Thermoplastic film extrusion apparatus
AssigneeWestvaco Corporation
InventorsDouglas C. Miller, Terry W. Wolfe
Life of this patent
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Abstract
A viscous flow thermoplastic film is extruded as a variant thickness profile curtain by means of an extrusion die having a flow choke rod extending longitudinally parallel with the die jaws and positioned within one die jaw for chordal projection into the die flow channel. The choke rod is surface relieved by chordal flats at locations corresponding to film zones of greater thickness. A single rod may be provided with as many profile pattern sequences as space and dimension allows chordal segments around the rod circumference. Pattern selection may be changed under die running conditions by rotating the profile rod about its axis to align the flats of the desired pattern within the die flow channel.
Claims10
A thermoplastic film extrusion die having a viscous flow channel between a pair of opposed die jaw faces, one such jaw having a bore channel formed longitudinally therein to receive an axially elongated cylindrical rod means therewithin having a substantially smooth cylindrical surface, a chordal segment of the circular section of said rod projecting beyond said one jaw face partially into said flow channel to form a zone of open but restricted flow area extended continuously along the length of said flow channel between said smooth cylindrical surface and said other jaw face, said smooth cylindrical surface being interrupted at select locations along the length thereof by cordal flat means to increase the flow area and reduce the restriction to thermoplastic flow in said channel past said rod means in regions of said channel adjacent said chordal flat means.
A thermoplastic film extrusion die means having a viscous flow channel between a pair of spaced die jaws terminated between spaced, parallel extending die lips, the improvement comprising axially elongated and rotatable rod means positioned within one of said die jaws asymmetrically of said flow channel to project an axially extended first arc segment thereof partially into said channel, first sectional portions of said arc segment having first axial length projecting a first distance from a channel face of said one die jaw into said flow channel to provide a first flow area and viscous flow restriction in said channel between said rod means and the other of said die jaws in channel regions adjacent said first sectional portions, and second sectional portions of said arc segment having second axial length and projecting a second distance from said one die jaw face into said flow channel to provide a second flow area greater than said first flow area and viscous flow restriction less than said first flow restriction.
Dependencies are inferred from the claim text.