JP7508387B2 - Air filter media - Google Patents

Description

This disclosure relates to a filter material for dust-removing air filters for filtering gas, particularly dust in the air, and in particular to a filter material for air filters that is characterized by low pressure loss, high collection efficiency, and high dust retention capacity.

In recent years, with the changing environment and growing interest in the indoor living environment at the individual level, there is a demand for purifying the air in offices and residential spaces. The most common method for removing suspended dust in the air is to use dust-removing air filters, and there are various types of filter media for dust-removing air filters. Of these, larger ones are used in system air conditioning in buildings and factories, while smaller ones are widely used in air purifiers and air conditioners. From the perspective of reducing costs and environmental impact, there is a demand for filter media for dust-removing air filters that combine low pressure loss and high collection efficiency, which can remove dust with little energy consumption, as well as a strong demand for filter media with a long life, i.e., a high dust retention capacity, which can reduce the costs of both maintenance and the filter media themselves.

In order to increase the dust retention capacity, air filter media have been proposed that have at least two layers with a density gradient, with a coarse layer on the upstream side and a dense layer on the downstream side (see, for example, Patent Document 1). As another method, a method has been proposed in which fibers are bonded together using pieces of exploded foam particles (see, for example, Patent Document 2).

JP 2015-139739 A JP 2006-7209 A

Journal of Power Sources, Volume 78, Issue 1-2, p. 42-45, 1999

As mentioned above, the technology of Patent Document 1 has been proposed as a method for increasing the dust retention capacity of air filter media, but this method has problems with the labor and cost required for manufacturing, as well as the problem that the filter media becomes thicker, which limits the number of folds in the pleated filter unit, reducing the filter media area and increasing the pressure loss of the filter unit. Patent Document 2 has also been proposed, but this method has problems with the uniformity and collection efficiency of the filter media being reduced because the voids created by the expandable particles are too large.

Air filter media are required to have low pressure loss, high collection efficiency, and high dust retention capacity, but conventional technology has not been able to obtain filter media that combines all of these characteristics. Therefore, the objective of the present invention is to provide an air filter media that has low pressure loss, high collection efficiency, and high dust retention capacity.

The inventors have found that the above-mentioned problems can be solved by using Fiber Number (hereinafter, abbreviated as FN), which indicates the relationship between the fiber diameter of glass fiber and the pressure loss passing through a sheet formed from the fiber, in order to describe the appropriate glass fiber blending ratio in the air filter material of the present invention, and have completed the present invention. That is, the air filter material according to the present invention is an air filter material made of a wet nonwoven fabric mainly made of glass fibers, FN1 is defined by number 1, FN2 is defined by number 2 to number 5, FN1/FN2, which is the ratio of FN2 based on FN1, is 2.50 or more, and the density of the filter material is in the range of 0.17 to 0.20 g/cm ³ , and among the glass fibers contained in the filter material, the glass wool fibers having an average fiber diameter of less than 5.5 μm include ultrafine glass wool fibers having an average fiber diameter of less than 1.0 μm and thick glass wool fibers having an average fiber diameter of 2.0 μm or more and less than 5.5 μm, and the basis weight of the air filter material is in the range of 84.6 to 100.4 g/m ² . Among the glass fibers contained in the filter medium, the glass wool fibers having an average fiber diameter of less than 5.5 μm include ultrafine glass wool fibers having an average fiber diameter of less than 1.0 μm and thick glass wool fibers having an average fiber diameter of 2.0 μm or more and less than 5.5 μm, thereby improving the uniformity of the filter medium.

ここで、
ｄ_ｉ ： ｉ番目の階級の繊維の繊維径［μｍ］
ｘ_ｉ ： ｉ番目の階級の繊維の配合比率［質量％］

here,
d _i : Fiber diameter of the i-th class fiber [μm]
x _i : Blend ratio of fiber of the i-th class [mass%]

ここで、
ｄ_{ｔｏｔａｌ} ： 濾材全体の比表面積より計算した濾材全体の平均繊維径［μｍ］

here,
d _total : average fiber diameter of the entire filter medium [μm] calculated from the specific surface area of the entire filter medium

ここで、
Ｓ_{ｔｏｔａｌ} ： 各繊維の比表面積より計算した濾材全体の比表面積［ｍ^２／ｇ］

here,
S _total : Specific surface area of the entire filter medium calculated from the specific surface area of each fiber [m ² /g]

ここで、
Ｓ_ｉ ： ｉ番目の繊維の繊維径より計算した比表面積［ｍ^２／ｇ］

here,
S _i : Specific surface area calculated from the fiber diameter of the i-th fiber [m ² /g]

ここで、
ρ ： ガラスの密度 ２．４９［ｇ／ｃｍ^３］

here,
ρ: Glass density 2.49 [g/cm ³ ]

Here, d _i in Equations 1 and 5 is defined by Equation 8, and x _i in Equations 1 and 4 is defined by Equation 9.

ここで、
Ｎ_ｉ ： ｉ番目の階級の繊維の本数

here,
N _i : Number of fibers in the i-th class

However, _i in number 8 and x _i in number 9 are determined by the following method. First, the image of the cross section of the filter material cut along the CD direction (width direction of the filter material roll) is taken with an electron microscope or the like, and the fiber diameter is measured. The magnification at this time is not particularly limited, but 3000 times or more is preferable, and the fiber diameter of all fibers used in the same filter material is taken with the same magnification. When the cross section of the glass fiber that can be confirmed in the image of the cross section of the filter material is elliptical, its short diameter is taken as the fiber diameter. In the thickness direction of the cross section of the filter material, a plurality of electron microscope photographs are taken as necessary so as to cover the entire thickness from the front surface to the back surface of the filter material, and the fiber diameter of each fiber is measured with a set of these photographs as the minimum unit. The number of measurement points of fiber diameter is 400 or more, and when the total number of measurement points is less than 400, it is measured from a plurality of sets of photographs covering the entire thickness. The fiber diameters measured by the above method are classified in increments of 0.1 μm starting from 0 μm, with the first class being 0 μm or more and less than 0.1 μm, the second class being 0.1 μm or more and less than 0.2 μm, and the last n-th class being 0.1(n-1) μm or more and less than 0.1 n μm. Here, the fiber diameter of the i-th class is the median of each class calculated by the formula 8. Next, the number of fibers in each class is counted from the electron microscope photograph, and the number of fibers in the i-th class is designated as _Ni , and the blending ratio x _i of the fibers in the i-th class is calculated by the formula 9.

In the air filter medium of the present invention, the glass fibers contained in the filter medium preferably include glass wool fibers and chopped glass fibers, and the glass wool fibers preferably include at least two types of glass wool fibers each having a different average fiber diameter. This provides the filter medium with strength and stiffness, and makes it easy to adjust FN1/FN2 and the density of the filter medium.

In the air filter medium of the present invention, it is preferable that, of all the glass fibers contained in the filter medium, the ratio of glass wool fibers having an average fiber diameter of less than 5.5 μm is 60 to 95 mass %, and the blending ratio of chopped glass fibers having an average fiber diameter of 5.5 μm or more is 5 to 40 mass %. This provides a good balance between the required collection efficiency, the strength and stiffness of the filter medium, and the dust retention capacity of the filter medium.

In the filter material for air filters according to the present invention, the filter material preferably contains a binder and a water repellent as auxiliary materials. The strength and rigidity of the filter material can be increased, and the filter material can have water repellency. In the filter material for air filters according to the present invention, the blending ratio of the thick glass wool fiber in the total glass fiber contained in the filter material is preferably at least 70%.

The effect of the present disclosure is to obtain a filter medium for air filters that has low pressure loss, high collection efficiency, and high dust retention capacity.

FIG. 11 is a diagram showing the relationship between pressure loss and dust retention capacity in Examples and Comparative Examples.

The present invention will be described in detail below with reference to embodiments, but the present invention should not be interpreted as being limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

In order to describe the appropriate blending ratio of glass fiber in the air filter material of this embodiment, the inventors use Fiber Number, which indicates the relationship between the fiber diameter of glass fiber and the pressure loss passing through the sheet formed from this fiber.FN is defined as 1/10 of the pressure loss [Pa] passing through a 90g/ ^m2 sheet under the airflow load of 0.0167m/s, and is expressed by the empirical formula shown in Equation 6 (for example, see Non-Patent Document 1).

ここで、
ｄ ： ガラス繊維の繊維径［μｍ］

here,
d: fiber diameter of glass fiber [μm]

When FN is applied to a filter medium containing multiple glass fibers, each having a different fiber diameter, there are two possible calculation methods:
(1) After calculating the FN of each fiber individually, multiply the FN of each fiber by the blending ratio of that fiber and add up (hereinafter referred to as FN1).
(2) Calculate FN from the average fiber diameter of the entire filter medium (hereinafter referred to as FN2).
Here, FN1 is close to the pressure loss of the filter material that is actually made, but FN2 is smaller than the actual pressure loss because the contribution of thick fiber to the pressure loss of the entire filter material is smaller than the contribution of the average fiber diameter of the entire filter material.The value of FN2 is smaller when the difference in fiber diameter of each fiber is large and/or when the relative blending ratio of thick fiber is high.Note that FN1 is defined by formula 1, and FN2 is defined by formulas 2 to 5.

The inventors have found that the dust retention capacity of a filter medium is increased by adjusting the fiber diameter and blending ratio of the glass fibers in the filter medium so that the FN1/FN2 ratio is 2.50 or more. This means that the difference in fiber diameter of the fibers contained in the filter medium is large and/or the relative blending ratio of large-diameter fibers is high. Although the detailed mechanism is unclear, it is presumed that the coarse fiber network structure formed by the large-diameter fibers contributes to the dust retention capacity. It is more preferable that the FN1/FN2 ratio is 2.60 or more, and even more preferable that it is 2.70 or more. There is no particular limit to the upper limit of the FN1/FN2 ratio, but it is preferably 3.50.

The density of the filter medium in this embodiment is in the range of 0.17 to 0.20 g/cm ³ , more preferably 0.17 to 0.19 g/cm ^3. If the density of the filter medium exceeds 0.20 g/cm ³ , the size of the voids in the filter medium required to obtain a high dust retention amount is not sufficient. If the density is less than 0.17 g/cm ³ , the uniformity of the filter medium is low, and the collection efficiency may be low.

The air filter medium of this embodiment includes glass wool fibers and chopped glass fibers. The glass wool fibers referred to here are irregular, discontinuous wool-like glass fibers with a certain distribution width of fiber diameters, which are produced by drawing using a flame drawing method or a rotary method. The fiber diameter range is generally about 0.2 to about 10 μm, and since it has a certain distribution width, the fiber diameter value is generally expressed as the average fiber diameter. The grade of glass wool fibers varies depending on the value of the average fiber diameter. On the other hand, chopped glass fibers are regular, linear glass fibers obtained by cutting continuous glass fibers spun from a nozzle having a certain diameter to a certain fiber length, and the fiber diameter range is generally about 4 to about 30 μm, and the fiber length range is generally about 1.5 to about 25 mm. In the filter medium of this embodiment, the glass wool fibers with a small fiber diameter and irregular shape have the effect of increasing the collection efficiency and maintaining voids in the filter medium. Chopped glass fibers, which have a large fiber diameter and are straight, have the effect of imparting the strength and stiffness required during processing and use of the filter unit, but on the other hand, they tend to accumulate in a state oriented in the web plane direction during the production of the filter medium, so a high blend ratio of chopped glass fibers increases the density of the filter medium.

The glass wool fibers having an average fiber diameter of less than 5.5 μm used in this embodiment preferably include both ultrafine glass wool fibers having an average fiber diameter of less than 1.0 μm and thin glass wool fibers having an average fiber diameter of 2.0 μm or more and less than 5.5 μm, more preferably include both ultrafine glass wool fibers having an average fiber diameter of 0.3 μm or more and less than 1.0 μm and thin glass wool fibers having an average fiber diameter of 2.0 μm or more and less than 5.5 μm, even more preferably include both ultrafine glass wool fibers having an average fiber diameter of 0.3 μm or more and less than 0.7 μm and thin glass wool fibers having an average fiber diameter of 3.0 μm or more and less than 5.5 μm, and most preferably include both ultrafine glass wool fibers having an average fiber diameter of 0.3 μm or more and less than 0.6 μm and thin glass wool fibers having an average fiber diameter of 3.0 μm or more and less than 5.5 μm. The greater the difference in the average fiber diameters of the glass wool fibers used, the greater the ratio FN1/FN2; however, if the difference in the average fiber diameters of the glass wool fibers becomes too large, in other words, if the ultra-fine glass wool fibers become too thin, the blending ratio of the fibers to achieve a specified pressure loss becomes too low, impairing the uniformity of the filter medium.

The blending ratio of glass wool fibers in the filter medium is preferably 60 to 95% by mass, and more preferably 70 to 90% by mass. If the blending ratio is too low, less than 60% by mass, the required collection efficiency may not be obtained. If the blending ratio is too high, more than 95% by mass, the blending ratio of chopped glass fibers becomes relatively low, and the required strength and stiffness may not be obtained.

The average fiber diameter of the chopped glass fiber used in this embodiment is preferably 5.5 μm or more, more preferably 5.5 to 11 μm, and even more preferably 6 to 9 μm. If the fiber diameter is too small, less than 5.5 μm, the effect on strength and stiffness will be insufficient. If the fiber diameter is too large, cracks will occur during pleating of the filter unit, so the upper limit of the average fiber diameter of the chopped glass fiber is, for example, 13 μm. In addition, the fiber length of the chopped glass fiber is preferably 3 to 10 mm. If the fiber length is too short, less than 3 mm, the effect on strength and stiffness may be insufficient. If the fiber length is too long, more than 10 mm, the dispersibility when dispersing in water to form a slurry in the wet papermaking process may be poor, and the uniformity of the filter medium may be impaired.

The blending ratio of chopped glass fiber in the filter medium is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass. If the blending ratio is too low, less than 5% by mass, the required strength and stiffness may not be obtained. If the blending ratio is too high, more than 40% by mass, the density of the filter medium increases, lowering the dust retention capacity, and the blending ratio of glass wool fiber becomes relatively low, making it difficult to obtain the required collection efficiency.

In the air filter medium of this embodiment, the glass wool fibers preferably contain two or more types of glass wool fibers each having a different average fiber diameter. This is because, when designing the filter medium of this embodiment, it is preferable to first fix the blending ratio of the chopped glass fibers according to the strength and stiffness required for the application, and then adjust the FN1/FN2 ratio by changing the average fiber diameter and/or blending ratio of the two or more types of glass wool fibers. When there is only one type of glass wool fiber and one type of chopped glass fiber, changing the blending ratio of each fiber affects multiple physical properties simultaneously, making it difficult to achieve a balance.

When designing the air filter medium of this embodiment, the average fiber diameter of the glass wool fibers can be the manufacturer's nominal value, but it is also possible to use values actually measured using an electron microscope or values calculated from the specific surface area measured by the BET method using formula 7.

ここで、
ｄ ： 繊維径［μｍ］
Ｓ ： 繊維の比表面積［ｍ^２／ｇ］
ρ ： ガラスの密度 ２．４９［ｇ／ｃｍ^３］

here,
d: fiber diameter [μm]
S: specific surface area of fiber [ ^m2 /g]
ρ: glass density 2.49 [g/cm ³ ]

The d _i and _xi used in the calculation of FN1/FN2 defined in this embodiment are determined by the following method. First, an image of the cross section of the filter material cut along the CD direction (width direction of the filter material roll) is taken with an electron microscope or the like, and the fiber diameter is measured. The magnification at this time is not particularly limited, but 3000 times or more is preferable, and the fiber diameter of all fibers used in the same filter material is taken with the same magnification. When the cross section of the glass fiber that can be confirmed in the image of the cross section of the filter material is an ellipse, its short diameter is taken as the fiber diameter. In the thickness direction of the cross section of the filter material, a plurality of electron microscope photographs are taken as necessary so as to cover the entire thickness from the front surface to the back surface of the filter material, and the fiber diameter of each fiber is measured with a set of these photographs as the minimum unit. The number of measurement points of the fiber diameter is 400 or more, and when the total number of measurement points is less than 400, it is measured from a plurality of sets of photographs covering the entire thickness. The fiber diameters measured by the above method are classified into classes in increments of 0.1 μm starting from 0 μm, with the first class being 0 μm or more and less than 0.1 μm, the second class being 0.1 μm or more and less than 0.2 μm, and the last n-th class being 0.1(n-1) μm or more and less than 0.1 n μm. Here, the fiber diameter of the i-th class is the median of each class calculated by the formula 8. Next, the number of fibers in each class is counted from the electron microscope photograph, and the number of fibers in the i-th class is designated as _Ni , and the blending ratio x _i of the fibers in the i-th class is calculated by the formula 9.

ここで、
ｄ_ｉ ： ｉ番目の階級の繊維の繊維径［μｍ］

here,
d _i : Fiber diameter of the i-th class fiber [μm]

ここで、
ｘ_ｉ ： ｉ番目の階級の繊維の配合比率［質量％］
Ｎ_ｉ ： ｉ番目の階級の繊維の本数

here,
x _i : Blend ratio of fiber of the i-th class [mass%]
N _i : Number of fibers in the i-th class

The basis weight of the filter material for air filters of the present embodiment is preferably in the range of 10 to 100 g/m ² , more preferably 50 to 90 g/m ^2. If the basis weight is too low, such as less than 10 g/m ² , the strength and rigidity of the filter material may be insufficient, and the filter unit may tear or crack during processing or use, or may deform during ventilation, causing an increase in pressure loss. If the basis weight is too high, such as more than 100 g/m ² , the filter material area in the filter unit may become small, and pressure loss may become high. The basis weight can be appropriately changed according to the required standard.

Small pressure loss is preferable, but generally, small pressure loss leads to high PAO permeability, so pressure loss is adjusted appropriately depending on the desired PAO permeability.

In this embodiment, in order to provide the air filter medium with the required physical properties, secondary materials other than glass fiber can be included. Examples of such secondary materials include binders for providing strength and rigidity, and water repellents for providing water repellency. The type and content of these secondary materials can be appropriately selected within a range that does not impair the effects of the present invention. As the binder, binder fibers and non-fibrous binder resins can be used, and binder resins are mainly used. As the binder resin, for example, polyacrylic ester resins, polyvinyl alcohol resins, polystyrene butadiene resins, polyvinyl acetate resins, polyurethane resins, etc. are used. As the water repellent agent, for example, fluoroalkyl resins, silicone resins, paraffin wax, etc. are used. These secondary materials are dispersed in water together with glass fibers, or are impregnated in the form of an aqueous dispersion onto a wet sheet obtained by wet papermaking. The solid mass ratio of the binder to the water repellent is preferably 100/0 to 80/20. In addition, the content of the binder and water repellent in the filter medium is preferably 2.0 to 10.0% by mass.

In this embodiment, the filter medium is made of a wet nonwoven fabric mainly composed of glass fibers, and the proportion of glass fibers in the total fiber content of the filter medium is preferably 50% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

The method for producing the air filter medium in this embodiment is a wet papermaking method. Here, glass fibers and, if necessary, auxiliary materials are dispersed in water to obtain a raw material slurry, which is then formed into a sheet by wet papermaking to obtain a wet sheet, which is impregnated with auxiliary materials if necessary, and then dried to obtain the desired air filter medium.

Next, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the examples, "parts" and "%" respectively refer to "parts by mass" and "% by mass" calculated on a solid content basis, unless otherwise specified.

Glass wool fibers and chopped glass fibers were mixed in the ratios shown in Tables 1 to 4, and the mixture was disintegrated in a pulper using sulfuric acid acid water with a pH of 3.0 to a slurry concentration of 0.5% by mass. The resulting slurry was then paper-made in a hand-sheeting machine to obtain wet paper. Next, the wet paper was impregnated with an impregnation liquid in which an acrylic resin binder (product name: Boncoat AN-155-E, manufacturer: DIC Corporation) and a fluorine-based water repellent (product name: NK Guard S-07, manufacturer: Nicca Chemical Co., Ltd.) were mixed to a solid content ratio of 95/5, and the wet paper was dried in a rotary dryer at 130°C to obtain air filter media for each Example and Comparative Example. The solid content concentration of the impregnation liquid was adjusted so that the content of the impregnated components in the filter media was 6% by mass.

The glass wool fibers B-04-F, B-06-F, B-08-F, B-15-F, B-26-R, B-39-R, and B-50-R and chopped glass fiber EC6-6SP used in this example were all manufactured by Unifrax, and the average fiber diameter values of these fibers were the nominal values published by the manufacturers.

The fiber blend ratios and the physical property measurement results in the examples and comparative examples are shown in Tables 1 to 8. In Table 5, Example 14 was changed to Reference Example 14.

The air filter media obtained in the examples and comparative examples were evaluated using the methods described below.

(1) Pressure loss [Pa]
The differential pressure when air was passed through an air filter medium having an effective area of 100 cm ² at 5.3 cm/sec was measured with a micro-differential pressure gauge.

(2) PAO transmittance [%]
Air containing polydisperse polyalphaolefin (hereinafter abbreviated as PAO) particles generated by a Ruskin nozzle was passed through an air filter medium with an effective area of 0.01 ^m2 at a surface velocity of 5.3 cm/sec. The number of PAO particles upstream and downstream of the filter medium was measured using a laser particle counter KC-18 (manufactured by Rion Co., Ltd.), and the transmittance was calculated by the formula: downstream number/upstream number x 100. The target particle diameter was 0.3 to 0.4 μm.

(3) PF value The PF value was calculated from the measured values of pressure loss and PAO permeability using the formula 10. A higher PF value means that the filter medium has a higher collection efficiency (i.e., a lower permeability) with a lower pressure loss.

(4) Basis weight [g/ ^m2 ]
Measurement was performed in accordance with JIS P 8124:2011.

(5) Thickness [mm]
The measurement was performed in accordance with JIS P 8118; 1998. The measurement pressure was 50 kPa.

(6) Density [g/cm ³ ]
Measurement was carried out in accordance with JIS P 8118;1998.

(7) Dust retention capacity [g/m ² ]
The dust retention capacity is obtained by neutralizing the charge of the test dust by using the charged particle neutralizer CD2000 (manufactured by PALAS) with the air containing the test dust generated by aerosol generator RBG-1000, and then passing the air through the filter material for air filter with an effective area of 0.01 ^m2 at a surface wind speed of 10 cm/sec. When the pressure loss at 10 cm/sec reaches 250 Pa, the mass of the particles attached to the filter material is obtained from the difference in the mass of the filter material before and after the dust is attached, and this is divided by the effective area to obtain the dust retention capacity. Note that the test dust is made of JIS 11 type Kanto loam layer powder, and the generation concentration of the test dust is set to 14.5 mg/ ^m3 .

In Examples 1 to 6 and Comparative Examples 1 to 4 shown in Tables 1 and 2, the fiber diameter and blending ratio of the glass wool fiber were changed while the blending ratio of the chopped glass fiber was constant at 30 mass% so that the basis weight was about 85 g/m ² and the pressure loss was about 40 Pa. In all Examples and Comparative Examples, the density of the filter medium was lower than 0.20 g/cm ³ , but the Examples with FN1/FN2 of 2.50 or more had a dust retention capacity of 9 g/m ² or more, while the Comparative Examples with FN1/FN2 of less than 2.50 had a dust retention capacity of less than 8.00 g/m ² , which was lower than the Examples.

In Examples 2, 5, 7 to 13 and Comparative Examples 5 and 6 shown in Tables 3 and 4, the blending ratio of chopped glass fiber and glass wool fiber was changed so that the basis weight was about 85 g/m ² and the pressure loss was about 40 Pa. In all Examples and Comparative Examples, FN1/FN2 was 2.50 or more, but the Examples in which the density of the filter medium was less than 0.20 g/cm ³ had a dust retention capacity of 9 g/m ² or more, while the Comparative Examples in which the density of the filter medium was more than 0.20 g/cm ³ had a dust retention capacity of less than 8.15 g/m ² , which was lower than the Examples.

In Example 14 and Comparative Example 7 shown in Table 5, the fiber diameter and blending ratio of glass wool fiber are changed in each basis weight so that the basis weight is about 30 g/m ² and the pressure loss is about 40 Pa. In addition, in Example 15 and Comparative Example 8 shown in Table 6, the fiber diameter and blending ratio of glass wool fiber are changed in each basis weight so that the basis weight is about 100 g/m ² and the pressure loss is about 40 Pa. When comparing Example 14 and Comparative Example 7, or Example 15 and Comparative Example 8, the example in which FN1/FN2 is 2.50 or more and the density of the filter medium is 0.20 g/cm ³ or less has a higher dust retention capacity than the comparative example.

In Example 16 and Comparative Example 9 shown in Table 7, the average fiber diameter of the glass wool fiber and the blending ratio of the glass wool fiber and the chopped glass fiber were changed so that the basis weight was about 85 g/m ² and the pressure loss was about 25 Pa. In addition, in Examples 17 to 19 and Comparative Example 10 shown in Table 8, the average fiber diameter of the glass wool fiber and the blending ratio of the glass wool fiber and the chopped glass fiber were changed so that the basis weight was about 85 g/m ² and the pressure loss was about 75 Pa. When comparing Example 16 with Comparative Example 9, or Examples 17 to 19 with Comparative Example 9, the examples in which FN1/FN2 was 2.50 or more and the density of the filter medium was 0.20 g/cm ³ or less had a higher dust retention capacity than the comparative examples.

The relationship between pressure loss and dust retention capacity in the examples and comparative examples is shown in Figure 1.

As shown in FIG. 1, when compared at the same basis weight, the examples in which the FN1/FN2 was 2.50 or more and the density of the filter medium was 0.20 g/cm ³ or less had a higher dust retention capacity than the comparative examples.

Furthermore, in all examples, the PF value was 12 or more, and a filter medium was obtained that combined low pressure loss and low permeability, i.e., high collection efficiency.

The present invention relates to a filter material for dust-removing air filters for filtering gas, particularly dust in the air, which has low pressure loss and high collection efficiency, as well as high dust retention capacity, i.e., long life, and can therefore be used in system air conditioning, air purifiers, air conditioners, etc. in buildings or factories.

Claims (5)

In an air filter material made of a wet nonwoven fabric mainly composed of glass fibers,
FN1 is defined by the following equation:
FN2 is defined by numbers 2 to 5,
FN1/FN2, which is the ratio of FN2 to FN1, is 2.50 or more, and
The density of the filter medium is in the range of 0.17 to 0.20 g/ ^cm3 ;
Among the glass fibers contained in the filter medium, the glass wool fibers having an average fiber diameter of less than 5.5 μm include ultrafine glass wool fibers having an average fiber diameter of less than 1.0 μm and thick glass wool fibers having an average fiber diameter of 2.0 μm or more and less than 5.5 μm;
The filter material for air filters has a basis weight in the range of 84.6 to 100.4 g/ ^m2 .

here,
d _i : Fiber diameter of the i-th class fiber [μm]
x _i : Blend ratio of fiber of the i-th class [mass%]

here,
d _total : average fiber diameter of the entire filter medium [μm] calculated from the specific surface area of the entire filter medium

here,
S _total : Specific surface area of the entire filter medium calculated from the specific surface area of each fiber [m ² /g]

here,
S _i : Specific surface area calculated from the fiber diameter of the i-th fiber [m ² /g]

here,
ρ: glass density 2.49 [g/cm ³ ]
Here, d _i in Equations 1 and 5 is defined by Equation 8, and x _i in Equations 1 and 4 is defined by Equation 9.

here,
N _i : the number of fibers in the i-th class Where, _i in number 8 and x _i in number 9 are determined by the following method. First, the image of the cross section of the filter material cut along the CD direction (width direction of the filter material roll) is taken with an electron microscope or the like, and the fiber diameter is measured. The magnification at this time is not particularly limited, but 3000 times or more is preferable, and the fiber diameter of all fibers used in the same filter material is taken with the same magnification. If the cross section of the glass fiber that can be confirmed in the image of the cross section of the filter material is elliptical, its short diameter is taken as the fiber diameter. In the thickness direction of the cross section of the filter material, multiple electron microscope photographs are taken as necessary so that the entire thickness is covered from the front surface to the back surface of the filter material, and the fiber diameter of each fiber is measured with a set of these photographs as the minimum unit. The number of measurement points of fiber diameter is 400 or more, and if the total number of measurement points is less than 400, it is measured from multiple sets of photographs covering the entire thickness. The fiber diameters measured by the above method are classified in increments of 0.1 μm starting from 0 μm, with the first class being 0 μm or more and less than 0.1 μm, the second class being 0.1 μm or more and less than 0.2 μm, and the last n-th class being 0.1(n-1) μm or more and less than 0.1 n μm. Here, the fiber diameter of the i-th class is the median of each class calculated by the formula 8. Next, the number of fibers in each class is counted from the electron microscope photograph, and the number of fibers in the i-th class is designated as _Ni , and the blending ratio x _i of the fibers in the i-th class is calculated by the formula 9. The filter medium for air filters according to claim 1, characterized in that the glass fibers contained in the filter medium include glass wool fibers and chopped glass fibers, and the glass wool fibers include at least two types of glass wool fibers each having a different average fiber diameter. The filter medium for air filters according to claim 1 or 2, characterized in that, of all the glass fibers contained in the filter medium, the ratio of glass wool fibers having an average fiber diameter of less than 5.5 μm is 60 to 95 mass %, and the blending ratio of chopped glass fibers having an average fiber diameter of 5.5 μm or more is 5 to 40 mass %. The filter medium for air filters according to any one of claims 1 to 3 , characterized in that the filter medium contains a binder and a water repellent as auxiliary materials. 5. The filter material for air filters according to claim 1, wherein the blending ratio of the large diameter glass wool fibers to the total glass fibers contained in the filter material is at least 70%.

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