Meltblown nonwoven fabric and filter equipped with same

Abstract

To provide a melt blown non-woven fabric having a wider distribution range of fiber diameter and less variation in fiber coarseness in comparison with a conventional melt blown non-woven fabric produced with use of a different diameter nozzle.SOLUTION: A melt blown non-woven fabric containing a plurality of thermoplastic resin fibers having different fiber diameters has an average fiber diameter of the thermoplastic resin fibers of 5 μm or more, and a proportion of the thermoplastic resin fibers having fiber diameters 0.5 times or less of the average fiber diameter of 10% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a meltblown nonwoven fabric and a filter including the same. [Background technology]

[0002] Meltblown nonwoven fabrics are widely used as filters for substances such as gases and liquids, and there is a demand for longer filter life so that they can capture more substances for a longer period of time.

[0003] Patent Document 1 discloses a meltblown nonwoven fabric manufactured using a nozzle piece having a fixed ratio of small-diameter nozzles and large-diameter nozzles. This meltblown nonwoven fabric uses a mixture of thick and thin fibers, which allows the thick fibers to maintain space between the fibers while the thin fibers increase the surface area, thereby increasing collection efficiency. This results in a filter medium with low pressure loss and high particle collection efficiency.

[0004] Patent Document 2 discloses a melt-blown nonwoven fabric sheet characterized by having 10 to 30% of fibers with a fiber diameter of 0.1 μm to 1.5 μm and 30 to 60% of fibers with a fiber diameter of 3 to 10 μm. Patent Document 2 uses nozzle pieces with a different ratio of small-hole nozzles and large-hole nozzles than Patent Document 1 (small-hole nozzles:large-hole nozzles = 1:1). Furthermore, by converting such a melt-blown nonwoven fabric sheet into an electret, high collection performance and low pressure loss are achieved. The QF value of the melt-blown nonwoven fabric sheet in Patent Document 2 is 0.130 to 0.250 Pa. -1 It is as follows.

[0005] Patent Document 3 discloses a nonwoven fabric made of a mixture of two types of long fibers made from different thermoplastic resins. The different thermoplastic resins are spun from respective gear pumps and nozzles, and preferably the proportion of long fibers with a fiber diameter of 0.1 to 1.5 μm is 30% or more by number of constituent fibers, and the proportion of long fibers with a fiber diameter of 3 μm to 10 μm is less than 30%.

[0006] Patent Document 4 discloses a bulky nonwoven web having a wide range of fiber diameters, which is produced by spinning a plurality of filaments discharged from 2 to 20 rows of multi-stage nozzles.

[0007] Patent Document 5 discloses a method for producing a mixed fiber nonwoven fabric in which a resin constituting fiber group A and a resin constituting fiber group B are melted in separate extruders and discharged from separate spinning holes, and the polymer discharge rate per single hole from the discharge hole for fiber group A is set to be small and the polymer discharge rate per single hole from the discharge hole for fiber group B is set to be large, thereby obtaining a mixed fiber nonwoven fabric having a desired single fiber diameter. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 11-131353 [Patent Document 2] Patent Publication No. 2006-37295 [Patent Document 3] Patent Publication No. 2013-40412 [Patent Document 4] Special Table 2020-505530 [Patent Document 5] Patent Publication No. 2016-160542 Summary of the Invention [Problem to be solved by the invention]

[0009] Liquid filters and air filters are required to have high efficiency, low pressure loss, and a long lifespan. When nonwoven fabrics are produced using the nozzle piece of Patent Document 1, a long lifespan can be achieved. However, when the spun fibers are thicker or the basis weight is lower, the thicker the fibers, the more uneven the appearance of the nonwoven fabric becomes, consisting of densely packed areas and coarsely packed areas, i.e., the unevenness due to the density of the fibers increases. This fiber unevenness can cause deterioration in the formation, and the target substances to be filtered may be missed in areas with low fiber density, making it difficult to achieve high efficiency.

[0010] In Patent Document 2, the proportion of fine fibers is low, so the balance between efficiency and pressure loss is not fully improved.

[0011] When the devices disclosed in Patent Documents 3, 4 and 5 are used, the equipment becomes very large and the cost also increases.

[0012] If the distribution range of fiber diameters can be further expanded while minimizing unevenness due to fiber density in meltblown nonwoven fabrics, the material capture capacity can be improved, and the demand for longer filter life can be met.

[0013] An object of the present invention is to provide a melt-blown nonwoven fabric having a wide fiber diameter distribution range and little unevenness due to fiber density. [Means for solving the problem]

[0014] Under these circumstances, the present inventors have conducted extensive research and found that the above-mentioned problems can be solved even in a melt-blown nonwoven fabric containing thermoplastic resin fibers with a large average fiber diameter of 5 μm or more by increasing the proportion of thermoplastic resin fibers with a small fiber diameter. Accordingly, the present invention encompasses the following embodiments. Item 1. A melt-blown nonwoven fabric containing a plurality of thermoplastic resin fibers having different fiber diameters, A melt-blown nonwoven fabric in which the average fiber diameter of the thermoplastic resin fibers is 5 μm or more, and the proportion of thermoplastic resin fibers having a fiber diameter of 0.5 times or less the average fiber diameter is 10% or more. Item 2. The melt-blown nonwoven fabric according to Item 1, wherein the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter among the thermoplastic resin fibers in the melt-blown nonwoven fabric is 30% or more. Item 3. The melt-blown nonwoven fabric according to Item 1 or 2, wherein the proportion of thermoplastic resin fibers having a fiber diameter of 2.5 times or more the average fiber diameter among the thermoplastic resin fibers in the melt-blown nonwoven fabric is 1% or more. Item 4. The melt-blown nonwoven fabric according to any one of Items 1 to 3, wherein the resin component of the thermoplastic resin fibers is at least one selected from the group consisting of polyolefins, polyesters, and polyamides. Item 5. The melt-blown nonwoven fabric according to any one of Items 1 to 4, wherein the decrease in breathability due to compression after the melt-blown nonwoven fabric is passed through a calendar roll consisting of a pair of metal rolls with a clearance of 0.1 mm is 20% or less of the value before passing through. Item 6. The melt-blown nonwoven fabric according to any one of Items 1 to 4, wherein the thickness of the melt-blown nonwoven fabric is reduced by 35% or less after passing through a calender roll having a clearance of 0.1 mm and consisting of a pair of metal rolls. Item 7. The melt-blown nonwoven fabric according to any one of Items 1 to 4, wherein the ratio of the decrease in breathability to the decrease in thickness due to compression after the melt-blown nonwoven fabric is passed through a calendar roll consisting of a pair of metal rolls with a clearance of 0.1 mm is 0.8 or less. Item 8. Bursting strength to basis weight ratio (kPa / (g / m 2 8. The melt-blown nonwoven fabric according to any one of items 1 to 7, wherein )) is 1.0 or more. Item 9. The melt-blown nonwoven fabric according to any one of Items 1 to 8, which is an electret nonwoven fabric containing a hindered amine light stabilizer and / or a crystal nucleating agent as an additive, and has a QF value of 0.2 or more. Item 10. A filter comprising the melt-blown nonwoven fabric according to any one of items 1 to 9. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a melt-blown nonwoven fabric having a wide fiber diameter distribution range and little unevenness due to fiber density. Such a nonwoven fabric is resistant to reduction in thickness even when pressure is applied, and is resistant to reduction in air permeability even after filtering substances. Therefore, a filter using such a nonwoven fabric has an improved balance between collection efficiency and pressure loss, and is expected to have a longer life. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a process schematic diagram of a method for producing a meltblown nonwoven fabric of the present invention. [Figure 2] 2(A) is a partial front view showing the arrangement of the spinning nozzles in the nozzle 3c portion of the device in Fig. 1. (B) is a partial perspective view of the nozzle 3c. (C) is a cross-sectional view of the nozzle 3c shown in Fig. 2(A) taken along X1-X1. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments for carrying out the present invention will be described. The embodiments described below are examples of typical embodiments of the present invention, and the present invention is not limited thereto.

[0018] The present invention provides a melt-blown nonwoven fabric containing a plurality of thermoplastic resin fibers having different fiber diameters, wherein the average fiber diameter of the thermoplastic resin fibers is 5 μm or more, and the proportion of thermoplastic resin fibers having a fiber diameter of 0.5 times or less the average fiber diameter is 10% or more.

[0019] The average fiber diameter of the thermoplastic resin fibers in the meltblown nonwoven fabric of the present invention is 5 μm or more. The average fiber diameter of the meltblown nonwoven fabric, i.e., the average fiber diameter of the fibers constituting the meltblown nonwoven fabric, is determined by taking four electron micrographs of the meltblown nonwoven fabric at a magnification that allows about 25 fibers to fit in each image, measuring the fiber diameters of a total of 100 arbitrarily selected fibers to the order of 0.1 μm, and averaging the measured diameters.

[0020] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric having a fiber diameter of 0.5 times or less the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers having a fiber diameter of 0.5 times or less the average fiber diameter by 100 and multiplying the result by 100.

[0021] When the proportion of thermoplastic resin fibers having a fiber diameter of 0.5 times or less the average fiber diameter is 10% or more, a large proportion of fibers with relatively small fiber diameters are present in the melt-blown nonwoven fabric, reducing unevenness due to the density of the fibers in the melt-blown nonwoven fabric and improving particle collection efficiency.

[0022] The meltblown nonwoven fabric of the present invention has a higher proportion of fine fibers, a wider fiber diameter distribution range, and less unevenness due to fiber density than conventional meltblown nonwoven fabrics with an average fiber diameter of 5 μm or more. Such a nonwoven fabric is resistant to loss of thickness even when pressure is applied, and its air permeability is also resistant to loss after filtration of the substance to be filtered (hereinafter, the substance to be filtered may be simply referred to as "substance"). Therefore, filters using such a nonwoven fabric are expected to have a high ability to retain their fiber structure, and to have high filtering performance and a long life.

[0023] Preferably, the proportion of thermoplastic resin fibers in the meltblown nonwoven fabric that have a fiber diameter of 0.75 times or less the average fiber diameter is 30% or more.

[0024] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric having a fiber diameter of 0.75 times or less the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter by 100 and multiplying the result by 100.

[0025] When the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter is 30% or more, fibers with small fiber diameters are present in a large proportion in the melt-blown nonwoven fabric, reducing unevenness due to the density of the fibers in the melt-blown nonwoven fabric and improving particle collection efficiency.

[0026] Preferably, in the meltblown nonwoven fabric of the present invention, the proportion of thermoplastic resin fibers having a fiber diameter of 2.5 times or more the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is 1% or more.

[0027] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric that have a fiber diameter that is 2.5 times or more the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers that have a fiber diameter that is 2.5 times or more the average fiber diameter by 100 and multiplying the result by 100.

[0028] When the proportion of thermoplastic resin fibers having a fiber diameter 2.5 times or more the average fiber diameter is 1% or more, fibers with relatively large fiber diameters are present in the meltblown nonwoven fabric, ensuring gaps between the fibers of the meltblown nonwoven fabric, increasing breathability and improving compression resistance.

[0029] The standard deviation of the fiber diameter of the thermoplastic resin fibers in the meltblown nonwoven fabric of the present invention is not particularly limited, but may be 1.2 or more. When the standard deviation of the fiber diameter of the meltblown nonwoven fabric of the present invention is 1.2 or more, the fiber diameter distribution range is wide, resulting in a mixture of thinner and thicker fibers. This suppresses unevenness due to fiber density, resulting in good formation. Furthermore, when the meltblown nonwoven fabric is used as a filter, the thin fibers ensure high particle collection capacity, while the thick fibers suppress compression due to filtration pressure, allowing more particles to be collected in the thickness direction, thereby improving the filter life. In some embodiments, the standard deviation of the fiber diameter of the thermoplastic resin fibers in the meltblown nonwoven fabric is 4.0 or more and 14.0 or less.

[0030] In the present invention, the standard deviation u of the fiber diameter is calculated by dividing the fiber diameter x of each of 100 fibers in an electron microscope photograph. i and the average fiber diameter x ave and is calculated using the following formula (1).

[0031]

number

[0032] Preferably, the ratio of the formation index to the average fiber diameter of the meltblown nonwoven fabric of the present invention is 50 or less, more preferably 20 or more and 50 or less. When the ratio of the formation index to the average fiber diameter is 50 or less, there is less unevenness due to the density of the fibers, resulting in a more uniform formation, and stable, high collection ability can be expected.

[0033] The formation index of a nonwoven fabric is an index of the basis weight per unit area and indicates the uniformity of fiber orientation. It can be calculated by shining transmitted light on a sample and using the distribution of light and shade in the image. A smaller formation index indicates higher uniformity. Furthermore, a smaller formation index indicates a higher material capture ability of the nonwoven fabric. Specifically, a transmission-type fabric analyzer (Nomura Shoji Co., Ltd. FMT-M III) is used for measurement. With no sample set, the amount of transmitted light is measured with a CCD camera with the light source on and off. Next, an A4-sized piece of nonwoven fabric is set on the sample, and the amount of transmitted light is measured in the same way to determine the average transmittance, average absorbance, and standard deviation. The formation index can be calculated by dividing the standard deviation by the average absorbance and multiplying it by 1,000.

[0034] The average fiber diameter of the meltblown nonwoven fabric of the present invention is not particularly limited, but from the viewpoint of the application of the fluid filter and compression resistance, it is preferably 5 to 50 μm. In some embodiments, the average fiber diameter is 5 to 40 μm. In other embodiments, the average fiber diameter is 5 to 25 μm.

[0035] The basis weight of the meltblown nonwoven fabric of the present invention is not particularly limited, but the average basis weight is preferably in the range of 5 to 150 g / m 2 and more preferably 15 to 100 g / m 2 and more preferably 20 to 50 g / m2 From the viewpoint of improving strength (improved strength makes it easier to process into a filter), and from the viewpoint of preventing excessive rigidity during filter formation and improving adhesion with other materials to achieve more uniform lamination (more uniform lamination leads to effective filtration performance), it is preferable that the average basis weight of the meltblown nonwoven fabric be within the above range. The basis weight is preferably 20 g / m 2 More preferably, 40 g / m 2 At or above this, a formation index to average fiber diameter ratio of 50 or less is more easily achieved.

[0036] In some embodiments of the preferred meltblown nonwoven fabric, when the average fiber diameter is 5 to 25 μm, the basis weight is 20 g / m 2 In some preferred embodiments of the meltblown nonwoven fabric, when the average fiber diameter is 5 to 25 μm, the basis weight is 20 g / m 2 More than 50g / m 2 The following is the result.

[0037] The thickness of the melt-blown nonwoven fabric of the present invention is not particularly limited, but the average thickness per sheet of melt-blown nonwoven fabric is preferably 0.01 to 10 mm, more preferably 0.1 to 5 mm.

[0038] The air permeability of the melt-blown nonwoven fabric of the present invention is not particularly limited, but the value measured on a 100 mm × 100 mm melt-blown nonwoven fabric test piece using a Frazier type tester in accordance with JIS L1096 is 1 to 1700 cm 3 / cm 2 / sec, preferably 50 to 1000 cm 3 / cm 2 From the viewpoint of suppressing an increase in pressure resistance during filtration and obtaining a nonwoven fabric with a predetermined strength, it is preferable that the air permeability of the melt-blown nonwoven fabric be within the above range.

[0039] In some embodiments, the average fiber diameter of the thermoplastic resin fibers is 5 μm or more, and the air permeability of the meltblown nonwoven fabric is 50 cm 3 / cm 2In some other embodiments, the average fiber diameter of the thermoplastic resin fibers is 5 μm to 50 μm, and the air permeability of the meltblown nonwoven fabric is 50 cm 3 / cm 2 / sec~800cm 3 / cm 2 / seconds.

[0040] The burst strength of the meltblown nonwoven fabric of the present invention is not particularly limited, but it is preferable that the average fiber diameter is 5 to 50 μm and the basis weight is 20 g / m. 2 from 50g / m 2 In this case, the pressure is preferably 30 kPa or more, more preferably 40 kPa or more. If the meltblown nonwoven fabric has uneven fiber density, the pressure resistance of the filtration medium will decrease when used as a filter, which may lead to membrane rupture. There is no particular upper limit for the burst strength, but since there is a concern that the processability of the meltblown nonwoven fabric will decrease, it is usually preferably 1000 kPa or less, and more preferably 500 kPa or less. The burst strength of the meltblown nonwoven fabric is the average value of values ​​measured in three tests conducted in accordance with JIS P8112:2008 using a Mullen burst tester M2-LD manufactured by Toyo Seiki Co., Ltd.

[0041] The higher the basis weight, the higher the burst strength. Therefore, although there is no particular limitation, the ratio of burst strength / basis weight (kPa / (g / m 2 )) is preferably 1.0 or more, more preferably 1.0 or more and 2.0 or less. When the burst strength is 1.0 or more, the strength of the meltblown nonwoven fabric increases, and the fabric is less likely to crack or collapse.

[0042] Nonwoven fabrics may be converted into electrets for use in air filters and other applications to improve the efficiency of capturing airborne particles. Typically, electretization of nonwoven fabrics made from thermoplastic resin fibers is achieved using methods such as corona charging, which applies a high voltage to the nonwoven fabric, or water flow charging, which applies friction to the nonwoven fabric using a water flow. The charge generated in the nonwoven fabric gradually dissipates over time due to factors such as temperature and humidity. To prevent this, additives effective in maintaining the charge are typically incorporated into the thermoplastic resin. Additives that are particularly effective in maintaining the charge include crystal nucleating agents and hindered amine light stabilizers. Since both are effective in maintaining the charge, either one can be used. However, because using one additive alone can result in poor spinnability due to the high amount added, two or more additives can be used in combination to achieve the same or better charge retention effect while reducing the overall amount added.

[0043] Examples of the crystal nucleating agent include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, phosphoric acid-based nucleating agents, triaminobenzene derivative nucleating agents, and metal carboxylate nucleating agents.

[0044] Sorbitol-based nucleating agents include dibenzylidene sorbitol (DBS), monomethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(p-methylbenzylidene)sorbitol (p-MDBS)), dimethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (3,4-DMDBS)), and the like, including "Millad" (registered trademark) 3988 (manufactured by Milliken Japan Co., Ltd.) and "Gelall" (registered trademark) E-200 (manufactured by New Japan Chemical Co., Ltd.).

[0045] Nonitol-based nucleating agents include, for example, 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol, and examples thereof include "Millad" (registered trademark) NX8000 (manufactured by Milliken Japan Co., Ltd.).

[0046] Xylitol-based nucleating agents include, for example, bis-1,3:2,4-(5',6',7',8'-tetrahydro-2-naphthaldehyde benzylidene) 1-allyl xylitol.

[0047] Examples of phosphoric acid-based nucleating agents include aluminum-bis(4,4',6,6'-tetra-tert-butyl-2,2'-methylenediphenyl-phosphate)-hydroxide, and examples thereof include "ADK STAB" (registered trademark) NA-11 (manufactured by ADEKA CORPORATION) and "ADK STAB" (registered trademark) NA-21 (manufactured by ADEKA CORPORATION).

[0048] Examples of triaminobenzene derivative nucleating agents include 1,3,5-tris(2,2-dimethylpropanamido)benzene, and examples of commercial products containing 1,3,5-tris(2,2-dimethylpropanamido)benzene include "Irgaclear (registered trademark) XT386" (manufactured by BASF Japan Ltd.).

[0049] Examples of metal carboxylate nucleating agents include sodium benzoate and calcium 1,2-cyclohexanedicarboxylate.

[0050] The amount of the crystal nucleating agent added cannot be generalized because the effect and spinnability differ significantly depending on the type of nucleating agent, but is preferably 0.005 to 20% by mass of the entire melt-blown nonwoven fabric.

[0051] Examples of the hindered amine light stabilizer include poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethylene((2,2,6,6-tetramethyl-4-piperidyl)imino)] (manufactured by BASF Japan Ltd., "Chimassorb" (registered trademark) 944FDL), dimethyl succinate-1-( 2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 622SF), and 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate bis(1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 144).

[0052] The content of the hindered amine light stabilizer also depends on the type used, but is preferably 0.1 to 10 mass % of the entire melt-blown nonwoven fabric, and more preferably 1 to 5 mass %.

[0053] In addition to the above-mentioned crystal nucleating agent and hindered amine light stabilizer, additives such as a heat stabilizer, a weathering agent, and a polymerization inhibitor may also be added to the melt-blown nonwoven fabric of the present invention.

[0054] The NaCl collection efficiency of the meltblown nonwoven fabric of the present invention is 5% or more, preferably 40% or more, and more preferably 50% or more.

[0055] The pressure loss of the meltblown nonwoven fabric of the present invention is preferably 30 Pa or less, more preferably 0.1 Pa or more and 20 Pa or less.

[0056] The NaCl collection efficiency and pressure loss were measured using an automatic filter efficiency measuring device (TSI, model AFT8130) with an effective measurement area of ​​100 cm 2 Measurements can be made under conditions of a wind speed of 5.3 cm / s.

[0057] The QF value of an electret nonwoven fabric can be calculated using the following formula from the collection efficiency and pressure loss values.

[0058] QF value = -LN[(100 - collection efficiency (%)) / 100 (%)] / [pressure loss (Pa)] In the formula, LN represents the natural logarithm, i.e., the logarithm with Napier's number as the base.

[0059] The QF value is 0.1 or more, preferably 0.2 or more.

[0060] Preferably, the meltblown nonwoven fabric of the present invention undergoes compression after passing through a calender roll consisting of a pair of metal rolls with a clearance of 0.1 mm, with a decrease in air permeability of 20% or less compared to before passing through. Such meltblown nonwoven fabrics are pressure-resistant and do not easily lose air permeability even when pressure is applied. This leads to a longer lifespan and a maintained water permeability rate through the meltblown nonwoven fabric. The water permeability rate refers to the amount of pure water that can pass through the meltblown nonwoven fabric per unit area in one hour. The temperature during compression by the calender rolls is not particularly limited, but is preferably 5 to 40°C, more preferably 20 to 30°C.

[0061] Preferably, the meltblown nonwoven fabric of the present invention undergoes a thickness reduction due to compression of 35% or less after passing through a calender roll consisting of a pair of metal rolls with a clearance of 0.1 mm. Such a meltblown nonwoven fabric is pressure-resistant and does not easily lose thickness even when pressure is applied. This prevents a decrease in the amount of captured particles retained and helps maintain the water flow rate through the meltblown nonwoven fabric.

[0062] Preferably, the meltblown nonwoven fabric of the present invention has a ratio of decrease in air permeability to decrease in thickness due to compression after passing the meltblown nonwoven fabric through a pair of metal calender rolls with a clearance of 0.1 mm of 0.8 or less. Such a meltblown nonwoven fabric is pressure resistant, and when pressure is applied, both air permeability and thickness are unlikely to decrease equally, and the decrease in air permeability is less likely to occur than the decrease in thickness. This leads to a longer life and a maintained water permeability rate through the meltblown nonwoven fabric.

[0063] The polymer constituting the meltblown nonwoven fabric for filters according to the present invention is not particularly limited as long as it is a meltblown thermoplastic resin. Examples of polymers constituting the meltblown nonwoven fabric include polyolefins (e.g., polyethylene, polypropylene, etc., preferably polypropylene), polyesters, polyether ether ketones, polyphenylene sulfide, 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 certain thermoplastic resin can also be referred to as a meltblown nonwoven fabric containing the thermoplastic resin as the main component. In the present invention, a meltblown nonwoven fabric mainly composed of a certain thermoplastic resin means a meltblown nonwoven fabric obtained using a thermoplastic resin as a main raw material, and includes not only a meltblown nonwoven fabric obtained using only the thermoplastic resin, but also a meltblown nonwoven fabric obtained using the thermoplastic resin in an amount of, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, etc. For the meltblown nonwoven fabric of the present invention, polyolefins, polyesters, and polyamides are preferred, and polyolefins are particularly preferred.

[0064] Examples of the polyolefin include homopolymers of α-olefins such as propylene, ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene, as well as random or block copolymers of two or more of these α-olefins. Polypropylene is preferred. When polypropylene is used as a raw material for the nonwoven fabric of the present invention, its melt flow rate (MFR) is not particularly limited. For example, polypropylene having a melt flow rate (MFR) of 5 to 2,500 g / 10 min is preferred. When polypropylene with an MFR of less than 5 g / 10 min is used, the melt-mixing temperature and discharge temperature must be relatively high, which may result in the generation of carbonized polypropylene. Furthermore, when the MFR exceeds 2,500 g / 10 min, the elongation of the nonwoven fabric decreases, resulting in brittleness. When polypropylene is used as a raw material for 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 under a load of 2.16 kg and at a temperature of 230°C in accordance with JIS K7210.

[0065] 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 is preferred, 5 × 10 4 ~3×10 5 The molecular weight distribution of the polypropylene [weight average molecular weight (Mw) / number average molecular weight (Mn)] is not particularly limited, but is preferably 1.1-10, more preferably 1.5-8, and even more preferably 2-6.

[0066] In an embodiment of the present invention in which polypropylene is used as a raw material, the polypropylene may be a propylene homopolymer, or a random, block, or graft copolymer of predominantly polymerized propylene with other α-olefins (e.g., ethylene, butene, hexene, 4-methylpentene, octene, etc.), unsaturated carboxylic acids or derivatives thereof (e.g., acrylic acid, maleic anhydride, etc.), aromatic vinyl monomers (e.g., styrene, etc.), etc. In the present invention, these polypropylenes may be used alone, as a mixture of multiple types of polypropylenes, or as a mixture with a thermoplastic resin other than polypropylene (e.g., polyolefin, etc.).

[0067] In an embodiment of the present invention in which polyester is used as a raw material, the polyester is not particularly limited, but examples thereof include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc., and polyethylene terephthalate, polybutylene terephthalate, etc. are preferred.

[0068] In an embodiment of the present invention in which polyamide is used as a raw material, the polyamide is not particularly limited, but 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).

[0069] 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 flowability improver, and the like may be added to the above-mentioned thermoplastic resin within a range in which the effects of the present invention can be obtained.

[0070] Next, a method for producing a melt-blown nonwoven fabric according to a preferred embodiment of the present invention will be described with reference to the drawings, although the method is not limited to the following. Figure 1 shows an example of an apparatus for producing a melt-blown nonwoven fabric according to the present invention. This apparatus comprises a hopper 1a for introducing raw materials, an extruder 1b for melt-kneading the raw materials, a metering pump 2 for sending the molten polymer extruded from the extruder 1b downstream, a die 3a for horizontally discharging the molten polymer in a fibrous form, a temperature-regulating heater 3b for the high-temperature, high-velocity air discharged from the die 3a together with the molten polymer, a spinning nozzle 3c attached to the tip of the die, a collector 4a for collecting fibers provided near the die 3a, a suction blower 4b for sucking the collector 4a (and the fibrous molten polymer 5a collected by the collector 4a), the fibrous molten polymer 5a discharged from the die, a melt-blown 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 melt-blown nonwoven fabric 5b.

[0071] FIG. 2(A) is a partial front view showing the arrangement of the spinning nozzles in the nozzle 3c portion of the apparatus of FIG. 1. FIG. 2(B) is a partial perspective view of the nozzle 3c. FIG. 2(C) is a cross-sectional view of the nozzle 3c shown in FIG. 2(A) taken along X1-X1. In the embodiment shown in FIG. 2(A), the nozzle hole 3d of the spinning nozzle 3c in the die 3a consists of a nozzle hole 3d1 having a diameter D1 and a nozzle hole 3d2 located between the two nozzle holes 3d1 and having a smaller diameter at its tip than the diameter D1 of the nozzle hole 3d1. In FIG. 2(C), if the length of the nozzle hole 3d1 is L1 and the diameter, i.e., hole size, is D1, then the ratio L1 / D1 of the length L1 to the diameter D1 of the spinning nozzle hole 3d1 is preferably 3 or greater, more preferably 6 or greater, to ensure a uniform discharge flow rate of the molten polymer from the spinning nozzle 3c. In the embodiment of FIG. 2(C), the hole diameter D1 of the nozzle hole 3d1 is constant along the length direction. In order to efficiently obtain a melt-blown nonwoven fabric while preventing entanglement of the extruded polymer fibers, the density of the spinning nozzle holes 3d is preferably 3 to 40 holes per inch, more preferably 5 to 35 holes per inch.

[0072] Between two nozzle holes 3d1, n rows of nozzle holes 3d2 can be provided, where n is preferably in the range of 2 to 4 (n is 3 in the figure). The center-to-center distance between the nozzle holes 3d, or the so-called pitch interval, is equal between adjacent hole diameters 3d1-3d2 and 3d2-3d2.

[0073] The length L2 of the small-diameter nozzle hole 3d2 may 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 between the tip and base ends, with the tip diameter D2d being smaller than the base end diameter D2p. The length L1 of the large-diameter nozzle hole 3d1 and the length L2 of the small-diameter nozzle hole 3d2 are each preferably 0.3 to 20 mm, more preferably 3 to 10 mm.

[0074] The diameters D1 and D2 (D2d and D2p) of the nozzle holes 3d1 and 3d2 are preferably 0.1 to 2.0 mm, and the ratio R (D1 / D2d) of the diameter D1 of the nozzle hole 3d1 to the diameter D2d of the tip of the nozzle 3d2 is, for example, in the range of 1.3 to 2.0. When the diameter ratio R is 1.3 or more, the fiber diameter distribution becomes broad, and when the diameter ratio R is 2.0 or less, the resin discharge balance based on the difference in the diameters 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 of the tip of the nozzle hole 3d2 is 0.10 to 0.80 mm.

[0075] In the present application, in order to prevent or suppress the resin from being difficult to discharge even when the diameter of the small-diameter nozzle hole 3d2 of the spinning nozzle 3c is small and to widen the distribution range of fiber diameters, the pressure applied to the tip of the large-diameter nozzle hole 3d1 and the pressure applied to the tip of the small-diameter nozzle hole 3d2 are made closer than before. As will be easily understood by those skilled in the art of fluid dynamics, such pressure can be 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 in the longitudinal direction of the nozzle hole 3d2.

[0076] Preferably, the pressure applied to the tip of the large-diameter nozzle hole 3d1 and the pressure applied to the tip of the small-diameter nozzle hole 3d2 are substantially equal. 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 that the difference between the two pressures is within ±30%.

[0077] In some embodiments, the cross-sectional area of ​​the small-diameter nozzle hole 3d2 decreases in one or more steps between the base end and the tip in the longitudinal direction, so that the hole diameter D2 of the nozzle hole 3d2 also decreases stepwise from the hole diameter D2p at the base end to the hole diameter D2d at the tip. For example, in the case of two steps, L2 = L21 + L22, where the hole diameter for L21 is constant at D2p and the hole diameter for L22 is constant at D2d. In other embodiments, the cross-sectional area of ​​the small-diameter nozzle hole 3d2 continuously decreases between the base end and the tip in the longitudinal direction, so that the hole diameter D2 of the nozzle hole 3d2 also continuously decreases from the hole diameter D2p at the base end to the hole diameter D2d at the tip. The latter configuration can be achieved by tapering the wall defining the nozzle hole 3d2 from the base end to the tip or from a position between the base end and the tip to the tip.

[0078] The ratio R2 (D1 / D2p) of the pore diameter D2p to D1 is, for example, 0.3 to 0.95.

[0079] The melt-blown nonwoven fabric of the present invention can be produced by a method including the steps of melt-kneading a polymer, discharging the molten polymer from a spinning nozzle, and spraying heated air from another nozzle to form polymer fibers. Referring to the apparatus described above, when producing a melt-blown nonwoven fabric, the fibrous molten polymer 5a discharged from the spinning nozzle 3c is stretched with heated air sprayed from an air nozzle, and additional processes can be performed as necessary to obtain the melt-blown nonwoven fabric. The resulting melt-blown nonwoven fabric may be subjected to calendering, charging, hydrophilization, etc., as necessary.

[0080] (1) Melt-kneading process 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 The molten polymer is extruded from a number of spinning nozzles 3c, and heated air is sprayed from the nozzles to form fibers of the polymer. The temperature of the die 3a and 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 heated air is preferably 160 to 360°C, and more preferably 190 to 330°C. The above temperature range is preferable from the viewpoints of preventing the polymer from solidifying rapidly immediately after being extruded from the spinning nozzles 3c, preventing fusion of the formed polymer fibers, and suppressing variation in fiber diameter.

[0082] 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, more preferably 0.5 to 1 g / min / hole or less. From the viewpoint of obtaining a discharge pressure sufficient for fiber formation 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.

[0083] The amount of heated air ejected per width of the spinning nozzle is 1 to 50 Nm 3 / min / m is preferable, 3 to 40Nm 3 / min / m is more preferred.

[0084] The meltblown nonwoven fabric of the present invention has a wide fiber diameter distribution range and little unevenness due to fiber density. Therefore, the meltblown nonwoven fabric of the present invention and a laminate thereof are useful as filter materials for fluid filters. Fluids include gases and liquids. The meltblown nonwoven fabric of the present invention and a laminate thereof are particularly useful as filter materials for liquid filters.

[0085] The present invention also provides a fluid filter comprising this laminate. Because the meltblown nonwoven fabric of the present invention has the above-mentioned properties, even when the meltblown nonwoven fabric of the present invention is used alone as the meltblown nonwoven fabric constituting the filter material, a fluid filter can be obtained that has a wide fiber diameter distribution range and little fiber unevenness, and therefore has high substance capture capacity and a long life. Meanwhile, in another embodiment of the present invention, the meltblown nonwoven fabric of the present invention may be combined with other meltblown nonwoven fabrics as the meltblown nonwoven fabric constituting the filter material, depending on the purpose of filtration, and liquid filters comprising laminates containing such combinations of meltblown nonwoven fabrics are also encompassed by the liquid filter of the present invention. Therefore, in the present invention, the term "laminate for liquid filters comprising meltblown nonwoven fabrics" includes not only laminates for liquid filters comprising only 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, more than half of the number of meltblown nonwoven fabrics constituting the laminate) is a meltblown nonwoven fabric.

[0086] The meltblown nonwoven fabric and the method for producing the same of the present invention have been described above with reference to preferred embodiments, but the present invention is not limited to the specific embodiments described above.

[0087] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. [Example]

[0088] 1. Meltblown nonwoven fabric manufacturing Example 1 MFR40 homopolypropylene resin (weight average molecular weight 1.7 × 10) was placed in the raw material hopper of the melt-blown manufacturing equipment. 5The melt-kneading temperature was 305°C. The distance between the die and the collector was 400 mm, and 10 Nm of heated compressed air at 290°C was used. 3 The resin was discharged into the atmosphere from a nozzle with different hole diameters (3d1:3d2=1:3, D1=0.6 mm, D2d=0.4 mm, D2p=0.8 mm, L1=L2=8.0 mm, the same applies to the following examples) shown in FIG. 2, with a suction volume of 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 44 g / m² / min. The rotation speed of the collector was adjusted to obtain a resin mass of 44 g / m². 2 , thickness 1.05mm, breathability 686cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 17.7 μm was obtained.

[0089] The obtained melt-blown nonwoven fabric was subjected to a water supply rate of 0.2 g / cm using the electret processed product manufacturing apparatus described in Japanese Patent No. 6842022. 2 The fabric was then dried in a dryer to produce an electret. The resulting melt-blown nonwoven fabric had a collection efficiency of 46%, a pressure loss of 0.4 Pa, and a QF value of 1.5.

[0090] Example 2 As in Example 1, polypropylene resin and two types of additives were charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 310°C. The gap between the die and the collector was 400 mm, and 12 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from the nozzle described in Example 1, and the suction volume was 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 42 g / m² / min. The rotation speed of the collector was adjusted to obtain a resin mass of 42 g / m². 2 , thickness 0.61mm, breathability 189cm 3 / cm 2A melt-blown nonwoven fabric with a fiber diameter of 7.4 μm was obtained.

[0091] The obtained melt-blown nonwoven fabric was made into an electret in the same manner as in Example 1. The obtained melt-blown nonwoven fabric had a collection efficiency of 82%, a pressure loss of 4.0 Pa, and a QF value of 0.43.

[0092] Example 3 As in Example 1, polypropylene resin and two types of additives were charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 310°C. The gap between the die and the collector was 400 mm, and 12 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from the nozzle described in Example 1, and the suction volume was 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 21 g / m / min. The rotation speed of the collector was adjusted to obtain a mass of 21 g / m. 2 , thickness 0.39mm, breathability 271cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 8.0 μm was obtained.

[0093] The obtained melt-blown nonwoven fabric was made into an electret in the same manner as in Example 1. The obtained melt-blown nonwoven fabric had a collection efficiency of 72%, a pressure loss of 1.9 Pa, and a QF value of 0.67.

[0094] Example 4 The same MFR40 homopolypropylene resin (weight average molecular weight 1.7 × 10) as in Example 1 was placed in the raw material hopper of the melt-blown manufacturing equipment. 5 ) was added, and the melt-kneading temperature was set to 305°C. The distance between the die and the collector was 400 mm, and 8 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from the nozzle described in Example 1, and the suction volume was 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 47 g / m² / min. The rotation speed of the collector was adjusted to obtain a resin mass of 47 g / m². 2 , thickness 1.10mm, breathability 713cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 22.9 μm was obtained.

[0095] Comparative Example 1 Only the same homopolypropylene resin as in Example 1 was charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 308°C. The gap between the die and the collector was 400 mm, and 9 Nm of heated compressed air at 290°C was used. 3 / min / m, and the resin was discharged into the atmosphere from a single-hole nozzle (D = 0.9 mm, L = 8.0 mm), with a suction volume of 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 45 g / m² / min. The rotation speed of the collector was adjusted to obtain a mass of 45 g / m². 2 , thickness 1.10mm, breathability 645cm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 18.6 μm was obtained.

[0096] Comparative Example 2 Only the same homopolypropylene resin as in Example 1 was charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 308°C. The distance between the die and the collector was 400 mm, and 11 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from a nozzle with different hole diameters (3d1:3d2=1:3, D1=0.6mm, D2=0.4mm, L1=L2=6.0mm), and the suction volume was 100Nm 3 The fibrous resin was continuously collected on a collector at a rate of 47 g / m / min. The rotation speed of the collector was adjusted to obtain a resin mass of 47 g / m. 2 , thickness 1.20mm, breathability 801cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 14.5 μm was obtained.

[0097] Comparative Example 3 Only the same homopolypropylene resin as in Example 1 was charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 310°C. The gap between the die and the collector was 350 mm, and 12 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from the same single-hole nozzle as in Comparative Example 1, and the suction volume was 100 Nm 3The fibrous resin was continuously collected on a collector at a rate of 40 g / m² / min. The rotation speed of the collector was adjusted to obtain a mass of 40 g / m². 2 , thickness 0.37mm, breathability 88cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 5.2 μm was obtained.

[0098] Comparative Example 4 The same MFR40 homopolypropylene resin (weight average molecular weight 1.7 × 10) as in Example 1 was placed in the raw material hopper of the melt-blown manufacturing equipment. 5 99.99% by mass of crystalline nucleating agent (BASF Irgaclear® XT386) as an additive was added, and the melt-kneading temperature was set to 308°C. The gap between the die and the collector was 350 mm, and 11 Nm of heated compressed air at 290°C was used. 3 / min / m, the resin was discharged into the atmosphere from the same single-hole nozzle as in Comparative Example 1, and the suction volume was 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 20 g / m / min. The rotation speed of the collector was adjusted to obtain a mass of 20 g / m. 2 , thickness 0.30mm, breathability 220cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 5.5 μm was obtained.

[0099] The obtained melt-blown nonwoven fabric was made into an electret in the same manner as in Example 1. The obtained melt-blown nonwoven fabric had a collection efficiency of 48%, a pressure loss of 3.5 Pa, and a QF value of 0.19.

[0100] Comparative Example 5 As in Example 1, polypropylene resin and two types of additives were charged into the raw material hopper of the melt-blown manufacturing equipment, and the melt-kneading temperature was set to 305°C. The gap between the die and the collector was 400 mm, and heated compressed air of 290°C was used at 12 Nm 3 / min / m, the resin was discharged into the atmosphere from the same single-hole nozzle as in Comparative Example 1, and the suction volume was 100 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 20 g / m / min. The rotation speed of the collector was adjusted to obtain a mass of 20 g / m. 2 , thickness 0.27mm, breathability 220cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 7.6 μm was obtained.

[0101] The obtained melt-blown nonwoven fabric was made into an electret in the same manner as in Example 1. The obtained melt-blown nonwoven fabric had a collection efficiency of 85%, a pressure loss of 6.4 Pa, and a QF value of 0.30.

[0102] Measurement and evaluation of various physical properties Next, the physical properties of the obtained melt-blown nonwoven fabrics of Examples 1-4 and Comparative Examples 1-5 were measured and calculated as follows. The results are shown in Table 1.

[0103] (1) Average area weight The average basis weight was determined by measuring the mass (g) of 10 melt-blown nonwoven fabric test pieces of 100 mm x 100 mm in a moisture equilibrium state at a temperature of 23°C and a humidity of 50% and averaging the measured values.

[0104] (2) Thickness For a 100mm x 100mm melt-blown nonwoven fabric test piece, diameter 2.5cm, load 7g / cm 2 The thickness of the central part of the test piece, which corresponds to the center of gravity, was measured using a linear gauge equipped with a measuring probe, and the measured values ​​of 10 pieces were averaged to obtain the thickness.

[0105] (3) Breathability The air permeability was measured on 10 melt-blown nonwoven fabric test pieces of 100 mm x 100 mm using a Frazier type tester in accordance with JIS L1096, and the results were averaged. Since nonwoven fabrics with high air permeability exceed the upper limit of the measuring instrument, the air permeability was calculated by averaging 100 cm per piece. 3 / cm 2 For air permeability of 100mm x 100mm or more, three 100mm x 100mm test pieces were simply stacked together and the air permeability was measured. Ten sets of measurements were taken, and the average value for the three test pieces was calculated. Table 1 shows the average value for the three test pieces multiplied by three.

[0106] (4) Average fiber diameter The average fiber diameter was calculated by taking four electron micrographs at a magnification that allowed for approximately 25 fibers to be included in each image, measuring the fiber diameters of a total of 100 fibers to the order of 0.1 μm, and averaging these.

[0107] The fiber diameter fraction is the number of fibers having a particular fiber diameter expressed as a percentage of the total number of fibers.

[0108] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric having a fiber diameter of 0.25 times or less the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers having a fiber diameter of 0.25 times or less the average fiber diameter by 100 and multiplying the result by 100.

[0109] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric having a fiber diameter of 0.5 times or less the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers having a fiber diameter of 0.5 times or less the average fiber diameter by 100 and multiplying the result by 100.

[0110] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric having a fiber diameter of 0.75 times or less the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter by 100 and multiplying the result by 100.

[0111] The proportion of thermoplastic resin fibers in a meltblown nonwoven fabric that have a fiber diameter that is 2.5 times or more the average fiber diameter is determined by randomly selecting 100 fibers from an electron microscope photograph 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 dividing the number of thermoplastic resin fibers that have a fiber diameter that is 2.5 times or more the average fiber diameter by 100 and multiplying the result by 100.

[0112] (5) Formation index The formation index was determined by measuring three A4-sized melt-blown nonwoven fabric test pieces using a fabrication analyzer (FMT-M III manufactured by Nomura Shoji Co., Ltd.) and averaging the results.

[0113] (6) Bursting strength The burst strength was determined in accordance with JIS P8112:2008 "Paper - Bursting strength test method" using a Mullen burst tester M2-LD manufactured by Toyo Seiki Co., Ltd., and was the average value of the values ​​measured in three tests.

[0114] (7) NaCl collection efficiency and pressure loss The NaCl collection efficiency and pressure loss were measured using an automatic filter efficiency measuring device (TSI, Model AFT8130) on three A4-sized melt-blown nonwoven fabric test pieces with an effective measurement area of ​​100 cm. 2 The measurements were taken under a wind speed of 5.3 cm / s and the average was calculated.

[0115] (8) QF value The QF value can be calculated using the following formula from the collection efficiency and pressure loss values. QF value = -LN[(100 - collection efficiency (%)) / 100 (%)] / [pressure loss (Pa)] where LN is the natural logarithm.

[0116] (9) Thickness after 0.1mm clearance processing The thickness of each melt-blown nonwoven fabric of Examples 1-4 and Comparative Examples 1-5 was measured before and after passing each melt-blown nonwoven fabric through a calender roll consisting of a pair of metal rolls with a clearance of 0.1 mm at 25° C. The thickness was measured in accordance with the description of (2) Thickness above.

[0117] The thickness reduction rate (D) was calculated by (thickness of melt-blown nonwoven fabric before passing through the calender rolls - thickness of melt-blown nonwoven fabric after passing through the calender rolls) / (thickness of melt-blown nonwoven fabric before passing through the calender rolls)*100.

[0118] (10) Air permeability after 0.1mm clearance processing The air permeability of each of the melt-blown nonwoven fabrics of Examples 1-4 and Comparative Examples 1-5 was measured before and after passing each melt-blown nonwoven fabric through a calender roll consisting of a pair of metal rolls with a clearance of 0.1 mm at 25° C. The air permeability was measured in accordance with the description of (3) Air permeability above.

[0119] The air permeability reduction rate (T) was calculated by (air permeability of melt-blown nonwoven fabric before passing through the calendar roll - air permeability of melt-blown nonwoven fabric after passing through the calendar roll) / (air permeability of melt-blown nonwoven fabric before passing through the calendar roll) * 100.

[0120] As shown in Table 1, the melt-blown nonwoven fabrics of Examples 1 to 4 of the present invention have a wide fiber diameter distribution, with fine and thick fibers uniformly dispersed and little fiber unevenness. When used as a filter, such melt-blown nonwoven fabrics can be expected to have high particle collection performance and a long life.

[0121] [Table 1]

Claims

1. A meltblown nonwoven fabric containing a plurality of thermoplastic resin fibers having different fiber diameters, a resin component of the thermoplastic resin fiber containing at least one selected from the group consisting of polyolefins and polyamides, The average fiber diameter of the thermoplastic resin fibers is 5 μm or more, and the ratio of thermoplastic resin fibers having a fiber diameter of 0.5 times or less of the average fiber diameter is 10% or more. A meltblown nonwoven fabric, The decrease in air permeability due to compression after passing the melt-blown nonwoven fabric through a calendar roll having a clearance of 0.1 mm, which is made of a pair of metal rolls, is 20% or less of the air permeability before passing through the calendar roll, A melt-blown nonwoven fabric having a ratio of burst strength to basis weight (kPa / (g / m 2 )) of 1.0 or more.

2. The meltblown nonwoven fabric according to claim 1, wherein the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is 30% or more.

3. The meltblown nonwoven fabric according to claim 1, wherein the proportion of thermoplastic resin fibers having a fiber diameter of 2.5 times or more the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is 1% or more.

4. 2. The meltblown nonwoven fabric according to claim 1, wherein the thickness reduction due to compression after passing the meltblown nonwoven fabric through a calendar roll having a clearance of 0.1 mm consisting of a pair of metal rolls is 35% or less of the thickness before passing.

5. 2. The meltblown nonwoven fabric according to claim 1, wherein the ratio of the decrease in air permeability to the decrease in thickness due to compression after passing the meltblown nonwoven fabric through a calendar roll having a clearance of 0.1 mm and consisting of a pair of metal rolls is 0.8 or less.

6. The melt-blown nonwoven fabric according to claim 1, which is an electret nonwoven fabric containing a hindered amine light stabilizer and / or a crystal nucleating agent as an additive, and has a QF value of 0.2 or more.

7. A filter comprising the meltblown nonwoven fabric according to any one of claims 1 to 6.

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