JP2001226516A - Photocatalyst film and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a transparent photocatalyst film which can impart photocatalytic functions to a substrate merely by sticking it thereto when the pattern or handle of the substrate is required to be fully utilized or when photocatalytic functions are required to be imparted to a transparent body and which can be easily manufactured by a coating method. SOLUTION: This photocatalyst film is transparent and comprises a stretched porous polytetrafluoroethylene film comprising a skeleton and voids within the skeleton and titanium oxide particles carried by the porous polytetrafluoroethylene film. The voids may be filled with a transparency- enhancing substance. Preferably, the titanium oxide particles are carried with a binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent photocatalyst film and a method for producing the same. More specifically, the present invention relates to a transparent photocatalyst film which can be produced by a simple coating method and has a chemical effect on the oxidative decomposition of the photocatalyst itself. The present invention relates to a stable and transparent photocatalytic film and a method for producing the same.

[0002]

2. Description of the Related Art A flat sheet or film carrying a photocatalyst capable of decomposing and removing air pollutants and odorous substances can impart a photocatalytic function to a substrate simply by sticking it to the substrate. Various studies have been conducted on such a photocatalyst film in terms of easier handling and workability than a coating agent containing a photocatalyst. Here, when it is desired to make use of the pattern and texture of the base material or to impart a photocatalytic function to a transparent body such as glass, the photocatalytic film itself is required to be transparent.

In the case of producing a photocatalyst film using a plastic film as a support, it is necessary to use a support which is not easily affected by the oxidative decomposition of the photocatalyst. When a highly active photocatalyst film is desired, it is necessary to carry as much titanium oxide as possible.

A fluororesin sheet has been proposed as a plastic film for a support which is stable against photocatalysis. However, it is difficult to form a thick photocatalyst layer containing titanium oxide on a polymer film having a smooth surface, and a thick photocatalyst layer cannot be formed only by coating with a binder or the like. Furthermore, even if a thick photocatalyst layer can be formed by coating, the titanium oxide on the surface of the photocatalyst layer functions as a photocatalyst, but since there is little light that can reach the inside of the photocatalyst layer, the titanium oxide inside the photocatalyst layer is used as a photocatalyst. In many cases, it does not function sufficiently, and as a result, a photocatalytic ability corresponding to the content of titanium oxide cannot be obtained.

[0005] As a photocatalyst film for effectively obtaining not only the titanium oxide on the surface of the photocatalyst layer but also the photocatalyst inside the photocatalyst layer to obtain a photocatalytic ability corresponding to the amount of titanium oxide supported on the support, for example, JP-A-10-27236
No. 7, Japanese Patent Application Laid-Open No. 9-227828 discloses a method in which fine particles of photocatalyst are dispersed in expanded porous polytetrafluoroethylene (Japanese Patent Application Laid-Open No. 9-278928). One in which photocatalyst particles are fixed on the surface of the pores of a porous resin film provided with a group (prior art 2) has been proposed.

[0006] The prior art 1 is to form a paste by mixing photocatalyst particles and polytetrafluoroethylene powder together with a forming aid, form the paste into a sheet, and evaporate and remove the forming aid from the sheet-shaped body. Produces a photocatalyst film. Since a transparent photocatalyst film cannot be produced by such a method, it cannot be applied as a photocatalyst film used when it is desired to make use of the pattern or texture of the base material or to impart a photocatalytic function to a transparent body.

The prior art 2 is also not intended for a transparent photocatalyst film, and therefore is not sufficient as a photocatalyst film to be used when it is desired to make use of the pattern or texture of the base material or to impart a photocatalytic function to a transparent body.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object the purpose of making use of the pattern and texture of a base material or of providing a transparent body with a photocatalytic function. It is an object of the present invention to provide a transparent photocatalyst film that can provide a photocatalytic function simply by sticking when applied, and that can be easily manufactured by a coating method.

[0009]

The photocatalyst film of the present invention comprises an expanded porous polytetrafluoroethylene film having a skeleton and voids between the skeleton, and an expanded porous polytetrafluoroethylene film. And titanium oxide particles carried thereon, and are transparent.

[0010] The titanium oxide particles may be carried by being attached to the skeleton surface of the expanded porous polytetrafluoroethylene membrane or filled in pores.
It may be adhered to the skeleton surface of the expanded porous polytetrafluoroethylene film or filled in the pores, and may be supported by being laminated on one and / or both surfaces of the expanded porous polytetrafluoroethylene film. Good. Alternatively, the titanium oxide particles may be supported by being laminated on one surface and / or both surfaces of the expanded porous polytetrafluoroethylene film.

The photocatalyst film of the present invention is supported by laminating titanium oxide particles on one side and / or both sides of the expanded porous polytetrafluoroethylene film,
The pores of the expanded porous polytetrafluoroethylene film may be filled with a transparency improving substance. Preferably, the transparency improving substance is silica gel.

Further, the photocatalyst film of the present invention may further comprise a binder, and the titanium oxide particles may be carried on the expanded porous polytetrafluoroethylene film via the binder. The binder is preferably silica.

The photocatalytic film of the present invention preferably has a light transmittance at 550 nm of 20% or more.

In the photocatalyst film of the present invention, the thickness of the expanded porous polytetrafluoroethylene is preferably 30 μm or less, and the particle size of the titanium oxide particles is 5 nm to 1 nm.
μm is preferred.

In the method for producing a photocatalyst film of the present invention, a first step of imparting a transparency-improving substance to an expanded porous polytetrafluoroethylene film and a method of supporting titanium oxide particles on the expanded porous polytetrafluoroethylene film are described. Including two steps. The first step is a step of immersing the stretched porous polytetrafluoroethylene film in an alkoxysilane sol and then drying, and the second step is preferably performed after the first step.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The photocatalytic film of the present invention comprises an expanded porous polytetrafluoroethylene (ePTFE) film,
Having titanium oxide particles supported on a PTFE film,
And a transparent film.

Here, the expanded porous polytetrafluoroethylene (ePTFE) refers to a molding aid obtained by mixing a fine powder of polytetrafluoroethylene (PTFE) with a molding aid. Stretched after or without removal and obtained by baking if necessary.In the case of uniaxial stretching, the fibrous structure is oriented in the stretching direction and pores are formed between fibrils. It has become. In the case of biaxial stretching, fibrils spread radially and have a spider web-like fibrous structure in which a large number of pores defined by nodes and fibrils exist. That is, the nodes and fibrils form the skeleton of the ePTFE membrane, and voids are formed between the fibrils or portions defined by the nodes and fibrils corresponding to the interskeletal gaps.

Such an ePTFE membrane is excellent as a support for photocatalyst particles because it is chemically stable and does not need to be subjected to the oxidative decomposition action of the photocatalyst carried even when in contact with the photocatalyst. In addition, the ordinary PTFE film is opaque, but can be made transparent by controlling the thickness of the ePTFE film, or by using a transparency improving substance described later in combination.

As the ePTFE membrane to be used, an ePTFE membrane having high transparency is preferable. Specifically, 550 nm
EPTF having a light transmittance of 10% or more, particularly 50% or more
An E film is preferably used. In general, the transparency tends to be reduced by supporting titanium oxide particles.However, the transparency can be increased by using a transparency improving substance or the like, so that the ePTFE film as the support has such a light transmittance. It is enough to have.

The thickness of the ePTFE membrane is preferably about 30 μm or less. The light transmittance of the ePTFE film is mainly ePT
Because it depends on the thickness of the FE film, it is necessary to be 30 μm or less in order to secure the above light transmittance.

The porosity and pore size of the ePTFE membrane may be appropriately selected according to the size of the titanium oxide particles to be used, but the porosity is preferably about 20 to 98%. The size of the pores is preferably such that the maximum pore diameter is 0.2 to 6.5 μm. Here, the porosity (%) is obtained from the following equation. In the formula, the true specific gravity is 2.2, which is the specific gravity of polytetrafluoroethylene. Porosity = (true specific gravity−apparent specific gravity) ÷ true specific gravity × 100 The maximum pore diameter of the pore is a value obtained from the bubble point shown in the following equation. Wherein B.I. P. Is the pressure at which continuous air bubbles are generated when 2-propanol is poured into the upper surface of the membrane and air is injected from the lower surface. Maximum pore size = 0.65 ° B. P.

The titanium oxide particles are used as photocatalyst particles and may be of anatase type or rutile type. Of these, titanium oxide having a high photocatalytic function, particularly anatase type titanium oxide, is preferably used.

The particle size of the titanium oxide particles is preferably 5 nm or more, more preferably 7 nm or more. On the other hand, the preferred upper limit of the particle size is 1 μm, more preferably 0.2 μm. If the thickness is less than 5 nm, it is difficult to produce titanium oxide particles, and if it exceeds 1 μm, it is white and opaque.

As an embodiment in which the titanium oxide particles are supported on the ePTFE membrane, for example, as shown in FIG.
The titanium oxide particles 4 adhere to the surface of the skeleton 2 of the FE film 1, and the titanium oxide particles 4 are filled in the pores 3.
Or titanium oxide particles 4 are impregnated inside the ePTFE membrane 1 and further laminated on the surface of the ePTFE membrane 1 to form a titanium oxide layer 5 as shown in FIG. 3. As shown in FIG. 3, or as shown in FIG.
An embodiment in which the film is laminated on the surface of the E film 1 is given. In FIGS. 2 and 3, the titanium oxide layer 5 is laminated only on one side of the ePTFE membrane 1, but may be laminated on both sides.

As described above, the photocatalyst film of the present invention has eP
It is a transparent film in which titanium oxide particles are supported on a TFE film. The term “transparent” as used in the present invention means that the side facing the film can be seen through the film.
It means that the light transmittance at 0 nm is 20% or more. The light transmittance varies depending on the type (thickness, porosity, etc.) of the ePTFE film to be used, the amount of titanium oxide particles to be supported, the mode of supporting the titanium oxide particles, and the use of a binder or a transparency improving substance described later.

The photocatalyst film of the present invention having the above-described structure is prepared by adding a titanium oxide particle to a solvent and dispersing the same to prepare a titanium oxide-containing solution.
After immersing the TFE membrane, taking it out and drying,
Alternatively, it can be obtained by applying a titanium oxide-containing liquid to the ePTFE membrane and then drying it.

The thickness of the photocatalyst film is determined by the e
As compared with the thickness of the PTFE film, the thickness is increased by the thickness of the titanium oxide layer. Although it varies depending on the thickness of the ePTFE membrane, the amount of titanium oxide particles carried, and the like, it is generally about 2 to 50 μm. The type of ePTFE membrane used as a support,
The desired transparency can be achieved if the thickness is up to about 100 μm by a treatment for improving the transparency.

The photocatalyst film of the present invention having the above configuration is a transparent body having a constant light transmittance as the photocatalyst film. That is, since light can pass through the film, most of the titanium oxide particles carried on the ePTFE film are irradiated with light, and can function as a photocatalyst. Therefore,
The photocatalyst film of the present invention can exhibit a photocatalytic function corresponding to the amount of the supported titanium oxide. Moreover, the photocatalyst film of the present invention can support a large amount of titanium oxide particles based on the porous structure of the ePTFE film. That is, the titanium oxide particles can be supported in the pores. Further, since the surface of the ePTFE film is an uneven surface which can act as an anchor for the titanium oxide particles, a thick titanium oxide layer can be formed even by coating.

In the photocatalytic film of the present invention, the titanium oxide particles are preferably supported via a binder.
The effect of not only strengthening the adhesion of the titanium oxide particles to the ePTFE film, but also suppressing the decrease in the light transmittance due to the titanium oxide particles being supported and improving the light transmittance as a photocatalytic film, depending on the type and amount of the binder used. Because there is also.

As the binder to be used, a binder which is not decomposed by the photocatalysis, specifically, a fluorine-based binder, a silicon-based binder, or the like is used. Examples of the fluorine-based binder include an amorphous fluorine resin. Examples of the silicon-based binder include a silica solution, an alkoxysilane sol, silicone, and silicate. Among these, a silica solution is preferably used from the viewpoint of the light transmittance of the photocatalyst film to be produced.

When a binder is used, a binder is added to the titanium oxide-containing liquid or a liquid is prepared using the binder as a dispersion medium for the titanium oxide particles.
What is necessary is just to immerse the TFE membrane or apply this liquid to the ePTFE membrane, and thus, the ePTFE
A photocatalyst film having a strong adhesion to the E film skeleton or the ePTFE film surface is obtained.

In the present invention, since the ePTFE membrane is inherently water-repellent, its affinity with a titanium oxide-containing liquid is generally poor. In order to increase the affinity with the titanium oxide-containing liquid, a hydrophilic treatment may be performed in advance. Examples of the hydrophilic treatment include a method in which an ePTFE film is immersed in an alkoxysilane sol, washed with water or immersed in water to hydrolyze the alkoxysilane oligomer, and then dried. By such a hydrophilic treatment, ePTF
A state in which silica having a large amount of SiOH groups formed by hydrolysis adheres to the surface of the skeleton (especially fibrils) of the E film, and the alkoxysilane oligomer that has entered the pores is washed away by water washing to form pores. It is in a state. Therefore, ePTFE subjected to hydrophilization treatment
The light transmittance and the film thickness of the film are almost the same as the light transmittance and the film thickness before the hydrophilic treatment.

Here, an alkoxysilane sol is a solution of an alcohol solution of an alkoxide to which water required for hydrolysis, an acid or ammonia as a catalyst is added, and the solution is at room temperature to 80 ° C.
This refers to a solution of silica particles formed by performing hydrolysis and polycondensation of an alkoxide with stirring at a degree. The silane of the alkoxysilane contains silane oligomerized and further polymerized by a Si—O bond.

In the present invention, the pores of the ePTFE film may be filled with a transparency improving substance in order to increase the transparency of the ePTFE film and thus the photocatalytic film. here,
The transparency improving substance is a substance capable of increasing the light transmittance of the ePTFE film by filling the pores in the ePTFE film, and specific examples thereof include an amorphous fluororesin and silica gel. For example, after immersing the ePTFE membrane in an alkoxysilane sol, without hydrolysis
Upon drying, the sol of the alkoxysilane that has entered the pores is gelled by drying. That is, the pores are filled with the oligomerized or polymerized silica contained in the alkoxysilane sol, that is, the silica gel is filled. In the state of the silica gel filled in the pores of the ePTFE membrane, the ratio of the silanol group (Si-OH) is smaller than that in the case where the silica gel is hydrolyzed by the above-mentioned hydrophilization treatment.

Examples of the alkoxysilane that can be used include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetrabutoxysilane.

As a method for filling the pores of the ePTFE membrane with the particles of the transparency enhancing substance, a method of immersing the ePTFE membrane in a liquid containing the transparency enhancing substance and drying it; applying the liquid of the transparency enhancing substance to the ePTFE membrane, Drying method is mentioned.

EP filled with pores filled with a transparency improving substance
As shown in FIG. 4, the photocatalytic film using the TFE film
A state in which a portion corresponding to the pores of the gap between the skeletons 2 of the TFE film is filled with a transparency improving substance (eg, silica gel) 6 and a titanium oxide layer 5 is laminated on the surface of the ePTFE film 1 ′ filled with the transparency improving substance. It has become. Here, when the ePTFE membrane 1 'filled with the transparency improving substance is used,
In principle, the titanium oxide particles are not filled in the pores, but a thick titanium oxide layer 5 is actually formed. The ePTFE membrane 1 'surface is not a smooth surface of a non-porous plastic film such as a PET film,
It is considered that the uneven surface capable of functioning like an anchor is maintained.

When the amount of the transparency improving substance to be filled is large, not only the inside of the pores of the ePTFE membrane but also the ePTFE
A layer made of a transparency improving substance may be laminated on the surface of the E film.
For example, as shown in FIG. 5, a layer 7 made of a transparency improving substance is laminated on the surface of an ePTFE membrane 1 ′ in which pores of the ePTFE membrane are filled with a transparency improving substance, and further, on this transparency improving substance layer 7, A state in which the titanium oxide layer 5 is stacked is obtained. Also in this case, the surface of the transparency improving substance layer 7 is made of eP
Since the unevenness of the surface of the TFE film 1 'is reflected, ePT
As in the case where the titanium oxide layer 5 is directly laminated on the FE film 1 ', a thick titanium oxide layer 5 can be formed.
In other words, a titanium oxide-coated photocatalyst film or a PET film is pre-coated with SiO ₂ , and then a thicker titanium oxide layer can be formed as compared with a titanium oxide-coated photocatalyst film. Can be carried.

The process of improving the transparency of the photocatalyst film by filling the pores of ePTFE with the transparency improving substance may be performed before the titanium oxide particles are supported,
It may be carried out after supporting the titanium oxide particles,
It may be performed when titanium oxide particles are supported. In the case of carrying out before carrying the titanium oxide particles, the ePTFE film 1 ′ in which the pores are filled with the transparency improving substance is first prepared, and the titanium oxide-containing liquid is applied to the ePTFE film 1 ′ to increase the transparency. An improved photocatalytic film can be manufactured. When performing after supporting titanium oxide particles, eP
A photocatalytic film with improved transparency can be manufactured by applying a liquid for improving transparency to the surface of a photocatalytic film in which titanium oxide particles are supported on a TFE film. In the case of carrying the titanium oxide particles, the transparency is improved by mixing titanium oxide in the liquid containing transparency improving substance or mixing the liquid containing titanium oxide with the liquid containing titanium oxide and applying the prepared mixture to the ePTFE membrane. An improved photocatalytic film can be manufactured. Among the above-mentioned production methods, the method is particularly preferable as a method for producing a photocatalyst film for use in which transparency is important, since a photocatalyst film having the highest transparency is obtained.

Although silica gel as a transparency improving substance and a small amount of a silicon-based binder contained in the titanium oxide coating solution are common in that SiO ₂ is a constituent component, the binder is only titanium oxide. The difference is that the transparency-enhancing material is used in an amount sufficient to fill the pores of the ePTFE membrane, whereas the amount necessary and sufficient to support the particles on the ePTFE membrane is used.

The photocatalyst film of the present invention having the above-described structure can impart photocatalytic ability to the substrate by a simple operation of sticking to the substrate. And since the photocatalyst film of the present invention is transparent, even when a transparent material such as a window glass or a glass plate of a watch is used as the base material, it does not impair the transparency of the base material, and does not stain and deodorize. It is possible to provide a photocatalytic function such as antibacterial. It can also be used by sticking it to a base material that wants to make use of its own pattern and material, such as wallpaper, furniture, and crafts. The photocatalytic function can be provided without damaging the pattern and material of the base material. Further, as described above, the photocatalyst film of the present invention can support a large amount of titanium oxide based on the structure of the ePTFE film used as the support, and can be expected to have a photocatalytic ability commensurate with the supported amount. Furthermore, the photocatalytic film of the present invention can impart photocatalytic ability to a substrate by a simple operation of sticking, so that the time required for construction is shorter than a method of directly applying and drying a titanium oxide-containing coating agent on a substrate. And there is no need to raise the temperature for drying. Therefore, a photocatalytic function can be imparted to substrates of various materials, such as wallpaper having poor heat resistance, crafts and building materials that cannot be heated to a high temperature.

[0042]

[Example] [Evaluation and measuring method] Film thickness Digimatic micrometer No. manufactured by Mitutoyo Corporation.
293-421-20.

Transparency The light transmittance at 550 nm was measured and used as an index of transparency. The light transmittance was measured using an ultraviolet-visible spectrophotometer UV-240 manufactured by Shimadzu Corporation.

Photocatalytic ability The dye was attached to the photocatalytic film, and the photocatalytic film to which the dye was attached was placed in an ultraviolet box manufactured by Kagaku Kyoei Co., Ltd., where it was irradiated with black light (maximum wavelength 352 nm, ultraviolet output 0.6 W). The photocatalytic activity was evaluated by examining the degree of decomposition of the dye.

Coumarin 343 or Rose Bengal was used as the dye, and the decomposition of the dye was examined by measuring the change in absorbance. The measurement results are shown in a graph in which the horizontal axis represents the irradiation time and the vertical axis represents the absorbance ratio with respect to the initial absorbance. The larger the ratio of decrease from the absorbance ratio, the better the photocatalytic activity.

The absorbance of the dye was measured at the absorption maximum wavelength λ _{max of the} dye (448 nm for coumarin and 558 nm for Rose Bengal).

The adhesion of the dye to the photocatalyst film is performed by immersing the prepared photocatalyst film in an alcohol solution containing a dye (a coumarin solution in 2-propanol, a solution of rose bengal in ethanol), removing the photocatalyst film at 100 ° C. For 30 minutes under vacuum.

[EPTFE Membrane] In the production of the photocatalyst membrane, the ePTFE membrane serving as a support is as shown in Table 1
Different types of ePTFE membranes were used.

[0049]

[Table 1]

[Production of Photocatalyst Film] Example 1 Titanium oxide coating agent ST-K03 from Ishihara Techno Co., Ltd. (solid content: 10% by mass, content ratio of titanium oxide: alkyl silicate binder: 1: 1)
Was added with the same amount of 2-propanol to prepare a titanium oxide-containing liquid. Add ePTFE to the prepared titanium oxide-containing liquid.
The film A was immersed, ultrasonically cleaned for 15 minutes, and then dried at 150 ° C. for 30 minutes to produce a photocatalytic film, and the light transmittance and the film thickness of the photocatalytic film were measured. Table 2 shows the measurement results.

The photocatalyst film produced as described above was impregnated with an amorphous fluororesin, and the light transmittance after the impregnation was measured. Table 2 shows the measurement results.

The photocatalytic ability of the photocatalytic film before impregnation with the amorphous fluororesin was examined using the dye coumarin. FIG. 6 shows the results.

Example 2 A photocatalyst film was produced in the same manner as in Example 1 using the ePTFE film B, and the results of measurement of the thickness and light transmittance of the photocatalyst film are shown in Table 2.

The photocatalyst film produced as described above was impregnated with an amorphous fluororesin, and the light transmittance after the impregnation was measured. Table 2 shows the measurement results.

The photocatalytic ability of the photocatalytic film before impregnation with the amorphous fluororesin was examined using the dye coumarin. FIG. 6 shows the results.

Examples 3 and 4 Example 1 except that the titanium oxide coating agent used was changed to ST-K01.
Alternatively, a photocatalytic film was manufactured in the same manner as in Example 2, and the film thickness and the light transmittance were measured. Table 2 shows the results.

ST-K01 is a solid content of 10% by mass.
The content ratio of titanium oxide: binder is 4: 1, and the content ratio of titanium oxide is higher than K03.

The photocatalytic ability of the photocatalytic film of Example 4 was examined using the dye coumarin, and the results are shown in FIG.

Example 5: The ePTFE membrane A was subjected to a hydrophilic treatment by performing the following operation. That is, an ethanol solution of a tetraethoxysilane sol (a tetraethoxysilane sol diluted twice with ethanol)
Then, the ePTFE membrane A was immersed in water, and then left in water for 10 minutes. After being taken out of the water, it was vacuum dried at 150 ° C. for 30 minutes. The thickness of the ePTFE membrane after the hydrophilic treatment is 2 μm,
Light transmittance is 54%, ePTFE before hydrophilization treatment
It was almost the same as membrane A. Here, the tetraethoxysilane sol is a mass ratio of tetraethoxysilane (monomer): ethanol: dilute hydrochloric acid (1%) 1: 5:
The solution No. 4 was heated and stirred at 60 ° C. for 24 hours and then allowed to cool, and the state of progress of the hydrolysis and polymerization reaction is unknown.

The hydrophilized ePTFE membrane A was immersed in the titanium oxide-containing solution prepared in Example 1, washed with ultrasonic waves, and dried under vacuum to produce a photocatalyst membrane. Table 2 shows the results of measuring the thickness maintenance and light transmittance of the manufactured photocatalyst film.

The photocatalytic ability of this photocatalytic film was measured using the dye coumarin or rose bengal, and the results are shown in FIG.

Example 6 A photocatalytic film was produced in the same manner as in Example 5 except that the titanium oxide-containing liquid used for supporting titanium oxide was changed to the titanium oxide-containing liquid prepared in Example 3. The film thickness and light transmittance were measured. Table 2 shows the results.

The photocatalytic ability of this photocatalytic film was measured using a dye coumarin or rose bengal, and the results are shown in FIG.

Examples 7 and 8: Regarding ePTFE membrane A,
A process for improving transparency was performed as follows. That is, after immersing the ePTFE membrane in a liquid obtained by diluting tetraethoxysilane sol with ethanol,
For 30 minutes to obtain an ePTFE membrane filled with silica gel in the pores of the ePTFE membrane. The thickness and light transmittance of the ePTFE membrane after silica gel filling are as follows:
It is as shown in Table 2.

The titanium oxide-containing liquid prepared in Example 1 or Example 3 was applied to a silica gel-filled ePTFE membrane with a glass rod, and dried at 150 ° C. for 30 minutes under vacuum to produce a photocatalyst membrane. The photocatalyst film produced using the titanium oxide-containing liquid prepared in Example 1 is Example 7 and the photocatalyst film produced using the titanium oxide-containing liquid prepared in Example 3 is Example 8). The thickness of the manufactured photocatalytic film,
The light transmittance was measured, and the results are shown in Table 2.

Example 9 Titanium oxide powder ST-21 from Ishihara Techno Co., Ltd. was added to an ethanol solution of tetraethoxysilane sol (two-fold dilution) as a transparency improving substance to prepare a titanium oxide-containing liquid (titanium oxide). Concentration 10g /
dm ³ ).

EPTFE was added to the prepared titanium oxide-containing liquid.
After immersing the film A, it was dried to produce a photocatalytic film. The thickness and light transmittance of the manufactured photocatalyst film were measured, and the results are shown in Table 2.

Comparative Example 1 A support of titanium oxide was ePTF
A photocatalytic film was manufactured in the same manner as in Example 1 except that the film was changed to the E film C. Table 2 shows the results of measuring the thickness and light transmittance of the manufactured photocatalytic film.

Comparative Example 2 The support of titanium oxide was ePTF
A photocatalytic film was manufactured in the same manner as in Example 5, except that the film was changed to the E film C. Table 2 shows the results of measuring the light transmittance of the manufactured photocatalyst film.

Comparative Example 3: The support of titanium oxide was ePTF
A photocatalytic film was produced in the same manner as in Example 7, except that the film was changed to the E film C. Table 2 shows the results of measuring the light transmittance of the manufactured photocatalyst film.

Comparative Example 4: As a support of titanium oxide, P
A photocatalytic film was produced in the same manner as in Example 1, except that an ET film (film thickness 124 μm, light transmittance 82%) was used. Uniform application was more difficult than when applied to a porous ePTFE membrane, and colorless and transparent microcrystals were precipitated by drying, and most of the formed titanium oxide layer was peeled off. .

Table 2 shows the results of measuring the thickness and light transmittance of the manufactured photocatalyst film. Note that the thickness of the photocatalyst film was measured in a state where microcrystals were precipitated (a state before the titanium oxide layer was separated).

Comparative Example 5 An alcoholic solution of a tetraalkoxysilane sol was applied to the surface of the PET film used in Comparative Example 4, dried, and a silica layer was laminated. Next, the titanium oxide-containing liquid prepared in Example 1 was applied, and then dried to laminate a titanium oxide layer, thereby producing a photocatalyst film. However, colorless and transparent microcrystals were precipitated by drying, and the formed titanium oxide layer was peeled off.

Table 2 shows the results of measuring the thickness and the light transmittance of the produced photocatalyst film. The thickness of the photocatalyst film was measured in a state where microcrystals were deposited (a state before the titanium oxide layer was separated).

[0075]

[Table 2]

In the photocatalyst films of Examples 1 and 2, the transparency was considerably lower than that of the ePTFE film A used as the support because the thick titanium oxide layer was laminated. Was holding. Further, by impregnating an amorphous fluororesin which is a transparency improving substance, the transparency could be improved.

In the photocatalyst films of Examples 3 and 4, a thick titanium oxide layer was not formed because the content of the titanium oxide particles in the titanium oxide-containing liquid was small. Therefore, as for the transparency, the transparency of the ePTFE membrane used as the support could be almost maintained. In addition, from FIG. 6, the photocatalytic ability showed the same level of photocatalytic ability as that of Example 1, and the titanium oxide layer had the same level of photocatalytic ability even though the thickness of the titanium oxide layer was small. . This means
It is considered that the titanium oxide was impregnated in the ePTFE membrane because the titanium oxide was supported using the titanium oxide-containing liquid having a low titanium oxide concentration.

From a comparison between Examples 5 and 6, and Examples 1 and 2, it can be seen that the use of the hydrophilicized ePTFE film makes the titanium oxide layer thinner and has higher transparency. That is, it is considered that the titanium oxide-containing liquid was easily impregnated into the inside of the ePTFE membrane due to the hydrophilicity of the ePTFE membrane.

From Examples 7 and 8, it can be seen that transparency can be improved by filling the pores of the ePTFE membrane with silica gel. When an ePTFE film in which pores are filled with silica gel is used, a thick titanium oxide layer is formed on the surface of the ePTFE film because titanium oxide particles hardly penetrate into the ePTFE film. However, high transparency was maintained despite the formation of a thick titanium oxide layer.

Example 9 is a case where the transparency improving substance was filled when the titanium oxide particles were carried. That is, eP
The pores of the TFE film are filled with silica gel and titanium oxide particles, which are transparency improving substances. The degree of improvement in transparency in this case was not as high as in Examples 7 and 8. However, Example 1 in which no transparency improving substance was used
Before and after the impregnation of the amorphous fluororesin.

As can be seen from Comparative Examples 1 to 3, when an opaque white PTFE film was used, only an opaque photocatalyst film was obtained. Even if the treatment with the transparency improving substance was performed, the transparency could not be increased, and the opacity remained.

According to Comparative Examples 4 and 5, when a PET film was used as a support, it was difficult to form a thick and stable titanium oxide layer carrying an amount of titanium oxide as in the case of using an ePTFE membrane. could not. That is, even if a large amount of the titanium oxide-containing liquid was applied, colorless and transparent microcrystals precipitated on the surface of the PET film, and finally the titanium oxide layer was peeled off. This indicates that an ePTFE membrane must be used to support a large amount of titanium oxide.

[0083]

Since the photocatalyst film of the present invention is transparent, it can be used for glass products that need to maintain the transparency of the substrate, and for crafts and building materials that need to make use of the design of the substrate. The photocatalytic ability can be imparted to these substrates.
In addition, since it is transparent, most of the supported titanium oxide particles can effectively function as a photocatalyst.
Therefore, the photocatalyst film of the present invention can support a large amount of titanium oxide particles due to the ePTFE film of the support,
In addition, it is possible to expect a photocatalytic ability corresponding to the supported amount.

Furthermore, by using a transparency improving substance in combination, even if a large amount of titanium oxide is supported, considerable transparency can be maintained.

According to the method for producing a photocatalyst film of the present invention, it is possible to easily produce a photocatalyst film in which the reduction in transparency due to the support of titanium oxide particles is suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of an embodiment of a photocatalyst film of the present invention.

FIG. 2 is a schematic cross-sectional view showing the configuration of another embodiment of the photocatalyst film of the present invention.

FIG. 3 is a schematic sectional view showing the configuration of another embodiment of the photocatalyst film of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a configuration of an embodiment of a photocatalytic film in which holes are filled with a transparency improving substance.

FIG. 5 is a schematic cross-sectional view showing a configuration of one embodiment of a photocatalytic film in which holes are filled with a transparency improving substance.

FIG. 6 is a graph showing the results of measuring the photocatalytic ability of the photocatalytic film of the example.

FIG. 7 is a graph showing the results of measuring the photocatalytic ability of the photocatalytic film of the example.

[Explanation of symbols]

 1,1 'ePTFE membrane 2 skeleton 3 vacancy 4 titanium oxide particles 5 titanium oxide layer 6 transparency improving substance 7 transparency improving substance layer

Claims (13)

[Claims] 1. A stretched porous polytetrafluoroethylene film having a skeleton and a gap between the skeletons as pores, and titanium oxide particles supported on the stretched porous polytetrafluoroethylene film. A photocatalytic film characterized by being transparent. 2. The photocatalyst film according to claim 1, wherein the titanium oxide particles are carried by being attached to a skeleton surface of the expanded porous polytetrafluoroethylene film or filled in pores. 3. The titanium oxide particles are attached to the skeleton surface of the expanded porous polytetrafluoroethylene film or filled in the pores, and one and / or both surfaces of the expanded porous polytetrafluoroethylene film. The photocatalyst film according to claim 1, which is carried by being laminated on the photocatalyst. 4. The photocatalyst film according to claim 1, wherein the titanium oxide particles are carried by being laminated on one side and / or both sides of the expanded porous polytetrafluoroethylene film. 5. The photocatalyst film according to claim 4, wherein the pores of the expanded porous polytetrafluoroethylene film are filled with a transparency improving substance. 6. The photocatalyst film according to claim 5, wherein the transparency improving substance is silica gel. 7. The photocatalyst film according to claim 1, further comprising a binder, wherein the titanium oxide particles are supported on the expanded porous polytetrafluoroethylene film via the binder. 8. The photocatalyst film according to claim 7, wherein the binder is silica. 9. The photocatalyst film according to claim 1, which has a light transmittance at 550 nm of 20% or more. 10. The photocatalyst film according to claim 1, wherein the thickness of the expanded porous polytetrafluoroethylene is 30 μm or less. 11. The titanium oxide particles have a particle size of 5 nm.
The photocatalyst film according to any one of claims 1 to 10, which has a thickness of from 1 to 1 µm. 12. A method for producing a photocatalytic film, comprising: a first step of providing a transparency-improving substance to an expanded porous polytetrafluoroethylene film; and a second step of supporting titanium oxide particles on the expanded porous polytetrafluoroethylene film. Method. 13. The first step is a step of immersing the stretched porous polytetrafluoroethylene film in a sol of alkoxide silane and then drying, and the second step is performed after the first step. Item 1
3. The method for producing a photocatalyst film according to item 2.