Investigation of Carbon Black Properties Affecting Thermal Durability of Silicone Rubber

Satoshi WATANABE* and Hideyuki HISASHI

Technology Center,GE Toshiba Silicone Co., Ltd.; 133, Nishishinmachi, Ohta-shi 373-8505 Japan
Product Development Research Laboratories, Mitsubishi Chemical Corporation; 1, Toho-cho, Yokkaichi-shi 510-8530 Japan

We tried to find out the optimal carbon black (CB) properties which would effectively increase the thermal durability of CB/Silicone rubber compound, through verification of the correlation between CB properties and the thermal durability. For the purpose of this study, we selected eight CB properties, namely primary particle size, structure, ash content, sulfur content, toluene coloring transmittance, crystalline thickness (Lc), volatile materials and a new indicater (O/S) which is the content of oxygen per unit CB surface area. We examined 12 kinds of CB. The thermal durability of CB containing rubber was significantly improved when the CB content was between 0.5 and 1.0 phr. Lc and the thermal durability showed a correlation and the smaller value of Lc (which was related to the thermal history in CB production furnace) exhibited the better thermal durability. CB whose O/S value was greater than 0.14 mg/m2 gave good thermal durability for the compound. However, the other properties did not display a correlation to the thermal durability of the composit. Consequently, it is suggested that CB, which possesses a good ability for capturing radicals in the compound, effectively improves thermal durability.

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