JPH04198374A - Resin composition for aqueous coating for outside of metal can - Google Patents

Abstract

PURPOSE:To obtain the title composition having excellent storage stability and capable of providing coating film having good processability, hardness, adhesion, etc., by blending a specific copolymer resin with an alkyletherified methylol melamine resin capable of diluting with water at a definite ratio. CONSTITUTION:The objective composition obtained by blending (A) a copolymer resin obtained by copolymerizing (i) a vinyl monomer containing >=5wt.% carboxyl group-containing vinyl monomer and >=5wt.% vinyl monomer expressed by the formula (R is H or methyl) as essential components and containing a hydroxyl group, glycidyl group and (alkoxy)methylolamide group with (ii) other vinyl monomer and having 1000-50000wt. average molecular weight with (B) an alkyletherified methylolmelamine resin capable of diluting with water, being 20-95 to 80-5 in blend ratio of the component A to the component B and obtained by neutralizing a carboxyl group contained in the component A with amines at an amount of 0.3-2.0 equivalent weight.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a water-dilutable paint resin composition, which has excellent stability against thinning of the paint due to hydrolysis after dilution with water, and which can be obtained The coating film relates to a resin composition for water-based paint on the exterior surface of metal cans that has good physical properties such as processability, hardness, and adhesion.

[Prior art]

Various thermosetting resins are used as paints for the exterior of cans. For example, thermosetting acrylic resins using amino resin as a crosslinking agent, thermosetting polyester resins, or epoxy resins can be used in combination with the same size. Various coating films required depending on the type of content, molding method, etc. Various resins are used depending on their physical properties.

Furthermore, since paints for the exterior of cans have generally been applied diluted with organic solvents, the thermosetting resins used have also been soluble in organic solvents.

However, recently it has been volatilized during heat curing! Due to the problems of environmental pollution and toxicity of solvents to the human body, there is an increasing demand for thermosetting paint resins that can be diluted with water.

Resins that can be diluted with water are obtained by increasing the carboxyl group concentration in the resin composition of the thermosetting acrylic resin or polyester resin mentioned above, and neutralizing it with amines.
A common method is to increase the hydrophilicity of the resin to make it dilutable with water.

However, paints using water-dilutable resins obtained in this manner have various advantages and disadvantages in practical applications.

For example, in the case of polyester resin, the concentration of organic solvent in the paint can be significantly reduced, and it has the advantage of being excellent in processability of the paint film, but the hardness of the paint film is inferior, and the solvent is A fatal drawback is that some water causes hydrolysis of the resin, causing the paint to become thinner over time. In addition, acrylic resins have excellent hydrolyzability and can provide a hard coating film, but they have poor processability, and commercially available water-dilutable acrylic resins already have organic solvents mixed into the resin. This has the disadvantage that it is difficult to reduce the concentration of organic solvent in the paint.

[Problems to be Solved by the Invention] As a result of intensive study by the present inventors to solve the above problems,
It was discovered that by utilizing the excellent hydrolyzability of water-dilutable acrylic resins, it was possible to significantly reduce the concentration of organic solvents in paints within a specific molecular weight range. It was discovered that a coating film with excellent hardness and workability can be obtained by copolymerizing acid ester compounds, and this led to the completion of the present invention.

That is, the resin composition for a water-based paint on the exterior surface of a metal can of the present invention contains (a) 5% by weight of a vinyl monomer containing a carboxyl group.
Contains as an essential component 5% by weight or more of a vinyl monomer represented by the above and the general formula (R in the formula represents a hydrogen atom or a methyl group), and contains a hydroxyl group, a glycidyl group, a methylolamide group. , a copolymer resin made by copolymerizing one or more vinyl monomers containing an alkoxymethylolamide group and another vinyl monomer and having a weight average molecular weight specified in the range of 1,000 to 50,000; (b) water dilutable; an alkyl etherified methylol melamine resin, and the blending ratio of the copolymer resin (a) and the alkyl etherified methylol melamine resin is (a)/ra) = (20 to 95)/ (80-5)
(resin solid content ratio %), and the carboxyl group contained in the copolymer resin (a) is reduced by 0.3 to 2.0 by amines.
It is characterized by equivalent neutralization. The following are representative examples of the constituent components of the copolymer resin (a) in the present invention.

Examples of vinyl monomers containing carboxyl groups include (meth)acrylic acid, itaconic acid, fumaric acid, (anhydride)
Examples include maleic acid, and these vinyl monomers may be used alone or in combination. If the amount of copolymerization is 5% by weight or more, preferably 5 to 30% by weight, but less than 5% by weight, the dilution of the resulting paint with water may be poor and resin precipitation may occur.

The vinyl monomer represented by the general formula is isobornyl (
Examples include meth)acrylates. Copolymerization amount is 5% by weight
As mentioned above, if the content is preferably 5 to 30% by weight and 5% by weight or less, the hardness and processability of the cured coating film will be poor and the required properties will not be satisfied.

In addition, examples of vinyl monomers containing hydroxyl groups include β-hydroxyethyl (meth)acrylate, β
-Hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc., and examples of vinyl monomers containing a glycidyl group include (methyl)glycidyl (meth)acrylate, etc., vinyl monomers containing a methylolamide group. Monomers include, for example, N-methylol (meth)acrylamide, and vinyl monomers containing an alkoxymethylolamide group include, for example, methoxymethylol (meth)acrylamide, ethoxymethylol (meth)acrylamide, and propoxymethylol (meth)acrylamide. Examples include acrylamide, butoxymethylol (meth)acrylamide, and the like.

Typical examples of other vinyl monomers that do not have such functional groups include styrene, α-methylstyrene, paramethylstyrene, vinyltoluene, methyl (meth)acrylate, ethyl (meth)acrylate. Examples include alkyl esters of (meth)acrylic acid such as.

The molecular weight of the copolymer resin (a) in the present invention is specified in a weight average molecular weight range of 1,000 to 50,000, but when the weight average molecular weight is 1,000 or less, the processability of the resulting coating film tends to be significantly inferior, When it is 50,000 or more, it becomes difficult to reduce the amount of organic solvent in the paint.

The weight average molecular weight measurement described in the present invention is carried out by gel permeability chromatography (hereinafter abbreviated as GPC).

The measurement conditions at this time were: tetrahydrofuran was used as the solvent, the sample concentration was 0.00175 g/a, and the column temperature was 4.
0°C1 flow rate 1.0 j11! /win, detector is R
1 (SHO[]EXRI 5E-11 type x32), and the column conditions were GMHXL.

G2000) IXL (manufactured by TO5O■) in series, and standard polystyrene is used for the calibration curve.

The water-dilutable alkyl etherified methylol melamine resin (b) of the present invention is a low molecular weight methyl etherified methylol melamine resin (for example, cymel 30
3.350 (manufactured by Mitsui Sui Anamitsu Ltd.) or methyl-butyl (or other alkyl) mixed etherified methylol melamine resin, which can be diluted with water, can all be used.

In the resin composition for water-based paint on the outer surface of metal cans of the present invention, the copolymer resin (a) is 95 to 20%, and the alkyl etherified methylolmelamine resin (a) is 5 to 80%, but preferably (a). ) is 95-50%, and ■) is 5-50%.
is optimal.

Typical examples of amines used to neutralize the carboxyl groups contained in the copolymer resin (a) include aqueous ammonia, diethylamine, monoethanolamine, jetanolamine, monoisopropanolamine, Morpholine, 2-amino-2-methyl-1-
propatool, triethylamine, N,N-dimethylethanolamine, N,N-diethylethanolamine,
Examples include primary, secondary, and tertiary alkylamines and alkanolamines such as N-methyl-jetanolamine, triethanolamine, and triisopropanolamine, and these amines may be used alone or in combination. However, the neutralization rate of carboxyl groups by these amines is 0.3 to 2 based on the equivalent amount of amines to carboxyl groups.
．． If the amount is less than 0.3 equivalents, the water dilutability of the paint will be poor, resulting in resin precipitation, and if it is more than 2.0 equivalents, the resulting paint will have a strong amine odor, which is not favorable for the working environment. becomes.

Water-dilutable epoxy resin block urethane resin, phenol resin, etc. are added to the resin composition for water-based paint on the outside surface of metal cans of the present invention in order to improve adhesion to metals, and the smoothness of the coating film surface is improved. When applying any known coating film improvement method such as adding additives etc., the structure, blending ratio and neutralization rate of the copolymer resin and alkyl etherified methylol melamine resin in the paint resin composition will improve according to the present invention. If it falls within the scope defined in , it shall fall within the scope of this claim.

Furthermore, although the coating resin composition of the present invention is used diluted in water, water-soluble organic solvents such as alcohols,
There is no problem in using glycol ethers, etc., and it is desirable to use them within the allowable range of the working environment.

Colored paints can also be produced by using organic pigments and inorganic pigments (rust-preventing pigments, extender pigments, metal powder pigments, etc.) as necessary, using any known paint-forming method, such as mixing, or dissolving or mixing in a solvent. can do.

The obtained paint is applied to a metal can or plate using a roll coater or a known coating machine, and heated at 150 to 240°C for 1 to 30 minutes.
By heating for 30 minutes to form a cured coating film, excellent coating performance such as hardness, workability, and adhesion can be obtained.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples, and all parts and percentages are based on weight unless otherwise specified.

Production Example 1 15 parts of styrene, 15 parts of methyl methacrylate, 5 parts of butyl acrylate, 120 parts of isobornyl acrylate, 2-
Weigh out 15 parts of hydroxyethyl methacrylate, 10 parts of methacrylic acid, and 10 parts of azobisisobutyronitrile into a glass container, mix and stir to completely dissolve the azobisisobutyronitrile, and then add 200 parts of roughened butyl cellosolve. A reactor equipped with a thermometer, a stirrer, a reflux condenser, and a solvent recovery device was heated to 140
The above mixture was added dropwise using a dropping funnel over a period of 5 hours at a temperature below C.

Thereafter, stirring was continued for 1 hour at 140°C, and further 0.5 part of azobisbutyronitrile was added.

After further stirring under the same temperature conditions for 3 hours, butyl cellosolve was removed from the system and the heated residue (JISK 54
A vinyl copolymer resin of 000% was obtained.

Dimethylethanolamine was added to the obtained vinyl copolymer resin in an amount of 1.0 equivalent to the carboxyl group, and after thorough stirring, pure water was added until the heating residue was 50%.
I adjusted it so that The resulting resin had a number average molecular weight of 1,500 and a weight average molecular weight of 40,000.

Manufacturability 2 Styrene 15 parts, methyl methacrylate 15 parts, butyl acrylate 5 parts, ethyl acrylate 20 parts, isobornyl methacrylate 20 parts, 2-hydroxyethyl acrylate 15 parts, methacrylic acid 10 parts and azobisiso A vinyl copolymer resin was synthesized using 10 parts of butyronitrile in the same manner as in Production Example 1.

The resulting resin had a heating residue of 50%, a number average molecular weight of 1,600, and a weight average molecular weight of 45,000.

Comparative Production Example 1 20.5 parts of styrene, 20.5 parts of methyl methacrylate,
Butyl acrylate 6.8 parts, ethyl acrylate 27.2 parts
parts, 15 parts of 2-hydroxyethyl methacrylate, 10 parts of methacrylic acid, and 10 parts of abbisisobutyronitrile.
After weighing 200 parts of butyl cellosolve into a glass container and stirring, use a thermometer containing 200 parts of butyl cellosolve in advance.
A reactor equipped with a stirrer, a reflux condenser, and a solvent recovery device was heated, and the above mixture was added dropwise using a dropping funnel at 140° C. over 5 hours.

Thereafter, stirring was continued for 1 hour at 140'C, and 0.5 part of azobisisobutyronitrile was further added. After further stirring under the same temperature conditions for 3 hours, the butyl cellosolve was removed from the system and a vinyl copolymer resin with a heating residue of 100% was replaced.

Dimethylethanolamine was added to the obtained vinyl copolymer resin in an amount of 1.0 equivalent to the carboxyl group, and after thorough stirring, pure water was added until the heating residue was 5.
Adjusted so that it was 0%. The resulting resin had a number average molecular weight of 1,400 and a weight average molecular weight of 38,000.

Comparative Production Example 2 PPG PIN-1500 (manufactured by Mitsui Toatsu Chemical Co., Ltd., hydroxylated 110.KOHmg/g, ) 14.2
part, neopentyl glycol 29.06B, adipic acid 19.7 parts, trimellitic anhydride 17.3 parts with a thermometer,
It was charged into a reactor equipped with a stirrer, a reflux condenser, and a solvent recovery device, and the temperature was raised to 180"C. While stirring was continued, the reaction distillate water was removed from the system. Acid value (JrS, K 54
008-5-1) Measurement method) is 50. KOH #l g
After the dehydration condensation reaction was carried out until the reaction mixture reached 1.0 / H, dimethylethanolamine was added in an amount of 1.0 equivalent to the carboxyl group, and stirring was continued. Further, pure water was added to adjust the heating residue to 50%. The resulting resin had a number average molecular weight of 1,800 and a weight average molecular weight of 38,000.

Example 1.2 and Comparative Examples 1-3 Commercially available product Cymel 3o3 (Mitsui Suyanamitsu ■) as a water-dilutable alkyl etherified methylol melamine resin
A thermosetting paint resin composition was prepared using the formulations shown in Table 1 using the following materials:

The coating resin compositions obtained in Example 1.2 and Comparative Examples 1 to 3 were adjusted with pure water and some butyl cellosolve to give a clear coating time of about 100 seconds as measured using a Ford cup #4. .

This clear face was coated on ETIH so that the film thickness after drying at 200°C for 5 minutes was 5μ.

The obtained evaluation results are shown in Table 2.

Test methods for various performance evaluations were conducted under the following conditions.

Filtration: DuPont impact test (load 300g, perseverance %P,
Cracks on the surface of the coating film due to a height of 30C11 and a temperature of 25°C were visually observed.

◎; Good Δ: Cracks in the coating film are observed.

×: Significant cracks in the coating film were observed.

Soil observation: A cross cut was made in the paint film using a cutter knife, and the paint film was immersed in boiling water for 30 minutes, then immediately pulled up, cellophane tape was applied to the cross cut portion, and the state of peeling of the paint film was visually observed.

◎; Good △: Peeling of the coating film is observed.

×: Significant peeling of the coating film was observed.

Hard: According to the method of JIS K 5400.6.14.

>) zbl-: After retort treatment at 125°C for 30 minutes, a 3×3 camp was punched out and cracks in the coating film were visually observed.

◎; Good △: Slight whitening is observed on the coating surface.

×: Significant whitening of the coating surface was observed.

2''A0): Calculated value calculated from the amounts of pure water and organic solvent used for dilution.

In addition, the clear faces obtained from Example 1.2 and Comparative Examples 1 to 3 were placed in containers, sealed, and stored in an atmosphere at 40°C, and the viscosity of the clear faces for one month was measured.

The results are shown in Table 3.

〔Effect of the invention〕

The resin composition for water-based paint on the outside surface of metal cans of the present invention maintains excellent processability in terms of film performance, and provides a paint with good storage stability without impairing physical properties such as hardness and adhesion. You can.

Claims (1)

[Claims] (a) 5% by weight of vinyl monomer containing a carboxyl group
Contains as an essential component at least 5% by weight of vinyl monomer represented by the above and the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, R in the formula shall represent a hydrogen atom or a methyl group) Copolymerization in which one or more vinyl monomers containing hydroxyl groups, glycidyl groups, methylolamide groups, or alkoxymethylolamide groups are copolymerized with other vinyl monomers, and the weight average molecular weight is specified in the range of 1,000 to 50,000. (b) a water-dilutable alkyl etherified methylol melamine resin, and the blending ratio of the copolymer resin (a) and the alkyl etherified methylol melamine resin (b) is (a)/ (b) = (20-95)/(80-5) (resin solid content ratio %), and the carboxyl groups contained in the copolymer resin (a) are replaced by amines in 0.3 to 2.0 equivalents. A resin composition for water-based paint on the outer surface of metal cans, which is characterized by a water-based paint composition for the exterior surface of metal cans.