GB1105141A - Thermosetting epoxy resin compositions - Google Patents

Abstract

Solvent-free thermosetting epoxy resin compositions which are liquid in the absence of a filler comprise a mixture of (A) a polyglycidyl ether of a polyhydric phenol having a viscosity of less than 30,000 cps. at 24 DEG C. and containing at least 1.5 oxirane groups per average molecular weight, and (B) (1) castor oil having an iodine value of at least 50 or liquid esters of ricinoleic acid and polyhydric aliphatic alcohols which esters have a molecular weight of 35-1100, a hydroxyl number of 100-350, a functionality of 2-5 and a viscosity at 24 DEG C. of 30-4000 cps., the amount of oil or ester being 40-110 wt. per cent based on the wt. of (A), and (2) maleic anhydride or an adduct thereof with an olefin which adduct has a m.p. not greater than 40 DEG C. The composition includes 1-1.5 oxirane groups for every carboxyl group produced by reaction between the castor oil or ester and the anhydride and for every anhydride group of unreacted anhydride, and includes at least 20% more anhydride groups than are necessary to provide one anhydride group for each hydroxyl group originally present in the castor oil or ester. Preferably the oil or ester have been pre-reacted with the anhydride, otherwise an esterification catalyst is necessary in the composition. Monoepoxides, 2,4,6 - tris (di - methylaminomethyl)phenol, pigments, granular or fibrous fillers and thixotropes may be added. Components (A) and (B) are mixed immediately before use and may be coloured differently as an indication of complete mixing. Alternatively (A) and (B)(2) may be promixed. The compositions may be cast and are useful for encapsulating electrical components.ALSO:Castor oil is esterified with an excess of maleic or hexahydrophthalic anhydride by heating in the presence of stannous octoate.