JP2008221074A - Electret filter medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret filter medium which contains a charge stabilizer, can stably hold charges over a long period of time by using a superfine polymer fiber spun by a charge spinning method, and is excellent in filtering performance, and to provide its manufacturing method. <P>SOLUTION: The electret filter medium containing the charge stabilizer uses the polymer fiber spun by the charge spinning method, with an average fiber diameter of 0.01-1 &mu;m. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electret filter medium using a polymer fiber containing a charge stabilizer and spun by a charge spinning method, and a method for producing the same.

  Conventionally, a technique for improving heat resistance by blending at least one selected from a hindered amine, nitrogen-containing hindered phenol, metal salt hindered phenol, or phenol stabilizer in a polymer is known. (Patent Document 1).

  Patent Document 2 discloses that the electret performance can be improved in the range of 0.7 to 3% by weight of the hindered amine-based additive and the like for the electret processed product.

  However, in Patent Document 1, although the heat resistance is improved, the fiber diameter of the nonwoven fabric used is as large as 3 μm, and the fiber diameter of the nonwoven fabric constituting the electret processed product described in Patent Document 2 is also 2 μm. It is large and has a problem that sufficient filter performance cannot be obtained.

Japanese Examined Patent Publication No. 4-42812 JP 2002-115178 A

  In view of the above-described conventional problems, the present invention can maintain a stable charge over a long period of time by using an ultrafine polymer fiber that includes a charge stabilizer and is spun by a charge spinning method, and has excellent filter performance. It is an object of the present invention to provide an electret filter medium and a method for producing the same.

  The electret filter medium of the present invention uses a polymer fiber containing a charge stabilizer and having an average fiber diameter of 0.001 to 1 μm spun by a charge spinning method.

  In the electret filter medium of the present invention, the charge stabilizer is a hindered amine-based, nitrogen-containing hindered phenol-based, metal salt hindered phenol-based, phenol-based, hindered phenol-based, phenol-based sulfur-based weathering agent, or fatty acid metal salt. It is preferably at least one selected from the group consisting of

  In the electret filter medium of the present invention, the polymer fiber preferably contains at least one polymer selected from the group consisting of polyamideimide, polylactic acid, and polycarbonate.

  In the electret filter medium of the present invention, the content of the charge stabilizer is preferably 0.1 to 30% by weight in the polymer fiber.

  The method for producing an electret filter medium of the present invention includes a step of preparing an organic solution containing a polymer fiber containing a charge stabilizer and an organic solvent, and a step of spinning the organic solution using a charged spinning method. Is preferred.

  The electret filter medium of the present invention is excellent in filter performance by using polymer fibers having an average fiber diameter of 0.001 to 1 μm spun by the charge spinning method. In addition, by containing a charge stabilizer, the charge can be stably held for a long time. Further, when a large amount of charge stabilizer is contained, the polymer fiber is usually not thinned. However, in the present invention, the reason is not clear, but the polymer fiber contains a large amount of 0.1 to 30% by weight of the charge stabilizer. Nevertheless, the synergistic effect with the charged spinning method can reduce the average fiber diameter of the polymer fibers, improve the filter performance, and is extremely effective.

  As the method for producing the electret filter medium of the present invention, for example, after dissolving a polymer constituting a polymer fiber in an organic solvent, an organic solution in which a charge stabilizer is dissolved is prepared. And a method of producing an electret filter medium by spinning using a charged spinning method. Hereinafter, specific raw materials used and production methods will be described.

  Moreover, in order for the electret filter material of this invention to obtain high filter performance, it is a preferable aspect to use the electret nonwoven fabric which uses a polymer fiber.

  The polymer used in the present invention is not particularly limited as long as it retains high electrostatic permanent chargeability. For example, polyethylene, polypropylene, polystyrene, poly-4 methyl-1 pentene, poly-3 methyl-1 butene, polyphenyl sulfide, polyether I-terketone, polyether sulfone, polyarylate, polyamideimide, polyetherimide, polyimide , Polybenzoxazole, polysulfone, polyarylate, polybutylene terephthalate, polycarbonate, wholly aromatic polyester, polytetrafluoroethylene, chlorotrifluoroethylene-ethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene Tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro And alkyl vinyl ether copolymer, insulating organic fibers polyphenylene oxide and the like, alone product and biodegradable organic fibers such as polylactic acid having biodegradability can include mixtures thereof. In particular, polyamideimide, polycarbonate, and polylactic acid are preferable because of excellent charging characteristics. In particular, polyamide-imide is preferable because it is excellent in heat resistance, easily industrialized as an electret, and low in cost. Hereinafter, the polyamideimide will be described in detail.

  Polyamideimide is synthesized by an ordinary method such as an acid chloride method using trimellitic acid chloride and diamine or a diisocyanate method using trimellitic anhydride and diisocyanate, but the diisocyanate method is preferred from the viewpoint of production cost.

  The acid component used for the synthesis of polyamideimide is trimellitic anhydride or trimellitic chloride, but part of it can be replaced with other polybasic acid or anhydride or acid chloride. For example, tetracarboxylic acids such as pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenylethertetracarboxylic acid, ethylene glycol bistrimellitate, propylene glycol bistrimellitate and their anhydrides or Aliphatic dicarboxylic acids such as acid chloride, oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4′-dicyclohexylmethanedicarboxylic acid, dimer acid and other alicyclic dicarboxylic acids, Tal acid, isophthalic acid, diphenyl sulfone dicarboxylic acid, diphenylether dicarboxylic acid, and aromatic dicarboxylic acids such as naphthalene dicarboxylic acid.

  In addition, a part of the trimellitic acid compound can be replaced with glycol. Examples of glycols include alkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, and hexanediol, polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and one or two of the above dicarboxylic acids. Examples thereof include polyesters having terminal hydroxyl groups synthesized from the above and one or more of the above glycols.

  Examples of the diamine component used for the synthesis of polyamideimide include aliphatic diamines such as ethylenediamine, propylenediamine, and hexamethylenediamine, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, isophoronediamine, and 4,4′-dicyclohexylmethane. Alicyclic diamines such as diamine, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, benzidine, o-tolidine, 2 , 4-tolylenediamine, 2,6-tolylenediamine, aromatic diamines such as xylylenediamine, and diisocyanates thereof. Among these, 4,4'-diaminodiphenylmethane and o-tolidine are preferable from the viewpoint of reactivity and cost.

  Diisocyanate components used for the synthesis of polyamideimide include ethylene diisocyanate, propylene diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, m- Phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, benzidine, o-tolidine diisocyanate compounds, 2,4-tolylene diisocyanate 2,6-tolylene diisocyanate, xylylene diisocyanate and the like. Among these, 4,4'-diphenylmethane and o-tolidine diisocyanate compounds are preferable from the viewpoint of reactivity and cost.

  Solvents used for polymerization of polyamideimide include organic polar amide solvents such as N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, N-methylcaprolactam Water-soluble ether compounds such as tetrahydrofuran and dioxane, water-soluble ketone compounds such as acetone and methyl ethyl ketone, and water-soluble nitrile compounds such as acetonitrile and propionitrile. These solvents can be used as a mixed solvent of two or more, and are not particularly limited.

  In order to obtain polyamideimide, the amount of the diamine component used in the solvent is preferably 0.90 to 1.20, more preferably 0.95 to 1.05, as a ratio to the number of moles of the acid component. is there. Outside this range, the polymerization of the polymer is difficult to proceed.

  In order to obtain polyamideimide, the amount of the diisocyanate component used in the solvent is preferably 0.90 to 1.20, more preferably 0.95 to 1.20 as a ratio to the number of moles of the acid component. 05. Outside this range, the polymerization of the polymer is difficult to proceed.

  As a polymerization condition of polyamideimide, it can be easily produced by stirring while heating to 60 to 200 ° C. in an inert gas atmosphere in the above solvent. As necessary, amines such as triethylamine, diethylenetriamine, 1,8-diazabicyclo [5,4,0] -7-undecene (DBU), alkalis such as sodium fluoride, potassium fluoride, cesium fluoride, sodium methoxide A metal salt or the like can also be used as a catalyst. These may be used as a mixture of two or more, and are not particularly limited.

  The polymer concentration in the organic solution in which polyamideimide is dissolved is 0.1 to 30% by weight, particularly preferably 1 to 20% by weight as the solid content concentration. If the concentration of polyamideimide is less than 0.1% by weight, it is not preferable because the concentration is too low, making it difficult to form a nonwoven fabric. On the other hand, if it is larger than 30% by weight, the fiber diameter of the resulting non-woven fabric increases, which is not preferable.

  The organic solvent for forming the polyamideimide solution is not particularly limited as long as the polyamideimide is dissolved within the above concentration. In addition, when spinning, it is possible to use the polymerized solution in which the polyamideimide is produced as it is, and using a poor polymer solvent, the polyamideimide is precipitated, washed, and purified, and then the polymer is a good solvent. It is also possible to redissolve and use as a solution. When there is no problem in the obtained polyamideimide fiber, it is preferable to use the polymerization solvent as it is during spinning.

  Examples of the poor solvent used for precipitation of the polymer include acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dioxane, propanol, carbon tetrachloride, cyclohexane, and cyclohexanone. Volatile solvents such as methylene chloride, phenol, pyridine, trichloroethane, acetic acid, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N, N-dimethylacetamide (DMAc), 1-methyl- 2-pyrrolidone (NMP), ethylene carbonate, propylene carbonate, dimethyl carbonate, acetonitrile, N-methylmorpholine-N-oxide, butylene carbonate, γ-butyrolactone, diethyl -Bonate, diethyl ether, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dioxolane, ethyl methyl carbonate, methyl formate, 3-methyl oxazolidine-2-one, methyl propio Examples thereof include solvents having relatively low volatility such as nate, 2-methyltetrahydrofuran and sulfolane. Alternatively, it is possible to use a mixture of two or more of the above solvents.

  The polymer fibers constituting the electret nonwoven fabric of the present invention are formed from fibers having an average fiber diameter of 0.001 to 1 μm. When the average fiber diameter is smaller than 0.001 μm, the self-supporting property is poor, and problems such as a decrease in strength and a decrease in handling property occur, which is not preferable. On the other hand, if the average fiber diameter is larger than 1 μm, the surface area becomes small, which is not preferable. A more preferable average fiber diameter is 0.005 to 0.8 μm, and a particularly preferable average fiber diameter is 0.01 to 0.5 μm.

  The charge stabilizer used in the electret filter medium of the present invention is a hindered amine-based, nitrogen-containing hindered phenol-based, metal salt hindered phenol-based, phenol-based, hindered phenol-based, phenol-based sulfur weathering imparting agent, fatty acid metal salt It is preferably at least one selected from the group consisting of Use of these charge stabilizers is effective because the electretization can be stabilized during charge spinning and the fiber diameter can be reduced. Specifically, details will be described below.

  In the case of hindered amines as charge stabilizers, poly [{(6- (1,1,3,3, -tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) {(2,2 , 6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}} (Cimasorb 944LD under the trade name of Ciba Geigy), dimethyl succinate 1-hydroxyethyl] -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (Tinubin 622LD under the trade name of Ciba Geigy), 2- (3,5-di-t-butyl-4-hydroxy Benzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (Ciba Geigy's trade name Tinuvin 144) and the like.

  In the nitrogen-containing hindered phenol, 1,3,5-tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid (Nippon Cyanamide Co., Ltd., trade name Cyanox 1790) or 1,3,5 5-tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanuric acid (IR3114 under the trade name of Ciba Geigy) and the like.

  In the metal salt hindered phenol, 3,5-di-t-butyl-4-hydroxy-benzil-mono-ethyl-phosphonate calcium (IR1425WL), 3,5-di-t-butyl-4-hydroxy-benzyl- Examples thereof include nickel of mono-ethyl-phosphonate (Irgastave 2002 under the trade name of Ciba Geigy) or magnesium salt of the same compound.

  In the case of hindered phenols, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Irganox 1010, manufactured by Ciba Geigy), octadecyl-3- (3,5-di -T-butyl-4-hydroxyphenyl) propionate (Irganox 1076, manufactured by Ciba Geigy), tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate (Irganox 3114, manufactured by Ciba Geigy), 3 , 9-bis- {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) -propionyloxy] -1,1-dimethylethyl} -2,4,8,10-tetraoxa Spiro- [5,5] undecane (Sumilyzer GA-80, manufactured by Sumitomo Chemical Co., Ltd.) .

  In the phenol type, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxyl) benzene (IR1330 under the trade name of Ciba Geigy), pentaerythrityl-tetrakis [ 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (IR1010 under the trade name of Ciba Geigy) and the like.

  In the case of hindered phenols, 2,6-di-t-butyl-4-methylphenol (Sumilyzer BHT), n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) Propionate, 2,2'-methylene-bis- (4-methyl-6-tert-butylphenol), 2-t-butyl-6- (3'-tert-butyl-5'-methyl-2'-hydroxybenzyl) -4-methylphenyl acrylate, 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, tetrakis- [methylene-3- (3 ', 5'-di -T-butyl-4'-hydroxyphenyl) propionate] -methane (Sumilyzer BP-101), 3,9-bis- [2-3- (3-t-butyl-4-hydroxy-5 Methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-spiro [5,5] undecane.

  In addition, as a charge stabilizer, phenolic sulfur weathering imparting agents include dilauryl thiodipropionate (DLTDP), dimyristyl thiodipropionate, distearyl thiodipropionate (DSTDP), pentaerythritol-tetrakis. -((Beta) -lauryl thiopropionate), 2-mercaptobenzimidazole, etc. are mentioned.

  Although it does not necessarily limit about a fatty acid metal salt as a charge stabilizer, What has a linear fatty acid group is preferable. The fatty acid group preferably has 10 to 20 carbon atoms. Specific examples include aluminum laurate, aluminum myristate, aluminum palmitate, aluminum stearate, magnesium laurate, magnesium myristate, magnesium palmitate, and magnesium stearate, particularly preferably aluminum stearate. .

  In the present invention, the polymer fiber preferably contains at least one selected from the charge stabilizers in an amount of 0.1 to 30% by weight, more preferably 0.3 to 10% by weight, still more preferably. 0.5 to 2% by weight. If it is less than 0.1% by weight, the electretization effect is not sufficient, and if it exceeds 30% by weight, the content is large and there is a possibility of bleeding out.

  In the present invention, additives such as inorganic or organic fillers may be blended for the purpose of improving various properties of the electret nonwoven fabric obtained by spinning. In the case of an additive having a low affinity for polyamideimide, the size is preferably smaller than the diameter of the resulting polyamideimide fiber. If it is large, the additive precipitates during charge spinning, causing thread breakage. As a method of blending the additive, for example, there are a method of adding a necessary amount of the additive in the reaction system of the polyamideimide polymerization in advance and a method of adding the necessary amount of the additive after the reaction of the polyamideimide polymerization is completed. Can be mentioned. In the case of an additive that does not inhibit polymerization, the former is preferable because a nonwoven fabric in which the additive is uniformly dispersed can be obtained.

  In the case of a method in which a necessary amount of additive is added after completion of the polymerization reaction of polyamideimide, ultrasonic stirring, mechanical forced stirring using a homogenizer, or the like is used.

  As a method for producing an electret nonwoven fabric using the polymer fiber of the present invention, a charged spinning method is used in which fibers having an average fiber diameter of 0.001 to 1 μm are obtained. Hereinafter, a method for producing an electret nonwoven fabric by the charge spinning method will be described in detail.

  The charged spinning method used in the present invention is a kind of solution spinning. In general, a high positive voltage is applied to a polymer solution, and fiber formation is performed in the process of being sprayed on a grounded or negatively charged surface. It is a technique to wake you up. An example of the charge spinning apparatus is shown in FIG. In FIG. 1, a charged spinning device 1 is provided with a spinning nozzle 2 that discharges a polymer that is a raw material of a fiber, and a counter electrode 5 that faces the spinning nozzle 2. The counter electrode 5 is grounded. The polymer solution charged by applying a high voltage jumps out from the spinning nozzle 2 toward the counter electrode 5 and is fiberized at that time. Nonwoven fabric by discharging a solution in which polyamideimide is dissolved in an organic solvent into an electrostatic field formed between electrodes, spinning the solution toward a counter electrode, and accumulating the formed fibrous substance on a collection substrate Can be obtained. The term “nonwoven fabric” as used herein refers not only to the state where the solvent of the solution has already been distilled off to form a nonwoven fabric, but also to the state containing the solvent of the solution.

  In the case of a nonwoven fabric containing a solvent, the solvent is removed after the charged spinning. Examples of the method for removing the solvent include a method of immersing in a poor solvent and extracting the solvent, and a method of evaporating the residual solvent by heat treatment.

  The material of the solution tank 3 is not particularly limited as long as it is resistant to the organic solvent used. Further, the solution in the solution tank 3 can be discharged into the electric field by a mechanical push-out system, a pump-out system, or the like.

  The spinning nozzle 2 preferably has an inner diameter of about 0.1 to 3 mm. The nozzle material may be made of metal or non-metal. If the nozzle is made of metal, the nozzle can be used as one electrode. If the nozzle 2 is made of non-metal, an electric field is applied to the extruded solution by installing an electrode inside the nozzle. Can be made. In consideration of production efficiency, it is possible to use a plurality of nozzles. In general, a nozzle having a circular cross section is used, but a nozzle having an irregular cross section can be used depending on the type of polymer and intended use.

  As the counter electrode 5, various shapes of electrodes can be used depending on the application, such as a roll-shaped electrode shown in FIG. 1, a flat plate-like, or a belt-like metal electrode.

  Moreover, although the description so far is a case where an electrode also serves as a substrate that collects fibers, by installing an object to be a substrate that collects between the electrodes, even if polyamideimide fibers are collected there Good. In this case, for example, continuous production is also possible by installing a belt-like substrate between the electrodes.

  Moreover, although it is common to form with a pair of electrodes, it is also possible to introduce a different electrode. It is also possible to perform spinning with a pair of electrodes, and to control the spinning state by controlling the electric field state with electrodes having different potentials introduced.

  Although the voltage application apparatus 4 is not specifically limited, A direct current high voltage generator can be used and a Van de Graf electromotive machine can also be used. The applied voltage is not particularly limited, but is generally 3 to 100 kV, preferably 5 to 50 kV, and more preferably 5 to 30 kV. Note that the polarity of the applied voltage may be either positive or negative.

  The distance between the electrodes depends on the charge amount, the nozzle size, the spinning solution flow rate, the spinning solution concentration, etc., but a distance of 5 to 20 cm is appropriate when it is 5 to 120 kV.

  The spinning atmosphere is generally performed in the air, but by performing charge spinning in a gas having a higher discharge starting voltage than air such as carbon dioxide, spinning at a low voltage is possible, such as corona discharge. It is also possible to prevent abnormal discharge. Further, when water is a poor solvent for the polymer, polymer precipitation may occur near the spinning nozzle. Therefore, in order to reduce the moisture in the air, it is preferable to carry out in the air that has passed through the drying unit.

  Next, the step of obtaining an electret nonwoven fabric made of polymer fibers accumulated on the collection substrate will be described. In the present invention, while spinning the solution toward the collection substrate, the solvent evaporates depending on conditions to form a fibrous material. At normal room temperature, the solvent completely evaporates until it is collected on the collection substrate. However, if the solvent evaporation is insufficient, the solvent may be drawn under reduced pressure. The fibers of the present invention are formed at the latest when collected on the collection substrate. Further, the temperature at which the spinning is performed depends on the evaporation behavior of the solvent and the viscosity of the spinning solution, but is usually 0 to 50 ° C. And a porous fiber is further accumulated on a collection board, and a nonwoven fabric is manufactured.

  If necessary, the electret nonwoven fabric of the present invention can be subjected to post-treatment so as to suit various applications. For example, a calendar process, a hydrophilic process, a water repellent process, a surfactant adhesion process, a pure water washing process, etc. for densification or adjusting the thickness accuracy can be performed.

  The electret nonwoven fabric used in the present invention can further improve the collection performance by performing further charging treatment. The method for the charge treatment is not particularly limited, and examples include charging by corona discharge, charging by electron beam irradiation, charging under a high electric field, charging by water collision by sufficient pressure, and the like.

The basis weight of the electret nonwoven fabric used in the present invention is determined according to the intended use and is not particularly limited, but is preferably 0.05 to 10 g / m ² , for example. The basis weight here is in accordance with JIS-L1085. If it is less than 0.05 g / m ² , the filter collection efficiency is low, which is not preferable. On the other hand, if it exceeds 10 g / m ² , the filter ventilation resistance becomes too high, which is not preferable.

  Although the thickness of the electret nonwoven fabric used for this invention is determined according to a use application and is not specifically limited, It is preferable that it is 1-100 micrometers, More preferably, it is 10-50 micrometers. When the thickness is less than 1 μm, the ventilation resistance is increased, which is not preferable. The thickness here is measured with a micrometer.

  The electret nonwoven fabric used in the present invention can constitute an electret filter medium in combination with a reinforcing base material. Examples of the reinforcing base material include, for example, a fabric (nonwoven fabric, woven fabric, knitted fabric), a film, a drum, a net, a flat plate, a belt, a conductive material made of metal, carbon, etc., or a nonconductive material made of an organic polymer. Can be used. The electret filter medium which combined the base material for reinforcement and a nonwoven fabric can be manufactured by forming the nonwoven fabric which consists of a polymer fiber on it.

  The nonwoven fabric of the reinforcing substrate is not particularly limited, and examples thereof include a thermal bond method, an airlaid method, a wet papermaking method, a spunbond method, and a melt blown method nonwoven fabric. In particular, it is preferable to use a thermal bond method nonwoven fabric or a spun bond method nonwoven fabric.

  The fiber of the reinforcing nonwoven fabric is not particularly limited, but a short fiber and a long fiber made of a polymer such as polyolefin and polyester can be widely used, and also used as a core-sheath type composite fiber or a heterogeneous fiber mixture. be able to. In particular, a fiber mainly composed of a polyester fiber is a preferred embodiment because it has excellent pleatability.

  The use of the electret filter medium obtained by the present invention can be used for various air filter applications such as air cleaner filters, precision equipment filters, cabin filters for automobiles, trains, etc., engine filters, and building air conditioning filters. It is particularly suitable for air purification applications that require heat resistance, mechanical strength, and thermal dimensional stability.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Moreover, the evaluation items in the following examples were carried out by the following methods.

[Average fiber diameter]
A scanning electron micrograph (magnification of 10,000 times) of the surface of the obtained nonwoven fabric was taken, and an average value obtained by measuring the fiber diameter at n = 30 was calculated from the photograph.

[Evaluation of filter performance]
(Ventilation resistance)
A non-woven fabric sample was placed in the duct and controlled so that the linear velocity through the filter was 10 cm / second, and the difference in static pressure between the upstream and downstream of the filter was read with a pressure gauge.

(Particle collection efficiency)
The upstream and downstream sides of the filter were measured with a particle counter (KC01-C, manufactured by Rion Co., Ltd.) for the particle concentration of 0.3 to 0.5 μm when atmospheric dust was passed through the filter at 10 cm / sec. The collection efficiency was determined from the ratio of the particle concentration on the downstream side.

[Example 1]
A four-necked flask equipped with a thermometer, a cooling tube, and a nitrogen gas inlet tube contains 1 mol of trimellitic anhydride (TMA), 0.995 mol of diphenylmethane diisocyanate (MDI), and 0.01 mol of potassium fluoride in a solid content concentration. Was added together with N, N-dimethylacetamide so as to be 25%, heated to 90 ° C. and stirred for about 3 hours to synthesize polyamideimide.

To the obtained polyamideimide solution, 0.5% by weight of Irganox 1010 (manufactured by Ciba Specialty Chemicals) as a hindered phenol additive is added to the polyamideimide, and N, N-dimethylacetamide is further added to the solid content concentration. Was 8% by weight. Using the apparatus shown in FIG. 1, this polyamideimide solution is applied to a fibrous material collecting electrode 5 with a polyester nonwoven fabric having a basis weight of 80 g / m ² , a fiber diameter of 45 μm and a thickness of 0.2 mm, and discharged for 30 minutes. did. An 18G (inner diameter: 0.8 mm) needle was used for the spinning nozzle 2, the voltage was 15 kV, and the distance from the spinning nozzle 2 to the counter electrode 5 for collecting fibers was 10 cm.

  The average fiber diameter of the obtained electret nonwoven fabric was 73 nm. As a result of measuring the filter performance, the ventilation resistance was 4.7 mmAq, and the collection efficiency was 91.3%.

[Example 2]
Polyamideimide was synthesized in the same manner as in Example 1, and Irganox 1010 (manufactured by Ciba Specialty Chemicals) as a hindered amine additive was added to the obtained polyamideimide solution in an amount of 1.5% by weight based on the polyamideimide. N, N-dimethylacetamide was added so that the solid content concentration at the time of discharge was 10% by weight. This solution was discharged in the same manner as in Example 1, and the average fiber diameter of the obtained electret nonwoven fabric was 118 nm. As a result of measuring the filter performance, the ventilation resistance was 3.8 mmAq, and the collection efficiency was 90.2%.

[Example 3]
Polyamideimide was synthesized in the same manner as in Example 1, and 0.5% by weight of Chimasorb 944LD (manufactured by Ciba Geigy) as a hindered amine additive was added to the resulting polyamideimide solution with respect to the polyamideimide. N, N-dimethylacetamide was added so that the solid content concentration of was 8% by weight. When this solution was discharged in the same manner as in Example 1, the average fiber diameter of the obtained electret nonwoven fabric was 124 nm. As a result of measuring the filter performance, the ventilation resistance was 3.6 mmAq, and the collection efficiency was 89.8%.

[Example 4]
A polylactic acid resin Lacty 9800 (manufactured by Shimadzu Corporation) was mixed with 0.5% by weight of aluminum stearate and dissolved in acetone to adjust the solid content concentration to 8% by weight. When this solution was discharged in the same manner as in Example 1, the average fiber diameter of the obtained electret nonwoven fabric was 105 nm. As a result of measuring the filter performance, the ventilation resistance was 5.8 mmAq, and the collection efficiency was 90.0%.

[Comparative Example 1]
Polyamideimide was synthesized in the same manner as in Example 1, and N, N-dimethylacetamide was added so that the solid content concentration at the time of discharge was 8% by weight without adding an additive to the obtained polyamideimide solution. When this solution was discharged in the same manner as in Example 1, the average fiber diameter of the obtained nonwoven fabric was 264 nm. As a result of measuring the filter performance, the ventilation resistance was 7.6 mmAq, and the collection efficiency was 72.3%.

[Comparative Example 2]
Polyacrylonitrile powder was dissolved in N, N-dimethylformamide so as to be 10% by weight. When this solution was discharged similarly to Example 1, the average fiber diameter of the obtained electret nonwoven fabric was 242 nm. As a result of measuring the filter performance, the ventilation resistance was 8.7 mmAq, and the collection efficiency was 67.5%.

  As is clear from Table 1, in the examples, since the electret filter medium using the charge stabilizer and the ultrafine polymer fiber was used, it was confirmed that the air resistance and the collection efficiency were excellent. On the other hand, in Comparative Examples 1 and 2, since the charge stabilizer was not included, it was confirmed that the fiber diameter was large, the ventilation resistance was high, and the collection efficiency was low.

Schematic cross-sectional view of a charged spinning device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charge spinning apparatus 2 Spinning nozzle 3 Solution tank 4 High voltage power supply 5 Counter electrode (collection board)

Claims (5)

  An electret filter medium using a polymer fiber containing a charge stabilizer and having an average fiber diameter of 0.001 to 1 μm spun by a charge spinning method.   The charge stabilizer is selected from the group consisting of hindered amines, nitrogen-containing hindered phenols, metal salts, hindered phenols, phenols, hindered phenols, phenolic sulfur weathering agents, and fatty acid metal salts. The electret filter medium according to claim 1, which is at least one kind.   The electret filter medium according to claim 1 or 2, wherein the polymer fiber contains at least one polymer selected from the group consisting of polyamideimide, polylactic acid, and polycarbonate.   The electret filter medium according to any one of claims 1 to 3, wherein the content of the charge stabilizer is 0.1 to 30% by weight in the polymer fiber. Preparing an organic solution containing a polymer fiber containing a charge stabilizer and an organic solvent;
A method for producing an electret filter medium according to any one of claims 1 to 4, comprising a step of spinning the organic solution using a charged spinning method.

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