Filter medium for air filter and method for manufacturing the same

Abstract

The present invention aims to provide a filter medium for an air filter having sufficient rigidity and strength for practical use, a high PF value, and water repellency, and to provide such a filter medium using a simple production method. The filter medium for an air filter of the present invention comprises a wet-laid nonwoven fabric containing glass fibers, and is characterized in that the filter medium contains a cationic binder resin, a fluororesin, and a cationic surfactant, wherein the solid content mass ratio of the fluororesin to the surfactant is within a range of 30 / 70 to 80 / 20.

Description

Technical Field

[0001] The present invention relates to a filter medium for an air filter used in an air filter installed in a semiconductor, liquid crystal, clean room for the food industry, a building air conditioner, an air purifier, or the like. Background Art

[0002] To capture and remove submicron and micron particles from the air, air filters equipped with filter media are typically used. Air filters are categorized by particle size and capture efficiency into coarse dust filters, medium efficiency filters, HEPA (High Efficiency Particulate Air) filters, and ULPA (Ultra Low Penetration Air) filters, with higher performance grades increasing.

[0003] Pressure loss and capture efficiency are characteristics that indicate the filtration performance of air filter media. Higher pressure loss increases the energy consumption required for ventilation and the filter's operating costs. Therefore, ideal filter media have low pressure loss and high particle capture efficiency. One indicator of filtration performance based on this perspective is the PF value defined by equation 1. Furthermore, transmittance [%] = 100 - capture efficiency [%], so filter media with a high PF value are ideal.

[0004] [Number 1]

[0005]

[0006] Another physical property required of air filter media is water repellency. Low water repellency can lead to the infiltration of sealants used when processing the filter media into air filter units. Furthermore, sufficient water repellency prevents clogging of the filter media's pores by condensation caused by temperature fluctuations or water droplets generated by the passage of high-humidity air.

[0007] Furthermore, as physical properties required for the filter medium for air filters, rigidity and strength can be cited. If the rigidity is low, there is a risk that the peaks of the pleats will come into contact with each other due to deflection during ventilation, resulting in an increase in pressure loss. In addition, if the strength is low, there is a risk that the filter medium will break or crack when the filter medium pleats are processed into an air filter unit or when used for ventilation. Therefore, it is necessary to impart practically sufficient rigidity and strength to the filter medium. However, the glass fiber used in the filter medium does not have self-adhesive properties, and the rigidity and strength are insufficient. Therefore, adhesives such as adhesive resins and adhesive fibers are generally used. Among them, it is ideal to use an adhesive resin that can impart rigidity and strength at the same time, but if the adhesive resin is attached to the filter medium, the adhesive film may clog the pores of the filter medium, thereby increasing the pressure loss, or cover the mesh structure of the glass fiber having a large surface area, thereby hindering particle capture, thereby reducing the PF value.

[0008] As methods for improving the PF value of filter media for air filters, the following methods have been proposed: a method of imparting a cationic surfactant as a quaternary ammonium salt to the filter media for air filters (for example, see Patent Document 1); a method of imparting a fluorine-based water repellent in addition to a binder resin and a surfactant containing either or both of a sulfate ester salt or a sulfonate salt (for example, see Patent Document 2); and a method of imparting a binder resin, a fluorine-based surfactant containing a perfluoroalkyl compound, and a water repellent (for example, see Patent Document 3).

[0009] As a method for further improving the PF value, a method of providing a fully meltable binder fiber and a core-sheath binder fiber has been proposed (for example, see Patent Document 4).

[0010] [Background Art Literature]

[0011] [Patent Document]

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-94580

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-221456

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-42762

[0015] Patent Document 4: Japanese Patent Application Laid-Open No. 2018-38983 Summary of the Invention

[0016] [Problems to be solved by the invention]

[0017] As described above, the techniques of Patent Documents 1 to 3 have been proposed as methods for improving the PF value of a filter medium for an air filter. However, further improvements in the PF value and water repellency are required.

[0018] Furthermore, the method disclosed in Patent Document 4 can obtain sufficient strength, but has a problem of insufficient rigidity.

[0019] As described above, air filter media are required to have practically sufficient rigidity, strength, and water repellency, as well as a high PF value. However, conventional technologies have been unable to achieve these properties, particularly sufficient rigidity, PF value, and water repellency. Therefore, the present invention aims to provide an air filter media having practically sufficient rigidity and strength, a high PF value, and water repellency, and to provide such a filter media using a simple manufacturing method.

[0020] [Technical means to solve the problem]

[0021] The filter medium for an air filter of the present invention comprises a wet-laid nonwoven fabric containing glass fibers, characterized in that the filter medium comprises a cationic binder resin, a fluororesin, and a cationic surfactant, wherein the solid content mass ratio of the fluororesin to the surfactant is within a range of 30 / 70 to 80 / 20. When the glass fibers are bonded with the cationic binder resin, the fluororesin and the cationic surfactant are adsorbed simultaneously on the glass fibers at the aforementioned ratio, thereby achieving a filter medium for an air filter having sufficient rigidity and strength for practical use, a high PF value, and water repellency.

[0022] In the filter medium for an air filter of the present invention, the fluororesin is preferably a nonionic or cationic fluororesin. Since glass fiber has a negative surface charge, the fluororesin is more easily adsorbed on the glass surface, thereby improving the water repellency.

[0023] In the filter medium for an air filter of the present invention, the total solid content of the binder resin, the fluororesin, and the surfactant contained in the filter medium is preferably 2 to 12% by mass relative to the entire filter medium. The filter medium can have sufficient rigidity and strength with a high PF value.

[0024] In the filter medium for an air filter of the present invention, the wet-laid nonwoven fabric preferably comprises glass wool fibers having a fiber diameter of 1 to 10 μm, glass wool fibers having a fiber diameter of less than 1 μm, and chopped glass fibers having a fiber diameter of 4 to 30 μm as the glass fibers. This facilitates obtaining a high PF value and high strength.

[0025] In the filter medium for an air filter of the present invention, the filter medium further comprises binder fibers, and the solid content by mass of the binder fibers, the binder resin, the fluororesin, and the surfactant contained in the filter medium can be from 0% to 30% relative to the total filter medium. This can further improve the rigidity and strength of the filter medium without significantly reducing the PF value.

[0026] The method for producing a filter medium for an air filter according to the present invention comprises the following steps: forming a wet sheet from a slurry containing glass fibers using a wet papermaking method; impregnating the wet sheet with an aqueous dispersion containing a cationic binder resin, a fluororesin, and a cationic surfactant, wherein the solids mass ratio of the fluororesin to the surfactant is within a range of 30 / 70 to 80 / 20; and drying the wet sheet impregnated with the aqueous dispersion to obtain a dried sheet. This method produces a filter medium for an air filter that has sufficient rigidity and strength for practical use, as well as a high PF value and water repellency.

[0027] [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a filter medium for an air filter that has practically sufficient rigidity and strength and also has a high PF value and water repellency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a graph showing the relationship between the solid content mass ratio of fluororesin / surfactant and the PF value at 0.10 to 0.15 μm.

[0030] Figure 2 This is a graph showing the relationship between the solid content mass ratio of fluororesin / surfactant and water repellency. DETAILED DESCRIPTION

[0031] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. The embodiments can be modified in various ways as long as the effects of the present invention are achieved.

[0032] The filter medium for an air filter according to this embodiment comprises a wet-laid nonwoven fabric containing glass fibers. The filter medium contains a cationic binder resin, a fluororesin, and a cationic surfactant, with the solids mass ratio of the fluororesin to the surfactant being between 30 / 70 and 80 / 20. Furthermore, during the filter medium manufacturing process, a wet sheet formed from a slurry containing glass fibers by wet papermaking is impregnated with an aqueous dispersion containing a cationic binder resin, a fluororesin, and a cationic surfactant, with the solids mass ratio of the fluororesin to the surfactant being between 30 / 70 and 80 / 20. Through the impregnation, the fluororesin and the surfactant are simultaneously adsorbed onto the glass fibers. The impregnated sheet is then dried. In the filter medium, the glass fibers are uniformly dispersed, preventing aggregation of the glass fibers, thereby increasing the surface area of ​​the filter medium. Furthermore, the surface tension of the impregnation liquid is reduced by the surfactant, thereby preventing the surface or pores of the filter medium from being clogged by the binder resin. This allows for a filter medium having a higher PF value than when impregnated with only the binder resin.

[0033] The solid content mass ratio of the fluororesin and the cationic surfactant in the filter medium in this embodiment (fluororesin / surfactant) is 30 / 70 to 80 / 20, more preferably 40 / 60 to 80 / 20. By setting this mass ratio, a filter medium for an air filter having both a high PF value (for example, 11 or more) and high water repellency (for example, 508 mm water column height or more) can be obtained. If the mass ratio of the fluororesin is less than 30 and the mass ratio of the surfactant is greater than 70, the fluororesin will not be fully adsorbed on the glass fiber, and thus the PF value and water repellency will decrease. If the mass ratio of the fluororesin is greater than 80 and the mass ratio of the surfactant is less than 20, the surfactant will not be fully adsorbed on the glass fiber, and thus the PF value will decrease.

[0034] The fluororesin used in the present embodiment is a resin containing a fluoroalkyl group in the molecule, and has characteristics such as water repellency, oil repellency, and non-adhesiveness by the repulsive force generated by the fluorine atoms. Preferably, a fluororesin containing an aqueous emulsion type or an aqueous dispersion type containing a perfluoroalkyl resin commercially available as a water repellent, an oil repellent, or an antifouling agent is used. Fluororesin is preferably nonionic or cationic, more preferably a cationic fluororesin that is easily adsorbed on glass fiber. Because glass fiber has a negative surface charge, fluororesin is more easily adsorbed on the glass surface, and the water repellent effect is improved. Cationicity described herein refers to that the fluororesin itself or an emulsifier, etc. are cationic, and the colloidal particles of the fluororesin dispersed in water have a positive surface charge. By using a cationic fluororesin, it is easy to be adsorbed on glass fiber with a negative surface charge in water.

[0035] The surfactant used in this embodiment is selected from cationic surfactants. Examples of cationic surfactants include primary and tertiary amine salts and quaternary ammonium salts. In this embodiment, as long as the filter medium contains a cationic surfactant, it may also contain a nonionic surfactant, as long as the effects of the present invention are not affected.

[0036] In the present embodiment, in order to give the rigidity and strength required for the air filter filter medium, a binder resin is used and selected from cationic binder resins. Cationicity described herein refers to that the binder resin itself or an emulsifier is cationic, meaning that the colloidal particles of the binder resin dispersed in water have a positive surface charge. By using a cationic binder resin, the surface of the glass fiber can be efficiently coated, and therefore, the improvement of rigidity and strength and the manifestation of water repellency can be taken into account. On the other hand, if anionic binder resins are used, the effect brought by the surface of the glass fiber can not be obtained so efficiently, and when mixed with the cationic fluororesin and / or cationic surfactant used in the present embodiment, cohesion easily occurs, and it is difficult to use. As binder resin, for example, polyacrylate resin, polystyrene butadiene resin, polyvinyl acetate resin, polyurethane resin, an aqueous dispersion comprising them can be used. In addition, as mentioned above, the fluororesin used in the present embodiment is less effective in imparting strength because the fluorine atoms can produce repulsion, and therefore, is not included in the binder resin described herein.

[0037] The total solid content of the binder resin, fluororesin, and surfactant in the filter medium is preferably 2-12% by mass, more preferably 4-9% by mass, relative to the total weight of the filter medium. If the content of these components is less than 2%, sufficient strength may not be achieved, while if the content exceeds 12%, the PF value may decrease.

[0038] The filter medium for the air filter in this embodiment comprises a wet-laid non-woven fabric containing glass fibers. Since glass fibers have high rigidity, the gaps required for air to pass through the filter medium can be sufficiently maintained, and a high PF value can be obtained. As glass fibers, glass wool fibers and chopped glass fibers can be used. The glass wool fibers described herein are amorphous and discontinuous cotton-like glass fibers with a certain degree of distribution width of fiber diameter produced by flame extension or rotation. The fiber diameter generally ranges from about 0.1 to about 10 μm. Since there is a certain degree of distribution width, the value of the fiber diameter is generally expressed as an average fiber diameter. The fiber diameter of the glass wool fibers used in this embodiment is also an average fiber diameter. On the other hand, chopped glass fibers are shaped and straight glass fibers that are cut into a specific fiber length from continuous glass fibers spun from a spinneret having a specific diameter. The fiber diameter generally ranges from about 4 to about 30 μm, and the fiber length generally ranges from about 1.5 to about 25 mm. In the filter medium of this embodiment, glass wool fibers with a relatively fine fiber diameter and irregular shape improve capture efficiency and maintain voids within the filter medium. Chopped glass fibers with a relatively coarse fiber diameter and a straight shape provide the strength and rigidity required for filter unit processing and use. However, during the filter medium manufacturing process, the fibers tend to accumulate horizontally. Therefore, a high chopped glass fiber content tends to increase the density of the filter medium. In this embodiment, when chopped glass fibers are used as the glass fibers, the chopped glass fiber content is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 10% by mass, relative to the total fiber mass of the filter medium.

[0039] In this embodiment, the average fiber diameter of the glass wool fibers is not particularly limited, but is preferably 0.1 to 10 μm, more preferably 0.2 to 7 μm. In order to obtain a high PF value, it is preferred that at least a portion of the glass fibers have a fiber diameter of less than 1 μm.

[0040] In this embodiment, binder fibers may be used to assist the strength-imparting effect of the binder resin. Binder fibers are fibers that are added to a slurry containing glass fibers and impart strength through melt bonding, hydrogen bonding, physical crosslinking, etc., and can be freely selected within a range that does not impair the effects of this embodiment. For example, they may be polyvinyl alcohol fibers, polyester fibers, polyolefin fibers, etc. In this embodiment, among these fibers, melt-bonding binder fibers are preferably used. As forms of melt-bonding binder fibers, there are parallel-type binder fibers in which a meltable portion and a non-meltable portion are adjacently composited, core-sheath-type binder fibers having a non-meltable core and a meltable sheath, or fully molten binder fibers that melt as a whole and help to bond main fibers such as glass fibers to each other. The blending ratio of the binder fibers is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and even more preferably 0 to 10% by mass relative to the total fiber mass of the fibers in the filter medium. In addition to the form in which the filter medium for an air filter contains any one of parallel-type binder fibers, core-sheath-type binder fibers, and fully molten binder fibers, the melt-bonding binder fibers may also contain two or three types. Examples of the two types include a combination of side-by-side binder fibers and core-sheath binder fibers, a combination of side-by-side binder fibers and fully meltable binder fibers, or a combination of core-sheath binder fibers and fully meltable binder fibers.

[0041] In this embodiment, the filter medium further includes binder fiber. The solid content by mass of the binder fiber, binder resin, fluororesin, and surfactant contained in the filter medium can be between 0% and 30% relative to the total filter medium. In this embodiment, since the filter medium includes the binder resin, the binder fiber is not required, but may be included in the filter medium as an auxiliary agent. However, if the solid content by mass of the binder fiber, binder resin, fluororesin, and surfactant contained in the filter medium exceeds 30%, the PF value may be reduced, thereby reducing the flame retardancy of the filter medium.

[0042] In the production process of the air filter medium of this embodiment, raw material fibers are dispersed in water to obtain a raw material slurry, which is then formed into a sheet using a wet papermaking method to obtain a wet sheet. The water used for dispersion and papermaking is preferably acidic, more preferably having a pH of 2 to 4. Dispersion and papermaking under acidic conditions facilitates dispersion of the glass fibers, improves wet paper strength, and facilitates handling.

[0043] In the filter medium manufacturing process of this embodiment, the wet sheet obtained by the above method is impregnated with an aqueous dispersion containing a cationic binder resin, a fluororesin, and a cationic surfactant, and then dried to obtain an air filter medium. Impregnating the sheet with the binder resin, fluororesin, and surfactant before drying enhances the effectiveness of the present invention. Drying the sheet is preferably performed using a multi-drum dryer, Yankee dryer, or hot air dryer in a papermaking machine, or a rotary dryer or circulating dryer in a hand sheeting machine, at a temperature of, for example, 100 to 170°C, more preferably 120 to 160°C.

[0044] In the present embodiment, additives such as a defoaming agent may be appropriately added to the binder resin, the fluororesin, and the surfactant aqueous dispersion within a range that does not impair the effects of the present invention.

[0045] [Example]

[0046] The present invention is described below with reference to specific examples, but the present invention is not limited to these descriptions. In the examples, "parts" represent the solid content by mass of the fibers in the raw material slurry or the solid content by mass of the components in the impregnation liquid, assuming the total amount of all fibers in the raw material slurry is 100 parts, and the binder resin in the impregnation liquid is 100 parts. For impregnation liquids that do not contain a binder resin, the total amount is assumed to be 100 parts. In the examples, "%" represents the solid content by mass of the components in the impregnation liquid or the solid content by mass of the components in the filter medium.

[0047] <Example 1>

[0048] A raw material slurry was obtained by dissociating 60 parts of glass wool (B-06-F, manufactured by Unifrax Co.) with an average fiber diameter of 0.65 μm, 30 parts of glass wool (B-26-R, manufactured by Unifrax Co.) with an average fiber diameter of 2.44 μm, and 10 parts of chopped glass fibers (EC-6-6-SP, manufactured by Unifrax Co.) with an average fiber diameter of 6 μm and a cut length of 6 mm using a desktop dissociator and acidic water with a pH of 3.0. Next, 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Corporation), 1.5 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Corporation), 3.5 parts of a cationic surfactant (Cateogen TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water were mixed and the solid content was adjusted to 1.8% to obtain an impregnation solution. This impregnation solution was applied to wet paper to impregnate the wet paper, and the wet paper was dried using a rotary dryer at 130°C to obtain a basis weight of 70 g / m2. 2The filter medium for an air filter has an impregnation component content of 5.2%.

[0049] <Example 2>

[0050] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 2 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 3 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water, and adjusting the solid content concentration to 1.8%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was adjusted to 1.8%. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0051] <Example 3>

[0052] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 3 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 2 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water, and adjusting the solid content concentration to 1.5%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was adjusted to 1.5%. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0053] <Example 4>

[0054] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 4 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 1 part of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water, and adjusting the solid content concentration to 1.2%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was adjusted to 1.2%. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0055] <Example 5>

[0056] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 2 parts of a nonionic fluororesin (AsahiGuard AG-E550D, manufactured by AGC Co., Ltd.), 3 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water, and adjusting the solid content concentration to 1.8%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was adjusted to 1.8%. 2 The filter medium for an air filter has an impregnation component content of 4.0%.

[0057] <Example 6>

[0058] 60 parts of glass wool (B-06-F, manufactured by Unifrax Co.) having an average fiber diameter of 0.65 μm, 12 parts of glass wool (B-26-R, manufactured by Unifrax Co.) having an average fiber diameter of 2.44 μm, 10 parts of chopped glass fibers (EC-6-6-SP, manufactured by Unifrax Co.) having an average fiber diameter of 6 μm and a cut length of 6 mm, and 18 parts of core-sheath binder fibers having a core / sheath of polyester / polyester (Melty 4080, manufactured by Unitika Co., Ltd.) having a cut length of 5 mm were disintegrated using acidic water having a pH of 3.0 in a table disintegrator. A product having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the above-mentioned disintegration was carried out using acidic water having a pH of 3.0. 2 The filter medium for an air filter has an impregnation component content of 5.1%.

[0059] <Example 7>

[0060] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 2 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 3 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 4.8%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the above-mentioned impregnation liquid was mixed. 2 The filter medium for an air filter has an impregnation component content of 11.8%.

[0061] <Comparative Example 1>

[0062] The following impregnation liquid was used, which was obtained by mixing a cationic binder resin (Boncoat SFC-54, manufactured by DIC Corporation) and water and adjusting the solid content concentration to 0.40%. The same method as in Example 1 was used except that the impregnation liquid was obtained by mixing a cationic binder resin (Boncoat SFC-54, manufactured by DIC Corporation) and water and adjusting the solid content concentration to 0.40%. 2 The filter medium for an air filter has an impregnation component content of 5.5%.

[0063] <Comparative Example 2>

[0064] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 5 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 2.0%. The same method as in Example 1 was used except that the impregnation liquid was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 5 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 2.0%. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0065] <Comparative Example 3>

[0066] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 1 part of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 4 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water, and adjusting the solid content concentration to 2.0%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was adjusted to 2.0%. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0067] <Comparative Example 4>

[0068] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 4.5 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 0.5 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 1.1%. A film having a basis weight of 70 g / m2 was obtained in the same manner as in Example 1 except that the impregnation liquid was used. 2 The filter medium for an air filter has an impregnation component content of 5.2%.

[0069] <Comparative Example 5>

[0070] The following impregnation liquid was used, which was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 5 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), and water and adjusting the solid content concentration to 1.1%. The same method as in Example 1 was used except that the impregnation liquid was obtained by mixing 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Co., Ltd.), 5 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), and water and adjusting the solid content concentration to 1.1%. 2 The filter medium for an air filter has an impregnation component content of 5.5%.

[0071] <Comparative Example 6>

[0072] The following impregnation liquid was used, which was obtained by mixing 60 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 40 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 0.10%. The same method as in Example 1 was used except that the impregnation liquid was obtained by mixing 60 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Co., Ltd.), 40 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and water and adjusting the solid content concentration to 0.10%. 2 The filter medium for an air filter has an impregnation component content of 0.23%.

[0073] <Comparative Example 7>

[0074] A 70 g / m² slurry was obtained in the same manner as in Example 1 except for the impregnation step. 2 Filter media for air filters.

[0075] <Comparative Example 8>

[0076] When 100 parts of a cationic binder resin (Boncoat SFC-54, manufactured by DIC Corporation), 3 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Corporation), 2 parts of an anionic surfactant (Hytenol 330T, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and water were mixed to a solids concentration of 1.5%, agglomerates formed. Therefore, it was not possible to produce an air filter medium using this impregnation solution.

[0077] <Comparative Example 9>

[0078] 100 parts of an anionic binder resin (Boncoat AN-1190S, manufactured by DIC Corporation), 3 parts of a cationic fluororesin (AsahiGuard AG-E060, manufactured by AGC Inc.), 2 parts of a cationic surfactant (CATIOGEN TMP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and water were mixed so that the solid content concentration became 1.5%, and as a result, aggregates were produced. Therefore, it was impossible to produce a filter medium for an air filter using this impregnating liquid.

[0079] Regarding the evaluation of the filter media for air filters obtained in the examples and comparative examples, the method shown below was used.

[0080] <Pressure loss>

[0081] Regarding the pressure loss, the differential pressure when ventilating a filter medium for an air filter with an effective area of 100 cm² at a face velocity of 5.3 cm / sec was measured using a manometer (Manostar Gauge WO81, manufactured by Yamamoto Electric Works Co., Ltd.) as the pressure loss. 2 The ratio of the number of upstream and downstream PAO particles when air containing polydisperse poly-α-olefin (PAO) particles generated by a Raskin nozzle passed through a filter medium for an air filter with an effective area of 100 cm² at a face velocity of 5.3 cm / sec was measured using a laser particle counter (KC-18, manufactured by RION Co., Ltd.), and the transmittance was obtained from this ratio. The target particle size was set to 0.10 - 0.15 μm.

[0082] <Transmittance>

[0083] Regarding the transmittance, the number of upstream and downstream PAO particles when air containing polydisperse poly-α-olefin (PAO) particles generated by a Raskin nozzle passed through a filter medium for an air filter with an effective area of 100 cm² at a face velocity of 5.3 cm / sec was measured using a laser particle counter (KC-18, manufactured by RION Co., Ltd.), and the transmittance was obtained from the ratio of the number of upstream and downstream particles. The target particle size was set to 0.10 - 0.15 μm. 2 The ratio of the number of upstream and downstream PAO particles when air containing polydisperse poly-α-olefin (PAO) particles generated by a Raskin nozzle passed through a filter medium for an air filter with an effective area of 100 cm² at a face velocity of 5.3 cm / sec was measured using a laser particle counter (KC-18, manufactured by RION Co., Ltd.), and the transmittance was obtained from this ratio. The target particle size was set to 0.10 - 0.15 μm.

[0084] <PF value>

[0085] Regarding the PF value, it was calculated using the formula shown in Equation (1) based on the values of the pressure loss and particle transmittance. The target particle size was set to 0.10 - 0.15 μm.

[0086] <Gurley stiffness>

[0087] Regarding the Gurley stiffness, it was measured using a Gurley stiffness tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) under the conditions of a test width of 1 inch and a test length of 2 inches.

[0088] <Tensile strength>

[0089] Regarding the tensile strength, it was measured using an automatic stereoplotter AGX-S (manufactured by Shimadzu Corporation) under the conditions of a test width of 1 inch, a test length of 100 mm, and a tensile speed of 15 mm / min.

[0090] <Water repellency>

[0091] Water repellency is measured according to MIL-STD-282.

[0092] The evaluation results of the filter media for air filters conducted by the above method are shown in Tables 1 and 2. In addition, using the results of Examples 1 to 4 and Comparative Examples 2 to 5, graphs showing the relationship between the solid content mass ratio of fluororesin / surfactant and the PF value at 0.10 to 0.15 μm and water repellency are shown in Tables 1 and 2. Figure 1 and Figure 2 middle.

[0093]

[0094]

[0095] According to Examples 1 to 4, when a cationic binder resin is included and a cationic fluororesin and a cationic surfactant are included in a ratio ranging from 30 / 70 to 80 / 20, a filter medium having practically sufficient strength and rigidity, a high PF value (11 or more), and water repellency (508 mm water column height or more) can be obtained. According to Example 5, when a nonionic fluororesin is included, although the water repellency is lower than that of Example 2, a filter medium having the same characteristics can be obtained. In other words, it can be seen that Example 2 using a cationic fluororesin is more preferable. According to Example 6, when a binder fiber is used, although the PF value is lower than that of Example 2, a filter medium having high strength and rigidity can be obtained. According to Example 7, when the amount of impregnation component attached is increased to about 12%, although the PF value is lower than that of Example 2, a filter medium having high strength, rigidity, and water repellency can be obtained.

[0096] According to Comparative Example 1, when no fluororesin and surfactant were included, the PF value was low. According to Comparative Example 2, when no fluororesin was included, the PF value and water repellency were low. According to Comparative Example 3, when the fluororesin blending ratio was low, the PF value and water repellency were low. According to Comparative Example 4, when the surfactant blending ratio was low, the PF value was low. According to Comparative Example 5, when no surfactant was included, the PF value was low. According to Comparative Example 6, when no binder resin was included, the rigidity and strength were low. According to Comparative Example 7, when no impregnation component was included, the rigidity and strength were low, and water repellency could not be obtained at all. According to Comparative Example 8, when the surfactant was anionic, agglomeration occurred due to the compatibility of the chemicals, and thus a filter medium could not be produced. According to Comparative Example 9, when the binder resin was anionic, agglomeration occurred due to the compatibility of the chemicals, and thus a filter medium could not be produced.

Claims

1. A filter medium for an air filter comprising a wet-laid nonwoven fabric containing glass fibers, characterized in that: The filter medium contains a cationic binder resin, a fluororesin, and a cationic surfactant, and does not contain an anionic surfactant. The solid content mass ratio of the fluororesin to the surfactant is within a range of 30 / 70 to 80 / 20.

2. The filter medium for an air filter according to claim 1, wherein The fluororesin is a nonionic or cationic fluororesin.

3. The filter medium for an air filter according to claim 1, wherein The total solid content by mass of the binder resin, the fluororesin, and the surfactant contained in the filter medium is 2 to 12% relative to the entire filter medium.

4. The filter medium for an air filter according to claim 2, wherein: The total solid content by mass of the binder resin, the fluororesin, and the surfactant contained in the filter medium is 2 to 12% relative to the entire filter medium.

5. The filter medium for an air filter according to any one of claims 1 to 4, characterized in that The wet non-woven fabric includes glass wool fibers with a fiber diameter of 1 to 10 μm, glass wool fibers with a fiber diameter less than 1 μm, and short-cut glass fibers with a fiber diameter of 4 to 30 μm as the glass fibers.

6. The filter medium for an air filter according to any one of claims 1 to 4, characterized in that The filter medium further includes binder fibers, and the blending ratio of the binder fibers in the filter medium is 0 to 30% by mass relative to the total fiber mass of the fibers in the filter medium.

7. The filter medium for an air filter according to claim 5, wherein: The filter medium further includes binder fibers, and the blending ratio of the binder fibers in the filter medium is 0 to 30% by mass relative to the total fiber mass of the fibers in the filter medium.

8. A method for manufacturing a filter medium for an air filter, characterized in that The steps include: a step of forming a sheet of a slurry containing glass fibers by a wet papermaking method to form a wet sheet; impregnating the wet sheet with an aqueous dispersion comprising a cationic binder resin, a fluororesin, and a cationic surfactant, and containing no anionic surfactant, wherein the solid content mass ratio of the fluororesin to the surfactant is within a range of 30 / 70 to 80 / 20; as well as A step of drying the wet sheet impregnated with the aqueous dispersion to obtain a dry sheet.

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