JPH04318085A - Water-based coating composition for coating of inner surface of can - Google Patents

Abstract

PURPOSE:To obtain the subject composition having excellent processability, adhesivity, corrosion resistance, water-resistance, chemical resistance, etc., by reacting a specific carboxyl-containing resin with an epoxy resin and using an aqueous dispersion of the obtained modified epoxy resin, etc., as a main component. CONSTITUTION:The objective composition is composed mainly of an aqueous dispersion of (A) a modified epoxy resin produced by reacting (a) a carboxyl- containing resin consisting of a copolymer containing (i) one or more kinds of polybasic acid monomer containing an alpha, beta-ethylenic unsaturated group which is selected from maleic anhydride, maleic acid and fumaric acid and (ii) an ethylenic hydrocarbon as essential monomer components with (b) an epoxy resin and/or (B) a graft polymer produced by the graft polymerization of a polymerizable unsaturated vinyl monomer to the above modified epoxy resin.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an aqueous coating composition for the inner surface of cans useful for coating the inner surfaces of edible cans for beverages, meat, vegetables, fruits, etc. The present invention relates to an aqueous coating composition for the inside of a can that has excellent properties such as durability, chemical resistance, hygienic properties, and flavor properties.

0002

[Prior Art and its Problems] Conventionally, paints for the inside of cans that use organic solvents as solvents or dispersion media are not only unfavorable in terms of environmental hygiene and fire safety, but also reduce the molecular weight of the base resin in order to maintain an appropriate coating viscosity. There was a problem in that the flavor properties and the like deteriorated because of this. In order to solve these problems, efforts are being made to develop water-based paints for the inside of cans that contain no or almost no organic solvent. The main water-based paints for the inside of cans that have been developed so far include (I) a self-emulsifying emulsion paint obtained by esterifying a carboxyl group-containing vinyl resin and an epoxy resin in the presence of a tertiary amine ( JP-A-55-3
(II) Self-emulsifying emulsion paint obtained by graft polymerizing a vinyl monomer containing a polymerizable unsaturated acid monomer to an epoxy resin using a peroxide as a catalyst (Japanese Patent Laid-Open No. 1285/1985); and (III) reacting the reaction product of an epoxy resin and (meth)acrylic acid with a monomer mixture consisting of an aromatic vinyl monomer, an alkyl ester of an α,β-ethylenically unsaturated carboxylic acid, acrylic acid or methacrylic acid. Self-emulsifying emulsion paint obtained by (polymerization)
No. 13 and No. 60-106805).

However, as a result of various studies on the above emulsion paints (I) to (III), it has been found that these emulsion paints have excellent coating film curing properties, adhesion properties, processability, etc., but have poor flavor properties and It was found that corrosion resistance, water resistance, chemical resistance, etc. were insufficient. That is, it is presumed that the basic structure of the self-emulsifying resin in the paint is composed of a linear vinyl resin softened by an epoxy resin bonded to pendants. In the self-emulsifying resin, (1) suppresses the high melting point and high viscosity of the resin and gives flexibility to the coating film, (2) allows reaction between epoxy resin and vinyl resin and water dispersion of the resulting resin. In order to ensure that the curing reaction with the curing agent proceeds smoothly, and to suppress residual stress during curing of the coating film due to heating, and to improve adhesion and processability, The above-mentioned linear vinyl resin has monomer components such as α and β that have linear alkyl groups in their ester moieties.
- It has been found that softening vinyl monomers such as alkyl esters of ethylenically unsaturated carboxylic acids are essential. However, by using a softened vinyl monomer, the objectives of (1) to (3) above are almost achieved, but on the other hand, the sanitary properties and flavor properties of the coating film are not sufficient.
Furthermore, it has been found that the formed coating film has high permeability to oxygen, moisture, and ions and is susceptible to hydrolysis, resulting in poor chemical resistance, corrosion resistance, water resistance, etc.

0004

[Means for solving the problem] Therefore, the present inventors
As a result of intensive studies with the aim of eliminating the various defects mentioned above without degrading the excellent performance of the water-based paints for the inside of cans (I) to (III), we found that a carboxyl group-containing resin that reacts with epoxy resin. ,(anhydrous)
The present invention has been completed based on the discovery that the above object can be achieved by using a copolymer containing maleic acid and/or fumaric acid and an ethylene series hydrocarbon as essential monomer components.

Thus, the present invention provides (1) a modified epoxy resin (X) obtained by reacting a carboxyl group-containing resin (A) and an epoxy resin (B), and/or a polymerizable resin in the modified epoxy resin (X). It contains as a main component an aqueous dispersion of a graft polymer (Y) obtained by graft polymerization of an unsaturated vinyl monomer (C), and the carboxyl group-containing resin (A) contains maleic anhydride, maleic acid, and fumaric acid. At least one kind of α,β-ethylenically unsaturated group-containing polybasic acid monomer selected from acids (hereinafter sometimes abbreviated as “polybasic acid monomer”) and ethylene series hydrocarbon (hereinafter “ethylene”) ) and (2) the above-mentioned modified epoxy resin (X) and/or An aqueous coating composition for the inside of a can, characterized in that it contains as a main component an aqueous dispersion (Z) obtained by seed polymerizing a polymerizable unsaturated vinyl monomer (D) in an aqueous dispersion of a graft polymer (Y). It provides:

The main feature of the composition of the present invention is that a copolymer (a) containing a polybasic acid monomer and ethylene as essential components is used as the carboxyl group-containing vinyl resin reacted with the epoxy resin. Thus, the compositions of the present invention can achieve various advantages as described below. In the copolymer (a), the crystallinity of ethylene decreases due to copolymerization with the polybasic acid monomer, and it acts as a soft component. It is thought that the properties and processability will be improved. In addition, since ethylene and the polybasic acid monomer have significantly different polarities and are clearly separated, the carboxyl group of the polybasic acid monomer component of copolymer (a) acts intensively on the coated surface. On the other hand, it is presumed that ethylene concentrates on the surface of the coating film and contributes to significantly improving corrosion resistance, water resistance, chemical resistance, etc. Furthermore, since the ethylene component in the copolymer (a) does not undergo hydrolysis at all, it has an excellent ability to prevent water, oxygen, ions, etc. from permeating through the coating film, and as a result, the present invention The coating film formed from the composition also has improved water resistance and chemical resistance. Further, since the copolymer (a) is hardly extracted by water, alcohol, etc., the composition of the present invention has excellent flavor properties and hygienic properties.

Furthermore, the composition of the present invention comprises a copolymer (a
Since the carboxyl group derived from the polybasic acid monomer component in ) reacts with the secondary hydroxyl group or oxirane group in the epoxy resin (B), it can be cured even without a crosslinking agent. In addition, since the copolymer (a) has a low viscosity,
It is possible to suppress the increase in viscosity accompanying the curing reaction and allow the crosslinking reaction to proceed sufficiently, thereby making it possible to form a coating film with a high crosslinking density.

Furthermore, since the composition of the present invention can be used in an aqueous medium, it is advantageous in terms of environmental hygiene, fire safety, and resource saving.

The composition of the present invention is a modified epoxy resin (X
) and/or an aqueous dispersion of the graft polymer (Y) as a main component. The modified epoxy resin (X)
is a combination of one or more copolymers (a) as a carboxyl group-containing vinyl resin (A) and an epoxy resin (B).
), while the graft polymer (Y) is obtained by graft polymerizing the modified epoxy resin (X) with a polymerizable unsaturated vinyl monomer (C). Each of these components will be explained in more detail below.

Copolymer (a): This is a copolymer that is reacted with the epoxy resin (B) and contains ethylene and a polybasic acid monomer as essential monomer components. The ethylene includes, for example, ethylene, propylene, butylene, hexylene, and the like.

The copolymer (a) contains ethylene and a polybasic acid monomer as essential components, and further contains, if necessary,
It can be obtained by copolymerizing one or more other ethylenically unsaturated monomers such as vinyl acetate, vinyl chloride, vinylidene chloride, acrylic esters, methacrylic esters, vinyl ethers, and styrene.

The composition ratio of each monomer in the copolymerization is not particularly limited and can be arbitrarily selected depending on the properties required for the composition of the present invention, but generally, ethylene and polybasic acid monomers are used. Based on the total weight of both components, ethylene is preferably in the range of 98 to 5% by weight, particularly 95 to 90% by weight, and polybasic acid monomers are in the range of 2 to 5% by weight.
A content of 95% by weight, particularly in the range from 5 to 10% by weight, is suitable. Furthermore, other ethylenically unsaturated monomers such as vinyl acetate, which can be used as needed, are preferably used in an amount of 500 parts by weight or less per 100 parts by weight of the total of ethylene and polybasic acid monomers. In addition, copolymer (a) obtained using maleic anhydride as a polyhydrochloric acid monomer must be ring-opened with water to convert anhydride carboxyl groups into carboxyl groups before reacting with resin (B). It is.

The copolymer (a) can be obtained by copolymerizing the above monomer components, for example, by high-pressure polymerization reaction, and by graft copolymerizing a polybasic acid monomer in the presence of an ethylene (co)polymer.

Epoxy resin (B): A compound having an epoxy group in one molecule, a condensate of a bisphenol compound having two or more phenolic hydroxyl groups in one molecule and epichlorohydrin is generally preferred, and specifically, For example, 2,2'-bis(4-hydroxyphenyl)propane (common name: bisphenol A), halogenated bisphenol A, bis(4-hydroxyphenyl)methane (common name: bisphenol F), 2,2'-bis(4 -Hydroxyphenyl)butyl, bis(4-hydroxyphenyl)sulfone (common name: bisphenol S)
, resorcinol, tetrahydroxyethane, phenol, or a condensate of epichlorohydrin and a bisphenol compound such as a novolak type polyfunctional phenol that is condensed with cresol and formalin. More specifically, the bisphenol compound is 0.5 to 2.0 mol, preferably 0.8 mol per mol of epichlorohydrin.
A mixture containing ~1.2 mol is continued to react in the presence of an alkali metal catalyst or an alkaline earth metal catalyst until the reaction product has a molecular weight in the range of about 1,000 to about 29,000. Or, as a starting material for a low molecular weight condensate having two epoxy groups in one molecule obtained by reacting the above bisphenol compound and epichlorohydrin in the presence of the above catalyst, per mol of the low molecular weight condensate. A mixture containing 0.5 to 1.5 moles, preferably 0.8 to 1.2 moles, of a bisphenol compound is added in the presence of a condensation catalyst until the molecular weight of the reaction product is about 1,000 to about 29,00.
This includes those obtained by continuing the reaction until the value falls within the range of 0. Examples of the alkali (earth) metal catalysts include sodium hydroxide, potassium hydroxide, lithium hydroxide, barium hydroxide, calcium hydroxide, sodium carbonate, calcium carbonate, etc.; In addition to the above-mentioned alkali (earth) metal catalysts, n-butylamine, tri-n-butylamine, triethanolamine, pyridine, calcium carbonate, calcium chloride, quaternary ammonium salts, etc. can be used.

[0015] The epoxy resin (B) used in the present invention is
Generally, one molecule has an average of 0.6 to 2.0, preferably 0.8 to 1.9 epoxy groups, and has a molecular weight of about 1,000 to about 29,000, preferably 1, 600～
It is desirable that it be within the range of 6,000. When the number of epoxy groups in one molecule is less than 0.6, the copolymer (a)
There is a possibility that the amount of unreacted epoxy resin components chemically bonded to increases, and the water dispersibility and storage stability of the modified epoxy resin (X) thus formed may also deteriorate.

[0016] As the epoxy resin (B) that can be used in the composition of the present invention, for example, EPON8
28, 1001, 1007, 1009 and 1010 (all Shell Chemical Company products), XAC5025, 60
71, 7072, 6084, 7097, 6097 and 6
099 (all Ciba Geigy products), DER662
, 664, 667, 668 and 669 (all of which are products of Dow Chemical Company).

Modified epoxy resin (X): copolymer (a)
It is obtained by reacting at least one of the following with an epoxy resin (B). This reaction mainly involves, in the presence of a tertiary amine, (1) an esterification reaction between the carboxyl group of the copolymer (a) and the epoxy group in the epoxy resin (B); It seems that either one of the carboxyl group, the epoxy group in the epoxy resin (B), and the quaternary ammonium salt reaction formed from the tertiary amine, or both (1) and (2) are carried out simultaneously. In this reaction, the ratio of copolymer (a) and epoxy resin (B) can be arbitrarily selected depending on the desired physical properties of the modified epoxy resin (X) to be formed. Based on the total weight of and epoxy resin (B),
The copolymer (a) is 5 to 90% by weight, especially 10 to 50% by weight, and the epoxy resin (B) is 10 to 95% by weight, especially 50% by weight.
It is preferably within the range of 90% by weight.

Further, as a catalyst for promoting the above reaction, it is preferable to use, for example, dimethylethanolamine, dimethylbenzylamine, triethanolamine, monomethyldiethanolamine, morpholine, etc., and the amount used is determined depending on the copolymer (a ) and epoxy resin (
A suitable range is 1 to 20% by weight based on the total solids content with B).

[0019] The above copolymer (a) and epoxy resin (B)
It is preferable to carry out the reaction with an organic solvent capable of dissolving or dispersing each of these components. Examples of such organic solvents include alcohol solvents such as n-butyl alcohol, and cellosolve solvents such as ethylene glycol monobutyl ether. Examples include solvents. The reaction temperature and time vary depending on the type of resin, the type of solvent, etc., but generally the reaction temperature is preferably within the range of 40°C to 200°C, particularly 60°C to 150°C. It is convenient that the acid value of the resulting modified epoxy resin (X) is usually in the range of 10 to 400, particularly 20 to 100.

Graft polymer (Y): A polymer obtained by graft polymerizing a polymerizable unsaturated vinyl monomer (C) onto a modified epoxy resin (X) as described above. ) can be produced by graft polymerizing (C) onto a polymerizable unsaturated vinyl monomer in an organic solvent solution in the presence of a free radical generator.

The polymerizable unsaturated vinyl monomer (C) capable of graft polymerization is a compound having one or more polymerizable unsaturated bonds in one molecule, and examples thereof include the following.

■Methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n
-butyl acrylate, n-butyl methacrylate, i
-butyl acrylate, i-butyl methacrylate, t
ert-butyl acrylate, tert-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl acrylate,
Acrylic acid or methacrylic acid having 1 to 2 carbon atoms, such as 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, decyl acrylate, etc.
4 alkyl or cycloalkyl esters;

002
3] ■ Vinyl monomers such as styrene, vinyltoluene, vinyl propionate, α-methylstyrene, vinyl acetate, acrylonitrile, methacrylonitrile, vinyl propionate, vinyl pivalate, and beoba monomer (Shell Chemicals):

■2-Hydroxyethyl acrylate, 2
- The number of carbon atoms of acrylic acid or methacrylic acid, such as hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, etc. is 1 or more
8 hydroxyalkyl esters;

■Acrylamide, methacrylamide, N
- functional acrylic or methacrylamides such as methylacrylamide, N-ethylmethacrylamide, diacetone acrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-butoxymethylacrylamide;

[
■Acrylic acid, methacrylic acid, crotonic acid,
Carboxyl group-containing vinyl monomers such as itaconic acid. These monomers can be used alone or in combination of two or more.

Examples of free radical generators that can be used include benzoyl peroxide, perbutyl octate, t-butyl hydroperoxide, azobisisobutyronitrile, azobisvaleronitrile, 2,
Examples include 2'-azobis(2-aminopropane) hydrochloride, which is generally used in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the total amount of modified epoxy resin (X) and polymerizable unsaturated vinyl monomer (C). It can be used in parts by weight.

Modified epoxy resin in graft polymerization (
The composition ratio of X) and the vinyl monomer (C) is not strictly limited, but generally, based on the total weight of both components, the modified epoxy resin (X) is 10 to 95% by weight, In particular, the content is preferably 50 to 90% by weight, and the vinyl monomer (C) is preferably 90 to 5% by weight, particularly preferably 50 to 10% by weight.

The graft polymerization reaction is usually preferably carried out in an organic solvent system, and the organic solvents that can be used include the modified epoxy resin (X), the vinyl monomer (C), the polymer formed from the vinyl monomer, and the graft polymer. Combine (Y)
Solvents that can dissolve and have excellent miscibility with water are preferred. Such organic solvents include, for example, those of the general formula H
O-R1 HO-Cm H2m-O-R2 and HO-Cm H2m-O-Cm H2m-O-R2 In each of the above formulas, R1 represents an alkyl group having 1 to 12 carbon atoms, and R2 represents the number of carbon atoms Examples include alcohol solvents, cellosolve solvents, and carbitol solvents, each of which represents 1 to 6 alkyl groups, and m is an integer of 1 to 6. Specifically, such organic solvents include isopropanol, n-butyl alcohol, 2-hydroxy-4
-Methylpentane 2-ethylhexyl alcohol, cyclohexanol, ethylene glycol, diethylene glycol, 1,3-butylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and the like. In addition, inert organic solvents that are immiscible with water can also be used, such as aromatic hydrocarbons such as toluene and xylene;
These include esters such as ethyl acetate and butyl acetate; ketones such as acetone and methyl ethyl ketone. These organic solvents are preferably those that can be removed by distillation under normal pressure or reduced pressure after the completion of the reaction.

The monomer composition in the graft polymerization can be arbitrarily selected depending on the properties required of the final coating material and cured coating film. For example, by incorporating a carboxyl group-functional monomer into the graft polymerization monomer composition, it is possible to react with unreacted epoxy resin and make it water-based, thereby improving the stability of the paint and film-forming properties during curing. be able to.

[0031] Reaction conditions such as temperature and time during graft polymerization are not special, and conditions known per se can be used. This graft polymerization appears to be due to a hydrogen abstraction reaction in the presence of an initiator.

[0032] In addition, in the epoxy resin skeleton, the grafting reaction point is tertiary hydrogen (hydrogen on the carbon to which the secondary hydroxyl group is bonded), and in the vinyl resin skeleton, it is the tertiary hydrogen in the ethylene skeleton. Tertiary hydrogen on carbon generated by branches is considered.

Graft copolymer (Y) finally obtained
generally preferably has an acid value within the range of 10 to 400, particularly 20 to 100.

The composition of the present invention can be prepared by dispersing the above-mentioned modified epoxy resin (X) and/or graft polymer (Y) in an aqueous medium as it is, or by neutralizing it with a basic compound or the like and then dispersing it in an aqueous medium. It can be obtained by dissolving or dispersing in.

As the basic compound of the neutralizing agent, those known per se can be used, and preferred specific examples include those of the general formula R3 R4 R5 N (wherein R3 and R4
each represents a substituted or unsubstituted monovalent alkyl group containing 1 or 2 carbon atoms in the alkyl moiety, and R5 represents a substituted or unsubstituted monovalent alkyl group containing 1 to 4 carbon atoms. ), N-
Methylpyrrolidine, N-methylmorpholine, pyridine,
At least one selected from the group consisting of N-methylpyrrole, N-methylpiperidine, and mixtures thereof. Specific examples of compounds represented by the above formula R3R4R5N include the following: trimethylamine, dimethylethanolamine (dimethylaminoethanol), methyldiethanolamine, ethylmethylethanolamine, dimethylethylamine, dimethylpropylamine, dimethyl-3 -Hydroxy-1-propylamine, dimethylbenzylamine, dimethyl-2-hydroxy-1-propylamine, diethylmethylamine, dimethyl-1-
Hydroxy-2-propylamine and mixtures thereof. Most preferably trimethylamine or dimethylethanolamine is used.

Neutralization is preferably carried out at a neutralization equivalent of 0.1 to 2. When neutralized in this way, the modified epoxy resin (X) and/or the graft copolymer (Y) become self-emulsifying, and there is no need to use an emulsifier, dispersant, etc. in order to dissolve or disperse them in an aqueous medium.

Furthermore, according to the present invention, in another embodiment, in the aqueous dispersion of the modified epoxy resin (X) and/or graft polymer (Y), in the presence of a free radical generator, the polymerizable Also provided is an aqueous coating composition for the inside of a can, which contains as a main component an aqueous dispersion (Z) formed by seed polymerizing an unsaturated vinyl monomer (D).

As the polymerizable unsaturated vinyl monomer (D) that can be seed-polymerized, at least one monomer selected from the monomers described above as the polymerizable unsaturated vinyl monomer (C) is suitable.

[0039] Here, the seed polymerization is carried out using the water-dispersed modified epoxy resin (X) and/or graft polymer (X).
In this polymerization, the particles of Y) serve as polymerization sites for the vinyl monomer (D), and the monomer (D) is polymerized within the water-dispersed particles. Polymerization conditions such as temperature and time during seed polymerization vary depending on the monomer type and initiator type used, but
Typically, the reaction temperature is within the range of about 30 to about 100°C;
Further, the polymerization time can be about 30 minutes to 10 hours.

The amount of monomer (D) that can be used is generally determined by the amount of modified epoxy resin (X) and/or graft resin (Y).
1 to 300 parts by weight, preferably 10 to 150 parts by weight, based on 100 parts by weight of the solid content.

The aqueous dispersion (Z) obtained by such seed polymerization has a proportion of component (B) in the composition,
Since the coating composition can be made lower than the above-mentioned compositions containing the modified epoxy resin (X) and the graft polymer (Y) as main components, it is possible to reduce the cost of the coating composition.

According to the present invention, as a further aspect,
Maleic acid is further added as an essential monomer to a composition containing an aqueous dispersion of the modified epoxy resin (X) and/or graft polymer (Y) as a main component, or a composition containing an aqueous dispersion (Z) as a main component. An aqueous coating composition for the inner surface of a can is provided, which contains a polymer (E) as a component.

The copolymer (E) contains maleic acid (including anhydride) as an essential monomer component, and comonomer components that can be copolymerized with maleic acid include, for example, methyl vinyl ether, styrene, vinyl chloride, and acrylic acid ester. , methacrylic acid ester, ethylene, vinyl acetate, and the like.

The composition ratio of maleic acid and the comonomer component in the copolymer (D) is generally 2 to 100% by weight, particularly 3% by weight, based on the total weight of both components.
The content of the comonomer component is preferably 0 to 70% by weight, and the comonomer component is preferably 98 to 0% by weight, particularly 70 to 30% by weight.

[0045] The amount of copolymer (D) to be used is per 100 parts by weight of epoxy resin (B) contained in the composition.
Usually, a range of 5 to 100 parts by weight is suitable.

As described above, the composition of the present invention comprises the modified epoxy resin (X) and the graft polymer (Y).
This is an aqueous dispersion of one or more unneutralized or neutralized products selected from the following, or an aqueous coating composition for the inner surface of a can, which contains the aqueous dispersion (Z) as an essential component.

The composition of the present invention may further contain water-soluble or hydrophobic urea resins, melamine resins, phenol resins, etc. as curing agents (crosslinking agents) (these include methylol compounds and alkyl ether compounds), if necessary. ) can also be mixed. The coating film formed from the composition of the present invention is rapidly crosslinked and cured when heated, and can form a coating film with excellent boiling water resistance and processability. It is also possible to mix resins, vinyl chloride-vinyl acetate-copolymer resins, and the like.

[0048] To apply the composition of the present invention to the inner surface of a can,
For example, the composition is applied to the surface of a metal material for a can, and then the formed coating is baked. Metal materials for cans include aluminum plates, steel plates, plated steel plates whose surfaces are plated with zinc, chromium, tin, aluminum, etc., or steel plates whose surfaces are chemically coated with chromic acid, iron phosphate, or zinc phosphate. Treated steel plates etc. can be used. In addition, examples of means for applying the composition to the surface of the metal material for cans include roll coating, spray coating, brush coating, spray coating,
Any method known per se can be used, such as dipping, electrodeposition, etc. A coating thickness of 5 to 30 μm is usually considered sufficient. The baking of the paint film is generally about 150 to about 22
60 to 600 at 0°C, preferably about 180 to about 200°C
seconds, preferably about 60 to 300 seconds.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Parts and percentages in Examples and Comparative Examples are based on weight unless otherwise specified.

I. Manufacturing example 1. Modified epoxy resin (X) (X-1): Copolymer prepared by adding 1 part of deionized water to an ethylene/maleic anhydride = 95/5 (weight ratio) copolymer to open the ring (acid value 57) 101 Part, Epon 1010 (Shell Chemical Co., Ltd., trade name, epoxy resin, number average molecular weight 5500
, about 1 epoxy group/1 molecule, non-volatile content 100%) 27
and 190 parts of n-butanol into a reaction vessel,
After heating to 100°C to dissolve each component, 2 parts of dimethylaminoethanol was added and maintained at the same temperature for 2 hours. Most of the epoxy groups were reacted, and the resulting resin had an acid value of 43 and a nonvolatile content of 40%.

2. Graft polymer (Y) (Y-1): 200 parts of the above modified epoxy resin liquid (X-1) was heated to 100°C, and polymerizable unsaturated vinyl monomer (C-1) [10% methacrylic, 80% styrene] was added. A mixture of 20 parts of ethyl acrylate and 10% of ethyl acrylate and 1 part of benzoyl peroxide was added dropwise over a period of 5 hours, and the mixture was aged for 2 hours to carry out graft polymerization. The nonvolatile content of the obtained graft polymer was 45%.

3. Aqueous dispersion (Z) (Z-1): Add dimethylaminoethanol to 222 parts of the above graft polymer liquid (Y-1) to completely neutralize it, and then add water to prepare an aqueous dispersion with a nonvolatile content of 20%. did. Next, most of the n-butanol contained in the aqueous dispersion was removed by reduced pressure. The non-volatile content was 26%. n-
After heating the aqueous dispersion from which butanol has been removed to 80°C, 30 parts of a polymerizable unsaturated vinyl monomer [consisting of styrene/n-butyl acrylate = 80/20 (weight ratio)] and 1 part of azoisobutyronitrile are added. was added dropwise over a period of 3 hours, and the mixture was aged at the same temperature for 3 hours to perform seed polymerization.

II. Example The modified epoxy resin (X-1) and graft polymer (Y-1) obtained in the above production example were completely neutralized by adding dimethylaminoethanol to each, and then water was added to disperse them. Butanol was removed under reduced pressure to obtain a composition targeted by the present invention. Moreover, the aqueous dispersion (Z-1) can be used as it is as a composition of the present invention.

III. Performance test results The composition obtained in the above example and the composition obtained by adding a curing agent to the composition were coated on an aluminum plate (aluminum 5052 material) and a tin plate (#25) using a bar coater.
1 based on the cured coating on each of the electroplated tinplates)
It was coated to a thickness of 5 to 20 μm and heated at 180° C. for 25 minutes to cure the coating film. The performance test results of the cured coating film are shown in Table 1 below.

[Table 1]

In Table-1, (*1) Comparative Example (X-1'): 100 parts of the ethylene/maleic anhydride copolymer in (X-1) was mixed with acrylic acid/styrene/
Ethyl acrylate = 7.3/60/32.7 (wt%
), and the rest was replaced with 100 parts of a copolymer consisting of (X
The mixture was reacted in the same manner as in -1), then neutralized with dimethylaminoethanol, water was added and dispersed, and n-butanol was removed under reduced pressure.

(Y-1'): (Y-1) (
X-1) was replaced with the above (X-1') in the same amount based on the solid content, and everything else was graft polymerized in the same manner as (Y-1), and then neutralized with dimethylaminoethanol,
After water was added and dispersed, n-butanol was removed under reduced pressure. (z-1'): Substitute the same amount of (Y-1) in the above (Z-1) with the above (Y-1') based on the solid content, and otherwise do the same as (Z-1). Seed polymerization was performed.

(*2) Composition Each Example is an aqueous coating composition using each of (X-1)...(Z-1) described in the same column, and the coating film formed thereby Performance is also listed.

(*3) Hardening agent In the examples marked with "○" in the same column, as a hardening agent,
This indicates that 10 parts by weight of Hytanol 4010 (trade name, phenol resin, manufactured by Hitachi Chemical Co., Ltd.) was blended based on the solid content per 100 parts by weight of the resin solid content in the composition. Note that "-" in the same column indicates that no curing agent was blended.

(*4) Flavor properties: After coating each aqueous coating composition on the inner surface of the can and curing it by heating at 200°C for 5 minutes (film thickness 15-20μ), the inside of the can was treated with activated carbon. Filled with 250ml of tap water, tightened, and
After 30 minutes of sterilization at -30°C, the samples were stored at 37°C for 3 months and a flavor test was conducted. ◎ No change at all ○ Very slight change △ Slight change × Significant change

(*5) Hygiene: Fill the can obtained in (*4) with 250 ml of ion-exchanged water, seal it, and heat it at 60°C.
Treatments were carried out for 30 minutes and at 100°C for 30 minutes, and measurements were made according to the test method described in the Food Sanitation Law. The amount of potassium permanganate consumed was expressed in ppm. ◎ 0 to less than 2 ○ 2 to less than 5 △ 5 to less than 10 × 10 or more

(*6) Acid resistance: A test piece was immersed in a 10% aqueous hydrochloric acid solution, and the coating film was visually evaluated after being immersed at 20°C for one week. ◎ No abnormality at all ○ Very slight whitening △ Slight whitening × Significant whitening

(*7) Alkali resistance: A test piece was immersed in a 10% caustic soda aqueous solution, and the coating film was visually evaluated after being immersed at 20°C for one week. The evaluation is the same as (*6).

(*8) Corrosion resistance: Coated plate 150 x 70 mm
After cross-cutting the coating to reach the substrate, place it in a salt spray test equipment. After 3 weeks, the sample was taken out and the width of rust on one side from the cut portion was measured. ◎ 0 to less than 1 mm ○ 1 to less than 2 mm △ 2 to less than 6 mm × 6 mm or more

(*9) Water resistance: After cross-cutting in the same manner as (*8), immerse in water at 100°C for 30 minutes, dry the coating at room temperature, and apply cellophane adhesive tape to the coating. After applying the paint and strongly peeling it off, the painted surface was evaluated. ◎ No peeling at all ○ Very slight peeling △ Slight peeling × Significant peeling

(*10) Adhesion: Using a knife, make 11 vertical and horizontal cuts in the coating surface with a width of about 1.5 mm in a grid pattern. A cellophane adhesive tape with a width of 24 mm was attached to the sample, and when it was strongly peeled off, the number of remaining adhered goblets was observed. ◎: 100 pieces ○: 95-99 pieces △: 80-94 pieces ×: 79 pieces or less

(*11) Impact workability: Coated plate size 40
Cut into pieces of mm x 50 mm, fold in half so that the test area is 40 mm with the coating film on the outside, and sandwich two pieces of 0.23 mm thick stain-free steel between the folded test pieces. After dropping a 3kg load onto the bend from a height of 42cm, a voltage of 6.5V x
Electricity was applied for 6 seconds, and the current value (mA) of a 2 cm width of the processed area was measured. ◎ 0 to less than 1 ○ 1 to less than 3 △ 3 to less than 10 × 10 or more

(*12) Curability: The cured coating film separated from the object to be coated was subjected to solvent extraction for 2 hours under refluxing methyl ethyl ketone, and evaluated by the change in weight of the remaining coating film after solvent extraction. ◎ 100-97% ○ 96-90% △ 89-80% × 79% or less

(*13) Tensile workability: The elongation rate of the cured coating film was determined by Tensilon (“Tensilon UTN II-20”)
, manufactured by Toyo Baldwin Co., Ltd., trade name). The tensile speed was 4 mm/min at 20° C., and the workability was evaluated based on the average elongation rate of 10 samples. Elongation rate 0-10%: × 11%-20%: △ 21-30%: ○ 31% or more: ◎

(*14) A: Performance of the test plate painted on aluminum B: Performance of the test plate painted on tin

Claims (2)

[Claims] Claim 1: A modified epoxy resin (
X) and/or contains as a main component an aqueous dispersion of a graft polymer (Y) obtained by graft polymerizing a polymerizable unsaturated vinyl monomer (C) to the modified epoxy resin (X), and The resin (A) contains at least one α,β-ethylenically unsaturated group-containing polybasic acid monomer selected from maleic anhydride, maleic acid, and fumaric acid and an ethylene series hydrocarbon as essential monomer components. An aqueous coating composition for the inside of a can, characterized in that it is a copolymer (a). [Claim 2] The modified epoxy resin according to Claim 1 (
A can containing as a main component an aqueous dispersion (Z) obtained by seed polymerizing a polymerizable unsaturated vinyl monomer (D) in an aqueous dispersion of X) and/or a graft polymer (Y). Aqueous coating composition for internal surfaces.