FILTER MEDIUM FOR AIR FILTER, AIR FILTER UNIT, AND METHOD FOR PRODUCING FILTER MEDIUM FOR AIR FILTER

摘要

A filter medium for an air filter unit for collecting dust from an airflow contains: a pre-collection layer for collecting some of the dust in the airflow; a principal collection layer that comprises a porous polytetrafluoroethylene film, collects dust that passes therethrough the pre-collection layer, and is positioned downstream in the airflow relative to the pre-collection layer; and a gas-permeable cover layer that allows dust in the airflow to pass therethrough, suppresses deformation of the surface of the air filter medium caused by exterior pressure, and is positioned in the outermost surface layer on the upstream side of the airflow. When producing the filter medium, a first laminate is obtained by laminating a member that becomes a gas-permeable supportive layer and a film that becomes the principal collection layer, and a second laminate is separately obtained by laminating a member that becomes the gas-permeable cover layer and a member that becomes the pre-collection layer. The laminating is performed in a manner such that the principal collection layer in the first laminate and the pre-collection layer in the second laminate are positioned on the inside.