It has been found that the combination of liquid diene rubbers and a large amount of sulfur content leads to very high hardness to EPDM vulcanizates. The newly developed EPDM compounds have also good processability.
It order to investigate the hardening mechanism, the EPDM vulcanizates were analyzed by using electron microscope and electron prove micro-analyzer. In the vulcanizates, diene rubbers were in a dispersion phase and EPDM was in a continuous phase. The amount of sulfur contented in diene rubber phase was found to be about ten times as much as EPDM phase. From the result, it is concluded that diene rubbers from hard particles cross-linked by large quantity of sulfur and these hard particles harden the EPDM vulcanizates.

View full abstract

The consumptions of steel cord and polyester cord have increased in recent years due to the use of radial tires requiring high modulus materials for tire cord. The problem with polyester cord in actual use is the drop of adhesion caused by the heat build-up of tires during running when the cord is used for large-sized tires of trucks and buses. It was found that the reason for the adhesion drop is the decomposition of polyester resulting from the migration of the amine compounds in rubber to the polyester layer. Therefore, the latex which improves the heat-resistant adhesion of polyester tire cord has been developed by us for use in tire production as a result of our research on the latex adhesive having both the adhesion and amine penetration prevention functions.
For further improvement of the tire properties, the separation of the above mentioned two functions was studied. As the result, the adhesion almost equal to that of nylon tire cord, the target, has been obtained by using two latexes, one with the adhesion function and the other with the polyester protection function.
It has been found that the latexes having the polymer structure of high crosslinking density are preferable to prevent amine penetration. As for the preparation of these latexes, it has been confirmed that the following two methods are most effective:
a) To increase the crosslinking points by introducing a crosslinking agent into the latex polymer
b) To cause the formation of the crosslinkinig network structure made by hydrogen bonds composed of carboxyl groups and pyridyl groups.

View full abstract