JP2017064684A - Electret filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electret filter suitable for filter use of requiring durability to tobacco smoke, in the present invention.SOLUTION: The present invention is an electret filter for carrying a fluorine-containing component on a fiber surface, and uses the electret filter provided so that in the particle collection efficiency of 0.3-0.5 μm in a wind speed of 5 cm/s, an initial QF value is 0.5 mmAqor more, and a filter degradation rate by a tobacco smoke load is -8/(g/m) or more.SELECTED DRAWING: None

Description

  The present invention relates to an electret filter.

  Conventionally, porous filters have been used for dust collection, protection, ventilation, and the like in dust masks, various air conditioning elements, air purifiers, cabin filters, and the like.

  Among porous filters, a fiber layer filter made of a fibrous material has a high porosity, has an advantage of long life and low ventilation resistance, and is widely used. In the fiber layer filter, particles are captured on the fiber by a mechanical collection mechanism such as contact adhesion, diffusion, inertial collision, and the like. These mechanisms vary depending on the physical properties of the particles, the fiber diameter, the passing air speed of the particles, etc., but in practical use environments, the filter particles are used when the aerodynamic equivalent diameter is about 0.1 to 1.0 μm. It is known that the collection efficiency is the lowest.

  In order to improve the efficiency of collecting particles with a filter with respect to particles having an aerodynamic equivalent diameter of about 0.1 to 1.0 μm, a method using electric attractive force in combination is known. For example, a method of applying a charge to particles to be collected, a method of applying a charge to a filter, or a combination of both methods are known. As a method for applying a charge to a filter, a method in which a filter is disposed between electrodes and dielectric polarization is performed during ventilation, and a method in which a long-life electrostatic charge is applied to an insulating material are known. In particular, in the latter case, energy such as an external power source is not required. Therefore, a filter containing such an insulating material is widely used as an electret filter.

  An electret filter is a commercial air conditioning element for controlling the concentration of suspended dust in an office building, a domestic air cleaner installed in a general home or small office, a local dust collector attached to a smoking room or amusement equipment, etc. Etc. are known as main applications.

  In particular, in household air purifiers, tobacco smoke having a particle size distribution that is difficult to collect with a fiber layer filter and having a high filter deterioration rate is used as a standard evaluation particle. This is defined in the Japan Electrical Manufacturers' Association standard JEM1467 (household air cleaner), the Chinese national standard GB / T-18801, and the CADR (Clean Air Delivery Rate) in the American Home Appliances Association (AHAM). For machine filters, improving the dust collection efficiency and durability of tobacco smoke is a major technical issue.

  According to the Japanese standard (JEM1467), the time when the dust collection performance (= collection efficiency x air volume) in model tests is halved compared to when not in use is regarded as the life, and the air volume is regarded as equivalent. In this case, suppressing the decrease in the collection efficiency against tobacco smoke greatly contributes to durability when used as an air cleaner.

  Up to now, a method for increasing the filtration area and reducing the amount of collected tobacco smoke per unit area of the filter, a method for increasing the filter layer and reducing the amount of collected tobacco smoke and improving the collection efficiency, and a finer finer Measures such as using a filter that exceeds 50% in terms of collection efficiency alone have been used. However, user and social demands such as large air volume, size saving, energy saving, noise reduction and long life are increasing, and it is becoming difficult to cope with the conventional technology.

  In addition, the electret filter has a drawback that the electrostatic attractive force is reduced as the particles are collected. Particularly, the oil mist having a small surface tension significantly accelerates the disappearance of charges by covering the fiber surface thinly. For general electret filters, polyolefin, polyester, polycarbonate, phenol resin, etc. with excellent charge stability are used. Among these, polyolefins such as polypropylene, polyethylene, polymethylpentene and the like having the smallest surface tension are used. The oil mist does not exhibit sufficient oil repellency as a material property for oil mists represented by poly alpha olefin (PAO), dioctyl phthalate (DOP) and tobacco smoke, etc. There is a problem that the collection efficiency maintenance performance under load (hereinafter referred to as “oil mist resistance”) is low.

In order to solve this problem, oil repellency is provided by lowering the surface tension of the fibrous material constituting the filter, and the loss of electric charge is suppressed by suppressing the spread of mist on the fiber surface and the absorption and diffusion into the fiber material. There is known a method for improving oil mist resistance by reducing the resistance. Specifically, in order to improve oil repellency, a method of mixing an additive having a perfluoro group in a resin (for example, Patent Document 1), a method of melt spinning a thermoplastic fluororesin (for example, Patent Document 2 and Patent Document) 3) A method of coating the surface with an emulsion processing agent having a perfluoro group (for example, Patent Document 4), a method of introducing fluorine atoms by replacing hydrogen atoms using plasma and fluorine gas (for example, Patent Documents) The electret which reduced surface tension and improved oil mist resistance while maintaining charge stability by 5) etc. is used.
Hereinafter, the reduction in surface tension as a material is referred to as “oil repellency”, and the effect of suppressing the decrease in efficiency against oil mist is referred to as “oil mist resistance”. The oil repellency referred to in the present invention means an effect of suppressing the spread of liquid by lowering the surface tension, and includes the action (water repellency) against water having a large surface tension value in view of the principle of wetting. It is what

  However, fluorinated resins and fluorinated low-molecular additives are not suitable for melt spinning in environments where the temperature exceeds 320 ° C. Unsuitable. In addition, when introducing fluorine atoms by fluorine gas or plasma treatment, it is necessary to strictly control oxygen and moisture amounts in order to prevent leakage of fluorine gas and to suppress hydrophilicity, and special equipment with high airtightness is required. In addition, due to bioaccumulation problems, the use of PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid) and salts thereof, and a parent substance that produces a telomer, and its production are prohibited. It is not preferable to add a hydrogen atom, to randomly generate fluorine-hydrogen substitution, or to cause thermal decomposition or oxidative decomposition.

  In addition, a method of coating polytetrafluoroethylene (PTFE) by sputtering is also known, but the flying particles are unevenly distributed on the outermost layer on the evaporation source side, and PTFE may be decomposed and oxidation products are generated. There is a risk.

In addition, fluorine-containing acrylate processing agents developed for textiles contain emulsifiers and film-forming aids, and short-chain perfluoro groups of C ₆ F ₁₃ or less are used as side chains to comply with PFOA and PFOS regulations. Because it is used, the processing agent loses crystallinity. For this reason, there is a problem that the processing agent itself does not have the stability of electrostatic charge but also significantly impairs the charge stability of the fibrous material as the base material even if the amount of adhesion is low.

JP 2009-6313 A JP 2002-266219 A Japanese Patent Laid-Open No. 2007-18895 JP 2004-352976 A Special table 2008-540856 gazette

  An object of the present invention is to provide an electret filter suitable for use in a filter requiring durability against tobacco smoke (for example, an air cleaner used in a house or vehicle, a smoking room, a dust collector in a game machine, etc.). .

As a result of intensive studies by the inventor, the inventor finally completed the electret filter of the present invention. That is, the present invention is as follows.
1. An electret filter in which a fluorine-containing component is supported on a fiber surface, and has an initial QF value of 0.5 mmAq ⁻¹ or more at a particle collection efficiency of 0.3 to 0.5 μm at a wind speed of 5 cm / s, and a tobacco smoke load The electret filter characterized by having a filter deterioration rate of -8 / (g / m ² ) or more.
2. 2. The electret filter as described in 1 above, wherein an effective fiber diameter of the fiber is 0.1 μm to 20 μm.

  In particular, it is possible to obtain a filter excellent in durability against cigarette smoke, which is suitable for use as an air purifier.

It is the graph which showed the relationship between tobacco smoke adhesion amount and a performance maintenance rate.

  Although the specific example of this invention is illustrated below, the optimal structure can be selected for every use according to the meaning of this invention.

  In the electret filter of the present invention, a fluorine-containing component is supported on the fiber surface, and fibers are used as a carrier. The electret filter of the present invention preferably includes a fiber layer made of fibers and fluorine-containing particles attached to the surface of the fiber layer.

(Fiber layer)
The constituent material of the fiber layer is not particularly limited as long as it has desired characteristics, but it is preferable to use a synthetic resin from the viewpoint of the degree of freedom in shape, and more preferably, a synthetic resin containing no fluorine is used. It is. Examples of synthetic resins not containing fluorine include polyesters, polycarbonates, polyamides, polyolefins, cyclic olefins, polyvinyl chloride, polyvinylidene chloride, and polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclic olefins. A material and a polystyrene material are preferable. By using these materials, the electrical resistance is high and the balance between hydrophobicity and moldability is good, and the collection efficiency of particles having a particle size of 0.3 to 0.5 μm (hereinafter simply referred to as collection efficiency). An electret filter excellent in practicality, that is, an electret filter excellent in practicality can be obtained.

  In order to further improve the durability against tobacco smoke, a synthetic resin containing a fluorine atom as a carrier can be used. For example, polytetrafluoroethylene, perfluoroethylene propene copolymer (FEP), perfluoroalkoxyalkane (PFA), ethylene Tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer (THV), etc. Is more preferably polytetrafluoroethylene, FEP, PFA, or ETFE.

  The fiber layer used in the present invention may be a woven fabric shape, a nonwoven fabric shape, a cotton shape, or the like obtained by molding a fibrous material obtained by a known technique into an appropriate shape and thickness according to the application, From the viewpoint of particle removal performance, a non-woven fiber layer is preferable. The method for forming the non-woven fiber layer is not particularly limited. For example, melt blown method, wet method, dry method, spunbond method, flash spinning method, electrospinning method, force spinning method, supersonic stretching method In the present invention, the melt blown method, the electrospinning method, the force spinning method, or the supersonic stretching is used because the nonwoven fabric obtained has a small fiber diameter and good collection efficiency. The method is preferably adopted. Further, from the viewpoint of not requiring treatment of the residual solvent, it is preferable to employ a melt blown method, a melt electrospinning method, a melt force spinning method, or a supersonic stretching method. The fiber layer may be molded from only one type of material, or may be molded using two or more types of materials.

  The effective fiber diameter of the fiber used in the present invention is preferably 0.1 to 20 μm, more preferably 0.15 to 15 μm, further preferably 0.2 to 10 μm, and 0.3 to It is particularly preferably 5 μm, and most preferably 0.5 to 3 μm. The effective fiber diameter of the fibers can be found in Davies, C .; N. , “The Separation of Arborne Dust and Particles”, Institution of Mechanical Engineers, London, Proceedings 1B, 1952. If the effective fiber diameter of the fiber is within the above range, the air ventilation resistance in the fiber layer can be reduced while increasing the collection efficiency. When the effective fiber diameter of the fiber is larger than 20 μm, the collection efficiency may be reduced, and the efficiency of various performances during charge decay is greatly reduced. In addition, when the effective fiber diameter of the fiber is smaller than 0.1 μm, the airflow resistance becomes too large when using an amount of fiber that maintains strength and uniformity, so a sirocco fan with a large air volume and a low static pressure. It becomes difficult to use for the air cleaner use sucked in.

  The cross-sectional shape of the fiber may be circular, or may be an odd-shaped cross-section such as an ellipse, a rectangle, a star, or a clover. With irregular cross-section fibers, the liquid whose contact angle with the fiber surface is 90 ° or less is absorbed into the fiber groove by capillary action, so that the entire fiber can be prevented from being covered with the liquid, and the electret degradation can be suppressed. can do.

  The fibrous material in the present invention may be a single product or a uniform product made of a material, or may be a mixture made of two or more materials having different methods, materials and fiber diameters.

  A known compounding agent may be added to the resin in order to suppress the deterioration of the resin itself and increase the charge stability in the fiber layer. Examples of the compounding agent include various metal salts, antioxidants, light stabilizers and the like. In addition, in order to suppress deterioration of the resin itself and increase charge stability in the fiber layer, the fiber layer may be formed using a plurality of different materials. For example, two or more different resin components may be formed. A compatible or incompatible blend polymer, ionomer, maleic acid-modified polyolefin, hindered phenol resin, hindered amine resin, or the like obtained by mixing can be used.

(Fluorine-containing component)
The electret filter of the present invention is characterized in that a fluorine-containing component containing a fluorine atom is supported on the fiber surface on at least a part of the fiber surface in order to impart water repellency and oil repellency. The fluorine-containing material is composed of a fluorine-containing polymer obtained from a monomer component containing a fluorine-containing polycyclic compound, or a fluorine-containing olefin or a (meth) acrylate having a fluorine-containing side chain. 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 a carbon number of 8 or more and all hydrogen is replaced with carbon by hydrolysis. It is preferable that no fluorine telomer is generated.

  As the state of supporting the fluorine-containing component on the fiber surface, specifically, a state in which a substantially uniform coating layer is formed on the fiber surface from the fluorine-containing material, the coating layer has irregularities, at least one of which is fluorine When it is a containing material, it has an unevenness | corrugation by a coating layer, and the case where both are fluorine containing materials can be illustrated.

  Specific examples of creating irregularities include (1) a method of attaching a component that becomes a convex portion after obtaining a smooth fluorine-containing surface in advance, (2) a melting point or glass transition temperature, and solubility of the coating solution. A method of mixing two or more different components to form unevenness due to a difference in solubility, (3) a method in which the coating liquid is an emulsion or suspension, and a component having a low melting point or glass transition temperature is smoothened by heat treatment, (4) A method in which a convex component is formed on the support surface in advance, and then the solution is attached. (5) After a convex component is formed on the support surface in advance, a component having a low melting point or glass transition temperature is attached and smoothed by heat treatment. And (6) a method of etching the carrier side after supporting an oxidation-resistant or sputter-resistant material on the surface of the carrier. That.

  In the above, methods for obtaining a smooth fluorine-containing surface in advance include (1) a method in which a fluorine-containing component is mixed with a carrier component, (2) a method in which the carrier is fluorinated with fluorine gas, and (3) a method in which fluorine plasma is used. A method of fluorinating the carrier, (4) a method of obtaining a fluorine-containing resin layer on the surface of the carrier by surface polymerization, (5) a method of coating the surface of the carrier with a solution of a fluorine-containing component, and (6) an emulsion or suspension of the fluorine-containing component. And then smoothing by heat treatment, (7) A method of making the particulate matter of the fluorine-containing component adhere in the gas phase and then smoothing by heat treatment, and (8) Evaporating and smoothing the fluorine-containing component The method of making it can be illustrated. Of these, the methods (5) to (8) are preferred.

  In the above, as a method of attaching the component to be a convex part to a pre-processed fluorine-containing plane, (1) a method of applying an emulsion, suspension, etc. as a coating liquid, (2) spraying the emulsion, suspension, solution, etc. Examples thereof include spraying and particle forming methods, and (3) a method of depositing on the surface from vapor or droplets using transpiration or sublimation.

  In the above, as a method for forming the convex portion in advance, (1) a method using etching treatment of the carrier, (2) two or more components are adhered, and at least one component is removed by a difference in solubility or vapor pressure. A method, (3) a method in which a convex component is mixed in advance with a resin component to be a carrier, (4) a method of spraying and granulating an emulsion, suspension, solution, etc., (5) using transpiration or sublimation, A method of depositing on the surface from vapor or droplets can be exemplified.

  As a method for vapor deposition of the fluorine-containing component, there is used a method 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 held at a lower temperature. Such a method is preferably used for either a batch method in which the entire processed surface is processed at once or a method in which different processed surfaces of the support are continuously processed by moving the support or the reaction vessel. .

The vapor deposition processing in the present invention can be preferably carried out in any atmosphere of pressurization, normal pressure, reduced pressure, vacuum state and pressure swing, air, and inert gas.
By setting it to a reduced pressure or vacuum state, it is possible to improve the transpiration rate and reduce the transpiration temperature, and it is possible to promote precipitation of transpiration by pressurization. Moreover, although it is possible to suppress the oxidation of a fluorine-containing component or a support by using a vacuum or an inert atmosphere, the present invention uses an air atmosphere in terms of cost because it can be processed 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 a particle coated with metal and metal oxide, and the fluorine-containing component is not a mixture with metal and metal oxide. Is preferred. In 100% by mass of the fluorine-containing component, the content of metal and metal oxide is preferably 10% by mass or less, more preferably 5% by mass or less, and 0% by mass (including metal and metal oxide at all). More preferred).

When a fluorine-containing component is produced using a fluorine-based coating layer on the surface of a metal or metal oxide, (1) it is difficult to uniformly coat the surface of the metal oxide and oil repellency with respect to fine droplets is exhibited. (2) Compounds that utilize reactivity with metals have a normal temperature viscosity in single linear compounds of C ₆ or less, and charge stability of electret filters and adhesion / dispersibility between particles (3) Reactivity to tobacco smoke and poor hydrolysis resistance to acid / basic substances arise.

  Further, the fluorine-containing component preferably contains a small amount of surfactant or no surfactant. Specifically, in 100% by mass of the fluorine-containing component, the content of the surfactant is preferably 25% by mass or less, more preferably 10% by mass or less, and 0% by mass (with the surfactant completely More preferably). Particles containing a surfactant exceeding the above range may impair the water / oil repellency and charge stability of the particles themselves and the substrate.

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

The fluorine-containing polymer preferably has a melting point or glass transition temperature of 40 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 80 ° C. or higher, and most preferably 100 ° C. or higher. . This is because it has the following effects. (1) Since the viscosity of the emulsion or suspension is reduced, blocking of particles in the dispersion is reduced. (2) The fluidity of the fluorine-containing polymer is lowered, and the loss 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 during addition of oil mist is further suppressed. (4) By processing the fluorine-containing polymer, the rigidity and heat setability of the fiber are improved, and the pleatability and wind resistance are excellent. (5) Blocking between filters or between a filter and a packaging material during molding processing and storage is suppressed, and contamination of a processing machine and a mold is reduced. For example, PTFE, FEP, PFA, ETFE, PCTFE, PVDF, THV, a (meth) acrylic acid polymer having a perfluoro structure of C ₇ or less (preferably C ₆ or less) at least in the side chain, soluble in fluorine solvents Examples thereof include modified PTFE. The measuring method of melting | fusing point and glass transition temperature is mentioned later.

  Particularly in fluorine-containing (meth) acrylic acid polymers, in order to increase the glass transition temperature in the case of random polymerization, halogen atoms are introduced into the main chain of the polymer, rigid short-chain methyl methacrylate, Making it a copolymer with monomers such as fluoromethyl methacrylate, highly sterically hindered styrene-containing olefins, dicyclopentenyl group-containing olefins, dicyclopentanyl group-containing olefins, and introducing crystallinity polymerization This is a preferable method.

  Specific examples of fluorine-containing (meth) acrylic acid-based polymers include (co) polymers containing fluorine-containing olefins. Specific examples of fluorine-containing (meth) acrylic acid include fluoroalkyls. (Co) polymer containing (meth) acrylate having a group in the side chain.

  From the viewpoint of oil repellency, the fluorine-containing olefin preferably has a perfluoroalkyl group and / or a perfluoroalkylene group. A perfluoro group having 1 to 7 carbon atoms is preferably used, 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) acryloyl group having a trifluoromethyl group located at the terminal.

  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. In such a structure, since there are no unpaired atoms and asymmetric polar components, surface tension and hygroscopicity are reduced, and as a result, oil mist resistance and electret resistance are improved.

  It is also preferred that the fluorine-containing polymer has one or more aromatic hydrocarbon groups and linear / branched / cycloaliphatic hydrocarbon groups as a spacer with the main chain. Further, when α-chloro (meth) acrylate is used as the main chain, it is possible to incorporate a chlorine atom having a large steric hindrance into the main chain, so that the polymer content is maintained while maintaining a high content ratio of the fluorine-containing monomer. As a result, a high glass transition temperature can be obtained, and charge stability and oil repellency can be easily improved.

  In the case of using a monomer having a short-chain fluorine-containing alkyl group or fluorine-containing alkylene group, in order to obtain a desired glass transition temperature or crystallinity, a monomer having a carbon number of 12 to 30 is used as a monomer to be copolymerized with these fluorine-containing monomers. It is also preferable to use a (meth) acrylate having a chain aliphatic hydrocarbon group, such as lauryl (meth) acrylate, myristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, and behenyl (meth) acrylate. Can be mentioned. In addition to increasing the crystallinity of the side chain in the copolymer by using a (meth) acrylate having a long-chain aliphatic hydrocarbon group, and contributing to an improvement in the glass transition temperature of the copolymer, Since the ester group is shielded and the molecular mobility is reduced, the stability of the electret property is improved.

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

  Of these, more preferred are dicyclopentanyl acrylate (homopolymer Tg = 120 ° C.), dicyclopentanyl methacrylate (homopolymer Tg = 175 ° C.), isobornyl acrylate (homopolymer Tg = 94 ° C.), isobornyl. It is a methacrylate (homopolymer Tg = 180 ° C.), and a homopolymer having a cyclic aliphatic hydrocarbon group is significantly higher in glass transition temperature than a homopolymer having a linear aliphatic hydrocarbon group. A high glass transition temperature as a polymer can be obtained while maintaining a high content ratio of the fluorine-containing monomer.

  Further, as a monomer to be copolymerized with a fluorine-containing monomer, a halogen-free olefin having a branched aliphatic hydrocarbon group, a cyclic aliphatic hydrocarbon group, or an aromatic hydrocarbon group can be used, for example, styrene (Homopolymer Tg = 100 ° C.). Since it has only a hydrocarbon structure with a large steric hindrance group called an aromatic ring and a small amount of polar components, the glass transition temperature of the copolymer is increased and the hygroscopicity of the copolymer is also reduced. The stability of sex is improved.

  As the other monomer, a halogenated olefin, a functional group having crosslinkability, a non-fluorinated monomer having a hindered phenol structure or a hindered amine structure imparting an antioxidant action and charge stability can also be used. The halogenated olefin is preferably used as long as it has 2 or more carbon atoms. Examples thereof include vinyl chloride, vinyl bromide, vinyl iodide, vinylidene chloride, vinylidene bromide, and vinylidene iodide. In view of improving the glass transition temperature, vinyl halides such as vinyl chloride (homopolymer Tg = 87 ° C.) are preferably used.

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

  Moreover, when forming an uneven | corrugated | grooved part by attaching particle | grains to the surface, it is preferable that the fluorine-containing particle | grains with a particle diameter of 0.1 nm or more and 500 nm or less are made to adhere to a support | carrier. The particle diameter 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 is difficult to achieve uniformity in particle size at the time of dispersion, and the coating layer thickness is likely to be excessive, making handling difficult. Moreover, since the floating oil mist to be collected is usually 500 nm or less, it is difficult to impart oil repellency due to unevenness. On the other hand, if the particle size is less than 0.1 nm, it is not suitable as a coating application in terms of solubility, melting point and vapor pressure, and the oil repellency, durability stability and electret stability may be inferior.

  In particular, in applications where the carrier is fibrous and air permeability and filtration characteristics are required, the ratio of the diameter of the fibrous material to 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. In general, it is known that the smaller the fiber diameter is, the more the filtration characteristics (capture efficiency per unit ventilation resistance) are improved.

  As a method for adjusting the particle size, (1) a method of adjusting the particle size at the time of polymerization by performing emulsion polymerization or suspension polymerization, and (2) pulverizing the fluorine-containing polymer by physical action such as impact and friction. (3) A method in which a fluorine-containing polymer is dissolved in a fluorine-based solvent, supercritical carbon dioxide or the like, and then sprayed onto a carrier, and (4) a fluorine-containing polymer in a fluorine-based solvent, supercritical carbon dioxide, or the like. (5) A method of spraying onto a carrier after heating to a temperature higher than the melting point, (6) Transpiration and condensation due to changes in pressure and temperature. The method is preferable, and a preferable method can be used according to the target particle diameter. 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. In addition, a fluorine-containing polymer can be produced by a known method using the above monomer.

  As a method of pulverizing by physical action, various types of wet or dry pulverizers can be used. Specifically, a ball mill, a bead mill, a jet mill, a homogenizer, and the like can be exemplified. It can also be suspended.

  When dispersed in a liquid, water, a hydrocarbon organic solvent, a halogen organic solvent, or the like is 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 improved by the affinity with the synthetic resin used as the carrier. When water is used as the dispersion medium, various surfactants can also be used. Since the surfactant inhibits the development of oil repellency and the stability of the electret, it is preferable to finally remove and / or inactivate the surfactant from the fluorine-containing component. A method of evaporating the surfactant by heat treatment before or after adhesion, a method of removing the surfactant from the fluorine-containing component by thermal decomposition or oxidative decomposition, and removing the surfactant from the fluorine-containing component by washing with water or a solvent. For example, a method of sealing an ionic functional group with a transition metal ion or a reactive organic substance can be used. As a method of dispersing a fluorine-containing component without using a surfactant, it is preferable to use a fluorine-containing solvent as a dispersion medium.

  Examples of the method for atomizing by spraying include airless or air pressure spraying, ultrasonic atomization, Ruskin nozzle, collision, electrostatic spraying, and the like. In this case, the particle diameter proportional to the solution concentration can be easily adjusted by using a solution or a pre-particulate suspension. In particular, a method of spraying a solution or suspension is suitable as a method for obtaining monodisperse particles of 0.1 nm or more and 500 nm or less, and may be attached in any state of a solution state, a semi-transpiration state, and a solid state. Absent.

  As a method of making particles by transpiration, a method in which a fluorine-containing material is vaporized by heating or reduced pressure and then deposited directly on the surface of the carrier by cooling or pressurizing, or a method of making particles in gas adhere to the surface of the carrier. Etc. can be used.

  The present invention includes a step (vapor phase method) of attaching a fluorine-containing component to a carrier using a gas phase in which a fluorine-containing component is dispersed. When the carrier is used for a filter, if particles are attached to the carrier by a vapor phase method, the carrier can be processed without using a surfactant, and the particle collecting property of the carrier itself can be utilized.

(Electretization)
In the electret filter of the present invention, at least one of the carrier and the fluorine-containing component is electretized, that is, an electrostatic charge is imparted. The electretization method is not particularly limited as long as desired characteristics can be obtained at the time of use, and may be before or after supporting the fluorine-containing component. In the former case, there is an advantage in adhesion and processing by attracting the fluorine-containing powder by electrostatic attraction, and in the latter case, the electric lines of force of the carrier are not shielded, so that the electret effect can be expressed more. .

  The electretization method includes polarization by high voltage, collision of charged ions, method by electric action such as injection of charged particles, method by interaction with solids such as friction and collision, method utilizing contact and collision with liquid For example, a known method can be preferably used. From the viewpoint of oil repellency and oil mist resistance, a method utilizing contact with a liquid or friction is more preferable. When this method is used, it becomes possible to electret without increasing the oxidation product having polarity, and this is a more preferable method from the viewpoint of tobacco smoke resistance.

In the electret filter of the present invention, the collection efficiency (initial collection efficiency) of particles having a particle diameter of 0.3 to 0.5 μm at a wind speed of 5 cm / s is preferably 50% or more, and preferably 70% or more. More preferably, it is more preferably 90% or more, and most preferably 99% or more.
The initial collection efficiency is calculated from the following equation by measuring the number of particles having a particle size of 0.3 to 0.5 μm before and after passing through the filter.
Initial collection efficiency (%) = (1− (number of particles after passing through the filter / number of particles before passing through the filter)) × 100

The electret filter of the present invention has an initial QF value of a particle size of 0.3 to 0.5 μm at a wind speed of 5 cm / s is 0.5 mmAq ⁻¹ or more, preferably 1.0 mmAq ⁻¹ or more, more preferably 1 .5 mmAq ⁻¹ or more. The initial QF value is calculated from the following equation using the ventilation resistance (pressure loss due to filter passage) and the value of the initial collection efficiency.
Initial QF value (mmAq ⁻¹ ) = − [ln (1- [initial collection efficiency (%)] / 100)] / [ventilation resistance (mmAq)]

  Regarding the oil repellency of the electret filter of the present invention, a drop of a test liquid used in the AATCC-118 method and a liquid mixture for a wetting tension test used in JIS K 6768 is dropped, and the smaller the surface tension required for permeation is, the smaller the surface tension is. The oil repellency is high. The oil repellency of the electret filter of the present invention can be adjusted according to required properties (waterproof, antifouling, water repellent, oil repellent, etc.), but the test used in the AATCC-118 method In the wet tension test mixed liquid used in the liquid and JIS K 6768 method, the surface tension of the test liquid that gives the permeability within 30 seconds is at least a non-processed product (for example, the surface tension of polypropylene obtained by the melt blown method is 36 mN / If it is lower than m), it can be preferably used. Specifically, it is more preferably 31 mN / m or less, further preferably 29 mN / m or less, particularly preferably 27 mN / m or less, and most preferably 25 mN / m or less. These materials have a surface tension of 31 mN / m bis (2-ethylhexyl) phthalate (DOP), which is the standard for liquid particles in the national certification standards for dust masks, and are one of poly-α-olefins (PAO). The surface tension of this material is 29 mN / m, and the correspondence to minerals and vegetable oil mist in actual use is considered. According to the inventor's study, there is a correlation between the oil repellency in the sheet shape and the oil mist resistance when used as a filter, and if the oil repellency to the extent that no absorption occurs due to capillary action is obtained, the filter Even so, it has sufficient oil mist resistance (suppressing a decrease in collection efficiency). This is because there is a correlation between the oil mist resistance (contact angle) on the surface of the material and the absorption phenomenon into the porous material. If the material has sufficient oil repellency, the entire fiber is covered with liquid by capillary action. Can be suppressed, and a decrease in electret properties can be suppressed. The oil repellency has a correlation with the contact angle and the collected state of the aerosol collected on the fiber surface during the mist test. Moreover, since tobacco smoke is a mixture, the surface tension value is not clear, but the durability is remarkably improved as the liquid permeability decreases.

In order to compare with a filter generally used for air purifier applications, an indicator of tobacco smoke durability is standardized by the following method.
(1) Four Mobius (registered trademark) manufactured by Japan Tobacco Inc. are burned in a 1 m ³ acrylic container using a smoke absorber and procedure in accordance with the JEM1467 method.
(2) A filter (sample) punched to 72 mmφ is attached to an adapter with an effective ventilation diameter of 50 mmφ, and circulation ventilation is performed for 10 minutes at an air flow of 12 L / min.
(3) The particle concentration is reduced from 4000 CPM to 3000 CPM by Shibata Kagaku Digital Dust Meter P-2L. When the efficiency is maintained at 100%, four Mobius (registered trademark) are burned and the air volume is 12 L / min. When the air is ventilated for 10 minutes, the collected amount is about 1 cigarette / cycle.
(4) At the end of the initial stage (before cycle load) and 1 cycle (four Moebius (registered trademark) burned and ventilated for 10 minutes at an air flow of 12 L / min), particles having a particle size of 0.3 to 0.5 μm The collection efficiency and the collected mass of tobacco smoke are measured, and the cycle and measurement are repeated until the performance maintenance rate drops to less than 15%.
(5) The effective fiber diameter (μm) of the fiber is calculated using the Davies formula.
(6) The fiber surface area (m ² / m ² ) per 1 m ^{2 of} sample is calculated using the effective fiber diameter obtained in (5) above.
(7) From the initial collection efficiency of the filter, ln (initial transmission rate) (= ln (1- [initial collection efficiency (%)] / 100)) is calculated, and the performance maintenance rate falls below 15%. From the collection efficiency (collection efficiency at the end of the cycle) with a particle size of 0.3 to 0.5 μm at the end of the immediately preceding cycle, ln (transmittance at the end of the cycle) (= ln (1- [collection at the end of the cycle) Efficiency (%)] / 100)). Then, ln (transmittance at the end of the cycle) / ln (initial transmittance) is defined as the performance maintenance rate.
(8) above to calculate the tobacco smoke collection amount per filter 1 m ² by dividing by the area of 50mmφ a passage area of the adapter tobacco smoke collection amount obtained in (4), per filter 1 m ² The collected amount of tobacco smoke per 1 m ² of fiber surface area is calculated by dividing the collected amount of tobacco smoke by the fiber surface area obtained in (6) above.
(9) A semi-logarithmic graph is plotted with the horizontal axis plotted as the amount of cigarette smoke per 1 m ² of fiber surface area (mg / m ² ) (ordinary axis) and the vertical axis as the performance maintenance ratio (logarithmic axis). The slope of the downward-sloping graph is the filter deterioration rate. Specifically, with respect to the logarithmic axis, the calculated slope (unit: 1 / (g / m) is set to 1 (no unit) as an interval (for example, an interval between 0.1 and 1) at which the performance maintenance ratio becomes 10 times. ² )) is the filter deterioration rate. A specific method for calculating the inclination will be described later.
Note that the calculation of thickness and filter deterioration rate refers to the characteristics of a substantially homogeneous electret layer that contributes to collection performance and durability, and when a plurality of electret layers with different fineness are laminated. It is necessary that at least one layer has the performance of the electret filter of the present invention.

In the electret filter of the present invention, as the charge stability required during storage and shape processing, the performance maintenance rate described below is preferably 10% or more, more preferably 30% or more, and even more preferably 70% or more. Preferably, 80% or more is particularly preferable, and 90% or more is most preferable. The collection efficiency at the end of the cycle is determined at the end of the cycle immediately before the cycle in which the performance maintenance rate falls below 15% (when the performance maintenance rate is less than 15% at the end of the second cycle, The value of the collection efficiency having a particle size of 0.3 to 0.5 μm is used.
Performance maintenance ratio [%] = 100 × [ln (1- [capturing efficiency at end of cycle (%)] / 100)] / [ln (1- [initial collection efficiency (%)] / 100)]

According to the inventor's verification, in the polypropylene fiber obtained by a general melt blown method, the filter deterioration rate (hereinafter sometimes simply referred to as deterioration rate) is about −9 / (g / m ² ). The deterioration rate can be suppressed to −8 / (g / m ² ) or more by using the electret filter of the present invention, preferably −6 / (g / m ² ) or more, more preferably −5. / (G / m ² ) or more, preferably −2 / (g / m ² ) or less. For example, when a filter having a deterioration rate of −9 / (g / m ² ) and a filter having a deterioration rate of −3 / (g / m ² ) are compared, the deterioration rate is −9 / (g / m ² ). A filter with a degradation rate of −3 / (g / m ² ) deteriorates to the same extent as a filter with a degradation rate of −9 / (g / m ² ) due to the cigarette smoke load three times that of the filter. It will be the same level). In the electret filter manufactured by the method of coating the fluorine-containing component by the vapor deposition method, the deterioration rate is easily suppressed.

(Other layers)
The electret filter of the present invention is preferably used by further laminating a fiber layer (hereinafter referred to as a liquid absorbing layer) having an oil absorbing function or a water absorbing function. When a non-fluorine material is used as a carrier, it has an oil absorbing function even when a general-purpose resin such as polyethylene or polypropylene is laminated. By providing a liquid-absorbing layer having a liquid-absorbing function such as oil absorption and water absorption, the liquid droplets generated by oil repellency can be prevented from dripping, and the liquid droplets can be transferred from the surface of the electret filter and diffused into the liquid absorption layer. Loss of electret property and increase in ventilation resistance can be suppressed.

  The material of the liquid-absorbing layer is not particularly limited as long as it absorbs liquid droplets, but is a fiber sheet material composed of polypropylene, polyethylene, polystyrene, polyamide, polyacrylonitrile, polyester, polycarbonate, cellulose, rayon, activated carbon, zeolite In addition, a sheet material containing a porous material such as pulp in the gap or processed into a surface is preferable. More preferred are fiber sheet materials made of olefinic materials such as polypropylene, polyethylene and polystyrene, or polyester, and even more preferred are fiber sheet materials made of polypropylene.

  The fibers constituting the liquid absorbing layer preferably have a diameter of 0.005 to 100 μm, more preferably 0.01 to 20 μm, further preferably 0.5 to 10 μm, and 1 to 5 μm. Most preferably it is.

  The fibers used for the liquid absorbing layer can be used alone or in combination of two or more, and the material can be selected from the viewpoint of collecting coarse particles, ventilation resistance, and the like.

  The material used as the liquid absorbing layer may be a non-electret material or an electret material, but is preferably an electret material.

  The production method of the liquid absorbing layer is not particularly limited as long as the desired properties can be obtained, but it is not limited by the thermal bond method, the spun bond method, the spun lace method, the melt electro spinning method, the solution electro spinning method, the force spinning method, or the like. It can be produced using a sheet material.

  The electret filter of the present invention can 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. These layers may be layers formed by adhering the fluorine-containing polymer used in the present invention.

  Examples of the prefilter layer and the fiber protective layer include spunbond nonwoven fabric, thermal bond nonwoven fabric, and urethane foam. Examples of the functional fiber layer include antibacterial, antiviral, colored fiber layers for identification and design purposes. Examples of the reinforcing layer include a thermal bond nonwoven fabric and various nets. In addition, it is also preferable for the liquid absorbing layer to have these functions as a method for reducing the thickness and ventilation resistance.

  The electret filter of the present invention can be widely used for functions such as dust collection, protection, ventilation, antifouling, and waterproofing. The electret filter of the present invention can be suitably used as, for example, a dust mask, various air conditioning elements, an air cleaner, a cabin filter, a filter for the purpose of protecting various devices, and mainly collects tobacco smoke. It can be preferably used for air cleaners, air conditioning element applications, and the like.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

(1) Thickness Using a digital thickness gauge, the thickness of the nonwoven fabric was measured with a terminal diameter of 20 mm and a load of 7 g / cm ² .

(2) Effective fiber diameter Davies, C.I. N. The effective fiber diameter of the non-woven fabric was calculated according to the method shown in “The Separation of Airborne Dust and Particles”, Institution of Mechanical Engineers, London, Proceedings 1B, 1952.

(3) effective fiber diameter obtained in the fiber surface area (2), basis weight of the nonwoven fabric, and JIS density obtained by K 0061 fiber surface area per nonwoven 1 m ² using (true specific gravity) (m ² / m ² ) Was calculated.

(4) Glass transition temperature The glass transition temperature of the particles is measured in accordance with JIS K 7121. Specifically, 10 mg of a sample is put in a measurement closed pan, and the temperature rise rate is 20 ° C./min. The midpoint glass transition temperature measured using a differential scanning calorimeter manufactured by TA Instruments was used as the glass transition temperature.

(5) Melting point The melting point of the particles is measured in accordance with JIS K 7121. Specifically, 5 mg of a sample is put in a measurement pan and the TA instrument is heated at a rate of 10 ° C./min. Using a differential scanning calorimeter manufactured by KK, the peak temperature measured on an airtight closed pan was determined as the melting point by confirming the presence of a recrystallization peak.

(6) Ventilation resistance A sample punched out to 72 mmφ was attached to an adapter with an effective ventilation diameter of 50 mmφ, and a pipe with an inner diameter of 50 mm connected to a fine differential pressure gauge was connected vertically and ventilated at 12 L / min (5 cm / s). The ventilation resistance (pressure loss) in the absence was measured.

(7) Collection efficiency in the filter after electretization (initial collection efficiency)
A sample punched out to 72 mmφ is attached to an adapter with an effective air diameter of 50 mmφ, and a filter particle collection efficiency test (initial collection efficiency test) is performed using the light scattering particle counter KC-01E manufactured by Rion Co. ).
Evaluation particle: Air dust Ventilation speed: 5 cm / sec (12 L / min)
Efficiency calculation: The number of particles having a particle size of 0.3 to 0.5 μm before and after passing through the filter was measured, and the value calculated using the following formula was used as the initial collection efficiency.
Collection efficiency (%) = (1− (number of particles after passing through the filter / number of particles before passing through the filter)) × 100

(8) Initial QF value Using the ventilation resistance measured in the above (6) and the initial collection efficiency value measured in the above (7), an initial QF value was obtained from the following equation.
Initial QF value (mmAq ⁻¹ ) = − [ln (1- [initial collection efficiency (%)] / 100)] / [ventilation resistance (mmAq)]

(9) Durability against oil mist (amount of tobacco smoke collected)
The oil mist load resistance (to oil mist durability) test was conducted using tobacco smoke as composite particles containing a wide variety of polar molecules.

[Tobacco smoke load]
1 m ³ using a puff device and methods that conform to JEM1467 in acrylic container, Japan Tobacco Inc. Mobius was (R) is four combusting. A sample punched out to 72 mmφ was attached to an adapter having an effective ventilation diameter of 50 mmφ, and aeration was performed for 10 minutes at an air flow of 12 L / min. The particle concentration is reduced from 4000 CPM to 3000 CPM with Shibata Kagaku Digital Dust Meter P-2L. When the efficiency is maintained at 100%, four Mobius (registered trademark) are burned and the air volume is 12 L / min. By aeration for 10 minutes, the collected amount is about 1 cigarette / cycle. The mass of the filter immediately before and after the cigarette smoke load cycle is weighed each time, and the difference between the masses is taken as the collected amount in the cycle, and among the collected tobacco smoke-derived components, the time course between cycle tests Measurement errors due to the dissipation of volatile components and the adhesion of NaCl in the collection efficiency test under the cigarette smoke load described below were prevented. Then, the cigarette smoke load cycle is repeated until the performance maintenance rate described below becomes less than 15%. When the performance maintenance rate falls below 15%, the cigarette smoke load cycle ends, and the performance maintenance rate falls below 15%. The integrated value of the collected amount up to the cycle immediately before (when the performance maintenance rate was less than 15% at the end of 2 cycles, at the end of 2 cycles) was taken as the collected amount of tobacco smoke.

[Measurement method of collection efficiency at the time of cigarette smoke load]
For each of the above cycles (4 Moebius (registered trademark) burned and ventilated for 10 minutes at an air flow of 12 L / min), a sample punched out to 72 mmφ was attached to an adapter with an effective aeration diameter of 50 mmφ and manufactured by TSI Using CERTITEST Model 8130, the amount of tobacco smoke collected is measured for each cycle, the collection efficiency test described below (collection efficiency test at the time of tobacco smoke load) is performed, and the equation described in (7) above Was used to calculate the collection efficiency. The particle size of 0.3 to 0.00 at the end of the cycle immediately before the cycle in which the performance maintenance ratio falls below 15% (when the performance maintenance ratio is less than 15% at the end of the second cycle, at the end of the second cycle). The collection efficiency of 5 μm was defined as the collection efficiency at the end of the cycle.
Evaluation particle: Solid NaCl in an equilibrium charged state (generated from 2 mass% NaCl water)
Mode particle size 0.075μm
Ventilation speed: 5 cm / sec (6 L / min)
Concentration: 200 mg / m ³
Efficiency calculation: Concentration evaluation before and after passing through the filter by the light scattering concentration method Note that the collection efficiency of the particle size of 0.3 to 0.5 μm by the light scattering concentration method is the particle size of 0.3 to 0.5 μm by the light scattering counter. It is confirmed that it is almost the same as the value of collection efficiency.
Moreover, when the sample after the tobacco smoke load was used, interference was caused in the particle diameter measurement of the light scattering counter, and thus the efficiency was evaluated by the light scattering concentration method. In addition, since the particle concentration does not become balanced in the usual 4 seconds, the numerical value of the filter tester mode (efficiency measurement mode) for one cycle is set with a value of 20 seconds set as the time for the upper and lower detectors to equilibrate. Using.

(10) Tobacco smoke collected per 1 m ^{2 of} fiber surface area By dividing the collected amount of tobacco smoke obtained in (9) above by the area of 50 mmφ which is the passage area of the adapter, tobacco smoke collected per 1 m ² of filter The amount collected was calculated, and the amount of tobacco smoke collected per 1 m ² of fiber surface area was calculated by dividing the amount of collected tobacco smoke per 1 m ^{2 of} filter by the fiber surface area.

(11) Performance maintenance ratio Using the initial collection efficiency measured in the above (7) and the value of the collection efficiency at the end of the cycle measured in the above (9), the performance maintenance ratio was obtained from the following formula.
Performance maintenance ratio [%] = 100 × [ln (1- [capturing efficiency at end of cycle (%)] / 100)] / [ln (1- [initial collection efficiency (%)] / 100)]

(12) Filter deterioration rate The performance maintenance rate was calculated | required by the method similar to the said Formula (11) using the tobacco smoke collection amount (integral value) at the time of completion | finish of each cycle. Fiber surface area of 1 m at the end of each cycle in which the performance maintenance ratio is in the range of 15 to 75% (when the performance maintenance ratio is less than 15% at the end of two cycles, at the end of one cycle and at the end of two cycles) ^{Using the} collected amount of tobacco smoke per ² (integrated value) and performance maintenance rate, the horizontal axis represents the amount of cigarette smoke deposited per 1 m ² of fiber surface area (g / m ² ) (ordinary axis), and the vertical axis represents performance maintenance. A semi-logarithmic graph plotted as a percentage (logarithmic axis) was created. The tobacco smoke coating weight of 0 g / m ² per fiber surface area 1 m ^2, to obtain an approximate straight line by the least squares method through the points of performance retention rate is 1. For the logarithmic axis, the interval at which the performance maintenance ratio becomes 10 times (for example, the interval between 0.1 and 1) is 1 (no unit), and the slope of the above approximate line (the unit is 1 / (g / m ² )) Was calculated and taken as the filter deterioration rate. This semilogarithmic graph is shown in FIG.

<Example 1>
After preparing a solution in which n-C ₁₈ F ₃₈ (melting point: 149 ° C.) was dissolved in perfluorohexane, the solution was immersed in a polypropylene nonwoven fabric obtained by a melt blown method and dried to make the particles into a polypropylene nonwoven fabric. A solid content of 0.30 g / m ^{2 was} deposited. Thereafter, electretization was performed by a corona discharge method to produce an electret filter. The evaluation results of the obtained filter are shown in Table 1.

<Example 2>
The polypropylene nonwoven fabric obtained by the melt blown method was attached to a thermostat kept at 30 ° C. and placed on the reaction vessel ceiling made of cylindrical ceramic. A hot plate heated to 250 ° C. is installed at the bottom, and n-C ₁₈ F ₃₈ (melting point: 149 ° C.) is evaporated from the top of the metal boat, so that particles adhere to the polypropylene nonwoven fabric in a solid content of 0.30 g / m ^2. I let you. The polypropylene nonwoven fabric to which the particles were attached was subjected to an aging treatment at 60 ° C. for 15 minutes. Thereafter, electretization was performed by a corona discharge method to produce an electret filter. The evaluation results of the obtained filter are shown in Table 1.

<Example 3>
By suspension polymerization, a random copolymer (glass transition temperature of 81 ° C.) having a mass ratio of dicyclopentanyl methacrylate to 2- (perfluorohexyl) ethyl methacrylate of 1: 9 was obtained. The random copolymer was pulverized in perfluorohexane to prepare a dispersion having a concentration of 1% by mass. The dispersion was infiltrated into the polypropylene nonwoven fabric, and the undissolved portion of the random copolymer particles dispersed in advance was adhered to the nonwoven fabric, and then aging was performed at 100 ° C. for 15 minutes. The adhesion amount of the random copolymer was 0.30 g / m ² in terms of solid content. Thereafter, electretization was performed by a corona discharge method to produce an electret filter. The evaluation results of the obtained filter are shown in Table 1.

<Comparative Example 1>
A polypropylene nonwoven fabric obtained by the melt blown method was charged by a corona discharge method to prepare a filter, which was used for various evaluations. The evaluation results of the obtained filter are shown in Table 1.

<Comparative example 2>
A polypropylene non-woven fabric obtained by the melt blown method was immersed in ethyl alcohol to eliminate the charge and used for various evaluations after producing a filter. The evaluation results of the obtained filter are shown in Table 1.

  From Examples 1 to 3, Comparative Example 1 and Comparative Example 2, it is understood that the QF value is improved by the electretization process.

  From Examples 1 to 3 and Comparative Example 1, it can be seen that those having a fluorine-containing component on the surface have a small deterioration rate.

  From the comparison between Example 2 and Example 1, it can be seen that those having a fluorine-containing component deposited thereon by vapor deposition have a lower deterioration rate.

  The electret filter of the present invention can be suitably used as, for example, a dust mask, various air conditioning elements, an air cleaner, a cabin filter, a filter for the purpose of protecting various devices, and mainly collects tobacco smoke. It can be preferably used for air cleaners, air conditioning element applications, and the like.

Claims (2)

An electret filter in which a fluorine-containing component is supported on a fiber surface, and has an initial QF value of 0.5 mmAq ⁻¹ or more at a particle collection efficiency of 0.3 to 0.5 μm at a wind speed of 5 cm / s, and a tobacco smoke load The electret filter characterized by having a filter deterioration rate of -8 / (g / m ² ) or more.   The electret filter according to claim 1, wherein an effective fiber diameter of the fiber is 0.1 μm to 20 μm.