JP2001131490A - Matte anionic electrodeposition coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anionic electrodeposition coating excellent in finish appearance. SOLUTION: The anionic electrodeposition coating comprises a hydrotalcite compound represented by the formula: Mgy-xAlx(OH)2y.Ax/yn-.mH2O (wherein A- is an n-valent anion, for example, a monovalent or divalent anion such as OH-, Cl-, CO32- and the like; and x, y and m are each a number satisfying 0<x, 2x<=y and 0<m, respectively), preferably by the formula: Ma1-xAlx(OH)2.(CO3)x/2.mH2O (wherein 0<x<=0.5). The hydrotalcite compound has a specific surface area (BET) of preferably 1-50 m2/g, particularly preferably 2-40 m2/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel anionic electrodeposition coating.

[0002]

2. Description of the Related Art At present, an anodized aluminum sash or the like is coated with an anion-type electrodeposition paint having a good finish with a single coat.

[0003] The coating method includes, for example, a pretreatment process such as anodizing an aluminum material in a concentrated sulfuric acid aqueous solution to form an anodized film on the surface of the aluminum material, washing with water, and, if necessary, sealing. After the anodized aluminum material is obtained, the anodized aluminum material is electrodeposited on the surface of the anodized aluminum material by applying a voltage between the aluminum material as an anode and the counter electrode as a cathode in an electrodeposition paint bath. A method of forming a coating film is generally used.

[0004] In such an anion type electrodeposition coating line, since the concentrated sulfuric acid aqueous solution in the pretreatment step is brought into the electrodeposition coating bath, abnormal deposition occurs when the anion electrodeposition coating is performed, and the coating film is exposed. Causes paint defects such as pinholes,
For this reason, there is a problem that the finished appearance and performance of the coating film are deteriorated.

Further, as an anionic electrodeposition coating material used in aluminum sashes, etc., a radical copolymerization reaction of a (meth) acrylic acid monomer, a hydroxyl group-containing monomer and, if necessary, other alkyl (meth) acrylates is carried out. Although a water-dispersible acrylic copolymer is used as a base resin, unreacted (meth) acrylic acid remains in the copolymer resin in the radical copolymerization reaction. When the low molecular weight acid component is subjected to anionic electrodeposition coating, the electrodeposition deposition rate differs from the copolymer resin component due to different electrodeposition deposition rates, causing abnormal deposition on the coating film,
There is a problem that paint defects such as pinholes occur.

Conventionally, in order to solve such a problem, a low-molecular-weight solution such as an aqueous sulfuric acid solution introduced from a pretreatment step or unreacted (meth) acrylic acid in a copolymer was introduced in an anion electrodeposition coating line. Is generally removed by anion exchange.

[0007] However, in order to remove such low-molecular-weight acid components, frequent anion-exchange treatment is required, which is troublesome, that the regeneration treatment for anion-exchange is troublesome, and that wastewater treatment equipment is difficult. There were problems such as being large-scale.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to develop an anion-type electrodeposition paint in which the finish appearance of a conventional anion-type electrodeposition paint is improved.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, an anionic electrodeposition coating material containing a specific hydrotalcite compound has been developed. It has been found that the number of exchange treatments can be reduced and a coating film having an excellent finished appearance can be provided,
The present invention has been completed.

[0010] Namely, the present invention is, in anionic electrodeposition coating, the following general formula _{(1) Mg YX Al X (} OH) 2Y · A X / Y n ^over · mH ₂ O (1) (in the formula, A ^n-n-valent anion, for example OH ^over, Cl
^Represents a divalent anion such as ^— , CO ₃ ^{2 —} , and x represents 0
<X, y are 2x ≦ y, and m is a number satisfying 0 <m, respectively).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrotalcite compound used in the electrodeposition coating composition of the present invention is a general term for a compound mainly composed of Mg and Al and mainly represented by the following general formula.

[0012] _{Mg YX Al X (OH) 2Y} · A X / Y n ^over · mH ₂ O (1) (wherein, A ^{n over} the n-valent anion, such as OH ^{chromatography,} Cl
^Represents a divalent anion such as ^— , CO ₃ ^{2 —} , and x represents 0
<X and y are 2x ≦ y, and m is a number satisfying 0 <m). Such a hydrotalcite compound is a compound having a layered structure having a large adsorptivity, and is industrially an antacid or a thermoacid. It is used as a stabilizer. In the above formula (1), particularly, the following formula (2): Mg _1-x Al _x (OH) _2. (CO ₃ ) _{X / 2} .mH ₂ O (2) 0 <x ≦ 0.5 is preferable.

Specific examples of the hydrotalcite compound include, for example, Mg _{4 -3} Al ₂ (OH) _{12 -6} CO _{3 .m
H 2 O, Mg 6 Al 2} (OH) 16 CO 3 · 4H 2 O, Mg
_4.5 Al ₂ (OH) ₁₃ CO ₃ · 3.5 H ₂ O, Mg ₄ Al
₂ (OH) ₁₂ CO ₃ · 3H ₂ O, Mg _0.7 Al _0.3
O _{1.15 and the} like, and as a commercially available product, DHT-4
A, Kyoword 500, 1000, 2000, 210
0, 2200 (manufactured by Kyowa Chemical Industry Co., Ltd.) and these can be used alone or in combination. Among these, Mg _{4 -3} Al ₂ (OH) _{12 -6} CO ₃ .mH ₂
O's are preferred.

The hydrotalcite compound used in the present invention has a specific surface area (BET) of 1 to 50 m ² /
g, especially those in the range of ^{2 to} 40 m ² / g.
The larger the specific surface area is, the larger the amount of adsorption per unit particle is. Further, the particle size distribution of the hydrotalcite compound is preferably 1 μm or less, more preferably 80% or more, particularly preferably 85% or more. If the particle size distribution is less than 80%, the amount of adsorption per unit weight decreases, which is not preferable.

The hydrotalcite compound used in the present invention may be subjected to a surface treatment as required. Examples of such surface treatment agents include organic fatty acids, anionic surfactants, silane-based coupling agents, titanate-based coupling agents, cheeks of glycerin and fatty acids, and the like. Specific examples of such a surface treatment agent include, for example, higher fatty acid condyles such as stearic acid, oleic acid, and lauric acid; for example, sodium stearate, sodium oleate,
Anionic surfactants such as sodium laurylbenzenesulfonate; for example, vinyltriethoxysilane,
Silane-based or titanate-based coupling agents such as γ-methacryloxypropyltriethoxysilane, isopropyltriiristearoyl titanate, isopropyltridecylbenzenesulfonyl titanate, etc .; for example, glycerin monostearate, glycerin monooleate And esters of glycerin and a fatty acid such as

The surface treatment of the hydrotalcite compound of the formula (1) with the surface treating agent is carried out, for example, when the surface treating agent is itself liquid or when it is dissolved in water, alcohol cheek, or the like to make it liquid. Can be carried out by mechanically mixing the liquid surface treating agent and the hydrotalcite compound powder of the formula (1) or an aqueous suspension thereof under heating conditions or non-heating conditions. Alternatively, for example, when the surface treatment agent is melted under heating conditions, the surface treatment agent can be mechanically mixed with the hydrotalcite compound powder of the formula (1) under heat melting conditions. If necessary, the mixture may be sufficiently mixed and subjected to, for example, washing, dehydration, drying, pulverization, classification, or the like, as appropriate, to give a surface-treated product.

In the electrodeposition coating composition of the present invention, activated alumina and / or activated clay can be used in combination with the above-mentioned hydrotalcites as a pigment. Such activated alumina and activated clay are also compounds having a porous structure having an adsorbing ability, and are industrially used for decolorization and purification of fats and oils and petroleum mineral oils.

Activated alumina is an intermediate having a pore structure obtained by calcining an alumina hydrate such as gypsite, boehmite, bayerite, or amorphous hydrated gel at an appropriate temperature, usually 200 to 1,000 ° C. Alumina (transition alumina). Activated alumina is also called gamma-alumina. As commercially available products, activated alumina KC-501, KC-503 and gamma-alumina A-manufactured by Sumitomo Chemical Co., Ltd.
11; DN-1A manufactured by Mizusawa Chemical Co., Ltd., and the like. Activated clay is obtained by treating acidic clay, which is a kind of clay containing a montmorillonite family clay mineral and soluble silicic acid as main components, with an acid to elute a part of basic components. As commercial products, activated clay made by Nippon Activated Shirato Co., Ltd. and Galleon Earth N made by Mizusawa Chemical Co., Ltd.
V and the like.

The compounding amount of the hydrotalcite compound in the electrodeposition coating composition of the present invention is suitably in the range of 2 to 100 parts by weight based on 100 parts by weight of the solid content of the emulsion resin in the coating composition. More preferably, it is in the range of 50 parts by weight. If the amount is less than 2 parts by weight, the ion exchange capacity cannot be sufficiently exhibited, while if it exceeds 100 parts by weight, problems tend to occur in the storage properties of the paint and the adhesion of the coating film to be formed.

When a hydrotalcite compound and activated alumina and / or activated clay are used together as a pigment component, the mixing ratio is not particularly limited.
Preferably, it is suitable to be used at a weight ratio of 1:10 to 10: 1.

The method of blending the hydrotalcite compound into the electrodeposition paint can be blended without any particular limitation. For example, it can be produced by dispersing and mixing an aqueous base resin for electrodeposition and a hydrotalcite compound with a disperser, then blending a crosslinking agent and a neutralizing agent, and dispersing in water.

The anionic electrodeposition coating composition referred to in the present invention is generally known, and includes an aqueous base resin containing a carboxyl group and a hydroxyl group in a skeleton and an amino resin.
A crosslinking agent such as a blocked polyisocyanate compound is obtained by neutralizing a vehicle component with a neutralizing agent such as an amine and then dispersing in water.

As the above-mentioned aqueous base resin, for example,
Vinyl copolymer, polyester resin, alkyd resin,
Fluororesins, silicone resins and the like can be mentioned. These resins can be used alone or in combination of two or more. Among these, it is preferable to use the following vinyl copolymers. Examples of the vinyl copolymer include a vinyl copolymer obtained by subjecting a hydroxyl group-containing vinyl monomer, an ethylenically unsaturated carboxylic acid, and another unsaturated monomer as required to a radical copolymerization reaction.

The following are examples of these monomer components. (1) Hydroxyl-containing vinyl monomers: for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, (poly) ethylene glycol mono (meth) Acrylate, (poly) propylene glycol mono (meth) acrylate, hydroxybutyl vinyl ether,
(Meth) allyl alcohol and the above-mentioned hydroxyl-containing vinyl monomers and β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, γ-caprolactone, γ-caprylolactone, γ-
As a product name such as a reaction product with a lactone compound such as laurilolactone, ε-caprolactone, δ-caprolactone, etc., as a trade name, Praxel FM1 (manufactured by Daicel Chemical Co.,
Caprolactone-modified (meth) acrylic acid hydroxyesters), Praxel FM2 (same as left), Praxel FM
3 (same as left), Plaxel FA-1 (same left), Plaxel FA2 (same left), Plaxel FA3 (same left) and the like.

(2) Ethylenically unsaturated carboxylic acids: for example, (meth) acrylic acid, maleic acid, Placcel F
M1A (hereinafter, manufactured by Daicel Chemical Industries, caprolactone-modified carboxyl group-containing (meth) acrylic monomer, trade name), Praxel FM4A, Praxel FM10A and the like.

(3) Other unsaturated monomers: for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate , (meth) acrylate, octyl (meth) acrylate, lauryl (meth) alkyl or cycloalkyl esters of C ₁ -C ₁₈ (meth) acrylic acid such as cyclohexyl acrylate, aromatic such as styrene vinyl monomers - s , (Meta)
(Meth) acrylamides such as acrylamide, N-butoxymethyl (meth) acrylamide, N-methylol (meth) acrylamide and derivatives thereof, and (meth)
Acrylonitrile compounds, etc., alkoxysilyl groups such as γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropyltriethoxysilane, vinyltrimethoxysilane Containing vinyl monomers.

In the proportions of these monomers, the hydroxyl group-containing monomers have a hydroxyl value of about 3 in the copolymer.
It may be blended so as to fall within the range of 0 to 300 mgKOH / g, but the amount of the hydroxyl group-containing monomer is about 3 to 40% by weight, preferably about 5 to 5% in terms of the total amount of the above monomers.
It is in the range of 30% by weight.

The above ethylenically unsaturated carboxylic acid may be blended so that the acid value of the copolymer falls within the range of about 10 to 200 mg KOH / g. And the ethylenically unsaturated carboxylic acid ranges from about 3 to 30% by weight, preferably about 4 to 20% by weight.

As other unsaturated monomers, it is preferable to use C ₁ -C ₁₈ alkyl or cycloalkyl esters of (meth) acrylic acid and aromatic vinyl monomers such as styrene. The amount of the monomers is about 37 to 95 based on the total amount of the monomers.
%, Preferably in the range of about 60-91% by weight.

As a method for carrying out a radical copolymerization reaction,
Conventionally known solution polymerization methods can be used.

As the cross-linking agent, for example, part or all of the methylol group of the melamine resin is methanol, ethanol, propanol, butanol, octyl alcohol,
Those modified with one or more monohydric alcohols such as 2-ethylhexyl alcohol can be used. It is preferable that the melamine resin has a mononuclear to polynuclear (about 2 to 5) nucleus content of 50% by weight or more. Also,
The melamine resin may contain other functional groups such as an imino group and a methylol group. As the matte electrodeposition paint, C ₃ or more monohydric alcohols, in particular C ₄ -C ₁₈ monohydric alcohol modified ether group triazine ring 1 nucleus per average of about 2.0 or more, particularly 2 It is preferable to contain from 0.0 to 5.0.

Examples of the blocked polyisocyanate crosslinking agent include lactones such as ε-caprolactone, methanol, ethanol, propanol, butanol, and aliphatic or alicyclic polyisocyanate compounds such as isophorone diisocyanate and hexamethylene diisocyanate. Those blocked with alcohols such as pentanol and oximes such as methyl ethyl ketoxime and methyl isobutyl ketoxime can be used.

In the electrodeposition coating composition of the present invention, the mixing ratio of the aqueous base resin and the crosslinking agent is 40 to 85% by weight, preferably 50% by weight, based on the total solid content of both.
And the crosslinking agent ranges from 15 to 60% by weight, preferably from 20 to 50% by weight. When the blending ratio of the aqueous base resin is less than 40% by weight, and when the crosslinking agent exceeds 60% by weight, the coating performance such as weather resistance and workability deteriorates, while the blending ratio of the aqueous base resin is 85% by weight.
If the amount of the crosslinking agent is less than 15% by weight, the coating properties such as weather resistance, abrasion resistance and workability deteriorate, which is not preferable.

The electrodeposition coating composition of the present invention may contain a pigment, if necessary.
Dyes, fluidity modifiers and the like can be added.

The electrodeposition paint of the present invention may be any type of paint such as a building bath paint, a replenishment paint and a line paint, but it is particularly preferably used as a line paint.

The electrodeposition paint of the present invention is used as a glossy or matte paint, and a coating film can be formed by the following non-rinse or rinse coating method.

The electrodeposition paint of the present invention is preferably applied particularly to the field of aluminum building materials using a colored or uncolored anodized aluminum material.

In order to form a coating film using the electrodeposition paint of the present invention, the anion-type electrodeposition paint obtained above is used as an electrodeposition paint bath, the aluminum material is immersed in the bath, and then dried. Anion electrodeposition coating is performed so that the film thickness is about 5 to 30 microns, without water washing (non-rinsing) or with water washing (rinsing), and after setting at room temperature, baking (for example, about 160 to 200 C. for about 20 to 40 minutes) to form a coating film.

[0039]

EXAMPLES The present invention will be described in detail with reference to examples. The invention is not limited to the embodiments provided.

Production Example of Acrylic Copolymer (a) 70 g of isopropyl alcohol was charged into a reaction vessel and kept at 80 ° C., and 10 g of styrene, 31 g of methyl methacrylate, 10 g of n-butyl acrylate, 30 g of ethyl acrylate, 2-hydroxyethyl acrylate
A mixture of 12 g of acrylic acid, 7 g of acrylic acid, and 2 g of azobisdimethylvaleronitrile was added dropwise over 3 hours, and then 1 g of azobisdimethylvaleronitrile was added.
For 1 hour to produce a reactive varnish (a). The copolymer had a weight average molecular weight of about 20,000 and an acid value of 55 m.
gKOH / g and a hydroxyl value of 58 mgKOH / g.
This copolymer (a) is used for a glossy electrodeposition paint.

Production Example of Acrylic Copolymer (b) 70 g of isopropyl alcohol was charged into a reaction vessel and kept at 80 ° C., and 10 g of styrene, 24 g of methyl methacrylate, γ-methacryloxypropyltrimethoxy were added. 7 g of silane, 10 g of n-butyl acrylate, 30 g of ethyl acrylate, 2-hydroxyethyl acrylate
A mixture of 12 g of acrylic acid, 7 g of acrylic acid, and 2 g of azobisdimethylvaleronitrile was added dropwise over 3 hours, and then 1 g of azobisdimethylvaleronitrile was added.
For 1 hour to produce a reactive varnish (b). The copolymer has a weight average molecular weight of about 25,000 and an acid value of 5
5 mgKOH / g and a hydroxyl value of 58 mgKOH / g. This copolymer (b) is used for a matte electrodeposition paint.

Example 1 DHT-4A was added to 7 kg (solid content) of the above copolymer (a).
(Made by Kyowa Chemical Industry Co., Ltd., trade name, Mg _{4 -3} Al ₂
After mixing 350 g of (OH) _12-6 CO ₃ · mH ₂ O), the mixture was dispersed in a pebble mill to obtain a pigment paste. Then, the pigment paste was added in an amount of 0.1 to the carboxyl group of the copolymer (a) of the obtained pigment paste. After blending 4 equivalents of triethylamine,
Mix and disperse, then add to this Nikarac MX600
After mixing and dispersing 3 kg (trade name, butoxylated melamine resin, manufactured by Sanwa Chemical Co., Ltd.), deionized water was gradually added dropwise while stirring, and triethylamine was further added to adjust the pH to 8.0. The glossy electrodeposition paint of Example 1 having a solid content of 10% by weight was produced. After 100 ppm of sulfuric acid was added to the electrodeposition paint as a sulfate group, it was stored at 30 ° C. for 14 days.

Example 2 In Example 1, the acrylic copolymer (a) was replaced with the acrylic copolymer (b) and Nicalak MX-600 was replaced with Nicalack MX-430 (trade name, melamine manufactured by Sanwa Chemical Co., Ltd.). About 3 methyl groups and about 3 butyl groups per nucleus, and the amount of the nucleus is about 57%) except that the same amounts were used. Was manufactured. Sulfuric acid is added to this electrodeposition paint as sulfate group.
After adding ppm, it was stored at 20 ° C. for 14 days.

Example 3 DHT-4A was added to 7 kg (solid content) of the copolymer (a).
(Made by Kyowa Chemical Industry Co., Ltd., trade name, Mg _{4 -3} Al ₂
After mixing 350 g of (OH) _12-6 CO ₃ · mH ₂ O) and 1960 g of titanium dioxide, the mixture was dispersed in a pebble mill to obtain a pigment paste. Then, the carboxyl group of the copolymer (a) of the obtained pigment paste was After adding 0.4 equivalent of triethylamine to the mixture, the mixture was mixed and dispersed, and then added to Nicarac MX600 (manufactured by Sanwa Chemical Co., Ltd.,
After mixing and dispersing 3 kg of trade name, butoxylated melamine resin, deionized water was gradually added dropwise while stirring, and triethylamine was further added to adjust the pH to 8.0. A glossy white electrodeposition paint No. 3 was produced. 100 ppm of sulfuric acid as sulfuric acid group in this electrodeposition paint
After putting, it was stored at 20 ° C. for 14 days.

Example 4 In Example 3, the acrylic copolymer (a) was replaced with the acrylic copolymer (b), and Nicarac MX-600 was replaced with Nicarac MX-430 (trade name, melamine manufactured by Sanwa Chemical Co., Ltd.). About 3 methyl groups and about 3 butyl groups per nucleus, and the amount of the nucleus is about 57%), except that the same amounts were used. A paint was manufactured. Sulfuric acid was added to this electrodeposition paint as sulfate group.
After adding 0 ppm, it was stored at 20 ° C. for 14 days.

Comparative Example 1 A clear glossy electrodeposition paint of Comparative Example 1 was produced in the same manner as in Example 1 except that DHT-4A was not used. Sulfuric acid is added to this electrodeposition paint as sulfate group.
After adding ppm, it was stored at 20 ° C. for 14 days.

Comparative Example 2 A clear matte electrodeposition paint of Comparative Example 2 was produced in the same manner as in Example 2 except that DHT-4A was not used. Sulfuric acid is added to this electrodeposition paint as sulfate group.
After adding ppm, it was stored at 20 ° C. for 14 days.

Comparative Example 3 A clear white electrodeposition paint of Comparative Example 3 was produced in the same manner as in Example 1 except that DHT-4A was not used. Sulfuric acid is added to this electrodeposition paint as sulfate group.
After adding ppm, it was stored at 20 ° C. for 14 days.

Comparative Example 4 A clear matte white electrodeposition paint of Comparative Example 4 was produced in the same manner as in Example 1 except that DHT-4A was not used. Sulfuric acid was added to this electrodeposition paint as sulfate group.
After adding 0 ppm, it was stored at 20 ° C. for 14 days.

Coating method (non-rinse): The electrodeposition paints obtained in Examples 1 and 3 and Comparative Examples 1 and 3 were used as an electrodeposition bath, and this was coated with an object (anodized film having a film thickness of about 10 microns). Aluminum material (size is 1m long x 0.1m wide x
(0.5 mm thick) suspended vertically, and anion electrodeposition coating was performed so that the dry film thickness was about 10 microns.
% For about 2 minutes (time until the coating liquid does not drip) and left to stand. Next, baking was performed at 170 ° C. for 30 minutes to form coating films of Examples 1 and 3 and Comparative Examples 1 and 3.

Coating method (rinse): Example 2,
4 and the electrodeposition paint obtained in Comparative Examples 2 and 4 as an electrodeposition bath,
An object to be coated (anodized aluminum material having a film thickness of about 10 μm (size: 1 m long × 0.1 m wide × 0.5 mm thick) was immersed vertically in this material, and the dry film thickness was about 10
After performing anionic electrodeposition coating to a micron size, the coated product is taken out of the bath and washed with water at 20 ° C.
The coating films of Examples 2 and 4 and Comparative Examples 2 and 4 were formed by baking at 70 ° C. for 30 minutes.

Table 1 shows the results of the appearance and performance of the coating film of the electrodeposition paint.

[0053]

[Table 1] Table 1

The test evaluation of paint storage stability and coating film appearance is as follows.

Paint storage stability: The paint was placed in a test tube (height 20).
cm, capacity: 20 cc) and allowed to stand at 20 ° C. for 7 days, and then the height of the residue settled at the bottom of the container was examined. ◎ indicates that the residue is 0.5 mm or less, and ○ indicates that the residue is 0.6 to 5 mm.
ほ ぼ: Residue is slightly poor at 6 to 10 mm, X is poor at 11 mm or more Specular reflectance: Measured at 60 ° specular reflectance according to JIS K-5400 Smoothness: Surface of coating film And the like) were visually evaluated. ◎: good, ○: almost good, △: slightly poor, ×: bad

[0056]

Effect of the Invention The electrodeposition paint of the present invention, by blending hydrotalcite, allows unreacted sulfuric acid solution and unreacted () in the copolymer to be brought in from the pretreatment step accumulated in the anion-type electrodeposition coating line. By adsorbing a low-molecular-weight acid component such as (meth) acrylic acid, a remarkable effect of reducing the number of anion exchanges is exhibited.

Although the effect of the present invention is not clear, it is presumed as follows.

In the electrodeposition paint, Mg _{4 -3} Al ₂ (OH) _12-6
A hydrotalcite compound of CO ₃ · mH ₂ O is blended, and its effect is described assuming that the acid ions brought in from the pretreatment step are sulfate ions. The effect is described as follows: Mg _{4 -3} Al ₂ (OH) _12-6 CO ₃ · mH ₂ O + H ₂ SO ₄
→ Mg _{4 -3} Al ₂ (OH) _12-6 SO ₄ · mH ₂ O + H ₂ O
As can be represented by the reaction formula of + H ₂ CO ₃ , negative ions of CO ₃ constituting hydrotalcite are anion-exchanged with strong sulfate ions to be incorporated into the crystal structure of the hydrotalcite compound, and Since the sulfate ion is not released even when the temperature is increased to the baking temperature, there is no possibility that the paint and the coating film will be adversely affected.

Claims (1)

[Claims] To 1. A anionic electrocoating paint, the following general formula _{(1) Mg YX Al X (} OH) 2Y · A X / Y n ^over · mH ₂ O (1) (wherein, A ^{n over} the n valence of the anion, for example OH ^over, Cl
^Represents a divalent anion such as ^— , CO ₃ ^{2 —} , and x represents 0
<X, y are 2x ≦ y, and m is a number satisfying 0 <m, respectively).