US2479423A

US2479423A - Method of and materials for treating surfaces of iron, zinc, and alloys of each

Info

Publication number: US2479423A
Application number: US646210A
Authority: US
Inventors: Snyder Eugene
Original assignee: Amchem Products Inc
Current assignee: Henkel Corp
Priority date: 1946-02-07
Filing date: 1946-02-07
Publication date: 1949-08-16
Anticipated expiration: 1966-08-16

Description

Patented Aug. 16, 1949 METHOD OF AND MATERIALS FOR TREAT- ING SURFACES OF IRON, ZINC, AND

LOYS OF EACH Eugene Snyder, Philadelphia, Pa, assignor to American Chemical Paint Company, Ambler, Pa., a corporation of Delaware No Drawing. Application February Serial N0. 648,210

' Claims. (Cl. 148--6.15)

1 This invention relates to a method of as well as to improved materials for treating surfaces of metals from the class of iron, zinc and alloys of each, and it involves both a cleaning and a coat- 8 of the surface. More specifically, it is directed to the production of close grained phosphate coatings on the metal which will inhibit corrosion and act as a bonding film for organic finishing coats of paint, varnish, lacquer, Japan, or the like.

Among the objects of the invention are:

The production of coatings of the type described by the use of solutions a. which are inexpensive to prepare, and easy to control and replenish.

b. which areso slightly corrosive that they may be handled in ordinary mild steel equipment.

0. which do not form objectionable quantities of insoluble "sludge" in nor incrustations on the equipment used. Thus, no difficulties arise due to clogging of screens and spray nozzles, or to hard scale on heating coils, or to abrasion of pumps.

A further object of the invention is to make possible the production of uniform, very finely crystalline coatings on surfaces which may not be completely free of grease, oil, dirt and the like. By contrast, prior phosphate coating processes have required rigorously clean surfaces if the coating is to be satisfactory at all. Moreover, in order to assure even, fine-grained coatings, where strongly alkaline or acidic cleaning agents have been employed prior to the coating step per se, it has been necessary to provide a subsequent rinse at a carefully controlled pH or even that a special chemical treatment be given to the work followed by suitable rinses. The need for such special techniques is entirely eliminated by the improvements of the present invention, which improvements make possible a simultaneous cleaning and coating procedure.

Still another object is to provide a method of and materials for treating ferrous and zinciferous metal surfaces by the use of which the tendency for the coated work to develop a discolored blush" while still wet or to rust while in storage before final finishing is greatly minimized. At the same time my new process and compositions have the ability to improve the life and enhance the quality of applied organic finishes.

The invention is based very largely on the discovery that a solution containing both primary and secondary phosphates from the class of the alkali and ammonium phosphates will produce on ferrous and zinciferous metal surfaces an excellent close-grained, water insoluble adherent 2 7 coating. Further investigation has disclosed that when the solution is maintained within the pH range 5 to 6, and is higher than that corresponding to the mono-basic phosphates present alone and lower than that corresponding to the dibasic phosphates alone, the coatings produced are of exceptionally good quality. A further advantage of the use of such solutions within this pH range is based upon the discovery that a concentrated material suitable for making up the original bath is also ideally suited for replenishing constituents removed by reaction with the metal, by dragout, etc. A solution replenished in this manner remains within the specified pH range. This is particularly important where a long succession of surfaces must be processed in the same solution since make-up and replenishment may easily be carried out by unskilled labor by adding the same concentrated material.

It has been found that solutions of primary and secondary alkali or ammonium phosphates hav ing 8. DH as indicated above have the ability to remove grease, oil and dirt from the surfaces being treated while simultaneously coating them, provided the degree of contamination from such substances is not too great. However, I have discovered that the solutions which I employ lend themselves exceptionally well to a simultaneous cleaning and coating operation if there be added to them a water-soluble wetting and emulsifying agent, whereupon they will satisfactorily simultaneously clean and coat even very highly or grossly contaminated surfaces. Insofar as I am aware, the simultaneous cleaning and coating herein disclosed has never before been successfully attained and constitutes a major forward step in this art.

I have further discovered that when a solid, nearly insoluble, normal phosphate from the class of iron and aluminum phosphates is present in a solution of alkali and/ or ammonium phosphates such as is described above, the pH is not appreciably changed and the coatings produced on ferrous and zinciferous metal surfaces are further impoved as regards corrosion resistance and the life of applied organic finishes. Any tendency for the coated surfaces to "b1ush or discolor while they are wet is likewise minimized.

The coating action of my improved cleaning and coating solutions may be accelerated by the presence therein of small quantities of oxidizing agents such as soluble nitrites, nitrates, and organic nitro compounds. As preferred agents of this class sodium nitrite, sodium nitrate, and picric acid are recommended. Recommended quantitles of such agents are from 0.01 to 0.25% of sodium nitrite or the equivalent of other soluble nitrite; from 0.1 to 1.0% of nitrate calculated as sodium nitrate; from 0.1 to 0.5% of picric acid. (These quantities represent concentrations of these accelerators in the dilute treating bath.)

Acceleration of coating may also be effected by the presence in my improved coating solutions of small quantities of certain metallic ions. The dissolved metals which have been found useful in this connection are copper. silver, nickel, and ferrous iron. These metals are only soluble in the phosphate solutions of pH to 6 in very small amounts. The amount of dissolved accelerating metal to be used should be from 0.0002 to 0.01% of the solution. The use of silver or copper as accelerating agents may reduce the corrosion resistance of the coating produced. Both types of accelerating material may be used simultaneously.

For convenience in storage and transportation concentrated admixtures. either solid or liquid, may be prepared for making up and replenishing solutions used in my improved coating process. Examples of such admixtures are given in subsequent formulas.

All of these formulas are designed with the following points in mind. While my improved coating process is relatively insensitive to the presence of dissolved or suspended impurities, yet the continual replenishment of the operating solutions with the make-up and/or the replenishing material containing large amounts of inert diluents. soluble or insoluble, leads to an undesirable accumulation of such inert material in the solution. Therefore, experience has shown that materials to be used for make-up and replenishment of the working solutions used in my improved process should contain at least 75% of the total. primary and secondary phosphates from the class: of alkali and ammonium phosphates.

An example of a solid admixture suitable for preparing coating solutions in accordance with my invention is given in the following formula:

A solution of the above material in water is prepared. The strength of the solution may vary widely depending on the conditions of use.

If the metal is to be coated in a bath by immersion, I prefer to use from 2 to 8 ounces of the material of Formula No. 1 per gallon of water. When using spray equipment in which the solution is impinged against the work, I prefer a solution of from 0.5 to 2 ounces of the concentrated admixture per gallon of water. The solution may be used at room temperature although its action is accelerated by heat and I prefer to use it at a temperature of from 120 to 200 F., although these temperatures are not to be considered as limitlng.

It is to be understood, of course, that before attempting to employ my invention the surfaces to :be treated should be freed of rust and scale in any manner familiar to the art, as by pickling, sand blasting or other conventional means. This will be assumed in connection with all of the formulas given in the present specification.

When employing a solution prepared from the concentrate of Formula No. 1. I find that the work should be relatively free of oil, grease and dirt, that is, it should not be grossly contaminated. However, work which is only slightly soiled may be quite satisfactorily treated with solutions prepared from Formula No. 1, especially if the solution is violently impinged upon the surface or, in the case of an immersion, if the bath is rather violently agitated. Rigorous pre-cleaning, however, is not required as has been necessary in the technique heretofore familiar in the art.

In using the impingement method any suitable spraying equipment may be provided, the details of which are not illustrated because they may take various forms dependent upon individual requirements.

Circulation of the solution through the tanks to the spraying orifices is preferably provided by means of a centrifugal pump. and the material which runs down from the work is collected in suitable troughs and returned to the tank or reservoir from which the solution is pumped.

The work to be treated is subjected to the impinging action of the jets of solution for a period of from 30 seconds to 1 minute, although this time may vary considerably depending upon conditions, temperature or the solution, and the type of material being treated.

While materials such as stampings are being cleaned and coated, the pumping system is kept in continuous operation in order to provide for continuous circulation of the solution from the tank to the impinging nozzles at a steady and uniform rate thus allowing the coating operation to take place in a remarkably short period of time. The formation of little or no sludge or incrustation, due to my improved process, allows almost continuous operation.

After the coating operation is begun, whether .by dipping or spraying, the solution when it becomes weak, as shown by periodic chemical analysis, may be kept up to strength by the addition of the appropriate quantities of the concentrated material.

Examination of Formula No. 1 and subsequent formulas will show that the molar ratio of primary and secondary phosphates lies between 32:1 and 5.6:1 inclusive. The pH of the coating solution made from Formula No. 1 and subsequent formulas will lie between 5.0 and 6.0 inclusive and should be kept within these limits in order to secure optimum performance of the cleaning and coating operation. Furthermore, the pH should be greater than that corresponding to the monobasic phosphate present alone and lower than that corresponding to the di-basic phosphate present alone.

The organic detergent of the above formula may be of the class of the well-known organic detergents of good wetting and emulsifying ower. As examples of wetting agents suitable for use 11 the above formula, we may employ sodium alkyl sulfates such as sodium lauryl sulfate; sulfonated hydrocarbons such as alkylated naphthalene sulfonic acids, etc..'and non-ionic" detergents which are derivatives of poly ethylene glycol. Certain cation-active materials are likewise suitable. In general, an organic detergent suificiently soluble and stable at the p of the solution and of adequate surface tension depressant and emulsifying power may be used.

The active ingredients in thisand subsequent formulas are put into the solvent in the same ratio that was shown under Formula No. 1.

Solutions made from this formula and similar ones will act in practice in a similar manner to that given under Formula No. 1 but will have the added advantage of cleaning even heavily contaminated metal surfaces simultaneously with the coating action. This will eliminate the necessity for a critical pre-cleaning. In actual practice, if the metal surface is grossly contaminated with oil, grease, dirt. or other similar material, I have found it expedient to give the material a crude pro-cleaning which usually may be accomplished by spraying the surface with hot water and allowing the water to drain oil. This will avoid the accumulation of large quantities of the contaminants in the working solution.

Another benefit obtained by the use of this formula is that the inclusion of hepta decanol or other like substances will cut down on the foaming tendencies of the solution. Other anti-foaming agents useful in this invention are petroleum fractions, pine oil, and alcohols of from 8 to 18 carbon atoms.

Formula No. 3

Lbs. Primary ammonia phosphate 0.835 Secondary sodium phosphate 0.045 Normal aluminum phosphate 0.010 Sulfonated castor oil-- 0.080 Oleyl alcohol 0.010 Pine 0.020

Total 1.000 3 In using this formula in my improved process the dilution of active ingredients and use of the diluted solution are accomplished in a manner similar to the instructions given under Formula No. 1. However, by the use of this formula a more corrosion-resistant bonding film is obtained. Increased resistance to "blushing and after-rusting of the coated metal prior to painting, etc. is also obtained.

To Formula No. 4 add 0.80% by weight of copper sulfate pentahydrate.

Formula No. 4 is used and acts similarly but coats more rapidly than Formula No. 3. This formula is included as an example wherein sodium nitrite is used as an accelerator and where is wished to obtain a heavy phosphatic bonding coat.

Formula No. 5 acts similarly to Formula No. 4 except that the application of the bonding coat is accomplished even faster than when Formula No. 4 is used. However, I have found that the coating obtained from using Formula No. 5 is less corrosion-resistant than that obtainedbyusingaformulasimilartoflai.

The corrosion resistance of metal surfaces treated with any of the preceding formulas in accordance with the instructions given may be still further improved if given an after treatment with weak chromic acid as taught in tin co-pending application of Messrs. Douty and Romig, Serial No. 583,458, filed November 14, 1944, subsequently issued as Patent No, 2,403,426.

My improved process and materials are capable of producing a fine-grained, corrosion-inhibiting coating while simultaneously cleaning a contaminated ferrous or zinciferous surface without the necessity of paying particular attention to a critical pre-cleaning step. This presents a distinct advantage over any prior technique with which I am familiar. The advantages of the invention make it possible either to eliminate entirely a pre-cleaning step or to combine a precleaning step with the coating step in one simple unit. This, of course, effects a corresponding saving in floor space and a marked economy in construction and equipment costs.

What I claim is:

1. The method of providing metal surfaces from the class of iron, zinc' and alloys of each with a corrosion resistant and paint bonding fllm comprising treating the surfaces with a dilute aqueous solution consisting essentially of primary and secondary phosphates from the class which consists of alkali and ammonium phosphates and containing added solid, undissolved, normal phosphate from the class consisting of ferric phosphate and aluminum phosphate, the pH of the 5 said solution being between 5.0 and 6.0 and being greater than that corresponding to the monobasic phosphate present alone and lower than that corresponding to the di-basic phosphate present alone.

2. The method of simultaneously cleaning metal surfaces from the class of iron. zinc and alloys of each and providing them with a corrosion-resistant and paint bonding film comprising treating the surface with an aqueous preparation containing as its essential active ingredients both primary and secondary phosphates from the class which consists of alkali and ammonium phosphates, a water-soluble, surface-active emulsifying agent and added solid. undissolved, normal phosphate from the class consisting of ferric and aluminum phosphates, the pH of the preparation being between 5.0 and 6.0 and being greater than that corresponding to the monobasic phosphate present alone and lower than that corresponding to the di-basic phosphate present alone.

3. The method of claim 2 in which the said surface-active emulsifying agent is a watersoluble non-ionic emulsifying agent.

4. A material for making up and replenishing a metal treating solution being an admixture consistingessentially of at least of primary and secondary phosphates from the class consisting of alkali and ammonium phosphates, the molar ratio of primary to secondary phosphate being between 32:1 and 5.6:1, the remainder of the composition being composed substantially of inert diluent, nearly insoluble phosphate from the class of normal ferric and aluminum phosphate, emulsifying agent, and anti-foaming material.

5. A material for making up and replenishing a metal treating solution being an admixture consisting of at least 75% of primary and secondary phosphates of the class consisting of alkali and ammonium phosphates, the molar ratio of EUGENE SNYDER.

REFERENCES CITED The following references are oi. record in the iile of this patent:

Number UNITED STATE PA'IIN'I'B Home Dete Allen Jln. I, 1919 Grnvell July 13, 1928 Tanner et a1 Nov. 15, 1932 Romig Oct. 11. 193B Neilson Jen. I. 1941 Tanner et a1 Nov. 1'1, 1942 Boyle et a1 Dec. 8, 1942 Rnmig Apr. 20, 1943 Douty et a1 July 2, 1946