JP2000109750A - Aqueous coating composition for can inner surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition capable of resolving the endocrine disruptor problem involving bisphenol A, good in coating operability, capable of giving coating film of high performance by using, as base resin, an epoxy resin with its terminal modified with a carboxylic acid or phenol compound. SOLUTION: This coating composition is such one as to contain, as base resin, a bisphenol A-type epoxy resin modified product having, on average, 0.5-1.8 per molecule of modified group of formula I or formula II (R1 is H or a 1-15C hydrocarbon group; R2 is a 1-15C carboxylic acid residue except carboxyl group) on the molecular terminal of a bisphenol A-type epoxy resin, an epoxy equivalent of 2,500-30,000 and number-average molecular weight of 3,000-40,000. The above modified product is obtained, for example, by reaction of a phenol compound of formula III and/or a carboxylic acid of formula IV as modifier with a bisphenol A-type epoxy resin with an epoxy equivalent of 2,000-15,000 and number-average molecular weight of 2,500-39,500.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition for the inner surface of a can containing, as a substrate resin, a bisphenol A type epoxy resin modified at the terminal with a carboxylic acid or an alkylphenol, which is suitable for environmental hormones.

[0002]

2. Description of the Related Art
Bisphenol A type epoxy resin is disclosed in
As described in 79504 and the like, a resin in which bisphenol A is introduced at the terminal of the resin is known.
However, recently, the residual of bisphenol A has become a problem from the viewpoint of environmental hormones, and a large amount of bisphenol A remains in the resin solution when producing the above-mentioned resin having bisphenol A introduced at the terminal of the resin. There was a problem.

In order to solve the problem of global environmental pollution due to the volatilization of organic solvents, organic solvent-based paints are being replaced with water-based paints in the field of paints for inner surfaces of cans. JP-A-41934 and JP-A-7-138523 propose an acrylic resin-modified epoxy resin-based water-based paint in which a bisphenol-type epoxy resin and a carboxyl group-containing acrylic resin are essential components, and these are combined or mixed. . However, these water-based paints do not consider the problem of environmental hormones caused by bisphenol A, and at present, there is no acrylic resin-modified epoxy resin-based water-based paint that can solve the problem of environmental hormones caused by bisphenol A. It is in.

[0004] In order to solve the problem of environmental hormones caused by bisphenol A, in the production of bisphenol A type epoxy resin, in order to eliminate the residual bisphenol A, it is required that the epoxy groups be excessive in relation to the hydroxyl groups of bisphenol A. It is conceivable to react, but the high-molecular-weight epoxy resin having an epoxy group at the terminal formed in this way causes gelation when the resin becomes highly viscous and becomes a water-based paint, and the coating workability of the water-based paint becomes poor. There was a problem of lowering.

[0005] An object of the present invention is to solve the problem of environmental hormones caused by bisphenol A, to achieve good coating workability,
An object of the present invention is to obtain an aqueous coating composition for the inner surface of a can which can form a coating film having good coating film performance.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain an aqueous paint for the inner surface of a can that can solve the problem of environmental hormones caused by bisphenol A. The present inventors have found that the above object can be achieved by using an epoxy resin whose terminal is modified with a carboxylic acid or a phenol compound, and completed the present invention.

That is, the present invention provides the following formula (1) or (2) at the molecular terminal of a bisphenol A type epoxy resin.

[0008]

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(Wherein, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 15 carbon atoms, and R ² represents a carboxylic acid residue having 1 to 15 carbon atoms excluding a carboxyl group). Bisphenol A having an average of 0.5 to 1.8 modified groups per molecule, an epoxy equivalent of 2,500 to 30,000 and a number average molecular weight of 3,000 to 40,000 It is intended to provide an aqueous coating composition for the inner surface of a can, comprising a modified epoxy resin (a) as a substrate resin.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous coating composition for the inner surface of a can of the present invention comprises the following modified bisphenol A type epoxy resin (a)
Is contained as a substrate resin.

Bisphenol A type epoxy resin modified product
(A) In the composition of the present invention, a modified bisphenol A-type epoxy resin (a) [hereinafter sometimes referred to as “modified epoxy resin (a)”], which is contained as a substrate resin,
The following formula (1) or (2) is added to the molecular terminal of the bisphenol A type epoxy resin.

[0012]

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(Wherein, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 15 carbon atoms, and R ² represents a carboxylic acid residue having 1 to 15 carbon atoms excluding a carboxyl group). The modifying group shown is 0.5 to 1.8 on average in one molecule.
, Preferably 0.8 to 1.6, having an epoxy equivalent of 2,500 to 30,000, preferably 4,000 to 2,
10,000 and a number average molecular weight of 3,000 to 40,0
00, preferably in the range of 4,000 to 20,000. It is preferable that the epoxy resin modified product (a) has an epoxy equivalent and a number average molecular weight within the above ranges from the viewpoints of stability of the obtained water-based paint, coating workability, coating film performance, and the like.

In the modifying group represented by the above formula (1),
The hydrocarbon group having 1 to 15 carbon atoms represented by R ¹ may partially contain an oxygen atom, a nitrogen atom and the like, and among them, for example, methyl, ethyl, n-butyl,
Alkyl groups having 1 to 15 carbon atoms such as tert-butyl and nonyl groups are preferred.

In the modified group represented by the above formula (2),
1 to 1 carbon atoms excluding the carboxyl group represented by R ²
5 carboxylic acid residues include a hydrogen atom and a carbon atom 1
And hydrocarbon groups which may partially contain oxygen atoms, nitrogen atoms, and the like. Representative examples of the hydrocarbon group include, for example, methyl, ethyl, n-
Alkyl groups such as propyl, butyl and nonyl groups; hydroxyl-containing hydrocarbon groups such as 1-hydroxyethyl group; and phenyl groups.

In the present invention, examples of the method for obtaining the modified bisphenol A type epoxy resin (a) include the methods described below or below.

The epoxy equivalent is 2,000 to 15,000.
A bisphenol A type epoxy resin having a number average molecular weight of about 2,500 to about 39,500,

[0018]

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Wherein R ¹ and R ² have the same meanings as described above, and a modifying agent which is a phenolic compound and / or a carboxylic acid, having a relatively low molecular weight and a low epoxy equivalent. Bisphenol A type epoxy resin, 2,2-bis (4-hydroxyphenyl) propane [abbreviated as "bisphenol A"]
And a method of reacting the phenol compound and / or a carboxylic acid modifier.

In the above method, the above three components may be reacted from the beginning of the reaction. In order to eliminate low molecular weight components, a bisphenol A type epoxy resin is reacted with bisphenol A to give an epoxy equivalent of 2,2. 000 ~
About 15,000, number average molecular weight is 2,500-39,
After about 500 bisphenol A type epoxy resins are synthesized, a phenol compound and / or a carboxylic acid modifier may be reacted.

Examples of the bisphenol A type epoxy resin used in the above method include a resin obtained by condensing epichlorohydrin and bisphenol A to a high molecular weight, if necessary, in the presence of a catalyst such as an alkali catalyst, and epichlorohydrin. Bisphenol A, if necessary, in the presence of a catalyst such as an alkali catalyst, condensed to a low molecular weight epoxy resin, a resin obtained by polyaddition reaction of this low molecular weight epoxy resin and bisphenol, and The obtained resin or the low-molecular-weight epoxy resin may be any of epoxy ester resins obtained by reacting a dibasic acid, and preferably has a glycidyl group at a molecular terminal of the resin. .

As the dibasic acid used for the production of the epoxy ester resin, a compound represented by the following formula HOOC- (CH ₂ ) _n -COOH (where n is an integer of 1 to 12) is preferable. Specific examples include succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecandioic acid, and hexahydrophthalic acid.

The bisphenol A type epoxy resin used in the above method has an epoxy equivalent of 2,000.
~ 15,000, preferably 2,500-10,0
Approximately 00, the number average molecular weight is 2,500 to 39,500
Degree, and preferably about 3,500 to 29,500, from the viewpoint of the amount of the epoxy terminal modifier introduced into the epoxy resin terminal, the stability of the obtained water-based paint, coating workability, coating film performance, and the like. It is.

In the present specification, the number average molecular weight is based on polystyrene as determined by gel permeation chromatography.

Commercially available bisphenol A type epoxy resins usable in the above method include, for example, Epicoat 1009 (epoxy equivalent: about 3,000, number average molecular weight: about 3,75) manufactured by Yuka Shell Epoxy Co., Ltd.
0), Epicoat 1010 (epoxy equivalent of about 4,50
0, number average molecular weight of about 5,500); Araldite AER6099 (epoxy equivalent of about 3,500;
A number average molecular weight of about 3,800); and Epomic R-309 (epoxy equivalent of about 3,50) manufactured by Mitsui Chemicals, Inc.
0, a number average molecular weight of about 3,800).

The bisphenol A type epoxy resin having a relatively low molecular weight and a low epoxy equivalent used in the above-mentioned method includes a modified epoxy resin obtained by reacting bisphenol A with a modifying agent which is an alkylphenol and / or a carboxylic acid. Any bisphenol A type epoxy resin capable of producing (a) can be used without any particular limitation. Specific examples thereof include those mentioned as the bisphenol A type epoxy resin usable in the above method, and oiled shell epoxy. Epicoat 828EL, Epicoat 1001, Epicoat 1 manufactured by Co., Ltd.
004 and Epicoat 1007.

The mixing ratio of the bisphenol A type epoxy resin having a relatively low molecular weight and a low epoxy equivalent to the bisphenol A in the above method is not particularly limited, but is based on 1 equivalent of epoxy group of the epoxy resin. Usually, it is suitable that the hydroxyl group of bisphenol A is in the range of 0.5 to 0.97 equivalent, preferably 0.8 to 0.95 equivalent.

Specific examples of the alkylphenol used as a modifier in the above or the above method include phenol, o-cresol, p-cresol, p-tert-
Butylphenol, p-nonylphenol and the like can be mentioned. Specific examples of the carboxylic acid used as the modifier include formic acid, acetic acid, propionic acid, butyric acid, hexanoic acid, octylic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, lactic acid, benzoic acid, and the like.

The amount of the modifying agent used in the above methods and the above method is such that the modified group by the modifying agent in the modified bisphenol A type epoxy resin (a) obtained by these methods has an average of 0.1 in one molecule. The amount may be 5 to 1.8, and usually 0.1 to 10% by weight based on the raw material constituting the solid content of the modified epoxy resin (a).
It is preferable that the amount is such that

The reaction in the above method or in the above method is usually carried out in an organic solvent at 100 to 200 ° C., preferably at 120 to 200 ° C.
~ 160 ° C. Examples of the organic solvent include hydrocarbons, ethers, esters, ketones,
Solvents such as alcohols can be used.

In the above method, in order to promote the reaction between the epoxy group in the epoxy resin and the above modifier,
As a catalyst, tetramethylammonium chloride, tetraethylammonium chloride, tetraethylammonium bromide, caustic soda, sodium carbonate, tri-n
-Butylamine, dibutyltin oxide and the like can also be used. The use amount of the catalyst is preferably 5000 ppm or less based on the raw material constituting the solid content of the modified bisphenol A type epoxy resin (a).

Representative examples of the aqueous coating composition for the inner surface of a can of the present invention include aqueous coating compositions containing the following resins (I) and (II).

(I) a resin obtained by subjecting the modified epoxy resin (a) to a carboxyl group-containing acrylic resin (b) (hereinafter sometimes abbreviated as “acrylic resin (b)”) by an ester addition reaction; (II) A resin obtained by graft-polymerizing a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer to the modified epoxy resin (a).

In the above (I), the modified epoxy resin (a) and the acrylic resin (b) are easily subjected to an ester addition reaction by heating, for example, in an organic solvent solution in the presence of an esterification catalyst. be able to.

In the above (II), the polymerizable unsaturated monomer component is graft-polymerized to the modified epoxy resin (a) in the presence of a radical generator such as benzoyl peroxide in an organic solvent. it can.

The acrylic resin (b) used in the above (1) is a copolymer resin containing a carboxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer as monomer components.

Examples of the carboxyl group-containing polymerizable unsaturated monomer include one or a mixture of two or more of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. However, methacrylic acid is preferably used.

Other polymerizable unsaturated monomers which are monomer components of the carboxyl group-containing acrylic resin (b) include:
Any monomer that can be copolymerized with the above-mentioned carboxyl group-containing polymerizable unsaturated monomer may be used, and may be appropriately selected and used according to required performance. For example, styrene, vinyltoluene, 2-methylstyrene ,
aromatic vinyl monomers such as t-butylstyrene and chlorostyrene; methyl acrylate, ethyl acrylate,
N-propyl acrylate, 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-, i- or t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate,
C1-C18 alkyl or cycloalkyl esters of acrylic acid or methacrylic acid such as lauryl methacrylate and cyclohexyl methacrylate; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,
C2-C8 hydroxyalkyl esters of acrylic acid or methacrylic acid such as 3-hydroxypropyl methacrylate and hydroxybutyl methacrylate; N-methylolacrylamide, N-butoxymethylacrylamide, N-methoxymethylacrylamide, N-methylolmethacrylamide, N-butoxy One or a mixture of two or more N-substituted acrylamide-based or N-substituted methacrylamide-based monomers such as methyl methacrylamide can be exemplified. As the other polymerizable unsaturated monomer, a mixture of styrene and ethyl acrylate is particularly preferable, and the constituent weight ratio of styrene / ethyl acrylate is 99.9 / 0.1 to 40/60, and more preferably 9 / 0.1 to 40/60.
Suitably, it is in the range of 9/1 to 50/50.

The preparation of the acrylic resin (b) can be easily carried out, for example, by solution-polymerizing the above monomer composition in an organic solvent in the presence of a polymerization initiator. Acrylic resin (b) has a resin acid value of 100 to 400 KOHm
g / g and the number average molecular weight are preferably in the range of 5,000 to 100,000.

In the ester addition reaction in the above (I), the mixing ratio of the modified epoxy resin (a) and the acrylic resin (b) is based on the equivalent of the epoxy group in the modified epoxy resin (a). Under the condition that the equivalent of the carboxyl group in the acrylic resin (b) becomes excessive, the epoxy resin modified product (a) and the acrylic resin (b) may be appropriately selected according to the coating workability and the coating film performance. The former: the latter is usually 6: 4 to 9: 1, and more preferably 7:
Preferably it is in the range of 3 to 9: 1.

The ester addition reaction can be carried out by a conventionally known method. For example, the modified epoxy resin (a)
The esterification catalyst is compounded in a uniform organic solvent solution of the epoxy resin and the acrylic resin (b), and usually at a reaction temperature of 60 to 130 ° C. for about 1 to 6 until substantially all of the epoxy groups are consumed. It can be performed by reacting for a time. Examples of the esterification catalyst include tertiary amines such as triethylamine and dimethylethanolamine, and quaternary salt compounds such as triphenylphosphine. Of these, tertiary amines are preferable. is there. When an esterification catalyst is used at the time of the ester addition reaction, the amount of the esterification catalyst is usually 0.1 to 1 equivalent to 1 equivalent of the epoxy group in the modified epoxy resin (a).
It is good to use in the range of 1 equivalent.

When the acrylic resin-modified epoxy resin (A) is a resin according to the above (II), a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer to be graft-polymerized to the epoxy resin modified product (a) Examples of the monomer include carboxyl group-containing polymerizable unsaturated monomers and other polymerizable unsaturated monomers, which are monomer components used in the production of the carboxyl group-containing acrylic resin (b) in the above (I).

The organic solvent used for the ester addition reaction in the above (I) or the graft polymerization reaction in the above (II) includes epoxy resin (a) and acrylic resin (b) or carboxyl group-containing polymerizable resin. When the polymerizable unsaturated monomer component containing the unsaturated monomer is dissolved and the acrylic resin-modified epoxy resin (A), which is a reaction product of these components, is dissolved or neutralized, the formation of an emulsion is hindered. As long as the organic solvent is not used, a conventionally known organic solvent can be used.

As the above-mentioned organic solvent, water-miscible solvents such as alcohol solvents, cellosolve solvents and carbitol solvents are preferred. 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, and ethylene glycol. Examples thereof include glycol monobutyl ether, 1-methyl-2-propoxyethanol, and diethylene glycol monomethyl ether. As the organic solvent, any other organic solvent which is difficult to mix with water can be used as long as the stability of the carboxyl group-containing reaction product (A) in an aqueous medium is not hindered. Examples thereof include hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, and ketones such as methyl ethyl ketone.

The acrylic resin-modified epoxy resin (A) obtained by the above (I) or (II) has a carboxyl group and a resin acid value of 10 to 160, more preferably 20 to 10
It is preferable to be within the range of 0 from the viewpoint of water dispersibility, coating film performance, and the like.

The acrylic resin-modified epoxy resin (A) is
Neutralizing at least a part of the carboxyl groups in the resin with a basic compound allows the resin to be dispersed in an aqueous medium. As the basic compound used for neutralizing 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 0.1 to 2.0 with respect to the carboxyl group in the resin (A).
It is preferably within the range of equivalent neutralization.

The aqueous medium may be water alone, or may be a mixture of water and an organic solvent. As the organic solvent, any conventionally known organic solvent can be used as long as it is an organic solvent that does not interfere with the stability of the acrylic resin-modified epoxy resin (A) in an aqueous medium and is miscible with water. The 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 20% by weight or less from the viewpoint of environmental protection and the like.

The acrylic resin-modified epoxy resin (A) can be neutralized and dispersed in an aqueous medium by a conventional method, for example, by stirring in an aqueous medium containing a basic compound as a neutralizer. A method of gradually adding an acrylic resin-modified epoxy resin (A), after neutralizing the acrylic resin-modified epoxy resin (A) with a basic compound, adding an aqueous medium to the neutralized product under stirring, or A method of adding the neutralized product to an aqueous medium can be used.

The aqueous coating composition of the present invention may contain, in addition to the neutralized acrylic resin-modified epoxy resin (A), if necessary, a resol-type phenol resin or an amino resin such as a melamine resin or a benzoguanamine resin. A curing agent; a surfactant, an antifoaming agent, and the like.

The aqueous coating composition 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 and a tin plate, and a primer applied to these metal plates. Examples thereof include painted metal plates, PET-coated metal plates obtained by laminating a polyester film (PET) on these metal plates, and those obtained by processing these metal plates into cans.

As a method of applying the aqueous coating composition of the present invention to a substrate, various known methods such as roll coater coating, spray coating, dip coating, and electrodeposition coating can be applied. The thickness of the coating film may be appropriately selected depending on the application, but is usually preferably about 3 to 20 μm. As the drying conditions of the coated film, the maximum temperature at which the material reaches is usually 120 to 300 ° C.
The conditions are preferably 10 seconds to 30 minutes, and in the case of roll coater coating, the temperature is more preferably in the range of 200 to 280 ° C. for 10 seconds to 50 seconds.

[0052]

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

In an acrylic resin synthesis reaction vessel, 1160 parts of diethylene glycol monobutyl ether was blended, and the temperature was raised to 100 ° C. and maintained. A mixed solution of 350 parts of methacrylic acid, 500 parts of styrene, 150 parts of ethyl acrylate, 75 parts of “Perbutyl O” (manufactured by NOF CORPORATION, peroxide-based polymerization initiator) and 140 parts of diethylene glycol monobutyl ether was added thereto. It was added dropwise over 3 hours. After completion of the dropwise addition, the mixture was aged at 100 ° C. for 2 hours. Then, 285 parts of diethylene glycol monobutyl ether was added, and the solid content was 39%.
An acrylic resin solution of No. ₃ was obtained. The obtained resin had a number average molecular weight of 5,000 and a resin acid value of 228 KOHmg / g.

Production Example 1 of Aqueous Coating Composition In a reaction vessel, "Epicoat 1009" (trade name, a bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.)
Epoxy equivalent about 3,000, number average molecular weight about 3,75
0) Add 525 parts, 12 parts of a 90% aqueous lactic acid solution, 58 parts of diethylene glycol monobutyl ether and 0.1 part of a 50% aqueous solution of tetramethylammonium chloride, raise the temperature to 140 ° C. with stirring, and maintain the same temperature for 6 hours. An epoxy resin modified solution was obtained. The resulting modified epoxy resin had an epoxy equivalent of about 9,100 and a number average molecular weight of about 6,
000, and the ratio of the functional group represented by the formula (2) by lactic acid in the modified epoxy resin was 2.2% by weight.

Next, 353 parts of the acrylic resin solution having a solid content of 39% obtained in Production Example 1 and 1-methyl-2-propoxyethanol 2 were added to the modified epoxy resin solution.
After adding 0 parts and uniformly stirring and mixing, the temperature was lowered to 100 ° C., 9 parts of deionized water and dimethylethanolamine were added.
6 parts were added and kept at 100 ° C. for 3 hours. Then, after adding 52 parts of dimethylethanolamine and 30 minutes have passed,
94 parts of "Show CKS-3865" (trade name, manufactured by Showa Polymer Co., Ltd., phenol resin solution, solid content 70%), 1-
After adding 30 parts of methyl-2-propoxyethanol and stirring for 30 minutes, 767 parts of deionized water was added dropwise with stirring over 5 hours to give a solid content of 39.5% and a viscosity of 3,000 mP.
An aqueous coating composition which was an aqueous dispersion having a · s and a particle diameter of 450 nm was obtained.

Example 2 In a reaction vessel, 525 parts of “Epicoat 1009” and p-
20 parts of tert-butylphenol, 60 parts of diethylene glycol monobutyl ether and 0.1 part of a 50% aqueous solution of tetramethylammonium chloride are added, and 1 part is stirred.
The temperature was raised to 40 ° C. and maintained at the same temperature for 8 hours to obtain a modified epoxy resin solution. The resulting modified epoxy resin has an epoxy equivalent of about 9,100 and a number average molecular weight of about 6,000, and the functional group represented by the above formula (1) by p-tert-butylphenol in the modified epoxy resin. Was 3.7% by weight.

Then, 353 parts of the acrylic resin solution having a solid content of 39% obtained in Preparation Example 1 above and 1-methyl-2-propoxyethanol 2 in the above-mentioned modified epoxy resin solution.
After adding 0 parts and uniformly stirring and mixing, the temperature was lowered to 100 ° C., 9 parts of deionized water and dimethylethanolamine were added.
6 parts were added and kept at 100 ° C. for 3 hours. Then, 52 parts of dimethylethanolamine was added, and after 30 minutes, 94 parts of “Shaw CKS-3865” having a solid content of 70% was added.
-Methyl-2-propoxyethanol 30 parts and 3
After stirring for 0 minutes, 767 parts of deionized water was added dropwise with stirring over 5 hours to give a solid content of 38.5% and a viscosity of 3,500.
An aqueous coating composition as an aqueous dispersion having a mPa · s and a particle diameter of 380 nm was obtained.

Example 3 "Epicoat 828EL" (trade name, manufactured by Yuka Shell Epoxy, bisphenol A type epoxy resin, epoxy equivalent: about 190, number average molecular weight: about 350) was placed in a reaction vessel.
10 parts, bisphenol A 262 parts ("Epicoat 82
8EL "per 1 mole of epoxy group per bisphenol A
Then, 26 parts of p-tert-butylphenol, 89 parts of diethylene glycol monobutyl ether and 0.1 part of a 50% aqueous solution of tetramethylammonium chloride were added, and the mixture was heated to 140 ° C. with stirring. The mixture was kept at the same temperature for 10 hours to obtain a modified epoxy resin solution. The resulting epoxy resin modified product has an epoxy equivalent of about 9,100 and a number average molecular weight of about 12,000,
The ratio of the functional group represented by the above formula (1) due to p-tert-butylphenol in the modified epoxy resin was 3.3% by weight. Then, 526 parts of the acrylic resin solution having a solid content of 39% obtained in Production Example 1 and 30 parts of 1-methyl-2-propoxyethanol were added to the modified epoxy resin solution, and the mixture was uniformly stirred and mixed. 10
The temperature was lowered to 0 ° C., 14.3 parts of deionized water and 5.5 parts of dimethylethanolamine were added, and the mixture was kept at 100 ° C. for 3 hours. Then add 79 parts of dimethylethanolamine and add 3 parts.
After 0 minutes, “Show CKS-386” having a solid content of 70% was used.
142 ”and 45 parts of 1-methyl-2-propoxyethanol were stirred for 30 minutes, and 1157 parts of deionized water was added dropwise with stirring over 5 hours to give a solid content of 38.
An aqueous coating composition as an aqueous dispersion having a 5% viscosity of 4,000 mPa · s and a particle diameter of 350 nm was obtained.

Comparative Example 1 1800 parts of "Epicoat 828EL" and 1487 parts of bisphenol A ("Epicoat 828EL") were placed in a reaction vessel.
The amount of the hydroxyl group in bisphenol A becomes 1.35 mol per 1 mol of the epoxy group), 363 parts of diethylene glycol monobutyl ether and 1 part of a 50% aqueous solution of tetramethylammonium chloride, and 140 parts of the mixture are stirred.
C. and kept at the same temperature for 8 hours to obtain an epoxy resin solution. The obtained epoxy resin has an epoxy equivalent of about 9,
100, a number average molecular weight of about 5,500.

Next, the acrylic resin solution 216 having a solid content of 39% obtained in Production Example 1 was added to the epoxy resin solution.
3 parts and 1-methyl-2-propoxyethanol 123
After the mixture was uniformly stirred and mixed, the temperature was lowered to 100 ° C., 58.5 parts of deionized water and 22.6 parts of dimethylethanolamine were added, and the mixture was kept at 100 ° C. for 3 hours. Then, 326 parts of dimethylethanolamine was added, and after 30 minutes, 587 parts of “Show CKS-3865” having a solid content of 70% and 1-methyl-2-propoxyethanol 18 were added.
After adding 4 parts and stirring for 30 minutes, 4774 parts of deionized water was added dropwise with stirring over 5 hours to give a solid content of 39.0.
%, A viscosity of 4,000 mPa · s, and an aqueous coating composition as a water dispersion having a particle diameter of 300 nm was obtained.

Comparative Example 2 A reaction vessel was charged with 500 parts of "Epicoat 828EL" and 292 parts of bisphenol A (an amount in which the hydroxyl group in bisphenol A was 0.96 mol per 1 mol of epoxy group of "Epicoat 828EL"), and diethylene glycol mono. 66 parts of butyl ether and 0.5 part of a 50% aqueous solution of tetramethylammonium chloride were added, and the mixture was stirred at 140 ° C.
And kept at the same temperature for 9 hours to obtain an epoxy resin solution. The obtained epoxy resin has an epoxy equivalent of about 9.1.
00, had a number average molecular weight of about 16,000.

Next, the acrylic resin solution 389 having a solid content of 39% obtained in Production Example 1 was added to the epoxy resin solution.
Then, the mixture was uniformly stirred and mixed, the temperature was lowered to 100 ° C., 10.3 parts of deionized water and dimethylethanolamine were added.
When 0 parts were added, the mixture gelled.

Each of the aqueous coating compositions obtained in Examples 1 to 3 and Comparative Example 1 was naturally coated with a roll coater, and all the compositions showed good coating workability.

Coating Performance Test Each of the aqueous coating compositions obtained in Examples 1 to 3 and Comparative Example 1 was applied to clean chin-free steel having a thickness of 0.23 mm to a dry coating thickness of 10 μm. And 3 at 200 ° C
Various coating film performance tests were carried out using the coated plate baked and cured for minutes based on the following test methods. In addition, the concentration of bisphenol A in each aqueous coating composition was measured. The results of these tests are shown in Table 1 below.

Test Method Gel Fraction: The weight percentage (%) of the weight of the unextracted coating film after extraction with respect to the weight of the coating film before extraction when the cured coating film was subjected to solvent extraction under reflux of acetone for 6 hours. Properties: Nylon film sandwiched between two coated plates (150 mm × 5 mm) with the coated surface as the surface to be adhered.
The test piece was heated at 0 ° C. for 60 seconds and then pressurized at 200 ° C. for 30 seconds to fuse the nylon film to both coatings. Next, the T-peel adhesive strength of this test piece was measured using a tensile tester (Shimadzu Autograph AGS-500A). The tensile conditions were a temperature of 20 ° C. and a tensile speed of 200 mm / min.

Workability: The coated plate was cut into a size of 40 mm × 50 mm, and the test area was 40 mm with the coated surface facing outward.
, And two pieces of 0.23 mm thick chin-free steel are sandwiched between the folded test pieces, and a 3 kg weight is bent from a height of 42 cm. Then, a current value was measured when a voltage of 6.5 V was applied for 6 seconds during a length of 20 mm at the tip of the bent portion.

Corrosion resistance: The coated plate was cut into a size of 150 × 70 mm, and the coated film was cross-cut so as to reach a base material, and then the coated plate was subjected to a salt spray test for 3 weeks. The coated plate after the test was visually evaluated according to the following criteria. ：: Rust width from cut portion is less than 2 mm on one side △: Rust width from cut portion is 2 mm or more on one side and less than 5 mm ×: Rust width from cut portion is 5 mm or more on one side.

Acid resistance: A coated plate whose back surface and cut surface were sealed was immersed in a 10% aqueous hydrochloric acid solution at 20 ° C. for one week, and the coated surface was visually evaluated according to the following criteria. ：: No abnormality was observed Δ: Slight whitening was observed ×: Extremely whitening was observed.

Alkali resistance: The coated plate whose back surface and cut surface were sealed was immersed in a 10% aqueous sodium hydroxide solution at 20 ° C. for 1 week, and the coated surface was visually evaluated according to the following criteria.

：: No abnormality was observed Δ: Slight whitening was observed X: Extremely whitening was observed.

Bisphenol A concentration: The concentration of bisphenol A in the aqueous coating composition when the aqueous coating composition obtained in each example was dissolved in tetrahydrofuran and analyzed by high performance liquid chromatography is indicated.

[0072]

[Table 1]

[0073]

The aqueous coating composition for the inner surface of a can of the present invention has a very low content of bisphenol A and can cope with the problem of environmental hormones, and has good coating workability.

The coating film obtained from the composition of the present invention is excellent in coating film performance such as adhesion to a substrate and corrosion resistance.

Continuing from the front page (72) Inventor Takeshi Uchida 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture Inside Kansai Paint Co., Ltd. (72) Inventor Shin Shin Asakura 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint stock Inside the company (72) Inventor Shinichiro Maruki 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Pref. (72) Inventor Kaoru Morita 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Pref. F term (reference) 4D075 EA06 EB22 EB33 4J036 AD08 CA06 CA07 CA21 CD03 JA01 KA04 4J038 CP101 DB341 DB351 DB451 GA02 GA06 MA08 NA27 PB04 PC02

Claims (3)

[Claims] 1. A bisphenol A type epoxy resin having the following formula (1) or (2) (Wherein, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 15 carbon atoms, and R ² represents a carboxylic acid residue having 1 to 15 carbon atoms excluding a carboxyl group) Bisphenol A type epoxy resin having an average of 0.5 to 1.8 groups per molecule, an epoxy equivalent of 2,500 to 30,000 and a number average molecular weight of 3,000 to 40,000 An aqueous coating composition for the inner surface of a can, comprising the modified product (a) as a substrate resin. 2. The modified bisphenol A type epoxy resin has a functional group represented by the formula (1) or (2):
The aqueous coating composition according to claim 1, wherein the resin-modified product contains 0.1 to 10% by weight of the solid content. 3. A compound represented by the following formula (1) or (2): (Wherein, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 15 carbon atoms, and R ² represents a carboxylic acid residue having 1 to 15 carbon atoms excluding a carboxyl group) Bisphenol A type epoxy resin having an average of 0.5 to 1.8 groups per molecule, an epoxy equivalent of 2,500 to 30,000 and a number average molecular weight of 3,000 to 40,000 An acrylic resin-modified epoxy resin (A) obtained by subjecting the modified product (a) and the carboxyl group-containing acrylic resin (b) to an esterification reaction is neutralized and dispersed in an aqueous medium. Item 3. The aqueous coating composition according to Item 1 or 2.