JP2686610B2 - Manufacturing method of thermal transfer sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of a heat-sensitive transfer sheet, and more specifically, it prevents background stains on a transfer paper due to a heat-meltable ink layer and has a low surface smoothness. The present invention relates to a heat-sensitive transfer sheet capable of giving high-quality printing even to transfer paper. (Prior Art) Conventionally, when printing an output print of a computer or a word processor by a heat-sensitive transfer method, a heat-sensitive transfer sheet provided with a heat-meltable ink layer on one surface of a base film is used. This conventional heat-sensitive transfer sheet is used as a base film such as condenser paper or paraffin paper having a thickness of 10 to 20 μm or a thickness of 3 to 20 μm.
It is manufactured by using a film made of a plastic such as polyester or cellophane of m, and providing a hot-melt ink layer in which wax is mixed with a coloring agent such as a pigment or a dye by coating. When output printing is performed on a transfer paper sheet using a conventional heat-sensitive transfer sheet, the ink layer comes into direct contact with the transfer paper surface, and the friction between the two often causes scumming in the non-printed portion. Further, although the thermal transfer method can print on plain paper, it does not mean that clear printing can be performed on all kinds of plain paper. When the smoothness of the transferred paper is expressed as Beck's smoothness, the best printing is possible with high-quality paper or coated paper that has been subjected to a calendar process that shows a value of 100 seconds or more, and high-quality paper of about 50 seconds is sufficient. Good print quality. However, if a transfer paper with a low smoothness that does not reach 50 seconds is used, the sharpness of the print will deteriorate. This is because, on a paper having a highly uneven surface, the ink layer and the paper cannot be brought into complete contact with each other by the pressing pressure of the thermal head, and the portions that do not come into contact result in poor transfer. Further, the thermal transfer method has a drawback that the printing speed is slower than that of the impact method, and improvement is desired. In order to increase the printing speed, the level of heat energy applied to the thermal head must be increased, which may cause bleeding of the printing and further aggravates the above-mentioned background stain. A method of forming a wax layer on the surface of the heat-meltable ink layer is known as a method for eliminating the background stain and the bleeding of the print at the time of printing as described above. As a method of forming this wax layer, a method of applying an organic solvent solution of wax or a dispersion liquid in an organic solvent to the surface of the heat-meltable ink layer and drying it is performed. (Problems to be Solved by the Invention) According to the above-described conventional method, although the background stain on the transfer paper and the bleeding of the print can be solved to some extent, the organic solvent used for forming the wax layer causes Since the parts melt, the thickness of the ink layer becomes non-uniform and the pigment agglomerates, resulting in a problem that the quality of the ink layer deteriorates. Further, the wax layer formed in this manner reduces the pressure of the thermal head because the adhesiveness of the surface layer to the transferred paper is insufficient when the transferred paper has a lower surface smoothness. Then, high-speed printing has a problem in that sufficiently clear printing cannot be obtained. The present invention has been made in view of the above-mentioned circumstances, and its purpose is to produce clear images even on high-speed thermal transfer without causing scumming and even for transfer paper having low surface smoothness. Another object of the present invention is to provide a heat-sensitive transfer sheet capable of giving excellent printing. (Means for Solving Problems) As a result of trial production and testing of a heat-sensitive transfer sheet having various configurations, the present inventor achieved the object of the present invention by providing a specific surface layer on the surface in contact with the transferred paper. Found to be effective. That is, the present invention, on one surface of the base film,
In the method for producing a thermal transfer sheet, which comprises forming a heat-fusible ink layer and forming a surface layer on the surface of the ink layer, which stops the printed portion of the transfer paper when the ink layer is transferred, A dispersion obtained by dispersing a thermoplastic resin in a mixed medium of water and a water-soluble organic solvent is applied to the surface of the ink layer, dried at a temperature not higher than the melting point of the wax and the thermoplastic resin, and wax. The method for producing a thermal transfer sheet is characterized in that the thermal transfer sheet is formed so as to have fine surface irregularities formed of the particles of 1. and particles of a thermoplastic resin. (Function) By using a thermoplastic resin in addition to wax when forming the surface layer, the adhesiveness of the ink layer to the transfer material is further improved, and even if there is rough transfer paper, scumming or printing occurs. High-speed printing is possible without causing blurring. Further, in a preferred embodiment, by forming the surface layer from a dispersion of wax containing thermoplastic resin particles in water, without damaging the heat-meltable ink layer at all,
A surface layer having a fine uneven surface is formed, and at the time of printing, the pressure of the thermal head is at least concentrated on the convex portion of the uneven shape, which improves the adhesiveness between the surface layer and the transfer paper, High-speed printing is possible without causing stains. (Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments. The heat-sensitive transfer sheet of the present invention has a heat-meltable ink layer 2 on one surface of a base film 1 as shown in FIG. The surface layer 3 made of resin is formed. As the base film used in the present invention, the same base film as used in the conventional thermal transfer sheet can be used as it is, and other base films can be used without any particular limitation. Specific examples of the preferred base film include, for example,
Polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, plastic such as ionomer, condenser paper,
There are papers such as paraffin paper, non-woven fabrics and the like, and a base film in which these are combined may be used. The thickness of this base film can be appropriately changed according to the material so that its strength and thermal conductivity are appropriate, but the thickness is preferably, for example, 2 to 25 μm.
m. The hot-melt ink used in the present invention may be composed of a colorant and a vehicle, and may further contain various additives if necessary. As the colorant, among organic or inorganic pigments or dyes, those having good characteristics as a recording material, for example, those having sufficient coloring density and not fading due to light, heat, temperature and the like are preferable. Further, it may be a substance which is colorless when it is not heated but which is generated when it is heated, or a substance which develops a color when it comes into contact with a substance applied to the transferred material. In addition to the colorants that form cyan, magenta, yellow, and black, colorants of various other colors can also be used. As the vehicle, a mixture of wax as a main component, and other components such as a wax and a derivative of a drying oil, a resin, a mineral oil, cellulose, and rubber is used. Representative examples of the wax include microcrystalline wax, carnauba wax, and paraffin wax. Furthermore, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti, Ibota wax, wool wax, shellac wax, candelilla wax, petrolatum, partially modified wax, fatty acid ester, fatty acid amide and the like are used. Can be In addition, a heat conductive substance can be added to the heat fusible ink in order to provide the heat fusible ink layer with good heat conductivity and melt transferability. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum dioxide. As a method of directly or indirectly forming a heat-meltable ink layer on a base film, the above-mentioned ink is applied by hot melt coating, hot lacquer coating, gravure coating, gravure reverse coating, roll coating and many other means. Methods and the like. The thickness of the ink layer to be formed should be determined so as to balance the required density with the thermal sensitivity, and is in the range of 0.1 to 30 μm, preferably 1 to 20 μm. In the present invention, the surface layer formed on the ink layer is
It forms part of the transfer film and forms the surface on the side that comes into contact with the transfer paper to stop the printed part of the transfer paper during transfer, prevent scumming, and adhere the ink layer to the transfer paper. Has the function of improving The wax used for forming the surface layer is the same as the wax used for the above-mentioned hot-melt ink layer. As such a thermoplastic resin, for example, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid ester copolymer (EEA), polyethylene, polystyrene, polypropylene, polybutene, petroleum resin, vinyl chloride resin, polyvinyl Alcohol, vinylidene chloride resin,
Methacrylic resin, polyamide, polycarbonate, fluororesin, polyvinyl formal, polyvinyl butyral, acetyl cellulose, nitrocellulose, polyvinyl acetate, polyisobutylene, ethyl cellulose, polyacetal, etc. are used, especially comparative low conventionally used as a heat-sensitive adhesive. Those having a softening point, for example, a softening point of 50 to 80 ° C. are preferable. The ratio of wax and thermoplastic resin used is wax 10
A weight ratio range of 5 to 300 of the thermoplastic resin with respect to 0 is preferable. The surface layer composed of the wax and the thermoplastic resin is formed by applying and drying a dispersion liquid in which the particles of the both are dispersed in an aqueous medium, that is, a mixed medium of water and a water-soluble organic solvent. The surface layer preferably has a thickness of 0.1 μm or more so that the sensitivity does not become insufficient even when the printing energy becomes low as in a high speed type printer.
It is less than μm. If the thickness is less than 0.1 μm, the transfer paper and the ink layer may rub against each other to cause scumming. Aqueous dispersions of wax are known per se, and various ones are commercially available and any of them can be used in the present invention. For example, wax is preferably used in water, preferably a surfactant or a protective colloid. It can also be obtained by dispersion treatment with a wax, or by dissolving the wax in a water-soluble organic solvent and adding it to water, or by adding water to this to precipitate the wax and to form an aqueous solution. It can also be a dispersion. As the organic solvent, ketones such as acetone, alcohols, water-miscible organic solvents such as glycols can be used, but if the amount of the organic solvent in the aqueous dispersion of wax is too large, the ink layer as the base may be damaged. Therefore, it should be 70% or less, preferably 50% or less in the medium. The particle size of the wax in these aqueous dispersions is not particularly limited, but the preferred range is 0.05 to 5 μm.
It is about. Further, the particles of the thermoplastic resin can be obtained from the market as emulsions of various forms and used in the present invention, and can be easily produced as in the case of the wax.
Their particle size is preferably about 0.05 to 5 μm. A desired surface layer is formed by coating and drying the aqueous dispersion containing the above wax and the thermoplastic resin on the ink layer by the same method as for forming the ink layer. When the drying temperature after coating is a temperature at which the wax particles and the thermoplastic resin particles are dissolved, a flat and smooth surface layer is formed. On the other hand, in a preferred embodiment, it is carried out at a temperature at which at least one particle can maintain its particle shape without melting. For example, by drying at a temperature lower than the softening point of the wax or the thermoplastic resin, for example, at a temperature of about 40 to 60 ° C., the existing particles form a surface layer having fine irregularities on the surface. It is recommended that an appropriate amount of extender be added to the surface layer. As a result, bleeding and tailing of the print can be more favorably prevented. Particles with too large a particle size are inappropriate for the extender pigment. Suitable as extender pigments are inorganic fillers such as silica, talc, calcium carbonate, precipitated barium sulfate, alumina, titanium white, clay, magnesium carbonate, carbon black or tin oxide. With a small amount of extender pigment, the effect is poor, while
A large amount lowers the dispersibility and makes it difficult to prepare an ink, and the coated material easily comes off from the base film, so it is preferable to add it in the range of 0.1 to 60% by weight. As described above, the surface layer is added with a coloring agent if necessary,
Or, configure without adding. If a colorant is used, it will overlap with the colorant of the heat-fusible ink layer to give a record of sufficient density, and if only a colorless vehicle is used, the transfer paper and the heat-meltable ink layer will rub against scumming. It can be prevented from occurring. When a heat-sensitive material is used for the base film, it is preferable to provide a layer for preventing sticking of the thermal head on the surface in contact with the thermal head. The sticking prevention layer 5 has a heat-resistant resin and a substance acting as a thermal release agent or a lubricant as basic constituent components. As a heat resistant resin, a compound having two or more amino groups or a diisocyanate or triisocyanate is added to a synthetic resin having a glass transition point of 60 ° C. or more or a thermoplastic resin having an OH group or a COOH group, and a slight crosslinking curing is performed. It is preferable to cause the above. Thermal release agents or lubricants, such as waxes and amides, esters and salts of higher fatty acids, that act by melting when heated, and fluororesins and inorganic substance powders, remain useful as solid There are things. By providing such a sticking prevention layer, thermal printing can be performed without sticking even on a heat-sensitive transfer sheet using a plastic film that is weak against heat as a base material, and it is difficult to cut and process the plastic film. You can take advantage of advantages such as ease. In general, a heat-sensitive transfer image is glossy and beautiful in printing, but on the other hand, it may be difficult to read a document. Therefore, matte printing may be desirable. In such cases, for example,
As proposed by the applicant (Japanese Patent Application No. 58-208306), a base film is coated with an inorganic pigment such as silica or calcium carbonate dispersed in an appropriate solvent to form a mat layer. It is advisable to form a heat-sensitive transfer sheet by coating the above with a heat-meltable ink layer. Alternatively, the base film itself may be mat-processed before use (the technique of Japanese Patent Application No. 58-208307 proposed by the applicant). Needless to say, the present invention can be applied to a heat-sensitive transfer sheet for color printing, so that a multi-color heat-sensitive transfer sheet is also included in the scope of the present invention. (Effects) According to the present invention as described above, by using the thermoplastic resin in addition to the wax when forming the surface layer,
The adhesiveness of the ink layer to the material to be transferred is further improved, and high-speed printing is possible without causing scumming or bleeding of printing even on the transfer paper having a rough surface. Further, in a preferred embodiment, by forming the surface layer from a dispersion of wax containing thermoplastic resin particles in water, without damaging the heat-meltable ink layer at all,
A surface layer with a fine uneven surface is formed, and at the time of printing, the pressure of the thermal head concentrates at least on the convex portion of the uneven shape, so the adhesiveness between the surface layer and the transfer paper is improved and scumming occurs. High-speed printing is possible without causing (Examples) Hereinafter, the present invention will be described more specifically with reference to examples. In the description, parts and% are based on weight unless otherwise specified. Example 1 A polyethylene terephthalate film having a thickness of 3.5 μm was used as a base film, a heat-meltable ink and a surface layer material having the following compositions were prepared on one surface of the base film, and the coating and drying were carried out by the respective means described above to obtain a book. The thermal transfer sheet of the invention was obtained. Heat-fusible ink layer Carbon black (Dia Black G, manufactured by Mitsubishi Kasei) 15 parts Ethylene / vinyl acetate copolymer (EVA Flex 310, manufactured by Mitsui Polychemical) 8 parts Paraffin wax (paraffin 150F, manufactured by Nippon Seiro Co., Ltd.) 50 parts Carnauba wax 25 parts A kneader was kneaded at 120 ° C for 6 hours using an attritor, and was applied and dried at a rate of 3.5 g / m ² (dry state) by a hot melt roll coating method at an ink temperature of 120 ° C. Surface layer 155F Paraffin wax emulsion (WE-70, manufactured by Bond Wax, solid content 40% aqueous emulsion) 20 parts Ionomer resin (Chemipearl S-100, manufactured by Mitsui Petrochemical, solid content 27%) 10 parts 60% isopropanol aqueous solution 15 Part was applied by a gravure coating method at a rate of 0.8 g / m ² (dry state) and dried at 60 ° C. to form a surface mat-like surface layer. Using the above-mentioned thermal transfer sheets with ink layer and surface layer thicknesses of 3.5 μm and 0.8 μm respectively, several types of high-quality smooth paper to low-quality medium paper are selected as the transfer target paper, and a commercially available thermal head Was used for thermal transfer printing. High-speed printing of 40 characters / sec with thermal head energy of 0.7 W / dot was able to be performed on all transfer paper with high quality without scumming. Example 2 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention. Heat-fusible ink layer Carbon black (Dia Black G, Mitsubishi Kasei) 15 parts Ethylene / vinyl acetate copolymer (EVA Flex 310, Mitsui Polychemical) 8 parts Patafin wax (paraffin 150F, Nippon Seiro) 50 Part Carnauba wax 25 parts A kneader was kneaded at 120 ° C. for 6 hours using an attritor, and was applied and dried at a rate of 3.5 g / m ² (dry state) by an ink temperature of 120 ° C. hot melt roll coating method. Surface layer 155F Paraffin wax emulsion (WE-70, manufactured by Bond Wax, solid content 40% aqueous emulsion) 70 parts EVA resin emulsion (bond wax 62-357, manufactured by Bond Wax, solid content 40%) 10 parts 50% isopropanol Aqueous solution 50 parts It was applied by a gravure coating method at a rate of 0.5 g / m ² (dry state) and dried at 73 ° C to form a surface layer having a surface smoothness. Similar to Example 1, this thermal transfer sheet, in which the thicknesses of the ink layer and the surface layer were 3.5 μm and 0.5 μm, respectively, showed good transfer performance. Example 3 Using the same base film as in Example 1, two layers having the following compositions were formed to obtain a thermal transfer sheet of the present invention. Heat-fusible ink layer Carbon black (Dia Black G, manufactured by Mitsubishi Kasei) 15 parts Ethylene / vinyl acetate copolymer (EVA Flex 310, manufactured by Mitsui Polychemical) 8 parts Paraffin wax (paraffin 150F, manufactured by Nippon Seiro Co., Ltd.) 50 parts Carnauba wax 25 parts A kneader was kneaded at 120 ° C for 6 hours using an attritor, and then applied and dried at a rate of 3.5 g / m ² (dry state) by an ink temperature of 120 ° C hot melt roll coating method. Surface layer Carnauba wax 10 parts Ethylene / vinyl acetate copolymer resin (Eva Flex 31
0, manufactured by Mitsui Polychemicals) After melting 2 parts, emulsified (solid content 20%) is applied by a roll coating method at a rate of 0.3 g / m ² (dry state) and dried at 60 ° C. To form a mat-like surface layer. The transfer sheet of this example, in which the thickness of the ink layer was 3.5 μm and the thickness of the surface layer was 0.3 μm, also showed good transfer performance without background stains. Example 4 A heat-meltable ink of each color of yellow (Y), magenta (M), cyan (C), and black (B) having the following composition using a polyethylene terephthalate film having a thickness of 6 μm as a base film and a surface layer An ink layer and a surface layer were formed from the ink to obtain a thermal transfer sheet of the present invention. Heat-fusible ink layer pigment (yellow, magenta, cyan or black pigment), 4 parts ethylene / vinyl acetate copolymer (Smitate KC-10, manufactured by Sumitomo Chemical Co., Ltd.) 7.5 parts Oxidized paraffin ester composite compound (amide polymer T -820, electronic polymer) 12.5 parts Paraffin wax (paraffin SP-0145, manufactured by Nippon Seiro Co., Ltd.) 15 parts Microcrystalline wax (Himic 2065, manufactured by Nippon Seiro Co., Ltd.) 10 parts Isopropanol 5 parts Xylene 46 parts Ink composition of the above 4 colors The ink layer was formed by gravure printing using the material in the order of yellow, magenta, cyan and black in the order of plane. The coating weight at that time was 4 g / m ² (when dried). Surface layer carnauba emulsion (WE-95, manufactured by Bond Wax,
Solid content 40%) 30 parts Ethylene / vinyl acetate copolymer emulsion (Polysol EVAAD-5, Showa High Polymer, solid content 56%) 10 parts 75% isopropanol aqueous solution 60 parts By gravure printing method using the above ink composition. A surface layer was formed by applying a dry weight of 0.7 g / m ² on the previously printed yellow, magenta, cyan and black heat-meltable ink layers. The drying condition at that time was 65 ° C. for 3 seconds. When printing was performed with a color thermal printer using the thermal transfer sheet of the present invention produced by the above steps, there was no scumming caused by rubbing the paper and the film. Also, although the paper had a Bekk smoothness of 20 seconds, clear printing was possible. In addition, ethylene-
Since the vinyl acetate copolymer was contained, the adhesiveness to the paper as the transfer target paper was good and the printing effect was further improved. or,
Since color overprinting was performed, the transfer of the magenta layer onto the yellow layer that was initially printed was improved compared to the case where no thermoplastic resin was added. Example 5 A surface layer was formed by substituting the following ink composition for the surface layer of Example 4 in the same manner as above and applying a dry weight of 1.5 g / m ² . The drying condition at that time was 85 ° C. for 5 seconds. Surface layer Paraffin emulsion (61-137, bond wax, solid content 40%) 40 parts Ethylene-vinyl acetate copolymer emulsion (Polysol EVAAD-5, Showa High Polymer, solid content 56%) 10 parts 60% ethanol aqueous solution When the thermal transfer sheet of the present invention produced as described above was printed in the same manner as in Example 4, there was no background stain, and beautiful color printing was also possible on bond paper having a smoothness of 5 seconds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing a part of a cross section of a heat-sensitive transfer sheet of the present invention. 1: Base film 2: Hot-melt ink layer 3: Surface layer 4: Sticking prevention layer

Claims (1)

(57) [Claims] A method for producing a thermal transfer sheet, comprising forming a heat-fusible ink layer on one surface of a base film, and forming a surface layer on the surface of the ink layer, the surface layer blocking a printed portion of a transfer paper when the ink layer is transferred. , The surface layer, a dispersion liquid in which a wax and a thermoplastic resin are dispersed in a mixed medium of water and a water-soluble organic solvent, is applied to the surface of the ink layer, below the melting point of the wax and the thermoplastic resin A method for producing a thermal transfer sheet, characterized in that the thermal transfer sheet is formed by drying at a temperature of 5 to have fine surface irregularities composed of wax particles and thermoplastic resin particles.