Stable, thin-film organic passivates

Abstract

An aqueous liquid passivate composition for treating metal surfaces having dispersed therein solid particles which result in a transparent or translucent, preferably colorless, corrosion resistant coating, upon drying of the aqueous liquid passivate composition, the coating providing better resistance to heating by solar energy than the untreated metal surface at lower coating thicknesses than paint.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation in part of U.S. application Ser. No. 11 / 330869, filed 12 Jan. 2006, which claims priority to U.S. Provisional Application Ser. No. 60 / 644,191, filed 14 Jan. 2005, each of which is incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates to compositions and processes for passivating, i.e., forming a corrosion resistant surface layer, on metal surfaces preferably predominantly of aluminum and / or zinc, which also improves the metal surface's resistance to heating by electromagnetic radiation (hereinafter EMR), in particular solar radiation or energy. A wide variety of such surfaces are in normal use, including many kinds of galvanized and / or aluminized steel, and the invention is applicable to aluminiferous and / or zinciferous surfaces which differ from the underlying metal, as well as to solid alloys of aluminum and / or zinc which include zinc, such as hot-dip and electro...

AI Technical Summary

Benefits of technology

[0023] In a first embodiment of the invention, an essentially or substantially chromium-free composition and process for passivating metal surfaces has been developed that provides corrosion resistance comparable to, i.e. about the same as, previously used chromate-containing passivating agents. Another aspect of the first embodiment of the invention provides a new thin organic coating that reduces the tendency of surfaces of coiled or stacked metal

Problems solved by technology

While the underlying steel substrate is protected, the aluminum and zinc coating are sometimes susceptible to corrosion that can result in surface staining and white corrosion.

Inorganic passivates, typically using chromium, provide excellent passivation but have the drawbacks of poor paint adhesion and adverse environmental impact.

Many of these attempts failed where the latex became unstable and the formulation coagulated, due at least in part to the low pH and the presence of other ingredients, such as metal ions.

Often, even if the formulation did not immediately coagulate, the chromium-free products had little or no shelf life, either separating or coagulating over a matter of days or even hours.

Another drawback of prior art organic passivating compositions is their undesirable effects on the physical attributes of coils of metal.

In this industry, the nature of the passivate coating can have undesirable effects of binding or slippage between metal surfaces in the coil.

Each undesirable effect causes problems in manufacture; binding refers to the coils sticking together and interferes with uncoiling, and slipping / sliding of the metal surfaces relative to each other in a coil can cause coil collapse.

Aluminum-zinc alloy coated steel sheets have good solar reflecting properties, but poor emittance of solar energy that is not reflected.

Such non-reflected energy is largely translated into heat in the steel sheets and some of the heat is then transferred to the interior of the building increasing the cost of cooling the interior.

Typically, the corrosion and lubricious coatings of the prior art deposited on aluminum-zinc surfaces provide less than desirable resistance to heating by the electromagnetic radiation of the sun (solar radiation).

Corrosion resistant coatings, such as inorganic chromium passivates and organic thin film passivates do not substantially improve emittance.

Some non-white paints provide improvements in emittance of solar energy, but at an insufficient rate with increasing film build compared to their tendency to reduce the solar reflectance of the coated surface.

Overall, the non-white paints offer a less than desirable trade-off between emittance and reflectance.

White paints initially have good solar reflectance and provide improvements in emittance of solar energy, but white paints have other drawbacks.

White paints require a series of additional processing steps and tend to highlight any dirt deposition, easily becoming aesthetically displeasing and hiding the desirable appearance of the metal coating.

A drawback of painting metal surfaces white to improve resistance to electromagnetic heating is the limited life of the paint and the tendency of the paint to stain and age, which reduces solar reflectance.

Another drawback of conventional paints is the thickness required.

Over a large expanse of surface, such as a roof, this thickness adds significant weight that must be supported, which adds to the overall expense of construction.