Filter material for air filter and air filter comprising same

Abstract

[Problem] To provide: a filter material for an air filter, the filter material being free of PFAS and capable of achieving low pressure loss and high collection efficiency; and an air filter comprising the same. [Solution] Provided is a filter material for an air filter, the filter material comprising skeletal short fibers made from polyethylene terephthalate, collection short fibers made from polyethylene terephthalate, having a smaller diameter than the skeletal short fibers, and binder short fibers that bond the skeletal short fibers and the collection short fibers. The skeletal short fibers have an average fiber diameter from 1 to 50 μm. The collection short fibers have an average fiber diameter of 0.500 μm or less. The total fiber surface area per filter material unit area of the collection short fiber is from 50 to 160 m2 / m2. The binder short fibers consist only of composite fibers made of polyethylene terephthalate and polyethylene terephthalate copolymer or composite fibers made of polyethylene terephthalate and polyethylene.

Description

Air filter media and air filter including same

[0001] The present invention relates to a filter medium for an air filter and an air filter including the same.

[0002] Conventionally, air filter collection technologies for efficiently collecting submicron or micron-sized particles in the air have been known. For example, Patent Document 1 discloses a filter medium that is formed by binding uniformly dispersed skeletal short fibers and collection short fibers with uniformly dispersed organic binder fibers, and that has low pressure loss and a high collection rate for submicron or micron-sized particles.

[0003] Japanese Patent Application Laid-Open No. 2018-171582

[0004] In recent years, proposals have been made to restrict organic fluorine compounds (PFAS, Per and Polyfluoroalkylsubstances). PFAS are known as "forever chemicals" due to their environmental persistence and bioaccumulation, raising concerns about their harmful effects on humans. This issue is becoming a global issue, with various companies considering the manufacture of so-called PFAS-free products. Similarly, PFAS-free filter media are also being sought. However, no PFAS-free filter media capable of performing satisfactorily as a filter media has been proposed to date.

[0005] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a PFAS-free air filter medium that can achieve low pressure loss and high collection efficiency, and an air filter including the same.

[0006] In order to solve the above-mentioned problems, the air filter medium according to the present invention is an air filter medium comprising: skeletal short fibers made of polyethylene terephthalate; collecting short fibers made of polyethylene terephthalate having a diameter smaller than that of the skeletal short fibers; and binder short fibers that bond the skeletal short fibers and the collecting short fibers, wherein the skeletal short fibers have an average fiber diameter of 1 to 50 μm, the collecting short fibers have an average fiber diameter of 0.500 μm or less, and the total fiber surface area of ​​the collecting short fibers per unit area of ​​the filter medium is 50 to 160 m. 2 / m2 and the binder short fibers consist solely of composite fibers of polyethylene terephthalate and polyethylene terephthalate copolymer, or composite fibers of polyethylene terephthalate and polyethylene.

[0007] The air filter medium according to the present invention is PFAS-free and can achieve low pressure loss and high collection efficiency.

[0008] 1 is a table showing the configurations and properties of Examples 1 to 8 and Comparative Examples 1 to 4.

[0009] An embodiment of an air filter medium according to the present invention will be described with reference to the accompanying drawings. The air filter medium according to the present invention (hereinafter simply referred to as "filter medium") can be used in clean rooms and clean benches in the semiconductor, liquid crystal, bio and food industries, for example. The filter medium can also be used in building air conditioning air filters, air purifiers, and other air filter media used to filter fine particles in gas.

[0010] The filter medium includes skeletal short fibers, collection short fibers having a diameter smaller than that of the skeletal short fibers, and binder short fibers that bond the skeletal short fibers and the collection short fibers together.

[0011] The short skeletal fibers are made of polyethylene terephthalate (PET) and have an average fiber diameter of 1 to 50 μm. The fiber blending ratio of the short skeletal fibers during production is 30 to 90 mass %, preferably 50 to 70 mass %.

[0012] The collecting short fibers are made of PET, just like the skeletal short fibers. The collecting short fibers have an average fiber diameter of 0.500 μm or less. If the collecting short fibers have an average fiber diameter greater than 0.500 μm, the collection efficiency will decrease and the desired filter performance will not be achieved.

[0013] Specifically, the collected short fibers consist of first collected short fibers, second collected short fibers having a diameter smaller than that of the first collected short fibers, and third collected short fibers having a diameter smaller than that of the second collected short fibers. The first collected short fibers have a fiber diameter of 0.450 to 0.800 μm. The second collected short fibers have an average fiber diameter of 0.200 to 0.450 μm. The third collected short fibers have a fiber diameter of 0.050 to 0.200 μm.

[0014] The fiber diameter and amount of these first to third collected short fibers (collected short fibers) are preferably selected so that the average fiber diameter as a whole is 0.500 μm or less.

[0015] The fiber blending ratio of the collected short fibers during production is greater than 0 and not more than 35 mass%, the fiber blending ratio of the first collected short fibers is 0 to 15 mass%, the fiber blending ratio of the second collected short fibers is 0 to 15 mass%, and the fiber blending ratio of the third collected short fibers is 0 to 10 mass%.

[0016] A fiber blending ratio of the third collecting short fibers having a fiber diameter of 0.200 μm or less within the above range is preferred from the viewpoint of suppressing an increase in pressure loss. The third collecting short fibers contribute to improving the collection efficiency. However, if the blending ratio is high, the third collecting short fibers will aggregate together due to their small fiber diameter and act in the same way as thick fibers, which will actually cause a decrease in pressure loss. Furthermore, a fiber blending ratio of the first and second collecting short fibers having a fiber diameter of more than 0.200 μm within the above range is preferred from the viewpoint of suppressing a decrease in collection efficiency.

[0017] The fiber surface area per unit area of ​​the first collection short fiber in the filter medium is 10 to 50 m 2 / m 2 The fiber surface area per unit area of ​​the second collection short fiber filter medium is 20 to 90 m 2 / m 2 The fiber surface area per unit area of ​​the third collection short fiber filter medium is 5 to 30 m 2 / m 2 is.

[0018] These first to third collection short fibers have a total fiber surface area per unit area of ​​filter media of 50 to 160 m 2 / m2 It is preferable to suitably select the fiber diameter and amount so that the total fiber surface area is within the above range, thereby making it possible to obtain a filter medium having a suitable pressure drop and collection efficiency.

[0019] This fiber surface area per unit area of ​​the filter medium can be calculated from the average fiber diameter measured using a required microscope or the like and the fiber volume determined from the basis weight of the filter medium.

[0020] The binder staple fibers are composed solely of composite fibers of PET and polyethylene terephthalate copolymer (CoPET), or composite fibers of PET and polyethylene (PE). The binder staple fibers are composite fibers with structures such as core-sheath, laminated, sea-island, and split. Because the binder staple fibers are composite fibers, the CoPET or PE, which has a low melting point, melts during the drying process during production and acts to bond the skeletal staple fibers and the collected staple fibers. Furthermore, the PET can act similarly to the skeletal staple fibers without melting. This prevents the filter medium from excessively forming a membrane of the binder staple fibers, thereby preventing a decrease in pressure loss, and also provides a filter medium with excellent processability when processed into a filter unit. The binder staple fibers preferably have a core-sheath structure with a core made of PET and a sheath made of CoPET or PE.

[0021] The fiber blending ratio of the binder short fibers during production is 10 to 40% by mass, and preferably 20 to 30% by mass.

[0022] The filter medium in this embodiment is manufactured, for example, as follows.

[0023] The skeletal short fibers, collection short fibers, and binder short fibers are disintegrated in a mixer. The disintegrated dispersion is diluted with water. Then, a wet paper is made using a hand-sheet machine. This wet paper is dried in a roll dryer to become a filter medium.

[0024] The drying temperature in the roll dryer is preferably a temperature (for example, about 140° C.) at which the CoPET or PE sheath of the binder fiber can melt to bond the collected short fibers and skeletal short fibers.

[0025] The filter medium thus constructed is preferably designed so that the performance index Qf value, which indicates the performance of the filter medium and is calculated from the following formula, is 0.028 or more.

[0026] Formula (1) Qf value [1 / Pa] = -ln(1 - capture rate [%] / 100) / pressure loss [Pa] The target particle size for capture rate is the maximum penetrating particle size (MPPS), which is 0.05 to 0.2 μm, specifically around 0.1 μm, when the air speed passing through the filter medium is 5.3 cm / s.

[0027] The filter material is preferably designed to have a tensile strength of 0.28 kN / m or more, because if the tensile strength is less than 0.28 kN / m, the filter material may not have enough strength and may be broken.

[0028] When the filter material has a Qf value of 0.028 or more and a tensile strength of 0.28 kN / m or more, it can be used as a filter material for quasi-HEPA (High Efficiency Particulate Air Filter), HEPA, and ULPA filters.

[0029] Such a filter medium and an air filter incorporating the same are all made of PFAS-free materials, have good processability, and can achieve low pressure loss and high collection efficiency, making them suitable for use as filter medium for air filters.

[0030] [Example 1] The following skeletal staple fibers, collected staple fibers, and binder staple fibers were defibrated in a mixer. Skeletal staple fibers: Material: PET staple fibers, 62% by mass, average fiber diameter: 12.5 μm Collected staple fibers: First collected staple fibers: Material: PET staple fibers, 9% by mass, average fiber diameter: 0.650 μm Second collected staple fibers: Material: PET staple fibers, 9% by mass, average fiber diameter: 0.350 μm Binder staple fibers: Material: Composite staple fibers with a core-sheath structure, where the core is PET and the sheath is CoPET, 20% by mass, average fiber diameter: 12.5 μm

[0031] The dispersion of the disintegrated short fibers was in a uniform dispersion state. The disintegrated dispersion was then diluted with water to a concentration of 0.1% by mass and made into a wet paper using a hand-made papermaking machine. This was dried in a roll dryer at 140°C to obtain a filter medium. The filter medium had a basis weight of 70 g / m. 2 The thickness of the filter material was 0.5 mm.

[0032] Example 2 A filter medium was produced under the same conditions as in Example 1, except that the fiber blending ratio of the skeletal short fibers was 52 mass % and the fiber blending ratio of the binder short fibers was 30 mass %.

[0033] [Example 3] A filter medium was produced under the same conditions as in Example 1, except that the fiber blending ratio of the skeletal short fibers was set to 69.25% by mass, the fiber blending ratios of the first and second collecting short fibers were set to 5% by mass, and the following third collecting short fibers were further blended. Third collecting short fibers: Material: PET short fibers 0.75% by mass; Average fiber diameter: 0.150 μm

[0034] [Example 4] A filter medium was prepared under the same conditions as in Example 3, except that the fiber content of the skeletal short fibers was 64% by mass, the fiber content of the first and second collection short fibers was 7.5% by mass, and the content of the third collection short fibers was 1% by mass.

[0035] [Example 5] A filter medium was prepared under the same conditions as in Example 3, except that the fiber content of the skeletal short fibers was 56.5% by mass, the fiber content of the first and second collection short fibers was 11% by mass, and the content of the third collection short fibers was 1.5% by mass.

[0036] [Example 6] A filter medium was prepared under the same conditions as in Example 3, except that the fiber content of the skeletal short fibers was 48% by mass, the fiber content of the first and second collection short fibers was 15% by mass, and the content of the third collection short fibers was 2% by mass.

[0037] [Example 7] A filter medium was prepared under the same conditions as in Example 1, except that the fiber content of the skeletal short fibers was set to 66% by mass, the first collection short fibers were omitted, and the fiber content of the second collection short fibers was set to 14% by mass.

[0038] [Example 8] A filter medium was produced under the same conditions as in Example 1, except that the fiber blending ratio of the skeletal short fibers was 62% by mass and the binder short fibers were the following binder short fibers: Binder short fiber material: 20% by mass composite short fiber with a core-sheath structure in which the core is PET and the sheath is PE; Average fiber diameter: 12.5 μm

[0039] [Comparative Example 1] For comparison, a filter medium was produced under the same conditions as in Example 1, except that the binder short fibers were changed to the following binder short fibers: Binder short fiber Material: Polyvinyl alcohol (PVA) short fiber 20 mass % Average fiber diameter: 7 μm

[0040] [Comparative Example 2] For comparison, a filter medium was prepared under the same conditions as in Example 1, except that the blending ratio of the same binder short fibers as those used in Example 1 was 10 mass % and the following binder short fibers were further blended: Binder short fiber material: PVA short fiber 10 mass % Average fiber diameter: 7 μm

[0041] [Comparative Example 3] For comparison, a filter medium was produced under the same conditions as in Example 1, except that the binder short fibers were changed to the following binder short fibers: Binder short fiber Material: CoPET short fiber 20 mass % Average fiber diameter: 4.3 μm

[0042] [Comparative Example 4] For comparison, a filter medium was prepared under the same conditions as in Example 1, except that the fiber content of the skeletal short fibers was set to 54% by mass, the fiber content of the first collection short fibers was set to 26% by mass, and the second collection short fibers were omitted.

[0043] The collection efficiency (%) and pressure loss (Pa) were determined for the filter media of Examples 1 to 8 and Comparative Examples 1 to 4, and the performance index Qf value (1 / Pa) was also determined. The results are shown in FIG.

[0044] As can be seen from Comparative Examples 1 and 2, when the binder short fibers contain PVA short fibers, tensile strength is obtained, but the melted PVA short fibers form a film, increasing pressure loss. Furthermore, as can be seen from Comparative Example 3, when the binder short fibers are CoPET monofilaments, the binder short fibers are all melted during the drying process, resulting in insufficient tensile strength and insufficient performance as an air filter medium. Furthermore, the filter medium of Comparative Example 3 had poor processability and was not durable for use. Furthermore, the filter medium of Comparative Example 4 had a poor collection efficiency due to the large fiber diameter of the collected short fibers, and the desired filter performance could not be achieved.

[0045] In contrast, the filter media according to the present invention in Examples 1 to 8 all have performance index Qf values ​​and tensile strengths suitable for use as filter media for air filters, and are useful as suitable filter media that do not use PFAS.

[0046] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the claims. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions described in the claims and their equivalents.

Claims

1. An air filter medium comprising: skeletal short fibers made of polyethylene terephthalate; collecting short fibers made of polyethylene terephthalate having a diameter smaller than that of the skeletal short fibers; and binder short fibers that bond the skeletal short fibers and the collecting short fibers, wherein the skeletal short fibers have an average fiber diameter of 1 to 50 μm, the collecting short fibers have an average fiber diameter of 0.500 μm or less, and the total fiber surface area of ​​the collecting short fibers per unit area of ​​the filter medium is 50 to 160 m. 2 / m 2 The filter medium for an air filter, wherein the binder short fibers are made of composite fibers of polyethylene terephthalate and a polyethylene terephthalate copolymer, or composite fibers of polyethylene terephthalate and polyethylene.

2. The air filter medium according to claim 1, wherein the binder short fibers have a core-sheath structure in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene terephthalate copolymer.

3. The collecting short fibers include first collecting short fibers having an average fiber diameter of 0.450 to 0.800 μm and second collecting short fibers having an average fiber diameter of 0.200 to 0.450 μm, and the fiber surface area of ​​the first collecting short fibers per unit area of ​​the filter medium is 10 to 50 m 2 / m 2 The second collection short fibers have a fiber surface area per unit area of ​​the filter medium of 20 to 90 m 2 / m 2 2. The air filter medium according to claim 1, wherein:

4. The collecting short fibers further include third collecting short fibers having an average fiber diameter of 0.050 to 0.200 μm, and the fiber surface area of ​​the third collecting short fibers per unit area of ​​the filter medium is 5 to 30 m 2 / m 2 4. The air filter medium according to claim 3, wherein:

5. The air filter media according to claim 1, having a performance index Qf value expressed by the following formula (1) of 0.028 or more: Formula (1) Qf value [1 / Pa] = -ln (1 - capture rate [%] / 100) / pressure loss [Pa], where the target particle size for capture rate is the maximum penetrating particle size, which is 0.05 to 0.2 μm when the air velocity passing through the filter media is 5.3 cm / s.

6. The air filter medium according to claim 1, having a tensile strength of 0.28 kN / m or more.

7. An air filter using the air filter material according to any one of claims 1 to 6.