Thermal transfer sheet and use thereof

Abstract

To provide a thermal transfer sheet which is used for printing on an object by thermal transfer, has good adhesion and fastness between ink and the object, and has good sublimation resistance.SOLUTION: A thermal transfer sheet comprising a release film, an ink layer and a binder resin layer laminated in this order. The binder resin layer contains an acrylic resin having a weight average molecular weight of 50000 to 150,000 and a glass transition temperature of 15 to 25 °C. It is preferable that the acrylic resin contains an alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms as a constituent monomer. The thermal transfer sheet is thermocompression-bonded to the article body, and the release film is peeled off to produce an article including the article body, the binder resin layer, and the ink layer laminated in this order.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermal transfer sheet used for printing on an object by thermal transfer, and to uses thereof. [Background technology]

[0002] BACKGROUND ART As a method for printing a design onto textile products such as clothing, a method is known in which a thermal transfer sheet on which a design has been formed is heated and pressed onto the object to be printed, thereby thermally transferring the design.

[0003] Known examples of such thermal transfer sheets include those in which a pattern is formed on the surface of a peelable base film, and then an adhesive layer is formed on top of that (see, for example, Patent Document 1). It is disclosed that the adhesive layer can be made of various thermoplastic resins.

[0004] As one of such thermal transfer methods, DTF (Direct To Film) printing has been attracting attention in recent years.

[0005] DTF printing involves first forming an ink layer and a binder resin layer in that order on a release film, then thermally transferring the binder resin layer and ink layer onto the printing object, and then peeling off the release film, thereby forming an ink layer on the surface of the printing object, such as a textile product (see, for example, Patent Document 2). This method is environmentally friendly because it does not require the evaporation of large amounts of solvent or water during the printing process.

[0006] The binder resin layer functions as a binder that adheres the ink layer to the surface of the printing substrate. The resin layer is usually formed by supplying hot-melt powder onto the ink layer, allowing it to adhere, and then heating it to melt and solidify it. Such hot-melt powder is required to achieve adhesion and robustness between the ink and the printing substrate, and polyurethane resin is preferably used (see paragraph

[0132] of Patent Document 2).

[0007] On the other hand, although not related to the application of adhering ink to an object, Patent Documents 3 and 4 describe acrylic resin powder that can be used as a general hot melt adhesive. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-32727 [Patent Document 2] Japanese Patent Publication No. 2022-147673 [Patent Document 3] International Publication No. 2019 / 188930 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-128736 Summary of the Invention [Problem to be solved by the invention]

[0009] The polyurethane resin disclosed in Patent Document 2 has the advantage of good adhesion and fastness after thermal transfer.

[0010] However, when polyurethane resin is used, it has been found that pigments and dyes contained in the printed material, such as textiles, can migrate over time or after heat treatment into the binder resin layer and ink layer formed from the polyurethane resin, causing the color of the ink layer to bleed. This color transfer is particularly likely to occur when black or dark-colored textiles are used. Although it is desirable to suppress such color transfer, it has been difficult to suppress it with polyurethane resins. The property of being resistant to color transfer will be hereinafter referred to as sublimation resistance.

[0011] Patent Documents 3 and 4 describe acrylic resins that can be used as general hot melt adhesives, but there is no mention of using them as a binder resin layer that adheres ink to an object, and there is no consideration of adhesion, robustness, or sublimation resistance after thermal transfer. The acrylic resins disclosed in these documents cannot achieve these physical properties.

[0012] In view of the above-mentioned current situation, the present invention aims to provide a thermal transfer sheet used for printing on an object by thermal transfer, which has good adhesion and robustness between the ink and the object, and also has good sublimation resistance, and uses thereof. [Means for solving the problem]

[0013] The present inventors conducted extensive research to solve the above-mentioned problems and found that the problems can be solved by using an acrylic resin as a material constituting the binder resin layer of a thermal transfer sheet and controlling the weight-average molecular weight and glass transition temperature of the acrylic resin within specific ranges, thereby arriving at the present invention. That is, the present invention provides a thermal transfer sheet including a release film, an ink layer, and a binder resin layer laminated in this order, The present invention relates to a thermal transfer sheet, wherein the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C. The present invention also provides a method for producing the thermal transfer sheet, comprising the steps of: forming the ink layer on the surface of the release film; and forming the binder resin layer on the surface of the ink layer. The present invention further provides an article including an article body, a binder resin layer, and an ink layer laminated in this order, The present invention also relates to an article in which the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C. The present invention further provides a method for producing an article including an article body, a binder resin layer, and an ink layer laminated in this order, the method comprising the steps of: A step of thermocompression bonding the thermal transfer sheet to an article body; and and a step of peeling off the release film to obtain the article. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a thermal transfer sheet used for printing on an object by thermal transfer, which has good adhesion and robustness between the ink and the object, and also has good sublimation resistance, and uses thereof. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail. The thermal transfer sheet according to this embodiment is used for printing on an object by thermal transfer. The thermal transfer sheet includes a release film, an ink layer, and a binder resin layer laminated in this order, and the binder resin layer constitutes the outermost layer of the thermal transfer sheet.

[0016] (binder resin layer) The binder resin layer contains an acrylic resin. The binder resin layer may be composed solely of the acrylic resin, or may contain, in addition to the acrylic resin, a resin other than the acrylic resin or an inorganic substance. The proportion of the acrylic resin in the binder resin layer is preferably, for example, 70% by weight or more and 100% by weight or less. The lower limit may be 80% by weight or more, 90% by weight or more, or 95% by weight or more.

[0017] The acrylic resin refers to a thermoplastic resin containing a (meth)acrylic monomer as a constituent monomer. However, the acrylic resin may further contain a monomer other than the (meth)acrylic monomer as a constituent monomer. The term "(meth)acrylic" is used to refer collectively to acrylic and methacrylic.

[0018] The content of the (meth)acrylic monomer is preferably 50% by weight or more and 100% by weight or less of the total amount of monomers constituting the acrylic resin, and the lower limit may be 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more.

[0019] The (meth)acrylic monomer is not particularly limited, and examples thereof include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; alkoxy(meth)alkyl acrylates; (meth)acrylonitrile, substituted (meth)acrylonitrile, (meth)acrylamide, and 2-(dimethylamino)ethyl (meth)acrylate. The (meth)acrylic monomer may be used alone or in combination of two or more kinds, preferably in combination of two or more kinds, since this makes it easier to control the glass transition temperature of the acrylic resin.

[0020] Among these, (meth)acrylic acid alkyl esters are preferred, and methacrylic acid alkyl esters are particularly preferred. In this case, the methacrylic acid alkyl esters may be used alone, or the methacrylic acid alkyl esters may be used in combination with the acrylic acid alkyl esters and / or the aromatic vinyl compounds described below.

[0021] In particular, since it is easy to control the glass transition temperature of the acrylic resin within a predetermined range described below, it is preferable to use a (meth)acrylic acid alkyl ester having at least an alkyl group with a carbon number of 4 to 12, and it is particularly preferable to use a methacrylic acid alkyl ester having at least an alkyl group with a carbon number of 4 to 12. The content of such alkyl ester is preferably 50% by weight or more, and more preferably 60% by weight or more, of the total amount of monomers constituting the acrylic resin.

[0022] The constituent monomer other than the (meth)acrylic monomer is not particularly limited as long as it is a vinyl compound copolymerizable with the (meth)acrylic monomer, such as an aromatic vinyl compound.

[0023] The aromatic vinyl compound is not particularly limited, and examples thereof include unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; substituted vinyl aromatic compounds such as α-methylstyrene; ring-alkylated vinyl aromatic compounds such as 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; ring-alkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; ring-ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; and ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene. Among these, substituted or unsubstituted styrene is preferred, styrene and / or α-methylstyrene is more preferred, and styrene is particularly preferred. The aromatic vinyl compound may be used alone or in combination of two or more.

[0024] From the viewpoint of the physical properties of the binder resin layer, the acrylic resin is preferably a non-crosslinked acrylic resin that does not have a crosslinked structure, i.e., it is preferable that the acrylic resin does not contain a polyfunctional monomer such as allyl methacrylate or divinylbenzene as a constituent monomer.

[0025] (glass transition temperature) The glass transition temperature (hereinafter also referred to as "Tg") of the acrylic resin is set to 25°C or lower to improve adhesion and robustness between the ink and the printing object, and is preferably 20°C or lower. If the Tg of the acrylic resin exceeds 25°C, it becomes difficult to achieve sufficient adhesion and robustness. From the viewpoint of ease of recovery of the acrylic resin, it is desirable to set the lower limit of the Tg of the acrylic resin to 15°C or higher.

[0026] When the acrylic resin is a homopolymer formed from one type of monomer, the standard analytical value described in the Polymer Data Handbook compiled by the Society of Polymer Science, etc. can be used as the glass transition temperature of the acrylic resin. When the acrylic resin is a copolymer formed from n types of monomers, the Tg (°C) of the copolymer can be calculated from the following FOX formula using the standard analytical values ​​of Tg related to the homopolymers of each monomer. Formula: 1 / (273+Tg)=Σ(Wn / (273+Tgn)) In the formula, Wn represents the mass fraction of monomer n, and Tgn represents the standard analytical value of Tg (°C) of a homopolymer of monomer n, where the mass fraction is the ratio of the amount of monomer n charged to the total amount of all monomers charged.

[0027] The standard analytical values ​​of Tg (°C) of the homopolymers of each monomer are as follows: Methyl methacrylate: 105°C, n-butyl methacrylate: 20°C, n-butyl acrylate: -54°C, styrene: 100°C, 2-ethylhexyl acrylate: -70°C

[0028] (Weight average molecular weight) The weight-average molecular weight of the acrylic resin is set within the range of 50,000 to 150,000. The weight-average molecular weight is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC). If the weight-average molecular weight is less than 50,000, the adhesion or robustness between the ink and the printed object will be insufficient. On the other hand, if it is greater than 150,000, the resin will be difficult to melt during binder resin layer formation or thermal transfer, which may result in poor adhesion. The lower limit is preferably 80,000 or more. The upper limit is preferably 130,000 or less. The weight average molecular weight can be controlled by adjusting the amount of a chain transfer agent used during polymerization of the acrylic resin.

[0029] The binder resin layer according to this embodiment preferably contains inorganic particles in addition to the acrylic resin. This can prevent blocking during recovery of the acrylic resin. Materials constituting the inorganic particles are preferably those with a large specific surface area, such as silica, titanium dioxide, zinc oxide, and aluminum oxide.

[0030] Among these, titanium dioxide particles are preferably used in consideration of compatibility with white ink, which is a suitable example of a retention layer-forming ink described below. Furthermore, hydrophilic titanium dioxide particles are desirable in consideration of mixability with acrylic resins. The hydrophilic titanium dioxide particles refer to titanium dioxide particles that have not been subjected to a surface treatment, whereas titanium dioxide particles that have been subjected to a surface treatment using a silane compound or the like exhibit hydrophobic properties.

[0031] The amount of such inorganic particles, particularly titanium dioxide particles, used can be appropriately set from the viewpoint of the blocking suppression effect and the viewpoint of maintaining the flexibility of the binder resin layer, but is preferably 0.1 to 1 part by weight per 100 parts by weight of the acrylic resin. The lower limit is preferably 0.2 parts by weight or more, and the upper limit is preferably 0.8 parts by weight or less.

[0032] (Method of manufacturing acrylic resin) Acrylic resins can be produced by, for example, suspension polymerization, solution polymerization, etc., but suspension polymerization is preferred. Generally, suspension polymerization can produce large particles with a primary particle size of several μm to 1000 μm. Furthermore, particles obtained by suspension polymerization do not require post-polymerization steps such as coagulation or granulation and are easy to wash, which has the advantage of making it easy to remove the dispersion stabilizer or emulsifier used.

[0033] Suspension polymerization can be carried out by charging the above-mentioned monomers, dispersion stabilizer, polymerization initiator, chain transfer agent, etc. all at once, in portions, or continuously as required, and maintaining a predetermined polymerization temperature with stirring.

[0034] The dispersion stabilizer is not particularly limited, but examples thereof include the following: Anionic water-soluble polymers: polyacrylic acid, sodium polyacrylate, potassium polyacrylate, polymethacrylic acid, sodium polymethacrylate, potassium polymethacrylate, sodium methacrylate-methacrylic acid alkyl ester copolymer, etc. Nonionic water-soluble polymers: polyvinyl alcohol; modified celluloses such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose; polyvinylpyrrolidone, polyacrylamide; polyalkylene oxides such as polyethylene oxide, polyoxyethylene-polyoxypropylene block copolymer, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene nonylphenyl ether, polyethylene glycol fatty acid ester, and polyoxyethylene laurylamine. Poorly water-soluble inorganic salts: tricalcium phosphate, calcium sulfate, barium sulfate, sodium pyrophosphate, magnesium pyrophosphate, calcium carbonate, magnesium carbonate, titanium oxide, silicon dioxide, hydroxyapatite, kaolin, etc. The dispersion stabilizer may be used alone or in combination of two or more kinds, and among these, it is preferable to use modified cellulose and / or a poorly water-soluble inorganic salt.

[0035] From the viewpoints of dispersion stability and cost, the total amount of dispersion stabilizer added is preferably 0.2 to 15 parts by weight, more preferably 0.5 to 10 parts by weight, per 100 parts by weight of the total amount of monomers.

[0036] An emulsifier can also be used in combination as an auxiliary for the dispersion stabilizer. The emulsifier is not particularly limited, and anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used. From the viewpoint of maintaining stability during polymerization, anionic surfactants and nonionic surfactants are preferred. These emulsifiers may be used alone or in combination.

[0037] Furthermore, for the purpose of preventing emulsification, neutral salts such as sodium chloride, sodium sulfate, sodium dodecyl sulfate, and sodium nitrite may be added.

[0038] The polymerization initiator is preferably an initiator soluble in the monomer used, and is not particularly limited, but examples thereof include azo or diazo polymerization initiators such as 2,2'-azobis(dimethyl isobutyrate) and 2,2'-azobisisobutyronitrile; and peroxide polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, and lauryl peroxide. From the viewpoint of a balance between molecular weight adjustment and polymerization temperature control, lauryl peroxide is particularly preferred.

[0039] The amount of the polymerization initiator used is not particularly limited, but is preferably in the range of 0.02 to 2 parts by weight, more preferably 0.1 to 1 part by weight, per 100 parts by weight of the total amount of the monomers.

[0040] It is preferable to use a chain transfer agent to adjust the molecular weight of the acrylic resin. The chain transfer agent is not particularly limited, but examples thereof include mercaptans such as n-dodecyl mercaptan; thioglycolic acid esters such as octyl thioglycolate; and α-methylstyrene dimer. These may be used alone or in combination. Among these, n-dodecyl mercaptan is preferred because it has a large chain transfer constant and is relatively easy to suppress odor during melting.

[0041] The amount of the chain transfer agent used is preferably in the range of 0.1 to 2 parts by weight, more preferably 0.2 to 1 part by weight, and even more preferably 0.2 to 0.5 parts by weight, per 100 parts by weight of the total amount of monomers. By appropriately adjusting the amount within this range, it is possible to control the molecular weight of the polymer within the above-mentioned numerical range.

[0042] The temperature during polymerization is not particularly limited, but is, for example, 50 to 80° C., and preferably 60 to 80° C. After the polymerization progresses and the top of the exothermic peak can be confirmed, it is preferable to continue the polymerization at 80 to 90° C. for a certain period of time in order to increase the polymerization conversion rate.

[0043] After forming an acrylic resin by suspension polymerization, solid-liquid separation is performed to recover the acrylic resin. When a cellulose-based dispersion stabilizer is used in the suspension polymerization, if the dispersion stabilizer remains, the viscosity of the system increases due to the cellulose-based compound, making solid-liquid separation difficult. Therefore, by adding a cellulose-degrading enzyme before solid-liquid separation to decompose the cellulose-derived structure, the viscosity of the system can be reduced, making solid-liquid separation easier.

[0044] The amount of cellulolytic enzyme to be added is not particularly limited and can be set as appropriate, but is preferably 0.001 to 0.1 parts by weight per 100 parts by weight of the cellulose-based dispersion stabilizer.

[0045] Inorganic dispersion stabilizers may also be decomposed before solid-liquid separation. To decompose an inorganic dispersion stabilizer, an organic acid or an inorganic acid may be added. Among these, hydrochloric acid is preferably used from the viewpoints of treatment during solid-liquid separation and volatility.

[0046] In order to suppress blocking of the acrylic resin, it is preferable to add the inorganic particles described above to the acrylic resin. The timing of adding the inorganic particles is not particularly limited, and the inorganic particles may be added before solid-liquid separation or after solid-liquid separation and before drying.

[0047] (Release film) The release film is not particularly limited, but is preferably one having heat resistance and strength sufficient to withstand the thermal transfer conditions described below, and examples thereof include resin films and paper. Resin films are particularly preferred. The type of resin constituting the resin film is not particularly limited, but is preferably a polyester resin such as polyethylene terephthalate.

[0048] The surface of the release film on which ink is printed has releasability. To impart releasability, the film surface is preferably coated with a release agent. The type of release agent is not particularly limited, and examples include silicone-based, fluorine-containing silicone-based, and non-silicone-based release agents.

[0049] Furthermore, it is preferable that an ink-receiving layer be formed on the surface of the release film on which ink is printed, in order to ensure the clarity of the design, etc. Examples of materials constituting such ink-receiving layers include porous substances such as crystalline silica, amorphous silica, and aluminum silicate.

[0050] (ink layer) The ink constituting the ink layer is not particularly limited, and general pigments, dyes, etc. can be used.

[0051] (About the use of thermal transfer sheets) The thermal transfer sheet according to this embodiment is used to thermally transfer an ink layer onto the surface of a printing object. During thermal transfer, the thermal transfer sheet is placed on the surface of the printing object (also referred to as the transfer object). At this time, the thermal transfer sheet is placed so that the binder resin layer, which is the outermost layer of the thermal transfer sheet, is in contact with the surface of the printing object. In this state, the binder resin layer is thermocompression-bonded to the printing object by applying heat and pressure. After cooling, the release film is peeled off. Thereafter, heat pressing may be performed again to fix the ink layer to the surface of the printing object.

[0052] As a result, an article can be obtained in which a binder resin layer and an ink layer are laminated in this order on the surface of the printing substrate. The binder resin layer is a layer that realizes thermal transfer of the ink layer to the printing substrate and is interposed between the ink layer and the surface of the printing substrate, allowing the ink to adhere to the printing substrate.

[0053] The conditions for heating and pressing during thermal transfer are not particularly limited and may be set appropriately, but for example, the transfer can be carried out within the range of 100 to 200° C. using a heat press or iron.

[0054] The printing object is not particularly limited, but is particularly suitable for textile products. The textile product may be fabric or clothing (e.g., sportswear, T-shirts, underwear, sweatshirts, socks). The fibers may be natural or chemical.

[0055] The color of the textile product is not particularly limited, and it may be colored or uncolored. However, the thermal transfer sheet according to this embodiment has good sublimation resistance and is effective in suppressing color transfer from textile products to the ink layer surface over time or due to heat (transfer of dyes or pigments contained in textile products to the ink layer), making it particularly useful for printing on colored textile products (especially dark or black textile products). When the thermal transfer sheet according to this embodiment is used, changes in the appearance of the ink layer are unlikely to occur even when printing on colored textile products. Therefore, there is no need to limit the color of the textile product to be printed, and the range of textile products that can be printed on can be expanded.

[0056] The method for producing the thermal transfer sheet according to this embodiment is not particularly limited. First, an ink layer having a desired design is formed on the surface of a release film. The method for forming the ink layer is not particularly limited, and a known printing method such as inkjet printing may be used.

[0057] Next, a binder resin layer is formed on the ink layer. The method for forming the binder resin layer is not particularly limited, but examples include a method in which hot-melt powder composed of a raw material containing an acrylic resin is prepared, adhered to the surface of the ink layer, and then heated to melt and solidify, or a method in which a liquid in which a raw material containing an acrylic resin is dissolved or dispersed in a solvent or water is applied to the surface of the ink layer and then dried.

[0058] According to a preferred embodiment, the thermal transfer sheet according to the embodiment can be produced by DTF (Direct To Film) printing.

[0059] DTF printing is a method in which a hot melt powder is used to produce a thermal transfer sheet in which an ink layer and a binder resin layer are laminated in that order on a release film, and then the thermal transfer sheet is used to thermally transfer the binder resin layer and ink layer onto the surface of the object to be printed.

[0060] An example of a specific procedure for DTF printing will be described below. First, a desired design is printed on a release film (also called a peeling film or a base film) using design ink, then ink for forming a retention layer is printed on top of the design, and hot melt powder is then supplied onto the ink for forming the retention layer and allowed to adhere.

[0061] The design ink is not particularly limited, but is preferably a water-based ink containing a pigment. The type of pigment is not particularly limited, and examples thereof include azo-, indanthrene-, or imidazolone-based yellow pigments; azo-, quinacridone-, cromophthalic-, or diketopyrrolopyrrole-based red pigments; phthalocyanine-based blue pigments; carbon black; phthalocyanine-based green pigments; indanthrene-based orange pigments; oxazoline-based purple pigments; and white pigments such as titanium oxide, aluminum silicate, and zinc oxide. The water-based ink may also contain an organic resin for fixing to improve fastness.

[0062] The ink for forming the retention layer is not particularly limited, but is preferably a water-based ink containing a pigment. The same inks as the specific examples of the design inks described above can be used. Ink that does not contain a colorant such as a pigment, for example, a colorless ink or a colorless transparent ink, can also be used. Among these, it is preferable to use a white concealing ink containing a white pigment such as titanium oxide.

[0063] The method for printing the design ink or the ink for forming the retaining layer onto the release film is not particularly limited, but can be carried out by inkjet printing.

[0064] The hot melt powder is preferably supplied to the ink layer surface when the ink for forming the retention layer is not completely dry and is in a wet state, so that the hot melt powder adheres to the wet surface of the ink layer for forming the retention layer.

[0065] The method for supplying the hot melt powder is not particularly limited, but the resin powder may be scattered from above by utilizing gravity, or may be supplied by utilizing air currents or static electricity. Alternatively, the hot melt powder may be supplied by passing a release film having an ink layer through a container storing the hot melt powder.

[0066] Next, it is desirable to remove unnecessary resin powder from the supplied resin powder from the release film having the ink layer. The method for doing so is not particularly limited, but examples include a method of applying vibration to the back surface of the release film by means of striking or rotating contact with a rotating brush to cause the unnecessary resin powder to fall off, a method of suctioning and removing the unnecessary resin powder, and a method of applying an air current to remove the unnecessary resin powder.

[0067] Next, with the hot-melt powder attached to the surface of the ink layer for forming a retention layer, a heat treatment is performed to melt the resin powder, and then the resin powder is solidified and integrated by cooling. This forms a binder resin layer on the surface of the ink for forming a retention layer. At the same time, the drying of the ink layer can be accelerated.

[0068] The conditions for the heat treatment when forming the binder resin layer are not particularly limited, but for example, the heating temperature may be about 100 to 160° C. and the heating time may be about 1 to 5 minutes. Cooling may be natural cooling or forced cooling using a cooling device.

[0069] As a result of the above, a thermal transfer sheet is formed in which a design ink layer, a retention layer-forming ink layer, and a binder resin layer are laminated in this order on the surface of the release film. Such a thermal transfer sheet also constitutes one aspect of the present invention. The design ink layer and the retention layer-forming ink layer are sometimes collectively referred to as ink layers. However, the formation of the design ink layer can be omitted.

[0070] The thermal transfer sheets described above can be produced using a commercially available DTF printer.

[0071] The following items list preferred aspects of the present disclosure, but the present invention is not limited to the following items. [Item 1] A thermal transfer sheet comprising a release film, an ink layer, and a binder resin layer laminated in this order, The thermal transfer sheet, wherein the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C. [Item 2] the acrylic resin contains alkyl (meth)acrylate as a constituent monomer, Item 2. The thermal transfer sheet according to item 1, wherein the alkyl (meth)acrylate comprises an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms. [Item 3] the binder resin layer further contains titanium dioxide particles, 3. The thermal transfer sheet according to item 1 or 2, wherein the content of the titanium dioxide particles is 0.1 to 1 part by weight based on 100 parts by weight of the acrylic resin. [Item 4] A method for producing the thermal transfer sheet according to any one of items 1 to 3, forming the ink layer on the surface of the release film; forming the binder resin layer on the surface of the ink layer. [Item 5] forming the binder resin layer on the surface of the ink layer, 5. The manufacturing method according to Item 4, further comprising the steps of: preparing a hot-melt powder containing the acrylic resin; supplying the hot-melt powder to a surface of the ink layer; and melting and solidifying the hot-melt powder on the ink layer to form the binder resin layer. [Item 6] An article comprising an article body, a binder resin layer, and an ink layer laminated in this order, The article, wherein the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C. [Item 7] 7. The article according to item 6, wherein the article body is a textile product. [Item 8] A method for producing an article including an article body, a binder resin layer, and an ink layer laminated in this order, comprising: A step of thermocompression bonding the thermal transfer sheet according to any one of items 1 to 3 to an article body; and and peeling off the release film to obtain the article. [Example]

[0072] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0073] (Method for measuring volume average particle size) The volume average particle size of the powder was measured using a measuring device based on the laser diffraction / scattering method, MT3000II manufactured by Microtrac Corp. The measurement sample was prepared by dispersing the collected powder in soapy water.

[0074] (Method for measuring compacted bulk density) The bulk density was measured by adding powder to a 25 mL measuring cylinder and tapping it. The powder was gradually added while tapping, and when the powder volume stopped moving from 20 mL, the weight of the powder was measured and the weight / volume (= 20 cm 3 ) was calculated.

[0075] (Method for measuring weight-average molecular weight) The weight-average molecular weight was determined by dissolving a sample in tetrahydrofuran (THF), filtering the soluble fraction through a filter with a filter diameter of 0.2 μm, and then using a high-speed GPC system (HLC-8220, manufactured by Tosoh Corporation) (sample solution: 20 mg sample / 10 mL THF, columns: one TSKguardcolumn SuperHZ-H and two TSKgel SuperHZM-H, both manufactured by Tosoh Corporation, column temperature: 40°C, detector: differential refractometer, flow rate: 0.35 mL / min, injection volume: 10 μL, calibration curve: standard polystyrene).

[0076] Example 1 800g of deionized water, 0.55g of disodium hydrogen phosphate, 82.5g of 10% tribasic calcium phosphate solution, and 0.11g of sodium nitrite were charged into a 3L polymerization reactor. Separately, 330g of butyl methacrylate, 104.5g of butyl acrylate, and 115.5g of methyl methacrylate were mixed, and then 1.1g of normal dodecyl mercaptan and 3.3g of lauryl peroxide were dissolved in the mixture. After confirming dissolution, the monomer mixture was charged into the 3L polymerization reactor, allowed to stand for a while, and then stirred at 300 rpm for 10 minutes. After stirring, 110g of 2% hydroxypropyl methylcellulose was added and the temperature was raised to 70°C while flowing nitrogen to initiate polymerization. After confirming the exothermic peak due to polymerization, the temperature was raised to 85°C and held for 3 hours to complete the polymerization, yielding a suspension of acrylic resin particles.

[0077] After polymerization, the suspension was cooled to below 50°C, 0.01 g of cellulose-degrading enzyme was added, and the mixture was stirred for 30 minutes, resulting in the decomposition of the cellulose-derived structure of hydroxypropyl methylcellulose. Furthermore, 165 g of 10% hydrochloric acid was added to decompose tribasic calcium phosphate. The suspension after the treatment was subjected to solid-liquid separation and then washed with water to obtain a dehydrated cake. 2.8 g of hydrophilic titanium dioxide (AEROXIDE P25, manufactured by Nippon Aerosil Co., Ltd.) was mixed with this dehydrated cake and then dried to obtain a spherical acrylic resin particle powder. The volume average particle diameter of this powder was 203 μm, and the compacted bulk density was 0.72 g / cm. 3 The weight average molecular weight of the acrylic resin was 128,000 and the Tg was 14.8°C.

[0078] Example 2 550 g of deionized water, 110 g of 10% tribasic calcium phosphate solution, and 55 g of 1% sodium dodecylbenzenesulfonate solution were charged into a 3-L polymerization reactor. Separately, 330 g of butyl methacrylate, 88 g of butyl acrylate, and 132 g of methyl methacrylate were mixed, and then 1.1 g of normal dodecyl mercaptan and 3.3 g of lauryl peroxide were dissolved in the mixture. After confirming dissolution, the monomer mixture was charged into the 3-L polymerization reactor, allowed to stand for a while, and then stirred at 300 rpm for 10 minutes. After stirring, the temperature was raised to 70 °C while flowing nitrogen to initiate polymerization. After confirming the exothermic peak due to polymerization, the temperature was raised to 85 °C and held for 3 hours to complete the polymerization, yielding a suspension of acrylic resin particles.

[0079] After polymerization, the suspension was cooled to below 50°C, and 165 g of 10% hydrochloric acid was added to decompose the tricalcium phosphate. The suspension after the treatment was subjected to solid-liquid separation and then washed with water to obtain a dehydrated cake. 2.8 g of hydrophilic titanium dioxide (AEROXIDE P25, manufactured by Nippon Aerosil Co., Ltd.) was mixed with this dehydrated cake and then dried to obtain a spherical acrylic resin particle powder. The volume average particle diameter of this powder was 124 μm, and the compacted bulk density was 0.69 g / cm. 3 The weight average molecular weight of the acrylic resin was 129,000 and the Tg was 19.7°C.

[0080] Examples 3 to 9 A powder of spherical acrylic resin particles was obtained in the same manner as in Examples 1 or 2, except that the types and amounts of materials used were changed according to the description in Table 1. The volume average particle size, packed bulk density, weight average molecular weight and Tg of the acrylic resin of the powder are shown in Table 1.

[0081] (Comparative Example 1) 800g of deionized water, 0.55g of disodium hydrogen phosphate, 66g of 10% tribasic calcium phosphate solution, and 0.11g of sodium nitrite were charged into a 3L polymerizer. Separately, 330g of butyl methacrylate, 88g of butyl acrylate, and 132g of methyl methacrylate were mixed, and then 4.4g of normal dodecyl mercaptan and 5.5g of lauryl peroxide were dissolved in the mixture. After confirming dissolution, the monomer mixture was charged into the 3L polymerizer, allowed to stand for a while, and then stirred at 250 rpm for 10 minutes. After stirring, 55g of 2% hydroxypropyl methylcellulose was added and the mixture was heated to 70°C under nitrogen flow to initiate polymerization. After confirming the exothermic peak due to polymerization, the mixture was heated to 85°C and held for 3 hours to complete the polymerization, yielding a suspension of acrylic resin particles.

[0082] After polymerization, the suspension was cooled to below 50°C, 0.01 g of cellulose-degrading enzyme was added, and the mixture was stirred for 30 minutes, resulting in the decomposition of the cellulose-derived structure of hydroxypropyl methylcellulose. Furthermore, 165 g of 10% hydrochloric acid was added to decompose tribasic calcium phosphate. The suspension after the treatment was subjected to solid-liquid separation and then washed with water to obtain a dehydrated cake. 2.8 g of hydrophilic titanium dioxide (AEROXIDE P25, manufactured by Nippon Aerosil Co., Ltd.) was mixed with this dehydrated cake and then dried to obtain a spherical acrylic resin particle powder. The powder had a volume-average particle diameter of 220 μm and a compacted bulk density of 0.75 g / cm. 3 The weight average molecular weight of the acrylic resin was 32,000, and the polymer Tg was 19.7°C.

[0083] (Comparative Examples 2 to 4) A powder of spherical acrylic resin particles was obtained in the same manner as in Comparative Example 1, except that the types and amounts of materials used were changed according to the description in Table 1. The volume average particle size, packed bulk density, weight average molecular weight and Tg of the acrylic resin of the powder are shown in Table 1.

[0084] (Evaluation method) The acrylic resin particle powders obtained in each Example or Comparative Example, or polyurethane powder (volume average particle diameter 180 μm, irregular shape, polymer Tg: −48° C.) in Comparative Example 5 were used to carry out the following evaluations.

[0085] (Coating onto polyester resin film) A 25% titanium oxide white pigment dispersion was applied to one side of a polyester resin film (100 μm thick) coated with a silicone wax-containing release agent using a No. 26 bar coater and dried at 70°C for 1 minute to form a white ink layer. The acrylic resin particle powder or polyurethane powder obtained in each Example or Comparative Example was sprinkled on the surface of the white ink layer so that the powder adhered to the entire white ink layer. The film was then tapped to remove excess powder. The film was then heated at 125°C for 3 minutes and 30 seconds to melt and solidify the powder, forming a binder resin layer.

[0086] (Transfer process onto textile fabric) The film with the white ink layer and binder resin layer formed was placed on the surface of a black textile fabric with the binder resin layer facing the textile fabric, pressed at 150°C for 15 seconds, and cooled. After cooling, the polyester resin film was peeled off and pressed again at 150°C for 15 seconds, leaving the white ink printed on the textile fabric. The following evaluations were carried out using this textile fabric.

[0087] (Evaluation of Adhesion) After applying the adhesive cloth tape to the printed surface of the textile fabric, the surface of the adhesive tape was rubbed with the cap of a pen 50 times to firmly adhere the adhesive tape to the textile fabric, and then the adhesive tape was quickly peeled off by pulling it vertically. After peeling, it was checked whether the printed surface was adhering to the adhesive surface of the adhesive tape, and the adhesion to the textile fabric was evaluated. The evaluation criteria were as follows: Good: The printed surface does not adhere to the adhesive surface at all. ×: The printed surface is attached to the adhesive surface.

[0088] (Evaluation of washing resistance) Based on the household washing machine method (JIS L 1930), a textile fabric printed with white ink was washed 10 times in a washing machine using the C4M method, and the printed surface of the textile fabric was checked for peeling. The evaluation criteria were as follows: ⊚: No peeling is observed on the printed surface. ◯: Minute peeling is observed, but it is not noticeable macroscopically. △: Some peeling is observed. ×: Peeling is observed over the entire surface.

[0089] (Evaluation of sublimation resistance) Fabrics printed with white ink were heated at 60°C for 48 hours to check whether the black pigment contained in the fabric rose to the printed surface. If the printed surface changed from white to a dark color or black, it was judged to have poor sublimation resistance. ◎: No change in white color was observed compared to before heating. ◯: There is a slight change in the white color, but it is not a problem. △: A change to a darker color can be recognized. ×: Discolored to black. The results of each evaluation are shown in Table 1.

[0090] [Table 1]

[0091] From Table 1, it can be seen that the acrylic resins of the examples have good adhesion after thermal transfer, fastness (washing resistance), and sublimation resistance.

[0092] On the other hand, in Comparative Example 1, the weight-average molecular weight of the acrylic resin was smaller than the specified range, and in Comparative Example 2, the weight-average molecular weight was larger than the specified range. In both cases, the adhesion and robustness after thermal transfer, as well as the sublimation resistance, were insufficient. In Comparative Example 3, the glass transition temperature of the acrylic resin was lower than the specified range, causing blocking during drying and making it impossible to recover the acrylic resin.In Comparative Example 4, the glass transition temperature was higher than the specified range, and it was found that the adhesion and robustness after thermal transfer were insufficient. Furthermore, it is clear that the sublimation resistance is insufficient in Comparative Example 5, which uses polyurethane.

Claims

1. A thermal transfer sheet comprising a release film, an ink layer, and a binder resin layer laminated in this order, The thermal transfer sheet, wherein the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C.

2. the acrylic resin contains alkyl (meth)acrylate as a constituent monomer, The thermal transfer sheet according to claim 1 , wherein the alkyl (meth)acrylate comprises an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms.

3. the binder resin layer further contains titanium dioxide particles, 2. The thermal transfer sheet according to claim 1, wherein the content of the titanium dioxide particles is 0.1 to 1 part by weight per 100 parts by weight of the acrylic resin.

4. A method for producing the thermal transfer sheet according to any one of claims 1 to 3, comprising: forming the ink layer on the surface of the release film; forming the binder resin layer on the surface of the ink layer.

5. forming the binder resin layer on the surface of the ink layer, 5. The manufacturing method according to claim 4, further comprising the steps of: preparing a hot-melt powder containing the acrylic resin; supplying the hot-melt powder to a surface of the ink layer; and melting and solidifying the hot-melt powder on the ink layer to form the binder resin layer.

6. An article comprising an article body, a binder resin layer, and an ink layer laminated in this order, The article, wherein the binder resin layer contains an acrylic resin having a weight average molecular weight of 50,000 to 150,000 and a glass transition temperature of 15 to 25°C.

7. The article according to claim 6 , wherein the article body is a textile product.

8. A method for producing an article including an article body, a binder resin layer, and an ink layer laminated in this order, comprising: A step of thermocompression bonding the thermal transfer sheet according to any one of claims 1 to 3 to an article body; and and peeling off the release film to obtain the article.

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