Patent ID: 10537836

Abstract:
A filter medium for an air filter includes a pre-collection member, a first porous film, and a second porous film arranged in order from the side that is upstream of the air current. Each of the first porous film and the second porous film has a pressure loss of 30 Pa or more and 90 Pa or less when air is passed through each porous film at a flow rate of 5.3 cm/s, and has a collection efficiency of 95% or more and 99.9% or less for NaCl particles having a particle diameter of 0.3 μm when air containing the NaCl particles is passed through each of the porous films at a flow rate of 5.3 cm/s. The pre-collection member has a pressure loss of 5 Pa or more and less than 55 Pa when air is passed through the pre-collection member at a flow rate of 5.3 cm/s, has a collection efficiency of 15% or more and less than 85% for NaCl particles having a particle diameter of 0.3 μm when air containing the NaCl particles is passed through the pre-collection member at a flow rate of 5.3 cm/s, and has a thickness of more than 0.4 mm.