Patent Application
20180215657
The present specification generally relates to textured glass, in particular textured glass for use as cover glass for display devices.
Glass having a textured surface has been widely applied because of its functionality and aesthetic appearance. When incorporated into consumer electronic devices, textured cover glass may effectively reduce the surface glare and improve the tactile feeling of the device, in particular for touch screen devices. However, the presence of the textured surface on the cover glass has been shown to cause various modes of image distortion which can degrade the performance of a high definition display.
Accordingly, a need exists for glass having a textured surface with reduced distortion, known as sparkle, and for methods for making the textured glass.
In an embodiment, a transparent glass sheet includes at least one anti-glare surface having a plurality of discrete surface features having an average size equal to or less than 20 microns and one or more flat regions. At least a portion of the plurality of discrete surface features are spaced apart from one another, and each of the plurality of discrete surface features are bounded by the one or more flat regions. The transparent glass sheet has a sparkle of equal to or less than 3% as evaluated by an SMS bench tester using a display light source of 141 ppi.
In another embodiment, a method for producing an anti-glare surface treatment on a transparent glass sheet includes introducing a roughening solution to a surface of the transparent glass sheet. The roughening solution includes from 1 wt. % to 6 wt. % hydrofluoric acid, from 5 wt. % to 15 wt. % ammonium fluoride, from 2 wt. % to 20 wt. % potassium chloride. The method further includes maintaining the roughening solution in contact with the surface of the transparent glass sheet to form and grow a plurality of surface features on the surface of the transparent glass sheet, and removing the roughening solution from contact with the surface of the transparent glass sheet before the plurality of surface features grow to fill the entire surface of the transparent glass sheet, wherein upon removal of the roughening solution, the transparent glass sheet has a plurality of discrete surface features separated from one another by one or more flat regions.
It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.
Reference will now be made in detail to embodiments of transparent glass sheets having anti-glare surfaces having low sparkle and methods of making the anti-glare surface having low sparkle, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
One embodiment of an example transparent glass sheet 100 is schematically depicted in
Directional terms as used herein, such as 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.
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 specific orientations be required with any apparatus. 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.
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.
Display “sparkle” or “dazzle” is a generally undesirable side effect that can occur when introducing anti-glare or light scattering surfaces into a pixelated display system such as, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED), touch screens, or the like, and differs in type and origin from the type of “sparkle” or “speckle” that has been observed and characterized in projection or laser systems. Sparkle is associated with a very fine grainy appearance of the display, and may appear to have a shift in the pattern of the grains with changing viewing angle of the display. Display sparkle may be manifested as bright and dark or colored spots at approximately the pixel-level size scale.
Whereas the most common anti-glare surfaces used in the display industry are coated polymer films, the present disclosure is primarily concerned with the optical and surface properties of a transparent glass article or sheet that is used as a protective cover glass over an LCD or other pixelated displays. In particular, a transparent glass sheet having a roughened surface and optical properties that minimize display “sparkle” and a display system comprising such a transparent glass sheet are provided. Additionally, surfaces with preferred small-angle-scattering properties or distinctness-of-reflected-image (DOI) which lead to improved viewability in display applications, especially under high ambient lighting conditions, are provided. The anti-glare surface is formed without the application or other use of foreign coating materials (e.g., coatings, films, or the like).
The origin of display sparkle has previously not been well understood. There are many potential root causes that could be hypothesized, such as interference effects, Rayleigh or Mie-type scattering, and the like. As described herein, it has been determined that the type of display sparkle that is commonly observed in pixelated displays combined with anti-glare surfaces is primarily a refractive effect in which features have some macroscopic (i.e., much larger than optical wavelength) dimensions on the surface, which cause refraction or “lensing” of display pixels into varying angles, thus modifying the apparent relative intensity of the pixels.
Referring to
Referring now to
The transparent glass sheet 100 may be a soda lime glass, an alkali aluminosilicate glass, or an alkali aluminoborosilicate glass. As used herein, the glass is transparent if it transmits at least 70% of at least one wavelength in a range from 390 nm to 700 nm. In some embodiments, the transparent glass sheet 100 may comprise an alkali aluminosilicate glass that includes alumina, at least one alkali metal, and silica (SiO2). An amount of silica the transparent glass sheet 100 may be greater than 50 mol %, at least 58 mol % SiO2, or at least 60 mol % SiO2. Examples of aluminosilicate glass substrates suitable for use as the transparent glass sheet 100 may include, but are not limited to, GORILLA®, EAGLE XG®, or LOTUS™ brand glass manufactured by Corning Incorporated. Other suitable substrates are contemplated. The transparent glass sheet 100 may include a strengthened glass substrate, which has been strengthened using thermal or chemical strengthening techniques.
The discrete surface features 104 of the anti-glare surface 102 of the transparent glass sheet 100 may be protrusions 108 that extend outward from the transparent glass sheet 100, as shown in
Referring to
As described above, one or more flat regions 106 occupy the space between each of the discrete surface features 104. Additionally, the flat regions 106 are contiguous such that each flat region 106 is connected with one or more other flat regions 106 that extend around one or more other discrete surface features 104. For example, the flat regions 106 are interconnected so that the flat regions 106 form a contiguous flat region, which may form a contiguous network or matrix of flat regions 106. In this manner, the anti-glare surface 102 includes a flat surface over which the discrete surface features 104 are distributed at individual, spaced-apart positions. The flat regions 106 propagate across the entire anti-glare surface 102 in an interconnected two-dimensional irregular-shaped lattice and are not isolated in discrete pockets completely surrounded by discrete surface features 104. The flat regions 106 may be continuously interconnected across the entirety of the anti-glare surface 102.
Referring to
As described previously, the anti-glare surface 102 having discrete surface features 104, which may be spaced apart and separated by one or more flat regions 106, may be a combination of curved surfaces 114 and flat surfaces 116. Because the flat surfaces 116 do not contribute to sparkle, the overall sparkle value for the anti-glare surface 102 having discrete surface features 104 may be reduced as compared to the conventional anti-glare surface 12 having continuous surface features 14, which results in a continuously curved surface.
The transparent glass sheet 100 having the anti-glare surface 102 with the plurality of discrete surface features 104, as previously described, may have a sparkle value of less than 3%, or less than 2%. As used herein, the sparkle value of the transparent glass sheet 100 is evaluated using SMS Bench and a display light source of 141 ppi, unless otherwise indicated. The anti-glare surface 102 having the discrete surface features 104 may have an average surface roughness (Ra) of from 10 nanometers (nm) to 1000 nm, or from 10 nm to 200 nm. Additionally, the anti-glare surface 102 having the discrete surface features 104 may have a transmission haze value of equal to or less than 20% as measured in accordance with ASTM D1003 using a Haze-Guard transmittance and haze testing apparatus obtained from Elektron Technologies, PLC.
As shown in
In contrast, as shown in
The transparent glass sheet 100 having the anti-glare surface 102 that includes the plurality of discrete surface features 104 separated by the flat regions 106 may be compatible with high definition (HD) displays having pixel densities of 200 ppi or greater. The ability to provide a low sparkle textured glass, such as transparent glass sheet 100, that is compatible with HD displays having high pixel density may create opportunities for integrating textured surfaces with consumer electronic devices. The transparent glass sheet 100 having such an anti-glare surface 102 may provide a glass with low sparkle that exhibits positive aesthetic appearance, good tactile feel, and anti-glare functionality.
In one or more embodiments, the discrete surface features 104 that protrude from the transparent glass sheet 100 may be made by a chemical etching method. Referring to
The method 200 includes removing 208 the roughening solution from contact with the surface 101 of the transparent glass sheet 100 before the plurality of discrete surface features 104 grow to fill the entire surface 101 of the transparent glass sheet 100. Upon removal of the roughening solution, the transparent glass sheet 100 comprises the plurality of discrete surface features 104 separated from one another by one or more flat regions 106. The method 200 may also include acid polishing 210 the surface 101 of the transparent glass sheet 100 to reduce a transmission haze of the transparent glass sheet 100 and a size of the plurality of discrete surface features 104.
The method 200 may optionally include strengthening 212 the transparent glass sheet 100. As previously described, the transparent glass sheet 100 may be thermally strengthened or chemically strengthened 212. The method 200 may optionally include cleaning (not shown) the surface 101 of the transparent glass sheet 100 prior to introducing the roughening solution to the surface 101 of the transparent glass sheet 100. The method 200 may also optionally include rinsing or cleaning (not shown) the surface 101 of the transparent glass sheet after the acid polishing 210 step or between removing 208 the roughening solution from the surface 101 of the transparent glass sheet 100 and acid polishing 210 the surface 101 of the transparent glass sheet 100.
Referring to
Referring to
The formation and growth of the crystals 120 to form the discrete surface features 104 are controlled so that the discrete surface features 104 remain spaced apart and separated from one another by flat regions 106. Crystal formation may be controlled to control the density of the discrete surface features 104 on the surface 101 of the transparent glass sheet 100 so that the discrete surface features 104 are maintained spaced apart and separated by the flat regions 106 of the glass surface 101 extending between each of the discrete surface features 104. Crystal growth may be controlled to limit the average size of the discrete surface features 104 to prevent them from growing into each other to create a continuous array of surface features. Forming and growing the crystals 120, which become the discrete surface features 104, may be conducted simultaneously. For example, the roughening solution may promote both formation and growth of the crystals 120 (i.e., discrete surface features 104) on the surface 101 of the transparent glass sheet 100.
The roughening solution may include hydrofluoric acid, one or more roughening reagents, and a solvent. In embodiments, the roughening solution may include a weight percent (wt. %) of hydrofluoric acid (HF) of from 0.5 wt. % to 10 wt. %, from 0.5 wt. % to 6 wt. %, from 0.5 wt. % to 3 wt. %, from 0.5 wt. % to 1 wt. %, from 1 wt. % to 10 wt. %, from 1 wt. % to 6 wt. %, from 1 wt. % to 3 wt. %, from 3 wt. % to 10 wt. %, from 3 wt. % to 6 wt. %, or from 6 wt. % to 10 wt. %. In some non-limiting examples, the roughening solution may include from 1 wt. % to 8 wt. % hydrofluoric acid. Alternatively, the roughening solution may include from 1 wt. % to 6 wt. % hydrofluoric acid.
The roughening reagent may be a reagent or combination of reagents that promote crystal formation and crystal growth by providing the cations (M+) to the roughening solution. The roughening reagent may include one or more inorganic salts containing potassium, sodium, and/or ammonium ions or combinations of ions. Non-limiting examples of roughening reagents may include, but are not limited to, potassium chloride (KCl), potassium nitrate (KNO3), potassium sulfate (K2SO4), sodium chloride (NaCl), sodium nitrate (NaNO3), sodium sulfate (Na2SO4), ammonium fluoride (NH4F), ammonium chloride (NH4Cl), ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4), other inorganic salts, and combinations of inorganic salts. In some non-limiting examples, the roughening solution may include a plurality of roughening reagents. For example, the roughening solution may include ammonium fluoride and potassium chloride as the roughening reagents.
The roughening solution may have a weight percent of a single roughening reagent of from 2 wt. % to 20 wt. %, from 2 wt. % to 15 wt. %, from 2 wt. % to 10 wt. %, from 2 wt. % to 5 wt. %, from 5 wt. % to 20 wt. %, from 5 wt. % to 15 wt. %, from 5 wt. % to 10 wt. %, from 10 wt. % to 20 wt. %, from 10 wt. % to 15 wt. %, or from 15 wt. % to 20 wt. %. The roughening solution may have a total weight percent (wt. %) of the roughening reagent, including multiple roughening reagents, of from 5 wt. % to 35 wt. %, from 5 wt. % to 25 wt. %, from 5 wt. % to 20 wt. %, from 5 wt. % to 17 wt. %, from 5 wt. % to 15 wt. %, from 7 wt. % to 35 wt. %, from 7 wt. % to 25 wt. %, from 7 wt. % to 20 wt. %, from 7 wt. % to 17 wt. %, from 7 wt. % to 15 wt. %, from 15 wt. % to 35 wt. %, from 15 wt. % to 25 wt. %, from 15 wt. % to 20 wt. %, from 15 wt. % to 17 wt. %, from 17 wt. % to 35 wt. %, from 17 wt. % to 25 wt. %, from 17 wt. % to 20 wt. %, from 20 wt. % to 35 wt. %, or from 20 wt. % to 25 wt. %. In some non-limiting examples, the roughening solution may include a weight percent of NH4F of from 5 wt. % to 15 wt. % and a concentration of KCl of from 2 wt. % to 20 wt. %. Alternatively, the roughening solution may have a weight percent of NH4F of from 10 wt. % to 20 wt. %.
The solvent may include water, which may make up the balance of the solution. The solvent may optionally include an organic solvent. Examples of suitable organic solvents may include, but are not limited to, polyols, such as a propylene glycol for example; alcohols, such as ethanol for example; and/or water miscible polar organic solvents, such as acetic acid for example. In some non-limiting examples, the roughening solution may include propylene glycol. The volume percent (vol. %) of propylene glycol in the roughening solution may be from 1 vol. % to 20 vol. %, from 1 vol. % to 15 vol. %, from 1 vol. % to 10 vol. %, from 1 vol. % to 5 vol. %, from 5 vol. % to 20 vol. %, from 5 vol. % to 15 vol. %, from 5 vol. % to 10 vol. %, from 10 vol. % to 20 vol. %, from 10 vol. % to 15 vol. %, or from 15 vol. % to 20 vol. %. Alternatively, the roughening solution may be substantially free of an organic solvent. As used in this disclosure, “substantially free” of a component means less than 1 wt. % of that component in a particular composition. As an example, a roughening solution which is substantially free of an organic solvent may have less than 1 wt. % of ethylene. Example roughening solutions may include one or more other additives, such as a surfactant, for example. An example roughening solution may have 1 wt. % or less of the surfactant.
In one or more non-limiting examples, the roughening solution may comprise, consist essentially of, or consist of HF, NH4F, KCl, and water. More specifically, the roughening solution may comprise, consist essentially of, or consist of from 1 wt. % to 6 wt. % HF, from 10 wt. % to 20 wt. % NH4F, from 2 wt. % to 20 wt. % KCl, and water. Alternatively, the roughening solution may comprise, consist essentially of, or consist of from 1 wt. % to 6 wt. % HF, from 5 wt. % to 15 wt. % NH4F, from 2 wt. % to 20 wt. % KCl, and water. In other non-limiting examples, the roughening solution may comprise, consist essentially of, or consist of from 1 wt. % to 6 wt. % HF, from 10 wt. % to 20 wt. % NH4F, from 2 wt. % to 20 wt. % KCl, from 1 vol. % to 15 vol. % propylene glycol, and the balance water.
While the transparent glass sheet 100 is exposed to the roughening solution, crystal seeds are formed on the surface of the transparent glass sheet 100 and grow according to the following chemical equations:
6HF+SiO2→H2SiF6+2H2O Eq. 1
2M++SiF62−→M2SiF6↓; where M=K+,Na+,NH4+,etc. Eq. 2
In equation 1, hydrofluoric acid (HF) reacts with the silica (SiO2) of the glass to produce a fluorosilicate (H2SiF6) and water. The H2SiF6 may dissociate in water, and the SiF62− ions may reacts with a cation (M) provided by the roughening reagent to produce the M2SiF6, per equation 2. The M2SiF6 precipitates on the surface of the transparent glass sheet 100 to form and grow the crystals, which become the discrete surface features 104. As previously discussed, the cation M provided by the roughening reagent may be a metal ion, such as potassium ion (K+) or sodium ion (Na+) for example, or the cation M may be a non-metallic cation, such as ammonium ion (NH4+) for example.
The discrete surface features 104, which are small in size and separated from one another by interconnected flat regions 106, are made by controlling crystal formation 204 and/or crystal growth 206 during the roughening process. Limiting crystal formation 204 to reduce the crystal seed density may ensure the formation of discrete surface features 104 that are spaced apart from one another and separated by flat regions 106 rather than a continuous interconnected network of surface features. Limiting growth 206 of the crystals 210 may prevent individual crystals 210 from growing into one another and combining to bridge the gaps between the discrete surface features 104. Further, controlling crystal growth may ensure that the surface features are appropriately sized to provide a target surface roughness. The composition of the roughening solution, temperature of the roughening solution, and reaction time of the transparent glass sheet 100 with the roughening solution may all be manipulated to control the crystal formation and crystal growth on the glass surface. The reaction time is the time period over which the transparent glass sheet 100 is maintained in contact with the roughening solution.
Tuning the composition of the roughening solution can effectively control the surface seed density (i.e., crystal formation density) and crystal growth rate. The number of crystal seeds that form on the surface 101 of the transparent glass sheet 100 may be controlled by controlling the concentration of the roughening reagents in the roughening solution. Increasing the concentration of the roughening reagents increases the concentration of cations (e.g., K+, Na+, NH4+, etc.), which drives the reaction of Equation 2 to the right in favor of producing more M2SiF6. Increasing the concentration of M2SiF6 through production of more M2SiF6 results in increased precipitation of M2SiF6 and, thus, an increase in the number of seeds formed on the glass surface 101. Likewise, decreasing the concentration of the roughening reagents drive the reaction of Equation 2 to the left in favor of decreasing concentration of M2SiF6, which leads to fewer seed formed on the glass surface 101. Therefore, the number of crystals formed (i.e., seeds formed) on the glass surface 101 may be reduced by reducing the concentration of the roughening reagents in the roughening solution.
Additionally, initial crystal formation on the glass surface 101 may be controlled by manipulating the solubility of the M2SiF6 in the roughening solution, which may be accomplished by changing the temperature of the roughening solution or changing the concentration of organic solvents in the roughening solution. For example, decreasing the temperature of the roughening solution decreases the solubility of M2SiF6 in the roughening solution, which results in increased precipitation of the M2SiF6 and increased crystal formation on the glass surface 101. Conversely, increasing the temperature of the roughening solution increases the solubility of M2SiF6 in the roughening solution and decreases precipitation of M2SiF6, which reduces formation of crystals on the glass surface 101. Therefore, decreasing the temperature increases crystal formation, which results in a greater density of the discrete surface features 104 on the surface 101 of the transparent glass sheet 100. The roughening solution may be maintained at a temperature of from 10° C. to 40° C. In some non-limiting examples, the roughening solution may be maintained at room temperature, which may be from 20° C. to 30° C.
Increasing the concentration of organic solvent in the roughening solution also tends to decrease the solubility of M2SiF6 in the roughening solution, leading to increased crystal formation. Conversely, decreasing the concentration of organic solvents in the roughening solution may tend to reduce crystal formation on the glass surface 101. Crystal formation may be reduced, and therefore limited, by maintaining a reduced concentration of the roughening reagents in the roughening solution, maintaining a higher temperature of the roughening solution, and/or reducing the concentration of organic solvents in the roughening solution. Alternatively, increasing the concentration of organic solvent in the roughening solution may increase crystal formation, resulting in a greater density of discrete surface features 104 formed on the surface 101 of the transparent glass sheet 100.
Crystal growth may be controlled by manipulating the reaction rate and/or the reaction time of the roughening process. Referring to Equation 1 previously provided, decreasing the concentration of HF in the roughening solution will decrease the concentration of reactants of Equation 1 and, therefore, decrease the reaction rate of Equation 1, leading to a decrease in the reactants for Equation 2 and a corresponding reduction in the formation of M2SiF6. As previously described, decreasing the concentration of M2SiF6 in the roughening solution decreases crystal formation as well as crystal growth.
For transparent glass sheets 100 that are aluminosilicate glass sheets, the crystal growth may be further reduced by increasing the concentration of fluoride ions in the roughening solution. The following chemical Equations 3-5 describe the chemical reactions related to etching an aluminosilicate glass:
Al2O3+6H+→2Al3++3H2O Eq. 3
HF↔H++F− Eq. 4
F−+HF↔HF2− Eq. 5
In Equation 3, aluminum oxide (Al2O3) at the surface of the aluminosilicate glass sheet is etched by protons (H+) (i.e., hydronium ions) to form aluminum ions (Al3+) and water (H2O). Equation 4 is the equilibrium dissociation of hydrofluoric acid HF in solution into fluoride ions (F−) and hydronium ions (H+). Adding fluoride ions, such as by increasing the concentration of ammonium fluoride (NH4F) in the roughening solution, shifts the equilibrium reaction of Equation 4 to the left towards formation of hydrofluoric acid (HF). Shifting the equilibrium of Equation 4 to the left results in a decrease in the concentration of hydronium ions (H+) and, thus, an increase in the pH of the roughening solution. The equilibrium of Equation 4 may further be shifted towards formation of HF through consumption of HF by Equation 5, in which the HF reacts with the increased concentration of fluoride ion (F−) to produce hydrogen difluoride ion (HF2−). Consumption of HF decreases the concentration of HF in the roughening solution. As previously described, decreasing the HF concentration decreases the reaction rate of Equation 1, which reduces the crystal formation and crystal growth on the glass surface 101 of the transparent glass sheet 100. Therefore, increasing the fluoride ions (F−) by increasing the concentration of NH4F in the roughening solution may increase the pH of the roughening solution and slow down the reactions resulting in crystal formation and growth.
Crystal growth may be further controlled by adjusting the reaction time (i.e., the time that the glass surface 101 of the transparent glass sheet 100 is maintained in contact with the roughening solution). As reaction time increases, the reactions of Equations 1-5 continue to proceed, resulting in continued crystal growth. Limiting the reaction time results in less crystal growth. The final crystal size, and therefore, the final size of the discrete surface features 104, may be reduced by shortening the reaction time.
Referring to
Referring to
Referring to
As previously described, in an alternative embodiment of an anti-glare surface 102 for a transparent glass sheet 100, the plurality of discrete surface features 104 may be a plurality of depressions 110, as shown in
Optionally, the transparent glass sheet 100 having the anti-glare surface 102 with the plurality of discrete surface features 104 separated by flat regions 106 may be strengthened using a chemical or thermal strengthening process. In embodiments, the transparent glass sheet 100 may be thermally strengthened. Alternatively, the transparent glass sheet 100 may be chemically strengthened using an ion exchange process to form a strengthened transparent glass sheet having one or more ion exchanged surfaces, for example. In this process, metal ions at or near a surface of the transparent glass sheet 100 are exchanged for larger metal ions having the same valence as the metal ions in the glass. The exchange is generally carried out by contacting the transparent glass sheet 100 with an ion exchange medium such as, for example, a molten salt bath that contains the larger metal ion. The metal ions are typically monovalent metal ions such as, for example, alkali metal ions. In one non-limiting example, chemical strengthening of a glass substrate containing sodium ions by ion exchange is accomplished by immersing the glass substrate in an ion exchange bath comprising a molten potassium salt such as potassium nitrate (KNO3) for example.
The replacement of small metal ions by larger metal ions in the ion exchange process creates a region in the glass that extends from the surface to a depth (referred to as the “depth of layer”) that is under compressive stress. This compressive stress at the surface of the transparent glass substrate is balanced by a tensile stress (also referred to as “central tension”) within the interior of the glass substrate. In some embodiments, the surface of the transparent glass substrate described herein, when strengthened by an ion exchange process, has a compressive stress of at least 350 MPa, and the region under compressive stress extends to a depth of layer of at least 15 μm below the surface.
The transparent glass sheet 100 having the anti-glare surface 102 that includes the plurality of discrete surface features 104 spaced apart and separated by the flat regions 106, as previously described, may be used as a front cover or cover glass for high definition display devices for an electronic device, such as a consumer electronic device. Examples of high definition display devices may include, but are not limited to, liquid crystal displays (LCD), organic light emitting diode (OLED), touch screens, or the like, having a resolution equal to or greater than 200 ppi in some embodiments, or equal to or greater than 2000 ppi in other embodiments. Examples of consumer electronic devices having high definitions displays with cover glass made from the transparent glass sheet 100 having the anti-glare surface 102 that includes the discrete surface features 104 spaced apart and separated by flat regions 106 may include, but are not limited to, smartphones, tablets, laptop computer displays, monitors, television screens, or other display devices. In one or more embodiments, an electronic device comprises a transparent glass sheet 100 having the anti-glare surface 102 that includes the plurality of discrete surface features 104 spaced apart and separated by the flat regions 106. The electronic device (for example a high definition display device) may a housing having front, back, and side surfaces; electrical components that are at least partially inside or entirely within the housing and including at least a controller, a memory, and a display at or adjacent to the front surface of the housing; and a cover substrate at or over the front surface of the housing such that it is over the display, wherein the cover substrate is any of the glasses disclosed herein.
Average Size of the Discrete Surface Features
The average size of the discrete surface features 104 may be determined from a photomicrograph of the anti-glare surface 102 of the transparent glass sheet 100 at 200× magnification. Each of the discrete surface features 104 are identified and manually measured. The measurements for each of the discrete surface features 104 in the photomicrograph are averaged together to determine the average size of the discrete surface features 104.
Sparkle Value
SMS Bench
The sparkle value of the anti-glare surfaces 102 may be evaluated using a bench-top Sparkle Measurement System (“SMS Bench”), Version 3.0.3, obtained from Display-Messtachnik & Systeme GmBH and a display light source of 141 ppi. The display light source can be a model Lenovo model Z510 screen. The sparkle values for the anti-glare surfaces disclosed herein using SMS Bench are reported in percent (%).
PPDr Method
The sparkle value of the anti-glare surface 102 may also be evaluated in terms of “pixel power deviation” (PPD). PPD is calculated by image analysis of display pixels according to the following procedure. A grid box is drawn around each LCD pixel. The total power within each grid box is then calculated from the CCD camera data and assigned as the total power tier each pixel. The total power tier each LCD pixel thus becomes an array of numbers, for which the mean and standard deviation may be calculated. The PPD value is defined as the standard deviation of total power per pixel divided by the mean power per pixel (times 100). The total power collected from each LCD pixel by the eye simulator camera is measured and the standard deviation of total pixel power (PPD) is calculated across the measurement area, which typically comprises about 30×30 LCD pixels.
The details of a measurement system and image processing calculation that are used to obtain PPI) values are described in U.S. Pat. No. 9,411,180, granted on Aug. 9, 2016, to Jacques Gollier et al, and entitled “Apparatus and Method fix Determining Sparkle,” the contents of which are incorporated by reference herein in its entirety. The measurement system includes: a pixelated source comprising a plurality of pixels, wherein each of the plurality of pixels has referenced indices i and j; and an imaging system optically disposed along an optical path originating from the pixelated source. The imaging system comprises: an imaging device disposed along the optical path and having a pixelated sensitive area comprising a second plurality of pixels, wherein each of the second plurality of pixels are referenced with indices m and n; and a diaphragm disposed on the optical path between the pixelated source and the imaging device, wherein the diaphragm has an adjustable collection angle for an image originating in the pixelated source. The image processing calculation includes: acquiring; a pixelated image of the transparent sample, the pixelated image comprising a plurality of pixels; determining boundaries between adjacent pixels in the pixelated image; integrating within the boundaries to obtain an integrated energy for each source pixel in the pixelated image; and calculating a standard deviation of the integrated energy for each source pixel, wherein the standard deviation is the power per pixel dispersion.
The light source used for the PPDr method may be a Fiber-Lite® LMI-6000 light source obtained from Dolan-Jenner industries. The mask may be a Part ID 210 ppi custom target on B270 glass obtained from Applied image, Inc. Sparkle values for the anti-glare surfaces disclosed herein using the PPDr method are reported in percent (%).
Transmittance and Haze
The transmittance and transmission haze (or T-haze) values of the anti-glare surfaces may be measured according to ASTM D1003 using a Haze-Guard testing apparatus by Elektron Technologies, PLC. As used herein, the term “transmittance” is defined as the percentage of incident optical power within a given wavelength range transmitted through a material. The transmittance value and the transmission haze value may be reported as percentages (%).
Gloss and Distinctness of Image
The 20° gloss, 60° gloss, 85° gloss, and distinctness of image (DOI) values for the anti-glare surfaces may be measured using a geniophotometer, such as a Rhopoint geniophotometer obtained from Rhopoint Instruments. The gloss values may be measured in accordance with ASTM E430 using the geniophotometer, and the DOI values may be measured in accordance with ASTM D5767. The gloss and DOI values are reported as percentages (%).
Surface Roughness and Skew
The surface roughness (RA) was measured using an interferometer and a sample area of 200 micron by 200 micron. The interferometer used was a ZYGO® NEWVIEW™ 7300 Optical Surface Profiler manufactured by ZYGO® Corporation. The surface roughness is reported as a mean surface roughness.
The skew (RSK) is a measurement of the symmetry of the surface profile of the glass surface relative to a mean line of the surface profile. For surface textures having the same surface roughness (RA), the skew may differentiate between the surface textures according to whether each surface texture is more or less peaked. For example, a negative RSK indicates a surface texture having a plurality of valleys, whereas a positive RSK indicates a predominance of peaks in the surface contour. RSK may be derived from the surface roughness measurements as the third central moment of the roughness amplitude density function.
The embodiments described herein will be further clarified by the following examples. Unless otherwise indicated, the transparent glass sheet 100 for each of the examples was an aluminosilicate glass manufactured by Corning Incorporated having an approximate composition as follows on an oxide basis: 64.62 mol % SiO2; 5.14 mol % B2O3; 13.97 mol % Al2O3; 13.79 mol % Na2O; 2.4 mol % MgO; 0.003 mol % TiO2; and 0.08 mol % SnO2.
In Examples 1-8, the effects of changes in composition of the roughening solution and reaction time were investigated. In particular, the concentrations of hydrofluoric acid (HF), ammonium fluoride (NH4F), and potassium chloride (KCl) were tuned at two levels; a high concentration level and a low concentration level. Eight roughening solutions were prepared, each of the solutions comprising HF, NH4F, KCl, and water. The concentrations of HF, NH4F, and KCl for each of the eight roughening solutions prepared for Examples 1-8 are provided in the following Table 1 with the balance of each solution being water. No organic solvents were added to the roughening solution.
To prepare the anti-glare surface 102 on the transparent glass sheet 100, the transparent glass sheet 100 was first cleaned using a cleanline wash. Once cleaned, the transparent glass sheet 100 was introduced to a bath of one of the roughening solutions of Examples 1-8 and maintained in contact with the roughening solution for a reaction time of 1 minute. After 1 minute, the transparent glass sheet 100 was removed from the bath of roughening solution and cleaned with deionized water to remove residual roughening solution from the transparent glass sheet 100. The method was repeated on separate transparent glass sheet 100 samples for each of the eight roughening solutions at a reaction time of 1 minute. A second set of samples were prepared by the same method, but with a reaction time of 8 minutes. None of the samples were subjected to acid polishing prior to evaluation.
Each of the sixteen samples prepared for Examples 1-8 were evaluated for transmittance, transmission haze, gloss 20°, gloss 60°, gloss 85°, distinctness of image (DOI), sparkle, roughness (RA), and skew (RSK), and the results are provided in Table 2 below. The sparkle value for each of the samples of Examples 1-8 was determined using the PPD method previously described. The test results for each of the samples of Examples 1-8 at 1 minute reaction time and 8 minute reaction time are provided in Table 2 below. For the sample ID's in Table 2, the first number before the dash is the solution number and the number after the dash is the reaction time in minutes.
In addition to the evaluations performed and reported in the table above, photomicrographs of the anti-glare surface 102 of each of the samples prepared for Examples 1-8 were taken at a magnification of 200 times and are included in
Qualitative evaluation of the photomicrographs led to the observation that reducing the concentration of KCl in the roughening solution reduces the density of the discrete surface features.
Qualitative evaluation of the photomicrographs also confirmed that increasing the reaction time of the transparent glass sheet 100 with the roughening solution increases the average size of the discrete surface features 104 formed on the anti-glare surface 102. For Example,
Further, qualitative evaluation of the photomicrographs led to the observation that increasing the NH4F concentration slows down the reactions and leads to discrete surface features 104 that are smaller in size.
Sparkle values measured for the Samples in Table 2 above ranged from 1.2% to 8%. As indicated by the results provided above in Table 2, the lowest sparkle values were obtained for Sample ID's 1-1 and 2-1, both of which samples were made with roughening solutions having a lower concentration of HF (3 wt. %) and a higher concentration of NH4F (15 wt. %) as compared to solutions 3-4, which had lower NH4F concentrations of only 5 wt. %, and solutions 5-8, which had higher HF concentrations of 6 wt. %.
Further, it was observed that decreasing the concentration of KCl in the roughening solution resulted in an increase in the sparkle measurement of the anti-glare surface 102 of the transparent glass sheet 100. For Example, Sample ID 3-1 was made with solution 3 having 10 wt. % KCl, and Sample ID 4-1 was made with solution 4 having a reduced concentration of KCl of 2 wt. %. The sparkle measurement for Sample ID 4-1 was higher than the sparkle measurement for Sample ID 3-1, which had the greater concentration of KCl. Similar relationships were observed between Sample ID's 5-1 and 6-1, Samples ID's 7-1 and 8-1, Sample ID's 1-8 and 2-8, Sample ID's 3-8 and 4-8, Sample ID's 5-8 and 6-8, and Sample ID's 7-8 and 8-8. Thus, the sparkle measurements indicate that increasing the KCl concentration in the roughening solution tends to decrease the sparkle of the resulting anti-glare surface 102 of the transparent glass sheet 100.
Additionally, the surface roughness of the anti-glare surface 102 of the transparent glass sheet 100 increased substantially when the reaction time was increased from 1 minute to 8 minutes.
The objective of Examples 9-14 was to use the relationships observed in Examples 1-8 to make anti-glare surfaces 102 having discrete surface features 104 spaced apart and separated by flat regions 106, the anti-glare surface 102 exhibiting low sparkle values. Consistent with the observations of Examples 1-8, the solutions of Examples 9-14 included lesser concentrations of HF (e.g., 1 wt. % and 3 wt. %) and greater concentrations of NH4F (15 wt. %). The reactions times were also shortened relative to the method used in Examples 1-8. In Examples 9-14, the effects of changes in composition of the roughening solution and reaction time were further tuned. In particular, the concentrations of HF and KCl were tuned at two levels; a high concentration level and a low concentration level. The concentration of NH4F was maintained constant at 15 wt. %. Six roughening solutions were prepared, each of the solutions comprising HF, NH4F, KCl, and water. In Examples 13 and 14, propylene glycol was added at a volume concentration of 15 volume % (vol. %) to study the effects of adding a quantity of organic solvent to the roughening solution. The concentrations of HF, NH4F, KCl, and propylene glycol for each of the six roughening solutions prepared for Examples 9-14 are provided in the following Table 4 with the balance of each solution being water.
To prepare the anti-glare surface 102 on the transparent glass sheet 100 for Examples 9-14, the transparent glass sheet 100 was first cleaned using a cleanline wash. Once cleaned, a transparent glass sheet 100 was introduced to a bath of one of the six roughening solutions of Examples 9-14 and maintained in contact with the roughening solution for a reaction time of 1 minute. After 1 minute, the transparent glass sheet 100 was removed from the bath of roughening solution and cleaned with deionized water to remove residual roughening solution from the transparent glass sheet 100. The method was repeated on separate transparent glass sheet 100 samples for each of the six roughening solutions at a reaction time of 1 minute. A second set of transparent glass sheet 100 samples were prepared by the same method, but with a reaction time of 4 minutes. None of the samples were subjected to acid polishing prior to evaluation.
Each of the twelve total samples prepared for Examples 9-14 were evaluated for transmittance, haze, gloss 20°, gloss 60°, gloss 85°, DOI, sparkle, roughness (RA), and skew (RSK), and the results are provided in Table 5 below. The sparkle value for each of the samples of Examples 9-14 was measured by SMS Bench using a 141 ppi light source. The test results for each of the twelve samples of Examples 9-14, six samples at the 1 minute reaction time and 6 samples at the 4 minute reaction time, are provided in Table 5 below. For the sample ID's in Table 5, the first number before the dash is the solution number and the number after the dash is the reaction time in minutes.
As indicated in Table 4, the anti-glare surfaces 102 of the samples prepared for Examples 9-14 exhibited sparkle values less than 3%, in particular, the sparkle values for Examples 9-14 were in a range of 0.9 to 2.9.
Based on the foregoing, it should now be understood that the embodiments described herein relate to transparent glass sheets 100 having anti-glare surfaces 102 with discrete surface features 104 that result in low sparkle values. The transparent glass sheets 100 and anti-glare surfaces 102 described herein may provide an anti-glare surface 102 with low sparkle and low haze that may be used as cover glass for high definition displays incorporated into consumer electronic devices.
While various embodiments of the anti-glare surface 102 and techniques for producing the anti-glare surface 102 having the plurality of discrete surface features 104 have been described herein, it should be understood it is contemplated that each of these embodiments and techniques may be used separately or in conjunction with one or more embodiments and techniques.
In a first aspect, a transparent glass sheet comprises at least one anti-glare surface having a plurality of discrete surface features having an average size equal to or less than 20 microns and one or more flat regions, wherein at least a portion of the plurality of discrete surface features are spaced apart from one another and each of the plurality of discrete surface features are bounded by the one or more flat regions, wherein the transparent glass sheet has a sparkle of equal to or less than 3% as evaluated by an SMS bench tester using a display light source of 141 ppi.
A second aspect according to the first aspect, wherein the plurality of discrete surface features are protrusions extending outward from the at least one anti-glare surface.
A third aspect according to the first aspect, wherein the plurality of discrete surface features are depressions in the at least one anti-glare surface.
A fourth aspect according to any previous aspect, wherein an average size of the plurality of discrete surface features is 10 microns or less.
A fifth aspect according to any previous aspect, wherein a majority of the plurality of discrete surface features are spaced apart from one another and separated by the one or more flat regions.
A sixth aspect according to any previous aspect, wherein each of the plurality of discrete surface features are separated from one another by one or more flat regions.
A seventh aspect according to any previous aspect, wherein the one or more flat regions extend between each of the plurality of discrete surface features.
An eighth aspect according to any previous aspect, wherein a majority of the discrete surface features are circumscribed by the one or more flat regions.
A ninth aspect according to any previous aspect, wherein a majority of the one or more flat regions are contiguous.
A tenth aspect according to any previous aspect, wherein the one or more flat regions are interconnected to form a contiguous flat region.
An eleventh aspect according to any previous aspect, wherein any line, which is in a plane of the anti-glare surface, extending from one of the plurality of discrete surface features to another one of the discrete surface features passes through at least one of the one or more flat regions.
A twelfth aspect according to any previous aspect, wherein an area of the one or more flat regions is from 10% to 60% of the total surface area of the anti-glare surface.
A thirteenth aspect according to any previous aspect, wherein an area of the flat regions is from 15% to 50% of the total surface area of the anti-glare surface.
A fourteenth aspect according to any previous aspect, wherein the at least one anti-glare surface has a surface roughness (Ra) from 10 nm to 1000 nm.
A fifteenth aspect according to any previous aspect, wherein the at least one anti-glare surface has a surface roughness (Ra) of from 10 nm to 200 nm.
A sixteenth aspect according to any previous aspect, wherein the transparent glass sheet comprises a transmission haze of less than 20% measured according to ASTM D1003.
A seventeenth aspect according to any previous aspect, wherein the transparent glass sheet comprises a strengthened transparent glass sheet.
An eighteenth aspect according to the seventeenth aspect, wherein the strengthened transparent glass sheet comprises one or more ion-exchanged surfaces.
In a nineteenth aspect, an electronic device comprises: a housing having a front surface, a back surface and side surfaces; electrical components provided at least partially within the housing, the electrical components including at least a controller, a memory, and a display, the display being provided at or adjacent the front surface of the housing; and the glass of any preceding aspect disposed over the display.
In a twentieth aspect, a method for producing an anti-glare surface on a transparent glass sheet, comprises: introducing a roughening solution to a surface of the transparent glass sheet, the roughening solution comprising: from 1 wt. % to 6 wt. % hydrofluoric acid; from 5 wt. % to 15 wt. % ammonium fluoride; and from 2 wt. % to 20 wt. % potassium chloride; maintaining the roughening solution in contact with the surface of the transparent glass sheet to form and grow a plurality of discrete surface features on the surface of the transparent glass sheet; and removing the roughening solution from the surface of the transparent glass sheet before the plurality of discrete surface features grow to fill the entire surface of the transparent glass sheet, wherein upon removal of the roughening solution, the transparent glass sheet comprises the plurality of discrete surface features separated from one another by one or more flat regions.
A twenty first aspect according to the twentieth aspect, further comprising acid polishing the surface of the transparent glass sheet to reduce a transmission haze of the transparent glass sheet and a size of the plurality of the discrete surface features.
A twenty second aspect according to the twentieth or twenty first aspect, wherein the surface of the transparent glass sheet is maintained in contact with the roughening solution for a reaction time equal to or greater than 1 minute and equal to or less than 8 minutes.
A twenty third aspect according to any one of the twentieth through twenty second aspects, further comprising strengthening the transparent glass sheet.
A twenty fourth aspect according to the twenty third aspect, wherein the transparent glass sheet is thermally strengthened.
A twenty fifth aspect according to the twenty third aspect, wherein the transparent glass sheet is chemically strengthened.
In a twenty sixth aspect, a transparent glass sheet has an anti-glare surface treatment prepared by the method of any one of the twentieth through twenty fifth aspects.
A twenty seventh aspect according to the twenty sixth aspect, wherein the plurality of discrete surface features have an average size of 10 microns or less.
A twenty eight aspect according to the twenty sixth or twenty seventh aspect, wherein the transparent glass sheet has a sparkle of 3% or less as evaluated by SMS bench using a display light source of 141 ppi, and a transmission haze of equal to or less than 20% measured according to ASTM D1003.
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/452,042 filed on Jan. 30, 2017, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62452042 | Jan 2017 | US |
