Air filter filtration material

Abstract

This air filter filtration material comprises a plurality of layers of nonwoven fabric and has a performance index of at least 0.023. At least one of the layers of nonwoven fabric contains at least two kinds of organic fibers A and B having different fiber diameters. The average fiber diameter of the organic fibers A is 0.01-0.60 μm, and the average fiber diameter of the organic fibers B is 1.0-30 μm.　Provided is an air filter filtration material suitable for an air filter having both high collection efficiency and low pressure loss.

Description

Air filter media

[0001] The present invention relates to an air filter medium suitable for an air filter.

[0002] In recent years, the demand for space purification has been increasing, and in a wide range of fields from living environment to industry, such as the measures for the health problem caused by dust particles of 2.5 μ m or less, and the dust-free manufacturing of semiconductors and medicines, the air filter that removes fine dust in the air is used.Particularly, in the space that requires extremely high clean air such as clean room or semiconductor manufacturing equipment, high-performance air filter is used, as represented by HEPA filter (High Efficiency Particulate Air filter) or ULPA filter (Ultra Low Penetration Air filter), and the air filter material of HEPA filter or ULPA filter is made of glass fiber nonwoven fabric or PTFE (polytetrafluoroethylene) porous film.

[0003] However, the air filters that use glass fiber and PTFE air filter media are all disposed of in landfills after use, which causes a large environmental impact.Furthermore, ULPA filters are used in clean rooms and semiconductor manufacturing equipment in semiconductor manufacturing, etc., but using glass fiber filter media will release boron, which has a negative effect on semiconductor manufacturing, so PTFE filter media is generally selected and used.However, PFOA (perfluorooctanoic acid), which is a by-product of PTFE manufacturing, is an environmentally destructive substance that is difficult to decompose in nature, and it also accumulates in living organisms and is toxic, so there are problems such as the need for alternative materials.

[0004] In response to the recent increase in environmental awareness and compliance consciousness, various filter media have been proposed that are made of ultrafine polyester fibers and have excellent filtering performance, which have a smaller environmental impact.

[0005] For example, Patent Document 1 proposes a wetlaid nonwoven fabric having a multilayer structure of two or more layers with no interface between adjacent layers, using short-cut nanofibers made of a fiber-forming thermoplastic polymer and cut so that the single fiber diameter (D) is 100 to 1,000 nm and the ratio (L / D) of fiber length (L) to the single fiber diameter (D) is within the range of 100 to 2,500. This proposal claims to provide a filter with high collection efficiency, low pressure loss, and a long filter life.

[0006] Patent Document 2 proposes an air filter medium using a nonwoven fabric containing three types of polyester fibers: nanofibers with a fiber diameter of 200 to 800 nm, fibers thicker than the nanofibers, and binder fibers. This proposal claims to have excellent pleating properties and wind pressure deformation resistance, low pressure loss, and high collection performance.

[0007] JP 2013-126626 A JP 2015-140495 A

[0008] Although the method described in Patent Document 1 can obtain an air filter medium with excellent high collection efficiency and low pressure loss, it does not achieve the collection efficiency required for HEPA filters or ULPA filters, and is insufficient in terms of achieving both low pressure loss and high collection efficiency.

[0009] Furthermore, the method described in Patent Document 2 can obtain a thin air filter medium that is excellent in pleatability and can achieve the collection efficiency required for HEPA filters and ULPA filters, but the pressure loss is high, and the method is insufficient in terms of achieving both low pressure loss and high collection efficiency.

[0010] The object of the present invention is to solve the problems of the above-mentioned conventional technology and to provide an air filter medium suitable for air filters, which has both the high collection efficiency and low pressure loss required for HEPA filters and ULPA filters, and an air filter using the same.

[0011] (1) An air filter medium having a performance index of 0.023 or higher, wherein at least one of the nonwoven fabric layers contains at least two types of organic fibers A and B having different fiber diameters, with the organic fiber A having an average fiber diameter of 0.01 to 0.60 μm and the organic fiber B having an average fiber diameter of 1.0 to 30 μm. (2) The air filter medium described in (1), characterized by a particle collection efficiency of 99.97% or higher for particles with a particle diameter of 0.3 μm. (3) The air filter medium described in (1), characterized by a particle collection efficiency of 99.9995% or higher for particles with a particle diameter of 0.15 μm. (4) The air filter medium described in (1), characterized by at least one of the laminated nonwoven fabric layers having a performance index of 0.023 or higher. (5) The air filter medium described in (1), wherein the nonwoven fabric further contains binder fibers. (6) An air filter using the air filter medium according to any one of (1) to (5). (7) A fan filter unit equipped with the air filter according to (6). (8) A clean room or semiconductor manufacturing equipment equipped with the air filter according to (6).

[0012] According to the present invention, it is possible to obtain an air filter medium suitable for air filters, which has both high collection efficiency and low pressure loss required for HEPA filters and ULPA filters.

[0013] The air filter medium of the present invention is an air filter medium comprising at least two types of organic fibers, characterized in that it comprises a plurality of laminated nonwoven fabrics each containing fiber A having a fiber diameter of less than 0.8 μm and an average fiber diameter of 0.01 to 0.60 μm and fiber B having a fiber diameter of 0.8 μm or more and an average fiber diameter of 1.0 to 30 μm, and has a performance index of 0.023 or more.

[0014] [Nonwoven Fabric] First, the nonwoven fabric of the present invention will be described in detail.

[0015] The fibers A and B used in the nonwoven fabric of the present invention are organic fibers. The organic fibers of the present invention are fibrous materials primarily composed of organic matter. Specific examples of organic fibers include, but are not limited to, cellulose produced from wood pulp, natural fibers such as cotton, hemp, wool, and silk, regenerated fibers such as rayon, semi-synthetic fibers such as acetate, and synthetic fibers such as polyester, nylon, and acrylic. Among these, synthetic fibers made of thermoplastic polymers are preferred from the viewpoint of mechanical properties and dimensional stability. Specific examples of thermoplastic polymers include, but are not limited to, polyesters such as polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polylactic acid; polyamides such as polyamide 6, polyamide 66, and polyamide 610; polyolefins such as polyethylene, polypropylene, and polymethylpentene; thermoplastic polymers such as polycarbonate, polyacrylate, polyphenylene sulfide, and thermoplastic polyurethane, and copolymers thereof. Among these, polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, polyamides such as polyamide 6 and polyamide 66, and polyphenylene sulfide are preferred because they have both mechanical properties and heat resistance.

[0016] The organic fiber in the present invention may be modified in various ways by adding secondary additives, as long as the effects of the present invention are not impaired. Specific examples of secondary additives include, but are not limited to, compatibilizers, plasticizers, antioxidants, ultraviolet absorbers, infrared absorbers, fluorescent brighteners, release agents, antibacterial agents, nucleating agents, heat stabilizers, flame retardants, antistatic agents, coloring inhibitors, adjusters, matting agents, defoaming agents, preservatives, gelling agents, latex, fillers, inks, colorants, dyes, pigments, and fragrances. These secondary additives may be used alone or in combination.

[0017] The fiber A used in the nonwoven fabric of the present invention has a fiber diameter of less than 0.8 μm and an average fiber diameter of 0.01 to 0.60 μm. A smaller fiber diameter is preferable because it results in a higher specific surface area and exhibits high collection performance when made into a nonwoven fabric. However, an average fiber diameter of 0.01 μm or more not only provides high collection performance, but also improves handleability and moldability during processing, resulting in a nonwoven fabric with excellent durability during use. The average fiber diameter is more preferably 0.05 μm or more, and even more preferably 0.10 μm or more. On the other hand, if the average fiber diameter is 0.60 μm or less, the high specific surface area resulting from the small fiber diameter will result in excellent collection performance when made into a nonwoven fabric. The average fiber diameter is more preferably 0.50 μm or less.

[0018] The fiber B used in the nonwoven fabric of the present invention has a fiber diameter of 0.8 μm or more and an average fiber diameter of 1.0 to 30.0 μm. When the average fiber diameter is 1.0 μm or more, the fiber B serves as an aggregate for maintaining the shape of the nonwoven fabric, and the fiber A is not excessively densified, thereby suppressing an increase in pressure loss and enabling the production of a nonwoven fabric that combines high collection performance with low pressure loss. The average fiber diameter is more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. On the other hand, when the average fiber diameter is 30.0 μm or less, fiber A, which is thinner than fiber B, is prevented from falling off during the processing of the wetlaid nonwoven fabric described below, and serves as a scaffold for fiber A in the resulting nonwoven fabric, allowing the formation of three-dimensionally uniform microspaces. The average fiber diameter of fiber B is more preferably 28.0 μm or less, and even more preferably 25.0 μm or less.

[0019] The nonwoven fabric of the present invention can use various binders, such as fibrous or adhesive binders, to physically bond the fibers constituting the nonwoven fabric together by thermal bonding. The binder is not particularly limited, but suitable binders include, for example, sheath-core fibers in which a thermoplastic polymer with a melting point of 150°C or less is arranged in the sheath. When such sheath-core fibers are used, the nonwoven fabric is preferably subjected to a drying process using a Yankee dryer or air-through dryer, or a heat treatment process using a calendar, after formation, whereby the sheath component of the binder fiber on the surface melts and bonds to the other fibers constituting the nonwoven fabric, thereby enhancing the rigidity of the nonwoven fabric. Furthermore, the core component of the binder fiber is preferably responsible for ensuring the strength of the nonwoven fabric. It is preferable that the melting point of the core component of the binder fiber is higher than that of the sheath component, and the difference in melting points is 20°C or more. This facilitates sufficient melting of the sheath component on the surface of the binder fiber, suppresses the deterioration of the orientation of the core component, and achieves both sufficient thermal bonding and high rigidity. Furthermore, by making the crystallinity of fiber B into an undrawn yarn of 20% or less, it can be used as a binder. By softening and fluidizing it through heat treatment, it is possible to bond the fibers firmly and uniformly.

[0020] In the nonwoven fabric of the present invention, the blending ratio (weight ratio) of fibers A and B can be calculated by dividing the weight of fiber A or B by the total weight of fibers A and B. Furthermore, when binder fibers are used in addition to fibers A and B, the blending ratio can be calculated by dividing the weight of fiber A or B by the total weight of fibers A, B, and the binder. As a guideline for the blending ratio of fibers A and B, the blending ratio of fiber A is preferably 2 to 55 wt %, and the blending ratio of fiber B is preferably 5 to 90 wt %. A blending ratio of fiber A of 2.5 wt % or more is preferred because the high specific surface area resulting from the small fiber diameter of fiber A results in excellent collection performance when made into a nonwoven fabric. The blending ratio of fiber A is more preferably 3 wt % or more, and even more preferably 5 wt % or more. On the other hand, if the blending ratio of fiber A is 55% by weight or less, excessive densification of fiber A in the nonwoven fabric is suppressed, thereby suppressing an increase in pressure loss and enabling a nonwoven fabric that combines high collection performance and low pressure loss to be obtained, and a blending ratio of 50% by weight or less is even more preferable. Furthermore, if the blending ratio of fiber B is 5% by weight or more, fiber B can function as an aggregate for maintaining the shape of the nonwoven fabric, fiber A is not excessively densified, thereby suppressing an increase in pressure loss, and fiber A, which is thinner than fiber B, can fall off during processing of the wetlaid nonwoven fabric described below, and this is also preferable. The blending ratio of fiber B is more preferably 7% by weight or more, and even more preferably 10% by weight or more.

[0021] The basis weight of the nonwoven fabric in the present invention is 3 to 100 g / m ２ The basis weight of the nonwoven fabric in the present invention refers to a value measured by the method described in the Examples section. ２ If the weight is 5 g / m or more, it is possible to obtain a uniform nonwoven fabric with little density difference and excellent durability during use, which is preferable. ２ More preferably, it is 7 g / m or more. ２ On the other hand, it is more preferable that the basis weight is 100 g / m or more. ２ If the weight is less than 80 g / m, the handling property and molding processability during nonwoven fabric processing are good, which is preferable. ２ More preferably, it is 70 g / m or less. ２It is more preferable that:

[0022] [Collection Efficiency, Pressure Drop] The performance index is an index used to evaluate the performance of a filter, and indicates the potential capacity of the filter. Specifically, it can be calculated using the following formula from the filter's collection efficiency and pressure drop, which will be described later: Performance index = -ln[{1 - collection efficiency (%) / 100)} / pressure drop (Pa)] The higher this performance index, the higher the performance of the filter is evaluated to be, and the performance index is an important index for comprehensively evaluating the performance of a filter.

[0023] The collection efficiency is an index showing how much particles a nonwoven fabric or air filter medium can capture. For example, the number of particles supplied to the nonwoven fabric or air filter medium (the number of upstream particles) and the number of particles that have passed through the nonwoven fabric or air filter medium (the number of downstream particles) can be measured using a particle counter or the like to calculate the particle transmittance, and the collection efficiency can be calculated from the particle transmittance using the following formula: Particle transmittance [%] = (the number of downstream particles / the number of upstream particles) x 100 Collection efficiency [%] = 100 - particle transmittance [%] In the JIS standard (JIS Z 8122), HEPA is specified as having a collection efficiency of 99.97% or more for 0.3 μm particles, and ULPA is specified as having a collection efficiency of 99.9995% or more for 0.15 μm particles. When evaluating a nonwoven fabric or air filter medium, the particle size to be measured is selected according to the desired filter grade. The collection efficiency can be automatically measured using a filter collection efficiency tester (Model 3160 manufactured by TSI) or the like, using a particle counter built into the device.

[0024] When air passes through nonwoven fabric or air filter material, the flow of air is hindered and resistance occurs. This resistance causes a difference in air pressure (static pressure) before and after passing through nonwoven fabric or air filter material, and this differential pressure value is pressure loss (Pa). If the pressure loss is large, the energy (for example, the power of the fan) required to pass through the air filter increases, and energy efficiency decreases. In JIS standard (JIS Z 8122), the pressure loss of both HEPA and ULPA is specified as 245 Pa or less in the state of air filter. However, this is the value after the air filter material is processed into a pleated shape, and the pressure loss of the filter material itself before pleating is preferably 350 Pa or less when, for example, air flows at a surface velocity of 3.3 m / min. In addition, the pressure loss can be automatically measured by using a filter collection efficiency test device (TSI Model 3160) or the like from a pressure meter (including a differential pressure meter) built into the device.

[0025] [Air filter material] The air filter material of the present invention is a laminated nonwoven fabric, and is constructed by laminating a plurality of the above-mentioned nonwoven fabrics.By laminating a plurality of nonwoven fabrics, the particle permeability of the nonwoven fabric is the product of the particle permeability of each nonwoven fabric, so the particle permeability after laminating a plurality of sheets is reduced, and the collection efficiency is increased.On the other hand, the pressure loss is the sum of the pressure loss of each nonwoven fabric, so by laminating a plurality of sheets, it is increased.In an example of specific figures, when two nonwoven fabrics with a particle permeability of 10% (collection efficiency 90%) and a pressure loss of 100 Pa are laminated, the particle permeability is 1% (10% [= 0.1] x 10% [= 0.1] = 1% [= 0.01]), and the pressure loss is 200 Pa (100 Pa + 100 Pa = 200 Pa). Note that before lamination (one nonwoven fabric), the particle permeability was 10% (filtering efficiency 90%) and the pressure loss was 100 Pa, and after lamination (two nonwoven fabrics), the particle permeability was 1% (filtering efficiency 99%) and the pressure loss was 200 Pa. In both cases, the performance index, which indicates the potential performance of the filter, was 0.023, and the balance between filter efficiency and pressure loss itself remained unchanged. If an attempt is made to improve the filter efficiency with a single nonwoven fabric by increasing the basis weight or the blending ratio of fiber A, the increase in filter efficiency will be accompanied by a greater increase in pressure loss, which will likely worsen the balance between filter efficiency and pressure loss and lower the performance index. In other words, in order to improve the performance index, a multilayer structure can be manufactured more easily than a single nonwoven fabric. For this reason, when manufacturing a filter medium with a collection efficiency of 99.97%, a pressure drop of 350 Pa, and a performance index of 0.023 required for a HEPA filter, it is less difficult to manufacture by laminating two sheets of nonwoven fabric with a collection efficiency of 98.27%, a pressure drop of 175 Pa, and a performance index of 0.023, or by laminating three sheets of nonwoven fabric with a collection efficiency of 93.31%, a pressure drop of 117 Pa, and a performance index of 0.023, than by constructing it with a single sheet of nonwoven fabric. The performance of the laminated nonwoven fabrics does not need to be the same. For example, by laminating a nonwoven fabric with a collection efficiency of 70.00%, a pressure drop of 100 Pa, and a performance index of 0.012 on the first sheet and a nonwoven fabric with a collection efficiency of 99.90%, a pressure drop of 250 Pa, and a performance index of 0.028 on the second sheet, it is possible to achieve a collection efficiency of 99.97%, a pressure drop of 350 Pa, and a performance index of 0.023.In this way, by using a multilayer structure, it is expected that the difficulty of manufacturing the nonwoven fabric will be reduced, and as a result, manufacturing costs will be reduced. However, if the number of nonwoven fabrics to be laminated is too large, the work involved in the nonwoven fabric manufacturing process and lamination process will increase, and the cost advantage of the multilayer structure will be lost. For this reason, the number of nonwoven fabrics to be laminated is preferably 5 or less, and more preferably 3 or less.

[0026] The air filter medium of the present invention is required to have a performance index of 0.023 or more after laminating the nonwoven fabric. If the performance index is 0.023 or more, the air filter medium will have a good balance between collection efficiency and pressure drop, making it useful in various industries such as HEPA filter applications and ULPA filter applications.

[0027] The air filter material of the present invention can also be configured by laminating an air-permeable support material other than the nonwoven fabric of the present invention in order to improve the strength of the filter material.The material and structure of the air-permeable support material are not particularly limited, but for example, nonwoven fabric, woven fabric, metal mesh, resin net, etc. are used.Among them, dry nonwoven fabrics with heat fusion are preferred in terms of strength, collection ability, flexibility, and workability.Furthermore, the dry nonwoven fabric may be a nonwoven fabric in which some or all of the fibers constituting it have a core / sheath structure, or a two-layer nonwoven fabric consisting of two layers of low-melting point material and high-melting point material. The material of the dry nonwoven fabric is not particularly limited, and examples thereof include polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polylactic acid; polyamides such as polyamide 6, polyamide 66, and polyamide 610; polyolefins such as polyethylene, polypropylene, and polymethylpentene; thermoplastic polymers such as polycarbonate, polyacrylate, polyphenylene sulfide, and thermoplastic polyurethane; and copolymers or composites thereof. For dry nonwoven fabrics with a core / sheath structure, the core component preferably has a higher melting point than the sheath component. Examples of core / sheath material combinations include polyethylene terephthalate / polyethylene and high-melting-point polyethylene terephthalate / low-melting-point polyethylene terephthalate. The breathable support material can be bonded to the nonwoven fabric of the present invention by partially melting the breathable support material through heating, by melting a hot-melt resin, by utilizing the anchor effect, or by using adhesives such as reactive adhesives.

[0028] The basis weight and thickness of the breathable support material are not particularly limited, and it may be placed between the nonwoven fabrics of the present invention, or the nonwoven fabrics of the present invention may be laminated together in advance, and the breathable support material may be further laminated on the multi-layered nonwoven fabric.

[0029] In order to extend the life of the air filter material of the present invention, a pre-collection layer may be further laminated (usually on the upstream side of the airflow passing through the filter material).As the pre-collection layer, for example, one obtained by melt-blown method is used.The material of the pre-collection layer can be, for example, polyester such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyamide such as polyamide 6, polyamide 66, polyamide 610, polyolefin such as polyethylene, polypropylene, polymethylpentene, thermoplastic polymer such as polycarbonate, polyacrylate, polyphenylene sulfide, thermoplastic polyurethane, and copolymers thereof.The pre-collection layer can be bonded to the laminated nonwoven fabric by, for example, thermal lamination using hot-melt resin.

[0030] The air filter material of the present invention preferably has a particle collection rate of 99.97% or more for particles with a particle size of 0.3 μm.By doing so, it can be used as a HEPA filter in the clean room of pharmaceutical, medical, food, semiconductor fields, etc.Furthermore, if the particle collection rate of 99.99% or more for particles with a particle size of 0.15 μm, it is preferable that the filter material can be used in clean room, semiconductor manufacturing equipment, etc., because it can highly purify the air.

[0031] The air filter medium of the present invention preferably has a particle collection efficiency of 99.9995% or more for particles with a particle size of 0.15 μm, making it possible to use it as an ULPA filter that is compatible with semiconductor manufacturing equipment, etc.

[0032] The air filter medium of the present invention preferably has an average pore size of 0.1 to 10 μm. The average pore size in the present invention refers to the average size of the through-holes formed in the nonwoven fabric sheet, and refers to a value measured by the method described in the Examples. An average pore size of 0.1 μm or more is preferable because it ensures stable fluid flow. On the other hand, an average pore size of 10 μm or less is preferable because it allows the fluid to flow uniformly throughout the entire sheet without disrupting the flow of fluid passing through the wetlaid nonwoven fabric sheet.

[0033] The thickness of the air filter medium of the present invention is preferably 0.05 to 1.0 mm. The thickness of the air filter medium in the present invention refers to the value measured by the method described in the Examples. A thickness of 0.05 mm or more is preferable because it provides good handleability and molding processability during nonwoven fabric processing, allowing for an air filter medium with excellent durability during use. Furthermore, it is preferable because it provides good molding processability, such as pleating, when used as an air filter medium. The thickness is more preferably 0.1 mm or more, and even more preferably 0.15 mm or more. On the other hand, a thickness of 1.0 mm or less is preferable because it can suppress high pressure loss due to densification of the nonwoven fabric. Furthermore, when pleated into an air filter, the thickness of the filter medium reduces the contact area between adjacent filter materials, ensuring a sufficient filtration area and suppressing an increase in pressure loss, which is preferable. The thickness is more preferably 0.9 mm or less, and even more preferably 0.8 mm or less.

[0034] [Method for Producing Nonwoven Fabric] Next, an example of a method for producing a nonwoven fabric according to the present invention will be described below.

[0035] First, fiber B, and, if necessary, short fibers of a fibrous binder, are added to an aqueous medium and stirred with a disintegrator to uniformly disperse the fibers, thereby preparing a fiber dispersion. In this process, the dispersibility of the fibers can be adjusted by adjusting the amount of fiber charged, the amount of aqueous medium, the stirring time, etc., and it is preferable that each short fiber is dispersed as uniformly as possible in the aqueous medium. A dispersant may be added to improve the dispersibility of the fibers in the aqueous medium, but it is preferable to keep the amount of dispersant added to the minimum necessary so as not to affect the processability when the nonwoven fabric is subjected to post-processing.

[0036] Next, a fiber dispersion of fiber A is prepared in which fiber A is uniformly dispersed in an aqueous medium according to the method described below. This fiber dispersion of fiber A is mixed with the fiber dispersion of fiber B (to which a fibrous binder is added as necessary) to prepare a papermaking solution, which is then wet-laid to obtain a nonwoven fabric in which fiber A is uniformly distributed.

[0037] Fiber A in the present invention can be produced by using a sea-island fiber made of two or more polymers with different dissolution rates in a solvent. The sea-island fiber in the present invention has a structure in which island components made of a slightly soluble polymer are scattered in a sea component made of a readily soluble polymer.

[0038] The sea-island composite spinning method by melt spinning is suitable for spinning the sea-island composite fiber because it has high productivity and can be produced continuously. Furthermore, a method using a sea-island composite spinneret is preferred because it allows for excellent control of fiber diameter and cross-sectional shape.

[0039] Specific examples of the hardly soluble polymer used for the island component in the present invention include, but are not limited to, polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polylactic acid; polyamides such as polyamide 6, polyamide 66, and polyamide 610; polyolefins such as polyethylene, polypropylene, and polymethylpentene; thermoplastic polymers such as polycarbonate, polyacrylate, polyphenylene sulfide, and thermoplastic polyurethane; and copolymers thereof.

[0040] From the viewpoint of simplifying the dissolution step of the sea component, the readily soluble polymer used for the sea component in the present invention is preferably readily soluble in an aqueous solvent, hot water, etc. As the readily soluble polymer in the present invention, it is preferable to use a copolymerized polyester, polylactic acid, polyvinyl alcohol, etc., and in particular, it is preferable to use a polyester copolymerized with polyethylene glycol and / or sodium 5-sulfoisophthalate, or polylactic acid, from the viewpoint of ease of handling and easy solubility in a low-concentration aqueous solvent.

[0041] In the present invention, "easily soluble" means that the dissolution rate ratio (easily soluble polymer / slightly soluble polymer) is 100 or more when the slightly soluble polymer is used as a reference in the solvent used in the dissolution treatment. In consideration of simplifying the dissolution treatment and shortening the time, this dissolution rate ratio is preferably large, more preferably 1,000 or more, and even more preferably 10,000 or more. This range is preferable because the dissolution treatment can be completed in a short time and fiber A suitable for the present invention can be obtained without unnecessary deterioration of the slightly soluble polymer.

[0042] Furthermore, from the viewpoints of solubility in aqueous solvents and simplification of treatment of waste liquid generated during dissolution, polyesters copolymerized with polylactic acid, 3 to 20 mol % of sodium 5-sulfoisophthalate, and polyesters copolymerized with the aforementioned sodium 5-sulfoisophthalate and 5 to 15 wt % of polyethylene glycol having a weight-average molecular weight of 500 to 3,000 are particularly preferred.

[0043] As a result, examples of suitable polymer combinations for the aforementioned islands-in-sea fiber include, but are not limited to, a sea component made of either a polyester copolymerized with 3 to 20 mol % of sodium 5-sulfoisophthalate and 5 to 15 wt % of polyethylene glycol having a weight average molecular weight of 500 to 3000, or polylactic acid, and an island component made of either polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, or copolymers thereof.

[0044] The spinning temperature for the sea-island composite fiber is preferably set to a temperature at which the poorly soluble polymer and the easily soluble polymer, mainly those with high melting points and high viscosity, exhibit fluidity, as determined from the above-mentioned viewpoints. The temperature at which the fluidity is exhibited varies depending on the properties and molecular weight of the polymer, but the melting point of the polymer is used as a guide, and the spinning temperature may be set to a temperature not higher than 60°C above the melting point. This range is preferable because it prevents thermal decomposition of the polymer in the spinning head or spin pack, thereby preventing a decrease in molecular weight and enabling a good sea-island composite fiber to be produced.

[0045] As described above, in order to dissolve and remove the sea component from the sea-island composite fiber to obtain ultrafine fibers, the sea-island composite spinneret exemplified in Japanese Patent No. 5740877 can be suitably used in the present invention, but is not limited thereto.

[0046] The melted yarn extruded from the sea-island composite spinneret is cooled and solidified, and converged by adding an oil or the like, and taken up by a roller with a specified peripheral speed. The take-up speed can be determined based on the discharge rate and the target fiber diameter, and is preferably 100 to 7000 m / min from the viewpoint of stable production of the sea-island composite fiber. The spun sea-island composite fiber is preferably drawn from the viewpoint of improving mechanical properties and thermal stability. The drawn multifilament may be drawn after being wound up, or may be drawn immediately after spinning without being wound up.

[0047] The sea-island composite fiber is preferably formed into a tow of tens to millions of fibers and cut to the desired fiber length using a cutting machine such as a guillotine cutter, slicer, or cryostat. The fiber length L after cutting is preferably set so that the ratio (L / R1) of the sea-island composite fiber to the diameter R1 (corresponding to the average fiber diameter of fiber A) of the island component fiber is 1000 to 6000. This range is preferable because it increases the number of contact points between fibers in a nonwoven fabric, promotes the formation of a bridging structure between fibers, and enhances the reinforcing effect of the nonwoven fabric. An L / R1 ratio of 1000 or more is preferable because it prevents fiber A from falling out from the nonwoven fabric during wetlaid papermaking. An L / R1 ratio of 1500 or more is more preferable, and an L / R1 ratio of 2000 or more is even more preferable. On the other hand, an L / R1 ratio of 6000 or less is preferable because it prevents fiber A from aggregating in an aqueous medium, resulting in a highly uniform nonwoven fabric. L / R1 is more preferably 5,500 or less, and even more preferably 5,000 or less.

[0048] Fiber A can be produced by dissolving and removing the sea part from the aforementioned islands-in-sea fiber. That is, the sea part can be removed by immersing the cut sea-island fiber in a solvent capable of dissolving the soluble polymer of the sea part. When the soluble polymer is copolymerized polyethylene terephthalate or polylactic acid in which sodium 5-sulfoisophthalate or polyethylene glycol is copolymerized, an alkaline aqueous solution such as a sodium hydroxide aqueous solution can be used. When using an alkaline aqueous solution, the bath ratio of the sea-island fiber to the alkaline aqueous solution (weight (g) of the sea-island fiber:weight (g) of the alkaline aqueous solution) is preferably 1:5 to 1:10,000, more preferably 1:10 to 1:5,000. This range is preferable because it prevents unnecessary entanglement of fibers A when the soluble polymer of the sea part dissolves.

[0049] The alkali concentration of the alkaline aqueous solution is preferably 0.1 to 5 wt %, more preferably 0.5 to 3 wt %. This range is preferable because dissolution of the readily soluble sea component polymer is completed in a short time, and a fiber dispersion in which fibers A are uniformly dispersed can be obtained without unnecessarily deteriorating the sparingly soluble island component polymer. The temperature of the alkaline aqueous solution is not particularly limited, but is preferably 50°C or higher, because this can accelerate the dissolution of the readily soluble sea component polymer.

[0050] In the present invention, an aqueous solution of the readily soluble sea component polymer from the sea-island composite fiber may be used as a fiber dispersion of fiber A as is, or may be used after adjusting the pH by adding an acid or alkali, or after diluting with water. A dispersant may be added to the fiber dispersion to prevent fiber A from aggregating over time. Examples of dispersants include cationic compounds, nonionic compounds, and anionic compounds. Among these, anionic compounds are preferred for improving dispersibility in an aqueous medium due to electrical repulsion. The amount of dispersant added is preferably 0.001 to 10 times the weight of fiber A. This range is preferred because it ensures dispersibility of fiber A without impairing processability during wetlaid nonwoven fabric fabrication.

[0051] In the present invention, when the fiber B is a synthetic fiber made of a thermoplastic polymer, it can be produced by melt spinning, stretching as necessary, and then cutting to a desired fiber length as described above.Here, the fiber length of the fiber B is preferably 30 mm or less.If the fiber length is 30 mm or less, the formation of fiber agglomerates caused by the fibers being tightly entangled with each other during dispersion in an aqueous medium is suppressed, and a homogeneous nonwoven fabric can be obtained, which is preferable because it can be used as an air filter material.

[0052] The fiber dispersion of fiber A thus prepared is mixed with the fiber dispersion of fiber B (to which a fibrous binder may be added, if necessary), diluted to a certain concentration, and then dewatered on an inclined wire or cylinder to form a nonwoven fabric by wet papermaking. Apparatuses used for wet papermaking include, but are not limited to, a cylinder papermaking machine, a Fourdrinier papermaking machine, an inclined short-wire papermaking machine, or a combination thereof. In the papermaking process, a three-dimensionally homogeneous nonwoven fabric can be produced by adjusting the papermaking speed, the amount of fiber, and the aqueous medium, as well as the dispersibility of the fibers in the papermaking dope, to control the accumulation of the fibers during drainage.

[0053] The nonwoven fabric formed by wet papermaking is subjected to a drying process to remove moisture. As a drying method, a method using hot air ventilation (air through) or a method of contacting with a heated rotating roll (heated calendar roll, etc.) can be suitably adopted, from the viewpoint that the nonwoven fabric can be dried and the heat-bonding of the heat-bondable fibers can be carried out simultaneously.

[0054] [Manufacturing method of air filter medium] The air filter medium of the present invention can be manufactured by stacking and arranging a plurality of nonwoven fabrics. When stacking, the stacked nonwoven fabrics may be bonded together. When bonding, thermal lamination or adhesives may be used.

[0055] When bonding by thermal lamination, the rollers of the thermal laminating device are heated to a temperature higher than the glass transition temperature of the organic fibers and hot melt resin that make up the nonwoven fabric, and then the nonwoven fabrics are passed through the rollers, whereby the nonwoven fabrics are partially melted or the hot melt resin is melted, thereby utilizing the anchor effect to bond the nonwoven fabrics.

[0056] When an adhesive is used for bonding, the adhesive is applied in dots to the surface of the nonwoven fabric to be bonded using a dispenser or the like, and the adhesive-coated surface is then aligned with the surface of the other nonwoven fabric to be bonded, thereby bonding the two together. There are no particular restrictions on the type of adhesive used for bonding, and aqueous adhesives, solvent-based adhesives, resin-based adhesives, etc. can be used.

[0057] [Use] The nonwoven fabric of the present invention has high collection efficiency, so the air filter material using the nonwoven fabric of the present invention can be suitably used as the air filter material for air purifiers, air conditioners, building air conditioners, industrial clean rooms, and the cabins of automobiles, trains, etc.In addition, in spaces that require extremely clean air, such as clean rooms and semiconductor manufacturing equipment, it can be suitably used as the air filter material for the air filters of, for example, the air conditioner that takes in outside air into clean rooms, the air conditioner that circulates the air in clean rooms, and the fan filter unit that is installed on the ceiling of clean rooms and semiconductor manufacturing equipment.The clean rooms and semiconductor manufacturing equipment that are equipped with the air filter that uses these air filter material of the present invention are useful in various industries.

[0058] The present invention will now be described in detail with reference to examples. However, the present invention is not limited to these examples. The respective property values ​​in the examples were determined by the following methods.

[0059] A. Average Fiber Diameter In an image of the cross section of a fiber taken with a scanning electron microscope (electron microscope SU-1510 manufactured by Hitachi High-Technologies Corporation), the circumscribed circle diameter of the fiber cross section was measured for 100 random fibers, and the average was rounded to one decimal place to obtain the average fiber diameter.

[0060] B. Fiber length of organic fiber The fiber lengths of 100 randomly selected fibers were measured in an image of the side surface of the fiber taken with a stereomicroscope (Olympus SZ-61 stereomicroscope), and the average was rounded off to one decimal place to obtain the fiber length. The fiber length of fiber A was measured on the sea-island composite fiber before removing the sea part.

[0061] C. Total volume of organic fibers The volume of each fiber was calculated assuming a perfect circle cross section using the average fiber diameter and fiber length calculated in the above items A and B. The volume of all fibers was then calculated by adding up the volumes of all the fibers.

[0062] D. Basis Weight The nonwoven fabric obtained in each of the Examples and Comparative Examples was used as a sample. The nonwoven fabric was cut into a square of 250 mm x 250 mm and weighed. ２ The value converted to the weight per unit area (g / m) is rounded to the nearest tenth to obtain the basis weight of the nonwoven fabric (g / m ２ Measurements were taken from three randomly selected locations per sample, and the average value was rounded off to one decimal place to obtain the basis weight.

[0063] E. Thickness The nonwoven fabric used in the measurement in the above item D was used as a sample, and the thickness of the nonwoven fabric was measured using a dial thickness gauge (SM-114 manufactured by TECLOCK CORPORATION, probe shape 10 mmφ, graduation 0.01 mm, measuring force 2.5 N or less). Measurements were taken at any five points per sample, and the average value was rounded to two decimal places to calculate the thickness (mm) of the nonwoven fabric.

[0064] F. Porosity Using the basis weight and thickness of the nonwoven fabric calculated in the above sections D and E, the value calculated by the following formula was rounded to one decimal place to determine the porosity (%) of the nonwoven fabric. Porosity (%) = 100 - [basis weight (g / m ２ ) / {thickness (mm) × fiber density (g / cm ３ )}] × 0.1 The fiber density may be the density of the fibers constituting the nonwoven fabric, and in the case of PET, it is 1.38 g / cm ３ It was calculated as:

[0065] G. Collection Efficiency The nonwoven fabrics or air filter media obtained in the Examples and Comparative Examples were used as samples, and samples cut to a diameter of 12 cm were set using a filter collection efficiency tester (TSI Model 3160). The collection efficiency was measured using particles with a particle size of 0.15 μm or 0.3 μm. For the collection efficiency (%) for particles with a particle size of 0.15 μm, sodium chloride particles with an average particle size of 0.15 to 0.16 μm were collected at 20,000 to 30,000 particles / m. ３ The measurement was made by passing air containing sodium chloride particles at a flow rate of 31.5 L / min. The collection efficiency (%) for particles with a particle size of 0.30 μm was 20,000 to 30,000 particles / m for sodium chloride particles with an average particle size of 0.30 to 0.31 μm. ３ The air containing the fluorine-containing compound was passed through at a flow rate of 31.5 L / min and the measurement was carried out.

[0066] H. Pressure loss The nonwoven fabric or air filter media obtained in Examples and Comparative Examples is used as sample, and the sample cut out to 12 cm in diameter is set using a filter collection efficiency tester (TSI Model 3160).The evaluation part is opened with a diameter of 11 cm, and the sample is exposed.In order to make the surface velocity of the air flowing 3.3 m / min, air is passed through at a setting of 31.5 L / min, and pressure loss (Pa) is measured.

[0067] I. Performance Index Using the filtering efficiency and pressure loss of the nonwoven fabric calculated in the above sections G and H, the following formula was used to calculate the performance index (1 / Pa) of the nonwoven fabric. The value was rounded to three decimal places. Performance index = -ln[{1 - filtering efficiency (%) / 100)} / pressure loss (Pa)] Example 1 Polyethylene terephthalate (PET) was used as island components, and a copolymerized PET obtained by copolymerizing 8.0 mol % of 5-sodium sulfoisophthalate and 10 wt % of polyethylene glycol having a molecular weight of 1,000 was used as a sea component, and each was vacuum dried at 150°C for 12 hours. Subsequently, the island component and sea component were fed to an extruder-type multi-component spinning machine in a blending ratio of 50 wt % and 50 wt %, respectively, and melted separately. The resulting mixture was then introduced into a spinning pack incorporating a sea-island composite spinneret (number of island components: 2000, shape of island components: round) at a spinning temperature of 285°C, and the composite polymer stream was discharged from the discharge holes at a throughput rate of 12 g / min to obtain a spun yarn. The spun yarn was cooled with cooling air at a temperature of 20°C and a speed of 20 m / min, oiled with an oiling device to converge, taken up by a first godet roller rotating at 1000 m / min, passed through a second godet roller rotating at the same speed as the first godet roller, and wound by a winder to obtain an undrawn yarn. The undrawn yarn was then drawn 3.4 times between rollers heated to 85°C and 130°C using a drawing machine to obtain a sea-island fiber (island component diameter: 0.20 μm).

[0068] The resulting sea-island composite fiber was cut to a fiber length of 0.6 mm, treated in a 1 wt% aqueous sodium hydroxide solution at a bath ratio of 1:100 at 90°C for 30 minutes, and then neutralized with acetic acid to a pH of 7 to obtain a fiber dispersion of fiber A.

[0069] Next, PET staple fibers (fiber diameter 3.0 μm, fiber length 3.0 mm) were used as fiber B at a blending ratio of 65% by weight (compounding ratio in the papermaking solution), and core-sheath PET staple fibers (core component: PET, sheath component: a copolymer polyester having a melting point of 110°C copolymerized with dicarboxylic acid components of 60 mol% terephthalic acid and 40 mol% isophthalic acid, and diol components of 85 mol% ethylene glycol and 15 mol% diethylene glycol, core-sheath ratio (weight ratio) = 50:50, fiber diameter 10.0 μm, fiber length 5.0 mm) were used as binder fiber C at a blending ratio of 30% by weight (compounding ratio in the papermaking solution). These fibers were then uniformly mixed and dispersed with water using a disintegrator to prepare a fiber dispersion of fiber B and binder fiber C.

[0070] The fiber dispersion of Fiber B and Binder Fiber C was homogeneously mixed with the fiber dispersion of Fiber A described above so that the blending ratio of Fiber A was 5% by weight, thereby preparing a papermaking stock solution. This papermaking stock solution was made into paper using a square sheet machine (250 mm square) manufactured by Kumagai Riki Kogyo Co., Ltd., and then dried and heat-treated in a rotary dryer with a roller temperature set to 110°C, thereby obtaining Nonwoven Fabric 1. Nonwoven Fabric 2 was obtained in a similar manner.

[0071] The evaluation results of the obtained nonwoven fabric 1 and nonwoven fabric 2, as well as the evaluation results of the laminated nonwoven fabric (air filter medium) obtained by laminating nonwoven fabrics 1 and 2, are shown in Table 1. For particles with a particle size of 0.3 μm, nonwoven fabric 1 and nonwoven fabric 2 had a collection efficiency of 98.2314% and 98.3542%, respectively, and the performance index was 0.024. Although the collection efficiency of each nonwoven fabric was less than the HEPA standard of 99.97%, by laminating nonwoven fabric 1 and nonwoven fabric 2, the collection efficiency was 99.9715%, which exceeded the HEPA standard, and the performance index was 0.024, resulting in an air filter medium. In this way, it was confirmed that the collection efficiency could be significantly increased by laminating nonwoven fabrics.

[0072] Example 2 Nonwoven fabrics 3 and 4 were prepared in the same manner as in Example 1, except that the compounding ratio of fiber A and fiber B and the basis weight were changed as shown in Table 1.

[0073] The evaluation results of the obtained nonwoven fabrics 3 and 4, as well as the evaluation results of the laminated nonwoven fabric (air filter medium) obtained by laminating the nonwoven fabrics 3 and 4, are shown in Table 1. The nonwoven fabrics 3 and 4 had collection efficiencies of 99.3284% and 99.4135%, respectively, for particles with a particle size of 0.15 μm, and performance indexes of 0.027 and 0.029. By laminating the nonwoven fabrics 3 and 4, the collection efficiency was 99.9955%, resulting in an air filter medium with a high collection efficiency and a performance index of 0.028. It was thus confirmed that the collection efficiency could be significantly increased by laminating the nonwoven fabrics.

[0074] Example 3 Nonwoven fabrics 5 and 6 were prepared in the same manner as in Example 1, except that the blending ratio of fiber A and fiber B was changed as shown in Table 1.

[0075] The evaluation results of the obtained nonwoven fabrics 5 and 6, as well as the evaluation results of the laminated nonwoven fabric (air filter medium) obtained by laminating the nonwoven fabrics 5 and 6, are shown in Table 1. The nonwoven fabrics 5 and 6 had collection efficiencies of 99.9412% and 99.9135%, respectively, for particles with a particle size of 0.15 μm, and performance indexes of 0.037 and 0.038. Although both had collection efficiencies that did not meet the ULPA standard of 99.9995%, by laminating the nonwoven fabrics 7 and 8, the collection efficiency was 99.9999%, exceeding the ULPA standard, and the performance index was 0.036, resulting in an air filter medium. In this way, it was confirmed that the collection efficiency could be significantly increased by laminating the nonwoven fabrics.

[0076] Example 4 Nonwoven fabrics 7 and 8 were prepared in the same manner as in Example 1, except that the blending ratio of fiber A and fiber B was changed as shown in Table 2 and binder fiber C was not used.

[0077] The evaluation results of the obtained nonwoven fabrics 7 and 8, as well as the evaluation results of the laminated nonwoven fabric (air filter medium) obtained by laminating the nonwoven fabrics 7 and 8, are shown in Table 2. The nonwoven fabrics 7 and 8 had collection efficiencies of 99.7751% and 99.8742%, respectively, for particles with a particle size of 0.15 μm, and performance indexes of 0.036 and 0.038. Although both had collection efficiencies that did not meet the ULPA standard of 99.9995%, by laminating the nonwoven fabrics 7 and 8, the collection efficiency was 99.9996%, exceeding the ULPA standard, and the performance index was 0.036, resulting in an air filter medium. In this way, it was confirmed that the collection efficiency could be significantly increased by laminating nonwoven fabrics.

[0078] Example 5 Nonwoven fabrics 9 and 10 were prepared in the same manner as in Example 1, except that the blending ratio of fiber A and fiber B was changed as shown in Table 2.

[0079] The evaluation results of the obtained nonwoven fabrics 9 and 10 were as follows: Further, a spunbond nonwoven fabric ("Elves S0303WDO" manufactured by Unitika Ltd. (average fiber diameter 24 μm, basis weight 30 g / m) consisting of fibers with a core / sheath structure using PET as the core and PE as the sheath) was placed between the nonwoven fabrics 9 and 10 as a breathable support material. ２ Table 1 shows the evaluation results of the laminated nonwoven fabric (air filter medium) in which nonwoven fabric 9 and nonwoven fabric 10 were arranged and laminated. The nonwoven fabric 9 and nonwoven fabric 10 had collection efficiencies of 99.9125% and 99.9056%, respectively, for particles with a particle size of 0.15 μm, and both had performance indices of 0.038. Although both had collection efficiencies that did not meet the ULPA standard of 99.9995%, by laminating nonwoven fabric 9, nonwoven fabric 10, and a breathable support material, the collection efficiency became 99.9999%, exceeding the ULPA standard, and the performance index was 0.038, resulting in an air filter medium. In this way, it was confirmed that the collection efficiency could be significantly increased by laminating nonwoven fabrics.

[0080] Comparative Example 1 Nonwoven fabrics 11 and 12 were prepared in the same manner as in Example 1, except that the blending ratio of fiber A and fiber B was changed as shown in Table 2.

[0081] The evaluation results of the obtained nonwoven fabric 11 and nonwoven fabric 12, and the evaluation results of the laminated nonwoven fabric (air filter material) obtained by laminating the nonwoven fabrics 11 and 12 are shown in Table 2. The nonwoven fabrics 11 and 12 have a particle collection efficiency of 96.2653% and 97.8426%, respectively, for particles with a particle size of 0.3 μm, and their performance indexes are 0.020 and 0.023. When the nonwoven fabrics 11 and 12 are laminated, the collection efficiency is 99.9241%, which does not exceed the HEPA standard, and the performance index is 0.022, resulting in an air filter material. Thus, it has been confirmed that even if nonwoven fabrics with low potential performance are laminated together, the performance index itself, which indicates potential performance, does not improve.

[0082]

[0083]

Claims

1. An air filter medium having a performance index of 0.023 or more and comprising multiple layers of nonwoven fabric, at least one of the layers of nonwoven fabric containing at least two types of organic fibers A and B having different fiber diameters, the organic fibers A having an average fiber diameter of 0.01 to 0.60 μm and the organic fibers B having an average fiber diameter of 1.0 to 30 μm.

2. The air filter medium according to claim 1, characterized in that it has a particle collection rate of 99.97% or more for particles having a particle diameter of 0.3 μm.

3. The air filter medium according to claim 1, characterized in that it has a particle collection rate of 99.9995% or more for particles having a particle diameter of 0.15 μm.

4. The air filter medium according to claim 1, wherein at least one of the laminated nonwoven fabrics has a performance index of 0.023 or more.

5. The air filter medium of claim 1, wherein the nonwoven fabric further comprises binder fibers.

6. An air filter comprising the air filter medium according to any one of claims 1 to 5.

7. A fan filter unit comprising the air filter according to claim 6.

8. A clean room or semiconductor manufacturing equipment equipped with the air filter according to claim 6.

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