JPS63259100A - Coating method by electrodeposition - Google Patents

Abstract

PURPOSE:To considerably improve the rust preventiveness of parts of an automobile body, household electrical appliances or the like coated by electrodeposition, by post-treating the coated parts with an aq. soln. contg. specified metal ions before the formed paint films cure. CONSTITUTION:Parts of an automobile body, automotive parts, household electrical appliances or the like requiring rust preventiveness are coated with a cationic or anionic electrodeposition paint. Before the formed paint films cure, the coated parts are immersed in an aq. soln. contg. an inorg. or org. acid salt of one or more among Zn, Ni, Sn, Pb, Cr, Sr, Co, Mn, Mo and Zr at 0.1-20wt.% concn. of metal ions for about 3-300sec. The soln. may be sprayed on the coated parts under 30-200V voltage impressed. The corrosion preventiveness of the coated parts is remarkably improved.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to automobile bodies and automobiles! , <-tsu, When applying electrodeposition to areas that require anti-rust properties such as home appliances,
This relates to an electrodeposition coating method in which the wet film deposited by applying electricity to the object to be coated is subjected to post-treatment in order to further improve various properties such as rust prevention. be.

[Problems to be solved by conventional technology and invention]

Electrodeposition coating of objects that require high corrosion resistance, such as automobile bodies and automobile parts, is usually performed through steps such as pretreatment with zinc phosphate, electrocoating, washing with water, and baking.

In recent years, there has been an extremely strong demand for improving the corrosion resistance of automobiles, and in order to improve the rust prevention performance of the end face rust prevention welds in the undercarriage area, we are using high performance pre-treatment and high performance electrodeposition paints. Development is being actively carried out.

For example, in pre-treatment, studies are being conducted to improve the density of crystals, and in the case of cationic electrodeposition paints, studies are being conducted on thickening the film, imparting high throwing power, and mixing anti-corrosion pigments. ing.

However, none of these methods has yet achieved sufficient performance improvement.

Although a review of the coating system described above is being considered, a practical one has not yet been developed.

[Means for solving problems]

The inventors used an aqueous solution containing metal ions.

It was discovered that by post-treating the electrodeposition coating film, the rust prevention ability can be dramatically improved, especially the rust prevention ability of the edge surface, and the present invention was completed. This electrodeposition coating method is characterized in that the electrodeposition-coated object is post-treated with an aqueous solution containing metal ions before the coating film curing step.

The aqueous solution used in the post-treatment of the present invention contains metal ions, particularly inorganic or organic acid salts of zinc, nickel, tin, lead, chromium, strontium, cobalt, manganese, molybdenum, zirconium, and two of these. A mixture of more than one type dissolved in water is suitable.

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

Examples of such inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, and chromic acid.

Examples of organic acids include formic acid, acetic acid, lactic acid, oxalic acid, maleic acid, citric acid, and acrylic acid.

The post-treatment method of the present invention is carried out by immersing the electrocoated object in the aqueous solution, energizing it, or showering or spraying the aqueous solution.The liquid temperature, immersion time, energization conditions, spray conditions, etc. Although it is necessary to determine the above-mentioned metal ion species and concentration, or electrodeposition coating film thickness, etc., it is usually appropriate to use an aqueous solution with a metal ion concentration of 0.1 to 20% by weight, and spray or 30 to 30% by weight. Perform a 300 second soak. When electricity is applied, it is preferable to apply a voltage of 30 to 200 cm.

By performing the post-treatment in the present invention, the above metal ions permeate into the previous porous film or are plated on the base metal surface, resulting in the following effects (1). ) Corrosion resistance is improved. In particular, the corrosion resistance of the end face is significantly improved.

(2) Since there is no need to mix metals such as lead and tin, or pigments and catalysts containing them into the electrodeposition paint, the stability of the paint and the finish of the painted surface are improved.

(3) Even without pretreatment such as zinc phosphate treatment, it has corrosion resistance equivalent to or better than current coating systems, so the pretreatment step can be omitted.

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

(4) The catalytic action of the metal increases curing properties at low temperatures.

The electrodeposition paints used in the present invention include cationic and anionic paints.

Cationic electrodeposition paints are made of a basic resin that can be neutralized with an organic or inorganic acid and dispersed in water, an organic or inorganic acid, water, a curing agent, a curing catalyst, an organic solvent if necessary, It is a water-based paint that uses pigments, etc.

Examples of such basic resins include epoxy resins, polybutadiene resins, acrylic resins, and mixtures thereof having basic groups such as amine groups, ammonium groups, and sulfonium groups.

Examples of such organic or inorganic acids include formic acid, acetic acid, propionic acid, lactic acid, sulfuric acid, hydrochloric acid, and phosphoric acid. These acids are mixed with a basic resin at a ratio of 0.1 to 0.6 equivalents per equivalent of the base in the resin, and dispersed in water.

Anionic electrodeposition paints are made by neutralizing them with an organic or inorganic base, and combining an acidic resin that can be dissolved or dispersed in water, an organic or inorganic base, water, a curing agent, and a curing catalyst if necessary. It is a water-based paint that uses organic solvents, pigments, etc. Such acidic resins include epoxy resins having carboxyl groups, polybutadiene resins, acrylic resins, polyester resins, and mixtures thereof.

Examples of such organic or inorganic bases include alkylamines such as triethylamine and tributylamine, alkanolamines such as dimethylethanolamine, ethyljetanolamine, and diisopropanolamine, and inorganic bases such as sodium hydroxide and potassium hydroxide. It will be done. These bases are mixed with an acidic resin at a ratio of 0.1 to 1.5 equivalents per equivalent of acid groups in the resin, and dispersed in water.

〔Example〕

Examples will be given below for specific explanation.

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

(Manufacturing example 1 of cationic electrodeposition paint) In a clean 4 yen 4 yen flask, use Epicoat #1004 (
Dissolve 1,900 g of Ebibis type epoxy resin manufactured by Shell ■ in 700 g of ethyl cellosolve, add 200 g of jetanolamine, hold at 60-65°C for 1 hour, and then heat to 120°C.
Raise the temperature to and hold for 1 hour.

Subsequently, the resin was cooled to 80°C, 500g of blocked isocyanate type curing agent EH-117-20 (manufactured by Asahi Denka ■) was added, and the resin was thoroughly mixed while being kept at 80 to 85°C for 1 hour, and then taken out. This resin is referred to as A. .

45 g of resin A, 45 g of ethyl cellosolve, and 1 titanium oxide
Put 35 g of IY and 7 g of carbon black into a mayonnaise bottle, add 300 g of glass peas, and disperse with a quick mill. This is designated as (B-1>).

4' 340g of resin A and stainless steel bat (B-1)
232 g and 8.5 g of formic acid were added, and while stirring with a disper, 2179.5 g of ion-exchanged water was gradually added and mixed thoroughly to form a cationic electrodeposition paint (C-
1) was obtained.

(Production Example 2 of Cationic Electrodeposition Paint) 45 g of the above resin A, 45 g of ethyl cellosolve, 120 g of titanium oxide, 7 g of carbon black, and 3 g of basic lead silicate.
Put 5g into a 1'a mayonnaise bottle and add 300 glass peas.
g and disperse using a quick mill.

Let's call it (B-2).

4゛α stainless steel butt with 340g of resin A (B-2)
Add 252g of formic acid and 8.5g of formic acid, and gradually add 2259.5g of ion-exchanged water while stirring with a disper. Mix thoroughly to obtain a cationic electrodeposition paint (C-2>) with a solid content of 20%.
I got it.

(Examples 1 to 5. Comparative Examples 1 to 3) Using the above cationic electrodeposition paint and post-treatment liquid, the results of electrodeposition coating and post-treatment were as shown in Tables 2-3. The electrodeposited coating film formed by this method showed excellent corrosion resistance equivalent to or better than that without pretreatment.

(Note 1> L-shaped test = L-shaped bent object is immersed, held for 3 minutes without stirring, then electrodeposited and baked for 3 minutes with stirring. Finished appearance of the coated surface O: Good Δ : Fairly good (Note 2) MIBK rubbing 10 times ○: No scratches △: Scratches ×: Exposed base (Note 3) SST
(Salt spray test) Judgment based on the rust width after 1000 hours O: Rust width less than 3111 Δ: tt 3 to less than 5 mm ×: Not 5 mm or more (For flat parts, the rust width from the cut end surface is the rust width from the panel end surface) (Note 4) Judgment based on the finish of the electrodeposited film after stirring the paint at 40°C for one month O: No difference from the initial stage Δ: Some coating film defects ×: Many coating film defects [Effects of the invention] According to the method of the present invention This makes it possible to improve the corrosion resistance of steel sheet products, including those for automobiles, and even without the chemical pretreatment step, it is possible to provide corrosion resistance that is equivalent to or better than that of conventional products. This method is especially advantageous when corrosion resistance of the end face is required.

Claims (1)

[Scope of Claims] 1. An electrodeposition coating method, which comprises post-treating an object coated with an electrodeposition paint with an aqueous solution containing metal ions before the coating film curing step. 2. Metal ions include zinc, nickel, tin, lead, chromium,
The electrodeposition coating method according to claim 1, wherein the metal ion is one or more metal ions selected from strontium, cobalt, manganese, molybdenum, and zirconium.