GB577561A - Phenol-formaldehyde resins - Google Patents

Abstract

Resins which can be blended with drying oils to yield quick drying varnishes forming durable films of good resistance to water, acid and alkalies are prepared by heating a mixture of o-cresol with p-hydroxydiphenyl or with o-hydroxydiphenyl or with a mixture of p- and o-hydroxydiphenyls, the o-cresol constituting 20-90 per cent by weight of the mixture, with aqueous formaldehyde in the presence of a strongly alkaline catalyst, until the resole formed separates from the aqueous layer, removing the resole from the aqueous layer and heating it under dehydrating conditions. About 0.9 to 1.1 mols. of formaldehyde are generally used per mol. of mixed phenols. Suitable catalysts are caustic soda, ammonia, caustic potash, calcium hydroxide, or trimethyl benzene ammonium hydroxide. The reaction is preferably performed under a reflux condenser. Dehydration may be performed by heating in a stream of inert gas such as carbon dioxide up to a temperature of 130 DEG C. The resin may then be hardened for storage by heating for 5-75 minutes at 150 DEG C., or it may be cooked with a drying oil, e.g. tung oil, to yield a varnish to which conventional driers such as cobalt or lead linoleates or naphthenates may be added. Examples 1-8 give particular details of proportions, times and temperatures for the preparation of resins from mixtures of o-cresol with p-hydroxy-diphenyl. Example 9 describes the preparation of a resin from a mixture of o-cresol with o-hydroxydiphenyl. Example 10 describes the preparation of a resin from a mixture containing o-cresol, p-hydroxydiphenyl and o - hydroxydiphenyl. Specifications 347,737, 417,122, 433,539 and 467,081 (as open to public inspection under Sect. 91) are referred to.