JPH0995793A - Tervalent chromium plating bath depositing chromium plating having thermally hardening property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a working environment and also to produce an industrial and practical mirror face gloss hard chrome plating film by using a tervalent chromium as a main component of a plating bath and combining boric acid, glycine and ammonium salt. SOLUTION: In a plating both composition, (1) 30-500g/l at least one compd. making a tervalent chromium ion, (2) 20-50g/l boric acid, (3) 20-120g/l glycine and (4) 30-150g/l ammonium salt are incorporated in an aq. son. Further, ammonium sulfamate, ammonium sulfate or ammonium chloride are used as the ammonium salt. A plating layer obtained by using this plating bath has a hardness of about Hv700 by Micro Vickers hardness at electrodeposition. The hardness is increased to about Hv1,500 by a heat treatment at about 400 deg.C, and a wear resistance is increased remarkably. Further, >=40μm plating film thickness is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel plating bath composition for electrodeposition of hard chromium having thermosetting and specular luster from an electrolytic solution containing trivalent chromium as a main component.

[0002]

2. Description of the Related Art Hard chrome plating usually uses a bath prepared by adding sulfuric acid or a fluorine compound as a catalyst to a hexavalent chromic acid solution. The chrome plating layer obtained from these plating solutions is glossy, has excellent corrosion resistance, and has high hardness,
It shows a value in the range of HV700-1000 in terms of micro Vickers hardness. For this reason, chrome plating is often used for decoration and machine parts that require abrasion resistance.

However, the conventional chromium plating uses a hexavalent chromium compound that is toxic to the human body, which deteriorates the working environment and requires special wastewater treatment because it is regulated as a pollutant. Therefore, there is a strong demand for the development of a chromium plating solution containing trivalent chromium, which is less toxic, and has already been put to practical use in the field of decorative chromium plating used with a plating thickness of around 0.2 μm. However, a practical plating solution has not yet been developed in the field of industrial (hard) chromium plating, which requires a thick film having a thickness of 5-100 μm.

In recent years, environmental problems have been highlighted in countries all over the world, and in particular, development of alternative techniques for various processes using hexavalent chromium is strongly desired. For this reason, the development of trivalent chromium plating solutions for industrial chromium plating is urgent.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The plating solution according to the present invention solves the above-mentioned drawbacks, that is, environmental and pollution problems. Since the present invention is a plating method using a trivalent chromium compound, the working environment is remarkably improved, and since harmful hexavalent chromium is not used, wastewater treatment can be simplified.

[0006]

MEANS FOR SOLVING PROBLEMS AND EFFECTS OF THE INVENTION The present invention is directed to (a) at least one compound which forms trivalent chromium ions, (b) boric acid, (c) glycine and (d) in an aqueous solution. Provided is a trivalent chromium plating bath containing an ammonium salt for depositing a thermosetting chromium plating.

The trivalent chromium plating bath of the present invention is preferably an aqueous solution containing at least one compound (a) which forms trivalent chromium ions in an amount of 30 to 500 g / l and (b) boric acid in an amount of 20 to 50 g / l. , (C) Glycine 20-120 g /
1 and 30-150 g / l (d) ammonium salt.

As the ammonium salt, it is preferable to use ammonium sulfamate [R ₁ R ₂ N-SO ₃ -NH ₄ ], ammonium sulfate [(NH ₄ ) ₂ SO ₄ ] or ammonium chloride [NH ₄ Cl]. It is preferred to use ammonium sulfamate.

Compounds of trivalent chromium such as chromium chloride, chromium sulfate and chromium sulfamate are used as chromium ions in the chromium plating bath of the present invention. Boric acid, glycine and the like as additives are known as additives for trivalent chromium plating baths, but this alone cannot provide a thick, glossy and practical chromium plating. In the present invention, ammonium sulfamate or ammonium sulfate,
By adding an ammonium salt such as ammonium chloride, it has succeeded in electrodepositing thick chromium plating having a specular gloss. The chromium plating layer according to the present invention has a hardness of about HV700 at the time of electrodeposition.
The heat treatment at around 0 ° C. can increase the hardness up to around HV 1500 and significantly increase the abrasion resistance.

[0010]

Next, examples of the present invention will be described.

Example 1 Chromium plating bath composition (in aqueous solution) and plating conditions: Chromium chloride 300 g / l Boric acid 30 g / l Glycine 50 g / l Ammonium sulfamate 130 g / l Bath temperature 50 ° C. Current density 40 A / dm ² Above When chrome plating was carried out for 30 minutes under the conditions described above, chrome plating having a specular gloss of about 30 μm was deposited, and the hardness of this film was HV720. When this product was heat-treated at 400 ° C for 1 hour, the hardness value was HV.
It rose to 1500.

Example 2 Chromium chloride 200 g / l Boric acid 40 g / l Glycine 70 g / l Ammonium sulfamate 100 g / l Bath temperature 40 ° C. Current density 30 A / dm ² Plating under the above conditions for about 50 μm
Chrome plating is deposited, and the hardness value of this coating is HV65
It was 0. When this product was heat-treated at 400 ° C. for 1 hour, the hardness value increased to HV1400.

Example 3 Chromium sulfamate 50 g / l Boric acid 30 g / l Glycine 60 g / l Ammonium sulfamate 80 g / l Bath temperature 40 ° C. Current density 40 A / dm ^{2 When the} plating was performed for 1 hour under the above conditions, about 50 μm Chromium plating was deposited. The hardness value of this plating layer is HV
It was 700, but when this was heat-treated at 400 ° C. for 1 hour, the hardness value increased to HV1400.

[0014]

As described above, according to the present invention, by adding an ammonium salt in combination with boric acid and glycine, a thermosetting chromium plating which is industrially sufficiently practical is deposited. 3 It has become possible to provide a valent chromium plating bath.

Claims (3)

[Claims] 1. An (a) at least one compound that forms trivalent chromium ions in an aqueous solution, (b) boric acid,
(C) A trivalent chromium plating bath containing glycine and (D) ammonium salt for depositing a thermosetting chromium plating. 2. In an aqueous solution, (a) 30 to 500 g / l of at least one compound which forms trivalent chromium ions,
(B) Boric acid 20 to 50 g / l, (c) Glycine 20 to
120 g / l and (ni) ammonium salt 30-150 g
A trivalent chromium plating bath for depositing thermosetting chromium plating, which contains 1 / l. 3. The trivalent chromium plating bath according to claim 1, wherein ammonium sulfamate, ammonium sulfate or ammonium chloride is used as the ammonium salt.