Method and apparatus providing uniform resin distribution in a coextruded product
AssigneeMobil Oil Corporation
InventorFox J. Herrington
Life of this patent
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Abstract
Disclosed is a method and apparatus for ensuring uniform distribution of higher and lower viscosity or flow rate resins in a product produced by a coextrusion process. A flow restriction is provided in the flow path of the lower viscosity or flow rate resin to increase the pressure drop of this resin as it passes through a coextrusion die. The increased pressure drop introduced by the flow restriction causes the lower viscosity or flow rate resin to be more uniformly distributed in the extruded product. A specific die construction providing a uniform resin flow channel within the die is also described.
Claims10
A method of coextruding a first molten resin stream of relatively high viscosity or flow rate and a second molten resin stream of relatively low viscosity or flow rate through a tubular die orifice in uniform laminar flow comprising the steps of:
- flowing said first stream under pressure from a first molten resin supply through a first die channel to a flow junction region adjacent said die orifice;
- flowing said second stream under pressure from a second resin supply through a second die channel to said flow junction region, said second die channel containing a flow restriction for impeding the flow of said second stream and raising the pressure drop of said second molten resin at said junction region to a value considerably larger than the maximum difference in pressure drop of said second molten resin existing at said junction region along the terminus of said second channel in the absence of said flow restriction, said restriction also being sufficient to decrease the pressure differential that would exist from one side of the die to the other in the absence of said flow restriction said decrease being of a magnitude sufficient to prevent non-uniform coextrusion of said first and second resin streams;
- joining said first and second molten streams at said junction region;
- flowing said joined first and second molten streams from said junction region through said die orifice in laminar flow relationship to obtain a coextruded resin material having a uniform distribution of first and second resins therein.
An apparatus for coextruding a first molten resin stream of relatively high viscosity or flow rate and a second molten resin stream of relatively low viscosity or flow rate comprising:
- a source of said first molten resin;
- a source of said second molten resin;
- a tubular coextrusion die comprising an extrusion orifice for producing a coextruded resin material, a first resin flow channel coupled to said first molten resin source and terminating at a flow junction region adjacent said orifice, a second resin flow channel coupled to said second molten resin source and terminating at said flow junction region, said second flow channel containing a flow restriction therein for impeding the flow of said second molten resin therethrough and raising the pressure drop therein to a value considerably larger than the maximum difference in pressure drop of said second molten resin existing at said junction region along the terminus of said second channel in the absence of said flow restriction, said flow restriction also decreasing the pressure differential that would exist from one side of the die to the other in the absence of said flow restriction said decreasing being of a magnitude sufficient to prevent non-uniform coextruding of said first and second resin streams and, a flow channel coupling said junction region to said orifice.
Dependencies are inferred from the claim text.