Process for thermally spraying porous metal coatings on substrates

Abstract

A process for forming a substantially planar porous metal coating on a substrate which comprises thermal spraying of the metal on the substrate to form a porous metal coating on the substrate, rolling the sprayed coating to render it substantially planar and in the process close the pores, and then removing part of the surface to improve planarity and to reopen the surface-connected pores of the surface. The metal to be sprayed may be in the form of a wire, powder or molten metal mass and be selected from the group consisting of aluminum, zinc, tin, copper, nickel, or their alloys. Preferably, the substrate is selected from the group consisting of steel, aluminum, aluminized or galvanized steel, tin plate, and plastic. The spraying is preferably conducted in a non-oxidizing or reducing atmosphere. Preferably, the coating on the substrate is subjected to cold rolling. Most preferably, the rolling is conducted so as to reduce the coating thickness to approximately half of its original thickness. The coated substrates are useful for a number of purposes, particularly where the substrate metal would not be useful by itself because it does not have the proper physical or chemical properties. The substantially planar porous metal coated substrates are particularly desirable for subsequent coating with other materials, especially organic coatings, because of the 'tooth' for the coating provided by the pores of the metal coating on the substrate. The substantially planar porous metal coated substrates of the invention are particularly suited as the base for either a presensitized or 'wipe-on' lithographic printing plate.