Synthesis of novel microfilters with ion-exchange capacity and its application to ultrapure water production systems

Excellent hollow-fiber type microfilters which have both filtration and ion-exchange capability have been synthesized by the modification of polyethylene microfilters. It has been found that the novel microfilters can be applied to the ultrapure water producing systems in semiconductor industries. The water produced by a series of microfilters, containing anion-exchange and cation-exchange groups, has shown an electric resistivity of 18.1 M Omega cm which could be near to theoretical pure water. The anion-exchange microfilters have exhibited the rejection ability of particles and colloidal substances. Examining the microfilters containing chelate-forming groups, it is suggested that most metal ions exist as colloidal substances instead of as dissolved ions at the final point of the ultrapure water producing system. In 1 Gbit semiconductor industries, the reduction of the metal ions in the ultrapure water might be a serious problem, and the anion-exchange microfilters should take an important role to resolve that problem.