Environmentally durable lightning strike protection materials for composite structures

Claim 1

A fiber-reinforced thermosetting matrix resin prepreg/film adhesive/metal screen combination suitable for co-curing into lightning strike protected fiber-reinforced thermoset composite structures, comprising: a) one or more plies of a fiber-reinforced prepreg impregnated with a thermosettable matrix resin sufficient to prepare a composite structure of a desired thickness; b) a conductive metal screen having a nominal thickness of from 1 mil to 10 mils; and c) a thermosettable film adhesive; wherein the diffusion coefficient of the thermosettable prepreg matrix resin into the film adhesive satisfies the equation D<[T.sub.a ].sup.1.5 /V.sub.a ·[T.sub.p /V.sub.p ] where D is the diffusion coefficient, T a is the dwell time of the adhesive resin at minimum viscosity V a is the minimum viscosity of the adhesive resin, T p is the dwell time of the prepreg matrix resin at minimum viscosity, and V p is the minimum viscosity of the prepreg matrix resin, T a , V a , T p and V p having been determined from the viscosity profile of the respective resin during cure at the same temperature/time ramp of 1°-2° C./min, and wherein D=0.1 when T a 1 .5 /V a <0.3; or where irrespective of D, T a 1 .5 /V a <0.3.