Patent ID: 6902385
Filing Date: 2005-06-07
Classification: B29C

Abstract:
1. Extrusion die apparatus, for manufacturing blown plastic film, wherein: the apparatus includes a die-member; the die-member is of generally annular form, having a circumferentially-disposed outer-face and inner-face; the die-member has a groove-face-A, which is of annular configuration, and which has an inner-edge-A; the groove-face-A is formed with melt-conveying-channels-A; the die-member includes a melt-entry-port, which is located in the outer-face of the die-member; the apparatus includes an annular groove-opposing-surface-A; the melt-conveying-channels-A include N spiral-grooves-A, which are open, and are formed into the groove-face-A; the apparatus is so arranged that melt, in flowing towards the inner-edge-A, spills over lands between turns of the spiral-grooves-A; the melt-conveying-channels-A are arranged, in relation to the groove-opposing-surface-A, for conveying liquid melt under pressure from the melt-entry-port in the outer-face, in a progressively inwards sense, through the spiral-grooves-A, to the inner-edge-A of the groove-face-A; the melt-conveying-channels-A include at least N supply-channels-A; the melt-conveying-channels-A include flow-divider-channels-A, which receive melt from the melt-entry-port, and divide the same into at least N incoming-streams, and convey the incoming-streams one each into the supply-channels-A respectively, the melt-conveying-channels-A include flow-mixing-channels-A; the flow-mixing-channels-A include subdivider-junctions-A and recombiner-junctions-A; at the subdivider-junctions-A, respective ones of the at least N incoming-streams from the supply-channels-A are sub-divided into respective left and right subdivided-streams; the recombiner-junctions are positioned inwards of the subdivider-junctions, and between adjacent subdivider-junctions, in the sense of being positioned to receive the subdivided-streams moving inwards from the adjacent subdivider-junctions, the melt-conveying-channels are so configured that, in respect of each one of the recombiner-junctions, the recombiner-junction receives the left subdivided-stream from the adjacent one of the subdivider-junctions to the right of that recombiner-junction, and receives the right subdivided-stream from the adjacent one of the subdivider-junctions to the left of that recombiner-junction, and combines that said left and right subdivided-streams into one recombined-stream respective to that recombiner-junction; the melt-conveying-channels-A include N of the recombiner-junctions, and the arrangement of the melt-conveying-channels is such that the N recombined-streams flow inwards, one each respectively, to the N spiral-grooves-A; and the melt-conveying-channels-A are so arranged as to convey melt from the melt-entry-port in the outer-face inwards first through the flow-divider-channels, then inwards through the supply-channels-A, then inwards through the flow-mixing-channels-A, then inwards through the spiral-grooves-A, then inwards towards the inner-edge-A of the groove-face-A; wherein the annular die-member has grooves both sides, in that: the die-member also has a groove-face-B, on the opposite thereof from groove-face-A; the groove-face-B is of annular configuration, and has an inner-edge-B; the groove-face-B is formed with melt-conveying-channels-B; the melt-conveying-channels-B include M spiral-grooves-B, which are open, and are formed into the groove-face-B; the melt-conveying-channels-B are arranged for conveying liquid melt under pressure from the melt-entry-port in the outer-face, in a progressively inwards sense, through the spiral-grooves-B, to the inner-edge-B of the groove-face-B; the melt-conveying-channels-A include at least M supply-channels-A; the melt-conveying-channels-B include flow-divider-channels-B, which receive melt from the melt-entry-port, and divide the same into at least M incoming-streams, and convey the incoming-streams one each into the supply-channels-A respectively; the melt-conveying-channels-B include flow-mixing-channels-B; the flow-mixing-channels-B include subdivider-junctions-B and recombiner-junctions-B; at the subdivider-junctions-B, respective ones of the at least M incoming-streams from the flow-divider-channels-B are subdivided into respective left and right subdivided-streams; the recombiner-junctions are positioned inwards of the subdivider-junctions, and between adjacent subdivider-junctions, in the sense of being positioned to receive the subdivided-streams moving inwards from the adjacent subdivider-junctions; the melt-conveying-channels are so configured that, in respect of each one of the recombiner-junctions, the recombiner-junction receives the left subdivided-stream from the adjacent one of the subdivider-junctions to the right of that recombiner-junctions, and receives the right subdivided-stream from the adjacent one of the subdivider-junctions to the left of that recombiner-junction, and combines the said left and right subdivided-streams into one recombined-stream respective to that recombiner-junction; the melt-conveying-channels-B include M of the recombiner-junctions, and the arrangement of the melt-conveying-channels is such that the M recombined-streams flow inwards, one each respectively, to the M spiral-grooves-B; and the melt-conveying-channels-B are so arranged as to convey melt from the melt-entry-port in the outer-face inwards first through the flow-divider-channels, then inwards through the supply-channels-B, then inwards through the flow-mixing-channels-B, then inwards through the spiral-grooves-B, then inwards towards the inner-edge-B of the groove-face-B; wherein the N spiral-grooves-A have a spiral-sense that is clockwise when viewed from one side of the annular die-member; the M spiral-grooves-B have a spiral-sense that is also clockwise, when viewed from that same one side of the die-member.