METHOD AND APPARATUS FOR FINISHING GLASS SHEETS

Methods and apparatus for finishing an edge of a glass sheet are described. The edge of the glass sheet is finished using a grinding wheel mounted on one end of a spindle, the grinding wheel having a peripheral edge that contacts the edge of the glass sheet during the grinding. The edge of the glass sheet is further finished by polishing the edge of the glass sheet with a polishing wheel mounted on one end of a spindle, the polishing wheel having an end face which contacts the glass edge during polishing.

BACKGROUND

Glass sheets are finished by grinding and polishing an edge of the glass sheet in the manufacture of various products, for example, a light guide plate (LGP), which is used in the back-light of edge-lit liquid crystal display (LCD) device to distribute light evenly over the display panel. Side lit back light units for such devices include an LGP that is usually made of high transmission plastic materials such as polymethylmethacrylate (PMMA). The trend toward thinner displays has been limited by challenges associated with using polymer light guide plates (LGPs). Although such plastic materials present excellent properties such as light transmission, these materials have relatively poor mechanical properties such as rigidity, coefficient of thermal expansion (CTE) and moisture absorption. In particular, polymer LGPs lack the dimensional stability required for ultra-slim displays. When a polymer LGP is subjected to heat and humidity, the LGP can warp and expand, compromising the onto-mechanical performance. The instability of polymer LGPs requires designers to add a wider bezel and a thicker backlight with air gaps to compensate for this movement.

Glass sheets have been proposed as a LGP replacement solution for displays, but the glass sheets must have the appropriate attributes to achieve sufficient optical performance in terms of transmission, scattering and light coupling. Glass sheets for light guide plates must meet such edge specifications as perpendicularity, straightness and flatness. Glass sheets are cut to size to make LGPs by mechanical scoring, forming a “vent,” which is an indentation line that extends partially into the glass surface. The vent functions as a separation line for controlled crack propagation of the glass sheet into two discrete pieces by applying mechanical force to the glass at the vent line. Glass LGPs up to 1.78 meters diagonal are currently available for use in displays having thicknesses in the range 0.7 mm and 2.0 mm, with dimensional tolerances of +/−0.5 mm and an average roughness at the edge of less than 0.2 micrometers. Corning Incorporated sells a Corning Iris™ glass for LGP, exhibiting high transmission of near 90% or greater in a wavelength range of 650 nm.

In an attempt to achieve the desired roughness at the edge, after scoring, finishing of the glass edge can be accomplished by grinding and polishing the edge with grinding and polishing wheels. Alternatively, etching with hydrofluoric acid and/or slurry polishing can be used. However, HF etching has safety and environmental considerations, and the etched edge may not provide the desired glass transmittance. Slurry polishing requires longer times to remove material on the glass edge than polishing with a polishing wheel, and it is difficult to control the glass edge dimension using slurry polishing. Traditional grinding and polishing using multiple wheels can also be time consuming to change grinding and polishing wheels, and the polishing wheels can wear quickly. Accordingly, it would be desirable to provide methods and apparatus for the finishing edges of glass sheets, especially glass sheets used for LGPs. It would also be desirable to provide apparatus and methods that provide additional capabilities in addition to grinding and polishing, such as forming holes in glass sheets.

SUMMARY

A first aspect of the disclosure pertains to an apparatus for finishing an edge of a glass sheet by grinding and polishing the edge of the glass sheet. In an embodiment, such an apparatus comprises a worktable which supports the glass sheet while the edges are subjected to grinding and polishing, wherein an X-axis is a direction of lateral movement on a plane of a glass sheet on the worktable, a Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis, and a Z-axis is a direction of vertical movement with respect to the plane; a rotary table movable along the X-axis and the Y-axis, the rotary table having a rotary table axis of rotation; a first spindle and a second spindle mounted to the rotary table having a common spindle axis of rotation about which the first spindle and the second spindle rotate, the common spindle axis of rotation orthogonal to the rotary table axis of rotation; and a grinding wheel mounted on the first spindle and a polishing wheel mounted on the second spindle, the grinding wheel configured to grind an edge of the glass sheet with the common spindle axis of rotation parallel to the Z-axis and the polishing wheel configured to polish an edge of the glass sheet with the common spindle axis of rotation parallel to the X-axis.

A second aspect of the disclosure pertains to a method to finish an edge of a glass sheet. In an embodiment, the method comprises supporting a glass sheet on a surface, wherein an X-axis is a direction of lateral movement on a plane of a glass sheet on the surface, a Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis, and a Z-axis is a direction of movement orthogonal to the plane; grinding the edge of the glass sheet with a grinding wheel mounted on one end of a first spindle, the first spindle oriented along the Z-axis during grinding and the grinding wheel comprising a peripheral edge that contacts the edge of the glass sheet during the grinding; and polishing the edge of the glass sheet with an end face of a polishing wheel mounted on one end of a second spindle, the second spindle positioned parallel to the plane during polishing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying examples and drawings.

In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles “a,” “an,” and the corresponding definite article “the” mean “at least one” or “one or more,” unless otherwise specified. It also is understood that the various features disclosed in the specification and the drawings can be used in any and all combinations.

Described herein are methods and apparatus for finishing edges of glass sheets. In specific embodiments, the glass sheets are finished by grinding and polishing to provide light guide plates which may be used in backlight units in accordance with embodiments of the present disclosure. In specific embodiments, light guide plates are provided that have similar or superior optical properties to light guide plates made from PMMA and that have much better mechanical properties such as rigidity, coefficient of thermal expansion (CTE) and dimensional stability in high moisture conditions compared to PMMA light guide plates.

Referring now toFIGS. 1-6, an edge finishing apparatus100adapted to finish an edge12of a glass sheet10comprises a worktable102which supports the glass sheet10while an edge12is subjected to grinding and polishing. The apparatus can be used to grind and/or polish the edge12, and/or a second edge14, a third edge13and a fourth edge15according to one or more embodiments. While in the embodiment shown, the worktable102is shown parallel to a horizontal plane, the disclosure is not limited to the worktable102being in the horizontal plane. The phrase “horizontal plane” with respect toFIGS. 1-6is an X-Y plane, wherein inFIGS. 1 and 3, an X-axis labeled as X is a direction of lateral movement on a horizontal plane of the glass sheet10on the worktable102, a Y-axis labeled as Y, which is a direction of longitudinal movement on the horizontal plane which is perpendicular to the X-axis, and a Z-axis labeled as Z is a direction of vertical movement relative to the horizontal plane (X-Y Plane), indicated by the X, Y and Z coordinates shown inFIGS. 1 and 3. However, the X-Y plane can be a plane other than a horizontal plane according to alternative embodiments.

With reference toFIG. 5, the edge finishing apparatus100further comprises a rotary table104and movable along the X-axis and the Y-axis, the rotary table104having a rotary table axis of rotation105. The edge finishing apparatus100shown inFIGS. 1-6further includes a first spindle106and a second spindle108mounted to the rotary table104having a common spindle axis of rotation107about which the first spindle and the second spindle rotate, the common spindle axis of rotation107is orthogonal to the rotary table axis of rotation105. The edge finishing apparatus100further comprises a grinding wheel110removably mounted on the first spindle106and a polishing wheel112removably mounted on the second spindle108, wherein the grinding wheel110is configured to grind the edge12of the glass sheet10with the common spindle axis of rotation107in a vertical orientation (i.e., parallel with the Z-axis) and the polishing wheel112is configured to polish an edge12of the glass sheet10with the common spindle axis of rotation107in a horizontal orientation (i.e., parallel to the X-axis or Y-axis or in the X-Y plane or horizontal plane of the glass sheet10).

One or more embodiments of the edge finishing apparatus100further comprises a plurality of first peripheral liquid cooling nozzles120arranged in a ring, the plurality of first peripheral liquid cooling nozzles120positioned adjacent the grinding wheel110and positioned to direct cooling liquid toward a peripheral grinding edge111of the grinding wheel110. According to one or more embodiments, “adjacent” refers to first peripheral liquid cooling nozzles120being a distance in a range of about 1-10 cm, about 1-8 cm, about 1-6 cm, about 1-4 cm, or about 1-2 cm from the peripheral grinding edge111of the grinding wheel110. The cooling liquid for the first peripheral liquid cooling nozzles120can be flowed to the first peripheral liquid cooling nozzles120through first liquid coolant lines121. In one or more embodiments, the apparatus further comprises a plurality of second peripheral liquid cooling nozzles130arranged in a ring, the second peripheral liquid cooling nozzles130adjacent the grinding wheel110. The cooling liquid for the second peripheral cooling nozzles can be flowed to the second peripheral liquid cooling nozzles130by second liquid coolant lines131. The cooling liquid provided to the first liquid coolant lines121and second liquid coolant lines131can be supplied by first supply line127(best seen inFIGS. 2 and 4), which may be connected to a coolant source (not shown) such as a faucet supplying tap water or a pump connected to a tank (not shown) containing deionized and/or demineralized water. The ring-shaped arrangement of the first peripheral liquid cooling nozzles120and second peripheral liquid cooling nozzles130provides efficient cooling of the wheels during grinding and polishing as well as the edge being finished and reduces edge burnout and chipping of the edge12of the glass sheet10.

In one or more embodiments, the edge finishing apparatus100further includes a plurality of remote liquid cooling nozzles140positioned remotely from the grinding wheel110and the polishing wheel112, and the remote liquid cooling nozzles140direct cooling liquid towards an edge12of the glass sheet during grinding and/or polishing. In one or more embodiments, “positioned remotely” means that the remote liquid cooling nozzles140are a distance in a range of about 10-200 cm, about 40-200 cm, about 80-200 cm, about 100-200 cm or about 150-200 cm from the edge of the glass sheet and/or the grinding wheel110and the polishing wheel112. InFIGS. 1-4, the remote liquid cooling nozzles140are shown as positioned on housing150which holds the rotary table104to a gantry152. Cooling liquid can be flowed to remote liquid cooling nozzles140by third liquid coolant lines141. The cooling liquid provided to the third liquid coolant lines141can be supplied by second supply line147(best seen inFIGS. 2 and 4), which may be connected to a coolant source (not shown) such as a faucet supplying tap water or a pump connected to a tank (not show) containing deionized and/or demineralized water.

In one or more embodiments, the plurality of first peripheral liquid cooling nozzles and remote liquid cooling nozzles140are configured to be activated during grinding of the glass sheet. The plurality of first peripheral liquid cooling nozzles120can include any suitable number of nozzles to provide sufficient cooling during grinding and/or polishing. For example, three, four, five, six, seven, eight, nine, ten, eleven or twelve first peripheral liquid cooling nozzles120can be provided. Likewise, the plurality of second peripheral liquid cooling nozzles130can include any suitable number of nozzles to provide sufficient cooling during grinding and/or polishing. For example, three, four, five, six, seven, eight, nine, ten, eleven or twelve second peripheral liquid cooling nozzles130can be provided. Regarding the remote liquid cooling nozzles140, any number nozzles can be provided and affixed to the housing150. As shown inFIGS. 1-6, remote liquid cooling nozzles140are supplied on two sides of the housing150. Each side of the housing can have any suitable number of nozzles to provide sufficient cooling during grinding and/or polishing, for example one, two, three, four, five, six, seven, eight, nine or ten remote liquid cooling nozzles140. The remote liquid cooling nozzles140can be spaced at any appropriate distance from the edge of the glass sheet10during grinding and/or polishing. The remote liquid cooling nozzles140can be spaced 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm,50, cm, 60 cm, 70 cm, 80 cm, 90 cm, 100 cm, 125 cm, 150 cm, 200 cm or up to 500 cm away from the edge12of the glass sheet10during a grinding and/or polishing operation. Each of the first peripheral liquid cooling nozzles120, second peripheral liquid cooling nozzles130and remote liquid cooling nozzles140can be sized and shaped as needed to obtain the desired cooling effect. For example, the openings of the first peripheral liquid cooling nozzles120, second peripheral liquid cooling nozzles130and remote liquid cooling nozzles140can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm or to 10 mm in diameter. Conventional polyvinyl chloride (PVC) or other plastic tubing or metal tubing can be used for each of the first liquid coolant lines121, second liquid coolant lines131, third liquid coolant lines141and the first supply line127and the second supply line147. The cooling liquid may comprise water, chilled water or other cooling liquid.

Referring now toFIGS. 7A and 9C and 7B and 9A and 9B, in one or more embodiments, the grinding wheel110comprises a cylindrical wheel including a peripheral grinding edge111and the polishing wheel112comprises a cup-shaped or cup wheel including a peripheral polishing edge161and a polishing end face162. As shown inFIGS. 7B, 9A and 9B, the cup wheel comprises a hollowed region164. The polishing wheel112shown inFIG. 9Acomprises slots166positioned on the polishing end face162providing a slotted surface that contacts the edge12of the glass sheet during polishing. Suitable cup wheels include a 2000 mesh (2000#) epoxy resin cup wheel with slots, an epoxy resin wheel 5000 mesh (5000#), and an epoxy resin wheel 9000 mesh (9000#) for fine polishing with a Cu content up to 50% by volume to reduce heat.

As shown inFIGS. 7A and 9C, the grinding wheel110includes a chamfer125which can be used to form a chamfer19on the edge12of the glass sheet10. In one or more embodiments, the first spindle106and the grinding wheel110are configured such that the peripheral grinding edge111contacts an edge12of the glass sheet10during grinding and the second spindle108and the polishing wheel112are configured such that polishing end face162contacts an edge of the glass sheet during polishing.

Referring back toFIGS. 1-4, the rotary table104is mounted on a gantry152that is movable along the Y-axis and the rotary table104is movable along the X-axis. The gantry152is movable on a Y-axis carriage180along rails182. It will be understood that the arrangement shown is exemplary, and linear motion of the gantry152along the Y-axis can be accomplished in other ways, for example, using a worm gear assembly that includes a threaded shaft, a rotating nut and motor drive (not shown). The rotary table104is movable on an X-axis carriage190along rails192. It will be understood that the arrangement shown is exemplary, and linear motion of the rotary table104along the X-axis can be accomplished in other ways, for example, a worm gear assembly that includes a threaded shaft, a rotating nut and motor drive (not shown).

Operation of the edge finishing apparatus100will now be described. The edge finishing apparatus100can be part of a computer numerical control (CNC) machine200. A grinding wheel110comprising a shank195can be mounted on the first spindle106by a chuck or a collet (not shown), which can be driven by a motor (not shown) to rotate the first spindle106and the grinding wheel110about axis of rotation107. Similarly a polishing wheel112comprising a shank197can be mounted on the second spindle108by a chuck or a collet (not shown), which can be driven by a motor (not shown) to rotate the spindle and the polishing wheel112about axis of rotation107. The grinding wheel110can be rotated while being translated along the edge12in the direction of the Y-axis to remove material from the edge12of the glass sheet10. The CNC machine200includes a controller210, which controls rotation and translation of the grinding wheel110and the polishing wheel112. The controller210is in communication with the CNC machine200either via a hardwired or wireless connection. The controller210can be any suitable component that can control translation and rotation of the components of the CNC machine200and edge finishing apparatus100. For example, the controller210can be a computer including a central processing unit, memory, suitable circuits and storage. The CNC machine200may further include one or more position sensors212, which may, for example, comprise a machine vision system including cameras, e.g., charge coupled device (CCD) cameras, to accurately track the position of the grinding wheel, the polishing wheel, the edge of the glass sheet edge being ground and polished, and to provide information to the controller210to align the grinding wheel and polishing wheel. A camera having a resolution of 0.001 micrometers can monitor a flat single edge, rectangular parts and circular parts.

The positioning of the grinding wheel110and polishing wheel112in the X-Y plane can be controlled by roller type or sliding type rail systems to effect movement of the grinding wheel110and the polishing wheel112in the X-direction and Y-direction. As noted above, Y-translation of the gantry152occurs via the Y-axis carriage180on rails182, and X-axis translation occurs via the X-axis carriage190on rails192. The position sensors212communicate with the controller210to provide feedback to the controller on the position of grinding wheel110and polishing wheel112and the glass sheet10during finishing of the glass sheet. The controller210of the CNC machine200may also be used to control the flow of the cooling liquid, which can communicate with valves and pumps (not shown) to control the pressure, flow rate and duration of cooling liquid flow through each of the first peripheral liquid cooling nozzles120, the second peripheral liquid cooling nozzles130and remote liquid cooling nozzles140.

According to one or more embodiments, the rotary table104enables the grinding wheel110and polishing wheel112to rotate about the axis of rotation105, which is orthogonal to axis of rotation107of the first spindle106and the second spindle108. The rotary table104can index or rotate in any desirable number of increments, for example, increments of 1 degree, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 45 degrees, 90 degrees and 180 degrees. A suitable rotary table104is a Detron GX-170P, available from Detron Machine Co., Ltd. of Taiwan. According to some embodiments, in use, during a grinding operation, the first spindle106is in a vertical orientation parallel to or along the Z-axis as shown inFIG. 1. The first spindle106rotates about axis107and translates along the Y-axis to remove material from edge12. In one or more embodiments, edges13,15can be finished by rotating the first spindle106about axis of rotation107while translating the first spindle along the X-axis to remove material from the edges13,15. When the grinding operation is completed, the controller210of the CNC machine200sends a signal to rotate the first spindle106ninety degrees about axis of rotation105so that the second spindle108is now positioned parallel to the X-Y plane or the horizontal plane of the worktable102and the glass sheet10so that the end face162can contact the edge12of the glass sheet10during a polishing operation. It will be understood that the orientation of the worktable102and glass sheet can be other than horizontal, and in some embodiments, the worktable102and the glass sheet can be tilted on an angle to the horizontal. During a polishing operation of edge12, the second spindle108rotates about axis of rotation107and translates second spindle108along the Y-axis. The polishing operation can also be performed in a similar manner on edge14.

Thus, it will be appreciated that the rotary table104enables grinding wi spindle106in a vertical orientation (parallel to the Z-axis) and polishing with the second spindle108in a horizontal orientation (parallel to the horizontal plane or X-Y plane). With a grinding wheel110mounted on the first spindle106and a polishing wheel112mounted to the second spindle108, the polishing and grinding operations can proceed rapidly and efficiently on edges12,14of the glass sheet10without changing wheels. Cooling provided by the first peripheral liquid cooling nozzles120, second peripheral liquid cooling nozzles130and remote liquid cooling nozzles efficiently cools the edges of the glass sheet while being finished, as well as cooling the grinding wheel and polishing wheel during a grinding and polishing process.

Typically, it is difficult to maintain a flat end face162on the polishing wheel112especially after the polishing wheel112has polished many glass edges. A dressing process can make the wheel flatter and remove burnout area to improve polishing efficiency. Referring now toFIG. 8, conditioning tool300is shown including a motor302and dressing wheel304which rotates in direction of arrow305. The dressing wheel304contacts the end face162of the polishing wheel112while the polishing wheel112is rotated about axis of rotation107and translated along direction309. The conditioning tool300could be offline, that is, located away from or separately from the edge finishing apparatus100. Alternatively, the conditioning tool300can be mounted to or adjacent the edge finishing apparatus100. Dressing the polishing wheel112with a GC (green silicon carbide) 120 mesh (120#) dressing wheel with an outer diameter of 75 mm, an inner hole diameter of 12.7 mm and a thickness of 25 mm running at 147 rpm while the polishing wheel112is rotated at 3000 rpm while translating the polishing wheel at 800 mm/min at 0.01 mm depth of cut of a glass edge resulted in an improved end face162flatness from 14 micrometers and to <1 micrometer after dressing.

Referring now toFIG. 10, hole drilling tool400could also be coupled to the first spindle106or the second spindle108to form holes in a glass sheet10. Thus, in one or more embodiments, a method may include forming a hole in the glass sheet with a hole drilling tool coupled to the first spindle or the second spindle. Forming the hole in the glass sheet may occur before or after the grinding and polishing described herein.

According to one or more embodiments, the edge finishing apparatus100can form an edge12perpendicular to the major surfaces of a glass sheet and provide an edge with improved edge roughness to Ra<0.5 micrometers, Ra<0.4 micrometers, Ra<0.3 micrometers or Ra<0.2 micrometers without etching the edge with hydrofluoric acid and/or slurry polishing the edge. Stated another way, a glass sheet with an edge roughness of Ra<0.5micrometers, Ra<0.4 micrometers, Ra<0.3 micrometers or Ra<0.2 micrometers can be made according to one or more embodiments by grinding and polishing using the edge finishing apparatus100in this disclosure. Average roughness (Ra) of the edge of a glass sheet after grinding and polishing is measured according to ISO 4288:1996 using a Keyence Ultra-deep shape measuring microscope, model VK-8510/VK-8500 available from Keyence Corporation at www.keyence.com. The edge finishing apparatus100can process a variety of glass sheet sizes, e.g., glass sheets with X-Y dimensions in a range of 10×10 mm to 3600 mm×1725 mm and larger.

Another aspect of the disclosure pertains to a method of grinding and polishing an edge of a glass sheet. In an embodiment, the method comprises supporting the glass sheet on a surface such as the worktable102shown inFIGS. 1-2, wherein an X-axis is a direction of lateral movement on a plane of a glass sheet on the surface, a Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis, and a Z-axis is a direction of movement orthogonal to the plane. In specific embodiments, the X-axis is a direction of lateral movement on a horizontal plane of a glass sheet on the horizontal surface, the Y-axis is a direction of longitudinal movement on the horizontal plane which is perpendicular to the X-axis, and the Z-axis is a direction of vertical movement with respect to the horizontal plane. The method further includes grinding the edge of the glass sheet with a grinding wheel mounted on one end of a first spindle, the first spindle oriented along the Z-axis during grinding and the grinding wheel having a peripheral edge that contacts the edge of the glass sheet during the grinding. The method further comprises polishing the edge of the glass sheet with a polishing wheel mounted on one end of a second spindle, the second spindle positioned parallel to the plane of the glass sheet during polishing and the polishing wheel having an end face which contacts the edge during polishing. In specific embodiments in which the worktable and glass sheet are horizontal, the second spindle is positioned horizontally (i.e., parallel to the X-Y plane) during polishing.

In one or more embodiments, the method includes directing cooling fluid at the peripheral edge of the grinding wheel with first peripheral liquid cooling nozzles arranged in a ring, the first peripheral cooling nozzles adjacent the peripheral edge of the grinding wheel during grinding. In one or more embodiments, the method includes directing cooling fluid at the edge of the glass sheet during polishing with a plurality of remote liquid cooling nozzles positioned remotely from the edge of the glass sheet and/or the grinding wheel110and the polishing wheel112during polishing. In one or more embodiments, the method includes directing cooling fluid at the edge during grinding with the plurality of remote liquid cooling nozzles positioned remotely from the edge of the glass sheet and/or the grinding wheel110and the polishing wheel112during grinding.

In one or more embodiments, the method includes moving the first spindle and the second spindle relative to the glass sheet in a direction along the Y-axis during grinding and polishing of the edge of the glass sheet. In one or more embodiments of the method, the first spindle and second spindle have a common spindle axis of rotation107about which the first spindle and the second spindle rotate.

In one or more embodiments of the method, the polishing wheel is a cup wheel. In one or more embodiments of the method, the polishing wheel is a cup wheel with slots on an end face of the cup wheel. In one or more embodiments of the method, the glass sheet after finishing can be used as a light guide plate, wherein the edge is a finished edge after grinding and polishing, the finished edge having an average roughness of less than 0.2 micrometers.

In one or more embodiments of the method, the finished edge has a perpendicularity such that the glass sheet after grinding and polishing of the edge can be used as light guide plate having a light injection edge that scatters light within an angle less than 12.8 degrees full width half maximum (FWHM) in transmission. In one or more embodiments of the method, where the glass sheet finished edge has a light transmission at least 95% at a wavelength of 450 nm. A glass sheet having this high transmission is suitable for use as a light guide plate, the

In one or more embodiments, the edge of the glass sheet is a first edge subjected to grinding and polishing to provide an edge that can be used as a first light injection edge in the fabrication of a light guide plate. The method can further include grinding and polishing two edges adjacent the first light injection edge. In one or more embodiments of the method, the glass sheet comprises SiO2in a range of 50 mol % to 80 mol %, Al2O3in a range of 0 mol % to 20 mol %, and B2O3in a range of 0 mol % to 25 mol %, and less than 50 ppm by weight iron (Fe) concentration.

As indicated above, the apparatus and methods described herein can be utilized in the manufacture of glass light guide plates.FIG. 11illustrates an exemplary embodiment of a light guide plate that can be made by the methods and apparatus of the present disclosure to finish a glass sheet by grinding and polishing an edge. The glass sheet has the shape and structure of a typical light guide plate comprising a glass sheet having a first face610, which may be a front face, and a second face opposite the first face, which may be a back face. The first and second faces have a height, H, and a width, W. In one or more embodiments, the first and/or second face(s) have an average roughness (Ra) that is less than 0.6 nm.

The glass sheet600has a thickness, T, between the front face and the back face, wherein the thickness forms four edges. The thickness of the glass sheet is typically less than the height and width of the front and back faces. In various embodiments, the thickness of the light guide plate is less than 1.5% of the height of the front and/or back face. In one or more embodiments, the thickness, T, may be about 2 mm, about 1.9 mm, about 1.8 mm, about 1.7 mm, about 1.6 mm, about 1.5 mm, about 1.4 mm, about 1.3 mm, about 1.2 mm, about 1.1 mm, about 1 mm, about 0.9 mm, about 0.8 mm, about 0.7 mm, about 0.6 mm, about 0.5 mm, about 0.4 mm or about 0.3 mm. The height, width, and thickness of the light guide plate are configured and dimensioned for use as a LGP in an LCD backlight application.

In the embodiment shown, a first edge630is a light injection edge that receives light provided, for example, by a light emitting diode (LED). In some embodiments, the light injection edge scatters light within an angle less than 12.8 degrees full width half maximum (FWHM) in transmission. The light injection edge can be obtained by grinding and polishing the first edge630in accordance with apparatus and methods described herein.

The glass sheet further comprises a second edge640adjacent to the light injection edge630and a third edge660opposite the second edge640and adjacent to the light injection edge630, wherein the second edge640and/or the third edge660scatter light within an angle of less than 12.8 degrees FWHM in reflection. The second edge640and/or the third edge660may comprise a diffusion angle in reflection that is less than 6.4 degrees. The glass sheet includes a fourth edge650opposite the first edge630.

According to one or more embodiments, three of the four edges of the LGP have a mirror polished surface for two reasons: LED coupling and total internal reflection (TIR) at two edges. According to one or more embodiments, and as illustrated inFIG. 12, light injected into a first edge630can be incident on a second edge640adjacent to the injection edge and a third edge660adjacent to the injection edge, wherein the second edge640is opposite the third edge660. The second and third edges may also comprise a low average roughness at the edge of less than 0.5 micrometers, 0.4 micrometers, 0.3 micrometers or 0.2 micrometers without etching with hydrofluoric acid and/or slurry polishing the edge so that the incident light undergoes total internal reflectance from the two edges adjacent the first edge.

Light may be injected into the first edge630from an array of LED's700positioned along the first edge630. The LED's may be located a distance of less than 0.5 mm from the first edge630. According to one or more embodiments, the LED's may have a thickness or height that is less than or equal to the thickness of the glass sheet to provide efficient light coupling to the light guide plate600. According to one or more embodiments, the two edges640,660may also comprise a diffusion angle in reflection that is less than 6.4 degrees.

EXAMPLES

Transmittance values were determined with several glass sheets having an X-Y-Z dimension of 200 mm×200 mm×1.1 mm were subjected to grinding and polishing using the edge finishing apparatus100and different grinding and polishing wheels as described below. Transmittance after grinding and polishing was measured using a Keyence Ultra-deep shape measuring microscope, model VK-8510/VK-8500 available from Keyence Corporation at www.keyence.com. Transmittance was measured on the 200 mm×200 mm×1.1 mm glass sheet across the Y dimension (200 mm) using laser light source (EQ-99X LDLS available from Energetiq Technology, Inc., Woburn, Mass.) at a wavelength ranging from 400 nm to 700 nm by directing the light source at the ground and polished edge and measuring light transmitted through the sample at the opposite edge with the microscope. Measurements were taken at wavelengths of 400 nm, 560 nm, and 630 nm. The transmittance measurements of the samples having ground and polished edges were compared with the transmittance values measured through a glass sheet having the same X-Y-Z dimensions across the Y dimension (200 mm) after being cut but before grinding and polishing of the edge to provide a percentage value compared to the cut edge sample. The transmittance of the sample with the cut edge was measured by directing the light source at the cut edge and measuring light transmitted through the sample at the opposite edge. A sample measured after being cut but before grinding and polishing of the edge had a glass transmittance of 100.00% with an as cut edge. The transmittance values provided below are an average of the measurements taken at the wavelengths of 400 nm, 560 nm, and 630 nm.

Average roughness was determined with several glass sheets having an X-Y-Z dimension of 1219 mm×150 mm×1.1 mm were subjected to grinding and polishing using the edge finishing apparatus100and different grinding and polishing wheels as described below. Surface roughness of the edge after grinding and polishing was measured according to ISO 4288:1996 using a Keyence Ultra-deep shape measuring microscope, model VK-8510/VK-8500 available from Keyence Corporation at www.keyence.com.

An 800 mesh (800#) chamfered metal bonded diamond grinding wheel was used to grind the edge at a translation speed of 6000 mm/min, removing 0.10 mm of the edge. This was followed by a second edge polish step with an end face a slotted epoxy resin bonded cup wheel 2000 mesh (2000#) with a Cu content up to 50% by volume, removing 0.03 mm after one pass at a translation speed of 6000 mm/min. A third step involved polishing with an unslotted end face of a resin cup wheel 5000 mesh (5000#) with a Cu content up to 50% by volume, removing 0.005 mm with one pass at a translation speed of 6000 mm/min. The average roughness Ra measured using the Keyence microscope using the technique described above was 0.04 micrometers. The optical transmittance was measured as described above, and the optical transmittance exceeded 99.5%, measuring 99.8%.

An 800 mesh (800#) straight (not chamfered) metal bonded diamond grinding wheel was used to grind an edge of a glass sheet at a translation speed of 6000 mm/min, removing 0.10 mm of the edge. This was followed by a second edge grind step with a chamfered metal bonded diamond grinding wheel 800 mesh (800#), removing 0.05 mm after one pass at a translation speed of 6000 mm/min. A third step involved polishing with an end face of an unslotted epoxy resin cup wheel 5000# with a Cu content up to 50% by volume, removing 0.005 mm with three passes at a translation speed of 6000 mm/min. The average roughness Ra measured using the Keyence microscope using the technique described above was 0.035 micrometers.

The optical transmittance was measured using the technique described above and exceeded 99.5%, measuring 99.8%.

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.