Stock material or miscellaneous articles – Thermal transfer donor – Specialized non-transferable layer on support
Reexamination Certificate
2001-10-24
2004-01-20
Hess, B. Hamilton (Department: 1774)
Stock material or miscellaneous articles
Thermal transfer donor
Specialized non-transferable layer on support
C428S032810
Reexamination Certificate
active
06680089
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermal transfer sheet for use in a multicolor image formation method of forming a high-resolution full color image using laser light. More specifically, the present invention relates to a thermal transfer sheet which can be used in a multicolor image formation method useful in the manufacture of a color proof (DDCP (direct digital color proof)) or a mask image in the printing field.
BACKGROUND OF THE INVENTION
In the field of graphic art, an image is printed on a printing plate using a set of color-separation films prepared from a color original by using lithographic films. In general, a color proof is manufactured from the color-separation films before the main printing (i.e., actual printing operation) so as to check on errors in the color separation process or whether color correction or the like is necessary. The color proof is demanded to have capabilities such as realization of high resolution for enabling the formation of a middle tone image with high reproducibility, and high process stability. Furthermore, in order to obtain a color proof approximated to an actual printed matter, the materials used for the actual printed matter are preferably used for the materials of the color proof, for example, the substrate is preferably the printing paper and the coloring material is preferably the pigment. With respect to the method for manufacturing the color proof, a dry process of using no developer solution is highly demanded.
For manufacturing the color proof by a dry process, a recording system of manufacturing a color proof directly from digital signals has been developed accompanying the recent widespread of an electronized system in the pre-printing process (pre-press field). This electronized system is developed particularly for the purpose of manufacturing a high-quality color proof and by this system, a halftone image of 150 lines/inch or more is generally reproduced. For recording a high-quality proof from digital signals, laser light capable of modulating by the digital signals and sharply focusing the recording light is used as the recording head. Accordingly, the recording material used with the laser is required to exhibit high recording sensitivity to the laser light and high resolution for enabling the reproduction of high definition halftone dots.
With respect to the recording material for use in the transfer image formation method utilizing laser light, a heat-fusion transfer sheet is known, where a light-to-heat conversion layer capable of generating heat upon absorption of the laser light and an image forming layer containing a pigment dispersed in a heat-fusible component such as wax or binder are provided on a support in this order (see, JP-A-5-58045 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). According to the image formation method using this recording material, heat is generated in a region irradiated with the laser light of the light-to-heat conversion layer and the image forming layer corresponding to the region is fused by the heat and transferred to an image receiving sheet disposed on the transfer sheet, whereby a transfer image is formed on the image receiving sheet.
JP-A-6-219052 discloses a thermal transfer sheet where a light-to-heat conversion layer containing a light-to-heat conversion substance, a very thin (0.03 to 0.3 &mgr;m) thermal releasing layer (i.e., thermal peeling layer) and an image forming layer containing a coloring material are disposed in this order on a support. In this thermal transfer sheet, upon irradiation with laser light, the bonding strength between the image forming layer and the light-to-heat conversion layer bonded with an intervention of the thermal releasing layer is diminished and a high definition image is formed on an image receiving sheet stacked and disposed on the thermal transfer sheet. This image formation method utilizes so-called “ablation”, more specifically, a phenomenon such that a part of the thermal releasing layer in the region irradiated with the laser light is decomposed and vaporized and thereby the bonding strength between the image forming layer and the light-to-heat conversion layer is diminished in that region, as a result, the image forming layer in this region is transferred to an image receiving sheet stacked on the thermal transfer sheet.
The above-described image formation methods are advantageous in that a printing paper having provided thereon an image receiving layer (adhesive layer) can be used as the image receiving sheet material and a multicolor image can be easily obtained by sequentially transferring images of different colors to the image receiving sheet. In particular, the image formation method using ablation is advantageous in that a high definition image can be easily obtained and therefore, this method is useful for the manufacture of a color proof (DDCP (direct digital color proof)) or a high definition mask image.
In the transfer image formation method, the light-to-heat conversion layer reaches a high temperature upon irradiation of laser light and for improving the thermal resistance of the light-to-heat conversion layer, 1) a thermal transfer recording material using a resin having a Tg of 100° C. or more for the light-to-heat conversion layer (see, JP-A-11-348438), 2) a thermal transfer recording material using a resin having a thermal decomposition temperature of 360° C. or more (see, JP-A08-267916), 3) a thermal transfer recording layer using a crosslinked resin for the light-to-heat conversion layer (see, JP-A-2000-033780) and the like have been proposed. However, these thermal transfer recording layers using such a resin for the light-to-heat conversion layer have a limit in the elevation of sensitivity.
In particular, when high adhesive strength is present between the image forming layer and the underlying layer thereof of the thermal transfer sheet, the separation (i.e., peeling) from the underlying layer cannot be easily attained at the transfer for forming a transfer image on an image receiving sheet and this incurs not only insufficient sensitivity of the transferred image but also easy occurrence of layer fogging.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the above-described problems in conventional techniques and provide a thermal transfer sheet which is not affected by the illumination light source even in comparison with the pigment coloring material or printed matter and upon transfer of the coloring material thin film, ensures excellent sharpness of halftone dots, good sensitivity, reduced layer fogging and very stable transfer releasability.
In the CTP (computer to plate) times, a film-less processing is used and a contract proof taking the place of proof print or color art is necessary. For attaining acknowledgement of users, color reproducibility agreeing with the printed matter or color art is required and in order to meet this requirement, a DDCP system using a coloring material of the same pigment as the printing ink, enabling transfer to the printing paper and being free of moire and the like has been developed. The target is a large-size (A2/B2) digital direct color proof system enabling transfer to the printing paper, using a coloring material of the same pigment as the printing ink and ensuring high approximation to the printed matter. The thermal transfer sheet of the present invention is mainly used in the method where a laser thin film thermal transfer system is employed, a pigment coloring material is used and transfer to the printing paper can be attained by performing actual halftone recording.
As a result of various investigations on the prevention of layer fogging or elevation of sensitivity of the thermal transfer recording material, the present inventors have found that when binders each having a solubility parameter (SP value) falling within a specific range are used in combination and contained in respective layers of the thermal transfer sheet, an excellent effect can be obtained in the p
Miyake Kazuhito
Yamamoto Mitsuru
Fuji Photo Film Co. , Ltd.
Hess B. Hamilton
Sughrue & Mion, PLLC
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