Polymer-bonded fiber agglomerate, fiber-reinforced composite material and processes for producing the same

Abstract

A polymer-bonded fiber agglomerate includes short fibers selected from carbon, ceramic materials, glasses, metals and organic polymers, and a polymeric bonding resin selected from synthetic resins and thermoplastics. The fiber agglomerates have an average length, measured in the fiber direction, of from 3 mm to 50 mm and an average thickness, measured perpendicularly to the fiber direction, of from 0.1 mm to 10 mm. At least 75% of all of the contained fibers have a length which is at least 90% and not more than 110% of the fiber agglomerate average length. A fiber-reinforced composite material having the fiber agglomerate and processes for the production thereof are also provided.

1 . A polymer-bonded fiber agglomerate, comprising: 
 short fibers selected from the group consisting of carbon, ceramic materials, glasses, metals and organic polymers;    a polymeric bonding resin selected from the group consisting of synthetic resins and thermoplastics;    a fiber agglomerate average length, measured in a fiber direction, of from 3 mm to 50 mm;    a fiber agglomerate average thickness, measured perpendicularly to said fiber direction, of from 0.1 mm to 10 mm; and    at least 75% of all contained fibers having a length being at least 90% and at most 110% of said fiber agglomerate average length.    
   
   
       2 . The polymer-bonded fiber agglomerate according to  claim 1 , which further comprises a ratio of fiber agglomerate length to width of from 2:1 to 100:1.  
   
   
       3 . The polymer-bonded fiber agglomerate according to  claim 1 , which further comprises at most three fiber layers.  
   
   
       4 . The polymer-bonded fiber agglomerate according to  claim 1 , which further comprises carbon fibers.  
   
   
       5 . A process for producing a polymer-bonded fiber agglomerate, which comprises producing the polymer-bonded fiber agglomerate according to  claim 1 , by carrying out the following process steps: 
 soaking a filament yarn with a liquid or pulverulent synthetic resin or a liquid or pulverulent thermoplastic to form an impregnated filament strand;    pressing the impregnated filament strand to a laid material of filaments orientated in parallel;    if a synthetic resin is used, curing the synthetic resin by heat treatment;    cooling the pressed filament strand; and    cutting the filament strand to a defined width and length.    
   
   
       6 . The process according to  claim 5 , which further comprises carrying out at least one of the process steps continuously.  
   
   
       7 . The process according to  claim 5 , which further comprises fanning out the filament strand by blowing on the filament strand with a gas before the soaking and impregnating step.  
   
   
       8 . The process according to  claim 5 , which further comprises carbonizing the filament strand pressed to a tape by heating to the exclusion of oxidizing substances, before the cutting step.  
   
   
       9 . The process according to  claim 8 , which further comprises coating the carbonized tape with a pitch and thereafter carbonizing the tape again.  
   
   
       10 . The process according to  claim 8 , which further comprises coating the carbonized tape with a carbonizable polymer or a pitch.  
   
   
       11 . The process according to  claim 10 , which further comprises additionally applying fillers selected from the group consisting of carbon powders, ceramic powders and powders of carbide-forming elements, together with or after the coating with the carbonizable polymer or the pitch.  
   
   
       12 . The process according to  claim 8 , which further comprises carrying out at least one of the steps continuously.  
   
   
       13 . The process according to  claim 10 , which further comprises carrying out at least one of the steps continuously.  
   
   
       14 . The process according to  claim 11 , which further comprises carrying out at least one of the steps continuously.  
   
   
       15 . A fiber-reinforced composite material, comprising: 
 fiber agglomerates having a fiber agglomerate average length, measured in a fiber direction, of from 3 mm to 50 mm, and a fiber agglomerate average thickness, measured perpendicularly to said fiber direction, of from 0.1 mm to 10 mm; and    at least 75% of all contained fibers having a length being at least 90% and at most 110% of said fiber agglomerate average length.    
   
   
       16 . The fiber-reinforced composite material according to  claim 15 , which further comprises a matrix of a ceramic material.  
   
   
       17 . A process for the production of a fiber-reinforced ceramic composite material, which comprises the following steps: 
 producing the polymer-bonded fiber agglomerate according to  claim 1  by: 
 soaking a filament yarn with a liquid or pulverulent synthetic resin or a liquid or pulverulent thermoplastic to form an impregnated filament strand;  
 pressing the impregnated filament strand to a laid material of filaments orientated in parallel;  
 if a synthetic resin is used, curing the synthetic resin by heat treatment;  
 cooling the pressed filament strand; and  
 cutting the filament strand to a defined width and length;  
   mixing the fiber agglomerate with a carbonizable polymer;    forming the mixture under pressure and at elevated temperature to yield a shaped article;    heating the shaped article to the exclusion of oxidizing substances and forming a fiber-reinforced porous body having a matrix of carbon; and    infiltrating the porous carbon body with a melt of at least one carbide-forming element, and converting at least some of the carbon of the matrix into carbides.    
   
   
       18 . The process according to  claim 17 , which further comprises carbonizing the filament strand pressed to a tape by heating to the exclusion of oxidizing substances, before the cutting step.  
   
   
       19 . The process according to  claim 18 , which further comprises coating the carbonized tape with a pitch and thereafter carbonizing the tape again.  
   
   
       20 . The process according to  claim 18 , which further comprises coating the carbonized tape with a carbonizable polymer or a pitch.  
   
   
       21 . The process according to  claim 20 , which further comprises additionally applying fillers selected from the group consisting of carbon powders, ceramic powders and powders of carbide-forming elements, together with or after the coating with the carbonizable polymer or the pitch.