JP4754269B2 - Filter material for air filter, method for producing the same, and air filter - Google Patents

Description

The present invention relates to a semiconductor manufacturing industry, pharmaceutical manufacturing industry, cleaning of clean rooms used in the fields such as food industry and hospitals, office air conditioning, domestic air conditioner filter for an air filter used in air filters used for material and The present invention relates to a manufacturing method and an air filter .

Conventionally, as an air filter , a large-area filter medium is folded in a zigzag shape, and a filter pack is formed by holding the interval of the filter medium with a wave-shaped separator as an interval holding material. For example, a box-shaped filter having a depth of 290 mm An air filter housed in a frame is used. Such an air filter has an advantage that it has a long life because of a large filter medium area. Also, an air filter of a type in which a pleat type filter pack is formed in which a fine interval of filter media obtained by folding an electret nonwoven fabric or the like in a zigzag shape is held by a ribbon material and accommodated in a box-shaped filter frame having a depth of 610 mm, for example. Has also been used. This type of air filter has the advantage that dust or the like having an opposite charge is easily adsorbed because positive or negative charges are charged on the fibers constituting the nonwoven fabric as a filter medium. This type of air filter has been used for a long time by frequently changing the filter medium. Moreover, for example, as in Patent Document 1, a blow-off type air filter in which a frame is attached to an opening of a bag-shaped filter medium is also used. Such an airflow type air filter has a large depth of 610 mm, and thus has an advantage of a large filter medium area and a long life.

As the filter medium used for the air filter, in addition to the electret nonwoven fabric, a filter medium made of a sheet made by a wet paper making method by adding a binder to synthetic fibers or inorganic fibers has been used. As such a filter medium for an air filter , a filter medium having high strength, high dust collection efficiency, and low pressure loss is desired.
For example, as shown in FIG. 3, a conventional filter medium 10 made of a sheet made of glass fiber or the like by a wet papermaking method has a small average pore diameter in the thickness direction of the filter medium due to glass fibers 9 having a relatively small average fiber diameter. Since the gaps are formed uniformly, there is a problem that a large amount of dust 8 is collected on the air inflow side and the pressure loss increases. The filter medium 10 also includes glass fibers 16 having a slightly large average fiber diameter.

In order to reduce the pressure loss, it is conceivable to reduce the density of the filter medium by using fibers having a large average fiber diameter. However, when a sheet made with only fibers having a large average fiber diameter is used as a filter medium, the gap between the fibers increases, and the dust collection efficiency decreases. Therefore, in Patent Document 2, as shown in FIG. 4, a synthetic fiber 11 having a large average fiber diameter, a glass fiber 12 having a small average fiber diameter, and expandable particles are dispersed in a dispersion medium, and a wet papermaking method is used. After forming a sheet-like material, a sheet in which voids 13 are formed by foaming of expandable particles is used as a filter medium 15. When the foamable particles are foamed, the fibers constituting the sheet-like material are spread to form a void portion 13, and while maintaining the void portion 13, the outer wall 14 of the expandable particles is melted to surround the surrounding fibers. Is glued.
Japanese Patent Laid-Open No. 7-253028 JP-A-9-155127

However, as shown in FIG. 4, the filter medium 15 described in Patent Document 2 has an average fiber diameter of skeleton fibers, although the density of the filter medium 15 is reduced by the voids 13 formed by foaming of expandable particles. The large mesh structure formed by the large synthetic fibers 11 is filled with the glass fibers 12 having a small average fiber diameter, and gaps having a small average pore diameter are formed uniformly in the thickness direction of the filter medium 15. The problem that a large amount of dust 8 is collected on the inflow side is not improved. For this reason, the filter medium 15 has a problem that the pressure loss becomes high and the life of the filter medium is short. In addition, the filter medium 15 has an advantage that an air passage is ensured by the gap portion 13 formed by foaming of the expandable particles, but the air passage secured with great effort has a large average fiber diameter as a skeleton fiber. There was a problem that the pressure loss was increased due to obstruction by the synthetic fiber 11.
Therefore, the present invention secures air passages by the gaps in the sheet constituting the filter medium, and collects dust uniformly in the thickness direction of the filter medium without being biased toward the air inflow side and collecting dust. It can be condensed, and an object thereof is to provide a filter medium and method of manufacturing the same, and an air filter for possible air filter to long life.

Air filter medium of the present invention is a street for an air filter media comprising a sheet formed a gap portion by bonding a fiber around at debris rupture the expandable particles of claim 1, wherein sheet and 70 to 90 wt% short glass fibers having an average fiber diameter of 4-8 [mu] m, and 0 to 15 wt% short glass fibers less than the average fiber diameter of 2 [mu] m, an adhesive synthetic fibers 5-15 weight average fiber diameter of 10~35μm %, And 3 to 10% by mass of expandable particle fragments.
Moreover, the manufacturing method of the filter material for air filters of this invention is 70-90 mass% of short glass fibers with an average fiber diameter of 4-8 micrometers , and short glass fibers 0 with an average fiber diameter of less than 2 micrometers as described in Claim 2. An aqueous dispersion in which 15% by mass, 5 to 15% by mass of an adhesive synthetic fiber having an average fiber diameter of 10 to 35 μm, and 3 to 10% by mass of unfoamed expandable particles having an average particle diameter of 3 to 20 μm are used. The sheet is made into a sheet, the foamable particles are foamed to form a void portion, and then the surrounding fibers are adhered to each other by a fragment obtained by rupturing the foamable particles to form a sheet.
Moreover, the air filter of the present invention is characterized in that, as described in claim 3, the air filter medium according to claim 1 is used.

The filter material for an air filter of the present invention is a sheet in which voids are formed by adhering surrounding fibers with fragments obtained by rupturing foamable particles, and the sheet is formed of short glass fibers 70 to 70 having an average fiber diameter of 4 to 8 μm. From 90% by mass, from 0 to 15% by mass of short glass fibers having an average fiber diameter of less than 2 μm, from 5 to 15% by mass of adhesive synthetic fibers having an average fiber diameter of from 10 to 35 μm, and from 3 to 10% by mass of foamable particles. It will be. Therefore, the voids in the sheet serve as air passages, making it easier for air to move from the inflow side to the outflow side of the filter medium, and the average fiber diameter constituting the sheet over the entire thickness direction of the filter medium. Dust can be evenly collected in a relatively fine network structure formed by short glass fibers of 4 to 8 μm, and the filter medium comprising the sheet can have a long life. Further, when glass short fibers having an average fiber diameter of less than 2 μm are mixed, the fine glass short fibers are dispersed by a relatively fine network structure formed by glass short fibers having an average fiber diameter of 4 to 8 μm , and pressure loss As a result, a fine mesh structure can be formed so that the dust collection efficiency can be increased over the entire thickness direction of the filter medium, and the life of the filter medium can be further extended.
Further, since 3 to 10% by mass of expandable particle fragments are contained in the sheet, the surrounding fibers are firmly bonded to the extent that the fragments of expandable expandable particles do not deteriorate the air permeability, and the strength of the filter medium is improved. can do.
According to the method for producing a filter medium for an air filter of the present invention, since the surrounding fibers are bonded with the fragments obtained by rupturing the expandable particles, compared to the case where the fibers are bonded only with the adhesive synthetic fibers, The strength of the sheet is improved and a long-life filter medium can be produced.
Since the air filter using the air filter medium of the present invention has a high filter medium strength, the life of the filter medium may be increased by about twice as compared with the case where a sheet made of a conventional glass fiber is used as the filter medium. And an air filter using the filter medium can be formed compactly.

The filter material for an air filter of the present invention is a sheet in which voids are formed by adhering surrounding fibers with fragments obtained by rupturing expandable particles, and the sheet is a short glass fiber having an average fiber diameter of 4 to 8 μm. 70 to 90% by mass, 0 to 15% by mass of short glass fibers having an average fiber diameter of less than 2 μm, 5 to 15% by mass of adhesive synthetic fibers having an average fiber diameter of 10 to 35 μm, and 3 to 10 mass of foamable particles. %.
In the sheet, short glass fibers having an average fiber diameter of 4 to 8 μm are blended in an amount of 70 to 90% by mass. When the blending amount is less than 70% by mass, the blending amount of adhesive synthetic fibers and foam particles is small. Therefore, when the average fiber diameter exceeds 8 μm or the blending amount exceeds 90% by mass, the blending amount of the adhesive synthetic fiber and the debris of the expandable particles decreases. Therefore, there is a problem that the strength of the filter medium is lowered.
In order to reduce the gap between the fibers in the sheet and increase the dust collection efficiency within a range where pressure loss is not increased, a part of the short glass fibers are average fibers in the range of 0 to 15% by mass. It is also possible to use short glass fibers having a diameter of less than 2 μm. In addition, in order to use the short glass fiber of the stable quality, it is preferable to use a thing with an average fiber diameter of 0.3 micrometer or more.
As the short glass fibers, those formed by a steam spraying method, a spinning method, a flame insertion method, a rotary method, or the like can be used.

  In the sheet, 5 to 15% by mass of an adhesive synthetic fiber having an average fiber diameter of 10 to 35 μm is blended when the blending amount is less than 5% by mass or the average fiber diameter of the adhesive synthetic fiber is less than 10 μm. This is because the adhesive area with the short glass fiber is reduced and the adhesive strength is insufficient, which causes a problem that the strength of the filter medium is weakened. When the blending amount exceeds 15% by mass or the average fiber diameter of the adhesive synthetic fiber exceeds 35 μm, a film is formed between the fibers when the resin is melted to form a binder, and the pressure loss of the filter medium increases. This is because the filter life is shortened.

  A core-sheath type synthetic fiber can be used as the adhesive synthetic fiber. For example, core-sheath type synthetic fiber (for example, N720 manufactured by Kuraray Co., Ltd.) using polyester as the core component and low-melting modified polyester as the sheath component, or core-sheath type synthesis using polyester as the core component and polyethylene as the sheath component A fiber (for example, N710 manufactured by Kuraray Co., Ltd.) can be used. Further, the adhesive synthetic fiber is not limited to the core-sheath type synthetic fiber, for example, synthetic fiber made of thermoplastic resin such as acrylic resin, polyester resin, polyolefin resin, or synthetic resin made of thermosetting resin such as epoxy resin. Fiber etc. can also be used.

  In the sheet, 3 to 10% by mass of expandable particle fragments are incorporated in an amount of less than 3% by mass, and the amount of expandable particle fragments to be ruptured after foaming is reduced. There is a problem that the amount of the filter medium is small and the strength of the filter medium is weakened. If the amount exceeds 10% by mass, the amount of fragments of the expanded foam particles is increased, but the short glass fiber and the adhesive are bonded. This is because there is a problem that a large amount of explosive foam particles adhering to the gaps between the synthetic fibers deteriorates the air permeability, increases the pressure loss, and shortens the filter medium life.

Next, the manufacturing method of the filter material for air filters of this invention is demonstrated.
According to the production method of the present invention, a sheet is obtained by a wet papermaking method using an aqueous dispersion in which unfoamed expandable particles having an average particle diameter of 3 to 20 μm are dispersed in the short glass fibers and adhesive synthetic fibers having the above-mentioned composition. A filter medium for air filter is manufactured, which is made of a sheet, foamed with the foamable particles to form voids, and then a sheet in which surrounding fibers are bonded with fragments obtained by rupturing the foamable particles.
In addition, the unexpanded expandable particles having an average particle diameter of 3 to 20 μm are used because the expansion coefficient of the expanded foamed particles is that the average particle diameter of the unexpanded expandable particles is less than 3 μm. Since it is low, there is a problem that it is not possible to form a sufficiently large void portion serving as an air passage in the filter medium, and when the average particle diameter exceeds 20 μm, the void becomes large, so the collection efficiency of the filter medium is This is because, although improved, the expanded foam particles adhere to the gaps between the fibers in a large amount, so that there is a problem that the pressure loss is increased and the filter medium life is shortened.

As the expandable particles, those having a particle size of about 4 to 5 times and a volume of about 50 to 100 times due to foaming are used.
As the expandable particles, those in which a heat-expandable gas such as ethane, ethylene, propane, butane, or isobutane is included in the outer wall made of polystyrene, polyvinyl chloride, polyvinylidene chloride and / or a copolymer thereof are used. be able to. In particular, due to the degree of expansion of the expandable particles, the degree of adhesion between the expandable expandable particles and the short glass fibers, acrylonitrile-methyl methacrylate (MMA) is used on the outer wall of the expandable particles, and isobutane is used as the heat-expandable gas to be included. It is preferred to use particles. When the heat-expandable expandable particles are used, the expandable particles are expanded by heating, and the expandable particles are ruptured and the contained heat-expandable gas is released to the outside. The broken pieces of the expandable particles are melted and firmly adhere to the surface and / or intersection of the surrounding fibers. The mass of the expandable particles hardly changes before and after the gas is released to the outside.

  In the sheet, fibers such as ultrafine fibrillated synthetic fibers, natural fibers, and filamentous fibers such as long glass fibers are blended so long as the collection efficiency is not lowered and the pressure loss is not increased. May be. In addition, it is also possible to make a sheet by wet paper making method by adding a surfactant to uniformly disperse the fibers etc. in the dispersion, and after making the sheet, a binder is added to improve the strength It is also possible to do.

Next, an embodiment of a filter medium for an air filter and a method for producing the filter medium of the present invention will be described with reference to the drawings, and a comparative example and a conventional example of the filter medium will be described together.

Example 1
10% by mass of C glass short fibers 3 ′ having an average fiber diameter of 0.8 μm (MLF # 208 manufactured by Nippon Sheet Glass Co., Ltd.), 78% by mass of C glass short fibers 3 having an average fiber diameter of 4 μm (W50 manufactured by Mag Co., Ltd.) As an adhesive synthetic fiber, a core-sheath type synthetic fiber 2 having an average fiber diameter of 17 μm and an average fiber length of 5 mm (core component polyester, sheath component modified polyester, heat shrinkage rate of 140 ° C. 55%, N720 manufactured by Kuraray Co., Ltd.) 7% by mass And, as expandable particles, thermally expandable microcapsules 4 having an average particle diameter of 10 to 20 μm (foaming start temperature 100 to 105 ° C., acrylonitrile-methyl methacrylate (MMA) copolymer on the outer wall, and isobutane included in the thermally expandable gas) Matsumoto Yushi Seiyaku Co., Ltd. Matsumoto Microsphere F-55) 5% by mass was dispersed and mixed in water to obtain an aqueous dispersion. A cationic acrylamide adsorbent having a molecular weight of 1,500,000 is added to this aqueous dispersion to adsorb and carry the heat-expandable microcapsules 4 on the surfaces of the C glass short fibers 3, 3 ′ and the core-sheath type synthetic fiber 2. I let you.
As shown to Fig.1 (a), after making the said aqueous dispersion into a sheet-like material using the normal paper machine, surfactant processing was performed. As shown in FIG. 1 (b), the sheet-like material is dried at 140 ° C. to bond the C glass short fibers 3, 3 ′ and the core-sheath type synthetic fiber 2, and unexpanded thermally expandable microcapsules 4 was foamed about 20 times to obtain a foamed microcapsule 5, and the surrounding C glass short fibers 3, 3 ′ and the core-sheath type synthetic fiber 2 were spread along the spherical surface of the microcapsule 5. Then, as shown in FIGS. 1 (c) and 2, the foamed microcapsule 5 is ruptured, and the surrounding C glass short fibers 3, 3 ′ and the core-sheath type synthetic fiber 2 are bonded with the ruptured pieces 7. The sheet 1 having a thickness of 0.71 mm and a basis weight of 92 g / cm ² in which a plurality of voids 6 were formed was used as an air filter medium. In FIG. 2, 8 indicates dust.

(Example 2)
The thickness is the same as in Example 1, except that the short glass fiber C (W50 manufactured by Mag Co., Ltd.) having an average fiber diameter of 4 μm is 73% by mass, and the thermally expandable microcapsules are 10% by mass as expandable particles. A sheet having a thickness of 0.86 mm and a basis weight of 91 g / cm ² was used as a filter medium for an air filter .

(Example 3)
Other than the fact that C glass short fibers (MLF # 208 manufactured by Nippon Sheet Glass Co., Ltd.) with an average fiber diameter of 0.8 μm were 0% by mass and C glass short fibers (M50 W50) with an average fiber diameter of 4 μm were used. In the same manner as in Example 1, a sheet having a thickness of 0.70 mm and a basis weight of 90 g / cm ² was used as a filter medium for an air filter .

Example 4
Example except that C glass short fiber 3 (manufactured by Mag Co., Ltd. W50) having an average fiber diameter of 4 μm was used, except that C glass short fiber (NANJING AIXIN FIBREGRATION PRODUCT CO., LTD) was used. In the same manner as in Example 1, a sheet 1 having a thickness of 0.71 mm and a basis weight of 92 g / cm ² was used as a filter medium for an air filter .

(Comparative Example 1)
In the same manner as in Example 1 except that C glass short fibers (W50 manufactured by Mag Co., Ltd.) having an average fiber diameter of 4 μm were 83% by mass, and the thermally expandable microcapsules were 0% by mass as expandable particles, A sheet having a thickness of 0.60 mm and a basis weight of 95 g / cm ² was used as a filter medium for an air filter .

(Comparative Example 2)
In the same manner as in Example 1 except that C glass short fibers having an average fiber diameter of 4 μm (W50 manufactured by Mag Co., Ltd.) were 68% by mass, and the thermally expandable microcapsules were 15% by mass as expandable particles, A sheet having a thickness of 0.91 mm and a basis weight of 88 g / cm ² was used as a filter medium for an air filter .

(Conventional example 1)
A sheet having an average fiber diameter of 2 μm and a thickness of 0.36 mm and a basis weight of 64 g / cm ² made by a commercially available wet papermaking method was used as a filter medium for an air filter .

(Conventional example 2)
A sheet with an average fiber diameter of 2 μm and a thickness of 0.50 mm and a basis weight of 90 g / cm ² made by a commercially available wet papermaking method was used as a filter medium for an air filter .

Next, for each of the filter media for air filters of Examples 1 to 4, Comparative Examples 1 and 2 and Conventional Examples 1 and 2 thus obtained, the filtration efficiency of the filter media and the filter media life were measured by the following methods. The measurement results were evaluated. Moreover, the presence or absence of dust adhesion on the outflow side of the filter medium was evaluated. Further, based on these evaluation results, comprehensive evaluation was performed as follows. The results are shown in Table 1.

[Collection efficiency]
Air dust having an average particle size of 0.3 μm was passed through the filter medium for air filter at a wind speed of 0.5 m / s, and the collection efficiency in accordance with JIS B9908 was measured.
Collection efficiency (%) = (1−number of downstream particles / number of upstream particles) × 100
Evaluation criteria: A collection efficiency of 50% or more was evaluated as ◎, 40 to 50% as 、, and less than 40% as ×.

[Life of filter media]
Based on the method defined in JIS B9908, the life of the filter medium was measured as follows.
Using 15 kinds of powders as test powders specified in JIS Z8901, the amount of powder dust retained at a final pressure loss of 250 Pa at a dust density of 70 ± 30 mg / m ³ and a wind speed of 5.3 cm / s was measured. .
W = W ₂ −W ₁ (g / filter unit)
W: Dust retention amount W1: Filter unit weight at start of test (g)
W2: Filter unit weight at the end of the test (g)
Evaluation criteria: The life of the filter medium for the air filter of Conventional Example 1 measured based on the above method is set to 100, the filter medium whose life is twice as long as that of the filter medium of Conventional Example 1 is given as ◎, and A circle indicates that the filter medium has a lifetime of less than twice.

[Existence of dust on the outflow side]
Using the filter medium subjected to the life test, it was evaluated whether dust adhered to each filter medium on the outflow side. In the case where dust is adhered, the mark is “Yes” (Yes), and in the case where dust is not adhered, the mark is “No”.

[Comprehensive evaluation]
When the collection efficiency and life were all ○ or ◎, ◎, when the collection efficiency was x and the filter media life was ○, it was marked as ◯, and when the filter media life was x, it was marked as x.

The results shown in Table 1 revealed the following.
It was confirmed that the filter media for the air filters of Examples 1 to 4 have a filter media life of two or more times longer than that of the commercially available filter media of Conventional Example 1. Furthermore, it was confirmed that Examples 1, 2, and 4 had good collection efficiency. The filter material for an air filter of Examples 1 to 4 has a void portion in which foamable particles are foamed, and the surrounding fiber surface and / or the intersection is bonded with a fragment obtained by rupturing the foamable particles. The part becomes a passage and air easily passes in the thickness direction of the filter medium, and the fine mesh structure of short glass fibers having an average fiber diameter of 4 to 8 μm , which is the main component of the sheet constituting the filter medium, makes the thickness direction of the filter medium It was confirmed that the filter media life was prolonged because the dust was collected almost uniformly throughout. Moreover, when the fine glass short fiber with an average fiber diameter of less than 2 micrometers is mix | blended like Examples 1, 2, and 4, this fine glass short fiber is formed with the short glass fiber with an average fiber diameter of 4-8 micrometers. It was confirmed that the finer mesh structure was dispersed by the relatively fine mesh structure formed, and the efficiency of collecting dust was increased throughout the thickness direction of the filter medium, and the life of the filter medium was further prolonged.
In addition, as in Example 3, when no short glass fibers having an average fiber diameter of less than 2 μm are blended, the filter medium life is twice as long as that of the filter medium of Conventional Example 1, but the fibers and fibers constituting the filter medium Since the gap became larger, the dust collection efficiency was lower than in Examples 1, 2, and 4.
Further, as in Comparative Example 1, the filter medium containing no foamable particles does not form voids due to foaming of the foamable particles, so that no air passage is secured in the thickness direction of the filter medium, and the filter medium life is shortened. Similar to Conventional Example 1, it was shortened. In addition, since the filter medium of Comparative Example 1 had no dust adhering to the air outflow side, voids due to foaming of the foamable particles were not formed. It was speculated that dust was collected on the filter medium on the inflow side.
In addition, as in Comparative Example 2, the filter medium containing the foamable particles exceeding 10% by mass forms many voids due to foaming of the foamable particles, so that although apparent dust collection efficiency is increased, The part of the filter medium per unit volume, which is the part that collects water, is reduced, and dust is collected in this small part of the filter medium, so that the pressure loss increases and the life of the filter medium is shortened as in the conventional example 1. It was.
Moreover, even if it was a case where the basis weight of a commercially available filter medium was made the same as in Examples 1 to 4 as in Conventional Example 2, the filter medium did not prolong its life as in Examples 1 to 4.

The present invention, through the thickness direction of the filter medium, evenly collect dust in a relatively fine mesh structure, the filter media and long life, provides a filter medium and method of manufacturing the same, and an air filter air filter It has industrial applicability in that it can.

(A) a sheet before foaming expandable particles to be a filter medium for an air filter of the present invention, (b) a sheet in a state where foamable particles are foamed, and (c) a sheet in a state where foamable particles are ruptured. Conceptual diagram showing The conceptual diagram which shows the state which allowed air to pass through the filter medium for air filters of this invention The conceptual diagram which shows the state which allowed air to pass through the filter medium of a prior art example The conceptual diagram which shows the state which allowed air to pass through the filter medium which has a space | gap part in the sheet | seat of a prior art example.

1 Sheet as filter medium for air filter 2 Core-sheath type synthetic fiber as adhesive synthetic fiber 3 Short C glass fiber with average fiber diameter of 4 μm 3 Short C glass fiber with average fiber diameter of 0.8 μm 4 Unexpanded thermal expansibility Microcapsule 5 Microcapsule foamed by thermal expansion 6 Void part 7 Broken microcapsule piece 8 Dust 9 Glass fiber 10 Filter medium 11 Synthetic fiber with large average fiber diameter 12 Glass short fiber with small average fiber diameter 13 Void part 14 Outer wall 15 Filter medium 16 Glass fiber with slightly larger average fiber diameter

Claims (3)

A filter medium for an air filter comprising a sheet in which voids are formed by adhering surrounding fibers with fragments obtained by rupturing expandable particles, wherein the sheet is 70 to 90% by mass of short glass fibers having an average fiber diameter of 4 to 8 μm. And 0 to 15% by mass of short glass fibers having an average fiber diameter of less than 2 μm, 5 to 15% by mass of adhesive synthetic fibers having an average fiber diameter of 10 to 35 μm, and 3 to 10% by mass of foam particles. Characteristic air filter media . And 70 to 90 wt% short glass fibers having an average fiber diameter of 4-8 [mu] m, and 0 to 15 wt% short glass fibers less than the average fiber diameter 2 [mu] m, and 5 to 15 wt% adhesive synthetic fibers having an average fiber diameter of 10~35μm After making a sheet using an aqueous dispersion in which 3 to 10% by mass of unfoamed expandable particles having an average particle diameter of 3 to 20 μm are dispersed, the foamable particles are foamed to form voids. A method for producing a filter material for an air filter , characterized in that surrounding fibers are bonded to each other by a fragment obtained by rupturing the foamable particles to form a sheet. Air filter characterized by using the air filter media of claim 1.

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