IMPROVEMENT OF WELDLINE STRENGTH OF FIBER-REINFORCED POLYCARBONATE INJECTION-MOLDED ARTICLES USING SIMULTANEOUS COMPOSITE INJECTION-MOLDING

Fiber reinforced thermoplastics (FRTP) injection molded articles have many advantages. However, moldings with a complex geometry often encou nter weldline problems. Mechanical properties of the injection molding s are often reduced by weldlines, because the fibers at weldline regio ns orient perpendicularly to the flow directions. We have reported tha t weldline strength is improved by ''back-flow'' during the holding st age. In this article, we have attempted to adapt the SCI (Simultaneous Composite Injection) molding method to improve weld strength of FRTP injection moldings. The back-flow is expected to occur when there is a difference of holding pressure between two cylinders of the SCI moldi ng machine. The effect of pressure difference between two injection cy linders on the back-flow phenomena is discussed for fiber reinforced p olycarbonate. It is clear that the strength reduction by the weldline can be suppressed down to negligibly small levels in SCI molding. (C) 1995 John Wiley and Sons, Inc.