Improvements in felt-like polytetrafluoroethylene products and their production

摘要

836,678. Paper &c. containing polytetrafluoroethylene filaments. DU PONT DE NEMOURS & CO., E.T. May 2, 1958 [May 2, 1957], No. 14124/58. Class 96. Felt-like sheets or moulded articles &c. are formed, e.g. on a conventional paper-making machine &c. from at least 10% of polytetrafluoroethylene filaments less than 1.0 inch long and up to 90% of non-fibrous heat-resistant particles of diameters between 25 and 500 microns. The products which may be felt-like, are of high electrical, chemical and heat resistance. They may be used as gaskets, or for filtering corrosive liquids &c. The filaments may be extruded as rods or tubes 1/ 16 to 1/ 8 inch diameter and worked to fine filaments in a hammer-mill or shredder &c. and formed as suspension, of up to 10% solids, with the particles which may be of ground glass, glass beads or microballoons, diatomaceous earth, rock, or metal. The suspension may include wetting agents, e.g. octylphenyl polyglycol ether, sodium lauryl sulphate, or polyoxyethylene or -propylene, or thickeners, e.g. carboxymethyl cellulose or its sodium salt, polyvinyl alcohol, sodium, potassium or ammonium alginates or polyacrylates, or antifoamants, e.g. ethyl acetate. The products may be heated above 621‹ F. to fuse the P.T.F.E. filaments at their intersections; they may be embossed; and may be treated with a wetting agent and impregnated with an aqueous dispersion of P.T.F.E. The suspension may be deposited on an open mesh steel or glass fabric laid on the wire-cloth &c., and the web &c. turned over, a second web being deposited thereon, so that the reinforcing steel or glass is embedded in the composite web which is dried and fused. Specification 781,512 is referred to.