To provide a method of producing a uniaxially stretched
polytetrafluoroethylene gasket tape, which comprises: (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 the paste by means of an extruder equipped with a die which has
plural separators inside an orifice thereof having a rectangular cross
section, (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 obtained uniaxially stretched polytetrafluoroethylene
sheet. The die of the extruder has plural sheet-like separators in the
orifice thereof having a rectangular cross section. The separators are
mounted so that free ends thereof are located at a point exceeding a
center point of a long side of the orifice, and function to provide slit
lines inside the extrudate in parallel with the long side of the orifice.
The high performance inexpensive PTFE gasket tape is produced by the
uniaxially stretching method and has properties equal to those of
biaxially stretched PTFE gasket tape.
