JPH0563234B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field: The present invention relates to a method for forming a highly durable multilayer coating film. Conventional technology and its problems: Traditionally, organic coating materials include thermoplastic resin paint and thermosetting resin paint. It is said that thermosetting resin paints that form However, when using thermosetting resin,
Requires application of sufficient thermal energy. on the other hand,
So-called polyurethane paints that use a reaction between isocyanate groups and hydroxyl groups are widely used as curable resins that undergo a curing reaction at room temperature without using thermal energy. In an environment where there is water splash, the isocyanate group reacts with water, inhibiting the reaction between the resins and making it impossible to obtain a durable coating film. In particular, the application of curable paints that harden at room temperature to water-based paint films has traditionally been considered extremely difficult in terms of uniformity of quality, but in the field of manufacturing technology such as building exterior materials and cement mortar products. The emergence of such a coating film forming method is desired. Furthermore, in the field of high-end painting technology for automobiles, etc., in order to reduce the amount of organic solvents used and the thermal energy required for curing, water-based paints are used for the undercoat layer and highly durable coatings are applied to the topcoat layer at room temperature. There is a need for a coating film forming method that can provide a sufficiently dry state with slight heating. Means for solving the problem: The present inventors have conducted intensive studies on a method of forming a multilayer coating film of a water-based paint and a thermosetting paint that reacts at room temperature or low temperature, which has been thought to be difficult in the past. As a result, the present invention was achieved by discovering that the present invention can be achieved by using an organic solvent-type top coating material containing a specific monomer, a copolymer copolymerized therewith, and a specific compound. That is, the present invention applies a water-based paint using water as a solvent or dispersion medium to a base material to form an undercoat layer, and in a state where water remains in the undercoat layer, the general formula (However, in the formula, R represents hydrogen or a methyl group, R ₁ , R ₂
represents an alkyl group having 1 to 6 carbon atoms. ) and a monomer component (B) copolymerizable with said (A), and a copolymer formed by copolymerizing a monomer component (A) represented by Applying an organic solvent-type top coating containing a compound (C) in which at least one amino group of a polyvalent amine compound having a primary or secondary amino group is blocked by reaction with a ketone or aldehyde. This is a coating film forming method characterized by the following. In the present invention, water-based paints forming the undercoat layer include, for example, acrylic ester copolymer resin emulsion paints, vinyl acetate copolymer resin emulsion paints, vinyl chloride copolymer resin emulsion paints, synthetic rubber latex-based paints, and water-soluble alkyd resins. Commonly used water-based paints such as paints, epoxy emulsion paints, water-soluble acrylic resin paints, and mixtures thereof are widely used, but emulsion-based paints (colloidal dispersion and hydrosol It is preferable to use an emulsion of an acrylic acid ester copolymer resin having a weight average molecular weight of 10,000 or more. In the present invention, the monomer component (B) copolymerizable with the monomer component (A) represented by the above general formula includes α,
Vinyl monomer components having β-unsaturated groups, such as alkyl acrylates and methacrylates having 1 to 18 carbon atoms in the alkyl chain, styrene, α-
Examples include methylstyrene, acrylonitrile, acrylic acid and methacrylic acids, maleic acid and fumaric acid, or alkyl esters thereof having 1 to 18 carbon atoms, hydroxyethyl acrylate, hydroxypropyl acrylate or methacrylates, acrylamide, methacrylamide, etc. It will be done. The copolymer used in the present invention is usually
It preferably has a number average molecular weight of 2000 to 30000, and in the presence of a polymerization initiator that generates radicals,
Those obtained by solution polymerization in an inert solvent are preferred. Examples of the polymerization initiator used in this case include peroxides such as benzoyl peroxide and cumene hydroperoxide;
Examples include diazo compounds such as azobisisobutylnitrile. Examples of inert solvents include aromatic solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, alcohol solvents such as butanol and isopropyl alcohol, and butyl cellosolve. , cellosolve solvents such as ethyl cellosolve, and acetates thereof. The polymerization temperature in the solution polymerization method described above varies depending on the polymerization initiator used, but is generally in the range of 60 to 160°C. In the present invention, the copolymerization ratio of monomer (A) in the copolymer is preferably in the range of 5 to 50% by weight from the viewpoint of durability and coating performance. The compound (C) used in the coating film forming method of the present invention is 1
It is a compound in which at least one amino group of a polyvalent amine compound having two or more primary or secondary amino groups in the molecule is blocked by reaction with a ketone or aldehyde. Examples of polyvalent amine compounds include aliphatic amines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, nonamethylenediamine, and diethylenetriamine, isophoronediamine, 4,4'-diaminodicyclohexylmethane, and 4,4'-diaminodicyclohexylmethane. , 4'-diaminodicyclohexylpropane, hydrogenated xylylene diamine, alicyclic diamines such as dipentene diamine, diamines in which the amino group is not directly bonded to the aromatic ring such as xylylene diamine, piperazine, 2-methyl Examples include heterocyclic amines such as piperazine, 2,5-dimethylpiperazine, and dipiperidylpropane. Examples of ketones used in the present invention include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone,
Examples include 3,3,5-trimethylcyclohexanone, cyclopentanone, and the like. In addition, examples of aldehydes include isobutyraldehyde, n
-butyraldehyde, diethylacetaldehyde, 2-ethylcaproaldehyde, isotridecylaldehyde and the like. The compound (C) used in the present invention is as follows:
It can be obtained by dehydrating the above polyvalent amine compound and ketones or aldehydes. In this case, it is desirable that all the amino groups of the polyvalent amine compound be dehydrated, but it can be used in the present invention if at least one amino group in one molecule is dehydrated. The mixing ratio of the above copolymer and compound (C) is particularly preferably such that the ratio of the molar equivalent of monomer (A) to the amino group equivalent of compound (C) in the copolymer is 1:0.6 to 1:1.2. are mixed and used in a weight ratio ranging from 1:0.7 to 1:1. The compound (C) in the top coat described above returns to a polyvalent amine compound due to moisture from the undercoat.
Reacts with the copolymer to form a highly durable cured top coat. In the present invention, the water-based paint and top coat used for the undercoat usually contain various coloring pigments such as titanium oxide, iron oxide, carbon black, phthalocyanine blue, etc., and calcium carbonate, barium sulfate, talc, etc. Fillers such as mica, alumina, silica, glass fiber, asbestos, bentonite, metal powders such as aluminum powder and stainless steel powder, and leveling agents,
Auxiliary agents commonly used in paints, such as antifoaming agents, dispersion aids, ultraviolet absorbers, and antioxidants, may be mixed and dispersed. Alternatively, only the undercoat may be colored, and the topcoat may be in the form of a so-called clear varnish, in which no coloring pigment is added. Particularly in the case of top coatings for automobiles, it is common to apply a water-based paint containing aluminum powder as an undercoat, and then apply the above-mentioned clear varnish containing an ultraviolet absorber, an antioxidant, or a transparent pigment. The above-mentioned undercoat paint is applied to various base materials such as metals, plastics, slate, wood materials, cement moldings, etc. by spray painting, brush painting, roller painting, etc., and the above-mentioned top coat paint is applied immediately. It may be applied by coating, or it may be applied after being left at room temperature to allow some of the volatile components to scatter. Effect of the invention: The coating film obtained by such a coating film forming method is a coating film that is excellent in various durability points such as weather resistance, moisture resistance, solvent resistance, and stain resistance. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the scope of the present invention is not limited to these Examples. Note that parts in the examples indicate parts by weight. Production example 1 Preparation of water-based paint: (i) Emulsify 60% by weight of butyl acrylate, 10% by weight of styrene, 26% by weight of methyl methacrylate, 2% by weight of 2-hydroxyethyl methacrylate, and 2% by weight of methacrylic acid. 100 parts by weight of polymerized acrylic acid ester copolymer resin (50% concentration, average particle size 0.15μ) was adjusted to pH with ammonia water.
Neutralized to 7.5. Add 15 parts of aluminum paste (manufactured by Toyo Aluminum Co., Ltd., product name: Alpace) to this.
Disperse and mix 9173ML of butyl cellosolve (30% diluted product), and further add 21 to 22
Water was added until the viscosity of the paint reached within seconds to obtain a water-based undercoating paint (a). (ii) 30% by weight of ethyl acrylate, 2-acrylic acid
Acrylic copolymer resin hydrosol (30%
Weight % concentration, solvent is water, isopropanol 70/
Mixing ratio of 30, neutralization with ammonia water to PH7.5
Disperse 167 parts by weight of titanium oxide and 50 parts by weight of titanium oxide (average particle size: 0.015μ) in a sand mill, dilute with water in a #4 food cup until the paint viscosity reaches 30 seconds, and prepare a water-based undercoating paint (B). Obtained. Production Example 2 Production of copolymer: 800 parts by weight of toluene and 200 parts by weight of methyl isobutyl ketone were placed in a reactor equipped with a stirrer, a reflux condenser, a thermometer, and a dropping tank, and after heating to 85°C,
A mixture of each monomer and polymerization initiator shown in each experiment number in Table 1 was dropped from a dropping tank over a period of 4 hours,
During this time, the reaction solution was maintained at 85 to 90°C with stirring, and upon completion of the dropwise addition, 3 parts by weight of azobisisobutyronitrile as a polymerization initiator was further added twice every 2 hours, and the reaction was continued at the above temperature for 6 hours. A copolymer solution was obtained.

[Table] Production Example 3 Synthesis of Compound (C): In a reactor equipped with a stirrer, a condenser with a water separator, and a thermometer, each polyvalent amine compound of each experimental symbol (A) to (D) shown in Table 2 was added. , ketone or aldehyde and other raw materials were prepared and heated at the temperature shown in Table 2.
A time reaction was performed. Furthermore, the reactants of each experimental symbol were concentrated under reduced pressure and adjusted to a 50% solution. The total amino group content of each reactant solution was measured by hydrochloric acid titration and is also listed in Table 2.

【table】

[Table] Production Example 4 Preparation of top coat paint: 200 parts by weight of the copolymer shown in Table 1 and a solution of compound (C) shown in Table 2 were mixed at the polymerization ratio shown in Table 3, and then diluting thinner ( Add toluene and ethyl acetate (mixed in equal weights), add 0.1% by weight of silicone aid for leveling, and add Tinuvin 328 (trade name, ultraviolet absorber manufactured by Ciba Kaigy Co., Ltd.) per solid content.
35 in food cup #4 by adding 0.5% by weight.
The clear varnish was prepared by diluting and mixing so that

[Table] Examples 1 to 11 In the case of applying the water-based undercoating paints (a) and (b) described above to a chemically treated steel plate with a thickness of 0.6 mm (a), the dry coating thickness was 15
Spray coat to give a dry coating thickness of ~20μ, or 30 to 35μ in case of (b), and leave to stand at the temperature and time shown in Table 4. I spray painted it to look like this.
After applying the top coat and curing the coated board by heating at 80°C for 30 minutes, solvent resistance, stain resistance and durability tests were conducted. The results are shown in Table 5. Comparative Examples 1 to 3 After applying the water-based undercoating paint (a) in exactly the same manner as in the coating film formation of the examples, methyl methacrylate,
Curing Olestar NP-1000, a water adduct of acrylic polyol, which is a copolymer of butyl acrylate and hydroxyethyl methacrylate, and hexamethylene diisocyanate (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name, 75% non-volatile content solution). A two-component mixed urethane paint (clear) was applied as a top coat, and the coated board was heated at 80°C for 30 minutes in the same manner as in the example, and then the paint film was tested. The evaluation results are also listed in Table 5.

【table】

【table】

[Table] Evaluation method: Solvent resistance; Evaluated by soaking methyl ethyl ketone in gauze and rubbing the surface of the coating film back and forth until the base material comes out. Stain resistance; carbon black water slurry is placed on the coating.
After drying at 50°C for 2 hours, the coating was washed with water and the extent of traces remaining on the coating was determined. Cold/heat cycle test: The coating was placed in a constant temperature bath at temperatures of -40°C and 80°C every hour, and the state of the coating film was observed after 10 cycles. Humidity test: After placing the test plate in a constant temperature and humidity chamber at 50°C and 98% relative humidity for 240 hours, the surface condition of the coating film was observed. Weather-o-meter: After 2000 hours of irradiation with a sunshine-type weather-o-meter, the gloss and color difference before irradiation (NBS color difference)
was measured.

Claims (1)

[Claims] 1. A water-based paint using water as a solvent or dispersion medium is applied to a base material to form an undercoat layer, and then, in a state where water remains in the undercoat layer, the general formula (However, in the formula, R represents hydrogen or a methyl group,
R ₁ and R ₂ represent an alkyl group having 1 to 6 carbon atoms) and a monomer component (B) copolymerizable with said (A) are copolymerized. A copolymer consisting of
and at least one polyvalent amine compound having two or more primary or secondary amino groups in one molecule.
1. A method for forming a coating film, which comprises applying an organic solvent-type top coating material containing a compound (C) in which amino groups of 1 and 2 are blocked by reaction with a ketone or an aldehyde.