High Surface Quality Long Fiberglass PU Composite

摘要

Polyurethane (PU) structural composites reinforced with long glass fibers are widely employed in many differentapplications in particular for the transportation industry. The production processes utilized to manufacture these compositesare known as structural RIM (Low Density-SRIM or High Density-SRIM) and, more recently, Long Fiber Injection, knownas LFI-PUR [1]. In particular the LFI technology is based on the simultaneous pouring of polyurethane and choppedfiberglass.This production process is well established in the market for over a decade and it shows several advantages compared withthe continuous mat technique (Structural RIM) in terms of part design freedom, fiberglass handling, no needs forthermoforming, just to mention a few.One of the major limitations of all the above composite technologies is related to the lack of exterior finishing due to thevisible fiberglass on the surface of the manufactured item. This has been a strong restriction confining the use of this PUcomposite only for hidden or covered parts.Therefore Dow Polyurethane Systems, a business group of The Dow Chemical Company, has recently developed a nextgeneration of polyurethane systems for long glass fiber composites capable of bringing additional advantages to the currenttechnology and better meeting industry needs.Combined with excellent internal mold release performance, the next generation long glass fiber composite systems offerimproved thermal stability, better fiber wettability and distribution, with no bubble and defects on the visible surface of thefinished item even when heating the composite at temperatures up to 120°C when compared to current compositetechnologies.Thank to this and to an optimized reaction profile these next generation polyurethane systems developed by Dow canprovide a long fiber composite showing high surface quality.In addition to this, Dow also developed a high temperature resistant compact rigid layer system that can be sprayed on themold just before the long fiber composite distribution, providing enhanced surface quality to the final part. This combinationallows obtaining high quality painted items by using both in-mold and off-line painting procedures.