JPH0450199B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a thermal transfer sheet, and more particularly to a thermal transfer sheet used in combination with a thermal transfer sheet in which thermal printing is performed according to image information using a thermal head or laser. Regarding the seat.

Technical background of the invention and its problems Conventionally, thermosensitive coloring paper has been mainly used to obtain images according to image information using a thermal head or laser. In this heat-sensitive coloring paper, a colorless or light-colored leuco dye provided on a base paper and a color developer are brought into contact with each other by heating to obtain a colored image. As such color developers, phenolic compounds, zinc salicylate derivatives, rosin, clay minerals such as activated clay, and the like are generally used. However, heat-sensitive color paper as described above has the fatal drawback that the color image will fade if stored for a long period of time, and color printing is limited to two colors and has continuous gradation. It was not possible to obtain a color image.

On the other hand, thermal transfer paper in which a heat-fusible wax layer in which pigments are dispersed is provided on a base paper has recently begun to be used. When the thermal transfer paper and the transfer paper are placed one on top of the other and thermal printing is performed from the back side of the thermal transfer paper, the wax layer containing the pigment is transferred onto the transfer paper and an image is obtained. According to this printing method,
Durable images can be obtained, and multicolor images can be obtained by printing multiple times using thermal transfer paper containing pigments in the three primary colors, but photographs with essentially continuous gradations cannot be used. It is not possible to obtain such an image.

Incidentally, in recent years, there has been an increasing demand for obtaining photograph-like images directly from electrical signals, and various attempts have been made. One such attempt is a CRT
This method involves projecting an image on top and photographing it using silver halide film, but if the silver halide film is an instant film, the running cost increases, and if the silver halide film is 35mm film, has the disadvantage that it is not instantaneous because it requires development processing after photographing. As another method, an impact ribbon method or an inkjet method has been proposed, but the former has the disadvantage of poor image quality, and the latter requires image processing, making it difficult to easily obtain photographic images. It has the disadvantage of being ugly.

In order to solve these drawbacks, a thermal transfer sheet provided with a sublimable disperse dye layer that has the property of transferring when heated is used in combination with a thermal transfer sheet, and the sublimable disperse dye is transferred onto the thermal transfer sheet while controlling the sublimable disperse dye layer. A method has been proposed to obtain a photograph-like image with gradation by performing a transition. This method is attracting attention because an image having continuous gradation can be obtained from a television signal through simple processing, and the equipment used therein is not complicated. One of the conventional techniques similar to this method is the dry transfer printing method for polyester fibers, which involves dispersing or dissolving dyes such as sublimable disperse dyes in a synthetic resin solution. This paint is applied in a pattern onto thin paper, etc. and dried to form a thermal transfer sheet.The thermal transfer sheet is placed on polyester fibers, which are the heat transfer sheet, and heated in close contact to dye the polyester fibers with disperse dyes. This is a method to obtain an image.

Another conventional technique similar to the present invention is a dry transfer printing method for acrylic fibers. In this method, cationic dyes are used. By the way, it dyes acrylic fiber well,
Moreover, basic dyes with good light resistance are called cationic dyes, but since these cationic dyes are generally difficult to sublimate, sublimation properties can be improved by changing the cationic dye to a free base form, deprotonating it, or converting the counter ion. It is used at a higher level. Furthermore, the dyeing sites of acrylic fibers are generally sulfonic acid residues, which are usually in the form of -SO ₃ Na, but by changing this to -SO ₃ NH ₄ , dry transferability is improved. It is said.

However, even if a thermal transfer sheet as described above and a thermal transfer sheet made of polyester fiber or acrylic fiber are superimposed and printed by heating with a thermal head or the like, a high-density color image cannot be obtained. One of the reasons for this is that the surface smoothness of the polyester fiber cloth or acrylic fiber cloth is not good, but it is believed that this is mainly due to the following reasons. In other words, in the normal dry transfer printing method or wet transfer printing method,
The migration of sublimable dyes onto polyester fiber fabrics is
This is because, while heating is carried out over a sufficient period of time, heating using a thermal head or the like is usually extremely short, and as a result, the dye does not transfer sufficiently onto the fiber cloth. By the way, in the dry transfer printing method, dye transfer is achieved by heating at 200°C for about 1 minute, whereas heating with a thermal head is as short as several milliseconds at 400°C.

For this reason, it has been proposed to use dyes with higher sublimability in thermal transfer sheets, and such dyes with higher sublimability include leuco dyes that are colorless or light-colored at room temperature. When these leuco dyes come into contact with acidic substances such as aromatic carboxylic acids, phenolic compounds, and organic sulfonic acids, they undergo lactone ring opening, spiropyran ring opening, or deacylation reactions, resulting in color development.

However, no matter how highly sublimable a dye is used in a thermal transfer sheet, it has not been possible to obtain a practical colored image. This is because even if a clear colored image is temporarily obtained, this colored image has extremely poor light resistance and lacks long-term storage stability.
The poor light resistance of such colored images is due to the fact that the dye is oxidized by excited oxygen generated during light irradiation. The use of ultraviolet absorbers or excited oxygen scavengers to increase the apparent lightfastness of dyes and pigments is already known in the dye and pigment art.

However, when printing is performed using a combination of a thermal transfer sheet and a thermal transfer sheet, sufficient effects cannot be observed simply by including an ultraviolet absorber or an oxygen scavenger in the thermal transfer layer. This is because the ultraviolet absorber or oxygen scavenger, which cannot exert its full effect unless it is located at the top of the thermal transfer sheet, is located at the bottom of the colored image.

As a result of further research based on these facts, the present inventors discovered that the above-mentioned drawbacks could be solved at once by including a specific component in the color developer layer of the thermal transfer sheet. As a result, we have completed the present invention.

OBJECTIVES AND SUMMARY OF THE INVENTION The present invention seeks to solve the drawbacks associated with the prior art, and provides a thermal transfer sheet having a thermal transfer layer containing a heat-transferable dye, and a thermal transfer sheet containing a specific component. By using it in combination with a thermal transfer sheet, the following objectives are to be achieved.

(a) To provide a recording material from which a colored image with continuous gradations like a photograph can be directly obtained from an electrical signal.

(b) A recording material that can produce highly transparent colored images with high density, excellent light resistance, and clear, high-resolution colored images that do not fade even after long-term storage. to provide.

In order to achieve the above object, in the present invention, a heteropolyacid or a salt thereof is contained in the color developer layer of a thermal transfer sheet, and this thermal transfer sheet is used in combination with a thermal transfer sheet. Further, it is preferable to use the heteropolyacid after treating it with an ammonium compound or an amine derivative in advance.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, preferred specific examples of the present invention shown in the drawings will be described.

The thermal transfer sheet 1 according to the present invention is constructed by providing a color developer layer 3 on a base material 2 as shown in FIG. 1, but as shown in FIG. The thermal transfer sheet may be composed of: When the color developer layer 3 is provided on the base material 2, the thickness of the color developer layer 3 is about 3 to 50 μm, preferably about 5 to 15 μm. On the other hand, when the thermal transfer sheet is composed of the color developer layer 3 alone, the thickness of the color developer layer 3 is 60 to 200 μm.
m, preferably about 90 μm to 150 μm.

The base material 2 is preferably one that has excellent smoothness and does not deform due to the heat and pressure applied during printing, and specifically, various synthetic papers,
Silver salt photographic paper, mirror coated paper, calendar coated paper, various heat-resistant plastic films, etc. are used. Among these, synthetic paper and silver salt photographic paper are particularly preferred.

The binder resin that forms the color developer layer 3 has the ability to sufficiently retain the color developer, has good adhesion to the base material 2, does not fuse with the thermal transfer sheet during thermal printing, and is also able to be used easily from the thermal transfer sheet. It is preferable to use a material that does not hinder the movement of the migrating dye into the interior.
Specifically, polyester resins, modified EVA resins, acrylic resins, maleic anhydride resins,
Urethane resin, polyvinyl alcohol resin,
Vinyl acetate resin, EVA resin, styrene resin, styrene copolymer resin (for example, butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, acrylonitrile-butadiene-styrene copolymer resin, chlorinated polyethylene resin) acrylonitrile-styrene copolymer resin,
methyl methacrylate-butadiene-styrene copolymer resin, methyl methacrylate-styrene copolymer resin, etc.), rubber resin, silicone resin, cellulose resin, natural rosin resin, amino resin, nylon resin, polycarbonate resin, Ethylene-vinyl acetate-vinyl chloride copolymer resin, polymethylpentene resin, ionomer resin, acetal resin, phenol resin, epoxy resin, melamine resin, alkyd resin, etc. can be used.

Among the binders mentioned above, resins with a low glass transition temperature are preferred from the viewpoint of color development, and examples of such resins include polyester resins and modified EVA.
Examples include acrylic resins, maleic anhydride resins, urethane resins, and the like.

As described later, in the present invention, a heteropolyacid is added to the color developer layer 3, and this heteropolyacid tends to form a colored substance during heating or storage. This coloring phenomenon of heteropolyacids is caused by the use of resins containing sulfonic acid residues, resins containing carboxylic acid residues, resins containing phosphoric acid residues, or resins with an acid value of 100 or more as binder resins. effectively prevented by using Among these binder resins, resins containing sulfonic acid residues are particularly preferred.

In the present invention, a heteropolyacid or a heteropolyacid salt is added as a color developer to the color developer layer 3 of the thermal transfer sheet. Heteropolyacid refers to a polyacid formed by condensation of inorganic acids that has two or more types of central atoms, and specifically includes phosphotungstic acid, phosphomolybdic acid,
Preferred examples include those having vanadium, molybdenum, or tungsten as a central atom, such as phosphomolybdenum-tungstic acid, phosphovanadate, and silicon-molybdic acid. In addition, P.
As, Si, Ge, Ti, Zr, Sn, Ce, Th, Fe, Pt,
Examples include those having Mn, Co, Ni, Te, Cr, Al, Cu, B, H, etc. as a central atom. Further, as the heteropolyacid, ammonium salts, amine salts, alkanolamine salts, etc. of the above-mentioned heteropolyacids can be preferably used. Additionally, alkali metal and alkaline earth metal salts of heteropolyacids may also be used.

It is generally known that phosphotungstic acid and phosphomolybdic acid react with basic dyes in an aqueous solution to obtain pigments with excellent light resistance. When used as a chemical, heteropolyacids tend to react with reducing substances to form colored substances, but it is possible to prevent the coloring phenomenon by treating heteropolyacids with ammonium compounds or amine derivatives. Found out. Examples of ammonium compounds for treating heteropolyacids include ammonium hydroxide, ammonium salts such as ammonium hydrochloride, ammonium phosphate, and ammonium acetate, and examples of amine derivatives include primary aliphatic amines, secondary fatty acid amines,
Examples include tertiary aliphatic amines, aromatic amines, and salts of the above amines and organic or inorganic acids.

The heteropolyacid can be treated with the ammonium compound or amine derivative as described below.

When the ammonium compound or amine derivative is water-soluble and the binder resin is also water-soluble, the heteropolyacid, ammonium compound or amine derivative, and binder resin may be mixed in an aqueous solution.

In addition, if the ammonium compound or amine derivative is water-soluble and the binder resin is oil-soluble, first dissolve the heteropolyacid in a small amount of alcohol or ketone, and then add the resulting solution to the binder resin. Add to solution. Next, when an aqueous solution of an ammonium compound or an amine derivative is added to the obtained solution and mixed with stirring,
The reaction between the heteropolyacid and the ammonium compound or amine derivative proceeds at the interface, and when the mixture is left to stand, most of the heteropolyacid that has reacted with the ammonium compound or amine derivative is recovered in the binder resin solution.

In addition to these methods, a heteropolyacid may be reacted with an ammonium compound or an amine derivative using an emulsion.

The heteropolyacid as a color developer is contained in the color developer layer in an amount of 1 to 95% by weight, preferably 20 to 95% by weight of the total weight of the color developer layer.
Used in an amount of 60% by weight.

In order to provide the color developer layer 3 on the base material 2, a binder resin containing a heteropolyacid as a color developer is applied by a known coating method such as a roll coating method, a gravure coating method, or a Miyabur coating method. Then, it may be applied onto the base material 2. Color developer layer 3 is on base material 2
The film thickness is 0.1 μm to 1 μm, preferably 2 to 20 μm.

In addition to the heteropolyacid as a color developer, other color developers such as phenolic compounds, zinc salicylate derivatives, rosin, clay minerals such as activated clay, sulfonic acid groups, phosphoric acid groups, or carboxylic acids are contained in the color developer layer. It is also possible to add substances containing. Further, in order to improve the light resistance of a colored image, an ultraviolet absorber or an excited oxygen scavenger may be added to the developer layer. As the ultraviolet absorber, benzophenone compounds, diphenyl acrylate compounds, benzotriazole compounds, etc. can be used. Further, as the excited oxygen scavenger, dibutyldithiocarbamate metal salt, bisdithiobenzyl metal salt, etc. can be used. Alternatively, existing anti-aging agents for rubber or plastics are also effective in improving the light fastness of colored images. These ultraviolet absorbers, excited oxygen scavengers, and the like are used in an amount of 10% by weight or less based on the binder resin.

Further, in order to prevent the developer layer from fusing with the thermal transfer paper during heating, it is preferable to add curable silicone or non-curable silicone resin to the developer layer. Note that fusion between the color developer layer and the thermal transfer sheet during heating can also be prevented by crosslinking a portion or the entire surface of the binder resin. Crosslinking of the binder resin can be achieved by electron beam irradiation, peroxide addition, and the like.

The thermal transfer sheet 1 according to the present invention may have a color developer layer 3 on the base material 2 and a protective layer 4 on the color developer layer 3, as the case may be, as shown in FIG. It may be provided and configured.

As the resin for forming the protective layer 4, the same resin as that used for forming the color developer layer is used, but the resin for forming the protective layer has good mechanical strength, heat resistance, water resistance, and solvent resistance. They are selected with emphasis on characteristics such as gender. In particular, it is important to select a resin that does not fuse with the thermal transfer sheet during heating, and it is also important to improve surface releasability or improve mechanical strength through crosslinking.

Although the protective layer 4 is required to pass the dye transferred from the thermal transfer sheet, it has been found that the above-mentioned resin for forming the color developer layer has almost no problem in this respect. However, if the thickness of the protective layer 4 becomes too large, the passage of the dye may be hindered, so the thickness of the protective layer 4 is desirably 0.1 to 100 .mu.m, preferably 2 to 20 .mu.m.

In order to improve the light resistance of the colored image, an ultraviolet absorber or an excited oxygen absorber can be added to the protective layer 4. In addition, the protective layer 4 is replaced by the color developer layer 3.
There is also the effect that the image obtained by providing it above becomes clearer. The reason for this is not clear, but it is thought that it is because the protective layer 4 has the function of preventing the migrated dye from being dispersed and locally localized to develop color.

In addition to the above-mentioned role, the protective layer 4 provides water resistance and solvent resistance to the thermal transfer sheet, and
It also has the role of improving the storage stability of the resulting colored image.

The thermal transfer sheet as described above is used in combination with a thermal transfer sheet. A typical thermal transfer sheet 5 is constructed by providing a thermal transfer layer 7 on one side of a support 6, as shown in FIG.
When this thermal transfer layer 7 is heated, the dye contained therein is transferred onto the thermal transfer sheet.

The support 6 has the role of holding the thermal transfer layer 7, and since heat is applied during thermal transfer, it is desirable that the support 6 has a mechanical strength that does not cause any trouble in handling even when heated. Moreover, in many cases, thermal energy for thermal transfer is applied from the side of the support 6 on which the thermal transfer layer 7 is not provided, so it is desirable that the support 6 also has the property of easily transmitting thermal energy.

Specific examples of the support 6 include flexible thin sheets such as condenser paper, glassine paper, parchment paper, highly sized paper, and plastic film. Among these, condenser paper and polyethylene terephthalate film are often used.Condenser paper is mainly used when heat resistance is important, and polyethylene terephthalate film is used when emphasis is placed on preventing breakage during handling with mechanical devices. Mainly used. The thickness of this support 6 is usually 3 to 50 μm, preferably 5 to 15 μm.
That's about it.

The thermal transfer layer 7 contains a dye that can escape from the thermal transfer layer and transfer to the developer layer of the thermal transfer sheet when heated.

After such a dye migrates to the color developer layer of the thermal transfer sheet, it comes into contact with a heteropolyacid as a color developer contained in the color developer layer to develop color.

Examples of the above-mentioned dyes include the following types of compounds.

(a) Leuco dyes For example, diphenylmethane compounds, triphenylmethane compounds, phenothiazine compounds, spirodipyran compounds, indolinospiropyran compounds, fluoran compounds, rhodamine lactam compounds, etc. These leuco dyes are used in heat-sensitive coloring paper or pressure-sensitive coloring paper, and are colorless or light-colored at room temperature.

(b) Basic dyes For example, diarylmethane compounds, triarylmethane compounds, thiazole compounds, methine compounds, xanthene compounds, oxazine compounds, thiazine compounds, azine compounds, acridine compounds, azo compounds Such.

(c) Cationic dyes, such as triarylmethane compounds, methine compounds, azo compounds, azomethine compounds, anthraquinone compounds, etc.

The cationic dye refers to a basic dye that dyes acrylic fibers well and has excellent light resistance.

The above-mentioned basic dyes and cationic dyes can be used as they are or in the form of alkali-treated dyes, and counterion exchangers or leuco dyes of these dyes can also be used.

The above dye is dispersed in a suitable synthetic resin binder forming a thermal transfer layer and provided on the support 6. As such a synthetic resin binder, it is usually preferable to select one that has high heat resistance and does not hinder dye migration that occurs when heated, and for example, the following are used.

() Cellulose resins Ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate, cellulose acetate butyrate, etc.

() Vinyl resin polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinylpyrrolidone,
polyester, polyacrylamide, etc.

Among the above synthetic resin binders, polyvinyl butyral resin or cellulose resin is preferred from the viewpoint of heat resistance.

To provide the thermal transfer layer 7 on the support 6, a dye and a synthetic resin binder are kneaded with a solvent or a diluent to form a coating composition for the thermal transfer layer, and this is applied onto the support 6 by an appropriate printing or coating method. Just set it up. Note that optional additives may be added to the coating composition for the thermal transfer layer, if necessary.

The basic structure of the thermal transfer sheet is as described above, but when the surface of the support is directly heated by a contact heating means such as a thermal head, the support 6 is heated as shown in FIG. By providing a slippery layer 8 containing a lubricant such as wax or a mold release agent on the side where the thermal transfer layer is not provided,
It is possible to prevent the heating means such as a thermal head from being fused to the support, and to improve the sliding properties.

The thermal transfer sheet may be in the form of a single sheet cut to a required size, continuous or rolled, or may be in the form of a narrow tape.

The thermal transfer sheet and the thermal transfer sheet prepared as described above are stacked facing each other so that the thermal transfer layer of the thermal transfer sheet and the color developer layer of the thermal transfer sheet are in contact with each other, as shown in FIG. By applying thermal energy according to image information to the interface of the color developer layer, the dye in the thermal transfer layer is transferred to the color developer layer.

In addition to thermal heads, heat sources that provide thermal energy include laser light, infrared flash,
A known device such as a thermal pen can be used. Thermal energy can be applied from the thermal transfer sheet side, from the thermal transfer sheet side, or from both sides, but from the viewpoint of effective use of thermal energy, it is best to apply from the thermal transfer sheet side. good. However, it is better to apply thermal energy from the thermal transfer sheet side, because it is possible to control the applied thermal energy to express the gradation of light and shade of the image, or to promote the diffusion of dye on the thermal transfer sheet to create a continuous image. This method is preferable in the sense that the expression of gradation is more reliable, and the advantages of both methods can be enjoyed at the same time in the method of applying thermal energy from both sides.

When a thermal head is used as a heat source for providing thermal energy, the applied thermal energy can be varied continuously or in multiple steps by modulating the voltage or pulse width applied to the thermal head.

When a laser beam is used as a heat source for providing thermal energy, the amount of thermal energy provided can be changed by changing the amount of laser light or the irradiation area. If a dot generator with a built-in acousto-optic element is used, thermal energy can be applied depending on the size of the halftone dot. When using a laser beam, it is best to make sure that the thermal transfer sheet and the thermal transfer sheet are in close contact with each other, and the surface to be irradiated with the laser beam may be colored, for example, black to improve the absorption of the laser beam. good.

When using an infrared flash lamp as a heat source for providing thermal energy, it is best to use a colored layer such as black, similar to when using laser light, or a pattern that continuously expresses the shading of the image, such as black. Alternatively, it may be done through these patterns using halftone dot patterns,
Alternatively, a colored layer such as black on one side and a negative pattern corresponding to the negative of the pattern described above may be combined.

When thermal energy is applied to the interface between the thermal transfer layer and the color developer layer as described above, the amount of dye in the thermal transfer layer is vaporized or melted according to the applied thermal energy, and the color developer layer is heated. It is transferred, accepted, and develops color.

With the thermal transfer recording described above, a dye corresponding to the thermal energy is thermally transferred to the color developer layer, and a one-color image can be recorded. By sequentially replacing the black thermal transfer sheet as needed and performing thermal transfer according to each color, it is also possible to obtain a color photographic color image consisting of a combination of colors. Note that instead of using thermal transfer sheets for each color as described above, a single thermal transfer sheet having areas pre-painted in each color is used, and first, for example, a yellow color separation image is thermally transferred using the yellow area. Next, if you use a method that uses, for example, the red area of the thermal transfer sheet, and then repeat the process sequentially to thermally transfer the separated color images of yellow, red, indigo, and if necessary, black, there is no need to replace the thermal transfer sheet. It has the advantage of becoming

Note that the quality of the image obtained can be improved by appropriately adjusting the size of the heat source used to apply thermal energy, the adhesion between the thermal transfer sheet and the thermal transfer sheet, and the thermal energy.

The thermal transfer sheet according to the present invention can be used in combination with a thermal transfer sheet for printing using various thermal printing printers, facsimiles, photo prints using magnetic recording methods, printing from television screens, etc. can.

For example, a received television screen may be stored on a storage medium such as a magnetic tape or magnetic disk.
The signal of each color separation pattern of yellow, red, indigo, and black if necessary is stored, and the signal of each stored color separation pattern is output, and the thermal energy corresponding to this signal is transferred to a thermal head, etc. By applying heat to the stacked body of the thermal transfer sheet and the thermal transfer sheet using the heat source described above and performing thermal transfer for each color sequentially, the television screen can be reproduced as a sheet-like print. When a combination of a thermal transfer sheet and a thermal transfer sheet according to the present invention is used for printing out such a television screen, the thermal transfer sheet usually has a white color developer layer alone or a colorless color developer layer. It is convenient to use a transparent color developer layer lined with a base material such as paper, or a white color developer layer lined with a base material such as paper to obtain a reflective image.

The same thing as above can also be done when using a combination of characters, figures, symbols, colors, etc., or a graphic pattern formed on a CRT screen by computer operation as an original image.
Furthermore, when the original image is a fixed image such as a painting, photograph, or printed matter, or an actual object such as a person, still life, or landscape, the same method as described above can be performed by using an appropriate means such as a video camera as a medium. Furthermore, when creating signals for each color separation pattern from the original image, an electronic plate making machine (color scanner) used for photolithography for printing may be used.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A polyester film with a thickness of 9 μm that was corona-treated on one side was used as a support, and a coating composition for a thermal transfer layer () having the following composition was thoroughly and uniformly ground in a mortar on the corona-treated film surface. , this is 0.24mm so that the thickness when dry is 1μm.
It was coated with a wire bar wrapped with wire of φ and dried with a dryer to obtain a thermal transfer sheet ( ).

Coating composition for thermal transfer layer () CA solvent ⁽¹⁾ 7.5 parts by weight CA varnish ⁽²⁾ 7.5 parts by weight Eisen Carotene Blue 3GLH (manufactured by Hodogaya Chemical Industries) 0.3 parts by weight KOH 0.1 part by weight (1) Toluene: Butyl acetate: Butanol = 9:
2:1 mixed solvent (2) 10% by weight of ethyl cellulose resin dissolved in the above CA solvent A thermal transfer sheet () was prepared in the same manner except that a coating composition for a thermal transfer layer () having the following composition was used. Obtained.

Coating composition for thermal transfer layer () CA solvent 7.5 parts CA varnish 7.5 parts by weight Leuco dye TH1109 (manufactured by Hodogaya Chemical Industry)
0.2 parts by weight Next, a coating composition for the developer layer having the following composition ()
#32 on 100 μm thick synthetic paper as a base material.
It was coated with a wire bar to a dry film thickness of 5 μm, and then dried in an oven to obtain a thermal transfer sheet ( ).

Paint composition for developer layer () Polyvinyl alcohol (manufactured by Nippon Gosei Kagaku Kogyo)
0.4 parts by weight Phosphortungstic acid 0.5 parts by weight Saturated ammonium hydroxide solution 0.5 parts by weight Water 5 parts by weight Thermal transfer sheet obtained as above ()
When this and the thermal transfer sheet (2000) were superimposed and printed on this using a thermal printer, a cyan colored image was obtained. When we conducted a light fastness test by irradiating this colored image with light from a carbon arc lamp using a sunshine weather meter, we found that the colored image was JIS 3
It had a light resistance of 100%.

In addition, the thermal transfer sheet () obtained as described above and the thermal transfer sheet () are overlapped,
When this was printed using a thermal printer, a cyan colored image was obtained. When this colored image was subjected to a light fastness test by irradiating it with light from a carbon arc lamp using a sunshine weather meter, the colored image had light fastness of JIS class 2.

Example 2 A coating composition for a color developer layer () having the following composition was coated onto a 100 μm thick synthetic paper as a base material using a wire bar (#32) in which a wire of 0.8 mmφ was wound to give a dry film thickness of 5 μm. The film was coated in the same manner as above, and then dried in an oven to obtain a heat transfer sheet (2).

Coating composition for color developer layer () S varnish ⁽¹⁾ 4 parts by weight phosphotungstic acid 0.5 parts by weight water 2 parts by weight (1) Methyl methacrylate and 2-acrylamido-2-methylpropanesulfonic acid (AMPS)
Copolymer with (AMPS content 25% monomer units)
in isopropyl alcohol solution (the copolymer is
present in an amount of 32% by weight, AMPS is neutralized with ammonia).

Thermal transfer sheet obtained as above () and the thermal transfer sheet obtained in Example 1 ()
When these were superimposed and printed using a thermal printer, a cyan colored image was obtained. When this colored image was subjected to a lightfastness test by irradiating it with light from a carbon arc lamp using a sunshine weather meter, the colored image had lightfastness of JIS grade 4 or higher.

Example 3 Thermal transfer sheet obtained in Example 2 () and
When the thermal transfer sheet () obtained in Example 1 was superimposed and printed on this with a thermal printer, a cyan colored image was obtained. When we performed a lightfastness test by irradiating this colored image with the light of a carbon arc lamp using a sunshine weather meter, we found that
The colored image had light resistance of JIS grade 3 or higher.

Example 4 A saturated ammonium sulfate solution was added to a developer layer coating composition (2) having the following composition, stirred for several minutes to treat phosphotungstic acid with an ammonium compound, and then allowed to stand, after which the upper layer solution was separated. This was applied onto a 100 μm thick synthetic paper as a base material using a #32 wire bar so that the dry film thickness was 5 μm, and then dried in an oven.

Coating composition for color developer layer () Modified EVA resin (Elvaloiwa 41-P) (manufactured by Mitsui Polychemical Co., Ltd.) 2 parts by weight Phosphortungstic acid 0.3 parts by weight Zinc dibutyldithiocarbamate 0.01 parts by weight Ethanol 2 parts by weight Methyl ethyl ketone 3 parts by weight Benzene 2 parts by weight Toluene 9 parts by weight Next, on the developer layer of the heat transfer sheet obtained as above, a coating composition for a protective layer having the following composition was applied so that the dry film thickness was 2 μm. 0.4mmφ
It was applied with a wire bar (#16) wrapped with wire and allowed to dry.

Coating composition for protective layer Modified EVA resin (Elvaloiwa 41-P) (manufactured by Mitsui Polychemicals) 2 parts by weight Ultraviolet absorber (Tinupin 328) (manufactured by Ciba Geigy) 0.3 parts by weight Toluene 19 parts by weight Methyl ethyl ketone 2 parts by weight Next obtained The protective layer is cross-linked by irradiating the entire surface with an electron beam of 10 megarads to form a thermal transfer sheet ().
I got it.

This thermal transfer sheet ( ) and the thermal transfer sheet ( ) obtained in Example 1 were superimposed and printed on this with a thermal printer, resulting in a cyan colored image. When this colored image was subjected to a light fastness test by irradiating it with light from a carbon arc lamp using a sunshine weather meter, the colored image had light fastness of JIS class 3 or higher.

[Brief explanation of drawings]

1, 2 and 3 are cross-sectional views of a thermal transfer sheet according to the present invention, and FIGS. 4 and 5 are cross-sectional views of a thermal transfer sheet used in combination with the thermal transfer sheet. , and FIG. 6 is a schematic cross-sectional view when the thermal transfer sheet and the thermal transfer sheet are used in combination. DESCRIPTION OF SYMBOLS 1... Thermal transfer sheet, 2... Base material, 3... Color developer layer, 4... Protective layer, 5... Thermal transfer sheet, 6
. . . Support, 7. Thermal transfer layer, 8. Slip layer.

Claims (1)

[Scope of Claims] 1. A heat transfer sheet having a color developer layer, which is used in combination with a heat transfer sheet having a heat transfer layer containing a heat-transferable dye that develops color upon contact with a color developer. A thermal transfer sheet characterized in that a color developer layer contains a heteropolyacid or a salt thereof as a color developer. 2. The thermal transfer sheet according to claim 1, wherein the heteropolyacid is treated with an ammonium compound or an amine derivative. 3. The thermal transfer sheet according to claim 1, wherein the color developer layer is provided on the base material. 4. The thermal transfer sheet according to claim 3, characterized in that a protective layer is provided on the developer layer. 5. The thermal transfer sheet according to claim 4, wherein the protective layer contains an ultraviolet absorber, an excited oxygen scavenger, or both. 6. The thermal transfer sheet according to claim 1, wherein the binder resin forming the developer layer contains a sulfonic acid residue. 7. The thermal transfer sheet according to claim 1, wherein the binder resin forming the color developer layer is made of a synthetic resin with a low glass transition temperature.