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

Field of invention

The present invention provides titanium dioxide (TiO) for producing a transparent paint having a self-cleaning effect.₂) Or zirconium oxide (ZrO)₂) Photocatalytically active oxides of transition metals, such as catalysts (MO or MO₂) Containing photocatalytic activity (PCA) paint, the transparent self-cleaning paint is an organic compound or contaminant that deposits on the glass window, for example, from the ambient environment when irradiated with sunlight, especially containing ultraviolet light. Reacts with or decomposes. Organic pollutants are CO₂, H₂It is decomposed into simple inorganic compounds such as O and various inorganic acids, which are returned to the atmosphere and / or washed away by the effects of heat, wind and / or rain. The paint is MO₂Self-cleaning with an efficiency determined by the activity of the catalyst, which efficiency is the MO with which contaminants come into contact.₂It is directly proportional to the total surface area of the particles.

Anatase type TiO₂When a metal oxide such as powder is irradiated with ultraviolet light having a wavelength of about 390 nm or less, the electrons in the valence band are excited to the conduction band, and the remaining positively charged holes are absorbed water vapor. Reacts with oxide ions. As a result, positively charged hydroxyl radical (OH)⁺Is formed. Hydroacid radicals are CO from organic pollutants₂And H₂It is a strong oxidative radical that can react with or remove electrons to produce a simple, inert product such as O, or HCl if halogen contaminants are involved.

Commercially available TiO₂As a powder photocatalyst, there is Degussa P25, which is 55 ± 15 m in a 30 nm aggregate.²g^-170: 30% mixture of anatase type / rutile type having a BET specific surface area and a crystal size of 0.1 nm. Degussa P25 constitutes an aqueous suspension in dilute alcohol that forms a chalky, catalytic coating on the glass. As a reference, there is a paper entitled "Photocatalytic Degradation of A Gaseous Organic Pollutant" published in the Journal of Chemical Education (Vol. 25, No. 6, June 1998.) and written by Yu et al.

In order to form a transparent self-cleaning photocatalytic coating film, TiO can be applied to a surface such as a window glass or dried under a predetermined environment.₂It is desirable to produce a formulation. As a reference, the title Synthesis Of Peroxo-Modified Anatase Sol From Peroxo-Titanic Acid Solution (Vol. 104, pages 914-917 (1996)) was written by H. Ichinose et al. In the Journal Of The Ceramic Society Of Japan. And the paper "Photocatalytic Activities Of Coating Films Prepared From Peroxotitanic Acid Solution- Derived Anatase Sols" (Vol. 104, No. 8, pages 715-718 (1996)). These treatises show that titanium dioxide (TiO) in various forms or shapes (polyforms) in aqueous solution by hydrogen peroxide treatment.₂) Is added in small amounts (0.85% to 1.7%).

These solutions are titanium peroxidase TiO (OOH)₂is called. Amorphous titanium dioxide is a component that provides the film properties and adhesiveness of the product. The mixture comprises the same amount of amorphous titanium dioxide and anatase (crystalline) titanium dioxide, is soluble in water up to about 2 weight percent of the formulation and can be applied under predetermined circumstances.

US Pat. Nos. 6,107,241 (Ogata et al.) And 6,429,169 (Ichinose) disclose anatase-type titanium oxide sol having a pH of 7.5 to 9.5 and a particle size of 8 to 20 nm, and the anatase-type titanium oxide sol is ammonia. Water or sodium hydroxide is added to a titanium saline solution such as titanium tetrachloride to wash and separate the formed titanium hydroxide, and the formed titanium hydroxide is treated with an aqueous hydrogen hydrogen solution. A stable, amorphous hydrogen peroxide sol with a concentration of about 2.9% formed, a pH of 6.0-7.0, a particle size of 8-20 nm, and a transparent yellow color above 100 ° C. A yellow suspension produced by heating. It can then be heated above 250 ° C to convert the anatase-type titanium oxide sol to anatase-type titanium dioxide.

Amorphous titanium peroxide sol has good adhesive strength, but has poor wettability to a substrate, is not photocatalytic, and has a yellowish color. The anatase-type titanium formed by heating the amorphous titanium peroxide sol to a high temperature has photocatalytic properties. Therefore, a mixture of amorphous titanium peroxide sol and anatase-type titanium oxide sol is produced to provide a mixed sol paint. The mixed sol coating may be supplemented with a photocatalyst such as powdered titanium dioxide having a particle size of less than 10 nm and other inert additives such as inorganic and organic binders. The active additive is transparent and can be mixed with the peroxotitanium sol so as not to change the pH or clarity of the solution. TiO with a particle size of about 10 nm₂Such materials will be opaque and inadequate to be used as a self-cleaning coating on transparent substrates such as glass with only a small amount. The coating process requires the formation of multiple layers or the application of a dipping process to provide sufficient adhesion, but as a result the yellowish color of each layer increases, which is unsatisfactory on the window glass. Comes to form the appearance. The reason why multilayer films are needed is that the molded coatings of peroxides are highly hydrophobic, so the paint does not have good wettability to the glass, leaving a holiday or unapplied area on the glass. This is because it tends to be spherical and requires a plurality of layers on one surface.

The process for producing amorphous titanium peroxide aqueous solutions and anatase-type particles in the 6-10 nm range is described in US Pat. Nos. 6,107,241 and 6,429,169. Amorphous titanium peroxides form an insoluble film when the peroxide chemically changes or reacts with water. It serves as a carrier for anatase-type particles.

The use of the coating alone or the coating containing particles causes the following problems when used against glass, plastic or metal.

1. The film-forming agent is highly hydrophobic and not moist to form a continuous film. A large amount of paint or thick paint layer is required to form a continuous coating or covering. Surface tension or peroxide-containing coatings can be overcome to some extent by increasing the thickness and weight of the coating. The time and effort required to apply these makes the use of the product impractical.

2. It is difficult to form a film, and the film has a yellowish color due to the presence of residues and unreacted titanium peroxide. This is a problem when increasing the weight and thickness of the coating to form a continuous coating on the substrate and to overcome the surface tension of the titanium peroxide solution.

3. The thickness required to overcome the non-wetting property to the substrate will reduce the translucency and transparency of the paint when applied to the entire surface of the glass. The index of refraction and excess thickness of the film produced results in a moire pattern and an apparent rainbow effect when viewed through clear glass.

The photochemically active ingredient is an anatase-type polymorph. The polymorph of peroxytitanate has no photochemical function. Photochemically active polyforms are obtained by heating amorphous titanium peroxide at 100 degrees Celsius for 6 hours.

The polymorph of peroxytitanic acid retains a yellow coloration in the product, even when mixed with titanium peroxidase. This yellow coloration is not preferable for transparent window glass. But TiO₂Solubility is related to the addition of peroxide, TiO in the absence of peroxide₂Does not dissolve in solution. As a result, it is highly desirable and required for many applications to completely remove or reduce the yellow coloration as much as possible in order to provide a transparent self-cleaning window coating.

Outline of the invention

The present invention is a novel photochemically active metal oxide (MO) containing an aqueous formulation.₂), In order to form a novel photochemically active and colorless coating having high wettability and strong adhesion to a transparent substrate such as window glass. It can be applied or sprayed under a predetermined environment and dried. The photocatalysts of metal oxides that can be used in the present invention are TiO sub.2, ZnO, SrTiO sub.3, CdS, CdO, CaP, InP, In sub.2 O sub.3, CaAs, BaTiO sub.3, K sub.2 NbO sub.3, Fe sub.2 O sub.3, Ta sub.2 O sub.5, WO sub.3, SaO sub.2, Bi sub.2 O sub.3, NiO, Cu. Includes Sub.2 O, SiC, SiO sub.2, MoS sub.2, MoS sub.3, InPb, RuO sub.2, CeO sub.2, etc. Of these, titanium oxide is preferred. Titanium oxide may be used in the form of particles or powders or in the form of sol.

By using a suitable wetting agent or combination of chemicals, the non-wetting or hydrophobicity of the titanium peroxide-containing amorphous coating is alleviated, and the thin film can be easily applied. Since the thin film has few yellow properties, this also reduces moire patterns and yellowing, and also allows for the removal of peroxides and rapid curing that cause yellowing over time. A suitable wetting agent is polyethylene oxide silane in an amount of 0.01-1% of the dry weight of the film-forming agent (titanium peroxide sol). This material is commercially available as DowChemicals Silicone Q25211 superwetting agent (polyethylene oxide silane).

The use of the acrylic urethane polymer solution as the primary coating over the glass surface acts as a barrier to sodium and potassium ions that move from the substrate into the titanium layer and block the photocatalyst.

Aliphatic acrylic urethane polymers can be replaced entirely or partially with titanium peroxide sol, providing additional coating and wetting properties. Acrylic urethane polymers reduce or remove the amount of titanium peroxide required and, as a result, reduce or remove yellow coloration. Acrylic urethane is a film that forms a counterpart of titanium peroxide that forms an insoluble film. In addition, due to the high oxidation resistance of the polymer, acrylic urethane is not easily self-altered and can be mixed with a titanium amorphous film forming agent. In addition, acrylic urethane reduces the moire pattern by reducing the refractive index of the coating film as well as making it possible to apply a thin film. The chemical properties of the polymer are as follows.

Acrylic diol is capped with ethylene oxide. The molecular weight or number of hydroxyl groups of the diol formed corresponds to 110-150 mg of KOH per gram of solid diol polymer. At this point, aliphatic diisocyanate is added in a stoichiometric ratio of 2 to 3 per 1. The diisocyanate may be isophorone diisocyanate (IPDI Huls Chemical) or methylenebiscyclohexyldiisocyanate (Mondur W. Bayer Chemical). Other alicyclic diisocyanates can also be used. As the proportion of diisocyanate increases, the polymer becomes harder and more chemical resistant. This fact and the use of acrylic backbones guarantee high oxidation and chemical resistance. For example, marine paints are based on urethane acrylic.

The use of small amounts of dimethylolpropionic acid and the formation of secondary (subsequent) salts allow the urethane acrylic to dissolve in aqueous solution. The chain extender usually contains ethylene glycol. The use of methylenebiscyclohexylamine results in the formation of a particularly hard, oxidation-resistant film when used as a carrier for anatase-type particles.

The use of a peroxide mechanism, which is a controlled decomposition, has not been explicitly described in the prior art. Once the peroxide is MO₂(TiO₂) If formed from metal oxides and the inorganic compound is in a sol state and is also water soluble, the following process is used for nanofabrication.

By heating to a temperature of 100 degrees Celsius, the peroxide begins to decompose. Therefore, MO₂It becomes possible to combine in units and become a natural crystalline state. In the case of titanium dioxide, anatase-type particles are formed in the range of 6-10 nm. Achieving such a small range in milling is not considered possible at this time. Below 40 nm, TiO₂Is reannealed or recombined by the heat generated and the pressure of grinding. In addition, the degree of concentration with respect to the number of particles, that is, the distribution of particles, contains 1 to 1/2% of extremely large aggregates of particles. This means TiO₂In the case of, it hinders transparency.

The following examples are examples of compounding formulations suitable for use in coatings that are colorless and have a self-cleaning effect on substrates such as glass and metals.

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The DMPI adduct is the reaction product of 1 mole of dimethylpropionic acid and 2 moles of isophorone diisocyanate. The DMPI adduct is a water-soluble and stable cross-linking agent. The adduct is aliphatic, does not have a yellow color, and is water-soluble. Isocyanates have a stable usable time in water and can be reacted in several ways. One is the final reaction of the isocyanate with water, forming an amine that reacts immediately with the isocyanate to form a film. Polycat 41 is a tertiary amine catalyst that forms a trimer of isocyanate that can be mixed with anatase-type sol particles that form an active photocatalytic coating so as to form a hard coating. Trimer formation produces an optically transparent coating that is more transparent to visible light than the polyurethane polymer itself.

The present invention is preferably MO₂With respect to the use of all photochemically active transition elements indicated by, M is a transition metal and O₂Is an oxide of M, TiO₂And ZrO₂Is most preferable.

It should be understood that the above description is merely an example of the present invention. Various replacements and modifications can be made by one of ordinary skill in the art without departing from the present invention. Accordingly, the present invention includes any replacement, modification and modification within the appended claims.