WO2016088692A1

WO2016088692A1 - Method for producing electret filter

Info

Publication number: WO2016088692A1
Application number: PCT/JP2015/083522
Authority: WO
Inventors: 北川　義幸
Original assignee: 東洋紡株式会社
Priority date: 2014-12-03
Filing date: 2015-11-30
Publication date: 2016-06-09
Also published as: JPWO2016088692A1; JP6743706B2

Abstract

The present invention provides a method for producing an electret filter that can be produced by means of a low-cost, easy method even without using a long-chain perfluoro compound. Provided is a method for producing an electret filter in which fluorine-containing particles that contain substantially no metal or metal oxides are deposited on a carrier, said method being characterized in that: the fluorine-containing particles comprise a fluorine-containing polycyclic compound or a fluorine-containing polymer obtained from a monomer component that includes a (meth)acrylate that has a fluorine-containing olefin or fluorine-containing side chain; in the fluorine-containing polymer and fluorine-containing polycyclic compound, hydrolysis does not give rise to fluorotelomers which have a carbon number of 8 or more and in which all hydrogen is substituted with carbon; the melting point or glass transition temperature of the fluorine-containing particles is 40 °C or more; and the method includes a step of depositing the fluorine-containing particles on the carrier using a liquid phase or gas phase in which the fluorine-containing particles are dispersed.

Description

Manufacturing method of electret filter

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

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

Among the porous filters, the fiber layer filter made of a fibrous material has a high porosity, has the advantages 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 for 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.

In order to increase the initial particle collection efficiency, and to make the electret filter suppress performance degradation due to attenuation of electrostatic charge during filter processing and storage, the fiber layer filter can be electretized and has moisture resistance and stability. A material having excellent heat stability is used.

However, the electret filter described above has a drawback that electrostatic attraction decreases as the collection of particles proceeds. Especially when collecting oil mist with a small surface tension, the oil mist covers the entire fiber surface thinly. As a result, the loss of electric charge is significantly promoted.

Polyolefin, polyester, polycarbonate, phenol resin, etc. with excellent charge stability are used as materials for general electret filters. Among these, polypropylene, polyethylene, polymethylpentene, which have the smallest surface tension, are used. Even when using polyolefin resins such as poly-α-olefin (PAO) and dioctyl phthalate (DOP), they do not exhibit liquid repellency, so oil mist is added to the filter. There is a problem that the particle collection efficiency is low.

In order to solve such a problem, the oil repellency is improved by lowering the surface tension of the fibrous material constituting the filter, and the spread of the mist-like particles on the fiber surface and the diffusion into the fiber is suppressed. There is known a method of improving particle collection efficiency when oil mist is added to a filter by reducing the disappearance of the above charge. Specifically, a method of mixing an additive having a perfluoro group with 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 perfluoro group A method of coating the surface with an emulsion processing agent (for example, Patent Document 4), a method of introducing fluorine atoms into a polymer constituting a filter by replacing constituent elements by fluorine gas treatment or plasma treatment (for example, Patent Document 5) A technique is known in which the surface tension of an electret filter is reduced and oil mist resistance is increased while maintaining charge stability by such a method.
In the present specification, the effect of oil repellency by lowering the surface tension of the material is referred to as “oil repellency”, and the effect of suppressing reduction in the particle collection efficiency of the material when oil mist is added is referred to as “oil mist resistance”. . The oil repellency in the present invention means the effect of suppressing the spread of the liquid on the surface of the material by lowering the surface tension of the material, and acting on water having a large surface tension value in view of the principle of wetting. (Water repellency) is also included.

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, the fluorine atom introduction method by fluorine gas treatment or plasma treatment needs to prevent leakage of fluorine gas, and it is necessary to strictly manage oxygen and water content in order to suppress the increase in hydrophilicity due to residual oxygen. Yes, special equipment with high airtightness is required.

In addition, in fluorine-containing acrylate processing agents developed for textiles, long-chain perfluoroalkyl group-containing compounds represented by perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are useful for the environment and the human body. Since there is a concern about the influence on it, a fluorine compound containing a perfluoroalkyl group having 7 or less carbon atoms is used as a processing agent as an alternative. However, since a perfluoro group having 7 or less carbon atoms is used as a side chain, the processing agent loses crystallinity, and the processing agent itself does not have electret properties, and even if it has a low adhesion amount, There is a problem that the electret property of the fiber material used as a material is significantly inhibited.

In addition to the above, a fluorine-based resin (for example, Patent Document 6) that imparts solubility and thermoplasticity by amorphization and has both electret and coating properties is also known, but it is necessary to use a special monomer as the main skeleton. There is a problem that the manufacturing cost is remarkably increased.

In the above method, since the oil repellency is expressed by the chemical properties (surface tension value) of the material itself, the water repellency is obtained, but the oil repellency is insufficient. Therefore, a method of forming a surface having oil repellency superior to the material itself by combining fine unevenness or fractal surface and a fluorine-based material (for example, Patent Document 7, Patent Document 8, Patent Document 9, Non-Patent Document 1). ) Is disclosed. However, as a result of studies by the present inventors, a fluorine-based compound having a short-chain perfluoro group having 8 or less carbon atoms has viscosity and fluidity in a general environment at about 40 ° C. encountered during transportation and storage. However, even if a fluorine-based compound having a short-chain perfluoro group having 8 or less carbon atoms is simply deposited on an inorganic carrier, charge stability is hindered, and electret and oil repellency cannot be achieved. is doing. In addition, these methods take into consideration the water / oil repellency of droplets made of non-reactive hydrocarbon oil or pure water, so that they have reactivity or change pH when dissolved in water. Water and oil repellency is reduced for extremely fine particles such as tobacco smoke and mist-like particles that contain multiple components having functional groups (amino groups, phenolic hydroxyl groups, carboxyl groups, etc.) There is a risk that charge stability may be impaired.

JP 2009-6313 A JP 2002-266219 A JP 2007-18895 A JP 2004-352976 A Special table 2008-540856 gazette International Publication No. 2009/104699 Japanese Patent No. 4695278 Japanese Patent No. 4384898 Japanese Patent No. 3688042

In a conventional oil-resistant electret filter, when a short-chain perfluoro compound that complies with environmental regulations is used, it is difficult to obtain an electret filter having excellent oil repellency, oil mist resistance, and charge stability. Therefore, the present invention has been given as an object to provide an electret filter that can be manufactured by a low-cost and simple method and has oil repellency, oil mist resistance, and charge stability.

The present inventor uses a fluorine-containing polymer obtained from a monomer component containing a fluorine-containing polycyclic compound, or a monomer having a fluorine-containing alkyl group or fluorine-containing alkylene group having 7 or less carbon atoms, to provide oil repellency and oil resistance. The inventors have found a production method for obtaining an electret filter having excellent mist properties and charge stability.

Specifically, a method for producing an electret filter in which fluorine-containing particles substantially free of metal and metal oxide are attached to a carrier, using a liquid phase or a gas phase in which the fluorine-containing particles are dispersed. And a production method including a step of attaching the fluorine-containing particles to the carrier. The fluorine-containing particles are made of a fluorine-containing polymer obtained from a fluorine-containing polycyclic compound, or a monomer component containing a fluorine-containing olefin or a (meth) acrylate having a fluorine-containing side chain, and the fluorine-containing polycyclic compound and the above-mentioned The fluorine-containing polymer is characterized in that a fluorine telomer having 8 or more carbon atoms and all hydrogens substituted with carbon is not generated by hydrolysis. The melting point or glass transition temperature of the fluorine-containing particles is 40 ° C. or higher.

The particle size of the fluorine-containing particles is preferably 1 nm or more and 500 nm or less.

It is preferable to include a step of removing and / or inactivating the surfactant from the fluorine-containing particles, and it is preferable to include a step of manufacturing the carrier by a melt blown method.

The present invention also includes an electret filter manufactured by the above manufacturing method.

According to the present invention, an electret filter having excellent oil repellency, oil mist resistance, and charge stability can be obtained.

The electret filter produced according to the present invention is obtained by attaching fluorine-containing particles substantially free of metal and metal oxide to a carrier.

(Carrier)
The carrier used in the present invention is not particularly limited as long as it has desired characteristics, but it is preferable to use a synthetic resin having a high electrical resistance from the viewpoint of the degree of freedom in shape and the charge stability of the electret filter. Specific materials include polyester, polycarbonate, polyamide, polyolefin, cyclic olefin, polyvinyl chloride, polyvinylidene chloride, and the like, and polyolefin materials such as polyethylene, polybutene, polypropylene, polymethylpentene, and cyclic olefin, and polystyrene materials are preferable. . By using these materials, an electret filter having high electrical resistance, a good balance of hydrophobicity, moldability, etc., and excellent particle collection efficiency, that is, an electret filter excellent in practicality is obtained. be able to.

In order to further improve oil repellency, it is also preferable to use a synthetic resin containing a fluorine atom as a carrier. Synthetic resins containing fluorine atoms include, for example, polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymer (FEP), perfluoroalkoxyalkane (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoro Examples thereof include ethylene (PCTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer (THV), and PTFE, FEP, PFA, and ETFE are more preferable from the viewpoint of oil repellency.

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 carrier. 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 carrier, the carrier may be formed using a plurality of different materials. For example, two or more different resin components are mixed. A compatible or incompatible blend polymer, ionomer, maleic acid-modified polyolefin, hindered phenol resin, hindered amine resin, or the like can be used. In consideration of the initial charge amount and charge stability as an electret filter, it is preferable that at least one synthetic resin can be electretized.

The carrier used in the present invention may be a woven fabric shape, a nonwoven fabric shape, a cotton shape, or the like that is 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 nonwoven fabric is preferable.

The method for forming the nonwoven carrier is not particularly limited. For example, the melt blown method, the wet method, the dry method, the spunbond method, the flash spinning method, the electrospinning method, the force spinning method, the supersonic stretching method, Known methods such as a composite fiber splitting method may be mentioned. In order to obtain a nonwoven fabric having a small fiber diameter and good particle collection efficiency, the present invention uses a melt blown method, an electrospinning method, a force spinning method, or supersonic stretching. 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. Even if the fibrous material in the present invention is produced by a single production method or synthetic resin, the type of resin is the same, but the production method, fiber diameter, etc. may be produced from different synthetic resins. Alternatively, it may be made from two or more synthetic resins.

The diameter of the fiber used in the carrier of the present invention is preferably 0.001 to 100 μm, more preferably 0.005 to 20 μm, still more preferably 0.01 to 10 μm, and particularly preferably 0.02. To 5 μm, and most preferably 0.03 to 3 μm. If the fiber diameter is within the above range, the air ventilation resistance in the carrier can be reduced while increasing the collection efficiency. When the fiber diameter is thinner than 0.001 μm, it is difficult to give a charge to the carrier, and when the fiber diameter is thicker than 100 μm, the collection efficiency may be lowered. There is a large decrease in efficiency in various performances.

(Fluorine-containing particles)
The electret filter of the present invention is characterized by using fluorine-containing particles containing fluorine atoms for imparting water repellency and oil repellency to at least a part of the surface of the carrier. The fluorine-containing particles are made 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 characterized in that no fluorine telomer is generated.

From the viewpoint of charge stability and oil repellency, the fluorine-containing polycyclic compound preferably has a fluorine substitution rate of hydrogen atoms of 80% or more, more preferably 90% or more, and most preferably 95% or more. From the viewpoint of charge stability and oil repellency, the fluorine-containing polycyclic compound has a melting point of 40 ° C. or higher, preferably 60 ° C. or higher, more preferably 80 ° C. or higher, and still more 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.

In addition, the fluorine-containing polymer has a glass transition temperature of 40 ° C. or higher, preferably 60 ° C. or higher, more preferably 80, in order to suppress charge stability inhibition due to adhesion between particles or flow. It is 100 degreeC or more more preferably. 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.

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 charge stability and oil mist resistance, the fluorine-containing particles are preferably not a coating on a metal and a metal oxide, and the fluorine-containing particles are not a mixture with a metal and a metal oxide. Is preferred. In 100% by mass of fluorine-containing particles, 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 preferably).

When fluorine-containing particles are produced using a fluorine-based coating layer on the surface of metal or metal oxide, (1) it is difficult to perform uniform coating on the surface of metal oxide, and it exhibits oil repellency against fine droplets. (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.

Moreover, it is preferable that the fluorine-containing particles contain a small amount of surfactant or no surfactant. Specifically, in 100% by mass of the fluorine-containing particles, the content of the surfactant is preferably 25% by mass or less, more preferably 10% by mass or less, and 0% by mass (the surfactant is completely contained). 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 oil repellency, the fluorine-containing olefin preferably has a perfluoroalkyl group and / or a perfluoroalkylene group. The perfluoroalkyl group and / or the perfluoroalkylene group preferably has 1 to 7 carbon atoms, more preferably a perfluoroalkyl group having 4 to 6 carbon atoms at the end of the side chain. More preferably. 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 atoms. 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 resistance and electret properties 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 spacers with the main chain. In addition, 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 content can be 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 (meth) acrylate having a fluorine-containing side chain of the present invention, it is preferable to use a monomer having a short fluorine-containing side chain having 1 to 7 carbon atoms. In order to obtain a desired glass transition temperature or crystallinity, it is also preferable to use a (meth) acrylate having a linear aliphatic hydrocarbon group having 12 to 30 carbon atoms as a monomer to be copolymerized with these fluorine-containing monomers. Examples include lauryl (meth) acrylate, myristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, and behenyl (meth) acrylate. 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 group; polycyclic aliphatic hydrocarbon groups having 7 to 20 carbon atoms such as norbornyl group, bornyl group, isobornyl group, adamantyl group; phenyl group, naphthyl group, benzyl group, etc. (Meth) acrylate having an aromatic hydrocarbon group. Since these (meth) acrylates have a large steric hindrance, the resulting copolymer has a high melting point or glass transition temperature, and further blocks the ester group and reduces molecular mobility, so that it has electret properties. The stability of 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. Methacrylate (homopolymer Tg = 180 ° C.). A homopolymer having a cyclic aliphatic hydrocarbon group is characterized by a significantly higher glass transition temperature than a homopolymer having a linear aliphatic hydrocarbon group, while maintaining a high content ratio of the fluorine-containing monomer. As a polymer, a high glass transition temperature can be obtained.

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 another monomer, a monomer having a halogenated olefin, a functional group having crosslinkability, 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. ~ 30: 70.

In the present invention, it is preferable that fluorine-containing particles having a particle size of 0.1 nm to 500 nm are attached to the carrier. It 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 a fibrous material and air permeability and filtration characteristics are required, the diameter ratio of the fibrous material to the particle is important, and the value obtained by dividing the fiber diameter by the particle diameter (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 is, the more the filtration characteristics (capture efficiency per unit ventilation resistance) are improved, and the increase in the fiber diameter due to the coating layer is suppressed.

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 etc. are mentioned, 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 expression of oil repellency and the stability of the electret, it is preferable to finally remove and / or inactivate the surfactant from the fluorine-containing particles. A method of evaporating the surfactant by heat treatment before or after adhesion, a method of removing the surfactant from the fluorine-containing particles by thermal decomposition or oxidative decomposition, and removing the surfactant from the fluorine-containing particles 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 fluorine-containing particles 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, as a method for obtaining monodisperse particles of 0.1 nm to 500 nm or less, a method of spraying a solution or suspension is suitable, and it may be attached in any of a solution state, a semi-transpiration state, and a solidified 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. Can be used.

In the present invention, a step (liquid phase method or vapor phase method) of attaching fluorine-containing particles to a carrier using a liquid phase or a gas phase in which fluorine-containing particles are dispersed is included. When the carrier is used for a filter, if the particles are attached to the carrier by a liquid phase method or a gas 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 particles 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 particles. 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, electretization can be performed without increasing the oxidation product having polarity.

Regarding the oil repellency of the electret filter of the present invention, a drop of a test liquid used in the AATCC-118 method or a liquid mixture for a wet tension test used in JIS K 6768 is dropped and brought into contact for 30 seconds. The tension of the filter surface is measured based on the presence or absence of penetration of oil, and the smaller the surface tension required for penetration, the higher the oil repellency. The oil repellency of the electret filter of the present invention can be adjusted according to the required properties (waterproof, antifouling, water repellent, oil repellent, etc.), but was measured using the above liquid. It can be preferably used if the surface tension is at least lower than the unprocessed product (for example, the surface tension of polypropylene obtained by the melt blown method is 36 mN / m). 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 a 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 of the sheet shape and the oil resistance when used as a filter, and if the oil repellency is such that no absorption occurs due to capillary action, the filter can be used as well. It has sufficient oil resistance, that is, it can suppress a decrease in particle collection efficiency. This is because there is a correlation between the oil resistance (contact angle) of the surface of the material and the absorption phenomenon into the porous body. When 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.

(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, the liquid droplets can be transferred from the surface of the electret filter and diffused to 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 preferably, it is an olefin fiber sheet material such as polypropylene, polyethylene, polystyrene, or the like, or a fiber sheet material made of polyester, and more preferably a fiber sheet material made of polypropylene.

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

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

The material used for 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 a spunbond nonwoven fabric, a 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 due to functions such as dust collection, protection, ventilation, antifouling and waterproofing. The filter of the present invention can be suitably used as, for example, a dust mask, various air conditioning elements, an air purifier, a cabin filter, and a filter for the purpose of protecting various devices.

This application claims the benefit of priority based on Japanese Patent Application No. 2014-244810 filed on December 3, 2014. The entire contents of Japanese Patent Application No. 2014-244810 filed on December 3, 2014 are incorporated herein by reference.

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) 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.

(2) 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 airtight pan, and the temperature is increased by 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.

(3) Oil repellency in JIS K 6768 wetting tension test solution 16 kinds of wetting tension test solutions were prepared at intervals of 1 mN / m in the range of surface tension of 40 to 25 mN / m with the formulation specified in JIS K 6768. . And 50 microliters was left still on the surface of the sample (filter after electretization) using the micropipetter for microorganism tests using the test liquid of surface tension 40mN / m, and the penetration degree after 10 seconds was observed. Thereafter, the penetration degree was similarly observed in the order of a test liquid with a surface tension of 39 mN / m, a test liquid with a surface tension of 38 mN / m, and so on. The surface tension of the test liquid with the smallest surface tension that was not completely absorbed was measured according to JIS K 6768. The oil repellency was measured with a wet tension test solution. As a result of sequential measurement, if there is a difference between the front and back surfaces of the test material, the surface tension with the smaller surface tension is defined as the oil repellency (the same applies to the oil repellency at AATCC 118). ). Further, when the test solution of 25 mN / m was non-penetrating, there was no penetrating test solution, so the test result was set to 25 mN / m.

(4) Oil repellency at AATCC 118 First to eighth grade test solutions defined in AATCC 118 were prepared. Each was placed on the surface of a sample (filter after electretization) with a micropipettor for microbiological test, and 50 μL of each was left, and the degree of penetration after 30 seconds was observed. The series corresponding to the highest numbered test solution in which the test solution was not completely absorbed by the sample was defined as the oil repellency of AATCC118. When the first grade test solution was permeated, there was no non-penetrated test solution, so the test result was less than the first grade. Further, when the 8th grade test solution was non-penetrating, there was no test solution that had penetrated, so the test result was set to 8th grade.

(5) Oil repellency against PAO Prepare Emery 3004 (PAO (poly-α-olefin)) as a test solution, and leave it at 50 μL against the surface of the sample (filter after electretization) for 30 seconds with a micropipettor for microbiological test. The degree of subsequent penetration was observed. If the test solution was not completely absorbed by the sample, it was said to have oil repellency against PAO. When the test solution was not completely absorbed by the sample, it was assumed to have oil repellency (non-penetration) with respect to PAO.

(6) Water Repellency 50 μL of water was allowed to stand on the surface of the sample (filter after electretization) using a micropipetter for microbiological test, and the degree of penetration after 30 seconds was observed. When water was not completely absorbed by the sample, it was said to have water repellency.

(7) Collection efficiency in filter after electret For the sample (filter after electret), the particle collection efficiency test of the filter by the following method using KC-01E manufactured by Rion Co., Ltd. Carried out.
Evaluation particle: Air dust Ventilation speed: 10cm / sec
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 collection efficiency was determined from the following equation.
Collection efficiency (%) = (1− (number of particles after passing through the filter / number of particles before passing through the filter)) × 100

(8) Durability against oil mist The load resistance to oil mist (durability against oil mist) test was carried out by the following two methods. Tests were performed using PAO mist as low polarity mineral-based particles, and tobacco smoke as composite particles containing water and a wide variety of polar molecules.

(8-1) Durability test against oil mist (durability against PAO)
A sample punched to 72 mmφ (filter after electretization) was attached to an adapter with an effective air diameter of 50 mmφ, and ventilated under the following conditions using a CSI TITEST Model 8130 manufactured by TSI. When the particle collection efficiency is 50% (the particle concentration after passing through the filter is half of the particle concentration before passing through the filter) when the particle loading is performed continuously, the endurance value indicates the amount of collected particles in the sample. It was.
Evaluation particle: Emery 3004 (PAO) in an equilibrium charged state
Mode diameter 0.184μm
Ventilation speed: 5 cm / sec (6 L / min)
Concentration: 100 mg / m ³
Efficiency calculation: Concentration evaluation before and after passing through the filter by the light scattering concentration method The collection efficiency of particles having a particle size of 0.3 to 0.5 μm by the light scattering concentration method is 0.3 to 0.5 μm by the light scattering counter. It has been confirmed that it almost coincides with the value of the particle collection efficiency of 0.5 μm.

(8-2) Durability test against oil mist (durability against cigarette smoke)
[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 decreased from 4000 CPM to 3000 CPM with Shibata Kagaku Digital Dust Meter P-2L. When the efficiency was maintained at 100%, four Mobius (registered trademark) were burned and the air volume was 12 L / min for 10 minutes. By performing ventilation, the load amount is approximately one cigarette / cycle.

[Measurement method of collection efficiency at the time of cigarette smoke load]
Adapter with an effective ventilation diameter of 50 mmφ for the sample (filter after electretization) punched out to 72 mmφ for each load (combustion of 4 Mobius (registered trademark) and aeration for 10 minutes at 12 L / min) The efficiency and mass are measured by the following method using a certitest model 8130 manufactured by TSI, and the cycle is repeated until the efficiency falls below 50%. The end point is when the efficiency falls below 50%. Plotting the collection efficiency and the collected weight of cigarette smoke with the vertical and horizontal axes as normal axes, the numerical value at the time when the efficiency reaches 50% is read and calculated as the endurance life.
Evaluation particle: Solid NaCl in an equilibrium charged state (generated from 2% by mass NaCl water) mode particle size 0.075 μm
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 In addition, when using the sample after the tobacco smoke load, it causes interference in the particle size measurement of the light scattering counter. went. 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.

<Example 1>
A dispersion was prepared by dispersing n-C ₂₀ F ₄₂ in perfluorohexane so that L16828 (n-C ₂₀ F ₄₂ : melting point 167 ° C.) manufactured by Alfa Aesar was 1% by mass. When the dispersion is sprayed on a polypropylene nonwoven fabric (hereinafter simply referred to as a polypropylene nonwoven fabric) having a basis weight of 30 g / m ² , an average fiber diameter of 3 μm and a thickness of 0.25 mm obtained by the melt blown method using a Ruskin nozzle, the particles are polypropylene. 0.54 g / m ² adhered to the nonwoven fabric as a solid content. Differential electric mobility analyzer (DMA) that classifies based on the electric mobility of particles, and condensing nucleus particle counter (CNC) that detects after growing droplets in supersaturated vapor using particles as condensation nuclei The mode particle diameter after solvent volatilization was measured by the DMA-CNC method in combination with and was 83 nm. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Example 2>
A dispersion was prepared by dispersing n-C ₂₀ F ₄₂ in perfluorohexane so that L16828 (n-C ₂₀ F ₄₂ : melting point 167 ° C.) manufactured by Alfa Aesar was 0.03% by mass. When the dispersion liquid was sprayed onto a polypropylene nonwoven fabric using a Ruskin nozzle, particles adhered to the polypropylene nonwoven fabric in a solid content of 0.13 g / m ² . When the mode particle diameter after solvent evaporation was measured by the DMA-CNC method, it was 18 nm. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Example 3>
An aqueous dispersion of polytetrafluoroethylene (melting point: 330 ° C.) was heated to 300 ° C. and the surfactant component was removed and dispersed in perfluorohexane to a concentration of 1% by mass (solubility is 0.1). After that, the dispersion was sprayed onto a polypropylene nonwoven fabric using a Ruskin nozzle. As a result, 0.96 g / m ^{2 of} particles were adhered in solid content. When the mode particle diameter after solvent evaporation was measured by the DMA-CNC method, it was 210 nm. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Example 4>
By suspension polymerization, a random copolymer (glass transition temperature (Tg): 61 ° C.) in which the mass ratio of dicyclopentanyl methacrylate to 2- (perfluorohexyl) ethyl methacrylate was 1: 9 was obtained. The random copolymer was pulverized in perfluorohexane, allowed to penetrate into the polypropylene nonwoven fabric as a dispersion, and the non-dissolved portion of the random copolymer particles dispersed in advance was adhered to the nonwoven fabric, followed by air drying. . The adhesion amount of the random copolymer was 1.19 g / m ² in terms of solid content, and the mode particle diameter was measured using a scanning electron microscope to be 260 nm. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Example 5>
A random copolymer (Tg: 81 ° C.) having a mass ratio of dicyclopentanyl methacrylate to 2- (perfluorohexyl) ethyl methacrylate of 3: 7 was obtained by suspension polymerization. The random copolymer was pulverized in perfluorohexane, allowed to penetrate into the polypropylene nonwoven fabric as a dispersion, and the non-dissolved portion of the random copolymer particles dispersed in advance was adhered to the nonwoven fabric, followed by air drying. . The adhesion amount of the random copolymer was 1.08 g / m ² in terms of solid content, and the mode particle size was measured using a scanning electron microscope and found to be 240 nm. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Comparative Example 1>
An electret filter was prepared by corona discharge method without attaching particles to the nonwoven fabric. The evaluation results of the obtained electret filter are shown in Table 1.

<Comparative example 2>
Snowtex (registered trademark) 30 (particle diameter: 10 to 15 nm), a silica sol manufactured by Nissan Chemical Industries, was hydrolyzed so as to cover the entire particle surface of Snowtex (registered trademark) 30, and 1H, 1H, 2H, An excessive amount of 2H-perfluorooctyltrimethoxysilane was reacted. When a mixed solution of SNOWTEX (registered trademark) 30 and 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane was diluted with isopropyl alcohol, the diluted solution was infiltrated into a polypropylene nonwoven fabric. 0.87 g / m ² of solid content was supported on the nonwoven fabric. Finally, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1. The Tg of the particles was less than 40 ° C. and the particles were viscous.

<Comparative Example 3>
When Unidyne (registered trademark) TG-5502, which is an aqueous emulsion and is a C ₆ -based water and oil repellent, was impregnated into a polypropylene nonwoven fabric, the particles supported 1.02 g / m ^{2 in} solid content. Next, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1. The Tg of the particles was 30 ° C. or less, and the particles were viscous.

<Comparative example 4>
An aqueous dispersion in which perfluoroheptanoic acid and zirconium tetraisopropoxide are dispersed in dehydrated isopropyl alcohol is attached to a polypropylene non-woven fabric and dried to support 0.88 g / m ^{2 of} perfluoroheptanoic acid particles in solid content. I let you. The melting point and Tg of the perfluoroheptanoic acid zirconium particles were not observed, and the thermal decomposition temperature was 320 ° C. Next, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

<Comparative Example 5>
After only Snowtex (registered trademark) 30 (particle diameter: 10 to 15 nm) was diluted with isopropyl alcohol, this diluted solution was infiltrated into the polypropylene nonwoven fabric. As a result, the particles were 0.68 g / m ² in solid content in the polypropylene nonwoven fabric. Supported. The Tg of the particles is 600 ° C. or higher. Next, the polypropylene nonwoven fabric to which the particles were attached was electretized by a corona discharge method to produce an electret filter. The evaluation results of the obtained electret filter are shown in Table 1.

This is an electret filter that can be manufactured by a low-cost and simple method even when using short-chain perfluoro compounds that comply with environmental regulations, and has oil repellency, oil mist resistance, and charge stability. Electret filter can be obtained. The filter of the present invention can be suitably used as, for example, a dust mask, various air conditioning elements, an air purifier, a cabin filter, and a filter for the purpose of protecting various devices.

Claims

A method for producing an electret filter in which fluorine-containing particles substantially free of metal and metal oxide are adhered to a carrier,
The fluorine-containing particles are made 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, and the fluorine-containing polymer and the fluorine The containing polycyclic compound does not generate a fluorine telomer having 8 or more carbon atoms and all hydrogens substituted by carbon by hydrolysis,
The melting point or glass transition temperature of the fluorine-containing particles is 40 ° C. or higher,
A method for producing an electret filter, comprising a step of attaching the fluorine-containing particles to the carrier using a liquid phase or a gas phase in which the fluorine-containing particles are dispersed.
The method for producing an electret filter according to claim 1, wherein the particle diameter of the fluorine-containing particles is 1 nm or more and 500 nm or less.
The method for producing an electret filter according to claim 1 or 2, comprising a step of removing and / or inactivating the surfactant from the fluorine-containing particles.
The method for producing an electret filter according to any one of claims 1 to 3, comprising a step of producing the carrier by a melt blown method.
An electret filter manufactured by the manufacturing method according to any one of claims 1 to 4.