Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
  • B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
  • B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
  • B01D39/18—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being cellulose or derivatives thereof
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/04—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres having existing or potential cohesive properties, e.g. natural fibres, prestretched or fibrillated artificial fibres
  • D04H1/26—Wood pulp
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
  • D04H1/4266—Natural fibres not provided for in group D04H1/425
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
  • D21H11/18—Highly hydrated, swollen or fibrillatable fibres
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/04—Additives and treatments of the filtering material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
  • B01D2239/0604—Arrangement of the fibres in the filtering material
  • B01D2239/064—The fibres being mixed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/10—Filtering material manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
  • B01D2239/12—Special parameters characterising the filtering material
  • B01D2239/1225—Fibre length
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2401/00—Physical properties
  • D10B2401/02—Moisture-responsive characteristics
  • D10B2401/021—Moisture-responsive characteristics hydrophobic
• • D—TEXTILES; PAPER
  • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
  • D10B2505/00—Industrial
  • D10B2505/04—Filters

Definitions

• the present disclosure relates to filter media for air filters used in various fields such as air conditioning in factories and buildings, automobile cabins, air conditioners, air purifiers, personal protective equipment, etc. In particular, it has a small environmental load and is used for filtering. It relates to an air filter medium with little decrease in performance.
• Glass fiber filter media and meltblown non-woven fabric filter media are mainly used as medium- and high-performance filter media for air filters used in building air conditioning. Since glass fiber filter media are nonflammable, they are landfilled as industrial waste after use. For this reason, the environmental load at the time of disposal is large.
• the meltblown nonwoven fabric filter medium uses non-renewable and limited fossil resources (PP, etc.) as raw materials, and emits a large amount of carbon dioxide throughout its life cycle when incinerated. Also, if it is released into the environment after use, it will remain in the environment without being decomposed. For the reasons described above, there is a demand for a biodegradable filter medium that is mainly composed of renewable raw materials and has a low environmental load.
• 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).
• cellulosic fibers such as lyocell fibers are highly hygroscopic and water-absorbing, so when used in a high-humidity environment or when air currents containing moisture or dust pass through, the fibers swell and the structure of the filter media changes.
• the filtration performance of the filter material for air filters is lowered, for example, the PF value is lowered.
• the PF value is defined by Equation 1, and the higher the PF value, the higher the efficiency of collecting dust particles, the lower the pressure loss, and the higher the filtration performance of the filter medium.
• transmittance [%] 100 - collection efficiency [%]
• a method of imparting water repellency to the filter medium is effective, and as a method of imparting water repellency to the filter medium for air filters, a method using a fluorine-based water repellent agent is widely used.
• a fluorine-based water repellent agent is widely used.
• perfluoroalkyl compounds constituting fluorine-based water repellents are difficult to decompose and highly bioaccumulative, and there is a worldwide movement to restrict their use, and they are not suitable for the purpose of the present invention.
• JP 2006-167659 A Japanese Patent Application Laid-Open No. 2006-326470 JP-A-2001-79318 JP 2014-98082 A
• an object of the present disclosure is to provide an air filter filter medium that is mainly composed of renewable raw materials, is biodegradable, and has sufficient water repellency.
• fibers constituting the filter medium include beaten fibers and non-beaten fibers, the beaten fibers are fibrillated lyocell fibers, and the unbeaten fibers are biodegradable fibers,
• the mass ratio of the beaten fibers to the non-beaten fibers (beaten fibers/non-beaten fibers) is in the range of 3/97 to 20/80
• the filter medium comprises a hydrocarbon-based polymer containing no fluorine in its molecule. It is characterized by containing a water-repellent agent as a main component. According to such a configuration, it is possible to obtain a filter medium that has a small environmental load and a small drop in filtration performance during use.
• the biodegradable fiber that is the non-beaten fiber is preferably at least one selected from the group consisting of regenerated cellulose fiber, natural cellulose fiber and polylactic acid fiber.
• the hydrocarbon-based polymer which is the main component of the water repellent agent, is an acrylic polymer.
• the filter medium for an air filter according to the present invention includes a form in which the filter medium contains a surfactant. Thereby, high filtration performance can be obtained.
• the surfactant is preferably a quaternary ammonium salt.
• the water repellency specified by MIL-STD-282 is 100 mm or higher in the water column. As a result, deterioration in filtration performance during use can be suppressed.
• the fibrillated lyocell fibers which are the beaten fibers, have an average fiber diameter of 0.3 ⁇ m or more, a maximum fiber diameter of 8 ⁇ m or less, and a length-weighted average fiber length of 1 mm or more. is preferred. Reduction in collection efficiency and tensile strength of the filter material is unlikely to occur.
• the biodegradable fibers which are the non-beaten fibers, have a fiber diameter of 5 ⁇ m or more.
• the average fiber diameter is 5 ⁇ m or more, the voids necessary for uniformly distributing the beaten fibers can be maintained, and the increase in pressure loss is less likely to occur, and the collection efficiency of the filter medium is less likely to decrease.
• a filter medium that has a small environmental load and a small drop in filtration performance during use. That is, it is possible to obtain an air filter filter medium that is mainly composed of a renewable raw material, has biodegradability, and has sufficient water repellency to prevent moisture absorption of cellulosic fibers including fibrillated lyocell fibers. .
• the lyocell fiber in this embodiment is a regenerated cellulose fiber spun by an organic solvent spinning method using N-methylmorpholine-N-oxide as a solvent.
• organic solvent spinning method cellulose is dissolved as it is in an organic solvent and spun, so there is less molecular breakage, the average degree of polymerization is higher than that of other regenerated cellulose fibers, and the rigidity of the fiber is high. It has characteristics close to a circular shape. This rigidity and cross-sectional shape help maintain voids in the filter medium.
• the fibrillated lyocell fiber after beating also maintains the aforementioned characteristics of rigidity and cross-sectional shape. Furthermore, fibrillation by beating increases the surface area of the fibers that contribute to the collection of particles, thereby increasing the collection efficiency and increasing the entanglement of the fibers, thereby increasing the tensile strength of the filter medium.
• the beaten fiber in the present embodiment is a fibrillated lyocell fiber, and the blending amount of the beaten fiber is 3 to 20 parts, preferably 5 to 15 parts, based on 100 parts of the total fiber mass constituting the filter medium. , more preferably 5 to 13 parts. If the blending amount is less than 3 parts, it is difficult to obtain sufficient collection efficiency, and sufficient tensile strength cannot be obtained due to less entanglement between fibers. On the other hand, if the blending amount is more than 20 parts, the fibers are entangled with each other too much to clog the voids, resulting in a large increase in pressure loss and a decrease in the PF value compared to the increase in collection efficiency.
• a beater such as a Niagara beater, PFI mill, single disc refiner or double disc refiner can be used. In the beating, it is preferable to beat without applying an excessively strong load so as not to shorten the fiber length of the lyocell too much.
• the fibrillated lyocell fibers used in the present invention preferably have a length-weighted average fiber length of 1 mm or more, more preferably 1 to 3 mm, even more preferably 1 to 2 mm.
• the length-weighted average fiber length of fibrillated lyocell fibers was measured according to ISO 16065-2:2007 "Determination of fiber length by automated optical analysis-Part 2".
• Lyocell fibers are fibrillated by beating and the fiber diameter becomes smaller.
• the average fiber diameter of the fibril lyocell fibers used in the present embodiment is preferably 0.3 ⁇ m or more, more preferably 0.3 to 1.0 ⁇ m, and further preferably 0.3 to 0.8 ⁇ m. preferable.
• the maximum fiber diameter of the fibrillated lyocell fibers is preferably 8 ⁇ m or less, more preferably 6 ⁇ m or less, and even more preferably 4 ⁇ m or less. If the average fiber diameter is less than 0.3 ⁇ m, the fibers may be cut as the fibrillation progresses, lowering the tensile strength of the filter medium and making it impossible to maintain the voids, thereby lowering the collection efficiency. be. On the other hand, if the average fiber diameter exceeds 1.0 ⁇ m and the maximum fiber diameter exceeds 8 ⁇ m, the surface area of the fibers that contributes to particle trapping is reduced, and the trapping efficiency may be lowered.
• the fiber diameter in the present embodiment is obtained by taking a photograph of the surface of the filter medium using an electron microscope, drawing a straight line in the horizontal direction on the obtained electron microscope photograph, and measuring the fiber diameter at the intersection of the straight line and the fiber. was measured.
• the average fiber diameter was the arithmetic mean value of 200 measurements.
• the non-beaten fibers in this embodiment are biodegradable fibers that have not been beaten, and are preferably at least one selected from the group consisting of regenerated cellulose fibers, natural cellulose fibers and polylactic acid fibers. Fibers of the same type and having different fiber diameters may be blended.
• the blending amount of the non-beaten fibers in the present embodiment is 80 to 97 parts out of 100 parts of the total fiber mass constituting the filter medium. If the blending ratio is out of this range, it will be out of the range of the blending amount of the beaten fiber.
• Regenerated cellulose fibers are viscose rayon fibers spun from cellulose by the viscose method, and lyocell fibers spun by the organic solvent spinning method. These are renewable materials made from wood pulp, and have biodegradability in soil burial and biodegradability in the sea.
• Natural cellulose fibers are fibers mainly composed of cellulose extracted from plants, and include wood pulp, cotton linter pulp, hemp pulp, kenaf pulp, and mercerized pulp obtained by alkali-treating wood pulp. These are renewable raw materials made from plants, and are biodegradable when buried in the soil.
• Polylactic acid fiber is a fiber spun mainly from a polymer that chemically polymerizes lactic acid obtained by saccharification and fermentation of biomass-derived starch as a raw material. This is a renewable material made from corn or the like, and is biodegradable when buried in the ground.
• polylactic acid fibers have thermoplasticity unlike cellulosic fibers, they can impart tensile strength to the filter medium or impart thermoformability to the filter medium by heat fusion. Since polylactic acid fiber competes with food as a raw material, it is preferable to keep the blending amount low within a range in which the physical properties of the filter medium are acceptable.
• the blending amount of the polylactic acid fiber is preferably 0 to 30 parts, more preferably 0 to 20 parts, based on the total fibers in the filter medium. That is, the blending amount of the non-beaten fiber is 80 to 97 parts out of 100 parts of the total fiber mass constituting the filter medium. (80-n) to (97-n) parts of the total amount of fibers (including the case where only one side is used) are blended. However, n is preferably 30 parts or less.
• the non-beaten fibers in the present embodiment preferably have an average fiber diameter of 5 ⁇ m or more, more preferably 5 to 40 ⁇ m, still more preferably 7 to 35 ⁇ m. If the average fiber diameter is smaller than 5 ⁇ m, it becomes difficult to maintain the voids necessary for uniformly distributing the beaten fibers, which may cause an increase in pressure loss. On the other hand, if the average fiber diameter exceeds 40 ⁇ m, the difference in fiber diameter from that of the beaten fibers is large, so the pore diameter of the filter medium varies greatly, which may lead to a decrease in collection efficiency.
• the water repellent agent in the present embodiment is a repellent agent mainly composed of a hydrocarbon-based polymer containing no fluorine in the molecule, which is used to impart sufficient water repellency to prevent deterioration of filtration performance during use. It is a liquid agent, and preferably has an acrylic polymer as a main component.
• a hydrocarbon-based polymer containing no fluorine in the molecule as a main component means that the polymer component of the water repellent agent accounts for 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more.
• it is composed of a polymer composed of an organic compound having a hydrocarbon skeleton and containing oxygen, nitrogen, and the like.
• a water repellent agent containing an acrylic polymer as a main component can increase the water repellency by increasing the number of carbon atoms in the ester portion of the raw material monomer acrylic acid ester or methacrylic acid ester.
• the acrylic polymer as the main component means that 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more of the polymer component of the water repellent is acrylic acid ester and / or methacrylic It consists of a polymer polymerized using an acid ester as a main raw material monomer.
• the number of carbon atoms in the ester portion is preferably 9 or more, more preferably 12 or more.
• the water repellency of the filter medium in this embodiment is preferably 100 mm or higher, more preferably 150 mm or higher, and even more preferably 200 mm or higher.
• the content of the water repellent agent in the filter medium should be within a range that provides the required water repellency and does not impede the biodegradability of the filter medium.
• the content of the water repellent agent in the entire filter medium is preferably 0.3 to 2.0% by mass, preferably 0.3 to 1.0% by mass, and more preferably 0.3 to 0.5% by mass in terms of solid content. is.
• the surfactant in this embodiment is used to prevent the fibers in the filter medium from sticking too closely to each other to improve filtration performance.
• Surfactants having various compositions and ionic properties can be selected within a range that does not interfere with the effects of the present invention.
• quaternary ammonium salts are preferred because they are highly effective in improving filtration performance.
• the quaternary ammonium salt has antibacterial properties, it is possible to impart antibacterial properties to the filter medium.
• the surfactant content in the filter medium should be within a range that does not impede the biodegradability of the filter medium.
• the content of the surfactant in the entire filtering medium is preferably 0 to 1.0% by mass, preferably 0 to 0.5% by mass, more preferably 0.1 to 0.5% by mass in terms of solid content.
• the basis weight of the filter medium in this embodiment is not particularly limited, it is preferably 25 to 350 g/m 2 , more preferably 50 to 250 g/m 2 , still more preferably 70 to 150 g/m 2 .
• the PF value of the filter medium in this embodiment is not particularly limited, it is preferably 5 or more, more preferably 7 or more.
• the tensile strength of the filter medium in this embodiment differs depending on the application and post-processing method, and is not particularly limited. 6 kN/m or more.
• the filter medium of this embodiment is manufactured using a wet papermaking method. That is, the fibers constituting the filter medium are dispersed in water using a dispersing machine such as a pulper, and the obtained fiber slurry is deposited on a wire and dehydrated to form a sheet, and the obtained wet sheet is dried using a hot air dryer. It is dried using a dryer such as a cylinder dryer to obtain a filter medium as a dry sheet.
• a dryer such as a cylinder dryer to obtain a filter medium as a dry sheet.
• the water repellent agent and surfactant are applied, they are applied to the wet sheet before drying in the form of an aqueous dispersion by an impregnation treatment such as spraying or immersion, followed by drying.
• an impregnation treatment such as spraying or immersion
• it may be applied to the dry sheet after drying.
• Lyocell fiber fineness 1.7 dtex (fiber diameter 12 ⁇ m), fiber length 4 mm, manufacturer: Lenzing AG) is beaten using a Niagara beater, and the average fiber diameter is 0.7 ⁇ m and the maximum fiber diameter is 3.5 ⁇ m. , resulting in fibrillated lyocell fibers with a length-weighted average fiber length of 1.1 mm.
• Lyocell fiber fineness 1.7 dtex (fiber diameter 12 ⁇ m), fiber length 4 mm, manufacturer: Lenzing AG
• Rayon fiber (1) fineness 0.6 dtex (fiber diameter 7 ⁇ m), fiber length 4 mm
• product name rayon corona SD
• Rayon fiber (2) fineness 2.2 dtex (fiber diameter 14 ⁇ m), fiber length 5 mm
• product name: rayon corona SB manufacturer: Daiwabo Rayon Co., Ltd.
• Rayon fiber (3) fineness 9.0 dtex (fiber diameter 28 ⁇ m), fiber length 8 mm
• product name: rayon corona CD manufacturer: Daiwabo Rayon Co., Ltd.
• Mercerized pulp fiber average fiber diameter 34 ⁇ m, average fiber length 2.8 mm
• product name Porocenia
• Cotton linter fiber (average fiber diameter 18 ⁇ m, average fiber length 2 mm, product name: PS711, manufacturer: Shandong Silver Hawk Chemical Fiber Co.), Polylactic acid single fiber (fineness 1.7 dtex (fiber diameter 13 ⁇ m), fiber length 5 mm, melting point 170° C., product name: Terramac PL01, manufacturer: Unitika Ltd.), Or polylactic acid core-sheath fiber (fineness 2.2 dtx (fiber diameter 15 ⁇ m), fiber length 5 mm, core melting point 170 ° C., sheath melting point 130 ° C., product name: Terramac PL80, manufacturer: Unitika Ltd.), any of They were mixed at the part ratios shown in Tables 1 to 3, tap water was added so that the slurry concentration was 0.5% by mass, and the fibers were defiberized using a pulper to obtain a fiber slurry.
• Example 17 the resulting wet sheet was coated with a water repellent agent (product name: Unidyne XF-5005, manufacturer: Daikin Industries, Ltd.) and a quaternary ammonium salt surfactant (product Name: Cathiogen TMP, Manufacturer: Daiichi Kogyo Seiyaku Co., Ltd.), the water repellent content in the filter medium is 0.3 mass% in solid content, and the surfactant content is 0 in solid content. 0.2% by mass was imparted by impregnation treatment and dried in a rotary dryer at 130° C. to obtain a filter medium for an air filter.
• a water repellent agent product name: Unidyne XF-5005, manufacturer: Daikin Industries, Ltd.
• a quaternary ammonium salt surfactant product Name: Cathiogen TMP, Manufacturer: Daiichi Kogyo Seiyaku Co., Ltd.
• Thickness [mm] It was measured according to JIS P 8118;1998. In addition, the measurement pressure was set to 50 kPa.
• thermoformability A thermoforming mold having 3 mm deep irregularities on the top and bottom is heated to 200°C, a filter medium is sandwiched between them, and a pressure of 1 kgf/cm 2 is applied for 5 seconds to perform thermoforming. The molded depth and breakage of the filtered media were evaluated. When the molding depth was 2 mm or more and there was no breakage, it was rated as ⁇ . The thermoformability was evaluated only in Examples 2 and 14-16.
• Tables 1 and 2 show the effects of the blending amount of the beaten fiber and the type of the non-beaten fiber at a constant basis weight, and also the results when the water repellent is not contained and when the surfactant is contained. is shown. From these results, the PF values were as low as less than 5 in Comparative Examples 1 and 4, in which the blending amount of the beaten fiber was more than 20 parts. Comparative Examples 2, 3 and 5, in which the blending amount of the beaten fiber was less than 3 parts, had a low tensile strength of less than 0.4 kN/m. In Examples 14 to 16, in which polylactic acid fibers were blended as non-beaten fibers, the tensile strength was high and thermoformability was imparted. In Comparative Example 6 containing no water repellent, water repellency was not exhibited. Example 17 containing a surfactant had a higher PF value than Example 2 containing no surfactant.
• Table 3 shows the effect of basis weight when the ratio of the number of fibers is adjusted so that the maximum value of pressure loss is 40 Pa.
• Examples 18 to 28 are examples in which the basis weight was adjusted in the range of 25 to 350 g/m 2 , but all of them are biodegradable, and have good PF value and water repellency. became.
• the filter medium for air filters of the present invention can be used for filter mediums for air filters used in various fields such as factory and building air conditioning, automobile cabins, air conditioners, air purifiers, and personal protective equipment.

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