GB927582A - Foamed and drawn filaments and method for preparing same - Google Patents

Abstract

Foamed and drawn polyolefin filaments, having a density of 6-45 pounds per cubic foot, are made by extruding a mixture of a molten polyolefin and a foaming agent which is gaseous at the extrusion temperature. The filaments have a substantially smooth external surface and substantially greater strength than the filament before drawing, and are preferably drawn to a length ratio of 4:1 to 10:1. Suitable polyolefins are polymers or copolymers of ethylene, propylene, butene-1, hexene-1, octene-1, and particularly aliphatic mono-1-olefines having a maximum of 8 carbon atoms and no branches nearer the double bond than the 4 position. The preferred material is polyethylene having S.G. 0,95-0,98 and at least 70% crystallinity at 70 DEG F. The foaming agent (0,01 to 50% by weight of the polyolefin) may be gaseous, liquid or solid, provided that it or its decomposition products are gaseous at the extrusion temperature, usually 250 DEG -600 DEG F. Suitable foaming agents are nitrogen, steam, carbon dioxide, hydrocarbons, water, ammonia, p,p1-oxy-bis(benzenesulphonylhydrazide), diazoaminobenzene, dinitrosopentamethylene tetramine, 4-nitrobenzene sulphonic acid hydrazide, beta-naphthalene sulphonic acid hydrazide, diphenyl-4,41-di(sulphonyl azide) and mixtures of sodium bicarbonate and tartaric acid. Extrusion pressures may range from atmospheric to 700 or 800 p.s.i.g. In a preferred process, a heated extrusion device 10 is provided with hopper 12 and screw 14 fitted with hollow shaft 16 through which liquid or gaseous foaming agent may be admitted to molten polyolefin contained in 10. Solid foaming agent may be added to solid polyolefin prior to melting. The melt is extruded through orifices in die 24 to form filaments which are cooled by liquid coolant, e.g. water, in tank 30. Heat treatment in a steam cabinet 38 conditions the filaments for drawing by tension between rollers. Specification 790,195 is referred to.ALSO:Foamed and drawn polyolefin filaments, having a density of 6-45 pounds per cubic foot, are made by extruding a mixture of a molten polyolefin and a foaming agent which is gaseous at the extrusion temperature. The filaments have a substantially smooth external surface and substantially greater strength than the filament before drawing, and are preferably drawn to a length ratio of 4 : 1 to 10 : 1. Suitable polyolefins are polymers or co-polymers of ethylene, propylene, butene-1, hexene-1 octene-1, and particularly aliphatic mono-1-olefines having a maximum of 8 carbon atoms and no branches nearer the double bond than the 4 position. The preferred material is polyethylene having S.G. 0,95-0,98 and at least 70% crystallinity at 70 DEG F. The foaming agent (0,01 to 50% by weight of the polyolefin) may be gaseous, liquid or solid, provided that it or its decomposition products are gaseous at the extrusion temperature, usually 250-600 DEG F. Suitable foaming agents are nitrogen, steam, carbon dioxide, hydro-carbons, water, ammonia, p, p1-oxy-bis(benzenesulphonylhydrazide), diazoaminobenzene, dinitrosopentamethylene tetramine, 4-nitrobenzene sulphonic acid hydrazide, beta-naphthalene sulphonic acid hydrazide, diphenyl-4, 41-di(sulphonyl azide) and mixtures of sodium bicarbonate and tartaric acid. Extrusion pressures may range from atmospheric to 700 or 800 p.s.i.g. In a preferred process, a heated extrusion device 10 is provided with hopper 12 and screw 14 fitted with hollow shaft 16 through which liquid or gaseous foaming agent may be admitted to molten polyolefin contained in 10. Solid foaming agent may be added to solid polyolefin prior to melting. The melt is extruded through orifices in die 24 to form filaments which are cooled by liquid coolant e.g. water, in tank 30. Heat treatment in steam cabinet 38 conditions the filaments for drawing by tension between rollers. Specification 790,195 is referred to.