JPH093693A - Method for coating aluminum blank - Google Patents

Abstract

PURPOSE: To facilitate the adjustment of coating brightness, such as matte, by coating the surface of an anodically oxidized aluminum film with a cation electrodeposition coating material contg. a specific polymerized acrylic resin. CONSTITUTION: The cation electrodeposition coating material of the acrylic resin polymerized by using a polysiloxane compd. having the repeating units expressed by formula I or formula II and having at least one azo bonds in one molecule as a free radical polymn. initiator is used and the surface of the anodically oxidized film of the aluminum blank is coated with this coating material. In such a case, the first voltage is impressed on the aluminum blank for a prescribed time in the anodic oxidation treatment stage for the aluminum blank and thereafter, the second voltage lower by >=10% than this first impressed voltage and higher than 0V is impressed thereon to form the anodically oxidized film of the thin barrier layer, by which the conductivity of the material to be coated is previously enhanced. The barrier layer obtd. by the first impressed voltage is more dissolved as the second impressed voltage is made lower, by which the conductivity of the material to be coated is improved but if the second voltage is 0V, the barrier layer is completely dissolved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an aluminum material. More specifically, the present invention provides an aluminum material that can be easily adjusted in coating gloss and can form a coating excellent in appearance and weather resistance on an aluminum material that requires anodizing treatment such as aluminum sash. It relates to the method of painting the material.

[0002]

2. Description of the Related Art Generally, an anion electrodeposition coating is applied to an anodized aluminum material, but the anion electrodeposition coating uses a melamine resin with poor acid resistance. Weather resistance is not obtained. Also,
Cationic electrodeposition coatings have excellent weather resistance because they use a urethane curing mechanism, but the conventional matting method for cationic electrodeposition coatings is a method of physically delustering by adding a microgel or filler (JP-A-4- 55478, etc.), it tends to become glossy depending on the stirring state of the paint. Further, when cationic electrodeposition coating is applied to an anodized aluminum material, pinholes and the like are likely to occur, which has not been industrially put to practical use.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made for the purpose of providing a method for coating a cationic electrodeposition coating which is applicable to an anodized aluminum material and whose gloss adjustment such as matting is easy. Is.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that an acrylic resin obtained by polymerizing a polysiloxane compound having an azo bond in the molecule as a radical polymerization initiator is used. A thin anodic oxide film of a barrier layer formed by applying a first voltage for a short time at a second voltage lower than the first voltage in the anodizing treatment step of the contained cationic electrodeposition coating material. It has been found that the above-mentioned coating makes it possible to coat a cationic electrodeposition coating whose gloss can be easily adjusted, and the present invention has been completed based on this finding. That is, the present invention provides (1) an acrylic resin obtained by polymerizing a polysiloxane compound having a repeating unit represented by the general formula [1] and having at least one azo bond in one molecule as a radical polymerization initiator. A method of applying the contained cationic electrodeposition coating on an anodized film of an aluminum material, which comprises applying a first voltage for a predetermined time in an anodizing treatment step,
2nd higher than 0V and 10% lower than 1st voltage
Is applied for 5 minutes or less to form a thin anodic oxide film on the barrier layer.

Embedded image (In the formula, R ¹ is the same or different alkyl group having 6 or less carbon atoms or nitrile group, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³ is the same or different unsubstituted or A halogen-substituted alkyl group or a phenyl group, m is the same or different number from 0 to 6,
n is the number of 0 to 200, A is -O- or -NH-, D is _{- (CH 2) S - (} . However, s is the number of the same or different 0-6) or - _{(CH 2) 3 -O- (CH} 2) 2 -
It is. ), And (2) the polysiloxane compound having an azo bond further has a unit represented by the general formula [2], the method for coating an aluminum material according to the item (1),

Embedded image (In the formula, Y is a divalent hydrocarbon group, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³
It is the same or different unsubstituted or halogen-substituted alkyl group or a phenyl group, n is a number from 0 to 200, A is -O- or -NH-, D is - (CH _{2) S} -
(However, s is the number of the same or different 0-6.) Or _{- (CH 2) 3 -O- (} CH 2) 2 - is. ), Is provided.

In the method of the present invention, a polysiloxane compound having a repeating unit represented by the general formula [1] or the general formulas [1] and [2] and having at least one azo bond in one molecule is used. A cationic electrodeposition coating containing a polymerized acrylic resin is used as a radical polymerization initiator.

Embedded image In the general formula [1], R ¹ is the same or different and has 6 carbon atoms.
It is the following alkyl groups or nitrile groups, and m is the same or different number of 0-6. In the general formulas [1] and [2], R ² is the same or different alkyl group having 6 or less carbon atoms, R ³ is the same or different unsubstituted or halogen-substituted alkyl group or phenyl group, and n is 0. ~ 20
0 is a number, A is -O- or -NH-, and D is-.
(CH _{2) S} - (however, s is the number of the same or different 0-6.) Or _{- (CH 2) 3 -O- (} CH 2) 2 - is. In the general formula [2], Y is a divalent hydrocarbon group such as an alkylene group, an alkenylene group and a phenylene group. Examples of the alkyl group having 6 or less carbon atoms represented by R ¹ in the general formula [1] include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a t-butyl group, a pentyl group and a hexyl group. Linear or branched alkyl groups such as In the general formula [1] or [2],
Examples of the alkyl group having 6 or less carbon atoms represented by R ² include linear or branched alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, pentyl group and hexyl group. A group can be mentioned.
In the general formula [1] or [2], the unsubstituted alkyl group represented by R ³ is, for example, a methyl group, an ethyl group,
Examples thereof include linear or branched alkyl groups such as propyl group, isopropyl group, butyl group, t-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group and dodecyl group. . R
^The halogen-substituted alkyl group represented by ³ is a halogenated version of the above alkyl group, for example, a chloromethyl group, a bromomethyl group, a trifluoromethyl group, 2-
Chloroethyl group, 3-chloropropyl group, 3-bromopropyl group, 3,3,3-trifluoropropyl group, 1,1,
2,2-tetrahydroperfluorooctyl group and the like can be mentioned.

A polysiloxane compound having a repeating unit represented by the general formula [1] and having an azo bond is represented by the general formula [3]

[Chemical 6] (In the formula, R ¹ is the same or different alkyl group having 6 or less carbon atoms or nitrile group, and m is the same or different number of 0 to 6.) and the general formula [ 4]

[Chemical 7] (In the formula, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³ is the same or different unsubstituted or halogen-substituted alkyl group or phenyl group,
Is -O- or = NH-, D is _{- (CH 2) s - (} . However, s is the number of the same or different 0-6) or -
_{(CH 2) 3 -O- (CH} 2) 2 - and is, n is the number of 0 to 200. ) And constituent components represented by () are alternately combined. The polysiloxane compound having the repeating units represented by the general formulas [1] and [2] and having an azo bond is represented by the general formula [3] of the polysiloxane compound represented by the general formula [1]. Part of the constituent components was replaced with a constituent component represented by the general formula [5] -CO-Y-CO -... [5] (wherein Y is a divalent hydrocarbon group). It is a thing. The amount that can be replaced with the constituent component represented by the general formula [5] is limited to the amount at which the radical polymerization activity of the polysiloxane compound having an azo bond does not disappear. Examples of the dibasic acid which is the compound corresponding to the general formula [5] include, for example, malonic acid,
Examples thereof include succinic acid, glutaric acid, adipic acid, pimelic acid, corkic acid, azelaic acid, sebacic acid, fumaric acid, itaconic acid, terephthalic acid, isophthalic acid and phthalic acid.

The polysiloxane compound having the repeating unit represented by the general formula [1] and having an azo bond is, for example, the general formula [6].

Embedded image (In the formula, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³ is the same or different unsubstituted or halogen-substituted alkyl group or phenyl group,
Is -O- or -NH-, D is _{- (CH 2) s - (} . However, s is the number of the same or different 0-6) or -
_{(CH 2) 3 -O- (CH} 2) 2 - and is, E is -NH ₂ or -
OH and n is a number from 0 to 200. ) A diamine or dihydroxy compound having a polysiloxane segment represented by the general formula [7]

Embedded image (However, in the formula, R ¹ is the same or different alkyl group or nitrile group having 6 or less carbon atoms, X is halogen, and m is the same or different number of 0 to 6.) It can be produced in high yield by reacting with a dibasic acid dihalide having a bond. Further, among the polysiloxane compounds having an azo bond, the compounds having the constituent component represented by the general formula [5] are obtained by converting a part of the dibasic acid dihalide having the azo bond of the general formula [7] to the general formula [5]. 8] X-CO-Y-CO-X ... [8] (In the formula, X is a halogen and Y is a divalent hydrocarbon group.) In place of the dibasic acid dihalide. It can be produced using the mixture.

The polysiloxane compound having an azo bond can be produced by reacting the compound represented by the general formula [6] with the compound represented by the general formula [7] in the presence of a base. Examples of the base to be used include triethylamine, tributylamine, N, N-dimethylaniline, piberidine, pyridine, 1,5-diazabicyclo [4,3,0] nonene-5,1,8-diazabicyclo [5,4, [0] Undecene-7, tri-n-butylamine, sodium hydride, n-butyllithium and the like can be mentioned, and they can be appropriately selected from these. The synthesis of the polysiloxane compound having an azo bond is usually performed in a solvent. As the solvent used,
For example, ethers such as tetrahydrofuran, diethyl ether, dimethoxyethane and dioxane, halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride and trichlene, hydrocarbons such as n-hexane, benzene and xylene, acetonitrile, N. , N-dimethylformamide and the like can be mentioned. The solvent is 1
The seeds may be used alone or in combination of two or more. The ratio of the diamine or dihydroxy compound represented by the general formula [6] to the dibasic acid dihalide having an azo bond represented by the general formula [7] is not particularly limited and can be appropriately selected. In order to obtain a high molecular weight polysiloxane compound, it is preferable to use both in an approximately equimolar ratio. When a base is used, it is preferably used in an amount of about 0.5 to 1.5 mol times that of the compound represented by the general formula [7]. The reaction temperature for reacting the compound represented by the general formula [6] with the compound represented by the general formula [7] is not particularly limited,
The reaction temperature is preferably -10 to 80 ° C in order to prevent the decomposition of the azo bond and to make the product have a high molecular weight. The reaction time is not particularly limited, but it is preferably 0.5 to 24 hours. The reaction temperature can be increased stepwise or continuously from a low temperature. The generated polysiloxane compound can be fractionated appropriately depending on the type of raw material, base, solvent, etc. used. For example, the viscous reaction solution may be diluted with a solvent, the by-produced quaternary ammonium salt may be washed with water, removed, dried, and the solvent may be removed. General formula [7]
By replacing a part of the compound represented by the formula with the compound represented by the general formula [8] and performing the same synthesis, a repeating unit represented by the general formula [1] and a compound represented by the general formula [2] are represented. It is possible to produce a polysiloxane compound having an azo bond having a unit of

The polysiloxane compound having an azo bond thus obtained has a structure represented by the general formula [3] and the general formula [4], or a general formula [3] and a general formula [4] as the constituent components. And an oligomer or polymer having a structure represented by the general formula [5]. Its properties vary depending on the molecular weight and the content of the polysiloxane segment, but are usually colorless or pale yellow, powdery, viscous oily or rubbery substances. Also, the solubility in the solvent,
Depending on the molecular weight and content of polysiloxane segment, ethers such as tetrahydrofuran, diethyl ether, dimethoxyethane, dioxane, halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, trichlene, toluene, benzene, xylene. It is dissolved in aromatic hydrocarbons such as acetone, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, and acetic acid esters such as methyl acetate, ethyl acetate, propyl acetate, -n-butyl acetate and amyl acetate. In the method of the present invention, the polysiloxane compound having an azo bond has a number average molecular weight of 1,500 to 1
It is preferably 50,000 and 2,000 to 10
More preferably, it is 0000. When the number average molecular weight is less than 1,500, a large number of molecules having substantially no azo bond exist, so that the efficiency of block copolymerization with a polymerizable monomer decreases and the original function is not achieved. It may not be displayed. If the number average molecular weight exceeds 150,000, the solubility in the hydrophilic solvent used for block copolymerization will decrease and the solution viscosity will increase, so block copolymerization must be carried out at a low concentration. In this case, the polymerization rate of the polymerizable monomer used for block copolymerization is lowered, so that the reaction may be forced to take place for a long time.

In the method of the present invention, a cationic electrodeposition coating composition containing an acrylic resin polymerized with a polysiloxane compound having an azo bond as a radical polymerization initiator is used. For the production of the acrylic resin, an acrylic monomer having an amino group, an acrylic monomer having a hydroxyl group and, if necessary, a monomer copolymerizable with these monomers are used.
In the method of the present invention, the acrylic monomer having an amino group is necessary in the step of making the resulting block copolymer resin water-based or cationic electrodeposition coating. The acrylic monomer having an amino group to be used is not particularly limited, and examples thereof include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate, and dimethylaminopropyl methacrylate. it can. The amount of the acrylic monomer having an amino group is determined by the properties, performance, and
It depends on the type and amount of the polysiloxane compound having an azo bond, the acrylic monomer having a hydroxyl group to be copolymerized, and the properties or reaction conditions of the monomer copolymerizable therewith, but usually per 1 kg of resin solid content. 0.4-1.0
It is preferably molar. If the amount of the acrylic monomer having an amino group used is less than 0.4 mol / kg, the emulsifying property of the acrylic resin in water is lowered, and a stable coating composition may not be obtained. If the acrylic monomer having an amino group is used in an amount exceeding 1.0 mol / kg, the yellowing tendency of the finished coating film may be increased. The acrylic monomer having a hydroxyl group to be used is not particularly limited, and for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3
-Hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, diethylene glycol monoacrylate, diethylene glycol monomethacrylate, etc. may be mentioned. The preferred amount of the acrylic monomer having a hydroxyl group varies depending on various factors like the acrylic monomer having an amino group, but is usually 0.5 to 3.0 mol per 1 kg of resin solid content. preferable. When the amount of the acrylic monomer having a hydroxyl group is less than 0.5 mol / kg, the coating film performance may be deteriorated, and the amount of the acrylic monomer having a hydroxyl group is more than 3.0 mol / kg. If so, the water resistance of the coating film may decrease. There is no particular limitation on the monomer that is optionally copolymerized with the acrylic monomer having an amino group and the acrylic monomer having a hydroxyl group, and examples thereof include methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, and 2-. Ethylhexyl acrylate, caprolactone modified acrylate, methyl methacrylate, ethyl methacrylate,
Isopropyl methacrylate, butyl methacrylate,
2-Ethylhexyl methacrylate, t-butyl methacrylate, caprolactone-modified methacrylate, styrene, vinyltoluene, vinyl acetate, cyclohexyl methacrylate and the like can be used.

A polysiloxane compound having an azo bond is used as a radical polymerization initiator, and an acrylic monomer having an amino group, an acrylic monomer having a hydroxyl group, and a monomer copolymerizable therewith are copolymerized. By doing
A copolymer unit (Z) derived from a mixed monomer of an acrylic monomer having an amino group, a monomer having a hydroxyl group, and a copolymerizable monomer, and a polysiloxane compound having an azo group A block copolymer is obtained in which each unit with the polysiloxane unit (X) is mainly bonded to the structure of Z—X, Z—X—Z or — (Z—X) _n —. Having an azo bond in the copolymerization of an acrylic monomer having an amino group, an acrylic monomer having a hydroxyl group, and a monomer copolymerizable therewith, which uses a polysiloxane compound having an azo bond as a radical polymerization initiator The amount of the polysiloxane compound used is 2 to 60% by weight, and the amount of the monomer used is 9
It is preferably 8 to 40% by weight, more preferably 5 to 30% by weight of the polysiloxane compound having an azo bond and 95 to 70% by weight of the monomer. When the amount of the polysiloxane compound having an azo bond is less than 2% by weight, block copolymerization may be extremely difficult. When the amount of the polysiloxane compound having an azo bond exceeds 60% by weight, the block copolymerization may occur. Not only does the molecular weight of the copolymer resin decrease, but it may also be economically disadvantageous. Acrylic monomers having amino groups, acrylic monomers having hydroxyl groups, and block copolymer resins obtained by copolymerizing these monomers with a polysiloxane compound having an azo bond as a radical polymerization initiator. Can be produced in a solvent. There is no particular limitation on the solvent used, for example, methyl alcohol, ethyl alcohol, isopropyl alcohol, alcohol solvents such as n-butyl alcohol, methyl cellosolve, ethyl cellosolve, cellosolve solvent such as butyl cellosolve, other carbitol solvent,
A solvent such as a cellosolve acetate solvent can be used. These solvents can be used alone or in combination of two or more.

In the production of the resin for a cationic electrodeposition coating used in the method of the present invention, unlike the method employed for a conventional resin for a cationic electrodeposition coating, a polysiloxane compound having an azo bond is initiated by radical polymerization. Since it is used as an agent, it does not require a commonly used low-molecular radical polymerization initiator. That is, a hydrophilic solvent, an acrylic monomer having an amino group, an acrylic monomer having a hydroxyl group, and a mixed monomer composed of a monomer copolymerizable therewith as necessary, are added to a mixed monomer having an azo bond. By dissolving the siloxane compound and then raising the temperature, radicals generated by decomposition of the azo bond start polymerization. Therefore, the polymerization reaction of the monomer occurs from both extended molecular ends of the polysiloxane unit. In the copolymerization reaction, the raw materials may be charged all at once or separately, and the reaction temperature is usually 60 to 140 ° C. and the reaction time is about 4 to 20 hours. When the concentration of the polysiloxane compound having an azo bond is low, or when the concentration of the azo bond contained in the molecule is low due to the high molecular weight of the polysiloxane unit in the polysiloxane compound having an azo bond, or when the catalyst efficiency decreases. When it is feared that the polymerization rate will be lowered, a peroxide-based and / or azo-based radical polymerization initiator may be added in the latter half of the reaction to improve the polymerization rate. The radical polymerization initiator used is not particularly limited,
Known peroxide or azo initiators can be used. Examples of peroxide-based radical polymerization initiators include methyl ethyl ketone peroxide, lauroyl peroxide, benzoyl peroxide, cumene hydro-peroxide and t-butyl hydroperoxide. Further, as the azo-based radical polymerization initiator, for example,
2,2'-azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile) and the like can be mentioned. Further, in the copolymerization reaction, a chain transfer agent such as octyl mercaptan, lauryl mercaptan, β-mercaptopropionic acid, and octyl thioglycolate can be used for controlling the molecular weight, if necessary.

The resin solution containing the block copolymer resin as the main component thus obtained contains, in addition to the block copolymer resin as the main component, for example, a chain transfer caused by a solvent or a chain transfer agent during the reaction to block the block copolymer resin. It includes a polymer derived from an acrylic monomer having an amino group which does not become a copolymer resin, an acrylic monomer having a hydroxyl group, and a mixed monomer of a monomer copolymerizable therewith. Also, when a normal peroxide-type or azo-type polymerization initiator is used in combination with a polysiloxane compound having an azo bond, a polymer derived from a mixed monomer that does not become a block copolymer resin is produced. Strictly speaking, the polysiloxane compound in which the azo bond is deactivated during the block copolymerization reaction and the polydimethylsiloxane represented by the general formula [6] having an unreacted hydroxyl group or amino group are also included. The method for preparing the cationic electrodeposition coating composition used in the method of the present invention is not particularly limited and can be prepared by a known method. An example of the preparation method is shown below. That is, a block copolymer resin and a block isocyanate compound are mixed, and acetic acid, lactic acid, formic acid, etc. are added and emulsified in deionized water to obtain a solid content of 5 to 2.
A stable fine particle dispersion of 0% weight is obtained. Examples of the blocked isocyanate compound to be used include isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), IPDI, and oligomers of 10 or less of HDI, or IPDI and HDI in combination with a polyol such as diethylene glycol or trimethylol propane. Isocyanate groups such as reacted di or triisocyanate compounds, alcohol, caprolactam,
Examples include those blocked with oximes and the like. All of these are non-yellowing isocyanates. Further, a similar block of tolylene diisocyanate (TDI) or diphenylmethane diisocyanate can be used to such an extent that weather resistance does not deteriorate.

The method for coating an aluminum material of the present invention comprises an anodizing treatment step of forming an anodized film on aluminum or an aluminum alloy, and an electrodeposition method of forming a coated film on the surface of the anodized film using a cationic electrodeposition coating composition. In the anodizing treatment step, after the first voltage is applied for a predetermined time, it is lower than the first voltage by 10% or more and 0.
A second voltage higher than V is applied only for a time within 5 minutes to form a thin anodic oxide film of the barrier layer. The method of the present invention may include a coloring treatment step of electrolytically coloring the anodized film between the anodization treatment step and the coating treatment step. Therefore, the article to be coated according to the method of the present invention has an aluminum anodized film or an electrolytically colored aluminum anodized film. The electrolytic coloring can be performed by any known secondary electrolysis or tertiary electrolysis method. The anodizing method is not particularly limited, and a known method can be used. For example, sulfuric acid,
Inorganic acids such as phosphoric acid and chromic acid, organic acids such as oxalic acid, sulfosalicylic acid and malonic acid, alkaline aqueous solutions such as sodium hydroxide and trisodium phosphate, direct current, alternating current, pulse, PR wave Alternatively, a method of electrolysis can be used by the AC / DC superimposition method. The electrodeposition coating treatment is performed by applying a voltage of 50 to 300 V according to a conventional method. It is preferable to lower the initial applied voltage by the soft start method or the constant current method in order to suppress the occurrence of pinholes.

FIG. 1 is an explanatory view showing a specific procedure of the method of the present invention. First, anodization is performed at a constant current density according to a conventional method. The end voltage at this time is the formation voltage X volt,
That is, the first voltage is used. Next, after switching to constant voltage control and applying for a predetermined time, the voltage is gradually decreased to X
The voltage is 10% or more lower than the voltage and higher than 0 V, and this voltage is applied for 5 minutes or less. This voltage is Y volts, that is, the second voltage. The thus-obtained anodized film is preferably washed with a hot water bath at 80 to 90 ° C. for about 5 minutes and then subjected to electrodeposition coating. Incidentally, electrolytic coloring can be applied before the electrodeposition coating. FIG.
It is sectional drawing of an aluminum anodized film. Reference numeral 1 is an aluminum anodic oxide film, 1a is a hole, 2 is a base material made of aluminum or an aluminum alloy, 3 is a barrier layer, and 4 is an impurity. The barrier layer 3 is originally a film having low conductivity, but since it is a thin film of several tens of angstroms,
When the anion electrodeposition coating material is used for coating, a part of the barrier layer 3 is dissolved, an electric current flows through the object to be coated, and the coating material is deposited on the surface of the anodic oxide coating 1 to form a coating film. When the cationic electrodeposition coating is used, the barrier layer 3 is not dissolved, but an electric current flows through the barrier layer 3 of the anodized film 1 to deposit the coating and form a coating film. By the way, the defects of the anodic oxide film 1 are affected by the conditions of the anodic oxidation and the impurities 4 in the base material 2, and particularly when the impurities 4 such as magnesium, silicon, manganese, and copper are present, the defects are concentrated in that portion. When defects are locally concentrated, current is concentrated on that portion during coating, which causes a kind of film breakage, resulting in defects such as craters and pinholes in the coating film.
However, in the method of the present invention, in the anodizing step, after applying the first voltage for a predetermined time, a second voltage that is 10% or more lower than the first voltage and higher than 0 V is applied for a time within 5 minutes. As a thin anodic oxide film of the barrier layer is formed, the conductivity of the object to be coated is improved, current concentration on the defective part of the anodic oxide film is suppressed, and a coating film with excellent appearance without defects is obtained. To be The barrier layer 3 having a predetermined thickness obtained at the first voltage is melted and thinned by applying the second voltage. Therefore, the lower the second voltage is, the thinner the barrier layer 3 is, and the more the conductivity of the coated object is improved. However, the second voltage is higher than 0V. When the second voltage is 0V, the barrier layer 3 is completely melted.

[0016]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In addition, in Examples and Comparative Examples, the coating films were evaluated as follows. (1) Appearance It was visually determined. Good: The coating film is smooth and has no rough skin, uneven gloss, or pinholes. Poor: Rough skin, uneven gloss, pinnhole, etc. are observed. (2) Weather resistance According to JIS K 5400 (1990) 9.8.1, a sunshine carbon arc lamp type accelerated weather resistance test was conducted to evaluate the degree of chalking after irradiation for 4,000 hours. Pass: No chalking is observed. Fail: Chalkification is recognized. Production Example 1 A four-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a calcium chloride tube had a number average molecular weight of 10,000.
And polydimethylsiloxane having amino groups at both ends (in the general formula [6], R ² and R ³ are methyl groups, E is —NH ₂ , D is — (CH ₂ ) ₃ —, and n is 133 on average. A certain Shin-Etsu Chemical Co., Ltd. product, X-22-161F) 200 weight part, triethylamine 4.04 weight part, and chloroform 100 weight part were prepared and fully stirred. Then, a solution of 6.34 parts by weight of 4,4′-azobis (4-cyanopentanoic acid chloride) and 97.9 parts by weight of chloroform was added dropwise under ice cooling over 40 minutes. After dropping, add 2
Reacted for hours. Further, 100 parts by weight of chloroform was added and added dropwise to dilute the mixture, and water-soluble components such as triethylamine hydrochloride were removed by washing with water, followed by vacuum drying. The number average molecular weight of the obtained polydimethylsiloxane compound having an azo bond was 86,000 according to GPC analysis. The decomposition temperature of the azo bond determined by DSC (Differential Scanning Calorimeter) was 92.5 ° C, and the decomposition enthalpy was -16.1 mJ / mg, but the heat balance after heat treatment at 140 ° C for 5 hours was Didn't show up. Production Example 2 In a four-necked flask equipped with a thermometer, a stirrer, a reflux condenser and a calcium chloride tube, the number average molecular weight was 4,600,
Polydimethylsiloxane having amino groups at both ends (in the general formula [6], R ² and R ³ are methyl groups, and E is —N
H _2, D is _{- (CH 2) 3 -,} n is an average 60 a is Shin-Etsu Chemical Co., Ltd., X-22-161C) 100 parts by weight, 4.38 parts by weight of triethylamine and chloroform 86.8 parts by weight Was charged and thoroughly stirred. Then, under ice cooling, 4.4 '
-Azobis (4-cyanopentanoic acid chloride) 6.8
A solution consisting of 9 parts by weight and 86.8 parts by weight of chloroform was added dropwise over 40 minutes. After the dropping was completed, the reaction was carried out at room temperature for 2 hours. Further, 50 parts by weight of chloroform was added and added dropwise to dilute the mixture, and water-soluble components such as triethylamine hydrochloride were removed by washing with water, followed by vacuum drying. The number average molecular weight of the obtained polydimethylsiloxane compound having an azo bond was 29,000 by GPC analysis. Also, D
The decomposition temperature of the azo bond determined by SC (Differential Scanning Calorimeter) is 93.6 ° C, and the decomposition enthalpy is -39.3 mJ.
/ Mg, but the heat balance after heat treatment at 140 ° C. for 5 hours did not appear. Example 1 In a 3000 ml four-necked flask equipped with a stirrer, a heat exchanger and a thermometer, 9.6 g of the polydimethylsiloxane compound having an azo bond obtained in Production Example 1 and 2-dimethylaminoethyl methacrylate 8. 6 g, 2-hydroxyethyl methacrylate 17.3 g, methyl methacrylate 25.9 g, 2-ethylhexyl acrylate 34.6
g, isopropyl alcohol 54.4 g, and butyl cellosolve 9.6 g were charged all at once, and solution polymerization was carried out at a temperature of about 80 ° C. for 7 hours while stirring. Then, 36.9 g of an isophorone-based blocked isocyanate compound (Sumitomo Bayer Urethane Co., Ltd., BL-4165) was mixed with the reaction solution,
The temperature was adjusted to about 60 ° C., neutralized with 2.6 g of acetic acid, and then 100.5 g of deionized water was gradually added to make the solution water-soluble to obtain a stable fine particle dispersion to obtain a cationic electrodeposition coating composition. Next, A6063 aluminum material was placed in a 1.5 mol / liter sulfuric acid bath at 20 ° C. and a direct current density of 1.5 A / dm ² , 1
Anodization was performed for 5 minutes. The first applied voltage is 17
V. After switching to the constant voltage control, the step-down speed was set to 0.1 V / sec and the second applied voltage was lowered to 14 V and kept for 1 minute. The anodic oxide film thus obtained was washed with water and then washed with 150 g / liter of nickel sulfate and 40
It was subjected to direct current electrolysis for 60 seconds at -14 V in a g / liter boric acid bath to give a bronze color. After washing with water, use hot water at 80 ° C for 5
After washing for a minute, a cationic electrodeposition coating was performed at an applied voltage of 160 V according to a conventional method, and baking was performed at 170 ° C. for 20 minutes. The obtained test piece had a coating film thickness of 7 μm and a good appearance,
Chalking was not observed at all even in the accelerated weathering test. Examples 2 to 4 Using the raw materials shown in Table 1, the same operation as in Example 1 was repeated to produce a cationic electrodeposition coating composition comprising a stable fine particle dispersion. The aluminum material was subjected to anodization and cationic electrodeposition coating under the conditions shown in Table 1. The evaluation results of the coating film are shown in Table 1. Comparative Example 1 In a 3000 ml four-necked flask equipped with a stirrer, a heat exchanger, and a thermometer, 1.9 g of 2,2'-azobisisobutyronitrile and 2-dimethylaminoethyl methacrylate 9.
5 g, 2-hydroxyethyl methacrylate 18.8
g, 28.2 g of methyl methacrylate, 37.6 g of 2-ethylhexyl acrylate, 54.4 g of isopropyl alcohol, and 9.6 g of butyl cellosolve were charged all at once, and solution polymerization was carried out at a temperature of about 80 ° C. for 7 hours while stirring.
Next, an isophorone-based blocked isocyanate compound (Sumitomo Bayer Urethane Co., Ltd., BL-416) was added to the reaction solution.
5) Mix 36.9 g, bring the temperature to about 60 ° C., and add acetic acid 2.
After neutralization with 9 g, deionized water (100.2 g) was gradually added to make the solution water-soluble, and a stable fine particle dispersion was obtained to obtain a cationic electrodeposition coating composition. The aluminum material was subjected to anodization and cationic electrodeposition coating under the conditions shown in Table 2. The evaluation results of the coating film are shown in Table 2. Comparative Examples 2 to 4 Using the raw materials shown in Table 2, the same operation as in Comparative Example 1 was repeated to produce a cationic electrodeposition coating composition comprising a stable fine particle dispersion. The aluminum material was subjected to anodization and cationic electrodeposition coating under the conditions shown in Table 2. The evaluation results of the coating film are shown in Table 2.

[0017]

[Table 1]

[0018]

[Table 2]

[Note] IPA: isopropyl alcohol BC: butyl cellosolve MAI-1: polysiloxane compound having azo bond synthesized in Production Example 1 MAI-2: polysiloxane compound having azo bond synthesized in Production Example 2 AIBN : Azobisisobutyronitrile DM: 2-Dimethylaminoethylmethacrylate 2HEMA: 2-Hydroxyethylmethacrylate MMA: Methylmethacrylate CHMA: Cyclohexylmethacrylate BuA: Butylacrylate 2EHA: 2-Ethylhexylacrylate KBM-503: 3-methacryloxypropyltri Methoxysilane (Shin-Etsu Chemical Co., Ltd.) BL-4165: Isophorone-based blocked isocyanate compound (Sumitomo Bayer Urethane Co., Ltd., heating residue 65% by weight) BL-21 5: Isophorone-based blocked isocyanate compound (manufactured by Mitsubishi Chemical Corporation, heating residue 70% by weight) All the test pieces of Examples 1 to 4 coated by the method of the present invention had a good appearance, and after the accelerated weathering test The film passed the test without chalking. On the other hand, the coating film of Comparative Example 1 coated with the cationic electrodeposition coating composition having no polysiloxane block had a good appearance, but failed due to chalking in the weather resistance test. The coating film of Comparative Example 2 in which a cationic electrodeposition coating material made of a polysiloxane compound having an azo bond was applied to an anodized aluminum material under the condition that the first voltage and the second voltage were equal to each other was the weather resistance. The test passed, but the appearance was poor. Furthermore, a cationic electrodeposition coating that does not have a polysiloxane block,
The coating films of Comparative Example 3 and Comparative Example 4 coated on the anodized aluminum material under the condition that the first voltage and the second voltage were equal had a poor appearance and failed the weather resistance test.

[0020]

According to the method of the present invention, a coating film having a good matte appearance suitable for an aluminum material and excellent weather resistance can be formed on the aluminum anodized film. The coating method of the present invention is for building materials such as aluminum sashes,
It can be suitably applied to aluminum materials for automobiles and the like.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a specific procedure of the method of the present invention.

FIG. 2 is a cross-sectional view of an aluminum anodized film.

[Explanation of symbols]

 1 Anodized film 1a Pore 2 Base material 3 Barrier layer 4 Impurity

Claims (2)

[Claims] 1. A cationic electrode containing an acrylic resin obtained by polymerizing a polysiloxane compound having a repeating unit represented by the general formula [1] and having at least one azo bond in one molecule as a radical polymerization initiator. A method of applying a coating material on an anodized film of an aluminum material, which comprises applying a first voltage for a predetermined time in an anodizing step,
2nd higher than 0V and 10% lower than 1st voltage
Is applied for 5 minutes or less to form a thin anodic oxide coating on the barrier layer. Embedded image (In the formula, R ¹ is the same or different alkyl group having 6 or less carbon atoms or nitrile group, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³ is the same or different unsubstituted or A halogen-substituted alkyl group or a phenyl group, m is the same or different number from 0 to 6,
n is the number of 0 to 200, A is -O- or -NH-, D is _{- (CH 2) S - (} . However, s is the number of the same or different 0-6) or - _{(CH 2) 3 -O- (CH} 2) 2 -
It is. ) 2. The method for coating an aluminum material according to claim 1, wherein the polysiloxane compound having an azo bond further has a unit represented by the general formula [2]. Embedded image (In the formula, Y is a divalent hydrocarbon group, R ² is the same or different alkyl group having 6 or less carbon atoms, R ³
It is the same or different unsubstituted or halogen-substituted alkyl group or a phenyl group, n is a number from 0 to 200, A is -O- or -NH-, D is - (CH _{2) S} -
(However, s is the number of the same or different 0-6.) Or _{- (CH 2) 3 -O- (} CH 2) 2 - is. )