Coating composition

Abstract

To provide a coating composition having good resin solubility, excellent adhesiveness, chemical resistance and hydrolysis resistance.SOLUTION: There is provided a coating composition comprising an acrylic resin (A), a polyisocyanate curing agent (B) and a solvent (C), wherein the acrylic resin (A) has a glass transition temperature Tg of 70°C or more, the solvent (C) contains an alcohol solvent (C1) containing at least one of a secondary alcohol and a tertiary alcohol and the storage modulus of elasticity (unit: Pa) (E'1) of the flat area of a coating film formed by baking the coating composition at 80°C for 30 minutes and the storage modulus (unit: Pa) (E'2) of the flat area of the coating film formed by baking the coating composition at 60°C for 72 hours after baking the coating composition at 80°C for 30 minutes satisfy the following expression. (E'2)-(E'1)≤8.00×106 (1)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a coating composition. [Background technology]

[0002] Plastic molded products are used in mobile phones, home appliances, office automation equipment, etc., and the surfaces of the plastic molded products may be painted to provide decoration or functions. Therefore, in addition to providing decoration, a coating composition for painting plastics may be required to provide the coating film with functions such as abrasion resistance, discoloration resistance, sebum resistance, high gloss, high weather resistance, and electrical insulation depending on the application. In addition, plastic molded products that come into contact with human skin and hands for long periods of time, such as exterior parts of mobile phones and interior parts of automobiles, are also required to have excellent chemical resistance such as sweat resistance, lactic acid resistance, hand cream resistance, and sunscreen cream resistance.

[0003] As such a coating composition, for example, Patent Document 1 discloses a coating composition containing a polyol (a) having a hydroxyl value of 180 or more, an acrylic polyol (b) not corresponding to (a), and a polyisocyanate (c). Patent Document 2 discloses a coating composition containing a hydroxyl-containing acrylic resin (A) having a weight-average molecular weight of 3,000 to 20,000 and a hydroxyl value in the range of 100 to 200 mgKOH / g, a polyisocyanate compound (B), a curing catalyst (C), and a surface conditioner (D) essentially consisting of a silicon-based surface conditioner (D-1) and an acrylic-based surface conditioner (D-2). Furthermore, Patent Document 3 discloses a coating composition comprising a base material containing a hydroxyl-containing acrylic resin (A), a hydroxyl-containing polyester resin (B), and resin beads (C), and a polyisocyanate curing agent. Furthermore, Patent Document 4 discloses a resin composition which contains, as a resin component, a mixture of a cellulose derivative (B) other than an acrylic-modified cellulose derivative obtained by graft polymerization or simply bonding an acrylic component to a cellulose derivative and an acrylic resin (C), the composition in the mixture, the weight-average molecular weight of the cellulose derivative (B) and the glass transition temperature of the acrylic resin (C) being within specific ranges, and the resin component has an acid value and a hydroxyl value in the sum of 7 to 100 mgKOH / g. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-095131 [Patent Document 2] JP 2014-019714 A [Patent Document 3] JP 2015-105297 A [Patent Document 4] JP 2014-181343 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when attempting to improve adhesion, chemical resistance, and hydrolysis resistance of the compositions of the above patent documents, the solubility of the resin decreases, and the paint and coating film may become cloudy. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coating composition which has good resin solubility and is excellent in adhesion, chemical resistance, and hydrolysis resistance. [Means for solving the problem]

[0006] As a result of intensive research by the present inventors, it was found that in order to obtain sufficient adhesion, chemical resistance, and hydrolysis resistance, it is essential that the blended resin is one in which a large amount of low-molecular-weight hydrophilic monomers are polymerized and one having a high glass transition temperature Tg is essential. However, when a resin satisfying the above requirements is used, the resin does not dissolve in the current solvent and becomes cloudy. Therefore, the inventors of the present invention have achieved the present invention by setting the glass transition temperature (Tg) of an acrylic resin to 70°C or higher, using a low molecular weight monomer with high water solubility as a constituent element, and adding a solvent containing a tertiary alcohol during dissolution, thereby achieving a balance between adhesion, chemical resistance, and hydrolysis resistance, as well as solubility in the coating material.

[0007] That is, the present invention relates to a coating composition containing an acrylic resin (A), a polyisocyanate curing agent (B), and a solvent (C), wherein the glass transition temperature Tg of the acrylic resin (A) is 70°C or higher, the solvent (C) contains an alcohol solvent (C1) containing at least one of a secondary alcohol and a tertiary alcohol, and the storage modulus (unit: Pa) (E'min1) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and the storage modulus (unit: Pa) (E'min2) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and then curing it for 72 hours at 60°C satisfy the following formula (1): (E'min2)-(E'min1)≦8.00×10 6 (1)

[0008] It is preferable that the crosslink density (unit: mol / cc) (n1) of a coating film formed by baking the coating composition at 80°C for 30 minutes and the crosslink density (unit: mol / cc) (n2) of a coating film formed by baking the coating composition at 80°C for 30 minutes and then curing it at 60°C for 72 hours satisfy the following formula (2). (n2)-(n1)≦8.00×10 -4 (2)

[0009] The glass transition temperature Tg of the coating film formed by baking the coating composition at 80°C for 30 minutes and then curing at 60°C for 72 hours is preferably less than 100°C.

[0010] The solvent (C) preferably further contains an ester solvent (C2).

[0011] The contents of the alcohol solvent (C1) and the ester solvent (C2) contained in the coating composition preferably satisfy the following formula (3). 0.01≦(C1) / (C2)≦0.20 (3)

[0012] The acrylic resin (A) preferably contains 75% or more of a monomer having methacrylic acid as a constituent monomer.

[0013] The hydroxyl value of the acrylic resin (A) is preferably 140 mgKOH / g or less. Effect of the Invention

[0014] According to the present invention, it is possible to obtain a coating composition which has good resin solubility and is excellent in adhesion, chemical resistance, and hydrolysis resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, one embodiment of the present invention will be described.

[0016] [Paint composition] The coating composition of the present invention is a coating composition containing an acrylic resin (A), a polyisocyanate curing agent (B), and a solvent (C), in which the glass transition temperature Tg of the acrylic resin (A) is 70°C or higher, the solvent (C) contains an alcohol solvent (C1) containing at least one of a secondary alcohol and a tertiary alcohol, and the storage modulus (unit: Pa) (E'min1) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and the storage modulus (unit: Pa) (E'min2) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and then curing it for 72 hours at 60°C satisfy the following formula (1): (E'min2)-(E'min1)≦8.00×10 6 (1) The paint will be described in detail below.

[0017] <Acrylic resin (A)> The polymerizable monomer constituting the acrylic resin (A) includes a polymer having methacrylic acid and other polymerizable unsaturated monomers.

[0018] (Monomers containing methacrylic acid) Examples of monomers having methacrylic acid include monoesters of methacrylic acid and dihydric alcohols, such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; methacrylates having a polyoxyethylene chain with a hydroxyl group at the molecular end; methyl methacrylate, 2-isocyanatoethyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and 2-ethyl methacrylate. Examples of the methacrylic acid include esters of methacrylic acid and alcohols having 1 to 24 carbon atoms, such as n-hexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, tridecyl methacrylate, and stearyl methacrylate; epoxy group-containing polymerizable unsaturated monomers, such as glycidyl methacrylate and 3,4-epoxycyclohexylmethyl methacrylate; and aminoalkyl methacrylates, such as N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, and N,N-dimethylaminopropyl methacrylate.

[0019] (Other polymerizable unsaturated monomers) Other polymerizable unsaturated monomers include monoesters of methacrylic acid and dihydric alcohols, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate; acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular end; methyl acrylate, 2-isocyanatoethyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate, cyclohexyl acrylate, and the like. esters of acrylic acid and alcohols having 1 to 24 carbon atoms, such as acrylate, isobornyl acrylate, tridecyl acrylate, and stearyl acrylate; carboxyl group-containing monomers, such as acrylic acid, methacrylic acid, maleic acid, and maleic anhydride; epoxy group-containing polymerizable unsaturated monomers, such as glycidyl acrylate and 3,4-epoxycyclohexylmethyl acrylate; aminoalkyl acrylates, such as N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, and N,N-dimethylaminopropyl acrylate; vinyl group-containing aromatic compounds, such as styrene, α-methylstyrene, and vinyl toluene; and vinyl group-containing compounds, such as vinyl acetate.

[0020] The acrylic resin (A) preferably contains 75% or more of a monomer having methacrylic acid as a constituent monomer, which provides excellent adhesion, chemical resistance, and hydrolysis resistance.

[0021] [Characteristics of acrylic resin] The properties of the acrylic resin (A) will be described below.

[0022] (Acrylic resin glass transition temperature Tg) The glass transition temperature Tg of the acrylic resin (A) is 70° C. or higher. When the glass transition temperature Tg of the acrylic resin (A) is 70° C. or higher, a coating film having excellent scratch resistance and chemical resistance can be obtained. The glass transition temperature Tg of the acrylic resin (B) is preferably 75° C. or higher and 100° C. or lower, and more preferably 80° C. or higher and 95° C. or lower.

[0023] The glass transition temperature Tg of the acrylic resin (A) was calculated by the Fox formula. In this specification, the glass transition temperature (Tg) of an acrylic resin is calculated using the following FOX formula. 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In the FOX equation, Tg is the glass transition temperature (K) of a polymer consisting of n types of monomers, Tg(1, 2, i, n) is the glass transition temperature (K) of the homopolymer of each monomer, W(1, 2, i, n) is the mass fraction of each monomer, and W1+W2+···+Wi+···+Wn=1.

[0024] (Hydroxyl value of acrylic resin) The hydroxyl value of the acrylic resin (A) is preferably 140 mgKOH / g or less, more preferably 130 mgKOH / g or less, and even more preferably 120 mgKOH / g or less. The lower limit of the hydroxyl value of the acrylic resin (A) is preferably 30 mgKOH / g or more, and more preferably 60 mgKOH / g or more. When the hydroxyl value of the acrylic resin (A) is 140 mgKOH / g or less, sufficient curability to exhibit good coating performance can be ensured, and scratch resistance and coating hardness can be ensured. Also, when the hydroxyl value of the acrylic resin (A) is 30 mgKOH / g or more, unreacted hydroxyl groups can be reduced, resulting in excellent chemical resistance.

[0025] Here, the hydroxyl value of the acrylic resin (A) is the number of milligrams of potassium hydroxide required to completely acetylate the hydroxyl groups in 1 g of the resin with acetic anhydride and then neutralize the free acetic acid generated by acetylation.

[0026] (Weight average molecular weight Mw) The weight average molecular weight Mw of the acrylic resin (A) is preferably 3000 or more and 18000 or less. By being 3000 or more, a coating film having good scratch resistance and coating film hardness can be obtained when crosslinked. By being 18000 or less, the solubility in the paint is good. The weight average molecular weight Mw of the acrylic resin (A) is more preferably 5000 or more and 14000 or less.

[0027] The weight average molecular weight Mw can be measured by using a TSKgel column (manufactured by Tosoh Corporation) and a GPC equipped with an RI (trade name "HLC-8220GPC", manufactured by Tosoh Corporation). The GPC conditions are as follows: tetrahydrofuran is used as the developing solvent, the flow rate is 0.35 ml / min, and the temperature is 40° C., and TSK standard polystyrene (manufactured by Tosoh Corporation) is used as the standard substance.

[0028] <Polyisocyanate hardener (B)> The polyisocyanate curing agent (B) is a compound having two or more isocyanate groups in one molecule, and is not particularly limited. For example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethylcaproate, etc. aliphatic diisocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, and other alicyclic diisocyanates; Isocyanates; aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, 4,4'-diphenylether diisocyanate; 1,3- or 1,4-xylylene diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, 1 Examples of suitable polyisocyanates include aromatic aliphatic diisocyanates such as 1,3- or 1,4-bis(α,α-dimethylisocyanatomethyl)benzene; triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene; tetraisocyanates such as 4,4'-diphenyldimethylmethane-2,2',5,5'-tetraisocyanate; polymerized polyisocyanates such as dimers and trimers of tolylene diisocyanate, and polyphenylpolymethylene polyisocyanates.Among these, aliphatic diisocyanates and alicyclic diisocyanates are preferred from the viewpoint of the properties of the resulting coating film, particularly from the viewpoint of the coating film being less likely to yellow.

[0029] The polyisocyanate curing agent (B) may be a commercially available product, such as the Burnock (registered trademark) series from DIC Corporation, the Duranate (registered trademark) series from Asahi Kasei Chemicals Corporation, or the Sumidur (registered trademark) series from Sumika Covestro Urethane Co., Ltd.

[0030] The polyisocyanate curing agent (B) may be used alone or in combination of two or more kinds.

[0031] In the coating composition of the present invention, the content of the polyisocyanate curing agent (B) is not particularly limited, but usually, the molar ratio (NCO mol% / OH mol%) of the amount of isocyanate groups in the polyisocyanate curing agent (B) to the amount of hydroxyl groups in the acrylic polyol (A) is preferably 0.8 to 1.5, more preferably 0.9 to 1.3. When the content of the polyisocyanate curing agent (B) is within the above range, the amount of unreacted hydroxyl groups and isocyanate groups is reduced, so that a coating film with better properties can be obtained.

[0032] <Solvent (C)> The solvent (C) contains an alcohol solvent (C1) containing at least one of a secondary alcohol and a tertiary alcohol. Of the secondary alcohol and the tertiary alcohol, it is more preferable that the solvent (C) contains a tertiary alcohol. Examples of secondary alcohols include hydrocarbon alcohols such as 2-propanol, 2-butanol, 2- and 3-pentanol, 2- and 3-hexanol, 2-, 3- and 4-heptanol, 2-, 3- and 4-octanol, and 3,3-dimethyl-2-butanol; aromatic alcohols, such as cyclic alcohols such as diphenylmethanol, 1-phenylethanol, 1-phenylpropanol, 1-phenyl-2-propanol, 1-phenylbutanol, 1-phenyl-2-butanol, 4-phenyl-2-butanol, and cyclohexanol; and steroid alcohols. Examples of tertiary alcohols include hydrocarbon alcohols such as 2-methyl-2-butanol, 2,3-dimethyl-2-butanol, 2-methyl-2-pentanol, and 3-methyl-3-pentanol; cyclic alcohols such as 1-methylcyclopentanol, 1-ethylcyclopentanol, 1-propylcyclopentanol, 1-butylcyclopentanol, and 1-methylcyclooctanol; monoterpene alcohols such as α-terpineol; and alcohols having a ketone functional group such as diacetone alcohol. The solvent (C) preferably further contains an ester solvent (C2). Examples of the ester solvent (C2) include methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, propyl acetate, and 3-methoxy-1-butyl acetate.

[0033] The contents of the alcohol solvent (C1) and the ester solvent (C2) contained in the coating composition preferably satisfy the following formula (3). 0.01≦(C1) / (C2)≦0.20 (3) By ensuring that the contents of the alcohol solvent (C1) and the ester solvent (C2) fall within the above ranges, a coating material that is soluble in the substrate can be produced, and as a result, a coating film with excellent adhesion can be obtained.

[0034] The concentration of the solvent (C) in the coating composition is preferably from 0.1% by mass to 30.0% by mass, from the viewpoints of coatability and environmental considerations.

[0035] <Other ingredients> The coating composition of the present invention can contain a pigment. The pigment is not particularly limited, and pigments that are commonly used in the coating industry, such as color pigments, extender pigments, and scale-like pigments, can be used. The pigments can be used alone or in combination of two or more.

[0036] Examples of color pigments include titanium oxide, iron oxide, carbon black, yellow lead, molybdate orange, ultramarine, Prussian blue, phthalocyanine blue, phthalocyanine green, quinacridone red, naphthol red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet.

[0037] Examples of the extender pigment include silica, talc, mica, calcium carbonate, and barium sulfate.

[0038] The flake pigment is a pigment having a thin and flat shape like a foil, and specific examples thereof include metal pigments such as zinc, nickel, chromium, tin, copper, silver, platinum, gold, and aluminum, as well as glass flakes, talc, mica, kaolin clay, and micaceous iron oxide. Metal pigments also include alloy pigments such as stainless steel. Furthermore, the flake pigments, such as talc and mica, may be surface-treated with a metal oxide such as titanium oxide.

[0039] In the coating composition of the present invention, the amount of pigment is preferably 0 to 40% by mass, and more preferably 5 to 25% by mass. The amount of pigment in the coating composition affects the properties of the coating film. If the amount of pigment is too low, the amount of solid components remaining in the coating film will be small, resulting in a decrease in coating film hardness and scratch resistance, while if the amount of pigment is too high, the crosslink density of the coating film will be low, which may result in a decrease in chemical resistance.

[0040] In addition to the pigment, the coating composition of the present invention can appropriately use additives necessary for a coating composition. For example, various coating additives that are generally known and commonly used in the art, such as curing catalysts, pigment dispersants, defoamers, anti-sagging agents, UV absorbers, light stabilizers, anti-fungal agents, etc., can be used in conventional amounts.

[0041] Furthermore, the coating composition of the present invention can also be used in combination with other resins, such as acrylic-modified alkyd resins, alkyd resins, silicone resins, fluororesins, or epoxy resins, as appropriate, for the purpose of improving performance within a range that does not affect the effects of the present invention.

[0042] [Properties of the coating] The properties of the coating film formed using the coating composition of the present invention will now be described.

[0043] <Storage modulus> It is preferable that the storage modulus (unit: Pa) (E'min1) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and the storage modulus (unit: Pa) (E'min2) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and then curing for 72 hours at 60°C satisfy the following formula (1). (E'min2)-(E'min1)≦8.00×10 6 (1) Here, the storage modulus (unit: Pa) of the flat region of the coating film is a value determined by the method in the Examples described later.

[0044] <Cross-link density of coating film> It is preferable that the crosslink density (unit: mol / cc) (n1) of a coating film formed by baking the coating composition at 80°C for 30 minutes and the crosslink density (unit: mol / cc) (n2) of a coating film formed by baking the coating composition at 80°C for 30 minutes and then curing it at 60°C for 72 hours satisfy the following formula (2). (n2)-(n1)≦8.00×10 -4 (2) By adjusting the crosslink density of the coating film within the above range, it is possible to obtain a coating film having good coating film hardness, scratch resistance and chemical resistance. The crosslink density of the coating film is determined by the method described in the Examples below.

[0045] <Glass transition temperature Tg of coating film> The glass transition temperature Tg of the coating film formed by baking the coating composition at 80° C. for 30 minutes and then curing at 60° C. for 72 hours is preferably less than 100° C., and more preferably less than 95° C. If the glass transition temperature Tg of the coating film is within the above range, a coating film having excellent scratch resistance and chemical resistance can be obtained. The glass transition temperature Tg is a value determined by the method in the Examples section described later.

[0046] The resin composition of the present invention is capable of forming a coating film having excellent chemical resistance, particularly resistance to sunscreen agents, and is therefore useful for coating plastic molded products that will come into contact with human skin and hands for long periods of time, specifically, interior and exterior components of automobiles and motorcycles, components for home appliances such as audio equipment, video equipment, and televisions, and components for office equipment such as mobile phones, printers, and personal computers.

[0047] [Painting method] The method for applying the resin composition includes, for example, a step of applying the resin composition to the surface of a substrate and then forming a film by drying or the like. In the method for applying the resin composition of the present invention, in addition to directly applying the resin composition to the surface of the substrate, a primer may be applied to the substrate before applying the resin composition. By applying the primer in advance, the adhesion between the coating film and the substrate can be improved.

[0048] The method for applying the resin composition is not particularly limited, and examples thereof include known application methods such as dipping, spin coating, flow coating, roll coating, spray coating, blade coating, and air knife coating. Among these, spray coating and roll coating are preferred from the viewpoint of easily controlling the film thickness.

[0049] In the method of applying a resin composition, a coating film can be formed by drying the resin composition applied to the surface of a substrate, but for example, when the resin composition is a volatile drying type resin composition, a coating film can be obtained by leaving the resin composition at a temperature of 5° C. or higher and lower than 70° C. after application. Similarly, when the resin composition is a thermosetting resin composition, a coating film can be obtained by leaving the resin composition at a temperature of 5° C. or higher and lower than 70° C. after application.

[0050] (base material) In the coating method of the resin composition of the present invention, the substrate is not particularly limited, and substrates of various shapes can be selected according to the application of the substrate. Examples of the substrate include PPE (polyphenylene ether) resin, polystyrene resin, olefin polymer such as polypropylene and polyethylene, polycarbonate resin, acrylic resin such as polymethyl methacrylate, and plastic substrate such as ABS resin. EXAMPLES

[0051] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below.

[0052] [Preparation of acrylic resin solution] First, a resin solution containing an acrylic resin (A) containing a hydroxyl group (hereinafter referred to as a hydroxyl group-containing acrylic resin) to be used in the examples and comparative examples is prepared. [Resin solution 1] Resin solution 1 containing acrylic resin (A) was prepared according to the following procedure. Table 1 shows the solvent, monomer, and polymerization initiator required for preparing acrylic resin (A), as well as the properties of acrylic resin (A). In Table 1, the blending amount of each component is expressed in parts by mass. 38.0 parts by mass of butyl acetate, 12.0 parts by mass of 2-hydroxyethyl methacrylate, 6.5 parts by mass of methyl methacrylate, 4.0 parts by mass of butyl methacrylate, 0.5 parts by mass or more of acrylic acid, 3.5 parts by mass of 2-ethylhexyl acrylate, 24.5 parts by mass of styrene monomer, and 4.0 parts by mass of t-butylperoxy-2-hexanoate were reacted under nitrogen gas at 110° C. for 8 hours. Then, the mixture was diluted with 7.0 parts by mass of butyl acetate to obtain an acrylic resin solution 1 having a solid content of 55% by mass.

[0053] [Resin solutions 2 to 9] Resin solutions 2 to 9 were prepared in the same manner as resin solution 1, except that the compounds and compositions were changed as shown in Table 1.

[0054] [Characteristics of acrylic resin (A)] The properties of the acrylic resin (A) in Resin Solutions 1 to 9 were measured as follows. The measurement results are shown in Table 1.

[0055] (solid content) The solid content was calculated from the change in weight when a weighed amount of the resin solution was placed in a container and heated in a drying oven at 150° C. for 30 minutes.

[0056] (Hydroxyl value of acrylic resin (A)) The hydroxyl groups in 1 g of acrylic resin (A) were completely acetylated with acetic anhydride, and the amount of potassium hydroxide required to neutralize the free acetic acid generated by the acetylation was then determined in mg, and this value was taken as the hydroxyl value of the acrylic resin (A).

[0057] (Glass transition temperature Tg of acrylic resin (A)) The glass transition temperature Tg of the acrylic resin (A) was calculated by the Fox formula.

[0058] (Weight average molecular weight Mw) The weight average molecular weight Mw of the acrylic resin (A) was measured by SEC (size exclusion chromatography, product name "HLC-8420GPC", manufactured by Tosoh Corporation) equipped with a differential refractive index (RI) detector using a TSKgel column SuperMultiporeHZ-M (manufactured by Tosoh Corporation). The SEC conditions were tetrahydrofuran as the developing solvent, a flow rate of 0.35 ml / min, and a temperature of 40°C. TSK standard polystyrene (manufactured by Tosoh Corporation) was used as the standard substance.

[0059] [Table 1]

[0060] Next, using the above resin solution, the coating compositions of the examples and comparative examples and test specimens equipped with coating films formed by applying and curing the coating compositions were prepared according to the following procedure. The components used in the coating compositions and their blending ratios are shown in Tables 2 and 3. In Tables 2 and 3, the blending amount of each component is shown in parts by mass, and NV indicates the non-volatile content (mass%) of the resin. Details of the materials in Tables 2 and 3 are as follows: Curing catalyst: TOS-K (Osaka Shinyaku Co., Ltd.) Color pigment: NSP-CZ808(D)BLACK (manufactured by Nikko Bix Co., Ltd.) Additive: BYK-065 (manufactured by BYK-Chemie) BYK-307 (BYK-Chemie) BYK-325N (BYK) Hardener: Sumidur N3300 (manufactured by Covestro) Duranate 24A-100 (manufactured by Asahi Kasei Corporation) Burnock DN-980S (manufactured by DIC Corporation) Dilution solvent: ISOPAR E (manufactured by ExxonMobil)

[0061] [Example 1] (Preparation of Coating Composition) 67.5 parts by mass of resin solution 1 as a hydroxyl group-containing acrylic resin (A), 2.0 parts by mass of TOS-K as a curing catalyst, 2.0 parts by mass of butyl acetate (C2), 2.0 parts by mass of 3-methoxy-1-butyl acetate (C2), 4.0 parts by mass of methyl isobutyl ketone, 16.0 parts by mass of NSP-CZ808 (D) BLACK as a coloring pigment, 0.5 parts by mass of BYK-065, 0.1 parts by mass of BYK-307, 0.4 parts by mass of BYK-325N as additives, and 15.5 parts by mass of a polyisocyanate compound were mixed and stirred with a disperser to prepare the coating composition of Example 1.

[0062] (Preparation of painted body (base material: polypropylene resin)) The coating composition was air spray coated onto a substrate made of polypropylene resin, 3.0 mm thick, and 100 mm x 100 mm in size, so that the dry film thickness was 50 μm. The coating composition was then dried at 80°C for 30 minutes to form a coating film, and a coated body was produced. This coated body was used to measure the glass transition temperature Tg and crosslink density of the coating film.

[0063] [Examples 2 to 16, Comparative Examples 1 to 11] A coating composition and a test specimen were prepared in the same manner as in Example 1, except that the components and formulation of the coating composition were changed as shown in Tables 2 and 3.

[0064] [Characteristics evaluation of coating composition] The coating compositions were evaluated for the following properties, and the evaluation results are shown in Tables 2 and 3.

[0065] (solid content) The solid content of the coating compositions of the above examples and comparative examples was measured according to the test conditions of JIS K 5601_1_2. The measurement results are shown in mass %.

[0066] (Solubility when mixed with diluting solvent) The coating compositions of the above Examples and Comparative Examples were evaluated for solubility when mixed with a dilution solvent according to the following evaluation criteria. 〇: Easily soluble △: Not uniformly dissolved ×: Gel

[0067] (Evaluation of coating appearance after time has passed) For the coating compositions of the above Examples and Comparative Examples, the base agent, curing agent and dilution solvent were mixed, and the appearance after standing at room temperature for 6 hours was evaluated according to the following criteria. ○: Appearance of the coating film is the same as immediately after mixing ×: Occurrence of bumps, loss of gloss

[0068] [Table 2]

[0069] [Table 3]

[0070] [Coating film evaluation] The coating films of the above-mentioned Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Tables 4 to 7.

[0071] (Storage modulus) (1) No protection The coating composition was spray-coated on an ABS resin substrate (thickness 3.0 mm, size 100 mm x 100 mm) to a dry film thickness of 30 μm, and then baked at 80°C for 30 minutes to form a coating film and prepare a test specimen. The storage modulus (unit: Pa) (E'min1) of the flat region of the coating film was determined by the following measurement method. The loss modulus E'' was also determined in the same manner. <Measurement conditions> Measuring equipment: RSA-GII (manufactured by TA Instruments) Measurement mode: Temperature dependence Chuck distance: 20mm Measurement width: 5.0mm Sample thickness: Dry film thickness 30 μm Measurement temperature range: 10℃~200℃ Heating rate: 5℃ / min Frequency: 1Hz Displacement amplitude: 25μm Distortion: 0.05% (2) With protection The coating composition was baked at 80°C for 30 minutes and then cured at 60°C for 72 hours to form a coating film, and the storage modulus (unit: Pa) (E'min2) of the flat area of ​​the coating film was measured. The storage modulus (unit: Pa) (E'min2) after curing was determined by the above-mentioned measurement method. (3) Storage modulus difference: (E'min2)-(E'min1) The difference in storage elastic modulus was calculated from the storage elastic modulus (E'min2) and (E'min1).

[0072] (Crosslink density) (1) No protection In the same manner as in the measurement of the storage modulus, the coating composition was baked at 80° C. for 30 minutes to form a coating film, and the crosslink density (unit: mol / cc) (n1) of the coating film was measured. The crosslink density n [mol / cc] was calculated from the following logical formula (the molecular weight between crosslinks was calculated from 1 / n). n=E' min / (3×ρRT) E' min :Storage modulus in the plateau region [Pa] ρ: Membrane specific gravity R: Gas constant (8.31 x 10 6 [Pa cc mol -1 ·K -1 ]) T: Temperature of storage modulus plateau region [K] (2) With protection The coating composition was baked at 80°C for 30 minutes and then cured at 60°C for 72 hours to form a coating film, and the crosslink density (unit: mol / cc) (n2) of the coating film was measured. The crosslink density n2 in the case where curing was performed was determined by the above-mentioned method. (3) Crosslinking density difference: (n2)-(n1) The crosslink density difference was calculated from the crosslink densities (n2) and (n1).

[0073] (Glass transition temperature Tg of coating film) (1) No protection Tan δ was calculated from the storage modulus and loss modulus obtained above, and the peak value was taken as Tg. tanδ: Loss tangent (tanδ=E'' / E') E': Storage modulus E): Loss modulus (2) With protection The coating composition was baked at 80° C. for 30 minutes and then aged at 60° C. for 72 hours to form a coating film. Thereafter, the glass transition temperature Tg was determined in the same manner as above.

[0074] (Coating appearance) The coating composition was spray-painted onto an ABS resin substrate (thickness 3.0 mm, size 100 mm × 100 mm) to a dry film thickness of 30 μm, and then the coating composition was dried at 80°C for 30 minutes to form a coating film and prepare a test specimen. The gloss was measured at 60° using a product called "Micro-Tri-gloss" manufactured by BYK Gardner. The appearance of the coating film was evaluated according to the following criteria. 〇:85+ △:80 or more and 85 or less ×: Less than 80

[0075] (Adhesive) A straight cut was made on the coating surface of the above test specimen with a cutter knife at a cutting angle of 60°, and then another cut was made at an angle of 60° to the first cut, creating 100 grids (2mm x 2mm). Cellophane tape was then firmly attached to cover the cuts, and the cellophane tape was peeled off at an angle of 45° to the coating surface. The number of remaining grids out of the 100 was evaluated according to the following criteria. ○:100 △: 90 or more but less than 100 ×: Less than 90

[0076] (Chemical resistance 1: Sun oil) A 70 mm x 150 mm test piece was cut out from the above test body, a piece of gauze was placed on it, 1 g of sanitary oil was evenly applied on top of it, and it was kept at 80° C. for 24 hours. The gauze marks after washing were evaluated according to the following criteria. ◎: No gauze marks ○: Slight gauze marks can be seen △: Gauze marks can be seen on some parts of the test piece. ×: Gauze marks can be seen on the entire surface of the test piece.

[0077] (Chemical resistance 2: Hand cream) A 70 mm x 150 mm test piece was cut out from the above test body, a piece of gauze was placed on it, 1 g of sanitary oil was evenly applied on top of it, and it was kept at 80° C. for 24 hours. The gauze marks after washing were evaluated according to the following criteria. ◎: No gauze marks ○: Slight gauze marks can be seen △: Gauze marks can be seen on some parts of the test piece. ×: Gauze marks can be seen on the entire surface of the test piece.

[0078] (Scratch resistance 1: dry wipe) Using a Gakushin abrasion tester (Daiei Scientific Instruments Co., Ltd., dyed material abrasion fastness tester RT-300), a canvas (No. 6) was used, and a load of 500 g was applied to the coating surface of the test specimen, which was then run back and forth 1000 times at 60 rpm. After the 1000 runs, the coating surface was washed with running water and naturally dried, and the gloss of the coating was visually observed and evaluated according to the following criteria. ○: Very slight scratches △: There is a clear scratch ×: Base exposed

[0079] (Heat resistance) The test specimens were kept at 90°C for 24 hours, and then the adhesion was evaluated. A straight cut was made on the coating surface of the test specimen with a cutter knife at a cutting angle of 60°, and then another cut was made at an angle of 60° to the first cut, creating 100 grids (2mm x 2mm). Cellophane tape was then firmly applied to cover the cuts, and the cellophane tape was then peeled off at an angle of 45° to the coating surface. The number of remaining grids out of the 100 was evaluated according to the following criteria. ○:100 △: 90 or more but less than 100 ×: Less than 90

[0080] (Moisture resistance) The test specimens were kept for 96 hours under conditions of an environmental temperature of 50°C and humidity of 98%, and then the adhesion was evaluated. A straight cut was made on the coating surface of the test specimen with a cutter knife at a cutting angle of 60°, and then another cut was made at an angle of 60° to the first cut, creating 100 grids (2mm x 2mm). Cellophane tape was then firmly applied to cover the cuts, and the cellophane tape was then peeled off at an angle of 45° to the coating surface. The number of remaining grids out of the 100 was evaluated according to the following criteria. ○:100 △: 90 or more but less than 100 ×: Less than 90

[0081] [Table 4]

[0082] [Table 5]

[0083] [Table 6]

[0084] [Table 7]

[0085] As shown in Tables 4 to 7, the coating films of the examples using the coating composition of the present invention obtained good results in all evaluation items.

Claims

1. A coating composition comprising an acrylic resin (A), a polyisocyanate curing agent (B), and a solvent (C), The glass transition temperature Tg of the acrylic resin (A) is 70° C. or higher, The solvent (C) contains an alcohol solvent (C1) containing at least one of a secondary alcohol and a tertiary alcohol, A coating composition in which the storage modulus (unit: Pa) (E'min1) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and the storage modulus (unit: Pa) (E'min2) in the flat region of a coating film formed by baking the coating composition for 30 minutes at 80°C and then curing the coating composition for 72 hours at 60°C satisfy the following formula (1): (E'min2)-(E'min1)≦8.00×10 ６ (1)

2. The coating composition according to claim 1, wherein the crosslink density (unit: mol / cc) (n1) of a coating film formed by baking the coating composition at 80°C for 30 minutes and then curing the coating composition at 60°C for 72 hours satisfies the following formula (2): (n2)-(n1)≦8.00×10 －４ (2)

3. 2. A coating composition according to claim 1, wherein the glass transition temperature Tg of a coating film formed by baking the coating composition at 80°C for 30 minutes and then aging at 60°C for 72 hours is less than 100°C.

4. 3. The coating composition according to claim 1, wherein the solvent (C) further comprises an ester solvent (C2).

5. The coating composition according to claim 4, wherein the contents of the alcohol solvent (C1) and the ester solvent (C2) contained in the coating composition satisfy the following formula (3). 0.01≦(C1) / (C2)≦0.20 (3)

6. 3. The coating composition according to claim 1, wherein the acrylic resin (A) contains at least 75% of a monomer having methacrylic acid as a constituent monomer.

7. 3. The coating composition according to claim 1, wherein the acrylic resin (A) has a hydroxyl value of 140 mg KOH / g or less.

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