JP2022045847A - Electret filter medium, filter, and production method of electret filter medium - Google Patents

Abstract

To provide an electret filter medium having high charging property, high collection efficiency and excellent oil mist resistance.SOLUTION: An electret filter medium made of a carrier carried with a fluorine-containing component has: a quality coefficient of 0.4 or more before 2-propanol vapor exposure test; a quality coefficient of 0.2 or more after 2-propanol vapor exposure test; and a ratio (after test/before test) of quality coefficients of 0.2-0.8 after and before 2-propanol vapor exposure tests, where, quality coefficient=-Ln((100-collection efficiency [%])/100)/pressure loss [mmAq].SELECTED DRAWING: None

Description

The present invention relates to an electret filter medium, a filter, and a method for manufacturing an electret filter medium.

Conventionally, a porous filter has been used to collect dust in a gas in a gas mask, various air conditioning filters, an air purifier filter, a cabin filter, and the like.

Among the porous filters, filters made of fibrous materials such as non-woven fabrics have high porosity, low pressure loss, and high dust collection performance, and are widely used. These fibrous filters capture particles on the fibers by mechanical collection mechanisms such as blocking, diffusion, and inertial collision, but the aerodynamic equivalent diameter of the particles captured in a practical usage environment is 0.1. It is known that the filter collection efficiency has a minimum value when the size is about 1.0 μm.

In order to improve the filter collection efficiency at the above-mentioned minimum value, a method of using an electric attractive force together is known. For example, a method of charging the collected particles, a method of charging the filter, or a combination of both is used. As a method of applying an electric charge to a filter, a method of arranging a filter between electrodes and performing dielectric polarization at the time of ventilation and a method of imparting a long-life electrostatic charge to an insulating material are known. In particular, the latter method is an external power supply or the like. It is widely used as an electret filter because it does not require the energy of.

The electret filter enhances the initial collection efficiency and suppresses the deterioration of performance due to the attenuation of electrostatic charge during filter processing and storage. Therefore, an electret filter medium that can be made into an electret and has excellent moisture resistance and heat stability is available. Used.

A method of adding various additives to improve the heat resistance stability of the electret filter medium is disclosed (for example, Patent Document 1), and a charge strengthening additive is disclosed in order to improve the electrostatic charge amount and the filter collection efficiency. Is known to increase the amount of charge at the time of contact with a liquid (for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 1-287914 Japanese Patent Publication No. 2011-522137

However, as examined by the present inventor, the surface tension of the electret filter medium increases when the charge-enhancing additive is mixed, and the fiber surface is thinly coated, especially when oil mist having a small surface tension is collected. It has been found to have the problem that the loss of charge is significantly promoted.

That is, these electret filters do not exhibit sufficient oil repellency as material properties for oil mists typified by various mineral oils, vegetable oils, polyα-olefins (PAOs), dioctyl phthalates (DOP), tobacco smoke and the like. Therefore, although the initial collection efficiency is high, the durability in the presence of oil mist (hereinafter referred to as "oil mist resistance") is low, and there is a problem that the collection efficiency decreases as the amount of oil mist adhered increases.

The present inventor has finally completed the present invention as a result of diligent research in order to solve the above problems. That is, the present invention is as follows.
1. 1. An electret filter medium composed of a carrier carrying a fluorine-containing component, the following quality coefficient value before the 2-propanol steam exposure test is 0.4 or more, and the following quality coefficient value after the 2-propanol steam exposure test is 0. An electlet filter medium having a value of 2 or more and a ratio of the following quality coefficient values (after test / before test) of 0.2 to 0.8 before and after the 2-propanol steam exposure test. Quality coefficient value = -Ln ((100-collection efficiency [%]) / 100) / pressure loss [mmAq]
2. 2. The electret filter medium according to 1 above, wherein the carrier carries 0.1 to 2.0 g / m ² of polytetrafluoroethylene as the fluorine-containing component.
3. 3. The electret filter medium according to 1 or 2 above, wherein the carrier is a meltblown nonwoven fabric made of a thermoplastic resin having a melting point of 320 ° C. or lower.
4. A filter using the electret filter medium according to any one of 1 to 3 above.
5. In the method for manufacturing an electret filter medium according to any one of 1 to 3 above.
A method for producing an electret filter medium, which comprises supporting the fluorine compound on the carrier and then forming it into an electret by liquid contact charging.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an electret filter medium and a filter having high chargeability and high collection efficiency and excellent oil mist resistance.

Hereinafter, embodiments of the present invention will be described, but the optimum configuration can be selected for each application in accordance with the gist of the present invention.

The electret filter medium of the present invention is an electret filter medium composed of a carrier carrying a fluorine-containing component, and the quality coefficient value before the 2-propanol steam exposure test is preferably 0.4 or more, more preferably 0.6 or more. preferable. More preferably, it is 0.8 or more, and most preferably 1.0 or more. If the quality coefficient value before the 2-propanol vapor exposure test is less than 0.4, there is a problem that the collection efficiency is low.

The quality coefficient value is calculated from the following formula using the collection efficiency (%) and pressure loss (mmAq) of atmospheric dust particles having a particle diameter of 0.3 μm at a filter medium passing linear velocity of 10.4 cm / s.
Quality coefficient value = -LN ((100-collection efficiency) / 100) / pressure loss

The electret filter medium of the present invention has a quality coefficient value of 0.2 or more after the 2-propanol steam exposure test, and the ratio of the quality coefficient values before and after the 2-propanol steam exposure test (after test / before test) is 0. It is preferably 2 to 0.8. If the quality coefficient value after the 2-propanol vapor exposure test is less than 0.2, or if the ratio of the quality coefficient values before and after the 2-propanol vapor exposure test (after test / before test) is less than 0.2, oil resistance resistance Not enough mist. 2-Propanol If the ratio of quality coefficient values before and after the vapor exposure test (after test / before test) is 0.8 or more, it is difficult to manufacture.

The electret filter medium of the present invention is preferably made of a porous dielectric sheet. Examples of the porous dielectric sheet include a fiber sheet (for example, a woven fabric, a knitted fabric, a non-woven fabric, and a composite thereof), a porous film (for example, a perforated film), a foam, or a composite thereof. However, it is not limited to these.

The electret filter medium of the present invention is preferably a nonwoven fabric produced by a spunbond method or a melt blow method. This is because these non-woven fabrics have a large fiber surface area, which improves the collection efficiency.

The electret filter medium of the present invention may be a single sheet or a plurality of laminated sheets. Further, in order to increase the sheet strength, a reinforcing material such as a thermal bond nonwoven fabric, a chemical bonded nonwoven fabric, or a net may be laminated.

The electret filter medium of the present invention may be composed of one kind or a plurality of kinds of materials, but it is preferable to contain at least one kind of materials having a volume resistivity of 10 ¹⁴ Ωcm or more from the viewpoint of charge retention. If the electret filter medium is made of only a material having a volume resistivity of less than 10 ¹⁴ Ω cm, it is difficult for electric charges to accumulate, it cannot be highly charged, and the collection efficiency is lowered. In addition, there arises a problem that the charge life becomes extremely short.

Specific materials of the electret filter medium of the present invention include polyolefin, polyester, polylactic acid, polycarbonate, polyvinyl chloride, polyvinylidene chloride and the like. Of these, polyolefins are preferable, and polypropylene and polymethylpentene are more preferable.

When the electret filter medium of the present invention is a spunbond or melt blown nonwoven fabric made of polypropylene, the basis weight is preferably 5 to 200 g / m ² , and more preferably 10 to 100 g / m ² . The average fiber diameter is preferably 1 to 30 μm.

Although not particularly specified, the electret filter medium of the present invention preferably contains a general polymer additive as a charge enhancer, and for example, a hindered amine-based or triazine-based stabilizer, a hindered phenol-based stabilizer, and a sulfur-based stabilizer. It is preferable that at least one additive among a stabilizer, a phosphorus-based stabilizer, a fatty acid metal salt, and a crystal nucleating agent is contained. By containing these additives, the chargeability of the electret filter medium is improved.

The hindered amine-based or triazine-based stabilizer is not particularly limited, but specifically, 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)] (BASF, Kimasorb® 944), 1,3,5-triazine-2,4,6-triamine, N, N'-1,2-ethangylbis [N- [3-[[ 4,6-bis [butyl (1,2,2,6,6-pentamethylpiperidine-4-yl) amino] -1,3,5-triazine-2-yl] amino] propyl] -N', N '-Dibutyl-N', N'-bis (1,2,2,6,6-pentamethyl (BASF, Kimasorb® 119), dimethyl-1- (2-hydroxyethyl) succinate-4 -Hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (BASF, Tinubin® 622), 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2 -Bis n-butylmalonate (1,2,2,6,6-pentamethyl-4-piperidyl) (BASF, tinubin® 144), dibutylamine 1,3,5-triazine N, Polycondensate of N'-bis (2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine · N- (2,2,6,6-tetramethyl-4-piperidyl) butylamine) , Kimasorb (registered trademark) 2020), 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5-((hexyl) oxy) -phenol (manufactured by BASF, tinubin (registered) Trademark) 1577)
And so on.

The above-mentioned hindered phenol-based stabilizer is not particularly limited, but specifically, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (BASF). Irganox® (registered trademark) 1010), octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (BASF, Irganox® 1076), Tris- (3, 5-di-t-butyl-4-hydroxybenzyl) -isocyanurate (BASF, Irganox® 3114), N, N'-hexane-1,6-zylbis (3- (3,5-) Di-t-butyl-4-hydroxyphenylpropionamide (BASF, Irganox® 1098), 2,6-di-t-butyl-4- (4,6-bis (octylthio) -1,3 , 5-Triazine-2-ylamino) phenol (BASF, Irganox® 565), 3,9-bis- {2- [3- (3-t-butyl-4-hydroxy-5-methyl) Phenyl) -propionyloxy] -1,1-dimethylethyl} -2,4,8,10-tetraoxaspiro- [5,5] undecane (Sumilyzer (registered trademark) GA-80, manufactured by Sumitomo Chemical Co., Ltd.), etc. Can be mentioned.

The sulfur-based stabilizer is not particularly limited, but specifically, di-lauryl-3,3-thiodipropionic acid ester (DLTDP), di-stearyl-3,3-thiodipropionic acid ester. (DSTDP) and the like.

The phosphorus-based stabilizer is not particularly limited, but specifically, Tris (2,4-di-t-butylphenyl) phosphite (manufactured by BASF, Irgafos (registered trademark) 168), di (). 2,6-di-t-butyl-4-methylphenyl) -pentaeristol-diphosfite (PEP-36, manufactured by Adeka Corporation), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10. -Oxide (manufactured by Sanko Co., Ltd., HCA) and the like can be mentioned.

The fatty acid metal salt is not particularly limited, but one having a linear fatty acid group is preferable. The fatty acid group preferably has 10 to 20 carbon atoms. Specific examples thereof include aluminum laurate, aluminum myristate, aluminum palmitate, aluminum stearate, magmusium laurate, magmusium myristate, magmusium palmitate, magmusium stearate and the like.

The crystal nucleating agent is not particularly limited, but specifically, sodium phosphate (4-t-butylphenyl) sodium (manufactured by Adeca, NA-10) and 2,2′-methylenebis phosphate (4). , 6-di-t-butylphenyl) sodium (manufactured by Adeca, NA-11), rosin-based crystal nucleating agent pine crystal KM-1500 (manufactured by Arakawa Chemical Co., Ltd.) and the like.

The content of the additive is 0.01 to 5 parts by weight, preferably 0.025 to 4 parts by weight, and more preferably 0.05 to 2 parts by weight with respect to 100 parts by weight of the porous dielectric sheet. Is. If the content is low, the electretization effect is not sufficient, and conversely, if the content is high, the effect is saturated and the cost increases, which is not preferable.

In the electret filter medium of the present invention, in order to impart oil mist resistance, a fluorine-containing component containing a fluorine atom is supported on the fiber surface at least a part of the surface of the electret filter medium. The fluorine-containing material comprises a fluorine-containing polymer obtained from a monomer component containing a fluorine-containing polycyclic compound, a fluorine-containing olefin, or a (meth) acrylate having a fluorine-containing side chain. Further, from the viewpoint of avoiding adverse effects on the environment and the human body, the fluorine-containing polymer and the fluorine-containing polycyclic compound have 8 or more carbon atoms and all hydrogen is replaced with carbon by hydrolysis. It is preferable that no fluorine telomer is generated.

As a state in which the fluorine-containing component is supported on the surface of the electret filter medium, specifically, when a substantially uniform coating layer is formed on the surface of the electret filter medium by the fluorine-containing material, the coating layer has irregularities and at least. When one is a fluorine-containing material, the coating layer has irregularities, and a case where both are fluorine-containing materials can be exemplified.

Specific examples of creating unevenness include (1) a filter medium before election, or a filter medium after electletization (hereinafter referred to as a carrier) in which a smooth fluorine-containing surface is obtained in advance and then a component that becomes a convex portion is attached. Method of forming unevenness by mixing two or more components having different melting points or glass transition temperatures and solubility in the coating solution, and (3) using the coating solution as an emulsion or suspension and melting point. Alternatively, a method of forming a smooth surface by heat-treating a component having a low glass transition temperature, (4) a method of forming a convex component on the carrier surface in advance and then attaching a solution, and (5) forming a convex component on the carrier surface in advance. After that, a method of adhering a component having a low melting point or a glass transition temperature and smoothing by heat treatment, (6) after surface-supporting an oxidation-resistant or spatter-resistant material from the carrier, the carrier side is etched. The method of doing so can be exemplified.

In the above, as a method for obtaining a smooth fluorine-containing surface in advance, (1) a method of mixing a fluorine-containing component with a resin component of the carrier, (2) a method of fluorinating the surface of the carrier with fluorine gas, (3). A method of fluorinating the surface of a carrier with fluorine plasma, (4) a method of obtaining a fluorine-containing resin layer on the surface of a carrier by surface polymerization, (5) a method of coating the surface of a carrier with a solution of a fluorine-containing component, (6) a method of coating a fluorine-containing component. A method of adhering the emulsion or suspension of the above to the surface of the carrier and then smoothing it by heat treatment, (7) a method of adhering the particulate matter of the fluorine-containing component to the surface of the carrier in the gas phase and then smoothing it by heat treatment. (8) A method of depositing a fluorine-containing component on the surface of a carrier to smooth it can be exemplified. Of these, the methods (5) to (8) above are preferable.

In the above, as a method of adhering the component to be a convex portion to the pre-processed fluorine-containing surface, (1) a method of applying an emulsion, a suspension or the like as a coating liquid, or (2) an emulsion, a suspension, a solution or the like is sprayed. Examples thereof include a method of spraying and atomizing, and (3) a method of depositing on the surface from steam or droplets by using evaporation or sublimation.

In the above, as a method of forming a convex portion in advance, (1) a method of using a carrier surface subjected to an etching treatment, and (2) two or more components are adhered to the carrier surface, and the solubility or vapor pressure is determined. A method of removing at least one component by a difference, (3) a method of mixing a convex component in advance with a resin component of a carrier, (4) a method of spraying an emulsion, a suspension, a solution or the like by spraying, and (5). Examples thereof include a method of depositing on the surface from steam or droplets by using evaporation, sublimation, or the like.

As a method for vapor deposition of the fluorine-containing component, a method is used in which vapor is generated by heating the fluorine-containing component with various heat sources and deposited as droplets or crystals on the surface of the carrier kept at a lower temperature. Such a method is preferably used regardless of whether it is a batch method in which the entire processed surface is processed at one time, or a method in which different processed surfaces of the carrier are continuously processed by moving the carrier or the reaction vessel. ..

The vapor deposition process in the present invention can be preferably carried out in any of pressure, normal pressure, reduced pressure, vacuum state and swing of the pressure, and atmosphere of the atmosphere and the inert gas. By reducing the pressure or setting the vacuum, it is possible to improve the transpiration rate and reduce the transpiration temperature, and pressurization can promote the precipitation of transpiration. Further, it is possible to suppress the oxidation of fluorine-containing components and carriers by using a vacuum or an inert atmosphere, but the present invention uses an atmospheric atmosphere in terms of cost because it can be treated at a low temperature below the thermal decomposition temperature. It is also possible.

From the viewpoint of charge stability and oil mist resistance, the fluorine-containing component is preferably not coated particles on the metal and the metal oxide, and the fluorine-containing component is not a mixture with the metal and the metal oxide. Is preferable. The content of the metal and the metal oxide is preferably 10% by mass or less, more preferably 5% by mass or less, and 0% by mass (totally containing the metal and the metal oxide) in 100% by mass of the fluorine-containing component. Not) is more preferable.

When a fluorine-containing component is produced on the surface of a metal or metal oxide using a fluorine-based coat layer, (1) it is difficult to uniformly coat the surface of the metal oxide, and oil mist resistance to fine droplets is exhibited. Among the compounds that utilize the reactivity with metals, (2) single linear compounds of C6 or less have room temperature viscosity, and the charge stability of the electret filter media and the adhesion and dispersion of particles are dispersed. There are problems such as inhibition of sex, (3) inferior reactivity to tobacco smoke and inferior hydrolysis resistance to acid / basic substances.

Further, the fluorine-containing component preferably contains or does not contain a small amount of a surfactant. Specifically, the content of the surfactant is preferably 25% by mass or less, more preferably 10% by mass or less, and 0% by mass (totally no surfactant) in 100% by mass of the fluorine-containing component. (Not included) is more preferable. Particles containing a surfactant exceeding the above range may impair the oil mist resistance and charge stability of the particles themselves and the substrate.

From the viewpoint of charge stability and oil repellency, the fluorine-containing polycyclic compound preferably has a fluorine substitution rate of 80% or more, more preferably 90% or more, and most preferably 95% or more. Further, from the viewpoint of charge stability and oil mist resistance, the fluorine-containing polycyclic compound preferably has a melting point of 40 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 80 ° C. or higher. It is most preferably 100 ° C. or higher. As a specific substance, fluorinated graphite, fluorinated fullerene, fluorinated carbon nanotubes and the like are preferable for a three-dimensional structure, and fluorinated graphene and the like are preferable for a planar structure.

The fluorine-containing polymer preferably has a melting point of 40 ° C. or higher or a glass transition temperature, more preferably 60 ° C. or higher, still more preferably 80 ° C. or higher, and most preferably 100 ° C. or higher. .. The reason for this is that it has the following effects. (1) Since the viscosity of the emulsion or suspension is reduced, the blocking of particles in the dispersion is reduced. (2) The fluidity of the fluorine-containing polymer is lowered, and the disappearance of electric charge due to the spread of the fluorine-containing polymer on the fiber after electret processing can be suppressed. (3) Since the molecular mobility of the fluorine-containing polymer is low, the fluorine-containing polymer itself is electretized, so that deterioration at the time of oil mist addition is further suppressed. (4) The rigidity and heat settability of the fiber are improved by processing the fluorine-containing polymer, and the pleated workability and wind resistance are excellent. (5) Blocking between filters and between filters and packaging materials during molding and storage is suppressed, and contamination of processing equipment and molds is reduced. For example, PTFE, FEP, PFA, ETFE, PCTFE, PVDF, THV, (meth) acrylic acid-based polymer having a perfluoro structure of C7 or less (preferably C6 or less) in at least the side chain, modification having solubility in a fluorine solvent. PTFE and the like can be exemplified.

In particular, in the case of a fluorine-containing (meth) acrylic acid-based polymer, in order to raise the glass transition temperature in the case of random polymerization, a halogen atom is introduced into the main chain of the polymer, or a rigid short-chain methyl methacrylate or tri. Crystalline is exhibited by using a copolymer with a monomer such as fluoromethylmethacrylate, a styrene-containing olefin having a large steric disorder, a dicyclopentenyl group-containing olefin, and a dicyclopentanyl group-containing olefin, and by introducing stereoregular polymerization. This is the preferred method.

Specific examples of the fluorine-containing (meth) acrylic acid-based polymer include (co) polymers containing a fluorine-containing olefin, and specific examples of the fluorine-containing (meth) acrylic acid include fluoroalkyl. Examples thereof include (co) polymers containing (meth) acrylates having a group in the side chain.

From the viewpoint of oil mist resistance, the fluorine-containing olefin preferably has a perfluoroalkyl group and / or a perfluoroalkylene group. The perfluoro group preferably has 1 or more and 7 or less carbon atoms, but more preferably has a perfluoroalkyl group having 4 to 6 carbon atoms at the end of the side chain. preferable. Further, the fluorine-containing (meth) acrylate preferably has a (meth) acrylic group in which a trifluoromethyl group is located at the end.

The fluorine-containing polymer may contain oxygen, silicon, nitrogen atoms and the like as a linking group, but more preferably has a structure consisting of only hydrogen, fluorine and carbon. With such a structure, since it does not have unpaired atoms and asymmetric polar components, surface tension and hygroscopicity are reduced, and as a result, oil mist resistance and chargeability are improved.

It is also preferable that the fluorine-containing polymer has one or more aromatic hydrocarbon groups and linear / branched / cyclic aliphatic hydrocarbon groups as a spacer with the main chain. Further, when α-chloro (meth) acrylate is used as the main chain, a chlorine atom having a large steric hindrance can be incorporated into the main chain, so that the polymer can be maintained at a high content ratio of the fluorine-containing monomer. It is possible to obtain a high glass transition temperature, and it is easy to improve charge stability and oil mist resistance.

When a monomer having a short-chain fluorine-containing alkyl group or a fluorine-containing alkylene group is used, a direct polymer having 12 to 30 carbon atoms is used as a monomer to be copolymerized with these fluorine-containing monomers in order to obtain a desired glass transition temperature or crystallinity. It is also preferable to use a (meth) acrylate having a chain aliphatic hydrocarbon group, for example, lauryl (meth) acrylate, myristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate. Can be mentioned. By using a (meth) acrylate having a long-chain aliphatic hydrocarbon group, in addition to enhancing the crystallinity of the side chain in the copolymer and contributing to the improvement of the glass transition temperature of the copolymer, in addition to contributing to the improvement of the glass transition temperature of the copolymer. Since the ester group is shielded and the molecular motility is reduced, the stability of chargeability is improved.

Further, as the monomer to be copolymerized with the fluorine-containing monomer, a (meth) acrylate having a branched aliphatic hydrocarbon group, a cyclic aliphatic hydrocarbon group, and an aromatic hydrocarbon group can also be used, which is specific. Examples include cycloalkyl groups such as cyclohexyl groups; polycyclic aliphatic hydrocarbon groups having 7 to 20 carbon atoms such as norbornyl group, bornyl group, isobornyl group and adamantyl group; phenyl group, naphthyl group, benzyl group and the like. It is a (meth) acrylate having an aromatic hydrocarbon group; Since these (meth) acrylates have a large steric hindrance, the melting point or the glass transition temperature becomes high, and further, the ester groups are shielded and the molecular motion is reduced, so that the stability of chargeability is improved. .. Examples of the (meth) acrylate include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, bornyl (meth) acrylate, adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyl (meth) acrylate. Examples thereof include tricyclodecanyl (meth) acrylate, phenyl (meth) acrylate, naphthyl (meth) acrylate, benzyl (meth) acrylate, and 2-t-butylphenyl (meth) acrylate.

Of these, more preferably dicyclopentanyl acrylate (glass transition temperature of homopolymer = 120 ° C.), dicyclopentanyl methacrylate (glass transition temperature of homopolymer = 175 ° C.), and isobornyl acrylate (glass transition of homopolymer). (Temperature = 94 ° C.), isobornyl methacrylate (glass transition temperature of homopolymer = 180 ° C.), and homopolymers having cyclic aliphatic hydrocarbon groups are more than homopolymers having linear aliphatic hydrocarbon groups. The glass transition temperature is remarkably high, and a high glass transition temperature can be obtained as a polymer while maintaining a high content ratio of the fluorine-containing monomer.

Further, as the monomer to be copolymerized with the fluorine-containing monomer, a halogen-free olefin having a branched aliphatic hydrocarbon group, a cyclic aliphatic hydrocarbon group, and an aromatic hydrocarbon group can also be used, for example, styrene. (Glass transition temperature of homopolymer = 100 ° C.) and the like can be mentioned. Since it has a large steric hindrance group called an aromatic ring and has only a hydrocarbon structure with few polar components, the glass transition temperature of the copolymer is increased and the hygroscopicity of the copolymer is also reduced, so that the copolymer is charged. Improves sexual stability.

As another monomer, a halogenated olefin, a functional group having a crosslinking property, an antioxidant action, and a non-fluorine-based monomer having a hindered phenol structure or a hindered amine structure that imparts charge stability can also be used. The halogenated olefin is preferably used as long as it has two or more carbon atoms, and examples thereof include vinyl chloride, vinyl bromide, vinyl iodide, vinylidene chloride, vinylidene bromide, and vinylidene iodide. Therefore, vinyl halide such as vinyl chloride (glass transition temperature of homopolymer = 87 ° C.) is preferably used in terms of improving the glass transition temperature.

The copolymerization ratio of the fluorine-containing monomer and the non-fluorine-based monomer is preferably in the range of 100: 0 to 10:90 in terms of molar ratio, more preferably 100: 0 to 20:80, and further preferably 100: 0. ~ 30: 70.

When the particles are attached to the surface to form uneven portions, it is preferable that fluorine-containing particles having a particle diameter of 0.1 nm or more and 500 nm or less are attached to the carrier. The particle size is more preferably 0.5 nm or more and 300 nm or less, further preferably 1 nm or more and 200 nm or less, and most preferably 2 nm or more and 100 nm or less. When the particle size is larger than 500 nm, it becomes difficult to achieve uniformity of the particle size at the time of dispersion, and the layer thickness of the coating tends to be excessive, which makes handling difficult. Further, since the floating oil mist to be collected is usually 500 nm or less, it is difficult to develop oil mist resistance due to unevenness. On the other hand, if the particle diameter is less than 0.1 nm, it is not suitable for coating applications in terms of solubility, melting point and vapor pressure, and oil mist resistance may be inferior.

In particular, in applications where the carrier is a fibrous material and breathability and filtration characteristics are required, the diameter ratio between the fibrous material and the particles is important, and the fiber diameter (fiber diameter) is divided by the particle diameter (particle diameter). The value (fiber diameter / particle diameter) is preferably 1 or more, more preferably 10 or more, and most preferably 100 or more. Further, it is generally known that the smaller the fiber diameter, the better the filtration characteristics (collection efficiency per unit aeration resistance), and the increase in the fiber diameter due to the coating layer is suppressed.

The methods for adjusting the particle size include (1) a method of adjusting the particle size at the time of polymerization by performing emulsion polymerization or suspension polymerization, and (2) crushing the fluorine-containing polymer by physical action such as impact and friction. (3) A method of dissolving a fluorine-containing polymer in a fluorine-based solvent, supercritical carbon dioxide, etc. and then spraying it onto a carrier to form particles, (4) a fluorine-based solvent, a fluorine-containing polymer in supercritical carbon dioxide, etc. After dissolving, a method of atomizing by reprecipitation by mixing with a poor solvent, (5) a method of heating to a temperature above the melting point and then spraying on a carrier, (6) a method of utilizing evaporation and condensation due to a change in pressure temperature. However, a preferable method can be used depending on the target particle size. In the case of particles obtained by emulsion polymerization, suspension polymerization, reprecipitation, etc., they may be attached to the carrier in a solid-liquid mixed state, or may be taken out as particles through a drying step. The fluorine-containing polymer can be produced by a known method using the above-mentioned monomers.

As a method of crushing by physical action, various wet or dry crushers can be used, and specific examples thereof include ball mills, bead mills, jet mills, homogenizers, etc., which are emulsified at the same time as crushing. It can also be suspended.

When dispersed in a liquid, water, a hydrocarbon-based organic solvent, a halogen-based organic solvent, or the like can be preferably used as the dispersion medium, and two or more kinds of dispersion media can be mixed and used. When an organic solvent is used as the dispersion medium, the permeability and the uniformity of the coating can be enhanced by the affinity with the resin component of the carrier. When water is used as the dispersion medium, various surfactants can also be used. Since the surfactant inhibits the development of oil mist resistance and charge stability, it is preferable to finally remove the surfactant from the fluorine-containing component and / or inactivate it, and as a method thereof, for example, , A method of evaporating the surfactant by heat treatment before or after adhesion to the carrier, a method of removing the surfactant from the fluorine-containing component by thermal decomposition or oxidative decomposition, an interface from the fluorine-containing component by washing with water or a solvent. A method of removing the activator, a method of sealing the ionic functional group with a transition metal ion or a reactive organic substance, or the like can be used. As a method for dispersing the fluorine-containing component without using a surfactant, it is preferable to use a fluorine-containing solvent as the dispersion medium.

As a method of atomizing by spraying, an airless type or a pneumatic type spray, an ultrasonic atomization type, a ruskin nozzle type, a collision type, an electrostatic spray type and the like can be exemplified. In this case, the particle size proportional to the solution concentration can be easily adjusted by using a solution or a suspension that has been atomized in advance. In particular, a method of spraying a solution or suspension is preferable as a method for obtaining monodisperse particles of 0.1 nm or more and 500 nm or less, and the particles may be adhered in a solution state, a semi-transpiration state, or a solidified state. do not have.

As a method of atomizing by evaporation, a method of vaporizing a fluorine-containing material by heating or depressurization and then depositing it directly on the surface of the carrier by cooling or pressurizing, or a method of atomizing in a gas and then adhering to the carrier. A method or the like can be used.

The present invention includes a step (gas phase method) of adhering a fluorine-containing component to a carrier using a gas phase in which a fluorine-containing component is dispersed. Adhering the particles to the carrier by the vapor phase method is preferable because it can be processed without using a surfactant and the particle collection characteristics of the carrier itself can be utilized.

In the electret filter medium of the present invention, at least one of the carrier and the fluorine-containing component is electretized, that is, electrostatically charged. The method of electretization is not particularly limited as long as it can obtain desired characteristics at the time of use, and may be before or after carrying the fluorine-containing component. In the former case, the fluorine-containing powder is attracted by electrostatic attraction, which has an advantage in adhesion and processing, and in the latter case, the electric line of force of the carrier is not shielded, so that the electret effect can be further exhibited. ..

The method of electretizing the electret filter medium in the present invention includes polarization by high voltage, collision of charged ions, method by electric action such as injection of charged particles, method by interaction with solid such as friction and collision, and contact with liquid. And a known method such as a method using collision can be preferably used. From the viewpoint of high chargeability and oil mist resistance, it is more preferable to use contact with a liquid or friction, and it is possible to electret without increasing polar oxidation products. It is more preferable from the viewpoint of oil mist resistance.

The method using contact with a liquid in the method for converting an electret filter medium into an electret is not particularly limited with respect to the liquid to be contacted. For example, water treated with a reverse osmosis membrane, a liquid obtained by adding a compound to the water, or the like is preferable. Additives to the liquid include metal oxide sol, sodium hydroxide, potassium hydroxide, hypochlorite, ammonia, ammonium salts, amines, carbonates, bicarbonates, carboxylic acids such as citric acid, and , The salt is mentioned. It should be noted that the surfactant and the organic solvent are contained in the aqueous solution because they not only enhance the permeability of the aqueous solution into the porous dielectric sheet but also form a film on the surface of the sheet and prevent the sheet from becoming highly charged. Should not be. The concentration of the additive is preferably 1 to 10000 ppm. When the concentration of the additive is within the above range, the porous dielectric sheet can be highly charged.

In the method of making the electret filter medium into an electret, when the porous dielectric sheet and the liquid are brought into contact with each other, the sheet is made into a mesh support having an air permeability of 50 to 400 cm ³ / cm ² / sec. It is preferable that the liquid is placed and the liquid is sprayed from above the liquid, and the lower part of the reticulated support is depressurized. The air permeability is measured using the Frangial type tester described in JIS-L1096. Regarding the contact of the aqueous solution with the porous dielectric sheet, a method other than injection may be used as long as the liquid can be brought into contact with the porous dielectric sheet at a pressure sufficient to pass through the porous dielectric sheet. For example, with respect to the porous dielectric sheet in contact with the liquid, the side opposite to the surface of the porous dielectric sheet in contact with the liquid may be in a reduced pressure state, and the liquid may be brought into contact with the porous dielectric sheet.

The net-like support is specifically a porous structure made of a woven fabric of metal yarn or plastic yarn, and examples thereof include woven shapes such as plain weave, twill weave, and satin weave. Metal materials include stainless steel and bronze, and plastic materials include polypropylene, polyester, polyurethane, nylon and polyphenylene sulfide.

The liquid is sprayed from a nozzle having a large number of orifices along the width direction of the sheet, which is installed several cm above the porous dielectric sheet, at a pressure sufficient for the liquid to pass through the sheet. The pressure sufficient to pass through is not specified, but depends on the basis weight of the porous dielectric sheet. For example, it is preferably 0.3 to 3 MPa for a sheet having a basis weight of 5 to 50 g / m ² , and 1 to 4 MPa for a sheet having a basis weight of 50 to 200 g / m ² . If the injection pressure is too high, pinholes will open in the porous dielectric sheet and the filtration performance will deteriorate. Further, if the liquid cannot sufficiently pass through the porous dielectric sheet due to the pressure being too low, the porous dielectric sheet cannot be highly charged.

The nozzles preferably have orifices having a diameter of 0.05 to 0.2 mm arranged in one row or a plurality of rows at a pitch of 0.5 to 3 mm. Further, for example, it is preferable that the reticulated support is movable and the porous dielectric sheet is conveyed in the longitudinal direction thereof so that the injection process can be continuously performed. The transport speed is not particularly limited, but a preferable range is 1 to 100 m / min. Further, the optimum number of injections and the treated surface (single-sided or double-sided) depend on the basis weight of the porous dielectric sheet and the average fiber diameter, and are not particularly limited.

Further, at the same time as the injection of the liquid, it is preferable to reduce the pressure below the net-like support by using an exhaust blower or the like. The suction negative pressure is not particularly limited, but 0.1 to 10 mAq is preferable. When the pressure is reduced, the liquid can sufficiently pass through the porous dielectric sheet, and the porous dielectric sheet can be highly charged.

As a drying method after the liquid injection treatment on the porous dielectric sheet, any conventionally known method can be used. For example, a hot air drying method, a vacuum drying method, a natural drying method, or the like can be applied. Of these, the hot air drying method is preferable because continuous treatment is possible. In the case of the hot air drying method, the drying temperature must be set to a temperature that does not cause the electret to disappear. It is preferably 120 ° C. or lower, more preferably 100 ° C. or lower, and even more preferably 80 ° C. or lower. Further, it is more preferable to remove excess liquid by a liquid absorbing roll, suction suction or the like as preliminary drying before hot air drying.

As a pretreatment for the porous dielectric sheet to be performed before the contact treatment with the liquid, it is preferable to perform a DC corona treatment. By performing the DC corona treatment, the surface layer portion of the sheet changes to be liquid-friendly, the contact property between the porous dielectric sheet and the liquid is improved, and the sheet can be highly charged.

The electret filter medium of the present invention can also be used in combination with layers such as a prefilter layer, a fiber protective layer, a functional fiber layer, and a reinforcing layer, if necessary. Examples of the pre-filter layer and the fiber protective layer include spunbonded non-woven fabric, thermal-bonded non-woven fabric, and urethane foam. Examples of the functional fiber layer include antibacterial, antiviral, colored fiber layers for the purpose of identification and design, and the like. Examples of the reinforcing layer include thermal bond non-woven fabrics and various nets.

The electret filter medium of the present invention can be widely used due to its functions such as dust collection, protection, ventilation, antifouling, and waterproofing. The electret filter medium of the present invention can be suitably used as, for example, a dustproof mask, various air conditioner elements, an air purifier, a cabin filter, and a filter for the purpose of protecting various devices, such as an air purifier and an air conditioner element. Can be preferably used for.

The filter of the present invention uses the electret filter medium of the present invention, and may be pleated or attached to a frame or the like, for example. Further, the filter of the present invention may be formed by combining the electret filter medium of the present invention with another material.

Hereinafter, the effects of the present invention will be shown more specifically by way of examples. The following examples do not have the property of limiting the present invention, and any design change according to the purpose of the above and the following is included in the technical scope of the present invention.

(Evaluation of filtration characteristics)
The pressure loss PD (mmAq) is obtained by installing an electret filter medium sample in the duct, controlling the filter medium passage line velocity to 10.4 cm / sec, and reading the static pressure difference between the upstream and downstream of the electret filter medium with a pressure gauge. I asked.

The particle collection efficiency E (%) was evaluated using a filter tester using atmospheric dust particles having an average particle diameter of 0.3 μm under the condition of an air volume of 10.4 cm / sec. The quality coefficient value QF (1 / mmAq) was calculated from the following formula using the pressure loss PD (mmAq) and the particle collection efficiency E (%).

QF = -Ln ((100-E) / 100) / PD

(Evaluation of average fiber diameter)
As an evaluation of the average fiber diameter, the fiber diameter was measured for 100 fibers enlarged by the SEM photograph, and the arithmetic mean value Dfs (μm) was obtained.

(2-Propanol vapor exposure test)
A sample after the 2-propanol vapor exposure test is prepared by placing 300 mL of 2-propanol 100 mL and an electret filter medium sample in a closed container (volume 10 L) and allowing the container to stand in an atmosphere at 25 ° C for 72 hours. did.

(Oil mist load test)
An aerosol of dioctylphthalic acid (DOP) having a median diameter of 0.15 to 0.25 μm was loaded in an amount of 1 g per 1 m ² of a non-woven fabric sample.

(Example 1)
Melt blow with a grain size of 18 g / m ² and an average fiber diameter (Dfs) of 2.7 μm using a resin containing 0.5 parts by weight of Irganox 1010 (manufactured by BASF) with 100 parts by weight of polypropylene resin of Melt Flow Index 700. The non-woven fabric was produced by a conventionally known method.
Next, after preparing a solution in which n-C ₁₈ F ₃₈ (melting point 149 ° C.) was dissolved in perfluorohexane, the above solution was immersed in the above-mentioned non-woven fabric and dried to make the fluorine compound non-woven fabric. The solid content of 0.30 g / m ² was adhered to the substrate to obtain a fluorine-containing component-supporting nonwoven fabric.
Then, the fluorine-containing component-supporting nonwoven fabric obtained above was placed on a silicon sheet having a thickness of 0.5 mm laid on the ground electrode of an aluminum flat plate, and a DC height of +15 kV was used using a needle-shaped electrode installed 1 cm above the nonwoven fabric. A voltage was applied for 10 seconds. Furthermore, the liquid is sprayed at a pressure of 1 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec. Was done. The liquid used is an aqueous solution obtained by adding potassium carbonate to high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment to a concentration of 100 ppm. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 2)
Melt blow with a basis weight of 30 g / m ² and an average fiber diameter (Dfs) of 2.3 μm using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) with 100 parts by weight of polypropylene resin of Melt Flow Index 700. The non-woven fabric was produced by a conventionally known method.
Next, after preparing a solution in which n-C ₁₈ F ₃₈ (melting point 149 ° C.) was dissolved in perfluorohexane, the above solution was immersed in the above-mentioned non-woven fabric and dried to make the fluorine compound non-woven fabric. The solid content of 0.30 g / m ² was adhered to the substrate to obtain a fluorine-containing component-supporting nonwoven fabric. After that, it was placed on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec, and a liquid was sprayed at a pressure of 1 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric. Was done. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 3)
Using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) and 0.1 part by weight of magnesium stearate with 100 parts by weight of polypropylene resin of Melt Flow Index 1300, the grain size is 25 g / m ² . , A melt-blown nonwoven fabric having an average fiber diameter (Dfs) of 1.4 μm was produced by a conventionally known method.
Next, after preparing a solution in which n-C ₁₈ F ₃₈ (melting point 149 ° C.) was dissolved in perfluorohexane, the above solution was immersed in the above-mentioned non-woven fabric and dried to make the fluorine compound non-woven fabric. The solid content of 0.30 g / m ² was adhered to the substrate to obtain a fluorine-containing component-supporting nonwoven fabric.
After that, it was placed on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec, and a liquid was sprayed at a pressure of 1 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric. Was done. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 4)
Using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) and 0.3 part by weight of magnesium stearate with respect to 100 parts by weight of polypropylene resin of Meltflow Index 700, the grain size is 15 g / m ² . , A melt-blown nonwoven fabric having an average fiber diameter (Dfs) of 1.7 μm was produced by a conventionally known method.
Next, the non-woven fabric obtained above was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. By installing a hot plate heated to 250 ° C on the bottom and evaporating n-C ₁₈ F ₃₈ (melting point 149 ° C) from the metal boat, the fluorine compound adheres to the non-woven fabric with a solid content of 0.30 g / m ² . I let you. After adhering, it was allowed to stand in an atmosphere of 60 ° C. for 15 minutes to obtain a fluorine-containing component-supporting nonwoven fabric.
After that, it was placed on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec, and a liquid was sprayed at a pressure of 1 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric. Was done. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 5)
Using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) and 0.3 part by weight of magnesium stearate with 100 parts by weight of polypropylene resin of Melt Flow Index 1300, the grain size is 30 g / m ² . , A melt-blown nonwoven fabric having an average fiber diameter (Dfs) of 0.95 μm was produced by a conventionally known method.
Next, the non-woven fabric obtained above was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. By installing a hot plate heated to 250 ° C on the bottom and evaporating n-C ₁₈ F ₃₈ (melting point 149 ° C) from the metal boat, the fluorine compound adheres to the non-woven fabric with a solid content of 0.30 g / m ² . I let you. After adhering, it was allowed to stand in an atmosphere of 60 ° C. for 15 minutes to obtain a fluorine-containing component-supporting nonwoven fabric.
After that, it was placed on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec, and the liquid was liquid at a pressure of 0.5 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric. Injection processing was performed. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 6)
Using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) and 0.3 part by weight of magnesium stearate with 100 parts by weight of polypropylene resin of Melt Flow Index 1300, the grain size is 18 g / m ² . , A melt-blown nonwoven fabric having an average fiber diameter (Dfs) of 1.8 μm was produced by a conventionally known method.
Next, the non-woven fabric obtained above was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. By installing a hot plate heated to 250 ° C on the bottom and evaporating n-C ₁₈ F ₃₈ (melting point 149 ° C) from the metal boat, the fluorine compound adheres to the non-woven fabric with a solid content of 0.30 g / m ² . I let you. After adhering, it was allowed to stand in an atmosphere of 60 ° C. for 15 minutes to obtain a fluorine-containing component-supporting nonwoven fabric.
Then, the fluorine-containing component-supporting nonwoven fabric obtained above was placed on a silicon sheet having a thickness of 0.5 mm laid on the ground electrode of an aluminum flat plate, and a DC height of +15 kV was used using a needle-shaped electrode installed 1 cm above the nonwoven fabric. A voltage was applied for 10 seconds to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 7)
Melt blow with a basis weight of 25 g / m ² and an average fiber diameter (Dfs) of 3.1 μm using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) with 100 parts by weight of polypropylene resin of melt flow index 100. The non-woven fabric was produced by a conventionally known method.
Next, the non-woven fabric obtained above was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. By installing a hot plate heated to 250 ° C on the bottom and evaporating n-C ₁₈ F ₃₈ (melting point 149 ° C) from the metal boat, the fluorine compound adheres to the non-woven fabric with a solid content of 0.30 g / m ² . I let you. After adhering, it was allowed to stand in an atmosphere of 60 ° C. for 15 minutes to obtain a fluorine-containing component-supporting nonwoven fabric.
After that, it was placed on a mesh support (96 mesh) with a draft of 120 cm ³ / cm ² / sec, and the liquid was liquid at a pressure of 0.5 MPa from a nozzle with a diameter of 0.1 mmφ and a pitch of 0.6 mm located 2 cm above the non-woven fabric. Injection processing was performed. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Example 8)
Flame-retardant round-section polyester short fiber containing phosphorus ("Heim" (registered trademark) manufactured by Toyobo Co., Ltd., fineness 1.7 dtex, fiber length 44 mm) and round-section polypropylene fiber (manufactured by Ube Nitto Kasei Co., Ltd., fineness 2) .2dtex, fiber length 51mm) was mixed and carded at a weight ratio of 1: 1 to prepare a mixed fiber web with a grain of 65g / m2, and a polypropylene spunbonded non-woven fabric of 15g / ^m2 (manufactured by Shinwa Co., Ltd., After laminating the fineness 5.5dtex), 3
High-pressure water of MPa was continuously sprayed and entangled, and at the same time, the oil agent was removed and dried to prepare a non-woven fabric.
Next, the non-woven fabric obtained above was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. By installing a hot plate heated to 250 ° C on the bottom and evaporating n-C ₁₈ F ₃₈ (melting point 149 ° C) from the metal boat, the fluorine compound adheres to the non-woven fabric with a solid content of 0.30 g / m ² . I let you. After adhering, it was allowed to stand in an atmosphere of 60 ° C. for 15 minutes to obtain a fluorine-containing component-supporting nonwoven fabric.
Then, two layers of fluorine-containing component-supporting nonwoven fabrics were laminated, needle punching was performed at a needle density of 50 lines / cm ² , and triboelectric charging and entanglement were simultaneously performed to obtain an electret filter medium having a total basis weight of 123 g / m ² . The temperature and humidity during the needle punching process were 27 ° C. and 55 RH%.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Comparative Example 1)
Melt blow with a basis weight of 18 g / m ² and an average fiber diameter (Dfs) of 2.0 μm using a resin containing 1.0 part by weight of Chimassorb 944 (manufactured by BASF) with 100 parts by weight of polypropylene resin of Melt Flow Index 700. The non-woven fabric was produced by a conventionally known method.
Next, the non-woven fabric obtained above is placed on a mesh support (96 mesh) having an air permeability of 120 cm ³ / cm ² / sec, and is placed 2 cm above the non-woven fabric from a nozzle having a diameter of 0.1 mmφ and a pitch of 0.6 mm. The liquid injection treatment was performed at a pressure of 1 MPa. The liquid used is high-purity water obtained by subjecting general tap water to a reverse osmosis membrane treatment and then an ion exchange membrane treatment. The transport speed of the net-like support was set to 4 m / min, and the lower part of the net-like support directly under the nozzle was set to a reduced pressure state of 2 mAq. This process was performed twice for each of the front and back sides of the sheet. Then, this sheet was allowed to stay in a hot air oven at 80 ° C. for 1 minute and dried to prepare an electret filter medium.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

(Comparative Example 2)
Flame-retardant round-section polyester staple fiber containing phosphorus (“Heim” (registered trademark) manufactured by Toyo Spinning Co., Ltd., fineness 1.7 dtex, fiber length 44 mm) and round-section polypropylene fiber (manufactured by Ube Nitto Kasei Co., Ltd., fineness 2) .2 dtex, fiber length 51 mm) was mixed and carded at a weight ratio of 1: 1 to prepare a mixed fiber web with a grain of 65 g / m ² and a polypropylene spunbonded non-woven fabric of 15 g / m ² (manufactured by Shinwa Co., Ltd.). , Fineness 5.5 dtex) was laminated, and then 3 MPa of high-pressure water was continuously sprayed to entangle them, and at the same time, the oil agent was removed and dried to prepare a non-woven fabric.
Next, three layers of the nonwoven fabric obtained above were laminated, needle punching was performed at a needle density of 50 lines / cm ² , and triboelectric charging and entanglement were simultaneously performed to obtain an electret filter medium having a total basis weight of 155 g / m ² . .. The temperature and humidity during the needle punching process were 23 ° C. and 46 RH%.
The obtained electret filter media was evaluated for filtration characteristics before and after the 2-propanol vapor exposure test, and for filtration characteristics after the oil load test. The results are shown in Table 1.

As can be seen from Table 1, in Examples 1 to 8, the quality coefficient value before the 2-propanol steam exposure test is 0.4 or more, and the quality coefficient value after the 2-propanol steam exposure test is 0.2 or more. Yes, and the ratio of the quality coefficient values before and after the 2-propanol steam exposure test (after test / before test) is 0.2 to 0.8, so the quality coefficient values before the test and after the oil test load are compared. Then, it did not decrease significantly after the test. On the other hand, in Comparative Examples 1 and 2, the quality coefficient value after the 2-propanol steam exposure test was less than 0.2, and the ratio of the quality coefficient values before and after the 2-propanol steam exposure test (post-test / pre-test). ) Is less than 0.2, and when comparing the quality coefficient values before the test and after the oil test load, it is significantly reduced after the test. It can be seen that Examples 1 to 8 have higher particle collection efficiency and are excellent in oil mist resistance as compared with Comparative Examples 1 and 2.

The electret filter medium of the present invention has a high particle collection efficiency despite low pressure loss and is excellent in oil mist resistance, so that it can be widely used in various filter applications and can greatly contribute to industry.

Claims (5)

An electret filter medium made of a carrier carrying a fluorine-containing component.
The following quality coefficient values before the 2-propanol vapor exposure test are 0.4 or more.
The following quality coefficient values after the 2-propanol vapor exposure test are 0.2 or more, and
2-propanol An electret filter medium characterized in that the ratio of the following quality coefficient values (after test / before test) before and after the vapor exposure test is 0.2 to 0.8.
Quality coefficient value = -Ln ((100-collection efficiency [%]) / 100) / pressure loss [mmAq] The electret filter medium according to claim 1, wherein the carrier carries 0.1 to 2.0 g / m ² of polytetrafluoroethylene as the fluorine-containing component. The electret filter medium according to claim 1 or 2, wherein the carrier is a meltblown nonwoven fabric made of a thermoplastic resin having a melting point of 320 ° C. or lower. A filter using the electret filter medium according to any one of claims 1 to 3. In the method for manufacturing an electret filter medium according to any one of claims 1 to 3.
A method for producing an electret filter medium, which comprises supporting the fluorine compound on the carrier and then forming it into an electret by liquid contact charging.