Acrylic and para-aramid pulp and processes of making same

Abstract

The present invention relates to acrylic and para-aramid pulp for use as reinforcement material in products such as seals and friction materials. The pulp comprises (a) irregularly shaped, acrylic fibrous structures, (b) irregularly shaped, para-aramid fibrous structures, and (c) water, whereby acrylic fibrils and/or stalks are substantially entangled with para-aramid fibrils and/or stalks. The invention further relates to processes for making such acrylic and aramid pulp.

1 . A process for making an acrylic and para-aramid pulp for use as reinforcement material, comprising: 
 (a) combining pulp ingredients including: 
 (1) acrylic fiber comprising acrylonitrile units which are at least 85 wt % of the total acrylic fiber, the fiber being 10 to 90 wt % of the total solids in the ingredients, and having an average length of no more than 10 cm;  
 (2) para-aramid fiber being 10 to 90 wt % of the total solids in the ingredients, and having an average length of no more than 10 cm; and  
 (3) water being 95 to 99 wt % of the total ingredients;  
   (b) mixing the ingredients to a substantially uniform slurry;    (c) co-refining the slurry by simultaneously: 
 (1) fibrillating, cutting and masticating the acrylic fiber and the para-aramid fiber to irregularly shaped fibrillated fibrous structures with stalks and fibrils; and  
 (2) dispersing all solids such that the refined slurry is substantially uniform; and  
   (d) removing water from the refined slurry to no more than 60 total wt % water,    thereby producing an acrylic and para-aramid pulp with the acrylic and the para-aramid fibrous structures having an average maximum dimension of no more than 5 mm, a length-weighted average of no more than 1.3 mm, and the acrylic fibrils and/or stalks are substantially entangled with the para-aramid fibrils and/or stalks.    
   
   
       2 . The process of  claim 1 , wherein 
 the acrylic fiber having a linear density of no more than 10 dtex; and    the para-aramid fiber having a linear density of no more than 2.5 dtex.    
   
   
       3 . The process of  claim 1 , wherein the pulp being without substantial aggregates of the same material.  
   
   
       4 . The process of  claim 1 , wherein 
 the ingredients further comprise 
 substantially or completely fibril-free, granular, para-aramid particles being no more than 50 wt % of the total solids in the ingredients, and having an average maximum dimension of 50 to 2000 microns, and  
   in the refining step, masticating at least some of the para-aramid particles into smaller, rounder, substantially fibril-free, particles,    whereby in the produced acrylic and para-aramid pulp, the acrylic and para-aramid fibrous structures contact and are wrapped partially around at least some of the rounder, substantially fibril-free, para-aramid particles.    
   
   
       5 . The process of  claim 1 , wherein in the combining step, the acrylic fiber comprises 25 to 60 wt % of the total solids.  
   
   
       6 . The process of  claim 1 , wherein in the combing step, the para-aramid fiber comprises 40 to 75 wt % of the total solids.  
   
   
       7 . The process of  claim 1 , wherein after the removing step, the water being 4 to 60 wt % of the entire pulp, and the pulp having a Canadian Standard Freeness (CSF) of 100 to 700 ml.  
   
   
       8 . The process of  claim 1 , wherein the refining step comprises passing the mixed slurry through a series of disc refiners.  
   
   
       9 . A process for making an acrylic and para-aramid pulp for use as reinforcement material, comprising: 
 (a) combining ingredients including water and a first fiber from the group consisting of: 
 (1) acrylic fiber comprising acrylonitrile units which are at least 85 wt % of the total acrylic fiber, the fiber being 10 to 90 wt % of the total solids in the pulp; and  
 (2) para-aramid fiber being 10 to 90 wt % of the total solids in the pulp;  
   (b) mixing the combined ingredients to a substantially uniform suspension;    (c) refining the suspension in a disc refiner thereby cutting the fiber to have an average length of no more than 10 cm, and fibrillating and masticating at least some of the fiber to irregularly shaped fibrillated fibrous structures;    (d) combining ingredients including the refined suspension, the second fiber of the group of (a)(1 and 2) having an average length of no more than 10 cm, and water, if necessary, to increase the water concentration to 95-99 wt % of the total ingredients;    (e) mixing the ingredients, if necessary, to form a substantially uniform suspension;    (d) co-refining the mixed suspension by simultaneously: 
 (1) fibrillating, cutting and masticating solids in the suspension such that all or substantially all of the acrylic and para-aramid fiber is converted to irregularly shaped fibrillated acrylic and para-aramid fibrous structures with stalks and fibrils; and  
 (2) dispersing all solids such that the refined slurry is substantially uniform; and  
   (h) removing water from the refined slurry to no more than 60 total wt % water,    thereby producing an acrylic and para-aramid pulp with the acrylic and the para-aramid fibrous structures having an average maximum dimension of no more than 5 mm, a length-weighted average of no more than 1.3 mm, and the acrylic fibrils and/or stalks are substantially entangled with the para-aramid fibrils and/or stalks.    
   
   
       10 . The process of  claim 9 , wherein 
 the ingredients further comprise: 
 substantially or completely fibril-free, granular, para-aramid particles being no more than 50 wt % of the total solids in the ingredients, and having an average maximum length of 50 to 2000 microns; and  
   in either the first or second refining step, masticating at least some of the para-aramid particles into smaller, rounder, substantially fibril-free, particles,    whereby in the produced acrylic and para-aramid pulp, the acrylic and para-aramid fibrous structures contact and are wrapped partially around at least some of the rounder, substantially fibril-free, para-aramid particles.    
   
   
       11 . The process of  claim 9 , wherein after the removing step, the irregularly shaped acrylic fibrous structures being 25 to 60 wt % of the total solids.  
   
   
       12 . The process of  claim 9 , wherein after the removing step, the irregularly shaped, para-aramid, fibrous structures being 40 to 75 wt % of the total solids.  
   
   
       13 . The process of  claim 9 , wherein after the removing step, the water being 4 to 60 wt % of the entire pulp, and the pulp having a Canadian Standard Freeness (CSF) of 100 to 700 ml.  
   
   
       14 . An acrylic and para-aramid pulp for use as reinforcement material, comprising: 
 (a) irregularly shaped, acrylic fibrous structures comprising acrylonitrile units which are at least 85 wt % of the total acrylic fibrous structures, the structures being 10 to 90 wt % of the total solids;    (b) irregularly shaped, para-aramid fibrous structures being 10 to 90 wt % of the total solids; and    (c) water being 4 to 60 wt % of the entire pulp,    whereby the acrylic and the para-aramid fibrous structures having an average maximum dimension of no more than 5 mm, a length-weighted average of no more than 1.3 mm, and stalks and fibrils where the acrylic fibrils and/or stalks are substantially entangled with the para-aramid fibrils and/or stalks.    
   
   
       15 . The aramid pulp of  claim 14 , further comprising 
 substantially or completely fibril-free, granular, para-aramid particles being no more than 50 wt % of the total solids.    
   
   
       16 . The pulp of  claim 14 , wherein 
 the irregularly shaped, acrylic fibrous structures being 25 to 60 wt % of the total solids.    
   
   
       17 . The pulp of  claim 14 , wherein 
 the irregularly shaped, para-aramid, fibrous structures being 40 to 75 wt % of the total solids.    
   
   
       18 . The pulp of  claim 14 , wherein the water being 4 to 60 wt % of the entire pulp, and the pulp having a Canadian Standard Freeness (CSF) of 100 to 700 ml.  
   
   
       19 . A friction material, comprising: 
 a friction modifier;    a binder; and    a fibrous reinforcement material comprising the pulp of  claim 14 .    
   
   
       20 . The friction material of  claim 19 , wherein 
 the friction modifier is selected from the group consisting of metal powders, abrasives, lubricants, organic friction modifiers, and mixtures thereof; and    the binder is selected from the group consisting of thermosetting resins, melamine resins, epoxy resins and polyimide resins, and mixtures thereof.    
   
   
       21 . A sealing material, comprising: 
 a binder; and    a fibrous reinforcement material comprising the pulp of  claim 14 .    
   
   
       22 . The sealing material of  claim 21 , wherein 
 the binder is selected from the group consisting of nitrile rubber, butadiene rubber, neoprene, styrene butadiene rubber, nitrile-butadiene rubber, and mixtures thereof.