Leukapheretic filter medium

Abstract

A leukocyte-removing filter medium which comprises a matrix and ultra-fine fibers having a fiber diameter of less than 1.0 μm and not less than 0.01 μm which contains ultra-fine fibers in an amount of less than 50 wt % and not less than 0.1 wt %, the degree of curvature of the ultra-fine fibers being 1.2 or more, and/or the ultra-fine fibers form pores having a roundness of 1.7 or less.

We claim:  
     
         1 . A leukocyte-removing filter medium comprising a matrix and ultra-fine fibers, said ultra-fine fibers comprising fibril fibers having a fiber diameter of less than 1.0 μm and not less than 0.01 μm, said ultra-fine fibers being contained in an amount of less than 50 wt % and not less than 0.1 wt %.  
     
     
         2 . A leukocyte-removing filter medium according to    claim 1   , wherein the fibril fibers are fibers obtained by fibrillating fiber having a fibril index of 10 or more.  
     
     
         3 . A leukocyte-removing filter medium according to    claim 1   , wherein the fibril fibers are purified cellulose fibers.  
     
     
         4 . A leukocyte-removing filter medium according to    claim 1   , wherein the fibril fibers are fibers having a degree of swelling of fiber length with water of 1.0% or less.  
     
     
         5 . A leukocyte-removing filter medium according to    claim 2   , wherein the fibril fibers have a degree of curvature of 1.2 or more.  
     
     
         6 . A leukocyte-removing filter medium according to    claim 2   , wherein the fibril fibers form pores having a roundness of 1.7 or less.  
     
     
         7 . A leukocyte-removing filter medium according to    claim 6   , wherein the diameter in terms of a circle of the pores formed by the fibril fibers is less than 20 um and not less than 1 μm.  
     
     
         8 . A leukocyte-removing filter medium according to    claim 1   , wherein the matrix is a fiber assembly composed of fibers having a fiber diameter of less than 30 μm and not less than 1 um as a matrix material.  
     
     
         9 . A leukocyte-removing filter medium according to    claim 8   , wherein the matrix material is long fibers having a fiber length of 10 mm or more.  
     
     
         10 . A leukocyte-removing filter medium according to    claim 8   , wherein the matrix material is short fibers having a fiber length of less than 10 mm and not less than 0.1 mm.  
     
     
         11 . A leukocyte-removing filter medium according to    claim 1   , wherein the matrix is a porous membrane or a spongy structure, which has an average pore size of less than 100 μm and not less than 1 μm.  
     
     
         12 . A leukocyte-removing filter medium according to    claim 1   , wherein the matrix is a particle assembly composed of particles having an average particle diameter of less than 300 μm and not less than 1 μm as a matrix material.  
     
     
         13 . A leukocyte-removing filter medium comprising non-woven fabric of splittable cellulose containing ultra-fine fibers, i.e., cellulose microfibrils having a fiber diameter of less than 1.0 um and not less than 0.01 um.  
     
     
         14 . A leukocyte-removing filter medium according to    claim 13   , wherein the percentage of the area of the cellulose microfibrils is less than 50% and not less than 1% based on the area of the whole cellulose fiber.  
     
     
         15 . A process for producing a leukocyte-removing filter medium which comprises previously mixing a matrix material with fibril fibers having a fiber diameter of less than 1.0 um and not less than 0.01 um, or making a dispersion of said fibril fibers in a matrix made of a material into paper, and thereby producing a filter medium, said filter medium containing said fibril fibers in an amount of less than 50 wt % and not less than 0.1 wt %.  
     
     
         16 . A process for producing a leukocyte-removing filter medium which comprises fibrillating a portion of splittable cellulose fiber constituting non-woven fabric of splittable cellulose, to produce a filter medium, said filter medium being composed of the resulting non-woven fabric of splittable cellulose containing cellulose microfibrils having a fiber diameter of less than 1.0 μm and not less than 0.01 μm.  
     
     
         17 . A process for producing a leukocyte-removing filter medium which comprises mixing a matrix material with splittable fiber and then splitting the splittable fiber into ultra-fine fibers having a fiber diameter of less than 1.0 μm and not less than 0.01 μm, to produce a filter medium, said filter medium containing said ultra-fine fibers in an amount of less than 50 wt % and not less than 0.1 wt %, the degree of curvature of said ultra-fine fibers being 1.2 or more, and/or said ultra-fine fibers forming pores having a roundness of 1.7 or less.  
     
     
         18 . A production process according to    claim 17   , wherein a treatment for the splitting is treatment with a high-pressure liquid.  
     
     
         19 . A leukocyte-removing filter apparatus for removing leukocytes from a leukocyte-containing fluid, said filter apparatus comprising: 
 an inlet;    a filter comprising at least one sheet of the filter medium according to    claim 1   ; and    an outlet.