JP2007160275A - Filter unit and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter unit which keeps a reduction in trapping efficiency due to pleating and using suppressed while having a polytetrafluoroethylene (PTFE)-based filter medium. <P>SOLUTION: The filter unit for trapping particles contained in air to be filtered is equipped with: a pleated filter medium with a laminate including a polytetrafluoroethylene porous membrane and a permeable supporting material; and a supporting frame for supporting the filter medium, wherein valley parts of folds in the filter medium are filled with a filler or crest parts of the folds of the medium are filled by thermal bolding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a filter unit and a manufacturing method thereof.

  In the semiconductor industry, the pharmaceutical industry, the bio industry, etc., the demand for high performance filter units having high collection performance such as HEPA or ULPA is increasing year by year. As filter media used in such high performance filter units, conventionally, filter media using glass fine fibers (microfibers) and fiber filter media such as non-woven fabrics of fine polymer fibers are generally used. However, in recent years, a filter medium (PTFE filter medium: described in, for example, Patent Document 1) provided with a polytetrafluoroethylene (PTFE) porous membrane has attracted attention. The PTFE filter medium has the features that it can be made thinner and has a smaller pressure loss than a fibrous filter medium having an equivalent collection efficiency.

  When the filter medium is incorporated in the filter unit, the filter medium is usually pleated to increase the surface area of the filter medium and reduce the airflow resistance of the filter unit.

Patent Document 2 discloses a pleated electret filter. In the electret filter, the electric charge of the electret is almost eliminated by heat fusion. In consideration of this, Patent Document 2 proposes that when a multilayer electret filter is pleated, heat fusion is performed only at the ridges and valleys of the fold.
JP 2000-61280 A Japanese Patent Laid-Open No. 5-49835

  PTFE-based filter media are more likely to have a lower collection efficiency due to pleating than fiber filter media. This is because the thickness of the fibrous filter medium is usually 100 μm or more, whereas the thickness of the PTFE porous membrane is usually as thin as about 10 μm or less, and defects such as fine holes and cracks due to stress applied during pleating. This is considered to be caused by the tendency to occur in the PTFE porous membrane. In particular, such a defect tends to occur in a fold portion formed by pleating. In addition, even when used as a filter unit, the above-described defect tends to occur in the fold portion due to discharge due to static electricity or the like.

  Accordingly, an object of the present invention is to provide a filter unit in which a reduction in repair efficiency due to pleating and use is suppressed while including a PTFE filter medium as a filter medium, and a method for manufacturing the same.

  A first filter unit of the present invention is a filter unit that collects particles contained in a gas to be filtered, and a filter medium obtained by pleating a laminate including a PTFE porous membrane and a breathable support material; A support frame for supporting the filter medium, and the valleys of the folds in the filter medium are sealed with a sealant.

  The second filter unit of the present invention is a filter unit that collects particles contained in the gas to be filtered, and is a filter medium obtained by pleating a laminate including a PTFE porous membrane and a breathable support material; A support frame for supporting the filter medium, and the ridges of the folds in the filter medium are sealed by thermal fusion.

  A first manufacturing method of the filter unit of the present invention is the above-mentioned first filter unit manufacturing method, wherein the folds of the filter medium are pleated with a laminate including a PTFE porous membrane and a breathable support material. A step of disposing a sealant in the valley and sealing the valley, and a step of fixing the filter medium to a support frame that supports the filter medium.

  A second manufacturing method of the filter unit according to the present invention is a manufacturing method of the second filter unit described above, in which a fold of a filter medium is formed by pleating a laminate including a PTFE porous membrane and a breathable support material. A step of heat-sealing the ridges to seal the ridges, and a step of fixing the filter medium to a support frame that supports the filter medium.

  According to the present invention, the trapping efficiency of the filter unit by pleating and use can be obtained by sealing the valleys or peaks of the folds in the pleated filter media with a sealing agent or heat sealing, respectively. Can be suppressed.

  Further, according to the present invention, such a filter unit can be manufactured with high productivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A filter unit (first filter unit) 1 shown in FIG. 1 includes a filter medium 5 and a support frame 6 that supports the filter medium 5. As shown in FIG. 2, the filter medium 5 is a filter medium obtained by pleating a laminate 4 including the PTFE porous membrane 2 and the air-permeable support material 3, and has a fold 7 formed by pleating. In the filter unit 1, particles contained in the gas to be filtered can be collected by the filter medium 5, and since the filter medium 5 is a PTFE-based filter medium, the filter unit 1 should have the same collection efficiency as that of a filter unit including a fibrous filter medium. Thus, the pressure loss can be reduced. FIG. 2 is a cross-sectional view schematically showing a cross section of the filter medium 5 shown in FIG. 1 cut along a plane α.

  In the filter unit 1, the valleys of the folds 7 in the filter medium 5 are sealed with the sealing agent 9, and a reduction in collection efficiency due to pleating and use can be suppressed.

  Sealing means that the air permeability of the processed part of the filter medium 5 is reduced by closing the eyes of the filter medium 5, and the air permeability of the processed part may be lost. . Specifically, it means closing the pores of the PTFE porous membrane 2 or closing the space between the fibers when the breathable support material 3 is made of fibers. In the manufacturing method of the present invention to be described later, the air permeability of the part can be eliminated (lost) by appropriately selecting a method for sealing.

  The sealing agent 9 is not particularly limited as long as it can be sealed with respect to the filter medium 5. For example, silicone rubber may be used, and a commercially available caulking agent can also be used.

  In the filter unit 1, it is not necessary that all the valleys of the folds 7 in the filter medium 5 are sealed, but at least all the valleys existing on one main surface side of the filter medium 5 are sealed. Preferably, as shown in FIG. 2, it is more preferable that all of the valley portions of the fold line 7 in the filter medium 5 are processed.

  In the filter unit 1, the crest portion of the crease 7 may or may not be processed. When the crest portion is processed, the method for capping the crest portion is not particularly limited, and is similar to the trough portion. It may be processed with a sealant 9 or may be processed with heat fusion.

  As shown in FIG. 4, the filter unit (second filter unit) 11 shown in FIG. 3 does not have the valleys of the folds 7 in the filter medium 5, and the crests 10 of the folds 7 are heat-sealed. 1 has the same structure as the filter unit 1 shown in FIG. Also by using such a filter unit 11, it is possible to suppress a decrease in collection efficiency due to pleating and use. FIG. 4 is a cross-sectional view schematically showing a cross section of the filter medium 5 shown in FIG. 3 cut along a plane α.

  In the filter unit 11, it is not necessary that all the crests 10 in the filter medium 5 are processed to be sealed, but at least all the crests 10 existing on one main surface side of the filter medium 5 are processed to be capped. Is preferable, and it is more preferable that all of the peak portions 10 in the filter medium 5 are processed.

  In the filter unit 11, the valley portion of the crease 7 may or may not be sealed, and when it is sealed, it is sealed by a method other than heat fusion, for example, a sealant. It is preferable. In other words, it is preferable that the crease valley portion of the filter medium 5 is not subjected to sealing processing by heat fusion.

  As described above, Patent Document 1 discloses an electret filter medium made of a pleated nonwoven fabric, and the filter medium is formed by pleating a laminated body of nonwoven fabrics that are not integrated, and then a ridge portion of a fold. Both the valleys and the valleys can be fixed by thermal fusion. However, in the filter medium 5, when the valley portion of the crease 7 is sealed by thermal fusion, the portion other than the crease 7 is easily heated. In particular, the PTFE porous membrane 2 and the breathable support material 3 are integrated. In the case where the filter medium is present, the filter medium is thermally contracted and distortion is likely to be accumulated. When the sealing process by heat sealing | fusion is not given to the crease | fold part of the filter medium 5, the distortion of the filter medium 5 can be reduced and when it is set as the filter unit 11, a more stable shape can be hold | maintained.

  The number of the PTFE porous membrane 2 and the air-permeable support material 3 included in the laminate 4 is not particularly limited, and it is sufficient that one or more PTFE porous membranes 2 and / or the air-permeable support material 3 are included. For example, as shown in FIGS. 2 and 4, it may be a laminate 4 having a structure in which the PTFE porous membrane 2 is sandwiched by a pair of breathable support materials 3. In this case, the strength and shape of the filter medium 5 Retention can be improved. The laminate 4 may include any member other than the PTFE porous membrane 2 and the air-permeable support material 3.

  Each member included in the laminate 4 such as the PTFE porous membrane 2 and the air-permeable support material 3 may be simply overlapped, or may be integrated by a technique such as adhesive lamination or thermal lamination. Also good. Especially, it is preferable that the PTFE porous membrane 2 and the air-permeable support material 3 are integrated, and in this case, the strength and shape retention as the filter medium 5 can be improved.

  The structure of PTFE porous membrane 2 is not particularly limited as long as it has an appropriate performance as a filter medium. The average pore diameter of the PTFE porous membrane 2 is, for example, in the range of 0.01 μm to 1 μm, the porosity is, for example, about 95% or more, and the thickness thereof is, for example, in the range of 2 μm to 10 μm. is there.

  The pressure loss of the PTFE porous membrane 2 is preferably about 100 Pa to 300 Pa in terms of pressure loss when gas is permeated at a flow rate of 5.3 cm / sec. The collection efficiency of the PTFE porous membrane 2 is 99.97% when the flow rate of the gas to be filtered is 5.3 cm / sec and the particle size of the particles to be collected is in the range of 0.3 μm to 0.5 μm. Preferably, it is 99.99% or more, or more preferably 99.995% or more.

  The collection efficiency of the filter units 1 and 11 is usually the same as the collection efficiency of the PTFE porous membrane 2. That is, the collection efficiency of the filter unit 11 is 99.97% when the flow rate of the gas to be filtered is 5.3 cm / sec and the particle size of the particles to be collected is in the range of 0.3 μm to 0.5 μm. That is, that is, satisfying the standard as a HEPA filter, preferably 99.99% or more, or more preferably 99.995% or more.

  The breathable support material 3 has an effect of protecting the PTFE porous membrane 2 during pleating and use, and improving the strength and shape retention as the filter medium 5.

  The structure of the breathable support material 3 is not particularly limited as long as it has better breathability than the PTFE porous membrane 2. For example, a breathable support composed of fibers such as felt, nonwoven fabric, woven fabric, mesh, and mesh sheet. The material 3 is preferable, and among them, the breathable support material 3 made of a nonwoven fabric is preferable because it is excellent in strength, flexibility, workability in the manufacturing process, and the like.

  As a material for the breathable support material 3, a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate, a polyamide, an aromatic polyamide, or a composite material thereof may be used.

  When the air-permeable support material 3 contains a material A having a melting point lower than that of PTFE, such as polyolefin and polyester, and the air-permeable support material 3 and the PTFE porous membrane 2 are integrated by thermal lamination, the filter medium 5 Can be said to have a structure in which the PTFE porous membrane 2 and the breathable support material 3 are integrated by heat fusion of the material A.

The breathable support material 3 may be a composite material B including a _first material having a melting point T ₁ and a second material having a melting point T ₂ higher than the melting point T _{1. In} this case, T ₁ By performing thermal lamination at a temperature lower than T _{2 as described} above, thermal lamination can be performed while the shape of the breathable support material 3 is more reliably held by the second material. That is, the integration of the PTFE porous membrane 2 and the air-permeable support material 3 by thermal lamination becomes easier. At this time, the filter medium 5 has a structure in which the PTFE porous membrane 2 and the air-permeable support material 3 are integrated by heat fusion of the first material. Examples of such a breathable support material 3 include a non-woven fabric including a composite fiber having a so-called core-sheath structure, and the core portion of the composite fiber is made of the second material, and the sheath portion is made of the first material. It is preferable. Examples of the first material include polyolefin such as polyethylene and polypropylene, and examples of the second material include polyester such as polyethylene terephthalate.

As shown in FIG. 4, when the crest portion 10 of the fold line 7 of the filter medium 5 is sealed by thermal fusion, the air-permeable support material 3 is the composite material B, and the thermal fusion of the first material is performed. Thus, the PTFE porous membrane 2 and the air-permeable support material 3 may be integrated, and the crest portion 10 of the crease 7 may be sealed by heat fusion of the first material and the second material. Such a filter medium 5 can be formed by setting the temperature at the time of heat lamination to T ₁ or more and less than T ₂ and setting the temperature at the time of sealing to T ₂ or more.

  As shown in FIG. 4, when the peak part 10 of the fold line 7 of the filter medium 5 is sealed by heat sealing, it is preferable that the breathable support material 3 contains polyester. Since polyester has a greater degree of viscosity reduction than polyolefin when heated and dissolved, it easily penetrates into the pores of the PTFE porous membrane 2 and is excellent in sealing processability by thermal fusion. When the breathable support material 3 is the composite material B, polyester may be included as the second material.

  A general material for the filter unit may be used for the support frame 6, and the shape of the support frame 6 can be arbitrarily set. The support method of the filter medium 5 in the support frame 6 should just be the same as a general filter unit.

  In the first production method of the present invention, the method for disposing the sealant in the valley of the fold of the pleated filter medium is not particularly limited. For example, a predetermined amount of the sealant is applied to the valley. What is necessary is just to apply | coat and, after application | coating, you may perform processes, such as drying and a heating, as needed.

  In the second production method of the present invention, the method for heat-sealing the ridges of the folds of the pleated filter media is not particularly limited. For example, the ridges may be brought into contact with a heat source such as a heater or a hot plate. That's fine.

In the second production method of the present invention, the breathable support material is the composite material B, and the temperature of the ridge portion of the filter medium is equal to or higher than the melting point (T ₂ ) of the second material included in the breathable support material. The peak portion may be processed by heat sealing.

  The pleated filter medium may be formed by a general manufacturing method.

  In the first and second manufacturing methods of the present invention, the method of fixing the pleated filter medium to the support frame that supports the filter medium may be a general method for manufacturing the filter unit.

  The sealing process in the first and second production methods of the present invention may be performed before or after the filter medium is fixed to the support frame.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the examples shown below.

  In this example, filter units 1 and 11 as shown in FIGS. 1 and 3 were produced and their collection efficiency was evaluated. As the filter medium 5, a laminate 4 in which the PTFE porous membrane 2 was held by a pair of breathable support materials 3 was used.

  First, the PTFE porous membrane 2 was produced by the method shown below.

100 parts by weight of PTFE fine powder (Asahi ICI Fluoropolymers, Fullon CD-123) and 17 parts by weight of naphtha as a liquid lubricant were uniformly mixed to form a PTFE paste. Next, the formed PTFE paste was preformed at a pressure of ² MPa (20 kg / cm ² ), extruded into a round bar shape, and then rolled with a pair of metal rolls to form a 250 μm thick PTFE sheet. did. Next, the formed PTFE sheet was stretched 10 times in the longitudinal (length) direction at 290 ° C. and 30 times in the lateral (width) direction at 80 ° C. to form an unfired PTFE porous membrane. Next, the formed non-fired porous film was fired at 400 ° C. for 3 seconds to obtain a PTFE porous film 2 (thickness 10 μm).

Next, the obtained PTFE porous membrane 2 is set in a circular holder having an effective ventilation area of 100 cm ² , and a pressure difference is generated on both sides of the set porous membrane to allow gas (air) to permeate. The pressure loss was measured with a pressure gauge when the flow velocity of the permeating gas was 5.3 cm / sec. As a result of the measurement, the pressure loss of the PTFE porous membrane 2 was 150 Pa.

Next, a pair of nonwoven fabrics having a core-sheath structure of polyethylene terephthalate (PET) and polyethylene (PE) so as to sandwich the obtained PTFE porous membrane 2 (manufactured by Unitika, Elves TO303WDO, thickness 150 μm, basis weight) 30 g / m ² , average fiber diameter 25 μm, PE melting point 129 ° C., PET PET core 200 ° C.), and the whole is 135 ° C. which is higher than PE melting point and lower than PET melting point The PTFE porous membrane 2 is sandwiched between the pair of breathable support materials 3 and the breathable support material 3 and the PTFE porous membrane 2 are integrated. A PTFE-based filter medium (thickness 130 μm, PTFE porous membrane thickness 10 μm) was obtained. In addition, the average fiber diameter in the said nonwoven fabric takes the surface of a nonwoven fabric with a scanning electron microscope (SEM), measures 10 or more fiber diameters from the acquired photograph, and calculates the average of the measured value. Determined by

Next, the obtained PTFE filter medium is set in a square holder having an effective ventilation area of 100 cm ² , and a pressure difference is generated on both sides of the set PTFE filter medium to allow gas to permeate (permeation amount: 31). 0.8 L / min), the pressure loss was measured with a pressure gauge when the flow velocity of the permeating gas was 5.3 cm / sec. As a result of the measurement, the pressure loss of the PTFE filter medium was 170 Pa.

Subsequently, using a device similar to the measurement of the pressure loss, the PTFE filter medium is allowed to pass a gas containing polydispersed dioctyl phthalate (DOP) particles, and the concentration of the DOP particles on the downstream side of the filter medium is measured with a particle counter (Lion). The collection efficiency of the PTFE-based filter medium was measured by KC-18) manufactured by the company. However, the gas permeated through the filter medium has 4 × 10 ⁸ particles / L in the particle diameter range of 0.1 μm to 0.2 μm, and 6 × 10 particles in the particle diameter range of 0.2 μm to 0.3 μm. DOP particles are included so as to be ⁷ particles / L, the particle size of the particles to be measured by the particle counter is in the range of 0.3 μm to 0.5 μm, and the collection efficiency is the collection efficiency = (1− (downstream side) DOP particle concentration / upstream DOP particle concentration)) × 100 (%). As a result of the measurement, the collection efficiency of the PTFE filter medium was 99.995%.

  Next, the PTFE filter material obtained as described above was pleated to a mountain height (folded height) of 20 mm by a commercially available reciprocating pleat machine (Model TK-11, manufactured by Toyo Koki Co., Ltd.), and the filter media 5 Formed. Next, the formed filter medium 5 is cut at a length of 100 mm in a direction parallel to the crease 7 formed by pleating, and the cut filter medium 5 is cut into 100 mm square so that the number of peaks is 20 peaks. The filter unit was formed by fixing to a plastic support frame 6 having an opening. When fixing the filter medium 5 to the support frame 6, the space between the filter medium 5 and the support frame 6 was sealed with a commercially available caulking agent (Konishi Co., Ltd., Bond Silicon Coke).

It was 25 Pa when the pressure loss of the formed filter unit was measured similarly to the measuring method of the said pressure loss. The aeration area of the filter medium 5 provided in the formed filter unit is 800 cm ² (= 20 mm (mountain height) × 2 × 20 (number of peaks) × 100 mm). Theoretically, the pressure loss of the filter unit is the pressure of the PTFE filter medium. Although the loss should be about 1/8 of 1/8 of 170 Pa, the difference of 4 Pa is considered to be based on the pressure loss of the filter unit itself, that is, the structural pressure loss.

  Next, each filter unit sample shown below was produced using the filter unit obtained as described above. The method for producing each unit sample is shown below.

-Sample 1-
All the valleys of the crease 7 in the filter medium 5 of the filter unit are sealed by applying a commercially available caulking agent (bond silicon coke, manufactured by Konishi Co., Ltd.) from the valley direction of the crease 7, as shown in FIG. Such a filter unit 1 (sample 1) was produced.

-Sample 2-
The peak portion of the crease 7 in the filter medium 5 of the filter unit is brought into contact with a hot plate having a temperature equal to or higher than the melting point of the PET contained in the breathable support material 3 for 10 seconds to melt the PET, Sealing was performed by wearing, and a filter unit 11 (sample 2) as shown in FIG. 3 was produced.

-Sample A (comparative example)-
The filter unit obtained as described above was used as a sample A as a comparative example without being processed.

  About each sample produced in this way, the pressure loss and collection efficiency of each sample were measured in the same manner as the method performed on the PTFE filter medium.

  The measurement results are shown in Table 1 below.

  As shown in Table 1, in Sample A, which is a comparative example, the collection efficiency was greatly reduced by pleating, whereas in Samples 1 and 2, the collection efficiency was not reduced by pleating. 99.995%. In sample A, it is considered that minute defects were generated in the PTFE porous membrane by pleating, and the collection efficiency thereof was lowered.

  ADVANTAGE OF THE INVENTION According to this invention, the filter unit by which the fall of the collection efficiency by a pleating process and use was suppressed can be provided.

It is a perspective view which shows an example of the filter unit of this invention. It is a figure which shows typically the cross section which cut | disconnected the filter medium in the filter unit shown in FIG. 1 by plane (alpha) shown in FIG. It is a perspective view which shows another example of the filter unit of this invention. It is a figure which shows typically the cross section which cut | disconnected the filter medium in the filter unit shown in FIG. 3 by plane (alpha) shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter unit 2 Polytetrafluoroethylene (PTFE) porous membrane 3 Breathable support material 4 Laminated body 5 Filter filter medium 6 Support frame 7 Fold 9 Sealing agent 10 Mountain part 11 Filter unit

Claims (8)

A filter unit for collecting particles contained in a gas to be filtered,
A filter medium in which a laminate including a polytetrafluoroethylene porous membrane and a breathable support material is pleated, and a support frame that supports the filter medium,
A filter medium in which valleys of folds in the filter medium are sealed with a sealant. A filter unit for collecting particles contained in a gas to be filtered,
A filter medium in which a laminate including a polytetrafluoroethylene porous membrane and a breathable support material is pleated, and a support frame that supports the filter medium,
A filter medium in which ridges of the folds in the filter medium are sealed by heat sealing.   The filter medium according to claim 2, wherein a sealing process by heat fusion is not applied to a valley portion of the fold in the filter medium. The air-permeable support member is a composite material comprising a first material having a melting point T _1, and a second material having a melting point T ₂ than the melting point T _1,
The polytetrafluoroethylene porous membrane and the breathable support material are integrated by heat fusion of the first material,
The filter medium according to claim 2 or 3, wherein the ridges of the folds are processed by heat fusion of the first material and the second material. The first material is a polyolefin;
The filter medium according to claim 4, wherein the second material is polyester. When the flow rate of the gas to be filtered is 5.3 cm / sec and the particle size of the particles to be collected is in the range of 0.3 μm to 0.5 μm,
The filter unit according to any one of claims 1 to 5, wherein the collection efficiency is 99.97% or more. It is a manufacturing method of the filter unit according to claim 1,
Placing a sealant in the valley of the fold of the filter medium in which the laminate including the polytetrafluoroethylene porous membrane and the air-permeable support material is pleated, and sealing the valley;
Fixing the filter medium to a support frame that supports the filter medium. It is a manufacturing method of the filter unit in any one of Claims 2-5,
A step of heat-sealing the ridges of the folds of the filter medium in which the laminate including the polytetrafluoroethylene porous membrane and the air-permeable support material is pleated, and processing the crests;
Fixing the filter medium to a support frame that supports the filter medium.

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