JPH0694541B2 - Water-based paint for inner surface of can - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a water-based paint for the inner surface of a can, and in particular, it contains a beverage such as a carbonated beverage or an alcoholic beverage, which does not favor the deterioration of flavor. The present invention relates to a water-based paint useful for protecting the inner surface of a metal can.

(Prior Art) Conventionally, in the can manufacturing industry, there have been problems such as air pollution and deterioration of working environment due to organic solvent-based paints, and a shift to water-based paints is desired. In recent years, as a means for avoiding these problems, a water-based paint containing a self-emulsifying epoxy resin as a main component has been proposed. For example, JP-A-56-109243 discloses an aqueous coating composition of an esterification reaction composition of a carboxyl group-functional acrylic resin and an epoxy resin, and JP-A-53-1228 discloses a carboxyl group-functional compound. A graft polymer epoxy resin emulsion is further disclosed in JP-A-57-
Japanese Patent No. 105418 discloses an aqueous coating composition comprising a polymerization reaction composition of an epoxy resin modified with acrylic acid or methacrylic acid and an acrylic monomer.

The above self-emulsifying epoxy resin itself has excellent physical properties such as adhesion to metals, water resistance, and processability required as a paint for the inner surface of a can, and it has been put to practical use in some parts. When the contents are carbonated drinks containing fruit juice, fruit juice drinks, or alcoholic drinks such as shochu, wine, etc., the flavor of these drinks is not as good as the conventional can inner surface paint. It came to be recognized that it could not be retained.

(Problems to be Solved by the Invention) As a result of investigations by the inventors on improving the flavor characteristics of the self-emulsifying epoxy resin, the vinyl chloride resin as a can inner surface protective coating film has excellent flavor characteristics. The present invention has been arrived at by paying attention to the fact that it is present.

[Structure of Invention]

(Means for Solving Problems) That is, according to the present invention, a self-emulsifying epoxy resin (A) obtained by neutralizing a part or all of carboxyl groups introduced into a molecule with amine or ammonia is used. A water-based paint for the inner surface of a can, which is composed of a vinyl chloride resin (B) polymerized in the presence of a Japanese acrylic resin and has excellent flavor characteristics.

The vinyl chloride resin (B) aqueous dispersion in the present invention is
It is obtained by polymerizing vinyl chloride and, if necessary, other copolymerizable monomers with an aqueous dispersion of a resin obtained by neutralizing a carboxyl group-containing acrylic resin with a basic substance as a dispersion medium.

As the carboxyl group-containing acrylic resin, acrylic acid or methacrylic acid is used as an essential component,
In addition, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and 2-ethylhexyl acrylate, aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene, maleic acid Α or β-ethylenically unsaturated dicarboxylic acid mono or diesters such as mono or dibutyl, mono or dioctyl fumarate, vinyl acetate,
It is a copolymer of vinyl esters such as vinyl propionate, vinyl ethers, unsaturated nitriles such as acrylonitrile and methacrylonitrile, olefins such as ethylene, butadiene and isoprene, vinyl chloride, vinylidene chloride and chloroprene.

The polymerization reaction of acrylic resin preferably has a boiling point of 70-23.
Azobisisobutyronitrile, in a hydrophilic organic solvent at 0 ° C, for example, ether alcohols such as methyl cellosolve and butyl cellosolve, and ether esters such as methyl cellosolve acetate and ethyl cellosolve acetate,
60 to 150 using radical polymerization initiator such as peroxide
It can proceed at ° C.

To make the obtained acrylic resin into an aqueous resin dispersion,
In the acrylic resin solution, basic compounds such as monomethylamine, monoethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, monomethanolamine, dimethanolamine, triethanolamine, dimethylaminoethanol, and other amines,
Inorganic basic compounds such as caustic potassium, caustic soda and aqueous ammonia are added, partially or completely neutralized, and after mixing and stirring, a predetermined amount of water or a mixture of water and an organic solvent is added.

The vinyl chloride resin (B) aqueous dispersion of the present invention is obtained by emulsion polymerization of vinyl chloride or a mixture of vinyl chloride and a copolymerizable monomer in the presence of the acrylic neutralized acrylic resin obtained by the above-mentioned method. It can be obtained by

Monomers copolymerizable with vinyl chloride include vinyl acetate, vinyl stearate and other vinyl esters, methyl vinyl ether, cetyl vinyl ether and other vinyl ethers, acrylic acid, methacrylic acid or their esters, styrene, α-methylstyrene. And other aromatic vinyl compounds.

Vinyl chloride is used in a monomer composition ratio in the range of 30 to 100% by weight. If it is less than 30% by weight, it has an adverse effect on the hygiene properties and flavor storability, which are the characteristics of vinyl chloride resins, and is not preferable.

The aqueous dispersion of the vinyl chloride resin (B) is prepared by adding a monomer containing vinyl chloride to an aqueous dispersion of an alkali-neutralized acrylic resin and stirring with water as a medium, for example, potassium persulfate, ammonium persulfate, It can be obtained by carrying out a polymerization reaction using an aqueous polymerization initiator composed of a redox catalyst in which hydrogen peroxide or a peroxide thereof is combined with a reducing agent. At this time, the alkali-neutralized acrylic resin is used in the range of 3 to 60 parts by weight with respect to 100 parts by weight of the vinyl chloride-containing monomer.

The self-emulsifying epoxy resin (A) of the present invention is obtained by introducing a carboxyl group derived from acrylic acid or methacrylic acid into a bisphenol type epoxy resin and dispersing it in an aqueous medium in the presence of the basic compound described above. Is.
For example, a self-emulsifying epoxy resin can be obtained by subjecting an acrylic resin made of a monomer copolymerizable with acrylic acid or methacrylic acid as an essential component and an epoxy resin to an esterification reaction in a hydrophilic organic solvent. .

The water-based paint for the inner surface of a can of the present invention has a composition ratio (A) / (B) of 90 in terms of the resin dispersion of the self-emulsifying epoxy resin (A) and the vinyl chloride resin (B). / 10 ~ 20/80
Blend so that If the amount of component (A) exceeds 90 parts by weight, the flavor characteristics will be poor, and the amount of component (B) will be 80%.
If it exceeds the parts by weight, the water resistance tends to be poor.

The water-based paint for the inner surface of a can of the present invention is applied to a can material by a usual coating method such as roll coating or spray coating.
The protective coating can be formed on the inner surface of the metal can by baking at 1.5 ° C. for 1.5 to 3 minutes.

Hereinafter, the present invention will be specifically described with reference to examples. In the examples, "part" and "%" mean "part by weight" and "% by weight", respectively.

(Example) Example 1 (a) Production of acrylic resin Styrene 300 parts Ethyl acrylate 210 parts Methacrylic acid 90 parts Butyl cellosolve 388 parts Benzoyl peroxide 12 parts 1/4 of the mixture of the above composition was substituted with nitrogen. Place in a necked flask, heat to 80-90 ℃, and maintain the temperature while keeping the rest.
Gradually add 3/4 over 2 hours, and after the addition is complete, stir at that temperature for 2 hours and then cool to obtain a resin solution with acid value 93 (solid content conversion), solid content 59.7%, and viscosity 4100 cps. It was

(B) Manufacture of epoxy resin solution Epicoat 1007 500 parts Butyl cellosolve 333.3 parts The total amount was charged into a 4-necked flask replaced with nitrogen gas, gradually heated to raise the internal temperature to 100 ° C, stirred for 1 hour, and then completely dissolved. Then, it was cooled to 80 ° C to obtain an epoxy resin solution with a solid content of 60%.

(C) Manufacture of self-emulsifying epoxy resin water dispersion 100 parts of acrylic resin solution of (a) 100 parts of epoxy resin solution of (b) 50 parts 2-Dimethylaminoethanol 9.3 parts Deionized water 290.7 parts In a 4-neck flask The whole amount of was charged, and while stirring, was added to neutralize the contained carboxyl groups in an approximately equimolar amount, the internal temperature was raised to 80 ° C., the mixture was stirred for 30 minutes, and then cooled to room temperature. The reduction rate of oxirane was 63.5%, and the viscosity was 1.5 times higher than before the reaction. When added little by little while stirring, the solid content was 19.8% and the viscosity was 360c.
A ps aqueous dispersion was obtained.

(D) Production of alkali-neutralized acrylic resin water dispersion 100 parts of the acrylic resin solution of (a) 2-dimethylaminoethanol 8.6 parts ion-exchanged water 190 parts The total amount was charged into a 4-necked flask substituted with nitrogen gas, After heating to 60 ° C with stirring, was gradually added dropwise. Ten
After stirring for 1 minute, the mixture was cooled to room temperature and added little by little over 30 minutes to obtain an aqueous dispersion having a solid content of 20%, a viscosity of 130 cps and a pH of 6.9.

(E) Manufacture of vinyl chloride resin water dispersion Ion-exchanged water 50 parts Acrylic resin water dispersion of (d) 125 parts Vinyl chloride 100 parts Ammonium persulfate 10% solution 4 parts Nitrogen-gas substituted stainless steel autoclave with stirring device Then, and were mixed with 70 parts by weight while stirring. Then, after heating to 55 ° C, was added to start the reaction. The reaction proceeded while gradually adding 30 parts so that the internal pressure became constant, and stirring was continued until the internal pressure reached 0 kg / cm ₂ after the addition was completed. A uniform aqueous dispersion having a solid content of 31.5%, a viscosity of 10 cps and a pH of 8.4 was obtained.

(F) Preparation of paint Self-emulsifying epoxy resin water dispersion 300 of (c) above
Parts 81 parts of the above-mentioned (e) vinyl chloride resin aqueous dispersion were placed in a beaker and stirred to obtain a uniform aqueous coating. The solid content ratio was 70% self-emulsifying epoxy resin and 30% vinyl chloride resin.

(G) Flavor property test of water-based paint A glass rod having a diameter of 5 mm was dipped in the water dispersion of the sample and then pulled up to prevent spontaneous fall, and then baked in an electric oven set at 180 ° C for 4 minutes. The glass rod was immersed in 300 mm of carbonated drinking water which had been taken in a wide-mouthed bottle in advance and sealed, and then stored at 35 ° C for 2 months. Next, a taste test was carried out by 10 panelists using carbonated drinking water, which was kept at 35 ° C. without a glass rod baked with paint, as a standard solution, and scored.
When the statistical processing was performed based on the evaluation scores of the obtained panelists, almost no change in taste was observed.

(D) Paint test of water-based paint A sample was applied to a 0.2 mm thick aluminum plate using a No. 18 bar coater, and then placed in an electric oven set at 180 ° C.
Baked for a minute.

After immersing this coated plate in boiling water for 3 minutes and observing the whitening state of the coating film and evaluating the water resistance, no change was observed in the coating film.

Next, when a cellophane tape was pressure-bonded to the surface of the coating film on the coated plate and then rapidly peeled off to observe the state where the coating film peeled from the base metal, and the adhesion was evaluated, no peeling of the coating film was observed.

Example 2 Using the alkali-neutralized acrylic resin prepared in Example 1, an aqueous dispersion of vinyl chloride resin having the monomer composition shown in Table 1 was produced. The amount of acrylic resin used was 25 parts per 100 parts of the monomer mixture containing vinyl chloride. Next, the self-emulsifying epoxy resin produced in Example 1 and the proportion shown in Table 1 were placed to produce an aqueous coating, and the same flavor test as in Example 1 was conducted. The results of the flavor test are shown in Table 1 by classifying them into the following four stages.

A: Almost no change in taste O: A slight change in taste is observed.

Δ: A change in taste is recognized.

X: The taste has changed significantly.

The abbreviations of the compounds shown in the table are as follows.

VC: Vinyl chloride VAc: Vinyl acetate BA: Butyl acrylate MAA: Methacrylic acid [Effects of the Invention] The water-based paint of the present invention contains a vinyl chloride resin having excellent flavor characteristics, and therefore improves the performance of a water-based paint containing a self-emulsifying epoxy resin as a main component, which has a difficulty in flavor characteristics. It is possible to expand the range of application as a paint for the inner surface of water cans. In addition, since the vinyl chloride resin is water-dispersed with the alkali-neutralized acrylic resin, it has excellent adhesion to the metal surface itself, and the water resistance required as a paint for the inner surface of the can is also good. .

Claims (1)

[Claims] 1. A self-emulsifying epoxy resin, which is a partial reaction product of a carboxyl group-containing acrylic resin obtained by neutralizing a part or all of carboxyl groups introduced into a molecule with amine or ammonia and a bisphenol type epoxy resin. A) An aqueous dispersion and a vinyl chloride resin (B) aqueous dispersion polymerized in the presence of an alkali-neutralized acrylic resin, wherein (A) / (B) is 90 / by weight of the resin component. 10 ~ 2
A water-based paint for the inner surface of cans with excellent flavor characteristics of 0/80.