Importance

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Abstract

The invention offers a porous polytetrafluoroethylene membrane, which is a porous resin membrane produced by the following steps: preparing multiple types of polytetrafluoroethylene each having a different quantity of heat of fusion; using each of the multiple types of polytetrafluoroethylene to form a membrane composed of a fluororesin consisting mainly of polytetrafluoroethylene; heating each membrane to its melting point or above to bake it, so that multiple types of nonporous resin membranes are produced; stacking the multiple types of nonporous resin membranes in the order of the magnitude of the quantity of heat of fusion of the polytetrafluoroethylene used to produce each of the nonporous resin membranes; bonding the stacked membranes with each other; and stretching the bonded membranes to form the porous resin membrane. The porous polytetrafluoroethylene membrane has a mean flow pore diameter of 50 nm or less. It has through pores having a microscopic and uniform diameter, and when used as a filter, it has excellent efficiency in filtering treatment and is less likely to develop clogging. The invention also offers a composite of the membrane, a process of producing the composite, and a separation membrane element incorporating the composite as a filtering membrane.

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First Claim