JPH06256710A - Aqueous coating composition - Google Patents

Abstract

PURPOSE:To obtain an aqueous coating composition useful for coating cans for foods and drinks, having excellent roll coating workability, yellowing prevention of coating film, hygienic properties, adhesion, chemical resistance, etc., comprising a prescribed modified epoxy resin and a phenol resin. CONSTITUTION:This coating composition comprises an aqueous coating composition obtained by blending (A) 100 pts.wt. of an acrylic modified epoxy resin prepared by reacting a bisphenol type epoxy resin having 8,000-18,000 epoxy equivalent and 3,500-10,000 number-average molecular weight by gel permeation chromatography with an carboxy-containing acrylic resin having 130-500 acid value with (B) 5-40 pts.wt. of a highly alkoxymethylated phenol-formaldehyde resin having 200-2,000 number-average molecular weight, <=0.2 methylol per phenol ring and 0.8-2.5 alkoxymethyl number wherein the component A is neutralized with ammonia and dispersed into an aqueous medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an excellent workability in roll coating, has no yellow discoloration of the coating film, and is hygienic.
The present invention relates to an aqueous coating composition capable of forming a coating film having excellent properties such as flavor, adhesion, processability, retort resistance, and chemical resistance, and especially for the inner surface of a can for food and drink such as drinks, meats, vegetables and fruits. The present invention relates to an aqueous coating composition suitable for roll coating, and a method for forming a coating film using the composition.

[0002]

2. Description of the Related Art Conventionally, can paints and anticorrosion paints have been desired to be changed to water-based paints from the viewpoint of resource saving, energy saving or environmental pollution. At present, an epoxy resin system is mainly studied as a water-based paint for can inner surface for a two-piece can by spray coating, and various self-emulsifying epoxy resin emulsions have been proposed.

On the other hand, in recent years, there is an increasing demand for water-based three-piece cans that are usually coated with a coil coat. In the coil coat coating, the self-emulsifying epoxy resin emulsion for spray coating has a structural viscosity that is too strong, resulting in markedly poor surface smoothness.
Various proposals have been made to improve the above-mentioned structural viscosity. For example, JP-A-4-168176 discloses a paint using ammonia water or a low boiling amine as a neutralizing agent for a reaction product of an epoxy resin and an acrylic resin. Proposed. With this paint, the viscosity of the paint is suppressed to a low level, and the leveling during roll coat painting is good, but when the roll coat is painted, the coated part by the end of the roll becomes abnormally thicker than other parts. The phenomenon of "up" occurs and there is a problem that the paint flows from the end of the thick film coated portion to the non-painted portion during baking. When the roll coating is applied to the can body for the production of three-piece cans, it is usual to leave the unpainted margin as an adhesive surface, but if the paint flows into this margin, the adhesion strength of the can becomes weak. Cause the problem of becoming.

Further, Japanese Patent Publication No. 64-54076 proposes a phenolic resin suitable for a paint for the inner surface of an aqueous can for roll coating. Although the adhesive strength is remarkably improved by using this resin, when ammonia water, which is an inorganic amine in this coating system, is used as a neutralizing agent, a resin obtained by reacting an ammonia resol resin, that is, a methylol group of a phenol resin with ammonia Is produced, which not only significantly impairs the flavor and hygiene, but also tends to cause yellowing of the coating film.

[0005]

Therefore, the present inventors have found that there is no problem of poor smoothness or build-up even in roll coating, excellent flavor and hygiene, and no yellow discoloration of the coating film. As a result of earnest research to obtain a coating composition, the present invention has been achieved.

That is, the present invention is as follows. Epoxy equivalent 8,
000-18,000 and number average molecular weight 3,500-1 by gel permeation chromatography
Bisphenol type epoxy resin (A) which is 10,000
And a carboxyl group-containing acrylic resin (B) are reacted with 100 parts by weight of an acrylic modified epoxy resin, the number average molecular weight is 200 to 2,000, and the average number of methylol groups per phenol ring is 0. .2 or less,
What is claimed is: 1. An aqueous coating composition comprising 5 to 40 parts by weight of a highly alkoxymethylated phenol formaldehyde resin having an average number of alkoxymethyl groups of 0.8 to 2.5. The present invention provides an aqueous coating composition characterized by being neutralized with ammonia and dispersed in an aqueous medium.

The present invention also relates to 2. The aqueous coating composition according to item 1, wherein the alkoxymethyl group in the phenol-formaldehyde resin has 2 to 8 carbon atoms.

Further, the present invention relates to 3. The aqueous coating composition according to item 1 or 2, wherein the resin acid value of the carboxyl group-containing acrylic resin (B) is in the range of 130 to 500.

The present invention also relates to 4. Item 1 to 3 wherein the compounding ratio in the reaction between the bisphenol type epoxy resin (A) and the carboxyl group-containing acrylic resin (B) is 1/1 to 10/1 in terms of the solid content ratio of (A) / (B). To provide the aqueous coating composition according to any one of 1.

Further, the present invention relates to 5. An aqueous coating composition according to any one of Items 1 to 4 is roll-coated on a metal plate and baked to provide a coating film forming method.

The acrylic modified epoxy resin used in the present invention is obtained by reacting a bisphenol type epoxy resin (A) with a carboxyl group-containing acrylic resin (B).

The above bisphenol type epoxy resin (A)
Has an epoxy equivalent of 8,000 to 18,000, preferably 9,000 to 14,000 and a number average molecular weight of 3,500 to 3 by gel permeation chromatography.
Any bisphenol type epoxy resin in the range of 10,000, preferably 5,000 to 9,000 can be used without particular limitation. Epoxy resin (A)
Is an esterification catalyst of a bisphenol type epoxy resin having a relatively low epoxy equivalent and a bisphenol compound, for example, tetraethylammonium bromide (TE
ABr) or a solvent in the presence of a reaction temperature of about 120-180
It can be obtained by carrying out the reaction for about 2 to 10 hours until the epoxy equivalent of the resin becomes 8,000 to 18,000 at ℃.

The bisphenol type epoxy resin having a relatively low epoxy equivalent has an epoxy equivalent of about 140 to
Generally about 4,000, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin and these epoxy resins and acrylic acid, methacrylic acid, polycarboxylic acid or acid anhydride thereof, Fatty acids, polyether polyols,
Examples thereof include modified epoxy resins obtained by reacting polyester polyol, polyamidoamine, lactone and the like. Examples of commercially available products of this bisphenol type epoxy resin include Epicoat 82 manufactured by Yuka Shell Epoxy Co., Ltd.
8EL, Epicoat 807P, Epicoat 1001, Epicoat 1004, Epicoat 1007, Arbaldite GY250, Araldite GY manufactured by Ciba-Geigy
260, Araldite 6084, Araldite 709
7, Araldite 6097, Epomic R130, Epomic R140, Epomic R manufactured by Mitsui Petrochemical Co., Ltd.
302, Epomic R304, and Epomic R307.

The bisphenol compound which is reacted with the bisphenol type epoxy resin having a relatively low epoxy equivalent to obtain the epoxy resin (A) is, for example, bis (4-hydroxyphenyl) -2,2-propane.
4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -methane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4- Hydroxy-
tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,
1,2,2-ethane, 4,4'-dihydroxydiphenyl sulfone and the like can be mentioned.

[0015]

When the epoxy equivalent of the bisphenol type epoxy resin (A) in the present invention is less than 8,000, the emulsion obtained by modifying with an acrylic resin has a large interparticle interaction and exhibits a structural viscosity (thixotropic property). When coated with a coat, the coated part due to the end of the roll becomes abnormally thick, and the build-up of the coating film is remarkable, making it unsuitable for roll coat coating. On the other hand, if it exceeds 18,000, the reaction points will decrease and epoxy resin will be used. Since the amount of the bonded acrylic resin is very small, the water dispersion ability is remarkably inferior and storage stability becomes poor. The epoxy resin (A) has a number average molecular weight of 3,500 to 10,000, preferably 6,000.
When it is from 0 to 9,000 and less than 3,500, the processability such as bending property of the obtained coating film is inferior, and when it exceeds 10,000, the water dispersion ability of the obtained emulsion is remarkably inferior and the storage stability becomes poor. Wake up.

The carboxyl group-containing acrylic resin (B) in the present invention is an acrylic copolymer containing a polymerizable unsaturated carboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid as an essential monomer component. It is united. This copolymer has a resin acid value of 130 to 500,
Furthermore, the range of 200-400 is preferable. When the acid value of the acrylic resin (B) is less than 130, the solvent resistance of the resulting coating film is lowered, and the flavor property tends to be deteriorated in the can inner surface application. On the other hand, if the acid value exceeds 500, the viscosity of the reaction system during the acrylic resin polymerization or the production of the acrylic modified epoxy resin tends to be extremely high, and the water resistance of the resulting coating film tends to be poor, and it is particularly used for can applications. In that case, whitening is likely to occur in the coating film after boiling.

Other monomer components other than the polymerizable unsaturated carboxylic acid used for polymerizing the acrylic resin (B) include, for example, styrene, vinyltoluene, 2-
Styrene-based monomers such as methylstyrene, t-butylstyrene and chlorostyrene; methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate,
Acrylic esters such as isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n methacrylate
-Butyl, isobutyl methacrylate, n-methacrylic acid
Methacrylic acid esters such as amyl, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate; acrylic acid 2
-Hydroxyethyl, hydroxypropyl acrylate,
Hydroxyl group-containing monomers such as 2-hydroxyethyl methacrylate and hydroxypropyl methacrylate; N
Examples thereof include N-substituted (meth) acrylic monomers such as methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide, and one or more of these can be selected. When used for cans, styrene and ethyl acrylate are particularly preferable among the above-mentioned other monomer components.

The acrylic resin (B) is a monomer mixture of the polymerizable unsaturated carboxylic acid and the other monomer components, for example, an organic solvent and azobisisobutyronitrile, benzoyl peroxide, t-butyl perbenzoyl. It can be obtained by heating and copolymerizing at 80 to 150 ° C. for about 1 to 10 hours in the presence of a radical polymerization initiator such as octanoate. The molecular weight of the acrylic resin (B) is not particularly limited, but a number average molecular weight of 1,500 to 40,000 is preferable,
More preferably, it is in the range of 2,000 to 20,000.

In the present invention, in order to obtain an acrylic-modified epoxy resin by reacting the bisphenol type epoxy resin (A) with the carboxyl group-containing acrylic resin (B), both are treated with an esterification catalyst such as amine or ammonia. The reaction may be carried out by heating in the presence or absence of a solvent or in the presence or absence of a solvent. The performance of the resin obtained varies depending on the type and amount of catalyst. The amount of the catalyst is usually 0.1 to 3% with respect to 100 parts by weight of the resin solid content used in the reaction.
0 parts by weight is preferred.

As the solvent which can be used in the reaction,
Examples thereof include methoxypropanol, ethylene glycol monobutyl ether, n-butanol, and the like, which are good solvents for all of the epoxy resin (A), the acrylic resin (B), and the acrylic modified epoxy resin which is a reaction product. preferable. When the esterification catalyst is used, the reaction temperature is appropriately about 80 to 120 ° C, and when the catalyst is not used, about 120 to 160 ° C is suitable. The progress of the reaction can be followed by using a generally known method for measuring an acid value, and the reaction is usually completed in 1 to 8 hours.

Bisphenol type epoxy resin (A) and carboxyl group-containing acrylic resin (B) used in the above reaction
The blending ratio of and may be appropriately selected depending on the coating workability and coating film performance, but is usually 1 in the solid content ratio of (A) / (B).
The range of / 1 to 10/1 is preferable, and the range of 2/1 to 9/1 is more preferable.

The acrylic modified epoxy resin obtained by the above reaction has a number average molecular weight of 6,000 to 20,000,
It preferably has an acid value of 25 to 100, and preferably has substantially no epoxy group.

In the present invention, the highly alkoxymethylated phenol formaldehyde resin used together with the acrylic modified epoxy resin has a function as a crosslinking agent and has a number average molecular weight of 200 to 2,000, preferably 400 to 1,200. And, the average number of methylol groups per phenol ring is 0.2 or less, and the average number of alkoxymethyl groups is 0.8 or more, preferably 1.0.
It is a phenol formaldehyde resin which is ~ 2.0 pieces. When the number average molecular weight is less than 200, processability and hygiene are remarkably poor, while the number average molecular weight is 2,000.
When it exceeds, the workability of roll coat coating is deteriorated. The average number of methylol groups per phenol ring is 0.2
If the number exceeds the limit, the number of azomethine bonds produced by the reaction between the methylol group and ammonia, which is a neutralizing agent, increases, which impairs flavor and hygiene and causes yellow discoloration of the coating film. When the number of alkoxymethyl groups per phenol ring is less than 0.8 on average, sufficient curability cannot be obtained and hygiene and processability are impaired.

In the above-mentioned phenol formaldehyde resin, the number of carbon atoms of the alkoxymethyl group is preferably 2 to 8, and specific examples of the alkoxymethyl group include methoxymethyl, ethoxymethyl, n-butoxymethyl,
Examples thereof include isobutoxymethyl and hexoxymethyl groups.

The above-mentioned phenol-formaldehyde resin is
It can be obtained by producing a methylolated phenol resin by a known method, and then etherifying the methylol group with an alcohol by a known method.

In the composition of the present invention, the compounding ratio of the acrylic modified epoxy resin and the highly alkoxymethylated phenol formaldehyde resin is in the range of 5 to 40 parts by weight with respect to 100 parts by weight of the former. Former 100
If the latter is less than 5 parts by weight relative to parts by weight, the curability is poor and hygiene and processability are impaired, while if the latter exceeds 40 parts by weight, the processability, hygiene and flavor of the resulting coating film are impaired. In addition, storage stability is also reduced.

In the composition of the present invention, the acrylic modified epoxy resin is neutralized and dispersed in an aqueous medium, but ammonia is used as a neutralizing agent. When water is dispersed using an organic amine such as dimethylethanolamine or diethanolamine as a neutralizing agent, the viscosity is remarkably increased at the same solid content as compared with the case of dispersing using ammonia. The present inventors believe that the cause of this is the interaction between particles and the hydrogen bond due to the bulkiness of the neutralizing agent itself.

The neutralization equivalent of the acrylic modified epoxy resin with ammonia is 0. 1 with respect to 1 equivalent of the carboxyl group in the resin in view of dispersibility, storage stability and odor of the resin.
It is preferably 6 to 1.4 equivalents. As the neutralizing agent, a small amount of organic amine may be used in combination with ammonia, but the amount of the organic amine is preferably 30 mol% or less based on the total amount of the neutralizing agent.

In the composition of the present invention, the highly alkoxymethylated phenol formaldehyde resin is dissolved or dispersed in an aqueous medium. A method of dissolving or dispersing the acryl-modified epoxy resin and the highly alkoxymethylated phenol formaldehyde resin in an aqueous medium to make them aqueous is, for example, neutralizing a neutralizing agent after mixing these resins, and then neutralizing the neutralized product. Is added to water to make it aqueous, a method of adding water to the neutralized product to make it aqueous, a method of adding the resin mixture to water containing a neutralizing agent to make aqueous, and a neutralizing agent to the resin mixture. Examples include a method of adding water containing water to make it aqueous. Alternatively, the acrylic modified epoxy resin may be neutralized with a neutralizing agent, a phenol formaldehyde resin may be added, and then the mixture may be mixed with water to make it aqueous. Alternatively, the acrylic modified epoxy resin may be neutralized with a neutralizing agent, mixed with water, and then phenol formaldehyde resin may be added thereto.

The resin hydrate obtained as described above can be used after desolvation if necessary. The composition of the present invention may further contain a curing agent such as a melamine resin, a benzoguanamine resin, a urea resin or the like, another aqueous anion resin, a pigment, a paint additive such as a defoaming agent or a leveling agent, and the like. . The solid content concentration of the aqueous coating composition of the present invention is not particularly limited, but usually 20
Used in the range of up to 45% by weight.

The aqueous coating composition of the present invention is a metal such as tin plate, aluminum, tin-free steel, iron, zinc, copper, galvanized steel sheet, alloy-plated steel sheet, etc., and these metals are subjected to phosphate treatment or chromate treatment. It can be applied to chemical conversion treated metal, wood, plastics, concrete, etc. The coating thickness may be appropriately selected depending on the application, but is usually 3 to 20 μm, and roll coating
It can be applied by spray coating, brush coating, roller coating, or the like. The coating film is generally dried at 120 to 25
It can be performed at 0 ° C. for about 10 seconds to about 30 minutes.

When the aqueous coating composition of the present invention is roll-coated for in-can use, the coating viscosity is usually adjusted to 50 to 90 seconds with Ford Cup # 4, and the dry film thickness is about 3 to.
Natural roll coating is applied on a metal plate such as tin plate, aluminum, tin-free steel, etc. so that the thickness becomes about 8 μm, and the temperature reached to the material is about 180 to 240 ° C for about 10 seconds to 20 seconds.
Excellent baking flavor and hygiene,
Also, there is no yellow discoloration of the coating film, and the build-up that causes problems at the end of the coating part has been improved and there is no flow of paint,
It is possible to obtain a coating film with good smoothness and gloss.

[0033]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In the following, "part" and "%" are based on weight.

Production of bisphenol type epoxy resin Production Example 1 (1) Epicoat 828EL (Note 1) 1,000 parts (2) Bis (4-hydroxyphenyl) methane 551 parts (3) Tetraethylammonium bromide 0.2 part Reflux tube (1) to (3) were charged in a four-necked flask equipped with a thermometer and a stirrer, and the reaction was carried out at 140 ° C under a nitrogen stream. The reaction is epoxy equivalent and 40% solution viscosity (25 ℃
And 40% solid content diethylene glycol monobutyl ether diluted resin solution in Gardner-Holt viscosity, the same applies hereinafter), and reacted for about 4 hours to obtain an epoxy equivalent of 10,000, 40% solution viscosity Z ₄ , and a number average molecular weight of about 7, 800 bisphenol type epoxy resin (A-
1) was obtained. (Note 1) Epicoat 828 EL: manufactured by Yuka Shell Epoxy Co., bisphenol A type epoxy resin, epoxy equivalent of about 186, molecular weight of about 350.

Production Example 2 (1) Epicoat 828EL 1,000 parts (2) Bis (4-hydroxyphenyl) methane 607 parts (3) Tetraethylammonium bromide 0.2 parts Four equipped with a reflux tube, a thermometer and a stirrer (1) to (3) were charged in a one-necked flask, and the reaction was carried out at 140 ° C under a nitrogen stream. The reaction is tracked by the epoxy equivalent and the viscosity of the 40% solution, and by reacting for about 4 hours, the epoxy equivalent of 11, 2 is obtained.
00, 40% solution viscosity Z ₅ ⁺ , number average molecular weight about 8,500
To obtain a bisphenol type epoxy resin (A-2).

Production of Carboxyl Group-Containing Acrylic Resin Production Example 3 (1) Methoxypropanol 580 parts (2) Methacrylic acid 160 parts (3) Styrene 232 parts (4) Ethyl acrylate 8 parts (5) Benzoyl peroxide 20 parts Reflux A four-necked flask equipped with a tube, a thermometer, a monomer flow rate controller, and a stirrer was charged with 20% of the mixture of (2) to (5) and (1) in a flask and heated to 95 ° C under a nitrogen stream. The rest of the mixture of (2) to (5) was added dropwise over about 3 hours, and after the completion of the addition, stirring was continued at the same temperature for 2 hours, and then the mixture was cooled to room temperature to obtain an acrylic resin solution (solid content: about 40%). B-1) was obtained. The obtained resin (solid content) had an acid value of 261 and a number average molecular weight of about 7,800.

Production Example 4 (1) Methoxypropanol 580 parts (2) Methacrylic acid 120 parts (3) Styrene 240 parts (4) Ethyl acrylate 40 parts (5) Benzoyl peroxide 20 parts Reflux tube, thermometer, monomer flow rate A four-necked flask equipped with a regulator and a stirrer was charged with 20% of the mixture of (2) to (5) and (1) in the flask and heated to 95 ° C under a nitrogen stream (2) to (5). The rest of the mixture was added dropwise over about 3 hours, and after the addition was completed, stirring was continued for 2 hours at the same temperature and then cooled to room temperature to obtain an acrylic resin solution (B-2) having a solid content of about 40%. . The obtained resin (solid content) had an acid value of 195 and a number average molecular weight of about 6,900.

Production of Phenol Formaldehyde Resin Production Example 5 (1) Bisphenol A 228 parts (2) 37% formalin water 324 parts (3) 20% aqueous sodium hydroxide solution 5 parts (4) 20% sulfuric acid aqueous solution 6.1 parts ( 5) n-Butanol 300 parts (6) Phosphoric acid 5 parts (7) n-Butanol 600 parts (1) to (3) were charged in a four-necked flask equipped with a reflux tube, a thermometer and a stirrer, and a nitrogen stream was introduced. The reaction was carried out at 70 ° C in the middle. In the reaction, the amount of unreacted formaldehyde was traced by a known method, and by reacting for about 8 hours, a methylolated phenol resin having an average of 3.2 methylol groups added per bisphenol molecule was obtained. After adding (4) and (5) to the product and concentrating under reduced pressure, (6) and (7) were added and the reaction was carried out at the reflux temperature. The reaction followed the decrease of methylol groups by infrared spectrum. By reacting for about 6 hours, a phenol resin solution having a solid content of 70% (C-
1) was obtained. The obtained resin was alkoxymethylated on the average of 3.0 per bisphenol nucleus, and had a number average molecular weight of about 980.

Production Example 6 In Production Example 5, the compositions of (1) to (7) are changed to the following compositions, and the time for the etherification reaction of the methylol group is changed from about 6 hours to about 8 hours. Except for this, the same procedure as in Production Example 5 was carried out to obtain a phenol resin solution (C-2) having a solid content of 70%. The obtained resin is bisphenol nucleus 1
The average number of 2.8 was alkoxymethylated, and the number average molecular weight was about 1,250. (1) Bisphenol A 228 parts (2) 37% formalin water 324 parts (3) 20% sodium hydroxide aqueous solution 5 parts (4) 20% sulfuric acid aqueous solution 6.1 parts (5) amyl alcohol 350 parts (6) phosphoric acid 5 parts (7) Amyl alcohol 600 parts

Production Example 7 (1) p-cresol 108 parts (2) 37% formalin water 163 parts (3) 20% sodium hydroxide aqueous solution 3 parts (4) 20% sulfuric acid aqueous solution 3.66 parts (5) n- Butanol 300 parts (6) Phosphoric acid 4 parts (7) n-Butanol 300 parts (1) to (3) were charged in a four-necked flask equipped with a reflux tube, a thermometer, and a stirrer at 70 ° C. in a nitrogen stream. By heating for about 4 hours, an average of 1.
A methylolated phenolic resin having 9 methylol groups added was obtained. After adding (4) and (5) to this product and concentrating under reduced pressure, (6) and (7) were added and the mixture was refluxed at about 3
By performing the reaction for time, a phenol resin solution (C-3) having a solid content of 70% was obtained. The obtained resin was alkoxymethylated on the average of 1.8 per 1 molecule of p-cresol and had a number average molecular weight of about 420.

Production Example 8 (for comparison) (1) Bisphenol A 228 parts (2) 37% formalin water 324 parts (3) 20% aqueous sodium hydroxide solution 5 parts (4) 20% sulfuric acid aqueous solution 6.1 parts (5 ) Butanol 300 parts (1) to (3) were charged into a four-necked flask equipped with a reflux tube, a thermometer, and a stirrer, and the reaction was carried out at 70 ° C. for about 8 hours in a nitrogen stream, and then (4) and (5). ) Was added and concentrated under reduced pressure to obtain a phenol resin solution (D-1) having a solid content of 70%. The obtained resin was a phenol resin having an average of 3.2 methylol groups added per molecule of bisphenol and had a number average molecular weight of 324.

Production Example 9 (for comparison) (1) p-cresol 108 parts (2) 37% formalin water 163 parts (3) 20% sodium hydroxide aqueous solution 3 parts (4) 20% sulfuric acid aqueous solution 3.66 parts ( 5) n-Butanol 300 parts A four-necked flask equipped with a reflux tube, a thermometer and a stirrer was charged with (1) to (3), and the reaction was carried out at 70 ° C for about 4 hours in a nitrogen stream, and further (4). And (5) were added and concentrated under reduced pressure to obtain a phenol resin solution (D-2) having a solid content of 70%. The obtained resin was a phenol resin having an average of 1.9 methylol groups added per molecule of p-cresol and had a number average molecular weight of 165.

Example 1 (1) 80 parts of the epoxy resin (A-1) obtained in Production Example 1 (2) 50 parts of the acrylic resin solution (B-1) obtained in Production Example 3 (3) Methoxypropanol 69. 8 parts (4) N, N-dimethylaminoethanol 0.2 part (5) Phenolic resin solution (C-1) obtained in Production Example 5 21.4 parts (6) Aqueous ammonia solution (concentration 25%) 7.2 Parts (7) Deionized water 171.0 parts (1) to (3) were charged into a four-necked flask equipped with a reflux tube, a thermometer, and a stirrer, heated to 100 ° C. and dissolved, and then (4) was added. In addition, the temperature was maintained and the reaction was carried out for about 6 hours to obtain an acrylic modified epoxy resin solution. This reaction was confirmed by measuring the acid value of the resin. The obtained resin (solid content) has an acid value of 49 and a number average molecular weight of about 8,900.
Met. The temperature of the resulting acrylic-modified epoxy resin solution was adjusted to 60 ° C., (5) was added, (6) was further added to neutralize, and (7) was gradually added to perform water dispersion. Then, the solution was concentrated under reduced pressure to remove excess solvent to obtain an aqueous coating composition. The resulting composition has a solid content of about 42% and a pH of 7.
7. Viscosity (B type viscometer, 25 ° C, the same below) is 120 cp
s and the emulsion particle size of the composition is 0.30 μm
Met.

Examples 2 to 6 and Comparative Examples 1 to 5 In Example 1, (1) type and amount of epoxy resin, (2) type and amount of acrylic resin solution, (5) type and amount of phenol resin solution And (6) the same procedures as in Example 1 except that the type and neutralization equivalent of the neutralizing agent were as shown in Table 1 to obtain aqueous coating compositions having a solid content of about 42%. Table 1 shows the pH, viscosity, and emulsion particle size of the obtained composition.

[0045]

[Table 1]

The aqueous coating compositions obtained in each of the examples and comparative examples were tested for roll coatability and storage stability. The test results are shown in Table 2 below. These test methods are as follows.

Roll coating suitability: The viscosity of the emulsion is adjusted to about 85 seconds with a Ford cup # 4, and natural film thickness is 5 to 8 μm after baking on tin-free steel (TFS) with a roll coater. Painted 20
After baking at 0 ° C for 10 minutes, the coating surface smoothness,
Gloss, edge build-up, sagging, etc. were evaluated comprehensively. The case where there was no abnormality and which showed a good appearance was marked with ◯. When the surface smoothness is poor ... TH, when the build-up is remarkable ... BU is displayed. Storage stability: Adjust the solid content of the emulsion to 30%,
Store at 50 ° C for up to 3 months and separate emulsion,
The state of sedimentation and aggregation was visually evaluated. Good ones without these abnormalities were evaluated as ◯.

Further, the respective aqueous coating compositions obtained in Examples 1 to 6 and Comparative Examples 1 to 5 were coated on a tin-free steel plate or a 100 μm aluminum foil so that the dry film thickness was about 6 μm. The coated plate was obtained by baking at 10 ° C for 10 minutes. The coated plate obtained by coating on a tin-free steel plate was tested for workability, retort resistance, adhesion and coating yellowing degree. In addition, hygiene and flavor tests were carried out on a coated plate coated on aluminum foil. The test results are shown in Table 2 below.

Each of the above tests was conducted according to the following test methods. Processability: Fold the coated plate in two with the coating film on the outside,
Place two tin-free steel plates between the folded test pieces.
After the sheet is sandwiched and bent for 2T, 6.
The current value (mA) in the width of the processed portion of 2 cm was measured when a voltage of 5 V was applied for 6 seconds. The smaller the value, the better the workability. Retort resistance: The coated plate is immersed in water and treated in an autoclave at 125 ° C. for 30 minutes to determine the whitening state of the coating film. ○: No whitening, × marked whitening

Adhesion: Two coated plates (150 mm x 5.0 m)
Nylon film is sandwiched between the coated surface of m) and the surface to be adhered, and this is heated at 200 ° C for 60 seconds and then 200 ° C.
A test piece was prepared by pressing nylon for 30 seconds to fuse both coating films to each other. Next, the T-peel adhesive strength of this test piece was measured by a tensile tester (Shimadzu Autograph AGS-500A).
Was measured at a tension rate of 200 mm / min and a temperature of 20 ° C. The value was an average value of 5 times. Those having a T-peel adhesive strength of more than 3 kg / 5 mm were rated as ◯ and those having a T-peel adhesive strength of 3 kg / 5 mm or less were rated as x.

Hygiene: A test panel coated on 100 μm aluminum foil was placed in a heat-resistant glass bottle with a ratio of application area: activated carbon treated tap water of 1 cm ² : 1 cc, covered, and autoclaved. Was treated at 125 ° C. for 30 minutes, and the content liquid was measured according to the test method described in the Food Sanitation Law (Ministry of Health and Welfare No. 434). Consumption is expressed in ppm.

Flavor: A test panel coated on 100 μm aluminum foil was placed in a heat-resistant glass bottle so that the ratio of coating area: activated carbon treated tap water was 2 cm ² : 1 cc, and the lid was closed in an autoclave. A treatment is carried out at 125 ° C. for 30 minutes to carry out a flavor test of the content liquid.
The case where no change was observed is marked as ○. Yellowing degree of coating film: The yellowing degree was evaluated by visually observing the test panel coated on the tin plate. ○: Almost no coloration ×: Remarkably yellowing

[0053]

[Table 2]

[0054]

EFFECTS OF THE INVENTION The composition of the present invention is extremely excellent in roll coat coating workability, and can be built even by roll coat coating.
It is possible to form a coating film that does not have a problem of up. Further, the coating film obtained from the composition of the present invention has no yellow discoloration of the coating film and has good hygiene properties, flavor properties, adhesion properties, processability, retort resistance, chemical resistance and the like. Therefore, the composition of the present invention is particularly suitable for roll-coating the inner surface of a can for food and drink.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Ichiro Yoshihara 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd.

Claims (5)

[Claims] 1. Epoxy equivalent of 8,000 to 18,000
And 100 parts by weight of an acrylic modified epoxy resin obtained by reacting a bisphenol type epoxy resin (A) having a number average molecular weight of 3,500 to 10,000 by gel permeation chromatography with a carboxyl group-containing acrylic resin (B) On the other hand, the number average molecular weight of 200-
Highly alkoxymethylated phenol formaldehyde resin having a number of 2,000 and an average number of methylol groups of 0.2 or less and an average number of alkoxymethyl groups of 0.8 to 2.5 per phenol ring. An aqueous coating composition comprising 5 to 40 parts by weight, wherein the acrylic modified epoxy resin is neutralized with ammonia and dispersed in an aqueous medium. 2. The aqueous coating composition according to claim 1, wherein the alkoxymethyl group in the phenol formaldehyde resin has 2 to 8 carbon atoms. 3. A carboxyl group-containing acrylic resin (B)
3. The aqueous coating composition according to claim 1, which has a resin acid value of 130 to 500. 4. The mixing ratio in the reaction of the bisphenol type epoxy resin (A) and the carboxyl group-containing acrylic resin (B) is 1/1 to 1 in terms of the solid content ratio of (A) / (B).
It is 0/1, The aqueous coating composition in any one of Claims 1-3. 5. A method for forming a coating film, which comprises coating the aqueous coating composition according to claim 1, 2, 3 or 4 on a metal plate by roll coating and baking.