CN113164849A

CN113164849A - Filter medium and filter using same

Info

Publication number: CN113164849A
Application number: CN202080006611.0A
Authority: CN
Inventors: 平本晋平; 梅林阳; 伊东秀実
Original assignee: JNC Corp; JNC Fibers Corp
Current assignee: JNC Corp; JNC Fibers Corp
Priority date: 2019-01-21
Filing date: 2020-01-14
Publication date: 2021-07-23
Also published as: JP7216322B2; WO2020153174A1; JP2020116487A

Abstract

Provided are a filter medium which has high dust collection efficiency, low pressure loss, and excellent quick-drying properties, and which can easily remove dust with water without using chemicals or the like, and a filter using the filter medium. A filter medium comprising an ultrafine fiber layer and a base material layer, and the filterThe average flow pore diameter of the filter medium is 3.0 [ mu ] m or less, and the water adhesion energy on the surface of the ultrafine fiber layer is 3.0mJ/m²The following.

Description

Filter medium and filter using same

Technical Field

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

Background

High performance filters, such as High Efficiency Particulate Air (HEPA) filters, have High collection Efficiency and are therefore used in filters for clean rooms, filters for household appliances such as vacuum cleaners and Air cleaners, filters for Air conditioning in buildings, filters for industrial use, cabin filters (cabin filters) for automobiles, and the like. In the use of a high-performance filter, when the pressure loss due to clogging with dust reaches a predetermined value, the filter is replaced with a new one, but in order to save resources or to suppress running costs (running cost), a high-performance filter which can be cleaned and reused is desired.

As an example of such a filter, patent document 1 proposes a glass fiber filter material for realizing a 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 obtained by blending and producing a microfine glass short fiber having an average fiber diameter of 0.2 to 0.6 μm and a synthetic fiber having an average fiber diameter of 3 to 5 μm. Patent document 2 proposes an electret (electret) filter medium for increasing the amount of dust held. The filter material of patent document 2 has a laminated structure in which a polypropylene melt-blown nonwoven fabric and a support layer are bonded to each other, and the melt-blown nonwoven fabric has a fiber diameter of about 5 μm and is formed with a large number of small holes having a pore diameter of 1.0mm 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 laminate having a microporous Polytetrafluoroethylene (PTFE) membrane disposed on the surface thereof, the microporous membrane being capable of easily removing dust. Since the PTFE microporous membrane is a dense membrane in which very fine fibrils (fibrils) are formed between resin blocks called nodes (nodes), the collected dust is easily accumulated on the surface of the membrane, and the dust can be relatively easily washed away from such a filter medium.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012-077400

Patent document 2: japanese patent laid-open No. 2014-226629

Patent document 3: japanese patent laid-open No. 2016-209870

Disclosure of Invention

Problems to be solved by the invention

However, in the glass fiber filter or electret filter as in patent documents 1 and 2, the size of pores formed between fibers constituting the filter (average flow pore diameter) is relatively large, and the collected dust enters the filter. Therefore, the collected dust cannot be easily removed, and cleaning using chemicals or the like is necessary as appropriate, and therefore, there is a problem in terms of environment or cost.

On the other hand, in the filter medium of patent document 3, washing with water is sometimes performed to remove dust adhering to the surface of the filter medium, but the droplet removal performance of the PTFE microporous membrane is not necessarily sufficient, and a part of water containing dust may remain on the surface, which is problematic in terms of self-cleaning performance and quick-drying performance.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a filter medium having high dust collection efficiency and low pressure loss, and being capable of easily removing dust with water without using chemicals or the like, and having excellent quick-drying properties, and a filter using the filter medium.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems. As a result, it was confirmed that: by using an extremely fine fiber obtained by a method such as electrospinning and setting the average flow pore diameter to a constant or smaller, it is possible to achieve both low pressure loss and high collection efficiency at a high level. Further, it has been found that when water repellency is imparted to such an ultrafine fiber, the water repellency of the surface of the filter medium is improved, and droplets on the surface are easily removed after cleaning, so that quick-drying properties are improved, while water hardly penetrates into the filter medium, and cleaning properties are impaired. The present inventors have further studied to achieve both quick-drying properties and cleaning properties, and have found that quick-drying properties and cleaning properties can be expressed by using the adhesion energy of water on the surface of a filter medium as a parameter, and that a filter medium that achieves both cleaning properties and quick-drying properties in addition to dust collection efficiency and pressure loss can be obtained by using the adhesion energy of water on the surface of a filter medium at a constant value or less, thereby completing the present invention.

That is, the present invention has the following configuration to solve the above problems.

[1]A filter medium comprising an ultrafine fiber layer and a base material layer, wherein the average flow pore size of the filter medium is 3.0 [ mu ] m or less, and the water adhesion energy on the surface of the ultrafine fiber layer is 3.0mJ/m²The following.

[2] The filter medium according to [1], wherein the ultrafine fibers constituting the ultrafine fiber layer contain a water-repellent agent.

[3] The filter medium according to [2], wherein the water-repellent agent contains fluorine.

[4]According to [1]To [3]]The filter medium of any one of the above, wherein the ultrafine fiber layer has a weight per unit area of 0.1g/m²～20.0g/m²。

[5] The filter medium according to any one of [1] to [4], wherein the base material layer comprises a nonwoven fabric having an average fiber diameter of 1 μm to 30 μm.

[6] A filter comprising the filter medium according to any one of [1] to [5 ].

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention having the above configuration, it is possible to provide a filter medium having high dust collection efficiency, low pressure loss, easy dust removal by water without using chemicals or the like, and excellent quick-drying properties. In particular, it is possible to provide a filter medium suitable for household electric appliance filters such as vacuum cleaners and Air cleaners, Air filters for Air conditioning in buildings, industrial medium-performance and/or high-performance filters, HEPA filters or Ultra Low Permeability Air (ULPA) filters for clean rooms, Air filters for automobiles, and the like.

Drawings

FIG. 1 is an optical photograph showing the filter medium of example 1 after evaluation of cleanability.

FIG. 2 is an optical photograph showing the filter medium of comparative example 1 after evaluation of cleanability.

Detailed Description

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, and is characterized in that: the average flow pore diameter of the filter medium is 3.0 μm or less, and the water adhesion energy on the surface of the ultrafine fiber layer is 3.0mJ/m²The following. By having such a feature, it is possible to provide a filter medium which has high dust collection efficiency, low pressure loss, and excellent quick-drying property, and which can easily remove dust with water without using chemicals or the like.

< ultra fine fiber layer >

The filter medium of the present invention comprises an ultrafine fiber layer. In the present specification, the term "microfine fibers" means fibers having an average fiber diameter of less than 1 μm. The ultrafine fibers constituting such an ultrafine fiber layer are not particularly limited, and the average fiber diameter is preferably in the range of 10nm to 999.9nm, more preferably 50nm to 200nm, and still more preferably 80nm to 150 nm. When the average fiber diameter of the ultrafine fibers is small, the specific surface area is large, and therefore high filter characteristics such as high collection efficiency and low pressure loss can be easily obtained. Further, since the pore diameter formed between the fibers constituting the filter medium is reduced, dust is easily collected on the surface of the filter medium, and cleaning is easy. On the other hand, as the fiber diameter decreases, the mechanical strength per fiber decreases, and there is a possibility that fiber breakage is caused at the time of filter processing or use, and if the average fiber diameter of the ultrafine fibers is 10nm or more, satisfactory monofilament strength can be obtained. The coefficient of variation in the fiber diameter of the ultrafine fibers is not particularly limited, but is preferably 0.5 or less, and more preferably 0.3 or less. When the coefficient of variation of the first fibers is 0.5 or less, excellent filter characteristics and easy cleanability can be obtained. The average fiber diameter can be measured by a known method, and examples thereof include: the ultrafine fibers were observed with a scanning electron microscope, and the diameters of 50 ultrafine fibers were measured with image analysis software, and the average value thereof was defined as the average fiber diameter and the like.

The resin constituting the ultrafine fibers is not particularly limited, and examples thereof include: polymer materials such as polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, 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 derivatives, chitin (chitin), chitosan, collagen, gelatin, and copolymers thereof. From the viewpoint of reducing the water adhesion energy, the resin constituting the ultrafine fibers is preferably a hydrophobic resin, more preferably a polyolefin resin or a fluorine resin, and further preferably a polyvinylidene fluoride resin. The polyvinylidene fluoride resin is not particularly limited, and examples thereof include: vinylidene fluoride polymers, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and trifluoroethylene, and the like. The weight average molecular weight of the resin constituting the ultrafine fibers is not particularly limited, but is preferably within a range of 10,000 to 10,000,000, more preferably within a range of 50,000 to 5,000,000, and still more preferably within a range of 100,000 to 1,000,000. When the weight average molecular weight is 10,000 or more, the ultrafine fibers are excellent in fiber formability and can be easily obtained as ultrafine fibers having a small average fiber diameter, and therefore, 10,000,000 or less is preferable because the solubility and the thermoplasticity are excellent and the processability is easy.

The ultrafine fibers constituting the ultrafine fiber layer preferably contain a water-repellent agent. By containing a water-repelling agent, the ability of water to adhere to the surface of the filter medium can be reduced, and the cleaning properties and quick-drying properties can be improved. The water-repellent agent is not particularly limited as long as it exhibits an effect of reducing the adhesion energy of water, and examples thereof include: a silicon-based silane compound, a fluorine-containing polyhedral oligomeric silsesquioxane, a fluorine-modified polyurethane, and a silicon-modified polyurethane. Among them, from the viewpoint of water repellency, workability, and price, it is preferable to use a fluorine-containing water-repellent agent such as a fluorine-containing polyhedral oligomeric silsesquioxane or a fluorine-modified polyurethane. The content of the water-repellent agent is not particularly limited, but is preferably in the range of 0.1 to 20 wt%, more preferably 1 to 15 wt%, relative to the ultrafine fibers and the fine particles generated during spinning by the electrospinning method. The concentration of the water-repellent agent is preferably 0.1% by weight or more because the effect of reducing the water-binding ability is obtained, and 20% by weight or less because the effect corresponding to the amount used is improved.

The filter medium of the present invention is characterized in that: the surface of the ultrafine fiber layer had an energy of adhesion of water of 3.0mJ/m²Hereinafter, the water adhesion energy is an index indicating the degree of ease with which water slides off the surface. The water adhesion energy (E) is calculated by using the following formula (1) using a falling angle (α) at which water starts to fall off when the filter medium in which water is dropped on the ultrafine fiber layer is tilted, a contact radius (r) of water at this time point, and a mass (m) of liquid droplets. Specific measurement methods are shown in examples.

While not particularly limited by theory, it is believed that the ability of the ultrafine fiber layer to adhere to water 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. As an index for evaluating the water repellency of the surface, a value of a contact angle is generally used, but when evaluating the droplet removal performance of the surface, only the contact angle is insufficient, and a value of an adhesion energy of water is preferably used. In the filter medium of the present invention, it is important that the ability of water to adhere to the surface of the ultrafine fiber layer be 3.0mJ/m²Hereinafter, if it is 2.0mJ/m²The following is more preferable. The lower limit is not particularly limited, and may be set to 0.1mJ/m in consideration of industrial rationality²The above. If the adhesion energy of water is 3.0mJ/m²In the following, water easily slips in the ultrafine fiber layer during the cleaning process, and the filter is dehydrated well after being washed, so that quick-drying property can be obtained.

The weight per unit area of the ultrafine fiber layer can be appropriately selected depending on the required filter performance, cleaning property, quick-drying property, etc., and for example, 0.1g/m²～20.0g/m²The range of (1). If the weight per unit area is 0.1g/m²As described above, the fiber matrix composed of the ultrafine fibers becomes sufficiently dense to improve the collection efficiency and the cleaning property, and 20.0g/m²The pressure loss can be reduced as follows. From this viewpoint, the weight per unit area of the ultrafine fiber layer is more preferably 0.2g/m²～10.0g/m²More preferably 0.5g/m²～5.0g/m²The range of (1).

The ultrafine fiber layer may contain components other than those described above within a range in which the effects of the present invention are not significantly impaired.

The method for producing the ultrafine fiber layer is not particularly limited, and it is preferably produced by an electrospinning method. By using the electrospinning method, the ultrafine fibers can be uniformly spun, and excellent filter characteristics can be obtained.

The electrospinning method is a method in which a spinning solution is discharged and an electric field is applied to fibrillate the discharged spinning solution, and a nanofiber of submicron order is collected in a nonwoven fabric form on a collector (collector). The method of electrospinning is not particularly limited, and there may be mentioned a generally known method, for example, a needle method using one or more needles, an air blow (air blow) method in which productivity per needle is improved by blowing an air stream to the tip of a needle, a multi-hole spinneret method in which a plurality of solution discharge holes are provided in one spinneret (spinnet), a free surface (free surface) method using a cylindrical or spiral rotating electrode half-immersed in a solution tank, an electro bubble (electro bubble) method in which electrospinning is performed by using bubbles generated on the surface of a polymer solution by supplying air as a starting point, and the like, and the method may be selected according to the fiber diameter and physical properties of nanofibers to be required.

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

The solvent for dispersing or dissolving the resin is not particularly limited, and examples thereof include: water, methanol, ethanol, propanol, acetone, N-dimethylformamide, 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, a mixture of these, and the like. The mixing ratio in the mixing is not particularly limited, and may be appropriately set in consideration of the required spinnability or dispersibility and the physical properties of the obtained fiber or filter medium.

When the ultrafine fibers contain a water-repellent agent, the resin and the water-repellent agent are preferably mixed together in the spinning solution, although not particularly limited. The mixing method is not particularly limited, and a method such as stirring or ultrasonic treatment can be exemplified. The mixing order is not particularly limited, and the mixing may be carried out 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.

The spinning solution may further contain a surfactant for the purpose of improving the stability of electrospinning or fiber formation. Examples of the surfactant include: anionic surfactants such as sodium lauryl sulfate, cationic surfactants such as tetrabutylammonium bromide, and nonionic surfactants such as polyoxyethylene sorbitan monolaurate. The concentration of the surfactant is preferably in the range of 5 wt% or less with respect to the spinning solution. The content of 5% by weight or less is preferable because the effect corresponding to the use can be improved.

Components other than the above-mentioned components may be contained as the 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 electrospinning, the viscosity of the spinning solution is preferably set to a range of 10cP to 10,000cP, and more preferably to a range of 50cP to 8,000 cP. When the viscosity is 10cP or more, spinnability for forming a fiber can be obtained, and when it is 10,000cP or less, the spinning solution is easily discharged. The viscosity is more preferably in the range of 50cP to 8,000cP because good spinnability can be obtained in a wide range of spinning conditions. The viscosity of the spinning solution can be adjusted by appropriately changing the molecular weight and concentration of the fiber-forming material, the kind of the solvent, and the mixing ratio.

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

As a method for applying an electric field, there is no particular limitation as long as the electric field can be formed between the nozzle and the collector, and for example, a high voltage may be applied to the nozzle to ground the collector. The voltage to be applied is not particularly limited as long as the fiber can be formed, and is preferably in the range of 5kV to 100 kV. The distance between the nozzle and the collector is not particularly limited as long as the fibers can be formed, and is preferably in the range of 5cm to 50 cm. The collector is not particularly limited as long as it can collect the spun fibers, and the raw material, shape, and the like thereof are not particularly limited. As a material of the collector, a conductive material such as metal can be suitably used. The shape of the collector is not particularly limited, and examples thereof include a flat plate shape, a shaft (draft) shape, and a conveyor (conveyor) shape. The fiber aggregate can be collected in a sheet form if the collector has a flat plate shape, and in a tubular form if the collector has a shaft shape. In the case of a belt conveyor, a fiber aggregate collected in a sheet form can be continuously produced. In the present invention, it is preferable that the ultrafine fiber layer is directly formed on the base material layer by placing the base material layer on the collector and spinning the same.

< substrate layer >

The filter medium of the present invention includes a base material layer. By including the base material layer, the characteristics of the ultrafine fiber layer can be imparted with mechanical strength, durability, drape workability, adhesion characteristics, and the like. The substrate layer can be suitably selected according to the required characteristics and form of the filter medium, and examples thereof include nonwoven fabrics, woven fabrics, meshes, and microporous membranes.

The material constituting the substrate layer is not particularly limited, and for example, in the case of using a substrate layer made of a polyolefin material such as polypropylene or polyethylene, the substrate layer has a characteristic of excellent chemical resistance and can be suitably used for applications such as a liquid filter requiring chemical resistance. When a substrate layer made of a polyester material such as polyethylene terephthalate, polybutylene terephthalate, polylactic acid, or a copolymer containing these as a main component is used, the substrate layer is excellent in drape characteristics, and therefore, the substrate layer can be suitably used for applications such as an air filter that requires a drape process.

From the viewpoint of processability and air permeability of the filter medium, a nonwoven fabric is preferably used as the base layer. The nonwoven fabric is not particularly limited, and examples of the nonwoven fabric include: hot-air (through-air) nonwoven fabrics, air-laid (air-laid) nonwoven fabrics, spunlace (spunlace) nonwoven fabrics, wet-laid nonwoven fabrics, spunbond nonwoven fabrics, meltblown nonwoven fabrics, chemical bond (chemical bond) nonwoven fabrics, flash-spun (electrospinning) nonwoven fabrics, electrospun nonwoven fabrics, and the like.

The filter medium of the present invention is preferably formed by integrating an ultrafine fiber layer and a base material layer. The method of integration is not particularly limited, and the ultrafine fiber layer and the base material layer which are separately produced may be integrated by an adhesive or thermal fusion bonding, or may be integrated by directly spinning the ultrafine fiber layer on the base material layer, or may be subjected to a bonding process by heat after directly spinning the ultrafine fiber layer on the base material layer.

When the bonding process by heat is performed, although not particularly limited, it is preferable to use a nonwoven fabric including a heat-fusible conjugate fiber including a low-melting-point component and a high-melting-point component as the base material layer. The structure, composite form and cross-sectional shape of the material of the heat-fusible composite fiber are not particularly limited, and known ones can be used. Examples of the material structure include: combinations of copolymerized polyethylene terephthalate and polyethylene terephthalate, copolymerized polyethylene terephthalate and polypropylene, high density polyethylene and polyethylene terephthalate, copolymerized polypropylene and polypropylene, copolymerized polypropylene and polyethylene terephthalate, and the like. Further, in view of the availability of raw materials and the like, it is preferable to exemplify: copolymerized polyethylene terephthalate with polyethylene terephthalate, high density polyethylene with polypropylene, high density polyethylene with polyethylene terephthalate.

Examples of the composite form of the cross section include a sheath-core type, an eccentric sheath-core type, a parallel type, and the like. The cross-sectional shape of the fiber is not particularly limited, and may be any cross-sectional shape other than a general circular shape, such as a special cross-section, such as an oval shape, a hollow shape, a triangular shape, a rectangular shape, or an octagonal shape, and preferably has a flat shape substantially parallel to the surface of the ultrafine fiber layer from the viewpoint of improving the adhesion between the ultrafine fiber layer and the base material layer. The substrate layer having such fibers in a cross-sectional shape can be obtained, for example, by: a method of processing oval, flat, and semicircular fibers into a sheet shape, and then bonding the sheet by heat or an adhesive; or the non-woven fabric made of round fibers is compacted by a hot roller.

The method for producing the nonwoven fabric including the heat-fusible composite fiber is not particularly limited, and a known production method such as carding, papermaking, air-laying, melt-blowing, or spun-bonding can be used. The method of bonding fibers when they are processed into a nonwoven fabric is not particularly limited, and examples thereof include: thermal bonding based on air through (air) processing or thermal compression bonding based on embossing processing, fiber interlacing based on needle punching (needle punching) or water punching processing, chemical bonding using an adhesive, and the like.

The thickness of the fibers constituting the substrate layer is not particularly limited, and for example, fibers having an average fiber diameter of 1 to 100 μm can be used, and 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 base material layer can be suppressed, and when the average fiber diameter is 100 μm or less, the ultrafine fiber layer can be uniformly collected.

The basis weight of the base material layer is not particularly limited, but is preferably 15g/m²Above, more preferably 30g/m²Above, more preferably 60g/m²The above. If the basis weight of the substrate layer is 15g/m²As described above, the ultrafine fiber layer can be prevented from shrinking, wrinkling, curling (curl), and the like, and can be provided with processing strength. The specific volume of the substrate layer is not particularly limited, but is preferably 5cm³A value of less than or equal to g, and more preferably 3cm³The ratio of the carbon atoms to the carbon atoms is less than g. If the specific volume of the substrate layer is 5cm³Lower than g is preferable because the peeling strength and abrasion resistance of the ultrafine fiber layer are improved and the reduction in collection efficiency when washing is repeated is small. The thickness of the base material layer is not particularly limited, and may be appropriately selected depending on the desired physical properties and applications of the filter, and for example, may be 0.05mm to 10mm, and is preferably 0.1mm to 5 mm. For example, when the base material layer is used as a pleated filter, the suitability for pleating can be improved by setting the base material layer to 0.1mm to 5mm, which is preferable.

The air permeability of the base material layer is not particularly limited, but is preferably 10cc/cm²At least one second, more preferably 100cc/cm²At least one second, and more preferably 200cc/cm²More than one second. If the air permeability is 10cc/cm²A pressure loss can be reduced by more than one second, and therefore, this is preferable.

When the filter medium is produced by directly spinning the ultrafine fiber layer onto the base layer by the electrospinning method, the electrical leakage resistance value of the base layer is preferably 10¹⁰Omega is less, more preferably 10⁷Omega is less than or equal to. If the electrical leakage resistance value is 10¹⁰When Ω or less, the ultrafine fiber layer can be stably deposited on the base material layer without generating electric repulsion, and adhesion can be improved. 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 is preferably 30N/50mm or more, more preferably 60N/50mm or more, from the viewpoint of providing strength, rigidity, and processability.

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, or the like, within a range in which the effects of the present invention are not significantly impaired, and water repellent processing is preferably performed from the viewpoint of cleaning properties.

< Filter Medium >

The filter medium of the present invention comprises the ultrafine fiber layer and the base material layer, and at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a web, and a microporous membrane may be further laminated and integrated on the surface side of the ultrafine fiber layer. By laminating and integrating, the surface of the ultrafine fiber layer is less likely to be exposed to the outside, and abrasion resistance, durability, and processing strength can be improved. From the viewpoint of cleaning performance, it is preferable to laminate and integrate the webs. The method of integration is not particularly limited, and the following methods can be employed: thermal compression bonding treatment using a heated smooth roll or an embossing roll, bonding treatment using a hot melt or a chemical adhesive, thermal bonding treatment using circulating hot air or radiant heat, and the like.

The filter medium of the present invention is characterized in that: the average flow pore diameter is less than 3.0 μm. In the present specification, the average flow pore size of the filter medium means the average flow pore size of the entire filter medium including the ultrafine fiber layer and the base material layer. The average flow pore diameter is an index of the size of pores formed between fibers constituting the filter medium, and can be measured by a known method. For example, the measurement can be performed by a pore size distribution measuring instrument or the like, and details are shown in examples. It is considered that when the average flow pore size is 3.0 μm or less, both collection efficiency and pressure loss can be achieved, and dust is less likely to enter the inside of the filter medium, thereby improving cleanability. The lower limit of the average flow pore size is preferably 0.1 μm or more from the viewpoint of the pressure loss of the filter medium. The average flow pore size of the filter medium can be adjusted by appropriately changing the average fiber diameter and the basis weight 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 more, more preferably 99% or more, and still more preferably 99.97% or more. The pressure loss is not particularly limited, but is preferably 300Pa or less, more preferably 180Pa or less, and further preferably 160Pa or less. Here, the dust collection efficiency and the pressure loss are such that the particle diameter: 0.07 μm (number center diameter), particle concentration: 10mg/m³～25mg/m³The particle of (2) was measured at a flow rate of 5.3 cm/sec through the sample. The dust collection efficiency and the pressure loss can be adjusted by appropriately changing the average fiber diameter or 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 member, or a filter medium other than the filter medium of the present invention. The filter may be any of a pleated filter, a flat plate filter, a cylindrical filter, and the like, and is suitably used as the pleated filter. When used as a filter, it is preferable that the side of the filter medium on the side of the ultrafine fiber layer be used as the surface side (suction side) of the filter. The use of the filter is not particularly limited, and is preferably a household appliance filter for a vacuum cleaner, an air cleaner for an air conditioner in a building, an industrial medium-performance and/or high-performance filter, a HEPA filter or ULPA filter for a clean room, a vehicle cabin filter for an automobile, or the like.

Examples

The following examples are merely examples for illustrative purposes. The scope of the present invention is not limited to the present embodiment.

[ example 1]

A polyvinylidene fluoride homopolymer (weight average molecular weight: 30 ten thousand) was dissolved in N, N-dimethylacetamide at a concentration of 18 wt%, and sodium lauryl sulfate as a conductive aid was added at a concentration of 0.025 wt% relative to the total solution weight, and fluorooctyl silsesquioxane (manufactured by NBD Nanotechnologies) as a water repellent agent was added at a concentration of 10 wt% relative to the weight of polyvinylidene fluoride to prepare a spinning solution. Next, a through-air nonwoven fabric comprising a heat-bondable conjugate fiber comprising a copolymerized polyethylene terephthalate and a polyethylene terephthalate (fiber diameter: 10 μm, thickness: 60 μm, basis weight: 18 g/m) was prepared²) As a substrate, a substrate was prepared on which a needle tube (gauge) manufactured by terumo corporation was inserted: 27G, needle length: 19mm) was spun out of the spinning solution and electrospun so that the weight per unit area of the ultrafine fiber layer became 0.5g/m²The method (1) is followed. The spinning conditions of this example were such that the amount of the single-hole solution supplied was 1.0mL/hr, the applied voltage was 30kV, the spinning distance was 150mm, and the air temperature and humidity in the spinning space were 25 ℃ and 30%.

[ example 2]

A polyvinylidene fluoride homopolymer (weight average molecular weight: 30 ten thousand) was dissolved in N, N-dimethylacetamide at a concentration of 18 wt%, and sodium lauryl sulfate as a conductive aid was added at a concentration of 0.025 wt% relative to the total solution weight, and fluorooctyl silsesquioxane (manufactured by NBD Nanotechnologies) as a water repellent agent was added at a concentration of 10 wt% relative to the weight of polyvinylidene fluoride to prepare a spinning solution. Next, the hot air nonwoven fabric described in example 1 was used as a base material, and a needle (Teyi) was inserted into the base materialManufactured by lumo corporation, needle tubing diameter: 27G, needle length: 19mm) was spun out of the spinning solution and electrospun so that the weight per unit area of the ultrafine fiber layer became 1.5g/m²The method (1) is followed. The spinning conditions in this example were the conditions described in example 1.

[ example 3]

A polyvinylidene fluoride homopolymer (weight average molecular weight: 30 ten thousand) was dissolved in N, N-dimethylacetamide at a concentration of 18 wt%, sodium lauryl sulfate as a conductive aid was added at a concentration of 0.025 wt% relative to the total solution weight, and a fluorine-based copolymer (daia roman FF129D, manufactured by dai chemical) as a water-repellent agent was added at a concentration of 10 wt% relative to the weight of polyvinylidene fluoride to prepare a spinning solution. Next, the hot-air nonwoven fabric described in example 1 was used as a base material, and the spinning solution was spun from an injection needle (manufactured by Terumo corporation, needle diameter: 27G, needle length: 19mm) and electrospun so that the weight per unit area of the ultrafine fiber layer became 1.5G/m²The method (1) is followed. The spinning conditions in this example were the conditions described in example 1.

[ example 4]

A spinning solution was prepared by dissolving a thermoplastic polyurethane elastomer (T1190, manufactured by dicesenson scientific Polymer) in a mixed solvent (N, N-dimethylformamide: tetrahydrofuran 60 wt%: 40 wt%) at a concentration of 12 wt%, adding sodium lauryl sulfate as a conductive aid at a concentration of 0.025 wt% relative to the total solution weight, and adding fluorooctyl silsesquioxane (manufactured by NBD Nanotechnologies) as a water repellent at a concentration of 10 wt% relative to the weight of the thermoplastic polyurethane elastomer. Next, the hot-air nonwoven fabric described in example 1 was used as a base material, and the spinning solution was spun from an injection needle (manufactured by Terumo corporation, needle diameter: 27G, needle length: 19mm) and electrospun so that the weight per unit area of the ultrafine fiber layer became 3.0G/m²The method (1) is followed. The spinning conditions of this example are examples1 under the conditions described in (1).

Comparative example 1

A polyvinylidene fluoride homopolymer (weight average molecular weight: 30 ten thousand) was dissolved in N, N-dimethylacetamide at a concentration of 18 wt%, and sodium lauryl sulfate as a conductive aid was added at a concentration of 0.025 wt% relative to the total solution weight, and fluorooctyl silsesquioxane (manufactured by NBD Nanotechnologies) as a water repellent agent was added at a concentration of 10 wt% relative to the weight of polyvinylidene fluoride to prepare a spinning solution. Next, the hot air nonwoven fabric described in example 1 was used as a base material, and the spinning solution was spun from the injection needle described in example 1 thereon and electrospun so that the weight per unit area of the ultrafine fiber layer became 0.1g/m²The method (1) is followed. The spinning conditions in this comparative example were the conditions described in example 1.

Comparative example 2

A polyvinylidene fluoride homopolymer (weight average molecular weight: 30 ten thousand) was dissolved in N, N-dimethylacetamide at a concentration of 18 wt%, and sodium lauryl sulfate as a conductive aid was added at a concentration of 0.025 wt% relative to the total solution weight to prepare a spinning solution. Next, the hot air nonwoven fabric described in example 1 was used as a base material, and the spinning solution was spun from the injection needle described in example 1 thereon and electrospun so that the weight per unit area of the ultrafine fiber layer became 1.2g/m²The method (1) is followed. The spinning conditions in this comparative example were the conditions described in example 1.

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

< mean flow pore size >

The immersion liquid was measured using an automated Perm porosimeter (automated Perm Porometer) manufactured by Porous Materials (porus Materials), and the immersion liquid was measured in accordance with Japanese Industrial Standards (JIS) K3832 (bubble point method) using Garwick (GALWICK) (surface tension 15.6 dynes/cm). The results are shown in table 1.

< pressure loss of filter medium >

The pressure loss was measured by using an automatic filter efficiency measuring device (Model 8130) manufactured by TSI corporation, and setting the flow rate at 5.3 cm/sec. The results are shown in table 1.

< energy of adhesion of water to ultrafine fiber surface of filter medium >

The filter medium was allowed to stand on a flat glass substrate by using a contact angle measuring device DM-500 manufactured by Kyowa interface science Co., Ltd. In a state where the inclination of the glass substrate was 0 degrees, a 4.0 μ L droplet of water was dropped on the surface of the filter medium, and the static contact angle was measured 3 seconds after the droplet was stationary. Thereafter, the glass substrate was tilted at a speed of 0.5 degrees/sec, the landing angle of the droplet when the end point of the droplet was away from the rest position was α, the landing radius was r, the droplet mass was m, and the gravitational acceleration was g, and the adhesion energy E (mJ/m) was obtained from the following equation (1)²). The results are shown in table 1.

< evaluation of detergency >

On the filter medium surface (100 cm)²) The powder for JIS test was uniformly loaded with 1.0g of 8 types of soil in Guandong, and the mixture was sucked at a wind speed of 1 m/sec for 1 minute from the side opposite to the side on which the powder was loaded. The filter medium carrying the powder was inclined at an angle of 40 °, and 400mL of pure water was dropped from a height of 5cm from the surface of the filter medium to clean the filter medium. Thereafter, the mixture was left to stand at 70 ℃ for 1 hour in a dryer to be dried. After drying, the pressure loss of the filter medium was measured by the method described above. The operation was repeated a total of 5 times. Let P be the initial pressure loss₀Let P be the pressure loss after the evaluation of the cleanability₁The pressure loss increase rate R is calculated from the following formula (2). Regarding the cleanability, the case where the pressure loss increase rate R is 0% or more and less than 5% is "excellent", the case where it is 5% or more and less than 10% is "o", and the case where it is 10% or more is "x". Show the resultsIn table 1.

TABLE 1

When examples 1 to 4 and comparative example 1 were compared, examples 1 to 4 having an average flow pore size of 3.0 μm or less exhibited high detergency, and comparative example 1 having an average flow pore size of more than 3.0 μm exhibited low detergency. Comparative example 1 although the adhesion performance was not inferior to that of examples 1 to 4, no cleaning property was obtained. The reason is considered to be that: in the filter medium of examples 1 to 4 having an average flow pore size of 3.0 μm or less, dust hardly enters the inside of the filter medium, and the cleaning property is improved.

Examples 1 to 4 and comparative example 2 have sufficient dust trapping properties. However, when examples 1 to 4 and comparative example 2 were compared, the adhesion energy was 3.0mJ/m²The following examples 1 to 4 were high in the cleaning property and the adhesive ability was more than 3.0mJ/m²The cleaning property of comparative example 2 was low. Comparative example 2 no cleaning property was obtained although the average flow pore diameter was not inferior to those of examples 1 to 4. The reason is considered to be that: the adhesion energy is 3.0mJ/m²In the following, the liquid droplets containing dust are easily removed from the surface of the filter medium.

Fig. 1 and 2 are optical photographs showing the filter media of example 1 and comparative example 1 after evaluation of cleanability. The filter medium of fig. 1 (example 1) was cleaned and removed of dust to such an extent that it was almost visually undetectable. On the other hand, the filter medium of fig. 2 (comparative example 1) was visually recognized for dust remaining on the filter surface.

Industrial applicability

The filter medium of the present invention has high dust collection efficiency and low pressure loss, and can easily remove dust with water without using chemicals and the like, and therefore, can be suitably used for household electric appliance filters such as dust collectors and air cleaners, air filters for air conditioners in buildings, filters for middle and/or high performance in industry, HEPA filters and ULPA filters for clean rooms, filters for cars, and the like.

Claims

1. A filter medium comprising an ultrafine fiber layer and a base material layer, wherein the average flow pore size of the filter medium is 3.0 [ mu ] m or less, and the water adhesion energy on the surface of the ultrafine fiber layer is 3.0mJ/m²The following.

2. The filter medium of claim 1, wherein the ultrafine fibers constituting the ultrafine fiber layer contain a water-repellent agent.

3. The filter of claim 2 wherein the water-repellant contains fluorine.

4. The filter medium of any of claims 1-3 wherein the ultrafine fiber layer has a weight per unit area of 0.1g/m²～20.0g/m²。

5. The filter of any of claims 1 to 4 wherein the substrate layer comprises a nonwoven fabric having an average fiber diameter of 1 to 30 μm.

6. A filter comprising the filter of any of claims 1 to 5.