JP6648939B2 - Aqueous paint composition for can inner surface - Google Patents

Description

  The present invention relates to a water-based paint composition for a can inner surface having excellent corrosion resistance and processability.

  Conventionally, as a metal can material, metals such as aluminum, tinplate, and tin free steel have been used. In order to prevent the corrosion of these metals, an epoxy resin / phenol resin-based or epoxy resin / amino resin-based paint excellent in adhesion and corrosion resistance is generally used on the inner and outer surfaces of the can. However, in recent years, there has been a demand for a paint system containing no bisphenol A due to the problem of the elution amount of bisphenol A, which is suspected as an environmental hormone.

  For example, Patent Literature 1 discloses a bisphenol A-free thermosetting paint, in which a polyester-acrylic can paint having a significantly reduced amount of paint components and a paint for such a can have an acid value. A thermoplastic polyester resin (A) having a hydroxyl value of 30 or less and a hydroxyl value of 40 or less and a thermosetting acrylic resin (B) are contained in a weight ratio of A: B = 90: 10 to 40:60. A thermosetting can coating is disclosed. However, the paint described in Patent Document 1 was insufficient in workability and corrosion resistance.

  In addition, Patent Document 2 discloses that (B) 1 to 40 parts by weight of a resol-type phenol resin crosslinking agent and (B) based on 100 parts by weight of a hydroxyl group-containing polyester resin having a number average molecular weight of 1,000 to 100,000. C) A coating composition characterized by containing 0.1 to 5 parts by weight (as an acid amount) of an acid catalyst is disclosed. However, the coating composition described in Patent Literature 2 has insufficient corrosion resistance, and particularly when filled with highly corrosive contents, the coating film is significantly deteriorated.

  In addition, Patent Document 3 discloses a polymer containing a carboxyl group-containing component (B) containing a carboxyl group-containing acrylic copolymer (B1), a basic compound (C), and water (D). A polymer emulsion obtained by radical polymerization of a component (A) containing an ethylenically unsaturated monomer (A1) with a nonionic water-soluble radical initiator (E) in the presence of an aqueous solution or emulsion (1) of An aqueous coating composition containing (F), which does not use a component derived from bisphenol A at all, and which is preferably used for coating the inner surface of a can which can form a coating film having excellent workability and corrosion resistance is disclosed.

  However, in the case of the water-based paint described in Patent Literature 3, when a highly corrosive content was filled, the deterioration of the coating film was remarkable. Therefore, when the corrosion resistance is improved, the workability may be inferior. From such a background, there has been a demand for a paint containing no component derived from bisphenol A, which has both workability and corrosion resistance.

JP 2000-290585 A JP 2001-131470 A JP 2008-255204 A

  The problem to be solved by the present invention is to provide a water-based paint composition for the inner surface of a can which is excellent in processability and corrosion resistance.

The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, the specific urethane resin (A) has the above-mentioned aqueous coating composition for a can inner surface containing an aqueous dispersion dispersed in an aqueous medium. It was found that the task could be achieved.
That is, the present invention
1. A urethane resin (A) having a structural unit derived from a polyester polyol (a), a structural unit derived from a diisocyanate compound (b), and a structural unit derived from a carboxyl group-containing diol (c) having the following characteristics is contained in an aqueous medium. Aqueous paint composition for a can inner surface containing an aqueous dispersion that is dispersed,
Polyester polyol (a):
A polyester polyol containing an acid component (a1) and an alcohol component (a2) as components, and at least one polybasic acid component (a11) selected from aromatic polybasic acids and alicyclic polybasic acids; The total content of at least one diol component (a21) selected from an aromatic diol and an alicyclic diol is such that the total mass of the acid component (a1) and the alcohol component (a2) constituting the polyester polyol (a) is 1. Polyester polyol which is 50 to 100% by mass as a standard 2. The aqueous coating composition for an inner surface of a can according to item 1, which contains 1,4-cyclohexanedicarboxylic acid as the polybasic acid component (a11).
3. Item 3. The aqueous coating composition for a can inner surface according to Item 1 or 2, which contains 1,4-cyclohexanedimethanol as the diol component (a21).
4. The aqueous coating composition for a can inner surface according to any one of Items 1 to 3, which contains dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI) as the diisocyanate compound (b).
5. Further, the water-based paint for a can inner surface according to any one of items 1 to 4, further comprising 0.1 to 10 parts by mass of the wax (B) based on 100 parts by mass of the solid content of the urethane resin (A). Composition,
6. Furthermore, the water-based paint for can inner surface according to any one of Items 1 to 5, which contains 0.1 to 10 parts by mass of the phenol resin (C) based on 100 parts by mass of the solid content of the urethane resin (A). Composition,
7. The coating film obtained by heating and drying at 200 ° C. for 2 minutes has an oxygen permeability coefficient of 9 × 10 ⁻¹³ (ml · cm / cm ² · sec · cmHg) or less. Aqueous paint composition for a can inner surface according to any one of
8. A can having a cured coating film based on the aqueous coating composition for an inner surface of a can according to any one of 8.1 to 7 on the inner surface of the can.

  ADVANTAGE OF THE INVENTION The aqueous coating composition for can inner surfaces of this invention can provide the can body excellent in processability and corrosion resistance. The can body coated with the aqueous coating composition for the inner surface of the can of the present invention can suppress the deterioration of the coating film even if the contents of the can contain alcohol, acid, high-concentration salt and the like.

  The present invention relates to a urethane resin (A) having a structural unit derived from a specific polyester polyol (a), a structural unit derived from a diisocyanate compound (b), and a structural unit derived from a carboxyl group-containing diol (c). An aqueous coating composition for the inner surface of a can containing an aqueous dispersion dispersed in a medium.

Urethane resin (A)
The urethane resin (A) is desirably one produced by reacting a specific polyester polyol (a) with a diisocyanate compound (b) and a carboxyl group-containing diol (c).

Polyester polyol (a)
The polyester polyol (a) used for the urethane resin (A) is a polyester polyol containing an acid component (a1) and an alcohol component (a2) as components, and is an aromatic polybasic acid and an alicyclic polybasic acid. The total content of at least one polybasic acid component (a11) selected from the group consisting of at least one diol component (a21) selected from aromatic diols and alicyclic diols constitutes the polyester polyol (a). It is characterized in that it is 50 to 100% by mass, preferably 60 to 100% by mass, based on the total mass of the acid component (a1) and the alcohol component (a2).

Acid component (a1)
As the acid component (a1), a compound conventionally used as an acid component in the production of a polyester polyol can be used. For example, aromatic polybasic acids, aromatic monocarboxylic acids, and alicyclic polybases can be used. Acids, aliphatic polybasic acids and aliphatic monocarboxylic acids.

  The aromatic polybasic acid is generally an aromatic compound having two or more carboxyl groups in one molecule, and an acid anhydride of the aromatic compound. Examples thereof include phthalic acid, isophthalic acid, terephthalic acid, and naphthalene. Aromatic polycarboxylic acids such as dicarboxylic acid, 4,4′-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of these aromatic polycarboxylic acids; and the like. The aromatic polybasic acids can be used alone or in combination of two or more. Among these aromatic polybasic acids, isophthalic acid can be preferably used particularly from the viewpoint of corrosion resistance.

The alicyclic polybasic acid is generally a compound having one or more alicyclic structures (mainly a 4- to 6-membered ring) and two or more carboxyl groups in one molecule, and an acid anhydride of the compound. . Examples of the alicyclic polybasic acid include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, and 3-methyl Alicyclic polycarboxylic acids such as -1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; The anhydrides of these alicyclic polycarboxylic acids are exemplified. The alicyclic polybasic acids can be used alone or in combination of two or more. Among the alicyclic polybasic acids, 1,4-cyclohexanedicarboxylic acid can be suitably used, particularly from the viewpoint of improving workability, corrosion resistance and scratch resistance.
The aliphatic polybasic acid is generally an aliphatic compound having two or more carboxyl groups in one molecule, and an acid anhydride of the aliphatic compound, for example, succinic acid, glutaric acid, adipic acid, pimerine Aliphatic polycarboxylic acids such as acids, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, brassic acid, octadecandioic acid, and citric acid; anhydrides of these aliphatic polycarboxylic acids; No. Aliphatic polybasic acids can be used alone or in combination of two or more.

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

  Examples of the aromatic diol include bis (hydroxyethyl) terephthalate and 1,4-benzenedimethanol, and these can be used alone or in combination of two or more.

Examples of the alicyclic diol include dihydric alcohols such as 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A and hydrogenated bisphenol F; and these dihydric alcohols include ε-caprolactone and the like. Examples thereof include polylactone diols to which lactones have been added, and these can be used alone or in combination of two or more. As the alicyclic diol, 1,4-cyclohexanedimethanol can be suitably used, particularly from the viewpoint of improving processability, corrosion resistance, and scratch resistance.

  Examples of the aliphatic diol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, and 2,3. -Butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3 -Pentanediol, 1,6-hexanediol, 1 5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, neopentyl glycol, polyethylene glycol, polypropylene glycol, Examples thereof include polyether diols such as polybutylene glycol, and these can be used alone or in combination of two or more.

  Examples of the polyhydric alcohol other than the aromatic diol, alicyclic diol and aliphatic diol include glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, and pentaerythritol , Dipentaerythritol, tris (2-hydroxyethyl) isocyanurate, sorbitol, mannitol, etc .; polylactone polyols obtained by adding lactones such as ε-caprolactone to these trivalent or higher alcohols And the like.

  Further, if necessary, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; propylene oxide, butylene oxide, and glycidyl esters of synthetic hyperbranched saturated fatty acids (trade name “Kajura E10” HEXION) An alcohol compound obtained by reacting a monoepoxy compound such as Specialty Chemicals) with an acid can also be used.

  The production of the polyester polyol (a) is not particularly limited, and can be performed according to a usual method. For example, it can be produced by reacting the acid component (a1) and the alcohol component (a2) in a nitrogen stream at 150 to 250 ° C. for 5 to 10 hours to perform an esterification reaction or a transesterification reaction. In the esterification reaction or transesterification reaction, the acid component (a1) and the alcohol component (a2) may be added at once, or may be added in several portions.

  After the carboxyl group-containing polyester resin is first synthesized, a part of the carboxyl groups in the carboxyl group-containing polyester resin may be esterified using the alcohol component (a2). Furthermore, after first synthesizing a polyester polyol, the polyester polyol may be half-esterified by reacting with an acid anhydride.

  In the esterification or transesterification reaction, a catalyst may be used to promote the reaction. As the catalyst, a known catalyst such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used.

Diisocyanate compound (b)
Examples of the diisocyanate compound (b) include those containing two or more isocyanate groups in one molecule, for example, aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; Isocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), 1,3- (isocyanatomethyl) cyclohexane Alicyclic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate and the like; lysine Organic polyisocyanate itself such as tri- or higher polyisocyanate such as lithocyanate, or an adduct of each of these organic polyisocyanates with a polyhydric alcohol, a low molecular weight polyester resin or water, or between the above-mentioned organic diisocyanates Examples thereof include cyclized polymers (for example, isocyanurate) and bilet-type adducts. These can be used alone or in combination of two or more. These can be used alone or in combination of two or more.

  Among these diisocyanate compounds (b), dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI) is particularly preferable for improving processability, retort resistance, corrosion resistance and oxygen permeability. is there.

Carboxyl group-containing diol (c)
Examples of the carboxyl group-containing diol (c) include, for example, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, and a condensation product thereof. Examples thereof include polyester polyols and polyether polyols. 12-hydroxystearic acid, paraoxybenzoic acid, 2,2-dimethyl-3-hydroxypropionic acid, salicylic acid and the like can be used in combination.

  The mixing ratio of the carboxyl group-containing diol (c) is such that the urethane resin (A) has an acid value of 5 to 50 mgKOH / g, preferably 10 to 40 mgKOH / g, and has a water dispersibility and a coating film obtained. It is desirable from the viewpoint of corrosion resistance.

For the production of the urethane resin (A), the urethane resin (A) can be produced by a conventionally known method. For example, a polyester polyol (a), a diisocyanate compound (b), a carboxyl group-containing diol (c), Is reacted.

  Specifically, for example, the polyester polyol (a) is heated to 80 to 150 ° C. in an organic solvent solution, the carboxyl group-containing diol (c) is added, and then the diisocyanate compound (b) is gradually added. It can be carried out by holding at 150 ° C., preferably 60 to 130 ° C., for 1 to 10 hours, preferably about 2 to 8 hours.

The proportions of the polyester polyol (a), the diisocyanate compound (b) and the carboxyl group-containing diol (c) in the urethane resin (A) are as follows: polyester polyol (a), diisocyanate compound (b) and carboxyl group-containing diol (c). )
45 to 70% by mass, preferably 50 to 65% by mass of the polyester polyol (a), 23 to 48% by mass, preferably 30 to 46% by mass of the diisocyanate compound (b), based on the total solid mass of It is desirable from the viewpoint of dispersibility and stability that the carboxyl group-containing diol (c) is reacted at a ratio of 1 to 7% by mass, preferably 1 to 5% by mass.

  As the organic solvent, a conventionally known organic solvent can be used. Specific examples of the above organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, dimethylformamide, 3-ethoxyethyl propionate, and 3-methoxy-N, N -Dimethylpropionamide and the like. These organic solvents may be used alone or as a mixture of two or more.

  Further, in order to accelerate the above reaction, an amine-based catalyst such as triethylamine, N-ethylmorpholine, triethylenediamine and the like used in a usual urethanization reaction may be used as necessary. The urethane resin (A) thus obtained can be dispersed in an aqueous medium. Examples of the aqueous medium include water and a mixed solution of water and an organic solvent such as a water-soluble organic solvent.

  The aqueous dispersion can be performed by a conventionally known method without any particular limitation. A surfactant, a neutralizing agent and the like are added to the obtained urethane resin (A), and the mixture is stirred while gradually adding an aqueous medium. Can be dispersed.

  Examples of the surfactant include nonionic surfactants such as polyoxyethylene nonylphenyl ether and polyoxyethylene-oxypropylene block copolymer, and anionic surfactants such as sodium lauryl sulfate and sodium dodecylbenzene sulfonate. Agents.

  The neutralizing agent is not particularly limited as long as it can neutralize a carboxyl group. For example, sodium hydroxide, potassium hydroxide, trimethylamine, dimethylaminoethanol, 2-methyl-2-aminopropanol, triethylamine, Ammonium and the like. The neutralizing agent may neutralize a carboxyl group in addition to the urethane resin (A), or may be added to an aqueous medium as a dispersion medium and neutralized simultaneously with dispersion.

  The urethane resin (A) can be made higher in molecular weight by further reacting a chain extender if necessary. Examples of the chain extender include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4-dicyclohexylmethanediamine, and 3,3′-. Diamines such as dimethyl-4,4'-dicyclohexylmethanediamine and 1,4-cyclohexanediamine; polyamines such as diethylenetriamine, dipropylenetriamine, triethylenetetramine and tetraethylenepentamine; hydroxyethylhydrazine, hydroxyethyldiethylenetriamine, 2- [ (2-aminoethyl) amino] ethanol, 3-aminopropanediol and other compounds having an amino group and a hydroxyl group; hydrazines, acid hydrazides, and the like. These may be used alone or in combination of two or more. It can be used in combination with the above. The acid value of the urethane resin (A) thus obtained is desirably 5 to 50 mgKOH / g, preferably 8 to 40 mgKOH / g from the viewpoint of stability and corrosion resistance.

Wax (B)
The aqueous coating composition for a can inner surface of the present invention can contain a wax (B), if necessary. As the wax (B), natural waxes or synthetic waxes, glycerides and waxes, and oxides and acid-modified products thereof can be used. Examples of natural waxes include hydrogenated fats and oils obtained by hydrogenating beef tallow or lard, beeswax, lanolin wax, whale wax, hydrogenated whale wax, carnauba wax, candelilla wax, rice wax, wood wax, jojoba wax, shellac, etc. And mineral waxes such as paraffin wax, paraffin wax, microcrystalline wax, montan wax, and sericin wax. Examples of the synthetic wax include polyethylene wax, polypropylene wax, polytetrafluoroethylene wax, and silicone wax. These can be used alone or in combination of two or more.

  When the wax (B) is blended, the blending amount is preferably in the range of 0.1 to 10 parts by mass based on 100 parts by mass of the solid content of the aqueous dispersion of the urethane resin (A). It is desirable from the viewpoint of improving the properties.

Phenol resin (C)
The aqueous coating composition for a can inner surface of the present invention can contain a phenol resin (C), if necessary. Examples of the phenolic resin (C) include a methylolated phenolic resin in which a phenolic compound such as phenol or cresol is condensed with formaldehyde in the presence of a reaction catalyst to introduce a methylol group; And those obtained by alkyl etherifying a moiety with an alcohol having 1 to 6 carbon atoms.

  Examples of the phenol compound include o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, carboxylate, m-cresol, m-ethylphenol, 3, Examples thereof include phenol compounds such as 5-xylenol, m-methoxyphenol, and bisphenol F, and these can be used alone or in combination of two or more.

Examples of the formaldehydes include formaldehyde, paraformaldehyde, trioxane and the like, and they can be used alone or as a mixture of two or more. Examples of the alcohol used for alkyl etherifying a part of the methylol group of the methylolated phenol resin include monohydric alcohols having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, isobutanol and the like.

  The phenolic resin (C) has a number average molecular weight of 200 to 2,000, preferably 300 to 1200, and an average number of methylol groups per nucleus of the benzene nucleus of 0.3 to 3.0, preferably Is suitably in the range of 0.5 to 3.0. In particular, among the resole-type phenolic resins, a phenolic acid formaldehyde resin obtained by subjecting phenolic acid and formaldehyde to a condensation reaction can provide a coating film exhibiting good corrosion resistance even in a processed portion.

  In this specification, the number average molecular weight is a value obtained by converting the number average molecular weight measured using a gel permeation chromatograph (GPC) based on the molecular weight of standard polystyrene, unless otherwise specified. Specifically, "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) was used as the gel permeation chromatograph, and "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and Using four TSKgel G-2000HXL (trade names, all manufactured by Tosoh Corporation), measurement can be performed under the conditions of a mobile phase tetrahydrofuran, a measurement temperature of 40 ° C., a flow rate of 1 mL / min, and a detector RI.

  The amount of the phenolic resin (C) is 0.1 to 10 parts by mass, preferably 1 to 8 parts by mass based on 100 parts by mass of the solid content of the urethane resin (A). It is desirable from the point of view.

Aqueous paint composition for inner surface of can In the paint composition of the present invention, in addition to the aqueous dispersion of the urethane resin (A), the wax (B) and the phenolic resin (C), which are added as required, the composition is further acid-cured. Paint additives such as a catalyst, a lubricity-imparting agent, an organic solvent, a resin for modifying a coating film, a pigment, an anti-agglomeration agent, an antifoaming agent, and a leveling agent can be appropriately compounded.

  The acid curing catalyst promotes the curing reaction of the composition of the present invention, for example, an acid catalyst such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, phosphoric acid or the like. Specific examples include neutralized amines of these acids. Among them, the above-mentioned sulfonic acid compounds or amine-neutralized sulfonic acid compounds are preferred.

  The coating composition for the inner surface of a can of the present invention is generally blended with an organic solvent from the viewpoint of coatability and the like. Examples of the organic solvent include alcohols such as ethyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexanol, benzyl alcohol, cyclohexanol, ethylene glycol, propylene glycol, diethylene glycol, and 1,3-butylene glycol; , Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, ethylene glycol mono 2-ethylhexyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monophenyl ether, 3-methyl-3 -Methoxybutanol, diethylene glycol monoe Ethers such as toluene ether and diethylene glycol monobutyl ether; ketones such as acetone, methyl isobutyl ketone, cyclohexanone, isophorone and acetylacetone; esters such as ethylene glycol monoethyl ether acetate and ethylene glycol monobutyl ether acetate; Can be. These can be used alone or in combination of two or more.

  Examples of the resin for modifying the coating film that can be blended in the aqueous coating composition for a can inner surface of the present invention include, for example, an amino resin, an ethylene-polymerizable unsaturated carboxylic acid copolymer and an ethylene-polymerizable carboxylic unsaturated acid copolymer. Combined ionomers and the like can be mentioned.

  The amino resin is compounded for the purpose of improving the curability of the coating composition, improving the hardness of the obtained coating film, improving the adhesion, and the like. Amino resins are condensation products of aldehydes such as formaldehyde, acetaldehyde, crotonaldehyde and benzaldehyde with substances containing amino or amide groups such as urea, melamine and benzoguanamine, which may be alkyl etherified by alcohols. . Useful alcohols include monohydric alcohols such as methanol, ethanol, propanol, butanol, hexanol, benzyl alcohol, cyclohexanol and ethoxyethanol. Examples of the amino resin include a benzoguanamine-formaldehyde resin, a melamine-formaldehyde resin, and a urea-formaldehyde resin.

  Examples of the object to be coated with the aqueous coating composition for the inner surface of the can of the present invention include, for example, aluminum plates, steel plates, untreated or surface-treated metal plates such as tin plates, and epoxy resin-based primers on these metal plates. Metal plates coated with paint or a primer paint such as a vinyl resin primer paint, and those obtained by processing these metal plates into cans and the like are included.

  The coated metal sheet is obtained by applying the aqueous coating composition for the inner surface of the can of the present invention to the object to be coated by a known coating method such as roll coater coating or spray coating and baking by a heating means such as a continuous baking furnace. be able to. The baking conditions are not particularly limited. For example, the baking temperature is 90 ° C. to 300 ° C., preferably 180 ° C. to 260 ° C., and more preferably 190 ° C. to 230 ° C., for 1 second to 1 hour. Baking for 30 minutes, preferably 5 seconds to 10 minutes, more preferably 8 seconds to 3 minutes is suitable. The coating thickness of the coated metal plate is not particularly limited, but it is desirably in the range of 1 to 25 μm, preferably 2 to 18 μm in terms of dry film thickness from the viewpoint of workability and corrosion resistance.

Furthermore, the coating film obtained by applying the aqueous coating composition for the inner surface of a can of the present invention and drying by heating at 200 ° C. for 2 minutes has an oxygen permeability coefficient of 9 × 10 ⁻¹³ (ml · cm / cm ² · sec). CmHg) or less, and preferably in the range of 2 × 10 ^{−13 to} 5 × 10 ⁻¹³ (ml · cm / cm ² · sec · cmHg).

  Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited thereto. In each example, "parts" indicates parts by mass and "%" indicates mass%.

Production Example 1 of Polyester Polyol (a) Production of 1 A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser with a water separator, and a nitrogen inlet tube was set to a nitrogen atmosphere, and 216 parts of isophthalic acid and 332 parts of 1,4-cyclohexanedimethanol were charged. The temperature was raised to 140 ° C. under stirring.
Thereafter, the temperature was raised to 230 ° C. over 4 hours while removing generated water. Subsequently, reflux was continued by adding 55 parts of toluene, and the reaction was carried out until the acid value became 2 mgKOH / g or less. After completion of the reaction, toluene was distilled off under reduced pressure at 180 ° C. 1 was obtained.

Synthesis Examples 2 to 14 Polyester polyol No. 2-No. Preparation of Polyester No. 14 The reaction was carried out until the acid value became 2 mgKOH / g or less in the same manner as in Synthesis Example 1 except that the content of the mixture was as shown in Table 1. 2-No. 14 was obtained.

Comparative Synthesis Examples 1 to 5 15-No. Preparation of Polyester No. 19 The reaction was carried out until the acid value became 2 mgKOH / g or less in the same manner as in Synthesis Example 1 except that the content of the mixture was as shown in Table 1. 15-No. 19 was obtained.

Production example 1 of urethane resin (A) Preparation of Polyester No. 1 obtained in Synthesis Example 1 under a nitrogen atmosphere in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, nitrogen inlet tube, and dropping funnel. 150 parts, 14.2 parts of dimethylolpropionic acid, and 60 parts of N-methylpyrrolidone were charged and heated to 120 ° C. with stirring. After the temperature was raised, 133 parts of Desmodur W (Note 1) were added dropwise over 10 minutes.
About 2 hours after the completion of the dropwise addition, when the NCO value (Note 2) became 32.0 mg / g or less, heating was stopped, and the mixture was cooled to 40 ° C. or less while 200 parts of methyl ethyl ketone was added dropwise. Thereafter, 9.8 parts of triethylamine was added as a neutralizing agent, and after uniformly stirring, 730 parts of deionized water was added dropwise over 20 minutes.
Thereafter, a solution prepared by dissolving 2.1 parts of diethylenetriamine in 20 parts of deionized water was added dropwise over 20 minutes, and the temperature was raised to 50 ° C. and maintained for 1 hour. Subsequently, the temperature was raised to 60 ° C., and methyl ethyl ketone was distilled off under reduced pressure. Then, the solid content concentration was adjusted to 30% by mass with deionized water. 1 was obtained. The obtained urethane resin solution No. The average particle size (Note 3) of No. 1 was 45 nm.

Production Examples 2 to 20
A urethane resin solution No. 1 was prepared in the same manner as in Production Example 1 except that the content of the mixture was as shown in Table 2. 2-No. 20 was obtained.

Comparative Production Examples 1 to 5
A urethane resin solution No. 1 was prepared in the same manner as in Production Example 1 except that the content of the mixture was as shown in Table 3. 21-No. 25 was obtained.

  (Note 1) Death Module W: Sumika Bayer Urethane, trade name, hydrogenated MDI.

(Note 2) NCO value: It was determined by the following measurement method.
The sample (g) is measured correctly in an Erlenmeyer flask, the sample dissolved by adding 10 ml of dioxane is heated to 50 ° C., 10 ml of a dioxane solution of dibutylamine (1/5 normal) is added, and the sample is mixed with the dibutylamine for 2 minutes. Is reacted. Next, 2-3 drops of an ethyl alcohol solution of bromophenol blue are added, and titration is performed with a hydrochloric acid solution (1/10 normal). When the color changes from blue to yellow-green, the end point is determined.
N = {0.1 × 42 × (A−B) × f} / (0.01 × S × W) Formula N: NCO value (mg of NCO contained in 1 g of sample)
A: Amount (ml) of N / 10 hydrochloric acid solution used to neutralize the blank N / 5 dibutylamine-dioxane solution
B: Amount (ml) of hydrochloric acid solution (1/10 normal) used for titration of sample
f: Factor of N / 10 hydrochloric acid solution S: Heating residue of sample (%)
W: Amount of sample (g)
42: molecular weight of NCO.

  (Note 3) Average particle diameter: Measured using COULTER N4 type (trade name, manufactured by Beckman Coulter, submicron particle size distribution analyzer).

Preparation of Phenol Resin Solution (C) Synthesis Example 15 Preparation of Phenol Resin A Solution 70 parts of m-cresol, 30 parts of p-cresol, 180 parts of a 37% aqueous formaldehyde solution and 1 part of sodium hydroxide were added and reacted at 60 ° C. for 3 hours. After that, dehydration was performed at 50 ° C. for 1 hour under reduced pressure.

  Next, 100 parts of n-butanol and 3 parts of phosphoric acid were added and reacted at 110 to 120 ° C. for 2 hours. After the completion of the reaction, the resulting solution was filtered to remove the generated sodium phosphate, thereby obtaining a phenol resin A solution having a solid content of about 50%. The obtained phenolic resin A had a number-average molecular weight of 800, an average number of methylol groups of 0.5 and an average number of butoxymethyl of 0.9 per benzene nucleus.

Manufacture of paint composition for can inner surface Example 1 Paint No. for can inner surface Production of urethane resin solution No. 1 having a solid content of 30% obtained in Production Example 1 1 (solid content) and 10 parts of ethylene glycol monobutyl ether were mixed and diluted with deionized water to obtain a paint No. No. 27 having a solid content of 27%. 1 was obtained.

Examples 2 to 29 Paint No. for Can Inner Surface 2-No. Production of Can No. 29 In the same manner as in Example 1 except that the compositions shown in Tables 4 and 5 were used, the paint No. 29 for the inner surface of the can was obtained. 2-No. 29 was obtained.

Comparative Example 1 Paint No. Production of No. 30 Urethane resin solution No. 30 having a solid content of 30% obtained in Comparative Production Example 1. No. 21 (solid content) and 10 parts of ethylene glycol monobutyl ether were mixed and diluted with deionized water. 30 was obtained.

Comparative Examples 2 to 5 Paint No. 31-No. Preparation of Can No. 34 In the same manner as in Comparative Example 1 except that the composition shown in Table 6 was used, paint No. 31-No. 34 were produced.

Trace Comparative Example 6 of Example 1 of Patent Document 1 (JP-A-2000-290585) Production of 35 In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser with a water separator, and a nitrogen inlet tube, 400 parts of dimethyl terephthalate, 370 parts of propylene glycol, 50 parts of 1,4 butanediol, and 0.29 parts of -n-butyl titanate was added, the temperature was gradually raised, and the reaction was continued for 4 hours until the reaction temperature reached 220 ° C. Next, the temperature was raised to 250 ° C., the pressure in the reaction system was gradually reduced, and the reaction was carried out under a reduced pressure of 0.2 mmHg or less for 4 hours to obtain a thermoplastic polyester resin. The resulting thermoplastic polyester resin had an acid value of 2 mgKOH and a hydroxyl value of 5 mgKOH. The number average molecular weight was 16,000.
Then, 330 parts of butoxymethylacrylamide, 420 parts of ethyl acrylate, 300 parts of methyl methacrylate, 450 parts of styrene, 75 parts of benzoyl peroxide, and 550 parts of Solvesso 150 were mixed, and 750 parts of cyclohexanone and 200 parts of Solvesso 150 were mixed in a solvent. At 110 ° C. in an air stream, the mixture was dropped over 1 hour to carry out a polymerization reaction.
After completion of the dropwise addition, the temperature was maintained at 110 ° C. for another 2 hours to polymerize the thermosetting acrylic resin. The number average molecular weight of the obtained thermosetting acrylic resin was 3,800.
A part of the thermosetting acrylic resin solution is taken, the thermoplastic polyester resin (the mixing ratio of the thermoplastic polyester resin and the thermosetting acrylic resin solution is 80/20 by mass ratio), and cyclohexanone-solvesso 150 mixed solvent ( (Mixing ratio = 1: 1 by mass, hereinafter referred to as a mixed solvent) was added, and the mixture was dissolved and mixed at 110 ° C. for 3 hours while stirring. It was adjusted using a mixed solvent, and the paint No. for inner surface of a can having a solid content of 27%. 35 was obtained.

Trace Synthesis Example 16 of Example 1 of Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-131470) Production of Polyester Resin A Solution
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 The esterification reaction was carried out while removing water generated by charging, heating and stirring to obtain a resin having a number average molecular weight of 24,000, a hydroxyl value of 10 mgKOH / g and an acid value of 0.5 mgKOH / g. The obtained resin was diluted while adjusting with a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 (mass ratio) to obtain a polyester resin A solution having a solid content of 27%.

Synthesis Example 17 Production of phenolic resin B solution 100 parts of bisphenol A, 178 parts of a 37% aqueous formaldehyde solution and 1 part of caustic soda were added, reacted at 60 ° C for 3 hours, and dehydrated at 50 ° C for 1 hour under reduced pressure. Next, 100 parts of n-butanol and 3 parts of phosphoric acid were added and reacted at 110 to 120 ° C. for 2 hours. After the completion of the reaction, the resulting solution was filtered to remove sodium phosphate produced, thereby obtaining a phenol resin B solution having a solid content of 50%. The obtained resin had a number average molecular weight of 880, an average number of methylol groups of 0.4 and an average number of butoxymethyl of 1.0 per benzene nucleus.

Comparative Example 7 Can inner surface paint No. Preparation of 36 The polyester resin solution A obtained in Synthesis Example 16 was 300 parts (solid content: 90 parts), the phenol resin solution B obtained in Synthesis Example 17 was 20 parts (solid content: 10 parts), and carnauba wax was 1.0 part. And Nailure 5225 (manufactured by King Industries, trade name, amine neutralized salt of dodecylbenzenesulfonic acid, content of dodecylbenzenesulfonic acid is 25%) 4.0 parts (dodecylbenzenesulfonic acid content is 1. 0 parts by weight), and then a mixed solvent of methyl ethyl ketone / cyclohexanone = 50/50 (mass ratio) was added thereto. 36 was obtained.

Trace Synthesis Example 18 of Example 1 of Patent Document 3 (Japanese Patent Application Laid-Open No. 2008-255204) Production of Aqueous Acrylic Copolymer A Reaction vessel equipped with stirrer, thermometer, reflux cooling pipe, dropping tank, and nitrogen gas inlet pipe Then, 100 parts of ethylene glycol monobutyl ether and 100 parts of ion-exchanged water were charged and heated to 90 ° C.
While maintaining the temperature in the reaction vessel at 90 ° C., a mixture consisting of 96 parts of methacrylic acid, 52 parts of styrene, 42 parts of ethyl acrylate, 10 parts of N-butoxymethylacrylamide, and 2 parts of benzoyl peroxide was dropped from the dropping tank for 4 hours. Continuously.
One hour and two hours after the completion of the dropping, 0.2 parts of benzoyl peroxide was added, and the reaction was continued for 3 hours after the completion of the dropping. The number average molecular weight was 45,000, the glass transition temperature was 73 ° C, and the acid value was 312 mg KOH. / G of a solution of the acrylic copolymer A (solid content 50%). Next, 29.8 parts of dimethylethanolamine was added, and the mixture was stirred for 10 minutes. Then, 368.2 parts of deionized water was added to make the mixture water-soluble, thereby obtaining an aqueous solution of an acrylic copolymer A having a solid content of 25%.

Comparative Example 8 Paint No. Preparation of 37 In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet pipe, 120 parts of the acrylic copolymer A aqueous solution obtained in Synthesis Example 18 and 88.9 deionized water. The temperature was raised to 70 ° C. while stirring while introducing a nitrogen gas.
Next, dropping tank No. 1 was charged with 39.0 parts of styrene, 23.5 parts of ethyl acrylate, and 7.5 parts of N-butoxymethylacrylamide. No. 2 was charged with 3.0 parts of a 1% aqueous hydrogen peroxide solution. Then, 3.8 parts of a 1% aqueous solution of sodium erythorbate were charged into 3 and added dropwise with stirring while maintaining the temperature in the reaction vessel at 70 ° C. over 3 hours simultaneously to obtain an emulsion. Thereafter, 114.3 parts of deionized water, 50 parts of n-butanol, and 50 parts of ethylene glycol monobutyl ether were added. 37 was obtained.

Creating a test plate
Each can inner coating obtained in the above Examples and Comparative Examples was coated on a # 5021 aluminum plate having a thickness of 0.25 mm with a bar coater so that the dry coating weight was 50 mg / 100 cm ^2, and was applied at 200 ° C. for 2 minutes. Was baked to obtain each test coated plate. Various tests were performed on each of the obtained test coated plates based on the following test methods. The test results are shown in Tables 4 to 6 above.
(Note 4) SR-16: manufactured by Koyo Chemical Co., Ltd., microcrystalline wax, melting point 83 ° C.
(Note 5) HD-3028: Carnauba wax, manufactured by Gifu Seratsuku Co., Ltd., melting point 82 ° C. (Note 6) Super Heart Run: lanolin alcohol, manufactured by CRODA, melting point 65 ° C.
(Note 7) Lanco 1370LF: manufactured by Lubrizol Japan Ltd., polypropylene wax, melting point 150 ° C., average particle size 9 μm
(Note 8) CERAFLOUR 991: manufactured by BYK, polyethylene wax, melting point 115 ° C, average particle size 5 µm
(Note 9) CKS-3898: manufactured by Showa Denko KK, trade name, resol type phenol resin, normal butanol solution
Test method
(Note 10) Appearance of coating film:
The appearance of the coating film of the test coated plate was visually observed.
◎: No abnormalities in the coated surface such as repelling, dents, cloudiness, and turbidity were observed on the coated surface.
○ indicates a level where there is no problem as a product although the painted surface is slightly cloudy
Δ indicates that any coating surface abnormality such as cissing, dent, cloudiness, or turbidity was observed on the coating surface. × indicates that any abnormalities in the coating surface such as repelling, dents, cloudiness, and turbidity are remarkably observed.

(Note 11) Workability:
Using a special goby fold type Dupont impact tester, insert two 0.27 mm thick aluminum plates between the bent parts of the test coating plate with the lower part folded in two so that the coating surface is on the outside. After placing a 1kg iron weight with a flat contact surface from a height of 50cm to give an impact to the bent part, a voltage of 6.5V was passed through the bent tip for 6 seconds. The current value (mA) at a width of 20 mm at the bending tip was measured and evaluated according to the following criteria.
◎ indicates that the current value is less than 5 mA,
○ indicates that the current value is 5 mA or more and less than 20 mA,
Δ indicates that the current value is 20 mA or more and less than 50 mA,
X: Current value is 50 mA or more.

(Note 12) Retort resistance:
The test coated plate was immersed in water and treated in an autoclave at 125 ° C. for 30 minutes, and the state of whitening and blistering of the coating film was evaluated according to the following criteria.
◎ indicates no whitening or blistering,
○ indicates no swelling and very slight whitening,
△ indicates a little swelling,
X indicates remarkable whitening or remarkable swelling.

(Note 13) Corrosion resistance:
The test coated plate was immersed in a corrosion liquid (citric acid / alcohol / salt / water = 3/3/3/91 [mass ratio]), which is a simulated liquid in the contents of a can, and the degree of corrosion was visually evaluated according to the following criteria. . The immersion was performed at two levels of 40 ° C. for 7 days and 40 ° C. for 14 days.
◎ indicates no corrosion
○ indicates very slight corrosion
△ indicates considerable corrosion
× indicates significant corrosion.

(Note 14) Scratch resistance:
Using a Bowden friction tester (Shinko Zoki Co., Ltd., Soda-type adhesion slide tester), perform a friction test under the conditions of a 3/16 inch steel ball with a friction part, a load of 1 kg, and a friction speed of 7 reciprocations / min. The number of times of friction until the occurrence of friction was measured. Evaluation was made according to the following criteria.
◎ indicates that no scratch occurs even if the number of frictions is 200,
○ indicates that scratches occur when the number of times of friction is 150 to 200 times,
Δ indicates that scratches occur at 50 to 149 times of friction,
X: Scratches occurred when the number of frictions was 49 or less.

(Note 15) Oxygen permeability resistance:
Each coating composition obtained in Examples and Comparative Examples was coated on a tin plate with a bar coater so that the dry coating weight was 10 μm, and baked at 200 ° C. for 2 minutes.
The obtained coating film was peeled off using the amalgam method, and the coating film was cut into a diameter of 17 mmφ and mounted on a measurement cell. Next, oxygen permeability was measured at a measurement temperature of 25 ° C. using a Kakenhi type film oxygen permeability meter (K-316, manufactured by Toyo Rika Co., Ltd.). Next, an oxygen permeability coefficient (ml · cm / cm ² · sec · cmHg) converted to a film thickness of 1 µm (temperature 25 ° C, relative humidity 50%) was determined.
◎ indicates that the oxygen permeability coefficient is 5 × 10 ⁻¹³ or less,
○ indicates that the oxygen permeability coefficient exceeds 5 × 10 ⁻¹³ and is 9 × 10 ⁻¹³ or less,
Δ indicates that the oxygen permeability coefficient exceeds 9 × 10 ⁻¹³ and is 12 × 10 ⁻¹³ or less,
× indicates that the oxygen permeability coefficient exceeds 12 × 10 ⁻¹³

  The aqueous coating composition for a can inner surface of the present invention can provide a can body having excellent corrosion resistance and workability.

Claims (8)

A urethane resin (A) having a structural unit derived from a polyester polyol (a), a structural unit derived from a diisocyanate compound (b), and a structural unit derived from a carboxyl group-containing diol (c) having the following characteristics is contained in an aqueous medium. An aqueous coating composition for the inner surface of a can, comprising a dispersed aqueous dispersion.
Polyester polyol (a):
A polyester polyol containing an acid component (a1) and an alcohol component (a2) as components, and at least one polybasic acid component (a11) selected from aromatic polybasic acids and alicyclic polybasic acids; The total content of at least one diol component (a21) selected from an aromatic diol and an alicyclic diol is such that the total mass of the acid component (a1) and the alcohol component (a2) constituting the polyester polyol (a) is Polyester polyol which is 50 to 100% by mass as a standard The aqueous coating composition for the inner surface of a can according to claim 1, comprising 1,4-cyclohexanedicarboxylic acid as the polybasic acid component (a11). The aqueous coating composition for a can inner surface according to claim 1 or 2, wherein the diol component (a21) contains 1,4-cyclohexanedimethanol. The aqueous coating composition for a can inner surface according to any one of claims 1 to 3, wherein the diisocyanate compound (b) contains dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI). The aqueous solution for a can inner surface according to any one of claims 1 to 4, further comprising 0.1 to 10 parts by mass of the wax (B) based on 100 parts by mass of the solid content of the urethane resin (A). Paint composition. The aqueous solution for a can inner surface according to any one of claims 1 to 5, further comprising 0.1 to 10 parts by mass of the phenol resin (C) based on 100 parts by mass of the solid content of the urethane resin (A). Paint composition. The coating film obtained by heating and drying at 200 ° C. for 2 minutes has an oxygen permeability coefficient of 9 × 10 ⁻¹³ (ml · cm / cm ² · sec · cmHg) or less. The aqueous coating composition for an inner surface of a can according to any one of the preceding claims. A can body having a cured coating based on the aqueous coating composition for a can inner surface according to any one of claims 1 to 7 on the inner surface of the can.