JPH0692560B2 - Aqueous coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a water-based coating composition, and more specifically, it can form a coating film excellent in corrosion resistance, water resistance and coating film hardness. It relates to an aqueous coating composition.

(Prior Art) In recent years, from the viewpoint of environmental protection, resource saving and non-hazardous substances, the conversion from the conventional so-called solvent type paint using an organic solvent as a diluent to an aqueous paint using water as a diluent has been promoted. There is.

Water-based paints based on water-dispersible or water-soluble resins such as alkyd resins, acrylic resins, polyester resins, epoxy ester resins, and acrylic grafted polyester resins are known. For example, as a water-dispersible resin system, a type obtained by emulsion polymerization of a monomer or the like in water in the presence of an emulsifier, a surfactant, a dispersant, or a solvent-free polymerized and neutralized water There are known types that can be obtained by phase transformation by addition of the above, but in both cases, there is a limitation in the polymerization method, and the workability is poor because it does not contain an organic solvent, and there are those with wide coating performance. There were drawbacks such as difficulty in obtaining.

On the other hand, a water-soluble resin can use a water-miscible solvent during or after the polymerization, so that the polymerization method is not limited, and a resin with a wide range of coating performance and workability can be obtained, but the corrosion resistance is high. However, the water resistance and coating hardness were insufficient.

Further, most of the resins used in the above water-based paints themselves do not have good corrosion resistance and water resistance. The reason for this is the use of emulsifiers, surfactants, dispersants, etc., the inclusion of hydrophilic carboxyl groups in the resin skeleton width, or the introduction of components with excellent corrosion resistance into the resin skeleton. There are difficult things. In particular, paints for cans have such properties as corrosion resistance to prevent corrosion of can materials, water resistance to high temperature hot water treatment for sterilizing foods as contents, and coating hardness that the can outer surface coating is not easily scratched during transportation. Performance is required, but conventional water-based paints have not been able to meet all of these requirements.

[Structure of Invention]

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and introduces phosphoric acid, which is a component having excellent corrosion resistance, into the resin itself, and at the same time, it functions as a curing catalyst to improve water resistance. It has excellent corrosion resistance, water resistance and coating hardness due to improvement of coating hardness with aromatic epoxy resin as basic skeleton resin and improvement of water easiness and reactivity by introducing high hydroxyl value compound. An aqueous coating composition is provided.

That is, the present invention is an aqueous coating composition in which the following (a), (b) and (c) are dispersed or dissolved in an aqueous medium containing most of water and a water-miscible solvent.

(A) Aromatic epoxy resin with phosphoric acid and low molecular weight alcohol or its derivative or number average molecular weight of 30
Modified epoxy resin composition obtained by reacting alcoholic hydroxyl group-containing low molecular weight resin having a hydroxyl value of 00 or less and 150 or more, (b) acrylic resin or polyester resin soluble or dispersible in the presence of alkali, (c) Aminoplast resin.

The aromatic epoxy resin in the present invention is, for example, bisphenol A diglycidyl ether or bisphenol A.
There are diglycidyl ether type epoxy resins such as di-β-methyl-diglycidyl ether, tetrahydroxyphenylmethane tetraglycidyl ether, novolac glycidyl ether and diglycidyl ether of bisphenol A alkylene oxide adduct. Particularly preferred is a diglycidyl ether type epoxy resin of bisphenol A. The epoxy equivalent of these aromatic epoxy resins is 170 to 4000, preferably 170 to 1500. When the epoxy equivalent is 170 or less, the coating film hardness, which is a characteristic of epoxy resin, does not appear, and when it is 1500 or more, it may be difficult to make it aqueous.

Examples of the alcohol component used for producing the modified epoxy resin in the present invention include low molecular weight alcohol, alcoholic hydroxyl group-containing polyester resin, acrylic resin and the like. These alcohol components, together with phosphoric acid, contribute to making the modified epoxy resin water-soluble and have a function of adjusting the molecular weight to a preferable range.

As low molecular weight alcohols, n-butanol, isobutanol, n-amyl alcohol, active amyl alcohol, isoamyl alcohol, secondary amyl alcohol, tertiary amyl alcohol, n-hexyl alcohol, methylamyl alcohol, 2-ethylbutanol, n -Heptanol, 2-heptanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, n-nonyl alcohol, undecyl alcohol, n-dodecyl alcohol, trimethylnonyl alcohol, n-tetradecyl alcohol, heptadecyl alcohol, cyclo Monohydric alcohols such as hexanol and 2-methylcyclohexanol, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol Dihydric alcohols such as triethylene glycol, trimethylolethane, trimethylolpropane, trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol, and dihydric alcohols such as diglycerin and some of the hydroxyl groups of polyhydric alcohols Alkyl etherified, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, diethylene glycol monoisopro Ether, diethylene glycol mono-butyl ether,
Examples include dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monoisopropyl ether, and dipropylene glycol monobutyl ether. These low molecular weight alcohols can be used as a solvent in the production of the modified epoxy resin.

Examples of the alcoholic hydroxyl group-containing polyester resin include polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, triethylene glycol, dipropylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diether. One or one of pentaerythritol, 1,3-butylene glycol, pentanediol, trimethylpentanediol, 1,6-hexanediol, 1,4-dicyclohexanedimethanol, (hydrogenated) bisphenol A, bisphenol dihydroxypropyl ether, etc. Used as a mixture of two or more kinds, as polyvalent carboxylic acid or its anhydride, (anhydrous) phthalic acid, isophthalic acid, terephthalic acid,
(Anhydrous) succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydro (anhydrous) phthalic acid, hexahydro (anhydrous) phthalic acid, (anhydrous) hymic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, (anhydrous) It is obtained by synthesizing trimellitic acid, methylenecyclohexanetricarboxylic acid (anhydride), (anhydrous) pyromellitic acid, etc. in the form of one kind or a mixture of two or more kinds while controlling the molecular weight under the addition of hydroxyl equivalents.

Examples of the alcoholic hydroxyl group-containing acrylic resin include hydroxyl group-containing vinyl monomers such as hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyamyl acrylate, hydroxyhexyl acrylate, and corresponding methacrylates, and vinyl monomers copolymerizable therewith, for example, , Ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, etc. Acrylic acid alkyl ester or alkyl methacrylate ester , N- (methoxymethyl) acrylamide, N- (isobutoxymethyl) acrylamide, N
Vinyl monomers containing N-alkoxyalkyl-substituted amides such as-(butoxymethyl) acrylamide, styrene,
Aromatic vinyl monomers such as vinyltoluene, α-methylstyrene, etc., vinyl monomers containing carboxyl groups such as (meth) acrylic acid, maleic acid, fumaric acid, etc. to reduce the reaction solid content, or to add a large amount of initiator, Alternatively, it is obtained by controlling the molecular weight using a chain transfer agent and synthesizing it.

The alcohol component is reacted in a molar excess with respect to the epoxy groups of the aromatic epoxy resin in the presence of phosphoric acid.

The phosphoric acid in the present invention includes, for example, metaphosphoric acid, hirophosphoric acid, orthophosphoric acid, triphosphoric acid, tetraphosphoric acid, and the like, which are obtained by hydrating diphosphorus pentoxide, and are used as one kind or a mixture of two or more kinds. It is preferably orthophosphoric acid. It is preferable to use 0.05 to 0.75 mol of phosphoric acid based on the epoxy group. If it is less than 0.05 mol, the corrosion resistance is poor, and if it is more than 0.75 mol, the coating stability is poor.

The modified epoxy resin composition (a) of the present invention is obtained by adding a molar excess of low molecular weight alcohol or alcoholic hydroxyl group-containing low molecular weight resin and phosphoric acid to an aromatic epoxy resin. It is obtained by reacting at a temperature of about 150 ° C and ending the reaction when the epoxy equivalent is 10,000 or more.

When a low molecular weight alcohol is used as a modifier, the modified epoxy resin composition becomes aqueous by adding this solution as it is to an aqueous medium. When a resin is used as the alcohol component, a water-miscible solvent such as a low-molecular alcohol can be added after the reaction to make it aqueous in the same manner. At this time, the addition of a volatile base such as an organic amine, which will be described later, facilitates water-solubilization, which is effective when the amount of the modified epoxy resin to be blended is large or when an epoxy resin having a high epoxy equivalent is used as a raw material.

The acrylic resin as the component (b) in the present invention is, for example,
Carboxyl group-containing vinyl monomers such as (meth) acrylic acid, maleic acid, and fumaric acid, and vinyl monomers copolymerizable therewith, such as hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyamyl acrylate, hydroxyhexyl acrylate, and the like. Hydroxyl group-containing vinyl monomer such as methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate,
Acrylic alkyl ester or methacrylic acid alkyl ester such as ethyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, N- (methoxymethyl) acrylamide, N- (isobutoxymethyl) acrylamide, N- (butoxymethyl) N-alkoxyalkyl-substituted amide-containing vinyl monomers such as acrylamide, styrene, vinyltoluene,
Obtained by copolymerizing with an aromatic vinyl monomer such as α-methylstyrene, preferably having a number average molecular weight of 4000 to
There are 30,000 acrylic resins.

The aqueous polyester resin as the component (b) in the present invention is
For example, ethylene glycol, propylene glycol,
1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, dihydric alcohols such as (hydrogenated) bisphenol A, trimethylolethane, trimethylolpropane, trishydroxy Dihydric or higher alcohols such as methylaminomethane, pentaerythrite, dipentaeryt, diglycerin, etc. are used as alcohol components, and (anhydrous) phthalic acid, isophthalic acid, terephthalic acid (anhydrous) succinic acid, adipic acid, azelaic acid, Sebacic acid, tetrahydro (anhydrous) phthalic acid, hexahydro (anhydrous) phthalic acid, (anhydrous) hymic acid, (anhydrous) maleic acid, fumaric acid itaconic acid, (anhydrous) trimellitic acid, methylenecyclohexene tricarboxylic acid (anhydride), ( Anhydrous) An oil-free polyester resin obtained by condensing a polyvalent carboxylic acid such as lomellitic acid or an anhydride thereof, and a monobasic acid such as benzoic acid or t-butylbenzoic acid which is optionally used in combination, as an acid component,
Or, in addition to the alcohol component and the acid component, castor oil, dehydrated castor oil, tung oil, safflower oil, soybean oil,
Alkyd resin obtained by reacting linseed oil, tall oil, coconut oil, etc., and an oil component, which is one or a mixture of two or more of those fatty acids, with the above-mentioned acid component and alcohol component and by reacting three components Also, there is a graft-modified polyester resin obtained by grafting a polyester resin having an unsaturated bond with an acrylic resin modified by grafting. The number average molecular weight of polyester resin is 1
000 to 20000 is preferable.

Volatile bases required to make these acrylic resins and polyester resins water-soluble include ammonia and monoethanolamine, dimethylamine, diethylamine, triethylamine, triethanolamine, diethylethanolamine, dimethylethanolamine, monophorine, etc. There are organic amines. The amount of the volatile base used may be an amount that at least partially neutralizes the carboxylic acid of the acrylic resin or the polyester resin.

The aminoplast resin (c) in the present invention is an alkyl etherified melamine resin, an alkyl etherified benzoguanamine resin, an alkyl etherified urea resin, an alkyl etherified resin of diguanamine having two triazine rings bonded to a phenylene nucleus, or an alkyl etherified resin. A glycol resin or the like is used alone or in combination of two or more. Preference is given to fully etherified hexamethoxymelamine.

In the water-based coating composition of the present invention, the modified epoxy resin composition (a) is used in an amount of 2 to 30 in the coating resin solid content in order to exert a good balance of corrosion resistance, water resistance, coating film hardness and coating stability.
It is preferable to add parts by weight. Water-based acrylic resin or water-based polyester resin (b) is in the coating resin solids
20 to 83 parts by weight are blended. If it is less than 20 parts by weight, the flexibility is inferior, and if it exceeds 83 parts by weight, the coating film is inferior. Also, the aminoplast resin (c) is preferably 15% in the solid content of the coating resin.
~ 50 parts by weight are used. If it is less than 15 parts by weight, water resistance and coating film hardness are poor, and if it exceeds 50 parts by weight, flexibility tends to be poor.

The aqueous coating composition of the present invention is used by dispersing or dissolving it in an aqueous medium composed of water and a water-miscible solvent. The proportion of the water-miscible solvent in the aqueous medium is 10 to 50% by weight. As the water-miscible solvent, any of the aforementioned low molecular weight alcohols can be used.

The water-based coating composition of the present invention comprises an amine-blocked acid catalyst such as p-toluenebenzenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenedisulfonic acid as a curing aid, if necessary, per 100 parts by weight of the resin solid content.
Add 0.1 to 1 part to make a paint.

A pigment, a leveling agent, an antifoaming agent, and a lubricant can be added to the water-based coating composition of the present invention. To blend the pigment, the aqueous acrylic resin or aqueous polyester resin solution of the component (b) is kneaded to prepare a pigment paste, and then the pigment can be blended. Furthermore, water-soluble resin, water-dispersible resin,
For example, maleated fatty acid, maleated butadiene resin,
It is also possible to mix a water-soluble or water-dispersible epoxy resin.

The water-based coating composition of the present invention comprises a roll coat, a spray,
The base material can be coated by a known means such as splash coating. As the base material, there are metal base materials such as electric tin-plated steel plate, tin-free steer, and aluminum.

Further, the aqueous coating composition of the present invention can be cured under a wide range of baking conditions from baking at 150 to 200 ° C. for about 10 minutes to high temperature short time baking at about 250 ° C. for 5 seconds.

(Examples) Hereinafter, the present invention will be described with reference to Examples. In the examples, "part" means "part by weight" and "%" means "% by weight".

Production Example 1 (Production of modified epoxy resin solution A1) 60 parts of diethylene glycol monobutyl ether in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen gas blowing tube, Epicoat 828 (trade name of Yuka Shell Epoxy Co., Ltd.) ) 40 parts was charged and dissolved by heating at 70 ° C, 10.4 parts orthophosphoric acid (0.5 mol with respect to the epoxy group) was charged and heated to 130 ° C while stirring while introducing nitrogen gas until the epoxy equivalent became 11,000. After the reaction, the mixture was cooled to below 50 ° C. to obtain a modified epoxy resin solution A1 having a solid content of 60%.

Production Example 2 (Production of Modified Epoxy Resin Solution A2) The same four-necked flask as in Production Example 1 was charged with 35 parts of ethylene glycol monoethyl ether and 65 parts of Epicoat 1001 and heated and dissolved at 90 ° C. to obtain orthophosphoric acid 1.34 parts (epoxy). (0.1 mol relative to the base) was added and heated to 130 ° C with stirring while introducing nitrogen gas, and reacted until the epoxy equivalent reached 11,000, then ethylene glycol monobutyl ether
After adding 27.2 parts, the mixture was further cooled to 50 ° C or lower to obtain a modified epoxy resin solution A2 having a solid content of 60%.

Production Example 3 (Production of Modified Epoxy Resin Solution A3) Neopentyl glycol 5 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser with a separation tank, and a nitrogen gas blowing tube.
0.0 part, adipic acid 23.4 parts, terephthalic acid 26.6 parts were charged and heated to 230 ° C while stirring while introducing nitrogen gas, reacted until the acid value became 5 or less, then cooled and hydroxyl value 18
A polyester resin having a number average molecular weight of 1,500 was obtained. Next, at 100 ° C, 1,100 parts of Epicoat 100 were charged, and after heating and dissolution, 6.31 parts of orthophosphoric acid (0.3 mol based on epoxy group) was charged and heated to 130 ° C, reacted until the epoxy equivalent was 12,000 or more, and then cooled. Modified epoxy resin solution A with a solid content of 60% by adding 131 parts of ethylene glycol monobutyl ether
3 was obtained.

Production Example 4 (Production of Modified Epoxy Resin Solution A4) The same four-necked flask as in Production Example 3 was charged with 48.4 parts of neopentyl glycol and 51.6 parts of terephthalic acid and heated to 230 ° C. while stirring while introducing nitrogen gas, After reacting until the acid value becomes 5 or less, it is cooled and the hydroxyl value is 180 and the number average molecular weight is
1600 polyester resins were obtained. Next, at 100 ° C, 1,98.8 parts of Epicoat 100 was charged, and after heating and melting, orthophosphoric acid 1
Charge 0.2 parts (0.5 mol based on epoxy group), heat to 130 ° C, react until the epoxy equivalent exceeds 12,000 and then cool, add 132 parts ethylene glycol monobutyl ether and add 60% solid modified epoxy. Resin solution A4 was obtained.

Production Example 5 (Production of Modified Epoxy Resin Solution A5) The same four-necked flask as in Production Example 1 was charged with 145 parts of ethylene glycol monoethyl ether and 5 parts of propyl mercaptan and stirred at 115 ° C. while introducing nitrogen gas.
After heating to 20 ° C, 20 parts of α-methylstyrene, 5 parts of acrylic acid, 40 parts of 2-hydroxypropyl acrylate,
A mixture of 35 parts of ethyl acrylate and 0.1 part of benzoyl peroxide was added dropwise over 3 hours. Then keep at 115 ℃,
After reacting for 1 hour, 0.8 part of benzoyl peroxide was added and reacted for another hour, then cooled and ethylene glycol monoethyl ether was distilled off under reduced pressure at 80 ° C to give a hydroxyl value of 174, a number average molecular weight of 2100 and a solid content of 85. % Acrylic resin solution was obtained. Next, 100 parts of Epicoat 100, 97.4 parts were charged and dissolved by heating at 90 ° C, and then 10.0 parts of orthophosphoric acid (0.
(5 mol) was charged and heated to 130 ° C, and the epoxy equivalent was 12,000.
After reacting until the reaction was completed, the mixture was cooled and 121 parts of ethylene glycol monoethyl ether was added to obtain a modified epoxy resin solution A5 having a solid content of 60%.

Production Example 6 (Production of Modified Epoxy Resin Solution A6) Modified Epoxy Resin Solution A1 produced in the same manner as in Production Example 1.
Then, 18.9 parts of dimethylethanolamine and 5.8 parts of water were added to obtain a modified epoxy resin solution A6 having a solid content of 50%.

Production Example 7 (Production of Modified Epoxy Resin Solution A7) 20.5 parts of ethylene glycol monoethyl ether and 79.5 parts of Epicoat 1004 were charged in the same four-necked flask as in Production Example 1 and heated at 90 ° C. and dissolved, and then 5.6 parts of orthophosphoric acid (epoxy) (0.5 mol with respect to the base) was heated to 130 ° C with stirring while introducing nitrogen gas, reacted until the epoxy equivalent reached 11000, then cooled to 70 ° C, 10.1 parts of dimethylethanolamine and 64.9 parts of water , 10 parts of monoglycol ether was added to obtain a modified epoxy resin solution A7 having a solid content of 50%.

Production Example 8 (Production of Modified Epoxy Resin Solution A8) 101.4 parts of Epicoat 1001 were charged into a polyester resin produced in the same manner as in Production Example 3 and dissolved by heating at 100 ° C., and then 10.5 parts of orthophosphoric acid (0.5 mol based on epoxy group). ) Was heated to 130 ° C, reacted until the epoxy equivalent reached 12000, 100 parts of ethylene glycol monobutyl ether was added, and further cooled to 70 ° C, dimethylethanolamine 19.0
Parts and 81.4 parts of water were added to obtain a modified epoxy resin solution A8 having a solid content of 50%.

Production Example 9 (Production of Modified Epoxy Resin Solution A9) Modified Epoxy Resin Solution A5 produced in the same manner as in Production Example 5.
18.2 parts of ethylene glycol monobutyl ether was added to the mixture, and after cooling, 18.2 parts of dimethylethanolamine and 10 parts of water were added.
0 part was added to obtain a modified epoxy resin solution A9 having a solid content of 50%.

Production Example 10 (Production of Aqueous Acrylic Resin Solution B1) n-Butanol 100 was placed in a four-necked flask similar to Production Example 1.
Parts were charged and kept at 105 ° C while introducing nitrogen gas, from the dropping tank, acrylic acid 10 parts, 2-hydroxyethyl methacrylate 20 parts, styrene 40 parts, butyl acrylate.
A mixture of 30 parts and 3 parts of benzoyl peroxide was added dropwise over 3 hours. After that, the temperature was kept at 105 ° C and the reaction was carried out for 1 hour. Then, 0.3 part of benzoyl peroxide was added, and the reaction was carried out for 1 hour to finish. 60
After cooling to below ℃, add 12.3 parts of dimethylethanolamine and 200 parts of water, distill off n-butanol together with water at 80 ℃ under reduced pressure, solid content 60%, residual n-butanol 10%
A transparent and viscous aqueous acrylic resin solution B1 having an acid value of 78 before neutralization and a number average molecular weight of 1000 was obtained.

Production Example 11 (Production of Aqueous Polyester Resin Solution B2) The same four-necked flask as in Production Example 3 was charged with ethylene glycol.
12.9 g, neopentyl glycol 21.6 parts, adipic acid 23.3
g, terephthalate 3.26.5 parts was charged and heated to 230 ° C while stirring while introducing nitrogen gas, reacted until the acid value became 5 or less, then cooled to 160 ° C and added 15.8 parts adipic acid, The reaction was further continued and terminated when the acid value reached 35. After cooling to below 80 ℃, 17.5 parts of ethylene glycol monobutyl ether, 4.8 parts of dimethylethanolamine and 55.2 parts of water were added, and the solid content was 50% and the organic solvent was 11%. Transparent and viscous acid value before neutralization 35, number average molecular weight 3800 aqueous polyester resin solution B2 was obtained.

Example 1 Modified epoxy resin solution A1 5.8 parts, aqueous acrylic resin solution B1 35.0 parts, hexamethoxymelamine (Cymel 303 manufactured by Mitsui Toatsu Chemicals, Inc .; the following examples are the same) 10.5 parts, amine-blocked paratoluene sulfone Acid 0.1 parts, ethylene glycol monobutyl ether 3.2 parts, ion-exchanged water 4
5.3 parts and 0.1 part of a silicone leveling agent were mixed to form a paint. The resin solid content of each component is the ratio shown in Table 1.

Examples 2 to 13 In the same manner as in Example 1, the resin compositions were changed as shown in Table 1 to form coating materials.

In addition, Comparative Examples 1 and 2 show water-based paints containing no modified epoxy resin of the present invention. The coating tests of the paints obtained in Examples 1 to 13 and Comparative Examples 1 and 2 and the paint film physical property test after paint baking and curing and the paint stability test were conducted, and the results are shown in Table 1.

○ Paint stability test: After each paint was stored at room temperature for 2 months, the state of gelation and separation of the resin was observed.

○ Physical property test of coating film: An electroplated tin plate with a plate thickness of 0.23 mm was coated by roll coating to a film thickness of 7 μ after drying, and baked in a gas oven at an ambient temperature of 190 ° C for 10 minutes to prepare a coated panel. .

○ Water resistance test; dip the coated panel in water, 100 ℃ -30 minutes and 125 ℃
After heat treatment for -30 minutes, the whitening state of the coating film was evaluated.

Workability test: An Erichsen test was conducted.

○ Impact resistance test: Using a DuPont impact tester, a 1/2 inch diameter impact core is brought into contact with the sample, and then a 500 g weight is dropped. Impact resistance was evaluated by the height at which the coating film did not crack.

○ Pencil hardness test: Followed the method registered in JIS standard "Pencil scratch test" (JIS No.K5400).

○ Adhesion test; After putting cuts reaching the base material of 11 pieces on each side of the coating film at intervals of 2 mm, a cellophane adhesive tape was attached, and then the peeling ratio of the peeled and cut coating film was examined. .

○ Salt water spray resistance test: After cutting a test piece that has a sealed part other than the coated surface until it reaches the base, put it in a salt water spray tester (JIS-Z-2371).
Either blister or rust from the cross cut part has a width of 3 mm
Indicates the time to reach.

○ Salt water immersion resistance test: Cut the test piece under seal except for the coated surface until it reaches the base material, and then dip it in 5% saline solution at 37 ° C to give the same width as above.
The time required to reach 3 mm is shown.

〔The invention's effect〕

The water-based coating composition of the present invention is excellent in corrosion resistance, water resistance and coating film hardness. Therefore ,. When the water-based coating composition of the present invention is used as a coating material for the outer surface of a can, it is a coating film that prevents corrosion of the can material, withstands high temperature hot water treatment for sterilizing food, and the coating film on the outer surface of the can is not easily damaged during transportation. Can be provided.

Continuation of the front page (56) Reference JP-A-60-210623 (JP, A) JP-A-61-98724 (JP, A) JP-A-63-189419 (JP, A) JP-A-63-189420 (JP , A) JP-A-61-246263 (JP, A) JP-A-58-500170 (JP, A)

Claims (1)

[Claims] 1. An aqueous coating composition comprising the following (a), (b) and (c) dispersed or dissolved in an aqueous medium consisting of most of water and a water-miscible solvent. (A) Aromatic epoxy resin with phosphoric acid and low molecular weight alcohol or its derivative or number average molecular weight of 30
Modified epoxy resin composition obtained by reacting alcoholic hydroxyl group-containing low molecular weight resin having a hydroxyl value of 00 or less and 150 or more, (b) acrylic resin or polyester resin soluble or dispersible in the presence of alkali, (c) Aminoplast resin