Cleaning Of Metals With Compositions Containing Alkali Metal Silicate And Chloride

Abstract

Metal surfaces are cleaned, prior to phosphating or the like, with compositions containing alkali metal (especially sodium) silicates and chlorides, and preferably also containing surfactants and chelating agents. These compositions have cleaning power comparable to phosphate-containing cleaners and cause less water pollution upon discharge into natural waterways.

Parent Case Text

This application is a continuation-in-part of copending application Ser. No. 58,182, filed July 24, 1970, now abandoned.

Description

This invention relates to methods for cleaning metal surfaces during processing thereof, especially prior to phosphating. More particularly, it relates to a method for cleaning a metal surface which comprises contacting said surface with an aqueous cleaning composition wherein the active ingredients comprise water-soluble alkali metal silicate and alkali metal chloride, the weight ratio of said silicate to said chloride being between about 4:1 and 10:1.

In the processing of metals, it is common practice to follow a drawing operation with a phosphating treatment to produce a phosphate coating on the metal which is resistant to corrosion and serves as a paint base. The metal emerging from the drawing operation almost always has foreign matter adhering to it, chiefly drawing oils and the like. Such foreign matter is extremely difficult to remove, but it must be removed before the metal can be phosphated. It has been customarily removed by heavy-duty alkaline cleaners containing various combinations of ingredients such as phosphates, silicates and surfactants. Phosphate-containing cleaners are particularly effective. However, the recent emphasis on avoidance of water pollution has aroused interest in cleaners which do not contain phosphate, since phosphates apparently promote algae growth in natural waterways such as lakes and rivers into which the cleaners are discharged after use.

A principal object of the present invention, therefore, is to provide a new method for heavy-duty cleaning of metal surfaces.

A further object is to provide a metal cleaning method in which the use of phosphates is avoided or substantially avoided, thereby decreasing the tendency of such compositions to pollute water.

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

The essential ingredients in the compositions used in the method of this invention are a water-soluble alkali metal silicate and an alkali metal chloride. By "alkali metal" is meant the metals in Group IA of the Periodic Table; that is, lithium, sodium, potassium, rubidium and cesium. Sodium and potassium are preferred, and because of their ready availability and low cost, the sodium salts are most often used.

Any water-soluble alkali metal silicate may be used in the method of this invention. Thus, suitable sodium silicates include sodium disilicate, Na.sub.2 Si.sub.2 O.sub.5 ; sodium metalsilicate, Na.sub.2 SiO.sub.3, and its hydrates; sodium orthosilicate, Na.sub.4 SiO.sub.4 ; and so-called "water glass," which is a liquid mixture of various sodium silicates. Sodium metasilicate is, however, preferred.

The alkali metal chloride may likewise be from any suitable source, but the preferred chlorides consist of crystals with high absorbent power. Particularly useful is a form of common salt sold by the Morton Salt Company and identified as "North Star Fine."

The weight ratio of silicate to chloride in the compositions used in the method of this invention should be between about 4:1 and 10:1. Weight ratios on the order of 7:1 or 8:1 are preferred.

In addition to the alkali metal silicate and chloride, the compositions used in the method of this invention ordinarily contain other ingredients such as surfactants, chelating agents, fillers and pH control agents. The preferred surfactants are non-ionic ones, chiefly polyethoxylated derivatives of phenols, alkyl phenols and alcohols, and amphoteric ones, especially those listed in McCutcheon's Detergents and Emulsifiers Annual as being suitable for metal cleaning. These include but are not limited to salts (especially alkali metal salts) of amino acids derived from long-chain amines, of carboxylic acids derived from long-chain alkyl-substituted imidazolines, of long-chain polycarboxylic acids, of betaine sulfonates derived from long-chain fatty acids, and of sulfonates of oxyethylated amines. Surfactants are particularly desirable in the compositions used in the method of this invention because they are ordinarily instrumental in starting the cleaning process which is continued by the alkaline ingredients.

The presence of chelating agents is preferred partly because of the absence of phosphates, which ordinarily serve that purpose when they are present. Suitable chelating agents include the various amainopolycarboxylic acids and their water-soluble salts, such as ethylenediaminetetraacetic acid, trimethylenediaminetetraacetic acid, nitrilotriacetic acid and the like. Particularly useful is the tetrasodium salt of ethylenediaminetetraacetic acid, sold under the trade name "Versene."

The proportions of surfactants and chelating agents used are usually about 3-10 parts by weight per 100 parts of active ingredients (excluding water).

Suitable for use as fillers and pH control agents are such materials as sodium carbonate (soda ash) and similar alkaline materials which are water-soluble and inexpensive.

For certain purposes, especially when the material to be removed from the surface is very stubborn and persistent, the compositions may also contain conditioners or activators of the type used to prepare metal surfaces for phosphating. Exemplary of such conditioners or activators are the titanium phosphate compositions described in U.S. Pat. No. 2,322,349.

The preferred cleaning compositions contain about 65-80 parts by weight of sodium metasilicate, about 5-15 parts of sodium chloride, about 5-15 parts of sodium carbonate, about 0-10 parts of ethylenediaminetetraacetic acid or a water-soluble salt thereof (an optional ingredient), about 4-10 parts of at least one non-ionic or amphoteric surfactant, and optionally about 4-10 parts of colloidal titanium phosphate.

Exemplary concentrates for preparing the cleaning compositions used in the method of this invention are listed in the following table.

______________________________________ Parts by weight Ingredient Example 1 2 3 ______________________________________ Sodium metasilicate 75 73 67 Sodium chloride 10 10 9 Sodium carbonate 10 10 9 "Versene" -- 2 5 "Triton X-114" (octylphenoxy polyethoxy ethanol) 2 -- -- "Triton DF-16" (modified linear alcohol ethoxylate) 3 -- -- "Triton CF-10" (alkaryl polyether) -- -- 2.5 "Tergitol 15-S-7" (linear alcohol ethoxylate) -- 2 -- "Tergitol Min-Foam 1X" (modified linear alcohol ethoxylate) -- 3 -- "Triton QS-15" (sulfonate of poly- ethoxylated C.sub.12.sub.-15 tertiary alkyl primary amine) -- -- 2.5 Colloidal titanium phosphate -- -- 5 ______________________________________

For use, concentrates such as those listed in the table are dissolved in water to a concentration of about 5-20 grams per liter, preferably about 5-10 grams per liter. The aqueous cleaner thus prepared is contacted with the metal surface by spraying, dipping or the like, preferably at a temperature of about 50.degree.-100.degree.C. Contact between the metal and the cleaner is continued for a period of time sufficient to remove drawing oils and other foreign matters from the metal surface, usually about 30 seconds to 1 minute. The surface is then rinsed with water and a phosphate coating is applied thereto by conventional methods.

The effectiveness of the method of this invention is shown in a series of tests in which various drawing oils are applied by brush to 4 inches .times. 8 inches cold-rolled steel panels which are then sprayed with cleaning compositions prepared from the concentrates of Examples 1-3 by dilution with water to 7.5 grams per liter, the temperature of the cleaning composition during spraying being 71.degree.C. The cleaning compositions are used both pure and contaminated with 5, 10, 15 and 20 grams per liter of the drawing oil. The cleaning operation is continued for 30 seconds, after which the steel panels are rinsed with water, phosphated with a phosphating solution of the type disclosed in U.S. Pat. No. 3,090,709 containing zinc, calcium and ammonium ions, and rinsed with a conventional chromium-containing rinse solution. The appearance of the phosphate coating is then evaluated to determine the effectiveness of the cleaner.

When tested by this method, the cleaners of Examples 1 and 2 gave results equal to those of comparable phosphate-containing cleaners at all levels of contamination, when used to remove ordinary drawing oils. Rust-preventive drawing oils were resistant to the cleaners of Examples 1 and 2 but were removed by the cleaner of Example 3, to a degree comparable to that of known heavy-duty phosphate cleaners.

Claims

What is claimed is:

1. A method for cleaning the surface of metals during processing thereof which comprises contacting said surface at a temperature of about 50.degree.-100.degree.C. with an aqueous cleaning composition in the liquid state wherein the active ingredients comprise water-soluble alkali metal silicate and alkali metal chloride, the weight ratio of said silicate to said chloride being between about 4:1 and 10:1.

2. A method according to claim 1 wherein the alkali metal is sodium.

3. A method according to claim 2 wherein the cleaning composition additionally contains at least one non-ionic or amphoteric surfactant and a chelating agent, each being present in the amount of about 3-10 parts by weight per 100 parts of active ingredients.

4. A method according to claim 3 wherein the chelating agent is ethylenediaminetetraacetic acid or a water-soluble salt thereof.

5. A method according to claim 2 wherein the active ingredients in said cleaning composition consist essentially of about 65-80 parts by weight of sodium metasilicate, about 5-15 parts of sodium chloride, about 5-15 parts of sodium carbonate, about 0-10 parts of ethylenediaminetetraacetic acid or a water-soluble salt thereof, and about 4-10 parts of at least one non-ionic or amphoteric surfactant, said ingredients being dissolved in water to a concentration of about 5-20 grams per liter.

6. A method according to claim 5 wherein the composition additionally contains about 4-10 parts by weight of colloidal titanium phosphate.