Microporous polyethylene film through liquid-liquid phase separation mechanism and preparing method thereof
First Claim
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1. A method of manufacture of a microporous polyethylene film comprising the steps of:
- melt-extruding a resin mixture, containing 20-55 weight % of polyethylene (component I) and 80-45 weight % of a diluent (component II) characterized by liquid-liquid phase separation from the above component I at 160-280°
C., at a temperature higher than the temperature of liquid-liquid phase separation to make a thermodynamic single phase in an extruder;
extruding the above single-phase molten material through dies by progressing liquid-liquid phase separation by passing it through a zone controlled to be in a temperature range of liquid-liquid phase separation;
molding the molten material extruded as liquid-liquid phase separation is progressed in the form of a sheet;
stretching the above sheet to have a ratio of stretching of 4 times or greater each in the machine and traverse directions and the total ratio of stretching of 25-50 times in the sequential or simultaneous stretching method including the roll or tenter method;
extracting component II from the stretched film and drying it; and
heat-setting the dried film by removing its residual stress to have a ratio of shrinkage of the film in each of the machine and traverse directions of 5% or less.
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Abstract
Disclosed in the present invention are a microporous polyethylene film and a method of manufacture thereof. The polyethylene microporous film manufactured according to the present invention may contribute to an increased productivity of stable products as its extrusion and stretching may be done readily. And thus manufactured product may be used for battery separators and various filters owing to its high gas permeability, superior puncture strength, and small ratio of shrinkage.
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Citations
15 Claims
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1. A method of manufacture of a microporous polyethylene film comprising the steps of:
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melt-extruding a resin mixture, containing 20-55 weight % of polyethylene (component I) and 80-45 weight % of a diluent (component II) characterized by liquid-liquid phase separation from the above component I at 160-280°
C., at a temperature higher than the temperature of liquid-liquid phase separation to make a thermodynamic single phase in an extruder;
extruding the above single-phase molten material through dies by progressing liquid-liquid phase separation by passing it through a zone controlled to be in a temperature range of liquid-liquid phase separation;
molding the molten material extruded as liquid-liquid phase separation is progressed in the form of a sheet;
stretching the above sheet to have a ratio of stretching of 4 times or greater each in the machine and traverse directions and the total ratio of stretching of 25-50 times in the sequential or simultaneous stretching method including the roll or tenter method;
extracting component II from the stretched film and drying it; and
heat-setting the dried film by removing its residual stress to have a ratio of shrinkage of the film in each of the machine and traverse directions of 5% or less. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification