Coating liquid forming titanium oxide thin membrane, method for producing the same and substrate carrying the same

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention utilizes the photocatalytic effect of titanium oxide and NO._XThe present invention relates to a titanium oxide thin film forming coating liquid used for removing harmful substances such as, deodorizing, antifouling, antibacterial, etc., a method for producing the same, and a titanium oxide thin film supporting base material.

【0002】

[Conventional technology]

Titanium oxide photocatalyst is NO due to the chemical reaction that occurs by absorbing ultraviolet rays._XIt is known to show effects such as removal of harmful substances such as, deodorization, antifouling, and antibacterial. By the way, in order to industrially exhibit the photocatalytic effect, it is necessary to support the photocatalytic thin film on the base material. As a method of applying titanium oxide to the surface of a base material such as glass, metal, ceramics, and various plastics, a method of applying and baking titanium alkoxide, which is a titanium oxide precursor, titanium organic acid, titanium chloride, etc., titania There is a method of applying a powder or a mixture of a sol and a binder. In the case of a titanium oxide thin film mainly for antifouling purposes, the degree of contamination depends on the dirt component adsorbed on the surface, so it is preferable that the surface of the film is smooth and the surface area is small.

【0003】

However, when the effect of decomposing more substances such as deodorization is expected, it is necessary to increase the specific surface area of the membrane, and for that purpose, it is necessary to make the membrane structure porous and at the same time to thicken the membrane. Therefore, a titanium oxide thin film mainly for the purpose of decomposing organic substances such as deodorization often forms a film using relatively large titanium oxide particles. A thin film made of titanium oxide having a large particle size inevitably has a thick film thickness, and many gaps are formed in the packed structure of large particles, resulting in a porous structure. By the way, in order to support and immobilize titanium oxide particles having a large particle size, which are not self-bonding to themselves, on a substrate in a porous manner, a binder component is added and the particles are cured at low temperature or normal temperature to be supported. Is required. At this time, since the film made of titanium oxide having large particles has a rough surface and a porous structure, the film strength is low, and there is a problem that the film easily falls off or is damaged. The simplest way to improve the film strength is to increase the amount of binder, but in this method, the binder component covers the surface of the titanium oxide particles, and even if the film strength is improved, the expected catalytic activity is reduced. It will end up. On the other hand, if the titanium oxide particles are made smaller, the surface becomes smooth and the strength of the film is improved. Since it is reduced, the catalytic activity is also reduced by this method. As described above, in order to support and immobilize titanium oxide having a large particle size on a substrate with the aim of achieving a large catalytic effect, it is a major issue to achieve both film strength and catalytic effect.

【0004】

[Problems to be Solved by the Invention]

The present inventors have made a titanium oxide thin film having high catalytic activity and practical film strength with a smaller amount of binder by mixing titanium oxide having a large particle size and titanium oxide having a small particle size in a coating liquid at a constant ratio. We found that a supported substrate could be obtained, and came to solve the problem.

【0005】

[Means for solving problems]

That is, the present invention has an average particle size of 0.4 to 1.5 μm and a specific surface area of 50 m.²Titanium oxide particles (A) of / g or more 0.2 to 15% by weight, average particle size 200 nm or less, specific surface area 200 m²Titanium oxide particles (B) of / g or more 0.05 to 10% by weight, and silica compound (SiO)₂As) (C) contains 0.1 ~ 5% by weight, and (B) / ((A) + (B)) x 100 = 3 ~ 25% by weight, (C) / ((A) + (B) + (C))) = 5 to 30% by weight of titanium oxide thin film forming coating liquid. The present invention also relates to a titanium oxide thin film-supporting substrate treated with the coating liquid.

【0006】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. There are two types of titanium oxide particles used in the present invention. One type is titanium oxide particles having an average particle diameter of 0.4 μm to 1.5 μm, and anatase-type titanium oxide is preferably used. If the average particle size is smaller than 0.4 μm, the porosity of the film decreases and the catalytic effect decreases, and if it is larger than 1.5 μm, the porosity of the film increases and the catalytic effect increases, but the film surface Since the film becomes coarse, the film strength is remarkably lowered, and the film falls off or chokes, which poses a problem in practical use. In practice, it is preferable to select titanium oxide particles having an average particle size of 0.6 μm to 1.2 μm in order to practically achieve both a catalytic effect and a film strength. The degree of crystallinity of the anatase-type crystal, that is, the size of the crystallite is not particularly particular, but any anatase-type diffraction peak may be observed when subjected to powder X-ray diffraction. Considering this, the crystallite diameter is about 5 nm or more. There is no particular problem even if some rutile-type titanium oxide is mixed on the powder X-ray diffraction chart.

【0007】

The specific surface area of titanium oxide powder is 50 m after drying at 100 ° C.²Must be at least / g. Below this, even if the structure is porous in order to obtain a catalytic effect, a large catalytic effect cannot be expected. As these titanium oxides, commercially available anatase-type titanium oxide powder may be used, or titanium hydroxide-containing titanium obtained by thermally decomposing or neutralizing titanium sulfate or titanium chloride may be used.

【0008】

To adjust the particle size, the titanium hydroxide gel obtained by the neutralization decomposition method or the thermal decomposition method may be solified and the particles may be grown by hydrothermal treatment, etc., but the powdered titanium oxide particles are pulverized by a dry method or a wet method. The method to do is the simplest. The particles obtained by this method are aggregate particles themselves, and easily form a porous structure that can be expected to have a high catalytic effect. When added as a powder to the coating liquid, it precipitates in a short time, so it is preferable to use it in a state of being processed into a slurry or sol having less sedimentation property. A commercially available titanium oxide slurry or sol may be used as long as the required physical properties are satisfied.

【0009】

A dispersion stabilizer can coexist in the coating liquid in order to prevent a change in particle size and sedimentation due to agglomeration of particles. These dispersion stabilizers can coexist at the time of preparing the particles, or may be added at the time of preparing the coating liquid.

【0010】

As the dispersion stabilizer, various chemicals can be used without particular concern, but since titanium oxide tends to aggregate near neutrality, an acidic or alkaline dispersion stabilizer is preferably used. Examples of the acidic dispersion stabilizer include mineral acids such as nitric acid and hydrochloric acid, and organic acids such as carboxylic acid, oxycarboxylic acid and polycarboxylic acid. A good example of the alkaline dispersion stabilizer is one or more compounds selected from carboxylic acids, alkali metal salts and ammonia of polycarboxylic acids, 1st to 4th grade amines, and alkanolamines having a hydroxy group added thereto. Can be mentioned. In particular, it is preferable to use an organic acid because it has good miscibility with an organic solvent described later, does not have an extremely low pH, and does not easily corrode equipment used during production. As the organic acid, acetic acid, oxalic acid, glycolic acid, lactic acid, tartrate acid, malic acid, citric acid and the like can be preferably used, and dispersion stabilization can be performed with one or more kinds of acids selected from these.

【0011】

Further, a thickener such as a water-soluble polymer can be added to increase the viscosity of the coating liquid. Examples of the thickener include polysaccharides, polyvinyl alcohol, polyethylene oxide and the like. Amount of titanium oxide in the coating liquid (TiO₂) Is 0.2 to 15% by weight. If the amount of titanium oxide in the coating liquid is too high, the viscosity of the coating liquid becomes too high and the handleability deteriorates. On the contrary, if it is too low, the viscosity of the coating liquid decreases. Titanium oxide with a large particle size tends to settle. Considering the stability of the coating liquid, the amount of titanium oxide is more preferably 2 to 10% by weight.

【0012】

On the other hand, the other type of titanium oxide particles used in the present invention has an average particle diameter of 200 nm or less and a specific surface area of 200 m.²Titanium oxide fine particles of / g or more (hereinafter referred to as titanium oxide fine particles to distinguish them from titanium oxide particles of 0.4 μm to 1.5 μm). These titanium oxide fine particles increase the contact points between the particles in the porous film, so as to prevent the formation of the porous structure by the titanium oxide particles having a larger particle size as described above, and the entire titanium oxide thin film. As a result, it plays a role of forming a high-strength film that can withstand practical use even if the amount of binder is small. Further, since these titanium oxide fine particles themselves also exhibit a catalytic effect, the catalytic effect of the titanium oxide particles is hardly reduced.

【0013】

Since these titanium oxide fine particles need to have a so-called binder effect as described above, it is essential that the particle size is small and the specific surface area is large. When the particle size is 200 nm or more, the binding effect is reduced and the film strength is lowered, so that it is more preferably 100 nm or less. Also, it is preferable that the specific surface area is large, and it is usually 200 m.²/ g or more is required, especially 250m if you want to improve the film strength²More than / g is used. The crystallinity of these titanium oxide fine particles is not particularly particular, but an amorphous structure that does not show a diffraction peak at all in powder X-ray diffraction is not good because it contributes little to the catalytic effect. Therefore, it is preferable that the anatase-type titanium oxide has crystallinity at least to the extent that a peak can be confirmed at the diffraction peak position in the powder X-ray diffraction of the dry powder.

【0014】

The method for producing these titanium oxide fine particles is not particularly limited, but since it is difficult to produce by the dry method, powdered titanium oxide may be finely pulverized in a wet manner in the presence of a dispersant or a solubilizer. It is appropriate to use the sol-like titanium oxide obtained by decomposing and dissolving the titanium salt. These titanium oxide fine particles are dispersed in the coating liquid together with the titanium oxide particles having a large particle size. Basically, colloidal level fine particles with a particle size of 200 nm or less are difficult to precipitate, but a unique dispersion stabilizer can be used to prevent the particles from settling or agglomerating in the coating liquid. It is also possible to share the dispersion stabilizer used for one of the titanium oxide particles.

【0015】

The type of dispersion stabilizer can be selected from those exemplified in the above-mentioned dispersion of titanium oxide particles. In order to prevent gelation and agglomeration of particles during mixing, it is preferable that the stabilizers for both are acidic or alkaline. What is important is that each particle exists stably in the coating liquid without causing changes such as aggregation and precipitation. Amount of titanium oxide fine particles in the coating liquid (TiO₂) Is 0.05 to 10% by weight. The ratio of titanium oxide fine particles to the total amount of film solids is preferably 3 to 20% by weight, and the ratio of titanium oxide fine particles to the total amount of titanium oxide is preferably 3 to 25% by weight. If the proportion of titanium oxide fine particles is below the lower limit, sufficient adhesion and film strength cannot be obtained unless the amount of binder is increased, and above the upper limit, the catalytic effect is extremely reduced due to changes in the film structure, or the film is cracked. It will be easier to do.

【0016】

In order to firmly adhere these titanium oxide particles to the base material, the titanium oxide fine particles alone are not sufficient, and a binder component is inevitably required. What can be used as a binder component in the present invention is a silica compound.

【0017】

As the silica compound, 4, 3, or bifunctional alkoxysilanes, condensates of these alkoxysilanes, hydrolysates, silicone varnishes, and the like can be used. The trifunctional alkoxysilane is generally called a silane coupling agent, but in the present invention, a compound in which one or more alkoxy groups are bonded to one silicon molecule is referred to as an alkoxysilane. Specifically, tetrafunctional alkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane, and trifunctional alkoxysilanes include methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, and phenyltriethoxysilane. Vinyl trimethoxysilane, vinyl triethoxysilane, metharoxypropyltrimethoxysilane, glycidpropoxytrimethoxysilane, glyciropropylmethyldiethoxysilane, aminopropyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, mercaptopropyltrimethoxy Examples of the silane and the bifunctional alkoxysilane include dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane. Examples of the condensate include, but are not limited to, condensates of tetrafunctional alkoxysilanes such as ethyl silicate 40, ethyl silicate 48, and methyl silicate 51.

【0018】

As the hydrolyzate, one obtained by hydrolyzing alkoxysilanes using an organic solvent, water and a catalyst can be used. Among these silica compounds, tetramethoxysilane, tetraethoxysilane, ethyl silicate 40, ethyl silicate 48, methyl silicate 51 and their hydrolysis products, alcoholic silica sol, can firmly fix the film on the substrate. Moreover, it is particularly suitable because it is relatively inexpensive.

【0019】

The method for producing the alcoholic silica sol is not particularly limited, and the alkoxysilane may be hydrolyzed in the coating liquid, or the alkoxysilane is hydrolyzed or partially hydrolyzed to already form an alcoholic silica sol. May be added to the titanium oxide solution of the present invention.

【0020】

These binder liquids are mixed with the coating liquid and used, but when mixing the binder, a solvent can be used to mix and stabilize the binder liquid and the aqueous titanium oxide dispersion liquid. As the type of solvent, monohydric lower alcohols such as methanol, ethanol, propanol and butanol, polyhydric alcohols such as ethylene glycol and propylene glycol, and cellsolve which is an ester thereof can be used as a favorable solvent. The amount of these solvents is 5 to 90% by weight based on the entire coating liquid.

【0021】

The silica compound, that is, the binder may be mixed with the titanium oxide-containing coating solution in advance and stored, but if the binder component deteriorates by a usual storage method, it is mixed with the titanium oxide-containing coating solution immediately before use. It can also be used. If the amount of binder is too large, it not only hinders the stability of the coating liquid, but also covers the surface of titanium oxide and significantly reduces the catalytic effect, so the specific surface area is 50 m.²Titanium oxide particles of / g or more (A), titanium oxide fine particles (B), silica mixture of binder (SiO)₂) Is (C), (C) / ((A) + (B) + (C)) = 5 to 30% by weight is preferable. In particular, when a catalytic effect is expected, it is even better to be 5 to 20% by weight. The binder concentration in the coating liquid affects the viscosity and stability of the coating liquid, so SiO₂0.1 to 5% by weight is preferable. When the binder is added to the coating liquid and then stored for a long time, it is more preferably 2.5% by weight or less.

【0022】

As a result of applying the coating liquid of the present invention, it can be applied to any base material as long as practical adhesion is obtained. However, as a general base material, ceramics such as tiles, roof tiles, and glass are used. It can be applied to metals such as iron and aluminum, plastics such as acrylic, PET, polycarbonate and vinyl chloride, various painted surfaces, concrete, mortar surfaces, and cloth.

【0023】

The shape of the base material can be plate-shaped, film-shaped, molded body, or the like. Any method may be used to apply the coating liquid onto the substrate to form a titanium oxide thin film, and various coating methods such as brush coating, spray coating, spin coating, dip coating, roll coating, gravure coating, and bar coating are available. It can be selected in consideration of the shape of the base material. Drying of the coating liquid varies depending on the type of substrate, but is usually heat-treated at 300 ° C or lower. When glass or ceramics is used as the base material, the adhesion is improved by treating at a high temperature, but at 500 ° C or higher, the specific surface area is significantly reduced due to the sintering of titanium oxide, and the catalytic effect is reduced.

【0024】

When the base material is a plastic such as acrylic, PET, polycarbonate, or vinyl chloride, the heat treatment temperature is 150 ° C or less due to the heat resistance of the base material. The thicker the film thickness of the titanium oxide thin film, the higher the catalytic effect. However, when the film thickness is 3 μm or more, the increase in the film thickness and the increase in the catalytic effect are not proportional, so that the film thickness is generally uneconomical. In addition, if the film thickness is thick, it may cause cracks, so practically 0.2 to 2 μm is a film thickness that can achieve both catalytic effect and economy. However, it is not limited to this because it differs depending on the type of the base material.

【0025】

When the above plastics are used as a base material for forming a thin film, an adhesive layer containing a resin as a main component is provided between the base material and the titanium oxide thin film in order to further enhance the adhesion between the base material and the titanium oxide thin film. Can be provided. The adhesive layer preferably has a high affinity for both the base material and the titanium oxide thin film composition, but the one containing acrylic resin as a main component is most suitable because it can form a tough adhesive layer with high adhesion. If it is desired to further increase the adhesion, an organic silicon compound such as a silica sol, a silicone resin, or an alkoxysilane can be mixed with the acrylic resin and used. Further, instead of the acrylic resin, an acrylic-modified silicone resin compound and a silicone-modified silicone resin compound can also be used. The adhesive layer is generally formed by applying a solution containing the above resin compound. The solution may be one in which the resin is dispersed in a solvent such as toluene, xylene, ketone, alcohol, or an aqueous emulsion type. The method for forming the adhesive layer is not particularly limited, and the adhesive layer can be formed by applying the same method as the titanium oxide thin film. The thickness of the adhesive layer is not limited, but sufficient adhesion can be imparted if it is about 0.2 μm or more. As a matter of course, if the surface of the base material is already coated with the above-mentioned resin for some reason, these treatments can be omitted.

【0026】

[Example]

The details of the inventions described so far will be described below with specific examples, but the present invention is not limited to those examples. Unless otherwise specified,% indicates weight%.

【0027】

(Example 1) Titanium oxide P-25 manufactured by Nippon Aerosil Co., Ltd. (specific surface area 50 m)²Citric acid was added as a dispersant to / g) (0.1 mol with respect to titanium oxide), and wet pulverization was performed to obtain an average particle size of 0.8 μm (specific surface area 68 m).²Slurry (A) of / g) and titanium oxide sol M-6 manufactured by Taki Chemical Co., Ltd. (specific surface area 280 m)²/ G, average particle size 10 nm) (B), and tetraethoxysilane (C) manufactured by Kanto Chemical Co., Inc. are converted into oxides (TiO).₂, SiO₂) To make the ratio of (B) / ((A) + (B)) × 100 = 10%, (C) / ((A) + (B) + (C)) = 20%, and mix. Dilute with water and ethanol and convert to oxide (TiO₂, SiO₂), A coating solution having a total solid content concentration of 8% and ethanol of 50% was obtained. The titanium oxide thin film forming coating solution was spin-coated on a PET substrate coated with a 75 mm × 52 mm slide glass and a silicon-containing acrylic resin paint primer A manufactured by Taki Chemical Co., Ltd. to a thickness of 1 μm, and 100 ° C. After drying for 10 minutes in, it was used as a sample plate. At this time, the dry solid content of the coating liquid applied on the substrate was 0.003 g per substrate.

【0028】

(Example 2) Titanium oxide A-100 manufactured by Taki Chemical Co., Ltd. (specific surface area 295 m)²Oxalic acid was added as a dispersant to / g) (0.2 mol with respect to titanium oxide), and wet pulverization was performed to obtain an average particle size of 0.6 μm (specific surface area 300 m).²Average particle size 150 nm and specific surface area 325 m obtained by the same method as the slurry (A) of / g)²/ G sol (B) and tetramethoxysilane (C) manufactured by Shin-Etsu Chemical Co., Ltd. are converted into oxides (B) / ((A) + (B)) x 100 = 6%, (C) / Mix to a ratio of ((A) + (B) + (C)) = 20%, dilute with water and isopropyl alcohol, and apply 10% total solids concentration in terms of oxide and 35% isopropyl alcohol. Obtained liquid. The above titanium oxide thin film forming coating solution was spin-coated on an acrylic substrate coated with a 75 mm × 52 mm slide glass and an acrylic silicon resin emulsion paint Sunmall manufactured by Sanyo Kasei Kogyo Co., Ltd. to a thickness of 5 μm, and 100 ° C. After drying in C for 10 minutes, it was used as a sample plate. At this time, the dry solid content of the coating liquid applied on the substrate was 0.003 g per substrate.

【0029】

(Example 3) Titanium oxide sol A-6 manufactured by Taki Chemical Co., Ltd. was dried at 105 ° C, malic acid was added as a dispersant (0.1 mol with respect to titanium oxide), and wet pulverization was performed. Slurry (average particle size 0.65 μm, specific surface area 140 m²/ g) (A), the sol (B) used in Example 2, and the dilution 40 (C) manufactured by Tama Chemical Co., Ltd. are converted into oxides (B) / ((A) + (B)), respectively. Mix so that the ratio is × 100 = 18%, (C) / ((A) + (B) + (C)) = 15%, dilute with water and ethanol, and the total solid content concentration in terms of oxide. A coating solution of 5% and 40% ethanol was obtained. The above titanium oxide thin film forming coating liquid was spin-coated on a PET substrate coated with a 75 mm × 52 mm slide glass and a special acrylic emulsion resin paint Boncoat DV-759 film manufactured by Dainippon Ink and Chemicals Co., Ltd. with a thickness of 5 μm. After drying at 100 ° C for 10 minutes, it was used as a sample plate. At this time, the dry solid content of the coating liquid applied on the substrate was 0.003 g per substrate.

【0030】

(Comparative Example 1) Solid content (TiO) of titanium oxide sol M-6 (B) manufactured by Taki Chemical Co., Ltd. in Example 1.₂) The total amount is the solid content (TiO) of the wet pulverized slurry (A) of titanium oxide P-25 manufactured by Nippon Aerosil Co., Ltd.₂), And the titanium oxide component was used as one type, and the coating liquid and the sample plate were prepared by the same method as in Example 1.

【0031】

(Comparative Example 2) Solid content (TiO) of titanium oxide sol M-6 (B) manufactured by Taki Chemical Co., Ltd. in Example 1.₂) The total amount is the solid content (TiO) of the wet pulverized slurry (A) of titanium oxide P-25 manufactured by Nippon Aerosil Co., Ltd.₂), And tetramethoxysilane (C) (SiO)₂) The coating liquid and the sample plate were prepared by the same method as in Example 1 except that the amounts were mixed so as to be (C) / ((A) + (C)) = 35%.

【0032】

(Comparative Example 3) The amount of tetramethoxysilane (C) in Example 1 (SiO)₂) Was mixed so that (C) / ((A) + (B) + (C)) = 50%, and a coating liquid and a sample plate were prepared by the same method as in Example 1.

【0033】

(Comparative Example 4) Solid content (TiO) of titanium oxide sol M-6 (B) manufactured by Taki Chemical Co., Ltd. in Example 1.₂) Was increased to (B) / ((A) + (B)) × 100 = 30%, and the coating liquid and the sample plate were prepared by the same method as in Example 1.

【0034】

(Membrane strength test) 1 kg / cm on the glass substrate sample prepared in the above Examples and Comparative Examples²Evaluated by repeated scratching with a commercially available plastic eraser weighted with AA, if the film did not disappear after 200 scratches, A, 50 to 100 times if the film disappeared after 100 to 200 scratches. The one in which the membrane disappeared was designated as B, and the one in which the membrane disappeared less than 50 times was designated as C.

【0035】

(Gas decomposition activity test) One acrylic substrate sample sample plate prepared in the above Examples and Comparative Examples was placed in a Pyrex (registered trademark) glass separable flask having a volume of 1.9 L, and acetaldehyde gas was introduced from a cylinder. The inside of the container was set to 100 ppm and sealed. After this, a commercially available FL black light was applied from the outside of the flask, and the ultraviolet intensity of the sample surface was 1 mW / cm.²Irradiation was carried out for 120 minutes so that the residual acetaldehyde concentration was measured with a detector tube. The catalytic effect was expressed as a percentage of the acetaldehyde concentration that was decomposed and disappeared with respect to the initial aldehyde concentration. The results are shown in Table 1.

【0036】

[table 1]

(Test results)<img file="JP2002293542A_D0001.tif" />【0037】

[Effect of the invention]

The titanium oxide thin film forming coating liquid of the present invention is composed of two types of titanium oxide, and when this is applied to the surface of a base material, both interact with each other to have high catalytic activity and practical film strength. Titanium thin film-supported substrate can be obtained