Air filter medium

Abstract

An air filter media is provided, comprising multiple layers of nonwoven fabric, with a performance index of 0.023 or higher. At least one layer of the nonwoven fabric contains at least two types of organic fibers, A and B, with different fiber diameters. The average fiber diameter of organic fiber A is 0.01–0.60 μm, and the average fiber diameter of organic fiber B is 1.0–30 μm. This provides an air filter media suitable for air filters that combine high capture efficiency with low pressure loss.

Description

Technical Field

[0001] This invention relates to air filter media suitable for air filters. Background Technology

[0002] In recent years, the demand for air purification has increased. Air filters that remove fine airborne dust are used in a wide range of fields, from living environments to industries, including countermeasures against health problems caused by dust particles smaller than 2.5μm and cleanroom processes in semiconductor and pharmaceutical manufacturing. In particular, high-performance air filters, such as HEPA (High Efficiency Particulate Air) filters and ULPA (Ultra Low Penetration Air) filters, are used in spaces requiring extremely high levels of air purification, such as cleanrooms and semiconductor manufacturing facilities. The filter media of HEPA and ULPA filters utilize non-woven glass fiber fabric and porous PTFE (polytetrafluoroethylene) membranes.

[0003] However, air filters using glass fiber and PTFE filter media are often landfilled after use, posing a significant environmental burden. Furthermore, while ULPA filters are used in cleanrooms and semiconductor manufacturing equipment, glass fiber filters release boron, which negatively impacts semiconductor manufacturing; therefore, PTFE filters are generally preferred. However, PFOA (perfluorooctanoic acid), a byproduct of PTFE manufacturing, is an environmentally damaging substance that is difficult to decompose in nature. It also accumulates in organisms and is toxic, raising the need for alternative materials.

[0004] Therefore, with the increasing environmental awareness and compliance awareness in recent years, various filter media with lower environmental impact, made of extremely fine polyester fibers and with excellent filtration performance have been proposed.

[0005] For example, Patent Document 1 proposes a wet nonwoven fabric with a multilayer structure of two or more layers, consisting of short-cut nanofibers made of fiber-forming thermoplastic polymers, with individual fiber diameters (D) of 100–1,000 nm and cut in a manner where the ratio of fiber length (L) to the individual fiber diameter (D) (L / D) is in the range of 100–2,500. According to this proposal, a filter with high capture efficiency, low pressure loss, and long filter life can be provided.

[0006] Furthermore, Patent Document 2 proposes an air filter material using a nonwoven fabric comprising three types of polyester fibers: nanofibers with a diameter of 200–800 nm, fibers coarser than nanofibers, and adhesive fibers. According to this proposal, it can exhibit low pressure loss and high trapping performance with excellent wrinkle resistance and resistance to wind pressure deformation.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-126626

[0010] Patent Document 2: Japanese Patent Application Publication No. 2015-140495 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] While the method described in Patent Document 1 can produce air filter media with excellent high capture efficiency and low pressure loss, it does not achieve the capture efficiency required by HEPA and ULPA filters, and its effectiveness is insufficient from the perspective of achieving both low pressure loss and high capture efficiency.

[0013] Furthermore, the method described in Patent Document 2 can obtain a thin film with excellent corrugated processability for air filter media, and can further achieve the collection efficiency required by HEPA and ULPA filters. On the other hand, the pressure loss is high, and the effect is not sufficient from the viewpoint of having both low pressure loss and high collection efficiency.

[0014] The objective of this invention is to solve the problems of the prior art described above, and to provide an air filter media suitable for use in air filters that combine the high capture efficiency and low pressure loss required by HEPA and ULPA filters, and to provide an air filter using the air filter media.

[0015] Methods for solving problems

[0016] (1) An air filter material, characterized in that it is an air filter material with multiple layers of nonwoven fabric and a performance index of 0.023 or higher, wherein at least one layer of the nonwoven fabric contains at least two kinds of organic fibers A and organic fibers B with different fiber diameters, wherein the average fiber diameter of organic fiber A is 0.01 to 0.60 μm and the average fiber diameter of organic fiber B is 1.0 to 30 μm.

[0017] (2) The air filter material according to (1) is characterized in that it has a particle capture rate of more than 99.97% for particles with a particle size of 0.3 μm.

[0018] (3) The air filter material according to (1) is characterized in that it has a particle capture rate of more than 99.9995% for particles with a particle size of 0.15 μm.

[0019] (4) The air filter material according to (1) is characterized in that at least one of the laminated nonwoven fabrics has a performance index of 0.023 or higher.

[0020] (5) The air filter material according to (1) further comprises adhesive fibers in the nonwoven fabric.

[0021] (6) An air filter made using any one of (1) to (5) air filter media.

[0022] (7) A fan filter unit comprising the air filter described in (6).

[0023] (8) A cleanroom or semiconductor manufacturing apparatus comprising the air filter described in (6).

[0024] The effects of the invention

[0025] According to the present invention, an air filter media can be obtained that is suitable for air filters that combine the high capture efficiency and low pressure loss required by HEPA and ULPA filters. Detailed Implementation

[0026] The air filter material of the present invention is characterized in that it is an air filter material composed of at least two kinds of organic fibers, wherein multiple layers of nonwoven fabric comprising fiber A with a fiber diameter less than 0.8 μm and an average fiber diameter of 0.01 to 0.60 μm and fiber B with a fiber diameter of 0.8 μm or more and an average fiber diameter of 1.0 to 30 μm are laminated together, and the performance index is 0.023 or more.

[0027] [Non-woven fabric]

[0028] First, the nonwoven fabric in this invention will be described in detail.

[0029] The fibers A and B used in the nonwoven fabric of this invention are organic fibers. The term "organic fiber" in this invention refers to a fibrous material whose main component is organic matter. Specific examples of organic fibers include natural fibers such as cellulose made from wood pulp, cotton, hemp, wool, and silk; regenerated fibers such as rayon; semi-synthetic fibers such as acetate; and synthetic fibers represented by polyester, nylon, and acrylic fibers, but are not limited to these. From the viewpoint of mechanical properties and dimensional stability, synthetic fibers formed from thermoplastic polymers are preferred. Specific examples of thermoplastic polymers include polyesters such as polyethylene terephthalate (PET), polymethyl 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; polycarbonate, polyacrylate, polyphenylene sulfide, and thermoplastic polyurethane; and their copolymers, but are not limited to these. Polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, polyamides such as polyamide 6 and polyamide 66, and polyphenylene sulfide are preferred due to their combination of mechanical properties and heat resistance.

[0030] The organic fibers of this invention can be modified with various minor additives without impairing the effects of the invention. Specific examples of minor additives include compatibilizers, plasticizers, antioxidants, ultraviolet absorbers, infrared absorbers, fluorescent whitening agents, release agents, antibacterial agents, nucleating agents, heat stabilizers, flame retardants, antistatic agents, color-resistant agents, regulators, matting agents, defoamers, preservatives, gelling agents, latex, fillers, inks, colorants, dyes, pigments, fragrances, etc., but are not limited to these. These minor additives can be used alone or in combination.

[0031] The nonwoven fabric used in this invention has a fiber diameter of less than 0.8 μm and an average fiber diameter of 0.01 to 0.60 μm. A finer fiber diameter results in a higher specific surface area, leading to superior trapping performance in the produced nonwoven fabric, which is preferred. However, if the average fiber diameter is 0.01 μm or more, in addition to high trapping performance, the fabric also exhibits good workability and molding properties, resulting in a nonwoven fabric with excellent durability during use. An average fiber diameter of 0.05 μm or more is more preferred, and even more preferably 0.10 μm or more is preferred. On the other hand, if the average fiber diameter is 0.60 μm or less, excellent trapping performance is achieved in the produced nonwoven fabric due to the high specific surface area resulting from the fine fiber diameter. An average fiber diameter of 0.50 μm or less is more preferred.

[0032] The fiber B used in the nonwoven fabric of this invention has a fiber diameter of 0.8 μm or more and an average fiber diameter of 1.0 to 30.0 μm. If the average fiber diameter is 1.0 μm or more, it serves as aggregate to maintain the shape of the nonwoven fabric, and fiber A does not become excessively dense. Therefore, a nonwoven fabric that suppresses the increase in pressure loss and combines high trapping performance with low pressure loss can be obtained. 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, if the average fiber diameter is 30.0 μm or less, during the processing of the wet nonwoven fabric described later, the shedding of fibers A, which are finer than fiber B, is suppressed. In the resulting nonwoven fabric, fibers A serve as a support for fiber A, and a three-dimensional homogeneous micro-space can be formed. The average fiber diameter of fiber B is more preferably 28.0 μm or less, and even more preferably 25.0 μm or less.

[0033] In this invention, various adhesives, such as fibrous materials or adhesives, can be used to physically bond the fibers constituting the nonwoven fabric to each other via thermal bonding. The adhesive is not particularly limited in this case, and for example, core-sheath fibers containing a thermoplastic polymer with a melting point below 150°C can be suitable. When using such core-sheath fibers, after the nonwoven fabric is formed, a drying process such as a Yankee dryer or an air-permeable dryer, or a heat treatment process such as a calender, is performed, causing the sheath component on the surface of the adhesive fibers to melt and bond with the other fibers constituting the nonwoven fabric. This improves the rigidity of the nonwoven fabric and is therefore preferred. Furthermore, the core component of the adhesive fibers helps ensure the strength of the nonwoven fabric and is therefore preferred. Additionally, the melting point of the core component of the adhesive fibers is higher than that of the sheath component. If the difference in melting points is 20°C or more, the sheath component on the surface of the adhesive fibers easily and sufficiently melts, and the reduction of the core component's orientation is suppressed, resulting in both sufficient thermal adhesion and high rigidity, which is therefore preferred. Furthermore, by forming fiber B as an undrawn filament with a crystallinity of less than 20%, it can be used as an adhesive. Softening / flowing through heat treatment enables strong and uniform bonding between fibers.

[0034] In the nonwoven fabric of this 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 adhesive fibers are used in addition to fibers A and B, the ratio can be calculated by dividing the weight of fiber A or B by the total weight of fibers A, B, and the adhesive. As a standard for the blending ratio of fibers A and B, the blending ratio of fiber A is preferably 2 to 55% by weight, and the blending ratio of fiber B is preferably 5 to 90% by weight. If the blending ratio of fiber A is 2.5% by weight or more, excellent trapping performance is exhibited when the nonwoven fabric is produced due to the high specific surface area resulting from the fine fiber diameter of fiber A. The blending ratio of fiber A is more preferably 3% by weight or more, and even more preferably 5% by weight or more. On the other hand, if the blending ratio of fiber A is 55% by weight or less, excessive densification of fiber A is suppressed in the nonwoven fabric, thus a nonwoven fabric that suppresses the increase in pressure loss and combines high trapping performance with low pressure loss can be obtained, which is therefore preferred, and more preferably 50% by weight or less. Furthermore, if the blending ratio of fiber B is 5% by weight or more, it can function as an aggregate for maintaining the shape of the nonwoven fabric, and fiber A will not be excessively densified, thus suppressing the increase in pressure loss. Moreover, during the processing of the wet nonwoven fabric described later, fibers A that are finer than fiber B can detach, which is therefore preferred. The blending ratio of fiber B is more preferably 7% by weight or more, and more preferably 10% by weight or more.

[0035] The mesh size of the nonwoven fabric in this invention is preferably 3-100 g / m². 2 The so-called nonwoven fabric gloss in this invention refers to the value measured by the method described in the example section. If the gloss is 3 g / m²... 2 The above methods yield a uniform nonwoven fabric with minimal density variation and excellent durability during use, making it a preferred choice. A more preferable g / m² ... 2 The above is further preferred to be 7g / m 2 That's all. On the other hand, if the eye load is 100g / m 2 The following properties result in improved operability and formability during nonwoven fabric processing, making it a preferred option. A more preferable value is 80 g / m². 2 The following is a further preferred value: 70g / m 2 the following.

[0036] [Capture efficiency, pressure loss]

[0037] The performance index is a metric used to evaluate the performance of a filter, representing its potential capacity. Specifically, it can be calculated from the filter's capture efficiency and pressure loss using the following formula (described later).

[0038] Performance index = -ln[{1 - capture efficiency (%) / 100)} / pressure loss (Pa)]

[0039] The higher the performance index, the higher the filter is considered to have performance. The performance index has become an important indicator for comprehensively evaluating the performance of a filter.

[0040] The capture efficiency is an indicator of how many particles a nonwoven fabric or air filter media can capture. For example, a particle counter can be used to measure the number of particles supplied to the nonwoven fabric or air filter media (upstream particle count) and the number of particles that pass through the nonwoven fabric or air filter media (downstream particle count), and the particle transmission rate can be calculated. The capture efficiency is then calculated from the particle transmission rate using the following formula.

[0041] Particle transmittance [%] = (Number of downstream particles / Number of upstream particles) × 100

[0042] Collection efficiency [%] = 100 - Particle transmittance [%]

[0043] The JIS standard (JIS Z 8122) specifies that HEPA filters have a capture efficiency of 99.97% or higher for particles of 0.3 μm, and ULPA filters have a capture efficiency of 99.9995% or higher for particles of 0.15 μm. When evaluating nonwoven or air filter media, the particle size to be measured is selected according to the target filtration level. Furthermore, the capture efficiency can be automatically measured using a filter capture efficiency testing device (TSI Model 3160) or similar device, by a particle counter built into the device.

[0044] When air passes through nonwoven fabric or air filter media, it obstructs airflow and creates resistance. This resistance results in a pressure (static pressure) difference before and after passing through the nonwoven fabric or air filter media; this pressure difference is called pressure loss (Pa). If the pressure loss is large, the energy required to pass through the air filter (e.g., fan power) increases, and energy efficiency decreases. The JIS standard (JIS Z 8122) specifies that the pressure loss for both HEPA and ULPA filters is 245 Pa or less in the air filter state. However, this is the value after the air filter media has been processed into a pleated shape. The pressure drop of the filter media before pleating is preferably 350 Pa or less, for example, when air flows at a surface velocity of 3.3 m / min. Furthermore, the pressure loss can be automatically measured by a pressure gauge (including a differential pressure gauge) built into a filter trapping efficiency testing device (TSI Model 3160), etc.

[0045] [Air filter media]

[0046] The air filter material of the present invention is a laminated nonwoven fabric, which is constructed by laminating multiple sheets of the aforementioned nonwoven fabric. In the case of multiple laminations, the particle permeability of the nonwoven fabric is the product of the particle permeability of each individual nonwoven fabric. Therefore, the particle permeability after multiple laminations is reduced, and the capture efficiency is increased. On the other hand, since the pressure loss is the sum of the pressure losses of each individual nonwoven fabric, it is increased by laminating multiple sheets. To illustrate with a specific example, when two sheets of nonwoven fabric with a particle permeability of 10% (capture efficiency of 90%) and a pressure loss of 100 Pa are laminated, the particle permeability becomes 1% (10% [=0.1] × 10% [=0.1] = 1% [=0.01]), and the pressure loss becomes 200 Pa (100 Pa + 100 Pa = 200 Pa). Furthermore, the particle transmittance (10%, capture efficiency 90%) and pressure loss (100 Pa) before lamination (1 nonwoven fabric sheet) and the particle transmittance (1%, capture efficiency 99%) and pressure loss (200 Pa) after lamination (2 nonwoven fabric sheets) are both 0.023, indicating that the balance between capture efficiency and pressure loss remains unchanged. If the capture efficiency is improved by increasing the amount of fiber and the blending rate of fiber A using a single nonwoven fabric sheet, the increase in pressure loss becomes even greater with the increase in capture efficiency. Therefore, the balance between capture efficiency and pressure loss is easily deteriorated, leading to a decrease in the performance index. In other words, to improve the performance index, manufacturing a multi-layer structure is easier than using a single nonwoven fabric sheet. Therefore, when manufacturing filter media for HEPA filters, which requires a capture efficiency of 99.97%, a pressure loss of 350 Pa, and a performance index of 0.023, it is easier to manufacture by stacking two nonwoven fabrics with a capture efficiency of 98.27%, a pressure loss of 175 Pa, and a performance index of 0.023, or stacking three nonwoven fabrics with a capture efficiency of 93.31%, a pressure loss of 117 Pa, and a performance index of 0.023, compared to using a single nonwoven fabric. Furthermore, the properties of the stacked nonwoven fabrics do not need to be identical. For example, stacking a nonwoven fabric with a capture efficiency of 70.00%, a pressure loss of 100 Pa, and a performance index of 0.012 (as the first piece) with a nonwoven fabric with a capture efficiency of 99.90%, a pressure loss of 250 Pa, and a performance index of 0.028 (as the second piece) achieves a capture efficiency of 99.97%, a pressure loss of 350 Pa, and a performance index of 0.023. By creating a multi-layered structure, the manufacturing difficulty of nonwoven fabric is reduced, which can be expected to reduce manufacturing costs. However, if the number of layers of nonwoven fabric becomes too large, the operations related to the fabric-making and lamination processes increase, thus losing the cost advantage of creating a multi-layered structure. Therefore, the number of layers of nonwoven fabric is preferably 5 or less, and more preferably 3 or less.

[0047] The air filter material of the present invention needs to have a performance index of 0.023 or higher after the nonwoven fabric is laminated. If the performance index is 0.023 or higher, it can be used as an air filter material with a good balance between capture efficiency and pressure drop, and is useful in various industries such as HEPA filter applications and ULPA filter applications.

[0048] To improve the strength of the air filter material of the present invention, it may be further laminated with a breathable support material other than the nonwoven fabric used in the present invention. The material and structure of the breathable support material are not particularly limited, and for example, nonwoven fabric, woven fabric, metal mesh, resin mesh, etc., are used. Among these, a dry nonwoven fabric with heat-sealing properties is preferred from the perspectives of strength, trapping ability, softness, and workability. Furthermore, the dry nonwoven fabric may be a nonwoven fabric with a core / sheath structure consisting of some or all of its constituent fibers, or a two-layer nonwoven fabric composed of two layers of low-melting-point material and high-melting-point material. There are no particular restrictions on the materials used in dry nonwoven fabrics. Polyesters such as polyethylene terephthalate, polymethylene 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; polycarbonate, polyacrylate, polyphenylene sulfide, and thermoplastic polymers such as thermoplastic polyurethane, and their copolymers or composites, can be used. For core / sheath structured dry nonwoven fabrics, 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 heating to partially melt the breathable support material or by melting the hot melt resin, utilizing the anchoring effect or by bonding with reactive adhesives, etc.

[0049] There are no particular limitations on the size and thickness of the breathable support material. It can be arranged between the nonwoven fabrics in this invention, or it can be arranged by pre-laminating the nonwoven fabrics in this invention to each other, and then further laminating the breathable support material on the multi-layered nonwoven fabric.

[0050] To extend the lifespan of the air filter material of the present invention, a pre-trapping layer can be further laminated (typically, upstream of the airflow passing through the filter material). As the pre-trapping layer, a material obtained, for example, by melt-blowing is used. Examples of materials for the pre-trapping layer include, for example, polyesters such as polyethylene terephthalate, polymethylene 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; polycarbonate, polyacrylate, polyphenylene sulfide, thermoplastic polymers such as thermoplastic polyurethane, and copolymers thereof. The pre-trapping layer can be bonded to the laminated nonwoven fabric by, for example, hot lamination using a hot-melt resin.

[0051] The air filter media of the present invention preferably has a particle capture rate of 99.97% or higher for particles with a diameter of 0.3 μm. This allows it to be used as a HEPA filter in cleanrooms in the pharmaceutical / medical, food, and semiconductor industries. Furthermore, if it has a particle capture rate of 99.99% or higher for particles with a diameter of 0.15 μm, it is preferred as a filter media for cleanrooms, semiconductor manufacturing facilities, etc., as it can purify air to an extremely high degree.

[0052] The air filter media of the present invention preferably has a particle capture rate of 99.9995% or higher for particles with a diameter of 0.15 μm. This allows it to be used as a ULPA filter, which can also be used in semiconductor manufacturing equipment and the like.

[0053] The air filter material 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 is a value measured by the method described in the embodiments. An average pore size of 0.1 μm or more ensures stable fluid flow, and is therefore preferred. On the other hand, if the average pore size is 10 μm or less, the flow of fluid passing through the wet nonwoven fabric sheet is not disrupted, and the fluid can flow uniformly into the entire sheet, which is also preferred.

[0054] The thickness of the air filter material of the present invention is preferably 0.05 to 1.0 mm. The thickness of the air filter material in the present invention refers to a value measured by the method described in the examples. If the thickness is 0.05 mm or more, the operability and formability during nonwoven fabric processing become good, and an air filter material with excellent durability during use can be obtained, which is therefore preferred. Furthermore, it has good formability such as pleating when used as an air filter material, which is also preferred. A thickness of 0.1 mm or more is more preferred, and 0.15 mm or more is even more preferred. On the other hand, if the thickness is 1.0 mm or less, high pressure loss caused by the densification of the nonwoven fabric can be suppressed, which is also preferred. Furthermore, when an air filter is manufactured by performing pleating, the portion of adjacent filter material in contact with each other is reduced due to the thickness of the filter material, thus ensuring the filtration area and suppressing the increase in pressure loss, which is also preferred. A thickness of 0.9 mm or less is more preferred, and 0.8 mm or less is even more preferred.

[0055] [Manufacturing method of nonwoven fabric]

[0056] Next, an example of a method for manufacturing nonwoven fabric according to the present invention will be shown below.

[0057] First, fiber B, as needed, adds short fibers of the fibrous adhesive to an aqueous medium and disperses them uniformly using a dispersant, thus preparing a fiber dispersion. In this process, the fiber dispersibility can be adjusted by the amount of fiber added, the amount of aqueous medium, and the stirring time, preferably achieving a state where each short fiber is dispersed as uniformly as possible in the aqueous medium. Furthermore, a dispersant can be added to improve the fiber dispersibility in the aqueous medium; however, when post-processing the nonwoven fabric, the amount of dispersant added is preferably controlled to the minimum necessary to avoid affecting its processability.

[0058] Next, a fiber dispersion of fiber A, in which fiber A is uniformly dispersed in an aqueous medium, is prepared according to the method described later. By mixing this fiber dispersion of fiber A with the fiber dispersion of fiber B (with fibrous binder added as needed), a papermaking solution is prepared. This solution is then subjected to wet papermaking to obtain a nonwoven fabric in which fiber A is uniformly distributed.

[0059] The fiber A in this invention can be manufactured using island-island fibers composed of two or more polymers with different dissolution rates in solvents. The so-called island-island fiber in this invention refers to a fiber having a structure in which islands composed of poorly soluble polymers are dispersed within sea-like components composed of readily soluble polymers.

[0060] As a method for producing the island fiber, melt spinning of island composite spinning is suitable from the viewpoint that it can be continuously manufactured with high productivity. Furthermore, from the viewpoint that the control of fiber diameter and cross-sectional shape is excellent, the method of using an island composite die is preferred.

[0061] Specific examples of poorly soluble polymers used in the island components of this invention include, but are not limited to, polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, polyamides such as polyamide 6, polyamide 66, and polyamide 610, polyolefins such as polyethylene, polypropylene, and polymethylpentene, polycarbonate, polyacrylate, polyphenylene sulfide, thermoplastic polyurethane, and their copolymers.

[0062] From the viewpoint of simplifying the dissolution process of marine components, the readily soluble polymers used for marine components in this invention preferably exhibit readily soluble properties in aqueous solvents or hot water. As readily soluble polymers in this invention, copolyesters, polylactic acid, polyvinyl alcohol, etc., are preferred. From the viewpoint of operability and ease of dissolution in low-concentration aqueous solvents, polyesters and polylactic acid copolymerized with polyethylene glycol and sodium 5-sulfoisophthalate alone or in combination are particularly preferred.

[0063] In this invention, "ease of solubility" refers to a dissolution rate ratio (ease of solubility / reluctance of solubility) of 100 or more when using a poorly soluble polymer as a reference relative to the solvent used in the dissolution process. Considering the simplification and reduction of the dissolution process time, this dissolution rate ratio is preferably large, more preferably 1000 or more, and even more preferably 10000 or more. If it falls within such a range, the dissolution process is completed in a short time, without unnecessarily deteriorating the poorly soluble polymer, and fiber A suitable for this invention can be obtained, which is therefore preferred.

[0064] Furthermore, from the viewpoint of solubility in aqueous solvents and ease of treatment of waste liquid generated during dissolution, polylactic acid, polyester copolymerized with sodium 5-sulfoisophthalate in 3 to 20 mol% and polyester copolymerized with polyethylene glycol in 5 to 15 wt% (in addition to sodium 5-sulfoisophthalate) in 5 to 15 wt% are particularly preferred.

[0065] Based on the above, examples of suitable polymer combinations for the aforementioned island fibers include polyester or polylactic acid, in which the sea component is copolymerized with 3 to 20 mol% sodium 5-sulfoisophthalate and 5 to 15 wt% polyethylene glycol with a weight average molecular weight of 500 to 3000, and the island component is polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and copolymers thereof, but not limited to these.

[0066] The spinning temperature of the aforementioned island-island fibers is preferably set at a temperature at which high-melting-point, high-viscosity polymers, among those determined from the above perspective, exhibit fluidity. This fluidity-indicating temperature varies depending on the polymer's characteristics and molecular weight, but the polymer's melting point serves as a standard; setting the spinning temperature to below the melting point +60°C is sufficient. Within this range, thermal decomposition of the polymer within the spinning head or spinning assembly is suppressed, thus inhibiting molecular weight reduction and allowing for the efficient production of island-island fibers, which is therefore preferred.

[0067] As described above in this invention, in order to obtain ultrafine fibers by dissolving and removing sea components from island fibers, the island composite die illustrated in Japanese Patent No. 5740877 can be used, but is not limited thereto.

[0068] The filaments melted and discharged from the island-island composite die are cooled and solidified, then bundled by applying an oiling agent, and drawn by a roller at a specified circumferential speed. The drawing speed can be determined by the discharge rate, the target fiber diameter, etc., and from the viewpoint of stably manufacturing island-island fibers, it is preferably 100 to 7000 m / min. From the viewpoint of improving mechanical properties and thermal stability, it is preferable to stretch the spun island-island fibers. This can be done by temporarily winding the spun multifilaments before stretching, or by stretching them after spinning without winding.

[0069] The aforementioned island fibers are preferably bundled into fiber bundles consisting of tens to millions of units, and cut to the desired fiber length using a cutting machine such as a cutting knife, slicing machine, or cryogenic cutting machine. The cut fiber length L is preferably such that the ratio (L / R1) to the diameter R1 of the island component of the island fiber (equivalent to the average fiber diameter of fiber A) is 1000 to 6000. If this range is met, the number of contact points between fibers increases when the nonwoven fabric is produced, promoting the formation of cross-linked structures between fibers and improving the reinforcing effect of the nonwoven fabric; therefore, this is preferred. If L / R1 is 1000 or more, fiber A is suppressed from detaching from the nonwoven fabric during wet papermaking processing; therefore, this is preferred. L / R1 is more preferably 1500 or more, and even more preferably 2000 or more. On the other hand, if L / R1 is 6000 or less, fiber A is suppressed from agglomerating in an aqueous medium, resulting in a nonwoven fabric with high homogeneity; therefore, this is preferred. L / R1 is more preferably 5500 or less, and even more preferably 5000 or less.

[0070] Fiber A can be manufactured by dissolving and removing the marine components from the aforementioned island fibers. That is, the cut island fibers are simply impregnated in a solvent containing a readily soluble polymer capable of dissolving the marine components, and the readily soluble polymer is removed. When the readily soluble polymer is a copolymer of polyethylene terephthalate (PET) with sodium 5-sulfoisophthalate, polyethylene glycol, etc., or polylactic acid, an alkaline aqueous solution such as sodium hydroxide solution can be used. In the case of an alkaline aqueous solution, the bath ratio of the island fibers to the alkaline aqueous solution (weight of island fibers (g): weight of alkaline aqueous solution (g)) is preferably 1:5 to 1:10000, more preferably 1:10 to 1:5000. Within this range, unnecessary entanglement of fibers A with each other is suppressed when the readily soluble polymer containing the marine components dissolves, which is therefore preferable.

[0071] Furthermore, the alkali concentration of the alkaline aqueous solution is preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight. Within this range, the dissolution of the readily soluble polymers of the marine component is completed in a short time, preventing unnecessary deterioration of the poorly soluble polymers of the island component, and resulting in a homogeneous fiber dispersion of fiber A, which is therefore preferred. Additionally, the temperature of the alkaline aqueous solution is not particularly limited, but a temperature of 50°C or higher can accelerate the dissolution of the readily soluble polymers of the marine component, which is also preferred.

[0072] In this invention, an aqueous solution of a readily soluble polymer containing marine components dissolved from island fibers is used as the fiber dispersion of fiber A. This dispersion can be used directly, or the pH can be adjusted by adding acid or alkali, or it can be diluted with water before use. Furthermore, a dispersant can be added to the fiber dispersion to inhibit the aggregation of fiber A over time. Examples of dispersants include cationic compounds, nonionic compounds, and anionic compounds; however, from the viewpoint of improving dispersibility due to electrorepulsion in an aqueous medium, anionic compounds are preferred. The amount of dispersant added is preferably 0.001 to 10 times the weight of fiber A. Within this range, the processability during nonwoven fabric processing using wet papermaking is not impaired, ensuring the dispersibility of fiber A, and is therefore preferred.

[0073] In the case of fiber B in this invention being a synthetic fiber composed of a thermoplastic polymer, it can be manufactured by melt spinning, stretching as needed, and then cutting it to the desired fiber length as described above. Here, the fiber length of fiber B is preferably 30 mm or less. If the fiber length is 30 mm or less, the formation of fiber clumps that tightly entangle with each other during dispersion in an aqueous medium is suppressed, resulting in a homogeneous nonwoven fabric, which is suitable for use as an air filter media and is therefore preferred.

[0074] The fiber dispersion of fiber A prepared in this manner is mixed with the fiber dispersion of fiber B (with fibrous binder added as needed), diluted to a certain concentration, and then dehydrated on an inclined wire or cylinder wire, forming a nonwoven fabric through wet papermaking. Examples of apparatus used for wet papermaking include cylinder wire papermaking machines, long wire papermaking machines, inclined short wire papermaking machines, or combinations thereof, but are not limited to these. In the papermaking process, by adjusting not only the fiber dispersion in the papermaking liquor but also the papermaking speed, the amount of fiber and water medium, and controlling fiber aggregation during filtration, a three-dimensional homogeneous nonwoven fabric can be produced.

[0075] Nonwoven fabrics formed by wet papermaking undergo a drying process to remove moisture. From the viewpoint that the drying of nonwoven fabrics and the thermal bonding of fibers can be carried out simultaneously, methods such as using hot air ventilation (air penetration) or contact with hot rotating rollers (hot calendering rollers, etc.) are suitable drying methods.

[0076] [Manufacturing method of air filter media]

[0077] The air filter media of the present invention can be manufactured by laminating multiple sheets of nonwoven fabric. During lamination, the overlapping nonwoven fabrics can be joined together. When joining, heat lamination, adhesives, or the like can be used.

[0078] In the case of bonding by hot lamination, the rollers of the hot lamination device are heated to a temperature higher than the glass transition temperature corresponding to the organic fibers and hot melt resin constituting the nonwoven fabric, so that they can pass through, thereby bonding by means of partial melting between the nonwoven fabrics or by means of melting of the hot melt resin, utilizing the anchoring effect.

[0079] When using adhesives for bonding, the adhesive can be applied in dots to the surfaces of the nonwoven fabrics to be bonded using a dispenser or similar device. The adhesive-coated surfaces are then placed on the surfaces of the nonwoven fabrics to be bonded, causing them to come together and bond. There are no particular restrictions on the type of adhesive used; water-based adhesives, solvent-based adhesives, resin-based adhesives, etc., can be used.

[0080] [use]

[0081] Because of its high capture efficiency, the nonwoven fabric of the present invention is suitable for use as an air filter material in air purifiers, air conditioners, building air conditioning systems, industrial cleanrooms, and passenger compartments of automobiles, trains, etc. Furthermore, it is suitable for use in spaces requiring extremely high levels of air purification, such as cleanrooms and semiconductor manufacturing facilities, as an air filter material for air conditioners that introduce outside air into cleanrooms, air conditioners that circulate air within cleanrooms, and fan filter units installed on the ceiling of cleanrooms and semiconductor manufacturing facilities. Cleanrooms and semiconductor manufacturing facilities equipped with air filters using these air filter materials of the present invention are useful in various industries.

[0082] Example

[0083] The present invention will now be described in detail based on embodiments. However, the present invention is not limited to these embodiments. Furthermore, the characteristic values ​​in the embodiments were obtained by the following methods.

[0084] A. Average fiber diameter

[0085] In the images of fiber cross-sections taken using a scanning electron microscope (Hitachi High Tech Noroges SU-1510 electron microscope), the circumscribed circle diameters of any 100 measured fiber cross-sections are averaged, and the average value up to the first decimal place is rounded to the nearest decimal place and set as the average fiber diameter.

[0086] B. Fiber length of organic fibers

[0087] In images taken using a stereomicroscope (Olinpas SZ-61), the lengths of any 100 fibers were measured. The average length was calculated by rounding to the second decimal place, and the result was defined as the fiber length up to the first decimal place. Additionally, the fiber length of fiber A was measured for island fibers before the removal of marine components.

[0088] C. The overall volume of organic fibers

[0089] Using the average fiber diameter and fiber length of the organic fiber calculated from items A and B above, and assuming a perfect circle cross-section, the volume of each fiber was calculated. Then, the volumes of all fibers were added together to calculate the overall volume of the organic fiber.

[0090] D. Pay per payment

[0091] The nonwoven fabric obtained through the examples / comparative examples was used as a sample. The weight of the nonwoven fabric cut into 250mm × 250mm square pieces was measured and converted to the weight per unit area (m²). 2 Round the weight value of the nonwoven fabric to the second decimal place to calculate the fabric weight (g / m²). 2 For each sample, measurements are taken at any three locations, and the average value is rounded to the second decimal place, which is set as the mean value.

[0092] E. Thickness

[0093] The nonwoven fabric used in the above-mentioned measurement (item D) was used as the sample, and a graduated dial thickness gauge (TECLOCK SM-114, probe shape 10mm) was used. The thickness of the nonwoven fabric was measured using a minimum scale of 0.01 mm and a measuring force of less than 2.5 N. Measurements were taken at any 5 locations on a single sample, and the average value was rounded to the third decimal place to calculate the thickness (mm) of the nonwoven fabric.

[0094] F. Porosity

[0095] The value of the nonwoven fabric obtained by using the nonwoven fabric's patch and thickness calculated from items D and E above, rounded to the second decimal place, is set as the porosity (%) of the nonwoven fabric.

[0096] Porosity (%) = 100-[Basic payload (g / m 2 ) / {thickness (mm) × fiber density (g / cm³) 3 )}]×0.1

[0097] Furthermore, the fiber density can simply be the density of the fibers that make up the nonwoven fabric, which is 1.38 g / cm³ in the case of PET. 3 And calculated.

[0098] G. Capture efficiency

[0099] Nonwoven fabric or air filter media obtained through the examples / comparative examples were used as samples. Samples cut to a diameter of 12 cm were placed in a filter trapping efficiency test apparatus (TSI Model 3160). The trapping efficiency was determined using particles with a diameter of 0.15 μm or 0.3 μm. Regarding the trapping efficiency (%) for 0.15 μm particles, 20,000 to 30,000 sodium chloride particles with an average particle size of 0.15 to 0.16 μm were used. 3 The air was passed through at a set speed of 31.5 L / min, and the results were measured. The collection efficiency (%) for particles with a diameter of 0.30 μm was measured at 20,000–30,000 sodium chloride particles with an average diameter of 0.30–0.31 μm per m³. 3 The air was passed through at a rate of 31.5 L / min, and the measurement was performed.

[0100] H. Pressure Loss

[0101] Using nonwoven fabric or air filter media obtained through the examples / comparative examples as samples, a sample cut to a diameter of 12 cm was placed in a filter trapping efficiency test apparatus (TSI Model 3160). The evaluation section was opened with a diameter of 11 cm to expose the sample. To ensure that the surface velocity of the flowing air was 3.3 m / min, the air flow rate was set to 31.5 L / min, and the pressure loss (Pa) was measured.

[0102] I. Performance Indicators

[0103] The values ​​of the nonwoven fabric's capture efficiency and pressure loss calculated using the above G and H terms are rounded to the fourth decimal place and set as the performance index of the nonwoven fabric (1 / Pa).

[0104] Performance index = -ln[{1 - capture efficiency (%) / 100)} / pressure loss (Pa)]

[0105] Example 1

[0106] Polyethylene terephthalate (PET) was used as the island component, and a copolymer of PET containing 8.0 mol% sodium 5-sulfoisophthalate and 10 wt% polyethylene glycol with a molecular weight of 1000 was used as the sea component. Both were vacuum dried at 150°C for 12 hours. Next, the island components and sea components were mixed at a ratio of 50 wt% and fed into an extrusion-type composite spinning machine respectively to melt them. At a spinning temperature of 285°C, the melt flowed into a spinning assembly incorporating a sea-island composite die (number of island components: 2000, island component shape: round). The composite polymer flow was discharged from the discharge orifice at a discharge rate of 12 g / min to obtain spun filaments. The spun filament was cooled with cooling air at a temperature of 20°C and a speed of 20 m / min. Oil was applied using an oiling device to bind the filament together. It was then drawn by a first guide roller rotating at 1000 m / min and wound by a second guide roller rotating at the same speed as the first guide roller using a winding machine to obtain undrawn filament. Then, using a drawing machine, the obtained undrawn filament was stretched to 3.4 times its original length between rollers heated to 85°C and 130°C to obtain island-island fibers (island component diameter: 0.20 μm).

[0107] The obtained island-island fibers were cut to a length of 0.6 mm. The cut island-island fibers were then treated in a 1% (w / w) sodium hydroxide aqueous solution at a bath ratio of 1:100 at 90°C for 30 minutes, and then neutralized with acetic acid to pH=7 to obtain a fiber dispersion of fiber A.

[0108] Next, by adjusting the ratio of PET short fibers (fiber diameter 3.0 μm, fiber length 3.0 mm) as fiber B to 65 wt% (the mixing ratio in the papermaking liquor) and core-sheath PET short fibers (core component: PET, sheath component: a copolyester with a melting point of 110°C copolymerized in a ratio of 60 mol% terephthalic acid and 40 mol% isophthalic acid as dicarboxylic acid components, and 85 mol% ethylene glycol and 15 mol% diethylene glycol as diol components, core-sheath ratio (weight ratio) = 50:50, fiber diameter 10.0 μm, fiber length 5.0 mm) as adhesive fiber C to 30 wt% (the mixing ratio in the papermaking liquor), the fibers were uniformly mixed and dispersed with water using a dissociation machine to prepare a fiber dispersion of fiber B and adhesive fiber C.

[0109] The fiber dispersion of fiber B and adhesive fiber C was homogenized with the fiber dispersion of fiber A at a mixing ratio of 5% by weight to prepare a papermaking solution. After papermaking using a square paper machine (250mm square) manufactured by Kumagai Riki Kogyosha, the solution was dried / heat-treated using a rotary dryer with the roll temperature set at 110°C to obtain nonwoven fabric 1. Nonwoven fabric 2 was obtained using the same method.

[0110] The evaluation results of the obtained nonwoven fabric 1 and nonwoven fabric 2, and the evaluation results of the laminated nonwoven fabric (air filter media) further laminated with nonwoven fabric 1 and 2 are shown in Table 1. The capture efficiencies of nonwoven fabric 1 and nonwoven fabric 2 for particles with a diameter of 0.3 μm are 98.2314% and 98.3542%, respectively, with a performance index of 0.024 for both. While any nonwoven fabric would not meet the HEPA standard of 99.97% capture efficiency, by laminating nonwoven fabric 1 and nonwoven fabric 2, the capture efficiency becomes 99.9715%, exceeding the HEPA standard, with a performance index of 0.024 for the air filter media. It can be confirmed that by laminating nonwoven fabrics in this way, the capture efficiency can be significantly increased.

[0111] Example 2

[0112] The mixing ratio and mesh size of fiber A and fiber B were changed as shown in Table 1. Otherwise, nonwoven fabrics 3 and 4 were produced in the same manner as in Example 1.

[0113] The evaluation results of the obtained nonwoven fabrics 3 and 4, and the evaluation results of the laminated nonwoven fabric (air filter material) further laminated with nonwoven fabrics 3 and 4 are shown in Table 1. The capture efficiencies of nonwoven fabrics 3 and 4 for particles with a diameter of 0.15 μm are 99.3284% and 99.4135%, respectively, with performance indices of 0.027 and 0.029. By laminating nonwoven fabrics 3 and 4, an air filter material with a capture efficiency of 99.9955% and a performance index of 0.028 is obtained. It can be confirmed that by laminating nonwoven fabrics in this way, the capture efficiency can be significantly increased.

[0114] Example 3

[0115] The blending of fibers A and B was modified as shown in Table 1. Otherwise, nonwoven fabrics 5 and 6 were produced in the same manner as in Example 1.

[0116] The evaluation results of the obtained nonwoven fabrics 5 and 6, and the evaluation results of the laminated nonwoven fabric (air filter media) further laminated with nonwoven fabrics 5 and 6 are shown in Table 1. The capture efficiencies of nonwoven fabrics 5 and 6 for particles with a diameter of 0.15 μm are 99.9412% and 99.9135%, respectively, with performance indices of 0.037 and 0.038. Both are below the ULPA standard of 99.9995% capture efficiency. However, by laminating nonwoven fabrics 7 and 8, the capture efficiency becomes 99.9999%, exceeding the ULPA standard, resulting in an air filter media with a performance index of 0.036. It can be confirmed that by laminating nonwoven fabrics in this way, the capture efficiency can be significantly increased.

[0117] Example 4

[0118] The blending of fibers A and B was changed as shown in Table 2, and the adhesive fiber C was not used. Otherwise, nonwoven fabrics 7 and 8 were produced in the same manner as in Example 1.

[0119] The evaluation results of the obtained nonwoven fabrics 7 and 8, and the evaluation results of the laminated nonwoven fabric (air filter media) further laminated with nonwoven fabrics 7 and 8 are shown in Table 2. The capture efficiencies of nonwoven fabrics 7 and 8 for particles with a diameter of 0.15 μm are 99.7751% and 99.8742%, respectively, with performance indices of 0.036 and 0.038. Both are below the ULPA standard of 99.9995% capture efficiency, but by laminating nonwoven fabrics 7 and 8, the capture efficiency becomes 99.9996%, exceeding the ULPA standard, with a performance index of 0.036 for the air filter media. It can be confirmed that by laminating nonwoven fabrics in this way, the capture efficiency can be significantly increased.

[0120] Example 5

[0121] The blending of fibers A and B was modified as shown in Table 2. Otherwise, nonwoven fabrics 9 and 10 were produced in the same manner as in Example 1.

[0122] The evaluation results of the obtained nonwoven fabrics 9 and 10, as well as the evaluation results of the laminated nonwoven fabric (air filter material) in which a spunbond nonwoven fabric as a breathable support material is arranged between nonwoven fabrics 9 and 10, are shown in Table 1. The spunbond nonwoven fabric is a spunbond nonwoven fabric (manufactured by Unichika Co., Ltd., "Elbes S0303WDO") with a core / sheath structure of PET for the core and PE for the sheath (average fiber diameter 24 μm, mesh size 30 g / m²). 2(Thickness 0.15mm). Nonwoven fabrics 9 and 10 have capture efficiencies of 99.9125% and 99.9056% respectively for particles with a diameter of 0.15μm, with a performance index of 0.038 for both. While these are below the ULPA standard of 99.9995%, by laminating nonwoven fabrics 9, 10, and a breathable support material, the capture efficiency is increased to 99.9999%, exceeding the ULPA standard, resulting in an air filter media with a performance index of 0.038. It can be confirmed that this lamination of nonwoven fabrics significantly increases the capture efficiency.

[0123] Comparative Example 1

[0124] The blending of fibers A and B was modified as shown in Table 2. Otherwise, nonwoven fabrics 11 and 12 were produced in the same manner as in Example 1.

[0125] The evaluation results of the obtained nonwoven fabrics 11 and 12, and the evaluation results of the laminated nonwoven fabric (air filter media) further laminated with nonwoven fabrics 11 and 12 are shown in Table 2. The capture efficiencies of nonwoven fabrics 11 and 12 for particles with a diameter of 0.3 μm are 96.2653% and 97.8426%, respectively, with performance indices of 0.020 and 0.023. If nonwoven fabrics 11 and 12 are laminated, the capture efficiency becomes 99.9241%, which does not exceed the HEPA standard, and the performance index is 0.022 for air filter media. It can be confirmed that even if nonwoven fabrics with low potential performance are laminated together, the performance index, which represents potential performance, does not improve.

[0126] .

Claims

1. An air filter medium, characterized by, It is an air filter material with multiple layers of nonwoven fabric and a performance index of 0.023 or higher. At least one layer of the nonwoven fabric contains at least two kinds of organic fibers A and organic fibers B with different fiber diameters. The average fiber diameter of organic fiber A is 0.01 to 0.60 μm, and the average fiber diameter of organic fiber B is 1.0 to 30 μm.

2. The air cleaner filter medium of claim 1 wherein, It has a particle capture rate of over 99.97% for particles with a diameter of 0.3 μm.

3. The air filter media according to claim 1, characterized in that, It has a particle capture rate of over 99.9995% for particles with a diameter of 0.15 μm.

4. The air filter media according to claim 1, characterized in that, At least one of the laminated nonwoven fabrics has a performance index of 0.023 or higher.

5. The air filter media according to claim 1, further comprising adhesive fibers in the nonwoven fabric.

6. An air filter made using the air filter media according to any one of claims 1 to 5.

7. A fan filter unit comprising the air filter of claim 6.

8. A cleanroom or semiconductor manufacturing apparatus comprising the air filter of claim 6.

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