Abstract:
An epoxy-styrene solventless resin impregnating varnish, having an atmospheric catalyzed pot life at room temperature of at least 45 days, is made by mixing: (1) the product of the reaction of (a) 1 part of an epoxy resin mixture comprising solid epoxy resin having an epoxy equivalent weight of between about 390-2500 and liquid epoxy resin having an epoxy equivalent weight of between about 100-385, wherein the weight ratio of solid epoxy: liquid epoxy is between 1:1 to 1:10; with (b) between about 0.01 to 0.06 part of maleic anhydride and (c) between about 0.0001 to 0.005 part of a catalyst selected from the group consisting of piperidine, pyridine, imidazoles, and aliphatic tertiary amines; under such conditions that the reaction between the maleic anhydride and the epoxy resin mixture is substantially complete, and the epoxy diester formed has an acid number of between about 0.5 to 3.0; with (2) a coreactive vinyl monomer, and between about 0.00030 to 0.004 part of an aromatic acidic phenolic compound, selected from the group consisting of dinitrophenols and trinitrophenols; and finally with (3) between about 0.3 to 1.2 part of a polycarboxylic anhydride, which is soluble in the mixture of (1) and (2) at temperatures between about 0* to 35*C, and an amount of free radical catalyst selected from azo compounds and peroxides that is effective to provide a catalytic effect on the impregnating varnish to cure it at temperatures over about 85*C. Upon heating at a temperature over about 85*C, the impregnating composition cures to a thermoset resin.
Abstract:
COMPOSITIONS OF MONTHS-LONG CATALYZED POT LIFE AT ROOM TEMPERATURES AND HENCE ESPECIALLY SUITABLE FOR COATING LARGE OBJECTS, ARE MADE BY MIXING (A) THE PRODUCT OF THE UNCATALYZED HALF-ESTERIFICATION OF EPOXY RESIN WITH AN OLEFINCALLY UNSATURATED DICARBOXYLIC ACID ANHYDRIDE (E.G., MALEIC ANHYDRIDE) WITH (B) A COREACTIVE VINYL MONOMER (E.G., STYRENE), (C) A POLYCARBOXYLIC ANHYDRIDE CONTAINING NO OLEFINIC UNSATURATION (E.G., NADIC METHYL ANHYDRIDE (NMA) VISCOUS LIQUID METHYLBICYCLO (2.2.1) HEPTENE-2,3DIACARBOXYLIC ANHYDRIDE ISOMERS) AND (D) POLYMERIZATION CATALYSTS AND INHIBITORS. UPON HEATING, THE COMPOSITION CURES TO A THERMOSET RESIN. THE BASIC COMPOSITION IS MODIFIED WITH FILLERS AND ADDITIVES FOR USE AS POTTING COMPOUNDS, ENCAPSULANTS, CASTINGS, LAMINATE ADHESIVES, ETC.