Filter medium for air filter, manufacturing method for same, and air filter unit using same

Abstract

[Problem] To provide a high performance filter medium that combines high initial collection efficiency resulting from electret melt blowing with efficiency retention of nanofibers after discharge and ameliorating the problem that dust holding capacity and tobacco durability of nanofibers are low. [Solution] This filter medium for an air filter has at least a first layer, a second layer, and a third layer in this order from the upstream side. The second layer is an electret melt-blown nonwoven fabric, the third layer is a nanofiber layer having an average fiber diameter of 10-1000 nm, and the basis weight of the third layer is 0.1 g / m2 or more.

Description

Air filter material, its manufacturing method and air filter unit using the same

[0001] The present invention relates to a filter medium for air filters that is suitable for use in air filters, a method for producing the same, and an air filter unit using the same.

[0002] In recent years, in the air filter market for air purifiers and automobile air conditioner filters (cabin filters), the international standard for general ventilation filters, ISO 16890-2016, has been revised to reflect the collection efficiency after static elimination in the performance description, and there is a trend toward placing greater emphasis on dust collection performance after static elimination.

[0003] Conventionally, electret filters, in which a synthetic fiber nonwoven fabric such as polypropylene is subjected to electret processing, have been known as filter media for air filters intended for air purification, etc. (Patent Documents 1 and 2). However, electret filters have had the problem that the electret weakens due to oil mist and moisture in the air over long-term use, resulting in a decrease in collection performance.

[0004] Therefore, in order to improve the dust collection performance of air filters after static elimination, nonwoven fabrics using nanofibers, which are ultrafine fibers with a fiber diameter of 1000 nm or less, have been proposed (Patent Documents 3 and 4). However, although such nonwoven fabrics exhibit high collection efficiency without relying on electrets, they have the problem of being prone to clogging and having a short lifespan.

[0005] JP 2014-64969 A JP 2021-147711 A JP 2018-202295 A JP 2015-140495 A

[0006] One indicator of the lifespan of an air filter is the dust retention capacity, which is measured by loading dust until a specified pressure is reached and measuring the dust weight at that point. The greater the dust retention capacity, the longer the filter lifespan and the higher its performance. However, the nanofibers used in the filter media of the present invention have a small fiber diameter, resulting in a narrow interfiber distance and a small pore size for the filter media. This has led to problems such as dust easily accumulating on the surface of the nanofiber layer, rapidly increasing pressure loss and reducing dust retention. Another indicator of the lifespan of air purifier filters is the cigarette load test, which measures the performance of an air filter when cigarette smoke particles are loaded onto it. The results of the cigarette load test showed that nanofibers with small fiber diameters capture cigarette smoke particles by adhering spherically to the fibers. In particular, nanofibers with large basis weights and narrow interfiber distances were found to form a membrane with spherically adhering cigarette smoke particles, significantly increasing pressure loss. Furthermore, when the nanofibers are formed into a film, multiple holes of 100 μm or larger are observed, and it has been confirmed that the flow of particles is concentrated in these holes, reducing the collection efficiency. This indicates that nanofibers have the problem of low durability against cigarettes.

[0007] The present invention has been made with the objective of providing a filter medium for air filters that maintains high collection efficiency both before and after static elimination while improving the problems of nanofibers, namely, low dust retention and low cigarette durability.

[0008] In order to solve the above problems, the present invention and its preferred embodiments have the following configurations: (1) An air filter medium having at least a first layer, a second layer, and a third layer in this order from the upstream side, wherein the second layer is an electret melt-blown nonwoven fabric, the third layer is a nanofiber layer having an average fiber diameter of 10 to 1000 nm, and the basis weight of the third layer is 0.1 g / m ２(2) The air filter medium according to (1), wherein the constituent fibers of the electret meltblown nonwoven fabric of the second layer have an average fiber diameter of 0.5 to 50 μm. (3) The air filter medium according to (1) or (2), wherein the constituent fibers of the first layer have an average fiber diameter of 10 to 150 μm, and the initial collection efficiency Ian of the nth layer measured at a wind speed of 3.2 m / min using static-neutralizing NaCl particles having a particle diameter of 0.3 to 0.5 μm satisfies the following relationship: Ia1<Ia2 Ia1<Ia3 (4) The air filter medium according to any one of (1) to (3), wherein the initial collection efficiency Ian of the nth layer measured at a wind speed of 3.2 m / min using static-neutralizing NaCl particles having a particle diameter of 0.3 to 0.5 μm satisfies the following relationship: Ia1 / Ia2≦0.20 Ia2 / Ia3≧1.00 (5) The air filter material according to any one of (1) to (4), wherein the initial QF value QFan of the n-th layer, measured using anti-static NaCl particles having a particle diameter of 0.3 to 0.5 μm at an air velocity of 3.2 m / min and calculated by the following formula (1), satisfies the following relationships: QFa1 / QFa2≦0.1 QFa2 / QFa3≧1.0 QF=−Ln(1−I / 100) / P (1) In formula (1), I represents collection efficiency (%), and P represents pressure loss (Pa). (6) The filter material for air filters according to any one of (1) to (5), the initial collection efficiency IA (%) of the antistatic NaCl particle of particle diameter 0.03 μ m is measured at wind speed 3.2 m / min, the initial collection efficiency IB (%) of the antistatic NaCl particle of particle diameter 0.1 μ m is measured at wind speed 3.2 m / min, and the initial collection efficiency IC (%) of the antistatic NaCl particle of particle diameter 0.3 μ m is measured at wind speed 3.2 m / min satisfy the following relationship: 0.01≦(100−IB) / (100−IA)≦0.8 0.001≦(100−IC) / (100−IA)≦0.3 (7) The air filter material according to any one of (1) to (6), wherein the initial QF value QFa of the air filter material is measured at an air velocity of 3.2 m / min using static-eliminating NaCl particles having a particle diameter of 0.3 to 0.5 μm and calculated by the following formula (1), and satisfies the following relationship: QFa≧0.07 QF=−Ln(1−I / 100) / P (1) In formula (1), I represents collection efficiency (%), and P represents pressure loss (Pa).(8) The air filter material according to any one of (1) to (7), wherein the initial QF value QFa3 of the third layer, measured using antistatic NaCl particles having a particle diameter of 0.3 to 0.5 μm at an air velocity of 3.2 m / min and calculated by the following formula (1), satisfies the following relationship: QFa3≧0.05 QF=−Ln(1−I / 100) / P (1) In formula (1), I represents collection efficiency (%), and P represents pressure loss (Pa). (9) The air filter material according to any one of (1) to (8), wherein the initial QF value QFa of the air filter material, the QF value QFaD2 of the second layer after static elimination, the QF value QFaD3 of the third layer after static elimination, and the QF value QFaDall of the entire air filter material after static elimination are measured using static elimination NaCl particles with a particle diameter of 0.3 to 0.5 μm at an air speed of 3.2 m / min and calculated by the following formula (1), satisfy the following relationships: QFaD2 / QFa<0.20 QFaD3 / QFa>0.20 0.10≦QFaDall / QFa≦1.00 QF=-Ln(1-I / 100) / P (1) In formula (1), I represents collection efficiency (%), and P represents pressure loss (Pa). (10) The air filter medium according to any one of (1) to (9), wherein the maximum penetrating particle size (MPPS) Mn (μm) of the collection efficiency of the nth layer, measured using antistatic NaCl particles having a particle size of 0.015 to 0.300 μm at an air velocity of 3.2 m / min, satisfies the following relationship: M2<0.05 M3>0.05 (11) The air filter medium according to any one of (1) to (10), further comprising an adsorbent layer between the first layer and the second layer and / or between the second layer and the third layer. (12) The air permeability of the first layer is 100 to 600 cm. ３ / cm ２The air filter material according to any one of (1) to (11), wherein the time is 0.5 to 1.5 seconds. (13) The air filter material according to any one of (1) to (12), which has a fourth layer downstream of the third layer and is made of fibers with an average fiber diameter of 0.5 to 150 μm. (14) A method for producing the air filter material according to any one of (1) to (12), which comprises bonding the first layer and the second layer together, and then laminating the third layer on the surface of the second layer to form the air filter material consisting of the first, second, and third nonwoven fabric layers. (15) A method for producing the air filter material according to (13), which comprises laminating the third layer on the fourth layer, bonding the first layer and the second layer together, and then laminating the surface of the second layer and the surface of the third layer. (16) A method for producing the filter material for air filters according to (13), comprising laminating the first layer and the second layer together, and then laminating the third layer on the surface of the second layer, and laminating the fourth layer on the surface of the third layer. (17) An air filter unit using the filter material for air filters according to any one of (1) to (13).

[0009] According to the present invention, the problems of low dust retention and cigarette durability of nanofibers are improved, and a high-performance filter medium is obtained that combines the high initial collection efficiency of electret melt-blown with the maintenance of efficiency after de-ionization of nanofibers.

[0010] FIG. 1 is a schematic diagram of a collection efficiency measuring device.

[0011] The present invention will be described in detail below.

[0012] The filter material for air filters of the present invention has at least a first layer, a second layer, and a third layer in this order from the upstream side, wherein the second layer is an electret melt-blown nonwoven fabric, the third layer is a nanofiber layer having an average fiber diameter of 10 to 1000 nm, and the basis weight of the third layer is 0.1 g / m ２ The effects of the present invention are believed to be achieved by laminating layers each having the following properties.

[0013] (First Layer) The form of the first layer is not particularly limited and may be a thermal bonded nonwoven fabric, a chemical bonded nonwoven fabric, a needle punched nonwoven fabric, etc., but from the viewpoint of the thickness of the filter medium and the ease of pleating, a chemical bonded nonwoven fabric is preferred.

[0014] The average fiber diameter of the fibers constituting the first layer is preferably 10 to 150 μm, more preferably 10 to 120 μm, and even more preferably 10 to 80 μm. By laminating a nonwoven fabric having a larger fiber diameter and greater strength than the second to fourth layers on the first layer, the first layer is suitable for serving as an aggregate for the filter medium and also facilitates the formation of spaces for retaining coarse dust.

[0015] The first layer has an air permeability of 100 to 600 cm ３ / cm ２ It is preferable that the air permeability is 100 cm ３ / cm ２ seconds or more, more preferably 120 cm ３ / cm ２ A nonwoven fabric having a large void volume and an air permeability of 600 cm or more is less likely to clog when the amount of dust attached is small, and can more effectively extend the life of the fabric. ３ / cm ２ seconds or less, more preferably 500 cm ３ / cm ２ - The dust collection performance is improved by the time being less than 1 / 2 second.

[0016] (Second Layer) The electret meltblown nonwoven fabric of the second layer preferably has an average fiber diameter of 0.5 to 50 μm, more preferably 1 to 30 μm, and even more preferably 1 to 10 μm. A finer average fiber diameter provides sufficient collection efficiency, but at the same time increases pressure loss, so the average fiber diameter is preferably within the above range. Furthermore, electret processing enables the electrostatic capture of submicron- and nano-sized fine dust particles that are normally difficult to remove.

[0017] The raw material for electret meltblown nonwoven fabrics is a spinnable thermoplastic resin, including polyolefin resins such as polypropylene, polyethylene, polystyrene, polybutylene terephthalate, and polytetrafluoroethylene, aromatic polyester resins such as polyethylene terephthalate, and polycarbonate resins, all of which have high electrical resistivity. From the standpoint of spinnability, polyolefin resins are preferred, with polypropylene being particularly suitable. The electret processing method can be selected from known methods such as corona discharge, fluid contact, and triboelectric charging. Among fluid contact methods, the so-called hydrocharging method, in which pure water is sprayed onto the nonwoven fabric or the fabric is exposed to a water stream in a water tank to apply the electret, is particularly preferred. As the polar solvent used here, pure water is preferably used from the standpoint of productivity, such as wastewater discharge.

[0018] (Third Layer) The third layer is a nanofiber layer having an average fiber diameter of 10 to 1,000 nm. An average fiber diameter of 1,000 nm or less, preferably 800 nm or less, and more preferably 500 nm or less, enables low pressure loss due to the slip-flow effect. An average fiber diameter of 10 nm or more, preferably 20 nm or more, and more preferably 30 nm or more, ensures an appropriate pore size and prevents excessive pressure loss and clogging.

[0019] The resin forming the fibers of the nanofiber layer is not particularly limited, but examples of polymeric materials that can be used include polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyamide, polyurethane, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyglycolic acid, polycaprolactone, polyvinyl acetate, polycarbonate, polyimide, polyetherimide, cellulose, cellulose derivatives, chitin, chitosan, collagen, gelatin, and copolymers thereof.

[0020] The basis weight of the third layer is 0.1 g / m２ The basis weight of the third layer is 0.1 g / m ２ By setting the weight of the third layer to 5.0 g / m or more, the mechanical collection efficiency is increased, leading to an improvement in the collection efficiency after neutralization. ２ or less, more preferably 2.0 g / m ２ By setting the above, it is possible to more effectively suppress an increase in pressure loss and a decrease in lifespan due to clogging by dust.

[0021] By using nanofibers with the above average fiber diameter, low pressure loss and high collection efficiency can be achieved, and therefore, in terms of performance of the third layer, it is preferable that the initial QF value QFa3 of the third layer, which is measured using static-eliminating NaCl particles of 0.3 to 0.5 μm at an air velocity of 3.2 m / min and calculated from the following formula (1), satisfies the following relationship: QFa3≧0.05 QFa3 is more preferably 0.06 or greater, and even more preferably 0.07 or greater.

[0022] The QF value is an index of the filtering performance of an air filter medium, and shows the relationship between filtering efficiency I (%) and pressure loss P (Pa) as expressed by the following formula (1): QF = -Ln(1 - I / 100) / P (1) The higher the QF value, the higher the filtering efficiency and the lower the pressure loss. QF = -Ln(1 - I / 100) / P (1) The filtering efficiency I (%) required to calculate the QF value can be calculated using the following formula (2) from the number of particles D upstream of the sample and the number of particles d downstream of the sample when a certain number of particles are flowed through the measurement sample at a specified air volume. Filtering efficiency I (%) = [1 - (d / D)] x 100 (2) (Fourth Layer) The air filter medium of the present invention also preferably has a fourth layer downstream of the third layer, which is made of fibers with an average fiber diameter of 0.5 to 150 μm. The average fiber diameter of the fibers constituting the fourth layer is preferably 5 to 40 μm, and more preferably 10 to 40 μm. The fourth layer may be made of any suitable material, including thermally bonded nonwoven fabric, chemically bonded nonwoven fabric, melt-blown nonwoven fabric, needle-punched nonwoven fabric, cellulose nano-nonwoven fabric, and a fiber sheet containing thermally adhesive fibers. However, a spunbonded nonwoven fabric is more preferred because it has excellent processability, low air resistance, protects the third layer, and reduces tearing and resilience during pleating.

[0023] (Adsorbent layer) The filter material for air filter of the present invention preferably has an adsorbent layer between the first layer and the second layer, and / or between the second layer and the third layer.By providing an adsorbent layer, it can contain odorous organic low molecular weight compounds such as ammonia and toluene and not release them from filter material, so that it can further improve air purification performance.As the adsorbent, for example, generally, activated alumina, activated carbon, activated carbon fiber, silica gel, zeolite etc. can be listed, and activated carbon is more preferred from the viewpoint of odorous substance adsorption effect.

[0024] (Laminated structure) In the air filter material of the present invention, the initial collection efficiency Ian of the nth layer measured using 0.3 to 0.5 μm antistatic NaCl particles at an air velocity of 3.2 m / min preferably satisfies the following relationship: Ia1 / Ia2≦0.20 Ia2 / Ia3≧1.00 Ia1 / Ia2 is more preferably 0.15 or less, even more preferably 0.10 or less, even more preferably 0.07 or less, and even more preferably 0.05 or less. Ia2 / Ia3 is more preferably 1.05 or more, even more preferably 1.10 or more, and even more preferably 1.15 or more. That is, among the layer structure of the first layer / the second layer / the third layer, it is preferable to have a structure in which the collection efficiency of the second layer is the highest.

[0025] The nanofibers in the third layer are extremely fine, with an average fiber diameter of 10 to 1,000 nm, resulting in small pore sizes and a high mechanical collection effect due to interference, inertia, gravity, and diffusion, maintaining a certain collection efficiency regardless of whether the particles are charged or not. On the other hand, increasing the basis weight to improve performance tends to result in a too small pore size, leading to dust accumulation on the surface, a sharp increase in pressure loss, and a low dust retention capacity. Furthermore, because the fiber diameter is extremely fine, the fibers are susceptible to changes in fiber shape due to the influence of tobacco smoke particles, which tends to reduce performance.

[0026] Therefore, in order to satisfy the above relationship, Ian placed a higher performance electret meltblown nonwoven fabric as the second layer in the upstream layer of the nanofiber, which enabled low pressure loss and high collection efficiency by electrostatic force, and by adopting a coarse-dense structure, the electret meltblown nonwoven fabric captured the dust that caused clogging of the nanofiber, making it possible to more effectively suppress a sudden increase in pressure loss. In addition, the electret meltblown nonwoven fabric, which has a larger fiber diameter than the nanofiber and is less affected by tobacco smoke, absorbs tobacco dust in the upstream layer of the nanofiber, more effectively suppressing the performance degradation of the nanofiber and more effectively achieving a long life as a filter material.

[0027] Furthermore, it is preferable that the initial QF value QFan of the nth layer, measured using anti-static NaCl particles having a particle diameter of 0.3 to 0.5 μm at an air velocity of 3.2 m / min and calculated from the above formula (1), satisfies the following relationships: QFa1 / QFa2≦0.1 QFa2 / QFa3≧1.0 QFa1 / QFa2 is more preferably 0.07 or less, and even more preferably 0.05 or less, and QFa2 / QFa3 is more preferably 1.5 or more, and even more preferably 2.0. In other words, of the layer configuration of the first layer / second layer / third layer, it is preferable that the second layer has the highest QF value.

[0028] (Filter Medium Performance) The filter medium for air filters of the present invention preferably has the following performance.

[0029] The first layer serves as a reinforcing layer for the air filter, capturing a large amount of large dust particles on the most upstream side, so it is preferable to adjust both the fiber diameter and pore size to be relatively large. Therefore, it is preferable that the first layer exhibits lower filtering performance compared to the second and third layers, and it is preferable that the initial filtering efficiency Ian of the nth layer, measured using antistatic NaCl particles with a particle diameter of 0.3 to 0.5 μm at an air velocity of 3.2 m / min, satisfy the following relationships: Ia1<Ia2 Ia1<Ia3 It is even more preferable that Ian satisfy the following relationships: Ia1<Ia3<Ia2

[0030] The air filter material of the present invention preferably has an initial QF value QFa of the air filter material, which is measured using 0.3-0.5 μm static neutralizing NaCl particles at an air velocity of 3.2 m / min and calculated according to the above formula (1), satisfying the following relationship: QFa≧0.07 QFa is more preferably 0.09 or more, and even more preferably 0.12 or more. This is made possible by the laminated structure of the present invention, which has a low pressure loss and an electret melt-blown layer that shows high initial collection efficiency in the second layer, and keeps the basis weight of the nanofiber in the third layer to the minimum amount that can achieve the target static neutralization collection efficiency, thereby suppressing the increase in pressure loss.

[0031] The electret meltblown nonwoven fabric of the second layer in the air filter material of the present invention can capture fine dust particles using electrostatic force and has a high initial collection efficiency, but over long-term use, the electrostatic force decreases due to oil mist and moisture in the air, and the collection performance tends to deteriorate. On the other hand, the nanofibers of the third layer have an average fiber diameter of 10 to 1,000 nm, which is extremely fine, resulting in a small pore size and a high mechanical collection effect, and they have the characteristic of maintaining collection efficiency regardless of whether they are charged or not. The air filter material of the present invention enables the performance of both the high initial collection efficiency of the electret meltblown and the maintenance of collection efficiency after de-staticization of the nanofibers.

[0032] That is, the air filter material of the present invention is measured using the neutralization NaCl particle of particle diameter 0.3~0.5 μm at wind speed 3.2m / min, and is calculated by above-mentioned formula (1), the initial QF value QFa of said air filter material, and the QF value QFaD2 after neutralization of the second layer, the QF value QFaD3 after neutralization of the third layer and the QF value QFaDall of said air filter material after neutralization of the whole preferably satisfy the following relationship.QFaD2 / QFa<0.20 QFaD3 / QFa>0.20, and the QF value QFaDn after neutralization is preferably higher in the third layer compared with the second layer, and the Eall of the whole filter material in the whole filter material that is stacked thereon is: 0.10≦QFaDall / QFa≦1.00 QFaD2 / QFa is more preferably less than 0.15, and even more preferably less than 0.10. QFaD3 / QFa is more preferably greater than 0.30, and even more preferably greater than 0.40. QFaDall / QFa is more preferably 0.13 or greater, and even more preferably 0.15 or greater. Furthermore, QFaDall / QFa is more preferably 0.80 or less, and even more preferably 0.60 or less.

[0033] The smaller the particle diameter of electret meltblown nonwoven fabric is, the lower the collection efficiency tends to be, while the smaller the particle diameter of nanofiber is, the higher the collection efficiency tends to be. In air filter media, when the filtration speed is constant, there is a particle size (maximum penetration particle diameter) that is most difficult to collect. In the air filter media of the present invention, the maximum penetration particle diameter (MPPS) Mn (μm) of the collection efficiency of the nth layer measured using static-neutralizing NaCl with a particle diameter of 0.015 to 0.300 μm at an air speed of 3.2 m / min preferably satisfies the following relationship: M2<0.05 M3>0.05 M2 is more preferably less than 0.03 μm, and M3 is more preferably greater than 0.07 μm.

[0034] Furthermore, the air filter medium of the present invention preferably has an initial collection efficiency IA (%) measured using static-eliminating NaCl particles with a particle diameter of 0.03 μm at an air velocity of 3.2 m / min, an initial collection efficiency IB (%) measured using static-eliminating NaCl particles with a particle diameter of 0.1 μm at an air velocity of 3.2 m / min, and an initial collection efficiency IC (%) measured using static-eliminating NaCl particles with a particle diameter of 0.3 μm at an air velocity of 3.2 m / min, which satisfy the following relationships: 0.01≦(100-IB) / (100-IA)≦0.8 0.001≦(100-IC) / (100-IA)≦0.3 (100-IB) / (100-IA) is more preferably 0.1 or more, and (100-IC) / (100-IA) is more preferably 0.1 or more.

[0035] (Manufacturing Method) The air filter medium of the present invention can be laminated by a commonly used method such as a hot melt powder method, an ultrasonic embossing adhesion method, or a spray lamination method.

[0036] Furthermore, although not particularly limited, since the third nanofiber layer is very thin and lacks stability on its own, when forming the air filter material consisting of the first, second and third nonwoven fabric layers, it is preferable that the third layer be laminated on top of the second layer, and it is more preferable that after the first and second layers are bonded together, the third nanofiber layer be laminated on the surface facing the second layer.

[0037] Nanofibers can be produced by known methods, such as electrospinning (electrospinning), melt-blowing, sea-island melt spinning, and carbon dioxide gas supersonic laser drawing, with electrospinning (electrospinning) being more preferred because it allows for mass production of wide fibers.

[0038] Furthermore, when forming the air filter material consisting of the first, second, third and fourth nonwoven fabric layers, it is preferable that the third nanofiber layer is formed on the fourth layer, and in particular, it is preferable that the third layer is laminated on the fourth layer, the first layer and the second layer are bonded together, and then the surface of the second layer is bonded to the surface of the third layer.

[0039] In addition, as another manufacturing method for forming the air filter material consisting of the first layer, the second layer, the third layer, and the fourth layer of nonwoven fabric, a method is also preferred in which the first layer and the second layer are bonded together, the nanofibers of the third layer are laminated on the surface of the second layer, and the fourth layer is laminated on the surface of the third layer.

[0040] In addition, in the above-mentioned two-step lamination method, the first layer and the second layer need to be heat-pressed twice, and the difference in the thermal shrinkage rate of each layer may cause wrinkles.Therefore, as another manufacturing method for forming the air filter material that is made up of the nonwoven fabric layers of the first layer, the second layer, the third layer and the fourth layer, it is also preferable to laminate the third layer on the surface of the fourth layer, and then laminate the laminate of the first layer, the second layer, the third layer and the fourth layer at once.

[0041] The air filter unit of the present invention uses the air filter material of the present invention, and is suitable for use in air filters, particularly as a filter for an air purifier or a cabin filter for an automobile. Therefore, it can be processed into a shape such as pleats and used as a filter unit.

[0042] The present invention will be described in more detail below using examples, but the present invention is not necessarily limited to these embodiments. The measurement items in the examples were measured by the following methods.

[0043] [Measurement method, processing method] (1) Average fiber diameter Twenty sample acquisition locations were randomly selected from a 1000 mm × 1000 mm surface of each layer, and one measurement sample measuring 3 mm × 3 mm in length × width was taken from each sample acquisition location. Photographs of the surface of the nonwoven fabric were taken using a scanning electron microscope (KEYENCE Corporation, VHX-6000 / D500 / D510, magnification: 1000x), one for each measurement sample, for a total of 20 photographs. The fiber diameters of all fibers in the photographs were measured, and the arithmetic average value was calculated.

[0044] (2) Basis weight: Calculate the mass of the evaluation sample (nonwoven fabric, anti-static nonwoven fabric or filter material) and calculate 1 m from its area.２ The weight per unit area was calculated as the basis weight of each sample. The minimum sampling area was 0.01 m ２ The nanofiber layer was formed on a spunbond nonwoven fabric SB having a known basis weight, which will be described later, and the basis weight of the entire SB on which the nanofiber layer was formed was measured. The basis weight of the nanofiber layer was calculated by subtracting the basis weight of the SB from the measured basis weight.

[0045] (3) Air permeability: Measurement was performed according to the evaluation method of the Frazier type method described in JIS L1096 (1999). However, since the measurement using one sheet tends to cause variations in the measurement results, the measurement was performed using two sheets stacked together. The evaluation number was at least 5, and the arithmetic average was taken as the air permeability in the present invention.

[0046] (4) Collection Efficiency of 0.3-0.5 μm Anti-Static NaCl Particles Measurement samples measuring 150 mm x 150 mm were collected, and the collection efficiency of each sample was measured using the collection efficiency measurement device shown in Figure 1. The collection efficiency measurement device shown in Figure 1 has a dust storage box 2 and a static eliminator 9 connected upstream of a sample holder 1 in which the measurement sample M is set, and a flow meter 3, a flow control valve 4, and a blower 5 connected downstream. A particle counter 6 is attached to the sample holder 1, and the number of dust particles on the upstream and downstream sides of the measurement sample M can be measured via a selector cock 7. The sample holder 1 is also equipped with a pressure gauge 8, which allows the static pressure difference between the upstream and downstream sides of the measurement sample M to be read.

[0047] To measure the collection efficiency, a NaCl solution was filled in the dust collection box 2. Next, the measurement sample M was set in the sample holder 1, and the air flow rate was adjusted with the flow control valve 4 so that the filter passing speed was 3.2 m / min. The dust concentration was adjusted to 10,000 to 30,000 particles / 2.83×10 －４ m ３ (0.01 ft ３) and stabilized within the range, the number of dust particles D upstream and the number of dust particles d downstream of the measurement sample M were measured three times per measurement sample using a particle counter 6 (KC-01D, manufactured by Rion Co., Ltd.), and the collection efficiency (%) of 0.3 μm anti-static NaCl particles was calculated using the following formula based on JIS K 0901 (1991) "Test methods for shape, dimensions and performance of filter media for collecting dust samples in gas." The average value of the three measurement samples was taken as the final collection efficiency (Ia). Collection efficiency (%) = [1 - (d / D)] x 100, where d represents the total number of downstream dust particles measured three times, and D represents the total number of upstream dust particles measured three times.

[0048] The higher the collection efficiency of a nonwoven fabric, the fewer the downstream dust particles, and therefore the higher the collection efficiency. Regarding the nanofiber layer, a nanofiber layer was formed on a spunbond nonwoven fabric SB (described later) with a collection efficiency of about 1%, and the collection efficiency of the entire SB on which the nanofiber layer was formed was measured.

[0049] (5) Pressure Loss The pressure loss was determined by reading the static pressure difference between the upstream and downstream of the measurement sample M using a pressure gauge 8 when measuring the collection efficiency according to (4) above. The average value of five measurement samples was taken as the final pressure loss. For the nanofiber layer, a nanofiber layer was formed on a spunbond nonwoven fabric SB (described below) with a pressure loss of about 1 Pa, and the pressure loss of the entire SB on which the nanofiber layer was formed was measured.

[0050] (6) QF Value The QF value (QFa) was calculated from the following formula (1) using the collection efficiency according to (4) above as I (%) and the pressure loss according to (5) above as P (Pa): QF=-Ln(1-I / 100) / P (1).

[0051] (7) The collection efficiency of the antistatic NaCl particles of particle diameter 0.015~0.300 μm, MPPS (maximum penetration particle diameter) JIS B9928 Appendix 5 (regulation) NaCl aerosol generation method (pressure spray method) according to the method described in, the NaCl particles generated by atomizer are classified into designated particle size by electrostatic classifier (TSI company manufacture), and after neutralizing particle charge using americium-241, the permeation flow rate is adjusted to 3.2 m / min, and the particle counter (TSI company manufacture, CNC) is used to determine the particle number before and after the filter material of measurement sample, and measure collection efficiency.For nanofiber layer, a nanofiber layer is formed on the spunbonded nonwoven fabric SB of collection efficiency about 1% as described later, and the collection efficiency of the SB of the whole formed nanofiber layer is measured.

[0052] The particle collection efficiency for particle sizes of 0.015 to 0.300 μm was measured, and the particle size with the lowest collection efficiency as a result of the greatest number of particles passing through was designated as MPPS (maximum penetrating particle size) Mn.

[0053] (8) Destaticization method: The filter material is placed in a sealed bag, filled with the IPA vapor of IPA (isopropyl alcohol), and exposed to the IPA vapor at room temperature for 48 hours.Then, it is taken out of the bag, and dried at room temperature for 24 hours to obtain the destaticized filter material.

[0054] (9) Dust retention performance evaluation method: A flat filter medium is placed on a filter with an effective opening area of ​​0.1 m. ２ The test tube was set in a holder with a diameter of 10 mm, and air was passed through it vertically at a surface velocity of 20.0 m / min. 15 types of JIS test powder (Japan Air Cleaning Association) were sprayed from the upstream side at a concentration of 70 mg / m ３ The pressure difference between the upstream and downstream of the filter when the air was supplied at this rate was measured with a differential pressure gauge, and the dust retention amount was measured from the change in filter mass from the initial pressure loss until the pressure rose to 150 Pa. Measurements were carried out by sampling five randomly selected points from one specimen, and the average value was used.

[0055] (10) Cigarette durability test method 1m ３In an acrylic container, one 10 mg "Mevius Original" tar cigarette (manufactured by Japan Tobacco Co., Ltd.) was placed in a cigarette smoke evacuator in accordance with the JEMA standard (JEM1467 method) and burned. In the same container, an evaluation sample attached to an adapter with an effective ventilation diameter of 135 mm was blown through a 1.3 m ３ After aeration at 1 / min for 1 hour, the collection efficiency and pressure loss of the evaluation sample were measured. This was then repeated five times for the same evaluation sample.

[0056] (11) Pleating property Using a reciprocating pleating machine, pleat processing was carried out continuously for 400 pleats under the conditions of pleat height 25 mm, pleat processing speed 40 pleats / min, and back pressure 0.1 MPa. After pleating, the pleat shape and pitch of the air filter filter material when released from the pleating machine were observed, and the pleat processability was ranked in the following three stages, with "A" being acceptable. A: The peak shape and pitch of the peak are stable. B: The pleat shape can be formed, but the peak shape and pitch are disturbed. C: The pleat shape cannot be formed.

[0057] [Nonwoven fabric and its production] (1) Chemical bonded nonwoven fabric CB: A nonwoven fabric having a basis weight of 40.0 g / m2, comprising 16.5 mass% of polyvinyl alcohol (PVA) fiber (Vinylon) having a single fiber fineness of 1.5 dtex, 22 mass% of polyvinyl alcohol (PVA) fiber (Vinylon) having a single fiber fineness of 7.1 dtex, 16.5 mass% of polyethylene terephthalate (PET) fiber having a single fiber fineness of 2.0 dtex, and 45 mass% of an acrylic resin binder containing a phosphorus-based flame retardant. ２ Chemical bonded nonwoven fabric CB was used.

[0058] (2) Electret melt-blown nonwoven fabric EMB1: Made of polypropylene resin (PP), the fabric has an average fiber diameter of 4.5 μm and a basis weight of 18.0 g / m by the melt-blown method. ２ Next, the obtained nonwoven fabric was made to travel along the water surface of a water tank to which pure water was supplied, and a slit-shaped suction nozzle was brought into contact with the surface of the nonwoven fabric to suck the water, thereby allowing the water to penetrate into the entire surface of the fiber layer, and after draining the water, the nonwoven fabric was allowed to dry naturally, thereby obtaining an electret melt-blown nonwoven fabric EMB1.

[0059] (3) Electret melt-blown nonwoven fabric EMB2: Made of polypropylene resin (PP), it has an average fiber diameter of 2.8 μm and a basis weight of 20.0 g / m by the melt-blown method. ２ An electret melt-blown nonwoven fabric EMB2 was obtained in the same manner as in the production of EMB1, except that the production conditions were changed so that:

[0060] (4) Nanofiber layer NF1 Polyvinylidene fluoride (PVDF) with a degree of polymerization of 500 was dissolved in hot water to prepare a 25% by mass aqueous solution of polyvinylidene fluoride. This aqueous solution was used as a spinning solution, and polyvinylidene fluoride nanofibers with a basis weight of 0.4 g / m were fabricated by electrospinning. ２ The nanofiber layer NF1 was obtained by spinning the nanofibers onto the substrate so that the nanofiber layer NF1 was spun ...

[0061] (5) Nanofiber layer NF2: Made of polyvinylidene fluoride (PVDF) and fabricated by electrospinning to a basis weight of 0.6 g / m ２ The nanofiber layer NF2 was obtained in the same manner as in the production of the nanofiber layer NF1, except that the production conditions were changed so that the weight per unit area of ​​the nanofiber layer NF1 was adjusted by changing the running speed of the substrate receiving the nanofibers.

[0062] (6) Spunbonded Nonwoven Fabric SB Polypropylene resin (PP) consisting of a homopolymer with an MFR of 200 g / 10 min was melted in an extruder and spun through a rectangular spinneret with a hole diameter φ of 0.30 mm and a hole depth of 2 mm at a spinning temperature of 235°C and a single-hole throughput of 0.32 g / min to form a yarn. After cooling and solidifying, the yarn was pulled and stretched using a rectangular ejector with compressed air at an ejector pressure of 0.35 MPa and collected on a collection net. The obtained nonwoven fiber web was thermally temporarily bonded using a flat roll at a temperature of 120°C to form a web having a basis weight of 15.0 g / m. ２ A spunbonded nonwoven fabric SB having an average single fiber diameter of 10.1 μm was obtained.

[0063] Table 1 shows the basic physical properties and characteristics of each nonwoven fabric or layer.

[0064]

[0065] [Example 1] (Three-layer filter medium configuration) CB was used for the first layer, EMB2 for the second layer, and NF1 for the third layer. There was no layer corresponding to the fourth layer.

[0066] (Lamination) A laminate of the second and third layers was obtained by using the second layer previously prepared as a substrate for the production of the third layer. A polyethylene hot melt resin was applied at 6.0 g / m2 to the surfaces of the first layer and the second layer of this laminate. ２ The fiber layers were combined together to obtain a three-layer filter medium.

[0067] Example 2 (Four-layer filter medium configuration) CB was used for the first layer, EMB1 for the second layer, NF1 for the third layer, and SB for the fourth layer.

[0068] (Lamination) 6.0 g / m of polyethylene hot melt resin was applied to the first and second layers. ２ The fiber layers were combined to obtain a laminate of the first and second layers. The previously prepared fourth layer was used as a substrate for the third layer, resulting in a laminate of the third and fourth layers. A polyethylene hot-melt resin was applied to the surface of the second layer and the surface of the third layer of these two laminates at a rate of 6.0 g / m. ２ The fiber layers were combined together to obtain a four-layer filter medium.

[0069] Example 3 (Four-layer filter medium configuration) CB was used for the first layer, EMB1 for the second layer, NF2 for the third layer, and SB for the fourth layer.

[0070] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Example 2 to obtain a four-layer filter medium.

[0071] Example 4 (Four-layer filter medium configuration) CB was used for the first layer, EMB2 for the second layer, NF1 for the third layer, and SB for the fourth layer.

[0072] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Example 2 to obtain a four-layer filter medium.

[0073] [Example 5] (Four-layer filter medium configuration) CB was used for the first layer, EMB2 for the second layer, NF2 for the third layer, and SB for the fourth layer.

[0074] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Example 2 to obtain a four-layer filter medium.

[0075] Example 6 (Four-layer filter medium configuration) CB was used for the first layer, EMB2 for the second layer, NF2 for the third layer, and EMB2 for the fourth layer.

[0076] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Example 2 to obtain a four-layer filter medium.

[0077] [Example 7] (Four-layer filter medium configuration) SB was used in the first layer, EMB2 in the second layer, NF2 in the third layer, and SB in the fourth layer.

[0078] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Example 2 to obtain a four-layer filter medium.

[0079] [Comparative Example 1] (Three-layer filter medium configuration) CB was used for the first layer, EMB2 for the second layer, and SB for the fourth layer. There was no layer corresponding to the third layer.

[0080] (Lamination) 6.0 g / m of polyethylene hot melt resin was applied to the first and second layers. ２ The fiber layers were combined to obtain a laminate of the first and second layers. A polyethylene hot melt resin was applied to the surface of the second layer and the surface of the fourth layer of this laminate in an amount of 6.0 g / m. ２ The fiber layers were combined together to obtain a three-layer filter medium.

[0081] [Comparative Example 2] (Three-layer filter medium configuration) EMB1 was used for the second layer, NF1 for the third layer, and SB for the fourth layer. There was no layer corresponding to the first layer.

[0082] (Lamination) A laminate of the third and fourth layers was obtained by using the previously prepared fourth layer as a substrate when producing the third layer. A polyethylene hot melt resin was applied at 6.0 g / m2 to the surface of the second layer and the third layer of this laminate. ２ The fiber layers were combined together to obtain a three-layer filter medium.

[0083] [Comparative Example 3] (Three-layer filter medium configuration) EMB1 was used for the second layer, NF2 for the third layer, and SB for the fourth layer. There was no layer corresponding to the first layer.

[0084] (Lamination) With the above layer structure, the fiber layers were combined with each other in the same manner as in Comparative Example 2 to obtain a three-layer filter medium.

[0085] [Comparative Example 4] (Three-layer filter medium configuration) CB was used for the first layer, NF1 for the third layer, and SB for the fourth layer. There was no layer corresponding to the second layer.

[0086] (Lamination) A laminate of the third and fourth layers was obtained by using the previously prepared fourth layer as a substrate when producing the third layer. A polyethylene hot melt resin was applied at 6.0 g / m2 to the surfaces of the first layer and the third layer of this laminate. ２ The fiber layers were combined together to obtain a three-layer filter medium.

[0087] [Comparative Example 5] (Three-layer filter medium configuration) CB was used for the first layer, NF2 for the third layer, and SB for the fourth layer. There was no layer corresponding to the second layer.

[0088] (Lamination Method) With the above layer structure, the fiber layers were combined with each other in the same manner as in Comparative Example 4 to obtain a three-layer filter medium.

[0089] Tables 2 and 3 show the basic physical properties of the laminated filter media of Examples 1 to 7 and Comparative Examples 1 to 5, and Tables 4 and 5 show the dust collection and durability performance of the laminated filter media of Examples 1 to 7 and Comparative Examples 1 to 5.

[0090]

[0091]

[0092]

[0093]

[0094] As shown in Table 2, in Examples 1 to 7, an electret melt-blown nonwoven fabric such as EMB1 or EMB2 was provided as the second layer, and a nanofiber layer such as NF1 or NF2 was provided as the third layer. Therefore, it was found that the initial collection efficiency and the collection efficiency after static elimination showed high performance.

[0095] Furthermore, as shown in Table 2, in Examples 2 to 7, the fourth layer was provided downstream of the third layer, which protected the third layer, which is easily damaged by contact with the outside, and it was found that the electrostatic collection efficiency after static elimination was higher.

[0096] Furthermore, it was found that Examples 2 to 5 shown in Table 2 have excellent processability because they have a chemically bonded nonwoven fabric such as CB in the first layer, and also have high performance in terms of initial pressure loss because they have a spunbonded nonwoven fabric such as SB in the fourth layer.

[0097] On the other hand, as shown in Table 3, in Comparative Example 1, the third nanofiber layer was not provided, and therefore, although the initial collection efficiency was high and the pressure loss was small due to the second layer of electret melt-blown nonwoven fabric of EMB2, the collection efficiency after static elimination was insufficient.

[0098] Furthermore, as shown in Table 5, Comparative Examples 2 and 3 did not have the first layer, and therefore had weak strength and were unsuitable for use in air filters, which are generally assembled after pleating and then manufactured into products, due to poor processability.

[0099] Furthermore, as shown in Table 3, in Comparative Examples 4 and 5, an electret melt-blown nonwoven fabric like EMB1 or EMB2 was not provided in the second layer, and therefore, although the post-neutralization efficiency maintained high performance due to the nanofiber layer in the third layer, the initial collection efficiency was insufficient.

[0100] Furthermore, as shown in Tables 4 and 5, dust retention and tobacco durability are higher when an electret melt-blown nonwoven fabric layer such as EMB1 or EMB2 is provided in the upstream layer of the nanofiber, and it was found that even higher performance can be achieved by providing a reinforcing layer such as the chemical bonded nonwoven fabric of Synthesis Example 1 in the upstream layer of the electret melt-blown nonwoven fabric.

[0101] The air filter medium of the present invention can be suitably used for air filters, particularly as filters for air purifiers and cabin filters for automobiles.

[0102] 1: Sample holder 2: Dust storage box 3: Flow meter 4: Flow rate adjustment valve 5: Blower 6: Particle counter 7: Switch cock 8: Pressure gauge 9: Static neutralizer M: Measurement sample

Claims

1. A filter medium for an air filter having at least a first layer, a second layer, and a third layer in this order from the upstream side, wherein the second layer is an electret melt-blown nonwoven fabric, the third layer is a nanofiber layer having an average fiber diameter of 10 to 1000 nm, and the basis weight of the third layer is 0.1 g / m ２ or more. The filter medium for an air filter.

2. The filter medium for an air filter according to claim 1, wherein the average fiber diameter of the constituent fibers of the electret melt-blown nonwoven fabric of the second layer is 0.5 to 50 μm.

3. The filter medium for an air filter according to claim 1 or 2, wherein the average fiber diameter of the constituent fibers of the first layer is 10 to 150 μm, and the initial collection efficiency Ian of the nth layer measured using charged NaCl particles with a particle diameter of 0.3 to 0.5 μm at a wind speed of 3.2 m / min satisfies the following relationship: Ia1 < Ia2, Ia1 < Ia3.

4. The filter medium for an air filter according to claim 1 or 2, wherein the initial collection efficiency Ian of the nth layer measured using charged NaCl particles with a particle diameter of 0.3 to 0.5 μm at a wind speed of 3.2 m / min satisfies the following relationship: Ia1 / Ia2 ≤ 0.20, Ia2 / Ia3 ≥ 1.

00.

5. The filter medium for an air filter according to claim 1 or 2, wherein the initial QF value QFan of the nth layer measured using charged NaCl particles with a particle diameter of 0.3 to 0.5 μm at a wind speed of 3.2 m / min and calculated from the following formula (1) satisfies the following relationship: QFa1 / QFa2 ≤ 0.1, QFa2 / QFa3 ≥ 1.0, QF = -Ln(1 - I / 100) / P... (1). In formula (1), I represents the collection efficiency (%), and P represents the pressure loss (Pa).

6. The filter medium for an air filter according to claim 1 or 2, wherein the initial collection efficiency IA (%), the initial collection efficiency IB (%), and the initial collection efficiency IC (%) measured using charged NaCl particles with a particle diameter of 0.03 μm at a wind speed of 3.2 m / min, the initial collection efficiency IB (%) measured using charged NaCl particles with a particle diameter of 0.1 μm at a wind speed of 3.2 m / min, and the initial collection efficiency IC (%) measured using charged NaCl particles with a particle diameter of 0.3 μm at a wind speed of 3.2 m / min satisfy the following relationship: 0.01 ≤ (100 - IB) / (100 - IA) ≤ 0.8, 0.001 ≤ (100 - IC) / (100 - IA) ≤ 0.

3.

7. The filter medium for an air filter according to claim 1 or 2, wherein the initial QF value QFa of the filter medium for an air filter measured using charged NaCl particles with a particle diameter of 0.3 to 0.5 μm at a wind speed of 3.2 m / min and calculated from the following formula (1) satisfies the following relationship: QFa ≥ 0.07, QF = -Ln(1 - I / 100) / P... (1). In formula (1), I represents the collection efficiency (%), and P represents the pressure loss (Pa).

8. The filter medium for an air filter according to claim 1 or 2, wherein the initial QF value QFa3 of the third layer calculated from the following formula (1) satisfies the following relationship when measured using the charged NaCl particles with a particle size of 0.3 to 0.5 μm at a wind speed of 3.2 m / min. QFa3 ≧ 0.05 QF = -Ln(1 - I / 100) / P... (1) In formula (1), I represents the collection efficiency (%), and P represents the pressure loss (Pa).

12. The air permeability of the first layer is 100 to 600 cm ３ / cm ２ ·second, the filter medium for an air filter according to claim 1 or 2.

9. The initial QF value QFa of the filter medium for an air filter, the QF value QFaD2 after charging of the second layer, the QF value QFaD3 after charging of the third layer, and the overall QF value QFaDall after charging of the filter medium for an air filter, which are measured using the charged NaCl particles with a particle size of 0.3 to 0.5 μm at a wind speed of 3.2 m / min and calculated from the following formula (1), satisfy the following relationship. QFaD2 / QFa < 0.20 QFaD3 / QFa > 0.20 0.10 ≦ QFaDall / QFa ≦ 1.00 QF = -Ln(1 - I / 100) / P... (1) In formula (1), I represents the collection efficiency (%), and P represents the pressure loss (Pa).

10. The filter medium for an air filter according to claim 1 or 2, wherein the most penetrating particle size (MPPS) Mn (μm) of the collection efficiency of the nth layer measured using the charged NaCl particles with a particle size of 0.015 to 0.300 μm at a wind speed of 3.2 m / min satisfies the following relationship. M2 < 0.05 M3 > 0.05 11. The filter medium for an air filter according to claim 1 or 2, wherein an adsorbent layer is provided between the first layer and the second layer and / or between the second layer and the third layer in the filter medium for an air filter.

13. The filter medium for an air filter according to claim 1 or 2, wherein a fourth layer made of fibers with an average fiber diameter of 0.5 to 150 μm is provided on the downstream side of the third layer.

14. A method for manufacturing a filter medium for an air filter according to claim 1 or 2, comprising bonding the first layer and the second layer, and then laminating the third layer on the surface on the second layer side to form the filter medium for an air filter composed of the non-woven fabric layers of the first layer, the second layer, and the third layer.

15. A method for manufacturing a filter medium for an air filter according to claim 13, comprising laminating the third layer on the fourth layer, bonding the first layer and the second layer, and then bonding the surface of the second layer and the surface of the third layer.

16. A method for manufacturing a filter medium for an air filter according to claim 13, comprising bonding the first layer and the second layer, laminating the third layer on the surface of the second layer, and laminating the fourth layer on the surface of the third layer.

17. An air filter unit using the filter medium for an air filter according to claim 1 or 2.

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