TW202146729A - Electret melt-blown non-woven fabric, filter material and air filter obtained using same, and method for producing electret melt-blown non-woven fabric - Google Patents

Abstract

The present invention addresses the problem of providing: an electret melt-blown non-woven fabric which has high trapping efficiency and low pressure loss; and a filter material and an air filter obtained using same. This electret melt-blown non-woven fabric is constituted from polyolefin-based resin fibers, wherein the non-woven fabric contains: 0.1-5.0 mass% of a hindered amine-based compound; and 0.01-1 mass% of one or more types of metal oxide particle which are constituted from oxides of metallic elements selected from among copper, cobalt, aluminum, nickel, zinc, palladium, molybdenum and tungsten, and which have an average particle diameter of 500 nm or less.

Description

Electret melt-blown non-woven fabric, filter material and air filter using the same, and manufacturing method of electret melt-blown non-woven fabric

The present invention relates to non-woven fabrics. More specifically, the present invention relates to an electret meltblown nonwoven fabric having excellent collection efficiency, a filter medium and an air filter using the same.

Conventionally, an air filter has been used to remove pollen, dust, etc. in the gas, and as the filter medium of the air filter, non-woven fabrics are often used.

In general, it is difficult to improve the collection efficiency and reduce the pressure loss for a filter using a non-woven fabric. Therefore, the non-woven fabric is processed into an electret, and the physical effect is added to the electrostatic effect, so as to try to obtain a filter. Non-woven fabric suitable for use when the constituent elements are used.

For example, there has been proposed a method for producing an electret nonwoven fabric in which, in a state where the nonwoven fabric is brought into contact with a ground electrode, the ground electrode is moved together with the nonwoven fabric, and a non-contact type application electrode is used to apply a high voltage continuously. electretization (refer to Patent Document 1). In addition, as a method of bringing water into contact with the fibers to charge the fibers, a so-called hydrocharge method has been proposed. For example, for a nonwoven fabric, a jet or droplet of water is sprayed with sufficient pressure to allow water to penetrate inside the nonwoven fabric. A method of electretizing it so that positive and negative charges are uniformly mixed (refer to Patent Document 2); the non-woven fabric is passed through a slit-shaped nozzle, and the water is sucked by the nozzle to permeate the fiber sheet, A method of uniformly mixing positive and negative charges (refer to Patent Document 3).

In addition, other than these, a heat-resistant electret material is proposed, which is a high molecular polymer constituting fibers of a non-woven fabric, blended with hindered amine-based, nitrogen-containing hindered phenol-based, and metal-salt hindered phenol-based materials. Or at least one kind of stabilizer selected from phenol-based stabilizers, and the trapped charge amount of thermally stimulated depolarization current from a temperature of 100°C or higher is 2.0×10 ⁻¹⁰ coulombs/cm ² or more (refer to Patent Document 4). [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 61-289177 Patent Document 2: Specification of US Patent No. 6,119,691 Patent Document 3: Japanese Patent Laid-Open No. 2003-3367 Patent Document 4: Japanese Patent Laid-Open No. 63-280408

[The problem to be solved by the invention]

As in the proposals described in the above-mentioned Patent Documents 1 to 4, by electretizing the nonwoven fabric, the pressure loss can be maintained relatively low and the collection efficiency can be improved to some extent. However, by electretizing the nonwoven fabric only In the current situation where the demand for higher-performance filters is increasing, the effect cannot be said to be sufficient for processors.

Therefore, an object of the present invention is to provide an electret melt-blown nonwoven fabric which has a low pressure loss and an unprecedented high collection efficiency in view of the above-mentioned problems. [means to solve the problem]

In order to achieve the above object, the inventors of the present invention have repeatedly and earnestly examined and found that, when using metal oxide fine particles of a specific metal type and a specific average particle size, even if electret processing is performed, the charging characteristics are not deteriorated, and the following results are obtained. Insights: Low pressure loss can be maintained while further improving capture efficiency.

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.

The electret meltblown nonwoven fabric of the present invention is an electret meltblown nonwoven fabric composed of polyolefin resin fibers, and the electret meltblown nonwoven fabric contains 0.1% by mass to 5.0% by mass of a hindered amine compound. and 0.01 mass % or more and 1 mass % or less of one or more metal oxide particles composed of oxides of metal elements selected from copper, cobalt, aluminum, nickel, zinc, palladium, molybdenum, and tungsten structure and the average particle diameter is 500 nm or less.

According to a preferred aspect of the electret meltblown nonwoven fabric of the present invention, the aforementioned metal oxide particles are zinc oxide particles.

According to a preferred aspect of the electret meltblown nonwoven fabric of the present invention, the average single fiber diameter of the constituted fibers is 1.5 μm or less.

According to a preferred aspect of the electret melt-blown nonwoven fabric of the present invention, the cross-sectional area of the primary particle of the metal oxide particles contained in the polyolefin resin fiber is regarded as S ₀ , and the SEM-EDX of the metal oxide particles is regarded as S 0 . S ₁ when calculated as the area of the secondary particles, at least one line comprises 1000 or less S ₁ / S ₀ of the metal oxide particles in the range of 1,000 to 50,000 fibers 1.0 × 10 ^-2 mm ² of the.

In addition, the filter material of the present invention is formed by using the above-mentioned electret melt-blown nonwoven fabric, and the air filter of the present invention is formed by using the above-mentioned filter material.

Furthermore, the manufacturing method of the electret meltblown nonwoven fabric of the present invention has the following steps (1) to (3) in order. (1) a step of mixing at least two or more polyolefin-based resin compositions (polyolefin-based resin A and polyolefin-based resin B), Here, the polyolefin-based resin A contains 0.01 mass % or more and 1 mass % or less of one or more metal oxide particles based on 100 mass % of the electret meltblown nonwoven fabric, and the metal oxide particles are composed of copper, It is composed of oxides of metal elements selected from cobalt, aluminum, nickel, zinc, palladium, molybdenum, and tungsten and has an average particle diameter of 500 nm or less, and the polyolefin-based resin B contains an electret melt-blown nonwoven fabric in an amount of 100% by mass. 0.1 mass % or more and 5.0 mass % or less of hindered amine-based compounds; (2) a step of making a nonwoven fabric by melt blowing a mixture of the polyolefin-based resin A and the polyolefin-based resin B; and (3) The step of electret processing the non-woven fabric.

According to a preferred aspect of the method for producing an electret meltblown nonwoven fabric of the present invention, the absolute value of the difference between the melt flow rate of the polyolefin-based resin A and the melt flow rate of the polyolefin-based resin B is 650 g/ more than 10 minutes. [Effect of invention]

According to the present invention, in the fibers constituting the electret meltblown nonwoven fabric, an electret meltblown nonwoven fabric can be obtained by locally containing metal oxide particles of a specific metal species and a specific average particle diameter in the fibers, It is low pressure loss, but has hitherto high capture efficiency.

[Form for carrying out the invention]

Hereinafter, suitable embodiments of the electret meltblown nonwoven fabric of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented according to the purpose or application.

The non-woven fabric of the present invention is an electret melt-blown non-woven fabric composed of polyolefin resin fibers, and the electret melt-blown non-woven fabric contains 0.1 mass % or more and 5.0 mass % or less of a hindered amine compound and 0.01 mass % or more. 1 mass % or less of one or more metal oxide particles composed of oxides of metal elements selected from copper, cobalt, aluminum, nickel, zinc, palladium, molybdenum, and tungsten and having an average particle size is 500 nm or less. Hereinafter, the constituent elements will be described in detail, but the present invention is not limited by the scope of the following description at all unless it deviates from the gist.

First, the electret meltblown nonwoven fabric of the present invention is composed of polyolefin resin fibers. The term "polyolefin-based resin fiber" in the present invention means that the constituent fiber is made of a polyolefin-based resin composition. By making polyolefin-based resin fibers with high volume resistivity and low water absorption, the electret processing of melt-blown nonwoven fabrics can be enhanced in chargeability and charge retention, and high trapping can be achieved by these effects. efficient.

In the present invention, as the polyolefin-based resin composition used for the polyolefin-based resin fiber, there may be mentioned homopolymers such as polyethylene, polypropylene, polybutene, and polymethylpentene. In addition, a copolymer obtained by copolymerizing these homopolymers with different components, or a resin such as a blended product of two or more different polymers can also be used. Among these, from the viewpoint of charge retention, polypropylene-based resins and polymethylpentene-based resins are preferably used. In particular, polypropylene-based resins are preferably used from the viewpoints of being inexpensive and easy to reduce the fiber diameter. In addition, the term "polypropylene resin" refers to resins such as polypropylene homopolymers, copolymers with other components, and polymer blends with dissimilar resins that contain 80% of polypropylene homopolymers and propylene units. mass % or more of resin.

Moreover, in the polypropylene resin fiber used for this invention, as long as the effect of this invention is not impaired, additives, such as a heat stabilizer, a weathering agent, and a polymerization inhibitor, may be contained in a polyolefin resin fiber.

Next, the electret meltblown nonwoven fabric of the present invention is based on the electret meltblown nonwoven fabric, and contains 0.1 mass % or more and 5.0 mass % or less of the hindered amine compound. By containing the hindered amine compound in an amount of 0.1 mass % or more, preferably 0.7 mass % or more, an electret melt-blown nonwoven fabric excellent in chargeability and charge retention during electret processing can be obtained. On the other hand, by containing the hindered amine compound in an amount of 5.0 mass % or less, preferably 3.0 mass % or less, the above-mentioned chargeability and charge retention can be exhibited at a lower cost.

The content of the hindered amine compound can be obtained, for example, as follows. That is, after the non-woven fabric was subjected to Soxhlet extraction with a methanol/chloroform mixed solution, the extract was subjected to repeated HPLC fractionation, and each fraction was subjected to IR measurement, GC measurement, GC/MS measurement, and MALDI measurement. -MS measurement, ¹ H-NMR measurement, and ¹³ C-NMR measurement to confirm the structure. The mass of the fractions contained in the additive was totaled, the ratio relative to the whole nonwoven fabric was obtained, and this was regarded as the content of the hindered amine compound.

The hindered amine-based compound used in the present invention is a compound having a structural unit represented by the following general formula (1).

In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, and * represents a bonding portion.

-2,4-二基)((2,2,6,6-四甲基-4-哌啶基)亞胺基)六亞甲基((2,2,6,6-四甲基-4-哌啶基)亞胺基)](BASF JAPAN(股)製，「Chimassorb」(註冊商標)944LD)、琥珀酸二甲基-1-(2-羥基乙基)-4-羥基-2,2,6,6-四甲基哌啶聚縮合物(BASF JAPAN(股)製，「Tinuvin」(註冊商標)622LD)及2-(3,5-二第三丁基-4-羥基苄基)-2-正丁基丙二酸雙(1,2,2,6,6-五甲基-4-哌啶基)酯(BASF JAPAN(股)製，「Tinuvin」(註冊商標)144)等。Examples of hindered amine compounds having such a structure include poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-tris

-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)hexamethylene((2,2,6,6-tetramethyl- 4-Piperidinyl)imino)] (manufactured by BASF JAPAN Co., Ltd., "Chimassorb" (registered trademark) 944LD), dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2 succinate ,2,6,6-Tetramethylpiperidine polycondensate (manufactured by BASF JAPAN Co., Ltd., "Tinuvin" (registered trademark) 622LD) and 2-(3,5-di-tert-butyl-4-hydroxybenzyl) bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-2-n-butylmalonate (manufactured by BASF JAPAN Co., Ltd., "Tinuvin" (registered trademark) 144 )Wait.

系化合物。藉由含有0.1質量%以上、較佳0.7質量%以上的三

系化合物，可得到施予駐極體加工時的帶電性、電荷保持性優異之駐極體熔噴不織布。另一方面，藉由含有5.0質量%以下、較佳3.0質量%以下的三

系化合物，可以更低成本展現上述帶電性與電荷保持性。Furthermore, the electret melt-blown nonwoven fabric of the present invention preferably contains 0.1 mass % or more and 5.0 mass % or less of the trioxide in the electret melt-blown non-woven fabric.

series compounds. By containing 0.1 mass % or more, preferably 0.7 mass % or more of

It is a compound that can obtain electret melt-blown nonwoven fabrics excellent in electret chargeability and charge retention during electret processing. On the other hand, by containing 5.0 mass % or less, preferably 3.0 mass % or less of

It is a compound that can exhibit the above-mentioned chargeability and charge retention at a lower cost.

系化合物之含量係與受阻胺系化合物同樣地，例如可如以下地求出。亦即，以甲醇/氯仿混合溶液索氏萃取不織布後，對於其萃取物，重複HPLC分取，對於各個分取物，以IR測定、GC測定、GC/MS測定、MALDI-MS測定、¹ H-NMR測定及¹³ C-NMR測定來確認結構。合計該三

系化合物所有的分取物之質量，求出相對於不織布全體之比例，將其當作三

系化合物之含量。In the present invention, three

The content of the type compound is the same as that of the hindered amine type compound, and can be obtained, for example, as follows. That is, after Soxhlet extraction of the non-woven fabric with a methanol/chloroform mixed solution, HPLC fractionation was repeated for the extract, and each fraction was measured by IR, GC, GC/MS, MALDI-MS, and ¹ H. -NMR measurement and ¹³ C-NMR measurement confirmed the structure. total the three

It is the mass of all the fractions of the compound, and the ratio relative to the whole non-woven fabric is obtained, and it is regarded as three

The content of the compound.

系化合物係具有以下通式(2)表示的三

環結構之化合物。The third used in the present invention

The compound is a compound having three compounds represented by the following general formula (2)

Compounds with ring structure.

In addition, in the general formula (2), * represents a bond portion.

環結構的三

系化合物，例如可舉出[(6-(1,1,3,3-四甲基丁基)亞胺基-1,3,5-三

-2,4-二基)((2,2,6,6-四甲基-4-哌啶基)亞胺基)六亞甲基((2,2,6,6-四甲基-4-哌啶基)亞胺基)](BASF JAPAN(股)製，「Chimassorb」(註冊商標)944LD)及2-(4,6-二苯基-1,3,5-三

-2-基)-5-((己基)氧基)-苯酚(BASF JAPAN(股)製，「Tinuvin」(註冊商標)1577FF)等。as having these three

ring structure of three

system compounds, for example, [(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-tri

-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)hexamethylene((2,2,6,6-tetramethyl- 4-Piperidinyl)imino)] (manufactured by BASF JAPAN Co., Ltd., "Chimassorb" (registered trademark) 944LD) and 2-(4,6-diphenyl-1,3,5-tris

-2-yl)-5-((hexyl)oxy)-phenol (manufactured by BASF JAPAN Co., Ltd., "Tinuvin" (registered trademark) 1577FF) and the like.

系化合物之中，更佳使用具有通式(1)、(2)之兩者的結構之化合物，其係因為能減少添加於聚烯烴系樹脂中的化合物量，且能以低成本展現帶電性與電荷保持性。如此的化合物例如為聚[(6-(1,1,3,3-四甲基丁基)亞胺基-1,3,5-三

-2,4-二基)((2,2,6,6-四甲基-4-哌啶基)亞胺基)六亞甲基((2,2,6,6-四甲基-4-哌啶基)亞胺基)](BASF JAPAN(股)製，「Chimassorb」(註冊商標)944LD)。These hindered amine compounds are based on three

Among the compounds, it is more preferable to use a compound having a structure of both general formulas (1) and (2), because it can reduce the amount of the compound added to the polyolefin-based resin and can exhibit chargeability at low cost and charge retention. Such compounds are, for example, poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-tris

-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)hexamethylene((2,2,6,6-tetramethyl- 4-Piperidinyl)imino)] (manufactured by BASF JAPAN Co., Ltd., "Chimassorb" (registered trademark) 944LD).

Furthermore, the electret meltblown nonwoven fabric of the present invention contains 0.01 mass % or more and 1 mass % or less of one or more metal oxide particles, and the metal oxide particles are composed of copper, cobalt, aluminum, nickel, zinc, palladium, and molybdenum. , It is composed of oxides of metal elements selected from tungsten and has an average particle size of 500 nm or less. The details are described below.

First, as the oxide of the metal element constituting the metal oxide particles used in the present invention, from the viewpoint of excellent collection efficiency when electretizing the meltblown nonwoven fabric, copper, cobalt, aluminum, Oxides of metal elements selected from nickel, zinc, palladium, molybdenum, and tungsten. Among them, zinc oxides are particularly preferred from the viewpoint of being excellent in collection efficiency. Metal oxides composed of oxides of a plurality of metal elements can also be used.

That is, specific examples of oxides of metal elements used in the present invention include copper(I) oxide, copper(II) oxide, cobalt(II) oxide, cobalt(III) oxide, cobalt(II, III) oxide, Aluminum oxide (III), nickel (II) oxide, zinc (II) oxide, palladium (II) oxide, molybdenum (VI) oxide, tungsten (VI) oxide, etc., preferably zinc (II) oxide.

The electret meltblown nonwoven fabric of the present invention also preferably contains one or more of the metal oxide particles.

In addition, the metal oxide particles used in the present invention have an average particle diameter of 500 nm or less. Collection efficiency can be improved by setting the average particle diameter of the metal oxide particles to be 500 nm or less, preferably 300 nm or less, and more preferably 100 nm or less. On the other hand, although there is no particular lower limit on the average particle diameter of the metal oxide particles used in the present invention, in general, particles of 1 nm or more are preferably used from the viewpoint of nanomaterial handling.

In addition, as a method for measuring the particle size of the metal oxide particles, first, the electret melt-blown non-woven fabric is immersed in a non-polar hydrocarbon solvent such as xylene, decalin, and chlorobenzene to dissolve the polyolefin resin, and the metal is isolated. oxide particles. To uniformly disperse the isolated metal oxide particles in water until they become primary particles, a conventional laser diffraction-scattering particle size analyzer or the like can be used, and the arithmetic mean calculated from the volume-based particle size distribution can be calculated The value is taken as the average particle diameter (nm) of the metal oxide particles.

Furthermore, in the electret melt-blown nonwoven fabric of the present invention, one or more of the aforementioned metal oxide particles are contained in an amount of 0.01 mass % or more and 1 mass % or less. With respect to the mass of the electret melt-blown nonwoven fabric, by setting the content of the metal oxide particles to 0.01 mass % or more, preferably 0.1 mass % or more, when the melt-blown non-woven fabric is subjected to electret processing, it can be obtained. Electret meltblown nonwoven with excellent capture efficiency. On the other hand, by making it 1 mass % or less, preferably 0.5 mass % or less, not only the strength of the electret meltblown nonwoven fabric can be maintained, but also the clogging of the spinning nozzle or the occurrence of resin lumps (shots) can be suppressed. Wait for the spinning problem.

In the present invention, the content of the metal oxide particles can be determined using analytical methods such as fluorescence X-ray analysis, atomic absorption analysis (FLAAS), and emission spectroscopic analysis (ICP-AES). For example, fluorescent X-ray analysis is a method of irradiating X-rays to a nonwoven fabric and detecting the generated fluorescent X-rays. Since this fluorescent X-ray has energy inherent in the element, it can be quantitatively analyzed using the qualitative analysis of Moseley's law and the intensity of the fluorescent X-ray. The relationship (calibration curve) between the concentration of the element to be analyzed in quantitative analysis and the fluorescent X-ray can be prepared in advance, and the unknown sample can be measured based on the result, and the concentration can be obtained from the obtained fluorescent X-ray intensity.

In the electret melt-blown nonwoven fabric of the present invention, the cross-sectional area of the primary particles of the metal oxide particles contained in the polyolefin-based resin fiber is regarded as S ₀ , and the secondary value of the metal oxide particles obtained by SEM-EDX is regarded as S 0 . When the area of the particles is taken as S ₁ , it is preferable to contain one or more and 1,000 or less _{metal oxide particles having S 1} /S ₀ of 1,000 to 50,000 in ^{the range of 1.0×10 −2} mm ^{2 of fibers.} When S ₁ /S _{0 is} less than 1000, the exposure of the polyolefin resin constituting the electret meltblown nonwoven fabric to the fiber surface decreases, and the collection efficiency decreases. The upper limit of S ₁ /S ₀ is not particularly limited, but is usually a range in which problems in spinning such as clogging of the spinning nozzle and generation of resin lumps (shots) do not occur, and is preferably 50,000 or less.

In the present invention, the aggregation state of the metal oxide particles is described in detail by the method described in the examples, but can be obtained as follows. First, by SEM-EDX analysis, the aforementioned electret melt-blown nonwoven fabric was irradiated with electron beams, the generated specific X-rays were spectroscopic, and the constituent elements were identified. Furthermore, by performing element mapping based on the detected information, the metal elements constituting the metal oxide particles in the fibers constituting the electret melt-blown nonwoven fabric can be visualized as images. At this time, among the metal elements visualized by element mapping, the metal element with the highest detection intensity is defined, the area of the visible part of the metal element is calculated, and this is regarded as the area of the secondary particle of the metal oxide particle. S ₁ . In addition, the agglomeration state of the metal oxide particles was calculated from the following formula, using the cross-sectional area of the primary particle of the metal oxide particles as S _{0 .}・Agglomeration state of metal oxide particles = S ₁ /S _{0 The} specific method for determining the cross-sectional area S ₀ of the primary particle, when the primary particle of the metal oxide particle is spherical or nearly spherical in shape, it is considered to have a shape similar to that of the primary particle The area of a circle with the same diameter as the average particle size is taken as S ₀ . When the pulverized particle or the like has a polygonal cross section, the polygon can be divided into triangles, and the sum of the areas can be obtained, etc., and can be obtained according to each shape.

In addition, when performing SEM-EDX analysis, as long as the analysis range can be ensured to be 1.0×10 ^-2 mm ² or more, the surface of the aforementioned electret meltblown nonwoven fabric can be analyzed, and the cross section of the nonwoven fabric can also be analyzed.

As the polyolefin-based resin composition used in the electret meltblown nonwoven fabric of the present invention, the method for determining the melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastics-thermoplastics according to JIS K7210-1:2014 - Part 1: Standard Test Methods", "8 A: Mass Measurement Method" to obtain. The polyolefin-based resin composition preferably has a melt flow rate (MFR) of 50 g/10 minutes or more and 2500 g/10 minutes or less measured under the conditions of a temperature of 230° C., a load of 2.16 kg, and a measurement time of 10 minutes. The melt flow rate of the polyolefin-based resin composition is preferably 50 g/10 minutes or more, more preferably 150 g/10 minutes or more, thereby making it easier to reduce the diameter of the fibers constituting the electret melt-blown nonwoven fabric . On the other hand, the melt flow rate of the polyolefin-based resin composition is preferably 2500 g/10 minutes or less, more preferably 2000 g/10 minutes or less, whereby the strength of the nonwoven fabric can be improved.

The polyolefin-based resin fibers used in the electret meltblown nonwoven fabric of the present invention preferably have an average single fiber diameter of 0.1 μm or more and 15.0 μm or less. By setting the average single fiber diameter to preferably be 0.1 μm or more, more preferably 0.3 μm or more, and particularly preferably 0.5 μm or more, the strength of the nonwoven fabric can be improved. On the other hand, by setting it as 15.0 μm or less, preferably 5.0 μm or less, and more preferably 1.5 μm or less, the collection efficiency of the electret meltblown nonwoven fabric can be improved.

In addition, the average single fiber diameter of the polyolefin-based resin fibers used in the electret meltblown nonwoven fabric in the present invention refers to three points in the width direction of the nonwoven fabric (two points at the side end and one point in the center), which are in the long side of the nonwoven fabric. A total of 15 points of 5 points every 5 cm in the direction are collected, and 15 measurement samples of 3 mm × 3 mm are collected, and the magnification is adjusted to 3000 times with a scanning electron microscope (such as "VHX-D510" manufactured by KEYENCE Co., Ltd.), from Each of the collected measurement samples was photographed with one photograph of the fiber surface, for a total of 15 photographs. For fibers whose fiber diameters (single fiber diameters) in the photographs can be clearly identified, the single fiber diameters are measured, and the average value is rounded off to the second decimal place.

In addition, the polyolefin resin fiber may be a composite fiber, for example, a core-sheath type, an eccentric core-sheath type, a side-by-side type, a split type, a sea-island type, and an alloy type of composite fibers can be collected.

The electret meltblown nonwoven fabric of the present invention preferably has a weight per unit area of not less than 3 g/m ^{2 and not} more than 100 g/m ² . By electret melt-blown non-woven fabric to the weight of 3g / m ² or more, preferably to 5g / m ² or more, more preferably set to 10g / m ² or more, can improve an electret melt-blown non-woven fabric capture efficiency. On the other hand, by setting it as 100 g/m ² or less, preferably 70 g/m ² or less, and more preferably 50 g/m ² or less, it can be suppressed that the electret meltblown nonwoven fabric is applied as a filter unit. The collapse of the pleated mountain when formed with pleats.

In addition, the weight per unit area of the electret melt-blown nonwoven fabric in the present invention is collected from the electret melt-blown non-woven fabric, and a sample of vertical × horizontal = 15 cm × 15 cm is collected, the mass of the sample is measured, and the obtained value is converted into per 1 m ^{The value of 2} was rounded off to the nearest decimal point, and the basis weight (g/m ² ) of the nonwoven fabric was calculated.

The electret melt-blown nonwoven fabric of the present invention combines high collection efficiency and low pressure loss by collecting the above-mentioned structure. As an index of these collection performances, there is a QF value (Pa ^-1 ). The QF value is shown in the following formula, which represents the relationship between the collection efficiency and the pressure loss. The higher the QF value, the higher the collection efficiency and the lower the pressure loss.・QF value (Pa ^-1 )=-[ln(1-(capture efficiency (%))/100)]/(pressure loss (Pa)).

Here, the method for measuring the collection efficiency and pressure loss of the electret melt-blown nonwoven fabric in the present invention is a value calculated by measuring with the following procedure. (1) At 5 places in the width direction of the non-woven fabric, one measurement sample M each having a length x width = 15 cm x 15 cm (5 in total) was collected. (2) The collection efficiency measuring apparatus shown in the schematic side view of FIG. 1 was prepared. In this collection efficiency measuring apparatus, the dust storage box 2 is connected to the upstream side of the sample holder 1 in which the measurement sample M is installed, and the flow meter 3 , the flow rate adjustment valve 4 , and the blower 5 are connected to the downstream side. In addition, the particle counter 6 can be used in the sample holder 1, and the number of dusts on the upstream side and the number of dusts on the downstream side of the measurement sample M can be measured by switching the cock 7, respectively. (3) A 10% aqueous solution of polystyrene particles (for example, "OptiBind, model: 9100079710290" manufactured by ThermoScientific) was diluted 200 times with distilled water, and the dust container 2 was filled. (4) The measurement sample M is set in the sample holder 1, and the air volume is adjusted with the flow rate adjustment valve 4 so that the filter passing speed becomes 4.5 m/min, so that the dust concentration is stabilized at 10,000 to 40,000/2.83×10 ^-4 m ³ (0.01ft ³ ). (5) Measure the number D of dust upstream of the measurement sample M and the number d of dust downstream of the measurement sample M with a particle counter 6 (for example, "KC-01D" manufactured by RION Co., Ltd.), and each measurement sample is measured 3 times, according to JIS K0901:1991 "Shape, dimension and performance test method of filter medium for dust sample collection in gas", the following formula was used to obtain the collection efficiency (%) of 0.3-0.5 μm particles.・Collection efficiency (%)=[1-(d/D)]×100 (where d represents the total number of downstream dusts measured three times, and D represents the total number of upstream dusts measured three times). (6) At the same time, the static pressure difference between the upstream and downstream of the measurement sample M is read with the pressure gauge 8, and the pressure loss (Pa) of the measurement sample M is obtained. (7) For the five measurement samples M, calculate the average value of the collection efficiency (%), round off the fourth decimal place, and use the obtained value as the collection efficiency (%) of the electret meltblown nonwoven fabric. (8) For the five measurement samples M, the average value of the pressure loss (Pa) was calculated, the second decimal place was rounded off, and the obtained value was regarded as the pressure loss (Pa) of the electret meltblown nonwoven fabric.

The electret melt-blown nonwoven fabric of the present invention is preferably used as a filter in order to utilize the above-mentioned high collection efficiency.

In order to utilize the aforementioned high collection efficiency, the air filter material of the present invention is preferably made of the electret melt-blown nonwoven fabric of the present invention. As a method for obtaining the air filtration filter material of the present invention from the nonwoven fabric of the present invention, it is possible to use: spraying a moisture-curable urethane resin or the like to disperse the electret meltblown nonwoven fabric and an aggregate material with higher rigidity than the nonwoven fabric of the present invention. The method of laminating the sheet; or the method of laminating the electret melt-blown non-woven fabric with the higher rigidity of the aggregate sheet by distributing thermoplastic resin and thermal fusion fiber through the heat circuit.

This aggregate sheet is used to capture relatively large dust, and at the same time is joined to the electret meltblown non-woven fabric to obtain the necessary rigidity as a filter material. As the aggregate sheet, for example, non-woven fabrics, knitted fabrics, etc. made of polyester fibers, polypropylene fibers, rayon fibers, glass fibers, and natural pulp can be used.

The filter material of the present invention can be directly incorporated into the frame material in the form of a sheet and used as a filter unit. In addition, in the present invention, the filter medium can be pleated by repeating the mountain fold and the valley fold, and used as a pleated filter unit provided in the frame material.

Therefore, the air filter of the present invention is preferably the aforementioned filter material. The air filter is more preferably a filter for an air conditioner, a filter for an air purifier, or a filter for an automobile cabin. That is, the electret melt-blown nonwoven fabric or filter material for filters of the present invention can be used as filters for such high-performance applications.

Next, the manufacturing method of the electret meltblown nonwoven fabric of the present invention will be described.

In the manufacture of the electret melt-blown non-woven fabric of the present invention, the hindered amine-based compound and the metal oxide particles can also be mixed in the polyolefin-based resin at one time to form a polyolefin resin composition, which is used to form the melt-blown non-woven fabric. However, it is preferable to mix the polyolefin-based resin A and the polyolefin-based resin B described later to prepare a polyolefin resin composition for forming a melt-blown nonwoven fabric. By doing so, the metal oxide particles can be locally present in the polyolefin-based resin fibers constituting the melt-blown nonwoven fabric, and the collection efficiency can be improved.

The polyolefin-based resin A contains, in addition to the polyolefin-based resin, one or more oxides of metal elements selected from copper, cobalt, aluminum, nickel, zinc, palladium, molybdenum, and tungsten, and the average Metal oxide particles with a particle size of 500 nm or less. The polyolefin-based resin A preferably contains one or more metal oxide particles so as to be 0.01 mass % or more and 1 mass % or less of the electret meltblown nonwoven fabric. By doing so, the aforementioned effects, namely, the electret meltblown nonwoven fabric excellent in collection efficiency can be obtained, and the collection efficiency can be further improved because the metal oxide particles can be locally present in the polyolefin-based resin fiber.

Moreover, it is preferable that the polyolefin resin A and/or B contains a hindered amine-type compound so that it may become 0.1 mass % or more and 5.0 mass % or less of the formed electret meltblown nonwoven fabric. In this way, an electret meltblown nonwoven fabric excellent in chargeability and charge retention can be obtained.

Furthermore, the absolute value (|MFR _A -MFR _B |) of the difference between the melt flow rate (MFR _A ) of the polyolefin-based resin A and the melt flow rate (MFR _{B ) of the polyolefin-based resin B is preferable.} It is 650g/10min or more. By doing so, the dispersion state of the metal oxide particles in the polyolefin-based resin can be made more favorable, and the electret melt-blown nonwoven fabric which is more excellent in chargeability and charge retention can be obtained.

As a method for preparing a polyolefin resin composition containing metal oxide particles using the polyolefin resin A and the polyolefin resin B by the above method, the metal oxide particles can be mixed while extruding using a biaxial extruder or the like. In the polyolefin-based resin, after preparing the polyolefin-based resin A, the polyolefin-based resin B is mixed therewith, or a master batch is used to form chip blends (chip blends) and then extrude. When using a master batch, for example, a master batch of polyolefin-based resin A in which metal oxide particles are blended into a polyolefin-based resin such as polypropylene can be prepared, and the master batch can be shredded with polyolefin-based resin B such as polypropylene. Blending is performed in an extruder to prepare a polyolefin-based resin composition containing metal oxide particles.

Next, a melt-blown nonwoven fabric is formed from the obtained polyolefin-based resin composition. As a method for producing a melt-blown nonwoven fabric, a sliver can be formed while discharging a polyolefin resin composition from a melt-blown nozzle having a predetermined hole diameter. The diameter of the sliver is reduced by jetting hot air from a certain angle to the discharge portion, and the sliver is deposited on the collecting portion to form a melt-blown nonwoven fabric.

Furthermore, the obtained meltblown nonwoven fabric is subjected to electret processing. As a method of electretizing the melt-blown nonwoven fabric of the present invention, for example, in a state where the melt-blown non-woven fabric is brought into contact with the ground electrode, the ground electrode and the non-woven fabric are moved together and applied in a non-contact manner. The method of applying high pressure to the electrode and continuously electretizing it; for melt-blown non-woven fabrics, with sufficient pressure to allow water to penetrate into the interior of the melt-blown non-woven fabric, spray water jets or water droplets to electretize them , The method of making the positive and negative charges evenly mixed, or making the meltblown non-woven fabric run on the slit-shaped nozzle, and the nozzle attracts water to make the water penetrate the fiber sheet, so that the positive and negative charges are uniform. The method of mixed existence of earth (hydraulic charging method), etc. [Example]

Next, based on an Example, this invention is demonstrated concretely. However, the present invention is not limited only by these embodiments. In addition, in the measurement of each physical property, the measurement was performed according to the above-mentioned method unless otherwise stated.

[Measurement method] (1) Weight per unit area of electret melt-blown nonwoven fabric (g/m ² ): From the electret melt-blown non-woven fabric, a sample of length × width = 15 cm × 15 cm was collected, and the mass of the sample was measured, and the The obtained value was converted into a value per 1 m ² , and the weight per unit area (g/m ² ) of the nonwoven fabric was calculated by rounding off the first decimal place. (2) Average single fiber diameter (μm) of polyolefin-based resin fibers: The total of 3 points in the width direction of the non-woven fabric (2 points at the side edges and 1 point in the center) and 5 points every 5 cm in the longitudinal direction is 15 Point, collect 15 measurement samples of 3mm × 3mm. Using a scanning electron microscope ("VHX-D510" manufactured by KEYENCE Co., Ltd.), the magnification was adjusted to 3,000 times, and one photograph of the fiber surface was taken from the collected sample, for a total of 15 photographs. For fibers whose fiber diameters (single fiber diameters) in the photographs were clearly identified, the single fiber diameters were measured, and the average value was rounded off to the second decimal place, and the obtained value was regarded as the average single fiber diameter. (3) Measurement of Aggregation State of Metal Oxide Particles of Electret Meltblown Nonwoven Fabric by SEM-EDX: VE-9800 (manufactured by KEYENCE Co., Ltd.) was used as a measuring device (SEM), and Genesis-XM1 (manufactured by EDAX Co., Ltd.) was used as a measurement device (SEM). Detection device (EDX).

Three measurement samples of 3 mm×3 mm were collected from 3 points in the width direction of the nonwoven fabric (2 points at the side edges and 1 point at the center), and platinum coating was performed on the measurement samples.

Using a scanning electron microscope (SEM), the magnification was adjusted to 1000 times (measurement field of view: 1.1×10 ^-2 mm ² ), 1 point each on the surface of the fiber was photographed from the collected measurement sample, and a total of 3 points were accumulated. The time was set at 200 sec, and analysis and element mapping were performed. By performing element mapping, the metal elements constituting the metal oxide particles in the fibers constituting the electret melt-blown nonwoven fabric are visualized as images. Among the visible metal elements, the metal element with the highest detection intensity is defined, the area of the visible part of the metal element is calculated, and this is regarded as the area S ₁ of the secondary particle of the metal oxide particle. Next, with respect to the cross-sectional area S ₀ of the primary particle of the metal oxide particle, the number _{of the area S 1} of the secondary particle of the metal oxide particle which is 1000 times or more and 50000 times or less is counted. Specifically, when the primary particles of the metal oxide particles are spherical particles with a diameter of 20 nm, the number of places where the diameter of the secondary particles is 0.63 μm or more and 4.5 μm or less is counted. At this time, for the purpose of confirming the diameter, the magnification of a scanning electron microscope (SEM) is first magnified to 10,000 times, etc., and counted. The aggregated state of the metal oxide particles was calculated from the following formula, using the cross-sectional area of the primary particle of the metal oxide particles as S _{0 .} Agglomeration state of metal oxide particles=S ₁ /S ₀ As a method for measuring the cross-sectional area S ₀ of primary particles of metal oxide particles, first, the electret meltblown nonwoven fabric is immersed in a hydrocarbon-based solvent to dissolve the polyolefin resin, Isolated metal oxide particles. Using a scanning electron microscope ("VE-9800" manufactured by KEYENCE Co., Ltd.), the isolated metal oxide particles were magnified to 100,000 times and observed to confirm the shape of the metal oxide particles. When the metal oxide particles are spherical, the isolated metal oxide particles are uniformly dispersed in water until they become primary particles, using a laser diffraction scattering particle size analyzer (manufactured by Horiba Manufacturing Co., Ltd.) LA-920 ), and the arithmetic mean calculated from the volume-based particle size distribution was taken as the average particle diameter (nm) of the primary particles of the metal oxide particles.

When the primary particle of the metal oxide particle is spherical or nearly spherical, it is regarded as a circle having the same diameter as the average particle diameter of the primary particle, and its area is regarded as S ₀ . In the case of a cross section having a polygonal shape such as pulverized particles, the polygonal shape can be divided into triangles, and the sum of the areas can be regarded as S ₀ . (4) Collection efficiency, pressure loss, and QF value of electret melt-blown nonwoven fabric: "OptiBind, model number: 9100079710290" manufactured by ThermoScientific was used as a 10% aqueous solution of polystyrene particles. In addition, as the particle counter of the collection efficiency measuring apparatus, "KC-01D" manufactured by RION Co., Ltd. was used. (5) Spinnability of polyolefin-based resin fibers: The spinnability of polyolefin-based resin fibers is based on the observation of ^{a nonwoven fabric with a width of 1 m×length of 1 m (1 m 2} ), and the number of shots is 0 or more and less than 10 Those with 10 or more pellets and less than 30 pellets were rated as B, and those with 30 or more pellets were rated as C.

[Example 1] As the polyolefin-based resin A and the polyolefin-based resin B, the following polyolefin-based resin raw materials were used. ・Polyolefin resin A: A polypropylene resin containing 20% by mass of zinc oxide particles having a particle diameter of 20 nm in a polypropylene resin. In addition, the melt flow rate was 230 g/10 minutes. ・Polyolefin-based resin B: In polypropylene resin, 1 mass % of hindered amine-based compound "Chimassorb" (registered trademark) 944 (manufactured by BASF JAPAN Co., Ltd., described as "C944" in Tables 1 and 2) is contained Polypropylene resin. In addition, the melt flow rate was 1100 g/10 minutes.

The polyolefin-based resin A and the polyolefin-based resin B were mixed at a mass ratio of polyolefin-based resin A:polyolefin-based resin B=1:99 to obtain a chip blend. Next, this chip blend was put into the raw material hopper of the extruder, and was supplied to the gear pump while being melted and kneaded by the extruder. The polyolefin-based resin composition measured by the gear pump was arranged in a straight line using a spinneret with a discharge hole of 0.3 mm in diameter, and the discharge amount was 320 g/min and the nozzle temperature was 280 °C by the melt blowing method. , The air pressure is 0.19MPa under the condition of spraying, and by adjusting the speed of the collecting conveyor belt, the melt-blown non-woven fabric ^{with a unit area weight of 20g/m 2 is obtained.} Next, electretizing treatment is applied to the obtained meltblown nonwoven fabric to obtain electret meltblown nonwoven fabric.

For the obtained electret melt-blown nonwoven fabric, the composition and the like of the polyolefin-based resin composition are shown in Table 1, and the measurement results and evaluation results are shown in Table 3.

[Example 2] By the same method as in Example 1, except that the mixing ratio of the polyolefin-based resin A and the polyolefin-based resin B was set to a mass ratio of polyolefin-based resin A:polyolefin-based resin B=5:95, a resin was obtained. Polar body meltblown nonwoven.

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 1, and the measurement results and evaluation results are shown in Table 3.

[Example 3] An electret melt was obtained in the same manner as in Example 1, except that the type of polypropylene resin used for the polyolefin-based resin B was changed and the melt flow rate of the polyolefin-based resin B was changed to 900 g/10 minutes. Spray non-woven.

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 1, and the measurement results and evaluation results are shown in Table 3.

[Example 4] In addition to the polyolefin-based resin A, the following polyolefin-based resin raw materials were used, and the mixing ratio of the polyolefin-based resin A and the polyolefin-based resin B was set to a mass ratio of polyolefin-based resin A:polyolefin-based resin B=0.5:99.5 Other than that, by the same method as Example 1, an electret melt-blown nonwoven fabric was obtained. ・Polyolefin resin A: A polypropylene resin containing 40% by mass of zinc oxide particles having a particle diameter of 30 nm in a polypropylene resin. In addition, the melt flow rate was 230 g/10 minutes.

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 1, and the measurement results and evaluation results are shown in Table 3.

[Example 5] In addition to using a spinneret with a diameter of 0.15 mm arranged in a straight line, the melt blowing method was used under the conditions of a discharge rate of 160 g/min, a nozzle temperature of 280°C, and an air pressure of 0.19 MPa Under spraying, the electret meltblown nonwoven was obtained by the same method as in Example 1 except that the meltblown nonwoven fabric with a weight per unit area of 20 g/m ^{2 was obtained by adjusting the speed of the collecting conveyor belt.}

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 1, and the measurement results and evaluation results are shown in Table 3.

[Comparative Example 1] An electret melt-blown nonwoven fabric was obtained by the same method as in Example 1, except that the polyolefin-based resin A was not used, and only the polyolefin-based resin B was used to obtain a polyolefin-based resin composition.

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 2, and the measurement results and evaluation results are shown in Table 3.

[Comparative Example 2] An electret melt-blown nonwoven fabric was obtained by the same method as in Example 1, except that the following polyolefin-based resin raw materials were used as the polyolefin-based resin raw material. ・Polyolefin resin A: A polypropylene resin containing 20% by mass of zinc oxide particles having a particle diameter of 800 nm in a polypropylene resin. In addition, the melt flow rate was 230 g/10 minutes.

About the obtained electret melt-blown nonwoven fabric, the composition of the polyolefin resin composition and the like are shown in Table 2, and the measurement results and evaluation results are shown in Table 3.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Polyolefin resin A Polyolefin resin Resin type polypropylene polypropylene polypropylene polypropylene polypropylene metal oxide particles Types of metal oxides Zinc oxide Zinc oxide Zinc oxide Zinc oxide Zinc oxide Average particle size (nm) 20 20 20 30 20 Content (mass %) 20 20 20 40 20 Hindered amine compounds Compound name - - - - - Content (mass %) - - - - - MFR _A (g/10min) 230 230 230 230 230 Polyolefin resin B Polyolefin resin Resin type polypropylene polypropylene polypropylene polypropylene polypropylene metal oxide particles Types of metal oxides - - - - - Average particle size (nm) - - - - - Content (mass %) - - - - - Hindered amine compounds compound C944 C944 C944 C944 C944 Content (mass %) 1 1 1 1 1 MFR _B (g/10min) 1100 1100 900 1100 1100 ｜MFR _A -MFR _B ｜ (g/10min) 870 870 670 870 870 Polyolefin resin composition Mass ratio (resin A:resin B) 1:99 5:95 1:99 0.5:99.5 1:99 metal oxide particles Content (mass %) 0.2 1 0.2 0.2 0.2 Hindered amine compounds Content (mass %) 1 1 1 1 1

[Table 2] Comparative Example 1 Comparative Example 2 Polyolefin resin A Polyolefin resin Resin type - polypropylene metal oxide particles Types of metal oxides - Zinc oxide Average particle size (nm) - 800 Content (mass %) - 20 Hindered amine compounds Compound name - - Content (mass %) - - MFR _A (g/10min) - 230 Polyolefin resin B Polyolefin resin Resin type polypropylene polypropylene metal oxide particles Types of metal oxides - - Average particle size (nm) - - Content (mass %) - - Hindered amine compounds compound C944 C944 Content (mass %) 1 1 MFR _B (g/10min) 1100 1100 ｜MFR _A -MFR _B ｜ (g/10min) - 870 Polyolefin resin composition Mass ratio (resin A:resin B) - 1:99 metal oxide particles Content (mass %) - 0.2 Hindered amine compounds Content (mass %) - 1

[table 3] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 spinnability A A A A A A C Number of metal oxide particles with 1000≦S ₁ /S _{0 ≦50000} twenty three 108 20 46 28 0 0 physical properties Weight per unit area (g/m ² ) 20 20 20 20 20 20 20 Average single fiber diameter (µm) 2.2 2.3 2.4 2.2 1.4 2 2 Pressure loss (Pa) 26.8 27.4 25.7 27.0 37.0 31.3 27.2 Capture efficiency (%) 99.998 99.997 99.996 99.998 100 99.998 99.949 QF value (Pa ^-1 ) 0.41 0.37 0.39 0.40 0.44 0.34 0.28

As is clear from Table 3, the electret meltblown nonwoven fabrics described in Examples 1 to 5 achieved high collection efficiency and excellent collection performance (QF value) despite low pressure loss.

In contrast, the electret melt-blown nonwoven fabric described in Comparative Example 1, which does not contain only the components of metal oxide particles, is a collection of electret melt-blown non-woven fabrics described in Examples 1 to 5. Lower performance (QF value) results.

In addition, the electret meltblown nonwoven fabric described in Comparative Example 2 in which the particle diameter of the metal oxide particles contained in the polyolefin-based resin A was 800 nm was smaller than the electret meltblown nonwoven fabric described in Examples 1 to 4. In other words, not only the yarn breakage and the shot during spinning occurred frequently and the spinnability deteriorated, but also it was confirmed that the metal oxide particles were much agglomerated, the dispersion state was poor, and the trapping performance (QF value) was also low.

As described above, according to the present invention, by adding metal oxide particles having a predetermined particle diameter to the polyolefin-based resin fibers constituting the electret meltblown nonwoven fabric to locally exist, it is possible to obtain both high collection efficiency and low The pressure loss of electret meltblown nonwovens. Moreover, this electret melt-blown non-woven fabric can be applied to filter media and air filters, especially high-performance filters for air conditioners, filters for air purifiers, and filters for car compartments, or for masks or protective clothing to suppress Sanitary material use for the purpose of intrusion of pollen and dust in the gas.

1: Sample holder 2: Dust storage box 3: Flowmeter 4: Flow adjustment valve 5: Blower 6: Particle Counter 7: Switch the cock 8: Pressure gauge M: Assay sample

FIG. 1 is a schematic side view showing an example of a measuring device for collection efficiency and pressure loss.

none.

Claims (9)

A kind of electret melt-blown non-woven fabric, which is an electret melt-blown non-woven fabric composed of polyolefin resin fibers, in the electret melt-blown non-woven fabric, the electret melt-blown non-woven fabric is included relative to 100 mass % of the electret melt-blown non-woven fabric In particular, it is 0.1 mass % or more and 5.0 mass % or less of the hindered amine compound and 0.01 mass % or more and 1 mass % or less of one or more metal oxide particles, the metal oxide particles are composed of copper, cobalt, aluminum, nickel, and zinc. , palladium, molybdenum, and tungsten selected from the oxides of metal elements and the average particle size is 500nm or less. The electret meltblown nonwoven fabric according to claim 1, wherein the metal oxide particles are zinc oxide particles. The electret meltblown nonwoven fabric according to claim 1 or 2, wherein the average single fiber diameter of the fibers is 1.5 μm or less. The electret meltblown nonwoven fabric according to any one of claims 1 to 3, wherein the electret meltblown nonwoven fabric is used for filters. The electret meltblown nonwoven fabric according to any one of claims 1 to 4, wherein the cross-sectional area of the primary particle of the metal oxide particle contained in the polyolefin-based resin fiber is regarded as S ₀ , and the metal oxide When the area of the secondary particles obtained by SEM-EDX is regarded as S ₁ , the area of the particles is 1 or more and 1,000 or less in the range of 1.0×10 ^-2 mm ² _{of the fiber. S 1} /S ₀ is 1,000 to 50,000 of metal oxide particles. A filter material, which is formed by using the electret melt-blown nonwoven fabric according to any one of claims 1 to 5. An air filter using the filter material of claim 6. A method for producing an electret meltblown nonwoven fabric as claimed in any one of claims 1 to 5, which has the following steps (1) to (3) in sequence: (1) a step of mixing at least two or more polyolefin-based resin compositions (polyolefin-based resin A and polyolefin-based resin B), Here, the polyolefin-based resin A contains 0.01 mass % or more and 1 mass % or less of one or more metal oxide particles based on 100 mass % of the electret meltblown nonwoven fabric, and the metal oxide particles are composed of copper, It is composed of oxides of metal elements selected from cobalt, aluminum, nickel, zinc, palladium, molybdenum, and tungsten and has an average particle diameter of 500 nm or less, and the polyolefin-based resin B contains the electret melt-blown in an amount of 100% by mass. For non-woven fabrics, the hindered amine compound is 0.1 mass % or more and 5.0 mass % or less; (2) the step of making a non-woven fabric by melt blowing the mixture of the polyolefin-based resin A and the polyolefin-based resin B; and (3) The step of electret processing the non-woven fabric. The method for producing electret meltblown nonwoven fabric according to claim 8, wherein the absolute value of the difference between the melt flow rate of the polyolefin-based resin A and the melt flow rate of the polyolefin-based resin B is 650 g/10 minutes or more .

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