JPS5884996A - Electrolytic coloring method for aluminum - Google Patents

Abstract

PURPOSE:To form a superior colored film by supplying AC to anodic oxidized Al in a weakly acidic electrolytic soln. contg. nickel sulfate and stannous sulfate as principal coloring components. CONSTITUTION:A weakly acidic electrolytic soln. contg. 5-30g/l nickel sulfate and 3-10g/l stannous sulfate as principal coloring components is adjusted to 5-7pH (7 is not included). To the soln. may be added a proper amount of ammonium sulfate, boric acid or tartaric acid, and to increase the pH an aqueous ammonia soln. is used. AC is supplied to anodically oxidized Al in the electrolytic soln. to form a superior colored film while preventing decoloring and the aging of the coloring components and enhancing the throwing power.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic coloring method for aluminum or aluminum alloy (hereinafter referred to as aluminum) that has been subjected to anodizing treatment. This invention relates to an electrolytic coloring method for aluminum using a weakly acidic electrolyte containing as a main coloring component.

Conventionally, to color aluminum, a method is generally used in which the aluminum has been anodized to form an oxide film using a conventional method, and then an alternating current is applied in a coloring bath containing a metal salt to form the desired colored film. I came.

Acidic coloring baths are commonly used as such coloring baths, but while they have the advantage of providing relatively excellent dispersibility, they are highly acidic (in other words, have a low pH) and cannot be used immediately after coloring. It is known that it also has disadvantages such as color fading if not washed with water and bath management is still complicated.

On the other hand, an electrolytic coloring method for aluminum using a neutral or alkaline coloring bath has been proposed in JP-A-49-28544, etc., but such a neutral or alkaline coloring bath causes almost no color fading even without washing with water. Although it has no advantage, the aging rate of the bath is extremely fast.
It is known that bath management is difficult. - also conventional acidic, neutral and slightly alkaline pH
The coloring baths in the area mainly produced bronze-black tones, and problems such as the difficulty of easily obtaining other tones remained unresolved.

The present invention aims to solve the above-mentioned drawbacks of conventional coloring baths, and more specifically, the present invention uses nickel sulfate and stannous sulfate as main coloring components, and adjusts and maintains the electrolytic coloring bath to be slightly acidic. Electrolytic coloring of aluminum that prevents color fading and aging of coloring components, improves throwing power, and creates an excellent colored film that adds a dull color to the conventional bronze black color tone. The main purpose is to provide law.

Therefore, in the electrolytic coloring method of aluminum of the present invention, anodized aluminum is subjected to alternating current in a weakly acidic electrolyte containing nickel sulfate and stannous sulfate as main coloring components, thereby producing a color tone unique to added metal salts. It is characterized by obtaining.

The pH range of the weakly acidic electrolyte may vary depending on the desired color tone and other coloring processing conditions; for example, when obtaining a dull color tone, a pH range of 5 to 7 (excluding pH 7) is desirable. .

On the other hand, the concentrations of nickel sulfate and stannous sulfate in the weakly acidic electrolyte can also vary depending on the desired color tone and other coloring treatment conditions, similar to the pH above, but generally each is between 5 and 30 P. /Z and 3-10 P/l
A range of e is desirable. Especially sulfuric acid, stannous 10
If it is used in excess of ft/Z, a large amount of precipitation may occur in the coloring bath, which is undesirable.

Further, the electrolytic solution may further contain appropriate amounts of ammonium sulfate, halonic acid, and tartaric acid as necessary. Furthermore, the electrolytic solution can be adjusted as necessary, and when raising the pH (i.e. When approaching the neutral side), this is done by adding aqueous ammonia.

Other electrolytic coloring conditions, such as AC power voltage, frequency,
The current density, current application time, coloring bath temperature, etc. are appropriately selected from the ranges used in ordinary electrolytic coloring methods for aluminum. For example, it is preferable to select the voltage from the range of 16 to 17 V from the viewpoint of color tone and prevention of spalling.

Although the current application time can vary depending on the desired color tone and other coloring conditions, 1 to 10 minutes is usually appropriate. It is convenient to use a normal AC power source as is, and therefore the frequency is 50Hz or <5OHz. Further, as a counter electrode, carbon, tin, nickel plate, etc. are used as in the conventional electrolytic coloring method. According to the electrolytic coloring method of the present invention, in addition to the conventional bronze color tone, It is now possible to create dull colors that were previously unavailable.

Furthermore, the weakly acidic coloring bath used in the method of the present invention has superior corrosion resistance and throwing power compared to conventional acidic coloring baths,
In addition, it was found to have superior aging resistance than neutral or weakly alkaline coloring baths.

Next, examples of the present invention will be shown.

Example 1 After pre-treating an aluminum plate according to a conventional method, 150 P
Direct current electrolysis was carried out in a sulfuric acid bath of 14 μm to form an anodic oxide film of 14 μm.

Next, alternating current electrolysis was performed at 15 V for 5 minutes in an electrolytic coloring bath having the following composition and pH using carbon as a counter electrode, and a uniform bronze colored aluminum was obtained.

Bath composition: stannous sulfate 61/! Nickel sulfate 15P/l.

Tartaric acid 20 P/i Ammonium sulfate 20? -/l.

Boric acid 20 f/1 Bath pH: 5.5 Example 2 An aluminum plate was pretreated and anodized in the same manner as in Example 1 to form an anodic oxide film of 14 μm.

Next, in the electrolytic coloring bath used in Example 1, carbon was used as a counter electrode, and AC electrolysis was performed at 17 V for 105+.
A uniform black colored aluminum was obtained.

Example 3 An aluminum plate on which a 20 μm anodic oxide film was formed in the same manner as in Examples 1 and 2 was subjected to alternating current electrolysis at 15 V for 2 minutes in the electrolytic coloring bath used in Example 2, and a uniform gray colored aluminum was obtained. It was done.

Analysis of the electrolytic coloring bath used in the above examples revealed that
It was observed that virtually no aging occurred. In addition, after the completion of the electrolytic coloring treatment, each colored aluminum was left as it was without immediately washing with water, but almost no color fading was observed in any of the examples.

Claims (1)

[Claims] (1) Anodized aluminum is subjected to alternating current in a weakly acidic electrolyte containing nickel sulfate and stannous sulfate as main coloring components to obtain a color tone unique to added metal salts. An electrolytic coloring method for aluminum characterized by: (2) In the electrolytic coloring method according to claim 1, the weakly acidic electrolyte has a pH in the range of 5 to 7 (excluding pH 7). (3), Patent In the electrolytic coloring method according to claim 1, the concentrations of nickel sulfate and stannous sulfate in the weakly acidic electrolyte are in the range of 5 to 3011/I and 6 to 10 fl13, respectively. An electrolytic coloring method for aluminum. (4) In the electrolytic coloring method according to any one of claims 1 to 6, the weakly acidic electrolyte further contains ammonium sulfate, malic acid, and tartaric acid. (9) In the electrolytic coloring method according to any one of claims 1 to 4, the weakly acidic electrolyte contains salanium ammonia water, and Electrolytic coloring method for pH-adjusted aluminum.