Kawasaki, Japan —For plastics, or "solid gasoline" as it's sometimes called, fighting flames is tough enough. Sure, additives can offer ignition resistance—but usually at the expense of impact strength and other mechanical properties. What's more, formulations based on tried-and-true halogen compounds have raised environmental concerns and now face regulatory pressures in Europe and Japan. NEC Corp. and Sumitomo Dow Ltd. have extinguished these problems with the development of a new ignition-resistant (IR) polycarbonate.
Called "Nucycle," the material uses a proprietary silicone as the IR additive to achieve a UL 94 V-0 rating at 1 mm, according to Masatoshi Iji of NEC's R & D department. Iji adds that the material also offers "impact strength much higher" than that of polycarbonate-containing traditional halogen or phosphorus additives. And Nucycle hangs on to other important polycarbonate properties, including surface hardness and heat resistance (see table). It costs about the same as polycarbonate with halogen compounds.
In the U.S., Dow Plastics (Midland, MI) will market the silicone-IR materials under the PCX name. "The physical and thermal properties of the PCX materials are nearly identical to those of the base polycarbonate," says Mike Hus, global technology leader for electronics. Dow's initial line-up will consist of three grades. One targets a V-0 rating at 0.95 mm and 5V at 2.5 mm. A second grade offers V-0 at 1.5 mm and 5V at 2.5. And the third grade features a 20% glass filling and meets V-0 at 1.5 mm. Dow and NEC also have developed transparent grades of these materials with a flame performance of V-0 at 2.0 mm.
Contrasting Nucycle's proprietary aromatic-branch silicone with the earlier attempts to use methyl silicone as an IR additive, Iji explains that silicone exhibits better solubility in polycarbonate, higher heat resistance, and mobility within PC resin at high temperatures—all of which add up to better flame performance than earlier efforts with silicone.
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about ignition-resistant polycarbonate from Dow Plastics: Circle 539
Polycarbonate (PC) properties with different ignition resistant additives
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