JPH03108B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a metallic coating method for forming a coating film having an excellent metallic appearance and excellent weather resistance, corrosion resistance, chemical resistance, etc. [Prior art] In recent years, acrylic resins, polyester resins,
Paints containing scaly metal powders (hereinafter referred to as metallic paints), which have epoxy resins as resin components, are attracting attention as paints that provide excellent coating film appearance and anti-corrosion properties. It tends to be widely used in structures. Regarding the painting system, from the perspective of shortening the painting process, a metallic base paint is applied, followed by a top clear paint, and then both coatings are baked and hardened at the same time.
The one-bake method is becoming widely used. [Problems to be Solved by the Invention] In recent years, in order to extend the interval between repainting, there has been a demand for a longer lifespan of the paint film. However, the conventional metallic paints cannot provide coating films with excellent long-term weather resistance, corrosion resistance, chemical resistance, etc., and therefore do not satisfy the above requirements. For example, it has been found that acrylic resin metallic paints do not have sufficient long-term outdoor durability, and often cause coating defects such as loss of gloss, cracks, and peeling after 3 to 4 years. Therefore, in order to meet the market demands mentioned above, dispersion-type fluororesin paints, in which polyvinylidene fluoride resin powder with excellent long-term weather resistance is dispersed in solution-type resins such as acrylic resins, are attracting attention. ing. However, such dispersion-type fluororesin paints have low transparency and the orientation of the scaly metal powder is non-uniform, resulting in a lack of glitter, which is a characteristic of metallic paints, and the disadvantage of not being able to obtain a metallic feel. It was hot. Furthermore, its baking temperature was extremely high, at over 200°C, which placed considerable restrictions on its use. Due to these various drawbacks, dispersion-type fluororesin paints are said to still not have sufficient commercial value in application fields where coating film appearance and aesthetics are important, and therefore, they are not considered to have sufficient commercial value. There was a demand for some kind of drastic improvement, with a focus on gender, etc. [Means for Solving the Problems] In view of the above-mentioned current situation, the inventors of the present invention have made extensive studies to improve or eliminate the various drawbacks of known paints, and have developed a paint that has excellent long-term weather resistance and has a metallic appearance. The present invention was achieved by discovering an excellent coating method. That is, the present invention provides a scale-like metal powder-containing base paint (with a resin component of a hydroxyl group-containing acrylic copolymer containing 10 to 60% by weight of at least one monomer of methyl methacrylate and styrene as a copolymerization component). A method of applying a top clear paint (metallic base paint) on the object to be coated, then applying a top clear paint whose resin component is a fluorine-containing copolymer containing hydroxyl groups (wet on wet), and then curing both coatings at the same time. This invention relates to a metallic coating method characterized by: The present invention will be explained in detail below. First, the metallic base paint used in the present invention contains as a resin component an acrylic copolymer obtained from methyl methacrylate and/or styrene and an α,β-ethylenically unsaturated monomer having a hydroxyl group. Methyl methacrylate, styrene, or a mixed monomer thereof, which is a copolymerization component of the acrylic copolymer, is an essential component in order to obtain a coating film with an excellent metallic appearance, and its content is particularly preferably 10 to 60% by weight. is 20-50% by weight. In the above content range, the lower limit is
If it is too low than 10% by weight, the compatibility with the top clear paint described later will be poor, and as a result, the scaly metal powder in the metallic base paint will easily migrate to the top clear layer, causing so-called metallic unevenness and glossiness. It becomes easier. In addition, it is undesirable because it tends to significantly reduce the resistance to the stress of expansion and contraction due to cold-heat cycles, which is particularly experienced by coating films exposed outdoors for a long period of time. On the other hand, if the content is too high than the upper limit of 60% by weight, the flexibility of the coating film will decrease, making cracking and whitening more likely to occur, and interlayer adhesion with the top clear layer will also decrease, which is not preferable. In the present invention, the content of the α,β-ethylenically unsaturated monomer having a hydroxyl group is such that the hydroxyl value of the resulting acrylic copolymer is 10 to 150, particularly preferably 20.
An appropriate amount is ~120. Note that if the hydroxyl value is lower than the above range, the curability of the coating film will be poor, and water resistance and weather resistance will tend to decrease. On the other hand, if the hydroxyl value is higher than the above range, the flexibility of the coating film tends to decrease and cracks are more likely to occur. In the present invention, examples of "α,β-ethylenically unsaturated monomer having a hydroxyl group" include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, di(2-hydroxy )
Typical examples include ethyl maleate and di(4-hydroxybutyl) maleate. In the present invention, in addition to the above monomers, α,β-ethylenically unsaturated dicarboxylic acids such as monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, etc. Monoesters, α, β monoethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic anhydride, methyl acrylate, methyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, methacryl Acrylic acid and/or methacrylic acid esters such as acid lauryl, and one or more types of styrene, α-methylstyrene, vinyltoluene, vinylpyridine, acrylonitrile, etc. may be copolymerized. The acid value of the acrylic copolymer is suitably 1 to 20, and the number average molecular weight is suitably about 5,000 to 150,000. The acrylic copolymer is produced by carrying out a copolymerization reaction in a conventional manner by allowing a monomer mixture of a predetermined ratio to react with a polymerization solution such as xylene, toluene, ethyl acetate, or butyl acetate in the presence of a polymerization solution. can be manufactured. A metallic base paint containing such a hydroxyl group-containing acrylic copolymer as a resin component can be prepared according to a known method. That is,
Dispersing a curing agent, scaly metal powder, and, if necessary, various coloring pigments, additives, modifiers, etc. commonly used in paints, in an organic solvent solution of a hydroxyl group-containing acrylic copolymer. A paint containing scaly metal powder is obtained. Examples of the organic solvent include aromatic hydrocarbons such as xylene and toluene, alcohols such as n-butanol, esters such as butyl acetate, ketones such as methyl isobutyl ketone, and glycol ethers such as ethyl cellosolve. In addition, various commercially available thinners can also be used. Further, as the curing agent, in the case of a room temperature curing type (including forced drying), a polyvalent isocyanate having two or more isocyanate groups in one molecule is suitable. Examples of the polyvalent isocyanate include aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylene diisocyanate, and hydrogenated xylylene diisocyanate, or biuret forms, dimers, and trimers thereof. Typical examples include reaction products between polymers or excess of these isocyanate compounds and low-molecular polyols such as ethylene diglycol, glycerin, trimethylolpropane, and pentaerythritol. Needless to say, in the case of a room temperature curing type, the curing agent becomes a two-component paint, which is mixed with the hydroxyl group-containing acrylic copolymer solution as the main ingredient immediately before coating. In addition, the polyvalent isocyanate compounds may include phenols, alcohols, oximes, lactams,
Blocked isocyanate compounds masked with masking agents such as amines and amides can also be used, and in this case, by mixing with the polyol component in a predetermined ratio, a one-component paint that can be cured by baking can be obtained. The mixing ratio of the polyol component which is the acrylic copolymer and the polyvalent isocyanate compound curing agent component is determined by the equivalent ratio of isocyanate groups of the isocyanate compound to hydroxyl groups of the polyol component (NCO/
OH) is (0.15-1.5/1) particularly preferably (0.2-1.5/1)
1.2/1), and within this range it is possible to exhibit the original resin properties. Furthermore, an aminoplast compound can also be used as a curing agent. Aminoplast compounds include melamine,
It is a condensation product of an amino compound such as urea, benzoguanamine, or acetoguanamine and an aldehyde compound, or a compound obtained by further etherifying the condensation product with an alcohol such as butatanol.
In addition, when using an aminoplast compound,
By mixing it with the polyol component in a predetermined ratio, it becomes a one-component paint that can be cured by baking. The mixing ratio (by weight) of the polyol component, which is an acrylic copolymer, and the aminoplast compound curing agent component is (95:5 to 60:40), particularly preferably (90:10 to 70:30); It becomes possible to exhibit the original resin properties within this range. Further, as the "scaly metal powder" used in the metallic base paint, those normally used in paints containing scale-like metal powder can be used.
Examples include scaly aluminum powder, stainless steel powder, copper powder, bronze powder, iron oxide powder, and mica powder treated with titanium oxide. The particle size of such flaky metal powder is generally suitable to have an average particle size of 3 to 30 microns. In addition, the metallic base paint used in the present invention may further contain various inorganic or organic coloring pigments or anticorrosion pigments such as titanium oxide, carbon black, and phthalocyanine; ultraviolet absorbers, surface conditioners, and curing accelerators, as required. Agent: A modifier such as cellulose acetate butyrate can be added as appropriate. The blending ratio of the components constituting these metallic base paints can vary widely depending on the coating conditions, etc., but usually the total amount of the hydroxyl group-containing acrylic copolymer and curing agent in the metallic base paint is about 20 to
40% by weight, about 1-20% by weight of flaky metal powder is suitable. Next, the top clearer used in the present invention will be explained. The top clear paint used in the present invention contains a hydroxyl group-containing fluorine-containing copolymer as a resin component. Suitable examples of the fluorine-containing copolymer include the fluorine-containing copolymers described in JP-A-57-34107. That is, the fluorine-containing copolymer has fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether, and hydroxyalkyl vinyl ether as essential components, and has a content of 30 to 70% by weight, 5 to 60% by weight, and 3 to 60% by weight, respectively.
A fluorine-containing copolymer containing 20% by weight and having a weight average molecular weight of about 20,000 to about 100,000 is preferable. In the above, if the fluoroolefin content is too low, the weather resistance will decrease, and if the fluoroolefin content is too high, it will be difficult to manufacture. Furthermore, if the cyclohexyl vinyl ether content is too low, the hardness of the coating film will decrease, and if the alkyl vinyl ether content is too low, the flexibility will decrease. Furthermore, it is particularly important to contain hydroxyalkyl vinyl ether in a proportion within the above range from the viewpoint of improving curability without impairing various useful properties as a coating material. In other words, if the hydroxyalkyl vinyl ether content is too high, not only will the solubility of the copolymer in organic solvents decrease, but also the flexibility of the coating film will decrease, while if the hydroxyalkyl vinyl ether content is too low, the durability of the coating film will decrease. Both are unfavorable because the adhesion decreases. In the fluorine-containing copolymer, the fluoroolefin is preferably perhaloolefin, particularly chlorotrifluoroethylene or tetrafluoroethylene. In addition, as the alkyl vinyl ether, those containing linear or branched alkyl groups having 2 to 8 carbon atoms, particularly those in which the alkyl group has 2 to 4 carbon atoms, are preferable. In the present invention, the fluorine-containing copolymer may contain comonomers other than the above-mentioned essential constituents in an amount not exceeding 40% by weight. Typical examples of such comonomers include ethylene, propylene, isobutylene, vinyl chloride, vinylidene chloride, methyl methacrylate, and butyl acetate. The fluorine-containing copolymer can be produced by causing a copolymerization reaction by allowing a polymerization initiator to act on a monomer mixture in a predetermined proportion in the presence of a polymerization medium. Examples of such fluorine-containing copolymers include Lumiflon LF100, Lumiflon LF200, Lumiflon LF210, Lumiflon LF300, Lumiflon
LF400 (all product names manufactured by Asahi Glass Co., Ltd.) etc. are commercially available. The top clear paint used in the present invention contains this fluorine-containing copolymer and an organic solvent similar to that used in the metallic base paint.
Consists of hardening agents, additives, etc. Furthermore, if necessary, extender pigments may be added within a range that does not impair transparency, or a small amount of coloring pigments or coloring dyes may be added to form a color clear. The mixing ratio of the fluorine-containing copolymer and the curing agent is the same as that of the acrylic copolymer and the curing agent, and it is possible to exhibit the original resin properties. Next, in the present invention, the coating film forming method is as follows:
Do it in the normal way. For example, apply a metallic base paint to the surface of the object that has been previously treated with a primer, surfacer, etc. as necessary, and adjust the viscosity to 10 to 30 seconds (Food Cup #4/20℃) with an organic solvent for dilution as necessary. Then, coat the surface of the object to a dry film thickness of approximately 5 to 35 μm. Next, add top clear paint to a viscosity of 15 to 40 (Food Cup #4/
20℃) and apply the coating to a dry film thickness of approximately 10 to 50μ. As for the painting method, regular spray painting, electrostatic painting, etc. are used for both metallic base paint and top clear paint. However, other coating methods can be equally used, and there are no particular restrictions. In addition, in the present invention, the top clear paint is
Although it is possible to overcoat the metallic base paint film whether it is in an undried state or a dry state, the former is preferred in terms of shortening the painting process. When applying top clear paint when the metallic base paint film is still wet, apply for 30 seconds or more.
It is best to wait about 10 minutes for setting time before reapplying. 5-40 after painting with top clear paint
After about a minute of setting time to make the coating sufficiently smooth and to volatilize the internal solvent, both coatings are dried. When drying at room temperature, leave it at room temperature for about 1 to 5 days to dry and harden. In addition, in the case of baking and drying, it is dried and hardened at 60 to 240° C. for a predetermined period of time using a conventional hot air drying oven, far-infrared oven, or the like. The baking conditions should be appropriately selected depending on the type of hardening agent, etc. Normally, when using an aminoplast compound, the temperature is about 130 to 170℃, and the temperature is about 10 to 100℃.
50 minutes is appropriate. In addition, when using a blocking isocyanate compound, the baking temperature should be set according to the dissociation temperature of the masking agent, but it is usually about 140 to 180℃.
Approximately 10 to 50 minutes is appropriate. In addition, if high temperature and short time baking conditions are required, approximately 200 to 240℃ and approximately 30 to
It is also possible to dry and cure in 300 seconds. [Effects of the Invention] In the coating film obtained by the coating method of the present invention, the intermolecular bonds of the resin are extremely stable because the fluorine-containing copolymer is used as a resin component in the top clear coating. Therefore, it has extremely high durability against various damages caused to the paint film due to long-term outdoor exposure, such as ultraviolet rays, heat rays, moisture, acidic substances, oxides, dust, and pollutants. There is. Therefore, it can be said that a coating film with excellent weather resistance, corrosion resistance, chemical resistance, etc. can be obtained. Furthermore, even if the metallic base paint and the top clear paint are applied wet-on-wet, since a specific acrylic copolymer is used as the resin component, the scaly metal powder in the metallic base paint will be transferred to the top clear layer. It doesn't move much. Therefore,
A good metallic feel without metallic unevenness can be obtained, and a coating film with excellent appearance such as gloss and grain can be obtained. Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, "part" and "%" in the examples are based on weight. Furthermore, the following fluorine-containing copolymers and acrylic copolymers were used in Examples and Comparative Examples. <Fluorine-containing copolymer solution> (1) Fluorine-containing copolymer solution (A) Monomers consisting of 55.2% chlorotrifluoroethylene, 20.0% cyclohexyl vinyl ether, 15.0% ethyl vinyl ether, and 9.8% hydroxybutyl vinyl ether. Japanese Patent Publication No. 57-34107
A 60% xylene solution of a fluorine-containing copolymer (hydroxyl value 28.3, Tg 45°C) was prepared according to the method described in the publication. (This is referred to as fluorine-containing copolymer solution (A)) (2) Fluorine-containing copolymer solution (B) Consists of 47% tetrafluoroethylene, 30% cyclohexyl vinyl ether, 8% ethyl vinyl ether, and 15% hydroxybutyl ether. Monomers were polymerized in the same manner to prepare a 60% xylene solution of a fluorine-containing copolymer (hydroxyl value 43.4, Tg 35°C). (This is referred to as fluorine-containing copolymer solution (B)) <Acrylic copolymer solution> 70 parts of xylol and 30 parts of butyl acetate were charged into a reactor equipped with a thermometer, a stirrer, a cooling tube, and a dropping roll. After raising the temperature to 80°C, a mixture of 100 parts of the monomer mixture shown in Table 1 and 1.5 parts of azobisisobutyronitrile was added dropwise over about 2 hours, and the mixture was reacted with stirring. Furthermore, 0.5 part of azobisisobutyronitrile was added, the temperature was raised to 85°C, and the reaction was stirred for about 4 hours to prepare an acrylic copolymer solution with a nonvolatile content of 50% and a number average amount of 12,000 to 25,000.

[Table] <Metallic base paint> The components shown in Table 2 were mixed to prepare a metallic base paint. For Metallic Base paint No., a polyvalent isocyanate solution was mixed immediately before painting.

[Table] <Top clear paint> The components shown in Table 3 were mixed to prepare a metallic base paint. In Top Clear Paint No. (4), a polyvalent isocyanate solution was mixed immediately before painting.

【table】

[Table] Examples 1 to 7 and Comparative Examples 1 to 4 The table below was applied to a coated object prepared by applying a cationic electrodeposition coating film and a polyester-melamine resin intermediate coating film to a mild steel plate.
Adjust the metallic base paint shown in 4 to a viscosity of 12 seconds (Food Cup #4, 20℃) with a mixed solvent of butyl acetate/ethylene glycol monoethyl ether acetate/xylene (30/20/50), then dry with air spray. The coating was applied to a film thickness of 25μ. After setting for 3 minutes, the top clear paint shown in Table 4 was adjusted to a viscosity of 30 seconds using the above-mentioned mixed solvent, and then coated with air spray until the dry film thickness was 30 μm.
After setting for 10 minutes, it was baked and dried at 150°C for 20 minutes. The results of various performance tests of the resulting coating film are shown in the lower row of Table 4. Example 8 The metallic base paint and top clear paint shown in Table 4 were coated in the same manner as in Example 1 after adjusting the viscosity. Thereafter, it was left to dry at room temperature for 2 days. The results of various performance tests of the resulting coating film are shown in the lower row of Table 4. As is clear from Table 4, the coating film obtained by the method of the present invention has a metallic feel, gloss, and sharpness, and has an excellent coating appearance.
Furthermore, the weather resistance and acid resistance were also excellent. On the other hand, Comparative Examples 1 and 3, in which the contents of styrene and methyl methacrylate in the acrylic copolymer were too high, had poor flexibility and poor impact resistance. On the other hand, Comparative Example 2, in which the content of styrene and methyl methacrylate in the acrylic copolymer was too low, had a very poor metallic feel.

【table】

【table】

Claims (1)

[Claims] 1. Methyl methacrylate, styrene, or a mixture of these monomers is added as a copolymerization component to the object to be coated.
A base paint containing scale-like metal powder containing 10 to 60% by weight of an acrylic copolymer with a hydroxyl value of 10 to 150 as a resin component is applied, followed by a top coat containing a fluorine-containing copolymer containing hydroxyl groups as a resin component. A metallic coating method characterized by applying multiple coats of clear paint and then curing both coats at the same time.