WO2020153174A1

WO2020153174A1 - Filter medium and filter using same

Info

Publication number: WO2020153174A1
Application number: PCT/JP2020/000881
Authority: WO
Inventors: 晋平平本; 陽梅林; 秀実伊東
Original assignee: Jnc株式会社; Ｊｎｃファイバーズ株式会社
Priority date: 2019-01-21
Filing date: 2020-01-14
Publication date: 2020-07-30
Also published as: CN113164849A; JP7216322B2; JP2020116487A

Abstract

Provided are: a filter medium that has a high dust trapping efficiency and less pressure loss, is capable of easily removing dust by using water without having to use chemicals, etc., and that exhibits excellent fast-dry properties; and a filter formed by using said filter medium. This filter medium includes an ultrafine fiber layer and a base material layer and has a mean flow pore size of at most 3.0 µm, wherein the adhesion energy of water on the surface of the ultrafine fiber layer is at most 3.0 mJ/m2.

Description

Filter medium and filter using the same

The present invention relates to a filter medium for collecting dust and a filter using the filter medium.

High-performance filters such as High Efficiency Particulate Air (HEPA) filters have high collection efficiency, so they are filters for clean rooms, home appliances filters for vacuum cleaners and air purifiers, filters for building air conditioning, industrial use. It is used for automobile filters, automobile cabin filters, etc. When using a high-performance filter, replace it with a new one when the pressure loss reaches a specified value due to clogging of dust, but a high-performance filter that can be washed and reused is used to save resources and reduce running costs. Is desired.

As an example of such a filter, Patent Document 1 proposes a glass fiber filter medium for achieving low pressure loss of a high performance filter. The filter medium of Patent Document 1 is a filter medium having a composition gradient in the thickness direction by blending ultrafine glass short fibers having an average fiber diameter of 0.2 to 0.6 μm and synthetic fibers having an average fiber diameter of 3 to 5 μm and making a paper. Is what you get. Further, Patent Document 2 proposes an electret filter medium for increasing the dust holding amount. The filter medium of Patent Document 2 has a laminated structure in which a polypropylene melt-blown non-woven fabric and a support layer are joined, and the melt-blown non-woven fabric has a fiber diameter of about 5 μm and a large number of small holes with a pore diameter of 1.0 mm or less. The filter medium of Patent Document 2 is folded and used as a pleated filter.

On the other hand, Patent Document 3 proposes a filter medium which is a laminated body having a PTFE microporous membrane on the surface, which can easily remove dust. Since the PTFE microporous membrane is a dense membrane in which very thin fibrils are formed between resin blocks called nodes, the collected dust is easily deposited on the surface of the membrane, and such a filter medium is Dust can be washed off relatively easily.

JP 2012-077400 A JP, 2014-226629, A JP, 2016-209870, A

However, in the glass fiber filter media and the electret filter media as disclosed in Patent Documents 1 and 2, the size of the pores formed between the fibers constituting the filter media (average flow rate pore diameter) is relatively large, and the collected dust is the filter media. It goes inside. For this reason, the collected dust cannot be easily removed, and in some cases it is necessary to wash with a chemical or the like, which causes a problem in terms of environment and cost.

On the other hand, the filter medium of Patent Document 3 may be washed with water in order to remove dust adhering to the surface of the filter medium, but the PTFE microporous membrane does not always have sufficient droplet removability, and water containing dust cannot be removed. It may remain partially on the surface, and there was a problem in terms of self-cleaning and quick-drying.

The object of the present invention is to solve the above problems, high dust collection efficiency, low pressure loss, and easily remove dust with water without using chemicals, etc. A filter material and a filter using the filter material.

The present inventors have conducted intensive research to solve the above problems. As a result, it was confirmed that low pressure loss and high collection efficiency can be achieved at a high level by using an extremely fine fiber obtained by a method such as electrostatic spinning and keeping the average flow pore diameter to be a certain value or less. When water repellency is imparted to such ultrafine fibers, the water repellency of the surface of the filter medium is improved, and the droplets on the surface are easily removed after washing, which improves the quick-drying property, while water permeates into the filter medium. It was found that it becomes difficult to do so and the cleaning property is impaired. Therefore, the inventors have further studied in order to achieve both quick-drying property and detergency, and by using the adhesion energy of water on the surface of the filtering material as a parameter, it is possible to express the rapid-drying property and detergency. The present invention has been completed by finding that a filter medium that has both a dust collection efficiency and a pressure loss, and also has a cleaning property and a quick drying property, can be obtained by controlling the adhesion energy of water on the surface to a certain value or less.

That is, the present invention has the following configurations that solve the above problems.

[1] A filter medium comprising an ultrafine fiber layer and a base material layer, wherein the filter medium has an average flow pore diameter of 3.0 μm or less, and water has an adhesion energy of 3.0 mJ on the surface of the ultrafine fiber layer. /M ² or less, a filter medium.
[2] The filter medium according to the above [1], wherein a water repellent is contained in the ultrafine fibers constituting the ultrafine fiber layer.
[3] The filter medium according to the above [2], wherein the water repellent contains fluorine.
[4] The filter medium according to any one of [1] to [3], wherein the basis weight of the ultrafine fiber layer is 0.1 to 20.0 g/m ² .
[5] The filter medium according to any one of [1] to [4], wherein the base material layer is made of a nonwoven fabric having an average fiber diameter of 1 to 30 μm.
[6] A filter comprising the filter medium according to any one of [1] to [5] above.

According to the present invention having the above structure, a filter medium having high dust collection efficiency, low pressure loss, easy removal of dust with water without using chemicals, and excellent quick-drying property is provided. It becomes possible to do. In particular, filter media suitable for home appliances filters for vacuum cleaners and air cleaners, air filters for building air conditioning, medium/high performance filters for industry, HEPA filters and ULPA filters for clean rooms, air filters for automobiles, etc. Can be provided.

FIG. 1 is an optical photograph of the filter medium of Example 1 after the cleaning property was evaluated. FIG. 2 is an optical photograph of the filter medium of Comparative Example 1 after the cleaning property was evaluated.

The present invention will be described in detail below.

The filter medium of the present invention is a filter medium including an ultrafine fiber layer and a base material layer, the average flow pore size of the filter medium is 3.0 μm or less, and the adhesion energy of water on the surface of the ultrafine fiber layer is It is characterized by being 3.0 mJ/m ² or less. By having such characteristics, the dust collection efficiency is high, the pressure loss is low, the dust can be easily removed with water without using chemicals, etc., and it is possible to provide a filter medium having excellent quick drying property. It will be possible.

<Ultra fine fiber layer>
The filter medium of the present invention comprises an ultrafine fiber layer. In addition, in this specification, the ultrafine fibers mean fibers having an average fiber diameter of less than 1 μm. The ultrafine fibers constituting such an ultrafine fiber layer are not particularly limited, but the average fiber diameter is preferably in the range of 10 to 999.9 nm, more preferably 50 to 200 nm, and more preferably 80 to 150 nm. The range is more preferable. When the average fiber diameter of the ultrafine fibers is small, the specific surface area is large, and it is easy to obtain high filter characteristics such as high collection efficiency and low pressure loss. In addition, since the pore size formed between the fibers constituting the filter medium becomes small, dust is easily collected on the surface of the filter medium, and cleaning is facilitated. On the other hand, as the fiber diameter decreases, the mechanical strength per fiber decreases, which may cause fiber breakage during filter processing and during use. However, if the average fiber diameter of the ultrafine fibers is 10 nm or more, it is satisfactory. Yarn strength is obtained. The coefficient of variation of the fiber diameter of the ultrafine fibers is not particularly limited, but is preferably 0.5 or less, more preferably 0.3 or less. If the coefficient of variation of the first fiber is 0.5 or less, it is possible to obtain excellent filter characteristics and easy cleaning. The average fiber diameter can be measured by a known method. For example, using a scanning electron microscope, the ultrafine fibers are observed, and the diameter of 50 ultrafine fibers is measured using image analysis software. Is used as the average fiber diameter.

The resin forming the ultrafine fibers is not particularly limited, and includes polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyamide, polyurethane, polystyrene, polysulfone, polyether sulfone, and polyvinylidene fluoride. , Polyacrylonitrile, polymethylmethacrylate, polyglycolic acid, polycaprolactone, polyvinyl acetate, polycarbonate, polyimide, polyetherimide, cellulose, cellulose derivatives, chitin, chitosan, collagen, gelatin and copolymers thereof The material can be illustrated. From the viewpoint of reducing the attachment energy of water, the resin forming the ultrafine fibers is preferably a hydrophobic resin, for example, a polyolefin resin, more preferably a fluorine resin, more preferably a polyvinylidene fluoride resin. Is more preferable. The polyvinylidene fluoride-based resin is not particularly limited, and examples thereof include a vinylidene fluoride polymer, a vinylidene fluoride-hexafluoropropylene copolymer, and a vinylidene fluoride-trifluoroethylene copolymer. The weight average molecular weight of the resin constituting the ultrafine fibers is not particularly limited, but is preferably in the range of 10,000 to 10,000,000, and more preferably in the range of 50,000 to 5,000,000. More preferably, it is more preferably 100,000 to 1,000,000. When the weight average molecular weight is 10,000 or more, it is excellent in the fiber forming property of the ultrafine fibers, and it becomes easy to obtain the ultrafine fibers having a small average fiber diameter, which is preferable. It is preferable because it has excellent plasticity and can be easily processed.

It is preferable that the ultrafine fibers constituting the ultrafine fiber layer contain a water repellent. By containing the water repellent, it becomes possible to reduce the attachment energy of water on the surface of the filter medium, and improve the cleaning property and the quick drying property. The water repellent is not particularly limited as long as it has an effect of lowering the adhesion energy of water, and is not particularly limited, and silicon-based silane compounds, fluorine-based silane compounds, fluorine-containing cage silsesquioxane, fluorine-modified polyurethane, silicon-modified Polyurethane can be exemplified. Above all, it is preferable to use a water repellent containing fluorine such as a fluorine-containing cage silsesquioxane or fluorine-modified polyurethane from the viewpoint of water repellency, workability and cost. The content ratio of the water repellent agent is not particularly limited, but is preferably in the range of 0.1 to 20% by weight, and preferably 1 to 15% by weight, based on the ultrafine fibers and the fine particles generated during the spinning by the electrostatic spinning method. Is more preferable. When the concentration of the water repellent is 0.1% by weight or more, the effect of lowering the adhesion energy of water can be obtained, and when it is 20% by weight or less, the effect commensurate with the amount used can be obtained, which is preferable.

The filter medium of the present invention is characterized in that the adhesion energy of water on the surface of the ultrafine fiber layer is 3.0 mJ/m ² or less, and the adhesion energy of water indicates how easily water slides off the surface. It is an index to represent. The adhesion energy (E) of water is determined by tilting the filter medium in which water is dropped on the ultrafine fiber layer, sliding angle (α) when water begins to slide, contact radius (r) of water at that time, and droplet It is calculated from the following formula (1) using the mass (m). A specific measuring method will be shown in Examples.

Although not particularly bound by theory, it is considered that the water attachment energy in the ultrafine fiber layer depends on the fine uneven structure of the surface formed by the ultrafine fibers, the water repellency of the ultrafine fibers, and other properties. Has been. The contact angle value is generally used as an index for evaluating the water repellency of the surface, but the contact angle alone is not enough to evaluate the droplet removal performance on the surface. It is preferable to use. Filter medium of the present invention, it is essential that water adhesion energy of the surface of the ultrafine fiber layer is 3.0 mJ / ^{m 2} or less, more preferably not more than 2.0 mJ / ^{m 2} or less. The lower limit is not particularly limited, but can be 0.1 mJ/m ² or more in consideration of industrial rationality. When the attachment energy of water is 3.0 mJ/m ² or less, water easily slips off the ultrafine fiber layer during washing, drains water well after washing the filter, and provides quick drying.

The basis weight of the ultrafine fiber layer can be appropriately selected depending on the required filter performance, cleaning property, quick drying property and the like, and for example, a range of 0.1 to 20.0 g/m ² can be exemplified. If a basis weight of 0.1 g / m ² or more, the fiber matrix ultrafine fibers constituting becomes sufficient dense, it is possible to improve the collection efficiency and cleaning properties, when 20.0 g / m ² or less, the pressure The loss can be reduced. From such a viewpoint, the basis weight of the ultrafine fiber layer is more preferably in the range of 0.2 to 10.0 g/m ² , and further preferably in the range of 0.5 to 5.0 g/m ^2. preferable.

The ultrafine fiber layer may contain components other than the above as long as the effects of the present invention are not significantly impaired.

The method for producing the ultrafine fiber layer is not particularly limited, but it is preferably produced by the electrostatic spinning method. By using the electrostatic spinning method, it is possible to uniformly spin the ultrafine fibers and obtain excellent filter characteristics.

The electrostatic spinning method is a method in which a spinning solution is discharged and an electric field is applied to make the discharged spinning solution into fibers, and the submicron-order nanofibers are collected in a non-woven fabric on the collector. The electrospinning method is not particularly limited, and is a generally known method, for example, a needle method using one or more needles, productivity per needle by spraying an air stream at the needle tip. Air blow method to improve the performance, 1 spinneret porous spinneret method with multiple solution discharge holes, free surface method using a cylindrical or spiral wire-shaped rotating electrode semi-immersed in the solution tank, polymer solution surface by supply air An electro-bubble method in which electrostatically spinning is performed from a bubble generated at the starting point, and the like, can be selected according to the fiber diameter and physical properties of the desired nano fiber.

The spinning solution is not particularly limited as long as it has spinnability, but a resin dispersed in a solvent, a resin dissolved in a solvent, a resin melted by heat or laser irradiation, etc. Can be used. In the present invention, in order to obtain very fine and uniform fibers, it is preferable to use a solution prepared by dissolving a resin in a solvent as a spinning solution.

The solvent for dispersing or dissolving the resin is not particularly limited, and water, methanol, ethanol, propanol, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, Toluene, xylene, pyridine, formic acid, acetic acid, tetrahydrofuran, dichloromethane, chloroform, 1,1,2,2-tetrachloroethane, 1,1,1,3,3,3-hexafluoroisopropanol, trifluoroacetic acid and mixtures thereof. Can be exemplified. The mixing ratio in the case of mixing and using is not particularly limited, and can be appropriately set in consideration of the required spinnability and dispersibility, and the physical properties of the obtained fiber and filter medium.

When the ultrafine fiber contains a water repellent, it is not particularly limited, but it is preferable to mix the water repellent with the resin in the spinning solution. The mixing method is not particularly limited, and examples thereof include stirring and ultrasonic treatment. The order of mixing is also not particularly limited, and they may be mixed simultaneously or sequentially. The mixing time is not particularly limited as long as the water repellent is uniformly dispersed or dissolved in the spinning solution, and stirring or ultrasonic treatment may be performed for 1 to 24 hours.

A surfactant may be further contained in the spinning solution for the purpose of improving the stability of electrostatic spinning and the fiber-forming property. Surfactants include, for example, anionic surfactants such as sodium dodecyl sulfate, cationic surfactants such as tetrabutylammonium bromide, and nonionic surfactants such as polyoxyethylene sorbitamon monolaurate. Can be mentioned. The concentration of the surfactant is preferably in the range of 5% by weight or less based on the spinning solution. When the content is 5% by weight or less, the effect commensurate with the use can be improved, which is preferable.

Other components than the above may be included as components of the spinning solution as long as the effects of the present invention are not significantly impaired.

In order to obtain ultrafine fibers by electrostatic spinning, it is preferable to adjust the viscosity of the spinning solution in the range of 10 to 10,000 cP, more preferably 50 to 8,000 cP. When the viscosity is 10 cP or more, spinnability for forming fibers is obtained, and when it is 10,000 cP or less, the spinning solution can be easily discharged. When the viscosity is in the range of 50 to 8,000 cP, good spinnability can be obtained in a wide range of spinning conditions, which is more preferable. The viscosity of the spinning solution can be adjusted by appropriately changing the molecular weight and concentration of the fiber-forming material, the type of solvent, and the mixing ratio.

The spinning solution may be spun at room temperature, or may be heated and cooled before spinning. Examples of the method of discharging the spinning solution include a method of discharging the spinning solution filled in a syringe from a nozzle using a pump. The inner diameter of the nozzle is not particularly limited, but is preferably in the range of 0.1 to 1.5 mm. The discharge amount is not particularly limited, but is preferably 0.1 to 10 mL/hr.

The method of applying the electric field is not particularly limited as long as the electric field can be formed in the nozzle and the collector. For example, a high voltage may be applied to the nozzle and the collector may be grounded. The applied voltage is not particularly limited as long as fibers are formed, but it is preferably in the range of 5 to 100 kV. The distance between the nozzle and the collector is not particularly limited as long as fibers are formed, but it is preferably in the range of 5 to 50 cm. The collector may be any as long as it can collect spun fibers, and its material and shape are not particularly limited. As a material for the collector, a conductive material such as metal is preferably used. The shape of the collector is not particularly limited, and examples thereof include a flat plate shape, a shaft shape, and a conveyor shape. When the collector is flat, the fiber assembly can be collected in a sheet shape, and when the collector is in a shaft shape, the fiber assembly can be collected in a tube shape. If it is in the form of a conveyor, the fiber aggregate collected in the form of a sheet can be continuously produced. In the present invention, it is preferable to form the ultrafine fiber layer directly on the base material layer by placing the base material layer on the collector and spinning the base material layer on the collector.

<Base material layer>
The filter medium of the present invention includes a base material layer. By including the base material layer, mechanical strength, durability, pleating processability, adhesive property and the like can be imparted to the characteristics of the ultrafine fiber layer. The base material layer can be appropriately selected according to the required characteristics and form of the filter medium, and examples thereof include non-woven fabric, woven fabric, net or microporous film.

The material constituting the base material layer is not particularly limited, but in the case of a base material layer using a polyolefin-based material such as polypropylene or polyethylene, it is characterized by excellent chemical resistance, and a liquid requiring chemical resistance is used. It can be suitably used for applications such as filters. In the case of a base material layer using a polyester-based material such as polyethylene terephthalate, polybutyl terephthalate, polylactic acid, or a copolymer containing these as the main components, it has excellent pleating characteristics, and therefore an air filter that requires pleating. Can be suitably used for

From the viewpoint of processability and air permeability of the filter medium, it is preferable to use a non-woven fabric as the base material layer. The non-woven fabric is not particularly limited, and examples of the non-woven fabric include a through-air non-woven fabric, an air-laid non-woven fabric, a spun lace non-woven fabric, a wet non-woven fabric, a spun bond non-woven fabric, a melt blown non-woven fabric, a flash spun non-woven fabric, and an electrostatic spun non-woven fabric. You can

In the filter medium of the present invention, it is preferable that the ultrafine fiber layer and the base material layer are integrated. The method of integration is not particularly limited, but the separately manufactured ultrafine fiber layer and the base material layer may be integrated by an adhesive or heat fusion, or the ultrafine fiber layer may be directly spun on the base material layer. It may be integrated by doing so, and after the ultrafine fiber layer is directly spun on the base material layer, it may be further subjected to an adhesion process by heat.

When performing the bonding process by heat, although not particularly limited, it is preferable to use a non-woven fabric made of a heat-fusible composite fiber composed of a low melting point component and a high melting point component as the base material layer. The material constitution, the composite form, and the cross-sectional shape of the heat-fusible conjugate fiber are not particularly limited, and known ones can be used. The material composition includes copolymer polyethylene terephthalate and polyethylene terephthalate, copolymer polyethylene terephthalate and polypropylene, high density polyethylene and polypropylene, high density polyethylene and polyethylene terephthalate, copolymer polypropylene and polypropylene, copolymer polypropylene and polyethylene terephthalate, polypropylene and polyethylene terephthalate. And the like can be exemplified. Further, considering the availability of materials, preferably, any combination of copolymerized polyethylene terephthalate and polyethylene terephthalate, high density polyethylene and polypropylene, and high density polyethylene and polyethylene terephthalate can be exemplified.

The composite form of the cross section may be, for example, a sheath-core type, an eccentric sheath-core type, or a parallel type. The cross-sectional shape of the fiber is not particularly limited, and in addition to the general round shape, any cross-sectional shape such as an oval shape, a hollow shape, a triangular shape, a quadrangular shape, and a modified cross-section such as a octagonal shape can be adopted. From the viewpoint of enhancing the adhesion between the fiber layer and the base material layer, it is preferable that the fiber layer has a flat shape substantially parallel to the surface of the ultrafine fiber layer. The substrate layer having fibers having such a cross-sectional shape is formed by, for example, a method in which elliptical, flat, or semicircular fibers are processed into a web shape and then bonded by heat or an adhesive, or a circular fiber. It can be obtained by consolidating a non-woven fabric with a hot roll.

The method for producing the non-woven fabric made of the heat-fusible composite fiber is not particularly limited, and known methods such as carding method, papermaking method, airlaid method, meltblown method, and spunbond method can be used. The fiber bonding method when processing into a non-woven fabric is not particularly limited, and examples thereof include thermal fusion bonding by air-through processing, thermocompression bonding by embossing, fiber entanglement by needle punching or spunlacing, and chemical bonding by an adhesive. To be

The thickness of the fibers constituting the base material layer is not particularly limited, but for example, fibers having an average fiber diameter of 1 to 100 μm can be used, preferably 5 to 50 μm, and more preferably 10 to 30 μm. .. If the average fiber diameter is 1 μm or more, the pressure loss of the base material layer can be suppressed, and if the average fiber diameter is 100 μm or less, the ultrafine fiber layer can be collected uniformly.

The basis weight of the base material layer is not particularly limited and is preferably 15 g/m ² or more, more preferably 30 g/m ² or more, and further preferably 60 g/m ² or more. When the basis weight of the base material layer is 15 g/m ² or more, shrinkage, wrinkling, curling and the like of the ultrafine fiber layer can be suppressed and processing strength can be imparted. The specific volume of the base material layer is not particularly limited, and is preferably 5 cm ³ /g or less, more preferably 3 cm ³ /g or less. When the specific volume of the base material layer is 5 cm ³ /g or less, the peeling strength and abrasion resistance of the ultrafine fiber layer are improved, and the decrease in collection efficiency after repeated washing is reduced, which is preferable. The thickness of the base material layer is not particularly limited and can be appropriately selected depending on the desired physical properties of the filter and the intended use, but can be, for example, 0.05 to 10 mm, and preferably 0.1 to 5 mm. For example, when it is used as a pleat filter, it is preferable that the base material layer has a thickness of 0.1 to 5 mm since the pleat processing suitability is improved.

The air permeability of the base material layer is not particularly limited, but is preferably 10 cc/cm ² /sec or more, more preferably 100 cc/cm ² /sec or more, and 200 cc/cm ² /sec or more. Is more preferable. It is preferable that the air permeability is 10 cc/cm ² /sec or more because the pressure loss can be reduced.

When a filter medium is manufactured by directly spinning an ultrafine fiber layer on a base material layer by an electrostatic spinning method, the electric leakage resistance value of the base material layer is 10 ¹⁰ Ω or less. It is more preferably 10 ⁷ Ω or less. When the electric leakage resistance value is 10 ¹⁰ Ω or less, the ultrafine fiber layer can be stably deposited on the base material layer without being electrically repulsed, and the adhesion can be improved. The average value of the tensile strength in the machine direction and the transverse direction of the base material layer is not particularly limited, but from the viewpoint of imparting strength, rigidity and workability, it is preferably 30 N/50 mm or more, and 60 N/50 mm or more. Is more preferable.

The base material layer may be subjected to electret processing, antistatic processing, water repellent processing, antibacterial processing, ultraviolet absorption processing, near infrared absorption processing, antifouling processing, coloring processing, etc., as long as the effect of the present invention is not significantly impaired. Although it may be applied, it is preferably water-repellent from the viewpoint of cleanability.

<Filter media>
The filter medium of the present invention includes the above-mentioned ultrafine fiber layer and a base material layer, and at least one layer selected from the group consisting of non-woven fabric, woven fabric, net and microporous film on the surface side of the ultrafine fiber layer. May be laminated and integrated. By laminating and integrating the layers, the surface of the ultrafine fiber layer is less likely to be exposed on the surface, and wear resistance, durability, and processing strength can be improved. From the viewpoint of cleanability, it is preferable that the nets are laminated and integrated. The integration method is not particularly limited, and thermocompression bonding treatment with a heated flat roll or embossing roll, adhesion treatment with a hot melt agent or a chemical adhesive, thermal adhesion treatment with circulating hot air or radiant heat, and the like can be adopted.

The filter medium of the present invention is characterized by having an average flow pore diameter of 3.0 μm or less. In the present specification, the average flow pore size of the filter medium refers to the average flow pore size of the entire filter medium including the ultrafine fiber layer and the base material layer. The average flow pore size is an index of the size of the pores formed between the fibers constituting the filter medium, and can be measured by a known method. For example, it can be measured by a pore size distribution measuring device or the like, and details are shown in Examples. When the average flow pore size is 3.0 μm or less, it is considered that both the collection efficiency and the pressure loss are compatible with each other, the dust hardly enters the inside of the filter medium, and the cleaning property can be improved. The lower limit of the average flow pore size is preferably 0.1 μm or more from the viewpoint of pressure loss of the filter medium. The average flow pore diameter of the filter medium can be adjusted by appropriately changing the average fiber diameter of the ultrafine fibers, the basis weight, and the like. It is believed that the substrate layer does not contribute significantly to the average flow pore size.

The dust collection efficiency of the filter medium of the present invention is not particularly limited, but is preferably 90% or more, more preferably 99% or more, and further preferably 99.97% or more. The pressure loss is not particularly limited, but is preferably 300 Pa or less, more preferably 180 Pa or less, and further preferably 160 Pa or less. Here, for the dust collection efficiency and pressure loss, particles having a particle diameter of 0.07 μm (median number diameter) and a particle concentration of 10 to 25 mg/m ³ were passed through the sample at a flow rate of 5.3 cm/sec. It is the measured value when. The dust collection efficiency and the pressure loss can be adjusted by appropriately changing the average fiber diameter and the basis weight of the ultrafine fibers.

The filter medium of the present invention is used as a filter in combination with a known structure such as a frame, a reinforcing material and a filter medium other than the present invention. The filter may be in any form such as a pleated filter, a flat filter, a cylindrical filter, etc., but it can be suitably used as a pleated filter. When used as a filter, it is preferable to use the ultrafine fiber layer side of the filter medium as the surface side (intake side) of the filter. The use of the filter is not particularly limited, but it is a home appliance filter for vacuum cleaners and air purifiers, an air filter for building air conditioning, a medium/high performance filter for industry, a HEPA filter or ULPA filter for clean rooms, for automobiles. It is preferable that it is a cabin filter or the like.

The examples below are for illustration purposes only. The scope of the invention is not limited to this example.

[Example 1]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) was dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive additive was added at 0.025% by weight based on the total weight of the solution. Fluorooctylsilsesquioxane (manufactured by Nvidinano Technologies) was added as a water repellent at a concentration of 10% by weight based on the weight of polyvinylidene fluoride to prepare a spinning solution. Next, a through-air non-woven fabric (fiber diameter: 10 μm, thickness: 60 μm, basis weight: 18 g/m ² ) composed of a heat-adhesive composite fiber containing copolymerized polyethylene terephthalate and polyethylene terephthalate is used as a base material, and the spinning solution is applied thereon. Was spun from an injection needle (Terumo, gauge: 27 G, needle length: 19 mm) and electrostatically spun to prepare an ultrafine fiber layer having a basis weight of 0.5 g/m ² . The spinning conditions of this example were as follows: the single-pore solution supply rate was 1.0 mL/hr, the applied voltage was 30 kV, the spinning distance was 150 mm, the spinning space temperature was 25° C., and the humidity was 30%.

[Example 2]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) was dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive additive was added at 0.025% by weight based on the total weight of the solution. Fluorooctylsilsesquioxane (manufactured by Nvidinano Technologies) was added as a water repellent at a concentration of 10% by weight based on the weight of polyvinylidene fluoride to prepare a spinning solution. Next, using the through-air non-woven fabric described in Example 1 as a substrate, the spinning solution was spun on the needle from an injection needle (Terumo, gauge: 27G, needle length: 19 mm) to perform electrostatic spinning. It was prepared so that the basis weight of the ultrafine fiber layer would be 1.5 g/m ² . The spinning conditions of this example were those described in Example 1.

[Example 3]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) was dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive additive was added to 0.025% by weight based on the total weight of the solution. As a water repellent, a fluorinated copolymer (Dialom Seika Chemical Co., Ltd., Dialomer FF129D) was added at a concentration of 10% by weight based on the weight of polyvinylidene fluoride to prepare a spinning solution. Next, using the through-air non-woven fabric described in Example 1 as a substrate, the spinning solution was spun on the needle from an injection needle (Terumo, gauge: 27G, needle length: 19 mm) to perform electrostatic spinning. It was prepared so that the basis weight of the ultrafine fiber layer would be 1.5 g/m ² . The spinning conditions of this example were those described in Example 1.

[Example 4]
A thermoplastic polyurethane elastomer (T1190, manufactured by DIC Covestropolymer Co., Ltd.) was dissolved in a mixed solvent (N,N-dimethylformamide:tetrahydrofuran=60% by weight:40% by weight) at a concentration of 12% by weight to prepare a conductive auxiliary agent. Sodium lauryl sulphate was used in a concentration of 0.025% by weight based on the total weight of the solution, and fluorooctylsilsesquioxane (manufactured by Nvidin Nano Technologies) as a water repellent at a concentration of 10% by weight based on the weight of the thermoplastic polyurethane elastomer. And a spinning solution was prepared. Next, using the through-air non-woven fabric described in Example 1 as a substrate, the spinning solution was spun on the needle from an injection needle (Terumo, gauge: 27G, needle length: 19 mm) to perform electrostatic spinning. It was produced so that the basis weight of the ultrafine fiber layer would be 3.0 g/m ² . The spinning conditions of this example were those described in Example 1.

[Comparative Example 1]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) was dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive additive was added at 0.025% by weight based on the total weight of the solution. Fluorooctylsilsesquioxane (manufactured by Nvidinano Technologies) was added as a water repellent at a concentration of 10% by weight based on the weight of polyvinylidene fluoride to prepare a spinning solution. Next, using the through-air non-woven fabric described in Example 1 as a base material, the spinning solution was spun on the needle from the injection needle described in Example 1 and electrostatically spun. It was produced so as to be 1 g/m ² . The spinning conditions of this comparative example were those described in Example 1.

[Comparative example 2]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) was dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive additive was added in an amount of 0.025% by weight based on the total weight of the solution. The concentration was added to prepare a spinning solution. Next, using the through-air nonwoven fabric described in Example 1 as a base material, the spinning solution was spun on from the injection needle described in Example 1 and electrostatically spun, and the basis weight of the ultrafine fiber layer was 1. It was manufactured so as to be ² g/m ² . The spinning conditions of this comparative example were those described in Example 1.

The measurement methods and definitions of the physical properties shown in the examples are shown below.

<Average flow pore size>
Using an Automated Perm Porometer manufactured by Porous Materials Co., a Gullwick manufactured by Porous Materials Co., Ltd. (surface tension=15.6 dynes/cm) was used for the immersion liquid, and the measurement was performed according to JIS K3832 (bubble point method). The results are shown in Table 1.

<Pressure loss of filter media>
Using a filter efficiency automatic detection device (Model 8130) manufactured by TSI, pressure loss was measured at a flow rate of 5.3 cm/sec. The results are shown in Table 1.

<Adhesion energy of water on the ultrafine fiber surface of the filter medium>
Using a contact angle measuring device DM-500 manufactured by Kyowa Interface Science Co., Ltd., the filter medium was made to stand still on a flat glass substrate. A drop of 4.0 μL of water was dropped on the surface of the filter medium with the glass substrate tilted at 0 degrees, and the static contact angle was measured 3 seconds after the drop of the drop was stopped. After that, the glass substrate is tilted at a rate of 0.5 degree/second, the sliding angle of the droplet when the end point of the droplet is separated from the rest position is α, the landing radius is r, the droplet mass is m, Adhesion energy E (mJ/m ² ) was calculated from the following equation (1), where gravitational acceleration is g. The results are shown in Table 1.

<Evaluation of detergency>
1.0 g of Kanto loam, 8 types of JIS test powder, was uniformly loaded on the filter medium surface (100 cm ² ), and suctioned for 1 minute at a wind speed of 1 m/sec from the side opposite to the surface on which the powder was loaded. The filter medium loaded with the powder was tilted at an angle of 40°, and 400 mL of pure water was dropped from the height of 5 cm from the surface of the filter medium to wash. Then, it was left to stand in a dryer at 70° C. for 1 hour to be dried. After drying, it was measured according to the method of pressure loss of the filter medium. This operation was repeated 5 times in total. The pressure loss increase rate R was calculated from the following equation (2), where P _{0 is the} initial pressure loss and P ₁ is the pressure loss after the cleaning property evaluation is completed. Detergency was rated as ⊚ when the pressure loss increase rate R was 0% or more and less than 5%, and ◯ when the pressure loss increase rate R was 5% or more and less than 10%, and was rated as X when 10% or more. The results are shown in Table 1.

Table 1

Comparing Examples 1 to 4 with Comparative Example 1, Examples 1 to 4 having an average flow pore diameter of 3.0 μm or less showed high cleanability, but Comparative Example 1 having an average flow pore diameter of more than 3.0 μm. It showed low detergency. In Comparative Example 1, although the adhesion energy was not inferior to that of Examples 1 to 4, the cleaning property was not obtained. It is considered that this is because the filter media of Examples 1 to 4 having an average flow pore size of 3.0 μm or less made dust less likely to enter the interior of the filter media and improved the cleaning property.

Examples 1 to 4 and Comparative Example 2 had a sufficient dust collecting property. However, comparing Examples 1 to 4 and Comparative Example 2, Examples 1 to 4 in which the adhesion energy is 3.0 mJ/m ² or less have high detergency, but the adhesion energy exceeds 3.0 mJ/m ² . Comparative Example 2 had low detergency. In Comparative Example 2, the average flow pore size was not inferior to that of Examples 1 to 4, but the cleaning property was not obtained. It is considered that this is because when the adhesion energy was 3.0 mJ/m ² or less, the droplets containing dust were easily removed from the surface of the filter medium.

FIGS. 1 and 2 show optical photographs of the filter media of Example 1 and Comparative Example 1 after the cleaning property evaluation. In the filter medium of FIG. 1 (Example 1), the dust was washed and removed to the extent that it could hardly be visually confirmed. On the other hand, in the filter medium of FIG. 2 (Comparative Example 1), dust remaining on the filter surface was visible.

The filter medium of the present invention has high dust collection efficiency, low pressure loss, and can easily remove dust with water without using chemicals, etc. It can be suitably used as an air filter for building air conditioning, a medium/high performance filter for industry, a HEPA filter or ULPA filter for a clean room, a cabin filter for an automobile, and the like.

Claims

A filter medium comprising an ultrafine fiber layer and a base material layer, wherein the filter medium has an average flow pore diameter of 3.0 μm or less, and water has an adhesion energy of 3.0 mJ/m 2 on the surface of the ultrafine fiber layer. The following is a filter medium.
The filter medium according to claim 1, wherein the ultrafine fibers forming the ultrafine fiber layer contain a water repellent.
The filter medium according to claim 2, wherein the water repellent contains fluorine.
The filter medium according to any one of claims 1 to 3, wherein the basis weight of the ultrafine fiber layer is 0.1 to 20.0 g/m 2 .
The filter medium according to any one of claims 1 to 4, wherein the base material layer is composed of a nonwoven fabric having an average fiber diameter of 1 to 30 µm.
A filter comprising the filter medium according to any one of claims 1 to 5.