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Development of Class A Surface Polyurethane LFI Composites

SpecialChem / Nov 9, 2009

Recent advancements in the Polyurethane Long Fiber Composite Injection (LFI) process have resulted in a dramatic increase in its commercial interest for producing a wide range of products including PWC's, entry door skins, truck body and spa panels. One of the main reasons for this success is a development in the polyurethane chemistry of the LFI process that allows long gel times on an open hot mold while maintaining a relatively short demold time. The chemistry and processing of LFI material will be discussed, with emphasis on structure/property relationship, density reduction through dissolved CO2, and in particular, the development of high surface quality (Class A) composites. We developed two technologies to obtain Class A surfaces on LFI parts:-
1) The use of an in-mold, hybrid polyester gel coat which serves both as a barrier layer to the glass read-through as well as the glossy surface.
2) An in-mold polyurethane paint. This technology to produce Class A composites with paint involves the use of in-mold paint, followed by a unique polyurethane barrier coat spray, designed to resist both thermal and mechanical deformation, and finally the addition of the long fiber PU material. The use of the polyurethane barrier spray in conjunction with LFI serves to shorten demold time as well as improve the surface quality by preventing the glass from showing through the surface. However, the use of any barrier spray does not guarantee a good surface, because it can easily be both thermally and mechanically deformed by the reacting LFI, which often results in surface waviness best described as orange peel. In this presentation we will describe a new class of PU barrier coat which resists deformation, thus resulting in composite materials with very low orange peel, as measured by a smoothness index of 9 or greater.

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