JPH08309281A - Formation of coating film - Google Patents

Abstract

PURPOSE: To make the film thickness of an intermediate coating material thin in a process in which an udercaot, an intermediate coating material and a finish coating material are applied by using, as the intermediate coating material, a liquid thermosetting coating material which fine aluminum powder and a titanium oxide pigment are mixed with a thermosetting resin composition by specific quantities to form. CONSTITUTION: In a process in which an undercoat, an intermediate coating material and a finish coating material are applied, as the intermediate coating material, a liquid thermosetting coating material which 0.1-30 pts.wt. of, fine aluminum powder of <10μaverage particle diameter and 1-200 pts.wt. of a titanium oxide pigment are mixed with 100 pts.wt. of a thermosetting resin composition to form and whose coating film hiding power is >=25μis used. As the thermosetting resin composition of the intermediate coating material, acrylic resin or the like having two or more bridging functional groups such as an epoxy group and an isocyanate group in one molecule is used. As the undercoat, a cation electrodeposition coating material or the like is used. As the finish coating material, a coloring coating material containing a coloring pigment and a metallic coating material are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film by coating an undercoat paint (A), an intermediate paint (B) and an overcoat paint (C). B)
Is used to reduce the film thickness of the intermediate coating film without lowering the coating film performance.

[0002]

[Prior art and its problems] Undercoat paint (such as electrodeposition paint),
It is known to apply intermediate coatings and topcoats to form multilayer coatings. However, regarding the intermediate coating composition, in order to hide the lower layer and maintain the coating film performance, it is usually necessary to apply a thick film of 30 μm or more (as a cured coating film). Therefore, it is desired to reduce the total coating cost by thinning the intermediate coating film without reducing the hiding property and coating film performance.

[0003]

Means for Solving the Problems The inventors of the present invention have conducted earnest research to solve these problems, and as a result, in the above coating step, when both components of a fine aluminum powder and a titanium oxide pigment were used in combination as an intermediate coating material. The inventors have found that the hiding property is improved, and the chipping resistance is also improved, and the present invention has been completed.

That is, according to the present invention, in the step of applying the undercoat paint (A), the intermediate paint (B) and the overcoat paint (C), the thermosetting resin composition 1 is used as the intermediate paint (B).
0.1 to 30 parts by weight of fine aluminum powder having an average particle size of less than 10 μm, and 1 to 100 parts by weight of titanium oxide pigment
The present invention relates to a method for forming a coating film, which comprises blending 200 parts by weight and uses a liquid thermosetting coating material having a coating film hiding power of 25 μ or less.

The coating film forming method of the present invention will be described in more detail below.

Undercoat paint (A): A paint which is directly applied to an object to be coated, which improves corrosion resistance and adhesion. As the undercoat paint (A), those known per se can be used, and examples thereof include a cationic electrodeposition paint.

Cationic type electrodeposition paints are widely used as undercoat paints (primers) for metal products such as automobile bodies, and are optionally cross-linked to an aqueous solution or dispersion of a salt of a cationic polymer compound. In the present invention, agents known per se can be used, which are prepared by mixing agents, pigments and various additives. For example, examples of the cationic polymer compound include those obtained by introducing a cationic group obtained by modifying an acrylic resin or an epoxy resin with an amino compound or the like, and an aqueous solution obtained by neutralizing the cationic group with an organic acid or an inorganic acid. Alternatively, it can be an aqueous dispersion. Further, a block polyisocyanate compound, an alicyclic epoxy resin, or the like can be preferably used as the crosslinking agent.

In the method of the present invention, for example, a metallic object to be coated is immersed as a cathode in such a cationic electrodeposition coating bath, and an electric current is applied between it and the anode for electrodeposition coating. The film thickness is preferably in the range of 10 to 30μ based on the cured coating film, and it is 1
It is preferable to heat at 40 to 200 ° C. to crosslink and cure.

Intermediate coating composition (B): It is applied on the cured or uncured coating surface of the undercoat coating composition (A), and the fine aluminum powder having an average particle size of less than 10 μ is added to 100 parts by weight of the thermosetting resin composition. 1 to 30 parts by weight and 1 to 200 parts by weight of a titanium oxide pigment, and a liquid thermosetting paint having a coating film hiding power of 25 μm or less.

In the coating material (B), the hiding power is improved by using a fine aluminum powder and a titanium oxide pigment in combination, and the cured coating film has a thickness of 25 μm or less, particularly 10 to 25 μm. ) Can be hidden. Moreover, even if the top coating material (C) is applied to the uncured coating surface of the coating material (B), both coating films are not mixed at all. Further, since the particle size of the aluminum powder is fine, the coating film of the intermediate coating composition (B) does not become a glittering glittering metallic coating film.

The thermosetting resin composition of the intermediate coating composition (B) is
For example, a base resin such as an acrylic resin, a polyester resin and an alkyd resin having two or more crosslinkable functional groups such as a hydroxyl group, an epoxy group, an isocyanate group and a carboxyl group in one molecule, and a melamine resin and a urea resin. A composition comprising a cross-linking agent such as an amino resin, a polyisocyanate compound (including a block), a carboxyl group-containing compound and the like is preferable.

The fine aluminum powder used in the coating material (B) is a fine powder having an average particle size of less than 10 μm, preferably 3 to 7 μm. If the average particle size is 10 μm or more, the hiding property of the coating film decreases. Not preferable. Where "average particle size"
Is the median diameter measured by the laser diffraction scattering method (LA-500) (the same applies hereinafter). The component of the fine aluminum powder is preferably metallic aluminum, and its surface may be treated with a silane coupling agent or the like.

Known titanium oxide pigments can be used as coating pigments, and the average particle size thereof is preferably 5 μm or less. Further, the titanium oxide pigment whose surface is treated with alumina, silica or the like can also be used.

The fine aluminum powder and the titanium oxide pigment are blended in an amount of 0.1 to 30 parts by weight, preferably 1 to 7 parts by weight, based on 100 parts by weight (solid content) of the thermosetting resin composition. Titanium oxide pigment is 1-2
00 parts by weight, preferably 80 to 120 parts by weight. The fine aluminum powder is 1 to 15 parts by weight, preferably 2 to 7 parts by weight, per 100 parts by weight of the titanium oxide pigment.

In the intermediate coating composition (B), it is essential to use both the fine aluminum powder and the titanium oxide pigment in combination, and the total blending amount of both pigments is such that the hiding power of the coating film of the intermediate coating composition (B) is high. It is about 25 μm or less (as a cured coating film).

The hiding power is the minimum film thickness that makes it impossible to recognize the color of the base material, and specifically, the minimum film thickness that makes it impossible to visually distinguish black and white through a coating film painted on a black and white plate. It is thick. By using the fine aluminum powder and the titanium oxide pigment in combination, it becomes possible to form a thin film having a hiding power of 25 μm or less. If either of these is lacking, the hiding power of such a thin film cannot be obtained.

The intermediate coating composition (B) is obtained by mixing and dispersing the above components in an organic solvent and / or a solvent such as water, and if necessary, a coloring pigment other than the above-mentioned fine aluminum powder and titanium oxide pigment, An extender pigment, an anti-settling agent and the like can be appropriately added. The intermediate coating composition (B) is applied to the undercoating surface by electrostatic coating, air spray, airless spray, etc., with a concealing film thickness of 25 μm or less, particularly 10 to 25 μm based on the cured coating film. Preferably.

In the present invention, the top coating composition (C) is dried at room temperature or by heating (preferably 100 ° C. or lower) without crosslinking and curing the coating film of the intermediate coating composition (B) and then applying the top coating composition (C). It is preferable to paint.

Topcoat paint (C): It is applied to the hardened or uncured paint surface of the intermediate paint (B), and a colored paint (solid color) (C-1) and a metallic pigment containing a coloring pigment are used. The compounded metallic paint (C-2) is included. All of these are preferably thermosetting.

First, the colored coating material (C-1) is a liquid thermosetting coating material containing a thermosetting resin composition and a coloring pigment as main components, and in principle, no metallic pigment is mixed therein.

The thermosetting resin composition of the colored coating material (C-1) may be, for example, a hydroxyl group, an epoxy group, an isocyanate group,
Base resins such as acrylic resins, polyester resins and alkyd resins having two or more crosslinkable functional groups such as carboxyl groups in one molecule, amino resins such as melamine resins and urea resins, polyisocyanate compounds (also block products) Preferred), and a crosslinking agent such as a compound containing a carboxyl group.

The color pigment used in the paint (C-1) is
It is for imparting an external color tone to the multilayer coating film of the present invention, and examples thereof include organic or inorganic color pigments for ordinary paints, and the average particle diameter thereof is preferably 5 μm or less. The coating material (C-1) is obtained by mixing and dispersing the above components in a solvent such as an organic solvent and / or water, and if necessary, an extender pigment, a metallic pigment, an anti-settling agent, etc. are appropriately added. be able to. The paint (C-1) is
It is preferable to coat the intermediate coating surface by electrostatic coating, air spray, airless spray or the like to a film thickness of 15 to 60 μm, particularly 20 to 35 μm based on the cured coating film.

Next, the metallic paint (C-2) is applied on the hardened or uncured coating surface of the intermediate paint (B), and the average particle diameter is 10 μm or more per 100 parts by weight of the thermosetting resin composition. 0.1 to 20 parts by weight of the metallic pigment described above is blended, and the hiding power of the crosslinked cured coating film is 50 μm or more.

Since the coating film of the coating material (C-2) contains the metallic pigment having a larger particle diameter than the above-mentioned, it has a glittering feeling and a light interference pattern.

The thermosetting resin composition is, for example, an acrylic resin, a polyester resin or an alkyd resin having two or more crosslinkable functional groups such as a hydroxyl group, an epoxy group, an isocyanate group and a carboxyl group in one molecule. Base resin such as, amino resin such as melamine resin and urea resin, polyisocyanate compound (including block),
A composition comprising a crosslinking agent such as a carboxyl group-containing compound is preferred. The metallic pigment used in the metallic paint (C-2) is a scaly particle pigment having a light interference effect or a glittering sensation, and is, for example, aluminum, mica, mica coated with a metal oxide, or mica-like oxidation. Examples include iron and mica-like iron oxide coated with a metal oxide. The average particle diameter of the metallic pigment is 10 μ or more, preferably 10 to 50 μ, more preferably 15 to 40 μ.
If it is less than 10 μm, the metallic feeling is deteriorated, which is not preferable. The blending amount of this metallic pigment is 0.1 per 100 parts by weight of the thermosetting resin composition.
1 to 20 parts by weight, preferably 3 to 10 parts by weight,
If it deviates from this range, the color variation becomes large depending on the film thickness, and a uniform hue cannot be obtained, so that the object of the present invention cannot be achieved.

The metallic paint (C-2) is prepared by mixing the above-mentioned components, and mixing and dispersing them in an organic solvent and / or a solvent such as water.

The metallic paint (C-2) is applied to the coating film surface of the cured or powder-cured intermediate paint (B) by electrostatic coating, air spray, airless spray or the like in the range of 10 to 60.
It is preferable to apply the coating so that the film thickness (as a cured coating film) is μ. Even if the intermediate-coating paint (B) of the end-curing is applied on the surface of the coating, both coatings will not be mixed.

In the method of the present invention, first, the above-mentioned undercoat paint (A) is used.
Is applied to the surface of the object to be coated, and then the intermediate coating material (B) and the top coating material (C) are sequentially applied to the coating surface. That is, the undercoat paint (A) (for example, cationic electrodeposition paint) is applied to a film thickness of 10 to 30 μm based on the cured coating film,
After heat-curing at 140 to 200 ° C (even if it is uncured), the intermediate coating composition (B) is electrostatically coated on the undercoat surface, and air-
It is coated with a film thickness of 25 μm or less, preferably 10 to 25 μm based on the cured coating film by spraying or airless spraying, and the coating film is not heat-cured (or 120 to 18).
After being cured by heating at 0 ° C.), the top coating composition (C) is applied to the surface of the intermediate coating film by electrostatic coating, air spray, airless spray or the like to give a film thickness of 10 to 60 μm (as a cured coating film). It is coated so that it is heated and cured at 120 to 180 ° C. That is, the above paints (A), (B) and (C)
3 types of paint are 3 coat 1 bake method, 3 coat 2
It can be performed by a baking method, a three-coat three baking method.

In the present invention, the clear coating material (D) can be applied to the coating film surface of the above-mentioned top coating material (C), if necessary.

Clear coating (D): This is a liquid composition to be applied on the coating surface of the uncured or cured top coating (C), which is a liquid composition prepared by mixing a thermosetting resin composition and a solvent. To form a transparent coating film. The thermosetting resin composition is a substrate such as an acrylic resin, a polyester resin and an alkyd resin having two or more crosslinkable functional groups such as hydroxyl group, epoxy group, isocyanate group and carboxyl group in one molecule. A composition comprising a resin and an amino resin such as a melamine resin and a urea resin, a polyisocyanate compound (including a block), and a crosslinking agent such as a carboxyl group-containing compound is preferable. An organic solvent and / or water can be used as the solvent, and the solvent is prepared by dissolving or dispersing the thermosetting resin composition. If necessary, the clear coating material (D) may be mixed with a coloring pigment, the above-mentioned metallic pigment, an ultraviolet absorber or the like to the extent that transparency is not impaired.

The clear coating material (D) is obtained by mixing the above-mentioned components, and is obtained by mixing and dispersing these components in an organic solvent and / or a solvent such as water. The clear coating material (D) is applied to the coating film surface of the top coating material (D) by electrostatic coating, air spray, airless spray or the like to give a film thickness of 10 to 60 μm (as a cured coating film). It is coated so that it is heated and cured at 120 to 180 ° C.

[0032]

【The invention's effect】

1. The thickness of the intermediate coating film is thinner than the conventional one (30μ or more) (2
5 μm or less, preferably 10 to 25 μm), so that the cost can be reduced in the entire multilayer coating film.

2. Even if the top coat is applied to the surface of the uncured intermediate coating, both layers are not mixed.

3. Even if the intermediate coating material is applied in a thin film, the hiding property is excellent, so the color stability of the top coating film is good, and the color design can be arbitrarily selected according to the purpose.

4. Improved chipping resistance.

[0036]

EXAMPLES Examples and comparative examples relating to the present invention will be described below.

I. Sample (1) Cationic electrodeposition paint (A) "Electron 9400HB" (Kansai Paint Co., Ltd.,
Product name, epoxy resin polyamine / block polyisocyanate compound type) (2) Intermediate coating (B) Polyester resin, melamine resin, fine aluminum powder and titanium oxide pigment are mixed in the ratio shown in Table 1 below. Organic solvent type paint. The blending amount of each component in Table 1 is a solid content ratio.

[0038]

[Table 1]

* 1: Phthalic anhydride / hexahydrophthalic anhydride type polyester resin (number average molecular weight of about 400)
0, hydroxyl value 82, acid value 7).

* 2: Yuban 28-60 (Mitsui Toatsu) * 3: K-9800 (Asahi Kasei), average particle size 5 to 6 μ * 4: Titanium JR701 (Teikoku Kako), average particle size 0.3
~ 0.6μ * 5: KNO-W iron oxide (Toda Kogyo), average particle size 0.2
˜0.5 μ * 6: The minimum film thickness (μ) at which black and white cannot be discriminated by the naked eye was measured through a coating film applied on a checkerboard-patterned black and white plate.

(3) Topcoat paint (C) An organic solvent-based paint prepared by mixing an acrylic resin, a melamine resin, and a coloring pigment or a metallic pigment in the ratio shown in Table 2 below. The blending amount of each component in Table 2 is a solid content ratio.

[0042]

[Table 2]

* 7: Methyl methacrylate type acrylic resin, number average molecular weight of about 2000, hydroxyl value of 70, acid value of 8
Is.

* 8: Yuban 28-60 Mitsui Toatsu * 9: Titanium CR93 Ishihara Sangyo * 10: Carbon FW200 DEGUSSA * 11: EUROPAL MALL, average particle size 14-
18μ (5) Clear paint (E) "Magiclon clear" (trade name, acrylic resin / melamine resin type, organic solvent type, manufactured by Kansai Paint Co., Ltd.).

II Examples and Comparative Examples Using the above samples, coating was performed according to the coating process shown in Table 3 and heat curing was performed to form a multilayer coating film. The performance test results of the multilayer coating film are also shown.

[0046]

[Table 3]

A cation electrodeposition coating (A) is applied to a degreased and zinc phosphate-treated steel sheet by a conventional method in a film thickness of 20 or less)
And electrodeposition coating was performed so that the coating film was cured by heating at 170 ° C. for 30 minutes. The intermediate coating composition (B-1) to the electrodeposition coated surface
(B-3) was applied to a film thickness of 25 μ, and (B-4) to (B-5) were applied to a film thickness of 50 μ, and left at room temperature for 5 minutes. Then, on this intermediate coating surface, top coating materials (C-1) to (C-5)
Using a mini bell type rotary electrostatic coating machine, discharge amount 150C
C, rotation speed 50000 rpm, shaping pressure 1 kg / c
m ^2, cancer distance 30 cm, Bed - scan temperature 20 ° C., Bed - were painted with scan humidity of 75%. The coating film thickness was 15 to 25 µ.
The top coating film is allowed to stand in the booth for 5 minutes, and then the clear coating (D) is applied to the uncured coating surface using a minibell type rotary electrostatic coating machine, the discharge amount is 300 CC and the rotation number is 40,000 rp.
m, shaping pressure 5 kg / cm ² , gun distance 30 cm, boo
The coating temperature was 20 ° C and the booth humidity was 75%. The coating film thickness was 45 to 50 μm. After coating, the mixture is left at room temperature for 3 minutes and then heated at 140 ° C. for 30 minutes in a hot-air circulation type drying oven to consist of the above intermediate coating composition (B), top coating composition (C) and clear coating composition (D) 3 The layer coatings were allowed to cure simultaneously.

The coating film performance test method and evaluation criteria are as follows.

Smoothness: Visual evaluation. ◯: Good, Δ: Slight discoloration, X: Remarkable discoloration Finished appearance: Visual evaluation of the color development of the metallic pigment.は indicates good color development, Δ indicates slightly good, and × indicates poor.

Claims (1)

[Claims] 1. An average particle size per 100 parts by weight of a thermosetting resin composition as the intermediate coating composition (B) in the step of applying the undercoat coating composition (A), the intermediate coating composition (B) and the top coating composition (C). A fine aluminum powder having a particle size of less than 10 μ can be used as a 0.2
1 to 30 parts by weight, 1 to 200 parts by weight of a titanium oxide pigment are mixed, and a liquid thermosetting coating material having a coating film hiding power of 25 μm or less is used.