GB772475A - Process for the manufacture of thermosetting condensation products and new products produced by this process - Google Patents

Abstract

Resins suitable for casting, lacquers, textile finishing, or as adhesives, are prepared by heating 1 mol. of urea melamine or a mixture of urea and melamine, hexamethylolmelamine, phenol, cresol, or a phenol-cresol mixture, with 2-2.4 mols. of formaldehyde, at an initial pH of 6.9-8.0 for 1-9 hours, the pH during heating being kept between 6.1 and 6.85 (measured at 18 DEG C. twenty minutes after sampling), removing most of the water in the precondensate, reducing the pH below 5.1, adding an alcohol with at least three carbon atoms and etherifying and further condensing in vacuo. Part of the formaldehyde may be replaced by acetaldehyde, acrylaldehyde or glyoxal. A precondensate from urea and/or melamine may be mixed before the pH is reduced below 5.1 with a separately prepared substantially dehydrated phenol - formaldehyde condensate. The pH during heating may be maintained at the desired value by use as catalyst of finely pulverized Pb, CoO, Cd, Zn, ZnO, or Mn2O3 containing traces of iron salts, or by heating in an oxygen-free atmosphere, e.g. of CO, H2 or N2, or by addition of a buffer, e.g. a mixture of primary potassium phosphate with secondary sodium phosphate or of sodium acetate with acetic acid. When using a catalyst, as above, the heating may be done under a pressure of up to 4 atmospheres. Up to 25 per cent by weight of thiourea based on the weight of urea may be added to the reaction product before the removal of water or before lowering the pH below 5.1. Part of the water remaining in the resins may be removed in vacuo at 30-50 DEG C. The resin may then be cast in a mould permeable to water, vapour (see Group V), water being allowed to evaporate and diffuse at 20-65 DEG C., or the cast resin may be heated in the mould at 20-65 DEG C. until it reaches the plastic gel state, when it is removed from the mould and the remainder of the water evaporated. Reduction of the pH below 5.1 may be effected by addition of formic, lactic, acrylic, methacrylic, succinic, benzoic hydroxybenzoic or aminobenzoic acid, acetic or maleic anhydride or aluminium sulphate or iron chloride. Alcohols suitable for the etherification are n-butyl, n-amyl, benzyl, hydroxybenzyl, or polyvinyl or glycerol. Plasticizers, e.g. o- or p-toluene sulphonamide, or formaldehyde condensates thereof, or borneol, camphor, turpentine oil, or methyl or ethyl esters of abietic or dihydroabietic acid may be added to the resins. Some alcohol may be added to the initial reaction mixture to ensure solubility of the ingredients. In Example 1 the pH of formaldehyde solution is adjusted to 7 with ammonia. Urea, cadmium dust and n-butanol are added and the mixture brought to boiling in about 1 hour and boiled for 4 hours (pH 6.4). The catalyst is filtered off and water removed in vacuo. Acetic anhydride and butanol are added and the mixture condensed and etherified in vacuo. Other examples illustrate some of the modifications referred to above.ALSO:Articles may be made from modified aminoplasts (see Group IV(a)) by casting them in forms permeable to water-vapour, water in the resin being allowed to evaporate and diffuse at 20 DEG -65 DEG C. The cast product may alternatively be heated in forms at 20 DEG -65 DEG C. until it reaches the plastic gel state, then removed and the water evaporated. Suitable materials for the forms are terracotta, plaster of paris, concrete, wood, cellulose, cellulose derivatives, polyvinyl chloride, polyvinyl acetate, polyethylene or polyethyleneoxide. They may be perforated or very thin to permit evaporation or diffusion of water. The forms may be coated with nitrocellulose to permit the resin to be removed more easily.