Water-based coatings for wood

Abstract

To provide an aqueous coating composition for wood, which has excellent pigment sedimentation stability, shows almost no volume shrinkage due to heat hardening, has excellent fillability, and is also excellent in performance such as water resistance and the like.SOLUTION: Provided is an aqueous coating composition for wood, comprising: acrylic resin particles (A) having a glass transition temperature of 20°C or higher; a surfactant (B) having a weight average molecular weight of 2400 or more and having a triblock structure comprising a polyoxypropylene group and two polyoxyethylene groups sandwiching the former; a polyisocyanate compound (C); and pigment (D), where the pigment (D) is contained in an amount of 600 mass% or more relative to a total solid content of the (A) component, the (B) component, and the (C) component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous wood coating composition that is excellent in pigment sedimentation stability and filling, and in performance such as water resistance. [Background technology]

[0002] When using wood materials such as plywood, various coatings are applied as needed depending on the purpose. Until now, hardwoods have been the mainstream for wood materials, but due to environmental protection and the decrease in the supply of hardwoods, softwoods are increasingly being used.

[0003] However, coniferous wood has many fine irregularities on its surface compared to hardwood, making it difficult to achieve sufficient smoothness with conventional sealer compositions. Furthermore, coniferous wood often has knot holes originating from the coniferous tree as defects, and these defects are often filled with putty, sealer, etc. in addition to painting.

[0004] For example, Patent Document 1 discloses a curable composition suitable for use as a sealer or the like, which contains (A) a synthetic resin emulsion, (B) a highly water-absorbent resin, (C) an extender pigment, and (D) a polyisocyanate compound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-63403 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the curable composition of Patent Document 1 is used as a putty material to fill the above-mentioned defects, the volume shrinkage during drying and hardening can result in insufficient filling of the repaired area, and the resulting wood material may have insufficient performance, such as water resistance.

[0007] The problem to be solved by the present invention is to provide an aqueous wood coating composition that has pigment sedimentation stability, almost no volume shrinkage upon heat curing, excellent filling properties, and excellent performance such as water resistance. [Means for solving the problem]

[0008] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a composition containing acrylic resin particles having a specific glass transition temperature, a surfactant having a specific triblock structure, a polyisocyanate compound, and a pigment, and have thus completed the present invention.

[0009] That is, the present invention provides: 1. A water-based wood coating composition comprising: acrylic resin particles (A) having a glass transition temperature of 20°C or higher; a surfactant (B) having a weight-average molecular weight of 2,400 or higher and a triblock structure consisting of a polyoxypropylene group and two polyoxyethylene groups sandwiching it; a polyisocyanate compound (C); and a pigment (D), wherein the pigment (D) accounts for 600% by mass or more of the total solid content of components (A), (B), and (C); 2. The aqueous wood coating composition according to item 1, wherein the acrylic resin particles (A) are crosslinked acrylic resin particles. 3. The aqueous wood coating composition according to item 1 or 2, wherein the acrylic resin particles (A) are core-shell type acrylic resin particles. 4. The aqueous wood coating composition according to any one of items 1 to 3, wherein the weight-average molecular weight of the polyoxypropylene group of the surfactant (B) is 1,450 or more. 5. The aqueous wood coating composition according to any one of items 1 to 4, wherein the surfactant (B) has a polyoxyethylene group content in the molecule of 20% by mass or more. 6. The aqueous wood coating composition according to any one of items 1 to 5, wherein the polyisocyanate compound (C) is an alicyclic polyisocyanate and / or a derivative of an alicyclic polyisocyanate. 7. The aqueous wood coating composition according to any one of items 1 to 6, wherein the polyisocyanate compound (C) is a nonionic group-containing polyisocyanate compound. [Effects of the Invention]

[0010] The coating composition of the present invention can provide an aqueous coating composition that undergoes almost no volumetric shrinkage upon curing, has excellent application properties such as filling ability and workability, and is excellent in pigment sedimentation stability, as well as excellent coating film performance such as water resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to an aqueous wood coating composition (hereinafter sometimes simply referred to as the present coating composition) that contains acrylic resin particles (A) with a glass transition temperature of 20°C or higher, a surfactant (B) with a weight-average molecular weight of 2400 or higher and a triblock structure consisting of a polyoxypropylene group sandwiched between two polyoxyethylene groups, a polyisocyanate compound (C), and a pigment (D), wherein the pigment (D) accounts for 600 mass% or more of the total solid content of components (A), (B), and (C).

[0012] The present invention will be described in detail below. <Paint composition> Acrylic resin particles (A) The acrylic resin particles (A) are characterized by having a glass transition temperature in the range of 20°C or higher.

[0013] The acrylic resin particles (A) are generally obtained by copolymerizing a polymerizable unsaturated monomer, which is a monomer having a polymerizable unsaturated group.

[0014] In this specification, the term "polymerizable unsaturated group" refers to an unsaturated group that can undergo radical polymerization. Examples of the polymerizable unsaturated group include a vinyl group, a vinylidene group, an acryloyl group, and a methacryloyl group.

[0015] In addition, in this specification, "(meth)acrylate" means "acrylate or methacrylate." "(meth)acrylic acid" means "acrylic acid or methacrylic acid." "(meth)acryloyl" means "acryloyl or methacryloyl." "(meth)acrylamide" means "acrylamide or methacrylamide."

[0016] Examples of the polymerizable unsaturated monomer include a polymerizable unsaturated monomer having one polymerizable unsaturated group in one molecule and a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule.

[0017] Examples of polymerizable unsaturated monomers having one polymerizable unsaturated group per molecule include methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, i-propyl(meth)acrylate, n-butyl(meth)acrylate, i-butyl(meth)acrylate, tert-butyl(meth)acrylate, n-hexyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, nonyl(meth)acrylate, tridecyl(meth)acrylate, and the like. alkyl or cycloalkyl (meth)acrylates such as acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate -; polymerizable unsaturated monomers having an adamantyl group, such as adamantyl (meth)acrylate; polymerizable unsaturated monomers having a tricyclodecenyl group, such as tricyclodecenyl (meth)acrylate; polymerizable unsaturated monomers containing an aromatic ring, such as benzyl (meth)acrylate, styrene, α-methylstyrene, and vinyltoluene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltrimethoxysilane, polymerizable unsaturated monomers having an alkoxysilyl group, such as methyloxypropyltriethoxysilane; perfluoroalkyl (meth)acrylates, such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; polymerizable unsaturated monomers having a fluorinated alkyl group, such as fluoroolefins; polymerizable unsaturated monomers having a photopolymerizable functional group, such as a maleimide group; vinyl compounds, such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, and vinyl acetate;Monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, ε-caprolactone-modified products of the monoesters, N-hydroxymethyl (meth)acrylamide, allyl alcohol, and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminal, as well as hydroxyl group-containing polymerizable unsaturated monomers; carboxyl group-containing polymerizable unsaturated monomers, such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; (meth)acrylonitrile, (meth)acrylamide, N,N-diol, Examples of such polymerizable unsaturated monomers include nitrogen-containing polymerizable unsaturated monomers such as methylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and adducts of glycidyl (meth)acrylate and amines; epoxy group-containing polymerizable unsaturated monomers such as glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, and allyl glycidyl ether; and (meth)acrylates having a polyoxyethylene chain whose molecular terminal is an alkoxy group.

[0018] These monomers can be used alone or in combination of two or more depending on the performance required of the acrylic resin particles (A).

[0019] Of the above polymerizable unsaturated monomers, the acrylic resin particles (A) preferably contain a hydroxyl group-containing polymerizable unsaturated monomer as a copolymerization component from the viewpoint of reactivity with the polyisocyanate compound (C).

[0020] 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, 1,6-hexanediol di(meth)acrylate, pentaerythritol acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-butane ... Examples of suitable monomers include taerythritol 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, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, triallyl isocyanurate, diallyl terephthalate, and divinylbenzene. These monomers can be used singly or in combination of two or more.

[0021] The polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule has the function of imparting a crosslinked structure to the copolymer. When using a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule, the proportion used can be appropriately determined depending on the degree of crosslinking of the copolymer, but is usually preferably within the range of about 0.1 to 30% by mass, particularly about 0.5 to 10% by mass, and more particularly about 1 to 7% by mass, based on the total amount of the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule and the polymerizable unsaturated monomer having one polymerizable unsaturated group in one molecule.

[0022] From the viewpoint of water resistance and blocking, the acrylic resin particles (A) are preferably crosslinked acrylic resin particles synthesized using a polymerizable unsaturated monomer having two or more of the above polymerizable unsaturated groups in one molecule as a copolymer component.

[0023] The acrylic resin particles (A) can be obtained by emulsion polymerization of a polymerizable unsaturated monomer mixture.

[0024] As the emulsifier, anionic emulsifiers and nonionic emulsifiers can be suitably used.

[0025] Examples of the anionic emulsifier include sodium salts and ammonium salts of alkylsulfonic acid, alkylbenzenesulfonic acid, alkylphosphate, etc. Examples of the nonionic emulsifier 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 trioleate, polyoxyethylene sorbitan monolaurate, etc. Also usable are polyoxyalkylene group-containing anionic emulsifiers having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule; and reactive anionic emulsifiers having an anionic group and a radically polymerizable unsaturated group in one molecule.

[0026] Examples of the reactive anionic emulsifier include sodium salts of sulfonic acid compounds having a radically polymerizable unsaturated group such as an allyl group, a methallyl group, a (meth)acryloyl group, a propenyl group, or a butenyl group, and ammonium salts of the sulfonic acid compounds.

[0027] The amount of the emulsifier used is preferably within the range of about 0.1 to 15 mass %, particularly about 0.5 to 10 mass %, and more particularly about 1 to 5 mass %, based on the total amount of all monomers used.

[0028] Examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; 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. Examples of organic peroxides include azo compounds such as azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), azobis(2-methylpropionitrile), 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}. These polymerization initiators can be used alone or in combination. Furthermore, the above polymerization initiators can also be used in combination with reducing agents such as sugars, sodium formaldehyde sulfoxylate, and iron complexes to form redox initiators, if necessary.

[0029] The amount of the polymerization initiator used is generally about 0.1 to 5% by mass, and particularly about 0.2 to 3% by 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 can be previously added to the monomer mixture or aqueous medium, or can be added all at once or dropwise during polymerization.

[0030] The acrylic resin particles (A) are preferably core-shell type acrylic resin particles having a core-shell structure from the viewpoint of pigment sedimentation stability and water resistance.

[0031] In the present invention, the "shell portion" of the core-shell acrylic resin particle means the polymer layer present in the outermost layer of the resin particle, the "core portion" means the polymer layer in the inner layer of the resin particle excluding the shell portion, and the "core-shell structure" means a structure having the core portion and the shell portion.

[0032] The core-shell structure is generally a layer structure in which the core is completely covered by the shell, but depending on the mass ratio of the core to the shell, the amount of monomer in the shell may be insufficient to form a layer structure. In such cases, the above-described complete layer structure is not necessary, and a structure in which only a portion of the core is covered by the shell may also be used. The concept of the multilayer structure in the core-shell structure also applies to the case in which a multilayer structure is formed in the core of a core-shell acrylic resin particle.

[0033] The core-shell acrylic resin particles can be obtained by emulsion-polymerizing a polymerizable unsaturated monomer mixture to obtain an emulsion of the core copolymer (I), then adding a polymerizable unsaturated monomer mixture to this emulsion and further emulsion-polymerizing it to prepare the shell copolymer (II).

[0034] The monomer mixture may contain, as needed, the above-mentioned polymerization initiator, chain transfer agent, reducing agent, emulsifier, and other components.

[0035] The monomer mixture may be added dropwise as it is, but it is preferable to add dropwise the monomer mixture as a monomer emulsion obtained by dispersing the monomer mixture in an aqueous medium.

[0036] The emulsion polymerization for preparing the emulsion of the core copolymer (I) can be carried out by a conventionally known method, for example, by emulsion polymerizing a mixture of polymerizable unsaturated monomers in the presence of an emulsifier using a polymerization initiator.

[0037] As a method for polymerizing the monomer mixture for forming the shell copolymer (II), for example, the monomer mixture or its emulsion may be added all at once or gradually dropwise to the emulsion of the core copolymer (I), and then heated to an appropriate temperature while stirring.

[0038] The core-shell type acrylic resin particles thus obtained have a multi-layer structure in which the copolymer (I) forms the core and the copolymer (II) forms the shell.

[0039] Furthermore, the core-shell acrylic resin particles can also be made into acrylic resin particles consisting of three or more layers by adding a step of supplying a polymerizable unsaturated monomer (one type or a mixture of two or more types) that forms another resin layer and carrying out emulsion polymerization between the step of obtaining the core copolymer (I) and the step of obtaining the shell copolymer (II).

[0040] When the acrylic resin particles (A) are of a core-shell type, from the viewpoint of the stability of the resin particles, the mass ratio of the core portion to the shell portion (core portion / shell portion) is preferably 90 / 10 to 50 / 50, particularly 85 / 15 to 60 / 40, and further particularly 80 / 20 to 65 / 35.

[0041] The acid value of the acrylic resin particles (A) is preferably within a range of 1 to 50 mgKOH / g, particularly 5 to 30 mgKOH / g, from the viewpoint of resin stability and water resistance.

[0042] If the acid value is less than 1 mgKOH / g, the dispersion stability of the particles may be poor, and if it exceeds 50 mgKOH / g, the coating film may become too hydrophilic and have poor water resistance. As a monomer for imparting an acid value to the acrylic resin particles (A), it is preferable to contain a carboxyl group-containing polymerizable unsaturated monomer, from the viewpoint that the neutralizing agent volatilizes, the hydrophilicity is significantly reduced after film formation, and water resistance is improved.

[0043] As the carboxyl group-containing polymerizable unsaturated monomer, acrylic acid and / or methacrylic acid can be particularly preferably used.

[0044] In this specification, the acid value (mgKOH / g) is the amount of acid groups contained in 1 g of sample (solid content in the case of resin) converted into potassium hydroxide, expressed in mg of potassium hydroxide. The molecular weight of potassium hydroxide is assumed to be 56.1.

[0045] The acid value is measured in accordance with JIS K-5601-2-1 (1999). The sample is dissolved in a mixed solvent of toluene and ethanol in a volume ratio of 2:1, and titrated with potassium hydroxide solution using phenolphthalein as an indicator, and the acid value is calculated using the following formula.

[0046] Acid value (mgKOH / g)=56.1×V×C / m V: titration volume (ml), C: concentration of titrant (mol / l), m: weight of solids of sample (g) The hydroxyl value of the acrylic resin particles (A) is preferably within a range of 5 to 150 mgKOH / g, particularly 10 to 100 mgKOH / g, from the viewpoints of reactivity with the polyisocyanate compound (C) and water resistance.

[0047] If the hydroxyl value is less than 5 mgKOH / g, the water resistance may be poor, and if it exceeds 150 mgKOH / g, the film-forming ability may be poor.

[0048] The monomer for imparting a hydroxyl value to the acrylic resin particles (A) preferably contains the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer.

[0049] As the hydroxyl group-containing polymerizable unsaturated monomer, among the above, particularly preferred are monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0050] The glass transition temperature (Tg) of the acrylic resin particles (A) is preferably 20°C to 80°C, particularly 25°C to 70°C, and more particularly 30°C to 60°C, from the viewpoint of blocking resistance and film-forming properties.

[0051] If the glass transition temperature (Tg) is less than 20°C, blocking may occur when plywood is stacked on top of it, and if the glass transition temperature (Tg) is more than 80°C, film-forming properties may be poor.

[0052] In this specification, the glass transition temperature (° C.) of the copolymer can be calculated by the following formula.

[0053] 1 / Tg(゜K)=(W1 / T1)+(W2 / T2)+·· Tg(℃)=Tg(゜K)-273 In each formula, W1, W2, ... represent the weight percent of each monomer used in the copolymerization, and T1, T2, ... represent the Tg (°K) of the homopolymer of each monomer. Note that T1, T2, ... are values ​​taken from pages III-139-179 of Polymer Handbook (Second Edition, edited by J. Brandup and E. H. Immergut).

[0054] Furthermore, when the Tg of the homopolymer of the monomer is unclear, the glass transition temperature (°C) is taken as the static glass transition temperature. For example, using a differential scanning calorimeter "DSC-220U" (Seiko Instruments Inc.), a sample is placed in a measuring cup and vacuum suction is used to completely remove the solvent, after which the change in heat quantity 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 is taken as the static glass transition temperature.

[0055] When the acrylic resin particles (A) are of a core-shell type, from the viewpoint of water resistance, it is preferred that the acid value of the core portion is in the range of 0 to 50 mgKOH / g, particularly 0 to 30 mgKOH / g, the hydroxyl value of the core portion is in the range of 5 to 150 mgKOH / g, particularly 10 to 100 mgKOH / g, and the Tg of the core portion is in the range of 20 to 80°C, particularly 30 to 60°C.

[0056] From the viewpoint of the stability of the resin particles, it is preferable that the acid value of the shell portion is in the range of 10 to 100 mgKOH / g, particularly 30 to 70 mgKOH / g, the hydroxyl value of the shell portion is in the range of 5 to 150 mgKOH / g, particularly 10 to 100 mgKOH / g, and the Tg of the shell portion is in the range of 20 to 80°C, particularly 25 to 60°C.

[0057] In addition, from the viewpoint of the film-forming properties and water resistance of the resulting coating film, the acrylic resin particles (A) preferably have a weight-average molecular weight of 50,000 or more, particularly within the range of 100,000 to 500,000 (except when the acrylic resin particles (A) are crosslinked resin particles). In this specification, the average molecular weight is a value obtained by converting the retention time measured using a gel permeation chromatograph into the molecular weight of polystyrene using the retention time of standard polystyrenes with known molecular weights measured under the same conditions.

[0058] Specifically, for example, a gel permeation chromatograph "HLC-8120GPC" (trade name, manufactured by Tosoh Corporation) is used, and four columns are used: one "TSKgel G4000HXL," two "TSKgel G3000HXL," and one "TSKgel G2000HXL" (trade names, all manufactured by Tosoh Corporation). A differential refractometer is used as the detector, and measurements can be performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL / min.

[0059] The average particle size of the acrylic resin particles (A) is preferably within a range of 50 to 500 nm, particularly 60 to 400 nm, and further particularly 70 to 300 nm, from the viewpoint of the stability of the resin particles.

[0060] If the average particle size is less than 50 nm, the resin particles may become unstable, resulting in poor paint stability, whereas if it exceeds 500 nm, the dispersion stability may be poor.

[0061] The average particle size can be measured by a common measuring means such as laser light scattering. In this specification, the average particle size of resin particles is a value measured using a submicron particle size distribution analyzer at 20°C after diluting 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.

[0062] To improve the mechanical stability of the acrylic resin particles (A), the acid groups, such as carboxyl groups, of the acrylic resin particles can be neutralized with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize the acid groups, and examples thereof include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and aqueous ammonia. These neutralizing agents can be used in an amount such that the pH of the aqueous dispersion of the acrylic resin particles (A) after neutralization is approximately 6.5 to 9.0.

[0063] In the aqueous coating composition of the present invention, resin particles other than acrylic resin particles (A) can also be used as needed.Specific examples include acrylic resins, acrylic / styrene resins, urethane resins, phenolic resins, vinyl chloride resins, vinyl acetate resins, vinyl acetate / acrylic resins, ethylene / vinyl acetate resins, epoxy resins, epoxy ester resins, polyester resins, alkyd resins, acrylonitrile / butadiene resins, styrene / butadiene resins, polybutadiene, polyisoprene, silicone resins, and fluororesins, as well as modified versions of these resins, such as carbonate-modified urethane resins, acrylic resin-modified epoxy resins, alkyd-modified epoxy resins, polybutadiene-modified epoxy resins, (poly)amine-modified epoxy resins, and urethane-modified epoxy resins.Resin particles (excluding acrylic resin particles (A)) consisting of at least one type selected from the following resins can be mentioned.These resin particles may also be so-called rubber.

[0064] The resin particles may be prepared by blending a plurality of resins or may be a blend of a plurality of types of resin particles. These resin particles can usually be incorporated into the composition of the present invention in the form of an emulsion.

[0065] Surfactant (B) The surfactant (B) is a nonionic surfactant, a block copolymer having a block structure of ethylene oxide, propylene oxide, and ethylene oxide addition polymers, and a copolymer having a triblock structure consisting of a polyoxypropylene group sandwiched between two polyoxyethylene groups. Although the surfactant (B) is highly hydrophilic overall, it has amphiphilic properties because the polyoxypropylene chain is more lipophilic than the polyoxyethylene chain.

[0066] From the viewpoint of pigment dispersibility, the surfactant (B) of the present coating composition preferably has a weight average molecular weight in the range of 2400 to 13,000, particularly 2600 to 10,000, and even more particularly 2800 to 9,000.

[0067] Furthermore, in each block structure, from the viewpoint of pigment dispersibility, it is preferable that the weight average molecular weight of the polyoxypropylene group is 1200 to 4000, particularly 1450 to 3250, and even more particularly 1450 to 2250, and the content of the polyoxyethylene group in the molecule is preferably within the range of 10 to 90% by mass, particularly 20 to 80% by mass, and even more particularly 30 to 70% by mass.

[0068] By including surfactant (B), the viscosity of the coating composition is less temperature-dependent, and the viscosity does not decrease even in the temperature range of about 30 to 60°C, maintaining a high viscosity. This prevents the pigment from settling during storage (especially in summer) and during the curing process, resulting in excellent storage stability and filling properties. Furthermore, when coating plywood, the plywood may be warm shortly after the completion of the bonding process before plywood production, but the coating viscosity remains high, resulting in excellent filling properties.

[0069] Polyisocyanate Compound (C) The polyisocyanate compound (C) is a compound having at least two isocyanate groups in one molecule, and examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanates.

[0070] Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (trivial name: lysine diisocyanate), aliphatic diisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0071] Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, Alicyclic diisocyanates such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), and norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)- 2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-bicyclo(2.2.1)heptane Examples include alicyclic triisocyanates such as (2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0072] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as methylenebis(4,1-phenylene)diisocyanate (common name: MDI), 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0073] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0074] Furthermore, examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetrione, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the above polyisocyanates.

[0075] The above polyisocyanates and derivatives thereof may be used alone or in combination of two or more kinds.

[0076] Among these polyisocyanates, alicyclic polyisocyanates and derivatives of alicyclic polyisocyanates are preferred.

[0077] From the viewpoint of pot life, among alicyclic polyisocyanates and derivatives of alicyclic polyisocyanates, isophorone diisocyanate and derivatives thereof are particularly preferred.

[0078] The polyisocyanate compound may be a prepolymer obtained by reacting the polyisocyanate or a derivative thereof with a compound reactive with the polyisocyanate under conditions of excess isocyanate groups. Examples of the compound reactive with the polyisocyanate include compounds having an active hydrogen group such as a hydroxyl group or an amino group, and specific examples include polyhydric alcohols, low-molecular-weight polyester resins, amines, and water.

[0079] Furthermore, as the polyisocyanate compound, a polymer of an isocyanate group-containing polymerizable unsaturated monomer, or a copolymer of the isocyanate group-containing polymerizable unsaturated monomer and a polymerizable unsaturated monomer other than the isocyanate group-containing polymerizable unsaturated monomer may be used.

[0080] As the polyisocyanate compound, hydrophilic polyisocyanate compounds (C1) for aqueous coatings, such as hydrophilized polyisocyanate compounds in which a hydrophilic group has been introduced into a polyisocyanate compound, and water-dispersible polyisocyanate compounds in which a polyisocyanate compound can be dispersed in water using a surfactant, can be suitably used.

[0081] Examples of the hydrophilic group include anionic groups such as acid groups and nonionic groups containing polyoxyalkylene (polyether chain) units. Examples of the acid group include carboxyl groups, phosphate groups, and sulfonic acid groups.

[0082] Among the hydrophilized polyisocyanate compounds, from the viewpoint of water resistance, nonionic group-containing polyisocyanate compounds are preferred, and polyisocyanate compounds having polyoxyalkylene (polyether chain) units as the nonionic group are particularly preferred.

[0083] In the present coating composition, from the viewpoint of water resistance, the solid content of the acrylic resin particles (A), surfactant (B) and polyisocyanate compound (C) is preferably such that, relative to the total solid content of the acrylic resin particles (A), surfactant (B) and polyisocyanate compound (C), the solid content of the acrylic resin particles (A) is 50 to 99 mass%, particularly 60 to 95 mass%, and even more particularly 60 to 90 mass%, the solid content of the surfactant (B) is 1 to 50 mass%, particularly 5 to 40 mass%, and even more particularly 10 to 30 mass%, and the solid content of the polyisocyanate compound (C) is 0.1 to 20 mass%, particularly 1 to 20 mass%, and even more particularly 3 to 15 mass%.

[0084] Pigment (D) The pigment (D) is contained mainly to improve the ability of the coating composition to fill defects and recesses in wood materials.

[0085] Examples of the pigment (D) include extender pigments and color pigments.

[0086] As the extender pigment, inorganic pigments and organic pigments known as extender pigments can be used without any particular limitation, and examples thereof include clay, silica, kaolin, barium sulfate, talc, calcium carbonate, white carbon, diatomaceous earth, magnesium aluminum carbonate flakes, and mica flakes.

[0087] Of the above extender pigments, calcium carbonate is preferably used.

[0088] Examples of commercially available extender pigments include the following:

[0089] Examples of calcium carbonate include "NS-300, 400" (manufactured by Nippon Funka Kogyo Co., Ltd.), "CaCO3 Super SS" (manufactured by Kyushu Calcium Co., Ltd.), "CaCO3 Sunlight No. 300" (manufactured by Takehara Kogyo Co., Ltd.), and "Calcium Carbonate NN-200" (manufactured by Nitto Funka Kogyo Co., Ltd.).

[0090] Examples of talc include "Microace L-1" (manufactured by Nippon Talc Co., Ltd.), "Talc MG115," "Talc MS410," and "Talc RL119" (manufactured by Fuji Talc Kogyo Co., Ltd.), "Talc TST-1," "Talc TST-2," and "FC-1 Talc" (manufactured by Fukuoka Talc Kogyo Co., Ltd.).

[0091] In addition to improving filling properties, color pigments can be used to achieve a desired color.

[0092] Specific examples of color pigments include titanium white, 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, monoazo yellow, ochre, disazo, isoindolinone yellow, metal complex azo yellow, and quinoftha. Examples of the pigments include quinacridone 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, pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet.

[0093] The pigment (D) can be used alone or in combination of two or more kinds.

[0094] In the present coating composition, from the viewpoints of the ability to fill recesses in a substrate and the solid content concentration of the composition, the solid content of the pigment (D) is preferably 600% by mass or more, particularly 700% by mass or more, and even more particularly 800% by mass or more, based on the total solid content of the acrylic resin particles (A), surfactant (B), and polyisocyanate compound (C).

[0095] paint composition In addition to the acrylic resin particles (A), surfactant (B), polyisocyanate compound (C), and pigment (D), the present coating composition may further contain, as necessary, coating additives such as a rheology control agent, a suspending agent, an antifoaming agent, a pigment dispersant, an anti-flocculating agent, and a leveling agent.

[0096] The coating composition contains water as a volatile component, and may also contain solvents other than water, such as organic solvents such as alcohol, if necessary.

[0097] The present coating composition can be produced by mixing the above components.

[0098] The present coating composition can be prepared by mixing all of the components simultaneously or sequentially. However, since the polyisocyanate compound (C) is reactive with the acrylic resin particles (A) and the surfactant (B) even at room temperature, it is preferable from the viewpoint of storage stability to prepare a two-component coating composition by premixing the components other than component (C) to form the main component, to which the polyisocyanate compound (C) is added as a curing agent.

[0099] The viscosity of the coating composition can be adjusted to any desired value for application. Specifically, for example, when used as a sealer or putty for filling defects in softwood, the viscosity is preferably in the range of 1 to 30 Pa s, particularly 5 to 20 Pa s, as measured at 60 revolutions using a B-type rotational viscometer.

[0100] The viscosity can be adjusted by appropriately adding and mixing water, an organic solvent, a rheology control agent, etc.

[0101] From the viewpoint of filling properties, the solid content concentration of the present coating composition is preferably in the range of 75% by mass or more, particularly 80% by mass or more.

[0102] From the viewpoint of storage stability of the paint, the aqueous paint composition of the present invention preferably has a pH in the range of 5.0 to 10.0, preferably 6.0 to 9.0.

[0103] The paint composition has excellent workability, such as excellent filling and application properties, and has excellent filling properties for substrates with recesses, and also has excellent properties such as small volume shrinkage upon hardening. Therefore, it can be particularly suitably used as a sealer composition or putty composition for smoothing out wood materials with defects such as knotholes and recesses.

[0104] The use of the present coating composition is not particularly limited, but it is preferably applied to wood having defects or depressions on the surface, and specifically, it can be suitably applied to the surfaces of wooden materials such as plywood, flooring, wall materials, ceilings, handrails, and furniture.

[0105] The present coating composition can be applied to wood, filled in, and then cured to form a coating film or cured body on the wood surface and in the filled area.

[0106] The applied and filled coating composition can be cured generally at a temperature of 0 to 180°C, preferably 60 to 140°C, for a curing time of 30 seconds to 1 hour.

[0107] When the present coating composition is applied to wood as a wood sealer composition or wood putty composition, it can be applied using a coating machine such as a natural reverse coater, sponge reverse coater or knife coater.

[0108] A knife coater is most preferred for filling knot holes in softwood plywood.

[0109] When a knife coater is used, the blade is placed against a dummy plate set in the knife coater, the composition of the present invention is dropped on the front side of the blade, and the substrate is conveyed, thereby easily filling recesses such as knotholes. From the viewpoint of the filling ability of the composition, the conveying speed of the substrate is preferably 10 to 30 m / min, and the blade angle is preferably 30° to 60°.

[0110] After application with a knife coater, forced drying (for example, at 100°C for 30 seconds) allows the paint composition to efficiently fill knotholes and depressions as a dried and hardened coating or hardened body, eliminating the surface irregularities that are a drawback of softwood plywood, making it possible to move on to the next process, such as painting.

[0111] As the wood, coniferous wood, hardwood wood, various plywoods, etc. can be used without limitation, but in the present invention, it is particularly suitable for use with coniferous wood having depressions or defects such as knotholes on the surface.

[0112] After application, the present coating composition can be used to form a coating film on the cured portion, and can also be laminated. The separate paint refers to a paint to be applied on top of the coating film (sealer layer) of the present paint composition, and includes a top coat paint to be applied to the top surface of the wood, as well as a primer paint and an intermediate coat paint. Known paints can be used in appropriate combinations. [Example]

[0113] The present invention will be explained in more detail below with reference to examples. Here, "parts" and "%" mean "parts by mass" and "% by mass," respectively. Note that the "parts by mass" of raw materials in the following production examples, examples, and comparative examples represent the parts by mass of the solid content (sometimes referred to as active ingredients) of the raw materials.

[0114] Production of acrylic resin particles (A) Manufacturing Example 1 A polymerization apparatus equipped with a stirrer, thermometer, and reflux condenser was charged with deionized water and Newcol 707SF (trade name, Nippon Nyukazai Co., Ltd., anionic surfactant, solids content 30% by mass) in the amounts shown in Table 1. After thorough nitrogen replacement, the temperature was raised. While stirring at approximately 100 rpm, the internal temperature was maintained at 82°C. A homomixer-prepared emulsion of component (A) shown in Table 1 (hereinafter referred to as the component (A) emulsion; the same applies to component (B)) and an aqueous solution of initiator 1 (Table 1) were added dropwise over 3 hours to polymerize the mixture. After the addition was complete, the mixture was allowed to react at 82°C for 0.5 hours, and then an aqueous solution of initiator 2 was added dropwise over 0.5 hours. After the addition was complete, the mixture was allowed to react at 82°C for 1 hour, after which it was cooled to 25°C. Finally, a neutralizer shown in Table 1 was added to obtain an emulsion of acrylic resin particles (A-1) (Tg: 20.9°C, acid value: 13.0 mgKOH / g, hydroxyl value: 64.7 mgKOH / g) with a solid content of 40.0 mass %.

[0115] The emulsion had a viscosity (measured with a Brookfield viscometer at 60 rpm and 20°C) of 400 mPa·s, a pH of 7.3, an average particle size of 100 nm, and a weight-average molecular weight of 140,000.

[0116] Manufacturing Example 2 A polymerization apparatus equipped with a stirrer, thermometer, and reflux condenser was charged with deionized water and Newcol 707SF in the amounts shown in Table 1. After thorough nitrogen replacement, the temperature was raised. While stirring at approximately 100 rpm, the internal temperature was maintained at 82°C. 5% by mass of the component (A) shown in Table 1, emulsified using a homomixer, and an aqueous solution of initiator 1 (see Table 1) were added dropwise to polymerize. After the dropwise addition was completed, the reaction was continued for 0.5 hours at 82°C. The remaining 95% by mass of the emulsion of component (A) and an aqueous solution of initiator 2 (see Table 1) were then added dropwise over 3 hours to polymerize. After the dropwise addition was completed, the reaction was continued for 0.5 hours at 82°C. Then, the emulsion of component (B) and an aqueous solution of initiator 3 (see Table 1) were added dropwise over 1 hour to polymerize. After the dropwise addition was completed, the reaction was continued for 1 hour at 82°C, and then cooled to 25°C. Finally, a neutralizer shown in Table 1 was added to obtain an emulsion of acrylic resin particles (A-2) (Tg: 21.5°C, acid value: 13.0 mgKOH / g, hydroxyl value: 64.7 mgKOH / g) with a solid content of 40.0 mass %.

[0117] The emulsion had a viscosity (measured with a Brookfield viscometer at 60 rpm and 20°C) of 400 mPa·s, a pH of 7.4, and an average particle size of 110 nm.

[0118] Manufacturing Example 3 An emulsion of acrylic resin particles (A-3) (Tg: 35.0°C, acid value: 13.0 mgKOH / g, hydroxyl value: 64.7 mgKOH / g) with a solid content of 40.0 mass % was obtained in the same manner as in Production Example 2, except that the formulation was as shown in Production Example No. 3 in Table 1.

[0119] The emulsion had a viscosity (measured with a Brookfield viscometer at 60 rpm and 20°C) of 410 mPa·s, a pH of 7.4, and an average particle size of 110 nm.

[0120] Production Example 4 An emulsion of acrylic resin particles (A-4) (Tg: 35.0°C, acid value: 13.0 mgKOH / g, hydroxyl value: 64.7 mgKOH / g) with a solid content of 40.0 mass% was obtained in the same manner as in Production Example 2, except that the formulation was as shown in Production Example No. 4 in Table 1.

[0121] The emulsion had a viscosity (measured with a Brookfield viscometer at 60 rpm and 20°C) of 400 mPa·s, a pH of 7.3, an average particle size of 130 nm, and a weight-average molecular weight of 180,000.

[0122] Manufacturing Example 5 An emulsion of acrylic resin particles (A-5) (Tg: 11.3°C, acid value: 13.0 mgKOH / g, hydroxyl value: 64.7 mgKOH / g) with a solid content of 40.0 mass % was obtained in the same manner as in Production Example 1, except that the formulation was as shown in Production Example No. 5 in Table 1.

[0123] The emulsion had a viscosity (B-type viscometer, 60 rpm, 20°C) of 400 mPa·s, a pH of 7.2, an average particle size of 120 nm, and a weight-average molecular weight of 150,000.

[0124] The acrylic resin particles (A-5) are for comparative purposes.

[0125] The Tg (°C), acid value, and hydroxyl value of each of the obtained acrylic resin particles (A) are also shown in Table 1. The core Tg / shell Tg / total Tg (°C) of the core-shell type acrylic resin particles (A-2), (A-3), and (A-4) is 21.7 / 21.1 / / 21.5 for the acrylic resin particles (A-2), 39.4 / 25.1 / / 35.0 for the acrylic resin particles (A-3), and 39.5 / 25.1 / / 35.0 for the acrylic resin particles (A-4).

[0126] [Table 1]

[0127] Preparation of coating compositions Example 1 The raw materials were mixed in a disperser to obtain the solid content shown in Table 2 below, and the paint solids concentration was adjusted to 75 mass% with deionized water to obtain Paint Composition No. 1. The viscosity of the resulting paint composition (measured with a Brookfield viscometer at 60 rpm and 23°C) was 5.0 Pa s.

[0128] Examples 2 to 16 and Comparative Examples 1 to 5 Coating composition Nos. 2 to 21 were obtained in the same manner as in Example 1 except for the formulations shown in Table 2 below. Coating composition Nos. 17 to 21 are comparative coating compositions.

[0129] The raw materials other than the acrylic resin particles (A) in the table are as follows:

[0130] Surfactant (B) L62: Weight average molecular weight 2500, weight average molecular weight of polyoxypropylene group 1750, content of polyoxyethylene group in molecule 20% by mass L64: Weight average molecular weight 2900, weight average molecular weight of polyoxypropylene group 1750, content of polyoxyethylene group in molecule 40% by mass F68: Weight average molecular weight 8400, weight average molecular weight of polyoxypropylene group 1750, content of polyoxyethylene group in molecule 80% by mass P84: Weight average molecular weight 4200, weight average molecular weight of polyoxypropylene group 2250, content of polyoxyethylene group in molecule 80% by mass L44: Weight average molecular weight 2200, weight average molecular weight of polyoxypropylene group 1200, content of polyoxyethylene group in molecule 40% by mass All five of the above are manufactured by Adeka Pigment (D) Calcium carbonate: Sunlight No. 300 (Takehara Kogyo Co., Ltd.) Talc: Microace L-1 (manufactured by Nippon Talc Co., Ltd.) Polyisocyanate compound (C) Desmodur Z4470BA; isocyanurate of isophorone diisocyanate Sumidur N3300; Hexamethylene diisocyanate isocyanurate Bayhydur 304; isocyanurate of hexamethylene diisocyanate with polyoxyethylene units, hydrophilic polyisocyanate compound All three are manufactured by Sumika Covestro Urethane Co., Ltd. Antifoaming agents BYK-028; Silicone defoamer manufactured by BYK-Chemie Creating test painted panels A piece of softwood plywood (120 mm thick, manufactured by Hayashi Veneer Industry Co., Ltd.) was cut into a 30 cm x 30 cm piece, and then four artificial holes, each 2.5 cm in diameter and 2.0 mm deep, were drilled using a Bosch DIY power tool, the PMR 500 Power Trimmer. The surface was then sanded with #180 sandpaper to obtain wood material for the test coating board.

[0131] Each coating composition obtained in the above Examples and Comparative Examples was applied to a wooden test board using a knife coater at a speed of 20 m / min, an angle of 45°, and a press pressure of 0.2 MPa, and then dried at 140°C for 1 minute to obtain test boards corresponding to each coating composition.

[0132] The test methods and evaluation methods are as follows.

[0133] Pigment settling stability For each paint composition, 4 kg of the base agent (composition obtained by excluding the polyisocyanate compound from the paint formulation) was placed in a 4 L can and stored in a constant temperature room at 40°C for one week, after which the state of pigment sedimentation at the bottom was checked with a spatula.

[0134] ◎: No pigment sediment is observed ○: A small amount of pigment sediment adhering to the spatula is observed △: There is pigment sediment, but it becomes uniform when stirred. ×: Pigment sediment is present and the mixture is not uniform even after stirring. Potlife Each coating composition was left in a thermostatic chamber at 23°C, and the condition of the coating was checked after 1 hour.

[0135] ◎: No change from the initial stage, fluidity is maintained 〇: Viscosity is slightly higher than initially, but it is fluid and can be applied. Fillability The condition of the cured coating that filled the artificial holes in each test panel was observed. The convex bulge is advantageous because it makes the filled area of ​​the coating smooth after sanding. If there are dents due to thinning, it will have a negative effect on the smoothness after sanding.

[0136] ◎: Fully convex ○: Convexly bulging △: Slightly dented ×: There is a dent Blocking resistance Immediately after removing the test boards from the dryer, they were cooled for about one minute, and then an unpainted wooden test board was placed on top of the painted surface. A 50 kg load was applied, and the boards were left in a thermostatic chamber at 50°C for one hour. After that, the overlapping wooden test boards were peeled off, and the condition of the coating in the filled area was observed.

[0137] ◎: No abnormalities observed ○: A small amount of paint film is attached to the overlapping wooden test boards, but most of it remains in the filling area. ×: Most of the coating film was peeled off from the filled portion of the artificial hole in the test coated panel.

[0138] water resistance Each test coated plate was immersed in water at 70°C for 2 hours, and then left at room temperature for 1 hour and 24 hours, after which the state of the coating film in the filled area was observed.

[0139] ◎: No abnormalities after leaving at room temperature for 1 hour ○: After leaving it at room temperature for 1 hour, it absorbed water and became swollen, but after leaving it at room temperature for 24 hours, it returned to its original state before the test. ×: The coating film has dissolved in water and disappeared from the filled part of the artificial hole.

[0140] [Table 2]

[0141] [Table 3] [Industrial Applicability]

[0142] It is possible to provide an aqueous coating composition that undergoes almost no volumetric shrinkage upon curing, has excellent application properties such as filling properties and workability, pigment sedimentation stability, and also has excellent coating film properties such as water resistance.

Claims

1. A composition comprising: acrylic resin particles (A) having a glass transition temperature of 20°C or higher; a surfactant (B) having a weight-average molecular weight of 2,400 or higher and a triblock structure composed of a polyoxypropylene group and two polyoxyethylene groups sandwiching the polyoxypropylene group; a polyisocyanate compound (C); and a pigment (D), An aqueous wood coating composition comprising a pigment (D) in an amount of 600 mass% or more relative to the total solid content of components (A), (B), and (C).

2. 2. The water-based wood coating composition according to claim 1, wherein the acrylic resin particles (A) are crosslinked acrylic resin particles.

3. 3. The aqueous wood coating composition according to claim 1, wherein the acrylic resin particles (A) are core-shell type acrylic resin particles.

4. 4. The aqueous wood coating composition according to claim 1, wherein the weight average molecular weight of the polyoxypropylene group of the surfactant (B) is 1,450 or more.

5. 5. The aqueous wood coating composition according to claim 1, wherein the surfactant (B) has a polyoxyethylene group content in the molecule of 20% by mass or more.

6. 6. The aqueous wood coating composition according to claim 1, wherein the polyisocyanate compound (C) is an alicyclic polyisocyanate and / or a derivative of an alicyclic polyisocyanate.

7. 7. The aqueous wood coating composition according to claim 1, wherein the polyisocyanate compound (C) is a nonionic group-containing polyisocyanate compound.

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