Even in years when vehicle sales are slow, there are always a few new cars and trucks in hot demand when the new model year starts. The same is true in automotive materials. The hot new material this year -- at least in interiors -- is a real mouthful: low-density structural reaction-injection molded polyurethane (LD-SRIM), or RIM-Urethanes.

Vehicle interiors are dominated by just two plastic materials in the U.S.: polypropylene (PP) and acrylonitrile butadiene styrene (ABS), and they are locked perpetually in a life-and-death struggle for market share. But as the new '96 models roll out, materials experts warn that as these two plastics giants continue to grapple, they should keep an eye on this young newcomer that's beginning to win respect and a following in North America. LD-SRIM is low-cost, very lightweight, and it has won applications on 20 or more major vehicle programs through the '98 model year. It's use -- measured in pounds consumed in North American-built vehicles -- is growing 15% to 20% annually.

"It's made impressive gains from a year ago because it's lightweight, and that's an awfully strong incentive to offer Detroit," says Jim Best, President of Market Search Inc., a Toledo, OH-based automotive plastics consulting company.

In 1990, LD-SRIM wasn't even used in the auto industry. Now the North American automotive market consumes well over 3 million lbs. (1.4 million kg) of the material annually. Market Search predicts consumption will increase to at least 15 million lbs. (6.8 million kg) by 2005. Some industry insiders say that's far too conservative, arguing that LD-SRIM use could grow to 20 million lbs. (9 million kg) or more in the next 10 years.

That's small potatoes compared with the 62 million lbs. (28 million kg) of PP that Market Search says will be consumed by the North American auto industry in 1995 and the 224 million lbs. (102 million kg) it's predicted to use by 2005, but still nothing to sneeze at. LD-SRIM parts are made by placing a continuous-strand glass fiber mat into a mold and then injecting two reactive water-blown polyurethane liquids into the mold. In a chemical reaction, the two polyurethane components harden into a foam that encapsulates the glass mat, resulting in a glass-reinforced structural composite.

Unlike thermoplastics or wood-fiber composites used to make interior trim panel substrates, the structural RIM process has the unique capability of yielding parts in a wide range of densities and physical properties, producers say.

By varying the density of the foam, the glass content and the thickness, a design engineer can create everything from a featherweight door panel to a tough, stiff, structural part such as a bumper beam, proponents say.

LD-SRIM got its foot in the door, so to speak, with door panels on heavy American luxury cars. LD-SRIM's ability to chop weight by 40% to 60% won it applications for door panel substrates on General Motors Corp.'s Oldsmobile 88 and Aurora/Riviera in the early '90s as engineers fought to save weight any way they could. Applications on other beefy models such as Ford Motor Co.'s Lincoln Town Car and Continental have followed.

These successful applications, coupled with the material's low tooling costs, have led OEM engineers to specify LD-SRIM for numerous other interior trim substrates, including package trays, seat pans, seat backs, sunshades and sun visors.

LD-SRIM also has expanded out of the luxury car niche and now is used for door panels on high-volume, mainstream vehicles such as the Buick Skylark/ Oldsmobile Achieva, and GM's Astro/ Safari M-vans. It also is scheduled for the door panels on Chrysler Corp.'s '98 LHS, and several new high-volume light-truck programs.

The Ford Probe package tray is a typical example of what the material can do, says ICI polyurethanes Group. Substituting LD-SRIM for molded wood fiber reduced part weight by 40% and cut production costs by 20%.

What's driving the demand? "Weight is the number one factor," says Bharat G. Naik, technical supervisor at ICI Polyurethanes Sterling Heights Div. However. he says far cheaper tools and high durability and impact strength also have helped the material gain acceptance -- especially in trucks.

LD-SRIM's small, but growing, niche has been especially rewarding to ICI Polyurethanes. Competitors such as Bayer Corp. and Dow Automotive Materials & Services Group were doing developmental work with the material in the 1980s similar to ICI's, but they didn't push hard into low-density interior panel applications. ICI's pioneering work in this area has won it more than 90% of the current applications.

Now, as market growth skyrockets, Bayer and Dow are starting to circle hungrily. "We are supplying several molders with materials that are making parts, and we intend to be a bigger player in the future," affirms Dave Ahlgren, director of automotive polyurethane sales at Bayer.

Even so, there may be room enough for everyone as SRIM expands into new areas such as higher density, structural applications including seat pans and backs and possibly load floors. LD-SRIM already is used for seat pans on Olds Aurora rear seats and the front seat backs. Structural seat parts may soon be in the cards. Other applications include spare tire covers, instrument panel retainers and consoles.

What's next on the agenda for this swiftly growing material? Further productivity increases, aided by the introduction of internal mold releases (UMRS), says ICI's Mr. Naik.

Productivity issues likely will become a major issue for LD-SRIM producers as competition heats up. For instance, Bayer's Mr. Ahlgren is quick to point out that his company has had a proprietary IMR product "from the get-go."

IMRs are lubricating compounds mixed with the polyurethane components that prevent the finished part from sticking to the mold. Without them, workers have to manually spray on solvent-based mold releases before each part is formed. That can add 15 to 30 seconds to the overall molding time, and spews pollution-causing solvent fumes (also known as volatile organic compounds or VOCs) into the work environment.

IMRs improve productivity in another way, too: They don't gum up molds like external mold releases. That means molding tools are down less often for cleaning.

"It's an exciting area," sums up Bayer's Mr. Ahlgren.