IKV develops gap impregnation molding system for polyurethanes

The German research and development group Institute of Plastics Processing (IKV) reports that it has worked with BASF to develop a gap impregnation process for the molding of fiber-reinforced polyurethane composite parts.

The German research and development group Institute of Plastics Processing (IKV) reports that it has worked with BASF to develop a gap impregnation process for the molding of fiber-reinforced polyurethane composite parts.

The Institute of Plastics Processing (IKV, Aachen, Germany) has announced the development of a gap impregnation molding process for polyurethanes. Gap impregnation is a fairly new process for the production of high-performance parts of fiber-reinforced plastics (FRP) in only a few minutes. In this process, which is similar to resin transfer molding (RTM), a temporary flow gap is created. This temporary flow gap and the inclined position of the mold result in rapid, reproducible injection of the resin system with low resistance. The exceptionally fast impregnation of the preform in the space of only a few seconds allows the use of the highly reactive resin systems that are needed for part production on an industrial scale.

At the Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University, an automated gap impregnation unit was developed in 2009 and installed in the IKV pilot plant. Recent tests with the unit have been aimed at using not only epoxy resin systems but also alternative resin systems such as polyurethanes (PU) for the series production of composite parts. In cooperation with IKV, BASF Polyurethanes GmbH (Lemförde, Germany) has developed a new, highly reactive and compact crosslinking PU system for FRP.

In this project, attention is focused on the verification and optimization of a long open processing time of the PU system during injection and impregnation of the FRP parts in combination with fast, latent crosslinkage with isothermal mold temperature control. Furthermore, demolding behavior is analyzed with the use of internal release agents.

For the tests, both flat and curved parts with varying thicknesses and a projected surface area of 250,000 mm²/387.5 inches2 are used. The parts are made of glass- and carbon fiber-reinforced plastics. Irrespective of the reinforcing fiber, the fiber volume fraction of the continuous fiber-reinforced parts is between 45 and 50 percent. Process times of less than six minutes – from mold closure to removal of the crosslinked part – were achieved. Depending on the volume of the part, the injection, impregnation and consolidation account for a maximum of 23 seconds, while crosslinkage of the parts in the mold, heated isothermally to 80°C/176°F, takes about four minutes. It was thus possible to successfully demonstrate a sufficiently long processing time of the latent reacting PU systems in the impregnation and consolidation process. Furthermore, a new modification of the PU systems with internal release agents allows reliable demolding. The impregnation quality of the parts is very good and comparable with that of highly reactive epoxy resin systems. This means, says IKV, that the PU systems developed by BASF are an attractive alternative to epoxy resin systems.