Melt-blown non-woven fabrics and filters incorporating such materials.

Abstract

DEPCT6609 / 06 / 2566 Melt-blown nonwoven fabric is a material composed of resin fibers. Thermoplastic filaments with varying fiber diameters, where the fiber diameter... It has a standard deviation of 1.2 or more and the fibers have a fabric index to diameter ratio. Average fiber content is less than 33;

Description

Meltblown nonwoven fabric and filter equipped with same

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

[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] Meltblown nonwoven fabrics are produced by discharging molten polymer from multiple meltblown nozzles installed at a fixed pitch and spinning the discharged molten polymer. While nozzle orifice diameters are typically uniform, the applicant previously created a nozzle with a specific ratio of small-diameter and large-diameter nozzles. It was confirmed that meltblown nonwoven fabrics produced using the nozzle with different orifice diameters have a wider fiber diameter distribution than those produced using a standard nozzle (Patent Document 1). A wider fiber diameter distribution allows for more uniform capture of substances not only on the surface layer but also inside the nonwoven fabric, resulting in a filter that is less susceptible to clogging and has a longer filtration life.

[0004] Patent Document 2 describes the production of a meltblown nonwoven fabric in which the cumulative frequency of fiber diameters of 1 μm or less is 5% or more and the cumulative frequency of fiber diameters of 10 μm or more is in the range of 0.1 to 5% by using nozzle pieces with a different ratio of small-hole nozzles and large-hole nozzles than those in Patent Document 1. This meltblown nonwoven fabric has excellent sound absorption properties.

[0005] Patent Document 3 discloses a high-loft nonwoven web having a wide range of fiber diameters 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 mixed fiber nonwoven fabric in which a resin constituting a fiber group A and a resin constituting a fiber group B are melted in separate extruders and discharged from separate spinning holes, and the single-hole polymer discharge rate from the discharge hole for fiber group A is set to be small and the single-hole polymer discharge rate 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.

[0007] Patent Document 5 discloses the production of a nonwoven fabric in which the fiber diameter of the thermoplastic resin fiber has two peaks using a nozzle with a single nozzle hole diameter, by using polypropylene and polypropylene wax as the thermoplastic resin raw material for the thermoplastic resin fiber contained in the nonwoven fabric.

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

[0009] JP 11-131353, JP 2013-147771, JP 2020-505530, JP 2016-160542, WO 2017 / 142021, WO 2018 / 030057

[0010] Although the use of a variable-diameter nozzle can achieve a longer filter life than the use of a single-diameter nozzle, the distribution range of the fiber diameter of the polymer fibers that can be produced is limited due to constraints on the nozzle design. For example, as the fibers become thinner, it becomes more difficult for the resin to come out of the small-diameter nozzle holes, and the thin fibers break, resulting in the generation of numerous shots, which are polymer agglomerates, which can degrade the appearance and quality of the nonwoven fabric. On the other hand, as the fibers become thicker, the appearance of the nonwoven fabric becomes uneven, consisting of dense and coarse fiber areas, i.e., unevenness due to fiber density becomes greater, resulting in greater variation in physical properties and the generation of shots due to insufficient cooling of the thick fibers, which can degrade the quality of the nonwoven fabric.

[0011] 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.

[0012] 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.

[0013] Under these circumstances, the present inventors conducted extensive research and found that the above-mentioned problems can be solved by providing a meltblown nonwoven fabric containing a plurality of thermoplastic resin fibers with different fiber diameters, in which the standard deviation of the fiber diameters is 1.2 or more and the ratio of the formation index to the average fiber diameter is less than 33. Therefore, the present invention encompasses the following embodiments.

[0014] Item 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 1.2 or more and the ratio of the formation index to the average fiber diameter is less than 33.

[0015] Item 2. The meltblown nonwoven fabric according to Item 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 4% or more.

[0016] Item 3. The meltblown nonwoven fabric according to Item 1 or 2, 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 46% or more.

[0017] Item 4. The melt-blown nonwoven fabric according to any one of Items 1 to 3, wherein the thermoplastic resin fibers have an average fiber diameter of 1 μm to 50 μm.

[0018] Item 5. The meltblown nonwoven fabric according to any one of Items 1 to 4, wherein the resin component of the thermoplastic resin fiber is at least one selected from the group consisting of polyolefin, polyester, and polyamide.

[0019] Item 6. A filter comprising the melt-blown nonwoven fabric according to Item 5.

[0020] According to the present invention, a melt-blown nonwoven fabric can be provided that has a wide fiber diameter distribution range and little unevenness due to fiber density. Such a nonwoven fabric is resistant to loss of thickness even when pressure is applied, and its air permeability is also resistant to loss of air permeability after filtering. Therefore, a filter using such a nonwoven fabric is expected to have a high ability to maintain its fiber structure and a long life.

[0021] 2A and 2B are schematic diagrams of a process for producing a melt-blown nonwoven fabric of the present invention. (A) A partial front view showing the arrangement of spinning nozzles in the nozzle 3c portion in the apparatus of FIG. 1. (B) A partial perspective view of the nozzle 3c. (C) A cross-sectional view of the nozzle 3c at X1-X1 shown in FIG. 2A. Graph showing particle filtration efficiency of the melt-blown nonwoven fabrics of Example 1, Comparative Example 1, and Comparative Example 2.

[0022] 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.

[0023] The present invention provides a meltblown nonwoven fabric containing a plurality of thermoplastic resin fibers having different fiber diameters, wherein the standard deviation of the fiber diameters is 1.2 or more and the ratio of the formation index to the average fiber diameter is less than 33.

[0024] The meltblown nonwoven fabric of the present invention has a standard deviation of fiber diameter of 1.2 or more. When the standard deviation of fiber diameter is 1.2 or more, the fiber diameter distribution range is wide, resulting in a mixture of thinner and thicker fibers. When 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. When the standard deviation of fiber diameter is less than 1.2, the majority of the fibers constituting the nonwoven fabric will be fibers with a certain limited range of fiber diameters. A bias toward fine fibers improves particle collection capacity, but the gaps between fibers are crushed by filtration pressure, making it difficult to return to the original structure, making the fabric more susceptible to clogging. Furthermore, a bias toward thick fibers results in greater unevenness due to fiber density, resulting in poor formation and insufficient particle collection capacity.

[0025] In the present invention, 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 such that about 25 fibers are included in each image, measuring the fiber diameters of a total of 100 arbitrarily selected fibers to the order of 0.1 μm in diameter, and averaging the measured values.

[0026] 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 the value is calculated using the following formula (1).

[0027]

[0028] n is the total number of fibers measured (n = 100), x i is the fiber diameter of each fiber, x ave is the average fiber diameter.

[0029] In the meltblown nonwoven fabric of the present invention, the proportion of thermoplastic resin fibers having a fiber diameter of at least 2.5 times the average fiber diameter among the thermoplastic resin fibers in the meltblown nonwoven fabric is at least 4%.

[0030] 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 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 2.5 times or more the average fiber diameter by 100 and multiplying the result by 100.

[0031] When the proportion of thermoplastic resin fibers having a fiber diameter 2.5 times or more the average fiber diameter is 4% or more, fibers with a relatively large average fiber diameter are present in the meltblown nonwoven fabric, and gaps between the fibers of the meltblown nonwoven fabric are secured, increasing breathability and improving compression resistance.

[0032] The upper limit of the proportion of thermoplastic resin fibers with a large average fiber diameter is not particularly limited, but in some embodiments, in terms of reducing unevenness due to fiber density 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 more the average fiber diameter is preferably 20% or less. The proportion of thermoplastic resin fibers having a fiber diameter of 5 times or more the average fiber diameter is determined by randomly selecting 100 fibers (n = 100) from a photograph of the surface of the nonwoven fabric taken with an electron microscope, measuring the diameters of the selected fibers, and calculating the value expressed as the number of fibers having a fiber diameter of 5 times or more the average fiber diameter / the total number of fibers measured (n = 100) x 100. The meltblown nonwoven fabric of the present invention preferably has a proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter of 46% or more of the thermoplastic resin fibers in the meltblown nonwoven fabric.

[0033] 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 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.

[0034] When the proportion of thermoplastic resin fibers having a fiber diameter of 0.75 times or less the average fiber diameter is 46% or more, a large proportion of fibers having a relatively small average fiber diameter 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.

[0035] The melt-blown nonwoven fabric of the present invention has 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 its air permeability is also resistant to reduction after filtration of the target substance (hereinafter, the target substance may be simply referred to as "substance"). Therefore, a filter using such a nonwoven fabric is expected to have a high ability to maintain its fiber structure, and to have high filtering performance and a long life.

[0036] The meltblown nonwoven fabric of the present invention has a ratio of the formation index to the average fiber diameter of less than 33. When the ratio of the formation index to the average fiber diameter is less than 33, the formation is more uniform due to less unevenness caused by fiber coarseness and density, and stable, high particle collection ability can be expected. When the ratio of the formation index to the average fiber diameter is 33 or more, the unevenness caused by fiber coarseness and density is large, and there are portions with large gaps between fibers, which is undesirable as the particle collection efficiency is unstable.

[0037] The formation index of a nonwoven fabric is an index of the basis weight per unit area and represents the uniformity of fiber orientation. The formation index of a nonwoven fabric can be calculated by irradiating a sample with transmitted light and using the distribution of shades in the image. A smaller formation index indicates higher uniformity. Furthermore, a smaller formation index indicates a higher substance capture ability of the nonwoven fabric. Specifically, a transmission-type fabric analyzer (FMT-M III manufactured by Nomura Shoji Co., Ltd.) is used for measurement, and the amount of transmitted light is measured with a CCD camera with the light source on and off without a sample set. Subsequently, the amount of transmitted light is measured in the same manner with an A4-sized piece of nonwoven fabric set, and the average transmittance, average absorbance, and standard deviation are calculated. The formation index can be calculated by dividing the standard deviation by the average absorbance and multiplying it by 1,000.

[0038] The average fiber diameter of the meltblown nonwoven fabric of the present invention is not particularly limited, but from the viewpoints of application to a fluid filter and compression resistance, it is preferably 1 to 50 μm. In some embodiments, the average fiber diameter is 1 to 40 μm. In other embodiments, the average fiber diameter is 1 to 10 μm.

[0039] 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 20 to 100 g / m 2 and more preferably 40 to 90 g / m 2From the viewpoint of improving strength (improved strength makes it easier to process into a filter), and from the viewpoint of preventing the rigidity from becoming too high when forming a filter and improving adhesion with other materials to perform more uniform lamination (more uniform lamination leads to effective filtration performance), it is preferable that the average basis weight of the melt-blown nonwoven fabric is set to the above range. The basis weight is preferably 40 g / m 2 More preferably, 45 g / m 2 At or above this level, a formation index to average fiber diameter ratio of less than 33 is more easily achieved.

[0040] In some preferred embodiments of the meltblown nonwoven fabric, when the average fiber diameter is 1 to 10 μm, the basis weight 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 basis weight 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 basis weight is 80 g / m 2 That's all.

[0041] 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.

[0042] 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 x 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, and 10 to 800 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.

[0043] 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 ~ 400cm 3 / cm 2 In some other embodiments, the average fiber diameter of the thermoplastic resin fibers is 1 μm or more and less than 5 μm, and the air permeability of the meltblown nonwoven fabric is 1 to 50 cm 3 / cm 2 / second.

[0044] The shot of the meltblown nonwoven fabric of the present invention is not particularly limited, but may be 1 m 2 For melt-blown nonwoven fabric, there are 3 transparent spots (resin lumps) with a diameter of 0.5 mm or more per m 2 Preferably, 1 piece / m or less 2 If shot is present in the meltblown nonwoven fabric, the maximum pore size around the shot increases, and the filtration performance decreases.

[0045] The burst strength of the meltblown nonwoven fabric of the present invention is not particularly limited, but when the average fiber diameter is 1 to 5 μm, it is 100 kPa or more, more preferably 150 kPa or more, more preferably 160 kPa or more, more preferably 170 kPa or more, and when the average fiber diameter is 5 to 50 μm, it is 150 kPa or more, more preferably 190 kPa. If the meltblown nonwoven fabric has uneven fiber density, the pressure resistance of the filtration medium may decrease when used as a filter, leading to membrane rupture. The upper limit of the burst strength is not particularly limited, but due to concerns about reduced processability of the meltblown nonwoven fabric, it is usually preferably 1000 kPa or less, 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.

[0046] The burst strength improves as the basis weight increases, and is not particularly limited, but the burst strength / basis weight ratio is 2 or more, more preferably 2.2 or more.

[0047] The pore size of a meltblown nonwoven fabric is the gap between fibers and can be adjusted by the fiber diameter, fiber diameter distribution, basis weight, thickness, etc. When used as a filter, the preferred pore size varies depending on the particle size of the substance to be captured. Generally, from the viewpoint of particle capture capacity, the smaller the maximum pore size, minimum pore size, and average pore size, the more preferable, and from the viewpoint of filter life, the larger the pore size. The pore size (maximum pore size, minimum pore size, average pore size) is measured by the bubble point method (ASTM F316-86, JIS K3832). In terms of particle capture capacity and life, the average pore size is preferably within the range of 5 to 50 μm.

[0048] The initial water flow rate represents the amount of pure water that can pass through a melt-blown nonwoven fabric per unit area in one hour in an initial state where filtrate containing particles and the like has not yet been filtered. This value is determined by measuring the time it takes for a certain amount of pure water to pass through the melt-blown nonwoven fabric under its own weight after alcohol substitution of the melt-blown nonwoven fabric. The initial water flow rate is an indicator of the filtration rate as a filter, and the faster the initial water flow rate, the greater the initial filtration throughput of the filter. The initial water flow rate of the melt-blown nonwoven fabric of the present invention is not particularly limited, but is preferably 600 mL / cm. 2 / h or more, and 650 mL / cm 2 / h or more, and more preferably 680 mL / cm 2 The melt-blown nonwoven fabric of the present invention has a high initial water permeability rate relative to the basis weight, which is thought to be due to the fact that there is little unevenness due to the density of the fibers.

[0049] The amount of deposited particles when the water flow rate is halved is the amount of particles captured by the meltblown nonwoven fabric at the point when the water flow rate is halved during the process of filtering filtrate containing particles, etc., and is an index of clogging of the meltblown nonwoven fabric. Generally, a filter needs to be replaced when the water flow rate is reduced to a certain level, and the longer the filtration amount before replacement, the longer the filter life can be evaluated. The amount of deposited particles is 40 g / m 2 More than 50 g / m 2 The above is more preferable.

[0050] The filtration efficiency evaluation (0-100%) is the efficiency with which particles can be collected when a filtrate containing particles is filtered through a melt-blown nonwoven fabric, and the higher the efficiency, the better. Generally, the filtration efficiency decreases as the filtered particle size decreases, and improves as the average pore size of the melt-blown nonwoven fabric decreases.

[0051] The polymer constituting the meltblown nonwoven fabric for filters according to the present invention is not particularly limited as long as it is a meltblownable thermoplastic resin. Examples of polymers constituting meltblown nonwoven fabrics 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. Furthermore, in the present invention, a meltblown nonwoven fabric composed primarily of a certain 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 using only the thermoplastic resin, but also meltblown nonwoven fabrics obtained using the thermoplastic resin in a proportion of 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. In the melt-blown nonwoven fabric of the present invention, polyolefins and polyesters are preferred, with polyolefins being particularly preferred.

[0052] 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 the raw material for the nonwoven fabric in the present invention, its melt flow rate (MFR) is not particularly limited, but polypropylenes having a melt flow rate (MFR) of 5 to 2,500 g / 10 min are preferred. When using polypropylene with an MFR of less than 5 g / 10 min, relatively high melt-mixing and extrusion temperatures are required, 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, 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, and 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.

[0053] 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 x 10 5 is preferred, and 5 × 10 4 ~3 x 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 to 10, more preferably 1.5 to 8, and even more preferably 2 to 6.

[0054] 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.).

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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, but 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 includes 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 together with the molten polymer from the die 3a, 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.

[0059] 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 the 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 diameter, is D1, then in order to uniformly discharge the molten polymer from the spinning nozzle 3c, the ratio L1 / D1 of the length L1 to the diameter D1 of the spinning nozzle hole 3d1 is preferably 3 or more, more preferably 6 or more. 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 fibers of the discharged polymer, the density of the spinning nozzle holes 3d is preferably 3 to 40 holes per inch, more preferably 5 to 35 holes per inch.

[0060] 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, i.e., the so-called pitch interval, is equal between adjacent hole diameters 3d1-3d2 and 3d2-3d2.

[0061] 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.

[0062] The D1 and D2 (D2d, D2p) of the nozzle holes 3d1 and 3d2 are preferably 0.1 to 2.0 mm, and the ratio R (D1 / D2d) of the hole diameter D1 of the nozzle hole 3d1 to the hole diameter D2d at the tip of the nozzle 3d2 is, for example, in the range of 1.3 to 2.0. When the hole diameter ratio R is 1.3 or more, the fiber diameter distribution becomes broad, and when the hole diameter ratio R is 2.0 or less, the resin discharge balance based on the difference in hole diameter is maintained, resulting in a stable spinning state. For example, the hole diameter D1 of the nozzle hole 3d1 is 0.20 to 1.20 mm, and the hole diameter D2d at the tip of the nozzle hole 3d2 is 0.10 to 0.80 mm.

[0063] In the present application, in order to prevent or suppress the resin from being difficult to come out 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.

[0064] 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%.

[0065] 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 decreases continuously between the base end and the tip in the longitudinal direction, so that the hole diameter D2 of the nozzle hole 3d2 also decreases continuously 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.

[0066] The ratio R2 (D1 / D2p) of the hole diameter D2p to D1 is, for example, 0.3 to 0.95.

[0067] 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 if necessary to obtain the melt-blown nonwoven fabric. The obtained melt-blown nonwoven fabric may be subjected to calendering, charging, hydrophilization, etc., as necessary.

[0068] (1) Melt-Kneading Step 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.

[0069] (2) Fiber Formation Step The molten polymer is discharged 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 (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, more preferably 190 to 330°C. The above temperature range is preferred from the viewpoints of preventing the polymer from rapidly solidifying immediately after being discharged from the spinning nozzles 3c, suppressing fusion of the formed polymer fibers, and suppressing variation in fiber diameter.

[0070] 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.

[0071] The amount of heated air ejected per width of the spinning nozzle is 5 to 50 Nm 3 / min / m is preferred, and 10 to 40 Nm 3 / min / m is more preferred.

[0072] 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.

[0073] The present invention also provides a fluid filter comprising the 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) uses meltblown nonwoven fabric.

[0074] 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.

[0075] 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.

[0076] 1. Production of Melt-Blown Nonwoven Fabric Example 1 A homopolypropylene resin with an MFR of 40 (weight average molecular weight 1.7 × 10) was placed in the raw material hopper of a melt-blown nonwoven fabric production apparatus. 5 The same applies to the following Examples and Comparative Examples) was added, and the melt-kneading temperature was set to 375°C. The gap between the die and the collector was 250 mm, and 13 Nm of heated compressed air at 290°C was used. 3 The resin was discharged into the atmosphere from the nozzle shown in FIG. 2 (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) at a speed of 1 / min / m, and the suction volume was 394 Nm 3The fibrous resin was continuously collected on a collector at a rate of 1 / min / m, and the rotation speed of the collector was appropriately adjusted to obtain a mass of 61 g / m. 2 , thickness 0.91 mm, breathability 12 cm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 1.9 μm and a formation index of 46 was obtained.

[0077] Example 2 A homopolypropylene resin with an MFR of 40 was charged into the raw material hopper of a melt-blown manufacturing apparatus, and the melt-blending temperature was set to 375°C. The gap between the die and the collector was 300 mm, and 15 Nm of heated compressed air at 290°C was blown. 3 At the same time, the resin was discharged into the atmosphere from the same nozzle as in Example 1, and the suction volume was 217 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 82 g / min / m, and the rotation speed of the collector was appropriately adjusted to obtain a mass of 82 g / m. 2 , thickness 1.33 mm, breathability 18 cm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 2.5 μm and a formation index of 53 was obtained.

[0078] Example 3 A homopolypropylene resin with an MFR of 40 was charged into the raw material hopper of a melt-blown manufacturing apparatus, and the melt-blending temperature was set to 365°C. The gap between the die and the collector was 500 mm, and 22 Nm of heated compressed air at 290°C was blown. 3 At the same time, the resin was discharged into the atmosphere from the same nozzle as in Example 1, and the suction volume was 197 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 82 g / min / m, and the rotation speed of the collector was appropriately adjusted to obtain a mass of 82 g / m. 2 , thickness 1.13 mm, breathability 65 cm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 6.5 μm and a formation index of 117 was obtained.

[0079] Comparative Example 1 A homopolypropylene resin with an MFR of 40 was charged into the raw material hopper of a melt-blown manufacturing apparatus, and the melt-blending temperature was set to 414°C. The gap between the die and the collector was 200 mm, and 290°C heated compressed air was used at 29 Nm 3 At the same time, the resin was discharged into the atmosphere from a single-hole nozzle (D = 0.4 mm, L = 4.0 mm) at a speed of 1 / min / m, and the suction volume was 327 Nm3 The fibrous resin was continuously collected on a collector at a rate of 1 / min / m, and the rotation speed of the collector was appropriately adjusted to a basis weight of 60 g / m. 2 , thickness 1.10 mm, air permeability 10 ccm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 1.6 μm and a formation index of 61 was obtained.

[0080] Comparative Example 2 A homopolypropylene resin with an MFR of 40 was charged into the raw material hopper of a melt-blown manufacturing apparatus, and the melt-blending temperature was set to 408°C. The gap between the die and the collector was 160 mm, and 290°C heated compressed air was blown through at 29 Nm 3 At the same time, the resin was discharged into the atmosphere from a nozzle with a different hole diameter (3d1:3d2 = 1:3, D1 = 0.6 mm, D2 = 0.4 mm, L1 = L2 = 6.0 mm), and the suction volume was 327 Nm 3 The fibrous resin was continuously collected on a collector at a rate of 1 / min / m, and the rotation speed of the collector was appropriately adjusted to a basis weight of 60 g / m. 2 , thickness 1.01 mm, breathability 12 cm 3 / cm 2 A melt-blown nonwoven fabric having a fiber diameter of 1.3 μm and a formation index of 57 was obtained.

[0081] Measurement and Evaluation of Various Physical Properties Next, the physical properties of the obtained melt-blown nonwoven fabrics of Examples 1-3 and Comparative Examples 1-2 were measured and calculated as follows. The results are shown in Table 1. (1) Average basis 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 results. (2) Thickness 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 results. 2The thickness of the central part corresponding to the center of gravity of the test piece was measured using a linear gauge equipped with a measuring probe, and the measurements of 10 pieces were averaged to determine the value. (3) Air Permeability Air permeability was measured for 10 meltblown nonwoven fabric test pieces measuring 100 mm x 100 mm using a Frazier-type testing machine according to JIS L1096, and the average was determined. (4) Average Fiber Diameter The average fiber diameter was determined by taking four electron micrographs at a magnification that allowed for approximately 25 fibers per image, measuring the fiber diameters of a total of 100 fibers to the order of 0.1 μm in diameter, and averaging these. The fiber diameter ratio is the ratio of the number of fibers having a specific fiber diameter to the total number of fibers, expressed as a percentage.

[0082] (5) Formation Index The formation index was determined by measuring three A4 size meltblown nonwoven fabric test pieces using a fabrication totalizer (FMT-M III manufactured by Nomura Shoji Co., Ltd.) and averaging the results. (6) Shot The shot was measured at 1 m 2 The presence or absence of film formation was determined by visually observing the presence or absence of transparent spots with a diameter of 0.5 mm or more on the meltblown nonwoven fabric test pieces. (7) Burst strength Burst strength was measured in accordance with JIS P8112:2008 "Paper - Burst strength test method" and was taken as the average value of the values ​​measured in three tests using a Mullen burst tester M2-LD manufactured by Toyo Seiki Co., Ltd. (8) Measurement method for maximum pore size, minimum pore size, and average pore size The maximum pore size, minimum pore size, and average pore size were measured using an automatic pore size distribution measuring instrument (model "CFP-1200AX", manufactured by Porous Materials Co., Ltd.) based on the bubble point method (ASTM F316-86, JIS K3832) shown below. During the measurement, a melt-blown nonwoven fabric specimen wetted with a test liquid (GALWICK or SILWICK) was set, and air pressure applied to one side was gradually increased.

[0083] (9) Evaluation of Initial Water Passage Rate and Amount of Deposited Particles at Half the Water Passage Rate The initial water pass rate and the amount of deposited particles at half the water pass rate were measured by the following method. 1. The weight (mg) of a melt-blown nonwoven fabric test piece cut to a size of 47 mm in diameter was measured. 2. After immersing the test piece in isopropanol, the diameter of the filtrate-passing portion of the test piece was set to 43 mm, and 400 mL of pure water was passed through it by its own weight, replacing the isopropanol contained in the test piece with water. 3. 100 mL of pure water was poured into the test piece, and the time it took for this pure water to pass through the test piece by its own weight was measured. The amount of water passing per unit area and unit time was calculated as the initial water pass rate (mL / cm 2 / h). 4. Next, 100 mL of pure water containing 10 mg of JIS Class 7 powder (Kanto loam, calcined product) was passed through the test piece. 5. After step 4 was completed, a pressure of 5 kPa was applied to the test piece from the upstream side. 6. 100 mL of pure water was poured into the test piece, and the time it took for the water to pass through under its own weight was measured, and the water flow rate was calculated. 7. Steps 4 to 6 were repeated until the initial water flow rate measured in step 3 was reduced by half. 8. Thereafter, the test piece was naturally dried for 24 hours at a temperature of 23°C and a humidity of 50%, and its weight was measured. The difference from the weight measured in step 1 was taken as the amount of particles (mg) deposited on the test piece, and the particles per unit area was taken as the amount of deposited particles (g / m) when the water flow rate was reduced by half. 2 )

[0084] (10) Evaluation of filtration efficiency: 200 mL of a test solution prepared by mixing JIS Class 7 powder with pure water to a concentration of 200 ppm was filtered through a test piece (diameter of the test solution passage part: 43 mm). + ) was used to measure the number of particles and evaluate the filtration efficiency. As shown in Table 1, the melt-blown nonwoven fabric of the present invention has a wide fiber diameter distribution, with fine and thick fibers uniformly dispersed and little fiber unevenness. It also has no shot and a good appearance. When used as a filter, such a melt-blown nonwoven fabric can be expected to have high particle collection performance and a long life. Furthermore, as shown in Figure 3, 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.

[0085]

Claims

DEPCT6609 / 06 / 25661. Melt-blown nonwoven fabric composed of multiple thermoplastic resin filaments of varying filament diameters, where the filament diameter has a standard deviation of 1.2 or more and the filaments have a fabric index to average filament diameter ratio of less than 33.

2. Melt-blown nonwoven fabric under claim 1 where thermoplastic resin filaments with a filament diameter equal to 2.5 times or more of the average filament diameter account for at least 4% of the thermoplastic resin filaments present in the melt-blown nonwoven fabric.

3. Melt-blown nonwoven fabric under claim 1 or 2 where thermoplastic resin filaments with a filament diameter equal to 0.75 times or less of the average filament diameter account for at least 46% of the thermoplastic resin filaments present in the melt-blown nonwoven fabric.

4. Melt-blown nonwoven fabric under claim 1 or 2 where thermoplastic resin filaments have an average filament diameter in the range of 1 micrometer to 50 micrometers.5.

6. Melt-blown non-woven fabrics under claim 1 or 2 in which thermoplastic resin fibers are incorporated with resin components, at least one of which is selected from a group consisting of polyolefin, polyester and polyamide.