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Puncture-resistant polyolefin membranes

  • US 6,096,213 A
  • Filed: 08/14/1998
  • Issued: 08/01/2000
  • Est. Priority Date: 08/14/1998
  • Status: Expired due to Term
First Claim
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1. A method of making microporous material, comprising:

  • (a) melt blending to form a substantially homogeneous mixture comprising;

    (i) from about 25 to about 60 parts by weight of a melt-processable semi-crystalline thermoplastic polymer component; and

    (ii) from about 40 to about 75 parts by weight of a second component comprising either (1) a compound that is miscible with the thermoplastic polymer component at a temperature above the melting temperature of the thermoplastic polymer but the phase separates from the thermoplastic polymer component when cooled below the crystallization temperature of the thermoplastic polymer component or (2) a compatible liquid that is miscible with the thermoplastic polymer component at a temperature above the liquid-liquid phase separation temperature but that phase separates from the thermoplastic polymer component when cooled;

    (b) forming shaped material of the melt blended mixture;

    (c) cooling the shaped material to a temperature at which phase separation occurs between the compound or compatible liquid and the thermoplastic polymer component through crystallization precipitation of the thermoplastic polymer component; and

    (d) stretching the shaped material in at least two perpendicular directions to an area expansion ratio of greater than nine and provide a network of interconnected pores;

    (e) then removing the compound to provide a microporous material having a puncture resistance of at least 350 g/25 microns;

    wherein said melt-processable thermoplastic polymer component is selected from the group consisting of polypropylene, ethylene vinyl alcohol copolymer, poly (ethylene chlorotrifluoroethylene), polyvinylidene fluoride, polymethylpentane poly(vinyl fluoride), polyoxymethylene, poly(ethylene oxide), and compatible blends thereof.

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