阅读说明：本技术 过滤器滤材及过滤器单元 (Filter medium and filter unit ) 是由 正木俊辅 森将明 于 2020-04-03 设计创作，主要内容包括：本公开的过滤器滤材具有第1聚四氟乙烯(PTFE)多孔膜、第1通气性支撑材料、第2PTFE多孔膜及第2通气性支撑材料依次层叠而成的层叠结构。第1PTFE多孔膜构成过滤器滤材的一个露出面。第1PTFE多孔膜的透过率相对于第2PTFE多孔膜的透过率的比为100以上。本公开的过滤器滤材包含PTFE多孔膜,容易除去因使用而堆积在表面上的尘埃,并且抑制了由尘埃除去操作导致的过滤性能下降,再利用性优异。透过率由使用平均粒径0.1μm的单分散癸二酸二辛酯颗粒在透过流速5.3cm/秒下测得的PTFE多孔膜的捕集效率通过式：透过率(％)＝100-捕集效率(％)求出。(The filter medium of the present disclosure has a laminated structure in which a 1 st porous Polytetrafluoroethylene (PTFE) membrane, a 1 st air-permeable support material, a 2 nd porous PTFE membrane, and a 2 nd air-permeable support material are laminated in this order. The 1 st porous PTFE membrane forms one exposed surface of the filter medium. The ratio of the permeability of the 1 st porous PTFE membrane to the permeability of the 2 nd porous PTFE membrane is 100 or more. The filter medium of the present disclosure contains a PTFE porous membrane, easily removes dust deposited on the surface by use, and is excellent in recyclability while suppressing a decrease in filtration performance due to the dust removal operation. The permeability is determined from the collection efficiency of the porous PTFE membrane measured at a permeation flow rate of 5.3 cm/sec using monodisperse dioctyl sebacate particles having an average particle size of 0.1 μm by the formula: the transmittance (%) was determined as 100-trapping efficiency (%).)

1. A filter medium comprising a 1 st porous Polytetrafluoroethylene (PTFE) membrane, a 1 st air-permeable support, a 2 nd porous PTFE membrane, and a 2 nd air-permeable support,

the filter medium has a laminated structure in which the 1 st porous PTFE membrane, the 1 st air-permeable support, the 2 nd porous PTFE membrane, and the 2 nd air-permeable support are laminated in this order,

the 1 st porous PTFE membrane constitutes one exposed surface of the filter medium,

a transmittance TR of the 1 st porous PTFE membrane₁A transmittance TR to the 2 nd porous PTFE membrane₂Ratio of (TR)₁/TR ₂The content of the organic acid is more than 100,

wherein the transmittance TR is₁And a transmittance TR₂The collection efficiency CE of each porous PTFE membrane 1₁(unit:%) and collection efficiency CE of the porous PTFE membrane 2₂(unit:%) the trapping efficiency was measured at a permeation flow rate of 5.3 cm/sec using monodisperse dioctyl sebacate particles having an average particle size of 0.1 μm,

transmittance TR₁(100%) trapping efficiency CE₁

Transmittance TR₂(100%) trapping efficiency CE₂。

2. The filter media of claim 1 wherein the ratio TR is₁/TR ₂Is more than 300.

3. The filter medium of claim 1 or 2, wherein the filter medium has a transmittance TR_FLess than 0.5 percent of the total weight of the composition,

wherein the transmittance TR is_FIs the collection efficiency CE of the filter medium measured at a permeation flow rate of 5.3 cm/sec using monodisperse dioctyl sebacate particles having an average particle diameter of 0.1 μm_F(unit:%) is a value obtained by the following formula,

transmittance TR_F(100%) trapping efficiency CE_F。

4. The filter medium according to any one of claims 1 to 3, wherein the pressure loss PL of the filter medium at a permeation flow rate of 5.3 cm/sec_FLess than 300 Pa.

5. A filter unit comprising the filter medium according to any one of claims 1 to 4 and a frame for supporting the filter medium.

Technical Field

The present invention relates to a filter medium and a filter unit.

Background

Filter media using a porous polytetrafluoroethylene (hereinafter referred to as "PTFE") membrane are used in various ventilation filters such as air filters for clean rooms and dust filters for cleaners. Patent document 1 discloses a filter medium including a 1 st porous PTFE membrane, a 1 st air-permeable support material, a 2 nd porous PTFE membrane, and a 2 nd air-permeable support material, the 1 st porous PTFE membrane constituting one exposed surface. The filter medium is sometimes required to be reusable, i.e., reusable, by removing dust accumulated on the surface, and when one exposed surface is formed of a porous PTFE membrane as in the filter medium of patent document 1, dust accumulated on the exposed surface is easily removed.

Documents of the prior art

Patent document

Patent document 1 Japanese patent laid-open publication No. 2016-209869

Disclosure of Invention

Problems to be solved by the invention

The dust removal can be performed by blowing air or washing with water, and in this case, many users want to wipe the exposed surface with a brush. However, the porous PTFE membrane is a very thin membrane and is easily damaged by external force, and the damage may cause a decrease in filtration performance of the filter medium. In fact, even a filter medium designed in consideration of removal of dust cannot sufficiently cope with a case where a user uses a brush in combination.

The purpose of the present invention is to provide a filter medium that contains a porous PTFE membrane, is easy to remove dust that has accumulated on the surface during use, and has excellent recyclability while suppressing the deterioration of filtration performance due to the dust removal operation.

Means for solving the problems

The present invention provides a filter medium, comprising: a 1 st porous PTFE membrane, a 1 st air-permeable support material, a 2 nd porous PTFE membrane, and a 2 nd air-permeable support material,

the filter medium has a laminated structure in which the 1 st porous PTFE membrane, the 1 st air-permeable support, the 2 nd porous PTFE membrane, and the 2 nd air-permeable support are laminated in this order,

the 1 st porous PTFE membrane constitutes one exposed surface of the filter medium,

the transmittance TR of the 1 st porous PTFE membrane₁A transmittance TR to the 2 nd porous PTFE membrane₂Ratio of (TR)₁/TR₂Is 100 or more.

Wherein the transmittance TR is₁And a transmittance TR₂The collection efficiency CE of each of the porous PTFE membranes 1₁(Unit:%) and collection efficiency CE of the porous PTFE membrane described above 2₂(unit:%) the trapping efficiency was measured at a permeation flow rate of 5.3 cm/sec using monodisperse dioctyl sebacate particles having an average particle size of 0.1 μm.

Transmittance TR₁(100%) trapping efficiency CE₁

Transmittance TR₂(%) 100-captoCollection efficiency CE₂

In another aspect, the present invention provides a filter unit including the filter medium of the present invention and a frame supporting the filter medium.

ADVANTAGEOUS EFFECTS OF INVENTION

In the filter medium of the present invention, one exposed surface of the filter medium is formed of a porous PTFE membrane, and dust deposited on this surface is more easily removed than dust deposited on the air-permeable support material. By disposing the filter medium so that the exposed surface is on the upstream side with respect to the air flow passing through the filter medium, dust deposited on the surface during use can be easily removed. In the filter medium of the present invention, the 1 st porous PTFE membrane and the 2 nd porous PTFE membrane have a large difference in filtration performance in terms of transmittance, and the exposed surface is formed of the 1 st porous PTFE membrane having a high transmittance. Thus, the filter performance as a filter medium can be borne by the 2 nd porous PTFE membrane having a low permeability and being hardly affected by an external force because it is sandwiched between air-permeable support members, and the exposed surface as a dust accumulation surface can be formed by the 1 st porous PTFE membrane having a high permeability and being less affected by the filter performance of the filter medium even if the filter medium is slightly damaged by an external force. In other words, in the filter medium of the present invention, the 2 nd porous PTFE membrane has a function of playing a role of a filtering function as a filter medium, and the 1 st porous PTFE membrane has a function of an exposed layer (a layer on which dust is deposited, a layer to which an external force is applied when removing dust) which allows some damage by an external force. In the filter medium of the present invention, the above-described functions are shared by the 1 st porous PTFE membrane and the 2 nd porous PTFE membrane, thereby suppressing a decrease in filtration performance due to a dust removal operation.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of the filter medium of the present invention.

Fig. 2 is a perspective view schematically showing an example of the air filter unit of the present invention.

Detailed Description

Embodiments of the present invention are described below with reference to the drawings. The present invention is not limited to the embodiments described below.

[ Filter Medium for Filter ]

Fig. 1 shows an example of a filter medium of the present invention. The filter medium 1 of fig. 1 includes a 1 st porous PTFE membrane 11, a 1 st air-permeable support 12, a 2 nd porous PTFE membrane 13, and a 2 nd air-permeable support 14. The filter medium 1 has a laminated structure 15 in which a 1 st porous PTFE membrane 11, a 1 st air-permeable support 12, a 2 nd porous PTFE membrane 13, and a 2 nd air-permeable support 14 are laminated in this order. The 1 st porous PTFE membrane 11 forms one exposed surface 16 of the filter medium 1. The other exposed surface 17 of the filter medium 1 is formed of the 2 nd air-permeable supporting member 14.

Transmittance TR of the 1 st porous PTFE membrane 11₁Transmittance TR to the 2 nd porous PTFE membrane 13₂Ratio of (TR)₁/TR₂Is 100 or more. Ratio TR₁/TR₂When the amount is less than 100, the above-mentioned functions of the porous PTFE membranes 11 and 13 are not sufficiently shared, and the degree of deterioration of the filtration performance of the filter medium due to the dust removal operation increases. Ratio TR₁/TR₂The amount of the organic solvent may be 300 or more, 400 or more, 440 or more, 500 or more, 1000 or more, 2500 or more, 5000 or more, 10000 or more, 25000 or more, 50000 or more, 75000 or more, 100000 or more, 110000 or more, 125000 or more, 150000 or more, 175000 or more, and further 190000 or more. Ratio TR₁/TR₂The larger the size, the more reliably the filter medium can be prevented from deteriorating in filtering performance due to the dust removing operation. Ratio TR₁/TR₂The upper limit of (b) is, for example, 5000000 or less.

The transmittances TR of the 1 st porous PTFE membrane 11 and the 2 nd porous PTFE membrane 13₁、TR₂The collection efficiency CE of the porous PTFE membranes 11 and 13 is₁、CE₂(unit:%) the trapping efficiency was measured at a permeation flow rate of 5.3 cm/sec using monodisperse dioctyl sebacate particles having an average particle size of 0.1 μm (hereinafter, the term "dioctyl sebacate" is referred to as "DEHS").

Transmittance TR₁(100%) trapping efficiency CE₁

Transmittance TR₂(100%) trapping efficiency CE₂

The collection efficiency CE of the porous PTFE membrane can be measured as follows. A porous PTFE membrane as an object to be evaluated was placed so as to cover the vent hole and to have a vent hole (circular shape, effective area 100 cm)²) On the holder. Then, a pressure difference is generated between one surface and the other surface of the holder, and air is allowed to permeate through the object to be evaluated in the vent. Then, after adjusting the pressure difference so that the linear flow rate of the air passing through the object to be evaluated is maintained at 5.3 cm/sec at the flow rate measurement timing, the air passing through the object to be evaluated is caused to pass through at 10⁴Per cm³The above concentrations contained monodisperse DEHS particles with an average particle size of 0.1 μm. Here, the concentration of DEHS particles contained in the air after passing through the object to be evaluated is measured using a particle counter disposed on the downstream side of the object to be evaluated, and the collection efficiency CE of the object to be evaluated is obtained by the following equation.

Collection efficiency CE ═ 1- (particle concentration on the downstream side)/(particle concentration on the upstream side) ] × 100 (%)

Transmittance TR of the 1 st porous PTFE membrane 11₁May be, for example, 10 to 90%. Transmittance TR₁The lower limit of (b) is 15% or more, 20% or more, 24% or more, 30% or more, 35% or more, and further 40% or more. Transmittance TR₁The upper limit of (b) may be 80% or less, 70% or less, 60% or less, 50% or less, 44% or less, and further 40% or less.

The permeability TR of the 2 nd porous PTFE membrane 13₂The concentration of the surfactant may be, for example, 0.000001 to 5%. Transmittance TR₂The upper limit of (b) is 1% or less, 0.5% or less, less than 0.5%, 0.25% or less, 0.15% or less, 0.11% or less, 0.1% or less, 0.01% or less, 0.001% or less, and further 0.0005% or less. Transmittance TR₂The lower limit of (b) may be 0.0001% or more.

Pressure loss PL of the 1 st porous PTFE membrane 11 at a permeation flow rate of 5.3 cm/sec₁For example, 1 to 150 Pa. Pressure loss PL₁The lower limit of (b) may be 10Pa or more, 20Pa or more, 30Pa or more, and further 40Pa or more. Pressure loss PL₁The upper limit of (b) may be 120Pa or less, 100Pa or less, 80Pa or less, 60Pa or less, and further 40Pa or less.

Pressure loss PL of the 2 nd porous PTFE membrane 13 at a permeation flow rate of 5.3 cm/sec₂For example, 50 to 500 Pa. Pressure loss PL₂The lower limit of (b) may be 75Pa or more, 100Pa or more, 110Pa or more, 125Pa or more, 150Pa or more, further 175Pa or more. Pressure loss PL₂The upper limit of (b) may be 400Pa or less, 350Pa or less, 300Pa or less, 250Pa or less, 200Pa or less, and further 180Pa or less.

Pressure loss PL of 1 st porous PTFE membrane 11₁Is generally smaller than the pressure loss PL of the 2 nd porous PTFE membrane 13₂. Pressure loss PL of the 2 nd porous PTFE membrane 13₂Pressure loss PL with respect to the 1 st porous PTFE membrane 11₁Ratio of (A to (B))₂/PL₁For example, 1.5 or more, and may be 2 or more, 2.75 or more, 3 or more, 4 or more, 4.5 or more, 5 or more, 7 or more, 8 or more, or even 9 or more. Ratio PL₂/PL₁The upper limit of (b) is, for example, 30 or less.

The pressure loss PL of the porous PTFE membrane can be measured as follows. Relative to the structure with air vents (circular, effective area 100 cm)²) The holder of (1) is provided with a porous PTFE membrane as an evaluation object so that the membrane closes the vent hole. Then, a pressure difference is generated between one surface and the other surface of the holder, and air is allowed to permeate through the object to be evaluated in the vent. Next, the pressure difference was measured by a pressure gauge (a meter) at a time when the linear flow rate of air passing through the evaluation object was measured to be 5.3 cm/sec by a flow meter. The pressure difference was measured 3 times for 1 evaluation object, and the average value thereof was defined as the pressure loss PL of the evaluation object.

The PF (Performance Factor) value of the 1 st porous PTFE membrane 11 is, for example, less than 20, and may be 19 or less, 18 or less, 17.5 or less, and further 17 or less. The lower limit of the PF value of the 1 st porous PTFE membrane 11 is, for example, 5 or more, and may be 8 or more, 10 or more, 12 or more, 13 or more, 14 or more, 15 or more, or further 15.2 or more. The PF value of the 2 nd porous PTFE membrane 13 may be, for example, 15 or more, 20 or more, 23 or more, 25 or more, 27 or more, 29 or more, or even 30 or more. The upper limit of the PF value of the 2 nd porous PTFE membrane 13 is, for example, 40 or less. The PF value of the 1 st porous PTFE membrane 11 is generally smaller than that of the 2 nd porous PTFE membrane 13. The ratio of the PF value of the 1 st porous PTFE membrane 11 to the PF value of the 2 nd porous PTFE membrane 13 is, for example, 0.9 or less, and may be 0.8 or less, 0.7 or less, or even 0.6 or less. The lower limit of the PF value ratio is, for example, 0.1 or more, and may be 0.3 or more, 0.36 or more, 0.4 or more, or further 0.5 or more.

The PF value of the porous PTFE membrane is the pressure loss PL of the porous PTFE membrane (wherein the unit of the pressure loss PL when the PF value is determined is mmH₂O) and collection efficiency CE (unit: %) is determined by the following formula.

PF value { -l o g [ (100-CE)/100]/PL } × 100

The thickness of the 1 st porous PTFE membrane 11 constituting the exposed surface 16 is, for example, 0.1 μm or more, and may be 1 μm or more, 2 μm or more, 5 μm or more, and further 10 μm or more. The upper limit of the thickness of the 1 st porous PTFE membrane 11 is, for example, 50 μm or less. The thickness of the 2 nd porous PTFE membrane 13 sandwiched between the 1 st and 2 nd air-permeable supports 12 and 14 is, for example, 0.1 to 50 μm, and may be 1 to 10 μm, 5 to 10 μm, or further 6 to 9 μm.

The water contact angle of the exposed surface 16 of the 1 st porous PTFE membrane 11 may be less than 154 °, and may be 153 ° or less. The water contact angle can be evaluated by the sessile drop method specified in Japanese Industrial Standard (JIS) R3257. In addition, although JIS R3257 specifies a method for evaluating the water contact angle of the substrate glass surface, the water contact angle of the exposed surface 16 can be evaluated according to a test method and test conditions specified in the standard. The contact angle is defined as an average of measured values at 5 positions on the surface to be evaluated. The volume of the water droplets used for the evaluation was set to 2 μ L.

The porous PTFE membranes 11 and 13 may be formed of a single layer, or may be formed of 2 or more layers.

The porous PTFE membranes 11 and 13 can be obtained, for example, as follows: the porous PTFE sheet is obtained by forming a mixture of the unfired PTFE powder and the liquid lubricant into a sheet by a method such as extrusion and/or rolling, removing the liquid lubricant from the obtained unfired sheet, and then stretching the sheet to make the sheet porous. The stretching is typically biaxial stretching in which stretching in the MD direction (longitudinal direction) and stretching in the TD direction (width direction) of the sheet are combined. In the biaxial stretching, stretching in the MD direction and stretching in the TD direction are preferably performed in this order. The liquid lubricant is not limited as long as it can wet the surface of the PTFE particles and can be removed later, and examples thereof include hydrocarbon oils such as naphtha, white oil, and liquid paraffin. The sheet may be subjected to firing in which the sheet is exposed to an atmosphere of 327 ℃ which is the melting point of PTFE or higher at any time after the liquid lubricant is removed. Firing may be performed simultaneously with stretching. The strength of the porous PTFE membrane can be increased by firing. By controlling the production conditions, typically the stretching conditions, of the porous PTFE membranes, porous PTFE membranes having different transmittances can be obtained.

The 1 st and 2 nd air-permeable supports 12 and 14 have a function of reinforcing the porous PTFE membranes 11 and 13 to maintain the shape of the filter medium 1, and a function of protecting the 2 nd porous PTFE membrane 13 from being damaged by an external force. The air-permeable supporting members 12 and 14 are made of, for example, nonwoven fabric, woven fabric, or net of fibers such as short fibers and long fibers. The air-permeable supporting members 12 and 14 made of nonwoven fabric are preferable because they are excellent in air permeability, strength, flexibility and handleability. The air permeability in the thickness direction of the air permeable supports 12 and 14 is generally higher than that of the porous PTFE membranes 11 and 13.

The materials constituting the air-permeable supporting materials 12, 14 are, for example: polyolefins such as Polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET); a polyamide comprising an aromatic polyamide; and composites of these. The breathable support materials 12, 14 may comprise more than 2 of these materials. From the viewpoint of excellent adhesion to the PTFE porous membranes 11 and 13, the material is preferably polyolefin, and more preferably PE. When the material is a composite material, polyolefin, particularly PE, is preferably exposed at the joint surfaces of the air-permeable supports 12 and 14 and the porous PTFE membranes 11 and 13.

One example of the composite material that can constitute the air-permeable supporting members 12 and 14 is a composite fiber having a core-sheath structure in which a core portion made of different materials is formed and a sheath portion covering the core portion is formed. In this composite fiber, the melting point of the material constituting the sheath portion is preferably lower than the melting point of the material constituting the core portion. The material constituting the core is, for example, polyester such as PET. The material constituting the sheath portion is, for example, polyolefin such as PE.

The average fiber diameter of the fibers constituting the air-permeable supporting members 12 and 14 may be, for example, 1 to 50 μm, 1 to 30 μm, or 10 to 30 μm.

The weight per unit area of the air-permeable supporting members 12, 14 is, for example, 20 to 70g/m². The upper limit of the weight per unit area may be 50g/m²Below, 40g/m²Less than 40g/m²And further 35g/m²The following. The lower limit of the weight per unit area is, for example, 25g/m²The above.

The composition of the 1 st air-permeable support member 12 may be the same as that of the 2 nd air-permeable support member 14.

Each of the breathable support materials 12 and 14 may be formed of a single layer, or may be formed of 2 or more layers.

The thickness of the filter medium 1 is, for example, 50 to 1000 μm, and may be 100 to 500 μm.

The weight per unit area of the filter medium 1 is, for example, 10 to 1000g/m²And may be 30 to 500g/m²。

Transmittance TR of filter medium 1_FFor example, the content is 5% or less, and may be 1% or less, 0.5% or less, 0.11% or less, 0.1% or less, less than 0.5%, 0.25% or less, 0.15% or less, 0.01% or less, 0.001% or less, and further 0.0005% or less. Transmittance TR_FThe lower limit of (b) is, for example, 0.00001% or more, and may be 0.0001% or more.

Transmittance TR of filter medium 1_FTo achieve the collection efficiency CE of the filter medium 1_F(unit:%) the collection efficiency CE, which is a value obtained by the following formula_FMeasured at a permeation flow rate of 5.3 cm/sec using monodisperse DEHS particles having an average particle diameter of 0.1. mu.m. Trapping efficiency CE_FThe collection efficiency CE of the porous PTFE membranes 11 and 13 can be measured by using the object to be evaluated as the filter medium 1₁、CE₂The same method as described above. Wherein the filter medium 1 is provided so that the 1 st porous PTFE membrane 11 is located on the upstream side with respect to the air permeation direction at the time of measurementIs placed on the holding member.

Transmittance TR_F(100%) trapping efficiency CE_F

Pressure loss PL of filter medium 1_FFor example, less than 300Pa, 250Pa or less, 230Pa or less, 220Pa or less, 210Pa or less, and further 200Pa or less. Pressure loss PL_FThe lower limit of (B) is, for example, 10Pa or more. Pressure loss PL_FThe pressure loss PL of the porous PTFE membranes 11 and 13 can be measured by using the object to be evaluated as the filter medium 1₁、PL₂The same method as described above. The filter medium 1 is provided in the holder so that the 1 st porous PTFE membrane 11 is on the upstream side with respect to the direction of air permeation during measurement.

The PF value of the filter medium 1 is, for example, 15 or more, and may be 19 or more, 20 or more, 22 or more, 24 or more, and further 25 or more. The PF value of the filter medium 1 is the pressure loss PL from the filter medium 1_F(wherein the pressure loss PL when the PF value is determined_FIs set as mmH₂O) and trapping efficiency CE_F(unit:%) is a value obtained by the following formula.

PF value { -l o g [ (100-CE)_F)/100]/PL_F}×100

The filter medium 1 may be Japanese Industrial Standard (JIS) Z8122: the filter medium for the HEPA (high-efficiency particulate air grade) filter specified in 2000 may be a filter medium for an ULPA (ultra-low-penetration air grade) filter.

The filter medium 1 may further include a layer and/or a member other than the porous PTFE membranes 11 and 13 and the air-permeable supports 12 and 14, as long as the filter medium has the laminated structure 15.

In the filter medium 1, adjacent porous PTFE membranes 11 and 13 and air-permeable supports 12 and 14 are bonded to each other. The bonding method is not limited, and examples thereof include thermal lamination and lamination with an adhesive. Bonding by thermal lamination is preferable from the viewpoint of suppressing an increase in pressure loss at the bonded portion. The filter medium 1 can be formed by, for example, subjecting a laminate in which a 1 st porous PTFE membrane 11, a 1 st air-permeable support 12, a 2 nd porous PTFE membrane 13, and a 2 nd air-permeable support 14 are laminated in this order to various lamination processes such as thermal lamination.

The filter medium 1 is generally used as a ventilation filter that allows gas such as air to pass therethrough and removes objects to be filtered such as particles contained in the gas. The filter medium 1 is generally used such that the 1 st porous PTFE membrane 11 is disposed upstream of a gas flow containing a substance to be filtered. The ventilation filter is, for example, an air filter for a clean room, a dust filter for an electrical product such as a cleaner and an air cleaner. The filter medium 1 is excellent in recyclability, and therefore is particularly suitable for use as a dust filter. However, the use of the filter medium 1 is not limited to the above example.

[ Filter Unit ]

Fig. 2 shows an example of the filter unit 21 of the present invention. The filter unit 21 shown in fig. 2 includes a filter medium 1 and a frame 22 for supporting the filter medium 1. In the filter unit 21, the filter medium 1 is in a state of the filter pleat pack 23 having been subjected to the pleating process. In the filter pleat pack 23, the filter medium 1 is folded in a continuous W shape when viewed from the side surface thereof. By the pleating process of the filter medium 1, the gas permeation amount can be increased while suppressing an increase in pressure loss as the filter unit 21.

The frame 22 supports the peripheral edge of the filter pleat pack 23. The frame 22 is made of, for example, metal, resin, or a composite material thereof. The frame 22 may have the same structure as that of a frame provided in a conventional filter unit.

The filter unit 21 may further include a member other than the air filter medium 1 and the frame 22. This member is, for example, a resin strip commonly referred to as a "bead". The rib is one of separators for maintaining the shape of the pleated air filter medium 1. The beads are generally disposed on the surface of the folded air filtering member 1 so as to run in a direction intersecting the gather lines (mountain fold lines and/or valley fold lines) of the air filtering member 1. The air filter medium 1 may have ribs on one surface or both surfaces, and is preferably arranged not on the porous PTFE membrane but on the air-permeable support member. The reinforcing rib can be formed by melting and applying a resin in a band shape, for example. The resin is not limited, and examples thereof include polyamide and polyolefin.

The filter unit 21 is generally used as a ventilation filter unit that allows gas such as air to pass therethrough and removes objects to be filtered such as particles contained in the gas. The filter unit 21 is usually used such that the 1 st porous PTFE membrane 11 is disposed upstream of the gas flow containing the object to be filtered. The ventilation filter unit is, for example, an air filter unit for a clean room, a cleaner, a dust filter unit for an electrical product such as an air cleaner, and the like. The filter unit 21 is particularly suitable as a dust filter unit because of its excellent recyclability. However, the use of the filter unit 21 is not limited to the above example.

The filter unit 21 can be formed by a known method using the filter medium 1. The pleating process of the filter medium 1 may be performed, for example, as follows: the air filter medium 1 is continuously folded by a pleating machine in mountain fold lines and valley fold lines set alternately and in parallel to the surface.

Examples

The present invention will be described in further detail below with reference to examples. However, the present invention is not limited to the examples shown below.

First, evaluation methods of the porous PTFE membrane and the filter medium produced in examples and comparative examples are shown.

[ thickness ]

The thicknesses of the porous PTFE membrane, the air-permeable support material, and the filter medium were evaluated by a digital dial gauge.

[ transmittance ]

The permeability of the porous PTFE membrane and the filter medium was evaluated as follows. First, a porous PTFE membrane or a filter medium as an evaluation object was provided with a vent hole (circular shape, effective area 100 cm) so that the vent hole was closed by the evaluation object²) On the holder. Then, a pressure difference is generated between one surface and the other surface of the holder to make air flowPermeate through the object to be evaluated in the vent. Then, after adjusting the pressure difference so that the linear flow rate of the air passing through the object to be evaluated is maintained at 5.3 cm/sec at the flow rate measurement timing, the air passing through the object to be evaluated is caused to pass through at 10⁴Per cm³The above concentrations contained monodisperse DEHS particles with an average particle size of 0.10 μm. The concentration of DEHS particles contained in the air after passing through the object to be evaluated was measured using a particle counter disposed downstream of the object to be evaluated, and the collection efficiency (unit:%) of the object to be evaluated was determined by the following formula (1). Then, the transmittance of the evaluation object is determined from the determined trapping efficiency by the following formula (2).

Formula (1): capture efficiency (%) [1- (particle concentration on the downstream side)/(particle concentration on the upstream side) ] × 100

Formula (2): transmittance (%) of 100-trapping efficiency

[ pressure loss ]

The pressure loss of the porous PTFE membrane and the filter medium was evaluated as follows. First, a porous PTFE membrane or a filter medium as an evaluation object was provided with a vent hole (circular shape, effective area 100 cm) so that the vent hole was closed by the evaluation object²) On the holder. Then, a pressure difference is generated between one surface and the other surface of the holder, and air is allowed to permeate through the object to be evaluated in the vent. Next, the pressure difference was measured by a pressure gauge (a meter) at a time when the linear flow rate of air passing through the evaluation object was measured to be 5.3 cm/sec by a flow meter. The pressure difference was measured 3 times for 1 evaluation object, and the average value was defined as the pressure loss of the evaluation object.

[ PF value ]

The PF values of the porous PTFE membrane and the filter medium were determined from the respective pressure losses PL (wherein the unit of the pressure loss PL when the PF value was obtained was mmH₂O) and collection efficiency CE (unit: %) was obtained by the following formula.

PF value { -l o g [ (100-CE)/100]/PL } × 100

[ washability ]

The water washability of the filter medium was evaluated as follows. First, will be evaluatedThe filter medium of the object was cut into a circular shape having a diameter of 47mm to obtain a test piece. Then, 0.2g of "8 types of soil for Guandong" as test powder described in JIS Z8901 was fully placed on the exposed surface of the 1 st porous PTFE membrane (examples 1 to 3 and comparative example 1) or the exposed surface of the air-permeable support (comparative example 2) of the test piece, and the test piece was sucked at a linear velocity of 20 cm/sec for 60 seconds from the opposite side thereof. Subsequently, the powder was washed with about 10mL of water using a wash bottle while keeping the mounting surface of the powder vertical. Next, the pressure loss PL of the filter medium was evaluated_FPressure loss PL before placing the powder_FThe case where the difference is less than 20% was evaluated as "good", and the case where the difference is 20% or more was evaluated as "poor".

[ durability test ]

The filter medium was subjected to a durability test as described below. First, the transmittance TR (transmittance before durability test) of the filter medium before the durability test was measured_F1. Next, a toothbrush was brought into contact with the exposed surface of the 1 st porous PTFE membrane (examples 1 to 3 and comparative example 1) or the exposed surface of the air-permeable support material (comparative example 2) in the filter medium, and the toothbrush was reciprocated 50 times in the contact state to perform a durability test. Subsequently, the filter medium subjected to the durability test was measured for its transmittance (transmittance after the durability test) TR_F2. The transmittance TR after the durability test was determined_F2Transmittance TR before durability test_F1The magnification of (2) is evaluated as "good" when the magnification is 10 times or less, and as "poor" when the magnification exceeds 10 times.

Production example 1

100 parts by weight of PTFE fine powder (made of Dajin, Polyflon (registered trademark) PTFE F-104) and 20 parts by weight of dodecane as a liquid lubricant were mixed uniformly to obtain a mixture. The resulting mixture was extruded into a rod-like shape by an extruder, and the rod-like shape was passed between a pair of metal reduction rolls to obtain a tape-like PTFE sheet (thickness: 200 μm). Subsequently, the PTFE sheet was held at 150 ℃ in an atmosphere to remove the liquid lubricant. Subsequently, the PTFE sheet was stretched at a stretching temperature of 280 ℃ and a stretching ratio of 85 times in the longitudinal direction, and then stretched at a stretching temperature of 150 ℃ and a stretching ratio of 200 times in the width direction. The stretched PTFE sheet was heated with hot air at 500 ℃ in a state in which the sheet had a fixed dimension, to obtain a porous PTFE membrane a. The porous PTFE membrane A thus obtained had a thickness of 2 μm, a transmittance of 44% and a pressure loss of 20 Pa.

Production example 2

100 parts by weight of PTFE fine powder (manufactured by AGC, Fluon (registered trademark) CD129E) and 20 parts by weight of dodecane as a liquid lubricant were mixed uniformly to obtain a mixture. The resulting mixture was extruded into a rod-like shape by an extruder, and the rod-like shape was passed between a pair of metal reduction rolls to obtain a tape-like PTFE sheet (thickness: 200 μm). Subsequently, the PTFE sheet was held at 150 ℃ in an atmosphere to remove the liquid lubricant. Next, the PTFE sheet was stretched in the longitudinal direction at a stretching temperature of 375 ℃, a stretching ratio of 20 times in the first stage, and a stretching ratio of 4.5 times in the second stage, and then stretched in the width direction at a stretching temperature of 150 ℃, and a stretching ratio of 6 times, to obtain a porous PTFE membrane B. The porous PTFE membrane B thus obtained had a thickness of 12 μm, a transmittance of 24% and a pressure loss of 40 Pa.

(production example 3)

100 parts by weight of PTFE fine powder (made of Dajin, Polyflon (registered trademark) PTFE F-104) and 20 parts by weight of dodecane as a liquid lubricant were mixed uniformly to obtain a mixture. The resulting mixture was extruded into a rod-like shape by an extruder, and the rod-like shape was passed between a pair of metal reduction rolls to obtain a tape-like PTFE sheet (thickness: 200 μm). Subsequently, the PTFE sheet was held at 150 ℃ in an atmosphere to remove the liquid lubricant. Subsequently, the PTFE sheet was stretched at a stretching temperature of 280 ℃ and a stretching ratio of 18 times in the longitudinal direction, and then stretched at a stretching temperature of 120 ℃ and a stretching ratio of 35 times in the width direction. The stretched PTFE sheet was heated with hot air at 500 ℃ in a state in which the sheet had a fixed dimension, to obtain a PTFE porous membrane C. The porous PTFE membrane C thus obtained had a thickness of 9 μm, a transmittance of 0.00022% and a pressure loss of 180 Pa.

Production example 4

100 parts by weight of PTFE fine powder (made of Dajin, Polyflon (registered trademark) PTFE F-104) and 20 parts by weight of dodecane as a liquid lubricant were mixed uniformly to obtain a mixture. The resulting mixture was extruded into a rod-like shape by an extruder, and the rod-like shape was passed between a pair of metal reduction rolls to obtain a tape-like PTFE sheet (thickness: 200 μm). Subsequently, the PTFE sheet was held at 150 ℃ in an atmosphere to remove the liquid lubricant. Subsequently, the PTFE sheet was stretched at a stretching temperature of 280 ℃ and a stretching ratio of 20 times in the longitudinal direction, and then stretched at a stretching temperature of 120 ℃ and a stretching ratio of 35 times in the width direction. The stretched PTFE sheet was heated with hot air at 500 ℃ in a state in which the sheet had a fixed dimension, to obtain a porous PTFE membrane D. The porous PTFE membrane D thus obtained had a thickness of 6 μm, a transmittance of 0.054% and a pressure loss of 110 Pa.

(example 1)

A filter medium having a 4-layer structure of 1 porous PTFE membrane/air-permeable support/2 porous PTFE membrane/air-permeable support was obtained by bonding a porous PTFE membrane A as a 1 st porous PTFE membrane, a porous PTFE membrane C as a 2 nd porous PTFE membrane, and a nonwoven fabric of PET/PE composite fibers (manufactured by Unitika, ELEVES S0303WDO, thickness 210 μm) as an air-permeable support by thermal lamination using a heating roll set at 130 ℃.

(example 2)

A filter medium having a 4-layer structure of 1 porous PTFE membrane/air-permeable support/2 porous PTFE membrane/air-permeable support was obtained in the same manner as in example 1, except that the porous PTFE membrane B was used as the porous PTFE membrane 1.

(example 3)

A filter medium having a 4-layer structure of 1 porous PTFE membrane/air-permeable support/2 porous PTFE membrane/air-permeable support was obtained in the same manner as in example 2, except that the porous PTFE membrane D was used as the porous PTFE membrane 2.

Comparative example 1

A filter medium having a 4-layer structure of 1 porous PTFE membrane/air-permeable support/2 porous PTFE membrane/air-permeable support was obtained by bonding a porous PTFE membrane D as a porous 1PTFE membrane and a porous 2PTFE membrane and a nonwoven fabric of PET/PE composite fibers (manufactured by Unitika, ELEVES T0303WDO, thickness 160 μm) as an air-permeable support by thermal lamination using a heating roll set at 130 ℃.

Comparative example 2

A filter medium having a 5-layer structure of air-permeable support material/1 porous PTFE membrane/air-permeable support material/2 porous PTFE membrane/air-permeable support material was obtained by bonding a porous PTFE membrane D as a 1 st porous PTFE membrane and a porous PTFE membrane D as a 2 nd porous PTFE membrane and a nonwoven fabric of PET/PE composite fibers (manufactured by Unitika, ELEVES T0303WDO, thickness 160 μm) as an air-permeable support material by thermal lamination using a heating roll set at 130 ℃.

The evaluation results are summarized in table 1 below.

[ Table 1]

^1*)The numerical value in parentheses is the transmittance TR of the filter medium after the durability test_F2The value of (D) is relative to the transmittance TR of the filter medium before the durability test_F1Magnification of value of

Industrial applicability

The filter medium of the present invention can be used for the same purpose as a conventional filter medium. The filter medium is used for, for example, a ventilation filter for electrical products such as a cleaner and an air cleaner.