Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-11-17
2003-01-14
Anthony, Joseph D. (Department: 1714)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S274000, C148S275000, C148S276000, C252S389530, C252S389610, C252S395000, C252S400530, C252S400610, C252S406000
Reexamination Certificate
active
06506263
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a composition for sealing anodically oxidized aluminum and aluminum alloy surfaces. More particularly, the invention relates to a sealant composition having improved sealing properties, such as resistance to stains and corrosive substances.
BACKGROUND OF THE INVENTION
Articles of aluminum or an aluminum alloy may be subjected to an anodic oxidation process to provide a protective coating or film of aluminum oxide on the aluminum surface. Such a process improves the hardness and corrosion resistance of the surface of the article and results in the formation of a uniform, translucent, highly porous aluminum oxide film. Generally, these anodic aluminum oxide films may be produced by placing the aluminum article in an acidic electrolyte solution and passing a direct electric current through the solution. Although the resulting anodic oxide layer is more resistant to corrosion than the untreated aluminum surface, the porous structure of the aluminum oxide layer ultimately renders it vulnerable to corrosion and degradation, particularly to that caused by external chemicals.
Therefore, to account for this porous structure, anodized aluminum oxide films and surfaces are commonly sealed with a sealing composition. It is currently theorized that the sealing process closes or fills the pores via hydration and/or precipitation of one or more compounds in the sealant composition. Aluminum articles treated in such a manner generally exhibit stronger resistance to the natural elements as well as external chemicals. Thus, sealed anodically oxidized aluminum surfaces are widely used when the aluminum surfaces may be subjected to severe environmental conditions.
Sealant compositions are well-known in the art. U.S. Pat. No. 3,852,124, herein incorporated by reference, describes a duplex sealing process which utilizes cobalt. U.S. Pat. Nos. 5,362,317 and 5,374,455, herein incorporated by reference, describe aluminum oxide sealant compositions comprising an alkaline earth metal salt and certain sulfonated compounds. U.S. Pat. No. 5,478,415, herein incorporated by reference, relates to a process and a composition for sealing anodically oxidized aluminum surfaces, the composition having an effective amount of a source of alkali metal ions, especially lithium ions. U.S. Pat. No. 4,939,001, herein incorporated by reference, describes a process of sealing decorative anodized aluminum oxide coatings in a hot aqueous solutions that contain 1-phosphonopropane-1,2,3-tricarboxylic acid, 1,1-diphosphonopropane-2,3-dicarboxylic acid, and/or alkali metal and/or alkanolamine salts of these acids. British Patent No. GB 2,254,622, herein incorporated by reference, discloses an aqueous sealant composition comprising at least one alkaline earth metal salt and a particular anti-smut compound. In addition to the patents described hereinabove, those references cited in these patents are also incorporated herein by reference.
There is a continuing need in the art for improved sealant compositions. Further, there is a need in the art for a sealant composition that exhibits enhanced sealant properties, such as corrosion inhibition and acid inhibition. This invention satisfies such needs.
SUMMARY OF THE INVENTION
This invention relates to an aqueous composition for sealing anodically oxidized aluminum surfaces. The composition contains at least one surfactant, a magnesium salt, and a cobalt(II) salt. This composition demonstrates enhanced sealant properties.
This invention also relates to a method of sealing anodically oxidized aluminum surfaces. In this method, the aluminum is contacted with a composition containing at least one surfactant, a magnesium salt and a cobalt(II) salt.
DETAILED DESCRIPTION
The sealant composition of this invention contains at least one surfactant, an effective amount of magnesium ion to achieve a seal, and a potentiating amount of cobalt(II).
The surfactants of this invention may be any surfactants known to be used in sealing compositions. Suitable surfactants include sodium dodecyl diphenyl oxide disulfonate (sold by Pilot Chemical Company under the product name Calfax DB-45), polytergent 2A-1, nonylphenol ethoxylate (sold by Huntsman Corporation under the product name Surfonic N-200), Monateric LF-100, Monateric LF-811, Monateric Cyna-50, Polystep B-27, steol, tamol and the nonoxynol series of surfactant under the Igepal name (e.g., Igepal CO-660, Igepal CO-710, Igepal CO-720, etc.).
Preferred surfactants are compounds of the following formula:
wherein Y is a direct bond or a group of the formula:
wherein R
1
and R
2
are each individually selected from H or C
5
-C
22
alkyl, provided that R
1
and R
2
may not both be H; n has a value in the range of 1 to 4; and X is a counter-ion, such as H
+
or an alkali metal ion, such as Na
+
.
The most preferred surfactants are compounds of the following formula:
wherein R
1
and R
2
are each independently H or C
12
-C
16
alkyl, provided that R
1
and R
2
may not both be H.
The source of magnesium ion used in a sealant composition of this invention is generally one or more of the magnesium salts that are well-known in the art. Suitable salts of magnesium include, without limitation, acetates, sulfates, hydroxides, nitrates, halides, and sulfamates, and mixtures thereof. Anions which contribute a buffering effect to the sealant composition are preferred. The acetate salt of magnesium is the most preferred salt.
The amount of magnesium ion needed to achieve a seal is well-known in the art. In this invention, the molar ratio of the magnesium salt to surfactant is preferably in the range from about 2:1 to about 20:1, more preferably in the range from about 4:1 to about 20:1, and most preferably in the range from about 10:1 to about 16:1. The weight ratio of the magnesium salt to the surfactant is preferably in the range from about 0.1:1 to about 30:1, more preferably in the range from about 0.5:1 to about 15:1, even more preferably in the range from about 1:1 to about 10:1, and most preferably in the range from about 3:1 to about 5:1.
The total combined concentration in the sealing composition of the magnesium salt and the surfactant is preferably in the range from about 1 to about 25 g/L, more preferably in the range from about 2 to about 10 g/L. Higher concentrations may be employed as needed to produce the desired sealant effect.
Suitable sources of cobalt(II) ion are those cobalt-containing compounds that, upon addition to an aqueous solution, result in disassociation of the cobalt(II) ion. Preferably, the cobalt(II) ion is an inorganic or organic salt of cobalt(II). Suitable sources of cobalt(II) ion include: cobalt(II) acetates, cobalt(II) nitrates, cobalt(II) chlorides, cobalt(II) carbonates, cobalt(II) bicarbonates, cobalt(II) oxides, cobalt(II) hydroxides, cobalt(II) bromates, and cobalt(II) oxalates. Cobalt(II) acetates and cobalt(II) acetate precursors are most preferred.
Although a wide number of cobalt(II) compounds may be used as the source of the cobalt(II) ion, certain counter ions are believed to interfere or inhibit the sealing process. Cobalt(II) compounds which are not well suited for sealant compositions include cobalt(II) phosphates and cobalt(II) silicates. Magnesium phosphates and magnesium silicates are also not well suited for sealant compositions. When the phosphates interact with unsealed aluminum oxide films, the surfaces of the films become difficult to seal. In particular, it has been found that phosphate concentrations of less than 20 ppm in a sealing bath can degrade sealing quality. Similar effects have been observed with silicate concentrations greater than 40 ppm.
The potentiating amount of cobalt(II), when used in accordance with this invention, produces a sealant which exhibits enhanced sealant properties, and, in particular, improved resistance to corrosive substances. A “potentiating amount” of cobalt(II) is an amount of cobalt(II) which, when added with the magnesium ion, improves the properties of the magnesium in the sealant composition. The potent
Basaly Mores
Rothwell Dana
Anthony Joseph D.
Houghton Metal Finishing Company
Morgan & Lewis & Bockius, LLP
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