GB646080A - A process for the preparation and application of reactive phenol-aldehyde resins - Google Patents

Abstract

Phenol-aldehyde resins, which are suitable for modifying rosin or ester gum in making drying oil varnishes, are prepared by reacting phenol and an aldehyde in two steps: (1) forming a Novolak in acid medium by condensing all the phenol with less than an equi-molecular ambient of aldehyde; and (2) condensing the Novolak with aqueous formaldehyde in a medium of strong alkali without addition of further phenol at a temperature not above 40 DEG C. to convert it into a Novolak polyalcohol, i.e. a Novolak in which the reactive positions have been wholly or partly substituted by methylol groups. The second amount of aldehyde is added in sufficient quantity to bring the ratio of total combined aldehyde to phenol up to at least 1 : 1. At the end of the first (acid) reaction the mixture contains about 20 per cent free phenol which may be distilled off or reacted with the aldehyde in the second stage. In examples: (1a) phenol, 470 g., and 37 per cent aqueous formaldehyde, 243 g., are reacted at 100 DEG C. in acid solution for 1 to 2 hours, 70 g. of 50 per cent NaOH is added, and the mixture reacted 4 to 5 days at 30 DEG C. with 485 g. aqueous formaldehyde. The mixture is neutralized with HCl and the resin filtered off; (1b) the product of (1a) is reacted with a mixture of gum rosin and glycerol; (2) similar procedure to that of (1) is followed, using, however, paraformaldehyde in forming the Novolak; (3a and 3b) similar procedure to that in (2) is followed. The product is then (3c) cooked with linseed oil and diluted with mineral spirits to form a varnish. Specification 261,472, [Class 81 (ii)], and U.S.A. Specification 1,699,727 are referred to.