二軸押出機内の樹脂挙動解明―可塑化ステップにおける(懸濁重合)PVC配合紛の圧縮および輸送挙動―
Study on the Resin Behavior in Intermeshing Twin Screw Extruder-Compacting and Conveying Behavior of (Suspension) PVC Compound in Plasticizing Step-
元田武彦・石原 誠
Motoda, Takehiko / Ishihara, Makoto
This study was conducted both experimentally and theoretically in order to elucidate the behavior of particulate resin such as PVC compound in the compacting and plasticizing step in an intermeshing counter-rotating twin screw extruder. Firstly, the compaction and friction characteristics of PVC compound were measured, since they play an important role in the plastication of solid polymer. Then by using a counter-rotating twin screw extruder of 91.2mm diameter, measurements of bulk density distribution, pressure and temperature rise in the plasticizing step were undertaken under various processing conditions in order to clarify the compacting and conveying behavior and to theoretically formulate the solids conveying efficiency and in-channel pressure rise.
It was found that the bulk density distribution is formed along the C-shaped chamber while exponential pressure rise is generated. The particulate solids conveying characteristic is determined by the amount of backward leakage flow through the intermeshing region and formulated as a conveying efficiency depending upon the screw shape and bulk density distribution due to the frictional forces on the plug state resin in the C-shaped chamber. Also, it has been clarified that over 80% of the plug temperature rise in the compacting and plasticizing step is due to frictional and viscous heat generation during passage through the intermeshing region. Observations of in-channel resin sampled after the barrel was pulled out, confirmed that material through the intermeshing region leaks backwards with a thin folded pattern being developed.
Key words: Intermeshing (counter-rotating) twin screw extruder / Polyvinylchloride / Plasticizing / Friction coefficient / Conveying efficiency