Filter material for air filter, method for using filter material for air filter, and air treatment device

Abstract

The invention provides an air filter material capable of inhibiting the generation of mildew, a method for using the air filter material, and an air treatment device. The air filter material comprises a porous membrane, the average height Rc of the surface of the porous membrane being 6 [mu] m or more, and the contact angle of water on the surface of the membrane being 90 degrees or more.

Description

Technical Field

[0001] This disclosure relates to an air filter media, a method of using the air filter media, and an air treatment device. Background Technology

[0002] In the past, mold sometimes grew in the filter media of air filters used to capture dust and other particles in the air.

[0003] For example, according to Patent Document 1 (Japanese Patent Application Publication No. 2003-205211), an air filter material is proposed, which has an antibacterial reinforcing material using inorganic, organic, or natural antibacterial agents laminated on a polytetrafluoroethylene porous membrane. Summary of the Invention

[0004] The technical problem that the invention aims to solve

[0005] For such air filter media, new methods are expected to be developed to achieve antibacterial properties.

[0006] Technical solutions adopted to solve technical problems

[0007] The first viewpoint's air filter media includes a porous membrane, wherein the average height Rc of the surface of the porous membrane is 6 μm or more, and the water contact angle on the membrane surface is 90 degrees or more.

[0008] As an air filter media, the preferred choice is an air filter media that is resistant to mold.

[0009] This air filter media can inhibit the growth of mold.

[0010] The second viewpoint's air filter media is based on the first viewpoint's air filter media, with the average height Rc of the porous membrane surface being above 36μm.

[0011] In addition, the average height Rc of the surface of the porous membrane is preferably 37 μm or more, and more preferably 38 μm or more.

[0012] This air filter media can inhibit mold growth for a longer period of time.

[0013] The air filter material of the third viewpoint is based on the air filter material of either the first or second viewpoint, and the arithmetic mean roughness Ra of the porous membrane surface is greater than 6 μm.

[0014] The filter media of this air filter easily inhibits the growth of mold.

[0015] The air filter media of the fourth viewpoint is based on the air filter media of any of the first to third viewpoints, with the average pore size of the porous membrane being 2μm or more.

[0016] The filter media of this air filter easily inhibits the growth of mold.

[0017] The air filter media of the fifth viewpoint is based on the air filter media of any of the first to fourth viewpoints, with the average pore size of the porous membrane being less than 10 μm.

[0018] The air filter material of the sixth viewpoint is based on the anti-mildew air filter material of any of the first to fifth viewpoints, with a porous membrane thickness of 100μm or more.

[0019] In addition, the thickness of the porous membrane is preferably 150 μm or more.

[0020] The filter media of this air filter easily inhibits the growth of mold.

[0021] The air filter media of the seventh viewpoint is based on the air filter media of any of the first to sixth viewpoints, wherein the contact angle between the air filter media and the isopropanol aqueous solution with a concentration of 30% by volume is greater than 127 degrees.

[0022] This air filter media can inhibit mold growth for a long time.

[0023] The air filter media of the eighth viewpoint is based on the anti-mildew air filter media of any of the first to seventh viewpoints, and the porous membrane contains fluororesin.

[0024] This air filter media can inhibit the growth of mold in porous membranes containing fluoropolymers.

[0025] The air filter media of the ninth point is based on the air filter media of any of the first to eighth points, and the porous membrane does not contain antifungal agents.

[0026] This air filter media can inhibit mold growth even when the porous membrane does not contain anti-mold agents.

[0027] The air filter media of the tenth point is based on the air filter media of any one of the first to ninth points, and the air filter media is used in an environment with a relative humidity of 60% or higher.

[0028] This air filter media can inhibit mold growth even when used in environments prone to mold.

[0029] The method of using the air filter media of the eleventh point is to use the air filter media of any one of the first to ninth points in an environment with a relative humidity of 60% or higher.

[0030] According to the usage method of this air filter media, it can be used to suppress the growth of mold in the air filter media even in environments where mold is prone to occur.

[0031] The air handling unit of the twelfth viewpoint includes the air filter media of any one of the first to tenth viewpoints.

[0032] According to this air handling device, air can be treated using air filter media. Attached Figure Description

[0033] Figure 1 This is a schematic cross-sectional view showing the layer structure of the anti-mildew air filter media 30a.

[0034] Figure 2 This is a schematic cross-sectional view showing the layer structure of the anti-mildew air filter media 30b.

[0035] Figure 3 This is a schematic cross-sectional view showing the layer structure of the anti-mildew air filter media 30c.

[0036] Figure 4 This is a schematic cross-sectional view showing the layer structure of the 30d filter media for mildew prevention.

[0037] Figure 5 This is a 3D view of the filter bag.

[0038] Figure 6 This is a 3D view of the air filter unit.

[0039] Figure 7 This is a schematic diagram of the air handling unit.

[0040] Figure 8 These are photographs showing the state of Example 1 and Comparative Example 1 three days after the start of the antifungal test according to JIS Z2911.

[0041] Figure 9 These are photographs showing the state of Example 1 and Comparative Example 1 one week after the start of the antifungal test according to JIS Z2911.

[0042] Figure 10 These are photographs showing the state of Example 1 and Example 3 after being cultured in the ISO846 test for four weeks. Detailed Implementation

[0043] Hereinafter, taking an embodiment as an example, an anti-mildew air filter material of one embodiment, an anti-mildew air filter material of one embodiment, a method of using the air filter material of one embodiment, and an air handling device will be described.

[0044] (1) Anti-mildew air filter media

[0045] The air filter media for mold prevention includes a porous membrane. The average surface height Rc of the porous membrane is 6 μm or more. The water contact angle on the membrane surface of the porous membrane is 90 degrees or more. Based on this mold-proof air filter media, the growth of mold in the porous membrane can be suppressed.

[0046] When air containing NaCl particles with a particle size of 0.1 μm passes through the filter at a flow rate of 5.3 cm / s, the particle capture efficiency of the anti-mildew air filter material can be 95.0% or more, more preferably 99.5% or more, and even more preferably 99.95% or more.

[0047] The pressure loss of the air filter material for mildew prevention when air flows through at a velocity of 5.3 cm / s is preferably less than 250 Pa, more preferably less than 200 Pa, and can also be more than 30 Pa and less than 190 Pa.

[0048] (2) Example of the structure of anti-mildew air filter media

[0049] The specific structure of the anti-mildew air filter material described above is not particularly limited.

[0050] For example, it can be like Figure 1 As shown in the anti-mildew air filter media 30a, it is formed by sequentially overlapping an air-permeable support member 21 and a porous membrane 31 in the airflow direction. Here, the porous membrane 31 can be disposed upstream of the airflow support member 21 or downstream of it.

[0051] For example, it can be like Figure 2 As shown in the anti-mildew air filter media 30b, it is composed of an upstream ventilable support member 21a, a porous membrane 31, and a downstream ventilable support member 21b stacked sequentially in the airflow direction.

[0052] In addition, it can also be like Figure 3 As shown in the anti-mildew air filter material 30c, it is composed of an upstream ventilable support member 21a, a first porous membrane 31a, a second porous membrane 31b, and a downstream ventilable support member 21b stacked sequentially in the airflow direction.

[0053] Alternatively, it can be like Figure 4 As shown in the anti-mildew air filter material 30d, it is composed of an upstream ventilatory support member 21a, a first porous membrane 31a, an intermediate ventilatory support member 21c, a second porous membrane 31b, and a downstream ventilatory support member 21b, which are sequentially overlapped in the airflow direction.

[0054] Alternatively, a pre-trapping layer can be provided on the upstream side of the porous membrane 31 or the first porous membrane 31a. This pre-trapping layer is a membrane with low pressure loss and low trapping efficiency.

[0055] Furthermore, there are no particular limitations on the overlapping methods of the various films or components mentioned above. They can be bonded by utilizing the anchoring effect generated by local melting caused by heating or the melting of hot melt resin, or by using reactive adhesives, or simply by stacking.

[0056] (3) Porous membrane

[0057] The average surface height Rc of the porous membrane is 6 μm or more, and the water contact angle at the membrane surface is 90 degrees or more. When the average surface height Rc of the porous membrane is 6 μm or more, it is easy to inhibit the permeation of water that promotes mold growth into the porous membrane, thus making it easier to maintain the porous membrane in a dry state. Furthermore, the water contact angle at the surface of the porous membrane is 90 degrees or more, resulting in good water repellency; water is easily repelled and therefore difficult to retain on the surface of the porous membrane. Therefore, mold growth in the porous membrane can be suppressed. This disclosure was made by first discovering that in porous membranes with a water contact angle at the membrane surface of 90 degrees or more, the degree of mold growth is correlated with the average surface height Rc of the porous membrane.

[0058] Furthermore, from the viewpoint of suppressing mold growth over a longer period of time, the average height Rc of the porous membrane surface is preferably 36 μm or more, more preferably 37 μm or more, even more preferably 38 μm or more, even more preferably 40 μm or more, and most preferably 100 μm or more.

[0059] The average height Rc of the surface of the porous membrane is not particularly limited, but is preferably 300 μm or less, and more preferably 200 μm or less.

[0060] In addition, the average height Rc of the surface was measured according to the method described in JIS B 0601 (2013).

[0061] Furthermore, the average height Rc of the porous membrane surface, for example in the case of a fluoropolymer porous membrane, can be reduced by decreasing the amount of liquid lubricant used in the manufacturing process (added when extruding powder obtained by condensation using a slurry extrusion device to obtain a sheet-like molded body), and increased by increasing the amount of liquid lubricant. Additionally, the average height Rc of the obtained porous membrane can be adjusted by regulating the type or ratio of the components mixed during the process of obtaining the fluoropolymer porous membrane. Furthermore, the average height Rc of the porous membrane surface, for example in the case of a fluoropolymer porous membrane, can be increased by decreasing the stretching ratio when stretching an unfired fluoropolymer membrane, and decreased by increasing the stretching ratio.

[0062] From the viewpoint that water is difficult to retain on the surface of a porous membrane and that the contact area between water and the porous membrane is easily reduced, the water contact angle of the porous membrane is 90 degrees or more, preferably 120 degrees or more, and more preferably 140 degrees or more.

[0063] Furthermore, the water contact angle refers to the contact angle obtained using the θ / 2 method. Additionally, the water contact angle is obtained by measuring the contact angle of a droplet after it has been dropped onto the surface of a porous membrane for 30 seconds.

[0064] From the viewpoint that water is difficult to retain on the surface of a porous membrane and is prone to reducing the contact area with the porous membrane, the contact angle of a 20% volume concentration of isopropanol aqueous solution is preferably 127 degrees or more, and more preferably 130 degrees or more.

[0065] Furthermore, the contact angle of the 20% (v / v) isopropanol aqueous solution is the contact angle obtained by the θ / 2 method. Additionally, the contact angle of the 20% (v / v) isopropanol aqueous solution was obtained by measuring the contact angle of the droplet after it had been dropped onto the porous membrane surface for 30 seconds. Moreover, the 20% (v / v) isopropanol aqueous solution is a solution with a water:IPA volume ratio of 80:20.

[0066] From the viewpoint that water is difficult to retain on the surface of a porous membrane and is prone to reducing the contact area with the porous membrane, the contact angle of a 30% volume concentration of isopropanol aqueous solution is preferably 127 degrees or more, and more preferably 129 degrees or more.

[0067] Furthermore, the contact angle of the 30% (v / v) isopropanol aqueous solution is the contact angle obtained by the θ / 2 method. Additionally, the contact angle of the 30% (v / v) isopropanol aqueous solution was obtained by measuring the contact angle of the droplet after it had been dropped onto the porous membrane surface for 30 seconds. Also, the 30% (v / v) isopropanol aqueous solution is a solution with a water:IPA volume ratio of 70:30.

[0068] Furthermore, compared to contact angle evaluation using water, the surface tension of an aqueous solution mixed with isopropanol is reduced; therefore, it can be said to be a liquid that is more easily absorbed than water. Consequently, the contact angle measured in tests using an aqueous solution mixed with isopropanol is often smaller than the contact angle measured in tests using water.

[0069] From the viewpoint of suppressing mold growth over a longer period of time, the arithmetic mean roughness Ra of the porous membrane surface is preferably 6 μm or more, more preferably 7 μm or more, and even more preferably 20 μm or more. The arithmetic mean roughness Ra of the porous membrane surface is not particularly limited, but is, for example, 100 μm or less. Furthermore, the arithmetic mean roughness Ra of the surface is a value measured according to the method described in JIS B0601 (2013).

[0070] Furthermore, the arithmetic mean roughness Ra of the porous membrane surface, for example in the case of a fluoropolymer porous membrane, can be adjusted by regulating the amount of liquid lubricant used in the manufacturing process. Additionally, the arithmetic mean roughness Ra of the obtained porous membrane can also be adjusted by regulating the type or ratio of the components mixed during the production of the fluoropolymer porous membrane.

[0071] From the viewpoint that water is difficult to retain in a porous membrane, the average pore size of the porous membrane is preferably 2 μm or more, more preferably 2.2 μm or more. Alternatively, the average pore size of the porous membrane can be, for example, 10 μm or less. This average pore size, also known as the average flow path diameter, is measured according to ASTM F316-86.

[0072] The thickness of the porous membrane is preferably 100 μm or more, more preferably 130 μm or more, and even more preferably 150 μm or more. A greater membrane thickness allows for the formation of a structure with larger pore sizes, making it harder for water to be retained and improving capture efficiency. Furthermore, when multiple porous membranes are stacked, the membrane thickness refers to their total thickness. Here, when two or more porous membranes are stacked, it is preferable that the porous membrane located upstream of the airflow has a greater thickness and larger pore size than the porous membrane located downstream of the airflow. This makes it easier to suppress mold growth upstream of the porous membrane. Additionally, the thickness of the porous membrane, for example in the case of a fluoropolymer porous membrane, can be increased by increasing the amount of liquid lubricant used in the manufacturing process or by decreasing the elongation ratio.

[0073] The aforementioned porous membrane can inhibit mold growth even without containing a fungicide. If a fungicide is included, there is a risk that the fungicide may detach from the porous membrane, leading to a deterioration in the performance of the air filter material. Therefore, it is preferable that the porous membrane does not contain fungicides such as antibacterial agents. Furthermore, the fungicide is not particularly limited and can include organic fungicides such as benzimidazole compounds, pyridinethiones, and isothiazolinone compounds, as well as inorganic fungicides such as photocatalysts containing transition metal elements.

[0074] Furthermore, the pressure loss of the porous membrane when air flows through it at a velocity of 5.3 cm / s is preferably less than 250 Pa, more preferably less than 200 Pa, and can also be 30 Pa or more but less than 190 Pa. The pressure loss of the porous membrane, for example in the case of a fluoropolymer porous membrane, can be reduced by increasing the amount of liquid lubricant used in the manufacturing process, by increasing the elongation ratio, or by increasing the calendering temperature.

[0075] (4) Porous membrane containing fluororesin

[0076] As the aforementioned porous membrane, a porous membrane comprising fluororesin is preferred, i.e., a fluororesin porous membrane. More specifically, the porous membrane is mainly composed of fluororesin, and preferably has a porous membrane structure, wherein the porous membrane structure has fibrils (not shown) and nodes (nodules) connected to the fibrils. Here, "mainly" means that, in the case of containing multiple components, the content of fluororesin is the highest.

[0077] As a component different from fluoropolymers, one example that can be cited is the non-melt-processable component (component B) that does not undergo fibrosis, i.e., inorganic filler, which is described later.

[0078] Fluororheological membranes used in fluoropolymer porous membranes can be composed of one component or two or more components. Furthermore, examples of fluoropolymers composed of two or more components include mixtures of three components: fibrous PTFE (hereinafter referred to as component A), a non-fibrous, non-thermally melt-processable component (hereinafter referred to as component B), and a non-fibrous, thermally melt-processable component with a melting point below 320°C (hereinafter referred to as component C). Fluororheological porous membranes are preferably composed of a combination of these three components. Compared to fibrous PTFE (high molecular weight PTFE) porous membranes, fluoropolymer porous membranes composed of these three components have a membrane structure with more pores and a thicker membrane thickness, thereby enabling the capture of microparticles in the gas over a wide area in the thickness direction of the filter media, thus increasing dust storage capacity. By using these three components to construct the porous membrane, the dust storage capacity for liquid particles can be increased, especially compared to solid particles.

[0079] The following is a further detailed explanation of the three components mentioned above.

[0080] (4-1) Component A: PTFE capable of fiberization

[0081] Fiberizable PTFE is, for example, high molecular weight PTFE obtained by emulsion polymerization or suspension polymerization of tetrafluoroethylene (TFE). Here, "high molecular weight" refers to a substance that readily fibers during the stretching process in porous membrane fabrication, yielding long fibrils. This substance has a standard specific gravity (SSG) of 2.130–2.230 and high melt viscosity, meaning it has a molecular weight that does not substantially melt and flow. From the viewpoint of easy fiberization and obtaining long fibrils, the SSG of fiberizable PTFE is preferably 2.130–2.190, more preferably 2.140–2.170. If the SSG is too high, the stretchability of the mixture of components A–C may deteriorate; if the SSG is too low, the calendering properties deteriorate, thereby potentially worsening the uniformity of the porous membrane and increasing the pressure loss of the porous membrane. Furthermore, from the viewpoint of obtaining easily fiberizable and long fibrils, PTFE obtained through emulsion polymerization is preferred. The standard specific gravity (SSG) is determined according to ASTM D4895.

[0082] Whether a material possesses fibrous properties, or is capable of becoming fibrous, can be determined by whether it can undergo paste extrusion, a representative method for shaping high-molecular-weight PTFE powder made from TFE polymers. Typically, paste extrusion is possible because high-molecular-weight PTFE possesses fibrous properties. If the unfired molded body obtained through paste extrusion lacks substantial strength or elongation—for example, if the elongation is 0% and it breaks upon stretching—it can be considered to lack fibrous properties.

[0083] The aforementioned high molecular weight PTFE can be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolymer PTFE (hereinafter referred to as homopolymer PTFE), or a mixture of modified PTFE and homopolymer PTFE. Homopolymer PTFE is not particularly limited, as long as it is as described in Japanese Patent Application Publication Nos. 53-60979, 57-135, 61-16907, 62-104816, 62-190206, 63-137906, and 2000-143727. Homopolymer PTFE disclosed in Japanese Patent Application Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, International Publication No. 2009 / 001894, International Publication No. 2010 / 113950, and International Publication No. 2013 / 027850 may be used appropriately. Among them, homopolymer PTFE disclosed in Japanese Patent Application Publication No. 57-135, Japanese Patent Application Publication No. 63-137906, Japanese Patent Application Publication No. 2000-143727, Japanese Patent Application Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, and International Publication No. 2010 / 113950, which have high elongation properties, is preferred.

[0084] Modified PTFE is composed of TFE and monomers other than TFE (hereinafter referred to as modified monomers). Examples of modified PTFE include substances that have been uniformly modified using modified monomers, substances that have been modified at the beginning of the polymerization reaction, and substances that have been modified at the end of the polymerization reaction, but are not particularly limited to these. Modified PTFE may appropriately use modified PTFE disclosed in, for example, Japanese Patent Application Publication No. 60-42446, Japanese Patent Application Publication No. 61-16907, Japanese Patent Application Publication No. 62-104816, Japanese Patent Application Publication No. 62-190206, Japanese Patent Application Publication No. 64-1711, Japanese Patent Application Publication No. 2-261810, Japanese Patent Application Publication No. 11-240917, Japanese Patent Application Publication No. 11-240918, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, International Publication No. 2011 / 055824, and International Publication No. 2013 / 027850. Among them, modified PTFE with high elongation properties is preferred, as disclosed in Japanese Patent Application Publication No. 61-16907, Japanese Patent Application Publication No. 62-104816, Japanese Patent Application Publication No. 64-1711, Japanese Patent Application Publication No. 11-240917, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, and International Publication No. 2011 / 055824.

[0085] Modified PTFE comprises TFE-based TFE units and modified monomer units based on modified monomers. The modified monomer units are part of the molecular structure of the modified PTFE and are derived from the modified monomers. Preferably, the modified PTFE comprises 0.001 to 0.500% by weight of all monomer units, more preferably 0.01 to 0.30% by weight of all monomer units. All monomer units are the portion of the molecular structure of the modified PTFE derived from all monomers.

[0086] There are no particular limitations on the modified monomers as long as they can copolymerize with TFE. Examples include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as trifluorochloroethylene (CTFE); hydrofluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluorovinyl ethers; perfluoroalkyl ethylene (PFAE); and ethylene. The modified monomers used can be one or more.

[0087] There are no particular limitations on perfluorovinyl ethers; for example, perfluorounsaturated compounds represented by the following general formula (1) can be cited.

[0088] CF2 = CF - ORf···(1)

[0089] In the formula, Rf represents a perfluorinated organic group.

[0090] In this specification, a perfluorinated organic group is an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The aforementioned perfluorinated organic groups may also have ether oxygen.

[0091] Examples of perfluorovinyl ethers include perfluoro(alkyl vinyl ethers) (PAVE) in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, as described in general formula (1). The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of perfluoroalkyl groups in PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl. Perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred as PAVE.

[0092] There is no particular limitation on the above-mentioned perfluoroalkyl ethylene (PFAE), and examples such as perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE) can be cited.

[0093] The modifying monomer used in modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE and ethylene.

[0094] In particular, from the viewpoint of easy fiberization and easy to obtain long fiber lengths of fibrils, it is preferable that the content of homopolymer PTFE in the PTFE that can be fiberized is more than 50% by weight.

[0095] In addition, PTFE, which can be fibrous, can also combine multiple of the above-mentioned components.

[0096] From the viewpoint of maintaining the fibrous structure of the porous membrane, it is preferable that the content of fibrous PTFE in the porous membrane exceeds 50% by weight.

[0097] (4-2) Component B: Non-thermally meltable components that do not undergo fibrosis.

[0098] The non-thermally meltable components that do not undergo fibrosis are mainly located in the nodular region as non-fibrous particles, which helps to inhibit the fibrosis of PTFE that is capable of fibrosis.

[0099] Examples of non-thermo-melting processable components that do not undergo fibrosis include thermoplastic components such as low molecular weight PTFE, thermosetting resins, inorganic fillers, and mixtures thereof.

[0100] Thermoplastic components are preferably those with a melting point above 320°C and a high melt viscosity. For example, low molecular weight PTFE has a high melt viscosity, so it can remain at the nodule even when processed at temperatures above its melting point. In this specification, low molecular weight PTFE is defined as having an index-average molecular weight of 600,000 or less, a melting point of 320°C to 335°C, and a melt viscosity of 100 Pa·s to 7.0 × 10⁻⁶ Pa·s at 380°C. 5 PTFE of Pa·s (see Japanese Patent Application Publication No. 10-147617).

[0101] Examples of methods for manufacturing low molecular weight PTFE include: a method of thermally decomposing high molecular weight PTFE powder (molded powder) obtained by suspension polymerization of TFE or high molecular weight PTFE powder (FP: fine powder) obtained by emulsion polymerization of TFE with a specific fluoride through a contact reaction at high temperature (see Japanese Patent Application Publication No. 61-162503); a method of irradiating the aforementioned high molecular weight PTFE powder or molded body with ionizing radiation (see Japanese Patent Application Publication No. 48-78252); and a method of directly polymerizing TFE together with a chain transfer agent (see International Publication No. 2004 / 050727, International Publication No. 2009 / 020187, International Publication No. 2010 / 114033, etc.). Low molecular weight PTFE, like fibrous PTFE, can be homopolymer PTFE or modified PTFE containing the aforementioned modified monomers.

[0102] Low molecular weight PTFE is not fibrous. Whether or not it is fibrous can be determined using the methods described above. Unfired molded bodies obtained by extruding low molecular weight PTFE from a paste do not possess substantial strength or elongation; for example, elongation is 0%, and it will break if stretched.

[0103] The low molecular weight PTFE is not particularly limited, but preferably has a melt viscosity of 1000 Pa·s or more at 380°C, more preferably 5000 Pa·s or more, and even more preferably 10000 Pa·s or more. In this way, if the melt viscosity is high, even if the non-fibrous, heat-melt-processable components (C component) melt during the manufacture of the porous membrane, the non-fibrous, non-heat-melt-processable components can remain at the nodule portion, thereby suppressing fibrosis.

[0104] Examples of thermosetting resins include epoxy resins, silicone resins, polyesters, polyurethanes, polyimides, phenolic resins, and mixtures thereof. From the viewpoint of workability in co-condensation (described later), thermosetting resins that are dispersed in water in their uncured state are preferred. These thermosetting resins are all commercially available.

[0105] Examples of inorganic fillers include talc, mica, calcium silicate, glass fiber, calcium carbonate, magnesium carbonate, carbon fiber, barium sulfate, calcium sulfate, and mixtures thereof. Among these, talc is preferred considering its affinity for and specific gravity with high molecular weight PTFE, which can be fibroinated. From the viewpoint of forming a stable dispersion during the manufacture of porous membranes, inorganic fillers with a particle size of 3 μm to 20 μm are preferred. The particle size is the average particle size, determined by laser diffraction / scattering. These inorganic fillers are all commercially available.

[0106] In addition, non-melt-processable components that do not undergo fibrosis can combine multiple of the above-mentioned components.

[0107] The content of the non-thermally melt-processable component that does not undergo fibrosis in the porous membrane is preferably 1% by weight or more and 50% by weight or less. By keeping the content of the non-thermally melt-processable component that does not undergo fibrosis at 50% by weight or less, it is easier to maintain the fibrous structure of the porous membrane. More preferably, the content of the non-thermally melt-processable component that does not undergo fibrosis is 20% by weight or more and 40% by weight or less, and even more preferably 30% by weight. By keeping the content at 20% by weight or more and 40% by weight or less, the fibrosis of fibrous PTFE can be more effectively suppressed.

[0108] (4-3) C component: Components with a melting point less than 320℃ that do not undergo fibrosis and can be thermally melted.

[0109] Components that do not undergo fibrosis and can be thermally melted (hereinafter also referred to as components that do not undergo fibrosis and can be thermally melted) with a melting point of less than 320°C have fluidity when melted. Therefore, when manufacturing porous membranes (during stretching), they can be melted and solidified in the nodule, which can improve the overall strength of the porous membrane and suppress the deterioration of filter performance even when compressed in subsequent processes.

[0110] The component that does not undergo fibrosis and is suitable for thermal melting preferably exhibits a melt viscosity of less than 10,000 Pa·s at 380°C. Furthermore, the melting point of the component that does not undergo fibrosis and is suitable for thermal melting is the peak of the following heat of fusion curve, which is obtained as follows: The component is heated to above the melting point using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min until it is completely melted once, then cooled to below the melting point at a cooling rate of 10°C / min, and then heated again at a heating rate of 10°C / min.

[0111] Examples of heat-meltable components that do not undergo fibrosis include heat-meltable fluoropolymers, polystyrene, polyethylene terephthalate (PET), polyesters, polyamides, and other resins, or mixtures thereof, which are substances that can fully utilize their meltability and flowability at the stretching temperature during the manufacture of porous membranes. Among these, heat-meltable fluoropolymers are preferred from the perspective of excellent heat resistance and chemical resistance at the stretching temperature during the manufacture of porous membranes. Examples of heat-meltable fluoropolymers include those comprising the following general formula (2).

[0112] RCF=CR2 (2)

[0113] (In the formula, R is independently selected from H, F, Cl, alkyl with 1 to 8 carbon atoms, aryl with 6 to 8 carbon atoms, cyclic alkyl with 3 to 10 carbon atoms, and perfluoroalkyl with 1 to 8 carbon atoms. In this case, all R can be the same, or any two R can be the same and the remaining R can be different from them, or all R can be different from each other.) represents at least one fluorinated olefinic unsaturated monomer, preferably a copolymer unit derived from two or more monomers, of a fluorinated polymer.

[0114] Examples of compounds represented by general formula (2) are not limited and can be cited as follows: perfluoroolefins such as fluoroethylene, VDF, trifluoroethylene, TFE, HFP, etc.; fluorochloroolefins such as CTFE, dichlorodifluoroethylene, etc.; (perfluoroalkyl) ethylene such as PFBE, PFHE, perfluoro-1,3-dioxane and mixtures thereof, etc.

[0115] Furthermore, fluoropolymers may also contain at least one monomer represented by the above general formula (2), With respect to the above general formula (1) and / or the following general formula (3) R2C=CR2 (3) (In the formula, R is independently selected from H, Cl, alkyl with 1 to 8 carbon atoms, aryl with 6 to 8 carbon atoms, and cyclic alkyl with 3 to 10 carbon atoms. In this case, all R can be the same, or any two or more R can be the same and these two or more R are different from the remaining R, or all R can be different from each other. If there are multiple R, they can be different from each other.) represents a copolymer derived from at least one copolymerizable comonomer.

[0116] Examples of compounds represented by general formula (1) include perfluoro(alkyl vinyl ether) (PAVE). Among these PAVEs, perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred.

[0117] Examples of compounds represented by general formula (3) include ethylene, propylene, etc.

[0118] More specific examples of fluoropolymers include: polyvinylidene fluoride derived from the polymerization of vinyl fluoride, polyvinylidene fluoride (PVDF) derived from the polymerization of vinylidene fluoride (VDF), polychlorotrifluoroethylene (PCTFE) derived from the polymerization of chlorotrifluoroethylene (CTFE), fluoropolymers derived from the copolymerization of two or more different monomers represented by the above general formula (2), and fluoropolymers derived from the copolymerization of at least one monomer of the above general formula (2) with at least one monomer of the above general formula (1) and / or at least one monomer of the above general formula (3).

[0119] Examples of such polymers include polymers having copolymer units derived from VDF and hexafluoropropylene (HFP), and polymers derived from at least 3% by weight of a comonomer other than TFE. Examples of the latter type of fluoropolymer include TFE / PAVE copolymers (PFA), TFE / PAVE / CTFE copolymers, TFE / HFP copolymers (FEP), TFE / ethylene copolymers (ETFE), TFE / HFP / ethylene copolymers (EFEP), TFE / VDF copolymers, TFE / VDF / HFP copolymers, TFE / VDF / CTFE copolymers, and mixtures thereof.

[0120] In addition, components that do not undergo fibrosis and can be thermally melted can be combined with various of the above-mentioned components.

[0121] The content of the non-fibrous, heat-melt-processable component in the porous membrane is preferably 0.1% by weight or more and less than 20% by weight. By having a content of less than 20% by weight, it is possible to prevent the non-fibrous, heat-melt-processable component from dispersing into portions other than the nodules in the porous membrane, thus preventing an increase in pressure loss. Furthermore, by having a content of less than 20% by weight, it is easy to achieve a high-ratio elongation of 40 times or more, as described later. With a content of 0.1% by weight or more of the non-fibrous, heat-melt-processable component in the porous membrane, even when compressed or subjected to pressure in subsequent processes, it is easy to sufficiently suppress the deterioration of the filtration performance of the porous membrane. The content of the non-fibrous, heat-melt-processable component in the porous membrane is preferably 15% by weight or less, more preferably 10% by weight or less. Furthermore, from the viewpoint of ensuring the strength of the porous membrane, the content of the non-fibrous, heat-melt-processable component in the porous membrane is preferably 0.5% by weight or more. Particularly preferred is about 5% by weight.

[0122] In order to achieve a good elongation ratio of 40 to 800 times, the content of the component that can be thermally melted without fiberization is preferably 10% by weight or less.

[0123] In the porous membrane composed of the above three components, the fibrils are mainly composed of component A, and the nodules are composed of components A to C. These nodules are formed relatively large within the porous membrane, resulting in a thicker porous membrane. Furthermore, because these nodules contain components that are heat-meltable and do not undergo fibrosis, they are relatively rigid, thus acting as supports in the thickness direction of the porous membrane. Therefore, even when subjected to compressive forces in the thickness direction during subsequent processing such as the lamination of the breathable support or the pleating process described later, the filtration performance of the porous membrane can be suppressed.

[0124] (4-4) Other properties of porous membranes

[0125] The fiber diameter (average fiber diameter) of the fluoropolymer porous membrane is preferably 50 nm or more and 250 nm or less, more preferably 60 nm or more and 200 nm or less. Furthermore, it is preferable that the fiber diameter of the first fluoropolymer porous membrane disposed on the upstream side of the airflow is larger than that of the second fluoropolymer porous membrane.

[0126] Furthermore, the aforementioned fluoropolymer porous membrane is not particularly limited, but it can be manufactured, for example, by referring to the manufacturing method described in Japanese Patent Application Publication No. 2017-159281.

[0127] (5) Ventilation support

[0128] Even if a porous membrane is difficult to stand upright due to its thinness, it can be supported by a breathable support to make it stand up.

[0129] The material and structure of the breathable support are not particularly limited, and examples include nonwoven fabric, woven fabric, metal mesh, and resin mesh. Among these, nonwoven fabric with thermal adhesion is preferred from the perspectives of strength, trapping properties, softness, and workability. The nonwoven fabric preferably consists of a core / sheath structure comprising part or all of the fibers, a two-layer nonwoven fabric formed by a layer of fibers made of a low-melting-point material and a layer of fibers made of a high-melting-point material, or a nonwoven fabric with a surface coated with a thermally adhesive resin. Examples of such nonwoven fabrics include, for example, imitation adhesive nonwoven fabric. Furthermore, the core / sheath structure of the nonwoven fabric is preferably a nonwoven fabric where the melting point of the core component is higher than that of the sheath component. For example, combinations of core / sheath materials include PET / PE and high-melting-point polyester / low-melting-point polyester. Combinations of low-melting-point and high-melting-point materials in the two-layer nonwoven fabric include, for example, PE / PET, PP / PET, PBT / PET, and low-melting-point PET / high-melting-point PET. Examples of nonwoven fabrics coated with a heat-adhesive resin include nonwoven fabrics coated with EVA (ethylene vinyl acetate copolymer resin) on PET nonwoven fabrics and nonwoven fabrics coated with olefin resin on PET nonwoven fabrics.

[0130] There are no particular restrictions on the material of nonwoven fabrics; polyolefins (PE, PP, etc.), polyamides, polyesters (PET, etc.), aromatic polyamides, or their composites can be used.

[0131] The ventilated support can be bonded to the porous membrane by heating to melt a portion of the ventilated support, or by melting a hot melt resin and using an anchoring effect or by using a reactive adhesive.

[0132] Compared with the porous membranes mentioned above, the pressure loss, collection efficiency, and dust storage capacity of the ventilated support are extremely low. Its pressure loss and collection efficiency can be less than 5% of those of the porous membranes, or even practically zero.

[0133] The pressure loss of the ventilated support is preferably 10 Pa or less, more preferably 5 Pa or less. The collection efficiency of the ventilated support for NaCl particles with a particle size of 0.1 μm can be substantially considered to be 0 or approximately 0.

[0134] Furthermore, the thickness of the ventilable support member is preferably 0.3 mm or less, and more preferably 0.25 mm or less.

[0135] Furthermore, the weight per unit area of ​​the ventilable support is preferably 20 g / m² or more and 50 g / m² or less.

[0136] Because the openings of the above-mentioned ventilation support components are very large and lack moisture retention, the anti-mold performance of the air filter media for mildew prevention essentially depends on the anti-mold properties of the porous membrane.

[0137] (6) Pre-capture collection

[0138] Air filter media for mold prevention may include a pre-collector positioned upstream of the porous membrane to capture a portion of the dust in the airflow.

[0139] From the viewpoint of minimizing the overall pressure loss of the air filter media for mildew prevention, the pressure loss of the pre-collector when air passes through at a flow rate of 5.3 cm / s is preferably 5 Pa or more and less than 55 Pa, more preferably 15 Pa or more and less than 45 Pa.

[0140] Furthermore, the collection efficiency of the pre-collector for NaCl particles with a diameter of 0.3 μm is preferably 15% or more and 85% or less, more preferably 30% or more and less than 75%.

[0141] Furthermore, from the viewpoint of facilitating the folding operation when folding the air filter media into pleats, the thickness of the pre-collector is preferably 0.8 mm or less, more preferably 0.7 mm or less, and may also be less than 0.4 mm. In addition, the thickness of the pre-collector is not particularly limited, but may, for example, be 0.1 mm or more.

[0142] The average fiber diameter of the pre-collecting element is preferably 0.8 μm or more and less than 2.0 μm.

[0143] The unit area weight of the pre-capture element is not particularly limited, but it can be, for example, 10 g / m² or more and 70 g / m² or less, preferably 30 g / m² or more and 67 g / m² or less.

[0144] Such pre-capture elements are not particularly limited, but can be made of glass fiber filter media, or nonwoven fabrics or fiber layer structures made of fibrous materials manufactured by one of the following methods: melt-blowing, electrospinning, island-type process, or a combination thereof. Combination methods include, for example, melt spinning and electret melt-blowing. The island-type process is, for example, a method in which different raw materials are arranged according to the discharge path to form fibers, with one portion of the raw material forming the sea portion and other different raw materials forming the island portion, so that the cross-section forms an island structure. Here, the bicomponent or multicomponent polymers of the islands can be spun, and the sea component can be dissolved in subsequent processing, leaving the island portion to form fibers. Furthermore, the bulk density, tensile properties, etc., can be adjusted by the combination of raw materials in the discharge path. In the melt-blowing process, heated air is blown out along the nozzle while molten polymer is discharged from the nozzle through an extruder, thereby forming filaments. Here, finer diameter filaments can be obtained by adjusting the amount of polymer discharged from the nozzle per unit time, the blowing speed of the heated air, etc. Furthermore, the physical properties of the filament can be altered by the melt viscosity of the polymer used. Examples of materials used in manufacturing pre-capture components by methods such as meltblowing, electrospinning, island spinning, and mixtures thereof include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyurethane (PU), and mixtures thereof.

[0145] (7) Examples of uses

[0146] Anti-mildew air filter media is used for applications such as the following.

[0147] ULPA filters (ultra-low permeability air filters) (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN (registered trademark) filters (for industrial use), catalyst filters (for exhaust gas treatment), filters with adsorbent (for HDD installation), ventilation filters with adsorbent (for HDD installation), ventilation filters (for HDD installation, etc.), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt materials, cartridge filters for gas turbines (compatible products for gas turbines), cooling filters (for electronic equipment housings), etc. Freeze-drying containers and other freeze-drying materials; automotive ventilation materials for electronic circuits and lighting fixtures; container applications such as container caps; protective ventilation applications for electronic equipment; and ventilation / internal pressure regulation applications for medical use. Applications include semiconductor liquid filters (for semiconductor manufacturing), hydrophilic filters (for semiconductor manufacturing), chemical filters (for pharmaceutical processing), filters for pure water production lines (for pure water production), and backwash liquid filters (for industrial wastewater treatment).

[0148] Anti-mildew air filter media is particularly preferred for use in any of the following: food factories, pharmaceutical factories, clean rooms, and air purifiers.

[0149] Furthermore, anti-mold air filter media is more effective when used in environments where mold growth is a particular concern. Anti-mold air filter media is preferably used in environments with a relative humidity of 60% or higher, more preferably in environments with a temperature of 20°C or higher and a relative humidity of 60% or higher, and even more preferably in environments with a temperature of 25°C or higher and a relative humidity of 70% or higher.

[0150] (8) Filter pack

[0151] Next, refer to Figure 5 The filter pack will be explained.

[0152] Figure 5 This is a 3D view of the filter pack 20.

[0153] Filter pack 20 includes the anti-mildew air filter media described above (e.g., anti-mildew air filter media 30a to 30d, etc.). The anti-mildew air filter media of filter pack 20 is a finished filter media processed into a serrated shape (pleating) by repeatedly alternating outward and inward folds. Pleating can be performed, for example, by a rotary pleating machine. The pleating width of the filter media is not particularly limited, for example, it is 25mm or more and 280mm or less. By implementing pleating, filter pack 20 can increase the pleated area of ​​the filter media when used in an air filter unit, thereby obtaining an air filter unit with higher capture efficiency.

[0154] In addition to the anti-mildew air filter media, the filter pack 20 may also include spacers (not shown) for maintaining the pleat spacing when used in an air filter unit. The material of the spacers is not particularly limited, but hot-melt resin is preferred.

[0155] (9) Air filter unit

[0156] Next, refer to Figure 6 The air filter unit 1 will be described below.

[0157] Figure 6 This is a perspective view of the air filter unit 1.

[0158] The air filter unit 1 includes: the anti-mildew air filter media or filter bag described above; and a frame 25 for holding the anti-mildew air filter media or filter bag. In other words, the air filter unit can be manufactured by holding the anti-mildew air filter media without peak-valley folding in the frame, or by holding the filter bag 20 in the frame 25. Figure 6 The air filter unit 1 shown is made using a filter bag 20 and a frame 25.

[0159] The frame 25 is made, for example, by assembling sheets or molding resin, and the filter bag 20 and the frame 25 are preferably sealed with a sealant. The sealant is used to prevent leakage between the filter bag 20 and the frame 25, and sealants made of resins such as epoxy, acrylic, and polyurethane can be used.

[0160] The air filter unit 1, which includes a filter pack 20 and a frame 25, can be a micro-pleated air filter in which a single filter pack 20 extending in a flat shape is housed inside the frame 25, or it can be a V-shaped air filter unit or a single-unit air filter unit in which multiple filter packs extending in a flat shape are arranged in the frame.

[0161] (10) Air handling unit

[0162] Next, refer to Figure 7 The air handling unit 100 will be described.

[0163] Figure 7 This is a perspective view of the air handling unit 100.

[0164] The air handling unit 100 includes the anti-mildew air filter material (e.g., anti-mildew air filter material 30a to 30d, etc.) described above, a housing 50, a heat exchanger 51, a humidity control unit 52, and a fan 53.

[0165] The housing 50 has an intake 50a and an outlet 50b, and houses anti-mildew air filter media 30a-30d, a heat exchanger 51, a humidity control unit 52, and a fan 53 inside. Furthermore, the anti-mildew air filter media 30a-30d, the heat exchanger 51, the humidity control unit 52, and the fan 53 are arranged in this order from the intake 50a toward the outlet 50b.

[0166] Heat exchanger 51 forms part of a refrigerant circuit (not shown) for refrigerant to flow through. Air that has passed through anti-mold air filter media 30a to 30d is heated or cooled as it passes through heat exchanger 51.

[0167] The humidity control unit 52 is not particularly limited, but may include a rotor or the like that containing an adsorption element. The adsorption element's ability to adsorb moisture is temperature-dependent, and dehumidification can be achieved by heating the adsorbed moisture. In this case, a heater that can be controlled together with the adsorption element is used.

[0168] The air handling unit 100 described above can be used as an external air handling unit with the intake port 50a of the housing 50 opening to the outside and the outlet port 50b of the housing 50 opening to the inside.

[0169] Example

[0170] The following examples and comparative examples are shown, and the contents of this disclosure are described in detail.

[0171] (Example 1)

[0172] As an example of the anti-mildew air filter material, the following were prepared: Figure 3 The air filter media for mildew prevention has the structure shown.

[0173] Specifically, both the upstream ventilation support 21a and the downstream ventilation support 21b are made of spunbond nonwoven fabric (average fiber diameter 20 μm, area weight 40 g / m², thickness 0.2 mm) composed of fibers with a core / sheath structure of PET core and PE sheath. Furthermore, the first porous membrane 31a disposed upstream of the airflow through the filter material and the second porous membrane 31b disposed downstream use products obtained through the following process.

[0174] A mixture of 66.5 wt% (polymer conversion) of an aqueous PTFE dispersion (PTFE-A) with an SSG of 2.160, 28.5 wt% (polymer conversion) of a low molecular weight aqueous PTFE dispersion (PTFE-B) with a melt viscosity of 20000 Pa·s measured by a flow meter at 380°C, and 5 wt% (polymer conversion) of an aqueous FEP dispersion with a melting point of 215°C was prepared. 500 ml of a 1% aluminum nitrate aqueous solution was added as a co-condensate, and the mixture was stirred to induce co-condensation. The resulting powder was then sieved to remove water and subsequently dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the three components.

[0175] Next, 36 parts by weight of hydrocarbon oil (IP Solvent 2028 manufactured by IDEMITSU) was added to every 100 parts by weight of the mixed powder at 20°C as a liquid lubricant (extrusion aid) and mixed. The resulting mixture was then extruded using a slurry extrusion apparatus to obtain a sheet-like molded body. A sheet-like die with a rectangular extrusion nozzle of 2 mm in the short side and 180 mm in the long side was mounted at the front end of the slurry extrusion apparatus. The sheet-like molded body was formed into a film shape using calendering rollers heated to 70°C, thereby obtaining a fluoropolymer film. The film was then passed through a hot air drying oven at 200°C to evaporate and remove the hydrocarbon oil, resulting in a strip-shaped unburned fluoropolymer film (first unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm. In addition, except that the amount of liquid lubricant mixed is set to 34 parts by weight, a strip-shaped unburned fluoropolymer film (second unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm is obtained in the same manner as the first unprocessed strip.

[0176] Next, the first and second unprocessed strips are overlapped and stretched along the length direction (longitudinal direction) at a stretch ratio of 6.5. The stretching temperature is 280°C. Then, using a tenter frame capable of continuous clamping, the overlapped and stretched unprocessed strips are stretched along the width direction (transverse direction) at a stretch ratio of 12.0, and heat-fixed. The stretching temperature at this time is 290°C, and the heat-fixing temperature is 390°C. Thus, a multilayer porous membrane formed by overlapping the first and second porous membranes is obtained. Then, using a laminating device, the upstream ventilable support member 21a and the downstream ventilable support member 21b are joined to both sides (outer layer side) of the obtained double-layer porous membrane by thermal fusion, thereby obtaining… Figure 3 The filter media shown has a four-layer structure.

[0177] (Example 2)

[0178] As the anti-mildew air filter material in Example 2, a following was prepared Figure 3 The air filter media for mildew prevention has the structure shown.

[0179] Specifically, in Embodiment 2, the same upstream ventilable support member 21a and downstream ventilable support member 21b as in Embodiment 1 are used. Furthermore, the first porous membrane 31a disposed upstream of the airflow through the filter material and the second porous membrane 31b disposed downstream use products obtained through the following process.

[0180] A mixture of 66.5 wt% (polymer conversion) of an aqueous PTFE dispersion (PTFE-A) with an SSG of 2.160, 28.5 wt% (polymer conversion) of a low molecular weight aqueous PTFE dispersion (PTFE-B) with a melt viscosity of 20000 Pa·s measured by a flow meter at 380°C, and 5 wt% (polymer conversion) of an aqueous FEP dispersion with a melting point of 215°C was prepared. 500 ml of a 1% aluminum nitrate aqueous solution was added as a co-condensate, and the mixture was stirred to induce co-condensation. The resulting powder was then sieved to remove water and subsequently dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the three components.

[0181] Next, 33.5 parts by weight of hydrocarbon oil (IP Solvent 2028 manufactured by IDEMITSU) was added to every 100 parts by weight of the mixed powder at 20°C as a liquid lubricant (extrusion aid) and mixed. The resulting mixture was then extruded using a slurry extrusion apparatus to obtain a sheet-like molded body. A sheet-like die with a rectangular extrusion nozzle of 2 mm in the short side and 180 mm in the long side was mounted at the front end of the slurry extrusion apparatus. The sheet-like molded body was formed into a film shape by calendering rollers heated to 70°C, thereby obtaining a fluoropolymer film. The film was then passed through a hot air drying oven at 200°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unburned fluoropolymer film (first unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm. In addition, except that the amount of liquid lubricant mixed is set to 30 parts by weight, a strip-shaped unburned fluoropolymer film (second unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm is obtained in the same manner as the first unprocessed strip.

[0182] Next, the first and second unprocessed strips are overlapped and stretched along the length direction (longitudinal direction) at a stretch ratio of 6.5. The stretching temperature is 280°C. Then, using a tenter frame capable of continuous clamping, the overlapped and stretched unprocessed strips are stretched along the width direction (transverse direction) at a stretch ratio of 13.7, and heat-fixed. The stretching temperature at this time is 290°C, and the heat-fixing temperature is 390°C. Thus, a multilayer porous membrane formed by overlapping the first and second porous membranes is obtained. Then, using a laminating device, the upstream ventilable support member 21a and the downstream ventilable support member 21b are joined to both sides (outer layer side) of the obtained double-layer porous membrane by thermal fusion, thereby obtaining… Figure 3 The filter media shown has a four-layer structure.

[0183] (Example 3)

[0184] As the anti-mildew air filter material in Example 3, a following was prepared Figure 3The air filter media for mildew prevention has the structure shown.

[0185] In Example 3, the same upstream ventilating support 21a and downstream ventilating support 21b as in Example 1 are used. Furthermore, the first porous membrane 31a disposed upstream of the airflow through the filter material and the second porous membrane 31b disposed downstream use products obtained through the following process.

[0186] As the raw material for Example 3, a mixed powder was obtained by co-condensing and mixing a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, namely perfluoroalkyl vinyl ether modified polytetrafluoroethylene fine powder, and polytetrafluoroethylene fine powder with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) at a weight ratio of 75:25.

[0187] Using a mixture obtained by mixing the powder with an extrusion aid (liquid lubricant) at 29% of its weight, and attaching a sheet mold with a rectangular extrusion orifice having a short side length of 2 mm × a long side length of 170 mm, a strip-shaped unburned fluoropolymer film (first unprocessed strip) with an average thickness of 300 μm and an average width of 170 mm is obtained according to the method of Example 1.

[0188] Furthermore, using a mixture obtained by mixing the above-mentioned mixed powder with an extrusion aid (liquid lubricant) at 24% of its weight, a strip-shaped unburned fluoropolymer film (second unprocessed strip) with an average thickness of 300 μm and an average width of 170 mm was obtained according to the method of Example 1.

[0189] The first and second unprocessed strips are overlapped and stretched along the length direction (longitudinal direction) at an elongation ratio of 8. The stretching temperature is 250°C. Next, using a tenter frame capable of continuous clamping, the overlapped and stretched unprocessed strips are stretched along the width direction (transverse direction) at an elongation ratio of 20.0, and then heat-fixed. The stretching temperature at this point is 290°C, and the heat-fixing temperature is 390°C. This yields a multilayer porous membrane formed by overlapping the first and second porous membranes. Then, using a laminating device, the upstream ventilatory support 21a and the downstream ventilatory support 21b are joined to both sides (outer layer side) of the resulting double-layer porous membrane via thermal fusion, thereby obtaining… Figure 3 The filter media shown has a four-layer structure.

[0190] (Example 4)

[0191] As the anti-mildew air filter material in Example 4, a following was prepared Figure 3 The air filter media for mildew prevention has the structure shown.

[0192] In Example 4, the same upstream ventilable support member 21a and downstream ventilable support member 21b as in Example 1 are used. Furthermore, the first porous membrane 31a disposed upstream of the airflow through the filter material and the second porous membrane 31b disposed downstream use products obtained through the following process.

[0193] As the raw material for Example 2, a mixed powder was obtained by co-condensing and mixing a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether, namely perfluoroalkyl vinyl ether modified polytetrafluoroethylene fine powder, and polytetrafluoroethylene fine powder with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) at a weight ratio of 75:25.

[0194] Using the mixture obtained by mixing the powder with an extrusion aid (liquid lubricant) at 28% of its weight, a strip-shaped unburned fluoropolymer film (first unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm was obtained according to the method of Example 1.

[0195] Furthermore, using a mixture obtained by mixing the above-mentioned mixed powder with an extrusion aid (liquid lubricant) at 24% of its weight, a strip-shaped unburned fluoropolymer film (second unprocessed strip) with an average thickness of 300 μm and an average width of 180 mm was obtained according to the method of Example 1.

[0196] The first and second unprocessed strips are overlapped and stretched along the length direction (longitudinal direction) at an elongation ratio of 8. The stretching temperature is 280°C. Next, using a tenter frame capable of continuous clamping, the overlapped and stretched unprocessed strips are stretched along the width direction (transverse direction) at an elongation ratio of 22.0, and then heat-fixed. The stretching temperature at this point is 290°C, and the heat-fixing temperature is 390°C. This yields a multilayer porous membrane formed by overlapping the first and second porous membranes. Then, using a laminating device, the upstream ventilable support member 21a and the downstream ventilable support member 21b are joined to both sides (outer layer side) of the resulting double-layer porous membrane by thermal fusion, thereby obtaining… Figure 3 The filter media shown has a four-layer structure.

[0197] (Example 5)

[0198] As the anti-mildew air filter material in Example 5, a following was prepared Figure 2 The air filter media for mildew prevention has the structure shown.

[0199] In Example 5, the same upstream ventilating support 21a and downstream ventilating support 21b as in Example 1 are used.

[0200] In addition, the porous membrane 31 uses a product obtained through the following process.

[0201] As the raw material for Example 5, polytetrafluoroethylene (PTFE) fine powder with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) was used. 33 parts by weight of liquid lubricant were added to every 100 parts by weight of the PTFE fine powder and mixed. The resulting mixture was extruded using a slurry extrusion apparatus to obtain a cylindrical molded body. This cylindrical molded body was formed into a film using calendering rollers heated to 70°C, thereby obtaining a PTFE film. The film was then passed through a hot air drying oven at 200°C to evaporate and remove hydrocarbon oils, thereby obtaining a strip-shaped unburned PTFE film with an average thickness of 200 μm and an average width of 150 mm. This unburned PTFE film was stretched along its length at a stretch ratio of 6.5. The stretching temperature was 280°C. Next, using a tenter frame capable of continuous clamping, the unburnt PTFE is stretched along its width at a stretch ratio of 32.0, and then heat-fixed. The stretching temperature is 290°C, and the heat-fixing temperature is 390°C. Using a laminating device, the upstream ventilable support 21a and the downstream ventilable support 21b are thermally fused to both sides (outer layer side) of the porous membrane obtained above, thereby obtaining… Figure 2 The filter media shown has a three-layer structure.

[0202] (Example 6)

[0203] As the anti-mildew air filter material of Example Six, a following was prepared Figure 2 The air filter media for mildew prevention has the structure shown.

[0204] Specifically, the upstream breathable support 21a, the intermediate breathable support 21c, and the downstream breathable support 21b all use spunbond nonwoven fabric made of fibers with a core / sheath structure of PET core and PE sheath (average fiber diameter 20μm, unit area weight 30g / m², thickness 0.2mm).

[0205] In addition, the porous membrane 31 uses a product obtained through the following process.

[0206] In a mixture of three components with the same raw materials as in Example 1, 34 parts by weight of hydrocarbon oil (IP Solvent 2028 manufactured by IDEMITSU) was added as a liquid lubricant (extrusion aid) at 20°C to every 100 parts by weight of the powder. The mixture was then extruded using a slurry extrusion apparatus to obtain a sheet-like molded body. A sheet-like die with a rectangular extrusion nozzle of 2 mm in the short side and 220 mm in the long side was mounted at the front end of the slurry extrusion apparatus. The sheet-like molded body was formed into a film by calendering rollers heated to 70°C to obtain a fluoropolymer film. The film was then passed through a hot air drying oven at 200°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unburned fluoropolymer film with an average thickness of 300 μm and an average width of 220 mm.

[0207] The unburned PTFE membrane is stretched along its length (longitudinal direction) at a stretch ratio of 6.5. The stretching temperature is 280°C. Next, using a continuously clamping tenter frame, the stretched unburned PTFE membrane is stretched along its width (transverse direction) at a stretch ratio of 11.0, and then heat-fixed. The stretching temperature is 290°C, and the heat-fixing temperature is 390°C. Using a laminating device, the upstream ventilable support 21a and the downstream ventilable support 21b are joined to both sides (outer layer side) of the porous membrane obtained above by thermal fusion, thereby obtaining… Figure 2 The filter media shown has a three-layer structure.

[0208] (Comparative Example 1)

[0209] As a comparative example, the air filter media used was prepared using commonly available materials. Figure 2 The air filter material shown is PTFE.

[0210] Furthermore, the physical properties measured in the examples and comparative examples are as follows.

[0211] (film thickness of porous membrane)

[0212] Using a film thickness gauge (1D-110MH type, manufactured by Mitutoyo Co., Ltd.), five sheets of the object to be measured are overlapped and the overall film thickness is measured. The value obtained by dividing the overall thickness by 5 is taken as the film thickness of one sheet.

[0213] In addition, for embodiments using two porous membranes, their combined thickness is taken as the membrane thickness.

[0214] (Average pore size of the porous membrane)

[0215] The mean flow pore size, as measured according to ASTM F316-86, is used as the mean pore size (mean flow path diameter) of the porous membrane. The actual measurement was performed using a PMI Capillary Flow Porometer CFP-1100A (manufactured by PIM).

[0216] In addition, for cases where multiple porous membranes exist, the average pore size is measured using the product of overlapping multiple porous membranes.

[0217] (The average height Rc of the porous membrane surface)

[0218] The average height Rc of the porous membrane surface was measured using a VK-9710 laser microscope (manufactured by Keyence Corporation) according to the method described in JIS B 0601:2013 (ISO 4287:1997, Amd.1:2009). The measurement conditions were: microscope magnification: 20x (monitor magnification: 400x), measurement area: 130 μm, roughness specification: ISO 4287 (JISB0601:2013). The average height Rc of the porous membrane surface was calculated from the obtained images using image analysis software (VK Analyzer). Furthermore, under the above conditions, measurements were performed at three locations on the porous membrane surface while varying the measurement sites, and the average value was calculated as the average height Rc.

[0219] In addition, for cases where multiple porous membranes exist, the surface of the porous membrane located upstream of the passing airflow is used as the object of measurement.

[0220] (Arithmetic mean roughness Ra of the porous membrane surface)

[0221] The arithmetic mean roughness Rc of the porous membrane surface was measured using a laser microscope VK-9710 (manufactured by Keyence Corporation) according to the method described in JIS B 0601 (2013). The measurement conditions were: microscope magnification: 20x (monitor: 400x), measurement area: 130 μm, roughness specification: ISO 4287 (JIS B 0601:2013). The arithmetic mean roughness Ra of the porous membrane surface was calculated from the obtained images using image analysis software (VK Analyzer). Furthermore, based on the above conditions, measurements were performed at three locations on the porous membrane surface while varying the measurement sites, and the average value was calculated as the arithmetic mean roughness Ra.

[0222] In addition, for cases where multiple porous membranes exist, the surface of the porous membrane located upstream of the passing airflow is used as the object of measurement.

[0223] (Contact angle of water on the surface of a porous membrane)

[0224] The contact angle was determined using the Drop Master501 (manufactured by Kyowa Interface Science Co., Ltd.) via the 2 / θ method.

[0225] (Contact angle of a liquid with a water:IPA ratio of 80:20 on the surface of a porous membrane)

[0226] The contact angle was determined using the Drop Master501 (manufactured by Kyowa Interface Science Co., Ltd.) via the 2 / θ method.

[0227] (Contact angle of a liquid with a water:IPA ratio of 70:30 on the surface of a porous membrane)

[0228] The contact angle was determined using the Drop Master501 (manufactured by Kyowa Interface Science Co., Ltd.) via the 2 / θ method.

[0229] In addition, in the case of multiple porous membranes, the contact angles mentioned above are measured on the surface of the porous membrane located upstream of the passing airflow.

[0230] (Weight per unit area of ​​the porous membrane)

[0231] The weight per unit area is the value obtained by dividing the mass (g) of a sample cut into a rectangle of a specified area using a precision balance by the area. Furthermore, for embodiments using two porous membranes, the weight per unit area is determined based on the product of multiple overlapping porous membranes.

[0232] (Pressure loss)

[0233] The test sample of the anti-mildew air filter media was placed on a filter holder with a diameter of 100 mm. The inlet side was pressurized with a compressor, and the air flow rate was adjusted to 5.3 cm / s using a flow meter. Then, the pressure loss at this time was measured using a pressure gauge.

[0234] (Collection efficiency of NaCl particles with a diameter of 0.1 μm)

[0235] According to the method described in Annex 5 of JIS B9928 (specified) on the method for generating NaCl aerosol (pressurized spray method), the NaCl particles generated by the sprayer are classified into particles with a diameter of 0.1 μm using an electrostatic classifier (manufactured by TSI Corporation). After neutralizing the charge of the particles with Americium 241, the flow rate is adjusted to 5.3 cm / s. The number of particles before and after the anti-mildew air filter material used as the test sample is determined using a particle counter (manufactured by TSI Corporation, CNC). The collection efficiency is then calculated according to the following formula.

[0236] Transmittance (%) = (CO / CI) × 100

[0237] Collection efficiency (%) = 100 - Transmission rate (%)

[0238] CO = The number of 0.1 μm NaCl particles downstream of the sample.

[0239] CI = The number of 0.1 μm NaCl particles on the upstream side of the sample.

[0240] (JIS Z2911 Antifungal Test (Wet Method))

[0241] Using the above-described Examples 1, 5, and Comparative Example 1 as subjects, anti-mold tests were conducted according to JIS Z2911.

[0242] The samples were cut into specified sizes and placed on an agar medium containing ammonium nitrate, potassium dihydrogen phosphate, magnesium sulfate heptahydrate, potassium chloride, ferric sulfate (II) heptahydrate, agar, and purified water. A mixed spore solution containing spores of Aspergillus niger, Penicillium citrinum, Chaetomium globosum, and Trichophyton verruciformis was sprayed onto the samples. The growth of mold on the sample surface was observed at a temperature of 26±2℃.

[0243] Here, as an evaluation of the mold growth status in the anti-mold test, the situation where mycelial growth cannot be judged by the naked eye is evaluated as 0, the situation where the area of ​​confirmed mycelial growth does not exceed 1 / 3 of the total area is evaluated as 1, and the situation where the area of ​​confirmed mycelial growth exceeds 1 / 3 of the total area is evaluated as 2.

[0244] (Based on the anti-mildew test according to JIS Z2911)

[0245] For the above embodiments and comparative examples, as a test of anti-mold according to JIS Z2911, the samples were cut into specified sizes, placed on potato dextrose agar medium, inoculated with a suspension of Aspergillus niger (1000 RLU), placed at room temperature, and the changes in mold growth on the sample surface over time (3 days, 1 week, 2 weeks) were observed with the naked eye.

[0246] (ISO 846 Plastics - Evaluation of microbial activity)

[0247] To investigate the resistance of the samples from Examples 1 and 3 to mold, tests were conducted using ISO 846:2019 (Method A). In the tests, the test mold was inoculated onto malt extract agar medium and cultured at 29±1℃ for 10–20 days. Spore numbers of 10-1 were then prepared using an inorganic salt solution. 6 The spore solution was prepared at a concentration of / mL, and an equal volume of the mixture was used as the test spore solution. Additionally, *Aspergillus niger* (NBRC 105649), *Penicillium pineophilum* (NBRC 100533), *Penicillium pseudomonadum* (NBRC 107725), *Trichoderma viride* (NBRC 6355), and *Chaetomium globosum* (NBRC 6347) were used as test molds. The test spore solution was sprayed onto the test samples and cultured for four weeks at 29±1℃ and a relative humidity of ≥95%. Mold growth on the test samples was observed visually and microscopically during the second and fourth weeks of culture.

[0248] In addition, as a result corresponding to mycelial growth, the following conditions were evaluated: no mold growth was detected under a microscope ("0"); no mold growth was detected by the naked eye, but the area of ​​mold detected under a microscope was less than 25% of the total sample area ("1a"); no mold growth was detected by the naked eye, but the area of ​​mold detected under a microscope was less than 50% of the total sample area ("1b"); no mold growth was detected by the naked eye, but the area of ​​mold detected under a microscope was more than 50% of the total sample area ("1c"); the area of ​​mycelial growth detected by the naked eye was less than 25% of the total sample area ("2"); the area of ​​mycelial growth detected by the naked eye was less than 50% of the total sample area ("3"); the area of ​​mycelial growth detected by the naked eye was more than 50% of the total sample area ("4"); and the case of vigorous mycelial growth covering the entire sample surface ("5").

[0249] The properties of the anti-mildew air filter media and the properties of the porous membranes of each embodiment and comparative example are shown in Table 1 below.

[0250] also, Figure 8 , Figure 9 Photographs of the samples taken three days after the start of the antifungal test according to JIS Z2911 in Example 1 and Comparative Example 1 are shown, respectively. Additionally, the blackened areas in the photographs indicate the locations of the identification text written on the samples and petri dishes, where no mold was identified.

[0251] [Table 1]

[0252] In addition, the contact angle (water) mentioned above was measured using the droplet method, but since the water droplet did not move, it represents the value measured with a needle attached.

[0253] Furthermore, in Examples 1 and 5, the antifungal resistance test in JIS Z2911 achieved a result of 0 (no mycelial growth was observed in the inoculated portion of the sample or specimen). In Comparative Example 1, the result was 1 (the area where mycelial growth was observed did not exceed 1 / 3 of the total area).

[0254] In the ISO 846 evaluation of the role of microorganisms in plastics, Examples 1 and 3 both achieved 0 (no mold growth was detected under a microscope) in both the second and fourth weeks of culture. Figure 10 Photographs of the samples from Example 1 and Example 3 at the fourth week of cultivation are shown respectively.

[0255] (Postscript)

[0256] The embodiments of this disclosure have been described above. However, it should be understood that various changes in form and detail can be made without departing from the spirit and scope of this disclosure as set forth in the claims.

[0257] Symbol Explanation

[0258] 1. Air filter unit; 20 filter packs; 25. Frame; 30a, 30b, 30c, 30d Anti-mildew air filter media (air filter media); 21. Ventilation support components 21a Upstream ventilation support; 21b Downstream ventilation support; 21c Intermediate ventilated support component; 31 porous membrane; 31a First porous membrane; 31b Second porous membrane; 50. Housing; 50a suction port; 50b blowout outlet; 51 Heat Exchanger 52 Humidity control unit; 53 Fans; 100 External air handling unit.

[0259] Existing technical documents

[0260] Patent documents

[0261] Patent Document 1: Japanese Patent Application Publication No. 2003-205211

Claims

1. An air filter media, characterized in that, It includes a porous membrane, wherein the average height Rc of the surface of the porous membrane is 6 μm or more, and the contact angle of water on the membrane surface is 90 degrees or more.

2. The air filter media according to claim 1, characterized in that, The average height Rc of the surface of the porous membrane is above 36 μm.

3. The air filter media according to claim 1 or 2, characterized in that, The arithmetic mean roughness Ra of the surface of the porous membrane is greater than 6 μm.

4. The air filter media according to any one of claims 1 to 3, characterized in that, The average pore size of the porous membrane is greater than 2 μm.

5. The air filter media according to any one of claims 1 to 4, characterized in that, The average pore size of the porous membrane is less than 10 μm.

6. The air filter media according to any one of claims 1 to 5, characterized in that, The thickness of the porous membrane is 100 μm or more.

7. The air filter media according to any one of claims 1 to 6, characterized in that, The contact angle of a 30% (v / v) aqueous solution of isopropanol is greater than 127 degrees.

8. The air filter media according to any one of claims 1 to 7, characterized in that, The porous membrane contains a fluoropolymer.

9. The air filter media according to any one of claims 1 to 8, characterized in that, The porous membrane does not contain any antifungal agents.

10. The air filter media according to any one of claims 1 to 9, characterized in that, The air filter media is used in environments with a relative humidity of 60% or higher.

11. A method of using an air filter media, characterized in that, The anti-mildew air filter material according to any one of claims 1 to 9 is used in an environment with a relative humidity of 60% or higher.

12. An air handling device, characterized in that, The air handling device includes the air filter media according to any one of claims 1 to 10.

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