Patent Application
20190337112
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.
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.
The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.
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
With reference to
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
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
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
Referring now to
As shown in
Referring back to
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
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
Referring now to
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
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 SiO2 in a range of 50 mol % to 80 mol %, Al2O3 in a range of 0 mol % to 20 mol %, and B2O3 in 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.
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
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.
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.
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.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/013495 | 1/12/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62445782 | Jan 2017 | US |
