Filter media for air filters and method for manufacturing the same

Abstract

To provide a filter medium for an air filter including a renewable material, having biodegradability, and having sufficient water repellency.SOLUTION: A filter medium for an air filter according to the present disclosure is a filter medium including a wet-type non-woven fabric. The fibers forming the filter medium includes beaten fibers and non-beaten fibers. The beaten fibers are fibrillated Lyocell fibers. The non-beaten fibers are biodegradable fibers. The filter medium includes an alkyl ketene dimer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to filter media for air filters used in various fields such as factory and building air conditioning, automobile cabins, air conditioners, air purifiers, and personal protective equipment, and more particularly to filter media for air filters that have a low environmental impact and a small decrease in filtration performance during use. [Background technology]

[0002] For air filters used in building air conditioning systems and other applications, glass fiber filters and meltblown nonwoven fabric filters are the main types of medium- and high-performance filter media used. Glass fiber filters are non-combustible and are therefore disposed of as industrial waste in landfills after use. This results in a significant environmental impact during disposal. On the other hand, meltblown nonwoven fabric filters mainly use non-renewable and finite fossil resources (such as PP) as raw materials, resulting in high carbon dioxide emissions throughout their entire lifecycle if incinerated. Furthermore, if released into the environment after use, they do not decompose and remain in the environment. For these reasons, there is a demand for filter media that have a low environmental impact, contain renewable materials, and are biodegradable.

[0003] To solve these problems, filter media containing fibrillated lyocell fibers, biodegradable fibers, and regenerated or semi-synthetic fibers have been proposed (see Patent Document 1 or Patent Document 2). However, cellulose fibers such as lyocell fibers have high hygroscopicity and water absorption, which can cause swelling of the fibers and changes in the filter media structure when used in high-humidity environments or when moisture-containing airflow or dust passes through them, leading to a decrease in the filtration performance of the air filter media, for example, a decrease in the PF value. The PF value is defined by formula 1, and a higher PF value means that the filter media has higher dust particle collection efficiency and lower pressure loss, resulting in higher filtration performance.

[0004]

number

[0005] To solve the aforementioned problems, a method of imparting water repellency to the filter material is effective, and a widely used method for imparting water repellency to air filter material is the use of a fluorine-based water repellent (see, for example, Patent Document 3 or Patent Document 4). However, perfluoroalkyl compounds that constitute fluorine-based water repellents are poorly degradable and highly bioaccumulative, and there is a global movement to restrict their use, making them unsuitable for the purpose of the present invention. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-167659 [Patent Document 2] Japanese Patent Publication No. 2006-326470 [Patent Document 3] Japanese Patent Publication No. 2001-79318 [Patent Document 4] Japanese Patent Publication No. 2014-98082 [Non-patent literature]

[0007] [Non-Patent Document 1] International Journal of Biological Macromolecules, 2022, Vol.207, p.31-39 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As described above, there is a demand for filter media that have a low environmental impact and maintain minimal degradation of filtration performance during use. However, conventional technologies have made it difficult to obtain filter media that possess all of these characteristics. Therefore, the objective of this disclosure is to provide an air filter media that contains renewable materials, is biodegradable, and has sufficient water repellency. [Means for solving the problem]

[0009] The filter medium for an air filter according to the present invention is a filter medium made of a wet non-woven fabric, and the fibers constituting the filter medium include beaten fibers and unbeaten fibers. The beaten fibers are fibrillated lyocell fibers, and the unbeaten fibers are biodegradable fibers. The biodegradable fibers are continuously distributed throughout the entire thickness direction of the filter material. The filter medium is characterized by containing an alkyl ketene dimer. According to such a configuration, a filter medium with a small environmental load and a small decrease in filtration performance during use can be obtained.

[0010] In the filter medium for an air filter according to the present invention, it is preferable that the content of the alkyl ketene dimer in the entire filter medium is in the range of 0.05 to 2.0% by mass. Thereby, a filter medium having sufficient water repellency and a high PF value can be obtained.

[0011] In the filter medium for an air filter according to the present invention, it is preferable that the biodegradable fiber is at least one selected from the group consisting of regenerated cellulose fiber, natural cellulose fiber, and polylactic acid-based fiber. Thereby, a filter medium having a high PF value and biodegradability can be obtained.

[0012] The filter medium for an air filter according to the present invention may contain a biodegradable binder. Thereby, a filter medium having biodegradability and sufficient strength and stiffness for the processing and use of the filter can be obtained.

[0013] In the filter medium for an air filter according to the present invention, the biodegradable binder may be polyvinyl alcohol and / or polylactic acid. Thereby, a filter medium having sufficient strength and stiffness without significantly reducing the PF value can be obtained.

[0014] In the filter medium for an air filter according to the present invention, it is preferable that the alkyl ketene dimer is not coated with a continuous film of the biodegradable binder. Thereby, a filter medium having sufficient strength and stiffness while maintaining water repellency can be obtained.

[0015] The manufacturing method of the filter medium for an air filter according to the present invention is Constituting the filter material Beaten fiber and A papermaking process of forming a wet sheet by sheet-forming a raw material slurry in which non-refined fibers are dispersed in water by a wet papermaking method, a step of applying an alkyl ketene dimer to the wet sheet, and a drying step of heat-drying the wet sheet to which the alkyl ketene dimer has been applied to form a dry sheet The filter material has the following properties: the beaten fibers are fibrillated lyocell fibers, the unbeaten fibers are biodegradable fibers, and the biodegradable fibers are continuously distributed throughout the entire thickness direction of the filter material. characterized by this. According to such a method, a filter medium having sufficient water repellency and a high PF value can be obtained.

[0016] In the method for manufacturing a filter medium for an air filter according to the present invention, a binder may be dispersed in the raw material slurry together with the fibers. Thereby, a filter medium having sufficient strength and stiffness can be obtained without inhibiting the effect of improving the water repellency and PF value by the alkyl ketene dimer.

Effect of the Invention

[0017] According to the present disclosure, a filter medium with a small environmental load and a small decrease in filtration performance during use can be obtained. That is, a filter medium for an air filter can be obtained that contains renewable materials, has biodegradability, and further has sufficient water repellency to prevent moisture absorption of cellulose-based fibers including fibrillated lyocell fibers.

Modes for Carrying Out the Invention

[0018] Next, embodiments of the present invention will be shown and described in detail, but the present invention is not construed as being limited to these descriptions. As long as the effects of the present invention are achieved, the embodiments may be variously modified.

[0019] The lyocell fibers in this embodiment are regenerated cellulose fibers spun by an organic solvent spinning method using N-methylmorpholine N-oxide as the solvent. Because the organic solvent spinning method involves dissolving cellulose directly in an organic solvent for spinning, there is less molecular cleavage, the average degree of polymerization is higher than other regenerated cellulose fibers, the fibers have high rigidity, and the cross-sectional shape of the fibers is close to circular. This rigidity and cross-sectional shape make it easier to maintain voids in the filter material. Furthermore, the fibrillated lyocell fibers after beating also maintain the aforementioned rigidity and cross-sectional shape, making it easier to maintain voids in the filter material. Moreover, when fibrillated by beating, the surface area of ​​the fibers that contribute to particle collection increases, thus increasing collection efficiency, and the tensile strength of the filter material increases due to increased entanglement between fibers.

[0020] In this embodiment, the beaten fibers are fibrillated lyocell fibers, and the amount of beaten fibers is preferably 2 to 30 parts, more preferably 3 to 20 parts, and even more preferably 5 to 15 parts, when the total amount of beaten fibers, non-beaten fibers, and binder constituting the filter material is 100 parts. If the amount is less than 2 parts, the surface area of ​​the fibers that contribute to particle collection is insufficient, and it is difficult to obtain sufficient collection efficiency. On the other hand, if the amount exceeds 30 parts, the fibers become too entangled, blocking the voids, and the pressure loss increases significantly compared to the increase in collection efficiency, which may lead to a decrease in the PF value.

[0021] For the beating method to fibrillate lyocell fibers, beating machines or disintegrators such as Niagara beaters, PFI mills, single disc refiners, double disc refiners, and deflakers can be used. In beating, it is preferable not to apply too much load so as not to shorten the length of the lyocell fibers too much.

[0022] As lyocell fibers are beaten, the fibers are cut and their length is shortened. If the fiber length becomes too short, it may fill the voids after sheet formation, potentially increasing pressure loss. On the other hand, if the fiber length is too long, the dispersibility when dispersed in water to form a raw material slurry will be poor, potentially resulting in an uneven structure of the filter material. The length-loaded average fiber length of the fibrillated lyocell fibers used in this invention is preferably 0.6 mm or more, more preferably 0.8 to 3 mm, and even more preferably 1 to 2 mm.

[0023] Furthermore, the length-weighted average fiber length of fibrillated lyocell fibers was measured according to ISO 16065-2:2014 "Determination of fiber length by automated optical analysis - Part 2: Unpolarized light method".

[0024] Lyocell fibers undergo fibrillation through beating, resulting in a reduction in fiber diameter. If the fiber diameter is too small, the fibers become easily broken, leading to the aforementioned problem of shortened fiber length. On the other hand, if the fiber diameter is too large, the surface area of ​​the fibers that contribute to particle collection becomes insufficient. The average fiber diameter of the fibrillated lyocell fibers used in this embodiment is preferably 0.3 μm or more, more preferably 0.4 to 1.5 μm, and even more preferably 0.5 to 1.0 μm.

[0025] Furthermore, the average fiber diameter of the fibrillated lyocell in this embodiment was calculated using Equation 2 from the specific surface area measured by the BET multipoint method using nitrogen.

[0026]

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[0027] The non-beaten fibers in this embodiment are biodegradable fibers that have not been beaten, have not been fibrillated, or have a slightly fuzzy surface. Examples of biodegradable fibers include regenerated cellulose fibers, natural cellulose fibers, polylactic acid-based fibers, polybutylene succinate fibers, and polyhydroxyalkanoate fibers. However, it is preferable that at least one selected from the group consisting of regenerated cellulose fibers, natural cellulose fibers, and polylactic acid-based fibers is used, as this prevents the fibers from melting during heat drying and prevents the phenomenon of the PF value decreasing due to melted fibers clogging the pores of the filter material. Non-beaten fibers of different types and / or different fiber diameters may be mixed and used.

[0028] In this embodiment, the amount of unbeaten fibers is preferably 50 to 98 parts, more preferably 60 to 95 parts, and even more preferably 70 to 90 parts, when the total amount of beaten fibers, unbeaten fibers, and binder constituting the filter material is 100 parts. If the amount of unbeaten fibers is less than 50 parts, the amount of beaten fibers and / or binder will be high, resulting in a decrease in the PF value. On the other hand, if the amount of unbeaten fibers exceeds 98 parts, sufficient collection efficiency and / or strength and rigidity cannot be obtained.

[0029] Regenerated cellulose fibers include viscose rayon fibers spun from cellulose using the viscose method, and lyocell fibers spun using the organic solvent spinning method. These are renewable materials made from wood pulp and possess soil biodegradability and marine biodegradability.

[0030] Natural cellulose fibers are fibers primarily composed of cellulose extracted from plants, and include wood pulp, cotton linter pulp, hemp pulp, kenaf pulp, and mercerized pulp obtained by alkali treatment of wood pulp. These are renewable materials made from plants and are biodegradable when buried in soil.

[0031] Polylactic acid fiber is a fiber spun from polylactic acid, which is produced by polymerizing lactic acid obtained from saccharification and fermentation of biomass-derived starch. It is biodegradable and can be buried in soil. Unlike cellulose fiber, polylactic acid fiber is thermoplastic, which allows it to impart thermoformability to filter media. In addition to main fibers made of ordinary polylactic acid with a melting point of 170°C or higher, binder fibers that partially use polylactic acid whose melting point has been lowered to below 170°C by modifying its molecular structure are also used. In this embodiment, the polylactic acid main fiber is used as a non-beaten fiber, and the polylactic acid binder fiber is used as a binder as described below.

[0032] In this embodiment, the non-beaten fibers preferably have an average fiber diameter of 5 μm or more, more preferably 6 to 50 μm, and even more preferably 7 to 40 μm. If the average fiber diameter is smaller than 5 μm, it becomes difficult to maintain the voids necessary for uniform distribution of the beaten fibers, which may lead to an increase in pressure loss. On the other hand, if the average fiber diameter exceeds 50 μm, the large difference in fiber diameter between the non-beaten fibers and the beaten fibers may lead to a large variation in the pore size of the filter material, which may cause a decrease in collection efficiency.

[0033] The alkyl ketene dimer in this embodiment is obtained by reacting naturally derived fatty acids (for example, palmitic acid with 16 carbon atoms or stearic acid with 18 carbon atoms) via an acid chloride to form a dimer. It is widely used as a sizing agent in paper to prevent ink from seeping in. It is also biodegradable, and its use as a water-resistant agent for biodegradable materials is being considered (see, for example, Non-Patent Document 1). In this embodiment, it is used to impart sufficient water repellency to the fibers constituting the filter material and to prevent a decrease in filtration performance during use of the filter material.

[0034] In this embodiment, the content of alkyl ketene dimer relative to the total filter media is preferably 0.05 to 2.0% by mass, more preferably 0.1 to 1.8% by mass, and particularly preferably 0.6 to 1.7% by mass. If the content is less than 0.05% by mass, sufficient water repellency (e.g., 100 mm water column height) may not be obtained. On the other hand, if the content is 0.05% by mass or more, sufficient water repellency (e.g., 100 mm water column height) can be obtained, and if the content is 0.1% by mass or more, even higher water repellency (e.g., 200 mm water column height) can be obtained. If the alkyl ketene dimer content exceeds 2.0% by mass, the PF value may decrease.

[0035] Furthermore, the inventors have discovered that the PF value of the filter media can be increased by adjusting the content of alkyl ketene dimer within an appropriate range for the entire filter media. Although the mechanism by which this increases the PF value is not clear, it is presumed that when an appropriate amount of alkyl ketene dimer is attached to the surface of fibrillated lyocell fibers, the aggregation of fibers is prevented, increasing the surface area of ​​the fibers and thereby increasing the collection efficiency, while the gaps between fibers are widened, reducing pressure loss and thus increasing the PF value. On the other hand, it is presumed that when too much alkyl ketene dimer is attached, the alkyl ketene dimer fills the gaps between fibers, reducing the surface area of ​​the fibers and thus decreasing the collection efficiency, while clogging unnecessarily increases pressure loss and thus decreases the PF value. When the alkyl ketene dimer content relative to the entire filter media is in the range of 0.05 to 2% by mass, a higher PF value can be obtained than when alkyl ketene dimer is not present, and when the content is 0.1 to 1.5% by mass, an even higher PF value (for example, 0.8 points or more higher than when alkyl ketene dimer is not present) can be obtained.

[0036] In this embodiment, a biodegradable binder may be included in the filter material for the purpose of improving strength and rigidity. As the biodegradable binder, for example, polyvinyl alcohol, polylactic acid, or both polyvinyl alcohol and polylactic acid can be used. Polyvinyl alcohol is biodegradable and adheres fibers together, and can be in fibrous or powder form that can be dispersed in water together with beaten and unbeaten fibers to form a raw material slurry, or it can be made into an aqueous solution that can be mixed with alkyl ketene dimer and attached. Polylactic acid is the polylactic acid binder fiber mentioned above, which adheres fibers together when heated above its melting point. It is more preferable that the biodegradable binder is in powder form. Because it is uniformly dispersed and adheres to the fibers at points, high strength and rigidity can be obtained without significantly reducing the PF value. It is particularly preferable that the powdered binder is polyvinyl alcohol. Even higher strength and rigidity can be obtained.

[0037] In this embodiment, when a biodegradable binder is included in the filter material, the amount of biodegradable binder is preferably 0.5 to 20 parts, and more preferably 1 to 15 parts, when the total amount of fibers and binder constituting the filter material is 100 parts. If the amount is less than 0.5 parts, there is a risk that sufficient improvement in strength and rigidity cannot be obtained, and if it exceeds 20 parts, there is a risk that the PF value will decrease.

[0038] In this embodiment, additives such as defoaming agents and dispersants can be appropriately included in the filter media, as long as they do not hinder the effects of the present invention.

[0039] The method for manufacturing the filter material in this embodiment uses a wet papermaking method. Specifically, the fibers constituting the filter material are dispersed in water using a disperser such as a pulper, the resulting raw material slurry is deposited on a wire and dewatered to form a wet sheet, an alkyl ketene dimer is applied to the resulting wet sheet by impregnation or coating, and the sheet is dried using a dryer such as a hot air dryer or cylinder dryer to obtain a dried filter material sheet. When the alkyl ketene dimer is applied to the sheet after drying, the effect of improving the PF value by the alkyl ketene dimer is not sufficiently obtained.

[0040] In the method for manufacturing the filter material of this embodiment, when a biodegradable binder is included, it is preferable to disperse the biodegradable binder together with the fibers constituting the filter material in the raw material slurry during the manufacturing process using the wet papermaking method described above. If the biodegradable binder is added simultaneously with the alkyl ketene dimer, or added separately after the alkyl ketene dimer has been added, the alkyl ketene dimer may be covered by a continuous film of the biodegradable binder, which may result in insufficient water repellency. It is preferable to disperse the biodegradable binder together with the fibers constituting the filter material in the raw material slurry to form a wet sheet, and then add the alkyl ketene dimer to the wet sheet.

[0041] In this embodiment, additives such as defoaming agents and dispersants can be appropriately added to the raw material slurry, as long as they do not interfere with the effects of the present invention.

[0042] The basis weight of the filter material in this embodiment is not particularly limited, but is preferably 25 to 350 g / m². 2 , comfortably 50-250g / m 2 More preferably 70-150 g / m² 2 The basis weight is 25 g / m². 2 If the basis weight is less than 350 g / m², sufficient tensile strength and / or Gurley stiffness may not be obtained. 2 If this value is exceeded, the surface area of ​​the filter media that can be accommodated in the filter unit may become insufficient.

[0043] The PF value of the filter media in this embodiment is not particularly limited, but is preferably 4.5 or higher, more preferably 6.0 or higher, and even more preferably 7.0 or higher. This results in a filter media with a good balance between pressure loss and collection efficiency.

[0044] The tensile strength of the filter material in this embodiment is not particularly limited, as the required tensile strength varies depending on the application and post-processing method, but it is preferably 0.40 kN / m or more, and more preferably 0.45 kN / m or more. A tensile strength of 0.40 kN / m or more is sufficient for a wide range of applications.

[0045] The Gurley stiffness of the filter media in this embodiment varies depending on the application and post-processing method, and is not particularly limited, but is preferably 7.0 mN or higher, and more preferably 10.0 mN or higher. A Gurley stiffness of 7.0 mN is sufficient for many applications. [Examples]

[0046] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these.

[0047] <Example 1> Fourteen parts of fibrillated lyocell fibers (average fiber diameter 0.8 μm, length-weighted average fiber length 1.1 mm) obtained by beating lyocell fibers (manufactured by Lenzing AG) as the beaten fiber, and eighty-six parts of regenerated cellulose lyocell fibers (manufactured by Lenzing AG, average fiber diameter 12 μm, average fiber length 4 mm) as the unbeaten fiber, were mixed with tap water to a slurry concentration of 0.5% by mass and dissociated using a mixer to obtain a raw material slurry. Next, the raw material slurry obtained was made into paper using a hand-made papermaking device to obtain a wet sheet. Next, the obtained wet sheet was impregnated with an aqueous diluted solution of alkyl ketene dimer (SE2360, manufactured by Seikoh PMC Co., Ltd.) so that the alkyl ketene dimer content relative to the entire filter material was 0.01% by mass in solids. The sheet was dried using a rotary dryer at 130°C to obtain a dry sheet with a basis weight of 100 g / m².2 An air filter filter medium was obtained.

[0048] <Examples 2 to 12> An impregnation treatment was performed so that the alkyl ketene dimer content with respect to the entire filter medium was in the range of 0.05 to 10% by mass shown in Table 1 in terms of solid content. Otherwise, in the same manner as in Example 1, the basis weight was 100 to 110 g / m 2 An air filter filter medium in the range was obtained.

[0049] <Example 13> 86 parts of mercerized pulp (Porocenia, manufactured by Rayonier Inc., average fiber diameter 34 μm, average fiber length 2.6 mm), which is natural cellulose fiber as unbleached fiber, were used, and an impregnation treatment was performed so that the alkyl ketene dimer content was 1.0% by mass in terms of solid content. Otherwise, in the same manner as in Example 1, a basis weight of 101 g / m 2 An air filter filter medium was obtained.

[0050] <Example 14> 76 parts of lyocell fiber (manufactured by Lenzing AG, average fiber diameter 12 μm, average fiber length 4 mm) and 10 parts of polylactic acid-based fiber (PL01, manufactured by Unitika Ltd., average fiber diameter 13 μm, average fiber length 5 mm, melting point 170 °C) were used as unbleached fibers. Otherwise, in the same manner as in Example 13, a basis weight of 101 g / m 2 An air filter filter medium was obtained.

[0051] <Example 15> 84 parts of lyocell fiber (manufactured by Lenzing AG, average fiber diameter 12 μm, average fiber length 4 mm) and 2 parts of polyvinyl alcohol powder (Poval K-177, manufactured by Denka Co., Ltd.) as a binder were used to obtain a raw material slurry. Otherwise, in the same manner as in Example 13, a basis weight of 101 g / m 2 An air filter filter medium was obtained.

[0052] <Example 16> A raw material slurry was obtained using the same method as in Example 13, except that 76 parts of lyocell fibers (Lenzing AG, average fiber diameter 12 μm, average fiber length 4 mm) were used as non-beaten fibers and 10 parts of core-sheath type polylactic acid binder fibers (PL80, Unitika Ltd., average fiber diameter 15 μm, average fiber length 5 mm, core melting point 170°C, sheath melting point 130°C) were used as a binder, resulting in a basis weight of 101 g / m². 2 We obtained a filter material for an air filter.

[0053] <Example 17> Except for impregnating the filter material with a water-diluted solution prepared by mixing an aqueous solution of polyvinyl alcohol (POVA 28-98, manufactured by Kuraray Co., Ltd.) and alkyl ketene dimer (SE2360, manufactured by Seikoh PMC Co., Ltd.) so that the polyvinyl alcohol content was 2.0% by mass in solids and the alkyl ketene dimer content was 1.0% by mass in solids, the same method as in Example 1 was used, resulting in a basis weight of 103 g / m². 2 We obtained a filter material for an air filter.

[0054] <Comparative Example 1> Except for not performing the alkyl ketene dimer impregnation treatment, the same method as in Example 1 was used to obtain a basis weight of 100 g / m². 2 We obtained a filter material for an air filter.

[0055] <Comparative Example 2> Except for applying a diluted aqueous solution of paraffin wax water repellent (Petrox P-310, manufactured by Meisei Chemical Industry Co., Ltd.) to the filter media by impregnation treatment so that the paraffin wax water repellent content relative to the entire filter media was 1.0% by mass in solids, the same method as in Example 1 was used, resulting in a basis weight of 101 g / m². 2 We obtained a filter material for an air filter.

[0056] The filter media for air filters obtained in the examples and comparative examples were evaluated using the method described below.

[0057] <Basic weight> The basis weight was measured according to JIS P 8124:2011 "Paper and cardboard - Method for measuring basis weight".

[0058] <Thickness and density> The thickness and density were measured according to JIS P 8118:1998 "Paper and paperboard - Test method for thickness and density". The measurement pressure was 50 kPa.

[0059] <Pressure loss> The pressure loss was measured using a manometer (Manostage WO81, manufactured by Yamamoto Electric Mfg. Co., Ltd.) as the differential pressure when air was passed through the filter medium for an air filter with an effective area of 100 cm 2 at a face velocity of 5.3 cm / second.

[0060] <Transmittance> The transmittance was determined from the ratio of the number of upstream and downstream PAO particles when air containing polydisperse polyalphaolefin (PAO) particles generated by a Ruskin nozzle was passed through the filter medium for an air filter with an effective area of 100 cm 2 at a face velocity of 5.3 cm / second. The number of upstream and downstream PAO particles was measured using a laser particle counter (KC-22B, manufactured by Rion Co., Ltd.). The target particle diameter was 0.3 μm, and it was determined as the geometric mean value of the transmittance for 0.2 - 0.3 μm and 0.3 - 0.4 μm.

[0061] <PF value> The PF value was calculated using the formula shown in Equation (1) from the values of the pressure loss and the transmittance.

[0062] <Water repellency> The water repellency was measured according to MIL-STD-282.

[0063] <Tensile strength> The tensile strength was measured using a universal testing machine (Autograph AGS-X, manufactured by Shimadzu Corporation) under the conditions of a test width of 25.4 mm, a test length of 100 mm, and a tensile speed of 15 mm / min.

[0064] <Gurley stiffness> The Gurley stiffness was measured according to JAPAN TAPPI No.40:2000 "Paper and paperboard - Test method for stiffness by load bending - Gurley method".

[0065] The evaluation results of the air filter media performed using the method described above are shown in Tables 1 and 2.

[0066] [Table 1]

[0067] [Table 2]

[0068] From the results of Examples 1 to 12 in Table 1 and Comparative Example 1 in Table 2, it was found that by setting the alkyl ketene dimer content to 0.05% by mass or more, an air filter media with sufficient water repellency of 100 mm water column height or higher was obtained, and by setting it to 0.1% by mass or more, an even higher water repellency of 200 mm water column height or higher was obtained. Furthermore, by setting the alkyl ketene dimer content in the range of 0.05 to 2.0% by mass, an air filter media with a higher PF value than the case without alkyl ketene dimer was obtained, and by setting it in the range of 0.1 to 1.5% by mass, a PF value 0.8 points or more higher than the case without alkyl ketene dimer was obtained.

[0069] The results from Example 6 in Table 1 and Examples 13 and 14 in Table 2 show that by using regenerated cellulose fibers, natural cellulose fibers, and / or polylactic acid-based fibers as non-beaten fibers, sufficient water repellency (water column height of 100 mm or more), PF value (4.5 or more), tensile strength (0.4 kN / m or more), and Gurley stiffness (7.0 mN or more) were obtained.

[0070] The results from Example 6 in Table 1 and Examples 15 and 16 in Table 2 show that high tensile strength and Gurley stiffness were obtained by using a binder.

[0071] The results from Examples 15 and 17 in Table 2 show that applying alkyl ketene dimer to a sheet that already contains a binder resulted in higher water repellency than when the binder and alkyl ketene dimer were applied simultaneously.

[0072] The results from Example 6 in Table 1 and Comparative Example 2 in Table 2 show that applying an alkyl ketene dimer resulted in higher water repellency than when a paraffin wax water repellent was applied. [Industrial applicability]

[0073] The filter material for air filters of the present invention can be used in various fields such as air conditioning in factories and buildings, automobile cabins, air conditioners, air purifiers, and personal protective equipment.

Claims

1. It is a filter material made of wet nonwoven fabric, The fibers constituting the filter material include beaten fibers and unbeaten fibers. The beaten fibers are fibrillated lyocell fibers, The non-beaten fiber is a biodegradable fiber, A filter material for an air filter, characterized in that the biodegradable fibers are continuously distributed throughout the entire thickness direction of the filter material, and the filter material contains an alkyl ketene dimer.

2. The air filter material according to claim 1, characterized in that the content of the alkyl ketene dimer relative to the entire filter material is in the range of 0.05 to 2.0% by mass.

3. The filter material for air filters according to claim 1 or 2, characterized in that the biodegradable fiber, which is the non-beaten fiber, is at least one selected from the group consisting of regenerated cellulose fiber, natural cellulose fiber, and polylactic acid-based fiber.

4. The filter material for air filters according to claim 1 or 2, characterized by containing a biodegradable binder.

5. The air filter material according to claim 4, characterized in that the biodegradable binder comprises polyvinyl alcohol, polylactic acid, or polyvinyl alcohol and polylactic acid.

6. The filter material for an air filter according to claim 4, characterized in that the alkyl ketene dimer is not coated by a continuous film of the biodegradable binder.

7. A papermaking process involves forming a wet sheet by a wet papermaking method, in which a raw material slurry, in which beaten fibers and unbeaten fibers constituting the filter material are dispersed in water, and The process involves imparting an alkyl ketene dimer to the aforementioned wet sheet, The process includes a drying step of heat-drying the wet sheet to which the alkyl ketene dimer has been applied to form a dry sheet, A method for manufacturing an air filter material, characterized in that the beaten fibers are fibrillated lyocell fibers, the unbeaten fibers are biodegradable fibers, and the biodegradable fibers are continuously distributed throughout the entire thickness direction of the filter material.

8. The method for producing an air filter material according to claim 7, characterized in that the alkyl ketene dimer is added such that its content relative to the entire filter material after drying is in the range of 0.05 to 2.0% by mass.

9. The method for producing a filter material for an air filter according to claim 7 or 8, characterized in that the biodegradable fiber, which is the non-beaten fiber, is at least one selected from the group consisting of regenerated cellulose fiber, natural cellulose fiber, and polylactic acid-based fiber.

10. A method for producing an air filter material according to claim 7 or 8, characterized in that a biodegradable binder is dispersed in the raw material slurry together with the beaten fibers and the unbeaten fibers.

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