Water-based paint compositions, coatings, and painted products

Abstract

The present invention provides a water-based paint composition containing a melamine-based crosslinking agent, exhibiting excellent storage stability and recoatability. [Solution] A water-based paint composition containing a hydroxyl group-containing (meth)acrylic resin (A), a melamine-based crosslinking agent having an alkylation degree of 60% or more (B), a sulfonic acid compound (C), a flake-like pigment (D), and water.

Description

Technical Field

[0001] The present disclosure relates to an aqueous coating composition, a coating film and a coated article.

Background Art

[0002] In order to impart properties such as weather resistance, chemical resistance or abrasion resistance to a base material such as a metal base material, it has been practiced to apply a coating composition onto a metal base material, perform a baking treatment, and form a coating film. As baking coating compositions, melamine-based, (meth)acrylic-based or fluorine-based coating compositions are known (see, for example, Patent Documents 1 to 4).

[0003] In recent years, emission regulations for organic solvents have been tightened for the purpose of consideration for the natural environment or coating work environments. Aqueous coating compositions generally have a lower content of volatile organic compounds (VOC) than organic solvent-based coating compositions. One of the methods for achieving low VOC is to convert coating compositions into aqueous-based ones.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problem to be Solved by the Invention

[0005] The present inventors conducted studies on an aqueous coating composition containing a melamine-based crosslinking agent, and found that the composition may not have sufficient storage stability or recoatability in some cases. This disclosure aims to provide a water-based coating composition containing a melamine-based crosslinking agent that exhibits excellent storage stability and recoatability. [Means for solving the problem]

[0006] One embodiment of the water-based paint composition of the present disclosure contains a hydroxyl group-containing (meth)acrylic resin (A), a melamine-based crosslinking agent having an alkylation degree of 60% or more (B), a sulfonic acid compound (C), a flake-like pigment (D), and water. [Effects of the Invention]

[0007] One embodiment of the water-based coating composition of the present disclosure contains a melamine-based crosslinking agent and exhibits excellent storage stability and recoatability. [Modes for carrying out the invention]

[0008] Each component described herein may be used individually or in combination of two or more. The term "(meth)acrylic" can also be used with acrylic or methacrylic. The term "(meth)acrylate" can also be used with acrylate or methacrylate. The term "(meth)acrylic acid" can also be used with acrylic acid or methacrylic acid.

[0009] In this specification, a numerical range indicated by "~" means a range that includes the numbers before and after "~" as the lower and upper limits. In this specification, if the units of the numbers before and after the "~" indicating a numerical range are the same, the unit of the number before "~" may be omitted.

[0010] [Water-based paint composition] One embodiment of the water-based paint composition of the present disclosure (hereinafter also referred to as "the Composition") contains a hydroxyl group-containing (meth)acrylic resin (A), a melamine-based crosslinking agent (B), a sulfonic acid compound (C), a flake-like pigment (D), and water, as described below.

[0011] <Hydroxyl group-containing (meth)acrylic resin (A)> The hydroxyl group-containing (meth)acrylic resin (A) (hereinafter also referred to as "component (A)") has structural units derived from (meth)acrylic monomers. Component (A) may further have structural units derived from ethylenically unsaturated monomers other than (meth)acrylic monomers (hereinafter also referred to as "other ethylenically unsaturated monomers") that are copolymerizable with (meth)acrylic monomers.

[0012] Component (A) may be a homopolymer of (meth)acrylic monomers, a copolymer of two or more (meth)acrylic monomers, or a copolymer of a (meth)acrylic monomer and other ethylenically unsaturated monomers. The copolymer may be, for example, a random copolymer, a block copolymer, or a graft copolymer. Component (A) is preferably a water-soluble (meth)acrylic resin that can be dissolved in water, or a water-dispersible (meth)acrylic resin that can be dispersed in water, and more preferably a water-dispersible (meth)acrylic resin.

[0013] Examples of (meth)acrylic monomers include (meth)acrylic acid esters, (meth)acrylamides, (meth)acrylonitriles, and (meth)acrylic acid.

[0014] Examples of (meth)acrylic acid esters include alkyl (meth)acrylates, alicyclic hydrocarbon group-containing (meth)acrylates, aryl (meth)acrylates, aralkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, hydroxyl group-containing (meth)acrylates, amino group-containing (meth)acrylates, and epoxy group-containing (meth)acrylates.

[0015] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate is preferably 1 to 20, more preferably 1 to 12, and even more preferably 1 to 6. Examples of alicyclic hydrocarbon group-containing (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Examples of aryl (meth)acrylates include phenyl (meth)acrylate. Examples of aralkyl (meth)acrylates include benzyl (meth)acrylate. Examples of alkoxyalkyl (meth)acrylates include methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, and ethoxybutyl (meth)acrylate.

[0016] Examples of hydroxyl group-containing (meth)acrylates include hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; hydroxyalkylcycloalkyl (meth)acrylates such as hydroxymethylcyclohexyl (meth)acrylate; polyalkylene glycol monoesters of (meth)acrylic acid such as polyethylene glycol mono(meth)acrylate and polypropylene glycol mono(meth)acrylate; and lactone adducts to these compounds (such as ε-caprolactone). Examples of amino group-containing (meth)acrylates include aminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and butylaminoethyl (meth)acrylate. Examples of epoxy group-containing (meth)acrylates include glycidyl (meth)acrylate.

[0017] Examples of (meth)acrylamides include aminoalkyl (meth)acrylamides such as aminoethyl (meth)acrylamide, dimethylaminomethyl (meth)acrylamide, and methylaminopropyl (meth)acrylamide; and other amide group-containing (meth)acrylic monomers such as (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-methylol (meth)acrylamide, methoxybutyl (meth)acrylamide, and diacetone (meth)acrylamide.

[0018] Examples of other ethylenically unsaturated monomers include α-olefins such as ethylene, propylene, and 1-butene; conjugated dienes such as 1,3-butadiene, isoprene, and chloroprene; styrenic monomers such as styrene, α-methylstyrene, vinyltoluene, and halogenated styrene; vinyl esters such as vinyl acetate and vinyl propionate; unsaturated monocarboxylic acids such as crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; monoesters of unsaturated dicarboxylic acids such as ethyl maleate and butyl maleate; and diesters of unsaturated dicarboxylic acids such as diethyl maleate and dibutyl maleate.

[0019] In component (A), the content of structural units derived from (meth)acrylic monomers in 100% by mass of the total amount of structural units derived from polymerizable monomers is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more. The content of each structural unit in component (A) is measured by nuclear magnetic resonance spectroscopy (NMR). The above (meth)acrylic monomer preferably comprises a (meth)acrylic acid ester, more preferably an alkyl (meth)acrylate, and in one embodiment comprises an alkyl (meth)acrylate and a hydroxyl group-containing (meth)acrylate. The above (meth)acrylic monomer may further comprise at least one selected from the group consisting of (meth)acrylic acid, unsaturated monocarboxylic acids other than (meth)acrylic acid, and unsaturated dicarboxylic acids.

[0020] Component (A) has hydroxyl groups. The coating film can be cured by a crosslinking reaction between the hydroxyl groups in component (A) and the reactive functional groups in the melamine-based crosslinking agent (B). Component (A) can be synthesized by using, for example, a hydroxyl group-containing (meth)acrylate as a (meth)acrylic monomer.

[0021] The hydroxyl value of component (A) is preferably 5 to 100 mg KOH / g, more preferably 10 to 90 mg KOH / g, even more preferably 20 to 80 mg KOH / g, and particularly preferably 30 to 70 mg KOH / g, from the viewpoint of improving coating strength and adhesion. The hydroxyl value of component (A) may be, for example, 36 mg KOH / g or more, or 51 mg KOH / g or more. The hydroxyl value of component (A) is measured on a solid content basis in accordance with JIS K0070:1992 (neutralization titration method).

[0022] Component (A) may have acidic groups such as carboxyl groups and may have an acid value greater than 0 mgKOH / g. The acid value of component (A) is preferably 5 to 120 mgKOH / g, more preferably 10 to 100 mgKOH / g, even more preferably 15 to 80 mgKOH / g, and particularly preferably 20 to 50 mgKOH / g. Component (A) with an acid value above the lower limit tends to have excellent stability in the paint composition. Paint compositions containing component (A) with an acid value below the upper limit tend to form a coating film with excellent water resistance. The acid value of component (A) is the amount of potassium hydroxide (mg) required to neutralize acidic groups such as carboxyl groups per 1 g of solid content of the sample, and is measured in accordance with JIS K0070:1992 (neutralization titration method).

[0023] The glass transition temperature (Tg) of component (A) is preferably -50 to 90°C, more preferably -30 to 70°C, even more preferably -10 to 50°C, and particularly preferably 0 to 30°C, from the viewpoint of improving the strength of the coating film. The Tg of component (A) is the temperature (°C) at the onset value of the DSC during heating, obtained by measuring the change in heat quantity in the range of -50 to 150°C in a nitrogen atmosphere at a heating rate of 10°C / min using a differential scanning calorimeter (DSC).

[0024] The weight-average molecular weight (Mw) of component (A) is preferably 1,000 to 200,000, more preferably 5,000 to 150,000, even more preferably 10,000 to 120,000, and particularly preferably 20,000 to 100,000, from the viewpoint of obtaining a paint composition with excellent film-forming properties.

[0025] The Mw of component (A) is a value equivalent to standard polystyrene, measured by gel permeation chromatography (GPC) under the following conditions. • Equipment: EcoSEC Elite HLC-8420GPC (manufactured by Tosoh Corporation) • Column: One "TSKgel SuperH 4000" and two "TSKgel SuperH 2000" connected together (both manufactured by Tosoh Corporation, inner diameter 6mm x length 15cm) • Eluent: Tetrahydrofuran (THF) ·Flow rate: 0.600mL / min • Detector: Differential refractive index (RI) detector Column constant temperature bath temperature: 40°C Calibration curve: Standard polystyrene Sample preparation method: Dilute the sample by adding THF to achieve a solid content concentration of 0.4% by mass, then filter it through a membrane filter to obtain the filtrate, which will be used as the GPC measurement sample.

[0026] Known methods can be used to synthesize component (A), including, for example, polymerizing polymerizable monomers in the presence of a radical polymerization initiator using solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization. Component (A) is produced by appropriately selecting (meth)acrylic monomers and, if necessary, other ethylenically unsaturated monomers, taking into consideration the structural units and weight-average molecular weight, and using known methods, such as solution radical polymerization.

[0027] Component (A) is preferably a water-dispersible (meth)acrylic resin particle. Component (A) may be present in particulate form in the composition. The Z-average particle size of component (A) is preferably 1 nm to 1 μm, more preferably 1 to 500 nm, even more preferably 5 to 300 nm, and particularly preferably 10 to 100 nm. Component (A) with a Z-average particle size within the above range tends to be stable in the coating composition, and such compositions tend to form coatings with uniform coating properties. The Z-average particle size is measured at 23°C by dynamic light scattering (DLS) using a particle size analyzer (e.g., Zetasizer Nano-ZS manufactured by Malvern).

[0028] This composition may contain one type of component (A), or it may contain two or more types of component (A). From the viewpoint of improving coating strength and adhesion, the content of component (A) is preferably 5 to 60% by mass, more preferably 15 to 50% by mass, and even more preferably 25 to 45% by mass, of 100% by mass of the solid content of the composition. The total solid content in this composition is preferably 30-80% by mass, more preferably 35-75% by mass, and even more preferably 40-70% by mass, from the viewpoint of improving paintability and other factors.

[0029] The solid content of a substance (e.g., this composition or each component) refers to the heat residue (non-volatile content) obtained when the substance is dried in a constant temperature oven at 125°C for 1 hour. Specifically, the heat residue is the residue of the sample (including residue adhering to the wire) obtained by weighing 1.0 g of the above substance onto a flat-bottomed dish, spreading it uniformly using a wire of known mass, and drying it in a constant temperature oven at 1 atmosphere and 125°C for 1 hour. The solid content percentage (solid content concentration) (mass%) of the above substance is calculated from the mass of the heat residue.

[0030] In the production of this composition, it is preferable to use an aqueous dispersion of component (A) from the viewpoint of coating film properties, etc. This makes it easier for component (A) to exist stably and uniformly in the composition, and tends to result in the formation of a coating film with uniform properties.

[0031] The aqueous dispersion of component (A) may be prepared, for example, by self-dispersing component (A) in water, by emulsifying component (A) using a surfactant, or directly by emulsion polymerization of the polymerizable monomer that forms component (A). Examples of surfactants include cationic surfactants, anionic surfactants, and nonionic surfactants.

[0032] The content of component (A) in the aqueous dispersion is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, and even more preferably 30 to 60% by mass, from the viewpoint of dispersion stability and workability in paint manufacturing.

[0033] An aqueous dispersion of component (A) is a dispersion in which component (A) is dispersed in a dispersion medium containing water (hereinafter also referred to as the "aqueous medium"). The aqueous medium is not particularly limited as long as it contains water. From the viewpoint of reducing environmental burden, the water content in the aqueous medium is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0034] The aqueous medium may contain a medium other than water. Examples of such mediums include acetone, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diacetone alcohol, dioxane, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monohexyl ether. The above mediums may be one type or two or more types.

[0035] Component (A) may have its acidic groups, such as carboxyl groups, neutralized by a neutralizing agent. Examples of neutralizing agents include amine compounds such as diethylamine, triethylamine, 2-dimethylaminoethanol, and dibutylamine.

[0036] The pH of the aqueous dispersion of component (A) at 23°C is preferably 7 to 12, more preferably 7.5 to 11, and even more preferably 8 to 10, from the viewpoint of the stability of the aqueous dispersion. By using such an aqueous dispersion, component (A) is more likely to exist stably and uniformly in the composition. Therefore, a coating film with uniform properties can be formed using this composition.

[0037] <Coating resins other than component (A)> This composition may further contain a film-forming resin other than component (A). Examples of such film-forming resins include (meth)acrylic resins, urethane resins, vinyl acetate resins, fluororesins, and vinyl chloride resins that do not have hydroxyl groups. The amount of the above-mentioned coating film-forming resin in this composition is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of component (A).

[0038] <Melamine-based crosslinking agent (B)> This composition contains a melamine-based crosslinking agent (B) (hereinafter also referred to as "component (B)"). Component (B) is a compound having an average of more than one, preferably two or more, reactive functional groups (groups represented by -NR2, described later) per molecule that can react with the hydroxyl groups in component (A), and can crosslink with component (A) to form a coating film.

[0039] Component (B) has an alkylation degree of 60% or more. The alkylation degree of component (B) is preferably 63-98%, more preferably 65-95%, even more preferably 67-90%, and particularly preferably 67-80%. The alkylation degree of the melamine crosslinking agent refers to the proportion (mol%) of R = alkoxymethyl groups in the total R of the group represented by -NR2 bonded to the triazine ring contained in the melamine crosslinking agent.

[0040] Paint compositions containing a flake-like pigment (D) along with a component (B) having such a degree of alkylation exhibit excellent storage stability and recoatability. On the other hand, when only a melamine-based crosslinking agent with a low degree of alkylation is used along with the flake-like pigment (D), storage stability or recoatability tends to be poor. Furthermore, "recoatability" refers to the ability to recoat the same type of paint composition. For example, it refers to the interlayer adhesion between paint films when a paint film of the same type as the paint composition is formed on top of a paint film formed from the same paint composition.

[0041] Component (B) typically has a group represented as -NR2 bonded to a triazine ring. In the formula, each of the multiple Rs can independently be a hydrogen atom, a methylol group (-CH2-OH), or an alkoxymethyl group (-CH2-OR). 1 ) indicates R 1 This represents an alkyl group, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, or t-butyl group, and particularly preferably a methyl group, n-butyl group, or isobutyl group. The alkyl group may be linear or branched.

[0042] Specifically, component (B) is preferably at least one selected from the group consisting of compound (B1) represented by formula (B1) and condensates of compound (B1). Component (B) may be compound (B1), the above condensate, or a mixture of compound (B1) and the above condensate.

[0043] [ka]

[0044] In formula (B1), each of the multiple Rs is independently a hydrogen atom, a methylol group (-CH2-OH), or an alkoxymethyl group (-CH2-OR 1 ) is shown. However, R is selected such that the degree of alkylation of component (B) is within the above range. 1 This represents an alkyl group, and specific examples and preferred examples are as described above. Multiple -CH2-OR groups in the same molecule 1 If it includes multiple R 1 They may be the same or they may be different.

[0045] The degree of methylolation in component (B) is preferably 20% or less, more preferably 1 to 19%, even more preferably 3 to 18%, and particularly preferably 4 to 17%, from the viewpoint of storage stability and recoatability. The degree of methylolation of the melamine crosslinking agent refers to the proportion (mol%) of R = methylol groups in the group represented by -NR2 bonded to the triazine ring contained in the melamine crosslinking agent to the total R.

[0046] In component (B), the proportion of R = hydrogen atoms (mol%) in the group represented by -NR2 bonded to the triazine ring is preferably 19% or less, more preferably 1 to 18%, even more preferably 2 to 17%, and particularly preferably 3 to 16%, from the viewpoint of storage stability and recoatability.

[0047] The weight-average molecular weight (Mw) of component (B) is preferably 300 to 2,000, more preferably 300 to 1,500, even more preferably 300 to 1,000, and particularly preferably 300 to 800. When Mw is below the upper limit, the recoatability tends to be better. The Mw of component (B) is the value on a standard polystyrene basis obtained by the GPC method. Details of the measurement conditions for the GPC method are described in the Examples section.

[0048] The average degree of polymerization (average number of triazine rings) of component (B) is preferably 1 or more, more preferably 1 to 10, even more preferably 1.2 to 5, and particularly preferably 1.5 to 3. When the average degree of polymerization is below the upper limit, the recoatability tends to be better.

[0049] The degree of alkylation, degree of methylolation, and proportion of hydrogen atoms of component (B), as well as the average degree of polymerization, can be determined by analyzing the structure of component (B) using nuclear magnetic resonance spectroscopy (NMR).

[0050] Component (B) can be produced by conventionally known methods. For example, component (B) can be obtained by etherifying the methylol group of methylolated melamine and / or its condensate, which are obtained by the reaction of a melamine compound and an aldehyde compound, using an alcohol. A commercially available product may be used as ingredient (B).

[0051] This composition may contain one type of component (B), or it may contain two or more types of component (B). The content of component (B) in this composition is preferably 10 to 200 parts by mass, more preferably 20 to 150 parts by mass, even more preferably 30 to 120 parts by mass, and particularly preferably 50 to 90 parts by mass, per 100 parts by mass of component (A). When the content of component (B) is within the above range, the resulting paint composition is superior in storage stability, recoatability, and curability, and the resulting coating film is superior in chemical resistance and corrosion resistance.

[0052] <Sulfonic acid compound (C)> The sulfonic acid compound (C) can act as a catalyst to promote the reaction between component (A) and the melamine-based crosslinking agent (B). Therefore, the sulfonic acid compound (C) has the advantage of imparting high reactivity to the resulting paint composition. By using the sulfonic acid compound (C), a paint composition with excellent curability can be obtained even when the degree of alkylation of the melamine-based crosslinking agent (B) is within the above range.

[0053] The sulfonic acid compound (C) may be a monosulfonic acid compound or a polysulfonic acid compound. Examples of sulfonic acid compound (C) include aliphatic sulfonic acids such as methanesulfonic acid; aromatic sulfonic acids such as dodecylbenzenesulfonic acid, p-toluenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid; and amine neutralized products of these sulfonic acids. The amine in the amine neutralized product of the above sulfonic acid may be, for example, a primary amine, a secondary amine, or a tertiary amine. Among the sulfonic acid compound (C), at least one selected from the group consisting of dodecylbenzenesulfonic acid, p-toluenesulfonic acid, the amine neutralized product of dodecylbenzenesulfonic acid, and the amine neutralized product of p-toluenesulfonic acid is preferred.

[0054] This composition may contain one sulfonic acid compound (C), or it may contain two or more. The content of sulfonic acid compound (C) in this composition is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.3 to 3 parts by mass, per 100 parts by mass of component (A).

[0055] <Flecked pigment (D)> This composition contains a flake-like pigment (D). Such a composition can form a coating film with excellent adhesion and recoatability to the object to be coated, and in one embodiment, can form a coating film with suppressed initial gloss.

[0056] Examples of flake-like pigments (D) include mineral pigments, metallic pigments, glass flakes, and plastic flakes. Among these, at least one selected from the group consisting of mineral pigments and metallic pigments is preferred. Examples of mineral pigments and metallic pigments include talc, mica, aluminum flakes, and stainless steel flakes. Among these, at least one selected from the group consisting of talc and aluminum flakes is preferred.

[0057] The average aspect ratio (median diameter (D50) / average thickness) of the flake-like pigment (D) is preferably 5 to 150, more preferably 10 to 120, even more preferably 15 to 110, and particularly preferably 20 to 100, from the viewpoint of excellent recoatability and the ability to form a coating film with suppressed initial gloss in one embodiment. For similar reasons, the D50 of the flake-like pigment (D) is preferably 1 to 100 μm, more preferably 2 to 50 μm, even more preferably 3 to 30 μm, and particularly preferably 3 to 10 μm.

[0058] D50 is the 50th percentile diameter in the volume-based particle size distribution measured at a temperature of 23°C using a laser diffraction particle size distribution analyzer (e.g., "SALD 2200" manufactured by Shimadzu Corporation). The average thickness is calculated by observing the main surface (the surface with the largest area) of the flake-like pigment from a horizontal direction using a scanning electron microscope (SEM) (e.g., "XL-30" by Philips), measuring the thickness of 100 randomly selected pigment particles, and taking the average value.

[0059] This composition may contain one type of flake-like pigment (D), or it may contain two or more types. The content of the flake-like pigment (D) in this composition is preferably 10 to 200 parts by mass, more preferably 15 to 150 parts by mass, even more preferably 20 to 100 parts by mass, and particularly preferably 25 to 80 parts by mass, per 100 parts by mass of component (A). The content of the flake-like pigment (D) is preferably 3 to 40% by mass, more preferably 5 to 30% by mass, even more preferably 8 to 20% by mass, and particularly preferably 10 to 15% by mass, based on 100% by mass of the solid content of the composition. When the content of flake pigment (D) is above the lower limit, the recoatability is superior, and a coating film with, for example, more suppressed initial gloss can be formed. When the content of flake pigment (D) is below the upper limit, the chemical resistance of the resulting coating film is superior.

[0060] <Other ingredients> This composition may further contain pigments other than the flake pigment (D), and additives, as well as other components (hereinafter also referred to as "other components"). Examples of additives include film-forming aids, surface modifiers, dispersants, defoamers, anti-sagging agents, adhesion enhancers, matting agents, antifungal agents, preservatives, pH adjusters, UV absorbers, light stabilizers, and antioxidants. This composition may contain one or more other components.

[0061] Examples of pigments other than flake pigments (D) include extender pigments, coloring pigments, and rust-preventive pigments (however, those of these pigments that are flake-shaped are classified as flake pigments (D) above). Examples of pigments include organic pigments and inorganic pigments. This composition may contain one or more pigments.

[0062] Examples of extender pigments include silica, clay, potassium feldspar, kaolin, alumina white, white carbon, aluminum hydroxide, magnesium carbonate, calcium carbonate, barium carbonate, barium sulfate, zinc oxide, and zinc sulfide. When this composition contains an extender pigment, the extender pigment content is preferably 0.1 to 80% by mass, more preferably 1 to 70% by mass, and even more preferably 5 to 60% by mass, based on 100% by mass of the solid content of this composition.

[0063] Examples of coloring pigments include organic pigments and inorganic pigments. Examples of organic pigments include naphthol red, phthalocyanine blue, and phthalocyanine green. Examples of inorganic pigments include carbon black, iron oxide, titanium dioxide (titanium white), yellow iron oxide, and red iron oxide. When this composition contains a coloring pigment, the proportion of the coloring pigment is preferably 0.1 to 60% by mass, more preferably 1 to 50% by mass, and even more preferably 5 to 45% by mass, based on 100% by mass of the solid content of this composition.

[0064] As film-forming aids, film-forming aids commonly used in water-based paint compositions, such as organic solvents with a boiling point of 180°C or higher at 1 atm, can be used. Examples include alcohols, glycol ethers, and esters. Examples of alcohols include 2,2,4-trimethylpentanediol and benzyl alcohol. Examples of glycol ethers include ethylene glycol monobenzyl ether, ethylene glycol monophenyl ether, ethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol diethyl ether, propylene glycol diethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ether, and dipropylene glycol n-butyl ether. Examples of esters include 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. When this composition contains a film-forming aid, the proportion of the film-forming aid is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 8% by mass, of the total amount of this composition.

[0065] Examples of surface modifiers include silicone-based surface modifiers, fluorine-based surface modifiers, and (meth)acrylic-based surface modifiers. When the composition contains a surface modifier, the proportion of the surface modifier is 100% by mass of the solid content of the composition, preferably 0.01 to 2% by mass, more preferably 0.05 to 1.5% by mass, and even more preferably 0.1 to 1% by mass.

[0066] As a dispersant, a material that can improve the dispersibility of water-insoluble components (e.g., pigments) in the paint composition is preferred. By using a dispersant, for example, a paint film with a good appearance can be easily formed, and a paint film with excellent crack resistance can be easily formed. Examples of dispersants include polymers having pigment-adsorbing groups (pigment affinity groups) and compatible chains. Examples of pigment-adsorbing groups include carboxyl groups, acid anhydride groups, phosphate groups, amino groups, groups of their salts, and ammonium bases. Examples of compatible chains include fatty acids, polyaminos, polyethers, polyesters, polyurethanes, and poly(meth)acrylates. When this composition contains a dispersant, the proportion of the dispersant is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, of 100% by mass of the solid content of this composition.

[0067] Preferred defoaming agents are those that can suppress the generation of bubbles during the manufacture or application of the paint composition, or those that can break bubbles that have formed in the paint composition. By using a defoaming agent, for example, the occurrence of air bubbles or pinholes in the paint film can be suppressed, and therefore the film-forming properties and crack resistance of the paint film can be improved. Examples of defoaming agents include silicone-based defoaming agents, polymer-based (non-silicone-based) defoaming agents, and mineral oil-based defoaming agents. When this composition contains an antifoaming agent, the proportion of the antifoaming agent is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, based on 100% by mass of the solid content of this composition.

[0068] As an anti-sagging agent, a material that can suppress the settling of water-insoluble components (e.g., pigments) in the paint composition and improve the storage stability of the paint composition is preferred. Examples of anti-sagging agents include organic oxidizers such as hydrogenated castor oil-based oxidizers, amide wax-based oxidizers, polyethylene oxide-based oxidizers, and urethane-based oxidizers; as well as inorganic oxidizers such as clay minerals (e.g., bentonite, smectite, and hectorite) and synthetic fine silica. When this composition contains an anti-dripping agent, the proportion of the anti-dripping agent is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, of 100% by mass of the solid content of this composition.

[0069] <Water> This composition is a water-based paint composition. A "water-based" paint composition is a paint composition that contains water. Examples of water include tap water, ion-exchanged water, and deionized water, with ion-exchanged water or deionized water being preferred. Examples of water include water contained in the aqueous dispersion of component (A).

[0070] The water content in this composition is preferably 20-70% by mass, more preferably 25-65% by mass, and even more preferably 30-60% by mass, from the viewpoint of reducing environmental impact and improving paintability. The water content is measured according to the Karl Fischer method using a moisture content measuring device (e.g., CA-310, manufactured by Nitto Seikou Analytech Co., Ltd.).

[0071] <Organic solvents> This composition is a water-based paint composition, but it may contain an organic solvent with a boiling point of less than 180°C at 1 atmosphere. Examples of the organic solvent include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as butyl acetate; alcohol solvents such as methanol, isopropyl alcohol, isobutyl alcohol, n-butanol, propylene glycol monobutyl ether, and propylene glycol monomethyl ether; and aliphatic hydrocarbon solvents such as n-hexane, n-octane, 2,2,2-trimethylpentane, isooctane, cyclohexane, and methylcyclohexane. The proportion of organic solvents with a boiling point of less than 180°C at 1 atmosphere in this composition is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, out of 100% by mass of the total amount of this composition.

[0072] <Method for producing a water-based paint composition> This composition can be produced, for example, by mixing component (A), a melamine-based crosslinking agent (B), a sulfonic acid compound (C), a flake-like pigment (D), and water. This composition can also be produced by, for example, placing each of the above components into a stirring vessel all at once or in any order, mixing each component using a known device such as a mixer, disperser, or agitator, and then dispersing or dissolving them in water. In the production of this composition, it is preferable to use an aqueous dispersion of component (A) from the viewpoint of workability in paint manufacturing.

[0073] Examples of the above-mentioned equipment include paint shakers, homogenizers, high-speed dispersers, sand grind mills, basket mills, ball mills, three-roll mills, ring mills, loss mixers, and planetary mixers. Mixing (kneading) may be carried out with heating or cooling depending on the season and environment.

[0074] This composition may be a multi-dosage type composition kit having two or more components, but it is preferable to be a single-dosage type composition. The above multi-dosage type composition kit has a first component and a second component, and usually each component is stored, kept, or transported in separate containers and mixed immediately before use.

[0075] In one embodiment, this composition is preferably a one-component composition containing component (A), a melamine-based crosslinking agent (B), a sulfonic acid compound (C), a flake-like pigment (D), and water, and more preferably a one-liquid composition. Even as a one-component composition, this composition exhibits excellent storage stability. This composition is preferably a baking paint composition.

[0076] Since this composition is a water-based paint composition, it has minimal adverse effects on the environment or human health. This composition exhibits excellent storage stability and recoatability. One embodiment of this composition can form a coating film with suppressed initial gloss, i.e., a low initial gloss value. Another embodiment of this composition can form a coating film with excellent adhesion to the substrate.

[0077] Conventional water-based paint compositions containing melamine-based crosslinking agents and spherical pigments have problems with recoating properties. When the inventors considered adding flake-shaped pigments, they discovered a new problem: the storage stability of the paint composition may decrease. Further investigation revealed that this new problem can be solved by using a specific melamine-based crosslinking agent together with the flake-shaped pigment. Specifically, this composition contains a melamine-based crosslinking agent (B) with a specific degree of alkylation within a particular range, along with a flake-shaped pigment (D), and therefore exhibits excellent not only recoating properties but also storage stability. Furthermore, one embodiment of this composition can form a paint film with suppressed initial gloss.

[0078] [Uses of water-based paint compositions] One aspect of the coating film of the present disclosure (hereinafter also referred to as "the coating film") is formed from the composition. One aspect of the coated article of the present disclosure (hereinafter also referred to as "the coated article") comprises a substrate and the coating film provided on the substrate.

[0079] Examples of materials for the substrate to which this composition is applied include metal materials, specifically, iron and steel (e.g., iron, steel, ferroalloys, carbon steel, mild steel, alloy steel), and non-ferrous metals (e.g., zinc, aluminum, copper, magnesium, and their alloys, brass, galvanized steel, zinc spraying, zinc phosphate coating, stainless steel (SUS304, SUS410, etc.)). Among these, non-ferrous metals are preferred. The substrate may be pre-treated to remove rust or dirt adhering to it. Examples of pre-treatment include washing and blasting. The substrate may also be surface-treated, such as chemical conversion treatment. Examples of chemical conversion treatment include chromate treatment and non-chromate treatment such as zinc phosphate treatment.

[0080] Specific examples of the above-mentioned base material include automotive components, building components, and industrial machinery components. More specifically, these include parts for automobile transmissions, oil coolers for marine engines, components for office automation equipment such as printers, components for pneumatic control systems such as compressors, and hydraulic valves for agricultural vehicles. Die-cast components such as aluminum die-cast and zinc die-cast are particularly preferred. This composition can be suitably applied to such specific examples.

[0081] The thickness of the coating film is not particularly limited and can be appropriately selected depending on the application in which the coating film is used, but is preferably 10 to 100 μm, more preferably 15 to 90 μm, and even more preferably 20 to 80 μm. The coating film may be formed by applying the composition to a substrate one or more times.

[0082] The coating film included in this product may be a single layer or a multi-layer coating of two or more layers. As mentioned above, this composition has excellent recoatability, and therefore exhibits excellent adhesion between the coating films in a multi-layer coating. The painted product may further have a primer film between the substrate and the main coating film, for example, to improve adhesion or corrosion resistance. The painted product may further have a topcoat film on top of the main coating film.

[0083] One embodiment of the manufacturing method for this coated product includes a step of applying the composition to a substrate (object to be coated) to form a coating film. The coating film may be formed by drying the composition at room temperature at about 5 to 35°C or by forced drying at about 35 to 90°C, but it is preferable to form it by baking the composition as described below. In other words, in one embodiment, the above manufacturing method preferably comprises the steps of (1) coating the composition onto a substrate and (2) baking the composition coated on the substrate to form a coating film.

[0084] In step (1), known methods for coating the composition include, for example, spray coating such as airless spray coating and air spray coating, brush coating, or roller coating. The coating of the composition onto the substrate may be repeated multiple times.

[0085] In step (2), the conditions for the baking treatment are not particularly limited. The ambient temperature for the baking treatment is preferably 50 to 240°C, more preferably 60 to 200°C. The processing time for the baking treatment is preferably 1 to 60 minutes, more preferably 2 to 50 minutes. The baking process may be carried out in two or more stages with different conditions. For example, the baking process may include a first stage in which baking is performed at an ambient temperature of 50°C to 130°C, and a second stage in which baking is performed at an ambient temperature of over 130°C and 240°C. The ambient temperature for the first stage is preferably 60 to 100°C, and the processing time is preferably 1 to 30 minutes. The ambient temperature for the second stage is preferably 140 to 200°C, and the processing time is preferably 1 to 30 minutes. This baking process allows for the production of a fully cured resin coating.

[0086] The atmosphere during steps (1) and (2) is not particularly limited. Steps (1) and (2) may be carried out in air, or in an inert gas atmosphere such as nitrogen or argon. Steps (1) and (2) may be carried out at normal pressure, or under reduced pressure, etc.

[0087] The series of steps (1) and (2) may be performed two or more times. However, in steps (1) and (2) from the second time onward, "substrate" shall be read as "coating film". For example, the composition may be applied to a substrate, the composition applied to the substrate may be baked to form a first coating film, the composition may then be applied to the first coating film, the composition applied to the first coating film may be baked to form a second coating film on the first coating film. In this way, a multilayer coating film having a first coating film and a second coating film is formed. As described above, this composition has excellent recoatability. Therefore, the first coating film and the second coating film have excellent interlayer adhesion.

[0088] [Example of form] This disclosure relates, for example, to the following [1] to

[10] . [1] A water-based paint composition containing a hydroxyl group-containing (meth)acrylic resin (A), a melamine-based crosslinking agent having an alkylation degree of 60% or more (B), a sulfonic acid compound (C), a flake-like pigment (D), and water. [2] The water-based paint composition according to [1], wherein the degree of alkylation in the crosslinking agent (B) is 65 to 95%. [3] The water-based paint composition according to [1] or [2], wherein in the crosslinking agent (B), the proportion of R=hydrogen atoms in the group represented by -NR2 bonded to the triazine ring (wherein the formula, each of the multiple Rs independently represents a hydrogen atom, a methylol group, or an alkoxymethyl group) is 19% or less of the total R. [4] The water-based paint composition according to any one of [1] to [3], wherein the resin (A) has a hydroxyl value of 5 to 100 mg KOH / g. [5] The water-based paint composition according to any one of [1] to [4], wherein the flake-like pigment (D) is at least one selected from the group consisting of talc and aluminum flakes. [6] The water-based paint composition according to any one of [1] to [5], wherein the content of the resin (A) is 5 to 60% by mass, the content of the flake-like pigment (D) is 3 to 40% by mass, the content of the crosslinking agent (B) is 10 to 200 parts by mass per 100 parts by mass of the resin (A), and the content of the sulfonic acid compound (C) is 0.01 to 10 parts by mass. [7] The water-based paint composition according to any one of [1] to [6], wherein the water content in the water-based paint composition is 20 to 70% by mass. [8] A water-based paint composition according to any one of [1] to [7] above, which is a baking paint composition. [9] A coating film formed from any of the water-based paint compositions described in [1] to [8] above.

[10] A coated product having a base material and a coating film as described in [9] provided on the base material. [Examples]

[0089] The present composition will be described in more detail below based on the examples, but the present composition is not limited to these examples. In the following description, "parts by mass" will be simply referred to as "parts". The physical properties described below were measured using the method described above, except for the physical properties described in detail below.

[0090] [Structure of melamine-based crosslinking agents] The structure of the melamine-based crosslinking agent (for example, the structure and proportion of R in formula (B1) described above) was analyzed using nuclear magnetic resonance spectroscopy (NMR). Specifically, the above structure was analyzed under the following conditions: The melamine-based crosslinking agent was diluted with dimethyl sulfoxide (DMSO)-d6 to form a homogeneous solution, which was then used as the NMR sample solution. quantitative 13 Measurement conditions for 13C NMR • Equipment: AVANCE III 400 (manufactured by Bruker) • Measurement method: Inverse gated coupling method Observed nuclei: 13 C Observation frequency: 100.6MHz • Locking solvent: DMSO-d6 • Total number of times: 8192 ·Measurement temperature: room temperature

[0091] [Weight-average molecular weight (Mw) of melamine-based crosslinking agents] The Mw of the melamine-based crosslinking agent was measured by the GPC method under the following conditions. • Equipment: EcoSEC Elite HLC-8420GPC (manufactured by Tosoh Corporation) • Column: One "TSKgel SuperH 4000" and two "TSKgel SuperH 2000" connected together (both manufactured by Tosoh Corporation, inner diameter 6mm x length 15cm) • Eluent: Tetrahydrofuran (THF) ·Flow rate: 0.600mL / min • Detector: Differential refractive index (RI) detector Column constant temperature bath temperature: 40°C Calibration curve: Standard polystyrene Sample preparation method: THF was added to the sample to dilute it to a solid content concentration of 0.4% by mass, and the filtrate obtained by filtering through a membrane filter was used as the GPC measurement sample.

[0092] [raw materials] (Meth)acrylic resin (A) dispersion (water-dispersible type) Watersol ACD-2001, manufactured by DIC Corporation. Hydroxyl value of solids = 56 mg KOH / g, solids content = 40% by mass

[0093] As crosslinking agents, melamine-based crosslinking agents (1) to (7), detailed in Table 1, were used. In Table 1, the heating residue refers to the residue after drying the melamine-based crosslinking agent in a constant temperature oven at 125°C for 1 hour. Furthermore, melamine-based crosslinking agents (1) to (7) contain alcohols with 4 or fewer carbon atoms.

[0094] [Table 1]

[0095] Coloring pigments Typeque R-930, manufactured by Ishihara Sangyo Co., Ltd., titanium oxide (titanium white)

[0096] Sulfonic acid compounds (C) Nacure 5225, manufactured by Kusumoto Kasei Co., Ltd. Amine neutralized product of dodecylbenzenesulfonic acid, solid content = 25% by mass

[0097] Scale-like pigment (D) Micro Ace L-1, manufactured by Nippon Talc Co., Ltd., fine talc powder. Average aspect ratio = 30, D50 = 5.0 μm Barium sulfate Precipitating barium sulfate 100, manufactured by Sakai Chemical Industry Co., Ltd. Spherical pigment, D50 = 0.6 μm

[0098] Film-forming aid Butyl carbitol (diethylene glycol monobutyl ether), Solid content ratio = 0% by mass Surface modifier BYK-349, manufactured by Big Chemie Japan Co., Ltd. Silicone-based surface modifier (polyether-modified siloxane), Solid content ratio = 100% by mass

[0099] [Example 1] 43 parts (meth)acrylic resin (A) dispersion, 11.5 parts melamine-based crosslinking agent (1), 17 parts coloring pigment, and 7 parts deionized water were mixed and strongly dispersed to obtain a mixture. To the above mixture, 0.35 parts sulfonic acid compound (C), 7 parts flake-like pigment (D), 5 parts film-forming aid, 0.3 parts surface modifier, and 8.85 parts deionized water were added and stirred to obtain a paint composition.

[0100] [Examples 2-4, Comparative Examples 1-7] A paint composition was obtained in the same manner as in Example 1, except that the compound composition was changed as shown in Table 2.

[0101] [Evaluation Method] <Recoat Test> A zinc phosphate treated steel sheet (SPCC-SD, PB-3118) with dimensions of 150 mm in length, 70 mm in width, and 0.8 mm in thickness was coated once with the above-mentioned coating composition of the example or comparative example to a dry film thickness of 30 μm. A low-temperature baking treatment was performed at 80°C (ambient temperature) for 10 minutes, followed by another baking treatment at 150°C (ambient temperature) for 20 minutes to cure the resin and form a first coating film.

[0102] On the first coating film described above, the same type of coating composition was applied with an applicator (gap: 4 mil), and a low-temperature baking treatment was performed at 80°C (ambient temperature) for 10 minutes, followed by a baking treatment at 150°C (ambient temperature) for 20 minutes to cure the resin, thereby forming a second coating film on the first coating film. In this way, a test piece was obtained on a zinc phosphate treated steel sheet with a multilayer coating film including the first coating film and the second coating film formed thereon.

[0103] The adhesion of the above multilayer coating was evaluated by performing a cross-cut adhesion test (cross-cut method, cross-cut interval: 1 mm) in accordance with JIS K5600-5-6:1999. Specifically, using a cutter guide, 11 vertical x 11 horizontal cuts were made on the surface of the multilayer coating of the test piece to a depth reaching the base steel plate, forming a grid of 100 squares with right-angle grids. The interval between the cuts was 1 mm. Next, cellophane tape was firmly pressed onto the grid portion of the test piece, and the end of the cellophane tape was quickly peeled off at a 90° angle to the multilayer coating surface. The number of squares in which the second coating remained or adhered to the first coating was measured.

[0104] <Storage Stability Test> On the surface of the zinc phosphate treated steel sheet (SPCC-SD, PB-3118) described above, the above-mentioned coating composition of the example or comparative example was applied once to a dry film thickness of 30 μm. A low-temperature baking treatment was performed at 80°C (ambient temperature) for 10 minutes, followed by another baking treatment at 150°C (ambient temperature) for 20 minutes to cure the resin and form a coating film. A similar coating film was formed using a sample of the same coating composition that had been left to stand (stored) in a 50°C incubator for two weeks. The appearance of each coating film was compared, and the gloss retention rate was evaluated. Regarding the gloss of the coating film, in accordance with JIS K5600-4-7:1999, the reflectance of light incident at a 60° angle to the perpendicular direction of the coating film surface (60° gloss) was measured using a surface gloss meter (model: Microtrigloss 4563, manufactured by BYK-Gardner). The ratio of the 60° gloss of the coating film obtained using the above coating composition after storage to the 60° gloss value of the coating film obtained using the above coating composition before storage (gloss retention rate (%)) was calculated. The storage stability of the above coating composition was evaluated based on the gloss retention rate.

[0105] [Table 2]

[0106] Compared to Comparative Example 7, which used a melamine-based crosslinking agent with a low degree of alkylation and did not use talc (flak-like pigment) or barium sulfate (spherical pigment), and Comparative Example 6, which used a melamine-based crosslinking agent with a low degree of alkylation and barium sulfate, the example using a melamine-based crosslinking agent with a high degree of alkylation and talc (flak-like pigment) exhibits superior recoating properties. Compared to Comparative Examples 3-5, which used melamine-based crosslinking agents and talc with a low degree of alkylation, the examples using melamine-based crosslinking agents and talc with a high degree of alkylation showed superior storage stability (gloss retention) and recoatability. Compared to Comparative Example 2, which used a melamine-based crosslinking agent with a high degree of alkylation but did not use talc or barium sulfate, Example 1, which used a melamine-based crosslinking agent with a high degree of alkylation and talc, exhibited superior recoating properties. Although a melamine-based crosslinking agent with a high degree of alkylation was used, Example 1, which used a melamine-based crosslinking agent with a high degree of alkylation and talc, exhibited superior recoating properties compared to Comparative Example 1, which used barium sulfate.

Claims

1. Hydroxyl group-containing (meth)acrylic resin (A), Melamine-based crosslinking agent (B) having an alkylation degree of 60% or more, Sulfonic acid compounds (C), Scale-like pigment (D), and water A water-based paint composition containing the following:

2. The aqueous coating composition according to claim 1, wherein the degree of alkylation in the crosslinking agent (B) is 65 to 95%.

3. In the crosslinking agent (B), -NR bonded to the triazine ring 2 The aqueous coating composition according to claim 1, wherein in a group represented by (wherein the formula, each of the multiple Rs independently represents a hydrogen atom, a methylol group, or an alkoxymethyl group), the proportion of R = hydrogen atoms to the total R is 19% or less.

4. The aqueous coating composition according to claim 1, wherein the resin (A) has a hydroxyl value of 5 to 100 mg KOH / g.

5. The aqueous paint composition according to claim 1, wherein the flake-like pigment (D) is at least one selected from the group consisting of talc and aluminum flakes.

6. In the aqueous coating composition, the content of the resin (A) is 5 to 60% by mass of 100% by mass of the solid content, and the content of the flake-like pigment (D) is 3 to 40% by mass. With respect to 100 parts by mass of the resin (A), The content of the crosslinking agent (B) is 10 to 200 parts by mass, The content of the sulfonic acid compound (C) is 0.01 to 10 parts by mass. The water-based paint composition according to claim 1.

7. The water-based paint composition according to claim 1, wherein the water content in the water-based paint composition is 20 to 70% by mass.

8. The water-based paint composition according to claim 1, which is a baking paint composition.

9. A coating film formed from the water-based coating composition according to any one of claims 1 to 8.

10. Substrate and The coating film according to claim 9 provided on the substrate, Painted product having [a certain characteristic].

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