JP7417469B2 - Air filter and its manufacturing method - Google Patents

Description

The present invention relates to an air filter that cleans air containing oil mist and dust, and a method for manufacturing the same. More specifically, the present invention relates to an air filter in which a water- and oil-repellent film having water and oil repellency is formed on the surface of nonwoven fabric fibers, and a method for manufacturing the same.

Machine tools such as cutting machines and lathes that process metal products using cutting oil scatter cutting oil due to high-speed operation of the machines, generating oil mist and dust at the same time. These oil mist and dust deteriorate the working environment and reduce the working efficiency. For this reason, air filter media that can suppress clogging not only from dust floating in the air but also from oil mist have been proposed as air filters that clean air containing oil mist and dust (for example, Patent Document 1 (Claim 1, paragraph [0006], paragraph [0021], paragraph [0045], paragraph [0053] to paragraph [0060]).

This air filter medium includes a first PTFE (polytetrafluoroethylene) porous membrane and a second PTFE porous membrane, and air flow is directed from the first main surface of the air filter medium to 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 porous PTFE membrane is in the range of 4 to 40 μm, the specific surface area of the first porous PTFE membrane is 0.5 m ² /g or less, and the specific surface area of the second porous PTFE membrane is in the range of 4 to 40 μm. is in the range of 1.5 to 10 m ² /g or less, which is larger than that of the first PTFE porous membrane.

The first and second porous PTFE membranes are formed by molding a mixture of PTFE fine powder and liquid lubricant into a sheet-like molded body. The first PTFE porous membrane is produced by stretching a sheet-like molded body while heating it in the longitudinal (MD) direction at a temperature higher than the melting point of PTFE (327°C) and at a magnification of 50 times or higher, and then stretched in the transverse (TD) direction. It is produced by stretching at a temperature of 130 to 400° C. while heating so that the length becomes 5 to 8 times the length before stretching. The second PTFE porous membrane is produced by stretching a PTFE sheet-shaped body while heating it in the MD direction at a temperature below the melting point of PTFE (270 to 290°C) and at a magnification of 15 to 40 times, and then stretching it in the TD direction. Then, it is further produced by stretching at a temperature of 120 to 130° C. while heating at the same magnification as in the MD direction stretching so that the length is 15 to 40 times the length before stretching.

Japanese Patent Application Publication No. 2018-51546

In the air filter medium disclosed in Patent Document 1, the first porous PTFE membrane is manufactured at a higher stretching temperature and a higher stretching ratio than the second porous PTFE membrane. , the specific surface area of the first PTFE porous membrane is reduced to 0.5 m ² /g or less, thereby collecting large particle size dust and oil mist. On the other hand, the specific surface area of the second PTFE porous membrane is increased to 1.5 to 10 m ² /g, thereby collecting small particle size dust and oil mist.

However, in the air filter medium disclosed in Patent Document 1, even though the first and second PTFE porous membranes collect dust and oil mist with different particle sizes, the PTFE porous membranes generate static electricity. However, it is difficult to process the filter into a filter shape because it is difficult to remove the generated static electricity. Furthermore, since water repellency is higher than oil repellency, moisture contained in the atmosphere may clog the PTFE porous membrane, making it easy for dust to adhere there. Therefore, if you continue to use the air filter medium, oil mist will continue to remain inside the air filter medium, and the air filter medium will easily become clogged.As a result, the amount of air passing through the air filter will likely decrease, and a new air filter will be required. There was a problem in that it had to be replaced frequently.

An object of the present invention is to provide an air filter that cleans air containing oil mist and dust and suppresses clogging. Another object of the present invention is to provide a method for easily manufacturing an air filter that cleans air containing oil mist and dust and suppresses clogging.

A first aspect of the present invention is that a large number of pores are formed between the fibers, penetrating between one surface through which air containing oil mist and dust flows in and the other surface facing this one surface through which the air flows out. An air filter including a nonwoven fabric, wherein a water- and oil-repellent film is formed on the fiber surface of the non-woven fabric, and the water- and oil-repellent film has a perfluoroether structure represented by the following general formula (1) or formula (2). Metal oxide particles (B) with an average particle diameter of 2 nm to 90 nm to which a fluorine-based functional group component (A) is bonded, and a carboxyl group- and/or acetyl group-containing substance (hereinafter simply referred to as “carboxyl group-containing substance, etc.”). ) (C), the carboxyl group-containing substance (C) is contained in the water- and oil-repellent film in a proportion of 10% by mass to 70% by mass, and the fluorine-based functional group component (A) The metal oxide particles (B) are contained in the water- and oil-repellent film in a total proportion of 30% by mass to 90% by mass, and the fluorine-based functional group component with respect to the metal oxide particles (B). The mass ratio (A/B) of (A) is in the range of 0.05 to 0.80, and the mass ratio (A/B) of the fluorine-based functional group component (A) to the metal oxide particle (B) is in the range of 0.05 to 0.80, and the air filter has an air permeability of 1 ml/cm ² /sec to 30 ml/cm ² /sec.

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

To further describe Y, Y is a site that binds to the metal oxide particles (B). A specific example is a structure in which the Z portion is hydrolyzed as Y in formula (3) or formula (4) described below. Examples of Y include the main component of a silica sol-gel obtained by hydrolytically polymerizing a mixture of a silane compound of formula (3) or formula (4) and a silicon alkoxide such as tetraethoxysilane or tetramethoxysilane. Furthermore, as Y, a silane compound of formula (3) or formula (4), a silicon alkoxide such as tetraethoxysilane or tetramethoxysilane, and a silane containing an epoxy group, a vinyl group, an ether group, etc. are mixed, Also included are main components of hydrolyzed polymerized silica sol gel. Incidentally, the carboxyl group-containing material (C) is a binder used to adhere the metal oxide particles (B) to which the fluorine-based functional group component (A) is bonded to the nonwoven fabric base material.

A second aspect of the present invention is an invention based on the first aspect, wherein the metal oxide particles (B) are selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. This is an air filter made of oxide particles of one type of metal.

A third aspect of the present invention is an invention based on the first aspect, wherein the carboxyl group-containing material (C) is an aqueous polyolefin dispersion having a carboxyl group, an ethylene-vinyl acetate copolymer self-containing material, etc. The air filter is an emulsion or a self-emulsification liquid of ethylene-vinyl acetate-acrylic acid copolymer.

A fourth aspect of the present invention is an air filter based on the first aspect, in which the nonwoven fabric is composed of a single layer or a laminate of multiple layers.

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

A sixth aspect of the present invention is that, as shown in FIG. 3, the content ratio of an aqueous dispersion of fluorine-containing metal oxide particles, a carboxyl group-containing substance, etc., and water or an alcohol having 1 to 4 carbon atoms is 40% by mass. % or less of water as a solvent to prepare a water- and oil-repellent film-forming liquid composition (hereinafter sometimes simply referred to as a liquid composition), and the water- and oil-repellent film-forming liquid The method for manufacturing an air filter includes the steps of dipping a nonwoven fabric in a diluted solution of a composition, and removing liquid from the dipped nonwoven fabric and drying it.

A seventh aspect of the present invention is an invention based on the sixth aspect, wherein the aqueous dispersion of fluorine-containing metal oxide particles is obtained by adding and mixing a fluorine-based compound to the aqueous dispersion of metal oxide particles, In this method, an air filter is prepared by adding and mixing a catalyst to this liquid mixture.

An eighth aspect of the present invention is an invention based on the seventh aspect, in which the metal oxide particles are made of one metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. This is a method for manufacturing an air filter made of oxide particles.

A ninth aspect of the present invention is an invention based on the sixth aspect, wherein the carboxyl group-containing material is a carboxyl group-containing polyolefin aqueous dispersion, a self-emulsion of an ethylene-vinyl acetate copolymer, Alternatively, it is a method for producing an air filter that is a self-emulsified liquid of ethylene-vinyl acetate-acrylic acid copolymer.

In the air filter according to the first aspect of the present invention, a water- and oil-repellent film is formed on the fiber surface of a nonwoven fabric included in the air filter, and the water- and oil-repellent film is formed by the above-mentioned general formula (1) or formula (2). A metal oxide particle (B) having an average particle diameter of 2 nm to 90 nm to which a fluorine-based functional group component (A) shown as shown is bonded, and a carboxyl group-containing substance (C), and the carboxyl group-containing substance (C) is contained in the water- and oil-repellent film in a proportion of 10% by mass to 70% by mass, and the fluorine-based functional group component (A) and the metal oxide particles (B) are included in the water- and oil-repellent film in total. It is contained in the oily film in a proportion of 30% to 90% by mass, and the mass ratio (A/B) of the fluorine-based functional group component (A) to the metal oxide particles (B) is 0.05 to 0. 80, and the air permeability of the air filter is between 1 ml/cm ² /sec and 30 ml/cm ² /sec. Therefore, when air containing oil mist and dust flows into the air filter from one side of the air filter, the oil mist and dust are collected by the nonwoven fabric, and only the air passes through the pores of the nonwoven fabric and flows out from the other side of the air filter. This makes the air cleaner and prevents clogging.

At this time, because of the oil-repellent performance of the water- and oil-repellent film, and because the air permeability of the air filter is 1 ml/cm ² /sec to 30 ml/cm ² /sec, the oil mist repels the water- and water-repellent surface of the fibers of the nonwoven fabric. It does not stick to the oily film, but is repelled and sticks to the surface. As the air filter continues to be used and the amount of oil mist collected inside the nonwoven fabric increases, if the air filter is placed horizontally, the oil mist will liquefy and be entrained by the passing air, causing it to flow onto the other side of the air filter. If the air filter is arranged vertically, the collected oil mist will collect at the lower end of the air filter due to its own weight and will not block the pores of the nonwoven fabric. This suppresses clogging of the pores due to oil mist.

On the other hand, since the air permeability of the air filter is 1 ml/cm ² /sec to 30 ml/cm ² /sec, dust may directly adhere to the water- and oil-repellent film on the fiber surface of the nonwoven fabric, or It adheres to the oil mist that adheres to the surface. Therefore, when the air filter becomes clogged with dust after long-term use, applying an impact to the air filter with an air knocker or the like will easily remove the dust that has adhered to it along with the oil mist. Can be played.

In the air filter according to the second aspect of the present invention, the metal oxide particles contained in the water- and oil-repellent film are one metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. Since the particles are oxide particles, metal oxide particles suitable for the usage environment of the air filter can be included from among various types of metal oxide particles.

In the air filter according to the third aspect of the present invention, the carboxyl group-containing material is a polyolefin aqueous dispersion having a carboxyl group, a self-emulsion of an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic acid copolymer. Since it is a self-emulsifying liquid of coalescence, this aqueous dispersion or self-emulsifying liquid acts as a binder for the fluorine-containing metal oxide particles, and when the liquid composition is formed on the surface of the substrate, the film is formed on the surface of the substrate. It can be firmly attached to.

In the air filter according to the fourth aspect of the present invention, when the nonwoven fabric is composed of a single layer, the air filter has a simple configuration, and when the nonwoven fabric is composed of a laminate of multiple layers, the air filter has a simple structure. Each layer can be configured depending on the properties such as the particle size of dust and the size of oil particles of oil mist.

In the air filter according to the fifth aspect of the present invention, the material of the fibers constituting the nonwoven fabric is polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, It can be selected from nylon and metal depending on the properties such as the particle size of inflowing dust and the size of oil particles of oil mist.

In the method according to the sixth aspect of the present invention, as shown in FIG. A water- and oil-repellent film-forming liquid composition is prepared by mixing with a solvent which is 40% by mass or less of water, and a non-woven fabric is dipped in a diluted solution of this water- and oil-repellent film-forming liquid composition. Since an air filter is manufactured by removing liquid and drying, a water- and oil-repellent film can be uniformly formed on the fiber surface of the nonwoven fabric. Furthermore, since metal oxide particles whose particle surfaces are water and oil repellent are present in the carboxyl group-containing material, it becomes easy to lower the air permeability of the nonwoven fabric while maintaining water and oil repellency. Furthermore, unlike the porous PTFE membrane of Patent Document 1, the water- and oil-repellent membrane is less likely to generate static electricity, making it possible to easily manufacture an air filter.

In the method for manufacturing an air filter according to the seventh aspect of the present invention, a fluorine-based compound is added to and mixed with an aqueous dispersion of metal oxide particles, and a catalyst is added and mixed with this mixture, so that fluorine-containing metal oxide particles are mixed. A uniformly dispersed dispersion is obtained.

In the method for manufacturing an air filter according to the eighth aspect of the present invention, the metal oxide particles are one type of metal oxide particles selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. Therefore, an air filter containing metal oxide particles suitable for the environment in which the air filter is used can be manufactured from among various types of metal oxide particles.

In the method for producing an air filter according to the ninth aspect of the present invention, the carboxyl group-containing material is a carboxyl group-containing polyolefin aqueous dispersion, a self-emulsion of an ethylene-vinyl acetate copolymer, or an ethylene-vinyl acetate-acrylic Since it is a self-emulsified liquid of an acid copolymer, this aqueous dispersion or self-emulsified liquid acts as a binder for the fluorine-containing metal oxide particles, and when the liquid composition is formed into a film on the surface of a substrate, the film is formed. It can be firmly attached to the surface of the base material.

For comparison, as shown in Comparative Example 4, which will be described later, metal If an air filter is manufactured by a method different from the present invention shown in FIG. 3, in which an aqueous dispersion of oxide particles is added, the air permeability of the nonwoven fabric can be lowered, but the essential oil repellency cannot be maintained sufficiently. can't get to it. On the other hand, in the method for manufacturing an air filter according to any one of the sixth to ninth aspects of the present invention, in order to bind the water- and oil-repellent film to the fiber surface of the nonwoven fabric while lowering the air permeability, Sufficient oil repellency can be obtained. Furthermore, the metal oxide particles also have the effect of improving the abrasion strength of the film.

FIG. 2 is a side view of a single layer nonwoven fabric of this embodiment. FIG. 2 is a side view of the two-layer nonwoven fabric of this embodiment. FIG. 2 is a flow diagram for manufacturing the air filter of this embodiment.

Next, embodiments for carrying out the present invention will be described with reference to the drawings.

[Air filter]
As shown in FIG. 1, the air filter 10 of this embodiment includes a nonwoven fabric 20 and a water/oil repellent film 21 having water and oil repellency formed on the fiber surface of the nonwoven fabric. The nonwoven fabric 20, which is the main component of the air filter 10, is made of a single layer and has one surface 20a through which air containing oil mist and dust flows in, and the other surface 20b opposite to this one surface 20a through which the air flows out. . As shown in FIG. 2, an air filter 50 may be formed of a two-layer laminate of an upper nonwoven fabric 30 and a lower nonwoven fabric 40. In this case, the upper surface of the upper layer nonwoven fabric 30 becomes one surface 30a into which air containing oil mist and dust flows, and the lower surface of the lower layer nonwoven fabric 40 becomes the other surface 40b opposite to this one surface 30a. Note that the laminate is not limited to two layers, but may be composed of multiple layers such as three layers or four layers.

As shown in the enlarged view at the center of FIG. 1, the nonwoven fabric 20 is formed by intertwining a large number of fibers 20c, and pores 20d are formed between the fibers. The pores 20d penetrate between the one surface 20a and the other surface 20b of the nonwoven fabric 20. A water- and oil-repellent film 21 is formed on the surface of the nonwoven fabric fibers 20c. The basis weight of the nonwoven fabric is preferably in the range of 100 g/m ² to 400 g/m ² , but is not limited to this range. The water- and oil-repellent film 21 includes metal oxide particles (B) having an average particle diameter of 2 nm to 90 nm and a carboxyl group-containing material (C). The fluorine-based functional group component (A) represented by the aforementioned general formula (1) or formula (2) is bonded to the metal oxide particles (B). The fluorine-based functional group component (A) is contained in the water- and oil-repellent film 21 in a proportion of 1% by mass to 30% by mass. Further, the carboxyl group-containing substance (C) is contained in the water- and oil-repellent film 21 in a proportion of 10% by mass to 70% by mass. Further, the fluorine-based functional group component (A) and the metal oxide particles (B) are contained in the water- and oil-repellent film 21 in a total amount of 30% by mass to 90% 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 0.05 to 0.80.

As shown in the further enlarged view at the top of FIG. 1, the water- and oil-repellent film 21 includes a large number of metal oxide particles 21a whose particle surfaces are covered with a fluorine-based functional group component, and a carboxyl group-containing material 21b as a binder. It is composed of . Since the water- and oil-repellent film 21 contains the metal oxide particles 21a, it appears to be a thick film, and the pores 20d between the fibers can be narrowed. Further, the film thickness can be controlled by changing the particle diameter of the metal oxide particles and the content ratio of the metal oxide particles in the film components.

When the basis weight of the nonwoven fabric is less than 100 g/m ² , the pores between the fibers are too large, and the ability to collect dust is likely to be insufficient. If it exceeds 400 g/m ² , the air permeability will be less than 1 ml/cm ² /sec, and dust will easily get stuck in the pores between the fibers, or the air permeability will be too low and the air will not flow due to the resistance of the air sent to the air filter. Pressure loss tends to occur in the filter, and the efficiency of air blowing energy tends to deteriorate. More preferably, the basis weight of the nonwoven fabric is in the range of 200 g/m ² to 350 g/m ² .

In the state of the air filter 10 in which the water- and oil-repellent film 21 is formed on the fiber surface, the nonwoven fabric 20 is manufactured to have an air permeability of 1 ml/cm ² /sec to 30 ml/cm ² /sec. If the air permeability is less than 1 ml/cm ² /sec, the air permeability will be poor and it will be difficult for air containing oil mist and dust to pass through. When it exceeds 30 ml/cm ² /sec, the size of the pores 20d of the nonwoven fabric becomes far larger than the respective particle sizes of the oil particles 22 of the oil mist and the dust particles 23 in the inflowing air, and the oil particles 22 and Dust particles 23 pass through the air filter 10 through the pores of the nonwoven fabric along with the air, and oil mist and dust cannot be collected. The air permeability is preferably 1.5 ml/cm ² /sec to 25 ml/cm ² /sec. Air permeability is measured using a Frazier type tester described in JIS-L1913:2000.

If the content of the fluorine-based functional group component (A) in the water- and oil-repellent film 21 is less than 1% by mass, the oil-repellent effect will be poor and the oil mist repelling performance will be insufficient. That is, when the oil mist reaches the air filter, it wets and spreads over the fiber surface, making it easier to block the pores 20d. When the content of the fluorine-based functional group component (A) exceeds 30% by mass, the adhesion of the water- and oil-repellent film to the nonwoven fabric deteriorates. The content of the fluorine-based functional group component (A) in the water- and oil-repellent film 21 is preferably 5% by mass to 25% by mass.

The metal oxide particles (B) contained in the water- and oil-repellent film 21 have an average particle diameter in the range of 2 nm to 90 nm. In the water- and oil-repellent film 21, the fluorine-based functional group component (A) and the metal oxide particles (B) are contained in a total proportion of 30% by mass to 90% by mass, preferably 35% by mass to 85% 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 0.05 to 0.80, preferably 0.07 to 0.70. If the total amount of component (A) and particles (B) is less than 30% by mass in the water- and oil-repellent film 21, the oil-repellent performance of the water- and oil-repellent film will deteriorate. Moreover, when the total amount exceeds 90% by mass, the content of the carboxyl group-containing substance (C) becomes relatively low, and the water- and oil-repellent film does not firmly adhere to the surface of the nonwoven fabric. If the mass ratio (A/B) is less than 0.05, the water- and oil-repellent film will have poor oil repellency, and if it exceeds 0.80, the adhesion of the water- and oil-repellent film to the fiber surface will decrease.

The operation of such an air filter 10 will be explained. As shown in FIG. 1, air containing oil mist and dust reaches one surface 20a of the nonwoven fabric 20 that constitutes the air filter 10. As shown in FIG. Here, since the air filter 10 has a predetermined air permeability, and since the water- and oil-repellent film 21 exhibits oil-repellency, it goes without saying that the oil particles 22 of the oil mist have a particle size larger than the pore size of the pores 20d. Even if the particle size is slightly smaller than the pore size of the pores 20d, it cannot pass through the air filter 10, and is repelled by the water- and oil-repellent film 21 between the fibers 20c of the non-woven fabric 20. It sticks to 21 and stops. At the same time, dust particles 23 also adhere to the water- and oil-repellent film 21 and stop there. Since the metal oxide particles 21a are included in the water- and oil-repellent film 21, the film becomes uneven, and while the degree of adhesion of oil particles 22 to the film is low, dust particles 23 tend to adhere thereto. As a result, the oil particles 22 of the oil mist and the particles 23 of dust are collected on the nonwoven fabric, and the air containing the oil mist and dust is transferred to the pores formed between the fibers 20c and the fibers 20c shown in the enlarged view of FIG. 20d and reaches the other surface 20b, where it becomes air free of oil mist and dust and passes through the nonwoven fabric 20.

As the air filter continues to be used and the amount of oil mist trapped inside the nonwoven fabric increases, if the air filter is placed horizontally, the oil mist that adheres to the membrane to a low degree will liquefy and become absorbed by the air passing through. When the air filter is arranged vertically, the collected oil mist gathers at the lower end of the air filter due to its own weight and does not block the pores of the nonwoven fabric. This suppresses clogging of the pores due to oil mist. The dust adheres directly to the water- and oil-repellent film on the fiber surface of the nonwoven fabric, or to the oil mist that adheres to the water- and oil-repellent film. The oil mist and dust accumulated on the nonwoven fabric 20 can be removed from the air filter 10 by periodically impacting the air filter 10 with an air knocker or the like.

[Air filter manufacturing method]
The air filter is generally manufactured by the following method.
As shown in FIG. 3, a fluorine-based compound 52 containing a fluorine-based functional group component (A) is mixed with an aqueous dispersion 51 of metal oxide particles, and a catalyst 53 is further mixed therein. A dispersion liquid 54 is prepared. A water- and oil-repellent film-forming liquid composition 60 is prepared by mixing this aqueous dispersion 54, a carboxyl group-containing substance, etc. 55, and a solvent 56. This liquid composition 60 is diluted with a solvent 61 to prepare a diluted liquid 62, into which the nonwoven fabric 20 is dipped. Subsequently, the nonwoven fabric 20 is dehydrated and dried to produce the air filter 10.

The method for manufacturing the air filter will be described in detail below.
[Preparation of nonwoven fabric]
First, a nonwoven fabric having an air permeability of 1.1 ml/cm ² /sec to 40 ml/cm ² /sec is prepared. Specifically, a nonwoven fabric having an air permeability of 1 ml/cm ² /sec to 30 ml/cm ² /sec is prepared, with a water- and oil-repellent film described below acting as an air filter formed on the fiber surface of the nonwoven fabric. do. When the water- and oil-repellent film is formed into a thick film, a non-woven fabric with high air permeability is selected, and when the water- and oil-repellent film is formed into a thin film, a non-woven fabric with low air permeability is selected.

Examples of the nonwoven fabric include a cellulose mixed ester membrane filter, glass fiber filter paper, and a nonwoven fabric made of a mixture of polyethylene terephthalate fiber and glass fiber (manufactured by Azumi Roshi Co., Ltd., trade name: 340). In this way, the nonwoven fabric is one or two types selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal. Made from more than 100 fibers. The fiber may be a mixture of two or more fibers. The thickness of the fibers (fiber diameter) is preferably 0.01 μm to 10 μm so that the above air permeability can be obtained. The thickness of the nonwoven fabric is 0.2 mm to 0.8 mm when the air filter is a single layer, and 0.2 mm to 1.6 mm when the air filter is a laminate of multiple layers. It is preferable that the thickness is as follows.

[Method for producing water- and oil-repellent film-forming liquid composition]
[Preparation of aqueous dispersion of metal oxide particles]
First, metal oxide particles are dispersed in an aqueous solvent to prepare an aqueous dispersion of metal oxide particles. 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 diameter is less than 2 nm, the metal oxide particles tend to aggregate and become difficult to disperse in the medium. If it exceeds 90 nm, the metal oxide particles will fall off from the water- and oil-repellent film when the liquid composition is formed into a film. Examples of metal oxide particles include particles of SiO ₂ , Al ₂ O ₃ , MgO, CaO, TiO ₂ , ZnO, and ZrO ₂ .

Examples of the aqueous solvent include water or a mixed solvent of water and an alcohol having 1 to 4 carbon atoms. As the above-mentioned water, it is desirable to use ion exchange water, pure water, etc. to prevent contamination with impurities. Here, the reason why an aqueous solvent is used as a solvent and an organic solvent is not used is for safety in handling. In addition, in this specification, the average particle diameter of metal oxide particles refers to the average value of the particle sizes measured by image analysis at 200 points among the particle shapes observed with a transmission electron microscope (TEM).

[Preparation of fluorine-containing metal oxide particle dispersion]
Next, a fluorine-based compound containing a fluorine-based functional group component represented by the above-mentioned formula (1) or formula (2) is added to the prepared aqueous dispersion of metal oxide particles. A nanocomposite of particles and a fluorine-based functional group component is synthesized. A catalyst is added to further promote the reaction. In this way, an aqueous dispersion of fluorine-containing metal oxide particles is prepared.

Examples of the above-mentioned catalysts include organic acids, inorganic acids, alkalis, and titanium compounds; examples of organic acids include formic acid and oxalic acid; examples of inorganic acids include hydrochloric acid, nitric acid, and phosphoric acid; Examples include sodium oxide, 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 those listed above.

The fluorine-based compound containing a fluorine-based functional group component is represented by the following general formula (3) or formula (4). More specifically, the perfluoroether groups in these formulas (3) and (4) include perfluoroether structures represented by the following formulas (5) to (13).

Further, as X in the above formulas (3) and (4), structures represented by the following formulas (14) to (18) can be mentioned. In addition, the following formula (14) is an example containing an ether bond, the following formula (15) is an ester bond, the following formula (16) is an amide bond, the following formula (17) is an example containing a urethane bond, and the following formula (18) is an example containing a sulfonamide bond. It shows.

Here, in the above formulas (14) to (18), R ² and R ³ are hydrocarbon groups having 0 to 10 carbon atoms, and R ⁴ is a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group for R ³ include alkylene groups such as methylene and ethylene groups, and examples of the hydrocarbon group for R ⁴ include alkyl groups such as methyl and ethyl groups, as well as phenyl groups, etc. can also be mentioned.

Further, in the above formulas (3) and (4), R ¹ includes a methyl group, an ethyl group, and the like.

Furthermore, 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, benzyloxy groups, and phenethyloxy groups. Examples include aralkyloxy groups such as aralkyloxy groups, acetoxy groups, propionyloxy groups, butyryloxy groups, valeryloxy groups, pivaloyloxy groups, and acyloxy groups such as benzoyloxy groups. Among these, it is preferable to use an ethoxy group.

Here, specific examples of fluorine-based compounds containing a fluorine-based functional group component having a perfluoroether structure represented by the above formula (3) or formula (4) include the following formulas (19) to (27). The structures represented are listed. In addition, in the following formulas (19) to (27), R is a methyl group or an ethyl group.

As described above, the fluorine-based compound contained in the water- and oil-repellent film-forming liquid composition of the present embodiment has an oxygen atom in the molecule containing a short-chain perfluoroalkyl group having 6 or less carbon atoms and a perfluoroalkylene group. It has a perfluoroether group in which multiple groups are bonded, and the fluorine content in the molecule is high, so it can impart excellent water and oil repellency to the formed film.

[Carboxyl group-containing substances, etc.]
The carboxyl group-containing material is an aqueous polyolefin dispersion having a carboxyl group, a self-emulsion of an ethylene-vinyl acetate copolymer, or a self-emulsion of an ethylene-vinyl acetate-acrylic acid copolymer. Commercially available ethylene-vinyl acetate products include Sepolsion VA406N, Sepolsion VA407N (all manufactured by Sumitomo Seika Co., Ltd.), Sumikaflex S-201HQ, S-465HQ (all manufactured by Sumitomo Chemical Co., Ltd.), and Quatex EC. -1800 and EC-1200 (both manufactured by Japan Coating Resin Co., Ltd.). Examples of polyolefin-based polyolefins having carboxyl groups include Zaixen A, Zaixen L, and Zaixen N (all manufactured by Sumitomo Seika Co., Ltd.); examples of ethylene-vinyl acetate-acrylic acid-based products include Sumikaflex S-900HL ( manufactured by Sumitomo Chemical Co., Ltd.).

[Water- and oil-repellent film-forming liquid composition]
The water- and oil-repellent film-forming liquid composition of the present embodiment is produced by the above-mentioned production method, and comprises metal oxide particles (B) to which the aforementioned fluorine-based functional group component (A) is bonded, and a carboxyl group-containing material. etc. (C) and a solvent (D). This fluorine-based functional group component (A) has a perfluoroether structure represented by the above general formula (1) or formula (2), and when the total amount of components excluding the solvent (D) is 100% by mass, It is contained in the liquid composition in an amount of 1% to 30% by mass. If the content of the fluorine-based functional group component is less than 1% by mass, oil repellency cannot be imparted to the formed film, and if it exceeds 30% by mass, repellency of the film will occur, resulting in poor film formability. The preferred content of the fluorine-based functional group component is 2% by mass to 28% by mass. In addition, the total content of the fluorine-based functional group component (A) and the metal oxide particles (B) is 30% by mass in the liquid composition, when the total amount of components excluding the solvent (D) is 100% by mass. 90% by weight, preferably 35% to 85% by weight. 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 0.05 to 0.80, preferably 0.07 to 0.70.

If the total amount of component (A) and particles (B) in the liquid composition excluding the solvent is less than 30% by mass, the oil repellency of the water- and oil-repellent film will deteriorate. If the total content exceeds 90% by mass, the content of the carboxyl group-containing substance (C) becomes relatively low, and when the liquid composition is formed into a film on a base material, the water- and oil-repellent film is formed on the nonwoven fabric. It no longer binds firmly to the fiber surface. If the mass ratio (A/B) is less than 0.05, the water- and oil-repellent film will have poor oil repellency, and if it exceeds 0.80, the adhesion of the water- and oil-repellent film to the fiber surface of the nonwoven fabric will decrease. . The solvent (D) is water or water in which the content of alcohol having 1 to 4 carbon atoms is 40% by mass or less. The reason why the content of alcohol having 1 to 4 carbon atoms is 40% by mass or less is for handling safety and storage stability of the liquid composition. Further, by using a mixed solvent of water and an alcohol having 1 to 4 carbon atoms, the drying speed is increased and the film forming property is 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.

[Method for forming a water- and oil-repellent film on the fiber surface of a nonwoven fabric]
In order to form a water- and oil-repellent film on the fiber surface of the nonwoven fabric of this embodiment, a water- and oil-repellent film-forming liquid composition is mixed with water and an alcohol having a carbon number of 1 to 4 and a boiling point of less than 120°C. Prepare a solution diluted with a mixed solvent. The mixing ratio of water and alcohol in this solvent (water:alcohol) is 1:0 to 5 by mass. The mass ratio of the solvent to the liquid composition (liquid composition:solvent) is 1:0.1 to 10. The nonwoven fabric is dipped in the diluted solution prepared in this way, pulled out from the diluted solution, and spread on a horizontal wire mesh or the like in the atmosphere at room temperature to remove liquid until a constant liquid volume is reached. Alternatively, the pulled-up nonwoven fabric may be shaken off to remove excess liquid, or the pulled-up nonwoven fabric may be passed through a mangle roll to remove liquid. The dehydrated nonwoven fabric is dried in the air at a temperature of 25° C. to 140° C. for 0.5 hours to 24 hours. As a result, as shown in the enlarged view in the center of FIG. 1, a water- and oil-repellent film 21 is formed on the surface of the fibers 20c constituting the nonwoven fabric 20. When the amount of liquid removed is small, a thick water- and oil-repellent film is formed on the fiber surface of the non-woven fabric, and when the amount of liquid removed is large, a thin water- and oil-repellent film is formed on the fiber surface of the non-woven fabric. Ru.

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 an aqueous dispersion of fluorine-containing metal oxide particles will be explained, and then a method for forming a water- and oil-repellent film using these Synthesis Examples and Comparative Synthesis Examples will be explained. Examples 1 to 6 and Comparative Examples 1 to 3 regarding preparation of liquid composition and production of air filter, and preparation of liquid composition for forming water- and oil-repellent film and air filter without using these synthesis examples and comparative synthesis examples Comparative Example 4 regarding the production of will be explained.

[Synthesis Examples 1 to 6, Comparative Synthesis Examples 1 to 4 for preparing fluorine-containing metal oxide particle dispersion]
<Synthesis example 1>
A fluorine compound represented by the above formula (19) was placed in a beaker containing 50.0 g of an aqueous dispersion of silicon dioxide (ST-OXS, manufactured by Nissan Chemical Co., Ltd., SiO ₂ concentration 10%) with an average particle size of 5 nm. 4.00g of was added and mixed. Next, 0.013g of nitric acid was added and mixed at 40°C for 2 hours to form an aqueous dispersion of silicon dioxide (silica) particles in which silicon dioxide particles bonded to a fluorine-based compound (an aqueous dispersion of fluorine-containing silica particles). Obtained. The mass ratio (A/B) of the fluorine-based functional group component (A) to silicon dioxide, which is the metal oxide particle (B), was 0.75.

<Synthesis example 2>
A fluorine compound represented by the above formula (20) was placed in a beaker containing 50.0 g of an aqueous dispersion of silicon dioxide (ST-XS, manufactured by Nissan Chemical Co., Ltd., SiO ₂ concentration 30%) with an average particle size of 45 nm. 0.90g of was added and mixed. Next, 0.005 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of silicon dioxide (silica) particles (an aqueous dispersion of fluorine-containing silica particles). The mass ratio (A/B) was 0.05.

<Synthesis example 3>
A fluorine-based compound represented by the above formula (21) was placed in a beaker containing 50.0 g of an aqueous dispersion of silicon dioxide with an average particle diameter of 80 nm (ST-ZL, manufactured by Nissan Chemical Co., Ltd., SiO ₂ concentration 30%). 3.00g of was added and mixed. Next, 0.005 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of silicon dioxide (silica) particles (an aqueous dispersion of fluorine-containing silica particles). The mass ratio (A/B) was 0.19.

<Synthesis example 4>
A fluorine-based compound represented by the above formula (27) was placed in a beaker containing 50.0 g of an aqueous dispersion of zirconium dioxide with an average particle diameter of 3 nm (SZR-W, manufactured by Sakai Chemical Co., Ltd., ZrO ₂ concentration 30%). 3.00g of was added and mixed. Next, 0.009 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of zirconium dioxide particles (an aqueous dispersion of fluorine-containing zirconia particles). The mass ratio (A/B) of the fluorine-based functional group component (A) to zirconium dioxide, which is the metal oxide particle (B), was 0.19.

<Synthesis example 5>
A fluorine-based compound represented by the above formula (27) was added to a beaker containing 50.0 g of an aqueous dispersion of titanium dioxide with an average particle size of 6 nm (TKS-203, manufactured by Teika, TiO ₂ concentration 20%). 2.00g was added and mixed. Next, 0.006 g of nitric acid was added, and in the same manner as in Synthesis Example 1, an aqueous dispersion of titanium dioxide particles (aqueous dispersion of fluorine-containing titania particles) was obtained. The mass ratio (A/B) of the fluorine-based functional group component (A) to titanium dioxide, which is the metal oxide particle (B), was 0.19.

<Synthesis example 6>
In a beaker containing 50.0 g of an aqueous dispersion of zinc oxide with an average particle size of 25 nm (MZ-500, manufactured by Teika, ZnO concentration 30%), 3 fluorine-based compounds represented by the above formula (27) were added. .00g was added and mixed. Next, 0.005 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of zinc oxide particles (an aqueous dispersion of fluorine-containing zinc oxide particles). The mass ratio (A/B) of the fluorine-based functional group component (A) to zinc oxide, which is the metal oxide particle (B), was 0.19.

<Comparative synthesis example 1>
In a beaker containing 50.0 g of an aqueous dispersion of titanium dioxide with an average particle size of 230 nm (R32, manufactured by Sakai Chemical Co., Ltd., TiO ₂ concentration 30%), 3 fluorine-based compounds represented by the above formula (27) were added. .00g was added and mixed. Next, 0.005 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of titanium dioxide particles (an aqueous dispersion of fluorine-containing titania particles). The mass ratio (A/B) of the fluorine-based functional group component (A) to titanium dioxide, which is the metal oxide particle (B), was 0.19.

<Comparative synthesis example 2>
Into a beaker containing 50.0 g of the same aqueous dispersion of silicon dioxide as in Synthesis Example 2, 0.60 g of the fluorine-based compound represented by the above formula (27) was added and mixed. Next, 0.005 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of silicon dioxide (silica) particles (an aqueous dispersion of fluorine-containing silica particles). The mass ratio (A/B) was 0.04.

<Comparative synthesis example 3>
Into a beaker containing 50.0 g of the same silicon dioxide aqueous dispersion as in Synthesis Example 2, 13.50 g of the fluorine-based compound represented by the above formula (27) was added and mixed. Next, 0.043 g of nitric acid was added, and the same procedure as in Synthesis Example 1 was carried out to obtain an aqueous dispersion of silicon dioxide (silica) particles (an aqueous dispersion of fluorine-containing silica particles). The mass ratio (A/B) was 0.84.

Table 1 below shows the contents of the aqueous dispersions of fluorine-containing metal oxide particles of Synthesis Examples 1 to 6 and Comparative Synthesis Examples 1 to 3. In Table 1, all R's in the formulas of the fluorine-containing silanes represented by formulas (19) to (21) and formula (27) as fluorine-based compounds are ethyl groups.

[Examples 1 to 6 and Comparative Examples 1 to 4 for preparation of water- and oil-repellent film-forming liquid composition and production of air filter]
<Example 1>
Aqueous ammonia (ammonia concentration 20% by mass) was appropriately added to 6.43 g of the aqueous dispersion of fluorine-containing silica particles obtained in Synthesis Example 1, and this liquid and a carboxyl group, which is one type of carboxyl group-containing substance, were added. Mix 10.00 g of a polyolefin aqueous dispersion (Zaixen A, manufactured by Sumitomo Seika Co., Ltd.) with a solvent consisting of 94.86 g of water and 23.71 g of industrial alcohol (AP-7, manufactured by Nippon Alcohol Sangyo Co., Ltd.), 135.00 g of a water- and oil-repellent film-forming liquid composition was prepared. A diluted solution was prepared by diluting 135.00 g of the obtained water- and oil-repellent film-forming liquid composition with 65.00 g of a mixed solvent of water and industrial alcohol (mass ratio of water: industrial alcohol = 1:1). did. As the base material of the air filter, nonwoven fabric 356 manufactured by Azumi Filter Paper Co., Ltd., which is made of a mixed fiber of PET fiber and glass fiber (mass ratio of PET: glass = 80:20) and has an air permeability of 9.3 ml/m ² /s, is used. there was. The nonwoven fabric was dipped in the diluted solution, the excess solution was shaken off, and the fabric was dried at room temperature for 24 hours to produce an air filter with an air permeability of 6.5 ml/cm ² /sec. The contents are shown in Tables 2 and 3 below.

Table 2 shows the content ratio of "fluorine-based functional group component (A) in the liquid composition excluding solvent", the content ratio of "carboxyl group-containing substance, etc. (C) in the liquid composition excluding solvent", and the content ratio of " The total content ratio of the fluorine-based functional group component (A) and metal oxide particles (B) in the liquid composition excluding the solvent is also shown. In addition, the content ratio (%) of the fluorine-based functional group component (A) in the liquid composition excluding the solvent is expressed as [(A) /[(A)+(B)+(C)]], and the content ratio (%) of carboxyl group-containing substances, etc. (C) in the liquid composition excluding the solvent is [(C)/[ (A) + (B) + (C)]], which is the total content (%) of the fluorine-based functional group component (A) and metal oxide particles (B) in the liquid composition excluding the solvent. is expressed as a percentage of [[(A)+(B)]/[(A)+(B)+(C)]], taking into account the content ratio of carboxyl group-containing substances (C). be.

<Examples 2 to 7 and Comparative Examples 1 to 3>
As shown in Table 2, in Examples 2 to 6, the respective weights were determined using the aqueous dispersions of fluorine-containing metal oxide particles obtained in Synthesis Examples 1 to 6 shown in Table 1. In Example 7, the weight was determined using the aqueous dispersion of fluorine-containing metal oxide particles obtained in Synthesis Example 1 shown in Table 1. In Comparative Examples 1 to 3, the respective weights were determined using the aqueous dispersions of fluorine-containing metal oxide particles obtained in Comparative Synthesis Examples 1 to 3 shown in Table 1.
In Example 2 and Comparative Examples 1 to 3, Zaixen N (manufactured by Sumitomo Seika Chemical Co., Ltd.), a polyolefin aqueous dispersion having a carboxyl group, was used as the carboxyl group-containing substance, etc., and the weight of each was determined. In Examples 3 to 5 and Example 7, the respective weights were determined using Zaixen L (manufactured by Sumitomo Seika Chemical Co., Ltd.), which is a polyolefin aqueous dispersion having a carboxyl group. In Example 6, the weight was determined using Sepolsion VA406N (manufactured by Sumitomo Seika Chemical Co., Ltd.), which is a self-emulsified liquid of ethylene-vinyl acetate copolymer.
In this way, the water- and oil-repellent film-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 3 were prepared.

The diluted solutions of the water- and oil-repellent film-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 3 were prepared by selecting nonwoven fabrics with different air permeability and types of air filter base materials shown in Table 3. A base material made of the selected nonwoven fabric was dipped in the same manner as in Example 1, and the liquid was removed and dried to obtain an air filter having the characteristics shown in Table 3.

<Comparative example 4>
In Comparative Example 4, a water- and oil-repellent film-forming liquid composition was prepared by a method different from that in Examples 1 to 7 and Comparative Examples 1 to 3 above. That is, 10.00 g of a carboxyl group-containing polyolefin aqueous dispersion (Zaixen A, manufactured by Sumitomo Seika Co., Ltd.), which is a type of carboxyl group-containing material, and a fluorine-containing silane represented by formula (27) as a fluorine-based compound. 0.47 g (R: ethyl group), 94.86 g of water, and 23.71 g of industrial alcohol (AP-7, manufactured by Nippon Alcohol Sangyo Co., Ltd.) were mixed.
Next, 6 g of an aqueous dispersion of silicon dioxide (ST-OXS, manufactured by Nissan Chemical Co., Ltd., SiO ₂ concentration 10%) with an average particle size of 5 nm was added to this mixture, and the mixture was heated at 25°C in a separable flask for 50 minutes. A mixed solution was prepared by stirring for a minute, and a water- and oil-repellent film-forming liquid composition was prepared. The same nonwoven fabric as in Example 7 was dipped in the diluted solution of this water- and oil-repellent film-forming liquid composition in the same manner as in Example 1, and then the liquid was removed and dried to form an air filter having the characteristics shown in Table 3. I got it.

Note that, unlike the nonwoven fabric of Example 1, the nonwoven fabric used in Example 7 and Comparative Example 3 consists of two layers: a nonwoven fabric of glass fiber and a nonwoven fabric of PET fiber. The air permeability of the obtained air filters was 1.3 ml/cm ² /sec and 0.8 ml/cm ² /sec, respectively.

<Comparative test and evaluation>
To simulate the oil mist and dust scattered from machine tools that process metal products using cutting oil, hexadecane and iron (III) oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a mass ratio of 80:20. The mixture was poured into a rotation/revolution stirrer and stirred and mixed to obtain a simulated liquid. After dropping 1 ml of the obtained simulated liquid from above onto the 11 types of horizontally placed air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 4, the air filters were stood vertically and the simulated liquid was poured. Confirmed fallability. If the simulated liquid soaked into the air filter, the oil repellency of the air filter was considered to be "poor," and if the simulated liquid fell from the air filter, the oil repellency of the air filter was considered to be "good."

As is clear from Table 3, for the air filter of Comparative Example 1, a liquid composition for forming a water- and oil-repellent film was prepared from Comparative Synthesis Example 1 containing metal oxide (titanium dioxide) particles with an average particle size of 230 nm. However, since it was made by dipping a nonwoven fabric in this liquid composition, removing the liquid, and drying it, the average particle size of the metal oxide particles was too large, and the metal oxide particles were mixed with the nonwoven fabric due to the carboxyl group-containing binder component. It was difficult to bind to the fiber surface. As a result, the simulated liquid did not fall from the air filter, and the oil repellency was "poor."

In the air filter of Comparative Example 2, "(A)/(B)" in the aqueous dispersion of fluorine-containing metal oxide particles (aqueous dispersion of fluorine-containing silica particles) was 0.04, and the solvent (D) was The content ratio of "carboxyl group-containing substance, etc. (C)" in the liquid composition excluding the solvent (D) is 80% by mass, and the content ratio of "(A) + (B)" in the liquid composition excluding the solvent (D) is The content of the fluorine-based functional group component in the film was 20% by mass, which was too low. For this reason, the air permeability of the air filter was too high at 32.2 ml/cm ² /sec, and the simulated liquid soaked into the air filter and did not fall down, resulting in poor oil repellency.

In the air filter of Comparative Example 3, "(A)/(B)" in the aqueous dispersion of fluorine-containing metal oxide particles (aqueous dispersion of fluorine-containing silica particles) was 0.84, and the solvent (D) was The content ratio of "carboxyl group-containing substance, etc. (C)" in the liquid composition excluding the solvent (D) is 5% by mass, and the content ratio of "(A) + (B)" in the liquid composition excluding the solvent (D) is It was 95% by mass, and the content of the fluorine-based functional group component in the film was too high. Therefore, the simulated liquid did not fall from the air filter, and the oil repellency was "poor."

In the air filter of Comparative Example 4, the water- and oil-repellent film-forming liquid composition was prepared by adding and mixing an aqueous dispersion of metal oxide particles to the fluorine-containing carboxyl group-containing material, so the particle surface was lipophilic. The presence of a large number of metal oxide particles in the film significantly degraded the oil repellency. As a result, the oil repellency was "poor".

On the other hand, in the air filters of Examples 1 to 7, the fluorine-based functional group component is represented by formula (1) or formula (2), the average particle diameter of the metal oxide particles is in the range of 2 nm to 90 nm, and the solvent The content of (C) such as a carboxyl group-containing substance in the liquid composition excluding (D) is 10% by mass to 70% by mass, and the fluorine-based functional group component (A ) and metal oxide particles (B) is 30% to 90% by mass, "(A)/(B)" is in the range of 0.05 to 0.80, and the air Since the air permeability of the filter is in the range of 1 ml/cm ² /sec to 30 ml/cm ² /sec, which satisfies the scope of the invention in the first aspect, the simulated liquid falls from the air filter and is not repelled. It was confirmed that all oil properties were "good".

The air filter of the present invention is used in a work environment with machine tools such as cutting machines and lathes that process metal products using cutting oil.

10 Air filter 20 Nonwoven fabric 20a One side of nonwoven fabric 20b Other side of nonwoven fabric 20c Fibers of nonwoven fabric 20d Pores of nonwoven fabric 21 Water- and oil-repellent film 21a Fluorine-containing metal oxide particles 21b Carboxyl group-containing substance, etc. 22 Oil particles of oil mist 23 Dust particle

Claims (9)

An air filter including a non-woven fabric in which a large number of pores are formed between fibers, penetrating between one surface through which air containing oil mist and dust flows in, and the other surface facing this one surface through which the air flows out, the air filter comprising:
A water- and oil-repellent film is formed on the fiber surface of the nonwoven fabric,
The water- and oil-repellent film is made of metal oxide particles with an average particle diameter of 2 nm to 90 nm to which a fluorine-based functional group component (A) containing a perfluoroether structure represented by the following general formula (1) or formula (2) is bonded. (B) and a carboxyl group- and/or acetyl group-containing substance (C),
The carboxyl group and/or acetyl group-containing substance (C) is contained in the water- and oil-repellent film in a proportion of 10% by mass to 70% by mass,
The fluorine-based functional group component (A) and the metal oxide particles (B) are contained in the water- and oil-repellent film in a total proportion of 30% by mass to 90% 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 0.05 to 0.80,
An air filter characterized in that the air filter has an air permeability of 1 ml/cm ² /sec to 30 ml/cm ² /sec.

In the above formulas (1) and (2), p, q and r are each the same or different integers of 1 to 6, and may be linear or branched. In the above formulas (1) and (2), X is a hydrocarbon group having 2 to 10 carbon atoms, and is selected from an ether bond, a CO-NH bond, an O-CO-NH bond, and a sulfonamide bond. may contain one or more types of bonds. Furthermore, in the above formulas (1) and (2), Y is hydrolysis of silane or a main component of silica sol-gel. The air filter according to claim 1, wherein the metal oxide particles (B) are oxide particles of one type of metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. The carboxyl group- and/or acetyl group-containing material (C) is a polyolefin aqueous dispersion having a carboxyl group, a self-emulsion of an ethylene-vinyl acetate copolymer, or a self-emulsion of an ethylene-vinyl acetate-acrylic acid copolymer. The air filter according to claim 1, which is an emulsion. The air filter according to claim 1, wherein the nonwoven fabric is composed of a single layer or a laminate of multiple layers. The fibers constituting the nonwoven fabric are one or two selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethylene (PTFE), glass, alumina, carbon, cellulose, pulp, nylon, and metal. The air filter according to claim 1 or 4, wherein the air filter is made of at least one type of fiber. Mixing an aqueous dispersion of fluorine-containing metal oxide particles, a material containing a carboxyl group and/or an acetyl group, and a solvent that is water in which the content of water or an alcohol having 1 to 4 carbon atoms is 40% by mass or less. A step of preparing a water- and oil-repellent film-forming liquid composition;
Dipping the nonwoven fabric in a diluted solution of the water- and oil-repellent film-forming liquid composition;
A method for manufacturing an air filter, comprising: deliquifying and drying the dipped nonwoven fabric. The air according to claim 6, 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, and adding and mixing a catalyst to this mixture. How to manufacture filters. 8. The method for manufacturing an air filter according to claim 7, wherein the metal oxide particles are oxide particles of one type of metal selected from the group consisting of Si, Al, Mg, Ca, Ti, Zn, and Zr. The carboxyl group- and/or acetyl group-containing substance is a polyolefin aqueous dispersion having a carboxyl group, a self-emulsion of an ethylene-vinyl acetate copolymer, or a self-emulsion of an ethylene-vinyl acetate-acrylic acid copolymer. The method for manufacturing an air filter according to claim 6.

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