JPH01223169A - Process for formation of coating film - Google Patents

Abstract

PURPOSE:To obtain a coating film imparting the surface of automobiles etc., with beautiful decorativeness, durability etc., by applying on the substrate surface a specific acrylic base coating containing a colorant and further applying a specific clear coating in a wet-on-wet system followed by heating to effect curing. CONSTITUTION:The surface of a substrate is coated with a base coating comprising (I) a colorant and (II) a base coating binder made up of (A) 40-90pts.wt. of a copolymer produced from a monomer of formula I and a second monomer of formula II or III and (B) 10-60pts.wt. of an amino resin followed by, in a wet-on-wet system, further applying a clear coating comprising (C) 50-95pts. wt. of an acrylic copolymer produced by copolymerization between a hydroxyl group-contg. vinyl monomer, a carboxyl group-contg. vinyl monomer, a methacrylic ester of formula IV and so on and (D) 5-50pts.wt. of a polyisocyanate compound, and then heating to effect curing, thus obtaining the objective coating film.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides high cosmetic properties, coating film performance, and durability, especially when the coating is applied to the surface of a base material such as a plastic, which has a low heat deformation temperature in an automobile. The present invention relates to a method for forming a coating film that is useful in fields where it is required to provide cosmetic properties and has excellent gloss retention when exposed outdoors.

[Prior art]

Conventionally, in painting equipment such as automobile bodies, after performing electrodeposition coating and medium-me coating, a pace coat paint containing a coloring agent such as a colored pigment, a metallic pigment, and mica, and a top coat are applied. Generally, a so-called two-coat one-bake method is used, in which a clear paint is overcoated using a wet-on-wet method, and then both paints are heated and cured at the same time.

Under these circumstances, in recent years, demands for cosmetic properties have become stronger amidst international competition as automobile manufacturers and other companies expand overseas in various fields. Increasing the thickness of the coat (Japanese Unexamined Patent Publication No. 60-94175, etc.) and lowering the molecular weight of the Acrylic IJ A/thread copolymer that is commonly used in clear coat paints (4? Japanese Patent Application Laid-open No. 60-229961, etc.) being developed.

However, thicker clear coats have problems with sag in vertical areas after painting, two coats have problems such as complicated processes and peeling between two clear coat layers, and low molecular weight acrylic copolymers. However, there is a problem with the deterioration of coating film performance such as solvent resistance and weather resistance of the cured parts, and at present k has not been reached to the point where a coating film with satisfactory coating film performance can be obtained.

[Problem that the invention seeks to solve]

The purpose of the present invention is to use a 2-coat, 1-bake coating method in which a specific acrylic resin is cross-linked with iso-V anate as a clear coat film, and compared to the conventional acrylic-amino By maintaining the weather resistance, water resistance, and solvent resistance of the thermosetting coating film, and forming a coating film with excellent gloss and sharpness, at the same time, by using a specific acrylamine paint as a pace coat paint. The object of the present invention is to provide a method for forming a coating film that enables two-coat, one-bake coating at a low temperature of 80 to 120°C.

[Means for solving problems]

The gist of the present invention is to create a coating film characterized by: after coating a base material surface with a paste coating consisting of a coloring agent and the following binder, applying the following clear coating in a wet-on-wet manner, and then curing by heating. It's in the formation method.

Binder for Paste Paint> (4) (a) 5 to 40% by weight of a hydroxyl group-containing vinyl monomer, (b) 30 to 90% by weight of an alkyl (meth)acrylate ester represented by the following general formula [I], 0n, xQ -0000n1! , n+1 (
b) (In the formula, R1 represents hydrogen or a methyl group, and n represents an integer of 1 to 4, respectively.) (c) At least one unsaturated carboxylic acid selected from the following formula (b) and [Table], or its Alkyl Esthe A/as~8 Weight I RbiHOOOOH! 0HO
OOR, (…] a]I, = a(cooH)am, oooRs (I
I) In formula C, R3 and Rs may be the same or different and represent hydrogen or an alkyl group having 1 to 8 carbon atoms) (d) Copolymerized with components (a), (b) and (a) Possible 3: Obtained by copolymerizing a heptamine mixture consisting of 0 to 645% by weight of other vinyl monomers, with a hydroxyl value of 20 to 100 WIIKOH/f and an acid value α of 5 to 55 wg.
(0) (e) hydroxyl group-containing vinyl heptamer 10-5
0 weight section, (f) Carboxy VA/group-containing vinyl lv scolding tool α3
~5% by weight, @ below - (meth)acrylic acid ester A/ shown by the formula (mV) 15-827% by weight, and 011, ! 0-00OR, (II) In the formula C, R4 is hydrogen or methoxy group, R is carbon 5 to 1 to 4
~18 alkyl groups, phenyl groups or benzyl groups, respectively) % (e), (f) and -) and other vinyl/&/senomers copolymerizable with components 0 to 40% by weight. Obtained by copolymerization, hydroxyl value 60-16019Ko II/t, acid value (L5-
20 qK OII/f acrylic copolymer 50~
95 parts by weight, and 5 to 50 parts by weight of a polyisocyanate compound.The acrylic copolymer (4) used in the binder for the paste paint of the present invention is used to coat the paste coat film and the clear coat after curing. In terms of interlayer adhesion of the coating film, the hydroxyl value is 20 to 10.
It must be 0119KOII/t. or,
In terms of primary physical properties such as pot life after paint preparation and solvent resistance, it is necessary that the acid value be in the range of a5 to 55 qxon/f.

Further, it is necessary that the hydroxyl group-containing vinyl S/monomer C-, which is one of the monomers constituting the acrylic copolymer (j), be contained in an amount of 5 to 40% by weight.

If the amount of the hydroxyl group-containing vinyl monomer is less than 5% by weight, the crosslinking density of the cured coating film due to the crosslinking reaction with the amino resin will be low, and performances such as water resistance and weather resistance will deteriorate, which is not preferable. Moreover, if it exceeds 40% by weight, the solution viscosity of the Aku-137W copolymer (N) will be too high and the water resistance of the cured coating film will deteriorate, which is not preferable.

Hydroxyl group-containing vinyl monomers (specific examples of - include 2-, t-nitroxyethyl (meth)acrylate,
2- and droxypropyl (meth)acrylate 1,5-
e Doroquinpropylene, A/(meth)acrylate, 4-hydroxybuty A/(meth)acrylate, 6-hydroxybuty S/A/(meth)acrylate, and drooxyalkyl A/(meth)acrylates, manufactured by NOF ■ Examples include adducts of 2-hydroxypropyl methacrylate and propylene oxide or ethylene oxide, represented by Premmar PP1000, Prem-r-PP500, Prem-r PI-200, Prem-r-PK-90, and the like. (Meth)acrylic acid ester A/(b) is
It is used in the range of 30 to 90% by weight, and if it is less than 30% by weight, sufficient weather resistance of acrylic resin cannot be obtained, and 90% by weight is used.
If the weight exceeds the weight limit, the crosslinking density of the cured coating film after crosslinking with the amino resin will be low, resulting in insufficient weather resistance and water resistance. 4
Specific examples of (meth)acrylic acid ester (b) include methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl methacrylate, propyl acrylate, and n methacrylate.
-butyl, 1-butyl methacrylate, t-methacrylate
Examples include butyl, n-butyl acrylate, 1-butyl acrylate, t-butyl acrylate, and 5ea-butyl acrylate.

Unsaturated carboxylic acid or its fullkyl ester (c)
e 447v Inic acid (ester), fumaric acid (ESTE/I/) or high taconic acid (ESTE A/) can be used for crosslinking with amino resins, especially in melamine curing systems, from 80°C to 12°C.
It is an essential component in order to obtain sufficient coating film performance by baking at a relatively low temperature of 0°C. Among the melamine resins, when a butyl etherified melamine resin is used, it is particularly effective and contains 15 to 8 parts by weight, preferably 2 to 6 parts by weight. If the content is less than (b5 weight), the solvent resistance, water resistance, etc., which play a sufficient role as a catalyst for the crosslinking reaction, will decrease, and if it exceeds 8 weight, the pigment and the amino resin that is the curing agent will be degraded. It is undesirable because the storage stability of the paste coating paint containing it decreases.Specific examples include monomethyl maleate, motuptil maleate, octyl maleate, monomethyl thumarate, motupyl fumarate, octyl fumarate, and maleic acid, fumaric acid, and itaconic acid.

(a), (b) and other vinyl yarn yarn copolymerizable with the above-mentioned components (a) (a is styrene, a-methylstyrene, styrene derivatives such as vinyltoluene; acrylonitrile, methacrylonitrile exclusive); Polymerizable unsaturated nitriles; vinyl esters such as vinyl acetate and vinyl propionate; N-alkoxy substituted amides; glycidyl (meth)acrylate, (meth)allyl glycidyl ether, metaglycidyl/L/epoxy group-containing monomer in (meth)acrylic acid; dimethylaminoethyl/&/(meth)acrylic acid, diethylaminoethyl Basic polymers such as (meth)acrylic acid; amyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, (
(Meth)acrylic esters such as 2-ethylhexyl meth)acrylate; Also, forces other than the above items (b) and (c) such as acrylic acid and methacrylic acid; polyVA/group-containing vinyl monomers, sulfoethyl methacrylate, Examples include sulfonic acid group-containing vinyl septamers such as sulfoethyl acrylate and 2-acrylamido-2-methylpropanesulfonic acid, and these can be used as necessary.

In the present invention, the acrylic copolymer (Jl) can be obtained by any known method such as solution polymerization, bulk polymerization, and emulsion polymerization. In addition, when using the solution polymerization method, the organic solvent used is isopropyl alcohol.
Commonly used organic solvents such as AI, n-fi)-N, toluene, and xylene can be used, and commonly used polymerization initiators such as azobisisobutyronitrile, benzylic peroxide, and cumenehydroboroxide can be used. A polymerization initiator can be incorporated.

According to the present invention, the acrylic copolymer (when obtaining the material,
2-mercaptoethanol, n-
Chain transfer agents such as dodeFA/mercaptan can be used. The binder for the paste paint in the present invention comprises 40 to 90 parts by weight, preferably 60 to 85 parts by weight of the acrylic copolymer (A) and 10 to 60 parts by weight of the amino resin.
Preferably, 15 to 40 parts by weight of the amino resin is blended. This is not preferable because it reduces the water resistance and flexibility of the coating film.

As the amino resin (B) used in the present invention, aminotriazine, urea, dicyandiamide, or M,M-ethylene urea is methylolated, and then alkyl etherified with JCS' p O hexanol or an alkanol having 1 to 6 carbon atoms. For example, methyl etherified melamine resin, butyl etherified melamine resin, etc. obtained from aminotriazine are particularly suitable. Furthermore, when an amino resin is used as a curing agent as in the base coat paint of the present invention, parato-μenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalene disulfonic acid is added to the paste paint. or an amine-neutralized product thereof, etc. can be added as an external acid catalyst.

In the present invention, colorants used in the base paint include commonly known brightening agents such as aluminum paste, mica, and flaky iron oxide; and pigments such as titanium oxide, carbon black, quinacridone, and V-aniline blue.

In addition, in the present invention, resins other than acrylic resins such as polyester resins, epoxy resins, and cellulose resins, surface conditioners, ultraviolet absorbers, antioxidants, pigment sedimentation inhibitors, etc. may be added to the base paint as necessary. Various auxiliary additives can be added as necessary using common compounding methods.

In the present invention, since the base paint is used as a base paint in a two-coat one-bake method,
It becomes possible to perform baking at a relatively low temperature of 20° C. and without using a sulfonic acid catalyst.

The acrylic copolymer (C) used in the clear paint of the present invention must have a hydroxyl value of 60 to 160 KOH/l. If it is less than 60111110 H/, the crosslinking density of the coating film will be low, and the solvent resistance and hardness will decrease, so it is preferable, and if it exceeds 160wIIK OH/f, the viscosity of the resin solution will increase, and the cosmetic properties will decrease. This is not preferable because water resistance decreases.

The hydroxyl group-containing vinyl hexamer (e), which is one of the monomers constituting the acrylic copolymer (0), is used in an amount of 10 to 40% by weight. If it is less than 10% by weight, the crosslinking density of the cured coating film due to the crosslinking reaction with the amino resin will be low and sufficient coating performance will not be obtained, and if it exceeds 500% by weight, the viscosity of the acrylic copolymer will be high. Therefore, the water resistance of the coating film decreases, which is not preferable. Specific examples include 2-hydroxyethyl/I/(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl A
Hydroxy alkyl A/(meth)acrylates such as /(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyiv(meth)acrylate, etc. Adducts Premar Pm-550 and Premar P manufactured by NOF ■
lf-90, Premmar PP1000, Premmar PP
500; Deluxe A/FM1, Booksel FM2, Deluxe A/FM2, etc. manufactured by Daicel Chemical Company, which are adducts of 2-hydroxyethy A/(meth)acrylate and 6-caprolactone, can be mentioned.

Further, the vinyl monomer (f) containing Calhoki V is used in an amount of 13 to 5 by weight. If it is less than 15% by weight, the reaction rate of crosslinking reaction with the isocyanate compound is slow, and coating film performance such as water resistance, solvent resistance, and non-adhesiveness deteriorates.
If it exceeds % by weight, the storage stability of the clear paint will decrease,
Undesirable. Specific examples include methacrylic acid,
Acrylic acid, itaconic acid, fumaric acid, crotonic acid, maleic acid, monomethyl itaconate, motuputyl itaconate, monomethyl maleate, monooctyl maleate,
Examples include 2-sulfoethyl methacrylate and 2-sulfoethyl acrylate.

(Meth)acrylic acid ester tv (7) is used in an amount of 15 to 897% by weight, preferably 30 to 60% by weight.

If it is less than 15% by weight, the weather resistance and cosmetic properties of the acrylic resin will decrease, and if it exceeds 89.7% by weight, the crosslinking density will decrease and solvent resistance and water resistance will be low. Specific examples include n-butyl (meth)acrylate, 1-butyl (meth)acrylate, sea-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexV
(meth)acrylate, lauri A/(meth)acrylate V
-)%) (meth)acrylic acid esters such as lysosyl methacrylate, stearyl A/(meth)acrylate, cyclohexyl methacrylate-F1 methacrylate V-, benzyl methacrylate-F1 ethoxyV ethyl methacrylate V-) etc.

Other vinyl monomers copolymerizable with the above-mentioned components (e), (f), and (2) may be used in an amount of 0 to 40% by weight within a range that does not impair the cosmetic properties and coating performance that are the characteristics of the present invention. used. Specific examples include styrene derivatives such as styrene, a-methylstyrene, and vinyltoluene; polymerizable nitriles such as acrylonitrile and methacrylaterile; glycidyl (meth)acrylate, (meth)aryglycidyl ether, and metaglycidyl AP ( Epoxy-based polymers such as meth)acrylic acid esters; basic wall polymers such as dimethylaminoethy(meth)acrylic acid, diethylaminoethyl/I/(meth)acrylic acid; methoxymethylacrylamide, butoxymethylacrylamide etc. N-
Alkoxy-substituted amides; methyl (meth)acrylate,
(meth)ethyl acrylate, (meth)acrylic glln
Examples include (meth)acrylic acid esters having an alkyl group having 1 to 30 carbon atoms such as -propyl and 1-propyl (meth)acrylate.

In the present invention, as the method for polymerizing the acrylic copolymer (C), various commonly known polymerization methods can be used, similar to the method for polymerizing the acrylic copolymer (A) contained in the paste paint. However, the present solution polymerization method is particularly preferred.

The clear paint in the present invention contains 50 to 90 parts by weight of an acrylic copolymer (0) and a polyisocyanate compound (b) as a curing agent in order to satisfy the high level of cosmetic properties and performance quality required by automobile paints. ) Contains 5 to 50 parts by weight. If the amount of the polyisocyanate compound is less than 5 parts by weight, the crosslinking density of the cured coating film will be low, resulting in insufficient weather resistance, solvent resistance, and water resistance of the coating film, and if it exceeds 50 parts by weight, the gloss of the cured coating film will be insufficient. It is not preferable because it deteriorates the physical and chemical properties including the texture and metallic feel. Generally, it is blended so that the molar ratio of the Woo group of the isocyanate compound to the OH group of the acrylic resin is 1 (equivalent), but depending on the purpose and use, it may be blended so that there is an excess of Neo groups or OH groups. can. Specific examples of this polyisocyanate compound include known non-yellowing isocyanates such as hexamethylene diisocyanate, xylylene diisocyanate, tolylene diisocyanate, and isophorone diisocyanate. It is also possible to use these isocyanate compounds in which the Neo group is blocked.

〔Example〕

Hereinafter, the present invention will be specifically explained using Examples. still,
In the examples, "1 part" indicates "part by weight."

Example of production of acrylic copolymer (A) contained in paste paint In a reaction vessel equipped with a stirrer, temperature control device and condenser, 40 parts of toluene and isopropyl alcohol A/2 were added.
I prepared 0 copies. The contents of the reaction vessel were heated with stirring to raise the temperature to 80°C. Next, 53 parts of methyl methacrylate V-), 27.5 parts of n-butyl acrylate,
100% solution consisting of 15 parts of 2-hydroxyethyl methacrylate, 1 part of methacrylic acid, 5 parts of maleic acid monobutyl ester, and 1.0 part of azobisisobutyronitrile.
1 part of azobisisobutyronitrile was added dropwise over 4 hours.

After adding three times and heating and stirring for 2 hours to increase the conversion rate to resin, 40 parts of toluene was added to terminate the reaction. Obtained acrylic copolymer solution (non-volatile content: 50%)
is referred to as acrylic resin varnish O-1. In addition, when the weight average molecular weight of the obtained acrylic copolymer was measured using a Gelbermulle Simin Chroma F graph, it was found to be 5o.
It was ooo. Hereinafter, acrylic copolymer C- of the seven-mer composition shown in Table 1 for base coat paints will be similarly used.
2 to O-5 were manufactured according to the above method. However, a-4
In the FC, fumaric acid, component (C), was charged at the same time as the initial toluene and isopropyl alcohol.

Example of manufacturing base paint: Put the amounts of each material shown in Table 2 into a stainless steel container.
After sufficient stirring, the viscosity was adjusted with a mixed solvent for dilution to produce base paints B-1 to B-5.

Table 2 *1) Aluminum paste made by Toyo Aluminum *2) *
3) Production example of acrylic copolymer Cc) contained in butylated melamine resin clear paint manufactured by Mitsui Toatsu Chemical Co., Ltd. Each of the five mixtures having the seven-mer composition shown in Table 3 was polymerized in the following steps. The reaction was carried out. First, 60 parts of Tsurupez φ100 (manufactured by Etsuso Corporation) were charged into a reaction vessel equipped with a stirrer, a temperature control device, and a condenser.
The temperature was raised to 140 tl by heating while stirring. Next, 1 part of azobisisobutyronitrile A and 3 parts of t-butylperoxyisopropyl carbonate were added to 100 parts of each of the ointment mixtures listed in Table 3.
I let it drip over time. Then, four 11 parts each of azobisisobutyronitrile were added. After further heating and stirring at 140° C. for 2 hours to increase the conversion rate to resin, 7 parts of butylene orthoacetate was added to terminate the reaction.

The hydroxyl value and acid value of each of the obtained acrylic copolymers (P-1 to P-5) and the viscosity and nonvolatile content of the copolymer solution were as shown in Table 3.

Examples 1 to 5 and Comparative Examples 1 and 2 Using each of the above acrylic copolymers (Q solution), Schiff type clear paints were manufactured according to the paint formulation shown in Table 4, and Examples 1 to 5. Comparison Example 1.2.

Table 4 1) Numbers in the table indicate parts by weight *2) Made by Japan Polyurethane ■ (Socyanate Prebolimer *5) Made by Monnanto Co., Ltd. Surface conditioner Coating film formation and evaluation Bonderite + 144 dull steel plate (Japan Test Panel ■) is coated with automotive cationic electrodeposition paint and heated to 180°C.
Bake for 30 minutes. Next, an aminoacid intermediate paint was applied, and after baking at 160°C for 30 minutes, the coating film was sanded and dried. On this coating film, the base paint shown in Table 2 and the clear coat paint shown in Table 4 were coated in combinations shown in Table 5 (wet-on-wet method). This overlapping coating was performed as follows. First, a base paint was applied onto the intermediate coating film to give a dry film thickness of 15 to 20 μm, and after being left for 5 minutes, a clear paint was applied to give a dry film thickness of 50 pm.

Undried overcoating) The coating film was left at room temperature for 10 minutes and then baked at the drying temperature listed in Table 5 for 30 minutes to form a coating film.

Table 5 shows the results of evaluating various coating film performances such as cosmetic properties for each of the coating films thus obtained.

As is clear from these results, the method of forming a coating film by combining the pace coat paint and the clear coat paint of the present invention improves gloss sharpness, hardness, gasoline resistance, hot water resistance, isobaric and weather resistance. A coating film with excellent performance can be obtained.

$1) 60°G = Suga Test Machine ■Digital angle gloss meter
Measured using IUGV-4D. *2) PGD value, evaluated by Tokyo Koden ■Portable sharpness glossiness meter.
-*3) Use Uni (manufactured by Mitsubishi Pencil).

*4) Regular gasoline (manufactured by Nippon Oil Corporation) IIc After soaking at room temperature for 24 hours, the appearance was visually judged.

*S) S After immersing in warm water at 0°C for 10 days, the appearance was visually judged.

*6) Appearance was visually judged after 1000 hours on Sunshine Quasar-Ometer and after 240 hours of humidity test at 50°C and 984RH.

$7) 6% sulfite aqueous solution (after L2CC spot,
After leaving it at room temperature for 24 hours, wash it with water and check for any traces of spots.

[Effect of the invention] As detailed above, by the method of the present invention, two copies of one
In the baking method, it is possible to perform baking at a relatively low temperature of 80 to 120°C without using a sulfonic acid catalyst, and it also has a beautiful appearance with excellent texture and gloss, Moreover, it is possible to obtain a molded product with excellent coating film performance, and the effect is extremely large.6゜Patent applicant: Mitsubishi Rayon Co., Ltd. Daisanto Patent attorney: Toshio Yoshizawa

Claims (1)

[Scope of Claims] A method for forming a coating film, which comprises applying a base coating consisting of a coloring agent and the following binder onto the surface of a substrate, then coating the following clear coating in a wet-on-wet manner, and then heating and curing the coating. <Binder for base paint> (A) (a) hydroxyl group-containing vinyl monomer 5 to 40% by weight
, (b) 30-90% by weight of (meth)acrylic acid alkyl ester represented by the following general formula [I], ▲ Numerical formulas, chemical formulas, tables, etc. ▼ [I] (In the formula, R_1 is hydrogen or a methyl group, (n each represents an integer of 1 to 4) (c) 0.5 to 8% by weight of at least one unsaturated carboxylic acid or alkyl ester thereof selected from the following general formulas [II] and [III], and HOOCCH=CHCOOR_2 [II] CH_2=C(COOH) CH_2COOR_3 [III
] (In the formula, R_2 and R_3 may be the same or different and represent hydrogen or an alkyl group having 1 to 8 carbon atoms) (d) Can be copolymerized with components (a), (b) and (c) and other vinyl monomers, obtained by copolymerizing a monomer mixture consisting of 0 to 64.5% by weight, with a hydroxyl value of 20 to 100 mgKOH/g and an acid value of 0.5 to 35 mg.
Base paint binder <clear paint> consisting of 40 to 90 parts by weight of acrylic copolymer of KOH/g, and (B) 10 to 60 parts by weight of amino resin (C) (e) 10 to 50 parts by weight of hydroxyl group-containing vinyl monomer , (f) 0.3 to 5% by weight of a carboxyl group-containing vinyl monomer, (g) 15 to 89.7% by weight of a (meth)acrylic acid ester represented by the following general formula [IV], and ▲ mathematical formula, chemical formula, table etc. ▼ [IV] (In the formula, R_4 is hydrogen or a methyl group, R_5 is a carbon number of 4
~18 alkyl groups, phenyl groups or benzyl groups, respectively) (h) A monomer mixture consisting of 0 to 40% by weight of other vinyl monomers copolymerizable with components (e), (f) and (g). Hydroxyl value obtained by polymerization: 60 to 160 mgK
OH/g, a clear paint consisting of 50 to 95 parts by weight of an acrylic copolymer with an acid value of 0.5 to 20 mgKOH/g, and (D) 5 to 50 parts by weight of a polyisocyanate compound.