WO2016200853A1

WO2016200853A1 - Method of removing metallic deposits from glass

Info

Publication number: WO2016200853A1
Application number: PCT/US2016/036291
Authority: WO
Inventors: Satoshi TSUNEYAMA; Kiyotaka YOSHIMOTO
Original assignee: Corning Incorporated
Priority date: 2015-06-10
Filing date: 2016-06-08
Publication date: 2016-12-15
Also published as: TWI689475B; JP2018518444A; KR20180026727A; CN107873049A; TW201708150A

Abstract

A method of removing metallic deposits from a glass article, for example a glass substrate such as a glass sheet, includes exposing the glass article to a weak acid solution for a time effective to remove the metallic deposit.

Description

METHOD OF REMOVING METALLIC DEPOSITS FROM GLASS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/173,480, filed on June 10, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND Field

[0002] The present disclosure is generally directed to a method of processing glass articles, for example a glass substrate for example a glass sheet suitable for use in display applications, and in particular for processing the glass article to remove metallic deposits therefrom.

Technical Background

[0003] Glass substrates suitable for use in display applications, for example as substrates in a glass display panel or as a cover glass sheet for a display panel, must be extraordinarily clean and defect free, as the visual acuity of the average viewer of such displays is capable of discerning even minute defects on a viewing screen. In addition, contamination of the glass sheets used in such applications can impede the deposition and/or functioning of materials deposited on the glass sheet that are required for the proper operation of the display device. For example, contamination may impede the deposition of thin film transistors deposited on one or more glass substrates used in the manufacture of a display device.

[0004] Contamination of glass substrates can be, for example, organic or metallic. As no single cleaning material is capable of removing all such contaminates, the process may need to be tailored to employ different cleaning agents to remove different contaminants. That said, the need to constrain costs associated with the manufacture of glass sheets dictates that effective methods of removing contaminants from glass sheets that do not significantly increase processing costs should be employed.

SUMMARY

[0005] It has been discovered that a weak acid may be used to treat glass articles, for example glass substrates such as glass sheets comprising metallic deposits on surfaces thereof, and it has been shown to be effective even at very small concentrations. Moreover, in certain embodiments the use of hypochlorous acid from industrial water systems provides for a ready source of chlorinated water that advantageously 1) is plentiful and inexpensive, and 2) is not subject to the special handling required for more active acids such as sulfuric or hydrochloric acids.

Hypochlorous acid is widely used as a bleach and a deodorizer and to disinfect and prevent bacterial growth in water. For example, hypochlorous acid may be used in industrial

applications to prevent the growth of bacteria in water used as a cooling fluid in heat exchange systems. Hypochlorous acid may be easily formed, for example, by adding sodium chlorite to water.

[0006] Accordingly, in one aspect a method of removing a metallic deposit from a glass article with a weak acid is described comprising exposing the glass article to an aqueous solution of a weak acid in a concentration of from 0.5 to 1.0 ppm for a time effective to remove metallic deposits from a surface of the glass article. A dissociation constant K_a of the weak acid can be in a range from about 2.95 x 10^"8 to about 7.5 x 10^"3. For example, the weak acid may be selected from the group consisting of hypochlorous acid, boric acid and phosphoric acid. The metallic deposit may comprise at least one of iron, calcium, barium, zinc, cobalt, manganese, strontium and combinations or alloys thereof. In various particular embodiments the metallic deposit comprises iron and the the weak acid comprises hypochlorous acid.

[0007] In another aspect, a method of removing a metallic deposit from a glass sheet is disclosed comprising exposing the entirety of at least one major surface of the glass sheet to an acqueous solution of hypochlorous acid in a concentration of from 0.5 to 1.0 ppm for a time effective to remove a metallic deposit from the at least one major surface. The metallic deposit may include at least one of iron, calcium, barium, zinc, cobalt, manganese, strontium and combinations or alloys thereof.

[0008] It should be clear that while the present disclosure is directed largely to glass substrates (e.g. glass sheets) produced in a glass sheet manufacturing process, embodiments described herein may be applied to other glass articles as well. Accordingly, the present disclosure is not limited to glass sheets, plates or other glass substrates, but may be used to remove metallic deposits from glass articles in general, regardless of shape.

[0009] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments as they are described and claimed. The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure, and together with the description serve to explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic diagram of an exemplary glass manufacturing apparatus;

[0011] FIG. 2 is a block diagram of a glass substrate finishing process that may be located downstream of the apparatus of FIG. 1;

[0012] FIG. 3 is a microscopic view of a metallic deposit on a glass substrate manufactured by the apparatus of FIG. 1;

[0013] FIG. 4 is an embodiment of a treatment apparatus for treating a glass substrate with hypochlorous acid;

[0014] FIG. 5 is another embodiment of a treatment apparatus for treating a glass substrate with hypochlorous acid; and

[0015] FIG. 6 is a graph illustrating the number of occurrences of iron deposits on glass substrates on a daily basis over a time period of approximately 6 months and showing a dramatic decrease in iron deposits upon commencement of hypochlorous acid washing.

DETAILED DESCRIPTION

[0016] Apparatus and methods will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments of the disclosure are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0017] It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations. [0018] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0019] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0020] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus, specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0021] As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0022] Shown in FIG. 1 is an example glass manufacturing apparatus 10. In some examples, the glass manufacturing apparatus 10 can comprise a glass melting furnace 12 that can include a melting vessel 14. In addition to melting vessel 14, glass melting furnace 12 can optionally include one or more additional components such as heating elements (e.g., combustion burners or electrodes) configured to heat batch and convert the batch into molten glass. In further examples, glass melting furnace 12 may include thermal management devices (e.g., insulation components) configured to reduce heat lost from a vicinity of the melting vessel. In still further examples, glass melting furnace 12 may include electronic devices and/or electromechanical devices configured to facilitate melting of the batch material into a glass melt. Still further, glass melting furnace 12 may include support structures (e.g., support chassis, support member, etc.) or other components.

[0023] Glass melting vessel 14 is typically comprised of refractory material, such as a refractory ceramic material. In some examples glass melting vessel 14 may be constructed from refractory ceramic bricks, for example refractory ceramic bricks comprising alumina or zirconia.

[0024] In some examples, the glass melting furnace may be incorporated as a component of a glass manufacturing apparatus configured to fabricate a glass ribbon. In some examples, the glass melting furnace of the disclosure may be incorporated as a component of a glass manufacturing apparatus comprising a slot draw apparatus, a float bath apparatus, a down-draw apparatus (e.g., a fusion apparatus), an up-draw apparatus, a press-rolling apparatus, a tube drawing apparatus or any other glass manufacturing apparatus. By way of example and not limitation, FIG. 1 schematically illustrates glass melting furnace 12 as a component of a fusion down-draw glass manufacturing apparatus 10 for fusion drawing a glass ribbon for subsequent processing into glass sheets.

[0025] The glass manufacturing apparatus 10 (e.g., fusion down-draw apparatus 10) can optionally include an upstream glass manufacturing apparatus 16 that is positioned upstream relative to glass melting vessel 14. In some examples, a portion of, or the entire upstream glass manufacturing apparatus 16, may be incorporated as part of the glass melting furnace 12.

[0026] As shown in the illustrated example, the upstream glass manufacturing apparatus 16 can include a storage bin 18, a batch delivery device 20 and a motor 22 connected to the batch delivery device. Storage bin 18 may be configured to store a quantity of batch material 24 that can be fed into melting vessel 14 of glass melting furnace 12, as indicated by arrow 26. In some examples, batch delivery device 20 can be powered by motor 22 such that batch delivery device 20 is configured to deliver a predetermined amount of batch material 24 from storage bin 18 to melting vessel 14. In further examples, motor 22 can power batch delivery device 20 to introduce batch material 24 at a controlled rate based on a level of molten glass sensed downstream from melting vessel 14. Batch material 24 within melting vessel 14 can thereafter be heated to form molten glass 28. [0027] Glass manufacturing apparatus 10 can also optionally include a downstream glass manufacturing apparatus 30 that is positioned downstream relative to the glass melting furnace 12. In some examples, a portion of downstream glass manufacturing apparatus 30 may be incorporated as part of glass melting furnace 12. For instance, first connecting conduit 32 discussed below, or other portions of the downstream glass manufacturing apparatus 30, may be incorporated as part of the glass melting furnace 12. Elements of the downstream glass manufacturing apparatus, including first connecting conduit 32, may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group of metals consisting of platinum, iridium, rhodium, osmium, ruthenium and palladium, or alloys thereof. For example, downstream components of the glass manufacturing apparatus may be formed from a platinum-rhodium alloy including 70 to 90% by weight platinum and 10 to 30% by weight rhodium. However, other suitable metals can include molybdenum, palladium, rhenium, tantalum, titanium, tungsten and alloys thereof.

[0028] Downstream glass manufacturing apparatus 30 can include a first conditioning (i.e. processing) vessel such as fining vessel 34, located downstream from melting vessel 14 and coupled to melting vessel 14 by way of the above-referenced first connecting conduit 32. In some examples, molten glass 28 may be gravity fed from melting vessel 14 to fining vessel 34 by way of first connecting conduit 32. For instance, gravity may drive molten glass 28 through an interior pathway of first connecting conduit 32 from melting vessel 14 to fining vessel 34. It should be understood, however, that other conditioning vessels may be positioned downstream of melting vessel 14, for example between melting vessel 14 and fining vessel 34. In some embodiments, a cooling vessel (not shown) may be employed between the melting vessel and the fining vessel wherein molten glass from the melting vessel is cooled to a temperature lower than the temperature of the molten glass in the melting vessel before entering the fining vessel.

[0029] Within fining vessel 34, bubbles may be removed from molten glass 28 by various techniques. For example, batch material 24 may include multivalent compounds (i.e. fining agents) such as tin oxide that, when heated, undergo a chemical reduction reaction and release oxygen. Other suitable fining agents include without limitation arsenic, antimony, iron and cerium. Fining vessel 34 is heated to a temperature greater than the melting vessel temperature, thereby heating the fining agent. Oxygen bubbles produced by the temperature-induced chemical reduction of the fining agent(s) rise through the molten glass within the fining vessel, wherein gases in the melt produced in the melting furnace can coalesce into the oxygen bubbles produced by the fining agent. The enlarged gas bubbles can then rise to a free surface of the molten glass in the fining vessel and thereafter be vented out.

[0030] Downstream glass manufacturing apparatus 30 can further include a second conditioning vessel such as mixing vessel 36 for mixing the molten glass that may be located downstream from the fining vessel 34. The glass melt mixing vessel 36 can be used to provide a homogenous glass melt composition, thereby reducing or eliminating inhomogeneities that may otherwise exist within the fined molten glass exiting the fining vessel. As shown, fining vessel 34 may be coupled to molten glass mixing vessel 36 by way of a second connecting conduit 38. In some examples, molten glass 28 may be gravity fed from the fining vessel 34 to mixing vessel 36 by way of second connecting conduit 38. For instance, gravity may drive molten glass 28 through an interior pathway of second connecting conduit 38 from fining vessel 34 to mixing vessel 36. It should be noted that while mixing vessel 36 is shown downstream of fining vessel 34, mixing vessel 36 may be positioned upstream from fining vessel 34. In some embodiments, downstream glass manufacturing apparatus 30 may include multiple mixing vessels, for example a mixing vessel upstream from fining vessel 34 and a mixing vessel downstream from fining vessel 34. These multiple mixing vessels may be of the same design, or they may be of a different design from one another.

[0031] Downstream glass manufacturing apparatus 30 can further include another conditioning vessel such as delivery vessel 40 that may be located downstream from mixing vessel 36. Delivery vessel 40 may condition molten glass 28 to be fed into a downstream forming device. For instance, delivery vessel 40 can act as an accumulator and/or flow controller to adjust and provide a consistent flow of molten glass 28 to forming body 42 by way of exit conduit 44. As shown, mixing vessel 36 may be coupled to delivery vessel 40 by way of third connecting conduit 46. In some examples, molten glass 28 may be gravity fed from mixing vessel 36 to delivery vessel 40 by way of third connecting conduit 46. For instance, gravity may drive molten glass 28 through an interior pathway of third connecting conduit 46 from mixing vessel 36 to delivery vessel 40.

[0032] Downstream glass manufacturing apparatus 30 can further include forming apparatus 48 comprising the above-referenced forming body 42 including inlet conduit 50. Exit conduit 44 can be positioned to deliver molten glass 28 from delivery vessel 40 to inlet conduit 50 of forming apparatus 48. In a fusion forming process, forming body 42 can comprise a trough 52 positioned in an upper surface of the forming body and converging forming surfaces 54 that converge along a bottom edge (root) 56 of the forming body. Molten glass delivered to the forming body trough via delivery vessel 40, exit conduit 44 and inlet conduit 50 overflows the walls of the trough and descends along the converging forming surfaces 54 as separate flows of molten glass. The separate flows of molten glass join below and along the root to produce a single ribbon of glass 58 that is drawn from root 56 by applying tension to the glass ribbon, such as by gravity and pulling rolls (not shown), to control the dimensions of the glass ribbon as the glass cools and viscosity increases such that the glass ribbon 58 goes through a visco-elastic transition and has mechanical properties that give the glass ribbon 58 stable dimensional characteristics. The glass ribbon may subsequently be separated into individual glass substrates 59 by a glass separation apparatus (not shown).

[0033] It should be understood that the production of glass substrates suitable for sale and distribution to equipment manufacturers may require additional processing before the product can be shipped from the manufacturer. Accordingly, FIG. 2 illustrates an exemplary finishing line 60 arranged downstream from glass manufacturing apparatus 10. Finishing line 60 may include a variety of different stations configured to process one or more glass substrates 59, including one or more of a cutting station 62, a beveling station 64, a washing station 66, an inspection station 68 and a packaging station 70.

[0034] In an example first step along finishing line 60, glass substrate 59 can be cut to a predetermined size. For example, the glass substrate may be cut to a predetermined size from the much larger glass ribbon 58 produced from apparatus 10 described above. In various

embodiments, the glass ribbon may be a continuous glass ribbon that is cut in a direction substantially perpendicular to the length dimension of the glass ribbon, e.g., perpendicular to a draw direction. Glass substrate 59 may include a thickness in a range from about 0.05 to about 0.7 millimeters, for example in a range from about 0.1 millimeters to about 3 millimeters, in a range from about 0.3 millimeters to about 1 millimeter, in a range from about 0.5 millimeter to about 0.7 millimeters, and including all ranges and subranges therebetween. In many glass ribbon drawing operations, the glass ribbon acquires thickened edge portions, termed beads, due to a width-wise shrinkage of the glass ribbon as the glass ribbon cools from a viscous state to an elastic state. However, typical applications, such as the manufacture of display panels for incorporation into various display devices, require the removal of these beads. Additionally, the parent glass substrate cut from the ribbon may be further cut into several smaller glass substrates. Accordingly, glass substrate 59 may be processed at cutting station 62 where cutting operations can be performed to remove any edge portion beads that exist on the glass substrate, and, optionally, to cut the glass substrate to a predetermined size.

[0035] Once glass substrate 59 has been trimmed to remove beads and/or cut to a

predetermined size, edges of the glass substrate may be beveled at a beveling station 64. Any one or more edges of the glass substrate may be beveled. In various embodiments, all four edges of a rectangular substrate are beveled, either singly (one at a time), or simultaneously. The cutting process may leave damaged edge faces on the glass substrate. For example, mechanical score and break processes typically involve contacting a major surface of the glass substrate with a scoring tool. The contacting requires pressing the scoring tool into the glass substrate with sufficient force to create a vent crack that extends at least partially through a thickness of the glass substrate. At least a portion of the thickness of the glass substrate may therefore also be damaged by the forced contact with the scoring tool. This damage can provide the initial flaw required for a subsequent unwanted break to occur. Various laser scoring and/or cutting techniques may be used that produce less edge surface damage to the glass substrate, but even in the event that a perfect cut can be made without any damage to the edge surface, the cutting process still leaves sharp edges where the edge surface meets the major surfaces of the glass substrate. Such sharp edges are prone to damage during handling of the glass substrate.

Accordingly, processing the glass substrate to produce a bevel along the edges of the glass substrate may reduce the tendency for handling damage to the glass substrate. Beveling can be performed by grinding and/or polishing of the glass substrate edges. Water may be applied to the edge surfaces of the glass substrate, to the major surfaces of the glass substrate and/or to the grinding wheel used to bevel the edges to aid in rinsing particulate from the glass substrate, to prevent glass particulate from adhering to the glass substrate, and to cool the contact surfaces of the glass substrate and grinding wheel during the grinding process.

[0036] During the grinding and/or polishing of the glass substrate, glass particulate is produced by the removal of glass from the edges of the glass substrate, which glass particulate may become attached to the major surfaces of the glass substrate. If the particulate is not removed, the particulate can interfere with downstream processing, for example the deposition of thin films during the production of a display panel. Thus, the glass substrate may be further processed at a washing station 66 where particulate is washed from the major surfaces, and from edge surfaces if necessary. During the washing step, the glass substrate may be exposed to one or more detergent solutions and/or rinsing solutions. After rinsing, the glass substrate may be dried, inspected at an inspection station 68 and then packaged for shipping at a packaging station 70.

[0037] It has been found that in some instances one or both major surfaces of the glass substrate may become contaminated with metallic deposits (e.g., "staining"), wherein minute regions of the glass surface include a thin deposit of metal, such as but not limited to iron, calcium, barium, zinc, cobalt, manganese, strontium. While the mechanism for such depositing is not well understood, it is thought that such metallic deposits may occur during the drawing process when the glass is still at an appreciable temperature (for example in a range from about 100°C to about 600°C. For example, such metallic depositing may occur as a result of glass condensate dripping onto the glass substrate from the drawing machine structure.

[0038] FIG. 3 is a photograph of an example iron deposit, shown at 20X. The particular iron deposit in FIG. 3 has an overall length of approximately 460 micrometers, with a ring-shaped center region of about 150 micrometers in length, and both vertical and horizontal streaking. In some processes, metallic deposits can be removed by exposing the glass substrate to a relatively strong mineral acid, for example hydrofluoric acid (HF) and/or hydrochloric acid. However, such strong acids are expensive to use, both in terms of the cost of the acid itself, special handling requirements and the need to process the waste liquid as a hazardous waste. Moreover, such acid may cause unnecessary etching of the glass surface.

[0039] Accordingly, the inventors herein have discovered that exposing the glass substrate to a weak acid solution with an acid concentration in a range from about 0.5 ppm to about 1.0 ppm is sufficient to remove occasional metallic deposits, is inexpensive, does not require special handling and produces no discernible etching under conditions described herein. As defined herein, a weak acid is an acid comprising an acid dissociation constant K_a in a range from 1.8x l0^~16 to 55.5, or the logarithmic constant pK_a in a range from about 15.74 to about -1.74, (where pK_a = -log K_a). Suitable weak acid solutions include, but are not limited to hypochlorous acid (K_a = 2.95 x 10^"8, pK_a = 7.53), boric acid (K_a = 5.8 x 10^"10, pK_a= 9.24) and phosphoric acid (K_a = 7.5 x 10^"3, pK_a = 2.125), or combinations thereof. Accordingly, in various embodiments, a weak acid having a K_a value in a range from about 2.95 x 10^"8 to about 7.5 x 10^"3 may be used, including all ranges and subranges therebetween. In particular embodiments, hypochlorous acid may be used.

[0040] In accordance with an embodiment shown in FIG. 4, a glass substrate 72 (where glass substrate 72 designates a glass substrate cut from the mother glass substrate 59, although in further embodiments, the glass substrate may be the mother glass substrate cut from glass ribbon 58, with or without beads removed) is exposed to a weak acid solution 74. The glass substrate may be exposed, for example by spraying the weak solution from one or more nozzles 76 arranged to wet one or both major surfaces 78, 80 of the glass substrate. For example, in various embodiments described herein the one or both major surfaces 78, 80 should be entirely wetted with the weak acid. In particular, treatment of a glass surface with hypochlorous acid can be used to remove iron deposits according to the following chemical reactions:

Fe + 2HC10 FeCl₂ + H₂+0₂ (1) 2HC10 -> 2HCl+0₂ (2) Fe+2HC1 FeCl₂+H₂, (3) where FeCl₂ is water soluble and easily removed in a downstream washing step.

[0041] The exposure to the weak acid may occur at any time after the glass substrate forming process, but in some embodiments, the acid exposure is performed during the beveling process at beveling station 64. However, in various other embodiments the exposure to the weak acid can occur after the beveling process but before the washing process at washing station 66. In some embodiments, one or both major surfaces 78, 80 may be exposed to a weak acid by a drizzle 82 (i.e., low pressure stream) of the acid from one or more nozzles 76, as shown in FIG. 5. The glass substrate 72 may be positioned at an angle a equal to or greater than 0 degrees and equal to or less than 90 degrees relative to horizontal (wherein 0 degrees is horizontal and 90 degrees is vertical). In some examples, the weak acid may be applied at a rate in a range from about 7 liters per minute to about 9 liters per minute, for example 8.3 +/- liters per minute. It has been found that at the foregoing concentration and delivery rate, an exposure time in a range from about 20 seconds to about 60 seconds is sufficient to remove metallic deposits, for example in a range from about 20 seconds to about 30 seconds, in a range from about 20 seconds to about 25 seconds, and including all ranges and subranges therebetween. [0042] It should be apparent with the benefit of the present disclosure that the weak acid employed in any of the various embodiments described above may be purposely produced specifically for removing metallic staining of glass substrates. However, it should also be apparent that certain weak acids, such as hypochlorous acid, may already be available from other sources in a manufacturing facility. For example, hypochlorous acid, because of its ability to suppress bacterial growth, may already be an additive in, for example, cooling water used in air conditioning cooling elements (e.g. heat exchangers). Moreover, other systems within a manufacturing facility that may employ hypochlorous acid-treated water may be used as a hypochlorous acid supply. Hypochlorous acid may be recycled water that is reclaimed from other processes and, suitably filtered, may be used as a hypochlorous acid for treating glass substrates as described herein. Accordingly, a ready supply of a suitable hypochlorous acid solution may be available without significant added cost.

[0043] FIG. 6 is a graph illustrating the approximately daily occurrence of iron deposited on glass substrates over a period of approximately 6 months in a glass manufacturing facility. The period from the left of the graph to vertical dashed line 84 represents a period in which only washing with an alkali detergent (e.g., Parker 225x) was performed. The vertical axis represents the number of defects (metallic staining) detected per day. A wash with hypochlorous acid was instituted at beveling station 64, represented by line 84. The data show a dramatic reduction in deposited iron once a hypochlorous acid wash was begun.

[0044] It should be apparent from the present disclosure that treatment with a weak acid solution, for example hypochlorous acid, may be performed on any suitable glass article, including glass substrates, glass articles made from glass substrates, for example display panels, and any other glass article that might benefit from the removal of metal staining.

[0045] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments disclosed herein without departing from the spirit and scope of the disclosure. Thus it is intended that the present disclosure cover the modifications and variations of these embodiments provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method of removing a metallic deposit from a glass article comprising:

exposing the glass article to an aqueous solution of a weak acid in a concentration of from 0.5 to 1.0 ppm for a time effective to remove a metallic deposit from a surface of the glass article.

2. The method according to claim 1, wherein a dissociation constant K_a of the weak acid is in a range from about 2.95 x 10^"8 to about 7.5 x 10^"3.

3. The method according to claim 1, wherein the weak acid is selected from the group consisting of hypochlorous acid, boric acid and phosphoric acid, or combinations thereof.

4. The method according to claim 1, wherein the metallic deposit comprises at least one of iron, calcium, barium, zinc, cobalt, manganese, strontium and combinations or alloys thereof.

5. The method according to claim 1, wherein the metallic deposit comprises iron.

6. The method according to any one of claims 1 to 5, wherein the weak acid comprises hypochlorous acid.

7. A method for removing a metallic deposit from a glass sheet comprising:

exposing the glass sheet to an aqueous solution containing hypochlorous acid in a concentration of from 0.5 to 1.0 ppm for a time effective to remove metallic deposits from a surface of the glass sheet.

8. The method according to claim 7, wherein the metallic deposit comprises at least one of iron, calcium, barium, zinc, cobalt, manganese, strontium and combinations or alloys thereof.

9. The method according to claim 7, wherein the glass sheet is exposed to hypochlorous acid for a period of time equal to or greater than 20 seconds.

10. The method according to claim 7, wherein the glass sheet is exposed to hypochlorous acid for a time in a range between 20 seconds to 60 seconds.

11. The method according to claim 7, wherein the exposing step comprises exposing an entirety of at least one major surface of the glass sheet to hypochlorous acid.

12. The method according to claim 7, further comprising grinding edges of the glass sheet during the step of exposing the glass sheet to hypochlorous acid.

13. The method according to any one of claims 7 to 12, wherein the hypochlorous acid is provided from a cooling apparatus.