| 摘要 |
1,126,849. Microporous olefin polymers. W. R. GRACE & CO. 19 May, 1967 [19 May, 1966], No. 23338/67. Addition to 1,051,320. Headings C3C and C3P. A process for making shaped articles of microporous cross-linked olefin polymers comprises forming a homogeneous mixture of a solid polyethylene, polypropylene or ethylene/vinyl copolymer and 20-400% (on the weight of polymer) of a pore-forming solid of particle diameter 0À1-10 microns, shaping the mixture at a temperature between the m.pt. of the polymer and the gelling pt. of the mixture, cross-linking the olefin polymer, removing the pore-forming solid and, necessarily when the polymer is ethylene, optionally when it is polypropylene or an ethylene/vinyl copolymer, orienting the shaped article. The cross-linking may be achieved by either generating freeradicals in situ, e.g. by heating 1,4-bis-(t-butylperoxyisopropyl) benzene, or by submitting the article to ionizing radiation. The orientation may be uniaxial or, preferably, biaxial and may be achieved by stretching the material at a temperature not more than 10‹ C. below the m.pt. of the polymer and under reduced pressure. The pore-forming solids preferred are sodium chloride, sodium carbonate, sodium benzoate, sodium acetate, silica gel, starch, benzoic acid, hydroquinone, dimethylterephthalate, anthracene, but cane-sugar is the most preferable. In the examples articles of polyethylene, polypropylene, ethylene-propylene, ethylene-vinyl acetate and ethylene-ethyl acrylate copolymers are produced.
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