Methods for purging process lines of additives for thermoplastic materials

摘要

Methods are provided whereby additive for thermoplastic materials may be recovered in a primary additive supply system simultaneously with the supply of an additive from a secondary additive supply system to a molten thermoplastic stream. Each of the primary and secondary additive supply systems is provided with respective recirculation lines so as to prevent sedimentation of the additive. According to the present invention, therefore, a protocol is employed whereby substantially all of the additive in the additive supply system, including that quantity of additive in the recirculation lines, may be recovered so that a fresh supply of additive (which oftentimes is different from the previous additive) may be connected for injection into the molten thermoplastic stream at the appropriate time.