Process for preparing expandable plastic granules

摘要

In a process for prodn. of expandable plastic granules (C) from plastic melt where the blowing agent is only partially soluble in a specific high pressure region: i) blowing agent is dispersed in the melt; ii) melt is retained for a period within specific pressure limits; iii) melt is cooled to a few deg. above the solidification temp. and granulated. All process stages up to granulation are performed in static mixers to prevent demixing. Process appts. comprises several static mixers (1,2) for incorporating the blowing agent (B) in the melt (A), a cooler (3) with heat exchanger elements forming part of a static mixer and a granulator (4). Also claimed is a complete plant including the above units (1,2,3,4) and has additionally i) appts. (10) for melt prodn.; ii) storage (20) for blowing agent; iii) a metering pump (21), and (iv) a control unit for the blowing agent (B) supply to the melt (A'). A use is claimed for prodn. of expandable PS granules from new or recycled PS incorporating a low boiling pt. hydrocarbon blowing agent esp. pentane.