ポリスチレン射出成形品における並走流ウェルドラインの破壊挙動

抄録

Although V-notches at weldlines in injection moldings are regarded as the causes of the reduction of mechanical properties and visual defects, few researchers have investigated the role of V-notches in the fracture behavior of weldlines. The fracture behavior of an adjacent flow weldline occurring behind an obstructive pin in injection-molded polystyrene plates was investigated by a fracture test which followed the technique of the double torsion test. The behavior of crack propagation was quite different between the upstream side and the downstream side of the weldline. There was a distinct boundary point between the sides. We defined the length of the upstream side as weldline length of fracture, L_wf. The crack propagated first in the sub-layer below the V-notch along the weldline and second inwardly from the sub-layer within L_wf. On the other hand, the crack at the sub-layer and that at the inward part propagated simultaneously in the area beyond L_wf similar to non-weld specimens. The fracture behavior had a close relationship to the V-notch shape. The V-notch depth showed little change within L_wf, while the depth decreased drastically in the area beyond L_wf. This relationship suggested that the difference of the fracture behavior was caused by the degree of molecular entanglement at the sub-layer below the V-notch.