Porous membrane with low steam permeability

摘要

This invention relates to the field of producing membranes for dry metal-air chemical current sources which should possess a high oxygen permeability and provide at the same time high barrier properties towards steam. The authors proposed semipermeable porous asymmetric membranes based on copolymer of vinylidene fluoride with tetrafluoroethylene at 8 - 70% mass content of tetrafluoroethylene the pore size of which is 0.0015 - 0.030 mu m, and the volume porosity is within 35 - 60% range. Such membranes are characterized by oxygen permeability not less than 2.70 m<3>/m<2> atm h, and steam permeability not more than 0.178 mg/h.cm<2>. In order to improve stability it is possible to cover membranes additionally on the more dense side with a layer of hydrophobic film-forming polymer (polydimethylsiloxane, polyvinyltrimethylsilane, polytrimethylsilylpropyne, polyvinylidene fluoride or its copolymer with tetrafluoroethylene) at the surface coating density of not more than 5 g/m<2>. Moreover, in order to improve the strength they may additionally include a large-pore fibrous support of polypropylene or polyamide at mass ratio of the fibrous support and fluoropolymer membrane layer 1:(0.3 - 1.5).