JP2002126624A - Method for applying water based top coating material for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying a water based coating material and a solvent based clear coating material without using a flash off oven process. SOLUTION: In the method for applying the water based top coating material for an automobile, which includes a step for applying the water based coating material and a step for applying the solvent based clear coating material on the water based coating material, the atomized particle diameter of the water based coating material is <=25 μm and coating material solid content in the water based coating material to be applied at the time of starting the step for applying the solvent based clear coating material is >=40 mass%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying a paint for automobiles, and more particularly to a method for applying a solvent-based clear paint on a water-based paint.

[0002]

2. Description of the Related Art In the coating of automobiles and the like, a coating method in which a base coating and a clear coating are applied as a top coating on a coating plate on which an undercoat and an intermediate coating are formed to form an overcoat is generally used. It is used regularly. The base paint is used to provide good decorative properties to the final finish with organic or inorganic pigments, and the clear paint is applied on top of the base paint film and removes the pigment to the extent that it is transparent or does not impair transparency. Including.

[0003] Conventional automotive coatings, especially base coatings, contain large amounts of organic solvents. From the viewpoints of global environmental protection, resource saving, and safety during painting, it is not preferable to use such a large amount of organic solvent, and in order to reduce the amount of organic solvent, active research and development of water-based paints is underway. Have been done.

For example, JP-A-8-10690 discloses a method for applying a base paint and a clear paint using an aqueous base paint comprising a polyurethane dispersion in which an aqueous polyurethane resin is dispersed in water and a rheology modifier. Have been.

[0005] Film formation with a base paint and a clear paint is usually performed by wet-on-wet painting.
That is, after coating the base paint, a clear coat is continuously applied without baking, and two coats and one bake in which the base paint and the clear paint are baked at a time are generally used. However, if a large amount of water remains in the aqueous base paint, when the clear paint is painted and baked,
Rapid evaporation of water occurs, and a defect such as a bubble mark on the surface of the coating film occurs. Further, in order to obtain good film thickness uniformity of the aqueous base coating film, the solid content of the coating material is currently 15%.
It is common to use about 35% by mass of paint,
It is necessary to increase the paint solids before applying the clear paint.

[0006] In order to solve this problem, in the application of a water-based topcoat, a flash-off oven (drying) step for evaporating moisture is generally used between the water-based base coating step and the clear coating step. It is.

[0007]

However, the existing line configuration for applying a solvent-based top coat mainly includes only a base coating process and a clear coating process, and a flash-off oven process is not included in the line. . Therefore, in order to use a water-based paint using an existing line, it is necessary to modify the existing top-coating line to have a line configuration including a flash-off oven process, resulting in a huge capital investment cost. was there.

The present invention has been completed in view of the above problems, and provides a method for applying a water-based paint and a solvent-based clear paint without a flash-off oven process, that is, without modifying an existing line. The purpose is to:

[0009]

DISCLOSURE OF THE INVENTION The present invention relates to the effects of the solid content and the atomized diameter of a water-based base paint, the number of bell revolutions and the amount of shaping air of a bell-type coating machine used for coating on the properties of a coating film. It has been completed as a result of intensive studies.

That is, the present invention has the following constitution for each claim.

The invention according to claim 1 is a method of applying a water-based topcoat for automobiles, comprising a step of applying a water-based base paint and a step of applying a solvent-based clear paint on the water-based base paint, The atomized diameter of the applied aqueous base paint is 25 μm or less, and the solid content of the applied aqueous base paint at the time of starting the step of applying the solvent-based clear paint is 40% by mass or more. A method for applying a water-based overcoat for automobiles, characterized in that:

The invention according to a second aspect is characterized in that the water-based base coating material has a bell rotation speed of 3000 using a bell-type coating machine.
The method for applying a water-based topcoat paint according to claim 1, wherein the coating is performed at 0 rpm or more and the shaping air amount is 500 liters (Normal) / min or more.

According to a third aspect of the present invention, the coating of the water-based top coating according to claim 1 or 2, wherein the solid content of the water-based base coating before coating is 10 to 35% by mass. Is the way.

[0014]

According to the present invention configured as described above, the following effects can be obtained for each claim.

According to the first aspect of the present invention, when the step of applying the solvent-based clear paint is started, the atomized diameter of the applied aqueous base paint and the solid content of the applied aqueous base paint are determined. By the adjustment, it is possible to suppress the partial bias of the contained water and to suppress the occurrence of defects such as armpits. For this reason, even if the water-based topcoat is applied without the flash-off oven process, it is possible to suppress the occurrence of a defect such as an armpit. That is, it is possible to perform the coating of the water-based paint and the solvent-based clear paint using the conventional equipment without the need to modify the existing equipment, and a great economical effect can be obtained.

According to the second aspect of the present invention, when the water-based paint is applied, the atomization diameter of the water-based paint can be easily reduced by adjusting the number of revolutions of a bell-type coating machine. In addition, moisture in the water-based paint can be effectively removed by adjusting the amount of shaping air.

According to the third aspect of the present invention, by using a paint having a paint solid content of 10 to 35% by mass,
A coating film having excellent film thickness uniformity can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for producing a coating film structure shown in FIG. 1 will be described below. In FIG. 1, for the sake of explanation, the thickness of each coating film is the same.

First, the steel sheet 1 is pre-treated (degreasing, chemical conversion treatment).
Is applied. As a result, oils adhering to the steel plate are completely removed. Further, by forming a chemically stable inorganic film on the steel plate surface, the steel plate surface is inactivated, and rust prevention and adhesion between the steel plate and the coating film are enhanced. In the automotive coating line, emulsion and alkaline degreasing agents and zinc phosphate chemicals are mainly used from the viewpoints of rust prevention, relation with undercoating paint, and mass productivity. Or a continuous spray method. In the pretreatment, complete degreasing and uniform and dense conversion coating are important.

An undercoating film 2 is formed on the pretreated steel sheet by electrodeposition, powder coating, or the like, thereby improving the rust prevention of the coating film. Since it is the first paint to be applied, it is preferable to use a paint having excellent adhesion, rust prevention and coating strength. In addition, it is preferable to coat the entire surface of the steel sheet in order to impart rust resistance over the entire surface. Examples of the material include, but are not limited to, a cationic electrodeposition coating material having a blocked isocyanate-modified epoxy resin as a main resin, and a powder coating material having an epoxy or polyester resin as a main resin. The paint has rustproof properties such as hydroxides, oxides, organic acid salts, and inorganic acid salts of metals such as aluminum, nickel, zinc, strontium, zirconium, molybdenum, tin, antimony, lanthanum, tungsten, and bismuth. A curing catalyst, an antisettling agent and the like can be appropriately compounded. In the undercoat, the thickness of the coating film, uniformity of the film thickness, sufficient baking,
It is important to pay attention to the smoothness and gloss of the finished surface. As the coating conditions, for example, when electrodeposition is used, a car body is used as a cathode, a carbon plate is used as an anode, a bath temperature is 20 to 35 ° C., a voltage is 100 to 400 V, and a current density is 0.
The undercoat can be applied by electrodeposition under the conditions of 01 to 5 A and an energization time of 1 to 10 minutes, and then the undercoat 2 can be cured by baking. As the baking conditions, generally used conditions can be used. For example, in the case of cationic electrodeposition coating, 130 to 1 is used.
It is baked at 80 ° C. for about 10 to 40 minutes.

After that, sealing of the joint of the steel sheets, soundproof coating, and vibration-proof material fusion may be performed. For sealing, for example, a PVC sol or bituminous sealing material can be applied to the steel plate joint with a flow gun or tube, and if necessary, can be finished smoothly with a brush or spatula. , Waterproof. In addition, sound-proofing and vibration-proofing are applied by painting or setting rubber latex-based, bituminous-based sound-proofing and vibration-proofing paint on the back of the floor, the inner surface of the wheel house, the lower part of the outer surface of the vehicle body, the floor, the dash surface, and the inner surface of the door outer. Processing can be performed.

An intermediate coating is applied on the undercoat 2
By baking, the intermediate coating film 3 can be formed. By these coatings, pinholes and small irregularities on the undercoat surface are filled, surface adjustment for improving the finish appearance of the overcoat is performed, and protection against external impacts such as stepping stones can be enhanced. The coating means is not particularly limited, and various known means such as air spray, airless spray, and electrostatic coating can be appropriately used. As the baking conditions, generally used conditions can be used. For example, baking is performed at 130 to 180 ° C. for about 10 to 40 minutes.

As the intermediate coating, various known water-based intermediate coatings and solvent-based intermediate coatings can be used. Specifically, a coating containing a carboxylic acid group-containing resin, a urethane bond-containing diol and resin fine particles as main components, Water-based paints such as polycarboxylic acid resins, amino resins, paints containing linear low molecular weight polyester diol and benzoin as main components, epoxy ester resins, amino alkyd resins, or oil-free amino alkyd resins are the main resins. Solvent-based paints and the like can be used.

Note that, in order to prevent the occurrence of scratches (chipping) due to stepping stones or the like from a vehicle traveling in front, before applying the intermediate coating material, the tip of the hood or the roof may be located at a location where chipping is likely to occur. Anti-chipping paint for imparting anti-chipping property (hereinafter also referred to as ACC)
Can be painted. Specific examples of the anti-chipping paint include a paint containing a polyolefin resin as a main component, a polyamine in a blocked urethane prepolymer,
A one-part heat-curable urethane paint obtained by adding a curing agent component having active hydrogen such as a polyol, a polyester resin and a melamine resin, or a polyester resin and a block isocyanate compound as main components, and a high concentration of an appropriate pigment. And a coating 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, and a solvent-based intermediate coating is applied thereon by wet-on-wet, and the anti-chipping paint is baked and dried once. A forming method can be used, but is not limited to this method. When applying a solvent-based ACC to the vehicle body, it is not necessary to apply the solvent-based ACC to the entire vehicle body, but only to the parts where chipping resistance is required, such as the tip of the hood or roof. Can be.

Thereafter, a water-based paint and a solvent-based clear paint are applied on the intermediate coat 3. As described in detail below, by applying a water-based paint and a solvent-based clear paint by the method according to the present invention, without a flash-off oven step which was conventionally essential for controlling defects such as armpits, Water-based paints and solvent-based clear paints can be applied. In the case of the intermediate paint and the top paint (base paint and clear paint), attention should be paid to prevention of problems such as dust, bumps, and sagging, to ensure the required film thickness, and to properly bake and dry.

After applying the solvent-based clear paint, baking is performed to form the water-based base coating film 4 and the solvent-based clear coating film 5. This imparts aesthetic appearance and durability to the environment (weather resistance, chemical resistance, abrasion resistance, etc.). The baking conditions for the topcoat paint are not particularly limited, but are, for example, 10 to 40 at 120 to 160 ° C.
It is baked and dried for about a minute.

A coating film having the structure shown in FIG. 1 is formed by such a process. However, the coating method of the present invention is not limited to the above structure, and various modifications utilizing known techniques are also included in the present invention. Included. For example, in order to improve the finish, the baking conditions are appropriately adjusted in consideration of the properties of the paint, such as applying the middle coat paint by a two-coat method or removing baking before applying the middle paint. be able to.

Hereinafter, the method for applying a top coat according to the present invention will be described in detail.

The invention according to the present invention is a method for applying a water-based topcoat for automobiles, comprising a step of applying a water-based base paint and a step of applying a solvent-based clear paint on the water-based base paint. The atomization diameter of the aqueous base paint is 25 μm or less, and the solid content of the applied aqueous base paint at the start of the step of applying the clear paint is 40% by mass or more. This is a method of applying a water-based topcoat for automobiles.
Between the application of the water-based paint and the application of the solvent-based clear paint, a set time may be appropriately provided for the adjustment of the solid content of the paint, and the application of the solvent-based clear paint without the set time. Can also.

If the atomization diameter exceeds 25 μm, the smoothness of the coating film when applied to a substrate is impaired, and the smoothness of the finally baked and dried coating surface may be degraded. There is. In addition, when the atomization diameter is large, it is difficult to evaporate the water contained in the aqueous base paint at the stage of coating, and it becomes difficult to improve the proportion of the solid content of the paint in the aqueous base paint. The lower limit of the atomization diameter is not particularly limited. However, if the atomization diameter is too small, the mass becomes light, so that the amount of suspended particles may increase, and the yield may be reduced.

The coating solid content of the water-based base coating when applying the solvent-based clear coating reduces the total water content,
It is preferably at least 40% by mass in order to suppress the occurrence of armpits. The upper limit of the solid content of the paint is not particularly limited, but when the viscosity of the water-based paint is too high,
When the solvent-based clear paint is applied by wet-on-wet, it may be difficult to suppress the occurrence of repelling or the like, so that the content is preferably 60% by mass or less.

The coating method of the present invention is particularly effective when a paint having a solid content of 10 to 35% by mass of the aqueous base paint before coating is used as the aqueous base paint. 1
When the amount is less than 0% by mass, it is difficult to reduce the solid content of the coating material to 40% by mass when starting the step of applying the solvent-based clear coating material. This is because the uniformity of the coating film thickness may be reduced. Here, “before painting” means immediately before being used in the painting process.

In the case of using a water-based base coating material, if the atomization diameter is large, the contained water will be partially biased, which will cause fire. In the present invention, by controlling the atomization diameter of the water-based base paint as described above to suppress the partial deviation of the contained water, and also by adjusting the paint solid content, contained in the water-based base paint By adjusting the water content, the occurrence of armpits can be suppressed.

For this reason, the use of the coating method of the present invention can effectively suppress the occurrence of wrinkles without providing a flash-off oven step. That is,
It is not necessary to provide new equipment to suppress the occurrence of waki, and the existing equipment can be used to apply the water-based paint and the solvent-based clear paint, resulting in enormous economic effects.

In the present invention, the atomized diameter refers to the average diameter of the particles of the coated paint. As a measuring method, a grounding rod with a glass plate is vertically shaken down during coating by a coating machine. A method of obtaining the average value of the particle distribution by collecting paint particles and performing image analysis on the particles can be used.

As the aqueous base paint, various commercially available paints can be used, and also known solid base paints and metallic base paints can be used.

As the solid base paint, base resin,
A thermosetting coating containing a crosslinking agent, a coloring pigment, and water can be used. Examples of the base resin include resins such as an acrylic resin, a polyester resin, an alkyd resin, a fluorine resin, a urethane resin, and a silicon-containing resin containing a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a silanol group, and an epoxy group. . As the crosslinking agent, melamine resin, urea resin, (block) which can react with the above functional group
Polyisocyanate compound, epoxy compound or resin, carboxyl group-containing compound or resin, acid anhydride,
Examples thereof include an alkoxysilane group-containing compound and a resin. Examples of the coloring pigment include cadmium yellow, cadmium red, molybdenum red, chrome yellow, Prussian blue, zinc white, titanium dioxide, yellow iron oxide, carbon black, aluminum flake, titanium mica, calcium carbonate, barium sulfate, and barium carbonate. Silica, kaolin, barita, clay, azo yellow, azo orange, azo red, phthalocyanine green, phthalocyanine blue, isoindoline yellow,
Solid color pigments for paints, such as a sullen pigment and a perylene pigment, can be mentioned, and the amount of these can be adjusted according to a desired color tone.

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 coated with a metal oxide, mica-like iron oxide, and the like. The orientation of such a metallic pigment gives an excellent coating appearance.

The thickness of the solid base coating and the metallic base coating is usually 5 to 5 for the cured coating after baking.
The thickness is adjusted to 0 μm, preferably about 10 to 40 μm.

As the solvent-based clear coating, various commercially available coatings can be used. In addition, a liquid coating containing a base resin, a curing agent, and an organic solvent as a solvent or a dispersing medium, can be dried at about 40 to 110 ° C. Solidifying materials are preferred. In addition, various known solid base paints and metallic base paints containing a coloring pigment or the like as necessary can be used. 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 thereof (such as a graft resin). Can be The glass transition temperature of these base resins is usually 40
Those within the range of about to 120 ° C are preferred. Any curing agent may be used as long as it reacts with the above functional group of the base resin and is cross-linked and cured three-dimensionally. For example, an amino obtained by etherifying a part or all of the methylol group of a melamine resin or a urea resin is used. Examples include resins, polyisocyanate compounds, blocked isocyanate compounds, epoxy group-containing compounds, carboxyl group-containing compounds, and hydroxyl group-containing compounds. The thickness of the clear coating film is usually adjusted to about 15 to 70 μm in the cured coating film after baking.

In the base paint and the clear paint, the above-mentioned pigment, dispersant, defoamer, ultraviolet absorber, light stabilizer and the like can be dispersed as required.

The defoaming agent refers to a chemical used to remove air bubbles, and it is preferable to suppress the generation of air bubbles in coating a paint, since this may cause poor appearance. In general, various known materials can be used as the defoaming agent, and an oily substance having a small volatility and a large diffusing power, or a water-soluble surfactant can be suitably used.

The dispersant is a component added to disperse solid fine particles in a liquid to form a suspension as stable as possible. The dispersing agent includes an anticoagulant used to prevent the particles once dispersed from coagulating again, in addition to the peptizer and the protective colloid.

The coating composition can be adjusted to a specific viscosity by using additives such as a thickener to obtain a desired film thickness.

The method for measuring the solid content of the paint is not particularly limited. For example, an aqueous base paint is applied to an aluminum foil whose mass has been measured in advance, and the mass (mass a) of the aluminum foil alone and the aqueous base paint are measured. After coating, the mass (mass b) after a certain set time has elapsed and the mass after baking and drying (mass c) were measured, and the following formula (1):

[0046]

(Equation 1)

Accordingly, it is possible to calculate the paint solid content when a certain set time has elapsed.

The coating of the base paint according to the present invention is carried out by using a bell type coating machine at a bell rotation speed of 30,000 rpm or more and a shaping air amount of 500 liters (No.
rmal) / min or more.

The coating method is not particularly limited, but a bell-type coating machine is preferred from the viewpoint of coating efficiency.

In the present invention, the bell rotation speed is 3000
By setting the rotation speed to 0 rpm or more, the atomization diameter of the water-based paint can be easily reduced to 25 μm or less. In addition,
The upper limit of the number of rotations of the bell is not particularly limited, but may be set to 60 due to mechanical and safety reasons of the bell coating machine.
It is preferably at most 000 rpm. Also, the shaping air amount is set to 500 liters (Normal) / mi.
By setting it to n or more, water can be effectively removed when the water-based paint is applied. The upper limit is not particularly limited, but is preferably 800 liters (Normal) / min or less from the viewpoint of preventing quality deterioration due to dust adhesion or the like.

The bell-type device is generally used to atomize paint supplied toward a disc-shaped paint diffusion plate rotatably provided at the tip end side of a coating machine main body by centrifugal force, and radially outwardly extend the bell cup. This is a device for spraying and applying shaping air toward the surface, but when it is used in the coating method according to the present invention, various improved devices can be used. For example, in order to suppress coating unevenness caused by the behavior of the scale-like member included in the paint, an apparatus provided with a means for adjusting the air ejection pressure may be used.

[0052]

EXAMPLES In the evaluation of Examples and Comparative Examples, evaluations were made based on the following methods.

<Measurement of paint solid content> After a water-based base paint was applied to an aluminum foil whose mass had been measured in advance, the mass (mass a) of the aluminum foil alone and the water-based base paint were applied, a certain set time had elapsed. The mass at the time (mass b) and the mass after baking and drying (mass c) were measured, and the paint solid content was calculated according to the above formula (1).

<Atomization diameter> During the coating with a coating machine, a ground rod with a glass plate was shaken down vertically, paint particles were collected, and image analysis was performed. The average value of the major axis and minor axis of all particles observed in the image was determined as the particle diameter, and the average value was determined as the atomized diameter.

<Appearance evaluation of coating film> JIS K-5400
The surface of the overcoat film was visually observed according to 7.1 (1990).

Example 1 An SPC steel plate (0.8 mm (thickness) × 70 mm × 150 mm) test piece was degreased, subjected to zinc phosphate conversion treatment, washed with water, and then washed with a cationic electrodeposition paint (Powertop U-60; Nippon Paint) Was applied at 250 V for 3 minutes, washed with water, and baked at 160 ° C. for 20 minutes. An intermediate coating (OP-61; manufactured by Nippon Paint Co., Ltd.) was applied to the electrodeposition test piece in a dry film thickness of 3
Coating was performed so as to have a thickness of 0 to 35 μm, and after setting at room temperature for 3 minutes, baking was performed at 140 ° C. for 20 minutes. A water-based base paint having a paint solid content of 25% by mass (Aqua BC-3; manufactured by NOF CORPORATION) using a bell type coater with respect to the intermediate coating test piece and the aluminum foil whose mass was measured in advance.
The bell rotation speed 30000 rpm, shaping air amount 5
The coating was performed under the condition of 00 liter (Normal) / min so that the atomization diameter of the coating material was 25 μm and the dry film thickness was 10 to 15 μm, and the coating was set at room temperature for 3 minutes. Next, clear paint (Bellcoat 6000; manufactured by NOF Corporation)
Was applied to a dry film thickness of 30 to 35 μm, set at room temperature for 3 minutes, and baked at 140 ° C. for 20 minutes. The paint solid content before clear coating was 40% by mass.

<Example 2> The bell rotation speed of the bell type coating machine was changed to 45000 rpm, and the atomization diameter of the paint was 22 μm.
Coating was performed in the same manner as in Example 1 except that The paint solid content before clear coating was 48% by mass.

<Embodiment 3> The bell rotation speed of the bell type coating machine was changed to 55000 rpm, and the atomization diameter of the paint was 21 μm.
Coating was performed in the same manner as in Example 1 except that The paint solid content before clear coating was 53% by mass.

<Example 4> Coating was performed in the same manner as in Example 1 except that the shaping air amount of the bell type coating machine was changed to 600 liters (Normal) / min so that the atomization diameter of the coating material became 24 μm. did. The paint solid content before clear coating was 41% by mass.

<Example 5> Coating was performed in the same manner as in Example 2 except that the shaping air amount of the bell type coating machine was changed to 600 liters (Normal) / min so that the atomization diameter of the coating material became 22 μm. did. The paint solid content before clear coating was 49% by mass.

<Example 6> Coating was performed in the same manner as in Example 3 except that the shaping air amount of the bell type coating machine was changed to 600 liter (Normal) / min so that the atomization diameter of the coating material became 21 μm. did. The paint solid content before clear coating was 54% by mass.

<Comparative Example 1> Coating was performed in the same manner as in Example 1 except that the shaping air amount of the bell type coating machine was changed to 450 liter (Normal) / min so that the atomization diameter of the coating material became 24 μm. did. The paint solid content before clear coating was 38% by mass.

<Comparative Example 2> The bell rotation speed of the bell type coating machine was changed to 25000 rpm, and the atomization diameter of the paint was 28 μm.
Coating was performed in the same manner as in Example 1 except that The paint solid content before clear coating was 35% by mass.

With respect to Examples 1 to 6 and Comparative Examples 1 and 2, the solid content (% by mass) of the paint before the clear coating, the atomization diameter, and the properties of the coating film after the clear coating (arm, finished appearance, color) were investigated. The results are shown in Table 1 (o: good, x: bad). As shown in Table 1, Examples 1 to 6 according to the present invention
Were good in terms of the properties of each coating film after coating (clearing resistance, finished appearance, color), whereas in Comparative Examples 1 and 2, defects were found in the coating film properties after clear coating. Was.

[0065]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating one embodiment of a coating film configuration using a coating method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 steel plate 2 undercoat 3 intermediate coat 4 base coat 5 clear coat

Claims (3)

[Claims] 1. A method for applying a water-based topcoat for automobiles, comprising: a step of applying a water-based base paint; and a step of coating a solvent-based clear paint on the water-based base paint, wherein the coated water-based base paint is used. Wherein the atomized diameter of the water-based paint is 25 μm or less, and the solid content of the water-based paint is 40% by mass or more when the step of applying the solvent-based clear paint is started. How to apply water-based topcoat. 2. The water-based base coating is performed by using a bell-type coating machine at a bell rotation speed of 30,000 rpm or more and a shaping air volume of 500 liters (Normal) /
2. The method for applying a water-based top coating according to claim 1, wherein the coating is performed for at least min. 3. The method according to claim 1, wherein the solid content of the water-based base coating before coating is 10 to 35% by mass.