Radiation imagery chemistry: process – composition – or product th – Imaged product – Nonsilver image
Reexamination Certificate
2002-10-21
2004-02-17
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Nonsilver image
C430S941000, C430S964000, C430S201000, C503S227000, C428S447000, C428S532000
Reexamination Certificate
active
06692879
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermal transfer recording material and particularly to a thermal transfer image-receiving sheet which can yield images with high dyeability, is free from heat fusing to a thermal transfer sheet at the time of image formation, and has satisfactory separability from the thermal transfer sheet.
BACKGROUND ART
Various thermal transfer methods are known in the art. One of them is a method wherein sublimation-transferable dyes are provided as recording agents and are thermally transferred from a thermal transfer sheet comprising a substrate sheet, such as a polyester film, bearing thereon these dyes onto an object colorable with a sublimable dye, for example, an image-receiving sheet comprising a receptive layer provided on paper, a plastic film or the like to form various full-color images.
In this case, a thermal head in a printer is used as heating means, and a large number of color dots of three or four colors with regulated heat quantity are transferred onto the image-receiving sheet by heating in a very short time, whereby full color of an original is reproduced by multicolor dots.
Since colorants used are dyes which are very vivid and highly transparent, the formed images have excellent reproduction of intermediate colors and gradation and have high quality which is equal to images produced by conventional offset printing and gravure printing and is comparable to the quality of full-color photographic images.
What is important for effectively carrying out the thermal transfer method is the construction of the thermal transfer sheet, as well as the construction of the image-receiving sheet on which an image is to be formed. Regarding conventional image-receiving sheets, for example, Japanese Patent Laid-Open Nos. 169370/1982, 207250/1982, and 25793/1985 disclose resins for the receptive layer. Specifically, vinyl resins, such as polyvinyl chloride resins, polyvinyl butyral resins, acrylic resins, cellulosic resins, olefin resins, polystyrene resins, polyester resins, polycarbonate resins and the like are disclosed as resins for the formation of the receptive layer.
In recent years, an improvement in printing speed (high-speed printing), which can shorten printout time per sheet, and power saving (low energy) printing, which can be driven by batteries for portable convenience, have become demanded. A receptive layer formed of a vinyl chloride-vinyl acetate copolymer resin is preferred as the receptive layer for high-speed printing and low-energy printing, because satisfactory density can be provided and, in addition, at the time of thermal transfer, abnormal transfer such as fusing does not occur between the thermal transfer sheet and the thermal transfer image-receiving sheet. Environmental problems, however, have led to a demand for a reduction in or total abolition of the use of vinyl chloride-containing materials. Further, other conventional thermal transfer image-receiving sheets and thermal transfer sheets disadvantageously cannot provide satisfactory print density.
The adoption of a method wherein the amount of dyes added to a binder for holding dyes in the thermal transfer sheet is increased, a method wherein a large amount of a plasticizer is added to the receptive layer, or a method wherein thermal transfer is carried out at high energy or low speed, is considered effective for providing satisfactory print density.
Increasing the amount of dyes, however, causes migration of the dye to the backside of the thermal transfer sheet. This disadvantageously causes a lowering in print density with the elapse of time, contamination of the backside, and contamination of a thermal head which shortens the service life of the thermal head. Further, at the time of thermal transfer, fusing occurs between the thermal transfer sheet and the thermal transfer image-receiving sheet probably due to plasticization of the dye binder by the dye.
The addition of a large amount of a plasticizer to the receptive layer softens the resin constituting the receptive layer and thus can improve dyeability, but on the other hand, poses problems including that mere contact of the receptive layer with the dye layer at room temperature causes dyeing of the receptive layer, a problem called “smudge,” i.e., unfavorable dyeing by waste heat generated in printing; fusing between the receptive layer and the dye binder in the thermal transfer sheet is likely to occur in a region from halftone region to high density region and, in this case, a large noisy sound is produced in the separation of the thermal transfer image-receiving sheet from the thermal transfer sheet at the time of printing, and, in some cases, the receptive layer is completely fused to the thermal transfer sheet, and, consequently, normal printing cannot be carried out, that is, abnormal transfer occurs.
Further, the addition of the plasticizer poses a problem of a change with the elapse of time, for example, that the formed image blurs with the elapse of time and the sensitivity in printing varies depending upon an environment in which the image-receiving sheet before the formation of an image is stored, making it impossible to provide prints having stable color tone. High-energy printing or low-speed printing is contrary to the demand in recent years, and, further, the thermal transfer at high energy causes fusing between the thermal transfer sheet and the thermal transfer image-receiving sheet at the time of thermal transfer and consequently causes abnormal transfer.
A method for solving the problem of the plasticizer is to adopt a multilayer structure in the receptive layer wherein a plasticizer-containing layer is provided as the lower layer (substrate side). In this case, however, the dyeability of the upper layer (surface layer) is so small that, in the case of direct printing, the dye cannot be diffused into the lower layer and, thus, the print density is low. Further, due to the multilayer structure, the production of the image-receiving sheet is complicated, and, thus, the production cost is disadvantageously high.
Accordingly, in a first aspect, an object of the present invention is to solve the above problems of the prior art and to provide a thermal transfer image-receiving sheet which has dyeability high enough to realize high-speed printing and low-energy printing, permits a protective layer to be thermally transferred onto the formed image, can avoid heat fusing between the thermal transfer image-receiving sheet and a thermal transfer sheet at the time of image formation, and has satisfactory separability from the thermal transfer sheet.
In general, what is important for effectively carrying out the formation of an image by thermal transfer is the construction of the thermal transfer sheet for feeding colorants, as well as the construction of the image-receiving sheet for receiving colorants for the formation of an image.
Regarding conventional image-receiving sheets, as described above, for example, Japanese Patent Laid-Open Nos. 169370/1982, 207250/1982, and 25793/1985 disclose resins for the receptive layer. Specifically, vinyl resins, such as polyvinyl chloride resins, polyvinyl butyral resins, acrylic resins, cellulosic resins, olefin resins, polystyrene resins, polyester resins, polycarbonate resins and the like are disclosed as resins for the formation of the receptive layer. Release agents usable in the image-receiving sheet include various silicone release agents, fluoro release agents, waxes, and surfactants.
In recent years, a method for image formation wherein, after image formation, a proper protective layer is provided according to purposes, has been mainly used from the viewpoints of improving storage stability of prints, such as lightfastness and chemical resistance, and providing added values of practicality, design, and security, such as the impartation of writing quality to the surface of prints and the formation of a hologram layer. For this reason, the image-receiving sheet should have satisfactory separability high enough to avoid heat fusing to the dye
Ieshige Munenori
Kaida Hidemasa
Omata Takenori
Suzuki Shino
Yuki Masahiro
Dai Nippon Printing Co. Ltd.
Parkhurst & Wendel L.L.P.
Schilling Richard L.
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