JPS5931597B2 - Method of coating metal surfaces with insoluble salts of metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention achieves the objectives of improving corrosion resistance, preparing a surface for painting and adhesion, and decorating by coating the surface of metal with an insoluble salt. Can be applied.

Conventional methods for depositing insoluble metal salts on metal surfaces include immersing the metal in an aqueous solution of phosphoric acid or oxalic acid, dissolving the metal, and depositing phosphate or oxalate on the metal surface. I've been exposed to it.

However, this method has the following drawbacks because it melts the base metal.

1. Once the metal surface is coated with an insoluble salt, the reaction does not proceed any further and the resulting film is only very thin.

2. Therefore, this method alone cannot provide complete rust prevention treatment.

3 Also, because the coating is thin, the base metal can be seen through, which is not aesthetically pleasing.

4 Furthermore, metals that are difficult to dissolve, such as copper, stainless steel, and platinum, cannot be coated.

The present invention overcomes these drawbacks, succeeds in providing a sufficiently thick coating of insoluble salt, and solves problems 1 to 3 above. Regarding problem 4, even though anti-corrosion treatment is not a problem for these hard-to-dissolve metals, it is necessary to coat them as a base treatment for adhesion or painting.
In this respect, the present invention, which overcomes the above-mentioned problem 4, is highly useful. The method of the present invention will be explained below.

1 Dissolve diethyl oxalate, dimethyl oxalate, sodium picanate, sodium tripolyphosphate, or sodium hexametaphosphate in water, and in the case of ethyl silicate, dissolve in a mixed solvent of water and alcohol.

2 Calcium, magnesium, zinc, aluminum,
Hydrolysis products of reagents such as iron or barium and soluble salts of metal ions to form insoluble salts are added to the solution of part 1.

3 Derust and degrease the metal and immerse it in the above solution.

4 Using platinum as an anode, current is passed through the metal to cathodically polarize it.

By the above-described treatment, an insoluble salt can be attached to the metal surface.

The principle of this method can be briefly described as follows.

The reagent shown in 1 dissolves in an aqueous solution and causes a hydrolysis reaction.

This hydrolysis reaction is active in alkaline conditions, and is therefore considered to be active in the vicinity of the cathodically polarized metal surface. As a result of the hydrolysis reaction, the hydrolysis products shown in the claims are produced, and these react with calcium ions, zinc ions, etc. and precipitate on the metal surface as an insoluble salt. In this method, it is presumed that the insoluble salt of the metal is precipitated and coated by the mechanism described above, but other explanations are possible, and the fundamental mechanism has not yet been completely elucidated. . In any case, this method makes it possible for the first time to firmly coat a metal surface with an insoluble salt, and this method has never been thought of before.

In the present invention, the voltage applied to the metal must be such that the metal does not elute, and its value varies depending on the type of metal and the pH.

For example, in the case of iron -780mV (S.S.C.E.)
It is necessary to do the following. However, care must be taken because if a voltage of too large a value (absolute value) is applied, the coating may become non-uniform due to gas generation, etc. The pH of the solution varies depending on the concentration of the reagent shown in 1, but it needs to be approximately slightly acidic to weakly acidic, so adjust it by adding an appropriate pH adjuster (hydrochloric acid, sulfuric acid, sodium hydroxide). Must. Since there is a correlation between the concentration of the reagent shown in 1, the concentration of metal ions such as calcium and zinc, and the temperature, a typical example will be described below.

Example 1 When an experiment was conducted using the above configuration, complete coating could be achieved in one hour.

-400m (Vs.S.C.E.) when the metal is copper,
-1500mV (Vs.S.C.
E. ) was found to be acceptable.

It was also possible to coat zinc oxalate, magnesium oxalate, and barium oxalate by using zinc chloride (39/2), magnesium chloride (39/l), and barium chloride instead of calcium chloride, respectively.

Example 2 After conducting the experiment for 1 hour, a firm coating could be obtained.

Example 3 Isobutyl alcohol was added to carry out the experiment in a mixed solvent since ethyl silicate is difficult to dissolve in water.

A firm coating could be made in 2 hours.

Claims (1)

[Claims] 1 Diethyl oxalate, dimethyl oxalate, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, ethyl silicate and their hydrolysis products oxalic acid, silicic acid, orthophosphoric acid, acid phosphoric acid and A metal is immersed in an aqueous solution containing metal ions that combine to form an insoluble salt, and the metal is exposed to 0.2 to 0.01 A/dm^.
A method in which an insoluble salt is deposited on the metal surface by applying a current as described in step 2 to cause cathodic polarization.