JP2006297328A - Film forming method of aluminum base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film forming method which can obtain a film good in film performances such as corrosion resistance and moisture resistance on an aluminum base material with one coating using a water paint without generating a trouble such as foaming, does not require a large-scale air conditioner, and also does not use harmful hexavalent chromium. <P>SOLUTION: The surface treatment by a zirconium salt such that an amount of adhesion Zr is 5-100 mg/m<SP>2</SP>or the surface treatment by a trivalent chromium salt such that the amount of the adhesion trivalent chromium is 5-100 mg/m<SP>2</SP>, is carried out for the aluminum base material. When a water thermosetting paint containing a water base resin with a hydroxyl value of 1-250 mg KOH/g and a crosslinking agent is coated with two stages on the aluminum base material and a coating film is formed by one coat one bake method which is a themosetting method, the first-stage coating is carried out and thereafter the second-stage coating is carried out so that the concentration of a nonvolatile content of the coated paint by the first-stage coating in beginning of the second-stage coating is in the range of 30-95 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a coating on an aluminum substrate.

  Aluminum wheels, aluminum frames, and the like that are excellent in lightness, corrosion resistance, design, and the like are often used as automobile wheels and automobile body frames that are attachment members such as tires.

  For protection and aesthetics, for example, a thermosetting organic solvent-type metallic paint or a colored paint is usually applied to an aluminum base such as an aluminum wheel, followed by a thermosetting organic solvent-type clear paint. A metallic coating or a colored coating is often formed by the two-coat method.

  On the other hand, in recent years, from the viewpoint of energy saving and the like, there is a strong demand for process reduction, and there is a demand for a coating system for an aluminum base material that satisfies coating film performance, design properties, etc. with one coat.

  For example, a 1-coat metallic paint composition comprising a non-aqueous polymer dispersion, an acrylic resin, and a glittering material as a metallic paint capable of performing 1-coat metallic coating on an aluminum substrate, There has been proposed an organic solvent-type metallic coating composition in which the difference between the solubility parameter value and the solubility parameter value of the dispersion stabilizer of the non-aqueous polymer dispersion is within a specific range (see Patent Document 1).

  However, when one-coat metallic coating is performed using the above organic solvent-type metallic coating composition, since the coating contains a large amount of organic solvent at a low solid content concentration, a large amount of organic solvent is used in the coating operation. There is a problem of discharging.

  In order to reduce organic solvent emissions, it is an effective means to apply a water-based paint as a one-coat metallic paint composition. In this case, however, the coating performance such as moisture resistance and corrosion resistance deteriorates. was there.

  Also, water-based paints are less volatile than organic solvent-type paints and are susceptible to problems such as armpits and sagging. Therefore, when painting water-based paints, the entire painting booth is usually used to prevent such problems. In order to manage the temperature and humidity, large-scale air conditioning equipment is required, and there is a problem that a large amount of capital investment is required.

Furthermore, from environmental measures, it is also required that pretreatment of the aluminum base material does not contain harmful hexavalent chromium ions.
JP 2002-80776 A

  The object of the present invention is to solve the above-mentioned problems of the prior art, and use a water-based paint on an aluminum substrate to apply a coating film with good coating properties such as corrosion resistance, moisture resistance, water resistance, acid resistance and weather resistance. It is an object of the present invention to provide a method for forming a coating film that can be obtained in one coat without causing problems such as cracking and sagging, and that does not require large-scale air conditioning equipment and does not use harmful hexavalent chromium.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that an aqueous substrate having a hydroxyl value of 1 to 250 mgKOH / g is formed on a surface-treated aluminum substrate to which a specific amount of zirconium or trivalent chromium is attached. It has been found that the above-mentioned problems can be solved by coating a water-based thermosetting paint containing a resin and a crosslinking agent in two stages under a specific condition and forming a coating film by a one-coat one-bake method. It came to complete.

  The present invention relates to the following aluminum base film forming method.

1. On an aluminum substrate subjected to a surface treatment with a zirconium salt with a zirconium deposition amount of 5 to 100 mg / m ² or a surface treatment with a trivalent chromium salt with a trivalent chromium deposition amount of 5 to 100 mg / m ² , a hydroxyl value of 1 to In forming a coating film by a 1-coat 1-bake method in which an aqueous thermosetting paint containing 250 mg KOH / g of an aqueous base resin and a crosslinking agent is applied in two stages and then heat-cured, after the first stage, the second stage A method for forming a coating film on an aluminum base material, wherein the second stage coating is performed with the nonvolatile content concentration of the coating paint by the first stage coating at the start of coating being in the range of 30 to 95% by weight.

  2. Item 2. The coating film forming method according to Item 1, wherein the aluminum substrate is an aluminum wheel for automobiles or an aluminum frame for automobile bodies.

  3. Item 3. The method for forming a coating film according to Item 1 or 2, wherein the crosslinking agent of the aqueous thermosetting paint is at least one selected from the group consisting of an amino resin, a polyisocyanate compound, and a block polyisocyanate compound.

  4). Item 4. The method for forming a coating film according to any one of Items 1 to 3, wherein the amount of the crosslinking agent in the aqueous thermosetting coating is 10 to 100 parts by weight with respect to 100 parts by weight of the base resin.

  5. Item 5. The method for forming a coating film according to any one of Items 1 to 4, wherein the aqueous thermosetting paint further contains 0.1 to 50 parts by weight of a metallic pigment with respect to 100 parts by weight of the base resin.

  6). Item 6. The method for forming a coating film according to Item 5, wherein the metallic pigment is an aluminum flake that has been surface-treated to inactivate water.

  7). Item 7. The method for forming a coating film according to any one of Items 1 to 6, wherein the aqueous thermosetting paint further contains 0.1 to 8 parts by weight of an ultraviolet absorber with respect to 100 parts by weight of the base resin.

  8). Item 8. The method for forming a coating film according to any one of Items 1 to 7, wherein the aqueous thermosetting coating further contains 0.1 to 8 parts by weight of a light stabilizer with respect to 100 parts by weight of the base resin.

  9. Item 9. The method for forming a coating film according to any one of Items 1 to 8, wherein the content of the volatile organic solvent in the aqueous thermosetting coating is 20% by weight or less.

  10.2nd stage coating by applying room temperature air spray coating or hot air spraying to the 10.1st stage coating and / or preheating to warm the aluminum substrate temperature to 25-50 ° C. at the start of the first stage coating Item 10. The method for forming a coating film according to any one of Items 1 to 9, wherein the nonvolatile content concentration of the coating material by the first stage coating at the start is in the range of 30 to 95% by weight.

  Item 11. The method for forming a coating film according to Item 10, wherein the coating of the first stage is performed by hot air spray coating.

  Item 12. The coating film forming method according to Item 10, wherein the coating of the first stage is performed by hot air spray coating, and the aluminum base material is also heated before the first stage coating is started.

  13. The method for forming a coating film according to Item 10, wherein the second stage coating is performed by hot air spray coating.

  14. The coating film forming method as described in 10 above, wherein the wind speed of the coating environment from the end of the first stage coating to the start of the second stage coating is 0.05 m / sec or more.

  15. 15. An aluminum substrate on which a single-layer coating film is formed by the coating film forming method according to any one of items 1 to 14.

Coating method for forming aluminum substrate The coating film forming method of the present invention is an aqueous solution having a hydroxyl value of 1 to 250 mgKOH / g on an aluminum substrate that has been surface-treated so that a specific amount of zirconium or trivalent chromium adheres. In forming a coating film by a 1-coat 1-bake method in which an aqueous thermosetting paint containing a base resin and a crosslinking agent is applied in two stages and then heat-cured, the non-volatile content concentration of the paint applied by the first stage coating is 30 It is a method characterized by performing the second stage coating in a range of about ~ 95% by weight.

There are no particular restrictions on the aluminum substrate that is the object to which the coating film forming method of the present invention is applied, and examples include an aluminum wheel for automobiles and an aluminum frame for automobile bodies.

  Aluminum wheels for automobiles are attachment members such as tires and tubes for various automobiles such as passenger cars, trucks, four-wheel ATVs, and motorcycles.

  The aluminum frame for an automobile body is a member mainly used for an outer plate portion of various automobile bodies such as passenger cars, trucks, four-wheel ATVs, and motorcycles. More specifically, examples of the aluminum frame include a door frame portion, a roof portion, a bonnet portion, a front fender portion, a trunk lid portion and the like in a passenger car, and a handle portion and a cylinder in a motorcycle. A pipe part, a swing arm part, etc. can be mention | raise | lifted as a typical thing.

  The aluminum base material is usually made of an alloy containing aluminum as a main component and further containing magnesium, silicon and the like.

  As an aluminum base material, what was shape-processed in arbitrary shapes can be used for the objectives, such as lightweight property and design property. Further, an aluminum base material in which a shot blasted uneven casting surface, a cut smooth surface, and the like are mixed can also be used.

  In the present invention, prior to the formation of the coating film, the aluminum substrate may be subjected to a surface treatment with a zirconium salt or a trivalent chromium salt that has a specific amount of zirconium adhesion or trivalent chromium adhesion. is necessary.

  The surface treatment of the aluminum substrate usually comprises a degreasing step and a chemical conversion treatment step, and the chemical conversion treatment is performed after the degreasing.

  As the degreasing step, alkali degreasing is generally performed. In alkaline degreasing, for example, a degreasing treatment is performed by an immersion method, a spray method, or the like using an alkaline aqueous solution in which an alkaline component such as caustic soda, sodium silicate, sodium carbonate, or sodium phosphate and a surfactant are used in combination.

  In the present invention, after the degreasing step, a chemical conversion treatment step is performed using a zirconium salt or a trivalent chromium salt. In these chemical conversion treatments, zirconium or trivalent chromium is used as a metal that substitutes for chromate-treated hexavalent chromium.

  In the chemical conversion treatment step, a chemical conversion treatment film containing zirconium or trivalent chromium is formed by a dipping method, a spray method, or the like using a chemical conversion treatment solution that is an aqueous solution containing a zirconium salt or a trivalent chromium salt. It is done by.

  The chemical conversion treatment solution contains a metal salt other than these, for example, cobalt salt, zinc salt, titanium salt, vanadium salt, cerium salt, molybdenum salt, tungsten salt, etc. in addition to the zirconium salt or trivalent chromium salt. Also good. Moreover, you may mix | blend an epoxy resin, an acrylic resin, these modified resins, tannic acid, a silane coupling agent, etc. with a chemical conversion liquid as needed.

  Examples of acids that form metal salts such as zirconium, trivalent chromium, cobalt, zinc, titanium, vanadium, cerium, molybdenum, and tungsten include sulfuric acid, phosphoric acid, nitric acid, hydrofluoric acid, hydrochloric acid, and composites of these acids. And the like.

In the present invention, the amount of zirconium attached to the aluminum base material is set within a range of about 5 to 100 mg / m ² by the surface treatment with the zirconium salt, or 3 to the aluminum base material by the surface treatment with the trivalent chromium salt. It is necessary to make the amount of valent chromium adhered within a range of about 5 to 100 mg / m ² . These surface treatment-treated films are excellent in adhesion, and by applying the coating amount of zirconium or trivalent chromium within the above range, an aqueous thermosetting paint is applied by this coating film forming method. The coating film performance such as corrosion resistance and moisture resistance of the aluminum base material to which is applied can be satisfied.

The amount of zirconium attached to the aluminum substrate is preferably about 25 to 50 mg / m ² . Moreover, the adhesion amount of trivalent chromium with respect to an aluminum base material becomes like this. Preferably it is about 25-50 mg / m < ² >.

Aqueous thermosetting paint The aqueous thermosetting paint used in the coating film forming method of the present invention (hereinafter sometimes referred to as “the present paint”) comprises an aqueous base resin having a hydroxyl value of about 1 to 250 mg KOH / g and a crosslinking agent. It is a paint to contain.

Aqueous base resin The aqueous base resin is a basic component of the cured coating film of the present paint. Examples of the resin include acrylic resins, polyester resins (including alkyd resins), urethane-modified polyester resins, and epoxy resins, and at least one of these is used. These resins are usually used after being water-soluble or water-dispersed. All of these base resins preferably have a hydroxyl group, a carboxyl group or the like in their molecular structure. Among these, it is preferable to use an acrylic resin, a polyester resin, or the like.

Acrylic resin Examples of the acrylic resin that can be suitably used as the aqueous base resin of the present paint include the following acrylic resins (a) to (d).

  (A) Water-soluble acrylic resin: Acid value 20-150 mgKOH obtained by copolymerizing carboxyl group-containing vinyl monomer (M-1), hydroxyl group-containing vinyl monomer (M-2) and other vinyl monomers (M-3) / G, neutralized product of acrylic resin having a hydroxyl value of about 20 to 200 mgKOH / g and a number average molecular weight of about 3,000 to 100,000.

  The carboxyl group-containing vinyl monomer (M-1) is a compound having one or more carboxyl groups and one polymerizable unsaturated bond in one molecule, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, Itaconic acid and the like can be mentioned. Furthermore, acid anhydrides and half-esterified monocarboxylic acids of these compounds can also be used as the monomer (M-1).

  The hydroxyl group-containing vinyl monomer (M-2) is a compound having one hydroxyl group and one polymerizable unsaturated bond in one molecule, and this hydroxyl group mainly functions as a functional group that reacts with a crosslinking agent. As the monomer, specifically, monoesterified products of acrylic acid or methacrylic acid and a dihydric alcohol having 2 to 10 carbon atoms are suitable. For example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, Examples thereof include hydroxypropyl acrylate and hydroxypropyl methacrylate.

  As other vinyl monomers (M-3), compounds other than the above-mentioned monomers (M-1) and (M-2) and having one polymerizable unsaturated bond in one molecule can be used. Specific examples thereof are listed below in (1) to (8).

  (1) Monoesterified product of acrylic acid or methacrylic acid and monohydric alcohol having 1 to 20 carbon atoms: for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, and the like.

  (2) Aromatic vinyl monomers: For example, styrene, α-methylstyrene, vinyltoluene and the like.

  (3) Glycidyl group-containing vinyl monomer: a compound having one glycidyl group and one polymerizable unsaturated bond in each molecule, specifically, glycidyl acrylate, glycidyl methacrylate, and the like.

  (4) Nitrogen-containing alkyl (C1-20) acrylate: for example, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and the like.

  (5) Polymerizable unsaturated bond-containing amide compounds: for example, acrylic acid amide, methacrylic acid amide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide , Diacetone acrylamide and the like.

  (6) Vinyl compound: For example, vinyl acetate, vinyl propionate, vinyl chloride and the like.

  (7) Polymerizable unsaturated bond-containing nitrile compounds: for example, acrylonitrile, methacrylonitrile and the like.

  (8) Diene compounds: for example, butadiene, isoprene and the like.

  These other vinyl monomers (M-3) can use 1 type (s) or 2 or more types.

  The copolymerization reaction of each vinyl monomer can be performed by a known method.

  The acrylic resin thus obtained is difficult to dissolve in water if the acid value is less than about 20 mg KOH / g, and if it exceeds about 150 mg KOH / g, the coating film performance may be deteriorated due to the residual carboxyl group. A value of about 20 to 150 mgKOH / g is preferable. The acrylic resin is preferably rendered water-soluble by neutralization with an amine described later.

  (B) Water-dispersible acrylic resin-1: fine particle acrylic resin having an average particle size of about 0.05 to 1.0 μm obtained by emulsion polymerization of a vinyl monomer in the presence of a dispersion stabilizer such as a surfactant. And dispersed in water. The acrylic resin preferably has a hydroxyl value of about 1 to 50 mgKOH / g and an acid value of about 1 to 80 mgKOH / g.

  The vinyl monomer to be emulsion-polymerized is preferably selected from the monomer (M-1), the monomer (M-2) and the monomer (M-3), and further contains a polymerizable unsaturated bond in one molecule as necessary. When a small amount of a polyvinyl compound (M-4) having two or more is used in combination, a water-dispersible acrylic resin crosslinked within the particle is obtained, and the coating performance is further improved.

  Examples of the polyvinyl compound (M-4) include ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, allyl methacrylate, and allyl acrylate. , Divinylbenzene, trimethylolpropane triacrylate and the like, and the diene compound is not included here.

  The water-dispersible acrylic resin produced here is also preferably neutralized with an amine described later.

  (C) Water-dispersible acrylic resin-2: An aqueous dispersion in which fine particles of acrylic resin dispersed in water are stabilized by a stabilizer polymer. The particle is a core part, and the stabilizer polymer is a shell. A core / shell type emulsion. The acrylic resin preferably has a hydroxyl value of about 1 to 50 mgKOH / g and an acid value of about 1 to 80 mgKOH / g.

  Specifically, first, a vinyl monomer component containing no or little carboxyl group-containing vinyl monomer (M-1) was emulsion-polymerized, and then a large amount of carboxyl group-containing vinyl monomer (M-1) was contained. It is obtained by emulsion polymerization by adding a vinyl monomer component, and this is preferable from the viewpoint of coating workability because it is thickened by neutralization with an amine described later.

  (D) Water-dispersible acrylic resin-3: The polymer particles (core part) are cross-linked and there is a polymer (shell part) that stabilizes the polymer particles (core part), and the core part and the shell part are chemically bonded. A core / shell type emulsion. The acrylic resin preferably has a hydroxyl value of about 1 to 50 mgKOH / g and an acid value of about 1 to 80 mgKOH / g.

  The bond between the core part and the shell part is, for example, a polymerizable unsaturated bond introduced via a hydrolyzable functional group or silanol group provided on the surface of the core part, or an allyl remaining on the surface of the core part ( It is carried out by copolymerizing a vinyl monomer component containing a carboxyl group-containing vinyl monomer (M-1) to a polymerizable unsaturated bond by (meth) acrylate (a shell portion is formed), and then the carboxyl group of the shell portion is changed. It is preferable to neutralize with an amine or the like described later.

  Since this has thixotropic properties (thixotropic properties), it hardly causes sagging in the coating film even under high humidity. In addition, there are features such that no abnormality is observed even when an organic solvent is blended, and that smoothness, gloss, water resistance, adhesion and the like are excellent.

  As a neutralizing agent for the acrylic resins of (i) to (d) above, ammonia or a water-soluble amino compound such as monoethanolamine, ethylamine, dimethylamine, diethylamine, triethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine , Triethanolamine, butylamine, dibutylamine, 2-ethylhexylamine, ethylenediamine, propylenediamine, methylethanolamine, dimethylethanolamine, diethylethanolamine, 2-amino-2-methylpropanol, diethanolamine, morpholine and the like can be suitably used. .

Polyester resin A polyester resin that can be suitably used as the aqueous base resin of the present paint can be synthesized by an esterification reaction of a polybasic acid and a polyhydric alcohol according to a conventional method.

  A polybasic acid is a compound having two or more carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid Examples thereof include acid, het acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, and anhydrides thereof.

  Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule, such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, diethylene glycol, dipropylene glycol, triethylene glycol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanedimethanol, hydroxy Diols such as pivalic acid neopentyl glycol ester, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol, and hydrogenated bisphenol A Class: Trimethylolpropane, To Trimethylol ethane, mention may be made of glycerin, trivalent or higher polyols such as pentaerythritol and the like.

  In addition, as the polyester resin, (semi) drying oils such as oil oil fatty acid, palm oil fatty acid, safflower oil fatty acid, soybean oil fatty acid, sesame oil fatty acid, eno oil fatty acid, hemp oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, etc. A fatty acid-modified polyester resin modified with a fatty acid or the like can also be used. It is generally suitable that the modified amount of these fatty acids is 30% by weight or less in terms of oil length. Further, a product obtained by partially reacting a monobasic acid such as benzoic acid may be used. In addition, for example, after the esterification reaction of the polybasic acid and the polyhydric alcohol to introduce an acid group into the polyester resin, the polybasic acid such as trimellitic acid or trimellitic anhydride and the anhydride thereof are further reacted. It may be a

  The weight average molecular weight of the polyester resin is suitably in the range of about 500 to 200,000, preferably about 2,000 to 50,000 from the viewpoints of coating film hardness, scratch resistance, weather resistance and the like. The hydroxyl value of the polyester resin is about 1 to 200 mgKOH / g, preferably about 30 to 150 mgKOH / g, from the viewpoint of coating film hardness, weather resistance, and the like. The acid value of the polyester resin is suitably about 10 to 100 mgKOH / g, preferably about 30 to 70 mgKOH / g, from the viewpoint of dispersion stability.

  As the neutralizing agent for the polyester resin, those exemplified for the acrylic resin can be used in the same manner.

The kind of the crosslinking agent crosslinking agent is not particularly limited, for example, amino resin, polyisocyanate compound, blocked polyisocyanate compound, an epoxy compound or resin, a carboxyl group containing compound or resin, usually water-based paint such as an acid anhydride Can be used, and these can be used alone or in combination. Examples of amino resins include melamine resins and urea resins.

  In particular, amino resins, polyisocyanate compounds, and block polyisocyanate compounds described below can be suitably used.

  Specific examples of amino resins include dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine, and alkyl etherified products thereof (alkyl is methyl, ethyl, propyl, isopropyl, butyl, isobutyl, etc.) And melamine resins such as these partial condensates; urea resins; urea-formaldehyde condensates; urea-melamine cocondensates.

  Of the above, melamine resins are preferred. Examples of commercially available melamine resins include “My Coat 212”, “Cymel 254”, “Cymel 202”, “Cymel 303”, “Cymel 325”, “Cymel 1156” (above, manufactured by Mitsui Cytec Co., Ltd.), “ “Uban 20N”, “Uban 20SB”, “Uban 128” (manufactured by Mitsui Chemicals, Inc.), “Sumimar M-50W”, “Sumimar M-40N”, “Sumimar M-30W” (manufactured by Sumitomo Chemical Co., Ltd.) Etc.

  In addition, when an amino resin is used as a curing agent, if necessary, a sulfonic acid such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, or a salt of these sulfonic acids and an amine is used as a catalyst. Can be used.

  Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate (IPDI); and aromatic aliphatics such as xylylene diisocyanate (XDI). Diisocyanates; aromatic diisocyanates such as tolylene diisocyanate (TDI) and 4,4′-diphenylmethane diisocyanate (MDI); dimers and trimers of these diisocyanate compounds; polyhydric alcohols such as these diisocyanate compounds and trimethylolpropane And adducts of these diisocyanate compounds and water.

  A blocked polyisocyanate compound obtained by blocking a polyisocyanate compound with a blocking agent may be used as a crosslinking agent.

  Examples of the blocking agent include oximes such as methyl ethyl ketoxime, acetoxime, cyclohexanone oxime, acetophenone oxime, and benzophenone oxime; phenols such as m-cresol and xylenol; methanol, ethanol, butanol, 2-ethylhexanol, cyclohexanol, Examples thereof include alcohols such as ethylene glycol monoethyl ether; lactams such as ε-caprolactam; diketones such as malonic acid diester and acetoacetate; mercaptans such as thiophenol. When using a block polyisocyanate compound, for example, a tin compound such as dibutyltin dilaurate can be added as a catalyst.

  In the present paint, among the above-mentioned crosslinking agents, a butyl etherified melamine resin can be preferably used from the viewpoints of improvement of moisture resistance and water resistance of the coating film, adhesion to an aluminum substrate, and the like. For example, by setting the amount of butyl etherified melamine resin to 40% by weight or more, preferably 50% by weight or more in the total crosslinking agent, a coating film having good water resistance and adhesion can be obtained. Specific examples of commercially available butyl etherified melamine resins include “Uban 122”, “Uban 128”, “Uban 20N”, “Uban 20SB”, “Uban 20SE-60” (manufactured by Mitsui Chemicals, Inc.), etc. Can give.

  The blending amount of the crosslinking agent in the aqueous thermosetting coating is preferably about 10 to 100 parts by weight with respect to 100 parts by weight of the base resin because the curability of the coating is excellent. The blending amount of the crosslinking agent is more preferably about 20 to 65 parts by weight with respect to 100 parts by weight of the base resin. The base resin weight is the total solid content by weight of one or more base resins.

  In addition to this paint, additional resins such as polyurethane resins and urethane emulsions; metallic pigments, colored pigments, extender pigments, UV absorbers, light stabilizers, anti-sagging agents, thickeners, antifoaming agents, anti-settling agents, etc. These additives and solvents can be blended as needed. Water and organic solvents can be used as the solvent.

  Examples of metallic pigments include aluminum flakes, copper bronze flakes, mica-like iron oxides, mica flakes, mica-like iron oxides coated with metal oxides, mica flakes coated with metal oxides, and the like.

  In the present invention, it is most typical to use an aqueous metallic paint blended with aluminum flakes among the above metallic pigments as the aqueous paint, and in this case, a coating film having chemical resistance, acid resistance, alkali resistance, etc. In order to improve the performance, aluminum flakes that have been surface-treated to inactivate water can be used more suitably.

  Surface-treated aluminum flakes that are inactivated against water (hereinafter sometimes referred to as “surface-treated aluminum flakes”) are formed of aluminum in order to suppress reaction with water in the dispersion medium in water-based paints. Aluminum flakes stabilized against water by treating the surface of the flakes and making them inert to water.

  Examples of the surface treatment agent used for the treatment of the aluminum flake surface include a phosphate group-containing polymerizable unsaturated monomer, a hydroxyl group-containing polymerizable unsaturated monomer, and other polymerizable unsaturated monomers copolymerizable with these monomers. A phosphoric acid group-containing copolymer obtained by copolymerization can be preferably used, and the copolymer is usually preferably used as an organic solvent solution thereof.

  Examples of the phosphoric acid group-containing polymerizable unsaturated monomer include (2-acryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acid phosphate, (2-methacryloyloxyethyl) acid phosphate, (2-methacryloyloxypropyl) Examples include acid phosphate.

  The hydroxyl group-containing polymerizable unsaturated monomer is intended to introduce a hydroxyl group capable of reacting with an aqueous melamine resin contained in the aqueous coating composition, and includes 2-hydroxyethyl acrylate, 2 Examples include -hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate and the like.

  In addition, other polymerizable unsaturated monomers copolymerizable with phosphoric acid group-containing polymerizable unsaturated monomers and hydroxyl group-containing polymerizable unsaturated monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl (Meth) acrylic acid alkyl esters such as methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate; carboxyl group-containing unsaturated monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid; Examples thereof include styrene and acrylonitrile.

  A copolymer of these polymerizable unsaturated monomers can be prepared by a usual polymerization method using a known polymerization initiator. As polymerization initiators, azo-based initiators such as azobisisobutyronitrile, 2,2′-azobis (methylvaleronitrile), azocumene, peroxides such as cyclohexanone peroxide, cumene hydroperoxide, lauroyl peroxide, etc. Examples thereof include system polymerization initiators.

  The acid value of the obtained phosphoric acid group-containing copolymer is preferably about 20 to 200 mgKOH / g. Among these acid values, the acid value based on the phosphoric acid group-containing polymerizable unsaturated monomer is 10 to 150 mgKOH. / G is desirable. The hydroxyl value of the copolymer is preferably about 20 to 200 mgKOH / g, and the number average molecular weight is preferably about 2,000 to 30,000.

  Moreover, when using the said phosphate group containing copolymer as a surface treating agent, it is preferable to use it normally as a solution of hydrophilic organic solvents, such as ester solvent, alcohol solvent, and ketone solvent. . As these organic solvents, those usually used at the time of preparing the copolymer may be used as they are, but they may be appropriately added after preparing the copolymer.

  Examples of the hydrophilic organic solvent include ester organic solvents such as ethylene glycol monoethyl ether acetate, ethylene glycol monoisobutyl ether acetate, methoxypropyl acetate, and ethyl acetate; ethyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol Alcohol-based organic solvents such as ethylene glycol, propylene glycol and hexylene glycol; ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether and 3-methoxy-3-methylbutanol -Alcohol-based organic solvents; methyl ethyl ketone, methyl isobutyl ketone, diacetone alcohol, etc. It can be exemplified tons organic solvents. Hydrophobic organic solvents such as xylene and toluene can be used in combination with these hydrophilic organic solvents as appropriate.

  In addition, since the phosphoric acid group-containing copolymer is used in an aqueous coating material in the present invention, for example, ammonia; triethylamine, ethanolamine, N, N-dimethylethanolamine, dimethylamine, dimethylethanolamine, diisopropylamine, diisopropylamine, The neutralization treatment is preferably performed using an organic amine such as propylamine. The neutralization treatment can be performed simultaneously with the surface treatment of the aluminum flakes or before or after the surface treatment. Of course, it may be performed immediately after preparing the copolymer.

  The surface treatment of aluminum flakes using the surface treatment agent can be performed, for example, by adding aluminum flakes with stirring to an organic solvent solution of a phosphoric acid group-containing copolymer and mixing them uniformly. Thereby, the surface of the aluminum flakes can be surface-treated by adsorbing and coating the copolymer on the surface of the aluminum flakes by the action of the phosphate group in the copolymer.

  As the aluminum flakes to be surface-treated, any aluminum flakes known per se used in the paint field can be used without particular limitation. The particle diameter of the aluminum flakes is not particularly limited, but usually it is preferably 100 μm or less.

  When the metallic pigment is contained in the water-based paint used in the present invention, by using the surface-treated aluminum flakes, the aluminum flakes are densely arranged in the coating film formed according to the present invention. Since the permeation of corrosive substances such as moisture can be suppressed, the coating film performance such as corrosion resistance, chemical resistance, acid resistance, and alkali resistance can be improved.

  In the present paint, when the metallic pigment is blended, the blending amount is about 0.1 to 50 parts by weight with respect to 100 parts by weight of the base resin, and the metallic appearance of the formed coating film is excellent. To preferred. The compounding amount of the metallic pigment is more preferably about 1 to 30 parts by weight with respect to 100 parts by weight of the base resin. The base resin weight is the total solid content by weight of one or more base resins.

  Examples of coloring pigments that are optional components of the paint include inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate, and carbon black; phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, and flavanthrone. Examples thereof include organic pigments such as yellow, isoindoline yellow, indanthrone blue, quinacridone violet and the like.

  Examples of extender pigments include calcium carbonate, barium sulfate, and clay.

  In this coating material, in order to improve the weather resistance of the coating film, an ultraviolet absorber and a light stabilizer can be suitably used. As an ultraviolet absorber, well-known absorbers, such as a benzotriazole type absorber, a triazine type absorber, a salicylic acid derivative type absorber, a benzophenone type absorber, can be used, for example. As a light stabilizer, well-known things, such as a hindered amine light stabilizer, can be used, for example.

  The compounding amount in the case of using the ultraviolet absorber is usually about 0.1 to 8 parts by weight, particularly about 0.3 to 5 parts by weight, with respect to 100 parts by weight of the base resin. From the viewpoint of yellowing resistance, it is preferable. The amount of the light stabilizer used is usually about 0.1 to 8 parts by weight, particularly about 0.3 to 5 parts by weight with respect to 100 parts by weight of the base resin. It is preferable from the viewpoint of weather resistance and yellowing resistance. The base resin weight is the total solid content by weight of one or more base resins.

  The present paint comprises an aqueous base resin having a hydroxyl value of 1 to 250 mg KOH / g and a crosslinking agent, which are essential components, and optionally the optional components, usually in the range of about 10 to 40% by weight, preferably 20 to 30% by weight. It is prepared to have a solid weight concentration of about 400 to 3,000 mPa · s (B-type viscometer, measured value at 60 rpm / 20 ° C.), preferably about 600 to 1,500 mPa · s. . At this time, it is preferable that the volatile organic solvent content of the paint is 20% by weight or less from the viewpoint of minimizing organic solvent discharge during coating.

Coating process of aluminum substrate The coating film forming method of the present invention is a one-coat, one-baking method in which the water-based thermosetting paint is applied in two stages on an aluminum substrate that has been subjected to a specific surface treatment, followed by heat curing. When forming the coating film by the method, after the first stage coating, the second stage coating is performed with the non-volatile concentration of the coating paint by the first stage coating at the start of the second stage coating in the range of 30 to 95% by weight. Characterized by doing.

  In ordinary water-based paint painting, air-conditioning equipment is controlled to an appropriate temperature and humidity condition, and then the water-based paint is air sprayed, airless sprayed, electrostatically so as to have a cured film thickness of about 10 to 40 μm. Since the main component is water with high latent heat compared to organic solvents, the volatile component in the paint is usually 25% by preheating at about 60 to 80 ° C. The coating film is generally cured by drying at about 120 to 160 ° C. for about 15 to 30 minutes after drying to about 15% by weight or less, preferably about 15% by weight or less.

  On the other hand, in the coating film forming method of the present invention, when applying the water-based thermosetting coating, the coating and the coating are heat-cured by a one-coat one-bake method by two-stage coating, particularly the first-stage coating. After that, the second stage of coating is performed after the nonvolatile content concentration of the coating paint by the first stage coating at the start of the second stage coating is controlled within the range of 30 to 95% by weight. As a result, problems such as armpits and sagging occur without requiring large-scale air conditioning equipment that controls the temperature and humidity of the entire booth, which is necessary for normal water-based paint painting, and preheating before heat curing the coating film. The painting work can be performed without any problems.

  The non-volatile content concentration of the coating paint by the first stage coating is in the range of 30 to 95% by weight, preferably 35 to 90% by weight, and more preferably 40 to 85% by weight. When the non-volatile content weight concentration is 30% by weight or less, metal unevenness in the metallic coating color and deterioration of the color stability of the coating film tend to occur, and when it is 95% by weight or more, the coating film becomes rough and the metallic coating color. There is a tendency that defects such as disordered orientation of the metallic pigment tend to occur.

  In the coating film forming method of the present invention, when the two-stage coating is performed on the aqueous thermosetting coating so as to have a total cured film thickness of, for example, about 15 to 25 μm, the second-stage coating is performed after the first-stage coating. Control the non-volatile content of the coating material by the first stage coating at the start within the range of 30 to 95% by weight, then apply to the object by air spray coating, airless spray coating, electrostatic coating, etc. After setting for about 5 to 15 minutes (leaving at room temperature until the start of heating after coating is completed), the coating film is cured by heating at about 120 to 160 ° C. for about 15 to 30 minutes.

  The film thickness distribution of the first stage and the second stage in the two-stage coating is preferably in the range of 1: 4 to 4: 1.

  Of the above-mentioned methods, air spray coating is preferably used as the coating method. The air spray coating machine is more preferably capable of performing air spray coating with hot air by switching between normal temperature air and hot air of about 30 ° C. to 40 ° C.

  In the above, for example, in the case of air spray coating, if the concentration of the non-volatile content of the coating paint at the start of the second stage coating is less than 30% by weight due to a decrease in temperature such as in winter, the first stage coating is performed with hot air. As air atomization coating, by promoting the evaporation of volatile components in the coating material, the non-volatile concentration of the first stage coating material at the start of the second stage coating is in the range of 30 to 95% by weight. It is preferable to do this.

  Even if the first stage coating is air spray coating with hot air as described above, if the non-volatile content concentration of the coating paint at the start of the second stage coating is less than 30 wt%, The first stage at the start of the second stage coating is achieved by heating (25 ° C. to 50 ° C.) the aluminum substrate that is the object to be coated and further promoting the evaporation of the volatile components in the coating material. The non-volatile content concentration of the coating material is preferably in the range of 30 to 95% by weight.

  In addition, as a method for promoting evaporation of volatile components in the coating material, for example, the wind speed of the coating environment during the flash time (the time from the end of the first stage coating to the start of the second stage coating) is 0.05 m / second or more. Thus, the evaporation can be promoted, or the flash time can be extended (for example, 10 minutes or more).

  Furthermore, if necessary, the second stage coating can also be a hot air spray coating.

  By adopting the above-mentioned coating method, even when the temperature is low, such as in winter, it is possible to ensure good painting workability without requiring large-scale air conditioning equipment that requires a running cost to heat the entire painting booth. be able to.

  According to the coating film forming method of the present invention, the following remarkable effects can be obtained.

  (1) The surface of the aluminum substrate is treated with zirconium or trivalent chromium with excellent coating adhesion and corrosion resistance, and a specific two-stage coating is performed using an aqueous thermosetting paint. A coating film having good coating performance such as corrosion resistance, moisture resistance, water resistance, acid resistance, weather resistance and the like can be formed on the material with one coat without causing problems such as cracking and sagging. In addition, since it is difficult to cause cracks, sagging, etc., it is not necessary to preheat before heat curing.

  (2) There is no need for large-scale air conditioning equipment, and there is no need to use harmful hexavalent chromium.

  (3) Since the paint used is a water-based paint, the amount of organic solvent discharged can be greatly reduced, and since it is a one-coat system, energy savings due to process reduction can be achieved.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. However, the present invention is not limited to the following examples. In each example, “part” and “%” are both based on weight, and the film thickness of the coating film is based on the cured coating film.

  In Examples and Comparative Examples, after the first stage coating, the concentration of the non-volatile content of the coating paint by the first stage coating at the start of the second stage coating is the aluminum base immediately after the first stage coating and immediately before the second stage coating. A part of the paint applied on the material was sampled as a 2 g sample with a flat spatula, and the weight was calculated using the weight of the cured coating film measured after heating and curing at 110 ° C. for 1 hour.

Production Example 1 Production of water-dispersible acrylic resin In a reaction vessel, 140 parts of deionized water, 2.5 parts of a surfactant (trade name “Newcol 707SF”, manufactured by Nippon Emulsifier Co., Ltd., solid content 30%), and the following single amount 1 part of body mixture (1) (Note 1) was added and stirred and mixed in a nitrogen stream to 60 ° C., and 3 parts of 3% ammonium persulfate was added. Subsequently, after raising the temperature to 80 ° C., 79 parts of monomer mixture (1), surfactant (trade name “Newcol 707SF”, manufactured by Nippon Emulsifier Co., Ltd., solid content 30%) 2.5 parts, 3% A monomer emulsion consisting of 4 parts of ammonium persulfate and 42 parts of deionized water was added dropwise to the reaction vessel using a metering pump over 4 hours. After completion of dropping, aging was performed for 1 hour.

  Further, at 80 ° C., the following monomer mixture (2) (Note 2) was added dropwise to the reaction vessel using a metering pump over 1.5 hours. After completion of dropping, the mixture was aged for 1 hour, cooled to 30 ° C., and then filtered through a 200 mesh nylon cloth. Deionized water was further added to this product, adjusted to pH 7.5 with 2-amino-2-methyl-1-propanol, and a water-dispersible acrylic resin having a hydroxyl value of 43.5 mgKOH / g and a Tg of 46 ° C. (solid content) A weight concentration of 30%) was obtained.

  (Note 1) Monomer mixture (1): Mixture of 53 parts of methyl methacrylate, 10 parts of styrene, 9 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate, 1 part of methacrylic acid and 2 parts of allyl methacrylate. .

  (Note 2) Monomer mixture (2): 5 parts of methyl methacrylate, 8 parts of n-butyl acrylate, 4 parts of 2-hydroxyethyl acrylate, 3 parts of methacrylic acid, 0.5 parts of “Newcol 707SF”, 3 A mixture of 4 parts of an aqueous ammonium persulfate solution and 30 parts of deionized water.

Production Example 2 Production of water-soluble acrylic resin In a reactor equipped with a stirrer, a reflux condenser and a thermometer, 60 parts of dipropylene glycol butyl ether was placed and heated to 125 ° C., and 30 parts of methyl methacrylate and n-butyl were obtained. A mixture of 30 parts acrylate, 20 parts 2-ethylhexyl methacrylate, 13 parts 4-hydroxybutyl acrylate, 7 parts acrylic acid and 2 parts azobisisobutyronitrile was added dropwise over 3 hours. After dropping, the mixture is aged for 1 hour, a mixed solution of 0.5 part of 2,2′-azobis (2,4-dimethylvaleronitrile) and 16 parts of dipropylene glycol butyl ether is added dropwise over 1 hour, and further aged for 1 hour. Thus, a solution having a solid content weight concentration of 57% of a water-soluble acrylic resin (hydroxyl value 51 mgKOH / g, acid value 54 mgKOH / g, weight average molecular weight 30,000) was obtained.

Production Example 3 Production of Water Dispersible Polyester Resin 13.4 parts of trimethylolpropane, 46.2 parts of hexahydrophthalic anhydride, 93.6 parts of neopentyl glycol, 49.8 parts of isophthalic acid and 36.5 parts of adipic acid An esterification reaction was carried out at 0 ° C., followed by addition reaction by adding 5.7 parts of trimellitic anhydride to obtain a carboxyl group-containing polyester resin having a hydroxyl value of 95 mgKOH / g, an acid value of 15 mgKOH / g, and a weight average molecular weight of 10,000. It was. Thereafter, 10% of tripropylene glycol monomethyl ether is added to the resin and fluidized, and after neutralizing the carboxyl group by adding methylethanolamine, water is added, and water dispersion with a solid content of 50% is added. A functional polyester resin was obtained.

Production Example 4 Production of surface-treated aluminum flakes that are inert to water In a stirring vessel, aluminum flake pigment paste (trade name “Aluminum Paste 0780M”, manufactured by Toyo Aluminum Co., Ltd., 44 μm aperture sieve Add 40 parts of ethylene glycol monobutyl ether to 30 parts of pigment paste consisting of 64 to 67% aluminum flake powder of 0.5% or less, mineral spirits 30 to 35%, and a small amount of stearic acid as a leafing aid. Stir. In this, 25 parts (12.5 parts by solid content) of a 50% ethylene glycol monobutyl ether solution of the following phosphoric acid group-containing acrylic resin (Note 3) is added, and 2.6 parts of triethylamine is further added and mixed uniformly. Thus, a surface-treated aluminum flake paste was obtained. The obtained surface-treated aluminum flake paste had a non-volatile content of about 34% and an aluminum pigment content of about 21%.

  (Note 3) Phosphoric acid group-containing acrylic resin: (2-acryloyloxyethyl) acid phosphate 20 parts, 2-hydroxyethyl methacrylate 20 parts, styrene 38 parts, n-butyl acrylate 20 parts and methacrylic acid 2 parts Combined (acid value 115 mgKOH / g (of which the acid value based on the phosphate group-containing polymerizable unsaturated monomer is 100 mgKOH / g), hydroxyl value 86 mgKOH / g, number average molecular weight 4,800).

Production Example 5 Production of water-based thermosetting paint Water-soluble acrylic resin obtained in Production Example 2 in an amount of 20 parts by weight, 2 parts of dimethylethanolamine, and water-dispersible polyester resin obtained in Production Example 3 were solid An amount of 20 parts by weight, 31 parts of methyl / butyl mixed etherified melamine resin (trade name “Cymel 254”, manufactured by Mitsui Cytec Co., Ltd., solid content concentration 80%), 25 by solids weight obtained in Production Example 1 An amount of water-dispersible acrylic resin and 60 parts of deionized water were added and mixed with sequential stirring, and the mixture was further stirred for 30 minutes. Thereafter, an alkali-thickened acrylic emulsion (trade name “Primal ASE-60”, manufactured by Nippon Acrylic Chemical Co., Ltd.) and 15 parts of butyl cellosolve in an amount of 2 parts by weight were added and stirred for another 20 minutes. Thereafter, 100 parts of aluminum flake dispersion 1 (Note 4) was added with stirring, dimethylethanolamine and deionized water were further added, and the viscosity was 800 mPa at 20 ° C. as measured with a B-type viscometer at 60 rpm. -It adjusted so that s and pH might be 8.4, and the water-based thermosetting coating material (i) was obtained. The solid content concentration of the water-based thermosetting paint (i) was 24.5%.

  (Note 4) Aluminum flake dispersion 1: Disperse and dissolve 20 parts of “Alpaste 5654NS” (trade name, manufactured by Toyo Aluminum Co., Ltd., aluminum flakes, aluminum content 70%) in 20 parts of butyl cellosolve. 33.5 parts of the obtained water-dispersible acrylic resin (10 parts as a solid content weight), 0.5 part of dimethylethanolamine and 26 parts of deionized water were sequentially added with stirring to obtain 100 parts of aluminum flake dispersion 1 Got.

Production Example 6 Production of water-based thermosetting paint In Production Example 5, instead of 31 parts of methyl / butyl mixed etherified melamine resin (trade name “Cymel 254”, manufactured by Mitsui Cytec Co., Ltd., solid content concentration 80%) 15 parts of butyl mixed etherified melamine resin (trade name “Cymel 254”, manufactured by Mitsui Cytec Co., Ltd., solid concentration 80%) and butyl etherified melamine resin (trade name “Uban 122”, manufactured by Mitsui Chemicals, Inc., solid content concentration 60%) ) A water-based thermosetting paint (ii) was obtained in the same manner as in Production Example 5 except that 21 parts were used. The solid content concentration of the aqueous thermosetting paint (ii) was 24.2%.

Production Example 7 Production of water-based thermosetting coating In Production Example 5, Production Example 5 was used except that 147 parts of aluminum flake dispersion 2 (Note 5) was used instead of 100 parts of aluminum flake dispersion 1 (Note 4). In the same manner, an aqueous thermosetting paint (iii) was obtained. The solid content concentration of the aqueous thermosetting paint (iii) was 24.7%.

  (Note 5) Aluminum flake dispersion 2: In Note 4, instead of 20 parts of “Alpaste 5654NS”, 67 parts of the surface-treated aluminum flake paste obtained in Production Example 4 (14 parts as the aluminum flake pigment content) is used. In the same manner as in Note 4, 147 parts of aluminum flake dispersion 2 was obtained.

Production Example 8 Production of water-based thermosetting paint Water-soluble acrylic resin obtained in Production Example 2 in an amount of 20 parts by weight, 2 parts of dimethylethanolamine, and water-dispersible polyester resin obtained in Production Example 3 were solid 20 parts by weight, 2 parts UV absorber (trade name “Tinubin 400”, manufactured by Ciba Specialty Chemicals), 1 part light stabilizer (trade name “Sanol LS292”, manufactured by Sankyo), methyl / butyl 31 parts of mixed etherified melamine resin (trade name “Cymel 254”, manufactured by Mitsui Cytec Co., Ltd., solid content concentration 80%), water dispersible acrylic resin in an amount of 25 parts by weight of solid content obtained in Production Example 1 and desorption 60 parts of ionic water were added and mixed with sequential stirring, followed by further stirring for 30 minutes. Thereafter, an alkali-thickened acrylic emulsion (trade name “Primal ASE-60”, manufactured by Nippon Acrylic Chemical Co., Ltd.) and 15 parts of butyl cellosolve in an amount of 2 parts by weight were added and stirred for another 20 minutes. Thereafter, 100 parts of aluminum flake dispersion 1 (Note 4) was added with stirring, dimethylethanolamine and deionized water were further added, and the viscosity was 800 mPa at 20 ° C. as measured with a B-type viscometer at 60 rpm. -It adjusted so that s and pH might be 8.4, and the water-based thermosetting coating material (iv) was obtained. The solid content concentration of the aqueous thermosetting paint (iv) was 24.2%.

Example 1 Film formation by 1-coat 1-bake method Aluminum cast plate (“A5454P”) subjected to chemical conversion treatment with a surface treatment agent (trade name “CT-3769”, manufactured by Nihon Parkerizing Co., Ltd.) containing zirconium fluoride and zirconium nitrate 100 × 60 × 3.2 mm, the temperature of this substrate was 20 ° C., and the amount of zirconium adhered to the substrate was 47 mg / m ² ), spray gun (trade name “W-61”, Anest The water thermosetting paint (i) obtained in Production Example 5 was subjected to the first stage room temperature air spray coating so as to have a film thickness of 10 μm. After 7 minutes, the second stage room temperature air spray coating was performed so that the total film thickness was 20 μm in total with the first stage coating. After being allowed to stand for 7 minutes, the coating film was cured by baking at 140 ° C. for 30 minutes to form a coating film by the 1-coat 1-bake method on the aluminum substrate.

  After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 61.6%.

Example 2 Coating Formation by 1 Coat 1 Bake Method In Example 1, except that the water-based thermosetting paint (ii) obtained in Production Example 6 was used instead of the water-based thermosetting paint (i). In the same manner as in Example 1, a coating film was formed on an aluminum substrate by a 1-coat 1-bake method. After the first stage coating, the non-volatile content concentration of the coating material by the first stage coating at the start of the second stage coating was 59.4%.

Example 3 Coating film formation by 1-coat 1-bake method In Example 1, except that the water-based thermosetting paint (iii) obtained in Production Example 7 was used instead of the water-based thermosetting paint (i). In the same manner as in Example 1, a coating film was formed on an aluminum substrate by a 1-coat 1-bake method. After the first stage coating, the non-volatile content concentration of the coating material by the first stage coating at the start of the second stage coating was 57.9%.

Example 4 Coating film formation by 1-coat 1-bake system In Example 5, the water-based thermosetting paint (iv) obtained in Production Example 8 was used in place of the water-based thermosetting paint (i). In the same manner as in Example 1, a coating film was formed on an aluminum substrate by a 1-coat 1-bake method. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 60.8%.

Example 5 Film formation by 1-coat 1-bake method The substrate temperature before coating was 10 ° C., so the substrate temperature was raised to 35 ° C. by hot air blow at 35 ° C. A coating film was formed on an aluminum substrate by the 1-coat 1-bake method in the same manner as in Example 1 except that this was performed. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 62.8%.

Example 6 Film formation by 1-coating 1-bake system The same as in Example 1 except that the material temperature before painting was 10 ° C and that the first stage painting was air spray painting with hot air at 35 ° C. Then, a coating film by a 1-coat 1-bake method was formed on the aluminum substrate. After the first stage coating, the non-volatile content concentration of the coating material by the first stage coating at the start of the second stage coating was 55.6%.

Comparative Example 1 Coating Formation by 1 Coat 1 Bake Method According to the same manner as in Example 1 except that the substrate temperature of the aluminum wheel before coating was 10 ° C., the 1 coat 1 bake method was used. A coating film was formed. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 25.2%.

Comparative Example 2 Coating Film Formation by 1 Coat 1 Bake Method In Example 1, except that the coating of the first stage was made to have a film thickness of 2 μm, 1 coating was applied on the aluminum substrate in the same manner as in Example 1. A coating film by a 1-bake method was formed. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 96.2%.

Comparative Example 3 Coating Film Formation by 1 Coat 1 Bake Method In Example 1, except that the adhesion amount of zirconium to the base material was 3 mg / m ² , on the aluminum base material in the same manner as in Example 1, A coating film by a 1-coat 1-bake method was formed. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 63.1%.

Comparative Example 4 Film Formation by 1 Coat 1 Bake Method In Example 1, the water-based thermosetting paint (i) was a solvent-type metallic paint (trade name “Magicron YP-1 Silver”, manufactured by Kansai Paint Co., Ltd.), 1 stage A coating film by a 1-coat 1-bake method was formed on an aluminum substrate in the same manner as in Example 1 except that the eye coating was 12 μm and the total film thickness was 24 μm. After the first stage coating, the non-volatile content concentration of the paint applied by the first stage coating at the start of the second stage coating was 72.8%.

  About the test sample which is the aluminum base material which formed the coating film by Examples 1-6 and Comparative Examples 1-4 by the 1-coat 1-bake system, a metallic feeling, a coating-film external appearance, a crack resistance, sagging resistance, Adhesion and moisture resistance tests were performed. The test method is as follows.

  Metallic feeling: The metallic feeling was shown by the value of IV measured using a laser-type metallic feeling measuring apparatus (trade name “ALCORP LMR-200”, manufactured by Kansai Paint Co., Ltd.). The IV value is an index indicating the whiteness of the metallic coating film, and the larger the IV value, the more uniformly the metallic pigment is oriented in parallel to the coating surface and whitens, indicating that the metallic feeling is improved.

  Appearance of coating film: Appearance of the coated surface was evaluated by visual observation. A film having no rough skin was good, and a rough one was observed.

  Waki resistance: The presence or absence of bubbles in the coating film was visually evaluated. ○ indicates that bubbles of the coating film due to the armpit are observed, and × indicates that no bubbles of the coating film due to the armpit are observed.

  Sagging resistance: The presence or absence of sagging traces of the coating film was visually evaluated. ○ indicates that a sagging trace of the coating film is observed, and × indicates that no sagging trace of the coating film is observed.

  Adhesion: On the coating film, make 100 2mm x 2mm gobangs with a cutter knife so as to reach the substrate, stick an adhesive cellophane tape on the coating surface, and peel off the tape rapidly at 20 ° C Later peeling was evaluated. ○ indicates that no peeling is observed, and x indicates that one or more peeling is recognized.

  Moisture resistance: The sample was allowed to stand in an environment with a temperature of 50 ± 2 ° C. and a relative humidity of 95% for 10 days, and then the appearance and adhesion of the coating film were examined. Adhesion was evaluated by evaluating the peel after the X-shaped cross-cut was cut with a cutter knife so that it reached the substrate on the coating film, and an adhesive cellophane tape was applied to the cross-cut part, and then it was peeled off rapidly. . ○ indicates that no abnormality is observed in the appearance and adhesion test of the coating film, and x indicates that appearance abnormality such as blistering and blistering is observed or peeling is observed in the adhesion test.

  Moreover, about the test sample which is the aluminum base material in which the coating film by the 1 coat 1 baking system obtained in Examples 1-4 and Comparative Examples 3-4 was formed, the corrosion resistance test was done with the following method.

  Corrosion resistance: Corrosion resistance was examined according to the salt spray test defined in JIS Z-2371. That is, the occurrence of rust after a 480 hour salt spray test was performed by placing a cross mark with an X mark with a cutter knife so as to reach the substrate on the coating film. ○ indicates that rust is not generated, and x indicates that rust is generated.

  Moreover, about Examples 1-4 and the comparative example 4, the measurement test of the amount of VOC (volatile organic compound) of the water-based thermosetting coating material used for the coating was performed, respectively.

  VOC amount: solid content concentration, specific gravity (measured by specific gravity cup method according to JIS K-5400 4.6.2), and water content (automatic moisture measuring device (trade name “KF-100”) The VOC amount of each paint was calculated according to the following formula (1).

VOC amount (g / L) = {[100− (S + W)] × ρ} / [100− (W × ρ)] (1)
In the formula (1), S represents the solid content concentration (%) of the paint, W represents the water content (%) of the paint, and ρ represents the specific gravity (g / L) of the paint.

  Table 1 shows each test result and the amount of VOC.

Claims (15)

On an aluminum substrate subjected to a surface treatment with a zirconium salt with a zirconium deposition amount of 5 to 100 mg / m ² or a surface treatment with a trivalent chromium salt with a trivalent chromium deposition amount of 5 to 100 mg / m ² , a hydroxyl value of 1 to In forming a coating film by a 1-coat 1-bake method in which an aqueous thermosetting paint containing 250 mg KOH / g of an aqueous base resin and a crosslinking agent is applied in two stages and then heat-cured, after the first stage, the second stage A method for forming a coating film on an aluminum base material, wherein the second stage coating is performed with the nonvolatile content concentration of the coating paint by the first stage coating at the start of coating being in the range of 30 to 95% by weight. The coating film forming method according to claim 1, wherein the aluminum base material is an aluminum wheel for an automobile or an aluminum frame for an automobile body. The method for forming a coating film according to claim 1 or 2, wherein the crosslinking agent of the aqueous thermosetting paint is at least one selected from the group consisting of an amino resin, a polyisocyanate compound and a block polyisocyanate compound. The coating-film formation method of any one of Claims 1 thru | or 3 whose compounding quantity of the crosslinking agent of a water-based thermosetting coating is 10-100 weight part with respect to 100 weight part of base resin. The coating film forming method according to any one of claims 1 to 4, wherein the aqueous thermosetting paint further contains 0.1 to 50 parts by weight of a metallic pigment with respect to 100 parts by weight of the base resin. 6. The method of forming a coating film according to claim 5, wherein the metallic pigment is aluminum flake that has been surface-treated to be inactivated against water. The method for forming a coating film according to any one of claims 1 to 6, wherein the aqueous thermosetting paint further contains 0.1 to 8 parts by weight of an ultraviolet absorber with respect to 100 parts by weight of the base resin. The coating film forming method according to any one of claims 1 to 7, wherein the aqueous thermosetting paint further contains 0.1 to 8 parts by weight of a light stabilizer with respect to 100 parts by weight of the base resin. The method for forming a coating film according to any one of claims 1 to 8, wherein the content of the volatile organic solvent in the aqueous thermosetting paint is 20% by weight or less. At the start of the second stage coating, by applying room temperature air spray coating or hot air spray coating for the first stage coating and / or preheating to warm the aluminum substrate temperature to 25 to 50 ° C. at the start of the first stage coating. The method for forming a coating film according to any one of claims 1 to 9, wherein a non-volatile content concentration of the coating paint by the first stage coating is in the range of 30 to 95% by weight. The coating film forming method according to claim 10, wherein the first stage coating is performed by hot air spray coating. The coating film forming method according to claim 10, wherein the first stage coating is performed by hot air spray coating, and the aluminum base material is also heated before the first stage coating is started. The coating film forming method according to claim 10, wherein the second stage coating is performed by hot air spray coating. The coating-film formation method of Claim 10 which makes the wind speed of the coating environment from the completion | finish of 1st stage coating to the start of 2nd stage coating 0.05 m / sec or more. The aluminum base material with which the single layer coating film was formed by the coating-film formation method of any one of Claims 1 thru | or 14.