Patent ID: 6702971
Filing Date: 2004-03-09
Classification: B29C,B29K,B29L

Abstract:
A method of producing a polytetrafluoroethylene sheet or film, in which the following steps (1) to (5) are carried out in that order:(1) a step for preparing a paste comprising a mixture of a polytetrafluoroethylene powder obtained by emulsion polymerization and an extrusion aid, (2) a step for extruding said paste by means of an extruder equipped with a die having an orifice which has a rectangular cross section and is provided with plural separators inside thereof, (3) a step for rolling, in the extruding direction, an extrudate having slit lines to give a rolled polytetrafluoroethylene sheet, (4) a step for uniaxially stretching the rolled sheet in the rolling direction after removing the extrusion aid from the rolled sheet, and (5) a step for heat-treating the uniaxially stretched polytetrafluoroethylene sheet at a temperature within a range of 340Â° to 380Â° C., wherein the die of the extruder is provided with a plurality of sheet-like separators in the orifice having a rectangular cross section in parallel with a long side of the orifice, and the plural separators are mounted so that any of free ends of the separators is located at a point exceeding a center point of the long side of the orifice and function to slit the inside of the extrudate in parallel with the long side of the orifice.