Process and device for producing filtration-active fibers

Abstract

A process and a device for producing filtration-active fibers is described. An aqueous suspension is produced from a homopolymer of polyacrylonitrile, polyamide or cellulose acetate and the suspension is heated in a tank to a temperature T which is at least 60° above the boiling point of the water and at least 30° C. below the softening temperature of the polymer. The at least plasticized polymer mass which has been obtained in this way is discharged through at least one nozzle means at least using the autogenous pressure of superheated water. The device calls for that the suspension is prepared in a storage tank, that a mixing tank is connected to the storage tank and is made for heating an aqueous polymer suspension under pressure, and that furthermore there is a nozzle means for discharge of the plasticized polymer mass located at the output of the mixing tank.

1 . Process for producing filtration-active fibers, in which an aqueous suspension of a hydrophilic polymer which is both free of additives and which also has no organic solvents is heated in a tank and then discharged from the tank, characterized in that homopolymers from polyacrylonitrile, polyamide or cellulose acetate are used as the polymers, that the suspension is heated in a tank to a temperature T which is at least 60° above the boiling point of the water and at least 30° C. below the softening temperature of the polymer, and the at least plasticized polymer mass which has been obtained in this way is discharged through at least one nozzle means at least using the autogenous pressure of superheated water.  
     
     
         2 . Process as claimed in    claim 1   , wherein polyamide 6 or polyamide 6, 6 is used as the polyamide.  
     
     
         3 . Process as claimed in    claim 1   , wherein cellulose diacetate or cellulose triacetate is used as the cellulose acetate.  
     
     
         4 . Process as claimed in    claim 3   , wherein the cellulose acetate has an acetic acid content from 52 to 56%.  
     
     
         5 . Process as claimed in one of    claims 1    to    4   , wherein the suspension is kept at the temperature T for a maximum 240 sec.  
     
     
         6 . Process as claimed in one of    claims 1    to    5   , wherein the suspension is continuously mixed during heating.  
     
     
         7 . Process as claimed in one of    claims 1    to    6   , wherein the polymer concentration in the suspension is 1 to 10% by mass.  
     
     
         8 . Process as claimed in one of    claims 1    to    7   , wherein the fibers are discharged in a space with a pressure≦atmospheric pressure.  
     
     
         9 . Process as claimed in one of    claims 1    to    8   , wherein the suspension is exposed to a pressure between 15 and 25 bar during heating.  
     
     
         10 . Process as claimed in one of    claims 1    to    9   , wherein a polymer powder with grain sizes between 20 and 100 microns is used for the suspension.  
     
     
         11 . Use of the fibers produced as claimed in    claim 1    for liquid filtration or for gas filtration.  
     
     
         12 . Use as claimed in    claim 11    in microfiber networks.  
     
     
         13 . Use as claimed in    claim 11    in a matrix of coarser fibers or as a precoat material.  
     
     
         14 . Device for continuous production of filtration-active fibers of PAN, PA or cellulose acetate with a storage tank ( 2 ) for preparing the suspension, with a mixing tank ( 10 ) which is connected to the storage tank and which is made for heating an aqueous polymer suspension under pressure, and with a nozzle means ( 16 ) for discharge of the plasticized polymer mass located at the output of the mixing tank ( 10 ).  
     
     
         15 . Device as claimed in    claim 14   , wherein the nozzle means ( 16 ) has at least one capillary nozzle ( 24   a, b, c ), one pneumatic nozzle, one needle valve or one binary nozzle.  
     
     
         16 . Device as claimed in    claim 14    or    15   , wherein there are at least three capillary nozzles ( 24   a, b, c ) adjacent to one another, with their outlet openings ( 26   a, b, c ) aligned at an acute angle to one another.  
     
     
         17 . Device as claimed in one of    claims 14    to    16   , wherein the diameter of the capillary nozzles is preferably 0.1 to 10 mm.  
     
     
         18 . Device as claimed in one of    claims 14    to    17   , wherein the ratio of the length to the diameter of the capillary nozzle ( 24   a, b, c ) is 30-50.  
     
     
         19 . Device as claimed in one of    claims 14    to    18   , wherein the mixing tank ( 10 ) is an extruder.  
     
     
         20 . Device as claimed in one of    claims 14    to    18   , wherein the mixing tank ( 10 ) has a dispersing means.  
     
     
         21 . Device as claimed in one of    claims 14    to    20   , wherein a coarse mixer ( 8 ) is connected upstream of the mixing tank ( 10 ).  
     
     
         22 . Device as claimed in one of    claims 14    to    21   , wherein behind the nozzle means ( 16 ) there is a discharge tank ( 15 ) in which a pressure≦atmospheric pressure can be set.  
     
     
         23 . Device as claimed in one of    claims 14    to    22   , wherein there is a metering pump ( 12 ) in front of the nozzle means ( 16 ).  
     
     
         24 . Device as claimed in one of    claims 14    to    23   , wherein in front of the mixing tank ( 10 ) there is a heat exchanger ( 6 ).