US3689379A - Composition and method for sealing anodized surfaces - Google Patents

Abstract

THIS INVENTION IS ADDRESSED TO AN IMPROVED COMPOSITION AND METHOD FOR SEALING ANODIZED SURFACES OF ALUMINUM AND ALUMINUM BASE ALLOYS WHEREIN THE SEALING COMPOSITION IS AN AQUEOUS SOLUTION OF NICKEL ACETATE, COBALT ACETATE OR MIXTURES THEREOF, A SODIUM SALT OF AN ALKYL NAPHTHALENE SULFONIC ACID, SODIUM LAURYL SULFATE AND THE CONDENSATION PRODUCT OF OCTYL PHENOL WITH ETHYLENE OXIDE.

Description

UnitedStates Patent ,Oflice 3,689,379 Patented Sept. 5, 1972 US. Cl. 204-35 N Claims ABSTRACT OF THE DISCLOSURE This invention is addressed to an improved composition and method for sealing anodized surfaces of aluminum and aluminum base alloys wherein the sealing composition is an aqueous solution of nickel acetate, cobalt acetate or mixtures thereof, a sodium salt of an alkyl naphthalene sulfonic acid, sodium lauryl sulfate and the condensation product of octyl phenol with ethylene oxide.

This is a continuation-in-part of copending application Ser. No. 13,832, filed Feb. 24, 1970, now Pat. No. 3,647,649, and entitled Method and Composition for Sealing Anodized Aluminum Surfaces.

This invention relates to a composition and method for sealing anodized surfaces of aluminum and aluminum base alloys. More particularly, it relates to a composition and method for sealing such surfaces to obtain a harder, more abrasive-resistant surface of greater resistivity while eliminating or minimizing smut formation.

It is conventional to seal anodized aluminum surfaces in order to increase the resistance of the anodized coating to stains and corrosion, to increase the durability of any color produced in the coating, and to increase the resistance of the surface to abrasion and wear. Current sealing methods include treatment with hot water and with solutions of certain hydrolyzable metal salts.

Treatment with hot or boiling water is typically used for clear (undyed) surfaces. This method requires water which is free of impurities and ideally is conducted with deionized water. For use with colored anodized coatings, a sealing bath in common use comprises a solution of a hydrolyzable metallic salt, typically nickel acetate or cobalt acetate. Sealing with such a bath sets the dye, minimizes color bleeding and improves the permanence of the color. Nickel or cobalt acetate treatment, however, has the disadvantage that it produces a cloudy or filmy coating on the surface of the sealed material. This coating, referred to in the trade as smu is particularly serious with dark shades and necessitates an additional step in the processing procedure to remove the filmy layer by mechanically bufling or polishing the aluminum surface. The necessity for smut removal represents an added cost in the processing of aluminum articles, since each piece must be handled individually. In addition, in the case of complicated shapes it may be impossible to remove the smut effectively by mechanical means.

In copending application, Ser. No. 13,832, filed Feb. 24, 1970, description is made of a significantly improved sealing method and composition in which use is made as the sealing composition of nickel acetate, cobalt acetate or mixtures thereof, an ammonium salt of naphthalene sulfonic acid, sodium lauryl sulfate, the condensation product of 1 mole of octyl phenol with about 12-13 moles of ethylene oxide and malic acid. It has been found in accordance with the method and composition described in this copending application that such compositions eliminate or substantially minimize the formation of smut on the sealed aluminum surface while at the same time improving the wear and corrosion resistance of the treated aluminum surfaces as compared to those obtained by sealing methods and compositions heretofore known. While the composition and method as described in the foregoing copending application represent a significant improvement in the art of sealing anodized aluminum surfaces, it has been found that it is generally advisable to formulate the sealing composition described in this copending application in aqueous composition using deionized water for best results. The use of deionized water represents a disadvantage in that the cost of the deionized water add to the overall cost of the sealing operation.

It is accordingly an object of the present invention to provide an improved composition and method for sealing anodized aluminum surfaces which is effective to eliminate or substantially minimize the formation of smut on the sealed aluminum surfaces, which is capable of providing a sealed surface having improved wear and corrosion resistance and which can be formulated in aqueous medium using ordinary tap water.

The concepts of the present invention reside in a variant of the hydrolyzable metal salt sealing technique, in which use is made of a sealing bath formulated to contain nickel acetate, cobalt acetate or mixtures thereof, and a novel combination of additives, specifically a sodium salt of alkyl naphthalene sulfonic acid and two specific wetting agents, which enable the bath to be formulated with ordinary tap water having a hardness of up to 15, grains.

The sealing bath of this invention is formulated of an aqueous solution of the following components:

Concentration, weight percent Ingredient Broad Preferred Nickel acetate, cobalt acetate or mixtures thereof. 35-60 42-50 Sodium salt of alkyl naphthalene sulfonic acid (dispersant) 35-60 42-50 Sodium lauryl sulfate (wetting agent) 0. 03-0. 3 0. 05-0. 15 Octyl phenoxy polyethoxy ethanol (wetting agent) 0. 1-1. 0 0. 2-0. 5

. invention is T amol S from 'Rohm & Haas Co.

The octyl phenoxy polyethoxy ethanol referred to above, and which is contemplated for use in the invention, is the product produced by the condensation of one mole of isoor .n-octyl phenol with about 12-13 moles of ethylene oxide.

A particularly preferred embodiment of the sealing composition of the invention contains, on a water-free basis, about 49% of nickel acetate, cobalt acetate or mixtures thereof; about 49% of the sodium salt of the alkyl naphthalene sulfonic acid; about 0.1% of sodium lauryl sulfate; and, about 0.25% of octyl phenoxy polyethoxy ethanoL.

The sealing composition of the invention is used by dissolving it in water at a concentration of about 2-16 grams per liter, preferably about 25-10 grams per liter, and optimally about 5-8 grams per liter. The sealing solution is heated to a temperature of about F. to the boiling point of the solution and preferably about 185-205 F. for contact with the anodized surface to be sealed. The pH of the solution is adjusted as necessary with a suitable acid or base, such as acetic acid, ammonium hydroxide or sodium hydroxide, to achieve a value within the range of about 5.2-5.8 and preferably about 5.4-5.6. One of the advantages of the composition of this invention is that once the pH is adjusted to a value within the desired range, the pH remains constant over substantial periods of time and consequently does not require frequent readjustment of the pH.

Contact of the sealing solution with the surfaces to be treated is maintained in the conventional manner for about 3-20 minutes and preferably about 5-10 minutes. The manipulative aspects of the sealing operation are not critical and any of the methods which have been used in the past may be employed with the novel baths of the invention.

The resulting sealed anodized aluminum surface has been found to have significantly improved corrosion resistance as measured by surface resistivity. The surface resistivity is a measure of the breakdown of the sealed anodized coating, with the higher values of surface resistivity being characteristic of greater corrosion resistance. For example, anodized aluminum surfaces which have been sealed in accordance with the practice of this invention exceed 1000 hours as tested in accordance with MIL Spec A8625, in which the anodized surface is exposed to a 5% by weight salt spray at 95 C.

Having described the basic concepts of the present invention, reference is now made to the following examples which are provided by way of illustration, and not by way of limitation, of the practice of the invention in the formulation of sealing compositions and the use of same in sealing anodized aluminum surfaces.

EXAMPLE 1 A sealing bath is prepared by dissolving in ordinary tap water about 4.4 grams per liter of a composition consisting of 49 parts by weight of nickel acetate, 40 parts by weight of the sodium salt of an alkyl naphthalene sulfonic acid, 0.25 part by weight of the condensation product of one mole of iso-octyl phenol with about 12-13 moles of ethylene oxide, and 0.08 part by weight of sodium lauryl sulfate. The pH of the resulting solution, maintained at a temperature of about 192 F., is used to seal an Anoclad 11 sheet having a 215 R1 anodic finish for about minutes. The sealed sheet is essentially smut free. In comparison with control samples of the same aluminum sheet sealed in boiling deionized water for 30 minutes at a pH of about 6.4, the sheets sealed in accordance with the invention show greater resistance to acid dissolution and equivalent surface electrical resistivity.

EXAMPLE 2 Using the procedure described in Example 1, a sealing bath is prepared by dissolving in tap water about 4.5 g. of a composition containing 25 parts by weight nickel acetate, 24 parts by weight cobalt acetate, 49 parts by weight of the sodium salt of an alkyl naphthalene sulfonic acid, 0.3 part by weight of the condensation product of one mole octyl phenol with about 12-13 moles of ethylene oxide and 0.07 part by weight sodium lauryl sulfate.

The pH of the resulting solution is adjusted to about 5.5, and the composition is then used to seal an anodized aluminum surface using the procedure described in Example 1. Comparable results are obtained.

It will be apparent that Various changes and modifications can be made in the details of procedure, formulation and use without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A water-soluble composition for sealing anodized aluminum consisting essentially of about 35-60% by weight of nickel acetate, cobalt acetate or mixtures thereof; about 35-60% by weight of a sodium salt of an alkyl naphthalene sulfonic acid; about 0.030.3'% by weight of sodium lauryl sulfate; and, about 0.1-1.0% by weight of the condensation product of one mole of octyl phenol with about 12-13 moles of ethylene oxide.

2. A composition in accordance with claim 1 which contains about 42-50% by weight of nickel acetate, cobalt acetate, or mixtures thereof; about 42-50% by weight of the sodium salt of the alkyl naphthalene sulfonic acid; about 0.05-0.15% by weight of sodium lauryl sulfate; and, about 02-05% by weight of the condensation product of one mole of octyl phenol with about 12-13 moles of ethylene oxide.

3. A composition in accordance with claim 1 which contains about 49% by weight of nickel acetate, cobalt acetate, or mixtures thereof; about 49% by weight of the sodium salt of the alkyl naphthalene sulfonic acid; about 0.1% by weight of sodium lauryl sulfate; and, about 0.25% by weight of the condensation product of one mole of octyl phenol with about 12-13 moles of ethylene oxide.

4. A bath for sealing anodized aluminum comprising an aqueous solution containing about 2-16 grams per liter of a composition of claim 1.

5. A bath in accordance with claim 4 containing about 5-8 grams per liter of a composition of claim 1.

6. A bath in accordance with claim 4 wherein the aqueous solution is formed of ordinary tap water.

7. A method of sealing anodized aluminum surfaces comprising contacting said anodized surfaces with an aqueous solution containing about 2-16 grams per liter of a composition in accordance with claim 1, said solution having a temperature from about F. to the boiling point of the solution and a pH within the range of about 5.2-5.8, and maintaining contact between said aluminum surfaces and said solution for about 3-20 minutes.

8. The method of claim 7 wherein said solution contains about 5-8 grams per liter of a composition in accordance with claim 2, said contact being maintained for about 5-10 minutes at a temperature of about 185- 205 F.

9. A method in accordance with claim 7 in which said solution contains about 5-8 grams per liter of a composition of claim 3, said contact being maintained for about 5-10 minutes at a temperature of about 185-205 F.

10. An aluminum article having an anodized surface, said surface having been sealed by a process in accordance with the method of claim 7.

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