US3372064A - Method for producing black coatings on metal surfaces - Google Patents

Description

United States Patent 3,372,6l64 METHOD FOR PRGDUCING BLACK (IGATHNGS 0N METAL SURFACES Robert R. Jones, Perry, and Howard G. Pekar, Cleveland, (Ellie, assignors to The Lubrizol Corporation, Wickliffe, Ohio, a corporation of Ohio No Drawing. Filed Jan. 6, 1967, Ser. No. 607,622 filairns. (Cl. 148-615) ABSCT OF THE DISCLOSURE Black matte coatings which are uniform in appearance and thickness and stable under relatively severe wear conditions are produced on metal surfaces by treating the surface with an aqueous acidic solution of a trivalent antimony salt and then depositing a protective coating, preferably a phosphate coating, thereon. The coating is somewhat darker if the phosphate solution contains nickel, and the antimony-containing solution remains homogeneous over longer periods of time if it contains a small amount of a stannous salt.

This invention relates to coatings for metal surfaces and more particularly to a new method for producing a black matte finish on a metal object, which method comprises contacting the surface of said object with an aqueous acidic solution of a trivalent antimony salt and thereafter depositing a protective coating thereon.

The provision of a black coating of uniform appearance for metal articles is of increasing importance, especially in the automobile industry. Certain automobile manufacturers now require that parts furnished tov them have such a coating. The dificulty has been that uniform black coatings have not been capable of simple production. The methods heretofore used have involved paints, pigmented oils or additives to metal treatment baths (e.g., phosphating baths). Each of these is attended by serious disadvantages such as non-uniformity in appearance or coating thickness, smutting, evolution of flammable solvent fumes, and low resistance to abrasion and Wear.

A principal object of the present invention, therefore, is to provide an improved method for producing black coatings on metal surfaces.

A further object is to provide a method for blackening metal surfaces which is simple to use and compatible with a wide variety of metal treatment procedures.

A still further object is to produce black matte coatings on metal objects, said coatings being uniform in appearance and thickness and stable under relatively severe wear conditions.

Other objects will in part be obvious and will in part appear hereinafter.

The method of this invention may be used with any metal which will receive a phosphate coating. These include ferrous metals, cadmium, Zinc and aluminum. The method is particularly advantageous on ferrous metal surfaces.

As indicated above, the method of this invention involves an initial treatment of the metal object being coated with an acidic solution of a trivalent antimony salt. Any of the water-soluble salts of trivalent antimony are satisfactory for this purpose; however, antimony trichloride is preferred. Based on the chloride, the concentration of antimony salt in the solution should be about 0.310.0 grams per liter, and preferably about 0.53.1 grams per liter.

The acid should be one which does not react violently or passivate the surface of the metal being treated or oxidize the antimony salt. Thus, neither sulfuric or nitric acids are suitable for use, since each of these acids oxidizes trivalent to pentavalent antimony. Furthermore, nitric acid passivates the surface of steel. In general, a strong mineral acid is desired, and hydrochloric acid is generaly convenient and suitable. The concentration of hydrochloric acid in the solution is preferably about 25-80 grams per liter. If lower acid percentages are used, insoluble antimony oxychloride may form and precipitate, While if higher percentages are used, uniformity of the black coating is impaired.

The presence of a stannous compound in the antimony salt solution is often beneficial, since stannous salts seem to retard the precipitation of antimony trioxide. About 0.30.4 gram of stannous chloride per gram of antimony trichloride is sufficient to accomplish this purpose.

According to this invention, the metal object is first thoroughly cleaned and is then contacted with the antimonycontaining solution (e.g., by immersion or spraying) for a period of time sufficient to provide a black coating of the desired thickness. The preferred thickness is in the range of about 20-70 mg. per square foot, preferably about 50 mg. per square foot. The time required to form a coating of this thickness is usually between about 10 seconds and about 4 minutes. For a 50 mg. per square foot coating, about 2 minutes is suitable. The temperature of the antimony treatment is preferably about room temperature (e.g., -80 F.).

Following treatment With the antimony solution, the metal object may be rinsed with water or another suitable rinsing medium; this rinsing step is desirable but not necessary. The object is then coated with a protective coating.

Protective coatings suitable for use in the method of this invention-are of many types and include, for example, lacquers, plastic coatings, phosphate coatings and chromate conversion coatings. The phosphate coatings are preferred; they are prepared by contacting the surface of the object with an aqueous acidic solution containing phosphate ions, usually in combination with auxiliary ions such as zinc, manganese, lithium, beryllium, magnesium, calcium, strontium, cadmium, barium and nickel. The presence of anions such as nitrate, nitrite, chlorate, ferrocyanide, ferricyanide or the like is also advantageous. The composition of the phosphating solution is not critical, but excellent results are obtained with the solutions described in US. Patent 3,090,709 and in copending application Ser. No. 323,134, filed Nov. 12, 1963. These solutions generally contain as essential ingredients the phosphate ion, either .zinc or nickel ion and at least one other metal nitrate from the group listed above. Zinc, if present, usually comprises about 0.1-0.4% (by weight) of the solution, and nickel may comprise about 0.005 2.0% thereof. Nickel-containing solutions are especially desirable since the presence of nickel ion reduces the smutting tendency of the blackened surface. The presence in the phosphating solution of small amounts of antimony, due to drag-out from the pre-dip solutions, is not harmful and in some instances may increase the thickness of the black coating.

The following table gives the compositions of several phosphating solutions which may be used'in the method of this invention. All figures represent weight percentages of the various ions except for points total acid, which denotes the number of milliters of 0.1 N aqueous sodium hydroxide required to neutralize a 10 ml. sample of the solution, using phenolphthalein as an indicator. The examples given are not to be considered as limiting the in- Patented Mar. 5, 1968' 4 vention, since any of the numerous phosphating composi- This concentrate is diluted with water to 3% (by voltions known in the art may be used. ume).

Example No. Ions The preparation of some of the phosphating solutions 15 Example 12 in the above table is effected in the followingmanner.

A 3% (by volume) aqueous solution is prepared from a concentrate containing 59.3 grams of the zinc oxide- T 24 6 f i lf 1 dd d 1 4 f nitric acid solution described in Example 11, 14.5 grams 0 grams 0 W1 ere are a e grams 0 of 75% phosphoric acid, 16.9 grams of ammonium di- Iime Calcium Oxide) and grams of 75% hydrogen phosphate, 3.7 grams of nickel nitrate hexamercial phosphoric acid. The solution is then diluted by h d d 5,6 grams f water. s g; P i yf fl i) c l 1 p y Methods for treating metal surfaces with phosphating 0 Water. 0 1 "r f 0 t 6 illte S0 utiOn t 6T6 is a ded solutions are well known in the art and need not be degram of Sodium nitrite and 2 grams of nickel flitfati scribed in detail here. Suflice it to say that the phosphathexahydrate- 0 ing treatment is generally carried out at an elevated tem- Example 2 perature, usually about 150-210 F., and requires between about seconds and 2 minutes. Dipping, spraying or any other convenient means of contact may be used. 30 The blackened and phosphated metal surface is preferably rinsed again with water and finally treated with an aqueous chromate or chromic acid solution, a so-called water-soluble oil, or both. The latter term is generic to a number of complex metal salts of mineralacid (especially phosphoric acid) esters, said salts being soluble To 87.3 grams of water there are added 11.7 grams of lime (72% calcium oxide), 68.4 grams of 75 commercial phosphoric acid, and 12.6 grams of nickel nitrate hexahydrate. This concentrate, having a specific gravity of 1.3, is diluted by dissolving 2 parts (by volume) in 100 parts (by volume) of water.

Example 3 30 or dispersible both in water and in organic solvents. Exhis solution is prepared by dissolving 2.3 grams of amples of water-soluble oils are the products described in lime (72% calcium oxide), 10.7 grams of 75% commer- US. Patents 2,080,299; 2,820,723; 2,861,907; and 3,215,- cial phosphoric acid, 2.4 grams of nickel nitrate hexa- 715. Many of these are sold under the trademark Rusthydrate, 4.5 grams of 42 Baum nitric acid, and 10 4O arest. Either the chromate or water-soluble oil treatment grams of ammonium dihydrogen phosphate in 970 grams renders the metal surface resistant to corrosion. of water. The effectiveness of the method of this invention is Example 4 shown by the following examples. To 830 grams of water there are added 121 grams of Example 13 commercial phosphoric acid. 15 grams of Baum A panel of cold-rolled steel 4" X 6") is cleaned, pickled mtric and, 8 grams of lime calcium Oxide) and in 10% phosphoric acid for 4 minutes at 160 F., rinsed 15 grams of mckel nitrate haxahydratewith water and immersed for about one minute at 75 F. in an aqueous solution containing 0.75 gram per liter of Example 5 antimony trichloride and 63.5 ml. per liter of 38% hydro- An aqueous solution (1 liter) is prepared containing 00 acid (about grams P liter f L PP- 4.98 grams of zinc nitrate, 6.88 grams of ammonium di- 'proxlmately It 8 then rmsed with w hydrogen h h t d 6.32 grams of l i nitrate mersed for 15 minutes in the phosphate solutlon of Extrihydrate. ample 10 at 190 F., rinsed a third time and treated for 30 seconds at 160.F. with an aqueous solution of chromic Example 6 acid (0.25 g./l.). The panel is finally air-dried, coated An aqueous solution (one liter) is prepared containing with a water-soluble oil sold as Rustarest 14-40-SC and 14.2 grams of zinc nitrate hexahydrate, 7.8 grams of 75% air-dried again. The surface of the metal thus treated rephosphoric acid, 4.2 grams of zinc chloride, 8.7 grams ceives a uniform black coating.

of ammonium dihydrogen phosphate, and 14.3 grams of A second panel is treated as described above, except calcium nitrate trihydrate.

that the chromic acid treatment is replaced by a hot water rinse (20 seconds at 180 F.). A third panel is treated Example 10 with the antimony-containing and phosphate solutions,

A concentrate is prepared from 31 grams of 75% Phos rinsed with water, immersed for 20 seconds at 160 F. 111

Phoric acid 263 grams of 67% nitric acid grams 3.20% (by volume) aqueous solutlon of a water-soluble of Zinc Oxide, 120 grams of ammonium dihyzirogen Phos 011 sold as Rustarest 452, and finally air-dried. Both panels phate, 3.7 grams of 50% sodium hydroxide, and 14.1 receive Sumlar black coatmgs' grams of water. This concentrate is diluted with water to Example 14 3% (by volume). f l

- The procedure 0 Examp e 13 (with chromlc acid rinse Example H followed by air drying) is repeated; the antimony and A concentrate is prepared from 65.4 grams of an aqu phosphate baths are used continuously for coating steel ous solution containing 20.95% (by weight) Zinc oxide panels,with replenishment as needed. It is found that the and 31.2% nitric acid, 16.0 grams of phosphoric antimony bath must be recharged, after treatment of 24 acid, and 18.6 grams of ammonium dihydrogen phosphate. 75 and 36 square feet of steel, with 25 ml. of a concentrate containing 42.8 grams per liter of SbCl and 500 ml. per liter of 38% HCl.

Example 15 A continuous operation similar to that of Example 14 is conducted, except that the antimony solution also contains 0.25 gram per liter of stannous chloride. It is found that the bath remains homogeneous during the treatment of a considerably greater total surface area of metal.

Example 16 The procedure of Example 14 is repeated, using an antimony solution containing 0.67 gram per liter of SbCl and about 43.4 grams per liter of HCl, and the phosphate bath of Example 11. A similar procedure is followed using the nickel-containing phosphate bath of Example 12. The latter is found to produce a somewhat darker coating.

What is claimed is:

1. A method for producing a black matte finish on a ferrous metal, zinc, cadmium or aluminum object which comprises contacting the surface of said object with an aqueous acidic solution of a trivalent antimony salt, the acid in said solution being one which does not react violently with or passivate the metal surface or oxidize said antimony salt, and thereafter depositing a phosphate conversion coating on said surface.

2. The method of claim 1 wherein the phosphate coating is applied by contacting the metal surface with an aqueous acidic solution containing as essential ingredients the phosphate ion and one or both of zinc and nickel ions, the zinc comprising about 0.11.36% by weight of said solution and the nickel about 0.005-2.0% thereof.

3. The method of claim 2 wherein the phosphate solution contains nickel ion.

4. The method of claim 2 wherein the metal surface is a ferrous metal.

5. The method of claim 4 wherein the antimony salt is antimony trichloride and the acid used in the antimonycontaining solution is hydrochloric acid.

6. The method of claim 5 wherein the concentration of antimony salt in the antimony-containing solution is about 03-100 grams per liter and the concentration of HCl therein is about 25-80 grams per liter.

7. A method according to claim 6 which comprises (A) contacting the surface of said object with said antimony salt solution: (B) thereafter contacting said surface with an aqueous acidic solution containing as essential ingredients the phosphate ion and one or both of zinc and nickel ions, the zinc comprising about 0.11.36% by weight of said solution and the nickel about 0.0052.0% thereof; and (C) treating said surface with one or both of 1) an aqueous chromate or chromic acid solution and (2) a complex metal salt of a phosphoric acid ester.

8. The method of claim 7 wherein the antimony trichloride solution also contains a stannous salt, about 0.3- 0.4 gram of said stannous salt, calculated as stannous chloride, being present per gram of antimony trichloride.

9. A ferrous metal, zinc, cadmium or aluminum object carrying on its surface a black matte coating applied by the method of claim 1.

10. A ferrous metal object carrying on its surface a black matte coating applied by the method of claim 4.

References Cited UNITED STATES PATENTS 1,43 6,729 11/ 1922 Scanlan et al. 1,493,012 5/1924 Abraham 1486.15 X 1,770,828 7/1930 Arent 117-130 2,564,661 8/1951 Arent 117-130 OTHER REFERENCES Hopkins, The Scientific American Cyclopedia of Formulas, 1925, Scientific American Pub. Co., pp. 444, 448.

Meyer, Product Engineering, December 1943, pp. 792- 794, TJI, p. 93, 148-6.14.

RALPH S. KENDALL, Primary Examiner.