Meltblown nonwoven fabric and filter having the same

Abstract

The present invention provides a melt-blown nonwoven fabric, which comprises a plurality of thermoplastic resin fibers with different fiber diameters, wherein the standard deviation of the fiber diameters is greater than 1.2, and the ratio of the evenness index to the average fiber diameter is less than 33.

Description

Technical Field

[0001] The present invention relates to a melt-blown nonwoven fabric and a filter comprising the melt-blown nonwoven fabric. Background Art

[0002] Meltblown nonwoven fabrics are widely used as filters for substances such as gases and liquids. In order to capture more substances for a longer period of time, the filter life is required to be extended.

[0003] Meltblown nonwoven fabrics are produced by discharging a molten polymer from multiple meltblowing nozzles spaced at regular intervals and spinning the discharged molten polymer. While the nozzle aperture is typically constant, the applicant has previously demonstrated that using nozzles with different apertures, each containing smaller and larger diameter nozzles at a specific ratio, to produce meltblown nonwoven fabrics with a wider fiber diameter distribution compared to meltblown fabrics produced using conventional nozzles (Patent Document 1). A wide fiber diameter distribution allows for more uniform capture of substances not only on the surface of the nonwoven fabric but also within its interior, resulting in filters that are less susceptible to clogging and have a longer filtration life.

[0004] Patent Document 2 describes the use of a nozzle sheet with a different ratio from that in Patent Document 1, comprising small-aperture and large-aperture nozzles, to produce a meltblown nonwoven fabric having a cumulative frequency of 5% or more for fibers with a diameter of 1 μm or less and a cumulative frequency of 0.1% to 5% for fibers with a diameter of 10 μm or greater. This meltblown nonwoven fabric exhibits excellent sound absorption properties.

[0005] Patent Document 3 discloses a high-bulk nonwoven web having a wide fiber diameter, produced by spinning a plurality of filaments discharged from 2 to 20 rows of multi-stage nozzles.

[0006] Patent Document 4 discloses a method for producing a blended fiber nonwoven fabric, in which the resin constituting the fiber group A and the resin constituting the fiber group B are melted using separate extruders and discharged from separate spinning holes, the polymer single-hole discharge rate from the discharge holes of the fiber group A being reduced, and the polymer single-hole discharge rate from the discharge holes of the fiber group B being set to a large value, thereby obtaining a blended fiber nonwoven fabric having a desired single fiber diameter.

[0007] Patent Document 5 discloses that polypropylene and polypropylene wax are used as the raw materials of thermoplastic resin fibers contained in the nonwoven fabric, and a nonwoven fabric having two peaks in fiber diameter of thermoplastic resin fibers is produced using a nozzle having a single nozzle aperture.

[0008] Patent Document 6 discloses a nonwoven fabric characterized by a volume fraction of less than 40% of fibers having an average fiber diameter of 0.8 μm or less and 1.0 μm or less. In the method for producing the nonwoven fabric, the die temperature is set so that the resin discharge rate per spinning nozzle is at least 0.01 g / min and the polymer pressure in the die section is at least 2.3 MPa. A single spinning nozzle is used.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 11-131353

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-147771

[0013] Patent Document 3: Japanese Patent Application No. 2020-505530

[0014] Patent Document 4: Japanese Patent Application Laid-Open No. 2016-160542

[0015] Patent Document 5: WO2017 / 142021

[0016] Patent Document 6: WO2018 / 030057 Summary of the Invention

[0017] Using nozzles with varying aperture diameters can extend filter life compared to using a single-diameter nozzle. However, nozzle design limitations limit the range of polymer fiber diameters that can be produced. For example, thinning the fibers makes it difficult for the resin to escape from the small-diameter nozzle holes, causing thin fibers to break and resulting in a large amount of polymer clumps (shouts), potentially degrading the appearance and quality of the nonwoven fabric. On the other hand, thickening the fibers increases the unevenness of the nonwoven fabric's appearance, resulting from areas with denser fibers and areas with coarser meshes. This increases the variation in physical properties and can lead to the generation of shouts caused by insufficient cooling of the coarse fibers, potentially degrading the quality of the nonwoven fabric.

[0018] If the unevenness caused by the density of fibers in a meltblown nonwoven fabric can be suppressed and the distribution range of the fiber diameter can be further expanded, the ability to capture substances will be improved, and the demand for a longer life of the filter can be achieved.

[0019] An object of the present invention is to provide a melt-blown nonwoven fabric having a wide distribution range of fiber diameters and little unevenness caused by the density of the fibers.

[0020] Under the above circumstances, the present inventors conducted intensive research and found that, in a meltblown nonwoven fabric comprising a plurality of thermoplastic resin fibers having different fiber diameters, the above-mentioned problems can be solved by setting the standard deviation of the fiber diameters to 1.2 or greater and the ratio of the evenness index to the average fiber diameter to less than 33. Accordingly, the present invention includes the embodiments described below.

[0021] <1> A meltblown nonwoven fabric comprising a plurality of thermoplastic resin fibers having different fiber diameters, wherein the standard deviation of the fiber diameters is greater than 1.2 and the ratio of the evenness index to the average fiber diameter is less than 33.

[0022] <2> . <1> A meltblown nonwoven fabric, wherein the proportion of thermoplastic resin fibers having a fiber diameter that is 2.5 times or more of the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is 4% or more.

[0023] <3> . <1> or <2> A meltblown nonwoven fabric, wherein the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less of the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is 46% or more.

[0024] <4> . <1> ~ <3> The melt-blown nonwoven fabric according to any one of the preceding claims, wherein the average fiber diameter of the thermoplastic resin fibers is 1 μm to 50 μm.

[0025] <5> . <1> ~ <4> The melt-blown nonwoven fabric according to any one of the preceding claims, wherein the resin component of the thermoplastic resin fiber is at least one selected from the group consisting of polyolefin, polyester, and polyamide.

[0026] <6> A filter having <5> meltblown nonwoven fabric.

[0027] The present invention provides a meltblown nonwoven fabric with a wide fiber diameter distribution range and minimal fiber density variations. This nonwoven fabric is less likely to lose thickness even when subjected to pressure, and its air permeability is less likely to decrease after filtering. Consequently, filters using this nonwoven fabric have a high ability to maintain their fiber structure and are expected to have a longer lifespan. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process of the method for producing the meltblown nonwoven fabric of the present invention.

[0029] Figure 2 (A) means Figure 1 A partial front view of the arrangement of the spinning nozzles in the nozzle portion 3c of the device. Figure 2 (B) is a partial perspective view of the nozzle 3c. Figure 2 (C) is Figure 2(A) is a cross-sectional view of the nozzle 3 c taken along the line X1 - X1 .

[0030] Figure 3 This is a graph showing the particle filtration efficiency of the meltblown nonwoven fabrics of Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments for implementing the present invention will be described. The embodiments described below are examples of representative embodiments of the present invention, and the present invention is not limited thereto.

[0032] The present invention provides a melt-blown nonwoven fabric, which comprises a plurality of thermoplastic resin fibers with different fiber diameters, wherein the standard deviation of the fiber diameters is greater than 1.2, and the ratio of the evenness index to the average fiber diameter is less than 33.

[0033] The standard deviation of the fiber diameter of the meltblown nonwoven fabric of the present invention is greater than 1.2. If the standard deviation of the fiber diameter is greater than 1.2, the distribution range of the fiber diameter is large, and finer fibers and thicker fibers are mixed. When used as a filter, fine fibers ensure high particle capture capacity, and thick fibers suppress compression caused by filtration pressure, which can capture more particles in the thickness direction, thereby improving the filter life. If the standard deviation of the fiber diameter is less than 1.2, fibers with a certain limited range of fiber diameters account for the majority of the fibers constituting the nonwoven fabric. If the preference is for fine fibers, the particle capture capacity is improved, but the gaps between the fibers are destroyed due to filtration pressure, making it difficult to restore to the original structure, and therefore prone to clogging. In addition, if the preference is for coarse fibers, the unevenness caused by the density of the fibers becomes larger, the texture is poor, and the particle capture capacity is insufficient.

[0034] In the present invention, the average fiber diameter of the meltblown nonwoven fabric, that is, the average fiber diameter of the fibers constituting the meltblown nonwoven fabric, is calculated as follows: in an electron microscope photograph of the meltblown nonwoven fabric, four images are taken at a magnification such that about 25 fibers are included in each image, and the fiber diameters of a total of 100 randomly selected fibers are measured to a diameter of 0.1 μm, and the average is calculated.

[0035] In the present invention, the standard deviation u of the fiber diameter is the fiber diameter x of each fiber calculated from 100 fibers in the electron microscope photograph. i and average fiber diameter x ave , and the value obtained by the following formula (1).

[0036] [Mathematical formula 1]

[0037] ;

[0038] n is the total number of fibers measured (n=100), xi is the value of the fiber diameter of each fiber, x ave is the value of the average fiber diameter.

[0039] In the melt-blown nonwoven fabric of the present invention, the ratio of thermoplastic resin fibers having a fiber diameter that is 2.5 times or more of the average fiber diameter among the thermoplastic resin fibers in the melt-blown nonwoven fabric is 4% or more.

[0040] The ratio of thermoplastic resin fibers having a fiber diameter that is 2.5 times or greater than the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is a value obtained by randomly selecting 100 fibers from an electron micrograph of the meltblown nonwoven fabric, measuring the fiber diameter of each fiber to the order of 0.1 μm, calculating the average fiber diameter of the 100 fibers, and then dividing the number of thermoplastic resin fibers having a fiber diameter that is 2.5 times or greater than the average fiber diameter by 100 and multiplying the result by 100.

[0041] If the proportion of thermoplastic resin fibers having a fiber diameter that is 2.5 times or more of the average fiber diameter is 4% or more, fibers having a relatively large average fiber diameter are present in the meltblown nonwoven fabric, which ensures gaps between the fibers of the meltblown nonwoven fabric, increases air permeability, and improves compression resistance.

[0042] The upper limit of the proportion of thermoplastic resin fibers having a large average fiber diameter is not particularly limited. However, in some embodiments, from the perspectives of reducing unevenness caused by the density of the fibers in the meltblown nonwoven fabric and particle collection efficiency, the upper limit of the proportion of thermoplastic resin fibers having a fiber diameter of 5 times or greater than the average fiber diameter is preferably 20% or less. The proportion of thermoplastic resin fibers having a fiber diameter of 5 times or greater than the average fiber diameter is determined by measuring the diameter of 100 fibers (n=100) randomly selected from a photograph of the surface of the nonwoven fabric taken using an electron microscope, and the resultant value is expressed as: the number of fibers having a fiber diameter of 5 times or greater than the average fiber diameter / the total number of fibers measured (n=100) × 100.

[0043] The melt-blown nonwoven fabric of the present invention preferably contains 46% or more of thermoplastic resin fibers having a fiber diameter of 0.75 times or less of the average fiber diameter among the thermoplastic resin fibers in the melt-blown nonwoven fabric.

[0044] The ratio of thermoplastic resin fibers having a fiber diameter of 0.75 times or less of the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is a value obtained by randomly selecting 100 fibers from an electron micrograph of the meltblown nonwoven fabric, measuring the fiber diameter of each fiber down to the 0.1 μm diameter, calculating the average fiber diameter of the 100 fibers, and then dividing the number of thermoplastic resin fibers having a fiber diameter of 0.75 times or less of the average fiber diameter by 100 and multiplying the result by 100.

[0045] If the proportion of thermoplastic resin fibers having a fiber diameter of less than 0.75 times the average fiber diameter is 46% or more, fibers having a relatively small average fiber diameter are present in a larger proportion in the meltblown nonwoven fabric, the unevenness caused by the density of the fibers in the meltblown nonwoven fabric is reduced, and the particle collection efficiency becomes good.

[0046] The meltblown nonwoven fabric of the present invention has a wide fiber diameter distribution range and minimal variations due to fiber density. Even when pressure is applied, the nonwoven fabric's thickness is less likely to decrease, and its air permeability is less likely to decrease after filtering the target substance (hereinafter sometimes referred to simply as "substance"). Consequently, filters using this nonwoven fabric have a high ability to maintain their fiber structure, and can be expected to have superior filtration performance and a long life.

[0047] The ratio of the evenness index to the average fiber diameter of the meltblown nonwoven fabric of the present invention is less than 33. When the ratio of the evenness index to the average fiber diameter is less than 33, the unevenness caused by fiber density is reduced, resulting in a more uniform texture and a stable high capture capacity. When the ratio of the evenness index to the average fiber diameter is greater than 33, the unevenness caused by fiber density is large, and there are areas with large gaps between fibers, resulting in unstable particle capture efficiency, which is not preferred.

[0048] The uniformity index of a nonwoven fabric is an indicator of the weight per unit area of a fine unit and is an index that indicates the uniformity of the fiber orientation. The uniformity index of a nonwoven fabric can be calculated by irradiating a sample with transmitted light and using the density distribution of the image. The smaller the uniformity index, the higher the uniformity. In addition, the smaller the uniformity index, the higher the nonwoven fabric's ability to capture substances. Specifically, the measurement uses a transmission uniformity meter (FMT-M III manufactured by Nomura Corporation). Without setting a sample, a CCD camera is used to measure the amount of transmitted light when the light source is on and when it is off. Next, the amount of transmitted light is measured in the same manner when the nonwoven fabric is cut into A4 size, and the average transmittance, average absorbance, and standard deviation are calculated. The uniformity index can be calculated by dividing the standard deviation by the average absorbance by 1000.

[0049] The average fiber diameter of the meltblown nonwoven fabric of the present invention is not particularly limited, but is preferably 1 to 50 μm from the perspective of fluid filter use and compression resistance. In some embodiments, the average fiber diameter is 1 to 40 μm. In other embodiments, the average fiber diameter is 1 to 10 μm.

[0050] The unit weight of the meltblown nonwoven fabric of the present invention is not particularly limited, but the average unit weight is preferably in the range of 5 to 150 g / m 2 , more preferably 20 to 100 g / m 2 , more preferably 40 to 90 g / m 2 From the perspective of improving strength (if the strength is improved, it is easy to process into a filter), and from the perspective of suppressing excessive rigidity during filtration and improving the adhesion with other materials to achieve more uniform lamination (more uniform lamination brings effective filtration performance), it is preferred that the average unit area weight of the meltblown nonwoven fabric be set to the above range. The unit area weight is preferably 40g / m 2 More than 45g / m 2 When the ratio of the evenness index to the average fiber diameter is less than 33, it is easier to achieve.

[0051] In some embodiments of the preferred meltblown nonwoven fabric, when the average fiber diameter is 1 to 10 μm, the weight per unit area is 60 g / m 2 In some preferred embodiments of the meltblown nonwoven fabric, when the average fiber diameter is 1 to 5 μm, the weight per unit area is 60 g / m 2 In some preferred embodiments of the meltblown nonwoven fabric, when the average fiber diameter is 5 to 10 μm, the weight per unit area is 80 g / m 2 above.

[0052] The thickness of the meltblown nonwoven fabric of the present invention is not particularly limited, but the average thickness of one sheet of the meltblown nonwoven fabric is preferably 0.01 to 10 mm, more preferably 0.1 to 5 mm.

[0053] The air permeability of the meltblown nonwoven fabric of the present invention is not particularly limited, but is preferably 1 to 1700 cm / s as measured using a Frazier tester in accordance with JIS L1096 for a 100 mm x 100 mm meltblown nonwoven fabric test piece. 3 / cm 2 / second, more preferably 10 to 800 cm 3 / cm 2 From the viewpoint of suppressing an increase in pressure resistance during filtration and obtaining a nonwoven fabric having a predetermined strength, the air permeability of the meltblown nonwoven fabric is preferably within the above range.

[0054] In some embodiments, the average fiber diameter of the thermoplastic resin fiber is 5 μm or more, and the air permeability of the meltblown nonwoven fabric is 50 cm 3 / cm 2 In other embodiments, the average fiber diameter of the thermoplastic resin fiber is 5 μm to 50 μm, and the air permeability of the meltblown nonwoven fabric is 50 cm 3 / cm 2 / second~400cm 3 / cm 2 In other embodiments, the average fiber diameter of the thermoplastic resin fiber is greater than 1 μm and less than 5 μm, and the air permeability of the meltblown nonwoven fabric is 1 to 50 cm 3 / cm 2 / Second.

[0055] The bulk of the meltblown nonwoven fabric of the present invention is not particularly limited, and the bulk of the meltblown nonwoven fabric of the present invention is not particularly limited. 2 For meltblown nonwoven fabrics, the number of transparent spots (resin blocks) with a diameter of 0.5 mm or more is 3 per m 2 Below, preferably 1 / m 2 If there are loose particles in the meltblown nonwoven fabric, the maximum pore size around the loose particles becomes larger, and the filtration performance decreases.

[0056] The bursting strength of the meltblown nonwoven fabric of the present invention is not particularly limited, but is preferably 100 kPa or greater, more preferably 150 kPa or greater, more preferably 160 kPa or greater, and more preferably 170 kPa or greater, when the average fiber diameter is 1 to 5 μm. It is preferably 150 kPa or greater, more preferably 190 kPa, when the average fiber diameter is 5 to 50 μm. Uneven fiber density in the meltblown nonwoven fabric can reduce the pressure resistance of the filter medium when used as a filter, potentially leading to membrane rupture. The upper limit of the bursting strength is not particularly limited, but due to concerns about reduced processability of the meltblown nonwoven fabric, it is generally preferably 1000 kPa or less, more preferably 500 kPa or less. The bursting strength of the meltblown nonwoven fabric is the average of three measurements performed using a Toyo Seiki Mullen Burst Tester M2-LD in accordance with JIS P8112:2008.

[0057] The higher the basis weight, the higher the bursting strength. Therefore, although not particularly limited, the bursting strength / basis weight is 2 or more, more preferably 2.2 or more.

[0058] The pore size of a meltblown nonwoven fabric is the gap between fibers. It can be adjusted by adjusting the fiber diameter, fiber diameter distribution, basis weight, thickness, and other factors. When used as a filter, the preferred pore size varies depending on the particle size of the substance to be captured. Generally, from the perspective of particle capture capacity, smaller maximum pore diameters, minimum pore diameters, and average pore diameters are preferred, while from the perspective of filter life, larger pore diameters are preferred. Pore diameters (maximum pore diameter, minimum pore diameter, and average pore diameter) are measured using the bubble point method (ASTM F316-86, JIS K3832). From the perspective of particle capture capacity and filter life, the average pore diameter is preferably within the range of 5 to 50 μm.

[0059] The initial water flow rate indicates the amount of pure water that can pass through the meltblown nonwoven fabric per unit area in 1 hour in the initial state of the filtrate containing particles, etc., which has not been filtered. This value is obtained by measuring the time it takes for a certain amount of pure water to pass through the meltblown nonwoven fabric due to its own weight after the meltblown nonwoven fabric is replaced with alcohol. The speed of the initial water flow rate becomes an indicator of the filtration speed of the filter. The faster the initial water flow rate, the greater the initial filtration processing capacity of the filter. The initial water flow rate of the meltblown nonwoven fabric of the present invention is not particularly limited, and is preferably 600mL / cm 2 / h or more, more preferably 650mL / cm 2 / h or more, more preferably 680 mL / cm 2 The meltblown nonwoven fabric according to the embodiment of the present invention has a high initial water permeation rate relative to its high basis weight, which is believed to be due to a small amount of unevenness caused by the density of the fibers.

[0060] The amount of accumulated particles when the water flow rate is halved is the amount of particles captured by the meltblown nonwoven fabric at the moment when the water flow rate is halved during the filtration of the filtrate containing particles, etc., and becomes an indicator of the clogging of the meltblown nonwoven fabric. Generally, the filter needs to be replaced when the water flow rate drops to a certain level. The more filtration volume before replacement, the longer the filter life can be evaluated. The accumulated particle amount is preferably 40g / m 2 More than 50g / m 2 above.

[0061] Filtration efficiency (0-100%) is the efficiency with which meltblown nonwoven fabric can capture particles when filtering a filtrate containing particles. Higher values are preferred. Generally, smaller particle sizes decrease filtration efficiency. Similarly, smaller average pore sizes in meltblown nonwoven fabrics increase filtration efficiency.

[0062] The polymer that constitutes the meltblown nonwoven fabric for the filter of the present invention is not particularly limited, as long as it is a thermoplastic resin that can be meltblown. Examples of polymers that constitute the meltblown nonwoven fabric include polyolefins (e.g., polyethylene, polypropylene, etc., preferably polypropylene), polyesters, polyetheretherketones, polyphenylene sulfides, and polyamides. These thermoplastic resins can be used alone or in combination of two or more. When two or more thermoplastic resins are used in combination, the blending ratio is not limited. In the present invention, a meltblown nonwoven fabric composed primarily of a thermoplastic resin can also be referred to as a meltblown nonwoven fabric containing the thermoplastic resin as the main component. Furthermore, in the present invention, a meltblown nonwoven fabric composed primarily of a thermoplastic resin refers to a meltblown nonwoven fabric obtained using a thermoplastic resin as the main raw material. This includes not only meltblown nonwoven fabrics obtained solely using the thermoplastic resin, but also meltblown nonwoven fabrics containing the thermoplastic resin in proportions of, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more of the raw material. Among the melt-blown nonwoven fabrics of the present invention, polyolefins and polyesters are preferred, and polyolefins are particularly preferred.

[0063] Examples of the polyolefins include homopolymers of α-olefins such as propylene, ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene, and random or block copolymers of two or more of these α-olefins. Polypropylene is preferred. When polypropylene is used as the raw material for the nonwoven fabric in the present invention, its melt flow rate (MFR) is not particularly limited. For example, polypropylene having an MFR of 5 to 2,500 g / 10 min is preferred. When using polypropylene with an MFR of less than 5 g / 10 min, the melt kneading and discharge temperatures must be high, potentially leading to the formation of carbonized products derived from the polypropylene. Furthermore, an MFR exceeding 2,500 g / 10 min reduces the elongation of the nonwoven fabric, making it brittle. When polypropylene is used as the raw material in the present invention, the MFR is preferably 10 to 2,000 g / 10 min, more preferably 15 to 100 g / 10 min. The MFR of polypropylene can be measured at a load of 2.16 kg and a temperature of 230° C. in accordance with JIS K7210.

[0064] When polypropylene is used as a raw material in the present invention, the weight average molecular weight (Mw) of the polypropylene is not particularly limited, but is preferably 1×10 4 ~5×10 5 , more preferably 5×10 4 ~3×10 5 The molecular weight distribution [weight average molecular weight (Mw) / number average molecular weight (Mn)] of the polypropylene is also not particularly limited, but is preferably 1.1 to 10, more preferably 1.5 to 8, and even more preferably 2 to 6.

[0065] In the embodiments of the present invention using polypropylene as a raw material, the polypropylene may be a propylene homopolymer or a random, block, or graft copolymer of propylene in a majority polymerization ratio with another α-olefin (e.g., ethylene, butene, hexene, 4-methylpentene, octene, etc.), an unsaturated carboxylic acid or its derivative (e.g., acrylic acid, maleic anhydride, etc.), or an aromatic vinyl monomer (e.g., styrene, etc.). In the present invention, these polypropylenes may be used alone, as a mixture of multiple polypropylenes, or as a mixture with a thermoplastic resin other than polypropylene (e.g., a polyolefin, etc.).

[0066] In the embodiment of the present invention using polyester as a raw material, the polyester is not particularly limited, and examples thereof include polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate, with polyethylene terephthalate and polybutylene terephthalate being preferred.

[0067] In the embodiment of the present invention in which polyamide is used as a raw material, the polyamide is not particularly limited, and examples thereof include polyamide 3 (nylon 3) (registered trademark), polyamide 4 (nylon 4) (registered trademark), polyamide 6 (nylon 6) (registered trademark), polyamide 6-6 (nylon 6-6) (registered trademark), and polyamide 12 (nylon 12) (registered trademark).

[0068] In the present invention, a crystal nucleating agent, a matting agent, a pigment, an antifungal agent, an antibacterial agent, a flame retardant, a hydrophilic agent, a light stabilizer, a fluidity improver, etc. may be added to the above-mentioned thermoplastic resin within a range that can achieve the effects of the present invention.

[0069] Next, a method for producing a meltblown nonwoven fabric in a preferred embodiment of the present invention will be described with reference to the drawings. However, the method is not limited to the method described below. Figure 1 An example of an apparatus for producing a meltblown nonwoven fabric according to the present invention is shown. The apparatus comprises a hopper 1a for feeding raw materials; an extruder 1b for melting and kneading the raw materials; a metering pump 2 for conveying the molten polymer extruded from the extruder 1b downstream; a die 3a for horizontally discharging the molten polymer in the form of fibers; a temperature-regulating heater 3b for high-temperature, high-speed air, which is discharged from the die 3a along with the molten polymer; a spinning nozzle 3c mounted at the tip of the die; a collector 4a for collecting fibers, located near the die 3a; a suction blower 4b for sucking out the collector 4a (and the fibrous molten polymer 5a collected by the collector 4a); the fibrous molten polymer 5a discharged from the die; a meltblown nonwoven fabric 5b formed by cooling and solidifying the fibrous molten polymer 5a on the collector 4a; and a winder 6 for winding up the meltblown nonwoven fabric 5b.

[0070] Figure 2 (A) means Figure 1 A partial front view of the arrangement of the spinning nozzles of the nozzle 3c portion of the device. Figure 2 (B) is a partial perspective view of the nozzle 3c. Figure 2 (C) is the Figure 2 (A) is a cross-sectional view of the nozzle 3c taken at X1-X1. Figure 2 In the embodiment shown in (A), the nozzle hole 3d of the spinning nozzle 3c in the die head 3a includes a nozzle hole 3d1 with a hole diameter D1, and a nozzle hole 3d2 provided between the two nozzle holes 3d1 and having a hole diameter smaller than the hole diameter D1 of the nozzle hole 3d1. Figure 2 In (C), if the length of the nozzle hole 3d1 is L1 and the diameter, i.e., the hole diameter, is D1, then in order to make the discharge flow rate of the molten polymer from the spinning nozzle 3c uniform, the ratio L1 / D1 of the length L1 and the diameter D1 of the spinning nozzle hole 3d1 is preferably 3 or more, more preferably 6 or more. Figure 2 In embodiment (C), the diameter D1 of the nozzle holes 3d1 is constant along the longitudinal direction. To prevent the discharged polymer fibers from becoming entangled and to efficiently obtain a meltblown nonwoven fabric, the density of the spinning nozzle holes 3d is preferably 3 to 40 per inch, more preferably 5 to 35.

[0071] n rows of nozzle holes 3d2 can be arranged between two nozzle holes 3d1, with n preferably ranging from 2 to 4 (n is 3 in the figure). The center-to-center distance between the nozzle holes 3d, or so-called pitch spacing, is equal between adjacent holes 3d1-3d2 and 3d2-3d2.

[0072] The length L2 of the small-diameter nozzle hole 3d2 can be the same as or different from the length L1 of the large-diameter nozzle hole 3d1, but is preferably the same. The diameter D2 of the small-diameter nozzle hole 3d2 differs at the distal end and the proximal end, with the distal diameter D2d being smaller than the proximal diameter D2p. The length L1 of the large-diameter nozzle hole 3d1 and the length L2 of the small-diameter nozzle hole 3d2 are preferably 0.3 to 20 mm, more preferably 3 to 10 mm, respectively.

[0073] The diameters D1 and D2 (D2d and D2p) of the nozzle holes 3d1 and 3d2 are preferably 0.1 to 2.0 mm. The ratio R (D1 / D2d) of the diameter D1 of the nozzle hole 3d1 to the diameter D2d at the tip of the nozzle hole 3d2 is, for example, in the range of 1.3 to 2.0. When the diameter ratio R is 1.3 or greater, the fiber diameter distribution becomes wider. When the diameter ratio R is 2.0 or less, the resin discharge balance based on the diameter difference is maintained, resulting in a stable spinning state. For example, the diameter D1 of the nozzle hole 3d1 is 0.20 to 1.20 mm, and the diameter D2d at the tip of the nozzle hole 3d2 is 0.10 to 0.80 mm.

[0074] In the present application, to prevent or suppress the difficulty of resin ejection even when the diameter of the small-diameter nozzle hole 3d2 of the spinning nozzle 3c is small, the distribution range of fiber diameters is expanded, and the pressure applied to the tip of the large-diameter nozzle hole 3d1 is made closer than before to the pressure applied to the tip of the small-diameter nozzle hole 3d2. As will be readily understood by those skilled in fluid mechanics, this pressure is satisfied by designing the nozzle hole 3d2 so that the cross-sectional area of the small-diameter nozzle hole 3d2 is larger at the base end than at the tip end in the longitudinal direction of the nozzle hole 3d2.

[0075] The pressure applied to the tip of the large-diameter nozzle hole 3d1 is preferably substantially equal to the pressure applied to the tip of the small-diameter nozzle hole 3d2. In other words, the flow rate per unit area of the molten polymer discharged from the tip of the small-diameter nozzle hole 3d2 is substantially equal to the flow rate per unit area of the molten polymer discharged from the tip of the large-diameter nozzle hole 3d1. Here, substantially equal pressures means that the pressures are equal, or the difference between the two compared pressures is within a range of ±30%.

[0076] In some embodiments, the cross-sectional area of the small-diameter nozzle hole 3d2 decreases in one or more stages between the base and tip along the length direction. Consequently, the diameter D2 of the nozzle hole 3d2 decreases in stages from the base diameter D2p to the tip diameter D2d. For example, in a two-stage configuration, L2 = L21 + L22, where the diameter relative to L21 is constant at D2p, and the diameter relative to L22 is constant at D2d. In other embodiments, the cross-sectional area of the small-diameter nozzle hole 3d2 decreases continuously along the length direction between the base and tip. Consequently, the diameter D2 of the nozzle hole 3d2 also decreases continuously from the base diameter D2p to the tip diameter D2d. This latter configuration can be achieved by tapering the walls defining the nozzle hole 3d2 from the base to the tip, or from a point between the base and tip to the tip.

[0077] The ratio R2 (D1 / D2p) of the pore diameters D2p and D1 is, for example, 0.3 to 0.95.

[0078] The meltblown nonwoven fabric of the present invention can be produced by a method comprising a step of melt-kneading a polymer, discharging the molten polymer from a spinning nozzle, and then discharging heated air from another nozzle to form polymer fibers. Referring to the apparatus described above, in the case of meltblown nonwoven fabric production, the fibrous molten polymer 5a discharged from the spinning nozzle 3c is stretched by heated air discharged from an air nozzle, and additional steps are performed as needed to obtain the meltblown nonwoven fabric. The resulting meltblown nonwoven fabric can be subjected to calendering, charging, hydrophilization, and other treatments as needed.

[0079] (1) Melt mixing process

[0080] The melt kneading temperature of the polymer is preferably (melting point of the polymer + 50° C.) to (melting point of the polymer + 300° C.) In the case of polypropylene, the melt kneading temperature is preferably 210 to 460° C., more preferably 230 to 420° C.

[0081] (2) Fiber formation process

[0082] A molten polymer is discharged from a plurality of spinning nozzles 3c, and heated air is discharged from the nozzles to form fibers of the polymer. The temperature of the die 3a and the heated air is preferably set to (the melting point of the polymer) to (the melting point of the polymer + 200°C). In the case of polypropylene, the temperature of the die 3a and the heated air is preferably 160-360°C, more preferably 190-330°C. This temperature range is preferred from the perspective of suppressing rapid solidification of the polymer immediately after discharge from the spinning nozzles 3c, suppressing fusion of the formed polymer fibers, and suppressing variations in fiber diameter.

[0083] In order to form polymer fibers, the discharge rate of the molten polymer per spinning nozzle 3c is preferably 0.1 to 2 g / min / hole or less, and more preferably 0.5 to 1 g / min / hole or less. From the perspective of obtaining a sufficient discharge pressure for fiberization and avoiding damage to the nozzle due to excessive discharge pressure, the discharge rate of the molten polymer per spinning nozzle 3c is preferably within the above range.

[0084] The discharge rate of heated air per unit width of the spinning nozzle is preferably 5 to 50 Nm 3 / min / m, more preferably 10 to 40 Nm 3 / minute / m.

[0085] The meltblown nonwoven fabric of the present invention has a wide fiber diameter distribution range and exhibits minimal variations due to fiber density. Therefore, the meltblown nonwoven fabric of the present invention and its laminate are useful as filter materials for fluid filters. Fluids include gases and liquids. The meltblown nonwoven fabric of the present invention and its laminate are particularly useful as filter materials for liquid filters.

[0086] The present invention also provides a fluid filter comprising such a laminate. Because the meltblown nonwoven fabric of the present invention exhibits the aforementioned properties, even when using only the meltblown nonwoven fabric of the present invention as the meltblown nonwoven fabric constituting the filter material, a fluid filter can be obtained that has a wide fiber diameter distribution range and minimal fiber unevenness, resulting in high substance capture capacity and a long life. On the other hand, in another embodiment of the present invention, depending on the purpose of filtration, other meltblown nonwoven fabrics may be used in combination with the meltblown nonwoven fabric of the present invention as the filter material. A liquid filter comprising a laminate comprising such a combination of meltblown nonwoven fabrics is also encompassed by the liquid filter of the present invention. Therefore, in the present invention, a "laminate for a liquid filter comprising laminated meltblown nonwoven fabrics" includes not only laminates comprising only laminated meltblown nonwoven fabrics but also laminates comprising meltblown nonwoven fabrics other than meltblown nonwoven fabrics, as long as at least one layer of the laminate (preferably comprising at least half the number of meltblown nonwoven fabrics constituting the laminate) comprises a meltblown nonwoven fabric.

[0087] As mentioned above, although the melt-blown nonwoven fabric of the present invention and the manufacturing method thereof were described by giving examples of preferred embodiments, the present invention is not limited to the above-mentioned specific embodiments.

[0088] The present invention will be described in further detail with reference to the following examples, but the present invention is not limited to these examples.

[0089] Example

[0090] 1. Manufacturing of meltblown nonwoven fabrics

[0091] Example 1

[0092] Homopolypropylene resin (weight average molecular weight 1.7×10 5 The same is true in the following examples and comparative examples) and the melt kneading temperature is set to 375°C. The distance between the die and the collector is 250 mm, and the heated compressed air at 290°C is 13 Nm 3 / min / m together, from Figure 2 The nozzle holes shown (3d1:3d2=1:3, D1=0.6mm, D2d=0.4mm, D2p=0.8mm, L1=L2=8.0mm, the same in the following examples) discharge the resin into the atmosphere at a suction volume of 394Nm 3 The fibrous resin was continuously collected on a collector with a rotation speed of 1000 nm / min / m. The rotation speed of the collector was appropriately adjusted to obtain a unit area weight of 61 g / m 2 , thickness 0.91mm, air permeability 12cm 3 / cm 2 / s, fiber diameter 1.9μm, and evenness index 46 meltblown nonwoven fabric.

[0093] Example 2

[0094] A homopolypropylene resin of MFR40 was put into the raw material hopper of the melt-blown manufacturing device and the melt mixing temperature was set to 375°C. The distance between the die head and the collector was 300mm, and the heated compressed air at 290°C was 15Nm 3 / min / m, the resin was discharged into the atmosphere from the same nozzle as in Example 1. At a suction rate of 217 Nm 3 The fibrous resin was continuously collected on a collector with a rotation speed of 1000 nm / min / m. The rotation speed of the collector was appropriately adjusted to obtain a unit area weight of 82 g / m 2 , thickness 1.33mm, air permeability 18cm 3 / cm 2 / s, fiber diameter 2.5μm, and evenness index 53 meltblown nonwoven fabric.

[0095] Example 3

[0096] A homopolypropylene resin of MFR40 was put into the raw material hopper of the melt-blown manufacturing device and the melt mixing temperature was set to 365°C. The distance between the die head and the collector was 500mm, and the heated compressed air at 290°C was 22Nm 3 / min / m, the resin was discharged into the atmosphere from the same nozzle as in Example 1. At a suction rate of 197 Nm 3 The fibrous resin was continuously collected on a collector with a rotation speed of 1000 nm / min / m. The rotation speed of the collector was appropriately adjusted to obtain a unit area weight of 82 g / m 2 , thickness 1.13mm, air permeability 65cm 3 / cm 2 / s, fiber diameter 6.5μm, and evenness index 117 meltblown nonwoven fabric.

[0097] Comparative Example 1

[0098] A homopolypropylene resin of MFR40 was put into the raw material hopper of the melt-blown manufacturing device and the melt mixing temperature was set to 414°C. The distance between the die head and the collector was 200mm, and the heated compressed air at 290°C and 29Nm 3 / min / m, the resin is discharged into the atmosphere by a single aperture nozzle (D = 0.4mm, L = 4.0mm), with a suction capacity of 327Nm 3 The fibrous resin is continuously collected on a collector with a rotation speed of 1000 nm / min / m. The rotation speed of the collector is appropriately adjusted to obtain a unit area weight of 60 g / m 2 , thickness 1.10mm, air permeability 10ccm 3 / cm2 / s, fiber diameter 1.6μm, and meltblown nonwoven fabric with a uniformity index of 61.

[0099] Comparative Example 2

[0100] A homopolypropylene resin of MFR40 was put into the raw material hopper of the melt-blown manufacturing device and the melt mixing temperature was set at 408°C. The distance between the die head and the collector was 160mm, and the heated compressed air at 290°C and 29Nm 3 / min / m, the resin is discharged into the atmosphere from nozzles with different apertures (3d1:3d2=1:3, D1=0.6mm, D2=0.4mm, L1=L2=6.0mm). 3 The fibrous resin is continuously collected on a collector with a rotation speed of 1000 nm / min / m. The rotation speed of the collector is appropriately adjusted to obtain a unit area weight of 60 g / m 2 , thickness 1.01mm, air permeability 12cm 3 / cm 2 / s, fiber diameter 1.3μm, and meltblown nonwoven fabric with a uniformity index of 57.

[0101] Determination and evaluation of various physical properties

[0102] Next, various physical property values of the meltblown nonwoven fabrics of Examples 1-3 and Comparative Examples 1-2 obtained were measured and calculated as follows. The results are shown in Table 1.

[0103] (1) Average weight per unit area

[0104] The average basis weight was determined by measuring the mass (g) of 10 meltblown nonwoven fabric test pieces of 100 mm×100 mm in a water equilibrium state at a temperature of 23° C. and a humidity of 50%, and averaging the measured values.

[0105] (2) Thickness

[0106] For a 100 mm × 100 mm meltblown nonwoven fabric test piece, use a 2.5 cm diameter, 7 g / cm load 2 The thickness of the central portion of the test piece corresponding to the center of gravity was measured using a linear gauge of a probe and the measured values of 10 pieces were averaged to obtain the thickness.

[0107] (3) Air permeability

[0108] The air permeability was determined by measuring 10 melt-blown nonwoven fabric test pieces of 100 mm×100 mm using a Frazier tester in accordance with JIS L1096 and averaging the measured values.

[0109] (4) Average fiber diameter

[0110] The average fiber diameter was determined by taking four electron microscope images at a magnification such that approximately 25 fibers were captured per image, measuring the fiber diameters of a total of 100 fibers down to the 0.1 μm level, and averaging the measured diameters.

[0111] The fiber diameter ratio expresses the ratio of the number of fibers having a specific fiber diameter to the total number of fibers as a percentage.

[0112] (5) Evenness index

[0113] The evenness index was determined by measuring three A4-sized meltblown nonwoven fabric test pieces using a evenness meter (FMT-MIII manufactured by Nomura Corporation) and averaging the measured values.

[0114] (6) Particles

[0115] For bulk particles, for 1m 2 The melt-blown nonwoven fabric test piece was visually inspected to determine whether or not a transparent spot with a diameter of 0.5 mm was formed to determine whether or not film formation occurred.

[0116] (7) Bursting strength

[0117] The bursting strength was determined as the average value of values measured by three tests using a Mullen bursting tester M2-LD manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P8112:2008 “Paper—Burst strength test method”.

[0118] (8) Determination of maximum pore diameter, minimum pore diameter and average pore diameter

[0119] The maximum pore diameter, minimum pore diameter, and average pore diameter were measured using an automatic pore size distribution analyzer (Model "CFP-1200AX," manufactured by Porous Materials Co., Ltd.) according to the bubble point method described below (ASTM F316-86, JIS K3832). During the measurement, a meltblown nonwoven fabric test piece moistened with a test solution (GALWICK or SILWICK) was placed, and the air pressure applied to one side was gradually increased.

[0120] (9) Evaluation of the amount of accumulated particles at the initial water flow rate and at half the water flow rate

[0121] The initial water flow rate and the amount of accumulated particles when the water flow rate was reduced to half were measured by the following method.

[0122] 1. Measure the weight (mg) of a meltblown nonwoven fabric test piece cut into a size of 47 mm in diameter.

[0123] 2. After the test piece was immersed in isopropyl alcohol, 400 mL of pure water was passed through the filtrate passage portion of the test piece with a diameter of 43 mm by its own weight to replace the isopropyl alcohol contained in the test piece with water.

[0124] 3. Pour 100 mL of pure water into the test piece and measure the time it takes for the pure water to pass through the test piece due to its own weight. The amount of water flowing through per unit area and per unit time is taken as the initial water flow rate (mL / cm 2 / h).

[0125] 4. Next, 100 mL of pure water to which 10 mg of JIS 7 type powder (Kanto Rom, calcined product) was added was passed through the test piece.

[0126] After completion of 5.4, a pressure of 5 kPa was applied to the test piece from the upstream side.

[0127] 6. Pour 100 mL of pure water into the test piece and measure the time it takes for the water to pass through under its own weight to calculate the water flow rate.

[0128] 7. Repeat steps 4 to 6 until the initial water flow rate measured in step 3 is halved.

[0129] 8. Then, the test piece was naturally dried at a temperature of 23°C and a humidity of 50% for 24 hours, and the weight was measured. The difference from the weight measured in step 1 was taken as the amount of particles deposited on the test piece (mg), and the particles per unit area were taken as the amount of particles deposited at half the water flow rate (g / m 2 ).

[0130] (10) Filtration efficiency evaluation: 200 mL of a test solution with a concentration of 200 ppm was prepared by filtering JIS 7 types of powder using a test piece (diameter of the test solution passage portion 43 mm) with pure water. The test solution and the collected filtrate were filtered using an apparatus (HIAC 8011 + ) Measure the number of particles and evaluate the filtration efficiency.

[0131] As shown in Table 1, the meltblown nonwoven fabric of the present invention has a wide fiber diameter distribution, with fine and coarse fibers evenly dispersed and minimal fiber unevenness. Furthermore, there is no loose particles, and the appearance is excellent. When used as a filter, such a meltblown nonwoven fabric can be expected to exhibit high particle capture performance and a long life.

[0132] In addition, if Figure 3 As shown, the filtration efficiency of the melt-blown nonwoven fabric of Example 1 was high not only for large particles but also for relatively small particles, and was superior to the melt-blown nonwoven fabrics of Comparative Examples 1 and 2 in filtration efficiency.

[0133] [Table 1]

[0134]

Claims

1. A meltblown nonwoven fabric comprising a plurality of thermoplastic resin fibers having different fiber diameters, The thermoplastic resin constituting the thermoplastic resin fiber is one or more selected from polyolefin, polyester, polyetheretherketone, polyphenylene sulfide and polyamide. The standard deviation of the fiber diameter is greater than 1.2, and the ratio of the evenness index to the average fiber diameter is less than 33. Among the thermoplastic resin fibers in the meltblown nonwoven fabric, the proportion of thermoplastic resin fibers having a fiber diameter of 2.5 times or more of the average fiber diameter is 4% or more. Among the thermoplastic resin fibers in the meltblown nonwoven fabric, the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less of the average fiber diameter is 46% or more. The average fiber diameter of the thermoplastic resin fiber is 1 μm to 50 μm.

2. The meltblown nonwoven fabric according to claim 1, wherein The resin component of the thermoplastic resin fiber is at least one selected from the group consisting of polyolefin, polyester, and polyamide.

3. A filter comprising the meltblown nonwoven fabric according to claim 2.

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