Patent ID: 7879921

Claim:
A process for manufacturing a fluid permeable composite material including the steps of providing a curable composition for producing a fluid permeable composite material comprising: a particulate material; and a binding agent including: from 25 to 50 percent by weight of an acrylic polymer based on methacrylate; fibre, present in an amount of up to 25% by weight; from 10 to 35% by weight of a homopolymer of an isocyanate and corresponding isocyanate polymerising agent for forming a crosslinked polymer with said acrylic polymer; and from 20 to 60% by weight of a low molecular weight solvent selected from C1 to C6 esters, hydrocarbon solvents, or C1 to C6 ketones, which low molecular weight solvent flashes off or evaporates during curing of the composition to leave voids in the cured composition; compressing the curable composition and curing the composition at a temperature above the glass transition temperature of the binder such that the solvent flashes off or evaporates to leave voids in the cured composition, and subsequently reducing the temperature.