Encapsulant compositions based on anhydride-hardened epoxy resins

Claim 1

An epoxy molding composition, suitable for use as an encapsulant having improved high temperature wet electrical properties, comprising: a. an epoxide compound having at least two 1,2-epoxide groups; b. a hardener therefor selected from the group consisting of (1) a polyanhydride having a molecular weight below about 1,000 and being the reaction product of a maleic monomer and at least one alkyl styrene monomer and (2) prepolymers of said polyanhydride with said epoxide compound; c. a catalyst to promote the curing thereof; d. about 55 to 75% by weight, based on the weight of the composition, of a silica filler; e. about 10 to 20% by weight, based on the weight of the composition, of an additional filler selected from the group consisting of calcined clay, antimony trioxide, antimony tetraoxide, calcium silicate, titanium dioxide, calcium carbonate, zinc oxide, magnesium oxide, or mixtures thereof; f. about 0.05 to 2% by weight, based on the weight of the composition, of a silane coupling agent; and g. about 0.01 to 2% by weight, based on the weight of the composition, of a lubricant selected from the group consisting of carnauba wax, montanic acid ester wax, polyethylene wax, polytetrafluoroethylene wax and mixtures thereof, said composition, when heat cured, exhibiting improved high temperature wet electrical properties as indicated by a decreased percent change of the Dielectric Loss Index measured after exposure to 15 psig steam for 16 hours from the Dielectric Loss Index measured under dry conditions at 25° C.