JPH105545A - Cleaning filter and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cleaning filter to efficiently remove low concn. harmful gas in air by preparing the filter by entangling fluorocarbon resin fibers containing a photocatalyst which is activated by irradiation of light of specified wavelengths so as to increase the contact area between the photocatalyst and the harmful gas. SOLUTION: This filter is produced by entangling fluorocarbon resin fibers containing a photocatalyst which is activated by irradiation of light of <=400nm wavelengths to prepare a cloth (felt or nonwoven fabric). As for the fluorocarbon resin fibers, polytetrafluoroethylene fibers which are especially excellent in chemical stability are preferable. As for the photocatalyst, anatase- type titanium oxide having an excellent photocatalytic effect is preferably used. The average fiber diameter of the fluorocarbon resin fibers is preferably <=30μm, and it is preferable that the fluorocarbon resin fibers have lots of micropores and have 1.3g/cm density and >=1.0cm<2> /g specific surface area. The amt. of the photocatalyst in the fluorocarbon resin fibers is preferably 0.1 to 60wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a purifying filter capable of removing harmful gases (contaminants) such as odorous gas, nitrogen oxides, sulfur oxides and the like existing in the air, and a filter for the same. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Hitherto, there has been proposed a method and an apparatus for removing low-concentration harmful gases of environmental air (atmosphere) such as nitrogen oxides and sulfur oxides using a photocatalyst such as titanium oxide. .

For example, Japanese Patent Application Laid-Open No. 7-108138 discloses a device for capturing and removing harmful gases (contaminants) in environmental air (atmosphere) on a catalyst by removing a photocatalyst (titanium oxide and activated carbon) from a thin plate. An apparatus having a structure supported on the surface of a blade-like reaction plate is disclosed. In such devices, thin plates (reaction plates) of plastic, aluminum, iron, etc.
A photocatalyst is attached to the surface of the substrate using an adhesive. However, although this device has a relatively simple structure, the contact between the photocatalyst and the harmful gas is performed on the surface of the plate member, so that the contact area between the photocatalyst and the harmful gas is small.

As the adhesive for fixing the photocatalyst to the surface of the plate material, an organic adhesive is usually used. However, since the photocatalyst, particularly titanium oxide, has a strong organic substance decomposability, it is not supported. There is a disadvantage that the photocatalyst falls off from the reaction plate when used for a long period of time because the adhesive to be oxidized and deteriorates rapidly. This problem also occurs when a general-purpose resin is used after being filled with a photocatalyst.

On the other hand, JP-A-6-315614 discloses that a photocatalyst is made of polytetrafluoroethylene (PTFE).
An apparatus is disclosed in which a mixture obtained by rolling into a sheet or a panel is formed by rolling the mixture. In this technique, since PTFE which is not oxidized and deteriorated by the photocatalyst is used, the problem of the photocatalyst falling off does not occur. However, in this device, the contact between the photocatalyst and the harmful gas on the surface of the sheet-shaped or panel-shaped molded product, that is, the surface of the plate material, similarly to the device disclosed in JP-A-7-108138 described above. Since it is performed, there is a disadvantage that the contact area between the photocatalyst and the harmful gas is small.

[0006]

As described above, the conventional apparatus using the photocatalyst has a disadvantage that the contact area between the photocatalyst and the harmful gas (contaminant) to be removed is small. There is a problem that it is not possible to efficiently remove odor gas and odor gas.

Accordingly, an object of the present invention is to provide a purification filter and a manufacturing method capable of increasing a contact area between a photocatalyst and an object to be decomposed such as harmful gas (contaminant) or odorous gas. .

[0008]

In order to achieve the above object, a purification filter of the present invention is formed by entanglement of a fluororesin fiber containing a photocatalyst activated by irradiation with light having a wavelength of 400 nm or less. I have.

As described above, if a fluororesin which is not oxidized and degraded by a photocatalyst is used, the photocatalyst is contained therein to form a fiber, and the fibers are entangled to form a filter, which can be compared with a sheet or panel form. The exposed area of the photocatalyst can be increased, and as a result, the contact area between the photocatalyst and an object to be decomposed such as odor gas or harmful gas can be increased. Therefore, in this state, when the filter of the present invention is irradiated with light including light (ultraviolet light) having a wavelength of 400 nm or less such as sunlight, harmful gases and pollutants are efficiently decomposed and removed on the surface and inside of the filter. You.

In the purification filter of the present invention, the average fiber diameter of the fluororesin fibers is preferably 30 μm or less. If the fiber diameter is 30 μm or less, the specific surface area of the filter of the present invention is increased, and the contact area between the photocatalyst and harmful gas (contaminant) in the air can be further increased.

In the purification filter of the present invention, the content of the photocatalyst in the fluororesin fiber is 0.1 to 60% by weight.
Is preferable. When the content of the photocatalyst is within the above-mentioned predetermined range, the fluororesin fiber has high mechanical strength, and has excellent retention of the photocatalyst. As a result, the durability of the purification filter of the present invention is improved. Will be better.

In the purifying filter of the present invention, the fluororesin fibers are preferably PTFE fibers. This is because PTFE is particularly excellent in chemical stability.

In the purifying filter of the present invention, the photocatalyst is preferably an anatase type titanium oxide. This is because anatase type titanium oxide has particularly excellent photocatalytic action.

In the purifying filter of the present invention, the fluororesin preferably contains a gas adsorbent in addition to the photocatalyst. This is because the contact efficiency between the photocatalyst and the odor gas or the organic gas is improved by using the gas adsorbent together. It is preferable that the gas adsorbent is at least one of zeolite and activated carbon.

In the purifying filter of the present invention, the fluororesin fiber has a large number of micropores and a density of 1.3 g / g.
In cm ³ , the specific surface area is preferably 1.0 cm ² / g / or more. Since such a fluororesin fiber has a large specific surface area, it is possible to further increase the contact area between the photocatalyst and harmful gas or odorous gas.

Next, the purification filter of the present invention is prepared by, for example, mixing a fluororesin and a photocatalyst, dispersing and blending the mixture with an extrusion aid, and extruding the molded product, and rolling the molded product into a sheet. Simultaneously with or after the rolling, the extrusion aid is removed by evaporation to produce a fluororesin film, and the fluororesin film is heated and fired at a temperature equal to or higher than the melting point of the fluororesin, and the fired fluororesin film is stretched. Then, the stretched baked fluororesin film is defibrated to produce a photocatalyst-containing fluororesin fiber, and the photocatalyst-containing fluororesin fiber can be entangled to produce the fiber.

Further, in the method for producing a purification filter of the present invention, a first fluororesin film and a second fluororesin film containing a photocatalyst are laminated, and the laminated film is stretched to form the second fluororesin film. The surface of the fluororesin film is made porous, the stretched laminated film is defibrated to produce a fluororesin fiber containing the photocatalyst, and a filter can be formed by entanglement of the fluororesin fiber. .

According to this method for producing a filter, the laminated film in which the first fluororesin film composed of a single fluororesin alone and the second fluororesin film containing a photocatalyst are stretched is stretched. Even if a large amount of photocatalyst is contained, the strength of the entire film required at the time of stretching and after the stretching is obtained by the first fluororesin film composed of only the fluororesin,
The action of improving the denseness and molecular orientation of the film by stretching works sufficiently. Further, since the surface of the second fluororesin film is made porous, a filter having a large specific surface area can be formed. As a result, a purification filter having excellent decomposition efficiency of odorous gas, harmful gas and the like and excellent durability can be produced with good reproducibility.

Further, as a method for producing the purification filter of the present invention, the photocatalyst-containing unsintered fluororesin sheet is stretched to be porous, and the fluorine-containing sheet is substantially maintained in a porous state. The resin is heated at a temperature equal to or higher than the melting point of the resin and fired to produce a fired sheet having a density of 1.3 g / cm ³ or less. The fired sheet is defibrated to produce a photocatalyst-containing fluororesin fiber. It is preferable to form the filter by entanglement of the fibers, because a filter for purification having a large specific surface area can be further produced.

The above specific surface area refers to the surface area per unit weight and can be measured, for example, by a BET adsorption method.

In the method for producing a purifying sheet of the present invention, the method of fibrillating a fluororesin film to produce a fluorocarbon fiber comprises the steps of: applying a fluororesin film to a tip of a member having a large number of needle-like projections; A method of defibrating by scratching is preferred. According to this method, the shape of the obtained fluororesin fiber is a shape in which many branch fibers are branched from the trunk fiber. Since the fiber having such a shape has a high crimpability, the fiber can be easily entangled.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The filter for purification of the present invention is formed by entanglement of a fluororesin fiber containing a photocatalyst activated by irradiation with light having a wavelength of 400 nm or less to form a fabric (felt or nonwoven fabric). It is what it was.

The fluororesin used as the material for forming the fluororesin fiber is not particularly limited.
FE, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PF
A), polychlorotrifluoroethylene (PCTF
E), fluorine resins such as polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and tetrafluoroethylene-ethylene copolymer (PETFE) can be used.

The reason for using the fluororesin fiber in the purification filter of the present invention is that the fluororesin has excellent chemical resistance, heat resistance, water repellency, and the like. This is because the characteristic deterioration is extremely small even when left unattended. PTFE having outstanding chemical resistance and water repellency among the above various fluororesins
It is particularly preferred to use The PTFE is preferably obtained by emulsion polymerization. Further, in the present invention, the specific gravity of the PTFE fiber is usually 2.0 or more, preferably in the range of 2.15 to 2.30.

The photocatalyst is an ultraviolet light (wavelength: 310-4)
00nm) and other light having a wavelength of 400 nm or less
Harmful gases such as nitrogen oxides and sulfur oxides in the air
It is a compound that causes photocatalysis to decompose. like this
As the photocatalyst, in addition to the titanium oxide described above, for example,
ZnO, Fe_TwoO_Three, CdS, CdSe, SrTiO _Three
And so on. These photocatalysts can be used alone or
More than one type is used together. Among them, titanium oxide (TiO 2)
_Two) Includes anatase type, rutile type and hydrous type.
Also prefers anatase-type titanium oxide, which has strong photocatalysis
No. The shape of the photocatalyst is usually powdery (particle).
For example, the particle size of anatase-type titanium oxide is generally
Usually, it is 0.001 to 50 μm, preferably 0.01 to 50 μm.
〜１０10 μm. The content of the photocatalyst is fluorine
It is preferably 0.1 to 60% by weight in the resin fiber.

In the present invention, a gas adsorbent is used together if necessary. That is, the photocatalyst alone may be contained in the fiber, but by including both the fiber and the gas adsorbent in the fiber, the contact of the harmful gas or the like to the photocatalyst can be promoted by the gas adsorption action of the gas adsorbent. As a result, harmful gases and the like can be decomposed more efficiently than in the case of using only a photocatalyst.

Examples of the gas adsorbent include synthetic or natural zeolites such as high silica zeolite (synthetic), sodalite (synthetic), and mordenite (natural), apatite, and activated carbon. These are usually used in the form of powder (particles), and one or more of them are used, but it is preferable to use at least one selected from zeolite and activated carbon from the viewpoint of high adsorption effect. The particle size of such a gas adsorbent is generally 0.01
To 50 μm, preferably 0.1 to 10 μm.

When a photocatalyst and a gas adsorbent are used in combination, the mixing ratio of the photocatalyst and the gas adsorbent varies depending on the kind of the compound to be used.
1: 1.

In order to further increase the contact area between the photocatalyst and the harmful gas (contaminant) in the air in the entire filter, the average fiber diameter of the fluororesin fibers is made as small as possible to increase the specific surface area of the filter. It is desirable. The specific surface area of the filter is generally 0.2 m
² / g or more, preferably 0.5 m ² / g or more. The average fiber diameter of the fluororesin fiber is generally 30 μm.
m or less, preferably 20 μm or less.

The density of the fibers in the filter for purification of the present invention, that is, the basis weight varies depending on the thickness (average diameter) of the fibers, but is generally preferably in the range of 10 to 500 g / m ² . By being in such a range, air can be sufficiently distributed not only near the surface of the filter but also inside the filter.

The purifying filter of the present invention is not particularly limited in its application range as long as it requires air purifying. For example, it is used for indoor air purifying, a clean room for manufacturing semiconductors, a clean room for producing pharmaceuticals, and a pollution control. Applicable to prevention equipment.

As described above, in the present invention, it is desirable that the fluororesin fibers containing the photocatalyst constituting the filter be ultrafine fibers having an average fiber diameter of 30 μm or less. However, it is difficult to obtain ultrafine fluororesin fibers by the emulsion spinning method generally used as a conventional method for producing fluororesin fibers. Therefore, in the present invention,
According to the above-mentioned method, an ultrafine fluororesin fiber containing a photocatalyst is produced, and a filter is formed by using this. An example of the manufacturing method will be described below.

First, the PTFE resin and the photocatalyst particles are mixed. Here, the mixing amount of the photocatalyst particles is about 0.1 to 5% by weight. When a gas adsorbent is used together, it is mixed with the photocatalyst. Hydrocarbons (extrusion aids) are further dispersed and mixed into this mixture, and the mixture is preformed into a cylindrical shape. This preform is extruded into a rod shape and further rolled to obtain a rolled sheet. And about 100 ~
The mixture is heated at 300 ° C. to evaporate and remove the hydrocarbons to form a PTFE film. Further, by heating to a temperature higher than the melting point of the PTFE resin, specifically, about 320 to 400 ° C.,
Bake the TFE film. By this firing step, PT
The specific gravity of the FE film will be in the range of about 2.1 to 2.3.

Next, this PTFE film is made of PTFE
It is stretched at least uniaxially at or above the melting point of the E resin. This stretching can be performed by a conventional method using a roll stretching machine, a tenter stretching machine, or the like, and the stretching direction may be the longitudinal direction of the film or the width direction. The stretching ratio is
Based on the size before stretching (the same applies hereinafter), more than twice,
Preferably it is three times or more. In order to obtain fine fibers, it is desirable that the thickness of the film after stretching is small.
Specifically, the thickness of the film after stretching is usually 0.5
mm or less, preferably 0.1 mm or less.

Next, the stretched film is defibrated to produce a PTFE fiber containing a photocatalyst. The defibration can be performed, for example, by scratching with a tip of the needle of a scraper such as a brush provided with a large number of metal needles. The scraping member of the scraping device is not limited to a metal needle, but may be made of another material, or may be of any other shape than a needle as long as it has a sharp tip. The size of the sharp tip of the scraping member of the scraping device is, for example, when the scraping member is the needle, the needle diameter is generally 1.0 mm.
It is preferable to set the size as small as possible within a range where the scraping member is not broken or deformed by the scraping operation.

The average fiber diameter of the fibers obtained by defibration is
It depends on the degree of molecular orientation of the stretched film and the thickness of the stretched film. The average fiber diameter of the fiber obtained by this method is 3
0 μm or less, and the shape is a shape in which many branch fibers are branched from the trunk fiber. The fibers having such a shape are rich in crimpability and are easily entangled. For example, the fibers can be easily entangled with a needle and processed into a felt or a nonwoven fabric.
The confounding can be performed by, for example, a needle punching machine or the like. In addition, a web can be formed by a card machine using the above-mentioned fibers, and further entangled by a water jet machine. These felts, nonwoven fabrics and the like constitute the purification filter of the present invention.

In the purifying filter thus obtained, the photocatalyst particles protrude from the surface of the fiber constituting the filter, and efficiently react with low-concentration odorous gas and harmful gas in the air to remove them. It can be decomposed and made harmless.

Next, a purification filter in which a fluororesin other than PTFE resin contains photocatalyst particles can be produced, for example, as follows. That is, first, a fluororesin and a photocatalyst are mixed and melt-extrusion is performed to form a thin film. Next, it is drawn and defibrated into a fiber by the same method as the above-mentioned PTFE resin fiber. Alternatively, it is also possible to mix a fluororesin and a photocatalyst and continuously form them into a fibrous form at the time of melt-extrusion molding to obtain fibers as they are. When a gas adsorbent is used together, it is mixed with a fluororesin together with the photocatalyst.

Next, a preferred production method of the present invention will be described.

First, a dispersion is prepared by dispersing fluororesin particles and photocatalyst particles produced by emulsion polymerization in a solvent, and this is coated on a heat-resistant substrate to form a coating film.
After removing the dispersing solvent from the coating film, the coating film is fired at a temperature equal to or higher than the melting point of the fluororesin to bind the fluororesin particles together to form a film. The particle size of the fluororesin particles here is generally 1 μm or less, and the particle size produced by emulsion polymerization is 0.1 μm.
It is preferable to use fluororesin particles of up to 1.0 μm.
Then, after the fluororesin film in which the photocatalyst particles are dispersed is peeled off from the heat-resistant substrate, the stretching ratio is generally at least two times, preferably at least three times, at least uniaxially at a temperature not lower than or equal to the melting point of the fluororesin. The film is stretched so as to be at least twice the thickness to make the film a thickness of 0.1 mm or less, preferably 0.05 mm or less. In this stretching, by stretching the film so that the thickness of the film becomes as small as possible, the degree of molecular orientation of the fluororesin constituting the film is increased, and the diameter of the fiber obtained in the fiberization step by the next defibration can be reduced. it can. Next, the 0.
A fluororesin film stretched to a thickness of 1 mm or less,
For example, the fibers are defibrated in the same manner as described above to obtain fibers. Also,
Fabrication of a filter using the fiber is performed in the same manner as described above.

According to this production method, the purification filter of the present invention can be produced, but there is a problem that the content of the photocatalyst cannot be increased in consideration of the film stretching step.
This is because, as the blending amount of the photocatalyst particles increases, the role of the fluororesin particles as a binder is hindered, and the binding between the fluororesin particles and the binding between the fluororesin and the photocatalyst become insufficient. This is because the effect of improving the denseness and the degree of molecular orientation does not work sufficiently, and the film may have low mechanical strength, that is, a brittle film. Therefore, as a method for solving this problem, the film to be stretched is a laminated film in which a fluororesin film layer made of a single fluororesin containing no photocatalyst particles and a fluororesin film layer containing photocatalyst particles are laminated. With such a laminated film, even if a large amount of photocatalyst is contained in the fluororesin film layer containing one photocatalyst, the mechanical strength of the entire film required during and after stretching of the film is the same as that of the fluororesin alone. Of the fluororesin film layer. In addition, the surface of the fluororesin film containing the photocatalyst is cracked by the stretching of the film to make the surface porous, so that a filter having a large specific surface area can be formed. Note that the laminated film may be formed by first forming a fluororesin film layer made of a single fluororesin on a heat-resistant substrate, and then forming a fluororesin film layer containing photocatalyst particles thereon. A fluororesin film layer containing photocatalyst particles may be formed on a functional substrate, and a fluororesin film layer made of a single fluororesin may be formed thereon. Further, the laminated film may be provided with at least one fluororesin film layer made of a fluororesin alone, and a fluororesin film layer containing photocatalyst particles is arranged on both main surfaces of the fluororesin film layer made of a fluororesin alone. A laminate structure or a laminate structure in which two or more fluororesin film layers composed of a single fluororesin and a fluororesin film layer containing photocatalyst particles are alternately provided may be used. In addition, the fluororesin film layer made of a fluororesin alone can also be formed by paste extrusion and calendering.

Next, in the method for producing a purification filter of the present invention, which is a preferable method mainly when PTFE is used, a PTFE fiber containing a photocatalyst having a larger specific surface area is produced, and the photocatalyst and the photocatalyst are used by using this. A method for obtaining a purification filter having a larger contact area with harmful gas or odorous gas will be described below.

It is desirable that the PTFE used in this production method be one which is oriented to a higher order by stretching. As such PTFE, those obtained by an emulsion polymerization method are preferable in that they have a small particle diameter and can be stretched to a higher order. The specific gravity of PTFE (SS
G) is usually 2.1 to 2.2.

Such a PTFE emulsion polymer may be used, for example, in addition to a homopolymer of tetrafluoroethylene, for example, 0.5
It may be modified by copolymerizing a small amount of another comonomer of not more than mol% with tetrafluoroethylene. Examples of such other monomers include hexafluoropropylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), trifluoroethylene and the like.

On the other hand, a photocatalyst such as titanium oxide is mixed with an extrusion aid such as liquid paraffin.

Then, the PTFE and the extrusion aid obtained by mixing the photocatalyst are mixed and stirred. The ratio of these three is usually 28 to 35 parts by weight of the extrusion aid and 0.1 to 6 parts by weight of the photocatalyst based on 100 parts by weight of PTFE.

Next, the mixture was paste-extruded,
Formed into a sheet by rolling or the like, then removing the auxiliary by heating or extraction with trichloroethylene,
A green PTFE sheet containing a photocatalyst is prepared.

The unfired PTFE sheet containing the photocatalyst is stretched to form a porous film. This stretching is usually performed by PT
This is performed under heating conditions at a temperature lower than the melting point of FE (327 ° C.). The stretching is preferably uniaxial stretching in the longitudinal direction, and the stretching ratio is not particularly limited as long as it can be sufficiently made porous, but is usually 1.5 times or more, preferably 3 times or more.

The stretching method is not particularly limited.
Conventionally, stress is applied while passing the sheet through a heated oven, or a sheet or the like is heated by contacting a heated roller or the like with the surface of the sheet to apply stress and stretch the sheet. The method is applicable.
By this stretching, an unsintered PTFE porous film having a thickness of 0.05 to 0.5 mm, which is oriented at a high order, and in which a large number of micropores having an average pore diameter of 0.01 to 0.5 μm are formed. This film is sufficiently porous so as to have a density of 1.3 g / cm ³ or less, preferably 1.25 g / cm ³ or less. As described above, if the film is sufficiently porous, the density of the fibers obtained through the steps described below can be sufficiently reduced.

Next, the unfired PTFE porous film is fired at a temperature equal to or higher than the melting point of PTFE while maintaining its porosity substantially. That is, this baking is performed at a baking temperature and time that can maintain the porous state of the film. Usually, the firing temperature is 327-4.
The temperature is in the range of 00 ° C., and the firing time is in the range of 1 second to 1 hour. The porous film obtained through such a firing step has a porosity of 40% or more, but has a density of 1.3 g /
It is preferable that the porosity is well maintained at not more than cm ³ .

Then, the porous film is defibrated in the same manner as described above to obtain a photocatalyst-containing PTFE fiber. This PTFE fiber has a density of 1.3 g / cm ³ or less, preferably 1.25 g / cm ³ or less, and a specific surface area of 1.0 g / cm ³ or less.
m ² / g or more. The average fiber diameter of this PTFE fiber is usually 50 μm or less, preferably 30 μm.
m or less. In general, a large specific surface area of a fiber indicates that if the density of the fiber is constant, the fiber is a fine fiber having a small average fiber diameter. However, since the PTFE fiber is a low-density porous fiber, The specific surface area is extremely large as compared with conventional fibers having the same average fiber diameter.

Next, the PTFE fiber is entangled in the same manner as described above, whereby the purification filter of the present invention can be produced.

[0053]

Next, examples will be described together with comparative examples.

(Example 1) PTFE resin particles (particle size: 0.
A 0.5 mm thick stainless steel foil as a heat-resistant base material is immersed in an aqueous dispersion in which 3 μm) is dispersed as a solid content of 60% by weight, and pulled up to form a coating film of the aqueous dispersion on the surface of the stainless steel foil. After that, it was air-dried, baked by heating at 380 ° C. for 90 seconds, and having a thickness of 10 μm.
m of PTFE alone was formed.

Next, PTFE resin particles (particle diameter 0.3 μm)
Anatase type titanium oxide powder (particle size: 0.02 μm) is added to the aqueous dispersion in which is dispersed so as to be 20% by weight based on the PTFE resin particles, and zeolite powder (particle size: 1.0 μm) is further added to the PTFE resin. PTFE resin particles by adding 20% by weight to the particles,
The total amount of the titanium oxide powder and the zeolite powder was adjusted to be 60% by weight as a solid content in the aqueous dispersion.

Next, the above-mentioned stainless steel foil on which the film layer made of PTFE alone was formed was mixed with the above-mentioned PTFE resin particles,
After being immersed in the aqueous dispersion in which the titanium oxide powder and the zeolite powder are dispersed and pulled up to form a coating film of the aqueous dispersion on a film layer of a stainless steel foil made of PTFE alone, the same air drying and heating as described above are performed. By baking, a PTFE film layer having a thickness of 8 μm containing the titanium oxide powder and the zeolite powder was formed. Then, a laminated film in which the PTFE film layer containing the titanium oxide powder and the zeolite powder was laminated on the film layer composed of the PTFE alone was peeled off from the stainless steel foil.

Next, this laminated film was heated to 380 ° C. and stretched four times in the longitudinal direction to obtain a stretched film having a thickness of 0.01 mm.

Next, the stretched film was scratched with a brush having metal needles having a needle diameter of 0.5 mm to obtain fibers. The content of titanium oxide in the fiber was 16% by weight, and the average fineness was 2 denier (average fiber diameter: 8 μm). The average fiber diameter is a value obtained by measuring the fiber diameters of 10 arbitrary fibers and averaging the measured fiber diameters. The same applies to the following examples.

Finally, the obtained fiber was entangled with a needle punching machine to prepare a filter having a thickness of 3 mm, a basis weight of 400 g / m ² and a specific surface area of 0.8 m ² / g.

The decomposition reaction between ammonia and acetaldehyde was tested using this filter.

In the test, a transparent container in which a filter is housed and in which a gas to be decomposed (ammonia, acetaldehyde) is enclosed, and a light source (outside the container, which irradiates ultraviolet light (310 to 400 nm) in a sealed space) Black light), a cylinder for introducing a gas to be decomposed (ammonia, acetaldehyde) into the container, a gas syringe for extracting the gas after the decomposition reaction from the container, and a gas syringe for extracting the gas after the decomposition reaction extracted by the gas syringe. The measurement was performed using a device equipped with a gas chromatography for measuring the concentration. Here, the light source (black light) is ultraviolet light (310 to 400 n).
m) at an intensity of 1 mW / cm ² .

In a container, thickness 3 mm × width 50 mm × length 5
A filter (1 g) having a size of 0 mm is accommodated, a certain amount of gas to be decomposed (ammonia, acetaldehyde) is sealed in the container, and the container is sealed. Then, ultraviolet light (310 to 310) is transmitted from the light source (black light) to the filter. 400 nm) while irradiating for a certain period of time (30 minutes, 60 minutes, 12 minutes).
At 0 min), the gas was extracted from the container with a gas syringe, and the concentration was measured by gas chromatography. Table 1 shows the results.
Shown in

(Example 2) PTFE resin particles (particle diameter: 0.3 μm) using a stainless steel foil having a thickness of 0.5 mm as a base material
The titanium oxide powder (particle size 0.02 μm) was dispersed in the aqueous dispersion in which
% Of the PTFE resin particles.
And the total amount of the PTFE resin particles, the titanium oxide powder and the zeolite powder was adjusted to 60% by weight as a solid content in the aqueous dispersion. A 0.5 mm stainless steel foil is immersed in this solution and pulled up to form a coating film of the aqueous dispersion on the surface of the stainless steel foil, which is then air-dried and baked at 380 ° C. for 90 seconds to obtain a titanium oxide powder. And a PTFE film layer having a thickness of 8 μm containing zeolite powder.

Next, PTFE resin particles (particle diameter 0.3 μm)
Is immersed in an aqueous dispersion in which 60% by weight is dispersed as a solid content, the stainless steel foil on which the PTFE film layer containing the titanium oxide powder and the zeolite powder is formed is pulled up, and the titanium oxide powder and the zeolite powder are removed. A coating film of the aqueous dispersion was formed on the PTFE film layer containing the film, and this was air-dried.
By heating and baking for 2 seconds, a film layer made of PTFE alone having a thickness of 10 μm was formed.

Next, using the aqueous dispersion in which the PTFE resin particles, titanium oxide powder and zeolite powder used first were dispersed, the titanium oxide powder and zeolite powder were contained on the film layer composed of PTFE alone in the same manner as described above. An 8 μm thick PTFE film layer was formed.
Then, a laminated film in which a PTFE film layer containing a titanium oxide powder and a zeolite powder was formed on both surfaces of the film layer composed of PTFE alone was peeled off from the stainless steel foil.

This laminated film was heated to 380 ° C.
The film was stretched four times in the length direction to obtain a stretched film having a thickness of 0.013 mm.

Thereafter, the stretched film was used in Example 1
The fiber was defibrated in the same manner as described above to obtain a fiber having an average fiber diameter of 8 μm. The titanium oxide content in this fiber was 15
% By weight.

Finally, the obtained fiber was entangled with a needle punching machine to prepare a filter having a thickness of 3 mm, a basis weight of 410 g / m ² and a specific surface area of 0.8 m ² / g.

Using this filter, the decomposition reaction of ammonia and acetaldehyde was tested in the same manner as in Example 1. Table 1 shows the results.

Example 3 When forming a PTFE film layer containing a titanium oxide powder and a zeolite powder, a titanium oxide powder (particle diameter 0.0
2 μm) and zeolite powder (particle size: 1.0 μm), each comprising 10 wt% with respect to the PTFE resin particles to form a film layer having a thickness of 6 μm in the same manner as in Example 1, except that it is composed of PTFE alone. A laminated film in which a PTFE film layer containing a titanium oxide powder and a zeolite powder was laminated on the film layer was formed. Then, the laminated film was defibrated in the same manner as in Example 1 to prepare a fiber having a titanium oxide content of 6% by weight and an average fiber diameter of 7 μm. The fiber was entangled with a needle punching machine to a thickness of 3 μm.
mm, basis weight 410 g / m ² , specific surface area 0.9 m
^{A 2} / g filter was made. Using this filter, the decomposition reaction of ammonia and acetaldehyde was tested in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 Molding powder of PTFE resin (particle size: 550 μm), 20% by weight of titanium oxide powder (particle size: 0.02), and 20% by weight of the molding powder of PTFE resin The zeolite powder (particle size: 1.0 μm) was mixed by a mixer for 30 minutes, and the mixture was put into a mold and pressed by a press to 300 kg / cm.
Preformed at a pressure of ² . And this preform is 3
The resultant was fired in a firing furnace heated to 80 ° C. for 5 hours, and the fired product was cut with a blade to obtain a sheet having a thickness of 0.1 mm.

This sheet was 0.1 mm × 50 mm × 90
The sample was cut to a size of 1 mm (mm) to obtain a sample, and the same ammonia and acetaldehyde decomposition reaction test as in Example 1 was performed. Table 1 shows the results.

[0073]

[Table 1]

As can be seen from Table 1, the present invention (Example 1)
When the filters of (3) to (3) were used, the harmful gas removal (decomposition) efficiency was dramatically improved as compared with the case of using the sheet-like harmful gas removal material of the related art (Comparative Example 1).

(Example 4) PTFE obtained by emulsion polymerization
Resin (average particle size: 0.2 μm) and titanium oxide (particle size:
0.007 μm) was mixed at 3% by weight. In this mixture,
Naphtha was mixed and stirred at 24% by weight. This mixture was preformed into a cylindrical shape, and the preformed product was extruded and rolled to obtain a sheet having a thickness of 0.1 mm. The rolled sheet was heated to 280 ° C. to remove naphtha by evaporation. Next, the rolled sheet was heated and fired at 350 ° C., and after firing, stretched 3.5 times in the longitudinal direction at 380 ° C.

The stretched film was scratched with a brush-like scratching tool provided with a large number of needles having a needle diameter of 0.5 mm to obtain fibers. The average fiber diameter of this fiber was 15 μm. Using these fibers, a web was formed with a card machine, and the web was entangled with a water jet machine to prepare a filter. The basis weight of this filter was 41 g / m ² .

The filter thus obtained was subjected to an acetaldehyde decomposition reaction test using the measuring apparatus shown in FIG.

As shown in the figure, the measuring device includes a closed transparent container 2, a circulation pump 4, a valve 5, and a flow meter 6, which are connected by flow paths 7a and 7b. A valve 5 and a flow meter 6 are mounted in this order in the middle of a flow path 7a extending from the circulation pump 4, and the end of the flow path 7a is introduced into the closed transparent container 2, while the closed transparent container 2 And a leading end thereof is connected to the circulation pump 4, and a flow path 7 c for sampling is branched from the middle of the flow path 7 b. A black light 3 is disposed in front of the closed transparent container 2.

An acetaldehyde decomposition reaction test using this measuring device is performed as follows. First, the filter 1 is placed in the sealed transparent container 2. The sample area of the filter 1 is 25 cm ² . Then, acetaldehyde is injected into the closed transparent container 2 so as to have an initial concentration of 500 ppm in the air, and the circulation pump 4 is operated to circulate the air at a circulation speed of 1 liter / min. In this state, the black light 3 is turned on and 1 m
The filter 1 is irradiated with an intensity of w / cm ² . And
Air is sampled at regular intervals from the sampling channel 7C, the acetaldehyde concentration is measured by gas chromatography, and the decomposition ratio is calculated. The results are shown in Table 2 below.

Example 5 The mixing ratio of titanium oxide was set to 0.1.
A filter was produced in the same manner as in Example 4, except that the weight was 5% by weight and the basis weight of the filter was 40 g / m ² . This filter was subjected to an acetaldehyde decomposition test in the same manner as in Example 4. The results are shown in Table 2 below.

(Example 6) As a fluororesin, an ethylene tetrafluoride-perfluoroalkoxyethylene resin was used.
3% by weight of titanium oxide was mixed and dispersed in the resin. This mixed dispersion was formed into a film having a thickness of 0.05 mm using a melt extruder under heating conditions at a temperature of 400 ° C. This film was stretched three times in the longitudinal direction at a temperature of 250 ° C. Other than that was carried out similarly to Example 4, and produced the filter. The basis weight of the filter was 40 g / m ² . This filter was subjected to an acetaldehyde decomposition test in the same manner as in Example 4. The results are shown in Table 2 below.

Example 7 31.6 parts by weight of liquid paraffin was prepared based on 100 parts by weight of a PTFE resin powder having a specific gravity (SSG) of 2.154. This liquid paraffin and 3.1 parts by weight of titanium oxide (particle size: 0.007 μm) were mixed and stirred, and then mixed with 100 parts by weight of the above PTFE resin powder. The content of the titanium oxide is PT
It is 3% by weight based on the FE resin.

The mixture was paste-extruded, and then calendered to obtain a green sheet having a thickness of 0.1 mm.
Liquid paraffin is extracted from the sheet with trichloroethylene, and then the unsintered sheet is heated to a temperature of 120 ° C.
The film was stretched 2 times in the longitudinal direction while heating for 2 minutes at, to obtain an unfired stretched film. This film has a thickness of 0.08 m
m, the pores were formed with a large number of micropores having an average pore diameter of 0.5 μm, and the apparent density was 0.72 g / cm ³ . Then, the unfired stretched film is fired at 350 ° C. for 1 minute to have a porosity of 63% and an apparent density of 0.8 g / c.
Thus, a fired porous film of m ³ was obtained.

This porous film was defibrated in the same manner as in Example 4 to obtain a titanium oxide-containing porous PTFE fiber. The specific surface area of this fiber was measured by a bed adsorption method and found to be 3.4 m ² / g, and the specific surface area was extremely large. Then, a filter was prepared using this fiber in the same manner as in Example 4. This filter was subjected to an acetaldehyde decomposition test in the same manner as in Example 4. The results are shown in Table 2 below.

(Comparative Example 2) Titanium oxide (same as in Example 4) was blended in a molding powder of PTFE resin (particle size: 500 μm) at a ratio of 3% by weight, and mixed with a mixer.
Mix for 0 minutes. This mixture was put into a mold and preformed into a cylindrical shape at a pressure of 300 kgf / cm ² by a press. The preform was heated and fired in a firing furnace heated to 380 ° C. for 1 hour. This fired product is cut with a knife,
A sheet having a thickness of 0.1 mm was obtained. This sheet was subjected to an acetaldehyde decomposition test in the same manner as in Example 4 with a sample area of 25 cm ² . The results are shown in Table 2 below.

(Comparative Example 3) PTF was prepared in the same manner as in Example 4.
Titanium oxide was mixed with E resin fine powder at a ratio of 3% by weight. To this mixture, 24% by weight of naphtha was mixed and stirred. This mixture was preformed into a cylindrical shape, and the preformed product was extruded and further rolled to obtain a 0.1 mm
Was obtained. The rolled sheet was heated to 280 ° C. to remove naphtha by evaporation. Further, the rolled sheet was heated and fired at 350 ° C. to obtain a fired sheet having a thickness of 0.1 mm. For this sheet, a sample area of 25 cm ²
Then, an acetaldehyde decomposition test was performed in the same manner as in Example 4. The results are shown in Table 2 below.

[0087]

[Table 2]

As apparent from Table 2 above, Examples 4 to
The filter of 7 showed excellent gas resolution. Especially,
The filter of Example 7 having a large specific surface area of the fiber was excellent in gas resolution. In contrast, the sheets of Comparative Examples 2 and 3 were inferior in gas resolution.

[0089]

As described above, the purification filter of the present invention is formed by entanglement of a fluororesin fiber containing a photocatalyst which is activated by irradiation with light having a wavelength of 400 nm or less. The contact area with gas or the like can be increased. Further, in the purification filter of the present invention, if a porous fluororesin fiber is used as the fluororesin fiber, the contact area can be further increased. If the photocatalyst and the gas adsorbent are used in combination, the efficiency of decomposing odorous gas and harmful gas can be further improved. For this reason, by applying the purification filter of the present invention, it is possible to efficiently remove odorous gas and harmful gas in the air even at a low concentration,
It can contribute to environmental purification. Further, according to the method for producing a purification filter of the present invention, the purification filter of the present invention can be efficiently produced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of an apparatus for measuring a gas decomposition function of a purification filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Purification filter 2 Closed transparent container 3 Black light 4 Circulation pump 5 Valve 6 Flow meter 7a, 7b Circulation flow path 7c Sample collection flow path

Claims (10)

[Claims] 1. A purifying filter formed by entanglement of a fluororesin fiber containing a photocatalyst activated by irradiation with light having a wavelength of 400 nm or less. 2. The fluororesin fiber has an average fiber diameter of 30 μm.
The purifying filter according to claim 1, wherein: 3. The purification filter according to claim 1, wherein the fluororesin fiber is a polytetrafluoroethylene fiber. 4. The purification filter according to claim 1, wherein the photocatalyst is an anatase type titanium oxide. 5. The purification filter according to claim 1, wherein the content of the photocatalyst in the fluororesin fiber is in the range of 0.1 to 60% by weight. 6. The purification filter according to claim 1, wherein the fluororesin contains a gas adsorbent in addition to the photocatalyst. 7. The purification filter according to claim 1, wherein the gas adsorbent is at least one of zeolite and activated carbon. 8. The fluororesin fiber has a large number of micropores, a density of 1.3 g / cm ³ and a specific surface area of 1.0 cm.
The purification filter according to any one of claims 1 to 7, which has a ratio of ² / g / or more. 9. A first fluororesin film and a second fluororesin film containing a photocatalyst are laminated, and the laminated film is stretched to make the surface of the second fluororesin film porous. A method for producing a purification filter, in which a stretched laminated film is defibrated to produce a fluororesin fiber containing the photocatalyst, and the filter is formed by entanglement of the fluororesin fiber. 10. An unsintered fluororesin sheet containing a photocatalyst is stretched and made porous, and heated and heated at a temperature equal to or higher than the melting point of the fluororesin while the porous state of the porous sheet is substantially maintained. To produce a fired sheet having a density of 1.3 g / cm ³ or less, fibrillating the fired sheet to produce a photocatalyst-containing fluororesin fiber, and confounding the photocatalyst-containing fluororesin fiber to form a filter. Manufacturing method.