JP4748720B2 - Multi-layer coating formation method - Google Patents

Description

  The present invention relates to a method for forming a multilayer film of aluminum or aluminum alloy which is excellent in weather resistance and whiteness, and further excellent in adhesion and dice mark concealment.

  Conventionally, in aluminum or an aluminum alloy, various surface treatments are applied depending on the application. For example, in the case of aluminum or an aluminum alloy used for housing building materials, an anodized film is formed on the surface of the surface by anodizing, and after washing with hot water, anion electrodeposition is performed. Electrodeposition coating using paint is performed.

  As a result, a composite film of an anodic oxide film and an electrodeposition coating film is formed on the surface of aluminum or an aluminum alloy, and a film excellent in weather resistance, design and adhesion can be obtained. As a recent trend in design, a coating film with higher whiteness is required. Therefore, for example, increasing the pigment concentration of the white pigment in the anion electrodeposition paint decreases the weather resistance, while reducing the pigment concentration to ensure the weather resistance results in insufficient design and dice mark concealment. there were.

Conventionally, a surface treatment method for an aluminum material characterized in that anodized aluminum or an aluminum alloy is immersed in a phosphoric acid aqueous solution or a sulfuric acid aqueous solution, washed with water, and electrodeposited to form a milky white composite film. (Patent Document 1).
In addition, after cleaning the surface of the aluminum material with alkali, a large number of pits are generated on the surface of the aluminum material by an acid etching process using a mixed acid solution containing hydrochloric acid and sulfuric acid, and then the pits are expanded by an alkali etching process. Then, an invention is disclosed in which the unevenness of the surface of the aluminum material is increased to adjust the whiteness, and electrodeposition coating is applied on the film (Patent Document 2). In the above Patent Document 1 and Patent Document 2, it was insufficient to obtain a multilayer film excellent in weather resistance, whiteness, adhesion, and dice mark concealment.
JP 2000-226694 A JP 2001-59200 A

  The problem to be solved is to provide a multilayer film forming method capable of producing a coated article excellent in weather resistance, whiteness, adhesion and dice mark concealing property in aluminum or an aluminum alloy.

That is, the present invention sequentially includes the following steps (1) to (4):
Step (1): A step of energizing aluminum or an aluminum alloy and anodizing to form an anodized film,
Step (2): a step of rinsing with an aqueous solution of sulfuric acid (a1) or an aqueous solution (A2) of an aqueous solution of phosphoric acid (a2) and then rinsing with water.
Step (3): Electrodeposition coating of an anionic electrodeposition paint (B) containing a carboxyl group-containing resin, a crosslinking agent and a pigment to form an electrodeposition coating film, and Step (4): Curing by heating and drying A step of forming a film, and the pigment concentration in the anion electrodeposition coating is in the range of 6 to 18% by mass as a percentage of the pigment mass (b2) to the resin solids mass (b1) of the anion electrodeposition coating. And the pigment in the anion electrodeposition paint is a pigment dispersion paste (a) in which a pigment having an average particle size in the range of 1 to 3 μm is dispersed, and an average particle size of 3 μm.
And a pigment dispersion paste (b) in which a pigment in the range of 10 μm or less is dispersed with respect to the total mass of the pigment dispersion pastes (a) and (b). The lightness (L ^* value) based on the L ^* a ^* b ^* color system defined in JIS Z 8729 of the formed multilayer coating is 85 to 85% by mass as a solid content. The present invention relates to a multilayer film forming method characterized by being in the range of 95.

The multilayer film forming method of the present invention is characterized in that after anodization is performed on aluminum or an aluminum alloy, the film is immersed in an acid solution bath (A) and electrodeposition coating is performed with a specific electrodeposition paint (B). To do. The obtained multilayer film is excellent in weather resistance, designability (whiteness), adhesion, and dice mark concealment.
The reason why the above effect is obtained is that the cell wall of the anodized film is dissolved by immersing it in the acid solution tank (A), so that the film surface is rich in irregularities, and diffuse reflection is promoted. It is considered that a multi-layer film excellent in weather resistance, adhesion and dice mark concealment property can be obtained by an anionic electrodeposition paint having a pigment concentration adjusted.

The multilayer film forming method of the present invention comprises the following steps (1) to (4). Hereinafter, it demonstrates in order of a process.
[Multilayer coating formation method]
As the aluminum or aluminum alloy used in the step (1), those subjected to a pretreatment for removing foreign substances, impurities, altered (abnormal) layers and the like from the surface of the material can be suitably used. Specifically, as this pretreatment, mainly chemical pretreatment to degrease the material surface, etching treatment to remove uneven oxide film and altered layer on the material surface, and further neutralization treatment It is common to do.

  Step (1): A step of conducting anodization by energizing aluminum or an aluminum alloy. The anodizing treatment is carried out in accordance with the conventional anodizing treatment for the purpose of forming a porous anodized film on the surface of the aluminum alloy, and depending on the intended use of the aluminum or aluminum alloy, the sulfuric acid method or An anodic oxidation method such as an oxalic acid method, a chromic acid method, or other organic acid methods can be used.

Specifically, examples of the electrolyte include sulfuric acid, oxalic acid, chromic acid, sodium phosphate, and aromatic sulfonic acid. As the voltage, electrolysis is performed at 10 to 150 V in a direct current, alternating current, or pulse waveform. The electrolytic solution is processed at a temperature of about 10 to 60 ° C. for about 5 to 60 minutes. The film thickness is about 1 to 30 μm.
Step (2): This is a step of immersing the aluminum or aluminum alloy that has undergone step (1) in the acid solution bath (A) of the phosphoric acid aqueous solution bath (a1) or the sulfuric acid aqueous solution bath (a2). By immersing in these acid solution tanks, a multilayer film with higher whiteness is formed in the multilayer film after electrodeposition coating.

The reason for the increase in whiteness is that the surface layer of the anodized film dissolves by immersion in an acid solution bath, resulting in a film structure rich in irregularities, and diffuse reflection is promoted, so that the whiteness is improved. It becomes a layer film. The anodized film is composed of a barrier layer having a thickness of 10 to 20 nm and a porous layer having a thickness of 1 to 30 μm. It is known that when immersed in an acid solution bath, not only the surface layer part but also the porous inner wall causes chemical dissolution in a short time. Further, when the porous inner wall is included, the actual surface area is larger than the apparent surface area, and therefore, the effect of forming irregularities by this chemical dissolution is great. Since it is chemical dissolution, the higher the temperature of the acid solution tank and the longer the immersion time, the greater the effect, but practically the temperature of the acid solution tank (A) is 10 ° C. to
35 degreeC, Preferably it is 15-25 degreeC, As immersion time, 10 second-30 minutes, Preferably about 1 minute-15 minutes are preferable from the surface of whiteness and productivity.

Moreover, when the acid solution tank (A) is a sulfuric acid aqueous solution tank (a2), the same sulfuric acid aqueous solution as that in the step (1) can be used. This means that the treatment can be performed by immersing aluminum or an aluminum alloy for a certain time as it is in the state after the energization in the step (1) without newly providing a dissolution tank.
In the phosphoric acid aqueous solution tank (a1), a phosphoric acid aqueous solution having a concentration of 5 to 300 g / l is used. The liquid temperature of the phosphoric acid aqueous solution is 10 to 35 ° C., preferably 15 to 35 ° C., and the immersion time is 10 seconds to 30 minutes, preferably about 1 minute to 15 minutes.

In the sulfuric acid aqueous solution tank (a2), a sulfuric acid aqueous solution having a concentration of 20 to 500 g / l is used. The temperature of the sulfuric acid aqueous solution is 10 to 35 ° C., preferably 15 to 35 ° C., and the immersion time is 10 seconds to 30 minutes, preferably about 1 minute to 15 minutes.
Next, the acid solution and the like adhering to the surface is removed by washing with hot water or without hot water washing, and then sent to the electrodeposition coating process. The hot water washing not only removes the acid solution adhering to the surface but also seals the film formed on the aluminum or aluminum alloy, thereby enhancing the adhesion of the multilayer film. Deionized water having a temperature of 70 to 90 ° C. is used, and the treatment time is about 0.5 to 5 minutes.

Step (3): A step of forming an electrodeposition coating film by electrodeposition-coating an anionic electrodeposition coating material (B) containing a carboxyl group-containing resin, a crosslinking agent and a pigment on the article obtained in step (2). It is.
In the step (3), the pigment concentration in the anion electrodeposition coating is 6 to 18% by mass, preferably 8 to 8% as a percentage of the pigment mass (b2) to the resin solids mass (b1) of the anion electrodeposition coating. It is preferable that it exists in the range of 17 mass%, More preferably, it is 10-16 mass%.

(Note 1) Pigment concentration: The pigment concentration is represented by the following formula (1).
Pigment concentration (mass%) = (mass of pigment in anion electrodeposition paint (b2) / resin solid mass in anion electrodeposition paint (b1)) × 100 Formula (1)
For example, the anion electrodeposition paint No. in Production Example 8 described later is used. 1, the pigment mass (b2) is 6.6 parts × 0.818 = 5.4 parts, and the resin solid content mass (b1) in the anion electrodeposition coating is 100 parts + 6.6 parts (1-0 .818), and thus the pigment concentration (%) is 5.3 mass%. In the formula, 6.6 parts is the mass of the pigment dispersion paste in the formulation of the anionic electrodeposition paint, and 0.818 is the pigment (mass%) in the pigment dispersion paste described in Table 1 below.

When the pigment concentration is less than 6% by mass, the whiteness dice mark concealing property is insufficient, and when it exceeds 18% by mass, the weather resistance is insufficient, which is not preferable.
In the step (3), the pigment in the anion electrodeposition paint is a pigment dispersion paste (a) in which a pigment having an average particle diameter of 1 to 3 μm is dispersed and an average particle diameter exceeding 3 μm and not exceeding 10 μm. A ratio of 5 to 50% by mass of the pigment dispersion paste (a) as a solid content with respect to the total mass of the pigment dispersion paste (a) and (b) as a pigment dispersion paste (b) in which the pigment is dispersed Those obtained by mixing with are preferable.

In the case where the pigment concentration in the anionic electrodeposition coating is in the range of 6 to 18% by mass, transparency is developed when the average particle size of the pigment dispersed in the pigment dispersion paste is less than 1.0 μm, and the multilayer is formed. The whiteness of the film decreases.
When the average particle diameter of the pigment in the pigment dispersion paste exceeds 10 μm, the glossiness of the coating film and the paint stability are impaired.

Even if two types of pigment dispersion paste are mixed, if one of the pigment dispersion pastes is out of the above range, a defect occurs in any of whiteness, glossiness, and paint stability.
By mixing the pigment dispersion paste (a) of pigment having an average particle diameter of 1 to 3 μm and the pigment paste (b) of pigment having an average particle diameter of more than 3 μm and not more than 10 μm, the pigment can be densely packed and a multilayer coating can be obtained. Thus, it is possible to obtain a paint having an increased whiteness and excellent glossiness, weather resistance and paint stability.

  Examples of the pigment include, for example, colored pigments such as titanium dioxide, red pepper, carbon black, yellow iron oxide (ocher), copper phthalocyanine blue, copper phthalocyanine green; Bright pigments such as titanium oxide-coated mica flakes and iron oxide-coated mica flakes; for example, extender pigments such as clay (kaolin), talc, calcium carbonate, barium sulfate, silica, diatomaceous earth, and magnesium carbonate.

  In addition, the above-mentioned pigment is adjusted according to the film performance such as weather resistance, whiteness and dice mark concealment, and the pigment type and amount used are appropriately added, and a pigment dispersing resin, a surfactant and water are added appropriately. The pigment-dispersed paste can be produced by sufficiently stirring with a stirrer or by dispersing using a ball mill or a sand mill. This pigment-dispersed paste can be used for the production of an anionic electrodeposition paint (B) together with an emulsion formed by dispersing a carboxyl group-containing resin and a crosslinking agent in detail in the following.

  Carboxyl group-containing resin: The carboxyl group-containing resin is a resin having at least one carboxyl group in one molecule, and more preferably a resin having at least one hydroxyl group. Specific examples include resins such as acrylic resins, polyester resins, polyether resins, polycarbonate resins, and urethane resins. Among these, acrylic resins are preferred from the viewpoint of weather resistance.

The above acrylic resin is obtained by copolymerizing a carboxyl group-containing radical polymerizable unsaturated monomer, and optionally a hydroxyl group-containing radical polymerizable unsaturated monomer, and other radical polymerizable unsaturated monomers. Can be manufactured.
Examples of the carboxyl group-containing radical polymerizable unsaturated monomer include monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. Examples of the hydroxyl group-containing radical polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and Other than this, Plaxel FM1 (manufactured by Daicel Chemical Industries, trade name, caprolactone-modified (meth) acrylic acid hydroxy esters), Plaxel FM2 (same as left), Plaxel FM3 (same as left), Plaxel FA1 (same as left), Plaxel FA2 (same as left), Plaxel FA3 (same as left) and the like.

Examples of the other radical polymerizable unsaturated monomer include γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, and γ- (meth) acryloyloxypropyltriethoxy. Alkoxysilyl group-containing unsaturated monomers such as silane and vinyltrimethoxysilane; for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth C ₁ of (meth) acrylic acid such as hexyl acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, etc.
_C18 alkyl or cycloalkyl esters, aromatic vinyl monomers such as styrene, (meth) acrylic acid amide, N-butoxymethyl (meth) acrylamide, N-methylol (meth) acrylamide (meth) Acrylamide and its derivatives, (meth) acrylonitrile compounds, etc. are mentioned.

  As an acrylic resin, usually the above-mentioned carboxyl group-containing radical polymerizable unsaturated monomer, if necessary, a hydroxyl group-containing radical polymerizable unsaturated monomer, and other radical polymerizable unsaturated monomers in a solvent. Obtained by radical polymerization reaction with a polymerization initiator. In this polymerization reaction, the carboxyl group-containing polymerizable unsaturated monomer is 1 to 20% by mass, preferably 4 to 10% by mass, and the hydroxyl group-containing radical polymerizable unsaturated monomer is 0 to 40% by mass, preferably 5%. The range of -30 mass% and the other radical polymerizable unsaturated monomer is 40-99 mass%, preferably 60-91 mass%.

  Examples of the solvent used for the polymerization reaction include alcohols such as propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, isobutyl alcohol, diethylene glycol monobutyl ether, methyl carbitol, 2-methoxyethanol, 2-ethoxy. Ethanol, 2-isopropanoxyethanol, 2-butoxyethanol, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2- Ethers such as propanol and dipropylene glycol monomethyl ether can be preferably used.

  Other than these, for example, aromatics such as xylene and toluene; ketones such as acetone, methyl ethyl ketone, 2-pentanone, 2-hexanone, methyl isobutyl ketone, isophorone, and cyclohexanone; methyl acetate, ethyl acetate, Esters such as pentyl acetate, 3-methoxybutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate, methyl propionate and ethyl propionate can also be used in combination.

As the radical polymerization initiator used for radical copolymerization, for example, benzoyl peroxide, di-t-butyl hydroperoxide, t-butyl hydroperoxide, cumyl peroxide, cumene hydroperoxide, diisopropyl benzanthane hydroperoxide, peroxides such as t-butylperoxybenzoate, lauryl peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, α, α′-
Examples include azo compounds such as azobisisobutylnitrile, azobisdimethylvaleronitrile, and azobiscyclohexanecarbonitrile.

The weight average molecular weight (Note 2) of the acrylic resin is in the range of 5,000 to 150,000, preferably 20,000 to 100,000.
(Note 2) Weight average molecular weight: JIS K 0124-83 It calculated | required by calculation from the chromatograph obtained by RI refractometer and the calibration curve of polystyrene using tetrahydrofuran for GPC.

  Basic compounds used for neutralization of carboxyl group-containing resins are primary monoamines such as ethylamine, propylamine, butylamine, benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, and 3-aminopropanol; diethyl Secondary monoamines such as amidethanolamine, di-n- or di-iso-propanolamine, N-methylethanolamine, N-ethylethanolamine; dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanolamine, dimethylamino Tertiary monoamines such as ethanol; polyamines such as diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine There is.

The blending ratio of the basic compound in the anionic electrodeposition coating material (B) is preferably in the range of 0.1 to 1.2 equivalents as a neutralization equivalent, and is a base with respect to the total measurement of the solid content of the carboxyl group-containing resin and the crosslinking agent. The active compound is in the range of 0.01 to 10% by mass, preferably 0.05 to 5% by mass.
Crosslinking agent: Conventionally known compounds can be used as the crosslinking agent. For example, methylol obtained by reaction of an amino component such as melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, dicyandiamide and aldehyde. And an alkyl etherified product of the methylolated amino resin and a blocked polyisocyanate compound.

As the methylolated amino resin, a methylolated melamine resin is preferable, and a part or all of the methylol group of the methylolated melamine resin is one kind of methanol, ethanol, propanol, butanol, octyl alcohol, 2-ethylhexyl alcohol, or the like. A melamine resin modified with two or more monohydric alcohols can be used.
Commercially available products of the above melamine resins include, for example, Uban 20SE-60, Uban 225 (all are trade names manufactured by Mitsui Chemicals), Super Becamine G840, Super Becamine G821 (All are Dainippon Ink. Butyl etherified melamine resin such as Chemical Industry Co., Ltd. (trade name); Sumimar M-100, Sumimar M-40S, Sumimar M-55 (all are trade names made by Sumitomo Chemical Co., Ltd.), Cymel 232, Cymel 303, Cymel 325, Cymel 327, Cymel 350, Cymel 370 (all are made by Nihon Cytec Industries, Inc., trade name), Nicarak MS17, Nicarak MX15, Nicarak MX430, Nicarak MX600 (all are made by Sanwa Chemical Co., Ltd., trade name) ), Regimin 741 (M Methyl etherified melamine resins such as Santo Co., Ltd. (trade name); Cymel 235, Cymel 202, Cymel 238, Cymel 254, Cymel 272, Cymel 1130 (all of which are Mitsui Cytec Co., Ltd., trade name), Summir M66B (Sumitomo) Mixed etherified melamine resin of methylation and isobutylation, etc., manufactured by Kagaku Co., Ltd .; methylation of Cymel XV805 (trade name, manufactured by Mitsui Cytec Co., Ltd.), Nicalac MS95 (trade name, manufactured by Sanwa Chemical Co., Ltd.), etc. And n-butylated mixed etherified melamine resin.

  As the blocked polyisocyanate compound, those obtained by blocking the isocyanate group of a conventionally known polyisocyanate compound with a blocking agent can be used. Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate or trimethylhexamethylene diisocyanate; cyclic aliphatic diisocyanates such as hydrogenated xylylene diisocyanate or isophorone diisocyanate; tolylene diisocyanate or 4,4'-diphenylmethane diisocyanate. An organic diisocyanate itself such as an aromatic diisocyanate itself, or an adduct of each of these organic diisocyanates with a polyhydric alcohol, a low molecular weight polyester resin or water, or a cyclized polymer of each organic diisocyanate as described above, Furthermore, an isocyanate biuret body etc. are mentioned.

  Examples of commercially available block polyisocyanate compounds include Vernock D-750, -800, DN-950, -970 or 15-455 (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), Desmodur L, N, HL, IL or N3390 (manufactured by Bayer Products), Takenate D-102, -202, -110N or 123N (Takeda Pharmaceutical Company, trade name), Coronate L, HL, EH or 203 (Japan) A polyurethane industry company make, brand name) or Duranate 24A-90CX (Asahi Kasei Kogyo company make, brand name) etc. are mentioned.

The water-dispersion of the carboxyl group-containing resin and the cross-linking agent
An emulsion can be obtained while adding a basic compound and deionized water and stirring with a disper or the like.
The anionic electrodeposition coating material (B) used in the method for forming a multilayer film of the present invention includes, in addition to a pigment dispersion paste, a carboxyl group-containing resin, a crosslinking agent, and a basic compound, an ultraviolet absorber and a light stabilizer as necessary. A curing catalyst can be added.

  Examples of the ultraviolet absorber include 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5 [(hexyl) oxy] -phenol, 2- [4- [6 (2- Hydroxy-3-dodecyloxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine and 2- [4- [6 (2-hydroxy -3-dodecyloxypropyl) oxy] -2-hydroxyphenyl] -4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine, 2,4-bis (2,4- Dimethylphenyl) -6- (2-hydroxy-4-iso-octyloxyphenyl) -s-triazine, 2,4-bis (2,4-dimethylphenyl) -6- (2-hydroxy-4-octyloxyphenyl) ) Examples include triazine-based ultraviolet absorbers such as -1,3,5-triazine.

  For example, 2- (2'-hydroxy-5'-methyl-phenyl) benzotriazole, 2- [2'-hydroxy-3 ', 5'-di- (1,1-dimethylbenzyl) phenyl] -2H-benzo Triazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-tert-butylphenyl) -5-chlorobenzo Triazole, 2- (2'-hydroxy-3 ', 5'-di-isoamylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-butylphenyl) benzotriazol Benzotriazole ultraviolet absorber and the like.

As the light stabilizer, a hindered amine derivative can be used, and specifically, bis- (2,2 ′, 6,6′-tetramethyl-4-piperidinyl) sebatate, 4-benzoyloxy-2,2 ′. , 6,6'-tetramethylpiperidine and the like.
Curing catalysts include higher alkyl aryl sulfonic acids such as dodecyl benzene sulfonic acid, dibutyl benzene sulfonic acid, dodecyl naphthalene sulfonic acid, dinonyl naphthalene sulfonic acid, dinonyl naphthalene disulfonic acid, and salts thereof (for example, amine compounds, ammonia, etc.) ), Etc .; trimethylamine, triethylamine, dimethylcyclohexylamine, N-tetramethylhexane-1,6-diamine, N-pentamethyldiethylenetriamine, 2-methyl-1,4-diazabicyclo [2,2,2] Amine compounds such as tertiary amines such as octane; dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoateoxy, dioctyltin Benzoate, organotin compounds such as aliphatic or aromatic carboxylic acid salts of dialkyltin such as dibutyltin dibenzoate and the like.

The formation of the coating film using the anionic electrodeposition coating is performed by placing the anionic electrodeposition coating in an electrodeposition bath to form an electrodeposition bath, and after immersing the aluminum substrate in this bath, the bath temperature is usually reduced to about It can adjust to 15-about 35 degreeC, and can carry out on the conditions of load voltage 100-400V.
Step (4): A step of forming a cured film by heating and drying. The baking conditions are usually about 130 to 200 ° C., preferably 150 to 180 ° C., for about 15 to 50 minutes, preferably 15 to 30 minutes. The film thickness of the electrodeposition coating film is not particularly limited, but in general, it is preferably in the range of 10 to 40 μm, particularly 15 to 35 μm based on the dry coating film.

When the multilayer film forming method of the present invention is used, a coating film having an L value (Note 3) of 85 to 95, preferably 87 to 94, and more preferably 89 to 93 with excellent whiteness can be obtained.
(Note 3) L value: Lightness (L ^* value) based on L ^* a ^* b ^* color system specified in JIS Z 8729. The lightness (L ^* value) of the coating film is a value measured using a color meter, for example, “Color Computer SM-7” manufactured by Suga Test Instruments Co., Ltd.

Formation of top clear film:
On the multilayer film obtained in the steps (1) to (4), an overcoat clear coating can be further applied. Examples of the base resin of the top clear coating include acrylic resins, polyester resins, alkyd resins, epoxy resins, urethane resins, silicone resins, fluorine resins, and modified products thereof, amino resins, ( (Blocked) A clear clear coating formed by blending a polyisocyanate compound.

The type of the paint may be any of a solution-type paint using an organic solvent as a medium, a non-aqueous dispersion paint, a water-soluble and / or emulsion paint and a powder paint using water as a medium.
The top clear coating is applied to the surface of the anion electrodeposition coating film by the usual coating means such as brush coating, spray coating, dip coating, flow coating, roller coating, electrostatic coating, etc., and then dried (heated) A coating film can be formed. The applied film thickness varies depending on the required performance, but is usually in the range of about 10 to 100 μm in terms of dry film thickness. The drying can be performed at room temperature or by heating, but it is desirable to set conditions suitable for the type of paint.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited thereby. “Parts” and “%” indicate “parts by mass” and “% by mass”.
Production Example 1 Acrylic resin solution No. 1 Production of 1 Into a reaction vessel charged with 21 parts of a mixed solvent (Note 4) and kept at 85 ° C., the following “mixture (A)” was added dropwise over 3 hours, and then 3 parts of azobisdimethylvaleronitrile was added. The reaction was carried out by holding at 85 ° C. for 4 hours, and the solid content was adjusted with a mixed solvent (see Note 4). 1 was produced.

"Mixture (A)"
Styrene 5 parts Methyl methacrylate 36.0 parts Ethyl acrylate 37.5 parts 2-Ethylhexyl methacrylate 4.0 parts Acrylic acid 5.5 parts 2-Hydroxyethyl methacrylate 12.0 parts KBM-503 (Note 5) 1.2 parts Azo Bisdimethylvaleronitrile 2.1 parts (Note 4) Mixed solvent: propylene glycol monomethyl ether / isopropyl alcohol / n-butyl alcohol / ethylene glycol monobutyl ether = 4.2 parts / 42 parts / 42 parts / 84 parts (Note 5) KBM-503: manufactured by Shin-Etsu Chemical Co., Ltd., trade name, γ-methacryloyloxypropyltrimethoxysilane Production Example 2 Emulsion No. Production of 70% acrylic resin solution No. 1 obtained in Production Example 1 above. 1 was dispersed by adding 92.7 parts (solid content 65 parts), Cymel 232 (Note 6) 35 parts (solid content 35 parts), triethylamine 1.9 parts (0.4 neutralization equivalent), and water 164 parts. 34% emulsion N with solid content adjusted
o. 1 was obtained.
(Note 6) Cymel 232: trade name, methyl / butyl mixed etherified melamine resin, manufactured by Mitsui Cytec

Production Example 3 Emulsion No. Production of 70% acrylic resin solution No. obtained in Production Example 1 above. 1) 92.7 parts (solid content 65 parts), Cymel 232 (see Note 6) 35 parts (solid content 35 parts), Tinuvin 328 (Note 7) 2 parts, Tinuvin 292 (Note 8) 1 part, Triethylamine 1. 9 parts (0.4 neutralization equivalent) and 170.4 parts of water were added and dispersed, and the solid content was adjusted to obtain 34% emulsion No. 2 was obtained.
(Note 7) Tinuvin 328: Ciba Geigy Co., Ltd., trade name, ultraviolet absorber (Note 8) Tinuvin 292: Ciba Geigy Co., Ltd., trade name, light stabilizer Production Example 4 Production Example of Pigment Dispersion Paste 60% Amine Neutralization Acrylic resin pigment dispersion resin (weight average molecular weight 36,000, hydroxyl value 70 mgKOH / g, acid value 56 mgKOH / g) 9.6 parts (solid content 5.8), CR-97 (Note 9) 25 parts, Todacolor KN -O (Note 10) 0.1 part, TAROX LL50 (Note 11) 0.9 part, deionized water 22.2 parts, charged in a ball mill for 48 hours, average particle diameter (Note) 2 μm, solid content 55 % Of pigment dispersion paste (a) was obtained. Table 1 shows the composition.

Production Example 5 Production Example of Pigment Dispersion Paste 60% amine neutralized acrylic resin pigment dispersion resin (weight average molecular weight 36,000, hydroxyl value 70 mg KOH / g, acid value 56 mg KOH / g) 9.6 parts (solid content 5.8) ), 25 parts of CR-97 (Note 9), 0.1 part of Todacolor KN-O (Note 10), 0.9 part of TAROX LL50 (Note 11), 22.2 parts of deionized water, 8 hours in a ball mill Dispersion gave a pigment dispersion paste (b) having an average particle size (Note) of 8 μm and a solid content of 55%. Table 1 shows the composition.

(Note) Average particle size is BI-DCP (Brookheven Instruments Corporation, particle size analyzer)
It measured using.
(Note 9) CR-97: Ishihara Sangyo Co., Ltd., trade name, titanium white (Note 10) Toda Color KN-O: Toda Kogyo Co., Ltd., trade name, Bengala (Note 11) TAROX LL50: Titanium Kogyo Co., Ltd., trade name , Yellow iron oxide Production Example 6 Anion electrodeposition paint No. Production of emulsion No. 1 with a solid content of 34%. 1 is 294 parts (solid content 100 parts), 55% solid content pigment dispersion paste is diluted with 12.0 parts (solid content 6.6 parts), deionized water 760 parts, and anion electrodeposition with a solid content of 10% Paint No. 1 was obtained.

Production Examples 7 to 19 2-No. 14 Anion electrodeposition paint No. 14 was prepared in the same manner as in Production Example 6 except that the contents of Table 2 were used. 2-No. 14 was obtained.

Preparation of test plate Aluminum material (silver: size is 150 mm x 70 mm x 0.5 mm)
6063-T5 material was used. The aluminum material is degreased by immersing it in an aqueous sulfuric acid solution at 25 ° C. and 100 g / l for 5 minutes, and then etched for 4 minutes with an aqueous sodium hydroxide solution at 50 ° C. and 50 g / l. It was neutralized by immersion for 3 minutes and used as a test plate.
Example 1 Multi-layer coating No. 1 1
Step 1: The test plate was immersed in a 180 g / l sulfuric acid aqueous solution at 20 ° C. and electrolyzed at 15 V for 30 minutes to form an anodized film having a thickness of 10 μm.

Step 2: After immersing in the same sulfuric acid aqueous solution as in Step 1 for 5 minutes, washing was performed.
Step 3: Next, washing with hot water is performed, and the anion electrodeposition coating no. 2 was used for electrodeposition coating so that the dry film thickness was 17 μm.
Step 4: Baked and dried at 180 ° C. for 20 minutes to form a multi-layer coating No. 1 was obtained.
Examples 2 to 10 Multi-layer coating No. 2-No. 10
Except for the steps shown in Table 3, the multilayer film No. 2-No. 10 was obtained. In addition, the coating film performance is shown.

Comparative Example 1 11
Step 1: The test plate was immersed in a 20 ° C. sulfuric acid aqueous solution and electrolyzed at 15 V for 30 minutes to produce an anodized film having a thickness of 10 μm.
Step 2: After immersing in the same sulfuric acid aqueous solution as in Step 1 for 5 minutes, washing was performed.

Step 3: Next, washing with hot water is performed, and the anion electrodeposition coating no. 1 was used for electrodeposition coating so that the dry film thickness was 17 μm.

Step 4: Glossy multilayer coating No. 7 after baking and drying at 180 ° C. for 20 minutes. 11 was obtained.
Comparative Examples 2-13
Except for the steps shown in Table 4, the multilayer film No. 12-No. 23 was obtained. In addition, the coating film performance is shown.

(Note 12) Whiteness:
Each multi-layered film is subjected to L ^* a ^* b ^* color system defined by JIS Z 8729 using a colorimeter (trade name “Color Computer SM-7”, manufactured by Suga Test Instruments Co., Ltd.). ^* Measured value.
(Note 13) Weather resistance:
The gloss of each multilayer coating conforms to JIS H 8602 5.12 (1992) (water spray time 12 minutes, black panel temperature 60 ° C.), using a carbon arc lamp type accelerated weathering tester sunshine weatherometer. The time required for the gloss retention to be 80% of the gloss before the exposure test was measured. Furthermore, the coating film surface was observed visually.

◎: Time for gloss retention to break 80% exceeds 2,500 hours ○: Time for gloss retention to break 80% for 2,000 hours or more and less than 2,500 hours ○ △: Gloss retention The time when the rate is less than 80% is 1,500 hours or more and less than 2,000 hours. Δ is the time when the gloss retention is less than 80%. More than 1,000 hours and less than 1,500 hours.
X: less than 1,000 hours when gloss retention is less than 80% (Note 14) 60 degree specular gloss:
The gloss of each multi-layer coating was measured according to JIS K-5400 7.6 (1990) 60 degree specular gloss, and the reflectance when the incident angle and the light receiving angle were 60 degrees was measured. Expressed as a percentage when the glossiness of the reference surface is 100.
(Note 15) Adhesiveness: Each multilayer coating was immersed in warm water at 40 ° C. for 240 hours, then cross-cut with a cutter knife, and a cello tape (registered trademark) was applied and peeled off instantaneously.

○: No abnormality △: Part of the coating film peeled ×: Coating film peeled (Note 16) Dice mark concealment:
The state of the dice mark of each multilayer film was visually evaluated.
○ indicates good dice mark concealment,
△ is inferior in dice mark concealment,
X is remarkably inferior in dice mark concealment.

  An object of the present invention is to provide a coated article having excellent weather resistance, whiteness, adhesion, and dice mark concealing property by the multilayer film forming method of the present invention.

Claims (3)

Sequentially, the following steps (1) to (4):
Step (1): A step of energizing aluminum or an aluminum alloy and anodizing to form an anodized film,
Step (2): a step of rinsing with an aqueous solution of sulfuric acid (a1) or an aqueous solution (A2) of an aqueous solution of phosphoric acid (a2) and then rinsing with water.
Step (3): Electrodeposition coating of an anionic electrodeposition paint (B) containing a carboxyl group-containing resin, a crosslinking agent and a pigment to form an electrodeposition coating film, and Step (4): Curing by heating and drying A step of forming a film, and the pigment concentration in the anion electrodeposition coating is in the range of 6 to 18% by mass as a percentage of the pigment mass (b2) to the resin solids mass (b1) of the anion electrodeposition coating. And the pigment in the anion electrodeposition coating is a pigment dispersion paste (a) in which a pigment having an average particle size in the range of 1 to 3 μm is dispersed, and a pigment having an average particle size in excess of 3 μm and in the range of 10 μm or less. The dispersed pigment dispersion paste (b) is mixed at a ratio of 5 to 50% by mass of the pigment dispersion paste (a) as a solid content with respect to the total mass of the pigment dispersion paste (a) and (b). Formed multilayer film A multilayer film forming method, wherein the lightness (L ^* value) based on the L ^* a ^* b ^* color system defined in JIS Z 8729 is in the range of 85-95. The method for forming a multilayer film according to claim 1, wherein the anionic electrodeposition paint (B) contains an ultraviolet absorber and / or a light stabilizer. The method for forming a multilayer film according to claim 1 or 2, wherein the multilayer film is a matte multilayer film.