JPH1017816A - Water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-based coating composition improved in applicability, initial curability, hardness and processability by mixing a specified acrylic resin with an amino resin. SOLUTION: 10-30wt.% vinyl acetate monomer is copolymerized with 3.5-20wt.% α,β-monoethylenically unsaturated carboxylic acid monomer and 50-86.5wt.% other comonomers in the presence of a polymerization initiator in a water-soluble solvent, and the product is neutralized and made water-based to obtain a water-soluble acrylic resin having a weight-average molecular weight of 5,000-50,000. 60-80 pts.wt. this resin is mixed with 20-40 pts.wt. amino resin to obtain a coating composition having a solid content of 50wt.% or above, an organic solvent content of 15wt.% or below and a viscosity of 90sec or below as measured by using a #4 Ford cup at 25 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an aqueous coating composition. More particularly, the present invention relates to an aqueous coating composition having excellent paint properties as a metal can outer coating and having a coating film having good initial curing, hardness and workability.

[0002]

2. Description of the Related Art Conventionally, the outer surface of a metal can made of steel, aluminum, tin-free steel, or the like has been coated to prevent corrosion due to molding or external impact and to decorate the outer surface. . Conventionally, solvent-type paints such as acrylic resin / amino resin / epoxy resin and polyester resin / amino resin have been used for coating the outer surface of these cans. However, in recent years, there has been an increasing demand for water-based paints for reasons such as resource saving, improvement of working environment, low pollution and the like, and water-based paints composed of acrylic resin / amino resin have been used.

[0003] Paints for metal cans are required to have extremely strict workability, hardness and various resistances as well as extremely strict paintability and film forming properties.
Mist generation suppression and prevention, productivity and energy saving,
From the viewpoint of economy, the solid content is as high as possible,
Excellent curability is also required. When the viscosity of the paint becomes high, the flow becomes poor, the paintability is impaired, and it becomes difficult to obtain a uniform coating film. However, if the viscosity is simply reduced by adding an organic solvent or water, the solid content will be low.
When the solid content becomes low, in order to obtain a predetermined dry coating film thickness, the paint must be applied thicker on the roll at the time of coating than in the case of the high solid content. If the paint is applied thicker on the roll at the time of painting, the paint scatters around the roll (generation of mist) and contaminates the coater. Therefore, there is a demand for the development of a water-based paint having a low viscosity and excellent coatability, while having a high solid content that does not easily generate mist.

Acrylic resins used in water-based paints are copolymers containing a relatively large amount of methyl methacrylate, styrene monomer, etc., for the purpose of ensuring the curability of the coating film, especially the initial curability and hardness. I have. However, when the content of methyl methacrylate, styrene monomer, and the like increases, the viscosity tends to increase, and when the viscosity increases, the paintability is impaired. Then, in order to satisfy the paintability, there was a situation in which the paint had to be made to have a low solid content. Therefore, an attempt was made to reduce the viscosity and increase the solid content by reducing the amount of the methyl methacrylate and styrene monomers of the acrylic copolymer component and using a large amount of ethyl acrylate and butyl acrylate. However, a paint using an acrylic resin containing a large amount of butyl acrylate or the like has a drawback that the curability is inferior.

However, if a large amount of a catalyst is added to supplement the curability or a large amount of a monomer having a functional group such as 2-hydroxy methacrylate is introduced into the acrylic resin, the processability of the coating film is adversely affected and the cost is reduced. There was a problem of getting high. That is, in the water-based paint, the reduction of the amount of the organic solvent, the high solid content, the coatability, the film forming property, the curability, and the various properties required for the obtained coating film could not be satisfied in a well-balanced manner.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been conventionally difficult to satisfy. It has a low organic solvent content, a high solid content, and is excellent in coatability and curability, and has various properties of a coating film. The purpose is to obtain an excellent water-based paint.

[0007]

That is, the present invention provides a vinyl acetate monomer (a) of 10 to 30% by weight, an α, β monoethylenically unsaturated carboxylic acid monomer (b) of 3.5 to 20%.
% By weight, monomer (c) 5 copolymerizable with (a) and (b)
A copolymer obtained by copolymerizing 0 to 86.5% by weight (hereinafter, referred to as a copolymer)
Abbreviated as the copolymer. ) Comprising an acrylic resin and an amino resin obtained by neutralizing the above with an organic amine, having a solid content of 50% or more, an organic solvent content of 15% or less, and a viscosity at 25 ° C using a # 4 Ford cup of 90 seconds or less. Of the aqueous coating composition.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail.
In the copolymer used in the present invention, the content of the vinyl acetate monomer (a) is particularly important. That is, when the vinyl acetate monomer (a) is less than 10% by weight, the curability of the formed coating film becomes insufficient when the copolymer is used for a coating material. On the other hand, if it exceeds 30% by weight, the paint becomes high in viscosity and impairs paintability.

The α, β monoethylenically unsaturated carboxylic acid monomer (b) includes acrylic acid, methacrylic acid, fumaric acid and the like, and acrylic acid is particularly preferred. α, β
The monoethylenically unsaturated carboxylic acid monomer (b) is selected from the group consisting of:
It is necessary to contain 5% by weight or more, preferably 5% by weight.
% By weight or more. If it is less than 3.5% by weight, the copolymer cannot be made aqueous. Further, the content of the α, β monoethylenically unsaturated carboxylic acid monomer (b) needs to be 20% by weight or less, preferably 15% by weight or less. 2
If it exceeds 0% by weight, the processability of a coating film using the copolymer as a coating material will be poor.

The monomers (c) copolymerizable with (a) and (b) include alkyl acrylates such as methyl acrylate, methyl methacrylate, ethyl acrylate and ethyl methacrylate, and styrenes such as styrene and vinyl toluene. And a hydroxy group-containing monomer such as hydroxyethyl acrylate and hydroxypropyl acrylate.

The copolymer is prepared by converting a monomer comprising (a), (b) and (c) into isopropyl alcohol,
n-butanol, isobutanol, butyl cellosolve,
alcohol solvents such as n-amyl alcohol and isoamyl alcohol, ethylene glycol monomethyl ether,
It can be obtained by radical polymerization using a polymerization initiator in a water-soluble solvent such as an ester solvent such as ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether.
The molecular weight of the obtained copolymer is preferably from 5,000 to 50,000, more preferably from 1 to 50,000 in terms of weight average molecular weight.
0000 to 20,000. Weight average molecular weight 5000
When the amount is less than the above, the processability of the coating film of the coating material using the copolymer tends to deteriorate, and when it exceeds 50,000, the viscosity of the coating material becomes high and the coating property may be impaired.

The copolymer is neutralized and made aqueous using an organic amine to obtain a water-soluble acrylic resin. As the organic amine to be used, triethylamine, triethanolamine, ethanolamine, monoethanolamine,
Monoethylamine, monomethylamine, methylaminoethanol and the like are used, and these are used as one kind or as a mixture of two or more kinds.

The amino resin used in the present invention is an amino resin that can be dissolved or dispersed in an aqueous medium, and includes a melamine resin, a benzoguanamine resin, a spiro guanamine resin, and the like. Is a solid content, preferably 60 to 80 parts by weight / 20 to 40 parts by weight. When the amount of the amino resin is less than 20 parts by weight, poor curing of the coating film occurs, and when the amount is more than 40 parts by weight, the workability after curing becomes poor.

In the present invention, the viscosity of the paint for the outer surface of the can at 25 ° C. is # from the viewpoint of coating properties and film forming properties.
It should be less than 90 seconds for a 4 Ford Cup, preferably 60-90 seconds. A high-viscosity coating material having a viscosity of more than 90 seconds cannot be applied, or even if it can be applied, the coating film becomes non-uniform and the appearance of the finished product is impaired.

It is also possible to mix a water-soluble resin or a water-dispersible resin, such as an aqueous polyester resin, a maleic acid resin, or a polyol, which is generally used as a water-based coating resin, as long as the effects of the present invention are not impaired. . Also,
Similarly, leveling agents, defoamers, and lubricants can be added.

The aqueous paint of the present invention can be applied to a substrate by a known means such as roll coating, spraying and brushing. Examples of the base material include a metal base material such as an electro-tin-plated steel sheet and tin-free steel aluminum.
Further, the aqueous coating composition of the present invention can be heated and cured at 120 to 240 ° C.

[0017]

EXAMPLES The present invention will be described below with reference to examples. In the example,
Parts mean parts by weight and% means percent by weight. Production Example 1 Production of Aqueous Acrylic Resin Solution A1 30 parts of butyl cellosolve in a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, a dropping tank, and a nitrogen gas injection tube,
70 parts of 1-butanol was charged, the temperature was maintained at 105 ° C. while introducing nitrogen gas, and ethyl acrylate 60%, 2-hydroxyethyl methacrylate 10%, vinyl acetate monomer 20%, acrylic acid 10
A solution prepared by dissolving 5 parts of benzoyl peroxide in 100 parts of a 100% mixture was added dropwise over 3 hours. Thereafter, the temperature was maintained at 105 ° C., and the reaction was carried out for 1 hour to complete the reaction. The weight average molecular weight of the obtained copolymer was 12,400. The copolymer solution was distilled under reduced pressure at 110 ° C. to remove 1-butanol to a non-volatile content of 76%. Then, 12 parts of diethanolamine and water were added, and a clear and viscous solution having a solid content of 55% and a residual butyl cellulosolve of 17% was added. Aqueous acrylic resin solution A1 was obtained.

Production Examples 2 to 13 Aqueous acrylic resin solution A
Production of 2-A13 According to Production Example 1, aqueous acrylic resin solutions A2-A13 were obtained with the compositions shown in Table 1.

Examples 1 to 9 and Comparative Examples 1 to 8 After mixing the components according to Tables 2 and 3, butyl cellosolve and water were added to dilute the mixture, and the solid content, the amount of the organic solvent in the paint, # 4 The viscosity of the Ford cup was adjusted. To this, a phosphoric acid catalyst was added to 100 parts of the resin solids in the paint,
0.5 or 1.0 part was added to obtain a water-soluble coating composition. Tables 2 and 3 also show the paint properties. Table 3 shows the results obtained by examining paintability, curability, physical properties of the coating film, and the like using these water-soluble coating compositions.

The test methods for paint properties, paintability, curability, etc. are as follows. -Paint properties-Solids The coating was performed according to the method registered in JIS standard "Heating residue" (JIS K-5400). Viscosity The viscosity [second] of the coating composition at 25 ° C. was measured using a # 4 Ford cup. -Coatability A 0.28-mm-thick aluminum plate was dried by roll coating, dried and coated to a thickness of 5 µm, and baked in an electric oven at an ambient temperature of 200 ° C to prepare a test piece. The state of the obtained test piece was visually observed, observed, and evaluated. ：: The thickness of all coating films on the entire surface of the aluminum plate is uniform and the surface is uniform. Δ: A state in which the paint was applied to the entire surface of the aluminum plate, but the thickness of the coating film was uneven and a wave was obtained. X: The part where the paint is not applied is distributed over the entire surface of the aluminum plate. In addition, about the thing of coating property evaluation x, the test and evaluation with respect to the following coating films were not performed. ○ Generation of mist The mist generated around the coater was repaired and the amount was calculated. ：: Almost no mist was generated. Δ: Some mist was generated. X: Mist generation was remarkable and the periphery of the coater was significantly contaminated.硬化 Curability A 0.28-mm-thick aluminum plate was dried by roll coating, dried and coated to a thickness of 5 µm, and baked in an electric oven at an ambient temperature of 200 ° C for 90 seconds to prepare a test piece. Boil this panel in MEK for 30 minutes,
The rate of weight loss before and after boiling was measured and used as a measure of curability. Weight loss rate = [(weight after boiling)-(weight before boiling)]
/ (Weight before boiling) ○ Physical properties of the coating Film coated with aluminum having a thickness of 0.28 mm by roll coating and then dried to a coating thickness of 5μ, baked in a gas oven at an ambient temperature of 200 ° C for 3 minutes, and tested. Pieces were prepared and the following tests were performed. -Impact resistance test Using an impact resistant DuPont impact tester, a 1/2 inch diameter shooting pin is brought into contact with the sample, and then a 500 gr weight is dropped. Impact resistance was evaluated based on the height at which cracks did not occur in the coating film.・ Pencil hardness test JIS standard “pencil scratch test” (JIS No. K54)
(00).

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[0025]

According to the present invention, a specific amount of vinyl acetate is contained in an acrylic resin in an aqueous coating of an acrylic resin / amino resin. In addition, it has become possible to obtain a water-based paint having excellent coating properties, film-forming properties, and curability, and also having various properties of a coating film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location // (C08F 220/18 220: 28 220: 08 220: 06)

Claims (1)

[Claims] 1. A vinyl acetate monomer (a) 10 to 30% by weight, an α, β monoethylenically unsaturated carboxylic acid monomer (b) 3.5 to 20% by weight, a monomer copolymerizable with (a) and (b) (C) An acrylic resin obtained by copolymerizing 50 to 86.5% by weight and an amino resin, and having a solid content of 50%.
% Or less, an organic solvent content of 15% or less, and a viscosity at 25 ° C. of 90 seconds or less using a # 4 Ford cup.