Filter media for air filters and method for manufacturing the same

Abstract

The purpose of the present disclosure is to provide an air-filter filter material having an improved filtering performance and good water repellency as a result of using a polyvinyl alcohol, a cationic surfactant, and a water repellent, and disposing a mesh-like network of the polyvinyl alcohol in pores of a fluid permeable passage in a supporting body. A method for producing an air-filter filter material according to the present disclosure comprises: an application step for applying an aqueous polyvinyl alcohol solution to a supporting body having fluid permeability, to bring the supporting body into a wet state; and a drying step for drying the aqueous polyvinyl alcohol solution adhering to the supporting body in the wet state at 140°C or higher. The aqueous polyvinyl alcohol solution contains a cationic surfactant and a water repellent and does not contain any binder resin other than the polyvinyl alcohol; and the supporting body, after being subjected to the drying step, has a mesh-like network of the polyvinyl alcohol in pores that serve as fluid permeable passages, as a result the aqueous polyvinyl alcohol solution being dried.

Description

Technical Field

[0001] An object of the present disclosure is to provide a filter medium for an air filter that uses polyvinyl alcohol and significantly improves particle collection performance, and a method for manufacturing the same. More specifically, a method for manufacturing an air filter filter medium suitable for air purification applications such as clean rooms or clean benches related to semiconductors, liquid crystals, bio-food industries, building air conditioning, internal combustion engines, or indoor spaces in a relatively short time is provided.

Background Art

[0002] In general, a filter medium for an air filter is used to collect submicron to micron-sized particles in the air. Filter media for air filters are generally classified into those for coarse dust filters, medium-performance filters, HEPA (High Efficiency Particulate Air) filters, or ULPA (Ultra Low Penetration Air) filters according to their collection performance. As basic characteristics of these filter media for air filters, in addition to a low particle transmittance of fine dust particles, a low pressure loss is required to allow air to pass through the filter.

[0003] As a filter medium for an air filter, there is a proposal to use polyvinyl alcohol with a degree of partial saponification of up to 90% to hydrophobize the surface of glass fibers, improve the dispersibility of the fibers, and increase the filter performance (see, for example, Patent Document 1).

[0004] Also, as a non-woven fabric filter having high shape maintainability that is not easily crushed in the thickness direction even when wind pressure is applied, there is a proposal to form it by orienting microfibers of polyvinyl alcohol in the thickness direction (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In Patent Document 1, a fluorine-based water repellent is included in the binder liquid, resulting in a water-repellent filter material. However, although polyvinyl alcohol is included as one of the binder resins for binding glass fibers together, it does not rapidly dry the wet filter material and improves the dispersibility of the glass fibers. However, because other binder resins are also mixed in, it inhibits the formation of a mesh-like network of polyvinyl alcohol between the fibers, and a structure with a network cannot be obtained. Therefore, it was sometimes difficult to achieve good collection efficiency of even finer particles while maintaining water repellency. Patent Document 1 shows the PF value for target particle diameters of 0.30 to 0.40 μm, but the PF value under stricter conditions of target particle diameters of 0.10 to 0.15 μm is low. Therefore, there is a need for an air filter material that has a high PF value under the strict conditions of target particle diameters of 0.10 to 0.15 μm. Furthermore, while Patent Document 1 describes a water-repellent material, it achieves this by impregnating the air filter media with approximately 0.25% water-repellent agent, resulting in a large amount of water-repellent agent adhering to it. However, there is a need for an air filter media that exhibits water repellency with the addition of only a very small amount of water-repellent agent.

[0007] In Patent Document 2, since there are few microfibers of polyvinyl alcohol formed in directions other than the thickness direction, these microfibers do not necessarily contribute to an improvement in filter performance.

[0008] This disclosure aims to provide an air filter material that improves filter performance, particularly particle collection performance, and has good water repellency, by using polyvinyl alcohol, a cationic surfactant, and a water repellent to provide a mesh-like network of polyvinyl alcohol in the pores of the fluid permeation path of the support material, arranged relatively randomly in the planar and thickness directions of the support material. Furthermore, this disclosure aims to provide a method for manufacturing such an air filter material in a relatively short time. [Means for solving the problem]

[0009] The inventors have solved the above problem by finding that when a fluorine-based water repellent is added to an aqueous polyvinyl alcohol solution attached to a fluid-permeable support, water repellency is obtained, but the PF value decreases significantly compared to the case without the fluorine-based water repellent, for reasons that are not clear. On the other hand, when both a cationic surfactant and a fluorine-based water repellent are added to the aqueous polyvinyl alcohol solution, water repellency is obtained while maintaining a high PF value. In other words, the method for manufacturing an air filter material according to the present invention involves adding an aqueous polyvinyl alcohol solution to a fluid-permeable support. spray An adhesion step in which the support is attached and the polyvinyl alcohol aqueous solution attached to the wet support is Without wiping or wringing, It includes a drying process that dries at 140°C or higher, The support is a nonwoven fabric for filter media, mainly composed of glass fibers. The aforementioned aqueous solution of polyvinyl alcohol contains a cationic surfactant and a water repellent, and does not contain any binder resin other than polyvinyl alcohol. The cationic surfactant is a cationic surfactant that does not act as a water repellent, the degree of saponification of the polyvinyl alcohol is 80-98 mol%, and the degree of polymerization of the polyvinyl alcohol is 1500-6000, the amount of the cationic surfactant in the aqueous polyvinyl alcohol solution is 1-30 parts by mass per 100 parts by mass of polyvinyl alcohol, the amount of the water repellent in the aqueous polyvinyl alcohol solution is 5-50 parts by mass per 100 parts by mass of polyvinyl alcohol, and the amount of polyvinyl alcohol adhering to the support is 0.05-1.00% by mass. The support having undergone the drying process is characterized in that, as the aqueous solution of polyvinyl alcohol dries, it has a mesh-like network of polyvinyl alcohol in the pores that serve as fluid permeability paths.

[0010] In the method for manufacturing an air filter material according to the present invention, the mesh-like network is preferably made of nanofibers. This makes it possible to achieve both high particle collection performance and low pressure loss.

[0011] In the method for manufacturing filter media for air filters according to the present invention, the nanofibers are preferably nanofibers with a number-average fiber diameter of 10 to 500 nm. This makes it possible to achieve both higher particle collection performance and low pressure loss.

[0012] In the method for manufacturing an air filter material according to the present invention, the amount of the polyvinyl alcohol aqueous solution to be attached to the support is 1 m of the support. 2 It is preferable that the amount is 50g or more per unit. This makes it easier to form a mesh-like network in the pores that serve as fluid permeability paths in the support, and the PF value tends to increase.

[0013] In the method for manufacturing an air filter material according to the present invention, in the drying step, the evaporation rate of the solvent of the polyvinyl alcohol aqueous solution adhering to the wet support is such that the evaporation rate of the support is 1 m 2 It is preferable that the flow rate is 100 g / min or more. By rapidly drying the aqueous solution of polyvinyl alcohol, a more reliable network of polyvinyl alcohol can be formed.

[0016] In the method for manufacturing an air filter material according to the present invention, the total amount of polyvinyl alcohol, cationic surfactant, and water repellent adhering to the support after the drying step is 0.10 It is preferable that the concentration be ~1.50% by mass. This allows for a high PF value and water repellency.

[0017] In the method for manufacturing an air filter material according to the present invention, The cationic surfactant is a quaternary ammonium salt type or amine salt type surfactant. It is preferable that this be the case.

[0018] The filter material for an air filter according to the present invention comprises a fluid-permeable support and a mesh-like network of polyvinyl alcohol formed in the pores of the support that serve as fluid permeability paths, wherein the mesh-like network is made of nanofibers, the degree of polymerization of the polyvinyl alcohol is 1500 to 6000, and the degree of saponification of the polyvinyl alcohol is 80It is 90 mol% or less, the adhesion amount of polyvinyl alcohol to the support is 0.05 to 1.00 mass%, and it contains a cationic surfactant and a water repellent agent, The support is a nonwoven fabric for filter media mainly composed of glass fibers, the cationic surfactant is a cationic surfactant that does not act as a water repellent, the cationic surfactant is added in an amount of 1 to 30 parts by mass per 100 parts by mass of polyvinyl alcohol, and the water repellent is added in an amount of 5 to 50 parts by mass per 100 parts by mass of polyvinyl alcohol. It is characterized by not containing a binder resin other than the polyvinyl alcohol.

Effect of the Invention

[0019] According to the present disclosure, by using polyvinyl alcohol, a cationic surfactant, and a water repellent agent, and providing a network-like network of polyvinyl alcohol in the pores of the fluid permeation path of the support in a relatively random manner in the plane direction and the thickness direction of the support, the filter performance, particularly the particle collection performance, can be improved, and a filter medium for an air filter with good water repellency can be provided. Furthermore, according to the present disclosure, a method for manufacturing such a filter medium for an air filter in a relatively short time can be provided. [[ID=X]]

Brief Description of the Drawings

[0020] [Figure 1] It is an image (observation magnification: 10,000 times) obtained by observing the air filter of Example 8 with SEM. [Figure 2] It is an image (observation magnification: 10,000 times) obtained by observing the air filter of Example 9 with SEM. [Figure 3] It is an image (observation magnification: 10,000 times) obtained by observing the air filter of Comparative Example 4 with SEM. [Figure 4] It is an image (observation magnification: 10,000 times) obtained by observing the air filter of Comparative Example 9 with SEM. [Figure 5] It is an image (observation magnification: 10,000 times) obtained by observing the air filter of Comparative Example 15 with SEM.

Mode for Carrying Out the Invention

[0021] Next, embodiments of the present invention will be shown and described in detail, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified. <X

[0022] The method for manufacturing the filter material for an air filter according to this embodiment comprises an adhesion step of attaching an aqueous polyvinyl alcohol solution to a fluid-permeable support to wet the support, and a drying step of drying the aqueous polyvinyl alcohol solution attached to the wet support at 140°C or higher, wherein the aqueous polyvinyl alcohol solution contains a cationic surfactant and a water repellent, and does not contain any binder resin other than polyvinyl alcohol, and the support that has undergone the drying step has a mesh-like network of polyvinyl alcohol in the pores that serve as fluid permeability paths as the aqueous polyvinyl alcohol solution is dried.

[0023] A polyvinyl alcohol aqueous solution containing a cationic surfactant and a water repellent will hereafter also be simply referred to as "polyvinyl alcohol aqueous solution."

[0024] <Support> The support material is not particularly limited as long as it is permeable to fluids, and for example, porous materials such as nonwoven fabrics, woven fabrics, paper, or sponges can be used. Among these, nonwoven fabrics are preferred, and in particular, nonwoven fabrics for filter media mainly composed of fibers such as glass fibers or organic fibers are preferred. Nonwoven fabrics for filter media mainly composed of glass fibers are even more preferred in that they can stably maintain filter performance. "Mainly composed of fibers such as glass fibers or organic fibers" means that the mass of these fibers relative to the total mass of the support material is 50% by mass or more. More preferably, it is 80% by mass or more. When the support material is a nonwoven fabric mainly composed of these fibers, the basis weight is 10 to 300 g / m². 2 Preferably, it is 30-200 g / m 2 It is more preferable that it be such. Fluid permeability refers to the property of being able to permeate at least gas, and more preferably the property of being able to permeate both gas and liquid.

[0025] The pressure loss of the support is preferably 1 Pa to 500 Pa. More preferably 10 Pa to 300 Pa, and even more preferably 30 Pa to 200 Pa.

[0026] If the pressure drop of the support is less than 1 Pa, the pore size of the support is too large, making it difficult to form a polyvinyl alcohol network, which does not contribute to increasing collection efficiency, and the PF value may not increase. If the pressure drop of the support exceeds 500 Pa, the collection efficiency of the support itself is extremely high, and the polyvinyl alcohol network does not contribute much to the collection efficiency of the support, and the PF value may not increase.

[0027] The glass fibers used as the support are, for example, wool-like ultrafine glass fibers produced by flame drawing or rotary drawing, or chopped strand glass fibers produced by cutting bundles of glass fibers spun to a predetermined fiber diameter to a predetermined fiber length. From these, fibers with various fiber diameters and lengths are selected according to the required physical properties and used individually or in mixtures. For example, a nonwoven fabric made of glass fibers obtained by mixing two or more types of ultrafine glass fibers with mutually different average fiber diameters and chopped strand glass fibers is preferred. In addition, low-boron glass fibers or silica glass fibers can be used to prevent boron contamination of silicon wafers in semiconductor manufacturing processes. 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, organic fibers include, for example, polypropylene fibers, acrylic fibers, vinylon fibers, cellulose fibers, polyester fibers, or aramid 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 if they are short fibers, is preferably 0.5 to 10,000 μm. More preferably, it is 10 to 5,000 μm. The method for manufacturing the nonwoven fabric is not particularly limited, and may be, for example, a dry method or a wet method.

[0028] The shape of the support is not particularly limited, and it does not have to be a flat structure such as a sheet. For example, the support material may be processed three-dimensionally, such as by pleating, which creates zigzag folds by repeatedly folding mountain folds and valley folds. If a support that has been pre-pleated is used, a long support can be dried in a drying area with a limited volume, and a filter material for air filters to which polyvinyl alcohol has been efficiently attached can be obtained.

[0029] Furthermore, the average pore size of the support is preferably 0.1 to 50 μm, more preferably 0.5 to 10 μm. Below 0.1 μm, fluid permeability may be poor. Above 50 μm, it may be difficult for polyvinyl alcohol to uniformly form a mesh-like structure within the pores of the support. In this embodiment, an aqueous solution containing polyvinyl alcohol and water can be applied to the pores of the support and then dried to form an air filter. By using a support with an appropriate average pore size, the aqueous solution can be uniformly distributed within the pores, making it easier to maintain the mesh-like structure even after drying. Here, the average pore size can be measured according to ASTM E1294-89 "Half-Dry Method".

[0030] The support is preferably made of a material that can be used as a filter medium for an air filter. In the method for manufacturing an air filter according to this embodiment, using such a support makes it easy to obtain an air filter with higher particle collection performance than conventional air filter materials (the support itself). The support may also be in a wet state; for example, a liquid of polyvinyl alcohol may be applied to the wet support during the papermaking process.

[0031] Polyvinyl alcohol is produced from polyvinyl acetate as a raw material by saponification, or conversion, of the carboxyl groups in polyvinyl acetate to hydroxyl groups through alkaline hydrolysis. Here, the proportion of carboxyl groups converted to hydroxyl groups is specifically called the degree of saponification.

[0032] The degree of saponification of polyvinyl alcohol is preferably 80-98 mol%, and more preferably 82-90 mol%. If the degree of saponification of polyvinyl alcohol is less than 80 mol%, the polyvinyl alcohol may not dissolve completely, and a suitable PF value may not be obtainable. If the degree of saponification of polyvinyl alcohol exceeds 98 mol%, the degree of saponification becomes high, and the hydrophobic effect weakens, which may make it difficult to form a network.

[0033] The degree of polymerization of polyvinyl alcohol is preferably 1500 to 6000. More preferably, it is between 2000 and 5000. An example is PVA95-88 (saponification degree 88 mol%, degree of polymerization 3500, manufactured by Kuraray Co., Ltd.). If the degree of polymerization of polyvinyl alcohol is less than 1500, the network structure of polyvinyl alcohol is difficult to form, and the PF value may not increase. If the degree of polymerization of polyvinyl alcohol exceeds 6000, the polyvinyl alcohol is difficult to dissolve, and if undissolved portions remain, the PF value may not increase.

[0034] In this embodiment, it is preferable that the degree of saponification of the polyvinyl alcohol is 80 to 98 mol%, and the degree of polymerization of the polyvinyl alcohol is 1500 to 6000. By setting the degree of saponification and polymerization of the polyvinyl alcohol within these ranges, it becomes easier to form a mesh-like network of polyvinyl alcohol, and the PF value is improved.

[0035] In this embodiment, the polyvinyl alcohol aqueous solution may contain additives other than polyvinyl alcohol. These additives may include surfactants, water repellents, defoamers, fine fibers, and fine particles. However, the polyvinyl alcohol aqueous solution must not contain any binder resins other than polyvinyl alcohol. If the polyvinyl alcohol aqueous solution contains binder resins other than polyvinyl alcohol, the PF value of the resulting air filter media will not improve compared to the PF value measured with only the support. This is because the formation of the polyvinyl alcohol mesh network is inhibited.

[0036] In this embodiment, it is preferable that the aqueous polyvinyl alcohol solution contains a cationic surfactant as an additive other than polyvinyl alcohol. Comparing the form using an aqueous polyvinyl alcohol solution containing a cationic surfactant with the form using an aqueous polyvinyl alcohol solution without a cationic surfactant, the PF value is further improved in the form containing the cationic surfactant. Since no improvement in the PF value is observed when an anionic surfactant or amphoteric surfactant is added to the aqueous polyvinyl alcohol solution, this further improvement in the PF value is due to the addition of a cationic surfactant.

[0037] Cationic surfactants can be broadly classified into quaternary ammonium salt types and amine salt types, but quaternary ammonium salt types are preferred, and examples include alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and perfluoroalkyltrialkylammonium salts. Of these, perfluoroalkyltrialkylammonium salts are fluorine-based cationic surfactants. Examples of amine salt types include monoalkylamine salts, dialkylamine salts, and trialkylamine salts.

[0038] In an aqueous solution of polyvinyl alcohol, it is preferable that the cationic surfactant is added in an amount of 1 to 30 parts by mass per 100 parts by mass of polyvinyl alcohol. If the cationic surfactant is a perfluoroalkyltrialkylammonium salt, it is preferable that it is added in an amount of 1 to 30 parts by mass, and more preferably 15 to 30 parts by mass, per 100 parts by mass of polyvinyl alcohol. If the cationic surfactant is alkyltrimethylammonium chloride, it is preferable that it is added in an amount of 5 to 10 parts by mass per 100 parts by mass of polyvinyl alcohol.

[0039] In this embodiment, the polyvinyl alcohol aqueous solution contains a water repellent in addition to a cationic surfactant as an additive other than polyvinyl alcohol. Comparing the form using a polyvinyl alcohol aqueous solution containing a cationic surfactant and a water repellent with the form using a polyvinyl alcohol aqueous solution containing a cationic surfactant but not a water repellent, the form containing a cationic surfactant and a water repellent achieves water repellency while maintaining the PF value. When a water repellent is included in the polyvinyl alcohol aqueous solution without a cationic surfactant, water repellency is achieved, but a high PF value cannot be obtained. To obtain a high PF value and water repellency, it is necessary to use a polyvinyl alcohol aqueous solution containing both a cationic surfactant and a water repellent.

[0040] As the water repellent, a fluororesin is preferred, and more preferably a cationic and fluororesin. Even more preferably, a cationic and fluororesin has a zeta potential of +10mV or higher, more preferably +20mV or higher, and even more preferably +30mV or higher. For example, AG-E310 (manufactured by AGC Corporation) is one such example.

[0041] The amount of water repellent in the aqueous solution of polyvinyl alcohol is preferably 5 to 50 parts by mass, and more preferably 10 to 20 parts by mass, per 100 parts by mass of polyvinyl alcohol. If the amount is less than 5 parts by mass, water repellency may not be obtained, and if it exceeds 50 parts by mass, the balance between a high PF value and high water repellency may be disrupted.

[0042] The preferred mass ratio of cationic surfactant to water repellent is 1:0.3 to 1:5, and more preferably 1:1 to 1:3.5.

[0043] In the filter material for air filters obtained by the manufacturing method according to this embodiment, it is preferable that fibrous polyvinyl alcohol is intertwined within the pores of the support, forming voids between the fibrous polyvinyl alcohol, and that it does not have a film-like structure in which polyvinyl alcohol is laminated. This prevents an increase in pressure loss and can lower particle transmission. A film-like structure in which polyvinyl alcohol is laminated refers to a membrane-like material that blocks all or part of the pores of the support, formed by the physical entanglement or chemical aggregation of polyvinyl alcohol.

[0044] In this embodiment, it is preferable that the ratio of polyvinyl alcohol adhering to the support is 0.05 to 1.00 mass%. More preferably, it is 0.10 to 0.50 mass%. By setting the adhering amount to this level, an air filter with high particle collection performance and relatively low pressure loss can be obtained. If the ratio of polyvinyl alcohol adhering to the support is less than 0.05 mass%, the particle collection performance may be poor. Conversely, if it exceeds 1.00 mass%, it tends to form a film that clogs the pores of the support, affecting particle collection performance and potentially reducing filter performance. The amount of polyvinyl alcohol adhering to the support can be controlled mainly by the concentration of polyvinyl alcohol in the aqueous solution and the amount of aqueous solution adhering to the support. The higher the concentration of polyvinyl alcohol in the aqueous solution, and the greater the amount of aqueous solution adhering to the support, the greater the amount of polyvinyl alcohol adhering to the support.

[0045] In this embodiment, the ratio of the total amount of polyvinyl alcohol, cationic surfactant, and water repellent to the support is preferably 0.05 to 1.50% by mass. More preferably, it is 0.10 to 0.80% by mass.

[0046] In this embodiment, the amount of polyvinyl alcohol aqueous solution to be attached to the support is 1 m 2It is preferable to use 50g or more per unit. More preferably 100g or more. If the amount is less than 50g, it may be difficult to form a mesh-like network between the fibers of the support, and the PF value may not increase easily. The upper limit of the amount of polyvinyl alcohol aqueous solution to be attached to the support is, for example, 1m 2 Each portion is 300g.

[0047] In this embodiment, after attaching a polyvinyl alcohol aqueous solution to a support, a drying step is performed to dry the polyvinyl alcohol aqueous solution at 140°C or higher 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 in units of one or several molecules, or a form in which it is partially aggregated. Of these, the form of polyvinyl alcohol in the aqueous solution is preferably a form in which polyvinyl alcohol is stably dissolved in the aqueous solution in units of one or several molecules.

[0048] <Solvent> The solvent contained in the aqueous solution of polyvinyl alcohol is preferably water or a mixture of water and an organic solvent. More preferably, it is water.

[0049] <Polyvinyl alcohol aqueous solution> In this embodiment, it is preferable that the solid content concentration of polyvinyl alcohol in the aqueous solution be 0.01 to 0.20% by mass. More preferably, it is 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 may not increase. If it exceeds 0.20% by mass, a film-like structure of polyvinyl alcohol may be formed on the surface of the support. As described above, a cationic surfactant is added to the aqueous polyvinyl alcohol solution in parts 1 to 30 by mass per 100 parts by mass of polyvinyl alcohol. In addition, as described above, a water repellent is added to the aqueous polyvinyl alcohol solution in parts 5 to 50 by mass per 100 parts by mass of polyvinyl alcohol in addition to the cationic surfactant.

[0050] <Preparation of aqueous solution> In this embodiment, the method for preparing the aqueous solution is not particularly limited; it is sufficient to dissolve the polyvinyl alcohol described above in water to make an aqueous solution. As for the method of adding a cationic surfactant and a water repellent to the polyvinyl alcohol aqueous solution, after adding polyvinyl alcohol to water, when making the final adjustment of the concentration of the polyvinyl alcohol, the solution is diluted using an aqueous solution containing a cationic surfactant at a concentration of about 0.5 to 3% by mass and an aqueous solution containing a water repellent at a concentration of about 0.5 to 3% by mass, thereby adjusting the concentrations of polyvinyl alcohol, cationic surfactant, and water repellent, respectively.

[0051] The method for dissolving polyvinyl alcohol according to this embodiment is not particularly limited, but for example, a magnetic stirrer, a propeller-type agitator, etc., can be used to add the powder or liquid polyvinyl alcohol to water and stir at about 100 to 700 rpm for 10 minutes. Then, the temperature can be raised to 95°C during stirring and the mixture can be stirred for about 2 hours to completely dissolve it.

[0052] <Adhesion Process> 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 is adjusted appropriately according to the thickness, material, and average pore size of the support, but as mentioned above, in this embodiment, an amount of polyvinyl alcohol attached to the support of 0.05% to 1.00% is preferred. If the amount of polyvinyl alcohol attached to the support of less than 0.05% by mass is insufficient, it will be difficult to form a uniform polyvinyl alcohol network. As a result, the particle collection performance as a filter material for air filters may not be sufficiently improved. Conversely, if it exceeds 1.00% by mass, the mesh-like network of polyvinyl alcohol tends to aggregate into a film, which may prevent sufficient improvement in particle collection performance. Also, as mentioned above, in this embodiment, the ratio of the total amount of polyvinyl alcohol, cationic surfactant, and water repellent attached to the support of 0.05% to 1.50% by mass is preferred. In this embodiment, the method for calculating the ratio of polyvinyl alcohol adhering to the support is not particularly limited. For example, if the support is composed only of inorganic fibers, only polyvinyl alcohol can be burned. If it contains a cationic surfactant, both polyvinyl alcohol and the cationic surfactant can be burned. If it contains a cationic surfactant and a water repellent, all polyvinyl alcohol, the cationic surfactant, and the water repellent can be burned, and the ratio can be calculated from the weight loss after burning. Alternatively, the ratio of polyvinyl alcohol adhering to the support can be calculated from the wet adhering amount. That is, the ratio of polyvinyl alcohol adhering to the support (in %) is {(wet adhering amount × solid content concentration of polyvinyl alcohol in aqueous solution) / mass of the support before the aqueous solution is applied} × 100. Alternatively, the ratio of polyvinyl alcohol and cationic surfactant adhering to the support can be calculated from the wet adhering amount. That is, the ratio of polyvinyl alcohol and cationic surfactant adhering to the support (in %) is {(wet adhering amount × total solid content concentration of polyvinyl alcohol and cationic surfactant in aqueous solution) / mass of the support before the aqueous solution is applied} × 100.Furthermore, the ratio of the amount of polyvinyl alcohol, cationic surfactant, and water repellent to the support can be calculated from the wet adhesion amount. That is, the ratio (in %) of the amount of polyvinyl alcohol, cationic surfactant, and water repellent to the support is {(wet adhesion amount × total solid content concentration of polyvinyl alcohol, cationic surfactant, and water repellent in the aqueous solution) / mass of the support before the aqueous solution is applied} × 100. Here, the wet adhesion amount is the difference between the mass of the support in the wet state after the aqueous solution is applied and the mass of the support before application, and represents the mass of the aqueous solution attached to the support at the start of the drying process. For this reason, the wet adhesion amount is preferably a value measured immediately before the drying process, for example, preferably measured within 10 minutes before the start of the drying process, and more preferably within 5 minutes.

[0053] Impregnation methods include, for example, completely immersing the support in an aqueous solution or immersing only the surface of the support. Completely immersing the support in an aqueous solution is superior because it allows the aqueous solution to penetrate efficiently and reliably into the depths of the pores of the support, thus forming a more uniform polyvinyl alcohol network. Furthermore, reducing the pressure while the support is completely immersed in the aqueous solution makes it easier for air to escape from within the support, making it more effective for the aqueous solution to penetrate. It is preferable to remove any excess aqueous solution by squeezing it out with a roll dewatering machine or by removing it with an absorbent material such as absorbent felt or absorbent paper. Immersing only the surface of the support is effective when a density difference in the polyvinyl alcohol network structure within the pores is created in the thickness direction of the support (the ratio of the polyvinyl alcohol network structure differs between one side of the support and the other side).

[0054] 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 coaters and die coaters. The coating method is advantageous in that it allows for easy control of the amount of aqueous solution adhering to the support.

[0055] The spraying method is a method of spraying an aqueous solution onto the surface of a support using a known sprayer such as a misting or spray bottle. The spraying method is effective, for example, when it is desired to form a network structure of polyvinyl alcohol only near the surface of the support among the pores of the support, or when it is not desired to allow a large amount of impregnation liquid or the rolls or bars of a coating machine to come into contact with the support.

[0056] In this embodiment, the spraying method is more preferable. While the impregnation method has advantages in terms of liquid penetration, when wiping off excess liquid, for example, the liquid adhering between the glass fibers is wiped away, making it difficult to form a mesh-like network after drying. Also, if dewatering is performed using a suction device instead of wiping, the liquid film between the fibers disappears, preventing the formation of a network and thus failing to improve filter performance. On the other hand, with the spraying method, it is possible to control the amount of liquid adhering, eliminating the need to apply excessive liquid and allowing for a stable improvement in filter performance.

[0057] <Drying process> In this embodiment, the aqueous solution is applied to the support as described above, and after the support is made wet, it is dried at 140°C or higher. Preferably, the temperature is 140 to 250°C, and more preferably 170 to 220°C. The drying temperature here refers to the maximum drying temperature of the drying apparatus during the drying process.

[0058] In this embodiment, drum-type hot dryers, hot air dryers, infrared dryers, etc., are preferred as drying equipment. Alternatively, a combination of these drying methods may be used. Note that drying is performed at atmospheric pressure.

[0059] In this embodiment, in the drying process, the evaporation rate of the solvent in the polyvinyl alcohol aqueous solution adhering to the wet support is such that the evaporation rate of the support is 1 m² 2 The evaporation rate is preferably 100 g / min or more. More preferably 120 g / min or more. If it is less than 100 g / min, the drying rate is too slow, and it may not be possible to form a mesh-like network of polyvinyl alcohol. The upper limit of the evaporation rate is, for example, 300 g / min.

[0060] In this embodiment, air may be used during drying. The purpose of using air is to prevent evaporated water vapor from remaining around the support and to promote the evaporation of the liquid. However, if the airflow is strong enough to penetrate the inside of the filter material, the film of liquid adhering between the fibers may be destroyed, so a moderate amount of airflow is preferable.

[0061] When a cationic surfactant is added to an aqueous polyvinyl alcohol solution, the amount of solution adhering to the support is reduced compared to when the surfactant is not added. It is presumed that the addition of the cationic surfactant improves filtration, resulting in less adhesion. Furthermore, a reduction in the amount of aqueous solution adhering reduces the load during heat drying and shortens the drying time, thereby improving productivity.

[0062] In this embodiment, the solid form of the polyvinyl alcohol obtained after drying is preferably fibrous, specifically nanofibers, more preferably nanofibers with a number-average fiber diameter of 10 to 500 nm, and even more preferably 10 to 100 nm. To create an air filter that achieves both high particle collection performance and low pressure loss, it is important to form a uniform fiber network of extremely fine polyvinyl alcohol fibers in the support. When nanofibers, especially ultrafine polyvinyl alcohol with a number-average fiber diameter of 500 nm or less, are used, the number of fibers per unit volume in the air filter material increases significantly, making it easier to capture particles in the gas and enabling high collection performance. In addition, the slip-flow effect makes the airflow resistance of the single fibers extremely low, which prevents the pressure loss of the air filter from increasing. The number-average fiber diameter of the polyvinyl alcohol here is calculated as follows: A water-soluble polymer cast on a carbon film coated grid is observed using a transmission electron microscope (TEM) to obtain electron microscope images. For each obtained observation image, two random axes are drawn vertically and horizontally, and the fiber diameter of the fibers intersecting the axes is visually read. At this time, observation is performed at a magnification of 5000x, 10000x, or 50000x depending on the size of the constituent fibers. The sample or magnification is set so that 20 or more fibers intersect the axes. At least three images of the non-overlapping surface are taken with an electron microscope, and the fiber diameter values ​​of the fibers intersecting two axes are read for each. Thus, information on at least 20 fibers × 2 × 3 = 120 fibers is obtained. The number-average fiber diameter was calculated from the fiber diameter data obtained in this way. For branched fibers, if the length of the branched part is 50 nm or more, it is included in the calculation of the fiber diameter as a single fiber. Alternatively, the number-average fiber diameter may be calculated as follows: The polyvinyl alcohol present on or inside the support is observed using an electron microscope (SEM). For each obtained observation image, two random axes are drawn vertically and horizontally, and the fiber diameter of the fibers intersecting the axes is visually read. At this time, the observation is performed at a magnification of 5,000 to 50,000 times, depending on the size of the constituent fibers.Images of multiple non-overlapping surface areas are taken 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 from at least 120 fiber diameter data points. For branched fibers, if the length of the branched portion is 50 nm or more, it is included as a single fiber in the fiber diameter calculation. In order to obtain distortion-free observation images, the sample is either pre-coated with a conductive coating or the effect of the coating thickness is taken into consideration. For example, when using an ion sputter (E-1045, Hitachi High-Technologies 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, since the deposition direction of the coating film is perpendicular to the expected direction, the coating thickness is half of the expected value when measuring the fiber diameter. In other words, when coated under the above conditions, the 12 nm (6 nm + 6 nm) of the coating thickness at both ends is subtracted from the fiber diameter obtained from the SEM.

[0063] The filter material for air filters obtained by the manufacturing method according to this embodiment comprises a fluid-permeable support and a mesh-like network of polyvinyl alcohol formed in the pores of the support that serve as fluid permeability paths. The mesh-like network consists of nanofibers, the degree of polymerization of the polyvinyl alcohol is 1500 to 6000, the degree of saponification of the polyvinyl alcohol is 60 to 90 mol%, the amount of polyvinyl alcohol adhering to the support is 0.05 to 1.00 mass%, and it contains a cationic surfactant and a water repellent, but does not contain any binder resins other than polyvinyl alcohol. Here, it is preferable that the cationic surfactant is added in an amount of 1 to 30 parts by mass per 100 parts by mass of polyvinyl alcohol. It is also preferable that the water repellent is added in an amount of 5 to 50 parts by mass per 100 parts by mass of polyvinyl alcohol. Here, the filter material for air filters does not contain any binder resins other than polyvinyl alcohol. If the filter material for air filters further contains other binder resins other than polyvinyl alcohol, no improvement in the PF value is observed based on the PF value measured with the support alone. This is because the inclusion of other binder resins besides polyvinyl alcohol would prevent the formation of the mesh-like network of polyvinyl alcohol. Furthermore, the inclusion of a cationic surfactant and a water repellent results in higher PF values ​​and water repellency compared to the case without these ingredients. The air filter material obtained by the manufacturing method according to this embodiment preferably has a total amount of polyvinyl alcohol, cationic surfactant, and water repellent attached to the support of 0.05 to 1.50% by mass. In addition, the nanofibers preferably have a number-average fiber diameter of 10 to 500 nm.

[0064] The PF value of the air filter media obtained by the manufacturing method according to this embodiment is preferably 0.5 or more higher than the PF value of the support under the conditions of a face velocity of 5.3 cm / sec and target particles of 0.10 to 0.15 μm. The PF value is an index for evaluating the balance between pressure loss and particle collection performance, and is calculated using the formula shown in Equation 1. A higher PF value indicates that the air filter media has a low particle transmission rate for target particles and low pressure loss.

number

[0065] In equation 1, the pressure loss is measured, for example, using a manometer. The particle transmittance is the percentage of polydisperse polyalphaolefin (PAO) particles that pass through an air filter or filter media when air containing PAO particles generated by a Ruskin nozzle is passed through it. The particle transmittance is measured, for example, using a laser particle counter.

[0066] The PF value of an air filter media is affected by the type and composition of the support, but is greatly influenced by the packing density of polyvinyl alcohol or the degree to which a network is formed by polyvinyl alcohol. In the manufacturing method according to this embodiment, it is preferable that the aqueous solution concentration of polyvinyl alcohol attached to the support is 0.01 to 0.20 mass%. However, even with such an attachment concentration, if, for example, the attachment of polyvinyl alcohol concentrates inside and / or on the surface of the pores of the support, and the packing density of polyvinyl alcohol becomes excessively high in certain areas, it will lead to an excessive increase in pressure loss, and as a result the PF value will decrease. It is preferable that the air filter media has a mesh-like network of polyvinyl alcohol inside and / or on the surface of the support, and does not have a film-like structure of polyvinyl alcohol. More specifically regarding the film-like structure of polyvinyl alcohol, when an aqueous solution with a high concentration of polyvinyl alcohol is attached to the support, it is conceivable that the attachment of polyvinyl alcohol concentrates inside and / or on the surface of the pores of the support, and polyvinyl alcohol molecules are layered inside and / or on the surface of the support pores to form a film. As a result, a mesh-like network of polyvinyl alcohol may not form on the surface of the support, and a film-like structure may be formed. If an air filter material with such a film-like structure partially formed is used, it can lead to an increase in pressure loss and a decrease in particle collection performance (i.e., a decrease in the PF value), and in some cases, it may not be able to maintain its permeability as an air filter. However, even if the adhesion of polyvinyl alcohol is concentrated only near the surface of the support, if a moderate network of polyvinyl alcohol is formed (i.e., the packing density of polyvinyl alcohol is not excessively high), the pressure loss will not increase significantly, and a suitable PF value for an air filter can be obtained. In this embodiment, the form of "having a mesh-like network of polyvinyl alcohol in the pores that serve as fluid permeability paths" can be, for example, three forms in which a network structure formed by the intertwining of nanofibers made of polyvinyl alcohol exists inside, on the surface, or both inside and on the surface of the pores that serve as fluid permeability paths.When a cationic surfactant and a water repellent are included in an aqueous solution of polyvinyl alcohol to manufacture a filter material for air filters, the formation of the mesh-like network of polyvinyl alcohol is further optimized, resulting in improved PF value and water repellency. [Examples]

[0067] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified. Note that the number of added parts is the value on a solid content basis.

[0068] [Preparation process for aqueous polyvinyl alcohol solution] 998.0g of water was added to a 1000ml beaker, followed by 2.0g of polyvinyl alcohol powder (saponification degree 88mol%, polymerization degree 3500, PVA95-88, manufactured by Kuraray Co., Ltd.). The mixture was stirred for 10 minutes using a propeller-type stirrer. The temperature was then raised to 95°C during stirring, and the mixture was stirred for 2 hours until dissolved. The solid content concentration of polyvinyl alcohol relative to the total mass of the aqueous solution was 0.20%, and the solution was diluted with water to achieve the concentrations of the examples and comparative examples. All water used to prepare the aqueous solutions was distilled water.

[0069] (Example 1) [Polyvinyl alcohol adhesion and drying] The concentration of polyvinyl alcohol (saponification degree 88 mol%, degree of polymerization 3500, PVA95-88, manufactured by Kuraray Co., Ltd.) is 0.07%, the concentration of surfactant (perfluoroalkyltrialkylammonium salt, fluorine-based cationic surfactant, Surflon S-221, manufactured by AGC Seimi Chemical Co., Ltd.) is 0.0105%, and the concentration of water repellent (fluorine-based cationic water repellent, AG-E310, manufactured by AGC, zeta potential: 30.8 mV) is 0.0035 %and Prepare a polyvinyl alcohol aqueous solution to be used as a support with a basis weight of 51 g / m². 2A nonwoven fabric (hereinafter referred to as the "support") made of glass fibers with a pressure drop of 67 Pa (consisting of 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) was coated with the amounts shown in Table 1 using a two-fluid nozzle spray, and dried in a hot air dryer at 190°C to obtain a filter material for an air filter. The total amount of polyvinyl alcohol and surfactant coated on the support was 0.43%.

[0070] (Example 2) An air filter material was obtained in the same manner as in Example 1, except that the concentration of the water repellent was changed to 0.0105% in the polyvinyl alcohol aqueous solution and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 1. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.45%.

[0071] (Example 3) An air filter material was obtained in the same manner as in Example 1, except that the concentration of the water repellent was changed to 0.0140% in the polyvinyl alcohol aqueous solution and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 1. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.47%.

[0072] (Example 4) An air filter material was obtained in the same manner as in Example 1, except that the concentration of the water repellent was changed to 0.0350% in the polyvinyl alcohol aqueous solution and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 1. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.55%.

[0073] (Example 5) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration and the water repellent concentration were both 0.0070%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.43%.

[0074] (Example 6) The surfactant concentration is 0.0070%, and the water repellent concentration is 0.0140%. %and An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified to achieve the desired result, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.44%.

[0075] (Example 7) The surfactant concentration is 0.0070%, and the water repellent concentration is 0.0350%. %and An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified to achieve the desired result, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.57%.

[0076] (Example 8) The surfactant was changed to alkyltrimethylammonium chloride, a cationic surfactant, Cathiogen TML, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and the surfactant concentration was changed to 0.0070% and the water repellent concentration was changed to 0.0070%. %and An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified to achieve the desired result, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.43%.

[0077] (Example 9) The surfactant was changed to alkyltrimethylammonium chloride, a cationic surfactant, Cathiogen TML, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and the surfactant concentration was changed to 0.0070% and the water repellent concentration to 0.0140%. %and An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified to achieve the desired result, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.46%.

[0078] (Example 10) The surfactant was changed to alkyltrimethylammonium chloride, a cationic surfactant, Cathiogen TML, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., with the surfactant concentration at 0.0070% and the water repellent concentration at 0.0350%. %and An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified to achieve the desired result, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 2. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.55%.

[0079] (Comparative Example 1) The "support" made of glass fibers from Example 1 was used as the air filter material.

[0080] (Comparative Example 2) An air filter material was obtained in the same manner as in Example 1, except that the concentration of the polyvinyl alcohol aqueous solution was changed to 0.07%, the concentration of the surfactant was 0%, and the concentration of the water repellent was 0%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 1. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.39%.

[0081] (Comparative Example 3) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0% and the water repellent concentration was 0.0070%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.38%.

[0082] (Comparative Example 4) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0% and the water repellent concentration was 0.0140%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.40%.

[0083] (Comparative Example 5) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0% and the water repellent concentration was 0.0350%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.53%.

[0084] (Comparative Example 6) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0% and the water repellent concentration was 0.0420%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.57%.

[0085] (Comparative Example 7) An air filter material was obtained in the same manner as in Example 1, except that the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0% and the water repellent concentration was 0.0490%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.62%.

[0086] (Comparative Example 8) An air filter material was obtained in the same manner as in Example 1, except that the surfactant concentration was changed to 0%, the water repellent was changed to a non-fluorinated, cationic hydrocarbon polymer-based water repellent, Mayshield P-350K, manufactured by Meisei Chemical Industry Co., Ltd., with a zeta potential of 37.8 mV, the polyvinyl alcohol aqueous solution was modified so that the water repellent concentration was 0.0007%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.33%.

[0087] (Comparative Example 9) An air filter material was obtained in the same manner as in Example 1, except that the surfactant concentration was changed to 0%, the water repellent was changed to a non-fluorinated, cationic hydrocarbon polymer-based water repellent, Mayshield P-350K, manufactured by Meisei Chemical Industry Co., Ltd., with a zeta potential of 37.8 mV, the polyvinyl alcohol aqueous solution was modified so that the water repellent concentration was 0.0070%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.41%.

[0088] (Comparative Example 10) An air filter material was obtained in the same manner as in Example 1, except that the surfactant concentration was changed to 0%, the water repellent was changed to a non-fluorinated, cationic hydrocarbon polymer-based water repellent, Mayshield Z-1, manufactured by Meisei Chemical Industry Co., Ltd., with a zeta potential of 13.7 mV, the polyvinyl alcohol aqueous solution was modified so that the water repellent concentration was 0.0007%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.34%.

[0089] (Comparative Example 11) An air filter material was obtained in the same manner as in Example 1, except that the surfactant concentration was changed to 0%, the water repellent was changed to a non-fluorinated, cationic hydrocarbon polymer-based water repellent, Mayshield Z-1, manufactured by Meisei Chemical Industry Co., Ltd., with a zeta potential of 13.7 mV, the polyvinyl alcohol aqueous solution was modified so that the water repellent concentration was 0.0070%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 3. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.36%.

[0090] (Comparative Example 12) An air filter material was obtained in the same manner as in Example 1, except that an acrylic resin (product name: Ultrazol FB-19 / manufactured by Aica Kogyo Co., Ltd.) was added to an aqueous solution of polyvinyl alcohol to a concentration of 0.0007% in the aqueous solution, and the amount of the polyvinyl alcohol aqueous solution containing the acrylic resin attached was changed to the amount shown in Table 4. The total amount of polyvinyl alcohol and acrylic resin attached to the support was 0.42%.

[0091] (Comparative Example 13) An air filter material was obtained in the same manner as in Example 1, except that the drying temperature was changed to 120°C and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 4. The amount of polyvinyl alcohol attached to the support was 0.42%.

[0092] (Comparative Example 14) An air filter material was obtained in the same manner as in Example 1, except that the surfactant was changed to a perfluoroalkyl compound, a fluorinated amphoteric surfactant, Surflon S-232, manufactured by AGC Seimi Chemical Co., Ltd., the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0.0105%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 4. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.43%.

[0093] (Comparative Example 15) An air filter material was obtained in the same manner as in Example 1, except that the surfactant was changed to polyoxyethylene tridecyl ether sulfate sodium salt, an anionic surfactant, Hythenol 330T, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the polyvinyl alcohol aqueous solution was modified so that the surfactant concentration was 0.0105%, and the amount of polyvinyl alcohol aqueous solution attached was changed to the amount shown in Table 4. The total amount of polyvinyl alcohol and surfactant attached to the support was 0.42%.

[0094] The manufacturing conditions and physical properties of the air filter media obtained in each example and comparative example are shown in Tables 1 to 4. The physical properties were measured using the following method.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] "PF�" The PF value was calculated from the measured pressure loss and particle transmission rate using the formula shown in Equation 1. The target particle size was set to 0.10–0.15 μm. A higher PF value indicates an air filter with low particle transmission rate and low pressure loss.

number

[0100] "Network Observation" The network was observed by scanning electron microscope (SEM, Hitachi High-Technologies Corporation, SU8010) on the filter media for the air filter at a magnification of 5,000 to 10,000 times. Prior to observation, a conductive coating was applied using an ion sputter (E-1045, Hitachi High-Technologies Corporation) under the following conditions: discharge current of 15 mA, sample-target distance of 30 mm, vacuum of 6 Pa, and coating time of 2 minutes.

[0101] "Gurley stiffness measurement method" The test was conducted according to JAPAN TAPPI Paper and Pulp Test Method No. 40:2000, Paper and Cardboard - Stiffness Test Method by Load Bending - Gurley method. The equipment used was a Gurley Tefne tester (manufactured by Kumagai Riki Kogyo Co., Ltd.).

[0102] "Method for measuring tensile strength" Measurements were taken in accordance with JIS P8113:2006 Paper and cardboard — Test methods for tensile properties. The equipment used was an Autograph AGX (manufactured by Shimadzu Corporation).

[0103] In Examples 1 to 10 and Comparative Examples 2 to 11, it was confirmed that polyvinyl alcohol nanofibers were formed, and that a mesh-like network of polyvinyl alcohol was present in the pores that served as fluid permeability pathways. The number-average fiber diameter of the nanofibers was approximately 40 nm. However, in Comparative Examples 2 to 11, the amount of polyvinyl alcohol mesh-like network formed was small.

[0104] Figure 1 shows an SEM image of the air filter of Example 8. As shown in Figure 1, by rapidly drying polyvinyl alcohol with a saponification degree of 88 mol% at a high temperature of 190°C, a clean nanofiber network was obtained, and a suitable PF value was acquired. Figure 2 shows an SEM image of the air filter of Example 9. As shown in Figure 2, by rapidly drying polyvinyl alcohol with a saponification degree of 88 mol% at a high temperature of 190°C, a clean nanofiber network was obtained, and a suitable PF value was acquired.

[0105] Examples 1 to 10 all show higher PF values ​​compared to the support of Comparative Example 1. In the air filter media according to this embodiment, for example, a PF value of 11.0 or higher can be obtained for 0.10-0.15 μm. In this example, a PF value of 11.3 or higher was obtained for 0.10-0.15 μm.

[0106] In Comparative Example 12, a small amount of acrylic resin (1% acrylic resin relative to PVA) was added as a binder resin to the aqueous solution of polyvinyl alcohol. As a result, the mesh-like network of polyvinyl alcohol was not formed, and the PF value was almost the same as that of Comparative Example 1, showing no improvement.

[0107] In Comparative Example 13, the drying temperature was less than 140°C, resulting in insufficient drying, which prevented the formation of a clean mesh-like network, and thus the PF value did not increase.

[0108] In Comparative Examples 3 to 7, while water repellency was achieved compared to Comparative Example 2, the PF value was lower. In other words, the example in which a water repellent was added to the aqueous solution of polyvinyl alcohol without a surfactant resulted in a lower PF value compared to the example in which neither a cationic surfactant nor a water repellent was added to the aqueous solution of polyvinyl alcohol. Figure 3 shows an image of the air filter of Comparative Example 4 observed by SEM. Because no cationic surfactant was added, the mesh-like network of polyvinyl alcohol was not formed. On the other hand, in Examples 1 to 10, in which both a cationic surfactant and a water repellent were added to the aqueous solution of polyvinyl alcohol, both water repellency and a high PF value were obtained. The reason for this phenomenon is not clear, but the examples in which polyvinyl alcohol, a cationic surfactant, and a water repellent are added to the aqueous solution are shown to be useful in that they provide water repellency and a high PF value.

[0109] Comparative Examples 8 to 11 are also examples in which a water repellent was added to an aqueous solution of polyvinyl alcohol without adding a surfactant. Figure 4 shows an image of the air filter of Comparative Example 9 observed by SEM. Because no cationic surfactant was added, the mesh-like network of polyvinyl alcohol was not formed. The PF value was only the same as that of Comparative Examples 3 to 7, and the PF value was lower than that of Comparative Example 2. Furthermore, despite adding a non-fluorine-based water repellent to the aqueous solution of polyvinyl alcohol, water repellency was not obtained. A comparison of Comparative Examples 8 to 11 with Examples 1 to 10 also showed that the examples were useful in that water repellency was obtained and high PF values ​​were obtained. Comparative Examples 8 and 10 did not exhibit water repellency. Comparative Example 9, which had an increased amount of water repellent added to Comparative Example 8, and Comparative Example 11, which had an increased amount of water repellent added to Comparative Example 10, both did not exhibit water repellency despite the increased amount of water repellent added.

[0110] In Comparative Example 14, a fluorinated amphoteric surfactant was added to the polyvinyl alcohol aqueous solution, but the PF value was almost the same as that of Comparative Example 1, and even lower than that of Comparative Example 2, which did not contain any surfactant. From this, it was found that adding a cationic surfactant, rather than a fluorinated amphoteric surfactant, is more useful for obtaining a high PF value.

[0111] In Comparative Example 15, an anionic surfactant was added to the polyvinyl alcohol aqueous solution instead of a cationic surfactant, but the PF value was lower than that of Comparative Example 1 and considerably lower than that of Comparative Example 2, which had no surfactant added. From this, it was found that adding a cationic surfactant rather than an anionic surfactant is useful for obtaining a high PF value. Figure 5 shows an image of the air filter of Comparative Example 15 observed by SEM. Although an anionic surfactant was added, the mesh-like network of polyvinyl alcohol was not formed.

[0112] Normally, the stiffness and tensile strength of a filter are increased by adding binder resin, but this leads to a decrease in the PF value. Therefore, there has usually been a trade-off relationship between stiffness and PF value. According to the present invention, as shown in Tables 1 to 2, it is possible to improve stiffness and tensile strength without significantly decreasing the PF value. For example, compared to Comparative Example 1, Examples 1 to 10 show an improvement of 1 mN or more in Gurley stiffness and an improvement of 0.2 kN / m or more in tensile strength. When stiffness and tensile strength are improved compared to Comparative Example 1, deformation of the filter during ventilation after pleating can be suppressed, which can lead to increased structural pressure loss. For example, it is possible to prevent the filter from deforming over time during use.

[0113] From the above results, it can be seen that the method for manufacturing the filter material for air filters according to this embodiment can provide a method for manufacturing an air filter material with improved filter performance, particularly particle collection performance, and good water repellency in a relatively short time, using polyvinyl alcohol, a cationic surfactant, and a water repellent.

Claims

1. A bonding step involves spraying a polyvinyl alcohol aqueous solution onto a fluid-permeable support to wet the support, The process includes a drying step of drying the polyvinyl alcohol aqueous solution adhering to the wet support at 140°C or higher without wiping or dewatering, The support is a nonwoven fabric for filter media, mainly composed of glass fibers. The aforementioned aqueous solution of polyvinyl alcohol contains a cationic surfactant and a water repellent, and does not contain any binder resin other than polyvinyl alcohol. The cationic surfactant is a cationic surfactant that does not act as a water repellent. The degree of saponification of the polyvinyl alcohol is 80 to 98 mol%, and the degree of polymerization of the polyvinyl alcohol is 1500 to 6000. The cationic surfactant in the aqueous polyvinyl alcohol solution is added in an amount of 1 to 30 parts by mass per 100 parts by mass of polyvinyl alcohol. The water-repellent agent in the aqueous polyvinyl alcohol solution is added in an amount of 5 to 50 parts by mass per 100 parts by mass of polyvinyl alcohol. The amount of polyvinyl alcohol adhering to the support is 0.05 to 1.00% by mass. A method for manufacturing an air filter material, characterized in that the support having undergone the drying step has a mesh-like network of polyvinyl alcohol in the pores that serve as fluid permeability paths, due to the drying of the aqueous polyvinyl alcohol solution.

2. The method for manufacturing an air filter material according to claim 1, characterized in that the mesh-like network is made of nanofibers.

3. The method for manufacturing an air filter material according to claim 2, characterized in that the nanofibers have a number-average fiber diameter of 10 to 500 nm.

4. The amount of the polyvinyl alcohol aqueous solution to be attached to the support is 1 m of the support. ２ A method for manufacturing an air filter material according to any one of claims 1 to 3, characterized in that the amount per unit is 50 g or more.

5. In the drying process described above, the evaporation rate of the solvent in the polyvinyl alcohol aqueous solution adhering to the wet support is such that the evaporation rate of the support is 1 m ２ A method for manufacturing an air filter material according to any one of claims 1 to 4, characterized in that the flow rate is 100 g / min or more per unit.

6. A method for producing an air filter material according to any one of claims 1 to 5, characterized in that the total amount of polyvinyl alcohol, cationic surfactant, and water repellent adhering to the support after the drying step is 0.10 to 1.50% by mass.

7. A method for producing an air filter material according to any one of claims 1 to 6, characterized in that the cationic surfactant is a quaternary ammonium salt type or an amine salt type surfactant.

8. A support having fluid permeability, The support has a mesh-like network of polyvinyl alcohol formed in the pores that serve as fluid permeability pathways, The aforementioned mesh-like network consists of nanofibers. The degree of polymerization of the polyvinyl alcohol is 1500 to 6000. The degree of saponification of the polyvinyl alcohol is 80-90 mol%, The amount of polyvinyl alcohol adhering to the support is 0.05 to 1.00% by mass, and It contains a cationic surfactant and a water repellent, The support is a nonwoven fabric for filter media, mainly composed of glass fibers. The cationic surfactant is a cationic surfactant that does not act as a water repellent. The cationic surfactant is added in an amount of 1 to 30 parts by mass per 100 parts by mass of the polyvinyl alcohol. The water-repellent agent is added in an amount of 5 to 50 parts by mass per 100 parts by mass of the polyvinyl alcohol. A filter material for air filters characterized by not containing any binder resin other than the aforementioned polyvinyl alcohol.

Images