JP2005095803A - Filter medium for air filter, and air filter unit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for an air filter capable of forming more pleats, having large effective filtering area and small pressure loss. <P>SOLUTION: This air filter medium 1 comprises at least one layer of PTFE porous membrane 2 and multiple layers of air permeable support layers 3, the medium 1 has a thickness of 0.3mm or less. It is preferable that the pressure loss is 20-200 Pa when passing air at a velocity of 5.3 cm/sec, and a collection efficiency is 99.999% or more when measured using dioctyl phthalate of a particle size of 0.1-0.2 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an air filter medium and an air filter unit using the same.

  Conventionally, as a filter medium for an air filter used in a clean room, paper made by adding a binder to glass fiber has been used in many cases. However, such filter media have problems such as the presence of small fibers attached to the filter media and generation of dust during bending. Further, this filter medium has a problem that it generates dust when it comes into contact with certain chemicals such as hydrofluoric acid.

Polytetrafluoroethylene (hereinafter referred to as “PTFE”) is a clean material. In recent years, a filter medium including a PTFE porous membrane has begun to be used as a filter medium for a high-performance air filter used in a clean room such as the semiconductor industry ( For example, see Patent Documents 1 to 4). Generally, a porous PTFE membrane is laminated with a breathable support layer for reinforcement to form a filter material for an air filter. In practice, a filter medium for an air filter having a structure including a plurality of breathable support layers is often used to ensure strength. These air filter media are subjected to continuous W-shaped fold folding (hereinafter also referred to as “pleating”), and are further framed and used as an air filter unit.
JP-A-5-202217 (5th page, FIG. 25) Japanese Patent Laid-Open No. 10-30031 (page 8, FIG. 1-2) JP 2000-33244 A (page 5) Japanese Unexamined Patent Publication No. 2000-61280 (pages 4-5 and 2-5)

  However, in the air filter medium including a plurality of air-permeable support layers, the thickness of each is greater than, for example, 0.3 mm. Therefore, the number of pleats per unit area of the plane perpendicular to the gas passing through the air filter (folded) The number of peaks) must be less than the desired number. When the number of folds is reduced, the effective filtration area of the air filter unit is reduced, and the pressure loss is increased.

  The air filter medium of the present invention is an air filter medium including at least one PTFE porous membrane and a plurality of air-permeable support layers, and the thickness of the air filter medium is 0.3 mm or less. It is characterized by being.

  The air filter unit of the present invention is characterized by using the air filter medium of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the filter medium for air filters which can form more pleats, the air filter unit with a large effective filtration area and a small pressure loss can be provided.

  Hereinafter, an example of a filter medium for an air filter of the present invention and an air filter unit using the same will be described with reference to the drawings.

  As shown in FIG. 1, the air filter medium 1 of the present embodiment includes at least one PTFE porous membrane 2 and a plurality of air-permeable support layers 3, and the thickness of the air filter medium 1 is as follows. Since it is 0.3 mm or less, more pleats can be formed as shown in the following examples. Therefore, if the filter material 1 for air filters of this Embodiment is used, the air filter unit with a large effective filtration area and a small pressure loss can be provided. In addition, there is no restriction | limiting in particular about the minimum of the thickness of the filter medium 1 for air filters, Usually, it is 100 micrometers or more.

  In the present invention, the thickness of the air filter medium is a value measured according to the following method.

[Thickness of air filter media]
Using a dial thickness gauge (measuring element diameter 10 mm, minimum graduation 0.01 mm), the thickness of an arbitrary portion of the filter medium 1 for air filter is measured at five points, and the average value is obtained.

  The PTFE porous membrane 2 is not particularly limited with respect to the pore diameter and the like as long as the collection function according to the intended use is exhibited, but usually the average pore diameter is 0.01 to 5 μm and the thickness is 2 to 30 μm. It is preferable.

  The pressure loss of the PTFE porous membrane 2 may be determined so that the pressure loss of the air filter medium 1 when air is permeated at a flow rate of 5.3 cm / s is 20 Pa to 200 Pa. About 150 Pa is appropriate.

  The collection efficiency of the PTFE porous membrane 2 is preferably 99.9999% or more when measured using dioctyl phthalate having a particle size of 0.1 μm to 0.2 μm. When the collection efficiency of the PTFE porous membrane 2 is 99.9999% or more, the collection efficiency measured by the above method is 99.999% or more by laminating the air-permeable support layer 3 on the PTFE porous membrane 2. This is because it is easy to produce a filter medium for air filter.

  In addition, the pressure loss and the collection efficiency of the PTFE porous membrane 2 and the filter medium 1 for air filter are values measured as follows.

(1) Pressure loss Set the sample in a circular holder so that the effective area is 100 cm ² , supply air from the inlet side, give a pressure difference between the inlet side and the outlet side, and the flow velocity of air passing through this sample Was adjusted to 5.3 cm / s, and the pressure loss (initial value) was measured with a pressure gauge (manometer).

(2) Collection efficiency The sample is set in a circular holder so that the effective area is 100 cm ^2, and the particle size is 0 on the upstream side of the sample while adjusting the flow rate of air passing through the sample to 5.3 cm / s. .1 μm to 0.2 μm of dioctyl phthalate (DOP) is supplied so that the concentration is about 10 ⁷ pieces / liter. The upstream particle concentration (pieces / liter) and the downstream particle concentration (pieces / liter) that have permeated through the sample are measured with a particle counter, and the measured values are substituted into the following equation (Equation 1) for collection. Seeking efficiency.
(Equation 1)
Collection efficiency (%) = (1− (downstream concentration / upstream concentration)) × 100

A PF (Performance of filter) value is often used as a measure of the balance between collection efficiency and pressure loss. A filter medium with a larger PF value has higher particle collection efficiency and lower pressure loss. The PF value of the PTFE porous membrane 2 is preferably 22 or more, and the PF value of the air filter medium 1 is also preferably 22 or more. The PF value is given by the following equation (Equation 2). In addition, the transmittance | permeability in (Equation 2) is obtained from the relationship of the transmittance | permeability = (100-collection efficiency).
(Equation 2)
PF value = [− Log (transmittance / 100) / pressure loss (mmH ₂ O)] × 100

  Next, an example of a method for producing the PTFE porous membrane 2 will be described. First, a paste-like mixture obtained by adding a liquid lubricant to PTFE fine powder is preformed. There is no restriction | limiting in particular in PTFE fine powder, A commercially available thing can be used. The liquid lubricant is not particularly limited as long as it can wet the surface of the PTFE fine powder and can be removed by extraction or heating. For example, hydrocarbons such as naphtha and white oil can be used. The addition amount of the liquid lubricant is suitably about 5 to 50 parts by weight with respect to 100 parts by weight of PTFE fine powder. The preforming may be performed at a pressure that does not squeeze out the liquid lubricant.

  Next, the preform is extruded and rolled to form a sheet, and the sheet-like formed body thus obtained is stretched at least in a uniaxial direction to obtain a PTFE porous membrane. The stretching may be performed after removing the liquid lubricant. Stretching conditions can be set as appropriate, but usually the temperature is 30 to 320 ° C., and the stretching ratio is 2 to 30 times in both the longitudinal and transverse directions.

  Since the PTFE porous membrane produced as described above has low strength in an unfired state, it is desirable to perform heat treatment. The heat treatment is performed at a temperature equal to or higher than the melting point of the PTFE porous membrane, but is preferably performed at 350 to 450 ° C. Although there is no restriction | limiting in particular about a heating method, There exist the method of blowing a hot air, the method of allowing the inside of a high temperature furnace to pass, etc.

  The air-permeable support layer 3 is not particularly limited in terms of material, structure, form, and the like as long as a filter medium for an air filter having a thickness of 0.3 mm or less can be produced by joining with the PTFE porous membrane 2, but from the PTFE porous membrane Also, a material excellent in air permeability, for example, felt, non-woven fabric, woven fabric, mesh (mesh sheet), and other porous materials can be used. In particular, a nonwoven fabric is preferable from the viewpoints of strength, collection property, flexibility, and workability. Furthermore, it is preferable that a part or all of the fibers constituting the nonwoven fabric are composite fibers having a core-sheath structure, and the core component is a fiber having a relatively higher melting point than the sheath component, for example, a synthetic fiber. If the breathable support layer 3 is heated to a temperature higher than the melting point of the sheath component, the breathable support layer 3 and the PTFE porous membrane 2 can be easily heat-laminated.

  The material of the breathable support layer 3 is not particularly limited, but polyolefin (polyethylene (PE), polypropylene (PP), etc.), polyamide, polyester (polyethylene terephthalate (PET), etc.), aromatic polyamide, or a composite material thereof. Etc. can be used.

When the air-permeable support layer 3 is a nonwoven fabric, the basis weight is preferably 100 g / m ² or less. If the basis weight is 100 g / m ² or less, the breathable support layer 3 and the PTFE porous membrane 2 are pressure-bonded by, for example, a heat laminating method so that the thickness of the air filter medium 1 is 0.3 mm or less. This is because an air filter medium having a pressure loss of 20 Pa to 200 Pa can be easily produced. Although there is no restriction | limiting in particular about the minimum of the fabric weight, Usually, it is preferable that it is 10 g / m < ² > or more.

The thickness of the air-permeable support layer 3 is not particularly limited as long as the air filter medium 1 having a thickness of 0.3 mm or less can be produced by bonding with the PTFE porous membrane 2, but the air filter medium 1 is, for example, 2, when two layers of the PTFE porous membrane 2 and three layers of the air-permeable support layer 3 are included, and the basis weight of the air-permeable support layer 3 is 10 to 20 g / m ² , the PTFE porous material The thickness of the breathable support layer 3 before being bonded to the membrane 2 is usually 50 to 120 μm.

That is, in the method for manufacturing the air filter medium 1 of the present embodiment shown in FIG. 2, for example, after the PTFE porous membrane 2 and the air-permeable support layer 3 are superposed, pressurizing while heating, Including the step of bonding the PTFE porous membrane 2 and the air-permeable support layer 3, it is preferable to use the air-permeable support layer 3 having a thickness of 50 to 120 μm and a weight per unit area of 10 to ²⁰ g / m ² .

  The breathable support layer 3 and the PTFE porous membrane 2 can be joined by, for example, a method such as adhesive lamination, heat welding, ultrasonic welding, vibration welding, and adhesion using an adhesive, in addition to the above thermal laminate. For example, when the breathable support layer 3 and the PTFE porous membrane 2 are joined by heat lamination, a part of the breathable support layer 3 is melted by heating, and the breathable support layer 3 and the PTFE porous membrane 2 are bonded. What is necessary is just to adhere. Further, the PTFE porous membrane 2 and the air-permeable support layer 3 may be bonded with a fusing agent such as hot melt powder interposed.

  The air filter medium 1 is not limited to the example shown in FIG. 1 or FIG. 2, but the air filter medium 1 is formed from a plurality of air-permeable support layers 3 as in the examples shown in FIGS. Including at least one layer of the PTFE porous membrane 2 between at least one pair of the breathable support layers 3 selected can damage the at least one layer of the PTFE porous membrane 2 due to an external force or the like. preferable.

  Further, as shown in FIG. 2, the air filter medium 1 includes a structure in which two or more layers of the PTFE porous membrane 2 are included, and the air-permeable support layer 3 is disposed between the pair of PTFE porous membranes 2. In this case, for example, even if a pinhole is generated in one PTFE porous membrane 2 due to an external force or the like, the other PTFE porous membrane 2 is not easily damaged, and the function as a filter medium is not immediately impaired. .

  If the entire thickness of the air filter medium 1 is 0.3 mm or less, the PTFE porous membrane 2 and the air-permeable support layer 3 are alternately laminated as in the example shown in FIGS. 1 and 2. Alternatively, there may be a portion in which either one or both of the PTFE porous membrane 2 and the air-permeable support layer 3 are continuously laminated. A plurality of porous PTFE membranes 2 having different characteristics and a plurality of breathable support layers 3 having different characteristics may be included.

  In a form in which a plurality of layers of PTFE porous membranes 2 are continuously laminated, the plurality of layers of PTFE porous membranes 2 may be simply overlapped, or may be joined together by pressure bonding, heat fusion, or the like during film formation. Good.

  FIG. 3 is a cross-sectional view of an example of the air filter medium 1 that has been pleated. When a long filter medium is alternately fold-folded / valley-folded at a predetermined interval in the length direction (when pleating is applied), a continuous W-shaped filter medium for air filter 1 as viewed from the cross-sectional direction Can be obtained.

  The pleating process is, for example, a rotary method in which a pair of rotating drums having blades arranged on the outer periphery is rotated while the filter medium is folded, while a pair of blades arranged at a predetermined interval in the transfer direction of the filter medium is moved. A reciprocating method in which the filter medium is alternately folded from both sides can be adopted.

  For example, as shown in FIG. 4, the air filter medium 1 folded in a W shape is framed with a support frame 22 made of aluminum to form an air filter unit.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

(Example 1)
20 parts by weight of a liquid lubricant (Dodecane) is uniformly mixed with 100 parts by weight of PTFE fine powder (manufactured by Asahi Glass Co., Ltd., “Fluon CD-123”) to pre-form a paste-like mixture, and round by paste extrusion Molded into a rod shape. The molded product was rolled to a thickness of 0.2 mm, and the liquid lubricant was extracted and removed with normal decane, and then stretched in the biaxial direction to form a PTFE porous membrane (thickness 10 μm, porosity 93%, average pore diameter 1.0 μm, pressure A loss of 80 Pa, a collection efficiency of 99.95%, and a PF value of 41) were obtained. Next, this PTFE porous membrane and a PET / PE core-sheath nonwoven fabric (thickness 110 μm, basis weight 20 g / m ² ) are thermally laminated (roll temperature 180 ° C.) to form a five-layer structure (nonwoven fabric / PTFE porous membrane). / Filter / nonwoven fabric / PTFE porous membrane / nonwoven fabric).

(Example 2)
The PTFE porous membrane prepared in Example 1 and a PET / PE core-sheath nonwoven fabric (thickness 90 μm, basis weight 15 g / m ² ) are thermally laminated (roll temperature 180 ° C.) to form a five-layer structure (nonwoven fabric / PTFE porous The filter material for air filters of a membrane / nonwoven fabric / PTFE porous membrane / nonwoven fabric) was obtained.

(Comparative Example 1)
The PTFE porous membrane prepared in Example 1 and a PET / PE core-sheath nonwoven fabric (thickness 150 μm, basis weight 30 g / m ² ) are thermally laminated (roll temperature 180 ° C.) to form a five-layer structure (nonwoven fabric / PTFE porous The filter material for air filters of a membrane / nonwoven fabric / PTFE porous membrane / nonwoven fabric) was obtained.

  The thickness, pressure loss, collection efficiency, and PF value of the air filter media of Examples 1 and 2 and Comparative Example 1 were determined and shown in Table 1. Moreover, about the filter medium for air filters of Examples 1, 2 and Comparative Example 1, using a pleating machine, pleating (folding width 30 mm) is performed until the thickness in the folding direction of the filter medium for air filter is 610 mm, The number of folds was determined and shown in Table 1. The number of folds was calculated by dividing 610 mm by twice the thickness of the air filter medium.

表１に示すとおり、エアフィルタ用濾材の厚さが０．３ｍｍ以下であると、より多くのプリーツを形成可能であることが確認できた。

As shown in Table 1, it was confirmed that more pleats could be formed when the thickness of the air filter medium was 0.3 mm or less.

  As described above, the air filter medium of the present invention can form more pleats and is useful as an air filter medium. The air filter unit of the present invention using the air filter medium of the present invention is useful as an air filter unit or the like because it has a large effective filtration area and a small pressure loss.

Sectional drawing which shows an example of the filter medium for air filters of this invention Sectional drawing which shows the other example of the filter medium for air filters of this invention Sectional drawing which shows the other example of the filter medium for air filters of this invention The perspective view which shows an example of the air filter unit of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter medium for air filters 2 PTFE porous membrane 3 Breathable support layer

Claims (9)

  An air filter medium comprising at least one polytetrafluoroethylene porous membrane and a plurality of breathable support layers, wherein the thickness of the air filter medium is 0.3 mm or less. Air filter media.   The filter medium for an air filter according to claim 1, wherein a pressure loss when air is permeated at a flow rate of 5.3 cm / s is 20 Pa to 200 Pa.   The filter medium for an air filter according to claim 1 or 2, wherein the collection efficiency measured using dioctyl phthalate having a particle size of 0.1 µm to 0.2 µm is 99.999% or more.   The at least 1 layer of the said polytetrafluoroethylene porous membrane is arrange | positioned between the at least 1 pair of air permeable support layers chosen from the said several air permeable support layers. The filter medium for air filters described in 1.   A plurality of layers of the polytetrafluoroethylene porous membrane, and at least one layer of air-permeable support between at least one pair of polytetrafluoroethylene porous membranes selected from the plurality of layers of polytetrafluoroethylene porous membrane The filter medium for an air filter according to any one of claims 1 to 4, wherein a layer is disposed.   The air filter medium according to any one of claims 1 to 5, wherein the air-permeable support layer is made of a nonwoven fabric.   The filter medium for an air filter according to claim 6, wherein a part or all of the fibers constituting the nonwoven fabric are composite fibers having a core-sheath structure, and the core component is a fiber having a melting point higher than that of the sheath component.   The filter medium for an air filter according to any one of claims 1 to 7, which is folded into a continuous W shape.   An air filter unit using the air filter medium according to claim 8.

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