JP5526917B2 - Thermal transfer sheet - Google Patents

Description

  The present invention relates to a thermal transfer sheet having a protective layer for improving the durability of characters or images formed on a thermal transfer member.

  In general, a thermal transfer sheet is called an thermal ribbon and is an ink ribbon used in a thermal transfer type printer. A thermal transfer layer is formed on one surface of a substrate, and a backcoat layer (heat resistant layer) is formed on the other surface of the substrate. (Sliding layer). Here, the thermal transfer layer is a layer of ink that is sublimated (sublimation transfer method) or melted (melt transfer method) by the heat generated in the thermal head of the printer and transferred to the transfer target side. .

  At present, the thermal transfer system is widely used for self-printing of digital cameras, cards such as identification cards, amusement output products, and the like because various images can be easily formed in full color along with the enhancement of functions of the printer. In general, a protective layer is formed on the surface of these characters or images in order to improve durability, weather resistance and the like.

  The protective layer is peeled off from the thermal transfer body by the thermal transfer method and transferred onto the thermal transfer body, and the weather resistance from ultraviolet rays or the like is required as performance. For this reason, it is common to provide an adhesive layer on the release layer in order to improve the adhesion to the surface of the transfer object, except when the protective layer is composed of a weather-resistant release layer. . Further, a non-transferable release layer is often provided between the release layer and the substrate so that the release layer can be easily transferred from the substrate.

  As described above, since the performance enhancement of the protective layer is accompanied by the multilayering, it is necessary to reduce the thickness of each layer as much as possible to reduce the cost. However, when the thickness of the release layer is reduced, the adhesion between the release layer and the release layer is reduced, and thus the protective layer is easily peeled off by physical action such as friction even in a non-heated state. For this reason, powder falling during the driving of the printer (here, powder falling means that the protective layer of the non-thermal transfer part falls off from the thermal transfer sheet in the form of flakes or dots, the same applies hereinafter), If these fall on the transfer medium immediately before printing, black printing defects will occur during thermal transfer.

On the other hand, if the thickness of the release layer is increased to a level at which no powder falls off, the adhesive force between the release layer and the release layer becomes too strong, and there is an abnormality in transferring the entire release layer to the transferred material. Occur. Regardless of the magnitude of this abnormal transfer, the peeling start portion that requires the most peeling energy, that is, the application surface head always starts.
As a thermal transfer sheet that prevents powder falling while ensuring thermal transferability, a technical example in which a heat-meltable release layer is provided between a base material and a heat-meltable colored ink layer having a high cohesive force has been proposed. Yes. Patent Document 1 is characterized in that the release layer contains porous particles. During heating and melting, air in the micropores expands and is released to the outside of the particles, and voids generated at the interface with the substrate. Due to the foam, the contact area between the release layer and the substrate is reduced, and as a result, the peelability can be improved even when the melt viscosity of the release layer is high. Patent Document 2 discloses a first release layer mainly composed of paraffin wax and polyethylene wax on a base material, and a second melt viscosity lower than that of the first release layer and mainly composed of paraffin wax. It is characterized by sequentially laminating release layers, and by changing the adhesion between the substrate and the release layer in the film thickness direction, it is possible to achieve both the transferability and retention of the ink layer, which are contradictory properties. Yes.

JP-A-6-135160 JP-A-6-143844

  However, when the above-described technique for the hot-melt colored ink layer is diverted to the protective layer, several problems arise. When porous particles are added to the release layer as in Patent Document 1, irregularities are generated on the surface of the release layer, resulting in a decrease in glossiness, which is one of important performances required for the protective layer. In addition, it is not preferable in terms of cost to make the release layer into two layers as in Patent Document 2.

As means for solving the above problems, the invention according to claim 1 is a substrate sheet, and a thermal transfer ink provided on one surface of the substrate sheet in the surface direction in the longitudinal direction of the substrate sheet. Layer and a protective layer, and a heat-resistant slip layer provided on the other surface of the base sheet, and the protective layer was formed by laminating a release layer, a release layer, and an adhesive layer in the surface order. A thermal transfer sheet,
The release layer is disposed on a boundary line side with the thermal transfer ink layer, and a film thickness increasing region in which the film thickness increases as the distance from the boundary line increases in the longitudinal direction; A film thickness constant region whose thickness is constant with the same dimension as the maximum film thickness of the film thickness increase region in the direction, the length of the film thickness increase region is 1 and the minimum film thickness of the film thickness increase region is h _1, and the maximum thickness of the film thickness increased area and _{h 2, (h 2 -h 1} ) / l, and the value of _h 1 / _{h 2} is the formula,
7.0 × 10 ⁻⁶ ≦ (h ₂ −h ₁ ) /l≦1.5×10 ⁻⁵
0.6 ≦ h ₁ / h ₂ ≦ 0.8
It is a thermal transfer sheet characterized by satisfying the above.

  The invention according to claim 2 is the thermal transfer sheet according to claim 1, wherein the total thickness of the protective layer is constant in the longitudinal direction.

  By using the thermal transfer sheet of the present invention, it is possible to provide a character or an image that does not have a printing defect due to powder falling while ensuring the thermal transferability of the protective layer.

It is explanatory drawing of one Embodiment of the thermal transfer sheet of this invention.

  The thermal transfer sheet of the present invention will be described below in detail with reference to the drawings.

  As shown in FIG. 1, the thermal transfer sheet 1 is provided with a thermal transfer ink layer 3 and a protective layer 4 on one surface 2 a of the base sheet 2 in a surface sequence so as not to overlap in the longitudinal direction of the base sheet 2, The base sheet 2 has a structure in which the heat-resistant slip layer 5 is provided on the other surface 2b. The protective layer 4 is formed by laminating a release layer 6, a release layer 7, and an adhesive layer 8 in the surface order. Among these, the release layer 7 that is thermally transferred onto the thermal transfer member and the adhesive layer 8 are collectively referred to as a thermal transferable protective layer 9.

  First, since the base sheet 2 is required to have heat resistance and strength not to be softened and deformed by heat pressure in thermal transfer, for example, polyethylene terephthalate, polyethylene naphthalate, polypropylene, cellophane, acetate, polycarbonate, polysulfone, polyimide, polyvinyl alcohol In addition, a synthetic resin film such as aromatic polyamide, aramid, and polystyrene, and paper such as condenser paper and paraffin paper can be used alone or in combination. Among these, a polyethylene terephthalate film is preferable in view of physical properties, workability, cost, and the like. Further, the thickness can be in the range of 2 to 50 μm in consideration of operability and workability, but in consideration of handling properties such as transfer suitability and workability, the thickness is about 2 to 12 μm. preferable.

  Next, the thermal transfer ink layer 3 includes a sublimation thermal transfer layer composed of a heat sublimable dye and a binder, and a melt thermal transfer layer composed of a dye and / or a pigment and a binder.

  The ink for forming a sublimation heat transfer layer is prepared by blending, for example, a heat sublimation dye, a binder, a solvent, and the like. An appropriate coating amount of the ink for forming the sublimation heat transfer layer is about 1 μm (dry thickness).

  The ink for forming a thermal transfer layer is prepared by blending, for example, a dye and / or pigment, a binder, a solvent, a lubricant and the like. The coating amount of the melt heat transfer layer forming ink is suitably about 0.5 to 1 μm (dry thickness).

  As the sublimation dye used in the ink for forming a sublimation heat transfer layer, a sublimation disperse dye is preferable. For example, as yellow components, solvent yellow 56, 16, 30, 93, 33, disperse yellow 201, 231 and 33. Examples of the magenta component include C.I. I. Disperse thread 60, C.I. I. Disperse violet 26, C.I. I. Solvent Red 27, or C.I. I. Solvent Red 19 etc. are mentioned. As the cyan component, C.I. I. Disperse Blue 354, C.I. I. Solvent Blue 63, C.I. I. Solvent Blue 36, or C.I. I. Disperse Blue 24 and the like. As the ink dye, it is common to perform color matching by combining the above dyes.

  The binder used in the ink for forming the sublimation heat transfer layer is not particularly limited, but cellulose resins such as ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxy cellulose, hydroxypropyl cellulose, methyl cellulose, and cellulose acetate, polyvinyl alcohol, and polyacetic acid Examples thereof include vinyl resins such as vinyl, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone, and polyacrylamide, polyester resins, styrene-acrylonitrile copolymer resins, and phenoxy resins. Among these, polyvinyl butyral and polyvinyl acetal resins containing a hydroxyl group that can be cross-linked by isocyanate or the like are preferable.

  Here, the ratio (mass ratio) of the dye and the binder in the sublimation thermal transfer layer forming ink layer is preferably dye / binder = 10/100 to 300/100. This is because if the dye / binder ratio is less than 10/100, the amount of dye is too small and the color development sensitivity is insufficient, and a good thermal transfer image cannot be obtained, and if this ratio exceeds 300/100, the binder This is because the solubility of the dye in the ink is extremely lowered, and the storage stability of the ink layer is deteriorated when the thermal transfer sheet is formed, and the dye is likely to be precipitated.

  The sublimation thermal transfer layer forming ink may contain a lubricant to prevent sticking between the thermal transferable ink layer and the transfer target during printing, and may be a fluorine-based, silicone-based, or phosphate-based one. And various oils and surfactants.

  The dyes used in the ink for forming the thermal transfer layer include diarylmethane, triarylmethane, thiazole, methine, azomethane, xanthene, axazine, thiazine, azine, acridine, azo, and spirodipyran. Commonly used thermal transfer dyes such as those based on isodolin, spiropyrans, fluorans, rhodamines, and anthraquinones can be widely used. As the pigment, known organic pigments and inorganic pigments can be used. For example, carbon black, azo series, phthalocyanine series, quinacridone series, thioindigo series, anthraquinone series, isoindolinone series, etc. Pigments.

  The binder used for the ink for forming the thermal transfer layer is not particularly limited except for the thermal melting property. For example, styrene resins such as polystyrene and poly α-methylstyrene, polymethyl methacrylate, poly Acrylic resins such as ethyl acrylate, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, vinyl resins such as polyvinyl butyral and polyvinyl acetal, polyester resins, polyamide resins, epoxy resins, polyurethane resins, petroleum Resin, ionomer, synthetic resin such as ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, cellulose derivatives such as nitrocellulose, ethyl cellulose, cellulose acetate propionate, rosin, rosin modified maleic acid resin, ester gum , Li isobutylene rubber, butyl rubber, styrene - butadiene rubber, butadiene - acrylonitrile rubber, derivatives of natural resins and synthetic rubber polychlorinated olefins such as carnauba wax, a wax such as paraffin wax. Among these, polyester and epoxy resin are preferable.

  Here, the ratio (mass ratio) of the dye and / or pigment (hereinafter sometimes referred to as the colorant component) and the binder in the ink layer for forming the thermal transfer layer is as follows: Colorant component / binder = 5/100 To 200/100 is preferred. This is because when the ratio of the colorant / binder is less than 5/100, the colorant is too small to obtain a good thermal transfer image, and when this ratio exceeds 200/100, the molten thermal transfer layer is aggregated. This is because the storage stability of the ink layer is deteriorated when the thermal transfer sheet is formed because the force is extremely reduced.

  Next, the release layer 6 forming the protective layer 4 adjusts the degree of peeling of the protective layer 4 from the base sheet 2 within an appropriate range, and ensures stable peelability from the base sheet 2. It is provided to do.

  The material of the release layer 6 is not particularly limited, and examples thereof include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, and sodium alginate, chlorinated rubber, cyclized rubber, and the like. Natural rubber derivatives, waxes such as natural wax and synthetic wax, cellulose derivatives such as nitrocellulose, cellulose, cellulose acetate propionate, acrylic, polyurethane, polyamide, polyimide, polyacetal, chlorinated polyolefin, chlorinated Examples thereof include thermoplastic resins such as vinyl-vinyl acetate copolymer systems, and thermosetting resins such as melamine type, epoxy type, polyurethane type, and silicone type.

  Next, the release layer 7 forming the protective layer 4 (thermal transferable protective layer 9) is prepared by blending a functional additive that imparts releasability and slipperiness, a binder, a solvent, and the like.

  Examples of functional additives used in the ink for forming the release layer include silicone oil, release agents typified by phosphate esters, waxes, slip agents typified by resin fillers, ultraviolet absorbers, and light stabilizers. , Antioxidants, fluorescent brighteners, antistatic agents and the like. In addition, the binder is not particularly limited except for heat melting property. For example, styrene resins such as polystyrene and poly α-methylstyrene, acrylic resins such as polymethyl methacrylate and polyethyl acrylate. Resin, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl resins such as polyvinyl butyral, polyvinyl acetal, polyester resin, polyamide resin, epoxy resin, polyurethane resin, petroleum resin, ionomer, ethylene-acrylic Synthetic resins such as acid copolymers, ethylene-acrylic acid ester copolymers, cellulose derivatives such as nitrocellulose, ethyl cellulose, cellulose acetate propionate, rosin, rosin-modified maleic acid resin, ester gum, polyisobutylene rubber, butyl rubber , Styrene - butadiene rubber, butadiene - acrylonitrile rubber, derivatives of natural resins and synthetic rubber polychlorinated olefins such as carnauba wax, a wax such as paraffin wax. Among these, acrylic resins and cellulose derivatives are preferable.

Further, the release layer 7 of the present invention is disposed on the boundary line A side (application surface head side) with the thermal transferable ink layer 3, and the film thickness increases as the distance from the boundary line A increases in the longitudinal direction of the base sheet 2. The film thickness increasing region 7a to be performed and the film thickness increasing region 7a are arranged on one side (rear side) of the base sheet 2 so that the film thickness is the maximum of the film thickness increasing region 2a in the longitudinal direction of the base sheet 2. A constant film thickness region 7b having the same dimension as the film thickness (film thickness at the boundary line A) and having a constant thickness is sequentially provided. Even if the film thickness of the constant film thickness region 7b is originally such that a transfer failure occurs, the film thickness increasing region 7a is provided so that the film thickness of the coating surface head is made thinner than the back (the constant film thickness region 7b), and MD By continuously increasing the film thickness in the direction (longitudinal direction: Machine Direction), it is possible to eliminate the transfer failure that has occurred starting from the top of the coated surface. Specifically, the length of the thickness increase area 7a of the peeling layer 7 l, the thickness of (the release) the start point of the region 7a (minimum thickness) to h _1, (the release) of the region 7a If the thickness of the end point (maximum film thickness) and _{h 2, (h 2 -h 1} ) / value of l and _h 1 / _{h 2} is the formula,
7.0 × 10 ⁻⁶ ≦ (h ₂ −h ₁ ) /l≦1.5×10 ⁻⁵
0.6 ≦ h ₁ / h ₂ ≦ 0.8
It is preferable to satisfy.

  The film thickness increase rate in the film thickness increase region 7a does not need to be constant, but in order to ensure stable thermal transferability, the film thickness increase region 7a and the release layer over the film thickness increase region 7b behind it. It is preferable that the film thickness change of 7 is more continuous.

When (h ₂ −h ₁ ) / l and h ₁ / h ₂ do not satisfy the range of the above formula, the following problems occur. When (h ₂ −h ₁ ) / l is less than 7.0 × 10 ⁻⁶ or h ₁ / h ₂ is less than 0.6, there is a film thickness region that is insufficient for preventing powder falling on the coated surface head. As a result, a printing defect occurs. On the other hand, if (h ₂ −h ₁ ) / l exceeds 1.5 × 10 ⁻⁵ , the rate of increase in film thickness is high, and transfer failure occurs. Alternatively, when h ₁ / h ₂ exceeds 0.8, the effect due to the change in film thickness is not exhibited. When h ₂ is small, a printing defect is caused, and when h ₂ is large, a transfer defect is caused.

  Next, the adhesive layer 8 for forming the protective layer 4 (thermal transferable protective layer 9) is prepared by blending, for example, functional additives such as slipperiness and ultraviolet absorbers, a binder, a solvent, and the like. The amount of ink applied is suitably about 0.5 to 5 μm (dry thickness). Further, since the film thickness of the release layer of the present invention continuously changes in the MD direction, the film thickness of the adhesive layer may be changed in order to make the film thickness of the thermal transferable protective layer constant.

  Examples of functional additives used in inks for forming adhesive layers include calcium carbonate, kaolin, talc, silicone powder, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, satin white, zinc carbonate, magnesium carbonate, aluminum silicate , Calcium silicate, magnesium silicate, silica, colloidal silica, colloidal alumina, pseudoboehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrohalosite, magnesium hydroxide and other inorganic fillers, acrylic plastic pigment, styrene plastic pigment, Examples include particles represented by organic fillers such as microcapsules, urea resins, and melamine resins. Among them, a spherical shape such as silicone powder uniformly adjusts the slipperiness of the protective layer surface. In that it can be suitable. Furthermore, benzophenone, benzotriazole, benzoate, UV absorbers typified by triazines, light stabilizers typified by hindered amines, antioxidants typified by hindered phenols, fluorescent whitening agents, antistatic agents, etc. Can be mentioned.

  In addition, the binder is not particularly limited except for heat melting property. For example, styrene resins such as polystyrene and poly α-methylstyrene, acrylic resins such as polymethyl methacrylate and polyethyl acrylate. Resin, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl resins such as polyvinyl butyral, polyvinyl acetal, polyester resin, polyamide resin, epoxy resin, polyurethane resin, petroleum resin, ionomer, ethylene-acrylic Synthetic resins such as acid copolymers, ethylene-acrylic acid ester copolymers, cellulose derivatives such as nitrocellulose, ethyl cellulose, cellulose acetate propionate, rosin, rosin-modified maleic acid resin, ester gum, polyisobutylene rubber, butyl rubber , Styrene - butadiene rubber, butadiene - acrylonitrile rubber, derivatives of natural resins and synthetic rubber polychlorinated olefins such as carnauba wax, a wax such as paraffin wax. Among these, acrylic resins, polyester resins, and epoxy resins are preferable.

  Next, the heat-resistant slipping layer 5 is required to have performance such as prevention of fusion between the thermal transfer sheet and the thermal head or protection of the thermal transfer sheet itself against heat from the thermal head.

  The heat-resistant slip layer forming ink is prepared by blending, for example, a functional additive that adjusts releasability, slipperiness, and surface properties, a binder, a curing agent, a solvent, and the like. The ink coating amount of this heat resistant slipping layer is suitably about 0.1 to 2 μm (dry thickness).

  As an example of the heat-resistant slipping layer, examples of the binder include synthetic resins such as acrylic, polyester, polyurethane, polyacetal, polyamide, and polyimide. Examples of the functional additive include stearates such as zinc stearate. And phosphoric acid esters such as polyoxyalkylene alkyl ethers, silicone oils such as amino-modified silicone oils, and particles such as silica and talc. Examples of the curing agent include 2,6-tolylene diisocyanate. Mention may be made of isocyanates.

  The thermal transfer sheet can be obtained by applying and forming ink for forming each layer on each base sheet 2 by a known paintable method such as gravure coating or slot coating.

  Specific examples of the present invention will be described below.

First, materials used in the examples and comparative examples of the present invention are shown below. In the text, “part” is based on mass.
<Base material sheet>
Polyester film: Thickness 4.5μm
<Yellow ink for thermal transfer formation>
C. I. Solvent Yellow 93 2.5 parts C.I. I. Solvent Yellow 16 1.5 parts Polyvinyl butyral resin 4.7 parts Silicone surfactant 0.1 part 2,6-tolylene diisocyanate 0.2 part Toluene 45.0 parts Methyl ethyl ketone 46.0 parts <Magenta ink for thermal transfer formation >
C. I. Disperse thread 60 2.2 parts C.I. I. Disperse Violet 26 2.2 parts Polyvinyl butyral resin 4.3 parts Silicone surfactant 0.1 part 2,6-tolylene diisocyanate 0.2 part Toluene 45.0 parts Methyl ethyl ketone 46.0 parts <Cyan for thermal transfer formation Ink>
C. I. Solvent Blue 63 3.0 parts C.I. I. Solvent Blue 36 1.5 parts Polyvinyl butyral resin 4.2 parts Silicone surfactant 0.1 part 2,6-Tolylene diisocyanate 0.2 part Toluene 45.0 parts Methyl ethyl ketone 46.0 parts <For mold release layer formation Ink>
-Silicone resin 30.0 parts-Toluene 35.0 parts-Methyl ethyl ketone 35.0 parts <Ink for peeling layer formation>
Acrylic resin 18.0 parts Polyester resin 1.0 part Polyethylene powder 1.0 part Toluene 40.0 parts Methyl ethyl ketone 40.0 parts <Ink for forming adhesive layer>
Acrylic resin 10.0 parts Polyester resin 3.5 parts Epoxy resin 3.5 parts Benzophenone UV absorber 7.5 parts Silicone powder 0.5 parts Toluene 35.0 parts Methyl ethyl ketone 40.0 parts <For heat resistant slipping layer formation Ink>
Acrylic polyol resin 15.0 parts Zinc stearate 1.5 parts Polyoxyalkylene alkyl ether 1.5 parts Talc 1.0 parts 2,6-tolylene diisocyanate 5.0 parts Toluene 50.0 parts Methyl ethyl ketone 20.0 parts Acetic acid 6.0 parts of <ethyl base material>
Foamed polyester film: 188μm thick
<Ink for forming image receiving layer for thermal transfer>
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 19.5 parts Amino-modified silicone oil 0.5 part Toluene 40.0 parts Methyl ethyl ketone 40.0 parts

<Preparation of base sheet with heat-resistant slip layer of thermal transfer sheet>
By forming a heat-resistant slipping layer with a dry thickness of 0.9 μm on one surface of the base sheet by the gravure coating method with a dry thickness of 0.9 μm, and then aging at 40 ° C. for 5 days, A heat-resistant slip layer was prepared.

<Preparation of transfer object>
Using a gravure coating method, a thermal transfer image-receiving layer is formed on one surface of a transfer substrate using a thermal transfer image-receiving layer forming ink with a dry thickness of 5.0 μm, thereby producing a transfer object for thermal transfer. did.

<Example 1>
Using the gravure coating method, the color inks for thermal transfer formation of yellow, magenta, and cyan are formed in the surface direction of the base sheet in the longitudinal direction so that they do not overlap in the order of the surface. Then, a thermal transfer ink layer having a dry thickness of 0.7 μm for each color was formed. Further, a protective layer was provided on the surface of the base sheet where the heat-resistant slip layer was not formed so as not to overlap the thermal transfer ink layer in a plane order but in a plane order in the longitudinal direction of the base sheet. This protective layer was formed by laminating a release layer (dry thickness of 0.5 μm), a release layer, and an adhesive layer (dry thickness of 1.5 μm) in the surface order. In addition, about the peeling layer, it formed so that the dry thickness of the application | coating surface head might be 0.4 micrometer, the length of a film thickness increase area | region might be 10 mm, and the dry thickness of the film thickness fixed area | region of the back may be 0.55 micrometer.

<Example 2>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the length of the thickness increase region of the release layer was changed to 20 mm and the dry thickness of the constant thickness region was changed to 0.6 μm.

<Example 3>
The thickness of the adhesive layer is changed in the MD direction so that the total thickness of the protective layer is constant, the dry thickness of the application surface head is 1.7 μm, the thickness reduction region is 20 mm, and the dry thickness of the constant thickness region. The thermal transfer sheet of the present invention was obtained in the same manner as in Example 2 except that was changed to 1.5 μm.

<Comparative Example 1>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the dry thickness of the release layer was changed to a constant value of 0.3 μm.

<Comparative example 2>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the dry thickness of the release layer was changed to a constant value of 0.5 μm.

<Comparative Example 3>
The peeling layer was applied in two steps, and after the first layer was formed with a dry thickness of 0.4 μm, the second layer was laminated with a dry thickness of 0.15 μm from the back of the first coating surface head 10 mm. The thermal transfer sheet of the present invention was obtained in the same manner as in Example 1.

<Comparative Example 4>
The thermal transfer of the present invention was carried out in the same manner as in Example 1 except that the dry thickness of the application surface of the release layer was changed to 0.45 μm, the thickness increase area was changed to 5 mm, and the dry thickness of the constant thickness area was changed to 0.5 μm. A sheet was obtained.

<Comparative Example 5>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the dry thickness of the application layer head of the release layer was changed to 0.3 μm and the dry thickness of the film thickness constant region was changed to 0.5 μm.

<Comparative Example 6>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the thickness increase region of the release layer was changed to 20 mm and the dry thickness of the constant thickness region was changed to 0.5 μm.

<Comparative Example 7>
A thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the thickness increase region of the release layer was changed to 30 mm and the dry thickness of the constant thickness region was changed to 0.7 μm.

<Printing>
Regarding the thermal transfer sheets of Examples 1 to 3 and Comparative Examples 1 to 7, each thermal transfer ink layer was transferred by a printer using a combination of the thermal transfer sheet and a transfer target, and an image was formed. For printing, two types of images, a full solid that transfers each thermal transfer ink layer with full energy and a half solid that transfers each thermal transfer ink layer with half energy, were alternately performed 100 sheets in succession.

  The following evaluation was performed about the image obtained by printing the thermal transfer sheet of Examples 1-3 and Comparative Examples 1-7. The results are shown in Table 1.

<Printing defects>
A case where black spots (including flakes) having a size of 0.05 mm2 or more are not generated with respect to the half solid images obtained by printing the thermal transfer sheets of Examples 1 to 3 and Comparative Examples 1 to 7. ○, the case where it occurred was evaluated as x.
<Thermal transfer properties>
For all the images obtained by printing the thermal transfer sheets of Examples 1 to 3 and Comparative Examples 1 to 7, the case where no transfer failure occurred was evaluated as ◯, and the case where it occurred was evaluated as ×.

  By using the thermal transfer sheet of the present invention, it has become possible to provide characters or images free from printing defects due to powder falling while ensuring the thermal transferability of the protective layer.

DESCRIPTION OF SYMBOLS 1 ... Thermal transfer sheet 2 ... Base material sheet 3 ... Thermal transfer ink layer 4 ... Protective layer 5 ... Heat-resistant slipping layer 6 ... Release layer 7 ... Release layer 7a .... Thickness increase region 7b ... Constant thickness region 8 ... Adhesive layer 9 ... Thermal transferable protective layer A ... Boundary line between thermal transferable ink layer and release layer

Claims (2)

A base sheet, a thermal transfer ink layer and a protective layer provided on one surface of the base sheet in the longitudinal direction of the base sheet, and a heat-resistant slip provided on the other side of the base sheet. A thermal transfer sheet formed by laminating a release layer, a release layer, and an adhesive layer in a surface sequential manner,
The release layer is disposed on a boundary line side with the thermal transfer ink layer, and a film thickness increasing region in which the film thickness increases as the distance from the boundary line increases in the longitudinal direction; A film thickness constant region whose thickness is constant with the same dimension as the maximum film thickness of the film thickness increase region in the direction, the length of the film thickness increase region is 1 and the minimum film thickness of the film thickness increase region is h _1, and the maximum thickness of the film thickness increased area and _{h 2, (h 2 -h 1} ) / l, and the value of _h 1 / _{h 2} is the formula,
7.0 × 10 ⁻⁶ ≦ (h ₂ −h ₁ ) /l≦1.5×10 ⁻⁵
0.6 ≦ h ₁ / h ₂ ≦ 0.8
The thermal transfer sheet characterized by satisfying.   The thermal transfer sheet according to claim 1, wherein the total thickness of the protective layer is constant in the longitudinal direction.

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