Emulsion, coating film, and method for producing the same

Abstract

To provide an emulsion that enables formation of a coating film exhibiting superior film-forming capability and adequate hardness.SOLUTION: An emulsion is provided, the emulsion containing particles including a copolymer having structural units derived from α-methylene lactone and structural units derived from a (meth)acrylic ester, and an aqueous dispersion medium, wherein the (meth)acrylic ester includes a (meth)acrylic ester (A) whose glass transition temperature is 0°C or less when formed as a homopolymer, and the glass transition temperature of the copolymer is -40°C or more and 100°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to emulsions and coatings and methods for making the same. [Background technology]

[0002] In order to address environmental issues, paints for forming coating films are required to contain as few volatile organic compounds as possible, and in recent years, development of water-based paints that use less volatile organic compounds has been progressing. For example, Patent Document 1 proposes an emulsion containing a copolymer whose main component is a (meth)acrylic acid ester such as methyl methacrylate or n-butyl acrylate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-059622 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to improve the hardness of a coating film formed from a water-based paint, it is necessary to use a polymer with a high glass transition temperature in the water-based paint. However, when a polymer with a high glass transition temperature is used in a conventional paint (emulsion), problems with film-forming properties, such as the appearance of cracks in the resulting coating film, may occur. Therefore, a paint (emulsion) is required to have both film-forming properties and hardness.

[0005] Therefore, a main object of the present disclosure is to provide an emulsion that has excellent film-forming properties and is capable of forming a coating film with sufficient hardness. [Means for solving the problem]

[0006] The present inventors conducted studies to solve the above-mentioned problems and found that by introducing a structural unit derived from α-methylene lactone into a copolymer and further adjusting the glass transition temperature of the copolymer to fall within a predetermined range, an emulsion containing particles containing the copolymer has excellent film-forming properties and can produce a coating film with sufficient hardness, which led to the completion of the invention of the present disclosure.

[0007] The present disclosure provides the emulsions described in [1] to [6], the coating film described in [7], and the methods for producing the coating film described in [8] to

[12] . [1] A particle containing a copolymer having a structural unit derived from α-methylene lactone and a structural unit derived from a (meth)acrylic acid ester, and an aqueous dispersion medium, the (meth)acrylic acid ester includes a (meth)acrylic acid ester (A) having a glass transition temperature of 0°C or lower when made into a homopolymer, The emulsion, wherein the copolymer has a glass transition temperature of -40°C or higher and 100°C or lower. [2] The emulsion according to [1], wherein the (meth)acrylic acid ester (A) includes a (meth)acrylic acid ester (A1) having a glass transition temperature of −80° C. or higher and 0° C. or lower when made into a homopolymer. [3] The emulsion according to [1] or [2], wherein the α-methylene lactone includes α-methylene-γ-butyrolactone. [4] The emulsion according to any one of [1] to [3], wherein the (meth)acrylic acid ester (A) comprises at least one selected from the group consisting of ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl acrylate. [5] The emulsion according to any one of [1] to [4], further comprising a (meth)acrylic acid ester (B) having a glass transition temperature of more than 0°C and not more than 110°C when the (meth)acrylic acid ester is made into a homopolymer. [6] The emulsion according to any one of [1] to [5], which is a paint. [7] A method for producing a coating film, comprising the steps of applying the emulsion according to [6] and drying the applied emulsion to form a coating film. [8] A copolymer having a structural unit derived from α-methylene lactone and a structural unit derived from a (meth)acrylic acid ester, the (meth)acrylic acid ester includes a (meth)acrylic acid ester (A) having a glass transition temperature of 0°C or lower when made into a homopolymer, The copolymer has a glass transition temperature of -40°C or higher and 100°C or lower, A coating film with a pencil hardness of HB or higher and 4H or lower. [9] The coating film according to [8], wherein the (meth)acrylic acid ester (A) includes a (meth)acrylic acid ester (A1) having a glass transition temperature of −80° C. or higher and 0° C. or lower when made into a homopolymer.

[10] The coating film according to [8] or [9], wherein the α-methylene lactone comprises α-methylene-γ-butyrolactone.

[11] The coating film according to any one of [8] to

[10] , wherein the (meth)acrylic acid ester (A) comprises at least one selected from the group consisting of ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl acrylate.

[12] The coating film according to any one of [8] to

[11] , wherein the (meth)acrylic acid ester further contains a (meth)acrylic acid ester (B) having a glass transition temperature of more than 0°C and not more than 110°C when made into a homopolymer. [Effects of the Invention]

[0008] According to the present disclosure, an emulsion is provided that has excellent film-forming properties and is capable of forming a coating film having sufficient hardness. Also, according to the present disclosure, a method for producing a coating film using such an emulsion is provided. Furthermore, according to the present disclosure, a coating film having sufficient hardness is provided. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0010] In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0011] In the present disclosure, (meth)acrylic acid esters include acrylic acid esters and the corresponding alkyl methacrylates.

[0012] <Emulsion> An emulsion according to one embodiment contains particles containing a copolymer having structural units derived from α-methylene lactone and structural units derived from a (meth)acrylic acid ester, and an aqueous dispersion medium. The emulsion according to this embodiment can be suitably used as a paint.

[0013] [particle] The particles contain a copolymer having structural units derived from an α-methylene lactone and structural units derived from a (meth)acrylic acid ester.

[0014] (Structural unit derived from α-methylene lactone) α-Methylene lactone is a general term for compounds in which an exomethylene group is bonded to the α-carbon atom of a lactone ring. The number of ring members in the lactone is not particularly limited, but may be, for example, a 4- to 8-membered ring, a 5- to 6-membered ring, or even a 5-membered ring. By including structural units derived from α-methylene lactone in the copolymer, the hardness of the resulting coating film can be improved.

[0015] An example of the five-membered α-methylene lactone is a compound represented by the following formula (1).

[0016] [ka]

[0017] In formula (1), R 1 ~R 4 R each independently represents a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. 1 ~R 4 are preferably each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably all are hydrogen atoms.

[0018] The structural unit derived from α-methylene lactone is formed, for example, by polymerization of α-methylene lactone. The copolymer may contain only one type of structural unit derived from α-methylene lactone, or may contain two or more types. The structural unit derived from α-methylene lactone preferably contains a structural unit represented by the following formula (2). The structural unit represented by the following formula (2) is formed, for example, by polymerization of a monomer containing a compound represented by formula (1).

[0019] [ka]

[0020] In formula (2), R 1 ~R 4 is R in Eq. (1) 1 ~R 4 and each independently represents a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. 1 ~R 4 are preferably each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably all are hydrogen atoms.

[0021] The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, and a cyclohexyl group. Examples of the aromatic hydrocarbon group include a phenyl group, a tolyl group, and a benzyl group.

[0022] The structural unit derived from α-methylene lactone is represented by R in formula (2). 1 ~R 4 It is preferable that the compound contains a structural unit derived from α-methylene-γ-butyrolactone in which all of are hydrogen atoms.

[0023] The content of structural units derived from α-methylene lactone in the copolymer is preferably from 5 to 60% by mass, more preferably from 10 to 55% by mass, and even more preferably from 20 to 50% by mass. By keeping it in such a range, the hardness of the resulting coating film can be further improved.

[0024] (Structural units derived from (meth)acrylic acid esters) (Meth)acrylic acid ester is a general term for esters of (meth)acrylic acid and a compound having a hydroxy group. The (meth)acrylic acid ester includes a (meth)acrylic acid ester (A) (hereinafter sometimes simply referred to as "(meth)acrylic acid ester (A)") having a glass transition temperature (Tg) of 0°C or lower when made into a homopolymer, and may further include a (meth)acrylic acid ester (B) (hereinafter sometimes simply referred to as "(meth)acrylic acid ester (B)") having a glass transition temperature (Tg) of more than 0°C and not higher than 110°C when made into a homopolymer. When the (meth)acrylic acid ester includes the (meth)acrylic acid ester (A), film-forming properties can be improved. The Tg of a homopolymer (single polymer) can be confirmed, for example, from literature such as "POLYMER HANDBOOK Fourth Edition" by J. Brandrup.

[0025] The (meth)acrylic acid ester (A) preferably contains a (meth)acrylic acid ester (A1) (hereinafter sometimes simply referred to as "(meth)acrylic acid ester (A1)") having a glass transition temperature of -80°C or more and 0°C or less when made into a homopolymer. Examples of the (meth)acrylic acid ester (A) ((meth)acrylic acid ester (A1)) include ethyl acrylate (homopolymer Tg: -24°C), n-butyl acrylate (homopolymer Tg: -55°C), 2-ethylhexyl acrylate (homopolymer Tg: -70°C), 2-ethylhexyl methacrylate (homopolymer Tg: -10°C), 2-octyl acrylate (homopolymer Tg: -50°C), 2-octyl methacrylate (homopolymer Tg: -25°C), lauryl acrylate (homopolymer Tg: -3°C), lauryl methacrylate (homopolymer Tg: -65°C), and 2-hydroxyethyl acrylate (homopolymer Tg: -15°C). The (meth)acrylic acid ester (A) ((meth)acrylic acid ester (A1)) may be used alone or in combination of two or more. The (meth)acrylic acid ester (A) ((meth)acrylic acid ester (A1)) preferably contains at least one selected from the group consisting of ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl acrylate.

[0026] In the (meth)acrylic acid ester (A), the content of the (meth)acrylic acid ester (A1) is preferably 60% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, further preferably 90% by mass or more and 100% by mass or less, and may be 100% by mass.

[0027] In the (meth)acrylic acid ester, the content of the (meth)acrylic acid ester (A) is adjusted so that the glass transition temperature of the resulting copolymer is −40° C. or higher and 100° C. or lower. The content of the (meth)acrylic acid ester (A) in the (meth)acrylic acid ester is preferably 20% by mass or higher and 100% by mass or lower, more preferably 25% by mass or higher and 100% by mass or lower, even more preferably 30% by mass or higher and 100% by mass or lower, and may be 100% by mass.

[0028] Examples of the (meth)acrylic acid ester (B) include methyl methacrylate (homopolymer Tg: 105°C), ethyl methacrylate (homopolymer Tg: 65°C), n-butyl methacrylate (homopolymer Tg: 20°C), isobutyl methacrylate (homopolymer Tg: 67°C), cyclohexyl methacrylate (homopolymer Tg: 66°C), 2-hydroxyethyl methacrylate (homopolymer Tg: 55°C), isobornyl acrylate (homopolymer Tg: 97°C), and 2,2,6,6-tetramethyl-4-piperidyl methacrylate (homopolymer Tg: 110°C). The (meth)acrylic acid ester (B) may be used alone or in combination of two or more.

[0029] In the (meth)acrylic acid ester, the content of the (meth)acrylic acid ester (B) is adjusted so that the glass transition temperature of the resulting copolymer is from −40° C. to 100° C. The content of the (meth)acrylic acid ester (B) in the (meth)acrylic acid ester is preferably from 0% to 80% by mass, more preferably from 0% to 75% by mass, even more preferably from 0% to 70% by mass, and may be 0% by mass.

[0030] The structural unit derived from a (meth)acrylic acid ester is formed, for example, by polymerization of a (meth)acrylic acid ester such as a (meth)acrylic acid ester (A) or a (meth)acrylic acid ester (B). The copolymer may contain only one type of structural unit derived from a (meth)acrylic acid ester, or may contain two or more types.

[0031] The content of structural units derived from (meth)acrylic acid ester in the copolymer is preferably 40% by mass to 95% by mass, more preferably 45% by mass to 90% by mass, and even more preferably 50% by mass to 80% by mass, which can further improve the hardness of the resulting coating film.

[0032] (Other structural units) The copolymer may further have other structural units different from the structural units derived from α-methylene lactone and the structural units derived from (meth)acrylic acid ester. Examples of the other structural units include structural units derived from monomers such as acrylic acid (Tg of homopolymer: 106°C), methacrylic acid (Tg of homopolymer: 228°C), styrene, vinyl toluene, α-methylstyrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, and vinyl acetate. The copolymer may contain only one type of other structural unit, or may contain two or more types. Of course, the copolymer may not contain any other structural units. The content of the other structural units in the copolymer may be 0% by mass or more and 20% by mass or less, or 0% by mass or more and 10% by mass or less.

[0033] The content of each structural unit in the copolymer was determined by dissolving the copolymer in a heavy solvent and 1 It can be determined by measuring H-NMR and calculating the area ratio of the peaks corresponding to each structural unit.

[0034] The glass transition temperature (Tg) of the copolymer measured by the onset method is -40°C or higher and 100°C or lower. A glass transition temperature (Tg) of -40°C or higher can provide a coating film with sufficient hardness. A glass transition temperature (Tg) of 100°C or lower can improve the film-forming properties of the emulsion. The glass transition temperature (Tg) of the copolymer measured by the onset method is preferably -30°C or higher, more preferably -15°C or higher, even more preferably 0°C or higher, particularly preferably 15°C or higher, most preferably 30°C or higher, and extremely preferably 45°C or higher. The glass transition temperature (Tg) of the copolymer is measured in accordance with the provisions of JIS K 7121.

[0035] The weight-average molecular weight (Mw) of the copolymer is not particularly limited. As described below, the copolymer can be prepared by emulsion polymerization or the like. For example, when prepared without using a chain transfer agent, the weight-average molecular weight (Mw) of the copolymer can exceed 1,000,000 or 1,500,000.

[0036] The content of the copolymer-containing particles in the emulsion is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 40% by mass or less. By keeping the content in such a range, productivity of the coating film can be improved.

[0037] The average particle size of the copolymer-containing particles in the emulsion is preferably 80 to 400 nm, more preferably 100 to 300 nm, and even more preferably 100 to 350 nm. By keeping the average particle size within this range, it is possible to further improve the film-forming properties and the hardness of the resulting coating film. The average particle size of the particles is the cumulant average particle size measured by dynamic light scattering at a measurement temperature of 25°C.

[0038] [Aqueous dispersion medium] The aqueous dispersion medium is preferably water alone, but may contain a non-aqueous solvent (particularly a water-soluble organic solvent) as long as the effects of the present disclosure are not impaired. Examples of water-soluble organic solvents include alcohol solvents such as methanol, ethanol, propanol, butanol, 2-methylpropyl alcohol, and 2-methyl-2-propanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate; and ether solvents such as dioxane, diethyl ether, and tetrahydrofuran. The content of the non-aqueous solvent in the aqueous dispersion medium may be 5% by mass or less, 2% by mass or less, or 1% by mass or less.

[0039] The content of the aqueous dispersion medium in the emulsion is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less. By keeping the content in such a range, productivity of the coating film can be improved.

[0040] [Additives] The emulsion may further contain an additive (hereinafter, sometimes referred to as "additive A"). Examples of additive A include film-forming aids; antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; ultraviolet absorbers; near-infrared absorbers; flame retardants; antistatic agents; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic antiblocking agents; organic or inorganic fillers; resin modifiers; plasticizers; lubricants; fluidizing agents; and compatibilizers. The emulsion may contain only one type of additive, or may contain two or more types. Of course, the emulsion does not necessarily contain additive A. The content of the additives in the emulsion can be appropriately adjusted according to the composition of the coating film to be obtained.

[0041] <Emulsion manufacturing method> The emulsion can be produced by polymerizing monomers containing α-methylene lactone and a (meth)acrylic acid ester in an aqueous dispersion medium by emulsion polymerization, suspension polymerization, etc. Emulsion polymerization is preferred as the polymerization method, since it results in more uniform particle sizes of particles containing the copolymer and improves film-forming properties.

[0042] In emulsion polymerization, particles containing a copolymer are obtained by polymerizing monomers containing α-methylene lactone and a (meth)acrylic acid ester in an aqueous dispersion medium in the presence of a polymerization initiator and an emulsifier.

[0043] The polymerization initiator is not particularly limited as long as it is a substance that decomposes when heated to generate radical molecules. Examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; azo compounds such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 4,4'-azobis(4-cyanopentanoic acid), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, and 2,2'-azobis(2,4-dimethylvaleronitrile); organic peroxides such as tert-butylperoxy-2-ethylhexanoate, benzoyl peroxide, and di-tert-butyl peroxide; and redox polymerization initiators such as hydrogen peroxide and ascorbic acid, t-butyl hydroperoxide and Rongalite, potassium persulfate and metal salts, ammonium persulfate, and sodium disulfite. The amount of the polymerization initiator added may be adjusted as appropriate, but is preferably 0.01 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the monomer.

[0044] Examples of emulsifiers include anionic surfactants (anionic reactive surfactants or anionic non-reactive surfactants), nonionic surfactants (nonionic reactive surfactants or nonionic non-reactive surfactants), cationic surfactants, amphoteric surfactants, and polymer surfactants. Here, the reactive surfactant refers to a surfactant having a polymerizable group. The emulsifier may be a single type or a combination of two or more types. From the viewpoint of improving the water resistance of the coating film, it is preferable that the emulsifier contains a reactive surfactant.

[0045] Examples of anionic reactive surfactants include polyoxyethylene alkyl ether sulfates, polyoxyalkylene styrenated phenyl ether sulfates, sulfosuccinates, polyoxyethylene alkyl phenyl ether sulfates or polyoxyethylene alkyl phenyl ester sulfates, (meth)acrylate sulfates, and phosphates.

[0046] Examples of anionic non-reactive surfactants include higher fatty acid salts such as sodium oleate; alkylarylsulfonates such as sodium dodecylbenzenesulfonate; alkyl sulfates such as sodium lauryl sulfate; and polyoxyethylene alkyl ether sulfates such as sodium polyethylene lauryl ether sulfate.

[0047] Examples of nonionic reactive surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene styrenated phenyl ethers, and polyoxyethylene alkyl phenyl ethers.

[0048] Examples of nonionic non-reactive surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene styrenated phenyl ethers, polyoxyethylene alkyl phenyl ethers, polyglycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene lanolins, polyoxyethylene hydrogenated castor oils, and polyoxyethylene sterols.

[0049] Examples of cationic surfactants include alkyl ammonium salts such as dodecyl ammonium chloride.

[0050] Examples of amphoteric surfactants include betaine ester emulsifiers.

[0051] Examples of polymer surfactants include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; and polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate.

[0052] The amount of emulsifier added may be adjusted as appropriate, but is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the monomer.

[0053] In emulsion polymerization, when dispersing the monomer in the aqueous solvent, the dispersion may be carried out by stirring with a paddle blade or the like, or may be carried out using an apparatus such as a high-speed shear turbine type disperser, a high-pressure jet homogenizer, an ultrasonic type emulsifying disperser, a medium stirring disperser, or a forced gap passage type disperser.

[0054] When polymerizing the monomers, a chain transfer agent, an additive (hereinafter sometimes referred to as "additive B"), and the like may be added.

[0055] Examples of chain transfer agents include monofunctional thiol compounds such as n-dodecyl mercaptan, t-dodecyl mercaptan, and β-mercaptopropionic acid; bifunctional thiol compounds such as polysiloxanes modified at both ends with mercapto groups; and side-chain polyfunctional mercapto-modified polysiloxanes in which the side chains are modified with mercapto groups. A chain transfer agent may or may not be added, but if added, the amount of chain transfer agent added is preferably 0.001 to 1 part by mass per 100 parts by mass of the monomer.

[0056] Examples of additive B include a water-insoluble organic solvent such as an alkane, and a radical scavenger. The amount of additive added may be adjusted as appropriate, but is preferably 0.001 part by mass or more and 1 part by mass or less relative to 100 parts by mass of the monomer.

[0057] The polymerization temperature is preferably from 40° C. to 100° C., more preferably from 50° C. to 95° C., and even more preferably from 60° C. to 90° C. The polymerization time is preferably from 0.5 hours to 20 hours, and more preferably from 1 hour to 10 hours.

[0058] The reaction solution after polymerization can be used as an emulsion as it is. The reaction solution after polymerization may be purified by filtration or the like, if necessary.

[0059] If necessary, the above-mentioned additive A may be added to the obtained emulsion.

[0060] <Coating film and its manufacturing method> In one embodiment, the coating film contains a copolymer having structural units derived from α-methylene lactone and structural units derived from a (meth)acrylic acid ester. The (meth)acrylic acid ester includes a (meth)acrylic acid ester (A). The glass transition temperature of the copolymer is −40° C. or higher and 100° C. or lower. The copolymer is the same as the copolymer contained in the emulsion described above. Therefore, a redundant description will be omitted here.

[0061] The coating film can be produced by a method including the steps of applying the above-mentioned emulsion (paint) and drying the applied emulsion to form a coating film.

[0062] The emulsion is applied to a support, for example. Examples of the support material include organic materials such as polyolefin resins (such as polypropylene resins), polyamide resins, polyimide resins, ABS (acrylonitrile butadiene styrene) resins, PC (polycarbonate) resins, PET (polyethylene terephthalate) resins, PPS (polyphenylene sulfide) resins, acrylic resins, and transparent resins; inorganic materials such as steel, stainless steel (SUS), metals (aluminum, copper, nickel, chromium, and the like) or alloys of these metals, glass, and silicon wafers; wood; and rubber.

[0063] Examples of methods for applying the emulsion include methods using a die coater, doctor blade coater, roll coater, comma coater, lip coater, applicator, spray, and the like.

[0064] The emulsion can be dried, for example, by heating within a temperature range that does not cause foam marks on the coating film.

[0065] The heating temperature when drying the emulsion is preferably from 20° C. to 100° C., more preferably from 20° C. to 90° C., and even more preferably from 20° C. to 80° C. This makes it possible to improve the drying efficiency of the aqueous dispersion medium while suppressing the formation of foam marks.

[0066] The heating time for drying the emulsion is preferably from 5 to 120 minutes, more preferably from 10 to 80 minutes, which can improve the drying efficiency of the aqueous dispersion medium.

[0067] The thickness of the coating film is preferably 1 μm or more and 300 μm or less, and more preferably 5 μm or more and 100 μm or less.

[0068] From the viewpoint of improving the strength of the coating film, the pencil hardness of the coating film is HB or more and 4H or less, preferably H or more, more preferably 2H or more, and even more preferably 3H or more.

[0069] The coating film of this embodiment can be used in a variety of applications, and is useful for paints, coatings, inks, pressure sensitive adhesives, adhesives, electronic materials, cosmetics, medicines, heat storage materials, fibers, civil engineering, and the like. [Example]

[0070] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to these examples. Various physical properties were measured and evaluated as follows.

[0071] In the following examples and comparative examples, the abbreviations for each compound mean the following compounds. MBL: α-methylene-γ-butyrolactone (Tg of homopolymer: 187°C) 2-EHA: 2-ethylhexyl acrylate (Tg of homopolymer: -70°C) BA: n-butyl acrylate (Tg of homopolymer: -55°C) EA: Ethyl acrylate (Tg of homopolymer: -24°C) HEMA: 2-hydroxyethyl methacrylate (Tg of homopolymer: 55°C) CHMA: Cyclohexyl methacrylate (Tg of homopolymer: 66°C) IBOA: Isobornyl acrylate (Tg of homopolymer: 97°C) MMA: Methyl methacrylate (Tg of homopolymer: 105°C) LA-87: 2,2,6,6-tetramethyl-4-piperidyl methacrylate (manufactured by ADEKA Corporation, trade name: Adekastab LA-87) (Tg of homopolymer: 110°C) AA: Acrylic acid (Tg of homopolymer: 106°C)

[0072] <Various physical properties> [Glass transition temperature (Tg) of copolymer] The glass transition temperature of the copolymer was measured in accordance with the provisions of JIS K 7121. Specifically, using a differential scanning calorimeter (Rigaku Thermo plus EVO DSC-8230), the emulsion was dried to remove water and powdered to a weight of approximately 10 mg under a nitrogen gas atmosphere, and the temperature was raised from room temperature to 200°C (heating rate: 20°C / min) to obtain a DSC curve, from which the glass transition temperature was measured by the starting point method. An empty container (α-alumina) was used as a reference.

[0073] [Coating thickness] The thickness of the coating was measured using a Digimatic Micrometer (Mitutoyo, ID-C112).

[0074] [Evaluation of film-forming properties] The appearance of the resulting coating film was visually inspected. When a crack-free area of ​​40 mm x 40 mm or more was confirmed, the film-forming property was evaluated as excellent and rated as "A," while other cases were evaluated as "B." Note that "when a crack-free area of ​​40 mm x 40 mm or more was confirmed" means that when an imaginary square was placed on the coating film so as not to include the cracked area, the length of one side of the largest square that could be placed was 40 mm or more.

[0075] [Evaluation of pencil hardness] The pencil hardness of the coating films that were rated "A" for film-forming properties was evaluated. The pencil hardness was determined in accordance with the provisions of JIS K 5600-5-4. Specifically, using a test pencil specified in JIS S 6006, the evaluation was performed using a pencil scratch hardness tester No. 533 (manufactured by Yasuda Seiki Seisakusho) with a load of 750 g. The hardest pencil hardness that did not cause scratches was taken as the pencil hardness.

[0076] Example 1 <Preparation of coating film> [Preparation of emulsion] A flask equipped with a dropping funnel, a stirrer, a nitrogen inlet tube, a thermometer, and a reflux condenser was charged with 200 parts by weight of deionized water. A mixture was prepared by adding 22 parts by weight of deionized water, 10 parts by weight of a 25% by weight aqueous solution of an anionic reactive surfactant (manufactured by ADEKA Corporation, trade name: ADEKA REASOAP® SR-20), 10 parts by weight of a 25% by weight aqueous solution of a nonionic reactive surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: AQUALON® AN-20), 40 parts by weight of MBL, and 60 parts by weight of 2-EHA to the dropping funnel. 2.5 parts by weight of the mixture was added to the flask, and the flask was heated to 60°C while blowing in nitrogen gas. Polymerization was then initiated by adding 2 parts by weight of a 5% by weight aqueous solution of ammonium persulfate (APS) to the flask. Next, the remainder of the mixture in the dropping funnel, along with 2 parts by mass of a 5% by mass aqueous solution of APS and 2 parts by mass of a 5% by mass aqueous solution of sodium disulfite (SMBS) from separate dropping funnels, were added dropwise into the flask over 180 minutes. After the dropping was completed, the temperature inside the flask was maintained at 60°C for 60 minutes to terminate the polymerization reaction. The resulting reaction solution was cooled to room temperature and then filtered through a 300 mesh (JIS mesh) wire mesh to obtain an emulsion of Example 1 with a solids content of 30% by mass.

[0077] [Creating coating film] To 100 parts by mass of the resulting emulsion, 10 parts by mass of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (manufactured by JNC Corporation, trade name: CS-12) as a film-forming aid was added to prepare a sample. The sample was applied to a glass plate (70 mm × 150 mm, thickness: 2 mm) using an applicator with a coating width of 50 mm. The applied sample was dried at 23°C for 5 minutes and then dried in a dryer at 70°C for 15 minutes to produce the coating film of Example 1. The dimensions of the coating film were 50 mm × 100 mm × 20 μm. The physical properties of the coating film of Example 1 are shown in Table 1.

[0078] Example 2 Except for changing 40 parts by mass of MBL and 60 parts by mass of 2-EHA to 40 parts by mass of MBL and 60 parts by mass of BA, the emulsion and coating film of Example 2 were obtained in the same manner as in Example 1. The physical properties of the coating film of Example 2 are shown in Table 1.

[0079] Example 3 <Preparation of coating film> [Preparation of emulsion] A flask equipped with a dropping funnel, a stirrer, a nitrogen inlet tube, a thermometer, and a reflux condenser was charged with 200 parts by weight of deionized water. 22 parts by weight of deionized water, 10 parts by weight of a 25% by weight aqueous solution of an anionic reactive surfactant (manufactured by ADEKA Corporation, trade name: ADEKA REASOAP® SR-20), 10 parts by weight of a 25% by weight aqueous solution of a nonionic reactive surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: AQUALON® AN-20), 40 parts by weight of MBL, 20 parts by weight of 2-EHA, 38 parts by weight of CHMA, and 2 parts by weight of LA-87 were added to the dropping funnel to prepare a mixed solution. 2.5 parts by weight of the mixed solution was added to the flask, and the flask was heated to 70°C while blowing in nitrogen gas. Polymerization was then initiated by adding 2 parts by weight of a 5% by weight aqueous solution of ammonium persulfate (APS) to the flask. Next, the remainder of the mixture in the dropping funnel and 2 parts by mass of a 5% by mass aqueous solution of APS were added dropwise to the flask over 180 minutes from separate dropping funnels. After the addition was completed, the temperature in the flask was maintained at 70°C for 60 minutes to terminate the polymerization reaction. The resulting reaction solution was cooled to room temperature and then filtered through a 300 mesh (JIS mesh) wire mesh to obtain an emulsion of Example 3 with a solids content of 30% by mass.

[0080] [Creating coating film] The coating film of Example 3 was obtained in the same manner as in Example 1. The physical properties of the coating film of Example 3 are shown in Table 1.

[0081] Example 4 <Preparation of coating film> [Preparation of emulsion] A flask equipped with a dropping funnel, a stirrer, a nitrogen inlet tube, a thermometer, and a reflux condenser was charged with 200 parts by weight of deionized water. 22 parts by weight of deionized water, 10 parts by weight of a 25% by weight aqueous solution of an anionic reactive surfactant (manufactured by ADEKA Corporation, trade name: ADEKA REASOAP® SR-20), 10 parts by weight of a 25% by weight aqueous solution of a nonionic reactive surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon® AN-20), 20 parts by weight of MBL, 28 parts by weight of 2-EHA, 1 part by weight of HEMA, 50 parts by weight of CHMA, and 1 part by weight of AA were added to the dropping funnel to prepare a mixed solution. 2.5 parts by weight of the mixed solution was added to the flask, and the flask was heated to 60°C while blowing in nitrogen gas. Thereafter, 1.5 parts by mass of a 10% by mass aqueous solution of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-50) was added to the flask to initiate polymerization. Next, the remainder of the mixed solution in the dropping funnel and 1.5 parts by mass of a 10% by mass aqueous solution of V-50 were each added dropwise to the flask from separate dropping funnels over 180 minutes. After completion of the dropping, the flask was maintained at 60°C for 60 minutes to terminate the polymerization reaction. The resulting reaction solution was cooled to room temperature and then filtered through a 300 mesh (JIS mesh) wire mesh to obtain an emulsion of Example 4 with a solids content of 30% by mass.

[0082] [Creating coating film] The coating film of Example 4 was obtained in the same manner as in Example 1. The physical properties of the coating film of Example 4 are shown in Table 1.

[0083] Example 5 <Preparation of coating film> [Preparation of emulsion] A flask equipped with a dropping funnel, a stirrer, a nitrogen inlet tube, a thermometer, and a reflux condenser was charged with 200 parts by weight of deionized water. 22 parts by weight of deionized water, 15 parts by weight of a 20% by weight aqueous solution of an anionic reactive surfactant (manufactured by Kao Corporation, trade name: Latemul® PD-104), 10 parts by weight of a 25% by weight aqueous solution of an anionic reactive surfactant (manufactured by ADEKA Corporation, trade name: Adeka Reasoap® SR-20), 50 parts by weight of MBL, 15 parts by weight of EA, 34 parts by weight of IBOA, and 1 part by weight of AA were added to the dropping funnel to prepare a mixed solution. 2.5 parts by weight of the mixed solution was added to the flask, and the flask was heated to 60°C while blowing in nitrogen gas. Polymerization was then initiated by adding 2 parts by weight of a 5% by weight aqueous solution of ammonium persulfate (APS) to the flask. Next, the remainder of the mixture in the dropping funnel, along with 2 parts by mass of a 5% by mass aqueous solution of APS and 2 parts by mass of a 5% by mass aqueous solution of sodium disulfite (SMBS) from separate dropping funnels, were added dropwise into the flask over 180 minutes. After the addition was completed, the temperature inside the flask was maintained at 60°C for 60 minutes to terminate the polymerization reaction. The resulting reaction solution was cooled to room temperature and then filtered through a 300 mesh (JIS mesh) wire mesh to obtain an emulsion of Example 5 with a solids content of 30% by mass.

[0084] [Creating coating film] The coating film of Example 5 was obtained in the same manner as in Example 1. The physical properties of the coating film of Example 5 are shown in Table 1.

[0085] Example 6 The emulsion and coating film of Example 6 were obtained in the same manner as in Example 1, except that 40 parts by mass of MBL and 60 parts by mass of 2-EHA were changed to 30 parts by mass of MBL and 70 parts by mass of 2-EHA. The physical properties of the coating film of Example 6 are shown in Table 1.

[0086] (Comparative Example 1) Except for changing 40 parts by mass of MBL and 60 parts by mass of 2-EHA to 60 parts by mass of 2-EHA and 40 parts by mass of MMA, the emulsion and coating film of Comparative Example 1 were obtained in the same manner as in Example 1. The physical properties of the coating film of Comparative Example 1 are shown in Table 1.

[0087] (Comparative Example 2) Except for changing 40 parts by mass of MBL and 60 parts by mass of 2-EHA to 40 parts by mass of MBL and 60 parts by mass of MMA, an emulsion and a coating film of Comparative Example 2 were obtained in the same manner as in Example 1. The physical properties of the coating film of Comparative Example 2 are shown in Table 1.

[0088] [Table 1]

[0089] As shown in Table 1, the coating films formed from the emulsions of Examples 1 to 6 were excellent in both film-forming properties and hardness. In contrast, the coating films formed from the emulsions of Comparative Examples 1 and 2 were poor in either film-forming properties or hardness. The coating film formed from the emulsion of Comparative Example 1 is presumed to have poor pencil hardness because it does not contain structural units derived from MBL. The coating film formed from the emulsion of Comparative Example 2 is presumed to have poor film-forming properties because it has a high glass transition temperature. These results confirm that the emulsions of the present disclosure are excellent in film-forming properties and are capable of forming coating films with sufficient hardness.

Claims

1. The dispersion medium comprises particles containing a copolymer having a structural unit derived from α-methylene lactone and a structural unit derived from a (meth)acrylic acid ester, and an aqueous dispersion medium, the (meth)acrylic acid ester includes a (meth)acrylic acid ester (A) having a glass transition temperature of 0°C or lower when formed into a homopolymer, The emulsion, wherein the copolymer has a glass transition temperature of −40° C. or higher and 100° C. or lower.

2. The emulsion according to claim 1, wherein the (meth)acrylic acid ester (A) comprises a (meth)acrylic acid ester (A1) having a glass transition temperature of −80° C. or higher and 0° C. or lower when formed into a homopolymer.

3. The emulsion according to claim 1 or 2, wherein the α-methylene lactone comprises α-methylene-γ-butyrolactone.

4. The emulsion according to claim 1 or 2, wherein the (meth)acrylic acid ester (A) comprises at least one selected from the group consisting of ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl acrylate.

5. The emulsion according to claim 1 or 2, further comprising a (meth)acrylic acid ester (B) having a glass transition temperature of more than 0°C and not more than 110°C when the (meth)acrylic acid ester is made into a homopolymer.

6. 3. The emulsion according to claim 1 or 2, which is a paint.

7. A method for producing a coating film, comprising the steps of applying the emulsion according to claim 6 and drying the applied emulsion to form a coating film.

8. The copolymer contains a structural unit derived from α-methylene lactone and a structural unit derived from a (meth)acrylic acid ester, the (meth)acrylic acid ester includes a (meth)acrylic acid ester (A) having a glass transition temperature of 0°C or lower when formed into a homopolymer, the copolymer has a glass transition temperature of −40° C. or higher and 100° C. or lower; A coating film having a pencil hardness of HB or more and 4H or less.

9. The coating film according to claim 8, wherein the (meth)acrylic acid ester (A) comprises a (meth)acrylic acid ester (A1) having a glass transition temperature of −80° C. or higher and 0° C. or lower when formed into a homopolymer.

10. The coating film according to claim 8 or 9, wherein the α-methylene lactone comprises α-methylene-γ-butyrolactone.

11. The coating film according to claim 8 or 9, wherein the (meth)acrylic acid ester (A) comprises at least one selected from the group consisting of ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl acrylate.

12. The coating film according to claim 8 or 9, further comprising a (meth)acrylic acid ester (B) having a glass transition temperature of more than 0°C and not more than 110°C when formed into a homopolymer.

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