JPH0474068B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for forming a coating film that takes advantage of the metallic luster of a metal base material made of stainless steel, aluminum, copper, or brass and has excellent long-term weather resistance and corrosion resistance. <Prior Art> It has been widely practiced to coat metal substrates with colored paints in order to give them aesthetic appearance and corrosion resistance. On the other hand, metal substrates such as stainless steel, aluminum, copper, or brass are widely used without being coated with colored paint in order to take advantage of the metallic luster of the metal substrate itself. However, such metal substrates are also coated with clear paint to prevent stains such as hand marks from adhering to them and to maintain their metallic luster. However, when a commonly used clear paint based on acrylic resin thread or polyester resin is applied, there is a problem in that after being left outdoors for several years, the paint film itself develops yoking and the like, resulting in a decrease in metallic luster. Therefore, it has been considered to apply a fluororesin-based clear paint that has good long-term weather resistance. <Problems to be Solved by the Invention> However, when a fluororesin-based clear paint is applied to a metal base material such as stainless steel, the metallic luster can be maintained for a long period of time, but when exposed outdoors, the paint may unexpectedly deteriorate. Even though rust does not occur on metal substrates such as stainless steel, there has been a phenomenon in which rust occurs on the surface of the metal substrate under the coating on metal substrates coated with fluororesin-based clear paint. . Although the cause of this is not certain, it is probably predicted to be as follows. In other words, metal base materials such as stainless steel have a high reflectance of sunlight and other light rays, including ultraviolet rays, while fluororesin-based clear coatings have a higher reflectance than other general acrylic resin-based, polyester-based, etc. clear coatings. However, the transmittance of ultraviolet rays is high, so the paint film is exposed to sunlight (transmitted light and reflected light) outdoors.
Part of the fluororesin decomposes under the influence of heat, and the decomposition products, highly active low-molecular compounds such as fluorides and chlorides, become corrosion factors, corrode the surface of the metal base material, and cause rust. It is thought that this causes the occurrence of As a result of intensive studies in view of the current situation, the present inventors have found a method that maintains the metallic luster of the metal base material such as stainless steel for a long period of time, and takes advantage of the long-term weather resistance of the fluororesin clear coating. The present invention has been achieved by discovering a method for forming a coating film that also prevents the occurrence of rust. <Means for Solving the Problems> Therefore, the present invention involves coating a metallic base material made of stainless steel, aluminum, copper, or brass with metallic luster with an acrylic resin-based clear paint, and then coating the base material with an acrylic resin-based clear paint containing hydroxyl groups. applying a fluoroplastic clear paint containing a fluorine-containing copolymer and a curing agent;
The present invention provides a method for forming a coating film with metallic luster. Since a fluororesin-based clear coating is applied to the metal substrate by the method of the present invention, the metallic luster can be maintained for a long period of time, and the acrylic resin-based clear coating is protected by the fluororesin-based clear coating for a long time. Long-term weather resistance is achieved without causing paint film defects such as yoking, and an acrylic resin-based clear coating film with high absorption rate for ultraviolet rays is interposed between the metal base material and the fluororesin-based clear coating film. This makes it possible to alleviate the generation of the above-mentioned corrosion factors from the fluororesin, and to prevent the generation of rust on the surface of the metal base material since it does not come into direct contact with the metal base material. The present invention will be explained in more detail below. The acrylic resin-based clear paint used in the present invention is a lacquer type that is usually used for various metals such as automobiles, a two-component type consisting of a combination with a polyvalent isocyanate as a hardening agent, and a hardening agent. Various room-temperature-curing acrylic resin-based clear paints such as one-component types made of a combination with blocked polyisocyanate or aminoplast resin, bake-curing acrylic resin-based clear paints, and ultraviolet-curable acrylic resin-based clear paints. These paints can be used without any particular restrictions, and these paints may be of organic solvent type or water-based type. Acrylic copolymers used as binders for acrylic resin-based clear paints are esterified with alkanols such as methyl, ethyl, propyl, and 2-ethylhexyl acrylates, and methyl, ethyl, propyl, butyl, and 2-ethylhexyl metadalylates. The main components are acrylic esters and methacrylic esters, and in addition to these, α,β-monoethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid; 2-hydroxyethyl acrylate, 2-hydroxyethyl acrylate, etc. Hydroxyalkyl esters of α,β-monoethylenically unsaturated carboxylic acids such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate; acrylamide, N-methylolacrylamide, N-butoxymethylacrylamide, diacetone acrylamide , N-methylolmethacrylamide, N-butoxymethylmethacrylamide, diacetone methacrylamide, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, etc. Compound: monoethylenically unsaturated compound containing a glycidyl group such as glycidyl ester of acrylic acid and methacrylic acid; and a monomer mixture obtained by appropriately combining various monomers such as styrene, acrylonitrile, methacrylonitrile, etc., copolymerized by a conventional method. It is. In particular, in the present invention, a copolymer containing an amino group or a glycidyl group using the above-mentioned amino group- or glycidyl group-containing monoethylenically unsaturated compound has a remarkable effect in preventing the occurrence of rust. Although the reason for this is not clear, it is probably because the amino groups and glycidyl groups react with the corrosion factors and inactivate them. In addition, the monomer containing an amino group or a glycidyl group is 1 to 30 mol% in the acrylic copolymer,
Preferably, a content of 4 to 20 mol % is suitable, and in the above range, the effect of preventing rust generation appears to be significant. Incidentally, if the amount is too much above the above range, water resistance, weather resistance, etc. tend to be adversely affected. Further, the acid value of the acrylic copolymer is suitably 10 or less, and the number average molecular weight is suitably about 2,000 to 150,000. Furthermore, as the binder, an acrylic copolymer modified with silicone can also be used. The acrylic resin-based clear paint used in the present invention is made by blending the above-mentioned binder with various solvents, etc., and, if necessary, adding curing agents, ultraviolet absorbers, alumina, silica, etc. It contains a small amount of various additives such as additives, modifiers such as cellulose acetate butyrate, extender pigments, and coloring pigments and dyes to the extent that they do not inhibit metallic luster. In addition, when using the above-mentioned curing agent, it is appropriate that the acrylic copolymer has a hydroxyl value of about 20 to 120. 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 of polymers or excess of these isocyanate compounds with low-molecular polyols such as ethylene glycol, 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, blocked isocyanate compounds obtained by masking the polyvalent isocyanate compounds with masking agents such as phenols, alcohols, oximes, lactams, amines, amides, etc. can also be used, and in this case, they are mixed with the polyol component in a predetermined ratio. By doing so, it becomes a one-component paint that can be cured by baking. 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 (0.1-1.3/1) particularly preferably (0.2-1.3/1)
1.0/1), 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 butanol. still,
When an aminoplast compound is used, it becomes a one-component paint that can be cured by baking by mixing it with the polyol component in a predetermined ratio. 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. Next, the fluororesin-based clear paint used in the present invention is a fluororesin-based clear paint that contains a fluorine-containing copolymer containing a hydroxyl group and a curing agent, and can be cured at room temperature or by baking at a low temperature. Moreover, it is soluble in ordinary organic solvents for paints. For example, a fluororesin-based clear paint containing as a binder a fluorine-containing copolymer containing fluoroolefin and vinyl ether as main components described in JP-A-57-34107 is suitable. That is, the fluorine-containing copolymer contains fluoroolefin, cyclohexyl vinyl ether, alkyl vinyl ether, and hydroxyalkyl vinyl ether as constituent components, and contains 30 to 70% by weight and 5 to 5% by weight, respectively.
60% by weight, 5 to 60% by weight, and 3 to 25% by weight, and the number average molecular weight is about 3000 to about
A fluorine-containing copolymer of 100,000 is preferred. In the above, if the fluoroolefin content is too low, the weather resistance will deteriorate, 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, hydroxyalkyl vinyl ether is
It is appropriate to use the above content 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. Adhesion tends to decrease. Further, in the fluorine-containing copolymer, as the fluoroolefin, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, etc. are preferable. Further, as the alkyl vinyl ether, those containing a linear or branched alkyl group having 2 to 8 carbon atoms, particularly those in which the alkyl group has 2 to 4 carbon atoms, are preferable. Moreover, as the hydroxyalkyl vinyl ether, one containing a hydroxyalkyl group having 2 to 8 carbon atoms is suitable. The fluorine-containing copolymer may contain comonomers other than the above-mentioned constituents in an amount not exceeding 40% by weight. Such comonomers include ethylene, propylene, isobutylene, vinyl chloride,
Typical examples include vinylidene chloride, methyl methacrylate, butyl acetate, and the like. Examples of such fluorine-containing copolymers include Lumiflon LF100, 200, 210, 300, 400, 510, and 700.
(all brand names manufactured by Asahi Glass Co., Ltd.) etc. are commercially available. Also, JP-A-59-189108, JP-A-60-
Publication No. 67518, Japanese Patent Application Publication No. 61-264065, Japanese Patent Application Publication No. Sho 61-264065
The fluorine-containing copolymers described in Japanese Patent No. 61-272273 and the like can also be suitably used in the present invention because they are soluble in common organic solvents for paints. The curing agent used in the fluororesin-based clear paint in the present invention may be the same as the curing agent used in the acrylic resin-based clear paint, and may be a polyvalent isocyanate having two or more isocyanate groups in one molecule. compounds, blocked isocyanate compounds, aminoplast compounds, etc. can be used. Further, the blending ratio of the fluorine-containing copolymer containing hydroxyl groups and the curing agent may be the same as in the case of the acrylic resin-based clear paint. In other words, when using an isocyanate compound as a curing agent, the equivalent ratio of isocyanate groups to hydroxyl groups is 0.1 to 1.3/
1, preferably 0.2 to 1.0/1, and when using an aminoplast compound as a curing agent, the mixing ratio (by weight) of the polyol component and the aminoplast compound component of the fluororesin clear paint is 95: 5-60:40, preferably 90:10-
The time shall be 70:30. The fluororesin-based clear paint used in the present invention is composed of the above-mentioned fluorine-containing copolymer as a binder and a curing agent, and various solvents, etc., blended in the usual way, and if necessary, the above-mentioned Similar to acrylic resin-based clear paints, it contains small amounts of various additives such as ultraviolet absorbers and erasing agents, modifiers, extender pigments, and colored pigments and dyes to the extent that they do not inhibit metallic luster. Next, the coating film forming method of the present invention will be explained. In order to improve adhesion as necessary, the surface of the metal base material is made rough by etching, etc., or treated with a chelating agent, a coupling agent, etc., and then the acrylic resin-based clear paint is applied by spray coating, electrostatic coating, etc. Coating is done by means such as roll coating so that the dry film thickness is approximately 5 to 20 μm. In addition, if the film thickness is thinner than the above range, the ability to absorb ultraviolet rays will not be fully exhibited, and the corrosion factors will not be sufficiently blocked from the surface of the metal base material.On the other hand, if the film thickness is thicker than the above range, the ultraviolet rays will not be able to be fully utilized, and if the film thickness is thicker than the above range, the ultraviolet rays will not be able to be fully absorbed. As the amount of acrylic resin-based clear coating increases, chemical resistance, weather resistance, etc. tend to decrease. Next, the above-mentioned fluororesin clear paint is applied in the same manner so that the dry film thickness is about 5 to 60 μm. In addition, if the film thickness is thinner than the above range, the film performance such as long-term weather resistance and chemical resistance will not be fully exhibited, and the protection of the acrylic resin clear paint film will be insufficient. The metallic luster, which is the original objective of the present invention, tends to be impaired. The acrylic resin clear paint and the fluororesin clear paint may be applied after the former is dried, or the latter may be applied wet or on-wet while the former is undried. <Effects of the Invention> Since the clear coating film is applied to the metal substrate by the method of the present invention, the metallic luster can be maintained for a long period of time, and the acrylic resin-based clear coating film is protected by the fluororesin-based clear coating film. , long-term weather resistance has been improved, and since the acrylic resin clear coating film, which has a high absorption rate for ultraviolet rays, is interposed between the metal base material and the fluororesin clear coating film, corrosion factors from the fluororesin are not generated. Since it does not come into direct contact with the metal base material, it prevents the occurrence of rust on the metal base material. Therefore, by the method of the present invention, the metal substrate can maintain its metallic luster in good condition for a long period of time. The present invention will be explained in more detail below. In addition,
In the examples, "parts" and "%" are expressed on a weight basis. <Acrylic resin clear paint A> 44 parts of ethyl acrylate, 43 parts of isobutyl methacrylate, 12 parts of hydroxyethyl methacrylate
0.8 parts of methacrylic acid, and 0.2 parts of polymerization catalyst were added dropwise into a solvent consisting of 50 parts of xylene and 50 parts of butyl acetate, and solution polymerization was carried out in a conventional manner to form an acrylic resin with a non-volatile content of 50% (glass transition temperature: 14°C). , hydroxyl value
52, acid value 5) A solution was obtained. Acrylic resin clear paint A was prepared by adding 9 parts of hexamethylene diisocyanate as a binder ("Sumidyur N-75" (trade name, manufactured by Sumitomo Bayer), solid content 75%) to 90 parts of this solution. <Glycidyl group-containing acrylic resin clear paint B> 70 parts of 2-ethylhexyl acrylate, 16 parts of isobutyl methacrylate, 7 parts of hydroxyethyl methacrylate, 6 parts of glycidyl methacrylate
part, 1 part of polymerization catalyst, 50 parts of xylene, butyl acetate
The mixture was added dropwise to 50 parts of a solvent and solution polymerized using a conventional method to obtain an acrylic resin solution (glass transition temperature: 5° C., hydroxyl value: 30) with a nonvolatile content of 50%. Add 80 parts of this solution to butyl etherified melamine resin.
20 parts were added to prepare glycidyl group-containing acrylic resin clear paint B. <Amino group-containing acrylic resin clear paint C> 42 parts of methyl methacrylate, 3 parts of ethyl methacrylate, 30 parts of 2-ethylhexyl methacrylate
15 parts of hydroxypropyl methacrylate, 5 parts of styrene, 5 parts of dimethylaminoethyl methacrylate, and 1 part of the polymerization catalyst were added dropwise into a solvent consisting of 20 parts of cyclohexanone and 80 parts of toluene, and solution polymerization was carried out in a conventional manner to remove non-volatile components. A 50% acrylic resin solution (glass transition temperature: 42°C, hydroxyl value: 58) was obtained. On the other hand, 55.5 parts of a polyisocyanate having a cyanurate ring, which is a trimer of hexamethylene diisocyanate, was dissolved in 20 parts of methyl ethyl ketone,
To this, 24.5 parts of methyl ethyl ketone oxime was added and reacted to obtain a blocked isocyanate compound solution (NCO equivalent: 359, non-volatile content: 80%). 13 parts of this blocked isocyanate compound solution,
Amino group-containing acrylic resin clear paint C was prepared by mixing 87 parts of the acrylic resin solution and 1 part of γ-aminopropyltriethoxysilane. <Fluoroplastic clear paint D> A monomer consisting of 52 parts of chlorotrifluoroethylene, 21 parts of 4-hydroxy-n-butyl vinyl ether, 17 parts of cyclohexyl vinyl ether, and 10 parts of ethyl vinyl ether is described in JP-A-57-34107. A 60% xylene solution of a fluorine-containing copolymer (number average molecular weight 6800, hydroxyl value 100) was obtained according to the method described in . Fluororesin clear paint D was prepared by adding 1 part of a surface conditioner and 23 parts of the hexamethylene diisocyanate binder to 100 parts of this solution. <Fluoroplastic color clear paint E> Monomers consisting of 30 parts of chlorotrifluoroethylene, 25 parts of tetrafluoroethylene, 10 parts of 4-hydroxy-n-butyl vinyl ether, 18 parts of cyclohexyl vinyl ether, and 17 parts of ethyl vinyl ether were A 40% cyclohexanone solution of a fluorine-containing copolymer (number average molecular weight 45,000, hydroxyl value 52) was obtained according to the method described in Japanese Patent No. 57-34107.
To 100 parts of this solution, 1 part of the transparent iron oxide pigment and 5 parts of the aforementioned blocked isocyanate compound solution were added to prepare a fluororesin-based gold color clear paint E. <Fluororesin clear paint F> 49 parts of methyl methacrylate, 30 parts of isobutyl methacrylate, 1 part of methacrylic acid, and 20 parts of hydroxypropyl methacrylate were solution-polymerized in a mixed solvent consisting of xylol and butyl acetate (1:1), Acrylic resin with non-volatile content of 60% (number average molecular weight
5000, hydroxyl value 86, acid value 6.5) solution was obtained. 50 parts of the acrylic resin solution, 50 parts of the fluorine-containing copolymer solution used in Paint D, 1 part of γ-aminopropyltriethoxysilane, 1 part of ultraviolet absorber, 32 parts of the blocking isocyanate compound solution, surface preparation agent. 0.5 parts were mixed to prepare fluororesin clear paint F. Example 1 Degreased stainless steel (SUS) with a thickness of 0.5 mm
#304-HL), acrylic resin clear paint A adjusted to a viscosity of 20 seconds (FC #4/20°C) with a diluent of butyl acetate/xylol/cellosolve acetate = 40/40/10 to a dry film thickness of 10μ. It was air-sprayed and dried at 80℃ for 30 minutes. Next, fluororesin clear paint D, whose viscosity was adjusted to 20 seconds in the same manner, was applied by air spray to give a dry film thickness of 40 μm, and dried at 80° C. for 30 minutes. Measurement of initial gloss and accelerated weathering test (Du cycle, test time 500 hours) on the obtained coated board
The resulting gloss and color difference were measured and the state of the coated plate was observed. The results are shown in Table 1. Example 2 In the same manner as in Example 1, a glycidyl group-containing acrylic resin clear paint B adjusted to a viscosity of 20 seconds was air-sprayed onto a stainless steel plate to a dry film thickness of 10 μm, and baked at 150° C. for 30 minutes. Next, a fluororesin clear paint F adjusted to a viscosity of 20 seconds was applied by air spray to give a dry film thickness of 10 μm, and baked at 150° C. for 30 minutes. The obtained coated plate was subjected to the same test as in Example 1, and the results are shown in Table 1. Example 3 A stainless steel plate was coated with amino group-containing acrylic resin clear paint C adjusted to a viscosity of 140 seconds using a diluted solvent of cyclohexanone/isophorone = 90/10 to a dry film thickness of 5 μm using a roll coater.
It was baked by passing it through a baking oven at ℃ for 1 minute. Next, a fluororesin color clear paint E adjusted to a viscosity of 140 seconds in the same manner was coated to a dry film thickness of 20 μm and baked. The obtained coated plate was subjected to the same test as in Example 1, and the results are shown in Table 1. Example 4 In Example 2, plate thickness was used instead of stainless steel plate.
A coated plate was obtained in the same manner except that a 0.8 mm chromate-treated aluminum plate was used. Measurement of initial gloss and accelerated weathering test (Sunshine Weatherometer test)
After 5,000 hours), the gloss and color difference were measured and the state of the coated plate was observed. The results are shown in Table 1. Example 5 In Example 2, a plate thickness of 1 was used instead of the stainless steel plate.
A coated plate was obtained in the same manner except that a mm copper plate was used. The obtained coated plates were measured for initial gloss, gloss and color difference after an outdoor exposure test (5 years), and observation tests for the condition of the coated plates, and the results are shown in Table 1. Example 6 A coated product was obtained in the same manner as in Example 2 except that a polished brass cast product was used instead of the copper plate,
The same test as in Example 5 was conducted and the results are shown in Table 1. Comparative Example 1 A test similar to that of Example 1 was conducted without coating the stainless steel plate of Example 1, and the results were compared to the first example.
Shown in the table. Comparative Example 2 In Example 1, two layers of acrylic resin clear paint A were applied to a dry film thickness of 25 μm (total film thickness
A coated plate was obtained in the same manner except that 50μ) was used, and the same tests were conducted, and the results are shown in Table 1. Comparative Example 3 In Example 2, fluororesin clear paint F was applied in two layers to a dry film thickness of 10 μm (total film thickness
A coated plate was obtained in the same manner except that 20 μ) was used, and the same test was conducted. The results are shown in Table 1. Comparative Example 4 The same test as in Example 5 was conducted without coating the copper plate of Example 5, and the results are shown in Table 1. Comparative Example 5 A coated plate was obtained in the same manner as in Example 5 except that fluororesin clear paint F was used instead of glycidyl group-containing acrylic resin clear paint B.
A similar test was conducted and the results are shown in Table 1. As is clear from Table 1, the examples of the present invention had excellent performance. On the other hand, the stainless steel of Comparative Example 1, which was not coated, became completely white and the specular gloss of the metal was also reduced. Furthermore, in the stainless steel of Comparative Example 2, which was coated with two layers of acrylic resin-based clear paint, the paint film became opaque due to chalking, and red spot rust was generated around the cracks. Further, in the stainless steel of Comparative Example 3, which was coated with two layers of fluororesin-based clear paint, red spots of rust with a diameter of 0.2 to 1 mm were generated along the hairline processing lines of the stainless steel, and the metallic feel was significantly lost. In addition, the copper plate of Comparative Example 4, which was not coated, was completely blackened and green rust was generated in some parts. Further, in the copper plate of Comparative Example 5, which was coated with two layers of fluororesin-based clear paint, black rust occurred on the lower surface of the paint film, and the metallic luster of the copper disappeared.

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Claims (1)

[Claims] 1. An acrylic resin-based clear paint is applied to a metallic base material made of stainless steel, aluminum, copper, or brass that has a metallic luster, and then a fluorine-containing copolymer containing a hydroxyl group and a curing agent are applied. A method for forming a coating film with a metallic luster, characterized by applying a fluororesin-based clear paint containing. 2. The method for forming a coating film with metallic luster according to claim 1, wherein the acrylic resin has a glycidyl group or an amino group.