Coating composition

Abstract

To provide a coating composition enabling materialization of a coating film excellent in adhesion to a base material and excellent in scratch resistance.SOLUTION: The coating composition of the present disclosure includes a hydroxyl group-containing resin (A), a crosslinking agent (B), an acid catalyst (C) containing a naphthalene skeleton, and a compound (D) containing a phosphate ester group. The crosslinking (B) includes an amino resin (B1) and / or a blocked isocyanate (B2). With respect to a total of 100 pts.mass of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B), the solid content of the hydroxyl group-containing resin (A) is 60 to 90 pts.mass, the active ingredient of the acid catalyst (C) containing the naphthalene skeleton is 0.01 to 0.5 pts.mass, and the solid content of the compound (D) containing the phosphate ester group is 0.5 to 5 pts.mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to coating compositions. [Background technology]

[0002] Coated steel sheets, which are prepared by coating metal substrates such as cold-rolled steel sheets and plated steel sheets and then subjecting them to forming, are also called precoated steel sheets (hereinafter also referred to as "PCM") and are used for applications such as architectural components such as shutters, ceiling doors, doors, roofs, and siding; exterior materials for electrical equipment such as outdoor air conditioner units; and interior materials. The precoated steel sheets are usually produced by applying a coating composition to the surface of the metal substrate and then heating (baking) it at 200 to 270°C for 30 to 60 seconds to form a coating film, which is then processed into the desired product.

[0003] Patent Document 1 describes a coating composition for use in PCM, which contains a hydroxyl-containing resin, an amino resin, a covalently blocked acid catalyst, and a phosphoric acid-modified epoxy resin, and the coating composition contains 60 to 90 parts by mass of the hydroxyl-containing resin, 10 to 40 parts by mass of the amino resin, 1 to 10 parts by mass of the acid catalyst portion of the covalently blocked acid catalyst, and 1 to 10 parts by mass of the solid content of the phosphoric acid-modified epoxy resin, relative to 100 parts by mass in total of the resin solid content of the hydroxyl-containing resin and the resin solid content of the amino resin.

[0004] Patent Document 2 describes a coating composition containing a metal less noble than iron, a binder resin, an adhesion promoter, and water, in which the binder resin contains at least one resin selected from acrylic resins, epoxy resins, and epoxy ester resins, and the adhesion promoter is at least one compound selected from phosphate ester compounds and sulfonate ester compounds. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2022 / 027157 [Patent Document 2] Patent Publication No. 2021-129713 Summary of the Invention [Problem to be solved by the invention]

[0006] The coating film formed on the pre-coated steel sheet must have flexibility, high workability so that it does not crack or peel when processed, for example, when the pre-coated steel sheet is bent, and high hardness (scratch resistance) so that it does not get scratched or dented.

[0007] This tendency is particularly pronounced in polyester resin-based paints, and a method of adding silica as an aggregate has been used to improve scratch resistance, but in order to satisfy the required scratch resistance, a large amount of silica must be added, which has the problem of reducing the chemical resistance of the resulting coating film.

[0008] An object of the present disclosure is to provide a coating composition that can produce a coating film that has good adhesion to a substrate and good scratch resistance. [Means for solving the problem]

[0009] The present disclosure includes the following aspects. [1] The composition comprises a hydroxyl group-containing resin (A), a crosslinking agent (B), an acid catalyst (C) having a naphthalene skeleton, and a phosphate group-containing compound (D), the crosslinking agent (B) contains an amino resin (B1) and / or a blocked isocyanate (B2), per 100 parts by mass of the total of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B), the solid content of the hydroxyl group-containing resin (A) is 60 parts by mass or more and 90 parts by mass or less, the active ingredient of the acid catalyst (C) containing a naphthalene skeleton is 0.01 parts by mass or more and 0.5 parts by mass or less, A coating composition, wherein the solid content of the phosphate ester group-containing compound (D) is 0.5 parts by mass or more and 5 parts by mass or less. [2] The coating composition according to [1], wherein the acid of the acid catalyst (C) is a sulfonic acid. [3] The coating composition according to [1] or [2], wherein the acid of the acid catalyst (C) is a disulfonic acid. [4] The coating composition according to any one of [1] to [3], wherein the phosphate value of the phosphate ester group-containing compound (D) is 50 mgKOH / g or more and 200 mgKOH / g or less. [5] The coating composition according to any one of [1] to [4], wherein the number average molecular weight of the phosphate ester group-containing compound (D) is 300 or more and 5,000 or less. paint composition [6] The coating composition according to any one of [1] to [5], further comprising an anti-rust pigment (E). [7] The coating composition according to any one of [1] to [6], wherein the anti-rust pigment (E) contains magnesium hydroxide. [8] A step of applying the coating composition according to any one of [1] to [7] to at least one surface of a metal plate so that the film thickness after curing is 1 to 30 μm to form a coating film; A method for producing a precoated metal sheet, comprising a step of drying and / or curing the coating film at a temperature of the metal sheet reached by 180°C to 270°C. [Effects of the Invention]

[0010] The coating composition of the present disclosure can provide a coating film that has good adhesion to the substrate and good scratch resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] The coating composition of the present disclosure comprises a hydroxyl group-containing resin (A), a crosslinking agent (B), an acid catalyst having a naphthalene skeleton (C), and a phosphate ester group-containing compound (D), the crosslinking agent (B) contains an amino resin (B1) and / or a blocked isocyanate (B2), per 100 parts by mass of the total of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B), the solid content of the hydroxyl group-containing resin (A) is 60 parts by mass or more and 90 parts by mass or less, the solid content of the acid catalyst (C) containing a naphthalene skeleton is 0.01 parts by mass or more and 0.5 parts by mass or less, The solid content of the phosphate ester group-containing compound (D) is 0.5 parts by mass or more and 5 parts by mass or less.

[0012] The coating composition of the present disclosure can realize a coating film with good adhesion (scratch resistance) to the substrate. Although the present disclosure should not be interpreted as being limited to a particular theory, the reason why the coating composition of the present disclosure can exhibit such an effect is thought to be as follows.

[0013] That is, the coating composition of the present disclosure contains a hydroxyl group-containing resin and a crosslinker, and combines an acid catalyst having a naphthalene skeleton with a phosphate ester group-containing compound. Although the interaction between these is not clear, it is thought that the presence of a compound having a bulky skeleton in the composition causes the compounds to become entangled with each other during coating film formation, improving adhesion to the substrate and enhancing scratch resistance.

[0014] <Hydroxyl group-containing resin (A)> The hydroxyl-containing resin (A) is a resin having hydroxyl groups in its molecular structure. The hydroxyl-containing resin (A) reacts with the crosslinking agent (B) to form a coating film. Examples of the hydroxyl-containing resin (A) include polyester resins, epoxy resins, and acrylic resins, with polyester resins being preferred.

[0015] (polyester resin) The polyester resin is not particularly limited as long as it is a polyester resin generally used for coatings. In the present disclosure, unless otherwise specified, when simply referring to a polyester resin, it means including at least one selected from the group consisting of polyester resins and modified polyester resins.

[0016] The hydroxyl value of the polyester resin is preferably 30 mgKOH / g or more and 100 mgKOH / g or less, more preferably 40 mgKOH / g or more and 100 mgKOH / g or less. When the hydroxyl value of the polyester resin is within this range, the reaction with the crosslinking agent (B) proceeds smoothly, and the coating film obtained from the coating composition of the present disclosure can have high solvent resistance, bending processability, processing adhesion, and chemical resistance. In the present disclosure, the hydroxyl value refers to the hydroxyl value of the solid content, and can be measured in accordance with JIS K 0070.

[0017] The number-average molecular weight of the polyester resin is preferably 1,500 or more and 5,000 or less, more preferably 2,000 or more and 4,500 or less, and even more preferably 2,000 or more and 4,000 or less. When the number-average molecular weight of the polyester resin is within this range, the curing reaction with the crosslinking agent (B) proceeds sufficiently, allowing the formation of a coating film with high solvent resistance and chemical resistance. Furthermore, the crosslink density can be appropriately suppressed, allowing the formation of a coating film with sufficient elongation, for example, a coating film with sufficient bending workability and processing adhesion. Furthermore, such a coating composition has an appropriate viscosity, making it easy to handle. In the present disclosure, the number average molecular weight is a polystyrene equivalent value determined by gel permeation chromatography (GPC).

[0018] The glass transition temperature (Tg) of the polyester resin is preferably −35° C. or higher and 110° C. or lower, more preferably −30° C. or higher and 80° C. or lower, and even more preferably −30° C. or higher and 60° C. When the glass transition temperature (Tg) of the polyester resin is within the above range, the moisture permeability of the coating film does not become excessively high, and the coating film has sufficient moisture resistance and chemical resistance. In the present disclosure, the glass transition temperature (Tg) can be measured using, for example, a thermal analyzer TMA7100 (manufactured by Hitachi High-Tech Science Corporation).

[0019] The acid value of the polyester resin may be preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, and even more preferably 0.3 mgKOH / g or more and 30 mgKOH / g or less. When the acid value of the polyester resin is in the above range, for example, hydrolysis resistance can be improved, and a coating film having moisture resistance and chemical resistance can be formed. In the present disclosure, the acid value refers to the acid value of the solid content, and can be measured in accordance with JIS K 0070.

[0020] The polyester resin can be obtained by polycondensation of a polyhydric alcohol and a polybasic acid. Specific examples of polyhydric alcohols include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate (BASHPN), N,N-bis-(2-hydroxyethyl)dimethylhydantoin, polycaprolactone polyol, glycerin, sorbitol, mannitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, and tris-(hydroxyethyl)isocyanate. The polyhydric alcohol may be used alone or in combination of two or more kinds.

[0021] Specific examples of polybasic acids include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyl terephthalic acid, methyl tetrahydrophthalic anhydride, himic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid, and endo acid anhydride. One type of polybasic acid may be used alone, or two or more types may be used in combination.

[0022] Examples of modified polyester resins include modified polyester resins such as urethane-modified polyester resins, epoxy-modified polyester resins, acrylic-modified polyester resins, and silicone-modified polyester resins. For example, urethane-modified polyester resins are resins that have a polyester main chain and whose terminals are modified with isocyanate to form a urethane-modified resin. For example, silicone-modified polyester resins can be prepared by reacting a polyester resin with an organic silicone (e.g., an organic silicone having a number-average molecular weight of about 300 to 1,000 and containing —SiOCH3 and / or SiOH groups as functional groups). The amount of organic silicone used is usually about 5 to 50 parts by mass per 100 parts by mass of polyester resin. For example, urethane-modified polyester resins can be prepared by reacting the polyester resin with a polyisocyanate compound.

[0023] As the polyester resin, commercially available products can be used, and examples thereof include DYNAPOL LH820, DYNAPOL LH826, DYNAPOL LH727, DYNAPOL LH538, DYNAPOL LH724 (all manufactured by Evonik), ETERKYD 5084-R-60-6E, ETERKYD 3103-X-70, ETERKYD 50528-R-70, ETERKYD 5055R-65-3 (all manufactured by Eternal Materials), Beckolite M-6902-50 (manufactured by DIC Corporation), and SYNOLAC 9605 (manufactured by ARKEMA).

[0024] (epoxy resin) The epoxy resin is not particularly limited as long as it is an epoxy resin generally used for coatings. In the present disclosure, unless otherwise specified, the term "epoxy resin" simply refers to at least one selected from the group consisting of epoxy resins and modified epoxy resins.

[0025] The hydroxyl value of the epoxy resin may be preferably 40 mgKOH / g or more and 200 mgKOH / g or less, more preferably 60 mgKOH / g or more and 180 mgKOH / g or less. When the hydroxyl value of the epoxy resin is within the above range, the reaction with the crosslinking agent (B) proceeds smoothly. By containing such an epoxy resin, the coating film obtained from the coating composition of the present disclosure has the advantages of high solvent resistance, sufficient bending workability, processing adhesion, and chemical resistance.

[0026] The number-average molecular weight of the epoxy resin is preferably 1,500 or more and 5,000 or less, more preferably 2,000 or more and 4,000 or less. When the number-average molecular weight of the epoxy resin is within this range, the curing reaction with the crosslinking agent (B), which will be described later, proceeds sufficiently, allowing the formation of a coating film with good appearance. Furthermore, the crosslinking density of the coating film can be appropriately suppressed, allowing the formation of a coating film with sufficient elongation, for example, a coating film with sufficient bending workability and processing adhesion. Furthermore, such a coating composition has an appropriate viscosity, making it easy to handle.

[0027] The glass transition temperature (Tg) of the epoxy resin may be 120° C. or lower, 115° C. or lower, or 110° C. or lower. In one embodiment, the glass transition temperature (Tg) of the epoxy resin may be 50° C. or higher, or 55° C. or higher. When the glass transition temperature (Tg) of the epoxy resin is within the above range, the moisture permeability of the coating film does not become excessively high, and the coating film has sufficient moisture resistance and chemical resistance.

[0028] The epoxy resin may be a hydroxyl group-containing epoxy resin (including modified hydroxyl group-containing epoxy resins). Examples of the epoxy resin include a resin obtained by condensing epichlorohydrin and bisphenol to a high molecular weight, if necessary in the presence of a catalyst such as an alkali catalyst; bisphenol-type epoxy resins such as bisphenol A and bisphenol F; and novolac-type epoxy resins. Examples of modified epoxy resins include modified epoxy resins such as acrylic-modified epoxy resins, urethane-modified epoxy resins, and amine-modified epoxy resins. For example, acrylic-modified epoxy resins can be prepared by reacting the bisphenol-type epoxy resin or the novolac-type epoxy resin with a polymerizable unsaturated monomer component containing acrylic acid or methacrylic acid. For example, urethane-modified epoxy resins can be prepared by reacting the bisphenol-type epoxy resin or the novolac-type epoxy resin with a polyisocyanate compound.

[0029] Commercially available epoxy resins can also be used, such as jER825, jER828, jER835, jER1004, jER1007, jER1010, jER1255HX30, and jER YX8100BH30 (all bisphenol A type, manufactured by Mitsubishi Chemical Corporation), and jER 1009F (bisphenol F type, manufactured by Mitsubishi Chemical Corporation).

[0030] (acrylic resin) The acrylic resin is not particularly limited as long as it is an acrylic resin generally used for paints. In the present disclosure, unless otherwise specified, when simply referring to an acrylic resin, it means including at least one selected from the group consisting of acrylic resins and modified acrylic resins.

[0031] The hydroxyl value of the acrylic resin may be preferably 40 mgKOH / g or more and 100 mgKOH / g or less, more preferably 60 mgKOH / g or more and 100 mgKOH / g or less. When the hydroxyl value of the acrylic resin is within the above range, the reaction with the crosslinking agent (B) proceeds smoothly. By containing such an acrylic resin, the coating film obtained from the coating composition of the present disclosure has the advantages of having high solvent resistance, chemical resistance, sufficient bending processability, and processing adhesion.

[0032] The number-average molecular weight of the acrylic resin may be preferably 1,500 or more and 5,000 or less, more preferably 2,000 or more and 4,000 or less. When the number-average molecular weight of the acrylic resin is within the above range, the curing reaction with the crosslinking agent (B) proceeds sufficiently, and a coating film with good appearance can be formed. In addition, the crosslink density of the coating film can be prevented from becoming too high, and a coating film with sufficient elongation can be formed, for example, a coating film with sufficient bending processability can be formed. Furthermore, the coating composition of the present disclosure has an appropriate viscosity, resulting in good handleability.

[0033] The glass transition temperature (Tg) of the acrylic resin may be preferably −35° C. or higher and 110° C. or lower, more preferably −30° C. or higher and 80° C. or lower, and even more preferably −30° C. or higher and 60° C. When the glass transition temperature (Tg) of the acrylic resin is within the above range, the moisture permeability of the coating film does not become excessively high, and the moisture resistance and chemical resistance of the coating film become good.

[0034] The acid value of the acrylic resin (including modified products thereof) may be preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, and even more preferably 0.3 mgKOH / g or more and 30 mgKOH / g or less. When the acid value of the acrylic resin is in this range, for example, hydrolysis resistance can be improved, and a coating film having moisture resistance and chemical resistance can be formed.

[0035] Examples of acrylic resins include acrylic resins composed of one or more monomers selected from the group consisting of (meth)acrylic monomers having a hydroxyl group, such as hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and N-methylolacrylamide, and lactone adducts thereof; (meth)acrylic acid; (meth)acrylic acid esters such as alkyl (meth)acrylate; and (meth)acrylonitrile. In addition to the structural units derived from the above-mentioned monomers, the acrylic resin may also contain structural units derived from other monomers (e.g., acid group-containing ethylenic monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, fumaric acid, and maleic acid, and vinyl monomers such as styrene). Examples of modified acrylic resins include modified acrylic resins such as silicone-modified acrylic resins. For example, silicone-modified acrylic resins can be prepared by reacting an acrylic resin with the above-mentioned organosilicon. The amount of organic silicone used is usually about 5 to 50 parts by mass relative to 100 parts by mass of the acrylic resin. In the present disclosure, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0036] As the acrylic resin, commercially available products can be used, such as Acrydic A-608, Acrydic A-452, and Acrydic A-830 (all manufactured by DIC Corporation).

[0037] The hydroxyl group-containing resin (A) may be used alone or in combination of two or more kinds.

[0038] The hydroxyl value of the hydroxyl-containing resin (A) may be preferably 30 mgKOH / g or more and 200 mgKOH / g or less, more preferably 40 mgKOH / g or more and 180 mgKOH / g or less. A hydroxyl value within this range allows the reaction with the crosslinking agent (B) to proceed smoothly. This also provides the coating film obtained from the coating composition of the present disclosure with the advantages of high solvent resistance, chemical resistance, sufficient bending processability, and processing adhesion.

[0039] The acid value of the hydroxyl-containing resin (A) may be preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 0.1 mgKOH / g or more and 30 mgKOH / g or less, and even more preferably 0.3 mgKOH / g or more and 30 mgKOH / g or less. When the acid value is within this range, for example, hydrolysis resistance can be improved, and a coating film having moisture resistance and chemical resistance can be formed.

[0040] The glass transition temperature (Tg) of the hydroxyl group-containing resin (A) may be preferably −35° C. or higher and 120° C. or lower, more preferably −30° C. or higher and 115° C. or lower, and even more preferably −30° C. or higher and 110° C. When the glass transition temperature (Tg) is within the above range, the moisture permeability of the coating film does not become excessively high, and the coating film has sufficient moisture resistance and chemical resistance.

[0041] The number-average molecular weight of the hydroxyl-containing resin (A) is preferably 1,500 or more and 5,000 or less, more preferably 2,000 or more and 4,500 or less, and even more preferably 2,000 or more and 4,000 or less. Having a number-average molecular weight within this range allows the curing reaction with the crosslinking agent (B) to proceed sufficiently, resulting in the formation of a coating film with high solvent resistance and chemical resistance. Furthermore, the crosslink density can be appropriately controlled to form a coating film with sufficient elongation, for example, a coating film with sufficient bending workability and processing adhesion. Furthermore, such a coating composition has an appropriate viscosity, resulting in good handleability.

[0042] The solid content of the hydroxyl-containing resin (A) is preferably 60 parts by mass or more and 90 parts by mass or less, more preferably 70 parts by mass or more and 85 parts by mass or less, per 100 parts by mass of the total of the solid content of the hydroxyl-containing resin (A) and the solid content of the crosslinking agent (B). When the content of the solid content of the hydroxyl-containing resin (A) is within this range, the resulting coating film can have good adhesion and scratch resistance. Hereinafter, the total of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B) will also be simply referred to as the resin solid content. In this disclosure, the solid content of a certain component means the heating residue as defined in JIS K 5601-1-2:2008, and the solid content concentration is calculated by measuring the percentage of the mass of the residue after heating at 105°C for 60 minutes to the original mass.

[0043] <Crosslinking agent (B)> The crosslinking agent (B) may typically be a compound having two or more groups per molecule that can react with the hydroxyl groups of the hydroxyl group-containing resin (A). The crosslinking agent (B) includes an amino resin (B1) and / or a blocked isocyanate (B2).

[0044] (Amino resin (B1)) The amino resin (B1) reacts with the hydroxyl-containing resin (A) to form a cured coating film. The amino resin (B1) has excellent curing reactivity with the hydroxyl-containing resin (A) and the like, and can give a coating film with good appearance and moisture resistance.

[0045] Examples of the amino resin (B1) include melamine resin, urea resin, benzoguanamine resin, etc., and melamine resin and urea resin are preferred. In particular, from the viewpoint of weather resistance, the amino resin preferably includes a melamine resin, and more preferably is a melamine resin.

[0046] "Melamine resin" generally refers to a thermosetting resin synthesized from melamine and aldehyde, and contains three reactive functional groups -NX in one triazine nucleus molecule. 1 X 2 It has the following characteristics. Examples of melamine resins include four types: a fully alkyl type containing -N(CH2OR)2 (R represents 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 reactive functional groups.

[0047] In the present invention, among the above-mentioned melamine resins, it is preferable to use a fully alkylated melamine resin, and examples of such a resin include a methylated melamine resin, a butylated melamine resin, and an isobutylated melamine resin.

[0048] As the melamine resin, commercially available products can be used, and examples thereof include Cymel 303, Cymel 325, Cymel 350, Cymel 370, Mycoat 715 (all methylated melamine resins, manufactured by Allnex Japan Co., Ltd.), Cymel 202, Cymel 235, Cymel 254, Cymel 1123, Cymel 1128, Cymel 1170, Mycoat 212 (all methyl-butylated mixed melamine resins, manufactured by Allnex Japan Co., Ltd.), Sumimal M-40S (methylated melamine resin, manufactured by Sumitomo Chemical Co., Ltd.), Amidair J-820-60, Amidair L-127-60 (all butylated melamine resins, manufactured by DIC Corporation). The amino resin (B1) may be used alone or in combination of two or more kinds.

[0049] In one embodiment, a polyester resin is used as the hydroxyl group-containing resin (A) and a melamine resin is used as the amino resin (B1).

[0050] In one embodiment, the content of the amino resin (B1) in 100% by mass of the total amount of the crosslinking agent (B) may be preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 70% by mass or more and 100% by mass or less. In another embodiment, the content of the amino resin (B1) in 100% by mass of the total amount of the crosslinking agent (B) may be 0% by mass.

[0051] In the coating composition of the present disclosure, the solid content of the hydroxyl-containing resin (A) is preferably 60 to 90 parts by mass, more preferably 70 to 80 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. The solid content of the amino resin (B1) is preferably 10 to 40 parts by mass, more preferably 20 to 30 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. By setting the hydroxyl-containing resin (A) and the amino resin (B1) within the above ranges, the curing reaction between the hydroxyl-containing resin (A) and the amino resin (B1) can proceed smoothly, and the resulting coating film can have a good appearance. Furthermore, the coating film obtained from the coating composition of the present disclosure has good solvent resistance, bending processability, processing adhesion, and chemical resistance.

[0052] (Blocked isocyanate (B2)) The blocked isocyanate (B2) is understood to be a compound (sometimes referred to as "BI") in which the isocyanate group of a polyisocyanate compound is blocked with an active hydrogen-containing compound. By including the blocked isocyanate (B2), it is possible to exhibit excellent rust prevention properties over a long period of time and further to form a coating film that exhibits excellent moisture resistance.

[0053] The polyisocyanate compound constituting the blocked polyisocyanate (B2) is not particularly limited, and conventionally known compounds can be used. Specific examples include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- or 1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (also known as isophorone diisocyanate; IPDI), dicyclohexylmethane-4,4'-diisocyanate (also known as hydrogenated MDI), 2- or 4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethane, 1,3 Examples of suitable polyisocyanate compounds include 1,4- or 1,4-bis(isocyanatomethyl)cyclohexane, bis(4-isocyanato-3-methylcyclohexyl)methane, 1,3- or 1,4-α,α,α'α'-tetramethylxylylene diisocyanate, 2,4- or 2,6-diisocyanatotoluene, 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), 1,5-naphthalene diisocyanate, p- or m-phenylene diisocyanate, xylene diisocyanate, and diphenyl-4,4'-diisocyanate. Furthermore, polyisocyanate compounds that can be used include cyclized polymers of each diisocyanate (isocyanurate type), isocyanate-biuret products (biuret type), and adduct types. The polyisocyanate compound may be used alone or in combination of two or more kinds. Isocyanurate-type polyisocyanate compounds are one of those preferably used in the present invention.

[0054] As the polyisocyanate compound, for example, it is preferable to use an aromatic polyisocyanate compound containing one or more aromatic functional groups in the molecule. By using an aromatic polyisocyanate compound, it is possible to improve the moisture resistance of the coating film and also improve the coating film strength. Examples of preferred aromatic polyisocyanate compounds include 2,4- or 2,6-diisocyanatotoluene (TDI), 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI), etc.

[0055] The isocyanate group content of the polyisocyanate compound constituting the blocked polyisocyanate compound, measured in accordance with JIS K 7301-1995, is typically 3 to 20%, and preferably 5 to 15%, of the solid content of the polyisocyanate compound. By ensuring that the isocyanate group content is within this range, the curability of the coating film is further improved. Furthermore, the crosslink density of the resulting coating film can be prevented from becoming excessively high, which can improve corrosion resistance.

[0056] The active hydrogen-containing compound (blocking agent) used in the blocked polyisocyanate (B2) is not particularly limited, and examples thereof include compounds having an -OH group (e.g., alcohols, phenols), an =N-OH group (e.g., oximes), or an =NH group (e.g., amines, amides, imides, lactams), compounds having a -CH2- group (active methylene group), and azoles. Specific examples include phenol, cresol, xylenol, ε-caprolactam, σ-valerolactam, γ-butyrolactam, methanol, ethanol, n-, i-, or t-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol, formamide oxime, acetaldoxime, acetoxime, methylethylkedoxime, diacetylmonoxime, benzophenone oxime, cyclohexane oxime, dimethyl malonate, ethyl acetoacetate, acetylacetone, and pyrazole. The active hydrogen-containing compound may be used alone or in combination of two or more kinds.

[0057] The thermal dissociation temperature of the blocked polyisocyanate (B2) depends on the type of polyisocyanate compound and active hydrogen-containing compound that constitute it, and the presence and amount of a catalyst. In the present disclosure, the thermal dissociation temperature of the blocked isocyanate (B2) (catalyst-free state) is preferably 120 to 180°C. By using a blocked polyisocyanate (B2) that exhibits a dissociation temperature within this range, the stability of the coating material can be improved, and since it has excellent crosslinking reactivity with the coating film-forming resin (A), a coating film with good moisture resistance can be obtained. Examples of blocked polyisocyanate compounds having a dissociation temperature of 120 to 180°C include Desmodur BL3175 manufactured by Sumika Covestro Urethane Co., Ltd. and Coronate 2554 manufactured by Tosoh Corporation.

[0058] In one embodiment, the content of the blocked isocyanate (B2) in 100% by mass of the total amount of the crosslinking agent (B) may be preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 70% by mass or more and 100% by mass or less. In another embodiment, the content of the blocked isocyanate (B2) in 100% by mass of the total amount of the crosslinking agent (B) may be 0% by mass.

[0059] In the coating composition of the present disclosure, the solid content of the hydroxyl-containing resin (A) is preferably 60 to 90 parts by mass, more preferably 70 to 85 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. The solid content of the blocked isocyanate (B2) is preferably 10 to 40 parts by mass, more preferably 20 to 30 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. By keeping the hydroxyl-containing resin (A) and the blocked isocyanate (B2) within the above ranges, the curing reaction between the hydroxyl-containing resin (A) and the blocked isocyanate (B2) can proceed smoothly, and the resulting coating film can have a good appearance. Furthermore, the coating film obtained from the coating composition of the present disclosure has good solvent resistance, bending processability, processing adhesion, and chemical resistance.

[0060] In the coating composition of the present disclosure, the solid content of the hydroxyl-containing resin (A) is preferably 60 to 90 parts by mass, more preferably 70 to 85 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. The solid content of the crosslinker (B) is preferably 10 to 40 parts by mass, more preferably 15 to 30 parts by mass, per 100 parts by mass of the total resin solids in the coating composition. By keeping the hydroxyl-containing resin (A) and crosslinker (B) within the above ranges, the curing reaction between the hydroxyl-containing resin (A) and crosslinker (B) can proceed smoothly, and the resulting coating film can have a good appearance. Furthermore, the coating film obtained from the coating composition of the present disclosure has good solvent resistance, bending processability, processing adhesion, and chemical resistance.

[0061] In the coating composition of the present disclosure, the resin solid content, i.e., the sum of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B), may be preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less, based on 100% by mass of the solid content of the coating composition.

[0062] <Acid catalyst (C)> The acid catalyst (C) can have the effect of increasing the reaction rate of the hydroxyl group-containing resin (A) and the crosslinking agent (B), and can be a compound containing an acid group. The acid catalyst (C) in the present disclosure has a naphthalene skeleton.

[0063] Conventionally, a coating composition containing a hydroxyl group-containing resin (A) and a crosslinking agent (B) may contain an acid catalyst (B) for the purpose of increasing the curing rate. In the present disclosure, the acid group in the acid catalyst (C) may include both a group that exists as an acid group and a group that is blocked with a blocking agent.

[0064] The acid catalyst (C) may be a compound containing an acid group itself, or a compound in which the acid group of a compound containing an acid group is blocked with a blocking agent. The naphthalene skeleton may be contained in the compound containing an acid group.

[0065] The compound containing an acid group is preferably a sulfonic acid compound. Examples of the sulfonic acid compound include aliphatic sulfonic acids such as methanesulfonic acid, and aromatic sulfonic acids such as paratoluenesulfonic acid (p-TSA), dinonylnaphthalenesulfonic acid (DNNSA), dinonylnaphthalenedisulfonic acid (DNNDSA), and dodecylbenzenesulfonic acid (DDBSA). These compounds may be used alone or in combination of two or more. In the aromatic sulfonic acid, one or more alkyl groups having 1 to 15 carbon atoms may be bonded to a carbon atom constituting the aromatic ring, more specifically, one or two alkyl groups may be bonded, for example, one alkyl group may be bonded.

[0066] In the present disclosure, aromatic sulfonic acid refers to a compound having a structure in which one or more sulfonic acid groups (e.g., one or two, specifically one sulfonic acid group) are directly bonded to an aromatic ring. Examples of the aromatic ring in aromatic sulfonic acid include a benzene ring and a naphthalene ring. The compound containing an acid group is preferably an aromatic sulfonic acid, more preferably a sulfonic acid having a naphthalene skeleton, such as dinonylnaphthalenesulfonic acid or dinonylnaphthalenedisulfonic acid.

[0067] Of the acid groups contained in the acid catalyst (C), the proportion of sulfonic acid groups may be preferably 80 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and even more preferably 95 mol% or more and 100 mol% or less, based on 100 mol% of the total amount of acid groups.

[0068] In one embodiment, the acid catalyst (C) preferably does not contain a phosphate group. Specifically, the proportion of the phosphate groups in the acid catalyst (C) is preferably 0 mol% to 10 mol%, more preferably 0 mol% to 5 mol%, and even more preferably 0 mol% to 3 mol%, based on 100 mol% of the total amount of acid groups.

[0069] Examples of commercially available products of the acid catalyst (C) include NACURE 155 (dinonylnaphthalene disulfonic acid: King Industries) and NACURE 1051 (dinonylnaphthalene sulfonic acid).

[0070] The acid catalyst (C) is preferably one in which the acid groups contained therein are blocked with a blocking agent, more preferably one in which all of the acid groups contained therein are blocked with a blocking agent. In a preferred embodiment, the acid catalyst (C) is preferably one in which the sulfonic acid groups contained therein are blocked with a blocking agent, more preferably one in which all of the sulfonic acid groups contained therein are blocked with a blocking agent.

[0071] Examples of the blocking agent for blocking the acid group of the acid catalyst (C) include amine compounds, epoxy resins, etc. Hereinafter, they are also referred to as an amine-blocked compound and a glycidyl-blocked compound of the acid catalyst (C), respectively.

[0072] The amine compound is preferably a secondary or tertiary amine having a boiling point of 50°C or higher and 250°C or lower. The secondary or tertiary amine having a boiling point of 50°C or higher and 250°C or lower is not particularly limited, and examples thereof include diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine, di-n-butylamine, diamylamine, diallylamine, di-sec-, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, 3-piperidinemethanol, triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, pyridine, N,N-dimethylallylamine, N-methylpiperidine, 4-ethylpyridine, N-methylpiperazine, N-methylmorpholine, etc. These may be used alone or in combination of two or more.

[0073] Commercially available amine-blocked compounds of the acid catalyst (C) include, for example, NACURE 3525 (amine-blocked compound of naphthalenedisulfonic acid: manufactured by King Industries) and NACURE X49-110 (amine-blocked compound of naphthalenedisulfonic acid: manufactured by King Industries). Commercially available amine-blocked compounds of the acid catalyst (C) include, for example, NACURE 3525 (amine-blocked compound of dinonylnaphthalenedisulfonic acid: manufactured by King Industries) and NACURE X49-110 (amine-blocked compound of dinonylnaphthalenedisulfonic acid: manufactured by King Industries).

[0074] The epoxy resin is not particularly limited, and may be a hydroxyl group-containing epoxy resin (including modified hydroxyl group-containing epoxy resins). Examples of the epoxy resin include a resin obtained by condensing epichlorohydrin and bisphenol to a high molecular weight, if necessary in the presence of a catalyst such as an alkali catalyst; bisphenol-type epoxy resins such as bisphenol A and bisphenol F; and novolac-type epoxy resins. Among these, bisphenol-type epoxy resins are preferred, and bisphenol A-type epoxy resins are more preferred.

[0075] Commercially available glycidyl block compounds of the acid catalyst (C) include, for example, NACURE 1419 (glycidyl block compound of dinonylnaphthalenesulfonic acid: King Industries). The use of such a blocking agent has the advantage of improving the storage stability of the coating composition.

[0076] The active ingredient of the acid catalyst (C) is preferably 0.01 to 0.5 parts by mass, more preferably 0.05 to 0.4 parts by mass, and even more preferably 0.2 to 0.4 parts by mass, relative to 100 parts by mass of the total resin solids in the coating composition. When the content of the acid catalyst (C) is within this range, the adhesion and scratch resistance of the resulting coating film can be improved. In the present disclosure, the active ingredient of the acid catalyst (C) means the portion of the acid catalyst that corresponds to the compound having an acid group, and typically does not include an amine compound that neutralizes the acid group or a blocking agent.

[0077] <Phosphate Ester Group-Containing Compound (D)> The coating composition of the present disclosure contains a phosphate ester group-containing compound (D). The phosphate ester group-containing resin may be any compound containing a phosphate ester group, and examples thereof include resins containing a phosphate ester group in the side chain and alkyl phosphate ester compounds.

[0078] The phosphate value of the phosphate ester group-containing compound (D) may be preferably from 20 mgKOH / g to 250 mgKOH / g, more preferably from 50 mgKOH / g to 200 mgKOH / g, and even more preferably from 75 mgKOH / g to 150 mgKOH / g. When the phosphate value of the phosphate ester group-containing compound (D) is within this range, the adhesion and scratch resistance of the resulting coating film can be improved.

[0079] The structure of the phosphate ester group-containing compound (D) is not particularly limited. Examples of the phosphate ester group-containing resin include acrylic resins having phosphate ester groups, polyester resins having phosphate ester groups, polyether resins having phosphate ester groups, epoxy resins having phosphate ester groups, styrene resins having phosphate ester groups, urethane resins having phosphate ester groups, and alkyl phosphate ester compounds. Among these, from the viewpoint of weather resistance and water resistance, it is preferable to use acrylic resins having phosphate ester groups. These polymers containing phosphate groups may be used alone or in combination of two or more.

[0080] The acrylic resin having a phosphate ester group can be obtained, for example, by polymerizing only the phosphate ester group-containing monomer, with the phosphate ester group-containing monomer being an essential component, or by copolymerizing a mixture of the phosphate ester group-containing monomer and another monomer.

[0081] Examples of the phosphate ester group-containing monomer include 2-acryloyloxyethyl acid phosphate, 2-(methacryloyloxy)ethyl phosphate (also known as acid phosphooxyethyl methacrylate, Phosmer M, manufactured by Unichemical Co., Ltd.), 3-chloro-2-acid phosphooxypropyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate (Phosmer PE, manufactured by Unichemical Co., Ltd.), acid phosphooxypolyoxypropylene glycol monomethacrylate (Phosmer PP, manufactured by Unichemical Co., Ltd.), and vinylphosphonic acid.

[0082] Examples of the monomer not containing a phosphate group include (meth)acrylic acid esters, monomers having an acid group, monomers having a hydroxyl group, and other monomers not containing these groups. As the (meth)acrylic acid esters, monomers having an acid group, monomers having a hydroxyl group, and other monomers, any of the compounds exemplified as the monomers used in the production of the acrylic resin can be used. In preparing the phosphate group-containing acrylic resin, these α,β-ethylenically unsaturated monomers not containing a phosphate group can be appropriately selected and used.

[0083] The phosphate ester group-containing acrylic resin can be produced, for example, by (co)polymerizing the phosphate group-containing monomer alone, or a monomer mixture containing the phosphate group-containing monomer and another monomer not containing a phosphate group, using a commonly used method. For example, the phosphate ester group-containing acrylic resin can be prepared by polymerizing the monomer mixture using a polymerization initiator in the presence of an organic solvent, if necessary. The polymerization initiator may be the same as that used in preparing an acrylic resin emulsion. Examples of organic solvents that may be used as needed include ketones such as cyclohexanone and methyl 2-n-amyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono tert-butyl ether acetate.

[0084] The reaction temperature in the (co)polymerization may be, for example, 80 to 150° C., and the reaction time may be, for example, 1 to 8 hours.

[0085] The alkyl phosphate ester compound includes alkyl phosphate esters having an alkyl group having 4 to 30 carbon atoms. Examples of alkyl phosphate compounds having an alkyl group having 4 to 30 carbon atoms include monoalkyl phosphates, dialkyl phosphates, and mixtures of monoalkyl phosphates and dialkyl phosphates. In dialkyl phosphates, it is more preferable that the two alkyl groups are the same group.

[0086] Examples of alkyl groups having 4 to 30 carbon atoms include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, docosyl, tetracosyl, hexacosyl, and octacosyl groups. These alkyl groups may be linear or branched.

[0087] Specific examples of alkyl phosphate ester compounds having an alkyl group having 4 to 30 carbon atoms include butyl acid phosphate (a mixture of monobutyl ester and dibutyl ester), 2-ethylhexyl acid phosphate (a mixture of mono-2-ethylhexyl ester and di-2-ethylhexyl ester), isodecyl acid phosphate (a mixture of monoisodecyl ester and diisodecyl ester), dilauryl acid phosphate, and lauryl acid phosphate (a mixture of monolauryl ester and dilauryl ester). ), tridecyl acid phosphate (a mixture of monotridecyl ester and ditridecyl ester), monostearyl acid phosphate, distearyl acid phosphate, stearyl acid phosphate (a mixture of monostearyl ester and distearyl ester), isostearyl acid phosphate (a mixture of monoisostearyl ester and diisostearyl ester), oleyl acid phosphate (a mixture of monooleyl ester and dioleyl ester), behenyl acid phosphate (a mixture of monobehenyl ester and dibehenyl ester), and the like.

[0088] The number average molecular weight of the phosphate ester group-containing compound (D) may be preferably 300 or more and 7,000 or less, more preferably 1,000 or more and 5,000 or less, and even more preferably 1,500 or more and 3,500 or less.

[0089] In the present disclosure, the phosphate value of the phosphate ester group-containing compound (D) is a calculated phosphate value calculated in accordance with the definition of acid value in JIS K5601 2-1 (the number of milligrams of potassium hydroxide (KOH) required to neutralize free acid in 1 g of nonvolatile matter of the product).

[0090] The phosphate ester group-containing resin may be a phosphate ester group-containing resin other than the phosphate ester group-containing acrylic resin. Examples of such phosphate ester group-containing resins include AQ-330 (manufactured by Kusumoto Chemicals Co., Ltd., phosphate value: 12 mg KOH / g), AQ-320 (manufactured by Kusumoto Chemicals Co., Ltd., phosphate value: 14 mg KOH / g), and AQ-340 (manufactured by Kusumoto Chemicals Co., Ltd., phosphate value: 18 mg KOH / g), which are phosphate ester surfactants having polyalkylene oxide groups; Examples of lubricating and dispersing agents include BYK-111 (manufactured by BYK-Chemie, phosphate value: 120 mg KOH / g), BYK-180 (manufactured by BYK-Chemie, phosphate value: 90 mg KOH / g), LUBIRIZOL2061H (manufactured by Lubrizol Corporation, phosphate value: 83 mg KOH / g), and ETERKYD4901-B-72 (manufactured by Eternal Materials, phosphate value: 30 mg KOH / g).

[0091] The content of the phosphate ester group-containing resin may be preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on 100% by mass of the total amount of the phosphate ester group-containing compound (D).

[0092] The solid content of the phosphate ester group-containing compound (D) is preferably 0.5 to 5 parts by mass, more preferably 1 to 4 parts by mass, and even more preferably 1.5 to 3.5 parts by mass, relative to 100 parts by mass of the total resin solid content in the coating composition. When the content of the phosphate ester group-containing compound (D) is within this range, the resulting coating film can have good adhesion, scratch resistance, and water resistance.

[0093] <Other resins> The coating composition may contain other resins used in the coating composition field, provided that the effects achieved by the present disclosure are not impaired. Examples of other resins include polyester resins and modified products thereof (urethane-modified polyester resins, epoxy-modified polyester resins, silicone-modified polyester resins, etc.) other than those mentioned above; urethane resins and modified products thereof (ester-based urethane resins, ether-based urethane resins, carbonate-based urethane resins, epoxy-based urethane resins, etc.); phenolic resins and modified products thereof (acrylic-modified phenolic resins, epoxy-modified phenolic resins, etc.); phenoxy resins; alkyd resins and modified products thereof (urethane-modified alkyd resins, acrylic-modified alkyd resins, etc.); and fluororesins. These resins may be used alone or in combination of two or more.

[0094] <Other additives> The coating composition of the present disclosure may contain additives other than those described above, as necessary. Other additives include, for example, extender pigments, anti-rust pigments, colorants such as coloring pigments and dyes, luster pigments, aggregates (resin particles, silica particles, etc.), waxes, solvents, ultraviolet absorbers (benzophenone-based ultraviolet absorbers, etc.), antioxidants (phenolic, sulfoid, hindered amine antioxidants, etc.), plasticizers, coupling agents (silane-based, titanium-based, zirconium-based coupling agents, etc.), anti-sagging agents, thickeners, pigment dispersants, pigment wetting agents, surface conditioners (silicone-based, organic polymer-based, etc.), leveling agents, color separation inhibitors, precipitation inhibitors, antifoaming agents, antifreeze agents, emulsifiers, preservatives, mildew inhibitors, antibacterial agents, stabilizers, etc. These additives may be used alone or in combination of two or more.

[0095] Examples of extender pigments include calcium carbonate, barium sulfate, clay, talc, mica, glass fiber, etc. These may be used alone or in combination of two or more. In one embodiment, the amount of the extender pigment is preferably 1 part by mass or more and 40 parts by mass or less, for example, 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the total resin solids in the coating composition. Having the amount of the extender pigment within this range has advantageous effects such as improving the scratch resistance of the coating film.

[0096] Examples of anti-rust pigments include strontium chromate, molybdate pigments (such as zinc molybdate and strontium molybdate), phosphomolybdate pigments (such as aluminum phosphomolybdate pigments), calcium silica pigments, phosphate anti-rust pigments, silicate anti-rust pigments, vanadate anti-rust pigments, and hydroxides or oxides of secondary elements such as calcium hydroxide and magnesium oxide. These may be used alone or in combination of two or more. In one embodiment, the amount of the anti-rust pigment is preferably 1 part by mass or more and 50 parts by mass or less, for example, 20 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the total resin solid content in the coating composition. When the amount of the anti-rust pigment is within this range, advantageous effects such as improved corrosion resistance of the coating film can be achieved.

[0097] 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. These may be used alone or in combination of two or more.

[0098] In one embodiment, the coating composition may contain a heat-shielding pigment. The heat-shielding pigment used is not particularly limited, and examples thereof include the following heat-shielding pigments. In the present disclosure, the heat-shielding pigment refers to a pigment that does not absorb light in the near-infrared wavelength region (wavelength: 780 nm to 2,500 nm) or has a low absorptivity for light in the near-infrared wavelength region (wavelength: 780 nm to 2,500 nm).

[0099] The heat-shielding pigment includes inorganic heat-shielding pigments and organic heat-shielding pigments. Examples of inorganic heat-shielding pigments include metal oxide pigments such as titanium oxide, magnesium oxide, barium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, indium oxide, sodium titanate, silicon oxide, nickel oxide, manganese oxide, chromium oxide, iron oxide, copper oxide, cerium oxide, and aluminum oxide; iron oxide-manganese oxide, iron oxide-chromium oxide (e.g., Dipyroxide Color Black #9595 manufactured by Dainichi Seika Chemicals Co., Ltd., and Black 6350 manufactured by Asahi Kasei Kogyo Co., Ltd.), iron oxide-cobalt oxide-chromium oxide (e.g., Dipyroxide Color Brown manufactured by Dainichi Seika Chemicals Co., Ltd.), and Examples of suitable pigments include composite oxide pigments such as copper oxide-magnesium oxide (e.g., Dipyroxide Color Black #9290, Dipyroxide Color Black #9590 manufactured by Dainichiseika Chemicals), manganese oxide-bismuth oxide (e.g., Black 6301 manufactured by Asahi Kasei Kogyo Co., Ltd.), and manganese oxide-yttrium oxide (e.g., Black 6303 manufactured by Asahi Kasei Kogyo Co., Ltd.); metal pigments such as silicon, aluminum, iron, magnesium, manganese, nickel, titanium, chromium, and calcium; and alloy pigments such as iron-chromium, bismuth-manganese, iron-manganese, and manganese-yttrium. These pigments may be used alone or in combination of two or more. Examples of organic heat-shielding pigments include azo pigments, azomethine pigments, lake pigments, thioindigo pigments, anthraquinone pigments (such as anthranthrone pigments, diaminoanthraquinonyl pigments, indanthrone pigments, flavanthrone pigments, and anthrapyrimidine pigments), perylene pigments, perinone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, phthalocyanine pigments, quiniphthalone pigments, quinacridone pigments, isoindoline pigments, and isoindolinone pigments. These pigments can be used alone or in combination of two or more.

[0100] 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, foil pigment such as foil-like phthalocyanine blue, etc. These may be used alone or in combination of two or more.

[0101] As the wax, waxes known to those skilled in the art for use in paints can be used, such as microcrystalline, polyethylene, polypropylene, paraffin, carnauba, and modified products thereof, etc. These may be used alone or in combination of two or more.

[0102] Examples of solvents 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, and isopropyl alcohol; 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, T-SOL 100, T-SOL 150 (all aromatic hydrocarbon solvents, manufactured by JXTG Nippon Oil & Energy Corporation). These may be used alone or in combination of two or more.

[0103] The coating composition of the present invention may be a water-based coating or an organic solvent-based coating.

[0104] In the coating composition of the present disclosure, the proportion of solids may be preferably 20% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 85% by mass or less, based on 100% by mass of the total amount of the coating composition.

[0105] [Method for preparing coating composition] The method for preparing the coating composition according to the present disclosure is not particularly limited. For example, the coating composition can be prepared by mixing the components using a mixer, disperser, kneader, or the like, such as a roller mill, ball mill, bead mill, pebble mill, sand grind mill, pot mill, paint shaker, or disperser.

[0106] [Coating film manufacturing method] The method for producing a coating film according to the present disclosure includes: A step of applying the coating composition of the present disclosure to an object to be coated to form a coating film; and The method includes a step of drying and / or curing the coating film under conditions in which the temperature of the coated object reaches 180°C to 270°C and the drying and / or curing time is 10 to 60 seconds.

[0107] Examples of substrates include steel sheets, 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 a hot-dip method or an electrolytic method. 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 coating targets.

[0108] The substrate is preferably surface-treated. Specifically, the substrate is preferably subjected to a pretreatment such as alkaline degreasing, hot water washing, or water washing, and then a chemical conversion treatment. The chemical conversion treatment may be carried out by a known method, and examples thereof include chromate treatment and non-chromate treatment such as zinc phosphate 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. By applying the coating composition of the present disclosure to a substrate that has been subjected to such a chemical conversion treatment, the adhesion of the coating film to the metal sheet surface and the corrosion resistance are improved.

[0109] The method for applying the coating composition is not particularly limited, but any conventionally known method such as a roll coater, airless spray, electrostatic spray, or curtain flow coater can be used, and it is preferable to apply the coating composition using a roll coater or curtain flow coater.

[0110] In one embodiment, the coating composition of the present disclosure can form a single layer coating film (also referred to as one coat). In another embodiment, the coating composition of the present disclosure can be used as an undercoat coating composition, for example, when forming a multi-layer coating film consisting of two layers, an undercoat coating film and a topcoat coating film. This can be done by applying the undercoat coating composition and then baking it, and then applying the topcoat coating composition and baking the topcoat coating film, or by applying the undercoat coating composition and then applying the topcoat coating composition wet-on-wet without baking it, and simultaneously baking it.

[0111] The temperature at which the coating film formed by applying the coating composition is dried and / or cured, i.e., the ultimate temperature (the maximum temperature reached by the substrate such as a steel plate), is 180° C. to 270° C., and may be 200° C. to 250° C. The drying and / or curing time can be, for example, 10 to 60 seconds. The method for drying and / or curing the coating film is not particularly limited, but heating means such as hot air heating, infrared heating, and induction heating can be used.

[0112] The coating film obtained by baking the coating film and curing the resin (dry film thickness) is usually 1 to 30 μm, and for example, in the case of a primer coating film, the thickness is preferably 2 to 15 μm, and in the case of a one-coat coating film, the thickness is preferably 5 to 25 μm.

[0113] [Pre-coated metal sheet] The precoated metal sheet of the present disclosure has a coating film formed from the coating composition according to the present disclosure on at least one surface of the metal sheet. For example, the thickness of a coating film formed from a coating composition according to the present disclosure is 1 μm or more and 30 μm or less, and in one embodiment, the thickness is 5 μm or more and 25 μm or less. As the metal plate, the above-mentioned substrates can be used.

[0114] When a precoated metal sheet has a coating film formed from the coating composition according to the present disclosure on one side of the metal sheet, the other side may have a coating film formed from a known coating composition, such as a coating composition containing an epoxy resin.

[0115] In one embodiment, the precoated metal sheet of the present disclosure comprises: A step of applying the coating composition of the present disclosure to at least one surface of a metal plate so that the film thickness after curing is 5 to 25 μm to form a coating film; The coating film can be produced by a method including a step of drying and / or curing the metal plate at a temperature of 180°C to 270°C for a drying and / or curing time of 1 to 10 seconds. In the method for producing a precoated metal sheet, the formation of the coating film, and the drying and / or curing of the coating film can be carried out in the same manner as in the method for producing a coating film described above. [Example]

[0116] The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0117] Table 1 shows the details of the hydroxyl-containing resins (A1) to (A4) used in the examples, comparative examples, and reference examples.

[0118] [Table 1] The hydroxyl group-containing resin (A4) (epoxy resin 1) used was prepared by dissolving 90 parts by mass of jER1007 (manufactured by Mitsubishi Chemical Corporation; solid content: 100% by mass) in 210 parts by mass of cyclohexanone to adjust the solid content to 30% by mass.

[0119] <Crosslinking agent (B)> Details of the amino resin (B1) and the blocked isocyanate (B2) are as shown in Table 2.

[0120] [Table 2]

[0121] The properties of the acid catalyst (C) are shown in Table 3.

[0122] [Table 3]

[0123] <Preparation Example of Phosphate Ester Group-Containing Compound (D)> A reaction vessel equipped with a thermometer, condenser, dropping funnel, and stirrer was charged with 48 parts by weight of ethoxypropanol and heated to 120°C under a nitrogen atmosphere. A monomer solution consisting of a mixed solution (36 parts by weight) of 5 parts by weight of styrene, 59 parts by weight of n-butyl acrylate, 20 parts by weight of 2-ethylhexyl acrylate, and 16 parts by weight of Phosmer M dissolved in 20 parts by weight of ethoxypropanol and 3.4 parts by weight of azobisisobutyronitrile as a reaction initiator was added dropwise through the dropping funnel at a constant rate over 3 hours. The reaction mixture was then maintained at 120°C for 1 hour to prepare a phosphate ester group-containing compound (D1) (phosphoric acid value: 100 mgKOH / g, number average molecular weight: 3,000, solids concentration: 60% by weight).

[0124] <Preparation Examples of Phosphate Ester Group-Containing Compounds (D2) to (D9)> Phosphate ester group-containing compounds (D2) to (D9) were prepared in the same manner as in Preparation Example (D1), except that the type and amount of each component was changed as shown in the table. Table 4 shows the properties of each component and the prepared phosphate ester group-containing compounds (D1) to (D9).

[0125] [Table 4]

[0126] The compounds listed in Table 4 are as follows: Phosmer M: 2-(methacryloyloxy)ethyl phosphate (manufactured by Unichemical Co., Ltd.)

[0127] <Phosphate Ester Group-Containing Compounds (D10) and (D11)> In addition to the above, details of the phosphate ester group-containing compounds used in the examples and comparative examples are as follows. Phosphate ester group-containing compound (D10): BYK-111 (phosphate ester type wetting and dispersing agent having a polyalkylene oxide group), manufactured by BYK-Chemie; phosphate value: 120 mg KOH / g, solid content: 95% by mass Phosphate ester group-containing compound (D11): Lubrizol 2061 (epoxy-functional phosphate ester compound), manufactured by Lubrizol Corporation; phosphate value: 83 mg KOH / g, solid content: 66% by mass [others] Solvent: Ethoxypropanol, manufactured by Tokyo Chemical Industry Co., Ltd.

[0128] Example 1 107.7 parts by mass of the hydroxyl group-containing resin (A1), 50.0 parts by mass of cyclohexanone as a solvent, 50.0 parts by mass of T-SOL 100, and 40.0 parts by mass of Magseeds EP-1 as a pigment were stirred and mixed in a disper to obtain a mixture. Next, the entire mixture and glass beads (same amount as the total mass of the mixture) were placed in a tabletop SG Mill 1500W disperser (manufactured by Ohira System Co., Ltd.), and the pigment was dispersed until the particle diameter of the pigment became 10 μm or less, thereby preparing a pigment dispersion paint. Furthermore, 30 parts by mass of a crosslinking agent (B1), 1.2 parts by mass of an acid catalyst (C1), and 5.0 parts by mass of a phosphate ester resin (D1) were added to 179.5 parts by mass of the pigment dispersion paint, and the mixture was stirred and mixed with a disper to obtain a paint composition. The resulting coating composition was diluted with a mixed solution of cyclohexanone / T-SOL 100=1 / 1 so as to have a viscosity of 100 seconds (25° C.) in a Ford cup No. 4, thereby obtaining coating composition 1.

[0129] <Examples 2 to 20 and Comparative Examples 1 to 8> Each coating composition was prepared in the same manner as in Example 1, except that the type and amount of each component was changed as shown in Tables 5 to 7.

[0130] The other materials listed in Table 5 are as follows: Solvent: Cyclohexanone, manufactured by Shoei Chemical Co., Ltd. Solvent: T-SOL 100 (aromatic hydrocarbon solvent), manufactured by Eneos Corporation Anti-rust pigment (E1): Magseeds EP-1 (magnesium hydroxide), manufactured by Konoshima Chemical Co., Ltd. Catalyst: TVS#Tin Lau (dibutyltin dilaurate), manufactured by Nitto Kasei Co., Ltd.; Active ingredient concentration: 100% by mass Silane coupling agent: KBM-403 (3-glycidoxypropyltriethoxysilane), manufactured by Shin-Etsu Chemical Co., Ltd.; active ingredient concentration: 100% by mass

[0131] <Preparation Example of Coated Steel Sheet of Example 1> After alkaline degreasing of a 0.4 mm thick hot-dip galvanized steel sheet, a phosphate treatment agent, Surfcoat EC2310 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.), was applied to the front and back surfaces of the steel sheet to perform a non-chrome chemical conversion treatment, and the steel sheet was then dried. Next, Coating Composition 1 was applied to the surface of the steel plate using a bar coater to a dry coating thickness of 5 μm, and the plate was baked for 30 seconds at a maximum temperature of 210°C to form a surface primer coating. Furthermore, Nippe Super Coat 300HQ (Nippon Paint Industrial Coatings; polyester topcoat) was applied as a topcoat using a bar coater to a dry coating thickness of 10 μm, and the plate was baked for 40 seconds at a maximum temperature of 210°C to obtain a coated steel plate.

[0132] <Preparation Examples of Examples 2 to 20 and Comparative Examples 1 to 8> The coated steel sheets of Examples 2 to 20 and Comparative Examples 1 to 8 were prepared in the same manner as in Example 1 for preparing coated steel sheets.

[0133] <Evaluation items> 1) Coating appearance The appearance of the coating films obtained in the examples and comparative examples was visually observed, and the degree of striating was evaluated according to the following criteria. ○: No streaks appear on the coating film. △: Very slight streaks appear on the coating film. ×: Streaks appear on the entire coating film.

[0134] 2) Scratch resistance (scratch resistance test) At room temperature of 23°C, a coin scratch tester (manufactured by Nippon Paint Co., Ltd.) was used to scratch the coated surface of each test plate obtained in the Examples and Comparative Examples by pressing the edge of a 10-yen copper coin at a 45-degree angle with a load of 3 kg while pulling the coin 50 mm at a speed of 10 mm / sec, creating five scratches on the coated surface. The degree of exposure of the metal (coated steel plate test piece) relative to the total scratch area was evaluated according to the following criteria. A score of 3 or higher was evaluated as good. 5: No metal base is visible in the scratched area. 4: Metallic base is visible in less than 10% of the scratch area. 3: The metal base is visible in more than 10% but less than 25% of the area of ​​the scratch. 2: The metal base is visible over 25% but less than 50% of the area of ​​the scratch. 1: Metallic base material is visible over 50% but less than 75% of the area of ​​the scratch. 0: Almost no paint film remains in the scratched area, revealing the metal base.

[0135] 3) Alkali resistance The coated steel plates obtained in the Examples and Comparative Examples were cut into 5 cm x 10 cm pieces. Each specimen was immersed in a 5% aqueous sodium hydroxide solution at 23°C for 48 hours, removed, washed with water, and then dried at 20°C for 2 hours. The coated steel plate specimens were evaluated for blistering on the flat surface in accordance with ASTM D714-56. ASTM D714-56 evaluates the size (average diameter) and density of each blister by comparing it with a standard photograph and assigns a grade symbol. Size is graded into four levels: 8 (approximately 1 mm diameter), 6 (approximately 2 mm diameter), 4 (approximately 3 mm diameter), and 2 (approximately 5 mm diameter). Density is graded into five levels: F, FM, M, MD, and D, from smallest to largest. A grade of 10 indicates no blistering. A grade of 8FM or higher is considered a pass.

[0136] 4) Boiling water resistance The coated steel plates obtained in the examples and comparative examples were cut into 5 cm x 10 cm pieces, and each test piece was immersed in boiling water at approximately 100°C for 24 hours, then removed and the surface appearance of the coating film was evaluated for blistering on the flat surface in accordance with ASTM D714-56. The evaluation criteria were the same as those for the evaluation method of alkali resistance described above.

[0137] [Table 5]

[0138] [Table 6]

[0139] [Table 7]

[0140] Examples 1 to 20 are examples of the present invention, and were all good in terms of paint appearance, scratch resistance, alkali resistance, and boiling water resistance.

[0141] Comparative Example 1 is an example in which the phosphate ester group-containing compound (D) was not contained, and the scratch resistance of the resulting coating film was not fully satisfactory. Comparative Example 2 is an example in which the acid catalyst (C) was not included, and the scratch resistance of the resulting coating film was not fully satisfactory. Comparative Example 3 is an example that did not contain either the acid catalyst (C) or the phosphate ester group-containing compound (D), and the scratch resistance, alkali resistance, and boiling water resistance of the resulting coating film were not fully satisfactory. Comparative Example 4 is an example in which the content of the active ingredient of the acid catalyst (C) exceeded 0.5 parts by mass, and the alkali resistance and boiling water resistance of the resulting coating film were not fully satisfactory. Comparative Example 5 is an example in which the solid content of the phosphate ester group-containing compound (D) exceeded 5 parts by mass, and the alkali resistance and boiling water resistance of the resulting coating film were not fully satisfactory. Comparative Examples 6 and 7 are examples in which an acid catalyst not having a naphthalene skeleton was used as the acid catalyst, and the scratch resistance of the resulting coating film was not fully satisfactory. Comparative Example 8 is an example in which a silane coupling agent was used instead of the acid catalyst (C) and the phosphate ester group-containing compound (D), and the scratch resistance of the resulting coating film was not fully satisfactory. [Industrial Applicability]

[0142] The coating composition of the present disclosure can prepare a coating film with good adhesion (scratch resistance). The coating composition of the present disclosure can be suitably used for pre-coated steel sheets, particularly pre-coated steel sheets used for construction components such as shutters, ceiling doors, doors, roofs, and siding; exterior materials for electrical equipment such as outdoor units of air conditioners; and interior materials.

Claims

1. The composition comprises a hydroxyl group-containing resin (A), a crosslinking agent (B), an acid catalyst (C) having a naphthalene skeleton, and a phosphate group-containing compound (D), the crosslinking agent (B) contains an amino resin (B1) and / or a blocked isocyanate (B2), relative to 100 parts by mass of the total of the solid content of the hydroxyl group-containing resin (A) and the solid content of the crosslinking agent (B), the solid content of the hydroxyl group-containing resin (A) is 60 parts by mass or more and 90 parts by mass or less, the amount of the active ingredient of the acid catalyst (C) containing a naphthalene skeleton is 0.01 parts by mass or more and 0.5 parts by mass or less, A coating composition, wherein the solid content of the phosphate ester group-containing compound (D) is 0.5 parts by mass or more and 5 parts by mass or less.

2. 2. The coating composition according to claim 1, wherein the acid of the acid catalyst (C) is a sulfonic acid.

3. 2. The coating composition according to claim 1, wherein the acid of the acid catalyst (C) is a disulfonic acid.

4. 2. The coating composition according to claim 1, wherein the phosphate group value of the phosphate ester group-containing compound (D) is 50 mgKOH / g or more and 200 mgKOH / g or less.

5. 2. The coating composition according to claim 1, wherein the number average molecular weight of the phosphate ester group-containing compound (D) is 300 or more and 5,000 or less. paint composition

6. The coating composition of claim 1 further comprising an anti-rust pigment (E).

7. 2. The coating composition of claim 1, wherein the anti-rust pigment (E) comprises magnesium hydroxide.

8. A step of applying the coating composition according to any one of claims 1 to 7 to at least one surface of a metal plate so that the film thickness after curing is 1 to 30 μm to form a coating film; A method for producing a precoated metal sheet, comprising a step of drying and / or curing the coating film at a temperature of the metal sheet reached by 180°C to 270°C.

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