Aqueous coating composition

Abstract

This aqueous coating composition contains acrylic modified epoxy resin particles (A) having a glass transition temperature of 30°C or higher, acrylic resin particles (B) having a glass transition temperature of 30°C or lower, and an organic solvent (C). The composition includes, as solids content, 20-60 mass% of the acrylic modified epoxy resin particles (A) and 40-80 mass% of the acrylic resin particles (B) relative to the total solids content of the acrylic modified epoxy resin particles (A) and the acrylic resin particles (B). The weighted average boiling point of the organic solvent (C) is 200°C or lower.

Description

water-based paint composition

[0001] The present invention relates to an aqueous coating composition.

[0002] Conventionally, steel materials such as lightweight steel used in construction applications have been coated with anti-rust paint to provide rust prevention. Solvent-based paints have been used as anti-rust paints, but in recent years, water-based paints have been used as environmental measures.

[0003] In the production line of lightweight steel and other steel materials, painting is generally carried out by applying molding oil, degreasing the formed steel material, preheating it to the desired temperature (approximately 80 to 110°C), and then airlessly painting the anti-rust paint onto it.

[0004] Because the above process is carried out in a short time (about 5 minutes from forming the steel to bundling the coated steel), the anti-rust paint must be quick-drying and highly hard.Furthermore, because the coated steel is bundled, stacked, and transported by crane within a few minutes, the paint must also have excellent blocking resistance (the paint films do not stick to each other).

[0005] In addition, the Ministry of Land, Infrastructure, Transport and Tourism's "Standard Specifications for Public Building Construction" stipulates that paints that meet the standards of JIS K5674 (lead- and chromium-free rust-preventive paint) must be used as rust-preventive paints for steel products, steel structures, etc., and public buildings are required to use paints that have obtained JIS standard certification.

[0006] Patent Document 1 discloses an aqueous coating composition containing 10 to 80 parts by weight of a water-based acrylic-modified alkyd resin (A) and 20 to 90 parts by weight of a water-based acrylic-modified epoxy resin (B) as a binder, as a coating composition excellent in oily surface adhesion, high-temperature finish, roll-touch coating film peelability, blocking resistance, and rust prevention.

[0007] Patent Document 2 discloses an aqueous rust-preventive composition characterized by blending 100 parts by weight of an aqueous resin composition consisting of 20 to 100 parts by weight of a styrene-butadiene copolymer having a glass transition point of 30 to 80°C and 0 to 80 parts by weight of an ethylene-acrylic acid copolymer with 1 to 30 parts by weight of a water-soluble solvent and 0.01 to 2.0 parts by weight of an aqueous chromium compound in terms of chromate ions, and adjusting the pH to 7 or higher.

[0008] Patent Document 3 discloses an aqueous coating composition characterized by containing, as resin components, urethane resin particles having a specific weight-average molecular weight range and glass transition temperature range, and acrylic resin particles having a specific glass transition temperature range.

[0009] Japanese Unexamined Patent Publication No. 7-300574 Japanese Unexamined Patent Publication No. 11-172189 Japanese Unexamined Patent Application No. 2020-2327

[0010] However, the aqueous coating composition described in Patent Document 1 is excellent in rust prevention and film-forming properties (quick-drying), but is insufficient in blocking resistance. The aqueous rust-preventive composition described in Patent Document 2 is excellent in rust prevention, but contains harmful chromium compounds, making it undesirable from the viewpoint of environmental protection. The aqueous paint composition described in Patent Document 3 is excellent in quick-drying, blocking resistance, and rust prevention, but may have insufficient coating film performance such as water resistance (water-resistant adhesion).

[0011] The object of the present invention is to provide an aqueous coating composition that can be used for both room-dry coating and baking coating, that has excellent film-forming properties, water resistance (water-resistant adhesion), blocking resistance and rust prevention properties, and that is free of environmentally hazardous substances (such as lead and chromium) and can form a coating film of high hardness.

[0012] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an aqueous coating composition containing acrylic-modified epoxy resin particles having a specific glass transition temperature range, and acrylic resin particles having a specific glass transition temperature range and an organic solvent, wherein the weighted average boiling point of the organic solvent is a specific temperature or lower, and have thus completed the present invention.

[0013] That is, the present invention is characterized by the following items 1 to 4. 1. An aqueous coating composition containing acrylic-modified epoxy resin particles (A) having a glass transition temperature of 30°C or higher, acrylic resin particles (B) having a glass transition temperature of 30°C or lower, and an organic solvent (C), wherein the acrylic-modified epoxy resin particles (A) account for 20 to 60 mass% and the acrylic resin particles (B) account for 40 to 80 mass% in terms of solid content relative to the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B), and the weighted average boiling point of the organic solvent (C) is 200°C or lower.

[0014] 2. The aqueous coating composition according to item 1, further comprising at least one of a rust inhibitor (D) and a pigment (E).

[0015] 3. The aqueous coating composition according to item 2, wherein the total solid content of the rust inhibitor (D) and the pigment (E) is 10 to 400 mass% based on the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B).

[0016] 4. A coating method comprising the steps of preheating an object to be coated, coating it with the aqueous coating composition described in any one of items 1 to 3 above, and then drying it using residual heat.

[0017] The aqueous coating composition of the present invention uses, as its resin components, a combination of acrylic-modified epoxy resin particles with a high glass transition temperature and acrylic resin particles with a low glass transition temperature, and is characterized in that the weighted average boiling point of the contained organic solvent is below a specific temperature. This makes it possible to obtain a coating film that achieves both film-forming properties (quick drying) and blocking resistance, and that also has excellent rust prevention properties and performance such as water resistance.

[0018] Furthermore, the aqueous coating composition of the present invention can be used for both ambient dry coating and baking coating, and by applying the aqueous coating composition of the present invention, it can be used not only for outdoor coating (ambient dry coating) at construction sites and the like, but also for efficient coating (usually baking coating) in production lines for coated steel materials and the like, thereby achieving the effect of producing coated articles such as coated steel materials with excellent rust prevention properties.

[0019] The present invention will be described in detail below, but these are examples of preferred embodiments, and the present invention is not limited to these details. In this specification, "mass" has the same meaning as "weight."

[0020] The aqueous coating composition of the present invention contains acrylic-modified epoxy resin particles (A) having a glass transition temperature of 30°C or higher, acrylic resin particles (B) having a glass transition temperature of 30°C or lower, and an organic solvent (C), wherein the aqueous coating composition contains 20 to 60 mass% of the acrylic-modified epoxy resin particles (A) and 40 to 80 mass% of the acrylic resin particles (B) in terms of solid content relative to the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B), and the weighted average boiling point of the organic solvent (C) is 200°C or lower.

[0021] The aqueous paint composition of the present invention (hereinafter sometimes referred to as "the paint") will be described in detail below.

[0022] <Acrylic-Modified Epoxy Resin Particles (A)> Acrylic-modified epoxy resin particles (A) (hereinafter sometimes referred to as "component (A)") are particles of an epoxy resin modified with acrylic, and the acrylic-modified epoxy resin can be produced, for example, by the following methods (1) to (3): (1) A method in which a polymerizable unsaturated monomer, for example, an acrylic monomer, is graft-polymerized onto an epoxy resin by a hydrogen abstraction reaction; (2) A method in which a carboxyl-group-containing polymerizable unsaturated monomer, for example, a carboxyl-group-containing acrylic monomer, is esterified with the epoxy group of an epoxy resin, and the acrylic monomer is polymerized with the double bond introduced into the epoxy resin, thereby obtaining an acrylic-modified epoxy resin; (3) A method in which an epoxy resin (a1) is reacted with a carboxyl-group-containing acrylic resin (a2) to obtain an acrylic-modified epoxy resin.

[0023] Of the above, the acrylic-modified epoxy resin produced by method (3) is preferred from the viewpoint of obtaining a coating film having good film-forming properties and excellent rust prevention properties.

[0024] The production of an acrylic-modified epoxy resin by method (3) will be described below.

[0025] The epoxy resin (a1) is a resin obtained by reacting a polyphenol compound with an epihalohydrin, such as epichlorohydrin. Examples of the polyphenol compound include bis(4-hydroxyphenyl)-2,2-propane (also known as "bisphenol A"), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (also known as "bisphenol F"), and 4,4-dihydroxydiphenyl sulfone (also known as "bisphenol S"). From the viewpoint of rust prevention, the epoxy resin (a1) is preferably a bisphenol A epoxy resin.

[0026] Bisphenol A epoxy resins can be obtained, for example, by polymerization of bisphenol A and epichlorohydrin. Bisphenol A epoxy resins can also be obtained by a two-stage polymerization method in which bisphenol A is added to a bisphenol A epoxy resin having a relatively low epoxy equivalent.

[0027] The bisphenol A epoxy resins having a relatively low epoxy equivalent generally have an epoxy equivalent of 160 to 2,000, and examples of commercially available products thereof include jER828EL, jER1001, jER1004, and jER1007 manufactured by Mitsubishi Chemical Corporation; Araldite AER250, Araldite AER260, Araldite AER6071, Araldite AER6004, and Araldite AER6007 manufactured by Asahi Kasei Epoxy Corporation; Epomic R140, Epomic R301, Epomic R304, and Epomic R307 manufactured by Mitsui Chemicals, Inc.; and Adeka Resin EP-4100 and Adeka Resin EP-5100 manufactured by Asahi Denka Co., Ltd.

[0028] The bisphenol A epoxy resin may be a modified epoxy resin obtained by modifying a bisphenol A epoxy resin with a dibasic acid. In this case, the bisphenol A epoxy resin to be reacted with the dibasic acid preferably has a number average molecular weight of 2,000 to 8,000 and an epoxy equivalent weight of 1,000 to 4,000.

[0029] The dibasic acid may be a compound represented by the following general formula: HOOC—(CH ２ ) ｎ -COOH (wherein n is an integer of 1 to 12). Specific examples of dibasic acids include succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, and hexahydrophthalic acid, with adipic acid being preferred.

[0030] The bisphenol A-type modified epoxy resin can be obtained by reacting a mixture of the bisphenol A-type epoxy resin and a dibasic acid in the presence of an esterification catalyst such as tri-n-butylamine, an organic solvent, and the like at a reaction temperature of 120 to 180°C for 1 to 4 hours.

[0031] The bisphenol A type modified epoxy resin is preferred because the dibasic acid molecular chain introduced into the epoxy resin molecule acts as a plasticizing component, improving the substrate adhesion and rust prevention properties of the coating film.

[0032] The epoxy resin (a1) used in the production of the acrylic-modified epoxy resin preferably has a number average molecular weight in the range of 2,000 to 30,000, particularly 5,000 to 30,000, and an epoxy equivalent in the range of 1,000 to 10,000, particularly 1,500 to 10,000, from the viewpoints of the dispersion stability and viscosity of the resulting acrylic-modified epoxy resin in an aqueous medium, the rust prevention properties of the resulting coating film, and the finish.

[0033] The carboxyl group-containing acrylic resin (a2) (hereinafter, sometimes abbreviated as "acrylic resin (a2)") used to produce the acrylic-modified epoxy resin by reacting it with the above-mentioned epoxy resin (a1) is an acrylic copolymer containing, as a monomer skeleton, a carboxyl group-containing polymerizable unsaturated monomer such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, or fumaric acid.

[0034] From the viewpoints of stability in an aqueous medium and the film-forming properties and rust-preventing properties of the resulting coating film, it is preferred that the acrylic copolymer have a weight-average molecular weight in the range of 5,000 to 100,000, particularly 10,000 to 100,000, and a resin acid value in the range of 150 to 700 mgKOH / g, particularly 200 to 500 mgKOH / g.

[0035] Examples of other monomers used in the production of the acrylic resin (a2) other than the carboxyl group-containing polymerizable unsaturated monomer include C1-22 alkyl esters of acrylic acid or methacrylic acid such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, benzyl(meth)acrylate, and stearyl(meth)acrylate; cyclohexyl(meth)acrylate, isobornyl(meth)acrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene; 2-hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate, hydroxyamyl(meth)acrylate, and hydroxypropyl(meth)acrylate. Examples of the hydroxyl group-containing acrylic monomer include caprolactone-modified alkyl(meth)acrylates having a hydroxyl group, which are obtained by ring-opening addition reaction of 1 mole of ε-caprolactone with 1 to 5 moles of ε-caprolactone to 1 mole of a hydroxyalkyl(meth)acrylate such as hydroxyhexyl(meth)acrylate and a hydroxyalkyl(meth)acrylate such as hydroxyethyl(meth)acrylate; acrylamide-based monomers such as acrylamide, methacrylamide, N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, N-n-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, N-n-butoxymethyl(meth)acrylamide, N-sec-butoxymethyl(meth)acrylamide, and N-tert-butoxymethyl(meth)acrylamide; acrylonitrile, methacrylonitrile, vinyl acetate, ethylene, and butadiene.

[0036] In this specification, "(meth)acrylate" means "acrylate or methacrylate", "(meth)acrylic acid" means "acrylic acid or methacrylic acid", "(meth)acryloyl" means "acryloyl or methacryloyl", and "(meth)acrylamide" means "acrylamide or methacrylamide".

[0037] The acrylic resin (a2) can be obtained by copolymerizing a monomer mixture of the carboxyl group-containing polymerizable unsaturated monomer and the other monomer in an organic solvent, for example, in the presence of a radical polymerization initiator and / or a chain transfer agent at 80 to 150°C for 1 to 10 hours.

[0038] Examples of the polymerization initiator include organic peroxide initiators, azo initiators, etc. Examples of the organic peroxide initiators include benzoyl peroxide, t-butylperoxy 2-ethylhexanoate, di-t-butyl peroxide, t-butylperoxybenzoate, t-amylperoxy 2-ethylhexanoate, etc., and examples of the azo initiators include azobisisobutyronitrile, azobisdimethylvaleronitrile, etc. Examples of the chain transfer agent include α-methylstyrene dimer, mercaptans, etc.

[0039] The acrylic-modified epoxy resin can be obtained, for example, by esterifying the epoxy resin (a1) and the acrylic resin (a2) in an organic solvent in the presence of an esterification catalyst, for example, a tertiary amine such as triethylamine or dimethylethanolamine, or a trialkylphosphine such as triphenylphosphine, at 80 to 120°C for 0.5 to 8 hours.

[0040] In the acrylic-modified epoxy resin, the mass ratio of the epoxy resin (a1) to the acrylic resin (a2) may be appropriately selected depending on the coating workability, coating film performance, etc., but the solids mass ratio of resin (a1) / resin (a2) is preferably within the range of 10 / 90 to 95 / 5, particularly 20 / 80 to 90 / 10.

[0041] In this specification, "solid content" refers to the proportion of nonvolatile components in a sample excluding volatile components such as water and organic solvents, and can be determined by drying approximately 2 g of a sample at 105°C for 3 hours and then determining the mass before and after drying. In this specification, "solid content mass" refers to the mass of nonvolatile components in a sample.

[0042] From the viewpoints of stability in an aqueous medium, and the blocking resistance and rust prevention properties of the resulting coating film, the acrylic-modified epoxy resin preferably has an acid value in the range of 20 to 120 mgKOH / g, particularly 30 to 100 mgKOH / g, and a weight-average molecular weight in the range of 1,000 to 40,000, particularly 2,000 to 20,000.

[0043] In this specification, the weight average molecular weight and number average molecular weight are values ​​obtained by converting the retention time (retention volume) measured by gel permeation chromatography using tetrahydrofuran as a solvent, based on the average molecular weight of polystyrene.

[0044] The gel permeation chromatograph may be, for example, "HLC8120GPC" (manufactured by Tosoh Corporation), and four columns, "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (all trade names manufactured by Tosoh Corporation), are used under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL / min, and detector: RI.

[0045] The acrylic-modified epoxy resin particles (A) can be obtained by neutralizing the above-mentioned acrylic-modified epoxy resin and dispersing it in an aqueous medium to form an aqueous dispersion.

[0046] The neutralizing agent used for neutralization is not particularly limited as long as it is used as a neutralizing agent in the technical field, but is preferably an amine, ammonia, etc. Representative examples of the amines include triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, morpholine, etc.

[0047] Of the above amines, dimethylethanolamine and triethylamine can be preferably used from the viewpoint of particle stability.

[0048] The degree of neutralization of the acrylic-modified epoxy resin is not particularly limited, but it is preferable to neutralize the acrylic-modified epoxy resin in a range of 0.3 to 2.0 equivalents, particularly 0.5 to 1.0 equivalents, relative to the carboxyl groups in the acrylic-modified epoxy resin. Examples of aqueous media for producing an aqueous dispersion of the acrylic-modified epoxy resin particles (A) include water and mixtures of water and organic solvents.

[0049] As the organic solvent, any organic solvent known in the art can be used as long as it does not cause any problems in the stability of the acrylic-modified epoxy resin particles (A) and is uniformly miscible with water. Examples of the organic solvent include ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and diethylene glycol monoethyl ether.

[0050] Furthermore, as the organic solvent, even organic solvents that are not uniformly miscible with water can be used as long as they are inactive and not reactive with the acrylic-modified epoxy resin particles (A) and do not cause any problems in the stability of the acrylic-modified epoxy resin particles (A).

[0051] Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, and ketone solvents such as methyl ethyl ketone.

[0052] From the viewpoint of blocking resistance, the organic solvent preferably has a boiling point of 200° C. or less, particularly 170° C. or less.

[0053] The aqueous dispersion of the acrylic-modified epoxy resin particles (A) can be prepared according to a method commonly used in the art, and examples thereof include a method in which the acrylic-modified epoxy resin is gradually added to an aqueous medium containing a neutralizing agent while stirring the aqueous medium; a method in which the acrylic-modified epoxy resin is neutralized with a neutralizing agent and then an aqueous medium is added to the stirred acrylic-modified epoxy resin; or a method in which the acrylic-modified epoxy resin is added to a stirred aqueous medium.

[0054] In order to improve the dispersibility of the acrylic-modified epoxy resin particles (A), an emulsifier such as a surfactant may be used.

[0055] As the emulsifier, well-known general anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymeric surfactants, reactive surfactants, etc., which are used in epoxy emulsions, can be used. Of these, anionic surfactants and nonionic surfactants can be preferably used.

[0056] Examples of the anionic surfactant include alkyl sulfates such as sodium dodecyl sulfate, potassium dodecyl sulfate, and ammonium dodecyl sulfate; sodium dodecyl polyglycol ether sulfate; sodium sulforicinoleate; alkyl sulfonates such as alkali metal salts of sulfonated paraffin and ammonium salts of sulfonated paraffin; fatty acid salts such as sodium laurate, triethanolamine oleate, and triethanolamine abietate; alkylaryl sulfonates such as sodium benzenesulfonate and alkali metal sulfates of alkali phenol hydroxyethylene; high alkyl naphthalene sulfonate; naphthalene sulfonate-formalin condensate; dialkyl sulfosuccinate; polyoxyethylene alkyl sulfate salts; and polyoxyethylene alkylaryl sulfate salts.

[0057] Examples of the nonionic surfactant include ethylene oxide and / or propylene oxide adducts of alcohols having 1 to 18 carbon atoms, ethylene oxide and / or propylene oxide adducts of alkylphenols, and ethylene oxide and / or propylene oxide adducts of alkylene glycols and / or alkylenediamines.

[0058] Examples of the alcohols having 1 to 18 carbon atoms that constitute the nonionic surfactant include methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol, tertiary butanol, amyl alcohol, isoamyl alcohol, tertiary amyl alcohol, hexanol, octanol, decane alcohol, lauryl alcohol, myristyl alcohol, palmityl alcohol, and stearyl alcohol. Examples of alkylphenols include phenol, methylphenol, 2,4-di-tert-butylphenol, 2,5-di-tert-butylphenol, 3,5-di-tert-butylphenol, 4-(1,3-tetramethylbutyl)phenol, 4-isooctylphenol, 4-nonylphenol, 4-tert-octylphenol, and 4-dodecanol. Examples of alkylene glycols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 1,6-hexanediol. Examples of alkylene diamines include those in which the alcoholic hydroxyl group of these alkylene glycols has been substituted with an amino group. The ethylene oxide and propylene oxide adducts may be random adducts or block adducts.

[0059] When these emulsifiers are used, there are no particular limitations on the amount used, and any amount can be used. However, if the mass ratio relative to the acrylic-modified epoxy resin particles is less than 0.01, sufficient dispersibility may not be obtained, and if it exceeds 0.3, the water resistance of the resulting coating film may decrease. Therefore, the mass ratio is preferably 0.01 to 0.3, and more preferably 0.05 to 0.2.

[0060] The weight average molecular weight of the acrylic-modified epoxy resin particles (A) is preferably in the range of 1,000 to 40,000, particularly 1,500 to 30,000, and more particularly 2,000 to 20,000, from the viewpoint of blocking resistance and rust prevention.

[0061] From the viewpoint of blocking resistance and rust prevention, the glass transition temperature (Tg) of the acrylic-modified epoxy resin particles (A) is 30° C. or higher, preferably 40 to 100° C., and particularly preferably 50 to 90° C. When the acrylic-modified epoxy resin particles (A) have a glass transition temperature (Tg) of 30° C. or higher, the hardness can be increased, and the blocking resistance and rust prevention properties of the aqueous coating composition are improved.

[0062] In this specification, the glass transition temperature (Tg) of the acrylic-modified epoxy resin particles (A) is determined by differential scanning calorimetry (DSC). Specifically, using a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Inc.), a sample is placed in a measuring cup, and the solvent is completely removed by vacuum suction. Then, the change in calorific value is measured in the range of -20°C to +200°C at a heating rate of 3°C / min, and the first change point in the baseline on the low temperature side can be measured as the glass transition temperature.

[0063] From the viewpoint of dispersion stability of the particles, the average particle size of the acrylic-modified epoxy resin particles (A) is preferably within the range of 50 to 500 nm, more preferably 100 to 350 nm, and even more preferably 150 to 280 nm.

[0064] The average particle size can be measured using a common measurement method such as laser light scattering. In this specification, the average particle size of resin particles is a value measured at 20°C using a submicron particle size distribution analyzer after dilution with deionized water in a conventional manner. As the submicron particle size distribution analyzer, for example, a "COULTER N4 type" (trade name, manufactured by Beckman Coulter, Inc.) can be used.

[0065] As the acrylic-modified epoxy resin particles (A), commercially available products that satisfy the above-mentioned glass transition temperature requirements can also be used, such as Modelpics 304 and Modelpics 307 manufactured by Arakawa Chemical Industries, Ltd.

[0066] <Acrylic Resin Particles (B)> The acrylic resin particles (B) (hereinafter, sometimes referred to as “component (B)”) may be those synthesized by either emulsion polymerization or solution polymerization, and both may be used in combination. However, from the viewpoint of blocking resistance, those synthesized by emulsion polymerization are preferably used.

[0067] The acrylic resin of the acrylic resin particles (B) includes copolymer resins such as acrylic styrene resin, acrylic urethane resin, acrylic silicone resin, acrylic alkyd resin, and acrylic SBR resin (acrylic modified epoxy resins are excluded).

[0068] The emulsion polymerization can be carried out by a conventionally known method such as a seed polymerization method or a mini-emulsion polymerization method, and can be carried out, for example, by emulsion polymerizing a polymerizable unsaturated monomer using a polymerization initiator in the presence of an emulsifier.

[0069] More specifically, the emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol as needed, and the polymerizable unsaturated monomer and the polymerization initiator are added dropwise to the aqueous medium while heating and stirring. The polymerizable unsaturated monomer may also be added dropwise in a similar manner, by previously emulsifying the polymerizable unsaturated monomer using an emulsifier and water.

[0070] Suitable emulsifiers include anionic surfactants and nonionic surfactants. Examples of the anionic surfactants include sodium salts and ammonium salts of alkylsulfonic acids, alkylbenzenesulfonic acids, alkylphosphates, and the like. Examples of the nonionic surfactants include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monostearate, sorbitan trioleate, and polyoxyethylene sorbitan monolaurate. It is also possible to use a polyoxyalkylene group-containing anionic surfactant having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule, or a reactive anionic surfactant having the anionic group and a polymerizable unsaturated group in one molecule.

[0071] Specific examples of reactive anionic surfactants include ELEMINOL JS-1, ELEMINOL JS-2 (manufactured by Sanyo Chemical Industries, Ltd.), S-120, S-180A, S-180, LATEMUL PD-104, LATEMUL PD-420, LATEMUL PD-430S, LATEMUL PD-450 (manufactured by Kao Corporation), AQUALON HS-10, AQUALON KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), ADEKA REASOAP SE-10N, ADEKA REASOAP SE-20N, ADEKA REASOAP SR-1025, ADEKA REASOAP ER-10, ADEKA REASOAP ER-20, ADEKA REASOAP ER-30, ADEKA REASOAP ER-40 (manufactured by ADEKA Corporation), and ANTOX MS-60 (manufactured by Nippon Nyukazai Co., Ltd.).

[0072] The dispersion stabilizers such as the above emulsifiers may be used alone or in combination of two or more in the emulsion polymerization reaction.

[0073] The amount of the emulsifier used is preferably 0.1 to 15% by mass, particularly 0.5 to 10% by mass, and more particularly 1 to 5% by mass, based on the total amount of all monomers used.

[0074] Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butylperoxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; azobisisobutyronitrile, azobis(2,4-dimethylamino)methylpropional; Examples of suitable polymerization initiators include azo compounds such as azobis(2-methylpropiononitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These polymerization initiators can be used alone or in combination of two or more. Furthermore, the above polymerization initiators can also be used in combination with a reducing agent such as sugar, sodium formaldehyde sulfoxylate, or an iron complex, as needed, to form a redox initiator.

[0075] The amount of the polymerization initiator used is generally 0.1 to 5 mass %, and particularly preferably 0.2 to 3 mass %, based on the total amount of all monomers used. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on the type and amount. For example, the polymerization initiator may be previously added to the monomer mixture or aqueous medium, or may be added all at once or dropwise during polymerization.

[0076] A chain transfer agent can also be used for the purpose of adjusting the molecular weight of the resulting acrylic resin particles (B). Examples of such chain transfer agents include compounds having a mercapto group, such as lauryl mercaptan, t-dodecyl mercaptan, octyl mercaptan, 2-ethylhexyl thioglycolate, 2-methyl-5-tert-butylthiophenol, mercaptoethanol, thioglycerol, mercaptoacetic acid (thioglycolic acid), mercaptopropionate, and n-octyl-3-mercaptopropionate. When such a chain transfer agent is used, its amount is generally preferably within a range of 0.05 to 10% by mass, and particularly preferably 0.1 to 5% by mass, based on the total amount of all monomers used.

[0077] The concentration of all polymerizable unsaturated monomers during the emulsion polymerization reaction is usually within the range of 0.1 to 60% by mass, preferably 0.5 to 50% by mass, and more preferably 1.0 to 50% by mass.

[0078] The reaction temperature is mainly determined by the initiator, and for example, it is preferably 60 to 90° C. for azo compounds and 30 to 70° C. for redox initiators. Generally, the reaction time can be 1 to 8 hours.

[0079] As the polymerizable unsaturated monomer, conventionally known ones can be used, for example, reactive group-containing polymerizable unsaturated monomers and other polymerizable unsaturated monomers can be used. Examples of the reactive group of the reactive group-containing polymerizable unsaturated monomer include reactive functional groups such as a hydroxyl group, an acid group, a carbonyl group, an N-methylol alkyl ether group, an isocyanate group, an epoxy group, an amino group, an alkoxysilyl group, a carbodiimide group, and a hydrazide group.

[0080] Examples of hydroxyl group-containing polymerizable unsaturated monomers include 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, ε-caprolactone-modified tetrahydrofurfuryl (meth)acrylate, ε-caprolactone-modified hydroxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-butoxypropyl (meth)acrylate, and monohydroxyethyl phthalate (meth)acrylate.

[0081] Of these, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and ε-caprolactone-modified hydroxyethyl (meth)acrylate can be preferably used.

[0082] Examples of the acid group-containing polymerizable unsaturated monomer include carboxyl group- or acid anhydride group-containing polymerizable unsaturated monomers.

[0083] Examples of the carboxyl group- or acid anhydride group-containing polymerizable unsaturated monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, and β-carboxyethyl acrylate, or acid anhydrides thereof. Of these, acrylic acid and methacrylic acid are preferred.

[0084] Examples of polymerizable unsaturated monomers containing an acid group other than a carboxyl group or an acid anhydride group include 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, sodium styrenesulfonate, sulfoethyl methacrylate, and its sodium or ammonium salts.

[0085] Examples of carbonyl group-containing polymerizable unsaturated monomers include acrolein, diacetone acrylamide, diacetone methacrylamide, formyl styrene, and vinyl alkyl ketones having 4 to 7 carbon atoms, such as vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone. Of these, diacetone acrylamide and diacetone methacrylamide are particularly preferred.

[0086] Examples of N-methylol alkyl ether group-containing polymerizable unsaturated monomers include N-methylol acrylamide butyl ether.

[0087] The isocyanate group-containing polymerizable unsaturated monomer is a compound having at least one unblocked isocyanate group and at least one radically polymerizable double bond per molecule, and examples thereof include methacryloyl isocyanate, 2-isocyanateethyl methacrylate, m- or p-isopropenyl-α,α'-dimethylbenzyl isocyanate, or a 1:1 (molar ratio) adduct of a hydroxyl group-containing polymerizable unsaturated monomer and a diisocyanate compound (for example, an equimolar adduct of 2-hydroxyethyl acrylate and isophorone diisocyanate).

[0088] Examples of epoxy group-containing polymerizable unsaturated monomers include glycidyl acrylate, glycidyl methacrylate, etc. Commercially available products can also be used, such as "CYCLOMER A-200" (alicyclic epoxy group-containing monomer) and "CYCLOMER M-100" (alicyclic epoxy group-containing monomer) manufactured by Daicel Corporation.

[0089] Examples of the amino group-containing polymerizable unsaturated monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylamide, and dimethylaminopropyl methacrylamide.

[0090] Examples of alkoxysilyl group-containing polymerizable unsaturated monomers include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, (meth)acryloyloxymethyltrimethoxysilane, (meth)acryloyloxyethyltrimethoxysilane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, (meth)acryloyloxyethyltriethoxysilane, (meth)acryloyloxypropyltributoxysilane, vinyltris-β-methoxyethoxysilane, divinylmethoxysilane, and divinyldi-β-methoxyethoxysilane.

[0091] Other polymerizable unsaturated monomers include, for example, alkyl or cycloalkyl esters of (meth)acrylic acid having 1 to 24 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and cyclohexyl (meth)acrylate; alkoxyalkyl esters of (meth)acrylic acid having 1 to 16 carbon atoms, such as methoxybutyl acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate, ethoxybutyl acrylate, ethoxybutyl methacrylate, and phenoxyethyl (meth)acrylate; styrene, vinyl Examples of suitable vinyl monomers include aromatic unsaturated monomers such as toluene, α-methylstyrene, N-vinylpyrrolidone, and vinylpyridine; olefins such as ethylene, propylene, butylene, and pentene; diene compounds such as butadiene, isoprene, and chloroprene; cyclohexenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, N-butoxy (meth)acrylamide, and adducts of glycidyl (meth)acrylate with amines; vinyl propionate, vinyl acetate, vinyl pivalate, and Veova Monomer (a product of Shell Chemical Co., Ltd.).

[0092] Furthermore, crosslinked resin particles can also be obtained by using a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule as a monomer component.

[0093] Examples of polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule include allyl (meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 1,6-hexane. Examples of such monomers include diol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, 1,1,1-trishydroxymethylpropane tri(meth)acrylate, triallyl isocyanurate, diallyl terephthalate, and divinylbenzene. These monomers can be used alone or in combination of two or more.

[0094] Among the polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate can be suitably used.

[0095] From the viewpoint of rust prevention and film-forming properties, the glass transition temperature of the acrylic resin particles (B) is 30° C. or lower, preferably within the range of −20 to 30° C., and more preferably −10 to 30° C. When the glass transition temperature (Tg) of the acrylic resin particles (B) is 30° C. or lower, both the coating film hardness and the flowability of the applied coating can be achieved, thereby improving the rust prevention and film-forming properties of the aqueous coating composition.

[0096] In this specification, the glass transition temperature Tg (absolute temperature) of the acrylic resin particles (B) is a value calculated by the following formula: 1 / Tg=W ａ１ / T ａ１ +W ａ２ / T ａ２ +...W ａｎ / T ａｎ Tg (°C) = Tg (K) - 273 [wherein, W ａ１ , W ａ２ , ...W ａｎ is the mass fraction of each monomer, and T ａ１ , T ａ２ ...T ａｎ is the glass transition temperature (absolute temperature) of the homopolymer of each monomer.

[0097] The glass transition temperatures of the homopolymers of each monomer are values ​​according to POLYMER HANDBOOK Fourth Edition, edited by J. Brandrup, E. h. Immergut, and E. A. Grulke (1999). For the glass transition temperatures of monomers not described in the literature, the values ​​used are those obtained by synthesizing a homopolymer of the monomer so as to have a weight-average molecular weight of about 50,000 and measuring the glass transition temperature by differential scanning calorimetry.

[0098] As the acrylic resin particles (B), commercially available products that satisfy the above-mentioned glass transition temperature requirements can also be used, such as Pliotec HDT 12 (acrylic SBR resin) manufactured by OMNOVA, LX407S10 manufactured by Zeon Corporation, JONCRYL PDX-7616A, JONCRYL PDX-7787, JONCRYL PDX-7741, and JONCRYL PDX-7356 manufactured by BASF, and U-DOUBLE EF-015, U-DOUBLE EF-016, and U-DOUBLE EF-017 manufactured by Nippon Shokubai Co., Ltd.

[0099] From the viewpoint of particle dispersion stability, the acrylic resin particles (B) may have an average particle size within the range of preferably 10 to 1000 nm, more preferably 20 to 500 nm, and even more preferably 40 to 300 nm.

[0100] The acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B), particularly when they have an acid group, are preferably neutralized with a basic compound from the viewpoint of dispersion stability.

[0101] As the basic compound, ammonia or a water-soluble amino compound such as monoethanolamine, ethylamine, dimethylamine, diethylamine, triethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine, triethanolamine, butylamine, dibutylamine, 2-ethylhexylamine, ethylenediamine, propylenediamine, methylethanolamine, dimethylethanolamine, diethylethanolamine, 2-amino-2-methylpropanol, diethanolamine, or morpholine can be suitably used.

[0102] When the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B) have hydroxyl groups, the hydroxyl value is preferably 1 to 150 mgKOH / g, more preferably 2 to 100 mgKOH / g, and even more preferably 5 to 90 mgKOH / g.

[0103] The acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B) may also have a core / shell structure. The term "shell portion" refers to the polymer layer present in the outermost layer of the resin particle, the term "core portion" refers to the polymer layer present in the inner layer of the resin particle excluding the shell portion, and the term "core / shell structure" refers to a structure having the core portion and the shell portion. The core / shell structure is typically a layer structure in which the core portion is completely covered by the shell portion. However, depending on the mass ratio of the core portion to the shell portion, the amount of monomer in the shell portion may be insufficient to form a layer structure. In such cases, the complete layer structure described above is not necessary, and the core portion may be partially covered by the shell portion, or a polymerizable unsaturated monomer, a component of the shell portion, may be graft-polymerized onto a portion of the core portion. The concept of a multilayer structure in the core / shell structure also applies to the case in which a multilayer structure is formed in the core portion of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B). The core / shell structure can be obtained, for example, by reacting monomer compositions having different compositions in multiple stages.

[0104] In the present invention, it is generally considered that the acrylic-modified epoxy resin particles (A) form a core / shell structure in which the epoxy resin portion forms the core and the acrylic resin portion forms the shell.

[0105] The aqueous coating composition of the present invention contains, as resin components, 20 to 60 mass % of acrylic-modified epoxy resin particles (A) and 40 to 80 mass % of acrylic resin particles (B) in terms of solid content relative to the total solid content of both.

[0106] Preferably, component (A) is 25 to 55% by mass and component (B) is 45 to 75% by mass, and more preferably, component (A) is 30 to 50% by mass and component (B) is 50 to 70% by mass. When component (A) is 20% by mass or more, the blocking resistance and water-resistant adhesion of the resulting coating film are improved, and when component (B) is 40% by mass or more, the film-forming properties are improved.

[0107] The aqueous coating composition of the present invention may contain resins other than the components (A) and (B) as required.

[0108] Specific examples include epoxy resins other than component (A), acrylic resins other than component (B), urethane resins, polyester resins, and resins that are commonly used as curing agents, such as amino resins, phenolic resins, polyisocyanate compounds, and carbodiimide compounds.

[0109] <Organic Solvent (C)> In this specification, the term "water-based paint" is used in contrast to organic solvent-based paint, and generally refers to a paint in which a film-forming resin, pigment, etc. are dispersed and / or dissolved in water or a medium primarily composed of water (aqueous medium). When the paint composition of the present invention is an aqueous paint, the water content in the paint composition is preferably within the range of 10 to 90% by mass, preferably 20 to 80% by mass, and more preferably 30 to 70% by mass. Furthermore, the organic solvent-based paint is a paint that contains substantially no water as a solvent, or in which all or most of the solvent is an organic solvent.

[0110] Examples of the organic solvent (C) contained in the aqueous coating composition of the present invention include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate, butyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, and methyl propionate; alcohol solvents such as 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and 2-ethyl-1-hexanol; ether solvents such as tetrahydrofuran, dioxane, and dimethoxyethane; glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, etc. The organic solvent (C) can be used without particular limitation as long as it does not cause problems in the stability of the aqueous coating composition of the present invention, but it is preferable that it does not contain toluene, xylene, etc., from the viewpoint of its impact on the human body and the environment.

[0111] The organic solvent (C) preferably functions as a plasticizer during the film-forming process and disappears from the coating film after film formation.

[0112] Furthermore, from the viewpoint of compatibility with water-based paints, 50 to 100 mass % of the organic solvent component is selected from those having a 1-octanol / water partition coefficient (Log P ＯＷ ) is preferably 1 or less.

[0113] Examples of the organic solvent include propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, isopropyl alcohol, ethylene glycol monobutyl ether, and isopropyl alcohol.

[0114] 1-octanol / water partition coefficient (Log P ＯＷ The method for measuring the partition coefficient (1-octanol / water) is to follow the Japanese Industrial Standard Z7260-107 (2000) "Measurement of partition coefficient (1-octanol / water) - Shake flask method." Specifically, a certain amount of the test substance is dissolved in 1-octanol, and the solution is added to two solvent phases, 1-octanol and water, and mixed thoroughly. After the two phases are separated, the concentration of the test substance in each phase is measured, and the partition coefficient is calculated. The partition coefficient is calculated using the following formula (2): P = log １０ P ＯＷ (2) P ＯＷ : C Ｏ / C Ｗ C Ｏ : Test substance concentration in 1-octanol layer (mol / L) C Ｗ : test substance concentration in the aqueous layer (mol / L)

[0115] In the present invention, the organic solvent (C) is a concept that covers all organic solvents contained in the aqueous coating composition of the present invention, including those contained in the aqueous medium of the aqueous dispersion of the acrylic-modified epoxy resin particles (A) and the acrylic resin (B), as well as organic solvents contained in the medium of optional components described below, and organic solvents optionally added to the coating material to ensure coating film performance, coating workability, etc.

[0116] In the aqueous coating composition of the present invention, the weighted average boiling point of the organic solvent (C) contained is 200°C or less from the viewpoint of blocking resistance and film-forming ability. When the weighted average boiling point of the organic solvent (C) is 200°C or less, sufficient blocking resistance can be obtained. If the weighted average boiling point of the organic solvent (C) is too low, the film-forming ability of the aqueous coating composition may be reduced, so the weighted average boiling point is preferably 110°C or higher. In other words, the weighted average boiling point of the organic solvent (C) is preferably 110 to 200°C, more preferably 110 to 180°C, even more preferably 120 to 180°C, and particularly preferably 120 to 170°C.

[0117] In this specification, the weighted average boiling point (Tmb (°C)) of the organic solvent (C) refers to the average boiling point calculated from the boiling points of each component of the organic solvent (C) contained in the aqueous coating composition and the proportions of those components, and is a value calculated by the following formula: Tmb (°C) = W ｂ１ ×T ｂ１ +W ｂ２ ×T ｂ２ +...W ｂｎ ×T ｂｎ [In the formula, W ｂ１ , W ｂ２ , ...W ｂｎ is the mass fraction of each organic solvent, and T ｂ１ , T ｂ２ ...T ｂｎ is the boiling point of each organic solvent (°C).

[0118] The organic solvents mentioned above can be used singly or in combination of two or more depending on the purpose, particularly, of adjusting the viscosity as well as the blocking resistance and film-forming properties.

[0119] From the viewpoint of film-forming ability and blocking resistance, the content of the organic solvent (C) in the aqueous coating composition of the present invention is preferably within the range of 1 to 100 mass%, particularly 1 to 70 mass%, further particularly 2 to 50 mass%, and even more particularly 2 to 40 mass%, based on the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B).

[0120] The solids concentration of the aqueous coating composition of the present invention is preferably adjusted to a solids content of 10% by mass or more, particularly 25 to 50% by mass, and more particularly 30 to 45% by mass, from the viewpoint of coating workability and reducing the amount of organic solvent discharged.

[0121] In this specification, the term "solid content" refers to the residue remaining after removing volatile components, and the residue may be in a solid or liquid state at room temperature. The solid content mass can be calculated by multiplying the sample mass before drying by the solid content percentage, which is the ratio of the amount of material remaining after drying to the mass before drying.

[0122] The aqueous coating composition of the present invention preferably contains at least one of a rust inhibitor (D) and a pigment (E).

[0123] <Rust inhibitor (D)> The aqueous coating composition of the present invention preferably contains a rust inhibitor to improve rust prevention properties.

[0124] As the rust inhibitor, those usually used in paints can be used, such as zirconium compounds, vanadium compounds, silicon oxide, sulfur-containing organic compounds, and rust-preventive pigments.

[0125] Examples of anti-rust pigments include zinc oxide, phosphite compounds, phosphate compounds, nitrite compounds, molybdate compounds, bismuth compounds, and metal ion-exchanged silica.

[0126] <Pigment (E)> The aqueous coating composition of the present invention preferably contains a pigment to improve rust prevention properties, impart a desired color, etc. Examples of the pigment include coloring pigments and extender pigments.

[0127] Examples of coloring pigments include titanium oxide, zinc molybdate, calcium molybdate, carbon black, graphite, iron black, Prussian blue, ultramarine, cobalt blue, copper phthalocyanine blue, indanthrone blue, yellow lead, synthetic yellow iron oxide, red iron oxide, transparent red iron oxide, bismuth vanadate, titanium yellow, zinc yellow, ochre, monoazo yellow, disazo, isoindolinone yellow, metal complex azo yellow, quinophthalone yellow, benzimidazolone yellow, monoazo red, unsubstituted quinacridone red, azo lake (Mn salt), quinacridone magenta, anthanthrone orange, dianthraquinonyl red, perylene maroon, perylene red, diketopyrrolopyrrole chrome vermilion, chlorinated phthalocyanine green, brominated phthalocyanine green, and others; such as pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet.

[0128] Examples of extender pigments include clay, silica, barium sulfate, talc, calcium carbonate, white carbon, diatomaceous earth, magnesium aluminum carbonate flakes, and mica flakes.

[0129] Among the above extender pigments, barium sulfate and talc are preferably used from the viewpoint of rust prevention.

[0130] When the aqueous coating composition of the present invention contains a rust inhibitor (D) and / or a pigment (E), the total solid content of the rust inhibitor (D) and the pigment (E) is preferably 10 to 400% by mass, particularly 20 to 350% by mass, and even more particularly 50 to 300% by mass, relative to the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B), from the viewpoint of rust prevention and film-forming properties.

[0131] The aqueous coating composition of the present invention may further contain additives such as catalysts, pigment dispersants, film-forming aids, anti-settling agents, rheology control agents, antifoaming agents, coating surface conditioners, ultraviolet absorbers, ultraviolet stabilizers, and pH adjusters, as required.

[0132] The aqueous coating composition of the present invention is capable of forming a coating film that is excellent in quick drying, blocking resistance, and coating workability, as well as in rust prevention and water resistance, and is therefore particularly suitable for use as an anti-rust coating for steel materials used in construction materials, etc., particularly lightweight steel sections.

[0133] More specifically, examples of steel materials to be coated with the aqueous coating composition of the present invention include C-shaped steel such as lip channel steel, light channel steel and deformed light channel steel, L-angle steel such as equal leg light angle steel and unequal leg light angle steel, lightweight steel such as square steel pipes and deck plates, and steel materials that have been subjected to chemical conversion treatment such as phosphate treatment.

[0134] The aqueous coating composition of the present invention can be applied to the above-mentioned steel material by a known method such as roll coating, spray coating, brush coating, electrostatic coating, dipping, electrodeposition coating, curtain coating or roller coating, and then dried to form a coating film.

[0135] There are no particular limitations on the thickness of the coating film formed by the aqueous coating composition of the present invention, but it can usually be applied in the range of 10 to 100 μm, preferably 10 to 80 μm.

[0136] The coating method of the present invention includes the steps of preheating the substrate, applying the aqueous coating composition of the present invention, and then drying using residual heat. Coating using the aqueous coating composition of the present invention can be either ambient drying or baking. The heating and drying conditions for baking can be set appropriately, but for example, in steel production lines, coating can be carried out by typically preheating the substrate to a temperature of 70 to 200°C, preferably 80 to 120°C, and then drying for 3 to 5 minutes using residual heat (the substrate temperature immediately after coating (approximately 60 to 100°C)).

[0137] The present invention will be explained in more detail below with reference to Production Examples, Examples, and Comparative Examples. However, the present invention is not limited thereto. In each example, "parts" and "%" are based on mass unless otherwise specified. Furthermore, the film thickness of the coating film is based on the cured coating film.

[0138] (Production Example 1) Production of Carboxyl Group-Containing Acrylic Resin (a2-1) 30 parts of ethylene glycol monobutyl ether and 40 parts of propylene glycol monomethyl ether were charged into a four-necked flask and heated to 100°C under a nitrogen stream, and the following "monomer mixture" and 3.0 parts of t-butylperoxy-2-ethylhexanoate were added dropwise over 3 hours, and the mixture was aged for 1 hour after the dropwise addition. "Monomer mixture" Styrene 45 parts Ethyl acrylate 10 parts Methacrylic acid 45 parts

[0139] Next, a mixed solution of 1.0 part of t-butylperoxy-2-ethylhexanoate and 10 parts of ethylene glycol monobutyl ether was added dropwise over 30 minutes, and the mixture was aged for 2 hours after the addition.

[0140] Next, 75 parts of n-butanol was added to obtain a carboxyl group-containing acrylic resin (a2-1) solution with a solids content of 40%. The obtained resin (a2-1) had a glass transition temperature of 126°C, a resin acid value of 293 mgKOH / g, and a weight average molecular weight of 22,000.

[0141] (Production Examples 2 and 3) Production of Carboxyl Group-Containing Acrylic Resin (a2-2) and Carboxyl Group-Containing Acrylic Resin (a2-3) Carboxyl group-containing acrylic resin (a2-2) and carboxyl group-containing acrylic resin (a2-3) were obtained in the same manner as in Production Example 1, except that the formulations shown in Table 1 were used.

[0142] The glass transition temperature, acid value, weight average molecular weight and solid content of the resulting carboxyl group-containing acrylic resin are shown in Table 1.

[0143]

[0144] (Production Example 4) Production of Acrylic-Modified Epoxy Resin Particles (A-1) A four-neck glass flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet was charged with the following mixture of (1) and (2) and 40 parts of ethylene glycol monobutyl ether, and heated to 100°C to uniformly dissolve the mixture. Then, 4.5 parts of dimethylethanolamine was added at the same temperature, and the mixture was stirred for 2 hours to carry out a reaction. Next, 165 parts of deionized water was added over 2 hours to obtain an aqueous dispersion of acrylic-modified epoxy resin particles (A-1) with a solids content of 30% by mass. The acrylic-modified epoxy resin particles (A-1) had a glass transition temperature (Tg) of 85.4°C and a resin acid value of 37 mgKOH / g. The composition of the mixture of (1) and (2) was as follows: (1) 84 parts of jER1010 (Note 3) (2) 40 parts of carboxyl group-containing acrylic resin (a2-1) solution (16 parts as solids)

[0145] (Production Examples 5 to 10) Production of Acrylic-Modified Epoxy Resin Particles (A-2) to (A-7) Aqueous dispersions of acrylic-modified epoxy resins (A-2) to (A-7) with a solid content of 30% by mass were obtained in the same manner as in Production Example 4, except for using the formulations shown in Table 2. The glass transition temperature (Tg) and resin acid value of each of the obtained acrylic-modified epoxy resin particles are also shown in Table 2.

[0146] (Note 1) jER1001: Epoxy resin manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin with an epoxy equivalent of approximately 475. (Note 2) jER1007: Epoxy resin manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin with an epoxy equivalent of approximately 1975. (Note 3) jER1010: Epoxy resin manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin with an epoxy equivalent of approximately 4500.

[0147]

[0148] (Production Example 11) Production of Acrylic Resin Particles (B-1) A monomer mixture was obtained by mixing 47.8 parts of styrene, 47.8 parts of 2-ethylhexyl acrylate, 0.9 parts of 2-hydroxyethyl acrylate, and 3.5 parts of methacrylic acid. 40 parts of deionized water, 3.3 parts of "Newcol 707SF" (manufactured by Nippon Nyukazai Co., Ltd., an anionic surfactant having a polyoxyethylene chain, solids content 30%), and 1 part of the monomer mixture prepared above were added to a reaction vessel, stirred and mixed under a nitrogen stream, and 4 parts of a 3% aqueous ammonium persulfate solution were added at 60°C. The temperature was then raised to 80°C, and a pre-emulsion consisting of the remaining 99 parts of the monomer mixture, 3.3 parts of "Newcol 707SF," 8 parts of 3% ammonium persulfate, and 35 parts of deionized water was added to the reaction vessel over 4 hours using a metering pump. After the addition was completed, the mixture was aged for 1 hour. Thereafter, 10 parts of deionized water was added, and the pH was adjusted to 8.5 with aqueous ammonia to obtain an aqueous dispersion of acrylic resin particles (B-1) with a solids content of 50% by mass. The obtained acrylic resin particles (B-1) had a glass transition temperature of -6.0°C, an average particle size of 165 nm, a hydroxyl value of 4.4 mg KOH / g, and an acid value of 22.8 mg KOH / g. The average particle size was measured at 20°C by diluting with deionized water using a submicron particle size distribution analyzer "COULTER N4" (manufactured by Beckman Coulter, Inc.).

[0149] (Production Examples 12 and 13) Production of Acrylic Resin Particles (B-2) and (B-3) Dispersions of acrylic resin particles (B-2) and (B-3) were produced in the same manner as in Production Example 11. The glass transition temperature, average particle size, hydroxyl value, and acid value of each of the obtained acrylic resin particles (B), as well as the pH and solids concentration of each of the obtained aqueous dispersions of the acrylic resin particles (B) are shown in Table 3. The acrylic resin particles (B-2) are acrylic resin particles having a core-shell structure, and the acrylic resin particles (B-3) are for comparative purposes.

[0150]

[0151] (Examples 1 to 9 and Comparative Examples 1 to 9) <Production of aqueous coating compositions> The raw materials were thoroughly mixed with a stirrer according to the formulations shown in Tables 4 and 5 below, and the pigment was dispersed until the grains (particle size of the coarse pigment particles) were 30 μm or less. Deionized water was then added to adjust the solids content to produce aqueous coating compositions Nos. 1 to 18 with a solids content of 50 mass%. Aqueous coating compositions Nos. 10 to 18 are for comparative examples.

[0152] The compositions in Tables 4 and 5 are solid mass ratios, and the weighted average boiling point (°C) of the organic solvent (C) is also shown. The mass of the organic solvent (C) is the content in the aqueous coating composition relative to the total solid mass (100) of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B).

[0153] The acrylic resin particles used in the examples are Pliotec HDT12 (acrylic SBR resin, glass transition temperature (Tg) 27.6°C, average particle size 140 nm, solid content mass concentration 50%, pH 8.0) manufactured by OMNOVA, and JONCRYL PDX-7616A (glass transition temperature (Tg) 9.0°C, average particle size 100 nm, solid content mass concentration 44%, solid content acid value 30 mgKOH / g, pH 7.8) manufactured by BASF.

[0154] <Preparation of Test Plates> Preparation of test plates for aqueous coating composition No. 1 A 70 x 150 x 0.8 mm polished cold-rolled steel plate was surface-polished using waterproof abrasive paper with a grit size of 280, and then degreased using toluene to prepare a test material. Test plates I-1 to IV-1 were prepared using the test material according to the following steps (I) to (IV).

[0155] (I) The aqueous coating composition No. 1 obtained in Example 1 was applied to the above substrate using a film applicator so that the cured film thickness was 35 μm, and the coating was dried for 8 hours in an environment of 23°C and 50% humidity to obtain test panel I-1.

[0156] (II) After heating the two above-mentioned materials to a surface temperature of 100°C, the aqueous coating composition No. 1 obtained in Example 1 was spray-painted onto the two pieces to a cured film thickness of 35 μm, and the pieces were cured in an environment of 23°C and 50% humidity to obtain two test pieces II-1. The curing time varies depending on the blocking resistance test temperature, since the blocking resistance test is started once the test piece temperature has cooled to the following blocking resistance test temperatures (55°C, 45°C, 35°C), and is approximately 1 to 10 minutes (specifically, it is several minutes at 55°C and approximately 10 minutes at 35°C).

[0157] (III) The aqueous coating composition No. 1 obtained in Example 1 was spray-coated onto the above substrate so that the cured film thickness was 35 μm, and the coating was then cured for 7 days in an environment of 23°C and 50% humidity to obtain test panel III-1.

[0158] (IV) The above material was heated to a surface temperature of 100°C, and then the aqueous coating composition No. 1 obtained in Example 1 was spray-painted onto the material to a cured film thickness of 35 μm, followed by aging for 24 hours in an environment of 23°C and 50% humidity to obtain test panel IV-1.

[0159] Preparation of test panels for aqueous coating compositions Nos. 2 to 18 Test panels I-2 to I-18, II-2 to II-18, III-2 to III-18, and IV-2 to IV-18 were obtained using aqueous coating compositions Nos. 2 to 18 in the same manner as in the preparation of the test panels for aqueous coating composition No. 1.

[0160] <Performance Tests and Performance Evaluations> The test plates I-1 to I-18, II-1 to II-18, III-1 to III-18, and IV-1 to IV-18 obtained by the above test plate production were subjected to performance evaluations according to the following test methods. The test results are shown in Tables 4 and 5 below.

[0161] Film-forming properties: Each test panel I-1 to I-18 was evaluated for film-forming properties by visually inspecting and microscopically (30x magnification) for cracks in the coating. The evaluation criteria are as follows. In the following evaluation criteria, A is the pass level. A: No cracks in the coating are observed even when observed with a microscope (30x magnification). B: No cracks are observed with the naked eye, but cracks in the coating are observed when observed with a microscope (30x magnification). C: Cracks in the coating are observed with the naked eye.

[0162] Rust prevention: The back and edge of each test plate III-1 to III-18 were coated with the same aqueous coating composition No. 1 to 18 as the front and then dried. After making notches on the front and back according to JIS K 5600-7-9, 7.5 (Method of making notches) a), 36 cycles of cyclic corrosion tests were performed under the conditions specified in JIS K 5600-7-9, Appendix 1 (Cycle D). After 36 cycles, the test plate was thoroughly washed with ion-exchanged water, and the surface was wiped dry. The rust prevention properties were evaluated according to the following evaluation criteria. The area within 10 mm of the outer periphery of the test specimen was excluded from the evaluation, and rust staining was also excluded from the evaluation. In the evaluation criteria below, A and B are acceptable levels. A: No blistering, peeling, or rust was observed on the evaluation areas on the front and back of the test plate, and the blistering or maximum rust width around the notch was within 1 mm. B: No swelling, peeling or rust was observed in the evaluation areas on the front and back of the test plate, and the swelling around the cut or the maximum rust width exceeded 1 mm. C: Either swelling, peeling or rust was observed in part of the evaluation areas on the front and back of the test plate. D: Either swelling, peeling or rust was observed in the entire evaluation areas on the front and back of the test plate.

[0163] Blocking resistance: Two test plates from each of II-1 to II-18 were placed together with their coated surfaces facing each other, and subjected to a pressure of 40 kgf / cm ２A weight was placed on the test plate so that the pressure was equal to or greater than 100 psi, and the plate was held at each temperature (55°C, 45°C, 35°C) for 1 hour. The weight was then removed and the plate was cooled to room temperature, and blocking resistance was evaluated based on the state of compression and the degree of peeling. The evaluation criteria are as follows. In the evaluation criteria below, the higher the temperature, the more severe the test conditions, with A, B, and C being pass levels. A: Tested at 55°C, no compression between the two plates was observed. B: Tested at 45°C, no compression between the two plates was observed. C: Tested at 35°C, no compression between the two plates was observed. D: Tested at 35°C, compression between the two plates was observed, but no damage to the coating film was observed when the two plates were peeled off. E: Tested at 35°C, compression between the two plates was observed, and damage to the coating film was observed when the two plates were peeled off.

[0164] Water-resistant adhesion: The back and edges of each test panel IV-1 to IV-18 were protected with a paint or anticorrosive vinyl tape that was sufficiently water-resistant. According to JIS K 5600-6-1, Clause 7, Method 1 (immersion method), the panel was immersed in deionized water at 23°C for 24 hours, removed, and the water on the surface was wiped off with filter paper as specified in JIS P3801. After drying for 30 minutes in an environment of 23°C and 50% humidity, 100 2mm x 2mm cross-hatched patterns were made on the coated surface according to JIS K 5600-5-6 (1990). Adhesive tape was applied to the surface, and the remaining state of the cross-hatched coating film after rapid peeling was examined. Adhesion was evaluated according to the following evaluation criteria. In the following evaluation criteria, A and B are acceptable levels. A: Number of remaining patterns / total number = 100 / 100, and no chipping was observed on the edges of the cross-hatched patterns. B: Number of remaining pieces / total number = 100 pieces / 100 pieces, and chipped edges are observed on the cross-hatched pattern. C: Number of remaining pieces / total number = 80 to 99 pieces / 100 pieces. D: Number of remaining pieces / total number = 0 to 79 pieces / 100 pieces.

[0165] Pencil hardness: The pencil hardness of the coated surface of each test panel IV-1 to IV-18 was measured in accordance with JIS K 5600-5-4 (1999) "Scratch hardness (pencil method)." The order of pencil hardness is 2B<B<HB<F<H<2H. A hardness of B or higher is good and is at an acceptable level.

[0166]

[0167]

[0168] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-027231) filed on February 27, 2024, the contents of which are incorporated herein by reference.

[0169] The aqueous coating composition of the present invention can be used for both ambient drying and baking coating, and can be used efficiently not only for outdoor coating at construction sites and the like, but also on production lines for coated steel materials and the like. It allows for the highly productive production of coated articles such as coated steel materials that do not contain environmentally hazardous substances (such as lead or chromium) and have excellent film-forming properties, rust prevention properties, water resistance and blocking resistance.

Claims

1. An aqueous coating composition comprising acrylic-modified epoxy resin particles (A) having a glass transition temperature of 30°C or higher, acrylic resin particles (B) having a glass transition temperature of 30°C or lower, and an organic solvent (C), wherein the acrylic-modified epoxy resin particles (A) account for 20 to 60 mass% and the acrylic resin particles (B) account for 40 to 80 mass% in terms of solid content relative to the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B), and the weighted average boiling point of the organic solvent (C) is 200°C or lower.

2. The aqueous coating composition according to claim 1, further comprising at least one of a rust inhibitor (D) and a pigment (E).

3. The aqueous coating composition according to claim 2, wherein the total solid content of the rust inhibitor (D) and the pigment (E) is 10 to 400 mass% relative to the total solid content of the acrylic-modified epoxy resin particles (A) and the acrylic resin particles (B).

4. A coating method comprising the steps of preheating an object to be coated, coating the object with the aqueous coating composition according to claim 1 or 2, and then drying the coating with residual heat.

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