Controlled pore composite polytetrafluoroethylene article

Claim 1

A separation composite article having controlled void volume and mean pore size comprising: polytetrafluoroethylene (PTFE) fibril matrix, and insoluble, non-swellable sorptive particles enmeshed in said matrix, the ratio of non-swellable sorptive particles to PTFE is in the range of 40:1 to 1:4 by weight, the composite article having a porosity in the range of 30 to 80 percent void volume and a mean pore size in the range of 0.3 to 5.0 micrometers, said article being provided by a method comprising the steps of: admixing lubricant with a blend comprising insoluble, non-swellable, sorptive particles and polytetrafluoroethylene to form a soft dough-like mass, the lubricant being present in an amount to exceed the sorptive capacity of the particles by at least 3 weight percent, said mass having a cohesive consistency, and the ratio of insoluble particles to PTFE being in the range of 40:1 to 1:4; b) intensively mixing said mass at a temperature and for a time sufficient to cause initial fibrillation of said PTFE particles; c) biaxially calendering said mass between gaps in calendering rolls maintained at a temperature and for a time, while closing the gap between the calendering rolls with each successive calendering operation, to cause additional fibrillation of said PTFE particles to form a self-supporting tear-resistant sheet having a void volume in the range of 30 to 80 percent and a mean pore size in the range of 0.3 to 5.0 micrometers, wherein said void volume and mean pore size vary directly with and are controlled by the amount of lubricant present during processing and wherein said article has reproducible porosity and mean pore size.