Air filter and regeneration method of the same

Abstract

To provide an air filter which can simultaneously collect at least two kinds of object particles to be caught having different particle sizes through one layer and regenerate catching performance, and a regeneration method of the air filter.SOLUTION: An air filter 1 includes a filter fiber 2 including a surface modification layer 22 formed in a metal fiber 21 and on a surface of the metal fiber 21. The surface modification layer 22 includes: a plurality of projections 221 projecting from a layer surface to the outside; and a fine uneven part 222 formed on the surface of the projection 221. The air filter 1 collects first object particles P1 to be caught through physical adsorption into valley spaces 223 formed between the plurality of projections 221 and collects second object particles P2 to be caught whose particle diameter is smaller than that of the first object particles P1 through physical adsorption into the fine uneven part 222. A regeneration method of the air filter washes and / or heats the air filter 1 where the first object particles P1 to be caught and the second object particles P2 to be caught are collected to regenerate the air filter 1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an air filter and a method for regenerating an air filter. [Background technology]

[0002] Air filters have been used in the field of vehicles such as automobiles. Known air filters include activated carbon filters made of nonwoven fabric of resin fibers carrying activated carbon, and resin HEPA filters (High Efficiency Particulate Air Filters). In general, activated carbon filters are used to capture gas particles (gas molecules), and HEPA filters are used to capture virus particles and fine particles.

[0003] Incidentally, prior Patent Document 1 discloses a technology not related to an air filter but related to a heat exchanger having fins whose surfaces have bactericidal properties. Specifically, the heat exchanger has fins having a metal substrate and a porous anodized layer formed on the metal substrate, and the surface of the porous anodized layer has a submicron-order uneven structure, and the uneven structure includes a plurality of recesses whose two-dimensional size when viewed from the normal direction to the surface is more than 100 nm and less than 500 nm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2016 / 021367 Summary of the Invention [Problem to be solved by the invention]

[0005] The conventional technology has the following problem. Specifically, when the air contains first particles to be collected (e.g., virus particles or fine particles) and second particles to be collected (e.g., gas particles) that are smaller in particle size than the first particles to be collected, a conventionally known method requires stacking a first filter layer for collecting the first particles to be collected and a second filter layer for collecting the second particles to be collected. However, this method increases pressure loss because the first filter layer and the second filter layer are stacked.

[0006] Furthermore, conventionally known general air filters capture target particles by chemical adsorption, and therefore, once their collection performance reaches saturation through use, they are discarded and cannot be regenerated.

[0007] The present invention has been made in consideration of these problems, and aims to provide an air filter that can simultaneously capture at least two types of target particles with different particle diameters in a single layer and that can regenerate the collection performance, as well as a method for regenerating an air filter. [Means for solving the problem]

[0008] One aspect of the present invention is An air filter (1) having filter fibers (2), The filter fiber is Metal fibers (21); a surface modification layer (22) formed on the surface of the metal fiber, The surface modification layer is a plurality of protrusions (221) protruding outward from the layer surface; and fine irregularities (222) formed on the surface of the protrusion, First particles to be collected (P1) are collected by physical adsorption in valley spaces (223) formed between the plurality of protrusions; second target particles (P2) having a particle diameter smaller than that of the first target particles to be collected are collected by physical adsorption onto the fine irregularities; Located on the air filter (1).

[0009] Another aspect of the present invention is A method for regenerating the air filter (1), comprising: cleaning and / or heating the air filter that has trapped the first target particles and the second target particles; How to regenerate an air filter. [Effects of the Invention]

[0010] The air filter has the above-described configuration. When the air contains first particles to be collected and second particles to be collected that are smaller in particle size than the first particles to be collected, the first particles to be collected are physically adsorbed into the valley spaces formed between the protrusions in the surface-modified layer formed on the surface of the metal fibers that constitute the main body of the filter fiber, and the second particles to be collected are physically adsorbed into the fine irregularities formed on the surface of the protrusions. Therefore, the air filter can simultaneously collect at least two types of particles to be collected, the first particles to be collected and the second particles to be collected, that is, particles with different particle sizes, in a single layer, thereby suppressing an increase in pressure loss.

[0011] Furthermore, because the main body of the filter fiber of the air filter is made of metal fibers, after the filtering performance has reached saturation through use, the first and second target particles to be collected that have been captured by physical adsorption can be removed by heating or cleaning, thereby restoring filtering performance. Therefore, with the air filter, filtering performance can be restored without having to be discarded after filtering performance has reached saturation through use.

[0012] The air filter regeneration method has the above-described configuration. According to the air filter regeneration method, the air filter that has captured the first and second target particles to be captured is cleaned and / or heated, thereby removing the first and second target particles to be captured that have been captured by physical adsorption on the surface of the surface-modified layer of the filter fiber. Furthermore, because metal fibers are used for the filter fiber, deformation of the filter due to cleaning and / or heating can be suppressed. Therefore, the air filter regeneration method can regenerate an air filter whose filtering performance has saturated due to use.

[0013] In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram for explaining the structure of the filter fiber of the air filter of the first embodiment. [Figure 2] FIG. 2 is an explanatory diagram for explaining the microstructure of the surface modification layer formed on the surface of the filter fiber of the air filter of the first embodiment. [Figure 3] FIG. 3 is an explanatory diagram for schematically explaining the effects of the air filter of the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram for schematically explaining the relationship between the particle diameter of particles to be collected and the collection efficiency. [Figure 5] FIG. 5 is a diagram summarizing the surface SEM image of Sample 1 obtained in Experimental Example 1, where the current density during Ni plating was 1 A / dm2, the results of measurement of the protrusion pitch by AFM, and the results of measurement of the specific surface area by the BET method. [Figure 6] FIG. 6 is a diagram summarizing the surface SEM image of Sample 2 obtained in Experimental Example 1, where the current density during Ni plating was 4 A / dm2, the results of measurement of the protrusion pitch by AFM, and the results of measurement of the specific surface area by the BET method. [Figure 7] FIG. 7 shows a summary of the surface SEM image of Sample 3 obtained in Experimental Example 1, where the current density during Ni plating was 10 A / dm, the results of measurement of the protrusion pitch by AFM, and the results of measurement of the specific surface area by the BET method. [Figure 8] FIG. 8 shows a collection of SEM images and AFM images of the surfaces of Samples 1 to 3 obtained in Experimental Example 1. In FIG. [Figure 9] FIG. 9 is a diagram showing the results of one-pass collection efficiency (particle diameter of target particles to be collected: 100 nm) (%) of Sample 3 and Sample 3C obtained in Experimental Example 1. [Figure 10] FIG. 10 is a diagram showing the relationship between the pitch (nm) of the protrusions in the surface modification layer and the one-pass collection efficiency (particle diameter of target particles: 100 nm) (%) obtained in Experimental Example 1. [Figure 11] FIG. 11 is a diagram showing the nonwoven fabric (before surface treatment) made of metal fibers used to prepare the sample in Experimental Example 2. [Figure 12] FIG. 12 is a diagram showing the appearances, surface SEM images, and measurement results of the specific surface area by the BET method of Samples 5 to 7 obtained in Experimental Example 2. [Figure 13] FIG. 13 is a graph showing the relationship between the test time (hr) and the acetaldehyde removal rate (%) for Samples 5 to 7, obtained in Experimental Example 2. [Figure 14] FIG. 14 is a diagram showing a surface SEM image of Sample 5, obtained in Experimental Example 3, in which PSL particles were collected. DETAILED DESCRIPTION OF THE INVENTION

[0015] The air filter and the method for regenerating the air filter according to the embodiment will be described in detail below. The lower and upper limits of the numerical ranges shown below can be arbitrarily combined (omitted below).

[0016] (Embodiment 1) An air filter of embodiment 1 will be described with reference to FIGS. 1 to 4. As illustrated in FIGS. 1 to 3, the air filter 1 of this embodiment includes a filter fiber 2. The filter fiber 2 includes metal fibers 21 and a surface-modified layer 22 formed on the surfaces of the metal fibers 21. The surface-modified layer 22 includes a plurality of protrusions 221 protruding outward from the layer surface and fine irregularities 222 formed on the surface of the protrusions 221. The surface-modified layer 22 physically adsorbs and collects first target particles P1 to be collected in valley spaces 223 formed between the plurality of protrusions 221, and physically adsorbs and collects second target particles P2, which have a particle size smaller than the first target particles P1, on the fine irregularities 222. This will be described in detail below.

[0017] As illustrated in Figs. 1 to 3, the air filter 1 of this embodiment has a filter fiber 2. The filter fiber 2 has metal fibers 21 and a surface modification layer 22. The metal fibers 21 form the main body of the filter fiber 2. The surface modification layer 22 is formed on the surface of the metal fibers 21.

[0018] Specifically, the air filter 1 is preferably made of a nonwoven fabric of filter fibers 2 from the viewpoints of filter manufacturability, surface modification, strength, pressure loss, etc. In this case, the average fiber diameter of the metal fibers 21 can be preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The average fiber diameter of the metal fibers 21 can be preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. The average fiber diameter of the metal fibers 21 is the arithmetic mean value of the fiber diameter measurements of the metal fibers 21 at any 10 positions on the nonwoven fabric. The basis weight of the nonwoven fabric is preferably 100 g / m 2 More preferably, 125 g / m 2 More preferably, 150 g / m 2 The basis weight of the nonwoven fabric is preferably 500 g / m or more. 2 or less, more preferably 300 g / m 2 More preferably, 200 g / m or less 2It can be as follows:

[0019] When the average fiber diameter of the metal fibers 21 increases, it is necessary to increase the basis weight of the nonwoven fabric to increase the collection area, but in that case, it becomes difficult to surface treat the metal fibers 21 inside the nonwoven fabric when surface treating the nonwoven fabric made of the metal fibers 21 to form the surface modified layer 22, and there is a tendency for the pressure loss of the air filter 1 to increase. On the other hand, when the average fiber diameter of the metal fibers 21 decreases, there is a tendency for the metal fibers 21 to become difficult to process into a nonwoven fabric and to deform during the surface treatment. When the average fiber diameter of the metal fibers 21 and the basis weight of the nonwoven fabric are within the above ranges, these problems are unlikely to occur, and there are advantages such as suppressing pressure loss of the air filter 1, good processability into a nonwoven fabric, and suppressing deformation during the surface treatment.

[0020] The metal fibers 21 are made of a fibrous metal (including alloys, omitted below). Examples of metal materials that make up the metal fibers 21 include iron, iron alloys such as stainless steel, copper, copper alloys, aluminum, and aluminum alloys. Of these, copper and copper alloys are preferred from the viewpoint of surface modification properties.

[0021] The surface modification layer 22 has a plurality of protrusions 221 and fine irregularities 222. Therefore, the surface area of ​​the filter fiber 2 can be increased compared to a metal fiber 21 that does not have the surface modification layer 22. The protrusions 221 protrude outward from the layer surface of the surface modification layer 22. Valley spaces 223 are formed between the plurality of protrusions 221. The valley spaces 223 can also be said to be depressions formed between the plurality of protrusions 221. The fine irregularities 222 are formed on the surfaces of the protrusions 221. Specifically, the fine irregularities 222 are formed along the surfaces of the protrusions 221. Therefore, even if the fine irregularities 222 are formed on the surfaces of the protrusions 221, the valley spaces 223 still exist.

[0022] The first target particles P1 to be collected are collected in the valley spaces 223 by physical adsorption. The second target particles P2 to be collected are collected by physical adsorption on the fine irregularities 222. The second target particles P2 have a smaller particle diameter than the first target particles P1 to be collected. The particle diameter of the first target particles P1 to be collected is the peak value of the particle diameter distribution measured by a scanning mobility particle sizer. The scanning mobility particle sizer may be the "SMPS: Scanning Mobility Particle Sizer, Model 3938" manufactured by TSI. If this model is discontinued, a successor model or the like may be used. In the present disclosure, the second target particles P2 to be collected may include gas particles (gas molecules). Examples of the second target particles to be collected P2 include specific malodorous substances as defined in the Offensive Odor Control Act (ammonia, methyl mercaptan, hydrogen sulfide, methyl sulfide, methyl disulfide, trimethylamine, acetaldehyde, propionaldehyde, normal butyraldehyde, isobutyraldehyde, normal valeraldehyde, isovaleraldehyde, isobutanol, ethyl acetate, methyl isobutyl ketone, toluene, styrene, xylene, propionic acid, normal butyric acid, normal valeric acid, isovaleric acid), etc. All of these are low molecular weight molecules with a molecular weight of 110 or less and a molecular diameter of 1 nm or less.

[0023] Specifically, the shape of the plurality of protrusions 221 can be a shape that allows the first collection target particles P1 to enter the valley spaces 223 and that can generate an air flow that carries (transports) the first collection target particles P1 into the valley spaces 223. Specifically, FIG. 2 shows an example in which the shape of the protrusions 221 is tapered from the bottom to the top of the protrusions 221. In this case, the distance between the tops of adjacent protrusions 221 is larger than the distance between the bottoms of adjacent protrusions 221. This has the advantage that, compared to a case in which the protrusions 221 are formed in a columnar shape, the first collection target particles P1 can more easily enter the valley spaces 223 and an air flow that carries the first collection target particles P1 into the valley spaces 223 can more easily be generated. Note that the protrusions 221 may be formed so that the valley spaces 223 are, for example, columnar spaces, or may be formed in a columnar, conical, pyramidal, or other shape.

[0024] The pitch between adjacent protrusions 221 can be 300 nm or more and 600 nm or less. In this case, when the particle diameter of the first target particles P1 to be collected is 100 nm or more and 300 nm or less, the lower limit of the pitch of the protrusions 221 is equal to or greater than the upper limit of the particle diameter of the first target particles P1 to be collected, so that the first target particles P1 to be collected are more easily collected in the valley spaces 223. Furthermore, if the upper limit of the pitch of the protrusions 221 is 600 nm or less, a sufficient number of valley spaces 223 can be ensured throughout the air filter 1, and a decrease in the collection efficiency of the first target particles P1 to be collected can be suppressed.

[0025] From the viewpoint of ensuring the above-mentioned effects, the lower limit of the pitch of the protrusions 221 can be preferably 100 nm or more, more preferably 200 nm or more, and even more preferably 300 nm or more. Also, from the viewpoint of ensuring the above-mentioned effects, the upper limit of the pitch of the protrusions 221 can be preferably 800 nm or less, more preferably 600 nm or less, and even more preferably 500 nm or less.

[0026] The height of the protrusions 221 can be set to 100 nm or more and 1000 nm or less. In this case, when the particle diameter of the first target particles P1 to be collected is 100 nm or more and 300 nm or less, the lower limit of the height of the protrusions 221 is equal to or greater than the lower limit of the particle diameter of the first target particles P1 to be collected, and therefore the first target particles P1 to be collected are more easily collected in the valley spaces 223. Furthermore, if the height of the protrusions 221 is 1000 nm or less, the pressure loss when air is passed through the air filter 1 is not too large, and a decrease in air volume can be suppressed.

[0027] From the viewpoint of ensuring the above-mentioned effects, the lower limit of the height of the protrusions 221 can be preferably 100 nm or more, more preferably 200 nm or more, and even more preferably 300 nm or more. Also, from the viewpoint of ensuring the above-mentioned effects, the upper limit of the height of the protrusions 221 can be preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 600 nm or less.

[0028] The pitch and height of the protrusions 221 can be measured as follows. Using an atomic force microscope (AFM), the surface irregularities of the filter fiber 2 (surface with the surface modification layer 22 attached) are measured along a diagonal line of a predetermined scan size. The distance between the tops of adjacent protrusions 221 included in the measurement data is measured, and the arithmetic mean value of the measured values ​​of the distance between the tops is defined as the pitch of the protrusions 221. Furthermore, the distance between the top and bottom of each protrusion 221 included in the measurement data is measured, and the arithmetic mean value of the measured values ​​of the distance between the top and bottom is defined as the height of the protrusion 221. The atomic force microscope that can be used is the "AFM5500M" manufactured by Hitachi Corporation. If this model is discontinued, a successor model or the like can be used. The AFM measurement conditions are specifically as follows: measurement mode: DFM, probe: SI-DF3 (tip R=10 mm), scan size: 5 μm, scan rate: 0.5 Hz, lines: 512 (390 nm intervals).

[0029] The fine irregularities 222 formed on the surface of the protrusion 221 can be formed, for example, by dendrite crystals. This configuration has the advantage of easily providing a fine irregular shape suitable for capturing gas particles as the second target particles to be captured P2. The second target particles to be captured P2 contained in the air can diffuse by Brownian diffusion and be physically adsorbed to the fine irregularities 222.

[0030] The specific surface area of ​​the filter fiber 2 can be 100 times or more and 500,000 times or less. With this configuration, the surface area of ​​only the surface of the filter fiber 2 is increased, which makes it easier to improve the collection performance of the first target particles P1 and the second target particles P2 to be collected while suppressing an increase in pressure loss. From the viewpoint of improving the collection performance of the first target particles P1, the specific surface area of ​​the filter fiber 2 can be preferably 10 times or more, more preferably 50 times or more, and even more preferably 100 times or more. Furthermore, from the viewpoint of improving the collection performance of the second target particles P2 to be collected, the specific surface area of ​​the filter fiber 2 can be preferably 1,000 times or more, more preferably 10,000 times or more, and even more preferably 30,000 times or more. On the other hand, the specific surface area of ​​the filter fiber 2 can be preferably 100,000 times or less, more preferably 72,000 times or less, and even more preferably 36,000 times or less, from the viewpoint of suppressing an increase in pressure loss due to an increase in the film thickness of the surface modification layer 22.

[0031] The specific surface area of ​​the filter fiber 2 is the surface area of ​​the filter fiber 2 [m 2 ] / Projected area of ​​filter fiber 2 [m 2 ] is a dimensionless unit defined as the surface area of ​​a square or rectangular area. 2 ] is the BET surface area [m 2 / g] and multiply it by the weight of the sample used for the measurement. The sample is cut into a square or rectangle, and the vertical and horizontal dimensions are recorded. The projected area [m 2] can be estimated by multiplying the vertical dimension of the sample used for the BET surface area of ​​the filter fiber 2 by the horizontal dimension.

[0032] The thickness of the surface modification layer 22 is preferably 5 μm or more and 20 μm or less. The larger the thickness of the surface modification layer 22, the larger the specific surface area of ​​the surface modification layer 22, but the greater the pressure loss of the air filter 1 tends to be. From the viewpoint of increasing the specific surface area of ​​the surface modification layer 22, the thickness of the surface modification layer 22 is more preferably 5 μm or more, and even more preferably 10 μm or more. From the viewpoint of suppressing pressure loss of the air filter 1, the thickness of the surface modification layer 22 is more preferably 17.5 μm or less, and even more preferably 15 μm or less. The thickness of the surface modification layer 22 is the arithmetic average of thickness measurements taken at any 10 locations on the bottom of the protrusion 221 in a cross section along the radial direction of the filter fiber 2.

[0033] The surface modification layer 22 may be formed of one layer or multiple layers. The surface modification layer 22 may be formed directly on the surface of the metal fiber 21, or one or more base layers may be provided between the metal fiber 21 and the surface modification layer 22 in order to improve the adhesion of the surface modification layer 22 to the surface of the metal fiber 21.

[0034] The surface modification layer 22 is preferably made of an inorganic material from the viewpoints of resistance to cleaning and heating, and recyclability by cleaning, heating, and vacuuming. Specific examples of inorganic materials include various metals (including alloys), metal salts, and oxides. More specifically, examples of metals include chromium, nickel, titanium, zinc, copper, tin, stainless steel, gold, silver, platinum, palladium, and ruthenium. Examples of metal salts include phosphates such as zinc phosphate and manganese phosphate. Examples of oxides include zinc oxide, copper oxide, chromium oxide, and titanium dioxide. The material of the protrusions 221 and the material of the fine irregularities 222 may be the same or different. Furthermore, if a base layer is provided, the base layer is preferably made of the same inorganic material as described above. The material of the surface modification layer and the base layer may be the same or different.

[0035] The surface modification layer 22 can be formed by performing a surface treatment on the surfaces of the metal fibers 21. Examples of surface treatments include wet surface treatments such as plating (e.g., roughening plating), painting, anodizing, and phosphate treatment, and dry surface treatments such as sputtering, CVD, PVD, and thermal spraying. The surface treatment can be performed once or multiple times. When performing multiple surface treatments, the surface treatments may be performed under different conditions or the same conditions. When the air filter 1 is composed of a nonwoven fabric of the filter fibers 2, the surface modification layer 22 can be formed on the surfaces of the metal fibers 21 constituting the nonwoven fabric by performing a surface treatment on the nonwoven fabric of the metal fibers 21.

[0036] In the air filter 1 of this embodiment, examples of the first target particles to be collected P1 include virus particles (influenza virus, norovirus, coronavirus, etc.), air pollutants (PM0.1, etc.), etc. One or more of these may be contained.

[0037] The particle diameter of the first target particles P1 can be, for example, 100 nm to 300 nm. Particle diameters such as virus particles are approximately 100 nm to 300 nm. As shown in Figure 4, when the target particles are approximately 100 nm to 300 nm, it is generally considered difficult to achieve a collection effect using any collection method (Brownian diffusion, inertia, gravity, or obstruction). The Brownian diffusion mechanism occurs due to the thermal motion of molecules, becomes more pronounced as the particle size decreases, and is independent of air flow such as flow velocity. The inertial mechanism is a phenomenon in which particles cannot keep up with the air flow as the particle size increases. The gravity mechanism is a phenomenon in which particles settle due to gravity acting on them and is dependent on the particle's mass. The obstruction mechanism is a mechanism in which particles collide with the fiber surface and are captured even if they are able to move along the air flow, and is dependent on the particle size. In contrast, the air filter 1 of this embodiment employs a surface modification layer 22 having the above-described surface shape, thereby providing an air filter 1 with excellent collection performance for virus particles and the like as the first target particles P1 to be collected.

[0038] Examples of the second particles to be collected P2 include at least one substance selected from the group consisting of basic compounds, acidic compounds, aldehydes, and sulfur compounds. Specific examples of basic compounds include ammonia and amines. Specific examples of acidic compounds include acetic acid and isovaleric acid. Specific examples of aldehydes include formaldehyde, acetaldehyde, and nonenal. Specific examples of sulfur compounds include hydrogen sulfide and methyl mercaptan. These substances cause bad odors. Therefore, in this case, an air filter 1 with deodorizing properties can be obtained by capturing the substances that cause bad odors.

[0039] 2 and 3, when first particles to be collected P1 and second particles to be collected that are smaller in diameter than the first particles to be collected are present in the air, the first particles to be collected P1 are physically adsorbed and collected in valley spaces 223 formed between multiple protrusions 221 in a surface-modified layer 22 formed on the surface of metal fibers 21 that constitute the main body of the filter fiber 2, and the second particles to be collected P1 are physically adsorbed and collected in fine irregularities 222 formed on the surface of the protrusions 221. Therefore, the air filter 1 of this embodiment can simultaneously collect, in a single layer, at least two types of particles to be collected that are different in diameter, the first particles to be collected P1 and the second particles to be collected P2, and can suppress an increase in pressure loss. In FIG. 3, the member designated by the symbol 3, which is arranged on the upstream side of the air flow of the air filter 1, is a dust filter for removing dust particles larger than the first target particles to be collected P1 and the second target particles to be collected P2.

[0040] Furthermore, in the air filter 1 of this embodiment, the main body of the filter fiber 2 is made of metal fibers 21, so after the filtering performance becomes saturated through use, the first target particles P1 and second target particles P2 to be collected that have been captured by physical adsorption can be removed by heating or cleaning, thereby restoring the filtering performance. Therefore, with the air filter 1 of this embodiment, the filtering performance can be restored without having to be discarded after the filtering performance becomes saturated through use.

[0041] The use of the air filter 1 of this embodiment is not particularly limited. The air filter 1 of this embodiment can be used, for example, in vehicles (automobiles), air purifiers, and residential ventilation equipment. Among these uses, the air filter 1 of this embodiment is particularly suitable for vehicles (automobiles). Generally, ways to improve the filtering performance of an air filter include stacking the number of filters or increasing the density of the filter fibers. However, since in-vehicle air filters are required to achieve both the filtering performance and the air conditioner performance, there is a limit to the increase in pressure drop (for example, a pressure drop of 175 Pa or less at a wind speed of 2 m). Furthermore, once the filtering capacity is saturated, the filtering performance decreases, and the filter must be replaced (discarded) periodically. In contrast, when the air filter 1 of this embodiment is used in a vehicle, as described above, even when at least two types of first and second target particles with different particle diameters are present in the air, these can be simultaneously captured by a single layer, thereby suppressing an increase in pressure drop. Furthermore, the collection performance can be restored through simple maintenance such as heating or cleaning, thereby improving maintainability.

[0042] (Embodiment 2) A description will be given of a method for regenerating an air filter according to embodiment 2. Note that, among the symbols used in embodiment 2 and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0043] The air filter regeneration method of this embodiment is the same as the air filter 1 of Embodiment 1. In the air filter regeneration method of this embodiment, the air filter 1 that has trapped the first target particles to be collected P1 and the second target particles to be collected P2 is cleaned and / or heated.

[0044] The cleaning and / or heating removes the first target particles P1 and the second target particles P2 that have been captured by physical adsorption on the surface of the surface-modified layer 2 of the filter fiber 2. Furthermore, since the metal fibers 21 are used in the filter fiber 2, deformation of the filter fiber 2 due to cleaning and / or heating can be suppressed. Therefore, the air filter regeneration method of this embodiment can regenerate an air filter 1 whose filtering performance has saturated due to use.

[0045] Specifically, the cleaning can be performed by immersion in water, a weakly acidic aqueous solution such as a citric acid aqueous solution, a weakly alkaline aqueous solution such as a bicarbonate aqueous solution, or an organic solvent such as ethanol or acetone, or by spraying. The heating can be performed by various heating methods, such as placing the filter in a thermostatic bath or heating on a hot plate. The heating temperature during the heating can be preferably 50°C or higher, more preferably 70°C or higher, and even more preferably 90°C or higher, from the viewpoint of the desorption of the second target particles P2. The heating temperature during the heating can be preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower, from the viewpoint of suppressing deformation and discoloration of the air filter 1. The heating time during the heating can be preferably 10 minutes or higher, more preferably 20 minutes or higher, and even more preferably 30 minutes or higher, from the viewpoint of evaporation of the cleaning solution. The heating time during the heating process can be preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 15 minutes or less, from the viewpoint of reducing waiting times at stores for routine automobile inspections, for example. Furthermore, the use of vacuum drawing during heating can promote the detachment of the second target particles to be collected P2. The degree of vacuum can be preferably 0.1 MPa or less, more preferably 0.05 MPa or less, and even more preferably 0.01 MPa or less.

[0046] The washing and heating may be performed once or multiple times. When the washing and heating are repeated multiple times, the same washing and heating treatment may be repeated, or different washing and heating treatments may be performed.

[0047] The air filter and the method for regenerating the air filter according to the embodiment will be specifically described below using experimental examples.

[0048] (Experimental Example 1) -Sample preparation- A 1 μm thick Ni underlayer was formed on the surface of a 100-mesh copper wire mesh (Nilaco Corporation, "CU 1181009") to improve adhesion. In this experimental example, a readily available standardized wire mesh was used as a material capable of simulating metal fibers to simplify the test. The term "mesh" refers to the size of the mesh and indicates the number of meshes per inch. The surface of this Ni underlayer was then subjected to surface treatment using Ni electroplating to form a Ni plating layer with a target thickness of 5 μm. The current density during Ni electroplating was adjusted to form a predetermined surface irregularity on the surface of the Ni plating layer. Samples 1 to 4 were obtained as described above.

[0049] Sample 1C was obtained in the same manner as Sample 1, except that the surface treatment by Ni electroplating was not performed. Sample 2C was obtained in the same manner as Sample 2, except that the surface treatment by Ni electroplating was not performed. Sample 3C was obtained in the same manner as Sample 3, except that the surface treatment by Ni electroplating was not performed. Sample 4C was obtained in the same manner as Sample 4, except that the surface treatment by Ni electroplating was not performed.

[0050] The surface of each sample was observed using a scanning electron microscope (SEM) and the surface shape was measured using an atomic force microscope (AFM). As a result, it was confirmed that the surface-modified layer formed on the surface of the wire mesh had multiple protrusions protruding outward from the layer surface and fine irregularities formed on the surface of the protrusions. In addition, the protrusion pitch of each sample was measured using the AFM described above, and the specific surface area was measured using the BET method described above. These results are summarized in Figures 5 to 8.

[0051] -Evaluation of collection performance for target particles (particle diameter 100 nm)- For each sample, the collection performance of the first target particles, which had a particle diameter of 100 nm, was evaluated. This experimental example corresponds to a general alternative evaluation using polyalphaolein (PAO) particles with a particle diameter of 100 nm.

[0052] Specifically, PAO particles were generated using an atomizer (TSI, Model 3079A) from a 0.6% by mass PAO solution diluted with isopropanol (IPA). These particles were then monodispersed to a particle size of 100 nm using an electrostatic particle classifier (TSI, Model 3080). Air containing approximately 4000 particles / mL of the monodispersed particles was then passed through the sample. The particle number concentrations upstream and downstream were measured using a scanning mobility particle sizer (TSI, Model 3938 SMPS) to determine the single-pass collection efficiency. The single-pass collection efficiency was measured using 20 38 mm diameter cutouts of the sample, stacked and fixed in a jig, with the air flow rate set to 5 L / min. Figure 9 shows the measurement results of the one-pass collection efficiency (particle diameter of the target particles to be collected: 100 nm) for Sample 3 and Sample 3C. Figure 10 also shows the relationship between the pitch of the protrusions in the surface modification layer and the one-pass collection efficiency (particle diameter of the target particles to be collected: 100 nm).

[0053] As shown in Figure 9, Sample 3, in which a surface-modified layer having multiple protrusions protruding outward from the layer surface and microscopic irregularities formed on the surface of the protrusions is formed on the surface of the metal fiber, has a one-pass collection efficiency (for particles with a diameter of 100 nm) that is approximately twice as high as Sample 3C, in which a surface-modified layer is not formed on the surface of the metal fiber. Although not shown, Samples 1, 2, and 4 also showed improved one-pass collection efficiencies (for particles with a diameter of 100 nm) compared to Samples 1C, 2C, and 4C. This is because the 100 nm diameter particles were effectively captured by physical adsorption in the valley spaces formed between the multiple protrusions in the surface-modified layer.

[0054] Furthermore, as shown in Fig. 10, it was confirmed that when the pitch of the protrusions is 300 nm or more and 600 nm or less, the collection performance of the first target particles to be collected is more easily improved than when the pitch of the protrusions is less than 300 nm or more than 600 nm. In Fig. 10, the dotted line labeled "No Treatment" represents the data for Samples 1C, 2C, 3C, and 4C.

[0055] (Experimental Example 2) As shown in Figure 11, a nonwoven fabric (basis weight 150 g / m) made of copper metal fibers (average fiber diameter 20 μm) 2 ) was prepared. The specific surface area of ​​the metal fibers in this nonwoven fabric without surface treatment was 3.4 times larger. Next, a 3 μm thick Ni underlayer was formed on the surface of the metal fibers in the nonwoven fabric in order to improve adhesion. Next, the surface of this Ni underlayer was subjected to surface treatment by electroplating with Ni, aiming for a thickness of 5 μm, to form a Ni plating layer. At this time, the current density during the Ni electroplating was adjusted to form a predetermined surface irregularity on the surface of the Ni plating layer. As a result of the above, Samples 5 to 7 were obtained.

[0056] Figure 12 shows the appearance, surface SEM image, and specific surface area measurement results by the BET method for each sample.

[0057] -Evaluation of collection performance for target particles (particle diameter < 1 nm)- Each sample was evaluated for its ability to capture acetaldehyde, a second target particle. Acetaldehyde is a gas that causes odor and has a particle diameter of less than 1 nm.

[0058] Specifically, 2 L of acetaldehyde (20 ppm) and each sample (area 16 cm) were placed in a 5 L gas bag. 2 The removal rate of acetaldehyde was calculated from the difference between the concentration of the blank containing no sample and that of the sample. The results are shown in Figure 13.

[0059] 12 and 13, it was confirmed that the acetaldehyde removal rate increases and the acetaldehyde collection performance improves as the specific surface area of ​​the filter fiber increases. Furthermore, these results show that increasing the specific surface area of ​​the filter fiber by 1000 times or more makes it easier to improve the collection performance of the second target particles to be collected.

[0060] (Experimental Example 3) A PSL particle collection experiment was carried out for 3 hours on Sample 5 (protrusion pitch 502 nm) of Experimental Example 2, using PSL particles (polystyrene latex particles, particle diameter 100 nm) instead of the PAO particles used in Experimental Example 1. The surface of this sample was then observed using an SEM. The results are shown in Figure 14.

[0061] As shown in FIG. 14, it was confirmed that the first target particles to be collected were also collected in the valley space in this experimental example (the area surrounded by the white circle in the figure).

[0062] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible within the scope of the gist of the present invention.

[0063] For example, the air filter described above may have a catalyst, such as a solid catalyst (heterogeneous catalyst) capable of decomposing the first target particles to be collected and / or the second target particles to be collected, supported on the surface of the surface modification layer, specifically the surface of the fine irregularities. In this case, the collected first target particles to be collected and second target particles to be collected are decomposed by the catalyst, thereby lengthening the time until the air filter needs to be regenerated (extending its lifespan).

[0064] Furthermore, the configurations shown in the above embodiments and experimental examples can be combined in any manner. Furthermore, the claims as originally filed can be combined in any manner. [Explanation of symbols]

[0065] 1 air filter 2. Filter Fiber 21 Metal Fibers 22 Surface modification layer 221 Protrusion 222 Fine irregularities 223 Valley Space P1 First target particle to be collected P2 Second target particle to be collected

Claims

1. An air filter (1) having filter fibers (2), The filter fiber is Metal fibers (21); a surface modification layer (22) formed on the surface of the metal fiber, The surface modification layer is a plurality of protrusions (221) protruding outward from the layer surface; and fine irregularities (222) formed on the surface of the protrusion, First particles to be collected (P1) are collected by physical adsorption in valley spaces (223) formed between the plurality of protrusions; second target particles (P2) having a particle diameter smaller than that of the first target particles to be collected are collected by physical adsorption onto the fine irregularities; Air filter (1).

2. The filter fiber is composed of a nonwoven fabric.

2. The air filter according to claim 1.

3. The surface modification layer is made of an inorganic material.

2. The air filter according to claim 1.

4. The pitch between the adjacent protrusions is 300 nm or more and 600 nm or less.

2. The air filter according to claim 1.

5. The height of the protrusion is 100 nm or more.

2. The air filter according to claim 1.

6. The specific surface area of ​​the filter fiber is 100 times or more and 10,000 times or less.

2. The air filter according to claim 1.

7. The particle diameter of the first particles to be collected is 100 nm or more and 300 nm or less.

2. The air filter according to claim 1.

8. the second particles to be collected are composed of at least one substance selected from the group consisting of basic compounds, acidic compounds, aldehydes, and sulfur compounds; 2. The air filter according to claim 1.

9. The fine irregularities are formed by dendrite crystals.

2. The air filter according to claim 1.

10. A method for regenerating an air filter (1) according to any one of claims 1 to 9, comprising: cleaning and / or heating the air filter that has trapped the first target particles and the second target particles; How to regenerate an air filter.

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