JP2000167475A - Formation of double-layer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the interlayer adhesion of a double-layer coating film formed by applying a solid color paint and a clear paint on a face to be coated by electrodeposition without providing any intermediate layer. SOLUTION: A solid color paint and a clear paint are successively applied on a material coated with a film formed by electrodeposition to form a double- layer overcoating film. The solid color paint contains a fine aluminum powder and/or a white coated metal powder, and the light transmittance is controlled to <=0.15% at 15 μm cured coating film thickness. Although an anionic or a cationic electrodeposition paint can be used, the cationic paint excellent in corrosion resistance, etc., is preferably used. A well-known cationic electrodeposition paint prepared by mixing a pigment and various additives, as required, with the aq. soln. or dispersion of a cationic high molecular compd. is applicable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a step of applying a solid color paint as a top coat and a clear paint successively on the surface of an electrodeposition coating film applied to an object to be coated without applying an intermediate coat. The present invention relates to a method for forming a multilayer coating film.

[0002]

2. Description of the Related Art An electrodeposition paint is applied to a conductive outer plate of an automobile body or the like, and an intermediate paint is applied without coating.
It is known that a solid color paint and a clear paint are sequentially applied as a top coat on the electrodeposition coated surface to form a top coat. However, since the intermediate coating film is omitted in this multi-layer coating film, ultraviolet rays easily pass through the solid color coating film from the clear coating film, and reach the electrodeposition coating film, and this electrodeposition coating film And the like, and there is a defect that separation easily occurs between the layers and the solid color coating film. In order to prevent the transmission of ultraviolet light, solid color paints have been made darker or an ultraviolet absorber has been blended. Then, there is a defect that the efficacy gradually decreases.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-layer topcoat formed by sequentially applying a solid color paint and a clear paint without applying an intermediate paint to the surface of the electrodeposition coating film. It is an object of the present invention to prevent the transmission of ultraviolet light and the delamination of both coating films without the necessity of making the solid color coating film dark, and without containing an ultraviolet absorber. As a result of intensive studies, it has been found that the object can be achieved by adding a fine aluminum powder and / or a white-coated metal powder to a solid color paint and adjusting the light transmittance to a specific value, thereby completing the present invention.

That is, according to the present invention, when a solid color paint and a clear paint are successively applied to the surface of an electrodeposition coating film applied to an object to be coated to form an overcoating multi-layer coating film, the solid color paint is fine. A method for forming a multilayer coating film (hereinafter referred to as "the present invention") comprising aluminum powder and / or white-coated metal powder and having a light transmittance of 0.15% or less at a cured coating thickness of 15 μm. Method). In particular, it is preferable that the present method is carried out by using an outer plate portion of an automobile body as the object to be coated.

[0005] The object to be applied in the present method is not particularly limited as long as it is a conductive metal product that can be electrodeposited. Plates are particularly preferred. Prior to the electrodeposition coating, it is preferable that these objects to be coated are subjected to degreasing cleaning, surface conversion treatment with zinc phosphate, iron phosphate or the like, and further water washing.

As the electrodeposition paint, either an anionic type or a cationic type can be used, but a cationic type having excellent corrosion resistance and the like is preferable. As the cationic electrodeposition coating material, a known one obtained by mixing a pigment or various additives as necessary with an aqueous solution or aqueous dispersion of a salt of a cationic polymer compound can be used. For example, examples of the cationic polymer compound include those in which a base resin such as an acrylic resin or an epoxy resin is modified with an amino compound or the like to introduce a cationic group, and this is neutralized with an organic acid or an inorganic acid. This can make it water-soluble or water-dispersible. As a crosslinking agent, a block polyisocyanate compound, an alicyclic epoxy resin or the like can be suitably used.

[0007] The cationic electrodeposition coating can be performed by immersing the above-mentioned conductive coating material as a cathode in the cationic electrodeposition coating bath and energizing it under ordinary conditions. The film thickness is preferably from 10 to 30 μm based on the cured coating film, and the coating film can be crosslinked and cured by heating at 140 to 200 ° C. for 10 to 40 minutes.

[0008] Solid color paint is a top coat paint directly applied to the cured or uncured coating surface of the electrodeposition coating film,
In this method, the color pigment component contains one or more selected from fine aluminum powder and white-coated metal powder, and the light transmittance at a cured coating thickness of 15 μm is 0.15% or less. Is used.

[0009] Specifically, one or more selected from a fine aluminum powder and a white-coated metal powder as a resin component and a color pigment component (hereinafter, both powders are collectively referred to as "white metal powder"). As an essential component, and further, if necessary, by using other color pigments, extender pigments, anti-settling agents, curing catalysts, ultraviolet absorbers, light stabilizers, etc., by dissolving or dispersing these in a solvent. It is a liquid paint to be prepared. The single coating film formed by this solid color paint has a solid tone, and hardly shows glitter or light interference.

The resin component includes a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a polyurethane resin, a cellulose acetate butyrate resin having a crosslinkable functional group such as a hydroxyl group, a melamine resin and a (block) polyisocyanate. Examples include ordinary resin components for paints, which contain a crosslinking agent such as a compound.

The fine aluminum powder is mainly composed of metallic aluminum, and its surface may be treated with a silane coupling agent or the like. The shape of the aluminum powder may be any of square grains, round grains, needles, and scaly shapes. However, scaly shapes are preferred for improving the concealing property, and the average particle size thereof is 10 μm or less, particularly 3 to 7 μm.
A range of μm is suitable. The average particle diameter is a median diameter measured by a laser diffraction scattering method (LA-500).
This fine aluminum powder itself is a white powder,
The coating film containing this does not have any glittering glitter.

The white-coated metal powder is a powder in which the surface of the metal powder is coated in white. Here, the shape of the metal powder may be any of a square grain, a round grain, a needle shape, and a scaly shape, but a scaly shape is preferable for improving the concealing property. The average particle diameter of these particles is suitably 10 μm or less, and particularly preferably in the range of 3 to 7 μm. The average particle size is determined by a laser diffraction scattering method (LA-50).
0) means the median diameter. Examples of the material of the metal powder include aluminum, copper, stainless steel, brass and alloys containing these metals, and the surface thereof may be treated with a silane coupling agent or the like. By coating the surface of these metal powders with a white pigment such as titanium oxide by a method known per se, a white-coated metal powder can be prepared. The thickness of the coating is not particularly limited as long as the surface of the metal powder is concealed so as to appear white. This white-coated metal powder is a white powder, and the coating film containing the powder has no glitter.

In a solid color paint, by containing one or more selected from these white metal powders, the hiding power of the coating film is remarkably improved, and a coating film having low light transmittance even in a thin film is obtained. Can be formed. Specifically, 0.1 to 10 parts by weight, particularly 0.1 to 10 parts by weight of the white metal powder is added per 100 parts by weight (solid content) of the above resin component.
When the content is within the range of 5 parts by weight, the light transmittance at a cured film thickness of 15 μm can be 0.15% or less. Since the compounding amount of these powders is smaller than that using a conventional white pigment, there is no decrease in the flexibility, gloss, sharpness, weather resistance and the like of the coating film.

Solid color containing white metal powder
The color tone of the paint film is white, but if necessary, it can be adjusted to an arbitrary color tone of achromatic or chromatic without lowering the concealing property by blending other coloring pigments. . As other coloring pigments, organic pigments and inorganic pigments for ordinary paints can be used. Piperine, phthalone,
Examples include phthalocyanine, carbon black, and titanium oxide, but are not limited thereto.

The solid color paint can be prepared by mixing and dispersing the above resin composition, white metal powder and the like in a solvent (for example, an organic solvent or water), and has a solid content of 20 to 60% by weight. Preferably, the composition is adjusted to 25 to 50% by weight, the viscosity is 10 to 30 seconds / ford cup # 4/20 ° C., and the cured or uncured electrodeposition coating film is applied by electrostatic coating, air spray, airless spray, or the like. It is preferable to apply a film having a thickness of 15 to 50 μm based on the cured coating film. A single coat of solid color paint can be cross-linked and cured by heating at a temperature of about 100 to about 170 ° C for 10 to 40 minutes.

The light transmittance of a solid color paint film is 360 to 420 for a 15 μm-thick film.
The light transmittance in nm. Specifically, solid color
The paint is applied so as to have a gradient film thickness (cured coating film) of 8 to 20 μm, and three places having different thicknesses of the coating film are selected, and the wavelength at each place is measured using an integrating sphere photometer. 3
The light transmittance of 60 to 420 nm is measured. The integrated value of each light transmittance is defined as the light transmittance (%) of the film thickness, and based on the result, the light transmittance value (%) at the film thickness of 15 μm is estimated.

The clear paint is a paint which is applied to the uncured or cured coating surface of a solid color paint, and contains a resin component and a solvent as main components and, if necessary, to such an extent that the transparency of the coating film is not impaired. It is a liquid paint which forms a colorless or colored transparent coating film, which is formed by blending a coloring pigment and other paint additives. It may be a powder coating.

The resin component is preferably thermosetting. More specifically, melamine is added to a base resin such as an acrylic resin, a polyester resin, an alkyd resin, or a urethane resin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, or an epoxy group. Resin, urea resin, polyisocyanate compound (including block body), carboxyl group-containing compound (or resin),
Known coating resins used in combination with a crosslinking agent such as an epoxy group-containing compound (or resin) can be used. Organic solvents and / or water can be used as the solvent. The clear paint can be applied to the uncured or cured solid color coating surface by a method such as electrostatic coating, air spray, or airless spray.
１００100 μm, preferably about 100 to about 170
Crosslinking and curing can be performed by heating at a temperature of 10C for 10 to 40 minutes.

In this method, an electrocoat is first applied to a conductive coating object, the intermediate coating is omitted, a solid color coating is applied to the electrodeposition coating surface, and then the solid coating is applied to the electrocoating surface. A multi-layer coating film can be formed by a three-coat one-bake system, a three-coat two-bake system, and a three-coat three-bake system, which consist of applying a clear paint.

[0020]

According to the present invention, the solid color paint film containing the white metal powder used in the present method has an excellent concealing property, and has a light transmittance of 0.15 even with a thin film having a thickness of 15 μm or less.
% Or less, there is little or no light transmission. Therefore, even if such a solid color paint is directly applied to an electrodeposition coating film without an intermediate coating film and is exposed outdoors for a long period of time, no light penetrates into the electrodeposition coating film adjacent to the lower layer and the interlayer does not transmit light. Peeling could be prevented. Furthermore, since it is not necessary to make the color dark to prevent light transmission, the defect that the color tone is limited is eliminated, and since the blending amount of the color pigment is not increased, the flexibility, gloss, The sharpness, weather resistance, etc. could be improved.

[0021]

EXAMPLES Examples and comparative examples of the present invention will be described. Parts and% are based on weight in principle,
The film thickness of the coating film is for the cured coating film.

1. Specimen 1) Coating object: Degreasing and zinc phosphate treated steel sheet (JI
SG3141, size 400 × 300 × 0.8 mm).

2) Electrodeposition paint a): Cationic electrodeposition paint (“Electron 9400H”)
B ", manufactured by Kansai Paint Co., Ltd., trade name, epoxy resin polyamine-based cation resin using a block polyisocyanate compound as a curing agent) 3) Solid color paint a): Acrylic resin containing hydroxyl group (hydroxyl group) Value 80, number average molecular weight 20,000) 70 parts (solid content), butylated melamine resin 30 parts (solid content), titanium oxide pigment 80 parts, the surface of an aluminum flake having an average particle diameter of 3 to 7 μm is coated with a titanium oxide pigment. Is mixed with an organic solvent (toluene / xylene = 1/1 weight ratio) and adjusted to a viscosity of 15 seconds (for ford cup # 4/20 ° C.) to obtain a solid color paint. a) was obtained. The light transmittance of a single cured coating film (film thickness 15 μm) of this coating material is 0.10%.

Measurement method of light transmittance: The light transmittance at a wavelength of 360 to 420 nm at a film thickness of 15 μm of the solid color coating film is 8 to 20 μm.
Is applied so as to have a gradient film thickness, and three places having different film thicknesses are selected from the paint films, and the light transmittance at a wavelength of 360 to 420 nm at each place is measured using an integrating sphere photometer. I do. The integral value of each light transmittance is defined as the light transmittance (%) of the film thickness.
The light transmittance value at 5 μm was estimated.

B): 70 parts (solid content) of a hydroxyl group-containing acrylic resin (hydroxyl value 80, number average molecular weight 20,000), 30 parts (solid content) of butylated melamine resin, 80 parts of titanium oxide pigment, "K-9800" ( 1.2 parts of an aluminum flake having a mean particle size of 5 to 6 μm, a white metal powder (trade name, manufactured by Asahi Kasei Corporation) in an organic solvent (toluene / xylene = 1/1)
(Weight ratio) and a viscosity of 15 seconds (for ford cup # 4 /
20 ° C) to obtain a solid color paint b).
The light transmittance of a single cured film (thickness: 15 μm) of this paint is 0.14%.

C): 70 parts (solid content) of a hydroxyl group-containing acrylic resin (hydroxyl value 80, number average molecular weight 20,000), 30 parts (solid content) of butylated melamine resin, 100 parts of titanium oxide pigment and an organic solvent (toluene / toluene) (Xylene = 1/1 weight ratio) and a viscosity of 15 seconds (for ford cup # 4/2)
0 ° C.) to obtain a solid color paint c). The light transmittance of a single cured coating film (film thickness 15 μm) of this coating material is 0.31%. (For comparison) 4) Clear paint a): "Lu-Gabek clearer", Kansai Paint Co., Ltd.
Made, trade name, acrylic resin / amino resin type, organic solvent type.

2. EXAMPLES AND COMPARATIVE EXAMPLES The cationic electrodeposition paint a) is electrodeposited by a conventional method to a film thickness of 20 μm, cured by heating at 170 ° C. for 20 minutes, and then solid-colored paints a) to c) are applied to the coated surface. With a film thickness of 15 μm
After leaving at room temperature for 5 minutes, the clear paint a) was applied to a film thickness of 40 μm, and left at room temperature for 3 minutes.
C. for 30 minutes to simultaneously cure the solid color coating and the clear coating (3 coats 2 bake). Table 1 shows these coating steps and the performance test results of the multilayer coating film obtained by the coating steps.

[0028]

[Table 1]

Mitsuzawa: This is the result of measuring the 60 ° mirror reflectivity (%) using a gross tester (manufactured by Tokai Rika Electric Works).

Adhesion between layers: Cut into the multi-layer coating film with a cutter so as to reach the substrate, make 100 goban eyes of 1 mm x 1 mm, stick an adhesive cellophane tape on the surface, and remove it at 20 ° C. Was rapidly removed, and the coated surface was observed.は indicates that no peeling of the rubbing film was observed, △ indicates that 1 to 5 rubbing films were peeled, ×
Indicates that six or more peeled-off paint films are often observed.

Water resistance: 2 pieces of the above test plate in warm water of 40 ° C.
After immersing for 40 hours, pulling up and drying, cut the coating film with a cutter to reach the base, size 1 mm × 1 mm
Was prepared, and an adhesive cellophane tape was stuck on the surface thereof, and the coated surface was observed after rapidly peeling it off at 20 ° C. ○ indicates that there is no peeling of the painted film, no occurrence of blisters or dust is observed, Δ indicates that 1 to 5 painted films are peeled, and occurrence of blisters or dust is slightly observed. 6 or more pieces of Gobang eyes peel off,
This indicates that blisters and shrinkage are frequently observed.

Accelerated weathering resistance: The test plate was exposed to a sunshine weatherometer for 1000 hours, immersed in warm water of 40 ° C. for 24 hours, pulled up and dried, and then coated with a cutter to reach a substrate. Cut, size 1mm x 1m
100 m-thick mounds were prepared, an adhesive cellophane tape was stuck to the surface, and the coated surface was observed after rapidly peeling it off at 20 ° C. ○: no peeling of the mesmerized paint film at all, no occurrence of blisters or blemishes was observed; It shows that 6 or more pieces of the Goban eyes peeled off, and many occurrences of blisters and blemishes were observed.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 7/12 C09D 7/12 Z F-term (Reference) 4D075 AE12 BB89X DA06 DB02 DC12 EA43 EC10 4J038 BA041 CG141 DA162 DD001 DD121 DD231 DG001 DG232 HA066 KA03 KA15 KA20 NA01 NA17 PA04 PA13 PA14 PB07

Claims (2)

[Claims] When a solid color paint and a clear paint are sequentially applied to the surface of an electrodeposition coating film coated on an object to form an overcoating multilayer film, the solid color paint contains fine aluminum powder and fine powder. And / or contains a white-coated metal powder and has a light transmittance of 0.1 at a cured coating thickness of 15 μm.
A multi-layer coating film forming method characterized by being 15% or less. 2. The method according to claim 1, wherein the object to be coated is an outer plate portion of an automobile body.