Aqueous resin composition and film

Abstract

To provide an aqueous resin composition having good storage stability and capable of providing a film excellent in strength and stretchability.SOLUTION: Wherein the polymer contains a methyl acrylate unit and a unit having a carboxyl group, a content of the methyl acrylate unit is 80.0% by mass or more and 99.9% by mass or less with respect to a total unit constituting the polymer, and an acid number of the polymer is 0. 5mgKOH / g or more and 150. 0mgKOH / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an aqueous resin composition and a film. [Background technology]

[0002] In recent years, efforts to reduce environmental impact, such as the reduction of volatile organic compounds (VOCs), have led to active research into the development of water-based resin compositions, in which acrylic resins, urethane resins, etc. are dissolved or dispersed in an aqueous medium. Acrylic resins are relatively easy to design and have excellent hydrolytic stability and heat resistance, making them useful for a variety of applications, including films, various pressure-sensitive adhesives, paints, and inks. However, achieving both excellent film strength and elasticity has been a long-standing challenge. On the other hand, urethane resins are significantly superior to acrylic resins in terms of achieving both elasticity and film strength, but suffer from the drawbacks of inferior stability in water and inferior heat resistance of the resulting film.

[0003] Patent Document 1 discloses an acrylic resin that exhibits excellent coating film strength and elasticity due to its core-shell structure. Patent Document 2 discloses a urethane-acrylic composite resin that has excellent water resistance, coating film strength, and elasticity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-77707 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-322359 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 aims to improve the strength and elasticity of the film by using resin microparticles consisting of a core and a shell with different glass transition temperatures, but there is a possibility that sufficient effects will not be achieved in terms of elasticity. Patent Document 2 aims to achieve both excellent coating film strength and elasticity by combining a urethane resin, which has excellent strength and elongation, with an acrylic resin, but the urethane resin portion is easily hydrolyzed, and there is a possibility that the storage stability of the aqueous resin composition and the mechanical properties of the film will deteriorate significantly over time.

[0006] An object of the present disclosure is to provide an aqueous resin composition capable of providing a film having good storage stability and excellent strength and elasticity, and further to provide a film that remains excellent in strength and elasticity even after a moist heat resistance test. [Means for solving the problem]

[0007] Some embodiments of the present invention are illustrated below. [1] An aqueous resin composition comprising an aqueous medium and a polymer, the polymer containing methyl acrylate units and units having a carboxy group, the content of the methyl acrylate units being 80.0 mass% or more and 99.9 mass% or less relative to all units constituting the polymer, and the acid value of the polymer being 0.5 mgKOH / g or more and 150.0 mgKOH / g or less.

[0008] [2] The aqueous resin composition according to [1], which has a minimum film-forming temperature of 30°C or lower.

[0009] [3] The aqueous resin composition according to [1] or [2], wherein the polymer has a crosslinked structure.

[0010] [4] The aqueous resin composition according to any one of [1] to [3], wherein the polymer is a polymer of a monomer mixture containing methyl acrylate, an ethylenically unsaturated monomer having a carboxy group, and a crosslinkable monomer, the content of the methyl acrylate being 80.0% by mass or more and 99.9% by mass or less, based on the total mass of the monomer mixture, the content of the ethylenically unsaturated monomer having a carboxy group being 0.1% by mass or more and 20.0% by mass or less, based on the total mass of the monomer mixture, and the content of the crosslinkable monomer being 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the monomer mixture.

[0011] [5] A film which is a molded article of the aqueous resin composition according to any one of [1] to [4] above. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide an aqueous resin composition capable of providing a film having good storage stability and excellent strength and stretchability, and further to provide a film that remains excellent in strength and stretchability even after a moist heat resistance test. DETAILED DESCRIPTION OF THE INVENTION

[0013] Several embodiments of the present disclosure will be described in detail below, but these are merely examples and the present invention is not limited to the following examples.

[0014] <<Aqueous resin composition>> According to one embodiment, there is provided an aqueous resin composition comprising an aqueous medium and a polymer, the polymer comprising methyl acrylate units and units having a carboxyl group, the content of the methyl acrylate units being 80.0% by mass or more and 99.9% by mass or less of all units constituting the polymer, and the polymer having an acid value of 0.5 mg KOH / g or more and 150.0 mg KOH / g or less. This aqueous resin composition can provide a film having good storage stability and excellent strength and elasticity.

[0015] In the present disclosure, a polymer containing methyl acrylate units and units having a carboxy group, in which the content of the methyl acrylate units is 80.0 mass% or more and 99.9 mass% or less with respect to all units constituting the polymer, and in which the acid value of the polymer is 0.5 mgKOH / g or more and 150.0 mgKOH / g or less, is also referred to as polymer P.

[0016] In this disclosure, acrylic resin collectively refers to homopolymers and copolymers of acrylic acid, methacrylic acid, and their derivatives. Copolymers containing other units in acrylic resin and having an acrylic resin as the main skeleton are also referred to as acrylic resin. (Meth)acrylate collectively refers to acrylate and methacrylate, and the same applies to other similar descriptions.

[0017] Polymer P contains methyl acrylate units and units having a carboxy group, which allows the provision of a film with excellent strength and stretchability. Polymer P contains units having a carboxy group, which allows the storage stability of the aqueous resin composition to be further improved.

[0018] By making the content of methyl acrylate units 80.0% by mass or more relative to the total units constituting polymer P, the interaction between side chains derived from methyl acrylate monomers is more effectively enhanced, making it possible to provide a film with excellent strength and elasticity. By ensuring that the content of methyl acrylate units is 99.9 mass% or less relative to all units constituting polymer P, an appropriate amount of units having a carboxy group that contributes to improving dispersion stability and coating film strength can be introduced, thereby further improving the storage stability of the aqueous resin composition and providing a film with excellent strength and elasticity. By having this methyl acrylate unit content of 80.0% by mass or more and 99.9% by mass or less, the interaction between the side chains derived from the methyl acrylate monomer in the polymer P is more effectively enhanced, and the content of carboxy groups contained in the polymer P is appropriate, improving the stability of the polymer P in an aqueous medium and further improving the storage stability of the aqueous resin composition. Furthermore, in the polymer P, not only is the interaction between the side chains derived from the methyl acrylate monomer more enhanced, but the synergistic effect of the interaction between the carboxy groups also significantly improves the strength and stretchability of the film. Furthermore, this film can maintain good strength and stretchability even after a moist heat resistance test.

[0019] From these viewpoints, the content of methyl acrylate units relative to all units constituting polymer P is preferably 80.0% by mass or more and 99.9% by mass or less, more preferably 85.0% by mass or more and 99.0% by mass or less, and even more preferably 90.0% by mass or more and 98.0% by mass or less.

[0020] In the present disclosure, the content of each unit constituting polymer P can be determined from the blending amount of the monomer serving as the raw material for each unit relative to the total mass of the monomer mixture used to synthesize the polymer.

[0021] When the acid value of polymer P is 0.5 mgKOH / g or more, the stability and storage stability of polymer P in the aqueous resin composition are further improved, and the interaction between carboxy groups functions effectively, thereby further improving the strength and elasticity of the film. By making the acid value of the polymer P 150.0 mgKOH / g or less, the generation of water-soluble resin components (polycarboxylic acid components) that are not incorporated into the polymer P due to the introduction of excessive carboxy groups is further suppressed, improving the storage stability of the aqueous resin composition. In addition, the component homogeneity of the copolymer P is maintained and phase separation, etc. is suppressed, thereby significantly improving the strength and elasticity of the film.

[0022] From these viewpoints, the acid value of polymer P is preferably 0.5 mgKOH / g or more and 150.0 mgKOH / g or less, more preferably 1.0 mgKOH / g or more and 100.0 mgKOH / g or less, and even more preferably 10.0 mgKOH / g or more and 90.0 mgKOH / g or less.

[0023] The acid value is the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of dried resin. In this disclosure, the acid value of polymer P is a value calculated by potentiometric titration with a potassium hydroxide-ethanol solution in accordance with JIS K2501. The titration can be performed using an automatic titrator "COM-1600" manufactured by Hiranuma Sangyo Co., Ltd.

[0024] <Aqueous medium> The aqueous medium refers to an aqueous dispersion medium or an aqueous solvent. It is preferable to use water as the aqueous medium, but a water-soluble solvent can also be used if necessary. In the aqueous resin composition, the water content of the aqueous medium may be 10% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total mass of the aqueous medium, and may be 100% by mass. In the aqueous resin composition, it is preferable that the water content of the aqueous medium is the maximum.

[0025] Examples of the water-soluble solvent include monohydric alcohol solvents such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol; glycol solvents such as ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-butanediol, 1,4-butanediol, pentylene glycol, 1,2-hexanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol; and glycol solvents such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monoisopropyl ether. Examples of suitable solvents include glycol ether solvents such as ethanol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, and tripropylene glycol monomethyl ether; lactam solvents such as N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, and ε-caprolactam; and amide solvents such as formamide, N-methylformamide, N,N-dimethylformamide, and Idemitsu's Equamide M-100 and Equamide B-100. These may be used alone or in combination of two or more.

[0026] <Polymer> The polymer P is preferably an aqueous resin. An aqueous resin refers to a resin that can be dispersed or dissolved in an aqueous medium. The polymer P is preferably in a dispersed or dissolved form in an aqueous medium, and after being applied to a substrate or the like, forms a film upon drying to form a water-insoluble film. The polymer P is preferably contained in the aqueous medium in the form of dispersed resin particles, and the aqueous resin composition is preferably a resin emulsion.

[0027] The polymer P includes a methyl acrylate unit and a unit having a carboxy group. The polymer P may further include a crosslinked structure.

[0028] The content of units having a carboxy group relative to all units constituting polymer P is preferably 0.05% by mass or more and 25.0% by mass or less, more preferably 0.1% by mass or more and 20.0% by mass or less, even more preferably 0.5% by mass or more and 15.0% by mass or less, and even more preferably 1.0% by mass or more and 10.0% by mass or less. When the content of units having a carboxy group is within the above range, the storage stability of the aqueous resin composition can be further improved. Furthermore, interactions between carboxy groups are effectively expressed, and the stretchability and strength of the film can be further improved.

[0029] The content of the units constituting the crosslinked structure relative to the total units constituting the polymer P is preferably 0.05% by mass or more and 30.0% by mass or less, more preferably 0.1% by mass or more and 20.0% by mass or less, even more preferably 2.0% by mass or more and 15.0% by mass or less, and even more preferably 4.0% by mass or more and 10.0% by mass or less. When the content of the units constituting the crosslinked structure is within the above range, the strength of the film can be further improved. The content of the units constituting the crosslinked structure relative to the total units constituting the polymer P can be calculated from the amount of crosslinkable monomer blended relative to the total mass of the monomer mixture used in synthesizing the polymer.

[0030] Polymer P may contain units other than methyl acrylate units, units having a carboxy group, and units constituting a crosslinked structure. In this case, the content of the other units relative to all units constituting the polymer may be 1.0% by mass to 30.0% by mass, 3.0% by mass to 20.0% by mass, or 5.0% by mass to 15.0% by mass.

[0031] By having methyl acrylate units account for 80.0% by mass or more and 99.9% by mass or less of all units constituting polymer P, a film with excellent stretchability, strength, and moist heat resistance can be obtained. Preferably, the methyl acrylate units account for 80.0% by mass or more and 99.9% by mass or less of all units constituting copolymer P, the units having carboxy groups account for 0.1% by mass or more and 20.0% by mass or less, and the units constituting crosslinked structures account for 0.1% by mass or more and 10.0% by mass or less of all units constituting copolymer P. In this case, the content of each unit is adjusted so that the total of each unit contained in copolymer P is 100% by mass.

[0032] The content of polymer P relative to the total mass of the aqueous resin composition is preferably 10 to 50 mass %, 15 to 40 mass %, or 15 to 30 mass %, depending on the coating method and application.

[0033] [Ethylenically unsaturated monomers] The polymer P may be a polymer of a mixture of ethylenically unsaturated monomers including methyl acrylate and an ethylenically unsaturated monomer having a carboxy group. This mixture may further include a crosslinkable monomer. This mixture may also optionally include another ethylenically unsaturated monomer polymerizable with methyl acrylate and the ethylenically unsaturated monomer having a carboxy group. The polymerization of the mixture of ethylenically unsaturated monomers can be carried out by radical polymerization.

[0034] Examples of the ethylenically unsaturated monomer having a carboxy group include maleic acid, fumaric acid, itaconic acid, citraconic acid, or anhydrides, alkyl monoesters, or alkenyl monoesters thereof; succinic acid β-(meth)acryloxyethyl monoester, acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid.

[0035] <Crosslinking monomer> The crosslinkable monomer is preferably an ethylenically unsaturated monomer having a crosslinkable functional group. Examples of the crosslinkable functional group include ethylenically unsaturated double bond groups such as vinyl groups, allyl groups, and (meth)acryloyl groups, as well as alkoxysilyl groups, epoxy groups, and glycidyl groups. By using a crosslinkable monomer, a crosslinked structure is incorporated into the molecules of copolymer P, thereby further increasing the strength of the film. The crosslinkable monomer is preferably a compound having one ethylenically unsaturated double bond group and at least one (meth)acryloyl group, and more preferably a polyfunctional (meth)acrylate compound such as a di(meth)acrylate compound, a tri(meth)acrylate compound, or a tetra(meth)acrylate compound.

[0036] Examples of the crosslinkable monomer include allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, vinyl group- or (meth)acryloyl group-containing monomers such as methyl acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, divinylbenzene, divinyl adipate, diallyl isophthalate, diallyl phthalate, and diallyl maleate; Alkoxysilyl group-containing monomers such as γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-acryloxypropylmethyldiethoxysilane, γ-methacryloxymethyltrimethoxysilane, γ-methacryloxymethyltriethoxysilane, γ-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, and vinylmethyldimethoxysilane; Epoxy group- or glycidyl group-containing monomers such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and 3,4-epoxycyclohexyl (meth)acrylate; Examples include methylol group-containing ethylenically unsaturated monomers such as N-methylol(meth)acrylamide, N,N-dimethylol(meth)acrylamide, and alkyl-etherified N-methylol(meth)acrylamide.

[0037] From the viewpoint of the tensile strength and elongation of the film, the crosslinkable monomer is preferably a bifunctional or trifunctional ethylenically unsaturated monomer, and more preferably a bifunctional ethylenically unsaturated monomer. From the viewpoint of the tensile strength and elongation of the film, the crosslinkable monomer is such that the ethylenically unsaturated double bond group and the crosslinkable reactive functional group are bonded via a saturated hydrocarbon group preferably having 1 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 4 to 6 carbon atoms.

[0038] <Other ethylenically unsaturated monomers> Examples of other ethylenically unsaturated monomers include aromatic ethylenically unsaturated monomers such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, and phenyl (meth)acrylate; linear or branched alkyl group-containing ethylenically unsaturated monomers, such as methyl methacrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate; Alicyclic alkyl group-containing ethylenically unsaturated monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; Fluorinated alkyl group-containing ethylenically unsaturated monomers such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate; Sulfo group-containing ethylenically unsaturated monomers such as sodium 2-methylpropanesulfonate, methallylsulfonic acid, sodium methallylsulfonate, allylsulfonic acid, sodium allylsulfonate, ammonium allylsulfonate, and vinylsulfonic acid; (meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide, N,N-di(propoxymethyl)acrylamide, Amide group-containing ethylenically unsaturated monomers such as N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and diacetoneacrylamide; hydroxyl group-containing ethylenically unsaturated monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, and allyl alcohol; Polyoxyethylene group-containing ethylenically unsaturated monomers such as methoxypolyethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; Examples thereof include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methylethylaminoethyl (meth)acrylate, dimethylaminostyrene, and diethylaminostyrene, and amino group-containing ethylenically unsaturated monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methylethylaminoethyl (meth)acrylate; Examples include ketone group-containing ethylenically unsaturated monomers such as diacetone (meth)acrylamide and acetoacetoxy (meth)acrylate.

[0039] One or more types of ethylenically unsaturated monomers having a carboxy group may be used in combination. One or more types of crosslinkable monomers may be used in combination. One or more types of other ethylenically unsaturated monomers may be used in combination.

[0040] The polymer P may be a polymer of a monomer mixture containing methyl acrylate and an ethylenically unsaturated monomer having a carboxy group, and optionally containing a crosslinkable monomer, another ethylenically unsaturated monomer, or a combination thereof. In this case, the mass of each monomer relative to the total mass of the monomer mixture may be within the preferred range of the mass of each unit relative to the total mass of all units constituting the polymer P described above. Preferably, the copolymer P may be a polymer of a monomer mixture containing 80.0% to 99.9% by mass of methyl acrylate, 0.1% to 20.0% by mass of an ethylenically unsaturated monomer having a carboxy group, and 0.1% to 10.0% by mass of a crosslinkable monomer. In this case, the content of each monomer in the monomer mixture is adjusted so that the total amount of each monomer contained in the monomer mixture is 100% by mass.

[0041] [Physical Properties] The minimum film-forming temperature (MFT) of the aqueous resin composition is preferably 30° C. or less, more preferably 20° C. or less, even more preferably 10° C. or less, and even more preferably 5° C. or less. When the minimum film-forming temperature is within the above range, the film-forming properties of the aqueous resin composition are improved, the occurrence of defects such as cracks in the film is suppressed, and a decrease in the strength and stretchability of the film can be prevented.

[0042] In the present disclosure, the minimum film-forming temperature is measured in accordance with JIS K6828-1: 2003. The minimum film-forming temperature can be measured, for example, using a "TP-801MFT Tester" manufactured by Tester Sangyo Co., Ltd.

[0043] The glass transition temperature (Tg) of the polymer P is preferably -10 to 50°C, more preferably 0 to 20°C, and even more preferably 10 to 20°C. When the Tg is -10°C or higher, the stretchability and strength of the film can be further increased. Furthermore, the storage stability of the polymer P in an aqueous medium can be better maintained. When the Tg is 50°C or lower, the film-forming properties of the aqueous resin composition are further improved, the occurrence of defects such as cracks in the film is suppressed, and the stretchability and strength are further improved. In the present disclosure, the glass transition temperature (Tg) of a polymer is measured using a DSC (differential scanning calorimeter). Specifically, it can be measured according to the method described in the examples.

[0044] The average particle size of the polymer P is preferably in the range of 50 nm or more and 1000 nm or less, more preferably 80 nm or more and 800 nm or less, and even more preferably 100 nm or more and 700 nm or less.

[0045] In the present disclosure, the average particle size of polymer P is the particle size (median size) at which the cumulative value reaches 50% in the volume-based particle size distribution measured by dynamic light scattering. Specifically, the median size can be measured by measuring particle size distribution data (histogram) using a Nanotrac Wave II EX150 (manufactured by Microtrack Bell) using a sample prepared by diluting polymer P in an aqueous medium to 0.05% by mass.

[0046] [Polymer synthesis method] Polymer synthesis methods include solution polymerization, emulsion polymerization, bulk polymerization, and phase inversion emulsification, but emulsion polymerization is preferred from the viewpoints of controllability of reaction heat and not using organic solvents. Soap-free emulsion polymerization, which does not use surfactants, may also be used.

[0047] The emulsion polymerization can be carried out in the presence of a surfactant. Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. Among these, anionic surfactants, cationic surfactants, and nonionic surfactants are preferred, and anionic surfactants and nonionic surfactants are more preferred. The surfactant may be a reactive surfactant or a non-reactive surfactant.

[0048] Examples of non-reactive anionic surfactants include higher fatty acid salts such as sodium oleate, alkylarylsulfonates such as dodecylbenzenesulfonic acid, alkyl sulfates such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene alkyl ether sulfates (trade name: Hitenol NF-08, etc.), alkyl sulfosuccinate salts and derivatives thereof such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, and sodium polyoxyethylene lauryl sulfosuccinate, and polyoxyethylene distyrenated phenyl ether sulfate.

[0049] Examples of non-reactive nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether, sorbitan higher fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate, polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monostearate, polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate and polyoxyethylene monostearate, glycerin higher fatty acid esters such as oleic acid monoglyceride and stearic acid monoglyceride, polyoxyethylene-polyoxypropylene block copolymers, and polyoxyethylene distyrenated phenyl ether.

[0050] The reactive surfactant may be an anionic surfactant or a nonionic surfactant having one or more unsaturated double bonds capable of radical polymerization. The reactive anionic surfactant is preferably, for example, one whose main skeleton is a sulfosuccinate ester, alkyl ether, alkylphenyl ether, alkylphenyl ester, (meth)acrylate sulfate ester, phosphate ester, or the like. The reactive nonionic surfactant is preferably, for example, one whose main skeleton is an alkyl ether, alkylphenyl ether, alkylphenyl ester, or the like.

[0051] The surfactant is preferably used in an amount of 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, in terms of the content of the active ingredient relative to 100 parts by mass of the ethylenically unsaturated monomer mixture. By using an appropriate amount of surfactant, polymerization stability is improved, and the storage stability of the aqueous resin composition and strength of the film can be further improved.

[0052] For emulsion polymerization, it is preferable to use a radical polymerization initiator (hereinafter also simply referred to as "polymerization initiator"). Known oil-soluble and water-soluble polymerization initiators can be used as the polymerization initiator. Examples of oil-soluble polymerization initiators include organic peroxides such as benzoyl peroxide, tert-butyloxybenzoate, tert-butyl hydroperoxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy-3,5,5-trimethylhexanoate, di-tert-butyl peroxide, cumene hydroperoxide, and p-menthane hydroperoxide; and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 1,1'-azobis-cyclohexane-1-carbonitrile. Examples of the water-soluble polymerization initiator include ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

[0053] When carrying out polymerization, a reducing agent, a transition metal salt, or a combination thereof can be used in combination with a polymerization initiator. The use of these in combination promotes decomposition of the polymerization initiator. Examples of reducing agents include organic reducing compounds such as metal salts of ascorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, and formaldehyde sulfoxylate, and reducing inorganic compounds such as sodium sulfite, sodium bisulfite, sodium metabisulfite, and sodium hyposulfite. Examples of transition metal salts include ferrous chloride, ferrous sulfate, and copper sulfate.

[0054] A water-soluble polymerization initiator is preferably used for the emulsion polymerization of polymer P. The polymerization initiator is preferably used in an amount of 0.03 to 5 parts by mass relative to 100 parts by mass of the ethylenically unsaturated monomer mixture. The reducing agent is preferably used in an amount of 0.01 to 2.5 parts by mass relative to 100 parts by mass of the ethylenically unsaturated monomer mixture. The transition metal salt is preferably used in an amount of 0.0001 to 0.002 parts by mass relative to 100 parts by mass of the ethylenically unsaturated monomer mixture. The polymerization initiator may be added by, for example, initial lump-sum addition, divided addition, or continuous dropwise addition, but is not particularly limited thereto. Furthermore, in order to hasten the end point of the polymerization reaction, a portion of the polymerization initiator may be added to the reaction system before or after the completion of the addition of the monomers to the reaction system.

[0055] During emulsion polymerization, buffers, chain transfer agents, basic compounds, and the like can be used as needed. Examples of buffers include sodium acetate, sodium citrate, and sodium bicarbonate. Examples of chain transfer agents include n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, lauryl mercaptan, stearyl mercaptan, 3-mercaptopropionic acid, n-octyl 3-mercaptopropionate, 2-ethylhexyl 3-mercaptopropionate, n-octyl thioglycolate, and 2-ethylhexyl thioglycolate. Among these, 2-ethylhexyl 3-mercaptopropionate and 2-ethylhexyl thioglycolate are preferred, with 2-ethylhexyl thioglycolate being more preferred. It is preferable to use 0.01 to 0.1 parts by mass of the chain transfer agent per 100 parts by mass of the ethylenically unsaturated monomer mixture. The basic compound is used for neutralization, and examples thereof include alkylamines such as trimethylamine, triethylamine, and n-butylamine, alcoholamines such as 2-dimethylaminoethanol, diethylaminoethanol, diethanolamine, triethanolamine, and aminomethylpropanol, morpholine, ammonia, etc. The basic compound is preferably ammonia in view of its volatility when drying the adhesive.

[0056] Examples of emulsion polymerization methods include a batch reaction in which an ethylenically unsaturated monomer, a surfactant, and water are all charged into a reaction vessel and reacted, and a dropping reaction in which the monomer is gradually dropped into a reaction vessel and reacted. Among these, a dropping reaction is preferred from the viewpoint of easy control of heat generation in the polymerization reaction. In addition, in the dropping reaction, in order to further improve polymerization stability, it is preferable to mix and stir the monomer, water, and surfactant to form an emulsified pre-emulsion and then dropwise add the pre-emulsion.

[0057] Soap-free emulsion polymerization is a method of emulsion polymerization in a reaction solution that is substantially free of surfactants. In the present disclosure, "substantially free of surfactants" means that the surfactant content in the aqueous composition is 0.1% by mass or less, preferably 0.01% by mass or less, more preferably 0.001% by mass or less, and even more preferably 0% by mass. Polymerization using the soap-free emulsion polymerization method reduces the impact of residual surfactants on the quality of the aqueous resin composition, making it possible to obtain an aqueous resin composition in which the impact of the surfactant is significantly reduced. In a film formed using this aqueous resin composition, the impact of the surfactant on the polymer P is reduced, thereby further improving the tensile strength and elongation of the film.

[0058] The aqueous resin composition may further contain additives such as extender pigments, thickeners, moisturizers, preservatives, antifoaming agents, and wetting agents as optional components, as long as the problem can be solved. Examples of extender pigments include talc, silica, calcium carbonate, barium sulfate, titanium oxide, and diatomaceous earth. Examples of thickeners include alkali-swelling thickeners, associative polyurethanes, carboxyvinyl polymers, thickening polysaccharides, and clay minerals. Examples of humectants include sorbitol, xylitol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, glycerin, diglycerin, polyethylene glycol, hyaluronic acid, chondroitin sulfate, pyrrolidone carboxylate, and DL-pyrrolidone carboxylate. Examples of preservatives include methyl parahydroxybenzoate, ethyl parahydroxybenzoate, propyl parahydroxybenzoate, butyl parahydroxybenzoate, benzoic acid, sodium benzoate, sorbic acid, potassium sorbate, phenoxyethanol, 4-hydroxyacetophenone, dehydroacetic acid, caprylyl glycol, and pentylene glycol. Examples of the antifoaming agent include silicone-based antifoaming agents, mineral oil-based antifoaming agents, etc. Examples of the wetting agent include surfactants exemplified in the synthesis of the polymer.

[0059] <<Film>> According to one embodiment, it is possible to provide a film that is a molded article of the aqueous resin composition according to the above embodiment. For example, a film can be formed by coating the aqueous resin composition on a release substrate, removing the aqueous solvent, and peeling the release substrate from the film. The aqueous solvent can be removed by natural drying, heat drying, vacuum drying, or the like. Drying can be performed at room temperature, but is preferably performed at 30°C or higher, and even more preferably at 40°C or higher. On the other hand, the drying temperature is preferably 70°C or lower. Rapid drying at high temperatures can reduce the dispersion stability of the polymer P in the coating film, resulting in reduced film strength and stretchability. Any release substrate can be used as long as it does not adhere to the film. For example, substrates such as silicone-coated polyethylene terephthalate, release polyethylene terephthalate, and release polyolefin can be used.

[0060] The film formed from the aqueous resin composition according to the embodiment described above has excellent strength and stretchability, and can be used in a variety of applications. The thickness of the film is not particularly limited and may be 0.1 to 10 mm, or 0.5 to 5 mm, depending on the application. [Example]

[0061] The present invention will be described in more detail below with reference to examples, but is not limited to these. In the following description, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Numerical values ​​in tables without a unit indicate parts by mass of solid content, and blank spaces indicate empty spaces. The acid value, glass transition temperature (Tg), and minimum film-forming temperature (MFT) of resins were measured as follows:

[0062] [Calculation of acid value] The acid value was calculated by potentiometric titration with potassium hydroxide-ethanol solution in accordance with JIS K2501. The titration was performed using an automatic titrator "COM-1600" manufactured by Hiranuma Sangyo Co., Ltd.

[0063] [Calculation of glass transition temperature (Tg)] The glass transition temperature was measured using a DSC (differential scanning calorimeter, manufactured by TA Instruments). Specifically, an aluminum pan containing a precisely weighed amount of about 3 mg of the dried aqueous resin composition and an empty aluminum pan serving as a reference were set in a DSC measurement holder, and the glass transition temperature (Tg) was calculated from the baseline shift in the DSC curve obtained by measurement under a temperature increase condition of 10°C / min.

[0064] [Minimum film forming temperature (MFT)] The minimum film-forming temperature was measured in accordance with JIS K6828-2 using a thermal gradient tester manufactured by Rigaku Kogyosha.

[0065] [Production of aqueous resin composition] The composition of the monomers of the polymers contained in the aqueous resin composition and the evaluation results of the aqueous resin composition and its film are shown in Table 1. In the table, a1 represents methyl acrylate, a2 represents a monomer having a carboxyl group, a3 represents a crosslinkable monomer, and a4 represents another ethylenically unsaturated monomer.

[0066] Example 1 A four-necked flask equipped with a reflux condenser, stirrer, thermometer, nitrogen inlet, and raw material inlet was prepared as a reaction vessel. 560 parts of water, 82.00 parts of methyl acrylate, 4.00 parts of methacrylic acid, 0.50 parts of 3-methacryloxypropyltrimethoxysilane, 2.00 parts of styrene, 0.50 parts of 2-hydroxymethyl methacrylate, 10.0 parts of methyl methacrylate, and 1.00 parts of acrylamide were stirred while purging with nitrogen, and the internal temperature was raised to 70°C. After the temperature was raised, 10.0 parts of a 5% aqueous potassium persulfate solution was added, and the internal temperature was maintained at 70°C and reacted for 16 hours. The mixture was then cooled to obtain an aqueous resin composition with a solids concentration of 15.0% by mass.

[0067] <Examples 2 to 8 and Comparative Examples 1 to 5> Aqueous resin compositions were obtained in the same manner as in Example 1, except that the monomer compositions and blending amounts (parts by mass) were changed as shown in the table.

[0068] Example 9 34.0 parts of water and 5.0 parts (active ingredient content: 1.0 part) of an aqueous solution of Hitenol NF-08 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., polyoxyethylene alkyl ether sulfate) as an anionic surfactant were added to 100 parts of a mixture of ethylenically unsaturated monomers containing 80.50 parts of methyl acrylate, 0.500 parts of acrylic acid, 9.00 parts of n-butyl acrylate, and 10.00 parts of 2-ethylhexyl acrylate in a vessel, and the mixture was stirred to prepare an emulsion for the dropping tank.

[0069] A separate four-neck flask equipped with a reflux condenser, stirrer, thermometer, nitrogen inlet, and raw material inlet was prepared as a reaction vessel. 95.0 parts of water, 1.0 part of a 20% aqueous solution of Hitenol NF-08 (Dai-ichi Kogyo Seiyaku Co., Ltd., polyoxyethylene alkyl ether sulfate) (active ingredient content: 0.2 parts) as an anionic surfactant, and 8.5 parts of the emulsion prepared above were charged. The mixture was stirred while purging with nitrogen and heated to an internal temperature of 75°C. After the temperature was raised, 5.0 parts of a 5% aqueous solution of potassium persulfate was added, and the remaining emulsion was added dropwise over 4 hours while maintaining the internal temperature at 75°C. After the dropwise addition was completed, the internal temperature was maintained at 75°C for an additional 8 hours to complete the reaction. After the reaction, the mixture was cooled to below 40°C, and 25% aqueous ammonia was added to neutralize 100% of the carboxyl groups of the polymer. Further water was added to adjust the solids concentration to 40.0% by mass, yielding an aqueous resin composition.

[0070] <Examples 10 to 12, Comparative Examples 6 to 7> Aqueous resin compositions were obtained in the same manner as in Example 9, except that the monomer compositions and blending amounts (parts by mass) were changed as shown in the table.

[0071] <Comparative Example 8> A reactor equipped with a stirrer, thermometer, and reflux condenser was charged with 77.0 parts of P-2010 (Kuraray polycarbonate polyol (functionality 2, hydroxyl value 56.0, molecular weight 2000) as polyol, 70.0 parts of C-2090 (Kuraray polycarbonate polyol (functionality 2, hydroxyl value 56.0, molecular weight 2000)), 0.5 parts of neopentyl glycol, 15.8 parts of dimethylol butanoic acid, 36.0 parts of isophorone diisocyanate as polyisocyanate, and 50.0 parts of methyl ethyl ketone as solvent, and the mixture was heated to 78 ° C. under a nitrogen atmosphere with stirring. 0.03 parts of titanium diisopropoxybis(ethyl acetoacetate) was added as a catalyst and reacted for 8 hours to obtain a urethane prepolymer with isocyanate groups at both ends. After adding 13.5 parts of triethylamine as a neutralizing agent, 400 parts of water and 2.4 parts of ethylenediamine as a chain extender were added, and the solvent was removed under reduced pressure to cause phase inversion to an aqueous phase. After phase inversion, water was further added to adjust the solids concentration to 20.0% by mass, thereby obtaining an aqueous resin composition.

[0072] The acid value, Tg, and minimum film-forming temperature (MFT) of the resulting aqueous resin composition were measured by the methods described above, and the results are shown in the table.

[0073] [Storage stability test of aqueous resin composition] The obtained aqueous resin composition was diluted to a resin solid content of 0.05% by mass, and the average particle size was measured using approximately 5 mL of the diluted solution with a Nanotrac Wave II EX150 (manufactured by Microtrac-Bell Co., Ltd.) The median diameter of the obtained particle size distribution data (histogram) was taken as the average particle size. After further storage at 50°C for 6 months, the average particle size was measured in the same manner as before storage (initial period). The rate of change before and after high-temperature storage was calculated from the obtained average particle size using the following formula. Rate of change in average particle size [%] = [average particle size (after storage) - average particle size (initial)] / average particle size (initial) x 100

[0074] Evaluation criteria A: The rate of change in average particle size is less than 10% (good). B: The rate of change in average particle size is 10% or more and less than 30% (usable). C: The rate of change in average particle size is 30% or more (unusable).

[0075] [Film production] The aqueous resin compositions before (initial) and after (after storage) the storage stability test were each poured into a silicone frame and dried at 40°C until the water evaporated, producing a film with a thickness of approximately 0.5 mm. Furthermore, the film produced from the aqueous resin composition before the storage stability test was placed in a thermo-hygrostat and left to stand for 2 weeks at a temperature of 85°C and a humidity of 85%, and then removed to produce a film after the moist heat resistance test.

[0076] [Film tensile test] The resulting film was cut into 5mm wide x 60mm pieces to prepare test pieces, which were then left to stand for one day at 23°C and 50% humidity. Tensile tests were then performed on the films using a benchtop precision universal testing machine (Shimadzu Autograph AGS-X) at 23°C and 50% humidity, with a chuck width of 20mm and a tensile speed of 50mm / min. Taking into account the test force, stroke, and film thickness at break obtained from the measurements, the breaking strength and breaking elongation were calculated using the following formulas. Breaking strength (N / mm 2 ) = Test force at break (N) / (film width (mm) * film thickness (mm)) Breaking elongation rate (%) = (stroke at break (mm) / chuck width (mm)) x 100

[0077] Evaluation criteria S: Elongation at break is 600% or more and breaking strength is 10N / mm 2 That's it. (Very good) A: Elongation at break is 600% or more and breaking strength is 5N / mm 2 More than 10N / mm 2 or the elongation at break is 400% or more but less than 600% and the breaking strength is 10N / mm 2 That's all. (Good) B: Elongation at break is 600% or more and breaking strength is 2N / mm 2 More than 5N / mm 2 or the elongation at break is 400% or more but less than 600% and the breaking strength is 5N / mm 2 More than 10N / mm 2 Less than. (Can be used) C: Elongation at break is 600% or more and breaking strength is 1N / mm 2 More than 2N / mm 2 or less than 600% elongation at break and breaking strength of 2N / mm 2 More than 5N / mm 2 Less than. (Not available) D: Elongation at break is 600% or more and breaking strength is 1N / mm 2 or less than 600% elongation at break and breaking strength of 2N / mm 2 Less than (very poor)

[0078] [Table 1-1]

[0079] [Table 1-2]

[0080] [Table 1-3]

[0081] As shown in the table, the aqueous resin compositions of the Examples exhibited excellent storage stability, and films formed from these aqueous resin compositions were found to be tough films with excellent breaking strength and breaking elongation. Furthermore, films formed from the aqueous resin compositions after the storage stability test and the moist heat test also exhibited excellent breaking strength and breaking elongation. In particular, Examples 5 and 6 exhibited good elongation and high stress, exhibiting behavior similar to that of rubber. Furthermore, Example 7 exhibited behavior in which elongation occurred after reaching a high yield point. On the other hand, the films formed from Comparative Examples 1 to 3, which used aqueous resin compositions containing no methyl acrylate, and Comparative Example 6, which contained a low amount of methyl acrylate, exhibited poor breaking strength and breaking elongation. Furthermore, the aqueous resin compositions of Comparative Examples 4 and 7, which used aqueous resin compositions containing no carboxyl groups, and Comparative Example 5, which used a polymer with a high acid value, exhibited poor storage stability, and the films formed therefrom exhibited poor breaking strength and breaking elongation. Furthermore, since Comparative Example 8 also has a urethane resin skeleton, the storage stability of the aqueous resin composition is low, and both the film produced from the aqueous resin composition after the storage stability test and the film after the moist heat test showed significantly poor breaking strength and breaking elongation.

Claims

1. comprising an aqueous medium and a polymer; The polymer contains a methyl acrylate unit and a unit having a carboxy group, the content of the methyl acrylate units is 80.0% by mass or more and 99.9% by mass or less relative to all units constituting the polymer, The acid value of the polymer is 0.5 mgKOH / g or more and 150.0 mgKOH / g or less. Aqueous resin composition.

2. 2. The aqueous resin composition according to claim 1, wherein the minimum film-forming temperature is 30°C or lower.

3. The aqueous resin composition according to claim 1 or 2, wherein the polymer has a crosslinked structure.

4. the polymer is a polymer of a monomer mixture containing methyl acrylate, an ethylenically unsaturated monomer having a carboxy group, and a crosslinkable monomer; the content of the methyl acrylate is 80.0% by mass or more and 99.9% by mass or less based on the total mass of the monomer mixture, the content of the ethylenically unsaturated monomer having a carboxy group is 0.1% by mass or more and 20.0% by mass or less based on the total mass of the monomer mixture, 3. The aqueous resin composition according to claim 1, wherein the content of the crosslinkable monomer is 0.1% by mass or more and 10.0% by mass or less based on the total mass of the monomer mixture.

5. A film which is a molded article of the aqueous resin composition according to claim 1 or 2.

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