Air filter medium and method for manufacturing the same

Abstract

To provide an air filter medium that has low pressure loss and high collection efficiency without using electrification treatment, and to provide a method for manufacturing the same.SOLUTION: An air filter medium includes a nonwoven fabric. The nonwoven fabric contains first fibers of which number average fiber diameter containing a first polymer having a glass transition temperature of -20 to 70°C is 3.0 μm or less; and second fibers of which number average fiber diameter containing a second polymer having a glass transition temperature of 80 to 160°C is 7.0 μm or more, where an apparent density is 0.085 g / cm3 or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a dust-removing air filter medium for filtering gas, particularly dust in the air, and more particularly to an air filter medium characterized by low pressure loss and high collection efficiency, and a method for producing the same. [Background technology]

[0002] In recent years, with the increasing interest in the health impact of living environment and the prevention of infectious diseases, there is a demand for the air purification of living spaces or offices.The method of removing dust suspended in the air is generally to use dust-removing air filters, and various dust-removing air filter media are used.As air filter media, there is a strong demand for filter media that can remove dust with low energy consumption, have low pressure loss and high collection efficiency.

[0003] Melt-blown nonwoven fabrics are widely used as air filter media. Melt-blown nonwoven fabrics with low pressure loss and high collection efficiency can be obtained by blending two types of long fibers made of different resins and producing a melt-blown nonwoven fabric with a specific volume of 12 cm3. 3 / g or more (see, for example, Patent Document 1); a filter medium made of a nonwoven fabric containing thin low-melting-point fibers made of a polyolefin resin and high-melting-point fibers with a fiber diameter of 20 to 100 μm, whereby the high-melting-point fibers are present in the cross section of the nonwoven fabric at least one fiber per 1.00 mm of cross-sectional length (see, for example, Patent Document 2); a filter medium made of a nonwoven fabric containing fibers made of a polyolefin resin with a fiber diameter of 7 μm or less and fibers with a fiber diameter of 15 to 100 μm, whereby the tensile strength in the longitudinal direction is 0.45 (N / 5cm) / (g / m 2 ) or more, and 6kg / cm 2 A filter medium made of a nonwoven fabric in which the rate of increase in pressure loss after application of a load is 25% or less has been proposed (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-40412 [Patent Document 2] WO2013 / 089213 publication [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-161041 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in order to obtain the air filter material that has both low pressure loss and high collection efficiency, the filter material that is made of mixed fiber melt-blown nonwoven fabric has been proposed.However, these filter materials are all made of the filter material that is made of electret nonwoven fabric that is charged, and when the charge of fiber surface is attenuated during use, there is a risk that collection efficiency will be greatly reduced.Therefore, the problem of the present disclosure is to provide the air filter material that has both low pressure loss and high collection efficiency and its manufacturing method without using charging treatment. [Means for solving the problem]

[0006] The present inventors have found that a meltblown nonwoven fabric containing a mixture of fine filtration fibers that contribute to particle capture and stiff, thick skeletal fibers that form appropriate gaps between the fine fibers can provide an air filter medium that combines low pressure loss and high collection efficiency, and have completed the present invention. That is, the air filter medium of the present invention is an air filter medium having a nonwoven fabric, wherein the nonwoven fabric contains first fibers containing a first polymer with a glass transition temperature of -20 to 70°C and having a number average fiber diameter of 3.0 μm or less, and second fibers containing a second polymer with a glass transition temperature of 80 to 160°C and having a number average fiber diameter of 7.0 μm or more, and the nonwoven fabric has an apparent density of 0.085 g / cm. 3 The present invention is characterized by the following:

[0007] In the air filter medium according to the present invention, the nonwoven fabric may be a melt-blown nonwoven fabric.

[0008] In the air filter medium according to the present invention, it is preferable that the first polymer is polypropylene and the second polymer is polycarbonate, which allows the air filter medium to have a higher QF (Quality Factor).

[0009] In the air filter medium according to the present invention, the volume ratio of the first fibers to the second fibers contained in the nonwoven fabric (first fibers / second fibers) is preferably 90 / 10 to 20 / 80. With this configuration, an air filter medium having a higher QF value can be obtained.

[0010] In the air filter medium according to the present invention, the volume ratio of the first fibers to the second fibers contained in the nonwoven fabric (first fibers / second fibers) is preferably 90 / 10 to 30 / 70. With this configuration, an air filter medium having a higher QF value can be obtained.

[0011] In the air filter medium according to the present invention, the QF value after static elimination treatment in which the air filter medium is exposed to saturated isopropanol vapor for 24 hours is preferably 0.0220 or more, and more preferably 0.0230 or more. (Number 1) QF value [1 / Pa] = {-ln(transmittance [%] / 100)} / pressure loss [Pa] Here, transmittance [%] = 100 - collection efficiency [%]

[0012] The method for producing an air filter medium according to the present invention includes a discharging step of discharging a first polymer having a glass transition temperature of −20 to 70° C. from a plurality of first nozzle holes and simultaneously discharging a second polymer having a glass transition temperature of 80 to 160° C. from a plurality of second nozzle holes; a drawing step of stretching the first polymer discharged from the first nozzle holes and the second polymer discharged from the second nozzle holes by blowing drawing air at 250 to 350° C. to form first fibers containing the first polymer and having a number average fiber diameter of 3.0 μm or less, and second fibers containing the second polymer and having a number average fiber diameter of 7.0 μm or more; and a drawing step of stretching the first fibers and the second fibers to form a fiber having an apparent density of 0.085 g / cm. 3 The method includes a collecting step of collecting the toner on a collecting surface as follows, and is characterized in that the hole diameter of the second nozzle hole is larger than the hole diameter of the first nozzle hole.

[0013] In the method for manufacturing an air filter medium according to the present invention, the first nozzle holes and the second nozzle holes are preferably arranged in a row in a direction transverse to the collecting surface, and the hole number ratio between the number of the first nozzle holes and the number of the second nozzle holes (first nozzle holes / second nozzle holes) is preferably 12 / 1 to 4 / 1. Such a configuration makes it easy to obtain an air filter medium with an optimal volume ratio of first fibers / second fibers.

[0014] In the method for manufacturing an air filter medium according to the present invention, the arrangement of the first nozzle holes and the second nozzle holes has an arrangement unit in which the first nozzle holes and the second nozzle holes are arranged at the hole number ratio, and the number of repetitions of the arrangement unit is preferably 10 to 200.

[0015] In the method for producing an air filter medium according to the present invention, it is preferable that the MFR of the first polymer is 500 to 2000 g / 10 min, the MFR of the second polymer is 30 to 300 g / 10 min, and the MFR of the first polymer is 5 times or more the MFR of the second polymer. This allows the second polymer to be sufficiently solidified when discharged from a second nozzle having a relatively large hole diameter.

[0016] In the method for producing an air filter medium according to the present invention, it is preferable that the second polymer is a hydrophilic polymer, and that the method further includes a resin drying step of drying the second polymer before the discharging step. Hydrophilic resins such as polycarbonate resins may contain moisture, which can cause large variations in viscosity of the molten resin during spinning or generate water vapor, making the resin discharge rate unstable and resulting in non-uniform fiber diameters. However, by removing the moisture in the resin through the resin drying step, fibers with a more uniform fiber diameter can be obtained.

[0017] In the method for producing an air filter medium according to the present invention, the collecting step includes a step of sucking air from the opposite side of the collecting surface, and the suction volume of the sucked air is 40,000 to 200,000 m 3 / hour / m 2 It is preferable that the apparent density can be more appropriately adjusted. [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide an air filter medium that combines low pressure loss and high collection efficiency without using an electrification treatment, and a method for manufacturing the same. [Brief explanation of the drawings]

[0019] [Figure 1] 2 is a schematic diagram showing an example of an arrangement of nozzle holes in a nozzle used in the method for manufacturing an air filter medium according to the present embodiment. FIG. [Figure 2] 1 is a schematic cross-sectional view showing an example of a melt-blowing device used in a method for producing an air filter medium according to the present embodiment. FIG. [Figure 3] 1 shows transmission images of the filter media of Example 5, Example 8, and Comparative Example 4 taken using an X-ray CT. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, one aspect of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that components with the same reference numerals in this specification and drawings indicate the same components. Various modifications may be made as long as the effects of the present invention are achieved.

[0021] The air filter medium according to this embodiment is an air filter medium having a nonwoven fabric, the nonwoven fabric containing first fibers having a number average fiber diameter of 3.0 μm or less and containing a first polymer having a glass transition temperature of −20 to 70° C., and second fibers having a number average fiber diameter of 7.0 μm or more and containing a second polymer having a glass transition temperature of 80 to 160° C., and the nonwoven fabric having an apparent density of 0.085 g / cm 3 The following is the result.

[0022] In the air filter medium according to the present embodiment, the type of nonwoven fabric is not particularly limited, and the nonwoven fabric may be, for example, a melt-blown nonwoven fabric manufactured by a melt-blowing method, a spun-bonded nonwoven fabric manufactured by a spun-bonding method, or an electrospun nonwoven fabric manufactured by an electrospinning method. Of these, in the air filter medium according to the present embodiment, the nonwoven fabric is preferably a melt-blown nonwoven fabric.

[0023] The air filter medium according to this embodiment has first fibers with a number-average fiber diameter of 3.0 μm or less. The first fibers are small-diameter filtration fibers that contribute to particle capture. The first polymer contained in the first fibers has a glass transition temperature of −20 to 70°C. If the glass transition temperature is lower than −20°C, the filter medium is likely to deform due to the tendency to relax at room temperature. If the glass transition temperature is higher than 70°C, efficient thinning by hot air during melt-blowing is difficult. The glass transition temperature of the first polymer is more preferably −20 to 50°C. The glass transition temperature of the polymer can be measured by the inflection point of differential scanning calorimetry.

[0024] The melting point of the first polymer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 80 to 300°C, and more preferably 160 to 200°C. A melting point of 80°C or higher facilitates the formation of continuous fibers, while a melting point of 300°C or lower facilitates melt molding. When the first polymer does not exhibit a constant melting point, it is preferable that the flow temperature of the first polymer be within the above range.

[0025] The first polymer is not particularly limited and can be appropriately selected depending on the purpose as long as it has a glass transition temperature of −20 to 70° C. Examples of such polymers include polypropylene resin, polyester resin, polyamide resin, polyurethane resin, and polyvinyl acetate resin, and polypropylene resin is preferred.

[0026] The number average fiber diameter of the first fibers is 3.0 μm or less, preferably 0.1 to 3.0 μm, and more preferably 0.1 to 2.0 μm. If the number average fiber diameter is 0.1 μm or more, voids are formed inside the filter medium, preventing excessive increases in pressure loss. If the number average fiber diameter is 3.0 μm or less, the surface area of ​​the fibers is increased, improving collection efficiency.

[0027] The first fibers are preferably made of only the first polymer, but may contain other components in addition to the first polymer as long as the effects of the present invention are not impaired. The other components may be, for example, a thermoplastic resin other than the first polymer, or various additives such as an antioxidant, a light stabilizer, or an ultraviolet absorber. The first fibers preferably do not contain an electret additive for enhancing electrostatic chargeability.

[0028] The air filter medium according to this embodiment has second fibers with a number-average fiber diameter of 7.0 μm or more. The second fibers are stiff, thick skeletal fibers that form appropriate gaps between the individual thin fibers (first fibers). The second polymer contained in the second fibers has a glass transition temperature of 80 to 160°C. If the glass transition temperature is lower than 80°C, the rigidity required for the skeletal fibers decreases. If the glass transition temperature is higher than 160°C, melt molding becomes difficult. The glass transition temperature of the second polymer is more preferably 90 to 150°C.

[0029] The melting point of the second polymer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 220 to 300° C., more preferably 220 to 280° C. A melting point of 220° C. or higher makes it easier to form thick, rigid fibers, while a melting point of 300° C. or lower facilitates melt molding. When the second polymer does not exhibit a melting point, it is preferable that the flow temperature of the second polymer is within the above range.

[0030] The second polymer is not particularly limited and can be appropriately selected depending on the purpose as long as it is a polymer having a glass transition temperature of 80 to 160° C. Examples of such polymers include polycarbonate resin, polysulfone resin, polyether ether ketone resin, and polyphenylene sulfide resin, with polycarbonate resin being preferred.

[0031] The number-average fiber diameter of the second fibers is 7.0 μm or more, preferably 8.0 μm or more, more preferably 10 to 60 μm, and even more preferably 20 to 60 μm. There is no particular upper limit to the number-average fiber diameter of the second fibers, but it is preferably 50 μm or less, and more preferably 40 μm or less. When the fiber diameter is 7.0 μm or more, the necessary rigidity as a skeletal fiber is obtained. When the fiber diameter exceeds 60 μm, the spaces between the thin fibers may become too large, which may reduce the collection efficiency.

[0032] The second fibers preferably consist solely of the second polymer, but may contain other components in addition to the second polymer as long as the effects of the present invention are not impaired. The other components may be, for example, thermoplastic resins other than the second polymer, or various additives such as antioxidants, light stabilizers, or UV absorbers. The second fibers preferably do not contain electret additives for enhancing electrostatic chargeability.

[0033] In the air filter material according to the present embodiment, the first polymer is preferably polypropylene, and the second polymer is preferably polycarbonate.According to this configuration, it is possible to obtain an air filter material with a higher QF value (Quality Factor).QF value is generally used as an index that represents the performance of filter material, and is a value calculated by the following formula 1.

[0034] The number-average fiber diameters of the first and second fibers are calculated as follows. The number-average fiber diameters are calculated by measuring the fiber diameters of 200 fibers in an image of the surface of a nonwoven fabric taken using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer. The method for distinguishing the first and second fibers is not particularly limited and can be selected appropriately depending on the type of polymer selected. For example, in the case where the first polymer is PP and the second polymer is PC, fibers that do not contain oxygen can be distinguished as PP fibers (first fibers) and fibers that contain oxygen can be distinguished as PC fibers (second fibers). The presence or absence of oxygen can be confirmed using an energy-dispersive X-ray analyzer.

[0035] The air filter medium according to this embodiment has an apparent density of 0.085 g / cm 3 Below 0.080g / cm 3 Preferably, it is 0.075 g / cm or less. 3 More preferably, it is 0.070 g / cm or less. 3 It is more preferable that the apparent density is 0.085 g / cm or less. 3A filter medium with a high QF value can be obtained by satisfying the above conditions. The lower limit of the apparent density is not particularly limited, but is preferably 0.050 g / cm3 from the viewpoint of the strength of the nonwoven fabric in the conveyor movement direction (MD) required for continuous production. 3 It is preferable that the concentration is 0.060 g / cm or more. 3 More preferably, it is equal to or greater than this. The apparent density is a value calculated by the equation 2 described below, and it can be said that the smaller the apparent density, the higher the bulk. The apparent density can be adjusted, for example, in the melt-blowing method, by adjusting the suction air volume when collecting the fibers. The smaller the suction air volume, the lower the apparent density tends to be.

[0036] In the air filter medium according to this embodiment, the nonwoven fabric preferably has a volume ratio of the first fibers to the second fibers (first fibers / second fibers) in the range of 90 / 10 to 20 / 80, more preferably 90 / 10 to 30 / 70, and even more preferably 85 / 15 to 40 / 60. This configuration allows for an air filter medium with a higher QF value. If the ratio of the first fibers is greater than 90 / 10, i.e., if the volume ratio of the first fibers to the total volume of the first fibers and the second fibers exceeds 90 volume%, it may be difficult to obtain a sufficient void formation effect by the second fibers. If the ratio of the first fibers is less than 20 / 80, i.e., if the volume ratio of the first fibers to the total volume of the first fibers and the second fibers is less than 20 volume%, it may be difficult to obtain a sufficient collection efficiency.

[0037] The air filter medium according to this embodiment may consist of only the nonwoven fabric (sometimes referred to as the main filter material nonwoven fabric) described above, or may be a laminate in which another sheet is laminated on the main filter material nonwoven fabric. The sheet laminated on the main filter material nonwoven fabric is, for example, a sheet with higher rigidity than the main filter material nonwoven fabric, or a sheet with functionality such as deodorizing or antibacterial. The form of the sheet laminated on the main filter material nonwoven fabric is not particularly limited, and may be, for example, a nonwoven fabric such as a dry nonwoven fabric, a wet nonwoven fabric, or a direct spun nonwoven fabric, a woven fabric, or a knit, and its material is not particularly limited, and may be, for example, a synthetic resin, a synthetic fiber, a natural fiber, an inorganic fiber, or a metal fiber. The basis weight of the main filter material nonwoven fabric according to this embodiment is not particularly limited, and may be 40 to 210 g / m 2 It is preferable that the density is 40 to 150 g / m 2 More preferably, it is 50 to 120 g / m 2 It is more preferable that it is. In addition, the apparent thickness of the primary filter medium nonwoven fabric according to this embodiment is not particularly limited, and is preferably 0.40 to 6.00 mm, more preferably 0.70 to 4.00 mm, more preferably 0.40 to 2.25 mm, and even more preferably 0.60 to 1.80 mm. The apparent thickness refers to the thickness measured when the measurement pressure applied between the pressure surfaces during thickness measurement is 0.4 kPa. The apparent thickness is preferably measured using an air-type thickness meter.

[0038] In the air filter medium according to the present invention, the QF value after static elimination treatment in which the filter medium is exposed to saturated isopropanol vapor for 24 hours is preferably 0.022 or more. The QF value after static elimination treatment is more preferably 0.024 or more. The static elimination treatment is performed in accordance with Annex C of JIS B 9927-5:2022 "High-performance particulate filters (EPA, HEPA, and ULPA) and filter media—Part 5: Test methods for filter units." (Number 1) QF value [1 / Pa] = {-ln(transmittance [%] / 100)} / pressure loss [Pa] Here, transmittance [%] = 100 - collection efficiency [%]

[0039] The method for producing an air filter medium according to this embodiment includes a discharge step of discharging a first polymer having a glass transition temperature of −20 to 70° C. from a plurality of first nozzle holes and simultaneously discharging a second polymer having a glass transition temperature of 80 to 160° C. from a plurality of second nozzle holes; a stretching step of stretching the first polymer discharged from the first nozzle holes and the second polymer discharged from the second nozzle holes by blowing stretching air at 250 to 350° C. to form first fibers containing the first polymer and having a number average fiber diameter of 3.0 μm or less, and second fibers containing the second polymer and having a number average fiber diameter of 7.0 μm or more; and a stretching step of stretching the first fibers and the second fibers to form fibers having an apparent density of 0.085 g / cm. 3 The method includes a collecting step of collecting the particles on a collecting surface as follows, wherein the hole diameter of the second nozzle hole is larger than the hole diameter of the first nozzle hole.

[0040] The method for producing the air filter medium according to this embodiment is a melt-blowing method, and includes a discharge step, a stretching step, and a collection step, and may further include other steps as necessary.

[0041] (Discharge process) The ejection step is a step in which a first polymer having a glass transition temperature of -20 to 70°C is ejected from a first nozzle hole, and simultaneously a second polymer having a glass transition temperature of 80 to 160°C is ejected from a second nozzle hole.

[0042] The first polymer and the second polymer are stirred and melted uniformly under constant temperature conditions in separate raw material tanks of the melt-blowing device.

[0043] The melting temperature is not particularly limited and can be selected depending on the melting point of each polymer. The melting temperature of the first polymer is preferably 150 to 250°C, more preferably 200 to 250°C. The melting temperature of the second polymer is preferably 200 to 300°C, more preferably 220 to 280°C.

[0044] The discharge rates of the first polymer and the second polymer are not particularly limited and can be appropriately selected depending on the purpose. The discharge rate of the first polymer is preferably 0.03 to 0.30 g / min / hole, more preferably 0.10 to 0.25 g / min / hole. The discharge rate of the second polymer is preferably 0.10 to 3.00 g / min / hole, more preferably 0.20 to 2.50 g / min / hole. This allows the desired fiber diameter to be achieved.

[0045] In the manufacturing method of the air filter medium according to this embodiment, the MFR of the first polymer is preferably 500 to 2000 g / 10 min, and the MFR of the second polymer is preferably 30 to 300 g / 10 min, and the MFR of the first polymer is preferably 5 times or more the MFR of the second polymer. This allows the second polymer to be sufficiently solidified when discharged from the second nozzle having a relatively large pore size. The MFR of the first polymer is more preferably 600 to 1800 g / 10 min. The MFR of the second polymer is more preferably 100 to 250 g / 10 min. The MFR of the first polymer is more preferably 6 times or more the MFR of the second polymer. The upper limit of the ratio of the MFR of the first polymer to the MFR of the second polymer is not particularly limited, but for example, the MFR of the first polymer is preferably 70 times or less, more preferably 50 times or less, the MFR of the second polymer. The MFR of the first polymer and the MFR of the second polymer may be the nominal values ​​of the resin manufacturer, or may be values ​​measured in accordance with JIS K 7210-1:2014 "Plastics - Determination of melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics - Part 1: Standard test method."

[0046] The diameters of the first nozzle hole and the second nozzle hole are not particularly limited and can be appropriately selected depending on the purpose. The diameter of the first nozzle hole is preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.4 mm. The diameter of the second nozzle hole is preferably 0.5 to 2.0 mm, more preferably 0.6 to 1.5 mm. This allows the desired fiber diameter to be achieved.

[0047] In the manufacturing method of the air filter medium according to this embodiment, the first nozzle holes and the second nozzle holes are preferably arranged in a row in a direction transverse to the collecting surface. In this case, the ratio of the number of the first nozzle holes to the number of the second nozzle holes (first nozzle holes / second nozzle holes) is preferably 12 / 1 to 4 / 1, more preferably 12 / 1 to 6 / 1. This configuration makes it easy to obtain an air filter medium with an optimal volume ratio of the first fibers to the second fibers. Here, the collecting surface is, for example, the nozzle-side surface of a collector, such as the conveyor transport surface or the outer peripheral surface of a drum, provided in a melt-blowing device. The collecting surface may also be a base fabric.

[0048] Furthermore, when the first nozzle holes and the second nozzle holes are arranged in a row, the arrangement of the first nozzle holes and the second nozzle holes in the nozzle of the melt-blowing device is not particularly limited and can be appropriately selected depending on the purpose, but the arrangement of the first nozzle holes and the second nozzle holes has an arrangement unit in which the first nozzle holes and the second nozzle holes are arranged at the above-mentioned hole number ratio, and the number of repetitions of the arrangement unit is preferably 10 to 200. The number of repetitions of the arrangement unit is more preferably 30 to 200.

[0049] The arrangement unit preferably has a plurality of first nozzle holes and one second nozzle hole, and the first nozzle holes are preferably arranged adjacent to each other, and the second nozzle holes are preferably arranged between the first nozzle holes. In this case, the pitch p1 between the first nozzle holes is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.3 to 1.5 mm, more preferably 0.7 to 1.2 mm. The pitch p1 between the first nozzle holes is the shortest distance between the circumferences of the opposing first nozzle holes. The pitch p2 between the first nozzle holes and the second nozzle holes is also not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.5 to 2.5 mm, more preferably 1.5 to 2.3 mm. The pitch p2 between the first nozzle holes and the second nozzle holes is the shortest distance between the circumferences of the opposing first nozzle holes and the second nozzle holes. This allows the voids in the filter medium to be appropriately adjusted. In addition, fibers discharged from adjacent nozzle holes are less likely to fuse together. In the arrangement unit, it is preferable that the second nozzle holes are not arranged adjacent to each other. This allows the voids in the filter medium to be adjusted appropriately.

[0050] An example of a nozzle of a melt-blowing device will be described below with reference to the drawings, but the method for producing an air filter medium of the present invention is not limited to this.

[0051] FIG. 1 is a schematic diagram showing an example of the arrangement of nozzle holes in a nozzle used in the manufacturing method of an air filter medium according to this embodiment. In FIG. 1, as an example, the nozzle 100 has an arrangement unit in which three consecutively arranged first nozzle holes 10, one second nozzle hole 11, and three consecutively arranged first nozzle holes are arranged in this order, and the nozzle holes of the arrangement unit (number of first nozzle holes / number of second nozzle holes / number of first nozzle holes = 3 / 1 / 3) are repeated 35 times. The present invention is not limited to this, and for example, the number of first nozzle holes 10 arranged on both sides of the second nozzle holes 11 in the arrangement unit shown in FIG. 1 can be changed, or the number of repetitions of the arrangement unit can be changed as appropriate. Furthermore, the number of first nozzle holes 10 arranged on both sides of the second nozzle holes 11 in the arrangement unit can be the same on the left and right sides of the second nozzle holes 11, as shown in FIG. 1, or can be different numbers.

[0052] The material for forming the nozzle 100 is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include copper, stainless steel, and aluminum.

[0053] FIG. 2 is a schematic cross-sectional view showing an example of a melt-blowing apparatus used in the manufacturing method of the air filter medium according to this embodiment. As shown in FIG. 2, the melt-blowing apparatus 200 preferably includes a first polymer raw material tank 20, a second polymer raw material tank 21, a collector 22, a first polymer supply path 23, a second polymer supply path 24, a stretching air flow path 29, and a nozzle 100. While the collector 22 in FIG. 2 has a conveyor 27 as an example, the present invention is not limited thereto and may have, for example, a drum. The collector 22 also preferably has an air suction section 26. By suctioning the mixed fibers 25 through the air suction section 26, the mixed fibers 25 can be deposited on the collector 22 more efficiently. The first polymer solution melted in the first polymer raw material tank 20 passes through the first polymer supply path 23 and is transported to the nozzle 100. At the same time, the second polymer solution melted in the second polymer raw material tank 21 passes through the second polymer supply path 24 and is conveyed to the nozzle 100. The first polymer solution and the second polymer solution simultaneously discharged from the nozzle 100 are cooled while being stretched by high-pressure stretching air A ejected from the stretching air flow path 29 to form a mixed fiber 25 of the first fiber and the second fiber, and the mixed fiber 25 is deposited on the collector 22 by the air suction unit 26. Thereafter, in the collector 22, a conveyor 27 conveys the deposited resin in the direction of the arrow at a predetermined conveying speed, thereby forming a continuous nonwoven fabric 28.

[0054] (Stretching process) The drawing step is a step in which a first polymer discharged from a first nozzle hole and a second polymer discharged from a second nozzle hole are drawn using drawing air at 250 to 350°C. The drawing air is heated air for drawing the first polymer and the second polymer. The drawn first polymer becomes a first fiber, and the drawn second polymer becomes a second fiber.

[0055] The temperature of the drawing air (hereinafter sometimes referred to as the hot air temperature) is 250 to 350°C. The hot air temperature is more preferably 280 to 320°C. If the hot air temperature is less than 250°C, the discharged resin pressure increases, making it impossible to obtain the desired fiber diameter. If the hot air temperature exceeds 350°C, gelation of the resin is accelerated, causing deterioration, and the nonwoven fabric becomes difficult to peel from the collector, making stable production impossible.

[0056] The flow rate of the drawing air (hereinafter also referred to as hot air volume) is not particularly limited and can be appropriately selected depending on the purpose. 3 / hour / m 2 It is preferable that the thickness is 400,000 to 700,000 m 3 / hour / m 2 It is more preferable that:

[0057] (Collection process) The collecting step is a step of collecting the first fibers and the second fibers. The collection is preferably performed by a windable collector. The windable collector is, for example, a collector equipped with a reel device for winding.

[0058] The collector winding speed (hereinafter also referred to as conveyor speed) is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.5 to 60 m / min, more preferably 1.5 to 40 m / min.

[0059] The distance between the nozzle surface of the die including the first and second nozzle holes and the collecting surface of the collector (die-collector distance) is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 100 to 500 mm, and more preferably 300 to 400 mm. The nozzle surface is the surface on which the first and second nozzle holes of the nozzle 100 are opened, and for example, when the die has a cross section in the shape of an inverted isosceles triangle as shown in Figure 2, the nozzle surface is the ridge line formed by the vertices of the isosceles triangle.

[0060] In the method for producing an air filter medium according to this embodiment, the collecting step includes a step of sucking air from the opposite side of the collecting surface, and the suction volume of the sucked air is 40,000 to 200,000 m 3 / hour / m 2 It is preferable that the above ratio is 10 to 40%. The apparent density can be adjusted more appropriately. The suction air is air for sucking the first fibers and the second fibers. When the suction step is included, the collection surface of the collector is preferably made of a material with high breathability, and the collection surface is preferably made of, for example, a wire mesh or a punched material. The porosity of the collection surface is preferably 10 to 40%, and more preferably 20 to 35%. If the porosity of the collection surface is less than 10%, it may not be possible to suction at the desired suction air volume. If the porosity of the collection surface is more than 40%, the first fibers and the second fibers may pass through the pores of the collection surface.

[0061] The collection method is not particularly limited and can be selected appropriately depending on the purpose, but a method of suctioning with air is preferred. The amount of suction when suctioning with suction air (hereinafter also referred to as suction air volume) is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 40,000 to 200,000 m 3 / hour / m 2 It is preferable that the thickness is 40,000 to 130,000 m 3 / hour / m 2 It is more preferable that the suction air volume is 200,000 m 3 / hour / m 2 The desired apparent density can be obtained by setting the suction air volume to 40,000 m 3 / hour / m 2 By doing so, it is possible to form the sheet without scattering the fibers.

[0062] (Other processes) The other steps are not particularly limited and can be selected appropriately depending on the purpose. Examples include a drying step for drying the obtained nonwoven fabric and a thickness adjusting step for adjusting the thickness of the nonwoven fabric.

[0063] In the manufacturing method of the air filter medium according to this embodiment, the second polymer is preferably a hydrophilic polymer, and the method further comprises a resin drying step of drying the second polymer before the discharge step.Hydrophilic resins such as polycarbonate resins may contain moisture in the resin, which may cause the viscosity of the molten resin to vary greatly during spinning, or may generate water vapor, making the discharge amount of the resin unstable, resulting in uneven fiber diameters.However, by removing the moisture in the resin through the resin drying step, fibers with a more uniform fiber diameter can be obtained.Hydrophilic polymers are, for example, polycarbonate, polyamide, and polyester.

[0064] The fiber diameters of the first fiber and the second fiber can be adjusted, for example, by adjusting the nozzle hole diameter within a predetermined range. However, this is not particularly limited in the present invention, and examples include appropriately designing the lip width and setback of the spinneret, or appropriately adjusting the polymer MFR, the discharge rate in the discharge step, and the hot air flow rate in the drawing step. For example, the smaller the lip width, the smaller the fiber diameter tends to be. The smaller the setback, the smaller the fiber diameter tends to be. The higher the polymer MFR, the smaller the fiber diameter tends to be. The lower the discharge rate in the discharge step, the smaller the fiber diameter tends to be. The higher the hot air flow rate in the drawing step, the smaller the fiber diameter tends to be. [Example]

[0065] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of added parts is a value converted into solid content.

[0066] (Example 1: Preparation of PP / PC blended fiber nonwoven fabric 1) A different diameter blending nozzle (see Figure 1) having the following configuration was attached to a melt-type composite nonwoven fabric manufacturing apparatus (model: MB-0300, manufactured by Nippon Nozzle Co., Ltd., see Figure 2) set under the following conditions, and using the following polymer raw materials, polypropylene (PP) resin was extruded from a nozzle with a hole diameter of 0.3 mm, and polycarbonate (PC) resin was extruded from a nozzle with a hole diameter of 0.7 mm, to produce PP / PC blended fiber nonwoven fabric 1. <Device> Nozzle angle (α): 60° Setback distance (ds): 0mm Air gap distance (da): 0.5mm Lip distance: 1mm Lip height: 1.4mm First polymer raw material tank temperature (melting temperature): 180℃ Second polymer raw material tank temperature (melting temperature): 250℃ <Nozzle> The width is 400 mm, and 35 repeating units each consisting of six first nozzle holes (hole diameter 0.3 mm) and one second nozzle hole (hole diameter 0.7 mm) are arranged. Pitch between first nozzle holes: 1.1 mm Pitch between the first and second nozzle holes: 2.2 mm <Polymer raw materials> First polymer: Polypropylene (PP) resin (Prime Polypro S13B, manufactured by Prime Polymer Co., Ltd., MFR: 700 g / 10 min, glass transition temperature: -10°C, melting point: 170°C) Second polymer: polycarbonate (PC) resin (Eupilon HL-7001, manufactured by Mitsubishi Engineering Plastics Corporation, MFR: 113 g / 10 min, glass transition temperature: 130°C, flow temperature: 220°C) The PC resin used was dried at 120° C. for 12 hours using a resin drying device (P-30CDBS, manufactured by Kawata Corporation). <Condition> Conveyor speed: 1.6m / min ·Hot air volume: 625000m 3 / hour / m 2 ·Hot air temperature: 280℃ Die-collector distance: 400 mm ·Suction air volume: 123300m 3 / hour / m 2 Total polymer discharge volume of the first nozzle hole: 37.5 cm 3 / min Total polymer discharge volume of the second nozzle hole: 7.5 cm 3 / min Polymer discharge volume per nozzle hole: 0.18 cm 3 / min / hole Polymer discharge volume per second nozzle hole: 0.21 cm 3 / min / hole

[0067] (Examples 2 to 8: Preparation of PP / PC blended fiber nonwoven fabrics 2 to 8) PP / PC mixed fiber nonwoven fabrics 2 to 8 were produced in the same manner as in Example 1, except that some of the <conditions> were changed to the conditions shown in Table 1 below.

[0068] (Example 9: Preparation of PP / PC blended fiber nonwoven fabric 9) A melt-type composite nonwoven fabric manufacturing apparatus (model: MB-0300, manufactured by Nippon Nozzle Co., Ltd., see Figure 2) was set under the following conditions, and a different-diameter blended fiber nozzle (see Figure 1) having the following configuration was attached to it. Using the following polymer raw materials, polypropylene (PP) resin was extruded from a 0.3 mm nozzle and polycarbonate (PC) resin was extruded from a 0.7 mm nozzle to produce PP / PC blended fiber nonwoven fabric 9. <Device> Nozzle angle (α): 60° Setback distance (ds): -0.25mm Air gap distance (da): 0.5mm Lip distance: 1mm Lip height: 1.4mm First polymer raw material tank temperature (melting temperature): 180℃ Second polymer raw material tank temperature (melting temperature): 250℃ <Nozzle> The width is 400 mm, and 35 repeating units each consisting of six first nozzle holes (hole diameter 0.3 mm) and one second nozzle hole (hole diameter 0.7 mm) are arranged. Pitch between first nozzle holes: 1.1 mm Pitch between the first and second nozzle holes: 2.2 mm <Polymer raw materials> First polymer: polypropylene (PP) resin (PWHOON NE051183, manufactured by SunAllomer Co., Ltd., MFR: 1800 g / 10 min, glass transition temperature: -10°C, melting point: 170°C) Second polymer: polycarbonate (PC) resin (Eupilon HL-7001, manufactured by Mitsubishi Engineering Plastics Corporation, MFR: 113 g / 10 min, glass transition temperature: 130°C, flow temperature: 220°C) The PC resin used was dried at 120° C. for 12 hours using a resin drying device (P-30CDBS, manufactured by Kawata Corporation). <Condition> Conveyor speed: 1.6m / min ·Hot air volume: 625000m 3 / hour / m 2 ·Hot air temperature: 280℃ Die-collector distance: 400 mm ·Suction air volume: 70500m 3 / hour / m 2 Total polymer discharge volume of the first nozzle hole: 37.5 cm 3 / min Total polymer discharge volume of the second nozzle hole: 7.5 cm 3 / min Polymer discharge volume per nozzle hole: 0.18 cm 3 / min / hole Polymer discharge volume per second nozzle hole: 0.21 cm 3 / min / hole

[0069] (Examples 10 to 14: Preparation of PP / PC blended fiber nonwoven fabrics 10 to 14) PP / PC mixed fiber nonwoven fabrics 10 to 14 were produced in the same manner as in Example 9, except that some of the <conditions> were changed to the conditions shown in Table 2 below.

[0070] (Comparative Example 1: Preparation of PP nonwoven fabric 1) PP nonwoven fabric 1 was produced in the same manner as in Example 1, except that only the first polymer was used without the second polymer of the <polymer raw materials>, the lip distance of the <device> was set to 0.5 mm, the conveyor speed of the <conditions> was set to 1.7 m / min, and the conditions were changed to those shown in Table 1 below.

[0071] (Comparative Examples 2 to 4: Preparation of PP / PP Blended Fiber Nonwoven Fabrics 1 to 3) PP / PP blended fiber nonwoven fabrics 1 to 3 were produced in the same manner as in Example 1, except that a polypropylene (PP) resin (Prime Polypro S119, manufactured by Prime Polymer Co., Ltd., MFR: 60 g / 10 min, glass transition temperature: -10°C, melting point: 170°C) was used as the second polymer of the <polymer raw material>, the temperature of the second polymer tank of the <apparatus> was set to 180°C, and some of the <conditions> were changed to the conditions shown in Table 1 below.

[0072] [Table 1]

[0073] [Table 2]

[0074] The air filter media obtained in the examples and comparative examples were evaluated using the following methods.

[0075] <Number average fiber diameter> The number-average fiber diameter was determined by measuring the fiber diameters of 200 fibers in photographs taken using a scanning electron microscope (SU8010, Hitachi High-Technologies Corporation) equipped with an energy dispersive X-ray analyzer (EMAX X-act, Horiba, Ltd.). Regarding the distinction between the first and second fibers, for PP / PC blended nonwoven fabrics, fibers that did not contain oxygen were designated as PP fibers, and fibers that contained oxygen were designated as PC fibers. For PP / PP blended nonwoven fabrics where it was impossible to distinguish between the first and second fibers, measurements were not performed.

[0076] <Metsuke> The basis weight was measured according to ISO 9073-1.

[0077] <Apparent thickness and apparent density> The apparent thickness was measured at a measurement pressure of 0.4 kPa using an air-type offline thickness meter (manufactured by Yamabun Denki Co., Ltd.) The apparent density was calculated using the following formula (2). (Number 2) Apparent density [g / cm 3 ]=(weight [g / m 2 ] / apparent thickness [mm]) x 1000

[0078] <Static charge removal treatment> Prior to the measurements, samples used for pressure drop and transmittance measurements were subjected to static elimination treatment by exposing them to saturated isopropanol vapor for 24 hours in accordance with Appendix C of JIS B 9927-5:2022. This ensured that the samples used for pressure drop and transmittance measurements were in an uncharged state.

[0079] <Pressure loss> Pressure loss is calculated for an effective area of ​​100 cm 2 The differential pressure when air was passed through the air filter medium at a surface velocity of 5.3 cm / sec was measured for the samples that had been subjected to the above-mentioned static elimination treatment using a manometer (Manostar Gauge WO81, manufactured by Yamamoto Electric Works, Ltd.).

[0080] <Transmittance> The transmittance was measured for the sample that had undergone the charge removal treatment. Air containing polydisperse polyalphaolefin (PAO) particles generated using a Ruskin nozzle was passed through an air filter medium with an effective area of 100 cm 2 at a face velocity of 5.3 cm / sec. The number of PAO particles upstream and downstream was measured using a laser particle counter (KC-22B, manufactured by Rion Co., Ltd.), and the transmittance was determined from the ratio of the upstream and downstream particles. The target particle diameter was 0.3 μm, and it was determined as the geometric mean value of the transmittance at 0.2 - 0.3 μm and 0.3 - 0.4 μm.

[0081] <QF value> The QF value was calculated using the formula shown in Equation (1) from the values of the pressure loss and the transmittance. The target particle diameter was 0.3 μm. A higher QF value means that the filter medium has a high collection efficiency (i.e., a low transmittance) at a low pressure loss. (Equation (1)) QF value [1 / Pa] = {-ln(transmittance [%] / 100)} / pressure loss [Pa] Here, transmittance [%] = 100 - collection efficiency [%]

[0082] <X-ray CT imaging> X-ray CT imaging was performed using an X-ray CT (SkyScan1272, manufactured by Bruker). The imaging conditions were a voltage of 40 kV, a current of 200 μA, a resolution of 1 μm / pixel, a pixel number of 2452×1640 pixels, and a rotation angle of 0.1°.

[0083] The evaluation results of the air filter medium obtained by the above method are shown in Tables 3 and 4.

[0084]

Table 3

[0085]

Table 4

[0086] As shown in Tables 3 and 4, Examples 1 to 5 have lower apparent densities and higher QF values ​​after static elimination than Comparative Examples 1 to 4. This confirms that high QF values ​​can be obtained without electrostatic charging, and that blending PC fiber with PP fiber changes the filter medium structure and improves the QF value. Furthermore, a comparison of Examples 9 to 14 with Comparative Example 5 also confirmed the same effect of blending.

[0087] As shown in Tables 3 and 4, Examples 6 to 8 had lower apparent densities and higher QF values ​​than Examples 1, 2, and 5, confirming that adjusting the suction air volume reduced the apparent density and improved the QF value.

[0088] FIG. 3 shows transmission images of the filter media of Example 4, Example 8, and Comparative Example 4, in which the fiber volume ratio of the first fiber / second fiber is 42 / 58, taken using X-ray CT. Here, CD is the width direction of the collection surface (e.g., conveyor), ND is the thickness direction of the nonwoven fabric, the bottom end of the photograph is the conveyor side, and the top end of the photograph is the nozzle side. In FIG. 3, the fibers that appear relatively thin are the first fibers, and the fibers that appear relatively thick are the second fibers. In Examples 5 and 8, the thickness of the filter media is greater than in Comparative Example 4. In Example 8, the thickness of the filter media is even greater than in Example 5. From these photographs, it can be seen that the thickness of the filter media increases and the apparent density decreases. As a result, it was confirmed that the QF value of the filter media increases even when not subjected to electrostatic treatment. From this, it can be said that the presence of the second fibers contributes to the reduction of the apparent density of the filter media and the increase of the QF value. [Explanation of symbols]

[0089] 100 nozzles 200 Melt-blowing equipment 10 First nozzle hole 11 Second nozzle hole 20. First polymer raw material tank 21 Second polymer raw material tank 22 Collector 23 First polymer supply route 24 Second polymer supply route 25 Blended Fiber 26 Air suction section 27 Conveyor 28 Nonwoven fabric 29 Stretched air channel A. Stretching air p1 Pitch between first nozzle holes p2 Pitch between the first nozzle hole and the second nozzle hole

Claims

1. An air filter medium having a nonwoven fabric, The nonwoven fabric contains first fibers containing a first polymer having a glass transition temperature of −20 to 70° C. and having a number average fiber diameter of 3.0 μm or less, and second fibers containing a second polymer having a glass transition temperature of 80 to 160° C. and having a number average fiber diameter of 7.0 μm or more, and has an apparent density of 0.085 g / cm ３ An air filter medium characterized by the following:

2. 2. The air filter medium according to claim 1, wherein the nonwoven fabric is a melt-blown nonwoven fabric.

3. 3. The air filter medium according to claim 1, wherein the first polymer is polypropylene and the second polymer is polycarbonate.

4. The air filter medium according to claim 1 or 2, characterized in that the volume ratio of the first fibers to the second fibers contained in the nonwoven fabric (first fibers / second fibers) is 90 / 10 to 20 / 80.

5. The air filter medium according to claim 1 or 2, characterized in that the volume ratio of the first fibers to the second fibers contained in the nonwoven fabric (first fibers / second fibers) is 90 / 10 to 30 / 70.

6. 3. The air filter medium according to claim 1, wherein the QF value after a static elimination treatment in which the air filter medium is exposed to saturated isopropanol vapor for 24 hours is 0.022 or more.

7. a discharge step of discharging a first polymer having a glass transition temperature of −20 to 70° C. from a plurality of first nozzle holes and simultaneously discharging a second polymer having a glass transition temperature of 80 to 160° C. from a plurality of second nozzle holes; a drawing step of drawing the first polymer discharged from the first nozzle holes and the second polymer discharged from the second nozzle holes by blowing drawing air at 250 to 350°C to form first fibers containing the first polymer and having a number average fiber diameter of 3.0 μm or less, and second fibers containing the second polymer and having a number average fiber diameter of 7.0 μm or more; The first fibers and the second fibers are woven into a woven fabric having an apparent density of 0.085 g / cm ３ collecting on a collection surface such that: The method for manufacturing an air filter medium is characterized in that the hole diameter of the second nozzle hole is larger than the hole diameter of the first nozzle hole.

8. the first nozzle hole and the second nozzle hole are arranged in a line in a direction transverse to the collection surface, The manufacturing method of the air filter medium according to claim 7, characterized in that the number ratio of the number of the first nozzle holes to the number of the second nozzle holes (first nozzle holes / second nozzle holes) is 12 / 1 to 4 / 1.

9. an arrangement of the first nozzle holes and the second nozzle holes has an arrangement unit in which the first nozzle holes and the second nozzle holes are arranged at the hole number ratio; The method for producing an air filter medium according to claim 8, wherein the number of repetitions of the arrangement unit is 10 to 200.

10. The MFR of the first polymer is 500 to 2000 g / 10 min, and The second polymer has an MFR of 30 to 300 g / 10 min, and 9. The method for manufacturing an air filter medium according to claim 7, wherein the MFR of the first polymer is at least five times the MFR of the second polymer.

11. the second polymer is a hydrophilic polymer, 9. The method for manufacturing an air filter medium according to claim 7, further comprising a resin drying step of drying the second polymer before the discharging step.

12. the collecting step includes a step of sucking air from the opposite side of the collecting surface, The suction volume of the suction air is 40,000 to 200,000 m ３ / hour / m ２ 9. The method for producing an air filter medium according to claim 7, wherein the air filter medium is

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