Filter medium, filter unit, and method for manufacturing filter medium

Abstract

A filter medium (20) comprises a first polytetrafluoroethylene porous film (11), a first air-permeable support material (12), a second polytetrafluoroethylene porous film (13), and a second air-permeable support material (14). A surface of the filter medium (20) is formed through the first polytetrafluoroethylene porous film (11). The bending resistance (S20TD) of the filter medium (20) measured in accordance with the Gurley method described in JIS L 1913(2010) in the TD direction is 13 mN or more.

Description

Filter medium, filter unit, and method for manufacturing filter medium

[0001] The present invention relates to a filter medium, a filter unit, and a method for producing a filter medium.

[0002] The filter medium including polytetrafluoroethylene (PTFE) porous membrane is used in various situations, such as turbine intake filters, clean room air filters, and household appliance filters.For example, Patent Document 1 discloses a filter medium that includes a first PTFE porous membrane, a first breathable support material, a second PTFE porous membrane, and a second breathable support material, which are laminated and bonded together in this order.The surface of the filter medium is formed by the first PTFE porous membrane.

[0003] There are cases where a filter medium is required to be reusable by removing dust from the surface of the filter medium. As described in Patent Document 1, when the surface of the filter medium is formed of a PTFE porous membrane, dust adhering to the surface of the filter medium is easily removed.

[0004] Patent No. 6200031

[0005] In order to remove dust adhering to the surface of a filter medium, the filter medium may be washed with water, blown with air, or brushed. At this time, the filter medium is distorted and its shape is changed due to the strong pressure of the airflow or the like applied to the filter medium. The present inventors have discovered a new problem that the shape of the filter medium does not recover even after the pressure is released, and the deformation remains. If the deformation of the filter medium continues, the dust adhering to the surface cannot be effectively removed.

[0006] Therefore, an object of the present invention is to provide a filter medium with improved shape recovery, a filter unit including the same, and a method for manufacturing the filter medium.

[0007] The present invention provides a filter medium comprising a first porous polytetrafluoroethylene membrane, a first breathable support material, a second porous polytetrafluoroethylene membrane, and a second breathable support material, which are laminated and bonded to one another in this order, wherein the surface of the filter medium is formed by the first porous polytetrafluoroethylene membrane, and the bending resistance of the filter medium in the TD direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0008] From another aspect, the present invention provides a filter unit comprising: the filter medium of the present invention; and a support frame supporting the outer periphery of the filter medium.

[0009] From yet another aspect, the present invention provides a method for producing a filter filter medium, the method comprising: producing a long filter filter medium comprising a first breathable support material and a first porous polytetrafluoroethylene membrane; and pleating the filter filter medium along a TD direction, wherein the first breathable support material and the first porous polytetrafluoroethylene membrane are laminated and bonded to each other in this order in the filter filter medium, and the bending resistance of the filter medium in the TD direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0010] According to the present invention, it is possible to provide a filter medium with improved shape recovery, a filter unit including the same, and a method for manufacturing the filter medium.

[0011] Schematic cross-sectional view of a filter medium according to one embodiment of the present invention. Schematic cross-sectional view of a modified filter medium. Schematic view showing a method of a 90° peel test for measuring the adhesive strength between a second porous PTFE membrane and a first breathable support material. Schematic perspective view of an example of a filter medium according to one embodiment of the present invention. Illustrates an example of a thermal lamination step in the manufacture of the filter medium shown in FIG. 1. Illustrates another example of a thermal lamination step in the manufacture of the filter medium shown in FIG. 1. Illustrates a perspective view of a filter unit including the filter medium shown in FIG. 1. Illustrates a cross-sectional image of the filter medium of Example 1. Illustrates a cross-sectional image of the filter medium of Comparative Example 1.

[0012] A filter medium according to a first aspect of the present invention is a filter medium comprising a first porous polytetrafluoroethylene membrane, a first breathable support material, a second porous polytetrafluoroethylene membrane, and a second breathable support material, which are laminated and bonded to one another in this order, wherein the surface of the filter medium is formed by the first porous polytetrafluoroethylene membrane, and the bending resistance in the transverse direction of the filter medium measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0013] In a second aspect of the present invention, for example, in the filter medium according to the first aspect, the adhesive strength between the second porous polytetrafluoroethylene membrane and the first breathable support material measured by a 90° peel test is 1.0 N / 40 mm or more.

[0014] In the third aspect of the present invention, for example, the filter medium according to the first or second aspect has a basis weight of 150 g / m 2 That's all.

[0015] In a fourth aspect of the present invention, for example, in the filter medium according to any one of the first to third aspects, the first breathable support material and the second breathable support material are each a nonwoven fabric, and the nonwoven fabric is an embossed nonwoven fabric.

[0016] In a fifth aspect of the present invention, for example, in the filter medium according to any one of the first to fourth aspects, the filter medium is wound in a roll shape, and the direction perpendicular to the winding direction is the TD direction.

[0017] In a sixth aspect of the present invention, for example, in the filter medium according to any one of the first to fifth aspects, the filter medium is pleated along the TD direction.

[0018] A filter unit according to a seventh aspect of the present invention comprises: a filter medium according to any one of the first to sixth aspects; and a support frame supporting an outer periphery of the filter medium.

[0019] A method for producing a filter medium according to an eighth aspect of the present invention includes the steps of: producing a long filter medium comprising a first breathable support material and a first porous polytetrafluoroethylene membrane; and pleating the filter medium along a transverse direction, wherein the first breathable support material and the first porous polytetrafluoroethylene membrane are laminated and adhered to each other in this order in the filter medium; and the bending resistance of the filter medium in the transverse direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0020] In a ninth aspect of the present invention, for example, in the method for manufacturing a filter medium according to the eighth aspect, the filter medium further comprises a second breathable support material, and in the filter medium, the first breathable support material, the first porous polytetrafluoroethylene membrane, and the second breathable support material are laminated and adhered to one another in this order.

[0021] In a tenth aspect of the present invention, for example, in the method for producing a filter medium according to the eighth aspect, the filter medium further comprises a second porous polytetrafluoroethylene membrane and a second breathable support material, and in the filter medium, the first porous polytetrafluoroethylene membrane, the first breathable support material, the second porous polytetrafluoroethylene membrane, and the second breathable support material are layered and bonded to one another in this order.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0023] [Filter medium] Figure 1 is a schematic cross-sectional view of a filter medium 20 according to one embodiment of the present invention. As shown in Figure 1, the filter medium 20 includes a first PTFE porous membrane 11, a first breathable support material 12, a second PTFE porous membrane 13, and a second breathable support material 14. The first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are layered in this order and bonded to one another.

[0024] The filter medium 20 has a first surface 20a and a second surface 20b opposite to the first surface 20a. The first surface 20a of the filter medium 20 is formed by the first porous PTFE membrane 11. According to the configuration of this embodiment, even if dust accumulates on the first surface 20a of the filter medium 20, the dust can be easily removed from the first surface 20a.

[0025] In the filter medium 20 of this embodiment, the bending resistance S20 in the TD direction of the filter medium 20 measured in accordance with the Gurley method described in Japanese Industrial Standards (JIS) L 1913 (2010) TD is 13 mN or more.

[0026] The filter medium 20 has an MD (machine direction) and a TD (transverse direction) perpendicular to the MD. The MD direction is the longitudinal direction of the filter medium 20, and the TD direction is the width direction of the filter medium 20. The MD and TD directions may respectively coincide with the directions of the first PTFE porous membrane 11 and the second PTFE porous membrane 13 during manufacture. When the longitudinal direction and width direction of the filter medium 20 are unknown, the bending resistance of the filter medium 20 in multiple directions is measured according to the Gurley method described in JIS L 1913 (2010), and the direction with the smallest bending resistance is considered to be the TD direction, and the direction perpendicular to the TD direction is considered to be the MD direction.

[0027] The filter medium 20 can be placed in a predetermined location (e.g., inside a vacuum cleaner) so that dust accumulates on the first surface 20a formed by the first PTFE porous membrane 11. To remove dust adhering to the first surface 20a of the filter medium 20 after use, the filter medium 20 may be washed with water, blown with air, or brushed. At this time, the filter medium 20 is distorted and its shape is changed by the strong pressure of the airflow or the like applied to the filter medium 20. The inventors have discovered that the high bending resistance of the filter medium in the TD direction contributes to improving the shape recovery of the filter medium, and have thus constructed the filter medium 20 of this embodiment. The filter medium 20 of this embodiment has excellent shape recovery.

[0028] Bending resistance S20 of the filter medium 20 in the TD direction TD The lower limit of the bending resistance S20 in the TD direction of the filter medium 20 may be 13.5 mN or more, or 14 mN or more. TD The upper limit of the bending resistance S20 of the filter medium 20 in the transverse direction is preferably 50 mN or less. TD may be 13.5 mN or more and 50 mN or less, or 14 mN or more and 50 mN or less.

[0029] In the filter medium 20 of this embodiment, the bending resistance S20 in the MD direction of the filter medium 20 measured in accordance with the Gurley method described in JIS L 1913 (2010) MD The bending resistance S20 in the MD direction is preferably 25 mN or more. MD The filter medium 20 having a compressive strength of 25 mN or more has excellent shape recovery properties.

[0030] Bending resistance S20 in the MD direction of the filter medium 20 MD The lower limit of the bending resistance S20 in the MD direction of the filter medium 20 may be 26 mN or more, 27 mN or more, or 28 mN or more. MD The upper limit of the bending resistance S20 in the MD direction of the filter medium 20 is preferably 50 mN or less. MDmay be 26 mN or more and 50 mN or less, 27 mN or more and 50 mN or less, or 28 mN or more and 50 mN or less.

[0031] Bending resistance S20 of the filter medium 20 in the TD direction TD and bending resistance S20 in the MD direction MD is a value measured in accordance with the Gurley method described in JIS L 1913 (2010). In the Gurley method, the longitudinal direction of the test piece corresponds to the MD direction of the filter medium 20, and the lateral direction corresponds to the TD direction of the filter medium 20.

[0032] In this embodiment, the filter medium 20 is composed of four layers of membrane. However, the filter medium 20 may be composed of more than four layers of membrane. A filter medium composed of more than four layers of membrane is obtained by alternately stacking PTFE porous membranes and breathable support materials. In order to facilitate dust removal, it is preferable that at least one surface (first surface 20a) of the filter medium 20 is formed of a PTFE porous membrane. In detail, such a filter medium 20 includes an upstream main surface (first surface 20a) and a downstream main surface (second surface 20b) in the flow direction of the gas to be filtered, with the upstream main surface being formed of the first PTFE porous membrane 11. In this embodiment, the downstream main surface is formed of the second breathable support material 14. The "main surface" refers to the surface of the filter medium 20 having the largest area.

[0033] Fig. 2 is a schematic cross-sectional view of a modified filter medium 20. As shown in Fig. 2, the filter medium 20 may be composed of a three-layer membrane. The filter medium 20 composed of a three-layer membrane is obtained by stacking a first breathable support material 12, a first porous PTFE membrane 11, and a second breathable support material 14 in this order. Specifically, such a filter medium 20 includes an upstream main surface (first surface 20a) and a downstream main surface (second surface 20b) in the flow direction of the gas to be filtered, with the upstream main surface being formed by the first breathable support material 12. The downstream main surface being formed by the second breathable support material 14. Even with such a filter medium, the bending resistance S20 in the TD direction of the filter medium measured in accordance with the Gurley method described in JIS L 1913 (2010) is TD It is realized that the force is 13 mN or more.

[0034] The values ​​of basis weight, thickness, areal density, average pore size, porosity, etc. of the first PTFE porous membrane 11 can be the same as those of the second PTFE porous membrane 13. That is, the first PTFE porous membrane 11 and the second PTFE porous membrane 13 can be made of a single type of PTFE porous membrane (the PTFE porous membrane that is manufactured under the same conditions using the same material).Of course, the values ​​of basis weight, thickness, areal density, average pore size, porosity, etc. of the first PTFE porous membrane 11 can be different from those of the second PTFE porous membrane 13.

[0035] The basis weight of the PTFE porous membranes that can be used as the first PTFE porous membrane 11 and the second PTFE porous membrane 13 is, for example, 0.3 to 1.5 g / m 2 is in the range.

[0036] The average pore size of the PTFE porous membranes that can be used as the first PTFE porous membrane 11 and the second PTFE porous membrane 13 is, for example, in the range of 0.01 to 100 μm.

[0037] Porous PTFE membranes that can be used as the first porous PTFE membrane 11 and the second porous PTFE membrane 13 can be produced by the following method. PTFE fine powder is mixed with a solvent to prepare a paste. The paste is extruded into a sheet. The resulting PTFE sheet is stretched and fired to obtain a porous PTFE membrane. The areal stretch ratio of the PTFE sheet during stretching (typically biaxial stretching) (the product of the stretch ratio in one axial direction and the stretch ratio in the direction perpendicular thereto) is, for example, in the range of 50 to 900 times. In this specification, "PTFE" also includes "modified PTFE."

[0038] The first breathable support material 12 and the second breathable support material 14 have a sheet-like shape. Each of the first breathable support material 12 and the second breathable support material 14 has higher strength and breathability than, for example, the PTFE porous membrane used in at least one of the first PTFE porous membrane 11 and the second PTFE porous membrane 13. The first breathable support material 12 and the second breathable support material 14 can be made of woven fabric, nonwoven fabric, mesh, net, foam, etc. Among these, nonwoven fabric is most preferably used. The fibers constituting the nonwoven fabric can be synthetic fibers made of polymeric materials such as polyolefin (e.g., polyethylene, polypropylene), polyester (e.g., polyethylene terephthalate), polyamide, acrylic, and polyimide. The nonwoven fabric may also be a composite material composed of multiple types of fibers. The first breathable support material 12 and the second breathable support material 14 may be made of a single type (product number) of nonwoven fabric, or different types of nonwoven fabric. Each of the first breathable support material 12 and the second breathable support material 14 has a thickness in the range of, for example, 50 to 300 μm.

[0039] In the filter medium 20 of this embodiment, the adhesive strength A1 between the second porous PTFE membrane 13 and the first breathable support material 12 measured by a 90° peel test is preferably 1.0 N / 40 mm or more. The inventors have found that the bending resistance S20 of the filter medium 20 in the transverse direction can be adjusted by adjusting the adhesive strength A1. TDIt has been found that when the adhesive strength A1 is 1.0 N / 40 mm or more, the bending resistance S20 in the TD direction of the filter medium 20 can be controlled. TD It can be achieved that the force is 13 mN or more.

[0040] The lower limit of the adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12 may be 1.5 N / 40 mm or more, or even 2.0 N / 40 mm or more. The upper limit of the adhesive strength A1 is preferably 10 N / 40 mm or less. The adhesive strength A1 may be 1.5 N / 40 mm or more and 10 N / 40 mm or less, or even 2.0 N / 40 mm or more and 10 N / 40 mm or less.

[0041] The adhesive strength A1 is a value measured by a 90° peel test. The 90° peel test can be performed in accordance with Japanese Industrial Standard JIS Z 0237 (2009) by the method described below.

[0042] 3 is a schematic diagram showing a method of a 90° peel test for measuring the adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12. First, the filter medium 20 as a test piece is cut into a size of 100 mm x 25 mm. The test piece has a dimension of 100 mm along the MD direction of the second PTFE porous membrane 13 and a dimension of 25 mm along the TD direction of the second PTFE porous membrane 13. In order to cause peeling at the interface between the second PTFE porous membrane 13 and the first breathable support material 12, an unbonded portion 20p where the second PTFE porous membrane 13 and the first breathable support material 12 are not bonded is provided at the end of the test piece in the longitudinal direction. Next, the test piece is attached to a stainless steel plate 25 with double-sided tape 26 (Nitto Denko Corporation No. 500). Next, the unbonded portion 20p of the test piece is fixed to the chuck 24 of a tensile tester (Shimadzu Corporation Autograph AG-1). Then, the chuck 24 is pulled up at a speed of 300 mm / min, causing peeling at the interface between the second PTFE porous membrane 13 and the first breathable support material 12, thereby measuring the 90° peel strength. After the start of measurement, the measured value of the first 25 mm length is ignored, and the average value of the measured values ​​(unit: N) continuously recorded for the 50 mm length test piece peeled from the stainless steel plate 25 is taken as the adhesive strength A1 of the filter medium 20.

[0043] When measurement is performed using the method shown in Fig. 3, there are cases where no clear peeling occurs at the interface between the second porous PTFE membrane 13 and the first breathable support material 12, and cohesive failure occurs in the second porous PTFE membrane 13. In either the case where clear peeling occurs or where cohesive failure occurs, in this embodiment, the value obtained by the method described with reference to Fig. 3 is defined as "the adhesive strength A between the second porous PTFE membrane 13 and the first breathable support material 12."

[0044] In this embodiment, the basis weight of the filter medium 20 is 150 g / m 2 It is preferable that the basis weight of the filter medium 20 is 150 g / m or more. 2 When the above value is satisfied, the bending resistance S20 in the TD direction of the filter medium 20 is TD It is easy to achieve a value of 13 mN or more.

[0045] The lower limit of the basis weight of the filter medium 20 is 160 g / m 2 or more, and 170 g / m 2 or more, and 180 g / m 2 or more, and further 190 g / m 2 The upper limit of the basis weight of the filter medium 20 is 400 g / m 2 The basis weight of the filter medium 20 is preferably 160 g / m or less. 2 More than 400g / m 2 or less, and 2 More than 400g / m 2 or less, and 2 More than 400g / m 2 or less, and further 190 g / m 2 More than 400g / m 2 It may be the following:

[0046] The pressure loss of the filter medium 20 is, for example, in the range of 50 to 400 Pa. "Pressure loss" refers to the pressure loss that occurs when air passes through the filter medium 20 at a flow rate of 5.3 cm / sec. Specifically, the pressure loss can be measured by the method described below. That is, for an effective area of ​​100 cm 2 The filter medium 20 was set in the cylindrical holder, and a pressure difference was generated between both sides of the filter medium 20 to allow air to pass through the filter medium 20. The flow rate of the passing air was measured with a flow meter to be 5.3 cm / sec (flow rate 31.8 m 3 The pressure loss when the pressure is adjusted to 1 / min is measured using a pressure gauge (manometer).

[0047] The filter medium 20 exhibits a collection efficiency of more than 90% for particles having a particle diameter in the range of 0.1 to 0.2 μm, for example. Generally, filter mediums that exhibit high collection efficiency for small particles tend to have low breathability, making it difficult to achieve both durability and breathability. According to this embodiment, it is possible to achieve both durability and breathability for a filter medium that exhibits high collection efficiency for small particles.

[0048] The collection efficiency can be measured by the following method: 2 The filter medium 20 is set in the cylindrical holder, and a pressure difference is generated between both sides of the filter medium 20 to allow gas to pass through the filter medium 20. The linear velocity of the passing gas is 5.3 cm / sec (flow rate 31.8 m 3 Next, the pressure difference is adjusted so that polydisperse dioctyl phthalate (DOP) particles specified in JIS Z 8901 (2006) are applied to the upstream side (first surface 20a side) of the filter medium 20 so that the concentration of particles in a predetermined particle size range is 10 6 The DOP particles are mixed into the gas so as to be particles / liter, and the concentration of DOP particles on the downstream side of the filter medium 20 (the second surface 20b side) is measured using a particle counter. The particle size range of the particles to be measured using the particle counter is, for example, 0.1 to 0.2 μm. The collection efficiency can be calculated using the formula: Collection efficiency = (1 - (Downstream DOP particle concentration / Upstream DOP particle concentration)) × 100 (%). Note that polyalphaolefin (PAO) may be used instead of DOP particles.

[0049] The filter medium 20 may be a HEPA (High Efficiency Particulate Air Filter) or a ULPA (Ultra Low Penetration Air Filter). The HEPA filter and the ULPA filter are filters specified in JIS Z 8122 (2000).

[0050] In this embodiment, the first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are bonded to one another. The bonding method for these components is not particularly limited. These components may be bonded to one another using an adhesive or by thermal lamination. When the first breathable support material 12 and the second breathable support material 14 are nonwoven fabrics that have thermal adhesive properties, bonding by thermal lamination is suitable for this embodiment. Thermal lamination makes it easy to ensure the adhesive strength between the PTFE porous membrane and the breathable support material while suppressing a decrease in breathability.

[0051] For example, when a nonwoven fabric contains fibers made of a thermoplastic resin such as polyethylene, the nonwoven fabric exhibits thermal bonding at relatively low temperatures. When such a nonwoven fabric is placed on a porous PTFE membrane and pressure is applied to both sides while heating, some of the fibers in the nonwoven fabric melt and solidify, bonding the nonwoven fabric to the porous PTFE membrane. Because the bonding points are limited to the fibers of the nonwoven fabric, breathability is maintained in the areas where fibers are not present.

[0052] The nonwoven fabric may also be an embossed nonwoven fabric. An embossed nonwoven fabric is a nonwoven fabric having one or more recesses and one or more protrusions. An embossed nonwoven fabric has higher rigidity and strength than a nonwoven fabric of the same thickness that is not embossed. An embossed nonwoven fabric has a concave-convex pattern, in other words, has a sea-island structure in plan view.

[0053] The depth of the embossed pattern in the embossed nonwoven fabric is preferably small. When the depth of the embossed pattern is small, the number of bonding points of the first breathable support material 12 to the second PTFE porous membrane 13 is likely to increase compared to when the depth of the embossed pattern is large. Therefore, the adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12 is likely to improve. As a result, the bending resistance S20 in the TD direction of the filter medium 20 is TD It is easy to achieve a value of 13 mN or more.

[0054] The embossed nonwoven fabric is, for example, a double-sided embossed nonwoven fabric that is embossed on both sides. If a double-sided embossed nonwoven fabric is used as the first breathable support material 12, the two embossed surfaces of the first breathable support material 12 will contact the first PTFE porous membrane 11 and the second PTFE porous membrane 13, respectively. If a double-sided embossed nonwoven fabric is used for both the first breathable support material 12 and the second breathable support material 14, cost reduction effects can be expected by using the same material. Furthermore, since a double-sided embossed nonwoven fabric has no front or back, using a double-sided embossed nonwoven fabric makes it less likely that errors will occur when manufacturing the filter medium 20.

[0055] However, a single-sided embossed nonwoven fabric that is embossed on only one side may be used as the first breathable support material 12. A single-sided embossed nonwoven fabric that is embossed on only one side may be used as the second breathable support material 14.

[0056] The bending resistance S10 in the TD direction of the breathable support material that can be used as the first breathable support material 12 and the second breathable support material 14 TD The lower limit of the bending resistance S10 in the TD direction of the breathable support material may be 0.5 mN or more, or 1 mN or more. TD The upper limit of the bending resistance S10 in the TD direction of the breathable support material is preferably 10 mN or less. TD When the bending resistance S20 of the filter medium 20 in the TD direction is 0.5 mN or more, TD It is easy to achieve a value of 13 mN or more.

[0057] The bending resistance S10 in the MD direction of the breathable support material that can be used as the first breathable support material 12 and the second breathable support material 14 MD The lower limit of the bending resistance S10 in the MD direction of the breathable support material may be 0.5 mN or more, or 1 mN or more. MD The upper limit of the bending resistance S10 in the MD direction is preferably 10 mN or less. MD When the strain is 0.5 mN or more, this can contribute to improving the shape recovery of the filter medium 20 .

[0058] Stiffness S10 of breathable support material in TD direction TD and bending resistance S10 in the MD direction MDis a value measured in accordance with the Gurley method described in JIS L 1913 (2010). In the Gurley method, the longitudinal direction of the test piece corresponds to the MD direction of the breathable support material, and the lateral direction corresponds to the TD direction of the breathable support material.

[0059] The basis weight of the breathable support material that can be used as the first breathable support material 12 and the second breathable support material 14 is 50 g / m 2 It is preferable that the basis weight of the breathable support material is 50 g / m or more. 2 When the above value is satisfied, the bending resistance S20 in the TD direction of the filter medium 20 is TD It is easy to achieve a value of 13 mN or more.

[0060] The lower limit of the basis weight of the breathable support material that can be used as the first breathable support material 12 and the second breathable support material 14 is 60 g / m 2 or more, and 2 or more, and 2 or more, and further 90 g / m 2 The upper limit of the basis weight of the breathable support material is 350 g / m 2 It is preferable that:

[0061] Fig. 4 is a schematic perspective view showing an example of the filter medium 20 of this embodiment. As shown in Fig. 4, the filter medium 20 may be a wound body wound into a roll. When the filter medium 20 is a wound body, the winding direction (longitudinal direction) is the MD direction, and the width direction perpendicular to the winding direction is the TD direction.

[0062] As shown in Fig. 4, the filter medium 20 may be pleated along the transverse direction to form a continuous W-shape. The pleating of the filter medium 20 can be performed using a known pleating machine (such as a rotary pleating machine, a reciprocating pleating machine, or a creasing pleating machine). The filter medium 20 of this embodiment has a bending resistance S20 in the transverse direction. TDTherefore, even if the shape of the filter medium 20 is changed by a strong pressure such as an airflow when removing dust adhering to the first surface 20 a of the pleated filter medium 20 in the TD direction, the shape of the filter medium 20 is restored when the pressure is released.

[0063] [Method for manufacturing filter medium] Hereinafter, a method for manufacturing the filter medium 20 shown in Fig. 1 will be described. The manufacturing method includes a step (step S1) of manufacturing a long filter medium 20 including a first PTFE porous membrane 11, a first breathable support material 12, a second PTFE porous membrane 13, and a second breathable support material 14. The bending resistance of the filter medium 20 in the TD direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0064] 5A, in step S1, the first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are first prepared in rolls. The first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are unwound from the respective rolls and merged to form a laminate 20s. The laminate 20s is supplied toward a pair of lamination rolls 27a and 27b and passes through the gap between the lamination rolls 27a and 27b. At this time, heat and pressure are applied to the laminate 20s from the rolls 27a and 27b, and the fibers constituting the breathable support materials 12 and 14 (nonwoven fabrics) melt and solidify, thereby bonding the first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 together. This results in the filter medium 20.

[0065] The pair of lamination rolls 27a and 27b are configured to apply heat and pressure to the laminate 20s. In this embodiment, the rolls 27a and 27b are configured so that the surface temperature of the roll 27a in contact with one side of the laminate 20s can be made different from the surface temperature of the roll 27b in contact with the other side. For example, only one lamination roll 27a has a built-in heater, while the other lamination roll 27b does not. Typically, one lamination roll 27a is a heating roll, and the other lamination roll 27b is a nip roll. When the laminate 20s passes through the gap between the lamination rolls 27a and 27b, the first PTFE porous membrane 11 contacts the lamination roll 27a, and the second breathable support material 14 contacts the lamination roll 27b. This allows heat to be preferentially transferred to the first PTFE porous membrane 11 and the first breathable support material 12. The thermal lamination of the laminate 20s can be carried out so that the adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12 is 1.0 N / 40 mm or more. Of course, it is important to appropriately adjust conditions such as the surface temperature of the lamination roll 27a, the pressure applied to the laminate 20s, and the conveying speed of the laminate 20s. In this way, the bending resistance S20 in the TD direction can be adjusted. TD It is possible to obtain a filter medium 20 having a tensile strength of 13 mN or more.

[0066] Alternatively, as shown in FIG. 5B , the thermal lamination process can be performed in two stages. In the first stage shown in the upper diagram of FIG. 5B , the laminate 20s is heated from both the upper and lower sides by heaters 29 arranged along its transport path and guided into the gap between rolls 28a and 28b. Typically, roll 28a is a rotating roll, and roll 28b is a nip roll. The heater 29 is, for example, an infrared heater. For example, rolls 28a and 28b have the function of applying pressure to the laminate 20s but not the function of applying heat. Therefore, the first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are temporarily bonded to each other via rolls 28a and 28b, thereby obtaining the laminate 20k. Next, in the second stage shown in the lower diagram of Fig. 5B, the laminate 20k is fed toward lamination rolls 27a and 27b, similar to those described with reference to Fig. 5A. As the laminate 20k passes through the gap between the lamination rolls 27a and 27b, the heating lamination roll 27a comes into contact with the first PTFE porous membrane 11 in the laminate 20k. This allows the laminate 20k to be thermally laminated so that the adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12 is 1.0 N / 40 mm or more. In this way, the bending resistance S20 in the TD direction is TD It is possible to obtain a filter medium 20 having a tensile strength of 13 mN or more.

[0067] 5A and 5B, before forming the laminate 20s, the first porous PTFE membrane 11 and the first breathable support material 12 may be weakly bonded together in advance. Similarly, the second porous PTFE membrane 13 and the second breathable support material 14 may be weakly bonded together in advance.

[0068] The manufacturing method of the filter medium 20 may further include a step (step S2) of pleating the filter medium 20 along the TD direction. Step S2 makes it possible to produce a pleated filter medium 20 as shown in Fig. 4. As described above, step S2 can be performed using a known pleating machine (such as a rotary pleating machine, a reciprocating pleating machine, or a creasing pleating machine).

[0069] Next, another example of a manufacturing method for the filter medium 20 will be described. The manufacturing method includes a step (step ST1) of producing a long filter medium 20 including a first breathable support material 12 and a first porous PTFE membrane 11, and a step (step ST2) of pleating the filter medium 20 along the transverse direction. In the filter medium 20, the first breathable support material 12 and the first porous PTFE membrane 11 are laminated and bonded to each other in this order. The bending resistance of the filter medium 20 in the transverse direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

[0070] In this manufacturing method, the filter medium 20 may further include a second breathable support material 14, and in the filter medium 20, the first breathable support material 12, the first porous PTFE membrane 11, and the second breathable support material 14 may be laminated and bonded to one another in this order.

[0071] Step ST1 corresponds to step S1 described above. By performing step ST1, for example, the filter medium 20 shown in FIG. 2 can be produced.

[0072] Step ST2 corresponds to step S2 described above. By step ST2, a pleated filter medium 20 as shown in FIG. 4 can be produced.

[0073] [Filter Unit] Next, the filter unit of the present invention will be described.

[0074] Fig. 6 is a perspective view of a filter unit 30 including the filter medium 20 shown in Fig. 1. The filter unit 30 includes the filter medium 20 and a support frame 22. As shown in Fig. 6, the filter medium 20 included in the filter unit 30 may be pleated along the TD direction. Such a filter medium 20 is obtained by pleating the filter medium 20 shown in Fig. 1.

[0075] Although not shown, the filter unit 30 may include the filter medium 20 shown in FIG.

[0076] The support frame 22 supports the outer periphery of the filter medium 20. The support frame 22 is made of resin or metal. The filter medium 20 may be fixed to the support frame 22 with an adhesive. The support frame 22 may be provided with a structure that clamps and fixes the outer periphery of the filter medium 20. Furthermore, the outer periphery of the filter medium 20 may be embedded in the support frame 22. In other words, the support frame 22 and the filter medium 20 may be integrated by insert molding.

[0077] Next, a description will be given of an application example of the filter unit 30. The filter unit 30 can be used, for example, as an exhaust filter for an electric vacuum cleaner. Examples of electric vacuum cleaners include cyclone vacuum cleaners and paper bag vacuum cleaners.

[0078] The vacuum cleaner includes, for example, a mechanism (a cyclone or a paper bag) for separating dust from suctioned air, a motor for rotating a fan, and at least one filter unit 30. In the filter unit 30, the first porous PTFE membrane 11 is located upstream in the air flow direction, and the second breathable support material 14 is located downstream in the air flow direction. Therefore, dust mainly accumulates on the surface of the first porous PTFE membrane 11. Dust accumulated on the surface of the filter unit 30 (particularly on the surface of the first porous PTFE membrane 11) can be removed by a brush, airflow, water flow, or the like.

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0080] (Example 1) A filter medium having the structure described with reference to Fig. 1 was produced by the method described with reference to Fig. 5A. The first PTFE porous membrane and the second PTFE porous membrane were produced by the method described below.

[0081] A mixture was obtained by mixing 100 parts by weight of PTFE fine powder (manufactured by Daikin Corporation, Polyflon (registered trademark) PTFE F-104) and 20 parts by weight of a liquid lubricant (dodecane). Next, the mixture was extruded into a rod using an extruder, and further passed through a pair of metal rolling rolls to obtain a sheet-like PTFE sheet (thickness 200 μm). Next, the PTFE sheet was held in an atmosphere at 150 ° C. to remove the liquid lubricant. Next, the PTFE sheet was stretched in the longitudinal direction under conditions of a stretching temperature of 280 ° C. and a stretching ratio of 20 times, and then stretched in the width direction under conditions of a stretching temperature of 120 ° C. and a stretching ratio of 35 times. Furthermore, the PTFE sheet after stretching was heated with hot air at 500 ° C. while the dimensions of the PTFE sheet were fixed. This resulted in a PTFE porous membrane. The obtained porous PTFE membranes were used as the first porous PTFE membrane 11 and the second porous PTFE membrane 13 .

[0082] As the first breathable support material 12 and the second breathable support material 14, a nonwoven fabric of PET / PE composite fiber (manufactured by Unitika Ltd., Elves T1006WDO) was used.

[0083] The first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 14 are stacked in this order, and are bonded by thermal lamination using a heating roll set at 130 ° C. The surface temperature of the heating lamination roll (roll 27a) is 200 ° C. The other lamination roll (roll 27b) is a nip roll without a heater. The conveying speed of the laminate (laminate 20s) of the first PTFE porous membrane 11, the first breathable support material 12, the second PTFE porous membrane 13, and the second breathable support material 13 is 5 m / min. Thus, the filter medium 20 of Example 1 having a four-layer structure is obtained. Figure 7 shows a cross-sectional image of the filter medium 20 of Example 1.

[0084] (Example 2) As the first breathable support material 12, use the nonwoven fabric of PET / PE composite fiber (manufactured by Unitika Co., Ltd., Elves T1003WDO), except that, obtain the filter medium 20 of Example 2 with four-layer structure by the same method as Example 1.

[0085] (Example 3) As the second breathable support material 14, use the nonwoven fabric of PET / PE composite fiber (manufactured by Unitika Co., Ltd., Elves T1003WDO), except that obtain the filter medium 20 of Example 3 with four-layer structure by the same method as Example 1.

[0086] (Comparative Example 1) A filter medium 90 of Comparative Example 1 having a four-layer structure was obtained by the same method as in Example 1, except that a nonwoven fabric of PET / PE composite fiber (Elves T1003WDO, manufactured by Unitika Ltd.) was used as the first breathable support material 12 and the second breathable support material 14. Fig. 8 shows a cross-sectional image of the filter medium 90 of Comparative Example 1.

[0087] [Bending resistance] The bending resistance S10 in the TD direction was measured for the first breathable support material 12 and the second breathable support material 14 of Examples 1 to 3 and Comparative Example 1 by the method described above. TD and bending resistance S10 in the MD direction MD The bending resistance S20 in the transverse direction was measured for the filter media 20 of Examples 1 to 3 and the filter media 90 of Comparative Example 1 by the method described above. TD and bending resistance S20 in the MD direction MD The results are shown in Table 1.

[0088] [Adhesion strength A1] Using the method described above, the adhesion strength A1 between the second porous PTFE membrane 13 and the first breathable support material 12 was measured for the filter media 20 of Examples 1 to 3 and the filter media 90 of Comparative Example 1. The results are shown in Table 1.

[0089] [Shape recovery] The filter media 20 of Examples 1 to 3 and the filter media 90 of Comparative Example 1 were pleated along the TD direction to a pleat height of 15 mm to form pleat packs. After pressing the pleat packs with fingers from above, the pleat packs were evaluated as pass (A) if the pleat packs recovered from their original shape, and as fail (B) if the pleat packs maintained their original shape. The results are shown in Table 1.

[0090]

[0091] As shown in Table 1, the bending resistance S20 in the TD direction TD The filter media of Examples 1 to 3, which had a bending resistance of 13 mN or more, were excellent in shape recovery. TD The filter medium of Comparative Example 1, which had a compressive strength of less than 13 mN, was poor in shape recovery.

[0092] 7 and 8, the filter medium 20 of Example 1 had a larger number of bonding points between the second PTFE porous membrane 13 and the first breathable support material 12 than the filter medium 90 of Comparative Example 1. As a result, the filter medium 20 of Example 1 had a higher adhesive strength A1 between the second PTFE porous membrane 13 and the first breathable support material 12 than the filter medium 90 of Comparative Example 1, and as a result, the bending resistance S20 in the TD direction TD It is presumed that the compressive strength achieved was 13 mN or more, and that this resulted in excellent shape recovery.

[0093] The technology disclosed in this specification is applicable to various filters such as turbine intake filters, clean room air filters, filters for home appliances, etc. The technology disclosed in this specification particularly contributes to the improvement of filters for vacuum cleaners, which are often washed frequently.

Claims

1. A filter medium comprising a first polytetrafluoroethylene porous membrane, a first breathable support material, a second polytetrafluoroethylene porous membrane, and a second breathable support material, which are laminated and bonded together in this order, wherein the surface of the filter medium is formed by the first polytetrafluoroethylene porous membrane, and the bending resistance in the transverse direction of the filter medium measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

2. The filter medium according to claim 1, wherein the adhesive strength between the second porous polytetrafluoroethylene membrane and the first breathable support material measured by a 90° peel test is 1.0 N / 40 mm or more.

3. Weight per unit area is 150g / m 2 The filter medium according to claim 1, wherein the filter medium is a filter medium having the above structure.

4. The filter medium according to claim 1, wherein the first breathable support material and the second breathable support material are each a nonwoven fabric, and the nonwoven fabric is an embossed nonwoven fabric.

5. The filter medium according to claim 1, wherein the filter medium is wound in a roll shape, and the direction perpendicular to the winding direction is the transverse direction.

6. The filter medium of claim 1, wherein the filter medium is pleated along the TD direction.

7. A filter unit comprising: a filter medium according to any one of claims 1 to 6; and a support frame supporting the outer periphery of the filter medium.

8. A method for producing a filter medium, comprising: a step of producing a long filter medium comprising a first breathable support material and a first porous polytetrafluoroethylene membrane; and a step of pleating the filter medium along the transverse direction, wherein the first breathable support material and the first porous polytetrafluoroethylene membrane are laminated and adhered to each other in this order in the filter medium, and the bending resistance of the filter medium in the transverse direction measured in accordance with the Gurley method described in JIS L 1913 (2010) is 13 mN or more.

9. The method for producing a filter medium according to claim 8, wherein the filter medium further comprises a second breathable support material, and in the filter medium, the first breathable support material, the first porous polytetrafluoroethylene membrane, and the second breathable support material are layered and adhered to one another in this order.

10. The method for producing a filter medium according to claim 8, wherein the filter medium further comprises a second porous polytetrafluoroethylene membrane and a second breathable support material, and in the filter medium, the first porous polytetrafluoroethylene membrane, the first breathable support material, the second porous polytetrafluoroethylene membrane, and the second breathable support material are layered and bonded to one another in this order.

Images