Release agent and heat transfer sheet

Abstract

The present invention provides a release agent that uses an aqueous medium and exhibits excellent stain resistance and alcohol resistance to the release layer after heat transfer, as well as a heat transfer sheet that uses the same. To provide. [Solution] A release agent for forming a release layer of a heat transfer sheet, the release agent comprising at least (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), and a heat transfer sheet having a base film, a release layer provided on one side of the base film, and an ink layer provided on the release layer, wherein the release layer is a layer formed by the release agent comprising at least (meth)acrylic resin (A), a curing agent (B), and an aqueous medium (C).

Description

【Technical Field】 【0001】 The present invention relates to a release agent for a thermal transfer sheet and a thermal transfer sheet using the same. 【Background Art】 【0002】 Conventionally, as a method of forming a pattern layer including characters, symbols, images, etc. on the surface of an object such as plastic, metal, glass, etc., a method using a thermal transfer sheet is known. Specifically, it is a method of bringing a thermal transfer sheet having a transfer layer with a pattern layer on one side of a base film into close contact with the surface of the object and heating from the back surface of the thermal transfer sheet to thermally transfer the transfer layer. 【0003】 Generally, a thermal transfer sheet has a structure in which a release layer, an ink layer, and a heat seal (adhesive) layer are sequentially laminated on a base film. The release layer, which is one of the components, is formed by a release agent containing a resin, an additive, a diluent, etc. The release agent is required to have adhesion to the base film during circulation, while it is required to be easily peeled off during thermal transfer. Further, since the release layer becomes the outermost layer in the transferred material after thermal transfer, stain resistance, scratch resistance, alcohol resistance, etc. are also required. Furthermore, in recent years, environmental consideration is also required from the perspective of SDGs. 【0004】 Many release agents use an organic solvent as a medium (see, for example, Patent Document 1), but in consideration of the environment, studies on release agents using an aqueous medium have begun. However, release agents using an aqueous medium may be inferior in stain resistance and alcohol resistance to the release layer after thermal transfer, and at present, those that satisfy all the required characteristics have not yet been obtained. 【Prior Art Documents】 【Patent Documents】 【0005】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2010-76331 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0006】 The object of the present invention is to provide a release agent that uses an aqueous medium and has excellent stain resistance and alcohol resistance to the release layer after heat transfer, and a heat transfer sheet that uses the same. [Means for solving the problem] 【0007】 As a result of diligent research, the present inventors have found that a release agent containing at least (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C) solves the above problem. 【0008】 In other words, the present invention provides a release agent for forming a release layer of a thermal transfer sheet, which contains at least a (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), wherein the (meth)acrylic resin (A) contains at least a (meth)acrylic resin (a1) having a glass transition temperature (Tg) of 50°C or higher. 【0009】 The present invention also provides the release agent described above, wherein the curing agent (C) is a silane coupling agent. 【0010】 The present invention also provides the release agent described above, wherein the (meth)acrylic resin further contains a (meth)acrylic resin (a2) having a lower glass transition temperature (Tg) than the (meth)acrylic resin (a1). 【0011】 The present invention also provides the release agent described above, wherein the glass transition temperature of the (meth)acrylic resin (a2) is 0°C or higher and 50°C or lower. 【0012】 The present invention further provides the stripping agent described above, which contains wax (D). 【0013】 The present invention also provides the stripping agent described above, wherein the average particle size of the wax (D) is 2 μm or less. 【0014】 The present invention also provides the stripping agent described above, wherein the aqueous medium is water alone, or a mixture of water and an organic solvent that is miscible with water. 【0015】 The present invention also provides a thermal transfer sheet comprising a base film, a release layer provided on one side of the base film, and an ink layer provided on the release layer, wherein the release layer contains at least (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), and the (meth)acrylic resin (A) is formed of a release agent containing at least (meth)acrylic resin (a1) having a glass transition temperature (Tg) of 50°C or higher. 【0016】 The present invention also provides the thermal transfer sheet described above, having a heat seal layer on top of the ink layer. 【0017】 The present invention also provides the thermal transfer sheet described above, wherein the ink layer is a layer formed from an ink composition containing a curing agent. [Effects of the Invention] 【0018】 The present invention provides a release agent that uses an aqueous medium and exhibits excellent ink transfer properties and alcohol resistance onto a release layer coated with the release agent, and also provides a thermal transfer sheet that uses this release agent. [Modes for carrying out the invention] 【0019】 The present invention will be described in detail below. All instances of "parts" refer to "parts by mass," and all instances of "%" refer to "percentage by mass." 【0020】 ((meth)acrylic resin) The (meth)acrylic resin (A) used in the present invention is not particularly limited and includes homopolymers or copolymers of (meth)acrylate, and copolymers obtained by copolymerizing (meth)acrylate with vinyl monomers that can copolymerize with (meth)acrylate. Furthermore, it is preferable that the copolymer has an acid value in order to impart water dispersibility and water solubility. In this invention, "(meth)acrylate" refers to either acrylate or methacrylate, or both, and "(meth)acrylic" refers to either acrylic or methacrylic, or both. 【0021】 Examples of (meth)acrylates and vinyl monomers that can copolymerize with (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopropyl (meth)acrylate, and isobutyl (meth)acrylate; aromatic (meth)acrylates such as benzyl (meth)acrylate; and hydroxyl group-containing compounds such as 2-hydrodoxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Monomers; alkyl polyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and methoxypolypropylene glycol mono(meth)acrylate; fluorinated (meth)acrylates such as perfluoroalkylethyl (meth)acrylate; styrene, styrene derivatives (p-dimethylsilylstyrene, (p-vinylphenyl)methyl sulfide, p-hexynylstyrene, p-methoxystyrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert- Aromatic vinyl compounds such as t-butylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, and 1,1-diphenylethylene; glycidyl (meth)acrylate, epoxy (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylene glycol tetra(meth)acrylate, 2-hydroxy-1,3-diacryloxypropane, 2,2-bis[4-(acryloxymethoxy)phenyl]propane, 2,2-bi (meth)acrylate compounds such as s[4-(acryloxyethoxy)phenyl]propane, dicyclopentenyl (meth)acrylate, tricyclodecanyl (meth)acrylate, tris(acryloxyethyl) isocyanurate, and urethane (meth)acrylate; (meth)acrylates having alkylamino groups such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylate; vinylpyridine compounds such as 2-vinylpyridine, 4-vinylpyridine, and naphthylvinylpyridine;Examples of the conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-cyclohexadiene and the like. These monomers can be used alone or in combination of two or more. Among them, copolymers of an alkyl (meth) acrylate and an aromatic vinyl compound are preferred, and copolymers of an alkyl (meth) acrylate and styrene are particularly preferred.; 【0022】 In addition, for the purpose of introducing one or more acidic groups selected from the group consisting of a carboxyl group and a carboxylate group in which the carboxyl group is neutralized by a basic compound, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, β-(meth)acryloyloxyethyl hydrogen succinate, β-(meth)acryloyloxyethyl hydrogen phthalate and other (meth)acrylic monomers having a carboxyl group are copolymerized to obtain a copolymer having an acid value. When introducing an acidic group, as will be described in detail later, it is preferable to appropriately adjust the monomer amount so that the acid value falls within a desired range. 【0023】 The copolymer can be produced, for example, by polymerizing various monomers in a temperature range of 50°C to 180°C in the presence of a polymerization initiator, and a temperature range of 80°C to 150°C is more preferable. Examples of the polymerization method include bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like. Examples of the polymerization mode include random copolymer, block copolymer, graft copolymer and the like. 【0024】 The copolymer used in the present invention may be of a core-shell type. In the present invention, the core-shell type resin refers to a state in which the polymer (a2) is dispersed in an aqueous medium by the polymer (a1). Usually, the polymer (a1) exists on the outermost part of the resin particles to form a shell part, and a part or all of the polymer (a2) often forms a core part. Hereinafter, in the present invention, the resin forming the shell part is referred to as polymer (a1), and the resin forming the core part is referred to as polymer (a2). 【0025】 [Polymer (a1) constituting the shell part] The core - shell type resin used in the present invention is preferably composed of a polymer (a1) constituting the shell part, which contains an acrylic resin having at least one hydrophilic group selected from the group consisting of a carboxyl group and a carboxylate group formed by neutralizing the carboxyl group. At that time, the acid value of the shell part is preferably in the range of 40 mgKOH / g or more and 250 mgKOH / g or less, and more preferably 120 mgKOH / g or less. 【0026】 The carboxyl group of the polymer (a1) constituting the shell part is preferably neutralized with a basic compound to form a carboxylate group. 【0027】 As the basic compound that can be used for the neutralization, for example, ammonia, triethylamine, morpholine, monoethanolamine, diethylethanolamine, etc. can be used. Using ammonia or triethylamine is preferable for further improving the hot - water resistance, corrosion resistance and chemical resistance of the coating film. 【0028】 The amount of the basic compound used is preferably in the range of [basic compound / carboxyl group]=0.2 - 2 (molar ratio) with respect to the total amount of the carboxyl groups of the polymer (a1) in order to further improve the water - dispersion stability of the obtained core - shell type resin. 【0029】 Among the monomers having a polymerizable unsaturated double bond, it is preferable to use a product obtained by polymerizing a (meth)acrylic monomer containing a (meth)acrylic monomer having a carboxyl group. In particular, as the polymer (a1), in order to adjust the glass transition temperature (Tg1) of the polymer (a1) to the range of 20°C to 100°C, it is more preferable to use a product obtained by copolymerizing methyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylic acid, etc. for forming a coating film with excellent film - forming properties and excellent hot - water resistance, corrosion resistance and chemical resistance. 【0030】 [Polymer (a2) constituting the core] The polymer (a2) constituting the core portion can be a copolymer such as an acrylic monomer, similar to the acrylic resin described above. In this case, the weight-average molecular weight of the core is preferably in the range of 200,000 to 3,000,000, and more preferably 800,000 or more. The Tg is preferably in the range of -30°C to 30°C. 【0031】 The polymer (a2) constituting the core portion can be a copolymer such as an acrylic monomer, similar to the acrylic resin described above, but it is preferable to manufacture it in an aqueous medium. Specifically, it can be manufactured by supplying the monomer and a polymerization initiator, etc., all at once or sequentially to a reaction vessel containing an aqueous medium and polymerizing them. In this case, a pre-emulsion may be prepared in advance by mixing the monomer, the aqueous medium, and a reactive surfactant, etc., as needed, and then this pre-emulsion and the polymerization initiator, etc., may be supplied to a reaction vessel containing an aqueous medium and polymerized. 【0032】 Examples of polymerization initiators that can be used when producing the polymer (a2) include radical polymerization initiators such as persulfates, organic peroxides, and hydrogen peroxide, and azo initiators such as 4,4'-azobis(4-cyanovaleric acid) and 2,2'-azobis(2-amidinopropane) dihydrochloride. Furthermore, the radical polymerization initiator may be used in combination with a reducing agent, as described later, as a redox polymerization initiator. 【0033】 Examples of persulfates that can be used include potassium persulfate, sodium persulfate, and ammonium persulfate. Examples of organic peroxides that can be used include benzoyl peroxide, lauroyl peroxide, decanoyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, t-butyl peroxylaurate, t-butyl peroxybenzoate, cumene hydroperoxide, paramenthane hydroperoxide, and t-butyl hydroperoxide. 【0034】 Furthermore, as the reducing agent, for example, ascorbic acid and its salts, erythorbic acid and its salts (such as sodium salts), tartaric acid and its salts, citric acid and its salts, metal salts of formaldehyde sulfoxylate, sodium thiosulfite, sodium bisulfite, ferric chloride, etc. can be used. 【0035】 The amount of polymerization initiator used should be sufficient to ensure smooth polymerization. However, from the viewpoint of maintaining the excellent corrosion resistance of the resulting coating film, a smaller amount is preferable, preferably 0.01% to 0.5% by mass relative to the total amount of monomer used in the production of the vinyl polymer (a2). Furthermore, when the polymerization initiator is used in combination with the reducing agent, it is preferable that the total amount of both used is also within the above range. 【0036】 Furthermore, when producing the pre-emulsion, reactive surfactants, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc., may be used. 【0037】 The acid value of the copolymer is preferably 20 mg KOH / g or more and 120 mg KOH / g or less, and more preferably 25 mg KOH or more. If the acid value is 20 mg KOH / g or more, the abrasion resistance, water abrasion resistance, and scratch resistance of the laminate can be improved when a curing agent is added. 【0038】 The acid value referred to here indicates the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 gram of resin. 【0039】 The weight-average molecular weight of the copolymer is preferably in the range of 5,000 to 100,000. If the weight-average molecular weight is 5,000 or more, the heat resistance of the resin film tends to not decrease, and the abrasion resistance and water abrasion resistance of the laminate tend to be maintained. If it is 100,000 or less, the laminate tends to have both substrate adhesion and scratch resistance. 【0040】 The glass transition temperature (Tg) of the copolymer is preferably 50°C to 110°C, and more preferably 80°C to 100°C. If the Tg of the copolymer is 50°C or higher, it is possible to improve the surface properties of the transfer obtained by thermal transfer using a thermal transfer sheet, including alcohol resistance. In addition, the peelability when peeling the base film after thermal transfer can also be improved. If the peelability is too high, it may cause a load when peeling the film during thermal transfer, potentially leading to a decrease in productivity. On the other hand, if the peelability is too low, it may cause problems such as blocking due to a decrease in adhesion between the base film and the release layer. Therefore, control of the peelability by selecting an appropriate resin is required. 【0041】 In the present invention, only (meth)acrylic resin (a1) having a glass transition temperature of 50°C or more and 110°C or less may be used, or a mixture of multiple (meth)acrylic resins with different Tg values ​​may be used. An example of such a combination of multiple (meth)acrylic resins with different Tg values ​​is a combination of (meth)acrylic resin (a1) having a glass transition temperature of 50°C or more and 110°C or less, and (meth)acrylic resin (a2) having a glass transition temperature of 0°C or more and less than 50°C. In this case, the ratio of (a1) to (a2) is preferably in the range of 100:0 to 50:50, and more preferably in the range of 100:0 to 60:40. 【0042】 In this case, (a1) is preferably a styrene-acrylic resin, and more preferably an ammonium salt of styrene-acrylic resin. (a2) is preferably a styrene-acrylic resin, and more preferably an ammonium salt of styrene-acrylic resin. 【0043】 Furthermore, the glass transition temperature (Tg1) refers to the so-called calculated glass transition temperature, which is the value calculated by the following method. (Formula 1) 1 / Tg(K)=(W1 / T1)+(W2 / T2)+...(Wn / Tn) (Equation 2) Tg(°C) = Tg(K) - 273 In Equation 1, W1, W2, ...Wn represent the mass percentage of each monomer relative to the total mass of monomers used in the production of the polymer, and T1, T2, ...Tn represent the glass transition temperature (K) of the homopolymer of each monomer. The values ​​of T1, T2, ...Tn are those listed in the Polymer Handbook (Fourth Edition, edited by J. Brandrup, E. Himmmergut, and E. A. Grulke). Furthermore, for homopolymers of each monomer whose glass transition temperatures are not listed in the Polymer Handbook, the glass transition temperatures were measured using a differential scanning calorimeter "DSC Q-100" (manufactured by TA Instrument Co., Ltd.) in accordance with JIS K7121. Specifically, the polymer, from which the solvent had been completely removed by vacuum suction, was subjected to a heating rate of 20°C / min, and the change in heat was measured in the range of -100°C to +200°C. The point where a straight line equidistant in the vertical direction from the extended straight line of each baseline intersects with the curve of the stepwise transition portion of the glass transition was defined as the glass transition temperature. 【0044】 The (meth)acrylic resin (A) is preferably 50% by mass or more and 100% by mass or less, relative to the solid content of the release agent of the present invention, and more preferably 75% by mass or more and 95% by mass or less. 【0045】 (Aqueous medium (B) The aqueous medium (B) used in the present invention may be the polymerization solvent used when polymerizing the (meth)acrylic resin (A), or it may be added when neutralizing the (meth)acrylic resin (A) polymerized by solution polymerization. Specifically, examples include water, organic solvents miscible with water, and mixtures thereof. Examples of organic solvents miscible with water include alcohol solvents such as methanol, ethanol, n-propanol, and isopropanol; ketone solvents such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycols; and lactam solvents such as N-methyl-2-pyrrolidone. In the present invention, water alone may be used, a mixture of water and an organic solvent miscible with water may be used, or an organic solvent miscible with water may be used alone. 【0046】 (Hardening agent (C)) The present invention contains a curing agent (C). The curing agent can be any curing agent that can react and cure with the functional groups contained in the (meth)acrylic resin (A), and specific examples include silane coupling agents, epoxy compounds, carbodiimides, aziridines, etc. Among these, silane coupling agents are preferred. 【0047】 (Silane coupling agent) The silane coupling agent used in the present invention is a silane compound having one or more hydrolyzable groups and one or more organic polymerizable functional groups in one molecule. Examples of the hydrolyzable groups include alkoxy groups such as methoxy groups and ethoxy groups; acyloxy groups such as acetoxy groups; and halogen groups such as chloro groups. Examples of the organic polymerizable functional groups include vinyl groups, epoxy groups, methacryloxy groups, acryloxy groups, amino groups, mercapto groups, isocyanate groups, ureido groups, and isocyanurate groups. The silane coupling agent may contain one or more of these hydrolyzable groups and one or more of these organic polymerizable functional groups in one or more molecules. 【0048】 Examples of the silane coupling agents include vinyl group-containing silane coupling agents (silane compounds having vinyl group and hydrolyzable group), epoxy group-containing silane coupling agents (silane compounds having epoxy group and hydrolyzable group), (meth)acryloxy group-containing silane coupling agents (silane compounds having (meth)acryloxy group and hydrolyzable group), amino group-containing silane coupling agents (silane compounds having amino group and hydrolyzable group), mercapto group-containing silane coupling agents (silane compounds having mercapto group and hydrolyzable group), isocyanate group-containing silane coupling agents (silane compounds having isocyanate group and hydrolyzable group), ureido group-containing silane coupling agents (silane compounds having ureido group and hydrolyzable group), and isocyanurate group-containing silane coupling agents (silane compounds having isocyanurate group and hydrolyzable group). 【0049】 Examples of silane coupling agents having a vinyl group include vinyltrimethoxysilane, vinyltriethoxysilane, and p-styryltrimethoxysilane. 【0050】 Examples of silane coupling agents having the epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. 【0051】 Examples of silane coupling agents having a (meth)acryloxy group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane. 【0052】 Examples of silane coupling agents having an amino group include compounds having one hydrocarbon group with one amino group in the molecule and one or more hydrolyzable groups in the molecule, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane; and compounds having one hydrocarbon group with two amino groups in the molecule and one or more hydrolyzable groups in the molecule, such as N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane. 【0053】 Examples of silane coupling agents having a mercapto group include 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane. 【0054】 Examples of silane coupling agents having an isocyanate group include 3-isocyanatetopropyltriethoxysilane. 【0055】 Examples of silane coupling agents having a ureido group include 3-ureidopropyltrimethoxysilane and 3-ureidopropyltriethoxysilane. 【0056】 Examples of silane coupling agents having an isocyanurate group include tris-(trimethoxysilylpropyl)isocyanurate. 【0057】 Among these silane coupling agents, the silane coupling agent having the amino group is preferred from the viewpoint of further improving alcohol friction and long-term stability. 【0058】 The silane coupling agent is preferably contained in an amount of 1% to 10% by mass relative to the solid content of the release agent of the present invention, and more preferably in an amount of 3% to 7% by mass. 【0059】 By adding the silane coupling agent as a curing agent, it is possible to form a release layer with superior alcohol resistance, which is the objective of the present invention. Furthermore, although the silane coupling agent may affect the storage stability of the release agent itself, it is preferable to select a silane coupling agent that has an amino group in particular, as this will result in a release agent with superior storage stability. 【0060】 (wax) In the present invention, wax may be used in combination, and is preferable. As the wax, it is preferable to use a water-dispersible wax that is stable in an aqueous medium. Specifically, examples include paraffin wax, microcrystalline wax, montan wax, carnauba wax, rice bran wax, wood wax, beeswax, whale wax, lanolin, fatty acid amide wax, sazole wax, polyethylene wax, and oxidized polyethylene wax. Among these, polyethylene wax and oxidized polyethylene wax are more preferred. Generally, thermal transfer sheets form a printed layer by printing printing ink onto a release layer, but depending on the type of wax in the release agent, there is a risk of poor ink transfer. On the other hand, by adding polyethylene wax or oxidized polyethylene wax to the aqueous release agent of the present invention, a release layer with good ink transfer properties can be formed. 【0061】 The aforementioned wax is used by dispersing particulate matter in water using physical, chemical, or a combination thereof, and is also commercially available in a dispersed form. The average particle size of the wax is preferably 0.1 μm to 5 μm, and more preferably 0.3 μm to 2 μm. The average particle size is measured using the Cole counter method. 【0062】 The wax is preferably in an amount of 1% to 20% by mass, and more preferably 1% to 10% by mass, relative to the solid content of the release agent of the present invention. 【0063】 The release agent of the present invention is not particularly limited except that it contains the (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), and can be used in combination with general-purpose resins other than (meth)acrylic resins, additives, etc., as long as the effects of the present invention are not impaired. Examples of general-purpose resins other than (meth)acrylic resins include vinyl resins such as polyvinyl alcohol resin, polyvinyl acetate resin, vinyl chloride resin, polyvinyl butyral resin, polyvinyl acetal resin, and polyvinylpyrrolidone; polyester resins such as polyethylene terephthalate resin and polyethylene naphthalate resin; urethane resins such as polyurethane acrylate; cellulose resins such as ethyl cellulose resin, hydroxyethyl cellulose resin, ethyl hydroxycellulose resin, methyl cellulose resin, and cellulose acetate resin; polyamide resins such as polyamide resin, aromatic polyamide resin, and polyamide-imide resin; acetal resins; and polycarbonate resins. Examples of additives include well-known defoaming agents and leveling agents. 【0064】 (Method of manufacturing a release agent) The release agent of the present invention can be obtained by dispersing the (meth)acrylic resin (A), an aqueous medium (B), a curing agent (C), and various additives as needed in an aqueous medium using a known dispersion method. 【0065】 (Heat transfer sheet) The thermal transfer sheet of the present invention is a sheet having a known structure, except that it has a release layer obtained by coating and drying the release agent of the present invention. The most common configuration is one having a base film, a release layer provided on one side of the base film, and an ink layer provided on the release layer. Furthermore, a release layer may be provided between the base film and the release layer. Furthermore, a heat-seal layer may be provided on top of the ink layer. 【0066】 (Base film) The base film used in this invention has the role of holding the transfer layer, and since heat is applied during thermal transfer, it is preferable that the material has sufficient mechanical strength to handle without problems even when heated. Examples of such base materials include polyethylene terephthalate film, 1,4-polycyclohexylenedimethylene terephthalate film, polyethylene naphthalate film, polyphenylene sulfide film, polystyrene film, polypropylene film, polysulfone film, aramid film, polycarbonate film, polyvinyl alcohol film, cellophane, cellulose derivatives such as cellulose acetate, polyethylene film, polyvinyl chloride film, nylon film, polyimide film, and ionomer film. The thickness of the base film is generally 0.5 μm to 50 μm, and more preferably 1 μm to 30 μm. 【0067】 (Method for forming a peeling layer) The method for forming the release layer on the base film is not particularly limited, but it can be formed by conventionally known coating methods. Specifically, for example, it can be formed by coating and drying using known means such as gravure coating, roll coating, comma coating, gravure printing, screen printing, and gravure reverse roll coating. The thickness of the release layer is not particularly limited, but is preferably 0.05 μm or more and 5.0 μm or less, and more preferably 0.1 μm or more and 3 μm or less. 【0068】 (Ink layer) The ink layer in the present invention is a layer for forming images such as characters and numbers, which is peeled off from the release layer and / or release layer and transferred onto the transfer object by overlapping a thermal transfer sheet and a transfer object, and heating the back side of the substrate (the side of the substrate without the transfer layer) with a conventionally known heating means such as a printer equipped with a thermal head for thermal transfer. The ink layer is a layer on which printing ink has been printed. 【0069】 Printing inks used in the ink layer contain a binder resin, a colorant, and a solvent. Examples of binder resins include acrylic resins such as poly(meth)acrylate and poly(meth)acrylamide; vinyl resins such as polyvinyl alcohol resin, polyvinyl acetate resin, vinyl chloride resin, polyvinyl butyral resin, polyvinyl acetal resin, and polyvinylpyrrolidone; polyester resins such as polyethylene terephthalate resin and polyethylene naphthalate resin; polyurethane resins; cellulose resins such as ethylcellulose resin, hydroxyethylcellulose resin, ethylhydroxycellulose resin, methylcellulose resin, and cellulose acetate resin; polyamide resins such as polyamide resin, aromatic polyamide resin, and polyamide-imide resin; acetal resins; and polycarbonate resins. 【0070】 Furthermore, a curing agent may be used in combination with the binder resin. The most commonly used curing agent is an isocyanate-based curing agent. From the viewpoint of curing efficiency, the amount of isocyanate compound added is preferably in the range of 0.3% to 10.0% by mass relative to the solid content of the liquid printing ink, and more preferably 1.0% to 7.0% by mass. 【0071】 As the coloring agent, conventionally known coloring agents can be used, but those with good properties as a printing material are preferred, for example, those with sufficient color density and that do not change color or fade due to light, heat, temperature, etc. Furthermore, substances that develop color upon heating or substances that develop color upon contact with components applied to the surface of the transfer object may also be used. For example, colors such as black, white, silver, cyan, magenta, yellow, red, green, and blue are preferred, and it is preferable to use carbon black for black, titanium dioxide for white, an inorganic material such as aluminum for silver, and organic pigments for cyan, magenta, yellow, red, green, and blue. 【0072】 There are no particular limitations on the solvent; for water-based inks, a water-based solvent can be selected, and for organic solvent-based inks, an organic solvent can be selected. 【0073】 The method for forming the ink layer is not particularly limited, but it can be formed by conventionally known printing methods. For example, the above-mentioned binder resin and colorant can be added to a suitable solvent to dissolve or disperse each component to prepare a coating solution. Then, this coating solution can be printed onto the release layer using known methods such as gravure coating, roll coating, comma coating, gravure printing, screen printing, and gravure reverse roll coating, and dried to form the ink layer. 【0074】 (Release layer) The release layer is a layer provided to allow the transfer layer to be easily peeled off the substrate (at the interface between the release layer and the transfer layer) during thermal transfer. The release layer is formed from a material with release properties, preferably contains a binder resin, and further contains additives such as a release agent. Examples of binder resins include acrylic resins such as poly(meth)acrylate and poly(meth)acrylamide; vinyl resins such as polyvinyl alcohol resin, polyvinyl acetate resin, vinyl chloride resin, polyvinyl butyral resin, polyvinyl acetal resin, and polyvinylpyrrolidone; polyester resins such as polyethylene terephthalate resin and polyethylene naphthalate resin; polyurethane resins; cellulose resins such as ethyl cellulose resin, hydroxyethyl cellulose resin, ethyl hydroxycellulose resin, methyl cellulose resin, and cellulose acetate resin; polyamide resins such as polyamide resin, aromatic polyamide resin, and polyamide-imide resin; acetal resins; and polycarbonate resins. Examples of mold release agents include silicone oil, phosphate ester plasticizers, fluorine compounds, waxes, metal soaps, and fillers. 【0075】 (Heat seal layer) The heat seal layer (also called the adhesive layer) is a layer provided to ensure good adhesion of the printed layer to the transfer target. The heat seal layer is preferably formed with a heat sealant. The heat sealant is not particularly limited and any known heat sealant can be used. For example, heat sealants mainly composed of polyester, ethylene-vinyl acetate copolymer, chlorinated ethylene vinyl acetate copolymer, chlorinated polypropylene, etc., can be used. These heat sealants can be appropriately selected depending on the material of the material to be transferred. For example, if the material to be transferred is a polyolefin film, a heat sealant mainly composed of chlorinated ethylene vinyl acetate copolymer or chlorinated polypropylene can be selected, and if the material to be transferred is a polyester film, a heat sealant mainly composed of polyester can be selected. 【0076】 (Transferred object) The transfer substrate usable for transferring the thermal transfer sheet according to the present invention is not particularly limited, and examples include conventionally known substrates on which a dye-receiving layer is provided. Examples of substrates for the transfer substrate include ordinary paper, fine paper, tracing paper, plastic film, etc., and the substrate is not particularly limited. Examples of plastic films include polyethylene terephthalate (PET) film, polystyrene film, polyamide film, nylon film, polyacrylonitrile film, polyolefin films such as polyethylene film (OPE: biaxially oriented polyethylene film, LLDPE: low-density polyethylene film, HDPE: high-density polyethylene film) and polypropylene film (CPP: unoriented polypropylene film, OPP: biaxially oriented polypropylene film), polyvinyl alcohol film, ethylene-vinyl alcohol copolymer film, cellophane, etc. The receiving layer in the above-mentioned transfer substrate can be formed by a coating method, a thermal head or hot roll formation method, or the like. 【0077】 (Transfer method) Transferring the transfer sheet according to the present invention to a transfer target can be performed directly to the transfer target using a conventionally known thermal transfer printer. Furthermore, if direct transfer is difficult to perform on the transfer target, the transfer can also be performed by first transferring the sheet onto a receptive layer of an intermediate transfer recording medium (primary transfer), and then transferring the receptive layer of this intermediate transfer recording medium to the transfer target (re-transfer). The thermal transfer printer may have separate transfer conditions set for, for example, sublimation transfer, thermal melt transfer, and protective layer transfer, or a common printer may be used with appropriate adjustments to the printing energy for each. The heating means is not particularly limited, and transfer may be performed using a hot plate, hot stamper, hot roll, line heater, iron, etc. [Examples] 【0078】 The present invention will be described in more detail below with reference to specific synthesis examples and embodiments, but the present invention is not limited to these embodiments. In the following examples, "parts" and "%" represent "parts by mass" and "mass%", respectively, unless otherwise specified. 【0079】 <Example: Method for producing an aqueous release agent> (Example 1: Method for producing an aqueous release agent) A aqueous release agent was obtained by preparing a mixture of ion-exchanged water and isopropyl alcohol with 21.5 parts of acrylic resin a1 (ammonium salt of styrene acrylic resin: Tg=96℃), 9.2 parts of acrylic resin a2 (ammonium salt of styrene acrylic resin: Tg=16℃), 0.8 parts of lubricant A (low molecular weight polyethylene, modified polyolefin), 2.0 parts of leveling agent (acetylene glycol), 1.7 parts of curing agent (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane), and 0.1 parts of defoaming agent (polyether, silicone compound). 【0080】 (Example 2: Method for producing an aqueous release agent) A aqueous release agent was prepared by mixing 30.7 parts of acrylic resin a1 (ammonium salt of styrene acrylic resin: Tg=96℃), 0.8 parts of lubricant A (low molecular weight polyethylene, modified polyolefin), 2.0 parts of leveling agent (acetylene glycol), 1.7 parts of curing agent (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane), and 0.1 parts of defoaming agent (polyether, silicone compound) with a mixed solvent of deionized water and isopropyl alcohol. 【0081】 (Comparative Example 1: Method for producing an aqueous release agent for comparative examples) A aqueous release agent was obtained by preparing 21.5 parts of acrylic resin a1 (ammonium salt of styrene-acrylic resin: Tg=96℃), 9.2 parts of acrylic resin a2 (ammonium salt of styrene-acrylic resin: Tg=16℃), 0.8 parts of lubricant B, 2.0 parts of leveling agent, and 0.1 parts of defoaming agent with a mixed solvent of deionized water and isopropyl alcohol. 【0082】 (Comparative Example 2: Method for producing an aqueous release agent for comparative examples) A aqueous release agent was obtained by preparing 21.5 parts of acrylic resin a1 (ammonium salt of styrene-acrylic resin: Tg=96℃), 9.2 parts of acrylic resin a2 (ammonium salt of styrene-acrylic resin: Tg=16℃), 2.0 parts of leveling agent, and 0.1 parts of defoaming agent with a mixed solvent of ion-exchanged water and isopropyl alcohol. 【0083】 (Comparative Example 3: Method for producing an aqueous release agent for comparative examples) A aqueous release agent was obtained by preparing a mixture of ion-exchanged water and isopropyl alcohol with 21.5 parts of acrylic resin a1 (ammonium salt of styrene acrylic resin: Tg=96℃), 9.2 parts of acrylic resin a2 (ammonium salt of styrene acrylic resin: Tg=16℃), 0.8 parts of lubricant A, 2.0 parts of leveling agent, and 0.1 parts of defoaming agent. 【0084】 (Comparative Example 4: Method for producing an aqueous release agent for comparative examples) A aqueous release agent was prepared by mixing 25.2 parts of acrylic resin b (ammonium salt of styrene acrylic resin: Tg=113℃), 2.0 parts of lubricant C (polyethylene-paraffin emulsion), 0.05 parts of leveling agent, and 0.01 parts of defoaming agent with a mixed solvent of deionized water and isopropyl alcohol. 【0085】 (Comparative Example 5: Method for producing an aqueous release agent for comparative examples) A water-based release agent was prepared by mixing 25.2 parts of acrylic resin b (ammonium salt of styrene acrylic resin: Tg=113℃), 2.0 parts of lubricant C, 0.05 parts of leveling agent, 5.0 parts of curing agent b (sorbitol polyglycidyl ether), and 0.01 parts of defoaming agent with a mixed solvent of deionized water and isopropyl alcohol. 【0086】 (Comparative Example 6: Method for producing an aqueous release agent for comparative examples) A water-based release agent was prepared by mixing 25.2 parts of acrylic resin b (ammonium salt of styrene acrylic resin: Tg=113℃), 2.0 parts of lubricant C, 0.05 parts of leveling agent, 3.0 parts of curing agent c (aziridine crosslinking agent), and 0.01 parts of defoaming agent with a mixed solvent of deionized water and isopropyl alcohol. 【0087】 <Method for manufacturing heat transfer sheets> Using the aqueous release agent obtained in the examples or comparative examples, apply it to polyethylene terephthalate (PET) film with an AutoProofer (manufactured by Tester Industries Co., Ltd.) at a solid content of 2 g / m². 2 The coating was applied in such a manner. The material was dried in a drying oven at 80-100°C for 10-30 seconds to obtain a release layer. On the resulting release layer, a printed layer was obtained using ink that had been adjusted to a viscosity of 15-18 seconds using an Auto Proofer with a Zaan Cup #3 (manufactured by Rigosha). Next, an adhesive, adjusted to a viscosity of 15-30 seconds using an Auto Proofer and Zahn Cup #3 (manufactured by Rigosha), is applied to the printed layer, with a solid content of 1-3 g / m². 2After coating the material in this manner, it was dried in a drying oven at 80-100°C for 10-30 seconds to obtain a heat transfer sheet consisting of a PET film, a release layer, a printing layer, and an adhesive layer. 【0088】 <Evaluation Method> (Changes in coating solution over time) The coating solution was checked after 5 days. The evaluation was as follows: 5: Little to no change in appearance or increase in viscosity was observed. 4. No changes in appearance were observed. A slight increase in viscosity was observed, but dilution was not necessary. 3: No changes in appearance were observed. However, some thickening was observed, requiring dilution. 2: Excessive thickening was observed, which was deemed unsuitable for use. 1: Hardening was observed that made the material unusable. 【0089】 (Appearance of the coating) A water-based release agent was applied to a polyethylene terephthalate (PET) film using an AutoProofer (manufactured by Tester Industries Co., Ltd.) at a rate of 2g. After drying in a drying oven at 80-100°C for 10-30 seconds, the coating film was inspected. 5: No bleaching was observed at all; it was transparent. 4: It was almost transparent, but some whitening was observed. 3: Whitening was observed to the extent that the underlying surface could be seen. 2: Whitening was observed to the extent that the underlying surface could barely be seen. 1: Whitening was observed to such an extent that the underlying surface could not be seen at all. 【0090】 (defoaming) After adding 30cc of water-based release agent to a 112cc glass bottle, the mixture was shaken 20 times by hand, and the foaming action was observed. The evaluation was as follows: 4. After stirring, the amount of foam generated was extremely small, and the foam completely disappeared within 1 minute. 3. After stirring, the amount of foam generated was small, with only a small amount of foam remaining after 1 minute. 2. After stirring, foam was observed, but the amount of foam decreased over time. 1. After stirring, a very large amount of foam was generated, and the amount of foam did not decrease even after 10 minutes. 【0091】 (Ink transfer) A water-based release agent was applied to polyethylene terephthalate (PET) film using an AutoProofer (manufactured by Tester Industries Co., Ltd.) at a rate of 2g. Drying was performed in a drying oven at 80-100°C for 10-30 seconds. The obtained coated material was printed using an auto-proofer with ink adjusted to 15-18 seconds using a Zahn cup #3 (manufactured by Rigosha), and the ink was then printed using a proofer equipped with a gradient plate to evaluate the ink transfer properties on the release agent. 5: No metastatic failures occurred at all. 4: The lesions were mostly metastatic, but some slight fading was observed in the pale areas. 3: The lesions were generally present, but some fading was observed from the area between the dark and light parts of the lesion. 2: Overall, smudging was observed. 1: It did not transfer. 【0092】 (Transferable) Samples obtained by preparing the aforementioned coated material were placed on a plastic substrate such as polypropylene (PP), and then set in a heat transfer machine (manufactured by Navitas Corporation). Heat transfer was performed using a hot roll heated to 200-250°C. The film was peeled off the sample immediately after heat transfer or after cooling at room temperature, and the transferability and foil tearability were evaluated. 5. The coating on the heat transfer sheet was completely transferred to the plastic substrate. 4: 95% to less than 100% of the coating on the heat transfer sheet was transferred to the substrate. 3: 50% to less than 95% of the coating on the heat transfer sheet was transferred to the substrate. 2: More than 0% of the coating on the heat transfer sheet was transferred to the substrate but less than 50%. 1: Not all of the coating on the heat transfer sheet was transferred to the plastic substrate. 【0093】 (Transfer evaluation) The final product, the transfer material after the film has been peeled off, was evaluated according to the following criteria. (Adhesion of adhesive tape to PP substrate) 5: The transfer material on the PP substrate did not peel off at all. 4: More than 0% but less than 5% of the transfer material peeled off the PP substrate. 3: Between 5% and 20% of the transfer material peeled off the PP substrate. 2: Between 20% and 50% of the transfer material on the PP substrate peeled off. 1: More than 50% of the transfer material on the PP substrate peeled off. 【0094】 (Scratch-resistant (10 back-and-forth strokes with nails)) 5: No scratch marks were left at all. 4: Slight scratches were visible. 3: The paint film has partially peeled off. 2: The paint film peeled off. The paint film peeled off after 1:1 round trip. 【0095】 (Alcohol resistance test (rubbing)) A cotton swab soaked in alcohol was moved back and forth over a transfer material on a PP substrate until the transfer material peeled off, and the number of times this was done was recorded. 【0096】 The results are summarized in Table 1. Blank spaces indicate that the ingredient was not included. 【0097】 [Table 1]

Claims

[Claim 1] A release agent for forming a release layer on a thermal transfer sheet, A release agent comprising at least a (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), wherein the (meth)acrylic resin (A) comprises at least a (meth)acrylic resin (a1) having a glass transition temperature (Tg) of 50°C or more and 110°C or less. [Claim 2] The release agent according to claim 1, wherein the curing agent (C) is a silane coupling agent. [Claim 3] The release agent according to claim 1 or 2, wherein the (meth)acrylic resin further contains a (meth)acrylic resin (a2) having a lower glass transition temperature (Tg) than the (meth)acrylic resin (a1). [Claim 4] The release agent according to claim 3, wherein the glass transition temperature of the (meth)acrylic resin (a2) is 0°C or higher and 50°C or lower. [Claim 5] Furthermore, the stripping agent according to claim 1 or 2, further containing wax (D). [Claim 6] The stripping agent according to claim 5, wherein the average particle size of the wax (D) is 2 μm or less. [Claim 7] The stripping agent according to claim 1 or 2, wherein the aqueous medium is water alone, or a mixture of water and an organic solvent that is miscible with water. [Claim 8] The material comprises a base film, a release layer provided on one side of the base film, and an ink layer provided on the release layer. The release layer is a thermal transfer sheet in which the release layer contains at least a (meth)acrylic resin (A), an aqueous medium (B), and a curing agent (C), and the (meth)acrylic resin (A) is formed by a release agent containing at least a (meth)acrylic resin (a1) having a glass transition temperature (Tg) of 50°C or higher. [Claim 9] The thermal transfer sheet according to claim 8, further comprising a heat seal layer on the ink layer. [Claim 10] The thermal transfer sheet according to claim 8 or 9, wherein the ink layer is a layer formed from an ink composition containing a curing agent.

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