Thermal transfer image receiving sheet

Abstract: A thermal transfer image receiving sheet comprising a substrate sheet and a dye receptor layer provided on at least one side surface of the susbtrate sheet, wherein the substrate sheet is a paper substrate sheet having a basis weight in the range of 60 to 120 g/m 2 . A thermal transfer image sheet of this type can be easily folded and filed and has excellent texture characteristics and is obtainable at low cost.

Description: The present invention relates to a thermal transfer image receiving sheet, more particularly to a thermal transfer image receiving sheet capable of forming an image of high density and high resolution. Various thermal transfer methods have been heretofore known. Of these, there has been proposed a method in which a sublimable dye is used as a recording agent and is supported on a substrate sheet such as a paper or a plastic film to prepare a thermal transfer sheet, and using the thermal transfer sheet, various full color images are formed on a thermal transfer image receiving sheet which is capable of being deposited with a sublimable dye, for example, a thermal image receiving sheet having a dye receptor layer on a paper or a plastic film. In such a case, a thermal head of a printer is used as a heating means, so that a great number of color dots of three or four colors are transferred onto the thermal transfer image receiving sheet under heating for a short period of time, thereby to reproduce a full color image of an original. Such images as obtained above are very sharp because the used colorant is a dye, and are also excellent in transparency. Therefore, the images are excellent in half tone reproducibility and gradation properties, and are substantially the same as those formed by the conventional offset printing and gravure printing. Further, when the above image forming method is used, there can be formed images having high quality which are comparable to full color photographic images. As the substrate sheet of the thermal transfer image receiving sheet used in the above sublimation type thermal transfer method, a plastic sheet, a laminate sheet of a plastic sheet and a paper, a synthetic paper, etc. are employed. However, in order to widely utilize the sublimation type thermal transfer method also in common offices, it is required to use ordinary papers such as a coat paper (i.e., art paper), a cast coat paper and a PPC paper as the substrate sheet of the image receiving sheet. In conventional image receiving sheets in which the above-mentioned various substrate sheets are used and a dye receptor layer made of a thermal plastic resin such as a polyester resin, a vinyl chloride resin and a vinyl chloride/vinyl acetate copolymer resin is provided thereon, the dye receptor layer is easily peeled off due to the heat of the thermal head during the thermal transferring procedure or due to the adhesive tape. For the formation of a sharp image, a sufficient whiteness of the dye receptor layer is necessary. However, when a large amount of a white pigment is introduced into the dye receptor layer for that purpose, deposition properties of the dye are decreased. Further, for obtaining an image of high resolution free from color dropout, decoloring, etc., the image receiving sheet is required to have sufficient cushioning properties so as to bring the dye receptor layer into good contact with the thermal head. Such cushioning properties are generally obtained by forming an intermediate layer made of a resin having high cushioning properties between the substrate sheet and the receptor layer. A most effective layer as the intermediate layer is a layer containing bubbles. In this case, however, when an image is formed by the thermal head, the bubbles contained in the intermediate layer are expanded again owing to the heat of the thermal head to make the surface of the receptor layer depressed and protruded or to break through the receptor layer, whereby the receptor layer becomes defective to give an adverse effect to the resulting image. By providing the intermediate layer, the cushioning properties of the receptor layer can be improved, but the physical strength thereof is lowered. For example, if writing with a pencil or the like is intended to be made on the receptor layer before or after the image formation, a lead of the pencil scratches and writing is difficult because of low strength of the receptor layer. Otherwise, if the writing is compulsively made, the receptor later is peeled off. In the case of using the ordinary paper such as a PPC paper as the substrate sheet of the image receiving sheet as described before, there is brought about such a problem that unevenness occur on the surface of the dye receptor later correspondingly to the roughness of the surface of the paper substrate. For solving this problem, a transfer method in which the dye receptor layer is transferred onto the surface of the paper is known. In this method, a receptor layer-transfer film having a dye receptor layer and a adhesive layer laminated on a surface of a substrate film having high releasability is employed. However, since the adhesive layer of the conventional receptor layer transfer films uses a heat-sensitive thermoplastic resin, the transference of the receptor layer needs application of heat, so that it is difficult to conduct high-speed transference. Further, in the case of using a coarse substrate sheet (e.g., paper) as the substrate sheet, adhesion strength thereof is insufficient in the high-speed transference. Moreover, the resulting image receiving sheet does not have satisfactory cushioning properties. It is the object of the present invention to provide a thermal transfer image receiving sheet excellent in adhesion properties, whiteness, and cushioning properties. Accordingly the invention provides a thermal transfer image receiving sheet comprising a substrate sheet, an intermediate layer provided on at least one side surface of the substrate sheet and a dye receptor layer provided on the surface of the intermediate layer, wherein the intermediate layer is formed from a chlorinated polypropylene resin. Thus, a thermal transfer image receiving sheet excellent in adhesion properties and cushioning properties can be obtained. The present invention is described below in more detail with reference to preferred embodiments thereof. FIG. 1 is schematic sectional view showing an embodiment of the thermal transfer image receiving sheet according to the invention. In FIG. 1, the thermal transfer imaging receiving sheet 1 comprises a substrate sheet 2, an intermediate layer 3 provided on the substrate sheet 2 and a dye receptor layer 4 provided on the intermediate layer 3. An embodiment of the thermal transfer image receiving sheet according to the invention comprises a substrate sheet, an intermediate layer provided thereon and a dye receptor layer provided on the intermediate layer, and the intermediate layer is composed of a chlorinated polypropylene resin. Examples of the substrate sheets employable in this embodiment include synthetic paper (polyolefin type, polystyrene type, etc.), fine paper, art paper, coat paper, cast coat paper, wall paper, backed paper, synthetic resin impregnated paper, emulsion impregnated paper, synthetic rubber impregnated paper, synthetic resin containing paper, plate paper, cellulose fiber paper, and films or sheets of various plastics such as polyolefin, polyvinyl chloride, polyethylene terephthalate, polystyrene, polymethacrylate and polycarbonate. Also employable are white opaque films obtained by adding white pigment or filler to these synthetic resins and expanded sheets. Further, laminates obtained by optional combinations of the above substrate sheets are employable. Representative laminates include a laminate of a cellulose fiber paper and a synthetic paper, a laminate of a cellulose fiber paper and a plastic film or a plastic sheet. The thickness of the substrate sheet is optional, but generally in the range of 10 to 300 µm. The chlorinated polypropylene resin for forming the intermediate layer on a surface of the substrate sheet may be either low-chlorinated or high-chlorinated, but particularly preferred is a low-chlorinated polypropylene having chloride content of 20 to 40 wt.%. The chlorinated polypropylene may be those having been subjected to various modification, such as maleic acid modified, alcohol modified and epoxy modified chlorinated polypropylene. The intermediate layer in the invention may be formed from a mixture of a chlorinated polypropylene and other resin such as acrylic resin, urethane resin, polyester resin, vinyl chloride resin, vinyl acetate resin and ethylene/vinyl acetate copolymer. In this case, the amount of the chlorinated polypropylene is preferably not less than 10 wt.% of the total amount. The intermediate layer can be formed by various methods such as a gravure coating, a screen printing and a cast coat method, without limiting thereto. The intermediate layer may contain a white pigment, a filler and/or a fluorescent brightener. For introducing the white pigment or others into the intermediate layer, they are added to the coating liquid used for the formation of the intermediate layer. The white pigment or the filler serves to improve whiteness and opacifying power of the intermediate layer and to prevent adverse effects by a colour of the substrate sheet on the obtained image. Examples of the white pigments and the fillers include titanium oxide, zinc oxide, caolin clay, calcium carbonate and particulate silica. The amount of the white pigment or the like is generally in the range of 1 to 500 parts by weight based on 100 parts by weight of the resin used for the intermediate layer, though it varies depending on the kinds of the used pigment or the like. The fluorescent brightener serves to eliminate yellowness of the resin of the intermediate layer and to enhance whiteness, and employable are conventional fluorescent brighteners of stilbene type, diaminodiphenyl type, oxazole type, imidazole type, thiazole type, coumarin type, naphthalimide type, thiophene type, etc. The fluorescent brightener is dissolved in a resin for the intermediate layer, and it shows satisfactory effect in an extremely low concentration, for example, a concentration of 0.01 to 5 wt.%. The dye receptor later 4 formed on the surface of the above intermediate layer 3 serves to receive a sublimable dye transferred from a thermal transfer sheet and to maintain the formed image. Examples of binder resins for forming the dye receptor layer include polyolefin resins such as polypropylene; halogenated vinyl resins such as polyvinyl chloride and polyvinylidene chloride; vinyl resins such as polyvinyl acetate, vinyl chloride/vinyl acetate copolymer, ethylene/vinyl acetate copolymer and polyacrylic ester; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polystyrene resins; polyamide resins; copolymer resins of olefin (e.g., ethylene and propylene) and other vinyl monomers; ionomer; cellulose resins such as cellulose diacetate; and polycarbonate, etc. Of these, particularly preferred are vinyl resins and polyester resins. Using these resins, an aqueous resin liquid such as an aqueous emulsion is prepared, and if desired, to the aqueous resin liquid may be added additives such as a surface active agent, a releasing agent, an antioxidant and an ultraviolet absorbent. Thus prepared aqueous resin liquid is applied onto the intermediate layer by conventional coating means such as a gravure printing, a screen printing, a reverse roll coating using a gravure plate, and then dried to form the dye receptor layer. In the case where the aqueous emulsion containing a surface active agent is used, the dye receptor layer 4 can have moisture absorption characteristics as the pulp paper substrate because the surface active agent is hydrophilic. The dye receptor layer 4 preferably contains a releasing agent to give a high releasability from a thermal transfer sheet. Examples of the preferred releasing agents include silicone oils, phosphoric ester type surface active agents and fluorine type surface active agents. Of these, particularly preferred are silicone oils. As the silicone oils, desirable are epoxy modified, alkyl modified, amino modified, carboxyl modified, alcohol modified, fluorine modified, alkyl aralkyl polyether modified, epoxypolyether modified, and polyether modified silicone oils. One or more kinds of the releasing agents can be employed. The amount of the releasing agent used herein is preferably in the range of 1 to 20 parts by weight based on 100 parts by weight of the binder resin. If the amount thereof is not within the above range, a problem of fusion of the dye receptor layer 4 to the thermal transfer sheet or a problem of reduction of printing sensitivity may occur. The thickness of the dye receptor layer 4 formed as above is optional, but generally in the range of 1 to 50 µm. Further, the thickness of the dye receptor layer 4 is preferably in the range of 0.1 to 5% based on the thickness of the thermal transfer image receiving sheet. As described in the above thermal transfer image receiving sheets, a thermal transfer image receiving sheet having high adhesion between the substrate sheet and the dye receptor layer and having excellent cushioning properties can be obtained by forming the intermediate layer from the chlorinated polypropylene. The above embodiment is described below in more detail with reference to examples. In the examples, "part(s)" and "%" mean "part(s) by weight" and "% by weight", respectively, unless otherwise noted specifically. Example A (A-1) Onto a surface of a synthetic paper (trade name: Yupo, available from Oji Yuka K.K.) having a thickness of 200 µm was applied a coating liquid for an intermediate layer having the following composition in an amount of 1.0 g/m 2 (dry basis) using a bar coater, then dried by means of a dryer, and further dried in an oven at 100 °C for 5 minutes to form an intermediate layer. Onto the intermediate layer was applied a coating liquid for a receptor layer having the following composition in an amount of 3.0g/m 2 and dried in an oven at 100 °C for 5 minutes, to obtain a thermal transfer image receiving sheet (A-1) of the invention. Composition of coating liquid for intermediate layer Chlorinated polypropylene (Harden 13B, available from Toyo Kasei K.K.) 50 parts Ethylene/vinyl acetate copolymer (Everflex 40Y, available from Mitsui Dupont Chemical K.K.) 50 parts Fluorescent brightener (Ubitex OB, available From Ciba Geigy) 0.1 part Toluene 100 parts Composition of coating liquid for receptor layer Polyester resin (Bylon 103, available from Toyobo K.K.) 100 parts Amino modified silicone (X-22-343, available From Shinetsu Kagaku Kogyo K.K.) 3 parts Epoxy modified silicone (KF-393, available From Shinetsu Kagaku Kogyo K.K.) 3 parts Methyl ethyl ketone/toluene (1/1 by weight) 500 parts (A-2) Onto a foamed polypropylene sheet (Toyopearl SS#35, available from Toyobo K.K., thickness: 35µm) was applied a coating liquid for an intermediate layer having the following composition in an amount of 2.0 g/m 2 (solid content) using a bar coater and dried. Then, onto the surface was applied a coating liquid for a receptor layer having the following composition in an amount of 2.0 g/m 2 , then dried by means of a dryer and further dried in an oven at 100 °C for 30 minutes, to obtain a thermal transfer image receiving sheet (A-2) of the invention. Composition of coating liquid for intermediate layer Chlorinated polypropylene (Hardren 15LPB, available from Toyo Kasei K.K.) 100 parts Titanium oxide (TCR-10, available from Tochem Product) 100 parts Toluene 100 parts Composition of coating liquid for receptor layer Vinyl chloride/vinyl acetate copolymer resin (VYHD, available from Union Carbide) 100 parts Epoxy modified silicone (KF-393, available from Shinetsu Kagaku Kogyo K.K.) 3 parts Amino modified silicone (KP-343, available from Shinetsu Kagaku Kogyo K.K.) 3 parts Methyl ethyl ketone/toluene (1/1 by weight) 400 parts (A-3) Onto a surface of a polyester film (trade name: Lumiror, available from Toray Industries, Inc.) having a thickness of 100 µm was applied a coating liquid for an intermediate layer having the following composition in an amount of 3.0 g/m 2 (dry basis) using a bar coater and dried by means of a dryer, to form an intermediate layer. Onto the intermediate layer was applied a coating liquid for a receptor layer having the following composition in an amount of 4.0 g/m 2 (dry basis) using a bar coater and dried, to obtain a thermal transfer image receiving sheet (A-3) of the invention. Composition of coating liquid for intermediate layer Chlorinated polypropylene (Hardren 15LPB, available from Toyo Kasei K.K.) 50 parts Titanium oxide (TCA888, available from Tochem Product) 100 parts Toluene 100 parts Composition of coating liquid for receptor layer Vinyl chloride/vinyl acetate copolymer resin (VYHD, available from Union Carbide) 100 parts Amino modified silicone (K-22-343, available from Shinetsu Kagaku Kogyo K.K.) 2 parts Epoxy modified silicone (KF-393, available from Shinetsu Kagaku Kogyo K.K.) 2 parts Methyl ethyl ketone/toluene (1/1 by weight) 100 parts (a-1) The procedure for obtaining the thermal transfer image receiving sheet (A-1) was repeated except for using the following thermoplastic resin solution as the coating liquid for an intermediate layer, to obtain a thermal transfer image receiving sheet (a-1) for comparison. Composition of coating liquid for intermediate layer Acrylic resin (Daiyanal BR85, available from Mitsubishi Rayon K.K.) 20 parts Toluene 100 parts (a-2) The procedure for obtaining the thermal transfer image receiving sheet (A-2) was repeated except for not forming an intermediate layer, to obtain a thermal transfer image receiving sheet (a-2) for comparison. Separately, an ink having the following composition for a dye layer was prepared. The ink was applied onto a polyethylene terephthalate film (thickness 6 µm) having been subjected to a heat resistance treatment on the back surface in an amount of 1.0 g/m 2 (dry basis) by means of a wire bar, and dried. Further, on the back surface were dropped several drops of a silicone oil (X-414003A, available from Shinetsu Kagaku Kogyo K.K.) by means of a dropping pipette, and the silicone oil was extended all over the surface to perform a back surface treatment. Thus, a thermal transfer sheet was obtained. Composition of ink for dye layer Dye to be dispersed (Kayaset Blue 714, available from Nippon Kayaku CO., Ltd.) 4.0 part Ethylhydroxy cellulose (available from Hercures) 5.0 part Methyl ethyl ketone/toluene (ration by Weight: 1/1) 80.0 part Dioxane 10.0 part The thermal transfer sheet was superposed on the dye receptor layer of each of the thermal transfer image receiving sheets (A-1) to (A-3), (a-1) and (a-2), and they were subjected to a printing procedure using a thermal head under the conditions of an output of 1 W/dot, a pulse width of 0.3 to 0.45 msec. and a dot density of 3 dot/mm to form cyan images. In the case of using the thermal transfer image receiving sheets (A-1) to (A-3) of the invention, the dye receptor layers were free from problem of peeling, and images of high quality free from defects such as color dropout were obtained. On the other hand, in the case of using the thermal transfer image receiving sheets (a-1) and (a-2) for comparison, the dye receptor layers were partially peeled off, and some images were of low quality because of defects such as color dropout. The present invention should not be interpreted in a restricted manner. The scope of the present invention is defined by claims and is not confined by the body of the specification at all.

Claims: A thermal transfer image receiving sheet comprising a substrate sheet, an intermediate layer provided on at least one side surface of the substrate sheet and a dye receptor layer provided on the surface of the intermediate layer, wherein the intermediate layer is formed from a chlorinated polypropylene resin. The thermal transfer image receiving sheet as claimed in Claim 1, wherein the intermediate layer contains at least one of a white pigment, a filler and a fluorescent brightener. The thermal transfer image receiving sheet as claimed in Claim 1, wherein the substrate sheet is made of any one of a pulp paper, a synthetic paper or a synthetic resin film.

Inventors: ANDO JITSUHIKO, ASAJIMA MIKIO, IMOTO KAZUNOBU, OSHIMA KATSUYUKI, TAKAHARA HIDETAKE, UENO TAKESHI, YAMAUCHI MINEO, ANDO, JITSUHIKO, ASAJIMA, MIKIO, IMOTO, KAZUNOBU, OSHIMA, KATSUYUKI, TAKAHARA, HIDETAKE, UENO, TAKESHI, YAMAUCHI, MINEO
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON PRINTING CO., LTD.
Application year: 1992
Main classification: B41M5
IPC codes: B41M5