Oxidation-resistant metal coatings

#More particularly, there is disclosed catalytically-active surfaces, precursors thereof, and methods of preparing and using such surfaces, e.g. in the preparation of metal-coated fibers and films and in methods of making and using such fibers and films.

#Methods of preparing metal-coated articles are known. For instance, Orban in U.S. Pat. No. 4,645,573 discloses continuous processes for coating polyester filaments with copper and silver involving, as illustrated in FIG. 1A, a plurality of steps, including cleaning, wetting and etching of the filament prior to contacting with commercial palladium chloride/stannous chloride catalytic activator, followed by an acid bath, electroless copper plating, copper cyanide plating and silver cyanide plating. See also U.S. Pat. No. 4,645,574 where Orban discloses continuous processes for coating polyamide filaments which as illustrated in FIG. 1B requires the use of a preactivator. Matijevic et al. in a paper entitled: "The Characterization of the Stannous Chloride/Palladium Chloride Catalysts for Electroless Plating", Plating And Surface Finishing, Oct. 1975, p.958, indicate that colloidal palladium is necessary for catalytic activity and that solutions of palladium complexes do not act as catalysts.

#In view of methods disclosed in the prior art, e.g. as illustrated by Orban and Matijevic et al., one object of this invention is to provide simpler methods for the metal coating of articles, e.g. filaments, with fewer required process steps and the common intermediate washing steps that generate waste disposal problems. It is a further object of this invention to provide such articles with an oxidation-resistant, electrolessly-deposited copper coating that requires the additional treatment of electrodeposition to provide oxidation resistance.

#FIGS. 1A and 1B are schematic illustrations of flow charts of processes for metal coating of filaments according to the prior art, i.e. Orban as discussed above.

#FIG. 2 is a schematic illustration of an embodiment of a process of this invention for coating fibers with metal coatings.

#FIGS. 3 is a transmission electron micrograph (TEM) of an electrolessly-deposited copper coating prepared according to prior art procedures set forth in Comparative Example 5.

#Metal-coated articles are provided by the methods of this invention using solutions comprising low levels of catalytic compounds. As used herein the term "catalytic" is intended to refer to Group 1B or Group 8 elements. In certain preferred aspects of the inventions the catalytic element will be palladium, platinum, iridium, gold, rhodium or ruthenium. In many more-preferred aspects of the inventions the catalytic element will be palladium.

#Useful articles which provide substrates for such metal-coatings can comprise any of a variety of formed shapes, e.g. fibers, thin films, thick sheets, rods, spheres, extruded shapes, fabrics, containers and so forth. Such substrates can also comprise a variety of materials of construction, including organic materials such as natural or synthetic polymers or composites such as cellulose, wood, polyester, etc. or inorganic materials such as ceramics, glass, alumino-silicates, etc. In certain preferred aspects of this invention the substrates comprise films or fibers, e.g. organic or inorganic fibers which are monofilament or multifilament, e.g. a yarn or tow. Useful inorganic fibers can comprise glass, alumina, phosphate and the like; while useful organic fibers can comprise cellulose and its derivatives such as rayon, polyamides such as nylon 6, nylon 6,6 and the like, polyesters such as PET, polyolefins such as polyethylene, polypropylene and the like, acrylics such as acrylonitrile polymers and copolymers, polysulfones, polyimides, etc. Such exemplary materials for fibers can also be useful in substrates of other shapes.

#Because substrate surfaces are often coated with materials such as lubricants or other processing aids which hinder the adhesion of catalyst materials, it is often necessary to initially remove such materials by washing with detergent or other cleaning solutions, e.g. comprising volatile organic solvents. A particularly useful cleaning solution for cleaning polymeric substrates has been found to comprise acidified alcohol, e.g. muriatic acid-containing methanol. If necessary the cleaner can be rinsed from the substrate, e.g. with water. Such water-wetted substrate can be directly immersed in a solution of catalytic compound. In the case of volatile cleaners such rinsing is often not necessary. For instance, cleaning solvent-wetted substrates can be dried in a warm air stream, then immersed in a solution of catalytic element.