JPH06304519A - Formation of coating film - Google Patents

Abstract

PURPOSE:To coat by 2-coat 1-bake system, by making the surface tension of a powder coating material A larger than that of a powder coating material B by a specific value in forming the powder coating film of a polyester resin based powder coating material B or the like on the uncured coating surface of an epoxy resin based powder coating material A. CONSTITUTION:This coating film forming method suitable for the under coating of automotive body or the like is the one to form a multiple layered coating film by applying the polyester resin based or an acrylic resin based powder coating material B on the uncured coating surface coated with the epoxy resin powder coating material A and simultaneously hardening by heating both coating films. In this case, the surface tension of the powder coating film A is larger than that of the powder coating film B and the difference is setted to 1-15 dyne/cm, preferably 2-13 dyne/cm. As a result, the multiple coating film composed of two kinds of the powder coating materials A and B is formed by 2-coat 1-bake system and excellent chipping resistance and corrosion resistance due to the 1st layer and excellent light resistance due to the 2nd layer are secured.

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 multilayer coating film by a so-called two-coat one-bake system in which two types of powder coating materials are applied wet-on-wet and then both coating films are simultaneously cured by heating. Regarding

[0002]

2. Description of the Related Art In recent years, the use of powder coating materials free from environmental pollution due to solvent evaporation has been rapidly increasing from the viewpoint of pollution prevention. For example, in the undercoating of an automobile body, a powder coating having an epoxy resin type, a polyester resin type, an acrylic resin type or the like as a main component is used for coating. The epoxy resin system is excellent in corrosion resistance and chipping resistance but inferior in weather resistance, while the polyester resin system or particularly acrylic resin system is in excellent in weather resistance but inferior in corrosion resistance and chipping resistance. Although the resin has some performances, the features of the above resin systems have not been fully utilized in the painting of automobile bodies that require high performance. Further, in order to shorten the coating process and save resources, it is desired to apply the top coat directly on the undercoat coating film without applying the intermediate coat.

[0003]

Means for Solving the Problems As a result of intensive investigations on the undercoat coating by the powder coating, the present inventors have found that an epoxy resin powder coating and a polyester resin or acrylic resin powder having a specific surface tension difference. 2 coats of body paint 1
The present invention has been completed by finding that by applying the baking method, the characteristics of each resin system can be fully utilized to form a multilayer coating film having excellent performance.

That is, according to the present invention, a polyester resin-based or acrylic resin-based powder coating material (B) is applied to the surface of an uncured coating film obtained by coating the epoxy resin-based powder coating material (A), and both coating films are simultaneously coated. A method of forming a multilayer coating film by heating and curing, wherein the surface tension of the epoxy resin-based powder coating material (A) is the surface tension of the polyester resin-based powder coating material or the acrylic resin-based powder coating material (B). Greater and the difference is 1-15
It is intended to provide a coating film forming method characterized by being within the range of dyne / cm 2.

The epoxy resin powder coating material (A) used in the present invention can be used without particular limitation as long as it is a thermosetting powder coating material containing an epoxy resin as a main component. Specifically, the epoxy resin is a reaction product of bisphenols such as bisphenol A and bisphenol F and epihalohydrin such as epichlorohydrin and has an epoxy equivalent of 450 to
3,500 bisphenol glycidyl ether type epoxy resin, a reaction product of a phenol type or cresol type novolak resin and epichlorohydrin, an epoxy phenol novolac resin having an epoxy equivalent of 200 to 300, and further triglycidyl isocyanurate,
Examples thereof include alicyclic epoxy resin, and glycidyl ether type epoxy resin of bisphenol A can be preferably used. Examples of the curing agent for the epoxy resin include hydrazides such as adipic acid dihydrazide, aromatic amines such as diaminodiphenylmethane, polyamide amines which are condensation products of aliphatic amines and aliphatic dicarboxylic acids, amine-based compounds such as dicyandiamide and imidazole-based compounds. Curing agent; acid anhydride such as tetrahydrophthalic anhydride, benzophenone tetracarboxylic acid anhydride, trimellitic anhydride, acid curing agent such as dodecane diacid, sebacic acid, adipic acid; phenolic resin, phenolic compounds such as bisphenol A A curing agent can be used, which can be appropriately selected and used.

If desired, the powder coating material (A) may further contain pigments such as extender pigments, rust preventive pigments and coloring pigments, and additives for coating materials. Powder coating (A)
For the production of, the method of uniformly dispersing the above-mentioned constituents by the usual melting / kneading, dry blending method, etc., then pulverizing with a mechanical pulverizer and sieving into powder with a particle size of 1 to 300 μm is applied. it can.

The polyester resin-based or acrylic resin-based powder coating material (B) used in the present invention can be used without particular limitation as long as it is a thermosetting powder coating material containing a polyester resin or acrylic resin as a main component. Specifically, the polyester resin includes polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, maleic anhydride, azelaic acid and polyhydric alcohols such as ethylene glycol, neopentyl glycol and trimethylolpropane. Those obtained by condensation can be used, and as the curing agent, blocked isocyanates obtained by blocking isocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane diisocyanate with phenols, lactams, oximes, etc. Compounds: solid melamine resin, triglycidyl isocyanurate, etc. can be used.

The acrylic resin may be an alkyl ester of (meth) acrylic acid (wherein the alkyl group has 1 to 1 carbon atoms).
12), a vinyl-based monomer having a functional group such as a glycidyl group, a hydroxyl group, and a carboxyl group, and a copolymer with a vinyl-based monomer copolymerizable therewith, if necessary, can be used. As the polyacrylic acid, if the functional group of the acrylic resin is a glycidyl group, a polybasic acid is used. If it is a hydroxyl group, the blocked isocyanate compound or hexamethoxymethylmelamine or tetrabutoxybenzoguanamine mentioned as the curing agent for the polyester resin is used. The amino resin and the like can be used, and if it is a carboxyl group, a hydroxyalkylamide such as bis [N, N-di (hydroxyethyl)] adipamide can be used.
Among these, a combination of a glycidyl group-functional acrylic resin and an aliphatic dibasic acid such as dodecane diacid can be preferably used.

If necessary, the powder coating material (B) may further contain pigments such as inorganic or organic color pigments and extender pigments, coating surface adjusting agents, coating additives such as curing catalysts. You can The powder coating material (B) can be manufactured in the same manner as the powder coating material (A).

In the present invention, the surface tension of the powder coating material (A) is higher than the surface tension of the powder coating material (B), and the difference is 1 to 15 dyne / cm, preferably 2-1.
It is essential that it is within the range of 3 dyne / cm. If the difference in surface tension is less than 1 dyne / cm, mutual fusion or mixing is likely to occur at the boundary between both coatings, while if it exceeds 15 dyne / cm, the interlayer adhesion of both coatings is unfavorable.

In the present invention, the "surface tension" is measured as follows: deionized water is dropped onto the cured coating film of the above powder coating material (A) or (B). The contact angle (θ) with the membrane is measured. Next, the following Sell and N
The surface tension of the coating film is obtained from the Eumann's empirical formula.

[0012]

[Equation 1] (In the formula, γ _L : surface tension of water (72.8 dyne / cm), γ
_S : Surface tension of coating (dyne / cm))

In the method of the present invention, the powder coating material (A) is applied, and the powder coating material (B) is applied to the uncured coating surface without being heated and cured, and then the powder coating material (A) is heated to cure both of them. The coating is cured simultaneously. The powder coatings (A) and (B)
The coating is not particularly limited, and is performed using an ordinary electrostatic powder coating machine or the like, and the powder coating (A) is coated so that the dry film thickness is 10 to 500 μm, preferably 20 to 100 μm. Further, the powder coating material (B) is applied so as to have a dry film thickness of 10 to 500 μm, preferably 20 to 100 μm. The heating to cure both coatings is
It is suitable to carry out at 140 to 200 ° C., preferably 160 to 180 ° C. for 15 to 40 minutes.

In the present invention, the above-mentioned multi-layer coating film may be used alone, but the coating film may be further overcoated if necessary. As the top coating used for the top coating, conventionally known ones can be appropriately used without particular limitation. Specifically, acrylic resin, polyester resin, silicone resin, fluororesin and modified resins thereof are used as the base resin component, and Examples of the (block) polyisocyanate compound, a melamine resin, a metal chelate, an aqueous coating material containing an alkoxysilane compound as a crosslinking agent (or a catalyst), an organic solvent type coating material, or a non-aqueous dispersion type coating material. Further, the top coating composition can be finished by a one-coat one-bake method and a metallic / clear system can be finished by a two-coat one-bake method and a two-coat two-bake method. The top coating film is usually about 10 to 1 in dry film thickness.
It is applied to 100 μm and the heating conditions can be arbitrarily selected depending on the vehicle component and the material of the object to be coated, but generally about 60
To about 160 ° C, especially 80 to 140 ° C for 10 to 40 minutes are preferred.

In the method of the present invention, the article to be coated with the multilayer coating film is a cold rolled steel sheet, a hot dip galvanized steel sheet,
Electrogalvanized steel plate, alloy plated steel plate, aluminum plate, aluminum plated steel plate, stainless steel plate, copper plate,
Metal plates such as copper-plated steel plates and tin-plated steel plates are included.
Further, a surface-treated plate obtained by subjecting these metal plates to chemical conversion treatment such as phosphate-based or chromate-based is also included.

[0016]

According to the method of the present invention, a multi-layer coating film obtained by applying two kinds of powder coating materials having a specific difference in surface tension by a two-coat one-bake system is the first layer. The coating film can achieve excellent chipping resistance and anticorrosion property, and the second layer coating film can ensure excellent weather resistance. Moreover, the effects of no pollution and resource saving are remarkable.

[0017]

EXAMPLES Next, the present invention will be described more specifically by way of examples. In the examples, "parts" and "%" mean "parts by weight" and "% by weight", respectively.

Production Example 1 of Epoxy Resin Powder Coating Production Example 1 Bisphenol A type epoxy resin (manufactured by Shell Chemical Co.,
"Epicoat 1004") 100 parts, adipic acid dihydrazide 6 parts, titanium white 50 parts, carbon black 1 part,
A blend of 0.5 part of benzoin was dry-mixed using a Henschel mixer, and then melted and kneaded by a Cokneader manufactured by Buss. This is cooled, coarsely crushed with a cutter mill (Torai Iron Works), further finely crushed with a Fuji Atomizer (FA-SW-1 manufactured by Fuji Sangyo Co., Ltd.), and sieved with a wire mesh of 150 mesh to obtain powder coating (A-1 ) Got.

Production Example 2 100 parts of bisphenol A type epoxy resin, 5 parts of adipic dihydrazide, 50 parts of titanium white, 1 part of carbon black, 0.5 part of benzoin, silicone oil KP322.
A blend consisting of 0.5 part (manufactured by Shin-Etsu Chemical Co., Ltd., a coating surface adjusting agent) was melted, kneaded, pulverized and the like in the same manner as in Production Example 1 to obtain a powder coating (A-2).

Production Example 3 of Polyester Resin Powder Coating Manufacturing Example 3 100 parts of polyester resin ER6570 (manufactured by Nippon Ester Co., terminal hydroxyl group containing type), 50 parts titanium white, 0.5 parts benzoin, Modaflow (manufactured by Mitsubishi Monsanto Kasei Co., Ltd., Repelling agent) 1 part, VESTAGOH B1530 (manufactured by Daicel Hüls, 20 parts isophorone diisocyanate adduct), and 1 part of dibutyltin dilaurate. A paint (B-1) was obtained.

Production of acrylic resin powder coating Production Example 4 Acrylic resin (styrene 20 parts, methyl methacrylate 3
3 parts, a copolymer consisting of 17 parts of n-butyl methacrylate and 30 parts of glycidyl methacrylate) to 100 parts, 20 parts of dodecane diacid as a curing agent, silicone oil KP3
22 0.1 part, benzoin 0.5 part, and titanium white 30 parts were dry-mixed in advance, and then 11 using an extruder.
The mixture was melted and kneaded at 0 ° C., cooled, and then pulverized in the same manner as in Production Example 1 to obtain a powder coating (B-2).

Production Example 5 Acrylic resin (styrene 20 parts, methyl methacrylate 3
3 parts, copolymer of n-butyl methacrylate 17 parts, glycidyl methacrylate 30 parts) 100 parts, dodecane diacid 20 parts, benzoin 0.5 parts, titanium white 30 parts, silicone oil KP322 1.5 parts The same composition as in Production Example 4 was used to obtain a powder coating (B-3).

Examples and Comparative Examples 100 × 300 × 0.8 mm cold rolled steel sheet (SPCC-D)
Was treated with the chemical conversion treatment agent Palbond 3004 (Zinc phosphate-based, manufactured by Nippon Parkerizing Co., Ltd.) as a coated plate,
The epoxy resin-based powder coating material obtained in the above Production Example was applied to the coated plate by using an electrostatic powder coating machine (GEMA-721 type) under the condition that the dry film thickness was 30 μm (first layer), The uncured coated surface is coated with the polyester resin-based or acrylic resin-based powder coating material obtained in the above Production Example under the condition that the dry film thickness is 50 μm (second layer), and both coating films are heated at 170 ° C. It was heated for 25 minutes and cured at the same time to obtain a multilayer powder coated plate (2-coat 1-bake system). However, in Comparative Examples 3 and 4,
Epoxy resin-based and acrylic resin-based powder coatings were respectively applied twice with the same coating and heat-cured in the same manner as above.

Further, in Examples 3 and 4, a top coating "Amilak White" (manufactured by Kansai Paint Co., Ltd.
Amino alkyd resin-based paint) was applied to a film thickness of 25 to 40 μm (dry film thickness) and heated at 140 ° C. for 30 minutes for curing to obtain a coated plate. Table 1 below shows the performance test results of the powder coating materials used in each of the examples and comparative examples and the multilayer coating films formed.

[0025]

[Table 1]

The test methods in Table 1 above are as follows. (* 1) Surface tension: Deionized water was added dropwise to the cured coating film to measure the contact angle (θ) with the coating film, and the surface tension of the coating film was calculated from the experimental formula of Sell and Neumann described above. .

(* 2) Finishability: The appearance of the coating film was visually observed and evaluated according to the following criteria. ◯: Smooth and glossy appearance with no deposition of the first layer powder coating Δ: Slight spotted deposition of the first layer powder coating was observed ×: The first and second layers A state in which the powder coating material is remarkably mixed is recognized.

(* 3) Chipping resistance: A stepping stone tester (JA-400 type, manufactured by Suga Test Instruments Co., Ltd.) was used, a coated plate was vertically mounted on a sample holder of the tester, and 50 g of No. 7 was used. Crushed stones were jetted with a pressure gauge of the same tester at an air pressure of 4 kg / cm ² , and the crushed stones were made to collide vertically with a coated plate, and the degree of peeling scratches at that time was evaluated according to the following criteria. ◯: Slight scratches were observed on a part of the coating film Δ: Scratches on the coating film were observed and peeling between the first and second layers was observed ×: Impact on the coating film There are many scratches due to swelling, and large peeling that reaches the base is recognized

(* 4) Salt spray resistance: Cross-cut scratches were made on the multilayer coating film with a knife so as to reach the substrate, and a salt spray test was carried out for 300 hours in accordance with JIS-Z-2371. The rust and the blister width were measured. ◯: 0 to less than 1 mm △: less than 1 to 3 mm ×: 3 mm or more

(* 5) Weather resistance: Using a sunshine weatherometer, the state of the coating film surface after the 500-hour test was visually observed, and the 60 ° gloss value was determined. ◯: There is no abnormality on the surface of the coating film and the gloss value is maintained at 80 or more. ×: There is remarkable luster and the gloss value is 20 or less.

(* 6) Adhesion: 100 pieces of 2 × 2 mm goggles were formed on the multilayer coating film with a knife so as to reach the substrate, and an adhesive cellophane tape was adhered to the surface thereof, and it was rapidly peeled off. The later coated surface was evaluated. ◯: Peeling is not observed at all x: Delamination of the first and second layers is recognized

Claims (1)

[Claims] 1. A polyester resin-based or acrylic resin-based powder coating material (B) is applied to the surface of an uncured coating film formed by coating an epoxy resin-based powder coating material (A), and both coating films are heated and cured at the same time. A method for forming a multilayer coating film by using the epoxy resin powder coating material (A) having a surface tension higher than that of the polyester resin powder coating material or the acrylic resin powder coating material (B). And the difference is within the range of 1 to 15 dyne / cm.