JP2019018188A - Air filter and method for manufacturing the same - Google Patents

Abstract

To provide an air filter that can improve collection efficiency without an increase in pressure loss, and to provide a method for manufacturing the same.SOLUTION: An air filter 10 includes: a substrate 1; and an ultrafine fiber layer 2 formed of an ultrafine fiber with an average fiber diameter 1 μm or less on the substrate 1. The ultrafine fiber constituting the ultrafine fiber layer 2 is an electret ultrafine fiber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an air filter and a manufacturing method thereof.

  In recent years, air pollution due to PM2.5 (particulate matter having a particle size of 2.5 μm or less) has become a problem, and air filters for collecting them have been actively developed. As a material used for this type of air filter, a nonwoven fabric (nanofiber nonwoven fabric) made of ultrafine fibers (nanofibers) having a fiber diameter of less than 1 μm is attracting attention (for example, see Patent Documents 1 to 3).

  Nanofiber is a unique material that combines the functions derived from nanoscale diameter and the ease of handling derived from macroscale length. Typical effects of nanofibers are (1) large specific surface area (super specific surface area effect), (2) nanoscale size (nanosize effect), and (3) molecules arranged in the fiber. (Molecular arrangement effect).

International Publication No. 2008/084797 JP 2010-236133 A Japanese Patent No. 3534108

The performance of the air filter is indicated by the QF value represented by the following formula. The QF value is a value indicating the collection performance per unit ventilation resistance of the filter.
QF value (1 / Pa) = − ln [1-collection efficiency (%) / 100] / [pressure loss (Pa)]
The QF value is a value corresponding to particles in each particle size range. For example, if the particle size distribution of the particles to be collected is 0.300 μm or more and less than 10 μm, the QF value and particles when the particles included in the range of 0.300 μm or more and less than 0.374 μm are to be collected QF value when particles included in the range of 0.374 μm or more and less than 0.465 μm are collected, and particles included in the range of 0.465 μm or more and less than 0.579 μm are collected. Each case has a different QF value. This is because the collection efficiency varies depending on the size of the particles to be collected. Generally, the collection efficiency increases as the size of the particles to be collected increases. Therefore, from the above formula of the QF value, the QF value increases as the collection target particle diameter increases. For the same reason, the QF value when particles included in the range of 0.300 μm or more and less than 0.374 μm are collected is also targeted for collection of particles having a particle size of 0.374 μm or more. This is different from the QF value of the case. The case where the particle diameter is in the range of 0.300 μm or more and less than 0.374 μm is the target of collection includes the smaller particles than the case where the particle diameter of 0.374 μm or more is the target of collection. Therefore, the collection efficiency becomes small. Therefore, the QF value in the case where particles included in the range of 0.300 μm or more and less than 0.374 μm are targeted for collection is the case where the particles whose particle diameter is 0.374 μm or more is targeted for collection. It becomes smaller than the QF value. In addition, from the formula of the above QF value, when the collection efficiency becomes 100%, it becomes −ln (0), and thus the QF value cannot be calculated. For this reason, there is no QF value corresponding to a collection efficiency of 100%. The pressure loss is determined by the structure of the air filter and is constant regardless of the particle size.
In the case of an air filter, when the pressure loss increases, the collection performance evaluated by the QF value decreases. Therefore, it is required to improve the collection efficiency and improve the QF value without increasing the pressure loss.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the air filter which can improve collection efficiency, without increasing a pressure loss, and its manufacturing method.

  In the first aspect of the present invention, an ultrafine fiber layer (hereinafter referred to as “nanofiber”) formed of a substrate and an ultrafine fiber having an average fiber diameter of less than 1 μm (hereinafter sometimes referred to as “nanofiber”) on the substrate. A nanofiber layer), and the ultrafine fibers constituting the ultrafine fiber layer are electretized air filters.

  The second aspect of the present invention includes a step of producing ultrafine fibers having an average fiber diameter of less than 1 μm, a step of forming an ultrafine fiber layer containing the ultrafine fibers on a substrate, and the ultrafine fiber layer. It is a manufacturing method of an air filter which has the process of electretizing ultrafine fiber.

  According to the present invention, since the nanofibers are electretized, an electrostatic particle collecting mechanism is added to the conventional particle collecting mechanism. Thereby, collection efficiency can be improved rather than the nanofiber which is not electretized. Therefore, when higher collection efficiency is required, improvement in collection efficiency can be achieved without increasing the basis weight of the nanofiber layer. Also, if the required collection efficiency does not change, the amount of nanofibers can be reduced, and thus low pressure loss can be realized.

It is a cross-sectional schematic diagram which shows an example of the air filter in this embodiment. It is a figure which shows an example of the apparatus which manufactures the air filter in this embodiment. It is a cross-sectional schematic diagram which shows the modification of the air filter of this embodiment. It is a cross-sectional schematic diagram which shows the example of a change of the air filter of this embodiment. It is a graph which shows the result of an Example and a comparative example. It is a graph which shows the result of an Example and a comparative example.

<Air filter>
The air filter according to the present embodiment includes an ultrafine fiber layer (hereinafter referred to as “nanofiber”) formed of a substrate and an ultrafine fiber (hereinafter referred to as “nanofiber”) having an average fiber diameter of less than 1 μm on the substrate. And the ultrafine fibers constituting the ultrafine fiber layer are electretized.

  FIG. 1 is a schematic cross-sectional view showing an example of an air filter in the present embodiment. In the present embodiment, the air filter 10 includes a base material 1 and a nanofiber layer 2 formed of nanofibers on the base material 1, and the nanofiber layer 2 is made of electret nanofibers. ing.

(Base material)
In this embodiment, a base material refers to the thing generally known as what is called a nonwoven fabric.
Examples of the substrate 1 include a dry nonwoven fabric, a wet method nonwoven fabric, a spunbond nonwoven fabric, a melt blown nonwoven fabric, a thermal bond nonwoven fabric, a chemical bond nonwoven fabric, a needle punch nonwoven fabric, a spunlace nonwoven fabric, a stitch bond nonwoven fabric, and a steam jet nonwoven fabric.
Examples of the material of the substrate 1 include polyethylene, polypropylene, rayon, polyester, polyamide, polyolefin, acrylic, vinylon, aramid, glass, and cellulose. The substrate 1 may be made of one kind of material, or may be a mixture of two or more kinds of different materials.

  Although the kind of base material 1 is not specifically limited, According to various physical property values (collection efficiency, pressure loss, thickness, etc.) required for an air filter as a product, various physical property values (collection efficiency) required for the base material 1 , Pressure loss, thickness, porosity, etc.) are naturally specified. In general, an air filter is required to have a low pressure loss. Therefore, unless there is a problem in handling properties and strength, it is desirable that the substrate is thin, has a high porosity, and has good air permeability. There is no particular limitation on the porosity of the substrate, but as will be described later, the air filter before electretization when particles included in the range of particle size of 0.300 μm or more and less than 0.374 μm are collected. It is desirable that the QF value be kept at 0.018 or more.

(Nanofiber)
In the present embodiment, the nanofiber refers to a resin whose fiber has an average fiber diameter of less than 1 μm.

The nanofiber layer 2 preferably has a porosity represented by the following formula of 95% or more, and more preferably 96% or more. When the porosity of the nanofiber layer 2 is not less than the lower limit of the above range, an increase in pressure loss of the air filter can be further suppressed and a higher QF value can be maintained.
Porosity (%) = 100− {basis weight (g / m ² ) × 100 / resin density (g / cm ³ ) / thickness (μm)}
Here, the resin density (g / cm ³ ) refers to the material density of the resin constituting the nanofiber layer 2, and the thickness (μm) refers to the film thickness of the nanofiber layer 2.

In the present embodiment, the basis weight of the nanofiber layer 2 is preferably 5 g / m ² or less, more preferably 4 g / m ² or less, and even more preferably 3 g / m ² or less. When the basis weight of the nanofiber layer 2 is not more than the upper limit of the above range, an increase in pressure loss of the air filter can be suppressed.

  The resin that can be used as the raw material of the nanofiber layer 2 is a thermoplastic resin that can be processed into a thread shape. For example, polyethylene terephthalate, polyester including polylactic acid, polyamide including nylon (nylon 6, nylon 66), polypropylene, polyolefin including polyethylene, polyvinyl alcohol polymer, acrylonitrile polymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer Fluoropolymers such as (PFA), urethane polymers, vinyl chloride polymers, styrene polymers, (meth) acrylic polymers, polyoxymethylene, ether ester polymers, cellulose modified polymers such as triacetylcellulose, etc. are used Can be done. Among these, polyethylene terephthalate, polylactic acid, nylon (nylon 6, nylon 66) and polypropylene are preferable because they have good stretchability and molecular orientation. Among them, polypropylene is most preferable because it is easy to maintain the polarization state of the electret and is a material often used in electret filters.

  The nanofiber layer 2 in the present embodiment includes a fiber having a fiber diameter that is not less than 2 times and not more than 10 times the average fiber diameter (less than 1 μm) of the constituent fibers (that is, a relatively thick fiber) at a predetermined ratio. Is preferred. Specifically, in the air filter according to the present invention, it is preferable that fibers having a fiber diameter of 2 to 10 times the average fiber diameter occupy 2 to 20% of the total number of fibers. As a result, the air filter according to the present embodiment improves the pressure loss by increasing the air permeability as compared with the conventional nanofiber nonwoven fabric while achieving practically sufficient collection efficiency. It is possible to prolong the life of the.

(air filter)
The air filter 10 of the present embodiment has a QF value represented by the following formula of 0. 0 when electrification is performed when particles included in a range of 0.300 μm or more and less than 0.374 μm are collected. It is preferably 018 or more, and more preferably 0.020 or more. By using an air filter whose particle size is 0.300 μm or more and less than 0.374 μm and for which the QF value before electretization for collecting particles contained in the range is equal to or more than the lower limit of the above range, Good air filter performance can be obtained. As described above, the QF value when particles having a particle size of 0.374 μm or more are to be collected is the particles to be collected in the range where the particle diameter is 0.300 μm or more and less than 0.374 μm. Is basically larger than the QF value. Specifically, when particles having a particle diameter of 0.374 μm or more are targeted for collection, the QF value represented by the following formula is preferably 0.018 or more.
QF value (1 / Pa) = − ln [1-collection efficiency (%) / 100] / [pressure loss (Pa)]

  The air filter of the present embodiment can be applied to, for example, a coarse dust filter, a medium / high performance filter, a HEPA filter, a ULPA filter, a gas removal filter, a mask, an air element, an air conditioner filter, an air cleaner filter, and the like.

  According to the air filter in the present embodiment, since the nanofibers constituting the nanofiber layer 2 are electretized, an electrostatic particle collection mechanism is further added to the conventional particle collection mechanism. Thereby, collection efficiency can be improved rather than the nanofiber which is not electretized. That is, the collection efficiency can be improved without increasing the pressure loss. In addition, as the particle collection proceeds, particles adhere to the surface of the nanofiber layer 2 and apparently cancel each other with the charge inside the fiber, which may reduce the electrostatic collection performance. As the nanofiber layer 2 adheres and accumulates on the nanofiber layer 2, clogging of the nanofiber layer 2 avoids a decrease in the collection efficiency. As a result, the collection performance required as an air filter is long-term. continue.

<Air filter manufacturing method>
The method for producing an air filter according to the present embodiment includes a step of producing nanofibers, a step of forming a nanofiber layer containing the nanofibers on a substrate, and the nanofibers constituting the nanofiber layer electret. And a step of converting.

(Nanofiber production process)
A conventionally well-known method can be used for a nanofiber production | generation process. Examples thereof include an electrospinning method (electrospinning method), a melt blow method, a sea-island melt spinning method, a carbon dioxide supersonic laser drawing method, and the like. Among them, the carbon dioxide supersonic laser stretching method can be applied to (1) a thermoplastic polymer material, (2) the obtained nanofibers are infinitely long fibers, and (3) the fiber orientation is high ( 4) Work environment and safety of nanofiber are high because no solvent is used, (5) Nanofiber scattering can be prevented by collecting fiber by reducing pressure, and (6) Device is small and simple structure Therefore, it is preferable because it is excellent in expandability regardless of the installation location.

Hereinafter, a preferable example of the nanofiber generation step in the present embodiment will be described.
The nanofiber according to the embodiment of the present invention is generated using an apparatus in which the raw filament delivery means and the drawing chamber are connected via a nozzle and the pressure difference between the inlet and the outlet of the nozzle is 20 kPa or more. That is, the original filament delivery means sends out the original filament, and the delivered original filament passes through the nozzle and is guided to the drawing chamber. In the drawing chamber, laser irradiation is performed on the original filament that has come out of the nozzle, whereby the original filament is continuously melted and drawn to produce nanofibers.

  In this embodiment, a multifilament yarn (multifilament) is used as the original filament. Therefore, hereinafter, the original filament may be referred to as a multifilament. The multi-primary yarn (multifilament) refers to a bundle composed of a plurality of single yarns (monofilament). The cross-sectional shape of one monofilament constituting the multifilament is not particularly limited. That is, the monofilament may be various deformed yarns such as an elliptical shape, a quadrangular shape, a triangular shape, a trapezoidal shape, and other polygonal shapes as well as a circular sectional shape. Further, as the monofilament, composite yarn such as hollow fiber, core-sheath type yarn, side-by-side type yarn may be used. Furthermore, the monofilaments constituting the multifilament need not all be the same. Multifilaments may be configured by combining monofilaments having different shapes and materials.

  In this embodiment, a multifilament in which 10 or more monofilaments are bundled is used as the original filament. The number of monofilaments to be bundled can be adjusted according to the nozzle used. Specifically, the ratio (S2 / S1) of the total cross-sectional area S2 of the multifilament to the cross-sectional area S1 of the rectifying unit of the nozzle can be appropriately adjusted so as to be within an appropriate range. A multifilament in which 20 or more, more preferably 40 or more monofilaments are bundled is preferably used as the original filament. The diameter of each monofilament constituting the multifilament is preferably 10 to 200 μm. The multifilament is usually twisted so that a plurality of monofilaments do not lose their integrity as a bundle. The number of twists is appropriately adjusted depending on the number, shape, material, etc. of the monofilament (usually 20 times / m or more).

  The resin that can be used as the multifilament is a thermoplastic resin that can be processed into a thread shape. For example, polyethylene terephthalate, polyester including polylactic acid, polyamide including nylon (nylon 6, nylon 66), polypropylene, polyolefin including polyethylene, polyvinyl alcohol polymer, acrylonitrile polymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer Fluoropolymers such as (PFA), urethane polymers, vinyl chloride polymers, styrene polymers, (meth) acrylic polymers, polyoxymethylene, ether ester polymers, cellulose modified polymers such as triacetylcellulose, etc. are used Can be done. In particular, polyethylene terephthalate, polylactic acid, nylon (nylon 6, nylon 66), and polypropylene are suitable for producing nanofibers because they have good stretchability and molecular orientation. Among them, polypropylene is easy to maintain the polarization state of the electret, and is the most frequently used material as the material to be used as the electret.

  Further, in the multifilament, various substances such as various organic substances, organometallic complexes, and inorganic substances can be kneaded in the fiber, or attached to the surface of the fiber. In this case, when the nanofibers are generated, the kneaded and / or attached substances can be uniformly dispersed to impart functionality to the nanofibers.

FIG. 2 is a diagram illustrating an example of an apparatus for producing nanofibers in the present embodiment.
In FIG. 2, the original filament supply chamber C <b> 1 and the stretching chamber C <b> 2 are connected via a nozzle 30. An original filament sending device 25 that sends the original filament (multifilament) toward the nozzle 30 is provided on the upstream side of the original filament supply chamber C1. The original filament delivery device 25 is not particularly limited as long as it can deliver multifilaments at a constant delivery speed. Hereinafter, the original filament delivery device 25 and the original filament supply chamber C1 may be collectively referred to as “original filament delivery means”.

The nozzle 30 has an inner surface with a tapered inner portion 31 whose inner diameter becomes smaller toward the downstream, and a straight tube rectifying portion 32 formed continuously with the downstream end of the introducing portion 31 and having a uniform inner diameter. It is preferable to have.
The ratio (L / D) between the length L of the rectifying unit 32 and the diameter D of the rectifying unit 32 is preferably 1 to 100, more preferably 1 to 50, and even more preferably 1 to 10. The rectifying unit 32 may be appropriately subjected to processing for airflow adjustment according to the number, shape, material, and the like of monofilaments in the multifilament used.

The original filament supply chamber C1 is under an atmosphere of P1 atmospheric pressure. On the other hand, the stretching chamber C2 is maintained in an atmosphere of P2 atmospheric pressure lower than P1 atmospheric pressure. Due to the pressure difference (P1-P2) between the P1 atmospheric pressure original filament supply chamber C1 and the P2 atmospheric pressure stretching chamber (P1-P2), the nozzle 30 has an inlet (introduction section 31) to an outlet (downstream end of the rectification section 32). A heading airflow is generated. The multifilament fed into the nozzle 30 passes through the nozzle 30 by the air flow generated in the nozzle 30 and is sent to the stretching chamber C2.
P1 ≧ 2 × P2 is preferable, P1 ≧ 3 × P2 is more preferable, and P1 ≧ 5 × P2 is most preferable. Moreover, specifically, the pressure difference (P1−P2) between P1 and P2 is preferably 20 kPa or more, and more preferably 50 kPa or more.

  In the present embodiment, it is particularly preferable that P1 is an atmospheric pressure and P2 is a pressure lower than the atmospheric pressure. This is because the apparatus can be configured relatively simply. In addition, the temperature of the original filament supply chamber C1 and the drawing chamber C2 is normally set to room temperature (normal temperature). However, when it is desired to preheat the multifilament or heat treat the drawn filament, heated air can be used as appropriate. An inert gas such as nitrogen gas can be used to prevent the filament from being oxidized. In order to prevent the scattering of moisture, a gas containing water vapor or moisture can be used. Various other inert gases can also be used for the purpose of controlling the vibration (described later) of the multifilament.

  In this embodiment, in order to generate a sufficient air flow for sending the multifilament to the drawing chamber C2, the ratio of the total cross-sectional area S2 of the multifilament to the cross-sectional area S1 of the rectifying unit 32 of the nozzle 30 (= S2 / S1, hereinafter referred to as “nozzle rectification unit occupation ratio”) must be 50% or less. If the nozzle rectification unit occupancy (S2 / S1) is greater than 50%, the amount of high-speed airflow flowing through the rectification unit 32 is insufficient, and multifilament vibration (described later) cannot be obtained sufficiently. is there. If the vibration of the multifilament is insufficient, the melted multifilament does not form a thread and falls as a molten lump, so that nanofibers cannot be obtained. On the other hand, if the nozzle rectification unit occupancy (S2 / S1) is less than 5%, the vibration of the multifilament becomes too large or the force of the air current does not apply well to the multifilament, and the desired nanofiber is obtained. I can't. Therefore, the nozzle rectification unit occupation ratio (S2 / S1) needs to be 5 to 50%, and preferably 10 to 35%.

  The multifilament that has passed through the nozzle 30 is irradiated with laser, and the tip of the multifilament is heated and melted. At this time, it is necessary to generate vibration in the multifilament, and accordingly, laser irradiation conditions such as a laser irradiation position, a laser shape, and a laser power are appropriately adjusted.

  In order to obtain nanofibers from multifilaments, it is necessary to vibrate the multifilaments by laser irradiation, but it is not necessary to simply vibrate the multifilaments. In order to stably obtain a desired nanofiber, the angle of the multifilament (center of bundle) during vibration (hereinafter referred to as “vibration angle of multifilament”) is 5 ° to 80 ° with respect to the central axis of the nozzle 30. Must be in the range. Preferably, the vibration angle of the multifilament is in the range of 15 ° to 50 °, more preferably in the range of 20 ° to 40 °.

In order to generate vibration in the multifilament, the position where laser irradiation is performed is also important. Specifically, it is necessary to perform laser irradiation so that the center position of the melted part of the multifilament is a position of 1 mm to 15 mm vertically below the nozzle outlet. If the melted part of the multifilament is at a distance closer than 1 mm from the nozzle outlet, the vibration angle of the multifilament may exceed the upper limit of the above range due to the airflow flowing out from the nozzle, and the melted part of the multifilament This is because if the distance is more than 15 mm from the outlet, the airflow flowing out from the nozzle is weakened, and the vibration angle of the multifilament may fall below the lower limit of the above range. Preferably, the laser irradiation is performed such that the center position of the melting portion of the multifilament is a position of 3 mm or more and 10 mm or less vertically below the nozzle outlet, and more preferably, the laser irradiation is the center position of the melting portion of the multifilament. Is performed at a position 3 mm or more and 5 mm or less below the nozzle outlet.
Nanofibers are generated when vibration occurs in the multifilament that satisfies the above-described conditions.

  In the above process, the original filament used (multifilament), the delivery speed of the original filament (multifilament), the nozzle shape, the laser irradiation conditions, and / or the pressure difference (P1) between the original filament supply chamber and the drawing chamber. By changing -P2), it is possible to adjust the average fiber diameter and fiber diameter distribution of the nanofibers obtained. For example, when producing the nanofiber for air filters of this embodiment, the fiber (relatively thick fiber) which has a fiber diameter of 2 to 10 times the average fiber diameter of the constituent fiber in the constituent fiber Are included in a predetermined ratio, the original filament, the delivery speed of the original filament, the nozzle shape, the laser irradiation conditions, and / or the pressure difference (P1-P2) are selected or determined.

(Nanofiber layer formation process)
The nanofiber produced | generated in said process is formed into a film on the base material which consists of a nonwoven fabric, and the filter medium with which the nanofiber layer containing nanofiber was formed on the base material is obtained. Specifically, for example, while feeding a sheet-like base material in one direction, nanofibers are ejected from one of the surfaces of the above-described apparatus to form a nanofiber layer on the fiber surface of the base material. At this time, the injection amount of the nanofiber and the feeding speed of the sheet-like substrate are adjusted as appropriate so that the basis weight of the nanofiber layer on the substrate is preferably 5 g / m ² or less. In order to efficiently form the produced nanofibers on the substrate, for example, in the above-described apparatus, a plurality of nozzles may be arranged in a direction intersecting the moving direction of the sheet-like substrate. . In this case, the interval between the nozzles is adjusted as appropriate so that the vibrated multifilaments do not contact each other and / or are not adversely affected by the air flow of the adjacent nozzles.
The filter medium obtained by the method described above can be wound up with a roll or the like after, for example, a nip treatment.

(Electretization process)
The method for converting the nanofiber into an electret is not particularly limited, and is performed by corona discharge treatment, electron beam irradiation, radiation irradiation, or the like, and among these, the corona discharge treatment is most preferable.
The applied voltage in the corona discharge treatment is appropriately adjusted according to the basis weight of the nanofiber layer 2, the fiber diameter of the nanofiber, the voltage application time, and the like.

(Optional process: Lamination process)
In the manufacturing method of the air filter according to the present embodiment, a lamination process may be performed as desired.
In the laminating step, the filter medium roll produced in the above steps is cut into a predetermined size to form the air filter 10, and a plurality of these air filters 10 are further laminated to form the air filter 20. Here, when a plurality of air filters 10 are stacked, only some or all of the nanofibers constituting the plurality of nanofiber layers may be electretized.

FIG. 3 is a schematic cross-sectional view showing a modification of the air filter of the present embodiment. The air filter 20 in this example is a stacked air filter configured by stacking a plurality of air filters 10. 3 illustrates the air filter 20 in which three air filters 10 are stacked, the number of the air filters 10 to be stacked is appropriately adjusted according to the collection performance of the target filter.
In addition, in FIG. 3, the embodiment which laminated | stacked the air filter 10 so that it was the order of nanofiber layer 2 / base material 1 / nanofiber layer 2 / base material 1 / nanofiber layer 2 / base material 1 was illustrated. However, the present invention is not limited to this. For example, the order of lamination, the direction, and the like are not particularly limited, such as base material 1 / nanofiber layer 2 / nanofiber layer 2 / base material 1 / base material 1 / nanofiber layer 2 / nanofiber layer 2 / base material 1.
Moreover, you may laminate | stack the air filter 10 from which basic weight differs. For example, nanofiber layer 2a (basis weight 1g) / substrate 1a (basis weight 5g) / nanofiber layer 2b (basis weight 2g) / substrate 1b (basis weight 5g) / nanofiber layer 2c (basis weight 3g) / Configuration of substrate 1c (basis weight 5g) (FIG. 4 (a)), nanofiber layer 2d (basis weight 1g) / substrate 1d (basis weight 5g) / nanofiber layer 2e (basis weight 2g) / substrate 1e The basis weight of the nanofiber layer to be laminated and the substrate is not particularly limited, such as the configuration (basis weight 7 g) / nanofiber layer 2f (basis weight 3g) / substrate 1f (basis weight 10g) (FIG. 4B). . Further, materials other than the air filter 10 may be interposed. For example, the configuration of nanofiber layer 2 / base material 1 / nanofiber 2 / base material 1 / non-element non-woven fabric 3 / nanofiber layer 2 / base material 1 / non-element non-woven fabric 3 (FIG. 4 (c)), etc. The kind of nonwoven fabric and the position to insert are not specifically limited.
The method for laminating the plurality of air filters 10 is not particularly limited as long as the performance of the air filter can be exhibited. For example, it is possible to use hot melt powder bonding, embossing, thermocompression processing of only the outer peripheral portion, or ultrasonic fusion processing. Moreover, the part to process is not specifically limited. The processing may be performed on the entire surface of the laminated product or only on the outer peripheral portion.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited by these examples. Moreover, each value in an Example and a comparative example was calculated | required with the following method.

(1) Average fiber diameter The surface of the manufactured air filter was photographed (magnification 4000 times) with a scanning electron microscope (JCM-5000 manufactured by JEOL Ltd.). Twenty obtained photographs were selected at random, the number of fibers in the photograph was counted, and the diameters of all the fibers were measured. The data of 20 photos is treated as one data, and the average value of the fiber diameters is calculated based on the total number of fibers contained in the 20 photos and the fiber diameters of all the fibers. The fiber diameter was used.

(2) Porosity The porosity of the nanofiber layer was calculated by the following formula.
Porosity (%) = 100− {basis weight (g / m ² ) × 100 / resin density (g / cm ³ ) / thickness (μm)}
Here, the resin density (g / cm ³ ) refers to the density of the resin constituting the nanofiber layer, and the thickness (μm) refers to the film thickness of the nanofiber layer.

(3) Air filter test (initial performance test)
For the manufactured air filter, when a filter performance tester (DFT-4 manufactured by Tokyo Directec Co., Ltd.) is used to collect particles whose pressure loss and particle size are in the range of 0.300 μm or more and less than 0.374 μm. The particle collection efficiency was evaluated. The test particle type used atmospheric dust. The test wind speed was 10 cm / s. The collection efficiency was calculated using a light scattering particle counter (TSI Model 3330).
The QF value of the air filter was calculated by the following formula.
QF value (1 / Pa) = − ln [1-collection efficiency (%) / 100] / [pressure loss (Pa)]

Example 1
A multifilament made of polypropylene (830 dtex, 25 filaments) was prepared as a multifilament that is an original filament. As the nozzle, a nozzle having an inside diameter of 0.8 mm and a length of 2.4 mm was used, and 40 nozzles were arranged side by side at intervals of 10 mm. The nozzle occupation ratio is 18%, the multifilament is supplied at 0.2 m / min with the vacuum degree of the stretching chamber being 30 kPa, and the center position of the melting portion of the multifilament is 500 W so that the center position is 3 mm below the nozzle. A circular laser with a diameter of 6 m was irradiated. At this time, the multifilament vibrated at a vibration angle of 23 degrees at the nozzle outlet, and the produced nanofiber was received by a polyolefin-made wet nonwoven fabric (base material) to obtain a composite nonwoven fabric (filter material). The obtained composite nonwoven fabric was wound after being subjected to a nip treatment. In the obtained composite nonwoven fabric, more specifically, a composite nonwoven fabric composed of a nanofiber layer formed on a polyolefin wet nonwoven fabric, the average fiber diameter of the nanofiber was 300 nm. The porosity of the nanofiber layer was 96%. The basis weight of the nanofiber layer was 1.5 g / m ² .
The obtained composite nonwoven fabric was subjected to corona treatment at an applied voltage of -6 kV to obtain an air filter in which nanofibers in the air filter were electretized. The surface potential of the electretized air filter was -250V to -200V.
The obtained electret air filter was subjected to an air filter test. The results are shown in Table 1.

(Example 2)
An electret air filter was obtained in the same manner as in Example 1 except that the composite nonwoven fabric was manufactured so that the basis weight of the nanofiber layer was 3 g.
The obtained electret air filter was subjected to an air filter test. The results are shown in Table 1.

(Comparative Example 1)
A composite nonwoven fabric was obtained in the same manner as in Example 1 except that the corona treatment was not performed.
The obtained composite nonwoven fabric was subjected to an air filter test. The results are shown in Table 1.

(Comparative Example 2)
A composite nonwoven fabric was obtained in the same manner as in Example 2 except that the corona treatment was not performed.
The obtained composite nonwoven fabric was subjected to an air filter test. The results are shown in Table 1.

  As shown in the results of Table 1, in Examples 1 and 2 (with electretization), it was confirmed that the collection efficiency was improved and the QF value was higher than in Comparative Examples 1 and 2 (without electretization). It was done.

(Example 3-1)
For the electret air filter of Example 1, the particle collection efficiency in the particle diameter range shown in Table 2 was evaluated in the same manner as in Example 1. The results are shown in Table 2.
(Example 3-2)
The electretized air filter of Example 1 was checked for air filter performance after standing for 7 months after electret processing at normal temperature, normal pressure, and normal humidity. In the same manner as in Example 1, the particle collection efficiency in the particle diameter range shown in Table 2 was evaluated. The results are shown in Table 2.

(Comparative Example 3)
About the composite nonwoven fabric of the comparative example 1, the particle collection efficiency of the particle diameter range shown in Table 2 was evaluated by the same method as in Example 1. The results are shown in Table 2.

  FIG. 5 is a graph showing the relationship between the particle diameter (μm) and the collection efficiency (%) in Examples 3-1 and 3-2 and Comparative Example 3. As shown in FIG. 5, in Examples 3-1 and 3-2 (with electretization), the collection efficiency is improved particularly in a particle diameter range of less than 1 μm as compared with Comparative Example 3 (without electretization). It was confirmed. Moreover, it was confirmed from the comparison of Example 3-1 (after electretization) and Example 3-2 (after seven months progress) that the effect of electretization is maintained even after seven months have elapsed after electret processing. .

(Example 4-1)
For the electretized air filter of Example 2, the particle collection efficiency in the particle diameter range shown in Table 3 was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Example 4-2)
About the electret-ized air filter of Example 2, the air filter performance after standing for 7 months after electret processing at normal temperature, normal pressure, and normal humidity was confirmed. In the same manner as in Example 1, the particle collection efficiency in the particle diameter range shown in Table 3 was evaluated. The results are shown in Table 3.
(Comparative Example 4)
For the composite nonwoven fabric of Comparative Example 2, the particle collection efficiency in the particle diameter range shown in Table 3 was evaluated in the same manner as in Example 1. The results are shown in Table 3.

  FIG. 6 is a graph showing the relationship between the particle diameter (μm) and the collection efficiency (%) in Examples 4-1 and 4-2 and Comparative Example 4. As shown in FIG. 6, in Examples 4-1 and 4-2 (with electretization), the collection efficiency is improved particularly in a particle diameter range of less than 1 μm as compared with Comparative Example 4 (without electretization). It was confirmed. Moreover, it was confirmed from the comparison of Example 4-1 (after electretization) and Example 4-2 (after seven months elapse) that the effect of electretization is maintained even after elapse of 7 months after electret processing. .

DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Nanofiber layer, 10 ... Air filter, 20 ... Laminated air filter

Claims (11)

  An air filter comprising a substrate and an ultrafine fiber layer formed of ultrafine fibers having an average fiber diameter of less than 1 μm on the substrate, wherein the ultrafine fibers constituting the ultrafine fiber layer are electretized. The air filter according to claim 1, wherein a porosity of the ultrafine fiber layer represented by the following formula is 95% or more.
Porosity (%) = 100− {basis weight (g / m ² ) × 100 / resin density (g / cm ³ ) / thickness (μm)}
Here, the resin density (g / cm ³ ) refers to the density of the resin constituting the ultrafine fiber layer, and the thickness (μm) refers to the film thickness of the ultrafine fiber layer.   The air filter according to claim 1 or 2, wherein the ultrafine fiber layer occupies 2 to 20% of the total number of fibers having a fiber diameter of 2 to 10 times the average fiber diameter. The QF value before electret represented by the following formula is 0.018 or more represented by the following formula when particles included in the range of particle diameters of 0.300 μm or more and less than 0.374 μm are collected. The air filter according to any one of the above.
QF value (1 / Pa) = − ln [1-collection efficiency (%) / 100] / [pressure loss (Pa)] The air filter according to any one of claims 1 to 4, wherein a QF value represented by the following formula is 0.018 or more when particles having a particle diameter of 0.374 µm or more are collected.
QF value (1 / Pa) = − ln [1-collection efficiency (%) / 100] / [pressure loss (Pa)] Producing an ultrafine fiber having an average fiber diameter of less than 1 μm;
Forming an ultrafine fiber layer containing the ultrafine fibers on a substrate;
A process for producing an air filter, comprising: electretizing the ultrafine fibers constituting the ultrafine fiber layer. The nonwoven fabric manufacturing process is led from the nozzle to the drawing chamber using an apparatus in which the raw filament delivery means and the drawing chamber are connected via a nozzle, and the pressure difference between the nozzle inlet and the nozzle outlet is 20 kPa or more. Producing ultrafine fibers by irradiating the original filament with laser,
A multi-filament yarn (multifilament) in which 10 or more monofilament yarns (monofilaments) are bundled as the original filament, and the ratio (S2 / S1) of the cross-sectional area S1 of the nozzle rectifying unit and the total cross-sectional area S2 of the multifilament is The multifilament is guided to the drawing chamber under the condition of 50% or less, and laser irradiation is performed so that the center position of the melted portion is 1 mm or more and 15 mm or less vertically below the nozzle outlet with respect to the multifilament that has come out of the nozzle. As a result, the tip of the multifilament is melted, and at this time, the air flow generated by the pressure difference causes the entire multifilament to have a maximum angle of 5 ° to 80 ° with respect to the central axis of the nozzle, and a conical shape with the nozzle hole as the apex The tip melt part of the multifilament is stretched by swinging randomly inside the space. The manufacturing method of the air filter as described.   The manufacturing method of the air filter of Claim 7 whose said S2 / S1 is 10 to 35%.   The method for manufacturing an air filter according to claim 7 or 8, wherein the pressure difference is 50 kPa or more.   The method for producing an air filter according to any one of claims 7 to 9, wherein a ratio (L / D) of the rectifying portion diameter D and the rectifying portion length L of the nozzle is 0.1 to 100.   The manufacturing method of the air filter as described in any one of Claims 7-10 with which an original filament consists of thermoplastic resins.

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