Patent ID: 8431213

Claim:
A pressboard consisting of a plurality of plies having thermostable floc and at least 40 weight percent aramid fibrids, where the thermostable floc are fibers having a length of 2 to 25 millimeters and a diameter of 3 to 20 micrometers and losing not more than 10 percent of its tenacity after exposure to 250° C. for 10 minutes in air and where the fibrids are polymer products of particles having a length and width in order of 100 to 1000 micrometers and thickness in the order of 0.1 to 1 micrometer, the pressboard having a final average thickness of 0.9 mm or greater, the pressboard having an a void content of 25 volume percent or less, characterized in that the pressboard has a ply adhesion (Y) in megapascals defined by the equation Y>2.97(X) (−0.25 ) wherein (X) is the thickness of the pressboard in millimeters, and wherein the ply adhesion is the peak load delamination of the structure in z-direction (out of plane) of the pressboard as measured in accordance with ASTM D 952-02, wherein the pressboard has compressibility of 1.6 percent or less and compression set of 0.18 percent or less.