Method of co-extrusion of polyvinylidene fluoride/polystyrene multiple-layered sheeting

Claim 1

A process for the manufacture of composite sheeting having a major layer corresponding substantially to the final composite sheeting thickness of a styrene polymer selected from the group consisting of homopolystyrene, impact polystyrene and normal copolymers of styrene containing a minor amount of another copolymerizable monomer, and a minor layer of vinylidene fluoride polymer firmly united to the exterior surface of said major layer, comprising: conveying a heat plasticized stream of said styrene polymer in a conduit having a generally circular cross section, joining to the exterior surface of said styrene polymer stream within the said conduit a second, heat plasticized stream of said vinylidene fluoride polymer, thereby forming a single stratified stream of heat plasticized material conforming to the cross section of said conduit and being characterized by distinct, contiguous layers of said polymeric materials having a relatively sharply defined interface therebetween, said interface terminating at each end at a point on the inside surface of said conduit, adjusting the melt viscosity of the vinylidene fluoride polymer, by adjusting its temperature, to a value within the range of about 50 to 150% of the melt viscosity exhibited by said styrene polymer under extrusion conditions, conveying said stratified stream undisturbed through said conduit to a sheet-form extrusion die having its die lips generally aligned in parallel with the said interface between the two polymeric materials, and passing said stratified stream of heat plasticized material through the said die.