WO2019125968A1

WO2019125968A1 - Surface treatments to substrates to reduce display corrosion

Info

Publication number: WO2019125968A1
Application number: PCT/US2018/065877
Authority: WO
Inventors: Louis Joseph STEMPIN, Jr.; Wanda Janina Walczak
Original assignee: Corning Incorporated
Priority date: 2017-12-21
Filing date: 2018-12-15
Publication date: 2019-06-27
Also published as: TW201927713A

Abstract

Methods of treating glass-based substrates such as glass substrates to reduce or prevent corrosion on the surface of the glass-based substrates are disclosed. Treated glass-based substrates are configured to be used as light guide plates in displays and lighting devices.

Description

SURFACE TREATMENTS TO SUBSTRATES TO REDUCE DISPLAY

CORROSION

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S. Provisional Application Serial No. 62/608721 filed on December 21 , 2017, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] The disclosure relates generally surface treatments of substrates that can be used for example, in displays and display devices, and in particular in displays comprising light guide plates.

BACKGROUND

[0003] Conventional components used to produce diffused light have included diffusive structures, including polymer light guides and diffusive films which have been employed in a number of applications in the display industry. These

applications include bezel-free television systems, liquid crystal displays (LCDs), electrophoretic displays (EPD), organic light emitting diode displays (OLEDs), plasma display panels (PDPs), micro-electromechanical structures (MEMS) displays, electronic reader (e-reader) devices, and others.

[0004] The desire for thinner, lighter and more energy efficient displays have led to the development of so-called transparent displays. Transparent displays are now being commercially implemented in several variations, including vending machine doors, freezer doors, retail advertising, augmented reality screens, heads-up displays in the automotive industry, smart windows for offices, portable consumer electronics, and security monitoring.

[0005] Unfortunately, transparent displays are susceptible to several poor performance characteristics. Currently available displays only partially transmit and reflect light, thus the contrast ratio of the display is greatly limited. Commercially available transparent displays typically offer only about 15% transmission, and performance is even lower in reflection mode.

[0006] For many practical applications, a transparent display requires the support of backplane illumination (via a transparent back light element). To maintain transparency, the back light needs to be fully transparent in an OFF-state and fully illuminated in an ON-state. Back lights having a frosted appearance are generally unacceptable. Additionally, the use of a transparent back light necessarily eliminates the use of a conventional reflective medium. Existing technology for providing backplane illumination are not satisfactorily meeting certain cost and performance requirements of the marketplace for transparent displays.

[0007] A light emitter, which refers generically to a device configured to provide illumination, may include a back light element for use in a display device, or the light emitter may be configured to provide general illumination such as illumination for a room or vehicle. The light emitter includes a light guide plate into which light can be coupled by one or more light sources and through which the coupled light

propagates. The light guide plate is generally a substrate comprising opposing major surfaces. As used herein, the term substrate refers generally to a plate-like substrate and which in some embodiments is suitable for use as a light guide plate. For light emitter applications at least one of the opposing major surfaces includes a surface texture configured to scatter at least a portion of the light propagating within the light guide. The surface texture is specifically configured to render the light guide visually transparent, without appreciable haze, thereby making the light guide particularly useful in the construction of a back light element for use in a transparent display device. The configuration of the surface texture also provides excellent viewing angle performance.

[0008] The light emitter may be positioned behind a transparent display panel relative to a viewer of the display panel. Light may be coupled into the light guide plate along one or more edge surfaces of the substrate, and/or along one or more borders thereof, wherein the borders represent portions of the major surfaces proximate the edge surfaces. The light propagates in a waveguide fashion within the light guide plate, for example by total internal reflection, and is incident on the light scattering portion of the at least one major surface. Thus, light propagating through the light guide plate and which light may be incident on a textured surface of the substrate may be scattered out of the light guide to illuminate the display panel of the display device, such as an LCD display panel.

[0009] Etching can be used to make the textured surfaces, such as textured surfaces for display applications. In addition to etching, the process for preparing the light guide plate may include additional steps such as cleaning the substrate prior to etching, rinsing and drying.

[0010] When luminance of a display device is out of specification, a displayed image loses sharpness. Degradation in luminance on a display device has been traditionally addressed by determining the voltage degradation with reference to a non-degraded pixel and compensating for current through a correction factor. It would be desirable to provide other methods reducing or preventing degradation of luminance in display devices.

SUMMARY

[0011] A first aspect of the disclosure pertains to a method of processing a glass substrate, the method comprising processing the glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises treating the glass substrate to prevent sodium ion migration to a surface of the glass substrate.

[0012] In a second aspect, a method of processing a glass substrate comprises processing the glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises contacting the glass substrate with an etchant selected from the group consisting of hydrofluoric acid, ammonium fluoride, ammonium bifluoride, sodium fluoride, potassium fluoride acetic acid, oxalic acid HCI, HNO3, H₂S0₄, and H3P0₄ and subjecting the glass substrate to a leaching reaction in which silica enriches a surface of the glass substrate and metal ions are depleted from the surface of the substrate.

[0013] In a third aspect, a method of processing a glass substrate comprises processing the glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises treating the glass substrate comprises contacting the glass substrate with a solution containing a compound selected from the group consisting of ZnCh, AlC , CaCh, MgC , ZnCh, AIBr₃, CaBr2, MgBr2, ZnF2, AIF3,

CaF2, and MgF2.

[0014] A fourth aspect pertains to a method of processing a substrate comprising providing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm; and treating the glass substrate by at least one of (a) depleting monovalent metal ions in the glass substrate and (b) attracting a counter ion divalent cation. In some embodiments the method includes both depleting monovalent metal ions in the glass substrate and attracting a counter ion divalent cation. In some embodiments, monovalent metal ions comprise Na. In some embodiments, treating the glass substrate comprises depleting monovalent metal ions in the glass substrate by depleting a layer of the glass substrate having a thickness in a range of from 1 nm to 10 nm of Na. In some embodiments, treating the glass substrate further comprises contacting the glass substrate with an etchant and subjecting the glass substrate to a leaching reaction in which silica enriches a surface of the glass substrate and the metal ions are depleted from the surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following detailed description can be further understood when read in conjunction with the following drawings.

[0016] FIG. 1 illustrates a light guide assembly according to certain embodiments of the disclosure;

[0017] FIG. 2 schematically shows modifying a glass substrate surface by leaching and annealing according to one or more embodiments;

[0018] FIG. 3 schematically shows modifying a glass substrate surface by exposure to a divalent cation;

[0019] FIG. 4 shows the change in luminance as a function of aging time for samples processed in accordance with Example 1 ; [0020] FIG. 5 shows the change in luminance as a function of aging time for samples processed in accordance with Example 2;

[0021] FIG. 6 shows Dynamic Secondary Ion Mass Spectrometry (SIMS) data for samples processed in accordance with Example 1 ;

[0022] FIG. 7 shows Time of Flight(TOF) SIMS data for untreated control substrates aged for 96 hours;

[0023] FIG. 8 is a schematic diagram illustrating how luminance was measured on samples; and

[0024] FIG. 9 is a graph showing Zeta potential versus pH for samples treated in accordance with Example 2.

DETAILED DESCRIPTION

[0025] One of the components that can cause a luminance change as a function of time in a display device is the glass surface itself due to "weathering" or corrosion of the glass surface. Described herein are surface treatments that can reduce or prevent corrosion on surfaces of display devices. In specific embodiments, surface treatments are described which can reduce corrosion on glass-based surfaces that are used for light guide plates and light guide assemblies comprising a light guide plate.

[0026] As used herein, the phrases "glass-based article" and "glass-based substrates" are used in their broadest sense to include any object made wholly or partly of glass. Glass-based substrates include laminates of glass and non-glass materials, laminates of glass and crystalline materials, and glass-ceramics (including an amorphous phase and a crystalline phase). Unless otherwise specified, all glass compositions are expressed in terms of mole percent (mol%).

[0027] The glass-based substrates and glass substrates described herein can be used as light guide plates. The light guide plates and light guide assemblies described herein can be utilized in displays, lighting, and electronic devices, e.g., televisions, computers, phones, tablets, and other display panels, luminaires, solid- state lighting, billboards, and other architectural elements.

[0028] Glass-based substrates such as glass substrates used in display glass have been shown to corrode in humid environments (e.g., 90% relative humidity) and elevated temperatures (e.g., 60° C). It was determined that such corrosion causes an increase in luminance, and subsequently results in degradation of the display quality.

[0029] Embodiments of the disclosure pertain to surface treatments that can reduce or prevent such corrosion by utilizing an facile approach that can be readily applied to existing display manufacturing finishing lines in a relatively quick time frame (e.g., minutes). For example, one or more embodiments of the disclosure provide a process to remove a problematic cation in the corrosion byproduct by leaching and subsequent optional annealing of the glass surface. In one more embodiments of the disclosure provides for the use of corrosion inhibitors in the rinse water of the final step of the glass finishing process. In some embodiments, a surface treatment strategy is provided to reduce corrosion in the form of white spot formation on glass- based substrates such as glass substrates, subsequently reducing or eliminating the extent of the resultant luminance increase caused by such corrosion.

[0030] FIG. 1 illustrates an exemplary embodiment of a light guide plate (LGP) assembly 100 comprising a glass-based substrate 110 and a plurality of

microstructures 130. Of course, the depicted microstructures 130 are exemplary only. Moreover, the size and/or shape of the microstructures 130 can be varied depending on the desired light output and/or optical functionality of the LGP. The light guide plate (LGP) assembly 100 further comprises at least one light source 140 that can be optically coupled to an edge surface 150 of the glass-based substrate 110, e.g., positioned adjacent to the edge surface 150. As used herein, the term "optically coupled" is intended to denote that a light source is positioned at an edge of the LGP so as to introduce light into the LGP. A light source may be optically coupled to the LGP even though it is not in physical contact with the LGP. Additional light sources (not illustrated) may also be optically coupled to other edge surfaces of the LGP, such as adjacent or opposing edge surfaces. The disclosure is not limited to any particular lighting arrangement, and can include edge lit and direct lit configurations. A general direction of light emission from light source 140 is depicted in FIG. 1 by the solid arrow. Light injected into the LGP may propagate along a length L of the LGP due to total internal reflection (TIR), until it strikes an interface at an angle of incidence that is less than the critical angle. TIR is the phenomenon by which light propagating in a first material (e.g., glass, plastic, etc.) comprising a first refractive index can be totally reflected at the interface with a second material (e.g., air, etc.) comprising a second refractive index lower than the first refractive index.

TIR can be explained using Snell's law:

n sin(6? ) = n₂ sin(^)

which describes the refraction of light at an interface between two materials of differing indices of refraction. In accordance with Snell's law, m is the refractive index of a first material, ri2 is the refractive index of a second material, Q , is the angle of the light incident at the interface relative to a normal to the interface (incident angle), and Q _r is the angle of refraction of the refracted light relative to the normal. When the angle of refraction (Q _r) is 90°, e.g., sin(0 _r) = 1 , Snell's law can be expressed as:

9_C ⁼ q, = sin^_1(— )

n_x

The incident angle Q , under these conditions may also be referred to as the critical angle Q _c. Light having an incident angle greater than the critical angle (0 , > 0 _c) will be totally internally reflected within the first material, whereas light with an incident angle equal to or less than the critical angle (0 , < 0 _C) will be transmitted by the first material.

[0031] In the case of an exemplary interface between air (m= 1 ) and glass (ri2= 1.5), the critical angle (0 _C) can be calculated as 41°. Thus, if light propagating in the glass strikes the air-glass interface at an incident angle greater than 41°, all the incident light will be reflected from the interface at an angle equal to the incident angle. If the reflected light encounters a second interface comprising an identical refractive index relationship as the first interface, the light incident on the second interface will again be reflected at a reflection angle equal to the incident angle.

[0032] The plurality of microstructures 130 may be disposed on a major surface of the glass-based substrate 110, such as light emitting surface 160. The plurality of microstructures 130 may, along with other optional components of the LGP, direct the transmission of light in a forward direction (e.g., toward a user), as indicated by the dashed arrows. In some embodiments, light source 140 may be a Lambertian light source, such as a light emitting diode (LED). Light from the LEDs may spread quickly within the LGP, which can make it challenging to effect local dimming (e.g., by turning off one or more LEDs). However, by providing one or more

microstructures on a surface of the LGP that are elongated in the direction of light propagation (as indicated by the solid arrow in FIG. 1 ), it may be possible to limit the spreading of light such that each LED source effectively illuminates only a narrow strip of the LGP. The illuminated strip may extend, for example, from the point of origin at the LED to a similar end point on the opposing edge.

[0033] According to various embodiments, the surface 160 or second major surface 170 of the glass-based substrate 110 may be patterned with a plurality of light extraction features. As used herein, the term "patterned" is intended to denote that the plurality of light extraction features is present on or in the surface of the substrate in any given pattern or design, which may, for example, be random or arranged, repetitive or non-repetitive, uniform or non-uniform. In other embodiments, the light extraction features may be located within the matrix of the glass-based substrate adjacent the surface, e.g., below the surface. For example, the light extraction features may be distributed across the surface, e.g., as textural features making up a roughened or raised surface, or may be distributed within and throughout the substrate or portions thereof, e.g., as laser-damaged features.

[0034] In various embodiments, the light extraction features optionally present on the surface 160 or second major surface 170 of the LGP may comprise light scattering sites. According to various embodiments, the light extraction features may be patterned in a suitable density so as to produce substantially uniform light output intensity across the light emitting surface of the glass-based substrate. In certain embodiments, a density of the light extraction features proximate the light source may be lower than a density of the light extraction features at a point removed from the light source, or vice versa, such as a gradient from one end to another, as appropriate to create the desired light output distribution across the LGP.

[0035] The LGP may be treated to create light extraction features according to any method known in the art, e.g., the methods disclosed in co-pending and co-owned International Patent Application Publication Nos. WO2014058748 and

WO2015095288, each incorporated herein by reference in their entirety. For example, a surface of the LGP may be ground and/or polished to achieve the desired thickness and/or surface quality. The surface may then be optionally cleaned and/or the surface to be etched may be subjected to a process for removing contamination, such as exposing the surface to ozone. The surface to be etched may, by way of a non-limiting embodiment, be exposed to an acid bath, e.g., a mixture of glacial acetic acid (GAA) and ammonium fluoride (NH₄F) in a ratio, e.g., ranging from about 1 : 1 to about 9:1. The etching time may range, for example, from about 30 seconds to about 15 minutes, and the etching may take place at room temperature or at elevated temperature. Process parameters such as acid concentration/ratio, temperature, and/or time may affect the size, shape, and distribution of the resulting extraction features.

[0036] The glass-based substrate 110 can have any desired size and/or shape as appropriate to produce a desired light distribution. The glass-based substrate 110 may comprise a second major surface 170 opposite the light emitting surface 160. The major surfaces may, in certain embodiments, be planar or substantially planar, e.g., substantially flat. The first and second major surfaces may, in various embodiments, be parallel or substantially parallel. The glass-based substrate 110 may comprise four edges as illustrated in FIG. 1 , or may comprise more than four edges, e.g. a multi-sided polygon. In other embodiments, the glass-based substrate 110 may comprise less than four edges, e.g., a triangle. By way of a non-limiting example, the light guide plate may comprise a rectangular, square, or rhomboid sheet having four edges, although other shapes and configurations are intended to fall within the scope of the disclosure including those having one or more curvilinear portions or edges.

[0037] In one or embodiments of the disclosure of processing substrates, the glass- based substrate 110 such as a glass substrate may have a thickness di of less than or equal to about 3 mm, for example, ranging from about 0.1 mm to about 3 mm, from about 0.1 mm to about 2.5 mm, from about 0.3 mm to about 2 mm, from about 0.5 mm to about 1.5 mm, or from about 0.7 mm to about 1 mm, including all ranges and subranges therebetween. The glass-based substrate 110 can comprise any material known in the art for use in display devices. For example, the glass-based substrate may comprise aluminosilicate, alkali-aluminosilicate, borosilicate, alkali- borosilicate, aluminoborosilicate, alkali-aluminoborosilicate, soda lime, or other suitable glasses. Non-limiting examples of commercially available glasses suitable for use as a glass light guide include, for example, EAGLE XG^®, Lotus™, Willow^®, Iris™, and Gorilla^® glasses from Corning Incorporated.

[0038] Some non-limiting glass compositions can include between about 50 mol % to about 90 mol% S1O2, between 0 mol% to about 20 mol% AI2O3, between 0 mol% to about 20 mol% B2O3, and between 0 mol% to about 25 mol% R_xO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1.

In some embodiments, R_xO - AI2O3 > 0; 0 < R_xO - AI2O3 < 15; x = 2 and R2O - AI2O3 < 15; R₂0 - AI2O3 < 2; x=2 and R₂0 - AI2O3 - MgO > -15; 0 < (R_xO - AI2O3) < 25, - 11 < (R₂0 - AI2O3) < 11 , and -15 < (R₂0 - AI2O3 - MgO) < 11 ; and/or -1 < (R₂0 - AI2O3) < 2 and -6 < (R2O - AI2O3 - MgO) < 1. In some embodiments, the glass comprises less than 1 ppm each of Co, Ni, and Cr. In some embodiments, the concentration of Fe is < about 50 ppm, < about 20 ppm, or < about 10 ppm. In other embodiments, Fe + 30Cr + 35Ni < about 60 ppm, Fe + 30Cr + 35Ni < about 40 ppm, Fe + 30Cr + 35Ni < about 20 ppm, or Fe + 30Cr + 35Ni < about 10 ppm. In other embodiments, the glass comprises between about 60 mol % to about 80 mol% S1O2, between about 0.1 mol% to about 15 mol% AI2O3, 0 mol% to about 12 mol% B2O3, and about 0.1 mol% to about 15 mol% R2O and about 0.1 mol% to about 15 mol% RO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1.

[0039] In other embodiments, the glass composition can comprise between about 65.79 mol % to about 78.17 mol% S1O2, between about 2.94 mol% to about 12.12 mol% AI2O3, between about 0 mol% to about 11.16 mol% B2O3, between about 0 mol% to about 2.06 mol% U2O, between about 3.52 mol% to about 13.25 mol% Na₂0, between about 0 mol% to about 4.83 mol% K2O, between about 0 mol% to about 3.01 mol% ZnO, between about 0 mol% to about 8.72 mol% MgO, between about 0 mol% to about 4.24 mol% CaO, between about 0 mol% to about 6.17 mol% SrO, between about 0 mol% to about 4.3 mol% BaO, and between about 0.07 mol% to about 0.11 mol% Sn02.

[0040] In additional embodiments, the glass-based substrate 110 can comprise an R_x0/Al₂0₃ ratio between 0.95 and 3.23, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2. In further embodiments, the glass-based substrate may comprise an R_xO/AhC ratio between 1.18 and 5.68, wherein R is any one or more of Li, Na,

K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1. In yet further embodiments, the glass-based substrate can comprise an R_xO - AI2O3 - MgO between -4.25 and 4.0, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2. In still further embodiments, the glass-based substrate may comprise between about 66 mol % to about 78 mol% S1O2, between about 4 mol% to about 11 mol% AI2O3, between about 4 mol% to about 11 mol% B2O3, between about 0 mol% to about 2 mol% U2O, between about 4 mol% to about 12 mol% Na₂0, between about 0 mol% to about 2 mol% K2O, between about 0 mol% to about 2 mol% ZnO, between about 0 mol% to about 5 mol% MgO, between about 0 mol% to about 2 mol% CaO, between about 0 mol% to about 5 mol% SrO, between about 0 mol% to about 2 mol% BaO, and between about 0 mol% to about 2 mol% Sn02.

[0041] In additional embodiments, the glass-based substrate 110 can comprise between about 72 mol % to about 80 mol% S1O2, between about 3 mol% to about 7 mol% AI2O3, between about 0 mol% to about 2 mol% B2O3, between about 0 mol% to about 2 mol% U2O, between about 6 mol% to about 15 mol% Na₂0, between about 0 mol% to about 2 mol% K2O, between about 0 mol% to about 2 mol% ZnO, between about 2 mol% to about 10 mol% MgO, between about 0 mol% to about 2 mol% CaO, between about 0 mol% to about 2 mol% SrO, between about 0 mol% to about 2 mol% BaO, and between about 0 mol% to about 2 mol% Sn0_2. In certain embodiments, the glass-based substrate can comprise between about 60 mol % to about 80 mol% S1O2, between about 0 mol% to about 15 mol% AI2O3, between about 0 mol% to about 15 mol% B2O3, and about 2 mol% to about 50 mol% R_xO, wherein R is any one or more of Li, Na, K, Rb, Cs and x is 2, or Zn, Mg, Ca, Sr or Ba and x is 1 , and wherein Fe + 30Cr + 35Ni < about 60 ppm.

[0042] The glass-based substrate 110 may, in some embodiments, be chemically strengthened, e.g., by ion exchange. During the ion exchange process, ions within a glass sheet at or near the surface of the glass sheet may be exchanged for larger metal ions, for example, from a salt bath. The incorporation of the larger ions into the glass can strengthen the sheet by creating a compressive stress in a near surface region. A corresponding tensile stress can be induced within a central region of the glass sheet to balance the compressive stress.

[0043] Ion exchange may be carried out, for example, by immersing the glass in a molten salt bath for a predetermined period of time. Exemplary salt baths include, but are not limited to, KNO3, UNO3, NaN03, RbN03, and combinations thereof. The temperature of the molten salt bath and treatment time period can vary. It is within the ability of one skilled in the art to determine the time and temperature according to the desired application. By way of a non-limiting example, the temperature of the molten salt bath may range from about 400°C to about 800°C, such as from about 400°C to about 500°C, and the predetermined time period may range from about 4 to about 24 hours, such as from about 4 hours to about 10 hours, although other temperature and time combinations are envisioned. By way of a non-limiting example, the glass can be submerged in a KNO3 bath, for example, at about 450°C for about 6 hours to obtain a K-enriched layer which imparts a surface compressive stress.

[0044] Embodiments of the disclosure provide a method of processing a glass- based substrate, for example, a glass substrate configured for use in a display device, and in some embodiments, a glass substrate configured to be used as a light guide plate.

[0045] In one or more embodiments, treated glass-based substrates such as glass substrates exhibit reduced effects of weathering compared to control glass substrates that have not been treated in accordance with the methods provided in this disclosure. Reduced effects of weathering is determined by at least one of observing an effective reduction of white spot formation on treated glass substrate compared to untreated substrates and a prevention a luminance increase or reduction of the magnitude of a luminance increase when the glass substrate is aged at 60 °C and at 90% relative humidity when compared to an untreated substrate.

[0046] According to one or more embodiments, relatively mild treatment conditions can be used to prevent or reduce the magnitude of luminance increases in display devices. In some embodiments, high throughput can be achieved as treatment times can range from about one minute to about one hour. In some embodiments, the treatment can be effected by placing a suitable chemical in rinse water used to rinse glass substrates during processing.

[0047] In a first embodiment, a method of processing a glass substrate is provided, the method comprising processing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises treating the glass substrate to prevent sodium ion migration to a surface of the glass substrate. [0048] In a second embodiment, the glass-based substrate comprises a glass or glass ceramic or a display glass. In a third embodiment, the glass-based substrate of the second embodiment is selected from the group consisting of aluminosilicate glass, borosilicate glass, and soda-lime glass.

[0049] In a fourth embodiment, treating the glass-based substrate in any of the first through third embodiments comprises one of: (a) depleting monovalent metal ions in the glass-based substrate and (b) attracting a counter ion divalent cation. In a fifth embodiment, the method of the fourth embodiment comprises depleting monovalent metal ions in the glass-based substrate. In a sixth embodiment, the monovalent metal ions of the fifth embodiment comprise Na.

[0050] In a seventh embodiment, the method of any of the fourth through sixth embodiments comprises depleting a layer of the glass-based substrate having a thickness in a range of from 1 nm to 10 nm of Na.

[0051] In an eighth embodiment, the method of any of the first through seventh embodiments is conducted at a temperature in a range of from about 20° C to about 90 °C, of from about 20° C to about 80 °C, of from about 20° C to about 70 °C, of from about 20° C to about 60 °C, of from about 20° C to about 50 °C, or of from about 20° C to about 50 °C. In a ninth embodiment, in the method of any of the first through eighth embodiments, the treating is conducted over a time period in a range of from about 1 minute to about 120 minutes, about 1 minute to about 90 minutes, about 1 minute to about 60 minutes, about 1 minute to about 45 minutes, about 1 minute to about 30 minutes, about 1 minute to about 20 minutes, about 1 minute to about 15 minutes, about 1 minute to about 10 minutes, or about 1 minute to about 5 minutes.

[0052] In a tenth embodiment, in any of the first through ninth embodiments, treating the glass-based substrate comprises contacting the glass-based substrate with an etchant and subjecting the glass-based substrate to a leaching reaction in which silica enriches a surface of the glass substrate and the metal ions are depleted from the surface of the substrate. In an eleventh embodiment, the etchant of the tenth embodiment contains at least one fluoride compound. In a twelfth

embodiment, the fluoride compound of the eleventh embodiment is selected from the group consisting of hydrofluoric acid, ammonium fluoride, ammonium bifluoride, sodium fluoride, and potassium fluoride. [0053] In a thirteenth embodiment, subjecting the glass-based substrate to a leaching reaction of the tenth embodiment comprises contacting the glass based substrate with an acid selected from the group consisting of a mineral acid and an organic acid. In a fourteenth embodiment, the mineral acid of the thirteenth embodiment is selected from the group consisting of HCI, HNO3, H₂S0₄, and H3P0_4.

[0054] In a fifteenth embodiment, the organic acid acid of the thirteenth

embodiment is selected from the group consisting of acetic acid and oxalic acid. In a sixteenth embodiment, the etchant any of the thirteenth through fifteenth

embodiments in an acid: water ratio of about 1 :200 to about 1 :20, for example, a ratio of about 1 : 150, about 1 :20; about 1 :80, about 1 :60: about 1 :50 or about 1 :40.

In some embodiments, the etchant contains mineral acid alone.

[0055] In a seventeenth embodiment, in any of the thirteenth through sixteenth embodiments, the method further comprises annealing the glass-based substrate after the contacting, wherein annealing is conducted at a temperature in a range of about 250 °C to about 700 °C, about 250 °C to about 600 °C, about 250 °C to about 500 °C, or about 250 °C to about 400 °C for a time period in a range of from about 20 minutes to about 3 hours, from about 20 minutes to about 2 hours, from about 20 minutes to about 1 hour, from about 20 minutes to about 45 minutes, or from about 20 minutes to about 30 minutes.

[0056] In an eighteenth embodiment, treating the glass-based substrate according to any of the first through fourth embodiments comprises contacting the glass-based substrate with a divalent cation solution. In a nineteenth embodiment, the divalent cation solution of the eighteenth embodiment comprises a compound selected from the group consisting of ZnC , AICI3, CaC , MgCh, ZnC , AIBr3, CaBr2, MgBr2, ZnF2, AIF3, CaF2, and MgF2. In a twentieth embodiment, the solution of the eighteenth or nineteenth embodiment, comprises a rinsing solution further comprising water. In a twenty-first embodiment, the surface treatment according to any of the first through twentieth embodiments reduces or prevents formation of white spots on the glass- based substrate.

[0057] According to one or more embodiments, modifying the glass-based substrate surface by leaching and annealing can be shown schematically as in FIG. 2. As shown in FIG. 2, modification of a glass-based substrate surface by leaching and annealing a sodium-containing glass substrate is shown. In some embodiments, since only a surface layer (shown by cross-hatched sections) is modified, the leaching treatment time is of relatively short duration as described above, and the temperature is relatively mild (e.g., about room temperature in the ranges provided above). After the treatment, the glass surface layer contains no or very little sodium ions, and the ability of forming sodium carbonate and/or

magnesium carbonate by products is s significantly reduced.

[0058] As shown in FIG. 3, in an exemplary embodiment, a sodium-containing glass substrate can be modified by exposure to an opposing divalent cation. In some embodiments, since only a surface layer is modified, the treatment time is relatively short duration as described above, and temperature is relatively mild (e.g., about room temperature in the ranges provided above). After treatment, the glass surface layer contains no or very little sodium ions, and the ability of forming sodium carbonate and/or magnesium carbonate by products which lead to corrosion of the surface is significantly reduced.

[0059] According to one or more embodiments, methods of reducing white spot formation and resulting luminance change in glass-based substrates are provided by utilizing a surface chemical treatment that may be optionally used with a subsequent heating step. While the present disclosure should not be limited to a particular theory, some glass substrates contain many single valence species such as Na at the glass surface. Sodium ions (Na⁺) within the surface layer can react with carbonates in the air to form small white precipitates (less than a micrometer in size) which can either nucleate or grow during the weathering process. It has been discovered that nucleation and growth was accelerated in a humid chamber ( e.g., at 60 °C and 90% relative humidity), and these precipitates have been detected as sodium carbonate and/or sodium hydroxide (as shown in FIG. 7) and result in an increase in luminance as shown in Examples 1 and 2 below.

[0060] In some embodiments, a leaching treatment using acid can deplete the formation of these precipitates by selectively removing metal ions such as sodium and preventing nucleation behavior, propelling the few that remain into growth behavior which appears to have less of an effect on luminance or haze. In some embodiments, the acid treatment or leaching can be followed by annealing to help inhibit any penetration of the sodium in the glass from deeper in to migrate to the surface. [0061] In other embodiments, treatment with a multivalent species (e.g., Zn) provides a different counter ion for the carbonates in the air to react with any existing sodium surface species. This multivalent species has less of an effect on luminance behavior compared to sodium. Because only the surface layer needs to be modified, the treatment time is relatively short in duration and the temperature used is relatively mild. According to some embodiment, after the treatment, the glass surface layer contains no or very little sodium ions, and the change in luminance with aging is significantly reduced.

[0062] Various embodiments of the present disclosure are further illustrated by the following non-limiting examples.

[0063] EXAMPLES

[0064] The following examples provide non-limiting examples of chemical treatment procedures, the related test method for determination of particle size distribution and luminance and the corresponding results.

[0065] Luminance and Confocal Methods to determine particle size distribution.

[0066] The sample test setup for luminance measurement is shown in FIG. 8.

Images were obtained using a charge coupled device (CCD) Imaging Photometer and Colorimeter (Camera), model number PM1423F-1 , available from Radiant Imaging, Redmond, WA (www.radiantimaging.com). The camera CCD array was 1526 X 1024. The samples were illuminated by using an LED strip from a Sony 1080p TV Backlight Unit. The light was injected into a flat edge of the sample, and the resulting luminance was captured in nits. For optical measurements of particle size distribution, a Zeiss Imager Z1 m optical microscope was used in darkfield mode. 400 images were taken at 50X magnification and an ImageJ program was used to determine particle size and other relevant parameters.

[0067] Example 1

[0068] IRIS™ glass samples that were 1.1 mm thick and 4 inches by 4 inches in size were processed as follows:

[0069] Each substrate was washed with Semiclean KG detergent (Yokohama Oil and Fats, Japan) in a Crest ultrasonic washer (http://www.crest-ultrasonics.com/) to remove any organic residual. The washing cycle for each substrate included;

following:

[0070] Normal 4% Semiclean wash with ultrasonics: 15 minutes in 4% Semiclean solution @ 160°F in Basin #1.

5 minutes in Dl water rinse @ 160°F in Basin #3.

5 minutes in Dl water with ultrasonics @ 160°F in Basin #3.

5 minutes in Dl water with ultrasonics @ 160°F in Basin #1.

5 minutes in Dl water with ultrasonics @ 160°F in Basin #3.

7.75 minute slow pull @ 80°F in Basin #4.

[0071] The total time for a complete wash cycle was 42.75 minutes, and the ultrasonic frequency was 40 MFIz.

[0072] The resulting surface was then exposed to 1 :200 HCI for a time ranging between 1 minute and 60 minutes via dipping at 65 °C, followed by drying in N₂ for 1 minute. The resulting surface was optionally exposed to an annealing step at 700 °C for one hour. The resulting glass surface was then either left as is or aged for different times (96 hr, 240 hr, 480 hr, 960 hr), at 60 °C 90% Rh and sample substrates were periodically removed to analyze the surface for weathering behavior.

[0073] Luminance was measured as described above, and the greater aging time was subtracted from luminance at time = 0 for each substrate to determine

luminance increase.

[0074] Weathering was assessed by optically determining the number of white spots using the Zeiss Imager Z1 m optical microscope and scanning the surface in darkfield mode as described above. Spots were counted for size, % area and other attributes in 400 stitched images.

[0075] Weathering was alternatively assessed by looking at the luminance behavior of the surface and comparing it to unaged glass substrates (controls) treated in the same fashion. Results showed that the treatment can effectively reduce the amount of sodium present at the surface. Since the original control substrate surface was replete with white spots containing sodium adducts (as shown in FIG. 7), it was determined that these spots could be reduced if sodium was absent. FIG. 4 shows the resulting change in luminance. In addition, the particle size distribution that occurred with aging for HCI treated and untreated glass surface on the samples was observed. FIG. 4 shows that virtually no change in luminance is observed for the HCI treated surface compared to the untreated (control) substrate. [0076] Dynamic Secondary Ion Mass Spectrometry (SIMS) data showed that the samples processed in accordance with Example 1 showed a depletion of sodium ions that occurs with leaching and annealing. The results are shown in FIG. 6.

[0077] The particle size distributions for the untreated and treated surfaces of the samples were measured as described above. For the control substrates, the majority of particle sizes was 0 to 1 micrometers and independent of aging time. For the samples treated in accordance with Example 1 , particle size grew as a function of aging time. In particular, there were particles in a range of from 1 micrometer to 7 micrometers for the sample aged for 960 hours.

[0078] Untreated control substrates aged for 96 hours were scanned using Time of Flight (TOF) SIMS, and the species in the particles are shown in FIG. 7. Precipitates of sodium carbonate and/or sodium hydroxide were detected.

[0079] Example 2

[0080] Glass-based substrates of IRIS™ glass glass samples that were 1.1 mm thick and 4 inches by 4 inches in size were washed with Semiclean KG detergent in the Crest ultrasonic washer to remove any organic residual. The washing cycle is the same as described in Example 1. The resulting surfaces of the sample substrates was treated with an aqueous solution of ZnCI₂ (pH = 4.8) for 3 minutes at room temperature. Adsorption of Zn onto the surfaces was shown to occur in less than that time frame by zeta potential study where the adsorption results in altering the glass surface charge (See FIG. 9)

[0081] The substrates were then dried with N₂ and left as is or aged at various times in 60 °C at 90% relative humidity as in Example 1.

[0082] Luminance was measured as described above, and the greater aging time is subtracted from luminance at time = 0 for each substrate to determine luminance increase. FIG. 5 shows the change in luminance. It was shown that the ZnCI₂ treated surfaces had a reduced change in luminance behavior compared to the untreated surfaces.

[0083] The particle size distributions for the untreated and treated surface were measured as described above for Example 1

[0084] For the samples treated in accordance with Example 2, particle size grew as a function of aging time. In particular, there were particles in a range of from 1 micrometer to 100 micrometers for the sample aged for 480 960 hours [0085] TOF SIMS was performed on samples rinsed in accordance with Example 2 and aged for 480 hours. TOF SIMS showed the presence of Na, Mg, and Zn.

Flowever, no sodium carbonate species was detected.

[0086] Various modifications and variations can be made to the materials, methods, and articles described herein. Other aspects of the materials, methods, and articles described herein will be apparent from consideration of the specification and practice of the materials, methods, and articles disclosed herein. It is intended that the specification and examples be considered as exemplary. It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method of processing a glass substrate, the method comprising:

processing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises treating the glass substrate to prevent sodium ion migration to a surface of the glass substrate.

2. The method of claim 1 , wherein the glass substrate display glass.

3. The method of claim 2, wherein the glass substrate is selected from the group consisting of aluminosilicate glass, borosilicate glass, and soda-lime glass.

4. The method of claim 2, wherein treating the glass substrate comprises at least one of: (a) depleting monovalent metal ions in the glass substrate and (b) attracting a counter ion divalent cation.

5. The method of claim 4, wherein monovalent metal ions comprise Na.

6. The method of claim 4, wherein depleting monovalent metal ions comprises depleting a layer of the glass substrate having a thickness in a range of from 1 nm to 10 nm of Na.

7. The method of claim 4, wherein the method is conducted at a temperature in a range of from about 20° C to about 90 °C.

8. The method of claim 7, wherein treating is conducted over a time period in a range of from about 1 minute to about 60 minutes.

9. The method of claim 4, wherein treating the glass substrate comprises contacting the glass substrate with an etchant and subjecting the glass substrate to a leaching reaction in which silica enriches a surface of the glass substrate and the metal ions are depleted from the surface of the substrate.

10. The method of claim 9, wherein the etchant contains at least one fluoride compound.

11. The method of claim 10, wherein the fluoride compound is selected from the group consisting of hydrofluoric acid, ammonium fluoride, ammonium bifluoride, sodium fluoride, and potassium fluoride.

12. The method of claim 9, wherein subjecting the glass substrate to a leaching reaction comprises contacting the glass based substrate with an acid selected from the group consisting of a mineral acid and an organic acid.

13. The method of claim 12, wherein the mineral acid is selected from the group consisting of HCI, HNO3, H₂S0₄, and H3P0_4.

14. The method of claim 12, wherein the organic acid is selected from the group consisting of acetic acid and oxalic acid.

15. The method of claim 13, wherein the etchant contains a mineral acid alone in concentration ratio of acid:water in a range of from about 1 :200 to about1 :20 in water.

16. The method of claim 9, further comprising annealing the glass substrate after the contacting, wherein annealing is conducted at a temperature in a range of from 50 °C to 700 °C for a time period in a range of from 20 minutes to 3 hours.

17. The method of claim 4, wherein of treating the glass substrate comprises contacting the glass substrate with a divalent cation solution.

18. The method of claim 17, wherein the divalent cation solution comprises a compound selected from the group consisting of ZnCh, AlCh, CaCh, MgCh, ZnCh, AIBr₃, CaBr2, MgBr2, ZnF2, AIF3, CaF2, and MgF2.

19. The method of claim 18, wherein the solution comprises a rinsing solution further comprising water.

20. The method of claim 2, wherein treating the substrate reduces or prevents formation of white spots on the glass substrate.

21. A method of processing a glass substrate, the method comprising:

processing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises contacting the glass substrate with an etchant selected from the group consisting of hydrofluoric acid, ammonium fluoride, ammonium bifluoride, sodium fluoride, potassium fluoride acetic acid, oxalic acid HCI, FINO3, FhS0₄, and FhP0₄ and subjecting the glass substrate to a leaching reaction in which silica enriches a surface of the glass substrate and metal ions are depleted from the surface of the substrate.

22. A method of processing a glass substrate, the method comprising:

processing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm, the substrate configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibiting a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm, wherein the processing comprises treating the glass substrate comprises contacting the glass substrate with a solution containing a compound selected from the group consisting of ZnCh, AICI3, CaCh, MgCh, ZnCh, AIBr3, CaBr2, MgBr2, ZnF2, AIF3, CaF2, and MgF2.

23. A method of processing a substrate comprising:

providing a glass substrate comprising at least one major surface and an edge defining a thickness in a range of from about 0.1 mm to about 3 mm; and treating the glass substrate by at least one of (a) depleting monovalent metal ions in the glass substrate and (b) attracting a counter ion divalent cation.

24. The method of claim 23, wherein the method comprises depleting monovalent metal ions in the glass substrate and attracting a counter ion divalent cation.

25. The method of claim 23, wherein the substrate is configured to be used as a light guide plate of a liquid crystal display to distribute light throughout the display and exhibits a transmittance normal to the at least one major surface greater than 90% over a wavelength range from 400 nm to 700 nm.

26. The method of claim 23, wherein monovalent metal ions comprise Na.

27. The method of claim 23, wherein treating the glass substrate comprises depleting monovalent metal ions in the glass substrate by depleting a layer of the glass substrate having a thickness in a range of from 1 nm to 10 nm of Na.

28. The method of claim 23, wherein treating the glass substrate further comprises contacting the glass substrate with an etchant and subjecting the glass substrate to a leaching reaction in which silica enriches a surface of the glass substrate and the metal ions are depleted from the surface of the substrate.