CVD method for depositing a coating

Abstract

A CVD method is provided for applying a coating to a surface of a moving ribbon of hot glass by directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass. The method of the invention provides for a relatively simple and inexpensive method of correcting variations in coating thickness obtained in a CVD process. Further, a more uniform coating may be obtained regardless of the cause of the original lack of uniformity.

Description

[0001] 1-29930

[0002] TITLE

[0003] CVD METHOD FOR DEPOSITING A COATING

[0004] BACKGROUND OF THE INVENTION

[0005] The invention relates to a method and apparatus for coating a substrate, particularly a glass substrate. More particularly, the invention relates to a continuous chemical vapor deposition (CVD) process for producing coated glass, and the apparatus for producing such coated glass.

[0006] Chemical vapor deposition processes are well known in the art of coating substrates. The substrate is coated by directing a flow of a gaseous reactant mixture toward the surface of the substrate to cause the reactant mixture to deposit the desired coating on the substrate surface. The physical form of the coating reactants employed in such processes may be liquid, vapor, liquids or solids dispersed in gas mixtures, aerosols, or vaporized or vaporous coating reactants dispersed in gas mixtures.

[0007] One issue associated with CVD processes relates to the production of a coating of uniform thickness along the width of the substrate. In certain instances, such as the application of a reflective metal oxide coating to a sheet of glass, the requirement that the coating have a uniform thickness is especially important, since small variations in the coating thickness can result in the glass sheet having non-uniform color. For example, variations in thickness of the metal oxide coating of one millionth of an inch can produce an unaesthetic appearance in the glass.

[0008] Generally, to produce a coating having a constant thickness, it is necessary that the gaseous reactant mixture be uniformly applied to the entire sheet of glass. Various 1-29930 means have been proposed for applying the gaseous reactant mixture in a uniform manner to a sheet of glass. Despite the various means previously proposed, problems still arise regarding the application of a coating of uniform thickness on a substrate by a chemical vapor deposition process. The causes of such non-uniformity are uncertain, but may include problems of exhaust balancing, temperature gradients in the substrate to be coated, dimensional changes in the coater upon heating, changes in the entrance region Reynolds number with changes in total flow, and the accumulation of deposits in the coater. Whatever the cause, it would be advantageous to provide a method and apparatus for substantially eliminating any lack of uniformity in the thickness of a coating applied to a substrate in a chemical vapor deposition process.

[0009] SUMMARY OF THE INVENTION

[0010] The invention relates in certain embodiments to a method of applying a coating to a surface of a moving ribbon of hot glass comprising (a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated; (b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations; (c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface; (d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the 1-29930 thickness of the coating; and (e) injecting a gas through a nozzle into a selected one or more of the drop tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.

[0011] In other embodiments of the invention, a method is provided that comprises: (a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated; (b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations; (c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface; (d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; (e) injecting an equal base amount of gas into each of the two or more drop tubes, and (f) after step (e), varying the amount of gas injected into one or more of the drop tubes relative to the amount of gas injected into one or more of the other of the drop tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at 1-29930 least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.

[0012] In still further embodiments, a method of applying a coating to a surface of a moving ribbon of hot glass comprises: (a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated; (b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations, wherein a plurality of the drop tubes are provided with a tee fitting; (c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface; (d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; and (e) injecting a gas into a selected one or more of the drop tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating; wherein the combined total amount of gas injected into the various drop tubes from the 1-29930 respective tee fittings is from about 15 slpm to about 60 slpm, preferably from about 20 slpm to about 40 slpm.

[0013] In additional embodiments, the method of the invention comprises: (a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated; (b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations; (c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface; (d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; and (e) injecting a gas into a selected one or more of the drop tubes so as to achieve jet-mixing and / or jet-impaction in the selected one or more of the drop tubes, to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.

[0014] The invention thereby provides for a relatively simple and inexpensive method of correcting variations in coating thickness obtained in a CVD process. Further, a more 1-29930 uniform coating may be obtained regardless of the cause of the original lack of uniformity.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above, as well as other advantages of the invention, will become readily apparent to those skilled in the art from the following detailed description of preferred embodiments when considered in the light of the accompanying drawings, in which:

[0017] FIG. 1 is a somewhat schematic, partial cutaway perspective view of the coating apparatus of the present invention;

[0018] FIG. 2 is a schematic representation of the apparatus of the invention; and

[0019] FIG. 3 is an enlarged cross-sectional view of a portion of the apparatus shown in FIG. 1.

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0021] It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific layers, articles, methods and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise.

[0022] In the context of the present invention, where a layer is said to be “based on” a particular material or materials, this means that the layer predominantly consists of the 1-29930 corresponding said material or materials, which means that it comprises at least about 50 at.% of said material or materials.

[0023] When a layer is said to deposited or formed directly on another layer, it means that there are no intervening layers coatings therebetween.

[0024] A side of a glass substrate where a coating is formed may be referred to herein as the coated side. A second major surface of the glass substrate and an opposite side of the coated glass article may be uncoated.

[0025] Unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

[0026] Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of” or “consists essentially of’ means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% 1-29930 by weight, typically less than 3% by weight, more typically less than 1 % by weight of non-specified components.

[0027] The term “consisting of’ or “consists of’ means including the components specified but excluding other components.

[0028] Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to include the meaning “consists essentially of’ or “consisting essentially of”, and also may also be taken to include the meaning “consists of’ or “consisting of”.

[0029] References herein such as “in the range x to y” are meant to include the interpretation “from x to y” and so include the values x and y.

[0030] Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number.

[0031] Further, any feature set out above in relation to the first aspect of the present invention may also be utilised in relation to any other aspects of the present invention, and any invention described herein may be combined with any feature of any other invention described herein mutatis mutandis. It will also be appreciated that optional features applicable to one aspect of the invention can be used in any combination, and in any number. Moreover, they can also be used with any of the other aspects of the 1-29930 invention in any combination and in any number. This includes, but is not limited to, the dependent claims from any claim being used as dependent claims for any other claim in the claims of this application.

[0032] The method and apparatus of the present invention may be employed in combination with a variety of substrates and coatings, and may be used to coat a continuous sheet or a series of discrete substrates. In the preferred embodiments of the invention, a continuous glass sheet is coated. This may be a sheet produced by the plate process, by any sheet process, or by a float process. The description which follows relates to an especially preferred embodiment where coating is deposited on a newly formed float glass ribbon.

[0033] Furthermore, the method and apparatus of the present invention are applicable to the chemical vapor deposition of any one or more reactants. For example, in some embodiments, the method and apparatus of the present invention are used to deposit a silica coating on a newly formed float glass ribbon. A gaseous mixture of monosilane, oxygen, ethylene, and nitrogen is reacted at or near the surface of the glass upon which the silica coating is to be deposited. This method for preparing a silica coating is more fully set forth in the patent US 5798142, which is incorporated herein in its entirety by reference thereto.

[0034] In other exemplary embodiments, the method and apparatus of the present invention are used to deposit a fluorine doped tin oxide coating on a newly formed float glass ribbon. A gaseous mixture of dimethyltin dichloride, oxygen, water, hydrogen fluoride, and nitrogen is reacted at or near the surface of the glass upon which the fluorine doped tin oxide coating is to be deposited. This method for preparing a fluorine 1-29930 doped tin oxide coating is more fully set forth in the patent US 5698262, which is incorporated herein in its entirety by reference thereto.

[0035] In other embodiments, for example, the method and apparatus of the present invention are used to deposit a titania coating on a newly formed float glass ribbon. A gaseous mixture of titanium tetrachloride, ethyl acetate, and nitrogen is reacted at or near the surface of the glass upon which the coating is to be deposited. This method for preparing a titania coating is more fully set forth in the patent US 6840061 , which is incorporated herein in its entirety by reference thereto.

[0036] In still further exemplary embodiments, the method and apparatus of the present invention are used to deposit a titanium nitride film on a newly formed float glass ribbon. A mixture of a titanium tetrahalide and a reducing agent, preferably titanium tetrachloride and anhydrous ammonia, is reacted at or near the surface of the glass sheet upon which the titanium nitride coating is to be deposited. Both reactants are preferably supplied in helium as an inert carrier gas. This method for preparing a titanium nitride coating is more fully set forth in the patents US 4545000 and US 5087525, both of which are incorporated herein in their entirety by reference thereto.

[0037] Referring now to FIG. 1 , there is illustrated an apparatus, generally designated 10, for applying a coating to a substrate, such as a continuous glass ribbon or sheet 12. The glass sheet 12 is generally supported on rollers (not shown) which move the glass sheet 12 along a path such as is indicated by the arrow at the lower right of FIG. 1 . The process entails forming a glass substrate, generally in a float glass process, and continuously advancing the glass sheet 12, while hot, past the coating apparatus 10 illustrated in FIG. 1. The coating apparatus is generally positioned in a sealed zone in 1-29930 which a non-oxidizing atmosphere is maintained. When the method is utilized in conjunction with the float glass manufacturing process, the coating apparatus is preferably provided within the float bath section thereof. The non-oxidizing atmosphere is generally a gas comprising about 99% by volume nitrogen and 1 % by volume hydrogen. However, other inert gases can be substituted for the nitrogen, or the proportion of hydrogen can be increased or decreased, so long as the desired result is achieved; i.e. , oxidation of the tin bath is prevented.

[0038] The coating apparatus 10 more particularly comprises a vapor distributor 14 disposed in facing relation to the glass sheet 12 and spanning the width of the glass sheet 12. A mixture of vaporized reactants is supplied to the vapor distributor 14 by means of a supply assembly described in detail below. A first vaporized reactant, generally mixed with an inert carrier gas such as nitrogen or helium, is supplied through the supply line 16 to an optional mixing device 18. If an optional second vaporized reactant is supplied via a separate supply line 20, the first vaporized reactant can be mixed with the second vaporized reactant in mixer 18. In that case, the second vaporized reactant is also generally mixed with an inert carrier gas before being introduced to the mixer 18. It is generally preferred that the same carrier gas be used for both reactants. In alternate embodiments, all the vaporized reactants may be mixed together at some point (not shown) further upstream from the jacketed header 22.

[0039] The vapor mixture, comprised of a mixture of the first and second reactants and the carrier gas or gases, passes to the jacketed header 22. The jacketed header 22 may be used in the conventional manner to maintain the temperature of the vapor mixture in the desired range for the specific coating conditions of any particular application. The vapor mixture is supplied to the vapor distributor 14 from the header 22 by means of a series of drop tubes 24 providing fluid communication therebetween. The drop tubes 24 are generally spaced approximately evenly along the lengths of the header 22 and distributor 14.

[0040] From the drop tubes 24, the vapor mixture flows into a channel 26 formed in the distributor 14. The channel 26 may advantageously be provided with a plurality of baffles 28, which force the vapor mixture through a series of direction changes, more evenly distributing the vapor mixture along the length of the distributor 14. This improves the uniformity of the coating deposited on the glass sheet 12. The vapor mixture flows by the baffles 28 and out of the distributor 14 through the outlet 30, which is disposed adjacent the glass sheet 12. The first and second reactants in the vapor mixture react at or near the surface of the glass sheet 12, continuously depositing the desired coating on the glass sheet 12 as it passes by the distributor 14.

[0041] Despite the series of spaced drop tubes 24 which supply the vapor mixture to the distributor 14, and the series of baffles 28 provided therein, sometimes the thickness of the coating deposited on the glass sheet 12 is not uniform across the width of the glass sheet 12. As mentioned above, this may be due to a variety of factors, such as problems of exhaust balancing, temperature gradients in the substrate to be coated, dimensional changes in the coater upon heating, changes in the entrance region Reynolds number with changes in total flow, and the buildup of deposits in the coater. When a reflective coating is being deposited on the glass sheet 12, this non-uniformity may result in an unacceptable variation in transmission and reflected color across the width of the glass sheet 12. When a low emissivity coating is being deposited on the glass sheet 12, the non-uniformity may result in an unacceptable variation in emissivity across the width of the glass sheet 12, while when a conductive coating is being deposited on the glass sheet 12, the non-uniformity may result in an unacceptable variation in sheet resistance across the width of the glass sheet 12.

[0042] To remedy any detected non-uniformity in coating thickness, a plurality of the drop tubes 24 of the coating apparatus 10 are provided with a tee fitting 32. In a preferred embodiment, each of the drop tubes 24 is provided with a tee fitting 32. Preferably, each of the tee fittings 32 is provided with a separate supply line 34 connected to a supply of one or more of the reactants or an inert gas, preferably an inert gas, and more preferably the same inert gas used as the carrier gas for the reactants. In certain preferred embodiments, the supply lines 34 are each in fluid communication with a flow control means 36. The flow control means 36 controls the flow of one or more of the reactants or inert gas (or both) to any one or more of the tee fittings 32 through the individual supply lines 34 (shown schematically). The flow control means 36 may be any suitable device for controlling such flow, such as a mass flow controller, a rotameter or the like.

[0043] If it is determined that the coating being deposited on the glass sheet 12 is too thin in a particular area and an amount of an inert gas is being supplied to the drop tube in that area, then the flow control means 36 is activated to reduce the flow of inert gas into that drop tube to increase the concentration of reactants. In the alternative, the flow control means 36 could be activated to supply one or more of the reactants to one or more of the drop tubes 24, via the associated supply line 34 and tee fitting 32, which are positioned in that particular area. Since the reaction rate of film formation on the glass 1-29930 sheet 12 is dependent on the concentration of the reactants in the gas phase above the glass sheet 12, the increase in the concentration of one of the reactants in either case will increase the rate of deposition and the thickness of the coating deposited in that particular area. In this manner, a more uniform coating thickness, and resulting color, transmittance, and / or sheet resistance may be achieved across the width of the glass sheet 12.

[0044] On the other hand, if it is determined that the coating being deposited on the glass sheet 12 is too thick in a particular area, the flow control means 36 is activated to supply an inert gas to one or more of the drop tubes 24, via the associated supply line 34 and tee fitting 32, which are located in that particular area. The introduction of an inert gas into a particular drop tube 24 reduces the concentration of the reactants in the vapor mixture passing through that drop tube 24, thereby reducing the deposition rate on the glass sheet 12 in the area of the selected drop tube or drop tubes. In addition, the introduction of additional inert gas into a drop tube 24, if of sufficient volume, produces some static pressure increase in the drop tube 24 in which it is introduced. This decreases the total flow of the vapor mixture to that drop tube 24, and causes an increase in total flow of the vapor mixture to the surrounding drop tubes 24. This again results in the deposition of a thinner coating proximate the drop tube 24 in which the inert gas is introduced.

[0045] FIG. 2 illustrates schematically the method of the present invention. The vaporized reactants are supplied through the supply line 16 and optional supply line 20 to the jacketed header 22, down through the drop tubes 24 to the distributor 14. The vapor mixture flows out of the distributor 14 through an outlet disposed adjacent the 1-29930 glass sheet 12. The first and second reactants in the vapor mixture react at or near the surface of the glass sheet 12, continuously depositing the desired coating on the glass sheet 12 as it passes by the distributor 14.

[0046] While variations in the thickness of the coating on the glass may in some cases be determined simply by observing the coated glass, in preferred embodiments a thickness measuring device 38 for measuring the thickness of the coating deposited on the glass sheet 12 is preferred. Where a reflective coating has been deposited, the thickness may preferably be measured by means of a photometer 38 positioned downstream of the coating apparatus 10. A thinner reflective coating results in a higher transmittance and a change in reflected color, and this can be measured by the photometer. In the case of the deposition of a titanium nitride coating on a glass sheet, as an example, a thinner coating results in a more negative value for the b* component of reflected color, where b* measures the amount of yellow-blue color in the color scale system established by the Commission International de I'Eclairage (hereinafter "CIE- lab"). Thus, the uniformity of the thickness of the coating may be determined indirectly by measuring the b* component across the width of the glass sheet 12. In an especially preferred embodiment, an online scanning photometer is employed to determine the thickness of the coating deposited along the width of the glass sheet 12.

[0047] Manual control means 40 may be utilized to activate the flow control means 36 manually in response to visual output provided by whatever suitable means 38 is employed to determine the thickness of the deposited coating. In an alternate, preferred embodiment, the thickness measuring means 38 is connected to a programmable controller 42 which is connected to and automatically activates the flow 1-29930 control means 36 in response to receiving a signal from the thickness measuring means 38. When this signal indicates a non-uniformity of the coating thickness outside of a pre-determined acceptable range programmed in controller 42, the flow control means 36 is activated by the controller 42 to supply one or more of the reactants or an inert gas to one or more of the individual drop tubes 24 to alter the concentration of one or more of the reactants in the gaseous reactant mixture flowing through such drop tube or drop tubes 24. The rate of deposition of the coating in the proximity of such drop tube(s) is thereby altered to obtain a coating on the substrate having improved uniformity of thickness.

[0048] In certain preferred embodiments, each tee fitting 32 is provided with nozzle 33 to allow for the injection of a gas into the related drop tube 24. The nozzles comprise a taper or constriction, as illustrated in FIG. 3, resulting in a jet or increase in the flow rate of the gas injected into the drop tubes, which advantageously increases the mixing between the injected gas and the vaporized reactants flowing through the drop tube 24 from the header 22.

[0049] The flow of a jet or nozzle into the flow in a pipe such as a drop tube 24 has four basic geometric / flow parameters: the jet or nozzle diameter d, the pipe or drop tube diameter D, the jet-to-pipe velocity ratio r, and the pipe flow Reynolds number Re. The combination of rd, known as the jet momentum length, has been used as the parametric length scale for this flow. In accordance with the invention, the Reynolds number of the flow through each drop tube 24 is greater than 15,000, high enough that the flow is well developed turbulent flow. 1-29930

[0050] When a flow of gas is injected from a nozzle 33 into the fully developed turbulent flow in the drop tube 24 to which the nozzle 33 is connected, three scenarios can result: 1) where rd / D<0.07, known as the wall-source regime, the jet does not penetrate significantly into the pipe flow and does not create efficient mixing; 2) where 0.07<rd / D<1 , known as the jet-mixing regime, the jet penetrates the core of the pipe flow and creates efficient mixing; and 3) where rd / D>1 .0, known as the jet-impaction regime, the jet hits the opposite wall of the pipe and also creates efficient mixing, though not better mixing than the jet-mixing regime.

[0051] The volume of flow through and size of the jet or nozzle orifice 33 of tee fitting 32 are adjusted relative to the diameter and flow through the drop tube 24 so that operation in the wall-source regime is avoided. Thus, the volume of flow and size of the nozzle orifice are adjusted so that each injection of gas operates in the jet-mixing regime or the jet-impaction regime, and preferably so that each injection of gas operates in the jetmixing regime. In this way, more complete mixing is achieved before the vaporized reactants exit the outlet 30 of the distributor 14, enhancing the ability to improve the uniformity of the deposited coating.

[0052] In further embodiments of the invention, rather than only injecting a gas into one or more of the drop tubes 24 after observing a variation in the thickness of the coating deposited on the glass, an initial base amount of gas is injected into each one of the two or more drop tubes. Then, the amount of gas supplied through each of the tee fittings 32 can be either reduced or increased as needed to improve the uniformity of thickness of the coating. In these embodiments, once there is determined to be a variation in coating thickness, the amount of gas injected into one or more of the drop tubes can be 1-29930 varied relative to the amount of gas injected into one or more of the other of the drop tubes to selectively vary the concentration of at least one gaseous reactant in the gaseous coating mixture. In addition, supplying an initial base amount of gas through each of the tee fittings prevents any backflow through the tee fitting and any buildup of coating within the nozzle 33.

[0053] In other aspects of the invention, a constant volume of vaporized reactants flowing through the header 22 is preferably maintained. In certain preferred embodiments, the total volume of gas flowing through the tee fittings is also maintained at a constant amount throughout the process. In this way, the total flow into the distributor remains constant throughout the process.

[0054] It has also been surprisingly found that, in some especially preferred embodiments, the combined total amount of gas supplied through the two or more tee fittings is kept between about 15 slpm and about 60 slpm, preferably from about 20 slpm and about 40 slpm. A total flow of gas through the two or more tee fittings of less than about 15 slpm may not provide sufficient flexibility to vary the reactant concentrations at the locations needed to significantly improve the uniformity of the coating. A total flow of gas through the two or more tee fittings of more than about 60 slpm may not allow for complete mixing within each of the drop tubes, impeding the ability to improve the uniformity of the coating. In certain embodiments, the combined total amount of gas supplied through the two or more tee fittings is kept between about 2.5% and 10% of the total volume of gas flowing through the distributor 14, and preferably between about 3.3% and 6.7% of the total volume of gas flowing through the distributor 14. 1-29930

[0055] In this application and accompanying drawings there is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. The suggestions contained herein are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof, and will be able to modify it and embody it in a variety of forms, each as may be best suited in the condition of a particular case. For example, it will be understood that any number of drop tubes and associated side arms greater than one may be utilized in accordance with the invention, depending upon the particular application.

[0056] In accordance with the provisions of the patent statutes, the invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.

Claims

1-29930WHAT IS CLAIMED IS:1 . A method of applying a coating to a surface of a moving ribbon of hot glass comprising:(a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated;(b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations;(c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface;(d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; and(e) injecting a gas through a nozzle into a selected one or more of the drop tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.1-299302. A method as claimed in claim 1 , wherein the gaseous coating mixture consists of one or more gaseous reactants and an inert carrier gas.

3. A method as claimed in any preceding claim, wherein the concentration of the at least one gaseous reactant is selectively varied by adding additional gaseous reactant or inert gas to the selected one or more of the drop tubes.

4. A method as claimed in any preceding claim, wherein the concentration of the at least one gaseous reactant is selectively varied by adding additional inert gas to the selected one or more of the drop tubes.

5. A method as claimed in any preceding claim, wherein the thickness of the coating is determined indirectly by measuring an optical property of the coated glass.

6. A method as claimed in any preceding claim, wherein the thickness of the coating is determined indirectly by measuring reflected color in step (d).

7. A method as claimed in claim 6, wherein the thickness of the coating is determined indirectly by measuring glass side reflected color.

8. A method as claimed in claim 7, wherein the thickness of the coating is determined indirectly by measuring the b* component of the glass side reflected color.1-299309. A method as claimed in any of claims 6 to 8, wherein the reflected color is measured using a photometer.

10. A method as claimed in any of claims 6 to 9, wherein the reflected color is measured using an online scanning photometer.11 . A method as claimed in any preceding claim, wherein a mass flow controller supplies the one or more gaseous reactants or inert gas to the one or more drop tubes.

12. A method as claimed in any preceding claim, wherein one or more gaseous reactants is supplied to one or more of the drop tubes proximate a supply location where the thickness of the coating deposited was observed to be lower relative to the thickness of the coating observed proximate another supply location.

13. A method as defined in any preceding claim, wherein an inert gas is supplied to one or more of the drop tubes proximate a supply location where the thickness of the coating deposited was observed to be higher relative to the thickness of the coating observed proximate another supply location.

14. A method as claimed in any preceding claim, wherein the injection in step (e) is controlled by a programmable controller in response to the property observed in step (d).1-2993015. The method of any preceding claim, wherein each nozzle comprises a taper or constriction resulting in an increase in the flow rate of the gas injected into each of the drop tubes.

16. A method of applying a coating to a surface of a moving ribbon of hot glass comprising:(a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated;(b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations;(c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface;(d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating;(e) injecting an equal base amount of gas into each of the two or more drop tubes; and(f) after step (e), varying the amount of gas injected into one or more of the drop tubes relative to the amount of gas injected into one or more of the other of the drop1-29930 tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.

17. A method of applying a coating to a surface of a moving ribbon of hot glass comprising:(a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated;(b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations, wherein a plurality of the drop tubes are provided with a tee fitting;(c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface;(d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; and(e) injecting a gas into a selected one or more of the drop tubes to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating1-29930 mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating; wherein the combined total amount of gas injected into the various one or more drop tubes through the respective tee fittings is from about 15 slpm to about 60 slpm.

18. The method of claim 17, wherein the combined total amount of gas injected into the various one or more drop tubes through the respective tee fittings is from about 20 slpm to about 40 slpm.

19. A method of applying a coating to a surface of a moving ribbon of hot glass comprising:(a) providing a coating gas distributor having a length extending across the width of the ribbon to be coated;(b) supplying a gaseous coating mixture comprising at least one gaseous reactant from a supply header to the distributor at two or more supply locations spaced along the length of the distributor, wherein two or more drop tubes provide fluid communication between the header and the gas distributor, with a drop tube provided at each of the two or more supply locations;(c) directing the gaseous coating mixture from the distributor over the surface of the moving ribbon of hot glass to form a coating on the hot glass surface;1-29930(d) determining at least one property of the coated glass at spaced locations across the width of the coated ribbon, the property being one which varies with a variation of the thickness of the coating; and(e) injecting a gas into a selected one or more of the drop tubes so as to achieve jet-mixing and / or jet-impaction in the selected one or more of the drop tubes, to selectively vary the concentration of the at least one gaseous reactant in the gaseous coating mixture supplied at one or more of the supply locations relative to the concentration of the at least one gaseous reactant supplied at one or more of the other of the spaced supply locations in response to a detected lack of uniformity of the coating as determined by the property to improve the uniformity of thickness of the coating.

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