JP2012131680A - Laser thermal stress scribing method and apparatus for glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus which eliminate unsteadiness of laser output, in a method and apparatus for achieving surface scribing of a workpiece of glass or the like by irradiating the surface of the workpiece with a laser beam under scanning.SOLUTION: When the surface of a workpiece 1 of glass or the like is heated by irradiating the surface with a laser beam under scanning and the rear is cooled under scanning to thereby achieve surface scribing 4 of the workpiece 1, a liquid or impurities present on the surface of the workpiece 1 is blown off by a jetted gas from a blast nozzle installed just in front of the laser beam and the surface of the workpiece 1 is cleaned, so that COlaser beam absorption by the liquid such as a coolant or impurities present in the laser beam irradiation position of the workpiece 1 surface is prevented, and thus, reduction of required laser output and process stabilization are achieved.

Description

The present invention relates to a brittle material, especially a thermal stress scribing method and apparatus for glass for flat panels and touch panels. Hereinafter, although the case of glass will be introduced as an example of a workpiece, the present invention can be applied to all brittle materials.

Recently, in the glass cleaving, the thermal stress cleaving method by laser beam irradiation has been used in place of the diamond chip mechanical method which has been used over the past several centuries.

  According to this method, defects inherent in the mechanical method, that is, a decrease in glass strength due to the occurrence of microcracks, contamination due to the occurrence of cullet at the time of cleaving, existence of a lower limit value of the applied plate thickness, and the like can be eliminated.

As a result, according to the thermal stress cleaving method, polishing and cleaning, which are subsequent processes of mechanical cleaving, are not required, and a mirror surface with a surface roughness of 1 μm or less can be obtained, and the product external dimension accuracy exceeds the industry specification value of ± 25 μm. Become a thing. This method is currently used for flat panel and touch panel glass having a plate thickness of 0.33 mm to 1.1 mm, but is expected to be used for a wider range of plate glass in the future.

  The principle of this method is as follows. The glass is heated to the extent that cracks, melting, vaporization, etc. do not occur by locally irradiating the laser beam. At this time, the glass heating section tries to expand thermally, but cannot sufficiently expand due to the reaction from the surrounding glass, and compressive stress is generated around the irradiation point. Even in the peripheral non-heated region, the peripheral portion is further distorted by the expansion from the heating portion, and as a result, compressive stress is generated. These compressive stresses are radial. By the way, when an object has a compressive stress, a tensile stress related to the Poisson's ratio is generated in the orthogonal direction. Here, the direction is a tangential direction. This is shown in FIG.

This figure shows the change of the radial stress component σ _x and the tangential stress component σ _y depending on the location when there is a temperature rise in the Gaussian distribution centered at the origin. The former is compressive stress from the beginning to the end (negative value in the figure), while the latter is compressive stress at the heating center, but changes to tensile stress (positive value in the figure) when leaving the center. Based on the stress distribution shown in the figure, a general temperature distribution can be handled as a linear superposition of the stress distribution. Even in that case, there is no difference that compressive stress and tensile stress are generated in the orthogonal direction at each point on the glass plate.

Of these stresses, the tensile stress is directly related to the cleaving. When the stress exceeds the fracture toughness value, which is a material specific value, fracture occurs everywhere and cannot be controlled. This is a destructive phenomenon, not processing. In the case of the thermal stress cleaving as in the present invention, the tensile stress is selected to be equal to or less than the same value, so this fracture does not occur.

However, if there is a crack at the position where the tensile stress is present, stress expansion occurs at the tip, and if this amplified tensile stress exceeds the fracture toughness value of the material, the crack expands. That is, as the progress of the crack, controlled cleaving as processing occurs. By scanning the laser beam irradiation point, the crack can be extended. In this thermal stress cleaving, the fractured surface is similar to the cleavage plane of the crystal, so there is no generation of microcracks and cullet, and the disadvantages of the mechanical method described above can be eliminated, and the glass processing method is extremely excellent. Will have.

  There are two types of thermal stress cleaving. First, thermal stress generation and cleaving occur over the entire thickness of the workpiece, which is called full cut. Second, as shown in FIG. 3, as a result of the surface heating 2 and the surface cooling 3, the crack 4 is generated only in the surface layer (for example, a depth of 100 μm) of the workpiece 1 and is generally called a surface scribe. 5 indicates the scribe direction. The workpiece that produced the surface scribe can be easily cleaved by applying mechanical stress. In this technique, since the tensile stress increases due to cooling in addition to the generation of thermal stress due to the heating described above, cooling is necessary. These full cut and surface scribe have advantages and disadvantages, but the latter is currently in practical use at production sites, and this patent also relates to the improvement of this technology.

This surface scribing technology by laser beam irradiation of glass has been vigorously developed by Kondratenco Bradymier Stepanovic, and a Japanese patent of Patent Document 1 has been established. This patent is also established as a European patent and a US patent in Patent Documents 2 and 3. He chose a CO ₂ laser beam that achieves surface heating by absorbing the surface of the glass as the laser beam.

Similarly, a Japanese patent of Patent Document 4 has been established in which a surface sliver is performed using a CO ₂ laser, and a technique of converting a circularly symmetric laser beam into a plurality of beam spot arrays arranged in a straight line by a beam splitter.

Kondratenko V.S., method for cutting brittle non-metallic materials, Japanese Patent No. 3027768 Kondratenko Vladimir S., Method of splitting non-metallic materials, EP0633867B1 Kondratenko Vladimir S., Method of splitting non-metallic materials, USP5609284 Tsutomu Teramoto, cutting device, Japanese Patent No. 3792639

Thermal stress cleaving due to laser beam irradiation or the like is characterized by a high-quality processing method rather than a mechanical method. On the other hand, this processing method also has drawbacks. One of the disadvantages of the thermal stress surface scribing method is that the process is complexly dependent on a number of conditions, and if one of these conditions changes, the machining characteristics change. That is, the process lacks stability. For this reason, it is not easy to use this technology at a production site.

The inventor is the condition that the fluctuation of the heating energy greatly affects the instability of the surface scribe, and even if the laser output is constant, the stability of the proportion of the same output that is absorbed by the work and consumed for the same heating Was confirmed experimentally.

In particular, if a liquid such as cooling liquid or contaminants adheres to the surface of the workpiece being processed, a part of the CO ₂ laser beam for heating is absorbed by this, and all the energy of the stabilized laser beam is heated. Not used. This does not make effective use of energy, and if the amount of liquid adhering is uneven depending on the location, the depth of surface scribing will vary, and in some cases, scribing may not occur, resulting in lack of process stability. .

Even if the glass surface is clean before the start of processing, if several scribing processes are repeated with the same workpiece, the cooling liquid used for the previous processing may remain in the heating position. . In such a case, if the scribe does not enter at all or the amount of the adhering liquid is not uniform, the scribe depth varies. Therefore, it is important to clean the workpiece surface immediately before the occurrence of the surface scribe to prevent the workpiece from being disturbed.

According to the present invention, high efficiency and high stability of thermal stress cleaving can be realized. The inventor can reduce the required laser power to 40 W by applying the present invention under conditions that require a laser power of 100 W in a conventional CO ₂ laser surface scribe, while the stability can be greatly improved. It was. Conventional laser thermal stress glass cleaving has been able to replace many mechanical techniques with diamond tips that have been used over the past few centuries, with many great technical advantages in processing quality. The present invention changes such a situation.

The following are the merits of general thermal stress cleaving of glass realized by the present invention.
1) Cleaving can be realized at a significantly higher speed than the conventional method.
2) No post-process such as polishing or cleaning after cleaving is required.
3) There is no generation of micro cracks in the vicinity of the fractured surface, and the material strength of the workpiece becomes a high value.
4) There is no adhesion of cullet on the cut surface and it is clean.
5) The cleaving position accuracy is increased.
6) The fractured surface is sufficiently perpendicular to the glass surface.
7) The fractured surface is a mirror surface and the surface roughness is good.
9) The cleaving can be automated.
In addition to the above, there are the following merits compared with the conventional laser thermal stress scribing method. 10) The required laser output can be greatly reduced.
11) The scribe characteristic can be remarkably stabilized.

1 is a schematic diagram of a laser thermal stress surface scribe method and apparatus according to the present invention. The generated thermal stress distribution diagram by Gaussian temperature distribution. The surface scribe schematic diagram by laser beam irradiation and cooling of glass. Conversion of Gaussian laser beam to line beam by DOE.

A schematic diagram of the method and apparatus enabling this invention is shown in FIG. In the figure, the surface scribe 4 is started from the initial crack 8 along the scribe direction 5 on the workpiece 1 such as glass and is advanced. For this purpose, the workpiece 1 is scanned at a required speed in the heating region of the surface of the workpiece 1 by the CO ₂ laser beam 2 having a linear shape and the cooling region 3 by the coolant spray from the cooling nozzle 7 that follows the workpiece. Progressing the scribe line is equivalent to the prior art.

The present invention is characterized in that cleaning is performed by removing residual liquid and foreign matter from the heating area prior to heating the workpiece surface by the laser beam, and this cleaning is performed by a gas such as air blown off and ejected from the nozzle 6. is there. For this reason, all of the irradiated CO ₂ laser energy is absorbed by the workpiece surface and used for heating. For this reason, thermal stress generation is performed stably.

Now, examples will be described. The present invention belongs to the surface scribe shown in FIG. Therefore, as shown in FIG. 1, the glass surface is scanned by heating by CO ₂ laser beam irradiation and the cooling means by cooling liquid spray following the scanning. In addition, an initial crack is provided at the glass edge where scribing is started. The principles and methods of these techniques are now well known.

  A feature of the present invention is that the work surface is cleaned by using a blow-off nozzle prior to laser heating as described above, and the configuration of the nozzle is shown in FIG. The nozzle is a pipe made of stainless steel having an inner diameter of 1 to 10 mmφ, and the air release tip is provided perpendicularly to the workpiece surface at a position 0.5 to 10 mm away from the edge of the laser beam on the workpiece surface. The work surface is cleaned by injecting a cleaning gas having a pressure of 0.1 to 0.5 MPa. The distance between the pipe tip and the workpiece surface may be about 5 mm. In this case, in the case where the cleaning was not performed, the laser output of 100 μm and the scribe depth of 100 μm could be processed at a speed of 200 mm / s. According to the present invention, the laser output could be reduced to 40 W. In addition, the process stability could be greatly improved.

FIG. 3 shows the case where the cross-sectional shape is a small circle as the heating laser beam. However, when the scribe is linear or the depth is to be increased, the cross-sectional shape is set to increase the heating time of the glass. A laser beam that is a line beam may be used. Since the laser beam emitted from the laser oscillator is usually a Gaussian beam having a circular cross-sectional shape, the cross-sectional shape of the beam must be converted by various methods.

One such method is shown in FIG. It uses a Gaussian laser beam 10 emitted from a laser oscillator 9 converted into a line beam using a diffraction grating type optical element (DOE) 11 as a line beam homogenizer. FIG. 4 is a schematic diagram showing the state of this conversion. In FIG. 4, 12 indicates the laser beam after passing through the DOE, and the line beam 13 which is the design specification is realized at a predetermined position. As this line beam, a beam having a width of about 0.1-1 mm and a length of about 30 mm is typically used. In this case, the intensity distribution is uniform in the length direction, but the width direction can be uniform or Gaussian. Further, the intensity distribution in the length direction can be changed by adjusting the diameter and position of the incident laser beam. As a result, the cleaving position accuracy can be further increased, and the surface scribe depth can be increased.

After these steps, a machine break is performed along the scribe line.

What has been described above are several embodiments for realizing the functions of the present invention, and it goes without saying that the spirit of the present invention can be realized in many other ways.

In this way, if the thermal stress cleaving of glass is introduced into the manufacturing process of flat panel and touch panel glass, the effect cannot be measured in improving the processing speed, processing quality, economy, etc., and overcoming the weaknesses of the prior art. Become a thing. These processes are currently performed with a diamond cutter, which presents problems such as the necessity of a cleaning step after cutting for generating cullet and a reduction in material strength due to the presence of microcracks. These problems can be solved by the advancement of the thermal stress scribing technique according to the present invention.

1 Work
2 Laser heating area 3 Cooling area 4 Surface scribe 5 Scribing direction 6 Blow-off nozzle 7 Cooling nozzle 8 Initial crack 9 Laser oscillator 10 Gaussian laser beam 11 Diffraction grating type optical element (DOE)
12 Laser beam after passing through DOE 13 Line beam cross-sectional shape

Claims (4)

In a laser thermal stress surface scribing method of glass with a cooling unit that irradiates a workpiece surface such as glass while scanning with a CO ₂ laser beam and follows and scans the back of the scanned laser beam at the same speed, The work surface is cleaned by blowing away the liquid or impurities present on the work surface before heating with the cleaning gas blown to the work surface from the tip of the blow-off nozzle installed in front. In [Claim 1], which was converted into an appropriate rectangular heat stress scribing a circular a CO ₂ laser beam cross-sectional shape with a diffraction grating optical element. In a laser thermal stress surface scribing apparatus for glass with a cooling unit that irradiates a workpiece surface such as glass while scanning with a CO ₂ laser beam and follows and scans the back of the scanned laser beam at the same speed, The work surface is cleaned by blowing away the liquid or impurities present on the work surface before heating with the cleaning gas blown to the work surface from the tip of the blow-off nozzle installed in front. [Claim 3] The cross-sectional shape of the CO ₂ laser beam is converted from a circular shape to a rectangular shape suitable for thermal stress scribing using a diffraction grating optical element.

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