Filter material for air filters and method for manufacturing the same

Abstract

The present invention aims to provide an air filter filter material that improves particle capturing performance by relatively randomly arranging a network of polyvinyl alcohol in the pores of the fluid permeation path of a support in the planar direction and thickness direction of the support. The manufacturing method of the air filter filter material of the present invention includes the following steps: an attaching step in which an aqueous polyvinyl alcohol solution is attached to a support having fluid permeability, and the support is brought to a wet state; and a drying step in which the aqueous polyvinyl alcohol solution attached to the support in the wet state is dried at a temperature of 140°C or higher; and the aqueous polyvinyl alcohol solution does not contain an adhesive resin other than polyvinyl alcohol, and as a result of the aqueous polyvinyl alcohol solution being dried, the support after the drying step has a network of polyvinyl alcohol in the pores of the fluid permeation path.

Description

Technical Field

[0001] The purpose of this invention is to provide a filter material for air filters that uses polyvinyl alcohol and has significantly improved particle capture performance, as well as a method for manufacturing the same. More specifically, this invention provides a method for manufacturing a filter material for air filters suitable for air purification applications in cleanrooms or clean benches, high-rise air conditioning systems, internal combustion engines, or indoor spaces related to the semiconductor, liquid crystal, biological, and food industries, in a relatively short time. Background Technology

[0002] To capture submicron or micron-sized particles in the air, air filter media are typically used. Air filter media are broadly categorized based on their capture performance into coarse filter applications, medium-efficiency filter applications, HEPA (High Efficiency Particulate Air) filter applications, and ULPA (Ultra Low Permeability Air) filter applications. A fundamental characteristic of these air filter media is the requirement for low particle permeability of fine dust particles; in addition, low pressure loss is required for air to pass through the filter.

[0003] The following solution is proposed: using polyvinyl alcohol with a partial saponification degree of up to 90% as the filter material for air filters, thereby making the surface of glass fibers hydrophobic, improving the fiber dispersibility, and enhancing the filter performance (for example, see Patent Document 1).

[0004] In addition, the following solution is proposed: a nonwoven filter with high shape maintenance that is not easily broken in the thickness direction even when wind pressure is applied is formed by aligning the tiny fibers of polyvinyl alcohol in the thickness direction (for example, see Patent Document 2).

[0005] [Background Technical Documents]

[0006] [Patent Literature]

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-194584

[0008] Patent Document 2: WO2018 / 221063 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] In Patent Document 1, although polyvinyl alcohol is included as one of the adhesive resins used to bond glass fibers together, the filter material in a wet state is not rapidly dried. Although this improves the dispersibility of the glass fibers, other adhesive resins are also mixed in, which hinders the formation of a polyvinyl alcohol network between the fibers and makes it impossible to obtain a network structure.

[0011] In Patent Document 2, since there are fewer polyvinyl alcohol microfibers formed in directions other than the thickness direction, these microfibers may not necessarily contribute to the improvement of filter performance.

[0012] The present invention aims to provide a filter material for air filters that improves filter performance, particularly particle capture performance, by using polyvinyl alcohol (PVA) to form a relatively random network of PVA meshes in the pores of the fluid permeation path of a support, both in the planar and thickness directions of the support. Furthermore, the present invention aims to provide a method for manufacturing such a filter material for air filters in a relatively short time.

[0013] [Technical means to solve the problem]

[0014] The method for manufacturing the filter material for air filters of the present invention is characterized by comprising the following steps: an attachment step in which a polyvinyl alcohol aqueous solution is attached to a fluid-permeable support, thereby making the support wet; and a drying step in which the polyvinyl alcohol aqueous solution attached to the wet support is dried at a temperature of 140°C or higher; wherein the polyvinyl alcohol aqueous solution does not contain any adhesive resin other than polyvinyl alcohol, and the support after the drying step, due to the drying of the polyvinyl alcohol aqueous solution, has a polyvinyl alcohol mesh network in the pores that form the fluid permeation path.

[0015] In the method for manufacturing the filter material for air filters of the present invention, the mesh network preferably comprises nanofibers. This allows for both high particle capture performance and low pressure loss.

[0016] In the method for manufacturing the filter material for air filters of the present invention, the nanofibers are preferably nanofibers with an average fiber diameter of 10 to 500 nm. This allows for both higher particle capture performance and lower pressure loss.

[0017] In the method for manufacturing the filter material for air filters of the present invention, the degree of polymerization of the polyvinyl alcohol contained in the aqueous polyvinyl alcohol solution is preferably 1500 to 6000. This allows for a more robust formation of a polyvinyl alcohol network and improves the power factor (PF) value.

[0018] Furthermore, in the method for manufacturing the filter material for air filters of the present invention, the degree of saponification of polyvinyl alcohol contained in the aqueous polyvinyl alcohol solution is preferably 80-98 mol%. Polyvinyl alcohol is easily soluble in aqueous solution, which can more effectively form a polyvinyl alcohol network and improve the PF value.

[0019] In the method for manufacturing the filter material for air filters of the present invention, the concentration of the solid content of polyvinyl alcohol in the aqueous polyvinyl alcohol solution is preferably 0.01 to 0.20% by mass. This can suppress the formation of a polyvinyl alcohol film structure on the surface of the support.

[0020] In the method for manufacturing the filter material for air filters of the present invention, the amount of polyvinyl alcohol adhering to the support after the drying step is preferably 0.05 to 1.00% by mass. This allows for the production of a filter material for air filters with high particle capture performance and relatively low pressure loss.

[0021] In the method for manufacturing the filter material for air filters of the present invention, the amount of the polyvinyl alcohol aqueous solution attached to the support is preferably per 1m 2 The support weighs 50g or more. The pores in the support, which form the fluid permeation path, easily create a mesh network without excessive or insufficient formation, thus easily increasing the power factor (PF) value.

[0022] In the method for manufacturing the filter material for air filters of the present invention, during the drying step, the evaporation rate of the solvent in the polyvinyl alcohol aqueous solution adhering to the wetted support is preferably per 1m³. 2 Support speed of 100g / min or higher. By rapidly drying the polyvinyl alcohol aqueous solution, a more robust polyvinyl alcohol network can be formed.

[0023] In the method for manufacturing the filter material for air filters of the present invention, it is preferable that the aqueous polyvinyl alcohol solution further contains a cationic surfactant. This allows for both high particle capture performance and low pressure loss.

[0024] In the method for manufacturing the air filter material of the present invention, the amount of the cationic surfactant added to the polyvinyl alcohol aqueous solution is preferably 1 to 30 parts by weight relative to 100 parts by weight of polyvinyl alcohol. This results in an air filter material with further improved particle capture performance and relatively low pressure loss.

[0025] In the method for manufacturing the air filter material of the present invention, the total amount of polyvinyl alcohol and cationic surfactant adhering to the support after the drying step is preferably 0.05 to 1.30% by mass. This allows for the production of an air filter material with further improved particle capture performance and relatively low pressure loss.

[0026] In the method for manufacturing the filter material for air filters of the present invention, the support is preferably a nonwoven fabric for filter materials with glass fiber as the main component. This ensures stable maintenance of filter performance.

[0027] The filter material for air filters of the present invention is characterized by having: a support having fluid permeability; and a polyvinyl alcohol mesh network formed in the pores of the support that form fluid permeation paths; the mesh network comprising nanofibers, the polyvinyl alcohol having a degree of polymerization of 1500 to 6000, the polyvinyl alcohol having a degree of saponification of 80 to 98 mol%, the amount of polyvinyl alcohol adhering to the support being 0.05 to 1.00% by mass, and containing no adhesive resin other than the polyvinyl alcohol.

[0028] The filter material for air filters of the present invention is characterized by having: a support having fluid permeability; and a polyvinyl alcohol mesh network formed in the pores of the support that form fluid permeation paths; free of adhesive resins other than the polyvinyl alcohol, containing a cationic surfactant, and the mesh network comprising nanofibers.

[0029] The air filter material of the present invention preferably further contains a cationic surfactant. This provides an air filter material with improved filter performance, particularly particle capture performance.

[0030] [Invention Effects]

[0031] According to the present invention, a filter material for air filters is provided, which improves filter performance, especially particle capture performance, by using polyvinyl alcohol to form a mesh network of polyvinyl alcohol relatively randomly arranged in the pores of the fluid permeation path of the support in the planar and thickness directions of the support. Furthermore, according to the present invention, a method for manufacturing such a filter material for air filters in a relatively short time is also provided. Attached Figure Description

[0032] Figure 1 The image is obtained by observing the air filter of Example 1A using SEM (observation magnification 5000x).

[0033] Figure 2 The image is obtained by observing the air filter of Example 6A using SEM (observation magnification 5000x).

[0034] Figure 3 The image is obtained by observing the air filter of Example 8A using SEM (observation magnification 5000x).

[0035] Figure 4The image is obtained by observing the air filter of Comparative Example 2A using SEM (observation magnification 5000x).

[0036] Figure 5 The image is obtained by observing the air filter of Example 2B using SEM (observation magnification 5000x).

[0037] Figure 6 The image is obtained by observing the air filter of Example 12B using SEM (observation magnification 5000x). Detailed Implementation

[0038] Secondly, while embodiments of the present invention have been described in detail, the present invention is not to be interpreted as limited by these descriptions. Various variations of the embodiments are possible as long as the effects of the present invention are achieved.

[0039] The method for manufacturing the filter material for an air filter according to this embodiment includes the following steps: an attachment step in which a polyvinyl alcohol aqueous solution is attached to a fluid-permeable support, thereby making the support wet; and a drying step in which the polyvinyl alcohol aqueous solution attached to the wet support is dried at a temperature of 140°C or higher; wherein the polyvinyl alcohol aqueous solution does not contain any adhesive resin other than polyvinyl alcohol, and after the drying step, the support has a polyvinyl alcohol mesh network in the pores that form the fluid permeation path due to the drying of the polyvinyl alcohol aqueous solution.

[0040] The method for manufacturing the filter material for the air filter according to this embodiment includes an aqueous solution of polyvinyl alcohol further containing a cationic surfactant.

[0041] Hereinafter, polyvinyl alcohol aqueous solutions containing cationic surfactants will also be referred to as "polyvinyl alcohol aqueous solutions".

[0042] <Support>

[0043] The support material is not particularly limited as long as it is permeable to fluids; for example, porous materials such as nonwoven fabric, woven fabric, paper, or sponge can be used. Among these porous materials, nonwoven fabric is preferred, and nonwoven fabrics for filter materials with glass fibers, organic fibers, or the like as the main component are particularly preferred. For the purpose of stably maintaining filter performance, nonwoven fabrics for filter materials with glass fibers as the main component are further preferred. Using glass fibers, organic fibers, or the like as the main component means that the mass of such fibers is 50% or more by mass relative to the total mass of the support material. More preferably, it is 80% or more by mass. When the support material is a nonwoven fabric with such fibers as the main component, the weight per unit area is preferably 10 to 300 g / m². 2 More preferably 30–200 g / m 2Fluid permeability refers to the property that allows at least gas to pass through, and more preferably, the property that allows both gas and liquid to pass through.

[0044] The pressure loss of the support is preferably 1 Pa to 500 Pa. More preferably, it is 10 Pa to 300 Pa, and even more preferably, it is 30 Pa to 200 Pa.

[0045] When the pressure loss of the support is less than 1 Pa, the pore size of the support is too wide, making it difficult for the polyvinyl alcohol network to fill the pores. This results in a situation where it is difficult to improve the capture efficiency, and the PF value does not increase. When the pressure loss of the support exceeds 500 Pa, the capture efficiency of the support itself is extremely high, and the polyvinyl alcohol network may not contribute to the capture efficiency of the support, thus the PF value will not increase.

[0046] The glass fibers used for the support are, for example, hair-like ultrafine glass fibers manufactured using flame stretching or rotation methods, or chopped glass fibers made by cutting glass fiber bundles spun to a specific fiber diameter into specific fiber lengths. Depending on the desired physical properties, glass fibers with various fiber diameters and lengths are selected from these glass fibers and used alone or in combination. For example, a nonwoven fabric containing glass fibers obtained by mixing two or more ultrafine glass fibers with different average fiber diameters with chopped glass fibers is preferred. Furthermore, in semiconductor manufacturing applications, low-borosilicate glass fibers or silica glass fibers can be used to prevent boron contamination of silicon wafers. The average fiber diameter of the glass fibers is not particularly limited, but is preferably 0.05 to 20 μm, more preferably 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 1 to 1000 μm. On the other hand, organic fibers are, for example, polypropylene fibers, acrylic fibers, vinylon fibers, cellulose fibers, polyester fibers, or aromatic polyamide fibers. 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 when the organic fibers are short fibers, it is preferably 0.5 to 10,000 μm. More preferably, it is 10 to 5,000 μm. The manufacturing method of the nonwoven fabric is not particularly limited, for example, it can be a dry process or a wet process.

[0047] There are no particular limitations on the shape of the support, and it may not have a planar structure like a sheet. For example, the material of the support can be three-dimensionally processed, such as by pleating, which creates serrated pleats through repeated mountain-shaped and valley-shaped pleats. If a support that has been pre-pleated is used, the long strip support can be dried in a limited drying area, thereby efficiently obtaining filter material for air filters coated with polyvinyl alcohol.

[0048] Furthermore, the average pore size of the support is preferably 0.1 to 50 μm, more preferably 0.5 to 10 μm. If it is less than 0.1 μm, the fluid permeability is poor. If it exceeds 50 μm, it is difficult for polyvinyl alcohol to uniformly form a mesh structure within the pores of the support. In this embodiment, although an air filter can be obtained by adhering an aqueous solution containing polyvinyl alcohol and water to the pores of the support and then drying it, by using a support with an appropriate average pore size, the aqueous solution is uniformly distributed within the pores, and the mesh structure is easily maintained after drying. Here, the average pore size can be measured according to ASTM E1294-89 "Semi-dry method".

[0049] The support is preferably made of a raw material that can be used as a filter material for an air filter. In the air filter manufacturing method of this embodiment, by using such a support, an air filter with higher particle capture performance than conventional air filter filter materials (the support itself) can be easily obtained. Furthermore, the support can also be in a wet state; for example, during the papermaking step, a polyvinyl alcohol solution can be adhered to the wet support.

[0050] Polyvinyl alcohol is manufactured by using polyvinyl acetate as a raw material and saponifying the carboxyl groups in the polyvinyl acetate, in other words, converting them into hydroxyl groups through alkaline hydrolysis. Here, the ratio of carboxyl groups to hydroxyl groups is specifically referred to as the degree of saponification.

[0051] The saponification degree of polyvinyl alcohol is preferably 80–98 mol%, more preferably 82–90 mol%. If the saponification degree of polyvinyl alcohol is less than 80 mol%, the polyvinyl alcohol may not dissolve completely, resulting in an inability to obtain a suitable PF value. If the saponification degree of polyvinyl alcohol exceeds 98 mol%, the higher the saponification degree, the weaker the hydrophobic effect, making it difficult to form a network.

[0052] The degree of polymerization of polyvinyl alcohol (PVA) is preferably between 1500 and 6000, and more preferably between 2000 and 5000. For example, PVA95-88 (88 mol% saponification, 3500 degree of polymerization, manufactured by Kuraray Corporation) can be cited. If the degree of polymerization of PVA is less than 1500, it is difficult to form a network structure, and the PF value will not increase. If the degree of polymerization of PVA exceeds 6000, PVA is difficult to dissolve, resulting in undissolved residue and preventing an increase in the PF value.

[0053] In this embodiment, the degree of saponification of polyvinyl alcohol is preferably 80-98 mol%, and the degree of polymerization of polyvinyl alcohol is preferably 1500-6000. By keeping the degree of saponification and degree of polymerization of polyvinyl alcohol within this range, it is easier to form a polyvinyl alcohol network, and the PF value is increased.

[0054] In this embodiment, the polyvinyl alcohol aqueous solution may also contain additives other than polyvinyl alcohol. These additives include surfactants, water-repellent agents, defoamers, fine fibers, and fine particles. However, the polyvinyl alcohol aqueous solution must not contain any adhesive resins other than polyvinyl alcohol. If the polyvinyl alcohol aqueous solution contains adhesive resins other than polyvinyl alcohol, no increase in the PF value of the obtained air filter material is observed compared to the PF value measured using only the support. This is because the formation of the polyvinyl alcohol network is hindered.

[0055] In this embodiment, the polyvinyl alcohol aqueous solution preferably contains a cationic surfactant as an additive other than polyvinyl alcohol. Comparing the form of the polyvinyl alcohol aqueous solution containing a cationic surfactant with the form of the polyvinyl alcohol aqueous solution without a cationic surfactant, the PF value of the form containing the cationic surfactant is further increased. Even when the polyvinyl alcohol aqueous solution contains anionic or amphoteric surfactants, no increase in the PF value was observed; therefore, this further increase in the PF value is due to the formulation of the cationic surfactant.

[0056] As cationic surfactants, they can be broadly classified into quaternary ammonium salt type and amine salt type, with quaternary ammonium salt type being preferred. Examples include alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and perfluoroalkyltrialkylammonium salts. Among these, perfluoroalkyltrialkylammonium salts are fluorinated cationic surfactants. As amine salt type, examples include monoalkylamine salts, dialkylamine salts, and trialkylamine salts.

[0057] The amount of cationic surfactant added to the polyvinyl alcohol aqueous solution is preferably 1 to 30 parts by weight relative to 100 parts by weight of polyvinyl alcohol. When the cationic surfactant is a perfluoroalkyl trialkylammonium salt, it is preferable to add 1 to 30 parts by weight relative to 100 parts by weight of polyvinyl alcohol, more preferably 15 to 30 parts by weight. When the cationic surfactant is alkyltrimethylammonium chloride, it is preferable to add 5 to 10 parts by weight relative to 100 parts by weight of polyvinyl alcohol.

[0058] In the air filter material obtained by the manufacturing method of this embodiment, it is preferable that fibrous polyvinyl alcohol is entangled within the pores of the support, forming voids between the fibrous polyvinyl alcohol, and preferably it does not have a membrane structure formed by polyvinyl alcohol lamination. This prevents pressure loss from increasing and reducing particle permeability. A membrane structure formed by polyvinyl alcohol lamination refers to a membrane that blocks all or part of the pores of the support, formed by the physical entanglement or chemical coagulation of polyvinyl alcohol.

[0059] In this embodiment, the ratio of polyvinyl alcohol (PVA) adhering to the support is preferably 0.05 to 1.00% by mass, more preferably 0.10 to 0.50% by mass. By setting such an adhering amount, the air filter can achieve high particle capture performance and relatively low pressure loss. If the ratio of PVA adhering to the support is less than 0.05% by mass, the particle capture performance is poor. Conversely, if the ratio of PVA adhering to the support is greater than 1.00% by mass, it is prone to forming a membrane that clogs the pores of the support, affecting the particle capture performance and reducing the filter performance. The amount of PVA adhering to the support can be mainly controlled based on the concentration of PVA in the aqueous solution and the amount of aqueous solution adhering to the support. The higher the concentration of PVA in the aqueous solution or the higher the amount of aqueous solution adhering to the support, the more PVA will adhere to the support.

[0060] In this embodiment, the ratio of the total amount of polyvinyl alcohol and cationic surfactant attached to the support is preferably 0.05 to 1.30% by mass, more preferably 0.10 to 0.65% by mass.

[0061] In this embodiment, the amount of polyvinyl alcohol aqueous solution adhering to the support is preferably per 1m 2 The amount should be 50g or more. More preferably, 100g or more. If it is less than 50g, it is difficult to form a network between the fibers of the support, and the PF value is also difficult to improve. The upper limit of the amount of polyvinyl alcohol aqueous solution adhering to the support is, for example, per 1m 2 It weighs 300g.

[0062] In this embodiment, after attaching an aqueous polyvinyl alcohol solution to a support, a drying step of drying the aqueous polyvinyl alcohol solution at a temperature of 140°C or higher can be performed to obtain a filter material for an air filter. The aqueous solution can be obtained by dissolving polyvinyl alcohol in water. The form of polyvinyl alcohol in the aqueous solution is, for example, a form in which polyvinyl alcohol is stably dissolved in the aqueous solution at a unit of one or several molecules, or a partially condensed form. Among these forms, the preferred form of polyvinyl alcohol in the aqueous solution is a form in which polyvinyl alcohol is stably dissolved in the aqueous solution at a unit of one or several molecules.

[0063] <Solvent>

[0064] The solvent contained in the polyvinyl alcohol aqueous solution is preferably water, or a mixture of water and an organic solvent. Water is more preferred.

[0065] <Polyvinyl alcohol aqueous solution>

[0066] In this embodiment, the solid content concentration of polyvinyl alcohol in the aqueous solution is preferably 0.01 to 0.20% by mass, more preferably 0.03 to 0.10% by mass. If the solid content concentration of polyvinyl alcohol in the aqueous solution is less than 0.01% by mass, the solid content concentration is too low, making it difficult to form a polyvinyl alcohol network and the PF value will not increase. If it exceeds 0.20% by mass, a film-like structure of polyvinyl alcohol will form on the surface of the support. As described above, 1 to 30 parts by mass of a cationic surfactant are added to the polyvinyl alcohol aqueous solution relative to 100 parts by mass of polyvinyl alcohol.

[0067] <Preparation of Aqueous Solutions>

[0068] In this embodiment, the method for preparing the aqueous solution is not particularly limited, as long as the polyvinyl alcohol is dissolved in water to prepare an aqueous solution. As a method for adding a cationic surfactant to the polyvinyl alcohol aqueous solution, when making the final adjustment of the concentration of polyvinyl alcohol after adding polyvinyl alcohol to water, the solution is diluted with an aqueous solution containing a cationic surfactant at a concentration of about 0.5 to 3% by mass, and the concentrations of polyvinyl alcohol and cationic surfactant are adjusted separately.

[0069] The method for dissolving polyvinyl alcohol in this embodiment is not particularly limited. For example, a magnetic stirrer or a propeller mixer can be used to add polyvinyl alcohol powder or liquid to water and stir at about 100 to 700 rpm for 10 minutes. Next, the temperature is raised to 95°C during stirring, and stirring is carried out for about 2 hours to completely dissolve the polyvinyl alcohol.

[0070] <Attachment Steps>

[0071] Methods for attaching the aqueous solution to the support include, for example, impregnation, coating, or spraying. Spraying is preferred. The amount of aqueous solution attached to the support can be appropriately adjusted according to the thickness, material, and average pore size of the support, but as described above, in this embodiment, the amount of polyvinyl alcohol attached to the support is preferably 0.05% to 1.00%. If the amount of polyvinyl alcohol attached to the support is less than 0.05% by mass, the amount of polyvinyl alcohol attached to the support becomes insufficient, making it difficult to form a uniform polyvinyl alcohol network. As a result, there is a concern that the particle capture performance as a filter material for air filters cannot be sufficiently improved. Conversely, if it exceeds 1.00% by mass, it is easy to form a membrane formed by the aggregation of the polyvinyl alcohol network, and there is a concern that the particle capture performance cannot be sufficiently improved. Furthermore, as described above, in this embodiment, the ratio of the total amount of polyvinyl alcohol and cationic surfactant attached to the support is preferably 0.05% to 1.30% by mass. In this embodiment, the method for calculating the ratio of polyvinyl alcohol (PVA) adhering to the support is not particularly limited. For example, if the support is composed only of inorganic fibers, only PVA can be burned; or if a cationic surfactant is included, both PVA and the cationic surfactant can be burned, and the amount of adhering can be calculated based on the ratio of the amount reduced after burning. Furthermore, the ratio of PVA adhering to the support can also be calculated based on the amount of wet adhesion. That is, the ratio of PVA adhering to the support (in %) is {(wet adhesion amount × concentration of solid PVA in the aqueous solution) / mass of the support before the aqueous solution is applied} × 100. Furthermore, the ratio of PVA and cationic surfactant adhering to the support can also be calculated based on the amount of wet adhesion. That is, the ratio of PVA and cationic surfactant adhering to the support (in %) is {(wet adhesion amount × total concentration of solid PVA and cationic surfactant in the aqueous solution) / mass of the support before the aqueous solution is applied} × 100. Here, the amount of wetted material is the difference between the mass of the support in its wetted state to which the aqueous solution is attached and the mass of the support before attachment. It refers to the mass of the aqueous solution attached to the support at the start of the drying step. Therefore, the amount of wetted material is preferably a value measured just before the drying step, for example, preferably within 10 minutes before the start of the drying step, and more preferably within 5 minutes.

[0072] As an impregnation method, methods include either completely immersing the support in an aqueous solution or only immersing the surface of the support. Completely immersing the support in the aqueous solution allows the solution to efficiently and effectively penetrate deep into the pores of the support, thus forming a more uniform polyvinyl alcohol network, which is superior in this respect. Furthermore, if decompression is applied while the support is completely immersed in the aqueous solution, air within the support is easily released, thus allowing for more effective penetration of the aqueous solution. Additionally, for excessive amounts of adhering aqueous solution, it is preferable to use a spin dryer or similar device, or to remove it using absorbent materials such as absorbent felts or absorbent paper. The method of only immersing the surface of the support is effective when there is a density difference in the polyvinyl alcohol network structure within the pores along the thickness direction of the support (the ratio of the polyvinyl alcohol network structure on one side of the support differs from that on the other side).

[0073] The coating method involves applying an aqueous solution to the surface of a support using a known coating machine or brush. Known coating machines include, for example, curtain coating machines and nozzle coating machines. The advantage of the coating method is that it is relatively easy to control the amount of aqueous solution adhering to the support.

[0074] The spray method is a method of applying an aqueous solution to the surface of a support using a known atomizer or sprayer. The spray method is effective in situations where it is desired to form a polyvinyl alcohol network structure only near the surface of the support within its pores, or when it is undesirable for the support to come into contact with a large amount of impregnating liquid, or with the rollers or bars of a coating machine.

[0075] In this embodiment, a spray method is preferred. The advantage of the impregnation method lies in the penetration of the solution, but when too much solution is wiped away, for example, the solution adhering between the glass fibers will be wiped off, making it difficult to form a mesh network after drying. Furthermore, if dehydration is performed using a suction machine or the like instead of wiping, there is no solution film between the fibers, making it impossible to form a network and failing to improve filter performance. On the other hand, with the spray method, the amount of solution adhering can be controlled, thus eliminating the need for excessive solution and consistently improving filter performance.

[0076] <Drying Steps>

[0077] In this embodiment, as described above, after the aqueous solution is applied to the support and the support becomes wet, it is dried at a temperature of 140°C or higher. Preferably, the temperature is 140–250°C, and more preferably 170–220°C. Furthermore, the drying temperature mentioned here refers to the highest drying temperature of the drying apparatus used in the drying process.

[0078] In this embodiment, the preferred drying equipment is a rotary drum dryer, a hot air dryer, or an infrared dryer. Furthermore, these drying methods can be combined. Additionally, the drying described herein is performed at atmospheric pressure.

[0079] In this embodiment, during the drying step, the evaporation rate of the solvent in the polyvinyl alcohol aqueous solution adhering to the wetted support is preferably per 1m. 2 The drying rate of the support is 100 g / min or more, preferably 120 g / min or more. If it is less than 100 g / min, the drying rate is slow, and therefore the polyvinyl alcohol network may not be formed. In addition, the upper limit of the evaporation rate is, for example, 300 g / min.

[0080] In this embodiment, air can also be used during drying. The purpose of using air is to prevent water vapor generated by evaporation from remaining around the support or to promote the evaporation of the solution. However, if the airflow is strong enough to penetrate the interior of the filter material, the solution film adhering between the fibers may be damaged; therefore, a moderate airflow is preferred.

[0081] When a cationic surfactant is present in a polyvinyl alcohol aqueous solution, the amount of aqueous solution adhering to the support is reduced compared to the case without a cationic surfactant. It is speculated that the presence of a cationic surfactant improves filtration, resulting in reduced adhesion. Furthermore, the reduced adhesion of the aqueous solution allows for a decrease in the load during heat drying and a reduction in drying time, thereby improving productivity.

[0082] In this embodiment, the solid polyvinyl alcohol obtained after drying is fibrous, preferably nanofibers, more preferably nanofibers with a number average fiber diameter of 10 to 500 nm, and even more preferably nanofibers with a number average fiber diameter of 10 to 100 nm. To produce an air filter that combines high particle capture performance with low pressure loss, it is important to form a uniform fiber network of polyvinyl alcohol with extremely fine fiber diameters within the support. If nanofibers, especially extremely fine polyvinyl alcohol with a number average fiber diameter of 500 nm or less, are used, the number of fibers per unit volume in the filter material for the air filter increases significantly, making it easier to capture particles in the gas and achieving high capture performance. Furthermore, due to the slip-flow effect, the wind resistance of a single fiber becomes extremely low, and the pressure loss as an air filter is less likely to increase. The number average fiber diameter of the polyvinyl alcohol can be calculated as follows: The water-soluble polymer cast on the carbon film-coated grid is observed using a transmission electron microscope (TEM). For each image obtained, two random axes are drawn vertically and horizontally in each image, and the fiber diameters of the fibers intersecting these axes are visually read. The observation is then performed at magnifications of 5000x, 10000x, or 50000x, depending on the size of the fibers. Furthermore, the sample or magnification is conditional on at least 20 fibers intersecting the axes. In this way, at least three images of the non-overlapping surface portion are taken using an electron microscope, and the fiber diameter values ​​of the fibers intersecting the two axes are read. Therefore, information on at least 20 × 2 × 3 = 120 fibers can be obtained. The number-average fiber diameter is calculated based on the obtained fiber diameter data. Additionally, for branched fibers, if the length of the branch is 50 nm or more, it is included as one fiber in the fiber diameter calculation. Furthermore, the number-average fiber diameter can also be calculated as follows: Polyvinyl alcohol present on the surface or inside the support is observed using a scanning electron microscope (SEM) image. For each acquired observation image, two random axes are drawn in both the longitudinal and transverse directions within each image. The fiber diameters of the fibers intersecting these axes are visually read. The observations are then performed at any magnification from 5000 to 50000, depending on the size of the constituent fibers. Multiple images of the non-overlapping surface portion are captured using an electron microscope, and the fiber diameter values ​​of the fibers intersecting the two axes are read. The number-average fiber diameter is calculated based on the diameter data of at least 120 fibers. Furthermore, for branched fibers, any branch with a length of 50 nm or more is included as a single fiber in the fiber diameter calculation. Additionally, to obtain observation images free from deformation, a conductive coating is applied to the sample beforehand, and the effect of the coating thickness is also considered.For example, using an ion sputtering apparatus (E-1045, manufactured by Hitachi High Technology Corporation), with a discharge current of 15 mA, a sample-target distance of 30 mm, a vacuum of 6 Pa, and a coating time of 2 minutes, the coating thickness is 12 nm. However, when measuring the fiber diameter, the coating deposition direction is perpendicular to the assumed direction; therefore, the coating thickness when measuring the fiber diameter is half of the assumed thickness. In other words, when coating is performed under the above conditions, the thickness is calculated by subtracting the 12 nm coating thickness (6 nm + 6 nm) at both ends from the fiber diameter determined by SEM.

[0083] The air filter material obtained by the manufacturing method of this embodiment preferably comprises: a support having fluid permeability; and a polyvinyl alcohol (PVA) mesh network formed in the pores of the support that serve as fluid permeation paths; wherein the mesh network comprises nanofibers with an average fiber diameter of 10 to 500 nm, the PVA has a degree of polymerization of 1500 to 6000, the PVA has a degree of saponification of 80 to 98 mol%, the amount of PVA adhering to the support is 0.05 to 1.00% by mass, and it does not contain any adhesive resin other than PVA. Here, the air filter material does not contain any adhesive resin other than PVA. If the air filter material further contains other adhesive resins besides PVA, no increase in the PF value is observed based on the PF value measured using only the support. This is because if other adhesive resins besides PVA are further contained, the PVA mesh network cannot be formed.

[0084] The air filter material obtained by the manufacturing method of this embodiment preferably comprises: a support having fluid permeability; a polyvinyl alcohol (PVA) mesh network formed in the pores of the support that form fluid permeation paths; and contains no adhesive resin other than PVA, but contains a cationic surfactant, and the mesh network comprises nanofibers. Here, the amount of cationic surfactant added is preferably 1 to 30 parts by mass relative to 100 parts by mass of PVA. Here, the air filter material does not contain adhesive resin other than PVA. If the air filter material further contains other adhesive resins besides PVA, no increase in the PF value is observed based on the PF value measured using only the support. This is because if other adhesive resins besides PVA are further contained, the PVA mesh network cannot be formed. Furthermore, by containing a cationic surfactant, the PF value becomes higher compared to the case without a cationic surfactant. In the air filter material obtained by the manufacturing method of this embodiment, the total amount of PVA and cationic surfactant adhered to the support is preferably 0.05 to 1.30% by mass. Furthermore, the degree of polymerization of polyvinyl alcohol is preferably 1500 to 6000. Additionally, the degree of saponification of polyvinyl alcohol is preferably 60 to 90 mol%. Furthermore, the nanofibers are preferably nanofibers with an average fiber diameter of 10 to 500 nm.

[0085] The filter material for air filters obtained using the manufacturing method of this embodiment preferably has a PF value that is 0.5 or higher than that of the support under conditions of a surface wind speed of 5.3 cm / s and a target particle size of 0.10 to 0.15 μm. The PF value is an indicator of the balance between pressure loss and particle capture performance, and is calculated using the formula shown in Figure 1. A higher PF value indicates a lower particle permeability and a lower pressure loss for the filter material for air filters.

[0086] [Number 1]

[0087]

[0088] In number 1, pressure loss is measured, for example, using a pressure gauge. Furthermore, particle transmittance is the ratio of PAO particles that pass through an air filter or the filter material used in the air filter when air containing polydisperse poly-α-olefin (PAO) particles generated by a Laskin nozzle is passed through it. Particle transmittance is measured, for example, using a laser particle counter.

[0089] The pressure drop (PF) value of air filter materials is also affected by the type or composition of the support, but the packing density of polyvinyl alcohol (PVA) or the degree to which a network of PVA forms has a greater impact. In the air filter material obtained using the manufacturing method of this embodiment, the concentration of the aqueous PVA solution attached to the support is preferably 0.01 to 0.20% by mass. However, even at this concentration, if, for example, the PVA attachment is concentrated inside and / or on the surface of the pores of the support, resulting in an excessively high local PVA packing density, it will still lead to an excessive increase in pressure loss, resulting in a decrease in the PF value. Preferably, the air filter material has a network of PVA inside and / or on the surface of the support, rather than a membrane structure of PVA. More specifically, regarding the membrane structure of PVA, when a high-concentration aqueous solution of PVA is attached to the support, the PVA attachment is concentrated inside and / or on the surface of the pores of the support, and PVA molecules are stacked inside and / or on the surface of the pores of the support, thus forming a membrane. As a result, a membrane structure sometimes forms on the surface of the support, rather than a network of PVA. If a filter material for an air filter is used, even if it only partially forms a membrane structure, pressure loss may increase or particle trapping performance may decrease (i.e., the PF value may decrease), and in some cases, the air permeability as an air filter cannot be maintained. However, even if the polyvinyl alcohol (PVA) adhesion is concentrated only near the surface of the support, as long as a PVA network is formed appropriately (as long as the PVA packing density is not too high), the pressure loss will not increase too much, and a suitable PF value for use as an air filter can be obtained. In this embodiment, the form of "a network of PVA in the pores that form the fluid passage path" includes, for example, a network structure formed by the entanglement of PVA nanofibers, existing inside the pores that form the fluid passage path, on the surface, or both inside and on the surface. When a cationic surfactant is contained in the PVA aqueous solution, the formation of the PVA network is further optimized and the PF value is higher when manufacturing the filter material for an air filter.

[0090] [Example]

[0091] Secondly, embodiments are given to illustrate the invention in more detail, but the invention is not limited to these embodiments. Furthermore, unless otherwise specified, "parts" and "%" in the examples refer to "parts by mass" and "% by mass," respectively. Additionally, the number of parts added is a converted value of the solid content.

[0092] [Preparation steps for polyvinyl alcohol aqueous solution]

[0093] 998.0 g of water was added to a 1000 ml beaker, followed by 2.0 g of polyvinyl alcohol (88 mol% saponification, 3500 degree of polymerization) powder. The mixture was stirred for 10 minutes using a propeller stirrer. The temperature was then increased to 95°C during stirring, and the mixture was stirred for 2 hours to dissolve the polyvinyl alcohol. The solid content of the polyvinyl alcohol relative to the total mass of the aqueous solution was 0.20%. The solution was diluted with water to achieve the concentrations required for the examples and comparative examples. Distilled water was used to adjust the aqueous solution.

[0094] Experiment A: Study on the morphology of non-cationic surfactants

[0095] (Example 1A)

[0096] [Adhesion and drying of polyvinyl alcohol]

[0097] The aqueous solution of polyvinyl alcohol with a saponification degree of 88 mol% and a polymerization degree of 3500 was used to make the concentration of the aqueous solution 0.07%. The aqueous solution of polyvinyl alcohol was applied to the support as a substrate at the amounts shown in Table 1, with a unit area weight of 51 g / m². 2 A filter material for air filters was obtained by drying a nonwoven fabric (hereinafter referred to as the "support") composed of glass fibers (including 22 parts of ultrafine glass fibers with an average fiber diameter of 0.65 μm, 63 parts of ultrafine glass fibers with an average fiber diameter of 2.4 μm, and 15 parts of chopped glass fibers with an average fiber diameter of 6 μm) with a pressure loss of approximately 70 Pa and using a hot air dryer at 190°C. The polyvinyl alcohol content on the support was 0.31%.

[0098] (Example 2A)

[0099] The drying temperature was changed to 170°C, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.30%.

[0100] (Example 3A)

[0101] The drying temperature was changed to 150°C, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.29%.

[0102] (Example 4A)

[0103] The dryer was changed to a rotary drum dryer, the drying temperature was changed to 150°C, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.20%.

[0104] (Example 5A)

[0105] The dryer was changed to a rotary drum dryer, the drying temperature was changed to 180°C, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.34%.

[0106] (Example 6A)

[0107] The polyvinyl alcohol was changed to polyvinyl alcohol with a saponification degree of 88 mol% and a polymerization degree of 4500, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.37%.

[0108] (Example 7A)

[0109] The polyvinyl alcohol was changed to polyvinyl alcohol with a saponification degree of 98 mol% and a polymerization degree of 1700, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 1. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.31%.

[0110] (Example 8A)

[0111] The polyvinyl alcohol was changed to polyvinyl alcohol with a saponification degree of 98 mol% and a polymerization degree of 2400, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amount shown in Table 2. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.31%.

[0112] (Example 9A)

[0113] The polyvinyl alcohol was changed to polyvinyl alcohol with a saponification degree of 80 mol% and a polymerization degree of 2400, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amount shown in Table 2. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.36%.

[0114] (Example 10A)

[0115] The concentration of the aqueous solution was changed to 0.20%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 2. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.44%.

[0116] (Example 11A)

[0117] The concentration of the aqueous solution was changed to 0.25%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 2. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.50%.

[0118] (Comparative Example 1A)

[0119] The glass fiber "support" of Example 1A was used directly as the filter material of the air filter.

[0120] (Comparative Example 2A)

[0121] The drying temperature was changed to 120°C, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 2. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.31%.

[0122] (Comparative Example 3A)

[0123] The air filter material was dried by passing hot air directly through it, and the amount of polyvinyl alcohol adhering to it was changed to the amount shown in Table 2. Otherwise, the air filter material was obtained in the same manner as in Example 1A. The amount of polyvinyl alcohol adhering to the support was 0.31%.

[0124] (Comparative Example 4A)

[0125] An acrylic resin (trade name: Ultrasole FB-19 / manufactured by Aike Industrial Co., Ltd.) was further added to an aqueous solution of polyvinyl alcohol at a concentration of 0.0007% in the aqueous solution, and the amount of polyvinyl alcohol containing the acrylic resin adhering to the aqueous solution was changed to the amount shown in Table 3. Otherwise, the filter material for air filters was obtained in the same manner as in Example 1A. The total amount of polyvinyl alcohol and acrylic resin adhering to the support was 0.34%.

[0126] The manufacturing conditions and physical properties of the air filter materials obtained in each embodiment and comparative example are shown in Tables 1 to 3. Furthermore, each physical property value can be measured using the method described below.

[0127]

[0128]

[0129] "PF value"

[0130] The PF value is calculated using the formula shown in Figure 1, based on measured values ​​of pressure loss and particle permeability. Additionally, the target particle size is 0.10–0.15 μm. A higher PF value indicates a lower particle permeability and lower pressure loss for the air filter.

[0131] [Number 1]

[0132]

[0133] "Observations on the Internet"

[0134] The network was observed using a scanning electron microscope (SEM, Hitachi High-Tech Corporation, SU8010) at a magnification of 5,000 to 10,000 times on the filter material of the air filter. Before observation, a conductive coating was applied using an ion sputtering system (E-1045, Hitachi High-Tech Corporation) under the following conditions: discharge current of 15 mA, distance between sample and target of 30 mm, vacuum of 6 Pa, and coating time of 2 minutes.

[0135] "Greece method for determining stiffness"

[0136] The test was conducted according to the Japanese TAPPI Pulp Test Method No. 40:2000 Paper and Paperboard - Stiffness under Bending Load - Grimethamine method. The machine used was a Grimethamine Softness Tester (manufactured by Kumagai Riki Kogyo Co., Ltd.).

[0137] "Method for determining tensile strength"

[0138] The test was conducted according to JIS P8113:2006 Paper and paperboard - Test method for tensile properties. The machine used was an Autograph AGX (manufactured by Shimadzu Corporation).

[0139] It can be seen that, compared with the support of Comparative Example 1A, Examples 1A to 11A all show higher PF values. Figure 1 The image shows an SEM observation of the air filter of Example 1A. According to... Figure 1 By rapidly drying polyvinyl alcohol with a saponification degree of 88 mol% at a high temperature of 190℃, a perfect nanofiber network is obtained, thus achieving a suitable PF value. Figure 2 The image shows an SEM observation of the air filter of Example 6A. According to... Figure 2Because the degree of polymerization is higher than that of Example 1A, it can have a more perfect nanofiber network, thus enabling the production of air filter materials with higher PF values. Figure 3 The image shows a SEM observation of the air filter of Example 8A. According to... Figure 3 Although the polyvinyl alcohol used was fully saponified (98 mol% saponification), its degree of polymerization was as high as 2400. Furthermore, it was dried at a high temperature of 190°C, resulting in perfect nanofibers with an appropriate PF value. In Comparative Example 2A, due to a drying temperature below 140°C, the drying amount was insufficient, a perfect network was not formed, and the PF value did not improve. Figure 4 The image shows a SEM image of the air filter of Comparative Example 2A. According to... Figure 4 Due to insufficient drying, it became a film-like laminate of polyvinyl alcohol. In Comparative Example 3A, because the air filter was dried directly by blowing air through the filter material, the film of the PVA aqueous solution was damaged by strong wind, making it difficult to form a network, and the PF value did not increase. In Comparative Example 4A, because a small amount of acrylic resin (1% acrylic resin was added to PVA) was further added to the polyvinyl alcohol aqueous solution as a binder resin, a network of polyvinyl alcohol could not be formed, and the PF value was almost the same as that of Comparative Example 1A, with no increase.

[0140] Based on the above results, it can be seen that the method for manufacturing air filter filter material of this embodiment can provide a method for manufacturing air filter filter material with improved filter performance in a relatively short time using polyvinyl alcohol.

[0141] Experiment B: Study on the morphology of cationic surfactants

[0142] In Experiment B, it was observed that the PF value was higher compared to Experiment A, which did not contain a surfactant, due to the presence of a surfactant, particularly a cationic surfactant. In other words, Examples 1B to 8B and Example 10B, which contain cationic surfactants, have higher PF values ​​compared to Examples 12B to 18B, which do not contain cationic surfactants. However, the PF values ​​of Examples 12B to 18B are almost identical to those of Examples 1A to 11A in Experiment A.

[0143] (Example 1B)

[0144] [Adhesion and drying of polyvinyl alcohol]

[0145] A polyvinyl alcohol aqueous solution was prepared with a concentration of 0.07% for polyvinyl alcohol (88 mol% saponification, 3500 degree of polymerization, PVA95-88, manufactured by Kuraray Co., Ltd.) and a concentration of 0.0035% for a surfactant (alkyltrimethylammonium chloride, cationic surfactant, CATIOGEN TML, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.). The polyvinyl alcohol aqueous solution was then atomized using a two-fluid nozzle sprayer to adhere the solution to a substrate with a unit area weight of 51 g / m², as shown in Table 4. 2 A filter material for air filters was obtained by drying a nonwoven fabric (hereinafter referred to as the "support") composed of glass fibers (including 22 parts of ultrafine glass fibers with an average fiber diameter of 0.65 μm, 63 parts of ultrafine glass fibers with an average fiber diameter of 2.4 μm, and 15 parts of chopped glass fibers with an average fiber diameter of 6 μm) with a pressure loss of 65 Pa at 190°C using a hot air dryer. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.39%.

[0146] (Example 2B)

[0147] The polyvinyl alcohol aqueous solution was modified by setting the surfactant concentration to 0.0070%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.36%.

[0148] (Example 3B)

[0149] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0007%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.35%.

[0150] (Example 4B)

[0151] The concentration of the polyvinyl alcohol aqueous solution (perfluoroalkyl trialkylammonium salt, fluorinated cationic surfactant, Surflon S-221, manufactured by AGC Seimei Chemical Co., Ltd.) was changed to 0.0035%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.36%.

[0152] (Example 5B)

[0153] The concentration of the polyvinyl alcohol aqueous solution (perfluoroalkyl trialkylammonium salt, fluorinated cationic surfactant, Surflon S-221, manufactured by AGC Seimei Chemical Co., Ltd.) was changed to 0.0070%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.39%.

[0154] (Example 6B)

[0155] The concentration of the polyvinyl alcohol aqueous solution (perfluoroalkyl trialkylammonium salt, fluorinated cationic surfactant, Surflon S-221, manufactured by AGC Seimei Chemical Co., Ltd.) was changed to 0.0105%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.42%.

[0156] (Example 7B)

[0157] The concentration of the polyvinyl alcohol aqueous solution (perfluoroalkyl trialkylammonium salt, fluorinated cationic surfactant, Surflon S-221, manufactured by AGC Seimei Chemical Co., Ltd.) was changed to 0.0140%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.41%.

[0158] (Example 8B)

[0159] The concentration of the polyvinyl alcohol aqueous solution (perfluoroalkyl trialkylammonium salt, fluorinated cationic surfactant, Surflon S-221, manufactured by AGC Seimei Chemical Co., Ltd.) was changed to 0.0210%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.43%.

[0160] (Example 10B)

[0161] The polyvinyl alcohol (PVA) aqueous solution was modified to have a concentration of 0.07% (88 mol% saponification, 4500 degree of polymerization, PVA-245, manufactured by Kuraray Corporation) and a surfactant concentration of 0.0070%. The amount of PVA aqueous solution adhering to the solution was also modified to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of PVA and surfactant adhering to the support was 0.39%.

[0162] (Comparative Example 1B)

[0163] The glass fiber "support" of Example 1B was used directly as the filter material of the air filter.

[0164] (Example 12B)

[0165] The polyvinyl alcohol (PVA) aqueous solution was modified to have a concentration of 0.07% (88 mol% saponification, 3500 degree of polymerization, PVA95-88, manufactured by Kuraray Corporation) and a surfactant concentration of 0%. The amount of PVA aqueous solution adhering to the solution was also modified to the amounts shown in Table 4. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of PVA and surfactant adhering to the support was 0.39%.

[0166] (Example 13B)

[0167] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0035%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.39%.

[0168] (Example 14B)

[0169] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0070%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.38%.

[0170] (Example 15B)

[0171] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0105%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the filter material for the air filter was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.39%.

[0172] (Example 16B)

[0173] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0035%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.36%.

[0174] (Example 17B)

[0175] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0070%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.38%.

[0176] (Example 18B)

[0177] The concentration of the polyvinyl alcohol aqueous solution was changed to 0.0105%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to the amounts shown in Table 5. Otherwise, the air filter material was obtained in the same manner as in Example 1B. The total amount of polyvinyl alcohol and surfactant adhering to the support was 0.39%.

[0178] In Examples 1B to 8B, 10B, and 12B to 18B, the solvent evaporation rate of the polyvinyl alcohol aqueous solution was approximately 171 g / m³. 2 ) / minute.

[0179] The manufacturing conditions and physical property values ​​of the air filter materials obtained in each embodiment and comparative example are shown in Tables 4 and 5. Furthermore, each physical property value was measured using the method described below.

[0180]

[0181]

[0182] In Examples 1B to 8B, 10B, and 12B to 18B, polyvinyl alcohol nanofibers were confirmed to have been formed. Furthermore, the average diameter of the nanofibers was approximately 40 nm. Polyvinyl alcohol nanofibers were confirmed to have been formed, and a polyvinyl alcohol network was observed within the pores that served as fluid permeation pathways.

[0183] It can be seen that the supports of Examples 1B to 8B and Example 10B all showed higher PF values ​​compared with those of Comparative Example 1B. Figure 5 The image shows an SEM observation of the air filter of Example 2B. Figure 5 By rapidly drying polyvinyl alcohol at a high temperature of 190°C in the presence of cationic surfactants, a perfect nanofiber network can be obtained, resulting in a suitable PF value.

[0184] Figure 6 The image shows a SEM image of the air filter of Example 12B. Figure 5 and Figure 6 In comparison, both examples exhibit a polyvinyl alcohol (PVA) network within the pores that form the fluid permeation path, making them difficult to distinguish at the resolution level of SEM images. In Example 12B without the addition of a cationic surfactant, the PF value for the 0.10–0.15 μm region is sufficiently high at 13.9, while in Example 2B with the addition of a cationic surfactant, the PF value for the 0.10–0.15 μm region is even higher at 17.0. This is presumably because the PVA network of Example 2B permeates many more extremely fine areas that cannot be fully observed in the SEM images, further increasing the PF value. It is also presumed that the addition of a cationic surfactant in Examples 1B, 3B–8B, and 10B also resulted in a permeation of the PVA network, further increasing the PF value.

[0185] In Example 2B, the degree of polymerization of polyvinyl alcohol was 3500, and in Example 10B, the degree of polymerization of polyvinyl alcohol was 4500. Both Example 2B and Example 10B were able to obtain equally high PF values.

[0186] On the other hand, in Examples 13B to 15B, anionic surfactants were added to the polyvinyl alcohol aqueous solution. Although a better PF value was obtained compared to Comparative Example 1B, the PF value was only almost equal to or slightly lower than that of Example 12B without surfactants. Therefore, it can be concluded that adding cationic surfactants is more beneficial for obtaining a high PF value than adding anionic surfactants.

[0187] Furthermore, in Examples 16B to 18B, a fluorinated amphoteric surfactant was added to the polyvinyl alcohol aqueous solution. Although a better PF value was obtained compared to Comparative Example 1B, the PF value was only almost equal to or slightly lower than that of Example 12B without surfactant. This indicates that adding a cationic surfactant is more beneficial for obtaining a high PF value than adding a fluorinated amphoteric surfactant.

[0188] (Comparative Example 9B)

[0189] In an aqueous solution of polyvinyl alcohol, an acrylic resin (trade name: ultrasonic FB-19 / manufactured by Acrylic Industry Co., Ltd.) was further added to reduce the concentration in the aqueous solution to 0.0007% (1.0% acrylic resin-based adhesive relative to PVA), and the amount of the polyvinyl alcohol aqueous solution containing the acrylic resin was changed to 244.0 g / m³. 2 In addition, the air filter material was obtained in the same manner as in Example 12B. The total amount of polyvinyl alcohol and acrylic resin adhering to the support was 0.34%. The pressure loss was 68 Pa, the particle permeability was 77.08%, and the PF value for 0.10-0.15 μm was 9.2. In Comparative Example 9B, although no cationic surfactant was added to the polyvinyl alcohol aqueous solution, if a small amount of adhesive resin other than polyvinyl alcohol (1.0% acrylic resin adhesive relative to PVA) was added to the polyvinyl alcohol aqueous solution, a polyvinyl alcohol network could not be formed, and the PF value was not improved, remaining the same as or lower than that of Comparative Example 1B.

[0190] (Comparative Example 10B)

[0191] The concentration of the surfactant in the polyvinyl alcohol aqueous solution was changed to 0.0070%, and the adhesion amount of the polyvinyl alcohol aqueous solution was changed to 243.0 g / m³. 2In addition, the air filter material was obtained in the same manner as in Comparative Example 9B. Under the conditions of Comparative Example 9B, even if a cationic surfactant was further added to the polyvinyl alcohol aqueous solution, if a small amount of adhesive resin other than polyvinyl alcohol (1.0% acrylic resin adhesive relative to PVA) was added to the polyvinyl alcohol aqueous solution, a polyvinyl alcohol network could not be formed, and the PF value was not improved, and was the same as or lower than that of Comparative Example 1B.

[0192] (Comparative Example 11B)

[0193] The drying temperature was changed to 120℃, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to 241.0 g / m³. 2 The amount of polyvinyl alcohol adhering to the support was 0.31%, except that the filter material for the air filter was obtained in the same manner as in Example 12B. The solvent evaporation rate of the polyvinyl alcohol aqueous solution was approximately 87 g / m³. 2 The pressure drop was 71 Pa, the particle permeability was 82.24%, and the PF value for 0.10–0.15 μm was 10.3. In Comparative Example 10B, due to insufficient drying, a polyvinyl alcohol network could not be formed, resulting in a polyvinyl alcohol film laminate.

[0194] (Comparative Example 12B)

[0195] The concentration of the surfactant in the polyvinyl alcohol aqueous solution was changed to 0.0070%, and the amount of polyvinyl alcohol adhering to the aqueous solution was changed to 242.0 g / m³. 2 In addition, the air filter material was obtained in the same manner as in Comparative Example 11B. Under the conditions of Comparative Example 11B, even with the further addition of a cationic surfactant to the polyvinyl alcohol aqueous solution, the polyvinyl alcohol network could not be formed due to insufficient drying, thus failing to become a polyvinyl alcohol film-like laminate. The PF value of 0.10 to 0.15 μm was the same as that of Comparative Example 11B.

[0196] Based on the above results, it can be seen that the method for manufacturing air filter filter material according to this embodiment can provide a method for manufacturing air filter filter material with improved filter performance in a relatively short time using an aqueous solution of polyvinyl alcohol containing a cationic surfactant. In the air filter filter material of this embodiment, for example, the PF value of 0.10 to 0.15 μm can be 14.0 or higher. In this embodiment, the PF value of 0.10 to 0.15 μm can be 14.4 or higher.

[0197] Generally, adding adhesive resin is used to increase the stiffness or tensile strength of a filter, but this leads to a decrease in the pressure drop factor (PF). Therefore, there is usually a trade-off between stiffness and PF. According to the present invention, as shown in Tables 1 to 5, stiffness or tensile strength can be increased without significantly reducing the PF. For example, compared to Comparative Example 1A, the Grievous stiffness of Examples 1A to 11A is increased by more than 1 mN, and the tensile strength is increased by more than 0.2 kN / m. Furthermore, compared to Comparative Example 1B, the Grievous stiffness of Examples 1B to 8B, 10B, and 12B to 18B is increased by more than 1 mN, and the tensile strength is increased by more than 0.2 kN / m. If the stiffness or tensile strength is increased, it is possible to suppress the situation where the filter deforms during ventilation after pleating, resulting in increased structural pressure loss. For example, it is possible to prevent the filter from deteriorating over time during use and deforming.

Claims

1. A filter material for an air filter, characterized in that: It has: a support structure that is fluid-permeable; and A network of polyvinyl alcohol is formed in the pores of the support, which serve as fluid permeation paths; The mesh network comprises nanofibers. The degree of polymerization of the polyvinyl alcohol is 1500–6000. The degree of saponification of the polyvinyl alcohol is 80–98 mol%. The amount of polyvinyl alcohol adhering to the support is 0.05–1.00% by mass. It does not contain any adhesive resins other than the polyvinyl alcohol mentioned above.

2. The filter material for an air filter according to claim 1, characterized in that: It further contains cationic surfactants.

3. A method for manufacturing a filter material for an air filter, characterized in that: It is a method for manufacturing filter material for air filters according to claim 1, and includes the following steps: an adhesion step, in which a polyvinyl alcohol aqueous solution is adhered to a fluid-permeable support, thereby making the support wet; and The drying step involves drying the polyvinyl alcohol aqueous solution adhering to the moistened support at a temperature above 140°C; and The polyvinyl alcohol aqueous solution does not contain any adhesive resin other than polyvinyl alcohol, and after the drying step, the support has a polyvinyl alcohol network in the pores that form the fluid passage path because the polyvinyl alcohol aqueous solution is dried.

4. The method for manufacturing the filter material for an air filter according to claim 3, characterized in that: The mesh network contains nanofibers.

5. The method for manufacturing the filter material for an air filter according to claim 4, characterized in that: The nanofibers are nanofibers with an average fiber diameter of 10–500 nm.

6. The method for manufacturing filter material for air filters according to any one of claims 3 to 5, characterized in that: The degree of polymerization of the polyvinyl alcohol contained in the aqueous solution of polyvinyl alcohol is 1500 to 6000.

7. The method for manufacturing filter material for air filters according to any one of claims 3 to 5, characterized in that: The polyvinyl alcohol in the aqueous solution contains a saponification degree of 80–98 mol.

8. The method for manufacturing filter material for air filters according to any one of claims 3 to 5, characterized in that: The concentration of solids in the polyvinyl alcohol aqueous solution is 0.01 to 0.20 by mass.

9. A method for manufacturing a filter material for an air filter according to any one of claims 3 to 5, characterized in that: The amount of polyvinyl alcohol adhering to the support after the drying step is 0.05 to 1.00 by mass.

10. A method for manufacturing a filter material for an air filter according to any one of claims 3 to 5, characterized in that: The amount of the polyvinyl alcohol aqueous solution attached to the support body is 50 g or more per 1 m2of the surface area of the support body. 2 The support body 50 g or more.

11. A method for manufacturing a filter material for an air filter according to any one of claims 3 to 5, characterized in that: In the drying step, the solvent of the polyvinyl alcohol aqueous solution adhering to the wet support evaporates at a rate of 1 m. 2 Support volume 100 g / min or more.

12. The method for manufacturing filter material for air filters according to any one of claims 3 to 5, characterized in that: The polyvinyl alcohol aqueous solution further contains a cationic surfactant.

13. The method for manufacturing filter material for air filters according to claim 12, characterized in that: The amount of the cationic surfactant added to the polyvinyl alcohol aqueous solution is 1 to 30 parts by weight relative to 100 parts by weight of polyvinyl alcohol.

14. The method for manufacturing filter material for air filters according to claim 12, characterized in that: The total amount of polyvinyl alcohol and cationic surfactant adhering to the support after the drying step is 0.05 to 1.30 by mass.

15. A method for manufacturing a filter material for an air filter according to any one of claims 3 to 5, characterized in that: The support is a nonwoven fabric filter material with glass fiber as the main component.

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