Fibrous sheet materials

Claim 1

In a process for the production of a non-combustible asbestos-free board product comprising a matrix of ball clay reinforced with glassy inorganic fiber, including the steps of: (i) dewatering on a sieve or other filter medium an aqueous suspension containing glassy inorganic fiber and ball clay as the major ingredients, with a small proportion of starch as binder, and (ii) subsequently setting the dewatered suspension at elevated temperature, the improvement which consists in: (a) employing as the aqueous suspension one which has a higher content of ball clay than of glassy inorganic fiber and which also contains organic web-forming fibers, the proportions of the various ingredients by weight of total solids in the suspension being: ______________________________________ unfired ball clay 42-67% glassy inorganic fiber 18-42% starch 1.5-5% organic web-forming fiber up to 7% ______________________________________ in combination with (b) limiting the setting at elevated temperature to a drying procedure which is carried out (b1) until the board product has a tensile strength greater than 2 MPa and a density at least 500 kg/m 3 but less than 1200 kg/m 3 , and (b2) so as to leave the ball clay in the unfired state and the starch content in the range 1.5-5% by weight, to obtain a board product which is remoldable when rewetted with water.