JP7789487B2 - Air filter and its manufacturing method - Google Patents

Description

The present invention relates to an air filter that purifies 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 is formed on the fiber surface of a nonwoven fabric, and a method for manufacturing the same.

When cutting machines, turning machines, and other machine tools that process metal products using cutting oil operate at high speeds, the cutting oil scatters, generating oil mist and dust. This oil mist and dust worsen the working environment and reduce work efficiency. For this reason, air filter media have been proposed that can purify air containing oil mist and dust, not only by filtering out dust suspended in the air, but also by preventing clogging caused by oil mist (see, for example, Patent Document 1 (Claim 1, paragraphs [0006], [0021], [0045], [0053] to [0060])).

This air filter medium includes a first PTFE (polytetrafluoroethylene) porous membrane and a second PTFE porous membrane, and the airflow passes through the first PTFE porous membrane and the second PTFE porous membrane in this order from the first main surface of the air filter medium 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, 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 PTFE porous membrane is 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 each formed into a sheet-like compact from a mixture of PTFE fine powder and liquid lubricant. The first porous PTFE membrane is produced by heating and stretching the sheet-like compact in the longitudinal (MD) direction at a temperature above the melting point of PTFE (327°C) and at a stretching ratio of 50 times or more, and then heating and stretching it in the transverse (TD) direction at a temperature of 130-400°C to 5-8 times its original length. The second porous PTFE membrane is produced by heating and stretching a sheet-like compact of PTFE in the MD direction at a temperature below the melting point of PTFE (270-290°C) to 15-40 times its original length, and then heating and stretching it in the TD direction at a temperature of 120-130°C to 15-40 times its original length, the same stretching ratio as in the MD stretching.

Japanese Patent Application Laid-Open No. 2018-51546

In the air filter medium disclosed in Patent Document 1, the first PTFE porous membrane is produced at a higher stretching temperature and a larger stretch ratio than the second PTFE porous membrane, thereby reducing the specific surface area of the first PTFE porous membrane to 0.5 m ² /g or less, thereby capturing large particle diameter dust and oil mist, while the second PTFE porous membrane has a larger specific surface area of 1.5 to 10 m ² /g, thereby capturing small particle diameter dust and oil mist.

However, in the air filter medium disclosed in Patent Document 1, even though the first and second PTFE porous membranes capture dust particles and oil mist of different particle sizes, the PTFE porous membranes are prone to generating static electricity, which is difficult to remove, making it difficult to process into a filter shape. Furthermore, because the PTFE porous membrane is more water-repellent than oil-repellent, moisture in the air can clog the PTFE porous membrane, making it easy for dust particles to adhere to it. Therefore, with continued use of the air filter medium, oil mist continues to remain inside the air filter medium, easily clogging the air filter medium. As a result, the volume of air passing through the air filter is likely to decrease, posing the issue of having to frequently replace the air filter with a new one.

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

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 large number of pores formed among the fibers, the pores penetrating the surface, wherein a water- and oil-repellent film is formed on the fiber surface of the nonwoven fabric, The water- and oil-repellent film comprises a fluorine-based functional group component (A) having a perfluoroether structure represented by the following general formula (1) or (2), layered inorganic compound particles (B), and a carboxyl group- and/or acetyl group-containing material (C) as a binder component, wherein the layered inorganic compound particles (B) are montmorillonite, hectorite, or stevensite, and the carboxyl group- and/or acetyl group-containing material (C) is a polyolefin-based aqueous dispersion having a carboxyl group, the fluorine-based functional group component (A) is contained in the water- and oil-repellent film in a proportion of 0.5 to 10 mass % when the water- and oil-repellent film is taken as 100 mass %, the mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) is 0.01 to 0.50, and the air permeability of the air filter is 1 ml/cm ² /sec to 130 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. 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 the main component of a silica sol-gel.

Explaining Y further, Y is the moiety that bonds to the layered inorganic compound particles (B). Specific examples include structures in which Y is hydrolyzed in the Z moiety in Formula (3) or Formula (4) described below. Y also includes the main component of a silica sol-gel obtained by mixing a silane compound of Formula (3) or Formula (4) with a silicon alkoxide such as tetraethoxysilane or tetramethoxysilane and hydrolyzing and polymerizing the mixture. Y also includes the main component of a silica sol-gel obtained by mixing a silane compound of Formula (3) or Formula (4) with 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. Incidentally, the carboxyl group and/or acetyl group-containing material (C) is used as a binder component for adhering the layered inorganic compound particles (B) to which the fluorine-based functional group component (A) is bonded to the nonwoven fabric substrate.

A second aspect of the present invention is an invention based on the first aspect, and is an air filter in which the layered inorganic compound particles (B) are contained in the water- and oil-repellent film in a proportion of 5 to 50 mass % when the water- and oil-repellent film is taken as 100 mass %, and the air filter has an air permeability of 1 ml/cm ² /sec to 40 ml/cm ² /sec.

A third 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.

A fourth aspect of the present invention is an air filter based on either the first or third 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.

A fifth aspect of the present invention is a method for producing an air filter, as shown in FIG. 3 , comprising the steps of: preparing a water- and oil-repellent film-forming liquid composition by mixing an aqueous dispersion of fluorine-containing layered inorganic compound particles, a carboxyl group- and/or acetyl group-containing material (C) as a binder component, and a solvent (D) which is water or water containing 40 mass % or less of an alcohol having 1 to 4 carbon atoms; dipping a nonwoven fabric into a diluted solution of the water- and oil-repellent film-forming liquid composition; and dehydrating and drying the dipped nonwoven fabric, wherein the layered inorganic compound particles (B) are montmorillonite, hectorite, or stevensite, and the carboxyl group- and/or acetyl group-containing material (C) is a polyolefin-based aqueous dispersion having carboxyl groups .

A sixth aspect of the present invention is an invention based on the fifth aspect , and relates to a method for producing an air filter, wherein the aqueous dispersion of fluorine-containing layered inorganic compound particles is prepared by adding and mixing a fluorine-based compound to an aqueous dispersion of layered inorganic compound particles, and then adding and mixing a catalyst to the mixture.

An air filter according to a first aspect of the present invention has a water- and oil-repellent film formed on the fiber surfaces of a nonwoven fabric contained in the air filter, the water- and oil-repellent film comprising a fluorine-based functional group component (A) represented by the above-mentioned general formula (1) or (2), layered inorganic compound particles (B), and a carboxyl group- and/or acetyl group-containing substance (C), the fluorine-based functional group component (A) being contained in the water- and oil-repellent film at a ratio of 0.5% by mass to 10% by mass, where the water- and oil-repellent film is taken as 100% by mass, and the air filter has an air permeability of 1 ml/ ^cm2 /sec to 130 ml/ ^cm2 /sec. Therefore, when air containing oil mist and dust flows into the air filter from one side, 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 from the other side of the air filter, making the air clean and reducing clogging.

At this time, due to the oil-repellent properties of the water- and oil-repellent film and the air filter's air permeability of 1 ml/ ^cm² /sec to 130 ml/ ^cm² /sec, the oil mist is not adsorbed by the water- and oil-repellent film on the fiber surface of the nonwoven fabric, but is instead repelled and adheres 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 block the pores of the nonwoven fabric. This prevents the oil mist from clogging the pores.

On the other hand, because the air permeability of the air filter is 1 ml/cm ² /sec to 130 ml/cm ² /sec, dust adheres either directly to the water- and oil-repellent film on the fiber surface of the nonwoven fabric, or to the oil mist that has adhered to the water- and oil-repellent film. Therefore, when an air filter becomes clogged with dust or the like 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.
Since the layered inorganic compound particles contained in the water- and oil-repellent film are montmorillonite or the like, the multilayer structure and high swelling property of montmorillonite or the like result in a large interlayer volume, which results in a better appearance of the film and also increases the strength of the film.
Since the carboxyl group- and/or acetyl group-containing material (C) is a polyolefin-based aqueous dispersion having a carboxyl group, this aqueous dispersion acts as a binder for the fluorine-containing layered inorganic compound particles, and when the liquid composition is formed into a film on the surface of a substrate, the film can be firmly bound to the surface of the substrate.

In the air filter of the second aspect of the present invention, the layered inorganic compound particles (B) are contained in the water- and oil-repellent film in a proportion of 5 to 50 mass % when the water- and oil-repellent film is taken as 100 mass %, and the air filter has an air permeability of 1 ml/cm ² /sec to 40 ml/cm ² /sec. Therefore, when the layered inorganic compound particles are contained in the water- and oil-repellent film in the above proportion, the abrasion resistance of the water- and oil-repellent film is increased, and the effect of filling the air holes in the nonwoven fabric is improved, making it possible to block oil particles on the surface of the air filter.

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

In the air filter of the fourth aspect of the present invention, the material of the fibers making up 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 properties such as the particle size of the inflowing dust and the size of the oil particles in the oil mist.

In the method of the fifth aspect of the present invention, as shown in Figure 3, a water- and oil-repellent film-forming liquid composition is prepared by mixing an aqueous dispersion of fluorine-containing layered inorganic compound particles, a carboxyl group- and/or acetyl group-containing material (C), and a solvent that is water or water containing 40% or less by weight of an alcohol having 1 to 4 carbon atoms. An air filter is produced by dipping a nonwoven fabric into a diluted solution of this water- and oil-repellent film-forming liquid composition, dewatering the nonwoven fabric, and drying it, thereby forming a uniform water- and oil-repellent film on the fiber surface of the nonwoven fabric. Furthermore, since the layered inorganic compound particles, whose particle surfaces are water- and oil-repellent, are present in the carboxyl group- and/or acetyl group-containing material, it is easy to reduce the air permeability of the nonwoven fabric while maintaining water- and oil-repellency. Furthermore, unlike the PTFE porous membrane of Patent Document 1, the water- and oil-repellent film is less likely to generate static electricity, allowing for easy production of air filters.
Since the layered inorganic compound particles are montmorillonite or the like, the multilayer structure and large swelling property of montmorillonite or the like result in a large interlayer volume, which can improve the appearance of the membrane and further increase the strength of the membrane.
Since the carboxyl group- and/or acetyl group-containing material (C) is a polyolefin-based aqueous dispersion having a carboxyl group, this aqueous dispersion acts as a binder for the fluorine-containing layered inorganic compound particles, and when the liquid composition is formed into a film on the surface of a substrate, the film can be firmly bound to the surface of the substrate.

In the method for producing an air filter according to the sixth aspect of the present invention, a fluorine-based compound is added and mixed into an aqueous dispersion of layered inorganic compound particles, and a catalyst is then added and mixed into this mixture, thereby obtaining a dispersion in which the fluorine-containing layered inorganic compound particles are uniformly dispersed.

FIG. 1 is a side view of a single layer nonwoven fabric of the present embodiment. FIG. 2 is a side view of the two-layer nonwoven fabric of the present embodiment. FIG. 2 is a flow chart showing a method for manufacturing the air filter of the present embodiment.

Next, an embodiment of 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- and oil-repellent film 21 formed on the fiber surface of the nonwoven fabric, exhibiting water- and oil-repellent properties. 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 the first surface 20a through which the air exits. As shown in FIG. 2 , an air filter 50 may be formed as 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 a two-layer structure, and may be formed of multiple layers, such as three or four layers.

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 the first surface 20a and the second surface 20b of the nonwoven fabric 20. A water- and oil-repellent film 21 is formed on the surface of the fibers 20c of the nonwoven fabric. The basis weight of the nonwoven fabric is preferably in the range of 100 g/ ^m2 to 400 g/ ^m2 , but is not limited to this range. The water- and oil-repellent film 21 contains layered inorganic compound particles (B) and a carboxyl group- and/or acetyl group-containing substance (C) as a binder component. The layered inorganic compound particles (B) preferably have an average particle diameter of 0.1 μm to 10 μm. The layered inorganic compound particles (B) are bonded to a fluorine-based functional group component (A) represented by the aforementioned general formula (1) or formula (2). The fluorine-based functional group component (A) is contained in the water- and oil-repellent film 21 in a proportion of 0.5% by mass to 10% by mass, where the water- and oil-repellent film 21 is taken as 100% by mass. The carboxyl group- and/or acetyl group-containing substance (C) is preferably contained in a proportion of 10% by mass to 70% by mass, where the water- and oil-repellent film 21 is taken as 100% by mass. Furthermore, the mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) is preferably in the range of 0.01 to 0.50.

As shown in the further enlarged view at the top of Figure 1, the water- and oil-repellent film 21 is composed of numerous layered inorganic compound particles 21a, the particle surfaces of which are covered with fluorine-based functional group components, bound together by a binder component 21b containing a carboxyl group and/or acetyl group. Because the water- and oil-repellent film 21 contains layered inorganic compound particles 21a, it appears to be a thick film, which narrows the pores 20d between the fibers. Furthermore, the film thickness can be controlled by changing the particle size of the layered inorganic compound particles and the content ratio of the layered inorganic compound particles in the film components.

If the basis weight of the nonwoven fabric is less than 100 g/ ^m2 , the pores between the fibers will be too large, and the dust collection ability will be insufficient. If it exceeds 400 g/ ^m2 , the air permeability will be less than 1 ml/ ^cm2 /sec, and dust will easily clog the pores between the fibers, or the air permeability will be too low, causing pressure loss in the air filter due to resistance of the air sent into the air filter, and the efficiency of the air blowing energy will be easily reduced. It is more preferable that the basis weight of the nonwoven fabric is in the range of 200 g/ ^m2 to 350 g/ ^m2 .

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 130 ml/cm ² /sec. Air permeability less than 1 ml/cm ² /sec results in poor breathability, making it difficult for air containing oil mist and dust to pass through. Air permeability greater than 130 ml/cm ² /sec results in the size of the pores 20d of the nonwoven fabric being much larger than the particle sizes of the oil particles 22 and dust particles 23 of the oil mist in the incoming air, causing the oil particles 22 and dust particles 23 to pass through the pores of the nonwoven fabric along with the air, preventing the oil mist and dust from being captured. The air permeability is preferably 1.5 ml/cm ² /sec to 125 ml/cm ² /sec. The air permeability is measured using a Frazier type testing machine as described in JIS-L1913:2000.

When the water- and oil-repellent film 21 is taken as 100% by mass, if the proportion of the fluorine-based functional group component (A) in the water- and oil-repellent film is less than 0.5% by mass, the oil-repellent effect will be poor and the ability to repel oil mist will be insufficient. That is, when oil mist reaches the air filter, it will wet and spread over the fiber surface, making it more likely to clog the pores 20d. If the proportion of the fluorine-based functional group component (A) in the water- and oil-repellent film exceeds 10% by mass, the adhesion of the water- and oil-repellent film to the nonwoven fabric will be poor. The content of the fluorine-based functional group component (A) in the water- and oil-repellent film 21 is preferably 0.7% to 8% by mass.

The layered inorganic compound particles (B) contained in the water- and oil-repellent film 21 preferably have an average particle size in the range of 0.1 μm to 10 μm. The mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) is preferably 0.01 to 0.50. If the mass ratio (A/B) is less than 0.01, the water- and oil-repellent film will have poor oil repellency, and if it exceeds 0.50, the adhesion of the water- and oil-repellent film to the fiber surface will decrease.

The operation of this air filter 10 will now be explained. As shown in Figure 1, air containing oil mist and dust particles reaches one surface 20a of the nonwoven fabric 20 that constitutes the air filter 10. Because the air filter 10 has a predetermined air permeability and the water- and oil-repellent film 21 exhibits oil repellency, oil particles 22 of the oil mist cannot pass through the air filter 10, even if they are larger than the pore size of the pores 20d, and even if they are slightly smaller than the pore size of the pores 20d. Instead, they are repelled by the water- and oil-repellent film 21 and adhere to and remain on the 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 water- and oil-repellent film 21. The layered inorganic compound particles 21a contained in the water- and oil-repellent film 21 create an uneven film, 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 from the oil mist and dust particles 23 are captured by the nonwoven fabric, and the air containing the oil mist and dust passes through the pores 20d formed between the fibers 20c shown in the enlarged view of Figure 1 to reach the other surface 20b, where it becomes oil mist- and dust-free air and passes through the nonwoven fabric 20.

As the amount of oil mist trapped inside the nonwoven fabric increases with continued use of the air filter, if the air filter is positioned horizontally, oil mist that does not adhere to the membrane to a large extent liquefies and is carried along with the passing air, collecting on the other side of the air filter. If the air filter is positioned vertically, the captured oil mist collects at the bottom of the air filter due to its own weight and does not block the pores of the nonwoven fabric. This prevents the oil mist from clogging the pores. Dust adheres directly to the water- and oil-repellent membrane on the fiber surface of the nonwoven fabric, or adheres to the oil mist that has adhered to the water- and oil-repellent membrane. 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.

[Method for manufacturing air filters]
The air filter is generally manufactured by the following method.
3 , a fluorine-based compound 52 containing a fluorine-based functional group component (A) is mixed with an aqueous dispersion 51 of layered inorganic compound particles, and a catalyst 53 is further mixed therein to prepare an aqueous dispersion 54 of fluorine-containing layered inorganic compound particles. A water- and oil-repellent film-forming liquid composition 60 is prepared by mixing this aqueous dispersion 54 with a binder component 55 containing a carboxyl group and/or acetyl group, and a solvent 56. 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.

The method for manufacturing the air filter will be described in detail below.
[Preparing the nonwoven fabric]
First, a nonwoven fabric having an air permeability of 1.1 ml/cm ² /sec to 150 ml/cm ² /sec is prepared. Specifically, a nonwoven fabric having an air permeability of 1 ml/cm ² /sec to 130 ml/cm ² /sec is prepared in a state in which a water- and oil-repellent film, which will be described later, is formed on the fiber surface of the nonwoven fabric to form an air filter. When the water- and oil-repellent film is to be formed into a thick film, a nonwoven fabric with high air permeability is selected, and when the water- and oil-repellent film is to be formed into a thin film, a nonwoven fabric with low air permeability is selected.

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 (manufactured by Asaka Filter Paper Co., Ltd., product name: 336 or product name: 356), nonwoven fabrics made from polyethylene terephthalate fibers (manufactured by Toray Industries, Inc., product name: G2260-1S or Toyobo Co., Ltd., product name: 191001), nonwoven fabrics made from polypropylene fibers (manufactured by Mitsui Chemicals, Inc., product name: M03150), 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 to achieve the above-mentioned air permeability. The thickness of the nonwoven fabric is preferably 0.2 mm to 0.8 mm if the air filter is a single layer, and a thickness that results in a laminate thickness of 0.2 mm to 5 mm if the air filter is a multi-layer laminate.

[Method for producing a water- and oil-repellent film-forming liquid composition]
[Preparation of aqueous dispersion of layered inorganic compound particles]
First, an aqueous dispersion of layered inorganic compound particles is prepared by dispersing layered inorganic compound particles in an aqueous solvent. The layered inorganic compound particles preferably have an average particle size of 0.1 μm to 10 μm. If the average particle size is less than 0.1 μm, the layered inorganic compound particles are likely to aggregate and become difficult to disperse in the medium. If the average particle size exceeds 10 μm, the layered inorganic compound particles are likely to fall off from the water- and oil-repellent film when the liquid composition is formed into a film. Examples of layered inorganic compound particles include air filters made of montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, stevensite, or vermiculite.

Examples of aqueous solvents include water or a mixed solvent of water and an alcohol having 1 to 4 carbon atoms. It is preferable 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 instead of an organic solvent is to ensure safety in handling. In this specification, the average particle size of layered inorganic compound particles refers to the average value of the particle sizes measured by image analysis at 200 points among the particle shapes observed with a scanning electron microscope (SEM).

[Preparation of Dispersion of Fluorine-Containing Layered Inorganic Compound Particles]
Next, a fluorine-containing compound containing a fluorine-containing functional group component represented by the above formula (1) or (2) is added to the prepared aqueous dispersion of the layered inorganic compound particles to synthesize a nanocomposite material of the layered inorganic compound particles and the fluorine-containing functional group component. A catalyst is then added to further promote the reaction. This results in the preparation of an aqueous dispersion of fluorine-containing layered inorganic compound particles.

The catalyst may be an organic acid, an inorganic acid, an alkali, or a titanium compound. 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. Examples of titanium compounds include titanium tetrapropoxide, titanium tetrabutoxide, titanium tetraisopropoxide, and titanium lactate. The catalyst is not limited to the above.

Fluorine-based compounds containing fluorine-based functional group components are 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).

X in the above formulas (3) and (4) can include structures represented by the following formulas (14) to (18). Note that formula (14) below shows an example containing an ether bond, formula (15) below shows an ester bond, formula (16) below shows an amide bond, formula (17) below shows a urethane bond, and formula (18) below shows a sulfonamide bond.

In the above formulas (14) to (18), ^R2 and ^R3 are hydrocarbon groups having 0 to 10 carbon atoms, and ^R4 is a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group for ^R3 include alkylene groups such as a methylene group and an ethylene group, and examples of the hydrocarbon group for ^R4 include alkyl groups such as a methyl group and an ethyl group, as well as a phenyl group.

In the above formulas (3) and (4), R ¹ may be a methyl group, an ethyl group, or the like.

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 an Si-O-Si bond. Specific examples of such hydrolyzable groups include alkoxy groups such as methoxy, ethoxy, propoxy, and butoxy; aryloxy groups such as phenoxy and naphthoxy; aralkyloxy groups such as benzyloxy and phenethyloxy; and acyloxy groups such as acetoxy, propionyloxy, butyryloxy, valeryloxy, pivaloyloxy, and benzoyloxy. Of these, the ethoxy group is preferred.

Specific examples of fluorine-based compounds containing a fluorine-based functional group component having a perfluoroether structure represented by formula (3) or (4) above include structures represented by formulas (19) to (27) below. In formulas (19) to (27) below, R represents 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 this embodiment has a perfluoroether group in which multiple short-chain perfluoroalkyl groups and perfluoroalkylene groups each having six or fewer carbon atoms are bonded to an oxygen atom within the molecule, and the high fluorine content within the molecule can impart excellent water- and oil-repellency to the formed film.

[Carboxyl group and/or acetyl group-containing substance]
The carboxyl group and/or acetyl group-containing material (C) as a binder component is a polyolefin-based aqueous dispersion having a carboxyl group, a self-emulsifying liquid of an ethylene-vinyl acetate copolymer, or a self-emulsifying liquid of an ethylene-vinyl acetate-acrylic acid copolymer. Commercially available polyolefin-based products having a carboxyl group include ZAIXXEN A, ZAIXXEN L, and ZAIXXEN N (all manufactured by Sumitomo Seika Chemicals). 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-401Q, S-465HQ, S-483HQ, S-830, and S-950HQ (all manufactured by Sumitomo Chemical), and Quatex EC-1800 and EC-1200 (all manufactured by Japan Coating Resins). Furthermore, examples of ethylene-vinyl acetate-acrylic acid based resins 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 this embodiment is produced by the above-described production method and contains layered inorganic compound particles (B) to which the fluorine-based functional group component (A) is bonded, a carboxyl group- and/or acetyl group-containing material (C) as a binder component, and a solvent (D). The fluorine-based functional group component (A) has a perfluoroether structure represented by the above-described general formula (1) or (2), and is contained in the liquid composition at 0.5% to 10% by mass, assuming that the total amount of all components excluding the solvent (D) is 100% by mass. If the fluorine-based functional group component is less than 0.5% by mass, the formed film cannot be imparted with oil repellency, while if it exceeds 10% by mass, the film will repel, resulting in poor film-forming properties. Furthermore, the mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) is preferably in the range of 0.01 to 0.50.

If the mass ratio (A/B) is less than 0.01, the water- and oil-repellent film is likely to have poor oil repellency, while if it exceeds 0.50, the adhesion of the water- and oil-repellent film to the fiber surface of the nonwoven fabric is likely to decrease. The solvent (D) is water or water containing 40% by mass or less of an alcohol having 1 to 4 carbon atoms. The reason for limiting the content of the alcohol having 1 to 4 carbon atoms to 40% by mass is to ensure safety in handling and the storage stability of the liquid composition. Furthermore, by using a mixed solvent consisting of water and an alcohol having 1 to 4 carbon atoms, the drying rate is increased and film-forming properties are improved. Examples of alcohols 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-repellent and oil-repellent film on the fiber surface of a nonwoven fabric]
To form a water- and oil-repellent film on the fiber surface of a nonwoven fabric according to this embodiment, the nonwoven fabric is dipped into the water- and oil-repellent 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 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 dried in the air at a temperature of 25°C to 140°C for 0.5 to 24 hours. If the viscosity of the water- and oil-repellent film liquid composition is high, a liquid can be prepared by diluting the liquid composition with a solvent containing water and an alcohol having a boiling point below 120°C and a carbon number of 1 to 4. The mixture ratio of water to 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 by mass. The nonwoven fabric may be dipped in the diluted solution prepared in this manner.
As a result, as shown in the enlarged view in the center of Figure 1, a water- and oil-repellent film 21 is formed on the surface of the fibers 20c that make up 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 nonwoven 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 nonwoven fabric.

Next, examples of the present invention will be described in detail along with comparative examples. First, Synthesis Examples 1 to 7 and Comparative Synthesis Examples 1 and 2, which prepare aqueous dispersions of fluorine-containing layered inorganic compound particles, will be described. Next, Examples 1 to 7 and Comparative Examples 1 to 3, which relate to the preparation of water- and oil-repellent film-forming liquid compositions and the production of air filters using these Synthesis Examples and Comparative Synthesis Examples, will be described.

[Synthesis Examples 1 to 7 for preparing dispersions of fluorine-containing layered inorganic compound particles, and Comparative Synthesis Examples 1 and 2]
<Synthesis Example 1>
2 g of Sumecton ST (Stevensite, manufactured by Kunimine Industries Co., Ltd.) as a layered inorganic compound and 98 g of water were stirred in a beaker to obtain an aqueous dispersion of layered inorganic compound particles. 0.04 g of a fluorine-based compound containing a fluorine-based functional group component (A) represented by the above formula (19) was added to 90 g of the obtained aqueous dispersion and mixed. Next, 0.005 g of nitric acid was added and mixed at 40 ° C for 2 hours to obtain an aqueous dispersion of fluorine-containing layered inorganic compound particles in which the fluorine-based compound was bonded to the layered inorganic compound particles. The mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) was 0.019.
Table 1 below shows the conditions for preparing the aqueous dispersion of fluorine-containing layered inorganic compound particles in Synthesis Example 1.

<Synthesis Examples 2 to 7 and Comparative Synthesis Examples 1 and 2>
In Synthesis Examples 2 to 7 and Comparative Synthesis Examples 1 and 2, the type of layered inorganic compound particles was changed to a type different from that in Synthesis Example 1, the fluorine-based compound was changed to a type different from that in Synthesis Example 1, the amount of nitric acid used as a catalyst was the same as in Synthesis Example 1, and the mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) was changed to a different value from that in Synthesis Example 1. Otherwise, aqueous dispersions of fluorine-containing layered inorganic compound particles in Synthesis Examples 2 to 7 and Comparative Synthesis Examples 1 and 2 were prepared in the same manner as in Synthesis Example 1, as shown in Table 1 above. In Table 1, all of the Rs in the formulas of the fluorine-containing silanes represented by formulas (19) to (21) and (27) as fluorine-based compounds are ethyl groups.

[Examples 1 to 7 and Comparative Examples 1 and 2 for preparation of water- and oil-repellent film-forming liquid composition and production of air filters]
Example 1
90.04 g of the aqueous dispersion of fluorine-containing layered inorganic compound particles obtained in Synthesis Example 1 was mixed with 7.57 g of an acetyl-group-containing ethylene acetate emulsion (Sumikaflex S-355HQ, manufactured by Sumitomo Chemical Co., Ltd.) as a binder component and 2.39 g of water as a solvent to prepare 100 g of a water- and oil-repellent film-forming liquid composition. A nonwoven fabric G2260-1S manufactured by Toray Industries, Inc., made of PET fiber and having an air permeability of 15 ml/ ^m² /s, was used as the air filter substrate. The nonwoven fabric was dipped into the water- and oil-repellent film-forming liquid composition, excess liquid was shaken off, and the nonwoven fabric was dried at room temperature for 24 hours to produce an air filter with an air permeability of 11 ml/ ^cm² /s. The results are shown in Tables 2 and 3 below.

Table 2 also shows the content of the fluorine-based functional group component (A) in the liquid composition excluding the solvent, the content of the layered inorganic compound particles (B) in the liquid composition excluding the solvent, and the content of the binder component (C) in the liquid composition excluding the solvent. The content (%) of the fluorine-based functional group component (A) in the liquid composition excluding the solvent is the percentage of [(A)/[(A) + (B) + (C)]], the content (%) of the layered inorganic compound particles (B) in the liquid composition excluding the solvent is the percentage of [(B)/[(A) + (B) + (C)]], and the content (%) of the binder component (C) in the liquid composition excluding the solvent is the percentage of [(C)/[(A) + (B) + (C)]].

<Examples 2 to 7 and Comparative Examples 1 to 3>
As shown in Table 2, in Examples 2 to 7 and Comparative Examples 1 and 2, the weights were determined using the aqueous dispersions of fluorine-containing layered inorganic compound particles obtained in Synthesis Examples 1 to 7 or Comparative Synthesis Examples 1 and 2 shown in Table 1. In Comparative Example 3, the weight was determined using the aqueous dispersion of fluorine-containing layered inorganic compound particles obtained in Synthesis Example 7 shown in Table 1. As shown in Table 2, in Examples 2 to 7 and Comparative Examples 1 to 3, the weights were determined using binder components comprising carboxyl group- and/or acetyl group-containing substances.
In this manner, the water- and oil-repellent film-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 3 were prepared.

Nonwoven fabrics with different breathability shown in Table 3 and the types of air filter substrates were selected, and the substrates made of nonwoven fabric were dipped in each of the water- and oil-repellent film-forming liquid compositions of Examples 2 to 7 and Comparative Examples 1 to 3 in the same manner as in Example 1, followed by dewatering and drying to obtain air filters having the properties shown in Table 3. In Comparative Example 2, since the viscosity of the water- and oil-repellent film liquid composition increased, the liquid composition was diluted with a solvent, and the substrate made of nonwoven fabric was dipped in this diluted liquid, followed by dewatering and drying.
The mixed fibers of PET and glass fiber used in Examples 4 and 7 were manufactured by Azumi Filter Paper Co., Ltd. under the trade names of 356 and 336. The nonwoven fabrics of Examples 1 to 7 and Comparative Examples 1 to 3 all consisted of a single layer.

<Comparative testing and evaluation>
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 charged in a mass ratio of 80:20 into a planetary centrifugal mixer (ARE-310 manufactured by Thinky Corporation), stirred and mixed to obtain a simulated liquid. 1 ml of the resulting simulated liquid was dripped from above onto 10 types of horizontally placed air filters obtained in Examples 1 to 7 and Comparative Examples 1 to 3, and the air filters were then stood vertically to check the ability of the simulated liquid to fall. 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."

As is clear from Table 3, in the air filter of Comparative Example 1, the content of fluorine-based functional group component (A) in the liquid composition excluding the solvent was too low at 0.4 mass%, so the water- and oil-repellent film did not exhibit oil repellency. Although the simulated liquid was captured on the air filter, the simulated liquid passed through the air filter, resulting in a "poor" oil repellency rating.

In the air filter of Comparative Example 2, the content of fluorine-based functional group component (A) in the liquid composition excluding the solvent was too high at 11.3 mass%, so the water- and oil-repellent film liquid composition was not evenly applied to the nonwoven fabric, and the water- and oil-repellent film was not evenly formed on the fiber surface of the nonwoven fabric. As a result, the water- and oil-repellent film became porous and did not exhibit oil repellency. Although the simulated liquid was collected in the air filter, the simulated liquid passed through the air filter, resulting in a "poor" oil repellency rating.

In the air filter of Comparative Example 3, metal fibers were used as the nonwoven fabric, and the concentration of the coating liquid was low, so the air permeability was too high at 136 ml/ ^cm2 /sec. As a result, the simulated liquid was easily collected on the air filter and then easily passed through the air filter. The simulated liquid did not fall off the surface of the air filter, and the oil repellency was "poor."

In contrast, the air filters of Examples 1 to 7 met the scope of the first aspect of the invention, and it was confirmed that the simulated liquid was captured and fell off the air filter, and that the oil repellency of all of them was "fairly good" or "good."

Here, in the air filter of Example 6, a water- and oil-repellent film liquid composition was used in which the content of layered inorganic compound particles (B) in the liquid composition excluding the solvent was 4 mass %, so the water- and oil-repellent film had a low content of layered inorganic compound particles, while the binder component (C) consisting of ethylene-vinyl acetate copolymer was the main component. In addition, a nonwoven fabric with a high air permeability of 140 ml/cm ² /sec before coating was used. As a result, the simulated liquid was collected in the air filter, but a small amount passed through the air filter. Although the simulated liquid slid off the surface of the air filter, the amount of slid off was reduced, and the oil repellency was rated as "fairly good."

In addition, the air filter of Example 7 used a water- and oil-repellent film liquid composition in which the content of layered inorganic compound particles (B) in the liquid composition excluding the solvent was 55% by mass, which increased the viscosity of the liquid composition. Therefore, a nonwoven fabric was dipped in this liquid, and the liquid was drained and dried. However, because the coating liquid was highly viscous, a somewhat uneven film was formed. Therefore, the simulated liquid was captured in the filter and did not pass through the air filter. However, although the simulated liquid did fall off the surface of the air filter, the amount of this falling was reduced, and the oil repellency was rated "fairly good."

The air filter of the present invention is used in work environments where machine tools such as cutting machines and turning machines are used to process metal products using cutting oil.

REFERENCE SIGNS LIST 10 Air filter 20 Nonwoven fabric 20a One surface of nonwoven fabric 20b Other surface of nonwoven fabric 20c Fiber of nonwoven fabric 20d Pores of nonwoven fabric 21 Water- and oil-repellent film 21a Fluorine-containing layered inorganic compound particles 21b Binder component 22 Oil particles of oil mist 23 Dust particles

Claims (6)

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 water-repellent and oil-repellent film is formed on the fiber surface of the nonwoven fabric,
The water- and oil-repellent film comprises a fluorine-based functional group component (A) having a perfluoroether structure represented by the following general formula (1) or (2), layered inorganic compound particles (B), and a carboxyl group- and/or acetyl group-containing substance (C) as a binder component,
the layered inorganic compound particles (B) are montmorillonite, hectorite, or stevensite,
The carboxyl group- and/or acetyl group-containing substance (C) is a polyolefin-based aqueous dispersion having a carboxyl group,
the fluorine-based functional group component (A) is contained in the water- and oil-repellent film in an amount of 0.5% by mass to 10% by mass, where the water- and oil-repellent film is taken as 100% by mass;
the mass ratio (A/B) of the fluorine-based functional group component (A) to the layered inorganic compound particles (B) is 0.01 to 0.50;
The air filter has an air permeability of 1 ml/cm ² /sec to 130 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. 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. The air filter according to claim 1, wherein the layered inorganic compound particles (B) are contained in the water- and oil-repellent film in an amount of 5 to 50% by mass when the water- and oil-repellent film is taken as 100% by mass, and the air permeability of the air filter is 1 ml/cm ² /sec to 40 ml/cm ² /sec. The air filter of claim 1, wherein the nonwoven fabric is composed of a single layer or a laminate of multiple layers. 4. 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. a step of preparing a water- and oil-repellent film-forming liquid composition by mixing an aqueous dispersion of fluorine-containing layered inorganic compound particles, a carboxyl group- and/or acetyl group-containing substance (C) as a binder component, and a solvent (D) which is water or water containing 40 mass % or less of an alcohol having 1 to 4 carbon atoms;
a step of dipping a nonwoven fabric into a diluted solution of the water- and oil-repellent film-forming liquid composition;
and a step of dehydrating and drying the dipped nonwoven fabric,
the layered inorganic compound particles (B) are montmorillonite, hectorite, or stevensite,
The method for producing an air filter , wherein the carboxyl group- and/or acetyl group-containing substance (C) is a polyolefin-based aqueous dispersion having a carboxyl group . 6. The method for producing an air filter according to claim 5, wherein the aqueous dispersion of the fluorine-containing layered inorganic compound particles is prepared by adding and mixing a fluorine-based compound to an aqueous dispersion of the layered inorganic compound particles (B), and then adding and mixing a catalyst to the mixture.