JP2010269266A - Dispersion liquid of photocatalyst particle and method for preparing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion liquid in which photocatalyst particles are dispersed highly and to provide a method for preparing the dispersion liquid without using a dispersant. <P>SOLUTION: The dispersion liquid contains a dispersion medium, the photocatalyst particles and an acidic substance, wherein the photocatalyst particles having ≤50 nm average particle size (D<SB>50</SB>) when measured by a dynamic light scattering method are dispersed in the dispersion medium and the pH of the dispersion liquid is 1.0-6.5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dispersion of photocatalyst particles and a method for producing the same. Specifically, the photocatalyst particles are dispersed with an average particle size of 50 nm or less, and a thin film excellent in transparency, ultraviolet light and visible photocatalytic activity is formed. The present invention relates to a dispersion capable of producing a dispersion and a production method capable of producing the dispersion without using a dispersant.

  The photocatalytic thin film formed on the surface of the substrate cleans the surface of the substrate because the organic substance is decomposed and the film surface becomes hydrophilic by the catalytic action of a photocatalytic metal compound such as titanium oxide contained therein. It is used for deodorizing and antibacterial applications. Currently, such photocatalytic thin films are mainly applied to exterior tiles, glass, exterior wall coating, filters inside air cleaners, inorganic base materials (ceramics, metals, etc.), but organic materials such as plastic materials. In recent years, the application of these to the base material has been actively studied (Patent Documents 1 and 2). In order to apply the photocatalytic metal compound to the organic base material, a dispersion liquid in which the photocatalytic compound particles are dispersed is applied to the base material and dried. However, a photocatalytic thin film formed on an organic base material using a conventional dispersion has insufficient photocatalytic activity, particularly in visible light, and has a problem of hindering the design of the base material surface. It was. This is partly due to the large particle size of the photocatalytic compound particles in the dispersion.

  In order to disperse titanium oxide highly, a wet disperser such as a bead mill is used (Patent Document 3). In this case, there is a problem that coarse particles are formed by re-aggregation in the process of making the particles finer. In order to prevent this, dispersants such as polyacrylic acid and polycarboxylic ammonium carboxylic acid are used. However, since the dispersant remains in the photocatalyst film, it may cause deterioration of physical properties of the thin film.

JP 2006-116461 A JP 2006-272757 A JP 2005-60532 A

Accordingly, an object of the present invention is to provide a dispersion in which photocatalyst particles are highly dispersed, and a production method capable of producing the dispersion without using a dispersant.

That is, the present invention is a dispersion containing a dispersion medium, photocatalyst particles and an acidic substance, wherein the photocatalyst particles are dispersed in the dispersion medium with an average particle size (D ₅₀ ) of 50 nm or less determined by a dynamic light scattering method. And a dispersion having a pH of 1.0 to 6.5.
The present invention is also a method for preparing a dispersion of photocatalyst particles using a bead mill, the bead mill comprising a hollow cylindrical container, a stirring member and bead separation means arranged in the container. , The beads are spherical beads made of zirconia having a diameter of 5 to 100 μm,
(1) The stirring member is rotated at the first rotation speed (r1) to stir the bead dispersion liquid having a pH of 1.0 to 6.5 containing the photocatalyst particles, the dispersion medium, and the acidic substance, and the beads, and the photocatalyst particles. The step of setting the average particle size (D ₅₀ ) determined by the dynamic light scattering method of 250 to 350% of the particle size of the primary particles of the photocatalyst particles, and then (2) adjusting the stirring member to 50 to 90 of r1. % Rotating at a second rotation speed (r2) to make the average particle size of the photocatalyst particles 150-250% of the particle size of the primary particles,
It is a method including.

  In the dispersion of the present invention, photocatalyst particles are dispersed with an average particle size of 50 nm or less, and are applied onto a substrate to form a film excellent in ultraviolet light and visible photocatalytic activity and transparency. In addition, since the method of the present invention performs dispersion with a strong shearing force in the first step, no coarse particles remain, and after the average particle diameter of the photocatalyst particles reaches a predetermined size, a gentler shearing force is used. Since the dispersion is performed, the photocatalytic function does not deteriorate due to reaggregation of the particles and crushing of the particle surface. This makes it possible to prepare a dispersion in which photocatalyst particles are dispersed with a particle size of 50 nm or less efficiently and without using a dispersant.

[Dispersion]
The dispersion liquid of the present invention has a volume-based 50% cumulative distribution diameter (D ₅₀ ) (hereinafter referred to as “average particle diameter”) determined by dynamic light scattering / frequency analysis (FFT-heterodyne method) of photocatalyst particles of 50 nm. Hereinafter, it is preferably 45 nm or less. In addition, the lower limit of the average particle diameter is the particle diameter of the primary particles of the photocatalyst particles. When the average particle size exceeds 50 nm, photoresponsiveness, particularly visible light responsiveness, and transparency are not sufficient. The state in which the average particle size is less than the primary particle size is so-called “overdispersion”, which causes problems such as particle aggregation and is not preferable.

The pH of the dispersion is 1.0 to 6.5, preferably 2.0 to 5.0. Within this range, the photocatalyst particles are charged and aggregation between the particles is effectively suppressed. The pH can be adjusted by adding an acidic substance described later to the dispersion medium while monitoring the pH of the dispersion medium with a glass electrode or the like. Photocatalyst particles are added to the dispersion medium whose pH has been adjusted to obtain a raw material dispersion, which is then processed by a bead mill. During this time, the pH hardly varies, and the pH of the finally obtained dispersion is also in the above range.

Examples of the photocatalyst particles include titanium oxide-based, tungsten oxide-based, zinc oxide-based, niobium oxide-based, etc. metal oxide crystal particles having an n-type semiconductor-like band gap structure. For example, anatase type titanium dioxide, rutile type titanium dioxide, peroxotitanium crystal, tungsten trioxide (WO ₃ ), zinc oxide (ZnO), Ga doped zinc oxide (GZO), niobium oxide (Nb ₂ O ₅ ), etc. Can be mentioned. Preferably, these metal oxide crystals are doped with different elements such as nitrogen, sulfur, phosphorus and carbon, and the surface carries different metals or compounds such as copper, iron, nickel, gold, silver, platinum and carbon. Used. The particle size of these primary particles is 1 nm to 50 nm, preferably 1 nm to 40 nm, more preferably 1 to 25 nm. As such photocatalyst particles, rutile type titanium dioxide carrying platinum (MPT-623 (trade name), powder, manufactured by Ishihara Sangyo), rutile type titanium dioxide carrying iron (MPT-625 (trade name) ), Powder form, manufactured by Ishihara Sangyo) and the like. The particle size of the primary particles can be obtained by using, for example, Scherrer's equation in the X-ray diffraction method. The compounding quantity of photocatalyst particle is 0.01-20 mass% of a dispersion liquid, Preferably it is 0.5-10 mass%. If it is less than the lower limit, it takes time and energy to volatilize the dispersion medium to form a film, and if it exceeds the upper limit, it becomes difficult to prepare a thin film from the dispersion, and the resulting film tends to be less transparent. is there.

As the dispersion medium, water, alcohols such as methanol, ethanol, isopropanol, or a mixture thereof are used. Preferably water and a mixture of water and alcohol, more preferably water are used. Water does not have to contain impurities that hinder the pH adjustment. Preferably, purified water, distilled water, or ion exchange water is used, and more preferably purified water is used.

An acidic substance is added to the dispersion medium to adjust its pH to 1.0 to 6.5, preferably 2.0 to 5.0. The acidic substance is at least selected from the group consisting of Bronsted acidic substances such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid and camphorsulfonic acid, polymer compounds having acidic groups, and acidic ion exchange resins. A kind is used. These acidic substances may be added as water or an alcohol solution. Preferably camphor sulfonic acid is used.

Preferably, the dispersion of the present invention does not contain a dispersant and substantially consists of photocatalyst particles, a dispersion medium, and an acidic substance. Thereby, deterioration of the physical property of the photocatalyst thin film resulting from a dispersing agent can be prevented.

[Distribution method]
The dispersion of the present invention is a bead mill comprising a hollow cylindrical container, a stirring member and a bead separating means arranged in the container, and the following steps are performed using spherical beads made of zirconia having a diameter of 5 to 100 μm. It can be prepared by the method including.
(1) The stirring member is rotated at the first rotation speed (r1) to stir the bead dispersion liquid having a pH of 1.0 to 6.5 containing the photocatalyst particles, the dispersion medium, and the acidic substance, and the beads, and the photocatalyst particles. The step of setting the average particle size (D ₅₀ ) determined by the dynamic light scattering method of 250 to 350% of the particle size of the primary particles of the photocatalyst particles, and then (2) adjusting the stirring member to 50 to 90 of r1. % Rotating at a second rotation speed (r2) of 150% to make the average particle size of the photocatalyst particles 150-250% of the particle size of the primary particles.

  As the bead mill, a bead mill that can use fine beads having a diameter of 100 μm or less is used. The bead mill generally includes a hollow cylindrical container called “vessel” and a stirring member disposed in the container and for stirring the raw material dispersion and the beads. As the stirring member, one that is disposed coaxially with the container and has a hollow cylindrical shape or an impeller shape can be used. Preferably, a hollow cylindrical stirring member is used. Such a mill having a hollow cylindrical stirring member is called an annular bead mill in which particles are pulverized at an annular portion between the inner wall of the container and the outer wall of the stirring member (see, for example, JP-A-2006-751). Wanna)

  More preferably, a circulation type bead mill is used. In the circulation type bead mill, the raw material dispersion is fed from the tank to the bead mill and dispersed by the bead mill, and then separated from the beads by the bead separation means and returned to the tank. Repeat until. Means for separating the beads include a centrifugal separator, a gap separator, and a separation screen, and a centrifugal separator is preferably used. Such bead mills are described in JP-A-2007-275842, JP-A-2007-190447, and the like, and as commercially available, Nano Getter (manufactured by Ashizawa Finetech Co., Ltd.), And Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd.).

The beads to be used preferably have a diameter of 100 μm or less, and more preferably in the range of 5 to 50 μm. The beads are preferably made of zirconia or yttrium partially-stabilized zirconia because of less wear. As an example of such beads, PlasmaBeads PB ZrO ₂ : Y 50Φ (yttrium partially stabilized zirconia beads, particle size range 40-60 μm, manufactured by Induction Heat Refining Co., Ltd.) can be mentioned.

  In the step (1), the beads are used in an amount of 30 to 70%, preferably 40 to 60%, of the volume of the part to be pulverized, for example, the annular part. The first rotation speed (r1) is preferably as large as possible, and is about 60 to 90% of the maximum possible rotation speed of the stirring member of the mill to be used. In the case of the annular bead mill described above, the rotational speed is defined by the peripheral speed of the hollow cylindrical stirring member, and r1 is 10 to 20 m / s, preferably 12 to 15 m / s. The second rotational speed (r2) in the step (2) is 50 to 90%, preferably 70 to 80% of r1. Thus, excessive dispersion is prevented by reducing the rotation speed. In addition, when reducing from r1 to r2, you may reduce in steps.

The raw material dispersion is prepared by adding 0.01 to 20% by weight, preferably 0.5 to 10% by weight, of photocatalyst particles to the dispersion medium adjusted to pH by adding the acidic substance. Prepare. Alternatively, the photocatalyst particles may be added to the dispersion medium in the tank after only the dispersion medium is circulated between the bead mill and the tank for several minutes at the stage where the pH of the dispersion medium is adjusted.

  During steps (1) and (2), the particle size of the photocatalyst particles is monitored. In the step (1), stirring is performed at a rotational speed r1 until the particle size of the primary particles of the photocatalyst particles is 250 to 350%, preferably 280 to 320%. When the particle diameter is smaller than the lower limit value, overdispersion may occur. On the other hand, when the particle size exceeds the upper limit value, coarse particles may remain. In the step (2), stirring is performed at a rotational speed r2 until the particle size of the primary particles of the photocatalyst particles is 150 to 250%, preferably 100 to 200%.

The temperature in the vessel in the steps (1) and (2) is in the range of 5 ° C to 90 ° C, preferably 25 ° C to 70 ° C.

  Preferably, the method of the present invention does not use a dispersant. Thereby, deterioration of the physical property of the photocatalyst thin film resulting from a dispersing agent can be prevented.

  The resulting dispersion can be applied to a variety of substrates and is particularly suitable for application to organic substrates. Examples of the substrate include films and molded articles such as polyethylene terephthalate (PET), polyvinyl chloride, polyethylene, and polypropylene. Before forming the photocatalytic thin film on the substrate, it is preferable to perform surface treatment by, for example, corona treatment, normal pressure (or atmospheric pressure) plasma treatment, or low pressure low temperature plasma treatment.

  In order to apply the photocatalyst dispersion liquid to the substrate, a conventionally known method may be used. For example, a dip coating method, a spin coating method, and a brush coating method can be mentioned. The coating amount is such that the thickness after drying is about 50 to 500 nm. The coating film can be dried at 70 to 150 ° C.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to these examples.

<Examples 1-4, Comparative Examples 1-3>
Each dispersion shown in Table 1 was prepared. As photocatalyst particles, titanium oxide (MPT-623 (trade name), platinum-supported titanium dioxide fine particles / rutile type, primary particle size 20 nm, manufactured by Ishihara Sangyo), or titanium oxide (MPT-625 (trade name), iron (Supported titanium dioxide crystal fine particles / rutile type, primary particle size 20 nm, manufactured by Ishihara Sangyo) and purified water as a dispersion medium was prepared by the following method.
While adding camphor sulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) to the dispersion medium and measuring it with a pH meter (D-51S, manufactured by Horiba, Ltd.) at 25 ° C., the pH was adjusted to 3.0. It was. However, Comparative Example 3 did not adjust the pH. As a bead mill, a circular annular bead mill, Nano Getter DMR-110 (trade name) (manufactured by Ashizawa Finetech), a zirconia bead (Plasma Beads PB) in an amount of 30 to 70% of the grinding chamber volume. ZrO ₂ : Y (trade name), manufactured by Induction Heat Refining Co., Ltd.) was added. Next, the dispersion medium was fed from the tank into the vessel. The rotation of the stirrer of the bead mill was started at a rotational speed of 12 m / s to 13 m / s. Immediately after the start of rotation, photocatalyst particles in an amount corresponding to 1.0% by mass of the mass of the raw material dispersion were added to the tank while continuing stirring. At intervals of about 10 minutes, the dispersion was collected from the tank and the particle size was measured. In Examples 1 to 4, since the average particle diameter of the photocatalyst particles became 280 to 340% of the particle diameter of the primary particles of the raw material titanium oxide 10 minutes after the start of stirring, the rotation speed was reduced to 10 m / s. In Examples 1 and 2, the speed was reduced to 8 m / s after another 10 minutes. In contrast, in Comparative Examples 1 and 2, the initial rotation speed was maintained. Each was stirred for a total of 30 minutes, the equipment was stopped, and the liquid in the vessel was recovered to obtain a dispersion.

The obtained dispersion was evaluated by the following method.
<Particle size measurement>
The particle size was measured using Microtrac UPA-EX (manufactured by Nikkiso Co., Ltd.), and the average particle size D ₅₀ (nm) was determined.
<Dispersion stability>
The dispersion was taken in a 50 mL glass vial and allowed to stand in the dark with the lid on. In this state, the number of days until a white precipitate became visible at the bottom of the vial was confirmed.

A thin film was prepared by the following method using the dispersion.
<Evaluation of photocatalytic thin film>
The dispersion was applied to a substrate to produce a photocatalytic thin film. A polyethylene terephthalate film (thickness 50 μm) was used as the substrate. The surface of the film cut to A4 size was subjected to corona discharge treatment, and then the dispersion was applied by a bar coater and heated and dried in an oven at 100 ° C. to produce a dried photocatalytic thin film having a thickness of about 200 nm. The obtained film was subjected to the following measurements.
<Measurement of photocatalytic film thickness>
Measurement was performed using a thin film measuring apparatus (F-20 (product name), manufactured by FILMETRICS) and a scanning electron microscope (S-3400NX (product name), manufactured by Hitachi High-Technologies).
<Total light transmittance and haze>
It measured with the digital haze meter NDH-20D of Nippon Denshoku Industries Co., Ltd.
<Measurement of photocatalytic activity>
On the obtained photocatalyst thin film, an aqueous solution of methylene blue having a concentration of 1.0 mmol / L was applied and dried at 60 ° C. to adsorb an amount of methylene blue completely covering the thin film surface. Immediately after drying, using a photocatalyst evaluation checker PCC-2 (trade name, manufactured by ULVAC Riko Co., Ltd.), the measurement of the absorbance (wavelength 664 nm) of the blue dye on the methylene blue adsorption surface was started, and ultraviolet light 1 mW / cm ² (190-190) 400 nm) and 1 mW / cm ² of visible light (wavelength 400 to 600 nm) were irradiated for 10 minutes, respectively, and the decrease (× 10 ³ ) in the absorbance (wavelength 664 nm) of the blue dye on the methylene blue adsorption surface was measured.

  As shown in Table 1, in Comparative Example 3 in which the pH of the dispersion was outside the range of the present invention, the average particle diameter of the catalyst particles in the obtained dispersion was large. Moreover, the average particle diameter of the catalyst particles in the dispersions obtained in Comparative Examples 1 and 2 prepared without reducing the rotation speed was significantly larger than that in the Examples. In contrast, the photocatalyst particles were highly miniaturized in the dispersions obtained in the examples, and the obtained photocatalyst film had high catalytic activity for both ultraviolet light and visible light.

The dispersion of the present invention is useful for forming a photocatalytic thin film having high transparency and high catalytic activity on an organic substrate. The method of the present invention is also useful for rapidly preparing the dispersion.

Claims (16)

A dispersion containing a dispersion medium, photocatalyst particles and an acidic substance, wherein the photocatalyst particles are dispersed in the dispersion medium with an average particle size (D ₅₀ ) of 50 nm or less determined by a dynamic light scattering method, and the dispersion A dispersion in which the pH of the liquid is 1.0 to 6.5. The dispersion according to claim 1, wherein the photocatalyst particles are made of titanium dioxide, zinc oxide, peroxotitanium crystals, or tungsten oxide. The dispersion according to claim 2, wherein the photocatalyst particles are made of rutile titanium dioxide carrying platinum or rutile titanium dioxide carrying iron. The dispersion according to any one of claims 1 to 3, wherein the dispersion medium is water or a mixture of water and alcohol. The acidic substance is at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid, camphorsulfonic acid, a polymer compound having an acidic group, and an acidic ion exchange resin. A dispersion according to any one of -4. The dispersion according to any one of claims 1 to 5, which does not contain a dispersant. A method for preparing a dispersion of photocatalyst particles using a bead mill, wherein the bead mill includes a hollow cylindrical container, a stirring member and bead separation means arranged in the container, and the beads have a diameter of 5 ˜100 μm zirconia spherical beads,
(1) The stirring member is rotated at the first rotation speed (r1) to stir the bead dispersion liquid having a pH of 1.0 to 6.5 containing the photocatalyst particles, the dispersion medium, and the acidic substance, and the beads, and the photocatalyst particles. The step of setting the average particle size (D ₅₀ ) determined by the dynamic light scattering method of 250 to 350% of the particle size of the primary particles of the photocatalyst particles, and then (2) adjusting the stirring member to 50 to 90 of r1. % Rotating at a second rotation speed (r2) to make the average particle size of the photocatalyst particles 150-250% of the particle size of the primary particles,
Including methods. The method according to claim 7, wherein the stirring member has a hollow cylindrical shape, and the bead separating means is a centrifugal blade disposed coaxially with the stirring member inside the stirring member. The method according to claim 8, wherein the rotational speed is a peripheral speed of the stirring member, r1 is 10 to 20 m / s, and r2 is 6 to 10 m / s. The method which concerns on any one of Claims 7-9 whose temperature in the said container between process (1) and (2) is 25 to 70 degreeC. The method according to any one of claims 7 to 10, wherein the particle diameter of primary particles obtained by an X-ray diffraction method of the photocatalyst particles is 1 to 25 nm. The method according to any one of claims 7 to 11, wherein the photocatalytic particles comprise titanium dioxide, zinc oxide, peroxotitanium crystals, or tungsten oxide. The method according to claim 12, wherein the photocatalyst particles comprise rutile titanium dioxide carrying platinum or rutile titanium dioxide carrying iron. The method according to any one of claims 7 to 13, wherein the dispersion medium is water or a mixture of water and alcohol. The acidic substance is at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid, camphorsulfonic acid, a polymer compound having an acidic group, and an acidic ion exchange resin. The method according to any one of -14. The method according to any one of claims 7 to 15, wherein no dispersant is used.