JP2006116892A - Thermal transfer sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal transfer sheet which has high transfer sensitivity in thermal transfer printing, can obtain a high-density print, high clarity of a thermal transfer image, and can make sufficiently satisfactory printed matter available. <P>SOLUTION: This thermal transfer sheet has a heat-resistant lubricity layer formed on one surface of a base material, an undercoating layer consisting of a colloidal inorganic pigment ultrafine particle, formed on the other surface of the base material, and a dye layer laminated in that order. The undercoating layer consisting of the colloidal inorganic pigment ultrafine particle can enhance the adhesive properties between the base material and the dye layer. In addition, when an image is thermally transferred in combination with a thermal transfer image receiving sheet, the abnormal transfer of the dye layer to the image receiving sheet does not occur. Further, since the undercoating layer is hardly stained by a dye from the dye layer, it is possible to prevent the dye from migrating to the undercoating layer from the dye layer during printing, and increase the transfer sensitivity in printing and enhance a print density by effectively diffusing the dye to the acceptance layer side of the image receiving sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermal transfer sheet in which a heat-resistant slipping layer is provided on one surface of a substrate, and an inorganic oxide thin film layer and a dye layer are sequentially formed on the other surface of the substrate. In particular, the present invention relates to a thermal transfer sheet that can obtain a high density print.

  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 having a large number of three or four colors adjusted by heating with the thermal head of the printer are transferred to the receiving layer of the thermal transfer image receiving sheet, and the multicolored color dots are transferred. To reproduce the full color of the document. The image formed in this way is very clear and excellent in transparency because the coloring material used is a dye, so the resulting image is excellent in the 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.

  Further, as a prior art, Patent Document 1 discloses a thermal transfer in which a polyvinyl pyrrolidone as a main component and a hydrophilic barrier / undercoat layer using a mixture of 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.

Japanese Examined Patent Publication No. 7-102746 Japanese Patent Publication No. 5-69718 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.

  In the invention according to claim 1, a heat-resistant slipping layer is provided on one surface of the base material, and an undercoat layer and a dye layer made of colloidal inorganic pigment ultrafine particles are sequentially formed on the other surface of the base material. It is characterized by. The invention of claim 2 is characterized in that the colloidal inorganic pigment ultrafine particles of claim 1 are colloidal silica and alumina sol.

  In the thermal transfer sheet of the present invention, a heat-resistant slipping layer is provided on one surface of a substrate, and an undercoat layer and a dye layer made of colloidal inorganic pigment ultrafine particles are sequentially formed on the other surface of the substrate. . The subbing layer comprising the above-mentioned colloidal inorganic pigment ultrafine particles can improve the adhesion between the substrate and the dye layer, and when the thermal transfer image receiving sheet is heated and thermally transferred, the dye layer is applied to the image receiving sheet. There is no abnormal transcription. 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.

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

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 material as long as it has a conventionally known 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.

  In the base material, an adhesion treatment is often performed on the surface on which the undercoat layer and the dye layer made of colloidal inorganic pigment ultrafine particles are formed. When forming a thin film layer of an inorganic oxide on the plastic film of the base material, the adhesiveness between the base material and the thin film layer of the inorganic oxide 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 enhance the adhesion between the base material and the undercoat layer made of colloidal inorganic pigment ultrafine particles, among the above-mentioned adhesion treatment, the corona discharge can be easily obtained without increasing the cost. Treatment or plasma treatment is preferred.

(Undercoat layer consisting of ultrafine colloidal inorganic pigment)
In the subbing layer 2 made of 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 its hydrate, suspect boehmite, etc.), aluminum silicate, magnesium silicate, magnesium carbonate, magnesium oxide, oxidation Examples include titanium. In particular, colloidal silica and alumina sol are preferably used. These colloidal inorganic pigment ultrafine particles have a primary average particle size of 100 nm or less, preferably 50 nm or less, particularly preferably 3 to 30 nm, and thereby sufficiently exhibit the function of the undercoat layer. it can.

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. In consideration of coating suitability when the undercoat layer is applied, it is preferable that the coating liquid for the undercoat layer has a low viscosity and fluidity. The undercoat layer in the present invention is composed of the above-mentioned colloidal inorganic pigment ultrafine particles, and does not use a resin as a binder, and a gravure coating is applied to a coating liquid in which inorganic pigment ultrafine particles are dispersed in a sol form in an aqueous solvent. It is formed by applying and drying by a conventionally known forming means such as a method, a roll coating method, a screen printing method, or a reverse roll coating method using a gravure plate. The undercoat layer thus formed has a coating amount during drying of about 0.02 to 1.0 g / m ² , preferably about 0.03 to 0.1 g / m ² . The undercoat layer is coated on a substrate using a coating solution in which the above-mentioned inorganic pigment ultrafine particles are dispersed in a water solvent, and is dried with hot air, etc. , Formed by blowing moisture. 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 has a colloidal inorganic pigment ultrafine particle as a main component and has no other components or a solvent that remains a little. Thus, the undercoat layer made of 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 combination is heated and thermally transferred, the abnormal transfer of the dye layer to the image receiving sheet is prevented. Further, since the undercoat layer is made of a material that is difficult to dye the dye from the dye layer, the dye transfer from the dye layer to the undercoat layer during printing is prevented, and the receiving layer of the image receiving sheet By effectively diffusing the dye to the side, the transfer sensitivity in printing is high and the printing density can be increased.

(Dye layer)
In the thermal transfer sheet of the present invention, the dye layer 3 is provided on the other side of the base material provided with a heat-resistant slipping layer on one side through an inorganic oxide thin film 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. The selection is 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.

  Further, 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.

  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 on a polymer main chain. 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, since the undercoat layer is composed of colloidal inorganic pigment ultrafine particles and does not use a binder, the adhesion between the undercoat layer and the dye layer may be likely to deteriorate. Therefore, as the binder resin constituting the dye layer, among the above-mentioned examples, hydroxyl groups and carboxyl groups such as polyvinyl butyral, polyvinyl acetal, polyvinyl acetate, cellulose resins such as polyester resins, cellulose acetate, cellulose butyrate, etc. A resin having a high adhesive property and a mixture thereof are preferably 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 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 .

(Heat resistant slipping layer)
In the thermal transfer sheet of the present invention, a heat-resistant slipping layer 4 is provided on one surface of the substrate in order to prevent adverse effects such as sticking and printing wrinkles due to the heat of the thermal head. 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, 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 resin, polyamideimide resin, poly Boneto 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. Preferably, it is a layer made of a polyol, for example, a polyalcohol polymer compound, a polyisocyanate compound, and a phosphate ester compound, and a filler may be added. More preferred.

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. This can be formed by coating with a forming means such as gravure printing, screen printing, reverse roll coating using a gravure plate, and drying. The coating amount of the heat-resistant slip layer is a ^{solid, 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. As a base material, an undercoat layer coating solution having the following composition is applied onto 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 is applied to the other surface of the base material in advance by gravure coating and dried so that the dry coating amount becomes 1.0 g / m ² . A layer was formed.

<Undercoat layer coating solution 1>
Colloidal silica (Snowtech OXS, particle size 4-6 nm, manufactured by Nissan Chemical Industries, Ltd.) 50 parts Water 25 parts Isopropyl alcohol 25 parts

<Dye layer coating solution>
C. I. Solvent Blue 63 6.0 parts Polyvinyl butyral resin 3.0 parts (SREC 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

A thermal transfer sheet of Example 2 was produced in the same manner as in Example 1 except that the undercoat layer had the following composition in the thermal transfer sheet produced in Example 1.
<Undercoat layer coating solution 2>
Alumina sol (Alumina sol 200, feather shape, manufactured by Nissan Chemical Industries, Ltd.) 50 parts Water 25 parts Isopropyl alcohol 25 parts

In the thermal transfer sheet produced in Example 1, the thermal transfer sheet of Example 3 was produced in the same manner as in Example 1 except that the undercoat layer had the following composition.
<Undercoat layer coating solution 3>
Alumina sol (alumina sol 520, boehmite plate crystal form, manufactured by Nissan Chemical Industries, Ltd.) 25 parts Water 37.5 parts Isopropyl alcohol 37.5 parts

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

(Comparative Example 2)
A PET film substrate having the same conditions as in Example 1 was used, and a heat-resistant slipping layer similar to that in Example 1 was previously formed on the other surface of the substrate. The adhesive layer coating solution 1 having the following composition is applied to the surface of the substrate opposite to the surface where the heat resistant slipping layer is provided by gravure coating, and dried to a dry coating amount of 0.06 g / m ² and dried. Thus, an adhesive layer was formed. Further, a dye layer is formed on the adhesive layer in the same manner as in Example 1 to produce a thermal transfer sheet of Comparative Example 2.

<Adhesive layer composition 1>
Polyvinylpyrrolidone 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 Example 1 was used, and a heat-resistant slipping layer similar to that in Example 1 was previously formed on the other surface of the substrate. The adhesive layer coating liquid 2 having the following composition is applied to the surface opposite to the surface on which the heat-resistant slipping layer of the substrate is provided, by gravure coating, and dried to a dry coating amount of 0.06 g / m ² and dried. Thus, an adhesive layer was formed. Further, a dye layer is formed on the adhesive layer in the same manner as in Example 1 to produce a thermal transfer sheet of Comparative Example 3.

<Adhesive layer composition 2>
Polyester resin (WR-961, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) 3 parts Water 50 parts Isopropyl alcohol 50 parts

<Reflection density>
Using the thermal transfer sheets of each 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: 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, scotch tape (registered trademark) is rubbed twice on the dye layer with the thumb, rubbed and applied, and immediately, the dye layer adheres to the tape side when peeled off. Evaluation was made by examining the presence or absence.

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.

<Releasability evaluation>
Under the same printing conditions as in the case of the reflection density measurement described above, the entire surface of the printed material was printed with a solid printing pattern (gradation value 255/255: density max), and when the printing was performed, It was visually examined whether the dye layer and the thermal transfer image receiving sheet were thermally fused or whether so-called abnormal transfer occurred in which the entire dye layer was transferred to the thermal transfer image receiving sheet.

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 and the evaluation results of the adhesive strength and releasability of the dye layer are shown in Table 1 below.

  From the above results, all of the thermal transfer sheets of Examples 1 to 3 in which the undercoat layer composed of colloidal inorganic pigment ultrafine particles was provided between the base material and the dye layer had the above reflection density of 2.30 or more. The concentration was high. In addition, all the thermal transfer sheets of the examples give good results for releasability, and there is no problem with the adhesion of the dye layer to the substrate.

  In Comparative Examples 1, 2, and 3, the subbing layer made of colloidal inorganic pigment ultrafine particles is not provided between the base material and the dye layer, and the reflection density is less than 2.2, and the high density It is not satisfactory as a print product. Further, Comparative Example 1 has practical problems with respect to the adhesion of the dye layer to the substrate and the releasability from the thermal transfer image receiving sheet.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Undercoat layer which consists of colloidal inorganic pigment ultrafine particles 3 Dye layer 4 Heat resistant slipping layer

Claims (2)

  A thermal transfer sheet comprising a heat-resistant slipping layer provided on one surface of a substrate, and an undercoat layer and a dye layer made of colloidal inorganic pigment ultrafine particles formed in order on the other surface of the substrate. The thermal transfer sheet according to claim 1, wherein the colloidal inorganic pigment ultrafine particles are colloidal silica or alumina sol.

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