GB836431A - Improvements in aminoplast resinous compositions and method of making same - Google Patents

Abstract

A process for preparing an aminoplast thermosetting resinous moulding composition comprises reacting (a) an aqueous solution of formaldehyde and (b) a formaldehyde-reactable compound comprising urea, thiourea, dicyandiamide, melamine, a formoguanamine, an acetoguanamine, a benzoguanamine, or an aminotriazone in the presence of (c) zinc oxide, the weight ratios of (a) and (b) being in the range of from 1 : 1 to 6 : 1 and the weight of (c) being in amount from about 0.05% to about 5% based on the weight of (a), at a temperature of from 75 DEG F. to the reflux temperature of the reaction mixture, until the free formaldehyde content of the reacting mixture falls below 6% by weight, based on the total weight of (a) and (b), impregnating a filler with the resulting resinous syrup and drying the composition, the zinc oxide being present throughout the entire preparation of the moulding composition. Mixed resins, e.g. urea-melamine-formaldehyde or urea-thiourea-formaldehyde resins may be prepared. Mixtures containing 20 to 60% melamine-formaldehyde resin and the remainder urea-formaldehyde resin prepared according to the invention may also be used. Suitable fillers are wood flour, cotton, paper pulp, alphacellulose, sawdust, walnut shell flour, clay, asbestos, graphite, carbon black, diatomaceous earth, ground cork, silicon carbide, sand, powdered rutile, powdered or flaked mica or quartz, glass fibres and synthetic fibres. As curing catalysts phthalic acid or anhydride, tetrachloro-phthalic anhydride, ammonium chloride, ammonium silicofluoride or ammonium borofluoride are suitable. To inhibit premature curing of the product there may be added borax, amines such as hexamethylene tetramine or further amounts of zinc oxide. Zinc stearate, glycerol monostearate, ceresin, carnauba wax, montan wax, calcium stearate and zinc palmitate are specified mould lubricants. Suitable colorants are cadmium yellow, red or maroon, titanium dioxide, black iron oxide, chrome green, gold, silver, aluminium and copper, alizarine red, Prussian blue, auramin, naphthol and malachite green. Examples illustrate the process as applied to urea-formaldehyde and melamine-formaldehyde condensation products.