JPH0347985A - Chromium plating method - Google Patents

Abstract

PURPOSE:To obtain a high-quality uniform Cr plating film by adding Pb salts to a plating soln. and keeping Cr<3+> in the plating soln. at a prescribed concn. when Cr plating is carried out with the plating soln. such as a sergent bath or a fluoride bath and an insoluble electrode as the anode. CONSTITUTION:An insoluble metal electrode coated with the oxide of a Pt family metal or a ferrite electrode is prepd. as the anode. A sergent bath, a fluoride bath or a Cr plating soln. contg. an org. acid is also prepd. Pb salts are added to the Cr plating soln. and Cr<3+> in the plating soln. is kept at 1-8g/l concn. Electrolysis is carried out with the plating soln. and the anode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a chromium plating method capable of forming a stable homogeneous plating film using a single insoluble electrode as an anode.

[Conventional technology]

In chromium electroplating baths, lead or an alloy thereof has conventionally been widely used as an anode. However, lead
Although anodes made of lead alloys maintain an appropriate concentration of trivalent chromium ions, they dissolve in the plating solution during use, producing yellow precipitates of lead chromate, which can lead to the formation of sludge and a rough plating film. It causes an invitation. Particularly in chromium plating baths that use fluoride or organic acids as catalysts, dissolution progresses quickly, shortening the life of the anode to approximately 3 to 12 months, and also burdening maintenance costs due to the generation of a large amount of sludge. big.

In order to solve these problems with lead-based electrodes, attempts have been made to use insoluble electrodes made of metals such as titanium and niobium coated with iridium oxide, or ferrite. However, since the insoluble electrode has poor oxidation function, the concentration of trivalent chromium ions in the bath increases, causing problems such as an increase in bath voltage, a decrease in current efficiency, and poor plating.

Recently, lead dioxide coated electrodes have been used as anodes for chromium plating. Unlike lead or lead alloy electrodes, this lead dioxide-coated electrode generates little sludge and has a high oxidizing power as an electrode.

In addition, in order to compensate for the drawbacks of the insoluble electrodes mentioned above, a method of using an insoluble electrode and a lead dioxide coated electrode in combination (
JP-A-63-270490, JP-A-63-29319
Publication No. 7) has been proposed.

According to these methods, the trivalent chromium ion concentration in the plating bath can be reduced to 1.5 to 8 g/I! However, in addition to the short lifespan and high cost of lead dioxide-coated electrodes, the current density flowing through the insoluble electrode portion and the lead dioxide-coated electrode portion is different, making it difficult for plating. There are technical problems such as variations in film thickness.

[Problem to be solved by the invention]

The present invention has been made to solve the problems of the prior art described above, and it is possible to maintain trivalent chromium ions in a plating bath at a constant low concentration level even by using a single insoluble electrode. The purpose of the present invention is to provide a chromium plating method capable of forming a plating film of uniform thickness and high quality without the formation of sludge.

[Means to solve the problem]

The chromium plating method according to the present invention to achieve these objects consists of using an insoluble metal electrode or ferrite electrode coated with a platinum group oxide as an anode, a Sargent bath,
When performing chromium plating using a fluoride bath or a similar bath containing an organic acid, lead salts are added to the plating solution to increase the concentration of trivalent chromium ions in the plating solution by 1 to 8 g/
! A structural feature is that the concentration is maintained within the range of .

As platinum group oxides to be coated on the metal electrodes and ferrite electrodes, ruthenium oxide, palladium oxide, osmium oxide, iridium oxide, etc. can be used, but iridium oxide is the most preferred material for practical use.

When chromium plating is performed using such an electrode as a positive electrode, the plating bath targeted by the present invention is a Sargent bath (typical bath composition; Crys: 250 g/l, H
gSO4: 2.5g/IL), fluoride bath (typical bath composition; CrO3: 250g/j!, Hz
SOa: 1 g/l, F: 0.6 g/l or 5iFa: 2.5 g/l, or similar plating baths containing organic acids (typical bath composition; CrO+
: 250g/ 42.112sO4: 2.5g/
II! , meta-lower alkanesulfonic acid: 5g/142
). However, the solubility of lead ions varies slightly depending on the type of bath, but is generally 20 to 40 mg/
Since j2 is extremely small, the concentration level of trivalent chromium ions gradually increases during the plating operation, as described above.

Therefore, the present invention is to actively add lead salts to the plating solution so that the dissolved lead ions can control the concentration of trivalent chromium ions in the plating solution. 1~8g/! It is characterized by being held at.

For this purpose, lead salts added to the plating solution include inorganic lead compounds such as basic lead carbonate, lead carbonate, lead oxide, lead hydroxide, lead borofluoride, and lead chromate, or lead oxalate, Examples include organic lead compounds such as lead acetate, lead methanesulfonate, and lead ethanesulfonate, and one or more selected from these salts are used.

Further, the amount of lead salts required in the present invention is not uniform depending on the type of salts, plating conditions, etc., but it is added to the plating bath so that the amount of lead is in the range of 50 to 500 mg/l.

The reason for this is that if the lead concentration is less than 50 mg/1, a lead dioxide film will not be uniformly formed on the surface of the insoluble electrode, resulting in insufficient oxidizing power, and if the lead concentration exceeds 500 mg/1, the oxidizing power will be insufficient. Although it is possible to maintain the valent chromium ion concentration at a low level of 1 to 8 g/l, excessive lead salts can cause lead chromate precipitation, which can cause bath contamination and the formation of a rough plating film. This is because there is a tendency for

In addition, in the chromium plating method according to the present invention, except for the above-mentioned features, there is no difference from a normal electrolytic chromium plating method particularly in other operating conditions.

[For production]

According to the present invention, the lack of oxidizing power caused by using an insoluble electrode as an anode is smoothly compensated for by the lead salts added to the plating solution. In other words, lead ions dissolved in the plating solution are oxidized at the anode to form a thin film of lead dioxide on the surface of the insoluble electrode, and this film acts as an oxidizer to maintain a constant concentration of trivalent chromium ions in the plating solution. functions to keep it in the low level range. 50-500f of lead salts as lead
By adjusting the amount of addition so that the concentration is 1 g/Il, the concentration of trivalent chromium ions retained can be as low as 1 to 8 g/ffi, which always forms a high-quality plating film.
, and very little lead chromate precipitation occurs.

Through this series of actions, a homogeneous ROM plating layer with a beautiful surface texture is formed.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

Example 1 Chromic anhydride (Cr(h) 250g/l, sulfuric acid (oz
soa) Basic lead carbonate 125 ■/! (100■ as lead
/l) was added. Ferrite electrode (TDK■
chrome plating was performed under the following conditions.

Bath temperature 55°C Cathode current density 50 A/dm2 Anode current density
8 A/dn+” Current concentration: 28/l Plating time: 120 Hr This plating bath was in equilibrium with trivalent chromium ions at 5.0 g/it, and a good quality ROM plating was obtained. It was confirmed that a lead dioxide film was formed.

For comparison, when chromium plating was carried out under the same conditions as above except that basic lead carbonate was not added, the concentration of trivalent chromium ions was 18 g/l, making it impossible to obtain good quality plating.

Example 2 Chromic anhydride (CrOs) 250g/I! ,,Sulfur MC
H2S04) 1.0g/l, sodium silicofluoride (N
azSiF6) 4.0 g/l- in a plating solution with a fluoride bath composition, and a lead borofluoride aqueous solution (40%) 230 μ
/1 (50 mg//l of lead was added. Using an insoluble electrode with a niobium surface coated with indium oxide to a thickness of about 6μ steel as an anode, chromium plating was performed under the following conditions.

Bath temperature 55°C Cathode current density 45^/dm” Anode current density 45A/d+n” Current density
2A/I! .

Plating time: 120Hr In this plating bath, the trivalent chromium ion concentration is 4.5g/l
Equilibrium was reached at , and good quality chromium plating was obtained. It was also confirmed that a brown film was formed on the anode surface.

For comparison, when chromium plating was performed under the same conditions except that lead borofluoride was not added, the trivalent chromium ion concentration was as high as 15 g/l, and a good quality plating film could not be obtained.

Example 3 Chromic anhydride (Cr03) 250g/l, sulfuric acid (lh
sO4) 2.5gel, ethanesulfonic acid 5.0g/
Lead methanesulfonate (192/2) (100/1 as lead) was added to a plating solution having an organic acid-containing composition consisting of 42% lead. Approximately 6 μm of iridium oxide is applied to the titanium surface as an anode.
Chrome plating was performed under the following conditions using an insoluble electrode coated to a thickness of .

Bath temperature: 60°C Cathode current density: 45A/dm2 Anode current density: 45A/d is the current concentration 2A#2 Plating time: 120Hr In this plating bath, the trivalent chromium ion concentration is 4.6g/l
Equilibrium was reached and a high quality chromium plating film was obtained. Furthermore, a brown lead dioxide film was formed on the surface of the anode.

For comparison, when chromium plating was performed under the same conditions as above except that lead methanesulfonate was not added, the trivalent chromium ion concentration was 15g#! Therefore, a good quality plating film could not be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the trivalent chromium ion concentration can always be maintained within the range of 1 to 8 g/l even when an insoluble electrode is used alone. This ensures the formation of a high quality chrome plating film.

Furthermore, since only a small amount of lead salts are added, there is less contamination of the bath liquid, making maintenance easier. It is also possible to use the same type of insoluble electrodes, resulting in a uniform current distribution. Since it can be connected, various effects such as miniaturization of equipment can be brought about.

Procedural amendment August 21, 1999 1.Display of the incident 1999 Patent Application No. 182277 2. Name of the invention Chrome plating method 3. Person who makes corrections Relationship with the incident

Claims (1)

[Claims] 1. Chromium plating is performed using an insoluble metal electrode or ferrite electrode coated with platinum group oxide as an anode, using a Sargent bath, a fluoride bath, or a similar bath containing an organic acid. A chromium plating method characterized by adding lead salts to the plating solution to maintain trivalent chromium ions in the plating solution in a concentration range of 1 to 8 g/l. 2. The chromium plating method according to claim 1, wherein the platinum group oxide is iridium oxide. 3. The lead salts are one or two types selected from basic lead carbonate, lead carbonate, lead oxide, lead hydroxide, lead borofluoride, lead chromate, lead oxalate, lead acetate, and lead lower alkanesulfonate. The chromium plating method according to claim 1, which is the above.