Aramid paper blend

Abstract

The present invention relates to aramid paper which is suitable for composite structures and which is made using a combination of para-aramid pulp, floc, and, optionally, a polymer binder material.

1 . Aramid paper comprising 50 to 95 weight percent p-aramid pulp and 5-50 weight percent of floc with an initial modulus less than 3000 cN/tex.  
   
   
       2 . The aramid paper of  claim 1 , wherein p-aramid pulp is poly(p-phenylene terephthalamide) pulp.  
   
   
       3 . The aramid paper of  claim 1 , wherein the floc is meta-aramid.  
   
   
       4 . The aramid paper of  claim 3 , wherein the meta-aramid floc is poly(m-phenylene isophthalamide) floc.  
   
   
       5 . The aramid paper of  claim 1 , comprising a polymer binder material in the quantity of less than 20 weight percent based on the weight of the total composition.  
   
   
       6 . The aramid paper of  claim 5 , wherein at least a portion of the polymer binder material is in the form of fibrids.  
   
   
       7 . The aramid paper of  claim 6 , wherein the fibrids are made from poly(m-phenylene isophthalamide).  
   
   
       8 . The aramid paper of  claim 5 , wherein the polymer binder can be fused by one of the group consisting of drying and calendering.  
   
   
       9 . The aramid paper of  claim 5 , wherein at least a portion of the polymer binder material is a resin binder material, which can be fused during drying or calendering of the paper.  
   
   
       10 . The aramid paper of  claim 9 , wherein at least a portion of the resin binder material is thermoplastic floc.  
   
   
       11 . The aramid paper of  claim 9 , wherein at least a portion of the resin binder material is a water-soluble resin.  
   
   
       12 . The aramid paper of  claim 1 , wherein the basis weight of the paper is less than 70 g/m 2 .  
   
   
       13 . The aramid paper of  claim 1  or  5 , wherein the absolute value of the coefficient of thermal expansion of the paper in plane in the temperature interval between 20 and 100° C. is less than 4 ppm/C.  
   
   
       14 . The aramid paper of  claim 1  or  5 , comprising 70 to 95 weight percent p-aramid pulp.  
   
   
       15 . A printed wiring board, comprising one or more layers of the paper of  claim 1  or  5 .  
   
   
       16 . An electrical insulating material, comprising one or more layers of the paper of  claim 1  or  5 .  
   
   
       17 . A composite structure, comprising the aramid paper of  claim 1  or  5  impregnated with a resin.  
   
   
       18 . The composite structure of  claim 17 , wherein the resin is a phenol.  
   
   
       19 . A printed wiring board or electrical insulating material, comprising the composite structure of  claim 17 .  
   
   
       20 . A structural material, comprising the aramid paper of  claim 1  or  5 .  
   
   
       21 . The structural material of  claim 20 , wherein the aramid paper is incorporated into the cells of a honeycomb structure.  
   
   
       22 . The structural material of  claim 20 , wherein the aramid paper is incorporated into the facing of a sandwich panel.  
   
   
       23 . A process of making aramid paper, comprising the steps of 
 dispersing p-aramid pulp in water    blending the pulp/water slurry with a floc having an initial modulus less than 3000 cN/tex wherein the weight percent of the pulp and the floc in the solids is from 50 to 95 and from 5 to 50 respectively,    draining the water from the final slurry to yield a wet paper composition,    drying the wet paper composition.    
   
   
       24 . The process of  claim 23 , comprising a step of wet pressing of the wet paper composition before drying.  
   
   
       25 . The process of  claim 24 , comprising heat-treating the paper after drying.  
   
   
       26 . The process of  claim 23 , comprising a step of adding a polymer binder material in a quantity less than 20 weight percent of the total solids after blending the pulp/water slurry with the floc.  
   
   
       27 . The process of  claim 26 , comprising heat-treating the paper after drying.  
   
   
       28 . The process of  claim 23 , comprising densification of the dried paper.  
   
   
       29 . The process of  claim 28 , wherein densification is performed by selecting one of the group consisting of application of pressure in the nip of a calender and application of pressure in a press.  
   
   
       30 . The process of  claim 28 , comprising a step of heat-treating the paper after densification.