| abstract |
A method of manufacturing a filter medium that has a PF value that exceeds 32, the PF value calculated from the pressure loss and the collection efficiency of the filter medium according to the following formula:n nPF=[−log(permeability (%)/100)/(pressure loss (Pa)]×1000[Formula 1]n nin which permeability (%)=100−collection efficiency (%). In this method, 380 ml or more of a liquid lubricant at 20° C. is added per 1 kg of a PTFE fine powder, this compound is processed into a tape shape and elongated to obtain a PTFE porous film, and an air permeable support member is heat laminated to at least one surface of the PTFE porous film. |