JPS6123783A - Method for plating chromium with ion exchange membrane - Google Patents

Abstract

PURPOSE:To facilitate the maintenance of a plating bath and to prolong the life of the bath by feeding an aqueous soln. of a tervalent chromium salt to a cathode chamber and an acid soln. contg. the same kind of anion as the chromium salt to an anode chamber. CONSTITUTION:An electrolytic cell is divided into anode and cathode chambers with an ion exchange membrane, and an aqueous soln. of a tervalent chromium salt such as chromium sulfate or chloride is fed to the cathode chamber. An acid soln. contg. the same kind of anion as the chromium salt such as sulfuric acid in case of chromium sulfate or hydrochloric acid in case of chromium chloride is fed to the anode chamber. The plating bath is adjusted to about 0-4pH, and electrolysis is carried out at about 5-50A/dm<2> average current density and room temp. - about 60 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a chromium plating method containing pentavalent chromium, and more specifically to a chromium plating method using an ion exchange membrane.

Chrome plating is widely used in the plating industry because it provides a plated surface with beautiful luster and corrosion resistance.

[Conventional technology]

Conventionally, a hexavalent chromium plating bath has been used for chromium plating. The drawbacks of this bath are that it has poor uniform electrodeposition, poor covering power, and current efficiency for chromium deposition is only a low value of around 10 cm based on hexavalent chromium. Due to the toxicity of chromium, its use is a major problem due to concerns about environmental pollution.

Until now, various plating baths using trivalent chromium, which is less toxic, have been proposed. Many of these contain carboxylic acids or carboxylates as chromium complexing agents. (For example, JP-A-47-20050, JP-A-50-92
257. JP-A-55-106348) These trivalent chromium plating baths are plating baths that have improved the drawbacks of hexavalent chromium baths, but from a commercial perspective, they are not necessarily preferable and some Although some have been put into practical use, the majority of chrome plating baths still use hexavalent ROM baths.

Many of the shortcomings of conventional trivalent chromium plating baths are believed to be attributable to complex anodic reactions. That is, divalent chromium produced in the cathode chamber is reoxidized by the anode reaction during plating, hexavalent chromium is produced, and the organic carboxylic acid or carboxylate used as a complexing agent is Due to anodic decomposition, etc., the life of the plating bath is reduced and maintenance of the plating bath is significantly complicated.

[Problem that the invention seeks to solve]

The purpose of the present invention is to eliminate the complicated anodic reaction, which is a disadvantage of the conventional plating method using a trivalent chromium plating bath, to facilitate maintenance, and to increase the life of the plating bath, so as to provide a practical trivalent chromium plating method. The purpose is to provide a chrome plating method.

[Means for solving problems]

The gist of the present invention is to divide an anode chamber and a cathode chamber using an ion exchange membrane, supply an aqueous solution in which a trivalent chromium salt is dissolved to the cathode chamber, and supply an anion species of the chromium salt to one anode chamber. The chromium plating method is characterized by supplying acid solutions of the same anion species, and detailed measurements thereof will be explained below.

The ion exchange membrane used in the present invention is a cation exchange membrane.

Although an anion exchange membrane or the like is used, for example, a fluorine-based cation exchange membrane having a sulfonic acid group is used.

The plating tank is divided into a cathode chamber and an anode chamber by an ion exchange membrane, and the cathode chamber contains a chromium plating solution, that is, an aqueous solution containing trivalent chromium salt, chromium sulfate, chromium chloride solution, etc. is supplied and extracted. Furthermore, in the chromium plating solution, as necessary, a) carboxylic acid or carboxylic acid salt known as a complexing agent for trivalent chromium, such as formic acid or formic acid salt.

Known ingredients such as glycolic acid or glycolate, aminoacetic acid, etc., a) ammonium salt, c) alkali metal salt, d) boric acid or aluminum salt, etc. are added.

3 inorganic salts contained in Naso' and Kiba f) 7 = 7 types of yF
- It is desirable that 1 be the same in terms of plating bath management. Therefore, if the chromium salt used is a sulfate, it is desirable to use the sulfate, and if it is a chloride, it is desirable to use the chloride. In the anode chamber, an acid solution of the same anion species as that of the chromium salt supplied to the cathode chamber, that is, sulfuric acid in the case of a chromium sulfate solution.

In the case of chromium chloride solution, hydrochloric acid is supplied and extracted.

For other constituent elements of the trivalent chromium plating method using an ion-exchange membrane of the present invention, various known conditions can be appropriately adopted. P of plating bath
H is used in the range of 0 to 4.

In the case of a sulfuric acid solution, an electrode made of lead or titanium coated with a noble metal or a noble metal oxide is used as the anode, and in the case of a chloride solution, an electrode made of graphite or titanium coated with a noble metal or a noble metal oxide is used.

The average current density is 5 to s o Vdm'', and the plating bath temperature is in the range of room temperature to 60°C.

c' Effect] In the chromium plating method using the ion exchange membrane of the present invention, the anode chamber and the cathode chamber are completely separated by the ion exchange membrane.
In addition, metal ions such as chromium are not included in the mass transfer within the membrane, and trivalent chromium in the cathode chamber, divalent chromium, and carboxylic acid or carboxylate generated at the cathode remain in the cathode chamber and are not transferred to the anode. There will be no migration.

Therefore, undesirable anodic reactions such as reoxidation of VCZ-valent chromium, production of hexavalent chromium, decomposition of carboxylic acid or carboxylate salt, etc., do not occur as in the prior art.

The anodic reaction in the Meggi method of the present invention is an extremely simple reaction in which only chlorine or oxygen is generated.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, maintenance of the trivalent chromium plating bath is significantly facilitated.
The life of the plating bath is also increased, and as a result, it is suitable for practical use5.
It is possible to obtain a valent chromium plating method.

Examples will be described below, but the present invention is not limited thereto.

〔Example〕

Example 1 Fluorine-based ion exchange membrane containing sulfonic acid groups (Du
A cathode chamber and an anode chamber were separated using a Pont NafiOn membrane.

The hexavalent chromium plating bath used had the composition shown in Table 1, and the pH
was adjusted to 1 and supplied to the cathode chamber.

Table 15 valent chromium plating bath Chloride 9m [18mo4/7 aminoacetic acid
1.2〃 Aluminum chloride 0.5 1 Ammonium chloride 1,5I 1N hydrochloric acid was used as the anode chamber solution.

In order to keep the concentration and pH of the cathode chamber solution and anode chamber solution constant, a cathode chamber solution storage tank and a solution solution storage tank were provided outside the plating tank, and the liquids were circulated from the storage tanks to the plating tank.

The cathode used was a brass plate that had been subjected to conventional pretreatments such as degreasing and pickling, and the anode used graphite.

The distance between the electrodes was 1OL:nl, and the plating current density was 15
Plating was carried out at room temperature for 10 minutes, and this operation was repeated until the bath current flow amount was 10 AFVt.

As a result, all of the resulting platings were shiny chrome plating. Furthermore, almost no chromium ions were detected in the anode chamber solution, and there was no coloration of the solution.

Example 2 Plating was performed using an aqueous solution having the composition shown in Table 2 as a trivalent chromium plating bath, and other conditions were the same as in Example 1.

Table 2 Trivalent chromium plating bath Chromium chloride 0.4 mokl Potassium formate 1. or ammonium chloride 2. Ol Boric acid 0.6 # As a result of repeating plating until the bath current was 10 AH/l, glossy chrome plating was obtained in all samples.

Furthermore, almost no chromium ions were detected in the anode chamber solution, and there was no coloration of the solution.

Claims (1)

[Claims] An anode chamber and a cathode chamber are divided using an ion exchange membrane, an aqueous solution in which a trivalent chromium salt is dissolved is supplied to the cathode chamber, and an anion species of the same type as that of the chromium salt is supplied to the anode chamber. A chrome plating method characterized by supplying an acid solution.