Air filter and its manufacturing method

Abstract

To provide an air filter where air containing oil mist and dust is cleaned and clogging is suppressed.SOLUTION: An air filter includes unwoven fabric where many pores penetrating between one surface to which air containing oil mist and dust flows in and the other surface to which one surface opposes and from which air outflows are formed between fibers. A multi-functional coating film containing metal oxide particles (B) being bonded with a fluorine-based functional group component (A) containing a perfluoro ether structure and having an average particle diameter of 2-90 nm, a self-reaction type carboxyl group containing substance (C) and a thickener (D) is formed on the fiber surface of the unwoven fabric. The multi-functional coating film contains 1.5-15 mass% fluorine-based functional group component (A), 0.3-3.0 mass% thickener (D) and 15-70 mass% component (A) and particle (B). A mass ratio (A / B) is 0.02-0.5. The permeability of the air filter is 1-30 ml / cm2 / s.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an air filter that purifies air containing oil mist and dust, and a manufacturing method thereof. More specifically, the present invention relates to an air filter having a multifunctional coating film with weak hydrophilicity and oil repellency formed on the fiber surface of a nonwoven fabric, and a manufacturing method thereof. In this specification, weak hydrophilicity refers to a property in which, after 0.1 mL of water is dropped onto a horizontally placed air filter from above, the water remains on the filter for 60 seconds or more, and the water penetrates into the air filter after 1 hour. [Background technology]

[0002] When machine tools such as cutting machines and turning machines that process metal products using cutting oil operate at high speeds, the cutting oil scatters, generating oil mist and, at the same time, dust. This oil mist and dust worsen the working environment and reduce work efficiency. For this reason, air filter media that can suppress clogging due to not only dust floating in the air but also oil mist have been proposed as air filters that purify air containing oil mist and dust (for example, Patent Document 1 (Claim 1, paragraphs

[0006] ,

[0021] ,

[0045] , and paragraphs

[0053] to

[0060] ).

[0003] This air filter medium includes a first PTFE (polytetrafluoroethylene) porous membrane and a second PTFE porous membrane, and the airflow passes from the first main surface of the air filter medium through the first PTFE porous membrane and the second PTFE porous membrane in this order to the second main surface of the air filter medium. The thickness of the first PTFE porous membrane is in the range of 4 to 40 μm, and the specific surface area of ​​the first PTFE porous membrane is 0.5 m. 2 / g or less, and the specific surface area of ​​the second porous PTFE membrane is 1.5 to 10 m, which is larger than that of the first porous PTFE membrane. 2 / g or less.

[0004] The first and second porous PTFE membranes are each produced by molding a mixture of PTFE fine powder and a liquid lubricant into a sheet-like molding. The first porous PTFE membrane is produced by stretching the sheet-like molding in the longitudinal (MD) direction while heating at a temperature above the melting point of PTFE (327°C) and at a stretching ratio of 50 times or more, and then stretching it in the transverse (TD) direction while heating at a temperature of 130 to 400°C to 5 to 8 times its original length. The second porous PTFE membrane is produced by stretching a PTFE sheet-like molding in the MD direction while heating at a temperature below the melting point of PTFE (270 to 290°C) to 15 to 40 times its original length, and then stretching it in the TD direction while heating at a temperature of 120 to 130°C to 15 to 40 times its original length, the same stretching ratio as in the MD stretching. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-51546 Summary of the Invention [Problem to be solved by the invention]

[0006] In the air filter medium disclosed in Patent Document 1, the first porous PTFE membrane is produced at a higher stretching temperature and at a larger stretch ratio than the second porous PTFE membrane, thereby increasing the specific surface area of ​​the first porous PTFE membrane to 0.5 m 2 / g or less, thereby capturing large particle diameter dust and oil mist. On the other hand, the specific surface area of ​​the second PTFE porous membrane is set to 1.5 to 10 m 2 / g, which allows for the capture of small particle size dust and oil mist.

[0007] However, in the air filter material disclosed in Patent Document 1, even though the first and second PTFE porous membranes are used to capture dust particles and oil mist of different particle sizes, the PTFE porous membrane is prone to generate static electricity, and it is difficult to remove the generated static electricity, so it is not easy to process it into a filter shape.In addition, because it has higher water repellency than oil repellency, the moisture contained in the air can clog the PTFE porous membrane, and dust particles can easily adhere thereto.Therefore, if the air filter material is used continuously, oil mist will continue to remain inside the air filter material, and the air filter material will easily become clogged, and as a result, the air volume passing through the air filter is likely to decrease, and there is a problem that the air filter needs to be frequently replaced with a new one.

[0008] An object of the present invention is to provide an air filter that purifies air containing oil mist and dust and suppresses clogging. Another object of the present invention is to provide a method for simply producing an air filter that purifies air containing oil mist and dust and suppresses clogging. [Means for solving the problem]

[0009] A first aspect of the present invention is an air filter including a nonwoven fabric having a surface through which air containing oil mist and dust flows in and another surface opposed to the first surface through which the air flows out, and a number of pores formed between fibers, the pores penetrating between the surface of the fibers of the nonwoven fabric. Weakly hydrophilic and water-repellenta multifunctional coating film is formed, the multifunctional coating film comprising metal oxide particles (B) having an average particle size of 2 nm to 90 nm and bonded with a fluorine-based functional group component (A) containing a perfluoroether structure represented by the following general formula (1) or (2), a self-reactive carboxyl group- and / or acetyl group-containing substance (C), and a thickener (D), the fluorine-based functional group component (A) is contained in the multifunctional coating film in a proportion of 1.5 mass % to 15 mass % and the thickener (D) is contained in a proportion of 0.3 mass % to 3.0 mass % when the multifunctional coating film is taken as 100 mass %, the fluorine-based functional group component (A) and the metal oxide particles (B) are contained in a total proportion of 15 mass % to 70 mass % when the multifunctional coating film is taken as 100 mass %, the mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is in the range of 0.02 to 0.5, The air permeability of the air filter is 1 ml / cm 2 / sec~30ml / cm 2 / second.

[0010] [ka]

[0011] In the above formulas (1) and (2), p, q, and r are each the same or different integers of 1 to 6, and the carbon skeleton may be linear or branched. Furthermore, in the above formulas (1) and (2), X is a hydrocarbon group having 2 to 10 carbon atoms, and may contain one or more bonds selected from an ether bond, a CO-NH bond, an O-CO-NH bond, and a sulfonamide bond. Furthermore, in the above formulas (1) and (2), Y is a silane hydrolyzate or a main component of a silica sol-gel.

[0012] More specifically, Y is a moiety that bonds to the metal oxide particles (B). Specific examples include structures in which the Z moiety is hydrolyzed in the formula (3) or (4) described below. Another example of Y is the main component of a silica sol-gel obtained by mixing a silane compound of formula (3) or (4) with a silicon alkoxide such as tetraethoxysilane or tetramethoxysilane and hydrolyzing and polymerizing the mixture. Another example of Y is the main component of a silica sol-gel obtained by mixing a silane compound of formula (3) or (4), a silicon alkoxide such as tetraethoxysilane or tetramethoxysilane, and a silane containing an epoxy group, a vinyl group, or an ether group, and hydrolyzing and polymerizing the mixture. The carboxyl group-containing material (C) is used as a binder component for adhering the metal oxide particles (B) to which the fluorine-based functional group component (A) is bonded to the substrate of a nonwoven fabric.

[0013] A second aspect of the present invention is an air filter according to the first aspect, wherein the metal oxide particles (B) are oxide particles of one metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr.

[0014] A third aspect of the present invention is an air filter based on the first aspect, wherein the self-reactive carboxyl group-containing substance (C) is an ethylene-acrylic acid copolymer, an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic acid copolymer.

[0015] A fourth aspect of the present invention is an air filter according to the first aspect, wherein the thickener (D) is a layered inorganic compound or a thickening polysaccharide.

[0016] A fifth aspect of the present invention is an air filter according to the first aspect, wherein the nonwoven fabric is formed of a single layer or a laminate of multiple layers.

[0017] A sixth aspect of the present invention is an air filter based on either the first or fifth aspect, wherein the fibers constituting the nonwoven fabric are one or more types of fibers selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal.

[0018] A seventh aspect of the present invention is A method for producing an air filter according to any one of the first to sixth aspects of the present invention, comprising: As shown in FIG. 3, the method for producing an air filter includes the steps of: preparing a liquid composition for forming a multifunctional coating film (hereinafter, sometimes simply referred to as a liquid composition) by mixing an aqueous dispersion of fluorine-containing metal oxide particles, a self-reactive carboxyl group-containing substance, a mixed solvent of water and an alcohol having 1 to 4 carbon atoms, and an aqueous thickener solution or an aqueous thickener dispersion; dipping a nonwoven fabric into the liquid composition for forming a multifunctional coating film; and dehydrating and drying the dipped nonwoven fabric.

[0019] An eighth aspect of the present invention is an invention based on the seventh aspect, which is a method for producing an air filter, wherein the aqueous dispersion of fluorine-containing metal oxide particles is prepared by adding and mixing a fluorine-based compound to an aqueous dispersion of metal oxide particles. [Effects of the Invention]

[0020] An air filter according to a first aspect of the present invention comprises a multifunctional coating film formed on the fiber surface of a nonwoven fabric contained in the air filter, the multifunctional coating film comprising metal oxide particles (B) having an average particle size of 2 nm to 90 nm and having a fluorine-based functional group component (A) represented by the above-mentioned general formula (1) or (2) bonded thereto, a self-reactive carboxyl group-containing substance or the like (C), and a thickener (D), wherein the fluorine-based functional group component (A) accounts for 1.5 mass% to the fluorine-based functional group component (A) and the metal oxide particles (B) are contained in a proportion of 15% by mass to 70% by mass when the total mass of the multifunctional coating film is taken as 100% by mass, the mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is in the range of 0.02 to 0.5, and the air permeability of the air filter is 1 ml / cm 2 / sec~30ml / cm 2 Therefore, when air containing oil mist and dust flows into one side of the air filter, the oil mist and dust are captured by the nonwoven fabric, and only the air passes through the pores of the nonwoven fabric and flows out the other side of the air filter, making the air clean and preventing clogging.

[0021] At this time, due to the oil repellency of the multi-functional coating and the air permeability of the air filter, 2 / sec~30ml / cm 2 / sec, the oil mist is repelled and adheres to the multifunctional coating on the fiber surface of the nonwoven fabric without adsorbing to it. As the amount of oil mist trapped inside the nonwoven fabric increases with continued use of the air filter, if the air filter is placed horizontally, the oil mist liquefies and is carried along with the passing air, collecting on the other side of the air filter. If the air filter is placed vertically, the captured oil mist collects at the bottom of the air filter due to its own weight, and does not clog the pores of the nonwoven fabric. This prevents the oil mist from clogging the pores.

[0022] On the other hand, dust particles are filtered out when the air filter has a permeability of 1 ml / cm 2 / sec~30ml / cm 2 / sec, it adheres directly to the multi-functional coating on the fiber surface of the nonwoven fabric, or to the oil mist that has adhered to the multi-functional coating. Therefore, when an air filter becomes clogged with dust after long-term use, the dust that has adhered together with the oil mist can be easily removed by impacting the air filter with an air knocker or the like, and the air filter can be regenerated.

[0023] In the air filter of the second aspect of the present invention, the metal oxide particles (B) contained in the multifunctional coating film are oxide particles of one metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr, so that it is possible to select a metal oxide suitable for the environment in which the air filter will be used from among the many types of metal oxide particles.

[0024] In the air filter of the third aspect of the present invention, the self-reactive carboxyl group-containing substance (C) is an ethylene-acrylic acid copolymer, an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic acid copolymer, and therefore the copolymer acts as a binder for the metal oxide particles, and when a multifunctional coating film is formed on the fiber surface of the nonwoven fabric, the film can be firmly bound to the surface of the nonwoven fabric.

[0025] In the air filter of the fourth aspect of the present invention, the thickener (D) contained in the multifunctional coating film is a layered inorganic compound or a thickening polysaccharide, which increases the thickness of the multifunctional coating film and reduces the air permeability of the air filter, thereby preventing oil mist from passing through the air filter. It is also possible to impart weak hydrophilicity to the multifunctional coating film.

[0026] In the air filter of the fifth aspect of the present invention, if the nonwoven fabric is formed from a single layer, the air filter will have a simple configuration, and if the nonwoven fabric is formed from a laminate of multiple layers, each layer can be configured according to the properties such as the particle size of the inflowing dust and the size of the oil particles in the oil mist.

[0027] In the air filter of the sixth aspect of the present invention, the material of the fibers constituting the nonwoven fabric can be selected from polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal, depending on the particle size of the inflowing dust, the size of the oil particles in the oil mist, and other properties.

[0028] In the method of the seventh aspect of the present invention, as shown in Figure 3, an aqueous dispersion of fluorine-containing metal oxide particles, a self-reactive carboxyl group-containing material, a mixed solvent of water and an alcohol having 1 to 4 carbon atoms, and an aqueous thickener solution or thickener dispersion are mixed to prepare a liquid composition for forming a multifunctional coating film, and an air filter is produced by dipping a nonwoven fabric into this liquid composition for forming a multifunctional coating film, dewatering the nonwoven fabric, and drying it, thereby enabling the formation of a uniform multifunctional coating film on the fiber surface of the nonwoven fabric. Furthermore, the presence of fluorine-containing metal oxide particles in the carboxyl group-containing material and the inclusion of a thickener in the multifunctional coating film makes it easy to reduce the air permeability of the nonwoven fabric while maintaining weak hydrophilicity and oil repellency. Furthermore, unlike the PTFE porous membrane of Patent Document 1, the multifunctional coating film is weakly hydrophilic. Therefore, firstly, static electricity is less likely to occur in the multifunctional coating film, making it possible to easily manufacture an air filter; secondly, by absorbing the water vapor contained in the oil mist, the multifunctional coating film exhibits an oil-repellent effect, thereby further improving the anti-clogging effect of the air filter.

[0029] In the method for producing an air filter according to the eighth aspect of the present invention, a fluorine-based compound is added and mixed into an aqueous dispersion of metal oxide particles, so that a dispersion in which fluorine-containing metal oxide particles are uniformly dispersed can be obtained. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a side view of a single layer nonwoven fabric of the present embodiment. [Figure 2] FIG. 2 is a side view of the two-layer nonwoven fabric of the present embodiment. [Figure 3] FIG. 2 is a flow chart showing a method for manufacturing the air filter of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Next, an embodiment of the present invention will be described with reference to the drawings.

[0032] [Air filter] As shown in FIG. 1, the air filter 10 of this embodiment includes a nonwoven fabric 20 and a multifunctional coating film 21 formed on the fiber surface of the nonwoven fabric, which has weak hydrophilicity and oil repellency. The nonwoven fabric 20, which is the main component of the air filter 10, is a single layer having a first surface 20a through which air containing oil mist and dust enters and a second surface 20b opposite to the first surface 20a through which the air exits. As shown in FIG. 2, the air filter 50 may be a two-layer laminate consisting of an upper nonwoven fabric 30 and a lower nonwoven fabric 40. In this case, the upper surface of the upper nonwoven fabric 30 corresponds to the first surface 30a through which air containing oil mist and dust enters, and the lower surface of the lower nonwoven fabric 40 corresponds to the second surface 40b opposite the first surface 30a. The laminate is not limited to two layers, and may be composed of multiple layers, such as three or four layers.

[0033] As shown in the enlarged view in the center of Figure 1, the nonwoven fabric 20 is formed by intertwining numerous fibers 20c, with pores 20d formed between the fibers. The pores 20d penetrate between one surface 20a and the other surface 20b of the nonwoven fabric 20. A multifunctional coating film 21 is formed on the surface of the fibers 20c of the nonwoven fabric. The basis weight of the nonwoven fabric is 100 g / m 2 ~400g / m 2The multifunctional coating film 21 preferably contains metal oxide particles (B), a self-reactive carboxyl group-containing substance (C) as a binder component, and a thickener (D). The metal oxide particles (B) are bonded to a fluorine-based functional group component (A) represented by the general formula (1) or (2) described above. When the multifunctional coating film is taken as 100% by mass, the multifunctional coating film 21 contains the fluorine-based functional group component (A) in a proportion of 1.5% to 15% by mass, and the thickener (D) in a proportion of 0.3% to 3.0% by mass. The fluorine-based functional group component (A) and the metal oxide particles (B) are contained in a total proportion of 15% to 70% by mass when the multifunctional coating film is taken as 100% by mass. The mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is in the range of 0.02 to 0.5.

[0034] As shown in the enlarged view at the top of Figure 1, the multifunctional coating film 21 is composed of numerous metal oxide particles 21a, whose surfaces are coated with fluorine-based functional group components, bound together by a binder component 21b, typically a carboxyl group-containing material. Because the multifunctional coating film 21 contains the metal oxide particles 21a and a thickener (D), it appears thick and narrows the pores 20d between the fibers. The thickness of the coating film can be controlled by varying the particle size of the metal oxide particles and the proportion of thickener in the coating. Furthermore, the inclusion of the thickener (D) imparts weak hydrophilic properties to the multifunctional coating film, which firstly makes it less prone to static electricity generation and secondly absorbs water vapor contained in oil mist, providing the multifunctional coating with oil-repellent properties, further enhancing the anti-clogging effect of air filters.

[0035] The weight of the nonwoven fabric is 100g / m 2 If the density is less than 400g / m, the pores between the fibers will be too large, and the dust collection capacity will be insufficient. 2 When the air permeability exceeds 1 ml / cm 2 / sec, which means that dust particles easily get stuck in the pores between the fibers, or the air permeability is too low, so the resistance of the air being sent into the air filter tends to cause pressure loss in the air filter, which tends to reduce the efficiency of the air blowing energy. 2 ~350g / m 2 It is more preferable that the range is

[0036] In the state of the air filter 10 in which the multifunctional coating film 21 is formed on the fiber surface, the nonwoven fabric 20 has a flow rate of 1 ml / cm 2 / sec~30ml / cm 2 / sec. 2 If the flow rate is less than 30 ml / cm² / sec, the ventilation is poor and it becomes difficult for air containing oil mist and dust to pass through. 2 If the air permeability exceeds 1.5 ml / cm, the size of the pores 20d of the nonwoven fabric becomes much larger than the particle size of the oil particles 22 and dust particles 23 of the oil mist in the incoming air, and the oil particles 22 and dust particles 23 pass through the pores of the nonwoven fabric along with the air and pass out of the air filter 10, making it impossible to capture the oil mist and dust. 2 / sec~40ml / cm 2 The air permeability is measured using a Frazier type tester as described in JIS-L1913:2000.

[0037] When the multifunctional coating film 21 is taken as 100% by mass, if the proportion of the fluorine-based functional group component (A) in the multifunctional coating film is less than 1.5% by mass, the oil repellency effect is poor and the ability to repel oil mist becomes insufficient. That is, when oil mist reaches the air filter, the oil mist spreads over the fiber surface and is likely to clog the pores 20d. If the proportion of the fluorine-based functional group component (A) in the multifunctional coating film exceeds 15% by mass, the adhesion of the multifunctional coating film to the nonwoven fabric becomes poor. The content of the fluorine-based functional group component (A) in the multifunctional coating film 21 is preferably 1.2% to 12% by mass.

[0038] The thickener (D) contained in the multifunctional coating film 21 is contained in a proportion of 0.3% by mass to 3.0% by mass when the multifunctional coating film is taken as 100% by mass. If it is less than 0.3% by mass, the resulting film will be water-repellent and will not exhibit weak hydrophilicity. If it exceeds 3.0% by mass, the oil-repellency of the multifunctional coating film will deteriorate. The thickener (D) contained in the multifunctional coating film 21 is preferably 0.5% by mass to 2.8% by mass.

[0039] The operation of this air filter 10 will now be described. As shown in FIG. 1, air containing oil mist and dust particles reaches one surface 20a of the nonwoven fabric 20 constituting the air filter 10. Here, because the air filter 10 has a predetermined air permeability and the multifunctional coating film 21 exhibits oil repellency, oil particles 22 of the oil mist cannot pass through the air filter 10 even if they are slightly smaller than the pore size of the pores 20d, let alone if they are larger than the pore size of the pores 20d. Instead, they are repelled by the multifunctional coating film 21 and adhere to and remain on the multifunctional coating film 21 between the fibers 20c of the nonwoven fabric 20. At the same time, dust particles 23 also adhere to and remain on the multifunctional coating film 21. Because the multifunctional coating film 21 contains fluorine-containing metal oxide particles 21a, the film becomes uneven, which reduces the adhesion of oil particles 22 to the film while making it easier for dust particles 23 to adhere. As a result, oil particles 22 of the oil mist and dust particles 23 are captured by the nonwoven fabric, and the air containing the oil mist and dust passes through pores 20d formed between fibers 20c shown in the enlarged view of Figure 1 to reach the other surface 20b, where it becomes air free of oil mist and dust and passes through the nonwoven fabric 20.

[0040] As the amount of oil mist trapped inside the nonwoven fabric increases with continued use of the air filter, if the air filter is placed horizontally, oil mist that does not adhere to the membrane will liquefy and be carried along with the passing air, collecting on the other side of the air filter. If the air filter is placed vertically, the captured oil mist will collect at the bottom of the air filter due to its own weight and will not clog the pores of the nonwoven fabric. This prevents the oil mist from clogging the pores. Dust will either adhere directly to the multifunctional coating on the fiber surface of the nonwoven fabric or adhere to the oil mist that has adhered to the multifunctional coating. The oil mist and dust that have accumulated in the nonwoven fabric 20 can be removed from the air filter 10 by periodically impacting it with an air knocker or similar device. Furthermore, by including a thickener, weak hydrophilicity is imparted to the multifunctional coating film, which firstly makes the multifunctional coating film less susceptible to static electricity, and secondly, by absorbing the water vapor contained in the oil mist, the multifunctional coating film exhibits an oil-repellent effect, further enhancing the anti-clogging effect of the air filter.

[0041] [Air filter manufacturing method] The air filter is generally manufactured by the following method. As shown in FIG. 3 , an aqueous dispersion 54 of fluorine-containing metal oxide particles is prepared by mixing a fluorine-containing compound 52 containing a fluorine-containing functional group component (A) with an aqueous dispersion 51 of metal oxide particles. If the pH of the dispersion is neutral, the fluorine-containing compound 52 is mixed, followed by the addition and mixing of a catalyst 53 to prepare the aqueous dispersion 54 of fluorine-containing metal oxide particles. A carboxyl group-containing substance or the like 55 serving as a binder component is mixed with this aqueous dispersion 54 to prepare a mixture 56. A mixed solvent 57 of water and an alcohol having 1 to 4 carbon atoms is then added to dilute the mixture 56, and a thickener aqueous solution or thickener aqueous dispersion 58 is further added to prepare a liquid composition 60 for forming a multifunctional coating film. A nonwoven fabric 20 is dipped into this liquid composition 60. The nonwoven fabric 20 is then dewatered and dried to produce an air filter 10.

[0042] The method for manufacturing the air filter will be described in detail below. [Preparing the nonwoven fabric] First, 1.1 ml / cm 2 / sec~40ml / cm 2 Specifically, a nonwoven fabric having an air permeability of 1 ml / cm 2 is prepared in a state where a multifunctional coating film (described later) is formed on the surface of the fibers of the nonwoven fabric to form an air filter. 2 / sec~30ml / cm 2 A nonwoven fabric having an air permeability of 1 / 2 / sec is prepared. When a thick multifunctional coating film is to be formed, a nonwoven fabric with a high air permeability is selected, and when a thin multifunctional coating film is to be formed, a nonwoven fabric with a low air permeability is selected. The air permeability of the nonwoven fabric to be prepared is selected according to the content of a thickener that acts to thicken the multifunctional coating film.

[0043] Examples of such nonwoven fabrics include cellulose-mixed ester membrane filters, glass fiber filter paper, nonwoven fabrics made from a mixture of polyethylene terephthalate and glass fibers (product names: 336 and 356, both manufactured by Azumi Filter Paper Co., Ltd.), nonwoven fabrics made from polyethylene terephthalate fibers (product names: G2260-1S, manufactured by Toray Industries, Inc., and 191001, manufactured by Toyobo Co., Ltd.), nonwoven fabrics made from polypropylene fibers (product name: M03150, manufactured by Mitsui Chemicals, Inc.), and nonwoven fabrics made from metal fibers (manufactured by Nichie Techno Co., Ltd.). Nonwoven fabrics are made from one or more fibers selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal. The fibers may also be a mixture of two or more fibers. The fiber thickness (fiber diameter) is preferably 0.01 μm to 10 μm so as to obtain the above-mentioned air permeability. The thickness of the nonwoven fabric is preferably 0.2 mm to 0.8 mm when the air filter is a single layer, and is preferably a thickness that makes the thickness of the laminate 0.2 mm to 5 mm when the air filter is a laminate of multiple layers.

[0044] [Method for producing a multifunctional coating film-forming liquid composition] [Preparation of Aqueous Dispersion of Metal Oxide Particles] First, an aqueous dispersion of metal oxide particles is prepared by dispersing metal oxide particles in an aqueous solvent. The metal oxide particles have an average particle size of 2 nm to 90 nm, preferably 2 nm to 85 nm. If the average particle size is less than 2 nm, the metal oxide particles are likely to aggregate and become difficult to disperse in the medium. If the average particle size exceeds 90 nm, the metal oxide particles are likely to fall off from the multifunctional coating film when the liquid composition is formed into a film. Examples of metal oxide particles include particles of SiO2, Al2O3, MgO, CaO, TiO2, ZnO, and ZrO2. Examples of commercially available products include an aqueous dispersion of silicon dioxide (trade name: ST-ZL (manufactured by Nissan Chemical Industries, Ltd., SiO concentration 40%), trade name: ST-C (manufactured by Nissan Chemical Industries, Ltd., SiO concentration 20%), trade name: ST-CM (manufactured by Nissan Chemical Industries, Ltd., SiO concentration 30%)), an aqueous dispersion of zirconium dioxide (trade name: SZR-W (manufactured by Sakai Chemical Industries, Ltd., ZrO concentration 30%)), an aqueous dispersion of titanium dioxide (trade name: TKS-203 (manufactured by Teika Corporation, TiO concentration 20%)), and an aqueous dispersion of zinc oxide (trade name: MZ-500 (manufactured by Teika Corporation, ZnO concentration 30%)).

[0045] Examples of aqueous solvents include water or a mixed solvent of water and an alcohol having 1 to 4 carbon atoms. It is desirable to use pure water such as ion-exchanged water or distilled water as the water to prevent the inclusion of impurities. The reason why an aqueous solvent is used as the solvent, rather than an organic solvent, is to ensure safety in handling. In this specification, the average particle size of metal oxide particles refers to the average value of particle sizes measured by image analysis at 200 points among particle shapes observed with a scanning electron microscope (SEM).

[0046] [Preparation of Aqueous Dispersion of Fluorine-Containing Metal Oxide Particles] Next, a fluorine-based compound containing a fluorine-based functional group component represented by the above formula (1) or (2) is added to the prepared aqueous dispersion of metal oxide particles to synthesize a nanocomposite material of the metal oxide particles and the fluorine-based functional group component. A catalyst may be added to further promote the reaction. This results in the preparation of an aqueous dispersion of fluorine-containing metal oxide particles.

[0047] When a catalyst is used, examples of the catalyst include organic acids, inorganic acids, alkalis, and titanium compounds, and examples of organic acids include formic acid and oxalic acid, examples of inorganic acids include hydrochloric acid, nitric acid, and phosphoric acid, examples of alkalis include sodium hydroxide, lithium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia, and examples of titanium compounds include tetrapropoxytitanium, tetrabutoxytitanium, tetraisopropoxytitanium, and titanium lactate. The catalyst is not limited to the above.

[0048] The fluorine-based compound containing a fluorine-based functional group component is represented by the following general formula (3) or formula (4): More specific examples of the perfluoroether group in formula (3) or formula (4) include perfluoroether structures represented by the following formulas (5) to (13).

[0049] [ka]

[0050] [ka]

[0051] [ka]

[0052] Furthermore, examples of X in the above formulas (3) and (4) include structures represented by the following formulas (14) to (18): Formula (14) shows an example containing an ether bond, Formula (15) shows an ester bond, Formula (16) shows an amide bond, Formula (17) shows a urethane bond, and Formula (18) shows a sulfonamide bond.

[0053] [ka]

[0054] Here, in the above formulas (14) to (18), R2 and R 3 is a hydrocarbon group with 0 to 10 carbon atoms, R 4 is a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. 3 Examples of the hydrocarbon group include alkylene groups such as methylene and ethylene groups, and R 4 Examples of the hydrocarbon group include alkyl groups such as methyl and ethyl groups, as well as phenyl groups.

[0055] In addition, in the above formulas (3) and (4), R 1 Examples of the alkyl group include a methyl group and an ethyl group.

[0056] In addition, in the above formulas (3) and (4), Z is not particularly limited as long as it is a hydrolyzable group that can be hydrolyzed to form a Si-O-Si bond. Specific examples of such hydrolyzable groups include alkoxy groups such as methoxy, ethoxy, propoxy, and butoxy groups, aryloxy groups such as phenoxy and naphthoxy groups, aralkyloxy groups such as benzyloxy and phenethyloxy groups, and acyloxy groups such as acetoxy, propionyloxy, butyryloxy, valeryloxy, pivaloyloxy, and benzoyloxy groups. Among these, an ethoxy group is preferred.

[0057] Specific examples of the fluorine-based compound containing a fluorine-based functional group component having a perfluoroether structure represented by the above formula (3) or (4) include structures represented by the following formulas (19) to (27), in which R is a methyl group or an ethyl group.

[0058] [ka]

[0059] [ka]

[0060] As described above, the fluorine-based compound contained in the multifunctional coating film-forming liquid composition of this embodiment has a perfluoroether group in which multiple short-chain perfluoroalkyl groups and perfluoroalkylene groups each having 6 or less carbon atoms are bonded to an oxygen atom in the molecule, and since the fluorine content in the molecule is high, it can impart excellent oil repellency to the formed film.

[0061] [Self-reactive carboxyl group-containing substances, etc.] The self-reactive carboxyl group-containing material (C) as a binder component is an ethylene-acrylic acid copolymer, an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic acid copolymer. Commercially available ethylene-vinyl acetate-based products include Sepolsion VA406N and Sepolsion VA407N (all manufactured by Sumitomo Seika Chemicals), Sumikaflex S-201HQ, S-355HQ, S-401HQ, S-465HQ, S-951HQ, and S3950 (all manufactured by Sumika Chemtex Co., Ltd.), and Aquatex EC-1800 and EC-1200 (all manufactured by Japan Coating Resins Co., Ltd.). Examples of ethylene-acrylic acid copolymers include Zaixen A and Zaixen B. Examples of suitable acrylic resins include Xen L and Zaixen N (both manufactured by Sumitomo Seika Chemicals), and an ethylene-vinyl acetate-acrylic acid-based resin such as Sumikaflex S-900HL (manufactured by Sumika Chemtex Co., Ltd.). Other examples include Sumikaflex S-830, an ethylene-vinyl acetate-vinyl chloride copolymer, and Sumikaflex S-950HQ, an ethylene-vinyl acetate-vinyl versatate copolymer (both manufactured by Sumika Chemtex Co., Ltd.). An example of an acrylic-based resin is TOCRYL BCX-1160R-2 (manufactured by Toyochem Co., Ltd.).

[0062] After preparing a mixed solution by mixing the above-mentioned self-reactive carboxyl group-containing material with an aqueous dispersion of fluorine-containing metal oxide particles, the mixed solution is diluted by mixing a mixed solvent of water and an alcohol having 1 to 4 carbon atoms. Here, the mixed solvent is water with an alcohol content of 40 mass% or less. The reason for keeping the content of the alcohol having 1 to 4 carbon atoms at 40 mass% or less is to ensure safety in handling and storage stability of the liquid composition. Furthermore, by using a mixed solvent of water and an alcohol having 1 to 4 carbon atoms, the drying speed is increased and film-forming properties are improved. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-2-propanol.

[0063] After diluting the mixture, an aqueous thickener solution or aqueous thickener dispersion is added and mixed. In addition to water-insoluble layered inorganic compounds, water-soluble thickening polysaccharides can also be used as thickeners. An aqueous thickening solution is prepared by dissolving a thickening polysaccharide in water, and an aqueous thickening dispersion is prepared by dispersing a layered inorganic compound in water. Examples of water-soluble thickening polysaccharides include xanthan gum, hydroxyethyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, starch, dextrin, carrageenan, guar gum, and pectin. Examples of water-insoluble layered inorganic compounds include bentonite (trade name: Moistonite S (manufactured by Kunimine Kogyo Co., Ltd.)), smectonite (trade name: Sumecton SA (manufactured by Kunimine Kogyo Co., Ltd.)), and hectorite (trade name: Laponite RDS (manufactured by Rockwood Co., Ltd.)). These layered inorganic compounds are particulate, preferably having an average particle size of 0.1 μm to 10 μm. If the average particle size is less than 0.1 μm or more than 10 μm, it is difficult to prepare an aqueous dispersion. An example of xanthan gum is Xanthan G (manufactured by Sansho Co., Ltd.). The thickener aqueous solution or thickener aqueous dispersion is prepared by mixing the thickener with water and stirring. The preferred content of the thickener is 0.08% by mass to 0.45% by mass, assuming the multifunctional coating film-forming liquid composition to be 100% by mass.

[0064] [Multifunctional coating film forming liquid composition] The multifunctional coating film-forming liquid composition of this embodiment is produced by the above-described production method and includes metal oxide particles (B) bonded with the fluorine-based functional group component (A), a self-reactive carboxyl group-containing material (C) or the like as a binder component, a mixed solvent, and a thickener aqueous solution or thickener aqueous dispersion. The fluorine-based functional group component (A) has a perfluoroether structure represented by the general formula (1) or (2) above. The liquid composition contains 1.5 to 15% by mass of the fluorine-based functional group component (A) when the total amount of all components excluding the solvent is taken as 100% by mass. If the fluorine-based functional group component is less than 1.5% by mass, the formed film cannot be imparted with oil repellency, while if it exceeds 15% by mass, the film may repel water, resulting in poor film-forming properties. The preferred content of the fluorine-based functional group component (A) is 2 to 13% by mass. The total content of the fluorine-based functional group component (A) and the metal oxide particles (B) is 15 to 70% by mass, preferably 20 to 65% by mass, when the total amount of all components excluding the solvent is taken as 100% by mass. Furthermore, the mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is in the range of 0.02 to 0.5, preferably 0.05 to 0.4.

[0065] If the total amount of component (A) and particle (B) is less than 15% by mass, the oil-repellent properties of the multifunctional coating film will be reduced. If the total amount exceeds 70% by mass, the content of the carboxyl group-containing substance (C) will be relatively low, and when the liquid composition is applied to a substrate, the multifunctional coating film will not adhere firmly to the fiber surface of the nonwoven fabric. If the mass ratio (A / B) is less than 0.02, the multifunctional coating film will have poor oil-repellent properties. If it exceeds 0.5, the adhesion of the multifunctional coating film to the fiber surface of the nonwoven fabric will be reduced.

[0066] [Method for forming a multifunctional coating film on the fiber surface of a nonwoven fabric] To form a multifunctional coating film on the fiber surface of a nonwoven fabric according to this embodiment, the nonwoven fabric is dipped into a multifunctional coating film-forming liquid composition, removed from the diluted solution, and then spread on a horizontal wire mesh or the like in the air at room temperature to allow the nonwoven fabric to drain until a certain amount of liquid is reached. Alternatively, the removed nonwoven fabric can be shaken off to remove excess liquid, or the removed nonwoven fabric can be passed through a mangle roll (wringer) to drain the liquid. The drained nonwoven fabric is then dried in the air at a temperature of 25°C to 140°C for 0.5 to 24 hours. This results in the formation of a multifunctional coating film 21 on the surface of the fibers 20c constituting the nonwoven fabric 20, as shown in the enlarged view in the center of Figure 1. When the amount of liquid removed is small, a thick multifunctional coating film is formed on the fiber surface of the nonwoven fabric; when the amount of liquid removed is large, a thin multifunctional coating film is formed on the fiber surface of the nonwoven fabric. [Example]

[0067] Next, examples of the present invention will be described in detail together with comparative examples. First, Synthesis Examples 1 to 6 and Comparative Synthesis Examples 1 to 3 for preparing aqueous dispersions of fluorine-containing metal oxide particles will be described, followed by Examples 1 to 7 and Comparative Examples 1 to 4 for preparing multifunctional coating film-forming liquid compositions and producing air filters using these Synthesis Examples and Comparative Synthesis Examples.

[0068] [Synthesis Examples 1 to 6 and Comparative Synthesis Examples 1 to 3 for Preparing Aqueous Dispersions of Fluorine-Containing Metal Oxide Particles] <Synthesis Example 1> To a beaker containing 50 g of an aqueous dispersion of silicon dioxide with an average particle size of 70 nm (product name: ST-ZL (Nissan Chemical Industries, Ltd., SiO concentration 40%), 2.00 g of the fluorine-based compound represented by formula (19) was added and mixed. The mixture was stirred at 40°C for 2 hours to obtain an aqueous dispersion of silicon dioxide (silica) particles in which the silicon dioxide particles were bonded to the fluorine-based compound (aqueous dispersion of fluorine-containing silica particles). The mass ratio (A / B) of the fluorine-based functional group component (A) to the silicon dioxide, or metal oxide particles (B), was 0.09. Table 1 below shows the conditions for preparing the aqueous dispersion of fluorine-containing metal oxide particles in Synthesis Example 1.

[0069] [Table 1]

[0070] <Synthesis Examples 2 to 6 and Comparative Synthesis Examples 1 to 3> In Synthesis Examples 2 to 6 and Comparative Synthesis Examples 1 to 3, the type of metal oxide particles was changed to a different type from that in Synthesis Example 1, and the type of fluorine-based compound was changed to a different type from that in Synthesis Example 1. In Synthesis Examples 4 to 6 and Comparative Synthesis Example 1, the fluorine-based compounds were mixed, and then nitric acid was used as a catalyst. The amount of catalyst used was the value shown in Table 1. The mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) was changed to a different value from that in Synthesis Example 1. Otherwise, aqueous dispersions of fluorine-containing metal oxide particles in Synthesis Examples 2 to 6 and Comparative Synthesis Examples 1 to 3 were prepared in the same manner as in Synthesis Example 1, as shown in Table 1 above. In Table 1, all of the R in the formulas of the fluorine-containing silanes represented by formulas (19) to (21) and (27) as the fluorine-based compounds are ethyl groups.

[0071] [Examples 1 to 7 and Comparative Examples 1 to 4 for preparation of multifunctional coating film-forming liquid composition and production of air filter] Example 1 A mixed solution was prepared by mixing 13.0 g of the aqueous dispersion of fluorine-containing metal oxide particles obtained in Synthesis Example 1 with 10.00 g of a binder component, such as an ethylene-vinyl acetate-based carboxyl group-containing material having an acetyl group (trade name: Sumikaflex S-355HQ (Sumitomo Chemical Co., Ltd.)). This mixed solution was mixed with an aqueous dispersion containing 23.7 g of a mixed solvent (a solvent obtained by mixing 19.9 g of water and 3.8 g of industrial alcohol (trade name: Solmix AP-7 (Japan Alcohol Sales Co., Ltd.))) and 0.55 g of a thickener (trade name: Moistonite S (Kunimine Industries Co., Ltd.)), to prepare a multifunctional coating film-forming liquid composition. The thickener was contained in this liquid composition at a ratio of 0.28 mass% when the liquid composition was taken as 100 mass%. A PET fiber-based air filter having an air permeability of 15 ml / m was used as the base material for the air filter. 2 A nonwoven fabric G2260-1S (manufactured by Toray Industries, Inc.) of 1 / 2 ml / s was used. The nonwoven fabric was dipped in the multifunctional coating film-forming liquid composition, the excess liquid was shaken off, and the fabric was dried at room temperature for 24 hours. The air permeability was measured to be 6.0 ml / cm. 2The details of the air filters are shown in Tables 2 to 4 below.

[0072] Table 2 shows the types and weights of the "fluorine-containing metal oxide particles" used to prepare the liquid composition for forming a multifunctional coating film, the types and weights of the "self-reactive carboxyl group-containing substances (C)," details of the "mixed solvent," and the types, weights, and content ratios of the "thickeners" in the liquid composition. Table 3 shows the content of the "fluorine-based functional group component (A) in the liquid composition excluding the solvent," the content of the "carboxyl group-containing substance (C) excluding the solvent," and the content of the "total of the fluorine-based functional group component (A) excluding the solvent and the metal oxide particles (B)."

[0073] [Table 2]

[0074] [Table 3]

[0075] [Table 4]

[0076] <Examples 2 to 7 and Comparative Examples 1 to 4> As shown in Table 2, in Examples 2 to 7 and Comparative Examples 1 to 4, the respective weights were determined using the aqueous dispersions of fluorine-containing metal oxide particles obtained in Synthesis Examples 1 to 6 or Comparative Synthesis Examples 1 to 3 shown in Table 1. In Examples 2 to 7 and Comparative Examples 1 to 4, the respective weights were determined using binder components such as a self-reactive carboxyl group-containing substance, a mixed solvent, and a thickener, as shown in Table 2. The content of the thickener indicates the proportion of the thickener contained in the liquid composition when the liquid composition is taken as 100 mass %. In this manner, each of the multifunctional coating-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 4 was prepared.

[0077] Nonwoven fabrics with different breathability shown in Table 3 and the type of air filter substrate were selected, and the substrates made of nonwoven fabrics were dipped in each of the multifunctional coating film-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 4 in the same manner as in Example 1, followed by dewatering and drying to obtain air filters having the properties shown in Table 4.

[0078] <Comparative testing and evaluation> (1) Breathability The air permeabilities of the 11 types of air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were measured using the Frazier type testing machine described in JIS-L1913:2000, as described above.

[0079] (2) Oil repellency The oil repellency of the 11 types of air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was measured and evaluated by the following method. To simulate the oil mist and dust dispersed from machine tools that use cutting oil to process metal products, n-hexadecane and iron (III) oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a planetary centrifugal mixer (ARE-310, manufactured by Thinky Corporation) in a mass ratio of 80:20 and stirred and mixed to obtain a simulated liquid. 1 ml of the resulting simulated liquid was dropped from above onto each of the 11 types of horizontally placed air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4, and the air filters were then stood vertically to check the sliding properties of the simulated liquid. If the simulated liquid passes through the air filter after being captured on the air filter, the oil repellency of the air filter is deemed to be "poor." If the simulated liquid passes through the air filter to a certain extent after being captured on the air filter and falls off the surface of the air filter, but the amount of the simulated liquid that falls is reduced, the oil repellency of the air filter is deemed to be "fairly good." If the simulated liquid is captured on the air filter but does not pass through the air filter and falls off the surface of the air filter, the oil repellency of the air filter is deemed to be "good."

[0080] (3) Weakly hydrophilic After 0.1 mL of water was dropped from above onto each of the 11 types of horizontally placed air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4, the water was retained for 60 seconds or more. If the water had penetrated the air filter after 1 hour, the weak hydrophilicity was judged to be "good." If the water had penetrated the air filter after a retention time of less than 60 seconds, the air filter was judged to be hydrophilic. If the water was still retained after 1 hour, the air filter was judged to be water-repellent, and the weak hydrophilicity was judged to be "poor."

[0081] (4) Membrane strength The strength of the multifunctional coating film on the surface of the nonwoven fabric fibers constituting the 11 types of air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was measured in accordance with JIS K7136 using a static friction tester (TL201Tt, manufactured by Trinity Lab Co., Ltd.). The measurement conditions were: contact: urethane rubber, load: 500 gf, movement speed: 50 mm / sec, movement distance: 30 mm. After the contact was moved back and forth 10 times on the surface of the horizontally placed air filter, the simulant liquid used in measuring the oil repellency was dropped, and the oil repellency was evaluated using the same method as in (2) above. If the oil repellency did not change after the contact was moved, the film strength was considered "good." If the simulant liquid penetrated into the air filter and the oil repellency changed, the film strength was considered "poor."

[0082] As is clear from Table 3, the air filter of Comparative Example 1 was produced by preparing a multifunctional coating film-forming liquid composition from Comparative Synthesis Example 1 containing metal oxide (silicon dioxide) particles with an average particle size of 230 nm, dipping a nonwoven fabric into this liquid composition, dewatering, and drying. Therefore, the average particle size of the metal oxide particles was too large, making it difficult for the metal oxide particles to adhere to the fiber surface of the nonwoven fabric due to the binder component, such as a carboxyl group-containing substance, and the air permeability was too low. As a result, the simulated liquid did not fall off the air filter, and the oil repellency was "poor." Furthermore, the film strength was also "poor."

[0083] In the air filter of Comparative Example 2, the content of the fluorine-based functional group component (A) in the liquid composition excluding the solvent was too low at 0.4 mass%, and the "(A) / (B)" ratio in the aqueous dispersion of fluorine-containing metal oxide particles (aqueous dispersion of fluorine-containing silica particles) was 0.005, resulting in a too low content of the fluorine-based functional group component. Furthermore, the content of "(A) + (B)" in the liquid composition excluding the solvent was 80 mass%, resulting in a relatively low content of carboxyl group-containing substances and other binders in the film. As a result, the simulated liquid soaked into the air filter and did not fall off, resulting in a "poor" oil repellency. Furthermore, due to the low content of the binder component, the film strength was low and rated "poor."

[0084] In the air filter of Comparative Example 3, the content ratio of the fluorine-based functional group component (A) relative to the metal oxide particles (B) was too high at 4.7% by mass, resulting in polymerization of only the fluorine-based functional group component, resulting in a non-uniform coating liquid. Furthermore, the content ratio of "(A) + (B)" in the liquid composition excluding the solvent was 10% by mass, resulting in a too low content of the fluorine-based functional group component in the film. As a result, the multifunctional coating liquid composition was not uniformly applied to the nonwoven fabric, and the multifunctional coating film was not uniformly formed on the fiber surface of the nonwoven fabric. As a result, the multifunctional coating film became porous, resulting in an air permeability of too high at 36.0 ml / cm2 / sec. The multifunctional coating film did not exhibit oil repellency, and the simulated liquid passed through the air filter, resulting in a "poor" oil repellency rating. Furthermore, because the formed film was non-uniform, the weak hydrophilicity rating was "poor." Furthermore, for the same reasons as above, the film strength was low and "poor."

[0085] In the air filter of Comparative Example 4, the amount of thickener added was too high at 9.1 mass %, so the weak hydrophilicity was "good", but the fluorine-based functional group component was too high at 16.6 mass %, so the adhesion of the multifunctional coating film to the nonwoven fabric was poor and the oil repellency was "poor". Furthermore, because the fluorine-based functional group component was too high, the film was non-uniform for the same reason as in Comparative Example 3, so the film strength was weak and it was "poor".

[0086] In contrast to these, the air filters of Examples 1 to 7 satisfied the scope of the invention of the first aspect, and therefore the simulated liquid was collected and dropped off the air filter, and all of the oil repellency was "good", and because the multifunctional coating film was uniformly formed, all of the weak hydrophilicity was "good", and further all of the film strength was "good". [Industrial Applicability]

[0087] The air filter of the present invention is used in a working environment where there are machine tools such as cutting machines and turning machines that process metal products using cutting oil. [Explanation of symbols]

[0088] 10 Air Filter 20 Nonwoven fabric 20a One side of nonwoven fabric 20b Other side of nonwoven fabric 20c nonwoven fiber 20d nonwoven fabric pores 21 Multifunctional coating film 21a Fluorine-containing metal oxide particles 21b Carboxyl group-containing substances, etc. 22 Oil particles in oil mist 23 Dust particles

Claims

1. An air filter including a nonwoven fabric having a large number of pores formed between fibers, the pores penetrating between one side into which air containing oil mist and dust flows in and another side opposite to the one side through which the air flows out, a multifunctional coating film having weak hydrophilicity and water repellency is formed on the fiber surface of the nonwoven fabric, The multifunctional coating film comprises metal oxide particles (B) having an average particle size of 2 nm to 90 nm and bonded to a fluorine-based functional group component (A) containing a perfluoroether structure represented by the following general formula (1) or (2), a self-reactive carboxyl group- and / or acetyl group-containing substance (C), and a thickener (D), When the multifunctional coating film is taken as 100% by mass, the fluorine-based functional group component (A) is contained in the multifunctional coating film in a proportion of 1.5% by mass to 15% by mass, and the thickener (D) is contained in a proportion of 0.3% by mass to 3.0% by mass, the fluorine-based functional group component (A) and the metal oxide particles (B) are contained in a total amount of 15% by mass to 70% by mass when the multifunctional coating film is taken as 100% by mass, the mass ratio (A / B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is in the range of 0.02 to 0.5; The air permeability of the air filter is 1 ml / cm 2 / sec ~ 30ml / cm 2 / second. 【Chemistry 1】 In the above formulas (1) and (2), p, q, and r are the same or different and are integers of 1 to 6, and the carbon skeleton may be linear or branched. Furthermore, in the above formulas (1) and (2), X is a hydrocarbon group having 2 to 10 carbon atoms and may contain one or more bonds selected from an ether bond, a CO—NH bond, an O—CO—NH bond, and a sulfonamide bond. Furthermore, in the above formulas (1) and (2), Y is a hydrolyzate of silane or a main component of silica sol-gel.

2. 2. The air filter according to claim 1, wherein the metal oxide particles (B) are oxide particles of one metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn and Zr.

3. 2. The air filter according to claim 1, wherein the self-reactive carboxyl group and / or acetyl group-containing material (C) is an ethylene-acrylic acid copolymer, an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic acid copolymer.

4. 2. The air filter according to claim 1, wherein the thickener (D) is a layered inorganic compound or a thickening polysaccharide.

5. 2. The air filter according to claim 1, wherein the nonwoven fabric is formed of a single layer or a laminate of multiple layers.

6. 6. The air filter according to claim 1, wherein the fibers constituting the nonwoven fabric are one or more types of fibers selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal.

7. A method for manufacturing an air filter according to any one of claims 1 to 6, comprising: a step of preparing a multifunctional coating film-forming liquid composition by mixing an aqueous dispersion of fluorine-containing metal oxide particles, a self-reactive carboxyl group- and / or acetyl group-containing substance, a mixed solvent of water and an alcohol having 1 to 4 carbon atoms, and an aqueous thickener solution or aqueous thickener dispersion; a step of dipping a nonwoven fabric into the multifunctional coating film-forming liquid composition; a step of draining the dipped nonwoven fabric and drying it; A method for manufacturing an air filter comprising:

8. 8. The method for producing an air filter according to claim 7, wherein the aqueous dispersion of fluorine-containing metal oxide particles is prepared by adding a fluorine-based compound to an aqueous dispersion of metal oxide particles and mixing the mixture.

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