GB2327428A

GB2327428A - Photocatalytic glass article

Info

Publication number: GB2327428A
Application number: GB9815371A
Authority: GB
Inventors: Yoshihiro Nishida; Hiroshi Honjo; Takeshi Kondo; Hideki Yamamoto; Seiji Yamazaki
Original assignee: Central Glass Co Ltd; Nissan Motor Co Ltd
Current assignee: Central Glass Co Ltd; Nissan Motor Co Ltd
Priority date: 1997-07-15
Filing date: 1998-07-15
Publication date: 1999-01-27
Anticipated expiration: 2018-07-15
Also published as: GB2327428B; GB9815371D0; DE19831610A1

Abstract

A photocatalytic article has (a) a soda-lime glass substrate; (b) a first layer formed on the substrate; and (c) a second layer formed on the first layer comprising titania. The first layer contains a silica and at least one metal or alumina. The at least one metal is selected from the group consisting of titanium and metals each having an electronegativity close to that of titanium eg Zr,Al,V,Cv,Mn,Zn, or Sc. The photocatalytic article is excellent in durability, since the second layer is superior in adhesion to the first layer. The first layer is produced by decomposing a solution containing either a precursor of silica and a compound of at least one of said metals or a solution containing a precursor of silica and a precursor of alumina. The second layer is produced by applying a solution containing titania and/or a precursor of titania. The second layer may contain a further oxide selected from SiO 2 , Al 2 O 3 , P 2 O 5 , B 3 O 3 , ZrO 2 , SnO 2 or Ta 2 O 5 .

Description

2327428 PHOTOCATALYTIC GLASS ARTICLE AND METHOD FOR PRODUCING SAME

The contents of Japanese Patent Application Nos. g190294 and 9-224796, having filing dates of July 15, 1997 and August 21, 1997 respectively, are hereby incorporated by reference. BACKGROUND ()F THE INVENTION

The present invention relates to a photocatalytic glass article having an outermost photocatalytic film, for uses in io various fields such as architectural, automotive window panes and mirrors.

In recent years, there have been proposals to form photocatalytic films on various substrates for providing stain resistance, deodorizing property, antibacterial property, is hydrophilicity, and the like. For example, Japanese Patent First Publication JP-A-5-253544 discloses a method for producing a platelike member having a function of deodorization. In this method, a glaze (binder) layer is formed on a tile substrate. Then, a fine powder of anatase-type Ti02 in the form of sol is applied to the glaze layer. Then, the glaze layer is melted by heating and then solidified by cooling. With this, part of the Ti02fine powder is exposed on the glaze layer.

JP-A-7-232080 discloses a multifunctional material having a substrate, a binder layer formed thereon, and a photocatalytic layer made up of photocatalytic particles and filler particles for binding together the photocatalytic particles. It is disclosed therein that the photocatalytic particles may be made of Ti02, ZnO, SrTiO3, FC203,CdS, CdSe, WO,,, FeTi03, GaP, GaAs, RuO2, MoSs, LaRhO3, CdFeOa, Bi20a, MOS2, In203, CdO, and Sn02. It is further disclosed that the filler particles are preferably made of metals such as Sn, Ti, Ag, Cu, Zn, Fe, Pt, Co, Pd as well as Ni and oxides of these metals. JP-A-9-59042 discloses a transparent substrate having an antifogging coating thereon.

This coating is made of a mixture of a medium having a refractive index of less than 2 and titania particles having an average crystal particle diameter of not larger than about 0.1 u m. It is known, when a photocatalytic titania film is directly formed on a Na±containing glass (e.g., soda-lime glass) substrate, sodium ions and alkali metal oxides may diffuse from the glass substrate into the photocatalytic film. With this, the photocatalytic activity of titania may be damaged. In view of lo this, there have been several proposals for forming a metal oxide interlayer under a functional film in order to prevent migration of sodium ions from a substrate (e.g., soda-lime glass) into the functional film. For example, JP-A-4-182327 discloses a functional glass plate laving a Na.-containing glass substrate; an ultraviolet- absorbing functional film containing ZnO and having a thickness of at least 0.5 tt m; and an undercoat layer (Interlayer) interposed between the glass substrate and the functional film. This undercoat layer is made of a metal oxide such as Si02, SiO2-TiO2 or Si02-ZrO2.

JP-A-7-315880 discloses a glass plate intended to be used as a touch panel that is superior in visibility. This glass plate has a transparent glass substrate, a first Si02 filM formed on the substrate, a second T102 film formed on the first film, and a third SnO2 transparent conductive film formed on the second film. The third film has a resistance of 0.54,5 KO1D. JP-A 8-190088 discloses a coated glass article having (a) a transparent glass substrate containing alkali metal ions; (b) a barrier layer formed on the glass substrate, for preventing diffusion of the alkali metal ions; and (c) a metal-containing coating formed on the barrier layer. The barrier layer has a thickness of not greater than 120A and is made of a metal oxide selected from zirconium oxide and titanium oxide. The metalcontaining coating is made of a conductive metal oxide 0 selected from indium oxide, inclaluminum oxide. SUMMARY OF 111E INVENTION

It was found that, when a Si02 filln is used as an interlayer for preventing diffusion of sodium ions from a substrate into a photocatalytic film, the photocatalytic film may become inferior in adhesion to the interlayer. With this, the photocatalytic film may exfoliate from the interlayer, for example, in a revere environment.

It is therefore an object of the present invention to provide a photocatalytic article that is superior in durability.

It is a more specific object of the present invention to provide a photocatalytic article having a photocatalytic film that is superior in adhesion to an interlayer thereof.

It is another object of the present invention to provide a method for producing such photocatalytic article.

According to the present invention, there is provided a photocatalytic article comprising (a) a soda-hme glass substrate; (b) a first layer (interlayer) formed on the substrate; and (c) a second layer (photocatalytic layer) formed on the first layer and comprising a titania.

According to a first aspect of the present invention, the first layer compn- see (1) a silica and (2) at least one metal selected from the group consisting of titanium and metals each having an electronegativity close to that of titanium. In fact, the first layer is a Si02-based film containing the at least one metal as a special additive. The Si02-based film refers to a film containing S102 as a main component thereof. The second layer according to the first aspect of the invention is a Ti02based film or a Si02-based film in which titania fine particles are dispersed. The Ti02-based film also refers to a film containing TiO2 as a main component thereof. We unexpectedly found that the bond strength between the above is tin oxide, indium/tin oxide, and first and second layers improves remarkably. We assume that this improvement was induced by a good compatibility or interaction between the at least one metal of the first layer and titanium of the second layer. Thus, the photocatalytic article according to the first aspect of the invention becomes superior in durability tests with respect to water resistance, humidity resistance, alkali resistance and the like. We further unexpectedly found that it becomes possible to prevent migration of sodium ions from the soda-lime glass substrate to the second photocatalytic layer. In other words, the first layer contributes to the alkali passivation. We still further unexpectedly found that the photocatalytic activity of the second layer becomes sufficiently high by the provision of the above-mentioned special first layer.

According to the first aspect of the present invention, there is provided a method for producing the above-mentioned photocatalytic article. 'Phis method comprises the steps of (a) providing a first solution comprising a precursor of the silica and at least one compound containing the at least one metal; (b) applying the first solution to the substrate, thereby to form a first precursory layer; (c) providing a second solution comprising the titania and/or a precursor of the titania; (d) applying the second solution to the first precursory layer, thereby to form a second precursory layer; and (e) baking the first and second precursory layers into the first and second layers.

According to a second aspect of the present invention, the first layer comprises (1) a silica and (2) an alumina. In fact, the first layer is a Si02-based film containing the alumina as a special additive. The second layer according to the second aspect of the invention is a TiO2-based film. We unexpectedly found that the first layer becomes higher in compactness bythe addition of an alumina to the Si02-based first layer. We further unexpectedly found that it becomes possible to prevent dissolution of the first layer's silica and migration of sodium ions from the soda-lime glass substrate to the photocatalytic second layer. We still furthermore unexpectedly found that the bond strength between the first and second layers improves remarkably. We assume that this improvement was induced by an interaction between the alumina of the first layer and titanium of the second layer. Thus, the photocatalytic article according to the second aspect of the invention becomes superior in durability tests with respect to water resistance, humidity resistance, alkali resistance and the like. We further unexpectedly found that a high temperature treatment of the photo'catalytic article does not interfere with the prevention of sodium ion's migration.

According to the second aspect of the present invention, there is provided a method for producing the above-mentioned photocatalytic article. This method comprises the steps of (a) providing a first solution comprising a precursor of the silica and a precursor of the alumina; (b) applying the first solution to the substrate, thereby to form a first precursory layer; (c) providing a second solution comprising the titania andlor a precursor of the titania; (d) applying the second solution to the first precursory layer, thereby to form a second precursory layer; and (e) baking the first and second precursory layers into the first and second layers. DESCRIPTION OF THE PREFERRED EMBODIMENTS

A photocatalytic article according to the first aspect of the present invention will be described in detail as follows.

In the first aspect of the invention, the first layer of the photocatalytic article comprises at least one metal selected from the group consisting of titanium and metals each having an electronegativity close to that of titanium. In general, "electronegativity" refers to a relative tendency of an atom or group of atoms to attract electrons to itself. For example, according to J. Inorg. Nucl. Chem., 17, 215 (1961), electronegativity of titanium is 1.54. The above-mentioned metals of the first layer are preferably in a range of from 1.3 to 1.7 in electronegativity. These metals are preferably Zr, AI, V, Cr, Mn, Zn and Sc. According to J. Inorg. Nuel. Chem., 17, 215 (1961), these preferable metals are respectively 1.33, 1.61, 1.63, 1.66, 1.55, 1. 65, and 1.36 in electronegativity. When the first layer is required to be colorless, transparent and acid resistant, the at least one metal is preferably selected hom the group consisting of Ti, Zr, and AI.

In the first aspect of the invention, it is preferable that the first layer contains 1-30 mol% of the at least one metal. La case that the first layer contains titanium, its content therein is preferably 1-10 moM Similarly, in case of Zr, its content therein is preferably 2-15 moM Similarly, in case of AI, V, Cr, Mn, Zn, and Sc, they are preferably 5-12 mol%, 5-9 mol%, 6-10 mol%, 1-9 mol%, 5- 10 mol%, and 1-7 mol%, respectively. When the second layerls a Si02-based film containing therein titania fine particles, the content of the titania fine particles in the second layer is preferably from 10 to 90 wt%.

In the first aspect of the invention, it is preferable that the first solution of the step (a) of the method for producing the photocatalytic article contains a hydrolysate of an alkoxysilane as a precursor of the silica. Furthermore, it is preferable that the first solution further contains at least one compound containing the at least one metal, which is selected from the group consisting of (1) nitrates of the at least one metal, (2) salts prepared by combining organic acids and hydroxides of the at least one metal, (3) acetylacetonates of the at least one metal, and (4) alkoxides of the at least one metal. The content of the at least one metal in the first layer is preferably from 1 to 30 mol%, based on the total number of moles of the solid matter contained in the first solution. If it is greater than 30 mol%, the prevention of sodium ion's migration from the soda-lime glass substrate to the second layer may become insufficient. With this, the photocatalytic activity of the second layer may become poor. If it is less than 1 mol%, the bond strength between the first and second layers may become too low.

In the first aspect of the invention, the thickness of the first layer is preferably from about 50 to about 200 xim, more preferably from about 80 to about 160 nm. If it is less than 50 nm, the prevention of sodium ion's migration from the substrate 10 into the second layer may become insufficient. With this, the photocatalytic activity of the second layer may become too low. If it is greater than 200 nm, that is not favorable from the economical viewpoint and may cause cracks on the first layer. The thickness of the second layer is preferably from about 50 to is about 700 xim. If it is less than 50 nin, the photocatalytic activity of the second layer may become insufficient. If it is greater than 700 nin, the photocatalytic activity of the second layer does not improve further as compared with a case that it is in a range of 50-700 nm. Furthermore, the second layer may 2o become poor in strength.

A photocatalytic article according to the second aspect of the present invention will be described in detail as follows.

In the second aspect of the invention, the content of alumina in the first layer is preferably from 1 to 80 wt%, more preferably from 5 to 60 wt%. If it is greater than 80 wt%, the prevention of sodium ion's migration from the substrate to the second layer may become insufficient. With this, the photocatalytic activity of the second layer may become poor. Furthermore, the photocatalytic article may become inferior in 30 alkali resistance. If it is less than 1 wt%, adhesion of the second layer to the first layer may become inferior. The content of titania in the second layer is preferably from 10 to 100 wt%. The second layer may further comprise at least one oxide selected from the group consisting of SiO2, A120s, P2Or,, B203, ZrO2, Sn02, and Ta205. Of these, at least one oxide selected fromSi02, A1, 20.3, P206 and B20a serves to form a socalled network structure in the second layer. In contrast, at least one oxide selected from Zr02, Sn02, and Ta20r, serves to improve the second layer in compactness and strength. In particular, Zr02 serves to make the second layer superior in alkali resistance. Sn02 serves to make the second layer higher in conductivity. TazO.5 serves to cut ultraviolet rays of io wavelengths near 280 nm, which are not related to the photocatalytic action of tiltania in the second layer. The first and second layers are each preferably in a range of 50-500 nin in thickness. As stated above, the second layer may comprise the above-mentioned at least,, one oxide. In this case, the second is solution may contain a mixture of the titania precursor and the at least one oxide, or crystalline or amorphous titania fine particles dispersed in a sol of a precursor of the at least one oxide.

In the second aspect of the invention, it is preferable that the first solution for forming the first layer contains a hyd. rolysate of an alkoxysilane as a precursor of the silica and a precursor of the alumina selected from the group consisting of aluminum nitrates, salts prepared by combining organic acids and aluminum hydroxides, aluminum acetylacetonates, and aluminum alkoxides. As stated above, the second solution for forming the second layer comprises titania andlor a titania precursor. When the second solution is free of the titania precursor but comprises titamia in the form of crystalline fine particles, the titania is in an amount such that the titania content of the second layer is preferably 10-90 wt%, more preferably 20- 80 wt%. If it is less than 10 wt%, the photocatalytic activity of the second layer may become infarior. If it is greater than 90 wt%, the second layer may become inferior in strength. Furthermore, it may become difficult to form the second layer. In contrast, when the second solution is free of titania but comprises a titania precursor, the titania precursor is in an amount such that the titania content of the second layer is preferably 50-100 wt%, more preferably 70-100 wt%. If it is less than 50 wt%, the photocatalytic activity of the second layer may become poor. Examples of the titania precursor contained in the second solution are titanium alk-oxides, titanium acetylacetonatos, titanium chloride, and titanium sulfate. The second solution may contain at least one of various solvents for dissolving the titania precursor. The second solution may further contain a stabilizing agent. It is optional to add water to the second solution in order to hydrolyze a titanium alkoxide or acetylacetonato.

In the second aspect of the invention, the thickness of the first layer is preferably from about 50 to about 500 run, more preferably from about 70 to about 130 nm. If it is less than 50 nm, the prevention of sodium ion's migration from the substrate into the second layer may become insufficient. With this, the photocatalytic activity of the second layer may become too low. If it is greater than 500 nm, that is not favorable from the economical viewpoint and may cause cracks on the first layer. The thickness of the second layer is preferably from about 50 to about 500 nm, more preferably 70-150 nm. If it is less than 50 nm, the photocatalytic activity of the second layer may become insufficient. If it is greater than 500 nm, the photocatalytic activity of the second layer does not improve further as compared with a case that lit lie in a range of 50-500 nm. Furthermore, the second layer may become poor in strength, and cracks may occur thereon.

In the first and second aspects of the invention, the shape of the sodalime glass substrate is not particularly limited, and it may be a platelike shape. The substrate may be selected from conventional float glass plates, which are generally used for automotive and architectural window panes. The substrate may be colorless or may have one of various colors, such as,green and bronze. It may have one or various additional functions such as heat reflection. It may be a tempered glass, a laminated glass, or a multiple glass. It may be flat or curved in shape. For example, it may have a thickness of from about 1.0 to about 12 min. It is preferable to have a thickness of ftom about 2.0 to about 10 min in architectural use. Furthermore, it is preferable to have a thickness of from about 1.5 to about 6.0 min, more preferably from about 2.0 to about 5.0 min, in automotive use.

In the first and second aspects of the invention, the precursor of the silica, contained in the first solution of the step is (a), may be selected from silicon alkoxides, such as tetraethoxysilane, tetramethoxysilane, monomethyltriethoxysilane, monomethyltrimethoxysilane, di-methyldimethoxysilane, dimethyldietho.x- ysilane, other tetraalkoxysilanes and other alk-ylalkoxysilanes. The precursor of the titania, contained in the second solution of the step (c), may be selected from titanium alkoxides, such as titanium tetraisopropoxide and titanium tetra-n-butoxide, and titanium acetylacetonates, such as titanium trilsopropoxy monoacetylacetonate.

In the first and second aspects of the invention, it is preferable to use an alcohol as a solvent for preparing the first and second solutions. Examples of the solvent are alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol and hexylene glycol; esters such as ethyl acetate, butyl acetate and amyl acetate; cellosolves (monoethers of ethylene glycol) such as methyl cellosolve, ethyl cellosolve and butyl cellosolve; and mixtures thereof. A suitable solvent may be selected from the above examples, in view of the evaporation rate of the solvent and the viscosity of the first and second precursory layers. In the invention, it is optional to add a thickener to the first andlor second solution. Examples of the thickener are a polyethylene glycol having an average molecular weight of 200, 5 a polypropylene glycol having an average molecular weight of 400, hydroxypropyl cellulose, and polyvinyl pyrrolidone. It is further optional to add a levelling agent to the first andlor second solution. Examples of the levelling agent are methyl silicones (e.g., dimethyl silicone) and fluorine -containing ones.

In the first and second aspects of the invention, the manner of applying the first and second solutions to the substrate and the first layer respectively is not particularly limited. It may be spin coating, dip coating, reverse roller coating, flexograpy, roller coating, coating with nozzle, spraying, or screen printing. It is preferable that each of the first and second solutions has a solid matter concentration of from about 1 to about 30 wt% and a viscosity of from about 1 to about 100 centipoises.

In the method for producing the photocatalytic article according to the first and second aspects of the invention, it is preferable to dry the first precursory layer between the steps (b) and (d) and the second precursory layer between the steps (d) and (e) at a temperature of from room temperature to about 30W, more preferably from about 100 to about 250r, for about 0.5 to about 60 minutes, more preferably from about 1 to about 30 minutes. The first and second precursory layers, preferably after the drying thereof, are baked in the step (e) preferably at a temperature of about 400-700t for about 1-30 min. The thermal tempering andlor the thermal bending of the photocatalytic article is preferably conducted, more preferably at a temperature of about 550-7001C for about 0.5-10 min, while the step (e) is conducted. Even if the thermal tempering andlor the thermal bending of the photocatalytic article is conducted at this temperature, sodium ion's diffusion is effectively prevented.

The following nonlimitative Examples 1-4 are illustrative of the first aspect of the present invention.

EXAMPLE 1

A photocatalytic article was produced as follows. At first, a first solution (sol) for forming the first layer on the substrate was prepared by diluting 10 times 10 g of a sol, MTS TI-20 (trade name) of Daffiachi Kagaku Kogyo Co., having a molar ratio of Si/TI of 75125 and a solid matter concentration of wt%, and 80 g of another sol, MTS-2 (trade name) of Dailiachi Kagaku Kogyo Co., containing Si in an amount of 100% and having a solid matter concentration of 20 wt%, with a solvent mixture prepared by mixing 3 parts by volume of lisobutyl acetate with 1 part by volume of n-butanol. Then, 2 cc of the obtained first solution was dropped on a soda-lime glass substrate having widths of 15 cm, and a thickness of 3.5 mm.

After that, a first precursory layer was formed on the substrate by spin coating, then was dried at 250t for 30 minutes, and then was cooled down to room temperature. The thus dried first precursory layer of a mixture of TiO2 and Si02 had a thickness of 100 nm. Then, the coated glass substrate was dipped into a solution containing a partial hydrolysate of titanium alkoxide, ATRON NTi-500 (trade name) of Nippon Soda Co., Ltd., and then was taken out thereof. After that, the coated glass substrate was dried at 2009C for 15 minutes and then was baked at 5OWC, thereby to form on the first layer a second layer of T102 having a thickness of 100 nni.

EXAMPLE2

A photocatalytic article was produced as follows. At first, the first solution for forming the first layer on the substrate was prepared by diluting 10 times a sol, CG-TI-10 (trade name) of Dailiachi Kagaku Koggyo Co., having a molar 1 ratio of Si/Ti of 90110 and a solid matter concentration of 20 wt%, with a solvent that was the same as that of Example 1. Then, the obtained first solution was applied by a reverse roller coating to a soda-lime glass substrate having the same dimensions as those of Example 1. The coated substrate was dried at 200t for 15 minutes, and then was cooled down to room temperature. The thus dried first precursory layer of a mixture of TiO2 and Si02 had a thickness of 150 tim. Then, the coated glass substrate was dipped into a solution containing a lo partial hydrolysate of titanium alkoxide, DT002 (trade name) of Nippon Soda Co., Ltd., and then was taken out thereof. After that, the coated glass substrate was dried at 200r, for 15 minutes and then was baked at 500t, thereby to form on the first layer a second layer of Ti02 having a thickness of 120 nm.

is EXAMPLE 3

A photocatalytic article was produced as follows. At first, the first solution for forming the first layer on the substrate was prepared by diluting 15 times a sol, CG-Zr-10 (trade name) of Daihachi Kagaku Kogyo Co., having a molar ratio of Sil& of 90/10 and a solid matter concentration of 20 wt%, with a solvent mixture prepared by mixing 2 parts by volume of ethanol with 1 part by volume of butyl cellosolve- Then, the obtained first solution was applied by a spin coating to a soda lime glass substrate having the same dimensions as those of Example 1. The coated substrate was dried at 2009C for 15 minutes, and then was cooled down to room temperature. The thus dried first precursory layer of a mixture of Zr02 and Si02 bad a thickness of 120 nm. Then, a solution containing a silica precursor and titania fine particles, ST-K03 (trade name) of Ishiliara Techno Co., was applied by spraying to the first precursory layer. After that, the coated glass substrate was dried at 20WC for 15 minutes and then was baked at 5009C, thereby to form on the first layer a second layer having a thickness of 160 nm. The second layer was a Si02-based film containing titania fine particles.

EXAMPLE4

A photocatalytic article was produced as follows. At first, the first solution for forming the first layer on the substrate was prepared by diluting 10 times 50 g of a sol, CG-19 (trade name) of Dalhachi Kagaku Kogyo Co., containing 10 wt% of S102, with a solvent mixture prepared by mixing 3 parts by volume of ethanol with 1 part by volume of n-butanol, in which solvent mixture 5.1 g of aluminum diisopropoxyacetylacetonato was dissolved. Then, the obtained first solution was applied by a spin coating to a soda-lime glass substrate having the same dimensions as those of Example 1. The coated substrate was dried at 2009C for 15 minutes, and then was cooled down to room temperature. The thus dried first precursory layer of a mixture of A120s and Si02 had a thickness of 160 nm. Then, a solution containing a silica precursor and titania fine particles, TINOC CA-62 (trade name) of Taki Chemical Co., Ltd., was applied by spraying to the first precursory layer. After that, the coated glass substrate was dried at 200t for 15 minutes and then was baked at 5009C, thereby to form on the first layer a second layer having a thickness of 150 nm. The second layer was a Si02-based film containing titania fine particles.

COMPARATIVE EXAMPLE 1 A photocatalytic article was produced as follows. At first, a soda-lime glass substrate that was the same as that of Example 1 was dipped into a silica precursor sol having a solid matter concentration of 6 wt%, COLCOAT N-103X (trade name) of Taiyo Bussan Co., and then was taken out thereof After that, the coated glass substrate was dried in the same manner as in Example 1, thereby to form thereon a first film of SiO2 having a thickness of 150 nin. Then, the coated glass Gubstrate was dipped into ATRON NTi-500 (trade name) of Nippon Soda 1 -is- Co., Ltd., and then was taken out thereof. After that, the coated glass substrate was dried and then baked in the same manners as those of Example 1, thereby to form on the first layer a second layer of TiO2 having a thickness of 100 nin.

The following nonlimitative Examples 5-9 are illustrative of the second aspect of the present invention.

EXAMPLE5

A photocatalytic article was produced as follows. At first, a first solution was prepared by mixing together 2 - of tetraethoxysilane, 1 g of aluminum nitrate nonahydrate, 0.7 g of water for hydrolysis, 0.06 g of 60% nitric acid (catalyst), and 40 g of ethanol (solvent). In the first solution, the weight ratio of silicon to aluminum on an oxide basis (Si02/A1203)was 80120.

The first solution was applied by spin coating to a soda-lime glass substrate having widths of 10 em and a thickness of 2 mm, thereby to form thereon a first precursory layer. After that, the coated substrate was dried at 250C for 5 min and then cooled down to room temperature.

A second solution was prepared at first by mixing together 8 g of a titania precursor sol, ATRON NTi-600 (trade name) of Nippon Soda Co., Ltd., and 3.3 g of a silica precursor sol, CSGDI-0600 (trade name) ofChisso Co. and then by diluting this mixture 4 times with ethanol. In the second solution, the weight ratio of titanium to silicon on an oxide basis M02/Si02) Was 80120. The second solution was applied to the first precursory layer, thereby to form thereon a second precursory layer. After that, the coated substrate was dried at 2501C for 5 min, and then was baked at 500'C for 5 min and then at 68OTC, thereby to turn the first and second precursory layers into first and second layers each having a thickness of nm.

EXAMPLE6

In this example, Example 1 was repeated except in that the second solution was prepared by diluting 4 times 100 g of a titania sol, ATRON NTi-500, with ethanol. The obtained second layer (TiO,2 film) had a thickness of 90 nm.

EXAMPLE 7

In this example, Example 1 was repeated except in that the first solution was prepared by mixing together 1.3 of tetraethoxysilane, 2.8 g of aluminum nitrate nonahydrate, 0.7 g of water for hydrolysis, 0,06 g of 60% nitric acid (catalyst), and 46 g of ethanol (solvent). In the first solution, the weight ratio lo of silicon to aluminum on an oxide basis (Si02/A1203) was 50150.

The obtained first layer had a thickness of 100 nm.

EXAMPLES

In this example, Example 1 was repeated except in that a first solution was prepd.red at first by mixing 18 g of a silica precursor sol, CSG-DI-0600 (trade name) of Chisso Co., with 2 g of an alumina precursor sol and then by diluting the resultant mixture 3 times with ethanol. In the first solution, the weight ratio of silicon to aluminum on an oxide basis (Si02/A1208) was 90/10. The alumina precursor sol was prepared at first by mixing together 10.5 g of isopropyl alcohol, 6 g of aluminum see-butoxide, and 3 g of ethyl acetoacetate, then. by stirring the mixture for stabilizing the same, and then by adding 0.5 g of water for hydrolysis. The obtained first layer (Si02-AI203 filM) had a thickness of 100 nm.

EXAMPLE 9

In this example, Example 1 was repeated except in that the preparation of the first and second solutions was modified as follows. In fact, the first solution was prepared at first by mixing 20 g of a silica precursor sol, CSG-DI-0600 (trade name) of Chisso Co., with 10 g of an alumina nitrate nonahydrate and then by diluting the resultant mixture 4 times with ethanol.

In the first solution, the weight ratio of silicon to aluminum on an oxide basis (Si02/A1203) was 30170.The second solution was 11 prepared by diluting 5 times a silica precursor sol containing titania fine particles, ST-03 (trade name) of Ishihara Techno Co., with ethanol. In the second solution, the weight ratio of titanium to silicon on an oxide basis (Ti02/Si02) was 50150. The obtained first layer (Si02-AI203 film) had a thickness of 100 nin, and the obtained second layer had a thickness of 150 nm.

COMPARATIVE EXAMPLE 2 In this comparative example, Example 1 was repeated except in that a silica precursor sol, CSG-DI-0600 (trade name) of Chisso Co., having a solid matter concentration of 6 wt%, was used as the first solution. The obtained first layer (Si02 filM) had a thickness of 100 nm.

COMPARATIVE EXAMPLE 3 In this example, Example 1 was repeated except in that a first solution was prepared at first by mixing 16 g of a silica precursor sol, CSG-DI- 0600, with 4 g of a titania precursor sol and then by diluting the resultant mixture 3 times with ethanol. In the first solution, the weight ratio of silicon to titanium on an oxide basis (Si02/TiO2) was 80120. The titania precursor sol was prepared at first by mixing together 9 g of isopropyl alcohol,.3 g of titanium -iso-prop oxide, and 1 g of acetylacetone, then by stirring the mixture for stabilizing the same, and then by adding 0.2 g of water for hydrolysis. The obtained first layer (SiO2-TiO2 film) had a thickness of 100 nin.

COMPARATIVE EXAMPLE 4 In this example, Example 1 was repeated except in that a first solution was prepared at first by mixing 16 g of a silica precursor sol, CSG-DI- 0600, with 4 g of a zirconia precursor sol and then by diluting the resultant mixture 3 times with ethanol. In the first solution, the weight ratio of silicon to zirconia on an oxide basis (Si02/ZrOz) was 80120. The zirconia precursor sol was prepared at first by mixing together 15 g of isopropyl alcohol, 4 g of zirconium-n-butoxide, and 1 g of acetylacetone, then by stirring the mixture for stabilizing the same, and then by adding 0.2 g of water for hydrolysis. The obtained first layer (SiO2-ZrO2film) had a thickness of 100 nni.

EVALUATION TESTS Photocatalytic articles of Examples 1-9 and Comparative Examples 1-4 were subjected to the following evaluation tests.

A photocatalytic activity test was conducted by applying an acetone solution containing 1 wt% of oleic acid to the surface of the second layer of each photocatalytic article, thereby to form a uniform oleic acid film on the second layer. Then, the coated photocatalytic article was irradiated for 2 hrs with ultraviolet rays having an intensity of 0.5MWICM2and a wavelength of 365 nm, using a light source, BLACK LIGHT F15T8BLB (trade name).Df Sankyo Denki Co. Then, the photocatalytic activity of the photocatalytic article was evaluated by the difference of the contact angle of water drop disposed on the coated photocatalytic article before and after the irradiation. The contact angles before the irradiation with respect to the photocatalytic articles according to Examples 1-4 and Comparative Example 1 were in a range of 22-24 degrees, and those after the irradiation were respectively 5, 3, 6, 4, and 4 degrees. The results of Examples 5-9 and Comparative Example 2-4 are shown in Table. It can be understood that the photocatalytic articles according to Examples 1-9 and Comparative Examples 1-2 are superior in photocatalytic activity, as compared with those according to Comparative Examples 3-4.

Table

Contact ngles (p) Before Ultraviolet After Ultraviolet Irradiation Irradiation Example 5 48 5 E%ample 6 55 2 Example 7 45 5 Exe S 43 6 Example 9 46 4 Com. Ex. 2 54 2 Com. Ex. 3 64 19 Com. Ex. 4 51 24 A water resistance test was conducted by immersing the photocatalytic article in a hot water of WC for ten days in total.

At intervals of certain periods of time during the test, a gauze s cloth was strongly rubbed against the second layer of the photocatalytic article in the hot water. Then, the external appearance of the photocatalytic article was observed. With this, it was found that the photocatalytic articles according, to Examples 1-9 and Comparative Examples 3-4 did not change in io external appearance even after ten days of the test. In contrast, it was found that those according to Comparative Examples 1-2 had exfoliation of the second layer from the first layer after a lapse of two days of the test.

A humidity resistance test was conducted by allowing the photocatalytic article to stand still for 30 days in total in an atmosphere of 50r, and a relative humidity of 98%. At intervals of certain periods of time during the test, a gauze cloth was rubbed thereagainst in the same manner as in the water resistance test. With this, it was found that the photocatalytic:

articles according to Examples 1-9 and Comparative Examples 3-4 did not change in external appearance even after 30 days of the test. In contrast, it was found that the photocatalytic articles according to Comparative Examples 1-2 had exfoliation of the second layer from the first layer after a lapse of 12 days.

An acid resistance test was conducted by immersing the photocatalytic article in 0. 1% hydrochloric acid aqueous solution for 48 hr under room temperature. Then, a gauze cloth was rubbed thereagainst in the same manner as in the water resistance test. With this, it was found that all the s photocatalytic articles according to Examples 1-9 and Comparative Examples 1-4 did not have any visible change in external appearance.

An alkali resistance test was conducted by immersing the photocatalytic article in 20% sodium carbonate aqueous solution for 48 hr in total under room temperature. At intervals of certain periods of time during the test, a gauze cloth was rubbed thereagainst in the same manner as in the water resistance test. With this, it was found that the photocatalytic articles according to Examples 1-9 and Comparative Examples is 3-4 did not change in external appearance even after 48 hr of the test. In contrast, it was found that the photocatalytic articles according to Comparative Examples 1-2 had exfoliation of the second layer from the first layer after a lapse of 11 hr.

A salt water resistance test was conducted by immersing the photocatalytic article in 3% salt water of 60t for 48 hr in total. At intervals of certain periods of time during the test, a gauze cloth was rubbed thereagainst in the same manner as in the water resistance test. With this, it was found that all the photocataly-tic articles according to Examples 1-9 and 2-5 Comparative Examples 3-4 did not have any visible changes in external appearance even after a lapse of 48 hr. In contrast, it was found that the photocatalytic articles according to Comparative Examples 1-2 had an exfoliation of the second layer from the first layer. In fact, the exfoliation occurred after a lapse of 5 hr in Comparative Example 2.

Claims

-21CLAIMS

1. A photocatalytic article comprising:

(a) a soda-lime glass substrate; (b) a first layer formed on said substrate, said first layer comprising (1) silica and (2) at least one metal selected from titanium and metals each having an electronegativity close to that of titanium; and (c) a second layer formed on said first layer, said second layer comprising titania.

A photocatalytic article according to claim 1, said second layer is made of said titania.

A photocatalytic article according to claim 1, said second layer comprises silica in which fine particles are dispersed.

A photocatalytic article according to any one of claims 1 to 3, wherein said metals of said first layer have an electronegativity of from 1.3 to 1.7.

5. A photocatalytic article according to claim 4, wherein said metal of said first layer is selected from Zr, Al, V, Cr, Mn, Zn and Sc.

6. A photocatalytic article according to claim 5, wherein said metal is selected from Zr and Al.

7. A photocatalytic article according to any one of claims 1 to 6, wherein said first layer contains 130 mol% of said at least one metal.

8. A.photocatalytic article according to claim 3, 2. wherein 3.

wherein titania wherein said second layer contains 10-90 wt',' of said titania fine particles.

9. A photocatalytic article according to any one of claims 1 to 8, wherein said first layer has a thickness of from about 50 to about 200 nm, and said second layer has a thickness of from about 50 to about 700 nm.

10. A photocatalytic article according to any one of claims 1 to 9, wherein said first layer comprises at least one oxide of said at least one metal.

11. A photocatalytic article according to claim 10, wherein said first layer comprises an oxide of aluminum.

12. A method for producing a photocatalytic article as defined in claim 1, said method comprising:

(a) providing a first solution comprising a precursor of silica and at least one compound containing said at least one metal; (b) applying said first solution to said substrate, thereby forming a first precursory layer; (c) providing a second solution comprising titania and/or a precursor of titania; (d) applying said second solution to said first precursory layer, thereby forming a second precursory layer; and (e) baking said first and second precursory layers to form said first and second layers.

13. A method according to claim 12, wherein said precursor of silica in (a) is a hydrolysate of an alkoxysilane, and wherein said at least one compound containing said at least one metal in (a) is selected from nitrates of said at least one metal, salts prepared by combining organic acids and hydroxides of said at least one metal, acetylacetonates of said at least one metal, and alkoxides of said 14. A method according at least one metal. to claim 12 or 13, wherein said first solution contains l30 mol% of said at least one metal, based on the total number of moles of all solid matter present in said first solution.

15. A method according to any one of claims 12 to 14, wherein (e) is conducted at a temperature of from about 400 to about 7000C for about 1 to about 30 minutes.

16. A method according to any one of claims 12 to 15, wherein, prior to (d), said first precursory layer is dried at a temperature of from room temperature to about 3000C for about 0.5 to about 60 minutes, and wherein, second precursory layer is dried at room temperature to about 3000C for 60 minutes.

prior to (e), said temperature of from about 0.5 to about 17. A photocatalytic article comprising:

(a) a soda-lime glass substrate; (b) a first layer formed on said substrate, said first layer comprising (1) silica and (2) alumina; and (c) a second layer formed on said first layer, said second layer comprising a titania.

18. A photocatalytic article according to claim 17, wherein said first layer contains 1-80 wt% of alumina.

19. A photocatalytic article according to claim 17, wherein said second layer contains 10-100 wt% of said titania.

20. A photocatalytic article according to claim 18 or 19, wherein when said titania of said second layer is in the form of crystalline fine particles, said second layer containing 10-90 wt% of said titania.

21. A photocatalytic article according to any one of claims 17 to 20, wherein said second layer further comprises at least one oxide selected from SiO2, A12031 P205, B20,, Zr02. Sn02 and Ta205.

22. A photocatalytic article according to any one of claims 17 to 21, wherein each of said first and second layers has a thickness of from 50 to 500 nm.

23. A method for producing a photocatalytic article as defined in claim 17, said method comprising:

(a) providing a first solution comprising a precursor of silica and a precursor of alumina; (b) applying said first solution to said substrate, thereby forming a first precursory layer; (c) providing a second solution comprising -25titania and/or a precursor of titania; (d) applying said second solution to said first precursory layer, thereby forming a second precursory layer; and (e) baking said first and second precursory layers to form said first and second layers.

24. A method according to claim 23, wherein said precursor of silica in (a) is a hydrolysate of an alkoxysilane, and said precursor of alumina in (a) is selected from aluminum. nitrates, salts prepared by combining organic acids and aluminum hydroxides, aluminum. acetylacetonates, and aluminum alkoxides.

25. A method according to claim 23 or 24, wherein, when said second solution in (c) is free of said precursor of titania but comprises titania in the form of crystalline fine particles, and wherein the titania contained in said second solution is in an amount such that said second layer contains 10-90 wt% of titania.

26. A method according to claim 23 or 24, wherein, when said second solution in (c) is free of titania but comprises said precursor of titania, and wherein the precursor of titania contained in said second solution is in an amount such that said second layer contains 50-100 wt% of titania..

27. A method according to any one of claims 23 to 26, wherein (e) is conducted at a temperature of from -26about 400 to about 7000C for about 1 to about 30 minutes.

28. A method according to any one of claims 23 to 27, wherein, prior to (d), said first precursory layer is dried at a temperature of from room temperature to about 30CC for about 0.5 to about 60 minutes, and wherein, prior to (e), said second precursory layer is dried at a temperature of from room temperature to about 3000C for about 0.5 to about 60 minutes.

1.

&7 Amendments to the claims have been filed as follows 1.

A photocatalytic article comprising:

(a) a soda-lime glass substrate; (b) a first layer formed on said substrate, said first layer comprising (1) silica and (2) at least one metal containing compound, the metal(s) being selected from titanium and metals each having an electroneaativity close to that of titanium; and (c) a second layer formed on said first layer, said second layer comprising titania.

2. A photocatalytic article according to claim 1, wherein said second layer is made of said titania.

3. A photocatalytic article according to claim 1, wherein said second layer comprises silica in which titania fine particles are dispersed.

4. A photocatalytic article according to any one of claims 1 to 3, wherein said metals of said first layer have an electronegativity of from 1.3 to 1.7.

5. A photocatalytic article according to claim 4, wherein said metal of said first layer is selected from Zr, AI, V, Cr, Mn, Zn and Sc.

6. A photocatalytic article according to claim 5, wherein said metal is selected from Zr and AI.

7. A photocatalytic article according to any one of claims 1 to 6, wherein said first layer contains 1-30 mol% of said at least one metal.

8. A photocatalytic article according to claim 3, 04 fV2 C:P1 z:> 13. A method according to claim 12, wherein said precursor of silica in (a) is a hydrolysate of an alkoxysilane, and wherein said at least one compound containina said at least one metal in (a) is selected ftom nitrates of said at least one metal, salts prepared by combining organic acids and hydroxides of said at least one metal, acetylacetonates of said at least one metal, and alkoxides of said at least one metal.

14. A method according to claim 12 or 13, wherein said first solution contains 1-30 mol% of said at least one metal, based on the total number of moles of all solid matter present in said first solution.

15. A method according to any one of claims 12 to 14, wherein (e) is conducted at a temperature of from about 400 to about 700T for about 1 to about 30 minutes.

16. A method according to any one of claims 12 to 15, wherein, prior to (d), said first precursory layer is dried at a temperature of from room temperature to about 30TC for about 0.5 to about 60 minutes, and wherein, prior to (e), said second precursory layer is dried at a temperature of from room temperature to about 30CC for about 0.5 to about 60 minutes.

17. A photocatalytic article according, to claim 11, wherein said first layer comprises (1) silica and (2) alumina.

0: a 4 a c9 18. A photocatalytic article according to claim 17, wherein said first layer contains 1-80 wt% of alumina.

19. A photocatalytic article according to claim 17, wherein said second layer contains 10-100 wt% of said titania.

20. A photocatalytic article according to claim 18 or 19, wherein when said titania of said second layer is in the form of crystalline fine particles, said second layer containing 10-90 wt% of said titania.

21. A photocatalytic article according to any one of claims 17 to 20, wherein said second layer further comprises at least one oxide selected frOM Si02, A1203, P205, B203, Zr02, Sn02 and Ta20,.

22. A photocatalytic article according to any one of claims 17 to 21, wherein each of said first and second layers has a thickness of from 50 to 500 rim.

23. A method for producing a photocatalytic article as defined in claim 17, said method comprising:

(a) providing a first solution comprising a precursor of silica and a precursor of alumina; first precursory layer; (c) (b) applying said first solution to said substrate, thereby forming a I- providing a second solution comprising