Method for producing glass plate, glass plate produced by said method and use thereof

Abstract

To provide an economical method for manufacturing an ultrathin glass plate, capable of surely enhancing strength in the end part of the glass plate in spite of a high cooling rate.SOLUTION: A method for manufacturing a glass plate comprises steps of: hot-molding a continuous glass ribbon (4) having a predetermined glass thickness of 15 μm to 2 mm from a glass melt; cooling the glass ribbon (4) at a cooling rate selected depending on the predetermined glass thickness; forming a focus region of a laser beam (20) using a beam formation optical system so that the focus region is larger than the thickness of the glass ribbon (4); and introducing a target break line (12) from a filament-like scratch into the glass ribbon (4) by the laser beam (20) so as to preferably extend the filament-like scratch from one side surface of the glass ribbon (4) to the side surface on the opposite side.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the production of ultra-thin glass sheets, i.e. glass with a glass thickness of 15 μm to 2 mm, by laser filamentation in order to introduce targeted break lines in an endless glass ribbon and subsequently separate process-induced thickened ears, i.e. raised thickened areas at both longitudinal edges of the glass ribbon, as well as to separate glass sheets in the transverse direction of the glass ribbon, whereby so-called glass sheets are also included in said ultra-thin glass sheets. [Background technology]

[0002] Laser filamentation for cutting the edge and transverse singulation in the glass ribbon, and optionally in combination with subsequent separation of the glass, allows for higher glass ribbon or pulling and cutting speeds in the cutting process than, for example, in the case of wheel cutting, where the achievable cutting speed, especially for the edge and transverse scoring, is limited by the separation and storage process carried out by the operator. Furthermore, laser filamentation is a low-particle method, which results in less contamination and scratches in the glass.

[0003] The separation of glass sheets by introducing a filament by an ultrashort pulsed laser is known per se. Corresponding methods are described, inter alia, in WO 2018 / 020145 A1, WO 2017 / 055576 A1, US 2018 / 0057390 A1 and US 2017 / 0120374 A1.

[0004] For ultra-thin glasses, significant cooling rates are achieved at high pull rates, since certain minimum pull rates are required to maintain certain geometric coefficients with respect to warpage, thickness variation, etc. High cooling rates are usually disadvantageous, since they usually result in internal stresses in the glass, which reduces the edge strength when cutting the glass. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 020145 [Patent Document 2] International Publication No. 2017 / 055576 [Patent Document 3] US Patent Application Publication No. 2018 / 0057390 [Patent Document 4] US Patent Application Publication No. 2017 / 0120374 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is therefore to provide a particularly economical method for producing ultra-thin glass sheets, which takes into account the various cooling rates and ensures that the edge strength of the glass sheets produced by this method is high, in particular despite high cooling rates. This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the invention are respectively described in the dependent claims. [Means for solving the problem]

[0007] The present invention therefore relates to a method for producing a glass sheet, comprising the following steps: a continuous, in particular continuous, drawing of a glass ribbon from the glass melt having a predetermined glass thickness in the range of 15 μm to 2 mm for hot forming, cooling the glass ribbon with a cooling rate selected depending on the given glass thickness, preferably at lower or smaller glass thicknesses the cooling rate is increased, i.e. preferably the smaller the glass thickness, the higher the cooling rate is selected and the higher the glass thickness, the lower the cooling rate is selected. generating a laser beam by at least one ultrashort pulse laser; generating a focal area of ​​the laser beam using beam shaping optics such that the focal area is greater than a glass thickness of the glass ribbon; introducing target break lines from filamentary flaws into the glass ribbon by means of the laser beam, such that the filamentary flaws extend preferably from one side of the glass ribbon to the opposite side thereof, wherein the filamentary flaws are introduced at intervals along the target break line, and wherein a transverse target break line across the glass ribbon and two longitudinal target break lines on either side longitudinal to the glass ribbon, each having an edge with a thickened ear, are generated. - separating the tabs along the longitudinal target break lines to form an edge, preferably having a predetermined edge strength; and separating the glass sheets by separation at transverse targeted break lines running across the glass ribbon to form edges, preferably having a predetermined edge strength; The present invention provides a method having the following structure:

[0008] The laser beam can be shaped by beam-shaping optics, in particular as a Bessel beam.

[0009] An apparatus corresponding to the above-mentioned method for producing glass sheets preferably comprises: An apparatus for hot forming from a glass melt into a continuous glass ribbon having a predetermined glass thickness in the range from 15 μm to 2 mm, at least one ultrashort pulsed laser for generating depthwise spaced filamentary defects in a predetermined volume of the glass ribbon to form transverse target break lines across the glass ribbon and longitudinal target break lines on opposite longitudinal sides of the glass ribbon, each having edges with thickened ears; and beam forming optics for generating a Bessel beam that generates a focal region that is adjusted as the beam shape to be larger than the glass thickness; A movement device for positioning the laser beam along a predetermined path of a target break line on the glass ribbon; a cooling device which cools the glass ribbon before, during and / or after the introduction of filamentary scratches into the glass ribbon at a cooling rate selected as a function of the given glass thickness, with a cooling rate preferably being arranged and adjusted in such a way that the smaller the glass thickness, the higher the cooling rate selected. The method may further include a separating device positioned and adjusted to separate, preferably mechanically, the ears along longitudinal target break lines and the glass sheets at transverse target break lines running across the glass ribbon to form respective edges.

[0010] Positioning of the laser beam by the movement device can be accomplished by at least one of the steps of moving the glass ribbon, moving the at least one ultrashort pulse laser, and moving or adjusting the beam forming optics.

[0011] In this case, the glass thickness is preferably 100 μm or less, less than 70 μm, 50 μm or less, 30 μm or less, or less than 20 μm.

[0012] The glass ribbon is advantageously rapidly drawn by a downdraw process, preferably at a speed ranging from 1 meter per minute to 50 meters per minute, but said process is not limited to the downdraw process, it can also be drawn by an overflow fusion process or any other process suitable for producing thin glass ribbons.

[0013] The introduction of the targeted break line from the filamentary flaws preferably occurs according to one embodiment after the glass ribbon turns horizontally during the downdraw process.

[0014] The glass ribbon is preferably cooled rapidly, in particular a cooling rate of 40 K / s or more can be used. In particular the cooling rate can be significantly higher, preferably 100 K / s or more, particularly preferably 150 K / s or more or even 200 K / s or more.

[0015] According to a further aspect of the invention, the glass ribbon is cooled at a thickness-dependent cooling rate, preferably in the range of (1 / d)·4500 Kelvin / (sec·μm) to (1 / d)·9000 Kelvin / (s·μm), where d denotes the thickness of the glass ribbon. Thus, advantageously, the cooling rate is increased for a given smaller thickness of the glass ribbon or decreased / reduced for a given larger thickness of the glass ribbon.

[0016] In order to subsequently be able to reliably and easily separate the ears from the glass ribbon and to achieve separation of the individual glass sheets, the glass ribbon is preferably cooled before the introduction of the target break line in the range of the glass transition temperature, preferably at a temperature below the softening point, particularly preferably below the glass transition temperature. In order to optimize the method, cooling of the glass ribbon can optionally additionally also be carried out during and / or after the introduction of the target break line.

[0017] In a preferred embodiment of the method, the cooling is carried out in a cooling furnace, in particular by means of a heating element, or by blowing or spraying with a cooling fluid, in particular air, another gaseous medium or an aerosol. In the latter case, the cooling rate can be adapted / determined by the process parameters glass temperature and feed rate, for example by controlling the flow rate of the cooling fluid, to prevent undesirable stresses in the glass ribbon.

[0018] According to a particularly preferred embodiment, the intensity distribution in the glass and thus also the shape of the filamentary scratches can be adjusted in a targeted manner via the beam shaping optics. For this purpose, the beam profile is preferably adjusted by means of corresponding beam shaping optics in such a way that the light intensity or the divergence of the laser beam is greater in the direction of the target break line than across it.

[0019] In a further preferred embodiment of the method, the beam-forming optics also produces a beam profile with a horizontal preferred direction, preferably an elliptical, lancet-shaped, drop-shaped, two spaced apart beams (e.g. double Bessel beam), rhomboid, dumbbell-shaped, wedge-shaped or point-shaped beam profile, or a beam profile with a main beam and a periphery with a weaker intensity, whereby after separation of the ears and singulation of the glass sheets, an almost arbitrary contour with a particularly high edge quality or edge strength can be obtained.

[0020] The speed and repetition rate of the ultrashort pulse laser are preferably adjusted so that the filamentary scratches are introduced adjacent to each other with a distance of at most the size of the glass thickness, advantageously the filamentary scratches have an average distance from each other in the range of 1 μm to 10 μm, preferably 3 μm to 8 μm.

[0021] In a preferred embodiment of the method for producing a glass sheet, the introduction of the target break lines is first across the glass ribbon, thereby generating a transverse target break line, and then on both sides longitudinally of the glass ribbon, each having an edge with a thickened ear, generating a longitudinal target break line, in this manner, the glass ribbon is mechanically stabilized by still holding the ears together after the introduction of the transverse target break lines.

[0022] It has further been found that the edge strength decreases with higher cooling rates for thinner glasses, and conversely, the edge strength increases with lower cooling rates for thicker glasses. In a preferred embodiment of the method, the edge strength KG depending on cooling is determined according to the following formula: K A glass sheet is produced with an edge having: (1) KG K =KG / K, or (2) KG=KG K ·K. In the formula, KG denotes the value of the strength in MPa and K denotes the cooling rate in Kelvin / s. In particular, the separation method disclosed herein provides a coefficient KG of more than 0.2 MPa·s / Kelvin, preferably more than 0.5 MPa·s / Kelvin, for a glass thickness of at least 30 μm. K For glass thicknesses of at least 50 μm, the cooling-dependent edge strength KG K can be greater than 0.5 MPa·s / Kelvin, preferably greater than 0.9 MPa·s / Kelvin. For a glass thickness of at least 100 μm, according to a further embodiment the cooling-dependent edge strength KG K is greater than 1.5 MPa·sec / Kelvin, preferably greater than 2 MPa·sec / Kelvin.

[0023] In a further preferred embodiment, the displacement device for moving the glass ribbon advantageously comprises at least a pressing roll, a pressing edge or a suction device for fixing the position of the glass ribbon in the focal region, so that the glass ribbon is fixed with respect to the position of the focal point of the ultrashort pulsed laser and the location of the target break position from the filamentary flaw, and a deviation of the glass ribbon from the focal region of the Bessel beam is avoided.

[0024] In particular, said fixation makes it possible to avoid the abovementioned disadvantages while also increasing the speed of the production process, which has a positive effect on the economics of the process.

[0025] The separation of the edge at the longitudinal break line and the separation of the glass sheet by separation at the transverse break line running across the glass ribbon are preferably performed mechanically. It has been shown that the separation at the target break line generally requires little mechanical action. In many cases, the movements and stresses during the transport of the glass ribbon are already sufficient to separate the target break location.

[0026] With the method for producing ultra-thin glass sheets according to the present disclosure, particularly high cutting speeds can also be achieved, in particular cutting speeds of up to 5 m / s, particularly preferably 3 m / s to 5 m / s.

[0027] According to laser filamentation, for cutting the edge and for lateral singulation in the glass ribbon, i.e. for separating the edge and separating the individual glass sheets or for so-called full body cut (FBC), as mentioned above, very little or no separation force is required. In particular, the induction of thermal stress by bringing about a temperature, i.e. the induction of a temperature difference, is not required, and therefore for example the so-called thermal cleavage method and thermal shock cutting by a steep temperature drop, in particular by a cooling shock, is not required.

[0028] With the method disclosed herein, high edge strengths are achieved at various cooling rates, especially at high cooling rates, taking into account the glass thickness.

[0029] Thus, the thickness dependent cooling rate is not a drawback but an element of the solution to the problem.

[0030] The process results in particularly low particle and particularly stable edge strength and therefore increased projected yield.

[0031] Due to the reduced production costs of the glass ribbon and the stable quality achieved with the method, the method is furthermore particularly economical.

[0032] According to the method, glass sheets with a glass thickness of 15 μm to 2 mm, preferably with a glass thickness of 100 μm or less, 50 μm or less or 30 μm or less, and preferably with a thermal expansion coefficient of more than 6 ppm / K can be produced, with the glass sheets preferably having a Weibull modulus (according to DIN EN 843-5) of more than 7 and a characteristic fracture stress of more than 130 MPa, often even more than 150 MPa or even more than 200 MPa. In a preferred embodiment, the characteristic fracture stress is in the range from 150 MPa to 250 MPa. The 5% quantile σ at an edge length of 1.68 meters 5%@1.68 For σ, values ​​of more than 90 MPa, and in many cases even more than 130 MPa, are obtained.

[0033] The glass plate preferably has a rough surface having filament-like scratches and a flat surface therebetween having no filament-like scratches, and the area ratio of the flat surface to the rough surface is preferably 3:10 to 2:1.

[0034] The ultrathin glass sheets which can be produced by the method according to the invention can be used for a wide variety of applications: preferably, they are used as insulating intermediate substrates or spacers for electronic components, for the encapsulation of optoelectronic components, as supports for thin-film cells, for example thin-film batteries or solar cells, as composite substrates for displays and for microfluidic cells.

[0035] Said various applications are based on properties such as chemical resistance, resistance to temperature changes and heat, hermeticity, high electrical insulation, adapted expansion coefficient, bendability, high optical quality and light transmission or even high surface quality with very little roughness on both sides of the thin glass as well as high edge strength that are achieved by said separation method.

[0036] The invention will now be described in more detail with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 shows a glass sheet manufacturing apparatus. [Diagram 2] FIG. 2 shows the beam profile of the beam forming optics. [Diagram 3] FIG. 3 shows an arrangement for separating the glass ribbon into individualized glass sheets. [Figure 4] FIG. 4 is a graph showing the dependence of cooling rate on glass thickness. [Diagram 5] FIG. 5 is a graph of the glass thickness dependence of edge strength and cooling rate. [Figure 6] FIG. 6 is a graph of the cooling rate dependent edge strength coefficient as a function of glass thickness. [Figure 7] FIG. 7 shows a Weibull graph of failure probability as a function of fracture stress. [Figure 8] FIG. 8 shows a Weibull graph of failure probability as a function of fracture stress. [Figure 9] FIG. 9 shows a micrograph of the edge area of ​​the glass plate. [Figure 10] FIG. 10 shows a micrograph of the edge of a glass plate. [Figure 11] FIG. 11 shows a schematic graph of the progression 43 of the intensity of the focal region 22 along the target break line and the progression 44 of the intensity of the focal region 22 perpendicular to the target break line. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] 1 shows an exemplary embodiment of an apparatus 1 for producing a glass sheet 2 with a predetermined glass thickness d in the range of 15 μm to 2 mm. A continuous glass ribbon 4 is drawn from a glass melt 10 through a downward slit-like nozzle 6, which is part of a hot-forming apparatus 8. As hot-forming method for the glass ribbon, preferably the so-called down-draw method is used here, and the introduction of the target break line 12 from the filamentary scratches 14, i.e. laser filamentation, takes place preferably directly during the down-draw method, particularly preferably after the glass ribbon 4 has been redirected horizontally.

[0039] The glass ribbon 4 is introduced with a targeted break line 12 from a controlled filamentary flaw 14 by at least one ultrashort pulse laser 16, the laser pulses of which generate an approximate Bessel beam 20 by means of beam shaping optics 18, thereby generating a focal region 22 passing through the glass ribbon 4. In particular, the beam shaping optics 18 can focus the laser beam 20 to increase the power density in the glass. Via the beam shaping optics 18, the intensity distribution and thus also the morphology of the filamentary flaw 14 can be adjusted in a targeted manner.

[0040] The focal region is preferably adjusted to be longer than the glass thickness d to generate deep (spaced apart) filamentary scratches 14 in a given volume of the glass ribbon 4, preferably introduced from one side 51 to the opposite side 52 of the glass ribbon 4, i.e., preferably throughout the entire thickness d of the glass ribbon 4.

[0041] As an ultrashort pulse laser for the purposes of the present invention, for example a Nd:YAG laser with a wavelength of 1064 nm, an average power of 12 W (at 1064 nm, 100 kHz, one pulse per burst), a repetition rate of 100 kHz, a burst frequency of 50 MHz and a pulse duration of about 10 ps (at 1064 nm and 100 kHz) is suitable.

[0042] According to a further embodiment, a Yb:YAG-laser with 1030 nm can be used. Generally, said laser can be used as a frequency doubled (SHG) or frequency tripled (THG) version. The pulse length is according to one embodiment in the range of 300 fs to 20 ps, ​​or in the range of 400 fs to less than 10 ps. The repetition rate can be in the range of 50 kHz to 1 MHz, preferably 100 kHz to 500 kHz. The pulse energy can be more than 100 μJ, more than 200 μJ, or even more than 400 μJ. The number of burst pulses is ≦2, ≦4, or ≦8.

[0043] Furthermore, the apparatus 1 for producing the glass ribbon 2 preferably includes a moving device 24, e.g. by transport rolls, in particular by drawing rolls, for moving the glass ribbon 4, an ultrashort laser 16, and / or beam forming optics 18 for positioning the laser beam 20 along a predetermined path of the target break line 12 on the glass ribbon 4.

[0044] In so doing, the laser beam 20 can be guided over the glass ribbon 4 or the glass ribbon 4 can be guided relative to the laser beam 20. A combination of both aspects is also possible. In order to move the laser beam 20 perpendicular to the direction of movement of the glass ribbon 4, for example a galvanometer scanner can be used or a deflection mirror can be conveyed on a movable axis transverse to the glass ribbon.

[0045] In this case, a transverse target break line 121 across the glass ribbon 4 and two longitudinal target break lines 122 on either side of the glass ribbon 4 each having an edge with a thickened ear 13 are formed.

[0046] The invention is also based on the finding that the variation in the breaking force at the edge produced by the laser-assisted method according to the present disclosure can be reduced with a cooling rate adapted to the glass thickness.

[0047] The apparatus 1 for producing glass sheets 2 therefore further comprises a cooling device 26 which cools the glass ribbon 4 before the filamentary scratches 14 are introduced into the glass ribbon 4 at a cooling rate selected as a function of the given glass thickness d, preferably arranged and adjusted in such a way that a higher cooling rate is selected for smaller glass thicknesses.

[0048] The cooling of the glass ribbon 4 is preferably carried out before the introduction of the target break line 12 in the range of the glass transition temperature, preferably at a temperature below the softening point, particularly preferably below the glass transition temperature.

[0049] In a preferred embodiment, cooling of the glass ribbon 4 is carried out in a cooling furnace 27, in particular in a regulated manner using heating elements. Optionally, homogeneous cooling can also be promoted by blowing or spraying a cooling medium, in particular air, aerosol.

[0050] According to one embodiment, the apparatus 1 for producing the glass sheets 2 further comprises a separating device 28 arranged and adjusted to preferably mechanically separate the ears 13 along the longitudinal target break line 122 to form the edge 30, and to preferably mechanically separate the glass sheets 2 by separating them at the transverse target break line 121 running across the glass ribbon 4 to form the edge 30. For example, the separating device may comprise an arrangement with a spherical roller guided over the target break line. A heat source, for example a laser, may also be provided to induce thermal stresses at the target break line. In some cases, a mechanical action is no longer required to separate the glass at the target break line.

[0051] Furthermore, via the beam shaping optics 18, the intensity distribution in the glass and thus the shape of the filamentary scratches 14 can be adjusted as desired.

[0052] In a further preferred embodiment, the moving device 24 for moving the glass ribbon 4 comprises at least one pressing roll, pressing edge or suction device for fixing the axial position or the position of the glass ribbon 4 in the direction of the beam in the focal area, so that the glass ribbon 4 is not distorted in terms of the singulation of the glass sheets 2 and the separation of the edge portions 13, which would impair the shape and edge quality of the individual glass sheets 2. In particular, the fixing also increases the speed of the production process and makes it possible to avoid the above-mentioned disadvantages, which has a positive effect on the economics of the method. In the case of the example shown in FIG. 1, a pair of pressing rolls 15 is shown as a device for fixing the vertical position of the glass ribbon 4, which fixes the position of the glass ribbon in the direction of incidence of the laser beam 20 near the point of irradiation of the ultrashort pulsed laser 16.

[0053] In a preferred embodiment for producing the glass plate 2, the beam profile is adjusted by corresponding beam-forming optics 18, preferably in such a way that the intensity profile is formed in the form of a Bessel beam or similar to the form of a Bessel beam with a highly enhanced intensity on the optical axis. The beam-forming optics provides focusing to a linear focus. To achieve such focusing, for example one or more axicons or diffractive optical elements (DOEs) or combinations thereof with other optical elements are suitable as beam-forming optics.

[0054] In particular, the beam profile is preferably adjusted so that the spread of the laser beam in the direction of the target break line 12 is greater than in a direction transverse, in particular perpendicular, to said break line. In this way, the amount of beam integrated along the target break line is greater than along a line running perpendicular to the target break line and across the center of the beam. In other words, the beam-shaping optics preferably generates a beam with a cross section which is wider in the direction of the linear filament scratches 14 than in a direction transverse to this direction, the individual filament scratches 14 running across the surface of the glass ribbon 4 in the direction of spread of the laser beam 20 which preferably follows a longitudinal direction perpendicular to the surface of the glass ribbon 4. For this purpose, the beam-shaping optics 18 is preferably adjustable with respect to a larger beam-cross section spread, and the direction of the larger cross section spread preferably tracks the path of the linear filament scratches 14.

[0055] In a further preferred embodiment of the method, an asymmetric beam profile with a horizontal preferred direction is generated by the beam forming optics 18. Figure 2 shows various possibilities of beam profiles for this. Part (a) shows an elliptical beam profile 32, which is aligned such that its long semi-axis is aligned along the respective target break line. The spread A of the beam profile along the target break line is therefore p is the spread A perpendicular to the target break line s2(e) shows a profile 36 of a dumbbell-shaped beam, and in FIG. 2(f) a profile 37 of a wedge-shaped beam. Finally, FIG. 2(g) shows a profile 38 of a beam with a main beam and a weaker or smaller periphery. The embodiments of the sub-views (b), (e), (f) and (g) have in common that they are not only more widespread in the direction of travel than in the direction perpendicular to it, but also asymmetric with respect to the mirror axis perpendicular to the direction of travel. Such a shape can be very advantageous to make the separation even easier and to achieve higher edge strength. This is because asymmetric conditions also exist during the introduction of the filament, since no filament is yet present in front of the laser beam in the direction of travel for the target break line in the part already scanned by the beam. In general, and without being limited to a particular example, it is therefore assumed that the filament-like defects are introduced with a laser beam 20 having an asymmetric beam profile with respect to its mirror image perpendicular to the direction of travel.

[0056] This results in an adjustable shape with higher geometric accuracy of the target break line 12 from the resulting filamentary scratches 14 as well as higher edge strength after separation of the ears 13 and individualization of the glass pane 2.

[0057] To promote the formation of a crack in the direction of the target break line, the cross-sectional shape of the laser beam is purposefully selected to have an extension in the direction of the desired break.

[0058] The elliptical cross-sectional shape 32 in Figure 2(a) is obtained from the original circular cross-sectional shape of the laser beam, for example through a combination of cylindrical lenses. Further beam profiles can also be generated through suitable lenses, possibly using diffractive optical elements (DOEs).

[0059] In a preferred embodiment of the method for producing the glass sheet 2, in terms of process technology, the sequence of introduction of the target break lines 12 is first transverse to the glass ribbon, resulting in a transverse break line 121, and then on both sides longitudinal to the glass ribbon, each with an edge having a thickened ear, resulting in a longitudinal target break line 122, since the glass ribbon 4 is then still held together by the ears 13 and is thereby mechanically stabilized.

[0060] FIG. 3 shows an arrangement for separating the glass ribbon 4 into individualized glass sheets 2 and for separating the ears 3 .

[0061] For this method, a moving device 24 is preferably provided for transporting the continuously drawn glass ribbon 4, which in the illustrated example comprises a conveyor belt 240. In general, without being limited to the illustrated example, a plurality of ultrashort pulse lasers 16 may be advantageously used to introduce the target break line 12, with at least one first ultrashort pulse laser 16 introducing a transverse target break line 121 and at least one second ultrashort pulse laser 16 introducing a longitudinal target break line 122. In particular, in the illustrated example, it is also possible to use ultrashort pulse lasers 16 for two longitudinal target break lines 122. The beam forming optics 18 of the ultrashort pulse laser 16 are not shown in the drawing for the sake of simplicity. As in the illustrated example, the moving device 24 may also comprise beam deflection optics 241. According to one embodiment, the target break line 121 is then introduced by a laser beam 20 which moves over the glass ribbon 4 by means of the beam deflection optics 241. The beam forming optics 241 may include, for example, a galvanometer scanner.

[0062] As shown, in one preferred embodiment, the above-mentioned target break lines 121, 122 are introduced into the continuous glass ribbon 4, first transversely and then longitudinally.

[0063] The separation or so-called full body cut (FBC) of the individual glass sheets 2 by separation or breaking at a transverse target break line 121 running across the glass ribbon 4 can be carried out by a mechanical separating device 28, for which particularly low or no separating forces are required with laser filamentation. The cutting of the edge 13, i.e. the separation of the edge along the longitudinal target break line 122 of the glass ribbon 4, can also be carried out with particularly low separating forces, for example by simple pulling and / or by moving on an acceleration belt 29. The acceleration belt 29, which separates the individual glass sheets 2 in the moving direction, can for example be part of the separating device 28 or can be the separating device 28.

[0064] After separation or singulation of the glass sheets 2, they can be transported by means of the transfer device 24 to an inspection unit 39. The inspection unit 39 can be used to inspect, among other things, the dimensions of the glass sheets and their edge quality.

[0065] In particular, in order to achieve good edge quality, no thermal separation of the glass ribbon 4 by introducing stress is required or no induction of thermal separation by introducing temperature, i.e. inducing a temperature difference, for example by a CO2 laser, i.e. the so-called thermal cleaving method, is required for separation, and no thermal shock cutting, for example by a cooling shock, for example by a steep temperature drop, is required.

[0066] In this case, separation can take place, for example, by introducing mechanical stress with a spherical roller or by directing a targeted break line on a spherical roller. The ears 13 separated from the remaining glass ribbon 4 can then be stored (in a debris repository / other space), for example in a debris container, optionally removed from the glass ribbon.

[0067] In the method according to the invention, the glass ribbon 4 is cooled at a cooling rate which is selected as a function of the predefined glass thickness d, with a higher cooling rate being preferably selected the smaller the predefined glass thickness d, or a lower cooling rate being preferably selected the larger the predefined glass thickness, i.e. a higher cooling rate is preferably selected the smaller the glass thickness, and a lower cooling rate is preferably selected the larger the glass thickness.

[0068] Figure 4 is a graph of selected cooling rates as a function of glass thickness. In particular, in Figure 4 the dependence of cooling rates in the range of 40 K / s to 325 K / s on glass thickness d in the range of 25 μm to 110 μm for the example glass ribbon 4 of AF32 glass from Schott AG is shown (curve (a)).

[0069] The glass offered by Schott AG under the name AF32 is an alkali-free aluminum borosilicate thin glass from the class of alkali-free glasses well suited for the process and has the following components in weight percent: SiO258~65 B2O36~10.5 Al2O314~25 MgO 0~3 CaO 0~9 BaO 3~8 ZnO 0-2, Here, the total content of MgO, CaO and BaO is characterized by being in the range of 8 to 18 mass %.

[0070] The glasses on which the examples are based have the following composition in % by weight: SiO261 Al2O318 B2O310 CaO5 BaO3 MgO3.

[0071] The glass AF32 has a high light transmittance of 2430 kg / m 3 density ρ, surface tension γ of 0.3 N / m, thermal conductivity λ of 2 W / mK, and specific heat capacity c of 1360 J / kgK.p The transition temperature T g is 713°C. The glass AF32 has a small thermal expansion coefficient close to that of silicon. The downdraw process furthermore produces particularly flat surfaces with a small roughness of less than 1 nm (RMS). The application temperatures reach up to about 600°C.

[0072] A further class of glasses suitable for the method described herein contains the following components in % by weight: SiO250~70 Al2O310~20 B2O35~15 CaO 4~8 BaO 0.5~5 SrO4~8.

[0073] In one embodiment, the glass is made from the following ingredients: SiO260 mass% B2O310 mass% Al2O315% by mass SrO 6% by mass CaO 6% by mass BaO 2% by mass as well as 1% by weight of further ingredients.

[0074] According to a further embodiment, the glass ribbon is preferably drawn to a thickness of 50 μm±10 μm. For example, the overflow fusion method is suitable.

[0075] A further class of glasses well suited for the present invention, since they can be processed into thin glass ribbons and easily divided by the introduction of targeted break lines as described herein, has the following components in wt. %: SiO230~85 B2O33~20 Al2O30~15 Na2O 3~15 K2O 3~15 ZnO 0-12 TiO20.5~10 CaO 0~0.1.

[0076] Examples from this class of glasses have the following composition in wt. %: SiO264.0 B2O38.3 Al2O34.0 Na2O 6.5 K2O 7.0 ZnO 5.5 TiO24.0 Sb2O30.6 Cl - 0.1.

[0077] Glass sheets having this composition generally have the following characteristics: α (20-300) 7.2×10 -6 / K T g 557℃ Density 2.5g / cm 3 .

[0078] A further class of glasses which are chemically strengthenable and which are particularly suitable for processing in the manner described herein have the following components in weight percent: SiO250~65 Al2O315~20 B2O30~6 Li2O 0~6 Na2O 8~15 K2O 0~5 MgO 0~5 CaO 0-7, preferably 0-1 ZnO 0-4, preferably 0-1 ZrO20~4 TiO2 0-1, preferably essentially free of TiO2.

[0079] Furthermore, the glass may contain 0 to 1% by weight of P2O5, SrO, BaO, as well as 0 to 1% by weight of the fining agents SnO2, CeO2 or As2O3 or other fining agents.

[0080] According to one embodiment, from glasses with compositions from the above ranges, glass sheets are produced with the following thicknesses: 35 μm±5 μm, 50 μm±5 μm, 75 μm±5 μm, 100 μm±10 μm. The above-mentioned kinds of glasses can be drawn, both by the downdraw method and by the overflow fusion method, into thin glass ribbons that can be easily split by the method described herein by the introduction of a targeted break line and achieving high strength in the glass sheet. In some cases, if the achievement of the desired glass thickness is not possible or difficult in the drawing method, said desired glass thickness can be achieved by chemical or mechanical thinning.

[0081] Examples of glasses from this class have the following composition in weight percent: SiO260.7 Al2O316.9 Na2O 12.2 K2O 4.1 MgO 3.9 ZrO21.5 SnO20.4 CeO20.3.

[0082] All of the glasses mentioned here can be successfully processed by downdraw into glass ribbons having thicknesses in the range of 30 to 100 μm.

[0083] Without being limited to the given examples, a glass ribbon 4 having a given glass thickness d in the range of 15 μm to 2 mm is cooled according to the method of the invention preferably at a cooling rate of 50 K / s or more (40 K / s for FIG. 4), preferably at least 100 Kelvin / s, particularly preferably at least 150 Kelvin / s or even at least 200 Kelvin / s.

[0084] As shown in the graph of FIG. 4, when the thickness of the glass ribbon is 30 μm, a cooling rate in the range of 150 Kelvin / sec to 300 Kelvin / sec is preferably selected, when the thickness of the glass ribbon is 50 μm, a cooling rate in the range of 90 Kelvin / sec to 180 Kelvin / sec is preferably selected, and when the thickness of the glass ribbon is 100 μm, a cooling rate in the range of 45 Kelvin / sec to 90 Kelvin / sec is preferably selected.

[0085] Thus, without being limited to the examples shown or the glass compositions described herein, the glass ribbon is preferably cooled at a cooling rate ranging from 150 Kelvin / sec·30 μm / d to 300 Kelvin / sec·30 μm / d, where d is the thickness of the glass ribbon, where in FIG. 4 curve (b) shows the upper limit of (1 / d)·300 Kelvin / sec·30 μm and curve (c) shows the lower limit of (1 / d)·150 Kelvin / sec·30 μm. This preferred range can alternatively be expressed as follows: The glass ribbon is preferably cooled at a cooling rate ranging from 150 Kelvin / sec·30 μm / d to 300 Kelvin / sec·30 μm / d, where d is the thickness of the glass ribbon, where in FIG. 4 curve (b) shows the upper limit of (1 / d)·300 Kelvin / sec·30 μm and curve (c) shows the lower limit of (1 / d)·150 Kelvin / sec·30 μm. This preferred range can alternatively be expressed as follows: (1 / d) 4500 Kelvin μm / s (curve (c)) ~ (1 / d) 9000 Kelvin μm / s (curve (b)) [wherein d represents the thickness of the glass ribbon] The cooling rate is in the range of

[0086] With the method according to the invention, it is surprisingly possible to achieve glass sheets with high edge strengths even in the case of high cooling rates, taking into account the glass thickness, as is exemplarily shown in FIGS.

[0087] FIG. 5 is a graph showing the glass thickness dependency of edge strength and cooling rate, and FIG. 6 shows a graph showing the glass thickness dependency of the coefficient of edge strength depending on cooling rate.

[0088] FIG. 5 shows a graph of the glass thickness dependence in the range of 20 μm to 110 μm of the edge strength in the range of 85 MPa to 155 MPa (curve (f)) and the cooling rate in the range of 40 to 230 Kelvin / s (curve (e)) for the example of glass AF32 from Schott AG. As shown in FIG. 5, for a glass thickness of 30 μm and a cooling rate of 150 Kelvin / s, the edge strength is about 90 MPa, for a glass thickness of 50 μm and a cooling rate of 120 Kelvin / s, the edge strength is about 140 MPa, and for a glass thickness of 100 μm and a cooling rate of 70 Kelvin / s, the edge strength is about 155 MPa. All edge strengths are sufficient for the use of the glass. This is especially because thinner glasses show lower edge strengths, but due to their small thickness they also show very high flexibility. Due to their small thickness, the stresses that occur at the edge when bending the glass are also small.

[0089] This relationship is called "Cooling-Dependent Edge Strength" (KG K ) [MPa K / s]: KG K =KG / K [where KG is the edge strength in MPa and K denotes the cooling rate in K / sec].

[0090] Figure 6 shows a graph of the coefficient of edge strength depending on cooling in the range of 0.3-2.5 MPa·sec / K versus glass thickness in the range of 20 μm-110 μm for the example of glass AF32 from Schott AG. It is shown that with the separation method disclosed herein, the coefficient of edge strength versus cooling rate generally has a linear relationship to the layer thickness, without being limited to the example shown.

[0091] In the example for glass AF32, from the values ​​in FIG. KG K =KG / K (KG K =-0.16974+0.02434·d) [where d is the thickness of the glass in micrometers] The relationship is obtained.

[0092] Cooling rate dependent edge strength KG for glass thicknesses of at least 30 μm K is preferably greater than 0.2 MPa·sec / Kelvin, particularly preferably greater than 0.5 MPa·sec / Kelvin. The above relationship is expressed as KG=K·KG K For glass thicknesses of at least 30 μm, The coefficient "cooling-dependent edge strength" (KG K ) 0.6MPa·sec / K, end strength (KG) 90MPa, The coefficient "cooling-dependent edge strength" (KG K ) 0.2MPa·sec / K, end strength (KG) 30MPa, and The coefficient "cooling-dependent edge strength" (KG K ) 0.5MPa·sec / K, end strength (KG) 150MPa This results in:

[0093] Cooling-dependent edge strength KG for glass thicknesses of at least 50 μm K is preferably greater than 0.5 MPa·sec / Kelvin, particularly preferably greater than 0.9 MPa·sec / Kelvin. Thus, for a glass thickness of at least 50 μm, and The coefficient "cooling-dependent edge strength" (KG K ) 0.5MPa·sec / K, resulting in an edge strength (KG) of 45MPa, as well as The coefficient "cooling-dependent edge strength" (KG K ) 0.9MPa·s / K, resulting in an end strength (KG) of 162MPa.

[0094] Cooling rate dependent edge strength KG for glass thicknesses of at least 100 μm K is preferably greater than 1.5 MPa·sec / Kelvin, particularly preferably greater than 2 MPa·sec / Kelvin. Thus, for a glass thickness of at least 100 μm, and The coefficient "cooling-dependent edge strength" (KG K ) 1.5 MPa·sec / K, resulting in an edge strength (KG) of 67.5 MPa, and The coefficient "cooling-dependent edge strength" (KG K ) 2MPa·s / K, resulting in an end strength (KG) of 180MPa.

[0095] Thus, through selection of the cooling rate, a targeted given / specific glass sheet edge strength can be achieved for a given glass thickness.

[0096] According to the method of the invention, glass sheets can be produced with a glass thickness of 15 μm to 2 mm, preferably with a glass thickness of 100 μm or less, 50 μm or less, or 30 μm or less, and with a thermal expansion coefficient of more than 6 ppm / Kelvin, with the glass sheets preferably having a Weibull modulus (according to DIN EN 843-5) of more than 7, in particular more than 8, and an edge strength or breaking stress of more than 150 MPa, preferably more than 180 MPa.

[0097] [Table 1]

[0098] The table shows the characteristic fracture stress and Weibull modulus of strength distribution for laser cut Schott AF32 glass produced by downdraw process with various glass thicknesses of 30 μm, 50 μm and 100 μm.

[0099] The higher the Weibull modulus, the more homogeneous and less prone to failure the workpiece, i.e., in this application, the glass sheet, is. A high Weibull modulus is a particular feature of the glass sheet 2 produced by the method disclosed herein.

[0100] Figures 7 and 8 show by way of example Weibull graphs of the failure probability as a function of the breaking stress. The graph in Figure 7 shows the measurements from which the data for the table heading "AF32_50 μm" were taken. Thus, a glass plate from glass AF32 having a thickness of 50 μm was tested. Figure 8 shows the measurements for the table heading "Setting 1-AF32_100 μm". Accordingly, for this, an AF32 glass plate having a thickness of 100 μm was tested.

[0101] Glass sheets produced according to the invention typically have rough surfaces resulting from separation at the filamentary scratches and essentially flat surfaces between them. The area ratio of said flat surfaces to the rough surfaces is generally between 3:10 and 2:1. In this regard, the micrograph in FIG. 9 shows an example of a side surface 51 bounded by an edge 30 of a glass sheet 2 produced by the method according to this disclosure by introducing targeted break lines from side-by-side spaced filamentary scratches 14 and subsequently separating the glass ribbon at said targeted break lines. The filamentary scratches 14 are also still visible at the edge 30 as half-open channels. These channels form rough surfaces 41 at the edge 30. A flat surface 40 extends between these rough surfaces.

[0102] The structure of the edge 30 is also evident in the example of Figure 10, which shows a micrograph of the edge 30 of a glass plate 2 having a thickness of 30 μm, viewed from above. It can be clearly seen that the periodic structure of filamentary scratches 14 extending from one side 51 to the opposite side 52 forms a rough surface, with a relatively flat surface 40 extending between them.

[0103] As already discussed above, a particularly stiff end 30 having a high Weibull modulus is achieved by adjusting the beam profile such that the light intensity of the laser beam 20 is greater in the direction of the target break line 12 than across it. This is achieved by having the beam profile diverge more in the direction along the target break line than perpendicular to it. The divergence A in the direction perpendicular to the target break line is sand the spread A in the direction parallel to the target break line p is shown by way of example in the partial view (a) of Fig. 2. Fig. 11 further shows a schematic graph of the progression 43 of the intensity of the focal region 22 along the target break line and the progression 44 of the intensity of the focal region 22 perpendicular to the target break line. s and A p The light intensity is at its maximum value I max A value I reduced by a factor of 1 / e from 1 / e As shown, A s A p Generally, and not limited to the example shown, in one preferred embodiment, using suitable beam shaping optics 18, laser beam 20 is focused at its focal region 22 such that it has a divergence A of laser beam 20 in a direction along a target break line or along a direction of movement of laser beam 20 over glass ribbon 4 mediated by a moving device. p is the spread A in the direction perpendicular to the target break line s It is envisaged that the beam profile is formed to be 1.3-5 times, preferably 1.5-4 times, larger than the beam profile. If the beam profile is deformed too much, a too wide distribution of the light intensity may result, which is contrary to the effective formation of filamentary defects in the glass.

[0104] It is clear to the skilled person that the present disclosure is not limited to the embodiments specifically shown in the drawings, but can be modified in various ways within the scope of the features of the claims. For example, not only the examples (b), (f) and (g) but also many further shapes of the beam profile are possible, which are not mirror symmetric, especially with asymmetric beam profiles with respect to the mirror image perpendicular to the direction of travel. For example, the movement of the laser beam 20 to introduce a transverse target break line can also be performed by mechanically moving the optics, especially by moving the entire ultrashort pulse laser 16 together with the beam forming optics on the glass ribbon 4, in addition to the one shown in FIG. 3. For this purpose, the laser can be moved on a crossbeam, for example, by using a carriage, or the beam can be directed at the glass ribbon at various transverse positions using a deflection prism or mirror with a moving mirror. [Explanation of symbols]

[0105] 1 Glass plate 2 manufacturing equipment 2 Glass plate 4. Glass Ribbon 6 Slit-shaped nozzle 8. Hot forming equipment 10 Glass Melt 12 Target break line 121 Horizontal target break line 122 Vertical target break line 13 Ears 14 Filamentous scars 15 Pressing roll 16 Ultrashort Pulse Laser 18 Beam forming optics 20 Laser Beam 22 focal areas 24 Mobile Devices 26 Cooling device 27 Cooling Furnace 28 Separation device 29 Acceleration Belt 30 End 32~38 Beam Profile 39 Inspection Unit 40 Flat surface 41 Rough Surface 43 Progression of intensity of focal region 22 along the target break line 44 Progression of intensity of focal region 22 perpendicular to the target break line 51, 52 Side of glass ribbon 4 240 Conveyor Belt 241 Deflection optical system d Glass thickness

Claims

1. A method for producing a glass plate (2), comprising the following steps: hot forming from the glass melt (10) a continuous glass ribbon (4) having a predetermined glass thickness (d) in the range of 15 μm to 100 μm; - cooling the glass ribbon (4) at a selected cooling rate depending on the predetermined glass thickness (d), generating a laser beam (20) using at least one ultrashort pulse laser (16); using beam shaping optics to generate a focal area (22) of said laser beam (20) such that said focal area (22) is greater than a glass thickness of the glass ribbon (4); introducing, by means of the laser beam (20), targeted break lines (12) from the filamentary scratches (14) into the glass ribbon (4) such that the filamentary scratches (14) preferably extend from one side (51) to an opposite side (52) of the glass ribbon (4); In this case, the filamentary defects (14) are introduced at intervals along the target break line (12), In this case, a transverse target break line (121) across the glass ribbon (4) and two longitudinal target break lines (122) on either side of the glass ribbon (4) are generated, each having an edge with a thickened ear (13). - separating the ears (13) along the longitudinal intended break lines (122) to form ends (30); and - separating the glass sheets (2) by parting at transverse targeted break lines (121) running across the glass ribbon (4) to form edges (30); wherein the glass ribbon (4) is cooled at a cooling rate ranging from (1 / d)·4500 Kelvin / (sec·μm) to (1 / d)·9000 Kelvin / (sec·μm), where d represents a thickness of the glass ribbon (4).

2. 2. The method for producing a glass sheet (2) according to claim 1, characterized in that the glass ribbon (4) is cooled at a cooling rate of 100 Kelvin / s or more, particularly preferably 150 Kelvin / s or more or 200 Kelvin / s or more.

3. 3. The method for producing a glass sheet (2) according to claim 1 or 2, characterized in that the glass ribbon (4) is cooled before the introduction of the targeted break line (12) in the range of the glass transition temperature, preferably at a temperature below the softening point, particularly preferably at a temperature below the glass transition temperature, and in which the glass ribbon (4) is optionally additionally cooled during and / or after the introduction of the targeted break line (12).

4. 4. The method for producing a glass sheet (2) according to claim 1, characterized in that the cooling is carried out in a cooling oven (27), in particular by means of a heating element.

5. 5. The method for producing a glass sheet (2) according to claim 1, characterized in that the beam profile of the laser beam (20) is formed such that the divergence of the laser beam (20) is greater in the direction of the target break line (12) than in the direction transverse to the target break line (12).

6. 6. A method for producing a glass sheet (2) according to claim 1, characterized in that the beam-forming optics (18) produces a beam profile with a horizontal preferred direction, preferably an elliptical beam profile (32), or a drop-shaped beam profile (33), or a beam profile in the form of a double beam, or a rhomboid beam profile (35), or a dumbbell-shaped beam profile (36), or a wedge-shaped beam profile (37), or a beam profile with a main beam and a peripheral part with a weaker intensity or divergence (38).

7. 7. A method for producing a glass sheet (2) according to claim 1, characterized in that by means of the beam-shaping optics (18), the laser beam (20) is shaped in such a way that in its focal region (22) the divergence of the laser beam (20) in a direction along the target break line is in the range of 1.3 to 5 times, preferably in the range of 1.5 to 4 times, greater than the divergence in a direction perpendicular to the target break line.

8. 8. The method for producing a glass sheet (2) according to claim 1, characterized in that the filamentary scratches (14) are introduced by means of a laser beam (20) having an asymmetric beam profile with respect to a mirror image perpendicular to the direction of travel.

9. 9. The method for producing a glass sheet (2) according to claim 1, characterized in that the filamentary scratches (14) are introduced side by side at a distance of at most the size of the glass thickness (d), advantageously with an average distance between adjacent filamentary scratches (14) in the range of 1 μm to 10 μm, preferably in the range of 3 μm to 8 μm.

10. 10. The method for manufacturing a glass sheet (2) according to claim 1, characterized in that the introduction of the target break lines (12) is performed in the following sequence: first across the glass ribbon (4), to create a transverse target break line (121), and then longitudinally relative to the glass ribbon (4), to create a longitudinal target break line (122).

11. 11. A method for producing a glass sheet (2) according to claim 1, characterized in that a plurality of ultrashort pulse lasers (16) are used, wherein at least one first ultrashort pulse laser (16) introduces a transverse target break line (121) and at least one second ultrashort pulse laser (16) introduces a longitudinal target break line (122).

12. 12. Method for producing a glass sheet (2) according to any one of claims 1 to 11, characterized in that the axial position of the glass ribbon (4) is fixed in the focal area, preferably by means of at least one pressing roll, pressing edge or by suction.

13. 13. A method for producing a glass sheet (2) according to claim 1, characterized in that the separation of the ears (13) at the longitudinal targeted break lines (122) and the separation of the glass sheet (2) by parting at the transverse targeted break lines (121) running across the glass ribbon are performed mechanically.

14. Use of a glass sheet produced by a method according to any one of claims 1 to 13, for an insulating intermediate substrate or spacer for electronic components, for the encapsulation of optoelectronic components, as a support for thin-film cells, e.g. thin-film batteries or thin-film solar cells, as a composite substrate for displays and for microfluidic cells.

15. An apparatus (1) for the manufacture of a glass sheet (2) according to any one of claims 1 to 13, comprising: an apparatus (8) for hot forming from a glass melt (10) a continuous glass ribbon (4) having a predetermined glass thickness (d) in the range of 15 μm to 100 μm; at least one ultrashort pulsed laser (16) for generating depthwise spaced filamentary defects (14) in a predetermined volume of the glass ribbon (4) to form transverse target break lines (121) across the glass ribbon (4) and to form longitudinal target break lines (122) on opposite sides of the glass ribbon (4) each having an edge with thickened ears (13), and beam forming optics (18) for generating a laser beam (20) having a focal area (22) that is adjustable to be larger than the glass thickness (d); a movement device (24) for positioning the laser beam (20) along a predetermined path of a target break line (12) on the glass ribbon (4), and a cooling device (26) arranged and adjusted to cool the glass ribbon (4) at a selected cooling rate in dependence on a predetermined glass thickness (d) before introducing filamentary scratches (14) into the glass ribbon (4); The device (1).

16. 16. The apparatus (1) according to claim 15, characterized in that the separating device (28) is arranged and adjusted to separate, preferably mechanically, the ears (13) along the longitudinal target break lines (122) and the glass sheets by dividing them at transverse target break lines (121) running across the glass ribbon (4) to form respective ends (30).

17. 17. Apparatus (1) for producing glass sheets (2) according to claim 15 or 16, characterized in that the moving device (24) for moving the glass ribbon (4) comprises at least one pressing roll, pressing edge or suction device for fixing the position of the glass ribbon (4) in a focal region.

18. The beam forming optics (18) has at least one of the following characteristics: the beam shaping optics (18) are adjusted such that a beam profile of the laser beam (20) is formed such that the divergence of the laser beam (20) in the direction of the target break line (12) is greater than in the direction across the target break line (12); the beam-shaping optics (18) are adjusted such that the laser beam (20) is shaped in its focal region (22) such that the divergence of the laser beam (20) in a direction along the direction of movement of the laser beam (20) mediated by the movement device on the glass ribbon (4) is in the range of 1.3 to 5 times, preferably in the range of 1.5 to 4 times, greater than the divergence in a direction perpendicular to the target break line; 18. Apparatus (1) according to any one of claims 15 to 17, characterized in that it comprises:

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