GB497972A - Process for the manufacture of cast synthetic resins from carbamides, phenols and formaldehyde - Google Patents

Abstract

Machinable cast resins are produced by heating at least 3 and preferably 3-5 molecular proportions of phenol with one of a carbamide and with formaldehyde in at least 1,5 times and preferably twice the total molecular proportions of phenol and carbamide, in a medium rendered acid by addition of acid, to at least a point where the liquor would, if cooled, separate into layers, and then removing water and other volatiles by vacuum distillation with or without cooling and mechanical separation of the aqueous layer. Acidification of the reaction mixture is preferably effected by an organic acid such as lactic acid which is added in an amount comparable molecularly with the quantity of carbamide. The thick syrup obtained is cast into moulds and hardened by prolonged heating at moderate temperatures. In an example, urea, phenol and formalin are mixed together, lactic acid is added and the liquor heated to 60-70 DEG C. in a stream of carbon dioxide for 5-6 hours; the liquor is allowed to cool, the aqueous layer which separates is poured off and the resinous layer is vacuum-distilled at 60 DEG C. with carbon dioxide bubbling through. When most of the volatile matter has been distilled off a plasticizer such as glycerine, glycols, tracetin, diglyceryl tetra-acetate or dimethyl phthalate is added and, after further distillation of volatile matter, o-phosphoric acid dissolved in ethyl or isopropyl alcohol is added and vacuum distillation is continued. The syrup, which may be thickened by raising the temperature to 70-75 DEG C. for a brief period, is poured into greased glass &c. moulds and is hardened by heating, first at 60 DEG C. and later to 70-75 DEG C. for 48 hours or more. To increase light-stability of the product phthalic anhydride, acetic anhydride or cyclohexanone may be added to the syrup. Thiourea may be employed instead of urea; also mixtures of different carbamides and mixtures of different phenols may be employed. Specifications 256,711, 264,601, and 309,849, [all in Class 2 (iii)], are referred to.