Water-based paints, painted materials, and coated cans

Abstract

To provide an aqueous coating that has excellent adhesion to a metal substrate even with the absence of a primer layer and can form a top coat layer having high processability, blocking resistance and retort resistance, and provide a coated can and a metal container.SOLUTION: An aqueous coating comprises an acrylic modified polyester resin (A) which is a product resulting from a reaction among a polycarboxylic acid (a-1), a polyol (a-2), a fatty acid (a-3), and an ethylenic unsaturated monomer (a-4), at least one of which components having a carbon-carbon double bond, the acrylic modified polyester resin (A) having a specific oil length, a specific weight average molecular weight and a specific acid value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a water-based coating material that can be used to form a coating film on a coated can or the like. [Background technology]

[0002] On the outer surfaces of beverage cans for storing alcoholic beverages such as soft drinks, coffee, or beer, and food cans for storing fish and meat (hereinafter, both of these are collectively referred to as food and beverage cans), a topcoat coating film is formed using a topcoat paint, which as a coated can contributes to improving the appearance of the food and beverage cans and preventing scratches. For example, in the case of coated cans that are subjected to advanced processing, such as so-called bottle cans that have a cap and a recappable screw portion (threaded portion), in order to improve adhesion between the metal substrate and the topcoat coating during processing, a primer layer may first be formed on the metal substrate by size coating (also called white coating or anchor coating), and then a topcoat coating may be formed on the primer layer.

[0003] Patent Document 1 discloses a coating composition for drawn cans, which contains two types of polyester resins having different glass transition temperatures and weight average molecular weights, an amino resin, and an epoxy resin. Patent Document 2 discloses a thermosetting top coat varnish composition for metal containers such as drawn cans, which contains a polyester resin, an amino resin, an epoxy resin, and a blocked isocyanate.

[0004] In recent years, from the perspective of environmental protection and ensuring a safe working environment, the generation of organic solvents and formaldehyde emitted during the paint baking process has become a problem. Therefore, there is a demand for water-based paints and for the reduction of amino resins, which generate formaldehyde when the paint hardens. For applications requiring high processing performance and retort resistance, such as bottle cans, solvent-based paints are used to ensure practical coating film performance for the top coat. Furthermore, because amino resins have excellent short-term curing properties, they are widely used as one of the methods to prevent blocking, a condition where cans coated with exterior paint adhere to each other and leave marks when transported to the interior paint coating line.

[0005] Patent Document 3 discloses an aqueous resin composition for the outer surface of a drawn can, which contains a polyester resin, an amino resin, and a phosphoric acid compound. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-123861 [Patent Document 2] Patent Publication No. 2021-138822 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-024976 Summary of the Invention [Problem to be solved by the invention]

[0007] The paints described in Patent Documents 1 and 2 show good adhesion to metal substrates even without a primer layer, but are solvent-based paints. The drawing can paint described in Patent Document 3 is a water-based paint, but there is no description of the workability when size coating is omitted, and the reality is that no water-based paint for can exteriors that satisfies high workability without size coating has been developed. Furthermore, in all of the above Patent Documents 1 to 3, an amino resin, which is a curing agent, is an essential component. The present invention aims to provide a water-based paint, a coated can, and a metal container that can form a topcoat film that has good adhesion to metal substrates even in the absence of an undercoat layer and has high processability, blocking resistance, and retort resistance. [Means for solving the problem]

[0008] The water-based paint according to the present invention is a reaction product of a polycarboxylic acid (a-1), a polyol (a-2), a fatty acid (a-3), and an ethylenically unsaturated monomer (a-4), At least one of the (a-1) to (a-3) has a carbon-carbon double bond in its molecule, The proportion of (a-4) is 3 to 40 mass% out of 100 mass% in total of (a-1) to (a-4), an acrylic-modified polyester resin (A) having an oil length of 10 to 50% in terms of triglyceride, a weight-average molecular weight of 2,000 to 50,000, and an acid value of 5 to 50 mgKOH / g; Includes. [Effects of the Invention]

[0009] According to the present invention having the above-described configuration, it is possible to provide a water-based paint, a coated can, and a metal container that can form a topcoat film that has good adhesion to metal substrates even in the absence of an undercoat layer, and that has high processability, blocking resistance, and retort resistance. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of the structure of an acrylic-modified polyester resin (A). [Figure 2] FIG. 2 is a schematic diagram showing another embodiment of the structure of the acrylic-modified polyester resin (A). [Figure 3] FIG. 2 is a schematic diagram showing yet another embodiment of the structure of the acrylic-modified polyester resin (A). [Figure 4]FIG. 2 is a schematic perspective view of the upper part of the covered can according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The water-based paint, coated member, and coated can of the present invention will be described below. In the present invention, the term "(trimellitic anhydride)" used in the acrylic-modified polyester resin (A) includes "trimellitic acid" and "trimellitic anhydride." Furthermore, "(meth)acrylic acid" includes each of "acrylic acid" and "methacrylic acid," "(meth)acrylate" includes each of "acrylate" and "methacrylate," and "N-alkoxymethyl(meth)acrylamide" includes each of "N-alkoxymethylacrylamide" and "N-alkoxymethylmethacrylamide."

[0012] <Acrylic-modified polyester resin (A)> The acrylic-modified polyester resin (A) in the present invention is an addition polymerization product of a polycondensation reaction product of a polycarboxylic acid (a-1), a polyol (a-2), and a fatty acid (a-3), and an ethylenically unsaturated monomer (a-4). At least one of the above (a-1) to (a-3) has a carbon-carbon double bond in the molecule.

[0013] Polyester chains are formed by polycarboxylic acid (a-1) and polyol (a-2). If both (a-1) and (a-2) are divalent compounds, the polyester chain has a linear structure. If either (a-1) or (a-2), or both, contain trivalent or higher valent compounds, the polyester chain has a branched structure. Fatty acid (a-3) is located at the end of the polyester chain or forms a side chain of the polyester chain.

[0014] The structure of the acrylic-modified polyester resin (A) in the present invention is classified into the following three modes. (1): Of (a-1) to (a-3), (a-1) or (a-2) has a carbon-carbon double bond, and has a site where an ethylenically unsaturated monomer (a-4) is polymerized, including the carbon-carbon double bond derived from (a-1) or (a-2) (see Figure 1). Note that both (a-1) and (a-2) may have a carbon-carbon double bond. (2): Of (a-1) to (a-3), (a-3) has a carbon-carbon double bond and a site where an ethylenically unsaturated monomer (a-4) is polymerized, including the carbon-carbon double bond derived from (a-3) (see Figure 2). (3): Of (a-1) to (a-3), (a-1) or (a-2), and (a-3) have carbon-carbon double bonds, and have a site where the ethylenically unsaturated monomer (a-4) is polymerized, including the carbon-carbon double bonds derived from (a-1) or (a-2), and (a-3) (see Figure 3). Note that both (a-1) and (a-2) may have carbon-carbon double bonds.

[0015] It should be noted that conjugated double bonds in aromatic compounds do not fall under the category of "carbon-carbon double bonds" in the present invention. In addition, among (a-1) to (a-3), compounds having a carbon-carbon double bond are not included in the "ethylenically unsaturated monomer (a-4)" of the present invention.

[0016] <Polycarboxylic acid (a-1)> The polycarboxylic acid (a-1) is a divalent or higher carboxylic acid, and examples thereof include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trifunctional or higher polycarboxylic acids. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, and biphenyldicarboxylic acid. Examples of the aliphatic dicarboxylic acid include succinic acid (anhydride), fumaric acid, maleic acid (anhydride), adipic acid, sebacic acid, azelaic acid, himic acid, dodecanedioic acid, and dimer acid. Examples of the alicyclic dicarboxylic acid include 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and anhydrides thereof. Examples of tri- or higher functional polycarboxylic acids include pyromellitic acid (anhydride), trimellitic acid (anhydride), and ethylene glycol bistrimellitate dianhydride. Among these, polycarboxylic acids containing carbon-carbon double bonds undergo addition polymerization with the ethylenically unsaturated monomer (a-4), increasing the crosslink density of the coating film, thereby improving the processing adhesion and retort resistance of the coating film. Examples of polycarboxylic acids containing carbon-carbon double bonds include itaconic acid, fumaric acid, and maleic acid (anhydride).

[0017] The polycarboxylic acids (a-1) can be used singly or in combination of two or more. In the present invention, monocarboxylic acids such as benzoic acid, para-t-butylbenzoic acid, 12-hydroxystearic acid, myristic acid, and crotonic acid can also be used as the carboxylic acid component for the purpose of adjusting the molecular weight of the acrylic-modified polyester resin (A).

[0018] <Polyol (a-2)> The polyol (a-2) is preferably a dihydric alcohol or a tri- or higher functional polyhydric alcohol. Dihydric alcohols include, for example, aliphatic diols such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, 2-methylidene-1,4-butanediol, 2-methylidene-1,5-pentanediol, or 2-methylidene-1,6-hexanediol; Alicyclic diols such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 2-hydroxycyclohexyl-methanol, 3-hydroxycyclohexyl-methanol, 4-hydroxycyclohexyl-methanol, hydrogenated bisphenol A, hydrogenated bisphenol AP, hydrogenated bisphenol F, hydrogenated bisphenol S, and hydrogenated biphenol; aromatic diols such as propylene oxide adducts of bisphenol A (2 to 8 moles added), propylene oxide adducts of bisphenol F (2 to 8 moles added), and adducts of ethylene oxide with bisphenol A or bisphenol F; etc. Examples of tri- or higher functional polyhydric alcohols include trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, dipentaerythritol, mannitol, sorbitol, and α-methyl glucoside. Among these polyols, polyols containing carbon-carbon double bonds undergo addition polymerization with the ethylenically unsaturated monomer (a-4), increasing the crosslink density of the coating film, thereby improving the processing adhesion and retort resistance of the coating film. Examples of polyols containing carbon-carbon double bonds include 2-methylidene-1,4-butanediol, 2-methylidene-1,5-pentanediol, and 2-methylidene-1,6-hexanediol. The polyol (a-2) can be used alone or in combination of two or more kinds.

[0019] Furthermore, by using a trifunctional or higher polyhydric alcohol in addition to a dihydric alcohol as the polyol (a-2), the polyester chain exhibits a branched structure, and the fatty acid (a-3) becomes a side chain of the polyester chain, which gives the coating film flexibility and improves adhesion during processing.

[0020] <Fatty acid (a-3)> The fatty acid (a-3) is a compound extracted by decomposing the ester bond site of various animal and vegetable oils, and is used for the purpose of imparting workability to the coating film. Animal and vegetable oils contain saturated fatty acids with 8 to 24 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid; Unsaturated fatty acids with approximately 16 to 22 carbon atoms, such as palmitoleic acid, ricinoleic acid, oleic acid, linoleic acid, linolenic acid, eleostearic acid, and eicosenoic acid; The types and proportions of fatty acids contained vary depending on the type of animal or vegetable oil. In the present invention, the fatty acid containing a carbon-carbon double bond undergoes addition polymerization with the ethylenically unsaturated monomer (a-4), increasing the crosslink density of the coating film, thereby improving the processing adhesion, blocking resistance, and retort resistance of the coating film. Examples of fatty acids containing a carbon-carbon double bond include coconut oil, palm oil fatty acid, palm kernel oil fatty acid, soybean oil fatty acid, and dehydrated castor oil fatty acid. The fatty acids (a-3) can be used singly or in combination of two or more.

[0021] <Ethylenically unsaturated monomer (a-4)> The ethylenically unsaturated monomer (a-4) undergoes addition polymerization, including the carbon-carbon double bond derived from the polycarboxylic acid (a-1), polyol (a-2), or fatty acid (a-3), thereby increasing the crosslink density of the coating film and improving the processing adhesion, blocking resistance, and retort resistance of the coating film. Examples of the ethylenically unsaturated monomer include (meth)acrylamides, (meth)acrylates, vinyl monomers, and carboxyl group-containing monomers.

[0022] Examples of (meth)acrylamides include N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, Nn-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, Nn-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N-pentyloxymethyl(meth)acrylamide, N-hexyloxymethyl(meth)acrylamide, N-heptyloxymethyl(meth)acrylamide, N-octyloxymethyl(meth)acrylamide, N-2-ethylhexyloxymethyl(meth)acrylamide, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, isobutyl(meth)acrylamide, t-butyl(meth)acrylamide, t-octyl(meth)acrylamide, and diacetone(meth)acrylamide.

[0023] Examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, and lanthanum (meth)acrylate. Examples of such acrylates include uryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone-modified (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and N,N-dibutylaminoethyl (meth)acrylate.

[0024] Examples of vinyl monomers include styrene, p-methylstyrene, α-methylstyrene, Examples of the vinyl alcohol include vinyl toluene, vinyl acetate, and vinyl propionate. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid.

[0025] Among these, from the viewpoint of the blocking resistance of the coating film, it is preferable to use any of N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, Nn-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, Nn-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N-pentyloxymethyl(meth)acrylamide, N-hexyloxymethyl(meth)acrylamide, N-heptyloxymethyl(meth)acrylamide, N-octyloxymethyl(meth)acrylamide, and N-2-ethylhexyloxymethyl(meth)acrylamide as (a-4).

[0026] The ethylenically unsaturated monomer (a-4) can be used alone or in combination of two or more. The proportion of the ethylenically unsaturated monomer (a-4) is 3 to 40% by mass, preferably 10 to 30% by mass, based on 100% by mass of the total of (a-1) to (a-4). Using 3% by mass or more improves the crosslink density and the retort resistance of the coating film. Using 40% by mass or less makes it easier to achieve a suitable crosslink density and further improves the processing adhesion of the coating film.

[0027] In the addition polymerization of the ethylenically unsaturated monomer (a-4) containing the carbon-carbon double bond derived from at least one of (a-1) to (a-3), it is preferable to use a polymerization initiator.

[0028] Examples of the polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazoline- 2-yl)propane], and the like, and examples of peroxide compounds include benzoyl peroxide, t-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, t-butylperoxy-2-ethylhexanoate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide. The polymerization initiator is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the ethylenically unsaturated monomer (a-4).

[0029] The acrylic-modified polyester resin (A) has an oil length, calculated as triglyceride, of 10 to 50%, preferably 20 to 40%. A triglyceride length of 10% or more improves the adhesion of the coating film during processing, while a triglyceride length of 50% or less ensures stability when the acrylic-modified polyester resin is made water-based. The oil length can be calculated using the following formula (1). Oil length (%) converted to triglyceride = 100 × {amount of fatty acid (g) / total amount of raw materials constituting polyester resin (g)} × {(number average molecular weight of fatty acid + 12.677) / number average molecular weight of fatty acid} (Equation 1) In addition, "12.677" in the above (Equation 1) refers to the molecular weight of glycerin (92.0 9) minus the molecular weight of water (18.020). 92.09 / 3-18.020=12.677

[0030] The weight-average molecular weight of the acrylic-modified polyester resin (A) is 2,000 to 50,000, and preferably 5,000 to 30,000. By making it 2,000 or more, the retort resistance of the coating film formed is improved, and by making it 50,000 or less, it is easy to adjust the viscosity to an appropriate level when it is made into a water-based coating material. The acid value is 5 to 50 mgKOH / g. By keeping it within this range, it is easy to ensure the paint stability when it is made water-based.

[0031] As described above, the acrylic-modified polyester resin (A) can be synthesized by the polycondensation reaction (esterification reaction) of a polycarboxylic acid (a-1), a polyol (a-2), and a fatty acid (a-3), and the addition polymerization of an ethylenically unsaturated monomer (a-4) including the carbon-carbon double bond possessed by at least one of (a-1) to (a-3). During the polycondensation reaction (esterification reaction) of the polycarboxylic acid (a-1), the polyol (a-2), and the fatty acid (a-3), an antioxidant may be used to ensure polymerization stability, such as a phenol-based antioxidant (including a hindered phenol-based antioxidant). The antioxidant is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the total of the polycarboxylic acid (a-1), the polyol (a-2), and the fatty acid (a-3).

[0032] The polycondensation reaction of (a-1) to (a-3) can be carried out under either normal pressure or reduced pressure. The molecular weight of the reaction product is adjusted by adjusting the charging ratio (excess ratio: equivalent ratio of hydroxyl groups to acid groups) of the acid groups derived from the polycarboxylic acid (a-1) and fatty acid (a-3) to the hydroxyl groups derived from the polyol (a-2). The excess ratio is not particularly limited except that the polyol groups are in excess, but is preferably 1.20 to 1.70. If the ratio is 1.20 or higher, the esterification reaction of the polycarboxylic acid (a-1), polyol (a-2), and fatty acid (a-3) is facilitated, and bonding sites between the hydroxyl groups and the fatty acid (a-3) are secured, thereby ensuring resin stability and coating film processing adhesion. If the ratio is 1.70 or lower, a resin with an appropriate molecular weight is obtained, ensuring coating film processing adhesion and retort resistance. For the purpose of adjusting the acid value, a trivalent or higher polycarboxylic acid may be newly added during the synthesis reaction, and the reaction may be allowed to proceed until the required acid value is reached.

[0033] <Amino resin (B)> The aqueous coating material of the present invention can contain an amino resin (B). The amino resin (B) in the present invention is a resin obtained by adding an aldehyde compound to some or all of the amino groups of the amino component to generate N-methylol groups, and then etherifying some or all of the resulting N-methylol groups by dehydrating them with an alcohol to generate N-alkoxymethyl groups. Because it can react with the acrylic-modified polyester resin (A) described above and the polyester resin (C) described below, it acts as a curing agent.

[0034] Examples of the amino resin (B) include urea resin, melamine resin, benzoguanamine (also known as 2,4-diamino-6-phenyl-1,3,5-triazine) resin, acetoguanamine resin, steroguanamine resin, spiroguanamine resin, dicyandiamide resin, etc. Also included are melamine-benzoguanamine co-condensation resins obtained by reacting melamine with benzoguanamine. Examples of the aldehyde compound include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. The alcohol used for etherifying the N-methylol group is preferably, for example, a monoalcohol having 1 to 6 carbon atoms, more preferably methyl alcohol, ethyl alcohol, isobutyl alcohol, or n-butyl alcohol. The alcohol can be used alone or in combination of two or more kinds. From the viewpoint of hardness and processability of the coating film, it is preferable to use a melamine resin, a melamine-benzoguanamine co-condensation resin, or a benzoguanamine resin as the amino resin (B). The amino resin (B) can be used alone or in combination of two or more.

[0035] Commercially available amino resins (B) may be used, such as Cymel 301, 303LF, 304, 323, 325, 328, 370, 659, and 1123 manufactured by Allnex; Luwipal 014, 015, 018, 066, 070, 052, and B017 manufactured by BASF; and Amidia L-105-60, Amidia L-109-65, Amidia L-110-60, Amidia TD-126, and Amidia 15-594 manufactured by DIC. The amino resin (B) is preferably contained in an amount of 1 to 20% by mass, based on a total of 100% by mass of the acrylic-modified polyester resin (A) and the amino resin (B). Using 1% by mass or more improves the crosslink density, further improving the impact resistance and retort resistance of the coating film. Using 20% ​​by mass or less makes it easier to obtain an appropriate crosslink density, improving the processing adhesion of the coating film.

[0036] <Polyester resin (C)> The water-based coating material of the present invention may contain a polyester resin (C) other than the acrylic-modified polyester resin (A), which further improves the adhesion of the coating film during processing.

[0037] The polyester resin (C) is preferably contained in an amount of 1 to 60% by mass, and more preferably 20 to 40% by mass, based on a total of 100% by mass of the acrylic-modified polyester resin (A), the amino resin (B), and the polyester resin (C). If it is contained in an amount of 1% by mass or more, the processability, impact resistance, and processing adhesion of the coating film are further improved. Furthermore, if it is contained in an amount of 60% by mass or less, the retort resistance of the coating film is further improved. The polyester resin (C) can be synthesized, for example, by a polycondensation reaction (esterification reaction) between a polycarboxylic acid (including its anhydride) and a polyol. This reaction can be carried out under either normal pressure or reduced pressure. The molecular weight can be adjusted by adjusting the charging ratio of the polycarboxylic acid to the polyol. As the polycarboxylic acid and polyol used as raw materials for the polyester resin (C), it is preferable to use the polycarboxylic acid (a-1) and polyol (a-2) exemplified in the section describing the acrylic-modified polyester resin (A), and further, a fatty acid (a-3) can also be used in part.

[0038] <Other resins> The water-based paint of the present invention may contain other resins, such as acrylic resins, water-based polyether polyol resins, polyester polyol resins, and modified epoxy resins in which the glycidyl groups of epoxy resins are addition-modified with amines, phosphoric acid, or the like.

[0039] <Basic compounds> In the present invention, the acrylic-modified polyester resin (A) and the polyester resin (C) can be made water-soluble or water-dispersible by neutralizing the carboxyl groups in them. For neutralization, it is preferable to use a basic compound such as an organic amine compound, ammonia, or an alkali metal hydroxide. Examples of the organic amine compound include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine. Examples of the alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The basic compounds can be used singly or in combination of two or more.

[0040] <Organic solvents> The water-based paint of the present invention may contain an organic solvent. The organic solvent is preferably a hydrophilic organic solvent. This makes it easier to adjust the coatability of the water-based paint and further improves the storage stability of the water-based paint. Examples of the hydrophilic organic solvent include alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, iso-butanol, t-butanol, and diacetone alcohol; Examples of glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether. The organic solvents can be used alone or in combination of two or more kinds.

[0041] <Curing catalyst> The aqueous coating material of the present invention may contain a curing catalyst as needed, preferably an acid catalyst, which allows the curing rate to be appropriately adjusted. Examples of the curing catalyst include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, phosphoric acid, and block products thereof. The curing catalyst can be blended in an amount of 0.001 to 1 part by mass per 100 parts by mass of the total resin components of the water-based paint.

[0042] <Lubricity imparting agent> The water-based coating material of the present invention may contain a lubricity-imparting agent as needed. The lubricity-imparting agent improves the sliding properties of the coating film, and can, for example, prevent the coating film from being scratched when coated cans come into contact with each other. The lubricity imparting agent is preferably, for example, a wax or a silicone-based lubricity imparting agent. The wax may be a natural wax or a synthetic wax. Natural waxes include, for example, animal waxes such as lanolin, beeswax, and whale wax; Vegetable waxes such as carnauba wax, candelilla wax, and rice wax; Examples of the wax include mineral waxes such as paraffin wax, microcrystalline wax, and montan wax. Examples of synthetic waxes include polyolefin waxes, fluorine waxes, and fatty acid ester waxes. Examples of silicone-based lubricity-imparting agents include dimethylpolysiloxane and modified products thereof. The lubricity imparting agents can be used alone or in combination of two or more. The lubricity-imparting agent can be contained in an amount of 0.001 to 10 parts by mass relative to 100 parts by mass of the total of the resin components of the water-based paint.

[0043] <Curing aid> The aqueous coating material of the present invention may contain a curing aid. Examples of the curing aid include polyisocyanates. Examples of polyisocyanates include blocked isocyanates using active methylene, MEK oxime, or ε-caprolactam as a blocking agent; MEK oxime-type aqueous isocyanate is an example.

[0044] <Water-based paint> The water-based paint of the present invention can be prepared by stirring and mixing the materials that constitute it. The aqueous paint of the present invention is preferably used as a colored paint containing a colorant such as a pigment or dye, a clear paint containing no colorant, or a topcoat paint to protect a colored coating film formed by applying a colored paint. Examples of the pigment include chromatic pigments (for example, quinacridone) and achromatic pigments (for example, titanium oxide, aluminum pigments, etc.). The colored coating material is preferably prepared by blending a colorant and, if necessary, a dispersant, and using a dispersing machine such as a sand mill or a disperser.

[0045] <Painting materials> The coated member of the present invention comprises a metal member and a coating film formed from the aqueous paint of the present invention. Conventional coated members require a primer layer when subjected to advanced processing because the coating film cannot adapt to deformations caused by the processing and is prone to peeling off from the metal member as a base material. However, the coated member of the present invention can form a coating film with good adhesion that is less likely to peel off from the metal member even when subjected to advanced processing without a primer layer. It goes without saying that the coated member of the present invention also includes embodiments having a primer layer. Similarly, a coating film made from the aqueous paint of the present invention may be formed on the primer layer.

[0046] The coated member can be obtained by applying the water-based coating material of the present invention to a metal member such as a metal plate, followed by drying and curing. Examples of the coating method include roll coating, spray coating, and brush coating. When applying the coating, the coating may be allowed to dry naturally, but a coating with higher hardness can be formed by heating (a drying process, also known as baking) to perform thermal curing. Baking can be performed, for example, in an electric oven, far-infrared oven, gas oven, coil oven, etc. Baking conditions include heating in an atmosphere with a temperature of 150°C to 240°C for approximately 20 seconds to 10 minutes. The coating weight is 30mg / 100cm 2 ~100mg / 100cm 2 The degree is preferable. The metal member is preferably a metal plate or a metal molded product. Examples of the metal plate include a hot-stretched steel plate, a cold-rolled steel plate, a hot-dip galvanized steel plate, an electrogalvanized steel plate, an alloy-plated steel plate, an aluminum-zinc alloy-plated steel plate, an aluminum plate, a tin-plated steel plate, a stainless steel plate, a copper plate, a copper-plated steel plate, a tin-free steel plate, a nickel-plated steel plate, an ultra-thin tin-plated steel plate, a chromium-treated steel plate, etc. The metal plate may be treated, for example, with an anti-rust treatment or the like. Examples of the metal molded product include a three-dimensional molded product obtained by three-dimensionally molding a metal plate into, for example, a cup shape. The thickness of the metal member is about 50 to 500 μm. The coating may be carried out before or after molding, but is preferably carried out after molding.

[0047] <Coated can> The coated can of the present invention comprises a can body and a coating film formed from the water-based paint of the present invention. In terms of functionality, the coated can is a can used, for example, as a beverage can for storing coffee, soft drinks, etc., or a food can for storing fish, meat, fruit, etc. Needless to say, the coated can can also be used to store non-food and beverage items such as lotion, engine oil, etc. In terms of form, the coated can is preferably, for example, a two-piece can, a three-piece can, or a so-called bottle-shaped can. A two-piece can has a can lid and a can body member as the can body. A three-piece can has two can lids (upper and lower) and one can body member as the can body. A bottle-shaped can has a removable cap and a bottle member as the can body, as shown in Figure 4, with a screw-type drinking spout onto which the cap can be attached.

[0048] The covered can of the present invention can be produced by processing the metal member or coated member. Among coated cans, for example, when producing bottle-shaped cans, the drawing process to form a screw-type drinking spout from a cup-shaped three-dimensional aluminum molded product and the screw-forming process for a removable cap require advanced processing. Therefore, in conventional coated cans, a primer layer is essential to maintain the adhesion of the coating film when processing a coated member to obtain a can body. However, in the coated can of the present invention, even without a primer layer, the adhesion of the coating film to the can body is unlikely to decrease. Note that the coated can of the present invention includes an embodiment having a primer layer. [Example]

[0049] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. Unless otherwise specified, in the examples, "parts" means "parts by mass" and "%" means "% by mass".

[0050] [Manufacturing Example 1] <Synthesis of Acrylic Modified Polyester Resin (A-1)> A reaction vessel equipped with a thermometer, stirrer, nitrogen gas inlet, fractionator, and condenser was charged with 27 parts of isophthalic acid, 1 part of maleic anhydride, 21 parts of glycerin, 24 parts of coconut oil fatty acid (iodine value: 112g / 100g), and 0.04 parts of Irganox 1010 (BASF Japan Ltd.) as an antioxidant. The mixture was stirred and sparged with nitrogen gas at 230°C. The reaction was terminated and cooled when the acid value reached 15mgKOH / g. When the internal temperature reached 100°C, 70 parts of ethylene glycol monobutyl ether was added. Subsequently, 18 parts of methyl methacrylate, 9 parts of N-butoxymethylacrylamide, and 0.8 parts of t-butyl peroxybenzoate were added, heated to 140°C, and reacted for 2 hours. Next, 0.1 parts of t-butyl peroxybenzoate was added and reacted for 1 hour to obtain a solution of acrylic-modified polyester resin (A-1) with a weight average molecular weight of 15,000, a non-volatile content of 55%, and an oil length of 25% when converted to triglyceride. The weight average molecular weight was measured using a Tosoh Corporation GPC apparatus 8020 series (THF (tetrahydrofuran) solvent, column temperature 40 ° C, polystyrene standard). Four columns, G1000HXL, G2000HXL, G3000HXL, and G4000HXL, manufactured by Tosoh Corporation, connected in series, were used, and measurements were performed at a flow rate of 1.0 ml / min.

[0051] The acid value was measured by the following method. 0.2 g of resin calculated as nonvolatile matter was dissolved in 20 ml of THF (tetrahydrofuran), titrated with a 0.1 N KOH ethanol solution, and the acid value was calculated by the following (Equation 2). Acid value (mgKOH / g)=5.611×A×F / 0.2 (Formula 2) A: Titration volume of KOH ethanol solution (ml) F: Potency of 0.1N KOH ethanol solution

[0052] [Manufacturing Examples 2 to 11] <Synthesis of Acrylic-Modified Polyester Resins (A-2) to (A-11)> Solutions of acrylic-modified polyester resins (A-2) to (A-11) were obtained in the same manner as in Production Example 1, except that the type and amount (parts) of each component in Production Example 1 were changed as shown in Table 1.

[0053] [Manufacturing Example 12] <Synthesis of amino resin (B-1)> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 187 parts of benzoguanamine, 187.5 parts of 80% paraformaldehyde, and 518 parts of n-butanol. The pH was adjusted to 9.0 with 25% aqueous sodium hydroxide, and the mixture was heated to 100°C and reacted for 3 hours. Subsequently, 60% aqueous nitric acid was added until the reaction solution reached pH 4, and the mixture was allowed to react for another 3 hours while being dehydrated under reflux. After the reaction was complete, the mixture was neutralized with 25% aqueous sodium hydroxide, and the n-butanol and water were removed under reduced pressure. Ethylene glycol monobutyl ether was added to the product to obtain a solution of amino resin (B-1) with a nonvolatile content of 80%.

[0054] [Manufacturing Example 13] <Polyester resin (C-1)> A reaction vessel equipped with a thermometer, a stirrer, a nitrogen gas inlet, a fractionating apparatus, and a cooling tube was charged with 22 parts of 1,4-butanediol, 10 parts of diethylene glycol, 11.3 parts of trimethylolpropane, 29.8 parts of isophthalic acid, 16.4 parts of hexahydrophthalic anhydride, and 10.5 parts of adipic acid, and the mixture was stirred and esterified at 220 ° C. under nitrogen gas inlet. The reaction was terminated and cooled when the acid value reached 30 mg KOH / g. When the internal temperature reached 100 ° C., 25 parts of ethylene glycol monobutyl ether was added to obtain a solution of polyester resin (C-1) with a weight average molecular weight of 3,000 and a nonvolatile content of 65%.

[0055] [Comparative Manufacturing Examples 1 to 6] <Synthesis of Acrylic Modified Polyester Resins (D-1) to (D-6)> Solutions of acrylic-modified polyester resins (D-1) to (D-6) were obtained in the same manner as in Production Example 1, except that the type and amount (parts) of each component in Production Example 1 were changed as shown in Table 2. Note that the acrylic-modified polyester resin (D-5) thickened during synthesis and became gel-like, making it impossible to evaluate.

[0056] [Table 1]

[0057] [Table 2]

[0058] The abbreviations for the materials in Tables 1 and 2 represent the following: PA: Phthalic anhydride IPA: Isophthalic acid MAH: Maleic anhydride GL: Glycerin TMP: Trimethylolpropane PeE: Pentaerythritol MMA: Methyl methacrylate N-MMA: Nn-methoxymethylacrylamide N-BMA: Nn-butoxymethylacrylamide

[0059] [Example 1] A mixture of 100 parts (calculated as nonvolatile content) of the acrylic-modified polyester resin (A-1) obtained in Production Example 1, 0.5 parts of "BYK302" (manufactured by BYK-Chemie) as a silicone leveling agent, and 1 part of "CERACOL604" (manufactured by BYK-Chemie, carnauba wax) as a wax was prepared. Appropriate amounts of ethylene glycol monobutyl ether and ion-exchanged water were then added and mixed to obtain a nonvolatile content concentration of 45% and an organic solvent concentration of 25%, thereby obtaining a water-based coating material.

[0060] [Example 2] to [Example 19] A water-based paint was obtained in the same manner as in Example 1, except that the type and amount (parts) of each component in Example 1 were changed as shown in Table 3. In Tables 3 and 4, the blending amounts of the amino resin "Cymel303LF", the amino resin (B-1) and the polyester resin (C-1) are values ​​calculated as nonvolatile contents. Cymel 303LF: Melamine-based amino resin manufactured by Allnex (non-volatile content: 98%)

[0061] [Comparative Example 1] to [Comparative Example 7] A water-based paint was obtained in the same manner as in Example 1, except that the type and amount (parts) of each component in Example 1 were changed as shown in Table 4.

[0062] <Preparation of painted member 1> The resulting coating was applied to a 0.28 mm thick #5182 aluminum plate using a bar coater to a dry weight of 50 mg / 100 cm 2 The coated member was heated in a gas oven at an internal temperature of 220°C for 1 minute to obtain coated member 1.

[0063] <Production of painted member 2> The obtained coated member 1 was heated in a gas oven at an internal temperature of 200° C. for 3 minutes, simulating a baking treatment of the internal paint, to obtain a coated member 2.

[0064] <Drawing adhesion> The mouth of the bottle was formed, and a cap was produced as a substitute test for evaluating the adhesion between the coating film and the metal member, and the following test was carried out. Specifically, the resulting coated member 2 was punched into a circle to produce a disk with a diameter of 55 mm. The resulting disk was then drawn so that the coating film was on the outside, producing a cap with a diameter of 25 mm and a depth of 18 mm. The resulting cap was subjected to a retort treatment at 130°C for 30 minutes, and the adhesion between the coating film and the metal member after treatment was evaluated according to the following criteria. ◎: The coating film is completely free of peeling and cracking. Good. ◯: The coating film had some peeling and cracking, but no practical problems. ×: The coating film peeled off and cracked considerably. Not suitable for practical use.

[0065] <Screw processability> The following substitute test was conducted to evaluate the workability of forming a screw on the drinking spout of a bottle can. First, a cap was prepared in the same manner as in the above-mentioned drawing adhesion test, and then screw processing was performed. The obtained screw-processed cap was subjected to retort processing at 130°C for 30 minutes, and the adhesion between the coating film on the screw part and the metal plate after processing was evaluated according to the following criteria. ◎: The coating film is completely free of peeling and cracking. Good. ◯: The coating film had some peeling and cracking, but no practical problems. ×: The coating film peeled off and cracked considerably. Not suitable for practical use.

[0066] <Blocking resistance> The following substitute test was conducted to evaluate the blocking property between painted can bodies. Two test pieces of painted member 1, each measuring 30 mm in length and 90 mm in width, were prepared. The two test pieces were stacked so that the coating films were in contact with each other and secured with clips. After baking under conditions simulating the baking process of the interior paint, the pieces were allowed to cool to 25°C. The marks left at the contact points were then evaluated according to the following criteria. ◎: No contact marks on the coating film. Good. Good: There were some contact marks on the coating film, but no practical problems. ×: There are many contact marks on the coating film. Not suitable for practical use.

[0067] <Retort resistance> Coated member 2 was subjected to a retort treatment for 30 minutes at 130° C. After the treatment, the coated plate was thoroughly dried, and the surface condition of the coating film (presence or absence of whitening) was evaluated visually. ◎: No change from the untreated coating film. Good. ◯: Very thin whitening of the coating film is observed. No practical problems. ×: Obvious whitening of the coating film is observed. Not suitable for practical use.

[0068] <Storage stability> The water-based paint obtained above was stored at 25°C for 30 days and then used to prepare coated member 2, and the state of the coating film was evaluated visually. ◎: The coating film is transparent and no aggregates are visible. Good. ◯: The coating film is slightly cloudy, but no aggregates or the like are observed. No practical problems. ×: The coating film is clearly cloudy and contains many aggregates. Not suitable for practical use.

[0069] Tables 3 and 4 show the details of the water-based paints obtained in Examples 1 to 19 and Comparative Examples 1 to 7, and the evaluation results of the physical properties of the coating films obtained from these water-based paints. Note that the water-based paint in Comparative Example 3 separated during preparation and could not be evaluated. In addition, the symbol "-" in the "Iodine value" column in Tables 3 and 4 indicates that no data is available.

[0070] [Table 3]

[0071] [Table 4]

[0072] As shown in Tables 3 and 4, the water-based paints of Examples 1 to 19 had good physical properties in all respects, whereas the water-based paints of Comparative Examples 1 to 7 had poor physical properties in one respect or another, and no paints were found to have good properties in all respects. [Explanation of symbols]

[0073] 1 Fatty acid (a-3) 2. Polymer of ethylenically unsaturated monomer (a-4) 3 Bottle parts 4. Screw-type drinking spout

Claims

1. a reaction product of a polycarboxylic acid (a-1), a polyol (a-2), a fatty acid (a-3), and an ethylenically unsaturated monomer (a-4); At least one of the (a-1) to (a-3) has a carbon-carbon double bond in its molecule, an acrylic-modified polyester resin (A) in which (a-4) accounts for 3 to 40% by mass of the total of (a-1) to (a-4), and the resin has an oil length, calculated as triglyceride, of 16 to 50%, a weight-average molecular weight of 2,000 to 50,000, and an acid value of 5 to 50 mgKOH / g; Water-based paints, including

2. 2. The aqueous coating material according to claim 1, wherein the acrylic-modified polyester resin (A) has a site where an ethylenically unsaturated monomer (a-4) is polymerized, including a carbon-carbon double bond derived from the polycarboxylic acid (a-1) or the polyol (a-2).

3. 2. The aqueous paint according to claim 1, wherein the acrylic-modified polyester resin (A) has a site where the ethylenically unsaturated monomer (a-4) is polymerized, including a carbon-carbon double bond derived from the fatty acid (a-3).

4. 2. The aqueous coating material according to claim 1, wherein the acrylic-modified polyester resin (A) has a site where an ethylenically unsaturated monomer (a-4) is polymerized, including a carbon-carbon double bond derived from the polycarboxylic acid (a-1) or the polyol (a-2), and the fatty acid (a-3).

5. The aqueous paint according to any one of claims 1 to 4, further comprising an amino resin (B), wherein the proportion of the amino resin (B) is 1 to 20 mass% in a total of 100 mass% of the acrylic-modified polyester resin (A) and the amino resin (B).

6. The aqueous paint according to claim 5, further comprising a polyester resin (C) other than the acrylic-modified polyester resin (A), wherein the proportion of the polyester resin (C) is 1 to 60 mass% in a total of 100 mass% of the acrylic-modified polyester resin (A), the amino resin (B), and the polyester resin (C).

7. A coated member comprising a metal member and a coating film formed from the water-based paint according to any one of claims 1 to 6.

8. A coated can comprising a can body and a coating film formed from the water-based paint according to any one of claims 1 to 6.

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