US3726720A - Metal conditioning compositions - Google Patents

Abstract

CONCENTRATES AND AQUEOUS SOLUTIONS CONTAINING ORTHOPHOSPHATE ION, PYROPHOSPHATE ION, A COMPLEX FLUORINECONTAINING ION (I.E., FLUOSILICATE) AND MAGNESIUM ION ARE USEFUL FOR TREATING METAL SURFACES IN BOTH 3-STAGE AND 5STAGE SYSTEMS. THE PREFERRED COMPOSITIONS ALSO CONTAIN A NON-IONIC SURFACTANT, PREFERABLY AN ALIPHATIC POLYETHER.

Description

United States Patent 3,726,720 METAL CONDITIONING COMPOSITIONS Donald Joseph Guhde, Cleveland, Ohio, assignor to The Lnbrizol Corporation, Wickliiie, Ohio No Drawing. Filed May 24, 1971, Ser. No. 146,421 Int. Cl. C23f 7/08 US. Cl. 1486.15 R 17 Claims ABSTRACT OF THE DISCLOSURE Concentrates and aqueous solutions containing orthophosphate ion, pyrophosphate ion, a complex fluorinecontaining ion (i.e., fluosilicate) and magnesium ion are useful for treating metal surfaces in both 3-stage and 5- stage systems. The preferred compositions also contain a non-ionic surfactant, preferably an aliphatic polyether.

This invention relates to new solutions for the formation of phosphate coatings on metals and to concentrates for the preparation of such solutions. More particularly, it relates to a solid concentrate comprising compounds which will yield, when dissolved in water, a solution containing orthophosphate ion, pyrophosphate ion, a complex fluorine-containing ion, and magnesium ion, as Well as to solutions prepared by dissolution of said concentrates in water.

So-called non-coating iron phosphate solutions are well known in the art. The action of such solutions on metal surfaces is characterized by the fact that the solution itself contains no metal which enters into the coating as a major constituent thereof; the sole major metallic constituent is obtained by dissolution of metal from the surface of the object being treated. Thus, when the solution is used to coat a ferrous metal object (as is usually the case), the coating produced consists predominantly of iron phosphate.

In producing a phosphate coating of this type, the metal object to be coated is normally freed of surface dirt, possessing oil and the like by the use of an alkaline cleaner, subsequently rinsed with water, treated with the phosphating solution, rinsed again and finally treated with a postrinse such as a chromium-containing solution to produce a coated article in which the coating protects the surface from corrosion and serves as a paint base. A coating system employing these setsp is known as a S-stage system. More recently, systems have been developed which combine the first three of these five stages into one, with the phosphating solution also serving as a cleaning agent; these systems are known as S-stage systems. Their use naturally offers advantages from the standpoint of economy of both time and effort. At the same time, however, the phosphating solution for use in a S-stage system must have a number of properties not required in S-stage solutions. These include the ability to clean the metal surface and to disperse the material cleaned from the surface harmlessly in the solution, or to deposit it where it will not interfere with the solutions coating operation.

A principal object of the present invention, therefore, is to produce improved non-coating iron phosphate solutions and concentrates for their preparation.

A further object is to provide phosphating compositions which amy be conveniently and effectively used in a 3-stage phosphating system.

Still another object is to provide phosphating solutions which combine cleaning and phosphating capabilities.

3,726,720 Patented Apr. 10, 1973 Other objects will in part be obvious and will in part appear hereinafter.

As previously mentioned, the compositions of this invention contain as essential ingredients orthophosphate ion (1 0 pyrophosphate ion (1 0 a complex fluorine-containing ion such as fluosilicate, fiuoborate or the like, and magnesium ion. The concentrates are principally composed of compounds which will provide these ions upon dissolution in water. The preferred approximate concentration ranges for such ions in the concentrates and in the solutions are given in the following table.

Concentrate Solution (percent by (grams per Ion weight) liter) The orthophosphate and pyrophosphate ions are typically provided at least partially by alkali metal orthophosphates and pyrophosphates, preferably sodium and/ or potassium. Because of their ready availability, the sodium phosphates are preferred, especially monosodium dihydrogen orthophosphate and disodium dihydrogen pyrophosphate. Some or all of the orthophosphate ion may also be provided by phosphoric acid.

The complex fluorine-containing ion may, as previously mentioned, be fluosilicate, fluoborate or any other commonly available complex fluoride. It may be furnished as an alkali metal salt or as the magnesium salt; the latter is preferred since it also provides the requisite magnesium ions. However, it is within the scope of this invention to use other magnesium salts, such as the chloride or nitrate.

Especially when used in a 3-stage system, the compositions of this invention also contain a non-ionic surfactant to promote cleaning of the metal surface. The choice of a suitable surfactant is readily accomplished by those skilled in the art. Particularly effective are aliphatic polyethers, of which well known examples are sold with various product or grade designation under the trade names Alfonic Ethoxylates, Antarox, Aquet, Arosurf, Cedepal, Cerfak, Cimag, Cindet, Doxomean, Ethomid, Makon, Neodol, Nonionic, Plurafac, Pluronic, Poly Tergent, Retzanol, Sandopan, Siponic, Solar, Sterling, Sterox, Surfynol, Tergitol, and Triton. Straight-chain polyethers are preferred. The surfactant, when used, constituetes about 18% by weight of the concentrate, and is present in the solution at about 0.1-2.0 grams per liter.

The compositions of this invention may, in particular instances, also contain accelerators such as nitrate, nitrite, chlorate, peroxide or the like, or combinations of these. However, the presence of accelerators is usually unnecessary and and may sometimes increase the sludging tendency of the phosphating solution.

The solutions of this invention may be used as to coat such metals as aluminum, zinc and ferrous metals, with the latter being preferred.

To prepare the solutions of this invention, the appropriate concentrate is generally dissolved in water in the An illustrative composition of this invention is a solid concentrate prepared by blending, in the order listed herein, 70.5 parts by weight of monosodium phosphate (NaH P 15.0 parts of sodium acid pyrophosphate (Na H P O 3.0 parts of 75% aqueous phosphoric acid, 7.5 parts of magnesium fluosilicate hexahydrate, and 4.0 parts of Antarox Bl-344, a non-ionic, biodegradable, straight chain aliphatic polyether surfactant having a cloud point aqueous solution) of 44 C., a pour point of 9 C., a specific gravity of 1.06 and a pH (10% aqueous solution) of 2.8. The proportions of anions and cations in the resulting solid concentrate are as follows:

Percent Orthophosphate 58.0 Pyrophosphate 11.8 Fluosilicate 3.9 Magnesium 0.66 Sodium 16.6

When dissolved in water at 1-3 ounces per gallon, the ions and other ingredients are present in the following concentrations (expressed in grams per liter):

Orthophosphate 4.3-13.0 Pyrophosphate 0.9-2.7 Fluosilicate 0.3-0.9 Magnesium 0.05-0.15 Sodium 124-3 .72

Surfactant 0.3-0.9

In the ordinary S-stage phosphating operation, the metal surface is first cleaned by chemical and/or physical means to remove any grease, dirt and oxides. It is then rinsed with water and treated with the phosphating solution. The phosphating treatment may be by any of the commonly used techniques such as spraying, brushing, dipping, roller-coating and flow-coating; the solutions of the present invention are particularly useful in a spray phosphating system. The temperature of the phosphating solution may vary from about room temperature to about 240 F.; the solutions of the present invention are most conveniently used at about 50-145 F., preferably about 90-110" F. The phosphating operation is continued until a phosphate coating of the desired weight is obtained; this Weight may be as little as 25 mg. per square foot of surface area and is generally about 40-50 mg. per square foot. A particularly advantageous feature of the solutions of this invention is that they dissolve relatively little metal from the surface of the object being treated during the formation of a coating of this thickness. Usually, only about -20 milligrams of metal per square foot is lost, compared to about 100 milligrams for known iron phosphate solutions containing (for example) calcium as a modifying ion.

Upon completion of the phosphating operation, the metal article is rinsed with Water and/or a hot, dilute aqueous solution of chromic acid. The chromic acid rinse appears to seal the phosphate coating and improve its utility as a base for the application of a paint or other siccative organic coating. A dilute aqueous solution of a metal chromate or dichromate, a chromic acid-phosphoric acid mixture, or a mixture of chromic acid with a metal dichromate may be used in place of the aqueous chromic acid. Also useful, especially on galvanized surfaces, are solutions containing partially reduced chromic acid such as those described in U.S. Pats. 3,282,744; 3,404,045; and 3,477,882.

In a 3-stage phosphating operation, the initial cleaning and rinsing steps described hereinabove are omitted and the phosphating solution doubles as a cleaner. Solutions of this invention containing a non-ionic surfactant, such as the solution specifically described hereinabove, are particularly useful in this respect since they clean the metal surface efficiently without excessive foaming and without fouling of the solution to impair its phosphating capabilities.

The effectiveness of the solutions of this invention for forming phosphate coatings on metal is demonstrated by the Salt Fog Corrosion Test (ASTM B117). In this test, a number of cold-rolled steel test panels are sprayed with a phosphating solution prepared by diluting the concentrate described hereinabove with water to 2 ounces per gallon. The temperature of application of the phosphating solution is about -120 F. The total phosphating time varies between 20 and 60 seconds, and the weight of the resulting coating varies from 9.3 to 27.9 mg. per square foot. The pH of the phosphating solution is adjusted to 3.8-4.5.

The phosphated panels are rinsed with Water, postrinsed at F. with a dilute aqueous chromic acid solution partially reduced with methanol, dried and painted with a white alkyd-melamine baking enamel. The paint film on each panel is ruptured down to the bare metal by scoring a 6-inch line on the surface of the panel. The scored panel is placed in a cabinet containing a 5% aqueous sodium chloride solution at 95 F. Air is bubbled through the solution to produce a corrosive salt atmosphere which acts on the surface of the test panels, suspended above the level of the salt solution. The panels remain in this atmosphere for hours after which they are removed, washed with water and dried with a cloth. A pressure-sensitive tape is then applied to each panel and removed suddenly. This procedure is repeated until no more paint can be removed in this manner. The loss of adhesion caused by corrosion from the scribed line is measured in thirty-seconds of an inch.

When tested by this method, the panels phosphated with the solutions of this invention lose paint in an amount of from 0 to about 7 inch.

What is claimed is:

1. A solid concentrate comprising compounds which will yield, when dissolved in water, a solution consisting essentially of Water and about 40-75 parts by weight of orthophosphate ion, about 5-20 parts of pyrophosphate ion, about 1-8 parts of a complex fluorine-containing ion, and about 0.25-1.5 parts of magnesium ion.

2. A concentrate according to claim 1 which contains about l-8% by weight of a non-ionic surfactant.

3. A concentrate according to claim 2 which additionally contains alkali metal ions.

4. A concentrate according to claim 2 wherein the complex fluorine-containing ion is fiuosilicate ion.

5. A concentrate according to claim 2 wherein the surfactant is a straight-chain aliphatic polyether.

6. A concentrate according to claim 5 which comprises, in addition to said polyether, monosodium dihydrogen orthophosphate, disodium dihydrogen pyrophosphate, phosphoric acid and magnesium fluosilicate.

7. An aqueous solution prepared by dissolution in water of a concentrate according to claim 1.

8. An aqueous solution according to claim 7 which contains about 3-17 grams per liter of orthophosphate ion, about 0.4-4.6 grams per liter of pyrophosphate ion, about 0.07-1.9 grams per liter of a complex fluorinecontaining ion, and about 0.02-0.34 gram per liter of magnesium ion, and which has been adjusted to a pH of about 3-6.

9. An aqueous solution according to claim 8 which additionally contains about 0.1-2.0 grams per liter of a non-ionic surfactant.

10. An aqueous solution according to claim 9 which additionally contains alkali metal ions.

11. An aqueous solution according to claim 9 wherein the complex fluorine-containing ions are fiuosilicate ions.

12. An aqueous solution according to claim 9 wherein the surfactant is a straight-chain aliphatic polyether.

13. An aqueous solution prepared by dissolving a concentrate according to claim 6 in water to a concentration of about 0.5-5.0 ounces per gallon and adjusting to a pH of about 4.5.

14. A method for producing a phosphate coating on a metal article which comprises contacting said article, at a temperature of about 50-145 F., with the aqueous solution of claim 8.

15. A method for producing a phosphate coating on a metal article which comprises contacting said article, at a temperature of about 50 145 F., with the aqueous solution of claim 11.

16. A method for producing a phosphate coating on a metal article which comprises contacting said article, at a temperature of about 90-110" F., with the aqueous solution of claim 12.

17. A method for producing a phosphate coating on a metal article which comprises contacting said article, at a temperature of about 90-110 F., with the aqueous solution of claim 13.

References Cited UNITED STATES PATENTS 3,060,066 10/1962 Ross et a1. 1486.l5 R 2,067,007 1/1937 Darsey 148 6.1sz 3,484,304 12/1969 Beach 1486.15R 2,987,428 6/1961 Heller 148-615 R 2,337,856 12/1942 Rice et al. 1486.15 R

RALPH s. KENDALL, Primary Examiner US. or. X.R. l48-6.16