Offering high strength combined with low weight, glass or carbon fiber-reinforced composite materials are especially suited for the manufacture of motor vehicle components. Particularly for mass-produced automobiles, resin injection processes such as RTM now predominate.

Henkel has pooled its expertise in developing composite matrix resins and in fundamental research on adhesives and surface modification to engineer a complete and coherent system for the manufacture and integration of composite components in the automobile.

The polyurethane-based matrix resin technology Loctite MAX 2 offers an attractive properties profile tuned to the requirements of the automotive industry. Good handling capability in the RTM process combined with low injection viscosity and controllable cure speed permits short cycle times (< 5 min) in composite component manufacture. The excellent intrinsic toughness of the resin results in higher resistance to dynamic loading and greater fatigue tolerance.

Compared with the epoxy resins normally used for RTM, the new Loctite MAX 2 offers a combination of good mechanical properties and high damage tolerance.

One special feature of the polyurethane matrix resin is its high stress intensity factor, which is a measure of toughness. The specific interactions between the polyurethane molecules that take place in addition to chemical cross-linking help to enhance this property.

The toughness of the resin also has a positive effect on the fatigue behavior under load. The high tolerance to stress peaks delays the formation of critical cracks, thus prolonging the part life. In automobiles, which are constantly subjected to dynamic loading under driving conditions, materials with a high fatigue tolerance are essential in order to be able to exploit lightweighting potential to its fullest extent.

Loctite MAX 2 features extremely low viscosity, even at low temperatures, permitting very fast resin injection without distorting the fibers while also achieving good wetting even with high fiber volumes.

The polyurethane chemistry makes it possible to control the curing reaction more reliably, either by adjusting the temperature or adding an accelerator. The generally low heat generation during curing allows fast curing even of thick parts with many layers of fibers and reduces the risk of local overheating and resulting defects.

Henkel and KraussMaffei have demonstrated that using the new resin system on high-pressure RTM equipment can significantly reduce manufacturing cycle times. Loctite MAX 2 cures much faster than the comparable epoxy resins that are mainly used in the RTM process today. This was exemplified by achieving a cure time of just one minute with a real-life three-dimensional component.

The resin is injected into the preheated mold under vacuum and removed after one minute. The fiber volume was approximately 50%, with no fiber distortion being detected regardless of the laminate structure. Milling to the final shape was performed directly after cooling of the components.

Even though high-pressure polyurethane processing and high-pressure RTM are already state-of-the-art, the machine technology does require some adaptation for the polyurethane RTM process. Building on Henkel’s processing expertise, KraussMaffei’s engineers further optimized the mixing and dispensing stations and the mixing heads in order to improve the high-precision dispensing technology and thus the controllability in high temperature processes.

First applications are already in the commercialization phase.