阅读说明：本技术 热转印片 (Thermal transfer sheet ) 是由 广川纯子 石田忠宏 于 2018-02-28 设计创作，主要内容包括：[课题]提供一种热转印片,其能够防止箔脱落的发生,并且具有不产生剥离痕迹或拖尾等转印不良的高转印性。[解决手段]本发明的热转印片的特征在于,其依次具备基材、脱模层和转印层,上述脱模层包含氧化铝或氧化铝水合物中的至少一种和粘结剂树脂。([ problem ] to provide a thermal transfer sheet which can prevent the occurrence of foil peeling and has high transferability without causing transfer failures such as peeling marks and streaks. [ solution ] A thermal transfer sheet of the present invention is characterized by comprising a base material, a release layer and a transfer layer in this order, wherein the release layer comprises at least one of alumina and alumina hydrate, and a binder resin.)

1. A thermal transfer sheet comprising a base material, a release layer and a transfer layer in this order,

the release layer includes at least one of alumina or alumina hydrate and a binder resin.

2. The thermal transfer sheet according to claim 1, wherein the transfer layer is provided with a release layer.

3. The thermal transfer sheet of claim 2, wherein the release layer comprises wax.

4. The thermal transfer sheet according to claim 2 or 3, wherein the transfer layer further comprises a coloring layer on the release layer.

5. The thermal transfer sheet according to any one of claims 1 to 4, wherein the solid content ratio of the at least one of alumina or alumina hydrate to the binder resin, that is, alumina or alumina hydrate/binder resin, is from 7/3 to 9/1 on a mass basis.

6. The thermal transfer sheet according to any one of claims 1 to 5, wherein the binder resin is an aqueous resin.

7. The thermal transfer sheet according to claim 6, wherein the aqueous resin is an aqueous vinyl resin.

8. The thermal transfer sheet according to claim 7, wherein the aqueous vinyl resin is at least one of polyvinylpyrrolidone and a vinyl acetate-vinylpyrrolidone copolymer.

9. The thermal transfer sheet according to any one of claims 1 to 8, wherein the thickness of the transfer layer is 1 μm or more and 6 μm or less.

Technical Field

The present invention relates to a thermal transfer sheet, and more particularly, to a thermal transfer sheet including a base material, a release layer, and a transfer layer.

Background

Conventionally, the following thermal fusion transfer methods are known: a colored-layer transfer sheet including a base material such as a resin film and a colored layer containing a colorant is subjected to energy application by a thermal head or the like to transfer the colored layer onto a transfer-receiving body such as paper or a plastic sheet, thereby forming an image.

Since an image formed by the thermal fusion transfer method has high density and excellent sharpness, the method is suitable for recording binary images such as characters and line drawings. In addition, according to the thermal fusion transfer method, variable information such as a recipient name, customer information, a serial number, a barcode, and the like can be recorded on the transfer target by using a computer or a thermal transfer printer.

In order to improve durability such as abrasion resistance of an image or the like formed as described above, a protective layer transfer sheet having a protective layer is superimposed on the image, and energy is applied by a thermal head or the like to transfer the protective layer.

For the thermal transfer sheets such as the colored layer transfer sheet and the protective layer transfer sheet, it has been proposed to provide a release layer between a transfer layer such as a colored layer or a protective layer and a base material or the like (patent document 1); this adjusts the peel force between the transfer layer and the substrate, and prevents the transfer layer from peeling off from the substrate (so-called foil peeling) during non-heating such as storage.

However, the conventional release layer cannot provide sufficient adhesion force between the transfer layer and the substrate or the like at the time of non-heating, and cannot completely prevent the occurrence of foil peeling, or the release force at the time of heating becomes too high, and the transfer layer cannot be transferred satisfactorily, and a peeling mark is generated, and there is room for improvement.

Such a thermal transfer sheet is required to have high transferability, and not only to cause no peeling marks, but also to cause no transfer defects such as streaking at the time of transfer of the transfer layer.

In the present invention, "tailing" refers to the following phenomenon: when the transfer layer is transferred to the object, the transfer layer is transferred so as to protrude from the boundary between the transfer region and the non-transfer region of the transfer layer as a starting point toward the non-transfer region side from the boundary.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above circumstances, and a main object thereof is to provide a thermal transfer sheet which can prevent foil peeling and has high transferability without causing transfer failures such as peeling marks and streaking.

Means for solving the problems

The thermal transfer sheet of the present invention is characterized by comprising a base material, a release layer and a transfer layer in this order, wherein the release layer comprises at least one of alumina or alumina hydrate and a binder resin.

In one embodiment, the transfer layer includes a release layer.

In one embodiment, the release layer comprises a wax.

In one embodiment, the transfer layer further includes a coloring layer on the release layer.

In one embodiment, the solid content ratio of the binder resin to at least one of the alumina and the alumina hydrate (alumina or alumina hydrate/binder resin) is 7/3 or more and 9/1 or less on a mass basis.

In one embodiment, the binder resin is an aqueous resin.

In one embodiment, the aqueous resin is an aqueous vinyl resin.

In one embodiment, the aqueous vinyl resin is at least one of polyvinylpyrrolidone and a vinyl acetate-vinylpyrrolidone copolymer.

In one embodiment, the thickness of the transfer layer is 2 μm or more and 6 μm or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a thermal transfer sheet having high transferability which can prevent the occurrence of foil peeling and can prevent the occurrence of transfer failure such as peeling marks and streaking.

Drawings

Fig. 1 is a schematic cross-sectional view showing one embodiment of a thermal transfer sheet of the present invention.

Fig. 2 is a schematic cross-sectional view showing one embodiment of the thermal transfer sheet of the present invention.

Fig. 3 shows a trapezoidal barcode printed in the image formability test of the example.

Detailed Description

(thermal transfer sheet)

As shown in fig. 1, a thermal transfer sheet 10 of the present invention includes a base material 11, a release layer 12, and a transfer layer 13 in this order.

In one embodiment, as shown in fig. 1, the transfer layer 13 includes a release layer 14 and a coloring layer 15.

In one embodiment, as shown in fig. 1, the thermal transfer sheet 10 of the present invention includes a back surface layer 16.

In one embodiment, as shown in fig. 2, the transfer layer 13 includes an adhesive layer 17.

The layers of the thermal transfer sheet of the present invention will be described below.

(substrate)

The base material is not particularly limited as long as it has heat resistance that can withstand the heat energy applied at the time of thermal transfer (for example, heat generated by a thermal head) and has mechanical strength and solvent resistance that can support the transfer layer.

Examples of the substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene terephthalate-isophthalate copolymer, and terephthalic acid-cyclohexanedimethanol-ethylene glycol copolymer, polyamide resins such as nylon 6 and nylon 6, polyolefin resins such as Polyethylene (PE), polypropylene (PP), and polymethylpentene, polyolefin resins such as polyvinyl chloride, polyvinyl alcohol (PVA), polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl butyral, and polyvinyl pyrrolidone (PVP), vinyl resins such as polyacrylate, polymethacrylate, and polymethyl methacrylate, (meth) acrylic resins such as polyacrylate, polymethacrylate, and polymethyl methacrylate, polyimide resins such as polyimide, and polyether imide, polyimide resins, and the like, A film made of a styrene resin, a cellulose resin such as cellophane, cellulose acetate, cellulose nitrate, Cellulose Acetate Propionate (CAP) and Cellulose Acetate Butyrate (CAB) (hereinafter simply referred to as "resin film").

Among the above resins, polyester resins such as PET and PEN are preferable from the viewpoint of heat resistance and mechanical strength, and PET is particularly preferable.

In the present invention, "(meth) acrylic acid" is meant to include both "acrylic acid" and "methacrylic acid".

In addition, a laminate of the resin films may be used as a substrate.

The laminate of the resin film can be produced by a dry lamination method, a wet lamination method, an extrusion method, or the like.

When the substrate is a resin film, the resin film may be a stretched film or an unstretched film, and a stretched film stretched in a uniaxial direction or a biaxial manner is preferably used from the viewpoint of strength.

In addition, the substrate preferably has irregularities on the surface thereof in view of improving adhesion to the release layer and the back surface layer and improving blocking resistance.

Examples of the means for forming the irregularities on the surface of the substrate include rough material kneading, blasting, texturing, rough coating, and chemical etching. The rough material kneading process is a process of forming a base material by using a resin in which an inorganic substance or an organic substance is kneaded. The rough coating process is a process of applying a coating material containing an organic or inorganic substance to the surface of a base material to impart unevenness to the surface of the base material.

The thickness of the substrate is preferably 3.0 μm to 12.0 μm, more preferably 4.0 μm to 6.0 μm. By setting the thickness of the base material to the above numerical range, the mechanical strength of the base material and the thermal energy transfer at the time of thermal transfer can be improved.

(Release layer)

The release layer is provided between the base material and the transfer layer, and is a layer remaining on the base material side during thermal transfer.

The release layer provided in the thermal transfer sheet of the present invention is characterized by containing at least one of alumina and alumina hydrate and a binder resin, and thereby can improve the peeling force between the transfer layers during non-heating and prevent the occurrence of foil peeling. Further, the thermal transfer sheet can be provided with high transferability which can prevent the occurrence of transfer failure such as peeling marks or streaking.

The release layer can be formed using a release layer-forming composition containing a binder resin and a dispersion liquid in which alumina is dispersed in an appropriate solvent, a release layer-forming composition containing an alumina sol and a binder resin, or the like. Specifically, the composition for forming a release layer, which will be described later, is dispersed or dissolved in water or an appropriate solvent, and applied to a substrate by a known means such as a roll coating method, a reverse roll coating method, a gravure printing method, a reverse gravure coating method, a bar coating (bar coating) method, and a rod coating (rodcoating) method to form a coating film, and the coating film is dried.

In the release layer, the solid component ratio of at least one of alumina or alumina hydrate to the binder resin is preferably 6/4 or more and 95/5 or less, more preferably 7/3 or more and 9/1 or less, on a mass basis.

When the solid content ratio of at least one of alumina and alumina hydrate to the binder resin is within the above numerical range, the occurrence of foil peeling can be further prevented, and the transferability can be further improved.

In the present invention, the alumina sol is a sol in which colloidal particles of alumina hydrate are dispersed in an aqueous solvent. The alumina sol may contain unhydrated alumina.

As the alumina hydrate, Al (OH) may be mentioned₃AlO (OH) and Al₅O₇(OH), and the like.

Examples of the aqueous solvent include water, hydrochloric acid, an aqueous acetic acid solution, an aqueous nitric acid solution, alcohol, and methyl isobutyl ketone.

The crystal structure of the alumina hydrate is not particularly limited, and any structure such as boehmite crystal, pseudoboehmite crystal, and amorphous crystal can be used. The shape is not particularly limited, and any shape such as granular, rod-like, fibrous, and feather-like shapes can be used.

The primary particle diameter of the colloidal particles of alumina hydrate is preferably 2.0nm to 30.0nm, more preferably 5.0nm to 20.0 nm. When the primary particle diameter of the colloidal particles of the alumina hydrate is within the above numerical range, the occurrence of foil peeling can be further prevented, and the transferability can be further improved.

In the present invention, the "primary particle size" refers to a volume average particle size, and can be measured according to JIS Z8819-2 (2001) using a particle size distribution/particle size distribution measuring apparatus (nanosrac particle size distribution measuring apparatus, manufactured by japan electronics and electronics industries, inc.).

The solid content concentration of the alumina sol is preferably 5 mass% to 20 mass%, more preferably 7.5 mass% to 15 mass%. When the solid content concentration of the alumina sol is within the above numerical range, the occurrence of foil peeling can be further prevented, and the transferability can be further improved.

The solid content of the alumina sol in the composition for forming a release layer is preferably 60 mass% to 95 mass%, more preferably 70 mass% to 90 mass%, relative to 100 mass% of the total solid content of the composition for forming a release layer. When the content of the alumina sol is within the above numerical range, the occurrence of foil peeling can be further prevented, and the transferability can be further improved.

The alumina sol can be prepared by a conventionally known method such as hydrolysis of an aluminum alkoxide, neutralization of an aluminum salt with an alkali, and hydrolysis of an aluminate.

The alumina sol is not limited to the one produced by the above method, and a commercially available product may be used.

As the binder resin, an aqueous resin can be used.

In the present invention, the "aqueous resin" includes: a water-soluble resin soluble in a water-based solvent; and resins which are insoluble in an aqueous solvent but can be dispersed in an aqueous solvent as in an emulsion or dispersion (hereinafter simply referred to as "water-dispersible resins"). In addition, in the present invention, a resin which is a water-soluble resin or a water-dispersible resin and is also soluble in an organic solvent is also included.

The term "aqueous solvent" refers to water or a solvent containing water as a main component. Examples of the solvent which can be used in combination with water include alcohols such as methanol, ethanol, isopropanol, and n-propanol; glycols such as ethylene glycol and diethylene glycol; and ketones such as acetone and methyl ethyl ketone; and so on.

Examples of the aqueous resin include aqueous polyester resins, aqueous polyurethane resins, aqueous epoxy resins, aqueous (meth) acrylic resins, aqueous polyolefin resins, aqueous cellulose resins, aqueous vinyl resins, and aqueous (meth) acrylic resins.

In addition, casein, gelatin, agar, starch, and the like may be used without being limited to the above resin.

Examples of the aqueous polyester resin include polyester resins having hydrophilic functional groups such as a hydroxyl group, a carboxyl group, an amino group, a carboxylic acid group, and a sulfonic acid group. More specifically, there may be mentioned polymers of alcohol compounds such as ethylene glycol, propylene glycol, 1, 3-butanediol and dipropylene glycol and phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid and succinic anhydride.

Examples of the aqueous polyurethane resin include polymers of isocyanate compounds such as hexamethylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, 1, 4-cyclohexane diisocyanate and xylylene diisocyanate and the above alcohol compounds.

Examples of the water-based epoxy resin include: a substance obtained by forcedly emulsifying an epoxy resin such as a bisphenol a type epoxy resin or a bisphenol F type epoxy resin with a surfactant; a substance obtained by reacting an epoxy resin with a (meth) acrylic acid-based resin, neutralizing the reaction product with ammonia or the like, and dispersing the neutralized product; and so on.

Examples of the aqueous (meth) acrylic resin include poly (meth) acrylic acid, 2-methylolacrylate, and 2-hydroxyethyl acrylate.

Examples of the water-based polyolefin resin include: and a product obtained by copolymerizing ethylene with an unsaturated carboxylic acid such as methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, or the like at high temperature and high pressure, neutralizing with ammonia, an amine compound, or the like, and dispersing the neutralized product.

Examples of the aqueous cellulose resin include methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

Examples of the aqueous vinyl resin include PVP, a vinyl acetate-vinyl pyrrolidone copolymer, an ethylene-vinyl acetate copolymer, PVA, polyvinyl acetal, polyvinyl acetate, polyvinyl chloride, and the like.

Among the above resins, from the viewpoint of improving foil peeling resistance and transferability, aqueous vinyl resins are preferred, and PVP and a vinyl acetate-vinyl pyrrolidone copolymer are particularly preferred.

The solid content of the binder resin in the composition for forming a release layer is preferably 5 mass% or more and 40 mass% or less, more preferably 10 mass% or more and 30 mass% or less, with respect to 100 mass% of the total solid content of the composition for forming a release layer. By setting the content of the binder resin to the above numerical range, the occurrence of foil peeling can be further prevented, and the peelability can be further improved.

In one embodiment, the release layer contains a release material such as silicone oil, a phosphate plasticizer, a fluorine compound, wax, a metal soap, and a filler.

The thickness of the release layer is preferably 0.01 μm to 0.5 μm, more preferably 0.02 μm to 0.2 μm, from the viewpoint of improving foil peeling resistance and transferability.

(transfer layer)

The thermal transfer sheet of the present invention includes the transfer layer on the release layer, and the transfer layer includes at least one of the release layer, the colored layer, and the adhesive layer, as described above.

The thickness of the transfer layer is preferably 2 μm to 6 μm, more preferably 3 μm to 5 μm. By setting the thickness of the transfer layer to the above numerical range, the occurrence of foil peeling can be more effectively prevented.

In addition, when the transfer layer includes a colored layer, a favorable image can be formed even on a transfer target having an uneven surface.

The peeling force of the transfer layer from the release layer at room temperature (22 ℃) is preferably 4g/1.5cm to 20g/1.5cm, more preferably 6g/1.5cm to 15g/1.5 cm. By setting the peeling force of the transfer layer from the release layer at room temperature to the above numerical range, the occurrence of foil peeling can be more significantly prevented.

In the present invention, the peeling force of the transfer layer from the release layer is a value obtained by dividing the peeling force (g) when the transfer layer is peeled from the release layer by the peeling width (cm). The measurement of the peeling force between the transfer layer and the release layer can be performed by sticking a double-sided tape to a thermal transfer sheet and peeling the sheet in a 90-degree direction using a load cell.

The peeling force of the transfer layer from the release layer at 40 ℃ is preferably 20g/1.5cm or more and 70g/1.5cm or less, more preferably 30g/1.5cm or more and 50g/1.5cm or less. By setting the peeling force of the transfer layer from the release layer at 40 ℃ to the above numerical range, the transferability of the thermal transfer sheet can be improved.

(peeling layer)

In one embodiment, the thermal transfer sheet of the present invention includes a release layer between the release layer and the colored layer. The release layer is a layer constituting the transfer layer, and the transferability of the transfer layer can be improved by providing the thermal transfer sheet with this layer.

In one embodiment, the release layer includes, for example, a cellulose-based resin, a vinyl-based resin such as an ethylene-vinyl acetate copolymer, a urethane-based resin, a silicone-based resin, a (meth) acrylic resin such as an ethylene-ethyl acrylate copolymer, a fluorine-based resin, a wax, or the like.

In the above materials, the release layer preferably contains at least either one of an ethylene-vinyl acetate copolymer and an ethylene-ethyl acrylate copolymer, since the occurrence of foil peeling can be further prevented.

In addition, among the above materials, the release layer preferably contains wax, and more preferably contains wax having a melting point or softening point of 70 ℃ to 120 ℃.

Examples of the wax include natural waxes such as beeswax, spermaceti wax, wood wax, rice bran wax, carnauba wax, candelilla wax and montan wax, synthetic waxes such as silicone wax, paraffin wax, microcrystalline wax, oxidized wax, ozokerite, ceresin, ester wax and polyethylene wax, higher saturated fatty acids such as heptadecanoic acid, lauric acid, cinnamic acid, palmitic acid, stearic acid, furoic acid and behenic acid, higher saturated monohydric alcohols such as stearyl alcohol and behenyl alcohol, higher esters such as fatty acid esters of sorbitan, and higher fatty acid amides such as stearamide and oleamide.

The release layer may contain rubbers such as isoprene rubber, butyl rubber, and nitrile rubber. By including a rubber in the release layer, the elasticity of the release layer can be improved, and the adhesion between the thermal transfer sheet and the object to be transferred can be improved.

The thickness of the release layer is preferably 0.1 μm or more and 5.0 μm or less in a dry state. By setting the thickness of the release layer to the above numerical range, the transferability of the transfer layer can be improved. By setting the thickness of the dried coating film to the above numerical range, excessive adhesion between the release layer and the colored layer can be prevented, and a good peeling effect can be obtained, and a good transfer sensitivity can be obtained at the time of printing.

The release layer can be formed by a conventionally known method such as hot melt coating, hot varnish coating, gravure direct coating, gravure reverse coating, blade coating, air coating, and roll coating using a release layer forming coating liquid.

(colored layer)

The colored layer contains a colorant and a binder resin.

The coloring agent contained in the colored layer may be suitably selected from carbon black, inorganic pigments, organic pigments and dyes according to the desired color tone and the like. For example, in the case of barcode printing, a colorant having a particularly sufficient black density and not discolored or faded by light, heat, or the like is preferable. Examples of such a colorant include carbon black such as lamp black, graphite, and nigrosine dye. In addition, in the case where color printing is required, other color dyes or pigments are used.

The content of the colorant in the colored layer is preferably 20 parts by mass or more and 60 parts by mass or less, and more preferably 30 parts by mass or more and 50 parts by mass or less, with respect to 100 parts by mass of the binder resin contained in the colored layer.

Examples of the binder resin included in the colored layer include (meth) acrylic resins, polyolefin resins, vinyl resins, polyester resins, polyurethane resins, cellulose resins, amide resins, and phenol resins.

The content of the binder resin in the colored layer is preferably 40 mass% to 80 mass%, more preferably 50 mass% to 70 mass%.

In one embodiment, the colored layer comprises the wax described above. The colored layer may contain additives such as a filler, a plasticizer, an antistatic agent, and an ultraviolet absorber within a range not to impair the characteristics of the present invention.

The thickness of the colored layer is preferably 0.5 μm to 2.0 μm, more preferably 0.8 μm to 1.5 μm.

By setting the thickness of the coloring layer to the above numerical range, it is possible to improve the image formability for a transfer-receiving body having irregularities on the surface while maintaining the transferability of the thermal transfer sheet.

The colored layer can be formed by dispersing or dissolving the above-mentioned materials in water or an appropriate solvent, applying the resultant solution to a release layer by a known means such as a roll coating method, a reverse roll coating method, a gravure printing method, a reverse gravure coating method, a bar coating (bar coating) method, and a rod coating (rod coating) method, to form a coating film, and drying the coating film.

(adhesive layer)

In one embodiment, the thermal transfer sheet of the present invention includes an adhesive layer. By providing the thermal transfer sheet with the adhesive layer, the adhesiveness of the transfer layer to the object to be transferred can be improved.

The adhesive layer is composed of a thermoplastic resin that softens when heated and exhibits adhesiveness.

Examples of the thermoplastic resin include polyester resins, vinyl resins such as vinyl chloride, vinyl acetate, and ethylene-vinyl acetate copolymers, (meth) acrylic resins, polyurethane resins, cellulose resins, melamine resins, polyamide resins, polyolefin resins, and styrene resins.

The thickness of the adhesive layer is preferably 0.1 μm to 0.6 μm, more preferably 0.2 μm to 0.5 μm.

By setting the thickness of the adhesive layer to the above numerical range, the adhesion of the transfer layer to the object to be transferred can be improved while maintaining the transferability of the thermal transfer sheet.

The adhesive layer can be formed by dispersing or dissolving the above-mentioned materials in water or an appropriate solvent, applying the solution to a colored layer or the like by a known means such as a roll coating method, a reverse roll coating method, a gravure printing method, a reverse gravure coating method, a bar coating (bar coating) method, and a rod coating (rod coating) method, to form a coating film, and drying the coating film.

(Back layer)

In one embodiment, the thermal transfer sheet of the present invention includes a back surface layer on a surface of the substrate on which the transfer layer is not provided. By providing the thermal transfer sheet with the back surface layer, the occurrence of sticking, wrinkles, and the like due to heating at the time of thermal transfer can be prevented.

In one embodiment, the back layer comprises a binder resin. Examples of the binder resin include cellulose-based resins, styrene-based resins, vinyl-based resins, polyester-based resins, polyurethane-based resins, silicone-modified urethane-based resins, fluorine-modified urethane-based resins, and (meth) acrylic resins. Among these, styrene-based resins, specifically, styrene-acrylonitrile copolymers are preferably used from the viewpoint of preventing the thermal head and the back surface layer from being sintered and generating dregs.

In one embodiment, the back layer contains a two-component curable resin that is cured by being used in combination with an isocyanate compound or the like as a binder resin. Examples of such a resin include a polyvinyl acetal resin and a polyvinyl butyral resin.

As the isocyanate compound, conventionally known isocyanate compounds can be used without particular limitation, and among them, an adduct of aromatic isocyanate is preferably used. Examples of the aromatic polyisocyanate include 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, a mixture of 2, 4-tolylene diisocyanate and 2, 6-tolylene diisocyanate, 1, 5-naphthalene diisocyanate, tolidine diisocyanate, p-phenylene diisocyanate, trans-cyclohexane-1, 4-diisocyanate, xylylene diisocyanate, triphenylmethane triisocyanate, tris (isocyanatophenyl) thiophosphate, and particularly preferably 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, or a mixture of 2, 4-tolylene diisocyanate and 2, 6-tolylene diisocyanate.

In one embodiment, the back layer comprises inorganic or organic particles. By including such fine particles in the back surface layer, the occurrence of sticking, wrinkles, and the like due to heating at the time of thermal transfer can be further prevented.

Examples of the inorganic fine particles include clay minerals such as talc and kaolin, carbonates such as calcium carbonate and magnesium carbonate, hydroxides such as aluminum hydroxide and magnesium hydroxide, sulfates such as calcium sulfate, oxides such as silica, graphite, niter, and boron nitride.

Examples of the organic fine particles include organic resin fine particles formed of a (meth) acrylic resin, a teflon (registered trademark) resin, a silicone resin, a lauroyl resin, a phenol resin, an acetal resin, a styrene resin, a polyamide resin, or the like; or crosslinked resin fine particles obtained by reacting them with a crosslinking material; and so on.

The thickness of the back layer is preferably 0.01 μm to 0.5 μm, more preferably 0.02 μm to 0.4 μm. By setting the thickness of the back layer to the above numerical range, it is possible to prevent the occurrence of sticking, wrinkles, and the like while maintaining the thermal energy transferability at the time of thermal transfer.

The back layer can be formed by dispersing or dissolving the above-mentioned materials in water or an appropriate solvent, applying the solution to a substrate by a known means such as a roll coating method, a reverse roll coating method, a gravure printing method, a reverse gravure coating method, a bar coating (bar coating) method, and a rod coating (rod coating) method, to form a coating film, and drying the coating film.