HK1066524B - Photo-induced hydrophilic article and method of making same - Google Patents

Description

Photo-induced hydrophilic articles and methods of making the same

Cross reference to related applications

The present application is a continuation-in-part application, 09/282943, filed 1999, 4/1, entitled "photocatalytically activated self-cleaning appliance," a divisional application of U.S. patent application 08/899257, filed 1997, 7/23 (now US6027766), which claims priority to U.S. patent provisional application 60/040566, filed 1997, 3/14, the entire contents of which are incorporated herein by reference. This application also claims priority to U.S. provisional patent application 60/272197 entitled "photo-induced hydrophilic article and method of making same" filed on 28.2.2001, the entire contents of which are incorporated herein by reference.

1. Scope of the invention

The present invention relates to methods of depositing hydrophilic coatings on substrates (e.g., glass sheets or continuous float glass ribbons) and to articles made by these methods.

2. Technical considerations

In the following discussion, general technical considerations related to the present invention will be discussed. However, specific references discussed herein are not to be considered as constituting "prior art" in the U.S. patent specification, and no such admission is made.

For many substrates, such as glass substrates such as architectural windows, automotive light windows and aircraft windows, it is desirable for good visibility that the substrate surface be substantially free of surface contaminants, such as common organic surface contaminants and inorganic contaminants, for as long as possible. Traditionally, this has meant that these surfaces need to be cleaned often. Such cleaning operations are typically performed by manually wiping the surface, with or without the aid of a chemical cleaning solution. Such methods are laborious, time-consuming and/or costly. Therefore, there is a need for substrates, particularly glass substrates, having surfaces that are easier to clean than existing glass substrates, which reduces the need or number of such manual cleaning.

It is known that certain metal oxide semiconductors can be added to coatings to provide photocatalytically activated (hereinafter "PA") coatings with self-cleaning properties, i.e. coatings and coatings which are described above in connection with exposure to certain electromagnetic radiationOrganic contaminants on the surface interact with each other, degrading or decomposing the contaminants. Patents and articles relating generally to photocatalytic oxidation of organic compounds are in dHarmful chemical combination Bibliographic of work on photocatalytic removal of substances from water and air The photocatalytic Removal of Hazardous Compounds from Water and Air)National renewable energy laboratory (5 months 1994), renewed both 10 months 1995 and 10 months 1996.

Typically, these PA coatings are made thick enough to have sufficient photocatalytic activity to destroy or decompose organic contaminants on the coating in as short a time as possible. For example, WO00/75087 discloses a photocatalyst having a minimum photocatalytic activity of 5x10^-3cm^-1min^-1The photocatalytically activated coating of (a). Additional PA coatings are disclosed, for example, in US 5873203, 6027766 and 6054227.

In addition to self-cleaning properties, these PA coatings are generally also hydrophilic, i.e. water-wetting. The hydrophilicity of the PA coating helps to reduce fogging, i.e., the accumulation of water droplets on the coating, which can reduce the transmission of visible light and visibility through the coated substrate. This hydrophilicity has so far been linked to several factors, among which an increased surface roughness of the coating and an increased porosity of the coating. For example, US 6103363 discloses a hydrophilic photocatalytically activated self-cleaning coating having a preferred Root Mean Square (RMS) surface roughness of 5-15nm and a preferred porosity of 70-90%. However, this surface roughness can make cleaning of the surface more difficult, such as creating small grooves where dust and dirt can accumulate or drawing and breaking fibers from a cleaning cloth wiped over the surface. Furthermore, the increased porosity of the coating also creates channels that can chemically attack the underlying substrate.

To achieve the desired coating thickness, photocatalytic activity, surface roughness and coating porosity beforehand, many PA self-cleaning coatings have been deposited by sol-gel techniques. In a typical sol-gel process, an uncrystallized colloidal suspension is applied to a substrate at about ambient temperature and then heated to produce a crystallized coating. For example, US 6013372 discloses a hydrophilic photocatalytically activated self-cleaning coating produced by the steps of: photocatalyst particles are blended in a metal oxide layer, and then the blend is coated on a substrate by a sol-gel method.

However, the conventional sol-gel method is economically or practically incompatible with some application conditions or substrates. For example, in a conventional float glass process, the float glass ribbon in the molten metal bath may be so hot that the sol cannot be used due to vaporization or chemical reaction of the solvent used in the sol. In addition, the environment in the molten metal bath is also detrimental to the moving machinery required to apply the sol, such as the spraying equipment. Therefore, the sol must generally be applied after the float glass ribbon exits the molten bath and cools to about room temperature. The coated glass ribbon is then heated to a temperature sufficient to crystallize the coating. Such cooling and reheating operations require significant investment in equipment, energy and processing costs, while also significantly reducing production efficiency. In addition, reheating of sodium-containing substrates, such as soda-lime-silica glass, increases the chance of sodium ions in the substrate migrating to the coating, which is conventionally referred to as "sodium ion poisoning" of the deposited coating. The presence of these sodium ions can degrade or destroy the photocatalytic activity of the self-cleaning coating. Moreover, sol-gel processes typically produce thick coatings, i.e., several microns thick, which can have a negative impact on the optical and/or aesthetic properties of the coated article. Generally, as the thickness of the PA self-cleaning coating increases, the light transmission and reflection of the coating passes through a series of minima and maxima due to optical interference effects. Due to these optical effects, the reflected and transmitted colors of the coating are varied. Thus, coating thicknesses sufficient to provide the desired self-cleaning properties may have undesirable optical properties.

It would therefore be advantageous to provide an article having a coating, particularly a hydrophilic coating, and a method of making the article that reduces or eliminates at least some of these aforementioned disadvantages.

Summary of The Invention

The present invention relates to an article comprising a substrate having at least one surface and a hydrophilic coating, in particular a photo-induced hydrophilic coating (defined below), deposited on at least a portion of the surface. The coating may be deposited by a method selected from chemical vapor deposition (hereinafter "CVD"), spray pyrolysis and/or magnetron base-spray vacuum deposition (hereinafter "MSVD"). In an embodiment, the root mean square roughness of the outer surface of the coating, e.g., the coating, may be greater than or equal to 0nm to less than or equal to 4nm, e.g., less than or equal to 3nm, such as less than or equal to 2nm, such as 0.2-0.7nm, such as less than or equal to 1 nm. It is particularly advantageous if the substrate is a float glass ribbon and the coating is deposited by CVD in a molten tin bath during the production of the float glass ribbon. In another embodiment of the invention, the photo-catalytic activity of the photo-induced hydrophilic coating is greater than or equal to 0cm^-1min^-1To less than or equal to 3x10^-3cm^-1min^-1E.g. less than or equal to 2x10^-3cm^-1min^-1. In another embodiment of the invention, the substrate is a float glass ribbon in a molten metal bath, the thickness of the photo-induced hydrophilic coating is greater than 0 angstroms to less than or equal to 500 angstroms, and the photo-induced hydrophilic coating is deposited in the molten metal bath by chemical vapor deposition. The invention also relates to a method of making such an article.

It has been surprisingly found that very thin semiconductive metal oxide coatings, for example, from about greater than 0 angstroms to less than or equal to 500 angstroms, which retain their hydrophilicity even when the photocatalytic activity of the very thin coating is less than that typically required for the self-cleaning coating to decompose organic contaminants, are thinner than coatings typically used to achieve photocatalytic self-cleaning performance. Thus, while the thin semiconductive metal oxide coating still retains sufficient photoactivity for hydrophilicity, it may not have sufficient long-term optical activity for having measurable or commercially acceptable photocatalytic self-cleaning activity. This photo-induced hydrophilicity provides low fogging and/or also makes the coated article easier to clean, e.g., easier to wipe, than an uncoated article in order to remove dust and/or water spots. Furthermore, the light-induced hydrophilicity also spreads the water and dries faster, which reduces water spotting because water does not readily bead and leaves spots. Dust can also be removed more easily by simply rinsing the coating without manually wiping the coating. In addition, these very thin semiconductive metal oxide coatings are not compromised by the undesirable optical problems associated with thicker photocatalytic self-cleaning coatings. It has also been surprisingly found that these very thin semiconductive metal oxide coatings can be made smoother and denser than previously thought possible while still retaining their photo-induced hydrophilicity. Suitable semiconducting metal oxides that may be used in the practice of the present invention are oxides of titanium.

In one embodiment, the invention provides a substrate having at least one surface with a light-induced hydrophilic semiconductive metal oxide coating, such as a titanium dioxide coating, deposited on at least a portion of the surface by CVD, spray pyrolysis, or MSVD. The thickness of the coating can be greater than 0 angstroms to less than or equal to 500 angstroms, such as less than or equal to 400 angstroms, such as less than or equal to 300 angstroms, such as 50-250 angstroms, and the RMS roughness of the outer surface of the coating can generally be greater than or equal to 0nm to less than or equal to 2nm, such as 1.9nm or less, such as 0.2-1.5nm, such as 1nm or less. For coatings of the invention having a thickness of about 200 angstroms or less, the surface of the coating may be less smooth, for example the RMS roughness may be 5nm or less, for example 4.9nm or less, for example 4nm or less, for example 3nm or less, for example 2nm or less, for example 1nm or less. In a specific embodiment, the substrate is a float glass ribbon in a molten tin bath.

In one embodiment, the present invention provides an article comprising a float glass ribbon having at least one surface and a photo-induced hydrophilic coating deposited directly on at least a portion of the at least one surface. The photo-induced hydrophilic coating may be deposited directly on the float glass ribbon in the molten metal bath.

The present invention also provides an article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface. The substrate may be a float glass ribbon in a molten metal bath, the thickness of the photo-induced hydrophilic coating may be 500 angstroms or less, and the photo-induced hydrophilic coating may be deposited on the at least one surface in the molten metal bath using a chemical vapor deposition process.

The present invention also provides an article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface. The photo-induced hydrophilic coating can be deposited by chemical vapor deposition at 500-1200 deg.C, and the thickness of the photo-induced hydrophilic coating can be 500 angstroms or less.

A method of forming a photo-induced hydrophilic coating on at least a portion of a substrate is provided. The method includes providing a substrate having a first surface and a second surface, at least one of the surfaces having tin diffused therein; depositing a metal oxide precursor onto at least one of said surfaces from a coating apparatus by a method selected from the group consisting of chemical vapor deposition, spray pyrolysis and magnetron sputtering vacuum deposition; and heating the substrate to a temperature sufficient to decompose the metal oxide precursor to produce a photo-induced hydrophilic coating having a root mean square roughness of 2nm or less.

Another method of forming a photo-induced hydrophilic coating on at least a portion of a substrate, the method comprising providing a float glass ribbon in a molten metal bath; depositing a metal oxide precursor by chemical vapor deposition directly onto the top surface of the float glass ribbon from the coating apparatus; and heating the glass ribbon to a temperature sufficient to decompose the metal oxide precursor to produce the photo-induced hydrophilic coating.

Another method of forming a photo-induced hydrophilic coating on at least a portion of a substrate, said method comprising providing a substrate having at least one surface; depositing a metal oxide precursor from a CVD coating apparatus onto at least a portion of the at least one surface; heating the substrate to 400-1200 ℃ to decompose the metal oxide precursor to produce a photo-induced hydrophilic coating; and providing sufficient precursor material to render the thickness of the photo-induced hydrophilic coating 500 angstroms or less.

The invention also relates to products prepared by the method of the invention.

Drawings

FIG. 1 is a cross-sectional view (not to scale) of a portion of a substrate bearing a photo-induced hydrophilic coating of the present invention;

FIG. 2 is a side view (not to scale) of a coating process for applying a semiconductive metal oxide coating of the present invention to a glass ribbon in a molten metal bath for a float glass process;

FIG. 3 is a side view (not to scale) of an insulating glass structure incorporating features of the invention.

Detailed Description

As used herein, spatial or directional terms, such as "inner", "outer", "above", "below", "top", "bottom", and the like, relate to the invention as it is shown in the drawings. It is to be understood, however, that the invention can be embodied in various and alternative orientations and, accordingly, such terms are not to be considered as limiting. Moreover, all numbers expressing dimensions, physical characteristics, processing parameters, quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless otherwise indicated, the numerical values set forth in the following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical value should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, reference to a range of "1 to 10" is intended to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; i.e., all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 5. 5-10. Further, as used herein, the terms "deposited on …" or "provided on …" mean deposited or provided on …, but not necessarily in contact with a surface. For example, a substrate having a coating "deposited on …" does not preclude the presence of one or more coating films of the same composition or of different compositions between the deposited coating and the substrate. In addition, all percentages recited herein are weight percentages unless otherwise indicated. All photocatalytic activity values described herein are determined using the conventional stearic acid test disclosed in US6027766, incorporated herein by reference. All root mean square roughness values were determined by atomic force microscopy from Root Mean Square (RMS) measurements over a surface area of 1 square micron. In addition, all references incorporated by reference herein are to be understood as being incorporated in their entirety.

Referring now to FIG. 1, there is shown an article 20 embodying features of the invention. Article 20 comprises a substrate 22 having a surface 21, and a photo-induced hydrophilic (hereinafter PH) coating 24 of the present invention is deposited on at least a portion of surface 21. As used herein, the term "photo-induced hydrophilic coating" refers to a photo-activated hydrophilic material or coating. "photoactivated hydrophilic" refers to a coating in which the contact angle of a water droplet on the surface of the coating decreases over time as the coating is exposed to electromagnetic radiation. For example, the contact angle may be reduced to less than 15 °, such as less than 10 °, and may become superhydrophilic after exposure to 60min of ultraviolet radiation from a source sold by the Q-Panel Company of Cleveland, Ohio under the trade designation UVA340, such as to less than or equal to 5 °, such as less than or equal to 4 °, such as less than or equal to 35 °, at a location such that there is 24W/m at the surface of the PH coating²The strength of (2). Longer exposure to said lightThe contact angle may decrease even further, for example less than or equal to 2 °, for example less than or equal to 1 °, in a source or when exposed to different light sources and/or different illumination intensities.

While not limiting to the invention, it is contemplated that the PH coatings of the present invention are light activated or behave light activated. As understood by those skilled in the art, the term "photoactivated" refers to the generation of photogenerated hole electron pairs upon irradiation with radiation of a particular frequency. Exemplary photoactive materials suitable for use in the practice of the present invention include semiconducting metal oxides. Although the photoactivated hydrophilic coating 24 may not necessarily be photocatalytic to the extent that it is sufficiently self-cleaning, i.e., may not be sufficiently photocatalytic to decompose contaminants such as organic materials on the coating surface in a reasonable or economically effective time.

In the broad practice of the invention, the substrate 22 can be any desired material having any desired optical properties. For example, the substrate 22 may be transparent to visible light. By "transparent" is meant a transmission through the substrate 22 of greater than 0% up to 100%. By "visible light" is meant 395-800nm electromagnetic energy. Alternatively, the substrate 22 may be translucent or opaque. By "translucent" is meant allowing electromagnetic energy (e.g., visible light) to pass through, but diffusing such that objects on the other side are not clearly visible. By "opaque" is meant a visible light transmission of 0%. Suitable materials for the substrate 22 include plastics (e.g., polymethylmethacrylate, polycarbonate, polyurethane, polyethylene terephthalate (PET) or copolymers of any of the monomers from which these polymers are made, or mixtures thereof), ceramics, or glass. The glass can be any type of glass, such as conventional float or flat glass, and can be any composition having any optical properties, such as any value of visible light transmittance, ultraviolet light transmittance, infrared light transmittance, and/or total solar energy transmittance. By float glass' is meant glass made by the conventional float glass process wherein molten glass is deposited on a molten metal bath and controlled cooling produces a float glass ribbon. The glass ribbon is then cut and/or shaped and/or heat treated, if desired. Examples of float glass processes are disclosed in US 4466562 and 4671155. The glass may be, for example, a conventional soda-lime-silica glass, a borosilicate glass, or a leaded glass. The glass may be "clear glass", i.e. uncolored or colorless glass. In another aspect, the glass can be tinted or colored glass. The glass may be tempered, heat treated or heat strengthened glass. As used herein, the term "heat strengthened" refers to annealed, tempered, or at least partially tempered. Although not limiting to the invention, examples of glasses suitable for use in the substrate 12 are disclosed in US 4746347, 4792536, 5240886, 5385872 and 5393593, which are incorporated herein by reference. The substrate 22 can have any desired dimensions, such as length, width, shape, or thickness. For example, the substrate 22 may be a glass pane for an architectural window, a skylight, a pane for an insulating glass unit, or for a conventional automotive windshield assembly, a side or rear window, a skylight, or an aircraft light transmission device, to name just a few examples.

The PH coating 24 may be deposited directly on, i.e., in contact with, a surface, such as the surface 21 of the substrate 22 shown in fig. 1. It has been found that even sodium-containing substrates, such as soda-lime-silica glass, do not render the very thin PH coatings of the present invention hydrophilic by the sodium in the substrate when the coating is applied by the molten bath process described below. Therefore, soda-lime-silica glass can be more easily cleaned without a sodium barrier layer between the glass and the PH coating of the present invention. Optionally, such a barrier layer may be used.

Alternatively, one or more other layers or coatings, such as one or more functional coatings (e.g., an anti-reflective coating) or sodium ion blocking layers as described below, may be sandwiched between the PH coating 24 and the substrate 22. For example, the PH coating 24 may be an outer or outermost layer of a multi-stack coating present on the substrate 22, or the PH coating 24 may be embedded in such a multi-stack as one of the other layers in addition to the outermost layer. By "outer layer" is meant a layer that receives sufficient exciting electromagnetic radiation, such as ultraviolet light, to result in a photoactivated hydrophilic coating that is sufficiently photoactive, but not necessarily photocatalytic. Preferably, the PH coating 24 is the outermost coating of the substrate 22.

As discussed above, the PH coating 24 need not have a photocatalytic activity level on the order of that of previously known self-cleaning coatings. For example, the photocatalytic activity of the pH coating 24 can be greater than or equal to 0cm^-1min^-1To less than or equal to 5x10^-3cm^-1min^-1±2 x 10^-3cm^-1min^-1E.g. less than or equal to 4 x10^-3cm^-1min^-1E.g. less than or equal to 3x10^-3cm^-1min^-1±2 x 10^-3cm^-1min^-1E.g. less than or equal to 2x10^-3cm^-1min^-1±2 x 10^-3cm^-1min^-1。

The PH coating 24 may comprise any coating material that is hydrophilic in photoactivation and that can be deposited by CVD, spray pyrolysis, or MSVD methods. For example, and without limiting the invention, the PH coating 24 may include one or more metal oxides, metal alloy oxides, or semiconductor metal oxides or metal alloy oxides, such as, but not limited to, titanium oxides, silicon oxides, aluminum oxides, iron oxides, silver oxides, cobalt oxides, chromium oxides, copper oxides, molybdenum oxides, tungsten oxides, zinc/tin alloy oxides, zinc stannate, strontium titanate, and mixtures or combinations thereof. The metal oxide and/or metal alloy oxide may comprise an oxide, peroxide or sub-oxide of the metal.

One illustrative PH coating 24 that is particularly suitable for the practice of the present invention is titanium dioxide. Titanium dioxide exists in amorphous or three crystalline forms, namely anatase, rutile and brookite crystalline forms. Anatase phase titanium dioxide has a strong photoactivated hydrophilicity combined with excellent chemical resistance and excellent physical durability. The rutile phase of titanium dioxide may also have a photo-activated hydrophilic character. Mixtures or compositions of anatase and/or rutile and/or brookite and/or amorphous phases are suitable for use in the present invention, provided that the composition has photoactivated hydrophilicity.

The PH coating 24 should be of sufficient thicknessTo provide an acceptable level of photoactivated hydrophilicity. The absolute value of "acceptable" or "unacceptable" for the PH coating 24 is not achieved because the level of acceptable photoactivatable hydrophilicity of the PH coating is germane to the purpose and conditions of use of the PH coated article and the performance criteria chosen to match the purpose. As discussed above, however, the thickness of the PH coating 24 to achieve photoactivation hydrophilicity may be approximately as thick as is required for conventional commercially acceptable levels of photocatalytic self-cleaning activity, for example, the PH coating 24 may be 10-5000 angstroms thick, in which case thicker coatings may have photocatalytic self-cleaning activity as well as hydrophilicity. As the coating becomes thinner in this range, the photocatalytic self-cleaning activity generally decreases. As the coating thickness decreases within a range of 50-3000 angstroms, such as 100-. It has been found that when the substrate 22 is a float glass plate and the PH coating 24 has a coating of anatase titanium dioxide PH produced by CVD directly on the float glass plate, a thickness of 200-300 angstroms provides a thickness of 0-2 x10^-3cm^-1min^-1±2 x 10^-3cm^-1min^-1Photocatalytic activity of, e.g., 1.8-2.8 x10^-3cm^-1min^-1To remove the stearic acid test film, the intensity at the surface of the PH coating produced when the PH coating was exposed to a UVA-340 light source was 24W/m²Ultraviolet rays of (2). This PH coating is also super-hydrophilic under the same radiation, and the contact angle of a water droplet is 4 ° ± 2 ° to 7 ° ± 2 ° after 60min exposure to UVA-340 light. As will be appreciated by those skilled in the art, there may not be a uniform thickness throughout the entire area of the coating. Therefore, the thickness discussed herein should be understood to be the average thickness of the entire coating.

In another aspect of the present invention, the outer surface of the PH coating 24 of the present invention may be much smoother than previous hydrophilic self-cleaning coatings while still retaining its photoactivated hydrophilicity. For example, the RMS roughness of the coating 24, particularly the outer or top surface of the coating, may be greater than or equal to 0nm to less than 5nm, such as less than or equal to 4.9nm, such as less than or equal to 4nm, such as less than or equal to 3nm, such as less than or equal to 2nm, such as less than or equal to 1nm, such as 0.3-0.7nm, even for thin coatings within the above-described range, such as 200 angstroms and 300 angstroms, for example. For example, the RMS surface roughness of the 200-300A PH coating discussed immediately above is 0.55-0.65nm as measured by atomic force microscopy.

In another aspect of the present invention, the PH coating 24 may have low visible light reflectivity. As used herein, "visible light reflectance" refers to the traditional chromaticity coordinate designation (R)₁) Y (illuminant C, 2 ℃ observation). For example, the visible light reflectivity of the PH coated article can be 10 to 25%, such as 15 to 25%, such as 19 to 24%, such as 15 to 22%, such as less than or equal to 25%, such as less than or equal to 23%, such as less than or equal to 20%.

In another aspect of the present invention, the PH coating 24 can be made denser than previous hydrophilic self-cleaning coatings. For example, the PH coating 24 may be substantially non-porous. By "substantially non-porous" is meant that the coating is sufficiently dense that the coating can withstand conventional hydrofluoric acid drop tests. In the drop test, two drops of 0.5% (volume%) hydrofluoric acid aqueous solution (HF) were placed on the coated sample, and a conventional laboratory watch glass (watch glass) was placed on the sample at room temperature for 8 min. After 8min, the cover glass was removed and the coating was checked for damage. The denser PH coating 24 of the present invention provides the underlying substrate with greater protection from chemical attack than previous more porous self-cleaning coatings, and is also harder and more scratch resistant than previous sol-gel coated self-cleaning coatings.

In accordance with the present invention, a pH coating having a thickness of 10-500 angstroms, e.g., less than or equal to 400 angstroms, e.g., 200 and 300 angstroms, can be formed on the substrate 22 by any one or more of spray pyrolysis, CVD, or MSVD. In spray pyrolysis methods, the organic or metal-containing precursor is carried in an aqueous suspension, e.g., an aqueous solution; in CVD, however, the precursor is carried in a carrier gas, such as nitrogen, and delivered to the surface of the substrate 22 while the substrate 22 is at an elevated temperature sufficient to decompose the precursor and form a PH coating 24 on the substrate 22. In the MSVD process, a metal-containing cathode target is sputtered at negative pressure in an inert or oxygen-containing atmosphere to deposit a sputter coating on the substrate 22. The substrate 22 may be heated during or after coating to crystallize the sputtered coating to form the PH coating 24. Conventional spray pyrolysis, CVD and MSVD processes are well known to those skilled in the art and are therefore not described in detail herein.

Each of which has advantages and limitations depending on the desired characteristics of the coating 24 and the type of glass making process. For example, in a conventional float glass process, molten glass is poured into a bath of molten metal (tin), such as a tin bath, to form a continuous ribbon of float glass. The temperature of the float glass ribbon in the tin bath is typically 1203 ℃ (2200 ° f) (at the infeed end of the bath) to 592 ℃ (1100 ° f) (at the exit end of the bath). The float glass ribbon is removed from the tin bath and annealed, i.e., controlled cooled, in an annealing furnace before the glass is cut into glass sheets of the desired length and width. The temperature of the float glass ribbon between the tin bath and the annealing furnace can be between 480 ℃ (896 ° f) and 580 ℃ (1076 ° f), and the temperature of the float glass ribbon in the annealing furnace can be between 204 ℃ (400 ° f) and 557 ℃ (1035 ° f). US 4466562 and 4671155 provide a discussion of the float glass process and are hereby incorporated by reference.

In the float glass process, CVD and spray pyrolysis processes may be preferred over MSVD processes because they are more compatible with coating a continuous substrate, such as a float glass ribbon, at elevated temperatures. Exemplary CVD and spray pyrolysis coating processes are disclosed in US 4344986, 4393095, 4400412, 4719126, 4853257 and 4971843, which are hereby incorporated by reference.

In the practice of the invention, one or more CVD coating apparatuses may be used in several places during the float glass ribbon production process. For example, the CVD coating apparatus can be used when the float glass ribbon is conveyed through a tin bath, after it exits the tin bath, before entering an annealing lehr, as it is conveyed through an annealing lehr, or after it exits the annealing lehr. Because the CVD process can coat a moving float glass ribbon while withstanding the harsh environments associated with producing a float glass ribbon, the CVD process is particularly useful for providing a PH coating 24 on a float glass ribbon in a molten tin bath. US4853257, 4971843, 5536718, 5464657 and 5599387 disclose CVD coating apparatus and methods useful in the practice of the invention for coating a float glass ribbon in a molten tin bath.

For example, as shown in FIG. 2, one or more CVD applicators 50 may be in a tin bath 52 above a molten tin bath 54. As the float glass ribbon 56 moves through the bath 52, precursor material is fed to the top surface of the ribbon 56. The precursor material decomposes to form the PH coating of the present invention having photoactivatable hydrophilic activity. For example, the precursor material may be selected to decompose to form a semiconducting metal oxide, such as a crystalline metal oxide. Exemplary precursor materials that can be used in the practice of the present invention to produce a titanium dioxide PH coating by CVD include, but are not limited to, titanium tetrachloride (TiCl)₄) Titanium tetraisopropoxide (Ti (OC)₃H₇)₄) (hereinafter, referred to as "TTIP"), titanium tetrabutoxide, titanium tetraethoxide (Ti (OC)₂H₅)₄) (hereinafter "TTEt") and mixtures thereof. Exemplary carrier gases that can be used in the CVD process include, but are not limited to, air, nitrogen, oxygen, ammonia, and mixtures thereof. For the metal-containing precursor described above, the concentration of the metal-containing precursor in the carrier gas may be 0.01 to 0.4% by volume, such as 0.05 to 2% by volume, such as 0.05 to 1% by volume; however, as will be appreciated by those skilled in the art, these concentrations may vary for other metal-containing precursors.

For CVD processes (and spray pyrolysis processes discussed below), the temperature of the substrate 22 (e.g., float glass ribbon 56) during the formation of the PH coating 24 on the substrate should be within a range that will decompose the metal-containing precursor material and result in a photoactivated hydrophilic activity. The lower end of this temperature range is largely influenced by the decomposition temperature of the metal-containing precursor selected. For the titanium-containing precursor described above, the lower temperature limit for the substrate 22 that provides sufficient decomposition of the precursor may be from 400 ℃ (752 ° f) to 500 ℃ (932 ° f). The upper limit of this temperature range may be influenced by the substrate coating process. For example, where the substrate 22 is a float glass ribbon 56 and the PH coating 24 is applied to the float glass ribbon 56 in the molten tin bath 50 during the production of the float glass ribbon, the temperature of the float glass ribbon 56 may exceed 1000 ℃ (1832 ° f). The float glass ribbon 56 may be drawn or sized (e.g., stretched or compressed) above 800 ℃ (1472 ° f). If the PH coating 24 is applied to the float glass ribbon 56 before or during drawing, the PH coating 24 may crack or wrinkle as the float glass ribbon 56 is stretched or compressed, respectively. Thus, when the float glass ribbon 56 is dimensionally stable (in addition to thermal shrinkage upon cooling), such as soda-lime-silica glass below 800 ℃ (1472 ° f), the PH coating may be applied and the float glass ribbon 56 decomposes the metal-containing precursor above a certain temperature, such as above 400 ℃ (752 ° f).

For spray pyrolysis, US 4719126, 4719127, 4111150 and 3660061 disclose spray pyrolysis apparatus and methods that can be used with conventional float glass ribbon production processes and are therefore incorporated by reference. While spray pyrolysis processes are well suited for coating a moving float glass ribbon, like CVD processes, spray pyrolysis processes are more complex than CVD equipment and are typically used at the exit end of the tin bath and the entry end of the lehr.

Exemplary metal-containing precursors useful in the practice of the present invention for generating a PH coating by spray pyrolysis include relatively water-insoluble organometallic reactants, specifically metal acetylacetonates, which are jet or wet milled to a particle size of less than 10 μm and suspended in an aqueous medium with a wetting chemistry. The metal acetylacetonate suitable for forming the titanium dioxide PH coating is titanium oxide acetylacetonate (TiO (C)₅H₇O₂)₂). The relative concentration of the metal acetylacetonate in the aqueous suspension is preferably in the range from 5 to 40% by weight of the aqueous suspension. The wetting agent can be any relatively low foaming surfactant, including anionic, nonionic, or cationic compositions, although nonionic compositions are preferred. The wetting agent is generally added in an amount of 0.24% by weight, but may be added in an amount of 0.01 to 1% by weight or more. The aqueous medium is preferably distilled or deionized water. Aqueous suspensions for the pyrolytic deposition of metal-containing films are disclosed in US 4719127, in particular column 2, line 16 to column 4, line 48, and are hereby incorporated herein by reference.

As will be appreciated by those skilled in the art, the bottom surface (often referred to as the tin side ") of a float glass ribbon placed directly on molten tin has tin diffused on its surface, resulting in a tin side having a different tin adsorption pattern than the opposite surface (often referred to as the" air side ") that does not contact the molten tin. When the float glass ribbon is supported on tin, as described above, the PH coating of the present invention may be formed on the air side of the ribbon by a CVD process in the float process; after it leaves the tin bath, it is formed on the air side of the float glass ribbon by CVD or spray pyrolysis; and/or on the tin side of the float glass ribbon by a CVD process after it exits the tin bath.

With respect to MSVD, US 4379040, 4861669, 4900633, 4920006, 4938857, 5328768, and 5492750 (all incorporated herein by reference) disclose MSVD apparatus and methods for sputter coating metal oxide films onto substrates, including glass substrates. MSVD, which requires negative pressure during the sputtering operation and which is difficult to form on a continuously moving float glass ribbon, is generally not suitable for providing a PH coating on a float glass ribbon during its manufacture. However, the MSVD process is suitable for depositing the PH coating 24 on the substrate 22, such as a glass plate. The substrate 22 can be heated to 400 ℃ (752 ° f) to 500 ℃ (932 ° f) so that the MSVD sputter coating on the substrate crystallizes during deposition, thus eliminating the need for a subsequent heating operation. In some cases, heating of the substrate during sputtering may not be preferable because the additional heating operation during sputtering may reduce productivity. On the other hand, the sputter coating can be directly crystallized in the MSVD coating apparatus without post-heating treatment using high-energy plasma, and it is not a preferred method because of the tendency to lower the yield by the MSVD coater.

One exemplary method of obtaining a PH coating (particularly a PH coating of 300 angstroms or less with an RMS roughness of 2nm or less) using MSVD is to sputter the coating onto a substrate, remove the coated substrate from the MSVD coater, and heat treat the coated substrate to crystallize the sputtered coating to form the PH coating 24. For example, and without limitation, a titanium metal target may be sputtered at a pressure of 5-10 millitorr in an argon/oxygen atmosphere containing 5-50%, e.g., 20%, oxygen to sputter deposit a titanium dioxide coating of a desired thickness on the substrate 22. The as-deposited coating is not crystallized. The coated substrate is removed from the coater and heated to 400 ℃ (752 ° f) to 600 ℃ (1112 ° f) for a time sufficient to promote the formation of the PH crystalline form of titanium dioxide, resulting in PH activity. For example, the coated substrate can be heated at a temperature of 400 ℃ (752 ° f) to 600 ℃ (1112 ° f) for at least 1 hour. Where the substrate 22 is a float glass ribbon cut glass sheet, the PH coating 24 may be sputter deposited onto the air side and/or the tin side.

The substrate 22 with the PH coating 24 deposited by CVD, spray pyrolysis or MSVD may then be subjected to one or more post-PH coating annealing operations. As can be appreciated, the time and temperature of the anneal can be affected by several factors, including the fabrication of the substrate 22, the fabrication of the PH coating 24, the thickness of the PH coating 24, and whether the PH coating 24 is in direct contact with the substrate 22 or is one of multiple layers on the substrate 22.

Regardless of whether the PH coating is provided by CVD, spray pyrolysis, or MSVD, where the substrate 22 includes sodium ions that can migrate from the substrate 22 to the PH coating deposited on the substrate 22, the sodium ions can inhibit or destroy the photoactivatable hydrophilicity of the PH coating by generating an inactive compound while consuming titanium (e.g., by generating sodium titanate) or by recombination of photo-excited charges. Therefore, a Sodium Ion Diffusion Barrier (SIDB) layer may be deposited on the substrate prior to the deposition of the PH coating 24. Suitable SIDB layers are disclosed in detail in US6027766 and are therefore incorporated by reference and are not discussed in detail herein. For post-coating heating, a sodium-containing substrate such as soda-lime-silica glass with a sodium barrier layer may be preferred. For the application of the PH coatings of the present invention in a molten metal bath, a sodium barrier layer is optional.

The PH coatings of the present invention are preferably photoactivated hydrophilic when exposed to ultraviolet range radiation in the electromagnetic spectrum (e.g., 300-. Ultraviolet radiation sources include natural sources of light, such as sunlight; and artificial light sources such as black light or ultraviolet light sources, such as the UVA-340 light source described above.

As shown in fig. 1, in addition to the PH coating 24 of the present invention, one or more additional coatings, such as a functional coating 46 (described below), may be deposited on the substrate 22. For example, functional coating 46 can be deposited on a major surface 60 of substrate 22 that is opposite surface 21. The functional coating 46 may be deposited by any conventional method, such as, but not limited to, spray pyrolysis, CVD, MSVD, sol-gel, and the like. For example, US 4584206 and 4900110, which are incorporated herein by reference, disclose methods and apparatus for depositing metal-containing films on the bottom surface of a glass ribbon by CVD. Such known apparatus may be downstream of the molten tin bath of the float glass process to provide a functional coating on the underside of the ribbon, i.e., the opposite side of the PH coating of the present invention. Alternatively, one or more other CVD applicators may be placed in the tin bath to deposit the functional coating on or under the PH coating 24 of the float glass ribbon.

FIG. 3 shows an illustrative article made according to the present invention in the form of an Insulating Glass (IG) unit (unit) 30. The insulating glass unit has a first pane 32 spaced from a second pane 34 by a gasket assembly (not shown) and the panes are secured with a sealing system forming a chamber between the two panes 32, 34. The first pane 32 has a first surface 36 (number 1 surface) and a second surface 38 (number 2 surface). The second pane 34 has a first surface 40 (number 3 surface) and a second surface 42 (number 4 surface). The first surface 36 may be an exterior surface of the IG unit, i.e., the surface exposed to the environment, while the second surface 42 may be an interior surface, i.e., the surface forming the interior side of the structure. Examples of IG units are disclosed in US 4193236, 4464874, 5088258 and 5106663, which are incorporated herein by reference. As shown in fig. 3, the PH coating 24 is preferably on the number 1 or 4 surface, preferably on the number 1 surface. The PH coating 24 reduces fogging and makes the IG unit 30 easier to clean and maintain.

One or more optional functional coatings 46 may be deposited on at least a portion of the number 2, 3, or 4 surfaces. As used herein, the term "functional coating" refers to a coating that alters one or more physical properties of the substrate on which it is deposited, such as optical, thermal, chemical or mechanical properties, and which is not intended to be removed from the substrate during subsequent processing. The functional coating 46 can have one or more functional coatings having the same or different composition or function. As used herein, the term "layer" or "film" refers to a coated area of a desired or selected coating composition. The membrane may be uniform, non-uniform, or have a gradient of compositional variation. A film is "uniform" when the portions between the outer surface or portion (i.e., the surface or portion furthest from the substrate), the inner surface or portion (i.e., the surface or portion closest to the substrate), and the inner and outer surfaces have substantially the same composition. A film is "graded" when, from the inner surface to the outer surface, or vice versa, one or more components of the film have a substantially increasing fraction and one or more other components have a substantially decreasing fraction. When the membrane is different from a uniform membrane or a gradient-varying membrane, the membrane is "non-uniform". A "coating" consists of one or more "films".

The functional coating 46 can be electrically conductive, such as the conductively heated window coatings disclosed in US 5653903 and 5028759, or can be a single film or multi-film coating of the antenna. Likewise, the functional coating 46 can be a solar control coating, such as a visible, infrared, or ultraviolet light energy reflecting or absorbing coating. Examples of suitable solar control coatings can be found in the following patents: US 4898789, 5821001, 4716086, 4610771, 4902580, 4716086, 4806220, 4898790, 4834857, 4948677, 5059295 and 5028759, also found in US patent application 09/058440. Likewise, the functional coating 46 may be a low emission coating. The "low emission coating" allows visible wavelength energy (e.g., 400-780nm) to be transmitted through the coating while allowing longer wavelength solar and/or thermal infrared energy to be reflected, generally to improve the thermal insulating properties of architectural glazings. By "low emissivity" is meant an emissivity of less than 0.4, preferably less than 0.3, more preferably less than 0.2. Examples of low emissivity coatings are found for example in US 4952423 and 4504109 and GB 2302102. The functional coating 46 can be a single or multi-layer coating and can comprise one or more metals, non-metals, semi-metals, semiconductors, and/or alloys, compounds, composites, compositions, or blends thereof. For example, the functional coating 46 can be a single layer metal oxide coating, a multi-layer metal oxide coating, a non-metal oxide coating, or a multi-layer coating. Additionally, the functional coating may be an anti-reflective coating.

An example of a functional coating suitable for use in the present invention is SUNGATE from PPG industries, incAnd SOLARBANSeries of coatings are commercially available. Such functional coatings typically comprise one or more antireflective coating films comprising a dielectric or antireflective material, such as a metal oxide or metal alloy oxide, which is preferably transparent or substantially transparent to visible light. The functional coating 46 can also include an infrared light reflecting film comprising a reflective metal, such as a noble metal (e.g., gold, copper, or silver, or combinations or alloys thereof), and can comprise a base or blocking film, such as titanium, on or under the metal reflective layer, as is known in the art.

The functional coating 46 may be deposited by any conventional method, such as, but not limited to, Magnetron Sputter Vacuum Deposition (MSVD), Chemical Vapor Deposition (CVD), spray pyrolysis (i.e., pyrolytic deposition), atmospheric pressure CVD (apcvd), low pressure CVD (lpcvd), plasma enhanced CVD (pevcd), plasma assisted CVD (pacvd), thermal or electron beam vaporization, cathodic arc deposition, plasma spray deposition, and wet chemical deposition (e.g., sol-gel, mirror (silver), etc.). When the functional coating is applied to the PH coated side of the substrate, it is preferred that the functional coating be applied in a tin bath prior to the PH coating. When the functional coating is on the opposite side 60 of the PH coating, the functional coating can be applied after the tin bath in the float glass process, as discussed above, for example by CVD or MSVD on the tin side of the substrate 22.

While in the above discussion the PH coating is applied to the air side of the substrate and the functional coating is applied to the tin side of the substrate, it should be understood that the functional coating may be applied to the air side of the substrate, such as a float glass ribbon in a tin bath, and the PH coating subsequently applied to the tin side of the substrate by any desired method, such as those described above.

Advantages of the present invention over sol-gel processes for preparing self-cleaning coatings include the ability to produce thin, dense PH coatings on substrates, unlike the generally thicker, porous self-cleaning coatings produced by sol-gel processes. Because the PH coatings of the present invention are thin, e.g., less than or equal to 500 angstroms, preferably less than or equal to 300 angstroms, they are aesthetically acceptable for use as a clear coating on glass substrates. Another advantage is that the present invention provides a method of PH coating that does not require reheating of the substrate after application of the coating or coating precursor, as is required by currently available sol-gel processes. This not only results in lower cost and higher efficiency of the process, such as but not limited to lower equipment costs, lower energy costs, shorter production times, but also greatly reduces the chance of sodium ion migration and sodium ion poisoning of the PH coating of the present invention. Furthermore, the process of the present invention is readily adaptable to the production of PASC coatings on continuously moving substrates such as float glass ribbons, whereas currently available sol-gel processes are less readily adaptable.

The following examples of the present invention are intended to illustrate, but not limit the present invention.

Examples

A48 "(122 cm) wide coating of titanium dioxide PH was deposited in a thickness of 232 angstroms (as measured by ellipsometry and transmission data) on a 152" (386cm) float glass ribbon (3.3mm thick clear glass) moving at a speed of 484in/min (1229cm/min) in a conventional tin bath using a conventional CVD process. The coating was formed from 0.07% (mol) titanium tetraisopropoxide precursor material in a nitrogen-containing carrier gas and was applied at a glass ribbon temperature of 1220 ° f (659 ℃). The coated glass ribbon was then annealed, i.e., cooled at a controlled rate, and the sample was then cut into 3 "(7.5 cm) by 6" (15cm) coupons. By X-ray diffraction of the crystalline structure of the deposited coatingAnatase was determined by the method. The photocatalytic activity of the coating was 1.8 x10^-3cm^-1min^-1As determined with the conventional stearic acid test and the chromaticity coordinates (illuminant C, 2 ° observation): reflectance (R)₁) Y19.43, x 0.2741, Y78.50, x 0.3187, and Y0.3279.

To measure the photoactivated hydrophilicity of the coated articles, the coupons were cleaned at 145 ° f with a dilute aqueous cleaning solution (ph2.9) of DART 210 cleaner commercially available from Madison Chemical inc. The sample was then rinsed with room temperature deionized water followed by a second ultrasonic cleaning in deionized water at 155 ° f for 10 min. The sample was again rinsed with room temperature deionized water and then blown dry with compressed nitrogen. The samples were exposed to a UVA340 lamp at 24W/m²And measuring the change in contact angle of the water drop with time. The contact angle of a water drop was measured on a Rame-Hart Tele model 102-00-115 goniometer with the sample in a horizontal (non-tilted) position. For each measured sample, the contact angle of a water drop decreases from about 21-47 to about 4-11 after about 30min of UVA-340 exposure and to about 3-7 after about 60min of exposure.

Taber abrasion tests were performed on several test specimens with 1000 gram CS-10F wheels, 10 and 25 cycles. The transmission haze of each sample was measured using the Pacific Scientific XL211 HazeGuard System to be 0.0. Taber abrasion was also performed on 5 specimens following test No. 18 of the procedure ANSI Z26.1-1983 (1000 cycles, 500 grams per round) for abrasion resistance, giving an average increase in scattered light of 2.4%.

The samples were subjected to several conventional test methods and the results are shown in table 1 below. The results of film degradation were based on visual inspection, as well as reflectance color measurements. The results of the contact angles were determined as described above.

As shown in table 1, after each test, the PH coating did not degrade and retained its photo-induced hydrophilicity.

It will be readily appreciated by those skilled in the art that various modifications may be made to the invention without departing from the principles disclosed above. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims (52)

1. An article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface, wherein the photo-induced hydrophilic coating has an outer surface having a root mean square roughness of less than or equal to 2nm, and wherein the photo-induced hydrophilic coating is deposited by a method selected from the group consisting of chemical vapor deposition, magnetron sputtering vacuum deposition, and spray pyrolysis.

2. The article of claim 1, wherein the coating is exposed to 24W/m²After 60min under UVA340 radiation, the contact angle of a water drop on the product is less than 15 degrees.

3. The article of claim 1, wherein the coating is exposed to 24W/m²After 60min under UVA340 radiation, the contact angle of a water drop on the product is less than 10 degrees.

4. The article of claim 1, wherein the coating is exposed to 24W/m²After 60min under UVA340 radiation, the contact angle of a water drop on the product is less than 5 degrees.

5. The article of claim 1, wherein the coating is exposed to 24W/m²After more than 60min under UVA340 radiation, the contact angle of a water drop on the product is less than or equal to 1 deg.

6. The article of claim 1, wherein the photo-induced hydrophilic coating has a thickness of less than or equal to 500 angstroms.

7. The article of claim 1, wherein the photo-induced hydrophilic coating has a thickness of less than or equal to 400 angstroms.

8. The article of claim 1, wherein the photo-induced hydrophilic coating has a thickness of less than or equal to 300 angstroms.

9. The article of claim 1, wherein the photo-induced hydrophilic coating has a thickness of less than or equal to 200 angstroms.

10. The article of claim 1, wherein the photo-induced hydrophilic coating has a thickness of 50 to 500 angstroms.

11. The article of claim 1, wherein the photo-induced hydrophilic coating comprises at least one metal oxide and/or metal alloy oxide selected from the group consisting of titanium oxide, silicon oxide, aluminum oxide, iron oxide, silver oxide, copper oxide, tungsten oxide, zinc/tin alloy oxide, zinc stannate, molybdenum oxide, zinc oxide, strontium titanate, cobalt oxide, chromium oxide, and combinations thereof.

12. The article of claim 1, wherein the photo-induced hydrophilic coating comprises titanium dioxide.

13. The article of claim 12, wherein the titanium dioxide is selected from the group consisting of anatase, rutile, brookite, amorphous, and combinations thereof.

14. The article of claim 1, wherein the photo-induced hydrophilic coating is substantially non-porous.

15. The article of claim 1, wherein the coating has an outer surface having a root mean square roughness of less than or equal to 1 nm.

16. The article of claim 1, wherein the coating has an outer surface having a root mean square roughness of 0.2 to 0.7 nm.

17. The article of claim 1, wherein the photocatalytic activity of the coating is less than or equal to 5x10^-3cm^-1min^-1。

18. The article of claim 1, wherein the photocatalytic activity of the coating is less than or equal to 3x10^-3cm^-1min^-1。

19. The article of claim 1, wherein the photocatalytic activity of the coating is less than or equal to 2x10^-3cm^-1min^-1。

20. The article of claim 1, wherein the article has a visible light reflectance of from 15 to 25%.

21. The article of claim 1, further comprising at least one additional layer between the photo-induced hydrophilic coating and the substrate.

22. The article according to claim 21 wherein said additional layer is a functional coating selected from the group consisting of a sodium ion diffusion barrier, a solar control coating, and an anti-reflective coating.

23. The article of claim 1, wherein the substrate comprises a first surface and a second surface, the coating being deposited on at least a portion of the first surface, and the second surface having tin diffused therein.

24. The article of claim 1, wherein the substrate is a float glass ribbon and the process is selected from the group consisting of chemical vapor deposition and spray pyrolysis.

25. The article of claim 24, wherein the float glass ribbon is in a molten metal bath and the process is a chemical vapor deposition process.

26. The article of claim 1, wherein the article is a monolithic window or a laminated window unit having an inner surface and an outer surface, the photo-induced hydrophilic coating being deposited on said outer surface.

27. The article of claim 1, wherein the article is an insulating glass unit having a number 1, 2, 3, and 4 surface and the photo-induced hydrophilic coating is on at least one of the number 1 or 4 surfaces.

28. The article of claim 27, further comprising a functional coating on at least one of the number 2, 3, or 4 surfaces.

29. The article of claim 1, wherein the article is an automotive light transmitting glass.

30. The article of claim 1, wherein the article is an architectural window.

31. The article of claim 1, wherein the article is an automotive light transmitting glass having an interior surface and the coating is deposited on the interior surface.

32. The article as claimed in claim 1, wherein the coating comprises titanium dioxide having a thickness of 200-300 angstroms, a root mean square smoothness of less than or equal to 1nm, and a photocatalytic activity of less than or equal to 3x10^-3cm^-1min^-1。

33. The article of claim 1, wherein the substrate comprises a functional coating deposited on at least a portion of the substrate.

34. The article of claim 33, wherein the functional coating is a solar control coating.

35. The article of claim 1, wherein the substrate comprises a first surface and a second surface, the photo-induced hydrophilic coating is deposited on at least a portion of the first surface, and the functional coating is deposited on at least a portion of the second surface.

36. An article comprising a float glass ribbon having at least one surface and a photo-induced hydrophilic coating deposited directly on at least a portion of the at least one surface, wherein the photo-induced hydrophilic coating is deposited directly on the float glass ribbon in a molten metal bath, the hydrophilic coating having a root mean square roughness of less than or equal to 2 nm.

37. An article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface, wherein the photo-induced hydrophilic coating has a photo-catalytic activity of less than or equal to 3x10^-3cm^-1min^-1The hydrophilic coating has a root mean square roughness of less than or equal to 2 nm.

38. An article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface, wherein the substrate is a float glass ribbon positioned in a molten metal bath, wherein the photo-induced hydrophilic coating has a thickness of 500 angstroms or less, and wherein the photo-induced hydrophilic coating is deposited on the at least one surface in the molten metal bath using a chemical vapor deposition process, the hydrophilic coating having a root mean square roughness of less than or equal to 2 nm.

39. An article comprising a substrate having at least one surface and a photo-induced hydrophilic coating deposited on at least a portion of the at least one surface, wherein the photo-induced hydrophilic coating is deposited by chemical vapor deposition at 500-1200 ℃, and wherein the photo-induced hydrophilic coating has a thickness of 500 angstroms or less and the hydrophilic coating has a root mean square roughness of less than or equal to 2 nm.

40. A method of producing a photo-induced hydrophilic coating on at least a portion of a substrate, said method comprising the steps of: providing a substrate having a first surface and a second surface, at least one of said surfaces having tin diffused therein; depositing a metal oxide precursor from a coating apparatus onto at least one of said surfaces by a process selected from the group consisting of chemical vapor deposition, spray pyrolysis and magnetron sputtering vacuum deposition; and heating the substrate to a temperature sufficient to decompose the metal oxide precursor to produce a photo-induced hydrophilic coating having a root-mean-square roughness of 2nm or less.

41. The method of claim 40 wherein the coating apparatus is a chemical vapor deposition coater and the metal oxide precursor is selected from the group consisting of titanium tetrachloride, titanium tetraisopropoxide, titanium tetraethoxide, titanium tetrabutoxide, and mixtures thereof.

42. The method of claim 40, wherein the photo-induced hydrophilic coating comprises titanium dioxide.

43. The method of claim 40, wherein the photo-induced hydrophilic coating has a thickness such that the coating is exposed to 24W/m²After 60min under 340nm UV radiation of intensity, the contact angle of the water drop on the coated substrate is less than 15 deg..

44. The method of claim 40, wherein the photo-induced hydrophilic coating has a thickness of less than or equal to 300 angstroms.

45. The method of claim 40, wherein the photo-induced hydrophilic coating has a thickness of 50 to 250 angstroms.

46. The method of claim 40, wherein the coating apparatus is a pyrolytic applicator and the method comprises feeding a suspension of the metal oxide precursor from the pyrolytic applicator onto the first surface.

47. The method of claim 40, wherein the metal oxide precursor is deposited directly on the surface of the substrate.

48. The method of claim 40, wherein the photocatalytic activity of the coating is less than or equal to 3x10^-3cm^-1min^-1。

49. The method as claimed in claim 40, wherein the thickness of the coating is 200-300 angstroms and the root mean square is coarseRoughness of 0.2-1.5nm and a photocatalytic activity of less than or equal to 3x10^-3cm^-1min^-1。

50. A method of producing a photo-induced hydrophilic coating on at least a portion of a substrate, said method comprising the steps of: providing a float glass ribbon in a molten metal bath; depositing a metal oxide precursor material directly from the coating apparatus to the top surface of the glass ribbon by chemical vapor deposition; and heating the glass ribbon to a temperature sufficient to decompose the metal oxide precursor material to produce a photo-induced hydrophilic coating having a root mean square roughness of less than or equal to 2 nm.

51. The method of claim 50, comprising depositing a metal oxide precursor material to provide a photo-induced hydrophilic coating having a thickness of 500 angstroms or less.

52. A method of producing a photo-induced hydrophilic coating on at least a portion of a substrate, said method comprising the steps of: providing a substrate having at least one surface; depositing a metal oxide precursor material from a CVD coating apparatus onto at least a portion of the at least one surface; heating the substrate to 400-1200 ℃ to decompose the metal oxide precursor material to produce a photo-induced hydrophilic coating; and providing sufficient precursor material such that the photo-induced hydrophilic coating has a thickness of 500 angstroms or less, the hydrophilic coating having a root mean square roughness of less than or equal to 2 nm.