JPH11106700A - Water-based coating material composition and coated metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-based coating material composition excellent in processing resistance and water resistance, capable of forming a coated film having a high hardness. SOLUTION: This composition comprises 30-85 wt.% of an acrylic copolymer (a) obtained by copolymerizing (1) 1-25 wt.% of an α,β-monoethylenic unsaturated carboxylic acid with (2) 5-60 wt.% of an N-methylolalkoxy(meth)acrylamide containing 20-100 wt.% of an N-methylolalkoxy(meth)acrylamide obtained by etherifying an N-methylol(meth)acrylamide with an alcohol having >=120 deg.C boiling point and (3) 10-60 wt.% of a (meth)acrylate and/or a vinyl monomer copolymerizable with the components (1) and (2) and 15-70 wt.% of an imino group type benzoguanamine resin (b) containing 0.5-2.0 imino groups based on one benzoguanamine nucleus (with the proviso that the total of the acrylic copolymer (a) and the imino group type benzoguanamine resin (b) is 100 wt.%).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition, and more particularly, to an aqueous coating composition having excellent retort resistance, workability and hardness, and coating the aqueous coating composition with the aqueous coating composition. Metal plate.

[0002]

2. Description of the Related Art The outer surfaces of beverage cans containing soft drinks and the like and food cans containing food (hereinafter, both are referred to as beverage cans, etc.) prevent corrosion of can materials and enhance aesthetic commercial value. And is coated with a coating film that can withstand a heat treatment step during food sterilization. Conventional coating materials used for coating are organic solvent type coating materials obtained by dissolving resins such as epoxy / amino resin, acrylic / amino resin, polyester / amino resin in an organic solvent. And baked and cured in a gas oven to cover the above beverage cans and the like. However, since these solvent-type paints contain a large amount of organic solvents, they are not preferable in the Fire Service Law, and various water-based paints have been developed.

There are roughly two types of water-based paints, those containing a water-dispersible resin and those containing a water-soluble resin. Many water-dispersible resins are usually synthesized by emulsion polymerization using a surfactant, and the surfactant used remains in the coating film even after the formation of the coating film, and has a disadvantage of lowering the water resistance. Was. On the other hand, by synthesizing a resin having an acid component in an organic solvent without using a surfactant, for example, a resin having a carboxyl group, and neutralizing the carboxyl group with a volatile base, a resin dispersion or an aqueous resin solution is obtained. Although there is a method of obtaining, in this case, it is necessary that the basic resin has an acid value of 20 or more in order to make it aqueous, and since the coating film after the volatile base is volatilized is rich in acid value, However, there is a disadvantage that the coating film has poor water resistance, alkali resistance and the like.

In order to improve these drawbacks, a method of mixing a large amount of an aqueous amino resin such as hexamethoxymethyl melamine or fully methylated benzoguanamine has been proposed, but the processability of the coating film is significantly reduced. On the other hand, when the amount of the aqueous amino resin is reduced to improve the processability, the coating film hardness tends to decrease, and it has been difficult to balance water resistance, coating film hardness and processability.

[0005] Japanese Patent Application Laid-Open Nos. 5-202270 and 5-320564 disclose N-methylol (meth) acrylamide, methanol, ethanol, and the like.
N formed by etherification with lower alcohol such as butanol
An aqueous coating composition containing an acrylic copolymer obtained by copolymerizing methylolalkoxy (meth) acrylamide has been proposed. 2. Description of the Related Art In recent years, beverage cans and the like have become the mainstream in which cans with a reduced diameter for reducing resources and costs. Conventionally, beverage cans and the like have been provided with a process in which the mouth of the can provided with a lid is slightly thinner than the body of the can after applying and curing the paint. In the case of reduced diameter cans), the mouth of the can must be made thinner while the body of the can is the same as the conventional can. However, the coatings obtained from the paints did not fully satisfy the further requirements for such processability and the water resistance.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an aqueous coating composition which is excellent in processing resistance and water resistance and can form a coating film of high hardness. Another object of the present invention is to provide a coated metal obtained by applying the aqueous coating composition to a metal, heating and curing the metal.

[0007]

The object of the present invention is to provide an acrylic copolymer (a) or (d) having a specific structure and a benzoguanamine resin (b) having a specific structure. Is achieved.

That is, the first present invention provides the following (1) to
Acrylic copolymer (a) 30 obtained by copolymerizing (3)
８５85% by weight, and 0.1 per benzoguanamine core.
An aqueous coating composition comprising 15 to 70% by weight of an imino group type benzoguanamine resin (b) having 5 to 2.0 imino groups. However, the acrylic copolymer (a) and the imino group type benzoguanamine resin (b)
To 100% by weight. (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (2) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a boiling point of 120 ° C. or more N-methylolalkoxy (meth) acrylamide containing 20 to 100% by weight of (meth) acrylamide (A): 5 to 60% by weight (3) (meth) acrylate copolymerizable with the above (1) and (2) And / or vinyl monomer: 10 to 60% by weight

In the second invention, the following (1), (4), and (3) are copolymerized to obtain an acrylic copolymer (c), and the acrylic copolymer (c) and a boiling point of 120 ° C. The N-methylolalkoxy (meth) acrylamide (B) obtained by reacting the above-mentioned alcohol with the above-mentioned alcohol and subjecting the copolymer to 20 to 100
Acrylic copolymer (d) obtained by substituting the above-mentioned alcohol with ether having a boiling point of 120 ° C. or higher by ether at 30% to 85% by weight, and 0.5 to 2% by weight per benzoguanamine nucleus.
An aqueous coating composition comprising 15 to 70% by weight of an imino group type benzoguanamine resin (b) having 0 imino groups. However, the total amount of the acrylic copolymer (d) and the imino group type benzoguanamine resin (b) is 100% by weight. (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (4) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a temperature of 50 ° C. or more and less than 120 ° C. (Meth) acrylamide (B): 5 to 60% by weight (3) Alkyl (meth) acrylate and / or aromatic vinyl monomer copolymerizable with the above (1) and (2): 10 to 60% by weight

In a third aspect of the present invention, the following (1), (5) and (3) are copolymerized to obtain an acrylic copolymer (e), and the acrylic copolymer (e) and a boiling point of 120 ° C. Acrylic copolymer (f) obtained by reacting at least a part of N-methylolalkoxy (meth) acrylamide (B) which has been reacted with the above alcohol and subjected to copolymerization with the alcohol having a boiling point of 120 ° C. or higher. : 30 to 85% by weight,
And an aqueous coating composition comprising 15 to 70% by weight of an imino group type benzoguanamine resin (b) having 0.5 to 2.0 imino groups per benzoguanamine nucleus. The total amount of the union (a) and the imino group type benzoguanamine resin (b) is 10
0% by weight). (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (5) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a boiling point of 120 ° C. or more N-methylolalkoxy (meth) acrylamide (B) containing less than 20% by weight of (meth) acrylamide (A) and etherified with N-methylol (meth) acrylamide with an alcohol having a temperature of 50 ° C. or more and less than 120 ° C. ) Containing at least 80% by weight of N-methylolalkoxy (meth) acrylamide: 5 to 60% by weight (3) (meth) acrylates and / or vinyl monomers copolymerizable with the above (1) and (2) : 10 to 60% by weight

A fourth aspect of the present invention is a coated metal obtained by applying the aqueous coating composition according to any one of the first to third aspects to a metal, heating and curing the metal.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The α-β-monoethylenically unsaturated carboxylic acid (1) used in the present invention is obtained by converting the acrylic copolymer (a) or (d) to an aqueous solution (solubilizing or Water-dispersible), and includes acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc., with acrylic acid and methacrylic acid being particularly preferred. The α-β-monoethylenically unsaturated carboxylic acid (1) is used in an amount of 1 to 15% by weight when obtaining the acrylic copolymer (a) or (d). If it is less than 1% by weight, it is difficult to make the acrylic copolymer (a) or (d) aqueous, and if it exceeds 15% by weight, the water resistance of the coating film becomes poor.

N-methylolalkoxy (meth) acrylamide (A) (hereinafter abbreviated as acrylamide (A)) is obtained by reacting (meth) acrylamide with formalin to obtain N-methylol (meth) acrylamide. Such N-methylol (meth) acrylamide is reacted with an alcohol having a boiling point of 120 ° C. or higher. The outline of the reaction is shown below.

[0014]

Embedded image

As alcohols having a boiling point of 120 ° C. or higher,
n-amyl alcohol (boiling point: 138 ° C, the same applies hereinafter),
Isoamyl alcohol (130.8 ° C), 2-methyl-
1-butanol (128 ° C), cyclohexanol (1
61.1 ° C), n-hexanol (157.1 ° C), 2
-Heptanol (160.4 ° C), 3-heptanol (156.2 ° C), n-heptanol (176.3)
° C), 2-ethylbutanol (147 ° C), n-octanol (195 ° C), 2-octanol (178.5).
C), 2-ethylhexanol (184.7C), nonanol (193C), n-decanol (231C), and undecanol (243C).
Ethyl cellosolve (135.6 ° C), butyl cellosolve (171.2 ° C), methyl cellosolve (124.4)
° C), hexyl cellosolve (208.1 ° C), methyl carbitol (194.1 ° C), ethyl carbitol (24.1 ° C).
02.0 ° C), butyl carbitol (230.4 ° C),
3-methoxy-butanol (161.1 ° C), 3-methyl-3-methoxybutanol (174.0 ° C), ethylene glycol monoisopropyl ether (144
° C), propylene glycol monomethyl ether (12
1 ° C.), ethylene glycol monoisobutyl ether (160.5 ° C.), methyl glycol (124.5)
° C), methyldiglycol (194 ° C), methylpropylene glycol (121 ° C), propylpropylene glycol (149.8 ° C), isopropyl glycol (1
Cellosolve-based or carbitol-based alcohols such as 41.8 ° C) and polyhydric alcohols such as ethylene glycol (197.2 ° C) and diethylene glycol (244.3 ° C). Cellosolve alcohols such as 3-methoxy-butanol are preferred.

According to a first aspect of the invention, (2) N-methylolalkoxy (meth) acrylamide (hereinafter abbreviated as (2) acrylamide) contains two acrylamides (A).
It is important to contain 0 to 100% by weight. (2) in the acrylic copolymer (a) upon baking and curing of the paint
An alkoxy group derived from acrylamide (-OR, R
Elimination of the alcohol from the alkyl group) generates a methylol group (—CH ₂ —OH), and the methylol group is converted to a benzoguanamine resin (b) described later.
Or the methylol groups react with each other to form a cured coating film. Therefore, the ease with which the alcohol is eliminated greatly affects the reactivity (curability) of the paint and the physical properties of the coating film.

The more easily the alcohol is desorbed, the more
In other words, the lower the boiling point of the alcohol to be eliminated, the faster the methylol group is generated, so that the reactivity (curability) is excellent. However, the cured coating film obtained because it cures in an extremely short time has a low workability. Inferior to On the other hand, the more difficult the alcohol is to be eliminated, that is, the higher the boiling point of the alcohol to be eliminated, the more difficult it is for the reaction (curing) to occur because the methylol group is less likely to be generated. It is necessary to react (cur) at a high temperature or react (cur) over time, but a cured coating film having excellent workability can be obtained.

Therefore, in order to achieve both reactivity (curability) and processability of a cured coating film, (2) an acrylamide (A) capable of desorbing a relatively high boiling alcohol from the acrylamide is used in an amount of 20 to 100. It is important that it be contained by weight. Generally, exterior paints such as beverage cans are often baked and cured at about 150 to 200 ° C. Therefore, in consideration of curability, the boiling point of alcohol that can be released from acrylamide (A) is about 250 ° C. or less. Preferably, it is 120-180 ° C. When the content of the acryl amide (A) is less than 20% by weight, the acryl amide (B) from which low-boiling alcohols can be eliminated
(Described later), and only a coating film having excellent curability but poor workability can be obtained.

In the first invention, (2) N which may be contained in the acrylamide together with the acrylamide (A)
-Methylol alkoxy (meth) acryl amide (B) (hereinafter abbreviated as acryl amide (B))
(Meth) acrylamide and formalin are reacted to obtain N-methylol (meth) acrylamide, and the N-methylol (meth) acrylamide and boiling point of 50 are obtained.
It is obtained by reacting with an alcohol having a temperature of 120 ° C. or more. The outline of the reaction is the same as in the case of the N-methylolalkoxy (meth) acrylamide (A).
Examples of the alcohol having a boiling point of 50 to 120 ° C include methanol (boiling point: 64.7 ° C, the same applies hereinafter), ethanol (78.3 ° C), 1-propanol (97.2 ° C), n
-Butanol (117.7 ° C.), s-butanol (9
9.5 ° C.), t-butanol (82.5 ° C.), isobutyl alcohol (107.9 ° C.), isopropyl alcohol (82.3 ° C.), s-amyl alcohol (119.3 ° C.)
° C), t-amyl alcohol (101.8 ° C), 3-pentanol (115.6 ° C), 3-methyl-2-butanol (112 ° C) and the like. Among the (meth) acrylates and / or vinyl monomers (3) copolymerizable with the above (1) and (2), methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, -Alkyl (meth) acrylates such as ethyl acrylate, cyclhexyl (meth) acrylate, and stearyl (meth) acrylate; and hydroxyl group-containing monomers such as hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate. For example, aromatic vinyl monomers such as styrene and vinyl toluene, and vinyl carboxylate monomers such as vinyl acetate can also be used.

The acrylic copolymer (a) can be obtained by a usual solution polymerization method, and a mixture of the above monomers is dissolved in an organic solvent such as a peroxide such as benzoyl peroxide;
Alternatively, radical polymerization is carried out using an azo compound such as 2,2 'azobisisobutylnitrile as a catalyst. Examples of the organic solvent used for polymerization include alcohol solvents such as methanol, ethanol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-amyl alcohol, and isoamyl alcohol, butyl cellosolve, hexyl cellosolve, butyl carbitol, methyl glycol, and methyl. Propylene glycol, propyl propylene glycol, 3-methoxybutanol, 3-methyl-3
Cellosolves such as -methoxy-butanol, ethylene glycol monoisopropyl ether, and propylene glycol monomethyl ether;

To the acrylic copolymer (a) solution, a volatile base such as ammonia or an organic amine is added together with water, or a volatile base such as ammonia or an organic amine is added and then water is added to the acrylic copolymer (a). The acrylic copolymer (a) can be dissolved or dispersed in an aqueous medium by neutralizing all or a part of the carboxylic acid in the union (a). The volatile base preferably has a boiling point of 400 ° C. or lower. For example, as the organic amine, monoethanolamine, dimethylamine, diethylamine, triethylamine, triethanolamine,
Examples thereof include diethylethanolamine and dimethylethanolamine.

The first invention comprises (2) an acrylic copolymer (a) containing acrylamide (A) previously alkoxylated with a high-boiling alcohol in an amount of 20% by weight or more and copolymerized with acrylamide. While using
A second invention is to provide an acrylic copolymer (c) obtained by copolymerizing an acrylamide (B) obtained by alkoxylation with a low-boiling alcohol, and then to obtain a mixture of the acrylic copolymer (c) and the boiling point. An acrylic copolymer (d) obtained by reacting an alcohol having a boiling point of not less than 120 ° C. with an alcohol having a boiling point of not less than 120 ° C. by reacting an alcohol having a boiling point of not lower than 120 ° C. The purpose of the present invention is to control the generation of methylol groups during baking and curing, as in the first invention, to improve the reactivity (curability) as a paint and the workability of the coating film. It is to balance. The acrylic copolymer (d) is obtained by heating the alcohol having a boiling point of 120 ° C. or higher and the acrylic copolymer (c) under reduced pressure to effect ether substitution, or by heating using an acid catalyst to effect ether substitution. be able to.

Further, a third invention is a mixture of acrylamide (A) and acrylamide (B),
(5) The acrylic copolymer (e) containing less than 20% by weight of the acrylamide (A) is obtained by using the acrylamide, and then the acrylic copolymer (e) is obtained in the same manner as in the second invention. An acrylic copolymer (A) obtained by reacting the coalesced (e) with an alcohol having a boiling point of 120 ° C. or higher and substituting at least a part of the acrylamide (B) subjected to copolymerization with an ether having the boiling point of 120 ° C. or higher. f), and the purpose is the same as in the case of the first and second inventions.
The method for polymerizing the acrylic copolymers (c) and (e) and the method for making the obtained acrylic copolymers (d) and (f) aqueous are the same as those for the acrylic copolymer (a). Is the same as

The benzoguanamine resin (b) used in the present invention is a resin obtained by condensing a methylol compound obtained by subjecting a part or all of the amino groups in benzoguanamine to addition reaction with formaldehyde, or one of the methylol groups of the methylol compound. The benzoguanamine nucleus needs to have 0.5 to 2.0 imino groups per benzoguanamine nucleus. When the number of imino groups is 2.0 or more, the stability with time as a coating is poor, and when the number is 0.5 or less, curing reactivity is poor. Examples of the alcohol used for etherifying the methylol group include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
Alkyl alcohols such as isobutyl alcohol, s-butyl alcohol and t-butyl alcohol, butyl cellosolve, hexyl cellosolve, butyl carbitol,
Cellosolves such as methyl-3-methoxy-butanol, 3-methoxy-butanol, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether, and methyl propylene glycol may be mentioned, and these may be used as a mixture.

In the aqueous coating composition of the present invention, if necessary, an acid catalyst or an amine blocking agent thereof such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinolylnaphthalenesulfonic acid or the like may be used as a curing aid. 0.1 to 4 parts can be added to 100 parts of the resin solids. Similarly, conventionally known leveling agents, defoaming agents, lubricants and the like can be added. In addition, pigments such as titanium oxide, aluminum pigments and quinacridone can be kneaded with the above-mentioned acrylic resin using a known dispersing machine such as a sand mill or a disper, and can be formed into a paint by the same method as described above. Furthermore, water-soluble resins and water-dispersible resins generally used as resins for water-based coatings, such as polyester resins and polyol resins or water-soluble or water-dispersible epoxy resins modified with amine, phosphoric acid, etc., maleated fatty acids Etc. can be mixed.

The aqueous coating composition of the present invention can be applied to a substrate by a known means such as roll coating, spraying and brushing. The metal plate used in the present invention is a cold-rolled steel plate having a thickness of 0.01 to 2.0 mm, an aluminum public metal plate, or the like. In some cases, the surface of these metal plates is plated with one or two or more alloys or composites of inorganic metals such as chromium, tin, zinc, and nickel, and organic materials such as acrylic resins, vapor-deposited, painted, and further zirconium, Alumite, phosphoric acid treatment, etc. are applied. Further, a plastic film-coated metal plate in which a resin film such as polyethylene terephthalate or polybutylene terephthalate is bonded to these metal plates can also be used.

Hereinafter, the present invention will be described with reference to examples. In the examples, “parts” means “parts by weight” and “%” means “% by weight”.

Production Example 1 (Production of Aqueous Acrylic Copolymer a1) 100 parts of ethylene glycol monoisopropyl ether was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube. The temperature was kept at 105 ° C. while stirring and introducing nitrogen gas, and a solution prepared by dissolving 5 parts of benzoyl peroxide in a mixture of the following monomers was dropped from a dropping tank over 3 hours. Styrene: 20% ethyl acrylate: 52% of acrylic _{acid: 8% CH 2 = CHCONHCH 2} O-CH 3: 10% ( methoxymethyl _{acrylamide) CH 2 = CHCONHCH 2 O-} CH 2 CH 2 -O-C 4 H 9 : 10% (N-methylolalkoxyacrylamide obtained by etherifying N-methylolacrylamide with butyl cellosolve having a boiling point of 171.2 ° C) Then, the mixture was reacted at 105 ° C for 1 hour, and 5 parts of benzoyl peroxide was added. The reaction was carried out for 1 hour and the reaction was completed. The solvent was removed under reduced pressure at 100 ° C. until ethylene glycol monoisopropyl ether had a nonvolatile content of 80%. Thereafter, 9.4 parts of diethanolamine and water were added, and an aqueous acrylic copolymer a1 having a solid content of 50% was obtained. I got

Production Examples 2 to 10 (Production of aqueous acrylic copolymers a2 to a10) Aqueous acrylic copolymer having a solid content of 50% was polymerized in the same manner as in Production Example 1 with the monomer composition shown in Table 1. a2
To a10 were obtained.

Production Example 11 (Production of acrylic copolymer c1 and aqueous acrylic copolymer d1) A mixture of the following monomers was copolymerized using butyl cellosolve instead of ethylene glycol monoisopropyl ether used in Production Example 1. The same procedure was followed up to the removal of the solvent according to Production Example 1 to obtain an acrylic copolymer c1 solution having a solid content of 50%. Styrene: 20% ethyl acrylate: 52% of acrylic _{acid: 8% CH 2 = CHCONHCH 2} O-CH 3: 20% ( methoxymethyl acrylamide)

Then, the temperature was raised to 120 ° C.
Add 2 parts and react for 1 hour while distilling off methanol,
50% of the methoxy groups derived from the above CH ₂ ＣＨCHCONHCH ₂ O—CH ₃ are replaced with —O—CH ₂ CH ₂ —O—C ₄ H
_The methanol and ethylene glycol monoisopropyl ether were removed at 100 ° C. under reduced pressure until the nonvolatile content became 80%. Then, 9.4 parts of diethanolamine and water were added, and aqueous acrylic having a solid content of 50% was added. A system copolymer d1 was obtained.

Production Example 12 (Production of acrylic copolymer e1 and aqueous acrylic copolymer f1) A mixture of the following monomers was copolymerized using butyl cellosolve instead of ethylene glycol monoisopropyl ether used in Production Example 1. The same procedure was followed up to the removal of the solvent according to Production Example 1 to obtain an acrylic copolymer e1 solution having a solid content of 50%. Styrene: 20% ethyl acrylate: 52% of acrylic _{acid: 8% CH 2 = CHCONHCH 2} O-CH 3: 18% ( methoxymethyl _{acrylamide) CH 2 = CHCONHCH 2 O-} CH 2 CH 2 -O-C 4 H 9 : 2%

Then, the temperature was raised to 120 ° C.
Add 2 parts and react for 1 hour while distilling off methanol,
About 44.4% of the methoxy groups derived from the above CH ₂ ＣＨCHCONHCH ₂ O—CH ₃ are converted to —O—CH ₂ CH ₂ —O—.
C ₄ H _{9 was} converted to a non-volatile content of 8 at 100 ° C. under reduced pressure.
Methanol and ethylene glycol monoisopropyl ether were removed until the concentration became 0%, and then 9.4 parts of diethanolamine and water were added to obtain an aqueous acrylic copolymer f1 having a solid content of 50%.

Production Example 13 (Production of Benzoguanamine Resin b1) Benzoguanamine 187 was placed in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube.
Parts, 80% paraformaldehyde (281 parts) and methanol (320 parts), and a 25% sodium hydroxide solution 0.7
After the addition, the mixture was heated at 60 ° C. for 3 hours. Thereafter, a 60% nitric acid solution was charged until the solution reached a pH of 3.5, followed by 7
The reaction was performed at 0 ° C. for 4 hours. After completion of the reaction, the reaction mixture was neutralized with a 25% sodium hydroxide solution, and then the methanol water was removed under reduced pressure at 70 ° C. or lower. And
The solid content was adjusted to 75% with ethylene glycol monoisopropyl ether.

Production Examples 14 to 17 (Production of Benzoguanamine Resins b2 to b5) According to Production Example 13, the reaction was carried out with the amounts of benzoguanamine, paraformaldehyde and methanol shown in Table 2 to obtain benzoguanamine resins b2 to b5.

Table 2 shows the results of NMR analysis and calculation of the number of imino groups per benzoguanamine nucleus for the benzoguanamine resins b1 to b5 obtained in Production Examples 13 to 17.

Examples 1 to 15 and Comparative Examples 1 to 4 After mixing the components according to the formulation shown in Table 3 (however, in Example 15, the acrylic resin solution and the pigment were kneaded first), butyl cellosolve and water were added. Then, the amount of the organic solvent in the paint was adjusted to 10% and the solid content to 35%. To this, 0.3% of a paratoluenesulfonic acid amine salt and 0.3% of a silicone-based leveling agent were added to obtain an aqueous coating composition.

Table 4 shows the results of examining the stability of the coating compositions and the physical properties of the coating films prepared in Examples and Comparative Examples.
5 is shown. Each test method is as follows.

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

Test of physical properties of coating film A 0.23 mm-thick electroplated tin plate was dried by roll coating, dried and coated to a thickness of 7 μm, and baked in a gas oven at an ambient temperature of 200 ° C. for 10 minutes to prepare a coated panel. did. The scratch resistance was evaluated by preparing a three-piece can formed by molding a painted plate such that the painted surface was the outer surface of the can.

Water resistance test The coated panel was immersed in water and subjected to a hot water treatment at 100 ° C. for 30 minutes and a pressurized boiling water treatment at 130 ° C. for 30 minutes, and then the whitening state of the coating film was evaluated. . O Workability test According to the Erichsen test and JISZ-2247, the state of the coating film was evaluated after extruding until the base metal plate began to crack. ○ Adhesion A peeling test was performed. Similarly, evaluation after pressure b boiling water treatment at 130 ° C. for 30 minutes was also performed. ○ Impact resistance test Using a Dupont impact tester, 1/2 inch diameter, 500
Tested with g load. ○ Pencil hardness test JIS standard "pencil scratch test" (JIS No. K540
The procedure was performed according to the method registered in (0). O Scratchability The contents were packed in cans, and the outer surfaces of the cans were brought into contact with each other in hot water at 80 ° C to evaluate the degree of scratching of the coating film. Paintability test ○ Immediately after coating with a flow roll coater, baking was performed in a gas oven to evaluate the leveling state.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

The aqueous coating composition of the present invention has a reactivity as a coating material by using a specific N-methylolalkoxy (meth) acrylamide copolymer and a specific benzoguanamine resin as resin components. Curability), and provide a coating film having excellent processing resistance to processing into various can forms, especially to reducing the diameter, and excellent water resistance and hardness to withstand the heat treatment step of beverage can and food can sterilization treatment. . And even if the content of the organic solvent is 15% by weight in the aqueous medium,
Good paint stability and good paintability.

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification symbol FI C09D 133/06 C09D 133/06 161/26 161/26 // C09D 133/02 133/02 (72) Inventor Kenshiro Shimada Tokyo 2-13-13 Kyobashi, Chuo-ku, Tokyo Toyo Ink Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. An acrylic copolymer (a) obtained by copolymerizing the following (1) to (3): 30 to 85% by weight, and 0.5 to 2.0 imino groups per benzoguanamine nucleus. Having imino group type benzoguanamine resin (b) 15-7
An aqueous coating composition containing 0% by weight (provided that the total amount of the acrylic copolymer (a) and the imino group type benzoguanamine resin (b) is 100% by weight). (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (2) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a boiling point of 120 ° C. or more N-methylolalkoxy (meth) acrylamide containing 20 to 100% by weight of (meth) acrylamide (A): 5 to 60% by weight (3) (meth) copolymerizable with the above (1) and (2) ) Acrylates and / or vinyl monomers: 10 to 60% by weight 2. After copolymerizing the following (1), (4) and (3) to obtain an acrylic copolymer (c), the acrylic copolymer (c) and an alcohol having a boiling point of 120 ° C. or higher are mixed with each other. N-methylolalkoxy (meth) reacted and subjected to copolymerization
Acrylic copolymer (d) in which 20 to 100% by weight of acrylamide (B) is ether-substituted with the alcohol having a boiling point of 120 ° C. or higher: 30 to 85% by weight, and 0.5 to 2 per benzoguanamine nucleus Imino group type benzoguanamine resin (b) having 0.0 imino groups
An aqueous coating composition containing 70% by weight (provided that the total amount of the acrylic copolymer (d) and the imino group type benzoguanamine resin (b) is 100% by weight). (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (4) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a temperature of 50 ° C. or more and less than 120 ° C. (Meth) acrylamide (B): 5 to 60% by weight (3) Alkyl (meth) acrylate and / or aromatic vinyl monomer copolymerizable with the above (1) and (2): 10 to 60% by weight 3. An acrylic copolymer (e) is obtained by copolymerizing the following (1), (5), and (3), and the acrylic copolymer (e) and an alcohol having a boiling point of 120 ° C. or higher are obtained. N-methylolalkoxy (meth) reacted and subjected to copolymerization
At least a part of the acryl amide (B) has the boiling point of 1
Acrylic copolymer (f) obtained by ether substitution with an alcohol at 20 ° C. or higher: 30 to 85% by weight, and an imino group type benzoguanamine resin having 0.5 to 2.0 imino groups per benzoguanamine nucleus ( b) 15-70
A water-based coating composition characterized by containing 100% by weight of an acrylic copolymer (a) and an imino group-type benzoguanamine resin (b). (1) α, β-monoethylenically unsaturated carboxylic acid: 1 to 25% by weight (5) N-methylolalkoxy obtained by etherifying N-methylol (meth) acrylamide with an alcohol having a boiling point of 120 ° C. or more N-methylolalkoxy (meth) acrylamide (B) containing less than 20% by weight of (meth) acrylamide (A) and etherified with N-methylol (meth) acrylamide with an alcohol having a temperature of 50 ° C. or more and less than 120 ° C. ) Containing at least 80% by weight of N-methylolalkoxy (meth) acrylamide: 5 to 60% by weight (3) (meth) acrylates and / or vinyl monomers copolymerizable with the above (1) and (2) : 10 to 60% by weight 4. A coated metal obtained by applying the aqueous coating composition according to any one of claims 1 to 3 to a metal, heating and curing.