Study of the effect of latex binder on the green and fired properties of ZnO varistor discs and estimation of Weibull parameters

The formation of green compact body is a major processing operation for manufacturing ZnO varistors. The density and strength of the green body is crucial not only for proper handling but also for avoiding introduction of further flaws through sintering. The green body may have a wide range of flaw sizes, resulting in corresponding variation of green strength. The green density and strength and consequently the fired strength of the varistor discs can be enhanced by proper selection of the binder, thereby, reducing flaw distribution. Shrinkage of the fired discs can also be reduced with discs of increased green density. Several commercial latex binders and their blends have been studied and compared with the conventional plasticized polyvinyl alcohol for the production of zinc-oxide varistor discs. It was found that discs with improved green density, green and fired strength and less shrinkage were achievable by the use of latex binder. Moreover, estimation of Weibull parameters showed that by using latex binder green and fired discs with more uniform distribution of strength can be produced.