JP2008080297A - Coating method of aluminum alloy wheel and aluminum alloy wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method of an aluminum alloy wheel capable of obtaining the aluminum alloy wheel excellent in sufficient chipping resistance, cutting processability, water resistance, corrosion resistance and adhesiveness in spite of the aluminum alloy wheel subjected to chemical forming treatment by non-chromate type chemical forming treatment, and also to provide the aluminum alloy wheel. <P>SOLUTION: The coating method of the aluminum alloy wheel includes a process (1) for treating the surface of the aluminum alloy wheel with a non-chromate chemical forming treatment agent and a process (2) for coating the surface of the aluminum alloy wheel treated in the process (1) with a powder coating and baking the coated aluminum alloy wheel. The powder coating is composed of powder coating particles containing a carboxyl group-containing polyester resin, polycaploractam and a β-hydroxyalkylamide curing agent represented by the general formula (1) (wherein R<SP>1</SP>is a hydrogen atom, a methyl group or an ethyl group; R<SP>2</SP>is a hydrogen atom; a 1-5 C alkyl group or HOCH(R<SP>1</SP>)CH<SB>2</SB>- and A is a divalent hydrocarbon group). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an aluminum alloy wheel coating method and an aluminum alloy wheel.

In recent years, for the purpose of environmental protection, a non-chromate chemical conversion treatment capable of imparting high corrosion resistance and adhesion equivalent to the chromate chemical conversion treatment to an aluminum metal surface is required. As such a non-chromate chemical conversion treatment agent, for example, a zirconium chemical conversion treatment agent, a titanium chemical conversion treatment agent, and the like are known (see Patent Document 1 and Patent Document 2).

On the other hand, in the coating of aluminum alloy wheels, coating is generally performed by sequentially applying powder primer coating, base coating, and clear coating on a metal surface that has been subjected to chemical conversion treatment. However, when such coating is performed on an aluminum surface treated with a non-chromate chemical conversion treatment agent, properties such as cutting workability, chipping resistance, water resistance, corrosion resistance, and adhesion are insufficient. In particular, a decrease in the machinability is an important problem, and there is a need for an improvement in the machinability of the coating film that does not cause peeling of the coating film during the cutting process.

Further, the molded aluminum alloy wheel is preferably hardened at a low temperature because the strength is lowered when it is treated at a high temperature. As a low-temperature curable powder coating for coating a wheel, a powder coating composition containing a β-hydroxylalkylamide curing agent as described in Patent Document 3 is known. However, in such a powder coating composition, improvement of cutting workability and chipping resistance has not been studied.

Patent Document 4 describes that a powder coating primer containing calcium carbonate and having a specific dynamic viscoelastic value forms a coating film having good cutting workability. However, such a powder paint primer for an aluminum alloy wheel is not intended to improve the above-mentioned problems on the metal surface after the non-chromate chemical conversion treatment.

JP 2004-018929 A JP 2004-018930 A JP 2001-294804 A JP 2003-221550 A

In view of the above, the present invention is an aluminum alloy wheel that is excellent in sufficient chipping resistance, cutting workability, water resistance, corrosion resistance, and adhesion, despite being subjected to chemical conversion treatment with a non-chromate chemical conversion treatment agent. It is an object of the present invention to provide an aluminum alloy wheel coating method and an aluminum alloy wheel capable of obtaining the above.

The present invention includes a step (1) of treating the surface of an aluminum alloy wheel with a non-chromate chemical conversion treatment agent, and a step (2) of applying and baking a powder coating on the surface treated in the step (1). A method of painting an aluminum alloy wheel,
The powder coating material includes a carboxyl group-containing polyester resin, polycaprolactone, and the following general formula (1);

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or HOCH (R ¹ ) CH ₂ —, and A represents a divalent group. Represents a hydrocarbon group.)
A coating method of an aluminum alloy wheel characterized by comprising powder coating particles containing a β-hydroxyalkylamide curing agent represented by the formula:

The powder coating particles preferably further contain an acrylic resin and / or an epoxy resin.
It is preferable that content of the said polycaprolactone is 1-20 mass parts with respect to 100 mass parts of carboxyl group-containing polyester resins.
In the powder coating particle, the ratio (number of hydroxyl group equivalents / number of carboxyl group equivalents) of the hydroxyl group equivalent number of the β-hydroxyalkylamide curing agent to the carboxyl group equivalent number of the carboxyl group-containing polyester resin is 0.5. / 1 to 1.5 / 1 is preferable.

It is preferable that the coating method of the aluminum alloy wheel of the present invention further includes a top coating step after the step (2).
The top coating step includes a step (3) of applying a metal pigment-containing base coating on the powder coating film formed in the step (2), and a metal pigment containing step formed in the step (3). It is preferable to consist of the process (4) of apply | coating a clear coating material on a base coating film.
The top coating step also includes a step (3) of applying a metal pigment-containing base paint on the powder coating film formed in the step (2), and a metal pigment-containing base formed in the step (3). A step (X) of partially cutting the coating film, a step (Y) of non-chromate treatment of the aluminum alloy material exposed in the step (X), and a clear paint on the surface of the aluminum alloy material treated in the step (Y) It is preferable to consist of the process (4 ') which apply | coats.

In the top coating step, the first base coating film is further formed on the powder coating film formed in the above step (2) by applying a first base coating material and curing it by heating (3). -A) a step (3-b) of applying a second base paint (brilliant pigment-containing base paint) on the first base paint film, and a second base paint (brilliant pigment-containing base paint). It is preferable to consist of a process (4 '') which applies a clear paint on top.

It is preferable that the heating temperature of the powder coating material in the said process (2) is 150-170 degreeC.
The powder coating particles preferably have a volume average particle size of 25 to 35 μm.
The non-chromate chemical conversion treatment agent is preferably a zirconium-based treatment agent and / or a titanium-based treatment agent.
The present invention is also an aluminum alloy wheel that is coated by the above-described method for coating an aluminum alloy wheel.
The present invention is described in detail below.

In the method for coating an aluminum alloy wheel of the present invention, a powder coating containing a carboxyl group-containing polyester resin, polycaprolactone, and a β-hydroxyalkylamide curing agent is used as a primer coating. After performing non-chromate conversion treatment, by using the above powder coating as a primer paint, it has sufficient chipping resistance even when non-chromate conversion treatment is performed, cutting workability, water resistance, corrosion resistance, adhesion An aluminum alloy wheel with excellent properties can be obtained. Moreover, since the powder coating material used here has low-temperature curability, the physical properties of the aluminum alloy are not reduced by high-temperature treatment.

In the aluminum alloy wheel coating method of the present invention, first, the step (1) of treating the surface of the aluminum alloy wheel with a non-chromate chemical conversion treatment agent is performed. The non-chromate chemical conversion treatment agent is a treatment agent that does not contain chromium metal, and examples thereof include a zirconium treatment agent, a titanium treatment agent, and a phosphoric acid treatment agent. It is preferable to use a titanium-based treatment agent. The zirconium-based treatment agent and / or titanium-based treatment agent preferably contains zirconium ions and / or titanium ions and fluorine ions, and may further contain phosphate ions.

The content of the zirconium ions and / or titanium ions is preferably 0.01 to 0.125 g / L in terms of metal elements in the non-chromate chemical conversion treatment agent. If it is less than 0.01 g / L, the mass of the formed film may be insufficient, and performance such as corrosion resistance may be insufficient. If it exceeds 0.125 g / L, the mass of the formed film is large. For this reason, the film becomes thick and the metal feeling of the aluminum alloy wheel may be impaired.

Here, the metal element conversion is a metal element conversion coefficient (a coefficient for converting the metal compound amount into the metal element amount to the content of the metal compound, specifically, the atomic weight of the metal element in the metal compound , Which means the value divided by the molecular weight of the metal compound).

The supply source of zirconium ions of the non-chromate chemical conversion treatment agent is not particularly limited. For example, soluble fluorozirconates such as fluorozirconate and fluorozirconate; (NH ₄ ) ₂ ZrF ₆ ; alkali metal fluorozirconate; Zirconium fluoride and the like can be mentioned.

The source of titanium ions of the non-chromate chemical conversion treatment agent is not particularly limited. For example, soluble fluorotitanates such as fluorotitanate and fluorotitanate; (NH ₄ ) ₂ TiF ₆ ; alkali metal fluorotitanate; titanium fluoride and the like Can be mentioned.

The fluorine ion content (total fluorine ion concentration in the treatment agent) is preferably 0.01 g / L or more and 0.5 g / L or less in terms of fluorine element in the non-chromate chemical conversion treatment agent. If it is less than 0.01 g / L, etching of the surface of the aluminum alloy wheel becomes insufficient, and the mass of the formed film may be insufficient. If it exceeds 0.5 g / L, the aluminum alloy wheel The surface will be improperly etched, and the surface of the aluminum alloy wheel may be in a blurred state as if covered with frost. The fluorine supply source in the chemical conversion treatment agent is not particularly limited, and examples thereof include hydrofluoric acid, hydrofluoric acid salt, and fluoroboric acid in addition to the above-described zirconium compound and titanium compound. it can.

When using the above-mentioned non-chromate chemical conversion treatment agent containing phosphate ions, the phosphate ion supply source is not particularly limited. For example, it is soluble in acid solutions such as phosphoric acid, ammonium phosphate, and alkali metal phosphates. And phosphoric acid compounds. In addition, although it is desirable to use orthophosphoric acid as the phosphate ion supply source, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, hypophosphoric acid, or salts thereof may be used. The phosphate ion content in the non-chromate chemical conversion treatment agent is preferably 0.003 to 0.33 g / L in terms of phosphorus element.

The pH of the non-chromate chemical conversion treatment agent is preferably 1.5 to 4.0. If the pH is less than 1.5, the surface of the aluminum alloy wheel may be unduly etched, and if it exceeds 4.0, the surface of the aluminum alloy wheel may be insufficiently etched.

The adjustment of the pH of the non-chromate chemical conversion treatment agent is preferably performed using an acid or base that does not adversely affect the chemical conversion treatment, such as nitric acid, ammonium hydroxide, perchloric acid, sulfuric acid and the like. When sulfuric acid is used, the pH of the non-chromate chemical conversion treatment agent is preferably 2 or more.

Processing by the non-chromate chemical conversion treatment agent can be carried out by conventional treatment by spraying or the like, as a condition for the chemical conversion process, it is preferred that the coating weight of ^{10mg / m 2 ~40mg / m 2} , more preferably it is ^{20mg / m 2 ~40mg / m 2} . If it is less than 10 mg / m ² , the corrosion resistance performance may be reduced, and if it exceeds 40 mg / m ² , the film may be too thick and the brightness of aluminum may be impaired.
The chemical conversion treatment may be performed so that the amount of the formed film falls within the above range. In general, the treatment temperature is preferably 30 to 50 ° C., and the treatment time is preferably 0.5 minutes to 3 minutes. The processing time is 40 ° C. and the processing time is 45 seconds.

The treatment with the non-chromate chemical conversion treatment agent (step (1)) is preferably performed on the surface of the aluminum alloy wheel subjected to pickling treatment. It is preferable to perform the said pickling process with the process liquid of pH 0.5-2.0 containing a ferric ion 0.1-0.4g / L and a sulfate ion.

The source of ferric ions is not particularly limited. For example, water-soluble ferric salts such as Fe ₂ (SO ₄ ) ₃ , Fe (NO ₃ ) ₃ , and Fe (ClO ₄ ) ₃ ; FeSO ₄ , Examples thereof include water-soluble ferrous salts such as Fe (NO ₃ ) ₂ . Among these, Fe ₂ (SO ₄ ) ₃ and FeSO ₄ that can provide sulfate ions are preferably used.

The pickling treatment is generally performed at a treatment temperature of 30 to 75 ° C, preferably 35 to 45 ° C, and a treatment time of 1 to 5 minutes, preferably about 3 minutes. The method for the pickling treatment is not particularly limited, and examples thereof include an immersion method and a spray method. The surface of the aluminum alloy wheel that has been subjected to the pickling treatment is preferably washed with water before the treatment with the non-chromate chemical conversion treatment agent. The washing method is not particularly limited, and can be carried out by a method generally used for metal surface treatment. A degreasing treatment with a surfactant may be performed before the pickling treatment.

In the present invention, after the step (1) of treating the surface of the aluminum alloy wheel with a non-chromate chemical conversion treatment agent, a step (2) of applying and baking a powder coating on the surface treated in the step (1). I do. As a result, an aluminum alloy wheel having excellent chipping resistance, cutting workability, water resistance, corrosion resistance, and adhesion can be obtained as described above. The powder coating used in the step (2) includes a carboxyl group-containing polyester resin, polycaprolactone, and the following general formula (1);

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or HOCH (R ¹ ) CH ₂ —, and A represents a divalent group. It represents a powder coating particle containing a β-hydroxyalkylamide curing agent represented by the following formula: By using such a powder coating material, a coating film excellent in smoothness, cutting workability and chipping resistance can be obtained even when primer coating is performed on the non-chromate chemical conversion coating film.

The polycaprolactone used in the powder coating is a resin capable of imparting flexibility to the formed coating film, and formed on the aluminum alloy wheel by using the polycaprolactone. It is presumed that the physical properties of the multilayer coating film, particularly the cutting workability, will be good.

The polycaprolactone preferably has a number average molecular weight of 10,000 to 100,000. If the number average molecular weight is less than 10,000, there may be a problem that the anti-blocking property of the paint is lowered, and if it exceeds 100,000, there may be a problem that the smoothness of the coating film is lowered. The polycaprolactone may be modified with polybasic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone or the like to the extent that the physical properties of the paint are not adversely affected.

Commercially available polycaprolactone can also be used. Examples of commercially available polycaprolactone include Plaxel H5, Plaxel H7, Plaxel H1P (manufactured by Daicel Chemical Industries), and the like.

It is preferable that the said polycaprolactone is mix | blended in the said powder coating particle in the ratio used as 1-20 mass parts with respect to 100 mass parts of carboxyl group-containing polyester resins. There exists a possibility that a coating-film physical property cannot fully be improved as a compounding quantity is less than 1 mass part. If the amount exceeds 20 parts by mass, the fluidity or transportability of the powder coating may be reduced, and coating may be difficult.

The carboxyl group-containing polyester resin preferably has a resin solid content acid value of 10 to 100 (mg KOH / g solid content; the same shall apply hereinafter), more preferably 15 to 80, and still more preferably 20 to 60. It is a range. When the acid value is less than 10, the curability is lowered and the mechanical properties may be lowered. On the other hand, when the acid value is more than 100, the water resistance of the obtained coating film may be lowered. The carboxyl group-containing polyester resin has a softening point of 80 to 150 ° C, preferably 90 to 130 ° C. When the softening point is lower than 80 ° C, the blocking resistance may be lowered, and when higher than 150 ° C, the smoothness of the obtained coating film may be lowered.

The carboxyl group-containing polyester resin preferably has a mass average molecular weight of 1000 to 150,000, more preferably 3000 to 70000, and still more preferably 4000 to 50000. If the mass average molecular weight is less than 1000, the performance and physical properties of the resulting coating film may be reduced. On the other hand, if it is greater than 150,000, the smoothness and appearance of the resulting coating film may be reduced. is there.

In addition, the acid value of the resin solid content in the present invention can be determined by a method based on JIS K 0070, and the softening point can be determined by a method based on JIS K 2207. Moreover, the mass average molecular weight and the number average molecular weight in the present invention can be determined by methods well known by those skilled in the art, such as a method obtained by converting to styrene by gel permeation chromatography (GPC).

The carboxyl group-containing polyester resin can be obtained by polycondensation by an ordinary method using an acid component mainly composed of a polyvalent carboxylic acid and an alcohol component mainly composed of a polyhydric alcohol as raw materials. By selecting the respective components and the conditions for condensation polymerization, a carboxyl group-containing polyester resin having the above physical property values and special values can be obtained.

Examples of the acid component include, but are not limited to, aromatics such as terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid and anhydrides thereof, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. Examples thereof include dicarboxylic acids and anhydrides thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, saturated aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and anhydrides thereof. In addition, lactones such as γ-butyrolactone and ε-caprolactone, and corresponding hydroxycarboxylic acids, aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid, and the like can be mentioned. Two or more acid components may be used. Of these, isophthalic acid and terephthalic acid are preferable from the viewpoint of durability, physical properties, and price. The total proportion of terephthalic acid and isophthalic acid in the total acid component is 70 mol% or more, preferably 75 mol% or more, and particularly preferably 80 mol% or more. Here, when the total proportion of terephthalic acid and isophthalic acid is used as the acid component by 70 mol% or more, it means that these are used as the main raw materials. About the upper limit of the said terephthalic acid and isophthalic acid content, it is good also considering the whole quantity of the acid component used for preparation of a polyester resin as a terephthalic acid and / or isophthalic acid. Further, when particularly improving weather resistance, the proportion of isophthalic acid in the total acid component is 70 mol% or more, preferably 80 mol% or more, particularly preferably 90 mol% or more. Here, using 70 mol% or more of the ratio of isophthalic acid in the total acid component means using isophthalic acid as a main raw material.

The alcohol component is not particularly limited. For example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3 -Butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol, 1 Diols of 2 octadecanediol etc., trimethylol propane, glycerine, may be mentioned polyhydric alcohols such trivalent or more such as pentaerythritol and the like. Two or more alcohol components may be used.

The β-hydroxyalkylamide curing agent has the following general formula (1);

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or HOCH (R ¹ ) CH ₂ —, and A represents a divalent group. Represents a hydrocarbon group.).

Further, R ¹ in the formula is preferably a hydrogen atom or a methyl group, R ² is preferably HOCH (R ¹ ) CH ₂ —, and A preferably has 2 to 10 carbon atoms, preferably 4 to 8 carbon atoms. An alkylene group is more preferred.

The curing agent can be obtained, for example, by reacting a carboxylic acid and / or a carboxylic acid ester with β-hydroxyalkylamine in the presence of an alkoxide catalyst such as sodium or potassium.

Examples of the carboxylic acid and carboxylic acid ester used here include succinic acid, adipic acid, glutaric acid, dimethyl succinate, diethyl succinate, and dimethyl adipate.

Examples of the β-hydroxyalkylamine include N-methylethanolamine, diethanolamine, N-methylpropanolamine and the like. As the β-hydroxyalkylamide curing agent, commercially available products such as “Primid” series manufactured by EMS-PRIMD can also be used.

The powder coating particle may further contain an acrylic resin and / or an epoxy resin.
As the acrylic resin, an epoxy group-containing vinyl resin which is a vinyl copolymer having an epoxy group at the terminal or side chain of the molecule is preferable. The epoxy group-containing vinyl resin preferably has an epoxy equivalent of 250 to 1500, more preferably 300 to 1000, from the viewpoints of storage stability of the paint, mechanical properties of the resulting coating film, water resistance, and the like. More preferably, it is 400 to 900. If it is less than 250, the solid-phase reaction tends to proceed and the storage stability may be lowered. If it exceeds 1500, the mechanical properties and water resistance may be lowered.

The epoxy group-containing vinyl resin can be obtained by copolymerizing a vinyl monomer having an epoxy group and, if necessary, another vinyl monomer. Alternatively, it can be obtained by introducing an epoxy group into the vinyl copolymer.

Examples of the vinyl monomer having an epoxy group that can be used when the epoxy group-containing vinyl resin is obtained by copolymerization include (meth) such as glycidyl (meth) acrylate and β-methylglycidyl (meth) acrylate. Examples include various alicyclic epoxy group-containing vinyl monomers such as various glycidyl esters of acrylic acid, 3,4-epoxycyclohexyl acrylate, and 3,4-epoxycyclohexyl methacrylate. Examples of the other vinyl monomers include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, and benzyl (meth) acrylate. -Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meta ) Hydroxyl group-containing (meth) acrylates such as acrylate, various α-olefins such as ethylene, propylene and butene-1, various aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene. , Vinyl acetate And vinyl esters such as vinyl propionate and vinyl butyrate.

On the other hand, when trying to obtain by the method of introduce | transducing an epoxy group into the vinyl type copolymer which is the latter method, the method etc. which make glycidol react with the vinyl copolymer which has an isocyanate group can be mentioned, for example.

The softening point of the acrylic resin is preferably 80 to 150 ° C. If it is outside this range, the blocking resistance and the smoothness of the coating film may be reduced.

The number average molecular weight of the acrylic resin is preferably 300 to 10,000, more preferably 1000 to 5,000 from the viewpoint of mechanical properties and smoothness of the coating film. When the number average molecular weight is less than 300, the mechanical properties are lowered, and when it is more than 10,000, the smoothness may be lowered.

Commercially available products of the epoxy group-containing vinyl resin include, for example, Finedick A229, Finedick A241, Finedick A244, Finedick A249, Finedick A261, Finedick A260, Finedick A266 (all of which are Dainippon Ink Kogyo Co., Ltd.), Almatex PD6300, Almatex PD6600, Almatex PD7210, Almatex PD7310, Almatex 7610, Almatex 7690 (all of which are manufactured by Mitsui Chemicals, Inc.).

Examples of the epoxy resin include those having an average of 1.1 or more epoxy groups in one molecule. Specifically, a reaction product of a novolac type phenol resin and epichlorohydrin, a bisphenol type epoxy resin (A type, B type, F type, etc.), a hydrogenated bisphenol type epoxy resin, a novolac type phenol resin and a bisphenol type epoxy resin ( A type, B type, F type, etc.) and epichlorohydrin reaction products, novolac type phenol resins and bisphenol type epoxy resins (A type, B type, F type, etc.) reaction products, cresol novolac, etc. Products obtained from the reaction of cresol compounds with epichlorohydrin, ethylene glycol, propylene glycol, 1,4-butanediol, polyethylene glycol, polypropylene glycol, neopentyl glycol, glycerol and other alcohol compounds with epichlorohydrin. Glycidyl esters obtained by reaction of carboxylic acid compounds such as sidyl ethers, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid, hexahydrophthalic acid and trimellitic acid and epichlorohydrin, p-oxybenzoic acid, Reaction product of hydroxycarboxylic acid such as β-oxynaphthoic acid and epichlorohydrin, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl Alicyclic epoxy compounds such as (3,4-epoxycyclohexane) carboxylate, triglycidyl isocyanurate (TGIC), and derivatives thereof can be used. Two or more of the above epoxy resins may be used in combination.

100-4000 are preferable and, as for the epoxy equivalent of the said epoxy resin, 100-2000 are more preferable. When the epoxy equivalent is less than 100, the storage stability of the paint may be lowered. On the other hand, when it is greater than 4000, the water resistance of the coating film may be lowered. In addition, the epoxy equivalent in this invention can be determined by JISK7236.

Examples of such commercially available epoxy resins include Epototo YD-128, Epotot YD-014, Epotot YD019, ST-5080, ST-5100, ST4100D (all manufactured by Toto Kasei), EHPA-3150 ( Daicel Chemical Industries, Ltd.), Araldite CY179 (Nippon Ciba-Geigy Corporation), Denacor EX-711 (Nagase Kasei Kogyo Co., Ltd.), Epototo YDPN-639, Epototo YDCN701, Epototo YDCN701 (all manufactured by Toto Kasei), Epicron N -680, Epicron N-695, Epicron HP-4032, Epicron HP-7200H (all manufactured by Dainippon Ink and Chemicals), Araldite PT 810, Araldite PT 910 (Nihon Ciba-Geigy), TEPIC (Nissan) Kogyo Co., Ltd.), and the like.

The content ratio of each component of the carboxyl group-containing polyester resin, the acrylic resin, the epoxy resin, and the curing agent in the powder coating is as follows.

When the acrylic resin is further contained, the content thereof is based on 100 parts by mass of the carboxyl group-containing polyester resin from the viewpoints of mechanical properties of the coating film, water resistance, smoothness, storage stability of the paint, and the like. Preferably it is 0.1-10 mass parts, More preferably, it is 1-10 mass parts, More preferably, it is 2-9 mass parts. If the amount is less than 0.1 parts by mass, the mechanical properties of the coating film are deteriorated and the water resistance is poor. The reaction proceeds and the storage stability of the paint may be reduced.

When the epoxy resin is further contained, the content thereof is preferably 0.1 to 10 mass with respect to 100 parts by mass of the carboxyl group-containing polyester resin from the viewpoints of water resistance of the coating film and storage stability of the paint. Parts, more preferably 1 to 10 parts by mass, still more preferably 2 to 9 parts by mass. If the amount is less than 0.1 parts by mass, the water resistance of the coating film becomes poor. If the amount exceeds 10 parts by mass, the reaction between the carboxyl group and the epoxy group proceeds during storage of the paint, and the storage stability of the paint may be deteriorated.

The ratio (hydroxyl group equivalent number / carboxyl group equivalent number) of the hydroxyl group equivalent number of the β-hydroxyalkylamide curing agent and the carboxyl group equivalent number of the carboxyl group-containing polyester resin is preferably 0.5 / 1 to 1. 1.5 / 1, more preferably 0.7 / 1 to 1.3 / 1. If it is within this range, the curing reaction proceeds normally, but if it is less than 0.5 / 1, the curing becomes insufficient, and the mechanical properties and water resistance of the coating film may be lowered. If it exceeds 1.5 / 1, the water resistance of the coating film may be lowered.

In particular, when the acid value of the carboxyl group-containing polyester resin is 10 to 45, the equivalent ratio is preferably 0.9 / 1 to 1.3 / 1. Within this range, the curing reaction proceeds without excess and deficiency, and the mechanical properties and water resistance of the coating film become favorable, which is preferable.

On the other hand, when the carboxyl group-containing polyester resin has an acid value of 45 to 100, which is higher than the acid value employed in ordinary powder coatings, and the low-temperature curability is particularly improved, the equivalent ratio Is preferably 0.7 / 1 to 1.1 / 1. If it is outside this range, the mechanical properties of the coating film and the water resistance may be lowered.

The powder coating material may contain various additives such as a surface conditioner, a plasticizer, an ultraviolet absorber, an antioxidant, an anti-waxing agent, and a charge control agent as necessary.

In particular, as the surface conditioner, from the viewpoint of applicability, (meth) such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, etc. A polymer obtained from an acrylic ester of acrylic acid and having a number average molecular weight of 300 to 50000, preferably 1000 to 30000, and a glass transition temperature of less than 20 ° C., preferably 0 ° C. or less. Is good. When the number average molecular weight is out of the above range, the surface adjustability cannot be sufficiently imparted, and the prevention of appearance defects such as dents becomes insufficient. Moreover, there exists a possibility that surface adjustability cannot fully be provided as glass transition temperature is 20 degreeC or more. The content of the surface conditioner is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and still more preferably 0.1 to 2% by mass in the powder coating particles. It is. If the amount is less than 0.01% by mass, the surface adjustability cannot be sufficiently imparted, and the probability of poor appearance is increased. If the amount exceeds 5% by mass, the blocking property of the paint may be lowered.

Examples of such commercially available surface conditioners include Acronal 4F (manufactured by BASF), Polyflow S (manufactured by Kyoeisha Chemical Co., Ltd.), Regiflow LV (manufactured by ESTRON CHEMICAL), etc. For example, Modaflow III (manufactured by Monsanto), Regisflow P67 (manufactured by ESTRON CHEMICAL), etc. are preferably used. Moreover, you may use the mixture of the acrylic polymer which is a surface adjusting agent, and an epoxy resin so that the usage-amount of an epoxy resin may become in the said range.

The powder coating material may be a pigment not added or a pigment added. The pigment is not particularly limited. For example, titanium dioxide, bengara, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigment, azo pigment and other colored pigments, talc, silica, calcium carbonate, precipitated And extender pigments such as basic barium sulfate.

The powder coating can be manufactured using a manufacturing method well known in the powder coating field. For example, the carboxyl group-containing polyester resin, the polycaprolactone, and the β-hydroxyalkylamide curing agent are essential, and further raw materials such as the acrylic resin, the epoxy resin, the other pigments, and the various additives are prepared. Thereafter, the raw materials are preliminarily mixed using a super mixer, Henschel mixer, or the like, and the raw materials are melt-kneaded using a kneader such as a kneader or an extruder. The heating temperature at this time must of course be lower than the bake hardening temperature, but it must be a temperature at which at least a part of the raw material can be melted and kneaded as a whole. Generally, it is melt-kneaded within a range of 80 to 120 ° C. Next, the melt is solidified by cooling with a cooling roll or a cooling conveyor, and is pulverized to a desired particle size through coarse pulverization and fine pulverization processes.

The volume average particle size of the powder coating particles is preferably 25 to 35 μm. When the thickness is less than 25 μm, there is a problem in the coating workability due to the decrease in fluidity of the powder coating, and when it exceeds 35 μm, a coating film having a high appearance may not be obtained. The volume average particle size can be measured by a particle size measuring device using light scattering such as Microtrac-II manufactured by Reed & Northrop.

The method for applying the powder coating is not particularly limited, and methods well known by those skilled in the art such as spray coating, electrostatic powder coating, and fluidized dipping can be used. From this point, the electrostatic powder coating method is preferably used. Although the coating film thickness at the time of apply | coating the powder coating composition of this invention is not specifically limited, It is preferable that it is 20-300 micrometers, and it is more preferable that it is 50-150 micrometers.

As conditions for baking the powder coating material, the heating temperature is preferably 100 to 230 ° C, more preferably 140 to 200 ° C, and still more preferably 150 to 170 ° C. The heating time can be appropriately set according to the heating temperature. Since the coating method of the present invention can be cured at a relatively low temperature to form a coating film, it is particularly suitable for coating aluminum alloy wheels.

It is preferable that the coating method of the aluminum alloy wheel of the present invention further has a top coating system on the powder coating film formed by the step (2). That is, it is preferable to further have a top coating step after the step (2). The following are mentioned as a 1st aspect of the said top coat process. That is, the step (3) of applying a metal pigment-containing base paint on the powder paint film formed by the step (2), and the metal pigment-containing base coat formed by the step (3) This is a top coating process comprising a step (4) of applying a clear paint on the surface. By having this top coating step, for example, a silver or metallic coating can be obtained.

Examples of the metal pigment that can be used in the metal pigment-containing base paint include flaky pigments such as aluminum flakes; non-colored or colored metallic glitter materials such as metals and alloys. Since it is excellent in dispersibility and can form a highly transparent coating film, a non-colored or colored metal pigment such as a metal or an alloy and a mixture thereof are preferable. Examples of the metal include aluminum oxide, copper, zinc, iron, nickel, and tin.

The shape of the metallic pigment, is not particularly limited average particle diameter and the thickness, for example, an average particle size (D ₅₀₎ is 2 to 50 [mu] m, that the thickness of the scaly is 0.1~5μm is preferred. The thing of the range of the said average particle diameter of 10-35 micrometers is excellent in glitter feeling, and is more preferable.

The total amount of the metal pigment concentration (PWC) relative to the solid content in the metal pigment-containing base coating is preferably 23.0% by mass or less. When it exceeds 23.0% by mass, the appearance of the coating film is deteriorated. More preferably, it is 0.01-20.0 mass%, More preferably, it is 0.01-18.0 mass%. The pigment concentration (PWC) in the base paint including the metal pigment and all other pigments is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass, Preferably it is 1-30 mass%. When it exceeds 50% by mass, the coating film appearance is deteriorated. Moreover, it is preferable that a dry film thickness is 1-50 micrometers.

As said metal pigment containing base coating material, the coating material containing an acrylic resin, a polyester resin, an epoxy resin, a urethane resin etc. can be used, for example. If necessary, it may be used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. The metal pigment-containing base paint can be in any form of water-based paint, solvent paint, and powder paint.

In the first aspect of the top coating step, it is preferable to further include a step (4) of further applying a clear paint on the metal pigment-containing base coating film formed by the step (3). That is, it is more preferable to carry out by two coats and one bake in which a clear coating film is formed by the step (4) on the uncured coating film formed by the step (3) and the two layers are simultaneously cured. A known method may be used for the curing.

The clear coating is not particularly limited, and examples thereof include those composed of a film-forming resin, a curing agent, and other additives. The film-forming resin is not particularly limited, and examples thereof include acrylic resins, polyester resins, epoxy resins, urethane resins, and the like. These are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. . As the clear paint, any form of water-based paint, solvent paint, and powder paint can be used.
In general, the dry film thickness of the clear coating formed by the clear coating is preferably in the range of 15 to 40 μm.

Moreover, the following coating process which has the cutting process for expressing the metallic luster of an aluminum alloy raw material as a 2nd aspect of the said top coat coating process is mentioned. That is, the step (3) of applying the metal pigment-containing base coating on the powder coating film formed by the above step (2), and the partial cutting of the metal pigment-containing base coating formed by the above step (3) Step (X), a step (Y) of subjecting the aluminum alloy material exposed in the step (X) to a non-chromate treatment, and a step of applying a clear paint to the surface of the aluminum alloy material treated in the step (Y) ( 4 ').
In this case, after the step (3), the step (X) of partial cutting is preferably performed after the coating film is cured and formed.

As said metal pigment containing base coating material, the thing similar to what was described in the said 1st aspect can be used.
The said hardening is not specifically limited, A well-known method can be used.
In the partial cutting step (X), in order to make use of the metallic luster of the aluminum alloy and to make it stand out, a part of the design surface of the aluminum alloy wheel (for example, the hatched portion in FIG. 2) is cut and processed. This is a process of exposing the metallic luster of the aluminum alloy material by exposing the material (FIG. 3). Examples of the cutting method include known methods such as bright lathe processing or buffing.
Examples of the non-chromate treatment step (Y) include the same method as the step (1) of treatment with the non-chromate chemical conversion treatment agent.

The step (4 ′) is for forming a clear coating film on the surface of the aluminum alloy material treated in the step (Y).
The clear coating film formed by the step (4 ′) may be one layer or two layers. That is, the clear coating film may be one in which, after forming the first clear coating film, a second clear coating is further applied to form a two-layer clear coating film.
The clear paint in the step (4 ′) is not particularly limited, and examples thereof include the same clear paint as described above. Moreover, the clear paints for forming the two-layer clear coating film may be the same or different.

The dry film thickness of the clear coating film is preferably in the range of 15 to 40 μm in the case of one layer, and is preferably in the range of 30 to 80 μm in the case of two layers.
The two-layer clear coating is formed by curing the first clear coating to form the first clear coating, and then applying the second clear coating to form the second clear coating. Alternatively, after the first clear coating is applied, the second clear coating may be applied, and then the two layers may be simultaneously cured to form a coating film.

Furthermore, as the third aspect of the top coating step, the following coating step, which is a coating system for obtaining a coating film appearance having a metallic luster, can be mentioned.
That is, on the powder coating film formed by the above step (2), the first base coating is further applied and cured by heating to form the first base coating (3-a), the above A step (3-b) of applying a second base paint (brilliant pigment-containing base paint) on the first base paint film; and a clear paint on the second base paint film (brilliant pigment-containing base paint). This is a top coating process comprising a coating process (4 ″).

It does not specifically limit as a 1st base coating material in the said process (3-a), The well-known base coating material which consists of binder resin, a pigment, an additive, and a solvent can be mentioned. As the pigment, a general pigment such as a luster pigment is used in addition to a color pigment and an extender pigment. As the binder resin, additive and solvent, known ones usually used in paints can be used.
As a commercial item which can be used as said 1st base coating material, the acrylic solvent type coating material "Super Lac 5000AS70 base black" by Nippon Paint Co., Ltd. can be mentioned, for example.
As a method for applying the first base paint and a method for heat curing, a known method may be used. Although the thickness of the said 1st base coating film is not specifically limited, Preferably it is 15-50 micrometers.

The second base paint (bright pigment-containing base paint) in the step (3-b) is a paint containing a bright pigment. By combining the second base paint (bright pigment-containing base paint) and the first base paint, it is possible to obtain a coating appearance having a metallic gloss. This second base coating (a glittering pigment-containing base coating) contains a glittering pigment as an essential component and further contains a binder resin, an additive, and a solvent. As the binder resin, additive, and solvent, known ones that are usually used in paints can be used.

The glitter pigment is not particularly limited as long as it is a glitter pigment obtained by pulverizing a deposited metal film into a metal piece. Such a luster pigment is generally obtained by vapor-depositing a metal film on a base film, peeling the base film, and then pulverizing the deposited metal film into a metal piece. The thickness of the deposited metal film, that is, the thickness of the metal piece obtained by pulverization is generally preferably about 100 to 1000 mm. Further, the degree of pulverization is preferably pulverized so that the particle size is about 5 μm to about 100 μm.

The material for the vapor-deposited metal film is not particularly limited, and examples thereof include metal films such as aluminum, gold, silver, copper, brass, titanium, chromium, nickel, nickel chromium, and stainless steel. Among these, an aluminum piece is preferable.
In the second base paint (bright pigment-containing base paint), the pigment mass concentration (PWC) of the bright pigment is preferably 20% or more, more preferably 25% or more.

The second base paint (brilliant pigment-containing base paint) may further contain a phosphate group-containing compound.
The content of the phosphoric acid group-containing compound is preferably 6 to 170 parts by mass (solid content), and 12 to 110 parts by mass (solid content) with respect to 100 parts by mass of the glitter pigment (solid content). It is more preferable.
As the phosphate group-containing compound, it is preferable to use a phosphate ester and a phosphate group-containing acrylic polymer in combination. In this case, the content of the phosphate ester is preferably 1 to 20 parts by mass (solid content) and preferably 2 to 10 parts by mass (solid content) with respect to 100 parts by mass of the luster pigment (solid content). More preferably. Moreover, it is preferable that content of the said phosphoric acid group containing acrylic polymer is 5-150 mass parts (solid content) with respect to 100 mass parts of luster pigments (solid content), and 10-100 mass parts (solid content). ) Is more preferable.

The coating amount of the second base paint (brilliant pigment-containing base paint) is not particularly limited, but it is applied such that the coating amount of the glitter pigment is about 0.1 to 10 g / m ^2. It is preferable.
The thickness of the second base coating film (bright pigment-containing base coating film) is preferably 5 μm or less, and more preferably 2 μm or less.

In the third aspect of the top coating step, a clear coating is applied on the second base coating film (brilliant pigment-containing base coating film) formed by applying in the step (3-b) (step ( 4 '')).
In the said 2nd aspect, the said process (3-b) and the said process (4 '') are the 2nd base coating films (luster pigment containing base coating film) formed at the said process (3-b). It is preferable that the coating is performed by 2-coat 1-bake in which the clear coating film formed in the step (4 ″) is simultaneously cured.
The curing can be performed by a known method.

The clear paint in the step (4 '') is not particularly limited, and examples thereof include the same clear paint as described above.
In general, the dry film thickness of the clear coating formed by the clear coating is preferably in the range of 15 to 40 μm.

In addition, this invention is also an aluminum alloy wheel coated by the said coating method.

According to the present invention, it is possible to obtain an aluminum alloy wheel having excellent chipping resistance, cutting workability, water resistance, corrosion resistance, and adhesion even though the chemical conversion treatment is performed with a non-chromate chemical conversion treatment agent. An aluminum alloy wheel coating method and an aluminum alloy wheel can be provided.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

Surface treatment method for an aluminum alloy wheel After degreasing the aluminum alloy wheel, it is washed with water, pickled, washed with water, chemically treated, washed with water, washed with pure water under the conditions shown below, dried, and then powdered. Painted with body paint. Washing with water was performed with a tap water shower, and washing with pure water was performed with a pure water shower. Each process was processed by the dip method. Drying was performed with an electric dryer at 120 ° C. for 25 minutes. The used processing liquid has the following composition.

(A) Degreasing solution: 2% (w / v) Surf Cleaner 53NF (manufactured by Nippon Paint)
Treatment temperature: 50 ° C. Treatment time: 3 minutes (B) pickling treatment solution: 3% (w / v) Surf Cleaner 355A (manufactured by Nippon Paint _{Co.; FeSO 4 · 7H 2 O 0.81g} / L, 98% sulfuric acid 12.1 g / L, pH 0.9)
Treatment temperature: 40 ° C. Treatment time: 3 minutes (C) Chemical conversion treatment solution: 2.5% (w / v) Alsurf 501N-1 (manufactured by Nippon Paint Co., Ltd .; zirconium phosphate-based treatment agent; (NH ₄ ) ₂ ZrF ₆ 0.12 g / L, 75% H ₃ PO ₄ 0.10 g / L, 55% HF 0.02 g / L, 42% HBF ₄ 0.16 g / L, pH 3.5)
Processing temperature: 40 ° C Processing time: 45 seconds

<Manufacture of powder paint>
Powder coating 1
Fine Dick M8962 (manufactured by Dainippon Ink & Chemicals, Inc., carboxyl group-containing polyester resin, number average molecular weight 3000, mass average molecular weight 8000, acid value 33, softening point 112 ° C.) 100 parts by mass, Primid XL552 (manufactured by EMS-PRIMD) , Β-hydroxyalkylamide curing agent, hydroxyl group equivalent 84) 5 parts by mass, acronal 4F (manufactured by BASF, acrylic polymer, Tg of −55 ° C., solubility parameter SP of 9.3, number average molecular weight of 16500 Surface mixer: 0.5 parts by mass, 1 part by mass of benzoin, 65 parts by mass of TYPEPE CR-90 (Ishihara Sangyo Co., Ltd., rutile titanium dioxide pigment) For about 3 minutes, and at about 110 ° C. using a melt-kneader Kneader (Bus). It was melt-kneaded. Here, Primid XL552 is a substance represented by the following formula.

Thereafter, the obtained melt-kneaded product was cooled to room temperature, and then pulverized using a pulverizer atomizer (Fuji Powdal Co., Ltd.). To obtain a powder coating composition by removing fine particles and coarse particles. The volume average particle diameter was 35 μm. The ratio of the equivalent number of hydroxyl groups of the β-hydroxyalkylamide curing agent to the equivalent number of carboxyl groups of the carboxyl group-containing polyester resin was 1.01 / 1.

Powder paint 2
The powder coating material was prepared in the same manner as the powder coating material 1 except that 5 parts by mass of Epototo YD-014 (Epto resin, epoxy equivalent 950) was used for the composition of the powder coating material 1 described above. A powder coating composition having a volume average particle size of 35 μm was obtained.

Powder coating 3
In addition to the composition of the powder coating 1 described above, 5 parts by weight of Finedic A241 (Dainippon Ink Chemical Co., Ltd., epoxy group-containing vinyl polymer, epoxy equivalent 600, softening point 109 ° C.), Epototo YD-014 ( A powder coating composition was produced in the same manner as the powder coating 1 except that 5 parts by mass of an epoxy resin (epoxy resin, 950) manufactured by Toto Kasei Co., Ltd. was added to obtain a powder coating composition having a volume average particle size of 35 μm. It was.

Powder coating 4
In addition to the composition of the powder coating 1 described above, 5 parts by weight of Finedic A241 (Dainippon Ink Chemical Co., Ltd., epoxy group-containing vinyl polymer, epoxy equivalent 600, softening point 109 ° C.), Epototo YD-014 ( A powder coating material is produced in the same manner as the powder coating material 1 except that 5 parts by mass of epoxy resin, epoxy equivalent 950) manufactured by Toto Kasei Co., Ltd. and 5 parts by mass of Plaxel H5 (manufactured by Daicel Chemical Industries, polycaprolactone) are added. As a result, a powder coating composition having a volume average particle size of 35 μm was obtained.

Powder coating 5
A paint is prepared with the same composition as the powder paint 4, and after pulverization using a pulverizer atomizer (manufactured by Fuji Powder Co., Ltd.) in the pulverization step, the resulting powder is converted into an air classifier DS-2 type (Japan) The powder coating composition was obtained by classifying using a Pneumatic Kogyo Co., Ltd. and removing fine particles and coarse particles. The volume average particle diameter was 27 μm.

Powder coating 6
A paint is prepared with the same composition as the powder paint 4, and pulverized using a pulverizer atomizer (Fuji Paudal), passed through a 100 mesh Tyler standard sieve (pore diameter 150 mm), and a volume average particle diameter of 45 μm. A powder coating composition was obtained.

Powder coating 7-12
Except that the blending amounts of polycaprolactone (flexible component), epoxy resin, epoxy group-containing vinyl polymer (acrylic resin component), and β-hydroxyalkylamide curing agent are as shown in Tables 3 and 4, respectively. A powder coating composition was obtained in the same manner as the powder coating 5.

<Evaluation of cutting workability>
Comparative Example 1
The powder coating 1 was coated on a surface-treated aluminum alloy wheel at an applied voltage of 80 kV using a corona discharge electrostatic powder coating machine (trade name “MXR-100VT-mini” manufactured by Asahi Sunac Corporation). Then, a coating film having a thickness of 100 μm was produced by baking at 160 ° C. for 20 minutes (coating object holding time).
Furthermore, Super Lac AS70 11SV-14 was applied to a dry film thickness of 20 μm, baked at 140 ° C. for 20 minutes to form a base coating film, and then a part of the painted aluminum alloy wheel was cut and processed again. After the non-chromate chemical conversion treatment, Super Lac 5000AC-1 (T) (manufactured by Nippon Paint Co., Ltd.) was applied so that the coating film thickness was 15 μm, and baked at 140 ° C. for 20 minutes. 5000 AW-10 (manufactured by Nippon Paint Co., Ltd.) was applied to a dry film thickness of 30 μm and heated at 140 ° C. for 20 minutes to produce a two-layer clear coating film.

Comparative Examples 2-5 and Examples 1-8
A coating film was formed on the aluminum alloy wheel in the same manner as in Comparative Example 1 except that the powder coating type used and the baking temperature and baking time of the powder coating were as shown in Table 1 or Table 2.

The cutting workability of the coating film obtained above was evaluated.
The cutting workability will be described with reference to the drawings. FIG. 1 is a plan view of the aluminum alloy wheel 1 used above, and FIG. 2 is an AB cross-sectional view of the spoke portion 2 shown in FIG. As shown in FIG. 2, first, after forming the powder coating film 11 and the base coating film 12, these coating films formed on the surface are cut to the cutting surface shown in FIG. At this time, as shown in FIG. 4, when a portion lacking in the coating film occurs, a two-layer clear coating film 13 is formed including that portion as shown in FIG. If this machinability is good, the coating film does not peel off as described above.

In order to confirm the presence or absence of abnormalities such as peeling of the coating film on the vertical and horizontal surfaces when the spokes on the design surface were cut, the state of the coating film in the vicinity of the cutting process was visually observed and evaluated according to the following evaluation criteria. The results are shown in Tables 1 and 2.
○: No abnormality is observed in the coating film near the cutting process ×: Peeling is recognized in the coating film near the cutting process

<Other performance evaluation>
Comparative Examples 6-9
Powder coatings 1 to 3 and powder coating 6 are aluminum alloys that have been surface-treated at an applied voltage of 80 kV using a corona discharge electrostatic powder coating machine (trade name “MXR-100VT-mini” manufactured by Asahi Sunac Corporation). Painted on the wheel. Then, a coating film having a thickness of 100 μm was produced by baking at 160 ° C. for 20 minutes (coating object holding time). Superlac AS70 11SV-14 (acrylic solvent-type paint, manufactured by Nippon Paint Co., Ltd.) was applied to the obtained coating film to a dry film thickness of 20 μm, set for 10 minutes, and then Superlac as a low solid solvent clear paint. 5000 AW-10 (acrylic solvent-based paint, manufactured by Nippon Paint Co., Ltd.), coated in one stage so as to have a dry film thickness of 40 μm, set for 7 minutes, and then heated at 140 ° C. for 20 minutes to produce a multilayer coating film .

Comparative Example 10
An attempt was made to form a coating film using the powder coating material 10 in the same manner as in Comparative Example 6, but the fluidity of the powder coating material was lowered and could not be applied.

Examples 9, 10
The powder coatings 4 and 5 were coated on a surface-treated aluminum alloy wheel at an applied voltage of 80 kV using a corona discharge electrostatic powder coating machine (trade name “MXR-100VT-mini” manufactured by Asahi Sunac Corporation). Then, a coating film having a thickness of 100 μm was produced by baking at 160 ° C. for 20 minutes (coating object holding time). Superlac AS70 11SV-14 (acrylic solvent-type paint, manufactured by Nippon Paint Co., Ltd.) was applied to the obtained coating film to a dry film thickness of 20 μm, set for 10 minutes, and then Superlac as a low solid solvent clear paint. 5000 AW-10 (acrylic solvent-based paint, manufactured by Nippon Paint Co., Ltd.), coated in one stage so as to have a dry film thickness of 40 μm, set for 7 minutes, and then heated at 140 ° C. for 20 minutes to produce a multilayer coating film .

Example 11
A multilayer coating film was formed using the powder coating material 5 in the same manner as in Example 10 except that the powder coating material was baked at 150 ° C. for 40 minutes.
Examples 12-14
A multilayer coating film was formed in the same manner as in Example 10 except that the powder coating materials 7 to 9 were used.
Examples 15 and 16
Using the powder coating materials 11 and 12, a multilayer coating film was formed in the same manner as in Example 10 except that the powder coating material was baked at 180 ° C. for 20 minutes.

<Performance evaluation method>
The performance evaluations were performed by using a surface-treated aluminum alloy wheel that was coated on a surface-treated aluminum alloy wheel and cut into an appropriate size. The appearance was evaluated using the painted wheels themselves. The obtained results are shown in Tables 3 and 4.

Adhesion test Adhesion test Each test piece is coated with 10 cuts in vertical and horizontal directions at intervals of 2 mm using a cutter. The remaining square eyes were counted (cross-cut test).

Water resistance test Hot water immersion test Each test piece was immersed in warm water at 60C for 72 hours, then left for 24 hours, and then subjected to the same cross-cut test as the adhesion test.

Corrosion resistance test Salt spray test The surface of each test piece is cross-cut with a cutter knife, sprayed with salt water at 35 ° C for 1200 hours using a 5 mass% NaCl aqueous solution, left for 24 hours, and around the cut part The degree of corrosion within 2 mm was measured.
○: No abnormalities such as blistering and rust of the coating film.
Δ: blistering or rusting occurs within 2 mm.
X: Blistering or rusting exceeds 2 mm.

Chipping resistance test Each specimen obtained was cooled to -30 [deg.] C., and then attached to a sample holder of a stepping stone testing machine (manufactured by Suga Test Instruments Co., Ltd.) so that the stone penetration angle was 90 [deg.]. 100 g of No. 7 crushed stone was sprayed at an air pressure of 3 kg / cm ² , and the crushed stone collided with the coating film of the test piece. The degree (number, size, location of destruction) of the scratches at that time was evaluated on a five-point scale.
1: Large peeling scratches on the entire surface, peeling from the substrate 2: Some peeling scratches on the entire surface, peeling from the substrate 3: Some peeling scratches on the entire surface, no peeling from the substrate 4: Partial peeling scratches on the substrate , No peeling from substrate 5: Almost no destruction

Appearance evaluation The finished appearance and smoothness of the coating film were evaluated according to the following criteria.
○: Good, △: Somewhat bad, ×: Bad

From Tables 1-4, the aluminum alloy wheel obtained by the coating method of the aluminum alloy wheel of the present invention has a particle size as long as the flexible component does not exceed 20 parts by mass with respect to 100 parts by mass of the carboxyl group-containing polyester. As long as the predetermined range was not exceeded, the appearance, various performances, and cutting workability were all excellent.

Since the coating method of the aluminum alloy wheel and the coated aluminum alloy wheel of the present invention are as described above, sufficient chipping resistance can be obtained after performing the chemical conversion treatment by the non-chromate chemical conversion treatment in accordance with the purpose of environmental conservation. In addition, an aluminum alloy wheel having excellent cutting workability after painting and baking can be provided.

1 is a plan view of an aluminum alloy wheel 1. FIG. It is AB sectional drawing in the spoke part 2 of FIG. It is drawing for demonstrating evaluation of cutting workability. It is drawing for demonstrating evaluation of cutting workability. It is drawing for demonstrating evaluation of cutting workability.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum alloy wheel 2, 2A, 2B, 2C Spoke part 10 Aluminum alloy raw material 11 Powder coating film 12 Base coating film 13 Two clear coating films

Claims (12)

An aluminum alloy wheel comprising: a step (1) of treating the surface of the aluminum alloy wheel with a non-chromate chemical conversion treatment agent; and a step (2) of applying and baking a powder coating on the surface treated by the step (1). Painting method,
The powder coating material includes a carboxyl group-containing polyester resin, polycaprolactone, and the following general formula (1):

(Wherein R ¹ represents a hydrogen atom, a methyl group or an ethyl group, R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or HOCH (R ¹ ) CH ₂ —, and A represents a divalent group. Represents a hydrocarbon group.)
A coating method for an aluminum alloy wheel, characterized by comprising powder coating particles containing a β-hydroxyalkylamide curing agent represented by the formula: The method for coating an aluminum alloy wheel according to claim 1, wherein the powder coating particles further contain an acrylic resin and / or an epoxy resin. The aluminum alloy wheel coating method according to claim 1 or 2, wherein the content of polycaprolactone is 1 to 20 parts by mass with respect to 100 parts by mass of the carboxyl group-containing polyester resin. In the powder coating particle, the ratio (number of hydroxyl group equivalents / number of carboxyl group equivalents) of the hydroxyl group equivalent number of the β-hydroxyalkylamide curing agent to the carboxyl group equivalent number of the carboxyl group-containing polyester resin is 0.5 / 1 to 1. The method for coating an aluminum alloy wheel according to claim 1, 2 or 3, which is 1.5 / 1. The method for coating an aluminum alloy wheel according to claim 1, further comprising a top coating step after the step (2). The top coating step includes a step (3) of applying a metal pigment-containing base coating on the powder coating film formed in step (2), and a metal pigment-containing base coating formed in the step (3). 6. The method for coating an aluminum alloy wheel according to claim 5, comprising a step (4) of applying a clear paint on the film. The top coating step includes a step (3) of applying a metal pigment-containing base coating on the powder coating film formed in step (2), and a step of applying the metal pigment-containing base coating formed in step (3). A step (X) of partially cutting, a step (Y) of non-chromate treatment of the aluminum alloy material exposed in the step (X), and a clear paint is applied to the surface of the aluminum alloy material treated in the step (Y). The method for coating an aluminum alloy wheel according to claim 5, comprising the step (4 ′). The top coating step is a step (3-a) in which a first base coating is further applied on the powder coating film formed in the step (2) and then heat-cured to form a first base coating. Applying a second base coating (bright pigment-containing base coating) on the first base coating (3-b); and clearing on the second base coating (bright pigment-containing base coating). The method for coating an aluminum alloy wheel according to claim 5, comprising a step (4 '') of applying a paint. The method for coating an aluminum alloy wheel according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the heating temperature of the powder coating in step (2) is 150 to 170 ° C. The method for coating an aluminum alloy wheel according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the powder coating particles have a volume average particle diameter of 25 to 35 µm. The method for coating an aluminum alloy wheel according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein the non-chromate chemical conversion treatment agent is a zirconium treatment agent and / or a titanium treatment agent. An aluminum alloy wheel, which is coated by the method for coating an aluminum alloy wheel according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11.

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