Biaxially oriented membranes from double layer, oil filled sheets
AssigneeAmtek Research International LLC
InventorsRichard W. Pekala, Don Spitz, Weston J. Wood
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Abstract
The present disclosure relates to a process for the formation of freestanding, biaxially-oriented, microporous polyolefin films. In this approach, at least two separate oil-filled, cast or calendered films are stacked on top of each other and then subjected to biaxial orientation, followed by solvent extraction of the process oil (i.e., plasticizer), evaporation of the solvent, and heat stabilization prior to separation into individual microporous membranes that are wound into rolls.
Claims20
A method of producing a freestanding, biaxially-oriented, microporous polyolefin membrane comprising the steps of:
- (a) preparing a composition comprising one or more polyolefins and a process oil, wherein the lowest molecular weight polyolefin component is greater than 300,000 g/mol,
- (b) passing the composition through a twin screw extruder and sheet die to form a cast oil-filled sheet,
- (c) stacking at least two layers of the oil-filled sheet on top of each other so that they can undergo biaxial orientation together without sticking to each other,
- (d) removing the process oil from the at least two oil-filled sheets with a solvent,
- (e) drying the solvent to form at least two microporous polyolefin membranes, and
- (f) heat stabilizing the at least two microporous polyolefin membranes to relieve residual stress prior to separating the two microporous polyolefin membranes and winding them into roll form.
A method of producing a freestanding, biaxially-oriented, microporous polyolefin membrane comprising the steps of:
- (a) preparing a composition comprising one or more polyolefins and a process oil, wherein the lowest molecular weight polyolefin component is greater than 300,000 g/mol,
- (b) passing the composition through a twin screw extruder and sheet die to form a cast oil-filled sheet,
- (c) stacking at least two layers of the oil-filled sheet on top of each other so that they can undergo biaxial orientation together without sticking to each other, wherein each of the at least two layers of the oil-filled sheet is subjected to biaxial orientation from 4 to 12 times in the machine direction and from 4 to 12 times in the transverse direction, and wherein the biaxial orientation occurs at a temperature of 60° C. and 100° C.,
- (d) removing the process oil from the at least two oil-filled sheets with a solvent,
- (e) drying the solvent to form at least two microporous polyolefin membranes, and
- (f) heat stabilizing the at least two microporous polyolefin membranes to relieve residual stress prior to separating the two microporous polyolefin membranes and winding them into roll form.
Dependencies are inferred from the claim text.