Photocatalytically-activated self-cleaning article and method of making same

to L

68.778/ZE

SBG & K.

International

H-1062 B^SX^b^AM

Phone: 34-24-950, ifk/J ΓJ S Fl I -U

Photocatalytically activated self-cleaning object and method for producing it

Reference to related invention applications

This application is incorporated by reference into U.S. Provisional Application No. 60/040566, filed March 14, 1997, and No. 60/040565, filed March 14, 1997.

With provisional application filed on 14th I and US 0/899265 No.:

It is also related to the co-filed application entitled "Photocatalytically Activated Self-Cleaning Devices", which is incorporated by reference. Subject of the Invention

The present invention relates to a method for producing a photocatalytically activated self-cleaning coating on a substrate (e.g., a glass sheet or a continuous, floated glass ribbon), a method for preventing sodium ion contamination of a photocatalytically activated self-cleaning coating deposited on a sodium ion-containing substrate, and articles produced by these methods.

Description of the state of the art

For many substrates (e.g. glass substrates), it is desirable that the substrate surface remains “clean,” i.e. free from surface contamination, such as common organic or inorganic surface contaminants. Traditionally, this has meant that such surfaces have had to be cleaned frequently. This cleaning operation is typically performed manually or by mechanical means. Both methods are labor-, time-, and/or cost-intensive. Therefore, there is a need for substrates that have a self-cleaning surface or at least are easier to clean, which would eliminate or reduce the need for such manual or mechanical cleaning.

Titanium dioxide (TiO₂) coatings are known to provide a photocatalytically activated self-cleaning surface (hereinafter "PASC") on a substrate. Publications on the formation of a PASC titanium dioxide coating on a glass substrate include USP 5,595,813 and Paz et al., "Photooxidative Self-cleaning transparent titanium dioxide films on glass" [Mater J. Res., Vol. 10, 11, 2842-48 (November 1995)]. Furthermore, a bibliography of patents and publications on the photocatalytic oxidation of organic compounds is included in Blake D.: “Bibliography of work on the catalytic removal of hazardous compounds from water and air”, National Renewable Energy Laboratory (May 1994, October 1995 and October 1996).

One available method for depositing a PASC coating (e.g., titanium dioxide PASC coating) onto a substrate is the sol-gel method. The sol-gel method involves applying a non-crystalline, alcohol solvent-based colloidal suspension (the sol) to a substrate at or around room temperature by spraying, spinning, or dipping. The substrate is then heated to about 100-800°C in order to bond the PASC coating to the substrate and/or to induce crystallization of the PASC coating to form a crystallized PASC coating (gel) on the substrate.

The application of a sol-gel PASC coating by sol-gel coating may not be compatible with certain application conditions or substrates. For example, if a PASC coating is applied to a supported web during its manufacture, the web may be too hot to accept the sol, depending in part on the solvent used in the sol solution. For many solvents used in the sol-gel process, it is necessary to cool the hot web of the support to about room temperature before applying the sol thereto, and then reheat the support to a temperature high enough to crystallize the sol into a PASC coating. Such cooling and reheating operations require significant equipment, energy, and handling costs, and significantly reduce production efficiency.

The PASC activity of PASC coatings can be significantly reduced or destroyed if sodium ions are present in the substrate and migrate from the substrate into the PASC coating. This phenomenon is known as sodium poisoning or sodium ion poisoning. For many types of substrates containing such sodium ions, the rate of sodium ion flux into the coatings increases with increasing substrate temperature. Thus, another limitation of the sol-gel coating method is that reheating the substrate increases the possibility of sodium ion migration and also sodium ion poisoning of the PASC coating.

Another limitation of the formation of PASC coatings by the sol-gel method is the thickness of the coatings (10'⁶ meter “M”) thickness of many microns. Such thick PASC coatings may have a detrimental effect on the optical and/or aesthetic properties of PASC-coated objects.

As is apparent from the foregoing, there is a need for an article of manufacture comprising a deposited PASC coating and a method for depositing such a PASC coating that does not have the disadvantages known in the art.

Summary of the invention

The invention relates to a PASC manufactured article comprising at least one surface and a PASC coating, for example titanium dioxide, deposited on the surface of a substrate by chemical vapor deposition (hereinafter referred to as "CVD"), spray pyrolysis or magnetron sputtering vacuum deposition (hereinafter referred to as "MSVD").

The invention also provides a PASC fabricated article having at least one surface coated with a sodium ion diffusion blocking layer (hereinafter referred to as "SIDB"), such as a layer of tin oxide, titanium dioxide, aluminum oxide, or a mixture thereof, deposited on the surface of the substrate, and a PASC layer, such as a layer of titanium dioxide, deposited on the SIBD layer. The PASC coating and the SIDB layer are each deposited by CVD, spray hydrolysis, or MSVD. The invention also provides a method for producing such a manufactured article.

Description of the drawings

Figure 1 is a cross-sectional view of a portion of a substrate having a PASC coating dispersed thereon, Figure 2 is a view similar to Figure 1 showing a SIDB layer disposed between the substrate and the PASC coating, Figure 3 is a schematic view of selected components of a CVD coating apparatus, and Figure 4 is a schematic view of selected components of a spray pyrolysis coating apparatus.

Description of the preferred embodiments

Referring to Figure 1, there is shown an article comprising components of the invention. The article 20 comprises a substrate 22 having a RASC coating 24 disposed thereon. The substrate 22 is not limited to the invention and may comprise a glass substrate, such as a glass plate or a continuous float glass ribbon, a plastic substrate, a metal substrate, and an enameled substrate.

The PASC coating 24 may be deposited directly on the substrate 22, as shown in FIG. 1, or alternatively, other layers may be interposed between the PASC coating 24 and the substrate 22, including, but not limited to, a SIDB layer 26, as shown in FIG. 2, which will be described below. Furthermore, those skilled in the art will recognize that the PASC coating 24 may be the topmost coating of a multilayer coating present on the substrate 22, or the PASC coating 24 may be incorporated into such a multilayer system as one of the layers other than the topmost layer, provided that sufficient actinic radiation can pass through any of the coatings above the PASC coating 24 to photocatalytically activate the PASC coating 24, and provided that that active radicals can pass through the coatings deposited over the 24 PASC coating and react with organic contaminants present in the top layer of the multilayer structure.

The 24 PASC coating may be any coating that can be activated to be self-cleaning and that can be deposited by CVD, spray pyrolysis, or MSVD. For example, although not limiting to the invention, the PASC coating 24 may comprise one or more metal oxides, such as titanium oxides, iron oxides, silver oxides, copper oxides, tungsten oxides, aluminum oxides, silicon oxides, zinc stannanes, molybdenum oxides, zinc oxides, zinc/tin oxides, strontium titanate, or mixtures thereof. The metal oxides may include oxides, superoxides, or metal suboxides.

A preferred 24 PASC coating is a titanium dioxide coating. Titanium dioxide exists in one amorphous and three crystalline forms, namely anatase, nitrile and brookite. Anatase phase titanium dioxide is preferred because it exhibits strong PASC activity while also having high resistance to chemical attack and excellent physical durability. Anatase phase titanium dioxide also has a high light transmittance in the visible wavelength range of the spectrum, which provides these anatase titanium dioxide coatings with excellent optical properties. Rutile phase titanium dioxide also exhibits PASC activity. Combinations of these anatase and/or rutile phases with brookite and/or amorphous phases are also acceptable for the purposes of the present invention, provided that these combinations exhibit PASC activity.

The PASC coating 24 must be sufficiently thick to provide an acceptable level of PASC activity. There is no absolute value for whether a PASC coating is “acceptable” or “unacceptable,” because whether a PASC coating has an acceptable level of PASC activity is largely determined by the purpose and circumstances under which the PASC-coated object is used, and the performance requirements associated with that purpose. In general, thicker PASC coatings have higher PASC activity. However, other considerations would suggest that a thinner coating is more appropriate, and thinner coatings are also advantageous when the object needs to have high light transmission for aesthetic or optical reasons; surface contaminants on the object's surface can be easily removed with a thinner PASC coating; the coating is exposed to significant radiation and/or the PASC coating is subject to sodium ion poisoning as discussed in more detail below. For a wide range of applications, it is preferred that the PASC coating be at least about 200 Angstroms thick, preferably at least about 400 Angstroms thick, more preferably at least 500 Angstroms thick. It has been found that where substrate 22 is a float glass piece and PASC coating 24 is an anatase titanium dioxide PASC coating formed directly on the float glass pieces by CVD, a thickness of about 500 Angstroms provides a PASC reaction rate of about 2x10'³ - 5x10'³/cm/minute (hereinafter referred to as 'cm')¹.what'¹”) range according to the stearic acid test film removal when the PASC coating is exposed to a light source, such as ultraviolet radiation, such as that sold under the name UVA-340 type by Q-Panel Company of Cleveland, Ohio, USA, with an intensity of approximately 20 Watts/square meter (hereinafter referred to as W/m²) on the surface of the PASC coating, which is acceptable for a wide range of applications.

According to the present invention, a thin layer, e.g., 1 μ (10') thick, is deposited on the substrate 22 by spray pyrolysis CVD or MSVD.⁶ m), more preferably less than 05 μ. In the spray pyrolysis method, a metal-containing precursor is carried in the form of an aqueous suspension, for example an aqueous solution, and in the case of the CVD method, in a carrier gas, and this solution or gas is directed onto the surface of the substrate 22 while maintaining the surface of the substrate 22 at a temperature high enough to cause decomposition of the metal-containing precursor and formation of the PASC coating 24 on the substrate 22. In the MSVD method, a sputtered coating is applied to a substrate 22 under negative pressure in an inert or oxygen-containing atmosphere. The substrate 22 is heated during or after the coating to induce crystallization of the sputtered coating and formation of the PASC coating 24.

Each of the methods has advantages and limitations, for example, the CVD method and the pyrolysis method are preferable to the spray pyrolysis method because the spray pyrolysis method may result in a 24 PASC coating in the presence of OH' ions, which in turn may prevent proper crystal formation in the 24 PASC coating, thereby reducing the PASC activity of the coating. The CVD method and the pyrolysis method are preferred over the MSVD method because they are compatible with the coating of continuous substrates, such as float glass ribbons, at higher temperatures. The CVD spray pyrolysis and MSVD methods for depositing the 24 PASC coating are discussed in more detail below. As can be understood, spray pyrolysis and CVD methods can be used to deposit thin (e.g., a few hundred Angstroms thick) metal oxide coatings (including titanium dioxide coatings) on a substrate. Such coatings are described in USP 4,344,986; 4,393,095; 4,400,412; 4,719,126; 4,853,257 and 4,971,843.

Metal-containing precursors that can form titanium dioxide PASC coatings using the VCD method in the practice of the present invention include, but are not limited to, titanium tetrachloride (TiCl₄), the titanium tetraisopropoxide [Ti(OC₃H₇)4] (hereinafter referred to as “TTIP”) and titanium tetraethoxide [Ti(OC₂H₅)4)] (hereinafter referred to as “TTEt”). Carrier gases that can be used in the CVD method include air, nitrogen, oxygen, ammonia and mixtures thereof. The preferred carrier gas is nitrogen and the preferred metal-containing precursor is TTIP. The concentration of the metal-containing precursor in the carrier gas is generally 0.1-0.4% by volume for the three listed precursors, but as will be understood by those skilled in the art, these concentrations may vary for other metal-containing precursors.

In the practice of the present invention, metal-containing precursors that can be used to prepare PASC coatings by spray pyrolysis include relatively water-insoluble organometallic reagents, particularly metal acetylacetonate compounds, which can be used dry or wet at about 10 μ (10'⁶ m) and suspended in an aqueous medium using a chemical wetting agent. A metal acetylacetonate suitable for the preparation of a titanium dioxide PASC coating is titanyl acetylacetonate [TiO(C₂H₇HE₂)₂J. The relative concentration of metal acetylacetonate in the aqueous suspension is preferably about 5 to 40% by weight. The wetting agent may be any low-foaming surfactant, such as anionic, nonionic or cationic compounds, but nonionic compounds are preferred. The wetting agent is typically used in an amount of about 0.24% by weight, but may be used in an amount of about 0.01% to 1% or more. The aqueous medium is preferably distilled or deionized water. Aqueous suspensions suitable for pyrolytic deposition of metal-containing films are described in USP 4,719,127, particularly in the portion from column 2, line 16 to column 4, line 48, which is incorporated herein by reference.

In both the VCD and spray pyrolysis methods, the temperature of the substrate 22 during the formation of the PASC coating 24 to be formed thereon must be maintained within a range that causes decomposition of the metal-containing precursor and a

PASC activity coating (e.g., a crystalline phase in the case of metal oxide PASC coatings). As will be appreciated, the lower limit of this temperature range is greatly influenced by the decomposition temperature of the metal-containing precursor chosen. For the titanium-containing precursors listed above, the minimum temperature of the substrate 22 that will cause adequate decomposition of the precursor will be in the range of about 400-500°C. The upper limit of this temperature range may be influenced by the substrate to be coated. For example, if the substrate 22 is a float glass ribbon and the PASC coating 24 is applied thereto during the manufacture of the glass ribbon, the float glass temperature may be greater than 1000°C. The float glass ribbon is typically thinned or formed (e.g., drawn or extruded) at temperatures greater than 800°C. If the 24 PASC coating is applied when the float glass is before or during thinning, the 24 PASC coating may crack or wrinkle when the float ribbon is stretched or compressed. Therefore, in the practice of the invention, it is preferred to apply the PASC coating when the floated strip is dimensionally stable, e.g., for soda lime silica glass at about 800°C, and the floated strip is at a temperature at which the metal-containing precursor decomposes, e.g., greater than 400°C.

In the production of float glass ribbon, the CVD or spray pyrolysis process is particularly suitable for producing the 24 PASC coating. Float glass ribbon is generally produced by batch production by melting the glass raw materials in a furnace and transferring the molten glass to a molten tin bath. The molten glass is drawn as a continuous glass ribbon through the tin bath while being sized and controllably cooled to form a dimensionally stable float glass ribbon. The floated strip is then removed from the tin bath and conveyed by conveyor rollers to a softening furnace to temper the floated strip. The tempered floated strip is then passed through shredding stations on conveyor rollers where the strip is cut into glass sheets of the desired length and width. The float glass process is described in USP 4,466,562 and 4,671,155, which are incorporated herein by reference.

The temperature of the strip floated in the tin bath decreases from about 1093.3°C in the bath to about 538°C when it leaves the bath. The temperature of the floated strip between the tin bath and the tempering annealing furnace is generally about 80-580°C; the temperature of the floated strip in the tempering annealing furnace is generally 204-557°C.

USP 4,853,257; 4,971,843; 5,536,718; 5,464,657; and 5,599,387, which are incorporated herein by reference, describe CVD coating equipment and methods that can be used in the practice of the present invention to coat floated strip during manufacture. Since the CVD method can coat a moving float strip, yet withstand the stringent requirements during float strip production, the CVD method is well suited to provide float strip with a 24 PASC coating. CVD coating equipment can be used at many points in the float strip production process. For example, the CVD coating apparatus can be used when the floated strip passes through the tin bath, after exiting the tin bath, before entering the tempering annealing furnace, while passing through the tempering annealing furnace, or after exiting the tempering furnace.

As will be appreciated by those skilled in the art, the concentration of the metal-containing precursor in the carrier gas, the flow rate of the carrier gas, the speed of the floating strip (the "line speed"), the ratio of the CVD coating apparatus to the floating strip surface area, in particular the flow rate of the exhausted carrier gas through the discharge ports of the CVD coating apparatus, the ratio of the discharge and the carrier gas feed rates within the CVD unit, which is known as the “outflow fit ratio” and the temperature of the floated strip are among the parameters that influence the thickness and morphology of the 24 PASC coating formed on the floated strip by the CVD process.

USP 4,719,136; 4,719,127; 4,111,150 and 3,660,061, which are incorporated herein by reference, describe spray pyrolysis apparatus and processes with which the floated strip manufacturing process can be employed. Although the spray pyrolysis method, like the CVD method, is well suited to coating a moving strip, spray pyrolysis requires more complex equipment than CVD equipment and is generally used between the exit end of the tin bath and the inlet end of the tempering annealing furnace.

As will be appreciated by those skilled in the art, the concentration of the pyrolytically sprayed aqueous suspension, the speed of the floated web, the number of pyrolytic spray nozzles, the spray pressure or spray rate, the spray pattern, and the temperature of the floated web during deposition are among the parameters that influence the final thickness and morphology of the PASC coating 24 formed on the floated web by spray pyrolysis.

As is known to those skilled in the art, the surface of a glass ribbon floated on molten tin (commonly referred to as the "tin side") contains diffuse tin, which provides a pattern of absorbed tin on the tin side that is different from the other surface of the glass ribbon not in contact with the molten tin (commonly referred to as the "air side"). This feature was described by Seiger J. discussed in: “Chemical characteristics of float glass surfaces”, Journal of non-crystalline solids, vol. 19, pp. 213-220, 1995; Columbin L. et al., “Penetration of tin in the bottom surface of float glass: a synthesis”, Journal of non-crystalline solids, vol. 38 and 39, pp. 551-556, 1980; and Williams, KF Ε. et al., “Tin oxidation state, depth profiles of Sn²⁺ and Sn⁴⁺ and oxygen diffusivity in float glass by Mossbauer spectroscopy, Journal of non crystalline solids, vol. 211, pp. 164-172, 1997, which are hereby incorporated by reference. As will be understood by one skilled in the art, the 24 PASC coating can be formed on the air side of the floated strip (by CVD) while it is carried by the tin bath; on the air side of the floated strip after it has left the tin bath by CVD or spray pyrolysis; and on the tin side of the floated strip after it has left the tin bath by CVD. If the PASC coating 24 is formed on the tin side of the floated strip, it is expected that the tin and/or tin oxide present on the glass surface will act as a SIDB layer 26 on the PASC coating 24 disposed thereon.

USP 4,379,040; 4,861,669; 4,900,633; 4,9220,006; 4,938,857; 5,328,768, and 5,492,750, all of which are incorporated herein by reference, describe an MSVD apparatus and method for sputtering a metal oxide film coating onto a substrate, including a glass substrate. The MSVD process is generally not compatible with the purpose of depositing a PASC coating on a float glass ribbon during its manufacture because the MSVD process requires a vacuum, which is difficult to provide on a continuously moving float ribbon during the sputtering operation. However, the MSVD method is acceptable for the purpose of depositing a PASC coating on a substrate 22, such as a glass plate. As will be appreciated by those skilled in the art, the substrate 22 can be heated to approximately 400-500°C so that the sputtered MSVD coating crystallizes during the deposition process, thereby avoiding subsequent heating operations. Heating the substrate during sputtering is not preferred as it may reduce performance during the subsequent heating process. Alternatively, the sprayed coating can be crystallized directly in the MSVD apparatus without post-heating treatment by using a high-energy plasma, but this is also not a preferred method because it reduces the performance of the MSVD coating apparatus.

The preferred method for producing a PASC coating by the MSVD method is to spray a coating onto the substrate, remove the coated substrate from the MSVD coating apparatus, and then heat treat to crystallize the sprayed coating into the PASC coating 24. In the MSVD method, for example, and without limiting the invention, titanium metal is sputtered in an argon/oxygen atmosphere containing about 5-50%, preferably 20% oxygen, at a pressure of about 5-10 millitorr (0.67-1.33 Pascal) to deposit a titanium dioxide coating of a desired thickness by sputtering onto the substrate 22. The coating is not crystallized. The coated substrate is removed from the coating apparatus and heated to about 400-600°C for a period of time sufficient to promote the formation of the crystalline form of the titanium dioxide PASC and to ensure PASC activity. Heating at 400-600°C for at least one hour is generally preferred. If the substrate 22 is a glass sheet cut from a float glass ribbon, the PASC coating 24 may be deposited by sputtering onto the air-facing or tin-facing side thereof.

The substrate having the PASC coating 24 deposited by CVD, spray pyrolysis, or MSVD may then be subjected to one or more PASC coating, leveling operations to enhance the self-cleaning activity of the PASC coating 24. It is believed that such post-PASC coating leveling may enhance the self-cleaning activity of the PASC coating 24 by promoting the formation of the desired crystalline PASC phase. As will be appreciated, the duration and temperature of the equalization operation can be influenced by a number of factors, including the makeup of the substrate 22, the makeup of the PASC coating 24, the thickness of the PASC coating 24, and whether the PASC coating 24 is directly on the substrate 22 or whether there is a multilayer layer on the substrate 22. It has been determined that if the substrate 22 is a piece of float glass and the PASC coating is a 400 Angstrom or 625 Angstrom thick anatase titanium dioxide coating - formed by the spray pyrolysis method - then the coating should have a thickness of 500^QEquilibration at 13°C for 13 minutes increases PASC activity.

As described above, when the PASC coating is prepared by either CVD, spray pyrolysis, or MSVD, if the substrate 22 contains sodium ions that can migrate from the substrate 22 to the PASC coating deposited on the substrate, the sodium ions can inhibit the photocatalytic activity of the PASC coating or destroy it by forming inactive compounds, while titanium is consumed through the formation of sodium titanates or by inducing recombination of photoactivated charges.

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We have found that a PASC coating can be formed on a sodium ion-containing substrate without loss of photocatalytic activity by: 1) providing a limited, partial sodium ion poisoning of a portion of the PASC coating and/or 2) providing a 26 SIDB layer. Both methods are described in more detail below.

We found that if the thickness of the PASC coating exceeds a minimum threshold, the PASC activity is not destroyed by sodium ion migration even if the PASC coating is deposited on a sodium ion-containing substrate at a temperature high enough to induce sodium ion migration from the substrate into the PASC coating. Although the mechanism of this result is not fully understood, it is believed that if the thickness of the PASC coating exceeds a minimum value, sodium ions can penetrate only a portion of the total thickness of the PASC coating during the time the substrate temperature exceeds the temperature that allows sodium ion migration. Then, when the temperature drops below the value that causes sodium ion migration, the migration of sodium ions stops or "freezes in place", resulting in the thickness of the PASC coating opposite the side of the substrate surface free from sodium ion poisoning and can maintain PASC activity. This minimum thickness of the PASC coating, as will be understood by one skilled in the art, varies with expected parameters such as, but not limited to, the time the substrate is held above the temperature at which sodium ion migration occurs, the application in which the manufactured PASC product is to be used, and the desired or required level of PASC activity. It has been found that for a titanium dioxide PASC coating deposited on a piece of plain soda-lime silicate glass by a CVD process, the thickness of the PASC coating should be a minimum of about 250 Angstroms, preferably a minimum of about 400 Angstroms, and more preferably a minimum of about 500 Angstroms, in order for a sufficient portion of the PASC coating 24 to remain free of sodium ion poisoning and retain PASC activity.

Referring to Figure 2, in an alternative method of preventing sodium ion poisoning of the PASC coating, a SIDB layer 26 is provided between the PASC coating 24 and the substrate 22. The SIDB layer 26 may be the only layer between the PASC coating 24 and the substrate 22 or may be one layer of a multi-layer stack. If a multilayer assembly is used, it is not necessary for the SIDB layer 26 to contact the substrate 22, provided that the SIDB layer 26 is positioned between the PASC coating layer 24 and the substrate 22 to prevent sodium ion migration from the substrate 22 to the PASC coating 24.

The SIDB layer 26 may be formed from amorphous or crystalline metal oxides, including but not limited to cobalt, chromium, iron, tin, silicon, and aluminum, magnesium, zinc oxides, or mixtures thereof. Mixtures include, but are not limited to, magnesium/aluminum oxides and zinc/tin oxides. As will be understood by those skilled in the art, the metal oxide may be a metal oxide, superoxide, or suboxide. Although the thickness of the SIDB layer required to prevent sodium ion poisoning of the PASC coating depends on several factors, such as the length of time the substrate is held above the temperature above which sodium ion migration occurs, the rate of sodium ion migration from the substrate, the rate of sodium ion migration through the SIDB layer, the thickness of the PASC coating, and the degree of photocatalytic activity required for a particular application, for most applications the thickness of the SIDB layer should be at least about 100 Angstroms, preferably at least 250 Angstroms, and more preferably at least about 500 Angstroms to prevent sodium ion poisoning of the PASC coating. The SIDB layer can be deposited on the substrate 22 by CVD, spray pyrolysis, or MSVD. If spray pyrolysis or CVD is used, the substrate 22 is preferably maintained at a temperature of at least about 400° C. to ensure decomposition of the metal-containing precursor to form the SIDB layer. The SIDB layer may also be formed by other methods, such as sol-gel methods, which, as mentioned above, are not compatible with float glass ribbon production.

A tin oxide SIDB layer can be deposited on the substrate by spray pyrolysis by preparing an aqueous solution of dibutyltin difluoride [(C₄Hg)₂SnF2] suspension and the aqueous suspension are applied to the substrate by spray pyrolysis. The aqueous suspension typically contains 100-400 g of dibutyltin difluoride per liter of water. Wetting agents can be used to aid suspension. During the preparation of the aqueous suspension, the dibutyltin difluoride particles are 1-10 μ (10'⁶ m) can be ground to an average particle size. The aqueous suspension is preferably vigorously stirred to evenly distribute the particles throughout the suspension. The aqueous suspension is applied by spray pyrolysis to the substrate, which is maintained at at least about 400°C, preferably about 500-700°C, where the aqueous suspension pyrolyzes and forms a tin oxide SIDB layer. As can be seen, the thickness of the SIDB layer formed depends, among other parameters, on the speed of the coating equipment, the dibutyltin difluoride concentration of the aqueous suspension, and the spraying speed.

Alternatively, the tin oxide SIDB layer can be formed on the substrate by CVD from a metal-containing precursor such as monobutyltin trichloride (hereinafter referred to as “MBTTCL”) vapor prepared with an air carrier gas mixed with water vapor. The concentration of MBTTCL vapor in the air carrier gas may be at least about 0.5%, while the substrate is maintained at a temperature sufficiently high to cause decomposition of the tin-containing layer, for example at least 400°C, preferably about 500-800°C, to form the tin oxide SIDB layer. As can be understood, the thickness of the SIDB layer formed by this process can be controlled by, among other parameters, the speed of the coating equipment, the concentration of MBTTCL vapor in the carrier gas, and the gas flow rate.

A SIDB layer produced by the MSVD process is described in USP 08/597,543, which is incorporated herein by reference, and which describes the formation of alkali metal diffusion barriers. The barrier layer described herein is generally about 20-180 Angstroms thick and its effectiveness increases with the density of the barrier.

The PASC coatings of the present invention are conventionally photocatalytically activated to self-clean by exposure to ultraviolet radiation in the wavelength range of the electromagnetic spectrum, for example, 300-400 nanometers (hereinafter "nm"). Sources of ultraviolet radiation include natural sources such as sunlight, artificial sources such as black light, or ultraviolet light sources such as UVA-340 light sources. If artificial ultraviolet light sources are used in such test ranges: <· is used in cases where it is desirable to determine how the PASC coating will respond to natural ultraviolet radiation. As is understood, the UVA-340 light source has a photon energy distribution that more closely approximates sunlight than the photon energy distribution of a black light source, which allows us to use a UVA-340 light source to better approximate how the PASC coating will behave when exposed to sunlight.

The ultraviolet radiation intensity should be at least approximately 20 Watt/m² (hereinafter referred to as “W/m²) on the surface of the coating to be tested. The intensity can be calibrated, for example, with an ultraviolet measuring device such as the J-221 type device sold under the BLACKRAY® trademark, manufactured by Ultraviolet Products, Inc., San Gabriel, CA. The light source is preferably directed normal to the coating surface to be tested.

The ultraviolet radiation source and the PASC coating should be positioned relative to each other so that the ultraviolet radiation first passes through the PASC coating and then through the substrate (i.e. the front or “coating side”). If the substrate is transparent to ultraviolet radiation, the PASC coating and the ultraviolet radiation source should be positioned relative to each other such that the ultraviolet radiation first passes through the substrate and then through the PASC coating (i.e., backside or "substrate side" first). In yet another embodiment, one or more ultraviolet radiation sources may be positioned on both sides of a substrate having a PASC coating on one or both sides.

As can be seen, it is difficult to precisely determine a preferred ultraviolet radiation source or ultraviolet radiation intensity or relative radiation source/PASC coating/substrate placement because these are influenced by so many factors. Such factors include, but are not limited to: the purpose for which the PASC coating is applied, such as whether the application is indoor or outdoor; the chosen ultraviolet radiation source, such as whether it is natural or artificial; seasonal or geographical effects, if the ultraviolet radiation source is natural; the desired or expected duration of ultraviolet radiation; the angle of incidence of the ultraviolet radiation on the surface of the PASC coating; the expected or desired rate of PASC activity; the extent to which the substrate and/or the coating or layers present on the substrate or PASC coating can reflect or absorb ultraviolet radiation; the contaminants that can be removed; the thickness of the PASC coating; the composition of the PASC coating; the possibility of sodium ion poisoning and the presence or absence of a SIDB layer. It has been found that an ultraviolet radiation source placed above the surface of the PASC coating, measured at the surface of the PASC coating, of about 5-100 W/m²-, preferably at least 20 W/m²Ultraviolet radiation intensity of 10

In order to assess the PASC activity of a PASC coating, it is useful to be able to measure and compare the effectiveness or activity of PASC coatings. A known, readily available organic contaminant can be applied to the PASC coating, and the ability of the PASC coating to remove the organic contaminant can be observed and measured by photocatalytic activation of the PASC coating. Stearic acid [CH₃(CH₂)i₆COOH] is an organic “contaminant” model to investigate the PASC activity of PASC coatings because stearic acid is a carboxylic acid with a long hydrocarbon chain and is therefore a good “model molecule” for molecules present in common contaminants such as household oils and dirt. Stearic acid can be easily applied to PASC coatings by appropriate techniques such as dipping, spraying, spin coating. Test stearic acid films approximately 100-200 Angstroms thick provide a suitable test film.

Stearic acid is methanolic, about 6x10³ It can be used in the form of a solution containing 100 mol/l stearic acid, which proved to be suitable.

The PASC activity of PASC coatings can be qualitatively calculated by coating the PASC coating with a stearic acid film (the film usually appears as a light brown coating on the PASC coating), irradiating the stearic acid film with ultraviolet radiation of a desired intensity for a desired time, and examining the stearic acid film with the naked eye to see if it has completely disappeared or how much the darkness of the stearic acid film has decreased compared to a part of the stearic acid film that has not been exposed to UV radiation. which was applied to a PASC coating but which was not irradiated with ultraviolet radiation.

The PASC activity of PASC coatings can also be quantitatively measured by measuring the carbon-hydrogen (hereinafter referred to as “CH”) stretching vibrational absorption bands of stearic acid present in the PASC coating. The integrated intensity is proportional to the thickness of the stearic acid film remaining on the surface of the PASC coating and the photocatalytically activated self-cleaning of the stearic acid film is expected to result in a decrease in the intensity of the CH stretching vibrational absorption bands. The CH bonds present in stearic acid absorb infrared radiation, which, unlike ultraviolet radiation, does not photocatalytically activate the PASC coating. This absorption is typically at 2800-3000 cm'¹ is performed at a wavenumber and is performed with a Fourier transform infrared spectrophotometer (hereinafter referred to as an “FTIR spectrophotometer”). The FTIR can be equipped with a detector such as a deuterated triglycine surface detector (hereinafter referred to as a “DTGS detector”) or a mercury-cadmium-telluride detector (hereinafter referred to as an “MTC detector”). The MTC detector is preferred because it has a higher signal-to-noise ratio than the DTGS detector. This may be important if the substrate and/or other coatings other than the PASC coating absorb the infrared radiation that the spectrophotometer uses to generate the absorption spectrum. If the infrared radiation is absorbed by the substrate and/or other coatings, the intensity of the infrared beam passing through the PASC coating and substrate with the stearic acid film to the detector is significantly reduced. This, combined with the low concentration of stearic acid present in the PASC coating (which gives a very weak infrared absorption), results in the infrared radiation signal obtained being not particularly intense. Therefore, an instrument equipped with an MCT detector provides a spectrum in which the signal-to-noise ratio is about an order of magnitude higher than that of an instrument equipped with DTGS detectors. When a stearic acid test film deposited on films and substrates PASC active through which the infrared beam can pass, the infrared beam can be directed through the films and substrates to a detector placed on the opposite side of the sample to be tested. If the films or substrates do not allow infrared radiation to pass through them, the infrared beam can be directed at the surface at an angle, pass through the stearic acid test film, and reflect off the substrate instead of passing through it to the detector. This latter method is known as reflectance IR spectroscopy.

The PASC reaction rate of a PASC coating can be determined by measuring the rate at which the PASC coating reacts to remove the stearic acid film on it when the PASC coating is exposed to photochemical (actinic) radiation. Specifically, the rate of decrease in the integrated intensity of the CH stretching vibrational feature (which is directly proportional to the surface coverage) is the actinic. gives the PASC reaction rate as a function of the duration of the radiation (which is assumed to be ultraviolet radiation here). For example, the initial PASC activity of a stearic acid test film present on a PASC coating is measured using an FTIR spectrophotometer. For this initial PASC activity measurement, the PASC coating is either irradiated with ultraviolet radiation or not. The stearic acid-coated PASC coating is then treated with ultraviolet radiation for a measured period of time, at the end of which a second PASC activity measurement is performed using the FTIR spectrophotometer. The integrated intensity of the CH bond stretching vibrations in the second measurement is expected to be lower than in the first due to the removal of part of the stearic acid test film by the ultraviolet radiation. From these two measurements, a curve can be constructed that shows the integrated intensity of the CH stretching vibrations as a function of time, and the slope of this curve gives the PASC reaction rate. Although two points are sufficient to construct a curve, it is advantageous to make more measurements during the PASC activity measurement to be able to construct a more accurate curve. Although the UV irradiation time during FTIR measurements can be kept constant or varied if more than two PASC activity measurements are performed (which corresponds to the cumulative UV exposure time during curve recording), the UV intensity and direction (coated side or substrate side) must be kept constant for each PASC measurement during PASC reaction rate determination.

The PASC reaction rate is cm¹ what¹ It is expressed in units of measurement, where higher values indicate higher PASC activity. There is no rate that would classify a PASC coating as “acceptable” or “unacceptable,” because whether a PASC coating has an acceptable PASC level is largely determined by the intended use of the PASC-coated article and the efficacy standards chosen for that purpose. For most applications, at least about 2x10'³, preferably at least about 5x10'³ PASC activity is desirable.

It is also useful to measure the thickness of the PASC coatings in order to properly determine and compare the PASC activity of the PASC coatings prepared according to the invention, because the PASC coating thickness can affect the photocatalytic activity, as demonstrated in the following examples. The thickness of the PASC coating 24 and/or SIDB layer 26 (if present) can be determined either by variable angle spectroscopic ellipsometry (hereinafter "VAS") or by profilometric measurement of an erased edge in the measured film, or calculated from interference colors, as is known in the art.

The thickness of the PASC coating 24 and/or, if present, the SIDB layer 26 can be calculated from X-ray diffraction data (hereinafter referred to as “XRD”) using the Scherrer equation. This equation is known in the art and is discussed in Chapter 9 of Klug and Alexander, “X-Ray diffraction procedures for polycrystalline and amorphous materials,” John Wiley & Sons, Inc.

The following examples of the present invention are provided for illustrative purposes and are not intended to limit the invention.

1. example

The 2100 Angstrom thick PASC coating formed by the CVD process

The PASC activity of a titanium dioxide PASC coating having a thickness of approximately 2100 Angstroms was tested as follows. The PASC coating was deposited by CVD onto a substrate 22 whose air-facing side was a piece of floated soda-lime quartz glass sold under the trade name SOLEX® by PPG Industries, Inc., Pittsburgh, Pennsylvania. Referring to Figure 3, the SOLEX® glass piece was 14 cm wide, 30.5 cm long, and 0.4 cm thick, and was placed in a 3. A titanium dioxide PASC coating was applied using a CVD coating apparatus 88 as shown in FIG. 3. The CVD coating apparatus 88 generally consists of three zones, separated by vertical dashed lines 90 and 92 in FIG. 3. The three zones include a preheating zone 94, a coating zone 96, and a leveling zone 98. The SOLEX® glass piece, hereinafter referred to as substrate 22, was moved through the three zones on an endless conveyor 102 in the direction of arrow 104.

The substrate 22 was placed in the preheating zone 94 and heated to a temperature of about 649°C by a series of heating elements 106 positioned above and below the conveyor 102. The substrate 22 was conveyed by the conveyor 102 to the CVD coating zone 96. The CVD coating zone 96 includes at least one coating unit 97. In order to deposit more than one coating layer in succession, the coating zone 96 may include a plurality of coating units 97. The coating unit includes lower support systems and control elements such as a lower gas supply system, a lower liquid supply system, temperature controllers, a lower discharge system, control elements, and a temperature and pressure recording system, none of which are shown in the figure. The inlet nitrogen flow was controlled to 113°C by heating elements not shown in the figure. The carrier gas was introduced at a rate of 20% of the total flow rate of NH3. The purge flow rate was 125% of the feed rate. The metal-containing precursor used for the titanium dioxide PASC coating deposited on substrate 22 was TTIP, which was present at 0.4% by volume in the total flow and was also supplied at approximately 113°C. The N₂, NH₃ and the amount of TTIP vapor passed through the CVD coating material 88 was 75 liters/minute (s.m.). The conveyor speed 102 was about 127 cm/minute and the nip width of the coating unit was about 0.48 cm. The substrate 22 was maintained at a temperature of about 554°C under the coating unit 97 while the coating 24 was deposited on the substrate 22 to form the coated pattern 100. A 24 titanium dioxide PASC coating of approximately 2100 Angstroms thick (as measured by VASE) was formed on the 100 coated sample.

The coated sample 100 was then transferred to the equilibration zone 98 where it was equilibrated from an initial temperature of about 549°C to a final temperature of about 121°C in about 26 minutes.

The 100 samples coated with PASC were subjected to XRD analysis. The grain size of the 24 PASC coatings was determined to be 309 Angstroms, calculated using the Scherer equation. The 100 coated samples showed strong peaks in the XRD curve corresponding to anatase titanium dioxide.

The 100 PASC coated sample was then coated with a stearic acid test film to measure its photocatalytic activity. An approximately 6x10'³ A 100 mol/L stearic acid solution was used by pipetting the stearic acid solution into the center of the 100 sample at a rate of approximately 2 ml/10 sec while the coated 100 sample was rotated at a speed of approximately 1000 rpm, causing the stearic acid to flow across the surface of the coated sample 100 under centrifugal force and forming a stearic acid film generally of approximately 100-200 Angstroms in thickness on the surface of the coated sample 100. By "generally" we mean that the thickness of the stearic acid layer was not constant along the length of the 100 coated samples, but was thickest at the ends of the 100 coated samples and thinnest in the middle of the 100 coated samples due to the centrifugal force applied. As will be appreciated, the given stearic acid solution concentration, rotation speed, sample size and pipetting speed can be modified to obtain a stearic acid coating of the desired thickness. With the parameters described above, the average thickness of the test stearic acid film was approximately 150 Angstroms, as determined by calibration with an IV intensity quartz crystal microbalance.

The 100 samples coated with the stearic acid test film/titanium dioxide were exposed to ultraviolet radiation from a light source placed perpendicular to the side of the 100 coated samples, which provided an irradiance of approximately 20 W/m on the surface of the 24 PASC coating.²intensity for approximately 30 minutes to initiate the photocatalytically activated self-cleaning of the test stearic acid. During the total 30 minutes of ultraviolet light irradiation, FTIR spectrophotometric measurements were performed periodically using an FTIR spectrophotometer equipped with an MCT detector for quantitative measurement of photocatalytic activity. Specifically, 100 samples coated with stearic acid test film, PASC, were exposed to ultraviolet radiation for a measured period of time, after which the 100 coated samples were placed in the FTIR spectrophotometer, where the CH absorption band of stearic acid was measured to determine PASC activity. The 100 coated samples were again exposed to ultraviolet radiation for an additional measured period of time to remove additional stearic acid, and then another FTIR measurement was performed. This procedure was repeated and a curve of the integrated IV absorption intensity of the CH stretching vibrations was obtained as a function of the cumulative time of ultraviolet light irradiation, the slope of which gave the PASC rate of 100 PASC samples coated with stearic acid test film/titanium dioxide. As can be seen, all FTIR measurements were performed on approximately the same surface of the 100 samples in order to minimize the aforementioned effect of the variation in the thickness of the stearic acid test film. The photocatalytic reaction rate was determined to be 3.53 x 10'³ cm'¹.we determined that it approximates the value of PASC-coated substrates that contain little or no sodium ions (such as quartz glass substrates), indicating that the 2100 Angstrom thickness of the titanium dioxide PASC coating is sufficient to prevent sodium ion poisoning.

2. example

700-800 Angstrom thick PASC coating formed by CVD process

A titanium dioxide PASC coating approximately 700-800 Angstroms thick was deposited by CVD on a glass substrate as in Example 1, with the following differences.

The glass composition used in Example 2 was 3 mm thick, transparent (i.e. low iron) soda-lime quartz glass. In Example 2, the preheating temperature was 593°C, the TTIP concentration was 0.1% at a total flow rate of 50 liters/min (smooth). The carrier gas was NH4Cl at 24% of the total flow rate.₃The coating speed was 76.2 cm/min and the gap width was 0.16 cm. The thickness of the 24 titanium dioxide PASC coating was calculated from interference colors, a known technique for measuring thin film thickness, and was approximately 700-800 Angstroms.

A stearic acid test sample was applied to the titanium dioxide PASC coating in the same manner as in Example 1, and after UV irradiation as described in Example 1, the PASC activity was periodically measured by an FTIR spectrophotometer over a cumulative period of 33 hours. The photocatalytic reaction rate was approximately 0.17x10'³cm-Vmin^, was determined.

The lower PASC activity in Example 2 is believed to be a consequence of the different thickness of the titanium dioxide coating in Examples 1 and 2 (approximately 2100 Angstroms versus approximately 700-800 Angstroms). Specifically, it is believed that the reaction rate in Example 2 was lower than in Example 1 because the sodium ion diffusion into the titanium dioxide coating in Example 2 is deeper because of the lower thickness of the titanium dioxide coating in Example 2. The titanium dioxide PASC coating of Example 2 has a greater total thickness percentage than that of Example 1. It is believed that sodium ions migrate from the glass sample into the PASC coating of Example 2 in the equalization annealing furnace 44. One conclusion that can be drawn from Examples 1 and 2 is that in the absence of a SIDB layer, thicker PASC coatings are less susceptible to sodium ion poisoning, thus maintaining greater PASC activity.

3. example

PASC coated on SIDB layer formed by CVD process

In this example, the effect of the presence of a tin dioxide SIDB layer on PASC activity was investigated. Specifically, a tin dioxide SIDB layer was formed on the air side of four pieces of float glass and certain physical properties of the SIDB layer were investigated. Then, 16 additional pieces of float glass were coated with a tin dioxide SIDB layer by CVD, each of which tin dioxide SIDB layers was then coated with a titanium dioxide PASC coating by CVD. A sample was cut from 16 pieces of PASC coated/SIDB coated/floated glass and these 16 pieces were coated with a stearic acid test film. The 16 pieces of stearic acid test film coated/titanium dioxide PASC coated/tin dioxide SIDB coated samples were irradiated with ultraviolet light and the PASC reaction rate of the samples was determined.

3A) Examination of the SIDB layer

The SIDB layer was deposited by CVD using the CVD apparatus described in Example 1 on the air-facing side of 4 glass pieces cut from a floated soda-lime quartz glass ribbon, the glass pieces measuring 12.7 x 30.48 x 0.4 cm. Specifically, the SIDB layer was a thin tin dioxide SIDB layer, and the effects of metal-containing precursor concentration, water vapor concentration, CVD apparatus speed, preheat temperature, and SIDB layer thickness on the tin dioxide SIDB layer were investigated. In all 4 glass pieces, the metal-containing precursor used to form the CVD tin oxide SIDB layer was a MBTTCL vapor mixed with water vapor in an air carrier gas.

One of the 4 glass pieces was coated with a tin oxide SIDB layer by CVD using the apparatus of Example 1 by directing an air carrier gas of about 1.5% MBTTCL vapor concentration and about 1.5% water vapor concentration to the air side of the glass piece. The preheat temperature was about 648°C and the apparatus speed was about 127 cm/min for this glass piece. The resulting tin oxide SIDB layer was approximately 3500 Angstroms thick, as determined by VASE. The resistivity and grain size of the SIDB layer were measured and found to be 4.6x10'³ We found it to be Ohm and 198 Angstroms.

A second piece of glass was coated with a tin oxide layer in a similar manner, but the speed of the apparatus was reduced to about 50.8 cm/min and the MBTTCL vapor concentration was reduced to about 0.5% and the water vapor concentration to about 0.5% in the air carrier gas. The preheat temperature was maintained at about 648°C. The tin oxide SIDB layer thus formed was about 430 Angstroms thick as determined by VASE. The resistivity was determined to be about 3.9x10'³ Ohm.cm, and the particle size was found to be approximately 185 Angstroms.

A third piece of glass was coated with a tin oxide SIDB layer in a similar manner, but the preheat temperature was reduced to about 480°C and the speed of the apparatus was increased to about 127 cm/min. The MBTTCL concentration in the air carrier gas was about 1.5% and the water vapor concentration was about 1.5%. The resulting tin oxide SIDB layer had a coating thickness of about 1000 Angstroms as determined by VASE and a resistivity of about 3.8x10-²Ohm.cm and its particle size is about 59 Angstroms.

A fourth piece of glass was coated with a tin oxide SIDB layer in a similar manner, but while the preheat temperature was maintained at about 480°C, the speed of the apparatus was reduced to 50.8 cm/min. The MBTTCL concentration was about 0.5%, and the water concentration was about 0.5% in the carrier gas. The tin oxide SIDB layer was about 1010 Angstroms thick, as determined by VASE, and the resistivity was about 2x10'² Ohm.cm and the particle size is about 78 Angstroms.

From the above, we conclude that for the given temperature ranges, concentrations, equipment speeds, and SIDB layer thicknesses, although the resistivities and grain sizes may vary, all four glass pieces have a cassiterite structure.

3B) Formation of a titanium dioxide PASC coating on a tin oxide SIDB layer by CVD process Each of the additional float glass pieces measuring 12.7x30.48x0.4 cm was coated with a tin oxide SIDB layer using the CVD coating equipment according to the method described in section 3A) and then coated with a titanium dioxide PASC coating using the CVD equipment and method as described in Example 1. In this coating operation, a pair of sequential coating units (one for the SIDB layer and one for the PASC coating) were used during the on-line CVD process. The PASC coating on the SIDB layer makes it difficult, if not impossible, to analyze SIDB separately, so we assumed that the PASC-coated tin oxide layers had the same properties as the uncoated tin oxide layers described in Section 3A) above, although both the SIDB layers and the PASC coatings were applied under specific coating parameters, as detailed below and shown in Table 1 below.

The 16 tin oxide SIDB layers were generally deposited using an air carrier gas mixed with water vapor and metal-containing precursor MBTTCL vapor. The MBTTCL vapor temperature was maintained at approximately 160° C. The total flow rate was 60 planes and the discharge ratio was 115%, with a partial width of 0.16 cm. For the SIDB layers formed in this example, the specific coating parameters included the temperature of the preheating zone 94, the speed of the equipment, the MBTTCL concentration, the water vapor concentration, and the thickness of the SIDB layer. The following 1. Table 1 shows the coating parameters of the tin oxide SIDB layers and the expected SIDB layer thicknesses for all 16 glass pieces. Actual thickness measurements were not performed; the expected thickness data is based on the results obtained in Section 3A) above. The 16 pieces are divided into four groups in Table 1, each group containing four substrates, according to preheat temperature and machine speed.

<img file="HUP0001814A2_D0001.tif" />

1,Table

S

n

HE

2

sodium ion diffusion barrier CVD coating parameters group number sample number preheating temperature (°C) equipment speed (cm/min) H

2

O concentration (vol.%) MBTTCL conc. (%) expected SIDB layer thickness (Angstrom) I. 1. 482.5 50.8 0.5 0.5 1010 2. 482.5 50.8 0.5 0.5 1010 3. 482.5 50.8 0.5 0.5 1010 4. 482.5 50.8 0.5 0.5 1010 II. 5. 482.5 127 1.5 1.5 1000 6. 482.5 127 1.5 1.5 1000 7. 482.5 127 1.5 1.5 1000 8. 482.5 127 1.5 1.5 1000 III. 9. 640.9 50.8 0.5 0.5 4340 10. 640.9 50.8 0.5 0.5 4340 11. 640.9 50.8 0.5 0.5 4340 12. 640.9 50.8 0.5 0.5 4340 ARC. 13. 482.5 127 1.5 1.5 3500 14. 482.5 127 1.5 1.5 3500 15. 482.5 127 1.5 1.5 3500 16. 482.5 127 1.5 1.5 3500

Each of the 16 SIDB-coated glass pieces was then coated with a titanium dioxide PASC coating, deposited from a second CVD coating unit located downstream of the first SIDB coating, which applied a nitrogen (N) layer to the SIDB-coated surface of the glass pieces.₂) carrier gas. In 8 of the 16 glass pieces, ammonia (NH₃) was added. The carrier gas temperature was maintained at approximately 113°C for all 16 glass pieces. The 16 glass pieces were equilibrated as described in Example 1. The TTIP quench temperature was maintained at approximately 104.4°C. Table 2 below shows the titanium dioxide PASC coating parameters for the 16 glass pieces. In Table 2, the 16 glass pieces were divided into four groups, each of which is indicated by the preheat temperature and the machine speed.

'54

2. Table

gap width (mm)** ta xr <ώ ·7 in b-_ in b- co xr co xr ΙΛ smb x-' xf cm' xf 1.58 4.74 1.58 4.74 co xr co xr in bms It was a security operation and this is when they would have entered the 88 CVD installation zone. * NH

3

conc. (%) oo ° ° CM CM qooo CM CM o OO o CM CM o OO o CM CM <u L. CD 4—» CD E TTIP conc.(%) r- XT XT vo' o' o' o' xr r- r- xr o' o' o' o' oh oh oh oh oh oh oh oh k in a preheating zone, before the 98 additional oh coating pan emptying setting (%) tn m in in OO CM CM x— t— X— x— in in m in CM CM oo in tn m in CM CM oox

-

x- v x- m in m in Ο O CM CM x- X— X— X— •natkoze. The pins got the front, what's ω co ro > total flow rate (l/min) in m in m CO b· CO b m in mm b- CO b· CO m in mm b- CO b- co in in io m CO b· CO b- PASC coating heated to room temperature 05 c 05 cd Σ5 s 05 equipment speed (cm/min) CO CO CO CO o' o' o o' m in in io CM CM CM CM τ— v— r— x— co co co co o' o' o' mmm in CM CM CM CM the 94 preheating zone temperatures, to which the glass pieces are first heated by the SIDB, then by the OOM— 04 o preheating temperature (°C)* m in in in cm' cm' cm cm' co co co co XT xt xT χφ in tn in in cm' cm' cm' cm' co co co co xr xr xr xr cd cd cd cd o' o' o' o' xr xr xr xr CO co co co CD CD CD CD o' o' o' o' xr xr xr xr CO CD CO CO sample number T-CM co XT m to b co cd o ™ CO IO CD T— T— The cooling temperature here passes through a heat transfer group number — ARC. *The preheater is a listed live-fire device

1/16 inch = 0.16 cm and 3/16 inch = 0.48 cm.

Table 3 below shows selected properties of each of the 16 glass pieces after application of the PASC coating described in Table 2. PASC coating thicknesses were not measured, but as expected, other deposition parameters such as machine speed and precursor concentration varied for each group. However, the surface roughness and grain size of the PASC coating were determined. The surface roughness measurements were calculated based on the atomic force microscope (hereinafter referred to as “AFM”) measurements performed on the PASC coating. It was found that there was a large variation in the surface roughness, grain size, and crystalline phase depending on the preheating temperature.

3. Table

oetrain properties I crystalline phase not detected not detected anatase/rutile anatase/rutile not detected not detected anatase/rutile anatase/rutile we did not detect anatase anatase anatase anatase not detected weak anatase ___ anatase * The grain size could not be calculated because either there were no detectable peaks in the X-ray diffraction pattern of the anatase phase (samples 1, 2, 5, 6, 8, 9 and 14) or the peaks were too broad and weak to be measured (samples 3, particle size (Angstroms) * * * * * * * * * 277 121 __________166 CD T v- * * m CM v- TiO

2

photocatalytically activated self-cleaning I surface roughness (Rms) co oo h- ττ r- v- oq co lo sh cn co ο o CO CO CD m <D Έ m heat <- co co co h- tn o cn xf in co' co r- r- hl r- CO CM CM CO T- h~ in σ>_ co in ττ in sample number CM CO O' in co rd co Ci θ ™ co ττ in co group number — Sub

7. and sample 15)

3C) Description of the PASC activity assay for 16 substrates

A 2.54 x 10.16 cm test strip was cut from each of the 16 PASC coated/SIDB coated glass pieces. Each of the 16 test strips was spin coated with a stearic acid test film as described in Example 1. The 16 test strips were then irradiated with ultraviolet light from a black light source at 20 W/m² intensity, over a cumulative period of 7 hours, to initiate photocatalytically activated self-cleaning of the stearic acid test film.

Since we found that the thickness of the stearic acid test film varied along the length of the 2.54x10.06 cm test strips (i.e., the stearic acid test film was thicker at each end of the test strips and thinner towards the center of each strip, which is a result of centrifugal force acting on the stearic acid when it was dropped into the center of the spun test strip), As described above (and as visually observed from the interference colors along the length of the test strips), the photocatalytic activity was measured at both ends of each of the 16 test strips using an FTIR spectrophotometer equipped with an MCT detector. The PASC reaction rates obtained from the FTIR spectroscopy studies for each pair of tests for each of the 16 test strips are shown in Table 4.

4. Table

Photocatalytically activated self-cleaning activity of 16 test strips group number sample number PASC activity rate on the left side of the strip X 10-

3

cm''.min·

1

PASC activity X 10-

3

cm\min·

1

| 1. 0.39 0.45 2. 0.32 0.28 3. 0.26 0.31 4. 0.4 0.39 II. 5. 0.5 0.57 6. 0.23 0.14 7. 0.27 0.22 8. 0.014 0.019 III. 9. 0.23 0.048 10. 0.96 0.77 11. 0.4 0.31 12. 0.52 0.43 ARC. 13. 1.18 0.94 14. 0.73 0.77 15. 0.42 0.41 16. 0.25 0.35

It is clear from Table 4 that for some test strips there is a very significant difference in activity between the two ends of the test strip. This difference is believed to be due to the uneven thickness of the stearic acid layer on the test strip.

Referring to Table 4, it seems that there is a lack of correlation between the conditions of deposition of PASC coating on SIDB layer and PASC activity. The three most active test strips, as shown in Table 4, are samples 13, 10 and 14, based on the activities of the left side of the test strips. These

Stripes 13, 10 and 14 correspond to the highest preheat temperature of 648.8°C. When sorted by PASC activity, the remaining 13 bands show a mix of preheat temperatures and other coating parameters, suggesting that the presence of a sodium ion diffusion barrier layer may act to prevent sodium ion poisoning of the PASC coating layer and allow for a wider range of coating conditions and parameters while still achieving photocatalytic activity.

4. example

PASC coating formed by spray pyrolysis

In this example, glass pieces were coated with titanium dioxide PASC coatings of varying thicknesses by spray pyrolysis to investigate the effect of PASC coating thickness on PASC activity.

The air-facing side of three 10.16x10.06x0.4 cm float glass pieces was coated with a titanium dioxide PASC coating by spray pyrolysis.

The main components of the pyrolytic spray apparatus used to apply the PASC coating to a glass piece are shown in Figure 4. The spray pyrolysis apparatus consisted of a preheating zone 120 and a pyrolytic spray zone 122. A glass piece 126 (not shown) was conveyed by a conveyor belt to the preheating zone 120 where it was heated to approximately 600-700°C by a series of electrical heating elements 130. The glass piece 126 was then conveyed by the conveyor to an oscillating atomizer valve 132, which was positioned approximately 25.4 cm above the air side of the glass piece 126. An aqueous suspension of the organometallic coating reagents 134 was maintained in suspension in the mixing chamber 138 by the mixer 136. The aqueous suspension 134 was conveyed by conduit 140 to atomizer valve 132 where it was mixed in any suitable manner with compressed air (which was supplied from compressed air source 142 to atomizer valve 132 by conduit 144). An atomization pattern 146 was formed as the aqueous suspension/compressed air mixture 134 was sprayed onto the surface of glass piece 126 and pyrolyzed on glass piece 126 to form PASC coating 24. The 126 pieces of glass coated with PASC were allowed to cool in air.

In this example, the organometallic coating reagent chosen was titanyl acetylacetonate and the rate of the aqueous suspension sprayed onto the surfaces of three 126 glass pieces was controlled to provide a PASC coating thickness on each glass piece. The thicknesses were 400, 725 and 1000 Angstroms. All other coating parameters were kept constant in order to determine the effect of PASC coating thickness on the photocatalytic activity of a titanium dioxide PASC coating deposited on transparent float glass by spray pyrolysis without a SIDB barrier layer.

The coating parameters for this example are shown in Table 5.

5. Table

PASC activity (x 10'

3

cm' '.min.

1

04 CM co TiO

2

thickness (Angstroms) oh 725 1000 deposition temperature (°C) 672 677 688 atomizing air pressure (kg/cm

2

) m co m cn 3.5 delivery rate (ml/min) 40 ml/min 55 ml/min 67 ml/min organometallic compound concentration (g/l) or rate 20g/ml 20g/ml 27 g/ml coating reagent titanyl acetylacetonate titanyl acetylacetonate titanyl acetylacetonate equipment speed (cm/min) 190.5 190.5 190.5 sample number < ω he

After deposition of the titanium dioxide PASC coating, each of the three glass pieces was cut into four 2.54x10.16 cm test strips, resulting in a total of 12 test strips.

A strip from each of the three original glass pieces was subjected to X-ray diffraction analysis. During the analysis, it was found that all three glass pieces exhibit strong anatase titanium dioxide X-ray diffraction lines.

To determine the photocatalytic activity of the three glass pieces, one test strip from each of the three glass pieces was coated with a stearic acid test film using the procedure described in Example 1. The three test strips were then exposed to ultraviolet radiation from a black light source, which was positioned perpendicular to the coated surface of each test strip and applied at a total of 20 W/m for 7 hours.² The photocatalytic reaction rates of each of the three test strips were quantitatively determined by FTIR spectroscopy using an MCT detector as described above. The photocatalytic reaction rates of the three glass pieces are shown in Table 5.

From the above, it can be concluded that small but acceptable photocatalytic reaction rates can be achieved for PASC coatings formed by spray pyrolysis technique without the PASC coating suffering from sodium ion poisoning. It can also be concluded that thicker PASC coatings have higher PASC activity, as demonstrated by Example C in Table 5.

5. example

Comparison of PASC coatings with and without SIDB layer by spray pyrolysis and investigation of the effect of post-PASC leveling

In this series of experiments, PASC-coated 8 glass pieces were prepared by spray pyrolysis to investigate the effect of the presence or absence of a SIDB layer, the effect of PASC coating thickness, the effect of substrate temperature during and after PASC coating deposition, and the effect of PASC coatings on the PASC reaction rate.

Specifically, 4 of the 8 4 mm SOLEX® float glass pieces were each coated with a 5010 Angstrom thick layer of tin dioxide SIDB, which was deposited using an aqueous solution of dibutyltin difluoride [(C₄H₉)2SnF2] suspension and a wetting agent. The tin dioxide SIDB layer was applied using the spray pyrolysis apparatus and procedure described in Example 4. After coating with the SIDB layer, the glass samples were cooled to room temperature and each of the other four glass pieces was coated with a titanium dioxide PASC coating over the SIDB coating and then cooled to room temperature. It should be noted that the four SIDB-coated glass pieces, which were cooled to room temperature between the application of the SIDB layer and the PASC coating and then reheated before the application of the PASC coating, were prepared in this manner because the laboratory pyrolytic atomization equipment used in the experiment had only one atomization pyrolysis station, so that the dibutyltin difluoride suspension (providing the SIDB coating) had to be replaced by a titanyl acetylacetonate suspension (providing the PASC coating). Such an intermediate cooling step would have been avoided by a preferred apparatus consisting of two spray pyrolysis stations where a SIDB layer and a PASC coating could be applied sequentially to a moving substrate, such as a continuous float glass ribbon, without any such intermediate cooling step.

After all 8 PASC-coated glass pieces were cooled to room temperature, they were coated with a stearic acid film as described in Example 1, and the films were then irradiated with a (JVA 340) light source placed perpendicular to the coated side of the stearic acid test film/PASC-coated glass pieces to irradiate the PASC-coated surface with 20 W/m² The PASC reaction rate for removing the stearic acid test film was quantitatively determined using the procedure described in Example 1. This PASC reaction rate is reported in the column labeled 0.00 minutes in Table 6 below. It should be noted that the parameter 0.00 minutes reflects the fact that the PASC-coated glass piece was not equilibrated after cooling to room temperature; it does not refer to the duration of ultraviolet irradiation.

The effect of equilibration time on stearic acid removal was investigated as follows. Residual stearic acid was washed off the PASC coating from each of the 8 glass pieces by rubbing the surface with a methanol-soaked cloth until no stearic acid film or haze was visible. Each of the 8 glass pieces was then placed in an oven maintained at approximately 500°C for approximately 3 minutes to heat them. The furnace heating was turned off, the door was opened, and the glass pieces were allowed to cool in the furnace to approximately room temperature. The slow cooling rate in the furnace ensured equilibration. Each glass piece was then coated with a new stearic acid test film, irradiated with ultraviolet light, and the PASC reaction rate was determined in the same manner as described for the unequilibrated PASC coating. The remaining stearic acid test film was again washed off each of the glass pieces as described above and each glass piece was heated for an additional 10 minutes and then cooled again in the same manner in the oven, for a total of 13 minutes of heating, then the stearic acid test film was reapplied as described and the PASC reaction rate was determined as described above. The procedure was repeated once more to achieve a total heating time of 73 minutes, followed by slow cooling in the furnace to ensure equilibration.

The properties of the SIDB layer and PASC coating and the PASC reaction rates as a function of the accumulated equilibration time for 8 glass pieces (D to K) are shown in the following Table 6.

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6. T A B L E

Photocatalytic activity reaction rate of PASC coatings with diffusion barrier layers containing and without sodium ions sample barrier layer TiO

2

thickness glass transition temperature of TiO

2

during coating (°C) photocatalytic activity* after equilibration at 500°C for the following time 0.00" 3 minutes 13 minute 73 minutes D no 400 Angstroms 618 0.72 1.05 1.94 **· This no 625 Angstroms 618 0.69 1.05 1.67 2.97 F 500 Angstroms SnOj 400 Angstroms 618 2.39 5.02 7.39 *«♦ G 500 Angstroms SnO

2

625 Angstroms 622 2.23 5.35 8.74 5.13 H no 400 Angstroms 682 2.05 6.59 5.14 • w* I no 625 Angstroms 682 4.71 7.99 9.95 5.39 J 500 Angstroms SnO

2

400 Angstroms 704.5 2.4 5.26 3.73 *** K 500 Angstroms SnO

z

625 Angstroms 690 4.64 12.29 5.57 4.4

PASC reaction rate for stearic acid removal (X 10^Λ cm'¹.min' )

The results of the photocatalytic analysis presented in Table 6 show that a titanium dioxide layer without a barrier layer, approximately 625 Angstroms thick (Sample 1), can approach the activity of a thinner 400 Angstroms thick PASC coating on a SIDB layer (Sample K). It should be noted that for the K samples, the SIDB layer was subjected to an intermediate cooling and the described reheating operation, which reheating operation may reduce the effectiveness of the SIDB layer, which would otherwise have a higher PASC activity.

Sample K in Table 6 also demonstrates that equilibration time can have a significant effect on the PASC reaction rate. After 3 minutes of equilibration time, the PASC activity of sample K increased from approximately 4.64 to approximately 12.29x10'³ cm'¹.min-¹increased to , but then decreased upon further equilibration. It is believed that the anatase phase of the titanium dioxide PASC coating formed during equilibration, when the PASC activity was measured within 3 min, and this formation occurred without significant sodium ion poisoning due to the presence of tin oxide in the SIDB layer. Although we do not wish to be bound by this specific theory, we believe that the equilibration is too long and its continuation could initiate sodium ion poisoning despite the presence of a SIDB layer, which would cause a decrease in the PASC activity of the K sample.

The above examples are provided for the purpose of illustrating the invention and are not intended to limit the invention.

Although the above methods of forming PASC coatings have been described in connection with forming such coatings on a continuously moving substrate, for example on a continuous, floated glass ribbon during substrate manufacturing, it is understood that these methods can also be applied downstream during the substrate manufacturing process. For example, PASC coatings can be applied to substrates, such as, but not limited to, glass substrates, as part of a process for bending and/or tempering the substrate. For example, if the substrate is to be heated for subsequent bending and/or tempering, the PASC coating with or without the SIDB layer can be applied prior to bending/tempering by spray pyrolysis or CVD or MSVD techniques. CVD and spray pyrolysis methods can be used during the bending/tempering process of the glass substrate. The PASC coating with or without a SIDB layer can be applied to the glass substrate with a bending/tempering reheat process using CVD, spray pyrolysis or MSVD.

It is believed that there are differences between PASC coatings prepared by the sol-gel process and those prepared by the methods described above. For example, it is expected that PASC coatings prepared by the sol-gel process are more porous, less dense, generally thicker, less suitable for transparent applications, and may contain more OH groups than PASC coatings prepared by the CVD or spray pyrolysis process. As mentioned above, excess OH groups are undesirable because they may prevent proper crystal formation in the PASC coating, which in turn may reduce PASC activity. It is believed that PASC coatings prepared by CVD or spray pyrolysis methods will have a finer grain structure than those prepared by the sol-gel process.

The advantages of forming PASC coatings according to the present invention over the sol-gel method include the ability to form a thin, dense PASC film on a substrate, as opposed to the much thicker porous coatings obtained by the sol-gel coating method. Because the PASC coatings of the present invention are thin, they are aesthetically acceptable as transparent coatings on glass substrates. A still further advantage is that the method of forming a PASC coating according to the invention avoids the need to reheat the substrate after application of the coating or coating precursor, as is required in the current sol-gel method. This makes the present method not only less expensive and more efficient by reducing equipment costs, energy costs, and production time, but also by significantly reducing the potential for sodium ion migration and sodium ion poisoning. A further advantage is that the method of the present invention can be easily applied to the formation of PASC coatings on continuously moving substrates, such as float glass ribbons, whereas currently available sol-gel methods cannot be so easily adapted for this purpose.

Various modifications of the invention are defined in the following claims.