Method for finishing edges of glass sheets

#The invention relates to a method and apparatus for finishing the edges of glass sheets, particularly sheets for use in flat panel displays.

#The manufacturing process of flat panel display substrates requires specific sized glass substrates capable of being processed in standard production equipment. The sizing techniques typically employ a mechanical scoring and breaking process in which a diamond or carbide scoring wheel is dragged across the glass surface to mechanically score the glass sheet, after which the glass sheet is bent along this score line to break the glass sheet, thereby forming a break edge. Such mechanical scoring and breaking techniques commonly result in lateral cracks about 100 to 150 microns long, which emanate from the score wheel cutting line. These lateral cracks decrease the strength of the glass sheet and are thus removed by grinding the sharp edges of the glass sheet. The sharp edges of the glass sheet are ground by a metal grinding wheel having a radiused groove on its outer periphery, with diamond particles embedded in the radiused groove. By orienting the glass sheet against the radiused groove, and by moving the glass sheet against this radiused groove and rotating the diamond wheel at a high RPM (revolutions per minute), a radius is literally ground into the edge of the glass sheet. However, such grinding methods involve removal of about 100 to 200 microns or more of the glass edge. Consequently, the mechanical scoring step followed with the diamond wheel grinding step creates an enormous amount of debris and particles.

#In addition, in spite of repeated washing steps, particles generated during edge finishing continue to be a problem. For example, in some cases particle counts from the edges of glass sheets prior to shipping were actually lower than subsequent particle counts taken after shipping. This is because the grinding of the glass sheets resulted in chips, checks, and subsurface fractures along the edges of the ground surfaces, all of which serve as receptacles for particles. These particles subsequently would break loose at a later time, causing contamination, scratches, and sometimes act as a break source in later processing. Consequently, such ground surfaces are “active”, meaning subject to expelling particles with environmental factors, such as, temperature and humidity. The present invention relates to methods for reducing these “lateral cracks” and “micro-checking” caused by grinding, thereby forming a glass sheet having edges that are more “inactive”.

#FIG. 1 illustrates a perspective view of a process in accordance with the present invention.

#FIG. 2A illustrates a partial cross-sectional view illustrating the grinding process illustrated in FIG. 1.

#FIG. 2B illustrates a partial cross-sectional view of the grinding process illustrated in FIG. 1.

#The present invention generally provides a method for grinding and polishing the edges of a sheet of glass, in particular, a flat panel display glass sheet. According to the present invention, the sheet of glass is held in place by securing means and the sheet of glass is conveyed on a conveyer system as shown in FIG. 1. FIG. 1 illustrates a preferred embodiment of the invention in which a plurality of grinding wheels and polishing wheels are used to finish the edges of a glass sheet. FIG. 1 shows a glass sheet designated generally by reference numeral 10 being conveyed on a conveyer system in the direction of arrow 15 while at least one edge of the glass sheet 10 is being ground and polished by the set of grinding wheels 20A and 20B and polishing wheels 30A and 30B. The major surface 19 and 23 of each of the grinding wheels 20A and 20B, respectively, and the major surface 33 and 29 of each of the polishing wheels 30A and 30B, respectively, are positioned parallel to the major surface 16 of the glass sheet 10. In the embodiment shown in FIG. 1, the grinding wheels 20A and 20B, each rotate in opposite directions. Specifically, grinding wheel 20A rotates in a counterclockwise direction, whereas grinding wheel 20B rotates in a clockwise direction. Similarly, polishing wheels 30A and 30B each rotate in opposite directions. Specifically, polishing wheel 30A rotates in a counterclockwise direction, whereas polishing wheel 30B rotates in a clockwise direction.

#As shown in FIG. 1, the grinding surface 21 of the grinding wheel 20B contacts one of the edges 14 of the glass sheet 10, whereas the grinding surface 22 of the grinding wheel 20A contacts an opposite edge 12 of the glass sheet 10. Similarly, the polishing surface 32 of the polishing wheel 30A contacts the edge 12 of glass sheet 10, whereas the polishing surface 31 of the polishing wheel 30B contacts the edge 14 of the glass sheet 10. In the preferred embodiment, each of the grinding wheels 20A and 20B and each of the polishing wheels 30A and 30B rotate simultaneously. Moreover, opposing edges 12 and 14 are simultaneously ground and polished in the preferred embodiment. In particular, each of the edges 12 and 14 first contact the grinding surfaces 22 and 21 of the grinding wheels 20A and 20B, respectively, and then the ground edges next contact the polishing surfaces 32 and 31 of each of the polishing wheels 30A and 30B, respectively. Also, as shown in FIG. 1, each of the grinding wheels 20A and 20B are spaced apart from each of the polishing wheels 30A and 30B, with grinding wheel 20A and polishing wheel 30A being positioned proximate to each other on one edge 12 of the glass sheet 10, and with grinding wheel 30A and polishing wheel 30B being positioned proximate to each other on the other edge 14 of the glass sheet 10.

#Furthermore, in the preferred embodiment, each of the grinding wheels 20A and 20B and each of the polishing wheels 30A and 30B are stationary, whereas, the glass sheet 10 is moved in the direction of arrow 15, so that each of the edges 12 and 14 are first ground and then polished. FIGS. 2A-2C show the details of one of the edges 12 being ground, whereas, FIGS. 3A-3C show details of the edge 12 being polished after the edge 12 has been ground. FIG. 2A shows a partial cross-sectional view of the grinding surface 22 of the grinding wheel 20A. As shown, the grinding surface 22 has at least one V-shaped groove 24 on the outer periphery, where a radial line passing through the center of the V-shaped groove 24 forms an angle θ with the V-shaped groove 24. The angle θ is in a preferred embodiment approximately between 15 and 40 degrees, most preferably, approximately 30 degrees. Although FIG. 2A shows only a single V-shaped groove 24, as shown in FIG. 1, the grinding wheels 20A and 20B each can have a plurality of V-shaped grooves 24, and in a preferred embodiment, each of the grinding wheels 20A and 20B have six V-shaped grooves 24. As shown in FIG. 2A, the edge 12 of the glass sheet 10 is aligned with the V-shaped groove 24. Specifically, the edge 12 has a flat region 12C located between a pair of corner regions 12A and 12B respectively. As shown in FIG. 2B, the edge 12 is inserted into the V-shaped groove 24 such that only the pair of corner regions 12A and 12B contact the V-shaped groove 24, whereas, the middle portion of the flat region 12C does not contact the grinding surface 22 of the grinding wheel 20A. As the corner regions 12A and 12B are chamfered by the V-shaped groove 24, the pair of corner regions 12A and 12B are transformed into a pair of ground beveled regions 12D and 12E, respectively, as shown in FIG. 2C. Also as shown in FIG. 2C, each of the rounded beveled regions 12D and 12E form an angle θ with the top surface 16A and the bottom surface 16B, respectively, of the glass sheet 10. In a preferred embodiment, the angle θ is approximately between 15 and 40 degrees, and most preferably, approximately 30 degrees. As shown in FIG. 2C, the middle portion of the flat region 12C of the edge 12 remains the same shape as before grinding, since this portion of the edge 12 is not contacted by the grinding wheel 20A.