초록 ▼

A method and apparatus for carrying out the method are for forming a sheet or film of thermoplastic polymer alloy by extruding an intimate blend of incompatible polymer materials, such as polypropylene dispersed in LLDPF, through an extruding die and stretching after extrusion. In the die upstream f

A method and apparatus for carrying out the method are for forming a sheet or film of thermoplastic polymer alloy by extruding an intimate blend of incompatible polymer materials, such as polypropylene dispersed in LLDPF, through an extruding die and stretching after extrusion. In the die upstream from the exit is a grid chamber comprising one or more grids, the grid or grids having at least 4 (in the longitudinal sections perpendicular to the main surfaces of the flow) closely spaced lamellae (303) having walls extending several millimeters in the direction of the flow which are interconnected (306) at intervals such that viewed in sections perpendicular to the direction of flow they form a network, the intervals being essentially longer than the distance between each pair of lamellae and between the lamellae apertures of a size selected to reduce the average size of the dispersed phase of P1 or P2 in the blend, the grid or grids being located at a position in the chamber where the gap is wider than the said exit gap, the grip chamber further comprising a gap reduction portion between the screen and the die exit wherein the gap through which the blend flows is reduced at least part way to the gap of the die exit. There may be two grids with parallel lamellae arranged so that the lamellae of the downstream grid are located mid-way between the lamellae of the upstream grid.

대표청구항 ▼

I claim: 1. A method of forming a thermoplastic film or sheet comprising the steps of:supplying at least a polymer material P1 and a polymer material P2 to a die, where the die comprises:inlets for the polymer materials P1 and P2,a chamber including:at least one screen (301, 302) positioned in the c

I claim: 1. A method of forming a thermoplastic film or sheet comprising the steps of:supplying at least a polymer material P1 and a polymer material P2 to a die, where the die comprises:inlets for the polymer materials P1 and P2,a chamber including:at least one screen (301, 302) positioned in the chamber perpendicular to a direction of flow, where each screen includes:flattened apertures sized to reduce an average size of a dispersed phase of the polymer material P1 or P2 in a blend of the polymer materials P1 and P2 and to form flattened fibrils of the dispersed phase in the blend, lamellae (303, 304, 305) interposed between adjacent apertures along their long sides, interconnections (306, 307, 308) portions interposed between adjacent apertures along their short sides, where intervals between interconnections between the lamellae are greater than a distance between each pair of where the apertures form a network of apertures having at least four lamellae interposed between apertures when viewed in cross-section,a gap reduction portion andan exit orifice having an exit gap,where the screens are located at a position in the chamber having a chamber gap wider than the exit gap, and where the gap reduction portion is disposed downstream of the screens and is adapted to dimensionally reduce the chamber gap to a dimension of the exit gap,extruding the blend of the polymer materials P1 and P2 through the chamber, the screens, the gap reduction portion and the exit orifice to form an extruded film having flattened fibrils of the dispersed phase in the blend, where each fibril extends substantially in one direction and where each fibril has a width and a thickness and the width is greater than the thickness, andstretching the extruded film to form a stretched film.