US 12,403,429 B2
Filter medium and filter unit
Shunsuke Masaki, Osaka (JP); and Masaaki Mori, Osaka (JP)
Assigned to NITTO DENKO CORPORATION, Osaka (JP)
Appl. No. 17/600,439
Filed by NITTO DENKO CORPORATION, Osaka (JP)
PCT Filed Apr. 3, 2020, PCT No. PCT/JP2020/015381
§ 371(c)(1), (2) Date Sep. 30, 2021,
PCT Pub. No. WO2020/204177, PCT Pub. Date Oct. 8, 2020.
Claims priority of application No. 2019-071843 (JP), filed on Apr. 4, 2019.
Prior Publication US 2022/0193618 A1, Jun. 23, 2022
Int. Cl. B01D 69/02 (2006.01); B01D 69/10 (2006.01); B01D 69/12 (2006.01); B01D 71/36 (2006.01)
CPC B01D 69/02 (2013.01) [B01D 69/107 (2022.08); B01D 69/1216 (2022.08); B01D 71/36 (2013.01); B01D 2239/0618 (2013.01); B01D 2313/2062 (2022.08); B01D 2325/0283 (2022.08)] 6 Claims
 
1. A filter medium comprising:
a first polytetrafluoroethylene (PTFE) porous membrane;
a first air-permeable supporting member having a mass per unit area of 20 to 70 g/m2;
a second PTFE porous membrane; and
a second air-permeable supporting member having a mass per unit area of 20 to 70 g/m2, wherein
the filter medium has a laminate structure composed of the first PTFE porous membrane, the first air-permeable supporting member, the second PTFE porous membrane, and the second air-permeable supporting member laminated in this order, and
the first PTFE porous membrane constitutes an exposed surface of the filter medium,
a thickness of the first PTFE porous membrane is 2 μm or more and 12 μm or less,
a thickness of the second PTFE porous membrane is 6 μm or more and 9 μm or less,
wherein the thickness of the one of the first PTFE porous membrane and the second PTFE porous membrane having the larger thickness is defined as a larger thickness (T1),
wherein the thickness of the other of the first PTFE porous membrane and the second PTFE porous membrane having the smaller thickness is defined as a smaller thickness (T2), and
wherein T2 divided by T1 satisfies the following inequity:
0.22≤T2/T1≤0.75, and
a thickness of the filter medium is more than 420 μm and 450 μm or less,
an average fiber diameter of the first air-permeable supporting member is 10 to 30 μm,
an average fiber diameter of the second air-permeable supporting member is 10 to 30 μm, and
a ratio TR1/TR2 of a transmittance TR1 of the first PTFE porous membrane to a transmittance TR2 of the second PTFE porous membrane is 100 or more and 5000000 or less,
where the transmittance TR1 and the transmittance TR2 are values determined by the following formulae from, respectively, collection efficiency CE1 (unit: %) of the first PTFE porous membrane and collection efficiency CE2 (unit: %) of the second PTFE porous membrane measured using monodisperse dioctyl sebacate particles having an average particle diameter of 0.1 μm at a permeate flow rate of 5.3 cm/sec:
transmittance TR1 (%)=100−collection efficiency CE1;
transmittance TR2 (%)=100−collection efficiency CE2; and
wherein a transmittance TRF of the filter medium is 5% or less,
where the transmittance TRF is a value determined by the following formula from collection efficiency CEF (unit: %) of the filter medium measured using monodisperse dioctyl sebacate particles having an average particle diameter of 0.1 μm at a permeate flow rate of 5.3 cm/sec:
transmittance TRF (%)=100−collection efficiency CEF.