JP4571793B2 - Aqueous photocatalyst coating solution - Google Patents

Description

  The present invention relates to a photocatalyst coating liquid used for imparting a photocatalytic function to a substrate surface. More specifically, the present invention is used to form a photocatalyst coating film excellent in durability, which is used for various applications such as ultraviolet absorption, antifouling, hydrophilicity, antifogging, and antibacterial on various substrates. The present invention relates to an aqueous photocatalyst coating solution.

  Conventionally, as a method of forming a photocatalyst layer on a substrate surface, a titanium alkoxide hydrolyzed solution is applied and baked (sol-gel method), and photocatalyst particles are mixed with an oxidation-resistant binder. A method of preparing a photocatalyst coating liquid, applying and drying the liquid is known.

  When using a binder, it is necessary to select a binder that can withstand photocatalytic oxidation such as titanium dioxide. As such an oxidation-resistant binder, a fluororesin binder such as PTFE by particles, silicon oxide, and Silicone binders and the like have been used.

  Among the conventional methods for forming a titanium oxide film, as a method of applying a hydrolyzed titanium alkoxide, that is, as a technique similar to the sol-gel method, for example, JP-A-4-83537 (Patent Document 1), A method of adding an amide or glycol to titanium alkoxide is described, and JP-A-7-1000037 (Patent Document 2) discloses a method of adding alcohol amines to titanium alkoxide.

However, none of the sol-gel method and the conventional method using a binder have a sufficiently high alkali resistance and coating film hardness and can form a photocatalyst layer having high durability. For example, fluororesin binders such as PTFE have problems of low hardness and adhesion and low transparency, and SiO ₂ binders such as silica have problems of insufficient alkali resistance and film hardness. These were all unsatisfactory in practice in terms of durability.

As means for solving these problems, Japanese Patent Laid-Open No. 9-71418 (Patent Document 3) discloses a sol solution composed of hydrogen peroxide and titanium oxide and a method for producing the same. This sol solution has the advantage that it can be neutral, but has problems such as insufficient mechanical strength of the film and insufficient storage stability of the solution.
JP-A-4-83537 Japanese Patent Application Laid-Open No. 7-100378 JP-A-9-71418

  The present invention solves the above-mentioned problems of conventional photocatalyst coating liquids, and is an aqueous photocatalyst that is excellent in durability and adhesion, can obtain a high hardness even when dried at room temperature, and can form a coating film excellent in alkali resistance. It is intended to provide a coating solution.

In order to solve the above-mentioned problems, the present inventors have searched for various coating film forming materials that can withstand the oxidative decomposition action of titanium oxide and have excellent alkali resistance. As a result, it has been found that zirconium oxide forms a coating film having particularly excellent alkali resistance and mechanical strength, and further includes a search for a compound to be a precursor for forming a zirconium oxide coating film, and includes it stably. We have eagerly studied the coating solution.
Then, by applying a coating liquid containing photocatalyst particles such as titanium dioxide dispersed on a substrate with a water-soluble zirconium compound such as an ammonium zirconium carbonate aqueous solution, which is a kind of zirconium compound, and an anionic dispersant, and drying it. The inventors have found that a photocatalyst coating material excellent in adhesion, durability, and alkali resistance can be obtained.
The present inventors further obtain inorganic titanium salts such as titanium chloride and titanium sulfate, orthotitanic acid produced when titanium alkoxide is reacted with water and hydrolyzed, and hydrogen peroxide acting on these. The present invention has been completed by finding that when amorphous titanium oxide such as peroxotitanic acid is allowed to coexist in the coating liquid, the film hardness and wear resistance are further improved.

Aqueous photocatalyst coating liquid of the present invention, an aqueous coating comprising 100 parts by mass of photocatalyst particles, a water-soluble zirconium compound of 1 to 40 parts by weight in terms of ZrO _2, and an anionic dispersing agent of 1 to 40 parts by weight Liquid,
The anionic dispersant contains at least one selected from phosphate, phosphorous acid, hypophosphorous acid, metaphosphate and hydroxycarboxylate;
The aqueous coating liquid further contains 20 to 200 parts by mass of amorphous titanium oxide with respect to 100 parts by mass of the photocatalyst particles .
In the aqueous photocatalyst coating liquid of the present invention, the water-soluble zirconium compound is preferably selected from zirconium carbonate / ammonium, zirconium carbonate / potassium, basic zirconium carbonate, acetylacetone-zirconium complex, zirconium oxychloride and zirconium acetate.

  The aqueous photocatalyst coating liquid of the present invention has a good coating property when coated on a desired substrate and can form a coating film having high hardness by drying at room temperature. The resulting coating film has durability and adhesion. And excellent in alkali resistance.

In the aqueous photocatalyst coating liquid of the present invention, 1 to 40 parts by mass of a water-soluble zirconium compound in terms of ZrO ₂ and 1 to 40 parts by mass of an anionic dispersant are required with respect to 100 parts by mass of the photocatalyst particles. is there. By the anionic dispersant, the charge of the photocatalyst particles becomes negative and can be stably dispersed in the aqueous liquid.

  The photocatalyst particles used in the present invention are not limited in type and composition as long as they can exhibit a practically sufficient photocatalytic action, but it is preferable to use a titanium oxide compound such as titanium dioxide. Preferred titanium oxide compounds for use in the present invention are anatase-type titanium dioxide (including metatitanic acid), methyl-type titanium dioxide, and brookite-type titanium dioxide, and in addition to visible light having a wavelength of 400 nm or more. So-called visible light responsive titanium oxide such as an oxygen defect type having a response property and a nitrogen dope type is preferably used. As these other photocatalyst particles, strontium titanate, barium titanate, zinc oxide, tin oxide, zirconium oxide and the like can also be used.

In addition, the aqueous photocatalyst coating liquid of the present invention further contains amorphous titanium oxide that can be crystallized by firing or electromagnetic wave irradiation , whereby the durability of the film can be improved. The usage-amount of an amorphous titanium oxide is 20-200 mass parts with respect to 100 mass parts of photocatalyst particles .

  Although there is no restriction | limiting in particular in the particle size of photocatalyst particle, Generally it is preferable to exist in the range of 1-100 nm, and 3-30 nm is more preferable.

  In order to produce the titanium compound used with the photocatalyst particles of the present invention, for example, titanium dioxide, an inorganic titanium compound such as titanium chloride, titanium oxychloride, titanium sulfate, or titanyl sulfate is dissolved in water. There is known a method of hydrolyzing a titanium compound by adding a catalyst such as hydrochloric acid or nitric acid to the mixture and heating. Other known methods include combustion oxidation of a compound such as titanium chloride, or hydrolysis of an organic titanium compound such as titanium alkoxide or titanium acetylacetonate. As a method for synthesizing visible light responsive titanium oxide, for example, a method in which hydrated titanium oxide or crystalline titanium dioxide is brought into contact with ammonia at a temperature of 300 to 600 ° C. is known.

  As the water-soluble zirconium compound contained in the aqueous photocatalyst coating liquid of the present invention, zirconium carbonate / ammonium, zirconium carbonate / potassium, basic zirconium carbonate, acetylacetone / zirconium complex, zirconium oxychloride, and / or zirconium acetate are used. be able to. Zirconium carbonate / ammonium carbonate is obtained by reacting zirconium ions with carbonate ions and ammonium ions, and carbon dioxide gas, ammonia and water are volatilized by dehydration and drying to change to zirconium hydroxide and zirconium dioxide. It has been.

Content of the water-soluble zirconium compound contained in the aqueous coating liquid of the present invention is 1 to 40 parts by mass in terms of ZrO ₂ with respect to 100 parts by mass of the photocatalyst particles. If it is less than 1 part by mass, the hardness of the resulting coating film is insufficient, and if it exceeds 40 parts by mass , the photocatalytic activity of the resulting coating film is reduced. When zirconium carbonate / ammonium carbonate is used as the water-soluble zirconium compound, the content ratio of zirconium ion, carbonate ion and ammonium ion is not particularly limited as long as the compound is within a substantially stable range, but 1: 0. It is preferable that it is 4-5: 0.4-5, for example, molar ratio of 1: 2: 2 can be used. As a preferable ammonium zirconium carbonate solution, there is an ammonium zirconium carbonate solution (trademark: Baycoat 20) manufactured by Nippon Light Metal Co., Ltd.

In the aqueous photocatalyst coating liquid of the present invention, an anionic dispersant is contained in an amount of 1 to 40 parts by mass with respect to 100 parts by mass of the photocatalyst particles. The anionic dispersant that can be used in the present invention has the effect of adsorbing to the photocatalyst particles as an anion, facilitating and stabilizing its dispersion in water, and stabilizing the water-soluble zirconium compound. As the anionic dispersant useful in the present invention, one or more of phosphate , phosphorous acid, hypophosphorous acid, metaphosphate, and hydroxycarboxylate are used. As the phosphate, an organic basic compound salt, an alkali metal salt, and / or an ammonium salt are preferably used. As a salt of a hydroxycarboxylic acid compound having a hydroxyl group , for example, a salt of a hydroxycarboxylic acid such as lactic acid or glycolic acid is preferred. These salts do not necessarily have to be added to the coating liquid after being synthesized into a salt, and the acid may be synthesized in an aqueous coating liquid by adding an acid and a base compound that reacts with it to form a salt.

  Although there is no restriction | limiting in particular in the pH value of a coating liquid, When using zirconium carbonate and ammonium, it is preferable that pH value exists in the range of 5-12. If the pH value is less than 5, carbon dioxide gas may be decomposed and separated from ammonium zirconium carbonate, and if it exceeds 3, ammonia may be decomposed and volatilized.

  In order to adjust the pH of the aqueous photocatalyst coating liquid to a preferable range, when an alkaline compound is used, the type thereof is not limited, but it is preferable to use an organic alkali compound such as ammonia or amines.

  The aqueous photocatalyst coating liquid of the present invention contains a solvent containing water as a medium. Although a solvent other than water is not necessarily required, ethanol, methanol, 2-propanol, ketone, dioxane, cellosolve, and / or glycol that are compatible with water can be used as the solvent other than water.

When the aqueous photocatalyst coating liquid of the present invention is applied on a desired substrate, it is preferable to apply the photocatalyst particles (for example, titanium dioxide) so that the adhesion amount thereof is in the range of ²⁰ to 2000 mg / m2. The coating layer of the aqueous photocatalyst coating solution can be dried at room temperature as well as heat drying, but the coating curing reaction is performed by irradiating with electromagnetic waves having a wavelength that the photocatalyst used during or after drying functions. It is preferable to promote.

EXAMPLES The present invention will be further described by the following examples, but the present invention is not limited by these examples.

The following materials were used in the following Reference Examples 1 to 4, 6 and 7 , Example 5 and Comparative Examples 1 to 4.
(Photocatalyst particles)
One of the following two types (A, B) was used.
A) Photocatalytic titanium dioxide (anatase type), manufactured by Ishihara Sangyo Co., Ltd .: ST-01
B ) Photocatalytic titanium oxide (visible light responsive type), manufactured by Sumitomo Chemical Co., Ltd .: TPS-201 (water-soluble zirconium compound)
Nippon Light Metal Co., Ltd., trademark: Baycoat 20 (20% strength aqueous solution as ZrO ₂ ) was used.
(Dispersant)
Anionic dispersant:
h) Ammonium pyrophosphate i) Neutralized phospholine morpholine j) Diammonium phosphate k) Neutralized monoethanolamine glycolic acid l) Ammonium lactate m) Polycarboxylic acid (Nikko Chemicals)
Nonionic dispersant:
n) Polyoxyethylene nonylphenyl ether (HLB: 11)
As the chemical, a reagent grade 1 product or an equivalent product was used.
(Amorphous titanium oxide)
Nippon Parkerizing Co., Ltd., trademark: PTI-5600 (concentration: 4%, pH: 8) was used.

In each of Reference Examples 1 to 4 , 6 and 7, Example 5, and Comparative Examples 1 to 4, photocatalyst coating liquids having the compositions shown in Tables 1 and 2 were prepared. As water-soluble zirconium compounds, Reference Examples 1 to 4 and 6, Example 5, Reference Example 7 and Comparative Example 2 used zirconium ammonium carbonate. In Comparative Example 1, silica sol (Nissan Chemical Co., Ltd.) was used instead of the water-soluble zirconium compound. Industrial Co., Ltd. Snowtex N) was added in an amount of 50 parts by weight in terms of SiO ₂ . Moreover, each coating liquid was apply | coated so that the dry film thickness might be set to about 0.5 micrometer using the stainless steel wire bar on the wash | cleaned glass substrate surface, and it dried at 80 degreeC for 20 minutes. The pencil hardness and alkali resistance of the obtained coating film were measured.

  In the preparation of the coating liquid, 50 g of the photocatalyst powder A) or B) is added to and dispersed in 600 g of an aqueous solution in which any of the dispersants h) to n) is dissolved in advance, and this is applied to a bead disperser. Add water-soluble zirconium compound (trademark: Baycoat 20), stir, add water or amorphous titanium oxide (trademark: PTI-5600), adjust the pH value with ammonia to the value listed in Table 1, and The total amount was adjusted to 1 kg.

The evaluation of the coating film performance was performed according to the following test method and evaluation criteria. Table 1 shows the measurement / evaluation results.
(Adhesion)
The adhesion of the test coating film was measured and judged according to JIS-K5400, a cross-cut tape method coating film adhesion test method. A sample without peeling was marked with ◯, and a piece with peeling was marked with ×.
(Film hardness)
The test coating film was scratched using JIS-K5400 and a pencil scratch test pencil, and the hardness of the coating film was expressed by pencil hardness. (Evaluated for substrates other than paper)
(Alkali resistance)
The test coating film was immersed in a 10% NaOH aqueous solution for 24 hours, washed with running water and dried, and then the adhesion of the coating film was determined according to a JIS-K5400 cross-cut tape method coating film adhesion test. A sample without peeling was marked with ◯, and a sample with peeling was marked with ×.

As is clear from Table 1, in Comparative Examples 1 to 3, satisfactory results could not be obtained when the conventional photocatalyst coating solution was used. When the aqueous photocatalyst coating liquid of Example 5 according to the present invention was used, practically excellent performance was obtained in coating film hardness, adhesion to a glass substrate, and alkali resistance.

  The aqueous photocatalyst coating liquid of the present invention can form a photocatalyst coating film that is highly resistant to abrasion and chemicals even in an environment where sufficient durability could not be obtained by the prior art. A photocatalytic film that can be used in a harsh environment for a longer period of time and can be used for various purposes such as dirt decomposition, ultraviolet absorption, sterilization, gas decomposition, and water purification is provided.

Claims (2)

An aqueous coating liquid containing 100 parts by mass of photocatalytic particles, 1 to 40 parts by mass of a water-soluble zirconium compound in terms of ZrO ₂ , and 1 to 40 parts by mass of an anionic dispersant ,
The anionic dispersant contains at least one selected from phosphate, phosphorous acid, hypophosphorous acid, metaphosphate and hydroxycarboxylate;
The aqueous photocatalyst coating liquid, wherein the aqueous coating liquid further contains 20 to 200 parts by mass of amorphous titanium oxide with respect to 100 parts by mass of the photocatalyst particles .   The aqueous photocatalyst coating liquid according to claim 1, wherein the water-soluble zirconium compound is selected from zirconium carbonate / ammonium carbonate, zirconium carbonate / potassium carbonate, basic zirconium carbonate, acetylacetone-zirconium complex, zirconium oxychloride and zirconium acetate.