US3106484A

US3106484A - Metal treating

Info

Publication number: US3106484A
Application number: US80535A
Authority: US
Inventors: Russell C Miller
Original assignee: Cowles Chemical Co
Current assignee: Brent Chemicals Corp; Cowles Chemical Co
Priority date: 1961-01-04
Filing date: 1961-01-04
Publication date: 1963-10-08
Anticipated expiration: 1980-10-08

Description

Oct. 8, 1963 R. c. MILLER 3,106,484

METAL TREATING Filed Jan. 4, 1961 CHROMIUM DEPOSITING sOLuTION I ZINC suRFACED ARTICLE ALL CONTAIN I Cr ZINC suRFACED ARTICLE CONTAINING AT LEAsT I SURFACE COATING OF CHROMIUM ONE ALSO I COIBIIITAINS I or R 5 CH OMIUM DEPOSITING SOLUTION AT LEAST :4 I ONE I ZINC SURFACED ARTICLE CONTAINING CONTAINS Two SURFACE COATINGs 0F CHROMIUM NO I I Cr ADDITIONAL CHROMIUM DEPOsITING SOLUTIONS (OPTIONAL) I ZINC suRFACED ARTICLE CONTAINING PLURALITY OF SURFACE COATINGS 0F CHROMIUM DYEING sOLuTION I DYED ARTICLE DRYING I DRIED DYED ARTICLE I I I HYDROPHOBIC PROTECTIVE COATING (OPTIONAL) I DYED ARTICLE CONTAINING HYDROPHOBIC COATING INVENTOR: RUSSELL C. MILLER 1 a-r M!- ATT'Ys United States Patent 3,106,484 METAL TREATING Russell C. Miller, Chicago, Ill., assignor to Ccwles Chemical Company, Cleveland, Ohio, a corporation of Ohio Filed Jan. 4, 1961, Ser. No. 80,535 16 Claims. (Cl. 117-.-71)

This invention relates to protective metal finishing compositions and more particularly to a process for finishing zinc surfaced articles to provide enhanced corrosion protection and an improved appearance. The invention is especially concerned :with the dyeing of zinc surfaced articles.

One of the objects of the invention is to provide a new and improved process for providing improved corrosion protection and a beautiful finish on Zinc surfaced articles.

Another object is to provide a process for making the surfaces of Zinc surfaced articles receptive to dyes.

A more specific object of the invention is to provide a process for treating electrodeposited zinc surfaces in order to make them receptive to dyes.

Another specific object of the invention is to provide a new and improved process for treating galvanized metal sheets in order to make them receptive to dyes.

An additional object is the provision of new and useful compositions suitable for application to zinc surfaced articles in order to provide enhanced corrosion protection and to make the surfaces of such articles receptive to dyes. Other objects will appear hereinafter.

In accordance with the present invention it has been found that new and improved dyed zinc surfaced articles can be obtained while enhancing the corrosion resistance by treating such articles in a plurality of treatments with chromium depositing solutions in at least one of which both Cr and Cr are present. In general, Cr" ions are predominant in the first chromium containing bath and Cr ions are predominant in the second chromium containing bath where the article treated has an electrodeposited zinc surface. If the zinc surface is a galvanize-d surface the Cr should be predominant in both baths and the Or may be omitted in one of the baths. The multiple or successive treatments should be effective to apply coatings containing a total of at least 20 milligrams of chromium per square foot of surface of said articles. Thereafter, a dye, preferably an acid dye, is applied to said chromium containing surface.

The specific compositions employed in the primary and secondary treatments will vary to some extent depending upon whether the zinc surfaced article is one in which the zinc has been electrodeposited or one in which the Zinc has been applied by galvanizing. In either case, there are certain additional optional treatments which may be desirable under some circumstances. For example, it is usually desirable in either case to treat the zinc surfaced article initially in order to remove from the surface foreign substances, such as, sulfur, cyanides, al-kalis, brightening agents, iron, and minerals. This is accomplished by rinsing with water, cold or hot, and by applying dilute acid solutions, such as, for example, dilute nitric acid solutions.

The invention also contemplates washing of the chrorniurn containing coatings with Water and, if necessary, leaching the coatings slightly under some circumstances.

The invention further contemplates the preparation of coated Zinc surfaced articles which are receptive to acid, direct or chromium containing dyes.

Finally, the invention contemplates the application of a protective organic film over the dyed surface in order to produce a dyed article having enhanced abrasion resistance. The chromium containing coatings provide zinc 3,106,484 Patented Oct. 8, 1963 ice I surfaced articles #with enhanced corrosion resistance. The dyes do not downgrade the corrosion resistance, but in the majority of instances (depending on the dye) increase the corrosion resistance.

In general, for the purpose of the invention the chromium containing coatings are sufiicient to provide 20 to 60 milligrams of chromium per square foot of surface area.

In practicing the invention where the zinc surfaced article is an electrodeposited zinc, the pH values of the compositions employed in the primary chromium depositing bath are important. The relative ratio' of Cr to Cr is also important and the ratio of Cr to Cr should always be greater than 4:1 for the primary chromium application. Furthermore, it is preferable in the first applied chromium-containing treating bath to employ a minimum of 12' grams per liter of Cr, preferably 30 to 40 grams per liter, and a minimum of 0.2 gram per liter of Cr In this primary treatment as applied .to electro-deposited zinc surfaced articles it is also desirable to apply a fairly heavy coat of chromium initially, preferably 20 to 40 milligrams of chromium per square foot of surface. In the secondary treatment, a minimum of 0.2 g'./liter and a maximum of 0.6 g./liter of Cr is preferably maintained at all times. Initially, the bath should have a small amount of Cr (0.05 g./liter) for quality finish and dye acceptance; the concentration of Cr can build up to a much larger amount (10-20 g./liter) and still function quite well. For best performance, however, the Cr level should be 0.1 to 3.0 g./ liter.

The accompanying drawing shows a flow diagram of the process. 7 Where the article to be treated is a galvanized ferrous metal article, that is to say, an article in which the zinc surface has been applied by dipping or passing the arti cle through molten zinc, it is desirable to apply as the primary treatment only a relatively small amount of chromium, preferably 2 to 5 milligrams per square foot of zinc surface. Furthermore, in this treatment the presence of trivalent chromium is immaterial and, in fact, the treatment is preferably carried out without introducing trivalent chromium into the treating composition.

In the secondary treatment where the article is a galvanized article and no trivalent chromium has been applied in the primary treatment, the (secondary treatment is preferably one which provides a rather heavy coating of chromium on the order of 30 to 60 milligrams of chromium per square foot and which also introduces trivalent chromium. Thus, in both types of articles trivalent chromium is introduced in at least one of the treatments but the order of introduction is different depending upon the type of surface.

The following compositions are given to illustrate different formulations which can be employed for various ohronrating treatments in accordance with the invention:

COMPOSITION A COMPOSITION C NaNO pounds 14.4 Na Cr O .2H O do 5.1 NaHF d 6 NH HF grams 57 d0. COMPOSITION D Pounds NaNO 84 NilzCI'zOq-ZHgO NaHF 64 Al(NO 2.0 NaNO 2.5 Zn dust 1.0

COMPOSITION E CrO i pounds 92 (NH4)2SO4 --d0. 8 Zn dust grams 4O NiSO do COMPOSITION F Percent NazCI' O'p2H2G CrO 17.8 (NI-1.02504 5.1 NaI-IF .5

Al (SO 1.2 Al(NO 1.8 N32C4H406 1 Na SiF 1.0 Zn dust 9 The invention will be further illustrated but is not limited by the following examples in which the quantities are stated in parts by weight unless otherwise indicated.

Example I A zinc plated wire rack of the type used in refrigerators was rinsed in fresh water at a temperature of 130 to 150 F., then dipped in a 0.5 to 1% by weight solution of HNO for about ten seconds at 70 to 80 F., and thereafter immersed in a solution prepared by dissolving 8 to 12 ounces per gallon of Composition A in a dernineralized water at a temperature of 80 to 100 F. for 10 to seconds with air agitation. The pH was maintained between .4 and .5 with a pH meter and by adding nitric acid when necessary. The trivalent chromium content of this first or primary chromating bath was not allowed to rise to more than 10 grams per liter. This was maintained by dumping a part of the solution and adding more of Composition A in any case where the trivalent chromium content began to approach 10 grams per liter. Regular additions of composition A were made to this bath every hour or two during the run.

After removal of the article from the primary chromating bath it was rinsed by dipping it in demineralized water at to F. Two separate rinses were applied in this manner. The article was then subjected to treatment in a dilute caustic soda solution containing .5 to 1 ounce of NaOH per gallon of water at a temperature of to F. for about 25 seconds. This is an optional treatment and is used to remove visible evidence of Cr which sometimes appears as a stain unless removed.

This treatment is usually referred to as a leaching treatment.

After the dilute caustic alkali leaching treatment the article is rinsed in demineralized water at 100 to F.

d A second rinse is also preferably applied which consists of equal parts of sulfuric acid and acetic acid added to a water bath to obtain a pH of 4 to 7 in the dilute solution (0.5 to 1%).

The resultant article was then immersed in the secondary chromating bath which was made up from composition C and contained an initial concentration of 1 ounce of said composition per gallon of solution, the remainder of said solution being Water. The pH of this solution was reduced to 0.9 to 1.5 by adding nitric acid. While no trivalent chromium was introduced into this solution, a check was maintained on the trivalent chromium at all times to be sure that it did not exceed 10 grams per liter of solution. The temperature of this bath was from 90 to 100 F. and the time of treatment was 10 to 20 seconds. The Cr in this solution was preferably maintained between 0.3 and 0.6 grams per liter.

After the secondary chromating treatment the resultant article was again given a cold rinse with a neutral or slightly acid solution, that is, either demineralized water or a dilute acid solution--maintained by addition of equal parts of sulfuric acid and acetic acid-40 a pH of 4 to 7.

After the primary chromating treatment the article has a clear, brilliant lustrous surface and this should not be diminished by the secondary treatment. Approximately 20 to 40 milligrams of chromium per square foot is applied in the primary treatment and 10 to 40 milligrams of chromium per square foot in the secondary treatment.

Prior to the secondary treatment the article does not readily accept a dye but after the secondary treatment it shows good receptivity.

The dye solution was prepared by dissolving in water A; to /2 ounce of dye per gallon of water and maintaining a pH of 5 to 7.5. The pH may be maintained by adding to the solution 1 part of sulfuric acid and 1 part of acetic acid in 80 parts of water, together with a sufficient amount of the dye to maintain the color. The dyeing is preferably effected at a temperature of 100 to F. and the solution is agitated during the dyeing operation.

Examples of dyes which can be employed are:

Brass, gold, yellow Ciba, Inc-Oxanal Yellow GR concentrated, Oxanal Orange G, Oxanal Orange REX concentrated Du Pont-Orange RO, Capracyl Orange R, Capracyl Brown 2R Green- Ciba, Inc.-Oxanal Green BL Du Pout-Pontacyl Green Bl, Anthraquinone Green GNN General Dyestutf-Tartrazine C Extra CF Black- Du Pont-Pontacyl Fast Black N2B concentrated,

Pontacyl Blue Black 3BA Red- Du Pout-Brilliant Crocein FL Blue Ciba, Inc.0xanal Blue C-200, Ox'anal Blue CB Du PontAnthraquinone Blue RXO, Anthraquinone Blue SWF Violet, purple Du Pont-Pontacyl Fast Violet 10B concentration Anthraquinone Violet 3RN General Dyestuff-Croseia Scarlet N Extra After dyeing, the article was rinsed at 100 to 110 F., the pH of this rinse being maintained between 6 and 7, either by the carryover from the preceding bath, or small additions of the very dilute acid mixture (equal parts sulfuric and acetic acids).

The article was then dried at a temperature of 200 to 250 F. for 3 to 10 minutes.

After cooling, the article was dipped in a clear enamel (e.g., Du Pont RIC-5912) and thereafter baked for 15 minutes at 400 F. Instead of applying an enamel, some other type of protective organic film may be applied to the final article, as, for example, an epoxy resin, a vinyl plastic, or a mixed epoxy-acrylic resin. The protective layer of organic film improves the abrasion resistance.

Example If This example illustrates the invention as applied to the treatment of galvanized sheets.

A galvanized sheet was dipped at a temperature of 180 to 200 F. in a solution containing 2 pounds per gallonof CrO 2 ounces per gallon of sodium acetate, 0.1 ounce per gallon of sulfuric acid and 1 ounce per gallon of nitric acid, together with traces of fluoride, the remainder being water. Instead of sodium acetate the corresponding amount of acetic acid may be used. The purpose of the acetate or acetic acid is to react with any lead that might be present on the surface of the zinc. This treatment serves to remove impurities, such as organic materials, detergents, oils, and other substances, which may be present on the surface of the sheet. The galvanized sheet does not necessarily have to be bright initially. The treatment not only removes impurities but produces a mircoetch on the surface of the sheet and provides a bright, clean surface containing a small amount of chromium which usually runs from 2 to 5 milligrams per square foot.

After the foregoing treatment, the sheet was rinsed in cold water and was then subjected to treatment with composition F dissolved in water in proportions of /2 to 2 ounces of composition F per gallon of water for 15 seconds at a temperature of 110 to 180 F. This normally produces a relatively heavy coating of chromium on the surface on the order of 30 to 60 milligrams of chromium per square foot of surface area.

The sheet containing the double chromium coating was then given a cold rinse with water at a temperature of 60 to 70 F. at a neutral pH.

Thereafter the sheet was dyed by immersing it in a dye solution containing 2 to 5' ounces of dye per gallon of Water at a pH of 6.0 and a temperature of 120 to 180 F. for 15 seconds. The dye can be any of the dyes set forth in Example I, and the procedure for preparing the dye solution can be the same as that set forth in Example 1.

After the dyeing operation the dyed sheet was rinsed again in cold water, 60 to 70 F., and at a neutral pH. Thereafter it was dried and an organic protective coating was applied to it as described in Example I.

The foregoing treatment produces a beautiful colored galvanized sheet in which the mechanical pattern of the sheet is visible through the dye coating.

It will be understood that the invention is susceptible to some variation in the manner of its practical application. Where the zinc surfaced sheet has a coating of electrodeposited zinc, pH control is very critical. The ratio of Cr to Cr is also very important and a ratio between 30:1 and 80:1 is preferred, with a ratio of 40:1 being approximately optimum. There is a slow rise in the Cr content of the bath as the latter is used successively in treating zinc surfaced articles and this is compensated for by adding the chromate containing compositions or by adding solid chromate in which the chromium has a valence of 6. For optimum results the weight ratio of NO :SO should be 8:1 to 10:1 in the first applied chromium depositing solution where the article has an electrodeposited zinc surface.

The various rinse operations are preferably carried out with demineralized water containing an acid where an acid has been specified. Water containing chlorine is undesirable. The same is true of water containing iron. The total solids present in the water preferably should not exceed 20 parts per million. Otherwise, spot-tiness and discoloration may result. Free nitric acid and soluble nitrates, when carried into the dye bath is detrimental to the dye-colored film.

The chromate film in itself enhances the utility of the article and the dye colored film is also corrosion resistant but both films can be easily scratched and therefore a coating of a hydrophobic film forming material, such as a vinyl resin, an'epoxy resin, polyethylene, polypropylene, an epoxy-acrylic resin, or a clear varnish is recommended.-

Various combinations of the chromate coating compositions may be employed in the practice of the invention. Good results have been obtained with double chromate treatments, for example, where the first treatment is carried out with composition A and the second treatment with composition C, or where the first treatment is carried out with composition B and the second treatment with composition C, or where the first treatment is carried out with composition A and the second treatment with composition D, or Where the first treatment is carriedout with composition B and the second treatment with composition D. An important feature of these treatments is that they are applicable to bright plates and do not degrade the lustre. However, proper dye acceptance is not obtained unles both treatments are used. Composition E can be substituted for composition A or composition B in any of the foregoing combinations.

In the foregoing compositions A to F, certain of the substances employed as ingredients other than chromates are used for specific purposes. Thus, Zn dust is used in order to partially reduce the hexavalent chromium and thereby provide trivalent chromium. Alternatively, trivalent chromium compounds can be employed. Sodium nitrite (NaNO is also used as a reducing agent. Ammonium sulfate is used to provide sulfate ion and to enhance corrosion protection. The ammonium ion also has a brightening effect. Aluminum compounds, such as aluminum sulfate and aluminum nitrate, improve the dye receptivity. The various fluoride compounds, ammonium acid fluoride (NH HF), sodium acid fluoride (N-aHF) and sodium silicofluoride (Na SiF6), are employed to improve corrosion resistance, provide a film containing chromium which adheres more tightly to the surface of the zinc and is more insoluble, provide a brightening effect, facilitate chemical polishing, provide resistance to the formation of swirl patterns caused by agitation in the various baths, and provide a buffer to maintain the pH.

Certain types of materials (organic, inorganic and metallo organic) are employed where it is desired to pro duce darker films. Examples of such substances are zinc, sodium and/ or potassium oxalates, tartrates, gluconates, bismuthates, oxynitrates, molybdates and antimonates, which can be incorporated, for example, as 1% to 2% by weight of composition F. They also serve as buffers in acid solutions and are especially useful where it is desirable to produce coatings having a green tint. All of these auxiliary materials are optional but enhance the results obtained in the practice of the invention.

The dyes which are employed in the practice of the invention are readily available dyes of the type which are ordinarily substantive to Wool. Acid dyes are preferred.

The invention is especially useful in producing wire racks such as are employed for refrigerator shelves. It can also be used for coloring zinc surfaced articles genenal-ly in order to enhance their appearance.

The invention is hereby claimed as follows:

1. A process of preparing a dyed zinc surfaced article which comprises subjecting a zinc surfaced article to a plurality of different treatments with chromium depositing solutions, all containing Cr? ions, at least one such chromium depositing solution containing an average amount of Cr ions of at least 0.2 gram per liter and a weight ratio of Cr to Cr greater than 4:1, and at least one other such chromium depositing solution containing substantially no Cr ions, said treatments being effective to apply coatings containing a total of at least 20 milligrams of chromium per square foot of sunface of said article, and thereafter applying a dye to said chromiuin containing surface of said article.

2. A product resulting from the process of claim 1.

3. A product resulting from the process of claim 1 which also contains a hydrophobic protective organic coating. it

4. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zinc surfaced article to a plurality of different treatments with chromium depositing solutions in the first applied of which the weight ratio of Cr to Cr is greater than 4:1 and the average amount of Cr is at least 0.2 gram per liter, at least one other chromium depositing solution containing substantially no trivalent chromium, said treatments being effective to apply coatings containing a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface of said article.

5. A process of preparing a dyed zinc surfaced article which comprises subjecting a zinc surfaced article having an electrodeposited zinc surface to a plurality of different treatments with chromium depositing solutions in one of which the weight ratio of Cr" to Cr is greater than 4:1, the average amount of Cr is at least 0.2 gram per liter, and the weight ratio of NO :SO is 8:1 to 10:1, at least one other chromium depositing solution containing substantially no trivalent chromium, said treatments being effective to apply coatings containing a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

6. A process of preparing a dyed zinc surfaced article which comprises subjecting a zinc surfaced article having a galvanized zinc surface to two different treatments with chromium depositing solutions in which Cr ions predominate over other Cr ions and in at least one of which the Weight ratio of Cr to Cr is at least 4:1 and the amount of Cr averages at least 0.2 gram per liter, the other chromium depositing solution containing substantially no trivalent chromium, said treatments being effective to apply coatings containing a total of 2 to milligrams of chromium in one treatment and 30 to 60 milligrams of chromium in the other treatment per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

7. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zinc surfaced article to a plurality of different treatments with chromium depositing solutions in one of which the ratio of Cr" to Cr is 30:1 to 80:1 and the average amount of Cr is 0.2 to 0.6 gram per liter, at least one other chromium depositing solution containing substantially no trivalent chromium, said treatments being effective to apply coatings containing a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

8. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zine surfaced article to two different treatments with chromium depositing aqueous solutions in the first of which the ratio of Cr to Cr is greater than 4:1 and the minimum amount of Cr is 0.2 gram per liter, the second of said chromium depositing solutions containing substantially no trivalent chromium, maintaining a pH of 0.4 to 1.5 during said treatments, said treatments being sufficient to apply a total of 20 to 40 milligrams of chromium per square foot of surface of said article in the first treatanent and to 40 milligrams of chromium per square foot in the second treatment, and thereafter applying a dye to said chromium containing surface.

9. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zinc surfaced article to a plurality of different treatments with chromium depositing solutions in one of which the ratio of Cr to Cr is greater than 4:1 and the minimum average amount of Cr is 0.2 gram per liter, at least one other chromium depositing solution containing substantially no trivalent chromium, at least one of said solutions also containing an aluminum salt of a mineral acid in suflicient amount to enhance dye receptivity of the resultant coating, said treatments being sufficient to apply a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

10. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited Zinc surfaced article to a plurality of different treatments with chromium depositing solutions in the first of which the ratio of Cr to Cr is greater than 4:1 and the minimum ave-rage amount of Cr is 0.2 gram per liter, the first of said solutions also containing a reducing agent adapted to reduce Cr to Cr at least one other chro mium depositing solution containing substantially no trivalent chromium, said treatments being sufiicient to apply a tota1 of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium surface.

11. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zinc surfaced article to a plurality of different treatments with chromium depositing solutions in one of which the ratio of Cr to Cr is greater than 4:1 and the minimum average amount of Cr is 0.2 gram per liter, at least one other chromium depositing solution containing substantially no trivalent chromium, at least one of said solutions also containing the fluoride ion, said treatments being sufficient to apply a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

12. A process of preparing a dyed zinc surfaced article which comprises subjecting an electrodeposited zinc surfaced article to a plurality of different treatments with chromium depositing solutions in one of which the ratio of Cr to Cr is greater than 4:1 and the minimum amount of Cr is 0.2 gram per liter, at least one other chromium depositing solution containing substantially no trivalent chromium, at least one of said solutions also containing at least one darkening agent from the group consisting of zinc, sodium and potassium oxalates, bismuthates, oxynitrates, molybdates and antimonates, said treatment being sufficient to apply a total of at least 20 milligrams of chromium per square foot of surface of said article, and thereafter applying a dye to said chromium containing surface.

13. A process of preparing a dyed zinc surfaced article which comprises applying to a clean zinc surfaced article having an electrodeposited coating of zinc, a chromium depositing aqueous solution containing Cr in the form of a substance from the group consisting of chromic acid and dichromates, ammonium sulfate, fluoride ions, an aluminum salt from the group consisting of aluminum sulfate and aluminum nitrate, a reducing agent in an amount sufficient to produce a weight ratio of the Cr to Cr of at least 4:1 but insuflicient to produce more than 10 grams per liter of Cr while maintaining a pH of 0.4 to 0.7 by adding nitric acid, thereafter rinsing the resultant treated article, contacting the resultant coating with a chromium depositing solution containing Cr nitrate ions, aluminum ions, fluoride ions, ammonium ions and sodium ions, while maintaining a pH of 0.9 to 1.5 by adding nitric acid, thereafter rinsing, thereafter dyeing with a dye which reacts with the chromium containing coating, thereafter rinsing the dyed article, then drying said article at a temperature below 250 F., and finally applying a hydrophobic protective organic coating to the resultant article.

14. A process for dyeing a galvanized zinc surfaced article which comprises applying to such article at to 200 F. a chromic acid containing solution, there after rinsing said article, thereafter applying a composition containing a dichromate, chromic acid, sulfate ions, ammonium ions, sodium ions, fluoride ions, aluminum ions, a reducing agent adapted to produce a weight ratio of Cr" to Cr of at least 4:1 but insufficient to produce more than 10 grams per liter of Cr at a temperature of 110 to 180 F. for a period of time sufficient to provide a chromium coating containing 20 to 60 milligrams of chromium per square foot, thereafter rinsing said article, thereafter dyeing said article with a dye capable of reacting with the chromium containing coating .at a slightly acid pH and a temperature of 120 to 180 F., rinsing the resultant article, drying, and finally applying a hydrophobic protective organic coating to said article.

15. A process of preparing a dyed zinc surfaced article which comprises applying to a zinc surfaced article having an electrodeposited coating of zinc a dilute acidic purifying bath, thereafter applying to the surface of said article a chromium containing aqueous solution containing 8 to 12 ounces per gallon of a composition having the following ingredients in the relative proportions given:

Na Cr O -2H O pounds 76 CrO do 19 NH4SO4 .d A1 (SO grams 59 NH HF do 240 Zn dust pound 1 at a temperature of 80 to 100 F. for to 25 seconds with air agitation while maintaining a pH of 0.4 to 0.7 by adding nitric acid, thereafter rinsing the resultant treated article, thereafter treating the rinsed article with an aqueous solution containing /2 to 1 ounce per gallon of sodium hydroxide at 90 to 100 F. for a short period of time sufficient to remove visible evidence of Cr, thereafter rinsing in water to which an acid has been added to a pH of 4 to 7, thereafter adding a composition containing the following ingredients in the relative proportions given:

in proportions of about 1 ounce of said composition per gallon of water at a temperature of to F. for 10 to 20 seconds while maintaining a pH of 0.9 to 1.5 by adding nitric acid, and a Cr content of 0.3 to 0.6 gram per liter, thereafter rinsing, and thereafter dyeing with a dye which reacts with the chromium containing coating with agitation at a temperature of to 140 F., thereafter rinsing the dyed article, then drying at a temperature below about 250 F., and finally applying a hydrophobic protective organic coating to the resultant article.

16. A process of preparing a dyed galvanized zinc surfaced article which comprises applying to such article at 100 F. to 200 F. a chromic acid containing solution for a period of time sufficient to form 2 to 5 milligrams per square foot of chromium on the surface of said article, thereafter rinsing said article with cold Water, thereafter contacting the surface of said article with an aqueous solution of /2 to 2 ounces per gallon of a composition containing the following ingredients in the relative proportions given:

at a temperature of F. to 180 'F. for a period 0 time sufficient to provide a chromium coating containing 30 to 60 milligrams of chromium per square foot, thereafter cold rinsing said article with water, thereafter dyeing said article with a dye capable of reacting with the chromium coating at a pH of about 6.0 and a temperature of F. to F., cold rinsing the resultant article with water, drying, and finally applying a hydrophobic protective organic coating to said article.

References Cited in the file of this patent UNITED STATES PATENTS King Jan. 29, 1946 McLean et a1. July 26, 1949 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 106,484 October 8, 1963 Russell C. Miller It is hereby certified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 27, for Na SiF read Na C H O Signed and sealed this 2nd day of June 19640 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Ailesting Officer Commissioner of Patents

Claims

1. A PROCESS OF PREPARING A DYED ZINC SURFACED ARTICLE WHICH COMPRISES SUBJECTING A ZINC SURFACED ARTICLE TO A PLURALITY OF DIFFERENT TREATMENTS WITH CHROMIUM DEPOSITING SOLUTIONS, ALL CONTAING CRVI IONS, AT LEAST ONE SUCH CHROMIUM DEPOSITING SOLUTION CONTAINING AN AVERAGE AMOUNT OF CRIII IONS OF AT LEAST 0.2 GRAM PER LITER AND A WEIGHT RATIO OF CRVI TO CRIII GREATER THAN 4:1, AND AT LEAST ONE OTHER SUCH CHROMIUM DEPOSITING SOLUTION CONTAINING SUBSTANTIALLY NO CRIII IONS, SAID TREATMENTS BEING EFFECTIVE TO APPLY COATINGS CONTAINING A TOTAL OF AT LEAST 20 MILLIGRAMS OF CHROMIUM PER SQUARE FOOT OF SURFACE OF SAID ARTICLE, AND THEREAFTER APPLYING A DYE TO SAID CHROMIUM CONTAINING SURFACE OF SAID ARTICLE.