Improvement of the crosslinking reactivity of polyvinyl acetal as an alternative to polyvinyl chloride

In order to conserve the global environment and improve the durability of particulate magnetic recording media, a new binder material, polyvinyl acetal (PVAc) has been developed to replace the current one, polyvinyl chloride (PVC). The crosslinking reactivity of PVAc synthesized at different temperatures was measured. It was found that the reactivity does not depend on the temperature when no magnetic particle is included, but that the reactivity of PVAc synthesized at a lower temperature (lower type) is higher than that of PVAc synthesized at a higher temperature (higher type) when magnetic particles are included. From NMR studies the lower type has larger amount of isolated hydroxyl groups than the higher type, which suggests that the lower type has more random distribution of hydroxyl groups than the higher type. The reactivity improvement is explained by examining the interaction between the particle surface and the hydroxyl groups of PVAc.