JP2001246311A - Method for forming multiple layer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming multiple layer coating films by applying a first colored base coating material, a second colored base coating material and a clear coating material on a material to be coated, such as the outer panel of an automobile. SOLUTION: This method for forming the multiple layer coating films consists in applying the first colored base coating material (A) to the material to be coated and half curing the coating film until the gel fraction of the coating film attains 5 to 95 wt.%, then applying the second colored base coating material (B) thereto and applying the clear coating material (C) thereto without curing the coating film, then heating the material to be coated to simultaneously cure the three-layered coating films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a multi-layer coating by applying a first colored base paint, a second colored base paint and a clear paint to an object to be coated such as an automobile outer panel. About the method.

[0002]

2. Description of the Related Art As a method of forming an overcoating multi-layer coating on an object to be coated such as an automobile outer panel, for example, a first colored base paint, a second colored base paint and a clear paint are used. A three-coat one-bake method (3 coats and 3 coats) in which these coatings are simultaneously cured by heating and then applying wet-on-wet coating.
C1B) After applying the first base paint and the second base paint, heating to completely cure both coatings, applying a clear coating, and heating again to cure the clear coating. 3
The coat 2 bake method (3C2B) is known. However, 3C1B is energy-saving because the heating of the coating film is performed in one step, but has a defect that it is easy to sag when a clear paint is applied to a thick film (40 μm or more).
B requires two heating steps and a second colored base.
It has defects such as insufficient interlayer adhesion between the paint film and the clear paint film.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to provide the above 3C
To eliminate defects in 1B and 3C2B,
The feature is that, in 3C1B, the second colored base paint is applied after being cured so that the gel fraction of the coating film of the first colored base paint is 5 to 95% by weight,
Thereby, the object was achieved, and the present invention was completed.

That is, according to the present invention, an object to be coated is coated with a first colored base coating material (A), and the coating film has a gel fraction of 5-9.
After semi-curing to 5% by weight, the second colored base
Forming a multi-layer coating film by applying a clear coating material (C) without applying the coating material (B) and curing the coating film, and then heating to simultaneously cure the three-layer coating film. About the law.

Hereinafter, the method for forming a multilayer coating film of the present invention will be described in detail.

[0006] The object to be coated is not particularly limited, but an outer plate portion of an automobile or an electric appliance is suitable. Examples of the automobile outer panel include hoods, roofs, trunk lids, fenders, bumpers, and door exteriors of passenger cars, mini cars, buses, trucks, and the like. The material of these objects to be coated is metal or plastic.

Prior to applying the first colored base paint (A) to the object to be coated, an undercoat or intermediate coating such as a cationic electrodeposition paint is applied to the object to be coated, and the coating is cured. It is preferable to keep it.

The first colored base paint (A) is a paint to be applied to an object to be coated prior to the second colored base paint (B), and is a paint containing a resin composition and a colored pigment. In addition, solid color paints, metallic paints, interference pattern paints, and the like are included, and the form can be applied to any of an organic solvent-based paint and an aqueous paint.

The resin composition comprises a hydroxyl group, a carboxyl group,
Base resins such as acrylic resins, polyester resins, and alkyd resins having functional groups such as epoxy groups, and melamine resins, urea resins, block polyisocyanate compounds, carboxyl group-containing compounds, and epoxy compounds that can react with these functional groups A thermosetting resin composition comprising a crosslinking agent such as a group-containing compound is suitable. The ratio of the base resin to the crosslinker is based on the total solid weight of both components, and the former is 5
0-90%, especially 60-80%, the latter 50-50%,
Particularly, 40 to 20% is suitable.

The color pigments include solid color pigments, metallic pigments and interference pattern pigments. As solid color pigments, for example, titanium oxide, zinc white,
Inorganic pigments such as carbon black, cadmium red, molybdenum red, chrome ero, chromium oxide, prussian bull, and cobalt bull; Organic pigments; scaly aluminum, mica, iron oxide, etc. as metallic pigments; and mica, mica surface-coated with metal oxide, etc. as interference pattern pigments. These pigments can be used alone or in combination of two or more. The compounding amount of these coloring pigments can be arbitrarily selected depending on the desired solid tone, metallic feeling and interference pattern, and there is no particular limitation. Any organic solvent may be used as long as it can mix and disperse the above-mentioned resin composition and color pigment, and ordinary paint solvents such as hydrocarbon-based, ester-based, ether-based, alcohol-based and ketone-based solvents are used. it can.

The first colored base paint (A) has, for example, a solid content at the time of coating of 10 to 50% by weight and a viscosity of 10 to 3%.
By adjusting the time to 0 second (for a hood cup # 4/20 ° C.), the object to be coated can be applied by electrostatic coating, air spray, airless spray or the like so that the thickness of the cured coating film becomes 10 to 40 μm.

In the present invention, the first colored base coating material (A) is applied to the object to be coated, and the gel fraction of the coating film is 5 to 95% by weight, preferably 20 to 75% by weight. After curing, it is necessary to apply the second colored base paint (B). When the gel fraction of the coating film of the first colored base coating material (A) is lower than 5% by weight, the coating film of the second colored base coating material (B) is easily sagged. Any of these is not preferred because the interlayer adhesion between the colored base paint (B) coating film and the clear paint (C) coating film is reduced.

The method of curing the coating film of the first colored base paint (A) so that the gel fraction falls within the above range can be arbitrarily selected depending on the resin composition used.
For example, a thermosetting composition is heated at a temperature of about 100 to 170 ° C. for an appropriate time, and a resin composition that cures at room temperature is left at a temperature of a room temperature to 100 ° C. or less for an appropriate time. A coating using an unsaturated resin composition can be easily applied by appropriately irradiating an active energy ray.

The gel fraction is determined by curing the first colored base paint (A) on a tin plate or a glass plate with a cured coating film of 20 to 50 μm.
It is coated so as to have a film thickness, and after being cured by the above-mentioned appropriate method so as to have a desired gel fraction, the coating film is peeled off from the object to be coated with a cutter or the like, and the acetone is put therein. Extraction was performed at the reflux temperature for 3 hours, and after drying, the following formula was obtained by (coating weight after extraction / coating weight before extraction) × 100.
It is calculated.

By semi-curing the coating film of the first colored base coating material (A) in this way, the second colored base coating material (B) becomes a cured coating film having a thickness of 30 μm or more as compared with the conventional 3C1B. No sagging even when painted, and 3C2
Since the number of heating steps is smaller than that of B, energy saving can be realized, and effects such as improvement in interlayer adhesion can be obtained.

The second colored base paint (B) is applied to the surface of the paint film obtained by semi-curing the coating film of the first colored base paint (A) in this manner.

The second colored base paint (B) is a first colored base paint (cured) cured so that the gel fraction of the coating film becomes 5 to 95% by weight, preferably 20 to 75% by weight. The paint to be applied to the coating surface of A), specifically, a resin composition, an organic solvent-based solid color paint containing a color pigment, a metallic paint, an interference pattern paint, and the like can be applied. By applying the second colored base paint (B), it is possible to improve the smoothness, sharpness and the like of the obtained multilayer coating film.

The resin composition comprises a hydroxyl group, a carboxyl group,
Base resins such as acrylic resins, polyester resins, and alkyd resins having functional groups such as epoxy groups, and melamine resins, urea resins, block polyisocyanate compounds, carboxyl group-containing compounds, and epoxy compounds that can react with these functional groups A thermosetting resin composition comprising a crosslinking agent such as a group-containing compound is suitable. The ratio of the base resin to the crosslinker is based on the total solid weight of both components, and the former is 5
0-90%, especially 60-80%, the latter 50-50%,
Particularly, 40 to 20% is suitable.

Examples of the coloring pigment include solid color pigments, metallic pigments and interference pattern pigments. As solid color pigments, for example, titanium oxide, zinc white,
Inorganic pigments such as carbon black, cadmium red, molybdenum red, chrome ero, chromium oxide, prussian bull, and cobalt bull; Organic pigments; scaly aluminum, mica, iron oxide, etc. as metallic pigments; and mica, mica surface-coated with metal oxide, etc. as interference pattern pigments. These pigments can be used alone or in combination of two or more. The compounding amount of these coloring pigments can be arbitrarily selected depending on the desired solid tone, metallic feeling and interference pattern, and there is no particular limitation. Any organic solvent may be used as long as it can mix and disperse the above-mentioned resin composition and color pigment, and ordinary paint solvents such as hydrocarbon-based, ester-based, ether-based, alcohol-based and ketone-based solvents are used. it can.

The second colored base paint (B) has, for example, a solid content at the time of coating of 10 to 50% by weight and a viscosity of 10 to 3%.
Adjust to 0 seconds (Ford cup # 4/20 ° C) and apply a half of the first colored base paint (A) by electrostatic coating, air spray, airless spray, etc., so that the cured coating film has a thickness of 10 to 40 µm. Can be applied to the cured coating surface. In the multilayer coating film of the present invention, the coating film of the second colored base paint (B) may be any of colored opaque, colored transparent, and colored translucent.

A second colored base paint (B) is applied, and the coating film is not cured (for example, a gel fraction of 5% by weight).
Hereinafter, a clear paint (C) is applied to the uncured coated surface.

The clear coating (C) is preferably a thermosetting coating which forms a colorless transparent or colored transparent coating containing a resin composition and an organic solvent as essential components and, if necessary, a coloring pigment. Can be used for The resin composition, the organic solvent, the color pigment, and the like are used in the first color base.
Paints (A) and the second colored base paint (B) can be suitably used.

The clear paint (C) is adjusted to, for example, a solid content of 10 to 60% by weight and a viscosity of 10 to 40 seconds (for ford cup # 4/20 ° C.) at the time of coating.
The uncured second colored base paint (B) can be applied to the uncured second colored base paint (B) by electrostatic coating, air spray, airless spray, or the like so as to have a thickness of about 60 μm.

In the present invention, after the first colored base paint (A) is applied, before the second colored base paint (B) is applied, the coating of the first colored base paint (A) is applied. Gel fraction is 5
It is necessary to cure to 95% by weight, preferably 20-75% by weight. When the gel fraction of the coating film of the first colored base paint (A) is lower than 5% by weight, the second
The coating film of the colored base coating material (B) tends to sag easily. On the other hand, if it exceeds 95% by weight, the interlayer adhesion with the coating film of the second colored base coating material (B) is reduced, and neither is preferable.

After applying the clear paint (C) as described above and leaving it at room temperature for about 1 to 10 minutes,
By heating at 0 ° C. for 10 to 40 minutes to simultaneously cure the three-layer coating film, the multilayer coating film intended for the present invention is obtained.

[0026]

The feature of the present invention is that when the second colored base paint (B) is applied, the colored base which is the surface to be coated is applied.
Paint (A) with a gel fraction of 5 to 95 in advance.
Weight percent. As a result, even if the second colored base coating material (B) was applied to a film having a thickness of 30 μm or more, there was no sagging, and the interlayer adhesion, smoothness and sharpness of the three-layer coating film were improved.

[0027]

EXAMPLES Examples and comparative examples according to the present invention will be described below. All parts and percentages are based on parts by weight, and the thickness of the coating is based on the cured coating.

1. Specimen (1) Coated object Cathode electrodeposition paint (“ELECRON 9800” Kansai Paint Co., Ltd.) was applied to a steel plate (size: 100 × 150 × 0.8 mm)
, Trade name, polyamine-modified epoxy resin, block polyisocyanate-based) and intermediate coating (Lugagabe T
P-37 "(manufactured by Kansai Paint Co., Ltd., trade name, polyester resin, melamine resin-based organic solvent type), and each was heated and cured.

(2) First colored base paint (A) a): Hydroxyl group-containing acrylic resin (number average molecular weight 1500
0, hydroxyl value 50, acid value 4) 75 parts, methyl / butyl mixed etherified melamine resin (“Yuvan 20SE” manufactured by Mitsui Toatsu Co., Ltd., trade name) 25 parts (solid content), titanium white pigment 7
0 parts and 1 part of carbon black were mixed and dispersed in a mixed solvent of ethyl acetate / toluene = 50/50 (weight ratio), the solid content at the time of coating was 40%, and the viscosity was 30 seconds (foam). Cup # 4/20 ° C).

(3) Second colored base paint (B) a): Acrylic resin containing hydroxyl group (number average molecular weight 1000)
0, hydroxyl value 100, acid value 5) 80 parts (solid content) and 20 parts (solid content) of "Uvan 20SE", 30 parts of titanium white pigment and 0.5 part of carbon black were dissolved in Solvesso 1
00 / Solvesso 150 (all manufactured by Cosmo Oil Co., Ltd., trade name, aromatic hydrocarbon solvent) = 50/50 (weight ratio)
Mixed and dissolved in a mixed solvent consisting of
It was adjusted to 0% and the viscosity to 20 seconds (for ford cup # 4/20 ° C).

(4) Clear paint (C) a): Acrylic resin containing hydroxyl group (number average molecular weight 1200
0, hydroxyl value 110, acid value 5) 80 parts (solid content) and 20 parts (solid content) of "Uvan 20SE" in Solvesso 1
00 / solvesso 150 = 50/50 (weight ratio), mixed and dissolved in a mixed solvent, and the solid content at the time of coating was 40%.
The viscosity was adjusted to 20 seconds (Ford cup # 4/20 ° C).

2. EXAMPLES AND COMPARATIVE EXAMPLES Example 1 A first colored base paint (A) (a) was applied to a substrate to a thickness of 25 μm, left at room temperature for 2 minutes, and then heated at 100 ° C. for 15 minutes. Then, the coating film of the first colored base paint (A) was semi-cured so that the gel fraction was 60%. Then, a second colored base coating material (B) (a) was applied to the semi-cured coating surface to a thickness of 35 μm, and left at room temperature for 2 minutes. After coating to a film thickness, heating at 140 ° C. for 30 minutes
The layer coating was simultaneously cured. As a result of a performance test of the obtained multilayer coating film, the thick film coating property was good, the interlayer adhesion was good, and the finished appearance was good.

COMPARATIVE EXAMPLE 1 A first colored base paint (A) (a) was applied to a substrate to a thickness of 25 μm, left at room temperature for 2 minutes, and then a second colored base paint (B) ( a) was applied to a film thickness of 35 μm, left at room temperature for 2 minutes, and then the clear paint (C)
After coating to a thickness of μm, the coating was heated at 140 ° C. for 30 minutes to simultaneously cure the three-layer coating. As a result of a performance test of the obtained multilayer coating film, the thick film coating property was poor, the interlayer adhesion was poor, and the finished appearance was poor.

The performance test method is as follows.

Thick film coatability: The second colored base paint (B) is applied on the coated surface (uncured or semi-cured) of the first colored base paint (A).
Is applied to a film thickness of 30 μm, and is heated at 140 ° C. for 30 minutes and cured to observe a coating film surface. Those with sagging, etc. were regarded as defective.

Interlayer adhesion: A cut line was made with a cutter knife so that the obtained multilayer coating film reached the base material, and 1 mm ×
One hundred squares of 1 mm square were made, and an adhesive cellophane tape was stuck to the coated surface, and the solid square paint film remaining on the trace of the sudden peeling was observed. A film in which no peeling of the coating film was observed between the first colored base coating film and the second colored base coating film was regarded as good, and a film in which one or more peeled-off painted films were peeled was regarded as poor.

Finished appearance: The surface of the obtained multilayer coating film was visually evaluated. Those with excellent sharpness and smoothness were evaluated as good, and those with inferior quality were evaluated as poor.

Claims (1)

[Claims] An object to be coated is coated with a first colored base coating material (A), semi-cured so that the gel fraction of the coating film becomes 5 to 95% by weight, and then coated with a second colored base paint. -A clear paint (C) is applied by applying a paint (B) without curing the paint film.
A method for forming a multi-layer coating film, wherein the method comprises the steps of: heating the three-layer coating film at the same time after coating the same.