Patent GB-609734-A (GB)
Title: Improvements in or relating to the manufacture of synthetic resins
IPC: C08G14/02
Filed: 1945-11-05
Abstract: In the manufacture of synthetic resins a porous filler is impregnated with hydrocarbons which are liquid and not p  polymerizable under the conditions of the reaction and at least the bulk of which boils above 250 DEG  C. and with an aqueous solution of formaldehyde and one or more of: urea, thiourea, dicyandiamide, dicyandiamidine and thiodicyandiamidine, the mixture is kneaded or agitated advantageously at 15 DEG -40 DEG  C. and then, preferably after standing for some time, heated and excess of water removed.  Some water may be removed, e.g. by evaporation or pressing out before the heating step.  The filler may be first impregnated with the resin-forming components, the mixture heated or dried to a certain degree and the hydrocarbons then added and mixing and drying completed, or the filler may be first soaked in water or in the hydrocarbons.  Part of the formaldehyde may be replaced by paraformaldehyde.  Paraffinic hydrocarbons which are partly branched chain are advantageous.  Suitable hydrocarbons mentioned are transformer oil, furfural or acid-treated paraffinic fractions, residual mixtures from straight run or cracked distillates.  A proportion of low-boiling hydrocarbons may be added.  They evaporate during drying, but leave a modified resin. If they contain wax, jelly or resins, heat or solvents may be added to maintain these in liquid state.  Suitable fillers are wood flour, straw, jute, cotton viscose and other vegetable matter with high cellulose content.  They may be pretreated by extraction of inorganic or organic matter, especially fatty materials, grinding or heating with superheated steam, followed by sudden expansion.  Fibrous fillers may be felted if desired into shapes before impregnation.  Mixtures of fillers may be used.  The filler may include comparatively large pieces of wood.  The fillers may be impregnated with a proportion of the components of the mixture and the remainder added at a later stage, the second lot of resin-forming components being different from the first, if desired. Products of the invention may if desired be mixed with those of the parent Specification.  Heating and removal of excess water may be carried out on trays or in revolving drums.  Up to 18 per cent moisture may be left in the product.  Curing temperatures range from 130 DEG -160 DEG  C. and pressures from 0.5-1.5 tons per sq. inch. Electronic heating may be used for large mouldings.  The moulding powders of the invention may be mixed with urea-formaldehyde, phenol-formaldehyde, furane-formaldehyde or melamine-formaldehyde resins or moulding powders. Alternatively the ingredients of these other resins may be added after the initial reaction has commenced. Small proportions of thermoplastic resins may also be added. Hexamethylenetetramine may be added after the initial impregnation, or when the initial reactive conditions are slightly acidic, ammonia may be added. Plasticisers, e.g. potato flour, tricresyl phosphate or calcium stearate may be added.  Condensing or curing agents, dyestuffs or pigments may be added before or after heating.  The filler may be impregnated with excess resin and further filler, if desired, impregnated with resins or plasticisers added later.  The curing conditions necessary for the resin may be varied and the drying temperature lowered by selection of the wood used as filler, by soaking the wood in water or an aqueous solution of one of the resin-forming components with or without added hydrocarbon, by adding a solution of wood extracts if desired after freeing it from organic matter, by adding a solvent for components of the wood other than cellulose or lignin, which solvent may contain cellulose derivatives or synthetic resins and which may be removed during drying, or by soaking the wood in acid solution in acid-resisting vessels if darkening of colour due to iron compounds is to be avoided.  If desired, however, iron compounds may be added since the darkening they cause is often accompanied by better flow properties.  In the examples: (1) wood flour is impregnated with an aqueous solution containing urea, formaldehyde and sulphuric acid and with a paraffinic gas oil boiling from 250 DEG -375 DEG  C. and the mixture kneaded.  The crumbly paste was allowed to stand and dried on trays in a current of air at 74 DEG -81 DEG  C.  The product could be cured at 140 DEG  C. and 1 ton/sq. inch pressure; (2) wood flour, formalin, urea, water, sulphuric acid and a mixture of paraffin gas oil and unbleached petroleum jelly were agitated in a mixer.  The temperature was raised to 50 DEG  C. and urea, hexamethylenetetramine, and ammonia were added with agitation.  The mixture was dried in air at 80 DEG -120 DEG  C. and the dried product crushed to yield a moulding powder.  Potato flour or tricresyl phosphate may be added before curing; (3) bleached cotton, water, formalin, urea, sulphuric acid and a mixture of paraffin gas oil, paraffinic transformer oil and unbleached petroleum jelly were mixed, and to the mixture were added urea, hexamethylene-tetramine and ammonia and the product was dried. Calcium stearate or tricresyl phosphate may be added before curing; (4) a mixture of beech, fir and oak sawdusts was soaked in urea solution and treated as in example (1) to produce a paste, part of which was dried at 105 DEG  C. and part at 95 DEG  C.  The second part cured better especially at low pressures, e.g. 600 lbs./sq. inch.  A tendency to sweat out oil was overcome by heating the cured products in a current of air at 100 DEG -140 DEG  C., wiping off oil on the surface every half-hour and finally buffing the bodies if desired, before or after cleaning their surfaces with petrol or solvent naphtha.