US2019229A - Coloration of aluminum articles - Google Patents

Description

a coloration of aluminum Patented Oct. 29, 1935 UNITED STATES PATENT oer-ice 2,019,229 4 COLORATION 0F ALUMINUM ARTICLES James Francis Leahy,

to Atlas Tack Corpor- Fairhaven, Mass., assignor ation, Fairhaven, Mass., at

No Drawing. Application November 16, 1931,

Serial No.

5 Claims.

The subject of this invention is the coloration of aluminum objects and more particularly small aluminum articles, such the like. It has been as buttons, eyelets and found possible to efiect by using the aluminum base itself as a component entering into the chemical formation of the coloring material. More specifically it has been found that the superficial oxidation of aluminum articles to produce surface films or coatings of aluminum oxide on such articles, followed by the treatment of the articles with lake-forming dyes, results in the generation of insoluble color lakes tenaciously adherent to the aluminum base, the reaction evidently being analogous to that occurring when mordant dyes are fixed on textile goods with mordants of the class of aluminum oxide.

I have now discovered that if the oxide film formed on aluminum articles is brought to a predetermined condition of hydrogen ion concentration, more especially on the alkaline side of neutrality, it is possible to control and extend the tones of color or color effects and the appearance developed on the articles with the available lake-forming dyes.

I have further found that by imparting a predetermined alkalinity to the aluminum oxide film, it is possible to ensure smooth and positive reaction between the film and the lake-forming dye to p roduce delicate and iridescent color lakes characterized by tenacious adherence to the metal base.

effect obtained in any particular upon the pH value or alkalini The color case depends y of the solution to which the oxide film is exposed, and upon such other factors as ment with the alkaline reagents.

While there are various ways 0 time and temperature of treatf superficially oxidizing aluminum articles, I prefer to bring about such oxidation disclosed in my application 452,525, filed May 14, 1930.

articles precisely as by a treatment such as Serial Number I shall therefore now give a specific example of procedure involving an initial oxidizing. treatment of aluminum described in that application.

Aluminum articles, such as buttons, are placed in a suitable perforated containe r of basket, and

the basket then immersed in a solution of about 2% sodium carbonate and about /z% sodium bichromate, preferably at boiling temperature, as

o accelerate the oxelevated temperature serves t idizing reaction.

The articles need remain in contact with the boiling solution for only five to fifteen minutes, coating or skin of at the end of which time a oxide of the desired depth has been produced and little further reaction takes place, probably owing to the impermeable character of the coating. then removed from the The The basket of articles is solution and may be washed free of entrained solution,

as by dipping oxide coating formed on the articles is a mixture of both aluminum and chromium oxides, the sodium bichromate evidently being reduced by the metallic aluminum into an oxide while serving to oxidize the metallic aluminum into an oxide. The coating has a'gray color characteristic of a mixture of both the aluminum and chromium oxides.

In accordance with the present invention, the batch of articles is then immersed in a solution of predetermined alkalinity, for instance, in a solution of both sodium carbonate and sodium tetraborate of about one tenth normality and in which the ratio of sodium carbonate to sodium tetraborate is about nine to one. The articles may be kept below the solution at about room temperature for about five minutes. The batch of articles may then be removed from the solution and subjected to the final dyeing operation. The alkaline treatment visibly modifies the oxide 20 film, changing it from an opaque, dull-gray color to a condition of translucency or transparency. The thickness of the film is also reduced owing -to the removal of considerable, if not all, of the chromium oxide as well as some of the aluminum 25 oxide.

The dyeing of the articles may be performed in various lake-forming dye solutions. For instance, the batch of articles may be lowered into a bath of dye solution at about boiling temperature containing, for instance, 1% alizarin dye of the desired color, say, red, blue, green or a mixture of colors. The dye bath preferably contains about 1% of a weakly ionized acid such as formic, acetic, lactic, tartaric, boric or phosphoric; and the articles are permitted to remain in'contact with the dye solution for about 15 minutes, at the end of which time practically equilibrium coloration has been efiected. When alizarin sapphire is the dye employed the articles acquire an iridescent blue coloration, whereas, when alizarin orange is the dye employed, a delicate, gold-colored lake is fixed on the articles. Theuse of a dye bath at elevated temperature is highly desirable in that the reaction to form the colored coating or color lake is greatly accelerated by increase of temperature, comparatively little reaction taking place at room temperature. The colored articles may then be dried; and, if desired, this may be effected 50 in a current of warm air, particularly inasmuch as no visible discoloration takes place under such conditions. The color lake formed on the article is resistant to scratching or abrasion and is characterized by its tenacity. It is firimly bonded with the aluminum base, although it can be removed by a hard, sharp instrument. The color lake also resists removal even by repeated treatment in solutions of alkali or soap, such as are used for laundering a0 density, hardness and 55,

The alkaline solution hereinbefore described for modifying the oxide film is subject to consid erable variation in composition, depending upon the final color effect to be produced. Thus, the

at about one-tenth normality, so that flexibility or control of the reaction on the film may be had.

It is highly likely that under the conditions given in the cited example, the chromium oxide content or the film is pracof relatively low alkalinity, may serve to cause the desired modification oi the oxide film. This modification is, as already indicated, accomdesired end-point of treatment.

I have adverted to the washing or rinsing oi the preliminarily oxidized articles before they undergo the second The articles may, however,

in wash water, and finally in the dye bath. It is desirable, however, to maintain the oxide film in a wet or freshly i'ormed state throughout the process, since when the oxide film is once dried out, it does not react as desired with the dye solution unless it is rehydrated by ored to the desired shade and that spoilage losses It is to be observed that although the initial treating solution may be slightly alka- 1 What I claim is: 1. A process which comprises treating aluminum articles with a. solution of an oxidizing agent to form a coating of aluminum oxide thereon,

on such articles.

2. A process of coloring small aluminum arti- 30 cles which comprises subjecting a batch of such articles to a succession of treatments, including ,10 and 11, and finally a treatment with a lakeforming dye solution to generate an insoluble color lake on such articles.

3. A process of coloring small aluminum articles which comprises subjecting a batch of such articles to a succession between about 10 and 11, ment with a lake-forming dye solution to generate an insoluble lake on such articles.

4. A process of coloring aluminum articles 11, and finally treating the articles with a lake-forming dye to generate an insoluble 70 color lake on such articles.

JAMES FRANCIS LEAHY.