Patent GB-766139-A (GB)
Title: Improvements in or relating to manufacturing process for the production of porous moulded bodies made of synthetic resins and moulding powder for use in said process
IPC: B29C44/34
Filed: 1954-08-05
Abstract: A process of moulding porous bodies from synthetic resin (see Group V) comprises : evenly covering the grains of a removable granular material, avoiding friction, with a thin layer of a resin of a sufficiently hard quality to obtain a moulding product in a powdered and granular state, moulding this powder under heat and pressure, and removing the removable material from the moulded bodies.  The invention is applicable to the manufacture of filters and diaphragms. For example, polyvinyl chloride is worked into a paste with butyl phthalate and alcohol, the paste mixed with crushed sodium chloride, the alcohol evaporated and the mixture gelified by heating.  The resulting powder is pre-heated and moulded under pressure, the sodium chloride is dissoved out from the moulded article by water, and the product dried.  In another example a moulding powder is made by mixing asbestos powder and sodium chloride with an alcohol solution of a phenolic resin and eliminating the alcohol, by heat, after homogenization.  The moulded product, when the sodium chloride has been dissolved out, is suitable for heat- and corrosion-proof filters.ALSO:A process of moulding porous bodies from synthetic resin comprises: evenly covering the grains of a removable granular material, avoiding friction, with a thin layer of a resin of a sufficiently hard quality to obtain a moulding product in a powdered and granular state, moulding this powder under heat and pressure and removing the removable material from the moulded bodies.  The means for imparting an even coating are known e.g. "atomizing" or mixing in slowly rotating drums.  During compression-moulding under heat the grains perforate the plastic material and make contact with one another.  The means by which the plastic material is applied to the granules of removable material are related to the nature of the plastic material.  With polyvinyl chloride, for example, the material may be worked into a paste with a plasticizer such as a mixture of butyl phthalate and alcohol and crushed sodium chloride mixed with this paste in a mixer, after which the alcohol is removed by evaporation and the mixture gelified by heating.  The powder so obtained is preheated before insertion in the mould, where it is moulded under pressure. The sodium chloride is dissolved out by water, resulting in a material suitable for filters or diaphragms. Moulding may be by extrusion, a suitable material for this being a paste of polyvinyl chloride and dioctyl phthalate mixed with granular sodium acetate which is dissolved out by water after the extrusion. The end product may be sound or heat insulation, obtained by cutting the extruded strip into granules and projecting them, by compressed air or electrostatically, onto a surface coated with an adhesive. If the plastic material is one for which there is no convenient solvent it may be melted and mixed with the granular material, for example crushed sodium chloride is heated in a mixer to a temperature higher than the melting point of the plastic, e.g. a super-polyamide, and the super-polyamide added and the mixing continued till the super-polyamide has melted, the mixer in this case being filled with nitrogen.  The resulting porous substance is cooled in nitrogen, moulded, and the sodium chloride dissolved out.  If the plastic is of a nature that can readily be dissolved the granules may be added to a solution of it, for example polystyrene dissolved in benzene may have added to it in a mixer crushed sodium chloride.  The benzene is eliminated, the remaining powder moulded, and the salt dissolved out. If the plastic material can be easily polymerized it may be applied to the granules before polymerization, for example polyester is mixed with a catalyst acting under heat, then mixed with crushed sugar, then polymerized by heating only to the extent necessary to produce a non-sticky powder.  The powder is moulded under heat and pressure and when polymerization is completed the moulded article is removed and the sugar dissolved out.  Glass fibre filling may be added to the sugar.  To ensure round pores, round-edged granules, such as result from grinding, may be used, or granules of a material which melts at a temperature below the moulding temperature.  Porous products of the invention mentioned are slabs, strips, tubes; articles such as cushions, shoes and toys; filters in which the filtering action on dust can be improved by the use of plastic materials which become charged electrostatically in circulating gas, e.g. polyvinyl chloride; light structure panels and vibration damping supports.