JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia - 76

KNOW-HOW Vacuum injection Initiator systems for vacuum injection The vacuum injection method is being used more and more for the production of polyester parts, particularly larger parts. Compared with other closed-mould methods, this process requires a relatively low investment and is currently the most attractive solution for solving the styrene emission problem. It is a very clean production method for both the environment and employees. will start the polymerization. When an inhibitor is used, care must be taken to make sure there is always enough peroxide left for curing the product properly. HARRY TER BEEK, TECHNICAL DEVELOPMENT MANAGER, THERMOSET PEROXYDES AKZONOBEL POLYMER CHEMICALS Gelcoat In vacuum injection, gelcoat application is a weakness in relation to styrene emission since it has to be carried out in the open air. The highest level of emissions is reached during spraying, but emissions continue during cure, up until the reinforcement has been applied and the equipment has been brought under vacuum. The emissions produced during spraying can be reduced by using a low-emission gelcoat, and this can be improved in the curing phase by using a fast-curing system. Akzo Nobel has developed a special fast-curing peroxide based on isopropylketone, Butanox P-50, for gelcoat application. This peroxide ensures rapid hardening of the gelcoat with the advantage of a lower styrene emission. It also shortens production time since the reinforcement and foil can be applied earlier. In addition, faster cure means higher gelcoat hardness when the laminate begins to harden, resulting in a smoother surface. T he mould and vacuum system can be developed with several specialized companies. The choice of the reinforcement material is very important and should not affect the flowability of the resin. The type of resin depends on the final application and it needs to have the right viscosity for injection. The peroxide formulation is often one of the last choices. The geltime of the formulation should be long enough to fill the mould properly, but the curing process has to start directly afterwards. Hardening should be fast and smooth so that the product can be demoulded as rapidly as possible without compromising quality. The end product should have optimum properties. For instance, the peak exotherm during cure should not be too high to avoid losing adhesion of the resin on the glass or even delamination. A good starting choice is Akzo Nobel’s standard, high-quality MEKP (methylethylketone peroxide) Butanox M-50. Due to its excellent composition of reactive and stable peroxide components, it ensures a good polymerization reaction under all circumstances. Long geltimes are generally needed, particularly for large products, and this can be achieved by using a special resin or peroxide. Using an inhibitor, such as the NLC-10 inhibitor, however, allows for more flexibility and is a more convenient way of adjusting the geltime. Ambient temperature, and especially the effects of summer and winter − always has a strong influence on reactivity. This can be directly corrected by the inhibitor, which acts in a very simple manner by destroying the first radicals generated before they can start the polymerization. As soon as the inhibitor is consumed, the next radicals generated Graph 1: Styrene emission after spraying − 15% lower emission with Butanox P-50 JEC Composites Magazine / No44 October 2008

JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #44 - October 2008 - Special Asia