JP6878298B2 - Water-based paint composition - Google Patents

Description

[Cross-reference of related applications]
This application claims priority based on Japanese Patent Application No. 2015-220860, which was filed on November 11, 2015, the entire disclosure of which is incorporated herein by reference.

The present invention relates to a water-based coating composition.

Recently, various paint compositions have been used for painting construction machines such as bulldozers, hydraulic excavators and wheel loaders or industrial machines. However, in the coating composition used for painting construction machinery or industrial machinery, when the coating film is dried, (1) the heat capacity is large and the heat of the drying furnace is not sufficiently transferred, and the curability is not sufficient (2). There are many vertical parts, and the glossiness of the matte coating film is not stable. (3) Furthermore, since construction machinery or industrial machinery is used outdoors, the finish, coating film hardness, coating film gloss stability, and water resistance There are problems such as requirements for properties, corrosion resistance, weather resistance, and the like.

Conventionally, in order to satisfy such a requirement, a coating composition has been developed in which two components, a base coating material and a curing agent component, are mixed and used immediately before coating.

For example, Patent Document 1 describes an aqueous resin (A) having an acid group and / or a tertiary amino and a hydroxyl group, a compound (B) having an epoxy group and a hydrolyzable silyl group, and a polyisocyanate compound (C). ) With a curable resin composition for water-based paints, which has excellent initial curability, raindrop stain resistance, gasoline resistance, solvent resistance, water resistance, weather resistance, etc. It is disclosed that a coating film can be obtained.

However, the curable resin composition for water-based paints described in Patent Document 1 has insufficient finishability, coating film hardness, and coating film gloss stability.
Good gloss stability of the coating film means that, for example, even when the object to be coated has a large heat capacity, the fluctuation of glossiness due to the baking temperature is small.

In addition, Patent Document 2 describes a water-based coating material containing a specific polyester resin (A), acrylic resin (B), water-dispersible polyisocyanate compound (C), and ion-exchanged amorphous silica fine particles (D). Disclosed is a water-based coating composition capable of forming a coating film having a long pot life (pot life) and excellent hardness, finish, gloss, water resistance and corrosion resistance. However, the water-based coating composition described in Patent Document 2 is insufficient in any of the finish property, the gloss stability of the coating film, and the weather resistance.

Japanese Unexamined Patent Publication No. 10-25450 JP-A-2007-284480

The problem to be solved by the present invention is water-based coating which is excellent in storage stability of the coating material and can form a coating film having excellent finish property, coating film hardness, gloss stability of the coating film, water resistance, corrosion resistance and weather resistance. To provide a coating composition.

As a result of diligent studies, the present inventors have conducted a hydroxyl group-containing resin (a), barium sulfate (b) having an average particle diameter of 0.01 to 2.0 μm, a coloring pigment (c), and a viscosity at 25 ° C. of 150 mPa · s or more. In order to complete the present invention, it has been found that the above-mentioned problems can be solved by an aqueous coating composition containing a specific amount of each of a polyisocyanate compound (d) of 800 mPa · s or less and a silane coupling agent (e). I arrived.

That is, the present invention includes the following aspects.

1. 1. A hydroxyl group-containing resin (a), barium sulfate (b) having an average particle diameter of 0.01 to 2.0 μm, a coloring pigment (c), and a polyisocyanate compound having a viscosity at 25 ° C. of 150 mPa · s or more and 800 mPa · s or less ( A coating composition containing d) and a silane coupling agent (e), wherein 1 to 50 parts by mass of barium sulfate (b) is added based on a total solid content of 100 parts by mass of the hydroxyl group-containing resin (a). , 1 to 100 parts by mass of the coloring pigment (c), 10 to 150 parts by mass of the polyisocyanate compound (d), and 0.1 to 10 parts by mass of the silane coupling agent (e). Paint composition.

2. Item 2. The aqueous coating composition according to Item 1, which contains 1 to 15 parts by mass of amorphous silica fine particles exchanged with metal ions based on 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a).

3. 3. Item 3. The water-based coating composition according to Item 1 or 2, wherein the hydroxyl group-containing resin (a) contains 0.1 to 10 parts by mass of a light stabilizer based on 100 parts by mass of the total solid content.

4. With the structure of the polyisocyanate compound (d) excluding the unreacted aliphatic diisocyanate, the 6-membered ring structure is 50 mol% or more, and the total of the uretdione structure and the allophanate structure is 20 mol. The water-based coating composition according to any one of Items 1 to 3, wherein the content is% or more and 50 mol% or less.

5. Item 2. The aqueous coating composition according to any one of Items 1 to 4, which contains 40 to 100 parts by mass of an ester-based hydrophilic solvent based on 100 parts by mass of the total solid content of the polyisocyanate compound (d).

6. A step of applying the water-based coating composition according to any one of Items 1 to 5 to a metal substrate, and a step of baking and drying an object to be coated with the coating composition at 50 to 170 ° C. for 10 to 120 minutes. A coating film forming method including.

7. A construction machine or an industrial machine having a cured coating film by the coating film forming method according to Item 6.

The water-based coating composition of the present invention has excellent storage stability of the base coating material, and the coating film obtained by coating the water-based coating composition has finishability, coating film hardness, coating film gloss stability, and water resistance. Excellent in corrosion resistance and weather resistance.

Specifically, the water-based coating composition of the present invention can be sufficiently cured in a short time at a low temperature even when (1) it is applied to an object to be coated having a large heat capacity, and (2) the cured coating film of the coating composition is It has excellent gloss stability, and the glossiness does not fluctuate much depending on the painted part (vertical part) and baking temperature. (3) The cured coating film has excellent water resistance, corrosion resistance, and weather resistance, so it can be used outdoors. The effect of the invention that it is useful can be achieved. The water-based coating composition of the present invention can be suitably used as, for example, a coating material for construction machinery or industrial machinery.

The present invention relates to a hydroxyl group-containing resin (a), barium sulfate (b) having an average particle diameter of 0.01 to 2.0 μm, a coloring pigment (c), and a viscosity at 25 ° C. of 150 mPa · s or more and 800 mPa · s or less. The present invention relates to an aqueous coating composition containing a predetermined amount of a polyisocyanate compound (d) and a silane coupling agent (e). Hereinafter, a detailed description will be given.

Hydroxy group-containing resin (a )
The hydroxyl group-containing resin (a) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl group-containing resin (a) include resins having a hydroxyl group, such as polyester resin, acrylic resin, polycarbonate resin, polyurethane resin, epoxy resin, and alkyd resin. These can be used alone or in combination of two or more. Among them, as the hydroxyl group-containing resin (a), it is preferable to use a hydroxyl group-containing acrylic resin from the viewpoint of coating film hardness and weather resistance. It is also preferable to use a hydroxyl group-containing acrylic resin and a hydroxyl group-containing polyester resin in combination.

The hydroxyl group-containing acrylic resin is an acrylic resin having at least one hydroxyl group in one molecule, and is usually a hydroxyl group-containing polymerizable unsaturated monomer and other polymerizable non-polymerizable monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. It is a copolymer of saturated monomers. Examples of the method for obtaining the copolymer include a method known per se, for example, a solution polymerization method in an organic solvent, an emulsion polymerization method in water, and the like.

The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule, and specifically, for example, 2-hydroxyethyl (meth) acrylate and 2-hydroxy. Propyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexytyl (meth) acrylate, 7-hydroxyheptyl (meth) ) A monoesterified product of a (meth) acrylic acid such as an acrylate or 8-hydroxyoctyl (meth) acrylate and a divalent alcohol having 2 to 8 carbon atoms (preferably 2 to 4 carbon atoms); the (meth) acrylic acid and the carbon number of carbon atoms. Ε-caprolactone modified product of monoesterified with 2 to 8 divalent alcohols; N-hydroxymethyl (meth) acrylamide; allyl alcohol, (meth) acrylate having a polyoxyethylene chain having a hydroxyl group at the molecular end, etc. Can be mentioned. In the present invention, the polymerizable unsaturated monomer having an ultraviolet absorbing functional group such as 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, which will be described later, is a hydroxyl group-containing polymerizable unsaturated monomer. Instead, it is included in other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomers.

Examples of other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and i-propyl (. Meta) 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, lauryl (meth) acrylate, stearyl (meth) acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth) acrylate, methyl Alkyl or cycloalkyl (meth) acrylates such as cyclohexyl (meth) acrylates, t-butylcyclohexyl (meth) acrylates, cyclododecyl (meth) acrylates; polymerizable unsaturated monomers having isobornyl groups such as isobornyl (meth) acrylates; adamantyl Polymerizable unsaturated monomer having an adamantyl group such as (meth) acrylate; vinyl aromatic compound such as styrene, α-methylstyrene, vinyltoluene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane , Γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane and other polymerizable unsaturated monomers having an alkoxysilyl group; perfluorobutylethyl (meth) acrylate, perfluorooctylethyl A (meth) acrylate having a perfluoroalkyl group such as a (meth) acrylate; a polymerizable unsaturated monomer having a fluorinated alkyl group such as a fluoroolefin; a polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group; Vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate; carboxyl group-containing polymerizable unsaturated monomers such as (meth) acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate; (Meta) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, glycidyl (meth) acrylate Nitrogen-containing polymerizable unsaturated monomer such as an adduct of and an amine compound; having two or more polymerizable unsaturated groups in one molecule such as allyl (meth) acrylate and 1,6-hexanedioldi (meth) acrylate. Polymerizable unsaturated monomer; glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4-epoxy Epoxy group-containing polymerizable unsaturated monomer such as cyclohexylpropyl (meth) acrylate and allylglycidyl ether; (meth) acrylate having a polyoxyethylene chain having an alkoxy group at the molecular end; 2-acrylamide-2-methylpropanesulfonic acid, Polymerizable unsaturated monomer having a sulfonic acid base such as allyl sulfonic acid, sodium styrene sulfonic acid salt, sulfoethyl methacrylate and its sodium salt, ammonium salt; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2 − A polymerizable unsaturated monomer having a phosphate group such as acryloyloxypropyl acid phosphate, 2-methacryloyloxypropyl acid phosphate; 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy- 4- (3-Acryloyloxy-2-hydroxypropoxy) benzophenone, 2,2'-dihydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2'-dihydroxy-4- (3-acryloyl) Polymerizable unsaturated monomer with UV-absorbing functional groups such as oxy-2-hydroxypropoxy) benzophenone, 2- (2'-hydroxy-5'-methacryloyloxyethylphenyl) -2H-benzotriazole; 4- (meth) Acryloyloxy-1,2,2,6,6-pentamethylpiperidin, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidin, 4-cyano-4- (meth) acryloylamino-2 , 2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidin, 1- (meth) acryloyl-4-cyano-4 -(Meta) acryloylamino-2,2,6,6-tetramethylpiperidine , 4-Crotonoyloxy-2,2,6,6-Tetramethylpiperidin, 4-Crotonoylamino-2,2,6,6-Tetramethylpiperidin, 1-Crotonoyl-4-Crotonoyloxy-2,2 , 6,6-Tetramethylpiperidin and other UV-stable polymerizable unsaturated monomers; achlorine, diacetoneacrylamide, diacetonemethacrylate, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketone with 4-7 carbon atoms Examples thereof include polymerizable unsaturated monomer compounds having a carbonyl group such as (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), and these can be used alone or in combination of two or more.

A hydroxyl group-containing polyester resin (oil-free hydroxyl group-containing polyester resin) is a polyester resin having at least one hydroxyl group in one molecule, and is usually produced by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction. be able to.

Polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid. Examples thereof include acids, phthalic acids, maleic acids, fumaric acids, itaconic acids, trimellitic acids, pyromellitic acids and anhydrides thereof. Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, for example, ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, bisphenol hydride. Examples thereof include A, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. The introduction of hydroxyl groups into the polyester resin is performed, for example, by using a trihydric or higher alcohol such as glycerin, trimethylolpropane, trimethylolethane, or pentaerythritol as a part of the polyhydric alcohol component in the production of the polyester resin. It can be carried out.

The hydroxyl group-containing polycarbonate resin is a polycarbonate resin having at least one hydroxyl group in one molecule, and a polycarbonate polyol is exemplified. Polycarbonate polyols can usually be produced by reacting a carbonate component such as alkylene carbonate, diaryl carbonate or dialkyl carbonate or a carbonic acid derivative such as phosgene with a polyhydric alcohol.

The hydroxyl group-containing polyurethane resin is a polyurethane resin having at least one hydroxyl group in one molecule, and is usually produced by reacting a polyhydric alcohol, a compound having an isocyanate group, and a chain extender in the presence of, for example, an emulsifier. can do. For example, a dispersion obtained by forcibly emulsifying or self-emulsifying a prepolymer in water can be mentioned.

The hydroxyl group-containing epoxy resin is an epoxy resin having at least one hydroxyl group in one molecule, and can be usually produced by reacting an epoxy resin with a polyhydric alcohol and, if necessary, a denaturing agent.

The hydroxyl group-containing alkyd resin is an alkyd resin having at least one hydroxyl group in one molecule, and can usually be produced by reacting an oil fatty acid with the oil-free hydroxyl group-containing polyester resin. Examples of the oil fatty acid include palm oil fatty acid, soybean oil fatty acid, flaxseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, millet oil fatty acid and the like. The reaction between the polyester resin and the oil fatty acid can also be carried out by a known method, and the oil length of the hydroxyl group-containing alkyd resin is preferably 30% or less.

The hydroxyl group-containing resin (a) preferably has a hydroxyl value in the range of 30 to 300 mgKOH / g, particularly 40 to 250 mgKOH / g, from the viewpoint of coating film hardness and corrosion resistance.

The hydroxyl group-containing resin (a) preferably has an acid value in the range of 10 to 40 mgKOH / g or less, particularly 15 to 30 mgKOH / g, from the viewpoint of water dispersibility and storage stability. The hydroxyl group-containing resin (a) generally preferably has a weight average molecular weight in the range of 3,000 to 100,000, particularly 3,000 to 50,000, and more preferably 4,000 to 30,000.

The "weight average molecular weight" in the specification is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by a gel permeation chromatograph according to the method described in JIS K 0124-2011.

As the gel permeation chromatograph, "HLC8120GPC" (manufactured by Tosoh Corporation) was used. As the column, four columns of "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation, trade name) are used, and the mobile phase; tetrahydrofuran. , Measurement temperature; 40 ° C., flow velocity; 1 ml / min, detector; RI conditions.

Barium sulfate (b)
The water-based coating composition of the present invention has a barium sulfate (b) having an average particle size of 0.01 to 2.0 μm, preferably an average particle size of 0.02 to 1.0 μm (hereinafter, abbreviated as barium sulfate (b)). Contains.

Commercially available products of such barium sulfate (b) include Varifine BF-20 (manufactured by Sakai Chemical Industry Co., Ltd., trade name, average particle size 0.03 μm), SS-50 (manufactured by Sakai Chemical Industry Co., Ltd., trade name). Average particle size 0.5 μm), barium sulfate 100 (manufactured by Sakai Chemical Industry Co., Ltd., trade name, average particle size 0.6 μm), precipitated barium sulfate PS-07 (manufactured by Guangxi Xiangzh, trade name, average particle size 0. 74 μm), Precipitated barium sulfate Blanc Fixe HD80 (manufactured by Solvery Barice Derivati SpA, trade name, average particle diameter 0.8 μm), barium sulfate HF (manufactured by Shenzhen Kashin Kako Co., Ltd., trade name, average particle diameter 0.9 μm) , SPARC W-5HB (manufactured by Wilbur Ellis, trade name, average particle size 1.6 μm). The average particle size in the present specification is a value obtained by measuring the particle size distribution by a dynamic light scattering method, more specifically, a value measured using UPA-EX250 (manufactured by Nikkiso Co., Ltd., trade name). means.

The blending amount of barium sulfate (b) in the water-based coating composition of the present invention is the total solid content of the hydroxyl group-containing resin (a) from the viewpoints of the coating film hardness of the obtained coating film, the gloss stability of the coating film, and the water resistance. It is desirable that the amount is 1 to 50 parts by mass, preferably 5 to 30 parts by mass, based on 100 parts by mass.

Color pigment (c)
The coloring pigment (c) can be blended for the purpose of adjusting the hue and brightness of the cured coating film of the aqueous coating composition of the present invention. The coloring pigment (c) is not particularly limited. Specifically, white-based coloring pigments such as titanium oxide and Neuburg silica clay (natural bond of plate-shaped kaolinite and massive quartz); black-based pigments such as carbon black, graphite (graphite), and iron black (iron black). Color pigments: Navy blue, ultramarine blue, cobalt blue, copper phthalocyanine blue, indanslen blue and other blue color pigments; synthetic yellow iron oxide, transparent red iron oxide (yellow), bismuth vanadate, titanium yellow, monoazo yellow, disazo yellow , Isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, benzimidazolone yellow and other yellow pigments; Bengara, transparent Bengara (red), monoazo red, unsubstituted quinacridone red, azolake (Mn salt), quinacridone magenta , Dianthraquinonyl red, perylene maroon, perylene red, diketopyrrolopyrrole chrome vermilion and other red pigments; chlorinated phthalocyanine green, brominated phthalocyanine green and other green pigments; pyrazolone orange, benzimidazo Other coloring pigments such as Ron Orange, Ansanthron Orange, Dioxazine Violet, Perylene Violet can be mentioned. These can be used alone or in combination of two or more.

The coloring pigment (c) can be blended in the coating composition as a powder, but the coloring pigment is mixed and dispersed with a part of the resin composition to prepare a pigment dispersion (pigment dispersion paste) in advance. It can also be made into a paint by mixing this with the remaining resin component and other components. In preparing the pigment dispersion (pigment dispersion paste), conventional paint additives such as antifoaming agents, dispersants, and surface conditioners can be used, if necessary.

The blending ratio of the coloring pigment (c) in the aqueous coating composition of the present invention is in the range of 1 to 100 parts by mass, preferably 5 to 50 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). Is preferable in that a coating film having excellent finish properties, gloss stability of the coating film, and weather resistance can be obtained.

Polyisocyanate compound (d)
The polyisocyanate compound (d) is a polyisocyanate compound having a viscosity (* 1) at 25 ° C. of 150 mPa · s or more and 800 mPa · s or less, preferably 250 mPa · s or more and 600 mPa · s or less. .. When the viscosity at 25 ° C. is in such a range, a coating film having good finish property, coating film hardness, coating film gloss stability, water resistance and corrosion resistance can be obtained.

(* 1) Viscosity: Using RE-85R (manufactured by Toki Sangyo Co., Ltd., trade name, viscometer), those with a viscosity of about 500 mPa · s or less at 25 ° C have a rotation speed of 20 rpm and a viscosity of about 500 mPa · s. Those with s or more were measured at a rotation speed of 10 rpm.

The polyisocyanate compound means a compound having at least two isocyanate groups in one molecule, for example, an aliphatic polyisocyanate, an alicyclic polyisocyanate, an aromatic aliphatic polyisocyanate, an aromatic polyisocyanate, or the polyisocyanate. Derivatives and the like can be mentioned.

Examples of the polyisocyanate derivative include the above-mentioned polyisocyanate dimer, trimmer, biuret, allophanate, uretdione, uretoimin, isocyanurate, oxadiazine trione and the like. The polyisocyanate compound (d) may contain one or more polyisocyanate compounds and derivatives thereof.

As the polyisocyanate compound (d), a compound obtained by self-emulsifying polyisocyanate in water, a compound in which polyisocyanate was forcibly dispersed by a stirrer or the like, and polyisocyanate were dispersed using an anionic or nonionic surfactant. Examples include compounds.

As the polyisocyanate compound (d), a polyisocyanate compound such as an aliphatic polyisocyanate (for example, an aliphatic diisocyanate) is used as a monomer and subjected to a mulching reaction (for example, an isocyanurate-forming reaction, an allophanate-forming reaction, a uretdione-forming reaction, etc.). The resulting multimer can be used. The multimerization reaction preferably includes at least a trimerization reaction (for example, an isocyanurate-forming reaction; a trimer is obtained).

The aliphatic diisocyanate is an aliphatic polyisocyanate having at least two isocyanate groups in one molecule. The aliphatic diisocyanate preferably has 4 to 30 carbon atoms, and examples thereof include tetramethylene-1,4-diisocyanate, pentamethylene 1,5-diisocyanate, and hexamethylene diisocyanate. Among these, hexamethylene diisocyanate is preferable from the viewpoint of finish property, water resistance and corrosion resistance.

The structure (* 2) of the polyisocyanate compound (d) is 50 mol% or more of the 6-membered ring structure among the structures derived from the isocyanate groups, and the uretdione structure and the allophanate structure, except for the unreacted aliphatic diisocyanate. It is desirable that the total is 20 mol% or more and 50 mol% or less from the viewpoints of finish property, gloss stability of the coating film, water resistance and corrosion resistance.

(* 2) Structure: The ratio of each structure in the polyisocyanate compound (d) ^{can be determined by 13} C-NMR measurement. Specifically, in ¹³ C-NMR measurement (measuring equipment: Bruker's Biospin Avance 600 (trade name), measuring solvent: chloroform-d, observation frequency: 150 MHz, number of integrations: 10000 times), isocyanurate group, imino. It can be calculated from the integrated value of peaks derived from the oxadiazinedione group, chloroformate group, uretdione group and other structures.

6-membered ring structure The 6-membered ring structure obtained by the quantification reaction of the isocyanate groups includes an isocyanurate ring and an iminooxadiazinedione ring, and an isocyanurate ring is preferable from the viewpoint of water resistance and corrosion resistance. The proportion of the 6-membered ring structure in the polyisocyanate compound (d) is 50 mol% or more and less than 80 mol%, preferably 55 mol% or more in terms of finish property, water resistance, corrosion resistance and coating stability. It is desirable that it is 75 mol% or less.

Uletdione structure / allophanate structure The above uretdione structure is generally formed by a dimerization reaction of isocyanate groups. The allophanate structure is generally formed by the reaction of two isocyanate groups with one alcohol.

The uretdione structure in the polyisocyanate compound (d) is not particularly limited. From the viewpoint of water resistance, corrosion resistance and weather resistance, the uretdione structure in the polyisocyanate compound (d) is 5 mol% or more and less than 45 mol%, preferably 15 mol% or more and 30 mol% or less. desirable.

The allophanate structure in the polyisocyanate compound (d) is not particularly limited. From the viewpoint of water resistance, corrosion resistance and weather resistance, it is desirable that the allophanate structure in the polyisocyanate compound (d) is 5 mol% or more and 20 mol% or less.

Other Structure The polyisocyanate compound (d) can include a urea structure, a biuret structure, and a urethane structure in addition to the 6-membered ring structure, the uretdione structure, and the allophanate structure.

Method for Producing Polyisocyanate Compound (d) The method for producing the polyisocyanate compound (d) is not particularly limited, and for example, an increase reaction (for example, isocyanurate-forming reaction, allophanate-forming reaction, uretdione-forming reaction) is excessive. Examples thereof include a method in which the unreacted diisocyanate monomer is removed after the reaction is completed in the presence of an aliphatic diisocyanate (for example, hexamethylene diisocyanate) monomer, and a method in which two or more kinds of polyisocyanates are separately produced and then mixed.

The aliphatic diisocyanate preferably has 4 to 30 carbon atoms, and examples thereof include tetramethylene-1,4-diisocyanate, pentamethylene 1,5-diisocyanate, and hexamethylene diisocyanate. Among these, hexamethylene diisocyanate is preferable from the viewpoint of finish property, water resistance and corrosion resistance.

The quantification reaction can be carried out in the presence of a known catalyst (for example, an isocyanurate-forming catalyst such as trimethyl-2-methyl-2-hydroxyethylammonium hydroxide), if necessary.

The conditions for the quantification reaction can be appropriately set by those skilled in the art. For example, the reaction temperature can be about 50 to 120 ° C., preferably about 60 to 90 ° C. The reaction time can be about 5 minutes to 24 hours, preferably about 30 minutes to 12 hours. The amount of the catalyst used can be about 10 to 1000 ppm, preferably about 10 to 500 ppm, and more preferably about 10 to 100 ppm with respect to the weight of the monomer used.

The proportions of the 6-membered ring structure, allophanate structure and uretdione structure of the polyisocyanate compound (d) can be adjusted based on, for example, the methods described in Japanese Patent No. 3995300 and WO2007 / 046470.

Commercially available products of such a polyisocyanate compound (d) include DURANATE TUL-100 (viscosity 300 mPa · sec / 25 ° C.), DURANATE TLA-100 (viscosity 500 mPa · sec / 25 ° C.), (Asahi Kasei Chemicals Co., Ltd.). Made) and the like.

The compounding ratio of the polyisocyanate compound (d) in the aqueous coating composition of the present invention ranges from 10 to 150 parts by mass, preferably 30 to 120 parts by mass, per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). It is preferable from the viewpoints of finish property, coating film hardness, coating film gloss stability, water resistance and corrosion resistance. Further, in addition to the polyisocyanate compound (d), a conventionally known polyisocyanate compound can also be used in combination.

Silane coupling agent (e)
The water-based coating composition of the present invention contains a silane coupling agent (e). The silane coupling agent (e) is, for example, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-). Aminoethyl) -γ-aminopropylmethyldimethoxysilane, N- (β-aminoethyl) -γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N- (β- (N-vinylbenzylaminoethyl)) Amino group-containing silane coupling agents such as −γ-aminopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane; γ-glycidoxypropylmethyldimethoxycisilane,
Epoxide group-containing silane coupling agents such as γ-glycidoxypropyltrimethoxyxisocyanate, γ-glycidoxypropyltriethoxyxisisilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane; β-carboxyethyl Carboxy-containing silane coupling agents such as phenylbis (2-methoxyethoxy) silane, N-β- (N-carboxymethylaminoethyl) -γ-aminopropyltrimethoxysilane; isocyanate groups such as 3-isocyanatepropyltriethoxysilane Containing silane coupling agent; examples thereof include isocyanurate group-containing silane coupling agents such as tris- (trimethoxysilylpropyl) isocyanurate. These silane coupling agents may be used alone or in combination of two or more.

Commercially available products of the silane coupling agent (e) include KBM-402, KBM-403, KBM-502, KBM-503, KBM-603, KBE-903, KBM-603, KBE-602, and KBE-603. , KBM-9007, KBM-9569 (above, manufactured by Shinetsu Silicone Co., Ltd., trade name), Silane Ace S530, Silane Ace S710 (above, manufactured by JNC Corporation, trade name) and the like.

The blending amount of the silane coupling agent (e) is 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass, based on 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). However, it is desirable for improving water resistance and corrosion resistance.

Metal ion-exchanged amorphous silica fine particles The aqueous coating composition of the present invention can contain metal ion-exchanged amorphous silica fine particles, if necessary. Amorphous silica fine particles exchanged with metal ions are silica fine particles in which alkaline earth metal ions such as calcium ions and magnesium ions are introduced into a fine porous silica carrier by ion exchange. Hereinafter, the calcium ion-exchanged amorphous silica fine particles will be referred to as calcium ion-exchanged silica, and the magnesium ion-exchanged amorphous silica fine particles will be referred to as magnesium ion-exchanged silica.

The metal ion-exchanged amorphous silica fine particles blended in the coating film are ion-exchanged with hydrogen ions and / or oxygen ions that have permeated the coating film, and calcium ions (Ca ²⁺ ) or magnesium ions (Mg). It is thought that alkaline earth metal ions such as ^{2+) are released to protect the metal surface.}

Examples of commercially available products of the calcium ion exchange silica include SHIELDEX C303, SHIELDEX AC-3, and SHIELDEX AC-5 (all of which are manufactured by WR Grace & Co., trade names). Examples of commercially available products of the magnesium ion exchange silica include silomask 52M (manufactured by Fuji Silysia Chemical Ltd., trade name) and Nova Nox ACE-110 (manufactured by SNCZ Co., Ltd., France, trade name).

When the amorphous silica fine particles exchanged with metal ions are blended in the aqueous coating composition of the present invention, the blending ratio is 1 to 15 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). The range of 3 to 12 parts by mass is preferable from the viewpoint of storage stability, water resistance and corrosion resistance of the coating material.

Light Stabilizer The water-based coating composition of the present invention may contain a light stabilizer, if necessary. Specific examples thereof include bis- (2,2', 6,6'-tetramethyl-4-piperidinyl) sebatate, 4-benzoyloxy-2,2', 6,6'-tetramethylpiperidine and the like. Be done.

Commercially available light stabilizers include, for example, TINUVIN123, TINUVIN144, TINUVIN152, TINUVIN292 (above, BASF, trade name), HOSTAVIN3058 (Clariant, trade name), ADEKA STAB LA-82 (ADEKA, Inc., product). First name) and so on.

When the above light stabilizer is blended, the blending amount is not particularly limited, but is preferably 0.1 to 10 parts by mass based on 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). Is preferably in the range of 0.5 to 5 parts by mass from the viewpoint of storage stability, finish and weather resistance of the base coating material.

Ester-based hydrophilic solvent The aqueous coating composition of the present invention may contain an ester-based hydrophilic solvent, if necessary. Specifically, for example, propylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, ethylene glycol monoternary butyl ether, tripropylene glycol monoethyl ether, dipropylene. Examples thereof include glycol monomethyl ether, diethylene glycol monoethyl ether acetate, and propylene glycol monopropyl ether.

The ester-based hydrophilic solvent contains 40 to 100 parts by mass of the ester-based hydrophilic solvent based on 100 parts by mass of the total solid content of the polyisocyanate compound (d).
It is preferably in the range of 50 to 90 parts by mass from the viewpoint of finishability.

Other Ingredients In the aqueous coating composition of the present invention, various additives widely used in this field, for example, pigments other than the coloring pigment (c) of the present invention, a catalyst, a pigment dispersant, etc. Japanese agents, dyes, plasticizers, anti-settling agents, UV absorbers, antioxidants, surface conditioners, surfactants, anti-sags, thickeners, defoamers, lubricants, crosslinkable polymer particles (microgels) , An anti-rust agent, an organic solvent other than an ester-based hydrophilic organic solvent, clean water, deionized water, and the like can be contained.

Examples of pigments other than the above coloring pigment (c) include extender pigments such as calcium carbonate, talc and kaolin; rust preventive pigments such as aluminum phosphate molybdenum; bismuth compounds such as bismuth oxide, bismuth hydroxide and bismuth lactate. Examples of the above catalyst include organic tin compounds such as dibutyltin oxide, dioctyltin oxide, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin dibenzoate, and dibutyltin dibenzoate.

Examples of the neutralizing agent include primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol and 3-aminopropanol; diethylamidiethanolamine and di-n-. Or secondary monoamines such as di-iso-propanolamine, N-methylethanolamine, N-ethylethanolamine; tertiary monoamines such as dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, dimethylaminoethanol Examples include polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine and methylaminopropylamine.

Examples of the rust preventive agent include sodium nitrite, organic acid amine salt, fatty acid salt and the like.

Commercially available rust preventives include, for example, Ruston N, Ruston RP11 (sodium nitrite, Koyo Kasei, trade name), Killeslite W7L (sodium nitrite, Kirest, trade name), Killeslite W511 (trade name). Organic acid amine salt, manufactured by Kirest, trade name), Killeslite WS410 (fatty acid salt, manufactured by Kirest, trade name) and the like can be mentioned.

Production of the water-based coating composition of the present invention The water- based coating composition includes, for example, a hydroxyl group-containing resin (a), barium sulfate (b) having an average particle diameter of 0.01 to 2.0 μm, a coloring pigment (c), and if necessary. A curing agent component containing a polyisocyanate compound (d) and a silane coupling agent (e) in a base coating material (1) containing metal ion-exchanged amorphous silica fine particles, a light stabilizer, and other components. It can be produced by mixing (2).

Further, the water-based coating composition of the present invention may include a state in which the base coating material (1) and the curing agent component (2) are not mixed, and a state in which the base coating material (1) and the curing agent component (2) are mixed. included. In the water-based coating composition of the present invention, the base coating material (1) and the curing agent component (2) are stored in separate containers, both are mixed immediately before use, and the solid content is adjusted with deionized water or the like. It is preferable to adjust the composition to obtain a water-based coating composition.

Coating film forming method The coating film forming method using the aqueous coating composition of the present invention is, for example, a step of coating the aqueous coating composition with or without applying an undercoat coating to an object to be coated. Next, a coating film forming method comprising a step of baking and drying an object to be coated with the water-based coating composition at 50 to 170 ° C. for 10 to 120 minutes is provided.

Examples of the object to be coated include cold-rolled steel sheets, black-skinned steel sheets, alloyed galvanized steel sheets, electrogalvanized steel sheets, metals such as aluminum, and the like. These metals and the like may be shot blasted, surface-adjusted, and chemical-converted, if necessary.

The method for coating the water-based coating composition of the present invention and the method for curing the coating film may be appropriately set depending on the intended use. As a coating method, for example, a coating method using dip coating, brush coating, roll brush coating, spray coating, roll coating, spin coating, dip coating, bar coating, flow coating, electrostatic coating, die coating or the like is preferable.

As the above-mentioned curing method, room temperature curing (for example, after forcibly drying at a temperature of more than 50 ° C. and 100 ° C. or lower for 5 to 40 minutes, then 24 hours to 10 days, preferably 3 to 7 days at 50 ° C. or lower). The coating film can be cured by heating (for example, curing the coating film at 100 to 200 ° C. for 10 to 120 minutes, preferably 120 to 180 ° C. for 20 to 90 minutes), and can be cured depending on the application. Conditions and the like may be set as appropriate. When the object to be coated is a part having a large heat capacity and cannot sufficiently heat the coating film and / or a part incorporating plastic, rubber, or the like, the above-mentioned room temperature curing is preferable. The coated article obtained by coating the water-based coating composition of the present invention has little change in glossiness due to the baking temperature even when the object to be coated has a large heat capacity. The above reason is considered to be due to the synergistic effect of barium sulfate (b), the coloring pigment (c), and the polyisocyanate compound (d) in the coating film. The film thickness of the cured coating film is 10 μm to 100 μm, preferably 20 μm to 80 μm. The storage container for the water-based coating composition is not particularly limited. For example, 1L to 200L cans can be used, and specifically, drum cans, oil cans and the like can be used.

Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited thereto. In each example, "part" indicates a mass part and "%" indicates a mass%.

Production Example 1 Acrylic resin solution production example Add 368.6 parts of ethylene glycol monobutyl ether to a 4-neck flask with a capacity of 2 liters equipped with a stirrer, thermometer, reflux tube, and nitrogen introduction tube, and after nitrogen substitution, stir 85 while stirring. Keeped at ° C.

Among these, 130 parts of styrene, 144 parts of methyl methacrylate, 150 parts of n-butyl methacrylate, 250 parts of i-butyl methacrylate, 200 parts of n-butyl acrylate, 426 parts of 2-hydroxyethyl methacrylate, 50 parts of acrylic acid, and 2, A mixture of 19.5 parts of 2'-azobis (2,4-dimethylvaleronitrile) was added dropwise over 3 hours, and from the end of the addition, the mixture was kept at 85 ° C. for an additional hour, followed by 65 parts of ethylene glycol monobutyl ether and 65 parts. A mixture of 6.5 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) was added dropwise over 1 hour. After keeping the temperature at 85 ° C. for 1 hour from the end of the dropping, the temperature was lowered to 40 ° C. Then, aqueous ammonia and deionized water were added to the flask to obtain an acrylic resin solution having a solid content of 45% by mass. The acrylic resin had a hydroxyl value of 138 mgKOH / g, an acid value of 29 mgKOH / g, and a number average molecular weight of 40,000.

Production Example 2 Production example of polyester resin solution 17 parts of trimethylolpropane, 21 parts of 1,6-hexanediol, in a reaction vessel equipped with a stirrer, thermometer, reflux tube, nitrogen introduction tube, rectification tower, and water separator. Condensation reaction of 15 parts of adipic acid, 29 parts of phthalic anhydride, and 12 parts of Cardura E10P (manufactured by HEXION Specialty Chemicals, trade name, glycidyl ester of synthetic highly branched saturated fatty acid) at 230 ° C. under reflux with toluene, resin acid value. Was 1.0 mgKOH / g or less, and then toluene was removed under reduced pressure to maintain the reaction temperature at 170 ° C.

To this reaction product, 6 parts of trimellitic anhydride was added, the reaction was added at 170 ° C. for 30 minutes, dipropylene glycol monomethyl ether was added, the temperature was cooled to 85 ° C., and the mixture was neutralized with dimethylethanolamine. A polyester resin solution having a solid content of 60% by mass was obtained by using water as an aqueous dispersion. The hydroxyl value of the polyester resin was 122 mgKOH / g, the acid value was 35 mgKOH / g, and the number average molecular weight was 2,000.

Production Example 3 Polyisosiart compound No. Example of production of 1 solution The inside of a 4-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen blowing tube, and dropping funnel is made into a nitrogen atmosphere, and 600 parts of hexamethylene diisocyanate and 2.5 parts of isobutanol are charged and stirred. The temperature inside the lower reactor was maintained at 80 ° C. for 2 hours. Then, 0.5 part of a solution obtained by diluting the isocyanurate-forming catalyst trimethyl-2-methyl-2-hydroxyethylammonium hydroxide with isobutanol to a concentration of 5% by mass was added to carry out an isocyanurate-forming reaction, and then phosphoric acid 85. The reaction was stopped by adding 0.06 part of a% aqueous solution.

Then, the reaction solution was further kept at 160 ° C. for 1 hour to form a polyisocyanate. The reaction solution was cooled to room temperature, filtered, and then unreacted hexamethylene diisocyanate was removed using a thin film distillation apparatus to remove the polyisosiato compound No. One solution was obtained.

Polyisosiart compound No. The viscosity (* 1) of one solution was 280 mPa · s. In addition, polyisosiart compound No. The structure (* 2) of 1 had a 6-membered ring structure of 63.4 mol%, a uretdione structure of 22.5 mol%, an allophanate structure of 13.6 mol%, and other structures of 0.5 mol%. ..

Production Example 4 Polyisosiart compound No. Example of production of 2 solutions The same procedure as in Production Example 3 was carried out except that the amount of isobutanol was 1.1 parts in Production Example 3. Two solutions were obtained. The obtained polyisosiart compound No. The viscosity (* 1) of the two solutions was 400 mPa · s. In addition, polyisosiart compound No. The structure of 2 (* 2) was 65.9 mol% for the 6-membered ring structure, 26.5 mol% for the uretdione structure, 7.3 mol% for the allophanate structure, and 0.3 mol% for the other structures. ..

Production Example 1 of water-based coating composition No. 1 of water-based coating composition. 1
By the following steps 1 to 4, the aqueous coating composition No. 1 having a solid content of 50% by mass was added. I got 1.

Step 1 20 parts (solid content) of the acrylic resin solution obtained in Production Example 1, 50 parts (solid content) of the precipitated barium sulfate PS-07 (* 4), 15 parts (solid content) of Typake CR-95 (* 8). ), 3 parts (solid content) of carbon MA-7 (* 11), 50 parts (solid content) of NEOLIGHT SA-200 (* 14) and an appropriate amount of ethyl acetate were added and dispersed in a sand mill for 1 hour to prepare a pigment dispersion paste. Obtained.

Step 2 The pigment dispersion paste obtained in Step 1 is added to 80 parts (solid content) of the acrylic resin solution obtained in Production Example 1 and stirred, and then 1.5 parts of AMP-95 (* 16) is added. , Deionized water was added to obtain a base paint having a solid content of 50% by mass.

Step 3 Solid content 63 containing 100 parts (solid content) of DURANATE TUL-100 (* 19), 60 parts (solid content) of diethylene glycol monoethyl ether acetate, and 4 parts (solid content) of Sila Ace S530 (* 23) as a curing agent component. % Hardener was obtained.

Step 4 100 parts of the base paint of the above step 2 and 15 parts of the curing agent of the step 3 were mixed, stirred with a disper for 3 minutes, and adjusted to the coating viscosity with deionized water.

Examples 2-35 Aqueous coating composition No. 2-No. 35
In the same manner as in Example 1, the water-based coating composition No. 2-No. I got 35.

Comparative Example 1 Aqueous coating composition No. 36
By the following steps 1 to 4, the aqueous coating composition No. 1 having a solid content of 50% by mass was added. I got 36.

Step 1 20 parts (solid content) of the acrylic resin solution obtained in Production Example 1, 50 parts (solid content) of Varifine BF-20 (* 3), 15 parts (solid content) of Typake CR-95 (* 8), 3 parts (solid content) of carbon MA-7 (* 11), 50 parts (solid content) of NEOLIGHT SA-200 (* 14) and an appropriate amount of ethyl acetate were added and dispersed in a sand mill for 1 hour to obtain a pigment-dispersed paste. ..

Step 2 The pigment dispersion paste obtained in Step 1 is added to 80 parts (solid content) of the acrylic resin solution obtained in Production Example 1 and stirred, and then 1.5 parts of AMP-95 (* 16) is added. , Deionized water was added to obtain a base paint having a solid content of 50% by mass.

Step 3 Solid content 63 containing 100 parts (solid content) of DURANATE TUL-100 (* 19), 60 parts (solid content) of diethylene glycol monoethyl ether acetate, and 4 parts (solid content) of Sila Ace S530 (* 23) as a curing agent component. % Hardener was obtained.

Step 4 100 parts of the base paint of the above step 2 and 15 parts of the curing agent of the step 3 were mixed, stirred with a disper for 3 minutes, and adjusted to the coating viscosity with deionized water.

Comparative Examples 2 to 21
Aqueous coating composition No. 1 was obtained in the same manner as in Comparative Example 1 except that the composition contents were shown in Tables 4 to 5. 37-No. I got 56.

(* 3) Varifine BF-20: manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate, average particle size 0.03 μm
(* 4) Precipitating barium sulfate PS-07: manufactured by Guangxi Xiangzh, trade name, barium sulfate, average particle size 0.74 μm
(* 5) SPARC W-5HB: manufactured by Wilbur Ellis, trade name, barium sulfate, average particle size 1.6 μm
(* 6) Barium sulfate BA: manufactured by Sakai Chemical Industry Co., Ltd., trade name, barium sulfate, average particle size 8 μm
(* 7) LAKABAR SF: LAKAVISUTH, trade name, barium sulfate, average particle size 14 μm
(* 8) Typake CR-95: manufactured by Ishihara Sangyo Co., Ltd., trade name, titanium dioxide (* 9) Siritin V85: manufactured by Hoffman Mineral Co., Ltd. -Mineral Co., Ltd., product name, Neuburg silica soil (* 11) carbon MA-7: Mitsubishi Chemical Co., Ltd., product name, carbon black (* 12) SHIELDEX C303: W. R. Grace & Co. Made by the company, trade name, calcium ion exchange silica, average particle size 3 μm
(* 13) NOVINOX ACE 110: SNCZ Society Nouvelle Deskur, manufactured by Ginsic, trade name, magnesium ion exchange silica, average particle size 4.8 μm
(* 14) NEOLIGHT SA-200: Takehara Chemical Co., Ltd., trade name, calcium carbonate (* 15) K-WHITE 140: Kikuchi Color Co., Ltd., trade name, aluminum dihydrogen dihydrogen tripolyphosphate (* 16) Adecanol UC-606: ADEKA, product name, hindered amine-based light stabilizer (* 17) TINUVIN292: Ciba Specialty Chemicals, product name, hindered amine-based light stabilizer (* 18) AMP-95: Dow Chemical, product name , 2-Amino-2-methyl-1-propanol (* 19) DURANATE TUL-100: manufactured by Asahi Kasei Chemicals Co., Ltd., trade name, hexamethylene diisocyanate-based polyisocyanate compound, viscosity 300 mPa · s / 25 ° C.
(* 20) DURANATE TLA-100: manufactured by Asahi Kasei Chemicals Co., Ltd., trade name, hexamethylene diisocyanate-based polyisocyanate compound, viscosity 500 mPa · s / 25 ° C.
(* 21) DURANATE TPA-100: manufactured by Asahi Kasei Chemicals Co., Ltd., trade name, hexamethylene diisocyanate-based polyisocyanate compound, viscosity 1,400 mPa · s / 25 ° C.
(* 22) BAYHYDUR304: Made by Sumika Bayer Urethane Co., Ltd., trade name, hexamethylene diisocyanate-based polyisocyanate compound, viscosity 3,800 mPa · s / 25 ° C.
(* 23) Sila Ace S530: JNC, trade name, silane coupling agent (* 24) KBM-403: Shin-Etsu Chemical, trade name, silane coupling agent, 3-glycidoxypropyltrimethoxysilane (* 24) 25) KBM-9007: manufactured by Shin-Etsu Chemical Co., Ltd., trade name, silane coupling agent, 3-isocyanatepropyltriethoxysilane.

The test plate was prepared and the performance was evaluated according to the following. The test results are also shown in Tables 1 and 2.

Preparation of test plate On a cold-rolled steel sheet (100 mm × 300 mm × 2.0 mm) treated with zinc phosphate, the coating composition No. 1 obtained in the above Examples and Comparative Examples was used. 1-No. 39 was spray-coated so as to have a dry film thickness of 50 μm. Then, each test plate was obtained by heating and drying at 95 ° C. for 20 minutes using an electric hot air dryer.

Performance evaluation (* 26) Storage stability of paint: Each base paint was placed in a 250 ml glass container and stored at 20 ° C. for 4 hours in a dark place to check the condition.

In S, no gelation, phase separation, or sedimentation of the coating composition was observed. In A, no gelation, phase separation, or sedimentation of the coating composition was observed, and some sedimentation was observed, but gentle stirring was observed. Return to original B shows slight gelation and phase separation of the paint composition.
In C, at least one of gelation and phase separation of the coating composition is remarkably observed.

(* 27) Finishability:
The appearance of the coated surface of the test plate heat-dried at 95 ° C. for 20 minutes was visually evaluated.

A has good smoothness and there is no problem. B has a slight decrease in finish such as swell, gloss, and dusty skin.
C has a large decrease in finish such as waviness, glossiness, and dusty skin.
(* 28) Coating film hardness: A test plate that has been heat-dried at 95 ° C. for 20 minutes is subjected to a pencil lead at an angle of about 45 ° with respect to the test coating plate surface according to JIS K 5600-5-4, and the lead is broken. The test plate was moved forward at a uniform speed by about 10 mm while being pressed against the coating film surface of the test plate as strongly as possible. The hardness of the hardest pencil that did not tear the coating film was defined as the coating film hardness.

(* 29) Glossy stability of coating film:
With the surface to be coated perpendicular to a cold-rolled steel sheet (70 mm × 300 mm × 2.0 mm) subjected to zinc phosphate chemical conversion treatment, each coating composition obtained in the above Examples and Comparative Examples was subjected to a dry film thickness. "Glossiness difference (Δ)" between the glossiness of a coated plate spray-coated to 50 μm and baked at 60 ° C. for 20 minutes and the glossiness of a coated plate baked at 160 ° C. for 20 minutes after preheating at 60 ° C. I asked.

The glossiness of each coating film follows the 60-degree mirror glossiness of JIS K 5600-4-7 (1999), and the reflectance when the incident angle and the light receiving angle are 60 degrees each is determined in the longitudinal direction of the test plate. The "average value" was obtained by measuring at n = 10 at intervals of about 2.5 cm, and evaluated according to the following criteria.

S has a glossiness difference (Δ) of 2 or less,
In A, the glossiness difference (Δ) exceeds 2, and is 5 or less.
In B, the glossiness difference (Δ) exceeds 5, and is 10 or less.
In C, the glossiness difference (Δ) exceeds 10.

(* 30) Water resistance:
Using a test plate that has been heat-dried at 95 ° C for 20 minutes, soak it in deionized water at 40 ° C for 240 hours, pull it up, and apply the coating plate according to the JIS K 5600-5-6 (1999) grid-tape method. Using a knife to reach the substrate on the film surface, make 11 vertical and horizontal cuts at intervals of about 2 mm to form a goban, and attach cellophane (registered trademark) adhesive tape to the surface. Then, the goban-coated surface after the tape was rapidly peeled off was evaluated according to the following criteria.

In S, no peeling of the coating film is observed. In A, slight peeling is observed in a part of the coating film in the knife scratch. In B, 1 to 20 of 100 Goban eyes are all peeled off. As for C, 21 or more of the 100 Goban eyes are all peeled off.

(* 31) Anticorrosion:
Using a test plate that has been heat-dried at 95 ° C for 20 minutes, make a cross-cut scratch with a knife, and perform a salt spray resistance test for 120 hours according to JIS Z-2371. Evaluated in.

For S, the maximum width of rust or blisters is less than 2 mm from the cut part (one side).
In A, the maximum width of rust or blisters is 2 mm or more and less than 3 mm (one side) from the cut part.
In B, the maximum width of rust or blisters is 3 mm or more and less than 4 mm (one side) from the cut portion.
In C, the maximum width of rust or blisters is 4 mm or more (one side) from the cut portion.

(* 32) Weather resistance:
Using a test plate heat-dried at 95 ° C. for 20 minutes, the test was carried out in the sunshine carbon arc lamp type light resistance and weather resistance test specified in JIS B-7533 until the irradiation time became a maximum of 1,200 hours. In the coating film of the test plate, the irradiation time at which the gloss retention rate with respect to the gloss before the test was 80% was measured.

S has a gloss retention rate of 80% or more even when the irradiation time is 1,200 hours. A has an irradiation time of less than 80% and an irradiation time of 1,000 hours or more and less than 1200 hours.
In B, the irradiation time in which the gloss retention rate is less than 80% is 800 hours or more and less than 1,000 hours.
For C, the irradiation time for which the gloss retention rate is less than 80% is less than 800 hours.

The water-based coating composition of the present invention can provide a coated article having excellent finish properties, coating film hardness, coating film gloss stability, water resistance, corrosion resistance and weather resistance.

Claims (5)

A hydroxyl group-containing resin (a), barium sulfate (b) having an average particle diameter of 0.01 to 2.0 μm, a coloring pigment (c), and a polyisocyanate compound having a viscosity at 25 ° C. of 150 mPa · s or more and 800 mPa · s or less ( A coating composition containing d) and a silane coupling agent (e), wherein 1 to 50 parts by mass of barium sulfate (b) is added based on a total solid content of 100 parts by mass of the hydroxyl group-containing resin (a). , 1 to 100 parts by mass of the coloring pigment (c), 10 to 150 parts by mass of the polyisocyanate compound (d), and 0.1 to 10 parts by mass of the silane coupling agent (e).
With the structure of the polyisocyanate compound (d) excluding the unreacted aliphatic diisocyanate, the 6-membered ring structure is 50 mol% or more, and the total of the uretdione structure and the allophanate structure is 20 mol. A water-based coating composition characterized by being% or more and 50 mol% or less. The water-based coating composition according to claim 1, which contains 1 to 15 parts by mass of amorphous silica fine particles exchanged with metal ions based on 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). The water-based coating composition according to claim 1 or 2, which contains 0.1 to 10 parts by mass of a light stabilizer based on 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a). The step of applying the water-based coating composition according to any one of claims 1 to 3 to a metal substrate, and the object to be coated with the coating composition is baked and dried at 50 to 170 ° C. for 10 to 120 minutes. A coating film forming method including a step. A construction machine or an industrial machine having a cured coating film according to the coating film forming method according to claim 4.