Thermal transfer method and apparatus therefor

Abstract: There is provided a receptor layer transfer sheet which is capable of providing images of high quality on a transfer receiving material having an unsmooth surface, even when it is used in combination with a conventional thermal transfer material. There is also provided a thermal transfer sheet which is capable of providing images of high quality on a transfer receiving material having an unsmooth surface. There is further provided a thermal transfer method and a thermal transfer apparatus which are capable of providing images of high quality and do not require a special detection mark provided in (or on) a thermal transfer sheet to be used in combination therewith.

Description: The present invention relates to a thermal transfer method and a thermal transfer apparatus to be used therein. According to the present invention, it is possible to form gradation images such as photographic images together with words and marks on ready made transfer receiving materials such as name cards, postcards, leaflets, curriculum vitaes, resumes, identification cards, licenses, commuter passes, membership cards, passports, notebooks and coupon tickets. Heretofore, various thermal transfer methods are known. Among these, there has been proposed a method wherein a sublimable dye (or subliming dye) is used as a recording agent, and is carried on a substrate sheet such as paper and plastic film to obtain a thermal transfer sheet, and various full colour images are formed on a transfer receiving material such as paper and plastic film having thereon a dye receptor layer by using the resultant thermal transfer sheet. In such a case, a thermal head of a printer is used as heating means so that a large number of colour dots of three or four colours are transferred to the transfer receiving material under heating in a very short period of time. As a result, a full colour image of an original is reproduced by using the multi-colour colour dots. The thus formed images are very clear and are excellent in transparency since the dyes are used therein as a colourant. Accordingly, these images are excellent in half tone reproducibility and gradation characteristic and are substantially the same as the images formed by the conventional offset printing and gravure printing. Further, when the above image forming method is used, there can be formed images of high quality which are comparable to full colour photographic images. In the above image forming method, however, the transfer receiving material on which the above mentioned images can be formed is restricted to a plastic sheet having a dyeing property (or dyeability) which is dyeable by a dye, paper on which a dye receptor layer has been formed in advance, etc. Accordingly, the above mentioned method cannot provide an image directly on ordinary plain paper, etc. As a matter of course, when a receptor layer is formed on the surface of ordinary plain paper, the resultant paper can be subjected to such image formation. However, such a method generally requires a high cost, and it is difficult to apply this method to generally ready made transfer receiving materials such as postcards, memo papers, letter papers and writing pads. As a measure of solving such a problem, there is known a receptor layer transfer sheet which is capable of easily providing a dye receptor layer on an essential part (i.e. a part on which an image is to be formed) of the ready made transfer receiving material such as paper when an image is intended to be formed on the ready made transfer receiving material. As such a receptor layer transfer sheet, there has been proposed one comprising a substrate sheet having a releasability and a resin layer disposed thereon for forming a receptor layer, e.g. as disclosed in Japanese Laid Open Patent Application (JP-A, KOKAI) No. 264994/1987. As a measure for further simplifying the above operation, there has been proposed a thermal transfer sheet such that dye layers of yellow, magenta and cyan (and optionally black, as desired) are sequentially formed on the surface of a continuous substrate film, and then a transfer receptor layer is formed on the same surface of the substrate film (Japanese Laid Open Patent Application Nos. 84281/1986 and 297184/1987). When such a thermal transfer sheet is used, the receptor layer is first transferred to a transfer receiving material, and then the dye layer of the respective colours are transferred to the receptor layer to form a full colour image. An example of this is to be found in EP-A-0333873. According to the present invention, there is provided a thermal transfer method, comprising: superposing a thermal transfer sheet on an image receiving sheet in a thermal transfer apparatus, and supplying heat to the thermal transfer sheet from the back surface side thereof, thereby to transfer a dye from the thermal transfer sheet to the image receiving sheet, the thermal transfer sheet comprising a continuous substrate sheet, and a dye layer of at least one colour and at least one transferable layer which are sequentially disposed on one side surface of the continuous substrate sheet, the thermal transfer sheet being white and comprising a dye receptor layer; wherein detection light is supplied from a light source provided in the thermal transfer apparatus to the thermal transfer sheet, and the resultant reflection or interception of the detection light based on the transferable layer is detected, thereby to detect the presence of the transferable layer. There is also provided a thermal transfer apparatus, comprising: an image receiving sheet, means for conveying the image receiving sheet, a thermal transfer sheet, means for conveying the thermal transfer sheet, heat application means for superposing the thermal transfer sheet on the image receiving sheet and supplying heat to the thermal transfer sheet from the back surface side therof, thereby to transfer a dye from the thermal transfer sheet to the image receiving sheet, and detection means comprising a light source and a light receptor, the thermal transfer sheet comprising a continuous substrate sheet, and a dye layer of at least one colour and at least one transferable layer which are sequentially disposed on one side surface of the continuous substrate sheet; the transferable layer being white and comprising a dye receptor layer; wherein detection light is supplied from the light source to the thermal transfer sheet and the resultant reflection or interception of the detection light based on the transferable layer is detected, thereby to detect the presence of the transferable layer. According to the above invention, the transferable layer comprising the dye receptor layer may function as a detection mark, and it is not necessary to form a special detection mark in the thermal transfer sheet and not necessary to provide a printing unit for printing a detection mark at production line of the thermal transfer sheet. Objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. Figure 1 is a schematic sectional view showing a thermal transfer sheet for use in the present invention. Figures 2 and 3 are schematic sectional views showing the thermal transfer method according to the present invention. Figure 1 is a schematic sectional view showing a thermal transfer sheet for use in the present invention. Figures 2 and 3 are schematic sectional views showing the thermal transfer method according to the present invention. Referring to Figure 1, the thermal transfer sheet 110 in this embodiment comprises a substrate sheet 111 and dye layers 112 of three colours (yellow layer 112Y, magenta layer 112M, and cyan layer 112C), a dye receptor layer 113 and a transferable protection layer 114 which are sequentially disposed on one surface side of the substrate sheet 111. The thermal transfer sheet 110 is characterised in that the dye receptor layer 113 is caused to be white and opaque. More specifically, the dye receptor layer 113 is opaque to such an extent that it may provide a substantial difference in light transmissivity with the dye layer 112 and the transfer protection layer 114. In such a case, the white pigment may preferably be added to the receptor layer 113 in an amount of 1 to 200 wt.parts with respect to 100 wt.parts of the resin constituting the receptor layer 113. Further, it is preferred to dispose an adhesive layer on the surface of the above receptor layer 113 so as to improve the transferability thereof. It is also possible to dispose an intermediate layer between the above receptor layer 113 and the above adhesive layer. It is also possible to add the white pigment to the above adhesive layer and/or the intermediate layer, and in such a case, the receptor layer 113 does not necessarily contain the white pigment. Next, there will be described a thermal transfer method using the thermal transfer sheet 110 shown in Figure 1, with reference to Figures 2 and 3. Referring to Figure 2, when the thermal transfer sheet shown in Figure 1 is loaded to a printer as shown in Figure 2 which has a floodlight device 116 and a light receiving sensor 117 on one side so as to effect thermal transfer operation, a detection light 118 ejected from the floodlight device 116 is reflected by a portion of the receptor layer 113, and the resultant reflection light is received by the light receiving sensor 117. Since the position other than the receptor layer, i.e., the dye layer 112 and the protection layer 114 are substantially light transmissive (or transparent), the detection light 118 is not detected by the light receiving sensor 117 with respect to these layers. Since the dye layers are formed according to a predetermined sequence of, e.g. yellow, magenta and cyan, when the light receiving sensor 117 detects the detection light, the printer recognises the presence of the dye receptor layer 113. Accordingly, in such a case, the printer can continuously and sequentially subject the layers of the yellow, magenta and cyan colours (and the protection layer) to the printing operation. Then, the printer again detects the receptor layer and the above steps are repeated. Figure 3 is a view showing another preferred embodiment wherein the floodlight device 116 and the light receiving sensor 117 are disposed opposite to each other by the medium of the thermal transfer sheet 110. In this embodiment, the same operations as described above with reference to Figure 2 are effected except that the receptor layer 113 is detected when the light receiving sheet 117 does not detect the detection light 118, whereby similar effects are provided. Apart from the features described above (including that the thermal transfer sheet to be loaded thereto has the specific structure as described hereinabove) the apparatus to be used in the present invention may be the same as those known in the prior art. For example, such an apparatus may be a thermal transfer apparatus which comprises an image receiving sheet, means for conveying the image receiving sheet, means for conveying the thermal transfer sheet, means for applying heat to the thermal transfer sheet and detection means comprising the floodlight device and the light receiving device. The transfer receiving material to which the transferable layer comprising the receptor layer is to be transferred by using the receptor layer transfer sheet as described hereinabove should not particularly be restricted. For example, specific examples of such a transfer receiving material may include any of various sheets such as plain paper, wood free paper, tracing paper and plastic film. The shape or form of the transfer receiving material may be any of various forms such as cards, postcards, passports, letter papers, writing papers, notepapers and catalogues. Particularly, the present invention is applicable to plain papers or rough papers having rough surface texture. The receptor layer may be transferred by use of any of various heating and pressing means which are capable of heating the receptor layer or adhesive layer so as to activate these layers. Specific examples of such heating and pressing means may include: general printers equipped with a thermal head for thermal transfer operation, hot stampers for transferable film or foil, and hot rollers. When thermal transfer operation is effected by using the transfer receiving material to which the receptor layer has been transferred, the means for applying heat energy to be used for the thermal transfer operation may be any of various known heat energy application means. For example, when a recording time is controlled by using a recording apparatus such as a thermal printer (e.g. Video printer VY 100, mfd. by Hitachi K.K.), so as to provide a heat energy of about 5 to 100 mJ/mm 2 , a desired image may be formed.

Claims: A thermal transfer method, comprising: superposing a thermal transfer sheet (110) on an image receiving sheet in a thermal transfer apparatus; and supplying heat to the thermal transfer sheet (110) from the back surface side thereof, thereby to transfer a dye from the thermal transfer sheet to the image receiving sheet, the thermal transfer sheet comprising a continuous substrate sheet (111), and a dye layer (112) of at least one colour (112Y, 112M, 112C) and at least one transferable layer (114) which are sequentially disposed on one side surface of the continuous substrate sheet (111), the transferable layer being white and comprising a dye receptor layer (113); wherein detection light is supplied from a light source (116) provided in the thermal transfer apparatus to the thermal transfer sheet, and the resultant reflection or interception of the detection light based on the transferable layer is detected (117), thereby to detect the presence of the transferable layer. A thermal transfer method according to Claim 1, wherein the transferable layer comprises the dye receptor layer (113) and an adhesive layer and optionally disposed therebetween an intermediate layer, and at least one layer selected from the adhesive layer, the intermediate layer and the dye receptor layer is white. A thermal transfer method according to Claim 1, or Claim 2, wherein the thermal transfer sheet comprises a white detection mark on the one side surface of the continuous substrate sheet. A thermal transfer method according to any of Claims 1 to 3, wherein the transferable layer is transferred to the image receiving sheet several times so as to provide a superposition of the transferable layers in advance of the thermal transfer of the dye. A thermal transfer apparatus, comprising: an image receiving sheet; means for conveying the image receiving sheet; a thermal transfer sheet (110); means for conveying the thermal transfer sheet; heat application means for superposing the thermal transfer sheet (110) on the image receiving sheet and supplying heat to the thermal transfer sheet from the back surface side thereof, thereby to transfer a dye from the thermal transfer sheet (110) to the image receiving sheet; and detection means comprising a light source (116) and a light receptor (117), the thermal transfer sheet (110) comprising a continuous substrate sheet (111), and a dye layer (112) of at least one colour (112Y, 112M, 112C) and at least one transferable layer (114) which are sequentially disposed on one side surface of the continuous substrate sheet, the transferable layer being white and comprising a dye receptor layer (113); wherein detection light is supplied from the light source (116) to the thermal transfer sheet, and the resultant reflection or interception of the detection light based on the transferable layer is detected, thereby to detect the presence of the transferable layer.

Inventors: ASAJIMA MIKIO, OSHIMA KATSUYUKI, TAKAHARA HIDETAKE, UENO TAKESHI, YAMAUCHI MINEO, ASAJIMA, MIKIO, OSHIMA, KATSUYUKI, TAKAHARA, HIDETAKE, UENO, TAKESHI, YAMAUCHI, MINEO, Asajima, Mikio, c/o Dai Nippon Print. Co., Ltd., Oshima, Katsuyuki, c/o Dai Nippon Print. Co., Ltd., Takahara, Hidetake, c/o Dai Nippon Print. Co., Ltd, Ueno, Takeshi, c/o Dai Nippon Print. Co., Ltd., Yamauchi, Mineo, c/o Dai Nippon Print. Co., Ltd.
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON PRINTING CO., LTD.
Application year: 1991
Main classification: B41M5
IPC codes: B41M5, B41J2