JP2022053689A - Thermal transfer sheet - Google Patents

Abstract

To provide a thermal transfer sheet capable of forming an excellent image onto each of a PET transfer target body and a PP transfer target body, capable of forming an image superior in scratch resistance even immediately after a formation, and having anti-blocking properties.SOLUTION: A thermal transfer sheet includes a substrate and a transfer layer disposed on one face side of the substrate in a peelable manner. In the thermal transfer sheet, the transfer layer sequentially includes, from a substrate side, a coloring layer and an adhesive layer. The adhesive layer includes a polyester and a polyolefin non-compatible to each other. The polyester contains a crystalline polyester having glass-transition temperature of lower than 50°C. The adhesive layer has a phase separation structure including two phases. When a surface of the adhesive layer is photographed by a digital microscope with a magnifying power of 500 to obtain an image, then the image is binarized using image processing software and the two phases are separated into a bright part and a dark part, an area of a surface region of the bright part or the dark part is 55% to 85%, with regard to a gross area of the image.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to thermal transfer sheets.

Conventionally, using a thermal transfer sheet including a base material and a transfer layer including a colored layer and an adhesive layer, energy corresponding to image information is applied by a heating device such as a thermal head to be transferred to paper or a plastic sheet or the like. A thermal transfer type image forming method for transferring a transfer layer onto a body is known.

In recent years, polyethylene terephthalate (PET) and polypropylene (PP) have been used as materials constituting the transferred body. Therefore, a thermal transfer sheet capable of forming a good image for both has been proposed. For example, Patent Document 1 proposes a thermal transfer sheet containing polyester and polyolefin and having an adhesive layer in which these materials form a sea-island structure. According to Patent Document 1, such a thermal transfer sheet is either a PET transferred body (hereinafter referred to as PET transferred body) or a PP transferred body (hereinafter referred to as PP transferred body). It is disclosed that a good image can be formed.

Japanese Unexamined Patent Publication No. 2020-116859

By the way, when an image is formed on the transferred body, the image immediately after the formation may have insufficient adhesion to the transferred body. If the adhesion between the image and the transferred object is insufficient, the scratch resistance of the image is lowered, so that there is a possibility that product defects may occur during the production of the printed matter.
Although the thermal transfer sheet of Patent Document 1 can form a good image for both the PET transferred body and the PP transferred body, there is room for improvement in the scratch resistance immediately after the image formation.

The present inventors examined the scratch resistance immediately after image formation. As a result of the study, the present inventors have found that by using a polyester having a low glass transition temperature in the adhesive layer of the above-mentioned thermal transfer sheet, an image having excellent scratch resistance can be formed even immediately after the formation. Further, the present inventors have found that the blocking resistance of the thermal transfer sheet can be improved by using crystalline polyester as the polyester.

Therefore, an object of the present disclosure is to be able to form a good image for both a PET transferred body and a PP transferred body (hereinafter referred to as image forming property), and also to have excellent scratch resistance even immediately after formation. It is an object of the present invention to provide a thermal transfer sheet capable of forming an image and having blocking resistance.

The present disclosure is a thermal transfer sheet comprising a substrate and a transfer layer removably provided on one surface side of the substrate.
The transfer layer includes a colored layer and an adhesive layer in order from the base material side.
The adhesive layer contains polyester and polyolefin, which are incompatible with each other.
Polyesters include crystalline polyesters with a glass transition temperature of less than 50 ° C.
The adhesive layer has a phase-separated structure containing two types of phases, and the surface of the adhesive layer is photographed with a digital microscope at a magnification of 500 times to acquire an image, and then the image is image-processed by image processing software. When the two phases are divided into a bright part and a dark part by binarization processing using the above, the area of the surface region of the bright part or the dark part is 55% or more and 85% with respect to the total area of the image. The following is a thermal transfer sheet.

According to the present disclosure, it is possible to provide a thermal transfer sheet which has image forming properties, can form an image having excellent scratch resistance even immediately after formation, and has blocking resistance.

It is a schematic sectional drawing which shows one Embodiment of the thermal transfer sheet of this disclosure. It is a schematic sectional drawing which shows one Embodiment of the thermal transfer sheet of this disclosure. It is a schematic sectional drawing which shows one Embodiment of the thermal transfer sheet of this disclosure. It is a schematic front view which shows one Embodiment of the phase separation structure which an adhesive layer has. It is a schematic front view which shows one Embodiment of the phase separation structure which an adhesive layer has.

[Thermal transfer sheet]
As shown in FIG. 1, the thermal transfer sheet 10 according to the present disclosure includes a base material 11 and a transfer layer 14 provided on one surface side of the base material 11 so as to be removable. The transfer layer 14 includes a colored layer 12 and an adhesive layer 13 in this order from the base material 11 side.
In one embodiment, as shown in FIG. 2, the transfer layer 14 further includes a release layer 15, and the release layer 15 is provided between the base material 11 and the colored layer 12.
Further, in one embodiment, as shown in FIG. 3, the thermal transfer sheet 10 includes the back surface layer 16 on the surface of the base material 11 opposite to the surface on which the transfer layer 14 is provided.
Further, in one embodiment, the thermal transfer sheet 10 of the present disclosure may further include a release layer and a primer layer on the substrate (not shown).

The layer configurations of the thermal transfer sheet 10 can be combined as appropriate.

Hereinafter, each layer included in the thermal transfer sheet according to the present disclosure will be described.

<Base material>
The base material has heat resistance to the heat energy applied during thermal transfer, and has mechanical strength and solvent resistance that can support each layer provided on the base material.

As the base material, a film composed of a resin material (hereinafter, simply referred to as "resin film") can be used. Examples of the resin material include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), 1,4-polycyclohexylene methylene terephthalate, and terephthalic acid-cyclohexanedimethanol-ethylene glycol copolymer. Polyester such as polyester, nylon 6 and polyamide such as nylon 6,6, polyolefin such as polyethylene (PE), polypropylene (PP) and polymethylpentene, polyvinyl chloride, polyvinyl alcohol (PVA), polyvinyl acetate, vinyl chloride-acetic acid. Vinyl copolymers, vinyl resins such as polyvinyl butyral and polyvinylpyrrolidone (PVP), (meth) acrylic resins such as polyacrylate, polymethacrylate and polymethylmethacrylate, imide resins such as polyimide and polyetherimide, cellophane, cellulose acetate, Examples thereof include cellulose resins such as nitrocellulose, cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB), styrene resins such as polystyrene (PS), polycarbonates, and ionomer resins.
Among the above-mentioned resins, polyesters such as PET and PEN are preferable, and PET is particularly preferable, from the viewpoint of heat resistance and mechanical strength.
As used herein, "(meth) acrylic" means to include both "acrylic" and "methacrylic". By "(meth) acrylate" is meant to include both "acrylate" and "methacrylate".

The above-mentioned laminate of resin films can also be used as a base material. The laminate of the resin film can be produced by using a dry lamination method, a wet lamination method, an extraction method, or the like.

When the base material is a resin film, the resin film may be a stretched film or an unstretched film, but from the viewpoint of strength, the stretched film stretched in the uniaxial direction or the biaxial direction is used. preferable.

The thickness of the base material is preferably 2 μm or more and 25 μm or less, and preferably 3 μm or more and 10 μm or less. This makes it possible to improve the mechanical strength of the base material and the transfer of thermal energy during thermal transfer.

<Transfer layer>
The transfer layer is a layer that is transferred from the thermal transfer sheet to the transferred body or the like by heating.

The transfer layer includes at least a colored layer and an adhesive layer. The transfer layer may further include a release layer.

(Adhesive layer)
The adhesive layer provided in the heat transfer sheet of the present disclosure includes polyester and polyolefin which are incompatible with each other. Further, the adhesive layer has a phase-separated structure containing two types of phases, and the surface of the adhesive layer is photographed with a digital microscope at a magnification of 500 times to obtain an image, and then the image is imaged. When binarization processing is performed using processing software and the two types of phases are divided into a bright portion and a dark portion, the area of the surface region (hereinafter, also referred to as surface region A) of the bright portion or the dark portion is the area of the image. It is 55% or more and 85% or less with respect to the total area. By using such an adhesive layer, the image formability of the thermal transfer sheet can be improved.
The area of the surface region A is preferably 60% or more and 83% or less, and more preferably 64% or more and 80% or less with respect to the total area of 100% of the image.
In taking the image, a VHX-1000 manufactured by KEYENCE CORPORATION is used as the digital microscope. In the binarization process, Image J is used as the image processing software. Further, the binarization process is performed with the default threshold value of ImageJ. The default threshold is determined by the IsoData algorithm described in Technical Document 1 (Ridler, TW & Calvard, S (1978), "Picture thresholding using an iterative selection method", IEEE Transactions on Systems, Man and Cybernetics 8: 630-632). It has been decided.
When the bright part corresponds to the surface area A, the dark part corresponds to the other surface area (hereinafter, also referred to as the surface area B), and when the dark part corresponds to the surface area A, the bright part corresponds to the surface area B. Equivalent to.

In one embodiment, the phase-separated structure of the adhesive layer includes a sea-island structure as shown in FIG. The sea-island structure is a structure including a sea phase 20 and discontinuous island phases 21 scattered in the sea phase 20.
When the phase separation structure of the adhesive layer is a sea-island structure, in the image after the binarization treatment, the bright part may be the sea phase and the dark part may be the island phase, or the bright part is the island phase. The dark part may be the sea phase.

When the phase separation structure of the adhesive layer is a sea-island structure, the value obtained by dividing the area of the surface region corresponding to the island phase by the number of island phases is preferably 50 μm ² / piece or more, and 50 μm ² / piece or more 2000 μm ² /. More preferably, 100 μm ² / piece or more and 1500 μm ² / piece or less, and further preferably 500 μm ² / piece or more and 1000 μm ² / piece or less.
By setting the value as described above, the image forming property for the PET transferred body and the PP transferred body can be improved.

In one embodiment, the sea phase is a phase containing polyester as a main component, and the island phase is a phase containing polyolefin as a main component.
In another embodiment, the sea phase is a phase containing polyolefin as a main component, and the island phase is a phase containing polyester as a main component.
In addition, in this specification, a principal component means a component of more than 50% by mass.

In one embodiment, the phase-separated structure of the adhesive layer includes a co-continuous structure as shown in FIG. The co-continuous structure is a structure in which the continuous phase A21 and the continuous phase B22 form a complicated network. In the co-continuous structure, the surface region corresponding to the continuous phase A21 is larger than the surface region corresponding to the continuous phase B22.
When the phase separation structure of the adhesive layer is a co-continuous structure, in the image after the binarization treatment, the bright part may be the continuous phase A and the dark part may be the continuous phase B, or the bright part may be the continuous phase. It may be B, and the dark part may be continuous phase A.

When the phase-separated structure of the adhesive layer is a co-continuous structure, the value obtained by dividing the area of the surface region corresponding to the continuous phase B by the number of continuous phases B is preferably 50 μm ² / piece or more, preferably 50 μm ² / piece or more. It is more preferably 4000 μm ² / piece or less, further preferably 500 μm ² / piece or more and 3000 μm ² / piece or less, and even more preferably 1000 μm ² / piece or more and 2000 μm ² / piece or less.
By setting the value as described above, the image forming property for the PET transferred body and the PP transferred body can be improved.

In one embodiment, the continuous phase A is a phase containing polyester as a main component, and the continuous phase B is a phase containing polyolefin as a main component.
In another embodiment, the continuous phase A is a phase containing polyolefin as a main component, and the continuous phase B is a phase containing polyester as a main component.

As used herein, polyester means a polymer polymerized by an ester bond. Such a polyester can be obtained, for example, by polycondensing at least a dicarboxylic acid compound and a diol compound.
Examples of the dicarboxylic acid compound include a dicarboxylic acid and a derivative of the dicarboxylic acid. Examples of the dicarboxylic acid include fats such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecandionic acid, eicosandionic acid, methylmalonic acid and ethylmalonic acid. Group dicarboxylic acid; alicyclic dicarboxylic acid such as adamantandicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid and decalindicarboxylic acid; terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid Acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylendandicarboxylic acid, anthracendicarboxylic acid Examples thereof include aromatic dicarboxylic acids such as acids, phenanthrangecarboxylic acids and 9,9'-bis (4-carboxyphenyl) fluorenic acid. Derivatives of the dicarboxylic acid include, for example, dicarboxylic acid anhydride, dicarboxylic acid ester and acid halide of the dicarboxylic acid. One kind or two or more kinds of dicarboxylic acid compounds can be used.
Examples of the diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, and cyclohexane. Diethanol, Decahydronaphthalenedimethanol, Decahydronaphthalenediethanol, Norbornanedimethanol, Norbornandiethanol, Tricyclodecanedimethanol, Tricyclodecaneethanol, Tetracyclododecanedimethanol, Tetracyclododecanediethanol, Decalindiethanol, Decalindiethanol, 5 -Methylol-5-ethyl-2- (1,1-dimethyl-2-hydroxyethyl) -1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis (4-hydroxy) Cyclohexylpropane), 2,2-bis (4- (2-hydroxyethoxy) cyclohexyl) propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamandiol , Paraxylene glycol, bisphenol A, bisphenol S and styrene glycol. One kind or two or more kinds of diol compounds can be used.

The polyester may contain a polymerization component other than the dicarboxylic acid compound and the diol compound, but the composition ratio thereof is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less.

The content of polyester in the adhesive layer is preferably 60% by mass or more and 85% by mass or less, and more preferably 65% by mass or more and 80% by mass or less with respect to the total solid content in the adhesive layer. Thereby, the image formability of the thermal transfer sheet can be further improved.

In the adhesive layer, the polyester comprises a crystalline polyester having a glass transition temperature (Tg) of less than 50 ° C. As a result, an image having excellent scratch resistance can be formed even immediately after formation, and a thermal transfer sheet having blocking resistance can be obtained.
In the image formed on the transferred body, the adhesive layer becomes familiar with the transferred body over time, so that the adhesion between the image and the transferred body is gradually improved, and the scratch resistance of the image is gradually improved accordingly. do. On the other hand, immediately after the image is formed, the adhesive layer is not yet familiar with the transferred body, the adhesion between the image and the transferred body is low, and the scratch resistance of the image is also low. By setting the Tg of the polyester to less than 50 ° C., the polyester of the adhesive layer is in a softened state immediately after the image is formed, so that the image is sufficiently adhered to the transferred object. As a result, the thermal transfer sheet of the present disclosure can form an image having excellent scratch resistance even immediately after formation.
Further, the amorphous polymer is in a molten state when it becomes Tg or less. Therefore, if the adhesive layer contains a large amount of low Tg amorphous polyester, the thermal transfer sheet tends to block. On the other hand, even if the amount of the crystalline polymer is Tg or more, the crystalline portion does not flow, so that the crystalline polymer does not become a molten state unlike the non-crystalline polymer. Therefore, even if the Tg is less than 50 ° C., the blocking resistance of the thermal transfer sheet can be maintained by using the crystalline polyester.
The Tg of the crystalline polyester is preferably −50 ° C. or higher and lower than 50 ° C., more preferably −40 ° C. or higher and 40 ° C. or lower, and further preferably −30 ° C. or higher and 25 ° C. or lower.
In this specification, Tg is a value obtained by differential scanning calorimetry (DSC) in accordance with JIS K 7121: 2012.

In the present specification, crystalline polyester is heated from −100 ° C. to 300 ° C. at 20 ° C./min and then from 300 ° C. to −100 ° C. at 50 ° C./min using a differential scanning calorimeter. It refers to a substance that shows a clear melting peak in either of the two heating processes, in which the temperature is lowered and then the temperature is raised from -100 ° C to 300 ° C at 20 ° C / min.

The melting point of the crystalline polyester is preferably 50 ° C. or higher and 150 ° C. or lower.
By setting the melting point of the crystalline polyester to 50 ° C. or higher, the blocking resistance of the thermal transfer sheet can be further improved. The melting point of the crystalline polyester is more preferably 70 ° C. or higher, further preferably 90 ° C. or higher.
By setting the melting point of the crystalline polyester to 150 ° C. or lower, the scratch resistance immediately after image formation can be further improved. The melting point of the crystalline polyester is more preferably 130 ° C. or lower, further preferably 120 ° C. or lower.
In this specification, the melting point is a value obtained by DSC in accordance with JIS K 7121: 2012.

The number average molecular weight (Mn) of the crystalline polyester is preferably 5,000 or more and 50,000 or less, and more preferably 8,000 or more and 40,000 or less. As a result, the scratch resistance immediately after image formation can be further improved, and the blocking resistance of the thermal transfer sheet can be further improved.
In this specification, Mn means a value measured by gel permeation chromatography using polystyrene as a standard substance, and is measured by a method according to JIS K 7252-3: 2016.

The content of the crystalline polyester is preferably 1% by mass or more and 30% by mass or less with respect to the total amount of solids in the adhesive layer.
By setting the content of the crystalline polyester to 1% by mass or more, the scratch resistance immediately after image formation can be improved. The content of the crystalline polyester is more preferably 3% by mass or more, further preferably 12% by mass or more.
By setting the content of the crystalline polyester to 30% by mass or less, the blocking resistance of the thermal transfer sheet can be improved. The content of the crystalline polyester is more preferably 23% by mass or less, further preferably 20% by mass or less.

In the adhesive layer, the polyester may further contain an amorphous polyester. This makes it possible to improve the blocking resistance of the thermal transfer sheet.

In the present specification, the amorphous polyester is heated from −100 ° C. to 300 ° C. at 20 ° C./min using a differential scanning calorimeter, and then from 300 ° C. to −100 ° C. at 50 ° C./min. In the two heating processes of lowering the temperature at -100 ° C and then raising the temperature from -100 ° C to 300 ° C at 20 ° C / min, the temperature does not show a clear melting peak in either of the heating processes.

The Tg of the amorphous polyester is preferably 50 ° C. or higher and 150 ° C. or lower.
By setting the Tg of the amorphous polyester to 50 ° C. or higher, the blocking resistance of the thermal transfer sheet can be improved. The Tg of the amorphous polyester is more preferably 60 ° C. or higher, further preferably 65 ° C. or higher.
By setting the Tg of the amorphous polyester to 150 ° C. or lower, the scratch resistance immediately after image formation can be improved. The Tg of the amorphous polyester is more preferably 120 ° C. or lower, further preferably 100 ° C. or lower.

The number average molecular weight (Mn) of the amorphous polyester is preferably 3000 or more and 30,000 or less, and more preferably 5000 or more and 15,000 or less. As a result, the scratch resistance immediately after image formation can be further improved, and the blocking resistance of the thermal transfer sheet can be further improved.

The content of the crystalline polyester is preferably 1% by mass or more and 30% by mass or less with respect to the total amount of solids in the adhesive layer.
By setting the content of the crystalline polyester to 1% by mass or more, the scratch resistance immediately after image formation can be improved. The content of the crystalline polyester is more preferably 3% by mass or more, further preferably 12% by mass or more.
By setting the content of the crystalline polyester to 30% by mass or less, the blocking resistance of the thermal transfer sheet can be improved. The content of the crystalline polyester is more preferably 23% by mass or less, further preferably 20% by mass or less.

In the present specification, the polyolefin is a polymer of an olefin, a copolymer of an olefin and another compound, an acid (maleic acid or the like) modified product (modified polyolefin) of these polymers, and a chlorinated product (chlorine) of these polymers. Polyolefins) and acid-modified products of these polymers. Polyolefins include chlorinated products (hereinafter referred to as acid-modified chlorinated polyolefins).
Among these, chlorinated polyolefin is preferable, and acid-modified chlorinated polyolefin is more preferable as the polyolefin of the adhesive layer from the viewpoint of image formability.
Examples of the olefin include ethylene, propylene, butene, pentene, hexene and octene.

The chlorination rate of the chlorinated polyolefin is preferably 10% or more and 55% or less, and more preferably 17% or more and 30% or less. Thereby, the image formability of the thermal transfer sheet can be further improved.
In the present specification, the chlorination rate of the polyolefin can be determined according to the method for quantifying chlorine in the chlorine-containing resin of JIS K 7229 (issued in 1995).

The Mn of the polyolefin is preferably 10,000 or more and 70,000 or less, and more preferably 30,000 or more and 60,000 or less. Thereby, the image formability can be further improved. In addition, the stability over time of the coating liquid for the adhesive layer used for forming the adhesive layer can be improved.

The Tg of the polyolefin is preferably 20 ° C. or higher and 90 ° C. or lower, and more preferably 50 ° C. or higher and 80 ° C. or lower. Thereby, the image formability of the thermal transfer sheet can be further improved.

The content of the polyolefin in the adhesive layer is preferably 15% by mass or more and 40% by mass or less, and more preferably 20% by mass or more and 35% by mass or less with respect to the total solid content in the adhesive layer.

When the polyester of the adhesive layer contains a non-crystalline polyester, the mass ratio of the crystalline polyester to the non-crystalline polyester is preferably 0.5 or more and 20 or less.
By setting the mass ratio of the crystalline polyester to the amorphous polyester to 0.5 or more, the blocking resistance of the thermal transfer sheet can be further improved. The mass ratio is more preferably 1.5 or more, further preferably 3 or more.
By setting the mass ratio of the crystalline polyester to the amorphous polyester to 20 or less, the scratch resistance immediately after image formation can be further improved. The mass ratio is more preferably 15 or less, and further preferably 6 or less.

In the thermal transfer sheet of the present disclosure, the storage elastic modulus of the adhesive layer is preferably 2.00 × 10 ⁵ Pa or less, more preferably 0.01 × 10 ⁵ Pa or more, and more preferably 2.00 × 10 ⁵ Pa or less at 70 ° C. .10 × 10 ⁵ Pa or more and 1.00 × 10 ⁵ Pa or less is more preferable.
By setting the storage elastic modulus of the adhesive layer to 2.00 × ¹⁰⁵ Pa or less, the scratch resistance immediately after image formation can be improved.
By setting the storage elastic modulus of the adhesive layer to 0.01 × ¹⁰⁵ Pa or more, the blocking resistance of the thermal transfer sheet can be improved.
The storage elastic modulus of the adhesive layer can be measured by a dynamic viscoelasticity measuring device (DMA) in accordance with JIS K 6394-2007. As the DMA, for example, an ARES reometer (manufactured by TA Instruments) can be used.

The colored layer may contain additives. Examples of the additive material include fillers, plastics, antistatic materials, ultraviolet absorbers, inorganic fine particles, organic fine particles, mold release materials and dispersants.

The thickness of the adhesive layer is preferably 0.05 μm or more and 1 μm or less, and more preferably 0.1 μm or more and 0.3 μm or less. Thereby, the image formability of the thermal transfer sheet can be improved.

The adhesive layer is formed by dispersing or dissolving the above-mentioned material in water or an appropriate solvent, and using known means such as a roll coating method, a reverse roll coating method, a gravure coating method, a reverse gravure coating method, a bar coating method and a rod coating method. , It can be formed by applying it on a colored layer or the like to form a coating film and drying it.

(Colored layer)
The colored layer contains at least a coloring material and a resin material.

As the coloring material contained in the coloring layer, carbon black, an inorganic pigment, an organic pigment or a dye can be appropriately selected and used according to the required color tone and the like. For example, in the case of bar code printing, it is particularly preferable to have a sufficient black density and not to be discolored or faded by light, heat or the like. Examples of such a coloring material include carbon black such as lamp black, graphite, niglocin dye and the like. Further, when color printing is required, other chromatic dyes or pigments are used.

The content of the coloring material in the colored layer is preferably 25% by mass or more and 45% by mass or less, and more preferably 30% by mass or more and 45% by mass or less. Thereby, the image formability of the thermal transfer sheet can be further improved.

Examples of the resin material contained in the colored layer include polyester, polyamide, polyolefin, vinyl resin, (meth) acrylic resin, vinyl chloride-vinyl acetate copolymer, cellulose resin, styrene resin, polycarbonate, phenoxy resin, and ionomer resin. Can be mentioned. Two or more of these resin materials may be combined. The resin material is preferably a combination of a (meth) acrylic resin and a vinyl chloride-vinyl acetate copolymer. Thereby, the image formability of the thermal transfer sheet can be further improved.

The content of the resin material in the colored layer is preferably 55% by mass or more and 75% by mass or less, and more preferably 55% by mass or more and 70% by mass or less. Thereby, the image formability of the thermal transfer sheet can be further improved.

When the colored layer contains a (meth) acrylic resin and a vinyl chloride-vinyl acetate copolymer, the mass ratio of the (meth) acrylic resin to the vinyl chloride-vinyl acetate copolymer is 0.2 or more and 5 or less. It is preferably 0.5 or more and 2 or less, more preferably. Thereby, the image formability of the thermal transfer sheet can be further improved.

The colored layer may contain the above-mentioned additive.

The thickness of the colored layer is preferably 0.3 μm or more and 1.2 μm or less, and more preferably 0.4 μm or more and 1 μm or less. As a result, the image formability can be improved and the image density of the printed matter can be improved.

The colored layer is formed by dispersing or dissolving the above-mentioned material in an appropriate solvent to prepare a coating liquid, and applying the above-mentioned coating means on a base material, a release layer, a release layer, or the like to form a coating film. , Which can be formed by drying.

(Release layer)
The release layer contains wax and a thermoplastic elastomer. Thereby, the image-forming property of the thermal transfer sheet can be improved.

Examples of the wax contained in the release layer include polyethylene wax, carnauba wax, paraffin wax, microcrystalline wax, candelilla wax, whale wax, wood wax, honey wax, partially modified wax, fatty acid ester, fatty acid amide and the like. Be done. The release layer may contain two or more of these waxes. As the wax, polyethylene wax or carnauba wax is preferable, and carnauba wax is more preferable, from the viewpoint of image forming property.
The carnauba wax is a wax derived from a plant of the family Palmaceae, and includes natural carnauba wax and its by-products and derivatives.

Examples of the thermoplastic elastomer contained in the release layer include styrene elastomers, olefin elastomers, urethane elastomers, polyester elastomers, polyamide elastomers, polyamide elastomers, 1,2-polybutadiene elastomers, vinyl chloride elastomers, and styrene-butadiene rubbers. .. The release layer may contain two or more of these thermoplastic elastomers. The thermoplastic elastomer is preferably styrene-butadiene rubber from the viewpoint of image formation.

In the release layer, the mass ratio of the wax to the thermoplastic elastomer is preferably 2 or more and 20 or less, and more preferably 5 or more and 15 or less. Thereby, the image formability of the thermal transfer sheet can be improved.

The release layer may contain the above-mentioned additive.

The thickness of the release layer is, for example, 0.1 μm or more and 3 μm or less.

For the release layer, the above-mentioned material is dispersed or dissolved in an appropriate solvent to prepare a coating liquid, and the above-mentioned coating means is applied onto a base material, a release layer or the like to form a coating film, which is then applied. It can be formed by drying.

<Back layer>
The back layer is a layer of the base material provided on the side opposite to the side on which the transfer layer is provided. Since the thermal transfer sheet is provided with a back layer, it is possible to suppress the occurrence of sticking and wrinkles due to heating during thermal transfer.

In one embodiment, the back layer comprises one or more resin materials. Examples of the resin material include cellulose resin, styrene resin, vinyl resin, polyester, polyurethane, silicone-modified polyurethane, fluorine-modified polyurethane, and (meth) acrylic resin.

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

In one embodiment, the back layer comprises inorganic or organic particles. This makes it possible to further suppress sticking, wrinkles, and the like due to heating during thermal transfer.

Examples of the inorganic 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, and oxides such as silica. , Graphite, sulphate, and inorganic particles such as boron nitride.
As the organic particles, organic resin particles made of (meth) acrylic resin, Teflon (registered trademark) resin, silicone resin, lauroyl resin, phenol resin, acetal resin, styrene resin, polyamide and the like, or these were reacted with a cross-linking material. Examples thereof include crosslinked resin particles.

The thickness of the back layer is preferably 0.1 μm or more and 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less. This makes it possible to suppress sticking, wrinkles, and the like while maintaining the transferability of thermal energy during thermal transfer.

The back layer is formed by dispersing or dissolving the above-mentioned material in an appropriate solvent to prepare a coating liquid, applying the above-mentioned coating means on a base material to form a coating film, and drying the coating film. can.

<Release layer>
The release layer is a layer that stays on the substrate during thermal transfer of the thermal transfer sheet.

The release layer contains one or more resin materials. Examples of the resin material contained in the release layer include (meth) acrylic resin, polyurethane, polyamide, polyester, melamine resin, polyol resin, cellulose resin, silicone resin and the like.

The release layer may contain a release material. Examples of the release material include silicone oil, phosphoric acid ester-based plasticizer, fluorine-based compound, wax, metal soap, filler and the like.

The thickness of the release layer is, for example, 0.2 μm or more and 2 μm or less.

For the release layer, the above-mentioned material is dispersed or dissolved in an appropriate solvent to prepare a coating liquid, and the above-mentioned coating means is applied on a base material or the like to form a coating film, which is dried. Can be formed by

<Primer layer>
The thermal transfer sheet of the present disclosure may be provided with a primer layer on one or both sides of a substrate. This makes it possible to improve the adhesion between the base material and the adjacent layer.

The primer layer contains one or more resin materials. Examples of the resin material contained in the primer layer include polyester, vinyl resin, polyurethane, (meth) acrylic resin, polyamide, polyether, cellulose resin and the like.

The thickness of the primer layer is, for example, 0.2 μm or more and 2 μm or less.

The primer layer is formed by dispersing or dissolving the above-mentioned material in an appropriate solvent to prepare a coating liquid, applying the above-mentioned coating means on a substrate or the like to form a coating film, and drying the coating film. Can be formed.

An embodiment of the thermal transfer sheet of the present disclosure is shown below. The thermal transfer sheet of the present disclosure is not limited to these embodiments.

The present disclosure is a thermal transfer sheet comprising a substrate and a transfer layer removably provided on one surface side of the substrate.
The transfer layer includes a colored layer and an adhesive layer in order from the base material side.
The adhesive layer contains polyester and polyolefin, which are incompatible with each other.
Polyesters include crystalline polyesters with a glass transition temperature of less than 50 ° C.
The adhesive layer has a phase-separated structure containing two types of phases, and the surface of the adhesive layer is photographed with a digital microscope at a magnification of 500 times to acquire an image, and then the image is image-processed by image processing software. When the two phases are divided into a bright part and a dark part by binarization processing using the above, the area of the surface region of the bright part or the dark part is 55% or more and 85% with respect to the total area of the image. The following is a thermal transfer sheet.

In one embodiment, the phase-separated structure is a sea-island structure that includes a sea phase and discontinuous island phases scattered within the sea phase.
The value obtained by dividing the area of the surface area corresponding to the island phase by the number of island phases is 50 μm ² / piece or more.

In one embodiment, the phase separation structure is a co-continuous structure including a continuous phase A and a continuous phase B.
The surface region corresponding to the continuous phase A is larger than the surface region corresponding to the continuous phase B.
The value obtained by dividing the area of the surface region corresponding to the continuous phase B by the number of the continuous phases B is 50 μm ² / piece or more.

In one embodiment, the polyester further comprises an amorphous polyester.

In one embodiment, the mass ratio of crystalline polyester to amorphous polyester is 0.5 or more and 20 or less.

In one embodiment, the storage elastic modulus of the adhesive layer is 2.00 × ¹⁰⁵ Pa or less at 70 ° C.

In one embodiment, the content of the crystalline polyester is 1% by mass or more and less than 30% by mass with respect to the total solid content in the adhesive layer.

The melting point of the crystalline polyester is 50 ° C. or higher and 150 ° C. or lower.

The number average molecular weight of the crystalline polyester is 5,000 or more and 50,000 or less.

The thickness of the adhesive layer is 0.05 μm or more and 1 μm or less.

The colored layer contains a vinyl chloride-vinyl acetate copolymer and an acrylic resin.

The transfer layer further comprises a release layer and
The release layer is provided between the base material and the colored layer, and is provided.
The release layer contains a wax and a thermoplastic elastomer.

Hereinafter, the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to these examples.
..

In Examples and Comparative Examples, the polyesters shown in Table 1 were used.

[Example 1]
As a base material, an easily adhesive-treated polyethylene terephthalate (PET) film having a thickness of 4.5 μm was prepared.
A coating liquid for a release layer having the following composition was applied to one surface of the PET film and dried to form a release layer having a thickness of 0.3 μm.
Next, a coating liquid for a colored layer having the following composition was applied onto the peeled layer and dried to form a colored layer having a thickness of 0.5 μm.
Next, a coating liquid for an adhesive layer having the following composition was applied onto the colored layer and dried to form an adhesive layer having a thickness of 0.2 μm.
Next, a coating liquid for a back layer having the following composition was applied and dried on the surface of the base material opposite to the release layer and the like to form a back layer having a thickness of 0.3 μm to obtain a thermal transfer sheet.

<Coating liquid for forming a release layer>
・ 10 parts by mass of carnauba wax (manufactured by Konishi Co., Ltd., WE-95, melting point 80 ° C)
1 part by mass of styrene-butadiene rubber (Nippon Zeon Co., Ltd., Nipol (registered trademark) LX430)
・ 20 parts by mass of water ・ 60 parts by mass of isopropanol (IPA)

<Coating liquid for forming a colored layer>
10 parts by mass of vinyl chloride-vinyl acetate copolymer (manufactured by Nissin Chemical Industry Co., Ltd., Solveine (registered trademark) CL, Mn25000)
・ Acrylic resin 10 parts by mass (manufactured by Mitsubishi Chemical Corporation, Dianal (registered trademark) BR87)
・ Carbon black 20 parts by mass ・ Toluene 30 parts by mass ・ MEK 30 parts by mass

<Coating liquid for forming an adhesive layer>
・ Crystalline polyester A 0.5 parts by mass ・ Non-crystalline polyester A 6.65 parts by mass ・ Maleic acid-modified chlorinated polypropylene 2.85 parts by mass (Nippon Paper Industries, Ltd., Supercron (registered trademark) 3221S, Mn50000 , Softening point 70 ° C, chlorine content 21.0% by mass)
・ Toluene 80 parts by mass ・ MEK 20 parts by mass

<Coating liquid for forming the back layer>
・ Styrene-acrylonitrile copolymer 11 parts by mass ・ Linear saturated polyester 0.3 parts by mass ・ Zinc stearyl phosphate 6 parts by mass ・ Melamine resin powder 3 parts by mass ・ MEK 80 parts by mass

[Examples 2 to 6, Comparative Examples 1 to 3]
A thermal transfer sheet was produced in the same manner as in Example 1 except that the composition of the adhesive layer and the thickness of the adhesive layer were changed as shown in Table 2.

<< Area measurement of surface area A and surface area B >>
The surface of the adhesive layer provided in the thermal transfer sheets obtained in the above Examples and Comparative Examples was photographed with a digital microscope (manufactured by KEYENCE CORPORATION, VHX-1000) at a magnification of 500 times, and an image was acquired.
Next, the obtained image was binarized using image processing software (National Institutes of Health, Image J), and the two phases constituting the phase separation structure were divided into a bright part and a dark part. .. The bright part corresponds to the surface area A, and the dark part corresponds to the surface area B.
Next, the area ratio of the surface area A to the total area of the image and the area ratio of the surface area B were obtained. The results are shown in Table 2.
The sea-island structure as shown in FIG. 4 was observed in the adhesive layer provided in the thermal transfer sheets of Examples 1, 2 and 5, and Comparative Example 2.
The adhesive layer provided in the thermal transfer sheets of Examples 3, 4 and 6 and Comparative Example 3 was observed to have a co-continuous structure as shown in FIG.

Further, the number of island phases or continuous phases B present in the obtained image was obtained, and the value obtained by dividing the area of the island phase or continuous phase B by the number was calculated. The results are shown in Table 2.
Table 2 shows the main components of the island phase or the continuous phase B. In Table 2, "PP" means polypropylene and "PEs" means polyester.

<< Measurement of storage elastic modulus >>
According to JIS K 6394-2007, the storage elastic modulus of the resin composition constituting the adhesive layer of the above-mentioned Example and Comparative Example was measured.
Specifically, first, the resin compositions constituting the adhesive layers of the above Examples and Comparative Examples were dissolved in a mixed solvent of toluene and MEK (toluene / MEK = 8/2), respectively. This solution was appropriately poured into a circular mold having a radius of 1 cm so that the thickness after drying would be about 1 mm, and a measurement sample was prepared. The prepared sample was measured using a dynamic viscoelastic device (ARES Leometer (manufactured by TA Instruments)) under the conditions of a temperature range of 30 to 120 ° C. and an angular velocity of 6.28 rad / s. From the obtained results, the value of the storage elastic modulus of the measurement sample at 70 ° C. was read. The measurement results are shown in Table 2.

<< Evaluation of image formation >>
Using the thermal transfer sheet obtained in each Example and Comparative Example and a printer (SD3C manufactured by Markem Image), a polyethylene terephthalate (PET) film which is a PET transfer body or a biaxial stretching which is a PP transfer body. A picket bar code image was formed on a polypropylene (OPP) film under the conditions of a printing density of 140%, a printing speed of 10 m / min, and a pressure of 0.35 MPa. The formed image was visually confirmed and evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2.
〔Evaluation criteria〕
A: It was confirmed that a good image was formed without any blurring or blurring in the image.
B: Blurring and / or blurring was observed in a part of the image, but there was no problem in practical use.
NG: Cannot transfer and could not form an image.

<< Scratch resistance evaluation >>
The surface of the image formed in the image formability evaluation was rubbed 20 times with a thumb or a nail in an environment of 22.5 ° C. and a humidity of 40%. The image after scraping was judged by a barcode checker and evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2. The image was scraped within 30 minutes after the image was formed.
〔Evaluation criteria〕
A: The judgment result by the barcode checker after rubbing was A judgment.
B: The judgment result by the barcode checker after rubbing was B or C judgment.
NG: The judgment result by the barcode checker after rubbing was D judgment or less.

<< Blocking resistance evaluation >>
The thermal transfer sheets of the above Examples and Comparative Examples were laminated in a sheet-fed state, a load of 0.196 MPa was applied, and the mixture was stored at 50 ° C. and 85% RH for 24 hours. The blocking resistance was evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2.
〔Evaluation criteria〕
A: No blocking occurred.
B: Slight blocking occurred.
NG: Blocking occurred on the entire surface.

10: Thermal transfer sheet, 11: Substrate, 12: Colored layer, 13: Adhesive layer, 14: Transfer layer, 15: Peeling layer, 16: Back layer, 20: Sea phase, 21: Island phase, 22: Continuous phase A , 23 continuous phase B

Claims (12)

A thermal transfer sheet including a base material and a transfer layer provided on one surface side of the base material so as to be peelable.
The transfer layer includes a colored layer and an adhesive layer in order from the base material side.
The adhesive layer contains polyester and polyolefin, which are incompatible with each other.
The polyester comprises a crystalline polyester having a glass transition temperature of less than 50 ° C.
The adhesive layer has a phase-separated structure containing two types of phases, and the surface of the adhesive layer is photographed with a digital microscope at a magnification of 500 times to obtain an image, and then the image is imaged. When binarization processing is performed using processing software to divide the two phases into a bright portion and a dark portion, the area of the bright portion or the surface region of the dark portion is relative to the total area of the image. A thermal transfer sheet of 55% or more and 85% or less. The phase-separated structure is a sea-island structure including a sea phase and discontinuous island phases scattered in the sea phase.
The thermal transfer sheet according to claim 1, wherein the value obtained by dividing the area of the surface region corresponding to the island phase by the number of the island phases is 50 μm ² / piece or more. The phase-separated structure is a co-continuous structure including a continuous phase A and a continuous phase B.
The surface region corresponding to the continuous phase A is larger than the surface region corresponding to the continuous phase B.
The thermal transfer sheet according to claim 1, wherein the value obtained by dividing the area of the surface region corresponding to the continuous phase B by the number of the continuous phases B is 50 μm ² / piece or more. The thermal transfer sheet according to any one of claims 1 to 3, wherein the polyester further contains an amorphous polyester. The thermal transfer sheet according to claim 4, wherein the mass ratio of the crystalline polyester to the non-crystalline polyester is 0.5 or more and 20 or less. The thermal transfer sheet according to any one of claims 1 to ⁵ , wherein the adhesive layer has a storage elastic modulus of 2.00 × 105 Pa or less at 70 ° C. The thermal transfer sheet according to any one of claims 1 to 6, wherein the content of the crystalline polyester is 1% by mass or more and less than 30% by mass with respect to the total solid content in the adhesive layer. The thermal transfer sheet according to any one of claims 1 to 7, wherein the crystalline polyester has a melting point of 50 ° C. or higher and 150 ° C. or lower. The thermal transfer sheet according to any one of claims 1 to 8, wherein the crystalline polyester has a number average molecular weight of 5,000 or more and 50,000 or less. The thermal transfer sheet according to any one of claims 1 to 9, wherein the thickness of the adhesive layer is 0.05 μm or more and 1 μm or less. The thermal transfer sheet according to any one of claims 1 to 10, wherein the colored layer contains a vinyl chloride-vinyl acetate copolymer and an acrylic resin. The transfer layer further comprises a release layer and
The release layer is provided between the base material and the colored layer.
The thermal transfer sheet according to any one of claims 1 to 11, wherein the release layer contains a wax and a thermoplastic elastomer.

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