Heat transfer image-receiving sheet

Abstract: The present invention relates to a transparent dye-receiving layer formed on the surface side of a transparent substrate sheet, wherein at least one side is provided with a light transmitting, colored detection mark.

Description: The present invention relates to a heat transfer image-receiving sheet used in combination with a heat transfer sheet. Among various heat transfer techniques so far known in the art, there is a sublimation type of transfer system wherein a sublimable dye as a recording material is carried on a substrate sheet such as paper or a plastic film to make a heat transfer sheet, which is in turn overlaid on a heat transfer sheet dyeable with a sublimable dye, for instance, a heat transfer sheet comprising paper or a plastic film having a dye-receiving layer on its surface to make various full-color image thereon. In such a system, the thermal head of a printer is used as heating means to transfer three-, four- or more-color dots onto the heat transfer image-receiving sheet by quick heating, thereby reproducing full-color images of manuscripts with said multicolor dots. When the heat transfer image-receiving sheet used with such a sublimation type of heat transfer system as mentioned above is required to form a light reflecting image, as is the case with generally available prints or photographs, it is formed of an opaque substrate sheet such as a paper or synthetic paper sheet having on its surface a dye-receiving layer of a resin capable of being well-dyed with a dye. When it is required to provide a light transmitting image which is used with an overhead projector (hereinafter OHP for short), etc., on the other hand, it is formed of a transparent sheet such as a polyester film having thereon such a dye-receiving layer as referred to above. When imaging is carried out with either one of such heat transfer image-receiving sheets, there is an increase in the temperature prevailing in the printer. This poses troubles or problems such as curling of the heat transfer image-receiving sheets or degradations of their slip properties and blocking resistance, which result in sheet jamming or multiple feeding of several sheets at one time. The curling problem may be solved by forming a curlproof layer of a suitable resin on the back side of the heat transfer image-receiving sheet. It is here noted that images obtained with the heat transfer techniques excel in clearness, color reproducibility and other factors and so are of high quality comparable to that of conventional photographic or printed images, because the colorant used is a dye. Especially when imaging is carried out with transparent films or sheets for OHPs, a transmission type of image of improved clearness and high resolution can advantageously be projected. The image-receiving sheet for OHPs is provided with a detection mark for positioning. However, conventional detection marks have been formed of black, white or silver inks, all having high shielding properties. As a result, an image projected on a screen becomes dull, since the detection mark throws a black shadow on the screen. Another problem with the image formed with OHPs is that an OHP film is so curled by the heat generated from a projector's light source that it is troublesome to handle and the projected image is distorted. EP-A-0 194 106, also filed by the applicant of the present invention, describes a thermal transfer sheet with a heat-resistant slipping layer and a heat transferable sheet with a receptive layer, whereby a detection mark can be provided on both sheets. Further the document discloses a heat transfer recording process which comprises reading of the detection marks for forming an image by use of these sheets. On page 38, lines 16 to 20 it is mentioned, that the detection marks may be provided with a transparent electroconductive substance. However, since the receiving sheets and detection marks disclosed in EP-A-0 194 106 are apparently opaque (see for example pages 33/34 where a white pigment is added) rather than transparent, this disclosure is in contrast to the features of the present invention. It is therefore an object of this invention to provide a transparent type of heat transfer image-receiving sheet which is free from the above-mentioned problems of the prior art and which provides an attractive image at the time of projection and is not curled in use. The above-mentioned object is achieved by the present invention. According to the present invention, there is provided a transparent type of heat transfer image-receiving sheet including a transparent substrate sheet having a transparent dye-receiving layer on the surface side, characterized in that said image-receiving sheet is provided on a part of at least one side with a light transmitting, colored detection mark. A transparent type of heat transfer image-receiving sheet for OHPs, etc. is provided on a part of at least one side with a light transmitting, colored detection mark, whereby said detection mark is projected in colors on a screen to prevent the projected image from becoming dull. By providing a curlproof layer, it is also possible to prevent curling of the image-receiving sheet by the heat emitted from a light source. Figs. 1 and 2 each are a sectional view of the heat transfer image-receiving sheet which embodies this invention. Figs. 3A, 3B, 3C, 3D, 3E and 3F each are a plan view of the heat transfer image-receiving sheet which embodies this invention. The present invention will now be explained in greater detail with reference to the preferred embodiments. As illustrated in Fig. 1 or 2, the heat transfer image-receiving sheet according to the present invention comprises a transparent substrate sheet 1, a dye-receiving layer 2 formed on the surface side of the substrate sheet 1 and a transparent detection mark 3 formed on at least one side of the substrate sheet 1. In a preferred embodiment, a curlproof layer 4 is provided on either one side of the substrate sheet 1. As is the case with conventional films for OHP (overhead projector), the transparent substrate sheet 1 used in this invention may be formed of a film or sheet of various plastics such as acetyl cellulose, polyolefin, polyvinyl chloride, polyethylene terephthalate, polystyrene, polymethacrylate and polycarbonate. Although not critical, these substrate sheets may generally have a thickness of about 50 to 200 µm for OHP purposes. Some of the substrate sheets as mentioned above are poor in the adhesion to the dye-receiving layer formed on the surface side thereof. In such cases, they should preferably be subjected on their surfaces to primer or corona discharge treatments. The dye-receiving layer 2 provided on the surface side of the substrate sheet 1 is to receive a sublimable dye coming from a heat transfer sheet and maintain the resulting image. The resins used to form the dye-receiving layer 2, for instance, may include polyolefinic resins such as polypropylene; halogenated vinyl resins such as polyvinyl chloride and polyvinylidene chloride; vinylic resins such as polyvinyl acetate and polyacryl ester; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polystyrene type resins; polyamide type resins; copolymeric resins such as copolymers of olefins such as ethylene and propylene with other vinyl monomers; ionomers; cellulosic resins such as cellulose diacetate; and polycarbonate. Particular preference is given to vinylic resins and polyester resins. The dye-receiving layer 2 of the heat transfer image-receiving sheet according to the present invention may be formed by coating on at least one major side of the substrate sheet a solution or dispersion in which the binder resin is dissolved or dispersed in a suitable organic solvent or water together with the required additives such as release agents, antioxidants and UV absorbers by suitable means such as gravure printing, screen printing or reverse roll coating using a gravure, followed by drying. The thus formed dye-receiving layer 2 may have any desired thickness, but is generally 1 to 50 µm in thickness. Such a dye-receiving layer should preferably be in a continuous film form, but may be formed into a discontinuous film with the use of a resin emulsion or dispersion. The present invention is primarily characterized in that the transparent type of heat transfer image-receiving sheet is provided on at least a part of its one major side with a light transmitting, colored detection mark 3. This detection mark 3 may be provided on either one major side of the heat transfer image-receiving sheet. As illustrated in Figs. 3A-3F, the detection mark 3 is generally provided on an edge of the transparent type of heat transfer image-receiving sheet, thereby achieving the alignment of the sheet with the surface of a projector's light source and enabling the projected image to be in correct alignment with a screen. In embodiments illustrated in Figs. 3A-3D, detection marks are provided on the side of each substrate sheet on which no dye-receiving layer is provided, whereas in embodiments in Figs. 3E and 3F, detection marks are provided on the surfaces of the dye-receiving layers. According to the present invention, the light transmitting detection mark 3, for instance, may be formed of an ink consisting of a dye solution or an ink with a transparent pigment dispersed in it. Alternatively, it may be formed by the heat transfer of a sublimable dye. This alternative embodiment is more preferred because, as illustrated in Fig. 3F, a detection mark 3 can be formed simultaneously with imaging. Preferred examples of the dye used to this end are an oil-soluble dye soluble in solvents, a disperse dye and a basic dye. Preferred examples of the transparent pigment, on the other hand, include a transparent pigment used for usual offset printing ink. The image-carrying light transmittance of each or the detection mark 3 is determined depending upon the concentration of the colorant used. According to the present invention, however, the image-carrying light transmittance is preferably in the range of 0.3 to 0.8. Difficulty would be encountered in the alignment of the projected image with a screen at below 0.3, whereas the detection mark becomes dim at above 0.8, casting a dark shadow on a screen. In accordance with a preferred embodiment of the present invention, a curlproof layer 4 of a less thermally expandable/shrinkable resin is provided on at least one side of the substrate sheet 1, as illustrated in Fig. 1 or 2, thereby providing an effective prevention of an OHP film from being curled by the heat emanating from a projector's light source during projection. Preferred examples of the less thermally expandable/shrinkable resin are acrylic, polyurethane, polycarbonate, vinylidene chloride, epoxy, polyamide and polyester resins. Some of these resins differ largely in thermal properties. Thus, the most preference is given to resins whose shrinkages upon heating are in the range of -1.0 to 1.5% as measured at 100°C for 10 minutes according to JIS-K-6734 and whose softening temperatures lie at 90°C or higher. By adding a filler to the resin, it is possible to impart good slip properties to the curlproof layer 4, when formed on the back side of the substrate 1 as shown in Fig. 2. Thus, the in-printer blocking and multiple feeding problems can be solved. The filler used may include plastic pigments of an increased transparency such as fluorine resin, polyamide resin, styrene resin, styrene/acrylic type of crosslinked resin, phenolic resin, urea resin, melamine resin, aryl resin, polyimide resin and benzoguanamine resin; and inorganic fillers of an increased transparency such as calcium carbonate, silica, clay, talc, titanium oxide, magnesium hydroxide and zinc oxide. Of these resins, preference is given to a resin having an increased heat resistance and a particle size of 0.5 to 30 µm. These fillers should be added to the resin in an amount sufficient to prevent a drop of the general transparency of the curlproof layer. In order to form the curlproof layer 4, such a resin as mentioned above is dissolved in a suitable organic solvent or dispersed in an organic solvent or water together with the necessary additives, thereby preparing a solution or dispersion. Then, the solution or dispersion is coated and dried on one side of the substrate sheet by suitable means such as gravure printing, screen printing or reverse roller coating with a gravure. In general, the thus formed slip layer has a thickness of about 1-10 µm. When the adhesion between the curlproof layer and the substrate sheet is not proper, it is preferred that the substrate sheet be previously provided on the side with a primer layer 5 made of resin such as polyurethane, polyester, acrylic or epoxy resin. According to the present invention, the image-receiving sheet may be wholly or partly colored with either a blue dye or a specific pigment in a specific manner. Such light transmitting bluing is not only effective in improving the storability of the image-receiving sheet but also greatly beneficial to making it easy to look at an image on a showing box, as is the case with roentgenography. In order to achieve such effects, it is preferred that the chromaticity value of the image-receiving sheet be such that it falls within a blue region the CIE system (CIE 1931) of color representation surrounded by the following three points: (x = 0.310, y = 0.316) (x = 0.285, y = 0.280) (x = 0.275, y = 0.320) Blue dyes so far known in the art may be used as the dyes for carrying out such dyeing. In consideration of heat stability, however, particular preference is given to anthraquinone type dyes. Use may also be made of organic and inorganic blue dyes such as phthalocyanine blue, cerulean blue and cobalt blue. To this end, at least one of the transparent substrate sheet, the transparent dye-receiving layer and the adhesive and curlproof layers laminated thereon additionally or if required may be blued. The heat transfer sheet used for carrying out heat transfer with the heat transfer image-receiving sheet according to the present invention includes a sublimable dye-containing layer on a polyester film. For the present invention, conventional heat transfer sheets known in the art may all be used as such. As heat energy applying means for heat transfer, conventional applicator means hitherto known in the art may be used. For instance, the desired object is successfully achievable by the application of a heat energy of about 5 to 100 mJ/mm 2 for a controlled recording time with recording hardware such as a thermal printer (e.g., Video Printer VY-100 made by Hitachi Co., Ltd.). In accordance with the present invention in which the colored, transparent detection mark is provided on a part of at least one side of the transparent type of heat transfer image-receiving sheet for OHP and other purposes, the projected image is allowed to look well, since the detection mark is projected in colors on a screen. Especially because the detection mark 3 is transparent, it may bear a graphic or symbolic title or caption written or marked in a black or white ink of high shielding properties. In this case, such characters, etc. may be projected in black on a screen against a colored background. Provision of the curlproof layer also makes it possible to prevent the film from being curled by the heat emanating from the projector's light source during projection. The present invention will now be explained more illustratively with reference to a number of examples and comparative examples in which, unless otherwise stated, the "part" and "%" are given by weight. Reference Example B1 A transparent polyethylene terephthalate film (of 100 µm in thickness; T-100 commercialized by Toray Industries, Inc.) was used as a substrate sheet. Next, the sheet was coated on one side with a coating solution having the following composition to a dry coverage of 5.0 g/m 2 by a bar coater, and was thereafter dried by a dryer and then in an oven of 80°C for 10 minutes to form a dye-receiving layer. Composition for Dye-Receiving Layer Polyester resin (Vylon 600 commercialized by Toyobo Co., Ltd.) 4.0 parts Vinyl chloride/vinyl acetate copolymer (#1000A by Denki Kagaku Kogyo K.K.) 6.0 parts Amino-modified silicone (X-22-3050C by The Shin-Etsu Chemical Co., Ltd.) 0.2 parts Epoxy-modified silicone (X-22-3000E by The Shin-Etsu Chemical Co., Ltd.) 0.2 parts Methyl ethyl ketone/toluene (at a weight ratio of 1:1) 89.6 parts With a bar coater, the aforesaid film was coated on the back side with a printer layer coating solution having the following composition to a dry coverage of 1.0 g/m 2 , followed by drying with a dryer. The resulting coating was further coated with a curlproof layer coating solution having the following composition to a dry coverage of 3.0 g/m 2 by means of a bar coater, and was thereafter dried with a dryer and then in an oven of 80°C for 10 minutes to form a curlproof layer. In this manner, a heat transfer image-receiving sheets according to this invention was obtained. Primer Layer Coating Composition Polyester polyol (Adcoat commercialized by Toyo Morton Co., Ltd.) 15.0 parts Methyl ethyl ketone/dioxane (at a weight ratio of 2:1) 85.0 parts Composition for Curlproof Layer Acrylic resin (BR-85 commercialized by Mitsubishi Rayon Co., Ltd.) 10.0 parts Filler (Orgasol 2002D by Nippon Rirusan K.K.) 0.1 part Methyl ethyl ketone/toluene (at a weight ratio of 1:1) 89.9 parts Example B1 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a transparent heat transfer image-receiving sheet according to this invention. Dye (C.I. Disperse Red 60) 1.0 part Binder (BR-85 commercialized by Mitsubishi Rayon Co., Ltd.) 5.0 parts Solvent (methyl ethyl ketone) 92.0 parts Example B2 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a transparent heat transfer image-receiving sheet according to this invention. Dye (C.I. Disperse Yellow 141) 0.5 parts Dye (C.I. Solvent Blue 63) 0.5 parts Binder (#1000A commercialized by Denki Kagaku Kogyo K.K.) 5.0 parts Solvent (methyl ethyl ketone and toluene) 91.0 parts Example B3 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a transparent heat transfer image-receiving sheet according to this invention. Dye (Phthalocyanine Blue) 3.0 parts Binder (BR-85 commercialized by Mitsubishi Rayon Co., Ltd.) 5.0 parts Solvent (methyl ethyl ketone and toluene) 92.0 parts Example B4 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a transparent heat transfer image-receiving sheet according to this invention. Pigment (Brilliant Carmine 6B) 1.5 parts Pigment (Pigment Yellow) 1.5 parts Binder (BR-85 commercialized by Mitsubishi Rayon Co., Ltd.) 5.0 parts Solvent (methyl ethyl ketone and toluene) 92.0 parts Comparative Example B1 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a comparative transparent heat transfer image-receiving sheet. Pigment (titanium oxide) 2.0 parts Binder (cellulose acetate L-70 commercialized by Daicel Chemical Industries, Ltd.) 5.0 parts Solvent (ethyl acetate) 93.0 parts Comparative Example B2 Such a detection mark as shown in Fig. 3A was provided on the back side of the transparent type of heat transfer image-receiving sheet of Ref. Ex. B1 with the following transparent ink, thereby obtaining a comparative transparent heat transfer image-receiving sheet. Pigment (carbon black) 2.0 parts Binder (cellulose acetate L-70 commercialized by Daicel Chemical Industries, Ltd.) 5.0 parts Solvent (ethyl acetate) 93.0 parts Usage Example B1 While the dye and dye-receiving layers were located in opposite relation, each of the heat transfer image-receiving sheets according to this invention and for the purpose of comparison was overlaid on a sublimation type of yellow heat transfer sheet (commercialized by Dai Nippon Printing Co., Ltd.). With a thermal sublimation transfer printer (VY-100 by Hitachi, Ltd.), a printing energy of 90 mJ/mm 2 was applied from the back side of the heat transfer sheet to the image-receiving sheet through the thermal head, followed by magenta and cyan printing to obtain a full-color image. The print was then projected through OHP hardware (Model 007 commercialized by Sumitomo 3M Co., Ltd.) on a white screen at a magnification of 3 for visually observing the projected detection mark and measuring the degree of curling of the image-receiving sheet at the time of projection. The results are reported in Table 1. Example B5 The heat transfer image-receiving sheet of Ref. Ex. B1 was used to form a full-color image in the same manner as in Usage Example B1. At the same time, such a detection mark as illustrated in Fig. 3F was printed in purple around the image. Estimation was made in the same manner as in Usage Example B1. Estimation (1) Color of Detection Mark: The projected mark was visually observed. (2) Transmission Density: The detection mark of the image-receiving sheet was measured with a transmission densitometer TD-904 (Macbeth Co., Ltd.). (3) Degree of Curling Each of the aforesaid image-receiving sheets was cut to an A4 size and then printed. The resulting print was horizontally placed on glass plate at a temperature of 45°C, and how much it was curled up at the four corners was measured. Estimation was made by averaging the four values. Sample Color of Detection Marks Color of Detection Marks at the time of projection Transmitting Density Degree of Curling Ex. B1 red red 0.68 5 mm Ex. B2 green green 0.58 ditto Ex. B3 blue blue 0.46 ditto Ex. B4 red red 0.60 ditto Ex. B5 purple purple 0.75 ditto Comp.Ex. B1 white black 0.30 ditto Comp.Ex. B2 black black 0.48 ditto Example C1 A 100 µm thick polyethylene terephthalate film was coated on one side with an adhesive layer coating solution (a-1) specified in Table 2 to a dry coverage of 1.0 µm, followed by drying. The resulting adhesive layer was further coated with a back layer coating solution (b-2) set out in Table 2 to a dry coverage of 1 µm, followed by drying. Then, a dye-receiving layer coating solution (c-2) was coated on the side of the film opposite to the back layer to a dry coverage of 5 µm, followed by drying. In this manner, an image-receiving sheet according to this invention was obtained. Examples C2 & C3 and Comparative Example C1 In place of the coated solutions employed in Example C1, the following coating solutions were used under otherwise similar conditions to those applied in Ex. C1. Example C2: (a-2), (b-1) and (c-2) Example C3: (a-2), (b-2) and (c-1) Comp. Ex. C1: (a-2), (b-2) and (c-2) Example C4 Added to 100 parts of polyethylene terephthalate were 0.03 parts of a dye (4), followed by heating and mixing at 290°C. Afterwards, the mixture was treated in known manners to obtain an unstretched film. This film was in turn stretched in the warp and weft directions, each at a stretching ratio of 3, and further thermally fixed at 220°C to obtain a blue polyester film of 100 µm in thickness. In the same manner as in Ex. C1, the coating solutions (a-2), (b-2) and (c-2) were coated on the polyester film to obtain an image-receiving sheet. Estimation (1) Chromaticity Value Transmitting spectra were measured through a spectrophotometer UV-3100 (commercialized by Shimadzu Corporation), and the values for x and y were found according to the standard CIE 1931 system of color representation. The x and y values are reported in Table 3. (2) Thermal Degradation Testing Color changes were visually observed before and after the samples were allowed to stand at 70°C for 300 hours. (3) Optical Degradation Testing Hue changes were visually observed before and after the samples were irradiated at a total dosage of 70 kJ/m 2 with a xenon fedeometer. x y Example C1 0.284 0.301 Example C2 0.280 0.295 Example C3 0.305 0.310 Example C4 0.293 0.307 Comp. Ex. C1 0.315 0.321 The image-receiving sheet according to Comp. Ex. C1 suffered a strong yellowing by heat and light, but the image-receiving sheets according to Examples C1-C4 did not substantially.

Claims: A heat transfer image-receiving sheet including a transparent dye-receiving layer formed on the surface side of a transparent substrate sheet, characterized in that it is provided on a part of at least one side with a light transmitting, colored detection mark. A heat transfer image=receiving sheet as recited in Claim 1, wherein said detection mark has a transmission density of 0.3 to 0.8. A heat transfer image-receiving sheet as recited in Claim 1 or 2, wherein said detection mark is formed of an ink containing a dye or transparent pigment. A heat transfer image-receiving sheet as recited in any one of Claims 1 to 3, wherein said detection mark is formed by the heat transfer of a sublimable dye. A heat transfer image-receiving sheet as recited in any one of Claims 1 to 4, wherein said substrate sheet is provided on either side with a curlproof layer formed of a less heat expandable/shrinkable resin. A heat transfer image-receiving sheet as recited in Claim 5, wherein said curlproof layer contains a filler, said filler accounting of 0.02 to 10.0% by weight of said curlproof layer. A heat transfer image-receiving sheet as recited in any one of Claims 1 to 6, which is colored by a blue dye or pigment. A heat transfer image-receiving sheet as recited in Claim 7, wherein the chromaticity value of said blued heat transfer image-receiving sheet lies in a region of the CIE 1931 system of color representation surrounded by the following three points: (x = 0.310, y = 0.316) (x = 0.285, y = 0.280) (x = 0.275, y = 0.320)

Inventors: EGUCHI HIROSHI, SUTO KENICHIRO, EGUCHI, HIROSHI, SUTO, KENICHIRO, EGUCHI, HIROSHI, C/O DAI NIPPON INSATSU K.K., SUTO, KENICHIRO, C/O DAI NIPPON INSATSU K.K.
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON INSATSU KABUSHIKI KAISHA
Application year: 1990
Main classification: B41M5
IPC codes: B41M5