Filter material and filter

Abstract

The present invention addresses the problem of providing a filter material and a filter having both high collection efficiency and low pressure loss and having high elongation. The filter material according to the present invention is a filter material comprising a fiber sheet comprising fibers containing a plurality of polyolefin resins having different melt flow rates (MFR), the total of the tensile elongation rates in the MD direction and the TD direction being 100% or more, and the quality coefficient value represented by the following formula being 1.8 or more. Quality coefficient value =-Ln ((100-trapping efficiency [%]) / 100) / pressure loss [mmAq]

Description

Technical Field

[0001] The present invention relates to a filter medium and a filter using the filter medium. Background Art

[0002] Conventionally, nonwoven fabrics are often used as filter materials for air filters. Among them, meltblown nonwoven fabrics are used for filter materials for air filters, battery separators, and the like (for example, Patent Document 1).

[0003] The melt-blowing method, which is a method for producing melt-blown nonwoven fabrics, is generally a method in which a thermoplastic polymer extruded from a spinneret is subjected to hot air jetting to be thinned into fibers, and the self-fusion characteristics of the obtained fibers are utilized to form a fiber web. Compared with other nonwoven fabric production methods such as spunbond, the melt-blowing method has the advantages of not requiring complicated processes and being easy to obtain thin fibers with a single fiber diameter of tens of μm to several μm or less.

[0004] However, the melt-blowing method is usually implemented using a resin with a relatively low molecular weight and a relatively high melt flow rate as a raw material, and the fibers produced by the melt-blowing method are relatively non-oriented. Therefore, the elastic stress of the fibers is relatively low, and the stress of the non-woven fabric produced using the fibers is also weak, making it difficult to achieve satisfactory performance.

[0005] Therefore, in Patent Document 2, stretchability is imparted to a melt-blown nonwoven fabric by using a composition containing an ethylene·α-olefin copolymer and a styrene-ethylene / butylene-styrene block copolymer.

[0006] In addition, Patent Document 3 discloses a nonwoven fabric having excellent softness and stretchability by embossing. However, the meltblown nonwoven fabrics of Patent Documents 2 and 3 lack the performance to be used as a filter material or filter.

[0007] On the other hand, the performance required of an air filter is a high collection efficiency capable of collecting a large amount of fine dust, and a low pressure loss with little resistance when the gas passes through the inside of the air filter. In order to obtain a filter material with a high collection efficiency, the single fiber constituting the nonwoven fabric is preferably fine in fineness. However, if the single fiber is fined, the nonwoven fabric made of the single fiber is easy to break, and the pressure loss becomes higher due to the increase in the fiber density of the nonwoven fabric.

[0008] In order to obtain a filter material with low pressure loss, the single fiber of the fiber constituting the nonwoven fabric for making the filter material is preferably coarse fineness. However, if the single fiber is coarse fineness, the fiber surface area in the nonwoven fabric is reduced and the collection efficiency is reduced. As described above, among the performances required for air filters, high collection efficiency and low pressure loss are in an inverse relationship.

[0009] Therefore, attempts have been made to simultaneously satisfy high collection efficiency and low pressure loss by making nonwoven fabric electret and utilizing electrostatic action in addition to physical action.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Publication No. 2017-94250

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 9-105056

[0014] Patent Document 3: Japanese Patent Application Publication No. 2000-8259 Summary of the invention

[0015] Problems to be solved by the invention

[0016] As described above, meltblown nonwoven fabrics used as filter materials and filters in the past have low elastic stress of fibers, so when elasticity, i.e. elongation, is insufficient, there is a problem that once some external force such as pleating is applied, they will immediately reach a complete breaking state.

[0017] Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a filter medium and a filter having both high collection efficiency and low pressure loss and high elongation.

[0018] In addition, it is desirable to provide a filter medium and a filter that are soft and have a high elongation.

[0019] Means for solving problems

[0020] The present inventors have conducted intensive studies to solve the above problems and have arrived at the present invention. The filter medium and filter of the present invention are as follows.

[0021] [1] A filter material, characterized in that it is a filter material made of a fiber sheet, wherein the fiber sheet is formed of fibers containing a plurality of polyolefin resins having different melt flow rates (MFRs), the total tensile elongation of the filter material in the MD direction and the TD direction is 100% or more, and the quality coefficient value expressed by the following formula is 1.8 or more.

[0022] Quality coefficient value = -Ln ((100 - collection efficiency [%]) / 100) / pressure loss [mmAq]

[0023] [2] The filter medium according to [1], wherein among the MFR values ​​of the plurality of polyolefin resins, the largest value is 10 times or more the smallest value.

[0024] [3] The filter material according to [1] or [2], which is an electret filter material that has been subjected to an electret treatment.

[0025] [4] The filter material according to any one of [1] to [3], wherein the fiber sheet is a meltblown nonwoven fabric.

[0026] [5] The filter medium according to any one of [1] to [4], wherein the average fiber diameter of the fibers constituting the fiber sheet is 5 μm to 40 μm.

[0027] [6] The filter material according to any one of [1] to [5], wherein the fiber contains 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of magnesium stearate per 100 parts by weight of the plurality of polyolefin resins.

[0028] [7] A filter using the filter medium described in any one of [1] to [6].

[0029] Effects of the Invention

[0030] According to the present invention, it is possible to provide a filter medium and a filter which have both high collection efficiency and low pressure loss and high elongation.

[0031] Therefore, the filter material of the present invention having high elongation is not easily broken even when external force is applied to the filter material during processing such as pleating, and can provide a thin filter and filter assembly with high fine dust capture performance, as well as a filter and filter assembly used in combination with an adsorbent such as activated carbon. DETAILED DESCRIPTION

[0032] The filter material of the present invention is made of a fiber sheet formed of fibers containing multiple polyolefin resins having different melt flow rates (MFR). The filter material is preferably made of a fiber sheet formed of fibers made of multiple polyolefin resins having different melt flow rates.

[0033] The total of the tensile elongation in the MD direction (longitudinal direction) and the TD direction (transverse direction) of the filter medium of the present invention is 100% or more, preferably 130% or more, and more preferably 150% or more.

[0034] If the total tensile elongation of the filter material in the MD direction and the TD direction is 100% or more, it is not easy to be damaged when the filter material is subjected to the desired processing such as pleating processing (hereinafter sometimes referred to as forming processing). In addition, if the total tensile elongation is 100% or more, even when the laminate of the filter material, the adsorbent material, the reinforcing material, etc. is subjected to forming processing such as pleating processing, the closeness of the filter material and the adsorbent material and the reinforcing material is improved, and the damage of the adsorbent material and the filter material can be suppressed, and the peeling of the filter material and the adsorbent material due to the stress applied during the forming processing and operation can also be suppressed. On the other hand, if the total tensile elongation of the MD direction and the TD direction is less than 100%, it is possible to break during the forming processing and operation.

[0035] The lower limits of the tensile elongation in the MD direction and the TD direction are each preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more.

[0036] In order to set the tensile elongation in the MD direction and the TD direction to the above-mentioned values, it is only necessary to adjust the manufacturing conditions. For example, it is preferred to adjust the fiber orientation and / or the degree of mutual fusion. Specifically, it is only necessary to adjust the conveying speed, conveyor belt angle, collection distance, discharge amount, nozzle spacing, resin temperature, hot air flow rate, etc.

[0037] Quality factor QF

[0038] The quality factor value QF represents the relationship between the collection efficiency and the pressure loss.

[0039] The quality coefficient value of the filter medium of the present invention is 1.8 or more, preferably 2.0 or more, more preferably 2.3 or more, and further preferably 2.5 or more.

[0040] The higher the quality coefficient value, the higher the collection efficiency and the lower the pressure loss, so the performance as a filter material is higher. Filter materials with a quality coefficient value less than 1.8 have problems such as low collection efficiency or high pressure loss.

[0041] The quality coefficient value was calculated from the following formula using the collection efficiency [%] of atmospheric dust particles with a particle diameter of 0.3 μm when the filter medium passes through a linear velocity of 10.4 cm / s and the pressure loss (mmAq) (it should be noted that the detailed conditions are based on the examples).

[0042] Quality factor QF = -Ln ((100 - collection efficiency) / 100) / pressure loss

[0043] The above-mentioned collection efficiency is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. Since the higher the collection efficiency, the better, there is no upper limit.

[0044] In addition, the pressure loss is preferably 0.2 to 20 mmAq, more preferably 0.5 to 10 mmAq.

[0045] The filter material of the present invention is made of a fiber sheet formed of fibers containing a plurality of polyolefin resins having different melt flow rates (MFRs).

[0046] Examples of the polyolefin resin include polypropylene resins and polyethylene resins. Examples of the polypropylene resin include homopolymers of propylene and copolymers of propylene and any one or more α-olefins. Examples of the polyethylene resin include homopolymers of ethylene and copolymers of ethylene and any one or more α-olefins.

[0047] As long as the melt flow rates are different, the combination of multiple polyolefin resins is not limited, and can be, for example, any combination of multiple polypropylene resins, multiple polyethylene resins, or a combination of one or more polyethylene resins and one or more polypropylene resins. In addition, these multiple polyolefin resins can be any of homopolymers, copolymers, or combinations thereof.

[0048] Among these materials, from the viewpoint of exerting electret performance, polyolefin resins mainly composed of polypropylene (for example, in 100% by mass of the polyolefin resin, preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 75% by mass or more, further preferably 90% by mass or more, and 100% by mass or less is polypropylene resin (total of homopolymer and copolymer)) are also preferred. In addition, other components may be copolymerized within a range that does not impair the properties of the polymer. More preferred are a plurality of polypropylene resins having different melt flow rates.

[0049] The fiber of the present invention may contain other polyolefin resins in addition to a plurality of polyolefin resins having different melt flow rates (MFR), such as polyethylene, polymethylpentene, polystyrene, cyclic olefins, various copolymerized olefin resins, thermoplastic elastomers, and other non-polyolefin resins.

[0050] When using a resin composition containing other resins, the other resins may be contained within a range that does not impair the properties of the polymer, and the content of the other resins is preferably 25% or less, more preferably 10% or less in 100% by mass of the resin composition. In the present invention, it is also preferred that the fiber contains no other resins and is made of the above-mentioned polyolefin resins with different melt flow rates, and more preferably is a fiber made of a plurality of polypropylene resins with different melt flow rates.

[0051] In the present invention, multiple polyolefin resins with different MFRs can be mixed in any proportion, but the first largest value (maximum value) of MFR is preferably 10 times or more relative to the first smallest value (minimum value), more preferably 20 times or more, further preferably 50 times or more, and further preferably 70 times or more. For example, among the multiple polyolefin resins with different MFRs used in the filter material of the present invention, if the minimum value of MFR is 18 and the maximum value is 1300, the maximum value is 72 times or more relative to the minimum value. It should be noted that sometimes the ratio of the minimum value to the maximum value is expressed as 18:1300.

[0052] The inventors of the present invention have conducted research and found that by mixing a plurality of polyolefin resins having different MFRs, the flexibility is improved by the high molecular weight component. The larger the MFR value, the better the fluidity and processability when melted, but the tensile strength is reduced. Therefore, in the present invention, a high molecular weight resin having a small MFR is mixed to improve the tensile strength.

[0053] In order to achieve the above effects, the minimum value of MFR is preferably 1 or more, more preferably 5 or more, and even more preferably 10 or more, and is preferably 1500 or less, more preferably 1000 or less, and even more preferably 500 or less.

[0054] The maximum value of MFR is preferably 100 or more, more preferably 200 or more, and even more preferably 300 or more, and is preferably 3500 or less, more preferably 2500 or less, and even more preferably 2000 or less.

[0055] The proportion of the polyolefin resin (preferably polypropylene resin) showing the minimum MFR value in the polyolefin resin (100% by mass) is preferably 0.5 to 80% by mass, more preferably 1 to 50% by mass. In addition, the proportion of the polyolefin resin (preferably polypropylene resin) showing the maximum MFR value is preferably 20 to 99.5% by mass, more preferably 50 to 99% by mass.

[0056] The mass ratio of the polyolefin resin (preferably polypropylene resin) showing the minimum MFR value to the polyolefin resin (preferably polypropylene resin) showing the maximum MFR value is preferably 0.5:99.5 to 80:20, more preferably 1:99 to 50:50.

[0057] The filter material of the present invention has the characteristic of excellent thermal stability. The filter material is sometimes exposed to high temperature during the forming process of the filter, etc. and during use, but the filter material of the present invention has a high quality coefficient value QF even after heating. The ratio of the quality coefficient value QF before heating to the quality coefficient value QF after heating (QF after heating / QF before heating) is preferably 0.75 or more, more preferably 0.8 or more, and further preferably 0.85 or more.

[0058] When manufacturing the fiber of the present invention containing multiple polyolefin resins having different melt flow rates (MFR), it is necessary to select a polyolefin resin that satisfies the ratio of the maximum value of MFR relative to the minimum value of MFR given above, preferably a polyolefin resin that satisfies the range of the maximum and minimum values ​​of MFR. In addition, it is preferred to adjust the mixing ratio in such a way that each polyolefin resin having the minimum and maximum values ​​of MFR has the above-mentioned preferred content. The additives described later may be contained in the polyolefin resin in advance, or may be added when the multiple polyolefin resins are melted and mixed.

[0059] The temperature (mixing temperature) when mixing the plurality of polyolefin resins is preferably about 5 to 250° C. higher than the melting point of the polyolefin resin. On the other hand, if the mixing temperature is too high, the molecular weight may be reduced and the strength of the filter material may be reduced. Therefore, it is preferably 450° C. or lower, more preferably 400° C. or lower.

[0060] The mixing time may be appropriately adjusted so that the mixture can be uniformly mixed, and may be, for example, about 1 to 30 minutes.

[0061] In addition, various known melt kneading machines such as an extruder, a stirrer, a kneader, and a kneading roll can be used for mixing.

[0062] In the filter material of the present invention, additives such as commonly used antioxidants, weather stabilizers, light stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, pigments, or other polymers may be added as needed within a range that does not impair the effects of the present invention.

[0063] Furthermore, additives such as a heat stabilizer, a weathering agent, and a polymerization inhibitor may be added to the filter material of the present invention.

[0064] The additives may be added during the production of the polyolefin resin, or may be added after processing into a fiber sheet or a filter material.

[0065] It is also a preferred embodiment that the filter material of the present invention is an electret filter material that has been subjected to an electret treatment.

[0066] When electret treatment is performed, electrostatic charge is imparted to the filter medium, thereby improving the collection efficiency and obtaining a filter medium with higher performance.

[0067] The electret treatment of the present invention may employ known techniques such as corona charging, friction charging, thermal electret, electron beam irradiation, charged particle injection, high pressure liquid stream irradiation, and photoelectret.

[0068] It is also a preferred embodiment that the filter medium of the present invention contains a hindered amine compound.

[0069] In particular, when the filter medium of the present invention is an electret filter medium, if the hindered amine-based compound is contained, the chargeability and charge retention during electret treatment will be further improved.

[0070] Compared with a filter material not containing a hindered amine compound, an electret filter material containing a hindered amine compound is less likely to lose its charge even when in contact with water, and thus exhibits more excellent collection performance.

[0071] Examples of hindered amine compounds include poly[{(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexylidene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidyl succinate polycondensate, and bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonate. These compounds may be used alone or in combination of two or more.

[0072] The content of the hindered amine compound is preferably 0.01 to 3 parts by mass relative to 100 parts by mass of the resin constituting the fiber sheet forming the filter medium, the lower limit is more preferably 0.2 parts by mass or more, further preferably 0.3 parts by mass or more, and further preferably 0.5 parts by mass or more, and the upper limit is more preferably 2.5 parts by mass or less. The upper and lower limits may be arbitrarily combined.

[0073] It is also a preferred embodiment that the filter medium of the present invention contains magnesium stearate.

[0074] In particular, when the filter medium of the present invention is an electret filter medium, if magnesium stearate is contained, the thermal stability of the electret filter medium in retaining electric charge is improved.

[0075] The content of magnesium stearate is preferably 0.025 to 0.25 parts by mass relative to 100 parts by mass of the resin constituting the fiber sheet forming the filter medium, with a lower limit of more preferably 0.02 parts by mass or more, further preferably 0.07 parts by mass or more, and an upper limit of more preferably 0.15 parts by mass or less. The upper and lower limits may be arbitrarily combined.

[0076] In the present invention, it is also a preferred embodiment to use magnesium stearate and a hindered amine compound together from the viewpoint of improving the collection efficiency and thermal stability of the electret filter material.

[0077] It is preferable that magnesium stearate and the hindered amine compound are added to the polyolefin resin so as to be contained in the above-mentioned content.

[0078] It is also a preferred embodiment that the filter medium of the present invention contains an arbitrary heat stabilizer.

[0079] By containing a heat stabilizer, the heat stability during spinning can be improved.

[0080] Examples of the heat stabilizer include nitrogen-containing hindered phenols, metal salt hindered phenols, phenols, sulfur stabilizers, and phosphorus stabilizers. These can be used alone or in combination of two or more. The content is preferably 0.01% to 5%.

[0081] It is also a preferred embodiment that the filter medium of the present invention contains various known additives.

[0082] As additives, for example, known additives that impart any of the following effects can be cited. Examples of the effects imparted to the filter material include dust removal, deodorization, antibacterial, mildew prevention, antiviral, insect repellent, insecticide, pest repellent, harmful substance removal, fragrance, dehumidification, humidity control, moisture absorption (drying), water (humidity) permeation, adsorption of oil, etc., adjustment of ion balance such as cationic adsorption, transpiration or slow release of water and / or volatile agents, etc. The additives can be used alone or in combination of two or more. The additives can be added to the resin, or added to the fiber sheet or filter material by spraying, etc. The content of the additive is preferably less than 10%.

[0083] The fiber sheet used in the filter medium of the present invention may be in the form of, for example, nonwoven fabric, woven fabric, knitted fabric, paper-like material, etc., preferably nonwoven fabric, more preferably melt-blown nonwoven fabric.

[0084] The fiber sheet can be produced by a known method. In addition, the fiber sheet may be a uniform product formed by a single production method or raw material, or a mixture of two types of fibers having different production methods, raw materials, and fiber diameters.

[0085] In the present invention, it is also a preferred embodiment when the basis weight of the fibrous sheet and / or the fiber diameter of the fibers are within a given range.

[0086] If the mass per unit area of ​​the nonwoven fabric is too small, the collection efficiency will be reduced. On the other hand, if the mass per unit area is too large, it will be easy to be clogged. For example, the mass per unit area of ​​the meltblown nonwoven fabric is preferably 5 to 100 g / m 2 , more preferably 10 to 60 g / m 2 .

[0087] If the fiber diameter of the fiber constituting the fiber sheet is too thick, it may be difficult to obtain a practical collection efficiency, and the collection efficiency may be greatly reduced when the charge decays in the electret filter material. On the other hand, if the fiber diameter is too thin, it is necessary to increase the mass per unit area in order to improve the collection efficiency, and the pressure loss may be increased, and sufficient electrostatic charge may not be imparted in the electret treatment.

[0088] For example, the average fiber diameter (diameter) of the melt-blown nonwoven fabric is preferably 1 to 30 μm, more preferably 5 to 20 μm.

[0089] Regarding the mass per unit area and the fiber diameter of the melt-blown nonwoven fabric, only one of them may be set within a given range. However, in consideration of the collection efficiency and the pressure loss, it is preferable to set both of them within a given range.

[0090] It is also a preferred embodiment to use the filter medium of the present invention as a filter composed of the filter medium alone, or to use the filter medium in combination with other materials to form a filter.

[0091] The shape of the filter is not particularly limited, and the filter may be a filter subjected to various processes such as pleating, corrugated plate processing, three-dimensional molding processing, or a sheet-shaped filter not subjected to these processes.

[0092] In particular, filters processed by wave-like processing, three-dimensional molding processing, etc. are preferred because they can increase the surface area of ​​the filter material, reduce pressure loss, improve the collection efficiency, and prolong the service life. In addition, compared with sheet-like filters, filters processed by wave-like processing and three-dimensional molding processing have high shape retention during use and excellent operability during installation and removal of the filter, so they are preferred.

[0093] For example, if the fiber sheet of the present invention is subjected to pleating, uniform pleats can be formed without breaking the fiber sheet. The preferred pleating conditions are not particularly limited, but the pleating temperature is preferably 60°C to 160°C. If it is higher than 160°C, the charge disappears and sufficient performance cannot be exhibited. If it is lower than 60°C, it is difficult to perform pleating. More preferably, it is 80°C to 110°C.

[0094] There are no particular limitations on other materials that can be combined with the filter medium of the present invention, and a filter can be constructed using various known materials such as reinforcing materials and activated carbon.

[0095] As described above, according to the present invention, a filter material that is soft and has a high elongation can be provided, and a filter having improved processability can be provided.

[0096] This application claims the benefit of priority based on Japanese Patent Application No. 2022-169192 filed on October 21, 2022. The entire contents of the specification of Japanese Patent Application No. 2022-169192 filed on October 21, 2022 are incorporated herein by reference.

[0097] Example

[0098] Hereinafter, the present invention will be specifically described by giving examples. However, the present invention is not limited to the following examples, and may be appropriately changed within the scope of the above-mentioned and later-described purports. Moreover, the modes after these appropriate changes are also included in the technical scope of the present invention.

[0099] First, processing conditions, measured characteristic values, and their measuring methods of Examples and Comparative Examples are shown below.

[0100] [Processing conditions]

[0101] (Electret treatment)

[0102] The nonwoven fabrics (fiber sheets) obtained in the examples and comparative examples were placed on a plate with an air permeability of 120 cm 3 / cm 2 / second mesh support (96 mesh), from the nozzle of 0.1mm diameter and 0.6mm spacing 2cm above the nonwoven fabric, the spraying treatment of the aqueous solution is carried out at a pressure of 1MPa. It should be noted that the aqueous solution is set as high-purity water obtained by performing reverse osmosis membrane treatment on ordinary tap water and then performing ion exchange membrane treatment. The conveying speed of the mesh support is set to 4m / minute, and the lower part of the mesh support immediately below the nozzle is set to a reduced pressure state of 2mAq. The surface and back of the nonwoven fabric are respectively treated twice. The electret treatment is carried out like this to obtain the electret filter material.

[0103] [Measurement method]

[0104] (Filter characteristics)

[0105] Quality factor QF

[0106] The quality factor value QF (1 / mmAq) is calculated by the following formula using the pressure loss PD (mmAq) and the particle collection efficiency E [%).

[0107] QF=-Ln((100-E) / 100) / PD

[0108] The pressure loss PD (mmAq) was obtained by placing a sample of the electret filter material in a conduit, controlling the linear velocity of the filter material to be 10.4 cm / sec, and reading the static pressure difference between the static pressure on the upstream side of the electret filter material (the air pressure before passing through the filter) and the static pressure on the downstream side (the air pressure after passing through the filter) (=static pressure on the upstream side - static pressure on the downstream side) using a micro differential pressure gauge.

[0109] The particle collection efficiency E [%] (=1-[mass of dust particles collected by the filter / mass of dust particles supplied] x 100%) was measured using a filter tester with 0.3 to 0.5 μm atmospheric dust particles at an air volume of 10.4 cm / sec.

[0110] (Average fiber diameter)

[0111] For the nonwoven fabrics obtained in the examples and comparative examples, 10 small samples were randomly collected, and photographs were taken at 500 to 3000 times using a scanning electron microscope. The fiber diameters of 10 fibers from each sample, for a total of 100 fibers, were measured, and the average value was calculated by rounding off to the first decimal place.

[0112] (Mass per unit area (g / m 2 )

[0113] According to 5.2 of JIS L1906 (2000 edition), three samples of 50 cm in length and 50 cm in width were collected from the nonwoven fabrics obtained in the examples and comparative examples, and the weight of each sample was measured. The average value of the obtained values ​​was converted into a value per unit area. It should be noted that the first decimal place was rounded off.

[0114] (Processability)

[0115] In the reinforcement material (PET thermal bonding non-woven fabric, 80g / m 2 ) and sprinkle activated carbon particles (average particle size 500μm: 250g / m 2 ) and polyethylene powder (average particle size 20 μm), and then laminated with an electret filter material, and then kept in a constant temperature layer at 130°C for 1 minute to produce an activated carbon sheet. The activated carbon sheet was pleated at a pleating temperature of 110°C using a reciprocating pleating machine so that the peak height was 3.0 cm, and evaluated using the following criteria.

[0116] ○: The pleats are uniform and there is no problem in processing.

[0117] △: The pleats are slightly uneven.

[0118] ×: The pleats are uneven, and there are processing problems. Or the nonwoven fabric is torn.

[0119] (Tensile elongation)

[0120] According to 5.3.1 of JIS L1906 (2000 edition), a sample with a size of 5 cm horizontal × 20 cm vertical is made of electret filter material, and the sample is placed longitudinally in the test machine. Under the conditions of a clamping interval of 15 cm and a tensile speed of 20 cm / min, the sample is subjected to three tensile tests in the longitudinal direction (MD direction) and the transverse direction (TD direction). The elongation [%] is calculated based on the displacement when the sample is stretched to break. It should be noted that the tensile elongation is the average value (n = 3).

[0121] (Thermal stability)

[0122] The thermal stability was evaluated by standing an electret filter material (size 10 cm×10 cm) in an oven heated and maintained at 100° C. for 30 minutes and using the ratio of the quality coefficient values ​​QF before and after standing in the oven (quality coefficient value after standing / quality coefficient value before standing).

[0123] (Melt flow rate)

[0124] The melt flow rate (MFR) is a value obtained by converting the amount of resin extruded from the die head in a certain period of time into the amount of resin extruded in 10 minutes under the conditions of 230°C and 2.16 kg load using a melt indexer F-01 (manufactured by Toyo Seiki Seisaku-sho, Ltd.) in accordance with JIS K7210:1999. The converted value is a value calculated using the MFR automatic calculation process (B method), and the calculation formula is as follows. It should be noted that the same method is also used to calculate when the melt flow rate is greater than 50 g / 10 minutes.

[0125] MFR (g / 10min) = (427×L×ρ) / t

[0126] In the formula,

[0127] L (interval of test conditions): 3 (cm);

[0128] ρ (melt density at test temperature): value calculated by the following formula using the cutting method (g / cm 3 ), but if the cutting method is not possible, set ρ = 0.75 (g / cm 3 ).

[0129] ρ=m / (0.711×L)

[0130] In the formula,

[0131] m: the mass of the sample that flows out when the piston moves the distance L, measured by the cutting method (g);

[0132] L: Same interval as above;

[0133] t (interval movement time): actual measured value (seconds).

[0134] [Example 1]

[0135] A master batch D was prepared by mixing 4.5 parts by weight of Chimassorb 944 (manufactured by BASF) as a hindered amine additive and 0.34 parts by weight of magnesium stearate with 100 parts by weight of polypropylene resin B (MFR=1300).

[0136] Polypropylene resin A (MFR = 18) and masterbatch D were mixed at a weight ratio of 5:1. The blended resin was used to produce a polypropylene resin with a unit area weight of 26 g / m 2 , meltblown nonwoven fabric (fiber sheet) with an average fiber diameter of 13μm.

[0137] The quality factor QF of the electret filter material obtained by electret treatment of the nonwoven fabric was 2.5, and the total tensile elongation in the longitudinal and transverse directions was 310%. In addition, the thermal stability was 0.9. The evaluation of pleat processability was 0. The ratio of the minimum value to the maximum value of the MFR of the resin constituting the fiber was 18:1300.

[0138] [Example 2]

[0139] Polypropylene resin A (MFR = 18), polypropylene resin B (MFR = 1300) and masterbatch D prepared in Example 1 were mixed at a weight ratio of A:B:D = 2:2:1. Using the blended resin, a polypropylene resin with a unit area weight of 26 g / m 2 , a meltblown nonwoven fabric with an average fiber diameter of 10 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=3.1, and the total tensile elongation in the longitudinal and transverse directions is 140%. In addition, the thermal stability is 0.92. The evaluation of pleat processability is 0. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 18:1300.

[0140] [Example 3]

[0141] The polypropylene resin C (MFR = 60) was mixed with the master batch D prepared in Example 1 at a weight ratio of C:D = 5:1. The blended resin was used to prepare a polypropylene resin with a unit area weight of 26 g / m 2 , a meltblown nonwoven fabric with an average fiber diameter of 10 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=2.3, and the total tensile elongation in the longitudinal and transverse directions is 280%. In addition, the thermal stability is 0.88. The evaluation of pleat processability is 0. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 60:1300.

[0142] [Example 4]

[0143] A master batch E containing 10 parts by weight of an antibacterial agent added to 100 parts by weight of a polypropylene resin B (MFR = 1300) was prepared. Polypropylene resin A (MFR = 18), master batch D prepared in Example 1, and master batch E were mixed at a weight ratio of A:D:E = 3.8:1:0.06, and the blended resin was used to prepare a polypropylene resin having a unit area mass of 26 g / m 2 , a meltblown nonwoven fabric with an average fiber diameter of 10 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=2.3, and the total tensile elongation in the longitudinal and transverse directions is 200%. In addition, the thermal stability is 0.9. The evaluation of pleat processability is 0. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 18:1300.

[0144] [Comparative Example 1]

[0145] The polypropylene resin B (MFR = 1300) was mixed with the master batch D prepared in Example 1 at a weight ratio of B:D = 4:1. The blended resin was used to prepare a polypropylene resin with a unit area weight of 30 g / m 2 , a meltblown nonwoven fabric with an average fiber diameter of 14 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=1.9, and the total tensile elongation in the longitudinal and transverse directions is 25%. In addition, the thermal stability is 0.86. The evaluation of pleat processability is ×. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 1300:1300.

[0146] [Comparative Example 2]

[0147] A master batch F was prepared in which Chimassorb 944 (manufactured by BASF) as a hindered amine additive was mixed at a ratio of 4.5 parts by weight with respect to 100 parts by weight of polypropylene resin B (MFR = 1300). The polypropylene resin B (MFR = 1300) and the master batch F were mixed at a weight ratio of B:F = 4:1, and the blended resin was used to prepare a polypropylene resin having a unit area weight of 22 g / m by the same method as in Example 1. 2 , a meltblown nonwoven fabric with an average fiber diameter of 10 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=2.0, and the total tensile elongation in the longitudinal and transverse directions is 30%. In addition, the thermal stability is 0.63. The evaluation of pleat processability is ×. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 1300:1300.

[0148] [Comparative Example 3]

[0149] Polypropylene resin B (MFR = 1300), polypropylene resin G (MFR = 900) and masterbatch D prepared in Example 1 were mixed at a weight ratio of B:G:D = 2:2:1. The blended resin was used to prepare a polypropylene resin with a unit area weight of 26 g / m 2 , a meltblown nonwoven fabric with an average fiber diameter of 14 μm. The quality coefficient of the electret filter material obtained by electret treatment of the nonwoven fabric is QF=2.2, and the total tensile elongation in the longitudinal and transverse directions is 48%. In addition, the thermal stability is 0.88. The evaluation of pleat processability is ×. The ratio of the minimum and maximum MFR of the resin constituting the fiber is 900:1300.

[0150]

[0151] It is found that the electret filter materials of Examples 1 to 4 of the present invention have a larger total value of longitudinal and transverse tensile elongation and are excellent in pleating processability than Comparative Examples 1 to 3. Therefore, it is found that the electret filter materials of Examples 1 to 4 have high flexibility.

[0152] In addition, Examples 1 to 4 containing magnesium stearate have higher quality factor values ​​QF even after heat treatment than Comparative Example 2 containing no magnesium stearate.

[0153] Industrial Applicability

[0154] The filter medium of the present invention has excellent flexibility and processability, can be widely used in various filter applications, and can make a great contribution to the industry.

Claims

1. A filter material, characterized in that: The filter material is made of a fiber sheet, wherein the fiber sheet is formed of fibers containing a plurality of polyolefin resins having different melt flow rates (MFRs), The total tensile elongation of the filter material in the MD direction and the TD direction is 100% or more, and the quality coefficient value represented by the following formula is 1.8 or more, Quality coefficient value = -Ln((100 - collection efficiency [%)) / 100) / pressure loss [mmAq].

2. The filter material according to claim 1, wherein Among the MFRs of the plurality of polyolefin resins, the largest value is 10 times or more the smallest value.

3. The filter material according to claim 1 or 2, wherein The filter material is an electret filter material that has been treated with electret.

4. The filter material according to claim 1 or 2, wherein The fiber sheet is a melt-blown nonwoven fabric.

5. The filter material according to claim 1 or 2, wherein The average fiber diameter of the fibers constituting the fiber sheet is 5 μm to 40 μm.

6. The filter material according to claim 1, wherein The fiber contains 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of magnesium stearate based on 100 parts by weight of the plurality of polyolefin resins.

7. A filter using the filter medium according to claim 1 or 2.

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