JP2904814B2 - Thermal transfer sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermal transfer sheet, and more particularly, to a novel thermal transfer sheet having an excellent heat-resistant slip layer (back layer) made of a specific material.

(Conventional technology and its problems) Conventionally, when printing an output print of a computer or a word processor by a thermal transfer method, a thermal transfer sheet provided with a heat-meltable ink layer on one surface of a base film is used. .

This conventional thermal transfer sheet has a thickness as a base film.
Using a 10 to 20 μm capacitor paper or a paper such as a paraffin paper or a 3 to 20 μm thick plastic film such as polyester or cellophane, and mixing a wax and a coloring agent such as a pigment or a dye with a hot-melt ink layer. It is manufactured by coating.

Also, when a heat-sensitive material such as a plastic film is used as the base film, the thermal head sticks (sticks) at the time of printing, and the peeling and slipping property of the thermal head is impaired, or the base film is broken. Or other problems occur.

As a method of solving such a problem, a method of incorporating inorganic particles or crosslinked resin particles having high heat resistance in the back layer has been proposed. The higher the amount of such heat-resistant particles added, the higher the heat resistance of the back layer, but there is a problem that the back layer strength of the back layer decreases as the amount of addition increases.

In particular, the back layer is preferably as thin as possible in consideration of the thermal sensitivity during thermal transfer. Recently, a back layer having a thickness of 0.5 μm or less has been demanded. The addition of a large amount of heat-resistant particles having a large particle diameter has a problem that the strength of the back layer is remarkably reduced, and a thin film back layer having sufficient heat resistance cannot be formed. Was. Of course, if particles having a thickness significantly smaller than the thickness of the back layer are used as the heat-resistant particles, a relatively large amount of heat-resistant particles can be included in the back layer, but in this case, sufficient heat resistance cannot be obtained. .

Accordingly, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a thermal transfer sheet provided with a back layer having excellent heat resistance.

(Means for Solving the Problems) The above object is achieved by the present invention described below.

That is, the present invention provides a thermal transfer sheet comprising a transfer ink layer which is melted by heating on one surface of a substrate film, and a back layer formed on the other surface of the substrate film in contact with a thermal head. The layer is composed of a binder and at least two kinds of heat-resistant particles having different particle diameters, and the particle diameter of the larger one of the two heat-resistant particles is 0.5X to X, where X is the thickness of the back layer. Wherein the particle size of the smaller particles is less than or equal to 粒径 of the particle size of the larger particles.

(Action) The larger heat-resistant particles act to provide sufficient heat resistance to the back layer, while the smaller particles fill the gaps between the larger particles without reducing the strength of the back layer. Thereby, the ratio of the heat-resistant particles in the back layer can be increased, and the heat resistance can be further improved without lowering the strength of the back layer.

By including at least two kinds of heat-resistant particles having different particle sizes in the back layer, excellent heat resistance is provided by large particles, and the total amount of the filler is increased by the action of small particles,
By the synergistic action of the large and small particles, a back layer having excellent heat resistance and strength of the back layer is formed.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

As the substrate film used in the present invention, the same substrate film as used in the conventional thermal transfer sheet can be used as it is, and other materials can be used without any particular limitation.

Specific examples of preferred base film include, for example, polyester, polypropylene, cellophane, polycarbonate, cellulose acetate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chloride rubber, ionomer, etc. Paper, such as plastic film, condenser paper, paraffin paper, and non-woven fabric.
A base film in which these are combined may be used.

The thickness of the substrate film can be appropriately changed depending on the material so that the strength and the thermal conductivity become appropriate, but the thickness is 0.5 to 50 μm, preferably 3 to 10 μm.
It is.

The back layer which mainly characterizes the present invention is provided on one surface of the above-mentioned base film, and as the base film, for example, one having relatively excellent heat resistance such as polyethylene terephthalate film is used. preferable.

In the present invention, the back layer is formed from at least two kinds of heat-resistant particles having different particle diameters from the binder resin and other necessary additives.

As the binder resin, for example, ethylcellulose, hydroxyethylcellulose, ethylhydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, cellulose acetate, cellulose acetate butyrate, cellulose resin such as a nitrified surface, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, Examples include vinyl resins such as polyvinylpyrrolidone, acrylic resin, polyacrylamide, acrylonitrile-styrene copolymer, polyester resin, polyurethane resin, silicone-modified or fluorine-modified urethane. Among these, it is preferable to use a compound having some reactive groups, for example, a hydroxyl group, and to use a polyisocyanate as a crosslinking agent in combination to form a crosslinked resin layer.

Further, as the binder resin, an acrylonitrile / styrene copolymer is particularly preferable because a back layer having excellent heat resistance can be formed without crosslinking.

The styrene / acrylonitrile copolymer is obtained by copolymerizing styrene and acrylonitrile, and includes, for example, Sebian AD, Sebian LD, and Sebian NA.
Various grades such as (manufactured by Daicel Chemical Industries, Ltd.) can be easily obtained from the market, and any of them can be used in the present invention, and can be easily manufactured according to a conventional method.

Particularly preferred styrene / acrylonitrile copolymers are
Among various grades, the molecular weight is 100,000 to 200,000, preferably 150,000 to 190,000, and the acrylonitrile content is 20 to 40.
Mol%, preferably 25 to 30 mol%, and those having a softening temperature of 400 ° C. or higher according to differential thermal analysis are preferable in view of dissolution stability in organic solvents and heat resistance.

When a polyethylene terephthalate film is selected as the base film, the styrene / acrylonitrile copolymer has insufficient adhesion to the base film. Therefore, in the production of the styrene / acrylonitrile copolymer, it is preferable to copolymerize a small amount, for example, a few mole% of a monomer having a functional group (for example, meth (acrylic acid or the like)).

As another method, a method in which a small amount of another adhesive resin is used in combination, or a method in which a primer layer is previously formed on a base film using these adhesive resins can be used.

A preferred adhesive resin is an amorphous linear saturated polyester resin having a glass transition point of 50 ° C. or higher, and examples thereof include products such as Byron (manufactured by Toyobo), Heritaire (manufactured by Unitika), Polyester (manufactured by Nippon Synthetic Chemical), and the like. Various grades by name are available from the market, all of which can be used in the present invention. As a particularly preferred example, Byron RV290
(Manufactured by Toyobo Co., Ltd., epoxy group-introduced product, molecular weight: 2,000 to 25,000, Tg: 77 ° C., softening point: 180 ° C., hydroxyl value: 5 to 8).

When the primer layer is formed from the polyester resin, it is preferable to form a layer having a thickness of about 0.05 to 0.5 μm. If the thickness is too thin, the adhesiveness is insufficient. Is unfavorably reduced.

When used in a mixture with the styrene / acrylonitrile copolymer, it is preferable to use 1 to 30 parts by weight per 100 parts by weight of the styrene / acrylonitrile copolymer. On the other hand, if the amount is too large, the heat resistance of the back layer decreases and sticking property is generated, which is not preferable.

Various heat-resistant particles per se used in the present invention are known in the art, for example, hydrotalcite DHT-4A (manufactured by Kyowa Chemical Industry), talc microace L-1 (manufactured by Nippon Talc),
Teflon Lubron L-2 (manufactured by Daikin Industries), graphite fluoride SCP-10 (manufactured by Sanbo Chemical Industry), graphite AT40S (manufactured by Oriental Industries) or silica, calcium carbonate, precipitated barium sulfate, urea resin crosslinked powder, melamine resin crosslinked Fine particles such as powder, crosslinked styrene / acrylic resin powder, crosslinked amino resin powder, silicone powder, wood powder, molybdenum disulfide, and boron nitride.

As the heat-resistant particles, those having various particle sizes are commercially available, but in the present invention, at least two types of heat-resistant particles having clearly different particle sizes are mixed and used.

The particle size of these particles is selected according to the thickness of the back layer to be formed. Since the thickness of the back layer is 0.1 to 0.5 μm, the particle size of the larger particles is in the range of 0.5X to X when the thickness of the back layer is X, for example, when the thickness of the back layer is 0.5 In the case of μm, it is preferable to use one having a thickness of 0.25 to 0.5 μm. If the particle size is less than half the thickness, the effect of improving the heat resistance is small. On the other hand, if the particle size is larger than the film thickness, it is difficult to form a smooth back surface layer and the thermal head is worn, which is not preferable.

On the other hand, the particle size of the smaller particles is less than half the particle size of the large particles, that is, when the particle size of the large particles is 0.3 μm, it is preferable to have a particle size of 0.15 μm or less. When the particle size is large, the difference from the large particles is small, so that it is difficult to fill the gaps between the large particles.

In the present invention, by using at least two kinds of heat-resistant particles having different particle diameters as described above, even if a relatively large amount of heat-resistant particles are included in the back layer, sufficient strength of the back layer can be maintained. I found it.

That is, the larger heat-resistant particles act to give sufficient heat resistance to the back layer, while the smaller particles fill the gaps between the larger particles without reducing the strength of the back layer. This has the effect of increasing the ratio of heat-resistant particles in the back layer and further improving the heat resistance of the back layer.

The heat-resistant particles as described above are preferably used in a ratio of 10 to 200 parts by weight per 100 parts by weight of the binder, and the ratio of large particles to small particles is preferably 20 to 80:80 to 20. If the amount and ratio are outside these ranges, excellent heat resistance and strength of the back layer are not compatible.

In the present invention, in forming the back layer from the above-mentioned materials, a heat releasing agent such as a wax, a higher fatty acid amide, an ester, a surfactant, a higher fatty acid metal salt, etc., as long as the object of the present invention is not hindered. And lubricants can be included.

A particularly preferred lubricant in the present invention is a polyvalent metal salt of an alkyl phosphate, wherein the polyvalent metal salt of the alkyl phosphate is obtained by substituting the alkali metal salt of the alkyl phosphate with a polyvalent metal. Which is itself known as an additive for plastics and is available in various grades from the market, all of which can be used in the present invention.

Particularly preferred polyvalent metal salts of alkyl phosphates in the present invention have the structural formula R is a cetyl group, a lauryl group, an alkyl group having 12 or more carbon atoms such as a stearyl group, particularly a stearyl group, and M is an alkaline earth metal such as barium, calcium, magnesium, zinc, or aluminum. There is something. Here, n represents the valence of M.

The amount of the polyvalent metal salt of the alkyl phosphate is preferably in the range of 10 to 150 parts by weight per 100 parts by weight of the binder.If the amount is less than the above range, sufficient slip properties cannot be obtained. On the other hand, if the above range is exceeded,
It is not preferable because the physical strength of the back layer decreases.

For the purpose of imparting an antistatic property to the back layer, a conductive agent such as carbon black and an antistatic agent such as a quaternary ammonium salt and a phosphoric ester can be added.

To form the back layer, the material as described above is acetone,
A coating solution is prepared by dissolving or dispersing in a suitable solvent such as methyl ethyl ketone, toluene, xylene and the like, and the coating solution is applied by a conventional coating means such as a gravure coater, a roll coater, a wire bar and dried. Formed by

The coating amount, that is, the thickness of the back layer is also important, and in the present invention, the solid content is 0.5 g / m ² or less, preferably 0.1 to 0.
A back layer having sufficient performance can be formed with a thickness of 5 g / m ² . If the back layer is too thick, the sensitivity at the time of transfer decreases, which is not preferable.

It is also effective to form a primer layer made of a polyester resin, a polyurethane resin, or the like on the base film before forming the back layer.

In the present invention, a heat-meltable ink layer is formed on the other surface of the base film from an ink containing necessary materials.

The ink for forming a hot-melt ink layer used in the present invention comprises a colorant and a vehicle, and may further contain various additives as necessary.

As the coloring agent, among organic or inorganic pigments or dyes, those having good characteristics as a recording material, for example, those having a sufficient coloring density and not discoloring by light, heat, temperature or the like are preferable.

In addition, a substance which is colorless when not heated but develops a color when heated, or a substance which develops a color when it comes into contact with a substance applied to a transfer target body may be used. In addition to the colorants that form cyan, magenta, yellow, and black, colorants of various other colors can also be used.

As the vehicle, a mixture of wax as a main component, and other components such as a wax and a derivative of a drying oil, a resin, a mineral oil, cellulose, and rubber is used.

Representative examples of the wax include microcrystalline wax, carnauba wax, and paraffin wax. Furthermore, various waxes such as Fischer-Tropsch wax, various low molecular weight polyethylenes, wood wax, beeswax, spermaceti, Ibota wax, wool wax, shellac wax, candelilla wax, petrolatum, partially modified wax, fatty acid ester, fatty acid amide and the like are used. Can be

Further, a heat conductive substance can be added to the heat fusible ink in order to give the heat fusible ink layer good heat conductivity and melt transferability. Examples of this substance include carbonaceous substances such as carbon black, aluminum, copper, tin oxide, and molybdenum disulfide.

As a method for forming a hot-melt ink layer directly or indirectly on a base film, a hot-melt coat, a hot lacquer coat, a gravure coat, a gravure reverse coat, a roll coat, and the like are applied by various methods. And the like. The thickness of the ink layer to be formed should be determined so as to balance the required density with the thermal sensitivity, and is in the range of 0.1 to 30 μm, preferably 1 to 20 μm.

In the present invention, a surface layer can be further formed on the ink layer. The surface layer forms part of a transfer film,
It forms a surface in contact with the paper to be transferred, has a function of stopping the printed portion of the paper at the time of transfer, preventing background stains, and improving the adhesiveness of the ink layer to the paper to be transferred.

The wax used for forming the surface layer is the same substance as the wax used for the above-mentioned hot-melt ink layer.

The surface layer made of the wax is formed by applying and cooling a wax melt, applying and drying an organic solvent solution containing the wax, and further applying and drying an aqueous dispersion containing the wax particles.

Coating of the surface layer can also be performed by various techniques as in the formation of the ink layer. In the present invention, the thickness of this layer is preferably 0.1 μm so that the sensitivity may not be insufficient even when the printing energy is low as in a high-speed type printer.
m or more and less than 5 μm.

It is recommended that an appropriate amount of extender be added to the surface layer. Thereby, bleeding and tailing of the print can be prevented more favorably.

A thermal transfer image generally has a glossy print and is beautiful, but on the other hand, matte printing may be desirable because the document may be difficult to read. In such a case, for example, as proposed by the applicant (Japanese Patent Application No. 58-208306), an inorganic pigment such as silica, calcium carbonate or the like dispersed in an appropriate solvent is dispersed on a base film. It is preferable to form a thermal transfer sheet by coating and providing a mat layer, and then coating a hot-melt ink layer. Alternatively, the base film itself may be used after mat processing (the technique of Japanese Patent Application No. 58-208307 also proposed by the applicant).

Needless to say, the present invention can be applied to a thermal transfer sheet for color printing, and a multicolor thermal transfer sheet is also included in the scope of the present invention.

(Effects) According to the present invention as described above, by including at least two types of heat-resistant particles having different particle sizes in the back layer, excellent heat resistance is imparted by large particles, and the total amount of the filler is reduced by the combined use of small particles. And a back layer having excellent heat resistance and film strength is formed by the synergistic action of large and small particles.

Examples Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the description, parts and% are based on weight unless otherwise specified.

Examples 1 to 5 Ink composition for back layer (1) Polyvinyl butyral resin (ESREC BX-1, manufactured by Sekisui Chemical Co., Ltd.) 6.0 parts zinc stearyl phosphate (LBT 1830, manufactured by Sakai Chemical Co., Ltd.) 6.0 parts urea resin Crosslinked powder (organic filler, particle size 0.14 μm, manufactured by Nippon Kasei Co., Ltd.) 0.8 parts Melamine resin crosslinked powder (Eposter S, particle size 0.3 μm)
m, Nippon Shokubai Kagaku Co., Ltd.) 1.0 part Solvent (MEK / toluene = 1/1) 86.2 parts Ink composition for back layer (2) Polyvinyl butyral resin (ESREC BX-1, Sekisui Chemical Co., Ltd.) 4.0 Part Polyvinyl butyral resin (ESLEK BLS, manufactured by Sekisui Chemical Co., Ltd.) 2.0 part Aluminum stearyl phosphate (LBT1813, manufactured by Sakai Chemical Co., Ltd.) 6.0 parts Acrylic cross-linked resin powder (GL-100, particle size 0.1 μm, Soken Chemical Co., Ltd.) ) 2.0 parts Melamine resin powder (Eposter S, particle size 0.3 μm, manufactured by Nippon Shokubai Chemical Co., Ltd.) 1.8 parts Solvent (MEK / toluene = 1/1) 84.2 parts Ink composition for back layer (3) Polyvinyl butyral Resin (Eslek BX-1, Sekisui Chemical Co., Ltd.) 4.0 parts Polyvinyl butyral resin (Eslec BLS, Sekisui Chemical Co., Ltd.) 2.0 parts Lithium stearate (S-7000, Sakai Chemical Co., Ltd.) 3.0 parts Zinc Steari Ruphosphate (LBT 1830, manufactured by Sakai Chemical Co., Ltd.) 1.0 part Urea resin powder (organic filler, particle size 0.14 μm, manufactured by Nippon Kasei Co., Ltd.) 2.0 parts Graphite fluoride (FC 2065, particle size 0.4 μm, Allied Chemical) 1.0 part Conductive carbon (Ketchen Black EC 600 manufactured by JD Lion Akzo Co., Ltd.) 1.5 parts Solvent (MEK / toluene = 1/1) 85.5 parts After stirring and mixing the above composition, 3 hours on a paint shaker After the dispersion treatment, a polyisocyanate curing agent (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) is applied to 100 parts of the processed material.
16 parts and an appropriate amount of a diluting solvent (MEK / toluene = 1/1) were added to obtain each back layer ink.

Each of the above inks was applied to a polyester film (thickness 6
μm, Lumirror F-53, manufactured by Toray Industries, Inc.) on a wire bar coater at a solid content of 0.5 g / m ^{2 at} a rate of 6 g.
Heat treatment was performed in an oven at 0 ° C. for 48 hours to form a back layer.

Back layer ink composition (4) Styrene / acrylonitrile copolymer (Sebian AD,
Daicel Chemical Co., Ltd. 6.0 parts Linear saturated polyester resin (Eritaire UE3200, Unitika Ltd.) 0.3 parts Zinc stearyl phosphate (LBT1830, Sakai Chemical Co., Ltd.) 3.0 parts Urea resin cross-linked powder (organic filler, particles) 0.14μm, Nippon Kasei Co., Ltd. 3.0 parts Melamine resin cross-linked powder (Eposter S, 0.3μ particle size)
m, Nippon Shokubai Chemical Co., Ltd.) 1.5 parts Solvent (MEK / toluene = 1/1) 86.2 parts Ink composition for back layer (5) Styrene / acrylonitrile copolymer (Sebian LD,
Daicel Chemical Co., Ltd. 6.0 parts Linear saturated polyester resin (Vylon # 200, Toyobo Co., Ltd.) 0.3 parts Aluminum stearate (SA 1000, Sakai Chemical Co., Ltd.)
4.5 parts Polyethylene wax (Mark FC113, manufactured by Adeka Argus Co., Ltd.) 3.0 parts Fluorocarbon (Mold Vitz F 57, particle size 0.1)
μm, manufactured by Axel Plastics Co., Ltd.) 2.0 parts Melamine resin crosslinked powder (Eposter S, particle size 0.3μ)
m, manufactured by Nippon Shokubai Chemical Co., Ltd.) 3.0 parts Solvent (MEK / toluene = 1/1) 81.2 parts Ink composition for back layer (6) Styrene / acrylonitrile copolymer (Sebian NA,
Daicel Chemical Co., Ltd.) 6.0 parts Linear saturated polyester resin (Polyester TP220, Nippon Synthetic Chemical Co., Ltd.) 0.3 parts Zinc stearate (SZ 2000, Sakai Chemical Co., Ltd.) 4.5 parts Urea resin crosslinked powder ( Organic filler, particle size 0.14 μm, manufactured by Nippon Kasei Co., Ltd. 1.5 parts Melamine resin crosslinked powder (Eposter S, particle size 0.3 μm)
m, Nippon Shokubai Chemical Co., Ltd.) 1.5 parts Conductive carbon (Ketchen Black EC 600JD, manufactured by Lion Akzo Co., Ltd.) 0.8 parts Solvent (MEK / toluene = 1/1) 85.4 parts Both styrene and acrylonitrile used above The contents of the polymer are as follows.

Ink composition for back layer (7) Nitrified cotton H1 / 2 second resin (Celnova BTH1 / 2, Asahi Kasei Corporation)
10.0 parts Linear saturated polyester resin (Eritaire UE3200, manufactured by Unitika Ltd.) 1.0 part Zinc stearyl phosphate (LBT 1830, manufactured by Sakai Chemical Co., Ltd.) 5.0 parts Urea resin crosslinked powder (organic filler, particle size 0.14 μm, Nippon Kasei Co., Ltd. 2.5 parts Melamine resin crosslinked powder (Eposter S, particle size 0.3μ)
m, manufactured by Nippon Shokubai Chemical Co., Ltd.) 1.5 parts Solvent (MEK / toluene = 1/1) 80.0 parts Ink composition for back layer (8) Cellulose acetate propionate resin (CAP 482)
−05, Eastman Kodak Co., Ltd.) 10.0 parts Linear saturated polyester resin (Vylon # 280, Toyobo) 1.0 part Zinc stearyl phosphate (LBT 1830, Sakai Chemical Co., Ltd.) 3.0 parts Urea resin cross-linked powder (organic) Filler, particle size 0.14μm, manufactured by Nippon Kasei Co., Ltd. 2.5 parts Melamine resin cross-linked powder (Eposter S, particle size 0.3μ)
m, manufactured by Nippon Shokubai Kagaku Co., Ltd.) 2.5 parts Solvent (MEK / toluene = 1/1) 81.0 parts After stirring and mixing the above composition, it was subjected to dispersion treatment with a paint shaker for 3 hours. / 1) was added to obtain an ink for each back layer.

Each of the above inks was applied to a polyester film (thickness 6
μm, Lumirror F-53, manufactured by Toray Industries, Inc.) on a wire bar coater at a solid content of 0.5 g / m ² , followed by hot-air drying to form a back layer.

Separately, a transfer ink composition having the following composition was kneaded for 6 hours while heating to 100 ° C. using a blade kneader.

Ink composition for forming transfer ink layer Paraffin wax 10 parts Carnauba wax 10 parts Ethylene / vinyl acetate copolymer (Smitate HC-10,
Sumitomo Chemical Co., Ltd.) 1 part Carbon black (Seast 3, Tokai Electrode Co., Ltd.) 2 parts The above ink composition was heated at a temperature of 100 ° C., and the back layer was formed by a roll coating method using a hot melt. On the other surface of each base film, a thermal transfer ink layer was formed by applying the applied amount to about 5.0 g / m ² to obtain a thermal transfer sheet of the present invention.

Using the thermal transfer sheet of the present invention obtained above, with a thermal printer, output 1W / dot, pulse width 0.3 to 4.5m
When printing was performed on plain paper under the conditions of sec. and a dot density of 3 dots / mm, the sticking phenomenon did not occur at all, no wrinkles occurred, and the thermal transfer sheet ran smoothly and had no problems.

Comparative Example 1 The urea resin crosslinked powder (organic filler,
A thermal transfer sheet of a comparative example was obtained in the same manner as in Example 1 except that only 1.8 parts of a particle size of 0.14 μm (Nippon Kasei Co., Ltd.) was used.

A printing test was performed in the same manner as in Example 1. As a result, sticking was severe and printing was impossible.

Comparative Example 2 A thermal transfer sheet of Comparative Example was obtained in the same manner as in Example 1, except that only 1.8 parts of the melamine resin crosslinked powder (Eposter S, particle size: 0.3 μm, manufactured by Nippon Shokubai Chemical Co., Ltd.) were used. Was.

When a printing test was performed in the same manner as in Example 1, a part of the back layer was peeled off, and the thermal head was broken.

Further, the coefficients of friction, sticking resistance and stain resistance of the thermal transfer sheets of Examples and Comparative Examples were measured. The results shown in Table 1 below were obtained.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-87295 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41M 5/38-5/40

Claims (4)

(57) [Claims] 1. A thermal transfer sheet having a transfer ink layer which is melted by heating on one surface of a base film, and a back layer provided on the other surface of the base film in contact with a thermal head. And at least two types of heat-resistant particles having different particle diameters, and among the two types of heat-resistant particles,
The particle size of the larger particles is 0.5X to X when the thickness of the back layer is X, and the particle size of the smaller particles is less than or equal to 1/2 of the particle size of the larger particles. Characteristic thermal transfer sheet. 2. The thermal transfer sheet according to claim 1, wherein the total amount of the heat-resistant particles is 10 to 200 parts by weight per 100 parts by weight of the binder. 3. The thermal transfer sheet according to claim 1, wherein the ratio of the large / small heat-resistant particles is 20 to 80/80 to 20 by weight. 4. The thermal transfer sheet according to claim 1, wherein the thickness of the back layer is 0.1 to 0.5 μm.