JP2010234733A - Thermal transfer sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal transfer sheet in which the sharpness of a thermal transfer image is high, and the generation of abnormal transfer in a print can be suitably inhibited even after being conserved under high temperature and high humidity; transfer sensitivity in a print of a thermal transfer is high, and a high-concentration print is obtained in a high-speed print; and the phenomenon of scorching (black solid blurring) can be inhibited in a black high density section in which dyes of three colors of yellow, magenta, and cyanogen are superposed one by one. <P>SOLUTION: The thermal transfer sheet comprises a primer layer and a dye layer formed one by one on one surface of a base material, wherein the primer layer contains a colloid-like inorganic pigment ultrafine particle and polyvinyl alcohol, in the polyvinyl alcohol, the content in the primer layer is at least 10 mass% and less than 50 mass%, the degree of saponification is larger than 80 mol%, and further in the primer layer, the application quantity (at the time of drying) is more than 0.03 g/m<SP>2</SP>, and less than 0.6 g/m<SP>2</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a thermal transfer sheet.

Conventionally, various thermal transfer recording methods have been used as simple printing methods. In such a variety of thermal transfer recording methods, when obtaining a color image, for example, yellow, magenta and cyan, and if necessary, a black color material layer is provided on one side of a continuous base sheet. A thermal transfer sheet is used in which a large number are repeatedly provided in sequence, and a heat-resistant slipping layer is provided on the opposite surface of the base sheet.
In such a thermal transfer recording method using a thermal transfer sheet, (1) a heat melting type in which a color material layer is melted and softened by heating and transferred to a transfer target to form an image; and (2) in the color material layer by heating. The dye is sublimated and is roughly classified into a sublimation type in which an image is formed by moving onto a transfer target.

A sublimation type thermal transfer sheet transfers a color dot in which a large number of heating colors of three or four colors are adjusted to the receiving layer of the thermal transfer image receiving sheet by heating with a thermal head of a printer. It reproduces the full color.
An image formed using a sublimation thermal transfer sheet is very clear and excellent in transparency because the color material used is a dye. For this reason, the reproducibility and gradation of intermediate colors are excellent, and it is possible to form a high quality image that is similar to an image by conventional offset printing or gravure printing and comparable to a full color photographic image.
Such a sublimation type thermal transfer sheet is required to have high adhesion between the dye layer and the substrate in order to prevent a problem that the dye layer (coloring material layer) is transferred to the transfer target. .

In recent years, the printing speed of a thermal transfer printer using a sublimation type thermal transfer sheet has been steadily increased, and it has become difficult to obtain a sufficient print density with a conventional thermal transfer sheet. In addition, a higher density and clearer image has been required for a printed image by thermal transfer.
Therefore, for example, when a black thermal transfer image is formed by sequentially superimposing three colors of dyes from the yellow, magenta, and cyan dye layers, an image quality defect occurs in the high density portion of black. It was. That is, at the time of dye thermal transfer, the dye receiving layer of the thermal transfer image receiving sheet is fused to the dye layer side of the thermal transfer sheet, thereby causing a hue fluctuation of the black portion, and as a result, the surface of the printed material becomes matte and loses gloss. The phenomenon called “koge” (black solid fade) has come to be seen. For this reason, many attempts have been made to improve the thermal transfer sheet and the thermal transfer image receiving sheet. For example, attempts have been made to improve transfer sensitivity in printing by reducing the thickness of the thermal transfer sheet, but wrinkles may occur due to heat, pressure, etc. during manufacture of the thermal transfer sheet or during thermal transfer recording. Had a problem of cutting.

In addition, attempts have been made to increase the printing density and the transfer sensitivity in printing by increasing the dye / resin (Dye / Binder) ratio in the dye layer of the thermal transfer sheet.
However, when such a thermal transfer sheet is stored in a wound state after production, the dye layer and the heat resistant slipping layer provided on the opposite side of the substrate come into contact with each other, whereby the dye is transferred from the dye layer to the heat resistant slipping layer. There was a problem of (kick) transition. The dye transferred to the heat-resistant slipping layer is rolled back to retransfer to another color dye layer, protective layer, etc. (back), and the contaminated layer is thermally transferred to the thermal transfer image receiving sheet. There is also a problem that the printing accuracy is remarkably deteriorated due to a hue different from the color designated by.

Further, high energy is also applied to the thermal transfer printer, not the thermal transfer sheet side, during thermal transfer during image formation.
However, in this case, so-called abnormal transfer, in which the entire dye layer of the thermal transfer sheet is transferred to the thermal transfer image receiving sheet, is likely to occur. On the other hand, in order to prevent abnormal transfer, a method of adding a large amount of a release agent to the receiving layer of the thermal transfer image-receiving sheet is also conceivable. It was.

For the purpose of improving transfer sensitivity in printing, for example, Patent Document 1 discloses a thermal transfer sheet having an adhesive layer containing a polyvinylpyrrolidone resin and a modified polyvinylpyrrolidone resin.
However, such a thermal transfer sheet can prevent abnormal transfer, but has a low printing density and has not reached a sufficient level.

For example, Patent Document 2 discloses a thermal transfer sheet including an undercoat layer containing a thermoplastic resin and colloidal inorganic pigment ultrafine particles between a base material and a dye layer. According to the thermal transfer sheet disclosed in Patent Document 2, it is possible to improve the transfer sensitivity to some extent and obtain a high-density print.
However, the thermal transfer sheet disclosed in Patent Document 2 cannot sufficiently prevent kogation and abnormal transfer after storage under high temperature and high humidity.

In addition, for example, in Patent Document 3, an undercoat layer formed mainly of a copolymer resin of vinyl pyrrolidone and vinyl acetate and colloidal inorganic pigment ultrafine particles is provided between a base material and a dye layer. A thermal transfer sheet is disclosed.
However, in recent years, the level of kogation and abnormal transfer prevention required for the thermal transfer sheet has become extremely high, and even with the thermal transfer sheet disclosed in Patent Document 3, the abnormal transfer prevention performance at such a high level is achieved. It was becoming something that could not be fully met.

JP-A-2005-231354 JP 2006-150956 A JP 2008-155612 A

In view of the above situation, the present invention has a high thermal transfer image sharpness, and can suitably prevent the occurrence of abnormal transfer in a print even after being stored at high temperature and high humidity. High transfer sensitivity in high-speed printing, high-density printing is obtained, and the phenomenon of kogation (solid black) in the black high-density area where three colors of yellow, magenta, and cyan dyes are sequentially stacked It aims at providing the thermal transfer sheet which can be suppressed.

The present invention is a thermal transfer sheet in which a primer layer and a dye layer are sequentially formed on one surface of a substrate, the primer layer containing colloidal inorganic pigment ultrafine particles and polyvinyl alcohol, and the polyvinyl alcohol Has a content in the primer layer of 10% by mass or more and less than 50% by mass, and a saponification degree is greater than 80 mol%, and the primer layer has an application amount (when dried) of 0.03 g / more than m ^2, and a thermal transfer sheet and less than 0.6 g / ^{m 2.}
In the thermal transfer sheet of the present invention, the polyvinyl alcohol preferably has a polymerization degree of 1000 to 3000.
The colloidal inorganic pigment ultrafine particles are preferably alumina sol and / or colloidal silica.
The present invention is described in detail below.

As a result of intensive studies on a thermal transfer sheet in which a primer layer and a dye layer are sequentially laminated on one surface of a base material, the present inventors have found that a conventional thermal transfer sheet becomes a primer layer when stored at high temperature and high humidity. It was found that moisture absorption occurred, and this primer layer moisture absorption caused abnormal transfer in printing.
Therefore, as a result of further intensive studies, the primer layer has a specific composition, specifically, a composition containing colloidal inorganic pigment ultrafine particles and polyvinyl alcohol having a predetermined degree of saponification and content, It has been found that the moisture absorption of the primer layer can be effectively suppressed, and abnormal transfer in printing can be sufficiently suppressed even after storage at high temperature and high humidity, and the present invention has been completed. Furthermore, the thermal transfer sheet having the primer layer having such a composition has high adhesion between the substrate and the dye layer, has high transfer sensitivity during image formation, and can suppress the occurrence of kogation.

(Base material)
The thermal transfer sheet of the present invention has a structure in which a primer layer and a dye layer are sequentially formed on one surface of a substrate.
The substrate is not particularly limited as long as it is made of a conventionally known resin having a certain degree of heat resistance and strength. For example, a plastic film having a thickness of about 0.5 to 50 μm, preferably about 1 to 10 μm. Are preferably used.
Examples of the resin constituting the plastic film include polyethylene terephthalate, 1,4-polycyclohexylenedimethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polystyrene, polypropylene, polysulfone, aramid, polycarbonate, polyvinyl alcohol, cellophane, and acetic acid. Examples thereof include cellulose derivatives such as cellulose, polyethylene, polyvinyl chloride, nylon, polyimide, and ionomer. Of these, polyethylene terephthalate is preferably used.
In addition, the said base material may consist only of 1 type of the above-mentioned resin, and may consist of 2 or more types of resin.

Moreover, it is preferable that the said base material has the adhesion process performed on the surface which forms the primer layer mentioned later. That is, when the base material is the above-described plastic film, it is preferable to perform an adhesion treatment because the adhesion between the base material and the primer layer tends to be insufficient when the primer layer is formed thereon.
Examples of the adhesion treatment include known resins such as corona discharge treatment, flame treatment, ozone treatment, ultraviolet treatment, radiation treatment, surface roughening treatment, chemical treatment, plasma treatment, low temperature plasma treatment, primer treatment, and grafting treatment. The surface modification technique can be applied as it is. Two or more of these treatments can be used in combination.
The primer treatment can be performed, for example, by applying a primer solution to an unstretched film at the time of film formation by melt extrusion of a plastic film and then stretching the film. In the present invention, in order to improve the adhesion between the base material, a colloidal inorganic pigment ultrafine particle described later, and a primer layer composed of polyvinyl alcohol, a general-purpose treatment method is used without increasing the cost among the above-mentioned adhesion treatments. Corona discharge treatment or plasma treatment is preferable in that it can be used and the adhesion between the substrate and the primer layer can be improved.

(Primer layer)
The primer layer is formed on one surface of the base material and plays a role of suitably bonding the base material and a dye layer to be described later, and even after being stored under high temperature and high humidity. This layer serves to prevent abnormal transfer in printing.
In the thermal transfer sheet of the present invention, the primer layer contains colloidal inorganic pigment ultrafine particles and polyvinyl alcohol.

The colloidal inorganic pigment ultrafine particles are not particularly limited and include conventionally known compounds. Specifically, for example, silica (colloidal silica), alumina or alumina hydrate (alumina sol, colloidal alumina, cationic aluminum oxide or hydrate, pseudoboehmite, etc.), aluminum silicate, magnesium silicate, magnesium carbonate , Magnesium oxide, titanium oxide and the like.
In the primer layer, these colloidal inorganic pigment ultrafine particles may be used not only under the same kind of conditions but also with different kinds.
As the colloidal inorganic pigment ultrafine particles, alumina sol and / or colloidal silica are preferably used.

The colloidal inorganic pigment ultrafine particles have an average particle size of 100 nm or less, preferably 50 nm or less, and particularly preferably 3 to 30 nm, whereby the function of the primer layer can be sufficiently exhibited.
The shape of the colloidal inorganic pigment ultrafine particles in the present invention may be any shape such as a spherical shape, a needle shape, a plate shape, a feather shape, or an amorphous shape. In addition, those treated in an acidic type so as to be easily dispersed in a sol form in an aqueous solvent, those obtained by converting fine particle charges into cations, and those obtained by surface treatment of fine particles can be used.

The primer layer preferably has a colloidal inorganic pigment ultrafine particle content of more than 50% by mass and 90% by mass or less. If it is 50% by mass or less, the adhesiveness to the dye layer described later may be insufficient, and if it exceeds 90% by mass, the releasability from the image receiving sheet at the time of thermal transfer is lowered, or the phenomenon of kogation May occur. The minimum with more preferable content of the said colloidal inorganic pigment ultrafine particle is 60 mass%, and a more preferable upper limit is 80 mass%.

In the thermal transfer sheet of the present invention, the polyvinyl alcohol constituting the primer layer is preferably a resin having a high saponification degree, and the saponification degree of the polyvinyl alcohol is greater than 80 mol%. When the saponification degree is 80 mol% or less, moisture absorption occurs in the primer layer when the thermal transfer sheet of the present invention is stored under high temperature and high humidity, and abnormal transfer in printing may not be effectively suppressed. The polyvinyl alcohol is more preferably completely saponified.
Here, even after a primer layer containing such a highly saponified polyvinyl alcohol, more preferably completely saponified polyvinyl alcohol, is stored under high temperature and high humidity, the so-called koge It is a fact that the present inventors have found for the first time that the printability can be particularly effectively suppressed due to the phenomenon or the releasability of the dye layer from the thermal transfer image-receiving sheet.

The polyvinyl alcohol preferably has a high molecular weight. This is because a primer layer containing a high molecular weight polyvinyl alcohol is more excellent in printability in printing.
That is, the polyvinyl alcohol preferably has a polymerization degree of 1000 to 3000. If it is less than 1000, the printability in printing may be reduced, and if it exceeds 3000, the viscosity becomes too high, and the coating suitability of the coating liquid used when forming the primer layer may be reduced. is there. A more preferable lower limit of the degree of polymerization is 1500, and a more preferable upper limit is 2600.
The degree of polymerization of the polyvinyl alcohol can be measured by an Ostwald viscometer according to JIS K 6726.

In the thermal transfer sheet of the present invention, the primer layer has a content of the polyvinyl alcohol of 10% by mass or more and less than 50% by mass. If it is less than 10% by mass, the releasability from the image-receiving sheet during thermal transfer may be lowered or the phenomenon of kogation may occur, and if it is 50% by mass or more, the adhesion of the primer layer to the dye layer Is insufficient.
The minimum with preferable content of polyvinyl alcohol in the said primer layer is 20 mass%, and a preferable upper limit is 40 mass%. When the content of polyvinyl alcohol in the primer layer is within this range, the printability of the thermal transfer sheet of the present invention and the adhesion of the primer layer to the dye layer can be made particularly excellent.

The primer layer containing the colloidal inorganic pigment ultrafine particles and polyvinyl alcohol can be formed by applying a primer layer coating solution on the substrate.
The primer layer coating liquid preferably has fluidity by lowering the viscosity in consideration of coating suitability.
The primer layer in the present invention is configured to contain the above-described colloidal inorganic pigment ultrafine particles and polyvinyl alcohol, the inorganic pigment ultrafine particles are dispersed in a sol form in an aqueous solvent, and the polyvinyl alcohol is dispersed or dissolved in the aqueous solvent. The primer layer coating solution can be applied and dried by a conventionally known forming means such as a gravure coating method, a roll coating method, a screen printing method, a reverse roll coating method using a gravure plate, and the like. .

The aqueous solvent in the primer layer coating solution is not particularly limited, and examples thereof include water; a mixture of alcohols such as ethanol and propanol and water, and the like. Furthermore, as the aqueous solvent, cellosolves such as methyl cellosolve and ethyl cellosolve; organic solvents such as ketones such as acetone and methyl ethyl ketone and water can be used, but water or water and alcohols can be used. It is preferable that it is a mixture.

When the primer layer is formed using the primer layer coating liquid having such a composition, the primer layer coating liquid is used to coat the substrate, and then, hot air drying or the like is performed, and the colloidal inorganic pigment is used. Moisture is removed so that the ultrafine particles are changed from a sol to a gel, and polyvinyl alcohol is formed by fixing inorganic pigment ultrafine particles as a binder. Therefore, the primer layer in the present invention is not subjected to a baking treatment by a general sol-gel method.

The coating amount of the coating solution for a primer layer is greater than 0.03 g / ^{m 2,} is 0.60 g / ^m of less than ² (dry). If it is 0.03 g / m ² or less, a sufficient print density cannot be obtained during thermal transfer, and the adhesiveness also deteriorates. If it is 0.60 g / m ² or more, the releasability from the image-receiving sheet in thermal transfer may be deteriorated or a kogation phenomenon may occur. Preferable lower limit is 0.05 g / ^{m 2,} the upper limit is preferably 0.50 g / ^{m 2.}

It is preferable that the primer layer formed as described above is mainly composed of colloidal inorganic pigment ultrafine particles and polyvinyl alcohol, with no other components, or with a little solvent remaining. Thus, the primer layer composed of colloidal inorganic pigment ultrafine particles and polyvinyl alcohol is formed as a film between the base material and the dye layer, and can enhance the adhesion between the base material and the dye layer. When heat transfer is carried out in combination with the image receiving sheet, abnormal transfer of the dye layer to the image receiving sheet can be prevented even after storage under high temperature and high humidity.
Furthermore, since the primer layer is composed of colloidal inorganic pigment ultrafine particles and polyvinyl alcohol that are difficult to dye from the dye layer, the dye layer is prevented from transferring from the dye layer to the primer layer during printing. By effectively diffusing the dye to the receiving layer side of the image receiving sheet, the transfer sensitivity in printing can be increased and the printing density can be increased. In addition, the primer layer in the present invention also prevents the point that the releasability from the image receiving sheet in printing is likely to deteriorate after storage at high temperature and high humidity, as compared with the conventional thermal transfer sheet.

(Dye layer)
In the thermal transfer sheet of the present invention, a dye layer is provided on one surface of a substrate via the primer layer.
The dye layer may be composed of a single layer of one color, or a plurality of dye layers containing dyes having different hues may be repeatedly formed on the same surface of the same substrate in the surface order.

The dye layer is a layer formed by supporting a heat transfer dye with an arbitrary binder.
As the dye to be used, a dye that melts, diffuses or sublimates by heat, and is used in a conventionally known sublimation transfer type thermal transfer sheet can be used in the present invention. Selection can be made in consideration of printing sensitivity, light resistance, storage stability, solubility in a binder, and the like.

Examples of the dye include methine series such as diarylmethane series, triarylmethane series, thiazole series, merocyanine, pyrazolone methine, indoaniline, acetophenone azomethine, pyrazoloazomethine, imidazolazomethine, imidazoazomethine, and pyridone azomethine. Azomethine series, xanthene series, oxazine series, dicyanostyrene, cyanomethylene series represented by tricyanostyrene, thiazine series, azine series, acridine series, benzeneazo series, pyridoneazo, thiophenazo, isothiazole azo, pyrrole azo, pyralazo, imidazole Azo, thiadiazole azo, triazole azo, diazo, etc., azo, spiropyran, indolinospiropyran, fluoran, rhodamine lactam, naphthoquinone Anthraquinone include the quinophthalone like.

As the binder for the dye layer, any conventionally known resin binder can be used. Examples of preferred binders include ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl cellulose, methyl cellulose, cellulose acetate propyrate, and cellulose acetate butyrate. And cellulose resins such as cellulose acetate and cellulose butyrate, vinyl resins such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone, and polyacrylamide, polyester resins, and phenoxy resins.

A silane coupling agent can be added to the dye layer. Examples of the silane coupling agent include those containing an isocyanate group such as γ-isocyanatopropyltriethoxysilane and γ-isocyanatopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N- Those containing an amino group such as β- (aminoethyl) -γ-aminopropyltriethoxysilane, γ-phenylaminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and β- (3,4- And those containing an epoxy group, such as epoxycyclohexyl) ethyltrimethoxysilane. These can be used alone or as a mixture of two or more.

In the silane coupling agent, for example, a silanol group generated by hydrolysis is condensed with a hydroxyl group of an inorganic oxide on the surface of the thin film layer to be chemically bonded to improve the adhesion. In addition, the epoxy group, amino group, etc. of the silane coupling agent react with the hydroxyl group, carboxyl group, etc. of the resin binder to chemically bond, improve the strength of the dye layer itself, cohesive failure of the dye layer during thermal transfer, etc. Can be prevented.

In the present invention, the following releasable graft copolymer can be used as a release agent or binder instead of the resin binder. This releasable graft copolymer is obtained by graft polymerizing at least one releasable segment selected from a polysiloxane segment, a fluorocarbon segment, a fluorinated hydrocarbon segment, or a long-chain alkyl segment on the polymer main chain. It is. Among these, a graft copolymer obtained by grafting a polysiloxane segment to a main chain made of a polyvinyl acetal resin is particularly preferable.

In the thermal transfer sheet of the present invention, the binder resin constituting the dye layer is as described above in that the adhesion between the primer layer and the dye layer can be maintained even after being left under high temperature and high humidity. Among them, single or a mixture of resins having a high adhesiveness having a hydroxyl group or a carboxyl group such as polyvinyl butyral, polyvinyl acetal, polyvinyl acetate, and cellulose resins such as polyester resins, cellulose acetate, and butyrate cellulose are preferably used. It is done.

The dye layer may contain the above-mentioned dyes, binders, and other various conventional additives as required. As the additive, for example, organic fine particles such as polyethylene wax, inorganic fine particles, silicone oil, silicone modified resin, fatty acid amide, fatty acid ester, phosphoric acid ester, which improve releasability from an image receiving sheet and ink coating suitability Etc. Such a dye layer is usually prepared by adding the above-mentioned dye, binder, and additives as necessary in an appropriate solvent, and dissolving or dispersing each component to prepare a coating solution. It can be formed by applying and drying the liquid on a substrate.
As this coating method, known means such as a gravure printing method, a screen printing method, a reverse roll coating method using a gravure plate, or the like can be used. The dye layer thus formed has a coating amount at the time of drying of about 0.2 to 6.0 g / m ² , preferably about 0.3 to 3.0 g / m ² .

Further, the thermal transfer sheet of the present invention is one in which a primer layer and a dye layer are sequentially formed on one surface of the above-described base material. However, the embodiment of the thermal transfer sheet of the present invention is limited to such a structure. For example, a protective layer, a color material layer such as a gold color layer, a silver color layer, or a hologram layer may be formed on the primer layer in the surface order with the dye layer. In addition, when several layers, such as the said dye layer, a protective layer, and a color material layer, are formed on a primer layer, the formation order of these each layer is not specifically limited.

(Heat resistant slipping layer)
The thermal transfer sheet of the present invention is provided with a heat-resistant slipping layer on the surface opposite to the surface on which the primer layer of the substrate is provided in order to prevent adverse effects such as sticking and printing wrinkles due to the heat of the thermal head. It may be.
The resin for forming the heat-resistant slipping layer may be any conventionally known resin such as polyvinyl butyral resin, polyvinyl acetoacetal resin, polyester resin, vinyl chloride-vinyl acetate copolymer, polyether resin, polybutadiene resin. , Styrene-butadiene copolymer, polyol (polyalcohol polymer compound, etc.), acrylic polyol, polyurethane acrylate, polyester acrylate, polyether acrylate, epoxy acrylate, urethane or epoxy prepolymer, nitrocellulose resin, cellulose nitrate resin, Cellulose acetate propionate resin, cellulose acetate butyrate resin, cellulose acetate hydrodiene phthalate resin, cellulose acetate resin, aromatic polyamide resin, Examples thereof include a polyimide resin, a polyamideimide resin, a polycarbonate resin, and a chlorinated polyolefin resin.

The slipperiness imparting agent added to or overcoating the heat resistant slipping layer made of these resins includes phosphate ester, metal soap, silicone oil, graphite powder, silicone graft polymer, fluorine graft polymer, acrylic silicone graft polymer, acrylic. Examples thereof include silicone polymers such as siloxane and arylsiloxane.
The heat-resistant slipping layer may further contain a known additive such as a filler or a crosslinking agent.
The heat-resistant slip layer in the present invention is preferably a layer made of a polyol, for example, a polyalcohol polymer compound, a polyisocyanate compound and a phosphate ester compound, and more preferably a filler added.

The heat-resistant slipping layer is prepared by dissolving or dispersing the above-described resin, slipperiness-imparting agent, and further a filler or the like with an appropriate solvent on the base material sheet to obtain a heat-resistant slipping layer coating solution. It can be prepared and applied by a forming means such as a gravure printing method, a screen printing method, a reverse roll coating method using a gravure plate, and dried to form. The coating amount of the heat resistant slipping layer is preferably 0.1 to 3.0 g / m ² in terms of solid content.

Since the thermal transfer sheet of the present invention has the above-described configuration, the thermal transfer image has high sharpness and suitably prevents occurrence of abnormal transfer in printing even after being stored at high temperature and high humidity. In addition, the transfer sensitivity is high in thermal transfer printing, high density printing is obtained in high speed printing, and in the high density portion of black where three colors of yellow, magenta, and cyan dyes are successively stacked, The phenomenon of black solid blurring can be suppressed.

The contents of the present invention will be described with reference to the following examples, but the contents of the present invention should not be construed as being limited to these embodiments. Unless otherwise specified, “part” and “%” are based on mass.

Example 1
As a base material, on a polyethylene terephthalate film (PET) having a thickness of 4.5 μm, a primer layer coating solution having the following composition is applied by gravure coating so that the dry coating amount is 0.15 g / m ² and dried. Thus, a primer layer was formed.
On the primer layer, a dye layer coating solution having the following composition was applied by gravure coating so that the dry coating amount was 0.7 g / m ² and dried to form a dye layer. Thermal transfer of Example 1 A sheet was produced.
On the other side of the substrate, a heat resistant slipping layer coating solution having the following composition was applied in advance by gravure coating and dried to a dry coating amount of 1.0 g / m ² , and heat resistant slipping was performed. A sex layer was formed.

<Primer layer coating solution>
700 parts of alumina sol (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
30 parts of polyvinyl alcohol (NH-18, manufactured by Nippon Synthetic Chemical Industry, degree of saponification 99 mol%, degree of polymerization 1800)
150 parts of water 150 parts of isopropyl alcohol

<Dye layer coating solution>
C. I. Solvent Blue 63 6.0 parts polyvinyl butyral resin 3.0 parts (S-REC BX-1 manufactured by Sekisui Chemical Co., Ltd.)
Methyl ethyl ketone 45.5 parts Toluene 45.5 parts

<Heat resistant slipping layer coating solution>
13.6 parts of polyvinyl butyral resin (manufactured by SREC BX-1 by Sekisui Chemical Co., Ltd.)
0.6 parts of polyisocyanate curing agent (Takenate D218, manufactured by Mitsui Chemicals Polyurethanes)
Phosphate 0.8 parts (Plysurf A208S, Daiichi Kogyo Seiyaku Co., Ltd.)
Methyl ethyl ketone 42.5 parts Toluene 42.5 parts

(Examples 2-13, Comparative Examples 1-12)
In the thermal transfer sheet produced in Example 1, the alumina sol and polyvinyl alcohol of the primer layer coating liquid were respectively used as the colloidal inorganic pigment ultrafine particles and resin shown in Table 1 below, and their blending amount (solid content) and coating Except having made the quantity into the following Table 1, it carried out similarly to Example 1, and produced the thermal transfer sheet of Examples 2-13 and Comparative Examples 1-12. The contents of the resin and colloidal inorganic pigment ultrafine particles in Table 1 are shown in Table 2 below.

(Evaluation)
The following evaluation was performed about the thermal transfer sheet obtained by each Example and the comparative example in the following procedure. The results are shown in Table 3.

(Printing suitability)
<Abnormal transcription evaluation>
Using the thermal transfer sheets prepared in each of the examples and comparative examples, after storing for one week in an environment of 40 ° C. and 90% RH, after leaving at room temperature for 1 hour, genuine for MEGA PIXEL III manufactured by Citizen Systems Attached to the Cy part of the ribbon and combined with a postcard size genuine thermal transfer image-receiving sheet for MEGA PIXEL III manufactured by Citizen Systems Co., Ltd. 15 under 3 environments of 25 ° C 50% RH, 35 ° C 85% RH, 40 ° C 90% RH A printing pattern with gradation steps (gradation values 0, 15, 30... 240, 255/255) is printed and transferred to the thermal transfer image receiving sheet together with the dye layer of the thermal transfer sheet. Evaluation was performed according to the following criteria.
(Evaluation criteria)
◎: Abnormal transfer cannot be confirmed in any environment ○: Abnormal transfer is observed in 40 ° C 90% RH environment, but abnormal transfer is visually observed by printing in 35 ° C 85% RH environment, 25 ° C 50% RH environment △: Abnormal transfer is observed in an environment of 40 ° C. and 90% RH and 35 ° C. and 85% RH, but abnormal transfer cannot be visually confirmed in a print in a 25 ° C. and 50% RH environment. But abnormal transcription is observed

<Evaluation of koge (solid black)>
Next, using the thermal transfer sheet of each example and comparative example, after being stored for one week in an environment of 40 ° C. and 90% RH, left at room temperature for 1 hour, and then used for MEGA PIXEL III manufactured by Citizen Systems. Attached to the Cy part of the genuine ribbon and combined with a postcard size genuine thermal transfer image-receiving sheet for MEGA PIXEL III manufactured by Citizen Systems Co., Ltd., yellow, magenta, and cyan under two environments of 25 ° C and 50% RH and 35 ° C and 85% RH Three-color dyes were sequentially stacked in order to perform black solid printing, and the occurrence of burnt in the black solid printed material was confirmed visually, and evaluated according to the following criteria.
(Evaluation criteria)
○: Kogation cannot be visually confirmed in printing at 35 ° C. and 85% RH environment, and at 25 ° C. and 50% RH environment. Δ: Kogation is observed in printing at 35 ° C. and 85% RH environment, but in 25 ° C. and 50% RH environment. No koge can be visually confirmed in the print of No. x: Koge is observed in a print in an environment of 35 ° C. and 85% RH and 25 ° C. and 50% RH. However, the koge is a dye from each dye layer of yellow, magenta, and cyan. 3 and the protective layer to be transferred from the protective layer transfer sheet at the end are sequentially stacked to form a black thermal transfer image, resulting in poor image quality at the high density portion of black, that is, the receiving layer of the thermal transfer image receiving sheet during transfer Is a phenomenon in which the hue of the black part changes (black solids) as a result of fusing to the thermal transfer sheet side, resulting in matting of the surface of the printed material and loss of glossiness.

<Print density>
Next, using the thermal transfer sheet of each example and comparative example, it is attached to the Cy part of a genuine ribbon for MEGA PIXEL III manufactured by Citizen Systems, and a postcard size genuine thermal transfer image receiving sheet for MEGA PIXEL III manufactured by Citizen Systems, Inc. In combination, a printing pattern of cyan solid (tone 255/255) was printed, and the maximum density (cyan) of the printing portion was measured with a reflection densitometer RD-918 manufactured by Gretag Macbeth. Then, using the ribbon (hereinafter referred to as a reference ribbon) to which the thermal transfer sheet according to Comparative Example 1 was attached as a reference, the ratio of the highest density with respect to the reference ribbon was evaluated according to the following criteria.
(Evaluation criteria)
○: Maximum density is 95 to 105% compared to the standard ribbon
Δ: Maximum density is 90 to 95% compared to the standard ribbon
×: The maximum density is less than 90% compared to the reference ribbon

<Adhesiveness of dye layer>
The thermal transfer sheets prepared in each of the examples and comparative examples were stored for one week in an environment of 40 ° C. and 90% RH, left at room temperature for 1 hour, and then placed on the dye layer of the thermal transfer sheet at a length of 200 mm × An evaluation was performed by examining the presence or absence of the dye layer on the tape side when the tape was peeled off, and the tape was peeled back and forth twice with a thumb. Evaluation was performed according to the following criteria.
○: Dye layer adhesion is not observed Δ: Dye layer adhesion is slightly observed, but there is no problem in printing under the above-mentioned kogation evaluation conditions ×: Dye layer adhesion is recognized over the entire surface

From Table 3, the primer layer contains colloidal inorganic pigment ultrafine particles and polyvinyl alcohol having a content of 10% by mass or more and less than 50% by mass and a saponification degree of more than 80 mol%. The thermal transfer sheet was excellent in printability (abnormal transfer, burnt), print density and adhesiveness. In addition, the thermal transfer sheet of Example 13 in which the polymerization degree of polyvinyl alcohol was 500 was inferior to the other examples in printing suitability (abnormal transfer).
On the other hand, the thermal transfer sheets of Comparative Examples 1 to 7 in which the colloidal inorganic pigment ultrafine particles and polyvinyl alcohol are not used in combination in the primer layer are excellent in printability (abnormal transfer, burnt), print density, and adhesiveness. It did not become.
Further, the thermal transfer sheet of Comparative Example 8 in which the content of polyvinyl alcohol in the primer layer is less than 10% by mass is inferior to printing suitability (koji), and the thermal transfer sheet of Comparative Example 9 having 50% by mass or more is suitable for printing (abnormal). Transfer) and adhesiveness.
In addition, the thermal transfer sheet of Comparative Example 11 in which the coating amount of the primer layer coating solution in the primer layer coating solution was 0.02 g / m ² was higher than the thermal transfer sheet of each example in terms of printing density and adhesiveness. The thermal transfer sheet of Comparative Example 12 in which the coating amount of the primer layer coating solution in the primer layer coating solution was 0.7 g / m ² was inferior, and the thermal transfer of each example in printability (koge). It was inferior to the sheet.

Since the thermal transfer sheet of the present invention has the above-described configuration, the thermal transfer image has high sharpness, can suitably prevent occurrence of abnormal transfer in a print after being stored at high temperature and high humidity, and thermal transfer High transfer sensitivity in printing, high-density printing is obtained in high-speed printing, and suppression of kogation (black solid blurring) in black high-density areas where three dyes of yellow, magenta, and cyan are sequentially stacked it can.

Claims (3)

A thermal transfer sheet in which a primer layer and a dye layer are sequentially formed on one surface of a substrate,
The primer layer contains colloidal inorganic pigment ultrafine particles and polyvinyl alcohol,
The polyvinyl alcohol has a content in the primer layer of 10% by mass or more and less than 50% by mass, and a saponification degree is larger than 80 mol%,
Furthermore, the thermal transfer sheet wherein a primer layer, the amount of coating (dry) is characterized in that more than 0.03 g / ^{m 2,} is less than 0.6 g / ^{m 2.} The thermal transfer sheet according to claim 1, wherein the polyvinyl alcohol has a degree of polymerization of 1000 to 3000. The thermal transfer sheet according to claim 1 or 2, wherein the colloidal inorganic pigment ultrafine particles are alumina sol and / or colloidal silica.