GB593924A - Process of forming granulated aminoplast resin compositions and products so produced - Google Patents

Abstract

<PICT:0593924/IV/1> A granulated amine-aldehyde resin moulding composition is prepared by a continuous process comprising preheating powdered amine-aldehyde resin moulding composition, passing the preheated powder through a set of differential rolls at a temperature less than the preheating temperature to form a loosely compacted sheet and granulating the sheet material. Preferably, the amine-aldehyde resin powder is treated continuously by passing it through two sets of differential pressure rolls, the temperature of the first set being below that required to form a self-sustaining sheet. The sheet is then formed as the material passes through the second set of hotter rolls. The material is then stripped off, granulated and screened, the rejected "fines" and "lumps" being reprocessed. The amine-aldehyde resin may be aminotriazine - aldehyde such as melamine - formaldehyde, dicyandiamide - aldehyde, melamine - modified dicyandiamide - formaldehyde, urea-aldehyde, thiourea-urea-aldehyde, melamine - urea formaldehyde, urea - aldehyde - alcohol, melamine - aldehyde - alcohol and mixtures of the separate resins or condensates in the presence of ammonia or ammonium hydroxide. Latent curing catalysts, mould lubricants such as zinc stearate, colouring matter and fillers such as wood flour, alpha cellulose, paper, cotton, canvas, asbestos, mica flakes, pearl shell chips, synthetic or natural filaments, glass fibres and fabrics may be added. In Fig. 1, powder from the pebble mill is charged through the hopper 12 to the nip of differential hot rolls 14, which may be corrugated, or the preheating may be effected on an endless belt in a heating chamber, in an inclined kiln or by induction heating. The preheated material is then passed through heated differential pressure sheeting rolls 18, preferably one roller only being heated and the sheet material stripped from the hot roll, granulated in a cutter equipped with a screen 28 through which the granules pass to the triple-decked sifter, the fines being recirculated and the lumps regranulated. A modification of the rolls comprises a three-roll calendar having two nips. In the examples: (1) a mixture of urea-formaldehyde condensate and paper pulp as filler, prepared as disclosed in U.S.A. Specification 2,338,464, was dried, ground in a ball-mill, preheated on differential rolls in which the fast roll was at 240-250 DEG F. and the slower roll at 220 DEG F., and sheeted on a second set of differential rolls closer together and at 140 DEG F. when the material was granulated and screened; (2) a melamine-formaldehyde resin with wood flour filler was dried, ball-milled, preheated in a chamber at 230 DEG F. and sheeted on differential hot rolls at 150 DEG F., when the material was granulated and screened.