Continuous process for producing reinforced resin laminates

Claim 1

In a continuous process for producing a metal clad reinforced resin laminate comprising the steps of (a) impregnating a fibrous cellulosic substrate with a liquid unsaturated polyester resin which is free of volatile solvent and is capable of curing without generating liquid and gaseous by-products; (b) laminating a plurality of the resin-impregnated substrates into a unitary member; (c) sandwiching the laminate between a pair of covering sheets, at least one of which is a cladding metal foil capable of permanently bonding to the resin-impregnated substrates after the laminate is cured; and (d) curing the laminate while supporting it between the pair of covering sheets without applying any appreciable pressure thereto; the improvement comprising: (e) pre-impregnating the cellulosic substrate with a solution of (i) an N-methylol compound having an unsaturated bond capable of copolymerizing with a vinyl monomer, or (ii) an N-methylol compound lacking such a copolymerizable bond in admixture with a modifying agent having both a group capable of condensing or adding to the N-methylol compound and an unsaturated bond copolymerizable with a vinyl monomer, and then drying the pre-impregnated substrate; (f) impregnating the substrate from step (e) to a final resin content of 10-90% by weight, based on the total weight of the resin-impregnated substrate; (g) partially curing the sandwiched laminate in step (d) at an elevated temperature until the metal foil is firmly bonded in position and the entire structure is sufficiently hard and self-supporting to be cut into lengths with a guillotine cutter or movable slicer; (h) cutting a continuous length of the partially cured laminate into a predetermined length; (i) fully curing the cut length of said laminate at an elevated temperature to decrease warp and residual strain in the laminate; and (j) mechanically correcting any distortion in the configuration of the fully cured laminate by geometrically modifying the warp in two directions which are perpendicular to each other to form a finished product which is substantially flat, free of residual strain or internal stress, and resistant to changes in physical and electrical properties upon exposure to elevated temperatures.