Impacts and Improvements of Twin-screw Extruder Co-extrusion Processes on the Wollastonite Dispersions in the High-temperature Nylon-based LED Support Materials
Impacts and Improvements of Twin-screw Extruder Co-extrusion Processes on the Wollastonite Dispersions in the High-temperature Nylon-based LED Support Materials
To solve the problems of low mechanical properties and frequent nozzle blockage leading to insufficient glue in the injection molded parts of high-temperature nylon(PPA)-based luminous diode(LED)support materials during the blending modification processes,the effects of the screw combinations and the key dimensional parameters of the twin-screw side feeder on the mechanical properties and dispersion of wollastonite were studied.The impacts of the presence of wollastonite aggregates in the products on the injection molding process were also investigated and analyzed.The results indicate that using an eccentric structure three-head meshing block to disperse and mix wollastonite and using a twin-screw side feeder with a low outer-inner diameter ratio and larger clearance with the main screw to feed wollastonite would cause the formations of wollastonite aggregates under mechanical extrusion pressure during the blending modification process,resulting to a decrease of product tensile strength from 79.9 MPa to the minimum of 52.2 MPa and a decrease of bending strength from 147.1 MPa to the minimum of 105.6 MPa.This also leads to a significant increase in nozzle blockages during the injection molding process,causing a severe abnormal rise in the rate of insufficient glue in the molded parts.However,replacing the eccentric structure three-head meshing block with a twin-head meshing block to disperse and mix wollastonite and using a more powerful feeding twin-screw side feeder(higher outer-inner diameter ratio and smaller clearance with the main screw)to feed wollastonite could effectively solve the problems of low mechanical properties caused by wollastonite aggregations and frequent glue insufficiency during the injection molding process.
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