Alkaline battery separator and process for producing the same

Abstract

An alkaline battery separator which enables the preparation of a battery with a good yield and workability is provided. The alkaline battery separator of the present invention comprises a fiber sheet mainly comprising hydrophilicity-imparted polyolefin fibers having a fiber diameter of 8 μm or more, and a part of the hydrophilicity-imparted polyolefin fibers is composed of high-strength fibers having a tensile strength of 5 g/d or more.

1. An alkaline battery separator comprising a fiber sheet comprising more than 75 mass percentage of hydrophilicity-imparted polyolefin fibers having a fiber diameter of 9 μm or more, based upon 100% total weight of constituent fibers of the fiber sheet, wherein a part of said hydrophilicity-imparted polyolefin fibers is comprised of fibers having a tensile strength of at least 5 g/d. 
     
     
       2. The alkaline battery separator according to  claim 1 , wherein said fiber sheet contains fibers having a tensile strength of 5 g/d or more and fusible fibers, as said hydrophilicity-imparted polyolefin fibers having a fiber diameter of at least 9 μm. 
     
     
       3. The alkaline battery separator according to  claim 2 , wherein the mass ratio of non-fusible fibers having a tensile strength of at least 5 g/d and said fusible fibers is 10:90 to 50:50. 
     
     
       4. The alkaline battery separator according to  claim 1 , wherein the maximum pore diameter of said fiber sheet is less than 50 μm. 
     
     
       5. The alkaline battery separator according to  claim 1 , wherein a 5% modulus strength with respect to at least a direction of said fiber sheet is at least 60 N/5 cm width. 
     
     
       6. The alkaline battery separator according to  claim 1 , wherein pores having a pore diameter of at least  30 μm or less in said fiber sheet accounts for at least 95% of the whole of pores. 
     
     
       7. The alkaline battery separator according to  claim 1 , wherein an air permeability of said fiber sheet is at least 4 cm/sec. 
     
     
       8. The alkaline battery separator according to  claim 1 , wherein an electrical resistance of said fiber sheet is less than 5 mΩ·100 cm 2 /sheet. 
     
     
       9. The alkaline battery separator according to  claim 1 , wherein polyethylene fibers whose surface consists substantially of a polyethylene resin account for at least 60 mass % of said hydrophilicity-imparted polyolefin fibers which are the major component of said fiber sheet. 
     
     
       10. The alkaline battery separator according to  claim 1 , wherein said fiber sheet is a non-woven fabric. 
     
     
       11. A process for producing an alkaline battery separator comprising a fiber sheet comprising more than 75 mass percentage of hydrophilicity-imparted polyolefin fibers having a fiber diameter of at least 9 μm, comprising steps of: forming a fiber sheet from polyolefin fibers which have a fiber diameter of at least 9 μm, said polyolefin fibers containing polyolefin fibers having a fiber diameter of at least 9 μm and a tensile strength of at least 5 g/d; and then imparting a hydrophilic property to the resulting fiber sheet.