Primer coating composition for aluminum wheels

Abstract

An object of the present invention is to find a primer coating composition for aluminum wheels, the composition having excellent stability and being capable of forming a coating film having excellent corrosion resistance, edge corrosion resistance, and filiform corrosion resistance. The invention provides (1) a primer coating composition for aluminum wheels comprising a copolymer resin (A), and 1 to 30 parts by mass of fumed silica (B) and 0.1 to 10 parts by mass of a magnesium-containing phosphoric acid-based compound (C), per 100 parts by mass of the total solids content of the copolymer resin (A). The invention also provides (2) the primer coating composition for aluminum wheels according to Item (1), further comprising 0.1 to 10 parts by mass of metal-ion exchanged silica (D), per 100 parts by mass of the total solids content of the copolymer resin (A).

Claims

1. A primer coating composition for aluminum wheels, the composition comprising: a copolymer resin (A) obtained by reacting a mixture containing a nitrogen-containing radical polymerizable unsaturated monomer (a1) represented by Formula (1) below in an amount of 5 to 35 mass %, a carboxyl-containing radical polymerizable unsaturated monomer (a2) in an amount of 1 to 10 mass %, and a radical polymerizable unsaturated monomer (a3) other than (a1) and (a2) in an amount of 55 to 94 mass %, relative to the sum of the constituting monomers, and 15 to 25 parts by mass of fumed silica (B) and 0.3 to 3 parts by mass of a magnesium-containing phosphoric acid-based compound (C), per 100 parts by mass of the total solids content of the copolymer resin (A), ##STR00004## wherein R.sup.1 represents a hydrogen atom or CH.sub.3, and R.sup.2 represents a hydrogen atom or a C.sub.1-6 alkyl group, and the magnesium-containing phosphoric acid-based compound (C) is at least one member selected from the group consisting of magnesium phosphate, magnesium tripolyphosphate, magnesium dihydrogen phosphate, and aluminum dihydrogen tripolyphosphate treated with magnesium oxide.

2. The primer coating composition for aluminum wheels according to claim 1, further comprising 0.1 to 10 parts by mass of metal-ion exchanged silica (D), per 100 parts by mass of the total solids content of the copolymer resin (A).

3. The primer coating composition for aluminum wheels according to claim 1, further comprising 1 to 20 parts by mass of an epoxy compound (E), per 100 parts by mass of the total solids content of the copolymer resin (A).

4. The primer coating composition for aluminum wheels according to claim 1, further comprising 1 to 20 parts by mass of a silane coupling agent (F), per 100 parts by mass of the total solids content of the copolymer resin (A).

5. The primer coating composition for aluminum wheels according to claim 1, further comprising 1 to 30 parts by mass of a dehydrating agent (G), per 100 parts by mass of the total solids content of the copolymer resin (A).

6. A method for forming a coating film, the method comprising: forming an uncured or cured coating film of the primer coating composition for aluminum wheels of claim 1 on an aluminum wheel whose surface is optionally treated; and forming at least one overcoating film on the uncured or cured coating film.

7. The primer coating composition for aluminum wheels according to claim 2, further comprising 1 to 20 parts by mass of an epoxy compound (E), per 100 parts by mass of the total solids content of the copolymer resin (A).

8. The primer coating composition for aluminum wheels according to claim 2, further comprising 1 to 20 parts by mass of a silane coupling agent (F), per 100 parts by mass of the total solids content of the copolymer resin (A).

9. The primer coating composition for aluminum wheels according to claim 3, further comprising 1 to 20 parts by mass of a silane coupling agent (F), per 100 parts by mass of the total solids content of the copolymer resin (A).

10. The primer coating composition for aluminum wheels according to claim 2, further comprising 1 to 30 parts by mass of a dehydrating agent (G), per 100 parts by mass of the total solids content of the copolymer resin (A).

11. The primer coating composition for aluminum wheels according to claim 3, further comprising 1 to 30 parts by mass of a dehydrating agent (G), per 100 parts by mass of the total solids content of the copolymer resin (A).

12. The primer coating composition for aluminum wheels according to claim 4, further comprising 1 to 30 parts by mass of a dehydrating agent (G), per 100 parts by mass of the total solids content of the copolymer resin (A).

13. A method for forming a coating film, the method comprising: forming an uncured or cured coating film of the primer coating composition for aluminum wheels of claim 2 on an aluminum wheel whose surface is optionally treated; and forming at least one overcoating film on the uncured or cured coating film.

14. A method for forming a coating film, the method comprising: forming an uncured or cured coating film of the primer coating composition for aluminum wheels of claim 3 on an aluminum wheel whose surface is optionally treated; and forming at least one overcoating film on the uncured or cured coating film.

15. A method for forming a coating film, the method comprising: forming an uncured or cured coating film of the primer coating composition for aluminum wheels of claim 4 on an aluminum wheel whose surface is optionally treated; and forming at least one overcoating film on the uncured or cured coating film.

16. A method for forming a coating film, the method comprising: forming an uncured or cured coating film of the primer coating composition for aluminum wheels of claim 5 on an aluminum wheel whose surface is optionally treated; and forming at least one overcoating film on the uncured or cured coating film.

17. The primer coating composition for aluminum wheels according to claim 1, wherein the maximum width of rust or blistering from the cut portion is less than 3 mm (on one side) when an aluminum wheel is treated with the primer coating composition, a cut is made in the surface of the coated aluminum wheel, a salt spray test is performed for 24 hours in accordance with JIS Z 2371, and wet conditions (humidity 85%, 40 C.) are maintained for 480 hours.

Description

EXAMPLES

(1) The present invention is described in further detail below with reference to Production Examples, Examples, and Comparative Examples. However, the scope of the present invention is not limited to these Examples.

Production Example 1

Production of Copolymer Resin No. 1 Solution

(2) 30.0 parts of a mixed solvent (xylene/n-butyl alcohol=80/20) was placed into a reaction vessel and maintained at 30 C. The mixture shown below was added thereto dropwise over a period of 4 hours. Subsequently, 0.5 parts of azobismethylvaleronitrile was added, and the resulting mixture was maintained at 80 C. for 3 hours to allow the reaction to occur. Then, a mixed solvent (xylene/n-butyl alcohol=80/20) was further added to produce a copolymer resin No. 1 solution having a solids content of 60 mass %.

(3) The copolymer resin No. 1 had a glass transition temperature (see Note 1) of 11.3 C., an acid value of 15.6 mgKOH/g, and a weight average molecular weight of 60,000.

(4) Mixture

(5) N-Butoxymethylacrylamide: 20 parts Acrylic acid: 2 parts Styrene: 30 parts Ethyl acrylate: 48 parts Azobismethylvaleronitrile: 5 parts

Production Examples 2 to 7

Comparative Production Examples 1 to 6

Production of Copolymer Resin No. 2 to No. 13 Solutions

(6) Copolymer resin No. 2 to No. 13 solutions were obtained as in Production Example 1, except that the formulations shown in Table 1 were used.

(7) TABLE-US-00001 TABLE 1 Production Production Production Production Production Production Production Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Copolymer resin No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 Mixture (a1) N-butoxymethylacrylamide 20 20 10 30 20 20 20 (a2) Acrylic acid 2 2 2 8 2 2 2 (a3) Styrene 30 30 30 16 30 25 Methyl methacrylate 10 15 10 40 Ethyl acrylate 48 15 10 16 10 46 35 n-Butyl acrylate 23 33 20 28 5 2-Hydroxyethyl methacrylate 2 13 Polymerization Azobismethylvaleronitrile 5 5 5 5 5 5 5 initiator Features Glass transition 11.3 12.1 10.8 10.8 10.8 12.9 13.9 temperature (see Note 1) Acid value (mgKOH/g) 15.6 15.6 15.6 62.3 15.6 15.6 15.6 Hydroxyl value (mgKOH/g) 0 0 0 0 0 9 56 Weight average 60,000 60,000 55,000 60,000 60,000 60,000 60,000 molecular weight Comp. Comp. Comp. Comp. Comp. Comp. Production Production Production Production Production Production Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Copolymer resin No. 8 No. 9 No. 10 No. 11 No. 12 No. 13 Mixture (a1) N-butoxymethylacrylamide 4 38 20 20 4 38 (a2) Acrylic acid 2 12 0.5 11 2 12 (a3) Styrene 30 20 30 4 30 20 Methyl methacrylate 10 10 12 Ethyl acrylate 33 10 15.5 47 30 0 n-Butyl acrylate 21 20 24 18 20 17 2-Hydroxyethyl methacrylate 2 13 Polymerization Azobismethylvaleronitrile 5 4.5 5 5 5 4.5 initiator Features Glass transition 8.5 7.9 10 12.6 12.7 19.6 temperature (see Note 1) Acid value (mgKOH/g) 15.6 93.4 3.9 85.6 15.6 93.4 Hydroxyl value (mgKOH/g) 0 0 0 0 8.6 56 Weight average 60,000 70,000 60,000 60,000 60,000 70,000 molecular weight

Production Example 6

Production Example of Magnesium-Ion Exchanged Silica

(8) 10 parts by mass of Sylysia 710 (produced by Fuji Silysia Chemical Ltd., trade name, silica particles, oil absorption: about 105 mL/100 g) was mixed and stirred, with 10,000 parts by mass of 5 mass % magnesium chloride aqueous solution for 5 hours. Thereafter, the solids content was collected by filtration, thoroughly washed with water, and dried to obtain magnesium-ion exchanged silica.

Production Example 7

Production Example of Phosphoric Acid-Modified Epoxy Resin Solution

(9) 280 parts of butyl glycidyl ether was added to 115 parts of 85% phosphoric acid, and reacted at 50 to 60 C. for 3 hours to obtain a phosphate ester compound.

(10) Subsequently, 190 parts of Adeka Resin EP-4100 (produced by Asahi Denka Kogyo K.K., trade name, bisphenol A epoxy resin, epoxy equivalent: 190), 58 parts of bisphenol A, and 1 part of dimethylbenzylamine were mixed, and the resulting mixture was reacted at 150 C. for 8 hours to obtain an epoxy compound having an epoxy equivalent of 500.

(11) 115 parts of xylene and 20 parts of the phosphate ester compound obtained above were added to 248 parts of the epoxy compound obtained above and reacted at 80 C. for 5 hours. Thereafter, the xylene was allowed to flow out of the reaction tank, followed by cooling to obtain a phosphoric acid-modified epoxy resin solution. The phosphoric acid-modified epoxy resin had a weight average molecular weight of 926.

Production Example 6

Production of Hydroxyl-Containing Acrylic Resin A Solution

(12) 30.0 parts of a mixed solvent (xylene/butyl acetate=80/20) was placed into a reaction vessel and maintained at 80 C. The mixture shown below was added thereto dropwise over a period of 4 hours. Subsequently, 0.5 parts of azobismethylvaleronitrile was added, and the resulting mixture was maintained at 80 C. for 3 hours to allow the reaction to occur. Then, a mixed solvent (xylene/butyl acetate=80/20) was further added to produce a hydroxyl-containing acrylic resin A solution having a solids content of 60 mass %.

(13) The hydroxyl-containing acrylic resin A had a glass transition temperature (see Note 1) of 38.2 C., an acid value of 15.0 mgKOH/g, a hydroxyl value of 103.5 mgKOH/g, and a weight average molecular weight of 15,000.

Mixture

(14) Acrylic acid: 2 parts Styrene: 30 parts Methyl methacrylate: 20 parts N-Butyl acrylate: 20 parts 2-Hydroxyethyl methacrylate: 24 parts Azobismethylvaleronitrile: 7 parts

Production Example 9

Production of Hydroxyl-Containing Acrylic Resin B Solution

(15) 30.0 parts of a mixed solvent (xylene/butyl acetate=80/20) was placed into a reaction vessel and maintained at 80 C. The mixture shown below was added thereto dropwise over a period of 4 hours. Subsequently, 0.5 parts of azobismethylvaleronitrile was added, and the resulting mixture was maintained at 80 C. for 3 hours to allow the reaction to occur. Then, a mixed solvent (xylene/butyl acetate=80/20) was further added to produce a hydroxyl-containing acrylic resin B solution having a solids content of 60 mass %.

(16) The hydroxyl-containing acrylic resin B had a glass transition temperature (see Note 1) of 28.7 C., an acid value of 15.6 mgKOH/g, a hydroxyl value of 301.3 mgKOH/g, and a weight average molecular weight of 15,000.

Mixture

(17) Acrylic acid: 2 parts Styrene: 8 parts N-butyl acrylate: 20 parts 2-hydroxyethyl methacrylate: 10 parts Azobismethylvaleronitrile: 7 parts

Production Example of Primer Coating Composition

Example 1

Production Example of Primer Coating Composition No. 1 Solution

(18) A mixed solvent (xylene/butyl acetate=50/50) was added to a mixture of 100 parts (solids content) of the copolymer resin No. 1 solution obtained in Production Example 1, 20 parts of Aerosil 380PE (Note 3), and 1.0 part of K-White G105 (Note 5). The resulting mixture was stirred with a stirrer (a stirring blade with a diameter of 7 cm, 700 rpm) for 1 hour to obtain a primer coating composition No. 1 having a solids content of 50 mass %.

Examples 2 to 23

Production Examples of Primer Coating Compositions No. 2 to No. 23

(19) Primer coating compositions No. 2 to No. 23 were obtained as in Example 1, except that the formulations shown in Table 2 were used.

(20) TABLE-US-00002 TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Primer coating composition No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 Formula- Copolymer (A) Copolymer resin No. 1 100 100 100 100 100 100 100 100 tion Copolymer resin No. 2 Copolymer resin No. 3 Copolymer resin No. 4 Copolymer resin No. 5 Copolymer resin No. 6 Copolymer resin No. 7 Fumed silica (B) Aerosil 380PE (Note 3) 20 20 20 20 20 20 20 Aerosil 130 (Note 4) 20 Magnesium- K-White G105 (Note 5) 25 25 25 25 containing LF Bousei CRF-15 (Note 6) 25 25 25 25 phosphoric acid-based compound (C) K-White 140E (Note 7) Metal-ion Magnesium-ion exchanged silica 25 25 exchanged obtained in Production Ex. 6 silica (D) Sylomask 52M (Note 8) 25 ShieldEx C303 (Note 9) 25 25 Epoxy resin (E) jER 1001 (Note 10) Phosphoric acid-modified epoxy resin obtained in Production Ex. 7 Silane coupling KBM-403 (Note 11) agent (F) Dehydrating agent (G) Orthomethyl acetate Other resins Hydroxyl-containing acrylic resin (A) Hydroxyl-containing acrylic resin (B) Properties Glass transtion temperature 65 65 65 62 61 63 65 64 (Coating film Tg)(Note 12) Corrosion resistance (Note 13) A A A S S S S S Edge corrosion resistance (Note 14) A A A A A A A A Fitform corrosion resistance A A A A A A A A (Note 15) Coating Composition Stability A A A A A A A A (Note 16) Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Primer coating composition No. 9 No. 10 No. 11 No. 12 No. 13 No. 14 No. 15 No. 16 Formula- Copolymer (A) Copolymer resin No. 1 100 100 100 100 100 100 50 tion Copolymer resin No. 2 100 Copolymer resin No. 3 50 Copolymer resin No. 4 Copolymer resin No. 5 Copolymer resin No. 6 Copolymer resin No. 7 Fumed silica (B) Aerosil 380PE (Note 3) 20 20 20 20 20 20 20 20 Aerosil 130 (Note 4) Magnesium- K-White G105 (Note 5) 25 25 25 25 25 25 25 25 containing phosphoric LF Bousei CRF-15 (Note 6) acid-based compound (C) K-White 140E (Note 7) Metal-ion Magnesium-ion exchanged silica 25 25 25 25 25 exchanged obtained in Production Ex. 6 silica (D) Sylomask 52M (Note 8) ShieldEx C303 (Note 9) 25 25 25 Epoxy resin (E) jER 1001 (Note 10) 100 100 Phosphoric acid-modified epoxy 80 10.0 12.0 100 100 100 resin obtained in Production Ex. 7 Silane coupling KBM-403 (Note 11) 100 100 100 100 agent (F) Dehydrating agent (G) Orthomethyl acetate 200 200 200 Other resins Hydroxyl-containing acrylic resin (A) Hydroxyl-containing acrylic resin (B) Properties Glass transtion temperature 64 68 68 68 70 70 67 64 (Coating film Tg)(Note 12) Corrosion resistance (Note 13) S S S S S S S S Edge corrosion resistance (Note 14) S S S S S S S S Fitform corrosion resistance A S A A A S S S (Note 15) Coating Composition Stability A A A A A A A A (Note 16) Ex. 17 Ex. 18 Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Primer coating composition No. 17 No. 18 No. 19 No. 20 No. 21 No. 22 No. 23 Formula- Copolymer (A) Copolymer resin No. 1 100 100 tion Copolymer resin No. 2 Copolymer resin No. 3 100 Copolymer resin No. 4 100 Copolymer resin No. 5 100 Copolymer resin No. 6 100 Copolymer resin No. 7 100 Fumed silica (B) Aerosil 380PE (Note 3) 20 20 20 20 20 20 20 Aerosil 130 (Note 4) Magnesium- K-White G105 (Note 5) 25 25 25 25 25 25 25 containing LF Bousei CRF-15 (Note 6) phosphoric acid-based compound (C) K-White 140E (Note 7) Metal-ion Magnesium-ion exchanged silica exchanged obtained in Production Ex. 6 silica (D) Sylomask 52M (Note 8) ShieldEx C303 (Note 9) 25 25 25 25 25 25 25 Epoxy resin (E) jER 1001 (Note 10) Phosphoric acid-modified epoxy 100 100 100 100 100 100 100 resin obtained in Production Ex. 7 Silane coupling KBM-403 (Note 11) 100 100 100 100 100 100 100 agent (F) Dehydrating agent (G) Orthomethyl acetate 200 200 200 200 200 200 200 Other resins Hydroxyl-containing acrylic resin (A) 100 Hydroxyl-containing acrylic resin (B) 100 Properties Glass transtion temperature 63 62 64 65 62 64 63 (Coating film Tg)(Note 12) Corrosion resistance (Note 13) S S S S S S S Edge corrosion resistance (Note 14) S S S S S S S Fitform corrosion resistance S S S S S S S (Note 15) Coating Composition Stability A A A A S S A (Note 16) The values in the formulation are solids content.
(Note 3) Aerosil 380PE: produced by Nippon Aerosil Co., Ltd., trade name, the fumed silica (B), specific surface area: 380 m.sup.2/g
(Note 4) Aerosil 130: produced by Nippon Aerosil Co., Ltd., trade name, the fumed silica (B), specific surface area: 130 m.sup.2/g
(Note 5) K-White G105: produced by Tayca Corporation, trade name, the magnesium-containing phosphoric acid-based compound (C) (magnesium oxide-treated aluminum dihydrogen tripolyphosphate)
(Note 6) LF Bousei CRF-15: produced by Kikuchi Color & Chemicals Corporation, trade name, the magnesium-containing phosphoric acid-based compound (C)
(Note 7) K-White 140E: produced by Tayca Corporation, trade name, aluminum dihydrogen tripolyphosphate
(Note 8) Sylomask 52M: produced by Fuji Silysia Chemical Ltd., trade name, the magnesium-ion exchanged silica (D) (average particle diameter: 2.30 to 3.30 m)
(Note 9) Shieldex C303: produced by W.R. Grace & Co., trade name, the calcium-ion exchanged silica (D) (average particle diameter: 3 m)
(Note 10) jER1001: produced by Mitsubishi Chemical Corporation, trade name, an epoxy resin, epoxy equivalent: 475, epoxy compound (E) (corresponds to the epoxy resin represented by Formula (2) above)
(Note 11) KBM-403; produced by Shin-Etsu Chemical Co., Ltd., trade name, silane coupling agent (F) (3-glycidoxypropyltrimethoxysilane)

Comparative Examples 1 to 14

Production of Primer Coating Compositions No. 24 to No. 37

(21) Primer coating compositions No. 24 to No. 37 were obtained as in Example 1, except that the formulations shown in Table 3 were used.

(22) TABLE-US-00003 TABLE 3 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Primer coating composition No. 24 No. 25 No. 26 No. 27 No. 28 No. 39 No. 30 Formulation Copolymer (A) Copolymer resin No. 1 100 100 100 100 100 100 Copolymer resin No. 8 100 Copolymer resin No. 9 Copolymer resin No. 10 Copolymer resin No. 11 Copolymer resin No. 12 Copolymer resin No. 13 Fumed silica (B) Aerosil 380OPE (Note 3) 20 20 20 20 20 20 Aerosil 130 (Note 4) Magnsium-containing K-White G105 (Note 5) 25 25 phosphoric acid-based LF Bousei CRF-15 (Note 6) compound (C) K-White 140E (Note 7) 25 Metal-ion exchanged Magnesium-ion exchanged silica 25 25 25 25 silica (D) obtained in Production Ex. 6 Sylomask 52M (Note 8) ShieldEx C303 (Note 9) 25 Epoxy resin (E) jER 1001 (Note 10) 100 100 100 100 Phosphoric acid-modified epoxy resin obtained in Production Ex. 7 Silane coupling KBM-403 (Note 11) 100 100 100 agent (F) Other resins Hydroxyl-containing acrylic resin (A) Hydrocyl-containing acrylic resin (B) Properties Glass transition temperature 69 66 63 69 66 64 52 (Coating film Tg)(Note 12) Corrosion resistance (Note 13) B B B A A A B Edge corrosion resistance (Note 14) C B B B B B B Fitform corrosion resistance (Note 15) B B B B B B B Coating composition stability (Note 16) A A A A A A A Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Primer coating composition No. 31 No. 32 No. 33 No. 34 No. 35 No. 36 No. 37 Formulation Copolymer (A) Copolymer resin No. 1 100 100 Copolymer resin No. 8 Copolymer resin No. 9 100 Copolymer resin No. 10 100 Copolymer resin No. 11 100 Copolymer resin No. 12 100 Copolymer resin No. 13 100 Fumed silica (B) Aerosil 380OPE (Note 3) 20 20 20 20 20 Aerosil 130 (Note 4) Magnsium-containing K-White G105 (Note 5) 25 25 25 25 25 25 25 phosphoric acid-based LF Bousei CRF-15 (Note 6) compound (C) K-White 140E (Note 7) Metal-ion exchanged Magnesium-ion exchanged silica 25 25 silica (D) obtained in Production Ex. 6 Sylomask 52M (Note 8) ShieldEx C303 (Note 9) 25 25 25 25 25 Epoxy resin (E) jER 1001 (Note 10) 100 100 Phosphoric acid-modified epoxy resin obtained in Production Ex. 7 Silane coupling KBM-403 (Note 11) 100 100 agent (F) Other resins Hydroxyl-containing acrylic resin (A) 100 Hydrocyl-containing acrylic resin (B) 100 Properties Glass transition temperature 71 90 35 30 76 69 69 (Coating film Tg)(Note 12) Corrosion resistance (Note 13) A A C B A B B Edge corrosion resistance (Note 14) B B B B B C C Fitform corrosion resistance (Note 15) B B B B B B B Coating composition stability (Note 16) A A B A A S A The values in the formulation are solids content.
(Note 12) Glass transition temperature (coating film Tg): Each primer coating composition was applied to a tin plate by spraying to a dry film thickness of 25 m, followed by baking at a substrate surface temperature of 140 C. for 20 minutes. The coating film was peeled off from the tin plate, and formed into strips (0.5 cm2 cm) to obtain a sample, and a measurement was performed using a dynamic viscoelasticity measuring device (FT Rheospectra DVE-V4, produced by Rheology K.K., trade name) under the conditions of a heating rate of 3 C./minute, a temperature range of 20 to 200 C., and a frequency of 110 Hz.

Preparation of Coated Aluminum Wheel Product

(23) Each primer coating composition was applied, to a non-chromium chemical conversion-treated aluminum wheel by spraying to a dry film thickness of 25 m, followed by setting at ordinary temperature for 5 minutes. Magicron EN-2 Clear (produced by Kansai Paint Co., Ltd., trade name, acrylic resin organic solvent-based clear coating composition) was then applied thereto to a dry film thickness of 25 m. Subsequently, heating was performed at 140 C. for 20 minutes to obtain a coated aluminum wheel product for the test.

(24) (Note 13) Corrosion resistance: a 10-cm cut was made using a cutter knife in the surface of the coating film of each coated aluminum wheel product to obtain samples, and a prepared CASS test solution at 502 C. was sprayed onto the samples for 120 hours, based on JIS Z 2371 (2000). The samples were left to stand for 24 hours, and the degree of corrosion around the cut portion was evaluated:
S: No defects such as blistering or rusting were observed in the coating film
A: Blistering or rusting of less than 1 mm from the cut portion was observed
B: Blistering or rusting of 1 mm or more and less than 2 mm from the cut portion was observed
C: Blistering or rusting of more than 2 mm from the cut portion was observed
(Note 14) Edge corrosion resistance: The coated aluminum wheel products were subjected to a salt spray test in accordance with JIS Z-2371, and rusting at the edge portion of the aluminum wheel products was evaluated according to the following criteria:
S: the number of rust occurrences: 0 on the entire aluminum wheel
A: the number of rust occurrences: 1 to 3 on the entire aluminum wheel
B: the number of rust occurrences: 4 to 10 on the entire aluminum wheel
C: the number of rust occurrences: 11 or more on the entire aluminum wheel
(Note 15) Filiform corrosion resistance: A cut was made in the surface of the coated aluminum wheel products, and a salt spray test was performed for 24 hours in accordance with JIS Z 2372. Thereafter, wet conditions (humidity 85%, 40 C.) were maintained for 480 hours, and the width of rust was measured from the cut portion. The width of rust or blistering from the cut portion was evaluated according to the following criteria:
S: the maximum width of rust or blistering from the cut portion was less than 2 mm (on one side)
A: the maximum width of rust or blistering from the cut portion was 2 mm or more and less than 3 mm (on one side) B; the maximum width of rust or blistering from the cut portion was 3 mm or more and less than 4 mm (on one side)
C: the maximum width of rust or blistering from the cut portion was 4 mm or more (on one side)
(Note 16) Coating composition stability: Each primer coating composition was sealed in a container and stored at 35 C. for 35 days. The state of each coating composition after storage was evaluated according to the following criteria:
S: Excellent, showing no change from that before storage
A: A small increase in viscosity, but stirring for about 1 minute brought it back to the original state
B: An increase in the viscosity or layer separation was observed
C: Layer separation was observed

INDUSTRIAL APPLICABILITY

(25) An aluminum wheel having excellent corrosion resistance, edge corrosion resistance, and filiform corrosion resistance can be provided.