Abstract: The present invention relates to a porous or microporous film of a high molecular weight polyolefin excellent in strength and air-permeability and suitable for use in filtering materials, separators for aqueous electrolyte batteries, separator films for batteries, separator films for electrolytic capacitors, and air-permeable films; for moisture-permeable water-proof use such as paper diapers and house-wrapping films; and for other uses such as cloths, package and printing, as well as a process for producing same. The feature of the present invention resides in an aspect that the film is composed of fibrils comprising extended-chain crystals and lamellar crystals and/or fibrils comprising helicoidal crystals.This porous film of a high molecular weight polyolefin is produced by subjecting an air-impermeable film of a high molecular weight polyolefin to thermal treatment followed by, if necessary, a stretching treatment and/or a thermosetting treatment.

Abstract: A process for producing a porous film of polypropylene comprises subjecting (1) an air-impermeable biaxially stretched film of polypropylene resin comprised predominantly of polypropylene having a crystallinity of at least 40% or (2) an air-impermeable inflation film of polypropylene resin comprised predominantly of polypropylene having a crystallinity of at least 46.5%, in the substantial absence of a plasticizer or a solvent, to a thermal treatment in the presence of a first liquid substantially incapable of dissolving the film while fixing the film in two orthogonal directions for making the film porous.

Abstract: A porous biaxially oriented film comprising a copolymer of an ethylene having an intrinsic viscosity ?.eta.! of from 3.5 to 10.0 dl/g and an .alpha.-olefin having 4 to 8 carbon atoms, the content of the .alpha.-olefin being in a number of from 1.0 to 7.5 per 1000 carbon atoms and the film retaining the structure which is based upon the microfibrils when it is heat-treated at 160.degree. C. under a constrained state and is then observed at room temperature, and a separator made of this film for batteries. The porous biaxially oriented film exhibits excellent gas permeating property over a practicable temperature range, exhibits excellent mechanical strength and, particularly, tensile strength, and loses gas permeating property when a maximum practicable temperature is exceeded. The film can be favorably used as a separator for batteries.

Abstract: A microporous film of high molecular weight polyolefin useful in the prepration of filter mediums or non-aqueous battery separators and a process for producing the film are disclosed. The microporous film of high molecular weight polyolefin contains leaf vein-like fibrils as a main constituent on each of which fibrils indeterminate-form crystallites of not more than 1 .mu.m in size flocculate and has an intrinsic viscosity, ?.eta.!, of 4 dl/g or more and, preferably, has:(a) a void content of 25% or more;(b) a gas permeability of 1900 sec/100 cc or less;(c) a tensile strength of 0.05 GPa or more; and(d) a gas impermeability-acquiring temperature of 140.degree. C. or lower. The microporous film is produced by subjecting a high molecular weight, biaxially oriented polyolefin film of 60% or more in crystallinity to a heat treatment and, if necessary, to a stretch treatment to thereby melt or dissolve the indeterminate-form portion of the film, then crystallizing it onto the fibrils as crystallites.

Abstract: Biaxially oriented films from high molecular weight polyethylene are characterized by a gas permeable structure formed from random-arranged microfibrils. The films have coefficients of static friction and kinetic friction of not more than 1.0. The biaxially oriented films are further characterized by service smoothness as well as tensile (tangent) modulus and tensile strength. The films may be used for lamination, filter, or for packaging for moisture absorbers. The biaxially oriented films may be obtained by extracting a hydrocarbon plasticizer from a sheet formed from the high molecular weight polyethylene and a hydrocarbon plasticizer, stretching the resulting sheet to obtain an oriented film having a specific surface area of at least 70 m.sup.2 /g and a fibril structure, and heating the oriented film under a standard length constraint to reduce the oriented film in specific area by at least 20 m.sup.2 /g.

Abstract: Biaxially oriented films from high molecular weight polyethylene are characterized by a gas permeable structure formed from random-arranged microfibrils. The films have coefficients of static friction and kinetic friction of not more than 1.0. The biaxially oriented films are further characterized by service smoothness as well as tensile (tangent) modulus and tensile strength. The films may be used for lamination, filter, or for packaging for moisture absorbers. The biaxially oriented films may be obtained by extracting a hydrocarbon plasticizer from a sheet formed from the high molecular weight polyethylene and a hydrocarbon plasticizer, stretching the resulting sheet to obtain an oriented film having a specific surface area of at least 70 m.sup.2 /g and a fibril structure, and heating the oriented film under a standard length constraint to reduce the oriented film in specific area by at least 20 m.sup.2 /g.

Abstract: Biaxially oriented films from high molecular weight polyethylene are characterized by a gas permeable structure formed from random-arranged microfibrils. The films have coefficients of static friction and kinetic friction of not more than 1.0. The biaxially oriented films are further characterized by service smoothness as well as tensile (tangent) modulus and tensile strength. The films may be used for lamination, filter, or for packaging for moisture absorbers. The biaxially oriented films may be obtained by extracting a hydrocarbon plasticizer from a sheet formed from the high molecular weight polyethylene and a hydrocarbon plasticizer, stretching the resulting sheet to obtain an oriented film having a specific surface area of at least 70 m.sup.2 /g and a fibril structure, and heating the oriented film under a standard length constraint to reduce the oriented film in specific area by at least 20 m.sup.2 /g.

Abstract: The biaxially oriented films of high molecular weight polyethylene is formed and its surface modified to provide a hydrophilic property to the resulting film. The film is prepared by melt-kneading the high molecular weight polyethylene with an ordinarily solid hydrocarbon plasticizer and a raw fabric sheet is formed from the resulting molten mixture. After the hydrocarbon plasticizer is extracted the resulting unstretched sheet is stretched under conditions providing a stretched film having a specific surface area of 70 m.sup.2 /g or more and a fibril structure. This stretched film is then heated under standard length constraint conditions to reduce the specific surface area of the stretched film by at least 20 m.sup.2 /g to obtain a biaxially oriented film of high molecular weight polyethylene.