US2302510A - Material and method for cleaning and coating metal - Google Patents

Description

Patented Nov. 17, 1942 MATERIAL AND METHOD FOR CLEANIN AND COATING METAL Robert R. Tamer, Detroit, and Herman J. Lodeesen, Berkley, Micln, assignors to Parker Rust Proof Company, Detroit, Mich.

No Drawing. Application November 11, 1935, Se-

rial No. 49,256. Renewed December 20, 1939. In Belgium September 23, 1931 23 Claims.

This invention relates to cleaning and coating metal, and more particularly to a method for removing small amounts of grease or other foreign substances from the surface of metal, and at the same time forming an integral coating upon the surface of the metal, which coating is adapted for uniting paint 'or enamel to the surface of the metal.

This application is a continuation in part of our co-pending application of the same title filed October 12, 1931, Serial No. 568,516.

The invention concerns preparing metal surfaces for receiving paint or enamel.

In general, the invention comprises the treatment of metals with solutions containing at least one phosphate, an oxidizing agent, an accelerating material, and an inert material. Included in the phosphates which may be employed are phosphates of iron, zinc, and manganese. Phosphoric acid may also be present if desired. Most of the common oxidizing agents except the chromates may be used in this invention. Generally, use can be made of an oxidizing agent having an oxidation potential not greater than the potential of the common bromates in a dilute phosphate solution. Nitrates, nitrites, sulphites may be employed. Nitric acid may be introduced in small quantities as such and has apparently an oxidizing efiect similar to that of the nitrates but it tends to increase the acidity of the bath and therefore, although it can be. used, it is not employed in the preferred form of the invention. Other specific oxidizing agents which may be employed are tungstates, such as sodium tungstate; acetates such as uranyl acetate; chlorates; bromates; iodate; methylene blue and the like. Among the accelerators which may be employed are soluble compounds, especially salts of copper and iron. It is understood that the metal of the accelerator must be lower in the electromotive series than the metal being treated. The preferred salt is copper sulphate, although other soluble salts may be employed, including copper nitrate and acetate. In some cases the oxidizing agent can be combined with the accelerator in a salt such as copper nitrate. When the metal being processed is zinc, soluble compounds of iron are especially suitable as accelerating agents. Examples are: ferrous sulphate and ferrous dihydrogen phosphate, the latter being preferred. For the inert material there may be employed any material which does not dissolve in, or react with the solution, such as fullers earth, talc, diatomaceous earth, wood flour and the like. Fulequivalent material may be substituted, the essential being merely an inert material preferably readily suspended in the solution and suitable to absorb impurities and to form a friable, non-adherent coating when dried.

The invention allows of considerable variation in the composition employed, in its manner of application, and in its manner of removal. For convenience, several examples of compositions, method of application and the manner of removalwill be described first, and then ways in which variations may be made will be indicated suiilciently to enable those skilled in the art to adapt the invention to the circumstances which confront them.

Example 1.-867 parts fullers earth, 95 parts zinc dihydrogen orthophosphate, 21 parts copper sulphate and 17 parts sodium nitrate, all by weight, are mixed with water until the composition has the desired consistency for spraying. This requires about 7% parts of the powder to a gallon of water.

Example 2.82 parts fuller's earth, 14.1 parts zinc dihydrogen orthophosphate, 3.9 parts copper nitrate (Cl1(NO3)2'3HsO) all parts by weight. This composition may be mixed with water as suggested in Example 1, the amount adjusted to give the desired consistency for spraying.

lers earth is the preferred material but any 55 While in the above examples the ingredients are mixed before being mixed with water it is possible to practice the invention by adding the ingredients separately or in any combination to each other or to the water.

Example 2 is an example showing the composition in which copper nitrate is employed both as an oxidizing agent and as an accelerator.

The composition above described is sprayed upon iron, steel or zinc surfaces which are to be cleaned and painted. The metal, before this treatment, should not be excessively dirty, but the treatment will remove some remaining grease, rust, and other foreign material from the surface of the metal. If too rusty, it may require treatment by other means, but slightly rusty surfaces can be readily cleaned and prepared for painting or enameling by this material.

After the solution has been sprayed upon the metal, it is dried, preferably at a somewhat elevated temperature. This temperature may be varied from only a littleabove ordinary room temperature to a point above the boiling point of water. However, there should be allowed some time for reaction to take place. When the material is sprayed on ordinary iron and steel articles, satisfactory results may be obtained by drying in such a way and at such a temperature that the material is completely dried in about fifteen minutes.

During this drying operation the rust is dissolved by the phosphoric acid resulting from hydrolysis of the solution, and the copper with the other phosphates forms a coating, integral with the surface of the metal and composedof substantially insoluble phosphates of iron and zinc with some copper embedded therein. Where copper compound is not employed in the composition there is, of course, no copper present in the coating. The dissolved rust and any grease upon the metal, as well as other foreign substances dissolved in the solution, is absorbedby and dried down with the fullers earth and forms a loose, powdery coating outside of the substantially integral coating described above, which is the result of chemical reaction with the metal of the article. This loose exterior coating of fullers earth and foreign material is readily brushed or washed off, leaving a surface which is clean except for the phosphate coating.

This phosphate coating is advantageous because, as previously indicated, it is substantially integral with the article, and it forms a much better bond with paint or enamel than does clean, smooth metal. As a result of this better bond, any pin holes through the coating of paint or enamel, or any scratches or accidentally formed regions where the enamel or paint is removed, are surrounded by the paint or enamel firmly adherent to the phosphate coating which in turn is substantially integral with the metal of the articles and, therefore, there is no opportunity for rust to spread between the painter enamel and the metal of the article, as frequently happens in the absence of such a bond between the paint or enamel and metal.

In the examples given above, the phosphates are introduced into the solution by means of zinc phosphate. While this is the most convenient method known for obtaining the desired result, it is obviously possible to form the phosphate in other ways, in the solution itself, or in a separate solution added to the water as a liquid, or by a differently formed composition which, upon addition to the solution, will produce the desired phosphates.

Instead of zinc dihydrogen phosphate, other phosphates may be employed such as manganese dihydrogen phosphate and mixtures. However, the zinc phosphate is preferable as it produces a coating more readily at low temperature than do phosphates of manganese or iron and the acidity of the zinc mixture remains more nearly the desirable ratio throughout the range of temperature employed. If manganese phosphate is employed, one or two ounces of sodium carbonate may be added to each gallon of water or some other material may be employed to reduce the acidity.

The purpose of the fullers earth, as indicated above, is to aid in the removal of the deleterious material from the surface of the article, including .the products of reaction between the solution oil. the friable coating from the surface, the article may be subjected to a washing or spraying with water, after allowing sumcient reaction to form the phosphate coating on the metal. In this way, the remnants of the solution, not exhausted in forming the phosphate coating, together with any material absorbed by the solution from the surface of the metal, can be washed oil. However, the method employing the fuller's earth or its equivalent is considered the most practical under most conditions.

If a stronger solution is used, and especially if the composition is such that a higher free acidity results, some neutralizing agent such as sodium carbonate may be employed.

The degree of acidity should be maintained within fairly close limits. The solutions given above require about 15 times as much alkali to affect phe'nolphthalein indicator as they do to affect methyl orange indicator. The proportion is even higher when the test is made with an unheated solution.

The essential is that there shall be phosphates, a proper degree of acidity, and an oxidizing agent. For speed in action, a soluble compound of copper is helpful. The desired copper may be introduced in other forms such as copper acetate, for example, and a separate oxidizing agent may be employed, with proper regard to total oxidizing power and to resultant acidity.

The formulas given above operate even more promptly upon a zinc or galvanized iron surface than upon the surface of iron or steel articles, and the elevation of temperature above ordinary room temperature is not necessary with zinc in order to form a coating, although it may be desirable for the purpose of quickly drying the material without an unnecassary lapse of time. Since the heating of the material is not as helpful when forming a coating with zinc, and the coating is formed quit promptly, there are more frequent circumstances which render desirable, when treating zinc, the substitution of the step of washing of! the residue of the solution instead of the use of an inert material and the drying and brushing 01! thereof.

Where preferred, this method of cleaning and coating may be employed with a final oxidizing treatment, such as raising the temperature of the final heating for drying purposes, so that the copper in the coating is oxidized. When this is done, the coating acts as an effective deterrent of rusting and has a black color acceptable as the finish coating for many purposes, especially where treating with oil.

To recapitulate, it may be pointed out that wide variation may be made both in the amount and kind of inert finely divided material which is employed, and under some circumstances this ingredient may be omitted entirely; the strength of the solution in phosphates may be varied within considerable limits, but it is desirable to have the solution fairly strong in order that sufflcient chemicals may be in contact with the metallic surface to cause the desired reaction; however, the phosphates should be introduced in such a manner that the acidity of the solution is of the order of that in the formulas given in order to obtain satisfactory results and a proportion similar to that given should be maintained between the free acid indicated by methyl orange and the total acidity indicated by phenolphthalein; phosphates of iron, manganese and zinc may be used substantially interchangeably,

although the zinc is preferable for reasons stated above; the amount of copper, or other metalless basic than iron, that is present in the solution may be varied to a considerable extent, if means are taken to avoid too great a departure from the desirable acidity as a result of the compounds containing the metal, and if an oxidizing agent is present. The amount of metal which can be used to form a satisfactory coating increases with the amount of oxidizing agent present. Silver may replace part or all of the copper and is added to the solution in the form of a soluble salt. Other similar soluble salts may be used, together with mixtures.

With the other chemicals substantially in the proportions given, increase of the copper content to 1% or above results in a softer less adherent coating, the quality of coating decreasing with the increase in copper until it is soon worthless. Decrease in the copper per cent below that specified results in some decrease in activity and the coating is unsatisfactory when the copper in a solution of the kind specified drops excessively, unless the oxidizing agent is increased.

Ordinarily the drying takes place concurrently with the chemical reaction which forms the coating, and the decrease in water substantially balances the depletion of the active chemicals, so that the solution remains at efilcient working strength until substantially complete drying, and at the same time substantially the entire effective coating-forming reagents are utilized before the drying becomes complete. If there is any dimculty in delaying evaporation long enough to secure substantially complete reaction, evaporation may be retarded by the use oflactic acid or some other material which retards drying without interfering with the chemical reaction and which does not render the dried residue difficult to remove.

Some alcohols may be added to the solution, if desired, and appear to aid in the spreading of the solution over the metal, but any great amount of alcohol slows up the chemical reaction. Ordinarily it is not needed to aid in removing grease. It appears that, when grease spots are on portions of the surface, the integral coating starts forming on the clean portions of the surface and follows along the surface under the grease, raising the grease oil! from the metal so that it is incorporated with the fuller's earth in the friable coating which is removed. At any rate, grease is effectivelyremoved from such spotted or slightly greasy surface without the use of any solvent of grease.

Any of the ordinary wetting agents may also b included in the compositions.

The preferred forms of the invention have been described, and sufllcient modifications and their results have been set forth so as to enable anyone skilled in the art to employ the invention. It will be understood that other modifications, obvious from the above disclosure, may be made within the termsof the appended claims.

What we claim is:

1. A method of coating a surface containing one of the group consisting of iron, steel or zinc which comprises applying to the surface a film of a solution containing, a phosphate of the group consisting of zinc, manganese, iron and mixtures; an oxidizing agent having an oxidation potential not greater than the potential of the common bromates in a dilute phosphate solution; and an accelerator of the group consisting of soluble compounds of copper and iron and mixtures thereof, which accelerator must be lower in the nitrate oxidizing agent and a material to conelectromotive series than the metal being treated, and maintaining such a film in contact with the surface until reaction of the solution with the surface produces on the surface a substantially integral coating,

2. A method as described in claim 1 in which thesolution contains an inert material which will not dissolve in or react with the solution and which will form a friable non-adherent coating when dried.

3. A method such as described in claim 1 in which the solution contains fuller's earth.

4. A method of treating a' surface of a metal included in the group of zinc and iron which comprises applying to the surface a film of a solution containing zinc dihydrogen phosphate, an oxidizing agent having an oxidation potential not greater than the potential of the common bromates in a dilute phosphate solution; and an accelerator of the class consisting of soluble compounds of copper and iron, which accelerator must be lower in the electromotive series than the metal being treated.

5. A method such as described in claim 4 in which the solution contains an inert material which will not dissolve in orreact with the solution and which will form a friable non-adherent coating when dried. I

6. A method in accordance with claim 4 in which thesolution contains fullers earth.

7. A material for cleaning and coating iron, steel and zinc surfaces comprising a dihydrogen phosphate of the. group consisting of zinc, iron and manganese, a water-soluble compound of copper, an oxidizing agent having an oxidation potential not greater than the potential of the common bromates in a dilute phosphate solution, and a material adapted to constitute a friable non-adherent mass after wetting and drying,

8. A material for cleaning and coating iron, steel and zinc surfaces comprising zinc dihydrogen phosphate, a water soluble salt of copper, a nitrate oxidizing agent and fuller's earth.

9. A material for cleaning and coating iron, steel and zinc surfaces comprising zinc dihydrogen phosphate, a water soluble copper salt, a

and their alloys, whichcomprises applying to such a surface a layer, of a mixture of fuller's earth and a phosphate coating solution, leaving the mixture on the surface until a coating is produced between the mixture and the surface and substantially integral with the surface, and then removing the mixture from the integral coating. v

13. The method of coating a surface containing iron which comprises applying to such a surface a layer of a mixture of fullers earth and a phosphate coating solution containing an oxidizing agent having sumcient expediting effect to enable the solution to produce on the surface a coating in not more than fifteen minutes, leaving the mixture on the surface until a coating is produced between the mixture and the surface and substantially integral with the surface, and then removing the mixture from the integral coating.

14. A method of treating a zinc surface which consists of applying to the surface a film of a solution containing zinc dihydrogen phosphate, a water soluble salt of iron and a nitrate oxidizing agent, and maintaining the solution in contact with the surface until a phosphate coating is formed on the surface.

15. A method of coating a surface containing metal of the class consisting of iron, steel and zinc, which comprises applying to the surface a film of a solution containing acid phosphate coating solution and an oxidizing agent having sufficient expediting effect to enable the solution to produce on the surface a coating in not more than fifteen minutes, leaving the film on the surface and heating it to a final heat above the boiling point of water, the heating being carried out at such a rate that a chemically .bonded coating is produced on the surface in not more than fifteen minutes.

16. A method of coating a surface containing metal of the class consisting of iron, steel and zinc, which comprises applying to the surface a film of a solution containing zinc dihydrogen phosphate and an oxidizing agent having sufficient expediting effect to enable the solution to produce on' the surface a coating in not more than fifteen minutes, leaving the film on the surface and heating it to a final heat above the boiling point of water, the heating being carried out at such a rate that a chemically bonded coating is produced on the surface in not more than fifteen minutes.

17. A method of coating 9. surface containing iron, which comprises applying to the surface a film of a solution containing an acid phosphate coating solution and a nitrate, leaving the film on the surface until a chemically bonded coating is produced on the surface, and then removing any residue.

18. A method of coating a surface containing iron, which comprises applying to the surface a film of a solution containing an acid phosphate coating solution and a nitrite, leaving the filrr. on the surface until a chemically bonded coating is produced on the surface, and then removing any residue.

19. A method of coating a surface containing iron, which comprises applying to the surface a film of a solution containing an acid phosphate coating solution and a sulphite, leaving the film 21. A method of coating a surface containing iron, which comprises applying to the surface a film of an acid phosphate coating solution containing a soluble salt of copper, and leaving the film on the surface 'until a chemically bonded coating is formed on the surface from ingredients of the surface and the film.

22. A method of coating a surface containing zinc, which comprises applying to the surface a film of an acid phosphate coating solution containing a soluble salt of iron, and leaving the film on the surface until a chemically bonded coating is formed, on the surface from ingredients of the surface and the film.

23. A method of coating a surface containing metal of the group consisting of iron, steel and zinc, which comprises applyingto the surface a film of an acid phosphate coating solution containing an accelerating tungstate, and leaving the film on the surface until a chemically bonded coating is formed on the surface from ingredients of the surface and the solution.

ROBERT E. TANNER. HERMAN J. LODEESEN,