Cutting method for glass sheet and glass sheet cutting apparatus

Abstract

Provided is a cutting method for a glass sheet, comprising radiating a laser beam to a cutting portion (C) of a glass sheet (G) having a thickness of 500 μm or less to fuse the glass sheet (G), wherein a narrowest gap between fused end surfaces (Ga1 and Gb1) of the glass sheet (G), which face each other in the cutting portion (C), is managed to satisfy a relationship of 0.1≦b/a≦2, where “a” is a thickness of the glass sheet (G) and “b” is the narrowest gap.

Claims

1. A cutting method for a glass sheet, comprising radiating a laser beam to a cutting portion of the glass sheet while jetting an assist gas to the cutting portion, to thereby divide the glass sheet by fusing into a product portion and a non-product portion using the cutting portion as a boundary, wherein the assist gas comprises: a center assist gas jetted just below from a position above the cutting portion to the cutting portion in a space above the glass sheet; and a side assist gas jetted obliquely downward from an upper position on a product portion side to the cutting portion in a space above the glass sheet, and wherein the side assist gas has a jetting pressure that is higher than a jetting pressure of the center assist gas so that a fused end surface of the product portion comprises a convex curved portion.

2. The cutting method for a glass sheet according to claim 1, wherein the side assist gas is jetted at an inclination angle of from 25° to 60° with respect to an upper surface of the glass sheet.

3. The cutting method for a glass sheet according to claim 1, wherein the assist gas further comprises an auxiliary side assist gas jetted obliquely upward from a lower position on the product portion side to the cutting portion in a space below the glass sheet.

4. The cutting method for a glass sheet according to claim 1, wherein the radiating the laser beam to the glass sheet is carried out in a defocus state.

5. The cutting method for a glass sheet according to claim 1, wherein a center line of the side assist gas is set to intersect with an upper surface of the glass sheet of the product portion side with respect to the cutting portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 A vertical sectional side surface of a glass sheet cutting device according to a first embodiment of a first invention.

(2) FIG. 2 A plan view of the glass sheet cutting device of FIG. 1.

(3) FIG. 3 A sectional view taken along the line X-X of FIG. 2.

(4) FIG. 4 A schematic view illustrating a state immediately after a glass substrate is fused by the glass sheet cutting device according to the first embodiment.

(5) FIG. 5 A vertical sectional view of a glass sheet cutting device according to a second embodiment of the first invention.

(6) FIG. 6 A vertical sectional view of a glass sheet cutting device according to a third embodiment of the first invention.

(7) FIG. 7 A vertical sectional view of a glass sheet cutting device according to a fourth embodiment of the first invention.

(8) FIG. 8 A vertical sectional view of a glass sheet cutting device according to a fifth embodiment of the first invention.

(9) FIG. 9 A perspective view of a second suction nozzle of FIG. 8.

(10) FIG. 10 A vertical sectional view of a glass sheet cutting device according to a sixth embodiment of the first invention.

(11) FIG. 11 A view illustrating another example of a glass sheet to be fused in the first invention.

(12) FIG. 12 A view illustrating a state in which strength of the glass sheet is evaluated in Examples of the first invention.

(13) FIG. 13 A sectional view of a glass sheet cutting device used in a laser fusing method for a glass sheet according to an embodiment of a fourth invention.

(14) FIG. 14 A sectional view illustrating how laser fusing is performed by the glass sheet cutting device of FIG. 13.

(15) FIG. 15 Another sectional view illustrating how laser fusing is performed by the glass sheet cutting device of FIG. 13.

(16) FIG. 16 Still another sectional view illustrating how laser fusing is performed by the glass sheet cutting device of FIG. 13.

(17) FIG. 17 Yet another sectional view illustrating how laser fusing is performed by the glass sheet cutting device of FIG. 13.

(18) FIG. 18 A view illustrating a problem that may occur in a case where a glass sheet is cut by laser fusing.

DESCRIPTION OF EMBODIMENTS

(19) In embodiments of first to fourth inventions described below, a glass sheet refers to a glass substrate for flat panel displays, which has a thickness of 500 μm or less. As a matter of course, the glass sheet to be cut is not limited to the glass substrate for flat panel displays, and may be glass substrates utilized in various fields, such as a glass substrate for solar cells, OLED illumination devices, touch panels, and digital signages, and laminated bodies formed of such glass substrates and organic resins. Note that, a thickness of the glass sheet is not particularly limited, but is preferably 300 μm or less, and particularly preferably 200 μm or less.

Embodiments of First Invention

(20) In the following, description is made of the above-mentioned embodiment of the first invention with reference to the drawings. Note that, in the following, a glass sheet refers to a glass substrate for flat panel displays, which has a thickness 500 μm or less. As a matter of course, the glass sheet to be cut is not limited to the glass substrate for flat panel displays, and may be glass substrates utilized in various fields, such as a glass substrate for solar cells, OLED illumination devices, touch panels, and digital signages, and laminated bodies formed of such glass substrates and organic resins.

(1) First Embodiment

(21) As illustrated in FIG. 1, a glass sheet cutting device 1 according to a first embodiment of the first invention comprises a support stage 2 for supporting from below a glass sheet G in a flat posture and a laser irradiator 3 for fusing and dividing the glass sheet G supported by the support stage 2.

(22) The support stage 2 comprises a stage main body 21 and a conveyer 22 which moves along an upper surface of the stage main body 21. The glass sheet G is conveyed downstream in a conveying direction (arrow A direction in FIG. 1) along a preset cutting line CL by movement of the conveyer 22. In this case, the stage main body 21 functions to guide the conveyer 22. Note that, the conveyer 22 comprises a large number of vents (not shown), and the glass sheet G is conveyed while being held on the conveyer 22 by attraction through intermediation of those vents. As a matter of course, there may be employed other conveying methods such as a method of conveying the glass sheet G with a conveyer while sandwiching widthwise end portions of the glass sheet G from both front and back sides without attracting the glass sheet G.

(23) As illustrated in FIG. 2, the stage main body 21 and the conveyer 22 are each divided at an interval in the width direction of the glass sheet G, and a non-support space S is formed at a position below the preset cutting line CL of the glass sheet G. In this non-support space S, a lower surface of the glass sheet G and the support stage 2 are out of contact with each other, and the lower surface of the glass sheet G is exposed to the non-support space S.

(24) As illustrated in FIG. 3, the laser irradiator 3 has an interior space for propagating a laser beam LB, and comprises a lens 31 provided in this space. In this embodiment, the laser beam LB is condensed onto a micro-focus spot by the lens 31, and radiated to a cutting portion (part under fusing by radiation of the laser beam LB) C under a state in which a focal position FP is focused on an upper surface of the glass sheet G. Then, the glass sheet G is fused with irradiation heat of the laser beam LB along the preset cutting line CL, and divided into a product portion Ga to be used as a product and a non-product portion Gb to be, for example, disposed of without being used as a product. Note that, the focal position FP of the laser beam LB may be an intermediate position in a thickness direction of the glass sheet G. Further, the focal position FP of the laser beam LB may be set above the glass sheet G so that the laser beam LB is radiated in a defocus state to the cutting portion C.

(25) The glass sheet cutting device 1 further comprises a side assist gas jet nozzle 4 for jetting a side assist gas A1 obliquely downward from an upper position on the product portion Ga side to the cutting portion C. This side assist gas A1 functions to blow off a molten foreign matter such as dross to the non-product portion Gb side.

(26) Description is made of an operation of the glass sheet cutting device 1 structured as described above.

(27) As illustrated in FIGS. 1 and 2, the glass sheet G is conveyed by the conveyer 22 of the support stage 2, and is scanned along the preset cutting line CL of the glass sheet G with the laser beam LB radiated from the laser irradiator 3 arranged statically on a conveyance path.

(28) While radiating the laser beam LB in this way, as illustrated in FIG. 3, the side assist gas A1 is jetted from the side assist gas jet nozzle 4 arranged on the upper position on the product portion Ga side of the glass sheet G obliquely downward to the cutting portion C positioned on the preset cutting line CL on the glass sheet G. With this, the molten foreign matter is removed from the cutting portion C, and hence fusing is efficiently performed. Further, the molten foreign matter is blown off to the non-product portion Gb side, and hence a situation where the molten foreign matter adheres to the product portion Ga can be prevented. The term “molten foreign matter” represents a foreign matter such as dross generated at the time of fusing of the glass sheet G, and includes a molten foreign matter and a solidified foreign matter.

(29) Further, in a space above the glass sheet G, only the side assist gas jet nozzle 4 is provided as means for jetting a gas to the glass sheet G. The side assist gas jet nozzle 4 jets the side assist gas A1 obliquely with respect to the cutting portion C of the glass sheet G. Thus, in comparison with a case where a gas is jetted substantially vertically from just above with respect to the cutting portion C of the glass sheet G (for example, in a case where a center assist gas is jetted), a force of pressing downward a vicinity of the cutting portion C in a molten state is less liable to act. Thus, the vicinity of the cutting portion C in a molten state of the glass sheet G can be prevented from hanging downward. Then, under a state in which the cutting portion C is prevented from hanging, the molten foreign matter generated at the cutting portion C is scattered by the side assist gas A1 preferentially to the non-product portion Gb side. Thus, the molten foreign matter is less liable to be deposited on a fused end surface Ga1 of the product portion Ga.

(30) Further, when the glass sheet G is fused as described above, a part of the cutting portion C of the glass sheet G is molten and removed, with the result that a gap is formed between the fused end surface Ga1 of the product portion Ga and a fused end surface Gb1 of the non-product portion Gb. Thus, the fused end surface Ga1 of the product portion Ga and the fused end surface Gb1 of the non-product portion Gb are spaced apart from each other by an amount corresponding to the gap. As a result, while preventing a situation where the fused end surfaces Ga1 and Gb1 are broken by contacting against each other, the product portion Ga and the non-product portion Gb can be smoothly separated from each other.

(31) Specifically, as illustrated in FIG. 4, management is performed so as to form, by fusing, a narrowest gap b which satisfies a relationship of 0.1≦b/a≦2, where “a” is the thickness of the glass sheet G and “b” is a narrowest gap between the fused end surface Ga1 of the product portion Ga and the fused end surface Gb1 of the non-product portion Gb after fusing. With this, the gap between the fused end surface Ga1 of the product portion Ga and the fused end surface Gb1 of the non-product portion Gb is strictly managed based on the relationship relative to the thickness of the glass sheet G. Thus, the product portion Ga and the non-product portion Gb can be safely separated from each other while satisfactorily maintaining a shape of the vicinity of the fused end surface Ga1 of the product portion Ga. In other words, when b/a exceeds 2, an excessively large amount of the glass sheet G is molten and removed by fusing, and the fused end surface Gb1 of the non-product portion Gb may be defectively shaped. Further, the glass sheet G may be deformed or broken by distortion. Meanwhile, when b/a is less than 0.1, the fused end surfaces Ga1 and Gb1 come excessively close to each other, and hence the fused end surfaces Ga1 and Gb1 may be brought into contact with each other at the time of separation, which may cause breakage of the product portion Ga (or non-product portion Gb).

(32) As a countermeasure, in order to adjust a width of the narrowest gap b, the following fused conditions may be changed.

(33) (1) Output power of the laser beam LB

(34) (2) A spot diameter size with respect to the glass sheet G

(35) (3) An inclination angle α1 (refer to FIG. 3) of an imaginary centerline L1 of the side assist gas A1 with respect to the surface (upper surface) of the glass sheet G

(36) (4) Jetting pressures of gases supplied to the glass sheet G, such as the side assist gas A1

(37) (5) Pulse duration and a pattern of the laser beam

(38) Conditions of the laser beam LB and the side assist gas A1 are as follows. Note that, as a matter of course, those conditions of the laser beam LB and the side assist gas A1 are not limited thereto.

(39) The spot diameter of the laser beam LB is set to be smaller than the narrowest gap b in FIG. 4.

(40) Irradiation energy of the laser beam LB on the upper surface of the glass sheet G is set to range from 100 W/mm.sup.2 to 100,000 W/mm.sup.2.

(41) The jetting pressure of the side assist gas A1 is set to range from 0.01 MPa to 0.5 MPa.

(42) The inclination angle α1 of the side assist gas A1 is set to range preferably from 25° to 60°, more preferably from 30° to 50°, and much more preferably from 35° to 45°. In other words, when the inclination angle of the side assist gas A1 with respect to the front surface of the glass sheet G is less than 25°, the side assist gas A1 is jetted at an excessively low angle with respect to the glass sheet G, which may cause a problem that the side assist gas A1 cannot be efficiently supplied to the cutting portion C. Meanwhile, when the inclination angle of the side assist gas A1 with respect to the front surface of the glass sheet G exceeds 60°, the side assist gas A1 is jetted at an excessively high angle with respect to the glass sheet G, which leads to a risk that a force of pressing the vicinity of the cutting portion C downward becomes larger. Thus, it is preferred that the inclination angle α1 of the side assist gas A1 fall within the above-mentioned numerical ranges. Within those ranges, the force of the side assist gas A1, with which the vicinity of the cutting portion C is pressed downward, can be appropriately suppressed while the side assist gas A1 is supplied sufficiently to the cutting portion C.

(43) Note that, in terms of preventing adhesion of a molten foreign matter to the product portion Ga, it is preferred that the inclination angle α1 of the side assist gas A1 be set to range from 15° to 45°. Thus, in consideration of the shape of the fused end surface Ga1 of the product portion Ga and prevention of adhesion of a molten foreign matter to the product portion Ga, it is preferred that the inclination angle α1 of the side assist gas A1 be set to range from 25° to 45°.

(44) An orientation of the side assist gas A1 is not particularly limited as long as being directed to the vicinity of the cutting portion C. For example, in the illustration, the imaginary center line L1 of the side assist gas A1 is set to intersect with the cutting portion C, but the imaginary center line L1 may be set to intersect with the upper surface or the lower surface of the glass sheet G on the product portion Ga side with respect to the cutting portion C.

(45) Examples of the side assist gas A1 comprise individual ones or mixtures of gases of oxygen (or air), water vapor, carbon dioxide, nitrogen, argon, and the like. Further, the side assist gas A1 may be jetted as hot blast.

(46) The glass sheet G fused as described above has the following features.

(47) First, as illustrated in FIG. 4, the fused end surface Ga1 of the product portion Ga is formed into a substantially circular-arc shape, specifically, satisfactory convex curved-surface shape. In detail, the fused end surface Ga1 of the product portion Ga comprises a fire-polished surface. Note that, the fused end surface Gb1 of the non-product portion Gb may undergo adhesion of a molten foreign matter (such as dross) blown off by the side assist gas A1, with the result that the fused end surface Gb1 may not be formed into the substantially circular-arc shape.

(48) Second, an arithmetic mean roughness Ra of the fused end surface Ga1 of the product portion Ga is 0.3 μm or less, and a mean length RSm of a roughness curve element thereof is 150 μm or more. In this context, regarding a lower limit value of Ra and an upper limit value of RSm, it is desired that the lower limit value of Ra be as close to zero as possible and that the upper limit value of RSm be as close to infinity as possible. However, practically, there are limitations owing to processing equipment and the like, and hence it is insignificant to define the lower limit value of Ra and the upper limit value of RSm. Therefore, in the above description, none of the lower limit value of Ra and the upper limit value of RSm is set.

(49) Third, a compressive residual stress of the fused end surface Ga1 of the product portion Ga ranges from 20 MPa to 500 MPa.

(2) Second Embodiment

(50) As illustrated in FIG. 5, the glass sheet cutting device 1 according to a second embodiment of the first invention is obtained by adding a center assist gas jet nozzle 5 to the structure of the glass sheet cutting device 1 according to the first embodiment. In the following, description is made only of differences while omitting description of common features.

(51) The center assist gas jet nozzle 5 is connected to a distal end portion of the laser irradiator 3, and supplies a center assist gas A2 into the interior space of the laser irradiator 3 (space below the lens 31). The center assist gas A2 supplied into the interior space of the laser irradiator 3 is jetted just below from a distal end of the laser irradiator 3 to the cutting portion C of the glass sheet G. In other words, from the distal end of the laser irradiator 3, the laser beam LB is emitted and the center assist gas A2 is jetted. The center assist gas A2 has functions to remove the molten foreign matter generated at the time of fusing the glass sheet G from the cutting portion C of the glass sheet G, to protect optical components such as the lens 31 of the laser irradiator 3 from the molten foreign matter, and further to reduce heat of the lens.

(52) On a premise that the jetting pressure of the side assist gas A1 is P1 and the jetting pressure of the center assist gas A2 is P2, P2/P1 is set to range from 0 to 2. In detail, for example, the jetting pressure of the center assist gas A2 is set to range from 0 MPa to 0.02 MPa, and the jetting pressure of the side assist gas A1 is set to range from 0.01 MPa to 0.5 MPa. It is preferred to set the jetting pressure of the side assist gas A1 to be higher than the jetting pressure of the center assist gas A2. For example, P2/P1 is set to range from 0.1 to 0.5, and in this case, it is preferred to set the jetting pressure of the center assist gas A2 to be sufficient for protection of the optical components such as the lens 31 of the laser irradiator 3 from the molten foreign matter.

(53) With this, the jetting pressure of the center assist gas A2 is relatively weakened, and hence mainly the side assist gas A1 blows off the molten foreign matter generated at the cutting portion C. This side assist gas A1 is jetted obliquely downward from the upper position on the product portion Ga side to the cutting portion C, and hence the force of pressing downward the vicinity of the cutting portion C in the molten state of the glass sheet G is weaker than that of the center assist gas A2. Therefore, by setting the jetting pressure of the side assist gas A1 to be higher than the jetting pressure of the center assist gas A2, the cutting portion C in the molten state of the glass sheet G can be prevented from hanging. Then, under the state in which the cutting portion C is prevented from hanging in this way, the molten foreign matter generated at the cutting portion C is scattered by the side assist gas A1 preferentially to the non-product portion Gb side. Thus, the molten foreign matter is less liable to be deposited on the fused end surface Ga1 of the product portion Ga. In this way, as in the case illustrated in FIG. 4, the fused end surface Ga1 of the product portion Ga can be maintained in the satisfactory substantially circular-arc shape.

(54) The side assist gas A1 and the center assist gas A2 may be of the same type or of types different from each other.

(3) Third Embodiment

(55) As illustrated in FIG. 6, the glass sheet cutting device 1 according to a third embodiment of the first invention is different from the glass sheet cutting devices 1 according to the first and second embodiments in that an auxiliary side assist gas jet nozzle 6 is provided in a space below the glass sheet G. In the following, description is made only of the difference while omitting description of common features. Note that, the center assist gas jet nozzle 5 is provided in the illustration, but may be omitted.

(56) The auxiliary side assist gas jet nozzle 6 is arranged at a lower position on the product portion Ga side of the glass sheet G, and jets an auxiliary side assist gas A3 obliquely upward to the cutting portion C.

(57) Further, in this embodiment, a side surface portion 21a on the product portion Ga side of the stage main body 21, which faces the non-support space S, is formed as a tapered surface inclined to be closer on an upper side to the cutting portion C of the glass sheet G than on a lower side. The side surface portion 21a formed as the tapered surface guides obliquely upward the auxiliary side assist gas A3 jetted from the auxiliary side assist gas jet nozzle 6 so that the auxiliary side assist gas A3 is supplied to the cutting portion C of the glass sheet G. Note that, in the illustration, another side surface portion 21a on the non-product portion Gb side of the stage main body 21, which faces the non-support space S, is also formed as a tapered surface inclined to be closer on an upper side to the cutting portion C of the glass sheet G than on a lower side. As a matter of course, only the side surface portion 21a on the product portion Ga side of the stage main body 21 may be formed as the tapered surface.

(58) With this, the molten foreign matter generated at the cutting portion C of the glass sheet G can be efficiently blown off by the side assist gas A1 and the side assist gas A3 toward the non-product portion Gb side. Further, the auxiliary side assist gas A3 acts on the lower surface of the glass sheet G, and hence an effect of supporting the vicinity of the cutting portion C of the glass sheet G from below can be expected, which is conceived to contribute to prevention of hanging of the vicinity of the cutting portion C.

(59) The jetting pressure of the auxiliary side assist gas A3 is set to range from, for example, 0.01 MPa to 0.5 MPa.

(60) An inclination angle α2 of the auxiliary side assist gas A3 with respect to the rear surface (lower surface) of the glass sheet G is set to range preferably from 15° to 70°, more preferably from 20° to 60°, and much more preferably from 25° to 45°.

(61) An orientation of the auxiliary side assist gas A3 is not particularly limited as long as being directed to the vicinity of the cutting portion C. For example, in the illustration, an imaginary center line L2 of the auxiliary side assist gas A3 is set to intersect with the cutting portion C, but the imaginary center line L2 may be set to intersect with the upper surface or the lower surface of the glass sheet G on the product portion Ga side with respect to the cutting portion C.

(62) The auxiliary side assist gas A3 may be of the same type as or of a type different from that of the side assist gas A1.

(63) Note that, in this third embodiment, the side assist gas A1 and the auxiliary side assist gas A3 are jetted simultaneously to the cutting portion C of the glass sheet G, but the present invention is not limited thereto. For example, jetting of the side assist gas A1 may be continued to blow off the molten foreign matter at the cutting portion C until the cutting portion C of the glass sheet G is penetrated, and after the cutting portion C of the glass sheet G is penetrated, jetting of the side assist gas A1 may be stopped so that the molten foreign matter at the cutting portion C is blown off with the auxiliary side assist gas A3.

(4) Fourth Embodiment

(64) As illustrated in FIG. 7, the glass sheet cutting device 1 according to a fourth embodiment of the first invention is different from the glass sheet cutting device 1 according to the third embodiment in how to supply the auxiliary side assist gas A3. In the following, description is made only of the difference while omitting description of common features.

(65) In the fourth embodiment, the stage main body 21 of the support stage 2 comprises a gas flow path 21b extending obliquely upward and having one end communicated to the non-support space S. Another end of the gas flow path 21b is connected to a jet port of the auxiliary side assist gas jet nozzle 6. The auxiliary side assist gas A3 jetted from the auxiliary side assist gas jet nozzle 6 is guided obliquely upward through the gas flow path 21b and discharged into the non-support space S. In this way, the auxiliary side assist gas A3 is supplied to the cutting portion C of the glass sheet G.

(5) Fifth Embodiment

(66) As illustrated in FIG. 8, the glass sheet cutting device 1 according to a fifth embodiment of the first invention is different from the glass sheet cutting device 1 according to the third embodiment in that there is provided a configuration for sucking the molten foreign matter generated in the fusing process. In the following, description is made only of the difference while omitting description of common features.

(67) Specifically, the glass sheet cutting device 1 according to the fifth embodiment comprises a first suction nozzle 7 arranged at an upper position on the non-product portion Gb side and a second suction nozzle 8 arranged at a lower position on the non-product portion Gb side.

(68) The first suction nozzle 7 is arranged to face the side assist gas jet nozzle 4 under a state in which an imaginary center line L3 thereof is orientated to the cutting portion C, and sucks the molten foreign matter in the space above the glass sheet G. An inclination angle β1 of the imaginary center line L3 of the first suction nozzle 7 with respect to the front surface (upper surface) of the glass sheet G is set within a range of α1±15°, preferably α1±10°, and more preferably α1±5°.

(69) Meanwhile, the second suction nozzle 8 is arranged to face the auxiliary side assist gas jet nozzle 6 under a state in which a suction port thereof is oriented upward, and sucks the molten foreign matter in the space below the glass sheet G, in other words, the non-support space S. The second suction nozzle 8 is arranged relatively on the non-product portion Gb side with respect to just below the cutting portion C. This is because, in the non-support space S, the molten foreign matter descends while being blown off by the side assist gas A1 and the auxiliary side assist gas A3 toward the non-product portion Gb side.

(70) The first suction nozzle 7 and the second suction nozzle 8 suck the molten foreign matter blown off by the side assist gas A1 and the auxiliary side assist gas A3 toward the non-product portion Gb side. With this, it is possible to reliably prevent a situation where the molten foreign matter blown off from the cutting portion C by the side assist gas A1 and the auxiliary side assist gas A3 floats in an ambient space and re-adhere to the product portion Ga.

(71) Note that, in this fifth embodiment, the first suction nozzle 7 and the second suction nozzle 8 suck the molten foreign matter simultaneously, but the present invention is not limited thereto. For example, suction of the molten foreign matter with the first suction nozzle 7 may be continued until the cutting portion C of the glass sheet G is penetrated, and after the cutting portion C of the glass sheet G is penetrated, the molten foreign matter may be sucked with the second suction nozzle 8. Alternatively, the first suction nozzle 7 may be omitted so that the molten foreign matter is sucked only with the second suction nozzle 8.

(72) As illustrated in FIG. 9, the second suction nozzle 8 arranged in the space below the glass sheet G comprises a suction port 81, which is elongated along a direction of the preset cutting line CL of the glass sheet G. This is because, in the space below the glass sheet G, the molten foreign matter tends to scatter over a wide range along the direction of the preset cutting line CL. Note that, when there is no spatial restriction due to the laser irradiator 3 and the like, the first suction nozzle 7 arranged in the space above the glass sheet G may also comprise a suction port elongated along the extending direction of the preset cutting line CL.

(6) Sixth Embodiment

(73) As a matter of course, as illustrated in FIG. 10, the glass sheet cutting device 1 according to the fourth embodiment (refer to FIG. 7) may further comprise the first suction nozzle 7 and the second suction nozzle 8.

(74) Note that, the first invention is not limited to the above-mentioned first to sixth embodiments, and various modifications may be made thereto. For example, when the glass sheet G is formed by an overflow downdraw method or the like, as illustrated in FIG. 11, a thickness of both the widthwise end portions of the glass sheet G is relatively larger than a thickness of a widthwise central portion of the glass sheet G. The widthwise central portion is produced as the product portion Ga, and both the widthwise end portions are each produced as the non-product portion (referred to as ear portions) Gb. Thus, the cutting methods and the cutting devices according to the present invention may be utilized for removing such ear portions each produced as the non-product portion Gb of the glass sheet G.

(75) Further, in the above-mentioned embodiments, description is made of a case where one of the thin flat glass G separated by fusing is the product portion Ga, and another is the non-product portion Gb. However, the cutting method and the cutting device according to the present invention are applicable to a case where both the one and the another of the thin flat glass G are produced as the product portions Ga.

Example 1

(76) As Examples of the first invention, the following comparative tests were carried out. Testing conditions are as follows. First, as in the embodiment illustrated in FIG. 3, while blowing an assist gas, a CO.sub.2 laser beam with a wavelength of 10.6 μm is radiated to a cutting portion of a thin flat glass having a size of 300 mm long and 300 mm wide so that the thin flat glass is cut by fusing. Next, annealing treatment is performed through a secondary process (such as laser annealing or electric heating annealing) performed on a vicinity of a fused end surface of the thin flat glass thus fused. Such a series of cutting steps is performed while changing the thickness a of the thin flat glass and the narrowest gap b between the fused end surfaces. Then, the following were inspected with respect to each of the thin flat glasses fused through the cutting steps.

(77) (1) Abrasion conditions of the fused end surfaces

(78) (2) Shapes of the fused end surfaces

(79) (3) Strengths

(80) Note that, the strengths of the fused thin flat glasses were evaluated, as illustrated in FIG. 12, by two-point bending of sequentially sandwiching the thin flat glasses G between two plate-like bodies 9 and gradually bending the thin flat glasses G into a U-shape by pressing at a speed of 50 mm/minute so that the thin flat glass G is curved in a longitudinal direction. These evaluations are obtained by calculating breaking strengths based on an interval between the two plate-like bodies 9 at the time of breakage through bending by pressing. Results of those tests are shown below.

(81) TABLE-US-00001 TABLE 1 Comparative Example Example Example Example Example Comparative Example 1 1 2 3 4 5 Example 2 a [μm] 100 100 100 100 100 100 100 b [μm] 5 10 50 70 100 200 220 b/a 0.05 0.1 0.5 0.7  1  2 2.2 Abrasion Observed Somewhat None None None None None observed Shape good good very very very good bad good good good Strength 350 450 1,000 1,000 900 600 600 [MPa] Comprehensive bad good very very very good bad evaluation good good good

(82) TABLE-US-00002 TABLE 2 Example Example Example Example Example Comparative 6 7 8 9 10 Example 3 a [μm] 100 200 300 400 500 700 b [μm] 50 50 50 50 50 50 b/a 0.5 0.25 0.17 0.13 0.1 0.07 Abrasion None None None None None Observed Shape very very very good good Good good good good Strength 1,000 1,000 850 750 500 300 [MPa] Comprehensive very very very very good bad evaluation good good good good

(83) According to Tables 1 and 2 above, it can be understood that, when b/a is 0.1 or more, abrasion is not caused at all by contact between the fused end surfaces of the thin flat glass at the time of separation, or can be suppressed to a substantially ignorable level. Thus, when the thickness a and the narrowest gap b are managed to fall within such ranges, it is possible to reliably reduce a risk of breakage of the fused end surfaces of the thin flat glass by contact to each other at the time of separation.

(84) Further, when b/a is 2 or less, it can be understood that the shapes of the fused end surfaces of the thin flat glass can be satisfactorily maintained. Thus, when the thickness a and the narrowest gap b are managed to fall within such ranges, it is possible to reliably reduce a risk of deterioration in product quality of the thin flat glass or a risk of breakage of the thin flat glass from the fused end surface in subsequent steps.

(85) Therefore, when the narrowest gap b is managed so that a relationship of 0.1≦b/a≦2 is satisfied, it is possible to reliably reduce a risk of breakage of the thin flat glass at the time of separation or in steps subsequent thereto while satisfactorily maintaining the shape of the vicinity of the fused end surface of the thin flat glass. Note that, such functions and advantages can be obtained without necessity to perform preheating or annealing treatment in addition to radiation of a laser beam for fusing.

(86) Note that, when more stable product quality is required, the annealing treatment may be performed with a laser beam and the like immediately after fusing.

(87) An arithmetic mean roughness Ra of the fused end surfaces formed in Examples 8 to 10 above ranged from 0.08 μm to 0.18 μm, and a mean length RSm of a roughness curve element thereof ranged from 250 μm to 400 μm. Thus, residues on the fused end surfaces were easily removed. Meanwhile, as for cleaved end surfaces of thin flat glasses in Comparative Examples, each formed by folding and cleaving the thin flat glass along a scribe line and then being subjected to diamond polishing, an arithmetic mean roughness Ra of the cleaved end surfaces ranged from 0.4 μm to 0.6 μm, and a mean length RSm of a roughness curve element thereof ranged from 80 μm to 140 μm. Thus, residues on the cleaved end surfaces were not sufficiently removed.

(88) Further, compression strains (residual compressive stresses) of the fused end surfaces formed in Examples 1 to 10 above ranged from 80 MPa to 180 MPa. When those end surfaces were each flawed to generate cracks, the cracks propagated along edges, with the result that performance of the glass sheet was not deteriorated. Meanwhile, compression strains of the end surfaces of the thin flat glasses prepared in Comparative Examples, which were subjected to laser cleaving, ranged from 0 MPa to 15 MPa. When those cleaved end surfaces were each flawed to generate cracks, the cracks propagated in an in-plane direction to divide the thin flat glass into two pieces, with the result that performance as the glass sheet was lost.

Embodiments of Second Invention

(89) Embodiments of the second invention are in common with the first to sixth embodiments of the first embodiment described above, and hence description thereof is omitted.

Embodiments of Third Invention

(90) Embodiments of the third invention are in common with the fifth and sixth embodiments of the first embodiment described above, and hence description thereof is omitted.

Embodiments of Fourth Invention

(91) In the following, description is made of a laser fusing method according to an embodiment of the fourth invention with reference to the drawings.

(92) FIG. 13 is a sectional view of a glass sheet cutting device 1 used for the laser fusing method according to the embodiment of the fourth invention. As illustrated in FIG. 13, the glass sheet cutting device 1 comprises an assist gas jet nozzle 2 for jetting an assist gas A1 in a direction inclined at a jetting angle α with respect to a front surface S of the glass sheet G while being oriented toward an irradiation portion C which is irradiated with a laser beam L, and a side assist gas jet nozzle 4 for jetting a side assist gas A2 in a direction inclined with respect to the front surface S of the glass sheet G while being oriented toward the irradiation portion C from an opposite side of the assist gas jet nozzle 2. Further, the laser irradiator 3 for radiating the laser beam L from just above to the irradiation portion C is arranged at a position facing the front surface S of the glass sheet G in the irradiation portion C, which is irradiated with the laser beam L.

(93) The laser irradiator 3 comprises therein a condenser lens 5 for condensing the laser beam L generated from a laser oscillating device (not shown) and radiating the laser beam L to the irradiation portion C. A focal point of the condenser lens 5 is adjusted to be positioned on a line of an imaginary cutting line Z indicated in FIG. 13 and on an extension line thereof. Further, the laser irradiator 3 comprises a side wall provided with a center assist gas introducing path 6 for introducing a center assist gas A3, which is jetted from a radiation port of the laser irradiator 3 to the irradiation portion C, into the laser irradiator 3.

(94) The glass sheet cutting device 1 structured as described above is configured to cut the glass sheet G placed on a support stage 7 by the laser fusing method using the irradiation portion C (imaginary cutting line Z) as a boundary into a product portion G1 on a side from which the assist gas A1 is jetted and a non-product portion G2 on a side to which the side assist gas A1 is jetted.

(95) In this context, a jetting pressure of the side assist gas A2 is set to be lower than a jetting pressure of the assist gas A1 so that an effect that a molten glass portion M generated at the irradiation portion C is scattered by the assist gas A1 is not impaired. It is preferred that the jetting pressures of the assist gas A1, the side assist gas A2, and the center assist gas A3 range from 0.2 MPa to 0.6 MPa, 0.0 MPa to 0.3 MPa, and 0.0 MPa to 0.3 MPa, respectively. It is more preferred that the jetting pressures of the assist gas A1, the side assist gas A2, and the center assist gas A3 range from 0.3 MPa to 0.5 MPa, 0.0 MPa to 0.2 MPa, and 0.0 MPa to 0.2 MPa, respectively. In addition, examples of the assist gas A1, the side assist gas A2, and the center assist gas A3 include inert gases exemplified by oxygen, air, water vapor, nitrogen, carbon dioxide, and argon.

(96) Further, the jetting angle α of the side assist gas A1 is selected based on a relationship between the sheet thickness of the glass sheet G and a clearance to be formed between cut surfaces of the glass sheet G after cutting. For example, when a ratio of the sheet thickness and the clearance formed after cutting is [0.1<(clearance/sheet thickness)<2.0], in order that the cut surfaces (cut surface of the product portion G1 and cut surface of the non-product portion G2) of the glass sheet G after cutting are prevented from contacting and sliding with respect to each other and that the molten glass is prevented from being unnecessarily scattered, the jetting angle α is set preferably within a range of 20°<α<65°, and more preferably 25°<α<60°. An optimum value of the ratio is adjusted with the sheet thickness.

(97) As the glass sheet G to be cut by laser fusing, there may be employed sheets of non-alkali glass, soda-lime glass, borosilicate glass, lead glass, crystallized glass, physical tempered glass, chemical tempered glass, and the like. In any case, the thickness of such glass sheets is preferably 1.0 mm or less, and more preferably 0.5 mm or less, while a lower limit value of the thickness is set to 0.02 mm.

(98) In the following, with reference to FIGS. 14 to 17 of the accompanying drawings, description is made of how to perform the laser fusing method according to the embodiment of the present invention for the glass sheet G, in which the glass sheet cutting device 1 described above is used. Note that, in the embodiment of the present invention, the non-alkali glass sheet is used as the glass sheet G, and a sheet thickness of the glass sheet G subjected to cutting is 0.5 mm, a ratio of the sheet thickness of the glass sheet G and a clearance formed between cut surfaces of the glass sheet G after cutting (clearance/sheet thickness) is 1.0, the jetting pressure of the assist gas A1 is 0.5 MPa, the jetting pressure of each of the side assist gas A2 and the center assist gas A3 is 0.1 MPa, and the jetting angle α is set to 35°.

(99) As illustrated in FIG. 14, through radiation of the laser beam L to the irradiation portion C of the glass sheet G, the glass is molten at the irradiation portion C by irradiation heat of the laser beam L, with the result of being formed as the molten glass portion M indicated by cross-hatching in FIG. 14. At this time point, the assist gas A1, the side assist gas A2, and the center assist gas A3 have been jetted to the irradiation portion C (molten glass portion M).

(100) Through jetting of the above-mentioned gases, as illustrated in FIG. 15, apart on a front surface side of the molten glass portion M is thickened in a direction from the product portion G1 side to the non-product portion G2 side mainly by pressure of the assist gas A1, and another part of the molten glass portion M is scattered in the same direction. In this way, a recessed portion H is formed in the irradiation portion C. The part of the molten glass portion M is thickened as described above at a wall portion in the recessed portion H, with which the assist gas A1 collides, with the result that an inclined wall portion W inclined oppositely to the inclination α of the jetting direction of the assist gas A1 is formed.

(101) By the inclined wall portion W thus formed, a jet flow of the assist gas A1 flowing in an oblique direction from the product portion G1 side to the non-product portion G2 side collides against the inclined wall portion W, and hence is turned in a vicinity of a central portion in a thickness direction of the irradiation portion C. Then, along the inclined wall portion W, the jet flow is turned from the non-product portion G2 side toward the product portion G1 side. In this way, the jet flow is guided to a back surface B side of the glass sheet G. At this time point, as illustrated in FIG. 15, an upper end of the inclined wall portion W is in a state of swelling from the front surface S of the glass sheet G, and hence the assist gas A1 is more easily guided to the back surface B side.

(102) In this way, the side assist gas A2 functions to prevent unnecessary scattering of the molten glass portion M with pressure thereof, and to support formation of the inclined wall portion W by cooling the wall portion in the recessed portion H, with which the assist gas A1 collides, so as to promote re-solidification of the molten glass portion M existing at the wall portion. Further, the jetting pressure of the side assist gas A2 is lower than the jetting pressure of the assist gas A1, and hence an effect of scattering the molten glass portion M with the assist gas A1 is not impaired.

(103) Further, at this time, the center assist gas A3 supports an effect of scattering the molten glass portion M with the assist gas A1 and functions as an air curtain for preventing partially volatilized molten particles M1 from scattering and adhering as dross to the above-mentioned condenser lens 5. Further, with respect to the recessed portion H formed in the irradiation portion C, the center assist gas A3 functions also to support, together with the side assist gas A2, the formation of the inclined wall portion W by cooling the wall portion, with which the assist gas A1 collides, so as to promote the re-solidification of the molten glass portion M existing at the wall portion.

(104) As described above, the wall portion of the recessed portion H, with which the assist gas A1 collides, is formed as the inclined wall portion W. Thus, as illustrated in FIG. 16, a part of the jet flow of the assist gas A1 is changed into flow turned in the vicinity of the central portion in the thickness direction of the irradiation portion C. By the flow and pressure of such an assist gas A1, the part of the molten glass portion M, which is molten and softened by the irradiation heat of the laser beam L, is gradually removed. In this way, cutting of the glass sheet G proceeds.

(105) After cutting of the glass sheet G is completed by continuously performing such an operation, as illustrated in FIG. 17, a cut surface F of the product portion G1 after cutting is formed as a cut surface F having a convex curved-surface shape substantially symmetrical with each other with respect to a central portion in the thickness direction. This cut surface F does not comprise corner portions liable to be subjected to chipping and the like. Thus, it is no longer necessary to perform a polishing process on the cut surface F after cutting. In addition, the assist gas A1 is jetted obliquely to the front surface S of the glass sheet G, and is turned in a midway so as to be discharged obliquely to the back surface B. In this way, it is also possible to avoid troubles in a case where the assist gas A1 is jetted perpendicularly to the front surface S of the glass sheet G, specifically, a trouble that a part of the molten glass portion M hangs from the back surface B by strong pressing of the irradiation portion C with the jetting pressure of the assist gas A1. As a result, an advantage of enhancing product quality of the cut surface F can be obtained.

(106) In the embodiment of the fourth invention, a total of three gases: the side assist gas A1; the side assist gas A2; and the center assist gas A3 are used. However, it is not necessary to use the side assist gas A2 and the center assist gas A3, and only the assist gas A1 may be used. Further, in the embodiment of the present invention, the side assist gas A2 is ceaselessly jetted from the start to the end of cutting of the glass sheet G. However, the side assist gas A2 may be jetted after the inclined wall portion W starts to be formed in the irradiation portion C. Further, the laser beam L is radiated to the irradiation portion C from just above. However, the laser irradiator 3 may be provided separately from the jetting port of the center assist gas A3 so that the laser beam is radiated from the product portion G1 side or the non-product portion G2 side. Further, it is not necessary to position the focal point of the laser beam L with respect to an intersecting portion between the imaginary cutting line Z and the front surface S of the glass sheet G, and the focal point of the laser beam L may be adjusted to be positioned on the central portion in the thickness direction of the irradiation portion C, on the back surface B, or above the front surface S of the glass sheet G.

Example 2

(107) As Examples of the fourth invention, tests of cutting glass sheets by the laser fusing method were carried out under six conditions shown in Table 3 below (four Examples and two Comparative Examples). After that, as quality evaluations of cut surfaces of products, quality levels were compared to each other based on the following three items. Note that, the CO.sub.2 laser beam with a wavelength of 10.6 μm was used as a laser beam for fusing.

(108) Item 1: whether or not dross adheres to any of the cut surfaces of the products

(109) Item 2: whether or not a melt hangs from any of the cut surfaces of the products

(110) Item 3: quality level of symmetry in the thickness direction of each of the cut surfaces of the products

(111) Table 3 below shows the test results. Note that, in Table 3, in rows of “jetting pressure of assist gas” and “jetting pressure of side assist gas,” cells of “0.0 MPa” mean that none of the assist gas and the side assist gas was jetted.

(112) TABLE-US-00003 TABLE 3 Example Example Example Example Comparative Comparative 1 2 3 4 Example 1 Example 2 Type of glass Non-alkali Non-alkali Non-alkali Soda-lime Non-alkali Soda-lime Sheet thickness of glass 0.1 0.3 0.5 1 0.1 1 [mm] Clearance /sheet 0.5 1 1 1.5 1 1 thickness Jetting pressure of 0.3 0.4 0.5 0.5 0 0.1 assist gas [MPa] Jetting angle of assist 43 35 35 28 85 gas [°] Jetting pressure of 0.1 0.1 0.1 0.1 0.3 0.5 center assist gas [MPa] Jetting pressure of side 0 0 0.1 0.1 0 0 assist gas [MPa] 1. Whether or not dross None None None None Observed Observed adhesion was observed 2. Whether or not None None None None Observed Observed hanging occurred 3. Quality level of good good good good bad bad symmetry of cut surface

(113) As shown in Table 3, when the assist gas was not used as in Comparative Example 1, adhesion of dross to the cut surfaces of the products was observed, and the inclined wall portion was not formed in the non-product portions. In addition, hanging of the molten glass was confirmed. Further, as in Comparative Example 2, also when the center assist gas was mainly used while jetting the side assist gas from substantially just above the irradiation portion, the inclined wall portion was not formed in the non-product portion, and satisfactory results were not obtained with regard to any of the comparison items. Meanwhile, in Examples 1 to 4, adhesion of dross to the cut surfaces of the products was not observed, and hanging of the molten glass was not confirmed. In addition, the symmetry in the thickness direction of each of the cut surfaces was very satisfactory.

REFERENCE SIGNS LIST

Reference Signs of Embodiments of First Invention

(114) 1 glass sheet cutting device 2 support stage 21 stage main body 22 conveyer 3 laser irradiator 31 lens 4 side assist gas jet nozzle 5 center assist gas jet nozzle 6 auxiliary side assist gas jet nozzle 7 first suction nozzle 8 second suction nozzle A1 side assist gas A2 center assist gas A3 auxiliary side assist gas C irradiation portion G glass sheet Ga product portion Ga1 fused end surface Gb non-product portion Gb1 fused end surface LB laser beam S non-support space

Reference Signs of Embodiments of Fourth Invention

(115) 1 glass sheet cutting device 2 assist gas jet nozzle 3 laser irradiator 4 side assist gas jet nozzle 5 condenser lens 6 center assist gas introducing path 7 support stage A1 assist gas A2 side assist gas A3 center assist gas L laser beam G glass sheet G1 product portion G2 non-product portion S front surface of glass sheet B back surface of glass sheet C irradiation portion H recessed portion F cut surface of product portion W inclined wall portion α jetting angle M molten glass portion M1 volatilized molten particle Z imaginary cutting line