JP2006026531A - Filter medium for air filter and air filter unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium of a large filtration effective area for an air filter and an air filter unit using the same. <P>SOLUTION: The filter medium for the air filter includes a PTFE (polytetrafluoroethylene) porous film having a plurality of pores and has a laminated structure, and is characterized in that two layers of the PTFE porous films are provided and among the two layers of the PTFE porous films, the PTFE porous film 2a arranged on the upstream side of the flow of a gas is formed with a plurality of openings 3a passing through in the thickness direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventionally, as an air filter medium used in a clean room, paper made by adding a binder to glass fiber has been used in many cases. However, such a filter medium has a problem that small fibers are present in the filter medium and dust is generated during bending. Furthermore, this filter medium also has a problem of generating dust when it comes into contact with chemicals such as hydrofluoric acid (see, for example, Patent Document 1).

Therefore, in recent years, air filter media including a porous film of polytetrafluoroethylene (hereinafter referred to as “PTFE”), which is a clean material, has been used in various fields. The PTFE porous membrane is a typical surface filtration type filter medium that captures dust and the like on its surface, and has excellent dust collection performance (see, for example, Patent Document 2).
JP-A 63-16019 Japanese Patent Application Laid-Open No. 07-196831

  However, the PTFE porous membrane has excellent dust collection performance, but has a drawback that pressure loss increases at an early stage when used for cleaning air containing a lot of dust. Therefore, an attempt has been made to increase the surface area of the porous PTFE membrane, that is, the effective filtration area by performing pleating or the like, thereby suppressing an increase in pressure loss due to use. There was a limit to the increase.

  An object of the present invention is to provide an air filter medium having a larger effective filtration area.

  An air filter medium according to the present invention includes a PTFE porous membrane having a plurality of pores and has a laminated structure, and includes two layers of the PTFE porous membrane, and the two-layer PTFE porous membrane. An opening penetrating in the thickness direction is formed in the PTFE porous membrane disposed upstream of the gas flow.

  In the present invention, an opening penetrating in the thickness direction is formed in the PTFE porous membrane disposed on the upstream side of the gas flow in the two-layer PTFE porous membrane. In addition to the upstream surface of the gas flow, the surface constituting the opening contributes to filtration. Dust and the like that have passed through the opening are captured by the other PTFE porous membrane. That is, in the air filter medium of the present invention, the effective filtration area is larger as the area of the surface constituting the opening than the conventional PTFE porous membrane in which the opening is not formed. Increase in pressure loss and clogging due to use is suppressed, and the service life is extended.

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

  1A shows a cross-sectional view of the air filter medium of the present embodiment, and FIG. 1B shows an exploded perspective view of the air filter medium of the present embodiment.

  As shown in FIG. 1, the air filter medium 1 of the present embodiment includes PTFE porous membranes 2a and 2b having a plurality of holes, and the gas flow of the two layers of PTFE porous membranes 2a and 2b. A plurality of openings 3a penetrating in the thickness direction is formed in the porous PTFE 2a disposed on the upstream side. Therefore, regarding the PTFE porous membrane 2a, not only the surface 21a on the upstream side of the gas flow but also the surface 31a constituting the opening 3a contributes to the filtration. Since the downstream end of the opening 3a is blocked by the surface 21b of the PTFE porous 2b, dust or the like passing through the opening 3a is captured by the surface 21b of the PTFE porous membrane 2b. That is, in the air filter medium 1 of the present embodiment, the effective filtration area is about the sum of the areas of the surfaces 31a constituting each opening 3a, compared to the single layer PTFE porous membrane in which the opening 3a is not formed. Become. Due to the increase in the effective filtration area, in the air filter medium 1 of the present embodiment, an increase in pressure loss and clogging due to use are suppressed, and the life is extended.

  In the example shown in FIG. 1, a plurality of openings 3a are formed and the openings 3a are independent from each other. However, the number of openings 3a is not limited to this, and may be one, for example.

  The shape of the opening 3a that can be seen when the PTFE porous membrane 2a is viewed in plan is a rectangle in the example shown in FIG. 1B, but is not limited to this, for example, a circle, an ellipse, a rectangle, a square, and a continuous shape Examples include at least one selected from the group consisting of W-shaped (see FIG. 6). In particular, the shape of the opening 3a is preferably a continuous W shape having a large area of the surface constituting the opening 3a.

  As shown in FIG. 2, in the air filter medium 1 of the present embodiment, the PTFE porous membrane 2a is used as the first PTFE porous membrane 2a, and the PTFE porous membrane 2b disposed in contact with the PTFE porous membrane 2a is used. When the second PTFE porous membrane 2b is used, not only the first PTFE porous membrane 2a but also the second PTFE porous membrane 2b are formed with a plurality of openings 3b penetrating in the thickness direction. Thus, if the opening 3b is formed also in the 2nd PTFE porous membrane 2b, pressure loss can be made lower than the example shown in FIG. 1, for example, and motive power cost can be reduced.

  However, in this case, the first PTFE porous membrane 2a is formed so that the opening 3a formed in the first PTFE porous membrane 2a and the opening 3b formed in the second PTFE porous membrane 2b do not communicate with each other. And the second PTFE porous membrane 2b are laminated.

  As shown in FIG. 2A, the deviation width L in the planar direction between the opening 3a and the opening 3b is, for example, the thickness D of the first PTFE porous film 2a and the thickness of the second PTFE porous film 2b. It is preferable that it is more than the sum total with E. When the opening 3a and the opening 3b are separated from each other by a sum of the thickness D of the first PTFE porous membrane 2a and the thickness E of the second PTFE porous membrane 2b in the plane direction, the opening 3a is passed. The possibility that dust will enter the opening 3b is reduced, and a reduction in the collection efficiency of the air filter medium can be suppressed.

  In the efilter medium 1 in which the opening 3b is also formed in the second PTFE porous membrane 2b, the first PTFE porous membrane 2a and the second PTFE porous membrane 2b are in contact with each other. desirable. When the first PTFE porous membrane 2a and the second PTFE porous membrane 2b are in contact with each other, the dust that has passed through the opening 3a of the first PTFE porous membrane 2a becomes the second PTFE porous membrane. It can further suppress that the collection efficiency of an air filter filter medium falls into the opening 3b of the film | membrane 2b.

  In addition, there is no restriction | limiting in particular about the shape of the opening 3b seen when the PTFE porous membrane 2b is planarly viewed, for example, what is necessary is just the same as the opening 3a.

  Although there is no restriction | limiting in particular about the pressure loss of PTFE porous membrane 2a, 2b in the location in which opening 3a, 3b is not formed, For example, 35 Pa-2000 Pa are suitable. In the present specification, the pressure loss is a value measured by adjusting the surface speed of the permeating air to 36 cm / sec.

  There is no particular limitation on the collection efficiency of the porous PTFE membranes 2a and 2b where the openings 3a and 3b are not formed. For example, 99.0% to 99.9999% is appropriate. In the present specification, the collection efficiency is a value measured by transmitting particles having a particle diameter of 0.3 μm to 0.5 μm.

  Although there is no restriction | limiting in particular about the thickness of PTFE porous membrane 2a, 2b, 1 micrometer-100 micrometers, Furthermore, 2 micrometers-50 micrometers are preferable.

  Next, an example of a method for producing a PTFE porous membrane will be described. First, a liquid lubricant is added to PTFE fine powder to produce a paste-like mixture. There is no restriction | limiting in particular as 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 liquid paraffin and naphtha can be used. These liquid lubricants may be used alone or in combination of two or more. The amount of liquid lubricant added varies depending on the type of PTFE fine powder, the type of liquid lubricant, the conditions of sheet molding described later, etc., for example, about 5 to 50 parts by weight is appropriate for 100 parts by weight of PTFE fine powder. It is.

  Next, the paste-like mixture is formed into a sheet. Examples of the molding method include (1) a method of extruding the admixture in a lot shape and then rolling with a pair of rolls, and (2) a method of extruding the plate shape into a sheet shape. Both methods (1) and (2) may be combined. Although the thickness of a sheet-like molded object changes with extending | stretching conditions etc. performed later, it is 0.1 mm-0.5 mm, for example. In addition, it is preferable to remove the liquid lubricant contained in the obtained sheet-like molded body by a heating method or an extraction method before the stretching step. Although there is no restriction | limiting in particular about the solvent used for an extraction method, For example, normal decane, dodecane, naphtha, kerosene, a liquid paraffin, etc. are mentioned.

  Next, the sheet-like molded body is stretched in a uniaxial direction or a biaxial direction to obtain a PTFE porous membrane. The stretching conditions can be appropriately set. For example, the stretching is performed at 30 ° C. to 320 ° C. so that the length in the longitudinal direction of the sheet-shaped molded body is 2 to 30 times, and then the width direction of the sheet-shaped molded body. The film is stretched at 30 ° C. to 320 ° C. so that the length thereof becomes 2 to 30 times. 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 (327 ° C.) of the PTFE porous membrane.

  Next, an opening is formed in the PTFE porous membrane. The opening can be formed by punching using a mold or cutting with a blade or the like.

  As shown in FIG. 3, the air filter medium 1 of this embodiment includes a breathable support layer 4 laminated on one of the two PTFE porous membranes 2a and 2b. Also good. In the example shown in FIG. 3, the air-permeable support layer 4 is disposed on the downstream side of the gas flow with respect to the two layers of the PTFE porous membranes 2a and 2b, but the PTFE porous membrane 2a and the PTFE porous membrane are arranged. 2b, or upstream of the gas flow with respect to the PTFE porous membrane 2a.

  The breathable support layer 4 preferably has a thickness of 10 μm to 500 μm and a pressure loss of 1 Pa to 100 Pa.

  As shown in FIG. 4, the air filter medium 1 of the present embodiment may include a prefilter 5 disposed further upstream than the PTFE porous membrane 2a. In this case, the thickness of the pre-filter 5 may be smaller than the thickness of the pre-filter of a conventional air filter medium composed of a pre-filter and a PTFE porous membrane in which no opening is formed, for example. The thicker the prefilter, the higher the function as a prefilter, but the worse the pleatability. In the air filter medium 1 of the present embodiment, since the effective filtration area of the PTFE porous membrane is larger than that of the conventional air filter medium, the thickness of the prefilter 5 is made thinner than the thickness of the prefilter of the conventional air filter medium. However, an increase in pressure loss and clogging associated with use can be suppressed to the same level or higher than conventional air filter media. Therefore, in the air filter medium 1 of the present embodiment, it is possible to achieve both an increase in pressure loss and clogging due to use and excellent pleatability.

  The prefilter 5 preferably has a thickness of 10 μm to 500 μm, a collection efficiency of 10% to 99%, and a pressure loss of 30 Pa to 700 Pa.

  The material of the breathable support layer 4 and the prefilter 5 is not particularly limited, but polyolefin (polyethylene (PE), polypropylene (PP), etc.), polyamide, polyester (polyethylene terephthalate (PET), etc.), aromatic polyamide or These composite materials can be used. For the air-permeable support layer 4 and the prefilter 5, for example, felt, non-woven fabric, woven fabric, mesh (mesh-like sheet), and other porous materials can be used.

  The breathable support layer 4 or the prefilter 5 and the PTFE porous membrane can be joined by a method such as thermal lamination, adhesive lamination, heat welding, ultrasonic welding, vibration welding, or the like. Adjacent PTFE porous membranes can be joined to each other by bonding with an adhesive or firing in a state where adjacent PTFE porous membranes are stacked.

  The thickness of the air filter medium is preferably 10 μm to 600 μm, and more preferably 20 μm to 500 μm. The collection efficiency is preferably 99.97% or more. There is no restriction | limiting in particular about the upper limit of collection efficiency, and it is so good that it is high. The pressure loss is preferably 0.05 kPa to 3.5 kPa, more preferably 0.1 kPa to 2.0 kPa.

  In the examples shown in FIGS. 1 to 4, each includes two layers of PTFE porous membranes. However, in the air filter medium of this embodiment, the number of layers of PTFE porous membranes is two or more. If there is no particular limitation, one or more other porous PTFE membranes may be included on the downstream side of the PTFE porous membranes 2a and 2b.

  FIG. 5 is a perspective view of an air filter unit using the air filter medium 1 of the present embodiment. The air filter medium 1 is pleated and framed with a support frame 22 made of aluminum or the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples. The pressure loss, the collection efficiency, and the thickness of the filter medium were measured according to the following methods.

(1) Pressure loss The sample is set in a circular holder so that the effective area is 100 cm ² , while atmospheric dust is supplied from the inlet side, a pressure difference is applied between the inlet side and the outlet side, and the air passing through this sample The transmission speed was adjusted to a surface speed of 36 cm / s with a flow meter. In this state, the pressure loss (initial value) was measured with a pressure gauge (manometer). Here, atmospheric dust refers to dust floating in the atmosphere.

(2) Collection efficiency The collection efficiency was measured in accordance with the aerosol collection test method of the sterilizing air filtration depth filter defined in JIS K 3803. The sample was set in a holder, and particles were supplied to the upstream side of the sample while adjusting the linear velocity of air passing through the sample to 5.3 cm / s. The upstream particle concentration (pieces / liter) and the downstream particle concentration (pieces / liter) that have passed through the sample are measured with a particle counter, and the measured value is substituted into the following equation (Equation 1) for collection. We asked for efficiency. In the test, dioctyl phthalate (DOP) particles having a particle size of 0.3 μm to 0.5 μm were used.

(Equation 1)
Collection efficiency (%) = (1− (downstream particle concentration / upstream particle concentration)) × 100
(3) Thickness of filter medium Three points were measured using a dial thickness gauge (measuring element diameter: 5 mmφ, minimum scale: 1 μm), and the average value was obtained.

  30 parts by weight of a liquid lubricant (liquid paraffin) is uniformly mixed with 100 parts by weight of PTFE fine powder (F-104, manufactured by Daikin Industries, Ltd.) to form a paste, and the resulting mixture is subjected to paste extrusion. Molded into a round bar. Next, the round bar-shaped molded product was rolled into a sheet shape so as to have a thickness of 0.2 mm, and then the liquid lubricant was extracted and removed from the obtained sheet-shaped molded product with normal decane. Next, the sheet-like molded body was stretched at 300 ° C. so that the length was 15 times, and then stretched at 100 ° C. so that the length in the width direction was 20 times using a tenter, and the PTFE porous membrane Got. The thickness of the PTFE porous membrane was 20 μm, the pressure loss was 0.82 kPa, and the collection efficiency was 99.98%.

  Next, as shown in FIG. 6A, a plurality of continuous W-shaped openings were formed in the PTFE porous membrane by a punching machine. The mountain interval G was 10 mm, the mountain height H was 8.7 mm, and the slit interval J was 1.2 mm. As shown in FIG. 6B, the slit width F was 0.5 mm.

  Next, a PTFE porous membrane with an opening formed thereon and a PTFE porous membrane with no opening formed thereon are overlaid and fired in an atmosphere at 380 ° C. for 20 seconds to form a two-layer air filter medium (thickness). 40 μm) was obtained. The pressure loss of the air filter medium measured with the porous PTFE membrane having openings formed toward the upstream side of the gas flow was 1.40 kPa, and the collection efficiency was 99.994%.

  Two porous PTFE membranes with openings formed in Example 1 were prepared, overlapped, and fired in an atmosphere of 380 ° C. for 20 seconds to form a two-layer air filter medium (thickness 40 μm). Got. The two PTFE porous membranes were superposed such that the opening of one PTFE porous membrane and the opening of the other PTFE porous membrane were shifted by 40 μm in the planar direction. The obtained air filter medium had a pressure loss of 1.15 kPa and a collection efficiency of 99.988%.

(Comparative example)
In the comparative example, two PTFE porous membranes prepared in Example 1 and having no openings were used as air filter media (thickness 40 μm, pressure loss 1.40 kPa, collection efficiency 99.994%).

  FIG. 7 shows the change with time of the pressure loss of the air filter medium. From the results shown in FIG. 7, it was confirmed that in the air filter media of Examples 1 and 2, an increase in pressure loss due to use was suppressed as compared with the air filter media of the comparative example.

  As described above, the air filter medium of the present invention and the air filter unit using the same have a large effective filtration area, so that the increase in pressure loss and clogging associated with use are suppressed, and the service life is extended. It is.

A is sectional drawing which shows an example of the air filter medium of this invention, B is an exploded perspective view of the air filter medium shown to A. A is an exploded perspective view showing another example of the air filter medium of the present invention, and B is a plan view of the air filter medium shown in A. FIG. Sectional drawing which shows the other example of the air filter medium of this invention Sectional drawing which shows the other example of the air filter medium of this invention Sectional drawing which shows an example of the air filter unit of this invention A is a top view explaining the shape of the opening formed in the PTFE porous membrane which comprises the air filter medium of an Example, B is an enlarged view of K part of A The graph which showed the time-dependent change of the pressure loss of the air filter medium of an Example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air filter medium 2a, 2b PTFE porous membrane 3a, 3b Opening 4 Breathable support layer 21 Air filter unit

Claims (6)

An air filter medium comprising a polytetrafluoroethylene porous membrane having a plurality of pores and having a laminated structure,
Including two layers of the polytetrafluoroethylene porous membrane,
The polytetrafluoroethylene porous membrane disposed on the upstream side of the gas flow in the two-layered polytetrafluoroethylene porous membrane has an opening penetrating in the thickness direction. Air filter media. The polytetrafluoroethylene porous film disposed on the upstream side is used as a first polytetrafluoroethylene porous film, and the other polytetrafluoroethylene disposed in contact with the first polytetrafluoroethylene porous film. When the ethylene porous membrane is the second polytetrafluoroethylene porous membrane,
A plurality of openings penetrating in the thickness direction is formed in the second polytetrafluoroethylene porous membrane,
The first polytetrafluoroethylene porous membrane and the first polytetrafluoroethylene porous membrane so as not to communicate with the opening of the second polytetrafluoroethylene porous membrane and the opening of the second polytetrafluoroethylene porous membrane. The air filter medium according to claim 1, wherein a second polytetrafluoroethylene porous membrane is laminated.   The air filter medium according to claim 2, wherein the first polytetrafluoroethylene porous membrane and the second polytetrafluoroethylene porous membrane are joined.   The air filter according to any one of claims 1 to 3, further comprising a breathable support layer laminated on any one of the two polytetrafluoroethylene porous membranes. Filter media.   The air filter medium according to any one of claims 1 to 4, wherein the collection efficiency of particles having a particle diameter of 0.3 µm to 0.5 µm is 99.97% or more.   An air filter unit using the air filter medium according to any one of claims 1 to 5.

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