JPH0333112A - Fluorinated copolymer and coating composition - Google Patents

Abstract

PURPOSE:To obtain a fluorinated copolymer adapted for use in a coating material excellent in appearance and film properties by constituting the copolymer from the units derived from a fluoroolefin, those derived from a perfluorovinyl ether and those having specified hydroxyls. CONSTITUTION:A fluoroolefin (A) (e.g. chlorotrifluoroethylene) is reacted with a perfluorovinyl ether (B) of the formula [wherein Rf is a perfluoro(alkoxyl) alkyl] and a hydroxylated monomer (C) containing at least 10mol% sec. hydroxyl-containing monomer (e.g. 4-hydroxybutyl vinyl ether) at -30 deg.C to 150 deg.C under a pressure of 1-100kg/cm<2> in the presence of a polymerization initiator in a polymerization solvent to obtain the title copolymer comprising 20-60mol% polymer units derived from component A, 1-40mol% polymer units derived from component B and 5-40mol% polymer units having hydroxyls and containing at least 10mol% polymer units having sec. hydroxyl and an intrinsic viscosity in an uncrosslinked state of 0.05-2.0dl/g (in tetrahydrofuran at 30 deg.C).

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a fluorine-containing copolymer and a coating composition. [Conventional technology] Conventionally, alkyd/melamine resin paints, acrylic melamine resin paints, etc. have been used as top coats for automobiles, but they are not necessarily sufficient in terms of weather resistance, water repellency, etc., and long-term beauty is not guaranteed. I have been carefully waxing to maintain this, but I am not satisfied with the result. Fluoroolefins to solve such problems. It has been proposed to use a fluorine-containing copolymer obtained by reacting a copolymer of cyclohexyl vinyl ether, alkyl vinyl ether, and hydroxyalkyl vinyl ether with an anhydride of a polybasic acid in a coating composition. (
(Refer to JP-A No. 61-200145) However, the resin in this case is required to contain 60 mol% or less of fluoroolefin in order to provide solubility in common paint solvents. . As a result, the fluorine content of the resin is lower than that of general fluororesins, and the surface properties unique to fluorine-containing resins, such as resistance to soot and dust on coatings and water and oil repellency, are not necessarily sufficient compared to PTFE. I can't say it anymore. On the other hand, in order to improve the stain resistance, water and oil repellency, etc. of the coating film, per 100 parts by weight of a fluorine-containing copolymer containing a fluoroolefin and a vinyl ether as essential constituents and having a crosslinked portion, the fluorine-containing copolymer and A coating resin composition containing 0.1 to 30 parts by weight of a co-crosslinkable polyfluoroalkyl group-containing polymer has been proposed (Japanese Patent Laid-Open No. 61-152).
(See Publication No. 771). However, the coating film obtained from the coating composition has weather resistance and stain resistance. Although it has excellent water and oil repellency, it has a disadvantage in that it has poor adhesion during recoating, so pretreatment such as sanding must be performed when repairing the coating film. [Problems to be solved by the invention] The present invention solves the above-mentioned problems that the prior art had, and improves the appearance and performance of the coating film (e.g., weather resistance, water repellency, recoat adhesion, etc.). The object of the present invention is to provide a fluorine-containing copolymer used in a coating composition that provides an excellent coating film, and a method for producing the same.

[Means to solve the problem]

The present invention was made in order to solve the above-mentioned problems, and consists of 20 polymerized units (1) based on fluoroolefins.
~60 mol%, 1 to 40 mol% of polymerized units (2) based on perfluorovinyl ether represented by CF, =CFORt (R, is a perfluoroalkyl group or perfluoroalkoxyalkyl group), and 1 to 40 mol% of polymerized units (2) having a hydroxyl group ( 3) in a ratio of 5 to 40 mol%, at least 10 mol% of the polymerized unit (3) having a hydroxyl group is a polymerized unit (3') having a secondary hydroxyl group, and in an uncrosslinked state it is The intrinsic viscosity at °C is 06
05 to 2.0 dl/g. In the fluorine-containing copolymer of the present invention, the fluoroolefins include tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, vinylidene fluoride, hexafluoropropylene, pentafluoropropylene, and fluoroolefins having about 2 to 4 carbon atoms. is preferably adopted. In particular, perhaloolefins such as tetrafluoroethylene 9-chlorotrifluoroethylene are preferred, and the fluoroolefins may be used alone or in combination. In addition, as perfluorovinyl ether, formula CFa
=CFORf is adopted. Here R
f is a linear 9-branched or cyclic perfluoroalkyl group or perfluoroalkoxyalkyl group. As R2, it is preferable to employ one having 1 to 8 carbon atoms. If the number of carbon atoms in R2 is too large, copolymerizability with fluoroolefins and other monomers will decrease, making it difficult to obtain the desired polymer. Specific R2 is −〇Fs, −
CFzCFs, -CF*CFtCF*. Ru. Furthermore, the polymerized unit (3) having a hydroxyl group is formed by copolymerizing a hydroxyl group-containing monomer, or by introducing a hydroxyl group into a polymer. Here, examples of the hydroxyl group-containing monomer include hydroxyl group-containing ethylenically unsaturated monomers such as hydroxyalkyl vinyl ether and hydroxyalkyl allyl ether.As a method for introducing hydroxyl groups into the tetrapolymer, after polymerization, hydration is performed. There are methods such as copolymerizing monomers that form hydroxyl groups through decomposition and then forming hydroxyl groups through hydrolysis. In addition, the polymerized unit having a secondary hydroxyl group is formed by a method such as copolymerizing a monomer having a secondary hydroxyl group or converting a primary hydroxyl group into a secondary hydroxyl group. . Examples of monomers having secondary hydroxyl groups include vinyl ethers having υ■ hydroxyl groups. In the above formula, n is an integer of 1 or more, but if n is too large, the coating film will become soft, sticky, or easily stained, which is undesirable, and preferably 1 to 6.
is an integer. Furthermore, if n is small, the coating film tends to become hard and brittle, but this does not cause any particular problem. Particularly preferably, n is an integer from 1 to 3. It is also possible to use vinyl ethers having secondary hydroxyl groups with different n's. Examples of the vinyl ether having a secondary hydroxyl group include 2-hydroxypropyl vinyl ether, 3
-Hydroxybutyl vinyl ether, 4-hydroxypentyl vinyl ether, etc. are exemplified. Further, as a method for converting a primary hydroxyl group into a secondary hydroxyl group, there is a method of adding an alkylene oxide such as propylene oxide. This alkylene oxide addition reaction can be carried out in the same manner as in the production of ordinary polyether compounds. The fluorine-containing copolymer of the present invention contains 20 to 60 mol% of polymerized units (1) based on fluoroolefins. Contains 1 to 40 mol% of a polymerized unit (2) based on perfluorovinyl ether represented by CFi=CFORf and 5 to 40 mol% of a polymerized unit (3) having a hydroxyl group. ) of at least 10
% by mole is the polymerized unit (3') having a secondary hydroxyl group. If the proportion of polymerized units (1) is less than the above range, sufficient weather resistance will not be obtained when used as a paint base, which is undesirable; if it is too large, solubility in various solvents will decrease, Difficult to use as paint base or paint additive. In addition, since the polymerized unit (2) is contained in the above ratio, when used as a paint base or paint additive, the paint film has excellent water and oil repellency and stain resistance. It exhibits non-adhesive properties. If the proportion of polymerized units (2) is less than the above, the properties of the coating film will not be satisfactory, and if it is too large, the solubility in solvents will decrease, making it difficult to use as a paint base or paint additive. If the proportion of polymerized units (3) is less than the above proportion, the solvent resistance of the cured coating may decrease when used as a paint base, which is undesirable; if it is too large, the coating will be hard and brittle. This is undesirable because it may cause the coating to become dry or cause a decrease in water resistance due to the hydroxyl groups remaining in the cured coating film. Furthermore, it is important that at least 10 mol% of the polymerized units (3) are polymerized units (3') having a secondary hydroxyl group. The fluorine-containing copolymer of the present invention containing polymerized units (3') in this proportion provides excellent adhesion when a coating film formed using the same is repainted with a paint. In addition, since the polymerized unit (3') is contained in this proportion, even when used in a paint, a surface modification effect can be obtained with a small amount, and the surface properties can be maintained over a long period of time. achieved. In other words, when conventionally known polyfluoroalkyl group-containing polymers are blended, a modification effect can be obtained with a small amount, but there are problems with repaintability and long-term durability, and polymers containing only primary hydroxyl groups have problems. do not,
In the case of a copolymer such as JP-A No. 63-218715,
Although the effect of surface improvement is maintained, the disadvantages of not being able to obtain a sufficient improvement effect when added in small amounts and having poor repaintability are also solved at the same time. Furthermore, the coating film using the polymer of the present invention has an advantage of superior image clarity compared to the coating film using a copolymer such as that disclosed in JP-A No. 63-218715. This is also considered to be due to the presence of a secondary hydroxyl group. Further, the fluorine-containing copolymer of the present invention has the above polymerized unit (1
) to (3), lowering the melting point or glass transition point of the fluorine-containing copolymer, further improving coating workability, and imparting physical properties such as appropriate hardness, flexibility, and gloss to the coating film. In addition to the above-mentioned polymerized units (1) to (3), polymerized unit (4) is included depending on the purpose of improving compatibility with curing agents, pigments, other resins, etc. Good too. The comonomer used to form the polymerized unit (4) is a comonomer that has an active unsaturated group to the extent that it can be copolymerized with fluorene and does not significantly impair the weather resistance of the coating film. alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, inbutyl vinyl ether, cyclohexyl vinyl ether, vinyl acetate, vinyl propylonate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl cyclohexanecarboxylate esters of alkyl carboxylic acids and vinyl alcohol such as, alkyl allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether, cyclohexyl allyl ether, ethyl allyl ester, propyl allyl ester,
Butyl allyl ester, inbutyl allyl ester. Alkyl allyl esters such as cyclohexyl allyl ester, alkenes such as ethylene, propylene, butylene, inbutylene, acrylic acid, methacrylic acid or ethyl acrylate. Propyl acrylate, butyl acrylate. Isobutyl acrylate% 2-ethylhexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate,
Examples include esters of acrylic acid or methacrylic acid such as 2-ethylhexyl methacrylate, and partially fluorine-substituted compounds thereof. Such comonomers may be used singly or in combination of two or more. In addition, as comonomers, vinyl compounds, allyl compounds, or alkenes having excellent copolymerizability with fluoroolefins are used. Preferably adopted. Furthermore, when a vinyl or allyl alkyl ester or alkyl ether is employed, the alkyl group is preferably a linear nine-branched or alicyclic alkyl group having about 2 to 10 carbon atoms; In addition to hydroxyl groups, the fluorine-containing copolymer may have groups that can react with isocyanate groups and groups that improve pigment dispersibility, such as carboxylic acid groups, epoxy groups, and amino groups. A fluorine-containing copolymer having groups can be obtained by copolymerizing monomers having those groups, or by reacting a hydroxyl group in the copolymer with a polyhydric carboxylic acid anhydride to introduce a carboxylic acid group. It can be produced by denaturation, etc. Further, the polymerized unit (4) may be composed of only one type, or may be composed of multiple types. The proportion of such polymerized units (4) in the fluorine-containing copolymer is preferably 0 to 60 mol%. If the proportion of polymerized units (4) is too high, sufficient weather resistance of the coating film may not be obtained when used as a paint base or paint additive.
Undesirable. Furthermore, the fluorine-containing copolymer of the present invention has an intrinsic viscosity (hereinafter referred to as

【η】
) is 0.05 to 2.0 di/g. [η]
If it is smaller than the above range, it will be difficult to obtain the strength of the coating when used as a paint base, and if it is larger,
It is not preferable because it has poor paintability and painting workability. The above copolymers are produced by causing a copolymerization reaction by applying a polymerization initiator or a polymerization initiation source such as ionizing radiation to a monomer mixture of a predetermined proportion in the presence or absence of a polymerization catalyst. It can be manufactured by Here, as the polymerization initiator, water-soluble or oil-soluble ones can be used as appropriate depending on the polymerization type or polymerization medium. Specifically, the water-soluble initiator is
A redox initiator consisting of a persulfate such as potassium persulfate, hydrogen peroxide, or a combination of these with a reducing agent such as sodium bisulfite or sodium thiosulfate, as well as small amounts of iron, ferrous salts, silver nitrate, etc. Inorganic initiators, such as systems in which the Examples of the soluble initiator include peroxy ester type peroxides such as t-butyl peroxyisobutyrate and t-butyl peroxy acetate, dialkyl peroxy dicarbonates such as diisopropyl peroxy dicarbonate, benzoyl peroxide, and azobis. Examples include isobutyronitrile. The amount of the polymerization initiator used can be changed as appropriate depending on the type, copolymerization reaction conditions, etc., but it is usually 0.005 to 100% based on the total amount of monomers to be copolymerized.
An amount of about 5% by weight, particularly about 0.05 to 0.5% by weight is adopted. In the above copolymerization reaction, the reaction format is not particularly limited, and bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization, etc. can be adopted, but the stability of the polymerization operation and the ease of separation of the produced copolymer Due to its properties, emulsion polymerization in an aqueous medium or alcohols such as t-butanol, esters, saturated halogenated hydrocarbons containing one or more fluorine atoms, aromatic hydrocarbons such as xylene, etc. are used as a solvent. Solution polymerization or the like is preferably employed. In addition, when carrying out a copolymerization reaction in an aqueous medium, a basic buffer is added so that the pH value of the liquid during polymerization is 4. Addition of a basic substance is also effective in the case of solution polymerization, which is preferably not less than 6. It goes without saying that these methods can be carried out by batchwise, semi-continuous, continuous, etc. operations. In this copolymerization reaction, the copolymerization reaction temperature is -30°C.
The optimum value can be appropriately selected within the range of ~+150°C depending on the type of polymerization medium, etc.; however, when performing the copolymerization reaction in an aqueous medium, the temperature is preferably 0°C ~ +100°C. A temperature of about 10°C to 90°C may be adopted. In addition, the reaction pressure can be selected as appropriate, but is usually 1 to 100 k.
g/cm", especially about 2 to 50 kg/cm. In addition, in order to suppress the intrinsic viscosity of the resulting copolymer within the above range, a reaction medium with a relatively large chain transfer constant may be used, It is preferable to carry out the copolymerization reaction in the presence of an appropriate chain transfer agent.The fluorine-containing copolymer of the present invention can be used as a coating material that provides a coating film having weather resistance, water and oil repellency, antifouling properties, and non-stick properties. It is useful as a base or paint additive.Especially when the fluorine-containing copolymer of the present invention is added to other synthetic resin paints, the fluorine-containing copolymer of the present invention tends to be oriented on the surface of the coating film.
A coating layer based on the fluorine-containing copolymer of the present invention is formed on the surface layer. Therefore, even when the fluorine-containing copolymer of the present invention is added in a small amount to a synthetic resin paint, it is possible to achieve excellent coating film properties such as weather resistance, water and oil repellency, and stain resistance. When the fluorine-containing copolymer of the present invention is added to a synthetic resin paint and used, 1 to 4 parts of the fluorine-containing copolymer of the present invention are added per ioo parts by weight of the film-forming resin component.
It is preferable to use the coating composition in an amount of about 0 parts by weight. If the amount of the fluorine-containing copolymer is too small, it will not be possible to impart excellent properties to the coating film, and if too much is added, no improvement can be expected, leading to economic disadvantages such as increased costs. This is not desirable. In particular, the blending amount is preferably 3 to 30% by weight. Here, the synthetic resin paint is acrylic. All general synthetic resin paints such as urethane-based, fluorine-based, phenol-based, epoxy-based, and silicone-based paints are used. Further, a steel plate coated with a top coat of a coating composition containing the fluorine-containing copolymer of the present invention as described above is extremely useful as an outer panel of an automobile. Usually, such automobile exterior panels are coated with a synthetic resin paint for aesthetic reasons. Top coating with the coating composition containing the fluorine-containing copolymer of the present invention is performed by drying the intermediate coating,
It may be applied before curing, so-called wet-on-wet painting, or it may be applied after drying and curing of the intermediate coating, so-called dry-on-wet painting. In addition, it is possible to apply a top coat to a product coated with a synthetic resin paint.For automobiles sold externally that have been top coated with a paint containing the fluorine-containing copolymer of the present invention, it is water repellent. Excellent properties such as oil repellency and stain resistance last for a long time, so
Work such as cleaning and waxing can be reduced. In addition, due to the excellent coating properties of this external sales beam for automobiles,
It is also possible to easily repair any scratches that occur. Of course, the fluorine-containing copolymer of the present invention can also be used as a paint base. When the fluorine-containing copolymer of the present invention is used as a paint base, it is preferable to add a curing agent and the like to form a paint composition. Here, the curing agent includes isocyanate curing agents, blocked isocyanate curing agents, aminoblast curing agents, metal alkoxides, etc., which are usually used as curing agents for paints, as well as silane coupling agents. Coupling agents such as these can be used. In addition, a curing catalyst that promotes the curing reaction may be blended as appropriate, and in addition, ultraviolet absorbers, light stabilizers, antifoaming agents, thickeners, leveling agents, and stabilizers that provide various functions. 1.Additives such as colorants may be blended, and it is preferable from the viewpoint of painting work that these are dissolved or dispersed in a liquid carrier.Liquid carriers include water-based, organic solvent-based, etc. However, when the above-mentioned compound and fluorine-containing copolymer are insoluble or non-dispersible in the liquid carrier, it is preferable to disperse them using a suitable dispersant, such as a surfactant. [Examples] The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples and Comparative Examples. Example 1 In a stainless steel autoclave with an internal volume of 200 cc and equipped with a stirrer, 50.7 g of xylene, 50.7 g of ethanol, and perfluorovinyl ether and cyclohexyl vinyl ether (hereinafter referred to as CHVE) in the proportions shown in Table 1 were placed.
4-hydroxybutyl vinyl ether (hereinafter referred to as 4-HBV)
E), 3-hydroxybutyl vinyl ether (hereinafter referred to as 3-HBVE) and potassium carbonate 0.8 g,
0.1 g of t-butyl baroxybiparate was charged and dissolved oxygen was removed by solidification and degassing with liquid nitrogen. Thereafter, chlorotrifluoroethylene (hereinafter referred to as CTFE) in the proportion shown in Table 1 was introduced into the autoclave, and the temperature was gradually raised. After the temperature in the autoclave reached 65° C., the reaction was continued with stirring for 24 hours, and then the autoclave was ice-cooled to stop the reaction. After reaching room temperature, unreacted monomers were purged and the autoclave was opened. The obtained polymer was mixed with water/methanol (1:1
), and after removing the supernatant liquid, heated to 60℃,
After drying under reduced pressure of 1 mmHg for 24 hours, the mixture was pulverized with an impact hammer mill to obtain a fluorine-containing copolymer. The composition of the obtained fluorine-containing copolymer calculated from the measurement results of the F-N MR spectrum and the intrinsic viscosity measured at 30°C in tetrahydrofuran

The values of [η] are shown in Table 2. Examples 2 to 3 The same procedures as in Example 1 were carried out except that the proportions of monomers were as shown in Table 1. The composition of the obtained copolymer and the value of [η] are shown in Table 2. Example 4 Internal volume 2. 960 g of xylene and 27 g of ethanol in a stainless steel autoclave with a stirrer. Perfluoropropyl vinyl ether (PPVE), cyclohexyl vinyl ether, 4-
Hydroxybutyl vinyl ether and potassium carbonate6.
2g and 1.4g of 2-butyl peroxyvivalate were charged and degassed under water cooling to remove dissolved oxygen. Thereafter, the mixture was introduced into an autoclave containing chlorotrifluoroethylene in the proportions shown in Table 1, and the temperature was gradually raised. After the temperature inside the autoclave reached 65° C., stirring was continued for 24 hours, and the autoclave was ice-cooled to stop the reaction. After purging unreacted monomers and opening the reactor, the reaction solution was filtered and the evaporator solvent was removed to obtain a fluorine-containing copolymer. The composition and [η] of this fluorine-containing copolymer are shown in Table 2. Next, 500 g of this fluorine-containing copolymer and 3 g of potassium hydroxide at a concentration of 95% were charged into a stainless steel autoclave with an internal volume of 21 cm, and 50 g of propylene oxide was added.
Gradually add g. The reaction was carried out at 110° C. for 10 hours, and the obtained transparent multicolored liquid was purified with synthetic magnesia to obtain a fluorine-containing copolymer. "From the C-NMR measurement results, it was confirmed that this fluorine-containing copolymer had a secondary hydroxyl group. Comparative Example 1 The same procedure as in Example 4 was carried out except that propylene oxide was not added. The procedure was carried out in the same manner as in Example 4. Comparative Example 2 The procedure was carried out in the same manner as in Example 1 except that the proportions of monomers were as shown in Table 1 and perfluorovinyl ether was not included.Table 1 PPVE: Barfluoro (Propyl vinyl) ether PHVE: Verfluoro(2-methyl-3-oxahexyl vinyl) ether VEOVA: Vinyl versatate Table 1 Fluorine-containing copolymers obtained in each example and comparative example
To 100 parts, add 110 parts of xylene and an isocyanate curing agent (Coronate EHJ manufactured by Nippon Polyurethane Co., Ltd.) [0
A coating composition was prepared by blending the ratio of old/[NCO]-1/1, and then a film was applied to the chromate-treated surface of a 0.8 mm thick aluminum plate (manufactured by Mitsubishi Aluminum Co., Ltd. "5052-H34°"). It was applied with an applicator to a dry film thickness of 20 to 30μ, and was heat cured at 140°C for 30 minutes.The results of tests conducted on the obtained coating film are shown in Table 3.Table 3*2 *3 The same paint composition is applied again on the coating film that has been formed,
100 goblin marks were made on the paint film at 1mm intervals,
``Sand with 400 sanding paper,
Peel off using cellophane adhesive tape. After 1 month of outdoor exposure, wipe with water to see how the dirt comes off. Store at 50°C for 1 month and measure the viscosity using an E-type viscometer. Example 5.6, Comparative Example 3.4 Addition amount shown in Table 4 (per 100 parts by weight of paint resin) to synthetic resin paint (mainly composed of Lumiflon L T-200 manufactured by Asahi Glass Co., Ltd. and containing incyanate curing agent) The fluorine-containing copolymer of Example 1 was added in an amount (addition amount), and the mixture was stirred and mixed to obtain a coating composition. This coating composition was coated and tested for physical properties of the coating film in the same manner as in Example 1, and the results are shown in Table 4. Table 4 *4 The fluorine-containing copolymer having no secondary hydroxyl group obtained in Comparative Example 1 was used. Example 7 When the coating composition of Example 5 was applied to a part of an automobile exterior panel, it was confirmed that this part clearly had superior water repellency compared to other parts. [Effects of the Invention] Since the fluorine-containing copolymer of the present invention has a perfluoro group, it has excellent water and oil repellency of the coating film compared to conventional solvent-soluble fluorine-containing copolymers. Since it has a secondary hydroxyl group, it has excellent easy-to-clean properties and recoat adhesion, so it exhibits excellent effects particularly when used as a paint resin for automobiles and the like. It is also recognized that the varnish has superior storage stability compared to fluorine-containing copolymers containing secondary hydroxyl groups.

Claims (3)

[Claims] (1) 2 polymerized units (1) based on fluoroolefins
0 to 60 mol%, 1 to 40 mol% of polymerized units (2) based on perfluorovinyl ether represented by CF_2=CFOR_f (R_f is a perfluoroalkyl group or perfluoroalkoxyalkyl group), and 1 to 40 mol% of polymerized units (2) having a hydroxyl group (3). ) in a ratio of 5 to 40 mol%, at least 10 mol% of the polymerized unit (3) having a hydroxyl group is a polymerized unit (3') having a secondary hydroxyl group, and the polymerization unit (3') has a secondary hydroxyl group in an uncrosslinked state at 30°C in tetrahydrofuran. A fluorine-containing copolymer having an intrinsic viscosity of 0.05 to 2.0 dl/g. (2) Per 100 parts by weight of the film-forming resin component, Claim 1
A coating composition containing 1 to 40 parts by weight of a fluorine-containing copolymer. (3) On the intermediate coating formed from the synthetic resin coating, a top coating is applied using a coating composition containing 1 to 40 parts by weight of the fluorine-containing copolymer of claim 1 per 100 parts by weight of the coating film-forming resin component. Automobile exterior panels.