JPH1199357A - Formation of composite coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form composite coating films of high saturation by forming a color base coating film on a substrate successively formed with primer coating and intermediate coating films and coating the surface of the color base coating film with a powder color clear coating material. SOLUTION: In the case of preparing a metallic material to be coated suitable for a vehicle body of an automobile, etc., a base material 1 is subjected to primer coating 2 and is then subjected to intermediate coating 3 thereon. The metallic material is subjected to black out coating for sashes as desired. The color base coating film 4 is thereafter formed thereon and the color base coating material is preferably a solvent based one in terms of coating workability. The solvent based color base material contains a thermosetting resin soluble or dispersible in water or org. solvent as a coating film forming component and a hardener. The surface of the color base coating film 4 is coated with the powder color clear coating material 5. The powder coating material 5 suitable for use consists of the thermosetting resin which is the coating film forming component and the hardener as essential components and further contains a pigment, surface control agent and other additives.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an automobile body and parts, which does not require any repair coating after repairing surface defects due to dust or the like.

[0002]

2. Description of the Related Art The coating method of a car body and parts is as follows.
Typically, a base coat with a high base concealing property (hiding the color of the base, undercoat and intermediate coat) is applied to the base coat and intermediate coat metal base material, and a clear paint is applied thereon. And then baking and hardening to form a composite coating. Here, the coating film formed from the clear paint is usually colorless and transparent.

For example, Japanese Patent Application Laid-Open No. 8-134385 proposes to use a liquid color clear paint obtained by adding a small amount of a coloring pigment to a liquid clear paint in the formation of the composite coating film. It is suggested that when such a color clear coating film is used, the color of the clear coating film can develop a high chroma hue in combination with the color of the color base coating film, thereby improving the design.

[0004] In the above-described composite coating film forming process, dust, dust and the like adhering to the surface layer of the coating film are usually removed by polishing the surface layer. However, the formed surface liquid color clear coating generally has a maximum of 40 μm.
Since the coating is as thin as about m, the hue changes due to polishing, and the polished portion has a disadvantage that the hue is thinner than the non-polished portion. For this reason, it is necessary to paint again to repair the polished portion.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for forming a high-chroma composite coating film which does not require the above-mentioned repair coating in order to overcome the above-mentioned problems.

[0006]

According to the present invention, there are provided (i) forming a color base coating film on a substrate on which an undercoat and an intermediate coating film are sequentially formed, and (ii) forming a powder on the color base coating film. Provided is a method for forming a composite coating film, which comprises applying a color clear paint.

[0007] In the present invention, the powder color clear paint is a color pigment 0.05 based on the total solid content in the paint.
-5% by weight, in particular 0.3-3% by weight,
The thickness of the formed powder color clear coating film is preferably 40 to 100 µm, more preferably 50 to 80 µm.

[0008] The present invention also provides an article having a composite coating formed by the above method.

[0009]

As described above, since a small amount of pigment is contained in the powder clear coating film in addition to the color base coating film, a composite film having high chroma can be formed. Further, since the clear coating film as the surface layer is sufficiently thick, it is not necessary to perform repair coating after removing the dust adhering to the surface layer by polishing. Further, since the number of manufacturing steps related to the repair painting is reduced, the production efficiency is also improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The base material suitable for the present invention is a metal-coated object suitable for a vehicle body such as an automobile (including motorcycles and buses), for example, iron, steel, aluminum, tin, zinc, and the like. And metal-plated or vapor-deposited products of these metals. The base material used is usually a degreased state or a base material which has been previously subjected to a chemical conversion treatment with a phosphate or a chromate.

[0011] The base material is usually coated with an undercoat,
A suitable intermediate coating is applied to provide weather resistance and flatness. The undercoat is preferably a cationic electrodeposition coating from the viewpoint of corrosion resistance. The intermediate coating can be performed using a weather-resistant dark gray, gray or white-based conventional intermediate coating or color intermediate coating.

If desired, a blackout coating for a sash may be performed after the undercoating and the intermediate coating.

In step (i) of the method of the present invention, a color base coating is formed on the undercoated and intermediate coated substrates.

As the color base coating, any of coatings commonly used in the art (ie, solvent-dilutable type, water-diluted type and powder coating) can be used. Dilution type or water dilution type) paints are particularly preferred.

The solution-based color base paint contains a thermosetting resin and a curing agent which can be dissolved or dispersed in water or an organic solvent as the above-mentioned components for forming a coating film. Examples of the thermosetting resin include a thermosetting acrylic resin, a polyester resin, an epoxy resin, and a urethane resin, and the thermosetting acrylic resin and the polyester resin are most preferable from the viewpoint of weather resistance. Examples of the curing agent generally include an amino resin, particularly a melamine resin and a block isocyanate. Preferably, an alkoxymethylmelamine resin can be used.

In the present invention, a combination of a base resin and a curing agent suitable for a solution-based color base paint is, for example, a combination of a thermosetting acrylic resin and an alkoxymethylmelamine resin.

In the method of the present invention, the weight ratio between the thermosetting resin and the curing agent in the solution-based color base coating composition is 90:10 to 10:10.
40:60, preferably 80:20 to 60:40.
Range. When the compounding ratio of the curing agent is less than 90:10, the crosslinking density of the coating film becomes low, so that the coating film strength is weak. Conversely, when the mixing ratio exceeds 40:60, the internal stress of the formed coating film is reduced. However, they are not preferable because they may become high and cause cracks and the like.

The color base paint contains a pigment.
Examples of pigments that can be added include titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, induthrone blue,
Coloring pigments such as dibromanzathrone red, perylene red, azo red, anthraquinone red, quinacridone red, and violet; barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, Extenders such as alumina white, gloss white, and satin white; and brilliant pigments such as mica powder, aluminum, stainless steel, iron, copper, nickel, tin, graphite, and flat coloring materials. The above pigments can be used alone or in combination of two or more.

The color base paint may optionally contain a dye in addition to the above pigment, and a dye having excellent weather resistance and solubility in water and / or an organic solvent is preferred. Specific examples of such dyes include 1: 2 chromium complex black, 1: 2 chromium complex yellow, 1: 2
Cobalt complex yellow, and one or more selected from these can be blended.

The color base paint may contain the above pigment (and dye) usually in an amount of 1 to 50% by weight based on the total solids in the paint.

Further, the color base coating may include additives known in the art, for example, a curing catalyst such as dodecylbenzenesulfonic acid, a surface modifier such as silicone or acrylic oligomer (typically, dimethyl Antioxidants such as silicone and methyl silicone), benzophenone and the like, plasticizers, ultraviolet absorbers, benzoins, anti-sagging agents, thickeners and the like.

As a solvent-diluted color base paint suitable for the present invention, for example, Super Lac M-155 (acrylic resin color base paint manufactured by Nippon Paint Co., Ltd.) is commercially available.

As the water-dilutable color base paint, for example, Super Nicks NWB-230 (manufactured by Nippon Paint Co., Ltd., acrylic color base paint) is commercially available.

When using any of the solution-based color base paints, an appropriate diluent (for example, an organic solvent or water) is used at a suitable coating viscosity (solvent dilution type: 10 to 30 seconds / # 4).
Ford cup / 20 ° C, water dilution type: 10-30 seconds / 2
0 ° C / # 4 Ford cup / 20 ° C).

The solution-based or water-based color base paint can be applied by coating methods known in the art.

After the color base paint is applied, the coating film is usually left for 1 to 10 minutes (setting) or subjected to preliminary drying (for example, at 60 to 120 ° C. for 1 to 10 minutes), and then subjected to the next coating step. Or 120
After baking and hardening at 200 ° C. for 5 to 60 minutes, the next coating step may be performed.

The dry film thickness of the color base coating film is usually 1
It can range from 0 to 50 μm, especially 13 to 25 μm.

In the step (ii) of the method of the present invention, a powder color clear paint is applied on the color base coating film.

A powder color clear paint suitable for use in the present invention contains a thermosetting resin and a curing agent as coating film forming components as main components, and further contains a pigment, a surface conditioner and other additives. .

Suitable thermosetting resins are preferably thermosetting resins that are solid at room temperature, and include, for example, acrylic resins and polyester resins (including alkyd resins). In some cases, two or more of the thermosetting resins may be mixed and included.

Typical examples of the acrylic resin include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, Tert-butyl (meth) acrylate,
Glycidyl acrylate, glycidyl methacrylate,
Or those obtained by polymerizing an acrylic monomer such as 2-methylglycidyl methacrylate by an ordinary method, and also includes a copolymer of them with styrene.

As a typical example of the polyester resin,
Polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane, pentaerythritol, and terephthalic acid, isophthalic acid, phthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid,
Examples thereof include those obtained by reacting a carboxylic acid such as β-oxypropionic acid by a conventional method, and alkyd resins.

The glass transition temperature (T
g) is preferably 25-80 ° C, more preferably 40-80 ° C.
７０70 ° C. If Tg is lower than 25 ° C., heat is generated during pulverization, and the resin particles are fused to the pulverizer, so that production is difficult. If Tg exceeds 80 ° C., the formed coating film has surface smoothness. Both are not preferred because they are difficult.

The curing agent suitable for the powder color clear coating used in the present invention can be appropriately selected depending on the type of the functional group of the resin. Examples thereof include aliphatic polycarboxylic acids such as blocked isocyanate and sebacic acid, and aminoplasts. resin,
Examples thereof include aliphatic acid anhydride, triglycidyl isocyanurate, amine-based curing agent, dicyandiamide, phenol resin, epoxy resin, alkylmethylmelamine resin, and benzoguanamine resin.

In the combination of the thermosetting resin and the curing agent, for example, the mixing ratio of an acrylic resin or a polyester resin and a melamine resin is 9: 1 to 5:
5, preferably 8: 2 to 6: 4. If the ratio is more than the above, the strength of the coating film is insufficient, and if the ratio is less than the above, cracks occur in the coating film. Alternatively, the mixing ratio of the thermosetting resin containing a hydroxyl group to the polyisocyanate compound is 0.3:
Preferred is between 1: 1 and 1.5: 1, especially between 0.7: 1 and 1.5: 1. If the amount is more than the above, the water resistance decreases, and if the amount is less than the above, poor curing results, which is not preferable. Alternatively, the mixing ratio of the glycidyl group-containing acrylic resin and the aliphatic polycarboxylic acid and / or acid anhydride thereof is 1: 0.5 to 1: 1.2, preferably 1: 0.0, in equivalent ratio. 6 to 1: 1. If the amount is more than the above-mentioned ratio, the strength of the coating film is insufficient.

The powder color clear paint preferably contains a coloring pigment as a pigment. Here, the coloring pigment includes, for example, titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, induthrone blue, dibromo Color pigments such as Anzathrone red, perylene red, azo red, anthraquinone red, quinacridone red, and violet; barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, alumina white , Gloss white, satin white and the like. The above pigments can be used alone or in combination of two or more.

The coloring pigment may be contained in an amount of 0.05 to 5% by weight, more preferably 0.3 to 3% by weight, based on the total solid content in the powder color clear coating composition.

As described above, additives that can be included in the powder color clear coating include curing catalysts such as dodecylbenzene sulfonic acid, surface modifiers such as silicone or acrylic oligomers (typically, dimethyl silicone,
Antioxidants such as methyl silicone), benzophenone and the like, plasticizers, ultraviolet absorbers, benzoins, anti-sagging agents, thickeners and the like.

The method for preparing the powder coating is a technique known in the art. It is, for example, after the raw material preparation step, pre-mixed, melt-kneaded, cooled, crushed,
Classifying for adjusting the particle size distribution.

The powder coating produced by the above process is preferably ground and classified to an average particle size of 5 to 40 μm.

In the method of the present invention, the powder color clear paint has an average particle size of 15 μm or less in order to facilitate the volatilization of the volatile matter at the time of forming a coating film and to make the coating film have a higher appearance. And the standard deviation of the particle size distribution is preferably 20 μm or less. Furthermore, in order to effectively prevent blocking during storage of the powder clear coating itself, the average particle diameter is 0.001 to 10 μm, and the glass transition temperature is 50 to
It is preferable to use a resin particle having a dissolution parameter (SP) of 9 to 15 at 150 ° C. which is present on at least the surface of the powder particle. The resin fine particles may be, for example, those obtained by spray-drying or freeze-drying a resin emulsion obtained by a conventional emulsion polymerization.

In the powder clear coating, silica fine particles may be added as an external additive in the same manner as when the resin fine particles are adhered to the surfaces of the powder coating particles. Examples of such silica fine particles include, for example, trade names HDKH2000 and HDKH3 whose surfaces are covered with trimethylsilyl groups.
0, HDK H20 (all manufactured by Hoechst) and those commercially available as Aerosil R972 (manufactured by Nippon Aerosil Co., Ltd.) in which silanol groups on the surface are reacted with dimethyldichlorosilane to impart hydrophobicity. . In the present invention, the above-mentioned hydrophobic silica is particularly effective.

The above-mentioned powder color clear paint is applied by electrostatic coating, particularly preferably by electrostatic spray coating (for example, a corona charging method or a tribocharging method). After coating, if desired, a continuous powder coating may be formed by predrying at 80 to 120 ° C for 5 to 30 minutes using a conventional heating means such as an oven. In forming such a continuous coating film, in order to obtain a desired hue and color depth, the above-mentioned coating step to the preliminary drying step may be usually repeated.

The undercoat concealing film thickness of the powder color clear coating film formed by the above-mentioned production method is preferably at least 200 μm.

The dry thickness of the formed powder color clear coating film is in the range of 40 to 100 μm, especially 50 to 80 μm. When the film thickness of the coating is less than 40 μm, after removing dust adhering to the surface layer after forming the coating by polishing,
Repair coating is required, and if it exceeds 100 μm, sagging is likely to occur, and neither is preferable.

The baking and curing conditions for the composite coating film formed as described above are usually at 120 to 200 ° C. for 5 to 60 minutes. The conditions may vary depending on the type of paint used.

[0047]

The present invention will be described below with reference to examples.
The present invention is not limited to the following examples. Preparation Example 1: Preparation of powder color clear paint A powder color clear paint composition was prepared using the following composition and according to the following production method. First, to 2L Kolben,
63 parts by weight of xylene was added, and the temperature was raised to 130 ° C. There, 55 parts by weight of glycidyl methacrylate, styrene 2
A mixture of 5 parts by weight, 20 parts by weight of methyl methacrylate, and 8 parts by weight of t-butylperoxy-2-ethylhexanoate was added dropwise over 3 hours while blowing nitrogen. Thirty minutes after the completion of the dropwise addition, 0.5 parts by weight of t-butylperoxy-2-ethylhexanoate was added dropwise over 30 minutes. After aging for 1 hour, the solvent was removed to obtain a solid resin. The conditions for removing the solvent were maintained at 5 mmHg and 130 ° C. for 1 hour after decompression. The glass transition temperature of the base resin thus obtained was 50 ° C., and the number average molecular weight was 2500. 70 parts by weight of the obtained base resin, coloring pigment: Irgazine DPP Red BO (manufactured by Ciba Specialty Chemicals) 0.5
Parts by weight, 1,10-decanedicarboxylic acid (DDA) 23.
After mixing 4 parts by weight, 1.0 part by weight of benzoin and 0.3 part by weight of a polysiloxane-based surface conditioner YF-3919 (manufactured by Toshiba Silicone), the mixture was melt-kneaded in a buscon kneader (manufactured by Buss).
This was pulverized and classified (150 mesh), and further classified with an airflow classifier DS-2 (Nippon Pneumatic Industries, Ltd.) to obtain a thermosetting powder color clear coating composition (I). In this powder coating composition, the COOH / epoxy functional group ratio was 0.75, the average particle size of the resin in the coating was 10 μm,
And the standard deviation of the particle size distribution was 20 μm or less. The particle size was measured using Microtrack MK-2 (manufactured by Nikkiso Co., Ltd.). The undercoat concealed film thickness of the thermosetting powder color clear coating composition was 200 μm or more.

Example 1 Dull steel sheet 1 pre-treated with zinc phosphate (dimensions: 0.8 mm
× 10cm × 30cm) First, cationic electrodeposition paint 2
(Nippon Paint Co., Ltd., “Power Top V-20”) is cationically electrodeposited to a dry film thickness of about 20 μm.
Baking was performed at 0 ° C. for 30 minutes to form a cationic electrodeposition coating film. Next, on the cationic electrodeposition coating film, a gray intermediate coating material 3 (Nippon Paint Co., Ltd., “Olga P-2 Gray”) is spray-coated so as to have a dry film thickness of about 35 to 40 μm,
It was baked at 140 ° C. for 30 minutes (formation of a base coat).

A super rack M-155 (manufactured by Nippon Paint Co., Ltd., acrylic resin-based red color base coat) 4 was coated on the base material formed as described above so as to have a dry film thickness of 20 μm. The color base coat used was diluted to a coating viscosity (14 seconds / # 4 Ford cup / 20 ° C.) with a diluent (ethyl acetate / xylol = 1/1) before use. 140 ° C.
After baking and curing for 20 minutes, the thermosetting powder color clear coating composition 5 prepared in Preparation Example 1 was applied so that the dry film thickness was 80 μm. Then 14
Baking was performed at 0 ° C. for 30 minutes to obtain a composite coating film 10.

Example 2 A composite coating film was formed in the same manner as in Example 1 except that the color base coating film was left (setting) at room temperature (25 ° C.) for 8 minutes without baking and curing.

Example 3 A composite coating film was formed in the same manner as in Example 1, except that the color base coating film was pre-dried at 80 ° C. for 5 minutes instead of baking and curing.

COMPARATIVE EXAMPLE A thermosetting powder color clear coating composition was prepared using a solvent-dilutable color clear coating composition (Nippon Paint Co., Ltd., Irgazine DPP Red BO; PWC = 1%) with a concealing film thickness of 20.
0 μm or more), and a composite coating film was formed in the same manner as in Example 1 except that the coating was performed so that the dry film thickness became 40 μm.

Table 1 summarizes the structures of the composite coating films formed in Examples 1 to 3 and Comparative Example.

[0054]

[Table 1]

Super rack M-155: manufactured by Nippon Paint Co., Ltd.
Acrylic resin-based color base coating composition Powder color clear: Thermosetting powder color clear coating composition from Preparation Example 1 Super Lac O-150: Nippon Paint, solvent dilution type color clear coating composition ⁺ "
This means that setting was performed at room temperature (25 ° C.) for 8 minutes without baking hardening.

Evaluation Method The surface layers (clear coating films) of the multilayer films prepared in the above Examples 1 to 3 and Comparative Example were each coated with a water-resistant abrasive paper and a compound to a predetermined thickness (5, 10, 15 and 20 μm). ) Just polished. Thereafter, the polished portion and the non-polished portion (the unpolished surface layer portion) were subjected to color difference (ΔE) measurement, visual appearance evaluation, and accelerated weather resistance test according to the following procedures.

(1) Measurement of Color Difference (ΔE) The lightness of the polished portion and the non-polished portion of the polished composite coating film was measured by “SM Color Computer SM-” manufactured by Suga Test Co., Ltd.
4 "Measured using a colorimeter. The difference in lightness between the polished portion and the non-polished portion was defined as a color difference (ΔE). However, the color difference was the absolute value of the difference in lightness. Table 2 shows the results.

(2) Visual Evaluation of Appearance In the polished composite coating film, the surface appearance of the polished portion and the non-polished portion was visually evaluated based on the following evaluation criteria. Table 2 shows the results. Evaluation criteria ○: The polished part and the non-polished part cannot be distinguished ×: The polished part stands out

(3) Accelerated Weathering Test Each polished composite coating film was subjected to an accelerated weathering test for 2000 hours in a sunshine weatherometer (accelerated weathering tester manufactured by Suga Test Instruments Co., Ltd.). The color difference (ΔE) was calculated in the same manner as in the above (1). Table 2 shows the results.

[0060]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a multilayer film manufactured by a multilayer film forming method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Dull steel plate, 2 ... Cationic electrodeposition coating, 3 ... Intermediate coating, 4 ... Solution color base coating, 5 ... Thermosetting powder color clear coating, 10 ... Multilayer film.

Claims (4)

[Claims] (1) forming a color base coating on a substrate on which an undercoat and an intermediate coating are sequentially formed; and (ii) forming a color base coating.
A method for forming a composite coating film, comprising applying a powder color clear paint on the color base coating film. 2. The method according to claim 1, wherein the powder color clear paint contains 0.05 to 5% by weight of a coloring pigment. 3. The method according to claim 1, wherein the thickness of the powder color clear coating formed by step (ii) is 40 to 100 μm. 4. An article having a composite coating formed by the method according to claim 1.