Toray Battery Separator Film Co., Ltd.

Tonen Chemical Corporation

Soichiro Yamaguchi

Kotaro Takita

Norimitsu Kaimai

Koichi Kono

Tetsuro Nogata

The invention relates to a twin screw extruder for preparing a polymeric solution. The extruder includes an elongated housing having an inlet end, an outlet end, an extruder shaft length L and a pair of interconnecting bores disposed within the housing, a pair of elongated extruder shafts, each having an axis of rotation, the pair of elongated extruder shafts disposed within the pair of interconnecting bores and drivable in at least one direction of rotation, a plurality of extruder screw segments positioned along the pair of elongated extruder shafts in a fixed angular relationship therewith, the plurality of extruder screw segments selected to form multiple extruder stages. The invention also relates to a process for extruding a mixture of polymer and diluent.

Extruder and process for preparing a mixture of polymer and diluent

A microporous polyolefin composite membrane, preferably for use as a battery separator, comprising a microporous polyolefin membrane and a polyolefin nonwoven fabric laminated on at least one surface of the microporous polyolefin membrane. The composite membrane has a thickness of 25 to 200 .mu.m, a porosity of 30 to 70%, an air permeability of 100 to 2000 sec/100 cc and a surface opening area ratio of 50 to 90% on at least one outer surface thereof. The microporous polyolefin membrane comprises a matrix polyolefin component which is a polyolefin having a weight average molecular weight of 5.times.10.sup.5 or more or a polyolefin mixture containing the polyolefin having a weight average molecular weight of 5.times.10.sup.5 or more, and has a porosity of 30 to 95%, an air permeability of 100 to 2000 sec/100 cc, an average open pore diameter of 0.001 to 1 .mu.m and a tensile strength at break of 500 kg/cm.sup.2 or more. The microporous polyolefin membrane may further comprise a shutdown polymer component to shut down the pores, thereby making the composite membrane impermeable. The polyolefin nonwoven fabric comprises fine fibers and has an air permeability of 0.1 to 100 sec/100 cc and a basis weight of 5 to 50 g/m.sup.2. The polyolefin nonwoven fabric prevents the composite membrane from melting down at a low temperature thereby preventing the short-circuit between the electrodes.

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Kanagawa, Japan

Soichiro Yamaguchi