Composite porous membrane, method for producing composite porous membrane, and battery separator using the composite porous membrane

Abstract

Disclosed is a composite porous membrane which can achieve both an excellent adhesiveness of a heat-resistant resin layer and a small rise in gas permeation resistance even in the case of further reducing the thickness of membranes to be used, for example, battery separators. Specifically disclosed is a composite porous membrane comprising a porous membrane (A) formed of a polyolefin-based resin and a porous membrane (B) containing a heat-resistant resin, said porous membrane (B) being laminated on said porous membrane (A), wherein said porous membrane (A) has a thickness being within a specific range, an average pore size being within a specific range and a porosity being within a specific range and the thickness of the entire composite porous membrane is within a specific range, characterized in that, in said composite porous membrane, the peel strength at the interface between the specific porous membrane (A) and porous membrane (B) is within a specific range and the difference between the gas permeation resistance of the entire composite porous membrane and the gas permeation resistance of the porous membrane (A) is also within a specific range.

Description

technical field [0001] The present invention relates to a composite porous membrane in which a porous membrane comprising a heat-resistant resin is laminated on a porous membrane formed of a polyolefin resin, and particularly relates to a polyolefin-based porous membrane having excellent ion permeability and a heat-resistant It is a composite porous membrane useful as a lithium-ion battery separator because of its excellent adhesion to a permanent resin film. Background technique [0002] Porous membranes made of thermoplastic resins are widely used as materials for separation, selective permeation and isolation of substances, and the like. For example, battery separators used in lithium secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, separators for electric double layer capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, precision filtration membranes, etc. Used in various filters, moisture-permeable wat...

AI Technical Summary

Problems solved by technology

[0013] In Patent Document 5, although the air permeability resistance does not increase significantly, the adhesion between the polyethylene porous film and the heat-resistant resin is extremely small. Like Patent Document 4, especially when the thickness of the polyethylene porous film is less than In the case of 10 μm, the heat-resistant resin layer may peel off, making it difficult to ensure safety

[0014] In this way, in a composite porous membrane in which a heat-resistant resin layer is laminated on a porous membrane of polyolefin or the like used as a base material, if the heat-resistant resin is intended to permeate into the porous membrane used as a base material to improve the If the adhesion of the heat-resistant resin layer increases, the increase in air resistance increases. If the penetration of the heat-resistant resin is reduced, the increase in air resistance can be suppressed to a small extent, but the adhesion of the heat-resistant resin layer decreases. Small, in particular, it is difficult to secure increasingly stringent safety requirements based on the speedup of the battery assembly process when advancing the thinning of the separator

In this way, there has been no composite porous membrane that has both the adhesion of the heat-resistant resin layer and the increase in air permeability resistance.

In addition, if the film thickness of a porous film such as a polyolefin-based film used as a base material is reduced, it becomes more and more difficult to achieve both the adhesion of the heat-resistant resin layer and the increase in air permeability resistance.

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