GB576745A - Improvements in or relating to resinous compositions - Google Patents

Abstract

Resins are made by heating a monohydric phenol with aqueous formaldehyde in presence of an acid catalyst to form a potentially heat-reactive resin, treating the resin for the removal therefrom or the neutralization therein of the acid, and before or after dehydrating, mixing therewith resorcinol and between 16 and 24 per cent of its weight of formaldehyde, paraformaldehyde or other polymer of formaldehyde (calculated as paraformaldehyde) and heating the mixture to bring it to the brittle stage. The phenol may be, for example, phenol itself, or a cresol, and the acid catalyst may be hydrochloric, sulphuric, or phosphoric acid and may be removed by washing with warm water or by neutralization with barium hydroxide. Preferably, the neutral potentially heat-reactive monohydric phenolic resin is melted after dehydration, the resorcinol is dissolved therein, and the formaldehyde or polymer thereof is added to the solution. The proportion of monohydric phenol resin in the resin should be about 10-90 per cent and preferably 50-80 per cent, and free phenol may be present. The amount of hardening agent, e.g. hexamethylene tetramine, required may vary from 2-10 per cent. The resins are used for moulding compositions, varnishes and adhesives, e.g. for bonding coating materials to walls of tanks, and may be incorporated with elastomers such as rubber or polyvinyl butyral. In examples, a resin obtained from equimolecular proportions of phenol and formaldehyde is: (1), (2) and (3), dehydrated and melted with varying proportions of resorcinol and paraformaldehyde, and (4) mixed with resorcinol and aqueous formaldehyde, followed by dehydration. Reference is made to the mixing of the product of example 1 with wood flour and to its solution in alcohol or acetone.