JP6691497B2 - Method for manufacturing filter material for air filter and method for manufacturing air filter - Google Patents

Description

  The present disclosure relates to a filter medium for an air filter and a method for manufacturing an air filter. More specifically, the present invention relates to a filter material for an air filter suitable for air purification applications such as semiconductors, liquid crystals, clean rooms or benches related to the bio / food industry, building air conditioning, internal combustion engines or indoor spaces, and a method for manufacturing an air filter.

  An air filter is generally used to collect particles in the submicron to micron units in the air. The term "air filter" used here refers to a filter material (sheet) for an air filter that is folded in, for example, a zigzag shape to increase the filtration area (pleating) and is integrated with a frame material such as metal or plastic to facilitate installation and replacement. This refers to a modified air filter unit. The air filter can be usually obtained by molding a long filter material for an air filter wound in a roll shape.

  Air filters are roughly classified into coarse dust filters, medium performance filters, HEPA (High Efficiency Particulate Air) filters, and ULPA (Ultra Low Penetration Air) filters according to their collection performance. The basic characteristics of these air filters are that, in addition to high collection efficiency of fine dust particles, low pressure loss is required in order to reduce the energy cost for passing air through the filter. ing. Therefore, in the air filter, generally, the filter material for the air filter is folded in a zigzag shape to increase the filtration area. Thereby, even if the air volume passing through the air filter is the same, the air volume per unit area of the filter medium can be reduced, and the pressure loss of the air filter can be reduced and the life of the air filter can be extended. Even a general air filter having a length of 610 mm and a width of 610 mm may have a length of several tens of meters because the filter medium is folded to have a large filtration area.

  In recent years, the use of nanocellulose has attracted attention. Generally, nanocellulose is also called cellulose nanofiber, and refers to (1) fine cellulose fibers having a number average fiber diameter of 1 to 100 nm, or (2) chemically treated (modified) fine cellulose fibers. As the nanocellulose of (1), for example, microfibrillated cellulose obtained by shearing and defibrating cellulose fibers under high pressure, nanofibrinated cellulose (hereinafter abbreviated as MFC, NFC), or fine particles produced by microorganisms Bacterial cellulose (hereinafter abbreviated as BC). Examples of the modified nanocellulose of (2) include cellulose nanocrystals (hereinafter abbreviated as CNC) obtained by treating natural cellulose with 40% or more concentrated sulfuric acid, or fibers of wood pulp. Microfibrils, which are the smallest unit, are isolated as an aqueous dispersion by mild chemical treatment at room temperature and normal pressure and mild mechanical treatment, and are ultrafine and uniform fine cellulose fibers (for example, see Patent Document 1). reference.).

  These nanocelluloses are expected to be used as filter materials or porous bodies. For example, a method for producing a leukocyte-removing filter material comprising a porous element having an average pore diameter of 1.0 μm or more and less than 100 μm and a fiber structure retained in the porous element and having an average fiber diameter of 0.01 μm or more and less than 1.0 μm. Are shown (for example, refer to Patent Document 2). In Patent Document 2, bacterial cellulose produced by acetic acid bacteria, or cellulose fiber obtained by treating rayon with sulfuric acid and finely treated with a homogenizer is used as the fiber structure.

  Since nanocellulose has high hydrophilicity, the cohesive force that works during drying is stronger than that of nanofibers derived from a thermoplastic polymer, and it is difficult to obtain a material having air permeability such as an air filter. Therefore, as a method for obtaining a material having air permeability using nanocellulose, nanocellulose is dispersed in a mixed solution of water and an organic solvent soluble in water, and cellulose is removed by freeze-drying the mixed solution. A method for producing a porous body is shown (for example, refer to Patent Document 3).

JP, 2008-1728, A Japanese Patent No. 3941838 JP, 2013-253137, A

R. Daoussi, E, Bogdani, S .; Vessot, J .; Andrieu, O .; Monnier, "Drying Technology" Vol. 29 (2011), p. 1853-1867

  Patent Document 2 uses bacterial cellulose produced by acetic acid bacteria as the thinnest fiber, and only discloses a method for producing a flat sheet having a small area at a laboratory level. The average fiber diameter is 0.02 μm (= 20 nm). As other fibers, cellulosic fibers obtained by treating rayon with sulfuric acid and refined with a homogenizer were used, and the thinnest had an average fiber diameter of 0.19 μm (= 190 nm). When bacterial cellulose is used, acetic acid bacteria are cultivated in the porous element, but there are many restrictions on the culturing conditions and the production amount is small, so that it is not suitable for industrial use. Further, the fibrous structure is formed only on the surface of the porous element, and the fibrous structure is not formed inside the holes of the porous element. Cellulose fibers obtained by refining rayon are submicron fibers rather than nanofibers, and conventional microglass fibers can be sufficiently substituted. Further, the filter material of Patent Document 2 is a filter material for liquid, and there is a problem that the porosity is too low as a filter material for air filters.

  Patent Document 3 does not discuss practical use of a porous cellulose body as a filter medium for an air filter. In Patent Document 3, a nanocellulose porous body is formed in a nonwoven fabric made of glass fibers by freeze-drying. However, freeze-drying requires a closed container to maintain a vacuum state during drying. Since the non-woven fabric used in Patent Document 3 is flat, a porous body having a size larger than that of the closed container cannot be obtained, and the porous body is used as a long filter medium for an air filter required for manufacturing an air filter. Was difficult to put into practical use. Further, the filter material for an air filter is usually pleated so that it is folded in a zigzag shape, but at that time, the nanocellulose network existing at the fold portion of the filter material for an air filter is broken or dropped, which deteriorates the filter performance. Sometimes. However, no means for solving this problem has been shown so far.

  An object of the present disclosure is to provide a method of manufacturing a filter medium for an air filter and a method of manufacturing an air filter, which use nanocellulose and have improved filter performance, particularly particle collection performance.

  The method for producing an air filter according to the present invention is a fixing step of fixing a fluid-permeable support, which has been subjected to pleating, to a frame material, and the support that has undergone the fixing step, and a dispersion liquid containing nanocellulose. Is attached, and a drying step of drying the support after the attaching step is performed.

  In the method for manufacturing an air filter according to the present invention, it is preferable that the drying method performed in the drying step is a freeze drying method. As a result, the aggregation of nanocellulose can be suppressed and a good nanocellulose network can be constructed, so that the filter performance of the air filter can be further improved.

  According to the present disclosure, it is possible to provide a method for manufacturing a filter medium for an air filter and a method for manufacturing an air filter, which use nanocellulose and have improved filter performance, particularly particle collection performance.

FIG. 3 is a diagram showing an image (observation magnification: 5000 times) obtained by observing the air filter of Example 1 with an SEM. FIG. 3 is a diagram showing an image (observation magnification: 10000 times) obtained by observing the air filter of Example 1 with an SEM. FIG. 6 is a diagram showing an image (observation magnification: 5000 times) obtained by observing the air filter of Comparative Example 1 with an SEM. FIG. 5 is a diagram showing an image (observation magnification: 10000 times) obtained by observing the air filter of Comparative Example 1 with an SEM.

  Next, the present invention will be described in detail by showing embodiments, but the present invention is not construed as being limited to these descriptions. The embodiments may be variously modified as long as the effects of the present invention are exhibited.

  The filter medium for an air filter according to the present embodiment has an adhesion step of adhering a dispersion liquid containing nanocellulose to a pleated support having fluid permeability, and drying the support after the adhesion step. And a drying step. By using a support that has been pleated in advance, it is possible to dry a long support in a drying area with a limited volume, and efficiently obtain a filter medium for air filters to which nanocellulose is attached. be able to. Furthermore, since the nanocellulose network at the fold portion is not broken or dropped due to the pleating process, it is possible to provide a filter medium for an air filter having high filter performance.

<Support>
The support is not particularly limited as long as it has fluid permeability, and for example, a porous material such as non-woven fabric, woven fabric, paper or sponge can be used. Among these, non-woven fabrics are preferable, and non-woven fabrics for filter media containing glass fiber or organic fiber as a main component are particularly preferable. The main component being glass fiber or organic fiber means that the mass of the fiber is 50 mass% or more with respect to the total mass of the support. More preferably, it is 80 mass% or more. When the support is a nonwoven fabric composed mainly of the fibers, the basis weight is preferably from 10 to 300 g / ^{m 2,} and more preferably 30 to 200 g / ^{m 2.} The fluid permeability is a property that allows at least a gas to pass therethrough, and more preferably a property that allows a gas and a liquid to pass therethrough.

  The glass fiber used for the support is, for example, a wool-like ultrafine glass fiber produced by a flame drawing method or a rotary method, or a bundle of glass fibers spun to have a predetermined fiber diameter into a predetermined fiber length. It is a chopped strand glass fiber produced by cutting. Among these, those having various fiber diameters and fiber lengths are selected according to the required physical properties, and they are used alone or as a mixture. Further, low boron glass fiber or silica glass fiber can be used for the purpose of preventing boron contamination of the silicon wafer in the semiconductor manufacturing process application. The average fiber diameter of the glass fibers is not particularly limited, but is preferably 0.05 to 20 μm. More preferably, it is 0.1 to 5 μm. The average fiber length of the glass fibers is not particularly limited, but is preferably 0.5 to 10000 μm. More preferably, it is 1 to 1000 μm. On the other hand, the organic fiber is, for example, polypropylene fiber, acrylic fiber, vinylon fiber, cellulose fiber, polyester fiber or aramid fiber. The average fiber diameter of the organic fibers is not particularly limited, but is preferably 0.05 to 100 μm. More preferably, it is 0.1 to 50 μm. The average fiber length of the organic fibers is not particularly limited, but in the case of short fibers, it is preferably 0.5 to 10000 μm. More preferably, it is 10 to 5000 μm. The method for manufacturing the nonwoven fabric is not particularly limited, and is, for example, a dry method or a wet method.

  The pleating process performed on the support is, for example, a process of forming a fold having a zigzag-like structure in which a mountain fold and a valley fold are repeated in the material of the support.

  The average pore size of the support is preferably 0.1 to 50 μm. More preferably, it is 0.5 to 10 μm. If it is less than 0.1 μm, the fluid permeability may be poor. When it exceeds 50 μm, it may be difficult for nanocellulose to uniformly form a network structure in the pores of the support. In the present embodiment, a dispersion containing nanocellulose can be deposited in the pores of the support and then dried to form an air filter, but by using a support having an appropriate average pore size, Since the cohesive force generated with respect to the nanocellulose during drying becomes easy to disperse, it becomes easy to maintain the network structure even after drying. Here, the average pore diameter can be measured according to ASTM E1294-89 "half-dry method".

  The support is preferably a material that can be used as a filter material for an air filter. In the air filter manufacturing method according to the present embodiment, by using such a support, it becomes easy to obtain an air filter having a higher particle trapping performance than the conventional filter material for air filter (support itself). .

<Nanocellulose>
Nanocellulose (hereinafter also referred to as nanofiber) includes chemically treated (modified) nanocellulose. In nanocellulose, the molecular chains of cellulose form two or more bundles. The term “two or more bundles of cellulose molecular chains” means a state in which two or more cellulose molecular chains are aggregated to form an aggregate called microfibril. In the present embodiment, in the cellulose molecular chain, a part or all of the hydroxyl group at the C6 position in the molecule is oxidized to an aldehyde group or a carboxyl group, and a part or all of the hydroxyl group other than the C6 position is oxidized to a carbonyl group. A part or all of the hydroxyl groups including hydroxyl groups other than C6 position are esterified such as nitrate ester, acetate ester or phosphate ester, or methyl ether, hydroxypropyl ether or carboxymethyl ether. Including a form substituted with another functional group such as an etherified product. When the cellulose molecular chain is modified to contain a carboxyl group, its counter ion is substituted with a cationic surfactant, those substituted with various metal ions, and the metal ion is reduced. Including those in the form of particles.

  In the present embodiment, the number average fiber diameter of nanocellulose is preferably 1 to 100 nm. In order to provide an air filter that achieves both high particle collection performance and low pressure loss, it is important to form a uniform fiber network of nanocellulose having a very small fiber diameter in the support. When ultrafine nanocellulose having a number average fiber diameter of 1 to 100 nm is used, the number of fibers per unit volume in the filter medium for an air filter remarkably increases, it becomes easy to capture particles in a gas, and high collection performance is obtained. Can be obtained. Further, due to the slip flow effect, the air flow resistance of the single fiber becomes extremely low, and the pressure loss as an air filter becomes difficult to increase. 2-30 nm is preferable and, as for the number average fiber diameter of nanocellulose, 3-20 nm is more preferable. When the number average fiber diameter is less than 1 nm, the single fiber strength of nanocellulose is weak and it may be difficult to maintain the fiber network in the filter medium for an air filter. When it exceeds 100 nm, the number of fibers per unit volume in the filter medium for an air filter decreases, and it may be impossible to form a nanocellulose network effective for capturing particles. Here, the number average fiber diameter is calculated according to the following. The nanocellulose cast on the carbon film-covered grid is observed with an electron microscope image using a transmission electron microscope (TEM, Transmission Electron Microscope). With respect to the obtained observed image, two vertical and horizontal axes are drawn for each image, and the fiber diameter of the fibers intersecting the axis is visually read. At this time, observation is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. The sample or the magnification is set under the condition that 20 or more fibers intersect the axis. In this way, at least three images of the non-overlapping surface portions are photographed by an electron microscope, and the value of the fiber diameter of the fiber intersecting the two axes is read. Therefore, at least 20 pieces × 2 × 3 = 120 pieces of fiber information can be obtained. The number average fiber diameter was calculated from the thus obtained fiber diameter data. In addition, regarding the branched fiber, if the length of the branched portion is 50 nm or more, it is incorporated into the calculation of the fiber diameter as one fiber. The number average fiber diameter may be calculated according to the following. The nanocellulose existing on the surface or inside the support is observed with an electron microscope image using a scanning electron microscope (SEM, Scanning Electron Microscope). With respect to the obtained observed image, two vertical and horizontal axes are drawn for each image, and the fiber diameter of the fibers intersecting the axis is visually read. At this time, observation is performed at any magnification of 5000 to 50000 times depending on the size of the constituent fibers. An image of a plurality of non-overlapping surface portions is taken with an electron microscope, and the value of the fiber diameter of the fiber intersecting each of the two axes is read. The number average fiber diameter is calculated from the fiber diameter data of at least 120 fibers. In addition, regarding the branched fiber, if the length of the branched portion is 50 nm or more, it is incorporated into the calculation of the fiber diameter as one fiber. The sample is previously coated with a conductive coating to obtain an observation image without distortion, but the effect of the coating film thickness is also taken into consideration. For example, when using ion sputtering (E-1045, manufactured by Hitachi High-Technology), the coating film thickness is 12 nm when the discharge current is 15 mA, the sample-target distance is 30 mm, the degree of vacuum is 6 Pa, and the coating time is 2 minutes. However, when measuring the fiber diameter, the coating film thickness should be half of the expected value because the deposition direction of the coating film is perpendicular to the expected direction. That is, when coating is performed under the above conditions, the coating film thickness of 12 nm (= 6 nm + 6 nm) at both ends is excluded from the fiber diameter obtained from SEM.

  The number average fiber length of nanocellulose is not particularly limited, but is preferably 0.01 to 20 μm. More preferably, it is 0.05 to 10 μm. More preferably, it is 0.08 to 1.0 μm. When the number average fiber length is less than 0.01 μm, the nanofibers are close to particles, and there is a possibility that a fiber network cannot be formed in the air filter medium. If it exceeds 20 μm, the entanglement of nanofibers increases, and the fibers may aggregate to fail to form a uniform network. The number average fiber length is calculated by observing the nanocellulose with an electron microscope image using a scanning electron microscope (SEM, Scanning Electron Microscope). With respect to the obtained observation image, 10 independent fibers are randomly selected for each image, and the fiber length is visually read. At this time, it is performed at any magnification of 1000 to 30000 times depending on the length of the constituent fibers. Note that the sample or the magnification is for the fiber whose start point and end point are within the same image. In this way, at least 12 images of the non-overlapping surface portion are photographed by SEM, and the fiber length is read. Therefore, at least 10 pieces × 12 pieces = 120 pieces of fiber information can be obtained. The number average fiber length can be calculated from the fiber diameter data thus obtained. For a branched fiber, the length of the longest part of the fiber is the fiber length.

  In the method for producing an air filter medium according to this embodiment, it is preferable that the number average fiber length of nanocellulose is smaller than the average pore diameter of the support. By making the number average fiber length of nanocellulose smaller than the average pore diameter of the support, nanocellulose can penetrate into the support and form a network inside the support. As a result, it is possible to obtain a filter medium for an air filter having a higher particle collecting performance even if the packing density of nanocellulose is relatively low. Since nanocellulose has a very high ability to form a network by connecting fibers, it is sufficient as a filter medium for air filters even if the number average fiber length is smaller than the average pore diameter of the support and the packing density is relatively low. Has a strong network strength. The value of the number average fiber length of nanocellulose is preferably 0.1 to 99%, and more preferably 5 to 36% with respect to the value of the average pore diameter of the support. If it is less than 0.1%, the number of contact points between the nanocelluloses or between the nanocellulose and the support becomes small, and the nanocellulose may drop off from the support. If it exceeds 99%, the nanocellulose may not be able to enter the inside of the support.

  The type of nanocellulose is not particularly limited, but is, for example, nanocellulose obtained by oxidizing cellulose using the above-mentioned MFC, NFC, CNC, or N-oxyl compound such as TEMPO described in Patent Document 1. Is. MFC and NFC are characterized by a wide distribution of fiber diameters because the cellulose fibers are sheared by mechanical treatment to form nanofibers. The CNC has a relatively uniform fiber diameter, but is characterized by a short fiber length of 0.1 to 0.2 μm. The nanocellulose described in Patent Document 1 is cellulose single microfibril. In natural cellulose, microfibrils are multibunched to construct a high-order individual structure. Here, the microfibrils are strongly aggregated by hydrogen bonds derived from the hydroxyl groups in the cellulose molecule. Cellulose single microfibrils are microfibrils isolated by subjecting natural cellulose to chemical treatment and slight mechanical treatment. As described in Patent Document 1, a cellulose raw material is oxidized with an oxidizing agent in the presence of an N-oxyl compound, a bromide, an iodide, or a mixture thereof, and the oxidized cellulose is further wet granulated. It is characterized as having a uniform fiber diameter, which is produced as an aqueous dispersion by chemical treatment, defibration, and nanofiber formation. Among these, the fine cellulose described in Patent Document 1 is particularly preferable in that it requires less energy for production than other cellulose fibers and has high productivity. The nanocellulose described in Patent Document 1 has a part of the hydroxyl groups of the cellulose molecule oxidized to at least one functional group selected from the group consisting of a carboxyl group and an aldehyde group, and has a cellulose type I crystal structure. The maximum fiber diameter is 1000 nm or less. This nanocellulose becomes a transparent liquid when dispersed in water.

  The cellulose raw material which is a raw material of nanocellulose is not particularly limited, but plant pulp, particularly wood pulp is preferable. The plant-based pulp includes, for example, kraft pulp derived from various woods such as bleached hardwood kraft pulp (LBKP) or bleached softwood kraft pulp (NBKP); sulphite pulp; waste paper pulp such as deinking pulp (DIP); grand pulp (GP). ), Pressurized groundwood pulp (PGW), refiner groundwood pulp (RMP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemimechanical pulp (CMP) or chemiground pulp (CGP); Powdery cellulose obtained by pulverizing them with a high-pressure homogenizer or a mill; or microcrystalline cellulose powder obtained by purifying them by a chemical treatment such as acid hydrolysis can be used. Further, plant-derived non-wood pulp such as kenaf, hemp, rice, bagasse, bamboo or cotton can also be used. This embodiment is not limited to the nanofiber raw material and the manufacturing method.

  The nanofiber manufacturing method is, for example, the manufacturing method described in Patent Document 1. According to Patent Document 1, a method for producing nanofibers comprises using natural cellulose as a raw material, an N-oxyl compound such as TEMPO in water as an oxidation catalyst, and oxidizing the natural cellulose by acting a co-oxidizing agent to produce a reaction product. It includes an oxidation reaction step of obtaining fibers, a purification step of removing impurities to obtain a reaction fiber containing water, and a defibration step of dispersing the reaction fiber containing water as nanocellulose in a dispersion medium.

  The filter medium for an air filter obtained by the manufacturing method according to the present embodiment, nanocelluloses are entangled with each other in the pores of the support to form voids between the nanocelluloses, and a membrane or nanocelluloses in which nanocelluloses are entangled. It is preferred to have no agglomerated membranes. It is possible to prevent the pressure loss from increasing and to enhance the particle collection efficiency. A membrane in which nanocellulose is entangled or a membrane in which nanocellulose is aggregated refers to a membrane-like material formed by physical entanglement or chemical aggregation of nanocellulose, which blocks all or part of the pores of the support. .

  In the method for manufacturing the air filter according to the present embodiment, the air filter can be obtained by fixing the filter material for air filter obtained by the method for manufacturing the filter material for air filter according to the present embodiment to the frame member. For example, the manufacturing method of the air filter according to the present embodiment, the support having a fluid permeable subjected to pleating, an adhesion step of adhering a dispersion liquid containing nanocellulose, and the support after the adhesion step And a fixing step of fixing the air filter material to the frame material.

  Further, the manufacturing method of the air filter according to the present embodiment, a fixing step of fixing the support having a fluid permeable subjected to pleating process to the frame material, the support after the fixing step, nanocellulose, The method includes an attaching step of attaching the dispersion liquid containing the adhesive, and a drying step of drying the support after the attaching step. That is, the air filter can be obtained by adhering the dispersion containing nanocellulose to the support previously fixed to the frame material and drying it. By attaching nanocellulose to the support fixed to the frame material, the support area can be folded in a zigzag shape without using the long filter media for air filters conventionally required for manufacturing air filters. It is possible to obtain an air filter having a large size. Further, the air filter can be obtained more efficiently by fixing the support to the frame material, attaching the dispersion liquid containing nanocellulose, and drying the dispersion liquid.

  As the frame material, for example, aluminum, aluminum alloy, stainless steel, thermoplastic resin, thermosetting resin, or a molded product obtained by solidifying fibrous material such as pulp can be used. There are various shapes for fixing the support or the filter medium for the air filter to the frame member. For example, the support or the filter medium for an air filter is folded and fixed in a zigzag shape. There are various shapes of the frame material, and there are a square shape having a square shape and a cylindrical shape. It is important that the air filter medium or the support and the frame member are adhered to each other without any leakage, and the adhesive is a method of fixing the frame member and the air filter medium or the support member so as not to create a gap. It is preferable. Here, as the adhesive, for example, a hot melt adhesive such as polyvinyl acetate resin can be used.

  In the present embodiment, the ratio of the amount of nanocellulose attached to the support is preferably 0.001 to 0.500 mass%. It is preferably 0.010 to 0.300% by mass, and more preferably 0.050 to 0.200% by mass. With such an amount of adhesion, an air filter having high particle collection performance and relatively low pressure loss can be obtained. If the amount of nanocellulose deposited on the support is less than 0.001% by mass, the particle collection performance may be poor. On the other hand, if it exceeds 0.500 mass%, the pressure loss may be too high. The amount of nanocellulose attached to the support can be controlled mainly by the concentration of nanocellulose in the dispersion and the amount of attachment of the dispersion to the support, which increases the concentration of nanocellulose in the dispersion. The more the adhesion amount of the dispersion liquid to the support increases, the more the adhesion amount of nanocellulose to the support increases.

  In this embodiment, the air filter can be obtained by adhering the dispersion liquid containing nanocellulose to the support fixed to the frame material and then drying the dispersion liquid. The dispersion liquid can be obtained by dispersing nanocellulose in a dispersion medium. The form of the nanocellulose in the dispersion liquid is, for example, a form in which the nanocellulose is dispersed dispersively or a form in which the nanocellulose is partially aggregated. Among them, the form of nanocellulose in the dispersion liquid is preferably a form in which nanocellulose is dispersed in pieces.

<Dispersion medium>
Water can be used as the dispersion medium. When water is used as the dispersion medium, a surfactant can be included. The surfactant has the effect of lowering the surface tension of the liquid, and the hydrophilic part of the surfactant is adsorbed on the nanocellulose, and the hydrophobic part is directed to the outside to make it hydrophobic. It is thought that there is a function to weaken. The surfactant is not particularly limited, and a cationic surfactant, an anionic surfactant, a nonionic surfactant or an amphoteric surfactant can be used. Preferably there is. Since the surface of the nanocellulose exhibits anionicity, the cationic surfactant is easily adsorbed, and the surface of the nanocellulose is easily covered with the surfactant. As a result, the effect of weakening the aggregation of nanocelluloses during drying is further enhanced, which contributes to the formation of a uniform network of nanocelluloses. Cationic surfactants are, for example, quaternary ammonium salts, alkylamine salts, sulfonium salts or phosphonium salts. From the viewpoint of high water solubility, a quaternary ammonium salt is more preferable. The content of the surfactant in the dispersion is not particularly limited, but it is preferably 0.10 to 100 mass% in terms of solid content concentration with respect to the dry mass of nanocellulose. More preferably, it is 0.50 to 50.0 mass%. Especially preferably, it is 1.00-40.0 mass%. If it is less than 0.10% by mass, the effect of adding a surfactant may not be obtained in some cases. If it exceeds 100% by mass, it may be difficult for the nanocellulose to maintain the fibrous state.

  Further, as the dispersion medium, a mixed dispersion medium in which water and an organic solvent soluble in water are mixed can be used. As described below, in the present embodiment, after the dispersion containing nanocellulose is attached to the support, it is possible to obtain a filter medium for an air filter by freeze-drying, but when performing this freeze-drying It is preferable to use a mixed dispersion medium in which water and an organic solvent that dissolves in water are mixed. Here, the organic solvent refers to an organic compound that is liquid at normal temperature and pressure. Further, “dissolving in water” means that, in a mixed dispersion medium in which water and an organic solvent are mixed, water and the organic solvent are mixed at an arbitrary ratio with each other at the molecular level and do not undergo phase separation. When the dispersion medium is a mixture of water and an organic solvent that dissolves in water, crystallization of the dispersion medium is suppressed during freeze-drying, which contributes to formation of a uniform nanocellulose network. In this embodiment, the concentration of the organic solvent in the mixed dispersion medium is preferably 2 to 50% by mass. It is more preferably 5 to 40% by mass, and even more preferably 10 to 30% by mass. If the concentration of the organic solvent exceeds 50% by mass, the dispersion medium becomes highly hydrophobic, and hydrophilic nanocellulose is not uniformly dispersed in the dispersion liquid, which may impair the formation of a uniform network of nanocellulose. . When the concentration of the organic solvent is less than 2% by mass, the formation of water crystals (ice crystals) during the freezing of the dispersion medium is remarkable, which causes aggregation and structural destruction of nanocellulose, which results in a uniform nano-scale on the support. It may not be possible to form a cellulose network.

  The organic solvent preferably contains at least one of alcohols, carboxylic acids, and carbonyl compounds. By including such an organic solvent, water crystals (ice crystals) produced during freeze-drying can be made smaller, and nanocellulose network formation on the support can be made more uniform. The organic solvent is (1) methanol, (2) ethanol, (3) 1-propanol or (4) t-butyl alcohol as alcohols, (5) acetic acid as carboxylic acids, and (6) acetone as carbonyl compounds. It is more preferable to include at least one of (1) to (6) from the viewpoint of compatibility with water. Of these, the organic solvent is particularly preferably t-butyl alcohol only. The freezing point of the mixed dispersion medium in which water and t-butyl alcohol are mixed is about -10 ° C at the lowest, which is higher than that of the mixed dispersion medium of other organic solvent and water, and it can be frozen. It's easy. It is known that in a t-butyl alcohol aqueous solution, when the t-butyl alcohol concentration is around 20 mass%, water and t-butyl alcohol form a eutectic and the crystal size upon freezing becomes small. When the organic solvent is only t-butyl alcohol, the concentration of t-butyl alcohol in the mixed dispersion medium is preferably 15 to 35% by mass, more preferably 20 to 30% by mass.

<Dispersion>
In this embodiment, the solid content concentration of nanocellulose in the dispersion is preferably 0.001 to 0.150% by mass. It is more preferably 0.005 to 0.100 mass%, and even more preferably 0.010 to 0.080 mass%. When forming a network of nanocellulose on a support having fluid permeability to provide a filter medium for an air filter, it is preferable that the network of nanocellulose is uniformly stretched without having a certain directionality. If the network of nanocellulose in the support is not stretched in a specific direction (orientated), it is easier to satisfy the particle capturing performance as a filter medium for an air filter. When the solid concentration of nanocellulose in the dispersion exceeds 0.150% by mass, many domains in which the fibers are oriented are likely to be formed. The orientation of the fibers means that the fibers are aligned in the same direction to some extent, and the orientation is not preferable for the filter medium for an air filter in which the higher the degree of dispersion of the fibers, the higher the particle capturing performance. Further, when the packing density of nanocellulose in the filter medium for air filters becomes excessively high, the distance between the nanocelluloses distributed in the filter medium for air filters cannot be maintained at an appropriate level, causing aggregation and the like due to moisture in the air, There is a possibility that the formation of a network by nanocellulose, which is suitable as a filter material for air filters, may be hindered. A nanocellulose dispersion obtained by oxidizing cellulose with an N-oxyl compound such as TEMPO has high transparency in water and is uniformly dispersed, but when the concentration is high, the fibers are particularly likely to be oriented. In the present embodiment, by setting the solid content concentration of nanocellulose in the dispersion liquid to 0.150% by mass or less, the distance between the fibers in the dispersion liquid is appropriately separated, and the nanocellulose is not or hardly oriented. Therefore, even when nanocellulose is incorporated into an air filter, a uniform fiber network can be formed without having a specific directionality, and it has an effect of remarkably enhancing the particle collecting performance as a filter medium for an air filter. On the other hand, if the concentration of nanocellulose in the dispersion liquid is less than 0.001% by mass, the entanglement of nanocellulose is reduced, and the network structure may not be maintained.

<Preparation of dispersion>
In the present embodiment, the method for preparing the dispersion liquid is not particularly limited, and nanocellulose may be dispersed in the above-mentioned dispersion medium to prepare a dispersion liquid. When using a mixed dispersion medium in which water and an organic solvent that dissolves in water are mixed, after preparing nanocellulose aqueous dispersion by dispersing nanocellulose in water, nanocellulose aqueous dispersion, with an organic solvent or water. It is preferable to add a mixed solvent with an organic solvent. When an aqueous dispersion of nanocellulose is added to the organic solvent, aggregates may be generated.

  In the present embodiment, various auxiliary agents may be added to the dispersion liquid. When freeze-drying is used in the drying step, sucrose, trehalose, L-arginine or L-histidine can be added as a freeze-drying stabilizer. Further, as the surface modifier for the nanocellulose, for example, a cationic surfactant, an anionic surfactant, a nonionic surfactant or an amphoteric surfactant can be blended.

<Adhesion process>
The method for attaching the dispersion liquid to the support is not particularly limited, and examples thereof include an impregnation method, a coating method and a spraying method. The amount of the dispersion liquid adhered to the support is appropriately adjusted according to the thickness, material and average pore diameter of the support, but as described above, in the present embodiment, the amount of nanocellulose adhered to the support. Is 0.001 to 0.500% by mass. The content is more preferably 0.010 to 0.300% by mass, and further preferably 0.050 to 0.200% by mass. By setting the ratio of the amount of nanocellulose adhered to the support to 0.001 to 0.500% by mass, it is possible to manufacture a highly efficient filter medium for air filters with improved particle collection performance. When the ratio of the attached amount of nanocellulose to the support is less than 0.001% by mass, the attached amount of nanocellulose to the support is insufficient, and it is difficult to form a uniform nanocellulose network. As a result, there is a possibility that the particle collection performance as the filter material for the air filter cannot be sufficiently improved. On the other hand, when it exceeds 0.500% by mass, the packing density of nanocellulose in the filter material for an air filter becomes excessively high, and the pressure loss may become excessively high. Further, in order to form a network of nanocellulose and obtain a high PF value, it is preferable to appropriately set the ratio of the amount of nanocellulose adhered to the support according to the drying method in the drying step performed later. For example, when the drying method is drying at room temperature or heat, the ratio of the amount of nanocellulose attached to the support is preferably 0.001 to 0.100 mass%, and 0.010 to 0.050 mass%. Is more preferable. When the drying method is freeze-drying, the ratio of the amount of nanocellulose attached to the support is preferably 0.001 to 0.500% by mass, and 0.010 to 0.300% by mass. Is more preferable. In the present invention, the method of calculating the ratio of the amount of nanocellulose adhered to the support is not particularly limited, but, for example, when the support is composed of only inorganic fibers, only nanocellulose is burned and burned. It can be calculated from the subsequent weight loss rate. When the support contains organic synthetic fibers, it can also be calculated from the amount of dissolution, for example, by dissolving only cellulose using a copper ethylenediamine solution. The ratio of the amount of nanocellulose attached to the support may be calculated from the wet amount of attachment. That is, the ratio (unit%) of the adhered amount of nanocellulose to the support is {(wet adhered amount × solid concentration of nanocellulose in the dispersion liquid) / mass of the support before the dispersion liquid is adhered} × 100 Is. Here, the wet adhesion amount is the difference between the weight of the support in the wet state to which the dispersion liquid is attached and the weight of the support before the attachment, and the dispersion attached to the support at the start of the drying step. It means the mass of liquid. Therefore, the wet adhesion amount is preferably a value measured immediately before the drying step, for example, it is preferably measured within 10 minutes before the start of the drying step, and more preferably within 5 minutes.

  The impregnation method includes, for example, a method of completely immersing the support in the dispersion liquid or a method of immersing only the surface of the support. The method of completely immersing the support in the dispersion liquid allows the dispersion liquid to efficiently and surely penetrate deep into the pores of the support, thereby forming a more uniform nanocellulose network. Excellent in terms. Further, when the pressure is reduced while the support is completely immersed in the dispersion, the air in the support is easily released, which is more effective for permeating the dispersion. The excessively adhered dispersion is preferably squeezed out by a roll dehydrator or the like, or removed by a water absorbing member such as water absorbent felt or water absorbent paper. The method of immersing only the surface of the support is such that the density difference of the network structure of nanocellulose in the pores in the thickness direction of the support (the presence of the network structure of nanocellulose on one surface side of the support and the other surface) It is effective in providing different ratios).

  The coating method is a method of coating the dispersion on the surface of the support with a known coating machine or brush. A known coating machine is, for example, a curtain coater (die coater). The coating method is excellent in that it is easy to control the amount of the dispersion liquid attached to the support.

  The spraying method is a method of spraying the dispersion liquid onto the surface of the support using a known sprayer such as a sprayer or a sprayer. The spraying method is, for example, when it is desired to form a nanocellulose network structure only in the vicinity of the surface of the support among the pores of the support, or a large amount of impregnating liquid, or a roll or bar of a coating machine is contacted with the support. It is effective when you do not want to let it. In the coating method and the spraying method, one surface of the support is depressurized to cause a flow of air, and the dispersion can be penetrated into the support by applying or spraying from the other surface.

  In the present embodiment, since nanocellulose is attached after the support is pleated, damage to the nanocellulose network during pleating can be suppressed. In the most common pleating process, a support is repeatedly subjected to a mountain fold process and a valley fold process to be pleated. The crests of the folds form an acute angle close to 180 degrees, and the support is damaged to some extent. A general support (conventional filter media for air filters) that is mainly composed of glass fibers or organic fibers is usually designed to withstand such folding, but the nanocellulose present on the surface of the support is The network of 1 may be broken or fallen off by the folding process, which may deteriorate the performance of the filter material for the air filter. On the other hand, in the present invention, since the nanocellulose is attached to the support after the support is pleated, the nanocellulose network can be formed even in the fold ridges.

<Drying process>
In this embodiment, the dispersion is attached to the support as described above, the support is made wet, and then dried. The drying method is not particularly limited, and drying at room temperature or heat or freeze drying can be used. Moreover, you may dry by pressure reduction. More preferably, the drying method is a freeze-drying method. As a result, aggregation of nanocellulose can be suppressed and a good nanocellulose network can be constructed, so that the filter performance of the air filter medium or the air filter can be further improved.

  In this embodiment, it is preferable to select the configuration of the dispersion liquid (dispersion medium) depending on the drying method. That is, when performing drying at room temperature or heat, it is preferable to use water (which may contain a surfactant) as the dispersion medium. Further, when performing freeze-drying, it is preferable to use a mixed dispersion medium in which water and an organic solvent soluble in water are mixed.

  The temperature for heat drying may be a temperature at which the support and the nanofibers are not decomposed or deformed. For example, a nonwoven fabric made of glass fiber is used as the support, and the nanofiber is disclosed in Patent Document 1. When the described nanofiber is used, the temperature may be 50 to 200 ° C. In the present embodiment, by using a porous support, the cohesive force generated on the nanofibers when the dispersion is dried is dispersed, and further, a large number of minute thin films are formed in each hole of the support. It is considered that, by drying, the nanofibers dispersed in the micro thin film remain in a network structure even when water is evaporated.

  Freeze-drying is a method in which the dispersion liquid is frozen together with the support (freezing step), and then dried by depressurizing the dispersion medium in the frozen state to sublime the dispersion medium (drying step). The method of freezing the dispersion in the freezing step is not particularly limited, for example, a method in which the support to which the dispersion is attached is put in a refrigerant such as liquid nitrogen to freeze, and the support to which the dispersion is attached is cooled. There are a method of placing the support on the top and freezing, a method of placing the support to which the dispersion is attached in a low temperature atmosphere to freeze, and a method of placing the support to which the dispersion is attached under reduced pressure to freeze. Preferred is a method in which the support to which the dispersion liquid is attached is put in a refrigerant and frozen. The freezing temperature of the dispersion must be equal to or lower than the freezing point of the mixed dispersion medium in the dispersion, preferably -50 ° C or lower, and more preferably -100 ° C or lower. If the freezing temperature is high, that is, the freezing rate is slow, the crystals of the dispersion medium may become large even if a mixed dispersion medium in which water and an organic solvent are mixed is used, and nanocellulose is concentrated around the crystals and aggregates are formed. May occur. On the other hand, by setting the freezing temperature sufficiently lower than the freezing point of the mixed dispersion medium, that is, by increasing the freezing rate, the dispersion medium can be frozen in a state close to amorphous.

  In the present embodiment, it is preferable to set the ambient temperature of the sample to a temperature equal to or lower than the melting point of the dispersion liquid in the drying step in the freeze-drying process. Here, the drying step in the freeze-drying process refers to a period during which the dispersion medium is sublimated from the frozen sample under reduced pressure. The ambient temperature of the sample is usually room temperature unless otherwise controlled. As described above, when the ambient temperature of the sample exceeds the melting point of the dispersion liquid, a part of the frozen dispersion liquid may be melted and the homogeneity of the nanocellulose network may be lost. For example, when the dispersion medium is a mixed dispersion medium of water and t-butyl alcohol and the concentration of t-butyl alcohol in the mixed dispersion medium is more than 0 and 50 mass% or less, the nanocellulose and the dispersion medium are The melting point of the contained dispersion is equal to the melting point of the dispersion medium. According to Non-Patent Document 1, the melting point of the mixed dispersion medium of water and t-butyl alcohol is at least -8.2 ° C. Therefore, when the dispersion medium is a mixed dispersion medium of water and t-butyl alcohol and the concentration of t-butyl alcohol in the mixed dispersion medium is more than 0 and 50 mass% or less, the ambient temperature of the sample is -8 It is preferably not higher than 2 ° C, more preferably not higher than -15 ° C, still more preferably not higher than -20 ° C. The lower limit of the ambient temperature of the sample varies depending on the type of the dispersion medium, but when using a mixed dispersion medium of water and t-butyl alcohol, it is preferably −30 ° C. or higher.

  The melting point of the dispersion can be determined from the first endothermic point that occurs when the dispersion changes from solid to liquid. The melting point of the dispersion liquid may be measured, for example, from the starting point of the first endothermic peak in the DSC curve obtained by a differential scanning calorimeter (DSC).

  In the present embodiment, the pressure of the drying step in the freeze-drying process is preferably 200 Pa or less, more preferably 50 Pa or less. If the pressure exceeds 200 Pa, the dispersion medium in the frozen dispersion liquid may melt.

<Air filter>
The air filter obtained by the manufacturing method according to the present embodiment is, for example, a coarse dust filter, a medium performance filter, a HEPA filter or a ULPA filter. The air filter obtained by the manufacturing method according to the present embodiment has a frame material and the filter material for an air filter obtained by the manufacturing method according to the present embodiment, and the filter material for an air filter is fixed to the frame material. Further, the air filter obtained by the manufacturing method according to the present embodiment can be applied as a dust mask or a mask for protecting pollutants such as pollen and virus.

The air filter or the filter medium for an air filter obtained by the manufacturing method according to the present embodiment preferably has a high PF value defined by the equation (1). The PF value is an index for evaluating the superiority or inferiority of the balance between pressure loss and particle collection performance, and is calculated using the formula shown in Formula 1. The higher the PF value, the higher the efficiency of collecting the target particles and the low pressure loss of the air filter or the filter material for an air filter.

  In Formula 1, the pressure loss is measured using, for example, a manometer. In addition, the particle transmittance is a ratio of PAO particles passing through an air filter or a filter medium for an air filter when passing air containing polydisperse polyalphaolefin (PAO) particles generated by a Ruskin nozzle. The particle transmittance is measured using, for example, a laser particle counter.

  Although the PF value of the air filter or the filter material for the air filter is also influenced by the type and structure of the support, the packing density of nanocellulose of the filter material for the air filter or the degree of formation of a network by nanocellulose has a great influence. In the filter medium for an air filter obtained by the production method according to the present embodiment, the ratio of the amount of nanocellulose adhered to the support is preferably 0.001 to 0.200% by mass, but such an adhered amount is not preferable. However, for example, if the adhesion of nanocellulose concentrates only near the surface layer of the support and the packing density of nanocellulose becomes excessively high partially, it causes an excessive increase in pressure loss, resulting in a decrease in PF value. To do. The filter material for an air filter preferably has a network network of nanocellulose on the inside and / or the surface of the support and does not have a film-like aggregate of nanocellulose. More specifically, when a dispersion having a high concentration of nanocellulose is adhered to the support, the adhesion of nanocellulose is concentrated on the surface of the support, which may cause aggregation of nanocellulose with each other on the surface of the support. To be As a result, a nanocellulose network is not formed in the surface layer of the support, and a film-like aggregate may occur. When the filter material for an air filter in which such a film-like aggregate is partially generated is used, an increase in pressure loss and a decrease in particle collection performance (that is, a decrease in PF value) occur, and in some cases, an air filter. As a result, it becomes impossible to maintain its breathability. Even if the adhesion of nanocellulose concentrates only near the surface layer of the support, if the nanocellulose network is formed appropriately (unless the packing density of nanocellulose is too high), the pressure loss will increase so much. Instead, a PF value suitable as an air filter can be obtained.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Further, “parts” and “%” in the examples represent “parts by mass” and “mass%”, respectively, unless otherwise specified. The number of parts added is a value in terms of solid content.

[Preparation process of nano cellulose aqueous dispersion]
NBKP equivalent to 2.00 g dry weight (consisting mainly of fibers having a fiber diameter of more than 1000 nm) and 0.025 g TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical) , 0.25 g of sodium bromide was dispersed in 150 ml of water, and a 13% aqueous solution of sodium hypochlorite was added to the pulp (NBKP) of 1.00 g to adjust the amount of sodium hypochlorite to 5.00 mmol. Sodium hypochlorite was added so that the reaction was started. During the reaction, 0.50 mol / l sodium hydroxide aqueous solution was added dropwise to maintain the pH at 10. After reacting for 2 hours, the reaction product was filtered and sufficiently washed with water to obtain an oxidized cellulose (TEMPO oxidized cellulose) slurry. A 0.5% by mass TEMPO oxidized cellulose slurry was defibrated at 15,000 rpm for 5 minutes using a biomixer (BM-2, manufactured by Nippon Seiki Seisakusho Ltd.) to dilute the solid content concentration to 0.2% by mass. After that, the fiber was further defibrated with an ultrasonic disperser (model US-300E, manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 8 minutes. Then, coarse fibers were removed by centrifugation to obtain an aqueous dispersion of nanocellulose in which TEMPO oxidized nanocellulose was dispersed in water. The number average fiber diameter was 4 nm as a result of analysis from an observation image obtained by observing this nanocellulose aqueous dispersion with a TEM (JEM2000-EXII, manufactured by JEOL Ltd.) at a magnification of 50000 times. The number average fiber length was 0.8 μm as a result of analysis from an observation image observed with a SEM (SU8010, manufactured by Hitachi High-Technology) at a magnification of 10,000 times. Water and t-butyl alcohol were added to the nanocellulose aqueous dispersion, and the container was covered and stirred with a magnetic stirrer for 5 minutes to obtain a nanocellulose dispersion. The solid content concentration of nanocellulose was 0.02% with respect to the total mass of the dispersion liquid. The mixing ratio of water and t-butyl alcohol in the nanocellulose dispersion was 70:30 by mass.

(Example 1)
A PP pleated compact cartridge filter (hereinafter referred to as "support air filter") (MCP-7-C10S, manufactured by Advantech) in which a support made of polypropylene fiber is pleated in a zigzag shape and fixed to a frame material is a nano. The cellulose dispersion was impregnated. One minute after the impregnation, pull up the "support air filter", remove the excess nanocellulose dispersion adhering to the frame material with water absorbent paper, and measure the mass of the "support air filter" in the wet state (before drying). It was measured. The wet adhesion amount of the dispersion liquid adhering to the support was obtained from the difference between the mass of the "support air filter" in the wet state and the mass of the "support air filter" before wetting. The ratio of the attached amount of nanocellulose to the support calculated from the wet attached amount was 0.1%. The wet “support air filter” was frozen with liquid nitrogen (−196 ° C.), and the frozen “support air filter” was put into a freeze-dried bottle that had been cooled to −20 ° C. in advance. After that, the entire freeze-drying bottle was placed in a freezer set at -20 ° C, depressurized by a freeze-dryer (VD-250F TAITEC Co., Ltd.) connected with a vacuum tube, and the dispersion medium in the "support air filter" was sublimated. By doing so, an air filter in which nanocellulose was attached to the “support air filter” was obtained. The pressure when the vacuum was reached was 50 Pa or less. The nominal pore size of the "support air filter" was 7 µm.

(Comparative Example 1)
The "support air filter" made of the polypropylene fiber of the example was used as it was as an air filter.

(Example 2)
In order to clarify the effect of the pleating process on the filter material for air filters to which nanocellulose adheres, the change in filter performance due to the pleating process was investigated. As the support, glass fibers having a basis weight of 70 g / m ² and a pressure loss of about 215 Pa (48 parts of ultrafine glass fibers having an average fiber diameter of 0.65 μm and 42 parts of ultrafine glass fibers having an average fiber diameter of 2.7 μm) were used. And 10 parts of chopped glass fibers having an average fiber diameter of 6 μm). The pleating process was performed by repeating a mountain fold and a valley fold at a mountain height of 1 cm. The pleated support was impregnated with the nanocellulose dispersion, and one minute after the impregnation, the support was pulled up, and the excess nanocellulose dispersion that had adhered was removed with water-absorbent paper, and then kept wet (before drying). The mass of the support was measured. The wet adhesion amount attached to the support was determined from the difference between the weight of the support in the wet state and the weight of the support before wetting. The ratio of the attached amount of nanocellulose to the support calculated from the wet attached amount was 0.1%. This support was freeze-dried in the same manner as in Example 1 to obtain an air filter medium.

(Comparative example 2)
A filter medium for an air filter was obtained in the same manner as in Example 2 except that the support was impregnated with the nanocellulose dispersion, lyophilized and then pleated.

"Pressure loss"
The pressure loss was measured by using a manometer (Manostar WO81, manufactured by Yamamoto Denki Seisakusho Co., Ltd.) as a differential pressure when air having a surface wind velocity of 5.3 cm / sec was passed through the air filter.

"Particle transmittance"
The particle transmittance is upstream and downstream when air containing polydisperse polyalphaolefin (PAO) particles generated by the Ruskin nozzle is passed so that the surface wind speed with respect to the filter material for the air filter is 5.3 cm / sec. The particle transmittance from the number ratio was measured using a laser particle counter (LASAIR-1001, manufactured by PMS).

"PF value"
The PF value was calculated from the measured values of pressure loss and particle transmittance using the formula shown in Formula 1. It should be noted that the higher the PF value, the higher the efficiency of collecting the target particles and the lower the pressure loss of the air filter.

"Observing the network"
The network was observed by observing the filter material for the air filter with a scanning electron microscope (abbreviated as SEM, SU8010 manufactured by Hitachi High Technology Co., Ltd.) at a magnification of 5,000 to 10,000 times. Before observation, conductive coating was performed using ion sputtering (E-1045, manufactured by Hitachi High-Technology) under the conditions of a discharge current of 15 mA, a sample-target distance of 30 mm, a vacuum degree of 6 Pa, and a coating time of 2 minutes.

  The performance of the air filter of Example 1 was as follows: pressure loss 130 Pa, particle permeability 52.8% at particle size 0.10 to 0.15 μm, PF value 2.09, particle permeability at particle size 0.30 to 0.40 μm. The rate was 21.0% and the PF value was 5.11. On the other hand, the performance of the air filter of Comparative Example 1 is that the pressure loss is 85 Pa, the particle transmittance is 71.6% when the particle size is 0.10 to 0.15 μm, the PF value is 1.67, and the particle size is 0.30 to 0.40 μm. The particle transmittance was 45.4% and the PF value was 3.96. Comparing the two filters, the pressure loss of the air filter of Example 1 is higher than that of the air filter of Comparative Example 1, but both the particle permeability and the PF value of the air filter of Example 1 are higher than those of the air filter of Comparative Example 1. Higher than the filter, the air filter of Example 1 was shown to have higher performance. Further, from FIGS. 1 to 4, in the air filter of Comparative Example 1, there are only voids between the fibers that form the support, whereas in the air filter of Example 1, between the fibers that form the support. In addition to the voids, it was confirmed that nanocelluloses were entangled with each other to form a network, and voids were further formed between the nanocelluloses.

  From the comparison between Example 2 and Comparative Example 2, the effect of the pleat processing on the filter material for air filters to which nanocellulose was attached was investigated. The air filter performance of the filter material for an air filter of Comparative Example 2 which was pleated after the adhesion of the nanocellulose had a pressure loss of 243 Pa, a particle transmittance of 0.053% at a particle diameter of 0.10 to 0.15 μm, and a PF value of 13.2. Met. On the other hand, the air filter performance of the filter material for an air filter of Example 2 to which nanocellulose was attached after pleating was as follows: pressure loss 289 Pa, particle transmittance 0.005% at particle diameter 0.10 to 0.15 μm, PF value 14 It was .6. Comparing the filter performances of the filter materials for both air filters, the filter material for the air filter of Example 2 to which nanocellulose was attached after pleating was more than the filter material for air filter of Comparative Example 2 to which pleating was performed after attaching the nanocellulose. The particle transmittance was low, the PF value was high, and the filter performance was improved. From these results, it was shown that a filter medium for a higher performance air filter and a higher performance air filter can be obtained by attaching nanocellulose after pleating the support.

  From the above results, the method for manufacturing the filter material for an air filter and the method for manufacturing an air filter according to the present embodiment use nanocellulose, and it is possible to provide a filter material for an air filter having improved filter performance and an air filter using the same. I understand.

Claims (2)

A fixing step of fixing a pleated processed support having fluid permeability to the frame material;
An attaching step of attaching a dispersion containing nanocellulose to the support that has undergone the fixing step,
And a drying step of drying the support that has undergone the attaching step. The method of manufacturing an air filter according to claim 1 , wherein the drying method performed in the drying step is a freeze-drying method.