Patent ID: 6929672

Claim:
A method for manufacturing a filter medium for an air filter to be used in the manufacture environment of a semiconductor device, comprising the steps of forming a non-woven fabric by binding fibers by a binder, said binder having its chief ingredient of a polymer dispersion having a copolymer of a hydrophilic monomer and a hydrophobic monomer dispersed in water, and obtaining said polymer dispersion by a polymerization step of dissolving the hydrophilic monomer in water, adding the hydrophilic monomer to this water solution and dispersing said hydrophobic monomer in said water solution, and adding a polymerization initiator to form said copolymer, wherein in said polymerization step, a hydrophilic organic peroxide of cumen hydroperoxide, 2 ,5-dimethylhexane-2, 5-hydroperoxide, or succinic acid peroxide is used as polymerization initiator.