JP2021112694A - Filter medium for air filter, and air filter unit using the same - Google Patents

Abstract

To provide a filter medium for air filter extremely superior in deodorizing speed and excellent in adsorption capacity under the kinetic condition in which air is circulated like an air filter.SOLUTION: A filter medium for air filter of this invention includes a layer including a granular gas adsorbent having an average particle diameter of 250 μm or less between two nonwoven fabric sheets. In the filter medium, a ratio of the average particle diameter of the granular gas adsorbent to the thickness of a layer including the granular gas adsorbent is 0.85 or more, and a pressure drop of the layer including the granular gas adsorbent at an air velocity of 6.5 m/min is 4.0 Pa or more.SELECTED DRAWING: None

Description

The present invention relates to a filter medium for an air filter and an air filter unit using the same.

In recent years, attention has been paid to indoor air chambers because the effects of VOCs (volatile organic compounds), tobacco smoke, air pollution, etc. emitted from building materials and interior materials on human health are serious. Gathering. At home and at work, a method of removing dust and odor by using an air purifier equipped with an air filter is widespread.

As a filter medium used for a dust-removing air filter having deodorizing performance, activated carbon and a heat-bonding powder or a heat-bonding sheet are sandwiched between two base sheets, and the two bases are fused by the heat-bonding component. Deodorizing filter media that integrates an agent sheet and activated carbon are widely used. (Patent Documents 1 and 2)
Further, for the purpose of improving the deodorizing performance, a deodorizing filter medium in which powdered activated carbon is adhered to a porous base material such as a non-woven fabric to increase the adsorption rate has been proposed. (Patent Document 3)

JP-A-2019-69405 Japanese Unexamined Patent Publication No. 2006-192333 Japanese Unexamined Patent Publication No. 2014-113214

Since the deodorizing filter medium for an air filter disclosed in Patent Documents 1 and 2 has a structure in which granular activated carbon is sealed between two non-woven fabrics, deodorizing performance such as deodorizing treatment speed (initial removal efficiency) and adsorption capacity can be obtained. In order to improve it, it is necessary to increase the amount of granular activated carbon enclosed. However, when the encapsulation amount of the granular activated carbon is increased, the granular activated carbon is compressed into two non-woven fabrics in a state of being overlapped in the filter medium thickness direction, so that the density of the granular activated carbon in the layer between the two non-woven fabrics increases. Therefore, the pressure loss of the deodorizing filter medium is not limited to the linear increase in proportion to the amount of granular activated carbon, but also has a secondary functional pressure loss increase behavior, and the pressure loss becomes very large.

Further, Patent Document 3 discloses a technique of adsorbing a powdery adsorbent on a base material sheet. In this technique, a fine powdery adsorbent is supported on the fiber surface to improve the contact efficiency with the target gas and improve the deodorizing treatment speed (initial removal efficiency). However, in reality, when the powdery adsorbent is fixed to the fiber surface with the binder, the adsorbent is coated on the binder, so that the deodorizing effect is less likely to be exhibited. Further, since the pressure loss tends to increase by adhering to the fiber surface in the form of a film, many adsorbents cannot be adhered, and as a result, the life of the deodorizing performance cannot be extended.

The present invention has been made in the background of the above problems, and the adsorption processing speed (initial removal efficiency) of the target gas component does not increase significantly under dynamic conditions such as an air filter in which air is flowing. ), And also provides a filter medium for an air filter having an excellent adsorption capacity.

The filter medium for an air filter of the present invention that solves the above problems is a filter medium for an air filter having a layer containing a granular gas adsorbent between two non-woven fabric sheets.
The average particle size of the granular gas adsorbent is 250 μm or less.
The ratio of the average particle size of the granular gas adsorbent to the thickness of the layer containing the granular gas adsorbent (average particle size of the granular gas adsorbent / thickness of the layer containing the granular gas adsorbent) is 0.85 or more. ,
The pressure loss of the layer containing the granular gas adsorbent is 4.0 Pa or more at a wind speed of 6.5 m / min.

The filter medium for an air filter of the present invention preferably has any of the following features (1) to (7).
(1) The ratio of the average particle size of the granular gas adsorbent to the thickness of the layer of the granular gas adsorbent (average particle size of the granular gas adsorbent / thickness of the layer containing the granular gas adsorbent) is 1.35 or less. Is.
(2) The compressibility of each of the two non-woven fabric sheets is 20% or less.
(3) The total thickness of the filter medium for the air filter is 0.90 mm or less.
(4) The amount of the granular gas adsorbent is in the range of ^{40 to 120 g / m 2.}
(5) The granular gas adsorbent contains granular activated carbon having a ^{specific surface area of 1100 m 2 / g or more.}
(6) The average pore diameters of the two non-woven fabric sheets are in the range of 20 μm to 200 μm, respectively.
(7) At least one of the above two non-woven fabric sheets is an electret non-woven fabric.

The air filter unit of the present invention is an air filter unit using the filter medium for the air filter of the present invention.

According to the present invention, it is possible to provide a filter medium for an air filter having an excellent deodorizing treatment speed and an excellent adsorption capacity under dynamic conditions such as an air filter in which air is flowing.

The filter medium for an air filter of the present invention has a layer containing a granular gas adsorbent (hereinafter referred to as a granular gas adsorbent layer) between two non-woven fabric sheets, and the granular gas adsorbent layer is a layer. The granular gas adsorbent is a single layer that is densely arranged.

The granular gas adsorbent contained in the granular gas adsorbent layer has an average particle size of 250 μm or less. Generally, a deodorizing filter medium for an air filter has a structure in which granular activated carbon having an appropriately designed particle size and amount is sealed between two non-woven fabric sheets. By increasing the amount of granular activated carbon enclosed, deodorizing performance such as deodorizing treatment speed (initial removal efficiency) and adsorption capacity is improved. On the other hand, if the encapsulation amount is too large, the activated carbon particles are compressed by two non-woven fabric sheets in a state of being overlapped in the thickness direction, resulting in a structure in which the activated carbon particles are excessively filled, which makes it very difficult for air to pass through. The pressure loss of the deodorizing filter medium generally increases in a linear function in proportion to the amount of activated carbon enclosed, but as described above, when the activated carbon particles are overlapped and densely packed, the pressure loss becomes a quadratic function. Pressure loss rises. Therefore, as a result of studies to improve the deodorizing performance without significantly increasing the pressure loss, the granular gas adsorbents were densely arranged in a single layer, and the average particle size of the granular gas adsorbents was reduced to 250 μm or less. , It was found that the contact efficiency between the granular gas adsorbent and the target treatment gas is improved, and the deodorizing performance can be improved. When the average particle size of the granular gas adsorbent exceeds 250 μm, even if the granular gas adsorbents are densely arranged in a single layer on the non-woven fabric, a gap through which the granular gas adsorbent cannot enter is likely to be formed. The contact efficiency with the granular gas adsorbent decreases, and the deodorizing treatment rate (initial removal efficiency) of the target gas tends to decrease. On the contrary, the smaller the average particle size of the granular gas adsorbent, the more difficult it is to form a gap, so that the contact efficiency between the granular gas adsorbent and the target gas increases, and the deodorizing treatment speed (initial removal efficiency) increases. However, if the average particle size of the granular gas adsorbent is too small and becomes smaller than the pore size of the non-woven fabric, the granular gas adsorbent tends to fall off from the filter medium for the air filter. Therefore, the average particle size of the granular gas adsorbent is preferably 50 μm or more.

The average particle size of the granular gas adsorbent in the present application corresponds to the size of a sieve through which 50% by mass of the total mass of the granular gas adsorbent is measured by measuring the particle size distribution by JIS-Z-8815 (1994). The particle size.

In the filter medium for an air filter of the present invention, the ratio of the average particle size (μm) of the granular gas adsorbent to the thickness (μm) of the granular gas adsorbent layer (average particle size of the gas adsorbent / layer containing the granular gas adsorbent). Thickness) is 0.85 or more. In the filter medium for an air filter of the present invention, it is important that the granular gas adsorbents are densely arranged in a single layer, and the above ratio of 0.85 or more is the average particle size and granularity of the granular gas adsorbent. This means that the thickness values of the gas adsorbent layers are close to each other, indicating that the granular gas adsorbents are densely arranged in a single layer without overlapping. If the ratio of the average particle size of the granular gas adsorbent to the thickness of the granular gas adsorbent layer is less than 0.85, the granular gas adsorbent is in a state of forming multiple layers instead of a single layer, as described above. The pressure loss increases quadratically.

On the other hand, the upper limit of the ratio of the average particle size of the granular gas adsorbent to the thickness of the granular gas adsorbent layer is preferably 1.35 or less. When the above ratio is larger than 1.35, it means that the thickness of the granular gas adsorbent layer is smaller than the average particle size of the granular gas adsorbent, and the granular gas adsorbents are not closely arranged and 2 It shows that there is a part where the non-woven fabric sheets are in direct contact with each other. Therefore, since the target gas passes through the two non-woven fabric sheets without coming into contact with the granular gas adsorbent, the deodorizing treatment speed (initial removal efficiency) tends to decrease.

The thickness of the granular gas adsorbent layer in the present application is a value calculated by subtracting the thickness of the two non-woven fabric sheets from the thickness of the filter medium for the air filter.

In the filter medium for an air filter of the present invention, the pressure loss of the granular gas adsorbent layer at a wind speed of 6.5 m / min is 4.0 Pa or more. If the granular gas adsorbents are densely arranged in a single layer in the granular gas adsorbent layer, the pressure loss naturally increases to some extent. Therefore, the pressure loss of the granular gas adsorbent layer at a wind speed of 6.5 m / min is 4. When it is 0.0 Pa or more, it means that the granular gas adsorbent is densely arranged between two non-woven sheets in a single layer. The pressure loss of the granular gas adsorbent layer at a wind speed of 6.5 m / min is the pressure of the two non-woven fabric sheets at a wind speed of 6.5 m / min from the pressure loss of the entire air filter filter medium at a wind speed of 6.5 m / min. It is a value calculated by subtracting the loss.

Specific examples of the granular gas adsorbent include activated carbon, silicon dioxide, zeolite, silica gel, activated alumina, activated clay, aluminum silicate, magnesium silicate, ion exchange resin, porous clay minerals, and chemicals described below for these particles. Can be mentioned, such as those attached with. Then, these granular gas adsorbents may be used alone or in combination. Further, it is preferable that these particles are porous bodies because they have better deodorizing performance. Of these, activated carbon is preferable because it has excellent physical adsorption ability and can remove gas over a wide range.

As a raw material for granular activated carbon, coconut shells, wood-based, coal-based, pitch-based and the like are known, but coconut shells are preferable. The pores of coconut shell activated carbon have a large proportion of small pores as compared with other raw materials, and the ash content, which is an impurity, is also small. That is, since the coconut shell activated carbon has small pores, an intermolecular force with the pore wall effectively acts on the adsorbed odor molecules, and it is difficult to desorb the adsorbed odor molecules, that is, secondary odor is generated. There is a feature that can suppress. Moreover, since it has a higher hardness than other raw materials, it can be supported between non-woven fabric sheets without being crushed.

The BET specific surface area of the granular activated carbon by the 77K nitrogen adsorption method ^{is preferably 1100 m 2} / g or more, and more preferably 1200 m ² / g or more in terms of BET specific surface area. By setting the specific surface area of the granular activated carbon to 1100 m ² / g or more, the effective area as a reaction field with the target gas is improved, so that the reaction rate with the target gas is further improved, and the granular gas adsorption of the present invention is performed. The dynamic adsorption performance of the agent is excellent. The upper limit of the BET specific surface area is not particularly limited, but ^{is preferably 3000 m 2} / g or less. This is because if it exceeds this range, there is an inconvenience that manufacturing becomes difficult, and the handleability is lowered due to a decrease in mechanical strength.

The average pore size of the granular activated carbon is specifically determined by using the adsorption-side isotherm obtained by the nitrogen adsorption method at 77 Kelvin (liquid nitrogen temperature), and the preferred average pore size range of the granular activated carbon is 1.0 to 5. It is 0 nm, more preferably 1.5 to 4.0 nm. When the average pore diameter is 1.0 nm or more, the target gas easily permeates into the pores of the granular activated carbon, and the dynamic adsorption performance of the granular gas adsorbent becomes more excellent. On the other hand, when the average pore diameter of the activated carbon is 5.0 nm or less, secondary odor (re-release of accumulated gas), which is a contradictory matter of the physical adsorption mechanism, can be suppressed.

Next, the hardness of the granular activated carbon according to JISK1474 is preferably 95% or more. When the hardness is 95% or more, it can be sandwiched between two non-woven fabrics and can maintain the conventional particle size without being crushed even when a strong pressure for fixing is applied.

As one form of the granular gas adsorbent, a chemical such as granular activated carbon or silicon dioxide particles may be impregnated. Hereinafter, the drug will be described.

Gases that are difficult to remove by physical adsorption to a granular gas adsorbent can be chemically removed by supporting the drug on a porous body such as activated carbon or silicon dioxide. As the drug, for example, when the purpose is to remove aldehyde gas, an amine compound is preferable, among which a primary amine compound having an amino group is preferable, and an acid hydrazide compound is more preferable.

Examples of the acid hydrazide compound include form hydrazide, acetohydrazide, propionate hydrazide, benzoate hydrazide island, acid monohydrazide having one acid hydrazide group in the molecule, dihydrazide oxalate, dihydrazide malonate, dihydrazide succinate, and adipine. Acid hydrazide having two acid hydrazide groups in the molecule, such as acid dihydrazide, fumaric acid dihydrazide, maleic acid dihydrazide, terephthalic acid dihydrazide, etc., and polyacrylic acid hydrazide, etc., having three or more acid hydrazide groups in the molecule. Acid polyhydrazide can be mentioned. Of these, dihydrazides are preferable, and adipic acid dihydrazide is particularly preferable in terms of adsorption performance of aldehydes.

_{The acid hydrazide compound is a compound having an acid hydrazide group represented by -CO-NHNH 2} derived from a carboxylic acid and hydrazine, and a nitrogen atom having an unshared electron pair is further bonded to the α position at the hydrazide terminal. As a result, the nucleophilic reactivity is significantly improved. It is considered that this unshared electron pair nucleophilically attacks the carbonyl carbon atom of the aldehydes and reacts to immobilize the aldehydes as a hydrazine derivative, whereby the adsorption performance of the aldehydes can be exhibited. Among the aldehydes, acetaldehyde has an electron-donating alkyl group at the α-position of the carbonyl carbon, so that the electrophilicity of the carbonyl carbon is low and it is difficult to be chemically adsorbed. However, the acid hydrazide compound has a nucleophilic reactivity as described above. Due to its high value, it exhibits good chemical adsorption performance even for acetaldehyde.

The amount of the acid hydrazide compound supported is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass with respect to 100 parts by mass of the granular gas adsorbent. When the supported amount is 1 part by mass or more, the removal efficiency of aldehydes and the effective adsorption capacity can be obtained. When the supported amount is 50 parts by mass or less, it is possible to suppress the crystallization of the acid hydrazide compound on the granular gas adsorbent and suppress the decrease in the gas adsorption rate of the granular gas adsorbent. Further, it is possible to suppress the dropping of the drug from the granular gas adsorbent.

Further, when the purpose is to remove acidic gases other than the above aldehydes, metal carbonates, specifically alkali metal carbonates such as potassium carbonate, potassium hydrogencarbonate, sodium carbonate and sodium hydrogencarbonate are preferably used. .. Acidic compounds are suitable for the purpose of removing basic gas, and phosphoric acid, sulfuric acid, nitric acid, malic acid, ascorbic acid and the like are preferably used as examples.

The amount of the metal carbonate supported is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the granular gas adsorbent. When the amount supported is 1 part by mass or more, the efficiency of removing acid gas by the granular gas adsorbent and the adsorption capacity become more excellent. When the amount supported is 20 parts by mass or less, the pores of the granular gas adsorbent are not blocked by the metal carbonate, so that a decrease in the adsorption rate can be suppressed. Further, it is possible to suppress the dropping of the drug from the granular gas adsorbent.

The amount of the acidic compound supported is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the granular gas adsorbent. When the supported amount is 1 part by mass or more, the efficiency of removing the basic gas by the granular gas adsorbent and the adsorbing capacity become more excellent. When the amount supported is 20 parts by mass or less, the pores of the granular gas adsorbent are not blocked by the acidic compound, so that a decrease in the adsorption rate can be suppressed. Further, it is possible to suppress the dropping of the drug from the granular gas adsorbent.

Next, a method for manufacturing the filter medium for an air filter of the present invention will be described. In the filter medium for an air filter, a granular gas adsorbent and a thermoplastic resin (binder) are arranged between two non-woven fabric sheets, and the two non-woven fabric sheets and granules are formed by the thermoplastic resin (binder) melted by heat treatment. It is obtained by integrating with a gas adsorbent by thermal adhesion. First, the granular gas adsorbent and the thermoplastic resin (binder) that have been sufficiently mixed and stirred are sprayed on one of the non-woven fabric sheets and heat-treated to melt the thermoplastic resin (binder). As a heating method, a heating furnace or the like can be used. Next, the other non-woven fabric sheet is put on the heat-treated granular gas adsorbent and the thermoplastic resin (binder), and the two non-woven fabric sheets are pressurized to be integrated.

Specific examples of the pressurizing method include a heat pressing method between rolls, a flat bed laminating method in which the heat belt conveyors are flat on both the top and bottom, and the like.

As the material of the thermoplastic resin (binder), a thermoplastic resin such as polyester, polyolefin, polyamide, polyurethane, ethylene-acrylic copolymer, polyacrylate, polyacrylic, polydiene, ethylene-vinyl acetate, polyvinyl chloride, polystyrene, etc. ( Binder), and among them, polyester and polyolefin are preferable as materials that generate less odor during heating.

The shape of the thermoplastic resin (binder) is not particularly specified as long as it is in the form of powder, but examples thereof include spherical, crushed, and fibrous forms.

The content of the thermoplastic resin (binder) is preferably 10 to 40 parts by mass with respect to 100 parts by mass of the granular gas adsorbent. Within this range, the adhesive force with the non-woven fabric is further improved, and the ventilation resistance and deodorizing performance of the filter medium for the air filter are further improved. The content is more preferably 15 to 35 parts by mass.

As the fibers forming the non-woven sheet, natural fibers, synthetic fibers, inorganic fibers such as glass fibers and metal fibers can be used, and among them, synthetic fibers of thermoplastic resin capable of melt spinning are preferable. Examples of the thermoplastic resin forming the synthetic fiber include polyester, polyamide, polyolefin, acrylic, vinylon, polystyrene, polyvinyl chloride, polyvinylidene chloride, polylactic acid, and the like, which can be selected according to the intended use. Further, a plurality of types may be used in combination.

As a method for producing the non-woven fabric sheet, a dry method, a wet method, a spunbond method, a thermal bond method, a chemical bond method, a spunlace method (water flow entanglement method), a spunbonded non-woven fabric, and a melt-blown non-woven fabric can be used. Of the two non-woven fabric sheets, at least one non-woven fabric sheet is preferably a wet non-woven fabric produced by a papermaking method, which can have a uniform basis weight and a uniform thickness and can arrange granular gas adsorbents precisely.

The fiber diameter of the fibers constituting the non-woven fabric sheet may be selected according to the target air permeability and dust collection performance in the application used as a filter medium for an air filter, but is preferably 1 to 2000 μm. When the fiber diameter is 1 μm or more, it is possible to prevent the gas adsorbent from clogging the surface of the fiber structure and prevent the air permeability from being lowered. More preferably, it is 2 μm or more. Further, when the fiber diameter is 2000 μm or less, it is possible to prevent a decrease in the carrying capacity of the granular gas adsorbent due to a decrease in the fiber surface area. More preferably, it is 100 μm or less.

The basis weight of the non-woven fabric sheet is preferably ^{10 to 200 g / m 2.} When the basis weight is 10 g / m ² or more, sufficient strength is obtained to withstand the processing for supporting the granular gas adsorbent, and the rigidity required to maintain the filter structure when air is aerated is obtained. .. When the basis weight is 200 g / m ² or less, it is possible to have high air permeability, and it is also excellent in handleability when the filter medium for an air filter is secondarily processed into a pleated shape or a honeycomb shape. More preferably, it is 150 g / m ² or less.

The thickness of the non-woven fabric sheet is preferably 0.10 mm to 0.60 mm. When the thickness is 0.10 mm or more, the non-woven fabric sheet is not torn and the granular gas adsorbent particles do not pop out. When the thickness is 0.60 mm or less, in addition to being easy to handle, the pressure loss does not increase due to the structure when the filter unit is used.

The compressibility of the non-woven fabric sheet is preferably 20% or less. When the compression rate is 20% or less, when the granular gas adsorbent is sprayed between two non-woven fabric sheets and pressure is applied for integration, the granular gas adsorbent is densely arranged in a single layer. Layer does not collapse. If the layer of the granular gas adsorbent collapses, the granular gas adsorbent is dispersed in the thickness direction, and there is a concern that the contact efficiency with the target gas is lowered and the initial deodorizing efficiency is lowered.

The average pore size of the non-woven fabric sheet is preferably 20 to 200 μm, more preferably 30 to 180 μm. When the average pore size of the non-woven fabric sheet is 20 μm or more, high air permeability can be ensured as a filter medium for an air filter. When the average pore size is 200 μm or less, the granular gas adsorbent can be suppressed from falling off from the non-woven fabric. When used as an air filter, the average pore size of the non-woven fabric sheet placed on the upstream side is increased, and the average pore size of the non-woven fabric sheet placed on the downstream side is reduced to prevent dust and dirt from clogging the filter. The increase in pressure loss can be suppressed.

The average pore diameter in the present application is a value calculated by the bubble point method (based on ASTMF-316-86). As the bubble point method, for example, "Perm-Porometer, a porous material automatic pore measurement system" (manufactured by PMI) can be used. The measurement by this Perm-Porometer is a method in which the non-woven fabric sheet is immersed in a liquid and supplied while increasing the gas pressure from the upper side of the non-woven fabric sheet, and the pore size is measured from the relationship between this pressure and the liquid surface tension on the surface of the non-woven fabric sheet. be.

Further, it is preferable that the two non-woven fabric sheets have different fiber configurations. For example, in use as a direct flow type filter, if a bulky and coarse non-woven fabric sheet is used on the upstream side, the amount of dust retained can be improved and the life of the filter can be extended. Further, if a non-woven fabric sheet made of ultrafine fibers is laminated on the downstream side, the collection efficiency can be increased.

It is preferable that at least one non-woven fabric sheet is electret-treated. Due to the electret treatment, submicron size and nano size fine dust, which is normally difficult to remove, can be collected by electrostatic force.

Materials constituting the electlet-treated non-woven sheet (electlet non-woven sheet) include polypropylene-based resins such as polypropylene, polyethylene, polystyrene, polybutylene terephthalate, and polytetrafluoroethylene, and aromatic polyester-based resins such as polyethylene terephthalate. A material having a high electrical resistance such as a polycarbonate resin is preferable.

The non-woven fabric sheet may be composed of components having ancillary functions such as an antibacterial agent, an antifungal agent, an antiallergen agent, an antiviral agent, a vitamin agent, and a flame retardant. These components may be kneaded into fibers or a non-woven fabric sheet, or may be attached and supported by post-processing. For example, a non-woven fabric sheet is obtained by preparing a non-woven fabric sheet by an arbitrary method, preparing an aqueous solution containing a flame retardant and a resin binder, impregnating and drying the non-woven fabric sheet, and fixing the flame retardant.

The amount of the granular gas adsorbent is preferably in the range of ^{40 to 120 g / m 2.} Within this range, when the filter unit obtained from the filter medium is mounted on an air purifier, etc., the contact efficiency with the target gas component increases and the deodorization processing speed (initial removal efficiency) increases, so the odor of the space is improved. The effect is noticeable.

The total thickness of the air filter filter medium is preferably 0.40 to 0.90 mm. When the thickness is within this range, it has strength against bending and can increase the area that can be accommodated in a certain volume when pleated.

The air filter unit of the present invention is configured by using the filter medium for the air filter of the present invention. As the shape of the filter medium for the air filter in the air filter unit, it may be used as it is in a flat shape, but a pleated type or a honeycomb type is adopted in order to put more filter media for the air filter within the limited dimensions. Is preferable. When the pleated type is used as a direct flow type air filter and the honeycomb type is used as a parallel flow type filter, the contact area of the treated air is increased to improve the collection efficiency and reduce the low voltage at the same time. Can be done.

The pleating method includes a reciprocating method and a rotary method, and any method may be used as long as it is processed in a mountain valley shape. Further, it is also preferable to perform separator processing in order to maintain the pleated shape, and from the viewpoint of production efficiency, a method of melting a thermoplastic resin such as bead processing or ribbon processing is desirable.

The distance between the pleats of the air filter unit using the filter medium for the air filter of the present invention is preferably 2 to 30 mm. When the distance between the fold peaks is 2 mm or more, the folds do not come into close contact with each other, the dead space is reduced, and the filter medium for the air filter can be used efficiently. When the distance between the fold peaks is 30 mm or less, the folding area of the filter medium for the air filter is sufficient, and the desired removal effect can be obtained.

Further, it is preferable that the air filter of the present invention is used by being housed in a frame from the viewpoint of air processing efficiency and handleability.

Hereinafter, the present invention will be specifically described with reference to Examples. The evaluation method of each characteristic of the filter medium in this example is described below.

[Measuring method]
(1) Average particle size (μm)
The average particle size of the granular gas adsorbent is measured by JIS-Z-8815 (1994), and the particle size corresponds to the size of the sieve through which 50% by mass of the total mass of the granular gas adsorbent passes. And said.

(2) Metsuke (g / m ² )
The basis weight of the non-woven fabric and the filter medium for the air filter was measured as follows. The mass of the measurement sample cut into 25 cm × 25 cm was measured for four sheets using a mass meter (FY-300 manufactured by A & D Co., Ltd.), and the average value was calculated. The average value ^{was converted into mass per 1 m 2} , and the second decimal place was rounded off to obtain a basis weight.

(3) Thickness (mm)
The thickness of the non-woven fabric and the filter medium for the air filter was measured as follows. A measurement sample cut into 10 cm x 10 cm was randomly measured at 10 points using a thickness gauge (manufactured by Daiei Kagaku Seiki Co., Ltd., model FS-60DS, stylus area 2500 mm ² , measurement load 0.5 KPa), and the average value was measured. Calculated and used as the thickness. The thickness of the granular gas adsorbent layer was calculated by subtracting the thickness of the two non-woven fabrics from the thickness of the filter medium for the air filter.

(4) Compressibility The compressibility of the non-woven fabric was measured as follows using a compressive elasticity tester. A test piece of about 5 cm x 5 cm was collected, the thickness (T ₀ ) was measured under a load of 0.5 KPa, and then the thickness (T ₁ ) was measured under a load of 5.0 KPa, and the results were calculated as follows. The compression ratio was calculated by applying it to the formula.
Compressibility% = (T _0- T ₁ ) / T ₀ x 100.

(5) Specific Surface Area of BET The specific surface area of the granular gas adsorbent was measured using NOVA2200e manufactured by Yuasa Ionics Co., Ltd. according to the BET multipoint method specified in JIS R 1626-1996. As a sample, 100 mg was sampled and evacuated at 100 ° C. for 4 hours, N ₂ was used as an adsorbent, and the sample was measured by a constant volume method.

(6) Average Pore Diameter The average pore diameter (D) from the specific surface area (S) and pore volume (V) obtained during the BET specific surface area measurement, assuming that the shape of the pores of the granular gas adsorbent is cylindrical. ) Was calculated.

(7) Content of impregnating agent The weight after impregnating the liquid in which the agent is dispersed or dissolved with the granular gas adsorbent and drying the granular gas adsorbent, and the weight of the granular gas adsorbent before the impregnation treatment described above. Calculated from the difference from the weight.
(8) Average pore size (μm)
The average pore size was calculated by the bubble point method (based on ASTMF-316-86) using the "porous material automatic pore measurement system Perm-Porometer" (manufactured by PMI). The pore size distribution was measured using a measurement sample diameter of 25 mm, using Galwick for the non-woven fabric having a pore diameter of 180 μm or less as the measurement liquid, and using pure water for the non-woven fabric having a pore diameter of more than 180 μm.

The mean flow pore diammeter (MEAN FLOW PORE DIAMETER) obtained by automatic calculation by a measuring instrument under the above conditions was used as the average pore diameter. The measurement was carried out by arbitrarily sampling 5 points from one sample, and the average value was obtained.

(9) Content of granular gas adsorbent and thermoplastic resin (binder) (g / m ² )
A mixed powder obtained by mixing and stirring a granular gas adsorbent and a thermoplastic resin (binder) was sprayed on a non-woven fabric, and then another non-woven fabric was further laminated and heat-pressed to integrate them, and the total texture was measured. The content of the granular gas adsorbent and the thermoplastic resin (binder) is calculated by multiplying the value obtained by subtracting the grain of the two non-woven fabrics from this total grain by the charge amount ratio of the granular gas adsorbent and the thermoplastic resin (binder). Calculated.

(10) Pressure loss (Pa)
A flat filter medium for an air filter ^{is set in a holder with an effective frontage area of 0.1 m 2} , and air is passed vertically from the upstream non-woven fabric to the downstream non-woven fabric at a surface wind speed of 6.5 m / min on the filter. The downstream pressure difference was measured with a MODUS digital manometer MA2-04P differential pressure gauge. The measurement was performed by arbitrarily sampling 5 points from one sample, and the average value was taken as the pressure loss of the filter medium for the air filter. The pressure loss of the granular gas adsorbent layer was calculated by subtracting the pressure loss of the two non-woven fabric sheets at a wind speed of 6.5 m / min from the pressure loss of the entire air filter filter medium at a wind speed of 6.5 m / min. .. The pressure loss of the two non-woven fabric sheets was arbitrarily sampled from one sample at five locations, and the average value was used.

(11) Dynamic adsorption performance (toluene)
The initial removal efficiency and adsorption capacity of toluene were measured as follows. A flat plate-shaped filter medium for an air filter was attached to an experimental column, and air having a temperature of 23 ° C. and a humidity of 50% RH was blown from the upstream non-woven fabric to the downstream non-woven fabric at a speed of 0.2 m / sec. Further, from the upstream side, toluene is volatilized by a permeator and added so that the upstream concentration becomes 80 ppm, air is sampled on the upstream side and the downstream side of the filter medium for the air filter, and each is used by an infrared absorption type continuous monitor. Toluene concentration was measured over time, and the removal efficiency was calculated by the following formula.
-Toluene removal efficiency (%) = [(C _0- C) / C ₀ ] x 100
C ₀ : Concentration on the upstream side (= 80 ppm)
C: Toluene concentration on the downstream side (ppm)
The removal efficiency 2 minutes after the start of toluene addition was defined as the initial removal efficiency. Furthermore, the removal efficiency after 2 minutes was measured over time. The adsorption amount is calculated from the upstream concentration (= 80 ppm) and the removal efficiency at each measurement time after 2 minutes, and the adsorption amount until the difference between the upstream concentration and the downstream concentration becomes 5%. It was integrated and used as the adsorption capacity.

(12) Dynamic adsorption performance (acetaldehyde)
The initial removal efficiency and adsorption capacity of acetaldehyde were measured as follows. A 12 cm square flat air filter filter medium is attached to a 10 cm square experimental duct, and air with a temperature of 23 ° C and a humidity of 50% RH is blown into the duct 0.2 m from the upstream non-woven fabric to the downstream non-woven fabric. Blow at a speed of / sec. Further, from the upstream side, acetaldehyde is added to an upstream concentration of 10 ppm using a standard gas cylinder, air is sampled on the upstream side and the downstream side of the filter medium for an air filter, and each acetaldehyde is sampled using an infrared absorption type continuous monitor. The concentration was measured over time, and the removal efficiency was calculated by the following formula.
-Acetaldehyde removal efficiency (%) = [(C _0- C) / C ₀ ] x 100
C ₀ : Acetaldehyde concentration on the upstream side (= 10 ppm)
C: Downstream acetaldehyde concentration (ppm)
The removal efficiency 100 seconds after the start of addition of acetaldehyde was defined as the initial removal efficiency. Further, the removal efficiency after 100 seconds was measured over time. The adsorption amount is calculated from the upstream concentration (= 10 ppm) and the removal efficiency at each measurement time after 100 seconds, and the adsorption amount until the difference between the upstream concentration and the downstream concentration becomes 5%. It was integrated and used as the adsorption capacity.

(13) Dynamic adsorption performance (ammonia)
The initial removal efficiency and adsorption capacity of ammonia were measured as follows. A 12 cm square flat air filter filter medium is attached to a 10 cm square experimental duct, and air with a temperature of 23 ° C and a humidity of 50% RH is blown into the duct 0.2 m from the upstream non-woven fabric to the downstream non-woven fabric. The air was blown at a speed of / sec. Further, from the upstream side, ammonia is added to an upstream concentration of 30 ppm using a standard gas cylinder, air is sampled on the upstream side and the downstream side of the filter medium for an air filter, and each ammonia is sampled using an infrared absorption type continuous monitor. The concentration was measured over time, and the removal efficiency was calculated by the following formula.
-Ammonia removal efficiency (%) = [(C _0- C) / C ₀ ] x 100
C ₀ : Ammonia concentration on the upstream side (= 30 ppm)
C: Ammonia concentration on the downstream side (ppm)
The removal efficiency 100 seconds after the start of addition of ammonia was defined as the initial removal efficiency. Further, the removal efficiency after 100 seconds was measured over time. The adsorption amount is calculated from the upstream concentration (= 30 ppm) and the removal efficiency at each measurement time after 100 seconds, and the adsorption amount until the difference between the upstream concentration and the downstream concentration becomes 5%. It was integrated and used as the adsorption capacity.

(14) Dynamic adsorption performance ((acetic acid))
A flat plate-shaped filter medium for an air filter was attached to an experimental column, and air having a temperature of 23 ° C. and a humidity of 50% RH was blown from the upstream non-woven fabric to the downstream non-woven fabric at a speed of 0.2 m / sec. Further, from the upstream side, acetic acid is volatilized by a permeator and added so as to have an upstream concentration of 80 ppm, air is sampled on the upstream side and the downstream side of the filter medium for an air filter, and an infrared absorption type continuous monitor is used for each. The acetic acid concentration was measured over time, and the removal efficiency was calculated by the following formula.
Acetate removal efficiency _{(%) = [(C 0} -C) / C0] × 100
C ₀ : Concentration on the upstream side (= 80 ppm)
C: Acetic acid concentration on the downstream side (ppm)
The removal efficiency 4 minutes after the start of acetic acid addition was defined as the initial removal efficiency. Further, the removal efficiency after 4 minutes was measured over time. The adsorption amount is calculated from the upstream concentration (= 80 ppm) and the removal efficiency at each measurement time after 4 minutes, and the adsorption amount until the difference between the upstream concentration and the downstream concentration becomes 5%. It was integrated and used as the adsorption capacity.

[Comprehensive judgment]
The evaluation as a filter medium for an air filter was judged as follows.
◎ (Very excellent): Satisfy the following criteria of “○” and satisfy the following (i) or (ii). (I) and (ii) show the ability to remove acetaldehyde and ammonia, which are polar gas components that are difficult to remove with activated carbon. (I): The initial removal efficiency of acetaldehyde is 40% or more and the adsorption capacity is 0.30 g / m ² or more (ii): Initial removal efficiency of ammonia is 50% or more and adsorption capacity is 0.50 g / m ² or more ○ (excellent): Pressure loss is less than 20 Pa,
X (inferior): The pressure loss is less than 20 Pa, the initial toluene removal efficiency is 75% or more, and the toluene adsorption capacity is 20 g / m ² or more.

[Non-woven fabric]
The non-woven fabrics used in each Example and Comparative Example were produced as follows.

(Non-woven fabric a)
A fiber aggregate having a basis weight of 35 g / m ² composed of polyester fibers and vinylon fibers was produced by a wet papermaking method. This fiber aggregate was impregnated with a dispersion of a styrene-acrylic polymer and a flame retardant (melamine phosphate) and then subjected to a dry heat treatment to prepare a non-woven fabric a having a texture of ^{50 g / m 2 and a thickness of 0.38 mm.} The produced nonwoven fabric a had an average pore diameter of 152.5 μm, a compressibility of 5.3%, and a pressure loss at a wind speed of 6.5 m / min of 1.0 Pa.

(Non-woven fabric b)
A polypropylene resin having a melting point of 163 ° C. was used as the thermoplastic resin, and a polypropylene resin composition to which a charge stabilizer was added was used as a raw material. From this polypropylene resin composition, a melt blow nonwoven fabric was produced using an apparatus including an extruder and a gear pump, a melt blow mouthpiece, a compressed air generator and an air heater, a collection conveyor, and a winder.
After adjusting the injection flow rate so that the melt blow fiber flow is tilted toward the sheet traveling direction to collect the melt blow fiber flow to form a sheet, electret processing is performed by the pure water suction method, and the grain size is 25 g / m ² , average. A non-woven fabric b having a fiber diameter of 8.2 μm and a thickness of 0.20 mm was obtained. The produced nonwoven fabric b had an average pore diameter of 85.0 μm, a compressibility of 10.0%, and a pressure loss at a wind speed of 6.5 m / min of 5.0 Pa.

(Non-woven fabric c)
A fiber aggregate having a basis weight of 40 g / m ² composed of polyester fibers and vinylon fibers was produced by a wet papermaking method. This fiber aggregate was impregnated with a dispersion of a styrene-acrylic polymer and a flame retardant (melamine phosphate) and then subjected to a dry heat treatment to prepare a non-woven fabric a having a grain size of ^{55 g / m 2 and a thickness of 0.42 mm.} The produced nonwoven fabric a had an average pore diameter of 125.5 μm, a compressibility of 7.1%, and a pressure loss at a wind speed of 6.5 m / min of 2.0 Pa.

(Non-woven fabric d)
A polypropylene resin having a melting point of 163 ° C. was used as the thermoplastic resin, and a polypropylene resin composition to which a charge stabilizer was added was used as a raw material. From this polypropylene resin composition, a melt blow nonwoven fabric was produced using an apparatus including an extruder and a gear pump, a melt blow mouthpiece, a compressed air generator and an air heater, a collection conveyor, and a winder.
After adjusting the injection flow rate so that the melt blow fiber flow is tilted toward the sheet traveling direction to collect the melt blow fiber flow to form a sheet, electret processing is performed by the pure water suction method, and the grain size is 20 g / m ² , average. A non-woven fabric d having a fiber diameter of 4.2 μm and a thickness of 0.17 mm was obtained. The produced nonwoven fabric d had an average pore diameter of 35.5 μm, a compressibility of 11.8%, and a pressure loss at a wind speed of 6.5 m / min at 8.0 Pa.

(Non-woven fabric e)
A PET spunbonded non-woven fabric with a 75 g / m ^{2 grain, a powdered activated carbon with a specific surface area of 1200 m 2} / g, a flame retardant melamine phosphate and a styrene acrylic binder with a mass ratio of 53.6: 28.6: 17.8. A non-woven fabric sheet e having a specific surface area of ^{78 g / m 2} was prepared by impregnating it in an aqueous solution uniformly dispersed in pure water and then drying it. The produced nonwoven fabric e had an average pore diameter of 125.5 μm, a compressibility of 6.8%, and a pressure loss at a wind speed of 6.5 m / min of 3.5 Pa.

The characteristics of the prepared non-woven fabric are summarized in Table 1.

[Granular gas adsorbent]
The granular gas adsorbent used in each Example and Comparative Example was prepared as follows.

[Activated carbon A]
Activated carbon A was a coconut shell activated carbon having an average particle size of 190 μm, a specific surface area of 1650 m ² / g (BET method), an average pore size of 1.8 nm, a hardness of 97.8% (JISK1474 method), and a pH of 10.2 according to the JISZ8815 method.

[Activated carbon B]
(Activated carbon)
A coconut shell activated carbon having an average particle size of 220 μm, a specific surface area of 1200 m ² / g (BET method), an average pore size of 1.7 nm, a hardness of 98.0% (JISK1474 method), and a pH of 9.8 according to the JISZ8815 method was used.
(Adhesive drug)
Phosphoric acid manufactured by Nacalai Tesque was used for adsorbing basic gas.
(Preparation of activated carbon B)
30.0 parts by mass of a phosphoric acid solution adjusted to a chemical concentration of 40% using the above phosphoric acid was sprayed onto 100.0 parts by mass of activated carbon to adhere, and then dried at 110 ° C. for 20 hours to obtain 100.0 parts of activated carbon. Activated carbon B to which 12.0 parts by mass of phosphoric acid was attached was obtained with respect to parts by mass.

[Activated carbon C]
(Activated carbon)
A coconut shell activated carbon having an average particle size of 190 μm, a specific surface area of 1200 m ² / g (BET method), an average pore size of 1.7 nm, a hardness of 98.0% (JISK1474 method), and a pH of 9.8 according to the JISZ8815 method was used.
(Adhesive drug)
Sodium hydrogen carbonate manufactured by Nacalai Tesque was used for acid gas adsorption.
(Preparation of activated carbon C)
An aqueous solution was prepared in which 8.0 parts by mass of sodium hydrogen carbonate was completely dissolved in 92.0 parts by mass of pure water. Then, 50.0 parts by mass of this aqueous solution was sprayed onto 100.0 parts by mass of the activated carbon and adhered, and then dried at 110 ° C. for 5 hours. Sodium hydrogen carbonate was added to 100.0 parts by mass of the activated carbon. Activated carbon C adhering to 0.0 parts by mass was obtained.

[Activated carbon D]
Activated carbon D was a coconut shell activated carbon having an average particle size of 170 μm, a specific surface area of 1650 m ² / g (BET method), an average pore size of 1.8 nm, a hardness of 97.8% (JISK1474 method), and a pH of 10.0 according to the JISZ8815 method.

[Activated carbon E]
Activated carbon E was a coconut shell activated carbon having an average particle size of 220 μm, a specific surface area of 1200 m ² / g (BET method), an average pore size of 1.7 nm, a hardness of 98.0% (JISK1474 method), and a pH of 9.4 according to the JISZ8815 method.

[Activated carbon F]
Activated carbon F was a coconut shell activated carbon having an average particle size of 400 μm, a specific surface area of 1100 m ² / g (BET method), an average pore size of 1.6 nm, a hardness of 97.2% (JISK1474 method), and a pH of 9.4 according to the JISZ8815 method.

[Aldehyde Adsorbent G]
(Porous silica)
Porous silica manufactured by Fuji Silysia Chemical Ltd. with an average particle size of 200 μm, a specific surface area of 480 m ² / g (BET method), and an average pore size of 12.0 nm according to the JISZ8815 method was used.
(Adhesive drug)
Adipic acid dihydrazide manufactured by Japan Finechem Company, Inc. was used.
(Preparation of aldehyde adsorbent G)
An 8.0% aqueous solution of adipic acid dihydrazide was prepared by completely dissolving 8.0 parts by mass of the above adipic acid dihydrazide in 92.0 mass "parts" of pure water. Then, 80.0 parts by mass of this aqueous solution was sprayed onto 100.0 parts by mass of the porous silica to adhere, and then dried at 110 ° C. for 4 hours. An aldehyde adsorbent G to which 6.4 parts by mass of acid dihydrazide was attached was obtained.

The characteristics of the prepared granular gas adsorbent are summarized in Table 2.

[Example 1]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Activated carbon A and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 75:30 (activated carbon A: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric a so as to have a total amount of 105 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for a filter was prepared.

[Example 2]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Granular gas adsorbent containing activated carbon A and aldehyde adsorbent G and low-density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive were used at 75:15:35 (activated carbon A: aldehyde). Weighed by the mass ratio of adsorbent G: low density polyethylene), stirred with a shaker, ^{and then uniformly sprayed on the non-woven fabric a so as to have a total amount of 125 g / m 2.} Hot melt adhesive in a drying oven at 150 ° C. A filter medium for an air filter was prepared by covering the non-woven fabric b with the non-woven fabric b in a melted state and heat-pressing.

[Example 3]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Granular gas adsorbent containing activated carbon A, activated carbon B and aldehyde adsorbent G, and low-density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999))) as a hot melt adhesive at 55:10:10: 30 (activated carbon A: activated carbon B: aldehyde adsorbent G: low-density polyethylene) was weighed, stirred with a shaker, and then uniformly sprayed ^{on the non-woven fabric a so as to have a total amount of 105 g / m 2.} In a state where the hot melt adhesive was melted in a drying oven at 150 ° C., a non-woven fabric b was placed over the melted hot melt adhesive and heat pressed to prepare a filter medium for an air filter.

[Example 4]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Activated carbon A and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 55:30 (activated carbon A: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric a so as to have a total amount of 85 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for a filter was prepared.

[Example 5]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Granular gas adsorbent containing activated carbon A and activated carbon B, and low-density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999))) as a hot melt adhesive at 80:30 (activated carbon A: activated carbon B). : Low density polyethylene) was weighed, stirred with a shaker, and then uniformly sprayed on the non-woven fabric a so as to have a total amount of 130 g / m ^{2. The} hot melt adhesive was melted in a drying oven at 150 ° C. A filter medium for an air filter was prepared by covering it with a non-woven fabric b and heat-pressing it.

[Example 6]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Granular gas adsorbent containing activated carbon A and activated carbon C, and low-density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999))) as a hot melt adhesive at 60:15:30 (activated carbon A: activated carbon C) : Low density polyethylene) was weighed, stirred with a shaker, and then uniformly sprayed on the non-woven fabric a so as to have a total amount of 105 g / m ^{2. The} hot melt adhesive was melted in a drying oven at 150 ° C. A filter medium for an air filter was prepared by covering it with a non-woven fabric b and heat-pressing it.

[Example 7]
The non-woven fabric c was used as the upstream non-woven fabric, and the non-woven fabric d was used as the downstream non-woven fabric. Activated carbon D and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 100:30 (activated carbon D: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric c so as to have a total amount of 130 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for a filter was prepared.

[Comparative Example 1]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Activated carbon E and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 150:50 (activated carbon E: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric a so as to have a total amount of 200 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for a filter was prepared.

[Comparative Example 2]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Activated carbon E and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 200:65 (activated carbon E: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric a so as to have a total amount of 265 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for use was prepared.

[Comparative Example 3]
The non-woven fabric a was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Activated carbon F and low density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) as a hot melt adhesive are weighed at a mass ratio of 55:25 (activated carbon F: low density polyethylene) and put into a shaker. After stirring, the mixture was uniformly sprayed on the non-woven fabric a so as to have a total amount of 80 g / m ^{2. With the} hot melt adhesive melted in a drying oven at 150 ° C. A filter medium for use was prepared.

[Comparative Example 4]
The non-woven fabric e was used as the upstream non-woven fabric, and the non-woven fabric b was used as the downstream non-woven fabric. Low-density polyethylene (melting point 98 ° C., MI 200 g / 10 min (JIS K7210 (1999)) ^{was uniformly sprayed on the non-woven fabric e so as to have a concentration of 7 g / m 2. The} hot melt adhesive was melted in a drying oven at 130 ° C. In this state, a non-woven fabric b was placed over the fabric and heat-pressed to prepare a filter medium for an air filter.

Tables 3 and 4 show the configurations, physical characteristics, and performance of the filter media for air filters produced in each Example and Comparative Example. The item of "average particle size of adsorbent / thickness of adsorbent layer" in Tables 3 and 4 is "average particle size of granular gas adsorbent / thickness of layer containing granular gas adsorbent".

[Evaluation of each example and comparative example]
In each of the filter media for air filters of Examples 1 to 7, the ratio of the average particle size of the granular gas adsorbent to the thickness of the granular gas adsorbent layer is 0.85 or more, and the granular gas in the granular gas adsorbent layer It was shown that the adsorbents were lined up without overlapping. Further, in each case, the pressure loss of the granular gas adsorbent layer was 4.0 Pa or more, indicating that the granular gas adsorbents were densely arranged in the granular gas adsorbent layer. On the other hand, in each of the examples, although the pressure loss of the granular gas adsorbent layer was 4.0 Pa or more, it was not excessively high, so that the pressure loss of the entire filter medium for the air filter was low at less than 20 Pa. Further, in each of the examples, since the average particle size of the granular gas adsorbent is 250 μm or less, the contact efficiency with the target gas is high, and the initial removal efficiency of toluene, which is a representative component of the organic gas, is 75% or more. The adsorption capacity was 20 g / m ² or more, which was excellent.

In addition to the above, in the filter medium for the air filter of Example 7, the average particle size of the granular gas adsorbent was as fine as 170 μm, so that the pressure loss of the granular gas adsorbent layer was slightly high at 7.0 Pa. The contact efficiency with the gas was high, the initial removal efficiency of toluene exceeded 90%, and the adsorption capacity was also excellent.

In the filter medium for an air filter of Example 2, since an aldehyde adsorbent was used in combination with activated carbon as a granular gas adsorbent, both the initial removal efficiency of acetaldehyde and the adsorption capacity were excellent.

In the filter medium for the air filter of Example 3, since activated carbon impregnated with an aldehyde adsorbent and phosphoric acid was used in combination as the granular gas adsorbent, both the initial removal efficiency of acetaldehyde and ammonia and the adsorption capacity were excellent. Was there.

In the filter medium for an air filter of Example 5, activated carbon impregnated with phosphoric acid was used in combination as a granular gas adsorbent for the purpose of removing basic gas in addition to activated carbon, so that the initial removal efficiency and adsorption capacity of ammonia were improved. Both were excellent.

In the filter medium for the air filter of Example 6, activated carbon impregnated with sodium hydrogencarbonate was used as the granular gas adsorbent in addition to activated carbon for the purpose of removing acid gas, so that the initial removal efficiency and adsorption capacity of acetic acid were improved. Both were excellent.

Air filter for medium of Comparative Example 1 and Comparative Example 2, the content of the activated carbon is particulate gas adsorbent, for each lot and ^{150g / m 2, 200g / m} 2, an initial removal efficiency and adsorption capacity of toluene together It was excellent. However, the ratios of the average particle size of the granular gas adsorbent to the thickness of the granular gas adsorbent layer were 0.79 and 0.71, respectively, and probably because the granular gas adsorbents overlapped, the granular gas adsorbent layer The pressure loss was as high as 19.0 Pa and 25.0 Pa, respectively, and the pressure loss of the filter medium for the air filter was also high.

Since the filter medium for the air filter of Comparative Example 3 uses activated carbon having a large average particle diameter of 400 μm as the granular gas adsorbent, the contact efficiency between the target gas and the granular gas adsorbent becomes low, and the gas adsorbent is contained. The amount was the same as in Example 4, but the initial removal efficiency and adsorption capacity of toluene were lower.

The filter medium for an air filter of Comparative Example 4 has a structure in which powdered activated carbon is fixed with a binder, but a large amount of activated carbon cannot be impregnated in consideration of pressure loss, and the initial removal efficiency of any gas is improved. The adsorption capacity became low.

The filter medium for an air filter and the air filter according to the present invention have a dramatically excellent deodorizing treatment speed and an excellent adsorption capacity under dynamic conditions such as an air filter in which air is flowing. It is preferably used as an air filter for purifying air in aircraft, automobiles, railroad vehicles, etc.

Claims (9)

A filter medium for an air filter having a layer containing a granular gas adsorbent between two non-woven fabric sheets.
The average particle size of the granular gas adsorbent is 250 μm or less, and the particle size is 250 μm or less.
The ratio of the average particle size (μm) of the granular gas adsorbent to the thickness (μm) of the layer containing the granular gas adsorbent (average particle size of the granular gas adsorbent / thickness of the layer containing the granular gas adsorbent) 0.85 or more,
A filter medium for an air filter, wherein the pressure loss of the layer containing the granular gas adsorbent is 4.0 Pa or more at a wind speed of 6.5 m / min. The ratio of the average particle size (μm) of the granular gas adsorbent to the thickness (μm) of the layer containing the granular gas adsorbent (average particle size of the granular gas adsorbent / thickness of the layer containing the granular gas adsorbent) The filter medium for an air filter according to claim 1, which is 1.35 or less. The filter medium for an air filter according to claim 1 or 2, wherein the compressibility of the two non-woven fabric sheets is 20% or less, respectively. The air filter filter medium according to any one of claims 1 to 3, wherein the total thickness of the air filter filter medium is 0.90 mm or less. The filter medium for an air filter according to any one of claims 1 to 4, wherein the amount of the granular gas adsorbent is in ^{the range of 40 to 120 g / m 2.} The filter medium for an air filter according to any one of claims 1 to 5, wherein the granular gas adsorbent contains granular activated carbon having a specific surface area of 1100 m ^{2 / g or more.} The filter medium for an air filter according to any one of claims 1 to 6, wherein the average pore diameters of the two non-woven fabric sheets are in the range of 20 μm to 200 μm, respectively. The filter medium for an air filter according to any one of claims 1 to 7, wherein at least one of the two non-woven fabric sheets is an electret non-woven fabric. An air filter unit using the air filter filter medium according to any one of claims 1 to 8.