Patent GB-591161-A (GB)
Title: Improvements in or relating to the preparation of moulding materials
IPC: B29B9/00
Filed: 1945-04-27
Abstract: Pelletted hot moulding compositions are prepared by incorporating with a mixture of liquid or powdered thermosetting resin, e.g. urea-formaldehyde or phenol-formaldehyde, and a filler such as barytes, silicates, metal oxides, powdered mica, wood flour, asbestos, cotton flock, chopped card and fabric, a substantially non-solvent wetting liquid in amount not exceeding the weight of filler and resin, and working the mixture to form pellets; the wetting liquid is evaporated under conditions which preserve the pellet form.  Water is the preferred wetting liquid, but hydrocarbons, e.g. benzene, toluene, xylene, gasolene, or mineral spirits can be substituted.  About 5-10 per cent of solvent, e.g. lower aliphatic alcohols or esters, glycols or ketones can be added to the wetting liquid.  A typical moulding composition of about equal parts of wood flour and powdered phenol formaldehyde resin requires about 30-60 per cent by volume of water.  The formation of pellets occurs when the mass has been brought to the crumbly state and is further agitated in a kneader, ribbon blender, pony mixer or a beading apparatus as disclosed in U.S.A. Specification 2,065,371. Tumbling in a smooth drum is sufficient for pelleting a typical wood flour, resin and water mixture.  The wetting liquid is evaporated by heating, preferably with continued agitation, e.g. by means of vibrating tables, until its content is reduced to about 2 per cent, when on cooling the conglomerates become hard and rigid.  The heating also serves to advance the resin.  Moulding material fines can be processed in this way either alone or as additions to resin-filler mixtures. In examples: (1) equal quantities of wood flour and powdered heat reactive phenol-formaldehyde resin with water to form a 45 per cent water content are pelleted with the apparatus disclosed in U.S.A. Specification 2,065,371, referred to above, and dried on a vibrating impact table at about 80 DEG  C. or an open-ended rotating tumbler is used, the water being sprayed in during the tumbling, or a kneader is used with partial evaporation of the moisture during kneading.  (2) A ball milled mixture of ground mica and powdered heat reactive phenol-formaldehyde resin is placed in a rotating tumbler, water sprayed on the mass and the pellets so formed dried in an oven. A graphite and resin mixture is similarly pelletized.  (3) A cotton flock was ball milled with dye and lubricant, agitated in a tumbler with an equal weight of a liquid water-soluble phenol-aldehyde resin and water was sprayed in, followed by benzene, when pellets produced on continued agitation were dried in an oven.  Cotton shearings and asbestos fibres were also made into pellets with powdered heat reactive phenol - formaldehyde resin.  (4) Moulding material fines and phenol-formaldehyde resin-cotton flock mixture were blended and sprayed with water until about one-third of the composition was water, when pellets formed were dried in a rotary drier. Wood-flour fines yielded pellets of slightly lower density. Example (5) describes the cold mixing in a kneader of a viscous heat-hardening ureaformaldehyde resin (10 per cent solids) with 40 per cent of the weight of the resin of wood flour, about 2 per cent of water and 1 per cent of ammonium chloride hardener for about 10 minutes to form a stiff granular mass.  Continued agitation resulted in pellets which were dried at about 160 DEG  F.