GB347738A - Improvements in or relating to bonded materials - Google Patents

Abstract

In a process of hot pressing a fibrous filler and a reactive resinoid wherein the binder is first liquefied by heat and set thereby, sufficient pressure being applied to cause the binder, before setting, to flow and fill completely the interspaces between the fibres, the resinoid is maintained before consolidation in a condition in which it will flow at about 170 DEG C. at pressures less than 500 lbs. per sq. in., or converted into such condition by the addition of a solvent, and then hot pressed under the comparatively low pressure needed. This characteristic may be obtained by regulating the drying of a varnish-impregnated material so as to leave a certain amount of solvent therein, by adding solvent to a dried impregnated material or by having the resinoid in a less advanced or polymerized state than is customary, e.g. by drying at low temperatures and under partial vacuum. In an example, fabric, felt or other suitable tissue or paper is coated or impregnated with a solution of a reactive cresol formaldehyde resinoid to yield a fabric containing about 50 per cent resinoid. The fabric is then dried leaving about 7 per cent volatile ingredients. A number of these sheets are then superposed and submitted to pressure at about 170 DEG C. With a pressure of about 55 and 100 lbs. per sq. in. laminated products with specific gravities of about 1,11 and 1,20 respectively, have been obtained. Fibrous fillers including paper, chopped fabric, asbestos, paper pulp, and wood flour may be employed in place of fabric and any of the resinoids suitable for moulding such as the phenol-formaldehyde or the glycerol-phthalic anhydride types may be used. In view of the low pressures employed, porous board such as is obtained from bagasse, cornstalks and the like can be used, particularly for an intermediate unexposed layer bonded with surface sheets of paper or fabric impregnated with a resinoid as specified. The intermediate board may itself be wholly or partially impregnated or the exposed edges only impregnated. Specification 345,228 is referred to.