A process for thermal transfer recording.

Abstract: The present invention is a heat transfer image-­ receiving sheet comprising a base sheet and a dye receiving layer formed on at least one surface of said base sheet, said dye receiving layer comprising an acidic resin with acid value of 2 or more, or being formed primarily of a polyester resin with a branched structure.

Description: This invention relates to a process for heat transfer recording using a heat transfer image-receiving sheet which can form a recorded image excellent in color forming density, sharpness and various fastnesses. Various heat transfer methods have been known in the art, and among them, there has been practiced the sublimation transfer method, in which a sublimable dye is used as the recording agent, this is carried on a base sheet such as paper to provide a heat transfer sheet, which is superposed on an image-receiving material capable of dyeing with a sublimable dye, for example, a fabric made of a polyester, and the sublimable dye is migrated to the image-receiving material by giving heat energy according to pattern information from the back of the heat transfer sheet. In the above sublimation transfer method, in the sublimation printing method, when the image-receiving material is, for example, a fabric made of a polyester, heat energy is imparted for a relatively longer time, and therefore the image-receiving material itself is heated by the heat energy imparted, whereby relatively good migration of the dye is accomplished. However, with the progress in recording method, when fine letters or figures or photographic images are to be formed on, for example, image-receiving materials having dye receiving layers provided on polyester sheets or papers at high speed by use of a thermal head, etc., heat energy is required to be imparted within a very short time of second units or less, and therefore, within such short time, the sublimable dye and the image-receiving material cannot be heated, whereby no image with sufficient density can be formed. Accordingly, in order to respond to such high speed recording, sublimable dyes excellent in sublimability have been developed, but dyes excellent in sublimability have generally smaller molecular weights, and hence pose problems such that the dyes may be migrated with lapse of time in the image-receiving material after transfer, or may be bleeded onto the surface, thus causing disturbance of the image elaborately formed to make them indistinct or contamination of surrounding articles. In order to avoid such problems, if a sublimable dye having relatively larger molecular weight is used, the sublimation speed is inferior in the high speed recording method as described above, and therefore no image with satisfactory density could be formed as described above. Accordingly, an object of the present invention is to provide a process for heat transfer recording using a heat transfer image-receiving sheet which gives a sharp image with sufficient density by imparting heat energy for a very short time as described above by use of a sublimable dye and yet an image is formed, which exhibits excellent various fastnesses. The present invention is a process for heat transfer recording comprising the steps of: providing (i) a heat transfer sheet comprising a base sheet and a heat transfer layer containing a dye formed on the base sheet and (ii) an image-receiving sheet comprising a base sheet and a dye receiving layer formed on at least one surface of the base sheet, the dye receiving layer comprising an acidic resin which is capable of receiving a sublimable dye and maintaining an image formed, the acidic resin having an acid value of from 2 to 20; bringing the heat transfer layer of the heat transfer sheet into contact with the image receiving layer of the image-receiving sheet; and carrying out thermal printing in accordance with the information for printing. In the present invention, the term "acid value" means the value indicating the quantity of a free acid such as a plasticizer. More particularly, this value means the quantity of potassium hydroxide in milligrams necessary for neutralizing the free acid contained in 1 gram of a sample to be determined. In this case, the acid value is measured according to the method defined by JIS-K-5400 8.5. By forming the receiving layer of a heat transfer image-receiving sheet of an acidic resin with an acid value of 2 or more, even when a dye with a relatively smaller molecular weight may be used, the bleed resistance of the dye received can be improved to form an image excellent in sharpness, density and storability, etc. Also, even when a dye with relatively higher molecular weight may be employed, due to excellent dye receptivity, an image excellent in sharpness, density and storability can be similarly formed. Particularly, when a sublimable dye having basic amine, e.g., amino group, imino group or amide group, is used, said dye is captured with acidic groups within the receiving layer and therefore bleed resistance can be made further better. Further, in the present invention, by forming the dye receiving layer of the heat transfer image-receiving sheet primarily of a polyester resin with a branched structure, the dye receiving layer will not be peeled off from the base material sheet even by imparting a high heat energy, whereby a heat transfer image-receiving sheet capable of giving a sharp image having sufficient density and resolution can be provided. The heat transfer image-receiving sheet to be used in the process of the present invention comprises a base sheet and a dye receiving layer formed on at least one surface thereof. Base sheet As the base sheet to be used in the present invention, there can be used synthetic papers (polyolefinic, polystyrenic, etc.), pure paper, art paper, coated paper, cast coated paper, wall paper, synthetic resin or emulsion impregnated paper, synthetic rubber latex impregnated paper, synthetic resin internally added paper, board paper, cellulose fiber paper, films or sheets of various plastics such as polyolefin, polyvinyl chloride, polyethylene terephthalate, polystyrene, polymethacrylate, polycarbonate which are not particularly limited. It is also possible to use a laminated product comprising any combination of the above base sheets. A typical example of the laminated product may be a combination of a cellulose fiber paper and a synthetic paper, or a combination of a cellulose fiber paper and a plastic film or sheet. First embodiment of dye receiving layer The receiving layer to be formed on the above base sheet is provided for receiving the sublimable dye migrated from the heat transfer sheet and maintaining the image formed. Said receiving layer is formed of various resins having acidic groups such as carboxyl group or sulfonic acid group in the molecules, and may be also formed from a mixture of a resin having these acidic groups and a resin having no acidic group. Particularly, it has been found in the present invention that excellent dye receptivity is exhibited when the acid value of the acidic resin employed is 2 to 20. If the acid value is less than 2, bleed resistance or contamination resistance of a dye with relatively smaller molecular weight is insufficient, while if the acid value is over 20, receptivity of the dye with relatively higher molecular weight is undesirably insufficient. The acidic resins to be used in the present invention may include acid modified resins modifying resins as mentioned below: (a) those having ester bond, such as polyester resin, polyacrylate resin, polycarbonate resin, polyvinyl acetate resin, styrene-acrylate resin, vinyl toluene-acrylate resin, etc.; (b) those having urethane bond, such as polyurethane resin, etc.; (c) those having amide bond, such as polyamide resin (nylon); (d) those having urea bond, such as urea resin, etc.; (e) otherwise those having high polarity bond, such as polycaprolactone resin, polystyrene resin, polyvinyl chloride resin, polyacrylonitrile resin, etc. Of the synthetic resins as mentioned above, particularly preferable is a polyester type resin. The acidic resin as mentioned above can be obtained by modifying the resin with a polycarboxylic acid during or after synthesis of the resin. As the modification method, for example, in the case of condensation type resin such as polyester, polyurethane resin, polyamide resin, etc., there may be employed the method in which a polycarboxylic acid is used in excess or an acid of trivalent or more is used during synthesis, or in the case of a vinyl type resin, there may be employed the method in which a monomer having an acidic group as a part of the monomers used is used, to give a resin having a desired acid value. Alternatively, when modified after synthesis, a resin having a group such as hydroxyl group, amino group, amide group, epoxy group, isocyanate group can be modified with a polycarboxylic acid to be modified into a resin with any desired acid value. The polycarboxylic acid to be used for modification may include, for example, aliphatic polycarboxylic acids such as di- or tri-carboxylic acids or anhydrides thereof, as exemplified by oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimellic acid, fumaric acid, maleic acid, methylmaleic acid, methylfumaric acid, itaconic acid, citraconic acid, mesacoic acid, acetylenic acid, malic acid, methylmalic acid, citric acid, isocitric acid, tartaric acid, edtc.; aromatic polycarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, 1,2,3-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, pyromellitic acid, benzenehexacarboxylic acid, naphthalene dicarboxylic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, diphenyltetracarboxylic acid, diphenylether tetracarboxylic acid, azobenzene tetracarboxylic acid or anhydrides thereof. In the present invention, particularly preferable aromatic polycarboxylic acid is benzene tricarboxylic acid, particularly trimellitic acid or anhydride thereof. The heat transfer image-receiving layer is obtained by coating and drying a solution of the above acidic resin or a mixture of this with a nonacidic resin dissolved in an appropriate organic solvent or a dispersion dispersed in an organic solvent or water on at least one surface of the above base sheet to form a dye receiving layer. When an acidic resin and a nonacidic resin are used in mixture, the acidic resin in the total of the both resins should be 5% by weight or more, preferably 10% by weight or more. In forming the above receiving layer, for further enhancing the sharpness of transferred image by improving the whiteness of the receiving layer, a pigment or filler such as titanium oxide, zinc oxide, kaolin clay, calcium carbonate, fine powdery silica, etc. can be added. Also, for further enhancing light resistance of the transferred image, a UV-ray absorber and/or a light stabilizer can be also added in the receiving layer. Such dye receiving layer may have any desired thickness, but generally a thickness of 3 to 50 µm. Also, such dye receiving layer should be preferably a continuous coating, but it may be also coated as an incontinuous coating by use of a resin emulsion or a resin dispersion. The heat transfer image-receiving sheet to be used in the process of the present invention is sufficiently useful with the constitution basically as described above, but inorganic powder for sticking prevention can be also included in the dye receiving layer, and by doing so, sticking between the heat transfer sheet and the heat transfer image-receiving sheet can be prevented even if the temperature during heat transfer may be increased to effect further excellent heat transfer. Particularly preferably, fine powdery silica may be employed. Also, in place of the inorganic powder such as silica as mentioned above, or in combination therewith, a resin with good releasability may be also added. A particularly preferable releasable polymer is a cured product of a silicone compound, for example, a cured product comprising an epoxy modified silicone oil and an amino modified silicone oil. Such release agent may be preferably added at a ratio comprising about 0.5 to 30% by weight of the dye receiving layer. The heat transfer sheet to be used in performing heat transfer by use of the heat transfer image-receiving sheet as described above comprises a dye layer containing a sublimable dye on a paper or a polyester film, and any of heat transfer sheets known in the art can be used as such in the present invention. According to the study of the present inventors, it has been found that the dye to be used in the heat transfer sheet should be preferably a dye having at least one primary to tertiary amine, particularly that the best image can be formed when it is an indoaniline type, cyanoacetyl type or anthraquinone type dye as represented by the formulae shown below. (In the above formulae, R 1 to R 4 each represent a C 1 to C 6 alkyl group, a cycloalkyl group or phenyl group, R 2 may be also hydrogen atom or alkoxy group, and R 3 and R 4 may also form a ring; X represents hydrogen atom, a substituent such as a halogen atom, a lower alkyl group, an alkoxy group, nitro group, etc.). As the means for imparting heat energy during heat transfer, any of the imparting means known in the art can be used. For example, the desired object can be sufficiently accomplished by means of a recording device such as thermal printer (e.g., Videoprinter VY-100, manufactured by Hitachi K.K., Japan) by controlling the recording time to give a heat energy of about 5 to 100 mJ/mm 2 . According to the present invention as described above, by forming the dye receiving layer of the heat transfer receiving sheet of an acidic resin, a sharp image can be formed at high density. Particularly, since these images have excellent bleed resistance and contamination resistance, even when the images may be stored for a long term, the images will not be lowered in sharpness and may be contacted with other articles without contamination thereof, thus solving various problems of the prior art. Second embodiment of the dye receiving layer In the second embodiment the above receiving layer is characterized by being formed primarily of a branched polyester resin. The branched polyester resin is one obtained by use of a polycarboxylic acid of 3 functionalities or more as a part of the acid component or a polyol of 3 functionalities or more as part of the alcohol component in preparing a linear polyester from a dicarboxylic acid and a diol. Examples of the dicarboxylic acid to be used in the present invention may include phthalic acid, isophthalic acid, terephthalic acid, 1,2-, 1,4-, 1,5-, 1,6-, 1,7- or 1,8-naphthalene dicarboxylic acid, diphenyl-2,2'-2,3'-2,4'-3,3'-4,4'-dicarboxylic acid, diphenylmethane-2,2'-2,3'-2,4'-3,3'-4,4'-dicarboxylic acid, diphenyl ether-4,4′-dicarboxylic acid, benzophenone-4,4′-dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid adipic acid, succinic acid, maleic acid, sebacic acid, isosebacic acid, dimeric acid, tetrachlorophthalic acid, 4,4′-dicarboxy-diphenylmethane, 4,4′-dicarboxyl-diphenylpropane, etc. Particularly preferable are isophthalic acid, terephthalic acid or derivatives thereof. Examples of trivalent or higher polycarboxylic acids may include trimellitic acid, trimesic acid, 1,2,5-, 2,3,6- or 1,8,4-naphthalene tricarboxylic anhydride, 3,4,4′-diphenyltricarboxylic anhydride, 3,4,4′-diphenylmethanetricarboxylic anhydride, 3,4,4′-diphenylethertricarboxylic anhydride and 3,4,4′-benzophenonetricarboxylic anhydride, and particularly useful is trimellitic acid. Of course, derivatives such as esters or anhydrides of the above di- or polyacides may be also employed. Examples of diol may include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,3-propane diol, various butane-, pentane- or hexane diols, such as 1,3- or 1,4-butane diol, 1,5-pentene diol, 1,6-hexane diol, 1,4-butene-2-diol, 2,2-dimethylpropane diol1,3, 2-ethyl-2-butyl-propane diol-1,3, 1,4-dimethylolcyclohexane, 1,4-butene diol, hydrogenated bisphenols ( e.g., hydrogenated P,P′-dihydroxydiphenylpropane or homologues thereof), cyclic glycol, such as 2,2,4,4-tetramethyl-1,3-cyclobutane diol, hydroquinone-di-β-hydroxyethyl ether, 1,4-cyclohexane dimethanol, 1,4-cyclohexane diethanol, trimethylene glycol, hexylene glycol, octylene glycol, etc. Particularly preferable are ethylene glycol, 1,2-propylene glycol and 1,6-hexane diol. Examples of trivalent or higher polyol may include glycerine, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, etc., particularly preferably glycerine or derivatives thereof. The branched polyester to be used in the present invention is prepared from the components as described above in conventional manner, and the trivalent or higher polycarboxylic acid or polyol used in this case should be preferably used at a ratio comprising 0.5 to 50 equivalent %, preferably 1.0 to 10 equivalent % in the acid components or the alcohol components to give a branched structure. If the amount of the polycarboxylic acid or the polyol used is too small, adhesiveness of the polyester resin obtained to the base material sheet is deficient, while if it is too much, gelling occurs to make the sheet unavailable. The heat transfer image-receiving sheet to be used in the process of the present invention is obtained by coating and drying a solution of the branched polyester resin as described above or a mixture of this with other resins dissolved in an appropriate organic solvent or a dispersion dispersed in an organic solvent or water to form a dye receiving layer. When the branched polyester and another resin are used in a mixture, the branched polyester resin should be preferably 5% by weight or more, preferably 10% by weight or more, in the total of the both. In forming the above receiving layer, for further enhancing the sharpness of transferred image by improving the whiteness of the receiving layer, a pigment or filler such as titanium oxide, zinc oxide, kaolin clay, calcium carbonate, fine powdery silica, etc. can be added. Also, for further enhancing light resistance of the transferred image, a UV-ray absorber and/or a light stabilizer can be also added in the receiving layer. Such dye receiving layer may have any desired thickness, but generally a thickness of 3 to 50 µm. Also, such dye receiving layer should be preferably a continuous coating, but it may be also coated as an incontinuous coating by use of a resin emulsion or a resin dispersion. The heat transfer image-receiving sheet to be used in the process of the present invention is sufficiently useful with the constitution basically as described above, but inorganic powder for sticking prevention can be also included in the dye receiving layer, and by doing so, sticking between the heat transfer sheet and the heat transfer image-receiving sheet can be prevented even if the temperature during heat transfer may be increased to effect further excellent heat transfer. Particularly preferably, fine powdery silica may be employed. Also, in place of the inorganic powder such as silica as mentioned above, or in combination therewith, a resin with good mold releasability may be also added. A particularly preferable mold releasable polymer is a cured product of a silicone compound, for example, a cured product comprising an epoxy modified silicone oil and an amino modified silicone oil. Such mold release agent may be preferably added at a ratio comprising about 0.5 to 30% by weight of the dye receiving layer. The heat transfer sheet to be used in performing heat transfer by use of the heat transfer image-receiving sheet as described above comprises a dye layer containing a sublimable dye on a paper or a polyester film, and any of heat transfer sheets known in the art can be used as such in the present invention. According to the study by the present inventors, it has been found that the dye to be used in the heat transfer sheet should be preferably a dye having at least one primary to tertiary amine, e.g., amino group, imino group or amide group, particularly that the best image can be formed when it is an indoaniline type, cyanoacetyl type or anthraquinone type dye. As the means for imparting heat energy during heat transfer, any of the imparting means known in the art can be used. For example, the desired object can be sufficiently accomplished by means of a recording device such as thermal printer (e.g., Videoprinter VY-100, manufactured by Hitachi K.K.) by controlling the recording time to give a heat energy of about 5 to 100 mJ/mm 2 . According to the present invention as described above, by forming the dye receiving layer of the heat transfer receiving sheet of a polyester resin having the branched structure, particularly a heat transfer image-receiving sheet can be provided, which give a sharp image having sufficient density and resolution even by imparting high energy without peel-off of the dye receiving layer from the base material sheet. The present invention is described in more detail by referring to Examples and Comparative examples. In the description, "parts" and "%" are based on weight unless otherwise particularly noted. Example A1 An ink composition for forming a dye carrying layer having a composition shown below was prepared, and applied and dried to a dried coating amount of 1.0 g/m 2 on a polyethylene terephthalate film with a thickness of 6 µm applied with heat-resistant treatment on the back to obtain a heat transfer sheet shown below in Table A1. Dye of the above formula 3.0 parts Polyvinyl butyral resin 4.5 parts Methyl ethyl ketone 46.25 parts Toluene 46.25 parts However, in the above composition, when the dye mixture was insoluble, DMF, dioxane, chloroform, etc. were employed as the solvent. Dye and Sheet No. R 1 R 2 R 3 R 4 X 1 -CH 3 -CH 3 -C 3 H 7 -C 3 H 7 Cl 2 -C 2 H 5 -CH 3 -C 2 H 5 -C 4 H 9 -CH 3 3 -CH 3 -CH 3 -CH 3 -C 4 H 9 Cl 4 -CH 3 -C 2 H 5 -CH 3 -C 2 H 5 -CH 3 5 -CH 3 -- -- -- -- 6 -CH 3 -CH 3 -- -- -- 7 -C 5 H 11 -- -- -- -- Also, by use of the following dye, heat transfer sheet 8 was obtained in the same manner as above method. Next, by use of a synthetic paper (Yupo FPG #150, manufactured by Oji Yuka K.K., Japan) as the base material sheet, a coating liquid with a composition shown below was coated on one surface to 10.0 g/m 2 on drying, followed by drying at 100°C for 30 minutes to give a heat transfer image-receiving sheet shown in Table A2. Acidic resin as in Table A2 shown below 11.5 parts Vinyl chloride-vinyl acetate copolymer (VYHH, manufactured by UCC) 5.0 parts Amino-modified silicone (KF-393, manufactured by Shinetsu Kagaku Kogyo K.K., Japan) 1.2 parts Epoxy-modified silicone (X-22-343, manufactured by Shinetsu Kagaku Kogyo K.K., Japan) 1.2 parts Methyl ethyl ketone/Toluene/Cyclohexanone (weight ratio 4:4:2) 102.0 parts No. 1: polyester resin (acid value 0.6) modified with trimellitic anhydride: acid value: 4.8; No. 2: the same as above with acid value of 2; No. 3: the same as above with acid value of 5; No. 4: the same as above with acid value of 6; No. 5: the same as above with acid value of 9; No. 6: the same as above modified with phthalic anhydride: acid value 4.7; No. 7: the same as above modified with maleic anhydride: acid value 4.4; No. 8: the same as above modified with succinic anhydride: acid value 4.7; No. 9: No modification (Comparative example): acid value 0.6 The above heat transfer sheet and the heat transfer image-receiving sheet were superposed with the respective dye layer and the dye receiving surface faced to each other, and recording was performed with a thermal head from the back of the heat transfer sheet under the conditions of a heat application voltage of 10V, a printing time of 4.0 ms. to obtain the results shown below in Table A3. Heat transfer sheet Image-receiving sheet Color forming density Fastness 1 1 1.20 o ○ 2 2 1.20 o ○ 3 3 1.30 o ○ 4 4 1.50 o ○ 5 5 1.40 ○ 6 6 1.02 o ○ 7 7 1.10 o ○ 1 8 1.05 o ○ 1 9 1.00 ▵ 8 1 0.80 X 8 1 0.75 X Color forming density is a value measured by Densitometer RD-918, manufactured by Macbeth, U.S. A. Fastness is represented by o ○ when sharpness of the image is not changed and also the white paper is not colored when the surface is frictioned with a white paper after the recorded image has been left to stand for a long time in an atmosphere of 50°C, by ○ when sharpness is slightly lost after the recorded image has been left to stand for a long time in an atmosphere of 50°C and the white paper is slightly colored, by ▵ when sharpness is lost and the white paper is colored, and by X when the image becomes indistinct and the white remarkably colored. Reference example B1 Terephthalic acid 66 parts (4 equivalents) Isophthalic acid 100 parts (6 equivalents) Ethylene glycol 28 parts (4.5 equivalents) Trimethylol propane 7 parts (0.5 equivalent) Bisphenol A 114 parts (5 equivalents) The above components were charged into a reactor, elevated in temperature to 150°C for 3 hours in a nitrogen atmosphere with the use of antimony trioxide as the catalyst, and the reaction was carried out at this temperature for one hour, followed further by dehydrating polycondensation under the conditions of 275°C, 0.1 to 0.15 mmHg for 2 hours, to obtain a branched polyester resin. Reference example B2 By use of the following components, a branched polyester resin was obtained in the same manner as in Reference example B1. Terephthalic acid 83 parts (5 equivalents) Isophthalic acid 66 parts (4 equivalents) Trimellitic acid 21 parts (1 equivalent) Ethylene glycol 31 parts (5 equivalents) Bisphenol A 68 parts (3 equivalents) Propylene glycol 15 parts (2 equivalents) Reference example B3 Terephthalic acid 66 parts (4 equivalents) Isophthalic acid 66 parts (4 equivalents) Trimellitic acid 42 parts (2 equivalents) Ethylene glycol 25 parts (4 equivalents) Trimethylol propane 13 parts (1 equivalent) Bisphenol A 114 parts (5 equivalents) Propylene glycol 15 parts (2 equivalents) Comparative reference example B1 Terephthalic acid 66 parts (4 equivalents) Isophthalic acid 66 parts (4 equivalents) Sebacic acid 40 parts (2 equivalents) Ethylene glycol 31 parts (5 equivalents) Bisphenol A 46 parts (2 equivalents) Propylene glycol 23 parts (3 equivalents) Examples B1 to B3 and Comparative example B1 By use of a polyethylene terephthalate sheet film (T-100, manufactured by Toray, Japan. 100 µm) as the base material sheet, a coating solution with a composition shown below was coated by a bar coater at a ratio to 5.0 g/m 2 on drying and dried to obtain heat transfer image-receiving sheets to be used in the process of the present invention and Comparative example. The peeling forces of the receiving layers of these image-receiving sheets were measured to obtain the results shown below in Table B1. Polyester of Reference examples B1-B3 or Comparative reference example B1 100.0 parts Epoxy-modified silicone (X-22-3000E, manufactured by Shinetsu Kagaku) 8 parts Amino-modified silicone (X-22-3050C, manufactured by Shinetsu Kagaku) 8 parts Methyl ethyl ketone/toluene (weight ratio 1/1) 400 parts On the other hand, an ink composition for dye carrying layer with a composition shown below was prepared and coated and dried by a wire var on a polyethylene terephthalate film with a thickness of 6 µm applied on the back with a heat-resistant treatment to a coated amount after drying of 1.0 g/m 2 to obtain a heat transfer sheet. C.I. Disperse Blue 24 1.0 part Polyvinyl butyral resin 10.0 parts Methyl ethyl ketone/toluene (weight ratio 1/1) 90.0 parts The above heat transfer sheet and the heat transfer image-receiving sheet to be used in the process of the present invention and Comparative example were superposed respectively with the respective dye layer and the dye receiving surface faced to each other, and printing was performed with a thermal head from the back of the heat transfer sheet under the conditions of an application voltage of 12.0 V, a pulse width of 16 ms. and a dot density of 6 dots/line. The resolutions of the images obtained were compared to give the results shown below in Table B1. Peeling force was measured by 180° test. Peeling force (g/cm) Resolution Example B1 500 Good Example B2 450 " Example B3 600 " Comparative example B1 150 "

Claims: A process for heat transfer recording characterized in that it comprises the steps of: providing (i) a heat transfer sheet comprising a base sheet and a heat transfer layer containing a dye formed on the base sheet and (ii) an image-receiving sheet comprising a base sheet and a dye receiving layer formed on at least one surface of the base sheet, the dye receiving layer comprising an acidic resin which is capable of receiving a sublimable dye and maintaining an image formed, the acidic resin having an acid value of from 2 to 20; bringing the heat transfer layer of the heat transfer sheet into contact with the image receiving layer of the image-receiving sheet; and carrying out thermal printing in accordance with the information for printing. The process according to claim 1, wherein said acidic resin is an acid modified polyester resin. The process according to claim 1 or 2, wherein the dye is a sublimable dye having an amine group. The process according to claim 1 or 2, wherein the dye is an indoaniline dye, cyanoacetyl dye or anthraquinone dye.

Inventors: EGASHIRA NORITAKA, NAKAMURA JOSHINORI, EGASHIRA, NORITAKA, NAKAMURA, JOSHINORI                            ., EGASHIRA, NORITAKA C/O DAI NIPPON INSATSU K. K., NAKAMURA, JOSHINORI C/O DAI NIPPON INSATSU K. K.
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON INSATSU KABUSHIKI KAISHA
Application year: 1989
Main classification: B41M5
IPC codes: B41M5