# Patent

## Title
Multicolor image-forming method and multicolor image-forming material

## Abstract

A method for forming a multicolor image comprises:
preparing: an image-receiving sheet having a support and an image-receiving layer; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the at least four thermal transfer sheets has a different color and each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.50 or more; superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to record an image, in which the transferred image onto the image-receiving sheet has a resolution of 2400 dpi or more, where in a color matching process is performed before the image is recorded on the image-receiving sheet.

## Background
FIELD OF THE INVENTION
The present invention relates to a multicolor image-forming method using a multicolor image-forming material for forming a full color image of high definition with a laser beam and the multicolor image-forming material, in particular, relates to a multicolor image-forming method using a multicolor image-forming material which is useful for forming a color proof (DDCP: direct digital color proof) from digital image signals by laser recording in the field of printing, or a mask image, and the multicolor image-forming material.
BACKGROUND OF THE INVENTION
In the field of graphic arts, printing of a printing plate is performed using a set of color separation films formed from a color original with a lith film. In general, color proofs are formed from color separation films before actual printing work for checking an error in the color separation step and the necessity for color correction. Color proofs are desired to realize high definition which makes it possible to surely reproduce a half tone image and have performances such as high stability of processing. Further, for obtaining color proofs closely approximating to an actual printed matter, it is preferred to use materials which are used in actual printing as the materials for making color proofs, e.g., the actual printing paper as the base material and pigments as the coloring materials. As the method for forming a color proof, a dry method not using a developing solution is strongly desired.
As the dry method for forming color proofs, a recording system of directly forming color proofs from digital signals has been developed with the spread of electronized system in preprocessing of printing (pre-press field) in recent years. Such electronized system aims at forming in particular high quality color proofs and generally reproduces a dot image of 150 lines/inch or higher. For recording a proof of high image quality from digital signals, laser beams capable of modulation by digital signals and capable of finely diaphragming recording light are used as recording heads. Therefore, the development of an image-forming material having high recording sensitivity to laser beams and exhibiting high definition capable of reproducing highly minute dots is required.
As the image-forming material for use in a transfer image-forming method using laser beams, a heat fusion transfer sheet comprising in the order of a support having a light-to-heat converting layer which absorbs laser beams and generates heat, and an image-forming layer which contains a pigment dispersed in components such as a heat fusion type wax and a binder is known (JP-A-5-58045 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). In the image-forming method using such an image-forming material, an image-forming layer corresponding to the area of a light-to-heat converting layer irradiated with laser beams is fused by heat generated in that area and transferred onto an image-receiving sheet arranged on the transfer sheet by lamination, thus a transferred image is formed on the image-receiving sheet.
Further, a heat transfer sheet comprising a support having provided thereon a light-to-heat converting layer containing a light-to-heat converting material, an extremely thin heat-releasing layer (from 0.03 to 0.3 μm), and an image-forming layer containing a coloring material in this order is disclosed in JP-A-6-219052. In this heat transfer sheet, the bonding strength between the image-forming layer and the light-to-heat converting layer bonded through the intervening heat-releasing layer is reduced by laser beam irradiation, as a result, a highly minute image is formed on an image-receiving sheet arranged on the heat transfer sheet by lamination. The image-forming method by the heat transfer sheet utilizes so-called ablation, specifically the heat-releasing layer partially decomposes at the area irradiated with laser beams and vaporizes, thereby the bonding strength of the image-forming layer and the light-to-heat converting layer at that area is reduced and the image-forming layer at that area is transferred to the image-receiving sheet laminated thereon.
These image-forming methods have various advantages that an actual printing paper provided with an image-receiving layer (an adhesion layer) can be used as the material of an image-receiving sheet, and a multicolor image can be easily obtained by transferring images different in colors in sequence on the image-receiving sheet. The image-forming method utilizing ablation, in particular, has the advantage that highly minute image can be easily obtained, and so these methods are useful for forming a color proof (DDCP: direct digital color proof) or a highly minute mask image.
DTP is prevailing more and more and the intermediate process using films is omitted when CTP (computer to plate) is used, and the need for proof is shifting from analog proof to DDCP. In recent years the demand for large sized high grade DDCP highly stable and excellent in coincidence in printing has increased.
High definition printing can be effected according to a heat transfer method by laser irradiation, and as the laser heat transfer methods, (1) a laser sublimation method, (2) a laser ablation method, and (3) a laser fusion method are conventionally used, but any of these methods has a drawback such that the shapes of recorded dots are not sharp. In (1) a laser sublimation method, the approximation of proofs to printed matters is not sufficient, since dyes are used as the coloring material, further, since this is a method of sublimating coloring materials, the outline of a dot is fuzzy, and so definition is not sufficiently high. On the other hand, since pigments are used as the coloring materials in (2) a laser ablation method, the approximation to printed matters is good, but this is a method of sputtering coloring materials, and so the outline of a dot is also fuzzy as in the sublimation method, and definition is not sufficiently high. Further, in (3) a laser fusion method, a molten substance flows, therefore, the outline of a dot is not also clear.
Further, there are the following drawbacks in the process of transferring an image-receiving sheet to an actual printing paper. That is, when an image-receiving sheet is transferred to an actual paper by a laminator, transferring is sometimes performed by superposing an actual paper and an image-receiving sheet on an aluminum guide plate and passing them through a heat roller. The aluminum guide plate is used for preventing the deformation of the actual paper. However, when an aluminum guide plate is adopted in the recording system of B2 size, an aluminum guide plate larger than B2 size is necessary, which results in the problemthat a large installation space is required. Accordingly, by adopting the structure of a carrier path rotating in a 180° arc to discharge the sheets on the side of insertion as shown in FIG. 3, not using an aluminum guide plate, the installation space can be largely saved. However, there arises a problem of the deformation of an actual paper, since an aluminum guide plate is not used in the laminator. Specifically, a pair of an actual paper and an image-receiving sheet curl with the image-receiving sheet being inside and roll on the discharge platform. It is very difficult work to release the image-receiving sheet from the curled actual paper.
SUMMARY OF THE INVENTION
Accordingly, the subjects of the present invention are to solve the above-described problems of the prior art technique and to accomplish the following objects. That is, an object of the present invention is to provide a large sized high grade DDCP which is highly stable and excellent in coincidence in printing. Specifically, the objects of the present invention are to achieve the following items: 1) a heat transfer sheet can provide dots showing sharpness and stability by membrane transfer of coloring materials, which are not influenced by light sources of illumination as compared with the pigment materials and printed matters, 2) an image-receiving sheet can receive stably and surely the image-forming layer in a heat transfer sheet by laser energy, 3) transfer to actual printing paper can be effected corresponding to the range of at least from 64 to 157 g/m2 such as art paper (coated paper), mat paper and finely coated paper, delicate texture can be imaged, and a high-key part can be reproduced accurately, and 4) extremely stable transfer releasability can be obtained. Another object of the present invention is to provide a method for forming a multicolor image having good image quality and stable transfer image density on an image-receiving sheet even when recording is performed by multi-beam laser beams of high energy under different temperature and humidity conditions.
A further object of the present invention is to provide a method for forming a multicolor image capable of preventing a pair of an actual paper and an image-receiving sheet discharged from a laminator from curling with the image-receiving sheet being inside when the image-receiving sheet on which a multicolor image has been printed is transferred to an actual paper, and preventing the actual paper from being deformed.
A still further object of the present invention is to make an image transferred to an actual printing paper sharper and high quality, and to prevent the reduction of image quality due to the invasion of foreign matters when an image-receiving sheet and a heat transfer sheet are fed to a recording unit.
That is, the means of the present invention for solving the above problems are as follows.
(1) A method for forming a multicolor image, which comprises:
preparing: an image-receiving sheet having a support and an image-receiving layer; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the at least four thermal transfer sheets has a different color;
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer;
irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to record an image, in which the transferred image onto the image-receiving sheet has a resolution of 2400 dpi or more,
wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.50 or more, and
a color matching process is performed before the image is recorded on the image-receiving sheet.
(2) The method for forming a multicolor image as described in the item (1), wherein the color matching process comprises:
a color image data conversion process of converting a color image data for forming a printed matter to a color image data for a proof outputting unit; and
a color·dot coincidence conversion process of performing a data conversion processing for making at least one of the color and dot of the printed matter coincide with at least one of the color and dot of the color image outputted from the proof outputting unit.
(3) The method for forming a multicolor image as described in the item (2), wherein the color-dot coincidence conversion process comprises:
a converting process of converting contone data (continuous tone data) to raster data;
a converting process of converting the received raster data according to four dimensional (black, cyan, magenta and yellow) table experimentally formed in advance so that the colors coincide with the colors of the printed matter formed based on the same raster data; and
a finally converting process of converting to binary data for dots so that the dots coincide with the dots of the printed matter.
(4) A method for forming a multicolor image, which comprises:
preparing: an image-receiving sheet having a support and an image-receiving layer; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the at least four thermal transfer sheets has a different color, and each of the at least four thermal transfer sheets has a recording area of a multicolor image being defined by a product of a length of 515 mm or more and width of 728 mm or more;
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer;
irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to record an image, and
transferring the image on the image-receiving layer to an actual printing paper, in which, when the image is transferred, the image-receiving sheet and the actual printing paper are disposed on a heat roller so that the image-receiving sheet is disposed over the actual printing paper.
(5) The method for forming a multicolor image as described in the item (1), wherein the at least four heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets.
(6) The method for a multicolor image as described in the item (5), wherein the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.
(7) The method for forming a multicolor image as described in the item (6), wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto an actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.
(8) The method for forming a multicolor image as described in the item (5), wherein the at least four of yellow, magenta, cyan and black heat transfer sheets and the image-receiving sheet each is fed to a recording unit in a roll, and each of the sheets is drawn out and carried automatically in the recording unit.
(9) The method for forming a multicolor image as described in the item (4), wherein the at least four heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets.
(10) The method for a multicolor image as described in the item (9), wherein the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.
(11) The method for forming a multicolor image as described in the item (10), wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto the actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.
(12) The method for forming a multicolor image as described in the item (9), wherein the at least four of yellow, magenta, cyan and black heat transfer sheets and the image-receiving sheet each is fed to a recording unit in a roll, and each of the sheets is drawn out and carried automatically in the recording unit.
(13) The method for forming a multicolor image as described in the item (1), wherein the irradiated area of the image-forming layer with laser beam is transferred to the image-receiving sheet in a thin film.
(14) The method for forming a multicolor image as described in the item (4), wherein the irradiated area of the image-forming layer with laser beam is transferred to the image-receiving sheet in a thin film.
(15) The method for forming a multicolor image as described in the item (1), wherein the transferred image onto the image-receiving sheet has a resolution of 2,600 dpi or more.
(16) The method for forming a multicolor image as described in the item (4), wherein the transferred image onto the image-receiving sheet has a resolution of 2,600 dpi or more.
(17) The method for forming a multicolor image as described in the item (1), wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.80 or more.
(18) The method for forming a multicolor image as described in the item (4), wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.80 or more.
(19) The method for forming a multicolor image as described in the item (1), wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 2.50 or more.
(20) The method for forming a multicolor image as described in the item (4), wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 2.50 or more.
(21) The method for forming a multicolor image as described in the item (1), wherein the image-forming layer in each of the at least four thermal transfer sheets and the image-receiving layer in the image-receiving sheet each has a contact angle with water of from 7.0 to 120.0°.
(22) The method for forming a multicolor image as described in the item (4), wherein the image-forming layer in each of the at least four thermal transfer sheets and the image-receiving layer in the image-receiving sheet each has a contact angle with water of from 7.0 to 120.0°.
(23) The method for forming a multicolor image as described in the item (1), wherein each of the at least four thermal transfer sheets has a recording area of the multicolor image being defined by a product of a length of 594 mm or more and width of 841 mm or more.
(24) The method for forming a multicolor image as described in the item (4), wherein each of the at least four thermal transfer sheets has a recording area of the multicolor image being defined by a product of a length of 594 mm or more and width of 841 mm or more.
(25) The method for forming a multicolor image as described in the item (1), wherein the ratio of an optical density (OD) of the image-forming layer in each of the at least four thermal transfer sheets to a thickness of the image-forming layer: OD/layer thickness (μm unit) is 1.80 or more and the image-receiving layer in the image-receiving sheet has a contact angle with water of 86° or less.
(26) The method for forming a multicolor image as described in the item (4), wherein the ratio of an optical density (OD) of the image-forming layer in each of the at least four thermal transfer sheets to a thickness of the image-forming layer: OD/layer thickness (μm unit) is 1.80 or more and the image-receiving layer in the image-receiving sheet has a contact angle with water of 86° or less.
(27) A multicolor image-forming material comprising:
an image-receiving sheet having an image-receiving layer and a support; and
at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the thermal transfer sheets has a different color,
wherein a multicolor image is formed by: superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form an image, and
each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.50 or more, and
the transferred image onto the image-receiving sheet has a resolution of 2,400 dpi or more, and
a color matching process is performed before the image is recorded on the image-receiving sheet.
(28) The multicolor image-forming material as described in the item (27), wherein each of the at least four thermal transfer sheets has a recording area of a multicolor image being defined by a product of a length of 515 mm or more and width of 728 mm or more, and the image on the image-receiving layer is transferred to an actual printing paper, in which, when the image is transferred, the image-receiving sheet and the actual printing paper are disposed on a heat roller so that the image-receiving sheet is disposed over the actual printing paper.
(29) The multicolor image-forming material as described in the item (27), wherein the at least four of heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets, and the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.
(30) The multicolor image-forming material as described in the item (29), wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto the actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a drawing showing the outline of the scheme of multicolor image-forming by heat transfer in thin layer by irradiation with a laser.
FIG. 2 is a drawing showing an example of constitution of a recording unit for laser heat transfer.
FIG. 3 is a drawing showing an example of constitution of a heat transfer unit.
FIG. 4 is a drawing showing the scheme of a system using a recording unit FINALPROOF for laser heat transfer.
FIG. 5 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 6 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 7 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 8 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 9 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 10 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 11 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 12 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 13 shows the shapes of the dots of the image obtained in Example 1-1. The center distance of dots is 125 μm.
FIG. 14 shows the reproducibility of the dots of the image obtained in Example 1-1. The axis of ordinate shows the dot area rate computed from the reflection density, and the axis of abscissa shows the dot area rate of the inputted signal.
FIG. 15 shows the repeating reproducibility of the image obtained in Example 1-1 in a*b* flat surface of L*a*b* color specification.
FIG. 16 shows the repeating reproducibility of the image obtained in Example 1-1.
FIG. 17 shows the letter quality of 2 points of the image (positive image) obtained in Example 1-1.
FIG. 18 shows the letter quality of 2 points of the image (negative image) obtained in Example 1-1.



DESCRIPTION OF REFERENCE CHARACTERS


    1: Recording unit
    2: Recording head
    3: By-scan rail
    4: Recording drum
    5: Heat transfer sheet-loading unit
    6: Image-receiving sheet roll
    7: Carrier roller
    8: Squeeze roller
    9: Cutter
    10: Heat transfer sheet
    10K, 10C, 10M, 10Y: Heat transfer sheet rolls
    12: Support
    14: Light-to-heat converting layer
    16: Image-forming layer
    20: Image-receiving sheet
    22: Support for image-receiving sheet
    24: Image-receiving layer
    30: Laminate
    31: Discharge platform
    32: Discard port
    33: Discharge port
    34: Air
    35: Discard box
    42: Actual paper
    43: Heat roller
    44: Insert platform
    45: Mark showing the position of placement
    46: Insert roller
    47: Guide made of heat resisting sheet
    48: Releasing claw
    49: Guide plate
    50: Discharge port


DETAILED DESCRIPTION OF THE INVENTION
As a result of eager investigation to provide a B2/A2 to B1/A1 or larger sized high grade DDCP which is highly stable and excellent in coincidence in printing, the present inventors have developed a heat transfer recording system for DDCP by laser irradiation which comprises an image-forming material of a B2 or larger size having performances of transfer to actual printing paper, reproduction of actual dots and of a pigment type, output driver, and high grade CMS software.
The characteristics of the performances of the heat transfer recording system by laser irradiation which has been developed by the present inventors, the constitution of the system and the outline of technical points are as follows. As the characteristics of performances, (1) since the dot shapes are sharp, dots which are excellent in approximation to the printed matter can be reproduced, (2) the approximation of hue to the printed matter is good, and (3) since the recorded quality is hardly influenced by the surrounding temperature and humidity and repeating reproducibility is good, a stable proof can be formed. The technical points of the material capable of obtaining such characteristics of performances are the establishment of the technique of membrane transfer, and the improvement of the retentivity of vacuum adhesion of the material required of a laser heat transfer system, following up of high definition recording, and the improvement of heat resistance. Specifically, (1) thinning of a light-to-heat converting layer by the introduction of an infrared absorbing dye, (2) strengthening of the heat resistance of a light-to-heat converting layer by the introduction of a polymer having a high Tg, (3) stabilization of hue by the introduction of a heat resisting pigment, (4) control of the adhesive strength and the cohesive strength of the material by the addition of low molecular weight components, such as a wax and an inorganic pigment, and (5) the provision of vacuum adhesion property to the material without being accompanied by the deterioration of an image quality by the addition of a matting agent to a light-to-heat converting layer, can be exemplified. As the technical points of the system, (1) carrying by air for continuous accumulation of multi sheets of films in a recording unit, (2) insert of a heat transfer unit on an actual paper for reducing curling after transfer, and (3) connection of output driver of a wide use having system connecting expendability, can be exemplified. The laser heat transfer recording system which has been developed by the present inventors is constituted by a diversity of characteristics of performances, the system constitution and technical points. However, these examples are illustrative of the present invention and should not be construed as limiting the scope of the present invention.
The present inventors have performed development on the basis of thoughts that individual material, each coating layer such as a light-to-heat converting layer, a heat transfer layer and an image-receiving layer, and each heat transfer sheet and image-receiving sheet are not present individually separately but they must function organically and synthetically, further these image-forming materials exhibit the highest possible performances when combined with a recording unit and a heat transfer unit. The present inventors have sufficiently examined each coating layer and the constituting materials of an image-forming material and prepared coating layers bringing out the best of their characteristics to make the image-forming material, and found proper ranges of various physical properties so that the image-forming material can exhibit the best performance. As a result, a high performance image-forming material could be found unexpectedly by thoroughly investigating the relationships between each material, each coating layer and each sheet and the physical properties, and functioning the image-forming material organically and synthetically with the recording unit and the heat transfer unit. The present invention in the system developed by the present inventors is an important invention concerning a multicolor image-forming method prescribing the combination with the color matching process and concerning a multicolor image-forming material for use therein for extracting the characteristics of the image-forming material of high performance supporting the system developed by the present inventors.
In the next place, the content, functions and effects of the color matching process for use in the present invention are described below.
In forming a color print, the finish of the print is confirmed in advance by forming a color proof approximating to the image to be obtained by printing with the printing plate formed beforehand from a color image data. Accordingly, for outputting the color image for a color proof on the basis of the color image data for forming a print, a variety of corrections and color conversion processes of the given color image data are necessary to obtain a color image faithfully reproducing the colors of the print, i.e., to obtain a color image having high approximation to the printed matter, by performing a color matching process.
In order to perform a variety of corrections and color conversion processes in the color matching process, for example, when the proof of a print is formed by a proof-outputting apparatus, a conversion table for printing condition correction for converting color image data with due regard to the printing condition concerning color printing machine (e.g., the kind of a printing paper and the kind of a printing ink), a standard color conversion table for performing standard color correction according to the proof-outputting apparatus and the outputting system of the color printing machine (e.g., a dot modulation system or a density modulation system) without depending upon the printing condition, and a conversion table for calibration for correcting machinery errors, use environment and aging fluctuation of the proof-outputting apparatus are necessary.
It is preferably that these various conversion tables for correction are experimentally formed in advance as four dimensional table (black, cyan, magenta and yellow), and the tables are preserved in the system for the present invention. The four dimensional table is formed so as to minimize the difference between measured values in the recorded image printed practically by a printer and the recorded image by the proof-outputting apparatus, and the recorded images are prepared in advance as to data of important colors under a variety of conditions (the printing condition, the outputting system, the use environment, etc.).
The color matching process of the present invention comprises the steps of: converting a color image data for forming a printed matter to a color image data for a proof outputting unit (a color image data conversion process); and
performing a data conversion processing for making at least one of the color and dot of the printed matter coincide with at least one of the color and dot of the color image outputted from the proof outputting unit (a color·dot coincidence conversion process).
The color dot coincidence conversion process of the present invention comprises the steps of: converting the color image data for the proof outputting unit (contone data(continuous tone data)) to raster data through an RIP (raster image processor) system, then performing data conversion according to a previously formed four dimensional table for color correction having a variety of correction data so that the colors of the data coincide with the colors of the print, and finally converting the data to binary data for dots so that the dots of the data coincide with the dots of the print.
A color proof image highly precisely approximating to the printed matter can be easily formed by performing data conversion processing of colors and dots by these color matching processes. Further, efficient color matching corresponding to a large sized image can be realized.
The details of data conversion is disclosed in JP-A-11-41475 and JP-A-2001-169110.
As one embodiment, there is one more invention within the multicolor image-forming method combined with the color matching process of the present invention. This one more invention in the system developed by the present inventors is an important technique prescribing the combination with the specific arrangement of an image-receiving sheet to an actual paper for extracting the characteristics of the image-forming material of high performance supporting the system developed by the present inventors.
This one more invention provides a method of preventing a pair of an actual paper and an image-receiving sheet from curling with the image-receiving sheet being inside. This curling prevention effect can be obtained by bimetallic effect of making use of the difference in shrinking amount between an actual paper and an image-receiving sheet and ironing effect of winding them around a heat roller. That is, when an image-receiving sheet and an actual paper are carried to be wrapped round a heat roller with the image-receiving sheet being inside as in conventional way at transferring to the actual paper, since the thermal shrinkage of the image-receiving sheet is larger than that of the actual paper, curling by bimetallic effect of the image-receiving sheet tends inward, which is the same direction as in the ironing effect and curling becomes serious by synergistic effect. Contrary to this, when the image-receiving sheet and the actual paper are carried to be wrapped round a heat roller with the actual paper being inside at transferring to the actual paper, curling by bimetallic effect and curling by ironing effect are offset each other, thus the problem of curling can be excluded.
As another embodiment, further one invention inheres in the multicolor image-forming method combined with the color matching process of the present invention. This further one invention in the system developed by the present inventors is an important technique prescribing the recording order of colors and the combination with an automatic roll feeder for extracting the characteristics of the image-forming material of high performance supporting the system developed by the present inventors.
In general, it is necessary to laminate image-forming layers of at least four colors of yellow, magenta, cyan and black on an actual paper for forming a color image. When image-forming layers of four colors are laminated on an actual paper in order of yellow, magenta, cyan and black from the actual paper side as in the present invention, the black color of the obtained image is very sharp and the image quality is excellent. This is a great advantage in the case of image-forming of a high definition image of 2,400 dpi or more. Further, OD/layer thickness of the image-forming layer is preferably higher than a definite value.
OD/layer thickness in the present invention is the ratio of the optical density (OD) of an image-forming layer to the layer thickness of the image-forming layer measured in μm unit. The optical density is the reflection optical density of each color of Y, M, C, K of the image which is transferred from the thermal transfer sheet to the image-receiving sheet and then is transferred from the image-receiving sheet to Tokuryo art paper, was measured in Y, M, C, K mode with a densitometer X-rite 938 (manufactured by X-rite Co.). The layer thickness of an image-forming layer is measured by observing the cross section of a heat transfer sheet before image-recording with a scanning electron microscope.
When the ratio of the optical density (OD) to the layer thickness (μm unit) of the image-forming layer in each heat transfer sheet, OD/layer thickness, is 1.50 or more, not only the image density required of a print proof can be easily obtained, but also the thickness of the image-forming layer can be thinned. As a result, the transfer to an image-receiving layer can be done efficiently, the breaking property of the image-forming layer becomes stable, a dot shape can be made sharp, in addition, pursuing of high definition recording responding to the image data and the reproduction of excellent dot shape can be realized. Further, since an image-forming layer can be made thinner, the influence of the surrounding temperature and humidity can be reduced to the utmost, the repeating reproducibility of an image can be improved, and stable transfer peelability can be obtained, thus an image highly approximating to the printed matter can be formed. By making OD/layer thickness 1.80 or higher, the effect can be promoted, and when OD/layer thickness is 2.50 or higher, the transfer density and the definition can be sharply increased.
When OD/layer thickness is less than 1.5, the image density become insufficient, or the breaking property of the image-forming layer is insufficient and the resolution reduce, as a result, the excellent image can not be obtained.
In the present invention, a heat transfer sheet and an image-receiving sheet are preferably fed in roll to a recording unit, and each of the sheets is draw out and carried by full automation in the unit. “Full automation” used here means a system of performing setting of a heat transfer sheet and an image-receiving sheet to a recording unit manually but the operation hereafter until the completion of recording is performed not using man power at all. An image is recorded in the present invention by superposing a heat transfer sheet and an image-receiving sheet vis-a-vis and irradiating with laser beams. At that time, if foreign matter is present between the heat transfer sheet and the image-receiving sheet, transfer of the image-receiving layer is hindered, resulting in the generation of a non-transferred area, i.e., a so-called “blank area”, and the deterioration of image quality. The invasion of minute foreign matters, e.g, dusts, into a recording unit can be prevented by full automation and the deterioration of the grade of image can be inhibited. In general, the probability of the occurrence of the defect due to foreign matters per one image plane is in proportion to the image area, and so a blank areas is a problem in practice when the image area is large. Particularly when the size of an image is 515 mm×728 mm or larger, a blank area is very big problem, but a good image hardly accompanied by a black area can be obtained by adopting a full automation system.
The present invention has the following further characteristics. That is, the characteristic is in the multicolor image-forming material. Specifically, the image-forming layer in each heat transfer sheet and the image-receiving layer in an image-receiving sheet have the contact angle with water of 7.0 to 120.0°, and thereby, sufficient adhesive strength can be obtained at image-forming time and the dot shape can be sharpened, which makes it possible to reproduce an excellent dot shape, and form a high grade proof free of transfer defect when transferred to an actual paper.
Also, in view of the above, in order to obtain a quality image having a sufficient density, it is preferably that the ratio of an optical density (OD) of the image-forming layer in each of the at least four thermal transfer sheets to a thickness of the image-forming layer: OD/layer thickness (μm unit) is 1.80 or more and the image-receiving layer in the image-receiving sheet has a contact angle with water of 86° or less.
The contact angle with water of each layer surface used in the present invention is a value obtained by the measurement with a contact angle meter CA-A model (manufactured by Kyowa Kaimen Kagaku Co., Ltd.).
The other characteristic is that the image-forming layer in the area irradiated with laser beams is transferred to an image-receiving sheet in a thin film.
By the membrane transfer method developed by the present inventors, high definition of from 0.9 to 1.1 of the line width reproducibility of a transferred image can be obtained in the present invention. This membrane transfer method is superiorto (1) a laser sublimation method, (2) a laser ablation method, and (3) a laser fusion method so far been used, however, of course, the multicolor image-forming method of the present invention is not limited thereto at all. On the contrary, many of the techniques incorporated in the above system developed by the present inventors can also be applied to each of the above conventional methods and can be improved, and contribute to the development of multicolor image-forming materials of high definition and multicolor image-forming methods.
The line width reproducibility used in the present invention is as follows: when the two dimensional energy distribution of laser beam spot is integrated in the main scanning direction and the half value width of the energy distribution in the by-scanning directions is taken as a, the ratio of the line width b of the transferred image to the length 2a obtained by multiplying a by 2 (b/2a) is the line width reproducibility.
In the next place, the system at large of the present invention will be described below together with the content of the present invention. In the system of the present invention, high definition and high image quality have been attained by inventing and adopting a membrane heat transfer system. A transferred image having definition of 2,400 dip or more, preferably 2,600 dip or more, can be obtained in the system of the present invention. The heat transfer system by membrane is a system of transferring a thin image-forming layer having a layer thickness of from 0.01 to 0.9 μm to an image-receiving sheet in the state of partially not melting or hardly melting. That is, since the recorded part is transferred as a membrane, an extremely high definition image can be obtained. A preferred membrane heat transfer method is to deform the inside of the light-to-heat converting layer to a dome-like form by photo-recording, push up the image-forming layer, to thereby enhance the adhesion of the image-forming layer and the image-receiving layer to make transferring easy. When the deformation is large, transferring becomes easy, since the force of pressing the image-forming layer against the image-receiving layer is great. While when the deformation is small, sufficient transferring cannot be effected in part, since the force of pressing the image-forming layer against the image-receiving layer is small. Deformation which is preferred for the membrane transfer can be observed by a laser microscope (VK8500, manufactured by Keyence Corporation), and the size of deformation can be evaluated by a deformation factor obtained by dividing [increased cross-sectional area of the recording area of the light-to-heat converting layer after photo-recording (a) plus cross-sectional area of the recording area of the light-to-heat converting layer before photo-recording (b)] by [cross-sectional area of the recording area of the light-to-heat converting layer before photo-recording (b)], and multiplying this value by 100. That is, deformation factor=[(a+b)/(b)]×100. The deformation factor is generally 110% or more, preferably 125% or more, and more preferably 150% or more. The deformation factor may be greater than 250% when the breaking elongation is made great but generally it is preferred to restrict the deformation factor to about 250%.
The technical points of the image-forming material in membrane transfer are as follows.
1. Compatibility of High Heat Responsibility and Storage Stability
For obtaining high image quality, transferring of a membrane of submicron order is necessary, but for obtaining desired density, it is necessary to form a layer having dispersed therein a pigment in high concentration, which is reciprocal to heat responsibility. Heat responsibility is also in the relationship reciprocal to storage stability (adhesion). By the development of novel polymer-additive, this reciprocal relationship has been solved.
2. Security of High Vacuum Adhesion
In membrane transfer pursuing high definition, the interface of transfer is preferably smooth, by which, however, sufficient vacuum adhesion cannot be obtained. Vacuum adhesion could be obtained by adding a little much amount of a matting agent having a relatively small particle size to the under layer of the image-forming layer, departing from general knowledge of obtaining vacuum adhesion, with maintaining proper gap uniform between the heat transfer sheet and the image-receiving sheet, without causing image dropout and securing the characteristics of membrane transfer.
3. Use of Heat Resisting Organic Material
A light-to-heat converting layer which converts laser beam to heat at laser recording attains the temperature of about 700° C. and an image-forming layer containing pigment materials reaches about 500° C. The present inventors have developed, as the material of a light-to-heat converting layer, modified polyimide capable of coating with an organic solvent, and at the same time pigments which are higher in heat resistance than pigments for printing, safe and coincident in hue, as the pigment materials.
4. Security of Surface Cleanliness
In membrane transfer, dust between a heat transfer sheet and an image-receiving sheet causes an image defect, which is a serious problem. Dust is coming from the outside of the apparatus, or is generated by cutting of materials, therefore dust cannot be excluded by only material control, and it is necessary that apparatus must be provided with a dust removing device. The present inventors found a material capable of maintaining appropriate viscosity and capable of cleaning the surface of a transfer material and realized the removal of dust by changing the material of the transfer roller without reducing the productivity.
In the next place, the system of the present invention will be described in detail below.
The present invention has realized a heat transfer image having sharp dots and transferring of an image to actual printing paper of a recording size of B2 size or larger (515 mm×728 mm or more). More preferably, B2 size is 543 mm×765 mm, and it is possible to record on this size or larger (preferably, 594 mm×841 mm or more) according to the present invention.
One characteristic of the performances of the system of the present invention is that sharp dot shape can be obtained. A heat transfer image obtained by this system is a dot image corresponding to print line number of definition of 2,400 dpi or more. Since individual dot obtained according to this system is very sharp and almost free of blur and chip, dots of a wide range from highlight to shadow can be clearly formed. As a result, output of dots of high grade having the same definition as obtained by an image setter and a CTP setter is possible, and dots and gradation which are excellent in approximation to the printed matter can be reproduced.
The second characteristic of the performances of the system of the present invention is that repeating reproducibility is good. Since a heat transfer image obtained by this system is sharp in dot shape, dots corresponding to laser beam can be faithfully reproduced. Further, since recording characteristics are little in dependency on the surrounding temperature and humidity, repeating reproducibility stable in hue and density can be obtained under wide temperature and humidity conditions.
The third characteristic of the performances of the system of the present invention is that color reproduction is good. A heat transfer image obtained by this system is formed with coloring pigments used in printing inks and since excellent in repeating reproducibility, highly minute CMS (color management system) can be realized.
The heat transfer image by the system developed by the present inventors can be almost in accord with the hues of Japan color and SWOP color, i.e., the hues of printed matters, and the colors appear similarly to the printed matters even when light sources of illumination are changed, such as a fluorescent lamp and an incandescent lamp.
The fourth characteristic of the performances of the system of the present invention is that the quality of a letter is good. Since a heat transferred image obtained by this system is sharp in dot shape, the fine line of a fine letter can be reproduced sharply.
The characteristics of the technical points of the materials for use in the system of the present invention are further described in detail below. As the heat transfer methods for DDCP, there are (1) a sublimation method, (2) an ablation method, and (3) a heat fusion method. Methods (1) and (2) are systems of sublimating or sputtering coloring materials, thus the outline of a dot becomes fuzzy. In method (3), since a molten substance flows, the outline of a dot is not also clear.
On the basis of a membrane transfer technique, the present inventors incorporated the following techniques to the system of the present invention for solving the new problems in laser transfer systems and obtaining further high image quality. The first characteristic of the technique of the materials is sharpening of dot shape. Image recording is performed by converting laser beams to heat in a light-to-heat converting layer and conducting the heat to the image-forming layer contiguous to the light-to-heat converting layer, to thereby adhere the image-forming layer to an image-receiving layer. For sharpening a dot shape, the heat generated by laser beams should not be diffused in the surface direction but be conducted to the transfer interface, and the image-forming layer rupture sharply at the interface of heating area/non-heating area. The thickness of the light-to-heat converting layer in the heat transfer sheet is thinned and dynamic properties of the image-forming layer are controlled for this purpose.
The first technique of sharpening of dot shape is thinning of the light-to-heat converting layer. The light-to-heat converting layer is presumed from simulation to reach about 700° C. in a moment, and a thin film is liable to be deformed and ruptured. When deformation and rupturing occur, the light-to-heat converting layer is transferred to the image-receiving layer together with the image-forming layer or a transferred image becomes uneven. On the other hand, a light-to-heat converting material must be present in the light-to-heat converting layer in high concentration for obtaining a desired temperature, which results in aproblem of precipitation of the light-to-heat converting material or migration of the material to the contiguous layer. Carbon black has been conventionally used in many cases as the light-to-heat converting material, but an infrared absorbing dye is used as the light-to-heat converting material in the present invention which can save the use amount as compared with carbon black. Polyimide compounds having sufficient dynamic strength even at high temperature and high retentivity of an infrared absorbing dye were introduced as the binder.
In this manner, it is preferred to make thin the light-to-heat converting layer up to about 0.5 μm or less by selecting an infrared absorbing dye excellent in light-to-heat converting property and a heat-resisting binder such as polyimide compounds.
The second technique of sharpening of dot shape is the improvement of the characteristics of an image-forming layer. When a light-to-heat converting layer is deformed or an image-forming layer itself is deformed due to a high temperature, thickness unevenness is caused in an image-forming layer transferred to an image-receiving layer corresponding to the by-scanning pattern of laser beams, as a result the image becomes uneven and apparent transfer density is reduced. The thinner the thickness of an image-forming layer, the more conspicuous is this tendency. On the other hand, when the thickness of an image-forming layer is thick, dot sharpness is impaired and sensitivity decreases.
To reconcile these reciprocal properties, it is preferred to improve transfer unevenness by adding a low melting point material to an image-forming layer, e.g., a wax. Transfer unevenness can be improved with maintaining dot sharpness and sensitivity by adding inorganic fine particles in place of a binder to adjust the layer thickness of an image-forming layer properly so that the image-forming layer ruptures sharply at interface of heating area/non-heating area.
In general, materials having a low melting point, such as a wax, are liable to ooze to the surface of an image-forming layer or to be crystallized and cause a problem in image quality and the aging stability of a heat transfer sheet in some cases.
To cope with this problem, it is preferred to use a low melting point material having no great difference from the polymer of an image-forming layer in an Sp value, by which the compatibility with the polymer of the image-forming layer can be increased and the separation of the low melting point material from the image-forming layer can be prevented. It is also preferred to mix several kinds of low melting point materials to prevent crystallization by eutectic mixture. As a result, an image showing a sharp dot shape and free of unevenness can be obtained.
The second characteristic of the technique of the materials is that the present inventors have found that recording sensitivity has temperature-humidity dependency. The dynamic properties and thermal physical properties of the coated layers of a heat transfer sheet in general vary by absorbing moisture, thus the humidity dependency of recording condition is caused.
For reducing the temperature-humidity dependency, it is preferred that the dye/binder system of a light-to-heat converting layer and the binder system of an image-forming layer should be organic solvents. Further, it is preferred to use polyvinyl butyral as the binder of an image-receiving layer and to introduce a hydrophobitization technique of polymers for the purpose of lowering water absorption properties of polymers. As the hydrophobitization technique of polymers, the technique of reacting a hydroxyl group with a hydrophobic group, or of crosslinking two or more hydroxyl groups with a hardening agent as disclosed in JP-A-8-238858 can be exemplified.
The third characteristic of the technique of the materials is the improvement of the approximation of hue to the printed matter. In addition to color matching of pigments in thermal head system color proof (e.g., First Proof, manufactured by Fuji Photo Film Co., Ltd.) and the technique of stable dispersion, the present inventors solved a problem newly occurred in the laser heat transfer system. That is, the first technique of the improvement of the approximation of hue to the printed matter is to use a highly heat resisting pigment. About 500° C. or more heat is also generally applied to an image-forming layer by laser exposure imaging, and so some of conventionally used pigments are heat-decomposed, but this problem can be prevented by using highly heat resisting pigments in an image-forming layer.
The second technique of the improvement of the approximation of hue to the printed matter is the diffusion prevention of an infrared absorbing material. For preventing the variation of hue due to the migration of an infrared absorbing dye from a light-to-heat converting layer to an image-forming layer by high heat at exposure, it is preferred to design a light-to-heat converting layer by combination of an infrared absorbing dye having high retentivity and a binder as described above.
The fourth characteristic of the technique of the materials is to increase sensitivity. Shortage of energy generally occurs in high speed printing and, in particular, time lag is caused in intervals of laser by-scanning and gaps are generated. As described above, using a dye of high concentration in a light-to-heat converting layer and thinning of a light-to-heat converting layer and an image-forming layer can improve the efficiency of generation and conduction of heat. It is also preferred to add a low melting point material to an image-forming layer for thepurpose of slightly fluidizing the image-forming layer at heating to thereby fill the gaps and improving the adhesion with the image-receiving layer. Further, for enhancing the adhesion of an image-receiving layer and an image-forming layer and sufficiently strengthening a transferred image, it is preferred to use the same polyvinyl butyral as used in the image-forming layer as the binder in the image-receiving layer.
The fifth characteristic of the technique of the materials is the improvement of vacuum adhesion. It is preferred that an image-receiving sheet and a heat transfer sheet are retained on a drum by vacuum adhesion. Since an image is formed by the adhesion control of both sheets, image transfer behavior is very sensitive to the clearance between the image-receiving layer surface in an image-receiving sheet and the image-forming layer surface in a transfer sheet, hence vacuum adhesion is important. If the clearance between the materials is widened with foreign matters, e.g., dust, as a cue, image defect and image transfer unevenness come to occur.
For preventing such image defect and image transfer unevenness, it is preferred to give uniform unevenness to a heat transfer sheet to thereby improve the air passage, to obtain uniform clearance.
The first technique of the improvement of vacuum adhesion is the provision of unevenness to the surface of a heat transfer sheet. For obtaining sufficient effect of vacuum adhesion even in superposed printing of two or more colors, unevenness is provided to a heat transfer sheet. For providing unevenness to a heat transfer sheet, a method of post treatment such as embossing treatment and a method of the addition of a matting agent to the coating layer are generally used, but in view of the simplification of manufacturing process and stabilization of materials with the lapse of time, the addition of a matting agent is preferred. The particle size of a matting agent must be larger than the thickness of the coating layer. When a matting agent is added to an image-forming layer, there arises a problem of coming out of the image of the part where the matting layer is present, accordingly, it is preferred to add a matting agent having an optimal particle size to the light-to-heat converting layer, thereby the layer thickness of the image-forming layer itself becomes almost uniform and an image free of defect can be obtained on the image-receiving sheet.
The characteristics of the technique of systematization of the system of the present invention will be described below. The first characteristic of the technique of systematization is the constitution of a recording unit. For surely reproducing sharp dots as described above, highly precise design is required also for a recording unit. The recording unit for use in the system of the present invention is the same as conventionally used recording units for laser heat transfer in fundamental constitution. The constitution is a so-called heat mode outer drum recording system and recording is performed such that a recording head provided with a plurality of high power lasers emit laser rays on a heat transfer sheet and an image-receiving sheet fixed on a drum. The preferred embodiments are as follows.
The first constitution of a recording unit is to prevent mixing of dusts. Feeding of an image-receiving sheet and a heat transfer sheet is performed by full automatic roll feeding. Mixture of dusts generated from the human body cannot be helped by sheet feeding of a small number, thus roll feeding is adopted.
Since heat transfer sheet comprises four colors each one roll, a roll of each color is switched to another by a rotating loading unit. Each film is cut to a prescribed length by a cutter during loading and fixed on a drum. The second constitution of a recording unit is to enhance the adhesion of an image-receiving sheet and a heat transfer sheet on a recording drum. An image-receiving sheet and a heat transfer sheet are adhered on a recording drum by vacuum adhesion, since the adhesion of an image-receiving sheet and a heat transfer sheet cannot be strengthened by mechanical fixing. Many vacuum suction holes are formed on a recording drum, and a sheet is sucked by a drum by reducing the pressure in a drum with a blower or a decompression pump. Since a heat transfer sheet is further suckedover the sucked image-receiving sheet, the size of the heat transfer sheet is made larger than the size of the image-receiving sheet. The air between the heat transfer sheet and the image-receiving sheet which most affects recording performance is sucked from the area outside of the image-receiving sheet where the heat transfer sheet is alone.
The third constitution of a recording unit is to accumulate multi sheets of films on a discharge platform stably. In the apparatus of the present invention, a multi sheets of large sized films of B2 size or larger can be accumulated on the discharge platform. When sheet B is discharged on the image-receiving layer of the already accumulated heat-adhesive film A, sometimes both cleave to each other. When the previous sheet cleaves to the previous of the previous sheet, the next sheet cannot be discharged correctly, which leads to the problem of jamming. For preventing cleaving, the prevention of the contact of film A and film B is the best. Some means are known as the contact preventing method, e.g., (a) a method of making difference in discharge platform level to make a gap between films by making film shape not plane, (b) a method of providing the discharge port at higher position than the discharge platform and dropping a discharged film from the above, and (c) a method of floating the film discharged later by blasting air between two films. In the system of the present invention, as the sheet size is very big (B2), the structures of the units are large scaled when methods (a) and (b) are used, hence, (c) a method of floating the film discharged later by blasting air between two films is adopted.
An example of the constitution of the apparatus of the present invention is shown in FIG. 2.
The sequence of forming a full color image by applying an image-forming material to the apparatus of the present invention (hereinafter referred to as image-forming sequence of the system of the present invention) is described below.

    1) By-scan axis of recording head 2 of recording unit 1 is reset by by-scan rail 3, main scan rotation axis of recording drum 4 and heat transfer sheet loading unit 5 are respectively reset at origin.
    2) Image-receiving sheet roll 6 is unrolled by carrier roller 7, and the tip of the image-receiving roll is fixed on recording drum 4 by vacuum suction via suction holes provided on the recording drum.
    3) Squeeze roller 8 comes down on recording drum 4 and presses the image-receiving sheet, and when the prescribed amount of the image-receiving sheet is conveyed by the rotation of the drum, the sheet is stopped and cut by cutter 9 in a prescribed length.
    4) Recording drum 4 further makes a round, thus the loading of the image-receiving sheet is finished.
    5) In the next place, in the same sequence as the image-receiving sheet, heat transfer sheet K of the first color, black, is drawn out from heat transfer sheet roll 10K, cut and loaded.
    6) Recording drum 4 starts high speed rotation, recording head 2 on by-scan rail 3 starts to move and when reaches the start position of recording, recording laser is emitted on recording drum 4 by recording head 2 according to recording signals. Irradiation is finished at finishing position of recording, operation of by-scan rail and drum rotation are finished. The recording head on the by-scan rail is reset.
    7) Only heat transfer sheet K is released with the image-receiving sheet remaining on the recording drum. For the releasing, the tip of heat transfer sheet K is caught by the claw, pulled out in the discharge direction, and discarded from discard port 32 to discard box 35.
    8) The procedures of 5) to 7) are repeated for the remaining three colors. Recording is performed in the order of black, cyan, magenta and yellow. That is, heat transfer sheet C of the second color, cyan, is drawn out from heat transfer sheet roll 10C, heat transfer sheet M of the third color, magenta, is from heat transfer sheet roll 10M, and heat transfer sheet Y of the fourth color, yellow, is from heat transfer sheet roll 10Y in order. This is the inverse of general printing order, since the order of the colors on actual paper becomes inverse by the later process of transfer to actual paper.
    9) After recording off our colors, the recorded image-receiving sheet is discharged to discharge platform 31. The releasing method from the drum is the same as that of the heat transfer sheet in above 7), but since the image-receiving sheet is not discarded differently from the heat transfer sheets, the image-receiving sheet is returned to the discharge platform by switch back when conveyed to discard port 32. When the image-receiving sheet is discharged to the discharge platform, air 34 is blasted from under discharge port 33 to make it possible to accumulate a plurality of sheets.


It is preferred to use an adhesive roller provided with an adhesive material on the surface as carrier roller 7 of either feeding part or carrying part of the heat transfer sheet roll and the image-receiving sheet roll.
The surfaces of the heat transfer sheet and the image-receiving sheet can be cleaned by providing an adhesive roller.
As the adhesive materials provided on the surface of the adhesive roller, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, a polyolefin resin, a polybutadiene resin, a styrene-butadiene copolymer (SBR), a styrene-ethylene-butene-styrene copolymer (SEBS), an acrylonitrile-butadiene copolymer (NBR), a polyisoprene resin (IR), a styrene-isoprene copolymer (SIS), an acrylic ester copolymer, a polyester resin, a polyurethane resin, an acrylate resin, a butyl rubber, and a polynorbornene can be exemplified.
An adhesive roller can clean the surfaces of the heat transfer sheet and the image-receiving sheet by being brought into contact with the surfaces of them, and the contact pressure is not particularly limited so long as they are in contact with each other.
Vickers hardness Hv of the material having viscosity used in the adhesive roller is preferably 50 kg/mm2 (approximately 490 MPa) or less in view of capable of sufficiently removing foreign matters and suppressing image defect.
Vickers hardness is hardness obtained by measurement with applying static load to a pyramid indenter of diamond having the angle between the opposite faces of 136°, and Vickers hardness Hv can be obtained by the following equation:
 Hardness Hv=1.854 P/d2(kg/mm2) approximately 18.1692 P/d2(Mpa)
wherein P: load (kg), d: the length of diagonal line of the square of depressed area (mm).
In the present invention, the modulus of elasticity at 20° C. of the material having viscosity used in the adhesive roller is preferably 200 kg/cm2 (approximately 19.6 MPa) or less in view of capable of sufficiently removing foreign matters and suppressing image defect similarly to the above.
The second characteristics of the technique of systematization is the constitution of the heat transfer unit.
The heat transfer unit is used for the steps of transferring the image-receiving sheet on which an image has been printed with a recording unit to an actual printing paper (hereinafter referred to as “actual paper”). This step is completely the same with First ProofTM. When the image-receiving sheet and an actual paper are superposed and heat and pressure are applied thereto, both are adhered, and then the image-receiving film is released from the actual paper, an image and the adhesion layer remain on the actual paper, and the support of the image-receiving sheet and the cushioning layer are peeled off. Accordingly, it can be said that the image is transferred from the image-receiving sheet to the actual paper in practice.
In First ProofTM, transferring is performed by superposing an actual paper and an image-receiving sheet on an aluminum guide plate and passing them through heat rollers. The aluminum guide plate is used for preventing the deformation of the actual paper. However, when an aluminum guide plate is adopted in the system of the present invention of B2 size, an aluminum guide plate larger than B2 size is necessary, which results in the problem that a large installation space is required. Accordingly, the system of the present invention does not use an aluminum guide plate and adopts the structure such that a carrier path rotates in a 180° arc and sheets are discharged on the side of insertion, thus the installation space can be largely saved (FIG. 3). However, there arises a problem of the deformation of an actual paper, since an aluminum guide plate is not used. Specifically, a pair of an actual paper and an image-receiving sheet curl with the image-receiving sheet being inside and roll on the discharge platform. It is very difficult work to release the image-receiving sheet from the curled actual paper.
In the present invention, it is preferable in view of curling prevention that the actual printing paper is disposed over the image-receiving sheet. The curling prevention is tried by bimetallic effect by making use of the difference in shrinking amount between an actual paper and an image-receiving sheet and ironing effect of winding them around a hot roller. In the case where an image-receiving sheet is superposed on an actual paper and inserted as in conventional way, since the thermal shrinkage of an image-receiving sheet in the direction of insertion is larger than that of an actual paper, curling by bimetallic effect is such that the upper tends inward, which is the same direction as in the ironing effect and curling becomes serious by synergistic effect. Contrary to this, when an image-receiving sheet is superposed under an actual paper, curling by bimetallic effect tends downward and curling by ironing effect tends upward, thus curls are offset each other.
The sequence of an actual paper transfer is as follows (hereinafter referred to as the transfer method of an actual paper for use in the system of the present invention). Heat transfer unit 41 for use in this method as shown in FIG. 3 is a manual apparatus differing from a recording unit.

    1) In the first place, the temperature of heat rollers 43 (from 100 to 110° C.) and the carrying velocity at transferring are set by dials (not shown) according to the kind of actual paper 42.
    2) In the next place, image-receiving sheet 20 is put on an insert platform with the image being upward, and the dust on the image is removed by an antistatic brush (not shown). Actual paper 42 from which dust has been removed is superposed thereon. At that time, since the size of actual paper 42 put upper side is larger than image-receiving sheet 20 put lower side, the position of image-receiving sheet 20 is not seen and alignment is difficult to do. For improving this work, marks 45 showing the positions of placement of an image-receiving sheet and an actual paper are marked on insert platform 44. The reason the actual paper is larger than image-receiving sheet 20 is to prevent image-receiving sheet 20 from deviating and coming out from actual paper 42 and to prevent the image-receiving layer in image-receiving sheet 20 from smearing heat rollers 43.
    3) The image-receiving sheet and the actual paper with being superposed are inserted into an insert port, and insert roller 46 rotates and feeds them to heat rollers 43.
    4) When the tip of the actual paper comes to the position of heat rollers 43, the heat rollers nip the image-receiving sheet and the actual paper and transfer is started. The heat rollers are heat resisting silicone rubber rollers. Pressure and heat are applied simultaneously to the image-receiving sheet and the actual paper, thereby they are adhered. Guide 47 made of a heat resisting sheet is installed on the down stream of the heat rollers, and a pair of the image-receiving sheet and the actual paper are carried upward through the upper heat roller and guide 47 with heating, they are released from the heat roller at releasing claw 48 and guided to discharge port 50 along guide plate 49.
    5) A pair of the image-receiving sheet and the actual paper coming out of discharge port 50 are discharged on the insert platform with being adhered. Thereafter, image-receiving sheet 20 is released from actual paper 42 manually.


The third characteristics of the technique of systematization is the constitution of the system.
By connecting the above units with a plate-making system, the function as color proof can be exhibited. As the system, it is necessary that a printed matter having an image quality approximating as far as possible to the printed matter outputted from certain plate-making data must be outputted from a proof, and in the present invention, the color matching process is performed. Therefore, a software for approximating dots and colors to the printed matter is necessary. The specific example of connection is described below.
When the proof of a printed matter is taken from the plate-making system CelebraTM (manufactured by Fuji Photo Film Co., Ltd.), the system connection is the followings as shown in FIG. 4. CTP (computer to plate) system is connected with CelebraTM. The final printed matter can be obtained by mounting the printing plate outputted from this system on a printing machine. As a color proof, the above recording unit Luxel FINALPROOF 5600 (manufactured by Fuji Photo Film Co., Ltd., hereinafter sometimes also referred to as “FINALPROOF”) is connected with CelebraTM, and as proof drive software for approximating dots and colors to the printed matter, PD SYSTEMTM (manufactured by Fuji Photo Film Co., Ltd.) is also connected with CelebraTM. CelebraTM and PD SYSTEMTM perform a color matching process in the system shown in FIG. 4.
Contone data (continuous tone data, image data) converted to raster data by CelebraTM are converted to binary data for dots and outputted to CTP system and finally printed. On the other hand, the same contone data (image data) is converted to the image data for the proof outputting apparatus, then to raster data, and is also outputted to PD system. PD system converts the received data according to four dimensional (black, cyan, magenta and yellow) table so that the colors coincide with the printed matter, and finally converts to binary data for dots so that the dots coincide with the dots of the printed matter and the data are outputted to FINALPROOF (FIG. 4).
The four dimensional table is experimentally prepared in advance and saved in the system. The experiment for the preparation of the four dimensional table is as follows. The printed image of important color data via CTP system and the outputted image of important color data from FINALPROOF via PD system are prepared, the measured color values of these images are compared and the table is formed so that the difference becomes minimum.
Thus, the present invention has realized the system constitution which can sufficiently exhibit the performance of the image-forming material having high definition.
The material of the heat transfer system for use in the system of the present invention is described below.
It is preferred that the absolute value of the difference between the surface roughness Rz of the front surface of the image-forming layer in the heat transfer sheet and the surface roughness Rz of the back surface of the image-forming layer is 3.0 or less, and absolute value of the difference between the surface roughness Rz of the front surface of the image-receiving layer in the image-receiving sheet and the surface roughness Rz of the back surface of the image-receiving layer is 3.0 or less. By such constitution of the present invention, conjointly with the above cleaning means, image defect can be prevented, jamming in carrying can be done away with, and dot-gaining stability can be improved.
The surface roughness Rz in the present invention means ten point average surface roughness corresponding to Rz of JIS (maximum height). The surface roughness is obtained by inputting and computing the distance between the average value of the altitudes of from the highest peak to the fifth peak and the average value of the depths of from the deepest valley to the fifth valley. A feeler type three dimensional roughness meter (Surfcom 570A-3DF, manufactured by Tokyo Seimitsu Co., Ltd.) is used for measurement. The measurement is performed in machine direction, the cutoff value is 0.08 mm, the measured area is 0.6 mm×0.4 mm, the feed pitch is 0.005 mm, and the speed of measurement is 0.12 mm/sec.
For further improving the above-described effects, it is more preferred that the absolute value of the difference between the surface roughness Rz of the front surface of the image-forming layer in the heat transfer sheet and the surface roughness Rz of the back surface of the image-forming layer is 1.0 or less, and absolute value of the difference between the surface roughness Rz of the front surface of the image-receiving layer in the image-receiving sheet and the surface roughness Rz of the back surface of the image-receiving layer is 1.0 or less.
Further, as another embodiment, it is preferred that the surface roughness Rz of the front surface and the back surface of the image-forming layer in the heat transfer sheet and/or the surface roughness Rz of the front surface and the back surface of the image-receiving layer in the image-receiving sheet is from 2 to 30 μm. By such constitution of the present invention, conjointly with the above cleaning means, image defect can be prevented, jamming in carrying can be done away with, and dot gaining stability can be improved.
It is also preferred that the glossiness of the image-forming layer in the heat transfer sheet is from 80 to 99.
The glossiness largely depends upon the surface smoothness of the image-forming layer and can affect the uniformity of the layer thickness of the image-forming layer. When the glossiness is higher, the image-forming layer becomes more uniform and more preferred for highly minute use, but when the smoothness is high, the resistance at conveying becomes larger, thus they are in relationship of trade off. When the glossiness is from 80 to 99, both are compatible and well-balanced.
The scheme of multicolor image-forming by membrane heat transfer using a laser is described with referring to FIG. 1.
Laminate 30 for image formation comprising image-receiving sheet 20 laminated on the surface of image-forming layer 16 containing pigment black (K), cyan (C), magenta (M) or yellow (Y) in heat transfer sheet 10 is prepared. Heat transfer sheet 10 comprises support 12, having provided thereon light-to-heat converting layer 14 and further thereon image-forming layer 16, image-receiving sheet 20 comprises support 22 and having provided thereon image-receiving layer 24, and image-receiving layer 24 is laminated on the surface of image-forming layer 16 in heat transfer sheet 10 in contact therewith (FIG. 1(a)). When laser beams are emitted imagewise in time series from the side of support 12 in heat transfer sheet 10 of laminate 30, the irradiated area with laser beams of light-to-heat converting layer 14 in heat transfer sheet 10 generates heat, thereby the adhesion with image-forming layer 16 is reduced (FIG. 1(b)). Thereafter, when image-receiving sheet 20 and heat transfer sheet 10 are peeled off, the area irradiated with laser beams 16′ of image-forming layer 16 is transferred to image-receiving layer 24 in image-receiving sheet 20 (FIG. 1(c)).
In multicolor image formation, the laser beam for use in irradiation preferably comprises multi-beams, particularly preferably comprises multi-beams of two-dimensional array. Multi-beams of two-dimensional array means that a plurality of laser beams are used when recording by irradiation with laser beam is performed, and the spot array of these laser beams comprises two-dimensional array comprised of a plurality of columns along the main scanning direction and a plurality of rows along the by-scanning direction.
The time required in laser recording can be shortened by using multi-beams of two-dimensional array.
Any laser beam can be used in recording with no limitation, such as gas laser beams, e.g., an argon ion laser beam, a helium-neon laser beam, and a helium-cadmium laser beam, solid state laser beams, e.g., a YAG laser beam, and direct laser beams, e.g., a semiconductor laser beam, a dye laser beam and an excimer laser beam, can be used. Alternatively, laser beams obtained by converting these laser beams to half the wavelength through second harmonic generation elements can also be used. In multicolor image formation, semiconductor laser beams are preferably used taking the output power and easiness of modulation into consideration. In multicolor image formation, it is preferred that laser beam emission is performed on conditions that the beam diameter of laser beam on the light-to-heat converting layer is from 5 to 50 μm (in particular from 6 to 30 μm), and scanning speed is preferably 1 m/second or more (particularly preferably 3 m/second or more).
In addition, it is preferred in multicolor image formation that the layer thickness of the image-forming layer in the black heat transfer sheet is larger than the layer thickness of the image-forming layer in each of yellow, magenta and cyan heat transfer sheet, and is preferably from 0.5 to 0.7 μm. By adopting this constitution, the reduction of density due to transfer unevenness by the irradiation of the black heat transfer sheet with laser beams can be suppressed.
By restricting the layer thickness of the image-forming layer in the black heat transfer sheet to 0.5 μm or more, transfer unevenness is not generated by high energy recording and image density is maintained, thus required image density as the proof of printing can be attained. Since this tendency becomes more conspicuous under high humidity conditions, density variation due to circumferential conditions can be prevented. On the other hand, by making the layer thickness 0.7 μm or less, transfer sensitivity can be maintained at recording time by laser and touching of small dots and fine lines can be improved. This tendency becomes more conspicuous under low humidity conditions. Definition can also be improved by the layer thickness of this range. The layer thickness of the image-forming layer in the black heat transfer sheet is more preferably from 0.55 to 0.65 μm and particularly preferably 0.60 μm.
Further, it is preferred that the layer thickness of the image-forming layer in the above black heat transfer sheet is from 0.5 to 0.7 μm, and the layer thickness of the image-forming layer in each of the above yellow, magenta and cyan heat transfer sheets is from 0.2 to less than 0.5 μm.
By making the layer thickness of each image-forming layer in yellow, magenta and cyan heat transfer sheets 0.2 μm or more, image density can be maintained without generating transfer unevenness when recording is performed by laser irradiation. On the other hand, by making the layer thickness 0.5 μm or less, transfer sensitivity and definition can be improved. The layer thickness of the image-forming layer in yellow, magenta and cyan heat transfer sheets is more preferably from 0.3 to 0.45 μm.
It is preferred for the image-forming layer in the black heat transfer sheet to contain carbon black, and the carbon black preferably comprises at least two carbon blacks having different tinting strength from the view point of capable of controlling reflection density with maintaining P/B (pigment/binder) ratio in a specific range.
The tinting strength of carbon black can be represented variously, e.g., PVC blackness disclosed in JP-A-10-140033, can be exemplified. PVC blackness is the evaluation of blackness, i.e., carbon black is added to PVC resin, dispersed by a twin roll mill and made to a sheet, and the blackness of a sample is evaluated by visual judgement, with taking the blackness of Carbon Black #40 and #45 (manufactured by Mitsubishi Chemicals Co., Ltd.) as 1 point and 10 points respectively as the standard values. Two or more carbon blacks having different PVC blackness can be used arbitrarily according to purposes.
The specific producing method of a sample is described below.
Producing Method of Sample
In a banbury mixer having a capacity of 250 ml, 40 mass % of sample carbon black was compounded to LDPE (low density polyethylene) resin and kneaded at 115° C. for 4 minutes.










Compounding condition


















LDPE resin
101.89 g 



Calcium stearate
1.39 g



Irganox ® 1010
0.87 g



Sample carbon black
69.43 g 










In the next place, dilution was performed in a twin roll mill at 120° C. so as to reach the concentration of carbon black of 1 mass %.










Preparation condition of diluted compound


















LDPE resin
58.3 g 



Calcium stearate
0.2 g



Resin compounded with 40 mass % of carbon black
1.5 g










The above-prepared product was made to s sheet having a slit width of 0.3 mm, the sheet was cut to chips, and a film having a thickness of 65±3 μm was formed on a hot plate at 240° C.
A multicolor image may be formed, as described above, by the method of using the heat transfer sheet, and repeatedly superposing many image layers (an image-forming layer on which an image is formed) on the same image-receiving sheet, alternatively a multicolor image may be formed by the method of forming images on a plurality of image-receiving sheet once, and then transferring these images to an actual paper.
With the latter case, for example, heat transfer sheets each having image-forming layer containing coloring material mutually different in hue are prepared, and independently four kinds (cyan, magenta, yellow, black) of laminates for image-forming comprising the above heat transfer sheet combined with an image-receiving sheet are produced. Laser emission according to digital signals on the basis of the image is performed to each laminate through a color separation filter, subsequently the heat transfer sheet and the image-receiving sheet are peeled off, to thereby form independently a color separated image of each color on each image-receiving sheet. Thereafter, the thus-formed each color separated image is laminated in sequence on an actual support, such as actual printing paper prepared separately, or on a support approximates thereto, thus a multicolor image can be formed.
It is preferred for the heat transfer sheet utilizing laser irradiation to form an image by the system of converting laser beams to heat and membrane-transferring the image-forming layer containing a pigment on the image-receiving sheet using the above converted heat energy. However, these techniques used for the development of the image-forming material comprising the heat transfer sheet and the image-receiving sheet can be arbitrarily applied to the development of the heat transfer sheets of a heat fusion transfer system, an ablation transfer system, and sublimation system and/or the development of an image-receiving sheet, and the system of the present invention may also include image-forming materials used in these systems.
A heat transfer sheet and an image-receiving sheet are described in detail below.
Heat Transfer Sheet
A heat transfer sheet comprises a support having thereon at least a light-to-heat converting layer and an image-receiving layer, and, if necessary, other layers.
Support
The materials of the support of the heat transfer sheet are not particularly restricted, and various supports can be used according to purposes. The support preferably has stiffness, good dimensional stability, and heat resistance capable of resisting the heat at image formation. The preferred examples of the support include synthetic resins, e.g., polyethylene terephthalate, polyethylene-2,6-naphthalate, polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene-acrylonitrile copolymer, polyamide (aromatic and aliphatic), polyimide, polyamideimide, and polysulfone. Biaxially stretched polyethylene terephthalate is preferred above all from the viewpoint of mechanical strength and dimensional stability against heat. When resins are used in the preparation of color proofs utilizing laser recording, it is preferred to form the support of a heat transfer sheet from transparent synthetic resins which transmit laser beams. The thickness of the support is preferably from 25 to 130 μm, particularly preferably from 50 to 120 μm. The central line average surface roughness Ra of the support of the side on which an image-forming layer is provided is preferably less than 0.1 μm (the value obtained by measurement using Surfcom, manufactured by Tokyo Seiki Co., Ltd., according to JIS B0601) The Young's modulus of the support in the machine direction is preferably from 200 to 1,200 kg/mm2 (approximately 2 to 12 GPa), and the Young's modulus of the support in the transverse direction is preferably from 250 to 1,600 kg/mm2 (approximately 2.5 to 16 GPa). The F-5 value of the support in the machine direction is preferably from 5 to 50 kg/mm2 (approximately 49 to 490 MPa), and the F-5 value of the support in the transverse direction is preferably from 3 to 30 kg/mm2 (approximately 29.4 to 294 MPa), and the F-5 value of the support in the machine direction is generally higher than the F-5 value of the support in the transverse direction, but when it is necessary to make the strength particularly in the transverse direction high, this rule does not apply to the case. Further, the heat shrinkage at 100° C. for 30 minutes of the support in the machine direction is preferably 3% or less, more preferably 1.5% or less, the heat shrinkage at 80° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. The breaking strength is from 5 to 100 kg/mm2 (approximately 49 to 980 MPa) in both directions, and the modulus of elasticity is preferably from 100 to 2,000 kg/mm2 (approximately 0.98 to 19.6 GPa).
The support of the heat transfer sheet may be subjected to surface activation treatment and/or one or two or more undercoat layers maybe provided on the support for the purpose of improving the adhesion with the light-to-heat converting layer which is provided on the support. As the examples of the surface activation treatments, glow discharge treatment and corona discharge treatment can be exemplified. As the materials of the undercoat layer, materials having high adhering property to both surfaces of the support and the light-to-heat converting layer, low heat conductivity, and excellent heat resisting property are preferably used. As the materials of such an undercoat layer, styrene, a styrene-butadiene copolymer and gelatin can be exemplified. The thickness of the undercoat layer is generally from 0.01 to 2 μm as a whole. If necessary, various functional layers such as a reflection-preventing layer and an antistatic layer may be provided on the surface of the heat transfer sheet of the side opposite to the side on which a light-to-heat converting layer is provided, or the support may be subjected to various surface treatments.
Backing Layer
It is preferred to provide a backing layer on the surface of the heat transfer sheet of the side opposite to the side on which a light-to-heat converting layer is provided. The backing layer preferably comprises a first backing layer contiguous to the support and a second backing layer provided on the side of the support opposite to the side on which the first backing layer is provided. In the present invention, the ratio of the mass A of the antistatic agent contained in the first backing layer to the mass B of the antistatic agent contained in the second backing layer, B/A, is less than 0.3. When B/A is 0.3 or more, a sliding property and powder dropout resistance of the backing layer are liable to be deteriorated.
The layer thickness C of the first backing layer is preferably from 0.01 to 1 μm, more preferably from 0.01 to 0.2 μm. The layer thickness D of the second backing layer is preferably from 0.01 to 1 μm, more preferably from 0.01 to 0.2 μm. The ratio of the layer thickness of the first backing layer to that of the second backing layer, C/D, is preferably from 1/2 to 5/1.
As the antistatic agents for use in the first and second backing layers, a nonionic surfactant, e.g., polyoxyethylene alkylamine, and glycerol fatty acid ester; a cationic surfactant, e.g., quaternary ammonium salt; an anionic surfactant, e.g., alkylphosphate; an ampholytic surfactant and an electrically conductive resin can be exemplified.
Electrically conductive fine particles can also be used as antistatic agents. The examples of such electrically conductive fine particles include oxides, e.g., ZnO, TiO2, SnO2, Al2O3, In2O3, MgO, BaO, CoO, CuO, Cu2O, CaO, SrO, BaO2, PbO, PbO2, MnO3, MoO3, SiO2, ZrO2, Ag2O, Y2O3, Bi2O3, Ti2O3, Sb2O3, Sb2O5, K2Ti6O13, NaCaP2O18 and MgB2O5; sulfide, e.g., CuS and ZnS; carbide, e.g., SiC, TiC, ZrC, VC, NbC, MoC and WC; nitride, e.g., Si3N4, TiN, ZrN, VN, NbN and Cr2N; boride, e.g., TiB2, ZrB2, NbB2, TaB2, CrB, MoB, WB and LaB5; silicide, e.g., TiSi2, ZrSi2, NbSi2, TaSi2, CrSi2, MoSi2 and WSi2; a metal salt, e.g., BaCO3, CaCO3, SrCO3, BaSO4 and CaSO4; and a complex, e.g., SiN4—SiC and 9Al2O3-2B2O3. These electrically conductive fine particles may be used alone or in combination of two or more. Of these fine particles, SnO2, ZnO, Al2O3, TiO2, In2O3, MgO, BaO and MoO3 are preferred, SnO2, ZnO, In2O3 and TiO2 are more preferred, and SnO2 is particularly preferred.
When the heat transfer sheet of the present invention is used in a laser heat transfer system, the antistatic agent used in the backing layer is preferably substantially transparent so that laser beams can be transmitted.
When electrically conductive metallic oxides are used as the antistatic agent, their particle size is preferably smaller to make light scattering as small as possible, but the particle size should be determined using the ratio of the refractive indices of the particles and the binder as parameter, which can be obtained according to the theory of Mie. The average particle size of the electrically conductive metallic oxides is generally from 0.001 to 0.5 μm, preferably from 0.003 to 0.2 μm. The average particle size used herein is the value of the particle size of not only the primary particles of the electrically conductive metallic oxides but the particle size including the particles having higher structures.
Besides an antistatic agent, the first and second backing layers may contain various additives, such as a surfactant, a sliding agent and a matting agent, and a binder. The amount of the antistatic agent contained in the first backing layer is preferably from 10 to 1,000 mass parts per 100 mass parts of the binder, more preferably from 200 to 800 mass parts. The amount of the antistatic agent contained in the second backing layer is preferably from 0 to 300 mass parts per 100 mass parts of the binder, more preferably from 0 to 100 mass parts.
As the binders for use for forming the first and second backing layers, homopolymers and copolymers of acrylic acid-based monomers, e.g., acrylic acid, methacrylic acid, acrylic ester and methacrylic ester, cellulose-based polymers, e.g., nitrocellulose, methyl cellulose, ethyl cellulose and cellulose acetate, vinyl-based polymers and copolymers of vinyl compounds, e.g., polyethylene, polypropylene, polystyrene, vinyl chloride-based copolymer, vinyl chloride-vinyl acetate copolymer, polyvinyl pyrrolidone, polyvinyl butyral and polyvinyl alcohol, condensed polymers, e.g., polyester, polyurethane and polyamide, rubber-based thermoplastic polymers, e.g., butadiene-styrene copolymer, polymers obtained by polymerization or crosslinking of photopolymerizable or heat polymerizable compounds, e.g., epoxy compounds, and melamine compounds can be exemplified.
Light-to-heat Converting Layer
The light-to-heat converting layer may comprise a light-to-heat converting material, a binder, and, if necessary, other additives.
A light-to-heat converting material is a material having a function of converting irradiated light energy to heat energy. A light-to-heat converting material is in general a dye (inclusive of a pigment, hereinafter the same) capable of absorbing a laser beam. When image-recording is performed by infrared laser irradiation, it is preferred to use an infrared absorbing dye as the light-to-heat converting material. As the examples of the dyes, black pigments, e.g., carbon black, pigments of macrocyclic compounds having absorption in the visible region to the near infrared region, e.g., phthalocyanine and naphthalocyanine, organic dyes which are used as the laser-absorbing material in high density laser recording such as photo-disc, e.g., a cyanine dye such as an indolenine dye, an anthraquinone dye, an azulene dye and a phthalocyanine dye, and organic metallic compound dyes, e.g., dithiol nickel complex, can be exemplified. Of the above compounds, cyanine dyes are particularly preferably used, since they show a high absorption coefficient to the lights in the infrared region, the thickness of a light-to-heat converting layer can be thinned when used as the light-to-heat converting material, as a result, the recording sensitivity of a heat transfer sheet can be further improved.
As the light-to-heat converting material, particulate metallic materials such as blackened silver and inorganic materials can also be used besides dyes.
As the binder to be contained in the light-to-heat converting layer, resins having at least the strength capable of forming a layer on a support and preferably having high heat conductivity. Heat resisting resins which are not decomposed by heat generated from the light-to-heat converting material at image recording are preferably used as the binder resin, since the surface smoothness of the light-to-heat converting layer can be maintained after irradiation even when light irradiation is performed with high energy. Specifically, resins having heat decomposition temperature (temperature at which the mass decreases by 5% in air stream at temperature increasing velocity of 10° C./min by TGA method (thermal mass spectrometry)) of 400° C. or more are preferably used, more preferably 500° C. or more. Binders preferably have glass transition temperature of from 200 to 400° C., more preferably from 250 to 350° C. When the glass transition temperature is lower than 200° C., there is a case where fog is generated on the image to be formed, while when it is higher than 400° C., the solubility of the resin is decreased, followed by the reduction of the productivity in some cases.
Further, the heat resistance (e.g., heat deformation temperature and heat decomposition temperature) of the binder in the light-to-heat converting layer is preferably higher than the heat resistance of the materials used in other layers provided on the light-to-heat converting layer.
Specifically, the examples of the binder resins which can be used in the light-to-heat converting layer include acrylate resins, e.g., polymethyl methacrylate, vinyl-based resins, e.g., polycarbonate, polystyrene, vinyl chloride-vinyl acetate copolymer and polyvinyl alcohol, polyvinyl butyral, polyester, polyvinyl chloride, polyamide, polyimide, polyether imide, polysulfone, polyether sulfone, aramid, polyurethane, epoxy resin and urea-melamine resin. Of these resins, polyimide resin is preferred.
Polyimide resins represented by the following formulae (I) to (VII) are soluble in an organic solvent and the productivity of the heat transfer sheet is improved when they are used. Further, these polymide resins are preferred in view of capable of improving the stability of viscosity, long term storage stability and moisture resistance of the coating solution for the light-to-heat converting layer. 




In formulae (I) and (II), Ar1 represents an aromatic group represented by the following formula (1), (2) or (3), and n represents an integer of from 10 to 100. 




In formulae (III) and (IV), Ar2 represents an aromatic group represented by the following formula (4), (5), (6) or (7), and n represents an integer of from 10 to 100. 




In formulae (V), (VI) and (VII), n and m each represents an integer of from 10 to 100. In formula (VI), the ratio of n/m is from 6/4 to 9/1.
As the criterion whether a resin is soluble in an organic solvent or not, when 10 mass parts or more of the resin is dissolved in 100 mass parts of N-methylpyrrolidone at 25° C., the resin can be preferably used in the light-to-heat converting layer, more preferably 100 mass parts is dissolved in 100 mass parts of N-methylpyrrolidone.
As the matting agent contained in the light-to-heat converting layer, inorganic and organic fine particles can be exemplified. The examples of the inorganic fine particles include metal salts, e.g., silica, titanium oxide, aluminum oxide, zinc oxide, magnesium oxide, barium sulfate, magnesium sulfate, aluminum hydroxide, magnesium hydroxide and boron nitride, kaolin, clay, talc, zinc flower, leadwhite, zeeklite, quartz, diatomaceous earth, pearlite, bentonite, mica and synthetic mica. The examples of the organic fine particles include resin particles, e.g., fluorine resin particles, guanamine resin particles, acrylic resin particles, styrene-acryl copolymer resin particles, silicone resin particles, melamine resin particles and epoxy resin particles.
The matting agents generally have a particle size of from 0.3 to 30 μm, preferably from 0.5 to 20 μm, and the addition amount is preferably from 0.1 to 100 mg/m2.
The light-to-heat converting layer may contain a surfactant, a thickener, and an antistatic agent, if necessary.
The light-to-heat converting layer can be provided by dissolving a light-to-heat converting material and a binder, adding, if necessary, a matting agent and other components thereto to thereby prepare a coating solution, coating the coating solution on a support and drying. As the organic solvents for dissolving polyimide resins, e.g., n-hexane, cyclohexane, diglyme, xylene, toluene, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, acetone, cyclohexanone, 1,4-dioxane, 1,3-dioxane, dimethyl acetate, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-butyrolactone, ethanol and methanol can be exemplified. Coating and drying can be performed according to ordinary coating and drying methods. Drying is generally performed at 300° C. or less, preferably 200° C. or less. When polyethylene terephthalate is used as the support, the drying temperature is preferably from 80 to 150° C.
If the amount of the binder in the light-to-heat converting layer is not sufficient, the cohesive strength of the light-to-heat converting layer lowers and the light-to-heat converting layer is liable to be transferred together when an image formed is transferred to an image-receiving sheet, which causes color mixture. While when the amount of the polyimide resin is too much, the layer thickness of the light-to-heat converting layer becomes too large to achieve a definite absorptivity, thereby sensitivity is liable to be decreased. The mass ratio of the solid content of the light-to-heat converting material to the binder in the light-to-heat converting layer is preferably 1/20 to 2/1, particularly preferably 1/10 to 2/1.
As described above, when the layer thickness of the light-to-heat converting layer is thinned, the sensitivity of the heat transfer sheet is increased and so preferred. The layer thickness of the light-to-heat converting layer is preferably from 0.03 to 1.0 μm, more preferably from 0.05 to 0.5 μm. Further, when the light-to-heat converting layer has the optical density of from 0.80 to 1.26 to the beam having wavelength of 808 nm, the transfer sensitivity of the image-forming layer is improved, more preferably the optical density of from 0.92 to 1.15 to the beam having wavelength of 808 nm. When the optical density at peak wavelength of laser beam is less than 0.80, irradiated light cannot be sufficiently converted to heat and sometimes transfer sensitivity is reduced. Contrary to this, when it exceeds 1.26, the function of the light-to-heat converting layer is affected at recording and sometimes fog is generated.
Image-forming Layer
An image-forming layer contains at least a pigment which is transferred to an image-receiving sheet and forms an image, in addition, a binder for forming the layer and, if necessary, other components.
Pigments are broadly classified to organic pigments and inorganic pigments, and they have respectively characteristics such that the former are particularly excellent in the transparency of the film, and the latter are excellent in shielding property, thus they may be used arbitrarily according to purposes. When the heat transfer sheet is used for the proofs of printing colors, organic pigments which are coincident with yellow, magenta, cyan and black generally used in printing ink or near to them in hue are preferably used. Further, metallic powder and fluorescent pigments are also used in some cases. The examples of the pigments which are preferably used include azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments and nitro pigments. The pigments for use in an image-forming layer are listed below by colors, however, these examples should not be construed as limiting the scope of the present invention.
1) Yellow Pigment


    Pigment Yellow 12 (C.I. No. 21090)
    Example:
    
        Permanent Yellow DHG (manufactured by Clariant Japan, K.K.), Lionol Yellow 1212B (manufactured by Toyo Ink Mfg. Co., Ltd.), Irgalite Yellow LCT (manufactured by Ciba Specialty Chemicals), Symuler Fast Yellow GTF 219 (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Yellow 13 (C.I. No. 21100)
    Example:
    
        Permanent Yellow GR (manufactured by Clariant Japan, K.K.), Lionol Yellow 1313 (manufactured by Toyo Ink Mfg. Co., Ltd.)
    
    
    Pigment Yellow 14 (C.I. No. 21095)
    Example:
    
        Permanent YellowG (manufactured by Clariant Japan, K.K.), Lionol Yellow 1401-G (manufactured by Toyo Ink Mfg. Co., Ltd.), Seika Fast Yellow 2270 (manufactured by Dainichi Seika K.K.), Symuler Fast Yellow 4400 (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Yellow 17 (C.I. No. 21105)
    Example:
    
        Permanent Yellow GG02 (manufactured by Clariant Japan, K.K.), Symuler Fast Yellow 8GF (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Yellow 155
    Example:
    
        Graphtol Yellow 3GP (manufactured by Clariant Japan, K.K.)
    
    
    Pigment Yellow 180 (C.I. No. 21290)
    Example:
    
        Novoperm Yellow P-HG (manufactured by Clariant Japan, K.K.), PV Fast Yellow HG (manufactured by Clariant Japan, K.K.)
    
    
    Pigment Yellow 139 (C.I. No. 56298)
    Example:
    
        Novoperm Yellow M2R 70 (manufactured by Clariant Japan, K.K.)

2) Magenta Pigment

    
    
    Pigment Red 57:1 (C.I. No. 15850:1)
    Example:
    
        Graphtol Rubine L6B (manufacturedbyClariant Japan, K.K.), Lionol Red 6B-4290G (manufactured by Toyo Ink Mfg. Co., Ltd.), Irgalite Rubine 4BL (manufactured by Ciba Specialty Chemicals), Symuler Brilliant Carmine 6B-229 (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 122 (C.I. No. 73915)
    Example:
    
        Hosterperm Pink E (manufactured by Clariant Japan, K.K.), Lionogen Magenta 5790 (manufactured by Toyo Ink Mfg. Co., Ltd.), Fastogen Super Magenta RH (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 53:1 (C.I. No. 15585:1)
    Example:
    
        Permanent Lake Red LCY (manufactured by Clariant Japan, K.K.), Symuler Lake Red C conc (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 48:1 (C.I. No. 15865:1)
    Example:
    
        Lionol Red 2B-3300 (manufactured by Toyo Ink Mfg. Co., Ltd.), Symuler Red NRY (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 48:2 (C.I. No. 15865:2)
    Example:
    
        Permanent Red W2T (manufactured by Clariant Japan, K.K.), Lionol Red LX235 (manufactured by Toyo Ink Mfg. Co., Ltd.), Symuler Red 3012 (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 48:3 (C.I. No. 15865:3)
    Example:
    
        Permanent Red 3RL (manufactured by Clariant Japan, K.K.), Symuler Red 2BS (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Red 177 (C.I. No. 65300)
    Example:
    
        Cromophtal Red A2B (manufactured by Ciba Specialty Chemicals)

3) Cyan Pigment

    
    
    Pigment Blue 15 (C.I. No. 74160)
    Example:
    
        Lionol Blue 7027 (manufactured by Toyo Ink Mfg. Co., Ltd.), Fastogen Blue BB (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Blue 15:1 (C.I. No. 74160)
    Example:
    
        Hosterperm Blue A2R (manufactured by Clariant Japan, K.K.), Fastogen Blue 5050 (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Blue 15:2 (C.I. No. 74160)
    Example:
    
        Hosterperm Blue AFL (manufactured by Clariant Japan, K.K.), Irgalite Blue BSP (manufactured by Ciba Specialty Chemicals), Fastogen Blue GP (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Blue 15:3 (C.I. No. 74160)
    Example:
    
        Hosterperm Blue B2G (manufactured by Clariant Japan, K.K.), Lionol Blue FG7330 (manufactured by Toyo Ink Mfg. Co., Ltd.), Cromophtal Blue 4GNP (manufactured by Ciba Specialty Chemicals), Fastogen Blue FGF (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Blue 15:4 (C.I. No. 74160)
    Example:
    
        Hosterperm Blue BFL (manufactured by Clariant Japan, K.K.), Cyanine Blue 700-10FG (manufactured by Toyo Ink Mfg. Co., Ltd.), Irgalite Blue GLNF (manufactured by Ciba Specialty Chemicals), Fastogen Blue FGS (manufactured by Dainippon Chemicals and Ink Co., Ltd.)
    
    
    Pigment Blue 15:6 (C.I. No. 74160)
    Example:
    
        Lionol Blue ES (manufactured by Toyo Ink Mfg. Co., Ltd.)
    
    
    Pigment Blue 60 (C.I. No. 69800)
    Example:
    
        Hosterperm Blue RL01 (manufactured by Clariant Japan, K.K.), Lionogen Blue 6501 (manufactured by Toyo Ink Mfg. Co., Ltd.)

4) Black Pigment

    
    
    Pigment Black 7 (carbon black C.I. No. 77266)
    Example:
    
        Mitsubishi Carbon Black MA100 (manufactured by Mitsubishi Chemicals Co., Ltd.), Mitsubishi Carbon Black #5 (manufactured by Mitsubishi Chemicals Co., Ltd.), Black Pearls 430 (manufactured by Cabot Co.)
    
    


As the pigments which can be used in the present invention, commercially available products can be arbitrarily selected by referring to Ganryo Binran (Pigment Handbook), compiled by Nippon Ganryo Gijutsu Kyokai, published by Seibundo-Shinko-Sha (1989), and COLOUR INDEX, THE SOCIETY OF DYES & COLOURIST, Third Ed. (1987).
The average particle size of the above pigments is preferably from 0.03 to 1 μm, more preferably from 0.05 to 0.5 μm.
When the particle size is 0.03 μm or more, the costs for dispersion are not increased and the dispersion solution does not cause gelation, while when it is 1 μm or less, since coarse particles are not contained in pigments, good adhesion of the image-forming layer and the image-receiving layer can be obtained, further, the transparency of the image-forming layer can also be improved.
As the binders for the image-forming layer, amorphous organic high polymers having a softening point of from 40 to 150° C. are preferably used. As the amorphous organic high polymers, styrene, derivatives of styrene, homopolymers and copolymers of the substitution products of styrene, e.g., butyral resin, polyamide resin, polyethyleneimine resin, sulfonamide resin, polyester polyol resin, petroleum resin, styrene, vinyltoluene, α-methylstyrene, 2-methylstyrene, chlorostyrene, vinylbenzoic acid, sodium vinylbenzene-sulfonate, and aminostyrene, methacrylic esters and methacrylic acid, e.g., methyl methacrylate, ethyl methacrylate, butyl methacrylate, and hydroxyethyl methacrylate, acrylic esters and acrylic acid, e.g., methyl acrylate, ethyl acrylate, butyl acrylate, and α-ethylhexyl acrylate, dienes, e.g., butadiene and isoprene, homopolymers of vinyl monomers or copolymers of vinyl monomers with other monomers, e.g., acrylonitrile, vinyl ethers, maleic acid, maleic esters, maleic anhydride, cinnamic acid, vinyl chloride and vinyl acetate can be used. Two or more of these resins may be used as mixture.
It is preferred for the image-forming layer to contain a pigment in an amount of from 30 to 70 mass %, more preferably from 30 to 50 mass %. It is also preferred for the image-forming layer to contain a resin in an amount of from 30 to 70 mass %, more preferably from 40 to 70 mass %.
The image-forming layer can contain the following components (1) to (3) as the above-described other components.
(1) Waxes
The examples of waxes include mineral waxes, natural waxes and synthetic waxes. As the examples of the mineral waxes, petroleum wax such as paraffin wax, microcrystalline wax, ester wax, and oxide wax, montan wax, ozokerite and ceresin can be exemplified. Paraffin wax is preferred above all. The paraffin wax is separated from petroleum, and various products are commercially available according to melting points.
As the examples of the natural waxes, vegetable wax, e.g., carnauba wax, Japan wax, ouriculy wax and esparto wax, and animal wax, e.g., beeswax, insect wax, shellac wax and spermaceti can be exemplified.
The synthetic waxes are generally used as a lubricant and generally comprises higher fatty acid compounds. As the examples of the synthetic waxes, the following can be exemplified.
1) Fatty Acid-based Wax
A straight chain saturated fatty acid represented by the following formula:

CH3(CH2)nCOOH

In the formula, n represents an integer of from 6 to 28. As the specific examples, stearic acid, behenic acid, palmitic acid, 12-hydroxystearic acid, and azelaic acid can be exemplified.
In addition, the metal salts of the above fatty acids (e.g., with K, Ca, Zn and Mg) can be exemplified.
2) Fatty Acid ester-based Wax
As the examples of the fatty acid esters, ethyl stearate, lauryl stearate, ethyl behenate, hexyl behenate and behenyl myristate can be exemplified.
3) Fatty Acid Amide-based Wax
As the examples of the fatty acid amides, stearic acid amide and lauric acid amide can be exemplified.
4) Aliphatic Alcohol-based Wax
A straight chain saturated aliphatic alcohol represented by the following formula:

CH3(CH2)nOH

In the formula, n represents an integer of from 6 to 28. As the specific examples, stearyl alcohol can be exemplified.
Of the above synthetic waxes 1) to 4), higher fatty acid amides such as stearic acid amide and lauric acid amide are preferred. Further, these wax compounds can be used alone or in arbitrary combination, as desired.
(2) Plasticizers
As the plasticizers, ester compounds are preferred, and well-known plasticizers can be exemplified, such asphthalic esters, e.g., dibutyl phthalate, di-n-octyl phthalate, di(2-ethylhexyl)phthalate, dinonyl phthalate, dilauryl phthalate, butyllauryl phthalate, and butylbenzyl phthalate, aliphatic dibasic acid esters, e.g., di(2-ethylhexyl)adipate, and di(2-ethylhexyl)sebacate, phosphoric triesters, e.g., tricresyl phosphate and tri(2-ethylhexyl)phosphate, polyol polyesters, e.g., polyethylene glycol ester, and epoxy compounds, e.g., epoxy fatty acid ester. Of these, esters of vinyl monomers, in particular, acrylic esters and methacrylic esters are preferred in view of the improvement of transfer sensitivity, the improvement of transfer unevenness, and the big controlling effect of breaking elongation.
As the acrylic or methacrylic ester compounds, polyethylene glycol dimethacrylate, 1,2,4-butanetriol trimethacrylate, trimethylolethane triacrylate, pentaerythritol acrylate, pentaerythritol tetraacrylate, dipentaerythritol polyacrylate can be exemplified.
The above plasticizers may be high polymers, and polyesters are preferred above all, since the addition effect is large and they hardly diffuse under storage conditions. As the polyesters, e.g., sebacic acid polyester and adipic acid polyester are exemplified.
The additives contained in the image-forming layer are not limited thereto. The plasticizers may be used alone or in combination of two or more.
When the addition amount of these additives in the image-forming layer is too much, there are cases where the definition of the transferred image is deteriorated, the film strength of the image-forming layer itself is reduced, or the unexposed area is transferred to the image-receiving sheet due to the reduction of the adhesion of the light-to-heat converting layer and the image-forming layer. From the above viewpoint, the content of the waxes is preferably from 0.1 to 30 mass %, more preferably from 1 to 20 mass %, based on the entire solid content in the image-forming layer. The content of the plasticizers is preferably from 0.1 to 20 mass %, more preferably from 0.1 to 10 mass %, based on the entire solid content in the image-forming layer.
(3) Others
In addition to the above components, the image-forming layer may further contain a surfactant, inorganic or organic fine particles (metallic powder and silica gel), oils (e.g., linseed oil and mineral oil), a thickener and an antistatic agent. Except for the case of obtaining a black image, energy necessary for transferring can be reduced by containing the materials which absorb the wavelength of the light sources for use in image recording. As the materials which absorb the wavelength of the light sources, either pigments or dyes may be used, but in the case of obtaining a color image, it is preferred in view of color reproduction to use dyes having less absorption in visible region and large absorption in the wavelength of light sources and use infrared light sources such as a semiconductor laser in image recording. As the examples of infrared absorbing dyes, the compounds disclosed in JP-A-3-103476 can be exemplified.
The image-forming layer can be provided by dissolving or dispersing the pigment and the binder, to thereby prepare a coating solution, coating the coating solution on the light-to-heat converting layer (when the following heat-sensitive releasing layer is provided on the light-to-heat converting layer, on the layer) and drying. As the solvent for use in the preparation of the coating solution, n-propyl alcohol, methyl ethyl ketone, propylene glycol monomethyl ether (MFG), methanol and water can be exemplified. Coating and drying can be performed according to ordinary coating and drying methods.
A heat-sensitive releasing layer containing a heat-sensitive material which generates gas by the action of the heat generated in the light-to-heat converting layer or releases adhesive moisture to thereby lower the adhesion strength between the light-to-heat converting layer and the image-forming layer can be provided on the light-to-heat converting layer in the heat transfer sheet. As such heat-sensitive materials, compounds (polymers or low molecular compounds) which themselves are decomposed by heat, or the properties of which are changed by heat, and generate gas, and compounds (polymers or low molecular compounds) which are absorbing, or are being adsorbed with, a considerable amount of easily-gasifying gases, such as moisture, can be used. These compounds may be used in combination.
As the examples of the polymers which themselves are decomposed by heat, or the properties of which are changed by heat, and generate gas, self oxidizing polymers, e.g., nitrocellulose, halogen-containing polymers, e.g., chlorinated polyolefin, chlorinated rubber, poly-rubber chloride, polyvinyl chloride, and polyvinylidene chloride, acryl-based polymers, e.g., polyisobutyl methacrylate which is being adsorbed with gasifying compound such as moisture, cellulose esters, e.g., ethyl cellulose which is being adsorbed with gasifying compound such as moisture, and natural high molecular compounds, e.g., gelatin which is being adsorbed with gasifying compound such as moisture can be exemplified. As the examples of low molecular compounds which are decomposed by heat, or the properties of which are changed by heat, and generate gas, diazo compounds and azide compounds which generate heat and decomposed, and generate gas can be exemplified.
Decomposition and property change by heat of the heat-sensitive material as described above preferably occur at 280° C. or less, particularly preferably 230° C. or less.
When low molecular compounds are used as the heat-sensitive material of the heat-sensitive releasing layer, it is preferred to combine the material with a binder. As the binder, the polymers which themselves are decomposed by heat, or the properties of which are changed by heat, and generate gas, can be used, but ordinary binders which do not have such property can also be used. When the heat-sensitive low molecular compound is used in combination with a binder, the mass ratio of the former to the latter is preferably from 0.02/1 to 3/1, more preferably from 0.05/1 to 2/1. It is preferred that the heat-sensitive releasing layer cover the light-to-heat converting layer almost entirely and the thickness of the heat-sensitive releasing layer is generally from 0.03 to 1 μm, and preferably from 0.05 to 0.5 μm.
When the constitution of the heat transfer sheet comprises a support having provided thereon a light-to-heat converting layer, a heat-sensitive releasing layer and an image-forming layer in this order, the heat-sensitive releasing layer is decomposed by heat conducted from the light-to-heat converting layer, or properties of which are changed by heat, and generates gas. The heat-sensitive releasing layer is partially lost or cohesive failure is caused in the heat-sensitive releasing layer due to the decomposition or gas generation, as a result the adhesion strength between the light-to-heat converting layer and the image-forming layer is lowered and, according to the behavior of the heat-sensitive releasing layer, a part of the heat-sensitive releasing layer migrates to the surface of the image finally formed with the image-forming layer and causes color mixture of the image. Therefore, it is preferred that the heat-sensitive releasing layer is scarcely colored, i.e., the heat-sensitive releasing layer shows high transmittance to visible rays, so that color mixture does not appear visually on the image formed, even if such transfer of the heat-sensitive releasing layer occurs. Specifically, the absorptivity of the heat-sensitive releasing layer to visible rays is 50% or less, preferably 10% or less.
Further, instead of providing an independent heat-sensitive releasing layer, the heat transfer sheet may take the constitution such that the light-to-heat converting layer is formed by adding the heat-sensitive material to the coating solution of the light-to-heat converting layer, and the light-to-heat converting layer doubles as the heat-sensitive releasing layer.
It is preferred that the coefficient of static friction of the outermost layer of the heat transfer sheet of the side on which the image-forming layer is provided is 0.35 or less, preferably 0.20 or less. When the coefficient of static friction of the outermost layer is 0.35 or less, the contamination of the roll for carrying the heat transfer sheet can be suppressed and the quality of the image formed can be improved. The measurement of coefficient of static friction is according to the method disclosed in paragraph [0011] of Japanese Patent Application No. 2000-85759.
It is preferred that the image-forming layer surface has Smooster value [means a value measured by apparatus called smooster: Digital Smooster DSM-2 Type manufactured by TOKYO ELECTRONIC INDUSTRY CO., LTD.] at 23° C., 55% RH of from 0.5 to 50 mm Hg (approximately, 0.0665 to 6.65 kPa), more preferably from 2.2 to 50 mm Hg (approximately, 0.293 to 6.65 kPa) and Ra of from 0.05 to 0.4 μm, which can reduce a great number of micro voids by which the image-receiving layer and the image-forming layer cannot be brought into contact with each other at the contact area, which is preferred in the point of transfer and image quality. The Ra value can be measured by a surface roughness meter (Surfcom, manufactured by Tokyo Seiki Co., Ltd.) according to JIS B0601. It is preferred that the surface hardness of the image-forming layer is 10 g or more when measured with a sapphire needle. When the heat transfer sheet is electrically charged according to U.S. test standard 4046 and then grounded, the electrification potential 1 second after grounding of the image-forming layer is preferably from −100 to 100 V. It is preferred that the surface resistance of the image-forming layer at 23° C., 55% RH is 109 Ω or less.
In the next place, the image-receiving sheet which can be used in combination with the heat transfer sheet is described below.
Image-Receiving Sheet
Layer Constitution
The constitution of the image-receiving sheet generally comprises a support having provided thereon one or more image-receiving layer(s) and, if necessary, any one or two or more layer(s) of a cushioning layer, a releasing layer and an intermediate layer is (are) provided between the support and the image-receiving layer. It is preferred in view of conveyance to provide a backing layer on the surface of the support opposite to the side on which the image-receiving layer is provided.
Support
A plastic sheet, a metal sheet, a glass sheet, a resin-coated paper, a paper, and ordinary sheet-like substrate materials, e.g., various complexes, are used as the support. As the examples of plastic sheets, a polyethylene terephthalate sheet, a polycarbonate sheet, a polyethylene sheet, a polyvinyl chloride sheet, a polyvinylidene chloride sheet, a polystyrene sheet, a styrene-acrylonitrile sheet, and a polyester sheet can be exemplified. As the examples of papers, an actual printing paper and a coated paper can be used.
It is preferred for the support to have minute voids inviewof capableof improving the image quality. Such supports can be produced by mixing a thermoplastic resin and a filler comprising an inorganic pigment and a high polymer incompatible with the above thermoplastic resin to thereby prepare a mixed melt, extruding the mixed melt by a melt extruder to prepare a monolayer or multilayer film, and further monoaxially or biaxially stretching the film. In this step, the void ratio is determined by the selection of the resin and the filler, a mixing ratio and stretching condition.
As the thermoplastic resins, a polyolefin resin such as polypropylene and a polyethylene terephthalate resin are preferred, since they are excellent in crystallizability and orientation property and voids can be formed easily. It is preferred to use the polyolefin resin or the polyethylene terephthalate resin as the main component and use a small amount of other thermoplastic resin arbitrarily in combination. The inorganic pigments for use as the filler preferably have an average particle size of from 1 to 20 μm, e.g., calcium carbonate, clay, diatomaceous earth, titanium oxide, aluminum hydroxide and silica can be used. As the incompatible resins for use as the filler, when polypropylene is used as the thermoplastic resin, it is preferred to combine polyethylene terephthalate as the filler. The support having minute voids is disclosed in detail in JP-A-2001-105752.
The content of the filler, e.g., an inorganic pigment, in the support is generally from 2 to 30% or so by volume.
The thickness of the support in the image-receiving sheet is generally from 10 to 400 μm, preferably from 25 to 200 μm. For enhancing the adhesion with the image-receiving layer (or the cushioning layer) or with the image-forming layer in the heat transfer sheet, the surface of the support in the image-receiving sheet may be subjected to surface treatment, e.g., corona discharge treatment and glow discharge treatment.
Image-receiving Layer
It is preferred to provide one or more image-receiving layer(s) on the support in the image-receiving sheet for transferring and fixing the image-forming layer on the image-receiving sheet. The image-receiving layer is preferably a layer formed with organic polymer binder as the main component. The binders are preferably thermoplastic resins, such as homopolymers and copolymers of acryl-based monomers, e.g., acrylic acid, methacrylic acid, acrylic ester, and methacrylic ester, cellulose-based polymers, e.g., methyl cellulose, ethyl cellulose and cellulose acetate, homomonomers and copolymers of vinyl-based monomers, e.g., polystyrene, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl alcohol and polyvinyl chloride, condensed polymers, e.g., polyester and polyamide, and rubber-based polymers, e.g., butadiene-styrene copolymer. The binder for use in the image-receiving layer is preferably a polymer having a glass transition temperature (Tg) of lower than 90° C. for obtaining appropriate adhesion with the image-forming layer. For that purpose, it is possible to added a plasticizer to the image-receiving layer. The binder polymer preferably has Tg of 30° C. or more for preventing blocking between sheets. As the binder polymer of the image-receiving layer, it is particularly preferred to use the same or analogous binder polymer as used in the image-forming layer from the point of improving the adhesion with the image-forming layer at laser recording and improving sensitivity and image strength.
It is preferred that the image-receiving layer surface has Smooster value at 23° C., 55% RH of from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and Ra of from 0.05 to 0.4 μm, which can reduce a great number of micro voids by which the image-receiving layer and the image-forming layer cannot be brought into contact with each other at the contact area, therefore, this constitution is preferred in the point of transfer and image quality. The Ra value can be measured by a surface roughness meter (Surfcom, manufactured by Tokyo Seiki Co., Ltd.) according to JIS B0601. When the image-receiving layer is electrically charged according to U.S. test standard 4046 and then grounded, the electrification potential 1 second after grounding of the image-receiving layer is preferably from −100 to 100 V. It is preferred that the surface resistance of the image-receiving layer at 23° C., 55% RH is 109 Ω or less. The coefficient of static friction of the surface of the image-receiving layer is preferably 0.2 or less. The surface energy of the surface of the image-receiving layer is preferably from 23 to 35 mg/m2.
When the image once formed on the image-receiving layer is re-transferred to an actual printing paper, it is also preferred that at least one image-receiving layer is formed of a photo-setting material. As the composition of such a photo-setting material, combination comprising a) a photopolymerizable monomer comprising at least one kind of a polyfunctional vinyl or vinylidene compound which can form a photopolymer by addition polymerization, b) an organic polymer, and c) a photopolymerization initiator and, if necessary, additives, e.g., a thermal polymerization inhibitor can be exemplified. As the above polyfunctional vinyl monomer, unsaturated ester of polyol, in particular, an acrylic or methacrylic ester (ethylene glycol diacrylate, pentaerythritol tetraacrylate) is used.
As the organic polymer, the polymers for use for forming the image-receiving layer can be exemplified. As the photopolymerization initiator, an ordinary photo-radical polymerization initiator, e.g., benzophenone and Michler's ketone, can be used in proportion of from 0.1 to 20 mass % in the layer.
The thickness of the image-receiving layer is generally from 0.3 to 7 μm, preferably from 0.7 to 4 μm. When the thickness of the image-receiving layer is 0.3 μm or more, the film strength can be ensured at re-transferring to an actual printing paper. While when it is 4 μm or less, the glossiness of the image after re-transferring to an actual printing paper can be suppressed, thus the approximation to the printed matter can be improved.
Other Layers
A cushioning layer may be provided between the support and the image-receiving layer. By providing a cushioning layer, it is possible to increase the adhesion of the image-forming layer and the image-receiving layer at heat transfer by laser and the image quality can be improved. Further, even if foreign matters enter between the heat transfer sheet and the image-receiving sheet during recording, the voids between the image-receiving layer and the image-forming layer are reduced by the deforming action of the cushioning layer, as a result the size of image defect such as blank area can be made small. Further, when the image formed by transfer is re-transferred to an actual printing paper, since the surface of the image-receiving layer is deformed according to the surface unevenness of the paper, the transferability of the image-receiving layer can be improved. Further, by reducing the glossiness of the transferred image, the approximation to the printed matter can be improved.
The cushioning layer is formed to be liable to be deformed when stress is laid on the image-receiving layer, hence for obtaining the above effect, the cushioning layer preferably comprises materials having a low modulus of elasticity, materials having elasticity of a rubber, or thermoplastic resins easily softened by heat. The modulus of elasticity of the cushioning layer at room temperature is preferably from 0.5 MPa to 1.0 GPa, more preferably from 1 MPa to 0.5 GPa, and particularly preferably from 10 to 100 MPa. For burying foreign matters such as dust, the penetration according to JIS K2530 (25° C., 100 g, 5 seconds) is preferably 10 or more. The cushioning layer has a glass transition temperature of 80° C. or less, preferably 25° C. or less, and a softening point of preferably from 50 to 200° C. It is also preferred to add a plasticizer to the binder for controlling these physical properties, e.g., Tg.
As the specific materials for use as the binder of the cushioning layer, besides rubbers, e.g., urethane rubber, butadiene rubber, nitrile rubber, acryl rubber and natural rubber, polyethylene, polypropylene, polyester, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, ethylene-acryl copolymer, vinyl chloride-vinyl acetate copolymer, vinylidene chloride resin, vinyl chloride resin containing a plasticizer, polyamide resin and phenol resin can be exemplified.
The thickness of the cushioning layer varies according to the resins used and other conditions, but is generally from 3 to 100 μm, preferably from 10 to 52 μm.
It is necessary that the image-receiving layer and the cushioning layer are adhered to each other until the stage of laser recording, but it is preferred that they are designed to be releasable for transferring an image to the actual printing paper. For easy release, it is also preferred to provide a releasing layer having a thickness of from 0.1 to 2 μm or so between the cushioning layer and the image-receiving layer. When the thickness of the releasing layer is too thick, the properties of the cushioning layer are difficult to be exhibited, thus it is necessary to adjust the thickness by the kind of the releasing layer.
The specific examples of the binders of the releasing layer include thermo-setting resins having Tg of 65° C. or more, e.g., polyolefin, polyester, polyvinyl acetal, polyvinyl formal, polyparabanic acid, methyl polymethacrylate, polycarbonate, ethyl cellulose, nitrocellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyvinyl chloride, urethane resin, fluorine resin, styrenes, e.g., polystyrene and acrylonitrile styrene, crosslinked products of these resins, polyamide, polyimide, polyether imide, polysulfone, polyether sulfone, aramid, and hardened products of these resins. As the hardening agent, generally used hardening agents, e.g., isocyanate and melamine, can be used.
When the binders of the releasing layer is selected taking the above physical properties into consideration, polycarbonate, acetal and ethyl cellulose are preferred in view of the storage stability, and further, when acrylic resins are used in the image-receiving layer, releasability at re-transferring of the image after laser heat transfer becomes good and preferred.
Further, a layer whose adhesion with the image-receiving layer extremely lowers by cooling can be used as the releasing layer. Specifically, layers containing waxes, heat fusion compounds such as binder, and thermoplastic resins as the main component can be used as such a layer.
The examples of the heat fusion compounds are disclosed in JP-A-63-193886. In particular, micro crystalline wax, paraffin wax, and carnauba wax are preferably used. As the thermoplastic resins, ethylene-based copolymers, e.g., ethylene-vinyl acetate resins and cellulose-based resins are preferably used.
As the additives, higher fatty acid, higher alcohol, higher fatty acid ester, amides, and higher amine can be added to the releasing layer, according to necessity.
As another constitution of the releasing layer, there is a layer which has releasability by causing cohesive failure due to fusion or melting by heating. It is preferred to add a supercooling substance to such a releasing layer.
As the supercooling substance, poly-ε-caprolactone, polyoxyethylene, benzotriazole, tribenzylamine and vanillin can be exemplified.
In still another constitution, a compound to reduce the adhesion with the image-receiving layer is added to the releasing layer. As such compounds, silicone-based resins, e.g., silicone oil; fluorine-based resins, e.g., Teflon and fluorine-containing acrylic resin; polysiloxane resins; acetal-based resins, e.g., polyvinyl butyral, polyvinyl acetal and polyvinyl formal; solid waxes, e.g., polyethylene wax and amide wax; and fluorine-based and phosphoric ester-based surfactants can be exemplified.
The releasing layer can be prepared by dissolving the above materials in a solvent or dispersing the above materials in a latex state, and coating the coating solution on the cushioning layer by a blade coater, a roll coater, a bar coater, a curtain coater, or a gravure coater, or extrusion lamination by hot melt. As another method, the solution or dispersion obtained by dissolving the above materials in a solvent or dispersing the above materials in a latex state is coated on a temporary base by the above coating method, the temporary base is adhered with the cushioning layer, and then the temporary base is released.
In the image-receiving sheet to be combined with the heat transfer sheet, the image-receiving layer may double as the cushioning layer, and in that case, the image-receiving sheet may take the constitution such as support/cushioning image-receiving layer, or support/undercoat layer/cushioning image-receiving layer. In this case, it is also preferred that cushioning image-receiving layer has releasability so as to be able to re-transfer to the actual printing paper. In this case, the image after being re-transferred to the actual printing paper becomes a glossy image.
The thickness of the cushioning image-receiving layer is from 5 to 100 μm, preferably from 10 to 40 μm.
It is preferred to provide a backing layer on the side of the support of the image-receiving sheet opposite to the side on which the image-receiving layer is provided for improving the traveling property of the image-receiving sheet. When a surfactant, an antistatic agent, e.g., fine particles of tin oxide, and a matting agent, e.g., silicon oxide and PMMA particles, are added to the backing layer, the traveling property in the recording unit is improved.
These additives can be added not only to the backing layer but also to the image-receiving layer and other layers, if desired. The kinds of the additives cannot be prescribed unconditionally according to purposes, but a matting agent having an average particle size of from 0.5 to 10 μm can be added in concentration of from 0.5 to 80% or so, and anantistatic agent can be added by selecting arbitrarily from among various surfactants and electrically conductive agents so that the surface resistance of the layer at 23° C., 50% RH becomes preferably 1012 Ω or less, more preferably 109 Ω or less.
As the binder for use in the backing layer, widely used polymers can be used, e.g., gelatin, polyvinyl alcohol, methyl cellulose, nitrocellulose, acetyl cellulose, aromatic polyamide resin, silicone resin, epoxy resin, alkyd resin, phenol resin, melamine resin, fluorine resin, polyimide resin, urethane resin, acrylic resin, urethane-modified silicone resin, polyethylene resin, polypropylene resin, polyester resin, Teflon resin, polyvinyl butyral resin, vinyl chloride-based resin, polyvinyl acetate, polycarbonate, organic boron compounds, aromatic esters, polyurethane fluoride, and polyether sulfone can be used.
When crosslinkable water-soluble binder is used as the binder of the backing layer and crosslinked, dropout prevention of a matting agent and scratch resistance of the backing layer are improved, further it is effective for blocking during storage.
The crosslinking means can be selected with no limitation from heat, actinic rays and pressure, according to the characteristics of the crosslinking agent to be used, and these may be used alone or in combination. For providing an adhering property to the support, an arbitrary adhesion layer may be provided on the same side of the support on which the backing layer is provided.
Organic or inorganic fine particles are preferably used in the backing layer as the matting agent. As the organic matting agent, polymethyl methacrylate (PMMA), polystyrene, polyethylene, polypropylene, fine particles of other radical polymers, and condensed polymers such as polyester and polycarbonate are exemplified.
The backing layer is preferably provided in an amount of about 0.5 to 5 g/m2. When the amount is less than 0.5 g/m2, coating property is unstable and a problem of dropout of the matting agent is liable to occur. While when the coating amount greatly exceeds 5 g/m2, the preferred particle size of the matting agent becomes extremely large and embossing of the image-receiving layer surface by the backing layer is caused during storage, and particularly in the heat transfer of transferring a thin image-forming layer, the dropout of the recorded image and unevenness are liable to occur.
The number average particle size of the matting agent is preferably larger than the layer thickness of the backing layer containing only a binder by 2.5 to 20 μm. Of the matting agents, particles having a particle size of 8 μm or more are necessary to be present in an amount of 5 mg/m2or more, preferably from 6 to 600 mg/m2, by which the defect due to foreign matters can be improved. Further, when a matting agent of narrow particle size distribution is used, i.e., when a matting agent having the value obtained by dividing the standard deviation of the particle size distribution by the number average particle size, σ/rn (variation coefficient of particle size distribution) of 0.3 or less is used, the defect which occurs when particles having an extraordinary big particle size are used can be improved, and further, the desired performance can be obtained with the less addition amount. The variation coefficient is more preferably 0.15 or less.
It is preferred to add an antistatic agent to the backing layer for the purpose of preventing adhesion of foreign matters due to the frictional electrification with a carrier roller. As the antistatic agent, a cationic surfactant, an anionic surfactant, a nonionic surfactant, a high molecular antistatic agent, electrically conductive fine particles, in addition, the compounds described in 11290 no Kagaku Shohin (Chemical Commercial Products of 11290), pp. 875 and 876, Kagaku Kogyo Nippo-Sha can be widely used.
As antistatic agents which can be used in the backing layer in combination, of the above compounds, carbon black, metallic oxide, e.g., zinc oxide, titanium oxide and tin oxide, and electrically conductive fine particles, e.g., organic semiconductors, are preferably used. In particular, when electrically conductive fine particles are used, the dissociation of the antistatic agent from the backing layer can be prevented, and stable antistatic effect can be obtained irrespective of the surroundings.
It is also possible to add a mold-releasing agent, e.g., various activators, silicone oil, and a fluorine resin, to the backing layer for providing a coating property and a mold-releasing property.
When the softening point of the cushioning layer and the image-receiving layer measured by TMA (Thermomechanical Analysis) is 70° C. or lower, the backing layer is particularly effective.
TMA softening point is obtained by observing the phase of the object with increasing the temperature of the object of measurement at constant rate and applying a constant load to the object. In the present invention, the temperature at the time when the phase of the object begins to change is defined as TMA softening point. The softening point by TMA can be measured with an apparatus such as Thermoflex (manufactured by Rigaku Denki-Sha Co.).
The heat transfer sheet and the image-receiving sheet can be used in image forming as the laminate by superposing the image-forming layer in the heat transfer sheet and the image-receiving layer in the image-receiving sheet.
The laminate of the heat transfer sheet and the image-receiving sheet can be produced by various methods. For example, the laminate can be easily obtained by superposing the image-forming layer in the heat transfer sheet and the image-receiving layer in the image-receiving sheet and passing through a pressure and heating roller. The heating temperature at this time is 160° C. or less, preferably 130° C. or less.
The above-described vacuum adhesion method can also be preferably used for obtaining the laminate. The vacuum adhesion method is a method of winding the image-receiving sheet around the drum provided with suction holes for vacuum sucking, and then vacuum-adhering the heat transfer sheet of a little larger size than the image-receiving sheet on the image-receiving sheet with uniformly blasting air by a squeeze roller. As other method, a method of mechanically sticking the image-receiving sheet on a metal drum with pulling the image-receiving sheet, and further mechanically sticking the heat transfer sheet thereon with pulling in the same manner can also be used. Of these methods, the vacuum adhesion method is especially preferred in the point of requiring no temperature control and capable of effecting lamination rapidly and uniformly.
EXAMPLE
The present invention will be described in detail with reference to the examples below, however, these examples should not be construed as limiting the scope of the present invention. In the examples, “parts” means “parts by mass” unless otherwise indicated.
Example 1-1
Preparation of Heat Transfer Sheet K (Black)
Formation of Backing Layer
Preparation of First Backing Layer Coating Solution

















Water dispersion solution of acrylic
2
parts



resin (Julymer ET410, solid content:



20 mass %, manufactured by Nippon Junyaku



Co., Ltd.)



Antistatic agent (water dispersion
7.0
parts



of tin oxide-antimony oxide,



average particle size: 0.1 μm,



17 mass %)



Polyoxyethylenephenyl ether
0.1
part



Melamine compound
0.3
parts



(Sumitic Resin M-3, manufactured



by Sumitomo Chemical Industry Co., Ltd.)



Distilled water to make the total amount
100
parts










Formation of First Backing Layer

One surface (back surface) of a biaxially stretched polyethylene terephthalate support (Ra of both surfaces: 0.01 μm) having a thickness of 75 μm was subjected to corona discharge treatment. The first backing layer coating solution was coated on the support in a dry coating thickness of 0.03 μm, dried at 180° C. for 30 seconds, thereby the first backing layer was prepared. The Young's modulus of the support in the machine direction was 450 kg/mm2 (approximately 4.4 GPa), and the Young's modulus of the support in the transverse direction was 500 kg/mm2 (approximately 4.9 GPa). The F-5 value of the support in the machine direction was 10 kg/mm2 (approximately 98 MPa), and the F-5 value of the support in the transverse direction was 13 kg/mm2 (approximately 127.4 MPa), the heat shrinkage at 100° C. for 30 minutes of the support in the machine direction was 0.3%, and that in the transverse direction was 0.1%. The breaking strength in the machine direction was 20 kg/mm2 (approximately 196 MPa), and that in the transverse direction was 25 kg/2(approximately 245 MPa), and the modulus of elasticity was 400 kg/mm2 (approximately 3.9 GPa).
Preparation of Second Backing Layer Coating Solution
















Polyolefin (Chemipearl S-120,
3.0 parts



27 mass %, manufactured by Mitsui



Petrochemical Industries, Ltd.)



Antistatic agent (water dispersion
2.0 parts



of tin oxide-antimony oxide,



average particle size: 0.1 μm,



17 mass %)



Colloidal silica
2.0 parts



(Snowtex C, 20 mass %, manufactured by



Nissan Chemical Industries, Ltd.)



Epoxy resin (Denacol EX-614B,
0.3 parts



manufactured by Nagase Kasei Co., Ltd.)



Distilled water to make the total amount
 100 parts 










Formation of Second Backing Layer

The second backing layer coating solution was coated on the first backing layer ina dry coating thickness of 0.03 μm, dried at 170° C. for 30 seconds, thereby the second backing layer was prepared.
Formation of Light-to-heat Converting Layer
Preparation of Light-to-heat Converting Layer Coating Solution
The following components were mixed by stirring with a stirrer and the light-to-heat converting layer coating solution was prepared.
Composition of Light-to-heat Converting Layer Coating Solution
















Infrared absorbing dye (NK-2014, manufactured by
7.6 parts



Nippon Kanko Shikiso Co., Ltd.,



cyanine dye having the following composition)





















In the formula, R represents CH3, and X represents ClO4−.













Polyimide resin represented by the following formula
29.3 parts


(Rika Coat SN-20F, manufactured by Shin Nihon Rika K.K.,


heat decomposition temperature: 510° C.)





















In the formula, R1 represents SO2, and R2 represents the following formula:































Exson naphtha
5.8 parts


N-Methylpyrrolidone (NMP)
1,500 parts


Methyl ethyl ketone
360 parts


Surfactant (Megafac F-176PF, manufactured by
0.5 parts


Dainippon Chemicals and Ink Co., Ltd., fluorine surfactant)


Dispersion of matting agent having the following composition
14.1 parts









Preparation of Dispersion of Matting Agent

Ten parts of pure spherical silica fine particles having an average particle size of 1.5 μm (Sea Hoster-KE-P150, manufactured by Nippon Shokubai Co., Ltd.), 2 parts of dispersant polymer (acrylate-styrene copolymer, Joncryl 611, manufactured by Johnson Polymer Co., Ltd.), 16 parts of methyl ethyl ketone, and 64 parts of N-methylpyrrolidone were mixed, this mixture and 30 parts of glass beads having a diameter of 2 mm were put in a reaction vessel made of polyethylene having a capacity of 200 ml, and dispersed with a paint shaker (manufactured by Toyo Seiki Co., Ltd.) for 2 hours and silica fine particle dispersion was obtained.
Formtion of Light-to-heat Converting Layer on Support Surface
The above light-to-heat converting layer coating solution was coated with a wire bar coater on one surface of a polyethylene terephthalate film (support) having a thickness of 75 μm, and the coated product was dried in an oven at 120° C. for 2 minutes, thus a light-to-heat converting layer was formed on the support. The optical density ODLH of the thus-obtained light-to-heat converting layer at wavelength of 808 nm measured by UV-spectrophotometer UV-240 (manufactured by Shimadzu Seisakusho Co. Ltd.) was 1.03, and the layer thickness measured with a scanning electron microscope was 0.3 μm on average.
In the present invention, the optical density (ODLH) of the light-to-heat converting layer in the heat transfer sheet means the absorbance of the light-to-heat converting layer at peak wavelength of the laser beams to be used when the image-forming material of the present invention is subjected to recording and can be measured with well-known spectrophotometers. UV-spectrophotometer UV-240 (manufactured by Shimadzu Seisakusho Co. Ltd.) was used in the present invention as described above. The optical density (ODLH) value obtained by subtracting the optical density of the support alone from the optical density including the support is taken as the above optical density.
Formation of Image-forming Layer
Preparation of Black Image-forming Layer Coating Solution
Each of the following components was put in a kneading mill, and pre-treatment was performed with adding a small amount of solvent and applying a shear force. A solvent was further added to the dispersion so as to reach the following composition, and dispersion was performed for two hours in a sand mill, thereby the mother solution of a pigment dispersion was obtained.
Composition of Black Pigment Dispersion Mother Solution
















Composition 1




Polyvinyl butyral
12.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Black 7 (carbon black,
 4.5 parts



C.I. No. 77266, Mitsubishi Carbon Black



#5, manufactured by Mitsubishi Chemicals



Co. Ltd., PVC blackness: 1)



Dispersion assistant
 0.8 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
79.4 parts



Composition 2



Polyvinyl butyral
12.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Black 7 (carbon black,
10.5 parts



C.I. No. 77266, Mitsubishi Carbon Black



MA100, manufactured by Mitsubishi Chemicals



Co., Ltd., PVC blackness: 10)



Dispersion assistant
 0.8 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
79.4 parts










The following components were mixed by stirring with a stirrer to prepare a black image-forming layer coating solution.
Composition of Black Image-forming Layer Coating Solution
















Above black pigment dispersion mother
185.7 parts 



solution (composition 1/composition 2:



70/30 (parts))



Polyvinyl butyral
11.9 parts 



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Wax-based compound



Stearic acid amide (Newtron 2,
1.7 parts



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Lauric acid amide (Diamid Y,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Oleic acid amide (Diamid O-200,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Rosin (KE-311, manufactured by
11.4 parts 



Arakawa Kagaku Co., Ltd.



components: resin acid 80-97%,



resin acid components:



abietic acid: 30 to 40%



neoabietic acid: 10 to 20%



dihydroabietic acid: 14%



tetrahydroabietic acid: 14%)



Surfactant (Megafac F-176PF,
2.1 parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



Inorganic pigment (MEK-ST,
7.1 parts



30% methyl ethyl ketone solution,



manufactured by Nissan Chemical



Industries, Ltd.)



n-Propyl alcohol
1,050 parts 



Methyl ethyl ketone
 295 parts 










It was found that the particles in the thus-obtained black image-forming layer coating solution had an average particle size of 0.25 μm, and the ratio of the particles having a particle size of 1 μm or more was 0.5% from the measurement by particle size distribution measuring apparatus of laser scattering system.
Formation of Black Image-forming Layer on Light-to-heat Converting Layer Surface
The above black image-forming layer coating solution was coated on the light-to-heat converting layer with a wire bar coater for 1 minute, and the coated product was dried in an oven at 100° C. for 2 minutes, thus a black image-forming layer was formed on the light-to-heat converting layer. By the above procedure, a heat transfer sheet (herein after referred to as heat transfer sheet K, similarly, a heat transfer sheet provided with a yellow image-forming layer is referred to as heat transfer sheet Y, a heat transfer sheet provided with a magenta image-forming layer is referred to as heat transfer sheet M, and a heat transfer sheet provided with a cyan image-forming layer is referred to as heat transfer sheet C) comprising a support having thereon a light-to-heat converting layer and a black image-forming layer in this order was prepared.
The optical density (OD) of the black image-forming layer in the thus-obtained heat transfer sheet K was 0.91 as a transmission density (transmission optical density) measured by Macbeth densitometer TD-904 (W filter), and the layer thickness of the black image-forming layer was 0.60 μm on average.
The obtained image-forming layer had the following physical properties.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 9.3 mm Hg (approximately 1.24 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 29 mJ/m2, and the contact angle with water was 94.8°.
The deformation rate of the light-to-heat converting layer was 168% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Preparation of Heat Transfer Sheet Y
Heat transfer sheet Y was prepared in the same manner as in the preparation of heat transfer sheet K, except that the yellow image-forming layer coating solution having the composition shown below was used in place of the black image-forming layer coating solution. The layer thickness of the image-forming layer in the obtained heat transfer sheet Y was 0.42 μm.
Composition of Yellow Pigment Dispersion Mother Solution










Yellow pigment composition 1


















Polyvinyl butyral
7.1 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Yellow (pigment yellow 180,
12.9 parts 



C.I. No. 21290)



(Novoperm Yellow P-HG, manufactured by



Clariant Japan, K.K.)



Dispersion assistant
0.6 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
79.4 parts 










Composition of Yellow Pigment Dispersion Mother Solution











Yellow pigment composition 2


















Polyvinyl butyral
7.1 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Yellow 139 (carbon black,
12.9 parts 



C.I. No. 56298)



(Novoperm Yellow M2R 70, manufactured by



Clariant Japan, K.K.)



Dispersion assistant
0.6 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
79.4 parts 










Composition of Yellow Image-forming Layer Coating Solution

















Above yellow pigment dispersion mother
 126 parts 



solution (yellow pigment composition 1/



yellow pigment composition 2: 95/5 (parts))



Polyvinyl butyral
4.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Wax-based compound



Stearic acid amide (Newtron 2,
0.7 parts



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Lauric acid amide (Diamid Y,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Oleic acid amide (Diamid O-200,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Nonionic surfactant
0.4 parts



(Chemistat 1100, manufactured by



Sanyo Chemical Industries, Co., Ltd.)



Rosin (KE-311, manufactured by
2.4 parts



Arakawa Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
0.8 parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
 793 parts 



Methyl ethyl ketone
 198 parts 










The obtained image-forming layer had the following physical properties.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 2.3 mm Hg (approximately 0.31 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.1.
The surface energy was 24 mJ/m2, and the contact angle with water was 108.1°.
The deformation rate of the light-to-heat converting layer was 150% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Preparation of Heat Transfer Sheet M
Heat transfer sheet M was prepared in the same manner as in the preparation of heat transfer sheet K, except that the magenta image-forming layer coating solution having the composition shown below was used in place of the black image-forming layer coating solution. The layer thickness of the image-forming layer in the obtained heat transfer sheet M was 0.38 μm.
Composition of Magenta Pigment Dispersion Mother Solution










Magenta pigment composition 1


















Polyvinyl butyral
12.6 parts



(Denka Butyral #2000-L, manufactured



by Denki Kagaku Kogyo Co., Ltd.,



Vicut softening point: 57° C.)



Pigment Red (pigment yellow 57:1,
15.0 parts



C.I. No. 15850:1)



(Symuler Brilliant Carmine 6B-229,



manufactured by Dainippon Chemicals



and Ink Co., Ltd.)



Dispersion assistant
 0.6 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
80.4 parts










Composition of Magenta Pigment Dispersion Mother Solution











Magenta pigment composition 2


















Polyvinyl butyral
12.6 parts



(Denka Butyral #2000-L, manufactured



by Denki Kagaku Kogyo Co., Ltd.,



Vicut softening point: 57° C.)



Pigment Red 57:1
15.0 parts



C.I. No. 15850)



(Lionol Red 6B-4290G, manufactured by



Toyo Ink Mfg. Co., Ltd.)



Dispersion assistant
 0.6 parts



(Solspers S-20000, manufactured by ICI)



n-Propyl alcohol
79.4 parts










Composition of Magenta Image-forming Layer Coating Solution


















Above magenta pigment dispersion mother
163
parts



solution (magenta pigment composition 1/



magenta pigment composition 2: 95/5 (parts))



Polyvinyl butyral
4.0
parts



(Denka Butyral #2000-L, manufactured



by Denki Kagaku Kogyo Co., Ltd.,



Vicut softening point: 57° C.)



Wax-based compound



Stearic acid amide (Newtron 2,
1.0
part



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Lauric acid amide (Diamid Y,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Oleic acid amide (Diamid O-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Nonionic surfactant
0.7
parts



(Chemistat 1100, manufactured by



Sanyo Chemical Industries, Co., Ltd.)



Rosin (KE-311, manufactured by
4.6
parts



Arakawa Kagaku Co., Ltd.)



Pentaerythritol tetraacrylate
2.5
parts



(NK ester A-TMMT, manufactured by



Shin-Nakamura Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
1.3
parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
848
parts



Methyl ethyl ketone
246
parts










The obtained image-forming layer had the following physical properties.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, specifically 200 g or more.
The Smooster value of the surface at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 3.5 mm Hg (approximately 0.47 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.8°.
The deformation rate of the light-to-heat converting layer was 160% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm 2 or more.
Preparation of Heat Transfer Sheet C
Heat transfer sheet C was prepared in the same manner as in the preparation of heat transfer sheet K, except that the cyan image-forming layer coating solution having the composition shown below was used in place of the black image-forming layer coating solution. The layer thickness of the image-forming layer in the obtained heat transfer sheet C was 0.45 μm.
Composition of Cyan Pigment Dispersion Mother Solution










Cyan pigment composition 1


















Polyvinyl butyral
12.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Blue (pigment blue 54:7,
15.0 parts



C.I. No. 74160)



(Cyanine Blue 700-10FG, manufactured



by Toyo Ink Mfg. Co., Ltd.))



Dispersion assistant
 0.8 parts



(PW-36, manufactured by Kusumoto Kasei



Co., Ltd.)



n-Propyl alcohol
 110 parts










Composition of Cyan Pigment Dispersion Mother Solution











Cyan pigment composition 2


















Polyvinyl butyral
12.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Pigment Blue 15
15.0 parts



(C.I. No. 74160, Lionol Blue 7027,



manufactured by Toyo Ink Mfg. Co., Ltd.)



Dispersion assistant
 0.8 parts



(PW-36, manufactured by Kusumoto Kasei



Co., Ltd.)



n-Propyl alcohol
 110 parts










Composition of Cyan Image-forming Layer Coating Solution


















Above cyan pigment dispersion mother
118
parts



solution (cyan pigment composition 1/



cyan pigment composition 2: 90/10 (parts))



Polyvinyl butyral
5.2
parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Inorganic pigment (MEK-ST)
1.3
parts



Wax-based compound



Stearic acid amide (Newtron 2,
1.0
part



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Lauric acid amide (Diamid Y,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Oleic acid amide (Diamid O-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Rosin (KE-311, manufactured by
2.8
parts



Arakawa Kagaku Co., Ltd.)



Pentaerythritol tetraacrylate
1.7
parts



(NK ester A-TMMT, manufactured by



Shin-Nakamura Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
1.7
parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
890
parts



Methyl ethyl ketone
247
parts










The obtained image-forming layer had the following physical properties.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 7.0 mm Hg (approximately 0.93 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.8°.
The deformation rate of the light-to-heat converting layer was 165% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Preparation of Image-receiving Sheet
The cushioning layer coating solution and the image-receiving layer coating solution each having the following composition were prepared.
















1) Cushioning layer coating solution




Vinyl chloride-vinyl acetate copolymer
20 parts



(main binder, MPR-TSL, manufactured by



Nisshin Kagaku Co., Ltd.)



Plasticizer
10 parts



(Paraplex G-40, manufactured by



C P. HALL. COMPANY)



Surfactant (fluorine surfactant,
0.5 parts 



coating assistant, Megafac F-177,



manufactured by Dainippon Chemicals



and Ink Co., Ltd.)



Antistatic agent (quaternary ammonium salt,
0.3 parts 



SAT-5 Supper (IC), manufactured by Nippon



Junyaku Co., Ltd.)



Methyl ethyl ketone
60 parts



Toluene
10 parts



N,N-Dimethylformamide
 3 parts



2) Image-receiving layer coating solution



Polyvinyl butyral
 8 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Antistatic agent
0.7 parts 



Sanstat 2012A, manufactured by



Sanyo Chemical Industries, Co., Ltd.)



Surfactant (Megafac F-177,
0.1 parts 



manufactured by Dainippon Chemicals



and Ink Co., Ltd.)



n-Propyl alcohol
20 parts



Methanol
20 parts



1-Methoxy-2-propanol
50 parts










The above-prepared cushioning layer coating solution was coated on a white PET support (Lumiler #130E58, manufactured by Toray Industries Inc., thickness: 130 μm) with a narrow-broad coater and the coated layer was dried, and then the image-receiving layer coating solution was coated and dried. The coating amounts were controlled so that the layer thickness of the cushioning layer after drying became about 20 μm and the layer thickness of the image-receiving layer after drying became about 2 μm. The white PET support was a void-containing plastic support of a laminate (total thickness: 130 μm, specific gravity: 0.8) comprising a void-containing polyethylene terephthalate layer (thickness: 116 μm, void ratio: 20%), and titanium oxide-containing polyethylene terephthalate layers provided on both sides thereof (thickness: 7 μm, titanium oxide content: 2%). The preparedmaterial was wound ina roll, stored at room temperature for one week, then used in the image recording by laser beam as shown below.
The obtained image-receiving layer had the following physical properties.
The surface roughness Ra is preferably from 0.4 to 0.01 μm, and specifically 0.02 μm.
The undulation of the surface of the image-receiving layer is preferably 2 μm or less, and specifically 1.2 μm.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 0.8 mm Hg (approximately 0.11 kPa).
The coefficient of static friction of the surface of the image-receiving layer is preferably 0.8 or less, and specifically 0.37.
The surface energy was 29 mJ/m2, and the contact angle with water was 85.0°.
Formation of Transferred Image
A transferred image to actual paper was obtained by the image-forming system shown in FIG. 4 according to the image-forming sequence of the system and the transfer method of the system including the color matching process as described above, and Luxel FINALPROOF 5600 (manufactured by Fuji Photo Film Co. Ltd.) was used as the recording unit.
The above-prepared image-receiving sheet (56 cm×79 cm) was wound around the rotary drum having a diameter of 38 cm provided with vacuum suction holes having a diameter of 1 mm (surface density of 1 hole in the area of 3 cm×8 cm) and vacuum sucked. Subsequently, the above heat transfer sheet K (black) cut into a size of 61 cm×84 cm was superposed on the image-receiving sheet so as to deviate uniformly, squeezed by a squeeze roller, and adhered and laminated so that air was sucked by suction holes. The degree of pressure reduction in the state of suction holes being covered was −150 mm Hg per 1 atm (approximately 81.13 kPa). The drum was rotated and semiconductor laser beams of the wavelength of 808 nm were condensed from the outside on the surface of the laminate on the drum so that the laser beams became a spot of a diameter of 7 μm on the surface of the light-to-heat converting layer, and laser image recording (line image) was performed on the laminate bymoving the laser beam at a right angle (by-scanning) to the rotary direction of the drum (main scanning direction). The condition of laser irradiation was as follows. The laser beams used in the example was multi-beam two dimensional array comprising five rows along the main scanning direction and three rows along the by-scanning direction forming a parallelogram.

    
    
        Laser power: 110 mW
        Drum rotation speed: 500 rpm
        By-scanning pitch: 6.35 μm
        Circumferential temperature and humidity conditions:
        
            Three conditions of 20° C. 40% (in case of using FIG. 15), 23° C. 50%, 26° C. 65%
        
        
    
    


The diameter of exposure drum is preferably 360 mm or more, and specifically 380 mm was used.
The size of the image was 515 mm×728 mm, and the definition was 2,600 dpi.
The laminate finished laser recording was detached from the drum and heat transfer sheet K was released from the image-receiving sheet manually. It was confirmed that only the irradiated area of the image-forming layer in heat transfer sheet K had been transferred from heat transfer sheet K to the image-receiving sheet.
In the same manner as above, the image was transferred to the image-receiving sheet from each of heat transfer sheet Y, heat transfer sheet M and heat transfer sheet C. The transferred images of four colors were further transferred to a recording paper and a multicolor image was formed. Even when high energy laser recording was performed under different temperature humidity conditions with laser beams of multi-beam two dimensional array, a multicolor image having excellent image quality and stable transfer density could be formed.
In the stage of transfer to the actual paper, the heat transfer unit having a dynamic friction coefficient against insert platform of polyethylene terephthalate of from 0.1 to 0.7 and traveling speed of from 15 to 50 mm/sec was used. The Vickers hardness of the material of the heat roller of the heat transfer unit is preferably from 10 to 100, and specifically the heat roller having Vickers hardness of 70 was used.
Every image obtained under three different surroundings of temperature humidity conditions was good.
The reflection optical density of each color of Y, M, C, K of the image transferred to Tokuryo art paper as a actual paper was measured in Y, M, C, K mode with a densitometer X-rite 938 (manufactured by X-rite Co.).
The reflection optical density, reflection optical density/image-forming layer thickness of each color are shown in Table 1 below.









TABLE 1






Reflection
Reflection Optical



Optical
Density/Layer Thickness


Color
Density
of Image-Forming Layer







Y
1.01
2.40


M
1.51
3.97


C
1.59
3.53


K
1.82
3.03









EXAMPLE 1-2
A transferred image was formed in the same manner as in Example 1-1 except for using Proof Setter Spectrum (manufactured by Creo Scitex Co.) as the recording unit.
REFERENCE EXAMPLES 1-1 to 1-2 AND EXAMPLE 1-3
Transferred images were formed in the same manner as in Example 1-1 except for using an approval material, Approval Digital Color Proofing Film (a sublimation type heat transfer material, manufactured by Eastman Kodak) in Reference Example 1-1, MATCH PRINT TM DIGITAL HALFTONE (an ablation type heat transfer material, manufactured by Imasion Co.) in Reference Example 1-2, and Color-Decision I material (a fusion type heat transfer material, manufactured by Konica Corp.) in Example 1-3, respectively, in place of the heat transfer sheet and the image-receiving sheet used in Example 1-1.
COMPARATIVE EXAMPLES 1-1 to 1-2
Transferred images were formed in the same manner as in Example 1-1 except for not performing the color matching process, in Comparative Example 1-1. Transferred images were formed in the same manner as in Example 1-3 except for not performing the color matching process, in Comparative Example 1-2.
The results obtained in the examples and the comparative examples are shown in Table 2 below.
The evaluation of each sample was performed visually according to the following criteria.

    o: Good
    _: A little insufficient
    x: Inferior











TABLE 2









Evaluation












Example
Line Width
Dot
Repeating
Reproduction
Quality of


No.
Reproducibility
Shape
Reproducibility
of Color
Letter





Example 1-1
1.05
∘
∘
∘
∘


Example 1-2
1.03
∘
∘
∘
∘


Reference
1.26
X
—
—
x


Example 1-1


Reference
1.23
X
—
∘
x


Example 1-2


Example 1-3
1.15
—
∘
∘
—


Comparative
1.05
∘
◯
X
◯


Example 1-1


Comparative
1.15
—
◯
X
—


Example 1-2









(1) Line Width Reproducibility

The two dimensional energy distribution of laser beam spot was integrated in the main scanning direction and the half value width a of the energy distribution in the by-scanning directions was taken, and the ratio of the line width b of the transferred image to the length 2a obtained by multiplying a by 2 (b/2a) was taken as the line width reproducibility.
(2) Dot Shape
As a result of comparison of the transferred images in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-2, the transferred images obtained by not performing the color matching process strikingly had a deteriorated color reproduction, and the recorded dot shapes of none of the Reference Examples were sharp. Since coloring materials are sublimated or sputtered in the laser sublimation method and the laser ablation method, the outline of dots becomes fuzzy. On the other hand, since molten substance flows in the laser heat fusion method, the outline of dots is not also clear. However, the samples of the present invention had an excellent color reproduction as the color matching process is performed, and as well as excellent color reproduction, the images exhibiting high image quality and sharp dots were obtained in the samples of the present invention.
The images obtained in Example 1-1 formed the dot image corresponding to print line number of definition of from 2,400 to 2,540 dpi. Since each dot is almost free of blur and chip and the shape is very sharp, dots of a wide range from highlight to shadow can be clearly formed as shown in FIGS. 5 to 12. Further, FIGS. 5 to 12 show the shapes of the dots of the image obtained in Example 1-1, and the center distance of dots is 125 μm. As a result, output of dots of high grade having the same definition as obtained by an image setter and CTP setter is possible, and dots and gradation which are excellent in approximation to the printed matter can be reproduced as shown in FIGS. 13 and 14. FIG. 13(b) shows the shapes of the dots of the image obtained in Example 1-1, and the center distance of dots is 125 μm. FIG. 13(a) is the enlarged view of the dots of the printed matter, and it can be confirmed that the dot shapes of FIG. 13(b) extremely resemble the dots of the printed matter in FIG. 13(a).
FIG. 14 shows the dot reproducibility of the image obtained in Example 1-1, wherein the axis of ordinate shows the dot area rate computed from the reflection density, and the axis of abscissa shows the dot area rate of the inputted signal. The dotted line shows the characteristic curve of the printed matter and the solid line shows the characteristic curve by Example 1.
The samples of the present invention also showed good results with definition of 2,600 dpi or higher.
(3) Repeating Reproducibility
Since the sample obtained in Example 1-1 is sharp in dot shape, dots corresponding to laser beam can be faithfully reproduced, further recording characteristics are hardly influenced by the surrounding temperature and humidity, and so repeating reproducibility stable in hue and density can be obtained as shown in FIGS. 15 and 16. FIG. 15 shows the repeating reproducibility of the image obtained in Example 1-1 in a*b* plane surface of L*a*b* color specification. FIG. 16 shows the repeating reproducibility of the image obtained in Example 1-1.
A transferred image to the actual paper was obtained in the same manner as in Example 1-1 using the image-forming material in Example 1-1 except for changing the temperature and humidity of the system to 19° C. 37% RH, 27° C. 37% RH, 19° C. 74% RH and 27° C. 74% RH, and the irradiated laser energy to 180 to 290 mJ/cm2, and the OD is shown in the axis of ordinate in FIG. 16. From FIG. 16, it can be seen that according to the present invention, a stable image can be obtained under wide surrounding temperature and humidity even if the laser energy load varies somewhat.
(4) Reproduction of Color
Pigments used in printing inks are used as the coloring material in the heat transfer sheet in Example 1-1, and since the heat transfer sheet is excellent in repeating reproducibility, highly minute CMS can be realized. The heat transfer image can almost coincide with the hues of the printed matters of Japan-Color, and the colors appear similarly to the printed matter even when light sources of illumination are changed, such as a fluorescent lamp, an incandescent lamp.
(5) Quality of Letter
Since the image obtained in Example 1-1 is sharp in dot shape, the fine line of a fine letter can be reproduced sharply as shown in FIGS. 17 and 18. FIG. 17 a positive image showing the letter quality of 2 points of the image obtained in Example 1-1, FIG. 18 a negative image showing the letter quality of 2 points of the image obtained in Example 1-1, and it can be seen that fine line of fine character is sharply reproduced both in FIG. 17 and in FIG. 18.
EXAMPLE 2-1
Preparation of Heat Transfer Sheet
Heat transfer sheets K (black), Y (yellow), M (magenta) and C (cyan) were prepared in the same manner as in Example 1-1 except for using each coating solution having the composition shown below.
Composition of Black Image-forming Layer Coating Solution
















The same pigment dispersion mother
185.7 parts 



solution as in Example 1-1



(composition 1/composition 2:



70/30 (parts))



Polyvinyl butyral
11.9 parts 



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Wax-based compound



Stearic acid amide (Newtron 2,
1.7 parts



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
3.4 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
3.4 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Rosin (KE-311, manufactured by
11.4 parts 



Arakawa Kagaku Co., Ltd.



components: resin acid 80-97%,



resin acid components:



abietic acid: 30 to 40%



neoabietic acid: 10 to 20%



dihydroabietic acid: 14%



tetrahydroabietic acid: 14%)



Surfactant (Megafac F-176PF,
2.1 parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



Inorganic pigment (MEK-ST,
7.1 parts



30% methyl ethyl ketone solution,



manufactured by Nissan Chemical



Industries, Ltd.)



n-Propyl alcohol
1,050 parts 



Methyl ethyl ketone
 295 parts 










It was found that the particles in the thus-obtained black image-forming layer coating solution had an average particle size of 0.25 μm, and the ratio of the particles having a particle size of 1 μm or more was 0.5% from the measurement by particle size distribution measuring apparatus of laser scattering system.
Composition of Yellow Image-forming Layer Coating Solution
















The same yellow pigment dispersion
 126 parts 



mother solution as in Example 1-1



(yellow pigment composition 1/yellow



pigment composition 2: 95/5 (parts))



Polyvinyl butyral
4.6 parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Wax-based compound



Stearic acid amide (Newtron 2,
0.7 parts



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
1.4 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
0.7 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
1.4 parts



(manufactured by Nippon Kasei



Co., Ltd.)



Nonionic surfactant
0.4 parts



(Chemistat 1100, manufactured by



Sanyo Chemical Industries, Co., Ltd.)



Rosin (KE-311, manufactured by
2.4 parts



Arakawa Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
0.8 parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
 793 parts 



Methyl ethyl ketone
 198 parts 










Composition of Magenta Image-forming Layer Coating Solution


















The same magenta pigment dispersion
163
parts



mother solution as in Example 1-1



(magenta pigment composition 1/magenta



pigment composition 2: 95/5 (parts))



Polyvinyl butyral
4.0
parts



(Denka Butyral #2000-L, manufactured



by Denki Kagaku Kogyo Co., Ltd.,



Vicut softening point: 57° C.)



Wax-based compound



Stearic acid amide (Newtron 2,
1.0
part



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
2.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Oleic acid amide (Diamid O-200,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Nonionic surfactant
0.7
parts



(Chemistat 1100, manufactured by



Sanyo Chemical Industries, Co., Ltd.)



Rosin (KE-311, manufactured by
4.6
parts



Arakawa Kagaku Co., Ltd.)



Pentaerythritol tetraacrylate
2.5
parts



(NK ester A-TMMT, manufactured by



Shin-Nakamura Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
1.3
parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
848
parts



Methyl ethyl ketone
246
parts










Composition of Cyan Image-forming Layer Coating Solution


















The same cyan pigment dispersion mother
118
parts



solution as in Example 1-1 (cyan pigment



composition 1/cyan pigment composition 2:



90/10 (parts))



Polyvinyl butyral
5.2
parts



(Eslec B BL-SH, manufactured by



Sekisui Chemical Industries, Ltd.)



Inorganic pigment (MEK-ST)
1.3
parts



Wax-based compound



Stearic acid amide (Newtron 2,
1.0
part



manufactured by Nippon Seika



Co., Ltd.)



Behenic acid amide (Diamid BM,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Lauric acid amide (Diamid Y,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Palmitic acid amide (Diamid KP,
1.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Erucic acid amide (Diamid L-200,
2.0
part



(manufactured by Nippon Kasei



Co., Ltd.)



Rosin (KE-311, manufactured by
2.8
parts



Arakawa Kagaku Co., Ltd.)



Pentaerythritol tetraacrylate
1.7
parts



(NK ester A-TMMT, manufactured by



Shin-Nakamura Kagaku Co., Ltd.)



Surfactant (Megafac F-176PF,
1.7
parts



solid content: 20%, manufactured by



Dainippon Chemicals and Ink Co., Ltd.)



n-Propyl alcohol
890
parts



Methyl ethyl ketone
247
parts










Each image-forming layer in the obtained heat transfer sheets K, Y, M and C had the following physical properties.
Physical Properties of Image-forming Layer in Heat Transfer Sheet K
The layer thickness was 0.60 μm.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 9.3 mm Hg (approximately 1.24 kPa).
The coefficient of static friction of the surface is preferably 0.8 or less, and specifically 0.08.
The surface energy was 29 mJ/m2, and the contact angle with water was 94.8°.
The deformation rate of the light-to-heat converting layer was 168% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Physical Properties of Image-forming Layer in Heat Transfer Sheet Y
The layer thickness was 0.42 μm.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 2.3 mm Hg (approximately 0.31 kPa).
The coefficient of static friction of the surface is preferably 0.8 or less, and specifically 0.1.
The surface energy was 24 mJ/m2, and the contact angle with water was 108.1°.
The deformation rate of the light-to-heat converting layer was 150% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Physical Properties of Image-forming Layer in Heat Transfer Sheet M
The layer thickness was 0.38 μm.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically, 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 3.5 mm Hg (approximately 0.47 kPa).
The coefficient of static friction of the surface is preferably 0.8 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.8°.
The deformation rate of the light-to-heat converting layer was 160% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Physical Properties of Image-forming Layer in Heat transfer Sheet C
The layer thickness was 0.45 μm.
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 7.0 mm Hg (approximately 0.93 kPa).
The coefficient of static friction of the surface is preferably 0.8 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.8°.
The deformation rate of the light-to-heat converting layer was 165% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Preparation of Image-receiving Sheet
An image-receiving sheet was formed in the same manner as in Example 1-1.
The heat transfer sheet obtained had the following physical properties.
The layer thickness was 2 μm.
The surface roughness Ra is preferably from 0.4 to 0.01 μm, and specifically 0.02 μm.
The undulation of the surface of the image-receiving layer is preferably 2 μm or less, and specifically 1.2 μm.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 0.8 mm Hg (approximately 0.11 kPa).
The coefficient of static friction of the surface of the image-receiving layer is preferably 0.8 or less, and specifically 0.37.
The surface energy was 29 mJ/m2, and the contact angle with water was 85.0°.
Formation of Transferred Image
A transferred image to actual paper was obtained by the image-forming system shown in FIG. 4 according to the image-forming sequence of the system and the transfer method of the system comprising the color matching process as described above, and Luxel FINALPROOF 5600 (manufactured by Fuji Photo Film Co., Ltd.) was used as the recording unit.
The above-prepared image-receiving sheet (56 cm×79 cm) was wound around the rotary drum having a diameter of 38 cm provided with vacuum suction holes having a diameter of 1 mm (surface density of 1 hole in the area of 3 cm×8 cm) and vacuum sucked. Subsequently, the above heat transfer sheet K (black) cut into a size of 61 cm×84 cm was superposed on the image-receiving sheet so as to deviate uniformly, squeezed by a squeeze roller, and adhered and laminated so that air was sucked by suction holes. The degree of pressure reduction in the state of suction holes being covered was −150 mm Hg per 1 atm (approximately 81.13 kPa). The drum was rotated and semiconductor laser beams of the wavelength of 808 nm were condensed from the outside on the surface of the laminate on the drum so that the laser beams became a spot of a diameter of 7 μm on the surface of the light-to-heat converting layer, and laser image recording (line image) was performed on the laminate by moving the laser beam at a right angle (by-scanning) to the rotary direction of the drum (main scanning direction) The condition of laser irradiation was as follows. The laser beams used in the example was multi-beam two dimensional array comprising five rows along the main scanning direction and three rows along the by-scanning direction forming a parallelogram.

    
    
        Laser power: 110 mW
        Drum rotation speed: 500 rpm
        By-scanning pitch: 6.35 μm
        Circumferential temperature and humidity conditions:
        
            Three conditions of 20° C. 40%, 23° C. 50%, 26° C. 65%
            The diameter of exposure drum is preferably 360 mm or more, and specifically 380 mm was used.
        
        
    
    


The size of the image was 515 mm×728 mm, and the definition was 2,600 dpi.
The laminate finished laser recording was detached from the drum and heat transfer sheet K was released from the image-receiving sheet manually. It was confirmed that only the irradiated area of the image-forming layer in heat transfer sheet K had been transferred from heat transfer sheet K to the image-receiving sheet.
In the same manner as above, the image was transferred to the image-receiving sheet from each of heat transfer sheet Y, heat transfer sheet M and heat transfer sheet C. The transferred images of four colors were further transferred to a recording paper and a multicolor image was formed. Even when high energy laser recording was performed under different temperature humidity conditions with laser beams of multi-beam two dimensional array, a multicolor image having excellent image quality and stable transfer density could be formed. The image-receiving sheet and an actual paper were superposed and carried to be wrapped round a heat roller with the image-receiving sheet outside at transferring to the actual paper. As a result, curling at laminator discharge port was 10 mm on average of four sides.
In the stage of transfer to the actual paper, the heat transfer unit having a dynamic friction coefficient against insert platform of polyethylene terephthalate of from 0.1 to 0.7 and traveling speed of from 15 to 50 mm/sec was used. The Vickers hardness of the material of the heat roller of the heat transfer unit is preferably from 10 to 100, and specifically the heat roller having Vickers hardness of 70 was used.
Every image obtained under three different surroundings of temperature humidity conditions was good.
The reflection optical density of each color of Y, M, C, K of the image transferred to Tokuryo art paper as the actual paper was measured in Y, M, C, K mode with a densitometer X-rite 938 (manufactured by X-rite Co.).
The reflection optical density, reflection optical density/image-forming layer thickness of each color are shown in Table 3 below.









TABLE 3






Reflection
Reflection Optical



Optical
Density/Layer Thickness


Color
Density
of Image-Forming Layer







Y
1.01
2.40


M
1.51
3.97


C
1.59
3.53


K
1.82
3.03









REFERENCE EXAMPLE 2-1
A transferred image was formed in the same manner as in Example 2-1 except that the image-receiving sheet and an actual paper were superposed and carried to be wrapped round a heat roller with the image-receiving sheet being inside at transferring to the actual paper. As a result, curling at laminator discharge port was tremendous and measurement was impossible. The results in Example 2-1 and Reference Example 1-1 are shown in Table 4 below.










TABLE 4








Curling at Laminator




Discharge Port at Transfer



Example No.
to Actual Paper









Example 2-1
10 mm



Reference
Measurement impossible



Example 1-1
(heavy curling)










As a measuring method of curling, the sheet is disposed on flat table so that the concave side of the curling sheet is disposed upward, and the lifting amount of the four corner in the sheet is measured and the average value thereof is evaluated as the curling.
When the other performances (Dot shape, Repeating reproducibility, Reproduction of color and Quality of letter) in Example 2-1 are evaluated, the results is excellent the same as in Example 1-1.
EXAMPLE 3-1
Preparation of Heat Transfer Sheet
Heat transfer sheets K (black), Y (yellow), M (magenta) and C (cyan) were prepared in the same manner as in Example 1-1 except for using each coating solution having the composition shown below.
Composition of Second Backing Layer Coating Solution
















Polyolefin (Chemipearl S-120,
3.0 parts



27 mass %, manufactured by Mitsui



Petrochemical Industries, Ltd.)



Antistatic agent (water dispersion
2.0 parts



of tin oxide-antimony oxide,



average particle size: 0.1 μm,



17 mass %)



Colloidal silica
2.0 parts



(Snowtex C, 20 mass %, manufactured by



Nissan Chemical Industries, Ltd.)



Epoxy resin (Denacol EX-614B,
0.3 parts



manufactured by Nagase Kasei Co., Ltd.)



Sodium polystyrenesulfonate
0.1 parts



Distilled water to make the total amount
 100 parts 










Each image-forming layer in the obtained heat transfer sheets K, Y, M and C had the following physical properties.
Physical Properties of Image-forming Layer in Heat Transfer Sheet K
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 9.3 mm Hg (approximately 1.24 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 29 mJ/m2, and the contact angle with water was 94.8°. The reflection optical density was 1.82, the layer thickness was 0.60 μm, and OD/layer thickness was 3.03.
The deformation rate of the light-to-heat converting layer was 168% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Physical Properties of Image-forming Layer in Heat Transfer Sheet Y
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 2.3 mm Hg (approximately 0.31 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.1.
The surface energy was 24 mJ/m2, and the contact angle with waterwas 108.1°. The reflection optical densitywas 1.01, the layer thickness was 0.42 μm, and OD/layer thickness was 2.40.
The deformation rate of the light-to-heat converting layer was 150% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm or more.
Physical Properties of Image-forming Layer in Heat Transfer Sheet M
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 3.5 mm Hg (approximately 0.47 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.80. The reflection optical density was 1.51, the layer thickness was 0.38 μm, and OD/layer thickness was 3.97.
The deformation rate of the light-to-heat converting layer was 160% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Physical Properties of Image-forming Layer in Heat Transfer Sheet C
The surface hardness of the image-forming layer is preferably 10 g or more when measured with a sapphire needle, and specifically 200 g or more.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 7.0 mm Hg (approximately 0.93 kPa).
The coefficient of static friction of the surface is preferably 0.2 or less, and specifically 0.08.
The surface energy was 25 mJ/m2, and the contact angle with water was 98.8°. The reflection optical density was 1.59, the layer thickness was 0.45 μm, and OD/layer thickness was 3.53.
The deformation rate of the light-to-heat converting layer was 165% when recording was performed at linear velocity of 1 m/sec or more with laser beams having light strength at exposure surface of 1,000 W/mm2 or more.
Preparation of Image-receiving Sheet
An image-receiving sheet was formed in the same manner as in Example 1-1.
The heat transfer sheet obtained had the following physical properties.
The layer thickness was 2 μm.
The surface roughness Ra is preferably from 0.4 to 0.01 μm, and specifically 0.02 μm.
The undulation of the surface of the image-receiving layer is preferably 2 μm or less, and specifically 1.2 μm.
The Smooster value of the surface of the image-receiving layer at 23° C., 55% RH is preferably from 0.5 to 50 mm Hg (approximately 0.0665 to 6.65 kPa), and specifically 0.8 mm Hg (approximately 0.11 kPa).
The coefficient of static friction of the surface of the image-receiving layer is preferably 0.8 or less, and specifically 0.37.
The surface energy was 29 mJ/m2, and the contact angle with water was 85.0°.
Formation of Transferred Image
A transferred image was formed in the same manner as in Example 1-1 except for using the each of thermal transfer sheets and the image-receiving sheet as described above. The transferring to the image-receiving sheet was performed in order of black, cyan, magenta and yellow.
The measuring method of reflection optical density and the results of measurement are described below.
The reflection optical density of each color of Y, M, C, K of the image transferred to Tokuryo art paper as the actual paper was measured in Y, M, C, K mode with a densitometer X-rite 938 (manufactured by X-rite Co.).
The reflection optical density, reflection optical density/image-forming layer thickness of each color are shown in Table 5 below.









TABLE 5






Reflection
Reflection Optical



Optical
Density/Layer Thickness


Color
Density
of Image-Forming Layer







Y
1.01
2.40


M
1.51
3.97


C
1.59
3.53


K
1.82
3.03









The evaluations of the image obtained according to the above system constitution was performed as follows.
(1) Measurement of Reflection Density (OD) of Black Image Area and Computation of Transfer Rate of Image
The image density of the transferred image obtained under each temperature and humidity condition was measured by Macbeth reflection densitometer RD-918 (W filter) using the heat transfer sheet K. Reflection density (OD) obtained are shown in Table 5 below.
The above heat transfer sheet K was transferred to an image-receiving sheet using a heat transfer unit and without laser recording, and the reflection density (OD) of the obtained black image measured according to the above method was 1.88. Image transferabilities of the heat transfer sheet K subjected to laser recording under temperature and humidity conditions of 18° C. 30% RH, 23° C. 50% RH and 26° C. 65% RH were respectively 98.4%, 96.8% and 96.3%.
Evaluation of Black Image Quality
Using the above heat transfer sheet K, the image qualities of the solid part and the line image part of a transferred image obtained under each temperature and humidity condition were observed with an optical microscope. The time lag in the solid part was not observed in every surrounding condition, definition of the line image was good, and transferred black image having less dependency on the surrounding condition could be obtained. The evaluation was performed visually according to the following criteria.
Solid Part


    o: Time lag in recording time and transfer failure were not observed.
    _: Time lag in recording time and transfer failure were observed partially.
    x: Time lag in recording time and transfer failure were observed all over the surface.

Line Image Part

    o: The edge of the line image was sharp and good definition was shown.
    o_: The edge of the line image was jagged slightly but bridging did not occur.
    _o: The edge of the line image was jagged but bridging did not occur.
    _: The edge of the line image was jagged and bridging occurred partially.
    x: Bridging occurred entirely.


A color image formed at surrounding temperature and humidity of 23° C. 50% RH was evaluated as follows. The results obtained are shown in Table 6 below.
(6) Evaluation of Hue of Black Area
The hue of black area of the color image transferred to a printing paper was visually evaluated according to the following three criteria.

    o: Even the areas transferred and superposed with other colors were neither yellowish nor reddish and good hue was obtained.
    _: The areas transferred and superposed with other colors were slightly yellowish and reddish but practicable.
    x: The areas transferred and superposed with other colors were yellowish and reddish and impracticable.


Good hue can be obtained in Example 3-1 and Reference Example 3-5 but the samples in Reference Examples 2-1 to 2-4 were not good.
(7) Evaluation of Blank Area
The white blank areas having a diameter of 1 mm or larger in the color image transferred to recording paper of a size of 515 mm×728 mm were counted.
When the other performances (Dot shape, Repeating reproducibility, Reproduction of color and Quality of letter) in Example 3-1 are evaluated, the results is excellent the same as in Example 1-1.
REFERENCE EXAMPLES 3-1 to 3-4
Reference Examples 3-1 to 3-4 were carried out in the same manner as in Example 3-1 except for changing the order of image formation as described in Table 6.
REFERENCE EXAMPLE 3-5
Reference Example 3-5 was carried out in the same manner as in Example 3-1 except for increasing the amounts of the pigments in yellow, magenta, cyan and black image-forming layers 0.5 times as much as those in Example 3-1. The optical density of each image-forming layer was adjusted to that in Example 3-1.
EXAMPLE 3-2
Example 3-2 was carried out in the same manner as in Example 3-1 using the same sample except for changing the image size to 594 mm×841 mm.
EXAMPLE 3-3
Example 3-3 was carried out in the same manner as in Example 3-1 using the same sample except for increasing the amounts of the pigments in the coloring layers 0.85 times as much as those in Example 3-1.
EXAMPLE 3-4
Example 3-4 was carried out in the same manner as in Example 3-1 using the same sample except for increasing the amounts of the pigments in the coloring layers 1.15 times as much as those in Example 3-1.
Color images were formed using the samples in Reference Examples 3-1 to 3-5 and Examples 3-2 to 3-4 at 23° C. 50% RH. Image quality, the hue of the black area and white blank area of each sample were evaluated. The results obtained are shown in Table 6 below.










TABLE 6







Example
Recording
OD/Layer Thickness
Contact Angle
















No.
Order
Yellow
Magenta
Cyan
Black
Yellow
Magenta
Cyan
Black





Example 3-1
K, C, M, Y
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-2
K, C, M, Y
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-3
K, C, M, Y
2.10
3.41
3.10
2.61
109.6
99.5
100.1 
97.6


Example 3-4
K, C, M, Y
2.71
4.32
3.95
3.39
106.2
96.5
96.8
92.2


Reference
Y, M, C, K
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-1


Reference
C, M, Y, K
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-2


Reference
M, Y, K, C
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-3


Reference
Y, K, C, M
2.40
3.97
3.53
3.03
108.1
98.8
98.8
94.8


Example 3-4


Reference
K, C, M, Y
0.79
1.58
1.19
1.15
101.2
88.1
91.5
82.6


Example 3-5












Results of Evaluation

















White







Blank



Example
Image Quality of
Image Quality of

Area



No.
Solid Part
Line Image
Hue
(number)







Example 3-1
∘
∘
∘
0



Example 3-2
∘
∘
∘
0



Example 3-3
∘
∘
∘
0



Example 3-4
∘
∘
∘
0



Reference
∘
∘
x
0



Example 3-1



Reference
∘
∘
x
0



Example 3-2



Reference
∘
∘
x
0



Example 3-3



Reference
∘
∘
x
0



Example 3-4



Reference
—
—
∘
0



Example 3-5










The materials for proof developed by the present inventors are based on the membrane transfer technique, and as a result for solving novel problems in laser transfer technique and further improving the image quality, the present inventors have developed a heat transfer recording system by laser irradiation for DDCP which comprises an image-forming material of B2 size or larger having performances of transfer to actual printing paper, reproduction of actual dots and of a pigment type, output driver, and high grade CMS software. Thus, a system capable of sufficiently exhibiting the performances of the materials of high definition could be realized according to the present invention. Specifically, the present invention can provide proof corresponding to CTP system and contract proof substituting analog style color proof. By this proof, color reproduction which coincides with printed matters and analog style color proofs for obtaining the approval of customers can be realized. The present invention can provide DDCP system by using the same pigment materials as used in the printing inks, effecting transfer to actual paper and generating no moire. The present invention can also provide a large sized high grade DDCP (A2/B2 or more) capable of transferring to actual paper, capable of using the same pigment materials as used in the printing inks, and showing high approximation to printed matters. The system of the present invention is a system adopting laser membrane transfer, using pigment coloring materials and capable of transferring to actual paper by real dot recording. According to the multicolor image-forming system according to the present invention, even when laser recording by high energy using multi-beam two dimensional array under different temperature humidity conditions is performed, an image having good image quality and stable transfer density can be formed on the image-receiving sheet.
Moreover, when an image-receiving sheet on which a multicolor image is formed is transferred to an actual paper, a pair of the image-receiving sheet and the actual paper discharged from a laminator can be prevented from curling with the image-receiving sheet being inside according to the present invention, thereby the deformation of the actual paper can be prevented.
While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.

## Claims

1. A method for forming a muiticolor image, which comprises:
preparing: an image-receiving sheet having a support and an image-receiving layer; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the at least four thermal transfer sheets has a different color; 
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; 
irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and 
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to record an image, in which the transferred image onto the image-receiving sheet has a resolution of 2400 dpi or more, 
wherein each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.50 or more, and 
a color matching process is performed before the image is recorded on the image-receiving sheet.

2. The method for forming a multicolor image as claimed in claim 1, wherein the color matching process comprises:
a color image data conversion process of converting a color image data for forming a printed matter to a color image data for a proof outputting unit; and 
a color·dot coincidence conversion process of performing a data conversion processing for making at least one of the color and dot of the printed matter coincide with at least one of the color and dot of the color image outputted from the proof outputting unit.

3. The method for forming a multicolor image as claimed in claim 2, wherein the color·dot coincidence conversion process comprises:
a converting process of converting contone data (continuous tone data) to raster data; 
a converting process of converting the received raster data according to four dimensional (black, cyan, magenta and yellow) table experimentally formed in advance so that the colors coincide with the colors of the printed matter formed based on the same raster data; and 
a finally converting process of converting to binary data for dots so that the dots coincide with the dots of the printed matter.

4. The method for forming a multicolor image as claimed in claim 1, wherein the at least four heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets.

5. The method for a multicolor image as claimed in claim 4, wherein the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.

6. The method for forming a multicolor image as claimed in claim 5, wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto an actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.

7. The method for forming a multicolor image as claimed in claim 4, wherein the at least four of yellow, magenta, cyan and black heat transfer sheets and the image-receiving sheet each is fed to a recording unit in a roll, and each of the sheets is drawn out and carried automatically in the recording unit.

8. The method for forming a multicolor image as claimed in claim 1, wherein the irradiated area of the image-forming layer with laser beam is transferred to the image-receiving sheet in a thin film.

9. The method for forming a multicolor image as claimed in claim 1, wherein the transferred image onto the image-receiving sheet has a resolution of 2,600 dpi or more.

10. The method for forming a multicolor image as claimed in claim 1, wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.80 or more.

11. The method for forming a multicolor image as claimed in claim 1, wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 2.50 or more.

12. The method for forming a multicolor image as claimed in claim 1, wherein the image-forming layer in each of the at least four thermal transfer sheets and the image-receiving layer in the image-receiving sheet each has a contact angle with water of from 7.0 to 120.00.

13. The method for forming a multicolor image as claimed in claim 1, wherein each of the at least four thermal transfer sheets has a recording area of the multicolor image being defined by a product of a length of 594 mm or more and width of 841 mm or more.

14. The method for forming a multicolor image as claimed in claim 1, wherein the ratio of an optical density (OD) of the image-forming layer in each of the at least four thermal transfer sheets to a thickness of the image-forming layer: OD/layer thickness (μm unit) is 1.80 or more and the image-receiving layer in the image-receiving sheet has a contact angle with water of 86° or less.

15. A method for forming a multicolor image, which comprises:
preparing: an image-receiving sheet having a support and an image-receiving layer; and at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the at least four thermal transfer sheets has a different color, and each of the at least four thermal transfer sheets has a recording area of a multicolor image being defined by a product of a length of 515 mm or more and width of 728 mm or more and each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.80 or more; 
superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; 
irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and 
transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to record an image, and 
transferring the image on the image-receiving layer to an actual printing paper, in which, when the image is transferred, the image-receiving sheet and the actual printing paper are disposed on a heat roller so that the image-receiving sheet is disposed over the actual printing paper.

16. The method for forming a multicolor image as claimed in claim 15, wherein the at least four heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets.

17. The method for a multicolor image as claimed in claim 16, wherein the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.

18. The method for forming a multicolor image as claimed in claim 17, wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto the actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.

19. The method for forming a multicolor image as claimed in claim 16, wherein the at least four of yellow, magenta, cyan and black heat transfer sheets and the image-receiving sheet each is fed to a recording unit in a roll, and each of the sheets is drawn out and carried automatically in the recording unit.

20. The method for forming a multicolor image as claimed in claim 15, wherein the irradiated area of the image-forming layer with laser beam is transferred to the image-receiving sheet in a thin film.

21. The method for forming a multicolor image as claimed in claim 15, wherein the transferred image onto the image-receiving sheet has a resolution of 2,600 dpi or more.

22. The method for forming a multicolor image as claimed in claim 15, wherein each of the image-forming layers in the at least four thermal transfer sheets has the ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 2.50 or more.

23. The method for forming a multicolor image as claimed in claim 15, wherein the image-forming layer in each of the at least four thermal transfer sheets and the image-receiving layer in the image-receiving sheet each has a contact angle with water of from 7.0 to 120.00.

24. The method for forming a multicolor image as claimed in claim 15, wherein each of the at least four thermal transfer sheets has a recording area of the multicolor image being defined by a product of a length of 594mm or more and width of 841 minor more.

25. The method for forming a multicolor image as claimed in claim 15, wherein the image-receiving layer in the image-receiving sheet has a contact angle with water of 86° or less.

26. A multicolor image-forming material comprising:
an image-receiving sheet having an image-receiving layer and a support; and 
at least four thermal transfer sheets each including a support, a light-to-heat converting layer and an image-forming layer, in which each of the thermal transfer sheets has a different color, 
wherein a multicolor image is formed by: superposing the image-forming layer in each of the at least four thermal transfer sheets on the image-receiving layer in the image-receiving sheet, in which the image-forming layer is opposed to the image-receiving layer; irradiating the image-forming layer in each of the at least four thermal transfer sheets with a laser beam; and transferring the irradiated area of the image-forming layer onto the image-receiving layer in the image-receiving sheet to form an image, and 
each of the image-forming layers in the at least four thermal transfer sheets has a ratio of an optical density (OD) to a layer thickness: OD/layer thickness (μm unit) of 1.50 or more, and 
the transferred image onto the image-receiving sheet has a resolution of 2,400 dpi or more, and 
a color matching process is performed before the image is recorded on the image-receiving sheet.

27. The multicolor image-forming material as claimed in claim 26, wherein each of the at least four thermal transfer sheets has a recording area of a multicolor image being defined by a product of a length of 515 mm or more and width of 728 win or more, and the image on the image-receiving layer is transferred to an actual printing paper, in which, when the image is transferred, the image-receiving sheet and the actual printing paper are disposed on a heat roller so that the image-receiving sheet is disposed over the actual printing paper.

28. The multicolor image-forming material as claimed in claim 26, wherein the at least four of heat transfer sheets comprises at least four of yellow, magenta, cyan and black heat transfer sheets, and the irradiated area of the image-forming layer in each of the at least four thermal transfer sheets is transferred onto the image-receiving layer in the image-receiving sheet in order of black, cyan, magenta and yellow.

29. The multicolor image-forming material as claimed in claim 28, wherein the irradiated area of the image-forming layer on the image-receiving sheet is transferred onto the actual printing paper in order of yellow, magenta, cyan and black from the side of the actual printing paper.