EP1257685A1

EP1257685A1 - Composition and process for sealing anodized aluminum

Info

Publication number: EP1257685A1
Application number: EP00979151A
Authority: EP
Inventors: Nelson Homma; Phillip M. Johnson; Lawrence R. Carlson
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1999-11-09
Filing date: 2000-11-09
Publication date: 2002-11-20
Also published as: AU1656101A; WO2001034872A1; EP1257685A4; CA2390994A1

Abstract

U.S. Patent 5,411,607 teaches that mid-temperature-range (76-93 °C) sealing of anodized aluminum can be accomplished effectively without any heavy metals, using a sealing composition that contains lithium cations (preferably from lithium acetate) and particular types of anionic surfactants made by sulfonating alkyl substituted diphenyl oxides or similar structures. It has now been found that the resistance of surfaces sealed in this way to yellowing after exposure to ultraviolet light and the tolerances of the sealing process itself for the presence of silicaceous impurities and sulfate ions in the sealing compositions can be considerably improved by using two kinds of these surfactants, one with alkyl substituents that contain 14 or fewer, preferably 12, carbon atomes each and one with alkyl substituents that contain 15 or more, preferably 16, carbon atoms each.

Description

COMPOSITION AND PROCESS FOR SEALING ANODIZED ALUMINUM

BACKGROUND OF THE INVENTION

This invention relates to a process for sealing anodically oxidized aluminum and aluminum alloy surfaces, so as to increase the resistance of the anodic oxide film to external corrosive agents, and to a composition for use in the process of the invention. More specifically, the invention provides an aqueous sealing composition substantially free of environmentally sensitive heavy metals.

Articles of aluminum or an aluminum alloy are typically subjected to an anodic oxidation process to improve the hardness and corrosion resistance of the surface of the article. As used herein the term aluminum includes pure or substantially pure aluminum as well as alloys of aluminum containing, in general, at least about 50 % by weight of aluminum. Examples of other metals which may be present in such aluminum alloys are silicon, bismuth, copper, nickel, zinc, chromium, lead, iron, titanium, manganese, and the like. The anodic oxidation of an aluminum surface results in the formation of a uniform, translucent, highly porous aluminum oxide film. The anodic oxide film can also serve an aesthetic or decorative function and may be clear, dyed with organic or inorganic substances, or electrolytically colored.

Generally, these anodic aluminum oxide films result from the passage of a direct electric current through an acidic electrolyte solution at temperatures ranging from 0 to 32 °C. Typically, the acidic electrolyte solution will employ sulfuric acid at concentrations from 140 to 200 grams of sulfuric acid per liter of anodizing electrolyte, this unit of concentration being hereinafter applicable to any ingredient in any composition and being hereinafter usually abbreviated as "g/l".

Anodic oxidation of aluminum is intended to provide a protective coating or film of aluminum oxide on the aluminum surface. Although this anodic oxide layer is more resistant to corrosion than the untreated aluminum surface, the porous structure of the aluminum oxide layer renders it vulnerable to corrosion and degradation, particularly to that caused by external chemical agents. As a result, anodized aluminum oxide films or surfaces are commonly subjected to a process known as sealing. (It is currently theorized, but without any intent to limit this invention, that the sealing process closes or fills the pores via hydration and/or precipitation of one or more compounds.) Aluminum articles treated in such a manner are generally valuable in a wide variety of end use applications, even those in which environmental conditions are severe. High quality sealed anodic aluminum oxide films should exhibit superior resistance to corrosion and degradation caused by most external chemical agents.

Prior art sealing processes can generally be divided into three categories: hydro- thermal sealing processes; mid-temperature sealing processes; and low temperature sealing processes. Hydrothermal sealing processes employ steam or boiling water to seal the anodic oxide coating. This process is believed to cause a hydration of the oxide coating, which results in the constriction of the surface pores. Although good quality sealed films are generally obtained, a disadvantage of this process is the cost of extremely high energy consumption associated with its operation. Mid-temperature sealing processes operate at temperatures between 76 and 93

°C. They generally employ, as the sealant compositions, aqueous solutions of heavy metal salts such as nickel or cobalt. Mid-temperature sealing processes enjoy a significant saving in energy consumption as compared to hydrothermal sealing processes, but present significant waste disposal problems in view of the presence of heavy metals. Such solutions often require expensive pretreatments prior to disposal.

Low temperature sealing processes also require the use of heavy metals. Such processes typically employ nickel salts such as nickel fluoride and operate at temperatures of about 32 °C. In addition to waste disposal problems because of the use of heavy metal ions, low temperature sealing processes suffer from the disadvantage of producing a sealed anodic film having a very low crazing temperature.

U. S. Patent 5,411 ,607 ("the '607 patent"), the entire disclosure of which except for any part that may be inconsistent with any explicit statement herein is hereby incorporated herein by reference, teaches what are believed to be the most advantageous mid-temperature processes yet in use, but experience since the application for this patent was filed has revealed some potential problems with the technology taught in it:

The most generally practiced teachings of this patent can produce sealed anodized films that are susceptible to a generally unwanted yellowing when exposed to sunlight or other ultraviolet light. Furthermore, the sealing compositions as most commonly used from the teachings of the '607 patent can be susceptible to a deterioration in performance from silicon compounds that tend to accumulate in the sealing baths during use. The deterioration in performance from accumulating silicon compounds can be reversed to a considerable extent by the addition of more of the type of organic smut inhibitor taught in the "607 patent, but it has been found that such increased concentrations of the preferred smut inhibitor taught in the examples of the '607 patent increase the yellowing tendency of the sealed coatings. The present invention is an improvement of the technology taught in the '607 patent that largely overcomes these deficiencies of the most common practice of the teachings of the '607 patent, while continuing to provide a process and composition for sealing anodized aluminum articles or surfaces which has relatively low energy costs, is environmentally friendly, and provides a sealed anodic aluminum oxide film of high quality, the aqueous sealing solution being substantially free of elements selected from the group consisting of the heavy metals and phosphorus.

Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout this description unless expressly stated to the contrary: percent, "parts of", and ratio values are by weight; the term "polymer" includes oligomer; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; specification of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole; any counterions thus implicitly specified should preferably be selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; and the term "mole" and its variations means "gram-mole" and its variations and may be applied to elemental, ionic, hypothetical, unstable, and any other chemical species defined by number and type of atoms present, as well as to compounds with well defined molecules.

BRIEF SUMMARY OF THE INVENTION

A sealing composition according to the present invention comprises, preferably consists essentially of, or more preferably consists of, water and the following components: (A) from 0.01 to 50 g/l of lithium cations;

(B) a first organic smut inhibitor selected from molecules conforming to the general formula given in column 5 lines 35 through 40 of the '607 patent, wherein: Y represents a direct bond or a divalent moiety selected from the group consisting of:

CH₃ O O

-L. -L, 1, -0-, an_d-S-;

CH ',3 O each of R, and R₂, these being alternatively designated hereinafter as the

"hydrophobe moieties" of the smut inhibitors corresponding to said gener- al formula, independently represents hydrogen or a C₅ - C₁₄ alkyl moiety, with the proviso that R, and R₂ are not both hydrogen; n is an integer from I to 4 inclusive; and

X^φ represents a counterion, such as H^β or an alkali metal cation; and (C) a second organic smut inhibitor selected from molecules conforming to the gen- eral formula given in column 5 lines 35 through 40 of the '607 patent, wherein: each of Y, n, and X^θ has the same meaning as for component (B); and each of R_t and R₂ independently represents hydrogen or a C₁₅ - C₂₅ alkyl moiety, with the proviso that R, and R₂ are not both hydrogen; and, optionally, one or more of the following components: (D) a component of pH adjusting agent, buffering agent, or both adjusting and buffering agent, that is not part of any of immediately previously recited components (A) through (C); (E) a component of antifoam agent that is not part of any of immediately previously recited components (A) through (D); and (F) a component of wetting agent that is not part of any of immediately previously recited components (A) through (E);

Various embodiments of the invention include working compositions for direct use in treating metals, concentrates from which such working compositions can be prepared by dilution with water, articles of manufacture including a surface contacted with a composition according to the invention, and processes. A process according to the invention in its most basic form requires only an operation of contacting an anodically oxidized aluminum surface with a sealing composition according to the invention as described above. Other operations, usually conventional in themselves, may be performed before and/or after such contacting in an extended process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS Anodized aluminum surfaces suitable for sealing according to the present inven- tion include all of those obtainable by anodic oxidation processes that produce an anodized coating that is at least partially porous. For example, preferred anodized aluminum surfaces will generally be those resulting from the process of passing direct electric current through an acidic electrolyte solution with the aluminum surface charged as the anode and a distinct counter electrode that is charged as the cathode. Suitable acidic electrolyte solutions are generally those containing sulfuric acid, oxalic acid or sulfamic acid. It will be appreciated by those skilled in the art that usually, prior to immersion of an aluminum article in the electrolyte solution, the article preferably will be degreased, washed, and optionally desmutted and/or deoxidized in a conventional manner. The characteristics of anodizing processes that are particularly preferred for preparing surfaces to be sealed according to the invention are set forth in the working examples below, but those skilled in the art will appreciate that it is not essential to the practice of the invention that the anodizing process be so limited.

Decorative anodized aluminum surfaces such as those which have been colored either electrolytically or with the use of organic and/or inorganic dyes may also be sealed with the use of the present invention. Suitable anodized aluminum oxide films to be sealed can be found on aluminum articles having a wide variety of shapes and configurations and will result from numerous manufacturing and processing means. Illustrative examples of suitable aluminum articles are plates, pipes, rods, extruded bars with irreg- ular or regular cross-sections, and articles formed by deep drawing and pressing.

Suitable sources of the lithium ions are those lithium containing compounds which, upon addition to water or an aqueous solution dissolve with disassociation of the lithium content into cations in the solution. Particularly suitable for use herein are lithium hydroxides and lithium salts. Illustrative examples of suitable sources of lithium ions are lithium acetate, lithium nitrate, lithium chloride, lithium carbonate, lithium acid carbonate, lithium oxide, lithium hydroxide, lithium bromate, and lithium oxalate. Lithium acetate and those compounds which are lithium acetate precursors are most preferred. (Lithium acetate precursors are compounds, such as lithium hydroxide and lithium oxide, that can react with acetic acid and/or precursors thereof, such as acetic anhydride, in aqueous solu- tion to form lithium acetate and water.)

The source(s) of lithium ions may be combined with generally available tap water provided that such water is substantially free from phosphate, sulfate, and silicaceous matter. (It has been found that, even in the most preferred compositions according to the invention, phosphate concentrations of less than 20 parts of phosphate per million parts of total sealing solution, a concentration unit that may be used hereinafter for any ingredient of any composition and is hereinafter usually abbreviated as "ppm", can degrade sealing quality, as can concentrations of silicaceous matter with a stoichiometric equivalent as silica that is greater than 90 ppm and/or concentrations of more than 4.1 parts of sulfate per thousand parts of total composition, this concentration unit being freely used hereinafter for any ingredient of any composition and being hereinafter usually abbre- viated as "ppt".) Accordingly, more preferably, the source(s) of lithium ions will be combined with deionized water. Deionized water is commercially available and may be defined as water from which all or substantially all ionic constituents have been removed, usually by passage of the water successively through acid form cation exchange resins and alkali form anion exchange resins or through a mixture of acid form cation exchange resins and alkali form anion exchange resins. (It should be noted that, because of the very low ionization constant of silicic acid, this constituent and some of its salts may not be effectively removed by conventional ion exchange processes and instead may be concentrated in the deionized water, because at the time of contact with the ion exchange resin, the silicic acid or salt thereof is mostly in nonionic form.) The concentration of lithium ions in a sealing composition according to the invention may be varied over quite a wide range with little or no variation in technical quality of the sealing obtained. More particularly, the concentration of lithium ions in a working sealing composition according to the invention preferably is at least, with increasing preference in the order given, 0.01 , 0.05, 0.10, 0.15, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, or 0.34 g/l and independently preferably is not more than, with increasing preference in the order given, 20, 15, 10, 5.0, 4.0, or 3.0 g/l and for economy more preferably is not more than, with increasing preference in the order given, 2.5, 2.0, 1.8, 1 .6, 1.4, 1.2, 1.00, 0.90, 0.80, 0.70, 0.60, 0.50, 0.45, or 0.40 g/l.

Each of surfactant components (B) and (C), independently for each and inde- pendently for each preference stated, is preferably selected from molecules that conform to the general formula in column 5 lines 35 - 40 of the '607 patent when: n is 2 or 3, more preferably exactly 2; when n is at least 2, each aromatic ring in the general formula has at least one of the -SO₃ moieties bonded directly to said aromatic ring; - Y represents a dimethylmethylene moiety or an -O- moiety, more preferably the latter; and

X^φ represents an alkali metal cation, most preferably a sodium cation. Additional individual preferences that are indicated below for components (B) and (C) separately are independent of these general preferences for both components, and any two or more of the general and the individual preferences may be combined to result in more particular preferences. Surfactant component (B) with shorter alkyl substituent(s) preferably consists of molecules that conform to the general formula in column 5 lines 35 - 40 of the '607 patent so that, independently for each preference stated, for the entire component: all R and R₂ moieties that are alkyl moieties contain an average number of car- bon atoms that has a value that is at least, with increasing preference in the order given, 6, 8, 10.0, 10.5, 11.0, 11.5, or 11.9 and independently preferably is not more than, with increasing preference in the order given, 13.5, 13.0, 12.5, or 12.1 ; and at least if all R, and R₂ moieties that are alkyl moieties have an average number of carbon atoms that is at least one of: not more than, with increasing preference in the order given, 10.5, 11 .0, 11.5, or 11.9; and not less than, with increasing preference in the order given, 14.0, 13.5, 13.0, or 12.5, the number average of the number of branching carbon atoms, which are defined as carbon atoms directly bonded to at least three other carbon atoms, in each of said R and R₂ moieties that are not hydrogen atom moieties, is at least, with increasing preference in the order given, 1.0, 1.5, 2.0, 2.5, or 3.0. Independently of its exact chemical nature, component (B) preferably is present in a working sealing composition according to the invention in a concentration that is at least, with increasing preference in the order given, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.65, 0.70, 0.72, 0.75, 0.80, 0.85, 0.88, 0.90, 0.92, or 0.94 g/l and independently preferably is not more than, with increasing preference in the order given, 4.0, 3.5, 3.0, 2.5, 2.0, 1.5, 1.3, 1.1 , or 1.02 g/l. If the concentration of component (B) is too low, an undesirable characteristic called "smutting", "smut", or "bloom" is likely to occur on the surface being sealed. These terms describe the deposition of hydrated aluminum oxide crystals on the surface of the anodic aluminum oxide film. Such smut or bloom greatly impairs the decorative or aesthetic appeal of anodized aluminum. The hydrated aluminum oxide is easily degraded by even light abrasion or touching and is particularly easily damaged by contact with human hands. Smut also interferes with attempts to bond smutted sealed anodized aluminum surfaces to other surfaces. Chemical and mechanical desmutting after-treatments are known in the art, but they introduce undesirable expense and may themselves adversely affect the overall quality of the sealed anodized aluminum film. If the concentration of component (B) is too high, smutting is usually prevented, but yellowing upon exposure to ultraviolet light becomes far more likely, and the amount of component (B) can also become an economic liability. Surfactant component (C) with longer alkyl substituent(s) preferably consists of molecules selected from the group that conform to the general formula in column 5 lines 35 - 40 of the '607 patent so that, independently for each preference stated, for the average of the entire component: - all R, and R₂ moieties that are alkyl moieties contain an average number of carbon atoms that is at least 16 and independently preferably is not more than, with increasing preference in the order given, 23, 21 , 19, or 17; and all R, and R₂ moieties that are alkyl moieties do not contain an average number of branching carbon atoms that is more than, with increasing preference in the order given, 2.0, 1.0, or 0.1.

Independently of its exact chemical nature, component (C) preferably is present in a composition according to the invention in a concentration that is at least, with increasing preference in the order given, 0.05, 0.10, 0.15, 0.25, 0.35, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, or 0.75 g/l and independently preferably is not more than, with increas- ing preference in the order given, 4.5, 4.0, 3.5, 3.0, 2.5, 2.1 , 1.8, 1.60, 1.50, 1.40, 0.90,

0.85, 0.82, or 0.79 g/l. If the concentration of component (C) is too low, smutting is likely to occur on the surface being sealed, while if the concentration of component (C) is too high, an excessive cost without any offsetting benefit will be incurred.

Independently of their actual values, the concentration of component (C) prefer- ably has a ratio to the concentration of component (B) in the same composition according to the invention that is at least, with increasing preference in the order given, 0.1 :1 .00, 0.3:1.00, 0.5:1.00, 0.55:1.00, 0.60:1 .00, 0.65:1 .00, 0.68:1 .00, 0.70:1.00, 0.72:1 .00, or 0.74:1 .00 and independently preferably is not more than, with increasing preference in the order given, 5.0:1 .00, 4.0:1 .00, 3.0:1.00, 2.5:1 .00, 2.0:1 .00, 1.8:1 .00, 1.6:1 .00, 1 .4:1.00, 1 .2:1 .00, 1.00:1.00, 0.90:1 .00, 0.85:1 .00, or 0.80:1 .00.

A working aqueous sealing composition according to the invention preferably has a pH value that is at least, with increasing preference in the order given, 1.0, 2.0, 3.0, 4.0, 4.5, 5.0, 5.3, 5.50, 5.60, 5.70, or 5.80 and independently preferably is not more than, with increasing preference in the order given, 9.5, 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.3, 6.20, 6.10, or 6.00. When the pH is either too low or too high, the protective value of the sealed anodized coating, as indicated by an acid dissolution test, will be impaired. The higher the concentration of silicaceous matter dissolved, dispersed, or both dissolved and dispersed in the working composition, the more easily the protective value of the coatings will be diminished by pH values outside the more preferred ranges. The preferred pH value is preferably stabilized by use of a buffer system in a working aqueous liquid composition according to the invention. Normally, the preferred buffer system consists of the anions of the salt(s) from which lithium cations are sourced to the aqueous liquid composition combined with the acid(s) corresponding to those anions. Accordingly, when lithium is sourced from lithium acetate as most preferred, acetic acid is also preferably present in the aqueous liquid composition according to the inven- tion in order to buffer the pH of the composition. If lithium cations are provided to the aqueous liquid composition by addition of lithium oxide or hydroxide, an amount of acetic acid that is more than sufficient to neutralize the oxide or hydroxide added is preferably also included in the aqueous liquid composition, in order to similarly constitute an acetic acid-acetate buffer system at the desired pH value. In either of these instances, the ratio of the molar concentration of unneutralized acetic acid to the molar concentration of acetate ions in the same composition preferably is at least, with increasing preference in the order given, 0.010:1 .00, 0.020:1.00, 0.030:1 .00, 0.040:1 .00, 0.045:1 .00, 0.050:1 .00, or 0.055:1.00 and independently preferably is not more than, with increasing preference in the order given, 0.6:1 .00, 0.4:1 .00, 0.2:1 .00, 0.100:1 .00, 0.080:1.00, 0.070:1 .00, 0.065:1.00, or 0.060:1.00 If any adjustment of pH should be required during prolonged use of a composition according to the invention in a process according to the invention, adjustments may be made as needed with the use of acetic acid to lower pH or ammonium hydroxide to raise pH.

Often, optional components (E) and (F), wetting and antifoam agents, are not needed in a composition according to the invention and when not needed are preferably omitted, at least for economy. If lack of wetting and/or excessive foam generation should be noted during a process according to the invention, those skilled in the art will know or will be able to determine with minimal experimentation what kinds of wetting and antifoam agents will overcome these problems without unacceptably interfering with the benefits of the invention. One suitable antifoam agent is FOAMBAN™ antifoam from

Ultra Additives, Paterson, New Jersey, but many others are also suitable.

For varied reasons, some of which have been indicated above, it is preferred that several materials, including some that have been included in previous sealing compositions for anodized aluminum, should be omitted or at least minimized in compositions according to the invention. More particularly, independently for each preferably minimized component listed below, a composition according to the invention preferably does not contain more than, with increasing preference in the order given, 1 , 0.5, 0.2, 0.08, 0.05, 0.02, 0.008, 0.005, 0.002, 0.0008, 0.0005, 0.0002, 0.00008, 0.00005, 0.00002, 0.000008, 0.000005, or 0.000002 percent of any of the following: any metal cations other than alkali metal cations; any anions that contain phosphorus atoms; any dispersed or dissolved substance that contains silicon atoms; sulfate anions; and any anions that contain fluorine atoms. (However, if optimum amounts of components (B) and (C) as described above are present, larger amounts of silicon atoms and sulfate anions may be tolerated without serious impairment of the results achieved.)

A concentrate make-up composition according to the invention preferably contains all of the ingredients other than water desired in a working sealing composition according to the invention and therefore is by definition a "single package" make-up concentrate, because it can be converted to a working sealing composition by dilution with water only, except that some further pH adjustment may possibly be required. In order to increase the savings from supplying a concentrate instead of a working composition and thereby avoiding transportation costs for water that can usually be added less expensively at the point of use, a single package make-up concentrate according to the invention preferably contains each ingredient as noted above in a concentration that is at least, with increasing preference in the order given, 2, 4, 8, 15, 20, 25, 30, 35, 40, or 45 times as great as one of the preferred concentrations indicated above for the particular ingredient in a working composition. In order to avoid phase separation and/or other instability during shipment or storage, a make-up concentrate composition preferably does not contain any ingredient in a concentration that is more than, with increasing preference in the order given, 100, 75, 50, 40, or 35 times greater than one of the preferred concentrations indicated above for the particular ingredient in a working composition.

As any particular volume of working composition is used, its ingredients will be depleted to some extent by incorporation into the sealed anodized coating and/or by mechanical drag-out. It has been found that components (B) and (C) as described above, along with component (E) if present, are consumed more rapidly than the lithium ions or buffering components. Accordingly, a replenisher concentrate preferably contains its surfactant components in a concentration with a higher ratio to the lithium ion concentration than in a preferred working sealing composition. More particularly, the ratio of the concentration of either of components (B) and (C) to the concentration of lithium ions in a replenisher concentrate preferably is at least, with increasing preference in the order given, 1 .2, 1 .4, 1.6, 1 .8, or 2.0 times higher than the ratio of the concentration of component (B) or (C) to the lithium ions concentration in the initial working sealing composition that is being replenished with a replenisher concentrate. Independently, the concentration of each of components (B) and (C) in a replenisher concentrate has one of the preferred ratios to the concentration of the same component in the working sealing composition being replenished as have been already described above for the ratios of these ingredients in a single package make-up concentrate to the concentration of the same ingredient in a working sealing solution made up from the make-up concentrate. The degree of preference of various ratios as specified for the make-up concentrate also applies to the ratios for the replenisher concentrate.

In a process according to the invention, anodized coatings formed on aluminum are preferably contacted with the aqueous sealing composition by immersion of the work piece in a composition according to the invention that is maintained at a temperature that is at least, with increasing preference in the order given, 30, 40, 50, 60, 65, 70, 73, 76, 79, 81 , 83, or 85 °C and independently preferably is not more than, with increasing preference in the order given, 94, 92, 90, or 88 °C during the period of immersion. The time of immersion or other contact of the anodized aluminum surface or article with the aqueous sealing composition is a function of the thickness of the anodized aluminum oxide film. In general, an anodized aluminum coating to be sealed preferably will remain in contact with the sealing composition for a minimum of 4.0 minutes with an additional 1.0 minute preferably added to this minimum for every 2.5 micrometres (hereinafter usually abbreviated as "μm") of thickness of the anodized aluminum coating to be sealed.

The practice of the invention may be further appreciated from the following, non- limiting operating examples and comparative examples, in which commercially available rectangular Type 6063 aluminum test panels with dimensions of 76x89 millimeters were subjected to the following cleaning and anodization processes in the order stated: Test panels were initially cleaned by immersion in an aqueous solution containing 50 g/l of

NOVACLEAN® 120 Cleaner Concentrate (commercially available from Henkel Surface Technologies Division of Henkel Corporation, Madison Heights, Michigan, this supplier being hereinafter usually abbreviated as "HST") at a temperature of 66 °C for approximately five minutes. Thus degreased panels were rinsed with tap water at room temperature (i.e., 18 - 23 °C), then etched at 66 °C by immersion for approximately five minutes in a solution containing 50 g/l of NaOH and 2.0 % by volume of EA-1010™ etch additive (from HST). Thus etched panels were next rinsed with tap water at room temperature, then were desmutted by immersion in NOVOX® 320 desmutting product (from HST) at a temperature of about 21 °C for one minute. The panels were subsequently rinsed with tap water at room temperature. The thus prepared test panels were anodized in an electrolyte solution in water of 180 g/l of sulfuric acid and 2.5 % of ANOMAX® 9000 hard coating additive (from HST). The anodizing electrolyte was maintained at 21 °C while the panels were anodized with direct current at a current density of 1.9 amps per square decimeter for about 32 minutes to produce an anodized coating thickness of 18 to 20 μm. Anodized test panels as thus prepared were sealed as described in specific examples below. The organic smut inhibitors, alternatively called "surfactants" below, that were used in these specific examples were all commercial products obtained from Dow Chemical, and their characteristics as described below are those reported in this manufacturer's technical literature. Each of them has as its active ingredients molecules that con- form to the general formula given in column 5 lines 35 through 40 of the '607 patent when: Y represents -O-; n is 2, and one of the sulfonyl groups is on each aromatic ring; R, is hydrogen in about half the molecules and is the same as R₂ in the remainder of the molecules; and X^® represents a sodium cation. The major distinction among them is the chemical nature of the hydrophobe moieties, which are n-hexyl for DOW FAX™ Hydro- trope surfactant, n-decyl for DOWFAX™ 3B2, "tetrapropylene" (believed to be tetra- methyl-1 -octyl) for DOWFAX™ 2A1 , and n-hexadecyl for DOWFAX™ 8390. Each of the surfactants contains from 35 to 47 % of its active ingredients in a solution in water. SPECIFIC EXAMPLE GROUP 1

In this group, the variable investigated was the concentration of lithium cations, which were provided to the composition according to the invention as lithium acetate di- hydrate. Each composition additionally contained 2.0 g/l of DOWFAX™ 2A1 , 2.0 g/l of DOWFAX™ 8390, and sufficient acetic acid to bring the solution to a pH value of 5.9 at 85 °C, at which temperature it was maintained for 12 minutes of contact with the anodized test panels in order to seal them. After this period of sealing, the panels were re- moved from contact with the aqueous liquid composition according to the invention, rinsed with deionized water, and dried. The dried panels were then evaluated visually for smut and according to American Society for Testing and Materials Test Methods B136-84 for dye stain resistance and B680-80 for acid dissolution resistance, for the last of which results are reported in grams per square meter, hereinafter usually abbreviated as "g/m²", or in milligrams per square inch. The concentrations of lithium acetate and the results of the acid dissolution resistance test are shown in Table 1 . In addition to these results, all of the sealed test panels prepared were completely free of smut and passed the dye stain resistance test. A value of 4.0 g/m² or its equivalent of 2.6 milligrams per square inch in the acid dissolution test is commercially acceptable. It is therefore apparent that all of the working compositions in Table 1 under the process conditions used in this Group produced satisfactory sealing.

SPECIFIC EXAMPLE GROUP 2

In this group, the pH value of the aqueous liquid sealing composition according to the invention was the independent variable studied. The panel test preparation before sealing was the same as for Group 1 , and the sealing compositions contained the same ingredients as for Group 1 except that: the concentration of lithium acetate dihydrate was 7.5 g/l in every instance; when needed to obtain high pH values, ammonium hydroxide was added to the composition to adjust the pH instead of acetic acid; for values under the column heading "With Silicate", each composition contained a concentration of sodium silicate that was stoichiometrically equivalent to 60 ppm of SiO₂ added to simulate contamination by silicaceous matter during prolonged use of a sealing composition; and the pH values of the compositions were as shown in Table 2 below. The dye stain resistance and acid dissolution resistance tests values obtained are also shown in Table 2. All of the compositions and processes shown in Table 2 produced sealed surfaces that were completely free of smut.

COMPARISON EXAMPLE GROUP 3

In this group, amounts of surfactant and of sodium metasilicate were independently varied, and acid dissolution test values and yellowing tendency of the resulting sealed specimens were quantitatively measured. The panel test preparation before sealing was the same as for Groups 1 and 2, and the sealing compositions contained the same ingredients as for Group 2 except that: the pH was constant at 5.9, the only surfactant in the sealing composition was DOWFAX™ 2A1 , and the concentrations of surfactant and of added silicate, the latter being measured as its stoichiometric equivalent as silica, were as shown in Table 3. The value of "ΔE" shown in Table 3 was measured on the samples sealed without any silicate added to the sealing composition and is the value calculated according to American Society for Testing and Materials ("ASTM") procedure D2244-85 after exposure to ultraviolet light for 720 hours according to ASTM Procedure G53-88. Lower values are preferred over higher ones in this test, and values of 1.5 or greater are generally not commercially acceptable, because of the danger of yellowing. Thus, it is clear from the results in Table 3 that the concentration of DOWFAX™ 2A1 should be limited to less than 6.0 g/l whenever yellowing tendencies in the sealed coating are not acceptable. Table 3

COMPARISON EXAMPLE GROUP 4

In this group the independent variables were the chemical structure of the sur- 5 factant used and the concentration of sodium metasilicate, measured as its stoichiometric equivalent as silica, in the sealing compositions. All other factors were the same as for Group 3, except that the surfactant used was varied as shown in Table 4, but its concentration was always 6.0 g/l. Results are shown in Table 4 below.

Table 4

The values in Table 4 indicate that at this relatively high concentration, only the surfactant with the highest number of carbon atoms in its hydrophobe moieties has good yellowing resistance. COMPARISON EXAMPLE GROUP 5

This group was substantially identical to Group 3, except that the surfactant used was DOWFAX™ 8390, with molecules having straight chain hexadecyl hydrophobe moieties, instead of DOWFAX™ 2A1. The results are shown in Table 5 below. The values in Table 5 show that this surfactant is much less effective at reducing the acid dissolution value than is the surfactant used in Group 3. However, the surfactant in this group also does not promote yellowing nearly as much as the surfactant used in Group 3.

Table 5

COMPARISON EXAMPLE GROUP 6

This group was like Group 4, except that the amount of surfactant in each instance was 4.0 g/l instead of 6.0 g/l as in Group 4, and the simulated contaminant added to most of the sealing compositions was sulfate ions (added as sodium sulfate) instead of silica. Results are shown in Table 6 below.

The results in Table 6 show that the surfactant with branched hydrophobe moieties is more tolerant of sulfate impurities, as it is of silica impurities, but when used alone at 4.0 g/l it does not give quite enough resistance to yellowing. EXAMPLE GROUP 7

In this group, two different surfactants were combined. Each sealing composition tested contained 2.0 g/l of DOWFAX™ 8390 and 2.0 g/l of another one of the surfactants used in the previous groups, the specific surfactant being specified in Table 7 below. Varying amounts of sulfate as simulated contamination were added as in Group 6, and Table 6

all other conditions were as specified for that Group. Results are shown in Table 7 below. In addition to these results, the ΔE value was measured for the sealed coating resulting from sealing with the "uncontaminated" sealing composition with each type of second surfactant, and in all instances the value was less than 1.0 and therefore satisfactory. The results in Table 7 indicate that the combination of DOWFAX™ 2A1 and DOWFAX™ 8390 produces better sealing quality at every level of sulfate concentration tested than does either of the other combinations of surfactants tested, and, as already noted, the yellowing resistance of this combination is also fully acceptable.

Table 7

EXAMPLE GROUP 8

Conditions for this group are substantially identical to those for Group 7, except that the simulated contaminant added to the sealing compositions was again sodium metasilicate, measured as its stoichiometric equivalent as silica, instead of sulfate, and 3.0 instead of 2.0 g/l of each surfactant were present in the sealing composition. Specific values and results are shown in Table 8.

In addition to the results shown in Table 8, the ΔE values were measured for the sealed coatings formed with the "uncontaminated" sealing compositions of each type used in this Group. The ΔE value was < 1.2 for either DOWFAX™ Hydrotrope Surfactant or DOWFAX™ 2A1 Surfactant as the second surfactant and was < 1.5 and therefore acceptable for DOWFAX™ 3B2 Surfactant as the second surfactant. Therefore, in this Group as well as in Group 7, the same combination of surfactants achieved the best results in the acid dissolution test, was satisfactory in yellowing resistance, and was highly tolerant of contamination.

Table 8

Claims

The invention claimed is: CLAIMS

1. An aqueous liquid composition suitable for sealing a coating formed on aluminum by anodization, said composition comprising water and the following components: (A) from about 0.01 to about 50 g/l of lithium cations;

(B) a first organic smut inhibitor selected from molecules conforming to the general formula given in column 5 lines 35 through 40 of the '607 patent, wherein:

Y represents a direct bond or a divalent moiety selected from the group consisting of:

- each of R^ and R₂, these being alternatively designated hereinafter as the

"hydrophobe moieties" of the smut inhibitors corresponding to said general formula, independently represents hydrogen or a C₅ - C₁₄ alkyl moiety, with the proviso that R, and R₂ are not both hydrogen; n is an integer from I to 4 inclusive; and - X^* represents a counterion; and

(C) a second organic smut inhibitor selected from molecules conforming to the general formula given in column 5 lines 35 through 40 of the '607 patent, wherein: each of Y, n, and X^s has the same meaning as for component (B); and each of R, and R₂ independently represents hydrogen or a C₁₅ - C₂₅ alkyl moiety, with the proviso that R, and R₂ are not both hydrogen.

2. An aqueous liquid composition according to claim 1 , wherein: there is a concentration of lithium ions that is from about 0.05 to about 3.0 g/l; there is a concentration of component (B) that is from about 0.2 to about 4.0 g/l; there is a concentration of component (C) that is from about 0.15 to about 3.0 g/l; and the concentration of component (C) has a ratio to the concentration of component (B) that is from about 0.3:1.00 to about 2.0:1 .00.

3. An aqueous liquid composition according to claim 2, wherein: each of components (B) and (C) is selected from molecules that conform to the general formula in column 5 lines 35 - 40 of the '607 patent when: n is 2 or 3; each aromatic ring in the general formula has at least one of the -SO₃ moieties bonded directly to said aromatic ring;

Y represents a dimethylmethylene moiety or an -O- moiety; and X^θ represents an alkali metal cation;

5 - for component (B) as a whole, all of R, and R₂ that are alkyl moieties have an average number of carbon atoms that is from about 6 to about 13.0; and for component (C) as a whole, all of R, and R₂ that are alkyl moieties have an average number of carbon atoms that is from about 16 to about 19.

4. An aqueous liquid composition according to claim 3, wherein: o - there is a concentration of lithium ions that is from about 0.20 to about 1.0 g/l; there is a concentration of component (B) that is from about 0.70 to about 1.1 g/l; there is a concentration of component (C) that is from about 0.45 to about 1.0 g/l; and the concentration of component (C) has a ratio to the concentration of 5 component (B) that is from about 0.60:1.00 to about 1.2:1.00.

5. An aqueous liquid composition according to claim 1 that is a make-up or replenisher concentrate composition, wherein: there is a concentration of lithium ions that is at least about 3.0 g/l; there is a concentration of component (B) that is at least about 6.0 g/l; 0 - there is a concentration of component (C) that is at least about 4.5; and the concentration of component (C) has a ratio to the concentration of component (B) that is from about 0.3:1.00 to about 2.0:1.00.

6. An aqueous liquid composition suitable for sealing a coating formed on aluminum by anodization, said composition having been made by mixing water and at least the fol- 5 lowing components:

(A) a source of lithium cations in an amount that provides from about 0.01 to about 50 g/l of lithium cations to the total composition;

(B) a source of a first organic smut inhibitor selected from molecules conforming to the general formula given in column 5 lines 35 through 40 of the '607 patent, o wherein:

5 ., -0-, and -S-; each of R, and R₂, these being alternatively designated hereinafter as the "hydrophobe moieties" of the smut inhibitors corresponding to said general formula, independently represents hydrogen or a C₅ - C₁₄ alkyl moiety, with the proviso that R, and R₂ are not both hydrogen; - n is an integer from I to 4 inclusive; and

X^θ represents a counterion; and (C) a source of a second organic smut inhibitor selected from molecules conforming to the general formula given in column 5 lines 35 through 40 of the '607 patent, wherein: - each of Y, n, and X^θ has the same meaning as for component (B); and each of R, and R₂ independently represents hydrogen or a C₁₅ - C₂₅ alkyl moiety, with the proviso that R^ and R₂ are not both hydrogen.

7. An aqueous liquid composition according to claim 6, wherein: the source of lithium cations provides to the aqueous liquid composition a con- centration of lithium cations that is from about 0.05 to about 3.0 g/l; the source of first organic smut inhibitor supplies the first organic smut inhibitor in an amount corresponding to a concentration of first organic smut inhibitor that is from about 0.2 to about 4.0 g/l; the source of second organic smut inhibitor supplies the second organic smut inhibitor in an amount corresponding to a concentration of second organic smut inhibitor that is from about 0.15 to about 3.0 g/l; and the source of second organic smut inhibitor supplies this inhibitor in an amount that has a ratio to the amount of first organic smut inhibitor supplied by the source thereof that is from about 0.3:1 .00 to about 2.0:1 .00.

8. An aqueous liquid composition according to claim 7, wherein: each of components (B) and (C) is selected from molecules that conform to the general formula in column 5 lines 35 - 40 of the '607 patent when: n is 2 or 3; each aromatic ring in the general formula has at least one of the -SO₃ moieties bonded directly to said aromatic ring;

Y represents a dimethylmethylene moiety or an -O- moiety; and X⁸ represents an alkali metal cation; for component (B) as a whole, all of R^ and R₂ that are alkyl moieties have an average number of carbon atoms that is from about 6 to about 13.0; and - for component (C) as a whole, all of R^ and R₂ that are alkyl moieties have an average number of carbon atoms that is from about 16 to about 19.

9. An aqueous liquid composition according to claim 8, wherein: the source of lithium cations provides to the aqueous liquid composition a concentration of lithium ions that is from about 0.20 to about 1.0 g/l; - the source of first organic smut inhibitor supplies the first organic smut inhibitor in an amount corresponding to a concentration of first smut inhibitor that is from about 0.70 to about 1.1 g/l; the source of second organic smut inhibitor supplies the second organic smut inhibitor in an amount corresponding to a concentration of second organic smut inhibitor that is from about 0.45 to about 1.0 g/l; and the source of second organic smut inhibitor supplies this inhibitor in an amount that has a ratio to the amount of first organic smut inhibitor supplied by the source thereof that is from about 0.60:1.00 to about 1.2:1.00.

10. An aqueous liquid composition according to claim 6 that is a make-up or replenisher concentrate composition, wherein: the source of lithium cations provides to the aqueous liquid composition a concentration of lithium ions that is at least about 3.0 g/l; the source of first organic smut inhibitor supplies the first organic smut inhibitor in an amount corresponding to a concentration of first smut inhibitor that is at least about 6.0 g/l; the source of second organic smut inhibitor supplies the second organic smut inhibitor in an amount corresponding to a concentration of second organic smut inhibitor that is that is at least about 4.5; and the source of second organic smut inhibitor supplies this inhibitor in an amount that has a ratio to the amount of first organic smut inhibitor supplied by the source thereof that is from about 0.3:1 .00 to about 2.0:1 .00.

11 . A process of sealing an anodized aluminum surface by contacting said surface with an aqueous liquid composition according to any one of claims 1 through 4 and 6 through 9 for a time of at least about 4.0 minutes, said aqueous liquid composition being maintained during said contacting within a temperature range from about 60 to about 94

°C.

12. A process according to claim 11 , wherein the anodized aluminum surface to be sealed has a known thickness in micrometres, said aqueous liquid composition is maintained during contacting within a temperature range from about 85 to about 93 °C, and said contacting is maintained for at least a number of minutes that is the sum of 4.0 plus the product of 0.4 times the number of micrometres in said known thickness of the anodized surface to be sealed.

13. An article of manufacture comprising a surface prepared by a process according to claim 11 or 12.