Air filter medium, filter pack, air filter unit, and method for producing the same
An air filter medium having a large thickness and a low filling factor, a filter pack, an air filter unit, and methods for producing the air filter medium, the filter pack, and the air filter unit are provided. The air filter medium includes a fluororesin porous film having a portion with a filling factor of 3.5% or less, and the portion with a filling factor of 3.5% or less has a thickness of 45 μm or more.
1 . An air filter medium comprising:
a fluororesin porous film having a portion with a filling factor of 3.5% or less and with an average pore diameter of 4.82 μm or more and 15.99 μm or less,
wherein the portion with the filling factor of 3.5% or less and with the average pore diameter of 4.82 μm or more and 15.99 μm or less has a thickness of 150 μm or more and 386.0 μm or less.
2 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film has a portion with a filling factor of 2.5% or less, and
the portion with a filling factor of 2.5% or less has a thickness of 50 μm or more and 380.0 μm or less.
3 . The air filter medium according to claim 1 ,
wherein a PF value of the air filter medium calculated from formula PF={−log((100−collection efficiency (%))/100)}/(pressure loss (Pa)/1000) using pressure loss and collection efficiency determined from polyalphaolefin particles having a particle size of 0.3 μm is 17 or more.
4 . The air filter medium according to claim 1 , wherein
a dust-holding capacity of polyalphaolefin particles having a number median diameter of 0.25 μm at which pressure loss increases by 250 Pa when air containing the polyalphaolefin particles is continuously passed through the air filter medium at a flow velocity of 5.3 cm/s is 30.0 g/m 2 or more.
5 . The air filter medium according to claim 1 , having a pressure loss of 200 Pa or less when air is passed through the air filter medium at a flow velocity of 5.3 cm/s.
6 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film includes:
a first fluororesin porous film having a filling factor of 3.5% or less and a thickness of 45 μm or more and 100.2 μm or less, and
a second fluororesin porous film disposed on a downstream side of an air flow with respect to the first fluororesin porous film and having a higher filling factor than the first fluororesin porous film.
7 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film includes at least one gradient density porous film having a higher density on a downstream side of an air flow than on an upstream side of the air flow.
8 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film is a single film.
9 . The air filter medium according to claim 1 , further comprising:
a pre-collection film disposed on an upstream side of an air flow with respect to the fluororesin porous film,
wherein the pre-collection film has a pressure loss of 15 Pa or more and 55 Pa or less when air is passed through the pre-collection film at a flow velocity of 5.3 cm/s,
a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the pre-collection film at a flow velocity of 5.3 cm/s is 25% or more and less than 80%, and
a PF value of the pre-collection film calculated from formula PF={−log((100−collection efficiency (%))/100)}/(pressure loss (Pa)/1000) using pressure loss and collection efficiency determined from polyalphaolefin particles having a particle size of 0.3 μm is 7 or more and 15 or less.
10 . The air filter medium according to claim 1 ,
wherein at least the portion with a filling factor of 3.5% or less of the fluororesin porous film contains a modified polytetrafluoroethylene.
11 . The air filter medium according to claim 1 ,
wherein at least the portion with a filling factor of 3.5% or less of the fluororesin porous film contains a fibril-forming polytetrafluoroethylene, a non-fibril-forming non-melting-processable component, and a non-fibril-forming melting-processable component having a melting point of lower than 320° C.
12 . The air filter medium according to claim 1 , further comprising:
an air-permeable supporting layer disposed on an upstream side and/or a downstream side of an air flow with respect to the fluororesin porous film.
13 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film having a portion with a filling factor of 3.5% or less and with an average pore diameter of 5.76 μm or more and 15.99 μm or less, and
the portion with a filling factor of 3.5% or less and with an average pore diameter of 5.76 μm or more has a thickness of 150 μm or more and 280.3 μm or less.
14 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film having a portion with a filling factor of 3.5% or less, with an average pore diameter of 4.82 μm and with a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the portion at a flow velocity of 5.3 cm/s is 99.999982% or more, and
the portion with a filling factor of 3.5% or less, with an average pore diameter of 4.82 μm or more and with a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the portion at a flow velocity of 5.3 cm/s is 99.999982% or more has a thickness of 150 μm or more and 179.3 μm or less.
15 . The air filter medium according to claim 1 ,
wherein the fluororesin porous film having a portion with a filling factor of 3.5% or less, with an average pore diameter of 5.76 μm and with a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the portion at a flow velocity of 5.3 cm/s is 99.997508% or more, and
the portion with a filling factor of 3.5% or less, with an average pore diameter of 5.76 μm or more and with a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the portion at a flow velocity of 5.3 cm/s is 99.997508% or more has a thickness of 150 μm or more and 198.7 μm or less.
16 . A filter pack comprising:
the air filter medium according to claim 1 ,
wherein the air filter medium is processed so as to have a zigzag shape in which mountain folds and valley folds are alternately repeated.
17 . An air filter unit comprising:
the air filter medium according to claim 1 ; and
a frame body holding the air filter medium.
18 . An air filter medium comprising,
a fluororesin porous film having a portion with a filling factor of 3.5% or less, with a pressure loss of 49 Pa or less when air is passed through the portion at a flow velocity of 5.3 cm/s, and with a collection efficiency of polyalphaolefin particles having a particle size of 0.3 μm at which air containing the polyalphaolefin particles is passed through the portion at a flow velocity of 5.3 cm/s is 99.277725% or more, wherein
the portion has a thickness of 150 μm or more and 386.0 μm or less.