US20190337112A1

US20190337112A1 - Method and apparatus for finishing glass sheets

Info

Publication number: US20190337112A1
Application number: US16/477,372
Authority: US
Inventors: Ting-Wei CHU; Hsueh-Hung Fu; Kai Yu Hsiao; Chi-Cheng Hsu; Tzu-Hen Hsu; Yuyin Tang
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2017-01-13
Filing date: 2018-01-12
Publication date: 2019-11-07
Also published as: TW201831266A; KR20190098768A; WO2018132661A1; CN110177647A; JP2020508226A

Abstract

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.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/445,782 filed on Jan. 13, 2017, the content of which is relied upon and incorporated herein by reference in its entirety.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

FIG. 1 is a perspective view of an apparatus for finishing an edge of a glass sheet showing a grinding wheel positioned to grind an edge of the glass sheet according to one or more embodiments;

FIG. 2 is a detailed perspective view of a portion of the apparatus shown in FIG. 1;

FIG. 3 is a perspective view of an apparatus for finishing an edge of a glass sheet showing a polishing wheel in position to polish an edge of the glass sheet according to one or more embodiments;

FIG. 4 is a detailed perspective view of a portion of the apparatus shown in FIG. 3;

FIG. 5 is a detailed perspective view of a polishing wheel on a spindle according to one or more embodiments;

FIG. 6 is a detailed perspective view of the grinding wheel of the apparatus shown in FIG. 1 according to one or more embodiments;

FIG. 7A is a side view showing a grinding wheel grinding an edge of a glass sheet;

FIG. 7B is a side view showing a polishing wheel polishing an edge of a glass sheet;

FIG. 8 is a side view showing a polishing wheel being dressed by a dressing wheel according to one or more embodiments;

FIG. 9A is a perspective view of a polishing wheel according to one or more embodiments;

FIG. 9B is a perspective view of a polishing wheel according to one or more embodiments;

FIG. 9C is a perspective view of a grinding wheel according to one or more embodiments;

FIG. 10 is a perspective view of a hole drilling tool according to an embodiment

FIG. 11 illustrates an exemplary embodiment of a light guide plate; and

FIG. 12 illustrates total internal reflection of light at two adjacent edges of a glass LGP.

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 to FIGS. 1-6, an edge finishing apparatus 100 adapted to finish an edge 12 of a glass sheet 10 comprises a worktable 102 which supports the glass sheet 10 while an edge 12 is subjected to grinding and polishing. The apparatus can be used to grind and/or polish the edge 12, and/or a second edge 14, a third edge 13 and a fourth edge 15 according to one or more embodiments. While in the embodiment shown, the worktable 102 is shown parallel to a horizontal plane, the disclosure is not limited to the worktable 102 being in the horizontal plane. The phrase “horizontal plane” with respect to FIGS. 1-6 is an X-Y plane, wherein in FIGS. 1 and 3, an X-axis labeled as X is a direction of lateral movement on a horizontal plane of the glass sheet 10 on the worktable 102, 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 in FIGS. 1 and 3. However, the X-Y plane can be a plane other than a horizontal plane according to alternative embodiments.
With reference to FIG. 5, the edge finishing apparatus 100 further comprises a rotary table 104 and movable along the X-axis and the Y-axis, the rotary table 104 having a rotary table axis of rotation 105. The edge finishing apparatus 100 shown in FIGS. 1-6 further includes a first spindle 106 and a second spindle 108 mounted to the rotary table 104 having a common spindle axis of rotation 107 about which the first spindle and the second spindle rotate, the common spindle axis of rotation 107 is orthogonal to the rotary table axis of rotation 105. The edge finishing apparatus 100 further comprises a grinding wheel 110 removably mounted on the first spindle 106 and a polishing wheel 112 removably mounted on the second spindle 108, wherein the grinding wheel 110 is configured to grind the edge 12 of the glass sheet 10 with the common spindle axis of rotation 107 in a vertical orientation (i.e., parallel with the Z-axis) and the polishing wheel 112 is configured to polish an edge 12 of the glass sheet 10 with the common spindle axis of rotation 107 in 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 sheet 10).
One or more embodiments of the edge finishing apparatus 100 further comprises a plurality of first peripheral liquid cooling nozzles 120 arranged in a ring, the plurality of first peripheral liquid cooling nozzles 120 positioned adjacent the grinding wheel 110 and positioned to direct cooling liquid toward a peripheral grinding edge 111 of the grinding wheel 110. According to one or more embodiments, “adjacent” refers to first peripheral liquid cooling nozzles 120 being 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 edge 111 of the grinding wheel 110. The cooling liquid for the first peripheral liquid cooling nozzles 120 can be flowed to the first peripheral liquid cooling nozzles 120 through first liquid coolant lines 121. In one or more embodiments, the apparatus further comprises a plurality of second peripheral liquid cooling nozzles 130 arranged in a ring, the second peripheral liquid cooling nozzles 130 adjacent the grinding wheel 110. The cooling liquid for the second peripheral cooling nozzles can be flowed to the second peripheral liquid cooling nozzles 130 by second liquid coolant lines 131. The cooling liquid provided to the first liquid coolant lines 121 and second liquid coolant lines 131 can be supplied by first supply line 127 (best seen in FIGS. 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 nozzles 120 and second peripheral liquid cooling nozzles 130 provides efficient cooling of the wheels during grinding and polishing as well as the edge being finished and reduces edge burnout and chipping of the edge 12 of the glass sheet 10.
In one or more embodiments, the edge finishing apparatus 100 further includes a plurality of remote liquid cooling nozzles 140 positioned remotely from the grinding wheel 110 and the polishing wheel 112, and the remote liquid cooling nozzles 140 direct cooling liquid towards an edge 12 of the glass sheet during grinding and/or polishing. In one or more embodiments, “positioned remotely” means that the remote liquid cooling nozzles 140 are 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 wheel 110 and the polishing wheel 112. In FIGS. 1-4, the remote liquid cooling nozzles 140 are shown as positioned on housing 150 which holds the rotary table 104 to a gantry 152. Cooling liquid can be flowed to remote liquid cooling nozzles 140 by third liquid coolant lines 141. The cooling liquid provided to the third liquid coolant lines 141 can be supplied by second supply line 147 (best seen in FIGS. 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 nozzles 140 are configured to be activated during grinding of the glass sheet. The plurality of first peripheral liquid cooling nozzles 120 can 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 nozzles 120 can be provided. Likewise, the plurality of second peripheral liquid cooling nozzles 130 can 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 nozzles 130 can be provided. Regarding the remote liquid cooling nozzles 140, any number nozzles can be provided and affixed to the housing 150. As shown in FIGS. 1-6, remote liquid cooling nozzles 140 are supplied on two sides of the housing 150. 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 nozzles 140. The remote liquid cooling nozzles 140 can be spaced at any appropriate distance from the edge of the glass sheet 10 during grinding and/or polishing. The remote liquid cooling nozzles 140 can 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 edge 12 of the glass sheet 10 during a grinding and/or polishing operation. Each of the first peripheral liquid cooling nozzles 120, second peripheral liquid cooling nozzles 130 and remote liquid cooling nozzles 140 can be sized and shaped as needed to obtain the desired cooling effect. For example, the openings of the first peripheral liquid cooling nozzles 120, second peripheral liquid cooling nozzles 130 and remote liquid cooling nozzles 140 can 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 lines 121, second liquid coolant lines 131, third liquid coolant lines 141 and the first supply line 127 and the second supply line 147. The cooling liquid may comprise water, chilled water or other cooling liquid.
Referring now to FIGS. 7A and 9C and 7B and 9A and 9B, in one or more embodiments, the grinding wheel 110 comprises a cylindrical wheel including a peripheral grinding edge 111 and the polishing wheel 112 comprises a cup-shaped or cup wheel including a peripheral polishing edge 161 and a polishing end face 162. As shown in FIGS. 7B, 9A and 9B, the cup wheel comprises a hollowed region 164. The polishing wheel 112 shown in FIG. 9A comprises slots 166 positioned on the polishing end face 162 providing a slotted surface that contacts the edge 12 of 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 in FIGS. 7A and 9C, the grinding wheel 110 includes a chamfer 125 which can be used to form a chamfer 19 on the edge 12 of the glass sheet 10. In one or more embodiments, the first spindle 106 and the grinding wheel 110 are configured such that the peripheral grinding edge 111 contacts an edge 12 of the glass sheet 10 during grinding and the second spindle 108 and the polishing wheel 112 are configured such that polishing end face 162 contacts an edge of the glass sheet during polishing.
Referring back to FIGS. 1-4, the rotary table 104 is mounted on a gantry 152 that is movable along the Y-axis and the rotary table 104 is movable along the X-axis. The gantry 152 is movable on a Y-axis carriage 180 along rails 182. It will be understood that the arrangement shown is exemplary, and linear motion of the gantry 152 along 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 table 104 is movable on an X-axis carriage 190 along rails 192. It will be understood that the arrangement shown is exemplary, and linear motion of the rotary table 104 along 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 apparatus 100 will now be described. The edge finishing apparatus 100 can be part of a computer numerical control (CNC) machine 200. A grinding wheel 110 comprising a shank 195 can be mounted on the first spindle 106 by a chuck or a collet (not shown), which can be driven by a motor (not shown) to rotate the first spindle 106 and the grinding wheel 110 about axis of rotation 107. Similarly a polishing wheel 112 comprising a shank 197 can be mounted on the second spindle 108 by a chuck or a collet (not shown), which can be driven by a motor (not shown) to rotate the spindle and the polishing wheel 112 about axis of rotation 107. The grinding wheel 110 can be rotated while being translated along the edge 12 in the direction of the Y-axis to remove material from the edge 12 of the glass sheet 10. The CNC machine 200 includes a controller 210, which controls rotation and translation of the grinding wheel 110 and the polishing wheel 112. The controller 210 is in communication with the CNC machine 200 either via a hardwired or wireless connection. The controller 210 can be any suitable component that can control translation and rotation of the components of the CNC machine 200 and edge finishing apparatus 100. For example, the controller 210 can be a computer including a central processing unit, memory, suitable circuits and storage. The CNC machine 200 may further include one or more position sensors 212, 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 controller 210 to 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 wheel 110 and polishing wheel 112 in the X-Y plane can be controlled by roller type or sliding type rail systems to effect movement of the grinding wheel 110 and the polishing wheel 112 in the X-direction and Y-direction. As noted above, Y-translation of the gantry 152 occurs via the Y-axis carriage 180 on rails 182, and X-axis translation occurs via the X-axis carriage 190 on rails 192. The position sensors 212 communicate with the controller 210 to provide feedback to the controller on the position of grinding wheel 110 and polishing wheel 112 and the glass sheet 10 during finishing of the glass sheet. The controller 210 of the CNC machine 200 may 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 nozzles 120, the second peripheral liquid cooling nozzles 130 and remote liquid cooling nozzles 140.
According to one or more embodiments, the rotary table 104 enables the grinding wheel 110 and polishing wheel 112 to rotate about the axis of rotation 105, which is orthogonal to axis of rotation 107 of the first spindle 106 and the second spindle 108. The rotary table 104 can 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 table 104 is a Detron GX-170P, available from Detron Machine Co., Ltd. of Taiwan. According to some embodiments, in use, during a grinding operation, the first spindle 106 is in a vertical orientation parallel to or along the Z-axis as shown in FIG. 1. The first spindle 106 rotates about axis 107 and translates along the Y-axis to remove material from edge 12. In one or more embodiments, edges 13, 15 can be finished by rotating the first spindle 106 about axis of rotation 107 while translating the first spindle along the X-axis to remove material from the edges 13, 15. When the grinding operation is completed, the controller 210 of the CNC machine 200 sends a signal to rotate the first spindle 106 ninety degrees about axis of rotation 105 so that the second spindle 108 is now positioned parallel to the X-Y plane or the horizontal plane of the worktable 102 and the glass sheet 10 so that the end face 162 can contact the edge 12 of the glass sheet 10 during a polishing operation. It will be understood that the orientation of the worktable 102 and glass sheet can be other than horizontal, and in some embodiments, the worktable 102 and the glass sheet can be tilted on an angle to the horizontal. During a polishing operation of edge 12, the second spindle 108 rotates about axis of rotation 107 and translates second spindle 108 along the Y-axis. The polishing operation can also be performed in a similar manner on edge 14.
Thus, it will be appreciated that the rotary table 104 enables grinding wi spindle 106 in a vertical orientation (parallel to the Z-axis) and polishing with the second spindle 108 in a horizontal orientation (parallel to the horizontal plane or X-Y plane). With a grinding wheel 110 mounted on the first spindle 106 and a polishing wheel 112 mounted to the second spindle 108, the polishing and grinding operations can proceed rapidly and efficiently on edges 12, 14 of the glass sheet 10 without changing wheels. Cooling provided by the first peripheral liquid cooling nozzles 120, second peripheral liquid cooling nozzles 130 and 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 face 162 on the polishing wheel 112 especially after the polishing wheel 112 has polished many glass edges. A dressing process can make the wheel flatter and remove burnout area to improve polishing efficiency. Referring now to FIG. 8, conditioning tool 300 is shown including a motor 302 and dressing wheel 304 which rotates in direction of arrow 305. The dressing wheel 304 contacts the end face 162 of the polishing wheel 112 while the polishing wheel 112 is rotated about axis of rotation 107 and translated along direction 309. The conditioning tool 300 could be offline, that is, located away from or separately from the edge finishing apparatus 100. Alternatively, the conditioning tool 300 can be mounted to or adjacent the edge finishing apparatus 100. Dressing the polishing wheel 112 with 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 wheel 112 is 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 face 162 flatness from 14 micrometers and to <1 micrometer after dressing.
Referring now to FIG. 10, hole drilling tool 400 could also be coupled to the first spindle 106 or the second spindle 108 to form holes in a glass sheet 10. 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 apparatus 100 can form an edge 12 perpendicular 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<0.5 micrometers, 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 apparatus 100 in 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 apparatus 100 can 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 worktable 102 shown in FIGS. 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 wheel 110 and the polishing wheel 112 during 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 wheel 110 and the polishing wheel 112 during 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 rotation 107 about 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. 11 illustrates 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 face 610, 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 (R_a) that is less than 0.6 nm.
The glass sheet 600 has 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 edge 630 is 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 edge 630 in accordance with apparatus and methods described herein.
The glass sheet further comprises a second edge 640 adjacent to the light injection edge 630 and a third edge 660 opposite the second edge 640 and adjacent to the light injection edge 630, wherein the second edge 640 and/or the third edge 660 scatter light within an angle of less than 12.8 degrees FWHM in reflection. The second edge 640 and/or the third edge 660 may comprise a diffusion angle in reflection that is less than 6.4 degrees. The glass sheet includes a fourth edge 650 opposite the first edge 630.
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 in FIG. 12, light injected into a first edge 630 can be incident on a second edge 640 adjacent to the injection edge and a third edge 660 adjacent to the injection edge, wherein the second edge 640 is opposite the third edge 660. 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 edge 630 from an array of LED's 700 positioned along the first edge 630. The LED's may be located a distance of less than 0.5 mm from the first edge 630. 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 plate 600. According to one or more embodiments, the two edges 640, 660 may 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 apparatus 100 and 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 apparatus 100 and 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.

Example 1

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%.

Example 2

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.

Claims

What is claimed is:

1. An apparatus for finishing an edge of a glass sheet comprising:

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.

2. The apparatus of claim 1, further comprising a plurality of first peripheral liquid cooling nozzles arranged in a ring, the first peripheral liquid cooling nozzles adjacent the first spindle and positioned to direct cooling liquid toward a peripheral edge of the grinding wheel.

3. The apparatus of claim 2, further comprising a plurality of second peripheral liquid cooling nozzles arranged in a ring, the second peripheral liquid cooling nozzles adjacent the second spindle.

4. The apparatus of claim 2, further comprising a plurality of remote liquid cooling nozzles positioned remotely from the grinding wheel and the polishing wheel and positioned to direct cooling liquid toward an edge of the glass sheet.

5. The apparatus of claim 4, wherein the plurality of first peripheral liquid cooling nozzles and remote liquid cooling nozzles are configured to be activated during grinding of the glass sheet.

6. The apparatus of claim 2, wherein the plurality of first peripheral liquid cooling nozzles includes four cooling nozzles.

7. The apparatus of claim 2, wherein the plurality of first peripheral liquid cooling nozzles includes six cooling nozzles.

8. The apparatus of claim 1, wherein the grinding wheel comprises a cylindrical wheel including a peripheral grinding edge and the polishing wheel comprises a cup wheel including a peripheral polishing edge and a polishing end face.

9. The apparatus of claim 8, wherein the first spindle and the grinding wheel are configured to contact an edge of the glass sheet by the peripheral grinding edge during grinding and the second spindle and the polishing wheel are configured to contact an edge of the glass sheet by the polishing end face.

10. The apparatus of claim 9, wherein the polishing end face of the cup wheel comprises a slotted surface.

11. The apparatus of claim 1, wherein the rotary table is mounted on a gantry movable along the y-axis and the rotary table is movable along the x-axis.

12. The apparatus of claim 11, wherein the gantry is movable along a y-axis carriage, and the rotary table is movable along an x-axis carriage.

13. A method of grinding and polishing an edge of a glass sheet comprising:

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.

14. The method of claim 13, further comprising directing cooling fluid at the peripheral edge of the grinding wheel with a plurality of first peripheral liquid cooling nozzles arranged in a ring, the first peripheral liquid cooling nozzles adjacent the peripheral edge of the grinding wheel.

15. The method of claim 14, further comprising directing cooling fluid at the edge during polishing with a plurality of remote liquid cooling nozzles positioned remotely from the edge of the glass sheet.

16. The method of claim 15, further comprising 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.

17. The method of claim 15, further comprising 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.

18. The method of claim 17, wherein the first spindle and second spindle rotate about a common spindle axis of rotation.

19. The method of claim 15, wherein the polishing wheel is a cup wheel.

20. The method of claim 19, wherein the cup wheel comprises slots on the end face thereof.

21. The method of claim 13, further comprising forming a hole in the glass sheet with a hole drilling tool coupled to the first spindle or the second spindle.

22. The method of claim 13, the edge being a finished edge after grinding and polishing, the finished edge having an average roughness of less than about 0.2 micrometers.

23. The method claim 22, wherein 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 Fe.