(US4613441-A)      Thermoplastic resin porous membrane is formed of resin having critical surface tension of 20-33 dyn/cm and having 3 dimensional network structure. Communicating pores having average pore dia. 0.1-2.0 micron are formed providing porosity of at least 60%.    The membrane has strength factor F, defined by F=A/(B(1-a)) of at least 1 measured in any direction; modulus factor F', defined by F=C/(D(1-a)) of at least 0.2 measured in any direction; max. pore dia. up to 3.25 times the average pore dia.; and thickness 5-500 micron. In the formulae, A is the tensile strength at break of the porous membrane and B the corresp. value for a non-porous film of the same resin. C is the tensile stress of the porous membrane at 5% deformation, and D the corresp. value for a non-porous film of the same resin. A is the porosity fraction of the membrane.    USE/ADVANTAGE -   The membrane is soft and excellent in water entry pressure, air permeability and oil permeability. It has good mechanical strength and dimensional stability. It can be used e.g. as an oil filter or a filter sepg. water from a gas or oil. (11pp)r    (DE3118924-C)      A porous membrane, 5-500 microns thick, having a critical surface tension not more than 35 mN/m and a 3-dimensional mesh-work structure, contg. interconnected pores of pore size 0.1-20 microns and a porosity at least 60%, is produced by a space drawing operation of a porous membrane made of a thermoplastic resin contg. interconnected pores of pore size 0.05-1 microns and having a porosity 30-70%. The drawing operation is carried out in at least 1 direction at a temp. 50-5 deg.C below the m.pt. or softening point of the resin.    The strength factor S of the membrane as defined by S=A/ (B(1-a)) is at least 1 and the modulus factor S' as defined by C/(D(1-a)) is at least 0.2, where A is the tear strength of the porous membrane, B is the tear strength of a non-porous film of the same resin, C is the tensile stress for the porous membrane and D is the tensile strength of a non-porous film of the same resin with both measured at a deformation of 5%, a is the porosity fraction of the porous membrane measured in all directions. The deformation of the membrane measured after being acted on by a tensile stress of 5% of the tear strength for 100 hrs. at 20 deg.C is not more than 15%. The permanent deformation after relief of the mentioned tensile stress is not greater than 5%.    The area shrinkage of the porous membrane at a temp. 50 deg.C below the m.pt. of softening point of the resin is pref. below 5%. The resin is high desnity polyethylene, polypropylene, polyvinylidene fluoride or a C2H4/C2F4 copolymer.    USE/ADVANTAGE -   Membrane can be used as microfilter; for sepn. of blood, as separator in an alkaline battery; the membranes have a high porosity combined with softness and an outstanding water input press property, air permeability, oil permeability as well as good mechanical strength and dimensional stability; the membranes are resistant to rotting and chemicals. (14pp)