To reduce the generation of copper foil wrinkles by a method in which after a fiber backing being impregnated with a kind of thermosetting resin varnish, the backing is heat-dried, a prepreg main body in which the thermosetting resin was cured to a B stage is pressurized while being cooled, and the surface is smoothed.
A lengthy fiber backing 1 such as a glass cloth, after being impregnated in an impregnation tank 3 with a kind of epoxy resin varnish 2 deformed by vacuum deaeration, is heat-dried continuously by a drier 4 to prepare a prepreg in a B stage. The prepreg which is discharged continuously from the drier 4, in the course of being cooled, is passed through two press rolls 6 and press-pinched, and the surface is smoothed. In this way, by using the remaining heat of the prepreg, the surface of the prepreg discharged continuously from the drier 4 can be smoothed. Even when the prepreg is used for copper-clad laminated board using very thin copper foil, the generation of copper foil wrinkles can be reduced.
MISAWA HIDETO
HIGASHIDA TOSHIYUKI
