Patent GB-686438-A (GB)
Title: Extrusion of tetrafluoroethylene polymer
IPC: B29C48/05
Filed: 1951-06-01
Abstract: A composition containing tetrafluoroethylene polymer particles of colloidal size mixed with a lubricant having a viscosity of at least 0.45 centipoise at 25 DEG  C. is extruded through a die at a temperature of 15 DEG  to 150 DEG  C.  The lubricant is liquid under the extrusion conditions and is present in an amount from 5 to 50 per cent by weght of the composition.  The extruded article, e.g. a sheet, rod, tube, filament or coating, is then baked at a temperature above the sintering temperature of the polymer.  The baking may be followed either by quenching in water or other coolant liquids or gases or by annealing.  When forming a tape, it may be passed between hot rollers after leaving the baking oven. The tetrafluoroethylene polymer may be polytetrafluoroethylene, in which the end groups of the polymer chain may be supplied by non-polymerizable compounds, e.g. methanol and ethanol or a copolymer of tetrafluoroethylene and another monomer, e.g. ethylene and chlorotrifluoroethylene.  An aqueous polymer suspension may be prepared by polymerizing tetrafluoroethylene at 0 DEG  to 100 DEG  C. in an aqueous medium in the presence of a water-soluble polymerization catalyst such as disuccinic acid peroxide and an alkali metal or ammonium salt of an acid of the formula H(CF2CF2)3-10COOH.  The lubricant may be a silicone oil such as polymethylsiloxane, and poly-(methyl, phenyl) siloxane; esters such as methyl benzoate, butyl acetate, dibutyl phthalate, and tricresyl phosphate; naturally occurring low-melting waxes; nuclear-chlorinated aromatic compounds such as chlorinated benzenes, naphthalenes, biphenyls, and phenols or di-n-propyl tetrachlorophthalate, methyl tetrachlorobenzoate, and chlorinated paraffins; fluorinated hydrocarbon oils; alcohols such as tertiary butanol; ethers such as methyl phenyl ether (anisole); amines; ketones; essentially saturated aliphatic and cycloaliphatic hydrocarbons such as n-octane, n-nonane, n-decane, 2 - methyl - decane, n - eicosane, petrolatum, paraffin waxes, and mixtures of two or more such hydrocarbons; aromatic hydrocarbons such as benzene, toluene, isomeric xylenes, tetrahydronaphthalene, decahydronaphthalene; and naturally occurring and/or synthetic mixtures of two or more of such lubricants.  The lubricant may be removed, prior to baking, by heating to volatilize the lubricant or by passing through a bath of solvent such as hexane, naphtha or toluene.  Fillers and pigments, e.g. carbon black, graphite, mica, talc, silica asbestos, and titanium dioxide, dyes, other lubricants, stabilizers, and plasticizers may be added to the composition.  In an example, an aqueous suspension of polytetrafluoroethylene is diluted with distilled water, petrolatum added and the mixture is whipped. Coagulation is effected by addition of aqueous acetone with agitation, and the lubricated polymer is filtered and dried at 110 DEG  C.ALSO:A composition containing tetrafluoroethylene polymer particles of colloidal size mixed with a lubricant having a viscosity of at least .45 centipoise at 25 DEG  C. is extruded through a die at a temperature of 15 DEG  to 150 DEG C.  The lubricant is liquid under the extrusion conditions and is present in amount from 5 to 50 per cent by weight of the composition.  The extruded article is then baked at a temperature above the sintering temperature of the polymer.  The baking may be followed either by quenching in water or other coolant liquids or gases or by annealing.  The lubricant may be removed prior to baking by heating the article to volatilize the lubricant or by passing the article through a bath of solvent or by evacuation under reduced temperatures.  When forming a tape, it may be passed between hot rollers after leaving the baking oven.  To form a coating on a wire, the composition is pressed into a cylindrical preform having a longitudinal hole. The preform is placed in an extrusion cylinder, and the wire to be covered is passed through the extrusion piston, the preform and the die assembly.  The composition is then extruded around wire. The wire may be precoated, spirally wrapped or braided, and several wires may be coated in one operation by using several dies.  The composition may also include fillers, pigments, dyes, other lubricants, stabilizers or plasticizers.  Two wires covered with polytetrafluoroethylene may be joined together by wrapping adjacent sections with extruded, unsintered, polytetrafluoroethylene tape and then heating the tape to sinter it.