Method for manufacturing air filter media and method for manufacturing air filter products

Abstract

Provided are an air filter filtration material and air filter product for which it is possible to extend the life thereof. The air filter filtration material comprises a filtration material layer containing first fibers having a mean fiber diameter of between 5 μm and 50 μm inclusive and second fibers interposed in gaps in-between the first fibers and having a mean fiber diameter of between 30 nm and 1 μm.

Description

[Technical field]

[0001] The present disclosure relates to an air filter medium. Manufacturing method and air filter products Manufacturing method Regarding. [Background technology]

[0002] Air filters are classified into ULPA (Ultra Low Penetration Air) filters, HEPA (High Efficiency Particulate Air) filters, and medium-performance filters based on their efficiency in capturing particles of a certain diameter. These filters are used for different purposes depending on their performance.

[0003] As an example of such air filters, Patent Document 1 (JP 2017-35684 A) proposes an air filter that uses a filter material that is a mixture of fibers with a small fiber diameter and fibers with a large fiber diameter, thereby suppressing clogging and extending the life of the filter. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] There is a demand for air filters with even longer life. [Means for solving the problem]

[0005] The air filter medium according to a first aspect includes a filter layer. The filter layer includes first fibers and second fibers. The first fibers have an average fiber diameter of 5 μm or more and 50 μm or less. The second fibers are interposed in the gaps between the first fibers and have an average fiber diameter of 30 nm or more and 1 μm or less.

[0006] The average fiber diameter of the first fibers can be specified as the average outer diameter of the fibers mainly composed of portions having a fiber diameter of 5 μm or more, and the average fiber diameter of the second fibers can be specified as the average outer diameter of the fibers mainly composed of portions having a fiber diameter of less than 5 μm.

[0007] This air filter medium can have a long life until a predetermined increase in pressure loss is observed.

[0008] The lifespan here can be defined as, for example, the time when the pressure loss when air is passed through the filter at a flow rate of 5.3 cm / sec increases by 50 Pa from the time of initial use.

[0009] The air filter medium according to the second aspect is the air filter medium according to the first aspect, and the first fiber is a fiber obtained by opening a tow band. The tow band is opened by applying tension. The tow band is obtained by crimping a tow in which a plurality of filaments are united.

[0010] The tow is, for example, a fiber bundle formed by assembling a large number of spun yarns, and may be in the form of a sheet.

[0011] The number of crimps may be 25 to 60 crimps per 25 mm in the longitudinal direction, and preferably 30 to 40 crimps per 25 mm in the longitudinal direction.

[0012] This air filter medium uses the first fibers obtained by opening the crimped tow band, so that the gaps between the first fibers are easily secured, and therefore it is possible for a larger portion of the second fibers to be sufficiently inserted into the gaps between the first fibers.

[0013] For example, by attaching a material that produces the second fibers to the tow band before it is opened, and then simultaneously producing the second fibers when the tow band is opened to produce the first fibers, the second fibers can be sufficiently attached to the first fibers to stabilize the integrated state of the two, and more of the second fibers can be interposed between the first fibers. This makes it possible to improve the homogeneity of the composite membrane in which the first fibers and the second fibers are sufficiently mixed.

[0014] An air filter medium according to a third aspect is the air filter medium according to the first or second aspect, wherein the first fibers are one or more types selected from the group consisting of cellulose acetate, rayon, polypropylene, polyethylene terephthalate, and polyethylene.

[0015] The cellulose acetate may be cellulose diacetate, cellulose triacetate, or a mixture thereof.

[0016] This air filter medium can have relatively thick fibers as the first fibers.

[0017] An air filter medium according to a fourth aspect is the air filter medium according to any one of the first aspect to the third aspect, wherein the second fibers are a stretched fiber-forming polymer.

[0018] As the fiber-forming polymer, for example, one or more types selected from the group consisting of fluororesin, polypropylene, polyethylene, and polyamide can be used.

[0019] This air filter medium can provide relatively fine fibers as the second fibers.

[0020] An air filter medium according to a fifth aspect is the air filter medium according to the fourth aspect, wherein the fiber-forming polymer includes a fluororesin.

[0021] Examples of the fluororesin include modified polytetrafluoroethylene, homopolytetrafluoroethylene, and mixtures thereof.

[0022] This air filter medium enables the chemical resistance and heat resistance of the second fibers to be increased.

[0023] An air filter medium according to a sixth aspect is the air filter medium according to any one of the first to fifth aspects, in which the filter medium layer contains resin granules having the same composition as the second fibers, and the ratio W1 / W2 of the weight W1 of the first fibers to the combined weight W2 of the second fibers and the resin granules is 3.0 or more and 18.0 or less.

[0024] In this air filter medium, by fully utilizing the functions of both the first fibers and the second fibers, it is possible to increase the collection efficiency and extend the lifespan of the air filter medium.

[0025] An air filter medium according to a seventh aspect is the air filter medium according to any one of the first to fifth aspects, wherein the filter medium layer contains resin granules having the same composition as the second fibers, and the ratio V1 / V2 of the volume V1 of the first fibers to the combined volume V2 of the second fibers and the resin granules is 1.9 or more and 124.0 or less.

[0026] Furthermore, it is preferable that the ratio W1 / W2 of the weight W1 of the first fibers to the combined weight W2 of the second fibers and the resin granules is 3.0 or more and 18.0 or less, and that the ratio V1 / V2 of the volume V1 of the first fibers to the combined volume V2 of the second fibers and the resin granules is 1.9 or more and 124.0 or less.

[0027] In this air filter medium, it is possible to achieve a good balance between the function of the first fibers to ensure space for capturing dust and the function of the second fibers to efficiently capture dust.

[0028] An air filter medium according to an eighth aspect is the air filter medium according to any one of the first aspect to the seventh aspect, wherein the thickness of the filter medium layer is 3 mm or more.

[0029] The thickness of the filter layer is more preferably 4 mm or more. Also, the thickness of the filter layer is, for example, 10 mm or less, and preferably 7 mm or less.

[0030] This air filter medium is capable of capturing a large amount of dust within the range of its thickness.

[0031] An air filter medium according to a ninth aspect is the air filter medium according to any one of the first to eighth aspects, wherein the filter medium layer has a pressure loss of 35 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec.

[0032] The filter layer may have a pressure loss of, for example, 3 Pa or more when air is passed through it at a flow rate of 5.3 cm / sec.

[0033] This air filter medium can reduce pressure loss and extend the life of the air filter.

[0034] An air filter medium according to a tenth aspect is the air filter medium according to any one of the first aspect to the ninth aspect, wherein the filter medium layer has a collection efficiency of 35% or more for NaCl having a particle diameter of 0.4 μm.

[0035] The filter layer preferably has a collection efficiency for NaCl having a particle diameter of 0.4 μm of 40% or more, and more preferably 43% or more.

[0036] The filter layer may have a collection efficiency for NaCl having a particle diameter of 0.4 μm of, for example, 99% or less, 90% or less, or 80% or less.

[0037] This air filter medium can ensure sufficient collection efficiency and extend the life of the air filter.

[0038] An air filter medium according to an eleventh aspect is the air filter medium according to any one of the first to tenth aspects, wherein the filter medium layer has a PF value, determined by the following formula: PF value={-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000), of 16 or more.

[0039] This air filter medium can produce an air filter with a good PF value and a long service life.

[0040] An air filter medium according to a twelfth aspect is the air filter medium according to any one of the first to eleventh aspects, wherein the filter medium layer has a dust amount of NaCl particles of 18 g / m when air containing NaCl having a particle diameter of 0.4 μm is continuously passed through the filter medium at a flow rate of 5.3 cm / sec and the pressure loss increases by 50 Pa. 2 That's all.

[0041] This air filter medium can achieve a sufficiently long service life.

[0042] An air filter product according to a thirteenth aspect is obtained by forming the air filter medium according to any one of the first to twelfth aspects into a bag shape.

[0043] This air filter product is bag-shaped and can be folded up into a small size. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of an air filter medium. [Diagram 2] FIG. 1 is a schematic diagram showing an embodiment of an air filter medium. [Diagram 3] 1 is an external perspective view showing an embodiment of an air filter product. [Figure 4] FIG. 1 is a schematic diagram of a tow band manufacturing apparatus according to one embodiment. [Diagram 5] 1 is a schematic diagram of a filter medium manufacturing apparatus according to one embodiment. [Figure 6] FIG. 1 is a schematic diagram of another example of a tow band manufacturing apparatus according to an embodiment. [Figure 7] 2 is a SEM photograph of the filter medium according to Example 1. [Figure 8] 2 is a SEM photograph of a filter medium according to Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Hereinafter, the air filter medium and the air filter product will be specifically described with reference to examples.

[0046] (1) Air filter media The air filter medium has a filter layer.

[0047] The air filter medium may be configured to have one sheet-like filter medium layer, or may be configured to have multiple filter medium layers overlapping in the airflow direction.

[0048] The air filter medium may be, for example, an air filter medium 80 configured by laminating or bonding a filter medium layer 65 and an air-permeable support material 70 as shown in Fig. 1. The air-permeable support material 70 may be disposed on the windward side of the filter medium layer 65, on the leeward side, or on both sides.

[0049] Preferred examples of such breathable support materials 70 include polyethylene terephthalate (PET) fiber nonwoven fabric, polybutylene terephthalate (PBT) fiber nonwoven fabric, core-sheath nonwoven fabric with a core component of PET and a sheath component of polyethylene (PE) (PET / PE core / sheath nonwoven fabric), core-sheath nonwoven fabric with a core component of PET and a sheath component of PBT (PET / PBT core / sheath nonwoven fabric), core-sheath nonwoven fabric with a core component of high melting point PET and a sheath component of low melting point PET (high melting point PET / low melting point PET core / sheath nonwoven fabric), nonwoven fabric made of composite fibers of PET fibers and PBT fibers, and nonwoven fabric made of composite fibers of high melting point PET fibers and low melting point PET fibers, and among these, those having heat-sealing properties are preferred.

[0050] The basis weight of the nonwoven fabric used in the breathable support material 70 is not particularly limited, but can be, for example, 15 g / m2 or more and 100 g / m2 or less. The thickness of the nonwoven fabric used in the breathable support material 70 may be preferably 0.1 mm or more and 1.0 mm or less. The pressure loss of the breathable support material 70 when air is passed through it at a flow rate of 5.3 cm / sec is smaller than that of the filter layer, and is preferably 10 Pa or less, and more preferably substantially 0.

[0051] 2, the air filter medium may be an air filter medium 80a provided with a pre-collection layer 69 for reducing the dust collection load in the filter medium layer 65 on the windward side of the filter medium layer 65. Here, the air filter medium 80a may also be provided with the breathable support material 70 as described above.

[0052] As the pre-collection layer 69, for example, at least one or two or more of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), and polyurethane (PU) can be used. The pre-collection layer 69 may be obtained by a melt-blown method. It is preferable that the pre-collection layer 69 has a pressure loss smaller than that of the filter layer 65 and larger than that of the breathable support material 70 when air is passed through it at a flow rate of 5.3 cm / sec. In addition, it is preferable that the pre-collection layer 69 has a collection efficiency of NaCl having a particle diameter of 0.4 μm smaller than that of the filter layer 65 and larger than that of the breathable support material 70.

[0053] (1-1) Filter medium layer The filter layer includes first fibers having an average fiber diameter of 5 μm or more and 50 μm or less, and second fibers interposed in gaps between the first fibers and having an average fiber diameter of 30 nm or more and 1 μm or less.

[0054] The first fibers and the second fibers are preferably present so that the second fibers are intercalated between the first fibers, and preferably form a composite membrane in which the first fibers and the second fibers are entangled so as not to be separated from each other.

[0055] The average fiber diameters of the first and second fibers can be evaluated based on fibers present within a predetermined range of an image observed using a microscope or the like.

[0056] The thickness of the filter layer is preferably 3mm or more, more preferably 4mm or more, from the viewpoint of capturing more dust within the range of thickness and extending the life span.In addition, the thickness of the filter layer is, for example, 10mm or less, preferably 7mm or less, from the viewpoint of preventing the first fiber from being excessively thick and being unable to position a sufficient number of the second fibers between the first fibers.

[0057] The basis weight of the filter layer is, for example, 100 g / m 2 More than 400g / m 2 and 170 g / m 2 More than 230g / m 2 It is preferable that:

[0058] The pressure loss of the filter layer when air passes through it at a flow rate of 5.3 cm / sec may be 35 Pa or less, preferably 30 Pa or less, more preferably 25 Pa or less. The pressure loss of the filter layer when air passes through it at a flow rate of 5.3 cm / sec may be, for example, 3 Pa or more, 5 Pa or more, 10 Pa or more, or 15 Pa or more.

[0059] The filter layer may have a collection efficiency of 35% or more, preferably 40% or more, more preferably 43% or more for NaCl with a particle diameter of 0.4 μm. Also, the filter layer may have a collection efficiency of 99% or less, 90% or less, or 80% or less for NaCl with a particle diameter of 0.4 μm.

[0060] The filter layer preferably has a PF value of 16 or more, more preferably 19 or more, as determined by the following formula: PF value={-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0061] When air containing NaCl particles of 0.4 μm in diameter is continuously passed through the filter layer at a flow rate of 5.3 cm / sec, the amount of NaCl particles retained is 18 g / m when the pressure loss increases by 50 Pa. 2It is preferable that the thickness is 20 g / m or more. 2 This makes it possible to sufficiently extend the life of the air filter medium.

[0062] (1-2) First Fiber The first fibers have an average fiber diameter of 5 μm or more and 50 μm or less, preferably 8 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less. By ensuring that the thickness of the first fibers is 5 μm or more, it is possible to make the first fibers function as a stable skeleton in the air filter medium, and to suppress deformation of the filter medium even when exposed to airflow during use. In addition, even if the thickness of the filter medium layer is increased, it is possible to suppress pressure loss to a low level. On the other hand, by making the thickness of the first fibers 50 μm or less, it is possible to suppress leakage of dust collection caused by the gap between the first fibers becoming too large.

[0063] The first fibers preferably mainly contain one or more selected from the group consisting of cellulose acetate, rayon, polypropylene (PP), polyethylene terephthalate (PET), and polyethylene (PE). Among them, cellulose acetate is preferable as the first fibers from the viewpoints of suppressing an increase in fiber diameter due to moisture absorption due to low hygroscopicity, suppressing mold growth, suppressing deterioration in a high temperature environment, and achieving high damage resistance. The cellulose acetate may be cellulose diacetate, cellulose triacetate, or a mixture thereof. This first fiber has a relatively large fiber diameter, and can more stably secure a wide space between the first fibers.

[0064] The first fiber may be, for example, a fiber obtained by a melt blowing method, a fiber obtained by an electrospinning method, a fiber obtained by an island-in-sea method, or a fiber obtained by opening a tow band. The tow band is obtained by crimping a tow formed by combining a plurality of filaments, which are the first fiber. The tow is, for example, a fiber bundle formed by assembling a large number of spun yarns, and may be in the form of a sheet. The fiber diameter and cross-sectional shape of the above-mentioned first fiber can be appropriately adjusted, for example, by changing the peripheral shape of the spinning hole at the stage of spinning the first fiber 2 by a dry spinning method. The opening of the tow band can be performed by applying tension to the tow band in the longitudinal direction. The tow band can be changed to a bulky form by opening the fibers, moving the arrangement of the crimped fibers, and reducing the overlap of the peaks and valleys. In addition, by using the first fibers obtained by opening a crimped tow band as the air filter medium, gaps between the first fibers are easily secured, and a larger portion of the second fibers can be sufficiently inserted into the gaps between the first fibers, and a large space capable of holding dust is secured, thereby suppressing clogging and extending the service life.

[0065] The number of crimps in the tow band can be, for example, 25 to 60 crimps per 25 mm in the longitudinal direction, and preferably 30 to 40 crimps per 25 mm in the longitudinal direction.

[0066] As described later, the air filter medium may be, for example, an air filter medium obtained by attaching a material that produces the second fiber to the tow band before opening so that it is dotted, and simultaneously generating the second fiber when the first fiber is generated by opening the tow band. This makes it possible to sufficiently attach the second fiber to the first fiber to stabilize the integrated state of both, while allowing more of the second fiber to be interposed between the first fibers. Therefore, it is possible to obtain a composite membrane in which the first fiber and the second fiber are homogeneously mixed. In addition, when the first fiber is generated by opening the tow band and the second fiber is also generated at the same time to obtain a filter layer, it is preferable to apply an aqueous dispersion in which a resin granular material that is the source of the second fiber is dispersed in water to the tow band, thereby attaching the resin granular material that is the source of the second fiber to the tow band. In this case, it is preferable that the tow band has a small contact angle θ1 of water immediately after water droplets are dropped on the surface of the tow band in order to increase the affinity of the aqueous dispersion to the tow band. In addition, it is preferable to open the tow band while it is attached with either or both of an oil emulsion containing a fiber oil and water used in spinning and water used in crimping.

[0067] (1-3) Second fiber The second fibers are fibers interposed between the first fibers and have an average fiber diameter of 30 nm to 1 μm. From the viewpoint of being able to efficiently capture dust by being positioned between the first fibers, the average fiber diameter of the second fibers is preferably 40 nm to 500 nm, more preferably 70 nm to 150 nm.

[0068] The second fibers are preferably heat-resistant and chemical-resistant like the first fibers. The second fibers preferably contain one or more fiber-forming polymers selected from the group consisting of fluororesin, polypropylene, polyethylene, and polyamide. In particular, the second fibers preferably contain fluororesin, and more preferably contain 50 wt% or more of fluororesin, because they are excellent in heat resistance and chemical resistance and can easily produce sufficiently fine fibers.

[0069] Examples of fluororesins include modified polytetrafluoroethylene, homopolytetrafluoroethylene, and mixtures thereof. Modified polytetrafluoroethylene (modified PTFE) is polymerized using tetrafluoroethylene (TFE) and a monomer (modified monomer) other than TFE. The modified PTFE may be one that is uniformly modified with the modified monomer, or may be a mixture obtained by adding the modified monomer at the beginning or end of the polymerization reaction. The modified monomer is not particularly limited as long as it can be copolymerized with TFE, and for example, a fluorine-containing monomer having an ethylenically unsaturated group can be used. Examples of fluorine-containing monomers having an ethylenically unsaturated group include hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), chlorotrifluoroethylene (CTFE), (perfluoromethyl)ethylene, (perfluorobutyl)ethylene, perfluorobutene-1, perfluorohexene-1, and perfluorononene-1. Examples of the PAVE include perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propyl vinyl ether) (PPVE). The monomer other than TFE may be used alone or in combination of two or more. The total amount of repeating units based on the monomer other than TFE is preferably 1% by mass or less, more preferably 0.5% by mass or less, of the total amount of repeating units based on all monomers forming polytetrafluoroethylene.

[0070] Polytetrafluoroethylene can be obtained, for example, by emulsion polymerization in which TFE or TFE and other modified monomers are polymerized in an aqueous medium containing a dispersant and a polymerization initiator, or by suspension polymerization. Polytetrafluoroethylene may be a component of fine powder obtained by emulsion polymerization. Fine powder can be obtained by recovering polytetrafluoroethylene fine particles from the polytetrafluoroethylene aqueous dispersion obtained by the above-mentioned emulsion polymerization, coagulating them, and then drying them. The fine powder preferably has an average particle size of 100 to 1000 μm, more preferably 400 to 600 μm. The average particle size here can be measured in accordance with ASTM D 1457.

[0071] Fine powder made of polytetrafluoroethylene has good extrusion processability and can be paste-extruded at an extrusion pressure of, for example, 20 MPa or less. The extrusion pressure is measured when paste-extrusion is performed through an orifice (diameter 2.5 cm, land length 1.1 cm, introduction angle 30°) under the conditions of a reduction ratio of 100, an extrusion speed of 51 cm / min, and a temperature of 25°C.

[0072] The above-mentioned fine powder made of polytetrafluoroethylene can be paste-extruded, rolled, and then stretched to produce fibers.

[0073] In addition, polytetrafluoroethylene is preferably one that is easily fibrous during the production of the filter layer, has a molecular weight that allows long fibrils to be obtained, has a standard specific gravity (SSG) of 2.130 or more and 2.230 or less, and has a high melt viscosity so that it does not melt and flow substantially.In addition, for such polytetrafluoroethylene, for example, the one described in International Publication No. 2013 / 157647 can be referred to.In addition, the standard specific gravity (SSG) can be measured by the water displacement method according to ASTM D-792 using a sample molded according to ASTM D4895-89.

[0074] The second fiber may be, for example, one obtained as a drawn fiber-forming polymer, a fiber obtained by a melt-blowing method, a fiber obtained by an electrospinning method, or a fiber obtained by a sea-island method.

[0075] When the second fiber is obtained as a stretched fiber-forming polymer, the second fiber can be obtained by stretching fiberizable polymer particles. Such fiberizable polymer particles are preferably polymers having a lamellar structure in which polymer chains are connected and folded, and are preferably polymers that can be paste extrusion molded. For example, the second fiber obtained by stretching the fiberizable polymer particles can be present together with the resin granules as fibers extending from the resin granules having the same structure as the second fiber.

[0076] When the second fibers are obtained by the melt-blowing method, a number of nozzles having a predetermined hole diameter are used, and the molten polymer discharged from each nozzle is spun in a high-temperature jet stream to obtain the second fibers. Here, the diameter of the obtained fibers can be changed by adjusting the production conditions of the melt-blowing method, such as the polymer discharge temperature, discharge amount, and air amount, and fibers with a relatively small fiber diameter can be obtained by increasing the polymer discharge temperature, decreasing the discharge amount, and increasing the air amount. It is also possible to obtain a composite membrane in which the first fibers and the second fibers are mixed by simultaneously producing the second fibers by the melt-blowing method and producing the first fibers by the melt-blowing method.

[0077] (1-4) Relationship between the first and second fibers In the case where the filter layer contains resin granules having the same composition as the second fibers, the ratio W1 / W2 of the weight W1 of the first fibers in the filter layer to the combined weight W2 of the second fibers and the resin granules is preferably 3.0 or more and 18.0 or less. This allows the functions of both the first fibers and the second fibers to be fully exerted, thereby increasing the collection efficiency and extending the lifespan.

[0078] In addition, when the filter layer contains resin granules having the same composition as the second fibers, the ratio V1 / V2 of the volume V1 of the first fibers in the filter layer to the combined volume V2 of the second fibers and the resin granules is preferably 1.9 or more and 124.0 or less. This makes it possible to achieve a good balance between the function of the first fibers to secure a space for capturing dust and the function of the second fibers to efficiently capture dust.

[0079] The lower limit of the ratio D1 / D2 of the outer diameter D1 of the first fibers to the outer diameter D2 of the second fibers may be, for example, 15.0, and preferably 60.0. The upper limit of the ratio D1 / D2 may be, for example, 1666.7, and preferably 1300.0, more preferably 714.3, and even more preferably 300.0. This makes it possible to ensure a sufficient space for capturing dust while suppressing the second fibers from falling off from the first fibers.

[0080] (2) Air filter products 20 FIG. 3 shows an external perspective view of an air filter product 100 according to one embodiment.

[0081] The air filter product 100 is constructed by folding air filter media 80 into bag-shaped pocket bodies 85, arranging the pocket bodies 85 with their inlets connected to each other, and fixing them to a frame body 90.

[0082] The air filter product 100 is known as a pocket filter, and since only the frame body 90 portion is made of a highly rigid material and each pocket body 85 can be folded, it can be made compact for easy transportation and storage.

[0083] The pocket body 85 is formed into a bag shape by joining the opposing filter medium portions folded back at the downstream end at the upper end and the lower end by sewing, heat fusion, adhesive, etc. Adjacent pocket bodies 85 are joined at the inlet portions by sewing, heat fusion, adhesive, etc.

[0084] A sealant may be used to seal between each pocket 85 and the frame 90. Examples of such sealants include resins such as epoxy, acrylic, and urethane.

[0085] (3) Manufacturing method Hereinafter, an example of a method for manufacturing a filter layer having a first fiber and a second fiber will be described with reference to the drawings. In the following, "upstream" and "downstream" may refer to the upstream and downstream in the conveying direction P of the tow band 64, respectively.

[0086] FIG. 4 shows an overall view of the tow band manufacturing apparatus 1. The tow band manufacturing apparatus 1 spins a filament 61, which is a first fiber, by a dry spinning method. The tow band manufacturing apparatus 1 also produces a yarn 62, an end 63, and a tow band 64 from a plurality of filaments 61. The filament 61 can be made of the material described above for the first fiber.

[0087] The tow band manufacturing apparatus 1 includes a mixing device 2, a filtration device 3, a spinning unit 4, an oil application unit 5, a godet roll 6, a guide pin 7, an application device 8, a first drying device 9, a winding device 10, and a second drying device 11.

[0088] In the tow band manufacturing apparatus 1, for example, a spinning stock solution 60 in which flakes such as cellulose diacetate are dissolved in an organic solvent at a predetermined concentration can be used. In the tow band manufacturing apparatus 1, the spinning stock solution 60 mixed by the mixer 2 and filtered by the filter 3 is discharged from a plurality of spinning holes 15a of the spinneret 15 provided on the spinning tube 14 of the spinning unit 4. The spinning holes 15a can have a predetermined shape such as a circular peripheral shape. By changing the diameter of the spinning holes 15a, the single fineness (FD) of the filament 61, which is the first fiber to be manufactured, can be adjusted. The spinning stock solution 60 discharged from each spinning hole 15a is exposed to hot air to evaporate the organic solvent, thereby obtaining a solid filament 61.

[0089] A plurality of filaments 61 that have passed through one spinning tube 14 are gathered by a guide pin 7 to become a yarn 62. The yarn 62 is applied with a fiber oil by an oil application unit 5 in order to suppress static electricity, and then taken up by a godet roll 6.

[0090] The spinning unit 4, the drying unit, the oil application unit 5, and the winding unit that manufacture the yarn 62 are collectively referred to as a station. The yarns 62 that have passed through each station are transported along the arrangement direction of the stations and are sequentially accumulated or stacked. As a result, the yarns 62 are converged to form an end (tow) 63 that is a flat aggregate of the yarns 62. The end 63 is formed by converging the yarns 62 to a predetermined total fineness (TD). The end 63 is transported and guided to the application device 8. The spinning method of the filament 61 is not limited, and may be a method other than a dry spinning method (for example, a melt spinning method or a wet spinning method).

[0091] The attachment device 8 conveys a plurality of first fibers (here, ends 63) while attaching a dispersion liquid containing resin granules that will be the source of the second fibers to the filaments 61 via an attachment roll (not shown). The dispersion liquid may contain a liquid other than water, but is preferably an aqueous dispersion liquid in which a plurality of resin granules are dispersed in water. The resin granules are preferably made of the material described above for the second fibers.

[0092] The resin granules are primary particles, and secondary particles are formed by bonding multiple resin granules to each other. When an external force is applied to these secondary particles (in other words, two bonded resin granules) so that the resin granules are separated from each other, fine fibers are pulled out from within the resin granules, and the resin granules form second fibers, i.e., resin fibers. The dispersion preferably contains primary particles made of multiple resin granules dispersed in a solvent. The attachment device 8 attaches the dispersion to the filament 61, so that multiple resin granules are dispersed and attached to the surface of the filament 61. The average particle diameter of the resin granules is, for example, 100 nm or more and 600 nm or less, and preferably 250 nm or more and 350 nm or less. The average particle diameter refers to the median diameter (cumulative 50% diameter (D50)) calculated from the measurement results by the dynamic light scattering method. The resin granules are preferably obtained by extrusion molding.

[0093] The first drying device 9 dries at least a part of the dispersion liquid applied to the filaments 61. By adjusting the degree of this drying, it is possible to reduce the amount of resin particles falling off from the filaments 61 and to easily adjust the weight ratio of the filaments 61 to the resin fibers.

[0094] The crimping device 10 crimps the filaments 61. The crimping device 10 has a pair of nip rolls N1, N2 and a stuffing box 18. The pair of nip rolls N1, N2 are arranged with their rotation axes parallel to each other, and press the ends 63 between their circumferential surfaces.

[0095] The stuffing box 18 is disposed downstream of the pair of nip rolls N1, N2, and includes a pair of plate materials C1, C2 having plate surfaces extending in the conveying direction P, and a biasing member 12. The pair of plate materials C1, C2 are disposed such that their plate surfaces face each other with a gap G therebetween and the gap G decreases from the upstream side to the downstream side. Into this gap G, the ends 63 (multiple filaments 61) that have passed through the pair of nip rolls N1, N2 are conveyed.

[0096] The urging member 12 is, for example, a plate material and extends along the plate surface of the plate material C1 in a direction perpendicular to the conveying direction P. The urging member 12 is pivotally supported by the plate material C1 at an upstream end in the conveying direction P so as to be rotatable about an axis Q extending in a direction perpendicular to the conveying direction P along the plate surface of the plate material C1. The urging member 12 is urged toward the plate surface of the plate material C2, and presses an end 63 conveyed between the pair of plate materials C1, C2.

[0097] The end 63 is pressed by the pair of nip rolls N1, N2 between the pair of nip rolls N1, N2, and then pushed into the stuffing box 18. The end 63 is pressed against the plate surface of the plate material C2 by the biasing member 12 while being conveyed in a serpentine manner between the plate surfaces of the plate materials C1, C2. The end 63 is pressed into the stuffing box 18 by the pair of nip rolls N1, N2 with a force greater than the force that the end 63 receives from the plate materials C1, C2 and the biasing member 12, so that the end 63 is crimped. The end 63 passes through the crimping device 10 to form a tow band 64. In addition, the multiple resin granules are bonded to each other by being pressurized in the crimping device 10, and secondary particles of the resin granules are formed.

[0098] In the crimping device 10, the degree of crimping, such as the number of crimps, of the filament 61 can be adjusted by adjusting the nip pressure of the pair of nip rolls N1 and N2, thereby reducing the amount of dispersion that falls off from the filament 61. The tow band 64 that has passed through the crimping device 10 is further dried by the second drying device 11. By applying a dispersion of resin granules to the filament 61 in a smooth state before crimping, the resin granules can be uniformly arranged on the filament 61 compared to the case where the dispersion is applied to the uneven portion after crimping.

[0099] The tow band 64 obtained as described above has a plurality of crimped filaments 61 and a plurality of resin granules dispersed inside the tow band 64 and supported by the filaments 61 and bonded to each other. By using the crimped filaments 61, the tow band 64 can be made bulky.

[0100] The FD of the tow band 64 can be, for example, 1.0 or more and 10.0 or less, and is preferably 2.0 or more and 6.0 or less from the viewpoint of properly securing the fiber gap while maintaining the moderate strength of the filament 61. The tow band 64 that has passed through the second drying device 11 is compressed and packed in a packing container 19 after being accumulated and formed into a bale shape.

[0101] 5 shows an overall view of a filter medium manufacturing apparatus 20 according to one embodiment. The filter medium manufacturing apparatus 20 includes, for example, a converging ring 21, a first opening unit 22, a turn baffle 23, a second opening unit 24, a pair of pretension rolls 25, a first opening roll pair 26, a second opening roll pair 27, a third opening unit 28, a pair of transport rolls 29, and a winding roll 30.

[0102] The converging ring 21 and the turn baffle 23 guide the bale-shaped tow band 64 raised from the packing container 19 from the upstream side to the downstream side. The first opening unit 22, the second opening unit 24, and the third opening unit 28 open the tow band 64 in its width direction by gas such as pressurized air. The pretension roll pair 25, the first opening roll pair 26, and the second opening roll pair 27 open the tow band 64 in the width direction and the conveying direction P while applying tension to the tow band 64 in the conveying direction P.

[0103] The pretension roll pair 25 has a pair of rolls R1, R2 arranged with their circumferential surfaces facing each other. The first opening roll pair 26 has a pair of rolls R3, R4 arranged with their circumferential surfaces facing each other. The second opening roll pair 27 has a pair of rolls R5, R6 arranged with their circumferential surfaces facing each other. The conveying roll pair 29 has a pair of rolls R7, R8 arranged with their circumferential surfaces facing each other. The conveying roll pair 29 conveys the tow band 64 that has passed through the second opening roll pair 27 to the downstream side. The winding roll 30 winds up the tow band 64 that has passed through the conveying roll pair 29.

[0104] When the filter medium manufacturing apparatus 20 is driven, the tow band 64 raised from the packing container 19 is inserted into the converging ring 21 and then spread in the width direction by the first spreading unit 22. The tow band 64 is then guided downstream by the turn baffle 23.

[0105] Next, the tow band 64 is further spread in the width direction by the second spreading unit 24, and then inserted between the rolls R1 and R2, between the rolls R3 and R4, and between the rolls R5 and R6 in order. The tow band 64 contacts the rolls R1 to R6. The rotation speed of the pair of rolls R5 and R6 is faster than the rotation speed of the pair of rolls R3 and R4. As a result, the tow band 64 is spread in the conveying direction P and the width direction by the first spreading roll pair 26 and the second spreading roll pair 27 while being given tension in the conveying direction P.

[0106] The tow band 64 is opened in the conveying direction P (left and right direction of the paper) and the width direction (perpendicular to the paper) by the roll pair 26, 27, so that tension acts on the filaments 61 and the resin granules in the conveying direction P and the width direction. As a result, the filaments 61 in the tow band 64 are opened to obtain a plurality of first fibers. At this time, tension (stretching force) acts on the resin granules so as to separate the bonded resin granules from each other, so that fine second fibers are drawn out from the resin granules. As a result, the tow band 64 becomes a fiber composite including a plurality of first fibers which are filaments 61 and a plurality of second fibers which are fine resin fibers.

[0107] The fiber diameter of the second fiber can be adjusted, for example, by the tension applied to the tow band 64 when the tow band 64 is opened. For example, by increasing the tension, the fiber diameter of the second fiber can be reduced and the length dimension of the second fiber can be increased. On the other hand, by reducing the tension applied to the tow band 64, the fiber diameter of the second fiber can be increased and the length dimension of the second fiber can be reduced.

[0108] The tow band 64 (fiber composite) that has passed between the second opening roll pair 27 is inserted between the rolls R7 and R8 of the transport roll pair 29. The rotation speed of the pair of rolls R7 and R8 is slower than the rotation speed of the pair of rolls R5 and R6. As a result, the tension acting on the tow band 64 in the transport direction P between the first opening roll pair 26 and the second opening roll pair 27 is relieved between the second opening roll pair 27 and the transport roll pair 29. This relief of tension adjusts the tow band 64 to a bulky state.

[0109] The tow band 64 that has passed through the conveying roll pair 29 is wound up on the winding roll 30. The tow band 64 is cut to a predetermined length to produce an air filter medium having a filter layer 65.

[0110] In addition, as the tow band manufacturing apparatus, for example, a tow band manufacturing apparatus 101 as shown in FIG. 6 may be used. This tow band manufacturing apparatus 101 omits the attachment device 8 and the first drying device 9, and instead includes a granular material adding device (feeder) 16. The granular material adding device 16 is arranged so that the resin granular material can be added to the filament 61 in powder form upstream of the crimping device 10 (here, downstream of the godet roll 6 and upstream of the crimping device 10). From the viewpoint of favorably attaching the resin granular material to the surface of the filament 61 and suppressing charging, it is preferable that water or a fiber oil is attached to the filament 61 introduced into the crimping device 10.

[0111] The method for producing the filter layer having the first and second fibers is not limited to the above-mentioned method, and for example, the filter layer may be obtained by applying a granular material of a polymer capable of being fiberized, which is the material of the second fiber, to a tow band, opening the obtained composite, cutting the opened fiber composite into short fibers, for example, about 5 mm, and forming it into a nonwoven fabric by a method such as needle punching. In addition, as another different method, for example, as described in International Publication No. 2017-022052 and International Publication No. 2018-221063, a mixed liquid containing cellulose nanofibers and a dispersion medium may be attached to a breathable support and freeze-dried to obtain a filter layer.

[0112] (4)Applications The air filter media and air filter products according to the present embodiment can be used in applications such as ventilation filters installed in ventilation paths connecting the outdoors and indoors of buildings such as offices, condominiums, and hospitals; heat-resistant filters used in specified high-temperature environments; chemical-resistant filters used in spaces where specified chemicals are handled; exhaust gas treatment filters, vacuum cleaner filters, and gas turbine filters.

[0113] <Example> (Examples 1 to 7, Comparative Examples 1 to 3) As the first fiber, acetate fiber was used. Specifically, cellulose diacetate was dissolved in acetone, and then spun into filaments by dry spinning to obtain a tow fiber material. As the second fiber, PTFE fine powder ("Polyflon Fine Powder F106" manufactured by Daikin Industries, Ltd.), which is widely used as a type of PTFE for porous membranes, was used. A surfactant was added to the corresponding freshly polymerized PTFE raw dispersion to make it 10 wt% relative to the PTFE solid content, to stabilize it, and the test was performed in a state where the handling properties were good. The PTFE used in the examples and comparative examples were all the same.

[0114] A PTFE aqueous dispersion was applied to the surface of a tow made of acetate fiber before it was subjected to crimping processing, and then the tow was passed through a crimping device to composite the PTFE and acetate fiber. The amount of PTFE applied was adjusted by changing the concentration, viscosity, and amount of coating applied to the tow surface. The composite that had passed through the crimping device was dried with hot air to remove moisture from the tow and PTFE. The dried composite was passed through a roll opening device at room temperature of about 25°C to extend the crimp, creating a bulky fiber structure in which the PTFE-derived second fiber was stretched between the first fibers.

[0115] The air filter media of each of the Examples and Comparative Examples was obtained by increasing the basis weight of the tow side to be used, or by stacking the fiber structures so as to obtain the required basis weight.

[0116] The physical properties of each sample were measured and evaluated under the conditions described below.

[0117] As a reference example, a glass fiber filter medium that has been conventionally used is shown for reference.

[0118] (PTFE fiber diameter and acetate fiber diameter) The surface of the test sample is photographed at 1000 to 5000 times magnification with a scanning electron microscope (SEM), two perpendicular lines are drawn on one photographed image, and the thickness of the image of the fiber that intersects with these lines is obtained as the fiber diameter. Here, the number of fibers to be measured is 200 or more. The fiber diameters thus obtained are plotted in a log-normal manner with the fiber diameter on the horizontal axis and the cumulative frequency on the vertical axis, and the value at which the cumulative frequency is 50% is defined as the average fiber diameter.

[0119] (Air filter media mesh size) The basis weight was calculated by dividing the mass (g) of a sample cut into a rectangle of 4.0 cm x 12.0 cm by the area (0.0048 m) measured on a precision balance. 2 ) was used as the value.

[0120] (PTFE loading amount per tow) The amount of PTFE dispersion applied to the tow surface was determined from the tow production speed and the flow rate of the PTFE dispersion applied during tow production.

[0121] (Air filter media thickness) Using a thickness gauge (1D-110MH, manufactured by Mitutoyo Corporation), five measurement targets were stacked and the total thickness was measured, and the value was divided by 5 to obtain the thickness of one sheet.

[0122] (Pressure loss of air filter media) A sample of air filter medium having a fluororesin porous membrane was set in a cylindrical filter medium holder with a diameter of 100 mm, the inlet side was pressurized with a compressor, and the air flow was adjusted so that the air passing through the filter medium was 5.3 cm / sec. The pressure was measured using a manometer on the upstream and downstream sides of the test sample in the air flow direction, and the difference in pressure between the upstream and downstream sides was calculated as the pressure loss.

[0123] (Air filter media collection efficiency (NaCl particles with a particle size of 0.4 μm)) According to the method described in JIS B9928 Appendix 5 (Regulations) NaCl aerosol generation method (pressure spray method), NaCl particles generated by an atomizer were classified to a particle size of 0.4 μm using an electrostatic classifier (TSI), and the particle charge was neutralized using americium 241. The permeation flow rate was then adjusted to 5.3 cm / sec. The number of particles before and after the filter material, which was the measurement sample, was determined using a particle counter (TSI, CNC), and the collection efficiency was calculated using the following formula. Collection efficiency (%) = (CO / CI) x 100 CO = Number of 0.4μm NaCl particles collected by the measurement sample CI = Number of 0.4 μm NaCl particles supplied to the measurement sample

[0124] (PF value of air filter media) Using the above pressure loss and collection efficiency, the PF value was calculated according to the following formula: PF value={-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0125] (Amount of dust held by air filter media) According to the method described in JIS B9928 Appendix 5 (Regulations) NaCl aerosol generation method (pressure spray method), NaCl particles generated by an atomizer were passed over americium 241, an alpha radiation source, to bring the particle's charge state to the same equilibrium charge state as atmospheric dust. After setting the filter medium, which was the measurement sample, in the same filter holder as that used for the pressure loss measurement, NaCl particles were introduced upstream of the filter medium, and the load of NaCl particles was continued until the pressure loss of the filter increased by +50 Pa from the initial value. The amount of dust was calculated using the following formula from the filter medium weight measurement before and after the load of NaCl particles. Dust retention amount (g / m 2 )=(MI-MO) / A MO = weight of test medium before loading with NaCl particles (g) MI = weight of test medium after loading with NaCl particles (g) A = effective filter area (100 cm 2 =0.01m 2 )

[0126] The physical properties of the air filter media (not in the form of a pocket air filter, but in the form of a sheet) of each Example and Comparative Example are shown in the following table. SEM photographs of Example 1 and Comparative Example 1 are shown in Figure 7 and Figure 8, respectively. JPEG0007678752000001.jpg95170

[0127] In addition, in the example of Comparative Example 2, the amount of PTFE attached to the tow was too much, so the acetate fiber could not be opened, and the PTFE could not be made into a fiber. Therefore, the filter medium of Comparative Example 2 could not be quantified in terms of collection efficiency, PF value, and dust amount.

[0128] In addition, for Comparative Examples 1 and 3, it took a considerable amount of time for the pressure loss to increase, and the test could not be continued until an increase of 50 Pa was confirmed, so the amount of dust held could not be quantified.

[0129] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure described in the claims. [Explanation of symbols]

[0130] 65 Filter media layer 69 Pre-collection layer 70 Breathable support material 80 Air filter media 80a Air filter media 85 Pocket Air Filter 90 Frame 100 Air Filter Products [Prior art documents] [Patent documents]

[0131] Patent Document 1: JP 2017-35684 A

Claims

1. First fibers having an average fiber diameter of 5 μm or more and 50 μm or less; second fibers interposed in gaps between the first fibers and having an average fiber diameter of 30 nm or more and 1 μm or less; A filter medium layer comprising: The filter layer has a pressure loss of 35 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec, The filter layer has a collection efficiency of 35% or more for NaCl having a particle diameter of 0.4 μm. A method for producing an air filter medium, comprising: The first fiber is produced by applying tension to a tow band obtained by crimping a tow formed by combining a plurality of filaments, to which a resin granule is attached, and opening the tow band to produce the first fiber, and by stretching the resin granule by opening the tow band to produce the second fiber, which is a fibrous polymer. A method for manufacturing air filter media.

2. First fibers having an average fiber diameter of 5 μm or more and 50 μm or less; second fibers that are interposed in gaps between the first fibers, have an average fiber diameter of 30 nm or more and 1 μm or less, and contain a fluororesin; Resin granules having the same composition as the second fibers; A filter medium layer comprising: a ratio W1 / W2 of a weight W1 of the first fibers to a combined weight W2 of the second fibers and the resin granules is 3.0 or more and 18.0 or less; The filter layer has a pressure loss of 35 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec, The filter layer has a collection efficiency of 35% or more for NaCl having a particle diameter of 0.4 μm. A method for producing an air filter medium, comprising: The first fiber is produced by applying tension to a tow band obtained by crimping a tow formed by combining a plurality of filaments, to which the resin granules are attached, and opening the tow band to produce the first fiber, and by stretching the resin granules by opening the tow band to produce the second fiber, which is a fibrous polymer. A method for manufacturing air filter media.

3. First fibers having an average fiber diameter of 5 μm or more and 50 μm or less; second fibers that are interposed in gaps between the first fibers, have an average fiber diameter of 30 nm or more and 1 μm or less, and contain a fluororesin; Resin granules having the same composition as the second fibers; A filter medium layer comprising: a ratio V1 / V2 of a volume V1 of the first fibers to a combined volume V2 of the second fibers and the resin granules is 1.9 or more and 124.0 or less; The filter layer has a pressure loss of 35 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec, The filter layer has a collection efficiency of 35% or more for NaCl having a particle diameter of 0.4 μm. A method for producing an air filter medium, comprising: The first fiber is produced by applying tension to a tow band obtained by crimping a tow formed by combining a plurality of filaments, to which the resin granules are attached, and opening the tow band to produce the first fiber, and by stretching the resin granules by opening the tow band to produce the second fiber, which is a fibrous polymer. A method for manufacturing air filter media.

4. The first fiber is one or more selected from the group consisting of cellulose acetate, rayon, polypropylene, polyethylene terephthalate, and polyethylene. A method for producing the air filter medium according to any one of claims 1 to 3.

5. The fiber-forming polymer includes a fluororesin. A method for producing the air filter medium according to claim 1.

6. The thickness of the filter layer is 3 mm or more. A method for producing the air filter medium according to any one of claims 1 to 5.

7. The filter layer has a PF value of 16 or more, as determined by the following formula: PF value = {-log ((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000). A method for producing the air filter medium according to any one of claims 1 to 6.

8. The filter layer has a dust amount of NaCl particles of 18 g / m when air containing NaCl particles of 0.4 μm in diameter is continuously passed through it at a flow rate of 5.3 cm / sec and the pressure loss increases by 50 Pa. ２ That's all. A method for producing the air filter medium according to any one of claims 1 to 7.

9. The air filter medium obtained by the method for producing an air filter medium according to any one of claims 1 to 8 is formed into a bag shape. Manufacturing method for air filter products.

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