JP7216322B2 - Filter medium and filter using the same - Google Patents

Description

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

High-performance filters such as High Efficiency Particulate Air (HEPA) filters have high collection efficiency, so they are used in clean room filters, home appliance filters for vacuum cleaners and air purifiers, building air conditioning filters, and industrial filters. It is used in filters for automobiles, cabin filters for automobiles, etc. When using a high-performance filter, if the pressure loss reaches the specified value due to clogging with dust, it is replaced with a new one, but in order to save resources and reduce running costs, a high-performance filter that can be washed and reused is recommended. Desired.

As an example of such a filter, Patent Literature 1 proposes a glass fiber filter medium for reducing the pressure loss of a high-performance filter. The filter medium of Patent Document 1 has a composition gradient in the thickness direction by blending ultrafine short glass fibers with an average fiber diameter of 0.2 to 0.6 μm and synthetic fibers with an average fiber diameter of 3 to 5 μm and making paper. is obtained. Further, Patent Document 2 proposes an electret filter medium for increasing the amount of dust retained. The filter material of Patent Document 2 has a laminated structure in which a polypropylene melt-blown nonwoven fabric and a support layer are joined together. The filter medium of Patent Document 2 is folded and used as a pleated filter.

On the other hand, Patent Literature 3 proposes a filter material which is a laminate having a PTFE microporous membrane on the surface thereof, which can easily remove dust. Since the PTFE microporous membrane is a dense membrane in which very fine fibrils are formed between resin masses called nodes, the collected dust tends to accumulate on the surface of the membrane. Dust can be washed away relatively easily.

Japanese Unexamined Patent Application Publication No. 2012-077400 JP 2014-226629 A JP 2016-209870 A

However, the glass fiber filter media and electret filter media such as those disclosed in Patent Documents 1 and 2 have a relatively large pore size (average flow pore size) formed between the fibers that make up the filter media, and the collected dust is removed from the filter media. enter the interior of For this reason, the collected dust cannot be easily removed, and depending on the situation, it is necessary to clean it using a chemical or the like, which causes environmental and cost problems.

On the other hand, the filter medium of Patent Document 3 may be washed with water to remove dust adhering to the surface of the filter medium. A part of it may remain on the surface, and there was a problem in terms of self-cleaning and quick-drying.

An object of the present invention is to solve the above-mentioned problems, and to provide a filter that has high dust collection efficiency, low pressure loss, can easily remove dust with water without using chemicals, etc., and is excellent in quick drying. An object of the present invention is to provide a filter medium and a filter using the filter medium.

The present inventors have made intensive studies to solve the above problems. As a result, it was confirmed that both low pressure loss and high collection efficiency can be achieved at a high level by using extremely fine fibers obtained by methods such as electrostatic spinning and by setting the average flow pore size to a certain value or less. In addition, by imparting water repellency to such ultrafine fibers, the water repellency of the surface of the filter medium is improved, making it easier to remove droplets on the surface after washing, improving quick-drying properties. It was found that it becomes difficult to clean and washability is impaired. Therefore, the inventors have made further studies to achieve both quick-drying and cleansing properties. The present inventors have found that by reducing the surface water adhesion energy to a certain value or less, it is possible to obtain a filter medium that achieves not only dust collection efficiency and pressure loss, but also cleanability and quick-drying properties, and completed the present invention.

That is, the present invention has the following configurations for solving the above problems.

[1] A filter medium comprising an ultrafine fiber layer and a substrate layer, wherein the average flow pore diameter 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 3.0 mJ. /m ² or less.
[2] The filter medium according to [1] above, wherein the microfibers constituting the microfiber layer contain a water-repellent agent.
[3] The filter medium according to [2] above, wherein the water repellent agent contains fluorine.
[4] The filter medium according to any one of [1] to [3], wherein the ultrafine fiber layer has a basis weight of 0.1 to 20.0 g/m ² .
[5] The filter medium according to any one of [1] to [4], wherein the substrate layer is composed 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.

ADVANTAGE OF THE INVENTION According to the present invention having the above configuration, there is provided a filter medium that has high dust collection efficiency, low pressure loss, can easily remove dust with water without using chemicals, etc., and is excellent in quick drying. It becomes possible to In particular, filter media suitable for household appliance filters for vacuum cleaners and air purifiers, air filters for building air conditioning, medium and high performance filters for industrial use, HEPA and ULPA filters for clean rooms, air filters for automobiles, etc. can be provided.

1 is an optical photograph of the filter medium of Example 1 after evaluation of washability. 4 is an optical photograph of the filter medium of Comparative Example 1 after evaluation of washability.

The present invention will be described in detail below.

The filter medium of the present invention is a filter medium comprising an ultrafine fiber layer and a base material layer, the average flow pore diameter 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, it is possible to provide a filter medium that has high dust collection efficiency, low pressure loss, can easily remove dust with water without using chemicals, etc., and is excellent in quick drying. It becomes possible.

<Ultrafine fiber layer>
The filter media of the present invention includes a microfiber layer. In this specification, 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. A range is more preferred. As the average fiber diameter of the ultrafine fibers becomes smaller, the specific surface area becomes larger, so it becomes easier to obtain high filter properties such as high collection efficiency and low pressure loss. In addition, since the pore diameter formed between the fibers constituting the filter medium is small, dust is easily collected on the surface of the filter medium, which facilitates cleaning. On the other hand, as the fiber diameter decreases, the mechanical strength per fiber decreases, which may cause fiber breakage during filter processing or use. Yarn strength is obtained. Although the coefficient of variation of the fiber diameter of the ultrafine fibers is not particularly limited, it 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 properties and easy washability. The average fiber diameter can be measured by a known method, for example, using a scanning electron microscope, observing the ultrafine fibers, measuring the diameter of 50 ultrafine fibers using image analysis software, and calculating the average as the average fiber diameter.

The resin constituting the ultrafine fiber is not particularly limited, and may be polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyamide, polyurethane, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride. , polyacrylonitrile, polymethyl methacrylate, polyglycolic acid, polycaprolactone, polyvinyl acetate, polycarbonate, polyimide, polyetherimide, cellulose, cellulose derivatives, chitin, chitosan, collagen, gelatin, and copolymers thereof Materials can be exemplified. From the viewpoint of reducing the adhesion energy of water, the resin constituting the ultrafine fiber is preferably a hydrophobic resin, for example, more preferably a polyolefin resin, a fluorine resin, or a polyvinylidene fluoride resin. is more preferred. Examples of the polyvinylidene fluoride-based resin include, but are not particularly limited to, vinylidene fluoride polymers, copolymers of vinylidene fluoride and hexafluoropropylene, and copolymers of vinylidene fluoride and trifluoroethylene. 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, more preferably in the range of 50,000 to 5,000,000. More preferably, it is from 100,000 to 1,000,000. If the weight average molecular weight is 10,000 or more, it is preferable because it is excellent in the fiber formation property of ultrafine fibers and it becomes easy to obtain ultrafine fibers with a small average fiber diameter. It is preferable because it has excellent plasticity and facilitates processing.

It is preferable that the ultrafine fibers constituting the ultrafine fiber layer contain a water-repellent agent. By containing a water repellent agent, it is possible to reduce the adhesion energy of water on the surface of the filter medium and to improve the washability and quick-drying properties. The water repellent is not particularly limited as long as it has the effect of lowering the adhesion energy of water, and includes silicon-based silane compounds, fluorine-based silane compounds, fluorine-containing cage-type silsesquioxanes, fluorine-modified polyurethanes, and silicon-modified water repellents. Polyurethane can be exemplified. Among them, it is preferable to use a fluorine-containing water repellent such as fluorine-containing cage silsesquioxane or fluorine-modified polyurethane from the viewpoint of water repellency, workability and cost. The content of the water repellent agent is not particularly limited, but it is preferably in the range of 0.1 to 20% by weight, preferably 1 to 15% by weight, based on the microfibers and fine particles generated during spinning by the electrostatic spinning method. is more preferable. If the concentration of the water repellent agent is 0.1% by weight or more, the effect of lowering the adhesion energy of water can be obtained, and if it is 20% by weight or less, an improvement in the effect corresponding to 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. It is an index that represents The adhesion energy of water (E) is determined by tilting the filter medium with water dropped on the ultrafine fiber layer, sliding down angle (α) when water starts to slide down, contact radius of water at that time (r) and drop It is calculated from the following formula (1) using the mass (m). A specific measuring method is shown in Examples.

Although it is not bound by any particular theory, it is believed that the adhesion energy of water in the ultrafine fiber layer is influenced by the fine uneven structure of the surface formed by the ultrafine fibers, the water repellency of the ultrafine fibers, and other properties. It is It is common to use the value of the contact angle as an index for evaluating the water repellency of a surface. It is preferable to use In the filter medium of the present invention, it is essential that the adhesion energy of water on the surface of the ultrafine fiber layer is 3.0 mJ/m ² or less, and more preferably 2.0 mJ/m ² or less. Although the lower limit is not particularly limited, it can be set to 0.1 mJ/m ² or more in consideration of industrial rationality. When the adhesion energy of water is 3.0 mJ/m ² or less, water easily slides down the ultrafine fiber layer during washing, and the filter can be easily drained after washing with water, and can be dried quickly.

The basis weight of the ultrafine fiber layer can be appropriately selected according to the required filter performance, washability, quick drying property, etc., and can be exemplified in the range of 0.1 to 20.0 g/m ² . If the basis weight is 0.1 g/ ^{m 2} or more, the fiber matrix composed of the ultrafine fibers will be sufficiently dense, and the collection efficiency and washability can be improved. 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 , more 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 they do not significantly impair the effects of the present invention.

Although the method for producing the ultrafine fiber layer is not particularly limited, it is preferably produced by an electrostatic spinning method. By using the electrostatic spinning method, it is possible to uniformly spin ultrafine fibers, and excellent filter properties can be obtained.

The electrostatic spinning method is a method in which a spinning solution is discharged and an electric field is applied to convert the discharged spinning solution into fibers, and nanofibers of submicron order are collected on a collector in the form of a non-woven fabric. The method of electrostatic spinning is not particularly limited, and generally known methods, for example, a needle method using one or more needles, and the productivity per needle by blowing an air flow to the tip of the needle A multi-hole spinneret method in which multiple solution ejection holes are provided in one spinneret. There is an electro-bubble method in which electrostatic spinning is performed using bubbles generated in the inner layer as a starting point, and the method can be selected according to the fiber diameter and physical properties of the desired nanofibers.

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

The solvent for dispersing or dissolving the resin is not particularly limited, and water, methanol, ethanol, propanol, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, 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 etc. can be exemplified. The mixing ratio in the case of using a mixture is not particularly limited, and can be appropriately set in consideration of the desired spinnability and dispersibility, and the physical properties of the obtained fiber and filter medium.

When the ultrafine fiber contains a water repellent agent, it is not particularly limited, but it is preferable to mix the water repellent agent with the resin in the spinning solution. The mixing method is not particularly limited, and methods such as stirring and ultrasonic treatment can be exemplified. Also, the order of mixing is not particularly limited, and they may be mixed simultaneously or sequentially. The mixing time is not particularly limited as long as the water repellent agent 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 added to the spinning solution for the purpose of improving the stability of electrospinning and fiber formation. 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 surfactant concentration is preferably in the range of 5% by weight or less relative to the spinning solution. If it is 5% by weight or less, it is preferable because the improvement of the effect corresponding to the use can be obtained.

Components other than those described above may be included as components of the spinning solution as long as they do not significantly impair the effects of the present invention.

In order to obtain ultrafine fibers by electrostatic spinning, the spinning solution preferably has a viscosity 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 can be obtained, and when it is 10,000 cP or less, the spinning solution can be easily discharged. If the viscosity is in the range of 50 to 8,000 cP, good spinnability can be obtained over 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 and the type and mixing ratio of the solvent.

As for the temperature of the spinning solution, the spinning can be carried out at room temperature, or the spinning can be carried out by heating and cooling. Examples of the method for discharging the spinning solution include a method for discharging the spinning solution filled in a syringe from a nozzle using a pump. Although the inner diameter of the nozzle is not particularly limited, it is preferably in the range of 0.1 to 1.5 mm. The discharge rate is not particularly limited, but is preferably 0.1 to 10 mL/hr.

The method for applying an electric field is not particularly limited as long as the electric field can be formed between 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 is preferably in the range of 5 to 100 kV. Also, the distance between the nozzle and the collector is not particularly limited as long as the fibers are formed, but it is preferably in the range of 5 to 50 cm. The collector is not particularly limited as long as it can collect the spun fibers, and its material and shape are not particularly limited. As the material of the collector, a conductive material such as metal is preferably used. The shape of the collector is not particularly limited, but examples thereof include a plate shape, a shaft shape, a conveyor shape, and the like. If the collector has a flat plate shape, it can collect the fiber aggregates in a sheet shape, and if it has a shaft shape, it can collect the fiber aggregates in a tubular shape. If it is conveyer-shaped, it is possible to continuously produce fiber aggregates collected in a sheet-like form. In the present invention, it is preferable to form the ultrafine fiber layer directly on the substrate layer by placing the substrate layer on a collector and spinning thereon.

<Base material layer>
The filter medium of the present invention includes a substrate layer. By including the base material layer, the properties of the ultrafine fiber layer, such as mechanical strength, durability, pleating workability, and adhesive properties, can be imparted. The base material layer can be appropriately selected according to the required properties and form of the filter medium, and examples thereof include nonwoven fabric, woven fabric, net, and 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 material such as polypropylene or polyethylene, it is characterized by excellent chemical resistance, and it is suitable for liquids that require chemical resistance. It can be suitably used for applications such as filters. In the case of a substrate layer using a polyester-based material such as polyethylene terephthalate, polybutyl terephthalate, polylactic acid, or a copolymer containing these as the main component, it has excellent pleat characteristics, so it is suitable for air filters, etc. that require pleating. It can be suitably used for the purpose of

From the viewpoint of the workability and air permeability of the filter medium, it is preferable to use a nonwoven fabric as the base material layer. The nonwoven fabric is not particularly limited, and nonwoven fabrics include through air nonwoven fabrics, airlaid nonwoven fabrics, spunlaced nonwoven fabrics, wet nonwoven fabrics, spunbond nonwoven fabrics, meltblown nonwoven fabrics, chemical bond nonwoven fabrics, flash spun nonwoven fabrics, electrostatic spun nonwoven fabrics, and the like. can be done.

In the filter medium of the present invention, it is preferable that the ultrafine fiber layer and the substrate layer are integrated. The method of integration is not particularly limited, but the separately manufactured ultrafine fiber layer and base layer may be integrated by adhesive or heat fusion, or the ultrafine fiber layer may be directly spun onto the base material layer. Alternatively, the ultrafine fiber layer may be directly spun onto the base material layer, and then heat-bonded.

Although there is no particular limitation when heat bonding is performed, it is preferable to use a nonwoven fabric made of heat-fusible conjugate fibers composed of a low-melting point component and a high-melting point component as the base material layer. The material configuration, composite form, and cross-sectional shape of the heat-fusible conjugate fiber are not particularly limited, and known ones can be used. The material composition includes copolymerized polyethylene terephthalate and polyethylene terephthalate, copolymerized polyethylene terephthalate and polypropylene, high-density polyethylene and polypropylene, high-density polyethylene and polyethylene terephthalate, copolymerized polypropylene and polypropylene, copolymerized polypropylene and polyethylene terephthalate, polypropylene and polyethylene terephthalate. A combination such as Furthermore, considering the availability of raw materials, combinations of copolymer polyethylene terephthalate and polyethylene terephthalate, high-density polyethylene and polypropylene, and high-density polyethylene and polyethylene terephthalate are preferable examples.

Examples of the composite form of the cross section include a sheath-core type, an eccentric sheath-core type, and a side-by-side type. The cross-sectional shape of the fiber is also not particularly limited, and any cross-sectional shape such as an elliptical, hollow, triangular, quadrangular, eight-shaped cross section, etc. can be adopted in addition to the general round shape. From the viewpoint of enhancing the adhesion between the fiber layer and the substrate layer, it is preferable to have a flat shape substantially parallel to the surface of the ultrafine fiber layer. The substrate layer having fibers with such a cross-sectional shape can be formed, for example, by processing elliptical, flattened, or semicircular fibers into a web and then bonding them with heat or an adhesive, or by using circular fibers. It can be obtained by consolidating a nonwoven fabric with a hot roll.

A method for producing a nonwoven fabric composed of the heat-fusible conjugate fibers is not particularly limited, and known production methods such as carding, papermaking, airlaid, meltblown, and spunbonding can be used. There are no particular restrictions on the method of bonding fibers when processing into a nonwoven fabric, and examples include thermal fusion bonding by air-through processing, thermocompression bonding by embossing, fiber entanglement by needle punching or spunlace processing, and chemical bonding with an adhesive. be done.

The thickness of the fibers constituting the base material layer is not particularly limited, but for example, those 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. . When the average fiber diameter is 1 μm or more, the pressure loss of the substrate layer can be suppressed, and when 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 even more preferably 60 g/m ² or more. If the basis weight of the base material layer is 15 g/m ² or more, shrinkage, wrinkling, curling, etc. of the ultrafine fiber layer can be suppressed, and processing strength can be imparted. The specific volume of the substrate 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 peel strength and wear resistance of the ultrafine fiber layer are improved, and the reduction in collection efficiency during repeated washing is reduced, which is preferable. The thickness of the substrate layer is not particularly limited, and can be appropriately selected according to the desired filter properties and application. For example, when used as a pleated filter, it is preferable that the substrate layer has a thickness of 0.1 to 5 mm to improve suitability for pleating.

The air permeability of the base 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 preferred. Air permeability of 10 cc/cm ² /sec or more is preferable because pressure loss can be reduced.

When a filter medium is produced by directly spinning an ultrafine fiber layer on a substrate layer by an electrostatic spinning method, the electrical leakage resistance value of the substrate layer should be 10 ¹⁰ Ω or less. It is preferably 10 ⁷ Ω or less, and more preferably 10 7 Ω or less. If 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 electrical repulsion, and adhesion can be enhanced. The average value of the tensile strength in the longitudinal 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 preferred.

The substrate 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 it does not significantly impair the effects of the present invention. Although it may be applied, from the viewpoint of washability, it is preferable to apply a water-repellent finish.

<Filter material>
The filter medium of the present invention includes the above-described ultrafine fiber layer and substrate layer, and on the surface side of the ultrafine fiber layer is further at least one layer selected from the group consisting of nonwoven fabrics, woven fabrics, nets and microporous films. may be laminated and integrated. By laminating and integrating, the surface of the ultrafine fiber layer becomes less likely to be exposed on the surface, and abrasion resistance, durability, and processing strength can be improved. From the viewpoint of washability, it is preferable that the net is laminated and integrated. The integration method is not particularly limited, and may be thermocompression bonding using a heated flat roll or embossing roll, bonding using a hot melt agent or chemical adhesive, or thermal bonding using circulating hot air or radiant heat.

The filter medium of the present invention is characterized by having an average flow pore size 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 substrate layer. The average flow pore size is an index of the size of the pores formed between the fibers that make up the filter medium, and can be measured by a known method. For example, it can be measured with a pore size distribution analyzer or the like, and the details are shown in Examples. If the average flow pore diameter is 3.0 μm or less, it is believed that both collection efficiency and pressure loss can be achieved, and dust is less likely to enter the inside of the filter medium, thereby improving washability. The lower limit of the average flow pore diameter 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, basis weight, etc. of the ultrafine fibers. It is believed that the substrate layer does not contribute significantly to the mean flow pore size.

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

The filter medium of the present invention is used as a filter in combination with known structures such as a frame, reinforcing material, filter medium other than the present invention, and the like. 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 application of the filter is not particularly limited, but home appliance filters for vacuum cleaners and air purifiers, air filters for building air conditioning, medium- and high-performance filters for industrial use, HEPA filters and ULPA filters for clean rooms, and automobile filters. is preferably a cabin filter or the like.

The following examples are for illustrative 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 was added as a conductive aid to the total solution weight at 0.025% by weight. A spinning solution was prepared by adding fluorooctylsilsesquioxane (manufactured by ND Nanotechnologies Co., Ltd.) as a water-repellent agent at a concentration of 10% by weight with respect to the weight of polyvinylidene fluoride. Next, a through-air nonwoven fabric (fiber diameter: 10 μm, thickness: 60 μm, basis weight: 18 g/m ² ) made of copolymerized polyethylene terephthalate and heat-adhesive composite fibers containing polyethylene terephthalate is used as a base material, and the spinning solution is applied thereon. was spun from an injection needle (manufactured by Terumo Corporation, gauge: 27G, 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 in this example were as follows: single hole solution supply rate: 1.0 mL/hr, applied voltage: 30 kV, spinning distance: 150 mm, temperature in the spinning space: 25°C, humidity: 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 was added as a conductive aid to the total solution weight at 0.025% by weight. A spinning solution was prepared by adding fluorooctylsilsesquioxane (manufactured by ND Nanotechnologies Co., Ltd.) as a water-repellent agent at a concentration of 10% by weight with respect to the weight of polyvinylidene fluoride. Next, the through-air nonwoven fabric described in Example 1 is used as a base material, and the spinning solution is spun onto the base material from an injection needle (manufactured by Terumo Corporation, gauge: 27G, needle length: 19mm) for electrostatic spinning, It was produced so that the fabric weight of the ultrafine fiber layer was 1.5 g/m ² . The spinning conditions for 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 was added as a conductive aid to the total solution weight at 0.025% by weight. A fluorine-based copolymer (Dialomar FF129D, manufactured by Dainichiseika Co., Ltd.) 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, the through-air nonwoven fabric described in Example 1 is used as a base material, and the spinning solution is spun onto the base material from an injection needle (manufactured by Terumo Corporation, gauge: 27G, needle length: 19mm) for electrostatic spinning, It was produced so that the fabric weight of the ultrafine fiber layer was 1.5 g/m ² . The spinning conditions for this example were those described in Example 1.

[Example 4]
A thermoplastic polyurethane elastomer (manufactured by DIC Covestro Polymer Co., Ltd., T1190) was dissolved in a mixed solvent (N,N-dimethylformamide: tetrahydrofuran = 60% by weight: 40% by weight) at a concentration of 12% by weight, and used as a conductive aid. 0.025% by weight of sodium lauryl sulfate with respect to the total weight of the solution, and 10% by weight of fluorooctylsilsesquioxane (manufactured by NVIDIA Nanotechnologies Co., Ltd.) as a water repellent with respect to the weight of the thermoplastic polyurethane elastomer. was added to prepare the spinning solution. Next, the through-air nonwoven fabric described in Example 1 is used as a base material, and the spinning solution is spun onto the base material from an injection needle (manufactured by Terumo Corporation, gauge: 27G, needle length: 19mm) for electrostatic spinning, It was produced so that the fabric weight of the ultrafine fiber layer was 3.0 g/m ² . The spinning conditions for 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 was added as a conductive aid to the total solution weight at 0.025% by weight. A spinning solution was prepared by adding fluorooctylsilsesquioxane (manufactured by ND Nanotechnologies Co., Ltd.) as a water-repellent agent at a concentration of 10% by weight with respect to the weight of polyvinylidene fluoride. Next, the through-air nonwoven fabric described in Example 1 is used as a base material, and the spinning solution is spun thereon from the injection needle described in Example 1 to perform electrostatic spinning. It was made to be 1 g/m ² . The spinning conditions for this comparative example were those described in Example 1.

[Comparative Example 2]
Polyvinylidene fluoride homopolymer (weight average molecular weight: 300,000) is dissolved in N,N-dimethylacetamide at a concentration of 18% by weight, and sodium lauryl sulfate as a conductive agent is added at 0.025% by weight based on the total solution weight. concentrations were added to prepare spinning solutions. Next, the through-air nonwoven fabric described in Example 1 is used as a base material, and the spinning solution is spun thereon from the injection needle described in Example 1 to perform electrostatic spinning. It was made to be 2 g/m ² . The spinning conditions for 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, Gullwick manufactured by Porous Materials (surface tension = 15.6 dynes/cm) was used as an immersion liquid, and measurement was performed according to JIS K3832 (bubble point method). Table 1 shows the results.

<Pressure loss of filter media>
Pressure loss was measured using an automatic filter efficiency detector (Model 8130) manufactured by TSI at a flow rate of 5.3 cm/sec. Table 1 shows the results.

<Adhesion energy of water on the ultrafine fiber surface of the filter material>
Using a contact angle measurement device DM-500 manufactured by Kyowa Interface Science Co., Ltd., the filter medium was allowed to rest on a flat glass substrate. A 4.0 μL water droplet 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 droplet stopped. After that, the glass substrate is tilted at a speed of 0.5 degrees/second, and α is the sliding angle of the droplet when the end point of the droplet separates from the stationary position, r is the landing radius, m is the droplet mass, Denoting the gravitational acceleration as g, the adhesion energy E (mJ/m ² ) was obtained from the following formula (1). Table 1 shows the results.

<Evaluation of washability>
1.0 g of JIS test powder Class 8 Kanto loam was uniformly loaded on the surface of the filter medium (100 cm ² ) and sucked from the side opposite to the powder-loaded surface at a wind speed of 1 m/sec for 1 minute. The filter medium loaded with the powder was tilted at an angle of 40°, and washed by dropping 400 mL of pure water from a height of 5 cm from the surface of the filter medium. After that, it was dried by leaving it in a dryer at 70° C. for 1 hour. After drying, it was measured according to the method of pressure drop of the filter media. This operation was repeated a total of 5 times. The initial pressure loss was P ₀ , the pressure loss after the evaluation of detergency was P ₁ , and the pressure loss increase rate R was calculated from the following equation (2). Detergency was evaluated as ⊚ when the pressure loss increase rate R was 0% or more and less than 5%, ∘ when it was 5% or more and less than 10%, and x when it was 10% or more. Table 1 shows the results.

Comparing Examples 1 to 4 with Comparative Example 1, Examples 1 to 4 with an average flow pore size of 3.0 μm or less showed high detergency, but Comparative Example 1 with an average flow pore size of more than 3.0 μm showed high detergency. It showed low detergency. Although Comparative Example 1 was not inferior to Examples 1 to 4 in terms of adhesion energy, cleanability was not obtained. It is believed that this is because the filter media of Examples 1 to 4, in which the average flow pore size is 3.0 μm or less, makes it difficult for dust to enter the inside of the filter media, thereby improving washability.

Examples 1 to 4 and Comparative Example 2 had sufficient dust trapping properties. However, when comparing Examples 1 to 4 and Comparative Example 2, Examples 1 to 4 with an adhesion energy of 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 washability. Comparative Example 2 was not inferior to Examples 1 to 4 in average flow pore diameter, but was not cleanable. This is considered to be because droplets containing dust are easily removed from the surface of the filter medium when the adhesion energy is 3.0 mJ/m ² or less.

1 and 2 show optical photographs of the filter media of Example 1 and Comparative Example 1 after evaluation of cleaning properties. 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 industrial use, a HEPA filter or ULPA filter for clean rooms, a cabin filter for automobiles, and the like.

Claims (9)

A filter medium comprising 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 3.0 mJ/m ² or less.
filter media. 2. The filter medium according to claim 1, wherein the ultrafine fibers constituting said ultrafine fiber layer contain a water-repellent agent. 3. The filter medium according to claim 2, wherein said water repellent agent is mixed with said ultrafine fibers constituting said ultrafine fiber layer. The filter medium according to claim 2 or 3 , wherein the water repellent agent contains fluorine. The filter medium according to any one of claims 1 to 4 , wherein the ultrafine fiber layer has a basis weight of 0.1 to 20.0 g/ ^m2 . The filter medium according to any one of claims 1 to 5 , wherein the base material layer is composed of a nonwoven fabric having an average fiber diameter of 1 to 30 µm. The ultrafine fibers constituting the ultrafine fiber layer are hydrophobic resins containing a fluorine-containing water repellent agent,
The filter medium according to any one of claims 1-6 . The hydrophobic resin is a fluororesin,
The filter media according to claim 7 . A filter comprising the filter media of any one of claims 1-8 .

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