GB541414A - Improvements in or relating to the production of resinous moulding compositions and moulded products - Google Patents

Abstract

541,414. Synthetic resin compositions moulding. CELLOMOLD., Ltd., DAVIES, D. N., and READ, L. M. May 22, 1940, No. 9073. [Class 2 (iii)] [Also in Group V] A composition of matter comprises a mass of loose substantially dry particles, so that the mass can be conveniently handed and distributed in a mould, and consists mainly of an intimate mixture of a heat hardenable phenolicaldehyde resin with wood sawdust in proportions within the limits 5 to 25 per cent. by weight of resin and 65 to 90 per cent. sawdust, the resin and sawdust amounting to at least 90 per cent. in the absence of any appreciable quantity of water or any more highly volatile substances other than such as may comprise a natural part of the resin or sawdust, the sawdust being in normal substantially non-pulverized condition and having a water content below 35 per cent. The resin may be obtained by condensing cresol, resorcinol or other phenol with formaldehyde or other aldehyde, and may be a solid resol or a novolak; if a novolak is used, hexamethylene tetramine or other appropriate hardening agent is incorporated in the composition ; fillers, lubricants, plasticizers, colouring matter, and oxides of alkaline earth metals, e.g. magnesia or lime, may be incorporated in the composition. The resin, either dry or in solution in a volatile solvent, is compounded with the other ingredients in a mixing machine which kneads but does not disintegrate the sawdust particles. In examples, a cresol-formaldehyde resol, sawdust, magnesia and a lubricant, e.g. olein, are mixed either in a heated Banbury mixer or in a cold ball mill, or a solution of the resol in a volatile solvent, e.g. methylated spirit, is mixed with the other ingredients either in a hot jacketed blade mixer, so that the volatile solvent is removed during mixing, or in a cold blade mixer of the Baker Perkins type, the mixture being then poured into a container and dried in an oven to remove the volatile solvent. The compositions have low flow properties, and can be moulded into sheets, blocks or similar articles of simple shapes in heated platen presses under a pressure of less than 600 lbs. sq. inch the product being removable from the mould whilst hot without blistering. A press comprising platens 3, 4, 5 connected by slotted links 6 may be employed, the composition being placed in a framework 8 of highly compressible material, e.g. strips of fibrous board having a base of sugar cane fibre, the strips being pinned together if desired. The composition and the framework are then compressed by applying a pressure of say 300 lbs. sq. inch hydraulically to the bottom platen 5, heat being applied simultaneously to cure the resin. Specifications 321,697, 336,754, [both in Class 2 (iii)], and 467,491 are referred to.