Analysis of the Mechanism for the Appearance of Bubbles in Rubber during Vulcanization

Appearance of bubbles in the rubber has been observed in real time by using X-ray imaging method in SPring-8. The behavior of diameter and quantity of bubbles has been measured for the samples which have the various contents of cure agent and moisture. The babbles appear after 30 to 50 sec from releasing curing pressure at the place where there are no any feature in the X-ray images pixel size is 0.5 μm. The diameter of bubbles increases linearly with time at first, and then it grows up to be closer to the limit diameter finally. This final diameter changes with cure time and amount of cure agent. And the quantity of bubbles changes with amount of moisture. The result shows the one of origin of bubbles is moisture, and even if the moisture content changes, the size of moisture particles does not change, the quantity of particles changes. The crosslink density participates in whether this particle changes to a bubble or keeps that state. That also participates in the final diameter of bubble. X-Ray experiments were performed at BL19B2, BL46XU in the SPring-8 with approval of the Japan Radiation Research Institute (JASRI) Proposal No. 2014A1571,2014A1572).