Title of invention: Meltblown nonwoven fabric and filter
Technical field
[0001]
　The present invention relates to a meltblown nonwoven fabric and a filter.
Background technology
[0002]
　Nonwoven fabrics manufactured by the meltblowing method (also referred to as meltblown nonwoven fabrics or meltblown nonwoven fabrics) have excellent flexibility, uniformity, and compactness, as compared to general spunbonded nonwoven fabrics, because the fibers that make up the nonwoven fabrics can be made finer. ing. Therefore, the melt blown non-woven fabric is used alone or laminated with other non-woven fabric, such as filters such as liquid filters and air filters, sanitary materials, medical materials, agricultural coating materials, civil engineering materials, building materials, oil adsorbent materials, automobile materials. , Electronic materials, separators, clothing, packaging materials, etc.
　As fibers constituting the non-woven fabric, fibers of thermoplastic resins such as polypropylene and polyethylene are known.
[0003]
　Generally, a filter is used for the purpose of collecting fine particles existing in a liquid or gas and removing the fine particles from the liquid or gas. It is known that the efficiency of collecting fine particles of the filter (hereinafter, also referred to as “collection efficiency”) tends to be excellent when the average fiber diameter of the fibers of the non-woven fabric forming the filter is small and the specific surface area is large. Has been. It is also known that the smaller the particle size of the fine particles, the lower the collection efficiency.
[0004]
　As a non-woven fabric having a small average fiber diameter, for example, a non-woven fabric obtained by molding a resin composition containing polyethylene and polyethylene wax by a melt blow method has been proposed (see, for example, Patent Documents 1 and 2).
[0005]
　Also proposed is a nonwoven fabric laminate in which a nonwoven fabric obtained by molding a resin composition containing polyethylene and polyethylene wax by a melt blow method is laminated with a spunbonded nonwoven fabric composed of a composite fiber formed of polyester and an ethylene polymer. (For example, see Patent Document 3).
[0006]
　As a method for producing a non-woven fabric having a small average fiber diameter, for example, a method of applying a high voltage to a fibrous resin in a melt blown method has been proposed (see, for example, Patent Document 4).
[0007]
　Further, as a method for producing a melt blown nonwoven fabric in which the entanglement of fibers and the adhesion of floating fibers are suppressed, the distance between the die and the suction roll is set so that the stretching of the molten polymer is completed, and the vibration of the obtained polymer fiber is substantially generated. Set within a range that does not occur, the distance between the outer peripheral surface of the suction roll and the die side end of the suction hood can be removed by suction even if the broken fiber adheres to or contacts the surface of the obtained meltblown nonwoven fabric. A method of setting the inside is proposed (for example, refer to Patent Document 5).
Prior art documents
Patent literature
[0008]
Patent Document 1: International Publication No. 2000/22219
Patent Document 2: International Publication No. 2015/093451
Patent Document 3: International Publication No. 2012/111724
Patent Document 4: International Publication No. 2012/014501
Patent Document 5: International Publication No. 2012/102398
Summary of the invention
Problems to be Solved by the Invention
[0009]
　As a result of examination by the present inventors, it was found that the nonwoven fabrics described in Patent Documents 1 and 3 have poor collection efficiency because the average fiber diameter is not sufficiently small. It was also found that the nonwoven fabric described in Patent Document 2 has a small specific surface area and poor collection efficiency.
　Further, it was found that the production methods described in Patent Documents 4 and 5 use a special device and have a slower production rate than the normal melt blown method.
　Therefore, in the present invention, it is an object of the present invention to provide a non-woven fabric which can be produced by a usual melt blown method and is excellent in collection efficiency, that is, a small average fiber diameter and a large specific surface area, and a filter using the non-woven fabric. ..
Means for solving the problem
[0010]
　Means for solving the above problems are as follows.
<1> The emission curve in gel permeation chromatography has at least one peak top at a position with a molecular weight of 20,000 or more and at least one peak top at a position with a molecular weight of less than 20,000, and the intrinsic viscosity [η] is A meltblown nonwoven fabric made of a propylene-based polymer having a density of 0.50 (dl/g) to 0.75 (dl/g).
<2> The propylene-based polymer contains at least a high-molecular-weight propylene-based polymer A having a weight average molecular weight of 20,000 or more and a low-molecular-weight propylene-based polymer B having a weight average molecular weight of less than 20,000 <1. The melt blown non-woven fabric as described in <>.
<3> The melt blown nonwoven fabric according to <2>, wherein the content of the low-molecular-weight propylene polymer B is 8% by mass to 40% by mass with respect to the total mass of the propylene polymer.
<4> The melt blown nonwoven fabric according to <2> or <3>, wherein the content of the high molecular weight propylene-based polymer A is 60% by mass to 92% by mass with respect to the total mass of the propylene-based polymer.
<5> The melt blown nonwoven fabric according to any one of <2> to <4>, wherein the high-molecular-weight propylene polymer A has a melt flow rate (MFR) of 1000 g/10 minutes to 2500 g/10 minutes.
<6> The melt blown nonwoven fabric according to any one of <1> to <5>, wherein the propylene-based polymer has a weight average molecular weight of 20,000 or more.
<7> The meltblown nonwoven fabric according to any one of <1> to <6>, which is composed of fibers having an average fiber diameter of less than 1.1 μm.
<8> Specific surface area of ​​2.0 m 2The melt-blown nonwoven fabric according to any one of <1> to <7>, wherein the melt-blown nonwoven fabric is /g to 20.0 m 2 /g.
<9> The meltblown nonwoven fabric according to any one of <1> to <8>, in which the ratio of the peak fiber diameter to the average fiber diameter exceeds 0.5.
<10> A nonwoven fabric laminate containing at least the meltblown nonwoven fabric according to any one of <1> to <9>.
<11> A filter including the meltblown nonwoven fabric according to any one of <1> to <9>.
<12> The filter according to <11>, which is a liquid filter.
Effect of the invention
[0011]
　According to the present invention, it is possible to provide a nonwoven fabric which can be manufactured by a usual melt blown method and has excellent collection efficiency, that is, a small average fiber diameter and a large specific surface area, and a filter using the nonwoven fabric.
Brief description of the drawings
[0012]
FIG. 1 is an emission curve in gel permeation chromatography of the propylene-based polymers used in Example 1 and Comparative Example 3.
FIG. 2 is an emission curve in gel permeation chromatography of the meltblown nonwoven fabric obtained in Example 1.
MODE FOR CARRYING OUT THE INVENTION
[0013]
　In the present disclosure, the numerical range indicated by using “to” indicates a range including the numerical values ​​before and after “to” as the minimum value and the maximum value, respectively.
[0014]
　The melt blown nonwoven fabric of the present disclosure has at least one peak top at a molecular weight of 20,000 or more and at least 1 at a molecular weight of less than 20,000 in an emission curve in gel permeation chromatography (GPC) (hereinafter, also referred to as “GPC chart”). A propylene-based polymer having two peak tops and an intrinsic viscosity [η] of 0.50 (dl/g) to 0.75 (dl/g).
[0015]
　The propylene-based polymer that constitutes the melt-blown nonwoven fabric of the present disclosure has not only at least one peak top at a position of molecular weight of 20,000 or more, but also at least one peak top at a position of less than 20,000, and When the viscosity [η] is 0.50 (dl/g) to 0.75 (dl/g), the average fiber diameter can be reduced and the specific surface area can be increased when the meltblown nonwoven fabric is manufactured. Becomes Therefore, by forming a meltblown nonwoven fabric with such a propylene-based polymer, the collection efficiency of particles is improved. Further, since it is not necessary to use a special device, the production speed is excellent.
[0016]

　The melt blown nonwoven fabric of the present disclosure is made of a propylene polymer. In the present disclosure, the propylene-based polymer means a polymer having a propylene content of 50% by mass or more.
[0017]
　The emission curve in GPC of a propylene-based polymer has at least one peak top at a molecular weight of 20,000 or more and at least one peak top at a molecular weight of less than 20,000. Hereinafter, the peak top appearing at the position of the molecular weight of 20,000 or more in the GPC emission curve is referred to as "high molecular side peak top", and the peak top appearing at the position of less than 20,000 of molecular weight is referred to as the "low molecular side peak top".
　The number of peak tops on the high molecular side and the peak tops on the low molecular side may be calculated by counting only the peak tops derived from the propylene polymer.
[0018]
　At least one of the polymer-side peak tops is located at a molecular weight of 20,000 or more, preferably at 30,000 or more, and more preferably at 40,000 or more.
　At least one of the polymer-side peak tops is preferably located in a molecular weight range of 20,000 to 80,000, preferably 30,000 to 70,000, and preferably 40,000 to 650,000. It is more preferable to be located. Within the above range, the average fiber diameter tends to be small, which is preferable.
[0019]
　At least one of the low molecular weight peak tops is located at a molecular weight of less than 20,000, preferably at 15,000 or less, more preferably at 14,000 or less, and at most 13,000. More preferably, it is located.
　At least one of the low molecular weight peak tops is preferably located in the range of molecular weight of 400 or more and less than 20,000, preferably in the range of 400 to 15,000, and in the range of 1,000 to 14,000. It is more preferably located in the range of 2,000 to 13,000, further preferably located in the range of 6000 to 13,000. Within the above range, fiber breakage during spinning hardly occurs, the spinnability remains high, and the average fiber diameter tends to be reduced, which is preferable.
[0020]
　The weight average molecular weight (Mw) of the propylene-based polymer is preferably 20,000 or more, more preferably 30,000 or more, and further preferably 35,000 or more. The Mw of the propylene-based polymer is preferably 100,000 or less, more preferably 80,000 or less, and further preferably 60,000 or less. When Mw is less than or equal to the above upper limit value, the average fiber diameter tends to be small, and when Mw is more than or equal to the above lower limit value, fiber breakage during spinning hardly occurs and spinnability is high, which is preferable.
[0021]
　In the present disclosure, the emission curve of propylene-based polymer in gel permeation chromatography (GPC) refers to the emission curve measured by the GPC method using the following apparatus and conditions. In addition, in the present disclosure, the weight average molecular weight (Mw) of the propylene-based polymer refers to a polystyrene-equivalent weight average molecular weight measured by a gel permeation chromatography method under the following apparatus and conditions.
[0022]
[GPC measuring device]
　Column: TOSO GMHHR-H(S)HT
　detector: RI detector for liquid chromatogram WATERS 150C
[0023]
[Measurement conditions]
　Solvent: 1,2,4-trichlorobenzene
　Measurement temperature: 145°C
　Flow rate: 1.0 ml/min
　Sample concentration: 2.2 mg/ml
　Injection volume: 160 μl
　Calibration curve: Universal Calibration
　analysis program: HT-GPC( Ver.1.0)
[0024]
　When thermal decomposition of the propylene-based polymer does not occur during spinning, the result of GPC measurement before spinning can be used as the result of GPC measurement of the nonwoven fabric.
[0025]
　The intrinsic viscosity [η] of the propylene-based polymer is 0.50 (dl/g) to 0.75 (dl/g). If the intrinsic viscosity [η] is less than 0.50 (dl/g), spinning defects such as yarn breakage are likely to occur. When the intrinsic viscosity [η] exceeds 0.75 (dl/g), the average fiber diameter is large and the specific surface area is small, so that the collection efficiency is poor.
　From the viewpoint of suppressing spinning defects and the average fiber diameter and specific surface area, the intrinsic viscosity [η] of the propylene-based polymer is preferably 0.52 (dl/g) to 0.70 (dl/g). , 0.55 (dl/g) to 0.60 (dl/g) is more preferable.
[0026]
　The intrinsic viscosity [η] of the propylene-based polymer is a value measured at 135° C. using a decalin solvent. Specifically, it is obtained as follows.
　About 20 mg of a propylene polymer is dissolved in 15 ml of decalin, and the specific viscosity ηsp is measured in an oil bath at 135°C. To this decalin solution, 5 ml of decalin solvent was added and diluted, and then the specific viscosity ηsp was measured in the same manner. This dilution operation is repeated twice more, and the value of ηsp/C when the concentration (C) is extrapolated to 0 is determined as the intrinsic viscosity (see the following formula).　
　　[Η]=lim (ηsp/C) (C→0)
[0027]
　The propylene-based polymer may be a homopolymer of propylene or a copolymer of propylene and α-olefin. The amount of α-olefin copolymerized with propylene is smaller than that of propylene, and one type may be used alone, or two or more types may be used in combination.
[0028]
　The α-olefin to be copolymerized preferably has 2 or more carbon atoms, and more preferably 2 or 4 to 8 carbon atoms. Specific examples of such α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 4-methyl-1-pentene.
[0029]
　The propylene-based polymer has a propylene content of preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and a propylene homopolymer. Is particularly preferable.
　When the content of propylene in the propylene-based polymer is within the above range, when the high-molecular-weight polypropylene-based polymer A described later and the low-molecular-weight polypropylene-based polymer B described later are included, the compatibility is excellent and the spinnability is good. And the average fiber diameter tends to be smaller, which is preferable.
[0030]
　The melt flow rate (MFR: ASTM D-1238, 230° C., load 2160 g) of the propylene-based polymer is not particularly limited as long as it can be melt-spun, and is usually 600 g/10 min to 2500 g/10 min. It is preferably in the range of 1200 g/10 minutes to 1800 g/10 minutes. By using a propylene-based polymer having an MFR within the above range, a meltblown nonwoven fabric having good spinnability and good mechanical strength such as tensile strength tends to be obtained.
[0031]
　The propylene-based polymer having a peak top at each position of the molecular weight of 20,000 or more and the molecular weight of less than 20,000 in the GPC emission curve is at least one of the high-molecular-weight propylene-based polymer A having Mw of 20,000 or more and Mw. It may be prepared by including at least one of the low molecular weight propylene-based polymer B having a molecular weight of less than 20,000. That is, it may be a mixture of the high molecular weight propylene polymer A and the low molecular weight propylene polymer B (hereinafter, also referred to as “propylene polymer mixture”).
　In addition, a propylene-based polymer having peak tops at respective positions of molecular weight of 20,000 or more and less than 20,000 on the GPC emission curve is subjected to multistage polymerization, and the kind of catalyst compound and the number of stages of multistage polymerization are appropriately adjusted. You may prepare it.
[0032]
The
　high molecular weight propylene-based polymer A has an Mw of 20,000 or more, preferably 30,000 or more, and more preferably 40,000 or more.
　Further, the Mw of the high molecular weight propylene polymer A is preferably 80,000 or less, more preferably 70,000 or less, and further preferably 650,000 or less.
　Within the above range, the average fiber diameter tends to be small, which is preferable.
[0033]
　The Mw of the high molecular weight propylene polymer A is preferably 20,000 to 80,000, preferably 30,000 to 70,000, and more preferably 40,000 to 650,000.
[0034]
　The high molecular weight propylene polymer A may be a homopolymer of propylene or a copolymer of propylene and α-olefin. Examples of the α-olefin to be copolymerized are as described above. From the viewpoint that the high molecular weight propylene polymer A has excellent compatibility with the low molecular weight polypropylene polymer B, the propylene content is preferably 70% by mass or more, and more preferably 80% by mass or more. Is more preferably 90% by mass or more, and particularly preferably a propylene homopolymer. It is preferable that the compatibility is excellent because the spinnability is improved and the average fiber diameter tends to be smaller.
　The high molecular weight propylene polymer A may be used alone or in combination of two or more.
[0035]
　Density of the high molecular weight propylene polymer A is not particularly limited, for example, 0.870 g / cm 3 ~ 0.980 g / cm 3 may be, preferably 0.900 g / cm 3 ~ 0. It is 980 g/cm 3 , more preferably 0.920 g/cm 3 to 0.975 g/cm 3 , and further preferably 0.940 g/cm 3 to 0.970 g/cm 3 .
[0036]
　When the density of the high-molecular-weight propylene polymer A is 0.870 g/cm 3 or more, the resulting meltblown nonwoven fabric tends to have further improved durability, heat resistance, strength, and stability over time. On the other hand, when the density of the high-molecular-weight propylene-based polymer A is 0.980 g/cm 3 or less, the heat-sealing property and the flexibility of the obtained meltblown nonwoven fabric tend to be further improved.
[0037]
　In the present disclosure, the density of the propylene-based polymer is such that the strand obtained at the time of measuring the melt flow rate (MFR) under a load of 2.16 kg at 190° C. is heat-treated at 120° C. for 1 hour, and then at room temperature for 1 hour ( It is a value obtained by measuring with a density gradient tube in accordance with JIS K7112:1999 after gradually cooling to 25°C).
[0038]
　The melt flow rate (MFR) of the high molecular weight propylene-based polymer A is not particularly limited as long as it can be used in combination with the low molecular weight propylene-based polymer B described later to produce a meltblown nonwoven fabric. The MFR of the high-molecular-weight propylene-based polymer A is preferably 1000 g/10 minutes to 2500 g/10 minutes, more preferably 1200 g/10 minutes to 2000 g from the viewpoints of fine fiber diameter, specific surface area, spinnability and the like. /10 minutes, more preferably 1300 g/10 minutes to 1800 g/10 minutes.
[0039]
　In the present disclosure, the MFR of a propylene-based polymer refers to a value obtained by measurement under the conditions of a load of 2.16 kg and 190° C. according to ASTM D1238.
[0040]
　The content of the high molecular weight propylene-based polymer A with respect to the total weight of the propylene-based polymer is preferably 60% by mass to 92% by mass, more preferably 62% by mass to 90% by mass, and 70% by mass. More preferably, it is from about 88% by mass.
　When the content of the high molecular weight propylene-based polymer A is within the above range, the average fiber diameter tends to be small and the specific surface area tends to be large. In addition, the spinnability, fiber strength, collection efficiency of fine particles, and filtration flow rate tend to be excellent.
　The total mass of the propylene-based polymer means the total mass of the polymers having a propylene content of 50% by mass or more based on all the constituent units.
[0041]
　When the content of the high molecular weight propylene polymer A is less than 70% by mass, it is preferable to design the Mw of the high molecular weight propylene polymer A to be higher. On the other hand, when the content of the high-molecular-weight propylene-based polymer A exceeds 95% by mass, it is preferable to design the Mw of the high-molecular-weight propylene-based polymer A to be low.
[0042]
The
　low-molecular-weight propylene-based polymer B has a Mw of less than 20,000 and has a relatively low molecular weight, and thus may be a waxy polymer.
[0043]
　The Mw of the low molecular weight propylene-based polymer B is preferably 15,000 or less, more preferably 14,000 or less, and further preferably 13,000 or less.
　The Mw of the low molecular weight propylene-based polymer B is preferably 400 or more, more preferably 1000 or more, further preferably 2000 or more, and particularly preferably 6000 or more.
　Within the above range, fiber breakage during spinning hardly occurs, the spinnability remains high, and the average fiber diameter tends to be reduced, which is preferable.
[0044]
　The Mw of the low molecular weight propylene polymer B is preferably 400 or more and less than 20,000, preferably 400 to 15,000, more preferably 1000 to 14,000, and 2000 to 1 It is more preferably 30000, particularly preferably 6000 to 13,000.
[0045]
　The low molecular weight propylene polymer B may be a homopolymer of propylene or a copolymer of propylene and α-olefin. Examples of the α-olefin to be copolymerized are as described above. From the viewpoint of excellent compatibility with the high molecular weight polypropylene polymer A, the low molecular weight propylene polymer B preferably has a propylene content of 70% by mass or more, and more preferably 80% by mass or more. Is more preferably 90% by mass or more, and particularly preferably a propylene homopolymer. In addition, if the compatibility is excellent, the spinnability becomes high, and the average fiber diameter tends to become smaller.
　The low molecular weight propylene polymer B may be used alone or in combination of two or more.
[0046]
　The softening point of the low molecular weight propylene polymer B is preferably higher than 90°C, more preferably 100°C or higher.
　When the softening point of the low molecular weight propylene-based polymer B exceeds 90°C, the heat resistance stability during heat treatment or use can be further improved, and as a result, the filter performance tends to be further improved. The upper limit of the softening point of the low molecular weight propylene polymer B is not particularly limited and may be 145° C., for example.
　In the present disclosure, the softening point of a propylene-based polymer refers to a value obtained by measurement according to JIS K2207:2006.
[0047]
　The density of the low molecular weight propylene polymer B is not particularly limited, for example, 0.890 g / cm 3 ~ 0.980 g / cm 3 may be, preferably 0.910 g / cm 3 ~ 0.980 g / cm 3 , more preferably 0.920 g/cm 3 to 0.980 g/cm 3 , and further preferably 0.940 g/cm 3 to 0.980 g/cm 3 .
　When the density of the low-molecular-weight propylene-based polymer B is within the above range, the low-molecular-weight propylene-based polymer B and the high-molecular-weight propylene-based polymer A are excellent in kneading property, and are excellent in spinnability and stability over time. There is a tendency. The method for measuring the density of the propylene-based polymer is as described above.
[0048]
　The content of the low-molecular-weight propylene-based polymer B with respect to the total weight of the propylene-based polymer is preferably 8% by mass to 40% by mass, more preferably 10% by mass to 38% by mass, and 12% by mass. More preferably, it is from about 30% by mass.
　When the content of the low molecular weight propylene polymer B is within the above range, the average fiber diameter tends to be small and the specific surface area tends to be large. In addition, the spinnability, fiber strength, collection efficiency of fine particles, and filtration flow rate tend to be excellent.
　The total mass of the propylene-based polymer means the total mass of the polymers having a propylene content of 50% by mass or more based on all the constituent units.
[0049]
　When the content of the low molecular weight propylene polymer B is less than 10% by mass, it is preferable to design the Mw of the low molecular weight propylene polymer B to be low. In this case, the Mw of the low-molecular-weight propylene polymer B is preferably 400 to 15,000, more preferably 1,000 to 13,000, and particularly preferably 1,000 to 8,000. is there.
[0050]
　On the other hand, when the content of the low molecular weight propylene-based polymer B exceeds 25% by mass, it is preferable to design the Mw of the low molecular weight propylene-based polymer B to be higher. In this case, the Mw of the low molecular weight propylene polymer B is preferably 1,000 to 15,000, more preferably 3,000 to 15,000, and further preferably 5,000 to 1.000. It is 50,000.
[0051]

　The average fiber diameter of the fibers constituting the meltblown nonwoven fabric is preferably less than 1.1 μm, more preferably 0.3 μm to 1.0 μm, and more preferably 0.5 μm to 0.9 μm. Is more preferable. By using the propylene-based polymer of the present disclosure, it is possible to make the average fiber diameter smaller.
　The average fiber diameter of the meltblown non-woven fabric is an average value of 100 selected non-woven fabric fibers from an electron micrograph (1000 times magnification) of the meltblown non-woven fabric, the diameter of the selected fibers is measured.
[0052]
　The meltblown nonwoven fabric preferably has a ratio of the peak fiber diameter to the average fiber diameter (hereinafter, also referred to as “peak fiber diameter ratio”) of more than 0.5 when the fiber diameter distribution is measured. When the peak fiber diameter ratio exceeds 0.5, the fiber diameter distribution is narrowed and the fiber diameter is made more uniform. Therefore, the generation of gaps caused by the non-uniform fiber diameter is suppressed, and the particle capturing efficiency tends to be further improved.
　The peak fiber diameter ratio is more preferably 0.53 or more, further preferably 0.55 or more. The upper limit of the peak fiber diameter ratio is not particularly limited and may be, for example, 0.95 or less, or 0.90 or less.
[0053]
　A method for measuring the average fiber diameter and the peak fiber diameter in the fiber diameter distribution will be described.
(1) Measurement of average fiber diameter The
　melt-blown nonwoven fabric was photographed at a magnification of 5000 times using an electron microscope “S-3500N” manufactured by Hitachi, Ltd., and the width (diameter: μm) of the fiber was 1000 points at random. The measurement is performed, and the average fiber diameter (μm) is calculated by number average.
　In order to make the measurement point of the fiber in the meltblown nonwoven fabric random, a diagonal line is drawn from the upper left corner to the lower right corner of the photograph taken, and the width (diameter) of the fiber at the intersection of the diagonal line and the fiber is measured. New photographs are taken and measurements are taken until the number of measurement points reaches 1000.
[0054]
(2) Peak fiber diameter (most frequent fiber diameter) A
　logarithmic frequency distribution is created based on the data of 1000 points of fiber diameter (μm) measured by the above-mentioned “(1) Method of measuring average fiber diameter”.
　In the logarithmic frequency distribution, the fiber diameter (μm) is plotted on the x-axis on a logarithmic scale with 10 as the base, and the y-axis is the frequency percentage. On the x-axis, a fiber diameter of 0.1 (=10 −1 ) μm to a fiber diameter of 50.1 (=10 1.7 ) μm is evenly divided into 27 on the logarithmic scale, and the frequency is the largest. The value of the geometric mean of the minimum value and the maximum value of the x axis in the divided section is defined as the peak fiber diameter (modal fiber diameter).
[0055]
　The specific surface area of melt blown nonwoven fabric, 2.0 m 2 /G～20.0M 2 is preferably / g, 3.0 m 2 /G～15.0M 2 more preferably from / g, 3.5 m 2 /G to 10.0 m 2 /g is more preferable. By using the propylene-based polymer of the present disclosure, it is possible to further increase the specific surface area. The specific surface area of ​​the meltblown nonwoven fabric is a value determined according to JIS Z8830:2013.
[0056]
　By using the propylene-based polymer of the present disclosure, the meltblown nonwoven fabric can have an average fiber diameter and a specific surface area within the above ranges, and has excellent collection efficiency when used as a filter.
[0057]
　The average pore diameter of the meltblown nonwoven fabric is preferably 10.0 μm or less, more preferably 3.0 μm or less, and further preferably 2.5 μm or less.
　The average pore size of the meltblown nonwoven fabric is preferably 0.01 μm or more, more preferably 0.1 μm or more. When the average pore diameter is 0.01 μm or more, when the meltblown nonwoven fabric is used for the filter, pressure loss is suppressed and the flow rate tends to be maintained.
[0058]
　The maximum pore size of the meltblown nonwoven fabric is preferably 20 μm or less, more preferably 6.0 μm or less, and further preferably 5.0 μm or less.
　The minimum pore size of the meltblown nonwoven fabric is preferably 0.01 μm or more, more preferably 0.1 μm or more.
[0059]
　The pore diameter (average pore diameter, maximum pore diameter, and minimum pore diameter) of the meltblown nonwoven fabric can be measured by the bubble point method. Specifically, in accordance with JIS Z8703:1983 (standard condition of the test place), a fluorine-based inert liquid (for example, a The pore size is measured with a capillary flow porometer (for example, Porous materials, Inc., product name: CFP-1200AE) impregnated with 3M, product name: Fluorinert.
[0060]
　The basis weight of the meltblown nonwoven fabric can be appropriately determined depending on the application, but is usually 1 g/m 2 to 200 g/m 2 , and preferably 2 g/m 2 to 150 g/m 2 .
　The porosity of the meltblown nonwoven fabric is usually 40% or more, preferably in the range of 40% to 98%, more preferably in the range of 60% to 95%. When the meltblown non-woven fabric of the present disclosure is embossed, the porosity of the meltblown non-woven fabric means the porosity at a portion excluding the embossing point.
[0061]
　Further, in the melt blown nonwoven fabric of the present disclosure, the volume occupied by the portion having the porosity of 40% or more is preferably 90% or more, and more preferably the porosity of 40% or more is almost all the portions. When using the meltblown nonwoven of the present disclosure in a filter, it is preferred that it is not embossed or is not embossed in almost all areas. When not embossed, the pressure loss when a fluid is passed through the filter is suppressed, and the filter flow path length is increased, which tends to improve the filtering performance. When the meltblown nonwoven fabric of the present disclosure is laminated on another nonwoven fabric, the other nonwoven fabric may be embossed.
[0062]
　The air permeability of the meltblown nonwoven fabric is preferably 3 cm 3 /cm 2 /sec to 30 cm 3 /cm 2 /sec, more preferably 5 cm 3 /cm 2 /sec to 20 cm 3 /cm 2 /sec, and further preferably Is 8 cm 3 /cm 2 /sec to 12 cm 3 /cm 2 /sec.
[0063]
　The meltblown nonwoven fabric preferably does not contain a solvent component. The solvent component means an organic solvent component capable of dissolving the polypropylene-based polymer forming the fiber. Examples of the solvent component include dimethylformamide (DMF). The term "containing no solvent component" means that the amount is below the detection limit by headspace gas chromatography.
[0064]
　The fibers of the meltblown nonwoven fabric preferably have entanglement points where the fibers self-bond together. The self-fused entanglement point means a branched portion where the fibers are bonded to each other by fusion-bonding the polypropylene-based polymer itself which constitutes the fiber, and the entanglement point where the fibers are bonded to each other through the binder resin. Is distinguished from. The self-fused entanglement points are formed during the process of thinning the fibrous polypropylene polymer by melt blown. Whether or not the fibers have the entanglement points where they are self-fused can be confirmed by an electron micrograph.
[0065]
　When the fibers of the meltblown nonwoven fabric have entanglement points due to self-fusion, an adhesive component for adhering the fibers need not be used. Therefore, the meltblown nonwoven fabric in which the fibers have the entanglement points due to self-fusion does not need to contain a resin component other than the polypropylene polymer constituting the fibers, and it is preferable not to contain it.
[0066]
　The meltblown nonwoven fabric may be used as a single-layer nonwoven fabric or may be used as a nonwoven fabric forming at least one layer of the nonwoven fabric laminate. Examples of other layers that make up the nonwoven fabric laminate include conventional meltblown nonwoven fabrics, spunbond nonwoven fabrics, other nonwoven fabrics such as needlepunching and spunlace nonwoven fabrics, and fabrics, knits, papers, and the like. In the nonwoven fabric laminate, at least one melt blown nonwoven fabric of the present disclosure may be contained, and two or more melt blown nonwoven fabrics may be contained. Further, other non-woven fabrics, woven fabrics, knitted fabrics, papers, etc. may be contained at least one of these, and may be contained in two or more. The nonwoven fabric laminate can be used as a filter, and may be used as a foam molding reinforcing material or the like.
[0067]

　The meltblown nonwoven fabric of the present disclosure may be used as a filter such as a gas filter (air filter) or a liquid filter.
　The melt blown nonwoven fabric does not include 1) no solvent component, 2) does not contain an adhesive component for adhering fibers to each other, and 3) is not embossed, satisfying at least one of these 1) to 3). In this case, the content of impurities is reduced. Therefore, such a melt blown nonwoven fabric has high cleanliness and filtering performance and is suitably used as a high performance filter.
[0068]
　The melt blown nonwoven fabric of the present disclosure can be suitably used as a liquid filter.
　The melt blown nonwoven fabric of the present disclosure tends to have a small average fiber diameter and a large specific surface area. For this reason, it is preferable to use the melt blown nonwoven fabric of the present disclosure as a liquid filter because the efficiency of collecting fine particles is excellent.
[0069]
　The liquid filter may be composed of a single layer of the meltblown nonwoven fabric of the present disclosure, or may be composed of a nonwoven fabric laminate of two or more layers of the meltblown nonwoven fabric of the present disclosure. When a nonwoven fabric laminate including two or more layers of meltblown nonwoven fabric is used as the liquid filter, two or more layers of meltblown nonwoven fabric may be simply stacked.
　Further, the liquid filter may be a combination of the meltblown nonwoven fabric of the present disclosure and another meltblown nonwoven fabric depending on the purpose and the liquid to be applied. In addition, spunbonded non-woven fabrics, nets and the like may be laminated to increase the strength of the liquid filter.
[0070]
　The liquid filter may be calendered using, for example, a pair of flat rolls having a clearance between the flat rolls in order to control the pore size to be small. The clearance between the flat rolls needs to be appropriately changed according to the thickness of the non-woven fabric so that the voids between the fibers of the non-woven fabric are eliminated.
[0071]
　When heat treatment is performed during calendering, it is preferable that the roll surface temperature is in the range of 15° C. to 50° C. lower than the melting point of the polypropylene fiber. When the roll surface temperature is lower than the melting point of polypropylene fiber by 15° C. or more, film formation on the surface of the meltblown nonwoven fabric is suppressed, and deterioration of filter performance tends to be suppressed.
[0072]
　Further, the melt blown nonwoven fabric of the present disclosure may be used as a reinforcing material for foam molding. The reinforcing material for foam molding is, for example, a reinforcing material that covers the surface of the foam molded article made of urethane or the like to protect the surface of the foam molded article or to increase the rigidity of the foam molded article. Is.
[0073]
　The melt blown nonwoven fabric of the present disclosure tends to have a small average fiber diameter and a large specific surface area, and therefore tends to have high liquid retention performance. Therefore, by arranging the foam molding reinforcing material including the melt blown nonwoven fabric of the present disclosure on the inner surface of the mold for foam molding and performing foam molding, it is possible to prevent the foaming resin such as urethane from leaching on the surface of the molded body. it can. The foaming reinforcing material may be a single-layer non-woven fabric consisting only of the melt-blown non-woven fabric of the present disclosure, but one or both sides of the melt-blown non-woven fabric of the present disclosure, using a spun-bonded non-woven fabric laminated body Is preferred. By laminating the spunbonded nonwoven fabric, for example, laminating with other layers becomes easy.
[0074]
　The spunbonded nonwoven fabric used in the foam molding reinforcement, preferably fiber diameter of 10 [mu] m ~ 40 [mu] m, more preferably from 10 [mu] m ~ 20 [mu] m, a basis weight of 10 g / m 2 ~ 50 g / m 2 to be It is preferably 10 g/m 2 to 20 g/m 2 . When the fiber diameter and basis weight of the spunbonded non-woven fabric layer are in the above ranges, it is easy to prevent the foaming resin from seeping out, and the reinforcement material for foam molding can be reduced in weight.
[0075]
　The foam-molding reinforcing material may further have a reinforcing layer or the like on the spunbonded nonwoven fabric, if necessary. As the reinforcing layer, various known non-woven fabrics can be used. When the foam molding reinforcing material has the reinforcing layer on only one surface, the foam molding reinforcing material is used by arranging the foam molding reinforcing material such that the reinforcing layer is on the foamed resin side of the melt blown nonwoven fabric of the present disclosure.
[0076]

　The method of manufacturing the meltblown nonwoven fabric of the present disclosure is not particularly limited, and a conventionally known method can be applied. For example, a manufacturing method including the following steps can be mentioned.
[0077]
　1) A step of discharging a molten polypropylene-based polymer from a spinneret together with a heating gas into a fibrous polypropylene-based polymer by a melt blown method
　2) A step of collecting the fibrous polypropylene-based polymer in a web shape
[0078]
　The meltblown method is one of the fleece forming methods in the production of meltblown nonwoven fabric. When a molten polypropylene-based polymer is discharged into a fibrous form from a spinneret, heated compressed gas is applied to both sides of the molten discharged product, and the heated compressed gas is accompanied to reduce the diameter of the discharged product. be able to.
[0079]
　In the melt blown method, specifically, for example, a polypropylene polymer as a raw material is melted using an extruder or the like. The molten polypropylene-based polymer is introduced into a spinneret connected to the tip of the extruder, and is discharged in a fibrous form from a spinning nozzle of the spinneret. By pulling the discharged fibrous molten polypropylene-based polymer with a high-temperature gas (for example, air), the fibrous molten polypropylene-based polymer is thinned.
[0080]
　The discharged fibrous molten polypropylene-based polymer is thinned to a diameter of usually 1.4 μm or less, preferably 1.0 μm or less by being pulled by a high temperature gas. Preferably, the fibrous molten polypropylene-based polymer is thinned to the limit of hot gas.
[0081]
　A high voltage may be applied to the thinned fibrous fused polypropylene-based coalesced material to further thin it. When a high voltage is applied, the fibrous molten polypropylene-based polymer is pulled toward the collection side by the attraction of the electric field and is thinned. The voltage to be applied is not particularly limited and may be 1 kV to 300 kV.
[0082]
　The fibrous molten polypropylene-based polymer may be irradiated with heat rays to be further thinned. It is possible to remelt the fibrous polypropylene-based polymer, which is thinned by irradiating with heat rays and has reduced fluidity. Also, by irradiating with heat rays, the melt viscosity of the fibrous polypropylene-based polymer can be further lowered. Therefore, even when a polypropylene polymer having a large molecular weight is used as a spinning raw material, sufficiently fine fibers can be obtained, and a high-strength meltblown nonwoven fabric can be obtained.
[0083]
　The heat ray means an electromagnetic wave having a wavelength of 0.7 μm to 1000 μm, and particularly a near infrared ray having a wavelength of 0.7 μm to 2.5 μm. The intensity of the heat ray and the irradiation amount are not particularly limited as long as the fibrous molten polypropylene-based polymer is remelted. For example, a near-infrared lamp or a near-infrared heater of 1V to 200V, preferably 1V to 20V can be used.
[0084]
　The fibrous molten polypropylene-based polymer is collected in a web shape. Generally, it is collected and deposited by a collector. This produces a meltblown nonwoven fabric. Examples of collectors include perforated belts, perforated drums, and the like. Further, the collector may have an air collecting portion, which may promote the collection of fibers.
[0085]
　The fibers may be collected in the form of web on a desired substrate previously provided on the collector. Examples of the substrate provided in advance include other non-woven fabrics such as melt blown non-woven fabric, spun-bonded non-woven fabric, needle punching and spun lace non-woven fabric, and woven fabric, knitted fabric, paper and the like. This makes it possible to obtain a meltblown nonwoven fabric laminate for use in high performance filters, wipers and the like.
[0086]
The manufacturing apparatus for manufacturing the meltblown nonwoven fabric of the present disclosure is not particularly limited as long as it can manufacture the meltblown nonwoven fabric of the present disclosure. For example,
　1) an extruder that melts and conveys the polypropylene-based polymer,
　2) a spinneret that discharges the molten polypropylene-based polymer that is conveyed from the extruder into a fibrous state, and
　3) a lower part of the spinneret, 　An example of the production apparatus includes a gas nozzle for injecting a high-temperature gas, and
　4) a collector for collecting the fibrous molten polypropylene-based polymer discharged from the spinneret into a web
.
[0087]
　The extruder is not particularly limited, and may be a single-screw extruder or a multi-screw extruder. The solid polypropylene polymer charged from the hopper is melted in the compression section.
[0088]
　The spinneret is located at the tip of the extruder. The spinneret is usually equipped with a plurality of spinning nozzles, for example, a plurality of spinning nozzles arranged in a row. The diameter of the spinning nozzle is preferably 0.05 mm to 0.38 mm. The molten polypropylene-based polymer is conveyed to the spinneret by the extruder and introduced into the spinning nozzle. Fibrous molten polypropylene-based polymer is discharged from the opening of the spinning nozzle. The discharge pressure of the molten polypropylene polymer is usually in the range of 0.01 kg /cm 2 to 200 kg/cm 2 , and preferably in the range of 10 kg/cm 2 to 30 kg/cm 2 . With this, the discharge rate is increased to realize mass production.
[0089]
　The gas nozzle injects high-temperature gas to the lower part of the spinneret, more specifically, near the opening of the spinning nozzle. The propellant gas can be air. It is preferable to provide a gas nozzle in the vicinity of the opening of the spinning nozzle and inject the high temperature gas onto the polypropylene-based polymer immediately after the ejection from the nozzle opening.
[0090]
　The velocity of the gas to be injected (the amount of discharged air) is not particularly limited, and may be 4 Nmm 3 /min/m to 30 Nmm 3 /min/m. The temperature of the injected gas is usually 5°C to 400°C or less, preferably 250°C to 350°C. The type of gas to be injected is not particularly limited, and compressed air may be used.
[0091]
　The apparatus for manufacturing the meltblown nonwoven fabric may further include voltage applying means for applying a voltage to the fibrous molten polypropylene-based polymer discharged from the spinneret.
　Further, a heat ray irradiation means for irradiating the fibrous molten polypropylene-based polymer discharged from the spinneret with heat rays may be further provided.
[0092]
　The collector (collector) that collects in a web shape is not particularly limited, and for example, fibers may be collected on a perforated belt. The mesh width of the perforated belt is preferably 5 mesh to 200 mesh. Further, an air collecting portion may be provided on the back side of the fiber collecting surface of the porous belt to facilitate the collection. The distance from the collecting surface of the collector to the nozzle opening of the spinning nozzle is preferably 3 cm to 55 cm.
[0093]
　The disclosure of Japanese Patent Application No. 2017-184520 filed on Sep. 26, 2017 is incorporated into the present disclosure in its entirety.
　All publications, patent applications, and technical standards in this disclosure are referred to in this disclosure to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. Incorporated by reference.
Example
[0094]
　Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
　Physical property values ​​and the like in Examples and Comparative Examples were measured by the following methods.
[0095]
(1) Average fiber diameter A
　melt-blown nonwoven fabric was photographed with an electron microscope (S-3500N manufactured by Hitachi, Ltd.) at a magnification of 1000 times, and 100 fibers (n=100) were arbitrarily selected, and the fibers were selected. Width (diameter) was measured, and the average of the obtained measurement results was defined as the average fiber diameter.
[0096]
(2) Specific surface area Based on
　JIS Z8830:2013, a BET specific surface area (specific surface area by BET method) of a meltblown nonwoven fabric by a pore distribution meter (Belsorb max, manufactured by Nippon Bell Co., Ltd.) using physical adsorption of nitrogen gas. (M 2 /g) was measured.
[0097]
(3) Peak fiber diameter ratio
　The average fiber diameter and the peak fiber diameter in the fiber diameter distribution were measured, and the obtained peak fiber diameter was divided by the average fiber diameter. The average fiber diameter and the peak fiber diameter in the fiber diameter distribution were measured as follows.
[0098]
(3-1) Average fiber diameter in fiber diameter distribution The
　melt blown nonwoven fabric was photographed at a magnification of 5000 times using an electron microscope “S-3500N” manufactured by Hitachi, Ltd., and the width (diameter: μm) of the fibers was randomly selected. ) Was measured at 1000 points, and the average fiber diameter (μm) was calculated by number average.
　In order to make the measurement point of the fiber in the meltblown nonwoven fabric random, a diagonal line is drawn from the upper left corner to the lower right corner of the photograph taken, and the width (diameter) of the fiber at the intersection of the diagonal line and the fiber is measured. New photographs were taken and measurement was performed until the number of measurement points reached 1000 points.
[0099]
(3-2) Peak fiber diameter in the fiber diameter distribution (most frequent fiber diameter)
　Based on the data of 1000 points of fiber diameter (μm) measured in the above-mentioned “(3-1) Method of measuring average fiber diameter” , A logarithmic frequency distribution was created.
　In the logarithmic frequency distribution, the fiber diameter (μm) was plotted on the x-axis on a logarithmic scale with 10 as the base, and the y-axis was the frequency percentage. On the x-axis, the fiber diameter of 0.1 (=10 −1 ) μm to the fiber diameter of 50.1 (=10 1.7 ) μm is evenly divided into 27 on the logarithmic scale, and the frequency is the highest. The value of the geometric mean of the minimum value and the maximum value of the x-axis in the divided section was defined as the peak fiber diameter (modal fiber diameter).
[0100]
[Example 1]
　85 parts by mass of Achieve 6936G2 (product name, manufactured by ExxonMobil, propylene-based polymer having a weight average molecular weight of 55,000, MFR: 1550) as a high-molecular-weight propylene-based polymer A and a low-molecular weight propylene-based polymer A As Polymer B, 15 parts by mass of Hiwax NP055 (product name, manufactured by Mitsui Chemicals, Inc., propylene-based polymer having a weight average molecular weight of 7700) is mixed to obtain 100 parts by mass of the propylene-based polymer mixture (1). It was
[0101]
　When the propylene polymer mixture (1) was measured by GPC by the method described above, peak tops were present at the positions of molecular weight 55,000 and 8,000. The number of peak tops was two. The weight average molecular weight (Mw) of the propylene polymer mixture (1) was 38,000. The intrinsic viscosity [η] of the propylene-based polymer mixture (1) was measured by the above-mentioned method and was found to be 0.56 (dl/g).
　A GPC chart of the propylene polymer mixture (1) is shown in FIG.
[0102]
　The propylene-based polymer mixture (1) was supplied to a die and discharged from a die having a set temperature of 280° C. at a rate of 50 mg/min per nozzle single hole, together with heated air (280° C., 120 m/sec) blown from both sides of the nozzle. A meltblown nonwoven fabric was obtained. The diameter of the nozzle of the die was 0.12 mm. The average fiber diameter, peak fiber diameter, peak fiber diameter ratio, and specific surface area of ​​the obtained meltblown nonwoven fabric were measured by the above-mentioned methods. The results are shown in Table 1.
[0103]
　GPC measurement was performed on the obtained meltblown nonwoven fabric by the method described above. The obtained GPC chart is shown in FIG. In GPC measurement of the meltblown nonwoven fabric, peak tops were present at the positions of molecular weight 55,000 and 8,000. The number of peak tops was two. The weight average molecular weight (Mw) of the meltblown nonwoven fabric was 38,000.
[0104]
　The intrinsic viscosity [η] of the obtained meltblown nonwoven fabric was measured by the following method.
　About 20 mg of the meltblown nonwoven fabric was dissolved in 15 ml of decalin, and the specific viscosity ηsp was measured in an oil bath at 135°C. To this decalin solution, 5 ml of decalin solvent was added and diluted, and then the specific viscosity ηsp was measured in the same manner. This dilution operation was repeated twice more, and the value of ηsp/C when the concentration (C) was extrapolated to 0 was determined as the intrinsic viscosity (see the following formula).　
　　[Η]=lim (ηsp/C) (C→0)
　The intrinsic viscosity [η] of the meltblown nonwoven fabric was 0.56 (dl/g), which was the same as that before spinning.
[0105]
[Example 2] In
　Example 1, instead of 100 parts by mass of the propylene polymer mixture (1), Achieve 6936G2 (product name, manufactured by ExxonMobil, weight average molecular weight: 5. 50,000 propylene-based polymer, MFR: 1550) 90 parts by mass, and high wax NP055 as a low-molecular-weight propylene-based polymer B (product name, manufactured by Mitsui Chemicals, Inc., weight-average molecular weight 7700 propylene-based polymer) 10 The same operation as in Example 1 was performed except that 100 parts by mass of the propylene-based polymer mixture (2), which was a mixture with parts by mass, was used.
　When the propylene polymer mixture (2) was measured by GPC by the method described above, peak tops were present at the positions of the molecular weights of 55,000 and 8,000. The number of peak tops was two. The weight average molecular weight (Mw) of the propylene polymer mixture (2) was 53,000. The intrinsic viscosity [η] of the propylene-based polymer mixture (2) was measured by the above-mentioned method and was found to be 0.56 (dl/g). Table 1 shows the average fiber diameter, peak fiber diameter, peak fiber diameter ratio, specific surface area, and intrinsic viscosity [η] of the obtained meltblown nonwoven fabric.
[0106]
Comparative Example 1 In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture (1), Achieve 6936G2 (product name, manufactured by ExxonMobil, weight average molecular weight: 5. The same operation as in Example 1 was performed except that 100 parts by mass of 50,000 propylene-based polymer, MFR: 1550) was used alone.
　When Achieve 6936G2 as the high molecular weight polypropylene-based polymer A was measured by GPC by the above method, a peak top was present only at the position of the molecular weight of 55,000. The intrinsic viscosity [η] of Achieve 6936G2 as the high-molecular-weight propylene-based polymer A was measured by the above-mentioned method and was 0.63 (dl/g). Table 1 shows the average fiber diameter, peak fiber diameter, peak fiber diameter ratio, specific surface area, and intrinsic viscosity [η] of the obtained meltblown nonwoven fabric.
[0107]
[Comparative Example 2] In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture (1), 650Y as a high-molecular weight propylene-based polymer A (product name, manufactured by Polymire, weight average molecular weight: 5.1). The same operation as in Example 1 was carried out except that 100 parts by mass of propylene-based polymer, MFR:1800) was used alone. When 650Y as the high molecular weight polypropylene polymer A was measured by GPC by the method described above, a peak top was present only at the position of the molecular weight of 51,000. The intrinsic viscosity [
η] of 650Y as the high-molecular-weight propylene polymer A was measured by the above-mentioned method and was found to be 0.56 (dl/g). The resulting Merutobu
average fiber diameter of the loan nonwoven peak fiber diameter, peak fiber diameter ratio, specific surface area, and the intrinsic viscosity [eta] shown in Table 1.
[0108]
[Comparative Example 3] In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture, Achieve 6936G2 (product name, manufactured by ExxonMobil, propylene-based polymer having a weight average molecular weight of 55,000, MFR: 1550) Using 100 parts by mass of a propylene-based polymer mixture (3), which is a mixture of 94 parts by mass and 6 parts by mass of Hiwax NP055 (product name, manufactured by Mitsui Chemicals, Inc., propylene-based polymer having a weight average molecular weight of 7,700). Except for this, the same operation as in Example 1 was performed.
　When the propylene-based polymer mixture (3) was measured by GPC by the method described above, a peak top was present only at the position of the molecular weight of 55,000. The weight average molecular weight of the propylene polymer mixture (3) was 54,000. Further, the intrinsic viscosity [η] of the propylene polymer mixture (3) was measured by the above-mentioned method, and it was 0.59 (dl/g).
　A GPC chart of the propylene polymer mixture (3) is shown in FIG.
　Table 1 shows the average fiber diameter, peak fiber diameter, peak fiber diameter ratio, specific surface area, and intrinsic viscosity [η] of the obtained meltblown nonwoven fabric.
[0109]
[Comparative Example 4] In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture, Achieve 6936G2 (product name, manufactured by ExxonMobil, propylene-based polymer having a weight average molecular weight of 55,000, MFR: 1550) Using 100 parts by mass of a propylene-based polymer mixture (4), which is a mixture of 50 parts by mass and 50 parts by mass of Hiwax NP055 (product name, manufactured by Mitsui Chemicals, Inc., propylene-based polymer having a weight average molecular weight of 7700). Except for this, the same operation as in Example 1 was performed.
　When the propylene polymer mixture (4) was measured by GPC by the method described above, peak tops were present at the positions of the weight average molecular weight of 55,000 and the molecular weight of 8,000. The number of peak tops was two. The weight average molecular weight of the propylene polymer mixture (4) was 29,000. The intrinsic viscosity [η] of the propylene polymer mixture (4) was 0.41 (dl/g) as measured by the above method.
[0110]
　An attempt was made to prepare a meltblown nonwoven fabric from the propylene polymer mixture (4) by the same method as in Example 1, but it could not be spun.
[0111]
[Comparative Example 5] In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture, S119 (product name, manufactured by Mitsui Chemicals, Inc., weight-average molecular weight: 171,000 propylene-based polymer, MFR: 60) Using 100 parts by mass of a propylene-based polymer mixture (5), which is a mixture of 85 parts by mass and 15 parts by mass of Hiwax NP055 (product name, manufactured by Mitsui Chemicals, Inc., propylene-based polymer having a weight average molecular weight of 7,700). Other than that, the same operation as in Example 1 was performed.
　When the propylene polymer mixture (5) was measured by GPC by the method described above, peak tops were present at the positions of molecular weight 170,000 and molecular weight 8,000. The number of peak tops was two. The weight average molecular weight of the propylene polymer mixture (5) was 162,000. The intrinsic viscosity [η] of the propylene-based polymer mixture (4) was measured by the above-mentioned method and found to be 1.2 (dl/g). Table 1 shows the average fiber diameter, peak fiber diameter, peak fiber diameter ratio, specific surface area, and intrinsic viscosity [η] of the obtained meltblown nonwoven fabric.
[0112]
[Comparative Example 6] In
　Example 1, instead of 100 parts by mass of the propylene-based polymer mixture, SP50500P (product name, manufactured by Prime Polymer Co., ethylene-based polymer having a weight average molecular weight of 38,000, JIS K 7210- 85 parts by weight of MFR:135 measured at 190° C. under a load of 2.16 kg according to 1:2014, and high wax 720P (product name, manufactured by Mitsui Chemicals, Inc., weight average molecular weight: 7,000 ethylene polymer). The same operation as in Example 1 was performed except that 100 parts by mass of the ethylene-based polymer mixture, which was a mixture of 15 parts by mass, was used.
　When the ethylene-based polymer mixture was measured by GPC by the above method, no peak top derived from the propylene-based polymer was found. The peak tops derived from the ethylene polymer were present at the positions of molecular weight 38,000 and 7,000. The weight average molecular weight of the ethylene polymer mixture was 31,000. The intrinsic viscosity [η] of the ethylene-based polymer mixture was measured by the above-mentioned method and was found to be 0.61 (dl/g). Table 1 shows the average fiber diameter, peak fiber diameter, peak fiber diameter ratio, specific surface area, and intrinsic viscosity [η] of the obtained meltblown nonwoven fabric.
[0113]
[Comparative Example 7] As a
　propylene/ethylene copolymer, Vistamaxx ™ 6202 [Product name, manufactured by ExxonMobil, weight average molecular weight: 70,000, MFR (230°C, 2.16 kg load): 20 g/10 min, ethylene content: 15 mass %] 40 parts by mass, propylene polymer wax [density: 0.900 g/cm 3 , weight average molecular weight: 7800, softening point 148° C., ethylene content: 1.7% by mass] 40 parts by mass, and propylene single weight 20 parts by mass of the combined product [MFR: 1500 g/10 minutes, weight average molecular weight: 54000] was mixed to obtain a propylene polymer composition (6).
[0114]
　When the propylene-based polymer mixture (6) was measured by GPC by the method described above, peak tops were present at a position of molecular weight 70,000, a position of molecular weight 54,000, and a position of molecular weight 8,000. The number of peak tops was three. The weight average molecular weight (Mw) of the propylene polymer mixture (6) was 48,000. The intrinsic viscosity [η] of the propylene polymer mixture (1) was 1.3 (dl/g) as measured by the above method. A meltblown nonwoven fabric was obtained in the same manner as in Example 1 except that the propylene polymer mixture (6) was used. The average fiber diameter, peak fiber diameter, and peak fiber diameter ratio of the obtained meltblown nonwoven fabric. Table 1 shows the specific surface area and the intrinsic viscosity [η].
[0115]
[table 1]

[0116]
　In Table 1, "-" means that the corresponding component was not included. PP represents polypropylene and PE represents polyethylene.
[0117]
　As is clear from Table 1, the meltblown nonwoven fabric of the example has a smaller average fiber diameter and a larger specific surface area than the meltblown nonwoven fabric of the comparative example. Therefore, it can be seen that when the meltblown nonwoven fabric of the example is used as a filter, the efficiency of collecting fine particles is excellent.
The scope of the claims
[Claim 1]
　The emission curve in gel permeation chromatography has at least one peak top at a molecular weight of 20,000 or more and at least one peak top at a molecular weight of less than 20,000, and an intrinsic viscosity [η] of 0.50. A meltblown nonwoven fabric made of a propylene-based polymer having a (dl/g) to 0.75 (dl/g).
[Claim 2]
　The propylene-based polymer contains at least a high-molecular-weight propylene-based polymer A having a weight average molecular weight of 20,000 or more and a low-molecular-weight propylene-based polymer B having a weight average molecular weight of less than 20,000. Meltblown nonwoven fabric.
[Claim 3]
　The melt blown nonwoven fabric according to claim 2, wherein the content of the low-molecular-weight propylene-based polymer B is 8% by mass to 40% by mass with respect to the total mass of the propylene-based polymer.
[Claim 4]
　The melt blown nonwoven fabric according to claim 2 or 3, wherein the content of the high-molecular-weight propylene-based polymer A relative to the total weight of the propylene-based polymer is 60% by mass to 92% by mass.
[Claim 5]
　The melt blown nonwoven fabric according to any one of claims 2 to 4, wherein a melt flow rate (MFR) of the high molecular weight propylene-based polymer A is 1000 g/10 minutes to 2500 g/10 minutes.
[Claim 6]
　The melt blown nonwoven fabric according to any one of claims 1 to 5, wherein the propylene-based polymer has a weight average molecular weight of 20,000 or more.
[Claim 7]
　The melt blown nonwoven fabric according to any one of claims 1 to 6, which is composed of fibers having an average fiber diameter of less than 1.1 µm.
[Claim 8]
　A specific surface area of 2.0 m 2 /G～20.0M 2 meltblown nonwoven fabric according to any one of claims 1 to 7 is / g.
[Claim 9]
　The melt blown nonwoven fabric according to any one of claims 1 to 8, wherein the ratio of the peak fiber diameter to the average fiber diameter exceeds 0.5.
[Claim 10]
　A nonwoven fabric laminate comprising at least the melt blown nonwoven fabric according to any one of claims 1 to 9.
[Claim 11]
　A filter comprising the meltblown nonwoven fabric according to any one of claims 1 to 9.
[Claim 12]
　The filter according to claim 11, which is a liquid filter.