JP6074617B2 - Air filter medium, air filter and air purifier using the same - Google Patents

Description

The present invention relates to air cleaning apparatus using the same and the air filter filtration material Contact and air filter.

  A conventional air filter medium used in, for example, an air cleaning device includes a base material layer and a fine fiber layer provided on the surface of the base material layer, and the base material layer has a first fiber diameter. The first fiber is laminated, and the fine fiber layer is formed by laminating the second fiber having the second fiber diameter on the surface of the base material layer, thereby forming the base material layer. While making the 1st fiber diameter of the 1st fiber thicker than the 2nd fiber diameter of the 2nd fiber which constitutes the above-mentioned fine fiber layer, the above-mentioned base material layer is the surface side rather than the density of the back side (The following patent document 1 exists as a related document relating to this).

JP 2010-274144 A

  According to the conventional example, since the fine fiber layer is provided on the surface of the base material layer, fine dust and the like can be collected.

  Further, the base material layer has a lower density on the front side than the density on the back side, and fine dust that could not be collected by the fine fiber layer is collected on the back side of the base material layer. The increase in pressure loss can be suppressed.

  However, the first fiber constituting the base material layer has an extremely large fiber diameter compared to the second fiber constituting the fine fiber layer, and therefore fine dust that could not be collected by the fine fiber layer. It is practically impossible to collect the above on the back side of the base material layer.

  Rather, when the density on the surface side of the base material layer is lowered in this way, the eyes (in plan view) formed by laminating the first fibers constituting the base material layer become a state of large eyes, As a result, the second fibers forming the fine fiber layer laminated on the first fibers are often laminated in a loose state in the large eye, and as a result, the second fibers As a result, the eyes (side view) formed are increased, and the dust collection efficiency as an air filter medium is reduced. Further, when air is passed through the air filter medium, pressure is applied to the fine fiber layer, and there is a possibility that the fine fiber is deformed by the pressure in the place where the large eyes are formed.

  In other words, the dust collection efficiency in the air filter medium having such a fine fiber layer has the greatest influence on the formation state of the fine fiber layer and the maintenance of the state. Then, the dust collection efficiency as the air filter medium is lowered.

  Then, an object of this invention is to make low pressure loss and high dust collection efficiency compatible.

In order to achieve this object, a substrate layer, a fine fiber layer provided on the surface of the substrate layer, and a protective layer provided on the surface of the fine fiber layer, the base layer Is a configuration in which the first fibers having the first fiber diameter are laminated, and the fine fiber layer has a configuration in which the second fibers having the second fiber diameter are laminated on the surface of the base material layer. The first fiber diameter of the first fiber constituting the base material layer is made thicker than the second fiber diameter of the second fiber constituting the fine fiber layer, and the protective layer is thermally meltable. the include resin fibers, before a air filter medium obtained by bonding the protective layer and KiHoso fiber layer, to lower the density of the back side than the density of the surface side of the base layer, the base layer an air filter filtration material provided with the fine fiber layer on the surface, thereby is to achieve the intended purpose.

Although the present invention as a base layer, and a fine fiber layer provided on the surface of the substrate layer, and a protective layer provided on the surface of the fine fiber layer, the base layer, The first fiber having a first fiber diameter is laminated, and the fine fiber layer is a structure in which a second fiber having a second fiber diameter is laminated on the surface of the base material layer. The first fiber diameter of the first fiber constituting the base material layer is made thicker than the second fiber diameter of the second fiber constituting the fine fiber layer, and the protective layer is a heat-meltable resin. includes fibers, before a air filter medium obtained by bonding the protective layer and KiHoso fiber layer, to lower the density of the back side than the density of the surface side of the base layer, on the surface of the base layer an air filter filtration material provided with the fine fiber layer, since the protective layer and the fine fiber layer is bonded, low pressure loss and Takashu Chiriko It is possible to achieve both.

  That is, the second fiber forming the fine fiber layer is in a state where the second fiber is fixed by the protective layer by bonding the surface in contact with the third fiber 19 forming the protective layer. As a result, even if pressure is applied to the fine fiber, it does not enter the open space of the base material layer, so the eye of the fine fiber layer 15 can be kept in the state at the time of manufacturing the air filter medium, As a result, both low pressure loss and high dust collection efficiency can be achieved.

  In addition, since the fine fiber layer is bonded to the contact surface of the protective layer, the position of the fine fiber is stable and difficult to shift, so that when the air filter medium is processed, a tensile or compressive force is applied. However, the second fiber does not enter the gap between the base material layers, the shape is maintained integrally with the protective layer, and high dust collection efficiency can be maintained.

  That is, the dust collection efficiency in an air filter medium having such a fine fiber layer has the greatest influence on the formation state and shape stability of the fine fiber layer. When the fine fiber layer is deformed, the air filter The dust collection efficiency as a filter medium is reduced.

Sectional drawing of the air purifying apparatus provided with the air filter which shows embodiment of this invention Perspective view of the air filter Enlarged perspective view of the filter media part Enlarged sectional view of the filter media Expanded sectional view of the same fine fiber layer (A) Perspective view of boundary portion between base material layer and fine fiber layer, (b) Perspective view of boundary portion between base material layer and fine fiber layer having low density on surface side Schematic showing the manufacturing method of air filter media Schematic showing the manufacturing method of air filter media

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the air purifier including the air filter of this embodiment includes a blower 2 and an air filter 3 in a main body case 1.

  The main body case 1 has a substantially vertically long box shape. The main body case 1 is provided with a substantially square-shaped intake port 4 on the front side surface portion thereof, and the main body case 1 is provided with a substantially square-shaped exhaust port 5. Yes. The exhaust port 5 is provided with a wind direction louver 6.

  The air blowing means 2 is provided in an air passage between the air inlet 4 and the air outlet 5 of the main body case 1, and has a scroll-shaped casing 7 and a blade 8 which is a centrifugal air fan provided in the casing 7. And the electric motor 9 that rotates the blade 8.

  The air filter 3 is located at the air inlet 4 of the main body case 1. The room air sucked into the main body case 1 from the air inlet 4 by the air blowing means 2 is sent to the air outlet 5 through the air filter 3. That is, the indoor air is cleaned by the air filter 3 and blown into the room.

  As shown in FIGS. 2 and 3, the air filter 3 includes a pleated filter medium part 10, and a frame-shaped shape holding part 11 provided on the outer periphery of the filter medium part 10 to hold the filter medium part 10 in a pleated shape. Formed from. The shape holding part 11 is formed from a square-shaped frame part 12 and an adhesive member 13 provided between the frame part 12 and the filter medium part 10. That is, the frame portion 12 is positioned on the periphery of the pleated filter medium portion 10, and the pleated filter medium portion 10 is fixed to the frame portion 12 by the adhesive member 13. The filter medium part 10 is an air filter medium.

  As shown in FIGS. 4 and 5, the filter medium part 10 before the pleating process includes a base material layer 14, a fine fiber layer 15 provided on the upstream side surface of the air flow blown to the base material layer 14, and this And a protective layer 16 for protecting the fine fiber layer 15.

  The average fiber diameter of the second fibers constituting the fine fiber layer 15 is 100 to 1000 nm. When the fiber diameter is on the order of nanometers, the effect of the slip flow effect based on the interaction at the interface between the air molecules and the fine fiber surface (the flow velocity hardly slows even when air flows) increases the pressure loss. Further, since the fiber diameter is small, the gap between the fibers is small, so that the dust collection efficiency is improved. Here, if the fiber diameter is less than 100 nm, the self-supporting property is poor and fuzzing occurs, which is not preferable. On the other hand, when the fiber diameter is 1000 nm or more, the gap between the fibers becomes large and the dust collection efficiency is lowered, which is not preferable.

  Moreover, the 1st fiber 17 which comprises the base material layer 14 is formed with glass fiber, a pulp fiber, a resin fiber, carbon fiber, an inorganic fiber, or those at least 1 fiber, As a manufacturing method of the base material layer 14, Examples thereof include a spunbond method, a dry or wet papermaking method, a melt blown method, a spunbond method, an airlaid method, and a thermal bond method. In particular, the wet papermaking method is preferable. By this manufacturing method, when the base material layer 14 is seen in the thickness direction as shown in FIG. You can have it.

The basis weight of the base material layer 14 is preferably 10 to 100 g / m ² . When the basis weight is less than 10 g / m ² , the bending resistance of the base material layer 14 is lowered, so that it becomes difficult to reduce the productivity of the pleating process and maintain the filter shape, and is 100 g / m ² or more. Then, since the pressure loss of the base material layer 14 is increased, the pressure loss of the air filter 3 is increased, and the low pressure loss characteristic of the fine fiber layer 15 is deteriorated.

  It is preferable that the average fiber diameter of the 1st fiber 17 which comprises the base material layer 14 is 1-50 micrometers. When the average fiber diameter is less than 1 μm, the strength of the single fiber is low and the strength as a reinforcing material is insufficient. When the average fiber diameter is 50 μm or more, the thickness of the base material layer 14 is increased and structural pressure due to pleating is increased. Since loss increases, it is not preferable.

  The protective layer 16 is a member that protects the fine fiber layer 15. As the third fiber constituting the protective layer 16, a heat-meltable resin fiber or the like may be used. In addition, a component constituting the protective layer 16 may be impregnated with a heat-meltable adhesive, or heat-meltable particles may be included. When a heat-meltable resin fiber is used, the protective layer 16 is melted by heating, and the fine fiber layer 15 and the protective layer 16 can be bonded and fixed. In addition, depending on the degree of heating, there is an effect that the three layers of the base material layer 14, the fine fiber layer 15, and the protective layer 16 can be bonded, and the filter medium portion 10 can be integrated. The same thing happens when a heat-meltable resin is included in part. As an example of the protective layer 16 containing a low melting point resin material, a spunbond nonwoven fabric or a thermal bond nonwoven fabric containing a low melting point resin material, or paper using a low melting point resin material as a binder can be used.

  In the present invention, the protective layer 16 includes a heat-meltable resin fiber, and the contact surface between the fine fiber layer 15 and the protective layer 16 is bonded by heating from the base material layer 14 side. Therefore, the heat-meltable resin contained in at least a part of the protective layer 16 is heat-melted at a melting temperature lower than the heat resistance temperature of each resin fiber constituting the base material layer 14 and the fine fiber layer 15. .

  The melting temperature of the resin used for the base material layer 14 and the fine fiber layer 15 differs depending on the type of resin, for example, 90 to 110 ° C. for polyethylene, 100 to 140 ° C. for polypropylene, 120 to 130 ° C. for polycarbonate, and 90 for polyurethane. ˜130 ° C., 400 ° C. or more for glass fiber. The protective layer 16 may be selected from those that melt at a temperature lower than the melting temperature of the base material and the fine fiber layer 15.

  Moreover, it is preferable that the average fiber diameter of the 3rd fiber which comprises the protective layer 16 is 1-10 micrometers. If the average fiber diameter is less than 1 μm, the self-supporting property is poor, and it is necessary to increase the weight per unit area in order to form the protective layer 16, and as a result, the pressure loss increases.

  On the other hand, if it is 10 μm or more, the collection efficiency of the protective layer 16 is lowered, which is not preferable. A preferable fiber diameter is 2 to 6 μm. Thereby, since it is a low pressure loss and a large dust can be collected upstream, the increase in the pressure loss of the air filter 3 at the time of long-term use can be suppressed.

  The protective layer 16 preferably has a pressure loss of about 1 to 10 Pa and does not hinder the inflow of air. When the pressure loss is 10 Pa or more, the pressure loss of the air filter 3 is increased, and the low pressure loss characteristic of the fine fiber layer 15 is deteriorated.

  As shown in FIG. 5, the filter medium portion 10 is constituted by the base material layer 14, the fine fiber layer 15 provided on the surface of the base material layer 14, and the protective layer 16, and the first base material 14 is constituted. While the fiber diameter of the fiber 17 is made thicker than the fiber diameter of the second fiber 18 constituting the fine fiber layer 15, the base material layer 14 has a configuration in which the density on the back surface side is lower than the density on the front surface side. Also good.

  In this configuration, since the density on the surface side of the base material layer 14 is increased, the eyes (plan view) formed by laminating the first fibers 17 constituting the base material layer 14 are small eyes. Therefore, the second fiber 18 forming the fine fiber layer 15 laminated on the first fiber 17 has small eyes (side view) as the fine fiber layer 15 in the small eyes. As a result, the dust collection efficiency as the air filter 3 is increased.

  That is, the dust collection efficiency in the air filter 3 having such a fine fiber layer 15 has the greatest influence on the formation state of the fine fiber layer 15, and when the fine fiber layer 15 has a large eye, the air filter As a result, the dust collection efficiency as 3 is reduced.

  Further, the second fiber 18 forming the fine fiber layer 15 is bonded to the third fiber 19 forming the protective layer 16 so that the second fiber 18 is fixed by the protective layer 16. As a result, even if pressure is applied to the second fibers 18 (fine fibers), the air does not enter the open space of the base material layer 14. Thus, the fine fiber layer 15 can be kept in a small state, and both low pressure loss and high dust collection efficiency can be achieved.

  As shown in FIG. 6 (a), when the fine fiber layer 15 is formed on the surface of the base material layer 14 with a small eye, the second fiber 18 forming the fine fiber layer 15 becomes a base material layer with a small eye. 14 is laminated in a stretched state, and as a result, the second fibers 18 (fine fibers) do not enter the large eyes of the base material layer 14, so that a uniform fine fiber layer 15 is obtained. Therefore, the eyes of the fine fiber layer 15 can be kept small, and as a result, the dust collection efficiency is increased.

  On the other hand, as shown in FIG. 6B, when trying to form a small fine fiber layer 15 on a large eye base layer 14, the second fibers 18 forming the fine fiber layer 15 are changed to a base material. Since the second fiber 18 constituting the fine fiber layer 15 is loosened as a result, the fine fiber layer 15 becomes non-uniform. The eye (side view) formed by 18 becomes large, and the dust collection efficiency is thereby lowered.

  Further, when the second fiber 18 is formed on the surface of the base material layer 14 in a slack state, the portion where the second fiber 18 and the third fiber 19 are not in contact with each other and the gap is increased, the As a result, the bonded area is reduced. When the adhesion area of the contact surface between the fine fiber layer 15 and the protective layer 16 is reduced, the position of the fine fiber layer 15 is not stable and easily deviates, and it is difficult to maintain high dust collection efficiency.

  The second fiber 18 constituting the fine fiber layer 15 is not particularly limited as long as it has a nano-order fiber diameter. However, since the fine fiber layer 15 is laminated on the surface of the base material layer 14, the electrostatic spinning method is used. Preferably, it is formed by. This method is a method of forming a fine fiber layer 15 by applying a high voltage to the solution and spraying the solution, and the fiber diameter of the second fibers 18 constituting the fine fiber layer 15 obtained is applied. Depending on the voltage, solution concentration, etc., an arbitrary fiber diameter can be obtained by adjusting these conditions.

  The material of the second fiber 18 constituting the fine fiber layer 15 produced by a known electrostatic spinning method may be any material that can be dissolved in a solvent. For example, polyacrylonitrile (PAN), polypropylene (PP), polyethylene (PE), polyethylene oxide (PEO), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyethersulfone (PES), polymethacrylic acid, polymethacrylic Methyl acid, polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polytetrafluoroethylene, polyvinyl alcohol (PVA), polycarbonate (PC), polystyrene, polyamide, polyimide, polyamideimide, aramid, polyimide benzazole, polyglycol Polymers such as acid (PGA), polylactic acid (PLA), polyurethane (PU), cellulose compounds, polypeptides, nylons such as nylon 66, and proteins Those solutions of, and an inorganic material such as alumina or titanium oxide may be obtained by a sol.

  The solvent for dissolving the polymer is not particularly limited as long as it is compatible with the polymer and can be dissolved. Examples of these solvents include water, alcohols, organic solvents, etc. Specific alcohols and organic solvents include acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, benzene, benzyl alcohol, 1, Highly volatile solvents such as 4-dioxane, propanol, carbon tetrachloride, cyclohexane, cyclohexanone, methylene chloride, phenol, pyridine, trichloroethane, acetic acid, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N , N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidone (NMP), ethylene carbonate, propylene carbonate, dimethyl carbonate, acetonitrile, N-methylmorpholine-N-oxide, Tylene carbonate, γ-butyrolactone, diethyl carbonate, diethyl ether, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dioxolane, ethyl methyl carbonate, methyl formate, 3-methyl oxazolidine Examples include solvents having relatively low volatility such as 2-one, methylpropionate, 2-methyltetrahydrofuran, and sulfolane.

  Next, an example of the manufacturing method of the air filter 3 of this embodiment is demonstrated.

  As shown in FIG. 7, the manufacturing facility includes a conveying means 20 that carries the base material layer 14 and conveys it in the horizontal direction, and a nozzle 21 located above the conveying means 20.

  The nozzle 21 sprays a polymer solution in order to form the fine fiber layer 15 on the surface which is the upper surface of the flat substrate layer 14 conveyed by the conveying means 20.

  In manufacturing the air filter 3, the polymer solution is discharged toward the base material layer 14 in order to form the fine fiber layer 15 from the nozzle 21 while the flat base material layer 14 is transported by the transport means 20. Here, a voltage of about +20 KV is applied to the nozzle 21, and the conveying means 20 is grounded. Due to this potential difference, the polymer polymer solution discharged from the nozzle 21 forms the fine fiber layer 15. The fine fiber layer 15 is formed by adhering to the surface of the base material layer 14 while being fiberized into the fibers 18 and laminating.

  Next, as shown in FIG. 8, a protective layer 16 is laminated on the surface of the fine fiber layer 15, and the layers are bonded and integrated through a heated pressure roll 22. Although the adhesion method is not particularly limited, adhesion by calendering or a heat oven is preferable. For example, in the case of thermocompression bonding by calendering, the thickness of the filter medium part 10 can be adjusted by appropriately selecting the heating temperature, pressure, and the like.

  Further, a resin adhesive such as hot melt or powder may be used for bonding the base material layer 14 to the fine fiber layer 15 and the protective layer 16.

  As shown in FIG. 5, the filter medium portion 10 is configured by the base material layer 14, the fine fiber layer 15 provided on the surface of the base material layer 14, and the protective layer 16, and the first base material 14 is configured. The fiber diameter of the fiber 17 is thicker than the fiber diameter of the second fiber 18 constituting the fine fiber layer 15, and the base material layer 14 has a lower density on the back side than a density on the front side, It is good also as a structure to which the contact surface of the fine fiber layer 15 and the protective layer 16 adhere | attaches.

  In this case, since the density on the surface side of the base material layer 14 is increased, the eyes (plan view) formed by laminating the first fibers 17 constituting the base material layer 14 are in a state of small eyes. Therefore, the second fiber 18 forming the fine fiber layer 15 laminated on the first fiber 17 has small eyes (side view) as the fine fiber layer 15 in the small eyes.

  The second fibers 18 formed in this manner are laminated in a stretched state on the surface of the base layer of the small eye, and the third fibers 19 constituting the protective layer 16 in contact therewith The contact area increases. In this state, the second fiber 18 that forms the fine fiber layer and the third fiber 19 that forms the protective layer 16 are densely melted by thermally melting the heat-meltable resin while applying pressure to the pressure-bonding roll 22. Glued in a state.

  The filter medium part 10 thus created is in a state where the second fibers are fixed by a protective layer. As a result, even if pressure is applied to the fine fibers, the base layer 14 does not enter the large eyes, so that the fine fiber layer 15 can be kept in the state of manufacture, and the fine fiber layer 15 can be Since it can be kept small, high dust collection efficiency can be maintained.

  In addition, since the contact surface of the fine fiber layer 15 and the protective layer 16 is bonded substantially uniformly, the adhesive strength is high, and the position of the fine fiber layer 15 is not stable and difficult to shift, so that the air filter medium is processed. Sometimes, the air filter medium can be obtained without being deformed and having a high dust collection efficiency.

  Further, the feature of this embodiment is that when the resin is thermally melted, the contact surface between the protective layer 16 and the fine fiber layer 15 is made higher by setting the temperature on the base layer 14 side higher than the temperature of the protective layer 16. This is to heat-melt almost uniformly. In this way, the third fiber 19 forming the protective layer 16 is formed from the surface side by thermally melting the resin with a temperature gradient so that the temperature decreases as it goes from the base material layer 14 to the protective layer 16. Also, the fine fiber layer 15 side becomes an air filter medium having many portions that are thermally melted. When the thermal melting of the resin proceeds excessively, the molten resin fills the gaps between the protective layer 16 and the fine fiber layer 15, and the pressure loss of the air filter medium increases. By thermally melting the resin with a temperature gradient, the third fiber 19 can be thermally melted with the minimum amount that contributes to the adhesive strength, and the pressure loss of the air filter medium accompanying the heat melting increases. Can be reduced.

  Making the temperature of the base material layer 14 side higher than the temperature of the protective layer 16 includes, for example, a method of heating with a heater from the base material side, a method of heating a portion in contact with the surface of the press roll 22 on the base material side, etc. Can be implemented.

  Moreover, the fiber diameter of the 1st fiber 17 which comprises the base material layer 14 is made thicker than the fiber diameter of the 2nd fiber 18 which comprises the fine fiber layer 15, and the base material layer 14 is the density of the surface side. In addition, the contact surface of the protective layer 16 and the fine fiber layer 15 is melted substantially uniformly by adopting a configuration in which the density on the back surface side is lower than that.

  The thermal conductivity (W / (m · K)) is 0.026 for air, 1.03 for glass, and 0.41 for polyethylene resin. That is, heat is more easily transmitted in the first fibers 17 and the second fibers 18 than in the air.

  When the resin is heated with a temperature gradient so that the temperature decreases as it goes from the base material layer 14 to the protective layer 16, in this embodiment, the resin is thermally deformed as shown in FIG. This is because the temperature of the second fibers 18 rises substantially uniformly through the first fibers 17 having good heat conduction, and the contact surfaces of the second fibers 18 and the third fibers 19 are melted substantially uniformly. It is to do.

  On the other hand, when the density of the base material layer 14 is reversed, the resin is thermally deformed as shown in FIG. This is because the temperature of the second fibers 18 increases non-uniformly through the first fibers 17 having good heat conduction and the air, and particularly the temperature near the second fibers 18 increases. This is because the contact surface between the second fiber 18 and the third fiber 19 is melted unevenly.

  When comparing FIG. 6A and FIG. 6B, the adhesive strength between fibers is stronger in (a), and the probability that the second fibers 18 (fine fibers) enter the eyes of the base material layer is reduced. Since an increase in loss can be suppressed to a low level, (a) is preferable as an air filter medium.

  Next, the filter medium part 10 is folded into a pleat shape by a folding machine (not shown), and finally the pleat-shaped filter medium part 10 is fixed to the frame part 12 by an adhesive member 13. The adhesive member 13 can be fixed in shape while securing the surface area of the air filter 3 by using, for example, a method in which only the apexes of the pleats are connected by hot melt resin or various adhesives.

  Also at this time, the structure of FIG. 6A has a stronger adhesive strength between the fibers and is less likely to be displaced, so that it is possible to obtain an effect that the air filter 3 is not easily damaged or crushed.

  As described above, since the air filter medium of the present invention has low pressure loss and high dust collection efficiency, it should be used as an air filter for removing allergens such as dust and pollen in home or commercial air purifiers. Can do.

DESCRIPTION OF SYMBOLS 1 Main body case 2 Air blower 3 Air filter 4 Intake port 5 Exhaust port 6 Wind direction louver 7 Casing 8 Blade 9 Electric motor 10 Filter material part 11 Shape holding part 12 Frame part 13 Adhesive member 14 Base material layer 15 Fine fiber layer 16 Protective layer 17 1st 1 fiber 18 second fiber 19 third fiber 20 conveying means 21 nozzle 22 pressure roll

Claims (5)

The has a base material layer, and a fine fiber layer provided on the surface of the substrate layer, and a protective layer provided on the surface of the fine fiber layer, the base layer, the first fiber diameter The first fiber constituting the base material layer has a structure in which the first fiber is laminated, and the fine fiber layer has a structure in which the second fiber having the second fiber diameter is laminated on the surface of the base material layer. of the first diameter of the fibers, while thicker than the second fiber diameter of the second fibers constituting the fine fiber layer, wherein the protective layer comprises a heat-meltable resin fibers, before KiHoso fibers An air filter medium in which a layer and the protective layer are bonded , wherein the density on the back side is lower than the density on the surface side of the base material layer, and the fine fiber layer is provided on the surface of the base material layer Air filter media. Air filter medium according to claim 1, wherein the fine fiber layer is composed of an average fiber diameter of 100 to 1000 nm. First fibers constituting the base layer, glass fibers, pulp fibers, resin fibers, air according to any of 2 claims 1 formed by the fibers comprising at least one of carbon fibers and inorganic fibers Filter media. The air filter which fixed the shape by pleating the air filter medium as described in any one of Claim 1 to 3 . The air purifier which has arrange | positioned the air filter of Claim 4 in the ventilation path.

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