Process for manufacturing prepreg

A process comprising

• impregnating a glass fiber substrate with a solvent to form a solvent-impregnated glass fiber substrate, then
• passing the solvent-impregnated glass fiber substrate through an air stream at a temperature lower than the boiling point of the solvent,
• impregnating the solvent-impregnated glass fiber substrate with a first epoxy resin to form an epoxy resin-impregnated glass fiber substrate,
• partially or completely curing the first epoxy resin in the epoxy resin-impregnated glass fiber substrate by heating at 140-200° C. for from 1 to 5 minutes to form a glass fiber substrate having an inner layer,
• impregnating the glass fiber substrate having the inner layer with a second epoxy resin which may be the same or different from the first epoxy resin to form an epoxy resin-impregnated glass fiber substrate having an outer layer, and
• partially or completely curing the first and second epoxy resins in the epoxy resin-impregnated glass fiber substrate having the inner layer by heating at 140-200° C. for from 1 to 5 minutes to form an outer layer,
• to form a prepreg,
• wherein the first epoxy resin in the inner layer has a degree of cure of 85% or more and the second epoxy resin in the outer layer has a degree of cure of 60% or less, and
• wherein the amount of solvent in the solvent-impregnated glass fiber substrate after passing the solvent-impregnated substrate through the air stream and before impregnating the solvent-impregnated glass fiber substrate with the first epoxy resin is 16 to 25 parts by weight per 100 parts by weight of the glass fiber substrate.