Microporous polyolefin film, separator for battery, and production processes therefor

Abstract

A polyolefin microporous membrane is suitable to provide thereon a porous layer having little variation in thickness, which has a fluctuation range of F25 value in the length direction of 1 MPa or less, and which has a length of 1,000 m or more (wherein the F25 value refers to a value obtained by: measuring a load value applied to a test specimen when the test specimen is stretched by 25% using a tensile tester; and dividing the load value by the value of the cross-sectional area of the test specimen).

1 . A polyolefin microporous membrane having a fluctuation range of F25 value in a length direction of 1 MPa or less, and having a length of 1,000 m or more (wherein the F25 value refers to a value obtained by: measuring a load value applied to a test specimen when the test specimen is stretched by 25% using a tensile tester; and dividing the load value by the value of the cross-sectional area of the test specimen). 
     
     
         2 . A battery separator comprising: a polyolefin microporous membrane having a fluctuation range of F25 value in a length direction of 1 MPa or less; and a porous layer formed on at least one surface of the polyolefin microporous membrane, which contains a water-soluble resin or a water-dispersible resin and heat resistance particles, and has an average thickness T(ave) of 1 to 5 μm (wherein the F25 value refers to a value obtained by: measuring a load value applied to a test specimen when the test specimen is stretched by 25% using a tensile tester; and dividing the load value by the value of the cross-sectional area of the test specimen). 
     
     
         3 . A battery separator comprising: a polyolefin microporous membrane having a fluctuation range of F25 value in a length direction of 1 MPa or less; and a porous layer formed on at least one surface of the polyolefin microporous membrane, which contains a water-soluble resin or a water-dispersible resin and heat resistance particles, and has an average thickness T(ave) of 1 to 5 μm (wherein the F25 value refers to a value obtained by: measuring a load value applied to a test specimen when the test specimen is stretched by 25% using a tensile tester; and dividing the load value by the value of the cross-sectional area of the test specimen), wherein the porous layer has a thickness fluctuation range (R) in the length direction of 1.0 p.m or less. 
     
     
         4 . A battery separator comprising: the polyolefin microporous membrane according to  claim 1 ; and a porous layer formed on at least one surface of the polyolefin microporous membrane, which contains a water-soluble resin or a water-dispersible resin and heat resistance particles, and which has an average thickness T(ave) of from 1 to 5 μm. 
     
     
         5 . The battery separator according to  claim 2 , wherein the porous layer has a thickness fluctuation range (R) in the length direction of 1.0 μm or less. 
     
     
         6 . The battery separator according to  claim 2 , wherein the water-soluble resin or the water-dispersible resin contains at least one of polyvinyl alcohol, an acrylic resin and a polyvinylidene fluoride resin. 
     
     
         7 . The battery separator according to  claim 4 , wherein the polyolefin microporous membrane has a length of 2,000 m or more. 
     
     
         8 . The battery separator according to  claim 4 , wherein the polyolefin microporous membrane has a length of 3,000 m or more. 
     
     
         9 . The battery separator according to  claim 4 , wherein the porous layer has a thickness fluctuation range (R) in the length direction of 1.0 μm or less. 
     
     
         10 . The battery separator according to  claim 4 , wherein the water-soluble resin or the water-dispersible resin contains at least one of polyvinyl alcohol, an acrylic resin and a polyvinylidene fluoride resin. 
     
     
         11 . The battery separator according to  claim 5 , wherein the water-soluble resin or the water-dispersible resin contains at least one of polyvinyl alcohol, an acrylic resin and a polyvinylidene fluoride resin. 
     
     
         12 . The battery separator according to  claim 5 , wherein the polyolefin microporous membrane has a length of 2,000 m or more. 
     
     
         13 . The battery separator according to  claim 6 , wherein the polyolefin microporous membrane has a length of 2,000 m or more. 
     
     
         14 . The battery separator according to  claim 5 , wherein the polyolefin microporous membrane has a length of 3,000 m or more.