Laminated nonwoven fabrics, laminated electrets, filters, and filter units

Abstract

To provide a laminated nonwoven fabric that achieves both high filtration performance and additional functions. [Solution] The present invention relates to a laminated nonwoven fabric comprising a nonwoven fabric A having constituent fibers containing a propylene polymer and an olefin polymer different from the propylene polymer, and a nonwoven fabric B having constituent fibers containing a propylene polymer, wherein the laminated nonwoven fabric has an average fiber diameter of 2 to 10 μm and an apparent density of 0.06 to 0.09 g / cm³. 3 That is the case.

Description

[Technical Field]

[0001] This invention relates to laminated nonwoven fabrics, etc. [Background technology]

[0002] Traditionally, air filters have been used to remove atmospheric dust and other particles, with fibrous sheets widely used as filter media. These fibrous filters capture particles on the fibers through mechanical collection mechanisms such as blocking, diffusion, and inertial collision. However, it is known that the filter collection efficiency is minimal when the aerodynamic equivalent diameter of the captured particles is around 0.1 to 1.0 μm in practical usage environments. To compensate for this weakness, electret filters that utilize the electrostatic attraction of electrets are used.

[0003] Air filters are required to have high collection efficiency and low pressure loss, but these two qualities are inversely related. Electret filters are widely used as a way to solve this problem.

[0004] To improve the collection efficiency of electret filters, it is known that it is preferable to impart an electrostatic charge to fibrous material by contacting or impacting it with a liquid (liquid contact charging method) to create an electret. For example, an electret that balances cost and performance is known in which an electrostatic charge is imparted to a fibrous material formed from a mixture of a resin mainly composed of polyolefin resin with nitrogen-containing compounds such as hindered amine compounds added, by contacting it with a liquid such as water.

[0005] Furthermore, attempts have been made to simultaneously satisfy high collection efficiency and low pressure loss by adding nucleating agents or electrostatic strengthening additives to thermoplastic resins, or by adding metal salts to fiber sheets (see Patent Documents 1-3).

[0006] In addition to high collection efficiency and low pressure loss, there is also a demand for functionalities such as low carbonization. Methods using plant-derived polyethylene resin or polylactic acid resin for the purpose of low carbonization are being considered (see Patent Documents 4-5). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-40098 [Patent Document 2] International Public Gazette 2018 / 105546 [Patent Document 3] Special Publication No. 2018-523761 [Patent Document 4] International Public Gazette 2024 / 048433 [Patent Document 5] Patent Application No. 2002-221662 [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, there has been a growing demand for improved filtration performance in air filters, such as those for air purifiers and cabin filters, including increased airflow and higher efficiency. In addition to improved filtration performance, there is also a demand for additional functions such as reduced carbon emissions and longer lifespan. To address these various additional functions, it is conceivable to utilize raw materials other than conventionally considered propylene-based polymers. However, since there are virtually no low-viscosity polymers other than propylene-based polymers suitable for nonwoven fabrics, it is difficult to obtain finely textured, dense nonwoven fabrics.

[0009] Thus, it has become clear that conventionally known methods make it difficult to achieve both high filtration performance and additional functions.

[0010] In view of the above problems, the present invention provides a nonwoven fabric and a filter that achieve both high filtration performance that simultaneously satisfies high collection efficiency and low pressure loss which could not be achieved conventionally, and additional functions such as low carbonization and long service life. [Means for Solving the Problems]

[0011] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by adopting the following constitution, and the present invention has been accomplished. That is, the present invention is as follows.

[0012] 1. A laminated nonwoven fabric obtained by laminating a nonwoven fabric A having constituent fibers containing a propylene-based polymer and an olefin-based polymer different from the propylene-based polymer, and a nonwoven fabric B having constituent fibers containing a propylene-based polymer, wherein the laminated nonwoven fabric has an average fiber diameter of 2 to 10 µm and an apparent density of 0.06 to 0.09 g / cm 3 A laminated nonwoven fabric, which is 2. The laminated nonwoven fabric according to the above 1, wherein the olefin-based polymer is a plant-derived polyethylene resin or a poly-4-methyl-1-pentene resin. 3. The laminated nonwoven fabric according to the above 1 or 2, wherein at least one of the nonwoven fabric A and the nonwoven fabric B contains a nitrogen-containing compound and a fatty acid metal salt having 10 to 50 carbon atoms. 4. The laminated nonwoven fabric according to the above 3, wherein both the nonwoven fabric A and the nonwoven fabric B are meltblown nonwoven fabrics. 5. A laminated electret obtained by applying an electric charge to the laminated nonwoven fabric according to the above 4, wherein the laminated electret has a filter medium quality factor (QF) value of 1.2 or more. 6. An electret filter or a filter unit using the laminated electret according to the above 5. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a nonwoven fabric and a filter that achieve both high filtration performance and additional functions such as low carbonization and long service life. [Mode for Carrying Out the Invention]

[0014] Hereinafter, the present invention will be specifically described, but the present invention is not limited to the following, and can be implemented with appropriate modifications within a range compatible with the gist set forth before and after this description, and all such modifications are included in the technical scope of the present invention.

[0015] The laminated nonwoven fabric of the present invention is a laminated nonwoven fabric obtained by laminating a nonwoven fabric A having constituent fibers containing a propylene-based polymer and an olefin-based polymer different from the propylene-based polymer, and a nonwoven fabric B having constituent fibers containing a propylene-based polymer. The polypropylene-based polymer of nonwoven fabric A and the polypropylene-based polymer of nonwoven fabric B may be the same or different. In the laminated nonwoven fabric, either nonwoven fabric A or nonwoven fabric B may serve as the first layer (back layer, lower layer) or the second layer (front layer, upper layer).

[0016] <Propylene-based polymer> The polypropylene-based polymer used in the present invention may be of only one type, or may be a combination of two or more types having mutually different melting points, molecular weights and crystal structures.

[0017] The propylene-based polymer used in the present invention is a polymer containing a constituent component derived from propylene. Specifically, it is a propylene homopolymer or a propylene copolymer. The propylene copolymer is preferably a copolymer of propylene and an α-olefin. Examples of the α-olefin in the propylene copolymer include ethylene, propylene, butylene, hexene, octene, butadiene, isoprene, chloroprene, methyl-1-pentene, and cyclic olefin. Among them, the propylene-based polymer preferably contains a propylene homopolymer, and is more preferably a propylene homopolymer.

[0018] The polypropylene polymer used in the present invention preferably has a stereoregularity of 85% or more, more preferably 90% or more, even more preferably 90% or more, and particularly preferably 95% or more. In this case, either isotactic or syndiotactic polymers can be preferably used. When two or more propylene polymers are used, it is preferable that one or more of them are included in the contained propylene polymers.

[0019] The melt flow rate (MFR) of the propylene-based polymer used in this invention is not particularly limited, but at a temperature of 230°C and a load of 2.16 kg in accordance with ASTM D 1238, It is preferable that the amount is 10g / 10 minutes or more, more preferably 50g / 10 minutes or more, even more preferably 100g / 10 minutes or more, and particularly preferably 200g / 10 minutes or more.

[0020] The proportion of propylene-based polymer to 100% by mass of laminated nonwoven fabric is not particularly limited, but is preferably 2 to 99% by mass, 5 to 98% by mass, and more preferably 10 to 97% by mass.

[0021] <Olefin polymers> The olefin polymer used in the present invention may be just one type, or it may be a combination of two or more types that have different melting points, molecular weights, and crystal structures.

[0022] The olefin polymer used in the present invention is an α-olefin alone or copolymer. (However, the propylene polymer mentioned above is excluded.) Examples of α-olefins in the olefin polymer include ethylene, butylene, hexene, octene, butadiene, isoprene, chloroprene, methyl-1-pentene, and cyclic olefins. Among these, the olefin polymer preferably includes an α-olefin homopolymer, and more preferably an α-olefin homopolymer. Specific examples of olefin polymers include polyethylene and poly-4-methyl-1-pentene.

[0023] To achieve low carbon content, it is preferable that polyethylene be plant-derived. "Plant-derived" means that it contains carbon derived from plant raw materials. In the case of a mixture with fossil raw materials, the carbon content can be calculated from the carbon ratio contained in the total weight. To achieve a longer lifespan, it is preferable to incorporate poly-4-methyl-1-pentene. Poly-4-methyl-1-pentene has a lower surface tension than polypropylene, which can reduce the coating of oily components and suppress the deterioration of electret performance. Therefore, it is possible to extend the lifespan by incorporating poly-4-methyl-1-pentene. As an indicator of extended lifespan, the tension of the nonwoven fabric obtained by a wet tensile strength test can be used. The wet tensile strength of a nonwoven fabric made of a polypropylene polymer containing nitrogen-containing compounds, which is generally used as a filter, is 36 mN / m, and a value lower than this is considered to indicate a longer lifespan.

[0024] The ratio of olefin polymer to 100% by mass of laminated nonwoven fabric is also not particularly limited, but is preferably 0.5 to 95% by mass, preferably 1 to 90% by mass, and more preferably 2 to 80% by mass.

[0025] <Nitrogen-containing compounds> The nitrogen-containing compound content relative to 100% by mass of the laminated nonwoven fabric of the present invention is 0.1 to 5% by mass, preferably 0.5 to 3% by mass, and more preferably 0.75 to 1.5% by mass. If the nitrogen-containing compound content is lower than 0.1% by mass, the amount of charge becomes low, resulting in a decrease in filtration characteristics, and if it is higher than 5% by mass, the stability of the charge is lost due to increased hygroscopicity.

[0026] The nitrogen-containing compound is not particularly limited as long as it provides the desired properties described above, but it is preferably a hindered amine compound containing at least one of a 2,2,6,6-tetramethylpiperidine structure and a triazine structure, and it is more preferably a hindered amine compound containing a 2,2,6,6-tetramethylpiperidine structure and a triazine structure.

[0027] Hindered amine compounds are not particularly limited, but examples include poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (Kimasorb® 944LD, manufactured by BASF Japan), dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine polycondensate (Tinuvin® 622LD, manufactured by BASF Japan), and 2-[[3,5-bis(1,1-dimethylethyl)-4-hydroxy Examples include phenylmethyl]-2-butylpropanediate bis[1,2,2,6,6-pentamethyl-4-piperidinyl] (Tinuvin® 144, manufactured by BASF Japan), dibutylamine 1,3,5-triazine·N,N-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexamethylenediamine·N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine polycondensate (Chimasorb® 2020FDL, manufactured by BASF Japan), and 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-(hexyloxy)-phenol (Tinuvin® 1577FF, manufactured by BASF Japan). In particular, it is preferable that the compound contains a 2,2,6,6-tetramethylpiperidine structure and a triazine structure, and more preferably Kimasove® 944LD or Kimasove® 2020FD. One of the above compounds may be used alone as the hindered amine compound, or two or more may be used in combination.

[0028] <Fatty acid metal salts> The content ratio of the fatty acid metal salt relative to 100% by mass of the laminated nonwoven fabric of the present invention is 0.01 to 1.0% by mass, preferably 0.025 to 0.5% by mass, and more preferably 0.05 to 0.1% by mass.

[0029] The fatty acid group is not particularly limited, but it is preferably a straight-chain saturated fatty acid group, and the fatty acid group has 10 to 50 carbon atoms. Specifically, examples include lauric acid, myristic acid, palmitic acid, and stearic acid. Zinc, aluminum, and magnesium are preferred as metal elements.

[0030] <Nonwoven fabric A> The nonwoven fabric A of the present invention is obtained as follows: A propylene-based polymer and an olefin-based polymer are melt-mixed in a twin-screw extruder at a melting temperature of 300°C or less to obtain a pelletized resin composition. This pelletized resin composition is then used to form a nonwoven fabric. Here, "using" means that the resin composition may be used alone, or it may be diluted with a propylene-based polymer or an olefin-based polymer as needed before use.

[0031] As a method for obtaining nonwoven fabric A, conventionally known methods can be used, such as methods for forming sheets from short fibers such as split fibers by carding, airlaid, or wet papermaking, or methods for forming sheets from continuous fibers using spunbond, meltblown, electrospinning, or force spinning methods. From the viewpoint of not requiring treatment of residual solvents or spinning oils adhering to the surface, nonwoven fabrics obtained by spunbond, meltblown, molten electrospinning, or molten force spinning methods are more preferred, and from the viewpoint of filtration performance, nonwoven fabrics obtained by meltblown are particularly preferred.

[0032] The basis weight of the nonwoven fabric A of the present invention is not particularly limited, but is preferably 1 to 50 g / m2, more preferably 3 to 40 g / m2, even more preferably 5 to 30 g / m2, and particularly preferably 7 to 20 g / m2, based on a balance between pressure loss and collection efficiency.

[0033] The thickness of the nonwoven fabric A of the present invention is not particularly limited, but is preferably 0.01 to 1.00 mm, more preferably 0.05 to 0.80 mm, even more preferably 0.10 to 0.60 mm, and particularly preferably 0.15 to 0.50 mm.

[0034] The nonwoven fabric A in the present invention may contain a compatibilizer as needed from the viewpoint of compatibility with the polymer used. The compatibilizer is used to control the dispersion structure, and examples of such compounds include commercially available products such as Dynalon (trademark registered) 6200P and Kraton (trademark) MD1648. Furthermore, the compatibilizer is not particularly limited, and compatibilizers described in "Plastic Compatibilizers: Development, Evaluation, and Recycling" (CMC Publishing) can also be suitably used. Moreover, these compatibilizers may be used individually or in mixtures of two or more.

[0035] If nonwoven fabric A contains nitrogen-containing compounds and fatty acid metal salts, they only need to be present on the surface of the molded nonwoven fabric, and can be introduced by methods such as solution coating, powder adhesion, solution mixing with polyolefin, polymerization mixing, or melt mixing.

[0036] Of the above methods, the melt mixing method is superior in terms of homogeneity and processability. It can be used by directly mixing it with the resin during melt molding into nonwoven fabric, or by using it as is or diluted as a pre-prepared additive masterbatch.

[0037] The nonwoven fabric A of the present invention may contain other polymers, colorants, stabilizers, nucleating agents, and other compounding agents as needed, as long as they do not impair the objectives of the present invention. Examples of components that may be optionally added include conventionally known antioxidants, heat-resistant stabilizers, weather-resistant stabilizers and other stabilizers, slip agents, anti-blocking agents, anti-fogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, and the like.

[0038] <Nonwoven fabric B> The nonwoven fabric B of the present invention is obtained by nonweaving mainly using a propylene-based polymer. Here, "using" means that commercially available polypropylene-based polymers may be used as is, or commercially available propylene-based polymers with reduced molecular weight or those melt-mixed with additives may be used as needed. Furthermore, "mainly" means 51% or more of the total weight of nonwoven fabric B.

[0039] As a method for obtaining nonwoven fabric B, conventionally known methods can be used, such as methods for forming sheets from short fibers such as split fibers by carding, airlaid, or wet papermaking, or methods for forming sheets from continuous fibers using spunbond, meltblown, electrospinning, or force spinning methods. From the viewpoint of not requiring treatment of residual solvents or spinning oils adhering to the surface, nonwoven fabrics obtained by spunbond, meltblown, molten electrospinning, or molten force spinning methods are more preferred, and from the viewpoint of filtration performance, nonwoven fabrics obtained by meltblown are particularly preferred.

[0040] The basis weight of the nonwoven fabric B of the present invention is also not particularly limited, but is 1 to 50 g / m², depending on the balance between pressure loss and collection efficiency. 2 Preferably, it is 3-40 g / m 2 It is more preferable that it be 5-30 g / m 2 It is even more preferable that the amount be 7-20 g / m 2 It is particularly preferable that this be the case.

[0041] The thickness of the nonwoven fabric B of the present invention is also not particularly limited, but is preferably 0.01 to 1.00 mm, more preferably 0.05 to 0.80 mm, even more preferably 0.10 to 0.60 mm, and particularly preferably 0.15 to 0.50 mm.

[0042] Even if nonwoven fabric B contains nitrogen-containing compounds and fatty acid metal salts, they only need to be present on the surface of the molded nonwoven fabric, and can be introduced by methods such as solution coating, powder adhesion, solution mixing with polyolefin, polymerization mixing, or melt mixing.

[0043] Of the above methods, the melt mixing method is superior in terms of homogeneity and processability. It can be used by directly mixing it with the resin during melt molding into nonwoven fabric, or by using it as is or diluted as a pre-prepared additive masterbatch.

[0044] The nonwoven fabric B of the present invention may also contain other polymers, colorants, stabilizers, nucleating agents, and other compounding agents as needed, to the extent that it does not impair the objectives of the present invention. Examples of components that may be optionally added include conventionally known antioxidants, heat-resistant stabilizers, weather-resistant stabilizers and other stabilizers, slip agents, anti-blocking agents, anti-fogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, and the like.

[0045] <Laminated nonwoven fabric> The laminated nonwoven fabric of the present invention is a state in which nonwoven fabric A and nonwoven fabric B are laminated together. Any conventionally known method for laminating nonwoven fabric A and nonwoven fabric B may be used, and is not particularly limited. For example, a method of directly fusing nonwoven fabric A and nonwoven fabric B together, a method of overlapping nonwoven fabric A and nonwoven fabric B and fusing both nonwoven fabrics by heating and pressing, or a method of bonding nonwoven fabric A and nonwoven fabric B together with an adhesive such as a hot melt adhesive or a solvent-based adhesive can be used. However, from the viewpoint of filtration performance, the method of directly fusing nonwoven fabric A and nonwoven fabric B together is the most suitable among these. Specifically, it is suitable to directly deposit nonwoven fabric A on top of nonwoven fabric B. In this case, nonwoven fabrics A and B may be spun using an apparatus having two nozzles and laminated in one step, or nonwoven fabric B may be spun using an apparatus having one nozzle, and then nonwoven fabric A may be spun in the same way and deposited on top of nonwoven fabric B to laminate in two steps.

[0046] The basis weight of the laminated nonwoven fabric of the present invention is not particularly limited, but from the viewpoint of the sum of nonwoven fabric A and nonwoven fabric B, it is 2 to 100 g / m². 2 Preferably, it is 6-80 g / m 2 It is more preferable that the amount be 10-60 g / m 2 It is even more preferable that the amount be 14-40 g / m².2 is particularly preferable.

[0047] The thickness of the laminated nonwoven fabric of the present invention is not particularly limited, but from the viewpoint of the total of nonwoven fabric A and nonwoven fabric B, the thickness is preferably 0.02 to 2.00 mm, more preferably 0.10 to 1.60 mm, still more preferably 0.20 to 1.20 mm, and particularly preferably 0.30 to 1.00 mm.

[0048] The average fiber diameter of the fibers of the laminated nonwoven fabric of the present invention is preferably 2 to 10 µm, more preferably 2 to 8 µm, still more preferably 2 to 6 µm, and particularly preferably 2 to 4 µm. When the average fiber diameter of the fibers is larger than 10 µm, it is difficult to obtain practical collection efficiency. Further, when the average fiber diameter of the fibers is smaller than 2 µm, fiber scattering occurs and productivity is significantly reduced. The fiber diameter is measured by using a scanning electron microscope, measuring the diameter of 100 fibers each on the back surface and the front surface (nonwoven fabric A and nonwoven fabric B) of the laminated nonwoven fabric such that there is no overlapping of fibers in the same field of view, and calculating the average fiber diameter as the geometric mean of the respective fiber diameters. By performing measurement from the back surface and the front surface of the laminated nonwoven fabric respectively, the average fiber diameter of each of nonwoven fabric A and nonwoven fabric B can be calculated.

[0049] The apparent density of the laminated nonwoven fabric of the present invention is 0.06 to 0.09 g / cm 3 , preferably 0.065 to 0.085 g / cm 3 , more preferably 0.065 to 0.08 g / cm 3 , and particularly preferably. When the apparent density is 0.09 g / cm 3 higher than the above value, the pressure loss increases, and a high filter medium quality factor (QF) value cannot be obtained. Further, when the apparent density is 0.06 g / cm 3 less than the above value, although the pressure loss is low and the filter medium quality factor (QF) value is high, it is difficult to obtain high collection efficiency.

[0050] In the above, apparent density is a value calculated by measuring the basis weight and thickness of the nonwoven fabric, as described later, and using the following formula. A lower apparent density indicates a bulkier nonwoven fabric. Apparent density (g / cm³) 3 ) = {Average weight (g / m 2 ) / Average thickness (mm) / 1000

[0051] The apparent density of the laminated nonwoven fabric of the present invention can be adjusted, for example, by adjusting the degree of fusion in the meltblown method, by adjusting the transport speed, conveyor angle, collection distance, discharge volume, nozzle pitch, nozzle L / D, resin temperature, hot air temperature, hot air flow rate, etc.

[0052] The laminated nonwoven fabric of the present invention, by providing additional functions to nonwoven fabric A and having a two-layer structure, yields a bulky laminated nonwoven fabric with a low apparent density, making it possible to achieve both high filtration performance and additional functions.

[0053] The present invention also includes nonwoven fabrics where the interlayers are not necessarily clearly defined or where the layers cannot be clearly separated. The constituent fibers of nonwoven fabric layer A are mainly composed of propylene polymers and olefin polymers different from the propylene polymers, and the constituent fibers of nonwoven fabric layer B are mainly composed of olefin polymers. Here, "mainly" refers to 51% or more of the total fibers in each layer.

[0054] In the present invention, the preferred method for electrostatic treatment is a method of contacting or impacting with a liquid (liquid contact charging method), and an electret with high filtration characteristics can be obtained by the liquid contact charging method. More specifically, it is preferable to use a method of contacting or impacting a laminated nonwoven fabric with a liquid by means of suction, pressurization, or ejection.

[0055] In the liquid contact charging method, the liquid to be contacted or impacted is not particularly limited as long as the desired properties can be obtained, but water is preferred in terms of handling and performance. A liquid obtained by adding a secondary component (a component other than water) to water may be used instead of water, and the conductivity and pH of the liquid can be adjusted by the type and amount of the secondary component added.

[0056] In the liquid contact charging method, the liquid to be contacted or impacted preferably has a pH of 1 to 11, more preferably 3 to 9, and even more preferably 5 to 7. Furthermore, the liquid to be contacted or impacted preferably has an electrical conductivity of 100 μS / cm or less, more preferably 10 μS / cm or less, and even more preferably 3 μS / cm or less.

[0057] The filter media quality factor (QF) is an index that shows the relationship between collection efficiency and airflow resistance, and is expressed by the following formula. The electret of the present invention has a QF value of 1.2 or higher, preferably 1.3 or higher, and more preferably 1.4 or higher. The higher the QF value, the higher the collection efficiency and the lower the airflow resistance, resulting in a high-performance filter. Electrets with a QF value of less than 1.2 have problems such as excessively low collection efficiency or excessively high airflow resistance. The QF value in this specification is calculated based on the airflow resistance when air is passed through in the thickness direction at an airflow velocity of 10.4 cm / s and the number of particles counted by a laser particle counter in the particle size category of 0.3 to 0.5 μm. QF value [mmAq] -1 ]=-[ln(1-(particle collection efficiency (%) / 100))] / [airflow resistance (mmAq)]

[0058] When the laminated electret of the present invention is used as a filter, the particle collection efficiency at a wind speed of 10.4 cm / s can be adjusted in various ways depending on the required characteristics, but it is preferably 50% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 99.9% or more. The particle collection efficiency described herein is calculated based on the number of particles in the particle size category of 0.3 to 0.5 μm measured by a laser particle counter before and after passing through the filter when air is passed through the filter in the thickness direction at a wind speed of 10.4 cm / s.

[0059] When the laminated electret of the present invention is used as a filter, the airflow resistance at a wind speed of 10.4 cm / s is preferably in the range of 5.0 to 30 mmAq, more preferably 5.5 to 20 mmAq, and particularly preferably 6.0 to 10 mmAq. If the airflow resistance is too low, the fibers are not fine enough, and a dense nonwoven fabric cannot be obtained, resulting in insufficient performance as a filter. If the airflow resistance is too high, the advantages of the electret filter are lost.

[0060] The laminated electret of the present invention may also be a filter consisting solely of electrets, or a filter made by combining electrets with other materials. The shape of the filter is not particularly limited and may be a sheet-like filter with pleating, corrugation, or other wavy processing.

[0061] When the laminated electret of the present invention is used as a filter or filter unit, it can be used in combination with other components as needed. That is, the filter of the present invention can be used in combination with a pre-filter layer, a fiber protection layer, a reinforcing member, a functional fiber layer, an adsorbent layer, and the like.

[0062] Examples of pre-filter layers and fiber protection layers include spunbond nonwoven fabrics, thermal bond nonwoven fabrics, and polyurethane foam, while examples of reinforcing members include dry-spun nonwoven fabrics, wet-spun nonwoven fabrics, and various types of nets. Functional fiber layers include antibacterial, antiviral, and colored fiber layers for identification and design purposes, while examples of adsorbent layers include activated carbon and silica gel.

[0063] The laminated nonwoven fabric, laminated electret, filter, and filter unit of the present invention can be used in a wide range of applications. In particular, they can be suitably used as filters for protection, ventilation, stain resistance, and waterproofing in dust masks, dustproof clothing, various air conditioning elements, air purifiers, cabin filters, and various devices. [Examples]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0065] First, the test method is as follows. (1) Air resistance A sample punched out to 72mmφ is attached to a 50mmφ effective airflow adapter, and a slight differential pressure is applied. Two pipes with an inner diameter of 50 mm, each connected to a meter, were linked vertically. Air was passed through the sample in the thickness direction at a wind speed of 10.4 cm / s, and the differential pressure between the top and bottom of the sample without any constriction was measured as the airflow resistance (pressure loss) (mmAq).

[0066] (2) Particle collection efficiency and particle transmission rate A sample punched to 72 mm in diameter was mounted in an adapter with an effective airflow diameter of 50 mm in diameter. Air was passed through the sample in the thickness direction at a wind speed of 10.4 cm / s, and the particle collection efficiency was measured using a light scattering particle counter KC-01E manufactured by Rion Co., Ltd. in the following manner. Particles evaluated: atmospheric dust particles Wind speed: 10.4cm / s Particle collection efficiency [%] = (1 - (Number concentration of particles with a particle size of 0.3 to 0.5 μm after sample transmission ÷ Number concentration of particles with a particle size of 0.3 to 0.5 μm before sample transmission)) × 100 Particle transmittance = (Number concentration of particles with a particle size of 0.3 to 0.5 μm after sample transmission ÷ Number concentration of particles with a particle size of 0.3 to 0.5 μm before sample transmission)

[0067] (3) Filter media quality factor (QF) value Using the values ​​of the airflow resistance measured in (1) above and the particle transmittance measured in (2) above, the QF value was calculated using the following formula. QF[mmAq -1 ]=-[ln(1-(particle collection efficiency (%) / 100))] / [airflow resistance (mmAq)]

[0068] (4) Inspection Six samples with a diameter of 72 mmΦ were collected, the weight of each sample was measured, the obtained values ​​were converted to a unit area, and the arithmetic mean of these values ​​was rounded to two decimal places.

[0069] (5) Thickness The thickness of each sample whose basis weight was measured was measured using a thickness gauge with a 7g load, and the arithmetic mean of these measurements was rounded to the third decimal place.

[0070] (6) Apparent density Using the weight and thickness obtained in (4) and (5) above, the calculation was performed using the following formula, and the result was rounded to two decimal places. Apparent density (g / cm³) 3 ) = {Average weight (g / m 2 ) / Average thickness (mm) / 1000

[0071] (7) Average fiber diameter Five arbitrary points were selected on both the front and back surfaces of the nonwoven fabric sample, and the diameter of the fibers was measured at each point using an electron microscope (n=20). The average fiber diameter was calculated by the arithmetic mean of the total of 100 fibers.

[0072] (8) Wetting tensile strength test Based on the wet tensile strength test method (JIS K 6768), formamide and ethylene glycol monoether were mixed to prepare test solutions with wet tensile strengths of 32 mN / m, 34 mN / m, and 36 mN / m. The samples were dropped onto one side of a nonwoven fabric, and the tensile strength of the samples that did not absorb the tensile strength was determined. The same procedure was performed on the other side of the nonwoven fabric, and the average value was determined as the wet tensile strength of the nonwoven fabric.

[0073] <Example 1> The following materials were used to obtain a resin composition: 46.350% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer; 50% by mass of plant-derived high-density polyethylene resin (biomass content of 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer; 1.5% by mass of Kraton® MD1648 as a compatibilizer; 1% by mass of Chimassorb® 944 as a nitrogen-containing compound; 0.15% by mass of magnesium stearate as a fatty acid metal salt; and 1% by mass of SumiLizer® GP as an additional additive. These materials were pelletized in a twin-screw extruder at a melting temperature of 200°C to obtain the resin composition. Separately, 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt were pelletized in a twin-screw extruder at a melting temperature of 180°C to obtain an additive masterbatch. Using a melt-blown apparatus with two nozzles, 20% by mass of the additive masterbatch was diluted with 80% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer from one nozzle and spun at 260°C to obtain nonwoven fabric B. From the other nozzle, 100% by mass of the resin composition was spun at 280°C and nonwoven fabric A was directly deposited on nonwoven fabric B to obtain a laminated nonwoven fabric in one step. In other words, a laminated nonwoven fabric containing 25% plant-derived resin was obtained for the purpose of reducing carbon emissions. Because the fibers of nonwoven fabric A, or both the fibers of nonwoven fabric A and nonwoven fabric B, melt due to the heat during spinning, the fibers of nonwoven fabric A and nonwoven fabric B fuse together to form a laminated nonwoven fabric. The resulting laminated nonwoven fabric was charged by passing water with an electrical conductivity of 0.7 μS / cm and pH 6.8 from nonwoven fabric A to nonwoven fabric B, and then air-dried at 25°C to obtain a laminated electret. It was evaluated according to (1) to (8) above.

[0074] In the following examples and comparative examples, the spinning of nonwoven fabric A was carried out at 280°C for the polypropylene resin and polyethylene resin system, and at 300°C for the polyethylene resin and poly-4-methyl-1-pentene resin system. <Example 2> The following materials were used to obtain a resin composition: 46.350% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer; 50% by mass of plant-derived high-density polyethylene resin (biomass content of 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer; 1.5% by mass of Kraton® MD1648 as a compatibilizer; 1% by mass of Chimassorb® 944 as a nitrogen-containing compound; 0.15% by mass of magnesium stearate as a fatty acid metal salt; and 1% by mass of SumiLizer® GP as an additional additive. These materials were pelletized in a twin-screw extruder at a melting temperature of 200°C to obtain the resin composition. Separately, 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt were pelletized in a twin-screw extruder at a melting temperature of 180°C to obtain an additive masterbatch. Using a melt-blown apparatus with one nozzle, 20% by mass of the additive masterbatch was diluted with 80% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer and spun to obtain nonwoven fabric B. Subsequently, using the same melt-blown apparatus, 100% by mass of the resin composition was spun and nonwoven fabric A was deposited on nonwoven fabric B, obtaining a laminated nonwoven fabric in two steps. In other words, a laminated nonwoven fabric containing 25% plant-derived resin for the purpose of reducing carbon was obtained. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. The evaluation was conducted according to (1) to (8) above.

[0075] <Example 3> A resin composition was obtained by pelletizing 60% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer and 40% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min as an olefin polymer using a twin-screw extruder at a melting temperature of 250°C. Separately, an additive masterbatch (1) was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Similarly, 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as the propylene polymer, 5% by mass of Chimassorb® 944 as the nitrogen-containing compound, and 0.375% by mass of magnesium stearate as the fatty acid metal salt were pelletized in a twin-screw extruder at a melting temperature of 180°C to obtain additive masterbatch (2). Using a melt-blown apparatus with two nozzles, 20% by mass of additive masterbatch (2) was diluted with 80% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as the propylene polymer through one nozzle and spun to obtain nonwoven fabric B. On the other hand, 12.5% ​​by mass of the resin composition and 20% by mass of the additive masterbatch (1) were diluted with 67.5% by mass of petroleum-derived polypropylene resin at a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer, spun, and nonwoven fabric A was directly deposited on nonwoven fabric B to obtain a laminated nonwoven fabric in one step. In other words, a laminated nonwoven fabric containing poly-4-methyl-1-pentene resin was obtained for the purpose of extending the lifespan. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. It was evaluated according to (1) to (8) above.

[0076] <Example 4> A resin composition was obtained by pelletizing 60% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer and 40% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min as an olefin polymer using a twin-screw extruder at a melting temperature of 250°C. Separately, an additive masterbatch (1) was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Similarly, 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as the propylene polymer, 5% by mass of Chimassorb® 944 as the nitrogen-containing compound, and 0.375% by mass of magnesium stearate as the fatty acid metal salt were pelletized in a twin-screw extruder at a melting temperature of 180°C to obtain additive masterbatch (2). Using a melt-blown apparatus with one nozzle, 20% by mass of additive masterbatch (2) was diluted with 80% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as the propylene polymer, and spun to obtain nonwoven fabric B. Next, using a similar meltblown apparatus, 12.5% ​​by mass of the resin composition and 20% by mass of the additive masterbatch (1) were diluted with 67.5% by mass of petroleum-derived polypropylene resin as a propylene-based polymer at a melt flow rate (MFR) of 1400 g / 10 min, spun, and nonwoven fabric A was deposited on nonwoven fabric B, thereby obtaining a laminated nonwoven fabric in two steps. In other words, a laminated nonwoven fabric containing poly-4-methyl-1-pentene resin was obtained for the purpose of extending its lifespan. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. It was evaluated according to (1) to (8) above.

[0077] <Example 5> The following materials were used to obtain a resin composition: 36.350% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer; 50% by mass of plant-derived high-density polyethylene resin (biomass content of 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer; 10% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min; 1.5% by mass of Kraton® MD1648 as a compatibilizer; 1% by mass of Chimassorb® 944 as a nitrogen-containing compound; 0.15% by mass of magnesium stearate as a fatty acid metal salt; and 1% by mass of SumiLizer® GP as an other additive. These materials were pelletized in a twin-screw extruder at a melting temperature of 200°C to obtain the resin composition. Separately, 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt were pelletized in a twin-screw extruder at a melting temperature of 180°C to obtain an additive masterbatch. Using a melt-blown apparatus with one nozzle, 20% by mass of the additive masterbatch was diluted with 80% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene-based polymer and spun to obtain nonwoven fabric B. Subsequently, using the same melt-blown apparatus, 100% by mass of the resin composition was spun and nonwoven fabric A was deposited on nonwoven fabric B, obtaining a laminated nonwoven fabric in two steps. In other words, a laminated nonwoven fabric containing 25% plant-derived resin and poly-4-methyl-1-pentene resin was obtained for the purpose of reducing carbon emissions and extending lifespan. Laminated electrets were obtained from the resulting laminated nonwoven fabric in the same manner as in Example 1. They were evaluated according to (1) to (8) above.

[0078] <Comparative Example 1> A resin composition was obtained by pelletizing a mixture of 71.350% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 25% by mass of plant-derived high-density polyethylene resin (biomass content of 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer, 1.5% by mass of Kraton® MD1648 as a compatibilizer, 1% by mass of Chimassorb® 944 as a nitrogen-containing compound, 0.15% by mass of magnesium stearate as a fatty acid metal salt, and 1% by mass of SumiLizer® GP as an additional additive, using a twin-screw extruder at a melting temperature of 200°C. Using a melt-blown apparatus with two nozzles, 100% by mass of the resin composition was spun from each nozzle to obtain a laminated nonwoven fabric. In other words, a laminated nonwoven fabric containing 25% plant-derived resin was obtained for the purpose of reducing carbon emissions. The resulting laminated nonwoven fabric was charged by passing water with an electrical conductivity of 0.7 μS / cm and a pH of 6.8 from the surface to the back, and then air-dried at 25°C to obtain a laminated electret. It was evaluated according to (1) to (8) above.

[0079] <Comparative Example 2> A resin composition was obtained by pelletizing a mixture of 71.350% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 25% by mass of plant-derived high-density polyethylene resin (biomass content of 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer, 1.5% by mass of Kraton® MD1648 as a compatibilizer, 1% by mass of Chimassorb® 944 as a nitrogen-containing compound, 0.15% by mass of magnesium stearate as a fatty acid metal salt, and 1% by mass of SumiLizer® GP as an additional additive, using a twin-screw extruder at a melting temperature of 200°C. 100% by mass of the resin composition was spun using a melt-blown device with a single nozzle to obtain a single-layer nonwoven fabric. In other words, a nonwoven fabric containing 25% plant-derived resin was obtained for the purpose of reducing carbon emissions. An electret was obtained from the obtained nonwoven fabric in the same manner as in Comparative Example 1. It was evaluated according to (1) to (8) above.

[0080] <Comparative Example 3> A resin composition was obtained by pelletizing 60% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer and 40% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min as an olefin polymer using a twin-screw extruder at a melting temperature of 250°C. Separately, an additive masterbatch (1) was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Using a meltblown apparatus with two nozzles, 12.5% ​​by mass of the resin composition and 20% by mass of the additive masterbatch (1) were diluted from each nozzle with 67.5% by mass of petroleum-derived polypropylene resin at a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer, spun, and a laminated nonwoven fabric was obtained. In other words, a laminated nonwoven fabric containing poly-4-methyl-1-pentene resin was obtained for the purpose of extending the lifespan. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Comparative Example 1. It was evaluated according to (1) to (8) above.

[0081] <Comparative Example 4> A resin composition was obtained by pelletizing 60% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer and 40% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min as an olefin polymer using a twin-screw extruder at a melting temperature of 250°C. Separately, an additive masterbatch (1) was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Using a meltblown apparatus with one nozzle, 12.5% ​​by mass of the resin composition and 20% by mass of the additive masterbatch (1) were diluted with 67.5% by mass of petroleum-derived polypropylene resin as a propylene polymer at a melt flow rate (MFR) of 1400 g / 10 min, spun, and a single-layer nonwoven fabric was obtained. In other words, a nonwoven fabric containing poly-4-methyl-1-pentene resin was obtained for the purpose of extending the lifespan. Electrets were obtained from the obtained nonwoven fabric in the same manner as in Comparative Example 1. They were evaluated according to (1) to (8) above.

[0082] <Comparative Example 5> A resin composition was obtained by pelletizing 97.85% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min as an olefin polymer, 1% by mass of Chimassorb® 944 as a nitrogen-containing compound, 0.15% by mass of magnesium stearate as a fatty acid metal salt, and 1% by mass of SumiLizer® GP as an other additive using a twin-screw extruder at a melting temperature of 200°C. Separately, an additive masterbatch was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Using a melt-blown apparatus with a single nozzle, 20% by mass of an additive masterbatch was diluted with 80% by mass of petroleum-derived polypropylene resin as a propylene-based polymer at a melt flow rate (MFR) of 1400 g / 10 min and spun. Subsequently, using the same melt-blown apparatus, 100% by mass of the resin composition was spun and directly deposited to obtain a laminated nonwoven fabric in two steps. In other words, to maximize low-carbonization, the polymer component of the layer corresponding to nonwoven fabric B was made solely of plant-derived resin. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Comparative Example 1. It was evaluated according to (1) to (8) above.

[0083] <Comparative Example 6> A resin composition was obtained by pelletizing 98.925% by mass of poly-4-methyl-1-pentene resin with a melt flow rate (MFR) of 180 g / 10 min as an olefin polymer, 1% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.075% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 250°C. Separately, an additive masterbatch was obtained by pelletizing 94.625% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 1400 g / 10 min as a propylene polymer, 5% by mass of Chimassorb® 944 as a nitrogen-containing compound, and 0.375% by mass of magnesium stearate as a fatty acid metal salt using a twin-screw extruder at a melting temperature of 180°C. Using a melt-blown apparatus with a single nozzle, 20% by mass of an additive masterbatch was diluted with 80% by mass of petroleum-derived polypropylene resin as a propylene-based polymer at a melt flow rate (MFR) of 1400 g / 10 min and spun. Subsequently, using the same melt-blown apparatus, 100% by mass of the resin composition was spun and directly deposited to obtain a laminated nonwoven fabric in two steps. In other words, to maximize the lifespan, the polymer component of the layer corresponding to nonwoven fabric B was made solely of poly-4-methyl-1-pentene resin. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. It was evaluated according to (1) to (8) above.

[0084] <Comparative Example 7> A laminated nonwoven fabric with an apparent density of 0.057 g / cm³ was obtained by adjusting the collection distance and resin temperature using the same method as in Example 1. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. It was evaluated according to (1) to (8) above.

[0085] <Comparative Example 8> A laminated nonwoven fabric with an apparent density of 0.092 g / cm³ was obtained by adjusting the collection distance and resin temperature using the same method as in Example 1. A laminated electret was obtained from the obtained laminated nonwoven fabric in the same manner as in Example 1. It was evaluated according to (1) to (8) above.

[0086] Table 1 shows the measured values ​​for Examples 1 to 5, and Table 2 shows the measured values ​​for Comparative Examples 1 to 8.

[0087] [Table 1]

[0088] [Table 2]

[0089] The results from the examples and comparative examples show that incorporating plant-derived polyethylene resin can contribute to reducing carbon emissions and impart additional functionality. By incorporating poly-4-methyl-1-pentene resin, the wettability is reduced, meaning that the coating of oily components can be reduced, which can be said to provide the additional function of extending the lifespan of the electret performance.

[0090] Examples 1-5 demonstrate high filtration performance while also possessing added functions such as reduced carbon dioxide emissions and extended lifespan. On the other hand, Comparative Examples 1-6 show that when attempting to add the added functions of reduced carbon dioxide emissions and extended lifespan, sufficient filtration performance is not achieved, as evidenced by low collection efficiency and low filter media quality factor (QF) values. Comparative Example 7 is manufactured using the same method as Example 1, but has a low apparent density and low collection efficiency. Comparative Example 8 is also manufactured using the same method as Example 1, but has a high apparent density and a low filter media quality factor (QF) value. Therefore, Examples 1-4 demonstrate that they are able to achieve both high filtration performance and added functions. [Industrial applicability]

[0091] The laminated nonwoven fabric, laminated electret, filter, and filter unit of the present invention possess not only high filtration performance but also additional functions such as low carbon emissions and extended lifespan. Therefore, they can be suitably used as filters in applications such as dustproof clothing, dustproof masks, and air purifiers, and can make a significant contribution to industry. However, their application range is not limited to those described herein.

Claims

1. A laminated nonwoven fabric is formed by laminating a nonwoven fabric A having constituent fibers containing a propylene polymer and an olefin polymer different from the propylene polymer, and a nonwoven fabric B having constituent fibers containing a propylene polymer. The laminated nonwoven fabric has an average fiber diameter of 2 to 10 μm and an apparent density of 0.06 to 0.09 g / cm³. ３ This is a laminated nonwoven fabric.

2. The laminated nonwoven fabric according to claim 1, characterized in that the olefin polymer is a plant-derived polyethylene resin or a poly-4-methyl-1-pentene resin.

3. The laminated nonwoven fabric according to claim 1 or 2, characterized in that at least one of the nonwoven fabric A and the nonwoven fabric B contains a nitrogen-containing compound and a fatty acid metal salt having 10 to 50 carbon atoms.

4. The laminated nonwoven fabric according to claim 3, characterized in that both nonwoven fabric A and nonwoven fabric B are meltblown nonwoven fabrics.

5. A laminated electret having an electric charge applied to a laminated nonwoven fabric as described in claim 4, wherein the filter material quality factor (QF) value is 1.2 or higher.

6. A filter or filter unit using a stacked electret as described in claim 5.

Images