The hot plate is impregnated with a thermosetting resin containing no halogen-based flame retardant on a substrate obtained by impregnation with a solution containing an alkoxysilane derivative and/or a condensate thereof, and dried by heating to obtain a prepreg. For the blank, the prepreg is stacked in several pieces, and copper foil is stacked on one side or both sides as needed, and laminated by heating and pressing.
It can be widely used in various plastic forming operations such as extrusion, pressing, stamping and drawing of various metal sheets. Such as silicon steel sheet, carbon steel, stainless steel, aluminum alloy, non-ferrous metals and their alloys. The concentration should be slightly increased when stamping silicon steel sheets and stainless steel.