JP2008221073A - Superfine fiber filter medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter having high filter performance by using superfine fiber filter medium formed by laminating a superfine nonwovn fabric layer and reinforcing base material, by using charging treatment. <P>SOLUTION: The superfine fiber filter medium is formed by laminating the superfine nonwovn fabric layer consisting of polymer fiber spun by a charge spinning method with fiber diameters of 0.001-1 μm, and the reinforcing base material. An average fiber diameter of the surface of the superfine nonwovn fabric layer of the reinforcing base material is 5-50 μm, and a bending resistance by the Ghare method of the reinforcing base material is 150 mg or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrafine fiber filter medium in which an ultrafine nonwoven fabric layer made of polymer fibers spun by a charge spinning method and a reinforcing base material are laminated, and a method for producing the same.

  Conventionally, a charge-treated filter has been obtained by subjecting a polypropylene web produced by using a melt-blowing device to a charge treatment, or by opening a charge-treated polypropylene film. It is widely used in applications for filtering charged foreign particles, such as breathing masks, air filters for air purifiers, water filters, soundproofing materials, and heat insulating materials. In addition, for the purpose of improving the collection efficiency, it has also been proposed to make the fiber diameter or fiber width in the nonwoven fabric used for the filter have a specific distribution.

  However, since the fiber diameter or slit width of nonwoven fabrics so far has been several μm, when manufacturing a charged nonwoven fabric filter, the collection efficiency is generally increased by increasing the basis weight. However, when the basis weight is increased, there is a problem that the thickness of the nonwoven fabric increases and the processability is lowered.

  In addition, because the fiber diameter and fiber width are large, the pore size of the filter is increased, physical collection such as interception and inertial collision does not contribute, and when dust is loaded, the electrostatic collection effect is reduced, There was a problem that collection efficiency fell.

  In recent years, nano-order fibers (nanofibers) having a fiber diameter of 1 μm or less have been widely studied. Examples of a method for producing an aggregate of fibers having a small fiber diameter include a composite spinning method, a high-speed spinning method, and a charged spinning method. Among them, the charged spinning method can be spun easily and with fewer man-hours than other methods. This applies a high voltage to a liquid (for example, a solution containing a polymer that forms a fiber, or a molten polymer) to charge the liquid, causing the liquid to move toward a counter electrode material, and forming a fiber. Is. Usually, the polymer forming the fiber is spun out of the solution and forms the fiber until it is captured by the counter electrode material. Fiber formation can be accomplished, for example, by solvent evaporation when using a solution containing the polymer that forms the fiber, by cooling when using a molten polymer, or by chemical curing (with curing steam). Process). The obtained fiber is collected on a collector arranged as necessary, and if necessary, it can be peeled off from the collector and used as a fiber aggregate. In addition, since it is possible to directly obtain an aggregate of non-woven fibers, there is no need to form an aggregate of fibers after spinning the fibers, and the operation is simple (see, for example, Patent Documents 1 to 3). ).

  Patent Document 4 discloses an ultrafine fiber aggregate layer having an average fiber diameter of 0.01 μm or more and less than 0.5 μm, and a fine fiber having an average fiber diameter of 0.5 μm or more and 5 μm or less. A filter medium characterized by comprising a fiber assembly layer has been proposed. However, since the filter medium is an aggregate of fine fibers, it does not have sufficient strength to hold the pleats when pleated, and a further reinforcing layer must be laminated to improve the strength. was there.

Japanese Patent Publication No. 48-1466 JP-A 63-145465 JP 2002-249966 A JP 2005-218909 A

  The present invention has been made in order to solve the above-described problems, and is highly effective by using a charge spinning method and using an ultrafine fiber filter medium in which an ultrafine nonwoven layer and a reinforcing substrate are laminated. An object is to provide an ultrafine fiber filter medium having filter performance and pleat strength.

  The present invention is an ultrafine fiber filter medium in which an ultrafine nonwoven fabric layer made of polymer fibers having an average fiber diameter of 0.001 to 1 μm spun by a charge spinning method and a reinforcing substrate are laminated, and the reinforcing substrate The material consists of a nonwoven fabric layer, the average fiber diameter of the nonwoven fabric layer on the surface of the ultrafine nonwoven fabric layer side of the reinforcing base material is 5 to 50 μm, and the Gurley stiffness of the reinforcing base material is 150 mg or more It is characterized by being.

The basis weight of the reinforcing base material used in the present invention is preferably 30 g / m ² or more.

  The method for producing an ultrafine fiber filter medium according to the present invention comprises a step of producing a polymer solution mainly comprising a polymer and an organic solvent, and the polymer polymer solution is spun using a charged spinning method. A step of collecting a polymer fiber having an average fiber diameter of 0.001 to 1 μm obtained by the spinning step on a collection substrate to form an ultrafine nonwoven fabric layer, and the ultrafine nonwoven fabric layer and a reinforcing substrate. The nonwoven fabric layer that is the reinforcing base material has an average fiber diameter of 5 to 50 μm, and the reinforcing base material has a Gurley stiffness of 150 mg or more. It is characterized by.

  In the step of laminating the ultrafine nonwoven fabric layer and the reinforcing base material of the present invention, it is preferable that the polymer solution is spun onto the reinforcing base material using a charge spinning method and laminated.

The basis weight of the reinforcing base material used in the method for producing an ultrafine fiber filter material of the present invention is preferably 30 g / m ² or more.

The ultrafine fiber filter medium of the present invention has an ultrafine nonwoven fabric layer made of polymer fibers having an average fiber diameter of 0.001 to 1 μm, and the average fiber diameter of the reinforcing substrate on the surface side of the ultrafine nonwoven fabric layer is 5 to 50 μm. In addition, since the Gurley bending resistance of the reinforcing base material is 150 mg or more, it has a very large surface area and is excellent in filtration performance, heat resistance, mechanical properties, and thermal dimensional stability. Moreover, since the basis weight of the reinforcing base material is 30 g / m ² or more, there is no large void, which is excellent in terms of filtration performance and strength. Furthermore, by using the method for producing an ultrafine fiber filter medium of the present invention, an ultrafine fiber filter medium excellent in filtration performance, heat resistance, mechanical properties, and thermal dimensional stability can be obtained and useful.

  The high molecular polymer constituting the ultrafine nonwoven fabric used in the present invention is not particularly limited as long as it retains high static permanent chargeability by charge treatment. 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 Alkyl vinyl ether copolymer or a mixture thereof is used. In order to increase the thermal stability of the charge after the charge treatment and also to increase the thermal dimensional stability in the production and use environment, the high molecular polymer used has a high melting point or has a melting point. Those that do not are preferred. One preferred example is polyamideimide. 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. .

  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 1.05 as a ratio to the number of moles of the acid component. It is.

  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.

  The polymer concentration in the polyamideimide solution is 0.1 to 30% by weight, particularly preferably 1 to 25% by weight, as the solid content concentration.

  In the present invention, additives such as inorganic or organic fillers may be blended for the purpose of improving various properties of the ultrafine nonwoven fabric made of polymer fibers 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.

  The ultrafine nonwoven fabric made of the polymer fiber of the present invention is 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, when 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 basis weight of the ultra-fine nonwoven fabric made of the polymer fiber of the present invention is determined according to the intended use, and is not particularly limited, but is preferably 0.01 to 3.0 g / m ^2. . The basis weight here is in accordance with JIS-L1085. If it is less than 0.01 g / m ² , the filter collection efficiency is low, which is not preferable. If it exceeds 3.0 g / m ² , the filter ventilation resistance becomes too high, which is not preferable.

  The thickness of the ultra-fine nonwoven fabric made of the polymer fiber of the present invention is determined according to the intended use and is not particularly limited, but is preferably 1 to 100 μm. The thickness here is measured with a micrometer.

  As a method for producing an ultrafine nonwoven fabric made of the polymer fiber of the present invention, a charged spinning method is used, which is a method for obtaining fibers having an average fiber diameter of 0.001 to 1 μm. Hereinafter, a method for producing 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 act. 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 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.

  Next, the production method of the present invention by the charge spinning method using polyamideimide as the polymer will be described in detail.

  First, a solution in which polyamideimide is dissolved in an organic solvent is produced. The concentration of polyamideimide in the solution in the production method of the present invention is preferably 0.1 to 30% by weight. 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. A more preferable polymer concentration of the polyamideimide is 1 to 20% by weight.

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

  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 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.

Inhibition or dispersion of fiber diameter, in stabilizing the spinning conditions, the water content of the spinning environment space (absolute humidity) is preferably ^{2g / m 3 ~12g / m 3} .

  Next, the step of obtaining an ultrafine 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.

  The ultra-fine nonwoven fabric used in the present invention can remarkably improve the filter performance by being charged. 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. For example, an ultra-fine nonwoven fabric mainly composed of polyamideimide is electretized by these charging treatments, and the collection performance is greatly improved.

  If necessary, the ultrafine nonwoven fabric made of the polymer fiber of the present invention can be post-treated so as to be adapted to various uses. 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 ultrafine nonwoven fabric comprising the polymer fiber of the present invention constitutes an ultrafine fiber 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. By forming an ultrafine nonwoven fabric made of polymer fibers thereon, an ultrafine fiber filter medium combining a reinforcing substrate and an ultrafine nonwoven fabric can be created.

  As the fabric, a nonwoven fabric can be most suitably used from the economical viewpoint. It is desirable that the average fiber diameter constituting the nonwoven fabric of the reinforcing substrate has an average fiber diameter larger than the average fiber diameter of the non-woven fabric of the present invention that has been subjected to the charge treatment. The reinforcing non-woven fabric is effective for increasing the rigidity of the filter and preventing the deformation of the filter.

  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. 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 average fiber diameter of the nonwoven fabric on the surface side of the ultrafine nonwoven fabric constituting the reinforcing substrate used in the present invention is 5 to 50 μm, preferably 10 to 45 μm, more preferably 15 to 40 μm. If the thickness is less than 5 μm, the ventilation resistance increases, and if it exceeds 50 μm, the ultrafine fibers enter between the fibers of the reinforcing base material during charge spinning, so that the ultrafine fiber layer becomes uneven and does not become uniform, and voids are formed. As a result, the collection efficiency decreases. In addition, the average fiber diameter of the nonwoven fabric on the side opposite to the surface of the ultrafine nonwoven fabric is not particularly limited, but is preferably 20 to 100 μm.

  Moreover, the average fiber diameter of the reinforcing nonwoven fabric is desirably 1000 times or less, more desirably 700 times or less, and particularly desirably 500 times or less the average fiber diameter of the ultrafine nonwoven fabric. If the fiber diameter exceeds 1000 times, the ultrafine fibers may enter between the fibers of the reinforcing nonwoven fabric during spinning, making it difficult to obtain uniform ultrafine fibers.

The basis weight of the reinforcing substrate is preferably 30 g / m ² or more, more preferably 60 to 200 g / m ² . If the basis weight is less than 30 g / m ² , the waist strength at the time of pleating decreases, which is not preferable. The basis weight here is in accordance with JIS-L1085.

  The thickness of the reinforcing substrate is determined according to the intended use, and is not particularly limited, but is preferably 100 to 2000 μm. If it is less than 100 μm, the strength as a reinforcing material becomes insufficient, and if it exceeds 2000 μm, the structural ventilation resistance during pleating increases, which is not preferable.

  The Gurley method bending resistance of the reinforcing substrate of the present invention is 150 mg or more, preferably 200 to 10000 mg, more preferably 300 to 5000 mg. If it is less than 150 mg, the pleated shape cannot be maintained after pleating, which is not preferable. If it exceeds 10,000 mg, a load is applied to the filter medium during pleating, which is not preferable. The Gurley method bending resistance in the present invention means a value measured in accordance with JIS L-1096 A method (Gurley method).

  The step of laminating the ultrafine nonwoven fabric layer and the reinforcing substrate in the method for producing an ultrafine fiber filter material of the present invention comprises the steps of laminating a polymer solution on the reinforcing substrate using a charge spinning method on the reinforcing substrate. It is a preferred embodiment to spin and laminate. Specifically, for example, using the apparatus shown in FIG. 1, the reinforcing base material is wound around the collecting electrode 5, the polymer polymer solution is filled in the solution tank 3, and a high voltage is applied. Then, the ultrafine fibers are spun from the spinning nozzle 2 toward the collecting electrode 5, and the ultrafine fibers are deposited and laminated on the reinforcing base material wound around the collecting electrode 5.

  The use of the ultrafine fiber filter medium obtained by the present invention is processed into a filter medium single plate or a pleat shape, thereby providing a filter for an air purifier, a filter for precision equipment, a cabin filter for an automobile, a train, an engine filter, and a building air conditioner. It can be used for various air filter applications such as filters. It is particularly suitable for air purification applications that require heat resistance, mechanical strength, and thermal dimensional stability.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples. The evaluation items in each of the following experimental examples were carried out by the following methods.

[Average fiber diameter]
For the reinforcing substrate, the surface on the side in contact with the ultrafine fibers was photographed with a scanning electron microscope (SEM), and 20 fibers were randomly selected from the many fibers displayed in the SEM image, The fiber diameter was measured.
For the ultrafine fibers, SEM photography was performed on the laminated state with the reinforcing base material, 20 fibers were randomly selected from the many fibers displayed in the SEM image, and the fiber diameter was measured. The average value of the measured fiber diameters was calculated and used as the average fiber diameter.

[Bending softness]
It measured based on JIS L-1096 A method (Gurley method).

[Evaluation of filter performance]
(Ventilation resistance) A non-woven fabric sample was placed in a duct and controlled so that the linear velocity through the filter was 10 cm / second, and the static pressure difference between the upstream and downstream of the filter was read with a pressure gauge.
(Particle collection efficiency) The concentration of particles having a particle diameter of 0.3 to 0.5 μm when air dust is passed through the filter at 10 cm / second is measured upstream and downstream of the filter using a particle counter (KC01-C, manufactured by Lion Co., Ltd.). And the collection efficiency was determined from the ratio of the upstream and downstream particle concentrations.

[pierced]
The surface of the ultrafine fiber was observed with an SEM at a magnification of 1000 times, and it was observed whether there were voids in the ultrafine fiber.

[Pleated]
The ultrafine fiber filter medium was pleated using a reciprocating pleating machine at a folding height of 30 mm and a pleat setting temperature of 80 ° C. After pleating, it was left at room temperature for 30 minutes to observe whether the pleated shape was retained. “Holded here” means a state in which a pleat crease is attached and the mountain does not fall down even if the pleat is spread a little.

[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. N, N-dimethylacetamide was added to the obtained polyamideimide solution to make the solid content concentration 8% by weight. Using this apparatus shown in FIG. 1, this polyamideimide solution is applied to the fibrous material collecting electrode 5 with a polyester thermal bond having a basis weight of 100 g / m ² , a surface fiber diameter of 25 μm, a thickness of 0.2 mm, and a bending resistance of 1540 mg. A nonwoven fabric (reinforcing substrate) was attached, and the polyamideimide solution was discharged for 30 minutes. 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 nonwoven fabric was 127 nm. The weight per unit area was 3.2 g / m ² . As a result of measuring the filter performance, the ventilation resistance was 7.6 mmAq, and the collection efficiency was 91.8%. There was no perforation in the ultrafine fiber part, and the ultrafine fiber was present uniformly. The pleat workability was good, and the pleated shape after processing was firmly held.

[Example 2]
An ultrafine fiber filter medium in the same manner as in Experimental Example 1, except that a polyester resin bond nonwoven fabric having a basis weight of 64 g / m ² , a surface fiber diameter of 15 μm, a thickness of 0.6 mm, and a bending resistance of 2934 mg was used for the fibrous material collecting electrode 5. Was made.
The average fiber diameter of the obtained nonwoven fabric was 133 nm. As a result of measuring the filter performance, the ventilation resistance was 7.8 mmAq, and the collection efficiency was 93.1%. There was no perforation in the ultrafine fiber part, and the ultrafine fiber was present uniformly. The pleat workability was good, and the pleated shape after processing was firmly held.

[Example 3]
A polyester thermal bond nonwoven fabric having a weight per unit area of 80 g / m ² , a thickness of 0.3 mm, and a bending resistance of 933 mg comprising a layer structure of polyester fibers having an average fiber diameter of 25 μm and polyester fibers having an average fiber diameter of 40 μm is applied to the fibrous material collecting electrode 5. An ultrafine fiber filter medium was prepared in the same manner as in Experimental Example 1 except that the polyamideimide solution was discharged from the average fiber diameter of 25 μm.
The obtained ultrafine fibers had an average fiber diameter of 120 nm. As a result of measuring the filter performance, the ventilation resistance was 6.8 mmAq, and the collection efficiency was 91.9%. There was no perforation in the ultrafine fiber part, and the ultrafine fiber was present uniformly. The pleat workability was good, and the pleated shape after processing was firmly held.

[Example 4]
An ultrafine fiber filter medium in the same manner as in Experimental Example 1, except that a polyester thermal bond nonwoven fabric having a basis weight of 80 g / m ² , a surface fiber diameter of 40 μm, a thickness of 0.2 mm, and a bending resistance of 520 mg was used for the fibrous material collecting electrode 5. Was made.
The average fiber diameter of the obtained nonwoven fabric was 207 nm. As a result of measuring the filter performance, the ventilation resistance was 6.1 mmAq, and the collection efficiency was 90.9%. There was no perforation in the ultrafine fiber part, and the ultrafine fiber was present uniformly. The pleat workability was good, and the pleated shape after processing was firmly held.
[Comparative Example 1]
An ultrafine fiber filter medium in the same manner as in Experimental Example 1 except that a polyester thermal bond nonwoven fabric having a basis weight of 90 g / m ² , a surface fiber diameter of 63 μm, a thickness of 0.2 mm, and a bending resistance of 882 mg was used for the fibrous material collecting electrode 5. Was made.
The average fiber diameter of the obtained nonwoven fabric was 221 nm. As a result of measuring the filter performance, the ventilation resistance was 1.6 mmAq, and the collection efficiency was 50.9%. Many perforations were seen in the ultrafine fiber part. The pleat workability was good, and the pleated shape after processing was firmly held.

[Comparative Example 2]
Ultrafine fibers in the same manner as in Experimental Example 1 except that a polypropylene melt blown nonwoven fabric having a basis weight of 30 g / m ² , a surface fiber diameter of 8.5 μm, a thickness of 0.2 mm, and a bending resistance of 89 mg was used for the fibrous material collecting electrode 5. A filter medium was prepared.
The average fiber diameter of the obtained nonwoven fabric was 121 nm. As a result of measuring the filter performance, the ventilation resistance was 10.2 mmAq, and the collection efficiency was 92.5%. There was no perforation in the ultrafine fiber part, and the ultrafine fiber was present uniformly. Although the pleating process was performed, the pleated shape collapsed after the process and could not be used as a pleated filter.

  From the results of Table 1, in the examples, by using an ultra-fine nonwoven fabric layer and a reinforcing base material made of a predetermined polymer fiber, ultra-fine fibers having excellent ventilation resistance and collection efficiency and excellent pleatability without perforations. It was confirmed that a filter medium could be obtained. On the other hand, in Comparative Example 1, since the average fiber diameter of the reinforcing base material was larger than a predetermined value, perforation was observed, and a decrease in collection efficiency was observed. Moreover, in Comparative Example 2, since the bending resistance of the reinforcing base material was smaller than a predetermined value, it was confirmed that the pleated shape could not be maintained after pleating and the pleating property was inferior.

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 ultrafine fiber filter medium in which an ultrafine nonwoven fabric layer made of polymer fibers having an average fiber diameter of 0.001 to 1 μm spun by a charge spinning method and a reinforcing base material are laminated,
An ultrafine fiber filter medium having an average fiber diameter of 5 to 50 μm on the surface of the reinforcing base on the side of the ultrafine nonwoven fabric layer, and a Gurley stiffness of the reinforcing base of 150 mg or more. The ultrafine fiber filter medium according to claim 1, wherein the basis weight of the reinforcing substrate is 30 g / m ² or more. Producing a polymer solution mainly comprising a polymer and an organic solvent;
Spinning the polymer solution using a charged spinning method;
A step of collecting a polymer fiber having an average fiber diameter of 0.001 to 1 μm obtained by the spinning step on a collection substrate to form an ultrafine nonwoven fabric layer;
Laminating the ultrafine nonwoven fabric layer and the reinforcing substrate,
The average fiber diameter of the said base material for reinforcement is 5-50 micrometers, and the Gurley method bending resistance of the said base material for reinforcement is 150 mg or more, The manufacturing method of the ultrafine fiber filter characterized by the above-mentioned.   The ultrafine nonwoven fabric according to claim 3, wherein the step of laminating the ultrafine nonwoven fabric layer and the reinforcing base material comprises spinning and laminating the polymer solution on the reinforcing base material using a charge spinning method. A method for producing a fiber filter medium. The method for producing an ultrafine fiber filter medium according to claim 3 or 4, wherein the basis weight of the reinforcing substrate is 30 g / m ² or more.

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