AIR FILTER MEDIUM, AIR FILTER PACK AND AIR FILTER UNIT COMPRISING THE SAME, AND METHOD FOR PRODUCING AIR FILTER MEDIUM

摘要

An air filter medium comprising a porous polytetra-fluoroethylene film and an air-permeable support member laminated on at least one surface of said porous film and having a PF1 value exceeding 22, which is calculated according to the following formula: PF1 = [-log (Penetration (%) /100) /Pressure loss (mmH2O)]x100 in which the penetration (%) - 100 - Collection efficiency from a pressure loss (unit: mmH2O) measured when an air is flowed through the air filter medium at a flow velocity of 5.3 cm/sec. and a collection efficiency (unit: %) measured using dioctyl phthalate having a particle size of 0.10 to 0.12 .mu.m. This air filter medium has a low pressure loss and a high collection efficiency.