Air filter medium, air filter pack, and air filter unit

Abstract

Provided is an air filter medium having a structure with a good PF value, an air filter pack, and an air filter unit. An air filter medium containing a resin has a plurality of first protrusions that protrude toward the passing direction of an air current with respect to the medium on a first face of the medium and a plurality of second protrusions that protrude toward the passing direction of the air current on a second face that is the back face of the first face of the medium, and the total projected area of the plurality of first protrusions and the plurality of second protrusions when the entire medium is projected in the passing direction of the air current is 50% or more and 100% or less of the projected area of the entire medium when the entire medium is projected in the passing direction of the air current. The ratio of the effective medium area of the medium with respect to the projected area of the entire medium when the entire medium is projected in the passing direction of the air current is 110% or more.

Description

Technical Field

[0001] This disclosure relates to an air filter media, an air filter bag, and an air filter unit. Background Technology

[0002] Currently, air filter media used to capture dust in gases are required to have good performance characteristics such as high capture efficiency and low pressure loss when the gas passes through.

[0003] For example, according to the air filter material described in Patent Document 1 (International Publication No. 2019 / 159654), it is proposed to utilize electrostatic effects by electretting nonwoven fabric, and to use a resin containing two components with different crystallization start temperatures as the resin constituting the nonwoven fabric fibers. Summary of the Invention

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

[0005] However, sufficient research has not been conducted on air filter media to reduce pressure loss while suppressing the decrease in capture efficiency through its structure. Air filter media with a good PF value (Power Factor) is required compared to flat-shaped air filter media. The PF value is a performance indicator of air filter media expressed using capture efficiency and pressure loss.

[0006] Technical solutions adopted to solve technical problems

[0007] The first-concept air filter media is a resin-containing air filter media with multiple protrusions. These protrusions project in the direction of airflow. The projected area of ​​the multiple protrusions when projected onto the entire filter media along the airflow direction is 50% to 100% of the total projected area of ​​the entire filter media when projected onto the entire filter media along the airflow direction. The ratio of the effective filter media area to the total projected area of ​​the entire filter media when projected onto the entire filter media along the airflow direction is 110% or more.

[0008] Compared to filter media with a flat shape that does not have multiple protrusions, this air filter media can improve the PF value.

[0009] The second viewpoint's air filter media is based on the first viewpoint's air filter media, and the PF value obtained is above 10.2 based on the dust collection efficiency of an airflow velocity of 9.63 cm / s and a particle size of 0.075 μm and the pressure loss at that time.

[0010] The air filter media is designed to perform well through its structure.

[0011] The third viewpoint's air filter media is based on the air filter media described in the first or second viewpoint, wherein the average protrusion ratio of the multiple protrusions in the direction of airflow is 0.10 to 0.85.

[0012] Here, the average protrusion ratio is the average of the protrusion ratios of multiple protrusions. The protrusion ratio refers to the protrusion height of the protrusion in the direction of airflow, relative to the equivalent diameter of the projected portion obtained by projecting the protrusion along the direction of airflow. Furthermore, the equivalent diameter is the value obtained by dividing four times the area of ​​the projected portion obtained by projecting the protrusion along the direction of airflow by the perimeter of that projected portion.

[0013] This air filter media can increase the effective area while suppressing filter media damage.

[0014] The air filter media of the fourth viewpoint is based on the air filter media described in any of the first to third viewpoints, and the resin includes fluororesin.

[0015] The air filter media is not easily damaged when forming multiple protrusions.

[0016] The fifth viewpoint's air filter media is based on the air filter media described in the fourth viewpoint, with the fluororesin including fibrous polytetrafluoroethylene. The air filter media has a PF value of 39 or higher, obtained based on the dust collection efficiency at an airflow velocity of 5.3 cm / s and a particle size of 0.3 μm, and the pressure loss at that point.

[0017] Here, fluoropolymers can also be resins composed of a single component, polytetrafluoroethylene, which is capable of being fibrous.

[0018] The air filter media is designed to perform well through its structure.

[0019] The sixth viewpoint's air filter media is based on the air filter media described in the fourth viewpoint. The fluororesin includes fibrous polytetrafluoroethylene, a non-fibrous, non-thermally meltable component, and a non-fibrous, thermoly meltable component with a melting point below 320°C. The air filter media has a PF value of 38 or higher, obtained based on the dust collection efficiency at an airflow velocity of 5.3 cm / s and a particle size of 0.3 μm, and the pressure loss at that point.

[0020] The air filter media is designed to perform well through its structure.

[0021] The air filter media of the seventh viewpoint is based on the air filter media described in any of the first to third viewpoints, wherein the resin comprises one or more selected from the group consisting of polypropylene, polyvinylidene fluoride, polyethylene, polyester, polyamide, aromatic polyamide, polyacrylonitrile, polyvinyl chloride, polyurethane, polylactic acid, polyphenylene sulfide, and polyimide. The air filter media has a PF value of 22 or higher, obtained based on the dust collection efficiency at an airflow velocity of 5.3 cm / s and a particle size of 0.3 μm, and the pressure loss at that point.

[0022] The air filter media is designed to perform well through its structure.

[0023] The air filter media of the eighth viewpoint is based on the air filter media described in any of the first to seventh viewpoints, wherein the plurality of protrusions include a plurality of first protrusions protruding upstream of the filter media relative to the direction of airflow and a plurality of second protrusions protruding downstream of the filter media relative to the direction of airflow. The total projected area of ​​the plurality of first protrusions and the plurality of second protrusions when projected onto the entire filter media along the direction of airflow is 50% to 100% of the total projected area of ​​the entire filter media when projected onto the entire filter media along the direction of airflow. The ratio of the effective filter media area to the total projected area of ​​the entire filter media when projected onto the entire filter media along the direction of airflow is 110% or more.

[0024] The air filter media has protrusions in both directions of the airflow path, thus suppressing the load applied to the filter media during processing.

[0025] The air filter media of the ninth point is based on the air filter media described in the eighth point, with multiple protrusions existing in a dotted pattern.

[0026] The filter media of this air filter makes it easy to increase the effective area.

[0027] The air filter media of the tenth viewpoint is based on the air filter media described in the ninth viewpoint, wherein the first protrusion is surrounded by three or more second protrusions. The second protrusions are surrounded by three or more first protrusions.

[0028] The filter media of this air filter makes it easy to increase the effective area.

[0029] The air filter media of the eleventh point is based on the air filter media described in the eighth point, wherein the plurality of first protrusions and the plurality of second protrusions are strip-shaped. The first protrusions and the second protrusions are arranged alternately.

[0030] The filter media of this air filter makes it easy to increase the effective area.

[0031] The air filter media of the twelfth viewpoint is based on the air filter media described in any of the eighth to eleventh viewpoints, with the first protrusion and the second protrusion connected together.

[0032] The air filter media can easily reduce the localized load generated when the first and second protrusions are formed.

[0033] The air filter media of the thirteenth viewpoint is based on the air filter media described in any of the first to twelfth viewpoints, wherein multiple protrusions are extended and formed by extrusion along the direction of airflow.

[0034] The air filter media is easy to process to form multiple protrusions.

[0035] The fourteenth viewpoint's air filter media is based on the thirteenth viewpoint's air filter media. It is obtained by extruding multiple extended sections relative to a flat filter media in the thickness direction of the flat filter media. The ratio of the PF value of the filter media with multiple extended sections to the PF value of the flat filter media, i.e., the PF value ratio (PF value after processing / PF value before processing), is 1.1 or higher. The PF value is obtained based on the collection efficiency of 0.3μm dust particles at an airflow velocity of 5.3cm / s and the pressure loss at that time.

[0036] This air filter media can achieve a good PF value by changing the shape of the flat filter media.

[0037] The air filter bag of the fifteenth point includes the air filter media described in any of the first through fourteenth points. In the air filter bag, the air filter media is processed into a serrated shape obtained by alternating and repeated outward and inward folds. In the air filter bag, multiple protrusions maintain the spacing between opposing portions of the air filter media.

[0038] The air filter pack has a large surface area that ensures it functions effectively even when folded.

[0039] The air filter unit of the sixteenth viewpoint includes the air filter housing and the housing of the fifteenth viewpoint. The housing holds the air filter housing. Attached Figure Description

[0040] Figure 1 This is a schematic cross-sectional view showing the layer structure of one of the air filter media.

[0041] Figure 2 This is a schematic cross-sectional view showing the layer structure of the air filter media (second one).

[0042] Figure 3This is a schematic cross-sectional view showing the layer structure of the air filter media (third type).

[0043] Figure 4 This is a partially enlarged perspective view of one example of an air filter media in which the protrusions are formed in a dotted pattern.

[0044] Figure 5 This is a schematic perspective view of an example of an embossing mold used to make an air filter media in which the first and second protrusions are connected.

[0045] Figure 6 This is a partially enlarged perspective view of an example (second example) of an air filter media in which the protrusions are formed in a strip shape.

[0046] Figure 7 This is a schematic 3D view of the air filter bag.

[0047] Figure 8 This is a schematic three-dimensional view of the air filter unit. Detailed Implementation

[0048] The following examples illustrate air filter media (hereinafter also referred to as filter media), air filter packs, and air filter units.

[0049] (1) Air filter media

[0050] Air filter media includes a main trapping layer composed of resin.

[0051] The main trapping layer can be composed of a porous membrane obtained by extending a sheet of resin, or it can be composed of a nanofiber layer, wherein the nanofiber layer is obtained by manufacturing nanofibers from resin using an electrospinning method.

[0052] Preferably, the air filter media also includes a support layer laminated to the main trapping layer to improve strength. By using the support layer, the air filter media can stand upright even if it is difficult to stand up due to the thinness of the main trapping layer. Furthermore, by ensuring the strength of the air filter media, it is easy to maintain the shape of the protrusions and further fold.

[0053] The support layer can be disposed only downstream of the main trapping layer, only upstream of the airflow, or both downstream and upstream. As such an air filter material, for example, it can be... Figure 1 The air filter media 30 shown has a main trapping layer 31 and a permeable support layer 32 stacked on the downstream side of the airflow direction passing through the main trapping layer 31. Furthermore, for example, it may also be as follows... Figure 2The air filter media 30 shown has a main trapping layer 31 and a permeable support layer 32 stacked on the upstream side of the airflow direction passing through the main trapping layer 31. Furthermore, for example, it may also be as follows... Figure 3 The air filter media 30 shown has a main trapping layer 31 and a permeable support layer 32 stacked on both the upstream and downstream sides of the airflow direction passing through the main trapping layer 31.

[0054] Furthermore, there are no particular limitations on the way the above layers are overlapped. 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.

[0055] (2) Main trapping layer

[0056] The resin constituting the main trapping layer is not specifically limited, and may include, for example, one or more selected from the group consisting of polytetrafluoroethylene (PTFE), nylon 6 and other nylons, polypropylene, polyethylene, polystyrene, polyester, polyphenylene sulfide, polyethylene oxide, polymethyl methacrylate, cellulose acetate, polycarbonate, polyvinyl chloride, polyetherimide, polyvinyl alcohol, polyethylene terephthalate, polyacrylonitrile, polyvinylidene fluoride, polystyrene, polyurethane and polycaprolactone.

[0057] Furthermore, when the main trapping layer is composed of a nanofiber layer obtained by electrospinning nanofibers using resin, it is preferable to select one or more from the group consisting of polypropylene, polyvinylidene fluoride, polyethylene, polyester, polyamide, aromatic polyamide, polyacrylonitrile, polyvinyl chloride, polyurethane, polylactic acid, polyphenylene sulfide, and polyimide. Additionally, as the nanofiber, for example, the average fiber diameter can be between 10 nm and 1000 nm.

[0058] The primary trapping layer is preferably composed mainly of fluororesin, and more preferably composed of a fluororesin porous membrane. Here, "mainly" means that, in the case of multiple components, the fluororesin has the highest weight proportion. The fluororesin porous membrane will be described later.

[0059] As the resin constituting the main trapping layer, when the sample is subjected to a load by applying a tensile speed of 100 mm / min in a specified tensile direction parallel to the extension direction of the reference plane, thereby stretching the sample by 50% in the specified tensile direction at 80°C, it is preferable that the PF value after stretching is 80% to 150% of the PF value before stretching, which is 100% (in addition, the PF value here is the PF value under the condition that the airflow velocity is 9.63 cm / s and the dust particle size is 0.075 μm).

[0060] From the viewpoint of achieving a good dust storage capacity, the thickness of the main trapping layer is preferably 10 μm or more. Furthermore, from the viewpoint of preventing the thickness of the folded portions from becoming excessive when used in a folded state, the thickness of the main trapping layer is preferably 50 μm or less. The thickness of the main trapping layer is the value of the thickness when a load of 0.3 N is applied to the test object in a specific measuring device. The main trapping layer used in the air filter media of this embodiment includes a protrusion. For example, it is possible to measure the thickness when a load of 0.3 N is applied while multiple main trapping layers are overlapped, and then measure the thickness when a load of 0.3 N is applied again while multiple additional main trapping layers are added and overlapped. The thickness is then determined as the difference in thickness divided by the number of additional main trapping layers.

[0061] (2-1) Fluoropolymer porous membrane

[0062] More preferably, the fluoropolymer porous membrane has a porous membrane structure including fibrils (not shown) and nodes (nodes) connected to the fibrils.

[0063] As a component that differs from fluororesin in porous fluororesin membranes, an example that is a non-thermally meltable component (component B) that does not undergo fibrosis, namely inorganic filler, can be mentioned later.

[0064] Fluororhines used in fluoropolymer porous membranes can consist of one component or two or more components. Furthermore, examples of fluoropolymers include those containing fibrous PTFE (hereinafter also referred to as component A). Additionally, examples of fluoropolymers include mixtures of component A, a non-fibrous, non-thermally melt-processable component (hereinafter also referred to as component B), and a non-fibrous, thermoly melt-processable component with a melting point below 320°C (hereinafter also referred to as component C).

[0065] (2-2) Component A: PTFE capable of fiberization

[0066] Fiberizable PTFEs, for example, possess extensibility and non-melt processability. Furthermore, "non-melt processability" refers to the fact that due to their high melt viscosity, they do not flow easily in the molten state, making melt processing difficult. Preferably, a fiberizable PTFE has a melt viscosity of 1×10⁻⁶ at 380°C. 8 Pa·S or above.

[0067] Fiberizable PTFE includes, 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 may deteriorate; if the SSG is too low, the calendering properties deteriorate, which may worsen the uniformity of the porous membrane and increase the pressure loss of the porous membrane. The aforementioned standard specific gravity (SSG) is determined according to ASTM D4895.

[0068] Furthermore, from the viewpoint of obtaining fibrils that are easy to fiberize and have long fiber lengths, PTFE obtained through emulsion polymerization is preferred. Emulsion polymerization can typically be carried out in an aqueous medium containing TFE or monomers other than TFE, a dispersant, and a polymerization initiator. Additionally, emulsion polymerization is preferably carried out under set stirring conditions with steady stirring to prevent the generated PTFE microparticles from agglomerating. In emulsion polymerization, the polymerization temperature is typically 20–100°C, preferably 50–85°C, and the polymerization pressure is typically 0.5–3.0 MPa. Free radical polymerization initiators, redox polymerization initiators, etc., are preferred as polymerization initiators in emulsion polymerization.

[0069] PTFE can also be formulated into a fine powder obtained by emulsion polymerization. This fine powder can be obtained by recovering PTFE microparticles from an aqueous PTFE dispersion obtained by emulsion polymerization, followed by condensation and drying. The fine powder formed from the above-mentioned PTFE exhibits good extrusion processability; for example, it can be extruded as a paste at an extrusion pressure of 20 MPa or less. Furthermore, the extrusion pressure was measured during paste extrusion through an orifice (diameter 2.5 cm, cross length 1.1 cm, lead angle 30°) at a reduction ratio of 100, an extrusion speed of 51 cm / min, and a temperature of 25°C. Paste extrusion molding typically involves pre-forming and extruding a mixture of the above-mentioned fine powder with an extrusion aid (lubricant). The extrusion aid is not particularly limited; existing known extrusion aids can be used, with petroleum-based hydrocarbons such as naphtha having a boiling point of 150°C or higher being preferred. The amount of extrusion aid used varies depending on the type of extrusion aid, but it is generally 5 to 50 parts by weight (P) per 100 parts by weight of PTFE powder. More preferably, it is 10 to 40 parts by weight, and even more preferably 25 to 35 parts by weight. Preforming and extrusion can be carried out using existing known methods, and suitable conditions can be selected.

[0070] Furthermore, the ability to form fibers can be determined by whether paste extrusion is possible. Paste extrusion is a representative method for molding high molecular weight PTFE powder made from TFE polymers. Generally, paste extrusion is possible because high molecular weight PTFE has fibrous properties. If the unfired molded body obtained by paste extrusion lacks substantial strength or elongation—for example, if the elongation is 0% and it breaks when stretched—it can be considered to lack fibrous properties.

[0071] 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. Furthermore, from the viewpoint of maintaining the moldability of polytetrafluoroethylene well, the content of modified PTFE in the high molecular weight PTFE is preferably 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less. There are no particular limitations on homopolymer PTFE, and homopolymer PTFE disclosed in Japanese Patent Application Publication No. 53-60979, Japanese Patent Application Publication No. 57-135, 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. 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, International Publication No. 2009 / 001894, International Publication No. 2010 / 113950, and International Publication No. 2013 / 027850 may be used. Among them, homopolymer PTFE with high elongation properties is preferred, as 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.

[0072] Modified PTFE consists 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. Preferably, modified PTFE is a TFE copolymer obtained by polymerizing trace amounts of monomers other than TFE with TFE within a range that does not significantly impair the properties of the TFE homopolymer. 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 Patent Application Publication No. 2003 / 033555, International Patent Application Publication No. 2005 / 061567, International Patent Application Publication No. 2007 / 005361, International Patent Application Publication No. 2011 / 055824, and International Patent Application 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.

[0073] 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.

[0074] 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.

[0075] There are no particular limitations on perfluorovinyl ethers; for example, perfluorounsaturated compounds represented by the following general formula (1) can be cited.

[0076] CF2 = CF - ORf · · · (1)

[0077] In the formula, Rf represents a perfluorinated organic group.

[0078] 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.

[0079] 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.

[0080] There is no particular limitation on the above-mentioned perfluoroalkyl ethylene (PFAE), and examples such as perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE) can be cited.

[0081] 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.

[0082] In particular, from the viewpoint of easy fiberization and obtaining protofibrils with longer fiber lengths, when using components B and C described later to construct fluoropolymer porous membranes, homopolymer PTFE preferably contains more than 50% by weight of fiber-forming PTFE.

[0083] As a fluoropolymer porous membrane, in addition to the aforementioned fibrous PTFE (component A), it also contains a non-fibrous, non-thermally meltable component (component B) and a non-fibrous, thermoly meltable component with a melting point below 320°C (component C). The following substances can be used as components B and C respectively. Compared to existing fibrous PTFE (high molecular weight PTFE) porous membranes, the fluoropolymer porous membrane composed of these three components has 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 direction of airflow through the filter media, thus increasing the dust storage capacity. By using these three components to construct the fluoropolymer porous membrane, the dust storage capacity for liquid particles can be increased, especially compared to solid particles.

[0084] (2-3) Component B: Non-thermally meltable components that do not undergo fibrosis.

[0085] The non-thermally meltable components that do not undergo fibrosis are mainly located at the junctions as non-fibrous particles, which helps to inhibit the fibrosis of PTFE that is capable of fibrosis.

[0086] 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.

[0087] 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 junction 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).

[0088] 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.

[0089] 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.

[0090] 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 junctions, thereby suppressing fibrosis.

[0091] Examples of thermosetting resins include epoxy resins, silicone resins, polyesters, polyurethanes, polyimides, phenolic resins, and mixtures thereof. From the viewpoint of co-condensation workability, thermosetting resins that are dispersed in water in their uncured state are preferred. These thermosetting resins are all commercially available.

[0092] 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.

[0093] In addition, non-melt-processable components that do not undergo fibrosis can combine multiple of the above-mentioned components.

[0094] The non-thermally meltable component that does not undergo fibrosis may contain 1% to 50% by weight of the porous membrane, preferably 20% to 40% by weight, and more preferably 30% by weight.

[0095] (2-4)C component: Components with a melting point less than 320℃ that do not undergo fibrosis and can be thermally melted.

[0096] 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 at the junctions, which can improve the overall strength of the porous membrane and suppress the deterioration of filter performance even when compressed in subsequent processes.

[0097] 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.

[0098] Examples of non-fibrous, heat-meltable components include heat-meltable fluoropolymers, polystyrene, polyethylene terephthalate (PET), polyesters, polyamides, and other resins, or mixtures thereof, which exhibit excellent meltability and flowability at the stretching temperature during porous membrane manufacturing. Among these, heat-meltable fluoropolymers are preferred due to their superior heat resistance and chemical resistance at the stretching temperature during porous membrane manufacturing. Examples of heat-meltable fluoropolymers include those comprising the following general formula (2).

[0099] RCF=CR2··· (2)

[0100] (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.

[0101] 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.

[0102] In addition, fluoropolymers may also contain at least one monomer represented by the above general formula (2), and the monomers represented by the above general formula (1) and / or the following general formula (3).

[0103] R2C=CR2· · · (3)

[0104] (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 of the above-mentioned other R, they can be different from each other.) represents a copolymer derived from the copolymerization of at least one copolymeric comonomer.

[0105] 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.

[0106] Examples of compounds represented by general formula (3) include ethylene, propylene, etc.

[0107] 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).

[0108] 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.

[0109] In addition, components that do not undergo fibrosis and can be thermally melted can be combined with various of the above-mentioned components.

[0110] 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.

[0111] 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.

[0112] (2-5) Method for manufacturing fluoropolymer porous membranes

[0113] Next, an example will be given to illustrate the manufacturing method of air filter media.

[0114] Fluoropolymers can be used in the fabrication of fluoropolymer porous membranes, and for example, component A or the three components described above are preferred.

[0115] There are no particular limitations on the form of the three components A to C described above; for example, they may be the compositions, mixed powders, or molding materials described later. The compositions, mixed powders, and molding materials all contain components A, B, and C as described above, and contain, for example, 0.1% by weight or more and less than 20% by weight of component C.

[0116] The raw materials for porous membranes can be in the form of mixed powders as described later, or non-powder mixtures, or molding materials or compositions as described later. Examples of mixed powders include, for example, the fine powder obtained by co-condensation used in the later examples, powder obtained by mixing two of the three raw materials by co-condensation and then mixing the other component using a mixer, and powder obtained by mixing the three raw materials using a mixer. Examples of non-powder mixtures include, for example, molded bodies such as porous bodies (e.g., porous membranes), and aqueous dispersions containing the three components.

[0117] Molding materials refer to materials that have been modified for processing in order to shape the composition. Examples include materials with added processing aids (such as liquid lubricants), materials with adjusted particle size, and pre-formed materials. Molding materials may also contain known additives in addition to the three components mentioned above. Examples of known additives include carbon materials such as carbon nanotubes and carbon black, pigments, photocatalysts, activated carbon, antibacterial agents, adsorbents, and deodorizing agents.

[0118] The composition can be manufactured by various methods. For example, when the composition is a mixed powder, it can be manufactured by the following methods: mixing powders of component A, component B, and component C using a general mixer or the like; obtaining a co-condensed powder by co-condensing three aqueous dispersions containing components A, B, and C respectively; mixing a mixed powder obtained by pre-co-condensing an aqueous dispersion containing any two of components A, B, and C with powder of the remaining component using a general mixer or the like.

[0119] As a method for the aforementioned co-condensation, the following methods can be cited as examples:

[0120] (i) A method of condensing a mixture of an aqueous dispersion of component A, an aqueous dispersion of component B, and an aqueous dispersion of component C;

[0121] (ii) A method of condensing a solution of an aqueous dispersion of any one of components A, B, and C by adding powders of the remaining two components.

[0122] (iii) A method of adding powder of any one of components A, B, and C to a mixed aqueous dispersion containing the remaining two components and then performing coagulation.

[0123] (iv) A method in which aqueous dispersions of any two of components A, B, and C are mixed in advance and then condensed to obtain a mixed powder of the two components, and the mixed powder is added to an aqueous dispersion of the remaining component and then condensed.

[0124] As for the co-condensation method described above, the method described in (i) is preferred from the perspective of easily dispersing the three components uniformly.

[0125] After co-condensation, the mixture is dehydrated and dried, then mixed with a liquid lubricant (extrusion aid) and extruded. There are no particular limitations on the liquid lubricant; it can be any substance capable of wetting the surface of the PTFE powder and removable after the mixture obtained through co-condensation is formed into a film. Examples include liquid paraffin, naphtha, white oil, hydrocarbon oils such as toluene and xylene, alcohols, ketones, and esters.

[0126] The mixture obtained by co-condensation is mixed with a liquid lubricant and then extruded and calendered using existing known methods to form a film. Here, regarding the amount of liquid lubricant mixed with the fluoropolymer (e.g., the mixture obtained by co-condensation), the amount of liquid lubricant mixed with 100 parts by weight of the fluoropolymer can be 10 parts by weight or more and 40 parts by weight or less, preferably 25 parts by weight or more and 35 parts by weight or less.

[0127] Extrusion can be performed by paste extrusion, plunger extrusion, etc., with paste extrusion being preferred. For the sheet extruded by paste extrusion, calendering is carried out under heating at a temperature of, for example, 40°C to 80°C using calendering rollers or the like. The thickness of the resulting calendered film is set based on the thickness of the target porous film, typically 100 μm to 1000 μm, but can also be 100 μm to 400 μm, preferably 150 μm to 350 μm.

[0128] Next, the liquid lubricant is removed from the uncalcined film, which is the calcined product. The removal of the liquid lubricant is carried out by heating, extraction, or a combination thereof.

[0129] Here, from the viewpoint of ensuring sufficient thickness of the obtained fluoropolymer porous membrane and reducing pressure loss, it is preferable that the calendered material after removing the liquid lubricant undergoes the following heat treatment before stretching: heating for more than one minute in a temperature atmosphere of 250°C to 325°C.

[0130] The calendered material, having had the liquid lubricant removed as described above, or the calendered material that has undergone further heat treatment, is then stretched. Furthermore, in cases containing both a non-fibrous hot-melt processable component and a non-fibrous non-hot-melt processable component, the stretching is performed at a temperature above the melting point of the non-fibrous hot-melt processable component and below the decomposition temperature of the non-fibrous non-hot-melt processable component.

[0131] Furthermore, when using a non-fibrous hot-melt processable component in the fabrication of a fluoropolymer porous membrane, this component melts during the stretching process and then solidifies at the junction, thereby enhancing the intensity of the airflow in the porous membrane. The stretching temperature can be set based on the temperature of the stretching furnace or the temperature of the heating rollers transporting the calendered material, or a combination of these settings.

[0132] The extension includes extension in a first direction and preferably extension in a second direction orthogonal to the first direction. Alternatively, the extension in the second direction may be performed after the extension in the first direction. Furthermore, the extension in the first direction and the extension in the second direction can be performed simultaneously. In this embodiment, the first direction is the length direction (longitudinal: MD direction) of the calender, and the second direction is the width direction (transverse: TD direction) of the calender. Additionally, the extension can be performed simultaneously while multiple calender sheets are overlapped.

[0133] The elongation area ratio of the calendered material can be more than 250 times and less than 800 times, preferably more than 300 times and less than 600 times, and more preferably more than 400 times and less than 580 times.

[0134] To obtain mechanical strength and dimensional stability, the resulting porous membrane is preferably heat-fixed. The temperature during heat fixing can be above or below the melting point of PTFE, preferably above 250°C and below 400°C.

[0135] Fluoropolymer porous membranes can be single-layered or multi-layered, obtained by stacking a first fluoropolymer porous membrane and a second fluoropolymer porous membrane.

[0136] (3) Support layer

[0137] The material and structure of the support layer 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 is preferably a two-layer nonwoven fabric formed by having a core / sheath structure as part or all of the fibers, 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, nonwoven fabrics with a core / sheath structure are preferably nonwoven fabrics where the melting point of the core component is higher than that of the sheath component. For example, combinations of core / sheath materials include, for example, PET / PE and high-melting-point polyester / low-melting-point polyester. Examples of combinations of low-melting-point and high-melting-point materials in two layers of nonwoven fabric include PE (polyethylene) / PET (polyterephthalic acid), PP (polypropylene) / PET, PBT (polybutylene terephthalate) / PET, and low-melting-point PET / high-melting-point PET. Examples of nonwoven fabrics with a surface 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 resins on PET nonwoven fabrics.

[0138] 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.

[0139] Compared to the main trapping layer, the pressure loss and trapping efficiency of the support layer are extremely low, and can be considered practically zero. When air passes through at a flow rate of 9.63 cm / s, the pressure loss of the support layer is preferably 10 Pa or less, more preferably 5 Pa or less, and even more preferably 1 Pa or less. When air passes through at a flow rate of 5.3 cm / s, the pressure loss of the support layer is preferably 5 Pa or less, more preferably 1 Pa or less. Furthermore, the trapping efficiency of the support layer, controlled by NaCl particles with a particle size of 0.075 μm, can be considered practically zero or approximately zero. The trapping efficiency of the support layer, controlled by NaCl particles with a particle size of 0.3 μm, can be considered practically zero or approximately zero.

[0140] The thickness of the support layer is preferably 500 μm or less, more preferably 300 μm or less. Furthermore, from the viewpoint of easily maintaining the shape of the protrusions provided on the air filter media, or from the viewpoint of easily maintaining the pleated shape when used in a folded form, the thickness of the support layer is preferably 50 μm or more, more preferably 75 μm or more. The thickness of the support layer is the value of the thickness when a load of 0.3 N is applied to the test object in a specific measuring device. The support layer used in the air filter media of this embodiment includes protrusions. For example, it is possible to measure the thickness when a load of 0.3 N is applied while multiple support layers are overlapped, and then measure the thickness when a load of 0.3 N is applied again while multiple support layers are further added and overlapped, and the thickness is determined as the difference in thickness divided by the number of additional support layers.

[0141] (4) Shape of air filter media

[0142] The air filter media has multiple protrusions projecting in the direction of airflow. This increases the effective filter area through which the airflow passes compared to flat-shaped air filter media. Furthermore, by increasing the effective filter area, the airflow velocity passing through the filter media can be reduced, resulting in better capture efficiency. Additionally, compared to flat-shaped air filter media, it is easier to increase rigidity, thus suppressing deformation of the filter media during use due to air pressure.

[0143] Furthermore, from the viewpoint of easily and sufficiently ensuring the effective filter media area of ​​the air filter media, the protrusions of the air filter media preferably include a plurality of first protrusions protruding upstream in the direction of airflow and a plurality of second protrusions protruding downstream in the direction of airflow.

[0144] Multiple first protrusions of the air filter media are located upstream of the airflow passing through the air filter media relative to the reference surface of the air filter media. The protrusion heights of the multiple first protrusions may all be the same or different from each other.

[0145] Multiple second protrusions of the air filter media are located downstream of the airflow passing through the air filter media relative to the reference surface of the air filter media. The protrusion heights of the multiple second protrusions may all be the same or different from each other.

[0146] Furthermore, the average protrusion height of the plurality of first protrusions may be the same as or different from the average protrusion height of the plurality of second protrusions. From the viewpoint of suppressing strain deviation during the response formation of either the first or second protrusion, the average protrusion height of the plurality of first protrusions is preferably 50% to 150% of the average protrusion height of the plurality of second protrusions, more preferably 70% to 130%, further preferably 90% to 110%, and most preferably the same.

[0147] Here, the reference plane of the air filter media is determined in the following order (i) to (iii).

[0148] (i) In the case where there are surfaces extending on the same plane between the protrusions of the air filter media, the surface is the reference plane.

[0149] (ii) Where there are no surfaces extending on the same plane between the protrusions of the air filter media, but there are surfaces extending on the same plane at the periphery of the air filter media, that surface is the reference surface.

[0150] (iii) In the case where there is no surface extending on the same surface between the protrusions of the air filter material and the periphery of the air filter material, an imaginary surface extending at the midpoint of the airflow direction between the first imaginary surface and the second imaginary surface is used as the reference surface, wherein the first imaginary surface is an imaginary surface that extends in such a way as to connect the protruding ends of a plurality of first protrusions of the air filter material, and the second imaginary surface is an imaginary surface that extends in such a way as to connect the protruding ends of a plurality of second protrusions.

[0151] When viewed along the direction of airflow, the protrusions of the air filter media can be, for example, as shown in the image. Figure 4 The protrusions are formed as shown in the diagram, appearing as dots. Furthermore, when observing the air filter material along the airflow direction, the ratio of the length of the protrusion in the longitudinal direction to the length of the direction perpendicular to the longitudinal direction can be 0.25 to 4.0, preferably 0.5 to 2.0. Additionally, the plurality of first protrusions and the plurality of second protrusions can each be formed as dots. In this case, when observing the air filter material along the airflow direction, one first protrusion can be surrounded by three or more second protrusions, or one first protrusion can be surrounded by four or more second protrusions. Furthermore, when observing the air filter material along the airflow direction, one second protrusion can be surrounded by three or more first protrusions, or one second protrusion can be surrounded by four or more first protrusions. Furthermore, for example, it is also possible to implement... Figure 5The air filter media shown is formed by embossing using a embossing mold, resulting in a first protrusion and a second protrusion that are connected to each other. In this case, the first and second protrusions can be continuously arranged when viewed along the airflow direction, thereby eliminating any intervening portion between the first and second protrusions when viewed along the airflow direction. Therefore, when the first and second protrusions are formed by embossing along the airflow direction, the non-uniformity of the filter media structure caused by the deformed area (first and second protrusions) and the undeformed area (intervening portion) can be minimized. Furthermore, when the first and second protrusions are raised along the airflow direction, it is easier to suppress the occurrence of stress that may locally occur near the boundary between the first and second protrusions and the intervening portion, and it is easier to suppress the occurrence of locally thinned portions due to elongation.

[0152] Furthermore, the protrusions on the air filter media, when viewed along the direction of airflow, can also be seen as... Figure 6 It is formed into a strip shape as shown. In addition, the first strip-shaped protrusion and the second strip-shaped protrusion in the protrusion can also be formed to be parallel to each other and arranged alternately.

[0153] The three-dimensional shape of the dot-like protrusions is not particularly limited, and can be selected from various shapes such as cuboids, cubes, prisms, cylinders, hemispheres, truncated spheres, truncated pyramids, cones, pyramids, truncated cones, etc. The top surface of the embossed protrusions can be a flat rectangular plane such as a rectangle or square, or a curved surface with curvature such as a hemisphere or cylinder.

[0154] The method for forming the protrusions is not particularly limited; for example, they can be formed by embossing a flat sheet of filter media. In the embossing process, an embossing mold with multiple embossed protrusions of a specific shape and multiple embossed recesses of a shape corresponding to the embossed protrusions is used. The air filter media is then clamped in the direction of airflow, causing the filter media to extend in the direction of airflow, thereby forming the protrusions. Furthermore, the atmosphere temperature during the embossing process can be between 50°C and 150°C, preferably between 70°C and 130°C, and can also be performed at 80°C. The shape, size, protrusion height, and formation density of the protrusions provided on the air filter media can be adjusted by changing the shape of the embossing mold. The embossing mold can be plate-shaped or roller-shaped.

[0155] In addition, to avoid localized damage, air filter media is preferably free of creases.

[0156] Furthermore, as an air filter material having multiple first protrusions and multiple second protrusions, it is more preferable to have a portion in which the first protrusions and second protrusions are connected without a flat surface sandwiched between them. For example, when the first protrusions and second protrusions are formed simultaneously by embossing, localized stretching loads between the first and second protrusions, or in any one of the first and second protrusions, are suppressed, making it easier to prevent damage to the air filter material.

[0157] The convexity ratio of air filter media can be 50% to 100%, 60% to 95%, or 70% to 90%. Here, "convexity ratio" refers to the proportion of the total area of ​​multiple convexities relative to the entire filter media. Specifically, it refers to the proportion of the total projected area of ​​multiple convexities when projected onto the entire filter media along the airflow direction to the total projected area of ​​the entire filter media when projected onto the entire filter media along the airflow direction. When the first and second convexities are included as convexities, their combined projected area is used for calculation. By setting the convexity ratio to 50% or more, the protrusion height of the convexities required to sufficiently increase the effective filter media area can be minimized. Therefore, damage to the filter media caused by embossing is easily suppressed, and the reduction in collection efficiency is easily suppressed. Furthermore, by setting the convexity ratio to 50% or more, the proportion of the boundary portion between the convexities and other areas can be reduced. Therefore, performance degradation of the filter media that may occur at this boundary portion can be suppressed. Alternatively, the entire surface of the air filter media may be composed of the first and second convexities.

[0158] The effective filter media area ratio of the air filter media is 110% or more, preferably 120% or more. By achieving an effective filter media area ratio of 110% or more, it is easier to suppress pressure loss of the air filter media and achieve good collection efficiency. Furthermore, from the viewpoint of suppressing damage to the air filter media, the effective filter media area ratio can be, for example, 300% or less, preferably 220% or less. Here, "effective filter media area ratio" refers to the ratio of the effective filter media area of ​​the air filter media to the projected area of ​​the entire filter media when projected along the airflow direction.

[0159] The average protrusion ratio of the protrusions of the air filter media is preferably 0.10 to 0.85, more preferably 0.14 to 0.78. By setting the average protrusion ratio to 0.10 or higher, it is easier to increase the effective filter media area of ​​the air filter media. Furthermore, by setting the average protrusion ratio to 0.85 or lower, damage to the air filter media can be suppressed. Here, "average protrusion ratio" refers to the average of the protrusion ratios of multiple protrusions. The protrusion ratio (mm / mm) refers to the protrusion height (mm) of the protrusion in the direction of airflow relative to the equivalent diameter (mm) of the projected portion obtained by projecting the protrusion along the direction of airflow. This protrusion height (mm) is the value after deducting the thickness of the filter media. Additionally, the equivalent diameter (mm) refers to the area (mm²) of the projected portion obtained by projecting the protrusion along the direction of airflow. 2 The value is obtained by dividing four times the perimeter (mm) of the projected portion.

[0160] Furthermore, the average height of the protrusion of the convex portion in the direction of airflow, without considering the thickness of the air filter media, can be, for example, between 1 mm and 8 mm.

[0161] In addition, the average value of 100 protrusions that exist in an adjacent manner can be used as the average value.

[0162] Furthermore, when observing the air filter media along the direction of airflow, from the viewpoint of easily increasing the effective filter media area while easily suppressing the occurrence of local thinning due to the stretching during embossing, the density of protrusions relative to the projected area of ​​the entire filter media (protrusions / cm²) is considered. 2 The preferred value is 0.1 to 10, but it can be 0.5 to 5, or 1.0 to 4.0.

[0163] (5) Properties of air filter media

[0164] The pressure loss of the air filter media when air passes through at a flow rate of 9.63 cm / s is preferably 160 Pa or less, more preferably 150 Pa or less. Furthermore, the pressure loss of the air filter media when air passes through at a flow rate of 9.63 cm / s is not particularly limited and can be 40 Pa or more. In addition, the capture efficiency of the air filter media that captures air at a flow rate of 9.63 cm / s and utilizes NaCl particles with a particle size of 0.075 μm is preferably 80% or more, more preferably 85% or more.

[0165] The pressure loss of the air filter media when air passes through at a flow rate of 5.3 cm / s is preferably 80 Pa or less, more preferably 75 Pa or less. Furthermore, the pressure loss of the air filter media when air passes through at a flow rate of 5.3 cm / s is not particularly limited and can be 20 Pa or more. In addition, the capture efficiency of the air filter media that captures air at a flow rate of 5.3 cm / s and utilizes NaCl particles with a particle size of 0.3 μm is preferably 90% or more, more preferably 95% or more.

[0166] The PF value of the air filter media, determined by the pressure loss when air passes through at a flow rate of 9.63 cm / s and the collection efficiency using NaCl particles with a particle size of 0.075 μm, is preferably 10.2 or higher, more preferably 11 or higher, based on the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0167] The PF value of the air filter media, determined by the pressure loss when air passes through at a flow rate of 5.3 cm / s and the collection efficiency using NaCl particles with a particle size of 0.3 μm, is preferably 38 or more, more preferably 39 or more, and even more preferably 40 or more, based on the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0168] The preferred dust storage capacity for NaCl particles with a diameter of 0.1 μm for the air filter media is 2.3 g / m³. 2 The above, more preferably 5.0 g / m 2 above.

[0169] Furthermore, all physical properties described in this embodiment represent values ​​in a non-charged state. Additionally, the non-charged air filter material refers to air filter material that has become uncharged after undergoing de-energization treatment according to "JIS B 9908-4 Part 4: Test Method for De-energization Treatment of Air Filter Units for Ventilation".

[0170] The thickness of the air filter media is preferably, for example, 200 μm or more and 500 μm or less. The thickness of the air filter media is the value of the thickness when a load of 0.3 N is applied to the test object in a specific measuring device. The air filter media of this embodiment includes a protrusion, and for example, it is possible to measure the thickness when a load of 0.3 N is applied while multiple sheets of air filter media are overlapped, and then measure the thickness when a load of 0.3 N is applied while multiple sheets of air filter media are further added and overlapped, and the thickness is determined as the value obtained by dividing the thickness difference by the number of additional sheets of air filter media.

[0171] Air filter media preferably does not include collapsed portions of 30% or less of the aforementioned thickness, or the area ratio of collapsed portions when viewed along the airflow direction is 1% or less. More preferably, it does not include collapsed portions of 20% or less of the aforementioned thickness, or the area ratio of collapsed portions when viewed along the airflow direction is 1% or less. Even air filter media with an uneven or textured surface can avoid performance degradation by not producing collapsed portions or minimizing collapsed portions.

[0172] When air filter media is formed by embossing flat filter media to create convex or concave shapes, the PF value ratio (PF value after processing / PF value before processing) of the embossed filter media relative to the PF value of the flat filter media is preferably 1.1 or more, more preferably 1.2 or more. Furthermore, the PF value here is obtained based on the collection efficiency of 0.3 μm dust particles at an airflow velocity of 5.3 cm / s and the pressure loss at that time. Thus, by forming convex or concave shapes along the airflow direction, a better PF value can be achieved compared to filter media with a flat shape.

[0173] When the main trapping layer of the air filter material is composed of a single component of fibrous polytetrafluoroethylene, the PF value of the air filter material, based on the trapping efficiency of dust with a particle size of 0.3 μm at an airflow velocity of 5.3 cm / s and the pressure loss at that time, is preferably 39 or more, more preferably 40 or more, and even more preferably 41 or more.

[0174] When the main trapping layer of the air filter material is composed of polytetrafluoroethylene that can be fibrous, a non-fibrous, non-thermally meltable component, and a non-fibrous, thermoly meltable component with a melting point of less than 320°C, the PF value of the air filter material obtained based on the trapping efficiency of dust with a particle size of 0.3 μm at an airflow velocity of 5.3 cm / s and the pressure loss at that time is preferably 38 or more, more preferably 39 or more, and even more preferably 40 or more.

[0175] When the main collection layer of the air filter material is composed of one or more of the following materials: polypropylene, polyvinylidene fluoride, polyethylene, polyester, polyamide, aromatic polyamide, polyacrylonitrile, polyvinyl chloride, polyurethane, polylactic acid, polyphenylene sulfide, and polyimide, the PF value of the air filter material is preferably 22 or higher, more preferably 23 or higher, and even more preferably 24 or higher, based on the collection efficiency of dust with a particle size of 0.3 μm at an airflow velocity of 5.3 cm / s and the pressure loss at that time.

[0176] (6) Applications of air filter media

[0177] The application of the air filter media in this embodiment is not particularly limited, but may be used for, for example, the following purposes.

[0178] 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.

[0179] 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.

[0180] Applications include semiconductor liquid filters (for semiconductor manufacturing), hydrophilic filters (for semiconductor manufacturing), chemical filters (for pharmaceutical treatment), filters for pure water production lines (for pure water production), and backwash liquid filters (for industrial wastewater treatment).

[0181] Furthermore, the air filter material of this embodiment can be used, for example, as a mask to prevent dust, fumes, bacteria, viruses, etc., from entering the body through the mouth and nose. The mask can be any of the following shapes: flat, pleated, or three-dimensional. Pleated masks can also be used with the folded pleats unfolded. Three-dimensional masks can also be beak-shaped, tapering towards the front.

[0182] (7) Air filter bag

[0183] Next, refer to Figure 7 The air filter pack of this embodiment will be described.

[0184] Figure 7 This is a perspective view of the air filter pack 20 of this embodiment.

[0185] The air filter bag 20 is a finished filter material in which the air filter media described above is processed into a serrated shape (pleated processing) by repeatedly alternating outward and inward folds. Pleating can be performed, for example, by a known rotary pleating machine. The pleated air filter bag has a V-shaped arrangement when viewed along the fold lines of the outward and inward folds. The fold width of the filter media is not particularly limited, for example, it is 25mm to 280mm. By performing pleating, the air filter bag 20 can increase the folded area of ​​the filter media when used in an air filter unit, thereby obtaining an air filter unit with higher capture efficiency. Thus, in the pleated air filter bag, the protrusions of the air filter media ensure that the opposing portions are spaced apart. In addition, in air filter media where multiple protrusions form more than 50% of the projected area of ​​the entire filter media, when used in a pleated shape, it is easy to maintain the spacing between the opposing parts on the downwind side and suppress deformation, even when used under relatively strong wind speeds. Therefore, pressure loss can be minimized.

[0186] Furthermore, in such an air filter pack, it is preferable that the hot-melt resin or similar material used to maintain the spacing between opposing portions of the air filter media is not provided on the surface of the air filter media, nor are there any retaining members or similar materials used to maintain the spacing between opposing surfaces; the opposing portions are only spaced apart by the aforementioned protrusions. In this case, hot-melt resin, retaining members, etc., are not required, thereby minimizing structural pressure loss.

[0187] (8) Air filter unit

[0188] Next, refer to Figure 8 The air filter unit 1 of this embodiment will be described.

[0189] Figure 8 This is a perspective view of the air filter unit 1 of this embodiment.

[0190] The air filter unit 1 includes the air filter bag 20 described above and a frame 25 for housing the air filter bag 20.

[0191] Furthermore, to prevent friction and dust generation due to varying degrees of expansion with temperature changes, and to achieve a lightweight design, the air filter unit preferably does not use a spacer retaining member. Moreover, by omitting a spacer retaining member, damage to the air filter media can be suppressed. Alternatively, a spacer retaining member, for example, can be a partition used to maintain the spacing between opposing portions of the air filter media, and is composed of a component different from the air filter media itself.

[0192] The frame 25 is made of a combination of sheets such as resin or metal, and the air filter 20 and the frame 25 are preferably sealed with a sealant. The sealant is used to prevent leakage between the air filter 20 and the frame 25, and sealants made of resins such as epoxy, acrylic, or polyurethane can be used.

[0193] Example

[0194] The following examples and comparative examples are shown, and the contents of this disclosure are described in detail.

[0195] (Comparative Example 1)

[0196] As the FP raw material for the fluoropolymer porous membrane, which is the main trapping layer of the air filter material used in Comparative Example 1, a mixed powder consisting of three components (fibrillable PTFE (component A), a non-fibrillable, non-thermally meltable component (component B), and a non-fibrillable, thermoly meltable component with a melting point of less than 320°C (component C)) was used.

[0197] More specifically, firstly, 66.5% by weight (polymer conversion) of an aqueous PTFE dispersion (component A) with an SSG of 2.160 prepared according to the method described in Comparative Example 3 of International Publication No. 2005 / 061567, 28.5% by weight (polymer conversion) of a low molecular weight aqueous PTFE dispersion (component B) with a melt viscosity of 20000 Pa·s measured by a flow tester at 380°C prepared according to the method described in International Publication No. 2009 / 020187, and 5% by weight (polymer conversion) of an aqueous FEP dispersion (component C) with a melting point of 215°C prepared according to the method described in Japanese Patent Application Publication No. 2010-235667, were mixed, and 500 ml of a 1% aluminum nitrate aqueous solution was added as a coagulant. The mixture was stirred to perform co-coagulation. Then, after sieving the water off the generated powder using a sieve, it is dried in a hot air drying oven at 135°C for 18 hours to obtain a mixed powder of the above three components.

[0198] Subsequently, 29.0 parts by weight (29.0 parts by weight relative to 100 parts by weight of the mixed powder) of hydrocarbon oil ("IPSolvent 2028" manufactured by IDEMITSU Co., Ltd.) was added as an extrusion liquid lubricant to every 100 parts by weight of the mixture at 20°C and mixed. Next, the obtained mixture was extruded using a slurry extrusion apparatus to obtain a cylindrical molded body. This cylindrical molded body was then formed into a film using a calendering roller heated to 70°C, thereby obtaining a PTFE film. The film was then passed through a hot air drying oven at 250°C to evaporate and remove the hydrocarbon oil, thereby obtaining a strip-shaped unburned PTFE film (unprocessed strip) with an average thickness of 300 μm and an average width of 150 mm. Next, the unburned PTFE film was stretched along its length (MD direction) at a specific stretch ratio (10x) and a specific stretching speed (13.8% / second) under a specific temperature environment (250°C). Next, using a tenter frame capable of holding the stretched, unburnt membrane, the membrane is stretched along the width direction (TD direction) at a specific stretch ratio (45 times) and a specific stretching speed (330% / second) under a specific temperature environment (288°C), and then heat-fixed at a temperature of 390°C. This yields a fluoropolymer porous membrane.

[0199] By thermally fusing a support layer onto a fluoropolymer porous membrane obtained as described above, the air filter media of Comparative Example 1 is obtained. Furthermore, the support layer uses a spunbond nonwoven fabric with a core / sheath structure, consisting of PET as the core and PE as the sheath (average fiber diameter 24 μm, area weight 40 g / m²). 2 (The thickness is 0.2 mm) (Furthermore, the capture efficiency can be considered to be 0 or approximately 0).

[0200] (Example 1)

[0201] The air filter media of Comparative Example 1 was embossed using an apparatus having a pair of roller embossing dies to obtain the air filter media of Example 1. The protrusions provided in the embossing dies are truncated pyramids, with one side of the base having a length of 9.5 mm, a height of 5.5 mm, and one side of the top of the truncated pyramid having a length of 2.0 mm. Furthermore, one of the pair of roller embossing dies has a plurality of protrusions for forming a plurality of first protrusions, and the other of the pair of roller embossing dies has a plurality of recesses corresponding to the protrusions for forming the plurality of first protrusions. Similarly, the other of the pair of roller embossing dies has a plurality of protrusions for forming a plurality of second protrusions, and the other of the pair of roller embossing dies has a plurality of recesses corresponding to the protrusions for forming the plurality of second protrusions. The air filter media of Example 1 was embossed using an embossing die that achieved a protrusion ratio of 95%. In addition, here, a pair of roller embossing dies are heated to 80°C and processed at a temperature that is above the glass transition temperature of the nonwoven fibers and below the temperature at which the nonwoven fabric undergoes film formation.

[0202] (Example 2)

[0203] In Example 2, the same filter media as Comparative Example 1 was used, except that an embossing die was used to emboss the material so that the convexity ratio reached 50% and the effective filter media area ratio was changed accordingly, thus obtaining the air filter media of Example 2.

[0204] (Example 3)

[0205] In Example 3, the same filter media as Comparative Example 1 was used, except that the embossing process was performed using an embossing mold that achieved an average protrusion ratio of 0.21, and the effective filter media area ratio was changed accordingly, thus obtaining the air filter media of Example 3.

[0206] (Comparative Example 2)

[0207] In Comparative Example 2, the same filter media as Comparative Example 1 was used, except that the embossing process was performed using an embossing mold with a protrusion height of 9.0 mm and an average protrusion ratio of 0.89, thereby changing the effective filter media area ratio. The air filter media of Comparative Example 2 was thus obtained. In this Comparative Example 2, damage was observed at the top of the protrusion.

[0208] (Comparative Example 3)

[0209] In Comparative Example 3, the same filter material as Comparative Example 1 was used, and the embossing process was the same as in Example 1 except that an embossing mold was used to achieve a convexity ratio of 40%, thereby obtaining the air filter material of Comparative Example 3.

[0210] (Comparative Example 4)

[0211] In Comparative Example 4, a nonwoven fabric made of glass fiber was used, and the same roller embossing die as in Example 3 was used to emboss the nonwoven fabric, thereby obtaining the air filter material of Comparative Example 4. Furthermore, according to the measurement method with a test wind speed of 5.3 cm / s and a test particle size of 0.3 μm, the pressure loss and dust collection efficiency of the glass fiber nonwoven fabric before embossing were 275 Pa and 99.98%, respectively, with PF = 13. In Comparative Example 4, damage was confirmed at the top of the protrusion.

[0212] (Comparative Example 5)

[0213] As the FP raw material for the fluoropolymer porous membrane, which is the main trapping layer of the air filter media used in Comparative Example 5, a mixed powder consisting of a single component was used.

[0214] More specifically, the process involves mixing finely powdered polytetrafluoroethylene (PTFE) with an average molecular weight of 6.5 million (manufactured by Daikin Industries, Ltd., trade name: F106) with an extrusion aid (liquid lubricant) in a specific amount (30 parts by weight) relative to 100 parts by weight of homopolymer PTFE. The resulting mixture is then extruded using a slurry extrusion apparatus to obtain a cylindrical molded body. This cylindrical molded body is then formed into a film using a calendering roller heated to 70°C, thereby obtaining a PTFE film. The film is then passed through a hot air drying oven at 200°C to evaporate and remove the extrusion aid, resulting in a strip-shaped unburned PTFE film (unprocessed strip) with a specific average thickness of 200 μm and an average width of 170 mm. Next, the unburned PTFE film is longitudinally stretched at 300°C along its length direction (MD direction) at a stretch ratio of 10 times and a stretching speed of 29.5% / second. Next, using a continuous stretching device of the tenter frame that can be continuously clamped, the device is stretched laterally in the width direction (TD direction) at a stretching ratio of 30 times and a stretching speed (330% / second) under a specific temperature environment (290°C), and then heat-fixed at a temperature of 390°C.

[0215] Similar to Comparative Example 1, a single-sided thermally fused support layer was applied to the fluoropolymer porous membrane obtained as described above to obtain the air filter media of Comparative Example 5. Furthermore, the support layer used a spunbond nonwoven fabric with a core / sheath structure, consisting of PET as the core and PE as the sheath (average fiber diameter 24 μm, area weight 40 g / m²). 2(The thickness is 0.2 mm) (Furthermore, the capture efficiency can be considered to be 0 or approximately 0).

[0216] (Example 4)

[0217] The air filter media of Comparative Example 5 was embossed using an apparatus with a pair of roller embossing dies to give it the same shape as that of Example 1, thereby obtaining the air filter media of Example 4. The air filter media of Example 4 was embossed using an embossing die that achieved a 95% convexity ratio, similar to that of Example 1.

[0218] (Comparative Example 6)

[0219] Comparative Example 6 uses polypropylene as the filter media, and nanofiber membranes are obtained by electrospinning. Specifically, polypropylene resin (manufactured by Prattmann: S315) is melt-blended at 300°C using a twin-screw extruder, followed by electrospinning. The spinning conditions are: needle inner diameter 0.2 mm, current collector distance 6 cm, and an applied voltage of 40 kV, resulting in an average fiber diameter of 480 nm and a basis weight of 5.5 g / m². 2 Nanofiber membranes.

[0220] Similar to Comparative Example 1, a single-sided thermally fused support layer was applied to the nanofiber membrane obtained as described above to obtain the air filter material of Comparative Example 6. Furthermore, the support layer used a spunbond nonwoven fabric with a core / sheath structure, consisting of PET as the core and PE as the sheath (average fiber diameter 24 μm, area weight 40 g / m²). 2 (The thickness is 0.2 mm) (Furthermore, the capture efficiency can be considered to be 0 or approximately 0).

[0221] (Example 5)

[0222] The air filter media of Comparative Example 6 was embossed using an apparatus with a pair of roller embossing dies to give it the same shape as that of Example 1, thereby obtaining the air filter media of Example 5. The air filter media of Example 4 was embossed using an embossing die that achieved a 95% convexity ratio, similar to that of Example 1.

[0223] In addition, the physical properties measured in Examples 1-5 and Comparative Examples 1-6 are as follows.

[0224] (Protrusion ratio)

[0225] The proportion of protrusions when projecting onto the air filter media along the direction of airflow, i.e., the protrusion ratio, is calculated by the following formula.

[0226] Convex ratio (%) = (total projected area of ​​multiple convex parts when projecting the entire filter media along the direction of airflow / projected area of ​​the entire filter media when projecting the entire filter media along the direction of airflow) × 100.

[0227] (Effective filter media area ratio)

[0228] The ratio of the effective filter media area of ​​an air filter media with protrusions to the effective filter media area assuming no protrusions, i.e., the effective filter media area ratio, is calculated using the following formula. Furthermore, the effective filter media area refers to the total surface area of ​​the air filter media on its upwind side.

[0229] Effective filter media area ratio (%) = (Effective filter media area of ​​the air filter / Projected area of ​​the entire air filter media when projected along the airflow direction) × 100

[0230] (Average Prominence Ratio)

[0231] The average protrusion ratio is calculated by taking the protrusion ratios of any 100 protrusions located in adjacent positions as the average. Furthermore, as described below, the protrusion ratio is the ratio of the height of the protrusion (excluding its thickness) to its equivalent diameter. The equivalent diameter (mm) is the area (mm²) of the bottom surface of the protrusion projected in the direction of airflow. 2 The equivalent diameter (mm) is obtained by dividing four times the perimeter (mm) of the protrusion. For example, in the case where the bottom surface of the protrusion is a square, it represents the length of one side of that square.

[0232] Protrusion ratio (mm / mm) = protrusion height of convex portion (mm) / equivalent diameter of convex portion (mm)

[0233] Equivalent diameter (mm) 2 / mm)=4×area of ​​the bottom surface of the convex part (mm²) 2 ) / Circumference of the bottom surface of the convex part (mm)

[0234] (Pressure loss of air filter media at a test air velocity of 9.63 cm / s)

[0235] The test sample of the air filter media was set at 65cm. 2 The filter media holder is used, and the inlet side is pressurized using a compressor. The airflow rate is adjusted to 9.63 cm / s using a flow meter. Then, the pressure loss at this time is measured using a differential pressure gauge.

[0236] (Pressure loss of air filter media at a test air velocity of 5.3 cm / s)

[0237] The test sample of the air filter media was set at 65cm.2 The filter media holder is pressurized using a compressor, and the airflow rate is adjusted to 5.3 cm / s using a flow meter. The pressure loss at this point is then measured using a differential pressure gauge.

[0238] (Collection efficiency of air filter media for NaCl particles with a diameter of 0.075 μm)

[0239] 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 0.075 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 9.63 cm / s, and the number of particles before and after the filter material used as the test sample is determined using a particle counter (manufactured by TSI Corporation, CNC). The capture efficiency is then calculated according to the following formula.

[0240] Transmittance (%) = (CO / CI) × 100

[0241] Collection efficiency (%) = 100 - Transmission rate (%)

[0242] CO = The number of 0.075 μm NaCl particles on the downstream side of the sample.

[0243] CI = The number of 0.075 μm NaCl particles on the upstream side of the sample.

[0244] (Collection efficiency of air filter media for NaCl particles with a diameter of 0.3 μm)

[0245] 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 0.3 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, and the number of particles before and after the filter material used as the test sample is determined using a particle counter (manufactured by TSI Corporation, CNC). Then, the capture efficiency is calculated according to the following formula.

[0246] Transmittance (%) = (CO / CI) × 100

[0247] Collection efficiency (%) = 100 - Transmission rate (%)

[0248] CO = The number of 0.3 μm NaCl particles downstream of the sample.

[0249] CI = The number of 0.3 μm NaCl particles on the upstream side of the sample.

[0250] (PF value of air filter media for NaCl particles with a diameter of 0.075μm)

[0251] Based on the pressure loss of the air filter media at the test wind speed of 9.63 cm / s and the collection efficiency of the air filter media using NaCl particles with a particle size of 0.075 μm, the PF value is calculated according to the following formula.

[0252] PF value = {-log((100 - capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000)

[0253] (PF value of air filter media for NaCl particles with a diameter of 0.3μm)

[0254] Based on the pressure loss of the air filter media at the test wind speed of 5.3 cm / s and the collection efficiency of the air filter media using NaCl particles with a particle size of 0.3 μm, the PF value is calculated according to the following formula.

[0255] PF value = {-log((100 - capture efficiency (%)) / 100)} / (pressure loss (Pa) / 1000)

[0256] (Dust storage capacity of air filter media for NaCl particles with a diameter of 0.1μm)

[0257] The evaluation was conducted through a pressure loss rise test during NaCl (solid particles) permeation. Specifically, a differential pressure gauge was used to measure the pressure loss rise over time when a flow rate of 5.3 cm / s was applied to an effective filtration area of ​​50 cm². 2 The pressure loss of the sample filter material when continuously passing through air containing NaCl particles was calculated. When the pressure loss increased by 300 Pa, the weight of the NaCl particles retained in the filter material per unit area, i.e., the dust storage capacity (g / m²), was determined. Furthermore, the NaCl particles used were NaCl particles generated by a sprayer (with a median particle size of 0.1 μm), and the NaCl particle concentration was set to approximately 5 million to 7 million particles / cm³. 3 Furthermore, the dust storage capacity of the air filter media for NaCl particles with a particle size of 0.1 μm was measured only for the air filter media of Example 1, Example 3, and Comparative Example 1. The dust storage capacity of the air filter media for NaCl particles with a particle size of 0.1 μm in Example 1 was 6.8 g / m³. 2 In Example 3, it was 2.4 g / m³. 2 In Comparative Example 1, it was 2.2 g / m³. 2 .

[0258] The physical properties of the air filter media of each of Examples 1-5 and Comparative Examples 1-6 are shown below.

[0259] [Table 1]

[0260]

[0261] [Table 2]

[0262]

[0263] In particular, as shown in Tables 1 and 2 above, compared with the flat filter media Comparative Examples 1, 5, and 6, the PF values ​​of Examples 1, 4, and 5 with protrusions were better. According to the ratio of PF values ​​before and after the protrusion processing (PF value of Example 1 / PF value of Comparative Example 1 = 1.34, PF value of Example 4 / PF value of Comparative Example 5 = 1.24, PF value of Example 5 / PF value of Comparative Example 6 = 1.27), it was confirmed that the same degree of improvement was obtained.

[0264] 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.

[0265] Symbol Explanation

[0266] 1 air filter unit;

[0267] 20 air filter packs;

[0268] 25 frame;

[0269] 30 air filter media;

[0270] 31. Main trapping layer;

[0271] 32. Support layer.

[0272] Existing technical documents

[0273] Patent documents

[0274] Patent Document 1: International Publication No. 2019 / 159654

Claims

1. An air filter media comprising fluororesin, characterized in that, The air filter media has multiple protrusions that project in the direction of airflow. The projected area of ​​the plurality of protrusions when projected onto the entire filter material along the direction of the airflow is more than 50% and less than 100% of the total projected area of ​​the filter material when projected onto the entire filter material along the direction of the airflow. The ratio of the effective filter media area to the projected area of ​​the entire filter media when projected along the direction of the airflow is 110% or more. The plurality of protrusions include a plurality of first protrusions projecting upstream of the filter material in the direction of airflow and a plurality of second protrusions projecting downstream of the filter material in the direction of airflow. The total projected area of ​​the plurality of first protrusions and the plurality of second protrusions when projected onto the entire filter material along the direction of the airflow is more than 50% and less than 100% of the total projected area of ​​the filter material when projected onto the entire filter material along the direction of the airflow. The ratio of the effective filter media area to the projected area of ​​the entire filter media when projected along the direction of the airflow is 110% or more. The plurality of protrusions are extended forming portions obtained by extrusion in the direction of the airflow. The air filter media is obtained by processing a flat filter media by extruding it in the thickness direction to form a plurality of elongated sections. The ratio of the PF value of the filter material having multiple extended molding portions to the PF value of the flat filter material, i.e., the PF value ratio (PF value after processing / PF value before processing), is 1.1 or higher. The PF value is obtained based on the collection efficiency of dust particles with a diameter of 0.3 μm when the airflow velocity is set to 5.3 cm / s and the pressure loss at this time. The air filter media does not have a collapsed portion of less than 30% of its average thickness, or the area ratio of the collapsed portion when viewed along the direction of airflow is less than 1%.

2. The air filter media according to claim 1, characterized in that, The PF value obtained based on the dust collection efficiency at an airflow velocity of 9.63 cm / s and a particle size of 0.075 μm, along with the pressure loss at that time, is above 10.

2.

3. The air filter media according to claim 1 or 2, characterized in that, The average protrusion ratio of the plurality of protrusions in the direction of airflow is 0.10 or more and 0.85 or less.

4. The air filter media according to claim 1 or 2, characterized in that, The fluoropolymer contains polytetrafluoroethylene, which is capable of being fibrous. The PF value is above 39, based on the collection efficiency of dust particles with a flow rate of 5.3 cm / s and a particle size of 0.3 μm, and the pressure loss at that time.

5. The air filter media according to claim 1 or 2, characterized in that, The fluororesin comprises fibrous polytetrafluoroethylene, a non-fibrous, non-thermally melt-processable component, and a non-fibrous, thermomeltable component with a melting point below 320°C. The PF value is above 38, based on the dust collection efficiency at an airflow velocity of 5.3 cm / s and a particle size of 0.3 μm, and the pressure loss at that time.

6. The air filter media according to claim 1 or 2, characterized in that, The multiple protrusions exist in a dot-like pattern.

7. The air filter media according to claim 6, characterized in that, The first protrusion is surrounded by three or more second protrusions. The second protrusion is surrounded by three or more of the first protrusions.

8. The air filter media according to claim 1 or 2, characterized in that, Both the first protrusions and the second protrusions are strip-shaped. The first protrusion and the second protrusion are arranged alternately.

9. The air filter media according to claim 1 or 2, characterized in that, The first protrusion and the second protrusion are connected.

10. An air filter bag, characterized in that, The air filter package includes the air filter media as described in claim 1 or 2. The air filter media is processed into a serrated shape by repeatedly alternating outward and inward folds, and the plurality of protrusions maintain the spacing between the opposing portions of the air filter media.

11. An air filter unit, characterized in that, include: The air filter pack of claim 10; as well as A frame that holds the air filter package.

Images