Disclosed is a method for producing a laminated porous polyolefin film, the method comprising steps of: providing a pair of tools for thermocompression bonding two resin films therebetween, laminating two films each comprising at least one layer made of a polyolefin resin composition comprising 100 parts by weight of a polyolefin resin having a melt index of 0.1 g/10 min or less and 80 to 300 parts by weight of a filler to form a laminated film by piling and thermocompression bonding the films between the thermocompressing portions of the tools, wherein the surface temperature of each thermocompressing portion is adjusted to a temperature higher than the melting point of the polyolefin resin by from 5 to 25.degree. C. during the lamination, and drawing the laminated film to form micropores therein, thereby yielding a porous film.

 
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> Process for removal of impurities from mother liquor in the synthesis of carboxylic acid using pressure filtration

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