| abstract |
Extruded articles having integral ribs and/or integral rows of spaced apart elements extending transverse to the direction of extrusion are formed by forcing a melt flowable material such as a thermoplastic polymer through an extrusion opening. The material is continuously extruded in a first lateral or annular extrusion zone in the extrusion opening while the material being extruded in a second lateral or annular extrusion zone, which is contiguous with the first zone, is periodically interrupted, modulated and/or restricted. |