Co-extrusion of acrylic ester polymer/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 CONSISYING OF HOMPOLYSTYRENE, IMPACT POLYSTYRENE AND NORMAL COPOLYMERS OF STYRENE CONTAINING A MINOR AMOUNT OF ANOTHER COPOLYMERIZABLE MONOMER, AND A MINOR LAYER CONSTITUTING LESS THAN 20% OF THE TOTAL FINAL TICKNESS OF AN ACRYLIC ESTER 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 ACRYLIC ESTER POLYMER, SAID SECOND STREAM CONSTITUTING LESS THAN ABOUT 20% BY VOLUME OF THE COMBINED FIRST AND SECOND STREAMS THEREBY FORMING A SINGLE STRATFIED STREAM OF HEAT PLASTICIZED MATERIAL CONFORMING TO THE CROSS SECTION OF SAID CONDUIT AND BEING CHARACTERIZED BY DISTINCT, CONTIGUOUS LAYERS OF SAID POLYMERIC MATEIRALS HAVING A RELATIVELY SHARPLY DEFINED INTERFACE THEREBETWEEN SAID INERTFACE TERMINAATING AT EACH END AT A POINT ON THE INSIDE SURFACE OF SAID CONDUIT ADJUSTING THE RESPECTIVE TEMPERATURES OF THE FIRST AND SECOND STREAMS UNDER CO-EXTRUSION CONDITIONS TO TEMPERATURES AT WHICH THE MELT VISCOSITY OF THE ACRYLIC ESTER POLYMER STREAM EXHIBITS A VALUE WITHIN THE RANGE OF ABOUR 50 TO 150% OF THE MELT VISCOSITY ESHIBITED BY SAID STYRENE POLYMER STREAM UNDER THE CONDTIONS OF A.S.T.M. TEST D-1238-63T, CONVEYING SAID COMPOSITE 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 MATERALS, AND PASSING SAID COMPOSITE, STREAM OF MOLTEN ATERIAL THROUGH THE SAID DIE TO FORM A SHEET, WHEREBY SAID SECOND STREAM SPREADS LATERALLY ACROSS SAID FIRST STREAM THEREBY FORMING SAID MINOR LAYER OF SAID COMPOSITE SHEETING.