Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Reexamination Certificate
2003-01-23
2003-12-16
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
C106S014210, C106S014410, C148S247000, C148S267000, C148S275000, C428S472000, C428S472100
Reexamination Certificate
active
06663700
ABSTRACT:
ORIGIN OF THE INVENTION
This invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process of post-treating metal coated substrates, and to the composition for treating metal coated substrates to provide color recognition and improve adhesion-bonding, abrasion, and corrosion-resistant properties of the coated substrates. More specifically, this invention relates to a novel composition, and to the process of using the composition to post-treat metal coated substrates. The composition comprises an acidic aqueous solution comprising effective amounts of at least one water-soluble trivalent chromium compound, an alkali metal hexafluorozirconate, at least one tetrafluoroborate and/or hexafluorosilicate, at least one water soluble zinc compound and effective amounts of water-soluble thickeners.
DESCRIPTION OF PRIOR ART
Current high-performance post treatments for metal coated substrates are based on hexavalent chromium chemistry. Hexavalent chromium is highly toxic and a known carcinogen. As a result, the solutions used to deposit post-treatment coatings and the coating, per se are toxic. These coatings do, however, yield outstanding paint adhesion and corrosion resistance to the base metal. Typically, post-treatments or coatings are deposited onto the metal at ambient temperatures and usually applied by immersion or spray processes. Post treatments are usually specified by the military or commercial specifications that govern each metal coating being treated. As such, there is not a unique “post treatment” specification for all metal coatings as there is for “conversion coated” aluminum and its alloys.
Further, environmental laws, executive orders, and local occupational, safety, and health (OSH) regulations are driving military and commercial users in the search for chromate-free post treatments. In the case of these coated metals, the metal substrates and the coatings per se are relatively non-toxic. With the addition of a chromate post treatment, however, these coatings become toxic. In addition, the use of chromate post treatments is becoming more expensive as regulations tighten and costs are becoming prohibitive with restrictions imposed by the EPA. Moreover, certain processes like spraying chromate coating solutions are forbidden at some facilities due to OSH risk, thereby forcing the use of less-than-optimum solutions. Thus, while existing chromate post treatments are outstanding in their technical performance in that they provide enhanced corrosion protection and adhesion bonding e.g. adhesion for paint and other coatings at a low application cost, from a life-cycle cost, environmental, and OSH perspective, chromate coatings are detrimental for people and the environment.
SUMMARY OF THE INVENTION
This invention relates to trivalent chromium post treatment (TCP) compositions and to the processes for providing color recognition and improved adhesion and corrosion resistant properties of metal coated substrates. These coatings and processes are generally known as “post-treatments”. Post-treatments are coatings in contact with the metal being treated after formation of the initial coating and therefore the post-treatments normally have no direct contact with the underlying substrate, except possibly through some pores in the outer metal coating.
Specifically, this invention relates to a composition and to the process of using said composition to post-treat metal coated substrates at ambient temperatures or higher e.g. temperatures ranging up to about 200° F. More specifically, this invention relates to compositions for post-treating metal coatings to provide color recognition, and to improve the corrosion-resistance, and adhesion bonding properties e.g. paint adhesion of the coatings. The composition comprises an acidic aqueous solution having a pH ranging from about 2.5 to 5.5 and preferably 3.7 to 4.0, and comprises, per liter of said solution, from about 0.01 to 22 grams of a water-soluble trivalent chromium compound, about 0.01 to 12 grams of an alkali metal hexafluorozirconate, about 0.0 to 12 grams and preferably 0.01 to 1.2 and more preferably 0.12 to 0.24 grams of at least one fluoro-compound selected from the group consisting of an alkali metal tetrafluoroborate, an alkali metal hexafluorosilicate and various combinations thereof, from about 0.001 to 10 grams per liter of at least one zinc compound, preferably divalent zinc salts, from about 0.0 to 10 grams per liter, preferably 0.5 to 1.5 grams of at least one water-soluble thickener and about 0.0 to 10 grams and preferably 0.5 to 1.5 grams per liter of at least one surfactant or wetting agent.
Compositions and processes based on trivalent chromium offer excellent technical performance compared to standard chromate-based coatings. However, a shortcoming of these compositions is the lack of a significant color change in the as-deposited metal coating, especially when used as a post treatment for aluminum-based sacrificial coatings. Chromate-based coatings of this type typically have an iridescent gold to brown color that is easily identified by processors, quality control personnel and other users in the field. A gold color on aluminum coated components generally means that a chromate post treatment is present and the color is useful for this type of quality control irrespective of technical coating performance such as resistance to corrosion or paint adhesion. TCP coatings typically have a light bluish to purplish to tan color, depending on the process conditions, that is very difficult to see in mixed light such as inside a production facility, at a repair depot or manufacturing plant. TCP coatings on some surfaces such as Ion Vapor Deposited (IVD) Aluminum is virtually colorless. Another shortcoming of these coatings is the relative performance of the TCP coatings as post treatments. As previously disclosed, TCP coatings yield about the same corrosion resistance as chromate post treatments on a variety of sacrificial coatings like cadmium, IVD aluminum, and zinc alloys such as zinc-nickel and tin-zinc. However, it would be desirable to have post treatment coatings that perform better than the presently known chromate post treatments.
It is therefore an object of this invention to provide an acidic aqueous solution comprising effective amounts of a trivalent chromium compound, an alkali metal hexafluorozirconate, a tetrafluoroborate and/or hexafluorosilicate and a divalent zinc compound for post-treating metal coated substrates to provide color recognition and identification, and to improve the adhesion bonding and corrosion resistance properties.
It is another object of this invention to provide a stable acidic aqueous solution having a pH ranging from about 2.5 to 5.5 containing a trivalent chromium salt, a hexafluorozirconate and a divalent zinc salt for post-treating metal coatings.
It is a further object of this invention to provide a stable acidic aqueous solution containing trivalent chromium having a pH ranging from about 3.7 to 4.0 for treating metal coated substrates at about room temperature wherein said solution contains substantially no hexavalent chromium.
These and other objects of the invention will become apparent by a further and more detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to compositions and processes for preparing corrosion-resistant coatings on sacrificial coatings such as cadmium, zinc, IVD aluminum, Alumiplate, zinc-nickel and tin-zinc. The process comprises treating said metal coated substrates with an acidic aqueous solution containing a trivalent chromium salt basic, an alkali metal zirconate such as potassium hexafluorozirconate, a cellulose-based thickener and an alkali metal compound such as a potassium tetrafluoroborate or hexafluorosilicate stabilizer. The composition must also c
Matzdorf Craig A.
Nickerson, Jr. William C.
Billi Ron
Green Anthony J.
The United States of America as represented by the Secretary of
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