US2471908A - Method of and material for preparing surfaces of ferriferous metals for the reception of a siccative finishing coat - Google Patents

Description

Patented 31, 11949 METHOD OF AND MATERIAL FOR PREPAR- ING SURFACES OF FERRIFEBOUS METALS FOR THE RECEPTION OF A SICCATIVE FIN ISHING COAT Eugene Snyder, Philadelphia, Pa., asslgnor to American Chemical Paint Company, Ambler,

Pa., a corporation of Delaware No Drawing. Application April 8, 1948, Serial No. 19,878

7 Claims.

This invention relates to the art of finishing ferriferous metals especially where such metals are to be covered with paint, varnish, enamel, japan or other siccative coating.

The principal objects of the invention are to increase the corrosion resistance of the surface and to improve the adherence and increase the life of the siccative coating especially under corrosive influences such as those which are associated with humid atmospheres, salt water. acid fumes and the like.

The invention relates generally to the phosphate coating art and before describing the details of my process I wish to point out that it has been known heretofore that a phosphate film with definite protective value can be formed on the surface of ferriferous metals by treating them with an aqueous solution containing primary or secondary phosphates of one or more of the alkali metals and of ammonium or, preferably, with combinations of both primary and secondary phosphate. One example of such a metal coating process is found in the United States patent to Douty and Romig No. 2,403,426. Due

to their cheapness and ease of control such phosphate coating systems have become increasingly important although they leave something to be desired insofar as speed of coating and range of optimum operating pH are concerned.

With the foregoing in mind. additional objects of my invention reside in the provision of a method and materials of the generalnature described which, however, will function to produce the coating far more rapidly and also to considerably increase the pH range over which the best quality of coating can be produced.

I have discovered that the coating time can be greatly decreased and the range of optimum operating conditions insofar as pH is concerned can be considerably extended if there be added tophosphate coating solutions of the character described a very small quantity of soluble peroxygen compound. Such compound should be present in the coating solution in an amount which is sufficient to give an available oxygen percent by weight of from about 0.008% to about 0.00016%. If the concentration of available oxygen falls below 0.00016% there is little or no beneflcialefl'ect and above the range given the peroxygen largely loses its value and finally becomes detrimental to the coating system in that the coating tends to become powdery and affords no protection whatsoever.

. 2 By way of specific example I cite the following: To a coating solution consisting of I add approximately 0.008% by weight of sodium perborate. In my preferred practice this solution is headed to approximately F. and is sprayed on the surface of the steel to be treated which surface should be scale-free. The spraying need be continued for as little as one minute although a longer period will do no harm. After treatment the steel should be rinsed preferably with a chromic acid rinse and then given a final finish of any desired siccative coating.

The solution described above will have a pH of approximately 5.5. However, I should like to point out that with my new method and material satisfactory operation may be had over a relatively wide range of pH such as from about 4.5

to about 6.0 and throughout this entire range the treated surface exhibits optimum characteristics both as to corrosion resistance, paint bonding ability, rapidity of coating, etc. Of course,

it must be .borne in mind that these factors may vary somewhat depending upon the type of fer.- riferous metal being treated, the temperature of the coating solution, the type of siccative coating employed, etc. but, for any given set of conditions, it will be found in all cases that marked improvement results from use of my invention as compared with previous practice with the type of phosphate coating solutions mentioned.

Peroxygen compounds other than sodium perborate can be employed such, for example, as stabilized hydrogen peroxide, organic peroxides, sodium peroxide, sodium persulfate, etc., but when used their quantities should be calculated in terms of the sodium perborate as given above.

-While the solution I have described is very good I have found that it is possible to improve it even further especially with respect to corrosion resistance in humid atmospheres by incorporating in the solution a small amount of metallic phosphate from the class of aluminum and ferric phosphates. Solutions containing such insoluble phosphate produce on the treated work a coating which has exceptionally great value for the prevention of atmospheric corrosion in humid surroundings. The quantity employed seems to be entirely unimportant because very small amounts will produce the desired effect and larger amounts make no difference in the results attained.

2,471,oos

For convenience in storage and transportation I prefer to prepare concentrated admixtures which may be either solid or liquid and these may be formulated in such a way as to serve both for making up and replenishing the working solutions. Such concentrated admixtures or materials should be prepared with the following points in mind. Although my improved coating process is relatively insensitive to the presence of dissolved approximately one ounce of the concentrate per gallon of water.

Additionally the concentrate should include from about 0.133% to about 1.66% by weight of peroxygen compound calculated as sodium perborate. With this quantity the diluted working solution will contain the compound within the range specified above.

The foregoing materials, of course, constitute the essentialcoating-producing ingredients of the concentrate and the balance can be made up of inert ingredients of one kind or another which have no substantial effect on the phosphating qualities of the working solution.

By way of specific example of a concentration which is suitable for use in preparing or replenishing a working solution attention is directed to the following:

Pounds Aluminum phosphate 0.010 Mono ammonium dyhydrogen phosphate 0.850 Disodium monohydrogen phosphate 0.040 Sodium perborate 0.01

The foregoing, of course, can be prepared as a solution if so desired but for ease in storage and transportation the dry material is preferable. The strength of the final coating solution may vary depending upon the conditions of use although I have found that a one ounce per gallon solution gives excellent results especially when sprayed for a period of approximately one to two minutes at a temperature of approximately 160 F.

In conclusion I wish to refer to the fact that solutions according to the present invention have a considerable ability to remove some small amounts of grease and oil from the surfaces being treated. In other words, they lend themselves to simultaneous cleaning and coating but this effect can be substantially augmented if there be added to the working solution an organic detergent soluble at the pH of the solution whereupon they will act to simultaneously clean and phosphate coat even very highly contaminated surfaces. For example, to attain the effect just described there can be added to the working solution a small amount of aryl aikyl polyethylene glycol ether alcohol condensate. This material is a non-ionic wetting agent the basic characteristic of which is an ethylene oxide chain having at one end of the chain a hydrocarbon radical linked through an oxygen atom and on the other end of the chain a hydrogen atom. The general formula for these compounds is RO(C2H4O)1H, where R" is a hydrocarbon radical and subscript a:" generally is between 3 and 30.

I claim:

1. In the art of coating ferriferousmetal the method which includes the step of treating the surface with a composition the essential coatingproducing ingredients of which consist of an aqueous solution of phosphate from the class which consists of alkali metals and ammonium, said solution also containing a quantity of soluble peroxygen compound suflicient to give an available oxygen per cent by weight of the total treating solution of from about 0.008% to about 0.00016% and the pH of said solution being from approximately 4.5 to 6.

2. The method of claim 1 where the peroxygen compound is sodium perborate.

3. The method of claim 1 where the treating solution also contains a small quantity of phosphate' from the class consisting of ferric and aluminum phosphate,

4. The method of claim 1 where the treating solution also contains a small amount of aryl alkyl polyethylene glycol ether alcohol having the general formula RO(C2H4O)H, where R is a hydrocarbon radical and subscript :0 generally is between 3 and 30.

5. A material for preparing and replenishing a metal-coating solution the essential coatingproducing ingredients of which material consist of phosphate from the class of alkali metal phosphates and ammonium phosphate, together with a quantity of peroxygen compound, the said phosphate constituting at least by weight of the material and said peroxygen compound being present in an amount from about 0.133% to about 1.66% by weight calculated as sodium perborate with the remainder of the material being made up of substantially inert ingredients.

6. The material of claim 5 which also includes a small amount of insoluble phosphate from the ,class of aluminum and ferric phosphates.

'7. The material of claim 5 in which the peroxygen compound is sodium perborate.

EUGENE SNYDER.

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

UNITED STATES PATENTS Number Name Date 2,298,312 Romig Oct. 13, 1942 2,326,309 Romig Aug. 10, 1943 2,403,426 Douty et a1. July 2, 1946