Process for producing micro-porous membrane of ultra-high-molecular-weight alpha-olefin polymer, micro-porous membranes and process for producing film of ultra-high-molecular-weight alpha-olefin polymer

A process for producing a micro-porous membrane of ultra-high-molecular-weight alpha-olefin polymer which comprises the steps of:

• (A) forming a gel-like object from a solution of an alpha-olefin polymer having a weight-average molecular weight of about 5.times.10.sup.5 or greater,
• (B) removing at least 10 wt. % of the solvent contained in the gel-like object so that the gel-like object contains 10 to 90 wt. % of the alpha-olefin polymer,
• (C) biaxially orientating the gel-like object obtained from step (B) at a temperature lower than that which is 10.degree. C. above the melting point of the alpha-olefin polymer and at a linear draw ratio greater than 2 and an areal draw ratio greater than 10, and
• (D) removing the residual solvent from the orientated product thereby obtaining a micro-porous membrane having a void ratio of 30 to 90%.

A process for producing film of ultra-high-molecular-weight alpha-olefin polymer which comprises the steps of:

• (A) forming a gel-like object from a solution of an alpha-olefin polymer having a weight-average molecular weight of about 5.times.105 or greater,
• (B) removing at least 10 wt. % of the solvent contained in the gel-like object so that the gel-like object contains 10 to 90 wt. % of the alpha-olefin polymer,
• (C) biaxially orientating the gel-like object at a temperature lower than that which is 10.degree. C. above the melting point of the alpha-olefin polymer at a linar draw ratio greater than 2 and an areal draw ratio greater than 10,
• (D) removing the residual solvent from the orientated product thereby obtaining a micro-porous membrane having a void ratio of 30 to 90%, and
• (E) pressing the orientated product at a temperature lower than the melting point of the alpha-olefin polymer.