Coating composition

Abstract

According to the present invention, a coating composition contains a prescribed amount of each of a polyester resin (A) that has a glass transition temperature of 30°C–80°C, a resol phenol resin (B), an acid catalyst (C), and an organic solvent component (D) that contains, as essential components, a hydrocarbon solvent (D1) that has a boiling point of at least 130°C, a ketone solvent (D2) that has a boiling point of at least 110°C, and an alcohol solvent (D3) that has a boiling point of at least 75°C.

Description

paint composition

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

[0002] As paints for the inner surface of cans, various paint compositions such as epoxy-based, polyvinyl chloride-based and polyester-based paints have been used from the viewpoints of coating film performance such as corrosion resistance and ease of painting.

[0003] In particular, coating compositions containing, as a base resin, an epoxy resin produced using raw materials containing bisphenol A and the like have been widely and generally used.

[0004] However, from the viewpoint of environmental impact, there is a demand for a coating composition for the inner surface of a can that does not use raw materials containing bisphenol A (BPA) (including raw materials that may contain residual levels of BPA). For example, Patent Document 1 discloses a polyester-acrylic resin-based thermosetting coating, Patent Document 2 discloses a coating containing a polyester resin and a phenolic resin, and Patent Document 3 discloses a coating containing a mixture of two types of polyester resins having specific glass transition temperatures, a crosslinking agent, and a curing catalyst.

[0005] Although the coating films obtained from these paints have excellent coating film performance, such as workability, required for use on the inner surface of cans, when used on the inner surface of can lids, there are problems in that the appearance of the coating film is insufficient depending on the coating curing conditions, and workability may decrease due to deterioration over time.

[0006] JP 2000-290585 A JP 2001-131470 A JP 2013-249376 A

[0007] The problem to be solved by the present invention is to provide a coating composition that does not use raw materials containing legally restricted substances such as bisphenol A, and that has excellent scratch resistance, processability, and coating film appearance, and is particularly suitable for use on the inner surfaces of can lids.

[0008] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by a coating composition containing a polyester resin having a glass transition temperature within a specific range, a resol-type phenolic resin, a curing catalyst, and an organic solvent component that satisfies specific requirements, and have thus completed the present invention.

[0009] Specifically, the present invention provides a coating composition containing a polyester resin (A) having a glass transition temperature of 30°C to 80°C, a resol phenolic resin (B), an acid catalyst (C), and an organic solvent component (D) containing as essential components a hydrocarbon solvent (D1) having a boiling point of 130°C or higher, a ketone solvent (D2) having a boiling point of 110°C or higher, and an alcohol solvent (D3) having a boiling point of 75°C or higher, wherein the coating composition contains 70 to 99 mass% of the polyester resin (A), 1 to 30 mass% of the resol phenolic resin (B), 0.1 to 5.0 mass% of the acid catalyst (C), and 100 to 600 mass% of the organic solvent component (D) relative to the total solids content of the polyester resin (A) and the resol phenolic resin (B).

[0010] The present invention also provides a coated metal sheet having a cured coating film of the above coating composition.

[0011] The present invention also provides a coated metal can having a cured coating film of the above coating composition on at least a portion of the can surface.

[0012] The coating composition of the present invention does not require the use of raw materials containing legally restricted substances such as bisphenol A, and provides a coating composition that is excellent in scratch resistance, processability, and coating film appearance, and is particularly suitable for use on the inner surfaces of can lids.

[0013] The present invention relates to a coating composition (hereinafter sometimes simply referred to as the present coating composition) characterized by containing a polyester resin (A) having a glass transition temperature of 30°C to 80°C, a resol-type phenolic resin (B), an acid catalyst (C), and an organic solvent (D) containing as essential components a hydrocarbon solvent (D1) having a boiling point of 130°C or higher, a ketone solvent (D2) having a boiling point of 110°C or higher, and an alcohol solvent (D3) having a boiling point of 75°C or higher, in amounts that satisfy specified quantitative requirements.

[0014] The present invention will be described in detail below. <Paint composition> Polyester resin (A) In this paint, the polyester resin, component (A), is a polyester resin containing hydroxyl groups, and may be any of oil-free polyester resin, alkyd resin, or modified products of these resins, such as urethane-modified polyester resin, urethane-modified alkyd resin, etc. Of these, oil-free polyester resin is preferably used. Oil-free polyester resin refers to a polyester resin that does not contain fatty acids.

[0015] The oil-free polyester resin is mainly an ester of a polybasic acid and a polyhydric alcohol.

[0016] The polybasic acid is primarily one or more dibasic acids selected from, for example, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, hexahydroterephthalic acid, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, etc. Instead of or in addition to the dibasic acid, a trivalent or higher polybasic acid such as trimellitic anhydride, methylcyclohexene tricarboxylic acid, pyromellitic anhydride, etc. These polybasic acids can be used alone or in combination of two or more.

[0017] If necessary, monobasic acids such as benzoic acid, crotonic acid, and pt-butylbenzoic acid can be used in combination with polybasic acids.

[0018] As the polyhydric alcohol, for example, dihydric alcohols such as ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, and 1,4-dimethylolcyclohexane are mainly used. Instead of or in addition to the dihydric alcohol, trihydric or higher polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol can also be used. These polyhydric alcohols can be used alone or in combination. The esterification reaction of both the polybasic acid and the polyhydric alcohol components can be carried out by known methods.

[0019] The oil-free polyester resin can also be obtained by carrying out a transesterification reaction using a lower alkyl ester of a polybasic acid (e.g., methyl ester, ethyl ester, etc.) instead of the polybasic acid in the esterification reaction. The transesterification reaction of both the lower alkyl ester of a polybasic acid and the polyhydric alcohol can be carried out by a known method.

[0020] In the oil-free polyester resin, it is preferable that the proportion of aromatic dicarboxylic acids among the dibasic acids is 80 to 100 mol %, and that the proportion of terephthalic acid among the aromatic dicarboxylic acids is 40 to 100 mol %.

[0021] An alkyd resin is a resin obtained by reacting an oil fatty acid with the acid component and alcohol component of the oil-free polyester resin by a known method. Examples of the oil fatty acid include coconut oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, safflower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and tung oil fatty acid.

[0022] The urethane-modified polyester resin is a resin obtained by reacting the above-mentioned oil-free polyester resin or a low-molecular-weight oil-free polyester resin obtained by reacting an acid component and an alcohol component during the production of the above-mentioned oil-free polyester resin, with a polyisocyanate compound by a known method.

[0023] The urethane-modified alkyd resin is a resin obtained by reacting the above-mentioned alkyd resin or a low-molecular-weight alkyd resin obtained by reacting the components used in producing the above-mentioned alkyd resin with a polyisocyanate compound by a known method. Examples of polyisocyanate compounds used in producing the urethane-modified polyester resin or urethane-modified alkyd resin include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 2,4,6-triisocyanatotoluene.

[0024] In the present invention, the polyester resin (A) has a glass transition temperature (hereinafter sometimes abbreviated as "Tg point") of 30 to 80°C, and preferably in the range of 40 to 65°C. If the Tg point is less than 30°C, it is not preferable in terms of scratch resistance. If the Tg point is more than 80°C, it is not preferable in terms of processability.

[0025] The number average molecular weight of the polyester resin (A) is preferably within the range of 3,000 to 100,000, more preferably within the range of 8,000 to 50,000, and even more preferably within the range of 10,000 to 30,000. The hydroxyl value of the polyester resin (A) is preferably 0.5 to 40 mgKOH / g, and more preferably 3 to 20 mgKOH / g. The acid value of the polyester resin (A) is preferably 20 mgKOH / g or less, more preferably 10 mgKOH / g or less, and even more preferably 2 mgKOH / g or less. These ranges are suitable from the viewpoints of ease of handling of the polyester resin, processability and hardness of the resulting coating film, etc.

[0026] The polyester resin (A) may be used alone or in combination of two or more kinds.

[0027] In this specification, the Tg point is measured by differential thermal analysis (DSC) using a differential scanning calorimeter, and the number average molecular weight is measured by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene according to the molecular weight measurement method described below.

[0028] (Molecular Weight Measurement Method) The number average molecular weight is a value obtained by converting the retention time (retention volume) measured using tetrahydrofuran as a solvent with a gel permeation chromatograph ("HLC8120GPC" manufactured by Tosoh Corporation) based on the number average molecular weight of polystyrene. Four columns, "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000XL" (all manufactured by Tosoh Corporation, trade names), were used, and the measurement was carried out under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 ml / min, detector: RI.

[0029] Resole-type phenolic resin (B) The resol-type phenolic resin, which is component (B) in the present coating material, is blended as a crosslinking agent to undergo a crosslinking reaction with the polyester resin (A) and harden.

[0030] The resol type phenolic resin is a resin obtained by condensation reaction of a phenol component and a formaldehyde component in the presence of an alkali catalyst.

[0031] Examples of the phenol component include difunctional phenols such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol; trifunctional phenols such as m-cresol, phenol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol; and tetrafunctional phenols such as bisphenol A and bisphenol F. These may be used alone or in combination of two or more.

[0032] Of the above, bisphenol A is not preferred for use in the present paint due to legal restrictions on the environment, etc.

[0033] Examples of the formaldehyde component include formaldehyde, paraformaldehyde, and trioxane, and these can be used alone or in combination of two or more.

[0034] As the resol type phenolic resin (B) in the present invention, a resol type phenolic resin (B1) obtainable by heating a phenolic component containing 50 to 100 mass % of m-cresol and 0 to 50 mass % of p-cresol (more particularly, 50 to 90 mass % of m-cresol and 10 to 50 mass % of p-cresol) and a formaldehyde component in the presence of a reaction catalyst to cause a condensation reaction to introduce methylol groups to obtain a methylolated phenolic resin, and then alkyl-etherifying a portion of the methylol groups of the obtained methylolated phenolic resin with an alcohol can be suitably used.

[0035] The resol-type phenolic resin (B1) has excellent reactivity, and the crosslinked coating film has excellent processability. By combining this resol-type phenolic resin (B1) with the polyester resin (A) in a predetermined amount to form a coating composition, a coating film having excellent corrosion resistance, particularly in highly processed areas, can be obtained.

[0036] In the production of the resol type phenolic resin (B1), the phenolic component as the starting material may be m-cresol or p-cresol, and the above-mentioned phenolic component may also be used in combination.

[0037] For the production of the resol type phenolic resin (B1), it is particularly preferable to use a phenol component containing 70 to 90 mass % of a trifunctional or higher phenol including m-cresol and 10 to 30 mass % of a difunctional phenol including p-cresol.

[0038] The alcohol used to alkyl-etherify a portion of the methylol groups of the methylolated phenolic resin is preferably a monohydric alcohol having 1 to 8 carbon atoms, preferably 1 to 4. Suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, and isobutanol.

[0039] In terms of reactivity with the polyester resin (A), the resol phenolic resin (B) preferably has an average number of alkoxymethyl groups per benzene nucleus of 70% or more based on the total number of alkoxymethyl groups and methylol groups, and more preferably has an average of 0.5 or more alkoxymethyl groups per benzene nucleus, and more preferably has 0.6 to 3.0 alkoxymethyl groups.

[0040] Acid catalyst (C) The acid catalyst (C) accelerates the curing reaction of the present coating material, and specific examples thereof include sulfonic acid compounds such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, etc.; acid catalysts such as phosphoric acid, or amine neutralized products of these acids. Among these, the above-mentioned sulfonic acid compounds or amine neutralized products of sulfonic acid compounds can be preferably used.

[0041] Organic Solvent Component (D) In ​​the present paint, the organic solvent component (D) contains as essential components a hydrocarbon solvent (D1) having a boiling point of 130°C or higher, a ketone solvent (D2) having a boiling point of 110°C or higher, and an alcohol solvent (D3) having a boiling point of 75°C or higher.

[0042] Examples of the hydrocarbon solvent (D1) include xylene (boiling point 139°C), Solvesso 100 (boiling point 150 to 185°C), Solvesso 150 (boiling point 178 to 209°C), and ethylcyclohexane (boiling point 133°C).

[0043] Examples of the ketone solvent (D2) include methyl isobutyl ketone (boiling point 116° C.), cyclohexanone (boiling point 156° C.), and isophorone (boiling point 215° C.).

[0044] Examples of the alcohol-based solvent (D3) include ethanol (boiling point 78°C), n-propanol (boiling point 97°C), isopropanol (boiling point 82°C), n-butanol (boiling point 118°C), sec-butanol (boiling point 100°C), tert-butanol (boiling point 83°C), isobutanol (boiling point 108°C), n-hexanol (boiling point 157°C), octanol (boiling point 197°C), and 2-ethylhexanol (boiling point 185°C).

[0045] As the organic solvent component (D), an organic solvent (D4) other than the above components (D1), (D2), and (D3) can also be used. Specific examples of such solvents include ester-based solvents such as ethyl propionate, methyl propionate, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate (boiling point 143°C), ethylene glycol monoethyl ether acetate (commonly known as "Celloace", boiling point 156°C), propylene glycol monomethyl ether acetate (commonly known as "PMAC", boiling point 146°C), isoamyl acetate (boiling point 142°C), methyl benzoate (boiling point 198 to 200°C), and ethyl ethoxypropionate (commonly known as "EEP", boiling point 169°C); ether-based solvents such as tetrahydrofuran, dioxane, and dimethoxyethane; ether alcohol-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and propylene glycol monopropyl ether; Examples of the acetic acid esters include oxohexyl acetate (commonly known as "OHA", boiling point 170°C), 3-methoxybutyl acetate (commonly known as "MBA" or "Metoacet", boiling point 172°C), methyl methoxybutyl acetate (commonly known as "Solphito acetate", boiling point 188°C), ethylene glycol monobutyl ether acetate (commonly known as "Butycel acetate", boiling point 191°C), diethylene glycol monoethyl ether acetate (commonly known as "Carbitol acetate", boiling point 217°C), and diethylene glycol monobutyl ether acetate (commonly known as "Butylcarbitol acetate", boiling point 246°C); and dibasic acid diesters such as dimethyl succinate (boiling point 196°C), dimethyl glutarate (boiling point 214°C), dimethyl adipate (boiling point 239°C), and diethyl succinate (boiling point 196°C).

[0046] The organic solvent component (D4) can be used alone or in combination with (D1), (D2), and (D3).

[0047] Coating Composition The coating composition contains the above-mentioned polyester resin (A), resol-type phenolic resin (B), acid catalyst (C), and organic solvent component (D) in the following blending ratio.

[0048] The blending ratio of the polyester resin (A) is 70 to 99 mass %, preferably 75 to 95 mass %, particularly preferably 80 to 95 mass %, in terms of solid content, based on the total solid content of the polyester resin (A) and the resol type phenolic resin (B).

[0049] If the blending ratio of the polyester resin (A) is less than 70% by mass, the processability may decrease, and if it exceeds 99% by mass, the water resistance may decrease.

[0050] The blending ratio of the resol type phenolic resin (B) is in the range of 1 to 30 mass %, preferably 2 to 25 mass %, particularly preferably 2 to 20 mass %, in terms of solid content, relative to the total solid content of the polyester resin (A) and the resol type phenolic resin (B).

[0051] It is preferable that the content is within the above range from the viewpoint of the curability, processability, water resistance, etc. of the resulting coating film.

[0052] The proportion of the acid catalyst (C) in the polyester resin (A) and the resol phenolic resin (B) is 0.1 to 5.0 mass %, preferably 0.2 to 3.0 mass %, in terms of the total solid content of the polyester resin (A) and the resol phenolic resin (B). A proportion within the above range is suitable from the viewpoints of the curability and physical properties of the resulting coating film.

[0053] In addition, when the acid catalyst (C) contains compounds other than acids (for example, amines in the case of amine-neutralized products of sulfonic acid compounds), the amount of the acid catalyst (C) does not include the portion of the compounds other than acids.

[0054] The blending ratio of the organic solvent component (D) is within the range of 100 to 600 mass%, preferably 100 to 400 mass%, and particularly preferably 150 to 300 mass%, based on the total solid content of the polyester resin (A) and the resol type phenolic resin (B). A blending ratio within the above range is suitable from the viewpoints of the appearance of the coating film, coating workability, etc.

[0055] Of the total amount of organic solvent component (D), the combined amount of hydrocarbon solvent (D1) having a boiling point of 130° C. or higher, ketone solvent (D2) having a boiling point of 110° C. or higher, and alcohol solvent (D3) having a boiling point of 75° C. or higher is preferably 50% by mass or higher, more preferably 60 to 95% by mass, and even more preferably 65 to 90% by mass. A ratio of 50% by mass or higher is favorable in terms of coating film appearance, coating workability, and coating storage stability.

[0056] Of the total amount of organic solvent component (D), the amount of hydrocarbon solvent (D1) having a boiling point of 130° C. or higher is preferably 5 to 80% by mass, more preferably 15 to 50% by mass. When the blending ratio of hydrocarbon solvent (D1) is 5% or higher, coating workability is good, and when it is 80% by mass or lower, it is suitable in terms of solubility of polyester resin (A) and coating storage stability.

[0057] Of the total amount of organic solvent component (D), the amount of the ketone solvent (D2) having a boiling point of 110° C. or higher is preferably 15 to 60% by mass, more preferably 25 to 55% by mass. A blending ratio of the ketone solvent (D2) of 15% or higher is suitable in terms of the solubility of the polyester resin (A) and the coating storage stability, while a blending ratio of 60% by mass or lower improves coating workability.

[0058] The amount of the alcohol-based solvent (D3) having a boiling point of 75° C. or higher is preferably 1 to 20% by mass, more preferably 3 to 12% by mass, of the total amount of the organic solvent component (D). If the blending ratio of the alcohol-based solvent (D3) is less than 1%, the solubility of the resol-type phenolic resin (B) may decrease, while if it exceeds 20% by mass, the solubility of the polyester resin (A) may decrease.

[0059] In addition to the polyester resin (A), resol-type phenolic resin (B), acid catalyst (C), and organic solvent component (D), the coating composition of the present invention may further contain, as appropriate, coating additives such as lubricity-imparting agents, coating film modifying resins (amino resins, etc.), pigments, anti-aggregating agents, anti-foaming agents, and leveling agents.

[0060] The lubricity-imparting agent is used for the purpose of improving the lubricity of the resulting coating film, and examples thereof include fatty acid ester waxes which are esters of polyol compounds and fatty acids, silicone waxes, fluorine-based waxes, polyolefin waxes such as polyethylene, lanolin waxes, montan waxes, microcrystalline waxes, carnauba waxes, etc. The lubricity-imparting agents can be used alone or in combination of two or more.

[0061] By incorporating a lubricity-imparting agent into the coating composition of the present invention, slipperiness can be imparted to the surface of the coating film obtained from the composition, reducing the frictional resistance of the coating surface, improving moldability and corrosion resistance after processing. The amount of lubricity-imparting agent incorporated is preferably within the range of 0.1 to 20% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 5% by mass, based on the total solids content of the polyester resin (A) and the resole phenolic resin (B), from the standpoint of moldability based on the flexibility and slipperiness of the coating film, corrosion resistance, etc.

[0062] Examples of the coating film modifying resin include amino resins, ethylene-polymerizable unsaturated carboxylic acid copolymers, and ethylene-polymerizable unsaturated carboxylic acid copolymer ionomers.

[0063] The amino resin is added for the purpose of improving the curability of the coating composition, and improving the hardness and adhesion of the resulting coating film.

[0064] The amino resin is a condensation product of an aldehyde such as formaldehyde, acetaldehyde, crotonaldehyde, or benzaldehyde with an amino- or amide-group-containing substance such as urea, melamine, or benzoguanamine, and may be alkyl-etherified with an alcohol, such as a monohydric alcohol such as methanol, ethanol, propanol, butanol, hexanol, benzyl alcohol, cyclohexanol, or ethoxyethanol.

[0065] Specific examples of amino resins include benzoguanamine-formaldehyde resin, melamine-formaldehyde resin, and urea-formaldehyde resin.

[0066] When an amino resin is added, the amount of the amino resin added is preferably in the range of 0.1 to 10 mass %, more preferably 0.2 to 5 mass %, in terms of solid content, relative to the total solid content of the polyester resin (A).

[0067] The above-mentioned ethylene-polymerizable unsaturated carboxylic acid copolymer and ethylene-polymerizable unsaturated carboxylic acid copolymer ionomer can be blended for the purpose of improving the flexibility of the coating film.

[0068] As the pigment, color pigments (for example, titanium oxide), extender pigments, etc., known in the paint field can be used.

[0069] The coating composition of the present invention can be applied to a variety of substrates such as metal plates, metal cans, plastics, and glass plates.

[0070] Coated Metal Sheet The coated metal sheet of the present invention can be obtained by applying the coating composition of the present invention to a metal sheet.

[0071] Examples of the metal sheet include hot-rolled steel sheets, cold-rolled steel sheets, hot-dip galvanized steel sheets, electrogalvanized steel sheets, alloy-plated steel sheets, aluminum-zinc alloy-plated steel sheets, aluminum sheets, tin sheets, tin-plated steel sheets, stainless steel sheets, copper sheets, copper-plated steel sheets, tin-free steel sheets, nickel-plated steel sheets, ultra-thin tin-plated steel sheets, and chromium-treated steel sheets. Steel sheets that have undergone various surface treatments or have been coated with a primer can also be used as needed.

[0072] When the coated metal sheet is processed into a can for use, any metal sheet that can be used for beverage cans, canned food cans, lids, caps, etc. can be used, such as aluminum sheet, tin-free steel sheet, tinplate sheet, etc.

[0073] The coated metal sheet of the present invention can be obtained by applying the coating composition of the present invention to a metal sheet by any of various known methods, such as roll coater coating, spray coating, dip coating, electrodeposition coating, etc., and baking the applied coating by a heating means such as a continuous baking oven. Of the above coating methods, roll coater coating or spray coating is preferred, and roll coater coating is particularly preferred.

[0074] The baking conditions are not particularly limited, but for example, baking is suitable under conditions in which the maximum temperature reached by the material is 120°C to 300°C, preferably 180°C to 260°C, for 5 seconds to 30 minutes, preferably 10 seconds to 10 minutes, and more preferably 10 to 60 seconds.

[0075] The amount of coating on the coated metal sheet can be determined appropriately depending on the application of the coated metal sheet, and the weight of the cured coating film is usually 10 to 200 mg / 100 cm ２ degree, especially 20 to 150 mg / 100 cm ２ The degree is preferable.

[0076] Coated Metal Can The coated metal can of the present invention is a metal can having a coating film made of the coating composition of the present invention formed on at least the inner surface and / or outer surface of the can body or can lid, and it is preferred that a cured coating film made of the coating composition of the present invention is formed on at least the inner surface of the metal can.

[0077] The coated metal can of the present invention can be formed from the coated metal plate described above, but can also be obtained by applying the coating composition of the present invention to a preformed metal container and curing it to form a cured coating film.

[0078] As the metal container on which the cured coating film is formed, any conventionally known metal can can be used, and there is no particular limitation. Examples include the can body of a three-piece can or two-piece can having a side seam.

[0079] The can lids can be formed from the coated metal sheet of the present invention by any conventionally known method for forming lids. Generally, they are formed into easy-open can lids of the stay-on-tab type or full-open type.

[0080] Examples of the form of cans to which the coating composition of the present invention can be applied include two-piece cans consisting of two parts, a lid and a body part integrated with the bottom, three-piece cans consisting of three parts, a lid, a bottom and a body part, and bottle cans, and the coating composition of the present invention can be applied to each of the above parts.

[0081] The coating film obtained from the coating composition of the present invention does not contain legally restricted substances such as bisphenol A and has excellent scratch resistance, processability, and coating film appearance, making it suitable for use in coating the inner surfaces of cans such as beverage cans. Furthermore, the coating film obtained from the coating composition of the present invention is particularly suitable for use on the inner surfaces of can lids.

[0082] The present invention also encompasses the following configurations: Item 1. A coating composition containing a polyester resin (A) having a glass transition temperature of 30°C to 80°C, a resole phenolic resin (B), an acid catalyst (C), and an organic solvent component (D) containing as essential components a hydrocarbon solvent (D1) having a boiling point of 130°C or higher, a ketone solvent (D2) having a boiling point of 110°C or higher, and an alcohol solvent (D3) having a boiling point of 75°C or higher, wherein the coating composition contains 70 to 99 mass% of the polyester resin (A), 1 to 30 mass% of the resole phenolic resin (B), 0.1 to 5.0 mass% of the acid catalyst (C), and 100 to 600 mass% of the organic solvent component (D) relative to the total solid content of the polyester resin (A) and the resole phenolic resin (B). Item 2. Item 1. A coating composition according to Item 1, wherein the total amount of the hydrocarbon solvent (D1) having a boiling point of 130°C or higher, the ketone solvent (D2) having a boiling point of 110°C or higher, and the alcohol solvent (D3) having a boiling point of 75°C or higher is 50% by mass or more of the total amount of organic solvent components (D). Item 3. A coating composition according to Item 1 or 2, wherein the amount of the hydrocarbon solvent (D1) having a boiling point of 130°C or higher is 5 to 80% by mass of the total amount of organic solvent components (D). Item 4. A coating composition according to any one of Items 1 to 3, wherein the amount of the ketone solvent (D2) having a boiling point of 110°C or higher is 15 to 60% by mass of the total amount of organic solvent components (D). Item 5. A coating composition according to any one of Items 1 to 4, wherein the amount of the alcohol solvent (D3) having a boiling point of 75°C or higher is 1 to 20% by mass of the total amount of organic solvent components (D). Item 6. Item 6. A coating composition according to any one of items 1 to 5, containing a resol-type phenolic resin (B) made from a phenolic component containing 50 to 100% by mass of m-cresol and 0 to 50% by mass of p-cresol as a starting material. Item 7. A coated metal sheet having a cured coating film of the coating composition according to any one of items 1 to 6. Item 8. A coated metal can having a cured coating film of the coating composition according to any one of items 1 to 6 on at least a portion of the can surface. Item 9. A coated metal can having a cured coating film of the coating composition according to any one of items 1 to 6 on the inner surface of a can lid.

[0083] The contents of all documents mentioned in this specification are incorporated herein by reference.

[0084] The present invention will be described in more detail below with reference to examples. Here, "parts" and "%" mean "parts by mass" and "% by mass," respectively. Note that the "parts by mass" of raw materials in the following production examples, examples, and comparative examples represent the parts by mass of the solid content (or active ingredient) of the raw materials (excluding the organic solvent component (D)).

[0085] Production of Polyester Resin (A) Production Example 1 Toyobo Co., Ltd.'s polyester resin "Vylon 103" (number average molecular weight 22,000, hydroxyl value 5 mg KOH / g, acid value 2 mg KOH / g or less, Tg point 45°C) was used as polyester resin (A-1).

[0086] Production Example 2 49.8 parts of terephthalic acid, 49.8 parts of isophthalic acid, 34.4 parts of hexahydroterephthalic acid, 28.3 parts of adipic acid, 99.8 parts of neopentyl glycol, 6.8 parts of trimethylolpropane, and a polycondensation catalyst were charged, heated and stirred to carry out an esterification reaction while removing the produced water, to obtain a polyester resin (A-2) having a number average molecular weight of 24,000, a hydroxyl value of 10 mgKOH / g, an acid value of 0.5 mgKOH / g, and a Tg point of 60°C.

[0087] Production Example 3 A polyester resin "Unitika Eliether UE-9100" manufactured by Unitika Ltd. (number average molecular weight 30,000, hydroxyl value 2 mgKOH / g, acid value 2 mgKOH / g or less, Tg point 18°C) was used as polyester resin (A-3).

[0088] Production Example 4 A polyester resin "Unitika Eliter UE-9900" (number average molecular weight 15,000, hydroxyl value 8 mgKOH / g, acid value 2 mgKOH / g, Tg point 101°C) manufactured by Unitika Ltd. was used as polyester resin (A-4).

[0089] The polyester resin (A-3) of Production Example 3 and the polyester resin (A-4) of Production Example 4 are for comparative purposes.

[0090] Preparation of Resole Phenolic Resin (B) Preparation Example 5: 70 parts of m-cresol, 30 parts of p-cresol, 180 parts of 37% aqueous formaldehyde solution, and 1 part of sodium hydroxide were added and reacted at 60°C for 3 hours, followed by dehydration at 50°C under reduced pressure for 1 hour. Next, 100 parts of n-butanol and 3 parts of phosphoric acid were added, and the reaction was carried out at 110-120°C for 2 hours. After completion of the reaction, the resulting solution was filtered to remove the resulting sodium phosphate, yielding a resol phenolic resin (B-1) solution with a solids content of approximately 50%. The resulting resin had a number-average molecular weight of 800, an average number of methylol groups per benzene nucleus of 0.5, and an average number of butoxymethyl groups per benzene nucleus of 0.9.

[0091] Production Examples 6 and 7 Production Example 5 was repeated except that 100 parts of the phenol component shown in Table 1 below were used instead of 70 parts of m-cresol and 30 parts of p-cresol, to obtain resol-type phenolic resin solutions (B-2) to (B-3) each with a solids content of approximately 50%.

[0092] The non-volatile component of each of the resol type phenolic resin solutions (B-1) to (B-3) is n-butanol.

[0093]

[0094] Example 1: 80 parts of the polyester resin (A-1) obtained in Production Example 1 was mixed with 40 parts of the resol-type phenolic resin (B-1) solution obtained in Production Example 5 (20 parts solids) and 1.2 parts of "Nakeure 5225" (*1) (0.3 parts dodecylbenzenesulfonic acid). The resulting mixture was then adjusted to 10 parts ethylcyclohexane, 120 parts methyl isobutyl ketone, 6 parts ethanol, 6 parts isopropyl alcohol, 20 parts butanol, and 38 parts ethylene glycol monobutyl ether per 100 parts of the total solids of the polyester resin (A-1) and resol-type phenolic resin (B-1), yielding a coating composition No. 1 with a solids content of 31.2%. (*1) Nakeure 5225: Trade name, manufactured by King Industries, USA, amine-neutralized solution of dodecylbenzenesulfonic acid, dodecylbenzenesulfonic acid content 25%.

[0095] Examples 2 to 40 and Comparative Examples 1 to 16 Paint compositions Nos. 2 to 56 with a solids content of 31.2% were obtained in the same manner as in Example 1, except for the formulations shown in Table 2 below. The amounts of Components A, B, and C in Table 2 are solids content amounts. The amount of Naicure 5225 is the solids content amount of dodecylbenzenesulfonic acid.

[0096] The total amount of solvent in Table 2 is the amount relative to 100 parts of the total solid content of Components A and B.

[0097] Coating compositions Nos. 41 to 56 are for comparative examples.

[0098] (*2) in Table 2 is as follows: (*2) Naicure 2500: Trade name, manufactured by King Industries, USA, amine-neutralized solution of p-toluenesulfonic acid, p-toluenesulfonic acid content 25%. The blending amount of Naicure 2500 in Table 2 is the solid content of p-toluenesulfonic acid.

[0099] Preparation of Test Coating Plates Each of the coating compositions obtained in the above Examples and Comparative Examples was applied to a 0.27 mm thick #5182 aluminum plate so that the dry coating weight was 80 to 90 mg / 100 cm ２ The test panels were roll coated so that the coating temperature was 255°C, and then baked by passing through a conveyor-type hot air drying oven to obtain each test panel. The baking conditions were a maximum temperature (PMT) of 255°C and a passage time through the oven of 20 seconds. The test panels obtained were subjected to various tests according to the following test methods. The test results are also shown in Table 2 below.

[0100] Test method: Coating appearance: The appearance of the test coated plate was observed with the naked eye. Those that showed no abnormalities on the coating surface such as cissing, dents, cloudiness, or turbidity were rated as (S), and those that showed slight abnormalities but were judged to be at a level that was not problematic for practical use were rated as (A). Those that showed abnormalities on the coating surface such as cissing, dents, cloudiness, or turbidity were rated as (B), and those that showed significant abnormalities were rated as (C).

[0101] Workability: The coated test plate was cut into a 5 cm length in the rolling direction and a 4 cm length perpendicular to the rolling direction. The 5 cm x 4 cm piece was then folded in half parallel to the short sides at a point closer to one of the short sides than the midline of the two short sides. The coated test plate was placed so that the larger folded half was on top and the smaller folded half was on the bottom. Two 0.26 mm thick aluminum plates were sandwiched between the folded portions of the coated test plate specimen in a room at 20°C, and the test plate was placed in a special fold-type DuPont impact tester. A 1 kg iron weight with a flat contact surface was dropped from a height of 50 cm to impact the folded portion. A voltage of 6.5 V was then applied to the folded tip for 6 seconds, and the current value (mA) over a 20 mm width of the folded tip was measured and evaluated according to the following criteria. If the coating is not easy to work, the coating at the bent section will crack, exposing the underlying metal plate and increasing the conductivity, resulting in a higher current value. S is less than 10mA A is 10mA or more and less than 20mA B is 20mA or more and less than 40mA C is 40mA or more

[0102] Scratch resistance: A friction test was conducted using a Bowden friction tester (Soda-type adhesion / slip tester, manufactured by Shinko Engineering Co., Ltd.) under conditions of a steel ball with a diameter of 3 / 16 inches at the friction part, a load of 4 kg, and a friction speed of 7 reciprocations per minute, and the number of frictions until scratches appeared on the coating film was measured. Evaluation was based on the following criteria: S: No scratches appeared even after 200 frictions; A: Scratches appeared after 150 to 200 frictions; B: Scratches appeared after 50 to less than 150 frictions; C: Scratches appeared after 10 to less than 50 frictions; D: Scratches appeared after less than 10 frictions.

[0103] Paint storage stability Each paint composition was left to stand at room temperature for one week and then visually evaluated. S: No precipitation observed A: Almost no precipitation observed B: Slight precipitation observed C: Considerable amount of precipitation observed

[0104]

[0105]

[0106]

[0107]

[0108] It is possible to provide an inner coated can lid that is excellent in scratch resistance, processability, and coating appearance, and to provide a coating composition that does not contain legally restricted substances such as bisphenol A.

Claims

1. A coating composition containing a polyester resin (A) having a glass transition temperature of 30°C to 80°C, a resol type phenol resin (B), an acid catalyst (C), and a hydrocarbon solvent (D1) having a boiling point of 130°C or higher, a ketone solvent (D2) having a boiling point of 110°C or higher, and an alcohol solvent (D3) having a boiling point of 75°C or higher as essential components, the organic solvent component (D), The coating composition is characterized by containing 70 to 99% by mass of the polyester resin (A), 1 to 30% by mass of the resol type phenol resin (B), 0.1 to 5.0% by mass of the acid catalyst (C), and 100 to 600% by mass of the organic solvent component (D) based on the total solid content of the polyester resin (A) and the resol type phenol resin (B).

2. The coating composition according to claim 1, wherein the total amount of the hydrocarbon solvent (D1) having a boiling point of 130°C or higher, the ketone solvent (D2) having a boiling point of 110°C or higher, and the alcohol solvent (D3) having a boiling point of 75°C or higher is 50% by mass or more of the total amount of the organic solvent component (D).

3. The coating composition according to claim 1, wherein the amount of the hydrocarbon solvent (D1) having a boiling point of 130°C or higher is 5 to 80% by mass of the total amount of the organic solvent component (D).

4. The coating composition according to claim 1, wherein the amount of the ketone solvent (D2) having a boiling point of 110°C or higher is 15 to 60% by mass of the total amount of the organic solvent component (D).

5. The coating composition according to claim 1, wherein the amount of the alcohol solvent (D3) having a boiling point of 75°C or higher is 1 to 20% by mass of the total amount of the organic solvent component (D).

6. The coating composition according to claim 1, containing a resol type phenol resin using a phenol component containing 50 to 100% by mass of m-cresol and 0 to 50% by mass of p-cresol as a starting material as the resol type phenol resin (B).

7. A coated metal plate having a cured coating film of the coating composition according to any one of claims 1 to 6.

8. A coated metal can having a cured coating film of the coating composition according to any one of claims 1 to 6 on at least a part of the can surface.

9. A coated metal can having a cured coating film of the coating composition according to any one of claims 1 to 6 on the inner surface of the can lid.