JP2003071379A - Coating method of top coat for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method of top coat for automobile which establishes the wet on wet coating between a water base coating or a solvent base coating and a solvent clear coating applied thereon and is excellent in appearance quality of coating film after baking. SOLUTION: This coating method of top coat for automobile comprises a process of applying the base coating and a process of applying the solvent clear coating on the base coating by means of the wet on wet coating. Therein, the coating is performed by using the clear coating having coating solid content NV in the coating of >=50% and the coating solid content in the clear coating after two minutes of setting is 60-70 mass%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcoating method for establishing wet-on-wet coating of a water-based paint or a solvent-based paint and a solvent-based clear paint applied thereon. More specifically, the present invention relates to a coating method for an automotive topcoating material for obtaining a coating film having a good coating quality, particularly a finished appearance even when a base coating and a clear coating are subjected to wet-on-wet coating.

[0002]

2. Description of the Related Art Conventionally, in the coating of automobiles and the like, there has been a coating method in which a base coating and a clear coating are applied as a top coating to a vehicle body on which an electrodeposition coating and an intermediate coating are formed to form a top coating. It is commonly used. The base paint is used to give a good decorative appearance by an organic pigment or an inorganic pigment, and the clear paint is applied on the base coating film, and the pigment is transparent or does not impair the transparency. It is contained to improve the appearance and finish.

Conventional automotive coatings, especially solvent-based base coatings and top-coating coatings such as clear coatings, contain a large amount of organic solvents, and from the viewpoints of global environmental protection, resource saving, and safety during coating. However, it is not preferable to use a large amount of such an organic solvent. Recently, high-solid paints, water-based paints, powder paints, and the like, which have a small amount of solvent, have been studied from the conventionally used solvent-based paints, and their application has been expanded.

At present, the coating process of a top coating for automobiles is
It consists of a process of applying a base paint and a process of applying a clear paint. After these are applied by wet-on-wet, they are baked at the same time after setting for a predetermined time. In the coating process of such a top-coat paint, setting of a predetermined time is essential for the process in order to evaporate the solvent in the paint. Here, a base paint is applied as the top coat paint, and a clear paint having a paint solid content of 50% by mass or less, which is conventionally used, is wet on the clear paint, for example, a clear paint having a paint solid content of 45% by mass. If you want to paint on-wet, see Figure 3.
As shown in Fig. 5, the solvent-based clear paint is applied in the range where the solid content of the base paint is 70 to 90% by mass, and after 2 minutes from setting, the clear paint solid content is in the range of 70 to 80% by mass. Since the above problem does not occur, conventionally, the overcoating is applied within the range where these relationships are satisfied.

[0005]

However, as described above, from the viewpoint of protecting the global environment, the specifications of clear coatings in which the amount of organic solvent in the coating is reduced as compared with conventional coatings, for example, coating solid content Is 50 mass% or more, when a solvent-based clear paint is used for coating, the clear paint solid content after setting for 2 minutes is 70 to 8 after setting, which was within an appropriate range in the past.
Under the condition of 0% by mass, there is a problem that the viscosity of the coating film itself becomes high, the coating film cannot flow in the setting state, and the appearance quality of the coating film remarkably deteriorates after baking.

Therefore, it has been a problem to secure the appearance quality of the coating film by establishing a wet-on-wet with the base coating material and the solvent-based clear coating material having a coating solid content of 50 mass% or more.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. As a water-based paint or a solvent-based paint, and a solvent-based clear paint to be applied on the water-based paint or a solvent-based paint, a conventional method is used from the viewpoint of protecting the global environment. An object of the present invention is to provide a method for coating an automotive topcoating paint which is excellent in the appearance quality of a coating film after baking by establishing wet-on-wet coating even when a clear coating having a reduced solvent content is used.

[0008]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, the step of applying a base paint and the wet-on-wet solvent-based clear paint on the base paint. In a method for coating a top coating composition for an automobile, including the step of coating with a coating composition, a clear coating composition having a coating solid content (NV) of 50% by mass or more is used for coating, and the coating composition in the clear coating composition after 2 minutes from setting. The present invention has been achieved by finding that the above-mentioned problems can be solved by using a method for coating an automobile topcoat paint having a solid content of 60 to 70% by mass.

Therefore, the method of coating a topcoat paint for automobiles according to the present invention comprises the steps of coating a base paint and wet-on-wet solvent-based clear paint on the base paint as described in claim 1. In a method for coating a top coating material for automobiles, including a step of coating, coating is performed using a clear coating material having a coating solid content (NV) of 50% by mass or more at the time of coating, and the coating solid content in the clear coating material after 2 minutes of setting. It is characterized in that the content is 60 to 70 mass%.

Further, in the method for coating a top coating composition for automobiles according to the present invention, as described in claim 2, the clear coating composition having a coating solid content (NV) of 50% by mass or more at the time of coating has a molecular volume of Is 100 cm ³ / mol or more and a solvent having a viscosity of 0.68 (mPa · s) or more is added in an amount of 2 to 10% by mass.

Further, according to the method of coating a top coating material for automobiles according to the present invention, as described in claim 3, the clear coating material has a bell rotational speed of 300 using a bell type electrostatic coating machine.
Over 00 rpm and shaving air pressure of 0.3 kg
The feature is that it is applied at a rate of / cm ² or more.

Furthermore, the coating method for a topcoat paint for automobiles according to the present invention is characterized in that, as described in claim 4, the base paint is a water-based or solvent-based base paint.

Further, according to the present invention, there is provided a method for applying a topcoat paint for automobiles, wherein when the step of applying the solvent-based clear paint is started after the base paint is applied, It is characterized in that the coating solid content of the coated base coating is 70 to 80% by mass.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for producing the coating film structure shown in FIG. 1 will be described below. It should be noted that, for convenience of description, FIG. 1 is illustrated with the same film thickness of each coating film.

First, the steel sheet 1 is pretreated (degreasing, chemical conversion treatment).
Thus, the stains and oils attached to the steel sheet are completely removed, and a chemical conversion film is formed on the surface of the steel sheet. The formed chemical conversion coating activates the steel sheet and enhances rust prevention and adhesion between the steel sheet and electrodeposition coating. In automobile coating lines, emulsion-based and alkaline-based degreasing agents and zinc phosphate-based chemical conversion treatment agents are mainly used from the viewpoints of rust prevention, relation to electrodeposition coating, and productivity, and the treatment method is dip. A method or a continuous spray method can be used. The pretreatment is an important step since complete degreasing and formation of a uniform and dense chemical conversion coating ensure rust prevention of the vehicle body and adhesion of the coating. Further, the undercoat coating film 2 is formed on the pretreated steel plate by electrodeposition coating, and this coating film ensures the rust prevention performance of the entire vehicle body. Since the electrodeposition paint is a paint that is first applied on a steel plate, it is preferable to use a paint that is excellent in adhesion, rust prevention and coating strength. Further, in order to ensure the rustproof property of the steel plate of the vehicle body by the electrodeposition coating, the entire vehicle body is coated by immersing the vehicle body in a bath of the electrodeposition coating material. Currently, as the electrodeposition paint, a cation type electrodeposition paint whose main raw material is a block isocyanate modified epoxy resin is generally used.
It is not limited to these. A in the electrodeposition paint
A curing catalyst having anticorrosive properties such as hydroxides, oxides, organic acid salts and inorganic acid salts of metals such as 1, Ni, Zn, Sr, Zr, Mo, Sn, W and Bi, and an anti-settling agent. It can be blended appropriately. The conditions for the electrodeposition coating were that the car body was the cathode, the carbon plate was the anode, and the bath temperature was 20-35.
C, voltage 100-400V, current density 0.01-5A,
The energization time is 1 to 10 minutes. Then 13
The electrodeposition coating is completed by baking at 0 to 180 ° C. for 10 to 40 minutes.

After that, sealing of seams of steel plates, soundproof coating, and vibration damping material fusion bonding may be applied. For sealing, for example, PVC sol or bituminous sealing material is applied to the joints of the steel plates with a flow gun and, if necessary, smoothed with a brush or spatula to prevent rust, dust, and waterproofing of the joints of the steel plates. It Also on the back of the floor, inside the wheel house,
The lower part of the outer surface of the vehicle body, the floor surface, the inner surface of the dash surface of the door outer surface, etc. can be subjected to soundproofing / vibrationproofing by painting or setting a rubber latex-based or bituminous-based soundproofing / vibrating coating.

Next, an intermediate coating material is applied onto the undercoat coating film 2 and baked to form the intermediate coating film 3. With these coating film configurations, pinholes and small irregularities on the undercoat surface are filled, surface adjustment is performed for the finish of the topcoat finish, and protection against external impact such as jump stones can be enhanced.
The coating means is not particularly limited, and various known means such as air spray, airless spray, electrostatic coating and the like can be appropriately used. The baking conditions are generally used conditions, for example, baking is performed at 130 to 180 ° C. for about 10 to 40 minutes.

As the intermediate coating material, various known water-based intermediate coating materials and solvent-based intermediate coating materials can be used. Specifically, a coating material containing a carboxylic acid group-containing resin, a urethane bond-containing diol and resin fine particles as main components, Polycarboxylic acid resin,
Aqueous paints such as paints containing amino resins, linear low-molecular polyester diols and benzoin as main components, and solvent-based paints containing epoxy ester resins, aminoalkyd resins, or oil-free aminoalkyd resins as main components. Can be used.

In addition, in order to prevent the occurrence of scratches (chipping) due to rocks from a vehicle traveling in front of the vehicle, the tip of the hood and roof should be protected against chipping before the intermediate coating is applied. It is also possible to apply an anti-chipping paint for imparting chipping property. As the anti-chipping paint, for example, a paint containing a polyolefin resin as a main component, a one-component heat-curable urethane paint obtained by adding a curing agent component having active hydrogen such as polyamine and polyol to a blocked urethane prepolymer, Examples thereof include a coating material containing a polyester resin and a melamine resin or a polyester resin and a blocked isocyanate compound as main components, in which an appropriate pigment is dispersed in a high concentration, and a coating material obtained by adding a polyamine curing agent to an epoxy polymer. As a method of forming a coating film containing an anti-chipping paint, a solvent-based or water-based anti-chipping paint is applied, a solvent-based intermediate coating paint is wet-on-wet over it, and an anti-chipping paint is baked and dried once. A forming method can be used, but is not limited to this method. In addition, when applying solvent-based anti-chipping paint to the vehicle body, it is not always necessary to apply solvent-based anti-chipping paint to the entire vehicle body,
It can be applied only to the parts where chipping resistance is required, such as the hood tip and roof tip.

Thereafter, an aqueous base paint or a solvent base paint is applied on the intermediate coating film 3, and then a solvent clear paint is applied. As will be described in detail below, by applying the coating method of the present invention, a wet-on-wet is established between the base coating material and the solvent-based clear coating material having a coating solid content of 50% by mass or more to secure coating film appearance quality. be able to. When coating automobile bodies, attention should be paid to preventing problems such as dust, bumps, and sagging, ensuring a stable required film thickness, and appropriate baking conditions.

A coating film having the constitution shown in FIG. 1 is formed by such steps, but the coating method of the present invention is not limited to the above constitution, and various modifications utilizing known techniques are also possible. Are included in. For example, in order to improve the finish appearance, a method of applying the intermediate coating paint by a two-coat method, or removing the baking before applying the intermediate coating paint, etc., the baking conditions are appropriately adjusted in consideration of the properties of the paint. can do.

The coating method of the automotive top coating material according to the present invention will be described in detail below. The present invention is a method for coating an automotive topcoat paint, which comprises a step of applying a base paint and a step of applying a solvent-based clear paint on the base paint by wet-on-wet. A coating method for a topcoat paint for automobiles, characterized in that a clear paint having an NV) of 50% by mass or more is used for coating, and the solid content of the clear paint after 2 minutes from setting is 60 to 70% by mass. is there. The clear coating composition having a coating solid content (NV) of 50% by mass or more at the time of coating has a molecular volume of 100 (cm ³ / mo) relative to the clear coating composition.
l) or more and a solvent having a viscosity of 0.68 (MPa · s) or more is added in an amount of 2 to 10% by mass.

When the clear paint is applied after the base paint is applied and the solid content of the clear paint is less than 60% by mass after 2 minutes from setting, the residual solvent in the base paint is rapidly evaporated during baking. Therefore, the traces of air bubbles, and coating defects commonly referred to as "armpits" occur on the surface of the clear coating film. Further, when the coating film solid content of the clear coating after 2 minutes from setting is higher than 70% by mass, the viscosity of the clear coating film itself becomes high and the coating film cannot flow in the setting state,
There is a problem that the finished appearance is significantly deteriorated.

The solvent used in the clear coating has a molecular volume of 1
At least 00 cm ³ / mol and a viscosity of 0.68 (MP
When the amount of the solvent which is more than a · s) is less than 2% by mass, the solid content of the coating film easily rises, the viscosity of the coating film itself becomes high, and the coating film in the set state cannot flow, There is a problem that the finished appearance is significantly deteriorated. When the amount of the solvent added is more than 10% by mass, the solid content of the coating film is unlikely to rise, and the residual solvent in the coating film evaporates rapidly during baking. Therefore, traces of bubbles on the surface of the clear coating, commonly known as waki A film defect is generated.

In the present invention, the solid content at the time of coating is 50
The solvent to be added to the clear coating material of mass% or more is specified by the molecular volume and the viscosity. Relative evaporation rates are often used when considering solvent volatilization. However, when the solid content of the coating material during actual coating is examined, no significant correlation is observed. Then, as a result of earnest studies, it was found that in order to control the volatility of the solvent present in the paint, it suffices to pay attention to the molecular volume and viscosity of the solvent itself, and the present invention has been accomplished. In the present invention, it is necessary to prevent the solid content during coating from increasing as much as possible, that is, the direction in which the solvent itself is less likely to volatilize. For that purpose, it is necessary to establish in the direction where the molecular volume is large (that is, the volume is large) and the viscosity is high.

The solvent having a molecular volume of 100 cm ³ / mol or more and a viscosity of 0.68 (MPa · s) or more is i-butyl acetate, 2,4-dimethylpentane, cyclohexane, diacetone. Alcohol, pent-
Examples thereof include o-xone, methylcyclohexane and methylcyclohexanone.

As the base paint used in the present invention, various commercially available water-based or solvent-based paints can be used, and also known solid base paints and metallic base paints can be used. For example, when using a water-based base paint, the solid base paint is a base resin,
A thermosetting paint containing a cross-linking agent, a color pigment and water can be used. Examples of the base resin include resins such as acrylic resin, polyester resin, alkyd resin, fluororesin, urethane resin, and silicon-containing resin having a crosslinkable functional group such as hydroxyl group, carboxyl group, silanol group, and epoxy group. As the cross-linking agent, melamine resin, urea resin, (block) that can react with the above functional groups
Examples thereof include isocyanate compounds, epoxy compounds or resins, carboxyl group-containing compounds or resins, acid anhydrides, alkoxysilane group-containing compounds or resins, and the like.
Examples of color pigments include cadmium yellow, cadmium red, molybdenum red, chrome yellow, Prussian blue, zinc white, titanium dioxide, yellow iron oxide, carbon black, aluminum flakes, titanium mica, calcium carbonate, barium sulfate, barium carbonate, silica. Solid color pigments for paints such as kaolin, barita, clay, azo yellow, azo orange, azo red, phthalocyanine green, phthalocyanine blue, isoindoline yellow, slene-based pigments, and berylene pigments, and their blending amount is a desired color tone. Can be adjusted accordingly.

Further, as the metallic base paint, a thermosetting paint containing a base resin, a crosslinking agent, a metallic pigment and water can be used. As the base resin and the cross-linking agent, those similar to the solid base paint can be used. Examples of the metallic pigment include aluminum powder, bronze powder, zinc powder, iron phosphide, mica, mica surface-coated with metal oxide, and mica-like iron oxide. An excellent coating film appearance is achieved by orienting such metallic pigments.

The solid base coating and the metallic base coating are usually 5 to 50 μm in the cured coating after baking.
m, preferably about 10 to 40 μm.

As the solvent-based clear paint, various commercially available paints can be used, and it is a liquid paint containing a base resin, a curing agent and a solvent or an organic solvent as a dispersion medium, which is dried at about 40 to 110 ° C. Materials that solidify are preferred. It is also possible to use various publicly known solid base paints and metallic base paints in which a coloring pigment or the like is blended if necessary. Examples of the base resin include an acrylic resin having a functional group such as a hydroxyl group, a carboxyl group, an epoxy group and an isocyanate group, a vinyl resin, a polyester resin, a fluororesin, a urethane resin and a modified resin (graft resin) thereof. The glass transition temperature of these base resins is usually 40 to
Those in the range of about 120 ° C. are preferable. The curing agent may be one that can be three-dimensionally crosslinked and cured by reacting with the above-mentioned functional groups of the base resin, and for example, a part or all of the methylol groups of the melamine resin or the urea resin can be an etherified cytenal amino resin, Examples thereof include isocyanate compounds, blocked isocyanate compounds, epoxy group-containing compounds, carboxyl group-containing compounds and hydroxyl group-containing compounds. The film thickness of the clear coating film is usually adjusted to about 15 to 70 μm in the cured coating film after baking. Further, the base paint and the clear paint may be dispersed with a pigment, a dispersant, an antifoaming agent, an ultraviolet absorber, a light stabilizer and the like, if necessary.

The method for measuring the solid content of the paint is not particularly limited. For example, the mass (mass a) of the aluminum foil alone whose mass is measured in advance, and when a certain set time has elapsed after applying the clear paint Mass (mass b) and mass after baking and drying (mass c) were measured, and the following formula (1): coating solid content (mass%) = 100 × (c−a) / (b−a) (1) ), It is possible to calculate the paint solid content (mass%) when a certain set time has elapsed.

Further, the clear coating according to the present invention is applied
Using a bell type coating machine, the bell speed is 30,000 rpm or more, and the shaving air pressure is 0.3 kg / cm ² ~
It is preferable to apply at 1.0 kg / cm ² .

Further, in the present invention, as shown in FIG. 2, when the step of applying the solvent-based clear paint by wet-on-wet is started after the base paint is applied,
The clear coating is applied when the coating solid content of the coated base coating is in the range of 70 to 80% by mass, and after 2 minutes of setting, the clear coating solid content is in the range of 60 to 70% by mass, and the bake hardening is performed. It is possible to obtain a coating film having good subsequent coating quality, particularly a finished appearance.

[0034]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

In the evaluation of the examples and comparative examples, the following methods were used for evaluation.

<Measurement of solid content of paint> The mass of the aluminum foil alone whose mass has been measured in advance (mass a), the mass when the set time has elapsed after applying the clear paint (mass b), and baking drying The subsequent mass (mass c) was measured, and the coating solid content (mass%) when a certain set time had elapsed was calculated by the above formula (1).

<Finishing Appearance of Coating Film> JIS K-54
The surface of the top-coat coating film was visually observed according to 00 7.1 (1990). (1) Evaluation of sharpness of coating film The sharpness of coating film was evaluated using a PGD meter (manufactured by Japan Color Research Institute). This PGD meter shows a test chart on the surface of the coating film, and the gloss and smoothness of the surface of the coating film can be numerically evaluated (0.1 to 0.1
It is obtained as a semi-functional evaluation in 1.5), and the larger the value, the better the finished appearance. (PGD: Portable dis
tinctness of image glossmeter) (2) Visual appearance Based on the above JIS, the finish of the coating film surface was evaluated. ◯: Good Δ: Normal ×: Poor (3) Presence or absence of cracks The presence or absence of cracks on the coating film surface was visually evaluated. ○: No armpit occurrence ×: There is armpit occurrence

Example 1 A test piece (0.8 mm thickness × 70 mm × 150 mm) was prepared using a cold-rolled steel sheet for automobiles, the test piece was degreased, zinc phosphate conversion treatment was performed, and washing with water was performed. It was Next, cationic electrodeposition paint (Power Top U-60:
(Nihon Paint Co., Ltd.) is electrodeposited at a voltage of 250 V for 3 minutes, washed with water, and then baked at 160 ° C. for 20 minutes,
An electrodeposition coating film having a film thickness of 20 μm was formed. Further, an intermediate coating composition (OP-61: manufactured by Nippon Paint Co., Ltd.) was coated on the electrodeposition coating film so that the dry film thickness was 35 μm, set at room temperature for 3 minutes, and then baked at 140 ° C. for 20 minutes. It was An aqueous base paint (N
WB260 silver (manufactured by Nippon Paint Co., Ltd.) was applied so as to have a dry film thickness of 15 μm, and hot air at 60 ° C. was applied for 3 minutes. The solid content of the obtained base paint was 80% by mass. Then, using a bell type electrostatic coating gun, the gun distance is 3
Clear paint (O-550: manufactured by Nippon Paint Co., Ltd.) under the conditions of 00 mm, applied voltage -60 KV, shaving air pressure 0.5 kg / cm ² , and bell rotation speed 35000 rpm.
Was coated to give a dry film thickness of 35 μm, and after setting for 10 minutes, baking was performed at 140 ° C. for 20 minutes to obtain a top coated plate for an automobile of Example 1.

The clear paint used in this example had a paint solid content of 62 mass%, a paint solid content at the time of coating was 52 mass%, and a paint solid content after setting for 2 minutes was 65.5 mass%.
Met. In addition, the clear paint has a molecular volume of 1 as a solvent.
26 cm ³ / mol, viscosity 0.685 (mPa · s)
2.0% by mass of methylcyclohexane was added.

Example 2 In Example 1, the shaving air pressure was 0.3 kg / c.
An automobile top-coat coated plate of Example 2 was obtained in the same manner except that the clear paint was applied under the conditions of m ² and bell rotation speed of 30,000 rpm. In this example, the coating solid content after setting for 2 minutes after the clear coating was 60.3% by mass.

Example 3 In Example 1, the shaving air pressure was 0.9 kg / c.
An automobile topcoat coated plate of Example 3 was obtained in the same manner except that the clear coating was applied under the conditions of m ² and a bell rotation number of 40,000 rpm. In this example, the coating solid content after setting for 2 minutes after the clear coating was 69.8% by mass.

Example 4 In Example 1, the shaving air pressure was 1.0 kg / c.
An automobile topcoat coated sheet of Example 4 was obtained in the same manner except that the clear coating was applied under the conditions of m ² and a bell rotation number of 45,000 rpm. In this example, the coating solid content after setting for 2 minutes after the clear coating was 69.9% by mass.

Example 5 In Example 1, 10.0% by mass of methylcyclohexane to be added to the clear paint, 1.0 shaving air pressure
A top coated plate for an automobile of Example 5 was obtained in the same manner except that the conditions were kg / cm ² and a bell rotation number of 45,000 rpm. In this example, the coating solid content after setting for 2 minutes after the clear coating was 60.8% by mass.

Comparative Example 1 In Example 1, a clear thinner (O-550: manufactured by Nippon Paint Co., Ltd.) was used without adding an aliphatic high-boiling point solvent, and an ordinary thinner was used. A shaving air pressure of 1.0 kg / cm was used.
² , an automobile topcoat coated plate of Comparative Example 1 was obtained in the same manner except that the bell rotation speed was 45,000 rpm. In this comparative example, the coating solid content after setting for 2 minutes after the clear coating was 70.2% by mass.

Comparative Example 2 In Comparative Example 2, the shaving air pressure was 0.2 kg / c.
A car top-coated plate of Comparative Example 2 was obtained in the same manner except that the conditions were m ² and a bell rotation speed of 25,000 rpm. In this comparative example, the solid content of the coating was 59.5% by mass 2 minutes after setting the clear coating.

Comparative Example 3 In Example 1, 1.5% by mass of methylcyclohexane to be added to the clear paint and shaving air pressure of 1.0 k
A top coated plate for an automobile of Comparative Example 3 was obtained in the same manner except that the conditions were g / cm ² and a bell rotation number of 45,000 rpm. In this comparative example, setting 2 is performed after clear paint is applied.
The solid content of the coating material after 7 minutes was 70.2% by mass.

Comparative Example 4 In Example 1, 10.5% by mass of methylcyclohexane added to the clear coating and 1.0 of shaving air were used.
A top coated plate for an automobile of Comparative Example 4 was obtained in the same manner except that the conditions were kg / cm ² and a bell rotation number of 45,000 rpm. In this comparative example, the coating solid content after setting the clear coating composition for 2 minutes was 59.8% by mass.

Table 1 shows the evaluation results of the finished appearance of the automobile top-coat coated plates obtained in Examples 1 to 5 and Comparative Examples 1 to 4.

[0049]

[Table 1]

[0050]

As described above, according to the present invention, an automobile including the steps of applying a base paint and applying a solvent-based clear paint onto the base paint by wet-on-wet. In the method of applying a top coating composition for coating, a clear coating having a coating solid content (NV) at the time of coating of 50% by mass or more is applied, and the coating solid content in the clear coating after setting for 2 minutes is 60 to 70% by mass. Since it was the coating method of the top coating for automobiles,
Even when the base paint and the clear paint are subjected to wet-on-wet coating, an excellent effect that a coating film having a good coating quality, particularly a finished appearance can be obtained can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of a coating film configuration in which a coating method of the present invention is used.

FIG. 2 is a diagram illustrating a relationship between a base coating solid content before clear coating and a clear coating solid content after 2 minutes of setting according to the present invention.

FIG. 3 is a diagram illustrating a relationship between a solid content of a base paint before clear coating and a solid content of clear paint after 2 minutes from setting in the related art.

[Explanation of symbols]

1 steel plate 2 Undercoat 3 Intermediate coating film 4 base coating 5 clear coating

Continued front page    F-term (reference) 4D075 AA09 AA13 AA23 AA84 AA85                       AE10 AE12 BB25Y CA47                       CB06 DA06 DB02 DC11 EA06                       EA08 EA43 EB32 EB33 EB35                       EB36 EB38 EB45 EB46 EB51                       EC30 EC51 EC52 EC54                 4F034 AA03 AA04 BA15 BA22 CA02                       CA22 DA06 DA25                 4J038 CD091 CG001 DD001 DG001                       DL001 EA011 JA02 JA17                       JA30 JA55 KA03 KA06 MA07                       MA08 NA01 PA03 PB07 PC02

Claims (5)

[Claims] 1. A method for applying a topcoat paint for automobiles, which comprises a step of applying a base paint and a step of applying a solvent-based clear paint on the base paint in a wet-on-wet manner. ) Is 50 mass% or more, and the solid content of the paint in the clear paint after setting for 2 minutes is 60 to 70 mass%. 2. The coating solid content (NV) at the time of coating is 50.
Clear coatings with mass% or more have a molecular volume of 100 cm ³ / m
2. The coating method for a top coating composition for automobiles according to claim 1, wherein a solvent having a viscosity of 0.68 (mPa · s) or more is added in an amount of 2 to 10% by mass. 3. The clear coating is applied by using a bell type electrostatic coating machine at a bell rotation speed of 30,000 rpm or more and a shaving air pressure of 0.3 kg / cm ² or more. 3. The method for coating a topcoat paint for automobiles according to 3. 4. The method for coating a topcoat paint for automobiles according to claim 1, wherein the base paint is a water-based or solvent-based base paint. 5. The coating solid content of the applied base paint is 70 to 80% by mass when the step of applying the solvent-based clear paint is started after the base paint is applied. A method for coating a topcoat paint for automobiles according to claim 1.