US2460898A

US2460898A - Process and composition for coloring copper and copper alloy surfaces

Info

Publication number: US2460898A
Application number: US562053A
Authority: US
Inventors: Walter R Meyer
Original assignee: Enthone Inc
Current assignee: MacDermid Enthone Inc
Priority date: 1944-11-04
Filing date: 1944-11-04
Publication date: 1949-02-08
Anticipated expiration: 1966-02-08

Description

Patented Feb. 8, 1949 H'EED PROCESS AND COMPOSITION FOR COLOR- ING COPPER AND COPPER ALLOY SUB- FACES Walter E. Meyer, Hamden, Conn.,. assignor, by

mesne assignments, to- Enthone, Inc.,

New

Haven, Conn., a corporation of Connecticut No Drawing. Application November 4, 1944, Serial No. 562,053

'1 Claims. (01. 148-614) This invention relates to the coloring of copper and copper alloy surfaces.

It is frequently desirable in the finishing of articles such as metal buttons and buckles, costume and cosmetic accessories, lamp bases and stands, urns, screens, tacks, particularly upholstery tacks, builders hardware and architectural items, and the like, fabricated from copper and copper alloys, such as brass, to treat the surfaces of the article to impart thereto a color not characteristic of the untreated metal. Various shades of brown including tan, greenish-brown, brownish-gold, etc., are considered particularly desirable. I

In accordance with the present invention, .I, produce these and other colors on copper and copper alloy surfaces by a process which comprises contacting the surface with an aqueous solution containing an alkali or alkaline earth metal chlorite, e. g. sodium, potassium, and calcium chlorites, and an alkaline salt. The alkali and alkaline earth metal chlorites are salts of chlorous acid and when chemically pure are essentially neutral in reaction. In the preferred mode of executing the process the surface to be cc]- ored is immersed in the salt solution.

Among the many alkaline salts which may be employed in the process of my invention may be mentioned: sodium carbonate, sodium metasilicate, sodium tetraborate, trisodium phosphate, tetrasodium pyrophosphate, sodium sesquisilicate, sodium orthosilicate, and the corresponding potassium and alkaline earth compounds where they are water-soluble. If desired, the process may be executed using a plurality of alkaline salts and/r chlorites. The presence of substantial amounts of a strong alkali such as sodium or potassium hydroxide in the coloring solution is without harmful efiect, in fact maybe advantageous particularly where it is desired to accomplish the coloring as rapidly as possible or to impart colors other than shades of brown, for example, a bluish, purplish, or greenish color.

It will be understood that the words color and coloring are used herein andv in the appended claims in the strict sense and do not include black or blackening. I

The exact color produced on the surface treated depends upon various factors including the composition of the surface, the particular salts being employed, the concentration of the salts, the temperature at which the solution is maintained, and the contact or treating time. tions necessary to achieve a particular color can be readily determined by simple experiments well 2 within the skill of those experienced in the metal coloring art.

I have found that in most cases the solution with proper adjustment of other conditions may be effectively operated at any temperature between 70 F. and its boiling point. However, I

" prefer to operate the solution at temperatures tains the chlorite and alkaline salt in a ratio The condiby weight within the range 1:1 to 122.5. Using such ratios of chlorite and alkaline salts, I have been able in many cases to obtain equivalent results from saturated solutions and solutions containing as little as a total of 4'. grams per liter of-the salts. The less concentrated solutions, however, must usually be operated at a higher temperature in order to accomplish the coloring in the same length of time. In operating at high concentrations, I have noticed that no adverse effect results from the presence of substantial amounts of undissolved salts in the solution. In general, I prefer to employ a solution in which the concentrations of the salts are within the following limits: chlorite- 10 g./l., alkaline salt-20 g./l. to chlorite g./l., alkaline saltg./l. I usually employ sodium chlorite in the practice of the invention because of its solubility and because it is readily available commercially.

Some combinations of the salts used in the execution of the invention give various colors while other combinations appear capable of imparting only a relatively few colors or of giving only a single color. I have found that the solution as prepared with sodium chlorite and either sodium carbonate or trisodium phosphate will give the greatest number of colors of the various chloritealkaline salt mixtures. When prepared with borax or sodium metasilicate in lieu of sodium carbonate or trisodium phosphate, the solution is relatively limited in coloring range. A very attractive brownish-gold color may be achieved, however, with a solution containing about 66 grams per liter of borax and an equal amount of sodium chlorite. This solution is best operated at the boiling point. If sodium metasilicate is used instead of borax, a greenish to brown color results depending upon the temperature of operation and the length of the treating period.

I prefer to carry out my process in a container formed of low carbon steel. The container or tank should be welded, not soldered,

ecause the solution will quickly dissolve solder. Inameled ware and ceramic vessels are not recommended for use with solutions which also coniin caustic because such solutions will gradually ttaclr the enamel or ceramic and frequently the Jlution may be poisoned by components of the camel.

In making up the solution, the tank is usually lied about three-quarters full of water after hich the pre-inixed salts are added with stirng until they are completely dissolved. The mk is then filled to the operatinglevel with iditional water.

I have found that unlike pure chlorlte a mixire of a chlorlte and an alkaline salt containing cm 1 to 2.5 parts of the alkaline salt for each tll". of chlorlte is not explosive upon percussion the presence of organic matter and does not arkedly increase the infiammability of ordinary brics when permitted to remain in contact lerewith. Also, the mixture or composition is as reactive with sulfur and when brought into ntact with acid is less prone to give oif danger-' LS amounts of chlorine dioxide. This last charteristic of my composition is particularly derable from the standpoint of safety since many etal surface treatments involve the use of acid iutions which are sometimes rather carelessly .ndled. Thus, when'accidentally spilled about plating room in which acid solutions are being ed, my composition does not involve the risk of lorine dioxide liberation that would be involved the chloritehandled separately were so spilled. consider the composition resulting from intiitely mixing an alkali or alkaline earth metal lorite with an alkaline salt a part ofmy inven- ,n. Where it is desired to practice the process ing a highly alkaline solution, the composition ty include substantial amounts, i.e. up to 50%, sodium or potassium hydroxide.

in commercial practice the composition conning 2 parts alkaline salt per part chlorlte is ded to water to form the coloring solution in a proportion of about 1 lb. for each gallon of ter.

During the coloring operation, water should-be led from time to time to replace that lost by lporation; otherwise, the solution may become l concentrated. No precise analytical control the solution is required. The need for more 50 ts is indicated by a slowing up of the coloring e. When the coloring rate has dropped about t, I usually add about 4 ounces of the original zture for each gallon of water present in the consider it highly important to thoroughly m the copper. or copper alloy surface. Cleancan he done with alkaline cleaners, vapor or or-solvent de-greasers, or by emulsion clean- The cleaning is not as critical as that for ting, but it is recommended to the end of ining uniform coloring that the surface be med to the extent that water when placed on surface remains thereon as a continuous film at least one minute without separating into plets i. e.. no water-break. n the case of highly buifed surfaces, it is ecially desirable to clean the surface to no lter-break." However, the work is preferably roughly rinsed after cleaning and then dipped :odiu'm cyanide solution as in the instance of itroplated copper.

have found that I can usually produce'the [red color on pure copper and high copper iys in from 1 to 10 minutes. In some cases 4 less than 30 seconds is suilicient. Low copper alloys may require as long as 20 minutes. After coloring, the work should be thoroughly rinsed in running cold water and then in hot water if it 5 is to be dried.

I In the immersion treatment, small parts can be supported in steel baskets or cylinders, and large objects on steel or iron racks, hooks, or wires. Where baskets are used, it is advisable to shake the work occasionally so that all surfaces will be exposed to the solution.

Following the coloring operation, the work may be subjected to various after-treatments such as tumbling in saw-dust, corn cob drying meal, or

paraffin coated ground cork." Where the work must withstand severe outdoor weathering, it is advisable to augment the protective effect of the finish with either lacquer, oil, or wax.

The herein described process is suitable for coloring all copper alloys containing as little as 60% of copper. Thus 60:40, 65:35, 70:30, 80:20, and 90:10 brasses are readily colored, as well as tin bronzes, silicon bronzes, beryllium coppers, and phosphor bronzes. Pure copper whether cast,

rolled, or electro-plated, is quickly given a deep finish. The process is also applicable to the coloring of electrolytically deposited brass alloys where the nominal copper content or the alloy is 60% or more.

I claim:

1. A solid composition in finely divided form adapted for use in aqueous solution to color copper surfaces or surfaces of copper alloys con taining not less than 60% copper which consists of about 1 part by weight of an alkali metal chlorlte and from about 1 to about 2.5 parts by weight of an alkaline salt having an alkalinity equal to or greater than that of tetrasodium pyrophosphate but less than that of caustic soda 40 or potash.

. 2. A solid composition in finely divided form' adapted for use in aqueous solution to color copper surfaces or surfaces of copper alloys comprising not less than 60% copper which consists of about 1 part by weight of sodium chlorlte and about 2 parts by weight of an alkaline salt having an alkalinity equal to or greater than that of tetrasodiumpyrophosphate but less than that of caustic sodayor potash.

.3. A process for coloring copper surfaces and surfaces of copper alloys containing not less than 60% copper which comprises contacting the surface with an aqueous solution consisting essentially of water. a chlorlte of the group consisting of alkali and alkaline earth metal chlo-.

rites, an alkaline salt having an alkalinity equal to,"or greater than, that of tetrasodium pyrophosphate but less than that of caustic soda or caustic potash, in proportions by weight within the range of 1 to 2.5 parts of the alkaline salt per part of the chlorlte, and 0 to 50%, based on the total weight of the chlorlte and alkaline salt, of a caustic alkali, the concentration of the salts in the solution being within the range of 4 grams per liter to saturation.

4. A process for coloring copper surfaces and A surfaces of copper alloys containing not less than V 60% copper whichcomprises immersing the surface in a hot aqueous solution consisting essentially of water, an alkali metal salt of chlorous acid, an alkaline salt having'an alkalinity equal to, or greater than, that of tetrasodium pyrophosphate but less, than that of caustic soda or caustic potash, in proportions by weight within the range of 1 to 2.5 parts of the alkaline salt per part of the chlorite, the concentration of the salts in the solution being within the range of 4 grams per liter to saturation.

5. A process for coloring copper surfaces and surfaces of copper alloys containing not less than 60% copper which comprises immersing the surface in a hot aqueous solution consisting essentially of water, sodium chlorite and an alkaline salt having an alkalinity equal to, or greater than, that of tetrasodium pyrophosphate but less than that of caustic soda or caustic potash, in proportions by weight of about 1 to 2, the concentration of the chlorlte in the solution being within the range of 10 grams per liter to 80 grams per liter.

6. A solid composition in finely divided form adapted for use in aqueous solutions to color copper surfaces and surfaces of copper alloys containing not less than 60% copper, the composition consisting essentially of a chlorite of the group consisting of the alkali and alkaline earth metal chlorites, an alkaline salt having an alkalinity equal to, or greater than, that of tetrasodium pyrophosphate, but less than that 01 caustic soda or caustic potash, in proportions by weight within the range of 1 to 2.5 parts of the alkaline salt per part of the chlorite, and 0 to 50% based on the total weight 01' the chlorite and alkaline salt of a caustic alkali.

7. A solid composition in finely divided form for use in aqueous solution to color copper surfaces or surfaces of copper alloys containing not less than 60% copper, the composition consisting essentially of an alkali metal chlorite, an alkaline salt having an alkalinity equal to, or greater than, that of tetrasodlum pyrophosphate but less than that of caustic soda or caustic potash, in proportions by weight within the range of 1 to 2.5 parts of the alkaline salt per part of the chlorite, and 0 to 50% based on the total weight of the chlorite and alkaline salt of a caustic alkali.

WALTER R. MEYER.

REFERENCES CITED The following references'are of record in the file of this patent:

UNITED STATES PATENTS Meyer Dec. 12, 1944