JP4974571B2 - Water-based paint composition - Google Patents

Description

  The present invention relates to a coating composition for cans useful for coating components of metal cans such as edible cans such as beverages and fruits and lids, and the obtained coating film has folding workability and water resistance. It is possible to form a coating film having an excellent balance of whitening property, acid resistance adhesion property, and flavor property.

Conventionally, can coating compositions such as inner and outer surfaces of cans and can lids having coating film performance such as processability, adhesion and corrosion resistance have been developed as can coating compositions.
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 (Patent Document 1).
In addition, an acid value of 150 to 450 mgKOH / g, a number average molecular weight of 2,000 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. An aqueous coating composition characterized by ˜50,000 emulsion resin dispersed in an aqueous medium is known (Patent Document 2).
In addition, 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. (Patent Document 3).
In addition, some of the epoxy groups in the epoxy resin are carboxyl groups 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, containing a basic compound and an aqueous medium An aqueous coating composition is known (Patent Document 4).
In addition, 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, and is present in a coating film. In view of mutual adhesion between the core-shell fine particles (islands) and the polymerized portion (sea) of the particulate self-emulsifying epoxy resin, there is an invention in which the adhesion and workability of the coating film are improved (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 (Patent Document 6). 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.

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

  An object of the present invention is to find a coating composition for cans which can form a coating film excellent in bending workability, water whitening resistance and flavor properties.

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 present invention provides the following aqueous coating composition and can coating composition.
[1] 100 parts by mass of an acrylic resin-modified epoxy resin (A) having the following characteristics, 0.1 to 20 parts by mass of a resol type phenol resin (B), and an acid value of 100 to 500 mgKOH / g having the following characteristics An aqueous coating composition comprising 0.1 to 20 parts by mass of an acrylic resin (C) dispersed in an aqueous medium.
Acrylic resin-modified epoxy resin (A): 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 the bisphenol type Resin acrylic resin (C) obtained by graft polymerization of polymerizable unsaturated monomer component containing carboxyl group-containing polymerizable unsaturated monomer (a3) to epoxy resin (a1) : acrylic acid, itaconic acid, 10 to 60% by mass of at least one radical polymerizable monomer selected from sulfonic acid or phosphoric acid group-containing radical polymerizable monomer and 40 to 90% by mass of other radical polymerizable unsaturated monomer (1). % Vinyl copolymer resin (c1) having a monomer component, 10 to 60% by weight of methacrylic acid and other radical polymerizable unsaturated monomers ( ) Low molecular weight having two or more complementary reactive groups in one molecule having a vinyl copolymer resin (c2) having 40 to 90% by mass as a monomer component and an acid group and a carboxyl group. A polymer obtained by reacting the compound (c3),
The vinyl copolymer resin (c1), the vinyl copolymer resin (c2), and the low molecular weight compound (c3) are based on the total solid content of the vinyl copolymer resin (c1) and the vinyl copolymer resin (c2). Vinyl copolymer resin (c1) / vinyl copolymer resin (c2) = 60/40 to 95/5 (% by mass), and [vinyl copolymer resin (c1) + vinyl copolymer Resin (c2)] / low molecular weight compound (c3) = 100 / 0.1 to 100/20 (parts by mass)
[2] The low molecular weight compound (c3) is at least one selected from 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 as described in [1] above.
[3] The aqueous coating composition according to the above [2] , 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.
[4] The above-mentioned [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) the aqueous coating composition according to any one of - [3].
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 A polymer having an acid value of 10 to 100 mgKOH / g, which is produced by polymerizing a radically polymerizable unsaturated monomer component composed of 40 to 96% by mass of a polymerizable unsaturated monomer (d3).
[5] above [1] to [4] or the aqueous coating composition according to 1, coating composition for cans, characterized in that intended to be painted can body.

  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 coating composition for cans of this invention is demonstrated.
[Coating composition for cans]
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 (a3) to a bisphenol type epoxy resin (a1). In the resin (2), for example, a polymerizable unsaturated monomer component can be graft-polymerized to the epoxy resin (a1) in an organic solvent in the presence of a radical generator such as benzoyl peroxide.

  As the bisphenol type epoxy resin (a1) used in the resin (1) and the resin (2), for example, epichlorohydrin and bisphenol are condensed to a high molecular weight in the presence of a catalyst such as an alkali catalyst as necessary. The resulting resin, epichlorohydrin, and bisphenol are condensed in the presence of a catalyst such as an alkali catalyst as necessary to obtain a low molecular weight epoxy resin, which is obtained by polyaddition reaction of the low molecular weight epoxy resin and bisphenol. Any of epoxy resins obtained by reacting a dibasic acid with these resins, and these obtained resins or the above low molecular weight epoxy resins.

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.

As a dibasic acid used for manufacture of the epoxy ester resin, the following formula (1)
HOOC- (CH _{2) n} -COOH ··· formula (1)
(Wherein, n is an integer of 1 to 12) is preferably used, and specifically, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexa Examples include hydrophthalic acid.

As a commercially available product of the epoxy resin (a1), for example, Epicoat 1007 (epoxy equivalent of about 1,700, number average molecular weight (Note 1) 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 manufactured by Asahi Ciba (epoxy equivalent of about 3,500, number average molecular weight of about 3) , 800); and Epomic R-309 (epoxy equivalent of about 3,500, number average molecular weight of about 3,800) manufactured by Mitsui Chemicals, Inc., and the like.
(Note 1) Number average molecular weight: Measured according to JIS K 0124-83, using TSK GEL4000H _XL + G3000H _XL + G2500H _XL + G2000H _XL (manufactured by Tosoh Corporation) as a separation column at a flow rate of 1.0 ml. / Min, using GPC tetrahydrofuran as the eluent, and calculated from the chromatogram obtained with the RI refractometer and the polystyrene calibration curve.

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 a copolymer comprising a carboxyl group-containing polymerizable unsaturated monomer (a3) and another polymerizable unsaturated monomer (a4) as monomer components. It is a polymer resin.
Examples of the carboxyl group-containing polymerizable unsaturated monomer (a3) include monomers such as (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, and fumaric acid. It can be used in combination of more than one species.

The other 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, vinyl toluene, 2-methyl styrene, t-butyl styrene, 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, methyl methacrylate , Ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n methacrylate , I- or t-butyl, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc. acrylic acid or methacrylic acid alkyl ester having 1 to 18 carbon atoms or Cycloalkyl esters; acrylics such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, hydroxybutyl methacrylate _C 2 -C ₈ hydroxyalkyl esters of acid or methacrylic acid; N- methylol acrylamide, N- butoxymethyl Accession Mention may be made of one or a mixture of two or more of N-substituted acrylamide or N-substituted methacrylamide monomers such as amide, N-methoxymethyl acrylamide, N-methylol methacrylamide and N-butoxymethyl methacrylamide. .
As the other 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, Is suitably in the range of 99/1 to 50/50.

In the carboxyl group-containing acrylic resin (a2), the constitutional ratio and type of the monomer are not particularly limited, but usually the carboxyl group-containing radical polymerizable unsaturated monomer is 15 to 80% by mass, particularly 20%. It is preferable that it is -60 mass%, and it is preferable that another 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 (see Note 1) in the range 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 normally used in the range of 0.1-1 equivalent with respect to 1 equivalent of epoxy groups in an epoxy resin (a1). Is good.

  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 at the same temperature for about 1 to 10 hours. Examples of the radical generator include azobisisobutyronitrile, benzoyl peroxide, t-butyl perbenzoyl octanoate, t-butyl peroxy-2-ethylhexanoate, and the like.

As an organic solvent in 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 can coating composition of the present invention is preferably in the range of 20% by mass or less from the viewpoint of environmental protection with respect to the resin solid content of the can 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 methylol group is introduced by the condensation reaction of phenols with an aldehyde such as formaldehyde in the presence of a reaction catalyst, 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 (Note 1) in the range of 200 to 2,000, preferably 300 to 1,200, and an average number of methylol groups per one benzene nucleus is 0. It is suitable that it is within the range of 0.3 to 3.0, 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 paint composition for cans 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, and flavor properties. Contributes to the formation of excellent coatings.
The acrylic resin (C) is a vinyl copolymer comprising at least one radical polymerizable monomer selected from acrylic acid, itaconic acid, sulfonic acid, or a phosphate group-containing radical polymerizable monomer as a constituent component. It has a vinyl copolymer chain (2) having a chain (1) and a monomer component containing methacrylic acid as constituent components.

Vinyl copolymer chain (1):
The vinyl copolymer chain (1) is preferably 10 to 60 mass of at least one radical polymerizable monomer selected from acrylic acid, itaconic acid, sulfonic acid, or phosphate group-containing radical polymerizable monomer. %, Preferably 20 to 55% by mass, more preferably 30 to 50% by mass, and other radical polymerizable unsaturated monomer (1) 40 to 90% by mass, preferably 45 to 80% by mass, more preferably It is a vinyl copolymer resin (c1) obtained by radical polymerization reaction of a mixture (1) containing 50 to 70% by mass of a monomer component in an appropriate solvent.
If at least one radical polymerizable monomer selected from acrylic acid, itaconic acid, sulfonic acid, or a phosphoric acid group-containing radical polymerizable monomer is less than 10% by mass, the adhesiveness decreases, and 60% by mass If it exceeds, water resistance may be impaired.

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.
The acrylic acid group-containing radical polymerizable monomer includes acrylic acid, and the itaconic acid group-containing radical polymerizable monomer includes itaconic acid.

Examples of the other radical polymerizable unsaturated monomer (1) include vinyl aromatic compounds such as styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, and vinylpyridine;
Such as 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) hydroxyalkyl (meth) acrylates of _C 2 -C ₈ acrylic acid or methacrylic acid such as acrylates, (poly ) Hydroxyl group-containing radical polymerizable unsaturated monomers such as ethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polybutylene glycol mono (meth) acrylate; Reaction products with lactone compounds such as β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, γ-caprolactone, γ-caprolactone, γ-lauryllactone, ε-caprolactone, and 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) etc .;
For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, etc. (meth) alkyl or cycloalkyl esters of _C 1 _{-C 18} acrylic acid, and the like;.
For example, N- (2-hydroxyethyl) (meth) acrylamide, N- (2-hydroxypropyl) (meth) acrylamide, N- (3-hydroxypropyl) (meth) acrylamide, N-methyl-N- (2-hydroxy Ethyl) (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-di- (2-hydroxypropyl) (meth) a Nitrogen-containing radical-polymerizable unsaturated monomers such as Riruamido;
For example, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, vinyltripropoxysilane, vinylmethyldipropoxysilane, vinyldimethylpropoxysilane, γ- ( An alkoxysilyl group-containing radical polymerizable unsaturated monomer such as meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, γ- (meth) acryloyloxypropyldimethylmethoxysilane; divinylbenzene , Ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene Recall 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) ethane di (meth) acrylate, , 1,1-tris (hydroxymethyl) Etantori (meth) polyvinyl compound such as acrylate; and the like.

  In the production of the vinyl copolymer resin (c1), at least one radical polymerizable monomer selected from acrylic acid, itaconic acid, sulfonic acid, or a phosphate group-containing radical polymerizable monomer and other radical polymerization The radical polymerization reaction using the mixture (1) containing the polymerizable unsaturated monomer (1) is carried out using an appropriate solvent in the presence of a polymerization initiator. The reaction temperature is usually 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, azobisisobutyronitrile (AIBN) and t-butylperoxy 2-ethylhexanoate (perbutyl O) can be used, and the blending amount is set to 0. 0 with respect to the total of the mixture (1). It is 05-3 mass%.

  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 chain (2):
The vinyl copolymer chain (2) is 10 to 60% by mass of methacrylic acid, preferably 15 to 55% by mass, more preferably 20 to 50% by mass, and other radical polymerizable unsaturated monomer (2) 40 to 40%. Vinyl copolymer resin obtained by radical polymerization reaction of mixture (2) containing 90% by mass, preferably 45 to 80% by mass, and more preferably 50 to 75% by mass in a suitable solvent. (C2) is preferred. 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 unsaturated monomer (2), one or more other radical polymerizable unsaturated monomers similar to those used for the vinyl copolymer chain (1) are selected and used. Can do.

  The vinyl copolymer chain (2) is at least one radical selected from acrylic acid, itaconic acid, sulfonic acid, or a phosphate group-containing radical polymerizable monomer used in the vinyl copolymer chain (1). It is characterized by not using a 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 chain (1) can be appropriately selected and used.

The acrylic resin (C) can be produced by synthesizing the vinyl copolymer resin (c1) and then reacting the vinyl copolymer resin (c2).
More preferably, the vinyl copolymer resin (c2) is added to the vinyl copolymer resin (c1) and stirred, and the low molecular weight compound (c3) described later is added to obtain the acrylic resin (C).

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. A polymer obtained by reacting two or more low molecular weight compounds (c3) is preferred.
The low molecular weight compound (c3) is an epoxy equivalent having two or more epoxy groups in one molecule of 180 to 5,000, preferably 200 to 1,000, selected from epoxy resins, resol type phenol resins and polycarbodiimide compounds. One type 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 equivalent) manufactured by Japan Epoxy Resin Co., Ltd. About 1,700, number average molecular weight about 2,900, Epicoat 1009 (epoxy equivalent about 3,500, number average molecular weight about 3,750), Epicoat 1010 (epoxy equivalent about 4,500, number average molecular weight 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 (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 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. Examples of commercially available products include Nisshinbo's Carbodilite (registered trademark) series such as Carbodilite V-02 and Carbodilite V-04.

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, more preferably 100 to 130 ° C, and the reaction time is usually about 10 hours or less, preferably about 0.5 to about 6 hours. Thereafter, it is diluted with an organic solvent such as propylene glycol n-propyl ether and cooled to obtain an acrylic resin (C).
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), the vinyl copolymer resin (c2), and the low molecular weight Compound (c3) is 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%), 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 an acid value of 100 to 500 mgKOH / g, preferably 200 to 480 mgKOH / g, more preferably 300 to 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 can coating composition in the present invention is 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass of the acrylic resin (C) with respect to 100 parts by mass of the acrylic resin-modified epoxy resin (A) obtained as described above. Parts, more preferably 2 to 5 parts by mass.

<Anionic polymer crosslinked fine particles (D)>
The can coating composition of the present invention may further contain anionic polymer crosslinked fine particles (D). The anionic polymer crosslinked fine particles (D) are composed of 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 70 to 90% by 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 crosslinked fine particles (D) include the following anionic polymer crosslinked fine particles (D1) and anionic polymer crosslinked fine particles (D2).

Anionic polymer crosslinked 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 First-stage emulsion polymerization is performed on the mixture (3) of the radically polymerizable monomer containing 60 to 96% by mass, preferably 75 to 90% by mass of the saturated monomer (d31), in the presence of water. An aqueous dispersion (I) is obtained.
Subsequently, carboxyl group-containing radical polymerizable monomer (d1) 10 to 35% by mass, preferably 15 to 25% by mass and other radical polymerizable unsaturated monomer (d32) 65 to 90% by mass, preferably 75 to A mixture of radically polymerizable monomers (4) containing 85% by mass is subjected to the second stage emulsion polymerization in the presence of the aqueous dispersion (I) and water, and anionic polymer crosslinked fine particles ( D1) is obtained.

Examples of the carboxyl group-containing radical polymerizable monomer (d1) used in the mixture (3) include monomers such as (meth) acrylic acid, maleic acid, crotonic acid, itaconic acid, fumaric acid, and the like. Can be used alone or in combination of two or more.
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.
As the polyvinyl compound (d2), an adduct formed 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 should also be used. Can do. Specifically, methacrylic acid and / or acrylic acid is 0.5 to 0.98 mol, preferably 0.65 to 0.95 mol, 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 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 and β-propiolactone, dimethylpro Piolactone, bu Reaction products with lactone compounds such as tyrolactone, 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 of the acrylic acid - ₁₈ alkyl or cycloalkyl esters of; 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, N-di- (2-hydroxypropyl) (meth) acrylamide; for example, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, Vinylmethyldiethoxysilane 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 unsaturated monomer (d31) is used as an emulsifier. The aqueous dispersion (I) can be produced by an emulsion polymerization reaction using 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 an emulsifier and 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) used in the mixture (4), at least one kind of the same monomers used in the mixture (3) can be selected and used.
Examples of the other radical polymerizable unsaturated monomer (d32) used in the mixture (4) include the polyvinyl compound (d2) used in the first stage polymerization reaction and the other radical polymerizable unsaturated monomer ( At least one or more types can be selected from d31).

  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).

  As the polymerization initiator, ammonium persulfate, potassium persulfate, and sodium persulfate can be used, and the blending amount is 0.05 to 3% by mass, preferably 0.1 to 1.0% by mass.

Examples of the emulsifier used in the first stage emulsion polymerization reaction and the second stage emulsion polymerization reaction 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 can be carried out usually in water at a temperature of about 60 to 95 ° C., preferably about 75 to 85 ° C. for about 1 to 5 hours, preferably about 2 to 4 hours. .

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 diameter (Note 2) of 0. 0.01 to 0.5 μm, preferably 0.1 to 0.35 μm, and 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.
(Note 2) Average particle size: Dilute the sample to a concentration suitable for measurement with deionized water with a submicron particle analyzer N4 (trade name, manufactured by Beckman Coulter, Inc., particle size distribution measuring device) (Measured at about 20 ° C.)

Anionic polymer crosslinked 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 mixture (5) of radically polymerizable monomer containing 45 to 65% by mass is subjected to radical polymerization reaction to obtain polymer (I). 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 crosslinked 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 as that used in the production of the anionic polymer crosslinked fine particles (D1). The group-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, and the like. Can be used.
As other radical polymerizable unsaturated monomer (d33), the polyvinyl compound (d2) used for the production of the anionic polymer crosslinked fine particles (D1) and the other radical polymerizable unsaturated monomer (d31) are used. 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, azobisisobromonitrile (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 in the production of the anionic polymer crosslinked fine particles (D1) can be selected and used. As the other radical polymerizable unsaturated monomer (d34), at least one of the other radical polymerizable unsaturated monomer (d31) and the carboxyl group-containing radical polymerizable monomer (d1) is used. It can be appropriately selected and used.
In the reaction, polymerization initiators such as ammonium persulfate, potassium persulfate, sodium persulfate, azobisisobutyronitrile (AIBN), t-butylperoxy 2-ethylhexanoate (perbutyl O), redox system start An agent can also be used.

  The mass ratio of the polymer (I) to the mixture (6) when used for the production of the anionic polymer crosslinked 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).

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 (Note 2) 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.

In the paint composition for cans of the present invention, the anionic polymer crosslinked fine particles (D1) or the anionic polymer crosslinked fine particles (D2) described above are further blended in the paint, thereby further bending workability and water resistance. A coating film having a good balance between whitening and flavor properties can be obtained.
The amount of the anionic polymer crosslinked fine particles (D1) or the anionic polymer crosslinked fine particles (D2) blended in the can coating composition is 1 to 100 parts by mass per 100 parts by mass of the acrylic resin-modified epoxy resin (A). A suitable range is 50 parts by weight, preferably 5-30 parts by weight. If it is less than 1 part by mass, it is not effective in improving the coating performance such as folding workability, water whitening resistance, and flavor, and if it exceeds 50 parts by mass, not only the coating stability is impaired, but the coating performance is not improved much. has no effect.

  The coating composition for cans of the present invention can be applied to various substrates, for example, an untreated or surface-treated metal plate such as an aluminum plate, a steel plate, a tin plate, and an epoxy system for these metal plates, Examples include metal plates coated with a vinyl primer or the like, and these metal plates processed into cans.

  Various known methods such as roll coater coating, spray coating, dip coating, and electrodeposition coating can be applied as a method for coating the base 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.

  The cross-section of the coating film obtained by applying the can coating composition of the present invention has a diameter of 0.01 to 0.5 μm, preferably 0.05 to 0.35 μm, and more preferably 0.08 to 0.00. It is characterized by forming a sea-island structure (see FIG. 1) having an island portion of 15 μm, and it is considered that the formation of such a sea-island structure contributes to improvement of bending workability.

  The present invention will be described more specifically with reference to examples. Hereinafter, “parts” and “%” mean “parts by mass” and “% by mass”, respectively.

[Production of acrylic resin-modified epoxy resin (A) (Production Examples 1 to 3)]
Production Example 1: Production of epoxy resin solution (a1)
A four-necked flask equipped with a reflux tube, thermometer, and stirrer was charged with 558 parts of Epicoat 828EL (Note 3), 329 parts of bisphenol A, and 0.6 part of tetrabutylammonium bromide, and reacted at 160 ° C. under a nitrogen stream. Went. 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 3) Epicoat 828EL: Japan Epoxy Resin, bisphenol A type epoxy resin, epoxy equivalent of about 190, molecular weight of about 350

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 of n-butanol, "180 parts of methacrylic acid, 240 parts of styrene, 180 parts of ethyl acrylate, t-butylperoxy-2" The mixture of “18 parts of ethylhexanoate” was heated to 100 ° C. under a nitrogen stream, and was added dropwise from the dropping funnel over about 3 hours. After the addition, the mixture was further stirred at the same temperature for 2 hours and then cooled. Thus, an acrylic resin solution having a solid content of 40% was obtained. 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 of the bisphenol A type epoxy resin obtained in Production Example 1 (solid content) and 50 parts of the 40% acrylic resin solution obtained in Production Example 2 (solid) 20 parts) and 33 parts of diethylene glycol monobutyl ether were added and heated to 100 ° C. to dissolve, then 2 parts of N, N-dimethylaminoethanol was added and reacted for about 2 hours, and then N, N-dimethyl was added. 3 parts of aminoethanol was added and the reaction was continued for 20 minutes. Thereafter, 165 parts 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%.

[Production of resol type phenolic resin (B)]
Production Example 4: Production of resol-type phenol resin solution A four-necked flask equipped with a reflux tube, thermometer, and stirrer was charged with 188 parts of phenol and 324 parts of a 37% formaldehyde aqueous solution and heated to 50 ° C. Was dissolved uniformly. 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. Subsequently, the mixture was cooled to 50 ° C., a 32% calcium hydroxide aqueous dispersion was slowly added to adjust the pH to 8.5, and the reaction was carried out at 50 ° C. for 4 hours.
After completion of the reaction, the pH was adjusted to 4.5 with 20% hydrochloric acid, and the resin was extracted with a mixed solvent of xylene / n-butanol / cyclohexane = 1/2/1 (mass ratio) to obtain catalyst, neutralization The salt was removed, followed by azeotropic dehydration under reduced pressure to obtain a light yellow and transparent resol type phenolic resin solution having a solid content of 60%.

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

(Note 5) Shonor BKS-377F: Showa Polymers, trade name, resol type phenol resin, solid content 50%

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 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, methyl methacrylate 40 parts, ethyl acrylate 50 parts) and a polymerization initiator solution (t-butylperoxy-2-ethylhexanoate 8 parts, propylene glycol npropyl ether 50 parts The mixture was dropped into the reactor with a metering pump over 4 hours, and aged for 0.5 hour after the completion of the dropping. Subsequently, a polymerization initiator solution (a mixed solution of 0.5 part of t-butylperoxy-2-ethylhexanoate and 30 parts of propylene glycol n-propyl ether) is dropped for 0.5 hour and ripened for 2 hours. It was. 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%, 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 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, methyl methacrylate 20 parts, ethyl acrylate 30 parts) and a polymerization initiator solution (t-butylperoxy-2-ethylhexanoate 8 parts, propylene glycol n-propyl ether 50 parts The mixture was dropped into the reactor with a metering pump over 4 hours, and aged for 0.5 hour after the completion of the dropping. Subsequently, a polymerization initiator solution (a mixed solution of 0.5 part of t-butylperoxy-2-ethylhexanoate and 30 parts of propylene glycol n-propyl ether) is dropped for 0.5 hour and ripened for 2 hours. It was. Then, it cooled to 60 degreeC, filtered and discharged | emitted with 100 mesh nylon cloth, and obtained the acrylic resin of 40% of solid content, an acid value of 390 mgKOH / g, and a number average molecular weight 4,000 (equivalent to resin (c1)) ). Next, the resin (c2) (Note 4) obtained in the same manner as in Production Example 5 was added to the reaction vessel at 100 ° C.
Next, 5 parts of Epicoat 834 (manufactured by Japan Epoxy Resin Co., Ltd., equivalent to epoxy resin, low molecular weight compound (c3)) was added, heated to 130 ° C. and aged for 3 hours. 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%, an acid value of 330 mgKOH / g, and a number average molecular weight of 4,500. 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.

(Note 5) Shonor BKS-377F: Showa Polymers, trade name, resol type phenol resin

[Production of anionic polymer crosslinked fine particles (D)]
Production Example 11 Production of Anionic Polymer Cross-Linked Fine Particles (D1) 150 parts of deionized water, “Newcol 562SF” (Note 6) in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device. 0.5 part (solid content) was charged, stirred and mixed in a nitrogen stream, and heated to 85 ° C.
Next, 1% of the following “monomer mixture 1” and 5.2 parts of “2% aqueous ammonium persulfate 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. Cool to 30 ° C., filter and discharge with 100 mesh nylon cloth to obtain anionic polymer crosslinked fine particles (D1) having an average particle diameter (Note 2) of 0.1 μm, a solid content of 25% and an acid value of 65 mgKOH / g. It was.
"Monomer mixture 1"
Deionized water 135 parts Styrene 30 parts Ethyl acrylate 50 parts Methacrylic acid 10 parts
Ethylene glycol dimethacrylate 10 parts “Newcol 562SF” (Note 6) 1 part (solid content)
"2% ammonium persulfate aqueous solution"
Ammonium persulfate 0.2 parts Deionized water 10 parts (Note 6) Newcol 562SF: Nippon Emulsifier Co., Ltd., trade name, ammonium polyoxyethylene alkylbenzenesulfonate, active ingredient 60%

Production Example 12 Production of Anionic Polymer Cross-Linked Fine Particles (D2) 95 parts of ethylene glycol monohexyl ether and 32 parts of n-butanol were charged into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device. The mixture was stirred and mixed in a nitrogen stream and heated to 100 ° C.
Subsequently, a monomer mixture (50 parts of methacrylic acid, 45 parts of styrene, 5 parts of ethyl acrylate) and a polymerization initiator (2 parts of perbutyl O, 10 parts of n-butanol) were dropped simultaneously over 3 hours, and after completion of dropping. Aged for 30 minutes. Thereafter, a polymerization initiator solution (0.4 parts of perbutyl O, 10 parts of n-butanol) was added dropwise for 30 minutes, and after aging for 2 hours, diluted with 63 parts of n-butanol to obtain a solid content of 32%, an acid value of 326 mgKOH / mg, polymer No. having 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. 25 parts (solid content) of 1 was neutralized with 3.88 parts of dimethylethanolamine, stirred for 15 minutes, and then 250 parts 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 an aqueous polymerization initiator solution (0.2 parts of ammonium persulfate, 22 parts of deionized water) was added dropwise for 1 hour in a nitrogen atmosphere, followed by aging for 2 hours. Then, it cooled to 30 degreeC, filtered and discharged | emitted with 100 mesh nylon cloth, adjusted with deionized water, and obtained the anionic polymer crosslinked fine particle (D2) of 20% of solid content. The anionic polymer crosslinked fine particles (D2) had an acid value of 82 mgKOH / g average particle size of 0.18 μm.
"Monomer mixture"
Deionized water 75 parts Ethylene glycol dimethacrylate 7.5 parts Ethyl acrylate 37.5 parts Styrene 30 parts (Note 6) Newcol 562SF 0.75 part

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

Examples 2-9
A can coating material No. 25 having a solid content of 25% was prepared in the same manner as in Example 1 except that the blending contents shown in Table 3 were used. 2-No. 10 was obtained.

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

Comparative Examples 2-10
A can coating material No. 25 having a solid content of 25% was prepared in the same manner as in Comparative Example 1 except that the content of Table 4 was used. 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.
(Note 7) Observation of coating film cross section (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, it was recognized in an area range of 10 μm × 10 μm. The average value (μm) of the width (major axis) in the longitudinal direction of 30 circular or elliptical island portions that were formed was determined.
(Note 8) T-bend bending workability:
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 are sandwiched and set in a tester. A 1 kg thick iron weight with a flat contact surface is dropped from a height of 50 cm to give an impact to the bent part, and then folded. 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.
A is less than 20 mA. A is 20 mA or more and less than 40 mA. A is 40 mA or more and less than 80 mA. X is 80 mA or more.

(Note 9) 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 iron weight 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, moisture is wiped off, the peeled portion of the processed part is subjected to a cello tape (registered trademark) , the portion is energized at an applied voltage of 6.5 V, and the current value (mA) of the bent tip 20 mm width is measured. evaluated.
A is less than 20 mA. A is 20 mA or more and less than 40 mA. A is 40 mA or more and less than 80 mA. X is 80 mA or more.
(Note 10) Retort whitening resistance A test coating plate was immersed in water, and the whitening state of a 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.

(Note 11) Acid resistance The test coating plate was immersed in an aqueous solution of 0.5% each 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 that full-surface swelling, full-surface peeling, or weakening of the coating film is remarkable (Note 12) Corrosion resistance after processing The test piece was prepared in the same manner as the above-mentioned T-bend processing test and bent in the same manner. After being immersed in a mixed aqueous solution in which 1% each of citric acid, malic acid and sodium chloride was dissolved and stored at 40 ° C. 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.
(Note 13) Flavor property Each test plate was added to a liquid in which 30 mg / l of d-limonene (fragrance) was added in deionized water and dispersed at 1 g / l of S-1170 (manufactured by Mitsubishi Chemical Corporation, sucrose fatty acid ester). Soaked at 35 ° C. for 1 month 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 a coating-film cross section which mix | blends a polymer crosslinked fine particle (D) in a coating material, and forms a sea-island structure.

Claims (5)

100 mass parts of acrylic resin-modified epoxy resin (A) having the following characteristics , 0.1-20 mass parts of resol type phenol resin (B), and acrylic resin having an acid value of 100-500 mgKOH / g having the following characteristics. (C) 0.1-20 mass parts is disperse | distributed in an aqueous medium, The aqueous coating composition characterized by the above-mentioned.
Acrylic resin-modified epoxy resin (A): 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 the bisphenol type Resin acrylic resin (C) obtained by graft polymerization of polymerizable unsaturated monomer component containing carboxyl group-containing polymerizable unsaturated monomer (a3) to epoxy resin (a1) : acrylic acid, itaconic acid, 10 to 60% by mass of at least one radical polymerizable monomer selected from sulfonic acid or phosphoric acid group-containing radical polymerizable monomer and 40 to 90% by mass of other radical polymerizable unsaturated monomer (1). % Vinyl copolymer resin (c1) having a monomer component, 10 to 60% by weight of methacrylic acid and other radical polymerizable unsaturated monomers ( ) Low molecular weight having two or more complementary reactive groups in one molecule having a vinyl copolymer resin (c2) having 40 to 90% by mass as a monomer component and an acid group and a carboxyl group. A polymer obtained by reacting the compound (c3),
The vinyl copolymer resin (c1), the vinyl copolymer resin (c2), and the low molecular weight compound (c3) are based on the total solid content of the vinyl copolymer resin (c1) and the vinyl copolymer resin (c2). Vinyl copolymer resin (c1) / vinyl copolymer resin (c2) = 60/40 to 95/5 (% by mass), and [vinyl copolymer resin (c1) + vinyl copolymer Resin (c2)] / low molecular weight compound (c3) = 100 / 0.1 to 100/20 (parts by mass) Low molecular weight compounds (c3) is an epoxy equivalent of 180～5,000 epoxy resin having two or more epoxy groups in one molecule, claim is at least one selected from resol type phenolic resin and polycarbodiimide compound 1 The water-based paint composition described in 1. The water-based coating composition according to claim 2 , 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. Per 100 parts by mass of the acrylic resin-modified epoxy resin (A), the one of the claims 1-3, characterized in that it further comprises 1 to 50 parts by weight of an anionic polymer crosslinked fine particles (D) having the following characteristics The water-based paint composition according to claim 1.
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 A polymer having an acid value of 10 to 100 mgKOH / g, which is produced by polymerizing a radically polymerizable unsaturated monomer component composed of 40 to 96% by mass of a polymerizable unsaturated monomer (d3). A water-based coating composition according to any one of claims 1 to 4 , which is intended to be applied to a can body.