JP2003226842A - Photocatalytic coating agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a photocatalytic coating agent having high chemical stability even in a neutral condition, and exerting substantial antimisting and antifouling effects even if used indoors. <P>SOLUTION: This photocatalytic coating agent contains a titanium oxide. Oxygen defects are present in the titanium oxide. A dispersion medium for this coating agent consists of an aqueous solvent. It is preferable that the pH of the dispersion medium is 5-9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a photocatalytic coating agent. INDUSTRIAL APPLICABILITY The present invention can be applied to an antifogging technique for preventing fogging of a base material and formation of water droplets by highly hydrophilicizing the surface of a base material such as a mirror, a lens, and plate glass. The present invention also prevents the surface from becoming dirty or self-cleans the surface by the effect of highly hydrophilicizing the surface of a building, window glass, mechanical device or article and the effect of decomposing organic substances attached to the surface ( It can also be applied to a technique of self-cleaning) or easy cleaning.

[0002]

2. Description of the Related Art The present inventors have conventionally proposed various applications utilizing the hydrophilizing ability of photocatalysts. For example, when the surface of the member is in a state where the contact angle with water is 10 ° or less, even if moisture or steam in the air is condensed, the condensed water is uniform without forming individual water droplets. The tendency to become a water film becomes remarkable. Therefore, the tendency that light-scattering haze does not occur on the surface becomes remarkable. Similarly, when window glass, vehicle rearview mirrors, vehicle windshields, eyeglass lenses, helmet shields, etc. are exposed to rain or splashes, discrete visual annoying water droplets are not formed and high visibility and visibility are achieved. To ensure the safety of vehicles and traffic, and to dramatically improve the efficiency of various work and activities.

Further, when the surface of the member is in a state of 20 ° or less in terms of contact angle with water, combustion products such as carbon black contained in exhaust gas from urban dust, automobiles, etc.
Both hydrophobic contaminants such as oils and fats and sealant elution components, and inorganic clay contaminants are difficult to attach, and even if they are attached, they can be easily removed by rainfall or washing with water.

In order for the member to have the above-described antifogging and antifouling functions, it is necessary to fix the photocatalyst material to the member. When titanium oxide generally used as a photocatalyst is used, mechanical durability cannot be obtained even if titanium oxide is applied to a member alone. For example, JP-A-8-164334
As described in (1), a method of using silicate as a binder for fixing titanium oxide to a member has been reported.

[0005]

Since the pH at the isoelectric point of titanium oxide is about 6 to 7, when it is attempted to disperse titanium oxide particles in water or alcohol to obtain a uniform titanium oxide sol, no acid or acid is used. Alkaline solvent must be added. Further, when the acidic or alkaline titanium oxide sol thus obtained and the binder are combined,
In order to prevent precipitation and aggregation, a binder having a pH close to that of the titanium oxide sol had to be selected. As the coating agent, it is desirable that the pH of the liquid is in the neutral range in consideration of the danger to the human body, the corrosiveness to the base material and the like. For example, when a neutral or weakly acidic silicone emulsion was used as the binder, the titanium oxide sol aggregated and precipitated, and a uniform coating agent could not be obtained.

As a method for dispersing titanium oxide in water in a neutral region, for example, as shown in JP-A-9-227832, the surface of titanium oxide is coated with an inorganic oxide having a pH of 5 or less or a pH of 9 or more. Is disclosed. However, in this method, since the surface of titanium oxide is covered with an inorganic substance having no photocatalytic activity, the oxidative decomposition power and the hydrophilization ability of titanium oxide are reduced.

On the other hand, when a member coated with a photocatalytic coating agent is to be used indoors for everyday use, the light source that can usually be expected is indoor lighting such as a fluorescent lamp or an incandescent lamp, and its UV illuminance is also 10 μW / cm. Very small, ² or less. Therefore, it is difficult to substantially exhibit the antifogging and antifouling functions indoors.

The present invention has been made to solve the above problems, and can provide a photocatalytic coating agent having high chemical stability in the neutral region. Further, since the photocatalytic coating agent has visible light responsiveness, it can exhibit substantial antifogging and antifouling functions indoors.

[0009]

In a photocatalytic coating agent containing titanium oxide, the titanium oxide has an oxygen defect, and the dispersion medium of the photocatalytic coating agent is an aqueous solvent. Provide a coating agent. The photocatalytic coating agent of the present invention has a pH
It is possible to stably disperse in an aqueous solvent in the neutral region of 5 to 9.

The effect of introducing oxygen vacancies into titanium oxide has not been clarified so far, but the presence of oxygen vacancies in titanium oxide crystals negatively charges the zeta potential in water. As a result, the pH at the isoelectric point shifts to the acidic side, and the pH falls within the range of 0-5. That is, the titanium oxide is negatively charged in a region where the pH is higher than 5, and can be dispersed even in neutral due to the electric repulsive force between the titanium oxide particles. Therefore, even if the titanium oxide is combined with another binder in the neutral region, a uniform coating agent can be obtained without precipitation or aggregation.

If the oxygen deficiency exists on the very surface of the titanium oxide crystal, the shift of the zeta potential to the negative side can be achieved. That is, it is not necessary to introduce oxygen defects into the entire area of the titanium oxide crystal. If oxygen defects are present in a region of 10 nm or less from the surface of titanium oxide, the zeta potential can be sufficiently shifted to the negative side. Needless to say, even if oxygen defects are introduced into the entire area of the titanium oxide crystal, the zeta potential can be shifted to the negative side.

Visible light responsiveness is exhibited by introducing oxygen defects. The photocatalytic coating agent of the present invention is
Antifogging, antifouling, and self-cleaning effects are exhibited even in a room with little ultraviolet light.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The crystal system of titanium oxide usable in the present invention is preferably anatase type, rutile type or brookite type. Alternatively, amorphous titanium oxide may be used.

The dispersion medium of the coating agent according to the present invention is
Aqueous solvents in the pH range of 5-9 can be used. As the aqueous solvent, tap water, pure water, intermediate water, etc. can be preferably used, and the aqueous solvent may contain carbonate ions.

The method of introducing oxygen defects into titanium oxide is achieved by, for example, heat treatment in a reduced pressure environment, heat treatment in a reducing gas such as hydrogen, or heat treatment in an inert gas such as helium or argon. It Further, oxygen defects may be introduced by plasma treatment.

The method of introducing oxygen defects into titanium oxide is more preferably achieved by heat treatment in a reducing gas such as ammonia, hydrocarbon, hydrogen sulfide or the like. In particular, when heat-treated in an ammonia stream, the surface zeta potential shifts to the negative side, and the photocatalyst has high visible light responsiveness. Further, in the present invention, if oxygen defects are present in the region of 10 nm or less from the surface of titanium oxide, a sufficient shift to the negative side of the zeta potential can be achieved, so that even at a relatively low temperature heat treatment of 600 ° C. or less. The effect of shifting the zeta potential to the negative side is sufficiently obtained.

Another method for introducing oxygen vacancies into titanium oxide can be achieved by firing a titanium oxide precursor containing anions other than oxygen at 600 ° C. or lower in the atmosphere. Due to the influence of anions other than oxygen, titanium oxide does not completely oxidize and becomes a state in which oxygen is less than the stoichiometric composition. For example, tetramethoxy titanium, tetraethoxy titanium, tetraisopropoxy titanium, tetra n-
Propoxy titanium, tetrabutoxy titanium, titanium chelate, acetylacetone titanium, titanium tetrachloride, titanium sulfate, at least one titanium oxide precursor selected from the group consisting of titanium hydroxide, ammonia, sulfuric acid, carbonic acid,
Those hydrolyzed with at least one catalyst selected from the group consisting of phosphoric acid, boric acid and hydrofluoric acid, titanium ammonium oxyoxalate, ammonium titanium sulfate and the like can be preferably used. At this time, the titanium oxide precursor may be in the form of powder or thin film.

The zeta potential in water of the surface of titanium oxide having oxygen defects is shifted to the negative side. The pH at the isoelectric point of general titanium oxide is about 6 to 7, but the pH at the isoelectric point of titanium oxide introduced with oxygen defects is 0 to 5. Therefore, since the surface is negatively charged in water or alcohol having a pH of 5 to 14, it is possible to disperse the particles uniformly by the electric repulsive force between the particles. In particular, the titanium oxide according to the present invention is neutral and can be dispersed. It is neutral and can be uniformly dispersed without causing aggregation or precipitation even when mixed with other binders.

As a binder contained in the photocatalytic coating agent of the present invention, a substance having a siloxane bond can be preferably used. A silanol group having a high affinity for water is present on the surface of the compound having a siloxane bond, and it has an effect of imparting or strengthening the hydrophilicity maintaining function in a dark place. As the substance having a siloxane bond, an alkali silicate such as water glass,
Colloidal silica and aluminosilicate compounds can also be used. The aluminosilicate compound is a compound in which a part of Si of the silicate compound is replaced with Al, and further H ⁺ , Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , in order to compensate the charge.
Alkali metal ions such as Fr ⁺ , Be ²⁺ , Mg ²⁺ , Ca ²⁺ , Sr
Alkaline earth metal ions such as ²⁺ , Ba ²⁺ and Ra ²⁺ may be contained. Of the compound having the silicate bond
It is possible to use a material in which a part of Si is replaced with Al, zeolite, or the like.

As the substance having a siloxane bond,
In a more preferred embodiment, silicone emulsions can be used. Examples of silicone emulsions include methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, and methyltri-t-silane.
-Butoxysilane; ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane,
Ethyltri-t-butoxysilane; n-propyltrichlorosilane, n-propyltribromosilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltriisopropoxysilane, n-propyltrit-butoxysilane; n-hexyltrichlorosilane, n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-hexyltriisopropoxysilane, n-hexyltrit-butoxysilane; n-decyltrichlorosilane, n -Decyltribromosilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, n-decyltriisopropoxysilane, n-decyltrit-butoxysilane; n-octadecyltrichlorosilane, n
-Octadecyltribromosilane, n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane, n-
Octadecyltri-t-butoxysilane; phenyltrichlorosilane, phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriisopropoxysilane, phenyltrit-butoxysilane; tetrachlorosilane, tetrabromosilane,
Tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane; dimethyldichlorosilane, dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane; diphenyldichlorosilane, diphenyldibromosilane, diphenyldimethoxysilane, Diphenyldiethoxysilane; phenylmethyldichlorosilane, phenylmethyldibromosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane; trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane, triethoxyhydrosilane, triisopropoxyhydrosilane, tri-t -Butoxyhydrosilane; vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyl Triethoxysilane, vinyltriisopropoxysilane, vinyltri-t-butoxysilane; trifluoropropyltrichlorosilane, trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane. , Trifluoropropyltri-t-butoxysilane;
γ-glycidoxypropylmethyldimethoxysilane, γ
-Glycidoxypropylmethyldiethoxysilane, γ-
Glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltriisopropoxysilane, γ-glycidoxypropyltrit-butoxysilane; γ-methacryloxypropylmethyldimethoxysilane , Γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacryloxypropyltri t-butoxysilane; γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ
-Aminopropyltriisopropoxysilane, γ-aminopropyltri-t-butoxysilane; γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane. , Γ-mercaptopropyltriisopropoxysilane, γ-mercaptopropyltri-t-butoxysilane; β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltriethoxysilane Partially hydrolyzed products and dehydrated in-polymerized products can be preferably used.

A fluororesin emulsion can be used as a binder contained in the photocatalytic coating agent of the present invention. The coating film containing the fluororesin emulsion has high chemical stability and high weather resistance.

Examples of the fluororesin emulsion include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotriethylene. Fluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, perfluorocyclopolymer, vinyl ether-fluoroolefin copolymer,
Vinyl ester-fluoroolefin copolymer, tetrafluoroethylene-vinyl ether copolymer, chlorotrifluoroethylene-vinyl ether copolymer,
At least one selected from an emulsion of a polymer having a fluoro group such as a tetrafluoroethylene urethane crosslinked product, a tetrafluoroethylene epoxy crosslinked product, a tetrafluoroethylene acrylic crosslinked product, and a tetrafluoroethylene melamine crosslinked product can be preferably used.

Since the titanium oxide according to the present invention has visible light responsiveness, light in the wavelength range up to 600 nm can be used for the photocatalytic reaction. The member coated with the photocatalytic coating agent of the present invention is highly hydrophilized to have a contact angle with water of 5 ° or less by light irradiation from indoor lighting such as a fluorescent lamp or an incandescent lamp, and has antifogging and antifouling properties. Exhibits self-cleaning effect. In addition, it also has a high function of decomposing the attached organic matter and exerts an antibacterial function. In addition, the photocatalytic member of the present invention has a high light intensity of a mercury lamp, a xenon lamp, a mercury-xenon lamp, a halogen lamp, a metal halide lamp, or the like, or sunlight incident from a window or scattered light of sunlight. Needless to say, when it is photoexcited by means of the above, the above-mentioned antifogging, antifouling, self-cleaning and antibacterial effects are exhibited.

[0024]

Example 1 Titanium oxide powder (ST01, Ishihara Sangyo) was heat-treated at 600 ° C. for 3 hours in an ammonia gas stream to produce nitrogen-introduced titanium oxide. The resulting powder had a pale yellow color, suggesting that titanium oxide was reduced in an ammonia atmosphere and oxygen vacancies were created. This powder was poured into pure water at a solid content concentration of 20% and pulverized with a ZrO2 bead mill (bead diameter: 0.3 mmΦ) for 48 hours to obtain a titanium oxide slurry. 0.1 g of this slurry to 200 g of 10 mmo
Electrophoretic light-scattering photometer (ELS-6000, Otsuka Electronics) to measure the zeta potential of the liquid that was added dropwise to a 1 / L sodium chloride solution
Was measured at various pH values. The pH was adjusted by using 10 mmol / L hydrochloric acid and sodium hydroxide.

The pH at which the zeta potential is 0 is the isoelectric point. As a result, the pH at the isoelectric point of the titanium oxide was 2.8. In other words, the surface is negatively charged in weak acidity to alkalinity, and the compounding with the binder having the pH in this region becomes easy.

Example 2 The titanium oxide slurry obtained in Example 1 was diluted with pure water,
A glass substrate was applied with a pH of 6 and a solid content concentration of 5 wt% by spin coating, and dried at 150 ° C. for 30 minutes.
In the obtained thin film, the zeta potential of the thin film surface was measured by the monitor particle method using the electrophoretic light scattering photometer used in Example 1. Monitor particles are latex coated with hydroxypropyl cellulose (particle size: 520n
m, Otsuka Electronics), and a drop was added dropwise to a 10 mmol / L sodium chloride aqueous solution. The method for adjusting pH is the same as in Example 1.

As a result, the pH at the isoelectric point of the titanium oxide thin film was 3.5.

Comparative Example 1 The zeta potential of a commercially available titanium oxide sol (STS01, Ishihara Sangyo) was measured. The measuring method is the same as in Example 1.

As a result, the pH of the commercially available titanium oxide at the isoelectric point was 6.7, and it was suggested that the dispersion in the neutral region is difficult because the charge amount in water in the neutral region is small.

Example 3 The acetaldehyde decomposition activity of the oxide thin film obtained in Example 2 was evaluated. A thin film sample was placed in an 800 mL glass cell, the cell was replaced with synthetic air, acetaldehyde was injected, and the mixture was allowed to stand in the dark for 2 hours and then the change in acetaldehyde concentration was measured when light was irradiated. The initial concentration of acetaldehyde was 500 ppm. Multi-gas monitor (Inno
va, 1312). The light source was a xenon lamp (LA-250Xe, manufactured by Hayashi Clock Industry Co., Ltd.), and visible light in the wavelength range of 430 nm or more was irradiated through an ultraviolet cut filter (Toshiba Glass, Y-43).

As a result, generation of carbon dioxide was recognized by irradiation with visible light, and the concentration of carbon dioxide generated became 1000 ppm after 3 days of irradiation, and it became clear that acetaldehyde was completely decomposed into carbon dioxide. .

[0032]

The neutral photocatalytic coating agent using various silicone emulsions as binders can be provided.
Further, it is possible to provide a photocatalytic coating agent exhibiting antifogging and antifouling functions indoors.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between pH and zeta potential according to Example 1 of the present invention.

FIG. 2 is a graph showing the relationship between pH and zeta potential according to Example 2 of the present invention.

FIG. 3 is a graph showing the relationship between pH and zeta potential according to Comparative Example 1 of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 5/00 C09D 7/12 7/12 183/04 183/04 B01D 53/36 J G F term (reference) ) 4D048 AA19 AB03 BA07X BA41X BA46X EA01 4G069 AA03 AA08 BA04A BA04B BA22C BA48A BD06B BE32C BE34C CA17 CD10 DA06 ED02 ED04 FA01 FA03 FB23 FC05 4J038 A08B05 HA08 HA05 HA08 HA05 HA08 HA05 HA08 DL081 HA11 DL081 HA08 DL1111

Claims (7)

[Claims] 1. A photocatalytic coating agent containing titanium oxide, wherein the titanium oxide has an oxygen defect, and the dispersion medium of the photocatalytic coating agent is an aqueous solvent. . 2. The photocatalytic coating agent according to claim 1, wherein the pH of the dispersion medium of the photocatalytic coating agent is 5-9. 3. The oxygen defects are formed from the surface of titanium oxide by 10
The photocatalytic coating agent according to claim 1, which is present in a region of not more than nm. 4. The photocatalytic coating agent according to claim 1, wherein a substance having a siloxane bond is used as a binder for fixing titanium oxide of the photocatalytic coating agent. 5. The photocatalytic coating agent according to claim 4, wherein the substance having a siloxane bond is a silicone emulsion. 6. The photocatalytic coating agent according to claim 1, wherein a fluororesin emulsion is used as a binder for fixing titanium oxide of the photocatalytic coating agent. 7. The photocatalytic coating agent according to claim 1, wherein the titanium oxide exhibits a photocatalytic function in response to irradiation with visible light.