VIEWPOINT | NEW RESINS SPEED CARBON-FIBER PARTS PRODUCTION

Carmakers are increasingly interested in composite parts reinforced with carbon fibers as a method to reduce vehicle weight and thereby improve fuel efficiency. But making such components is costly, largely because of the slow processing speed for the epoxy resins used to bind the fibers. Epoxies are tough and highly temperature resistant. They also are brittle, a characteristic that has further restricted the auto industry's use of carbon-reinforced parts.

But that is changing this year with the production debut of Loctite Max 2, a polyurethane resin from the adhesives technologies unit of Henkel AG & Co. KGaA. Max 2 significantly reduces processing speed and gives parts more flexibility.

Henkel also is unveiling Max 3, an even more advanced resin that retains the toughness and molding speed of Max 2 but adds an internal mold release, greater tolerance to paint oven temperatures and the ability to make in-mold parts with class A surface finishes. Scott Pergande, Director of Henkel's Adhesives Steering Unit, North America and Latin America North; and Scott Simmons, Business Development Specialist Lead for Composites, explain how the new resins expand the auto industry's options for adopting carbon-fiber reinforced components in high volumes.

Why is epoxy the current resin of choice for carbon-fiber composites?

Epoxy resins were developed for the aerospace industry and also are used to manufacture large windmill blades. They have become a proven material in those applications, so it was natural for carmakers to turn to epoxy-based composites as they looked for new ways to help them lightweight their vehicles. The challenge is cycle speed. It's not a big issue for the relatively low production volumes typical in the aerospace and wind energy industries. But it has been a major impediment to high-volume production parts for the automotive market.

What makes Loctite Max 2 and Max 3 attractive for automotive applications?

These new polyurethane resins enable manufacturers to make parts in minutes instead of hours. They are low-viscosity resins that penetrate and impregnate the fiber materials faster but more gently than traditional solutions, resulting in more consistent parts. We collaborated with Germany's KraussMaffei Technologies GmbH, a major maker of plastic molding equipment, to reduce the curing time for Max 2 to one minute.

Both resins are tougher and more flexible than epoxies, so they can be used in more places to make wheels, for example. Max 3 has a higher glass transition temperature (as great as 130 C compared with 90 C-115 C for Max 2), which makes it especially well suited for components that will go through a traditional paint oven. The inclusion of a release agent in the formulation means that production doesn't have to stop after approximately 1,000 pulls so mold release can be reapplied.

Are the new resins being used for production parts?

Max 2 is going into production right now. Benteler-SGL a venture between parts fabricators Benteler Automobiltechnik in Germany and SGL Carbon in Austria is using the resin to make a composite transverse leaf spring for Daimler AG's Sprinter van. The component weighs one-third as much as a conventional steel spring, and Benteler-SGL anticipates annual production of 100,000-150,000 parts.

What other applications are the auto industry developing?

Carmakers and suppliers recognize that Max 2 and Max 3 broaden their choices, and they are pursuing several options. Companies are looking at suspension parts, coil spring, B-pillars, bumper pillars and even some high-volume exterior body panels.

Isn't surface finish an issue for exterior carbon-fiber-reinforced composites?

Typically, there's a very significant amount of post processing required to achieve a class-A finish for these materials. But earlier this year we partnered with equipment and coatings suppliers to demonstrate a system that can make class-A finished roof panels at 120 C in less than six minutes. Parts emerge clean and with no need for further surface work.

The process begins by placing a preform in the mold. Then we infuse it for 3.5 minutes with Max 3 resin. Next, the mold is opened slightly and the part is sprayed with a two-part clear polyurethane topcoat and UV-resistant film. Finally the part is recompressed for two more minutes.

What about the cost?

The two big contributors to the cost of carbon-fiber-reinforced parts are cycle time and post processing. Loctite Max 2 and Max 3 significantly reduce the first and can eliminate the second, so these resins are real game-changers for the auto industry. Even greater savings are possible when multiple metal assemblies are replaced with a single molded part.

Click HERE to learn more about Henkel Adhesives Technologies. Visit www.HenkelNA.com/LightenUp to learn more about vehicle lightweighting or follow on Twitter: @henkelauto_na.