射出成形品のひけ発生位置に対する固化層の発達状況と樹脂−金型間の粘着性の影響
Location of Sink-marks on the Surface of Injection-molded Polymer Strips Controlled by the Heat Transfer
黒崎晏夫・佐藤 勲・斉藤卓志
Kurosaki, Yasuo / Satoh, Isao / Saito, Takushi
This paper deals with a technique for improving the shape quality of injection-molded polymer products by controlling the heat transfer within the mold. In this paper, the authors tried to find a refined technique for improving the sink-mark problem, and examined the mechanism governing the sink-mark generation on an asymmetrically cooled polystyrene strip from the standpoint of thermal engineering. Sink-marks due to the shrinkage are considered to be controlled by both the cohesion between the molten polymer and the mold wall, as well as the stiffness of the frozen layer which gradually develops within the molded polymer adjacent to the mold wall. Although limited to polystyrene strip, the results obtained in the present study showed that the cohesive power of the molten polymer increases rapidly when the mold wall temperature exceeds the thermal deformation temperature of the polymer, and that the thickness of the frozen layer, which dominates its stiffness, monotonously increases with increasing time elapsed after the shot and decreasing with the mold wall temperature.
Key words: Injection-molded polymer strips / Sink-marks / Cohesion / Frozen layer / Heat transfer control