Coextrusion process for overcoming the curtaining effect

Claim 1

A process for extruding thermoplastic materials, said process comprising the steps of (a) passing a molten thermoplastic stream that is flowing at a relatively greater pressure at a side-to-side midpoint than at the sides thereof, through a multimanifold die restriction channel of increasing cross-sectional area from the center thereof to each end thereof, so that the molten stream is subjected to an inverse resistance to flow and thereby caused to flow at substantially equal pressure from side to side; (b) while maintaining said substantially equal pressure, expanding the cross-sectional thickness of the molten stream; (c) while continuing to maintain said substantially equal pressure, reducing the cross-sectional thickness of the expanded stream; (d) converging the thickness-reduced molten stream with at least one other thickness-reduced stream that is flowing at substantially equal pressure from side to side, to form a melt-laminate; and (e) maintaining said substantially equal flow pressure for each stream of said melt-laminate, until said melt-laminate exits from said multimanifold die whereby the curtaining effect is minimized or eliminated in said melt-laminate.