Coatings for Metal Surfaces

Abstract

An iron-containing metal surface, such as a brushed stainless steel, comprises a heat-set layer of a metal phosphate reaction product formed between a surface metal and phosphate precursor wherein the reaction product layer has an average thickness less than 2 micrometers. A metal surface, that resists retention of environmental stains or marks as well as resisting tarnish at elevated temperatures, is formed by forming a reaction product with the metal surface by heat setting a surface liquid layer containing a phosphate precursor such as a phosphate ester-containing solution or phosphoric acid solution, and optionally containing a phospho alumina precursor, onto the metal surface. An article coated in accordance with this invention is similar in appearance to a similar article without such a coating for maintaining original aesthetic properties.

Description

CROSS-REFERENCE To RELATED APPLICATIONS[0001]This application claims priority to U.S. patent application Ser. No. 14 / 124,895, filed Dec. 9, 2013, which is a U.S. National Phase of PCT / US2012 / 050826, filed Aug. 14, 2012, which claims priority to U.S. Provisional Patent Application 61 / 523,946, filed Aug. 16, 2011, and to U.S. Provisional Patent Application 61 / 562,637, filed Nov. 22, 2011, each incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]This invention relates to inorganic protective systems for iron-containing metal substrates and more particularly relates to protective fillers or coatings applied to metal substrates particularly with heterogeneous surface microstructure, such as in brushed metal substrate surfaces, to inhibit fingerprint and stain retention, impart tarnish protection, be easy to clean, and maintain surface appearance.[0003]Common metal surfaces, such as brushed surfaces, may be subject to exposure with materials that leave lasting marks on the s...

AI Technical Summary

Benefits of technology

This patent describes a method for creating a metal surface that is resistant to staining and tarnish. The method involves heating a metal surface and applying a liquid layer containing phosphate precursors and optionally phospho alumina precursors. The resulting layer is less than 2 micrometers thick and helps maintain the metal surface's original appearance.

Problems solved by technology

Common metal surfaces, such as brushed surfaces, may be subject to exposure with materials that leave lasting marks on the surface.

Although fingerprint or stain resistant coatings are known, especially organic or polymeric coatings, such coated surfaces typically are soft, not uv resistant, not organic solvent resistant, and not tarnish resistant at elevated temperatures.

Further, polymeric coatings (such as may be applied to consumer appliances) may have a noticeable thickness and have poor aesthetics.

These valleys may be primarily responsible for poor fingerprint resistance and staining under common household use along with the need to use of aggressive and environmentally hazardous cleaning agents to remove them.

Thus, certain stainless finishes are more susceptible to such degradation in the valleys.

These valleys are chemically complex and are readily susceptible to oxidation or corrosion.

Organic (or substantially organic) fillers such as polymeric materials (including polymer-silica hybrids) are typical and used extensively in commercial brushed stainless steel appliances, but their durability and inertness for common use is limited, and in particular they are susceptible to attack under uv radiation, which limits their use in outdoor applications, and to organic cleaning solvents such as ketones.

Further, polymeric-based coatings may alter the surface appearance to form a duller or unattractive plastic-like appearance.