JP2020203402A - Thermal transfer image-receiving sheet and method for producing the same - Google Patents

Abstract

To provide a thermal transfer image-receiving sheet that gives a uniform image.SOLUTION: On one surface side of a base material 100, a hollow layer 200 and a dye receiving layer 300 are formed in the stated order. The hollow layer 200 has at least hollow particles and a binder resin. The binder resin has at least one of natural rubber and synthetic rubber as the main component. In one surface of the hollow layer 200, not the other surface on the base material side, a waviness curve maximum valley depth Wv (ISO4287-1997) is 2.0 um or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a thermal transfer image receiving sheet used in a thermal transfer printer and a method for producing the same.

Generally, the heat-sensitive transfer recording medium has an ink ribbon used in a heat-sensitive transfer printer and a heat transfer image receiving sheet which is a transfer target. The ink ribbon is provided with a heat-sensitive transfer layer on one surface of the base material and a heat-resistant slipping layer (backcoat layer) on the other side of the base material. Here, the heat-sensitive transfer layer is a layer of ink, and the ink is sublimated (sublimation transfer method) or melted (melt transfer method) by the heat generated in the thermal head of the printer and transferred to the heat transfer image receiving sheet side. It is a thing. The heat transfer image receiving sheet is provided with a dye receiving layer on one surface of a base material, and the dye receiving layer receives the ink transferred from the above-mentioned ink ribbon and forms an image.

Currently, among the heat-sensitive transfer methods, the sublimation transfer method can easily form various images in full color in addition to improving the functionality of the printer, so self-printing of digital cameras, cards such as identification cards, output products for amusement, etc. , Widely used.
Along with the diversification of the above-mentioned applications, there has been a growing demand for miniaturization, high speed, low cost, environmental compatibility, and durability to the obtained prints. In recent years, the same surface of the base material of the ink ribbon has been increasing. A heat-sensitive transfer recording medium provided with a plurality of dye layers provided on the side of the paper so as not to overlap with a protective layer or the like that imparts durability to a printed matter has become widespread.

Under the above circumstances, with the diversification and widespread use of thermal transfer image sheets, the purpose is to improve the heat insulation of the heat transfer image receiving sheet against heat from the thermal head and the cushioning property to improve the image quality of the printed matter. , A thermal transfer image receiving sheet in which a hollow layer having fine bubbles is provided on the surface of the base material or between the base material and the dye receiving layer has been proposed. The hollow layer is formed by the method described in Patent Document 1 in which a film having air bubbles inside is bonded to a base material, or by applying a coating liquid in which hollow particles and a binder resin are mixed. The method described in Patent Document 2 and the like can be mentioned.

Japanese Unexamined Patent Publication No. 1-130989 Japanese Unexamined Patent Publication No. 8-25813

However, the method of forming a hollow layer on the heat transfer image receiving sheet by adhering the film to the base material has a problem that curling is likely to occur due to heat shrinkage of the film. On the other hand, the method of forming the hollow layer by coating has an advantage that it is relatively easy to prevent the occurrence of curl.
Further, as described above, the hollow layer also has the purpose of enhancing the cushioning property. Therefore, it is desirable that the material forming the hollow layer has high flexibility. At the same time, in order to improve the smoothness of the surface after printing, it is desirable that the stability after applying pressure is also high. Examples of the material satisfying the above two performances include rubbers such as natural rubber and synthetic rubber such as styrene-butadiene rubber (SBR).

When the hollow layer is formed on the heat transfer image receiving sheet by coating the hollow particles and the binder resin, it is necessary to disperse the hollow particles evenly in the binder resin in order to give the printed matter a uniform appearance. Become. However, the dispersibility of the hollow particles is greatly affected by the pH in relation to the surface charge thereof, but the pH of the hollow particle dispersion is often about 8, and when the pH greatly deviates from this value, the hollow particles May start to agglomerate, causing irregularities on the surface of the hollow layer, resulting in non-uniform images of the resulting print.

On the other hand, various additives are added to the latex in which the rubber fine particles are dispersed in water. In particular, an alkaline stabilizer is added for the purpose of improving the stability by adjusting the surface charge of the rubber fine particles. May be done. Alkaline stabilizers are concentrated in the process of drying, and the pH of the coating solution may increase during drying, but the increase in pH becomes remarkable especially when the film thickness is high. In such a case, there is a problem that the dispersibility of the hollow particles cannot be sufficiently obtained due to the increase in pH, and as a result, the hollow particles are aggregated and only a non-uniform image can be obtained. If the alkali-based stabilizer is not added to the latex, the dispersibility of the hollow particles is maintained, a smooth coating film is obtained, and a uniform image can be obtained, but the stability of the latex is reduced, and storage and coating are performed. There is a problem that the viscosity of latex changes and gelation occurs due to slight changes in the environment.

The present invention has been made by paying attention to the above points, and an object of the present invention is to provide a thermal transfer image receiving sheet capable of obtaining a uniform image.

In order to solve the problem, in the thermal transfer image receiving sheet according to one aspect of the present invention, a hollow layer and a dye receiving layer are formed in this order on at least one surface side of the base material, and the hollow layer is formed with at least hollow particles. It has a binder resin, and the binder resin is mainly composed of at least one of natural rubber and synthetic rubber, and the maximum valley depth Wv (ISO4287-197) of the waviness curve on the surface of the hollow layer is 2.0 um or less. The gist is that.

The method for producing a thermal transfer image sheet, which is one aspect of the present invention, is a method for producing a thermal transfer image sheet in which a hollow layer and a dye receiving layer are formed in this order on at least one surface side of a base material, and is a natural rubber. Ink containing hollow particles and a pH buffer solution in an aqueous colloid of at least one of the synthetic rubbers is applied onto the substrate and dried to form the hollow layer, and the ink is formed in an environment of 25 ° C. The gist is that the pH is 8.0 or more and 9.0 or less, and the ratio of the solid content of the pH buffer solution to the solid content of the entire ink is 0.5% by weight or more and 5.0% by weight or less. And.

According to one aspect of the present invention, it is possible to obtain a heat-sensitive transfer image receiving sheet capable of obtaining a uniform image.

This is an example of a cross-sectional view showing a schematic configuration of a thermal transfer image receiving sheet used in carrying out the present invention.

Hereinafter, embodiments of the present invention (hereinafter, referred to as “the present embodiment”) will be described with reference to the drawings.
[Overall configuration of thermal transfer image receiving sheet]
As shown in FIG. 1, the heat transfer image receiving sheet of the present embodiment includes a base material 100, a hollow layer 200, and a dye receiving layer 300.

[Structure of base material 100]
The base material 100 is not limited except that heat resistance and strength that are not softened and deformed by heat pressure in thermal transfer are required, and conventionally known base materials 100 are used.

Examples of the material of the base material 100 include condenser paper, glassin paper, sulfated paper, high-sized paper, synthetic paper (dioxide-based, polystyrene-based), high-quality paper, art paper, coated paper, resin-coated paper, and cast. Coated paper, wallpaper, backing paper, synthetic resin or emulsion impregnated paper, synthetic rubber latex impregnated paper, synthetic resin inner sheet paper, paperboard, etc., cellulose fiber paper, or polyester, polyacrylate, polycarbonate, polyurethane, polyimide, polyetherimide, Cellulous derivatives, polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polystyrene, acrylic, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, nylon, polyether ether ketone, polysulfone, polyether sulfone, tetrafluoroethylene , Perfluoroalkyl vinyl ether, polyvinyl fluoride, tetrafluoroethylene / ethylene, tetrafluoroethylene / hexafluoropropylene, polychlorotrifluoroethylene, polyvinylidene fluoride and the like, and white pigments on these synthetic resins. A white opaque film formed by adding a filler or a filler can also be used, and is not particularly limited. Further, as the base material 100, a laminate made of any combination of base materials made of the above materials can also be used. Examples of typical laminates include synthetic paper made of cellulose fiber paper and synthetic paper, or synthetic paper made of cellulose synthetic paper and plastic film.

Further, the thickness of the base material 100 (the length in the vertical direction in FIG. 1) is appropriately changed according to the strength and heat resistance required for the heat transfer image receiving sheet and the material of the material used as the base material. It is possible, and specifically, it is preferably in the range of 50 μm or more and 1000 μm or less, and more preferably in the range of 100 μm or more and 300 μm or less.

[Structure of hollow layer 200]
The hollow layer 200 prevents the heat applied during image formation from being lost due to propagation to the base material 100 side, and enhances the cushioning property so that the surface of the heat transfer image receiving sheet can follow the thermal head. It is possible to increase and obtain a uniform printing screen.
The hollow layer 200 is a layer containing at least hollow particles and a binder resin. The binder resin contains at least one of natural rubber and synthetic rubber as a main component. The main component refers to, for example, 80% by weight or more, preferably 90% by weight or more of the binder resin.

The hollow layer 200 is formed by containing hollow particles and a pH buffer in an aqueous colloid of at least one of natural rubber and synthetic rubber constituting the binder resin, and further adding additives such as a surfactant and a stabilizer. An appropriately added ink is used as a coating solution for forming the hollow layer, and the coating solution is applied onto the base material 100 and dried to form the hollow layer 200.
The ratio of the solid content of the pH buffer solution to the solid content of the entire ink is preferably 0.5% by weight or more and 5.0% by weight or less.
If the solid content of the pH buffer is less than 0.5% by weight, the performance of the pH buffer is not sufficiently effective, and the pH of the coating solution changes abruptly in the process of coating and drying. As a result, agglomeration of hollow particles occurs. On the other hand, if it exceeds 5.0% by weight, the binding force of the binder resin constituting the hollow layer 200 decreases, the hollow layer cannot withstand the pressure applied to the image receiving sheet at the time of printing, and the image quality of the printed matter deteriorates. It will be.

Examples of the binder resin used for the hollow layer 200 include isoprene rubber, butadiene rubber, styrene-butadiene rubber (SBR), chloroprene rubber, nitrile rubber, butyl rubber, chlorinated butyl rubber, ethylene propylene rubber, and acrylic, in addition to natural rubber. Synthetic rubbers such as rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and silicone rubber are mentioned, and natural rubber, SBR, butadiene rubber, chlorinated butyl rubber, and acrylic rubber are preferable. In particular, at least one of natural rubber and SBR is more preferable. By using the rubber as the binder resin, the cushioning property of the hollow layer is improved, so that the followability of the heat transfer image receiving sheet to the thermal head is increased, and a uniform image can be obtained.

The binder resin used for the hollow layer 200 is required to be an aqueous colloid dispersed in an aqueous dispersion medium in its coating. By using an aqueous coating liquid, it is possible to suppress adverse effects on the environment during the production of the heat transfer image receiving sheet.
The pH of the coating liquid (ink) forming the hollow layer 200 is preferably pH 8.0 or more and 9.0 or less in the measurement in an environment of 25 ° C. before coating. By setting the pH in this range, the aqueous colloid of the binder resin is stable, does not cause viscosity change or gelation during storage or coating, suppresses the occurrence of particle agglomeration, and is hollow with a smooth surface. It is possible to obtain layers. In order to obtain this pH, a pH buffer solution or a pH adjuster described later may be added as appropriate.

Examples of the hollow particles used in the hollow layer 200 include hollow particles whose outer shell is made of silica, calcium carbonate, ceramic, acrylic resin, acrylic-styrene resin, or the like. The voids of the hollow particles may be porous as well as single pores. Further, the void portion of the hollow particles may contain not only air but also a liquid that can volatilize after drying, such as water. It is assumed that the hollow particles do not contain thermally expandable microcapsules.

The particle size of the hollow particles is preferably 0.1 μm or more and 5.0 μm or less. If the particle size is less than this range, sufficient voids are not formed in the hollow layer and the heat insulating property is insufficient, while if it exceeds this range, the surface of the hollow layer becomes excessively uneven, resulting in dye acceptance. The smoothness of the layered surface is also lost, resulting in poor image quality of the printed matter.
The porosity of the hollow particles is preferably 20% or more and 60% or less. If the porosity is less than 20%, sufficient voids are not formed in the hollow layer and the heat insulating property is insufficient, while if it exceeds 60%, the hollow layer cannot withstand the pressure applied to the image receiving sheet at the time of printing. The hollow layer is crushed, and a predetermined heat insulating property cannot be obtained, or the image quality of the printed matter is poor.

The pH buffer solution used for the coating solution forming the hollow layer 200 is a solution in which the pH does not change significantly even if some acid / alkali is added or the concentration is changed. Examples of the pH buffer solution include phosphate buffer solution, Tris hydrochloric acid buffer solution, ethylenediamine buffer solution, Tris EDTA buffer solution, Trisborate EDTA buffer solution, sodium citrate buffer solution, sodium borate buffer solution and the like. By adding these buffer solutions to the coating solution, it is considered that a rapid change in pH can be suppressed even when the concentration changes during drying after coating, and as a result, aggregation of hollow particles can be prevented.

It is desirable that the pH buffer be made of a material that does not decompose or volatilize, especially when heated. The coating film is placed in an environment exceeding 100 ° C. in the drying process, and by selecting a pH buffer material from those that do not decompose or volatilize even under such temperature, the performance of the pH buffer Will be more stable and it will be possible to prevent the agglomeration of hollow particles.
That is, it is preferable that the pH buffer solution is a pH buffer solution made of a material that does not decompose or volatilize even when heated at 105 ° C. for 60 minutes.
The pH buffer solution preferably further contains at least one of boric acid and a boric acid compound. Although the cause is unknown, the use of at least one of boric acid and a boric acid compound as the material of the pH buffer makes it possible to particularly prevent the agglomeration of hollow particles.

In the heat transfer image receiving sheet of the present embodiment as described above, the maximum valley depth Wv of the swell curve on the surface of the hollow layer 200 is 2.0 μm or less. The maximum valley depth Wv is determined in accordance with ISO 4287-1997.
In order to make the maximum valley depth Wv of the waviness curve of the surface of the hollow layer 200 2.0 μm or less, in addition to adjusting the manufacturing method of the ink forming the hollow layer, the surface of the base material 100 or the hollow layer 200 to be used The state may be adjusted by various conventionally known methods. If Wv is larger than 2.0 μm, uneven shading will occur in the printed matter, so it is necessary to set Wv to 2.0 μm or less.

[Structure of Dye Receiving Layer 300]
The dye receiving layer 300 receives the heat transfer dye transferred from the ink ribbon at the time of image formation by heat transfer, and also forms and maintains the image by retaining the received heat transfer dye.

The dye receiving layer 300 is formed by, for example, appropriately adding an additive such as a curing agent or a mold release agent to the binder resin to prepare a coating liquid for forming the dye receiving layer 300, applying the coating liquid, and drying the coating liquid.
Examples of the binder resin used for the dye receiving layer 300 include acrylic resin, vinyl chloride resin, polyolefin resin such as polyethylene and polypropylene, polyvinyl chloride, vinyl chloride / vinyl acetate copolymer (salt vinegar vinyl resin). , Halogenized polymer such as polyvinylidene chloride, polyvinyl acetate / acrylic copolymer, vinyl polymer such as polyacrylic acid ester, polystyrene resin, polyamide resin, olefin such as ethylene and propylene, and other vinyl monomers. Examples thereof include a polymerization system resin, a cellulose resin such as ionomer and cellulose diacetate, a polycarbonate and the like, and a mixed system of these resins, and a vinyl chloride resin is preferable. Among the vinyl chloride meter resins, at least one kind of vinyl chloride resin selected from vinyl chloride / vinyl acetate copolymer and vinyl chloride / acrylic copolymer is more preferable.

Further, as a curing agent, it may be appropriately added depending on the binder resin. As an example of the curing agent, isocyanates such as tolylene diisocyanate, triphenylmethane triisocyanate, and tetramethylxylene diisocyanate, and derivatives thereof can be used.

Further, a mold release agent may be appropriately added to the dye receiving layer 300. Examples of mold release agents include amino-modified silicone, alcohol-modified silicone, vinyl-modified silicone, urethane-modified silicone, epoxy-modified silicone, polyester-modified silicone, polyether-modified silicone, polyester-modified silicone, acrylic-modified silicone, aralkyl-modified silicone, and Examples thereof include silicone oils such as amide-modified silicones. In the present invention, these can also be mixed or polymerized using various reactions before use.
When the content of the silicone release agent increases, background stains occur. Therefore, the silicone release agent is preferably 2% or less with respect to the solid content of the binder resin of the dye receiving layer 300.

Further, an adhesive layer may be provided for the purpose of improving the adhesiveness between the base material 100 and the hollow layer 200, or between the hollow layer 200 and the dye receiving layer 300. The material constituting the adhesive layer is not particularly limited, and examples thereof include polyolefin resins such as polyethylene, urethane resins, acrylic resins, and polyester resins. Among these, urethane-based resin and acrylic-based resin are preferable. Further, a known additive such as a filler, an antistatic agent, or a fluorescent whitening agent may be added to the material forming the adhesive layer, if necessary.

Further, a back surface layer may be provided on the surface of the base material 100 opposite to the dye receiving layer 300. The back surface layer is provided for the purpose of improving the transportability in the printer, preventing blocking from the dye receiving layer 300 during storage, and improving the writing property. The material constituting the back surface layer is not particularly limited, but for example, polyolefin resins such as polyethylene resin and polypropylene resin, acrylic resins, polycarbonate resins, polyvinyl alcohol resins, polyvinyl acetal resins, polyester resins, etc. Examples thereof include polypropylene-based resins and polyamide-based resins. Further, a known additive such as a filler, an antistatic agent, or a fluorescent whitening agent may be added to the material forming the back surface layer, if necessary.

Hereinafter, the effects of the present invention will be verified using Examples (Examples 1 to 5 and Comparative Examples 1 to 3) with reference to FIG. In addition, when it is described as "part" in the following description, it indicates the mass standard unless otherwise specified. Moreover, the present invention is not limited to the following examples.
In the examples and comparative examples described below, the heat transfer image receiving sheet hollow layer base material and the heat transfer image receiving sheet were produced by the methods shown below.

-Preparation of a hollow layer base material for a heat transfer image receiving sheet-Example 1
As a base material, 188 μm easy-adhesion-treated PET (Wv = 0.2) was used. On one of the surfaces, a hollow layer ink having the composition shown below (ink for forming the hollow layer 200, hereinafter referred to as "hollow layer ink-1") is applied by a gravure coating method to a coating thickness after drying. The hollow layer 200 was formed by applying the ink so as to have a thickness of 4.0 μm and drying at a temperature of 100 ° C. for 10 minutes to prepare a heat transfer image receiving sheet hollow layer base material A.

・ Hollow layer ink-1
The composition of the hollow layer ink-1 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Low Pake SN-1055) 52.5 parts Pure water 12.0 parts

-Example 2
In the heat transfer image receiving sheet hollow layer base material produced in Example 1, the base material 100 is made of 190 μm double-sided resin coated paper (Wv = 1.4), and the hollow layer 200 is an ink having the composition shown below (hereinafter, “” A heat transfer image receiving sheet hollow layer base material B was obtained in the same manner as the heat transfer image receiving sheet A except that the ink was described as “hollow layer ink-2”).

・ Hollow layer ink-2
The composition of the hollow layer ink-2 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Lowpaque SN-1055) 52.5 parts Carbonate-bicarbonate buffer (0.1 mol / l pH 9.2) 12.0 parts

・ Example 3
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-3”). The heat transfer image receiving sheet hollow layer base material C was obtained.

・ Hollow layer ink-3
The composition of the hollow layer ink-3 is as follows.
Natural rubber latex (LATEX LA) 29.5 parts Hollow particle dispersion (trade name: LaTeX SN-1055) 58.5 parts Carbonic acid-bicarbonate buffer (0.1 mol / l pH 9.2) 12.0 parts

・ Example 4
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-4”). A thermal transfer image receiving sheet hollow layer base material D was obtained.

・ Hollow layer ink-4
The composition of the hollow layer ink-4 is as follows.
SBR Latex (trade name: LX430) 24.5 parts Hollow particle dispersion (trade name: Low Pake Ultra) 63.5 parts Carbonate-bicarbonate buffer (0.1 mol / l pH 9.2) 12.0 parts

・ Example 5
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-5”). A thermal transfer image receiving sheet hollow layer base material E was obtained.

・ Hollow layer ink-5
The composition of the hollow layer ink-5 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Low Pake SN-1055) 52.5 parts Phosphate buffer (0.2 mol / l pH 8.0) 12.0 parts

-Example 6
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-6”). The heat transfer image receiving sheet hollow layer base material F was obtained.

・ Hollow layer ink-6
The composition of the hollow layer ink-6 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Lowpaque SN-1055) 52.5 parts 2x Tris Boric acid EDTA (TBE) buffer (pH 8.1) 12.0 parts

・ Comparative example 1
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the heat transfer image receiving sheet hollow layer base material G was prepared in the same manner as the heat transfer image receiving sheet B except that the hollow layer 200 was the above hollow layer ink-1. Obtained.

・ Comparative example 2
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-7”). The heat transfer image receiving sheet hollow layer base material H was obtained.

・ Hollow layer ink-7
The composition of the hollow layer ink-7 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Low Pake SN-1055) 52.5 parts Citric acid-phosphate buffer (0.2 mol / l pH 7.2) 12.0 parts

・ Comparative example 3
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the same as the heat transfer image receiving sheet B except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-8”). The heat transfer image receiving sheet hollow layer base material I was obtained.

・ Hollow layer ink-8
The composition of the hollow layer ink-8 is as follows.
SBR Latex (trade name: LX430) 35.5 parts Hollow particle dispersion (trade name: Lowpaque SN-1055) 52.5 parts Sodium hydrogen carbonate aqueous solution (2.5% pH 8.0) 12.0 parts

・ Comparative example 4
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the base material 100 is the same as the heat transfer image receiving sheet B except that 190 μm double-sided resin coated paper (Wv = 2.6) is used. A sheet hollow layer base material J was obtained.

・ Comparative example 5
In the heat transfer image receiving sheet hollow layer base material produced in Example 2, the heat transfer image receiving sheet hollow layer group is used except that the hollow layer 200 is an ink having the composition shown below (hereinafter referred to as “hollow layer ink-9”). Material K was obtained.

・ Hollow layer ink-9
The composition of the hollow layer ink-9 is as follows.
Polyurethane aqueous dispersion (trade name: Superflex 210) 42.0 parts Hollow particle dispersion (trade name: Lowpaque SN-1055) 48.0 parts Carbonic acid-bicarbonate buffer (0.1 mol / l pH 9.2) 10 .0 copies

-Formation of Dye Receiving Layer Regarding the obtained thermal transfer image receiving sheet hollow layer base materials A to K, a dye receiving layer coating liquid was applied to the surface opposite to the base material of the hollow layer so that the thickness after drying was 3 μm. It was applied and dried to obtain thermal transfer image receiving sheets of Examples a to k, respectively.

-Dye receiving layer coating liquid The composition of the dye receiving layer coating liquid is as follows.
Vinyl chloride-acrylic emulsion (solid content 40%) 98.3 parts (trade name: Viniblanc 900)
Polyether-modified silicone (trade name: KF-6012) 0.4 parts Isocyanate-based curing agent (trade name: DNW-6000) 1.3 parts

-Preparation of thermal transfer recording medium A 4.5 μm polyethylene terephthalate film with easy-adhesion treatment on one side is used as a base material, and a heat-resistant slip layer coating liquid having the composition shown below is applied to the non-easy-adhesion-treated surface after drying. It was applied and dried so that the amount was 1.0 g / m ^2, and a base material with a heat-resistant slippery layer was obtained. Next, a thermal transfer layer coating solution having the composition shown below is applied to the easily adhesive-treated surface of the base material with a heat-resistant slipping layer so that the coating amount after drying is 1.0 g / m ² , dried and thermally transferred. A layer was formed to obtain a thermal transfer recording medium.

-Heat-resistant slip layer coating liquid The composition of the heat-resistant slip layer coating liquid is as follows.
Silicone acrylic graft polymer 50.0 parts (trade name: US-350)
Methyl ethyl ketone 50.0 parts

-Thermal transfer layer coating liquid The composition of the thermal transfer layer coating liquid is as follows.
C. I. Solvent Blue 36 2.5 parts C.I. I. Solvent Blue 63 2.5 parts Polyvinyl acetal resin 5.0 parts Toluene 45.0 parts Methyl ethyl ketone 45.0 parts

[Evaluation]
-Hollow layer smoothness evaluation The surface of the obtained thermal transfer image receiving sheet hollow layer base material was measured with a contact-type fine shape measuring machine ET4000 (manufactured by Kosaka Laboratory), and the maximum valley depth Wv of the swell curve was measured. Was done.
-Ink buffer component ratio For each hollow layer ink that was prepared, the ratio of the solid content of the pH buffer solution to the solid content of the entire ink was calculated.
-Ink pH measurement For each hollow layer ink prepared, the pH at 25 ° C. was measured using a pH meter (trade name: D-71, glass electrode type pH meter manufactured by Horiba Seisakusho).

-Evaluation of printing Using the thermal transfer image receiving sheets and thermal transfer recording media of Examples 1 to 6 and Comparative Examples 1 to 5, solid images were printed at settings of 300 dpi, 10 msec / line, and 0.5 mJ / dot to obtain image quality. Evaluation was performed. The image quality was evaluated according to the following criteria.
◯: The density of the printed matter is uniform and the image quality is excellent. ×: There is a problem in practical use due to uneven shading on the printed matter.

[Evaluation results]
Table 1 shows a list of evaluation results for each level.

As can be seen from the results shown in Table 1, the hollow layer is composed of hollow particles and a binder resin, the binder resin is mainly composed of at least one rubber of natural rubber and synthetic rubber, and the undulation curve of the surface of the hollow layer. By setting the maximum valley depth Wv to 2.0 μm or less, a heat transfer image receiving sheet having excellent image quality could be produced, and the effect of the invention could be confirmed.

On the other hand, in Comparative Example 1, since the pH buffer solution was not contained, sufficient dispersibility of the hollow particles could not be obtained, the maximum valley depth Wv was larger than 2.0 μm, and the resin coated paper was used as the base. When used as a material, sufficient image quality could not be obtained.
In Comparative Example 2, although the pH buffer solution was contained, the pH of the ink was lower than 8.0, so that sufficient dispersibility of the hollow particles could not be obtained, and sufficient image quality could not be obtained. It was.
In Comparative Example 3, the pH was adjusted by adding an aqueous sodium hydrogen carbonate solution instead of the pH buffer solution, but sufficient dispersibility of the hollow particles could not be obtained, and the maximum valley depth Wv became larger than 2.0 μm. , Sufficient image quality could not be obtained.

In Comparative Example 4, a hollow layer using SBR as a binder was formed by adding a pH buffer solution, but the base material was too rough to be sufficiently smoothed by the hollow layer, and the maximum valley depth was reached. Wv became larger than 2.0 μm, and sufficient image quality could not be obtained.
In Comparative Example 5, the maximum valley depth Wv is 2.0 μm or less, but since polyurethane is used as the binder, the hollow layer cannot be provided with sufficient cushioning properties, and sufficient image quality can be obtained. could not.

The thermal transfer image receiving sheet obtained by the present invention can be used in a sublimation transfer type printer, and various images can be easily formed in full color in addition to high speed and high functionality of the printer. Therefore, self-printing of a digital camera , Cards such as identification cards, output materials for amusement, etc. can be widely used.

100 Base material 200 Hollow layer 300 Dye receiving layer

Claims (4)

A hollow layer and a dye receiving layer are formed in this order on at least one surface side of the base material.
The hollow layer has at least hollow particles and a binder resin.
The binder resin contains at least one of natural rubber and synthetic rubber as a main component.
The maximum valley depth Wv (ISO4287-197) of the swell curve on the surface of the hollow layer is
A thermal transfer image receiving sheet characterized by being 2.0 um or less. A method for producing a heat transfer image receiving sheet in which a hollow layer and a dye receiving layer are formed in this order on at least one surface side of the base material.
The hollow layer is formed by applying and drying an ink containing hollow particles and a pH buffer solution in an aqueous colloid of at least one of natural rubber and synthetic rubber on the base material.
The pH of the above ink in a 25 ° C. environment is 8.0 or more and 9.0 or less.
A method for producing a heat transfer image receiving sheet, wherein the ratio of the solid content of the pH buffer solution to the solid content of the entire ink is 0.5% by weight or more. The method for producing a heat transfer image receiving sheet according to claim 2, wherein the pH buffer solution is a pH buffer solution made of a material that does not decompose or volatilize even when heated at 105 ° C. for 60 minutes. The method for producing a heat transfer image receiving sheet according to claim 2 or 3, wherein the pH buffer solution contains at least one of boric acid and a boric acid compound.

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