observed when 5.0 phr ZnO was used. Improvements
in E100 and E300 were also observed. t90 was
227 s when 1.0 phr nano-ZnO was used; however, it
was 256 s when 5.0 phr ZnO was used. This was
judged to be caused by the fact that the available
surface area of the nano-ZnO was increased compared
to when the nano-ZnO was used in the carbon-
black-filled compounds. This was due to the
excellent dispersion effect of the dispersing agent
used in the silica-filled compounds.