JP4562640B2 - Thermal transfer sheet - Google Patents

Description

The present invention relates to a thermal transfer sheet in which an inorganic oxide thin film layer and a dye layer are sequentially formed on one surface of a substrate, and more particularly to a thermal transfer sheet having high transfer sensitivity in printing and particularly capable of obtaining high-density printing. It is.

Conventionally, various thermal transfer recording methods are known. Among them, a thermal transfer sheet having a dye layer in which a dye for sublimation transfer is used as a recording material and this is supported on a base material such as a polyester film with a suitable binder. From the above, there are proposed methods for forming various full-color images by thermally transferring a sublimation dye onto a transfer material that can be dyed with a sublimation dye, for example, a thermal transfer image-receiving sheet having a dye-receiving layer formed on paper or a plastic film. Yes. In this case, as the heating means, the color dots in which a large number of heating amounts of three colors or four colors are adjusted are transferred to the receiving layer of the thermal transfer image receiving sheet by heating with the thermal head of the printer, and the multicolored color dots are transferred. This reproduces the full color of the original. The image formed in this way is very clear and excellent in transparency because the colorant used is a dye, so the resulting image is excellent in reproducibility and gradation of intermediate colors. It is possible to form a high-quality image similar to an image obtained by offset printing or gravure printing, and comparable to a full-color photographic image.

In such a thermal transfer recording system using sublimation transfer, as the printing speed of the thermal transfer printer is increased, there has been a problem that a sufficient print density cannot be obtained with the conventional thermal transfer sheet. Also, there has been a demand for higher density and clearer prints of thermal transfer images, and improved thermal transfer image-receiving sheets that accept images of sublimation dyes transferred from the thermal transfer sheet and the thermal transfer sheet. Many attempts have been made. 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. Causes the problem of cutting.

In addition, the dye / resin (Dye / Binder) ratio in the dye layer of the thermal transfer sheet was increased to try to improve the printing density and the transfer sensitivity in the printing. When the dye is transferred to the heat-resistant slipping layer of the material and the transferred dye is rolled back, it is re-transferred to the dye layer of another color (kickback), and the contaminated layer is thermally transferred to the image receiving sheet. The hue may be different from that of the original color, or the so-called background stain may occur. In the thermal transfer printer, not on the thermal transfer sheet side, high energy was applied during thermal transfer during image formation. However, the dye layer and the receiving layer are fused, and so-called abnormal transfer is likely to occur. When a large amount of a release agent is added to the receiving layer to prevent the abnormal transfer, blurring of the image, background smearing, etc. occur.

In addition, as a prior art, Patent Document 1 discloses a thermal transfer in which a hydrophilic barrier / undercoat layer using polyvinyl pyrrolidone as a main component and polyvinyl alcohol as a component for improving dye transfer efficiency is provided between a dye layer and a support. A sheet is disclosed. In Patent Document 2, there is provided a thermal transfer sheet in which an intermediate layer containing a sublimation dye having a diffusion coefficient smaller than that of the sublimation dye contained in the recording layer is provided between the base film and the recording layer containing the sublimation dye. Are listed. Only the use of hydroxyethyl cellulose is described as the contents of this intermediate layer. In any of the thermal transfer sheets disclosed in Patent Documents 1 and 2, the printed matter using the thermal transfer sheet has not yet reached a sufficient level as the maximum density.

Patent Documents 3 and 4 disclose that an intermediate layer containing a metal or metal oxide is provided between the base material of the thermal transfer sheet and the dye layer. In Patent Document 3, in a working example, a metal or a metal oxide is formed on a substrate by vapor deposition, and a dye thin film is deposited thereon to transfer the dye onto active clay paper. It is shown. However, in this thermal transfer sheet, the density of the thermal transfer image is not sufficiently high, and the sharpness of the thermal transfer image is not high. Moreover, a special apparatus for vapor deposition is required, resulting in high manufacturing costs.

In Patent Document 4, an easy-adhesion layer containing a homopolymer of N-vinylpyrrolidone or a copolymer of N-vinylpyrrolidone and other components is provided between the base material of the thermal transfer sheet and the dye layer, It has been shown that an inorganic filler such as an ultraviolet absorber and a filler such as silica and alumina are also used for the easy-adhesion layer in order to improve the adhesiveness. However, although this easy-adhesion layer can improve the adhesion of the dye layer to the substrate, it has high transfer sensitivity in thermal transfer printing, and does not provide high-density printing.
JP-A-5-131760 JP-A-60-232996 JP 59-78897 A Japanese Patent Laid-Open No. 2003-312151

Accordingly, in order to solve the above-described problems, a thermal transfer sheet having high transfer sensitivity in thermal transfer printing, high density printing, high thermal transfer image sharpness, and sufficiently satisfactory printing can be provided. For the purpose.

The invention according to claim 1 is such that an undercoat layer and a dye layer made of a thermoplastic resin and colloidal inorganic pigment ultrafine particles are sequentially formed on one surface of a substrate, and the colloidal inorganic pigment ultrafine particles are alumina sol der is, the thermoplastic resin is a polyvinylpyrrolidone resin, further, the content of said colloidal inorganic pigment ultrafine particles and a thermoplastic resin, by weight, colloidal inorganic pigment ultrafine particle / thermoplastic resin = wherein the 1 / 4-1 / 0.1 der Rukoto. The invention of claim 2 is a thermal transfer sheet according to claim 1 on the surface opposite to the surface to form an undercoat layer of the base material is provided with a heat-resistant slip layer.

The thermal transfer sheet of the present invention is obtained by sequentially forming an undercoat layer and a dye layer made of a thermoplastic resin and colloidal inorganic pigment ultrafine particles on one surface of a substrate. The subbing layer made of the above thermoplastic resin and colloidal inorganic pigment ultrafine particles can improve the adhesion between the base material and the dye layer, and the image receiving sheet can be used in combination with the thermal transfer image receiving sheet to perform thermal transfer by heating. The dye layer does not transfer abnormally. Furthermore, since the undercoat layer is difficult to dye the dye from the dye layer, it prevents the dye from transferring from the dye layer to the undercoat layer during printing, and prevents the dye from diffusing to the receiving layer side of the image receiving sheet. By performing it effectively, the transfer sensitivity in printing is high and the printing density can be increased. Further, compared with the case where the undercoat layer is composed only of colloidal inorganic pigment ultrafine particles, the releasability from the image receiving sheet in printing is less likely to deteriorate after storage at high temperature and high humidity.

FIG. 1 shows the best mode of one embodiment of the thermal transfer sheet of the present invention. In FIG. 1, a heat-resistant slip layer 4 is provided on one surface of a substrate 1 to improve the slipperiness of the thermal head and prevent sticking, and a thermoplastic resin and a colloidal inorganic pigment are disposed on the other surface of the substrate 1. 2 shows a thermal transfer sheet in which an undercoat layer 2 and a dye layer 3 made of ultrafine particles are sequentially formed.

Hereinafter, each layer constituting the thermal transfer sheet of the present invention will be described in detail.
(Base material)
The base material 1 of the thermal transfer sheet used in the present invention may be any conventionally known resin having a certain degree of heat resistance and strength. For example, it has a thickness of about 0.5 to 50 μm, preferably about 1 to 10 μm. Polyethylene terephthalate film, 1,4-polycyclohexylenedimethylene terephthalate film, polyethylene naphthalate film, polyphenylene sulfide film, polystyrene film, polypropylene film, polysulfone film, aramid film, polycarbonate film, polyvinyl alcohol film, cellophane, acetic acid Examples thereof include cellulose derivatives such as cellulose, polyethylene film, polyvinyl chloride film, nylon film, polyimide film, ionomer film, and the like. As the resin, polyethylene terephthalate is preferable.
The base material may be composed of only one kind of the above-described resin, or may be composed of two or more kinds of resins.

In the base material, an adhesion treatment is often performed on the surface on which the undercoat layer and the dye layer made of thermoplastic resin and colloidal inorganic pigment ultrafine particles are formed. When the undercoat layer is formed on the plastic film of the base material, it is preferable to perform an adhesion treatment because the adhesion between the base material and the undercoat layer tends to be insufficient. As the adhesion treatment, known resin surface modification 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, grafting treatment, etc. Quality technology 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 and the undercoat layer made of the thermoplastic resin and colloidal inorganic pigment ultrafine particles, among the above-mentioned adhesion treatments, the general treatment method is used without increasing the cost. Corona discharge treatment or plasma treatment is preferred in that it can be used and the adhesion between the substrate and the undercoat layer can be improved.

(Underlayer)
In the undercoat layer 2 made of the thermoplastic resin and the colloidal inorganic pigment ultrafine particles provided between the substrate and the dye layer in the thermal transfer sheet of the present invention, conventionally known compounds can be used as the colloidal inorganic pigment ultrafine particles. 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, oxidation Examples include titanium. In particular, colloidal silica or alumina sol is preferably used. In the undercoat layer, these colloidal inorganic pigment ultrafine particles may be used not only under the same type of conditions but also with different types such as colloidal silica and alumina sol. These colloidal inorganic pigment ultrafine particles have an average particle size of 100 nm or less, preferably 50 nm or less, particularly preferably 3 to 30 nm, and thereby the function of the undercoat 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, it is possible to use an acid type treated so as to be easily dispersed in a sol form in an aqueous solvent, a fine particle charge converted to a cation, or a fine particle surface treated.

The thermoplastic resin used in the undercoat layer is a hydrophilic resin. For example, polyester resin, polyacrylate resin, polyurethane resin, styrene acrylate resin, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl Examples thereof include cellulose resins such as cellulose, methyl cellulose, cellulose acetate, and cellulose butyrate, polyvinyl acetal resins such as polyvinyl acetoacetal and polyvinyl butyral, polyvinyl pyrrolidone resins, and polyvinyl alcohol resins. Further, these resins may be mixed and used. In particular, among the above hydrophilic resins, a polyvinyl pyrrolidone resin or a polyvinyl alcohol resin is preferably used because it has good adhesion to a substrate and a dye layer and has low dyeing properties.

Examples of the polyvinylpyrrolidone resin include homopolymers of vinylpyrrolidone such as N-vinyl-2-pyrrolidone and N-vinyl-4-pyrrolidone, and copolymers thereof. The polyvinyl pyrrolidone resin used in the present invention preferably has a K value in the Fickencher formula of 60 or more, and in particular, a grade of K-60 to K-120 can be used, and the number average molecular weight is 30. , 000 to 280,000. When the polyvinyl pyrrolidone resin having a K value of less than 60 is used, the effect of improving transfer sensitivity in printing is reduced.

As the polyvinyl alcohol resin used in the undercoat layer, those having a saponification degree of 50 to 100 mol% and a polymerization degree of 200 to 3500 are preferable. If the degree of saponification or the degree of polymerization is too low, the adhesion to the substrate or the dye layer tends to be lowered, and if they are too high, the viscosity becomes too high and the coating suitability is lowered.

The glass transition temperature Tg of the thermoplastic resin in the undercoat layer is preferably 60 ° C. or higher, and thermal fusion between the dye layer and the transfer material due to thermal damage from the thermal head to the undercoat layer, It is possible to further prevent the occurrence of abnormal transfer and uneven printing on the transfer material due to the generation of wrinkles on the thermal transfer sheet during thermal transfer recording. When the Tg of the binder resin of the undercoat layer is less than 60 ° C., the constituent resin of the primer layer is liable to flow due to heat at the time of printing, abnormal transfer is likely to occur, and the dye contained in the dye layer is the undercoat layer. Back diffusion is likely to reduce transfer sensitivity.

The blend of the thermoplastic resin and the colloidal inorganic pigment ultrafine particles in the undercoat layer is preferably colloidal inorganic pigment ultrafine particles / thermoplastic resin = 1/4 to 1 / 0.1 on a mass basis. The colloidal inorganic pigment ultrafine particles / thermoplastic resin is more preferably 1/4 to 1 / 0.5. If the blending ratio of the colloidal inorganic pigment ultrafine particles in the undercoat layer is too high, the releasability from the image receiving sheet in printing is likely to deteriorate after the thermal transfer sheet is left at high temperature and high humidity and stored. Also, if the blending ratio of the thermoplastic resin in the undercoat layer is too high, the thermal transfer sheet is left at high temperature and high humidity, and after storage, the releasability from the image-receiving sheet in printing tends to decrease, and the dye layer Adhesiveness may decrease.

In the case of coating the undercoat layer, it is preferable to give the fluidity by lowering the viscosity as a coating solution for the undercoat layer in consideration of the coating suitability.
The undercoat layer in the present invention is composed of the above thermoplastic resin and colloidal inorganic pigment ultrafine particles, the inorganic pigment ultrafine particles are dispersed in a sol form in an aqueous solvent, and the thermoplastic resin is dispersed in an aqueous solvent, or The dissolved 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, or a reverse roll coating method using a gravure plate.
The aqueous solvent in the 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. Further, as the aqueous solvent, cellosolves such as methyl cellosolve and ethyl cellosolve; aromatic solvents such as toluene, xylene and chlorobenzene; ketones such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; tetrahydrofuran Ethers such as dioxane, chlorine solvents such as chloroform and trichloroethylene, nitrogen-containing solvents such as dimethylformamide and N-methylpyrrolidone, dimethyl sulfoxide, and a mixture of an organic solvent and water can also be used. , Water, or a mixture of water and alcohols.
The thus formed undercoat layer, 0.02~1g / ^{m 2,} to 0.02~1.0g / ^{m 2,} preferably the coating during drying of about 0.03~0.1g / ^{m 2} The amount of work.
The undercoat layer is coated on the substrate using the above coating solution, dried with hot air, etc., so that the colloidal inorganic pigment ultrafine particles are changed from sol to gel, moisture is blown off, The thermoplastic resin is formed by adhering ultrafine inorganic pigment particles as a binder. Therefore, the undercoat layer of the present invention is not subjected to a baking treatment by a general sol-gel method.

It is desirable that the undercoat layer formed as described above is mainly composed of thermoplastic resin and colloidal inorganic pigment ultrafine particles, with no other components, or a little solvent remaining. . Thus, the undercoat layer composed of the thermoplastic resin and colloidal inorganic pigment ultrafine particles 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 the thermal transfer image receiving sheet is heated in combination with the thermal transfer image, abnormal transfer of the dye layer to the image receiving sheet can be prevented.
Furthermore, since the undercoat layer is composed of a thermoplastic resin that is difficult to dye the dye from the dye layer and the colloidal inorganic pigment ultrafine particles, the dye layer from the dye layer to the undercoat layer at the time of printing is used. By preventing the transfer and 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 undercoat layer in the present invention prevents the point that the releasability from the image-receiving sheet in printing is likely to decrease after storage at high temperature and high humidity, compared to the case where the undercoat layer is composed only of colloidal inorganic pigment ultrafine particles. ing.

(Dye layer)
In the thermal transfer sheet of the present invention, the dye layer 3 is provided on one surface of the substrate via the undercoat layer. The dye layer can be composed of a single layer of one color, or a plurality of dye layers containing dyes having different hues can be repeatedly formed on the same surface of the same base material in the order of surfaces. 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 azomethines such as diarylmethane, triarylmethane, thiazole, merocyanine, pyrazolone methine and the like, indoaniline, acetophenone azomethine, pyrazoloazomethine, imidazolazomethine, imidazoazomethine, and pyridone azomethine. , Xanthene, oxazine, dicyanostyrene, cyanomethylene represented by tricyanostyrene, thiazine, azine, acridine, benzeneazo, pyridoneazo, thiophenazo, isothiazoleazo, pyrroleazo, pyralazo, imidazoleazo, Azos such as thiadiazole azo, triazole azo, dizazo, spiropyran, indolinospiropyran, fluoran, rhodamine lactam, naphthoquinone, anne Rakinon system include the quinophthalone like.

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

A silane coupling agent can be added to the dye layer. Examples of silane coupling agents include those containing isocyanate groups such as γ-isocyanatopropyltriethoxysilane and γ-isocyanatopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β -(Aminoethyl) -γ-aminopropyltriethoxysilane, those containing amino groups such as γ-phenylaminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane and β- (3,4-epoxy And those containing an epoxy group such as (cyclohexyl) 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.

Further, in the present invention, the following releasable graft copolymer can be used as a release agent or binder in place 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 to a polymer main chain. Is. Of 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, as a binder resin constituting the dye layer, the adhesive resin between the undercoat layer and the dye layer can be maintained even after being left under high temperature and high humidity. Among them, polyvinyl butyral, polyvinyl acetal, polyvinyl acetate, polyester resins, cellulose resins such as cellulose acetate and cellulose butyrate, and the like are preferably used alone or in a mixture of highly adhesive resins having a hydroxyl group or a carboxyl group. Used.

The dye layer may contain the above-mentioned dyes, binders, and other various conventional additives as required. Examples of the additive include organic fine particles such as polyethylene wax and inorganic fine particles in order to improve releasability from the image receiving sheet and ink coating suitability. 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 thickness of 0.2 to 6 g / m ² , or 0.2 to 6.0 g / m ² , preferably 0.3 to 3 g / m ² , or 0.3 to 3.0 g. / M ² is the coating amount at the time of drying.

(Heat resistant slipping layer)
The heat transfer sheet of the present invention is provided with a heat resistant slipping layer 4 on the surface opposite to the surface on which the undercoat layer of the base material is provided in order to prevent adverse effects such as sticking and printing wrinkles due to heat of the thermal head. It may be a thing. 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 Polyimide resins, polyamideimide resins, polycarbonate resins, and chlorinated polyolefin resins.

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 layer added with a filler.

The heat-resistant slipping layer is prepared by dissolving or dispersing the above-described resin, slipperiness-imparting agent, and filler in an appropriate solvent on the base sheet to prepare a heat-resistant slipping layer coating solution. Then, this can be 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 slip layer is a ^{solid, 0.1g / m 2 ~3g / m} 2, to 0.1g ^{/ m 2} ~3.0g ^/ m 2 is preferred.

Next, an Example and a comparative example are given and this invention is further explained in full detail. In the text, “part” or “%” is based on mass unless otherwise specified.
(Reference Example 1)

As a base material, an undercoat layer coating solution having the following composition is applied on a polyethylene terephthalate film (PET) having a thickness of 4.5 μm by gravure coating so that the dry coating amount is 0.06 g / m ² and dried. Thus, an undercoat layer was formed. On the undercoat layer, a dye layer coating solution having the following composition was applied by gravure coating to a dry coating amount of 0.7 g / m ² and dried to form a dye layer. A thermal transfer sheet is prepared. In addition, a heat-resistant slipping layer coating solution having the following composition was applied to the other surface of the substrate in advance by gravure coating and dried so that the dry coating amount was 1.0 g / m ² . A layer was formed.

<Undercoat layer coating solution 1>
30 parts of colloidal silica (Snowtech OXS, particle size 4-6 nm, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Polyvinylpyrrolidone resin (K-90, manufactured by ISP) 3 parts Water 50 parts Isopropyl alcohol 50 parts

<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, Takeda Pharmaceutical Company Limited)
Phosphate 0.8 parts (Plysurf A208S, Daiichi Kogyo Seiyaku Co., Ltd.)
Methyl ethyl ketone 42.5 parts Toluene 42.5 parts ( Reference Example 2 )

A thermal transfer sheet of Reference Example 2 was prepared in the same manner as in Reference Example 1 except that the undercoat layer had the following composition in the thermal transfer sheet prepared in Reference Example 1.
<Undercoat layer coating solution 2>
30 parts of alumina sol (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
3 parts of polyvinyl alcohol resin (Gohsenol KH-20, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80 mol%, polymerization degree 2000 to 3000)
50 parts of water 50 parts of isopropyl alcohol (Example 3)

A thermal transfer sheet of Example 3 was produced in the same manner as in Reference Example 1 except that the undercoat layer had the following composition in the thermal transfer sheet produced in Reference Example 1.
<Undercoat layer coating solution 3>
30 parts of alumina sol (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Polyvinylpyrrolidone resin (K-90, manufactured by ISP) 3 parts Water 50 parts Isopropyl alcohol 50 parts ( Reference Example 3 )

A PET film substrate having the same conditions as in Reference Example 1 was used, and a heat-resistant slipping layer similar to that in Reference Example 1 was previously formed on one surface of the substrate. On the surface opposite to the surface on which the heat-resistant slip layer of the substrate is provided, the undercoat layer coating solution 4 having the following composition is applied by gravure coating so that the dry coating amount is 0.06 g / m ² . Dried to form an undercoat layer. Further, a dye layer is formed on the undercoat layer in the same manner as in Reference Example 1 to produce the thermal transfer sheet of Reference Example 3 .

<Undercoat layer coating solution 4>
Alumina sol 6 parts (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Polyvinylpyrrolidone resin (K-90, manufactured by ISP) 3 parts Water 35 parts Isopropyl alcohol 35 parts (Example 5)

A thermal transfer sheet of Example 5 was prepared in the same manner as in Reference Example 1 except that the undercoat layer had the following composition in the thermal transfer sheet prepared in Reference Example 1.
<Undercoat layer coating solution 5>
15 parts of alumina sol (alumina sol 200, feather-shaped, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Polyvinylpyrrolidone resin (K-90, manufactured by ISP) 3 parts Water 40 parts Isopropyl alcohol 40 parts (Example 6)

A thermal transfer sheet of Example 6 was prepared in the same manner as in Reference Example 1 except that the undercoat layer had the following composition in the thermal transfer sheet prepared in Reference Example 1.
<Undercoat layer coating solution 6>
40 parts of alumina sol (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Polyvinylpyrrolidone resin (K-90, manufactured by ISP) 1 part Water 35 parts Isopropyl alcohol 35 parts

(Comparative Example 1)
A PET film substrate having the same conditions as in Reference Example 1 was used, and a heat-resistant slipping layer similar to that in Reference Example 1 was previously formed on one surface of the substrate. The surface of the substrate opposite to the surface on which the heat-resistant slipping layer is provided is directly coated on the substrate with the dye layer coating solution used in Reference Example 1 by gravure coating, so that the dry coating amount is 0.7 g / The dye layer is formed by coating and drying so as to be m ^2, and the thermal transfer sheet of Comparative Example 1 is produced.

(Comparative Example 2)
A PET film substrate having the same conditions as in Reference Example 1 was used, and a heat-resistant slipping layer similar to that in Reference Example 1 was previously formed on one surface of the substrate. On the surface opposite to the surface on which the heat-resistant slip layer of the substrate is provided, the undercoat layer coating solution 7 having the following composition is applied by gravure coating so that the dry coating amount is 0.06 g / m ² . Dried to form an undercoat layer. Further, a dye layer is formed on the undercoat layer in the same manner as in Reference Example 1 to produce a thermal transfer sheet of Comparative Example 2.

<Undercoat layer coating solution 7>
Polyvinyl pyrrolidone resin (K-90, manufactured by ISP) 10 parts Water 100 parts Isopropyl alcohol 100 parts

(Comparative Example 3)
A PET film substrate having the same conditions as in Reference Example 1 was used, and a heat-resistant slipping layer similar to that in Reference Example 1 was previously formed on one surface of the substrate. On the surface opposite to the surface on which the heat-resistant slipping layer of the substrate is provided, the undercoat layer coating solution 8 having the following composition is applied by gravure coating so that the dry coating amount is 0.06 g / m ² . Dried to form an undercoat layer. Further, a dye layer is formed on the undercoat layer in the same manner as in Reference Example 1 to produce a thermal transfer sheet of Comparative Example 3.

<Undercoat layer coating solution 8>
50 parts of alumina sol (alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd., solid content 10%)
Water 25 parts Isopropyl alcohol 25 parts

Test Examples The following tests were conducted on the thermal transfer sheets obtained in each Example and each Comparative Example.

<Reflection density>
Using the thermal transfer sheets of the examples and comparative examples prepared above, in combination with a dedicated thermal transfer image-receiving sheet for an OLYMPUS P-400 printer, printing was performed under the following conditions, and a Macbeth reflection densitometer RD-918. The reflection density was measured.
(Printing conditions)
Thermal head: KGT-217-12MPL20 (manufactured by Kyocera Corporation)
Heating element average resistance value: 2994 (Ω)
Main scanning direction printing density; 300 dpi
Sub-scanning direction print density; 300 dpi
Applied power: 0.10 (w / dot)
1 line cycle: 5 (msec.)
Printing start temperature; 40 (° C)
Applied pulse (gradation control method); using a multi-pulse test printer that can vary the number of divided pulses from 0 to 255 in one line period and having a pulse length obtained by equally dividing one line period into 256 The duty ratio of the divided pulse was fixed to 70%, and the number of pulses per line period was divided into 15 from 0 to 255. Thereby, different energy can be given to 15 steps.

With respect to the prints in each of the above Examples and Comparative Examples, the reflection density of density max (255th gradation) was measured.

<Adhesive strength of dye layer>
Using the thermal transfer sheet prepared above, on the dye layer, scotch tape (registered trademark) of length 200 mm x width 12 mm is rubbed twice with the thumb and pasted. Evaluation was made by examining the presence or absence of adhesion of the dye layer.

Evaluation was performed according to the following criteria.
○: Adhesion of the dye layer is not recognized.
Δ: Slight adhesion of the dye layer is observed.
X: Adhesion of the dye layer is observed on the entire surface.

<Evaluation of releasability after storage>
The thermal transfer sheets prepared in each of the above examples and comparative examples were stored for 48 hours in an environment of 40 ° C. and 90% RH, and then subjected to the same printing conditions as in the above reflection density measurement. When the entire surface is printed with a printing pattern having a solid color (gradation value 255/255: density maximum) and printing is performed, the dye layer of the thermal transfer sheet and the thermal transfer image-receiving sheet are thermally fused, or for each dye layer It was examined visually whether so-called abnormal transfer, which is transferred to the thermal transfer image-receiving sheet, occurred.

Evaluation was performed according to the following criteria.
○: The dye layer and the thermal transfer image-receiving sheet are not thermally fused and abnormal transfer does not occur.
X: The dye layer and the thermal transfer image-receiving sheet are thermally fused or abnormal transfer occurs.

The measurement results of the reflection density, the adhesion strength of the dye layer, and the results of evaluation of releasability after storage are as shown in Table 1 below.

From the above results, thermal transfer of Reference Examples 1, 2, 3, and Examples 3, 5 and 6 in which an undercoat layer made of a thermoplastic resin and colloidal inorganic pigment ultrafine particles was provided between the base material and the dye layer. All of the sheets had a high density with the above reflection density of about 2.40 or more. Further, in the thermal transfer sheets of Reference Examples 1 and 2, Examples 3, 5 and 6, the ratio of the colloidal inorganic pigment ultrafine particles to the thermoplastic resin is such that the colloidal inorganic pigment ultrafine particles / thermoplastic resin = 1/4 to 1. Since it is within the range of /0.1, good results can be obtained particularly with respect to the releasability after storage, and the adhesion of the dye layer to the substrate is not problematic. Regarding the evaluation of releasability after storage, although the thermal transfer sheet of Reference Example 3 was inferior in evaluation to other examples, a better result than Comparative Example 3 was obtained.

The thermal transfer sheet of Comparative Example 1 does not have a subbing layer on the substrate, and is provided with a dye layer directly. The thermal transfer sheet and thermal transfer image receiver after adhesion to the substrate of the dye layer, high temperature and high humidity storage The releasability from the sheet has practical problems, and the reflection density is less than 2.2, which is not satisfactory as a high-density printed matter.
In Comparative Example 2, an undercoat layer made of only a thermoplastic resin is provided between the base material and the dye layer, and there is a problem in releasability between the thermal transfer sheet and the thermal transfer image receiving sheet after storage at high temperature and high humidity. The reflection density is less than 2.2, which is not satisfactory as a high density printed matter. In Comparative Example 3, an undercoat layer composed only of colloidal inorganic pigment ultrafine particles was provided between the substrate and the dye layer, and the reflection density of the printed matter and the adhesion of the dye layer to the substrate were good. However, there is a problem with the releasability between the thermal transfer sheet and the thermal transfer image-receiving sheet after storage at high temperature and high humidity.

Since the thermal transfer sheet of the present invention has the above-described configuration, the adhesiveness between the base material and the dye layer can be improved, and when the thermal transfer image is heated in combination with the thermal transfer image receiving sheet, the dye layer is transferred to the image receiving sheet. Does not transfer abnormally. The thermal transfer sheet of the present invention has little transfer of dye from the dye layer to the undercoat layer at the time of printing, and can effectively perform dye diffusion to the receiving layer side of the image receiving sheet, so the transfer sensitivity in printing is high, The print density can be increased. Furthermore, the thermal transfer sheet of the present invention is less likely to deteriorate the releasability from the image-receiving sheet in printing after storage at high temperature and high humidity, as compared with the case where the undercoat layer is composed only of colloidal inorganic pigment ultrafine particles.

It is a schematic sectional drawing which shows one best form of embodiment which is the thermal transfer sheet of this invention.

1 Substrate 2 Undercoat layer 3 Dye layer 4 Heat-resistant slipping layer

Claims (2)

Subbing layer on one surface of a substrate comprising a thermoplastic resin and colloidal inorganic pigment ultrafine particle is obtained by sequentially forming a dye layer, wherein the colloidal inorganic pigment ultrafine particles Ri alumina sol der,
The thermoplastic resin is a polyvinylpyrrolidone resin,
The content ratio between the colloidal inorganic pigment ultrafine particles and the thermoplastic resin is, based on mass, colloidal inorganic pigment ultrafine particles / thermoplastic resin = 1/4 to 1 / 0.1. Thermal transfer sheet. The thermal transfer sheet according to claim 1 on the surface opposite to the surface to form an undercoat layer of the base material is provided with a heat-resistant slip layer.

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