JP2000226542A - Aqueous resin composition for covering can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous resin composition for the inner surface of a can having adhesiveness and processability of an aqueous coating material having formerly been offered and undoubtedly having general safety and sanitary property and as various vessels of foods, cosmetics, medical supplies, etc., especially excellent in processing corrosion resistance of a coated film even after heat-sterilizing treatment without eluting bisphenol-A into an ingredient. SOLUTION: This aqueous resin composition for covering a can is composed of a carboxyl group-containing self-emulsifying aromatic epoxy resin, e.g. an acrylic-modified aromatic epoxy resin and an antioxidant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel and useful aqueous resin composition for coating cans. More specifically, the present invention relates to an improved aqueous resin composition for coating the inner surface of a can, which contains a specific antioxidant component and can suppress the elution amount of bisphenol A, particularly as a coating for the inner surface of the can.

[0002]

2. Description of the Related Art Conventionally, metals such as aluminum, tinplate and tin-free steel have been used as metal cans. These metals, to prevent their corrosion,
Usually, a coating film is formed on the inner and outer surfaces of the can. As a paint for the inner surface of a can, epoxy / phenolic resin, epoxy /
Amino resin-based or vinyl chloride organosol-based paints are used.

However, since the above-mentioned paint contains an organic solvent, it has a risk of air pollution, deterioration of working environment, fire and explosion, and as a means for avoiding these problems, Various methods have been proposed in which a so-called self-emulsifiable epoxy resin in which an emulsifying segment is introduced into a molecule by modifying an epoxy resin with an acrylic resin is dispersed in water.

For example, JP-A-53-1228 discloses that a monomer mixture containing a carboxyl group-containing vinyl monomer is polymerized using a free radical generator such as benzoyl peroxide in the presence of an epoxy resin. The resulting grafted epoxy resin is
A method of stably dispersing in an aqueous medium containing a base is disclosed.

JP-A-55-75460 and JP-A-56-109243 each disclose a carboxyl group-excess partial reactant obtained by reacting an acrylic resin with a relatively high molecular weight aromatic epoxy resin. Is dispersed in an aqueous medium in the presence of ammonia or an amine.

JP-A-55-3481 and JP-A-5-3481
JP-A-5-3482 discloses that a carboxyl group-containing vinyl polymer which is obtained by esterifying a carboxyl group-containing vinyl polymer with an epoxy resin in the presence of an amine-based esterification catalyst and substantially has no oxirane group of the epoxy resin. A method is disclosed in which a polymer-modified epoxy resin is neutralized with a base and dispersed in water.

Further, JP-A-57-105418 and JP-A-58-198513 each disclose an epoxy group in one molecule obtained by partially reacting an aromatic epoxy resin with (meth) acrylic acid. A method is disclosed in which a low-molecular compound having both acryloyl and acryloyl groups is copolymerized with a monomer mixture containing acrylic acid or methacrylic acid, and the copolymer is neutralized with a base and dispersed in water.

However, these aqueous resin compositions are excellent in general food hygiene, while
There is a problem in that bisphenol A suspected of environmental hormones elutes into the contents of the can. At present, no aqueous resin composition that does not elute bisphenol A in the contents of the can has been found.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to maintain the adhesion and processability of a conventionally proposed water-based paint and to have general safety and health. Of course, as a container for foods, cosmetics, medical products, etc., especially after heat sterilization, it has excellent coating corrosion resistance and does not elute bisphenol A into the contents. The purpose is to obtain an aqueous resin composition for use.

[0010]

Means for Solving the Problems The present inventors have eagerly sought to improve the above-mentioned drawbacks of the acrylic-modified epoxy resin,
As a result of the study, the present inventors have found an aqueous resin composition containing a specific antioxidant component and having a small amount of bisphenol A eluted into the contents of the can, thereby completing the present invention. That is, the constitution of the present invention is an aqueous resin composition for can coating, characterized by containing a carboxyl group-containing self-emulsifying aromatic epoxy resin and an antioxidant. Furthermore, the constitution of the present invention is an aqueous resin composition for can coating, wherein the carboxyl group-containing self-emulsifying aromatic epoxy resin is an acrylic-modified aromatic epoxy resin.

Further, in the constitution of the present invention, the antioxidant is preferably butylhydroxyanisole, dibutylhydroxytoluene, dilaurylthiodipropionate, nordihydroguaiaretic acid, propyl gallate, distearylthiodipropionate. Thiodipropionic acid, guaiac, 2,4,5-trihydroxybutyrophenone, d
The aqueous resin composition for can coating is at least one selected from the group consisting of l-α-tocophenol, erythorbic acid, and ascorbic acid. Further, the aqueous resin composition for can coating has a content of the antioxidant to the aromatic epoxy resin in the range of 0.1 to 2.0% by weight.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The aforementioned carboxyl group-containing self-emulsifiable aromatic epoxy resin used in the present invention [hereinafter also referred to as (resin A). ] Is obtained by modifying the epoxy resin with a copolymerizable monomer mixture containing an ethylenically unsaturated carboxylic acid as an essential component, or a carboxyl group-containing acrylic resin, has a carboxyl group, and separately has an emulsifier Refers to those that can be emulsified in an aqueous medium without the use of The aqueous resin composition for coating cans of the present invention contains a carboxyl group-containing self-emulsifying aromatic epoxy resin (resin A) and an antioxidant. The order of dispersing resin A in water and adding the antioxidant is as follows. Is not particularly limited, neutralization and water dispersion may be performed after mixing the resin A and the antioxidant, and on the other hand, the antioxidant may be added after the resin A is neutralized and dispersed in water. You may.

The epoxy resin used in the present invention includes:
In particular, the epoxy equivalent is 2,000 to 12,000,
It is preferable to use an aromatic epoxy resin having a number average molecular weight of 3,000 to 12,000, for example, bisphenol A (or F) / epichlorohydrin type epoxy resin, novolak type epoxy resin, and these epoxy resins as fatty acids and And / or a modified epoxy resin modified with a phenolic compound. Particularly, among these aromatic epoxy resins, the epoxy equivalent is 2,0.
00 to 12,000, more preferably 3,000
0 to 10,000, and a number average molecular weight of 3,000 to 12,000, particularly preferably
4,000 to 10,000 are designated.

The number average molecular weight is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene. Commercially available products include, for example, Epicoat 10 manufactured by Yuka Shell Epoxy Co., Ltd.
09, Epicoat 1010, Epicoat 1256, Epicoat 4010P, Epicron 9050 manufactured by Dainippon Ink and Chemicals, Inc. and the like.

The epoxy equivalent of the epoxy resin is 12,000.
If it exceeds 0, the curability is inferior and the phenomenon that the coating film becomes white after the hot water treatment is observed. On the other hand, if it is less than 2,000, it becomes inevitably too hard to cure. Worse.

On the other hand, the epoxy resin has a number average molecular weight of 1
When it exceeds 2,000, workability becomes good, but adhesion becomes inferior. When the number average molecular weight is less than 3,000, processability becomes inferior. However, it is not suitable for use as a resin for coating the inner surface of a can. Thus, as the resin for coating the inner surface of the can,
It is preferable to use an aromatic epoxy resin having an optimal range of epoxy equivalent and number average molecular weight, respectively.

In the present invention, not only the above-mentioned aromatic epoxy resin can be used alone, but also the control of the degree of curing,
For the purpose of giving optimum coating film properties such as adjustment of Tg,
Two or more aromatic epoxy resins can be used in combination.

For example, a resin prepared by the following production method, if necessary, is neutralized with a basic compound as a typical example.

(1) Aromatic epoxy resin (a-1)
In the presence of a mixture of copolymerizable monomers containing an ethylenically unsaturated carboxylic acid as an essential component, in the presence of a polymerization initiator, in an organic solvent, a method of copolymerizing,

(2) Aromatic epoxy resin (a-1)
And a carboxyl group-containing acrylic resin (a-2) obtained by copolymerizing a copolymerizable monomer mixture containing an ethylenically unsaturated carboxylic acid as an essential component in an organic solvent. A method in which a carboxyl group is excessively reacted with an epoxy group, and the esterification reaction is carried out in an organic solvent at a reactive group concentration, or

(3) An aromatic epoxy resin having a (meth) acryloyl group introduced therein and a copolymerizable monomer mixture containing an ethylenically unsaturated carboxylic acid compound as an essential component, The method of copolymerization in an organic solvent below is particularly typical.

Of course, a carboxyl group-containing self-emulsifying epoxy resin obtained by a method other than the above, that is, an epoxy resin modified with a carboxyl group-containing acrylic resin can also be used.

In the present invention, only typical representative examples of the ethylenically unsaturated carboxylic acids include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

Various monoalkyl esters of ethylenically unsaturated dicarboxylic acids, such as monomethyl maleate, monoethyl fumarate, mono-n-butyl itaconate,
It goes without saying that such an ethylenically unsaturated carboxylic acid may be used instead of such an ethylenically unsaturated carboxylic acid. In addition, if only particularly typical examples of other copolymerizable monomers are given as examples, methyl (meth) acrylate, ethyl (meth) acrylate,
Propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, Various (meth) acrylic esters such as octadecyl (meth) acrylate; various ethylenically unsaturated aromatic monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, and 2,4-dibromostyrene. Monomer (aromatic vinyl monomer; various (meth) acrylonitrile, various ethylenically unsaturated nitriles; vinyl acetate, vinyl propionate, various vinyl esters; vinylidene chloride, vinylidene bromide, various Vinylidene halide; 2-hydroxyethyl acrylate, 2-hydroxy acrylate Kishipuropiru, such as 2-hydroxyethyl methacrylate, various ethylenically unsaturated carboxylic acid hydroxyalkyl ester, (meth)
Various ethylenically unsaturated carboxylic acid glycidyl esters such as glycidyl acrylate; or (meth) acrylamide, N-methylol (meth) acrylamide, N
-So-called radically polymerizable compounds such as various (meth) acrylamide derivatives such as butoxymethylacrylamide and diacetoneacrylamide.

However, in the present invention, it is possible to use the above-mentioned various copolymerizable monomers.
It is preferable to use a monomer having an ester bond having a g of 300 ° K or less (hereinafter, referred to as a specific ester type monomer) so as to be within 2% by weight in the resin. This is because the resin component having a low Tg sorbs a large amount of the flavor component of the content and increases the water vapor permeability, and further, the ester bond undergoes hydrolysis in the heat sterilization process of the can content, resulting in processing. This is because the properties are remarkably deteriorated. Examples of such specific ester type monomers include acrylates such as ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

In the various production methods (1), (2) and (3) described above, the amount of the ethylenically unsaturated carboxylic acid used is based on 100 parts by weight of the total weight of the copolymerizable monomer. , 25 parts by weight to 65 parts by weight.

When the amount of the ethylenically unsaturated carboxylic acid used is 2
When the amount is within the range of 5 parts by weight to 65 parts by weight, it is used for the dispersion stability of the resin in the aqueous medium, the adhesion of the coated film to the metal, the solvent resistance, and the inner surface of the can, respectively. This is preferable because the hygiene and the like tend to be improved in each case.

The aromatic epoxy resin (a) in each of the production methods (1), (2) and (3)
-1) and various copolymerizable monomers as described above, or a carboxyl group-containing acrylic resin (a
The usage ratio of -2) is (a-1) / (a-2) in terms of solid content weight ratio when their total weight is 100 parts by weight.
= 50/50 to 90/10 is preferred, and the reactive group concentration range is such that the carboxyl group is excessive relative to the epoxy group.

When the proportion of the aromatic epoxy resin (a-1) is 50 to 90 parts by weight, the coating film has excellent adhesion to metal, and the obtained resin (A) has a stable dispersion. This is preferable because the property tends to be improved.

The proportion of the aromatic epoxy resin (a-1) and (meth) acrylic anhydride used in the production method of (3) above is defined as the solid content weight ratio when the total weight thereof is 100 parts by weight. Where, resin / anhydride = 90 / 10-9
A range of 9.95 / 0.05 is preferred.

The polymerization initiator used in each of the above-mentioned reactions is not particularly limited. For example, ordinary polymerization initiators such as azobisisobutyronitrile and benzoyl peroxide are particularly typical. It is listed as.

The use amount of these polymerization initiators is not particularly limited, but is preferably in the range of 0.01 to 20% by weight based on the total weight of the copolymerizable monomers.

If only typical organic solvents are exemplified, methanol, ethanol, n-propanol, isopropanol, n-butanol, se
Including c-butanol, tert-butanol, isobutanol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, methyl cellosolve acetate or ethyl cellosolve acetate, dioxane, dimethylformamide or diacetone alcohol Various hydrophilic organic solvents such as ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone,
Various lipophilic organic solvents such as toluene or xylene. These may be used alone or in combination of two or more. If necessary, water and these organic solvents may be used in combination.

As the basic compound that can be used for neutralizing the carboxyl group of the resin (A) obtained by the above-mentioned methods (1) to (3), any of ordinary inorganic bases and organic bases can be used.

Of these, only typical inorganic bases are exemplified, and examples thereof include sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate. Illustrative examples include ammonia, alkylamines such as trimethylamine, triethylamine or butylamine; alcoholamines such as dimethylaminoethanol, diethanolamine or aminomethipropanol; or morpholine. Also, polyvalent amines such as ethylenediamine and diethylenetriamine can be used.

As the above-mentioned basic compound, ammonia and volatile amines are preferable because they tend to improve water resistance without remaining in the coating film. The amount of the basic compound used is preferably such that the pH of the dispersion becomes 5 or more.

In particular, at least a part of the carboxyl group in the carboxyl group-containing self-emulsifying epoxy resin (A) used in the present invention is neutralized with a basic compound and dispersed in an aqueous medium. By heating the body, the reaction between the epoxy group and the carboxyl group remaining in the fine particles is performed, and microgel particles having a three-dimensional network structure can be obtained.

However, in the case of the method (2) for synthesizing the carboxyl group-containing self-emulsifying epoxy resin (A),
It is necessary to carry out a partial esterification reaction so as to leave an epoxy group.

In the present invention, the aqueous medium means water alone or a mixture with a hydrophilic organic solvent in which at least 10% by weight of water is water. If only typical representative examples of hydrophilic organic solvents that can be used in the present invention are given as examples, methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-
Alkyl alcohols such as butanol, tert-butanol and isobutanol; methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve,
Glycol ethers such as hexyl cellosolve, methyl carbitol, ethyl carbitol and butyl carbitol; or glycol ether esters such as methyl cellosolve acetate and ethyl cellosolve acetate; dioxane, dimethylformamide, tetrahydrofuran, methyl ethyl ketone, diacetone alcohol And so on.

The use of a lipophilic organic solvent, if necessary, can be used without any problem. When it is necessary to reduce the amount of the organic solvent contained in the aqueous resin composition thus obtained, when the carboxyl group-containing self-emulsifying epoxy resin (A) is produced, the boiling point is low and the azeotrope with water is reduced. An organic solvent such as acetone, methyl ethyl ketone, n-butanol or butyl cellosolve is dispersed in an aqueous medium in combination with water, and then distilled at normal pressure or reduced pressure, whereby the organic solvent can be stably obtained. An aqueous resin composition having a low content of is easily obtained.

The aqueous resin composition for coating the inner surface of a can according to the present invention comprises:
Consisting of a carboxyl group-containing self-emulsifying epoxy resin and a specific antioxidant, the resin contains 0.1% by weight to 2.0% by weight.
It is preferable that the content be contained by weight. If the content is less than 0.1% by weight, the required performance cannot be obtained, and if the content exceeds 2.0% by weight, the coating performance as a paint for the inner surface of the can, especially the hygiene, may be unfavorable.

As such antioxidants, butylhydroxyanisole, dibutylhydroxytoluene, dilaurylthiodipropionate, nordihydroguaiaretic acid,
Propyl gallate, distearyl thiodipropionate, thiodipropionic acid, guaiac, 2,4,5-trihydroxybutyrophenone, dl-α-tocophenol, erythorbic acid, ascorbic acid,
Among them, erythorbic acid and ascorbic acid have high safety and are useful.

The antioxidant has a function of suppressing the generation of bisphenol A, which is a decomposition product due to the oxidation reaction of the epoxy resin, reduces the amount remaining in the baking film on the inner surface of the can, and reduces the amount eluted into the contents. Can be reduced. The oxidation reaction is 170
It occurs at a sintering temperature of ℃ or more, becomes severe with an increase in the sintering temperature, and the amount of bisphenol A eluted increases. Even when an epoxy resin is used for the outer coating, the same reaction occurs, so that bisphenol A is sorbed to the inner coating film. Therefore, the effect can be further enhanced by adding an antioxidant to the outer coating. In this case, as the antioxidant, known substances other than the above substances can be used.

The aqueous resin composition for coating the inner surface of a can of the present invention may further contain a phenol resin as a curing agent, if necessary, in order to enhance the adhesion and curability of the coating film. . If only typical examples of such phenolic resins are given as examples, various tetrafunctional phenolic compounds such as bisphenol A or bisphenol F, phenolic acid, m-ethylphenol, 3,5-xylenol, m-methoxy Trifunctional phenol compounds such as phenol or p-cresol, o-cresol,
Various bifunctional phenols such as p-tert-butylphenol, p-ethylphenol, 2,3-xylenol and m-methoxyphenol were synthesized with formaldehyde in the presence of an alkali catalyst.

Further, it is also possible to use a form in which a part or all of the methylol group contained in the phenol resin is etherified with an alcohol having 1 to 12 carbon atoms.

The aqueous resin composition of the present invention can also contain, if necessary, various auxiliaries such as a solvent, a surfactant or an antifoaming agent for improving coating properties.

The aqueous resin composition for coating the inner surface of a can of the present invention is a lubricant for the purpose of preventing the coating film from being damaged during processing.
It is also possible to add various known and commonly used waxes. The wax used here may be used alone, but in consideration of friction and wear resistance, a combination of a hard wax having a penetration of 10 or less at 25 ° C and a soft wax having a penetration of more than 10 at the same time is required. It is even more effective.
Furthermore, since the aqueous resin composition for coating the inner surface of a can of the present invention has low affinity with wax, even a small amount of the resin composition floats on the coating film surface and exhibits good friction and wear resistance.

The aqueous resin composition of the present invention is useful for coating various kinds of metal materials or products such as aluminum, tin-plated steel sheet, pretreated metal, and steel. Needless to say, it may be used as a coating agent for other materials and processed products.

The most preferable use is for use in the inner surface coating of various metal containers used for foods and drinks, etc. There is no elution of molecular compounds, and in addition, the coating is extremely impervious to the coating, so it does not alter the natural taste or aroma of the food and drink stored inside the can and is also excellent in processability. Is obtained.

Further, the aqueous resin composition for coating the inner surface of a can of the present invention does not foam even under high-temperature and short-time baking conditions, is capable of thick film coating, and has good workability and corrosion resistance. From a certain point, it is also useful as a paint for correcting welds in welding cans.

As a method for applying the aqueous resin composition of the present invention, various types of spray coating such as air spray, airless spray or electrostatic spray, dip coating, roll coater coating, and electrodeposition coating are also possible.

The baking conditions are 120 to 280.
It is preferably within a range of 10 seconds to 30 minutes at a temperature of ° C.

The aqueous resin composition of the present invention is mixed with an appropriate rust inhibitor, a pigment, a filler, etc., depending on the use, and is used as a rust-preventive primer, a printing ink, a corrosion-resistant rust-preventive paint, or the like. Can also be used.

[0054]

EXAMPLES The present invention will be described more specifically with reference to examples. In the following, unless otherwise noted, parts and%
Are all based on weight.

Example 1 [Preparation Example of Carboxyl Group-Containing Self-Emulsifying Aromatic Epoxy Resin] (1) 120 parts of n-butanol (2) 150 parts of Epicoat 1010 (3) 25 parts of methacrylic acid (4) styrene 11 parts (5) Ethyl acrylate 1 part (6) Benzoyl peroxide 3 parts (7) n-butanol 10 parts Into a four-necked flask purged with nitrogen gas, (1) and (2) were charged and dissolved by heating. (3)-(7)
The resulting raw materials were uniformly added dropwise over 2 hours with stirring while keeping the inside of the flask at 110 ° C. After completion of the dropwise addition, the mixture was further stirred at the same temperature for 4 hours to obtain a carboxyl group-containing self-emulsifiable aromatic epoxy resin solution having a solid content of 58%. Epicoat 1010 used here is a bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd.

[Water dispersion of the carboxyl group-containing self-emulsifying aromatic epoxy resin] (8) 100 parts of the carboxyl group-containing self-emulsifying epoxy resin solution 100 parts (9) Dimethylethanolamine 4 parts (10) ion-exchanged water 260 parts of (8) was charged into a four-necked flask filled with nitrogen gas,
This was heated to 100 ° C., and a mixture of (9) and (10) was added dropwise over 10 minutes with stirring to obtain an aqueous dispersion of the target resin. Further, under reduced pressure, 130 parts of n-butanol and water were distilled off by azeotropic distillation to obtain a solvent-free aqueous dispersion of the target resin having a nonvolatile content of 25%.

[Formation of paint] (15) 100 parts of the above aqueous dispersion (16) 0.6 parts of phenolic resin (17) 6 parts of hexyl cellosolve (18) 0.3 parts of antioxidant 0.3 parts (15) to (18) The paint was obtained by mixing and stirring sufficiently. The phenolic resin used here is "EP-
560 "(Resol type phenolic resin manufactured by Monsanto Co., USA), and the antioxidant was" Antiox L "(distearyl thiodipropionate manufactured by NOF Corporation).

(Example 2) [Synthesis of carboxyl group-containing acrylic resin] (a) n-butanol 670 parts (b) styrene 250 parts (c) ethyl acrylate 10 parts (d) methacrylic acid 190 parts (e) peroxide 5 parts of benzoyl First, (a) was charged into a four-necked flask in which nitrogen gas had been replaced, and kept at 100 ° C. while stirring and dissolving.
What mixed and dissolved (b)-(e) was dripped gradually over 2 hours. After completion of the dropwise addition, the mixture was further stirred at the same temperature for 3 hours to obtain a carboxyl group-containing acrylic resin solution having a solid content of 40%.

[Synthesis of Carboxyl Group-Containing Self-Emulsifying Aromatic Epoxy Resin] (f) Epicoat 1010 150 parts (e) Carboxyl group-containing acrylic resin solution 125 parts (h) n-butanol 130 parts (i) dimethylethanol Amine 12 parts First, (f) to (h) were charged into a four-necked flask purged with nitrogen gas, and completely dissolved by stirring at 100 ° C for 2 hours, and then cooled to 80 ° C. In this solution,
By charging (i) and stirring for 1 hour, a solution of a carboxyl group-containing self-emulsifying epoxy resin having a solid content of 48% was obtained.

[Water dispersion of carboxyl group-containing self-emulsifying epoxy resin in water] (j) 100 parts of the above self-emulsifying epoxy resin solution (k) 194 parts of ion-exchanged water In a four-necked flask filled with nitrogen gas, (j) ) Was heated to 50 ° C., and (k) was added dropwise with stirring over 30 minutes to obtain an aqueous dispersion of a carboxyl group-containing self-emulsifying epoxy resin having a solid content of 16.3%. Was. Further, under reduced pressure, n-butanol and water were distilled off by azeotropic distillation to obtain a solvent-free aqueous dispersion of a carboxyl group-containing self-emulsifying epoxy resin having a nonvolatile content of 25%. Further, a paint was prepared in the same manner as in Example 1.

Example 3 An aqueous dispersion was obtained in the same manner as in Example 2 except that the antioxidant was changed to "ascorbic acid" (manufactured by Takeda Pharmaceutical Co., Ltd.).

Comparative Example 1 A control aqueous dispersion was obtained in the same manner as in Example 1 except that the antioxidant used in Example 1 was not used.

Comparative Example 2 A control aqueous dispersion was obtained in the same manner as in Example 2 except that the antioxidant used in Example 2 was not used.

Next, the respective paints obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated by the following evaluation methods. The results are summarized in Table 1.

[Preparation of test coated plate] Thickness 0.32 m
m on an aluminum plate with a dry coating weight of 60 m
Using a bar coater, apply each of the paints obtained in each Example so as to obtain g / dm2, bake them in an oven at 205 ° C for 10 minutes, cool them to room temperature, and paint them for testing. Board.

[Adhesion] 100 1 × 1 mm grids were formed on the coating film formed on the test coated plate with a cutter.
This sample piece was treated with hot water at 125 ° C. for 30 minutes. Thereafter, an adhesive tape was stuck on the grid, and then the adhesive tape was rapidly peeled off. The peeling state of the coating film was observed, and evaluated by the following three grades. …: No peeling at all △: 1 to 30% of the whole peeled ×: 31 to 100% of the whole peeled

[Workability] Using a special goby fold type Dupont impact tester, two unpainted aluminum plates were sandwiched between two folded samples placed at the bottom, and the contact surface was flat and weighed 1 kg of iron. Was dropped from a height of 50 cm, and a bent sample piece was prepared.
Hot water treatment for minutes. Then, in order to check the degree of damage of the coating film in the bent part, the current value was measured for the bent surface using an enamellator (electrical current tester) through an electrolyte solution of 1% saline, and The evaluation was made according to the following three grades. …: The current value is less than 10 mA △: The current value is 10 to 50 mA ×: The current value is 50 mA or more

[KMnO4 Consumption] The test coating plate of 160 cm 2 was immersed in 100 ml of purified water and subjected to a hot water treatment at 125 ° C. for 0.5 hour. Potassium consumption was measured and evaluated by the following three steps. …: Consumption amount is 5 ppm or less △: consumption amount exceeds 5 ppm, but 10 ppm or less ×: consumption amount exceeds 10 ppm

[Eluted amount of BPA] The test coating plate of 100 cm 2 was immersed in 100 ml of purified water, and subjected to a hot water treatment at 125 ° C. for 0.5 hour. Thereafter, the purified water was concentrated 100 times, the elution amount was measured by gas chromatography, and the elution amount from the coating film was evaluated by the following three steps. …: The amount of elution from the coating film is 5 ppb or less △: The amount of elution from the coating film is 5 to 10 ppb ×: The amount of elution from the coating film is 10 ppb or more

[0070]

[Table 1]

[0071]

EFFECT OF THE INVENTION The aqueous resin composition for coating cans according to the present invention has a low risk of fire and pollution, and has remarkably good general safety and hygiene, adhesion of the coating film, and processability after hot water treatment. In addition, since the amount of bisphenol A eluted in the contents is small, it is remarkably excellent as a coating agent used for food containers.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J026 AB04 AB05 AC24 BA05 BA10 BA19 BA20 BA24 BA25 BA27 BA33 BA34 CA03 DB09 DB12 DB15 GA09 4J038 BA012 BA232 DB061 DB071 DB341 DB351 GA06 JA64 JC06 KA02 MA10 NA02 NA05 PB04 PC02

Claims (4)

[Claims] 1. An aqueous resin composition for can coating, comprising a carboxyl group-containing self-emulsifying aromatic epoxy resin and an antioxidant. 2. The aqueous resin composition for can coating according to claim 1, wherein the carboxyl group-containing self-emulsifying aromatic epoxy resin is an acrylic-modified aromatic epoxy resin. 3. The antioxidant is butylhydroxyanisole, dibutylhydroxytoluene, dilaurylthiodipropionate, nordihydroguaiaretic acid, propyl gallate, distearylthiodipropionate, thiodipropionic acid. Guaiac fat, 2,4,5-
The aqueous resin composition for can coating according to claim 1, which is at least one member selected from the group consisting of trihydroxybutyrophenone, dl-α-tocophenol, erythorbic acid, and ascorbic acid. 4. The aqueous resin composition for can coating according to claim 1, wherein the content of the antioxidant with respect to the aromatic epoxy resin is in the range of 0.1 to 2.0% by weight.