WO2012075097A1

WO2012075097A1 - Methods for separating a sheet of brittle material

Info

Publication number: WO2012075097A1
Application number: PCT/US2011/062565
Authority: WO
Inventors: Gregory Scott Glaesemann; Xinghua Li
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2010-11-30
Filing date: 2011-11-30
Publication date: 2012-06-07
Anticipated expiration: 2013-05-30
Also published as: TW201231421A

Abstract

Methods for separating a sheet of brittle material include the step of providing a sheet of brittle material, such as a glass sheet, with a strain point and a melting point. The method further includes the step of providing a first heating irradiation to a first radiation zone on an outer surface of the sheet, wherein a radiated portion of the outer surface of the sheet is heated to a temperature above the strain point and below the melting point. The method further includes the steps of cooling the radiated portion to create residual stress within the cooled radiated portion, contacting the cooled radiated portion of the sheet such that the residual stress facilitates formation of an initial crack open to the outer surface of the sheet, and propagating the initial crack.

Description

METHODS FOR SEPARATING A SHEET OF BRH LE MATERIAL

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S. Provisional Application Serial No. 61/417998 filed on November 30, 2010 the content of which is relied upon and incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to methods of separating a sheet of brittle material, and more particularly to methods of separating a sheet of brittle material by forming an initial crack open to an outer surface of the sheet that extends some distance into the sheet.

BACKGROUND

[0003] The manufacturing of glass sheets typically involves cutting the glass sheet to a desired shape. Procedures are known for cutting glass sheets with a C0₂ laser to propagate a defect in a glass sheet previously produced by a scoring wheel, laser ablation, or laser induced damage inside the glass.

SUMMARY

[0004] The following presents a simplified summary of the disclosure in order to provide a basic understanding of some example aspects described in the detailed description.

[0005] In one example aspect, a method for separating a sheet of brittle material comprises the step (I) of providing a sheet of brittle material with a strain point and a melting point. The method further includes the step (II) of providing a first heating irradiation to a first radiation zone on an outer surface of the sheet, wherein a radiated portion of the outer surface of the sheet is heated to a temperature above the strain point and below the melting point. The method further includes the step (III) of cooling the radiated portion to create residual stress within the cooled radiated portion, the step (∑V) of contacting the cooled radiated portion of the sheet such that the residual stress facilitates formation of an initial crack open to the outer surface of the sheet, and the step (V) of propagating the initial crack.

[0006] In accordance with examples of the aspect, step (II) compacts the brittle material within the radiated portion of the sheet.

[0007] In accordance with further examples of the aspect, step (Π) is conducted by moving the first heating irradiation relative to the outer surface of the sheet along a path such that the radiated portion of the outer surface comprises an elongated radiated portion extending along the path.

[0008] In accordance with yet further examples of the aspect, the first heating irradiation substantially continuously heats the radiated portion within the first radiation zone as the first heating irradiation travels relative to the outer surface of the sheet along the path.

[0009] In accordance with still further examples of the aspect, a maximum average residual stress in the cooled radiated portion is distributed along a line substantially parallel to the path.

[0010] In accordance with examples of the aspect, the initial crack extends in a direction substantially orthogonal to the path.

[0011] In accordance with embodiments of the aspect, the elongated radiated portion includes opposed elongated edge regions and an elongated central region disposed between the opposed elongated edge regions, wherein a stress profile has the maximum average stress at the elongated central region of the elongated radiated portion.

[0012] In accordance with further embodiments of the aspect, the stress profile has a minimum average stress at the opposed edge regions of the elongated radiated portion.

[0013] In accordance with yet further embodiments of the aspect, the maximum average stress is from about 50 MPa to about 70 MPa.

[0014] In accordance with still further embodiments of the aspect, the center of the initial crack is positioned at the central region of the elongated radiated portion.

[0015] In accordance with additional examples of the aspect, wherein during step (TV) the central region of the elongated radiated portion is contacted to form the initial crack.

[0016] In accordance with still additional examples of the aspect, wherein the stress profile is predetermined to control a length of the initial crack.

[0017] In accordance with yet additional examples of the aspect, wherein the first radiation zone has an elliptical footprint with a major axis of the elliptical footprint extending along the path when moving the first heating irradiation relative to the outer surface of the sheet.

[0018] In accordance with further examples of the aspect, wherein during step (TV), contacting is carried out by mechanical contact. [0019] In accordance with yet further examples of the aspect, wherein step (V) includes propagating the initial crack by heating and then subsequently cooling the brittle material.

[0020] In accordance with still further examples of the aspect, wherein step (V) comprises: (VI) heating a second radiated portion of the outer surface of the brittle material within a second radiation zone using a second heating irradiation along a score-line starting from the initial crack; and then (V2) cooling the second radiated portion by a fluid jet to form a vent-line.

[0021] In accordance with embodiments of the aspect, wherein the fluid jet is a liquid jet, a gas jet or a combination thereof.

[0022] In accordance with further embodiments of the aspect, wherein the second radiation zone has an elliptical footprint.

[0023] In accordance with still further embodiments of the aspect, wherein the elliptical footprint of the second radiation zone has a major axis extending along the initial crack.

[0024] In accordance with yet further embodiments of the aspect, a cooling zone cools the second radiated portion during step (V2) and the cooling zone is spaced behind the second heating irradiation, wherein cooling during step (V2) is conducted immediately after heating during step (VI).

[0025] In accordance with further examples of the aspect, further comprising step (VI) of bending the sheet of brittle material along the score-line to separate the sheet into multiple pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and other aspects are better understood when the following detailed description is read with reference to the accompanying drawings, in which:

[0027] FIG. 1 is a schematic view one example apparatus that may be used for separating a sheet of brittle material in accordance with embodiments of the present disclosure;

[0028] FIG. 2 is an example radiation zone that may be used in accordance with aspects of the disclosure

[0029] FIG. 3 is a schematic view of a glass sheet wherein a first radiation zone is heating a radiated portion of the glass sheet; [0030] FIG. 4 is a schematic view of the glass sheet after cooling the radiated portion to create residual stress within the cooled radiated portion of the glass sheet;

[0031] FIG. 5 is an enlarged sectional view of the glass sheet along line 5-5 of FIG. 4;

[0032] FIG. 6 is a graph representing a residual stress profile along a width of the cooled radiated portion of the glass sheet;

[0033] FIG. 7 is an enlarged view of FIG. 6 demonstrating a pointed indenter just prior to contacting the cooled radiated portion of the glass sheet;

[0034] FIG. 8 is a view similar to FIG. 7 wherein the point indenter is mechanically contacting the cooled radiated portion of the glass sheet;

[0035] FIG. 9 is a view similar to FIG. 8 after the initial crack has been formed by mechanically contacting the cooled radiated portion of the glass sheet with the point indenter;

[0036] FIG. 10 illustrates the glass sheet of FIG. 4 after creating the initial crack;

[0037] FIG. 11 illustrates the glass sheet of FIG. 10 with a second radiation zone approaching the initial crack;

[0038] FIG. 12 illustrates the glass sheet of FIG. 11 with the second radiation zone passing over the initial crack;

[0039] FIG. 13 illustrated the glass sheet of FIG. 12 with a cooling zone beginning to propagate the initial crack along a score-line;

[0040] FIG. 14 is the glass sheet of FIG. 13 wherein the elongated radiation zone and cooling zone have been moved along the separation path to continue propagating the initial crack along the score-line to form a vent-line; and

[0041] FIG. 15 is the glass sheet of FIG. 14 after separating the glass sheet into two portions, for example, by mechanically breaking the glass sheet along the vent-line created by propagating the initial crack.

DETAILED DESCRIPTION

[0042] Examples will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, aspects may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. [0043] Various apparatus may be used for methods of separating a sheet of brittle material in accordance with aspects of the disclosure. For example, FIG. 1 is a schematic view one example apparatus 101 that may be used for separating a sheet of brittle material in accordance with embodiments of the present disclosure. The brittle material may be, for example, a glass, a ceramic, or a glass ceramic article. For the purpose of further discussion, a glass sheet, and in particular a glass sheet suitable for use in the manufacture of liquid crystal displays will be hereinafter assumed and described. However, it should be noted that the present invention has applicability to the scoring and separation of other sheets of brittle material.

[0044] Apparatus 101 comprises optical delivery apparatus 103 for irradiating a glass sheet 105 (or other brittle material), and a coolant fluid delivery apparatus comprising coolant nozzle 107, coolant source 109 and associated conduit 111 that may convey coolant to the coolant nozzle 107. In one example, optical delivery apparatus 103 can comprise a radiation source such as the illustrated laser 113 although other radiation sources may be provided in further examples. The optical delivery apparatus 103 can further include a circular polarizer 115, a beam expander 117, and beam shaping apparatus 119.

[0045] Optical delivery apparatus 103 may further comprise optical elements for redirecting a beam of radiation (e.g., laser beam 121) from the radiation source (e.g., laser 113), such as mirrors 123, 125 and 127. The radiation source can be configured as the illustrated laser 113 configured to emit a laser beam having a wavelength and a power suitable for heating the glass sheet at a location where the beam is incident on the glass sheet. In one embodiment, laser 113 is a C0₂ laser although other laser types may be used in further examples.

[0046] The laser 113 may be configured to initially emit the laser beam 121 with a substantially circular cross section (i.e. the cross section of the laser beam at right angles to the longitudinal axis of the laser beam). Optical delivery apparatus 103 is operable to transform laser beam 121 such that the beam has a significantly elongated shape when incident on glass sheet 105, producing an elongated footprint or "elongated radiation zone" 129 on the outer surface 131 of the glass sheet 105. The boundary of the elongated radiation zone 129 is determined as the point at which the beam intensity has been reduced to 1/e² of its peak value. The laser beam 121 passes through circular polarizer 115 and is then expanded by passing through beam expander 117. The expanded laser beam then passes through beam shaping apparatus 119 to form a beam producing elongated radiation zone 129 on a surface of the substrate. Beam shaping apparatus 119 may, for example, comprise one or more cylindrical lenses. However, it should be understood that any optical elements capable of shaping the beam emitted by laser 113 to produce an elongated radiation zone 129 on glass sheet 105 may be used.

[0047] FIG. 2 illustrates a diagrammatic view of the elongated radiation zone 129. As shown, the elongated radiation zone 129 may comprise an elliptical footprint 201 although other elongated footprint configurations may be provided in further examples. As shown the elliptical footprint 201 can include a major axis 203 that is substantially longer than a minor axis 205. In some embodiments, for example, major axis 203 is at least about ten times longer than minor axis 205. However, the length and width of elongated radiation zone 129 are dependent upon the desired scoring separation speed (beam translation speed), desired initial crack size, thickness of the glass sheet, laser power, etc., and the length and width of the radiation zone may be varied as needed.

[0048] Turning back to FIG. 1, the coolant nozzle 107 can be configured to deliver a coolant jet 133 of coolant fluid to the outer surface 131 of glass sheet 105. The coolant nozzle 107 can have various internal diameters to form a cooling zone 135 of a desired size. As with elongated radiation zone 129, the diameter of coolant nozzle 107, and the subsequent diameter of coolant jet 133, may be varied as needed for the particular process conditions. In some embodiments, the area of the glass sheet immediately impinged upon by the coolant (cooling zone) can have a diameter shorter than the minor axis of the radiation zone.

However, in certain other embodiments, the diameter of the cooling zone may be larger than the minor axis of elongated radiation zone 129 based on process conditions such as speed, glass thickness, laser power, etc. Indeed, the (cross sectional) shape of the coolant jet may be other than circular, and may, for example, have a fan shape such that the cooling zone forms a line rather than a circular spot on the surface of the glass sheet. A line-shaped cooling zone may be oriented, for example, perpendicular to the major axis of elongated radiation zone 129. Other shapes may be beneficial. [0049] In one example, the coolant jet 133 comprises water, but may be any suitable cooling fluid (e.g., liquid jet, gas jet or a combination thereof) that does not stain or damage the outer surface 131 of the glass sheet. The coolant jet 133 can be delivered to a surface of the glass sheet 105 to form the cooling zone 135. As shown in FIGS. 13-14, the cooling zone 135 can trail behind the elongated radiation zone 129 to propagate an initial crack formed by aspects of the disclosure described more fully below.

[0050] The apparatus 101 may further comprise a device for producing a relative motion between the glass sheet 105 and elongated radiation zone 129. This may be accomplished by moving the glass sheet 105 relative to laser beam 121, or by moving the laser beam 121 (and therefore elongated radiation zone 129) relative to the glass sheet 105. For instance, example configurations may provide a laser beam that moves relative to the glass sheet 105 wherein the outer surface 131 has a relatively large area, e.g., in excess of several square meters. In addition or alternatively, moving the laser beam relative to the glass sheet may also be desired for relatively thin glass sheets. For example, glass sheets 105 used in the

manufacture of optical displays can be less than 1 mm in thickness, and often less than about 0.7 mm, and may be larger than 10 square meters. Moving such large sheets of very thin glass may be impractical. Where moving the sheet is impractical, optical delivery apparatus 103 may be mounted on a suitable stage, such as an xy linear stage or gantry apparatus, so that laser beam 121 and coolant jet 133 can be traversed over glass sheet 105.

[0051] It should be noted that elongated radiation zone 129 and cooling zone 135 can move independent from one another. In further examples, the elongated radiation zone 129 and the cooling zone 135 move in unison so that the spatial relationship between the coolant zone and the radiation zone remain substantially constant. In further examples, many of the optical components, and glass sheet 105, may be maintained stationary during the scoring and separation process while the laser beam 121 is directed to a "flying head" 137 that is translated relative to and substantially parallel with glass sheet 105 for redirecting the laser beam 121 onto the glass sheet. For example, the flying head 137 may comprise the beam shaping apparatus 119 and the mirror 127. In this instance, only the flying head 137 may be configured to move to redirect the beam and traverse the elongated radiation zone 129 along the outer surface 131 of the glass sheet 105. [0052] Methods of separating a sheet of brittle material (e.g., glass sheet 105) will now be described with reference to FIGS. 3-15. The brittle material (e.g., glass sheet) is provided with a strain point and a melting point. For example, the strain point of a glass sheet is the temperatures at which viscosity of the glass reaches 10^14'5 Poise. In some examples, the strain point may be from about 450 °C to about 750 °C. The melting point for a brittle material, such as a crystalline material, is the temperature at which the material transitions from a solid state to a liquid state. For a glass material, the melting point can be defined as the temperature at which the material exhibits a viscosity of 200 Poise (20 Pa^»s). In some examples, the melting point of the glass sheet may be from about 550 °C to about 1000 °C.

[0053] As shown in FIG. 3, the method further includes the step of providing a first heating irradiation to a first radiation zone 301 on the outer surface 131 of the glass sheet 105. In some examples, the first radiation zone 301 may be formed from the elongated radiation zone 129 described in FIG. 1 wherein the coolant jet 133 is not used (i.e., turned off) and only the optical delivery apparatus 103 is used to generate the first radiation zone 301.

[0054] The first radiation zone 301 can include a variety of shapes and sizes. For instance, the first radiation zone may have a circular, square, polygonal or other footprint shape. Moreover, the radiation zone may have an elongated shape in further examples. Such elongated shapes may comprise an oblong shape such as a rectangular shape. As shown, the first radiation zone 301 can also have an oblong shape with an elliptical footprint similar to the elliptical footprint of the elongated radiation zone 129 illustrated in FIG. 2. Forming the first radiation zone 301 with an oblong shape can allow the radiation zone to substantially continuously heat the outer surface 131 as the first radiation zone 301 travels along a path 305.

[0055] By way of the first heating irradiation, a radiated portion 303 of the outer surface 131 of the glass sheet 105 is heated to a temperature above the strain point and below the melting point. As a result of heating the glass between the strain point and the melting point, the glass material within the radiated portion 303 of the glass sheets compacts. As shown in FIG. 3, the radiated portion 303 trailing behind the first radiation zone 301 naturally begins to cool, wherein residual stress is created within the cooled radiated portion 303. The residual tensile stress that is locked within the cooled radiated portion 303 after cooling.

[0056] The underlying concept of compaction of the glass to create the residual stress will now be described. Many glass materials, such as certain LCD glass substrates, are produced by fast cooling of a glass material in viscous state to visco-elastic state, and then to elastic state. The fast cooling, hence insufficient annealing and glass structure relaxation, results in a glass structure at a high temperature frozen in the elastic state. If the glass material with a high-temperature structure is subsequently heated to a temperature higher than the strain point thereof, the glass structure can relax to develop a structure

corresponding to a lower temperature. Such further relaxation (annealing) can lead to an increase of the local density of the glass, hence a shrinkage of local volume thereof. This annealing-induced density increase is called "compaction" that can lead to the tensile stress profile referenced in this disclosure.

[0057] In some examples, as shown in FIG. 3, the first radiation zone 301 can be moved along a path 305 when moving the first radiation zone 301 relative to the outer surface 131 of the glass sheet 105. If provided with the illustrated elliptical footprint, the major axis 307 of the elliptical foot print can extend along the path 305. As such, the first radiation zone 301 can be elongated in the direction of the path 305 to allow gradual and substantially continuous heating of the outer surface 131 as the first radiation zone 301 travels along the path 305 to create the radiated portion 303. The first radiation zone 301 may traverse only a part of the glass sheet 105 or, as shown, the entire first length "Li" of the glass sheet 105. As such, the first radiation zone 301 can travel relative to the outer surface 131 of the glass sheet 105 along the path 305 such that the radiated portion 303 of the outer surface 131 is elongated along the path as shown in FIG. 4. Traversing the entire first length "Li" to provide the elongated radiated portion 303 can allow subsequent initial crack formation at a later determined point anywhere along the first length "Li". As such, the glass sheet 105 may be subsequently cut with any desired dimension that can be subsequently determined during a future separating procedure described below.

[0058] As shown in FIG. 3, the trailing portion of the elongated radiated portion 303 begins to cool after leaving the first radiation zone 301. As shown in FIG. 4, eventually the entire elongated radiated portion 303 extending along the path 305 cools to lock in residual stress formed by heating the radiated portion 303. The radiated portion 303 cools sufficiently fast to avoid annealing of the glass sheet; thereby locking in the residual tensile stress.

[0059] The residual stress from heating with the first radiation zone 301 can be distributed along a stress profile substantially orthogonal to the path 305. Indeed, FIG. 5 is a section taken along line 5-5 of FIG. 4 illustrating a width "W" of the radiated portion 303 along a section orthogonal to the path 305. FIG. 6 shows a measured average stress profile 601 of the radiated portion 303 with a maximum average stress 603 at an elongated central region "Wi" disposed between opposed elongated edge regions "W2", W3". In one example, the maximum average residual stress in the cooled radiated portion 303 is distributed along a line substantially parallel to the path 305. As further illustrated, minimum average tensile stress 605a, 605b appears at opposed elongated edge regions "W2", W3". The size, power and speed of the first radiation zone 301 can affect the stress profile and, consequently, the length, depth and direction of the initial crack described more fully below. The larger average tensile stress appearing in the central radiated portion results from increased temperature experienced by a longer exposure time of the elongated central region "Wi" to the laser due to the elliptical footprint and orienting the major axis 307 along the path 305. Likewise, the minimum average tensile stress appearing at the opposed elongated edge regions "W2", W₃" is the result from a relatively short exposure time of the edge regions to the first radiation zone 301 due to the orientation of the elliptical footprint. As shown, the maximum average stress can be from about 50 MPa to about 70 MPa with the understanding that the tensile stress at the surface of the elongated central region "Wi" may be much higher than the maximum average stress through the depth of the elongated central region "Wi". For example, the maximum average stress of the central region can be from about 50 MPa to about 70 MPa while the stress at the surface of the central region may be greater than or equal to 100 MPa. In further examples, the maximum average stress and/or surface stress may have other values in further examples.

[0060] The width "W" of the radiated portion 303 can control the overall length of the initial crack. For example, the initial crack may have a length that is substantially equal to the width "W" of the radiated portion 303 although lengths less than or slightly greater than the width "W" can be provided in further examples. Moreover, the radiated portion 303 heats the surface of the glass to a depth shown in FIGS. 5 and 7. The depth of the radiated portion 303 selected to control the desired depth dimension of the initial crack. For example, the depth of the initial crack may be substantially equal to the depth of the radiated portion 303 although depths less than or slightly greater than the depth of the radiated portion 303 may be provided in further examples.

[0061] The method further includes the step of cooling the radiated portion 303 to create residual stress within the cooled radiated portion 303. Cooling can be conducted by exposing the radiated portion 303 to ambient environmental conditions after heating within the first radiation zone 301. In further examples, cooling may be facilitated by blowing air or other fluid (e.g., gas or liquid) over the surface to sufficiently cool the radiated portion 303 to generate and lock in the desired tensile stress profile.

[0062] The method further includes the step of contacting the cooled radiated portion 303 of the glass sheet 105 such that the residual stress facilitates formation of an initial crack. For example, a desired location for forming the initial crack is selected somewhere along the elongated length of the cooled radiated portion 303. In one example, as shown, in FIG. 7, a mechanical contacting mechanism, such as the illustrated point indenter 701 can be moved downward in direction 703 toward the outer surface 131 within the region of the cooled radiated portion 303.

[0063] As shown in FIG. 8, a point 801 of the indenter 701 contacts the outer surface 131 and begins creating the initial crack 803 that propagates in opposite directions 805a, 805b. Moreover, as shown, the indenter 701 can contact the center 807 of the cooled radiated portion 303 at the central region "Wi". As shown, the initial crack 803 propagates in the directions 805a, 805b from the maximum stress profile region to the minimum profile stress region. As such, as shown in FIG. 9, the initial crack 803 naturally tends to extend along a direction 901 that is substantially orthogonal to the path 305 of the first radiation zone 301 along the stress profile 601. As further illustrated, the center of the initial crack can be positioned at the central region "Wi" of the elongated radiated portion 303. Once complete, the initial crack 803 is open to the outer surface 131 of the glass sheet 105 as shown in FIG. 9. Based on process parameters, the stress profile 601 can be controlled during formation of the elongated radiated portion 303 by the first radiation zone 301.

Consequently, characteristics of the initial crack 803 (e.g., length, depth and direction) can be controlled based on a predetermined stress profile 601 and depth of the affected region.

[0064] The method further includes the step of propagating the initial crack 803 along a score-line to create a vent-line that may be used to immediately or subsequently separate the glass sheet 105. Propagating the initial crack 803 can be carried out in a wide variety of ways. In one example, the same apparatus illustrated in FIG. 1 may be used to propagate the initial crack 803. As such, the process may be simplified since the same apparatus can be used to create the stress profile 601 and propagate the initial crack 803. In the illustrated example, the initial crack can be propagated by heating and then subsequently cooling the glass sheet 105. For example, the method can involve the steps of heating a second radiated portion of the outer surface of the brittle material within a second radiation zone using a second heating irradiation along a score-line starting from the initial crack; and then cooling the second radiated portion by a fluid jet to form a vent-line.

[0065] Moreover, as shown in FIG. 10, the initial crack 803 extends along direction 901 that may be coincident with the desired separation path 1101 illustrated in FIG. 11. As the initial crack 803 already extends along the desired separation path 1101, proper control of the crack propagation can be improved such that the initial crack 803 is continued to extend along the separation path 1101 to properly form a vent-line along the score line to immediately or subsequently separate the glass sheet 105 in along the desired separation path 1101.

[0066] Turning to FIG. 11, in one example, the optical delivery apparatus 103 may then create a second radiation zone 1103 that may be similar to the elongated radiation zone 129 discussed in FIG. 1 and/or the first radiation zone 301 discussed above. Moreover, if provided with the illustrated elliptical footprint, the major axis of the second radiation zone 1103 can be aligned along the separation path 1101 and the initial crack 803 to maximize the temperature and resulting tensile stress along the separation path 1101. As shown in FIG. 12, the second radiation zone 1103 can then be passed over the initial crack 803. As shown in FIG. 13, the cooling zone 135 can then be created, for example, by the coolant jet 133 of fluid. As shown, the cooling zone 135 may be located behind the second radiation zone 1103 traveling in a direction of the separation path 1101. As such, the cooling zone may be spaced behind the second heating irradiation, wherein the cooling with the cooling zone 135 is conducted immediately after heating within the second radiation zone 1103.

[0067] As shown in FIG. 13, the cooling zone 135 propagates the crack at a bottom edge 1301 at one end of the initial crack 803 and continues propagating the crack at the opposite end of the initial crack 803 to a desired depth of the glass sheet 105. In some examples, the crack is propagated all the way through the thickness of the glass sheet 105 although the initial crack may only be propagated partially through the glass sheet to form a vent line along the desired separation path 1101. As shown in FIG. 14, the second radiation zone 1103 and cooling zone 135 then travel together across outer surface 131 of glass sheet 105. The second radiation zone 1103 heats the glass sheet 105 while the coolant jet 133 follows to rapidly cool or quench the heated radiated portion of the substrate (via cooling zone 135). Consequently, the crack continues to propagate partially or entirely through the thickness of the glass sheet 105 in the desired direction as the second radiation zone 1103 and the cooling zone 135 travel along the separation path 1101. The propagated crack eventually reaches the opposite top edge 1501. In one example, the propagated crack extends through the entire thickness of the glass sheet 105 such that, as shown in FIG. 15, the glass sheet 105 is completely separated into a first portion 1503a and a second portion 1503b without any further process steps. In alternative examples, the propagated crack only extends partially through the thickness of the glass sheet. As such, a vent line can be formed along the desired separation 1101. The sheet can then undergo an additional processing step wherein the sheet is bent to break the sheet along the vent line into the first portion 1503a and the second portion 1503b illustrated in FIG. 15.

[0068] In the following example, an elliptical C0₂ laser beam of dimension 2 mm by 24 mm was used to heat a glass substrate. The glass substrate used was Corning EAGLE XG glass substrate available from Corning, Inc. The glass sheet thickness was 0.7 mm and it strain point is 777°C. A laser power of 92 W was measured on the surface of the glass substrate. A water jet was used in the quenching process with an orifice of 75 μηι diameter and a flow of 7.8 seem of DI water. A typical laser scribing speed of 140 mm/s was achieved without any optimization process. [0069] A residual stress profile can be examined with the aid of a PolScope. FIG. 6 shows a PolScope measurement of the residual stress profile on a 0.7 mm thickness Corning EAGLE XG glass substrate when the relative moving speed was reduced to 50 mm/s and the water jet was turned off. The stress was assumed to be uniform to a depth of 0.2 mm from the surface of the glass sheet. The stress field was then used to create and limit the size of the starter defect to initiate the scribing process. A radial crack initiation was aided by the presence of the tensile residual stress profile.

[0070] As shown by FIG. 6, the residual stress profile is directional and promotes crack orientation orthogonal to the maximum principal stress. As such, the crack formation can be predetermined and the size of the residual stress profile can define the maximum initial crack size, thereby alone one to directly control the initial crack size and orientation with the laser.

[0071] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the claimed invention.

Claims

1. A method for separating a sheet of brittle material comprising the steps of:

(I) providing a sheet of brittle material with a strain point and a melting point;

(II) providing a first heating irradiation to a first radiation zone on an outer surface of the sheet, wherein a radiated portion of the outer surface of the sheet is heated to a temperature above the strain point and below the melting point;

(III) cooling the radiated portion to create residual stress within the cooled radiated portion;

(IV) contacting the cooled radiated portion of the sheet such that the residual stress facilitates formation of an initial crack open to the outer surface of the sheet; and

(V) propagating the initial crack.

2. The method according to claim 1, wherein step (II) compacts the brittle material within the radiated portion of the sheet.

3. The method according to any one of the preceding claims, wherein step (II) is conducted by moving the first heating irradiation relative to the outer surface of the sheet along a path such that the radiated portion of the outer surface comprises an elongated radiated portion extending along the path.

4. The method according to claim 3, wherein the first heating irradiation

substantially continuously heats the radiated portion within the first radiation zone as the first heating irradiation travels relative to the outer surface of the sheet along the path.

5. The method according to claims 3 or 4, wherein a maximum average residual stress in the cooled radiated portion is distributed along a line substantially parallel to the path.

6. The method according to claim 5, wherein the initial crack extends in a direction substantially orthogonal to the path.

7. The method according to claims 5 or 6, wherein the elongated radiated portion includes opposed elongated edge regions and an elongated central region disposed between the opposed elongated edge regions, wherein a stress profile has the maximum average stress at the elongated central region of the elongated radiated portion.

8. The method according to claim 7, wherein the stress profile has a minimum average stress at the opposed edge regions of the elongated radiated portion.

9. The method according to claims 7 or 8, wherein the maximum average stress is from about 50 MPa to about 70 MPa.

10. The method according to any one of claims 7 to 9, wherein the center of the initial crack is positioned at the central region of the elongated radiated portion.

11. The method according to any one of claims 7 to 10, wherein during step (TV) the central region of the elongated radiated portion is contacted to form the initial crack.

12. The method according to any one of claims 7 to 1 1, wherein the stress profile is predetermined to control a length of the initial crack.

13. The method according to any one of claims 3 to 12, wherein the first radiation zone has an elliptical footprint with a major axis of the elliptical footprint extending along the path when moving the first heating irradiation relative to the outer surface of the sheet.

14. The method according to any one of the preceding claims, wherein during step (TV), contacting is carried out by mechanical contact.

15. The method according to any one of the preceding claims, wherein step (V) includes propagating the initial crack by heating and then subsequently cooling the brittle material.

16. The method according to claims 15, wherein step (V) comprises:

(VI) heating a second radiated portion of the outer surface of the brittle material within a second radiation zone using a second heating irradiation along a score-line starting from the initial crack; and then

(V2) cooling the second radiated portion by a fluid jet to form a vent-line.

17. The method according to claim 16, wherein the fluid jet is a liquid jet, a gas jet or a combination thereof.

18. The method according to claim 16, wherein the second radiation zone has an elliptical footprint.

19. The method according to claim 18, wherein the elliptical footprint of the second radiation zone has a major axis extending along the initial crack.

20. The method according to claim 19, wherein a cooling zone cools the second radiated portion during step (V2) and the cooling zone is spaced behind the second heating irradiation, wherein cooling during step (V2) is conducted immediately after heating during step (VI).

21. The method according to any of claims 16 to 20, further comprising step (VI) as follows:

(VI) bending the sheet of brittle material along the score-line to separate the sheet into multiple pieces.