Photocatalytically-active, self-cleaning aqueous coating compositions and methods

Photocatalytic activity, self-cleaning water-based coating composition and method

Technical field

The present invention relates to a photocatalytically active (PCA) coating composition, which contains a photocatalytically active transition metal oxide (MO) or (MO2), such as titanium dioxide (TiO2) or zirconium oxide (ZrO2) catalyst, which is used to produce a transparent self A cleaning coating, such as a coating for glass windows, which reacts with organic compounds or pollutants deposited on it from the environment and decomposes them when exposed to sunlight, especially the ultraviolet radiation contained therein . The organic pollutants are decomposed into simple inorganic compounds, such as CO2, H2O and various inorganic acids, which enter the atmosphere and/or are washed away under the action of heat, wind and/or rain, so the coating The layer is self-cleaning, and its effectiveness depends on the level of the photocatalytic activity of the MO2 catalyst, which is proportional to the total surface area of the MO2 particles exposed to the pollutants.

Background technique

As we all know, when metal oxides, such as anatase TiO2 powder, are irradiated with ultraviolet light with a wavelength below about 390nm, electrons in the valence band will be excited to the conduction band, leaving positively charged holes that are related to the absorbed The water vapor hydroxide ion is reactive, leading to the formation of a positively charged hydroxyl group, (OH)+. The hydroxyl group is a strong oxidizing group that can react with organic pollutants and obtain electrons from organic pollutants, producing simple, non-hazardous products such as CO2 and H2O, or if halogen pollutants are included, producing HCl.

A commercially available TiO2 powder photocatalyst is Dggussa P25, a 70:30% anatase/rutile mixture, with a BET surface area of 55±15m2g-1, and a crystal size of 0.1nm in a 30nm aggregate. It forms an aqueous suspension in the diluted alcohol, which forms a chalky catalytic coating on the glass. Refer to the paper entitled "Photocatalytic Degradation of Gaseous Organic Pollutants" by Yu et al., published in Journal of Chemical Education, Volume 25, No. 6, June, 1998.

It is desirable to produce a TiO2 composition that can be applied to a surface such as window glass and dried under ambient conditions to form a transparent self-cleaning photocatalytic coating. Refer to the paper entitled "Synthesis of peroxy-modified anatase sol from peroxytitanic acid solution" in the Journal of The Ceramic SocietyOf Japan by H. Ichinose et al., Vol. 104, No. 914- 917 pages (1996), and the paper titled "Photocatalytic activity of coating films prepared from peroxotitanic acid solution-derived anatase sol", Volume 104, No. 8, pages 715-718 (1996 ). These papers describe a method of putting a small amount (0.85% to 1.7%) of various forms or morphologies (polymorphs) of titanium dioxide (TiO2) into an aqueous solution by reacting with hydrogen peroxide.

These solutions are called Titanium Peroxidase-TiO(OOH)2. Amorphous titanium dioxide is a component that causes the product to have film-forming and adhesive properties. The mixture is composed of equal weights of amorphous and anatase (crystalline) forms of titanium dioxide, can dissolve up to about 2% by weight of the composition in water, and can be applied under ambient conditions.

U.S. Patent 6,107,241 (Ogata, etc.) and 6,429,169 (H. Ichinose) disclose anatase titanium oxide sol with a pH of 7.5 to 9.5 and a particle size of 8-20 nanometers, which is a yellow suspension that is passed through the following Step manufacturing: adding ammonia or sodium hydroxide to a titanium salt such as a titanium tetrachloride solution, washing and separating the formed titanium hydroxide, treating the formed titanium hydroxide with an aqueous hydrogen peroxide solution, and heating the formed stable amorphous Titanium peroxide sol, the sol has a concentration of about 2.9%, a pH of 6.0 to 7.0, a particle size of 8 to 20 nanometers, and a yellow transparent color, reaching a temperature of 100°C or higher to form anatase titanium oxide Sol. The anatase titanium oxide sol may be subsequently heated to a temperature of 250° C. or higher to convert it into anatase titanium dioxide.

Amorphous titanium peroxide sol has good bonding strength, but has poor wettability to the substrate, is not photocatalytic, and is slightly yellow in color. The anatase titanium formed by heating the amorphous titanium peroxide sol to a high temperature is photocatalytic. Therefore, a mixture of amorphous titanium peroxide sol and anatase titanium oxide sol was manufactured to provide a mixed sol coating composition in which more photocatalysts can be added, for example, in powder form with a particle size of less than 10 nanometers Titanium dioxide, and other inert additives, such as inorganic and organic binder materials, which are transparent and compatible with titanium peroxide sol, so as not to change the pH or transparency of the solution. Even a small amount of TiO2 or other ingredients with a particle size of about 10 nanometers will make the composition opaque and therefore cannot be satisfactorily used as a self-cleaning coating on glass or other transparent substrates. The coating must be applied in the form of several layers or immersion liquids to provide sufficient adhesion, but the end result is that the yellowish color of each layer is enhanced, creating an unsatisfactory appearance on the window glass. Multiple layers are necessary because the peroxide-forming film is very hydrophobic, so the coating composition does not have good wettability to the glass, and tends to bead on the glass, leaving "blank spots" or uncoated Covered area, so multiple cover layers are required.

Methods of producing both an aqueous solution of amorphous titanium peroxide and anatase particles in the range of 6 to 10 nanometers are described in U.S. Patent Nos. 6,107,241 and 6,429,169. When the peroxide decomposes or reacts with water, the amorphous titanyl peroxide forms an insoluble film. This acts as a carrier for the anatase particles.

Applying the film alone, or embedding the particles therein, has the following problems when applied to glass, plastic, or metal.

1. The film former is very hydrophobic and cannot be wetted to form a continuous film. In order to form a continuous film or cover layer, a large amount of composition or a thick composition layer is required. The surface tension of the peroxide-containing film is to some extent offset by the additional thickness and weight of the film. This application time and labor make the use of the product impractical.

2. The formation of the film is difficult, and the color is slightly yellow due to the presence of residual and unreacted titanyl peroxide. If the weight and thickness of the film are increased to overcome the surface tension of the titanyl peroxide solution to form a continuous coating on the substrate, the above-mentioned problems will be exacerbated.

3. When applied to glass, the transparency and transparency of the coating is impaired because an excessive thickness is required to overcome the non-wettability of the substrate. The refractive index and excessive thickness of the film thus produced result in interference patterns and appear to have an iridescent effect when viewed through transparent glass.

The photochemically active component is anatase polymorph. The polymorph of peroxotitanic acid has no photochemical activity. The photochemically active polymorph is obtained by heating the amorphous titanyl peroxide sol at a temperature of 100 degrees Celsius for six hours.

The peroxytitanate polymorph has a yellow color, which remains in the product, even when it is mixed with titanium peroxidase-this yellow color is unfavorable for transparent window panes. However, the solubility of TiO2 is related to the addition of peroxide; without peroxide, TiO2 cannot be dissolved. Therefore, for many applications, it is highly desirable and necessary to completely remove or reduce this yellowness as much as possible to provide a transparent self-cleaning window coating.

Summary of the invention

The present invention relates to a novel method for producing a novel aqueous composition containing a photochemically active metal oxide (MO2), which can be coated or sprayed and dried under ambient conditions to form a novel photochemically active colorless coating , The coating has strong wettability and adhesion to transparent substrates such as window glass.

Metal oxide photocatalysts usable in the present invention include TiO2, ZnO, SrTiO3, CdS, CdO, CaP, InP, In2O3, CaAs, BaTiO3, K2NbO3, Fe2O3, Ta2O5, WO3, SaO2, Bi2O3, NiO, Cu2O, SiC, SiO2, MoS2, MoS3, InPb, RuO2, CeO2, etc. Among these, titanium oxide is preferable. Titanium oxide can be used in the form of particles or powder or in the form of sol.

The use of a suitable wetting agent or reagent mixture reduces the non-wetting or hydrophobicity of the amorphous film containing titanium peroxide, making it easier to apply a thinner film. This reduces interference patterns and yellowness, because thinner films have much less yellow characteristics, and also allow for faster curing, and can eliminate yellow-causing peroxides over time. A suitable wetting agent is polyethylene oxide silane in an amount of 0.01 to 1% of the dry weight of the film-forming agent (titanium peroxide sol). This material is commercially available, such as Dow Chemicals' silicone Q25211 superwetting agent (polyethylene oxide silane).

Applying an acrylic polyurethane polymer solution as a primer on the glass can act as a barrier layer, which can block the migration of sodium and potassium ions from the substrate to the titanium layer and hinder the photocatalysis.

Acrylic aliphatic polyurethane polymers can replace all or part of the titanium peroxide sol and provide additional film-forming and wettability properties. Acrylic polyurethane polymers reduce or eliminate the amount of titanyl peroxide required, and thereby reduce or eliminate the yellow color. Acrylic urethanes are the film-forming counterparts of titanyl peroxides that form insoluble films. Also because of the high oxidation resistance of the polymer, it is resistant to self-aging and is compatible with the titanium amorphous film-forming agent. In addition, by reducing the refractive index of the coating and allowing the application of thin films, it reduces interference patterns. The chemical properties of the polymer are as follows: the acrylic diol is terminated with ethylene oxide. The molecular weight or hydroxyl number of the diol formed is between 110 and 150 mg KOH per gram of solid diol polymer. At this time, the aliphatic diisocyanate is added at a stoichiometric ratio of 2 to 3 to one. The diisocyanate may be isophorone diisocyanate (IPDI, Huls Chemical), or methylene biscyclohexyl diisocyanate (Mondur W., Bayer Chemical). Other cyclic aliphatic diisocyanates can also be used. As the proportion of diisocyanate increases, the polymer becomes harder and more resistant to chemicals. The use of an acrylic backbone ensures a high degree of oxidation resistance and chemical resistance. For example, marine paint is based on polyurethane acrylic resin.

The use of a small amount of dimethylolpropionic acid and subsequent salt formation allows the urethane acrylic resin to enter the aqueous solution. The chain extender typically includes ethylene glycol. For this purpose, when used as a support for anatase particles, methylene biscyclohexyl diamine is used to form a particularly hard and oxidation resistant film.

In the prior art, there is no explicit mention of the use of a peroxide mechanism for controlled degradation. Once the peroxide is formed from the MO2 (TiO2) metal oxide, and the mineral is turned into a sol state, and if it is soluble in water, the following method can be used for nano-preparation.

By heating at 100 degrees Celsius, the peroxide starts to decompose. Therefore, it is allowed to mix MO2 units in their natural crystalline state. In the case of titanium dioxide, the anatase particles formed are in the range of 6 to 10 nanometers. At this time, it is considered impossible to obtain such a small range by grinding. Below 40 nanometers, TiO2 will be re-annealed or recombined due to the generated heat and grinding pressure. In addition, the distribution of particles, relative to the number of particles present, contains 1 to 1/2% of very large particle agglomerates. This hinders transparency in the case of TiO2.

The following examples are examples of preparing compositions suitable for applying colorless self-cleaning coatings on glass, metal, and other substrates.

Example 1 Material dry weight wet weight titanyl peroxide sol 1.00 100 nanometer anatase particles 1.00 100 polyethylene oxide silane 0.10 10.0 Example 2 titanyl peroxide sol 1.00 100 nanometer anatase particles 1.0 100 polyurethane acrylic copolymer 1.0 2.857 polyethylene oxide silane. 20 2.0 Example 3 nano anatase particles 1.00 100 diisocyanate (DMPA and 1.00 2.00 IPDI adduct) polyethylene oxide silane 0.10 10.0 tertiary amine catalyst (polycat .10 .1041, air products)

Example 4 Nano anatase particles 2.00 200 DMPA IPDI adduct 1.0 2.0 Polyethylene oxide silane 0.10 10.0 Polyurethane acrylic polymer 1.0 2.857 Polycat 41 .10 .10 Example 5 Nano anatase particles 2.0 200 DMPA IPDI addition 1.0 2.0 Polyethylene oxide silane. 10 10.0 Polycat 41 (tertiary amine) .10 .10 Example 6 Nano anatase particles 1.0 100 Titanium peroxide sol 0.5 50 Polyethylene oxide silane 0.10 10 polyurethane acrylic polymer 0.5 1.4285 Example 7 nano anatase particles 1.0 100 titanyl peroxide sol. 5 50 polyethylene oxide silane. 10 10 DMPA IPDI adduct. 5 1.0 Polycat 41 .10. The 10DMPI adduct is the reaction product of one mole of dimethylpropionic acid and two moles of isophorone diisocyanate. It is a water-soluble, stable crosslinking agent. The adduct is aliphatic and does not turn yellow. It is water-soluble. Isocyanates are stable in water for a practical period of time, so they can react in several ways. One will be the final reaction of the isocyanate with water to form an amine, which will immediately react with the isocyanate to form a film.

Polycat 41 is a tertiary amine catalyst that trimerizes isocyanate to form a hard film, which is compatible with anatase sol particles and forms an active photocatalytic film. The trimerization produces an optically transparent film that has a higher visible light transmittance than the polyurethane polymer itself.

The present invention preferably involves the use of all photochemically active transition elements represented by MO2, M is a transition metal, and O2 is its oxide, most preferably TiO2 and ZrO2.

It should be understood that the above description is merely an example of the present invention. Without departing from the present invention, those skilled in the art can design various alternatives and modifications. Therefore, the present invention intends to include all such alternatives, modifications and changes that fall within the scope of the appended claims.