JP2587934B2 - Electrodeposition method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrodeposition coating for a part requiring rust prevention such as an automobile body, an automobile part, a home appliance, etc. The present invention relates to an electrodeposition coating method characterized by performing post-treatment on a wet film deposited by energization in a bath in order to further improve various performances including rust prevention.

[Problems to be solved by conventional technology and invention]

Usually, electrodeposition coating on a coating object requiring high corrosion resistance, such as an automobile body or an automobile part, is performed through steps such as post-electrodeposition coating with zinc phosphate or the like, washing with water, and baking.

In recent years, the demand for the improvement of corrosion resistance of automobiles has become extremely strong, and high performance pretreatment and high performance electrodeposition paints have been used to improve the performance such as rust prevention in the joints between the end faces of the undercarriage. Is being actively developed.

For example, in the pretreatment, studies have been made to improve the density of crystals, and in the case of cationic electrodeposition paints, studies have been made on thickening, imparting high throwing power, mixing rust preventive pigments, and the like. ing. However, none of them has yet been sufficiently improved in performance.

In addition, a review of the coating system is also being considered, but a practical system has not yet come out.

[Means for solving the problem]

The present inventors have found that by post-treating the electrodeposition coating film with an aqueous solution containing metal ions, the rust-preventing power can be drastically improved, and particularly the rust-preventing power of the end face can be improved. That is, the present invention is characterized in that an object to be electrodeposited with a cationic electrodeposition paint is immersed in an aqueous solution containing metal ions before the coating film curing step, and the electrodeposition is performed. Is the way.

The aqueous solution used for the post-treatment of the present invention contains a metal ion, particularly zinc, nickel, tin, lead, chromium,
Inorganic or organic acid salts of strontium, cobalt, manganese, molybdenum, zirconium and their two salts
A mixture obtained by dissolving a mixture of two or more kinds in water is preferable.

Further, additives may be mixed for the purpose of improving the stability of the aqueous solution and improving the workability.

Such inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,
Carbonic acid, chromic acid and the like can be mentioned.

Organic acids include formic acid, acetic acid, lactic acid, oxalic acid,
Maleic acid, citric acid, acrylic acid and the like can be mentioned.

In the post-treatment method of the present invention, the object to be electrodeposited is immersed in the aqueous solution and energized. The post-treatment liquid temperature, immersion time, energizing conditions, and the like need to be appropriately determined according to the above-described metal ion species and concentration, or the thickness of the electrodeposition coating, but usually the metal ion concentration is 0.1 to 20% by weight. It is appropriate to use an aqueous solution, and immersion is performed for 30 to 300 seconds. When energizing, a voltage of 30 to 200 V is preferably applied.

By performing the post-treatment in the present invention, the above-described metal ions penetrate into the porous film before baking of the electrodeposition coating film, or are plated on the base metal surface, thereby obtaining the following effects (1). Corrosion resistance is improved. In particular, the corrosion resistance of the end face is significantly improved.

(2) It is not necessary to mix a metal such as lead or tin or a pigment or a catalyst containing them in the electrodeposition paint, so that the stability and finish of the paint surface are improved.

(3) Even without pre-treatment such as zinc phosphate treatment, the pre-treatment step can be omitted because it has corrosion resistance equal to or higher than that of the current coating system.

This also greatly reduces the economic burden in the painting process.

(4) The curability at low temperatures is increased by the catalytic action of the metal.

The electrodeposition paint used in the present invention is of a cationic type.

Cationic electrodeposition paint is neutralized with an organic or inorganic acid, and a basic resin and an organic or inorganic acid that can be decomposed into water, water, a curing agent, a curing catalyst, an organic solvent, if necessary, This is a water-based paint using a pigment or the like.

Examples of such a basic resin include an epoxy resin having a basic group such as an amino group, an ammonium group, and a sulfonium group, a polybutadiene resin, an acrylic resin, and a mixture thereof.

Examples of such organic or inorganic acids include formic acid,
Acetic acid, propionic acid, lactic acid, sulfuric acid, hydrochloric acid, phosphoric acid and the like can be mentioned. These acids are converted into a basic resin by a base 1 in the resin.
Mix at a ratio of 0.1 to 0.6 equivalent to the equivalent and disperse in water.

〔Example〕

 Hereinafter, specific examples will be described with reference to examples.

 Each aqueous solution was prepared according to the formulation shown in Table 1.

(Production example 1 of cationic electrodeposition paint) Epicoat # 1004 in a clean 4-liter 4-neck flask
1900 g (Epivis epoxy resin manufactured by Shell Co., Ltd.) was dissolved in 700 g of ethyl cellosolve, and diethanolamine 20
Add 0 g, hold at 60-65 ° C for 1 hour, then raise the temperature to 120 ° C and hold for 1 hour.

Subsequently, the mixture is cooled to 80 ° C., and 500 g of a blocked isocyanate-type curing agent EH-117-20 (manufactured by Asahi Denka Co., Ltd.) is added, and 80 to 85 ° C.
After mixing well for 1 hour, take out. This resin is designated as A.

45 g of resin A, 45 g of ethyl cellosolve, 135 g of titanium oxide and 7 g of carbon black are placed in a 1-liter mayonnaise bottle, 300 g of glass beads are added, and the mixture is dispersed by a quick mill.

4 liter stainless steel vat with resin A540g (B-
1) 232 g and 8.5 g of formic acid were added, and 2179.5 g of ion-exchanged water was gradually added while stirring with a disper and mixed well to obtain a cationic electrodeposition paint (C-1) having a solid content of 20%. .

(Production Example 2 of cationic electrodeposition paint) 45 g of the above resin A, 45 g of ethyl cellosolve and 120 of titanium oxide
g, 7 g of carbon black and 35 g of basic lead silicate are placed in a 1-liter mayonnaise bottle, 300 g of glass beads are added, and the mixture is dispersed with a quick mill.

This is designated as (B-2).

4 liter stainless steel vat with resin A540g (B-
2) 252 g and formic acid 8.5 g were added, ion-exchanged water 2259.5 g was gradually added while stirring with a disper, and mixed well to obtain a cationic electrodeposition paint (C-2) having a solid content of 20%.

(Examples 1 to 4, Comparative Examples 1 to 3) As a result of performing electrodeposition coating and post-treatment using the above-mentioned cationic electrodeposition paint and post-treatment liquid, as shown in Tables 2 and 3, the method of the present invention was carried out. The electrodeposited coating film formed by the method described above exhibited equivalent or superior corrosion resistance without any pretreatment.

[Effects of the Invention] According to the method of the present invention, it is possible to improve the anticorrosion properties of steel products, including those for automobiles, and to provide the same or higher anticorrosion performance as before even if the chemical conversion pretreatment step is omitted. can do. This is an advantageous method particularly when corrosion protection of the end face is required.

Claims (2)

(57) [Claims] 1. An electrodeposition coating method comprising: immersing an object to be electrodeposited with a cationic electrodeposition coating in an aqueous solution containing metal ions prior to a coating film curing step; 2. The method according to claim 1, wherein the metal ions are zinc, nickel, tin, lead,
The electrodeposition coating method according to claim 1, wherein the electrodeposition coating is one or more metal ions selected from chromium, strontium, cobalt, manganese, molybdenum, and zirconium.