FLAT GLASS HAVING AT LEAST ONE PREDETERMINED BREAKING POINT

Abstract

A flat glass is provided that includes a first side face, an opposite, second side face, and at least one edge face. The flat glass has a linear predetermined breaking location on the first or second side face. The flat glass also has two mutually separated points, where at least one of the two mutually separated points lies on the linear predetermined breaking location. The two mutually separated points are each configured as a point of attack for a force for breaking the flat glass. The two mutually separated points have breaking forces required to break the flat glass that differ from one another in magnitude and/or direction.

Claims

1. A flat glass comprising: a first side face; an opposite, second side face; at least one edge face; a linear predetermined breaking location on the first or second side face; and two mutually separated points, at least one of the two mutually separated points lies on the linear predetermined breaking location, the two mutually separated points each being configured as a point of attack for a force for breaking the flat glass, wherein the two mutually separated points have breaking forces required to break the flat glass that differ from one another in magnitude and/or direction.

2. The flat glass of claim 1, wherein both of the two mutually separated points lie on the linear predetermined breaking location, and wherein the breaking forces differ from one another in magnitude.

3. The flat glass of claim 1, further comprising a second linear predetermined breaking location.

4. The flat glass of claim 3, further comprising two further mutually separated points, the two further mutually separated points both lying on the second linear predetermined breaking location and each are configured as another point of attack for a force for breaking the flat glass, wherein the two further mutually separated points have breaking forces required to break the flat glass that differ from one another in magnitude.

5. The flat glass of claim 3, wherein at least one of the two mutually separated points lies on the second linear predetermined breaking location.

6. The flat glass of claim 3, wherein the linear predetermined breaking location is arranged on the first side face and the second linear predetermined breaking location is arranged on the second side face.

7. The flat glass of claim 1, wherein the magnitude of the breaking forces decrease continuously along the linear predetermined breaking location.

8. The flat glass of claim 1, wherein the magnitude of the breaking forces differ by at least 10% for a spacing between the two mutually separated points of at least 5 mm.

9. The flat glass of claim 1, wherein the magnitude of the breaking forces differ by at least 30% for a spacing between the two mutually separated points of at least 5 mm.

10. The flat glass of claim 1, further comprising a coating on the first side face and/or the second side face, wherein the coating comprises a material selected from a group consisting of epoxysilane, aminosilane, aldehydesilane, a polymer having a reactive N-hydroxysuccinimide terminal group, indium tin oxide, chromium, and any combinations thereof.

11. The flat glass of claim 1, wherein the linear predetermined breaking location is formed by a locally reduced thickness of the flat glass.

12. The flat glass of claim 1, wherein the linear predetermined breaking location comprises a trench indentation in the first side face and/or the second side face.

13. The flat glass of claim 1, wherein the linear predetermined breaking location comprises a crack along the first side face and/or the second side face.

14. The flat glass of claim 1, wherein the linear predetermined breaking location comprises a ultrashort-pulse laser microstructure of locally modified filamentations in the first side face and/or the second side face.

15. The flat glass of claim 1, wherein the linear predetermined breaking location comprises a modification of a microstructure of the glass.

16. The flat glass of claim 15, wherein the modification comprises a sequence of spatially restricted, nonoverlapping modifications of the microstructure, wherein the sequence of spatially restricted, nonoverlapping modifications at the two mutually separated points comprises a spacing and/or a volume that differ from one another.

17. The flat glass of claim 15, wherein the sequence of spatially restricted, nonoverlapping modifications comprise a spacing along the predetermined breaking location that increases or decreases continuously.

18. The flat glass of claim 15, wherein the sequence of spatially restricted, nonoverlapping modifications comprise a spacing along the predetermined breaking location that increases or decreases linearly.

19. The flat glass of claim 1, further comprising a thickness of from 0.7 mm to 10 mm.

20. The flat glass of claim 1, wherein the flat glass is configured as a substrate a medical diagnosis device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The sold FIGURE shows a schematic representation, not true to scale, of a measurement layout for determining the breaking force in cross section.

DETAILED DESCRIPTION

[0057] For the measurement of the breaking force, a flat glass 1 having square side faces with an edge length b and a thickness d is used. Conventionally, the edge length should be 30 mm and the thickness should be 1 mm. The edge length b of a measurement specimen must, however, in this case be at least 20 times the thickness of the flat glass: b≥20*d. Measurements on other, in particular rectangular, geometries are however likewise possible.

[0058] The flat glass 1 lies supported along a narrow contact line on two supports 3. The supports 3 in this case have a spacing L which is adjusted to 15 times the thickness of the glass: L=15*d. With a thickness of d=1 mm, the spacing is thus L=15 mm.

[0059] The breaking force under tensile stress is always measured for glass. This means that the side face on which the predetermined breaking location to be measured is arranged must be arranged on the lower side 7 for the measurement. Since with rigid bodies the point of attack of a force can always be displaced along the line of action, the action of a compressive force on the opposite side 9 from the predetermined breaking location and the action of a tensile force on the side of the predetermined breaking location 7 are equivalent. The direction and magnitude of these forces are then identical, and the forces are merely displaced along the line of action perpendicularly to the surface of the flat glass 1.

[0060] During the measurement, a force is applied to the flat glass 1 from the upper side 9 by means of a pin 5, this force being increased continuously during the measurement until the flat glass 1 breaks. The magnitude of the force at which the flat glass breaks corresponds to the breaking force. The pin 5 in this case acts only pointwise on the predetermined breaking location. In particular, the contact face of the pin, which comes into contact with the flat glass 1, is flat and circular with a diameter of 0.5 mm. The pin 5 may, for example, be made of stainless steel. The arrow represented in the FIGURE on the pin 5 indicates the movement direction of the pin 5 and therefore the direction of the force action, or the line of action.

[0061] For the present invention, it is not important to determine the absolute breaking force. It is sufficient merely to determine the relative breaking force differences at different points of a predetermined breaking location, or at points of different predetermined breaking locations. The dimensions mentioned above may therefore be varied in a wide range. They must, however, be kept constant for the measurement values to be compared. For example, instead of a flat circular contact face, a spherical pin 5 with a suitably chosen diameter, for example 2 mm, may also be selected for the pin.

[0062] For measurement of the breaking force at different positions of an individual predetermined breaking location, it is necessary to produce a multiplicity of identical specimens and to carry out the measurement at each position to be measured on the predetermined breaking location on a plurality of specimens. By means of the values determined in this way, it is then possible to average in order to obtain reliable information about the breaking force distribution along a predetermined breaking location produced in a defined way.

[0063] The way in which a flat glass according to the invention may be produced by laser filamentation will be described by way of example below.

[0064] One suitable laser source according to the present invention is a neodymium-doped yttrium aluminum garnet laser with a wavelength of 1064 nanometers. Such a laser may be operated in so-called burst mode. This means that instead of individual pulses, a train of a plurality of pulses in very close succession is emitted. The pulse repetition rate of a laser in burst mode is given by the time between the pulse trains. The burst frequency is given by the time between the individual pulses within a pulse train.

[0065] The laser source produces, for example, a raw beam with a (1/e.sup.2) diameter of 12 mm, and a biconvex lens with a focal length of 16 mm may be used as optics. Suitable beam shaping optics, for example a Galilean telescope, may optionally be used for producing the raw beam.

[0066] The laser source operates, in particular, with a pulse repetition rate that between 1 kHz and 1000 kHz, preferably between 10 kHz and 400 kHz, particularly preferably between 30 kHz and 200 kHz.

[0067] The pulse repetition rate and/or the forward speed may in this case be selected so that the desired spacing of neighboring modifications is achieved. In particular, the forward speed may be varied in order to alter the spacings between neighboring modifications, and therefore the breaking force.

[0068] The suitable pulse duration of a laser pulse lies in a range of less than 100 picoseconds, preferably less than 20 picoseconds.

[0069] The typical power of the laser source in this case particularly favorably lies in a range of from 20 to 300 watts. In order to achieve the filamentary modifications, a pulse energy in the burst of more than 400 microjoules is preferably used. A total burst energy of more than 500 microjoules is furthermore advantageous. The burst energy in this case corresponds to the sum of the energy of all pulses in the pulse train.

[0070] The pulse duration is substantially independent of whether a laser is operated in single-pulse operation or in burst mode. The pulses within a burst typically have a similar pulse length as a pulse in single-pulse operation. The burst frequency may lie in the interval of from 15 MHz to 90 MHz, preferably in the interval of from 20 MHz to 85 MHz, and is for example 50 MHz, and the number of pulses in the burst may be between 1 and 10 pulses, for example 6 pulses.

[0071] Because of the very high burst frequency, all pulses of a pulse train strike substantially the same position of the substrate and together generate the modifications there. The number of laser pulses for respectively producing a modification is in this case selected in particular from the interval of from 1 to 20, preferably from the interval of 1 to 10, particularly preferably from the interval of 2 to 8.

[0072] The spacing between neighboring modifications may in particular lie in the interval of from 1 μm to 20 μm, particularly in the interval of 2 μm to 10 μm.

[0073] The diameter of the modifications may for example lie in the interval of 0.5 μm to 5 μm, in particular 0.8 μm to 2 μm, and particularly in the interval of 1 μm to 1.5 μm.

[0074] The modifications may be arranged at different locations in the flat glass, depending on the way in which the focus of the laser beam is positioned relative to the side faces of the flat glass. For example, they may extend from the surface of the side face facing toward the laser into the volume of the flat glass. They may likewise extend from the surface of the side face facing away from the laser into the volume of the flat glass. They may furthermore extend from the surface of the side face facing away from the laser through the entire thickness of the flat glass as far as the opposite side face. They may likewise extend only in the volume of the flat glass, without contact with one of the side faces. In this way, it is possible in a particularly simple way to produce predetermined breaking locations on both side faces of the flat glass with a single laser, merely by varying the focal positioning.

[0075] The person skilled in the art will adjust, or vary, these parameters so that he achieves the desired breaking force behavior of the predetermined breaking locations.

LIST OF REFERENCE NUMERALS

[0076] 1 flat glass [0077] 3 support [0078] 5 pin [0079] 7 lower side [0080] 9 upper side