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Reduced thermal expansion.

U.S. Patent 8,974,729 (March 10, 2015), "Anti-Thermally-Expansive Resin and Anti-Thermally-Expansive Metal," Makoto Kubota, Kaoru Miura, Hisato Yabuta, Yoshihiko Matsumura, Yuichi Shimakawa, and Masaki Azuma (Canon Kabushiki Kaisha, Tokyo, and Kyoto University, Kyoto, Japan).

In long-term use under varying temperatures, large or mismatched thermal expansions between parts are a problem, especially for plastics with very large expansion. This can be especially critical in precision equipment. One approach is to fill a resin with a large positive thermal expansion with a filler with matching negative thermal expansion, but such fillers are not common.

Kubota et al. developed polymeric composites with small thermal expansion by mixing resins with fillers having negative thermal expansion. The high-expansion resins range from polybenzimidazole (PBI) to fluorocarbons and polycarbonates, including thermosets and thermoplastics. Typically the negative thermal expansion particles are special metal oxides like ([Bi.sub.1-x][M.sub.x])Ni[O.sub.3], where "M" is a rare-earth element (the negative expansion is due to complex phase transitions). In an example composite, the linear expansion coefficient of PBI at the glass transition temperature or lower is +23 x [10.sup.-6]/K. In contrast, the linear expansion coefficient of the oxide particle is about -20 x [10.sup.-6]/K. When the solid particle is dispersed in the PBI matrix, the usual interfacial thermal stress is cancelled at the contact interface, and local thermal strains are eliminated.

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Title Annotation:INDUSTRY PATENTS
Author:Corneliussen, Roger
Publication:Plastics Engineering
Article Type:Brief article
Geographic Code:1USA
Date:Jun 1, 2015
Words:233
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