TOYOTA, JAPAN - Japan's top automaker, abandoning its customary caution, is moving ahead boldly with a plastics plan that has the potential to reshape the industry's use of polypropylene. Three years ago, Toyota Motor Corp. officials based in Toyota commercialized an olefin-based polymer that is lighter, cheaper and more temperature-resistant than conventional PP. Developed jointly with nine Japanese resin makers, including Mitsubishi Chemical Corp. of Tokyo and Sumitomo Chemical Co. Ltd. of Osaka, the plastic already has been adopted for an estimated half of bumpers used on its cars, and the share is increasing.
Considering that Toyota produces a third of all vehicles built in Japan today, that constitutes a significant development.
Beginning last autumn with the RAV4, the automaker's popular sport-utility vehicle, the company expanded use of the material to include instrument panels and trim. In fact, one-fourth of the RAV4's plastic content - a total of 53 pounds, double the weight on any other Toyota vehicle - is the special polymer. Researchers insist that this share will increase gradually as new derivatives are developed.
The polymer, an advanced PP, first was used on the 1991 Crown as a bumper material. It now is being used for half of all Toyota bumpers and, within the next three years, the automaker plans to increase that share to 70 percent. In addition to the RAV4, which is scheduled to go on sale in North America in October, Toyota so far has adopted the material for bumpers on the Crown, Aristo, Mark II, Carina, Tercel and Camry.
About the time of the Toyota development, rival Nissan Motor Co. Ltd. of Tokyo introduced a bumper material of its own. Nissan's, called ultrahigh stiffnessbumper material, has characteristics similar to Toyota's, the chief one being crash-impact resistance.
In the near future, Toyota plans to expand applications for the bumper material to include side molding and lower back trim; the instrument panel grade, which resists both heat and shock, to include the lower cowl and upper door trim; and the trim derivative, featuring high flow qualities, to include the trim and scuff plate.
Longer term, after the year 2000, the automaker hopes to develop grades for outer body panels, including fenders and hoods. In the interim, researchers ex-pect to merge the instrument panel and trim grades. But for all three grades to be unified - a prerequisite for lowering costs to the level of steel, thus making it possible to use the material for body panels - a technological breakthrough is necessary.
The Toyota polymer not only is less costly than conventional PP, it also is 15 percent lighter - and stronger with more resistance to impact.
Its melt flow, which is twice that of PP, enables the material to achieve 30 percent more yield in molding.
Toyota characterizes the polymer as having a ``low molecule and high crystal structure,'' which allows it to flow easily when heated and maintain a high crystal structure when cool.
In tests, the automaker found the material retains its basic performance characteristics and shape at temperatures between 248§ F and minus 22§ F, enabling the material to pass through a paint oven without deforming, unlike conventional PP.
Like PP, the material resists road chemicals such as salt. Unlike conventional PP, its surface quality is equal to that of steel. Moreover, the polymer can be recycled as many as 10 times.
The automaker wants to sell the new polymer outside of the Toyota group and has instructed Mitsubishi Chemical to approach General Motors Corp. and Ford Motor Co. on its behalf. The two U.S. automakers still are evaluating the material.
