| abstract |
The present invention is a rubber composition that contains a rubber, and thermally-expandable microcapsules which undergo volumetric expansion through heating, and that is characterized in that the contained amount of the thermally-expandable microcapsules is 1.5-10.7 parts by mass with respect to 100 parts by mass of the rubber, and when a test piece including an uncrosslinked rubber composition that contains the rubber, the thermally-expandable microcapsules, a crosslinking agent, and a crosslinking accelerator is subjected to a heat treatment under conditions in which the temperature is 180°C, the frequency is 100 cpm, and the amplitude angle is 0.5 degrees in order to cause the crosslinking reaction and the volumetric expansion of the thermally-expandable microcapsules to proceed, a time difference Δt (= t 2 - t 1 ) between time t 1 when the test piece expanded by the heat treatment has exhibited the highest pressure, and time t 2 when an optimum crosslinking point defined in JIS K6300-2 is achieved, is 1.0-4.5 min. |