JP2008001888A - Aqueous coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition for cans capable of forming a coating film which excels in bending workability, water-whitening resistance, and flavor properties. <P>SOLUTION: The aqueous coating composition comprises 100 pts.mass of an acrylic-resin-modified epoxy resin (A), 0.1-10 pts.mass of a resol type phenol resin (B), 0.1-20 pts.mass of an acrylic resin (C) having an acid number of 100-500 mgKOH/g and the following characteristics wherein the resin (A), the resol type phenolic resin (B), and the resin (C) are stably dispersed in an aqueous medium. The acrylic resin (C) is prepared by reacting a vinyl copolymer resin (c1) having a glass transition temperature of -20°C to 70°C with a vinyl copolymer resin (c2) having a glass transition temperature of 20-150°C which is higher than that of the vinyl copolymer resin (c1) by 10°C or greater. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water-based coating composition useful for coating components of edible cans such as beverages and fruits, and metal cans such as lids, and the obtained coating film has folding processability, water whitening resistance, and acid resistance adhesion. Can be formed with a good balance between the properties and flavor.

  Conventionally, coating compositions for cans such as inner and outer surfaces of cans and can lids having coating performance such as processability, adhesion and corrosion resistance have been developed.

  Conventionally, an aqueous resin dispersion in which an acrylic resin (D) containing a monobasic acid as an essential component and containing at least 40% of an acrylic monomer component having a glass transition point of 0 ° C. or lower is added to an acrylic-modified epoxy resin. An invention relating to a body is known (see Patent Document 1).

  In addition, an acid value of 150 to 450 mg KOH / g obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of an aqueous dispersion of a carboxyl group-containing epoxy resin and a carboxyl group-containing acrylic resin, a number average molecular weight of 2,000 to An aqueous coating composition is known in which 50,000 emulsion resins are dispersed in an aqueous medium (see Patent Document 2).

  On the other hand, an aqueous coating composition containing at least one adhesion-imparting resin (C) selected from an acrylic resin-modified epoxy resin (A), a resol type phenol resin (B), a polyester resin, and a polyvinyl butyral resin is known. (See Patent Document 3).

  In addition, some of the epoxy groups in the epoxy resin may be a carboxyl having an acid value of 10 to 135 mgKOH / g, a glass transition temperature (Tg) of -20 to 20 ° C., and a weight average molecular weight of 10,000 to 200,000. A group-containing acrylic resin and an acrylic modified epoxy resin obtained by reacting with a part of carboxyl groups in a carboxyl group-containing acrylic resin having an acid value of 180 to 450 mgKOH / g, a basic compound and an aqueous medium An aqueous coating composition is known (see Patent Document 4).

  Furthermore, it is a paint for cans that has excellent adhesion and workability by dispersing core-shell fine particles in an aqueous resin composition in which fine-particle self-emulsifying epoxy resin is dispersed in an aqueous medium. Considering mutual adhesion between fine particles (islands) and polymerized portions (sea) of fine particle self-emulsifying epoxy resin, there is an invention in which the adhesion and processability of the coating film are improved (see Patent Document 5). .

  In addition, an aqueous coating composition containing an acrylic resin-modified epoxy resin, a resol type phenol resin, and a styrene copolymer rubber is known (see Patent Document 6).

JP-A-8-302275 JP-A-9-227824 JP-A-11-343456 JP 2005-187679 A JP-A-9-67543 Japanese Patent Application Laid-Open No. 11-263939

However, the coating films obtained by applying the paints described in Patent Documents 1 to 6 are not satisfactory in all of bending workability, water whitening resistance, acid adhesion resistance, flavor properties, and the like.
An object of the present invention is to find an aqueous coating composition capable of forming a coating film excellent in bending workability, water whitening resistance and flavor properties, and an aqueous coating composition for cans.

As a result of intensive studies to solve the above-mentioned problems, the present inventors blend a resol-type phenol resin (B) and a specific acrylic resin (C) with respect to the acrylic resin-modified epoxy resin (A). As a result, the inventors have found that the above problems can be solved, and have completed the present invention.
That is, the following aqueous coating composition is provided.

(1) Acrylic resin having an acid value of 100 to 500 mgKOH / g, having 0.1 to 10 parts by mass of resol type phenol resin (B) and 100 parts by mass of acrylic resin-modified epoxy resin (A) Containing 0.1 to 20 parts by mass of (C),
An aqueous coating composition comprising the acrylic resin-modified epoxy resin (A), the resol type phenolic resin (B) and the resin (C) dispersed stably in an aqueous medium.
Acrylic resin (C): a vinyl copolymer resin (c1) having a glass transition temperature of -20 to 70 ° C, and a glass transition temperature of 20 to 150 ° C, as compared with the vinyl copolymer resin (c1). It is obtained by reacting with a vinyl copolymer resin (c2) that is 10 ° C. or higher.
(2) The acrylic resin (C) is
At least one acid group-containing radical polymerizable unsaturated monomer 10 selected from acrylic acid, itaconic acid, sulfonic acid group-containing radical polymerizable unsaturated monomer and phosphoric acid group-containing radical polymerizable unsaturated monomer 10 Vinyl copolymer resin (c1) having ˜60 mass% and other radical polymerizable unsaturated monomers 40 to 90 mass% as monomer components;
A vinyl copolymer resin (c2) containing 10 to 60% by mass of methacrylic acid and 40 to 90% by mass of other radical polymerizable unsaturated monomer as monomer components;
The water-based paint composition according to the above (1), which is a polymer obtained by reacting a low molecular weight compound (c3) having two or more complementary reactive groups having reactivity with an acid group and a carboxyl group in one molecule. object.
(3) The ratio of the vinyl copolymer resin (c1), the vinyl copolymer resin (c2) and the low molecular weight compound (c3) constituting the acrylic resin (C) is as follows:
Based on the total solid content of vinyl copolymer resin (c1) and vinyl copolymer resin (c2), vinyl copolymer resin (c1) / vinyl copolymer resin (c2) = 60/40 to 95 / 5 (mass%) and [vinyl copolymer resin (c1) + vinyl copolymer resin (c2)] / low molecular weight compound (c3) = 100 / 0.1 to 100/20 (parts by mass) The water-based coating composition as described in (2) above, wherein
(4) The low molecular weight compound (c3) is at least selected from the group consisting of an epoxy resin having two or more epoxy groups in one molecule and having an epoxy equivalent of 180 to 5,000, a resol type phenol resin, and a polycarbodiimide compound. The water-based coating composition according to (2) or (3), which is one kind.
(5) The aqueous coating composition according to (4), wherein the low molecular weight compound (c3) is an epoxy resin having an epoxy equivalent of 200 to 1,000 having two or more epoxy groups in one molecule.
(6) The acrylic resin-modified epoxy resin (A) is obtained by esterifying a bisphenol type epoxy resin (a1) having a number average molecular weight of 2,000 to 35,000 and a carboxyl group-containing acrylic resin (a2). The above (1) to (1), wherein the resin or a resin obtained by graft polymerization of a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer (a3) to the bisphenol type epoxy resin (a1) (5) The water-based coating composition in any one of.
(7) The above (1), further comprising 1 to 50 parts by mass of anionic polymer crosslinked fine particles (D) having the following characteristics with respect to 100 parts by mass of the acrylic resin-modified epoxy resin (A) ) To (6).
Anionic polymer crosslinked fine particles (D): in the presence of water, carboxyl group-containing radically polymerizable monomer (d1) 2 to 30% by mass, polyvinyl compound (d2) 2 to 30% by mass and other radical polymerization It comprises a polymer having an acid value of 10 to 100 mgKOH / g, which is produced by polymerizing a radically polymerizable unsaturated monomer component comprising 40 to 96% by mass of a polymerizable unsaturated monomer (d3).
(8) An aqueous coating composition for cans, wherein the aqueous coating composition according to any one of (1) to (7) is applied to a can.

  According to the present invention, since the bending workability, water whitening resistance, and acid resistance adhesion are improved, a metal can having a coating film having excellent corrosion resistance to contents and excellent flavor properties can be obtained.

Below, the water-based coating composition of this invention is demonstrated.
[Water-based paint composition]

<Acrylic resin-modified epoxy resin (A)>
The acrylic resin-modified epoxy resin (A) may be any of the following resin (1) and resin (2).
Resin (1): Bisphenol type epoxy resin (a1) [hereinafter sometimes abbreviated as “epoxy resin (a1)”] and carboxyl group-containing acrylic resin (a2) [hereinafter abbreviated as “acrylic resin (a2)”. A resin obtained by an ester addition reaction. In the resin (1), the epoxy resin (a1) and the acrylic resin (a2) can be easily subjected to an ester addition reaction by heating, for example, in an organic solvent solution in the presence of an esterification catalyst.

  Resin (2): A resin obtained by graft polymerization of a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer to the bisphenol type epoxy resin (a1). In the resin (2), for example, in an organic solvent, a carboxyl group-containing polymerizable unsaturated monomer component can be graft-polymerized to the epoxy resin (a1) in the presence of a radical generator such as benzoyl peroxide. it can.

  As the bisphenol type epoxy resin (a1) used in the resin (1) and the resin (2), for example, epichlorohydrin and bisphenol may be used in the presence of a catalyst such as an alkali catalyst, if necessary, with an epoxy equivalent of 2000 to 10,000 ( A resin obtained by condensation to a high molecular weight having a number average molecular weight of 4000 to 30000), epichlorohydrin and bisphenol are condensed in the presence of a catalyst such as an alkali catalyst as necessary to obtain an epoxy equivalent of 180 to 1000 (number average molecular weight of 360 to 360). 2000) epoxy resin, a resin obtained by polyaddition reaction of this epoxy resin and bisphenol, and an epoxy ester obtained by reacting these resins or the above low molecular weight epoxy resin with a dibasic acid. Any of resins may be used.

  Examples of the bisphenol include bis (4-hydroxyphenyl) methane [bisphenol F], 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], 2, 2-bis (4-hydroxyphenyl) butane [bisphenol B], bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, p- (4-hydroxyphenyl) phenol, oxybis (4-hydroxyphenyl), sulfonylbis (4-hydroxyphenyl), 4,4′-dihydroxybenzophenone, bis (2-hydroxynaphthyl) methane and the like can be mentioned among others. Bisphenol A and bisphenol F are preferably used . The bisphenols can be used alone or as a mixture of two or more.

  Examples of the dibasic acid used in the production of the epoxy ester resin include succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, phthalic acid, hexahydrophthalic acid and the like.

  As commercially available products of the epoxy resin (a1), for example, Epicoat 1007 (epoxy equivalent of about 1,700, number average molecular weight of about 2,900) manufactured by Japan Epoxy Resin Co., Ltd., Epicoat 1009 (epoxy equivalent of about 3,500, number average) Molecular weight of about 3,750), Epicoat 1010 (epoxy equivalent of about 4,500, number average molecular weight of about 5,500); Araldite AER6099 (epoxy equivalent of about 3,500, number average molecular weight of about 3,800) manufactured by Asahi Ciba; And Epoxy R-309 (epoxy equivalent of about 3,500, number average molecular weight of about 3,800) manufactured by Mitsui Chemicals, Inc.

The number average molecular weight was measured according to JIS K 0124-83, and TSK GEL4000H _XL + G3000H _XL + G2500H _XL + G2000H _XL (Tosoh Corporation) was used as a separation column at a flow rate of 1.0 ml / min, eluent. In addition, GPC tetrahydrofuran was used to calculate from the chromatogram obtained with the RI refractometer and the calibration curve of polystyrene.

  The epoxy resin (a1) has a number average molecular weight of 2,000 to 35,000, preferably 4,000 to 30,000, and an epoxy equivalent of 1,000 to 12,000, preferably 3,000 to 3,000. A bisphenol-type epoxy resin in the range of 10,000 is preferable from the corrosion resistance of the obtained coating film.

  In the resin (1), during the ester addition reaction, the carboxyl group in the acrylic resin (a2) undergoes an ester addition reaction with the epoxy group in the epoxy resin (a1), so that the epoxy group in the epoxy resin (a1). The average number of epoxy groups per molecule of epoxy resin is 0.5 to 2, preferably 0.5 to 1.6.

  On the other hand, in the above (2), since the grafting reaction takes place by hydrogen abstraction of the epoxy resin main chain and the graft polymerization reaction proceeds, the epoxy resin (a1) may be substantially free of epoxy groups. The acrylic resin (a2) used in the resin (1) is composed of a carboxyl group-containing radical polymerizable unsaturated monomer (a3) and another radical polymerizable unsaturated monomer (a4) as monomer components. It is a copolymer resin.

  Examples of the carboxyl group-containing radical polymerizable unsaturated monomer (a3) include monomers such as (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, fumaric acid, and the like. Two or more types can be used in combination.

The other radical polymerizable unsaturated monomer (a4) may be any monomer that can be copolymerized with the carboxyl group-containing polymerizable unsaturated monomer (a3), and is appropriately selected according to the required performance. For example, aromatic vinyl monomers such as styrene, vinyltoluene, 2-methylstyrene, t-butylstyrene, chlorostyrene; methyl acrylate, ethyl acrylate, acrylic acid n-propyl, isopropyl acrylate, n-, i- or t-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl acrylate, methacrylic acid Methyl, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methacrylate C1-C18 of acrylic acid or methacrylic acid such as n-, i- or t-butyl acrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc. Alkyl ester or cycloalkyl ester of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, hydroxybutyl _C 2 -C ₈ hydroxyalkyl esters of acrylic acid or methacrylic acid such as methacrylate; N- methylolacrylamide, N- Butokishime Mention may be made of one or a mixture of two or more of N-substituted acrylamide or N-substituted methacrylamide monomers such as ruacrylamide, N-methoxymethyl acrylamide, N-methylol methacrylamide and N-butoxymethyl methacrylamide. it can.

  As the other radical polymerizable unsaturated monomer (a4), a mixture of styrene and ethyl acrylate is particularly preferable, and the constituent mass ratio of styrene / ethyl acrylate is 99.9 / 0.1 to 40/60, Furthermore, it is suitable to be in the range of 99/1 to 50/50.

  The carboxyl group-containing acrylic resin (a2) is not particularly limited in the constitutional ratio and type of the monomer, but usually the carboxyl group-containing polymerizable unsaturated monomer is 15 to 80% by mass, particularly 20 to 20%. It is preferable that it is 60 mass%, and it is preferable that another radically polymerizable unsaturated monomer (a4) is 85-20 mass%, especially 80-40 mass%.

  The carboxyl group-containing acrylic resin (a2) can be easily prepared, for example, by subjecting the above monomer composition to a solution polymerization reaction in an organic solvent in the presence of a polymerization initiator. The carboxyl group-containing acrylic resin (a2) may have a resin acid value of 100 to 400 mgKOH / g and a number average molecular weight of 5,000 to 100,000.

  The above reaction can be performed by a conventionally known method. For example, an esterification catalyst is blended in a uniform organic solvent solution of the epoxy resin (a1) and the acrylic resin (a2), so that substantially all of the epoxy groups are contained. In general, the reaction can be carried out by reacting at a reaction temperature of 60 to 130 ° C. for about 1 to 6 hours until it is consumed. Examples of the esterification catalyst include tertiary amines such as triethylamine and dimethylethanolamine, and quaternary salt compounds such as triphenylphosphine. Among them, tertiary amines are preferable. is there.

  The solid content concentration in the reaction system of the epoxy resin (a1) and the acrylic resin (a2) is not particularly limited as long as the reaction system is within a viscosity range that does not hinder the reaction. Moreover, when using an esterification catalyst at the time of carrying out ester addition reaction, the usage-amount is 0.01-1 equivalent normally with respect to 1 equivalent of epoxy groups in an epoxy resin (a1), Preferably it is 0.1. It is good to use in the range of -0.5 equivalent.

  Although it does not restrict | limit especially as a content rate of an epoxy resin (a1) and an acrylic resin (a2), Usually, it is preferable that an epoxy resin (a1) is 60-90 mass%, especially 70-85 mass%. The acrylic resin (a2) is preferably 15 to 30% by mass, particularly preferably 20% by mass.

  When the acrylic resin-modified epoxy resin (A) is a resin based on the resin (2), the polymerizable unsaturated monomer component to be graft-polymerized on the epoxy resin (a1) is a carboxyl group-containing acrylic resin in the resin (1). A polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer (a3) which is a monomer component used for the production of (a2) can be exemplified. Moreover, this component may further contain the other polymerizable unsaturated monomer (a4) used by resin (1).

  The graft polymerization reaction in the resin (2) can be performed by a conventionally known method. For example, in a solution of the epoxy resin (a1) heated to 80 to 150 ° C. in an organic solvent solution, a radical generator and polymerizable unsaturated. It can be carried out by gradually adding a uniform mixed solution with the monomer component and maintaining the same temperature for about 1 to 10 hours. Examples of the radical generator include benzoyl peroxide, t-butyl perbenzoyl octanoate, t-butyl peroxy-2-ethylhexanoate, and the like.

  As the organic solvent for preparing the resin (1) and the resin (2), a polymerizable containing an epoxy resin (a1) and an acrylic resin (a2) or a carboxyl group-containing polymerizable unsaturated monomer (a3). As long as it is an organic solvent that dissolves the unsaturated monomer component and does not interfere with the formation of the emulsion when the acrylic resin-modified epoxy resin (A) that is the reaction product is neutralized and made aqueous A conventionally well-known thing can be used.

  Specific examples of the organic solvent include isopropanol, butyl alcohol, 2-hydroxy-4-methylpentane, 2-ethylhexyl alcohol, cyclohexanol, ethylene glycol, diethylene glycol, 1,3-butylene glycol, ethylene glycol monoethyl ether, ethylene Examples include glycol monobutyl ether and diethylene glycol monomethyl ether.

  The acrylic resin-modified epoxy resin (A) obtained by the resin (1) or the resin (2) has a carboxyl group and has a resin acid value of 10 to 160 mgKOH / g, more preferably 20 to 100 mgKOH / g. It is preferable from the viewpoint of water dispersibility and coating film performance.

  The acrylic resin-modified epoxy resin (A) can be dispersed in an aqueous medium by neutralizing at least a part of the carboxyl groups in the resin with a basic compound.

  As the basic compound used for neutralization of the carboxyl group, amines and ammonia are preferably used. Representative examples of the amines include alkylamines such as trimethylamine, triethylamine, and tributylamine; alkanolamines such as dimethylethanolamine, diethanolamine, and aminomethylpropanol; and cyclic amines such as morpholine. The degree of neutralization of the acrylic resin-modified epoxy resin (A) is not particularly limited, but is usually in the range of 0.1 to 2.0 equivalent neutralization with respect to the carboxyl group in the resin (A). Is preferred.

  The aqueous medium may be only water, but may be a mixture of water and an organic solvent. Any known organic solvent can be used as the organic solvent, and those listed as organic solvents that can be used in the production of the acrylic resin-modified epoxy resin (A) can be suitably used. The amount of the organic solvent in the aqueous coating composition of the present invention is desirably in the range of 20% by mass or less from the viewpoint of environmental protection with respect to the resin solid content of the aqueous coating composition.

  In order to neutralize and disperse the acrylic resin-modified epoxy resin (A) in an aqueous medium, a conventional method may be used. For example, an acrylic resin modified with stirring in an aqueous medium containing a basic compound as a neutralizing agent. A method of gradually adding the epoxy resin (A), neutralizing the acrylic resin-modified epoxy resin (A) with a basic compound, and then adding an aqueous medium to the neutralized product with stirring or neutralizing the neutralized product Examples thereof include a method of adding a product into an aqueous medium.

<Resol type phenol resin (B)>
Although it is a resol type phenol resin (B) used for the paint composition for cans of this invention, it works as a crosslinking agent of an acrylic resin modified epoxy resin (A) and an acrylic resin (C), such as phenol and bisphenol A A phenol resin in which a phenolic and an aldehyde such as formaldehyde are condensed in the presence of a reaction catalyst to introduce a methylol group, and a part of the introduced methylol group is alkylated with an alcohol having 6 or less carbon atoms. Etherified ones are also included.

  The resol type phenol resin (B) has a number average molecular weight in the range of 200 to 2,000, preferably 300 to 1,200, and an average number of methylol groups per benzene nucleus of 0.3 to 3 It is appropriate that the number is within the range of 0.0, preferably 0.5 to 3.0, and more preferably 0.7 to 3.0. By using the above-mentioned resol type phenol resin, it is possible to form a coating film having excellent coating performance such as adhesion.

  In the can coating composition of the present invention, the resol-type phenol resin (B) is 0.1 to 20 parts by mass, preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the acrylic resin-modified epoxy resin (A). It is preferable to be within the range of 10 parts by mass. Furthermore, a surfactant, an antifoaming agent, a pigment, a wax, a fragrance and the like may be appropriately contained as necessary.

<Acrylic resin (C)>
The can coating composition of the present invention has particularly good acid resistance adhesion by blending the acrylic resin (C), and the obtained coating film has bending workability, water whitening resistance, corrosion resistance, flavor, and the like. This contributes to the formation of a coating film with excellent properties.

  The acrylic resin (C) has a glass transition temperature of −20 to 70 ° C. and a glass transition temperature of 20 to 150 ° C., and compared with the vinyl copolymer resin (c1). It is a resin obtained by reacting with a vinyl copolymer resin (c2) that is 10 ° C. or higher.

Here, the glass transition temperature (Tg) can be calculated by the following equation.
1 / Tg (° K) = (W1 / T1) + (W2 / T2) +
Tg (° C.) = Tg (° K) -273
In each formula, W1, W2,... Represent the respective weight percentages of the monomers used for copolymerization, and T1, T2,... Represent the Tg (° K) of the monomer homopolymer. T1, T2,... Are values according to Polymer Hand Book (Second Edition, edited by J. Brandup / E.H. Immergut).

  The glass transition temperature (° C.) when the Tg of the homopolymer of the monomer is not clear is the static glass transition temperature. For example, a differential scanning calorimeter “DSC-50Q type” (manufactured by Shimadzu Corporation, trade name) is used. The sample was taken into a measuring cup, and the solvent was completely removed by vacuum suction, and then the change in calorie was measured in the range of −100 ° C. to + 100 ° C. at a temperature rising rate of 3 ° C./min to obtain the glass transition temperature.

Vinyl copolymer resin (c1):
The vinyl copolymer resin (c1) is preferably at least one selected from acrylic acid, itaconic acid, a sulfonic acid group-containing radical polymerizable unsaturated monomer, and a phosphoric acid group-containing radical polymerizable unsaturated monomer. 10 to 60% by mass, preferably 20 to 55% by mass, more preferably 30 to 50% by mass of the acid group-containing radically polymerizable unsaturated monomer, and other radically polymerizable unsaturated monomers not containing an acid (1) A mixture (1) containing 40 to 90% by mass, preferably 45 to 80% by mass, and more preferably 50 to 70% by mass as a monomer component is obtained by radical polymerization reaction in an applicable solvent. .

  When at least one radical polymerizable monomer selected from acrylic acid, itaconic acid, sulfonic acid group-containing radical polymerizable unsaturated monomer and phosphoric acid group-containing radical polymerizable unsaturated monomer is less than 10% by mass If the adhesiveness is reduced and the content exceeds 60% by mass, the water resistance may be impaired.

  Examples of the acrylic acid group-containing radical polymerizable unsaturated monomer include acrylic acid, and examples of the itaconic acid group-containing radical polymerizable unsaturated monomer include itaconic acid. Examples of the sulfonic acid group-containing radical polymerizable monomer include 2-acrylamido-2-methylpropanesulfonic acid. Examples of the phosphoric acid group-containing radical polymerizable monomer include mono (2-hydroxyethyl methacrylate) phosphate.

Examples of the other radical polymerizable unsaturated monomer (1) include vinyl aromatic compounds such as styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, and vinylpyridine; for example, 2-hydroxyethyl (meth) acrylate. , 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) _C 2 -C ₈ hydroxyalkyl acrylic acid or methacrylic acid acrylate (meth) acrylate, (poly) ethylene glycol mono (meth) acrylate, Hydroxyl group-containing radical polymerizable unsaturated monomers such as polypropylene glycol mono (meth) acrylate and polybutylene glycol mono (meth) acrylate; these hydroxyl group-containing radical polymerizable unsaturated monomers and β-propiolactone, dimethylpropio Lactone, butyrolol Reaction products with lactone compounds such as kuton, γ-valerolactone, γ-caprolactone, γ-caprolactone, γ-laurolactone, ε-caprolactone, δ-caprolactone, etc., for example, Plaxel FM-1, Plaxel FM -2, Plaxel FM-3, Plaxel FA-1, Plaxel FA-2, Plaxel FA-3 (above, trade name, manufactured by Daicel Chemical Industries, caprolactone-modified (meth) acrylic acid hydroxy esters) and the like; for example, methyl (meta ) Acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, etc. acid of _C 1 _{~C 18} of Alkyl or cycloalkyl esters; for example, N- (2-hydroxyethyl) (meth) acrylamide, N- (2-hydroxypropyl) (meth) acrylamide, N- (3-hydroxypropyl) (meth) acrylamide, N- Methyl-N- (2-hydroxyethyl) (meth) acrylamide, N-ethyl-N- (2-hydroxyethyl) (meth) acrylamide, N-methyl-N- (2-hydroxypropyl) (meth) acrylamide, N -Methyl-N- (3-hydroxypropyl) (meth) acrylamide, N-ethyl-N- (2-hydroxypropyl) (meth) acrylamide, N-ethyl-N- (3-hydroxypropyl) (meth) acrylamide, N, N-di- (2-hydroxyethyl) (meth) acrylamide, N, N- -Nitrogen-containing radically polymerizable unsaturated monomers such as (2-hydroxypropyl) (meth) acrylamide; for example, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane Vinyldimethylethoxysilane, vinyltripropoxysilane, vinylmethyldipropoxysilane, vinyldimethylpropoxysilane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, γ- (meth) Acryloyloxypropyldimethylmethoxysilane, etc .; alkoxysilyl group-containing radical polymerizable unsaturated monomers; divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol Cold di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4-butanediol diacrylate, glycerin di (meth) Acrylate, glycerin tri (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate , Dipentaerythritol penta (meth) acrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, glycerol allyloxy di Meth) acrylate, 1,1,1-tris (hydroxymethyl) Etanji (meth) acrylate, 1,1,1-tris (polyvinyl compound such as hydroxymethyl) Etantori (meth) acrylate; and the like. The other radical polymerizable monomer (1) does not contain an acid.

  In the production of the vinyl copolymer resin (c1), at least one selected from acrylic acid, itaconic acid, a sulfonic acid group-containing radical polymerizable unsaturated monomer, and a phosphoric acid group-containing radical polymerizable unsaturated monomer. The temperature of the radical polymerization reaction by the mixture (1) containing the radical polymerizable monomer and the other radical polymerizable unsaturated monomer (1) is carried out using an appropriate solvent in the presence of a polymerizable initiator. . The reaction temperature is usually in the range of about 60 to 200 ° C., preferably about 70 to 160 ° C., and the reaction time is usually about 10 hours or less, preferably about 0.5 to about 6 hours.

  As said polymerization initiator, what is generally used as radical polymerization initiators, such as t-butyl peroxy 2-ethyl hexanoate (perbutyl O), can be used, and a compounding quantity is a mixture (1). It is 0.05-3 mass% with respect to the total amount of.

  Examples of the solvent include hydrocarbons such as toluene, xylene, cyclohexane and n-hexane; esters such as methyl acetate, ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and methyl amyl ketone; Examples include amide systems such as dimethylformamide and dimethylacetamide; alcohol systems such as methanol, ethanol, n-propanol, and iso-propanol; or a mixture thereof.

Vinyl copolymer resin (c2):
Vinyl copolymer resin (c2) is 10-60 mass% of methacrylic acid with respect to the sum total of the monomer which comprises vinyl copolymer resin (c2), Preferably it is 15-55 mass%, More preferably, 20 -50% by mass, other radical polymerizable monomer monomer (2) 40-90% by mass, preferably 45-80% by mass, more preferably 50-75% by mass as a monomer component ( 2) is a resin obtained by a radical polymerization reaction in an applicable solvent. The other radical polymerizable monomer (2) does not contain an acid.

  If the methacrylic acid is less than 10% by mass, the adhesiveness is lowered, and if it exceeds 60% by mass, the water resistance may be impaired. As the other radical polymerizable monomer (2), one or more other radical polymerizable unsaturated monomers similar to those used for the vinyl copolymer resin (c1) can be selected and used. .

  The vinyl copolymer resin (c2) is obtained from the acrylic acid, itaconic acid, the sulfonic acid group-containing radical polymerizable monomer, and the phosphate group-containing radical polymerizable monomer used in the vinyl copolymer resin (c1). It is characterized by not using at least one selected radically polymerizable monomer.

In the production of vinyl copolymer resin (c2), the radical polymerization reaction with mixture (2) containing methacrylic acid and other radical polymerizable unsaturated monomer (2) is carried out in the presence of a polymerization initiator, Use an appropriate solvent.
The reaction temperature is usually in the range of about 60 to 200 ° C., preferably about 70 to 160 ° C., and the reaction time is usually about 10 hours or less, preferably about 0.5 to about 6 hours. As the polymerization initiator and the solvent, the same solvents as those used for the vinyl copolymer resin (c1) can be appropriately selected and used.

Low molecular weight compound (c3):
In the acrylic resin (C), in the presence of the vinyl copolymer resin (c1) and the vinyl copolymer resin (c2), a complementary reactive group having reactivity with an acid group and a carboxyl group is contained in one molecule. It is preferably a polymer obtained by reacting a low molecular weight compound (c3) having two or more and having a number average molecular weight of 360 to 10,000. It is preferable that the number average molecular weight of the low molecular weight compound (c3) is within the above range because (c1) and (c2) are likely to react.

  As the low molecular weight compound (c3), an epoxy equivalent having two or more epoxy groups in one molecule is 180 to 5,000, preferably 200 to 1,000 epoxy resin, resol type phenol resin, and polycarbodiimide compound. At least one selected can be used.

  Examples of commercially available epoxy resins include Epicoat 828 (epoxy equivalent of about 180, number average molecular weight of about 360), Epicoat 834 (epoxy equivalent of about 235, number average molecular weight of about 470), and Epicoat 1007 (epoxy) manufactured by Japan Epoxy Resin Co., Ltd. Equicoat about 1,700, number average molecular weight of about 2,900, Epicoat 1009 (epoxy equivalent of about 3,500, number average molecular weight of about 3,750), Epicoat 1010 (epoxy equivalent of about 4,500, number average molecular weight of about 5, 500); Araldite AER6099 (epoxy equivalent of about 3,500, number average molecular weight of about 3,800) manufactured by Asahi Ciba; and Epomic R-309 (epoxy equivalent of about 3,500, number average molecular weight of about 3800) manufactured by Mitsui Chemicals, Inc. 3,800).

  Among these, as the epoxy resin, Epicoat 828 and Epicoat 834 are preferable from the viewpoint of reaction efficiency between the vinyl copolymer resin (c1) and the vinyl copolymer resin (c2).

  As the resol type phenol resin, the same one as the resol type phenol resin (B) can be used. For example, Shonor BKS377 (number average molecular weight of about 1000, manufactured by Showa Polymer Co., Ltd.) can be mentioned as a commercial product.

  The polycarbodiimide compound can be obtained by reacting a polyisocyanate compound in an inert solvent in the presence of a carbodiimidization catalyst. A dicarbodiimide compound such as dicyclohexylcarbodiimide can also be used as the polycarbodiimide compound. Examples of commercially available products include Nisshinbo's Carbodilite (registered trademark) series such as Carbodilite V-02 (number average molecular weight of about 1200), Carbodilite V-04 (number average molecular weight of about 700), and the like.

  Examples of the polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, bis (isocyanatomethyl) cyclohexane, tetramethylene diisocyanate, hexamethylene. Aromatic, alicyclic or aliphatic diisocyanate compounds such as diisocyanate, methylene diisocyanate, isophorone diisocyanate and the isocyanurate thereof, and of these isocyanate compounds Examples include terminal isocyanate-containing compounds obtained by reacting low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, trimethylolpropane, and hexanetriol with an excess amount.

  Examples of the inert solvent include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as dioxane; and solvents such as dimethylformamide. Various catalysts can be used as the catalyst for promoting the carbodiimidization of the polyisocyanate compound, but 1-phenyl-2-phospholene-1-oxide, 3-methyl-1-phenyl-2-phospholene-1-oxide, 1 -Phenyl-2-phospholene-1-sulfide, 1-ethyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene 1-oxide, their corresponding isomers, 3-phospholenes Etc. are good. The catalyst amount can be used within a range of 0.01 to 1% by weight based on the total amount of the polyisocyanate compound.

  In the production of the acrylic resin (C), the reaction temperature in the radical polymerization reaction using the vinyl copolymer resin (c1), the vinyl copolymer resin (c2) and the low molecular weight compound (c3) described above is: Usually, it is in the range of about 60 to 200 ° C., preferably about 70 to 160 ° C., and the reaction time is usually about 10 hours or less, preferably about 0.5 to about 6 hours.

  As a reaction ratio of the vinyl copolymer resin (c1), the vinyl copolymer resin (c2), and the low molecular weight compound (c3), the vinyl copolymer resin (c1) constituting the acrylic resin (C) and the vinyl copolymer resin are used. The polymer resin (c2) and the low molecular weight compound (c3) are converted into a vinyl copolymer resin (c1) / c based on the total solid content of the vinyl copolymer resin (c1) and the vinyl copolymer resin (c2). Vinyl copolymer resin (c2) = 60/40 to 95/5 (mass%), preferably 75/25 to 85/15 (mass%), and [vinyl copolymer resin (c1) + vinyl Copolymer resin (c2)] / low molecular weight compound (c3) = 100 / 0.1 to 100/20 (parts by mass), preferably 100/2 to 100/10 (parts by mass) . By setting the blending ratio in this range, a film excellent in adhesion and corrosion resistance can be obtained.

  The acrylic resin (C) thus obtained has a glass transition temperature of 20 to 90 ° C, preferably 30 to 70 ° C, more preferably 40 to 55 ° C, and an acid value of 100 to 500 mgKOH / g, preferably 200. It is -480 mgKOH / g, More preferably, it is 300-450 mgKOH / g. The number average molecular weight is 1,000 to 25,000, preferably 2,000 to 20,000, and more preferably 3,000 to 10,000.

  The aqueous coating composition in the present invention is 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight, more preferably 100 parts by weight of acrylic resin-modified epoxy resin (A). 2 to 5 parts by mass can be contained.

<Anionic polymer fine particles (D)>
The aqueous coating composition of the present invention can be appropriately mixed with anionic polymer fine particles (D). Examples of the anionic polymer fine particles (D) include radical polymerizable monomers comprising a carboxyl group-containing radical polymerizable monomer (d1), a polyvinyl compound (d2), and other radical polymerizable unsaturated monomers (d3). It consists of a polymer obtained from a saturated monomer. Here, the content of each radical polymerizable unsaturated monomer is 2 to 30% by mass of the carboxyl group-containing radical polymerizable monomer (d1) with respect to the total solid content of the constituting radical polymerizable monomer. , Preferably 5 to 15% by mass, polyvinyl compound (d2) 2 to 30% by mass, preferably 5 to 15% by mass, other radical polymerizable unsaturated monomer (d3) 40 to 96% by mass, preferably It is 70-90 mass%.

  If the carboxyl group-containing radical polymerizable monomer (d1) is less than 2% by mass, water dispersibility becomes insufficient, and if it exceeds 30% by mass, corrosion resistance may be impaired. If the polyvinyl compound (d2) is less than 2% by mass, the water whitening resistance is insufficient, and if it exceeds 30% by mass, the particle size becomes unfavorable. Specific examples of the anionic polymer fine particles (D) include the following anionic polymer fine particles (D1) or anionic polymer fine particles (D2).

Anionic polymer fine particles (D1):
Carboxyl group-containing radically polymerizable monomer (d1) 5% by mass or less, preferably 3% by mass, polyvinyl compound (d2) 4 to 35% by mass, preferably 10 to 25% by mass, and other radical polymerizable monomers A first stage of using a polymerization initiator in the presence of water, a mixture of radically polymerizable monomers (3) containing 60 to 96% by weight, preferably 75 to 90% by weight of a saturated monomer (d31). The aqueous dispersion (I) is obtained by emulsion polymerization.
Subsequently, the carboxyl group-containing radical polymerizable monomer (d1) is 10 to 35% by mass, preferably 15 to 25% by mass and the other radical polymerizable unsaturated monomer (d32) 65 to 90% by mass, preferably 75%. A mixture of radically polymerizable monomers (4) containing ˜85% by mass is subjected to a second stage emulsion polymerization using a polymerization initiator in the presence of the aqueous dispersion (I) and water, Anionic polymer crosslinked fine particles (D1) are obtained.

  Examples of the carboxyl group-containing radical polymerizable monomer (d1) include monomers such as (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, fumaric acid, etc., and these may be used alone or in combination of two or more. Can be used.

  Examples of the polyvinyl compound (d2) include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3- Butylene glycol di (meth) acrylate, 1,4-butanediol diacrylate, glycerin di (meth) acrylate, glycerin tri (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, penta Erythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate , Neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, glycerol allyloxy di (meth) acrylate, 1,1,1-tris (hydroxymethyl) ethanedi (meth) acrylate, 1,1,1- Tris (hydroxymethyl) ethane tri (meth) acrylate and the like can be mentioned, and can be appropriately selected from these.

  Furthermore, as the polyvinyl compound (d2), an adduct obtained by reacting an epoxy resin having an epoxy equivalent of 180 to 1,000 having two or more epoxy groups in the molecule with methacrylic acid and / or acrylic acid is also used. can do. Specifically, methacrylic acid and / or acrylic acid is 0.5 to 0.98 mol, preferably 0.65 to 0.95 mol, and more preferably 0.75 to 1 mol of the functional group in the epoxy resin. It is an adduct obtained by subjecting ˜0.9 mol to an addition reaction at a reaction temperature of 60 to 150 ° C. for 10 minutes to 180 minutes.

Other radical polymerizable unsaturated monomers (d31) include, for example, vinyl aromatic compounds such as styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, vinylpyridine, etc .; for example, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) _C 2 -C ₈ hydroxyalkyl acrylic acid or methacrylic acid acrylate (meth) acrylate, (poly) ethylene glycol mono (meth) acrylate Hydroxyl group-containing radical polymerizable unsaturated monomers such as polypropylene glycol mono (meth) acrylate and polybutylene glycol mono (meth) acrylate; these hydroxyl group-containing radical polymerizable unsaturated monomers β-propiolactone, dimethylpropio Lactone, buty Reaction products with lactone compounds such as lolactone, γ-valerolactone, γ-caprolactone, γ-caprolactone, γ-laurolactone, ε-caprolactone, δ-caprolactone, etc., for example, Plaxel FM-1, Plaxel FM -2, Plaxel FM-3, Plaxel FA-1, Plaxel FA-2, Plaxel FA-3 (trade name, manufactured by Daicel Chemical Industries, caprolactone-modified (meth) acrylic acid hydroxyesters) and the like; (Meth) acrylates such as (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, etc. _C 1 _~C of acrylic acid Etc. ₈ alkyl or cycloalkyl esters; for example, N- (2- hydroxyethyl) (meth) acrylamide, N-(2-hydroxypropyl) (meth) acrylamide, N-(3- hydroxypropyl) (meth) acrylamide N-methyl-N- (2-hydroxyethyl) (meth) acrylamide, N-ethyl-N- (2-hydroxyethyl) (meth) acrylamide, N-methyl-N- (2-hydroxypropyl) (meth) Acrylamide, N-methyl-N- (3-hydroxypropyl) (meth) acrylamide, N-ethyl-N- (2-hydroxypropyl) (meth) acrylamide, N-ethyl-N- (3-hydroxypropyl) (meth) ) Acrylamide, N, N-di- (2-hydroxyethyl) (meth) acrylamide, Nitrogen-containing radically polymerizable unsaturated monomers such as N-di- (2-hydroxypropyl) (meth) acrylamide; for example, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinyl Methyldiethoxysilane vinyldimethylethoxysilane, vinyltripropoxysilane, vinylmethyldipropoxysilane, vinyldimethylpropoxysilane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, γ -(Meth) acryloyloxypropyldimethylmethoxysilane and the like; alkoxysilyl group-containing radical polymerizable unsaturated monomer.

  A mixture (3) of a radical polymerizable monomer containing a carboxyl group-containing radical polymerizable monomer (d1), a polyvinyl compound (d2) and another radical polymerizable monomer (d31) in the presence of water. In step (1), the first stage emulsion polymerization reaction is performed using a polymerization initiator to produce an aqueous dispersion (I). The reaction temperature is usually in the range of about 60 to 90 ° C., preferably about 75 to 85 ° C., and the reaction time is usually about 10 hours or less, preferably about 0.5 to about 6 hours.

  Next, emulsion polymerization in the second and subsequent stages is performed using a polymerization initiator in the presence of the aqueous dispersion (I), the mixture (4) and water. As the carboxyl group-containing radical polymerizable monomer (d1) contained in the mixture (4), at least one kind of the same monomers used in the mixture (3) can be selected and used. As the other radical polymerizable monomer (d32) contained in the mixture (4), the polyvinyl compound (d2) used in the first stage emulsion polymerization reaction and the other radical polymerizable monomer (d31) are used. At least one type can be selected and used.

  In addition, the mass ratio of the aqueous dispersion (I) to the mixture (4) when used for the production of the anionic polymer crosslinked fine particles (D1) is based on the total amount of each mixture. I) / mixture (4) = 50/50 to 90/10 (mass ratio), preferably 70/30 (mass ratio) to 85/15 (mass ratio).

  In addition, as a polymerization initiator used in the first stage emulsion polymerization reaction and the second stage emulsion polymerization reaction, ammonium persulfate, potassium persulfate, and sodium persulfate can be used, and the blending amount is 0.05-3. The mass is preferably 0.1 to 1.0 mass%.

  Examples of the emulsifier include sodium salts and ammonium salts such as alkylsulfonic acid, alkylbenzenesulfonic acid, and alkylphosphoric acid. In addition, these anionic groups and nonionic anionic emulsifiers having nonionic groups such as polyoxyethylene or polyoxypropylene chains in one molecule, and reactivity having these anionic groups and polymerizable unsaturated groups in one molecule Anionic emulsifiers.

  Specifically, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, Nonionic emulsifiers such as polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate; dimethylalkyl Zwitterionic emulsifiers such as bedaines, dimethylalkyllauryl bedaines, alkylglycines, and the like.

  The concentration of the emulsifier is 0.1 to 20% by mass, preferably about 0.5 to 10% by mass, based on the total amount of monomers constituting the mixture (3) or the mixture (4). Also preferred for performance. The polymerization reaction after the first stage and the second stage is performed in a suitable solvent at a temperature of about 60 to about 95 ° C., preferably about 75 to about 85 ° C. for about 1 to 5 hours, preferably about 2 to 4 hours. It can be carried out.

  The obtained anionic polymer crosslinked fine particles (D1) have an acid value of 1 to 100 mgKOH / g, preferably 20 to 80 mgKOH / g, more preferably 40 to 75 mgKOH / g, and an average particle size of 0.01 to 0. 0.5 μm, preferably 0.1 to 0.35 μm, more preferably 0.10 to 0.25 μm. This range is preferable for forming a coating film excellent in drawing ironing processability and water whitening resistance.

  The average particle size was determined by diluting the sample with deionized water to a concentration suitable for measurement with a submicron particle analyzer N4 (trade name, manufactured by Beckman Coulter, Inc., particle size distribution measuring device) Degree).

Anionic polymer fine particles (D2):
First, carboxyl group-containing radical polymerizable monomer (d1) 20 to 60% by mass, preferably 35 to 55% by mass, and other radical polymerizable unsaturated monomer (d33) 40 to 80% by mass, preferably A polymer (I) is obtained by radical polymerization reaction of a mixture (5) of radically polymerizable monomers containing 45 to 65% by mass.

  Next, 4 to 33% by mass of the polyvinyl compound (d2), preferably 10 to 25% by mass, and 67 to 96% by mass of other radical polymerizable unsaturated monomer (d34), preferably 75 to 90% by mass. The mixture (6) of the radical polymerizable monomer contained is subjected to emulsion polymerization in the presence of the polymer (I) and water to obtain anionic polymer fine particles (D2).

  Regarding the production of the polymer (I), the carboxyl group-containing radical polymerizable monomer (d1) used in the mixture (5) is the same carboxyl group as that used in the production of the anionic polymer fine particles (D1). The containing radically polymerizable monomer (d1) can be used, and examples thereof include monomers such as (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, fumaric acid, etc., and these can be used alone or in combination of two or more. Can be used.

  Examples of the other radical polymerizable unsaturated monomer (d33) include the polyvinyl compound (d2) used for the production of the anionic polymer fine particles (D1) and the other radical polymerizable monomer (d31). At least one or more types can be appropriately selected and used.

  The radical polymerization reaction using the mixture (5) uses a polymerization initiator in a suitable solvent at a temperature of about 90 to about 170 ° C., preferably about 100 to about 150 ° C., preferably about 1 to 5 hours, preferably After about 2 to 4 hours, the polymer (I) can be obtained.

  Examples of the solvent used in the above reaction include hydrocarbons such as toluene, xylene, cyclohexane, and n-hexane; esters such as methyl acetate, ethyl acetate, and butyl acetate; acetone, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone. Examples include ketones; amides such as dimethylformamide and dimethylacetamide; alcohols such as methanol, ethanol, n-propanol, and iso-propanol; or a mixture thereof. As the polymerization initiator, azobisisobutyronitrile (AIBN), t-butylperoxy 2-ethylhexanoate (perbutyl O), or the like can be used.

  Subsequently, the polyvinyl compound (d2) is contained in an amount of 4 to 33% by mass, preferably 5 to 25% by mass, and other radical polymerizable unsaturated monomer (d34) 67 to 96% by mass, preferably 60 to 90% by mass. Using the mixture (6), an emulsion polymerization reaction is carried out in the presence of the polymer (I) and water.

  As the polyvinyl compound (d2), one or more monomers similar to those used for the production of the anionic polymer fine particles (D1) can be selected and used. As the other radical polymerizable monomer, the same carboxyl group-containing radical polymerizable monomer (d1) as used for the production of the anionic polymer fine particles (D1) or other radical polymerizable monomers At least one or more types can be appropriately selected from (d31).

  In addition, the mass ratio of the polymer (I) and the mixture (6) when used for the production of the anionic polymer fine particles (D2) is based on the total amount of each mixture, and the polymer (I) / Mixture (6) = 25/75 to 85/15 (mass ratio), preferably 60/40 (mass ratio) to 80/20 (mass ratio).

  In the reaction, a polymerization initiator such as ammonium persulfate, potassium persulfate, sodium persulfate, azobisisobutyronitrile (AIBN), t-butylperoxy 2-ethylhexanoate (perbutyl O), or the like can be used. As a density | concentration of the said polymerization initiator, it is 0.05-3 mass% with respect to the total amount of the monomer which comprises a mixture (6) or polymer (I), Preferably it is 0.1-10 mass%. is there.

  The concentration of the emulsifier is 0.3 to 3% by mass, preferably about 0.5 to 2% by mass, based on the total amount of monomers constituting the mixture (6) or the polymer (I). Also preferred for performance. If the conditions are selected, particles can be formed without an emulsifier.

  The reaction temperature in the emulsion polymerization reaction using the mixture (6) in the presence of the polymer (I) and water is usually about 60 to 95 ° C., preferably about 75 to 85 ° C., and the reaction The time is usually about 10 hours or less, preferably about 0.5 to about 6 hours.

  The obtained anionic polymer crosslinked fine particles (D2) have an acid value of 10 to 120 mgKOH / g, preferably 30 to 100 mgKOH / g, more preferably 50 to 90 mgKOH / g. The average particle diameter is 0.05 to 1.0 μm, preferably 0.10 to 0.50 μm, and more preferably 0.10 to 0.30 μm. This range is preferable for forming a coating film excellent in drawing ironing processability and water whitening resistance.

  The water-based coating composition of the present invention further comprises bending workability, water whitening resistance and flavor by blending the above-mentioned anionic polymer fine particles (D1) or anionic polymer fine particles (D2) in the paint. A coating film with an excellent balance of properties can be obtained.

  The amount of the anionic polymer fine particles (D1) or the anionic polymer fine particles (D2) blended in the aqueous coating composition of the present invention is 1 to 50 per 100 parts by mass of the acrylic resin-modified epoxy resin (A). A part by mass, preferably within a range of 5 to 30 parts by mass is appropriate. This range is also preferable for improving coating film performance such as bending workability, water whitening resistance and flavor.

  The water-based coating composition of the present invention can be applied to various base materials, such as untreated or surface-treated metal plates such as aluminum plates, steel plates, tin plates, etc., and epoxy-based, vinyl on these metal plates. Examples of such a metal plate coated with a primer such as a metal plate may include those obtained by processing these metal plates into cans.

  Various known methods such as roll coater coating, spray coating, dip coating, and electrodeposition coating can be applied as a method of coating the aqueous coating composition of the present invention on the substrate. Of these, roll coater coating or spray coating is preferred. The coating thickness may be appropriately selected depending on the use, but is usually preferably about 3 to 20 μm. As the drying conditions of the coated film, it is usually within the range of 10 seconds to 30 minutes, preferably at 200 to 280 ° C. for 15 seconds to 10 minutes under the condition that the maximum material arrival temperature is 120 to 300 ° C. Good.

  Moreover, the coating film cross-section obtained by coating the water-based coating composition with the anionic polymer crosslinked fine particles (D) is characterized by forming a sea-island structure as shown in FIG. By forming such a sea-island structure, it is thought that it contributes to the improvement of bending workability. As the sea-island structure, it is preferable that an island portion having a diameter of 0.01 to 0.5 μm, preferably 0.05 to 0.35 μm, more preferably 0.08 to 0.15 μm is observed.

  The present invention will be described more specifically with reference to examples.

Production Examples 1 to 3 [Production of acrylic resin-modified epoxy resin (A)]
Production Example 1 Production of epoxy resin solution (a1)
A four-necked flask equipped with a reflux tube, a thermometer, and a stirrer was charged with 558 parts by mass of Epicoat 828EL, 329 parts by mass of bisphenol A, and 0.6 parts by mass of tetrabutylammonium bromide at 160 ° C. under a nitrogen stream. Reaction was performed. The reaction was monitored by epoxy equivalent and reacted for about 5 hours to obtain a bisphenol A type epoxy resin having a number average molecular weight of about 11,000 and an epoxy equivalent of about 8,000.
Note that Epicoat 828EL is a bisphenol A type epoxy resin (epoxy equivalent: about 190, molecular weight: about 350, manufactured by Japan Epoxy Resin Co., Ltd.).

Production Example 2 Production of carboxyl group-containing acrylic resin solution (a2)
A four-necked flask equipped with a reflux tube, a thermometer, a dropping funnel, and a stirrer was charged with 882 parts by mass of n-butanol, “180 parts by mass of methacrylic acid, 240 parts by mass of styrene, 180 parts by mass of ethyl acrylate, and t-butyl. A mixture of “18 parts by mass of peroxy-2-ethylhexanoate” was heated to 100 ° C. under a nitrogen stream, and was added dropwise from the dropping funnel in about 3 hours. After the addition, the mixture was further stirred at the same temperature for 2 hours. Subsequently, the mixture was cooled to obtain an acrylic resin solution having a solid content of 40% by mass. The obtained resin (solid content) had a resin acid value of 196 mg KOH / g and a number average molecular weight of about 19,000.

Production Example 3 Production of acrylic-modified epoxy resin dispersion (A)
In a four-necked flask equipped with a reflux tube, a thermometer, and a stirrer, 80 parts by mass of the bisphenol A type epoxy resin obtained in Production Example 1 (solid content) and 50% by mass of the 40% acrylic resin solution obtained in Production Example 2 Parts (solid content 20 parts by mass), diethylene glycol monobutyl ether 33 parts by mass, heated to 100 ° C. and dissolved, then added 2 parts by mass N, N-dimethylaminoethanol and reacted for about 2 hours. N, N-dimethylaminoethanol (3 parts by mass) was added and the reaction was continued for 20 minutes. Thereafter, 165 parts by mass of deionized water was added dropwise over 1 hour to perform water dispersion to obtain an acrylic-modified epoxy resin dispersion having an acid value of 34 mgKOH / g and a solid content of 30% by mass.

Production Example 4 [Production of Resol Type Phenolic Resin (B)]
A four-necked flask equipped with a reflux tube, a thermometer, and a stirrer was charged with 188 parts by mass of phenol and 324 parts by mass of a 37% by mass aqueous formaldehyde solution, and heated to 50 ° C. to uniformly dissolve the contents. Next, zinc acetate was added and mixed to adjust the pH in the system to 5.0, and then heated to 90 ° C. and reacted for 5 hours. Next, the mixture was cooled to 50 ° C., and a 32% by mass calcium hydroxide aqueous dispersion was slowly added to adjust the pH to 8.5, followed by reaction at 50 ° C. for 4 hours.
After completion of the reaction, the pH was adjusted to 4.5 with 20% by mass hydrochloric acid, and then the resin was extracted with a mixed solvent of xylene / n-butanol / cyclohexane = 1/2/1 (mass ratio) to obtain a catalyst, The salt was removed and then azeotropically dehydrated under reduced pressure to obtain a light yellow and transparent resol type phenolic resin solution having a solid content of 60% by mass.

Production Examples 5 to 10 [Production of acrylic resin (C)]
Production Example 5
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device was charged with 70 parts by mass of propylene glycol n-propyl ether, stirred and mixed in a nitrogen stream, and heated to 100 ° C.
Then, a monomer mixture (methyl methacrylate 20 parts by mass, 2 ethylhexyl acrylate 30 parts by mass, acrylic acid 50 parts by mass) and a polymerization initiator solution (t-butylperoxy-2-ethylhexanoate 8 parts by mass, propylene glycol (mixture of 50 parts by mass of n-propyl ether) was dropped into the reactor with a metering pump over 4 hours, and aging was carried out for 0.5 hours after the completion of dropping. Subsequently, a polymerization initiator solution (a mixed solution of 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate and 30 parts by mass of propylene glycol n-propyl ether) was dropped for 0.5 hours and aged for 2 hours. Went. Thereafter, it is cooled to 60 ° C., filtered and discharged through a 100 mesh nylon cloth, an acrylic resin (c1) having a solid content of 40% by mass, a glass transition temperature of 38 ° C., an acid value of 390 mgKOH / g, and a number average molecular weight of 4,000. Got.
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device was charged with 70 parts by mass of propylene glycol n-propyl ether, stirred and mixed in a nitrogen stream, and heated to 100 ° C. Thereafter, a monomer mixture (50 parts by weight of methacrylic acid, 30 parts by weight of ethyl acrylate, 20 parts by weight of styrene) and a polymerization initiator solution (8 parts by weight of t-butylperoxy-2-ethylhexanoate, propylene glycol n- A mixed solution of 50 parts by mass of propyl ether) was dropped into the reactor with a metering pump over 4 hours, and aging was performed for 0.5 hours after the completion of the dropping. Subsequently, a polymerization initiator solution (a mixed solution of 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate and 30 parts by mass of propylene glycol n-propyl ether) was dropped for 0.5 hours and aged for 2 hours. Went. Thereafter, it is cooled to 60 ° C., filtered and discharged through a 100 mesh nylon cloth, and a resin (c2) having a solid content of 40% by mass, a glass transition temperature of 92 ° C., an acid value of 326 mgKOH / g, and a number average molecular weight of 4,000 is obtained. It was.
Next, the resin (c2) was added to the acrylic resin (c1) at 100 ° C. Next, 5 parts by mass of Epicoat 834 (manufactured by Japan Epoxy Resin Co., Ltd., epoxy resin, epoxy equivalent of about 235, number average molecular weight of about 470, corresponding to low molecular weight compound (c3)) was added, the temperature was raised to 130 ° C., and 3 hours Aged. Thereafter, it is diluted with propylene glycol n-propyl ether, cooled to 60 ° C., filtered and discharged through a 100 mesh nylon cloth, an acrylic resin having a solid content of 40% by mass, a glass transition temperature of 48 ° C., and an acid value of 347 mg KOH / g. No. 1 was obtained.

Production Examples 6 to 10
Acrylic resin No. 2 was prepared in the same manner as in Production Example 5 except that the monomer used was the content of Table 1. 2-No. 6 was obtained.
Shonor BKS-377F is a resol type phenolic resin (solid content 50 mass%, number average molecular weight about 1000, manufactured by Showa Polymer Co., Ltd.) (the same applies hereinafter).

Comparative production example 1 (according to JP-A-8-302275)
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device was charged with 70 parts by mass of propylene glycol n-propyl ether, stirred and mixed in a nitrogen stream, and heated to 100 ° C.
Thereafter, a monomer mixture (acrylic acid 10 parts by mass, methyl methacrylate 40 parts by mass, ethyl acrylate 50 parts by mass) and a polymerization initiator solution (t-butylperoxy-2-ethylhexanoate 8 parts by mass, propylene glycol n A mixed solution of 50 parts by mass of propyl ether) was dropped into the reactor with a metering pump over 4 hours, and aging was performed for 0.5 hours after the completion of the dropping.
Subsequently, a polymerization initiator solution (a mixed solution of 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate and 30 parts by mass of propylene glycol n-propyl ether) was dropped for 0.5 hours and aged for 2 hours. Went. Thereafter, the mixture was cooled to 60 ° C., filtered and discharged through a 100 mesh nylon cloth, an acrylic resin No. 1 having a solid content of 40% by mass, a glass transition temperature of 91 ° C., an acid value of 78 mgKOH / g, and a number average molecular weight of 3,500. 7 was obtained.

Comparative production example 2
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device was charged with 70 parts by mass of propylene glycol n-propyl ether, stirred and mixed in a nitrogen stream, and heated to 100 ° C.
Thereafter, a monomer mixture (acrylic acid 50 parts by mass, methyl methacrylate 20 parts by mass, ethyl acrylate 30 parts by mass) and a polymerization initiator solution (t-butylperoxy-2-ethylhexanoate 8 parts by mass, propylene glycol n A mixed solution of 50 parts by mass of propyl ether) was dropped into the reactor with a metering pump over 4 hours, and aging was performed for 0.5 hours after the completion of the dropping.
Subsequently, a polymerization initiator solution (a mixed solution of 0.5 parts by mass of t-butylperoxy-2-ethylhexanoate and 30 parts by mass of propylene glycol n-propyl ether) was dropped for 0.5 hours and aged for 2 hours. Went. Then, it cooled to 60 degreeC, filtered and discharged | emitted with 100 mesh nylon cloth, and obtained acrylic resin of solid content 40 mass%, glass transition temperature 105 degreeC, acid value 390 mgKOH / g, and number average molecular weight 4,000. .
Subsequently, resin (c2) having a glass transition temperature of 92 ° C. was added to the reaction vessel at 100 ° C. Next, 5 parts by mass of Epicoat 834 (manufactured by Japan Epoxy Resin Co., Ltd., equivalent to an epoxy resin and a low molecular weight compound (c3)) was added, the temperature was raised to 130 ° C., and the mixture was aged for 3 hours. Then, it is diluted with propylene glycol n-propyl ether, cooled to 60 ° C., filtered and discharged through a 100 mesh nylon cloth, solid content 40% by mass, glass transition temperature 98 ° C., acid value 330 mgKOH / g, number average molecular weight. 4,500 acrylic resin no. 8 was obtained.

Comparative Production Examples 3-6
Acrylic resin No. 2 was prepared in the same manner as in Comparative Production Example 2 except that the monomer used was blended in Table 2. 9-No. 12 was obtained.

[Production of Anionic Polymer Fine Particles (D)]
Production Example 11 Production of Anionic Polymer Fine Particles (D1) 150 parts by mass of deionized water and 0.5 parts by mass of “Newcol 562SF” in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device. (Solid content) was charged, stirred and mixed in a nitrogen stream, and heated to 85 ° C.
Next, 1% by mass of the following “monomer mixture 1” and 5.2 parts by mass of “2% by mass ammonium persulfate aqueous solution” were introduced into the reaction vessel and maintained at 85 ° C. for 20 minutes. Thereafter, the remaining monomer emulsion and ammonium persulfate aqueous solution were dropped into the reactor with a metering pump over 3 hours, and aging was performed for 2 hours after the completion of the dropping. The mixture was cooled to 30 ° C., filtered and discharged through a 100-mesh nylon cloth to obtain anionic polymer fine particles (D1) having an average particle size of 0.1 μm, a solid content of 25% by mass, and an acid value of 65 mgKOH / g.
"Monomer mixture 1"
Deionized water 135 parts by weight Styrene 30 parts by weight Ethyl acrylate 50 parts by weight Methacrylic acid 10 parts by weight
Ethylene glycol dimethacrylate 10 parts by weight Newcol 562SF 1 part by weight (solid content)
"2 mass% ammonium persulfate aqueous solution"
Ammonium persulfate 0.2 parts by mass Deionized water 10 parts by mass Newcol 562SF is polyoxyethylene alkylbenzene sulfonate ammonium (active ingredient 60% by mass, manufactured by Nippon Emulsifier Co., Ltd.) (the same applies hereinafter).

Production Example 12 Production of Anionic Polymer Fine Particles (D2)
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device was charged with 95 parts by mass of ethylene glycol monohexyl ether and 32 parts by mass of n-butanol, and stirred and mixed in a nitrogen stream to rise to 100 ° C. Warm up.
Next, a monomer mixture (50 parts by mass of methacrylic acid, 45 parts by mass of styrene, 5 parts by mass of ethyl acrylate) and a polymerization initiator (2 parts by mass of perbutyl O, 10 parts by mass of n-butanol) were dropped simultaneously over 3 hours. Then, after completion of dropping, the mixture was aged for 30 minutes. Thereafter, a polymerization initiator solution (0.4 parts by weight of perbutyl O, 10 parts by weight of n-butanol) was dropped for 30 minutes and aged for 2 hours, and then diluted with 63 parts by weight of n-butanol to obtain a solid content of 32% by weight, Polymer No. 3 having an acid value of 326 mgKOH / mg and a weight average molecular weight of 37,000. 1 was obtained.
Next, in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, and a reflux condenser, the above-mentioned polymer No. 1 was added. After neutralizing 25 parts by mass (solid content) of 1.88 with 3.88 parts by mass of dimethylethanolamine, the mixture was stirred for 15 minutes and then 250 parts by mass of deionized water was added.
Thereafter, at 30 ° C. or lower, the following “monomer mixture” was added to deionized water to give an emulsion, which was dropped into the reaction vessel over about 1 hour. Next, the temperature was raised to 85 ° C., and a polymerization initiator aqueous solution (0.2 parts by mass of ammonium persulfate, 22 parts by mass of deionized water) was dropped for 1 hour in a nitrogen atmosphere, and then aged for 2 hours. Then, it cooled to 30 degreeC, filtered and discharged | emitted with 100 mesh nylon cloth, and adjusted with deionized water, and obtained the anionic polymer microparticles | fine-particles (D2) of 20 mass% of solid content. The anionic polymer fine particles (D2) had an acid value of 82 mgKOH / g and an average particle size of 0.18 μm.
"Monomer mixture"
Deionized water 75 parts by weight Ethylene glycol dimethacrylate 7.5 parts by weight Ethyl acrylate 37.5 parts by weight Styrene 30 parts by weight Newcol 562SF 0.75 part by weight

Example 1 Production of a can coating composition
To 100 parts by mass (solid content) of an acrylic-modified epoxy resin dispersion having a solid content of 30% by mass obtained in Production Example 3, 1.7 parts by mass (solid content) of a resol-type phenol resin solution, and acid in advance with dimethylethanolamine, etc. Acrylic resin No. 1 obtained in Production Example 5 in which the molar amount was neutralized. After adding 5 parts by mass (solid content) of 1 and stirring for about 30 minutes, it was adjusted by gradually adding deionized water. 1 was obtained.

Examples 2-10
A can coating material No. 25 having a solid content of 25% by mass was prepared in the same manner as in Example 1 except that the blending contents in Table 3 were used. 2-No. 10 was obtained.

Comparative Example 1
To 100 parts by mass (solid content) of an acrylic-modified epoxy resin dispersion having a solid content of 30% by mass obtained in Production Example 3, 1.7 parts by mass (solid content) of a resol-type phenol resin solution, and acid in advance with dimethylethanolamine, etc. The acrylic resin No. 1 obtained in Comparative Production Example 1 with the molar amount neutralized. After adding 5 parts by mass (solid content) of No. 7 and stirring for about 30 minutes, it was adjusted by gradually adding deionized water. 11 was obtained.

Comparative Examples 2-10
Except for the blending contents in Table 4, in the same manner as in Comparative Example 1, the paint No. 12-No. 20 was obtained.

Preparation of test plate Each can paint obtained in the above Examples and Comparative Examples was spray-coated on a # 5182 aluminum plate having a thickness of 0.26 mm subjected to phosphoric acid chromate treatment so that the dry coating thickness was 10 μm. And it was set as the coating board hardened by baking for 3 minutes at 200 degreeC. The performance test was performed according to the following test method.

Observation of cross section of coating film (μm):
When the cross section of the coating film obtained by cutting the test plate was observed with a scanning electron microscope (5000 times magnification) and the sea-island structure could be confirmed, 30 circular or elliptical island portions that could be recognized in an area range of 10 μm × 10 μm The average value (μm) of the width (major axis) in the longitudinal direction was determined.

T-bend bendability:
After cutting the test coating plate to 5 cm in the rolling direction and 4 cm in the vertical direction, using a special goby folding DuPont impact tester in a room at 20 ° C., between the bent portions of the test coating plate with the lower part folded in two. Place two aluminum plates with a thickness of 0.26 mm, set them in a tester, drop a weight of 1 kg of iron with a flat contact surface from a height of 50 cm and give an impact to the bent part, then fold The bending tip part was energized for 6 seconds at an applied voltage of 6.5 V, and the current value (mA) of the bending tip part 20 mm width was measured and evaluated according to the following criteria.
◎ is less than 20 mA ○ is 20 mA or more and less than 40 mA △ is 40 mA or more and less than 80 mA × is 80 mA or more

T bent bent part retort adhesion:
After cutting the test coated plate to 5 cm in the rolling direction and 4 cm in the vertical direction, using a special goby-fold type DuPont impact tester in a room at 20 ° C., between the bent parts of the test coated plate with the lower part folded in two. Two aluminum plates with a thickness of 0.26 mm were sandwiched and set in a tester. After dropping a 1 kg weight of iron with a flat contact surface from a height of 50 cm to impact the bent part, The test piece was immersed in water at 125 ° C. for 30 minutes in an autoclave. Thereafter, the moisture was wiped off, and the peeled portion was subjected to a peel test with a cello tape. The portion was energized at an applied voltage of 6.5 V, the current value (mA) of the bent tip portion 20 mm wide was measured, and evaluated according to the following criteria.
◎ is less than 20 mA ○ is 20 mA or more and less than 40 mA △ is 40 mA or more and less than 80 mA × is 80 mA or more

Retort whitening resistance:
The test coating plate was immersed in water, and the whitening state of the coating film treated at 125 ° C. for 30 minutes in an autoclave was evaluated according to the following criteria.
◎ indicates no whitening at all,
○ indicates a slight whitening.
△ is slightly whitened,
X is markedly whitened.

Acid resistance:
The test coating plate was immersed in an aqueous solution of 0.5% by mass of citric acid and malic acid, treated in an autoclave at 125 ° C. for 30 minutes, and the state was visually evaluated according to the following criteria.
In ◎, no deterioration was observed.
○ indicates slight peeling or swelling.
Δ indicates blistering and peeling throughout.
X indicates remarkable swelling or peeling of the entire surface or weakening of the coating film

Corrosion resistance after processing:
A test piece was prepared in the same manner as in the above-mentioned T-bend processing test, and the sample that was bent in the same manner was immersed in a mixed aqueous solution in which 1% by mass of citric acid, malic acid, and sodium chloride was dissolved, at 40 ° C. After storing for 2 weeks, the state of the bent portion was visually evaluated according to the following criteria.
◎ indicates no corrosion.
○ shows slight corrosion.
Δ indicates considerable corrosion.
X: Corrosion is remarkable.

Flavor characteristics:
Each test plate was immersed in deionized water at 30 ° C. for 1 month in a solution in which 30 mg / l of d-limonene (fragrance) was added and dispersed at 1 g / l of S-1170 (manufactured by Mitsubishi Chemical Corporation, sucrose fatty acid ester). And stored. In order to measure d-limonene (fragrance) adsorbed on the coating film after storage, it was extracted by immersion in diethyl ether at 20 ° C for 1 week, and the extracted d-limonene (fragrance) was measured by gas chromatography. And evaluated according to the following criteria.
○ indicates that the extracted d-limonene (fragrance) is less than 0.6 mg per 120 mg of the coating film weight. Δ indicates that the extracted d-limonene (fragrance) is 0.6 mg or more per 120 mg of the coating film weight. Less than 6 mg × indicates that the extracted d-limonene (fragrance) is 1.6 mg or more per 120 mg of the coating weight.

  Since the bending workability and water whitening resistance have been improved, a metal can having a coating film having excellent corrosion resistance to contents and excellent flavor properties can be obtained.

It is an electron micrograph which shows an example of the coating-film cross section which forms a sea island structure of the aqueous coating composition which mix | blended the anionic polymer crosslinked fine particle (D).

Claims (8)

Acrylic resin (C) having an acid value of 100 to 500 mgKOH / g having the following characteristics: 0.1 to 10 parts by mass of resol type phenol resin (B) with respect to 100 parts by mass of acrylic resin-modified epoxy resin (A) 0.1 to 20 parts by mass,
An aqueous coating composition comprising the acrylic resin-modified epoxy resin (A), the resol type phenolic resin (B) and the resin (C) dispersed stably in an aqueous medium.
Acrylic resin (C): a vinyl copolymer resin (c1) having a glass transition temperature of -20 to 70 ° C, and a glass transition temperature of 20 to 150 ° C, as compared with the vinyl copolymer resin (c1). It is obtained by reacting with a vinyl copolymer resin (c2) that is 10 ° C. or higher. The acrylic resin (C) is
At least one acid group-containing radical polymerizable unsaturated monomer 10 selected from acrylic acid, itaconic acid, sulfonic acid group-containing radical polymerizable unsaturated monomer and phosphoric acid group-containing radical polymerizable unsaturated monomer 10 Vinyl copolymer resin (c1) having ˜60 mass% and other radical polymerizable unsaturated monomers 40 to 90 mass% as monomer components;
A vinyl copolymer resin (c2) containing 10 to 60% by mass of methacrylic acid and 40 to 90% by mass of other radical polymerizable unsaturated monomer as monomer components;
The water-based paint composition according to claim 1, which is a polymer obtained by reacting a low molecular weight compound (c3) having two or more complementary reactive groups in one molecule having reactivity with an acid group and a carboxyl group. . The ratio of the vinyl copolymer resin (c1), the vinyl copolymer resin (c2) and the low molecular weight compound (c3) constituting the acrylic resin (C) is as follows:
Based on the total solid content of vinyl copolymer resin (c1) and vinyl copolymer resin (c2), vinyl copolymer resin (c1) / vinyl copolymer resin (c2) = 60/40 to 95 / 5 (mass%) and [vinyl copolymer resin (c1) + vinyl copolymer resin (c2)] / low molecular weight compound (c3) = 100 / 0.1 to 100/20 (parts by mass) The water-based coating composition according to claim 2, wherein   The low molecular weight compound (c3) is at least one selected from the group consisting of an epoxy resin having an epoxy equivalent of 180 to 5,000 having two or more epoxy groups in one molecule, a resol type phenol resin, and a polycarbodiimide compound. The water-based coating composition according to claim 2 or 3.   The water-based coating composition according to claim 4, wherein the low molecular weight compound (c3) is an epoxy resin having an epoxy equivalent of 200 to 1,000 having two or more epoxy groups in one molecule.   The acrylic resin-modified epoxy resin (A) is a resin obtained by esterifying a bisphenol type epoxy resin (a1) having a number average molecular weight of 2,000 to 35,000 and a carboxyl group-containing acrylic resin (a2), or 6. The resin obtained by graft polymerization of a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer (a3) to the bisphenol type epoxy resin (a1). 2. The aqueous coating composition according to item 1. The anionic polymer crosslinked fine particles (D) having the following characteristics are further contained in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the acrylic resin-modified epoxy resin (A). The water-based coating composition according to any one of the above.
Anionic polymer crosslinked fine particles (D): in the presence of water, carboxyl group-containing radically polymerizable monomer (d1) 2 to 30% by mass, polyvinyl compound (d2) 2 to 30% by mass and other radical polymerization It comprises a polymer having an acid value of 10 to 100 mgKOH / g, which is produced by polymerizing a radically polymerizable unsaturated monomer component comprising 40 to 96% by mass of a polymerizable unsaturated monomer (d3).   A water-based paint composition for cans, wherein the water-based paint composition according to any one of claims 1 to 7 is applied to a can.