Coating composition

Abstract

To provide a coating composition that has excellent stain resistance to rainwater or the like in an initial period and over time, forms a matte coating film (particularly, a low-gloss coating film with a crepe pattern) having excellent weather resistance, and is also capable of suppressing fume generation, a method for forming a matte coating film (crepe pattern coating film) using the coating composition, and a coated metal plate.SOLUTION: Provided are a coating composition containing hydroxy group-containing resin (A), crosslinking agent (B), sulfonic acid compound (C), amine compound (D), and hydrophilic agent (E), wherein a water receding contact angle on the surface of a coating film formed by curing the coating composition is cured is 30° or less, and a minimum autocorrelation length (Sal) is 10 to 40 μm, a method for forming a coating film of the coating composition, and a coated metal plate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coating composition capable of forming a matte coating film (particularly a low-gloss coating film with a wrinkled pattern) that has excellent initial and aging resistance to contamination by rainwater and the like and excellent weather resistance, a method for forming a matte coating film using the coating composition, and a coated metal sheet. [Background technology]

[0002] Pre-coated steel sheets are widely used as exterior materials for architectural components such as shutters, storm shutters, doors, roofs, and siding, as well as for electrical equipment such as outdoor units of air conditioners. The coating films on these pre-coated steel sheets used outdoors require stain resistance and weather resistance to prevent streak stains caused by raindrops containing atmospheric dust, as well as deterioration of the coating due to sunlight, acid rain, and other factors. Furthermore, customer needs for the appearance of the above-mentioned products dictate a strong demand for a subdued, low-gloss design. To address these needs, various methods for hydrophilizing the coating surface have been proposed as a method for achieving coatings with excellent stain resistance. Meanwhile, coatings with a surface shape characterized by a finely textured pattern known as a crinkle pattern are known as pre-coated steel sheet coatings with high weather resistance and low gloss design. The crinkle pattern varies widely depending on the type and amount of the components of the coating material that forms the pattern.

[0003] Patent Document 1 discloses a coating composition that is capable of forming coating films with excellent retention of stain resistance against rainwater and the like, particularly coating films with a gloss of semi-gloss or less (60° gloss of about 50 or less), and that contains a resin binder containing a polyester resin component containing a specific fatty acid-modified polyester resin and a melamine resin component containing a butyl etherified melamine resin, and that contains a specific organosilicate and / or a condensate component thereof.

[0004] However, in the case of coating compositions using organosilicate compounds, problems have arisen, particularly in the high-temperature baking of precoated steel sheets, such as reduced productivity due to oven contamination by silicate fumes, and insufficient stain resistance due to variations in the initial development of hydrophilicity depending on the coating application environment.

[0005] Furthermore, Patent Document 2 discloses a coating composition containing a hydroxyl group-containing resin, a crosslinking agent, and a specific surfactant, which can suppress the amount of fume generated during baking and can form a coating film that maintains stain resistance for a long period of time when exposed outdoors.

[0006] However, in particular in matte coating films using matte filler particles such as synthetic silica, the effect of preventing a decrease in stain resistance due to outdoor exposure is insufficient, and in the case of low-gloss coating films in particular, there have been cases where problems have arisen with weather resistance due to water retention and detachment of the matting agent. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5705220 [Patent Document 2] Patent No. 6648938 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a coating composition that can form a matte coating film (particularly a low-gloss coating film with a shrinkage pattern) that has excellent initial and aging resistance to contamination by rainwater and the like and excellent weather resistance, and that can also suppress fume generation; a method for forming a matte coating film (shrinkage-pattern coating film) using the coating composition; and a coated metal sheet. [Means for solving the problem]

[0009] As a result of extensive research, the inventors have discovered that by forming a matte shape into a specific range of wrinkled pattern (design) and imparting moderate hydrophilicity, the increase in water receding contact angle over time is minimal, making it possible to maintain a low water receding contact angle, and thereby obtaining a matte coating film with excellent stain resistance, which has led to the completion of the present invention.

[0010] That is, the present invention provides the following.

[0011] 1. A coating composition comprising a hydroxyl group-containing resin (A), a crosslinking agent (B), a sulfonic acid compound (C), an amine compound (D), and a hydrophilizing agent (E), A coating composition characterized in that the surface of a coating film obtained by curing the coating composition has a water receding contact angle of 30° or less and a minimum autocorrelation length (Sal) of 10 to 40 μm.

[0012] 2. A coating composition according to item 1, wherein the hydroxyl-containing resin (A) contains a hydroxyl-containing polyester resin.

[0013] 3. A coating composition according to item 1 or 2 above, wherein the crosslinking agent (B) contains an amino resin.

[0014] 4. A coated metal plate having a metal plate and a coating film on at least one surface of the metal plate, the coating film being formed from the coating composition according to item 1 or 2 above; A coated metal sheet, characterized in that the coating film surface has a water receding contact angle of 30° or less and a minimum autocorrelation length (Sal) of 10 to 40 μm.

[0015] 5. A method for forming a coating film, comprising a coating step of applying the coating composition according to item 1 or 2 above to a substrate, and a step of drying and / or curing the applied coating composition at a temperature of 170°C to 270°C. [Effects of the Invention]

[0016] According to the present invention, by forming the matte shape into a specific range of wrinkled pattern (design) and imparting moderate hydrophilicity, the increase in water contact angle over time is small, and it is possible to maintain a low water contact angle, thereby obtaining a matte coating film with excellent stain resistance.

[0017] The range of matte shapes (shrinkage patterns) that provide not only good contamination resistance but also good corrosion resistance and weather resistance has also been clarified, making it possible to provide a coating composition that can form a matte coating film (shrinkage pattern coating film) that is excellent in contamination resistance, corrosion resistance, and weather resistance, and that can also suppress fume generation, as well as a method for forming a matte coating film (shrinkage pattern coating film) using the coating composition, and a coated metal sheet. DETAILED DESCRIPTION OF THE INVENTION

[0018] The coating composition of the present invention will now be described in detail.

[0019] The present invention provides a coating composition containing a hydroxyl group-containing resin (A), a crosslinking agent (B), a sulfonic acid compound (C), an amine compound (D), and a hydrophilizing agent (E), The coating composition is characterized in that the surface of a coating film obtained by curing the coating composition has a water receding contact angle of 30° or less and a minimum autocorrelation length (Sal) of 10 to 40 μm.

[0020] <Hydroxyl group-containing resin (A)> The hydroxyl-containing resin (A) is a resin having a hydroxyl group in one molecule, and may have a carboxyl group as needed.

[0021] Specific examples of the hydroxyl group-containing resin (A) include polyester resin, acrylic resin, epoxy resin, polyurethane resin, etc., but from the viewpoint of the processability and weather resistance of the coating film, hydroxyl group-containing polyester resin is preferred.

[0022] Examples of the hydroxyl group-containing polyester resin include oil-free polyester resin, alkyd resin, urethane-modified polyester resin, and silicon-modified polyester resin.

[0023] The oil-free polyester resin can usually be produced by an esterification reaction or transesterification reaction between a polybasic acid component (a1) and a polyhydric alcohol component (a2).

[0024] The polybasic acid component (a1) may be any compound commonly used as a polybasic acid component in the production of polyester resins, such as an alicyclic polybasic acid, an aliphatic polybasic acid, or an aromatic polybasic acid.

[0025] Alicyclic polybasic acids are compounds having one or more alicyclic structures (mainly 4- to 6-membered rings) and two or more carboxyl groups in one molecule, acid anhydrides of such compounds, and esterified products of such compounds.

[0026] Examples of the alicyclic polybasic acid include alicyclic polybasic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of these alicyclic polybasic carboxylic acids; and lower alkyl esters of these alicyclic polybasic carboxylic acids. The alicyclic polybasic acids can be used alone or in combination of two or more.

[0027] As the alicyclic polybasic acid, 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic anhydride can be particularly preferably used.

[0028] The aliphatic polybasic acid is an aliphatic compound having two or more carboxyl groups per molecule, an acid anhydride of the aliphatic compound, or an ester of the aliphatic compound. Specific examples include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, octadecanedioic acid, and citric acid; anhydrides of these aliphatic polycarboxylic acids; and lower alkyl esters of these aliphatic polycarboxylic acids. The aliphatic polybasic acids can be used alone or in combination of two or more.

[0029] As the aliphatic polybasic acid, it is preferable to use a dicarboxylic acid having an alkyl chain with 4 to 18 carbon atoms. Examples of the dicarboxylic acid having an alkyl chain with 4 to 18 carbon atoms include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, and octadecanedioic acid, and among these, adipic acid is preferably used.

[0030] The aromatic polybasic acid is an aromatic compound having two or more carboxyl groups per molecule, an acid anhydride of the aromatic compound, or an ester of the aromatic compound. Specific examples include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of these aromatic polycarboxylic acids; and lower alkyl esters of these aromatic polycarboxylic acids. The aromatic polybasic acids can be used alone or in combination of two or more.

[0031] As the alcohol component (a2), a polyhydric alcohol having two or more hydroxyl groups in one molecule can be suitably used. Examples of the polyhydric alcohol include alicyclic diols, aliphatic diols, and aromatic diols.

[0032] Alicyclic diols are compounds having one or more alicyclic structures (mainly 4- to 6-membered rings) and two hydroxyl groups per molecule. Examples of such alicyclic diols include dihydric alcohols such as 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, and hydrogenated bisphenol F; and polylactone diols obtained by adding a lactone compound such as ε-caprolactone to these dihydric alcohols. These can be used alone or in combination of two or more.

[0033] The aliphatic diol is an aliphatic compound having two hydroxyl groups in one molecule. Examples of the aliphatic diol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1 ,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, neopentyl glycol, etc. These can be used alone or in combination of two or more.

[0034] The aromatic diol is an aromatic compound having two hydroxyl groups in one molecule. Examples of the aromatic diol include ester diol compounds such as bis(hydroxyethyl) terephthalate and alkylene oxide adducts of bisphenol A. These compounds can be used alone or in combination of two or more.

[0035] Examples of polyhydric alcohols other than the alicyclic diols, aliphatic diols, and aromatic diols include polyether diol compounds such as polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanurate, sorbitol, and mannite; and polylactone polyol compounds in which a lactone compound such as ε-caprolactone is added to any of the above trihydric or higher alcohols.

[0036] Among the above other polyhydric alcohols, trihydric or higher alcohols can be preferably used from the viewpoint of increasing the molecular weight and improving the reactivity. Examples of the trihydric or higher polyhydric alcohols include trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannite; polylactone polyol compounds obtained by adding a lactone compound such as ε-caprolactone to these trihydric or higher alcohols; and tris(hydroxyalkyl)isocyanurates such as tris(2-hydroxyethyl)isocyanurate, tris(2-hydroxypropyl)isocyanurate, and tris(2-hydroxybutyl)isocyanurate. Of these, trimethylolpropane is particularly preferred.

[0037] Furthermore, as alcohol components other than the polyhydric alcohol (a2), for example, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting monoepoxy compounds such as propylene oxide, butylene oxide, and glycidyl esters of synthetic highly branched saturated fatty acids (trade name "Cardura E10" manufactured by HEXION Specialty Chemicals) with acids can also be used as needed.

[0038] The method for producing the hydroxyl group-containing polyester resin is not particularly limited and can be carried out according to a conventional method. For example, the hydroxyl group-containing polyester resin can be produced by reacting the polybasic acid component and the polyhydric alcohol component in a nitrogen stream at 150 to 250°C for 5 to 10 hours to carry out an esterification reaction or an ester exchange reaction.

[0039] In the esterification reaction or transesterification reaction, the acid component and the alcohol component may be added at once or in several portions. Alternatively, a carboxyl group-containing polyester resin may be first synthesized, and then a portion of the carboxyl groups in the carboxyl group-containing polyester resin may be esterified using the alcohol component. Furthermore, a hydroxyl group-containing polyester resin may be first synthesized, and then the hydroxyl group-containing polyester resin may be half-esterified by reacting with an acid anhydride.

[0040] In the esterification or transesterification reaction, a catalyst may be used to promote the reaction, such as dibutyltin dibenzoate, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, tetrabutyl titanate, or tetraisopropyl titanate.

[0041] The hydroxyl group-containing polyester resin can be modified with fatty acids, fats and oils, polyisocyanate compounds, organopolysiloxane compounds, etc. during the preparation of the resin, or after the esterification reaction or transesterification reaction.

[0042] Modification with fatty acids or fats and oils produces alkyd resins, modification with polyisocyanate compounds produces urethane-modified polyester resins, and modification with organopolysiloxanes produces silicone-modified polyester resins.

[0043] Examples of fatty acids used in producing the alkyd resin include coconut oil fatty acids, cottonseed oil fatty acids, hempseed oil fatty acids, rice bran oil fatty acids, fish oil fatty acids, tall oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids; lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc. Examples of fats and oils include coconut oil, cottonseed oil, hempseed oil, rice bran oil, fish oil, tall oil, soybean oil, linseed oil, tung oil, rapeseed oil, castor oil, dehydrated castor oil, and safflower oil.

[0044] Examples of polyisocyanate compounds used to modify the urethane-modified polyester resin include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,3-(isocyanatomethyl)cyclohexane. aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate; and organic polyisocyanates themselves, such as trivalent or higher polyisocyanates such as lysine triisocyanate, or adducts of these organic polyisocyanates with polyhydric alcohols, low-molecular-weight polyester resins, or water, or cyclized polymers (e.g., isocyanurates) or biuret-type adducts of the above-mentioned organic diisocyanates. These can be used alone or in combination of two or more.

[0045] Examples of organopolysiloxane compounds used to modify the silicone-modified polyester resin include organopolysiloxane (i) represented by the following formula (1) and organopolysiloxane (ii) having a hydrolyzable silyl group.

[0046] R 2 a Si(OH) b O (4-a-b) / 2 ...Equation (1) (In the formula, R 2 represents the same or different substituted or unsubstituted monovalent hydrocarbons having 1 to 8 carbon atoms, and a and b satisfy the relationships 0.2≦a≦2, 0.1≦b≦3, and a+b<4.

[0047] R 2 is preferably an alkyl group having 1 to 4 carbon atoms, or a substituted hydrocarbon group such as a phenyl group, a vinyl group, a 3-glycidoxypropyl group, a 3-methacryloyloxypropyl group, a 3-aminopropyl group, or a 3,3,3-trifluoropropyl group, and more preferably an alkyl group such as a methyl group or an ethyl group.

[0048] Such organopolysiloxane (i) can be obtained, for example, by hydrolyzing one or a mixture of two or more of methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, or the corresponding alkoxysilanes with a large amount of water by a known method.

[0049] Commercially available organopolysiloxane (i) includes KR-311, KR-282, and KR-271 (all trade names manufactured by Shin-Etsu Chemical Co., Ltd.).

[0050] The organopolysiloxane (ii) is an organopolysiloxane having hydrolyzable silyl groups at the molecular terminals or side chains, and the hydrolyzable silyl groups in the molecule, such as alkoxysilyl groups, react with moisture or water in the air to hydrolyze and form silanol groups. Any known organopolysiloxane (ii) can be used without limitation, as long as it undergoes hydrolysis and condensation at room temperature. The organopolysiloxane (ii) generally has a weight-average molecular weight in the range of 200 to 28,000, and preferably 300 to 18,000.

[0051] The weight average molecular weight of the hydroxyl group-containing resin is preferably 3,000 to 60,000, and more preferably has a number average molecular weight in the range of 5,000 to 40,000, from the viewpoint of the processability, chemical resistance and finished appearance of the resulting coating film.

[0052] In this specification, the number average molecular weight and weight average molecular weight are values obtained by converting the number average molecular weight and weight average molecular weight measured using gel permeation chromatography (GPC) based on the molecular weight of standard polystyrene.

[0053] Specifically, the gel permeation chromatograph used is "HLC8120GPC" (trade name, manufactured by Tosoh Corporation), and the columns are "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation), and measurements can be performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL / min, and detector: RI.

[0054] From the viewpoint of the processability of the coating film, the hydroxyl value of the hydroxyl-containing resin is preferably within a range of 5 to 250 mgKOH / g, particularly 10 to 200 mgKOH / g.

[0055] From the viewpoint of finished appearance, the acid value of the hydroxyl group-containing resin is preferably in the range of 30 mgKOH / g or less, particularly 20 mgKOH / g or less.

[0056] <Crosslinking agent (B)> The crosslinking agent (B) is a component that contributes to the formation of a cured coating film by reacting with the hydroxyl group-containing resin (A).

[0057] Examples of the crosslinking agent (B) include amino resins; polyisocyanate compounds; blocked polyisocyanate compounds (compounds in which the isocyanate groups of polyisocyanate compounds are blocked with active hydrogen-containing compounds); and phenol resins.

[0058] The crosslinking agent (B) can be used alone or in combination of two or more kinds.

[0059] As the crosslinking agent (B), amino resins can be preferably used from the viewpoints of crosslinking reactivity and finished appearance.

[0060] Examples of amino resins include melamine resins and urea resins, with melamine resins being preferred.

[0061] Melamine resin is generally a thermosetting resin synthesized from melamine and aldehyde, and contains a triazine nucleus and three reactive functional groups -NX per triazine nucleus. 1 X 2 The melamine resin may be of four types: a fully alkylated type containing -N(CH2OR)2 (R is preferably an alkyl group having 1 to 8 carbon atoms, the same applies below) as a reactive functional group; a methylol group type containing -N(CH2OR)(CH2OH) as a reactive functional group; an imino group type containing -N(CH2OR)(H) as a reactive functional group; and a methylol / imino group type containing -N(CH2OR)(CH2OH) and -N(CH2OR)(H) or -N(CH2OH)(H) as a reactive functional group.

[0062] Of the above melamine resins, it is preferable to use a fully alkylated melamine resin from the viewpoint of forming a shrinkable coating film.

[0063] Examples of fully alkylated melamine resins include methylated melamine resins, butylated melamine resins, methyl / butyl mixed melamine resins, isobutylated melamine resins, etc. Among these, methylated melamine resins, butylated melamine resins, and methyl / butyl mixed melamine resins are preferred.

[0064] Commercially available melamine resins can be used, such as Cymel 303, Cymel 254, Cymel 1170, Cymel 235, Cymel 238, Cymel 325, Cymel 1123, and Mycoat 715 (all manufactured by Daicel-Allnex Corporation), Sumimal M-40S (manufactured by Sumitomo Chemical Co., Ltd.), Super Beckamine J-820-60, and Super Beckamine L-121-60 (manufactured by DIC Corporation), and Yuban 20SE-60 (manufactured by Mitsui Chemicals, Inc.).

[0065] The above melamine resins can be used alone or in combination of two or more.

[0066] The polyisocyanate compound is a compound having two or more free isocyanate groups in one molecule, and examples thereof include aliphatic diisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate; alicyclic diisocyanate compounds such as hydrogenated xylylene diisocyanate, cyclohexylene diisocyanate, methylene bis(cyclohexyl isocyanate), and isophorone diisocyanate; tolylene diisocyanate and phenylene diisocyanate. aromatic diisocyanate compounds such as 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, and naphthalene diisocyanate; and trivalent or higher organic polyisocyanate compounds such as 2-isocyanatoethyl-2,6-diisocyanatocaproate, 3-isocyanatomethyl-1,6-hexamethylene diisocyanate, and 4-isocyanatomethyl-1,8-octamethylene diisocyanate (commonly known as triaminononane triisocyanate). Further examples include cyclized polymers or biuret forms of these polyisocyanate compounds; and combinations thereof.

[0067] Among the above polyisocyanate compounds, aliphatic polyisocyanate compounds are preferred from the viewpoint of obtaining a wrinkle-pattern coating film that is excellent in processability and weather resistance, and among these, nurate forms of aliphatic polyisocyanate compounds, adduct forms of aliphatic polyisocyanate compounds, and biuret forms of aliphatic polyisocyanate compounds are preferred.

[0068] In particular, nurates of hexamethylene diisocyanate, adducts of hexamethylene diisocyanate compounds, and biurets of hexamethylene diisocyanate are preferred.

[0069] The blocked polyisocyanate compound is a compound in which the isocyanate group of the polyisocyanate compound is blocked with an active hydrogen-containing compound.

[0070] Examples of the blocking agent as the active hydrogen-containing compound include pyrazoles such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-nitro-3,5-dimethylpyrazole, and 4-bromo-3,5-dimethylpyrazole; oximes such as methyl ethyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; phenols such as phenol, para-t-butylphenol, and cresol; lactams such as ε-caprolactam and γ-butyrolactam; aliphatic alcohols such as n-butanol and 2-ethylhexanol; aromatic alkyl alcohols such as phenyl carbinol and methylphenyl carbinol; ether alcohols such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; and active methylenes such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone.

[0071] Among these blocking agents, pyrazoles, oximes, phenols and lactams, especially oximes, can be preferably used from the viewpoint of obtaining a wrinkle-patterned coating film that is excellent in processability and weather resistance.

[0072] Commercially available blocked polyisocyanate compounds include, for example, hexamethylene diisocyanate nurates such as Burnock D-500, Burnock D-550, Burnock DB-980K (all trade names manufactured by DIC Corporation), Sumidur N3300, Desmodur N3600, Desmodur N3790BA, Desmodur N3900, and Desmodur XP2840; hexamethylene diisocyanate biurets such as Desmodur N75MPA / X and Desmodur N3200; and hexamethylene diisocyanate nurates such as Desmodur HT. Examples of suitable polyimide compounds include an adduct of Anate (all trade names manufactured by Sumika Bayer Urethane Products Co., Ltd.), Takenate D-102, Takenate D-202, Takenate D-110N, and Takenate D-123N (all trade names manufactured by Mitsui Chemicals, Inc.), Coronate L, Coronate HL, Coronate EH, Coronate 203, and Millionate MT (trade names manufactured by Nippon Polyurethane Industry Co., Ltd.), and Duranate MF-K60B, SBN-70D, MF-B60B, 17B-60P, TPA-B80E, and E402-B80B (all trade names manufactured by Asahi Kasei Chemicals Corporation).

[0073] In the coating composition of the present invention, the mixing ratio of the hydroxyl group-containing resin (A) and the crosslinking agent (B) is preferably 50 to 95 mass %, preferably 60 to 90 mass %, of the hydroxyl group-containing resin (A) and 5 to 50 mass %, preferably 10 to 40 mass %, of the crosslinking agent (B), based on the total solid content of the (A) and (B) components, from the viewpoint of obtaining a wrinkle-patterned coating film that is excellent in processability, weather resistance, and scratch resistance.

[0074] <Sulfonic acid compound (C)> The sulfonic acid compound (C) acts as a catalyst to promote the reaction between the hydroxyl group-containing resin (A) and the crosslinking agent (B). The sulfonic acid compound (C) and the amine compound (D) can form a salt. The salt of the sulfonic acid (C) and the amine compound (D) increases the difference between the surface cure and the internal cure of the coating film formed from the coating composition, promoting non-uniform curing of the entire coating film.

[0075] Examples of sulfonic acid compounds include paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalene disulfonic acid, methanesulfonic acid, dinonylnaphthalenesulfonic acid, etc. These can be used alone or in combination of two or more.

[0076] From the viewpoint of forming a good matte appearance (crinkle pattern), among the above, dodecylbenzenesulfonic acid and paratoluenesulfonic acid can be preferably used.

[0077] The content of the sulfonic acid compound (C) is preferably in the range of 0.1 to 3.0 mass %, particularly 0.2 to 2.5 mass %, and even more particularly 0.3 to 2.0 mass %, in terms of solid content, based on the total solid content of the hydroxyl group-containing resin (A) and the crosslinking agent (B), from the viewpoint of forming a good matte appearance (crinkle pattern) of the coating film.

[0078] <Amine compound (D)> The amine compound (D) contributes to neutralizing the sulfonic acid compound (C), and at least a portion of it may exist as a salt with the sulfonic acid compound (C) in the coating composition of the present invention. Furthermore, an excess amount of the amine compound (D) promotes non-uniform curing of the coating film and contributes to the formation of a good matte appearance (crinkle pattern).

[0079] Examples of the amine compound (D) include secondary amines such as diethylamine, diisopropylamine, di-n-propylamine, diallylamine, diamylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-, 2,6-, 3,5-lupetidine, and 3-piperidinemethanol; tertiary amines such as triethylamine, tributylamine, triallylamine, N-methyldiallylamine, N-methylmorpholine, N,N,N',N'-tetramethyl-1,2-diaminoethane, N-methylpiperidine, pyridine, and 4-ethylpyridine; and amines having secondary and tertiary amino groups such as N-methylpiperazine. These can be used alone or in combination of two or more.

[0080] The boiling point, type and amount of the amine compound (D) are important for obtaining a good matte appearance (uniform wrinkle pattern) of the coating film.

[0081] The boiling point of the amine compound (D) is preferably within the range of 30 to 250°C, particularly 70 to 200°C, and further particularly 75 to 160°C.

[0082] As the amine compound (D), triethylamine, diisopropylamine and di-n-butylamine are particularly preferred.

[0083] The amount of the amine compound (D) added is preferably in the range of a molar ratio relative to the sulfonic acid compound (C), amine compound (D) / sulfonic acid compound (C) = 1.5 to 30, particularly 3 to 25, and more particularly 5 to 20.

[0084] The sulfonic acid compound (C) and the amine compound (D) may be mixed in advance, or a mixture of these may be blended. Also, a blocked sulfonic acid compound in which a sulfonic acid is blocked with an amine compound (particularly a secondary amine or a tertiary amine) may be used, and further, may be used in combination with the amine compound (D).

[0085] Commercially available blocked sulfonic acid compounds include, for example, Naicure 5225 (manufactured by King Industries, an amine-neutralized solution of dodecylbenzenesulfonic acid, containing 25% dodecylbenzenesulfonic acid) and Naicure 2500 (manufactured by King Industries, an amine-neutralized solution of paratoluenesulfonic acid, containing 25% paratoluenesulfonic acid).

[0086] <Hydrophilic Agent (E)> The hydrophilizing agent may be any agent as long as it has hydrophilicity, and is usually a compound that imparts hydrophilicity to the coating film by floating and localizing on the surface layer of the coating film formed from the coating composition.

[0087] Examples of the hydrophilicity-imparting group include anionic groups, cationic groups, and nonionic groups.

[0088] Examples of the anionic group include a carboxyl group, a carbonyl group, a sulfonic acid group, and a phosphate group.

[0089] Examples of the cationic group include an amino group and an ammonium salt group.

[0090] Examples of the nonionic group include a morpholine group, an amide group, a hydroxyl group, and an oxyalkylene group.

[0091] Furthermore, the hydrophilicity-imparting group may include betaine, which is an amphoteric compound.

[0092] As the hydrophilicity-imparting group, a nonionic group is preferred from the viewpoint of wrinkle pattern stability, and among nonionic groups, an amide group is particularly preferred from the viewpoint of long-lasting hydrophilicity.

[0093] Furthermore, the hydrophilizing agent (E) preferably contains a low polarity functional group in order to impart surface orientation.

[0094] Examples of the low polarity functional group include an organosiloxane group and a perfluoroalkyl group from the viewpoint of surface orientation. As the hydrophilizing agent (E), a copolymer of constituent monomers containing at least one compound having, as a hydrophilicity-imparting group, any one of a morpholine group, an amide group, an oxyalkylene group, and a quaternary ammonium base, and at least one compound having, as a low-polarity functional group, any one of an organosiloxane group and a perfluoroalkyl group, can be particularly preferably used.

[0095] Specifically, for example, copolymers of constituent monomers containing at least a (meth)acrylate compound having an organosiloxane group and a (meth)acrylate compound having an acryloylmorpholine group, copolymers of constituent monomers containing at least a (meth)acrylate compound having a perfluoroalkyl group and a (meth)acrylate compound having an acryloylmorpholine group, copolymers of constituent monomers containing at least a (meth)acrylate compound having an organosiloxane group and a (meth)acrylamide compound, copolymers of constituent monomers containing at least a (meth)acrylate compound having a perfluoroalkyl group and a (meth)acrylamide compound, copolymers of constituent monomers containing at least an organosiloxane group and a (meth)acrylate compound having an oxyalkylene group; a copolymer of constituent monomers containing at least a (meth)acrylate compound having a perfluoroalkyl group and a (meth)acrylate compound having an oxyalkylene group; a copolymer of constituent monomers containing at least a (meth)acrylate compound having an organosiloxane group and a (meth)acrylate compound having a quaternary ammonium salt group; and a copolymer of constituent monomers containing at least a (meth)acrylate compound having a perfluoroalkyl group and a (meth)acrylate compound having a quaternary ammonium salt group.

[0096] Among the above, from the viewpoint of water-wet drying properties, copolymers of constituent monomers containing at least a (meth)acrylate compound having an acryloylmorpholine group as a hydrophilicity-imparting group, particularly copolymers of constituent monomers containing at least a (meth)acrylate compound having an acryloylmorpholine group and a (meth)acrylate compound having a perfluoroalkyl group, and copolymers of constituent monomers containing at least a (meth)acrylate compound having an acryloylmorpholine group and a (meth)acrylate compound having an organosiloxane group can be preferably used.

[0097] Organosilicates and / or condensates thereof, which are localized on the surface of the coating film during film formation and subsequently exhibit hydrophilicity through a hydrolysis reaction, can also be used as the hydrophilizing agent (E). Furthermore, by using the above-mentioned hydrophilizing agents in combination with organosilicates and / or condensates thereof, it is possible to achieve a balance between silicate fume generation and hydrophilicity.

[0098] From the viewpoint of water resistance, the solid content of the hydrophilizing agent (E) is preferably within the range of 0.1 to 20 mass %, particularly 0.1 to 15 mass %, and even more particularly 1 to 10 mass %, relative to the total solid content of the hydroxyl group-containing resin (A) and the crosslinking agent (B).

[0099] When an organosilicate and / or a condensate thereof is also used as the hydrophilizing agent (E), from the viewpoint of suppressing a decrease in productivity due to oven contamination by silicate fumes, the organosilicate and / or condensate thereof preferably accounts for 0.5 to 3 mass %, particularly 0.5 to 2.5 mass %, and even more particularly 1 to 2 mass %, in terms of solid content, relative to the total solid content of the hydroxyl group-containing resin (A) and the crosslinking agent (B).

[0100] In addition to the hydroxyl group-containing resin (A), crosslinking agent (B), sulfonic acid compound (C), amine compound (D), and hydrophilizing agent (E), the coating composition of the present invention can optionally use known raw materials that have been conventionally used in coating compositions, such as pigments such as aggregates, color pigments, luster pigments, extender pigments, rust-preventive pigments, and heat-shielding pigments; coating additives such as antifoaming agents, surface conditioners, UV absorbers (triazine-based UV absorbers, benzophenone-based UV absorbers, and the like), light stabilizers, and waxes; metal catalysts such as tin compounds and titanium compounds; and solvents such as water and organic solvents.

[0101] Examples of aggregates include organic resin particles such as acrylic resin particles, nylon resin particles, acrylonitrile resin particles, urethane resin particles, urea resin particles, and polyolefin resin particles; glass beads, ceramic fibers, and synthetic silica particles. These can be used alone or in combination of two or more.

[0102] The amount of aggregate is preferably in the range of 0.5 to 30 mass %, particularly 2 to 20 mass %, based on the total amount of solids of the hydroxyl group-containing resin (A) and the crosslinking agent (B).

[0103] By including an aggregate, a uniform matte coating film can be stably formed in the coating film obtained from the coating composition of the present invention.

[0104] Examples of color pigments include color inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and coal dust; color organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, industhrone blue, dibromoanzathrone red, perylene red, azo red, and anthraquinone red; and aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, and finely divided titanium.

[0105] Examples of the luster pigment include aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, alloy foil such as nickel-copper foil, and foil pigments such as foil-like phthalocyanine blue.

[0106] Examples of extender pigments include calcium carbonate, barium sulfate, clay, talc, mica, and glass fiber.

[0107] The above pigments can be used alone or in combination of two or more.

[0108] The amount of the pigment is preferably within a range of 3 to 150% by mass, particularly 5 to 100% by mass, based on the total solid content of the hydroxyl group-containing resin (A) and the crosslinking agent (B).

[0109] As the wax, waxes known to those skilled in the art for use in paints can be used, and examples thereof include microcrystalline, polyolefin, polytetrafluoroethylene, polypropylene, paraffin, carnauba, and modified products thereof.

[0110] The above waxes can be used alone or in combination of two or more.

[0111] The amount of wax is preferably in the range of 0.5 to 15 mass %, particularly preferably 1 to 7 mass %, based on the total solid content of the hydroxyl group-containing resin (A) and the crosslinking agent (B).

[0112] By including wax, it is possible to stably achieve good scratch resistance in the coating film obtained from the coating composition of the present invention.

[0113] Examples of the solvent include water; glycol-based organic solvents such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate; alcohol-based organic solvents such as methanol, ethanol, isopropyl alcohol, and Solfit (manufactured by Kuraray Co., Ltd.); ether-based organic solvents such as dioxane and tetrahydrofuran; ester-based organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and isophorone; and N-methyl-2-pyrrolidone, toluene, pentane, isopentane, hexane, isohexane, cyclohexane, solvent naphtha, mineral spirits, and Swazol 1500 (an aromatic hydrocarbon-based solvent, manufactured by ENEOS Corporation). The above solvents can be used alone or in combination of two or more.

[0114] The coating composition of the present invention may be an organic solvent-based coating material or a water-based coating material.

[0115] <Water receding contact angle> The coating film of the coating composition of the present invention has a receding water contact angle of 30° or less, preferably 0 to 25°, and more preferably 0 to 20°.

[0116] More specifically, the coating composition of the present invention is applied to a substrate surface to a cured film thickness of 22 μm and cured at 220°C for 40 seconds, forming a coating film that has a receding water contact angle of 30° or less, preferably 0 to 25°, and more preferably 0 to 20°.

[0117] In the present invention, the receding water contact angle was measured using the expansion / contraction method. Specifically, 2 μL of distilled water was deposited on a test specimen using an automatic contact angle measurement device to form a water droplet. Next, a stainless steel needle (SNS021 / 011, manufactured by Eiko Seiki Co., Ltd.) with an outer diameter of 0.21 mm and an inner bore diameter of 0.11 mm attached to a 500 μL glass syringe (DS500 / GT, manufactured by Eiko Seiki Co., Ltd.) was inserted into the center of the water droplet so that the tip of the needle was 0.2 mm above the test specimen surface. The contact angle immediately after 40 μL of distilled water was injected through the needle at a rate of 20 μL / s was taken as the advancing contact angle. After allowing the water to stand for 1 second, the contact angle immediately after aspirating 40 μL at a rate of 20 μL / s was taken as the receding contact angle.

[0118] The contact angle meter used in the present specification for measuring the contact angle is "DMo-502" (manufactured by Kyowa Interface Science Co., Ltd.).

[0119] <Minimum autocorrelation length (Sal)> The coating film of the coating composition of the present invention has a minimum autocorrelation length (Sal) of 10 to 40 μm, preferably 10 to 35 μm, and more preferably 15 to 30 μm.

[0120] More specifically, the coating composition of the present invention is applied to a substrate surface to a cured film thickness of 22 μm and cured at 220°C for 40 seconds, and the resulting coating film has a minimum autocorrelation length (Sal) of 10 to 40 μm, preferably 10 to 35 μm, and more preferably 15 to 30 μm.

[0121] By adjusting the content within the above range, a matte coating film having excellent stain resistance and weather resistance can be obtained.

[0122] Here, the minimum autocorrelation length Sal can be measured in accordance with the surface texture standard ISO 25178. If Sal is small, the surface shape will be regular and dense, and conversely, if it is large, the surface shape will be irregular and sparse.

[0123] The minimum autocorrelation length (Sal) was measured in accordance with ISO25178 using a three-dimensional white light interference microscope (BRUKER, ContourX).

[0124] The arithmetic mean height (Sa) is a parameter that indicates the surface roughness of a coating film, and represents the average absolute value of the difference in height between each point on the coating film and the average surface. A smaller Sa means that the coating film surface is flatter and less matte.

[0125] The arithmetic mean height (Sa) can also be measured in accordance with ISO 25178 using a three-dimensional white light interference microscope (Bruker, ContourX).

[0126] From the viewpoint of matte appearance and stain resistance, Sa is 1.0 μm or more, preferably 3.0 μm or more, more preferably 5.0 μm or more, and particularly preferably 6.0 μm or more. The upper limit of Sa is preferably 12.0 μm, more preferably 10.0 μm, and even more preferably 8.0 μm.

[0127] More specifically, the coating composition of the present invention is applied to a substrate to a cured film thickness of 22 μm and cured at 220° C. for 40 seconds to form a coating film with an arithmetic mean height (Sa) of 1.0 μm or more, preferably 3.0 μm or more, more preferably 5.0 μm or more, and particularly preferably 6.0 μm or more. The upper limit of Sa is preferably 12.0 μm, more preferably 10.0 μm, and even more preferably 8.0 μm.

[0128] In the present invention, the formation of a continuous water film on the coating surface during rainfall is important for the stain resistance of the coating film, and there is a very high correlation between the stain resistance of a matte coating film and the fact that, in dynamic contact angle measurements of water, there is no increase in the contact angle at the start of expansion and there is little reduction in the area of the water film on the coating film surface during contraction. It is presumed that when the specific wrinkle-patterned coating film formed using the paint composition of the present invention has a water receding contact angle of 30° or less, moisture remains in the shrinkage depressions after wetting with water when the film shrinks, so that a film can be formed with little apparent reduction in area when the water droplets contract and little increase in contact angle when the water expands, resulting in a coating film with excellent stain resistance and long-lasting stain resistance.

[0129] <Method of manufacturing the coating composition> The method for producing the coating composition of the present invention is not particularly limited. For example, the coating composition can be produced by mixing the components using a mixer, disperser, kneader, etc., such as a sand grind mill, ball mill, blender, paint shaker, or disperser.

[0130] <Object to be coated> Examples of substrates to be coated with the coating composition of the present invention include metal plates such as zinc-plated steel sheets, zinc-aluminum alloy-plated steel sheets, aluminum alloy-plated steel sheets, hot-dip zinc-aluminum-magnesium alloy-plated steel sheets, stainless steel sheets, and cold-rolled steel sheets, all of which are produced by hot-dip methods or electrolytic methods.

[0131] In addition to these steel sheets or plated steel sheets, metal sheets such as aluminum sheets (including aluminum alloy sheets) can also be used as substrates.

[0132] The metal sheet is preferably surface-treated. Specifically, the metal sheet is preferably subjected to a pretreatment such as alkaline degreasing, hot water washing, or water washing, followed by a chemical conversion treatment. The chemical conversion treatment may be carried out by a known method, and specific examples include non-chromate treatments such as chromate treatment, zinc phosphate treatment, and zirconium treatment. The surface treatment can be appropriately selected depending on the steel sheet to be used, but a treatment that does not contain heavy metals is preferred.

[0133] <Painted metal plate> The coated metal sheet of the present invention comprises a metal sheet and a coating film formed on at least one surface of the metal sheet from the coating composition of the present invention. The coating composition contains a hydroxyl group-containing resin (A), a crosslinking agent (B), a sulfonic acid compound (C), an amine compound (D), and a hydrophilizing agent (E). On the surface of the coating film, the water receding contact angle is 30° or less, and the minimum autocorrelation length (Sal) is 10 to 40 μm.

[0134] The thickness of the coating film is preferably within the range of 1 μm to 40 μm, particularly 15 μm to 30 μm, and further particularly 18 μm to 25 μm.

[0135] The coated metal sheet may have a coating film formed from the coating composition of the present invention on one surface and a coating film formed from a known coating composition on the other surface.

[0136] For example, the other surface may have a coating film formed from a known coating composition, such as a coating composition containing an epoxy resin.

[0137] The coated metal sheet may have an undercoat coating film (primer coating film) between the metal sheet and the coating film formed from the coating composition of the present invention.

[0138] The undercoat paint (primer paint) may be a conventionally known paint.

[0139] The primer paint is appropriately selected depending on the type of substrate and the type of metal surface treatment, but epoxy resin-based primer paints, polyester resin-based primer paints, and modified primer paints thereof are particularly suitable, and polyester-based primer paints are suitable when processability is particularly required. From the viewpoint of environmental protection, it is preferable to use a chromium-free primer paint that does not contain a chromium-based rust-preventive component.

[0140] The primer coating is applied by a known coating method such as roll coating or spray coating so that the dry film thickness is usually 1 to 30 μm, preferably 2 to 20 μm, and the material is then heated to a maximum temperature of 140 to 270°C, preferably 190 to 240°C, for 5 to 120 seconds, preferably 10 to 60 seconds, to form a cured primer coating film.

[0141] The primer coating may be a single layer, or may be a two-layer structure in which a second primer coating (intermediate coating) is formed on a first primer coating. When the primer coating is a two-layer structure, it is possible to impart different functions to the two primer coating layers, such as imparting corrosion protection to the first primer coating and imparting processability and chipping resistance to the second primer coating (intermediate coating).

[0142] The presence of an undercoat film can improve the adhesion and corrosion resistance of the coating film formed from the coating composition of the present invention.

[0143] The thickness of the undercoat film is preferably in the range of 2 μm to 20 μm, particularly 5 μm to 15 μm.

[0144] <Coating film formation method> The method for forming a coating film of the present invention comprises the steps of applying the coating composition of the present invention to an object to be coated, and drying and / or curing the coating composition at a temperature in the range of 170°C to 270°C.

[0145] It is preferable to apply a chemical conversion treatment such as phosphate treatment or chromate treatment to the surface of the substrate as a base treatment for painting, and then apply the coating composition thereon. By applying the coating composition of the present invention to a metal plate that has been subjected to such a chemical conversion treatment, the adhesion and corrosion resistance of the coating film to the metal plate can be improved.

[0146] Alternatively, a primer coating may be formed on a metal plate that has been subjected to a chemical conversion treatment, and then the coating may be applied on top of that.

[0147] A coating film made from the coating composition of the present invention can be formed by applying the coating composition to a substrate such as a metal plate, and then subjecting the substrate to a baking treatment in which the substrate is heated.

[0148] There are no particular limitations on the method for applying the coating composition to the substrate, and it can be applied using a bar coater, roll coater, roll curtain coater, curtain flow coater, die coater or spray gun.

[0149] Furthermore, the method for baking the substrate after painting is not particularly limited, but a cured coating can be obtained by baking the coating and crosslinking the resin using heating means such as hot air heating, infrared heating, induction heating, etc. The baking temperature (the maximum temperature reached by the coated substrate, such as a steel plate) is usually in the range of 180°C to 250°C, preferably 200°C to 235°C, and the baking time is usually in the range of 5 to 100 seconds, preferably 25 to 60 seconds.

[0150] The film thickness (dry film thickness) of the coating film obtained using the coating composition of the present invention is usually within the range of 1 μm to 40 μm, and for example, in the case of a topcoat coating film, it is preferably within the range of 15 μm to 30 μm, more preferably 18 μm to 25 μm. [Example]

[0151] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. In the examples, "parts" and "%" are by mass unless otherwise specified.

[0152] Preparation of coating compositions Example 1 Polyester resin 1 (Note 1) 85 parts (solid content), Cymel 303 (Note 4) 15 parts (solid content), dodecylbenzenesulfonic acid 0.5 parts, diisopropylamine 1.5 parts, polyethylene dispersion (Hiflat T-15P-2: Gifu Ceramics Manufacturing Co., Ltd., trade name) 1.5 parts (solid content), polytetrafluoroethylene (DYNEON TF9205: 3M DYNEON Corporation, trade name) 2 parts (solid content), organic resin particles 1 (Note 6) 2 parts (solid content), organic resin particles 2 (Note 7) 2 parts (solid content), hydrophilizing agent (E-1) 3 parts (solid content), and TIPAQUE 100 parts of CR-93 (titanium oxide, product name, manufactured by Ishihara Sangyo Kaisha) was mixed and diluted with an organic solvent (a mixed solvent of cyclohexanone / Swasol 1500 = 40 / 60 (mass ratio)) to obtain Coating Composition No. 1 with a viscosity of 80 seconds (Ford cup #4, 25°C).

[0153] Examples 2 to 33 and Comparative Examples 1 to 8 Coating compositions Nos. 2 to 41 were obtained in the same manner as in Example 1, except for the formulations shown in Table 1. Coating compositions Nos. 34 to 41 are comparative examples. In Table 1, the amounts of components excluding the amine compound are solid contents.

[0154] The notes in the table are as follows:

[0155] (Note 1) Polyester resin 1 Acid components: isophthalic acid / phthalic anhydride / adipic acid, alcohol components: 1,3-butylene glycol / neopentyl glycol / glycerin, polyester resin synthesized in a composition ratio of DBR 0.91, weight average molecular weight approximately 8000, hydroxyl value 100mgKOH / g, acid value 2.9mgKOH / g.

[0156] (Note 2) Polyester resin 2 Acid components: terephthalic acid / isophthalic acid / adipic acid, alcohol components: ethylene glycol / neopentyl glycol / glycerin. Polyester resin synthesized in a composition ratio of 0.98, weight average molecular weight approximately 19,000, hydroxyl value 20 mg KOH / g, acid value 8.1 mg KOH / g.

[0157] (Note 3) Polyester resin 3 Acid component: 1,2-cyclohexanedicarboxylic anhydride, alcohol component: neopentyl glycol / 2-butyl-2-ethyl-1,3-propanediol / trimethylolpropane, polyester resin synthesized in a composition ratio of DBR 0.98, alkyd resin modified with coconut oil fatty acid, weight average molecular weight approximately 30,000, hydroxyl value 75 mg KOH / g, acid value 6.0 mg KOH / g.

[0158] (Note 4) Cymel 303: Product name, fully alkylated methylated melamine resin, manufactured by Nippon Cytec Industries Co., Ltd. (Note 5) Cymel 325: Product name, imino group-type methylated melamine resin, manufactured by Nippon Cytec Industries Co., Ltd. (Note 6) Tuftic A-20: Toyobo Co., Ltd., trade name, polyacrylonitrile-based fine particles (Note 7) PERGOPAK M-3: Product name, urea / formaldehyde condensate, manufactured by JM Huber Corporation (Note 8) GASIL HP-560: A synthetic amorphous silica manufactured by PQ Corporation. (Note 9) GASIL HP-39: A synthetic amorphous silica manufactured by PQ Corporation. (Note 10) GASIL HP-395: A synthetic amorphous silica manufactured by PQ Corporation. The hydrophilizing agents (E) in the table are as follows:

[0159] Synthesis of hydrophilizing agent (E-1) 100 parts of cyclohexanone was added to a four-necked flask equipped with a reflux condenser, a thermometer, and a stirrer, and the temperature was raised to 100°C with stirring.

[0160] To this was added 5 parts of (e1) one-end methacrylate-modified dimethyl silicone (manufactured by Shin-Etsu Chemical Co., Ltd., product name "X-22-2475"), 91.9 parts of (e3) acryloylmorpholine (manufactured by KJ Chemical Co., Ltd., product name "ACMO"), 3.1 parts of (e7) 2-hydroxyethyl acrylate (manufactured by Nippon Shokubai, product abbreviation name "BHEA"), 1.0 part of 2,2'-azobis(2-methylbutyronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "V-59"), and 100 parts of cyclohexanone (manufactured by Sumitomo Chemical), and the mixture was added dropwise over 3 hours to a flask heated to 100°C.

[0161] After the dropwise addition was completed, the mixture was stirred for 30 minutes at 100°C, and then a solution of 0.3 parts of 2,2'-azobis(2-methylbutyronitrile) and 10 parts of cyclohexanone was added dropwise over 30 minutes, and the mixture was allowed to react for 1 hour at 100°C while continuing to stir. 26.4 parts of cyclohexanone was further added to obtain a hydrophilizing agent (E-1) with a solids mass concentration of 55%.

[0162] Synthesis of hydrophilizing agents (E-2) to (E-8) Hydrophilizing agents (E-2) to (E-8) each having a solid mass concentration of 55% were obtained by synthesizing in the same manner as hydrophilizing agent (E-1) except for using the compositions shown in Table 2.

[0163] The raw materials used other than the hydrophilizing agent (E-1) in Table 2 are as follows:

[0164] (e2): 2-(perfluorohexyl)ethyl acrylate (manufactured by Unimatec Co., Ltd., product name "CHEMINOX FAAC-6") (e4): Dimethylacrylamide (e5): Methoxypolyethylene glycol acrylate (product name "AM-90G" manufactured by Shin-Nakamura Chemical Co., Ltd.) (e6): Dimethylaminopropylacrylamide methyl chloride quaternary salt DMAPAA-Q manufactured by KJ Chemicals The hydrophilizing agents (E-9) to (E-10) are as follows:

[0165] Hydrophilizing agent (E-9): NEWCOL 290M: Product name, dioctyl sulfosuccinate sodium salt, manufactured by Nippon Nyukazai Co., Ltd. Hydrophilizing agent (E-10): NEWCOL 294-T: Product name, dioctyl sulfosuccinate calcium salt, manufactured by Nippon Nyukazai Co., Ltd. Hydrophilizing agent (E-11): MKC Silicate MS56S: a trade name of Mitsubishi Chemical Corporation, a methyl esterified silicate that is a condensation product of tetramethoxysilane. Hydrophilizing agent (E-12): MKC Silicate MS58B30: Mitsubishi Chemical Corporation, trade name, methyl / butyl mixed esterified silicate, a condensation product of tetraalkoxysilane Creating test panels A primer coating (KP Color 8635 Primer, trade name, polyester resin primer, manufactured by Kansai Paint Co., Ltd.) having a dry thickness of 4 μm was formed on an aluminum-zinc alloy zinc-plated steel sheet (GL material, sheet thickness 0.35 mm).

[0166] Next, each of the coating compositions Nos. 1 to 41 obtained in the above Examples and Comparative Examples was applied to the primer coating using a bar coater to a dry film thickness of 22 μm, and the coating was baked for 40 seconds under conditions where the maximum temperature reached by the material was 220°C, to obtain each test panel.

[0167] Each test plate was tested under the test conditions described below, and the results are shown in Table 1.

[0168] Fume generating: Using the test set shown in the model diagram in Figure 1, the fumes generated from the coated panels were evaluated according to the following process. ◎ and ◯ indicate acceptable levels.

[0169] Step 1: Preheat the test plate (1) at 140°C for 3 minutes.

[0170] Step 2: Next, the preheated test plate (1) is placed on a hot plate (3) set to 230°C, and the test plate (1) is surrounded by a frame (2) to prevent fumes from escaping from the coated plate.

[0171] Step 3: In order to capture the fumes coming out of the painted plate, a steel plate (4) is placed on top of the frame (2), and a 4-liter round can (5) filled with ice water is placed on top of the steel plate (4), and left for 40 seconds to immediately cool the fumes that are generated.

[0172] Step 4: A new test plate (1) was used, and the above steps 1 to 3 were repeated 10 times. Thereafter, the steel plate (4) was taken out and its appearance was evaluated according to the following criteria.

[0173] ◎ indicates that a small amount of fume has adhered to the steel plate (4), but there is no sense of interference. ○ indicates that fumes have adhered to the steel plate (4) and there is a sense of interference, but there is no cloudiness or adhesion of resin.

[0174] △ indicates that fumes have adhered to the steel plate (4), causing interference, and that cloudiness or adhesion of resin is observed.

[0175] X indicates that fumes have adhered to the steel plate (4), making it opaque or significantly stained with resin.

[0176] 60°G: The gloss value (60° gloss value) of each coating surface measured in accordance with the specular gloss (60°) of JIS K5600-4-7 (1999).

[0177] Arithmetic mean roughness (Sa) and minimum autocorrelation length (Sal): According to the method specified in ISO25178, the surface shape of two arbitrary points on the coated surface of each sample was measured using BRUKER's three-dimensional white light interference microscope ContourX (measurement and analysis software Vision64), and shape analysis was performed to determine the minimum autocorrelation length Sal and arithmetic mean roughness Sa of the coated surface.

[0178] Shape analysis was performed using a high-resolution CCD camera (resolution: 1280 × 960 pixels) with the VXI measurement method (resolution: high speed). The conditions were: white light source, measurement magnification: 5.0 × 1.0, measurement range: 0.9 mm × 4.0 mm, threshold: 2%, and filtering: terms removal (tilt only).

[0179] Water receding contact angle: Using an automatic contact angle measurement device, 2 μL of distilled water was deposited on the test plate to form a water droplet. Next, a stainless steel needle (SNS021 / 011, manufactured by Eiko Seiki Co., Ltd.) with an outer diameter of 0.21 mm and an inner bore diameter of 0.11 mm attached to a 500 μL glass syringe (DS500 / GT, manufactured by Eiko Seiki Co., Ltd.) was inserted into the center of the water droplet so that the tip of the needle was 0.2 mm above the surface of the test plate. 40 μL of distilled water was then injected through the needle at a rate of 20 μL / s. The contact angle immediately after this was recorded as the advancing contact angle. After allowing the water to stand for 1 second, the contact angle immediately after aspirating 40 μL at a rate of 20 μL / s was recorded as the receding water contact angle.

[0180] Rain streak staining: Test specimens (test panels cut to a size of 100 x 300 mm) were attached to a stand modeling an eaves at an angle of 4 degrees from the vertical with the coating facing north, and an exposure test was carried out on the roof of Kansai Paint Co., Ltd. in Ota Ward, Tokyo. Two months after the start of exposure, the color difference (ΔE) from the initial painted panel was measured in accordance with JIS Z 8370 using a multi-light source spectrophotometer MSC-5N made by Suga Test Instruments Co., Ltd., and rated according to the following criteria: ◎ and ◯ are passing levels.

[0181] ◎ indicates ΔE is less than 1 ○ indicates that ΔE is 1 or more and less than 2 △: ΔE is 2 or more and less than 5 × indicates ΔE of 5 or more Accelerated weathering: Each test panel was subjected to 3,000 hours of continuous irradiation with a xenon weather meter under repeated cycle conditions (18 minutes wet, 102 minutes dry) based on Method A of the Long-Term Durability Accelerated Weathering (Xenon Lamp) Test for Paint Films specified in JIS K 5600 7.7. Afterwards, the condition of the coating surface was evaluated based on the following criteria. ◎ and ◯ indicate passing levels.

[0182] ◎: No abnormalities such as blisters, cracks, cloudiness, or chalking are observed on the painted surface.

[0183] 〇: No abnormalities such as blisters, cracks, or chalking are observed on the painted surface, but cloudiness is observed on the painted surface. △: Any abnormality on the painted surface such as blisters, cracks, or chalking is observed. ×: Any of the following abnormalities on the painted surface, such as blisters, cracks, or chalking, is significantly observed.

[0184] [Table 1]

[0185] [Table 2]

[0186] [Table 3]

[0187] [Table 4]

[0188] [Table 5] [Industrial Applicability]

[0189] The present invention provides a coating composition capable of forming a matte coating film (crinkle-pattern coating film) that is excellent in stain resistance, corrosion resistance, and weather resistance, a method for forming a matte coating film (crinkle-pattern coating film) using the coating composition, and a coated metal sheet. [Brief explanation of the drawings]

[0190] [Figure 1] A model diagram of the device used to test the amount of fume generated during baking is shown below. [Explanation of symbols]

[0191] 1. Painted board 2. A coating to prevent fumes from escaping from the painted board 3. Hot plate 4. Steel plate for capturing fumes emitted from painted panels 5. A 4-liter round can filled with ice water to immediately cool the generated fumes.

Claims

1. A coating composition comprising a hydroxyl group-containing resin (A), a crosslinking agent (B), a sulfonic acid compound (C), an amine compound (D), and a hydrophilizing agent (E), A coating composition characterized in that the surface of a coating film obtained by curing the coating composition has a water receding contact angle of 30° or less and a minimum autocorrelation length (Sal) of 10 to 40 μm.

2. 2. The coating composition according to claim 1, wherein the hydroxyl-containing resin (A) comprises a hydroxyl-containing polyester resin.

3. 3. The coating composition according to claim 1, wherein the crosslinking agent (B) contains an amino resin.

4. A coated metal plate having a metal plate and a coating film on at least one surface of the metal plate, wherein the coating film is formed from the coating composition according to claim 1 or 2, and the coating film has a water receding contact angle of 30° or less and a minimum autocorrelation length (Sal) of 10 to 40 μm on the surface of the coated metal plate.

5. A method for forming a coating film, comprising a coating step of applying the coating composition according to claim 1 or 2 to a substrate, and a step of drying and / or curing the applied coating composition at a temperature of 170°C to 270°C.

Images