Glass pane and assembly of glass panes with low degree of fine waviness, and methods for producing and using same

Abstract

The invention relates to a glass pane, in particular a glass pane which is obtained by individualizing a floated glass strip formed by means of a hot forming process, in particular comprising a borosilicate glass, with a thickness (D) ranging from at least 1.75 mm to maximally 7 mm or a thickness (D) ranging from at least 0.7 mm to 7 mm, in particular from 1.1 mm to maximally 7 mm, and comprising an upper face and a lower face. The glass pane is characterized by a fine waviness of 10 nm to 26 nm, preferably between 10 nm and 15 nm, in at least one direction parallel to the surface of the glass pane on at least one surface of the upper face or the lower face of the glass pane. The invention also relates to an assembly of said glass panes and to methods for producing and using same.

Description

[0001] GLASS PANE AND ENSEMBLE OF GLASS PANES WITH LOW WAVEL AND METHOD FOR THE PRODUCTION AND USE THEREOF

[0002] Description

[0003] Field of the invention

[0004] The present application relates to a floated glass pane, preferably a glass pane with low optical defects, in particular low fine waviness, an ensemble of floated glass panes, a method for their production and their use.

[0005] Background of the invention

[0006] Glass panes can be used in a wide variety of applications, for example in vehicle windows, in architectural applications or as covers for electronic devices (so-called display panes).

[0007] For example, the German patent application DE 10 2007 025 687 B3 describes the use of a glass pane made of borosilicate glass in a

[0008] Flat glass display device and a flat glass display device equipped in this way.

[0009] International patent application WO 2018 / 114956 A1 describes a thin glass substrate as well as a method and apparatus for its production. In the process for producing the thin glass substrate, the viscosity of the glass is specifically adjusted.

[0010] The international patent application WO 2019 / 076492 A1 also describes a thin glass substrate, in particular a borosilicate glass thin glass substrate, as well as a method and a device for its production, wherein here too the viscosity of the glass is specifically adjusted in the production process.

[0011] Finally, German patent application DE 10 2020 104 973 A1 describes a glass substrate for a vehicle windshield, particularly for a vehicle windshield. For this purpose, the aging rate of the glass is specifically adjusted.

[0012] Documents WO 2021 / 216362 A1 and WO 2021 / 222161 A1 describe liquid crystal cells comprising low-waviness substrates produced using a fusion-draw process. WO 2022 / 115280 A1 discusses substrates for micro-LEDs and for the transfer of microelectronics and discloses low-waviness substrates produced using a fusion-draw process. None of these three documents provides a reproducible technical teaching of how these substrates are actually produced. These substrates do not comprise floated glass panes, meaning they do not comprise glass panes produced using a float process.

[0013] US 2002 / 0012160 A1 discloses a glass substrate for a display manufactured using a float process. A WcA value (filtered center line waviness, also referred to as "filtered center line waviness") of 0.03 to 0.5 pm is specified according to JIS B0651, which was determined using a surface roughness measuring device with a phase-compensated 2RC zone filter with limit values ​​of 0.8 to 25 mm over a measuring length of 200 mm. Glass substrates with lower center line waviness are obtained through surface treatment measures such as polishing. However, these low center line wavinesses obtained through surface treatment are considered unsuitable for display applications due to electrostatic charging.

[0014] State-of-the-art glass panes therefore generally still exhibit quite pronounced, particularly lens-like, optical defects, which may be caused, for example, by a relatively high degree of fine waviness, and require further surface treatment such as polishing. Therefore, there is a need for methods for producing glass panes that can further reduce optical defects, particularly fine waviness, as well as for glass panes with preferably minimal optical defects, particularly minimal waviness, which, in particular, do not require any further surface treatment.

[0015] Object of the invention

[0016] One object of the invention is to provide a glass pane that at least partially mitigates the above-described disadvantages of the prior art. A further aspect is to provide a method for producing such glass panes and the use of these glass panes.

[0017] The object of the invention is achieved by the subject matter of the independent claims. Preferred and specific embodiments can be found in the dependent claims, the description, and the drawings of the present disclosure.

[0018] In a glass pane, particularly as considered within the scope of the present disclosure, thus in a glass pane obtained by a hot-forming process comprising floating, with substantially parallel main surfaces, a deflection of the beam path of light passing through it can occur, as a result of which at least a portion of this light changes its direction of propagation. This deflection can occur due to deviations of the surface of the glass pane from an ideally flat surface, which then results in not only a merely parallel offset of the beam path of this light perpendicular to its direction of propagation, as in the ideal case, for example, when the light passes through the glass pane at an angle relative to the glass pane, but various types of deflection of the beam path can occur.Roughness of at least one of the surfaces of the glass pane can cause irregular scattered light, which, when viewed through such a glass pane, essentially only leads to a reduction in the contrast of objects lying behind the glass pane, i.e. on the side of the glass pane facing away from the viewer.

[0019] However, if the glass pane not only has irregular, thus statistically fluctuating surface structures, but also a wavy surface, i.e. periodic elevations extending spatially at least in one direction, this can cause disturbances which, when viewed through the glass pane, can change, in particular distort, the image of objects behind the glass pane. These image-changing periodic disturbances in the beam path are also referred to herein as optical disturbances and can be detected, for example, as waviness in the surface of the glass pane. Such distortions can be particularly disturbing, for example, when viewing a display or indicator device that uses a glass pane as a cover, for example.

[0020] One aspect of the present invention is intended in particular to also mitigate these image-altering structures on at least one of the surfaces of the glass pane, but preferably both on the surface of the upper side of the glass pane and on the surface of the lower side of the glass pane, in particular without having to undertake surface-treating measures, such as polishing.

[0021] The invention has made it possible, in a surprisingly effective manner, to reduce optical defects directly during the hot-forming of a glass pane, without the need for subsequent surface treatment of the respective glass pane. Thus, the values ​​of fine waviness specified in the claims as well as in the present description and the figures refer in each case to a hot-formed glass pane immediately after its removal from the float bath and, in particular, to a glass pane obtained by singulation from a floated glass ribbon formed according to the invention by hot-forming, which, however, was not subjected to any surface treatment, in particular surface-modifying measures that have a measurable influence on the fine waviness, either during or after hot-forming.

[0022] The periodic elevations on the surface of at least one side of the glass pane, which extend spatially at least in one direction, are also referred to as waviness in the context of the present disclosure and can be measured, for example, profilometrically using a variety of commercially available devices known to those skilled in the art.

[0023] However, since the present disclosure does not address any waviness, but rather specific forms of waviness within a defined spatial spectrum extending in a spatial direction, preferably perpendicular to the drawing direction, the present disclosure also distinguishes itself from any form of waviness by using the term "fine waviness." The metrological detection of this fine waviness is described in more detail below.

[0024] To determine the fine waviness, the surface of a glass pane was measured using a Surfcom 1400-350 surface and contour measuring device from ZEISS (release P000083259) along a line perpendicular to the drawing direction Y, thus running in the X direction, on the top surface and the bottom surface of the respective glass pane within a measuring area M1 to M8 and M1' to M8'. The aforementioned X direction can be seen, for example, in the Cartesian coordinate system shown in Figures 1 to 4. A lower limit wavelength Ac (cut-off) of 0.25 mm was selected, and 8 mm was chosen as the upper limit wavelength Zf (cut-off). A Gaussian filter was used for filtering. The fine waviness values ​​output by this contour measuring device are also referred to in the art as Wfpd values, and are also output accordingly by this measuring device.The unfiltered primary profile (P profile), thus the actually measured surface profile, can be converted into the waviness profile (W profile) and the roughness profile (R profile) by filtering it, in particular according to DIN EN ISO 11562 / DIN EN ISO 16610-21, whereby the determining variable for the boundary between waviness and roughness, thus the lower limit wavelength Ac (cutoff), was chosen to be 0.25 mm, in order in particular to also not include the roughness components mentioned above, which only lead to an irregularly statistically distributed deflection of light passing through the glass pane, in the results of the present measurement.

[0025] The upper limit wavelength f (cut-off) was chosen to be 8 mm in order to exclude wavinesses which are essentially no longer of interest for the application of the present invention from being recorded by the present measurement, since wavinesses with a wavelength of more than 8 mm are only very weakly noticeable as optical disturbances for the use of the glasses according to the invention.

[0026] The measurement data obtained here were reported in accordance with EN ISO 4287:1998, which specifies the geometric product specifications (GPS) of surface finish. The wavinesses measured within these cut-off wavelengths of Ac (cut-off) = 0.25 mm to f (cut-off) = 8 mm are referred to as fine wavinesses in the context of this disclosure and are specified with their respective values ​​in accordance with the standard.

[0027] The present invention relates to a glass pane, in particular a glass pane comprising a borosilicate glass or made of a borosilicate glass, with a thickness of between at least 1.75 mm and at most 7 mm or with a thickness of between 0.7 mm and at most 7 mm, in particular between 1.1 mm and at most 7 mm. The glass pane comprises a top side and a bottom side, each defining a surface of the glass pane, wherein these surfaces extend substantially parallel to one another. The thickness D of the glass pane 33, 33', 33" hot-formed by means of floating is referred to as the distance between the top surface, thus the top side, and the bottom surface, thus the bottom side, as is also shown, for example, in Figure 4 for the hot-formed glass ribbon 13 from which the glass panes 33, 33', 33" are individually cut.

[0028] According to a first aspect of the invention, a glass pane is provided, in particular a glass pane obtained by singulation from a floated glass ribbon formed by hot forming, in particular comprising a borosilicate glass, with a thickness D between at least 1.75 mm and at most 7 mm or with a thickness D between at least 0.7 mm and at most 7 mm, in particular between 1.1 mm and at most 7 mm, comprising an upper side and a lower side, characterized by a fine waviness on at least one surface of the upper side or the lower side of the glass pane of 10 nm to 26 nm, preferably between 10 nm and 15 nm, in at least one direction parallel to the surface of the glass pane.

[0029] In this case, the fine waviness is measured, for example, on the surface of the top side or the surface of the bottom side of the glass pane along a line ML with a length of 260 mm, preferably within a square area Ml to M8 and Ml 'to M8' of 260 mm by 260 mm and amounts to at least 10 nm to 26 nm, preferably between 10 nm and 15 nm. As can be seen, for example, from Figures 7a and 7b, the measuring surfaces Ml to M8 and Ml ' to M8' can also be located on a single contiguous region of the glass ribbon 13, in particular on a single glass pane 33, 33', 33" separated therefrom, so that the properties disclosed here also apply to separated glass panes 33, 33', 33" which have an extension in the X direction which is greater than the length of an individual one of the measuring surfaces Ml to M8 and Ml ' to M8'.

[0030] The above-mentioned at least one direction corresponded in each case to the X-direction of the Cartesian coordinate system shown in Figures 1 to 4 and thus ran perpendicular to the drawing direction Y used in hot forming, in which the distance from a component for throughput regulation, the tweel or control slide, is also indicated, wherein the side of the tweel or control slide facing the float bath, as shown in Figure 5, is at a distance of zero m at a location in the drawing direction Y and thus represents the starting point for distance information which is in each case indicated for the center Mi of the float bath with respect to the X-direction.

[0031] This at least one direction can be indicated on the glass pane or on the packaging of the glass pane to ensure the simplest possible further processing of the glass pane. Alternatively, this at least one direction can also be determined independently of any indication of the at least one direction, in particular independently of the indication "perpendicular to the drawing direction," by measuring the respective direction with the smallest fine waviness.

[0032] A preferred embodiment also relates to an ensemble of glass panes comprising a plurality of glass panes, in particular at least eight glass panes, according to claims 1 to 4, in which the median of the fine waviness of the ensemble has a value which is less than 20 nm. The ensemble of glass panes can, for example, as can be seen from Figures 7a and 7b, comprise glass panes 33, 33', 33", in which all or at least more than one of the measuring surfaces M1 to M8 and M1' to M8' are located on a single contiguous region of the glass ribbon 13, in particular on more than one single glass pane 33, 33', 33" separated therefrom. In this case, one of the separated glass panes of the ensemble can also have an extension in the X direction which is greater than that of one of the measuring surfaces M1 to M8 and M1' to M8'.

[0033] In other words, according to the present disclosure, a glass pane is provided which has particularly small optical defects, which can be caused in particular by fine waviness.

[0034] This was previously unknown. However, the low fine waviness of the glass pane according to the present application is particularly advantageous for applications of the glass pane, for example, in electronic devices and displays, where it can be used as a cover pane. The glass panes according to the invention are also advantageously suitable for use as glazing, in particular as architectural glazing.

[0035] It is furthermore advantageous, particularly with regard to the scratch resistance and chemical resistance of the glass pane, if it comprises a borosilicate glass comprising the following components in wt.%:

[0036] SiCh 70 to 87, preferably 75 to 85

[0037] B2O3 5 to 25, preferably 7 to 14

[0038] AI2O3 0 to 5, preferably 1 to 4

[0039] Na2O 0.5 to 9, preferably 0.5 to 6.5

[0040] K2O 0 to 3, preferably 0.3 to 2.0

[0041] CaO 0 to 3

[0042] MgO 0 to 2.

[0043] This type of borosilicate glass offers particularly good scratch and chemical resistance. It also makes it possible to produce glasses with a low coefficient of thermal expansion. The linear thermal expansion coefficient in the range between 20°C and 300°C is preferably less than 5 x 10' 6 / K, but preferably at least 3.0 * 10' 6 / K.

[0044] According to one embodiment, the glass pane is particularly preferably designed as a float glass pane. This preferably allows for particularly low fine waviness.

[0045] Advantageously, such a glass pane can be produced in a method according to a further aspect of the present disclosure. The present disclosure therefore also relates to a method for producing a glass pane, in particular a method for continuously producing a glass pane, in particular a glass pane according to one embodiment, comprising the steps

[0046] - Providing a mixture comprising glass raw materials, - Melting the mixture to obtain a glass melt,

[0047] - Adjusting the viscosity of the glass melt,

[0048] - Transferring the glass melt into a device for hot forming by means of floating to form a glass ribbon,

[0049] - separating the hot-formed glass ribbon to obtain a glass sheet, the viscosity in the hot-forming device being adjusted so that the sum of the decimal logarithms at the distance from a flow control component, at which the glass has reached its maximum width after impacting the float bath, is 1g (r|A / dPa*s) and at the end of hot-forming is 1g (r|E / dPa*s) between at least 11.4 and at most 11.8.

[0050] In a further preferred embodiment, the viscosity in the hot-forming device is adjusted such that the sum of the decimal logarithms at the distance from a flow control component, at which the glass has reached its maximum width after impacting the float bath, is 1g (r|A / dPa*s) and at the end of hot-forming is 1g (r|E / dPa*s) between at least 11.4 and at most 11.6.

[0051] In other words, the method according to the present disclosure comprises a step in which the viscosity of the glass melt is adjusted such that a certain minimum viscosity of the glass is never undercut. On the contrary, the viscosity is specifically adjusted, for example by deliberately cooling the glass before transferring it to the hot-forming device. However, the targeted adjustment of a relatively high viscosity does not only occur at the beginning of the method; rather, it is advantageous to specifically adjust the overall viscosity during the process. For this purpose, the sum of the decimal logarithms of the glass viscosity r| of the glass encompassed by the glass sheet at the distance from a component for throughput regulation, at which the glass has reached its maximum width after impacting the float bath and at the end of hot-forming, is a suitable measure.For this purpose, the decimal logarithm of the viscosity r|A, thus 1g (r|A / dPa*s), is determined at the distance from a component for flow regulation, at which the glass has reached its maximum width after hitting the float bath, and the decimal logarithm of the viscosity T|E, thus 1g (T|E / dPa*s), at the end of hot forming, and the sum of these values ​​is within the limits mentioned above, i.e. between at least 11.4 and at most 11.8 or preferably also between 11.4 and at most 11.6.Since in this sum the logarithmic values ​​of the viscosities r|A and r|E are added, thus forming 1g (r|A / dPa*s) + 1g (r|E / dPa*s), this also corresponds to the decimal logarithm of the multiplication of these viscosity values, 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 1g (r|A / dPa*s * r|E / dPa*s). Insofar as a multiplication of the viscosity values ​​r|A and r|E, or of viscosity values ​​in general, is mentioned within the scope of the present disclosure, such as in the legends to the attached figures, this is also intended to disclose the addition of their respective decimal logarithms.

[0052] Until now, it was known to set the viscosity at the beginning of the hot forming process to a specific value, and also to choose this value relatively low. However, it has been shown that a significant degree of fine waviness was still obtained in this way. This is particularly evident upon closer examination of the surface properties, especially the fine waviness disclosed here.

[0053] Until now, it was assumed that, in order to achieve minimal fine waviness, it was advantageous if the viscosity was low at the beginning of the hot forming process, i.e., during and shortly after transferring the molten glass to a hot forming device. The idea was that this would result in a low-viscosity liquid that could compensate for any waviness by flowing during the hot forming process itself.

[0054] Surprisingly, however, it has been shown that this is not the case. In fact, it surprisingly appears to be significantly more advantageous for the formation of particularly fine waviness if the viscosity is initially deliberately set high. The mechanism behind this is not yet fully understood. Furthermore, careful monitoring of the viscosity - and correspondingly of the temperature control - during the process is extremely advantageous. It has also been shown that good, i.e. low, fine waviness cannot be achieved simply by deliberately setting a high initial viscosity. Rather, it is important to take an overall view of the viscosity in the forming process. One measure for this is the sum of the decimal logarithms at the distance from a component for throughput regulation, at which distance the glass has reached its maximum width after hitting the float bath, and at the end of hot forming.According to the process, the viscosity is adjusted so that the sum of the decimal logarithms of the viscosity at the distance from a component for flow control, at which the glass has reached its maximum width after hitting the float bath, and at the end of hot forming is between at least 11.4 and at most 11.8.

[0055] The "distance from a flow control component at which the glass has reached its maximum width after impacting the float bath" and the "end" of hot forming are initially understood to be spatial limitations of the process. The start of the thickness-related forming process or the forming section Hs, within which a defined glass thickness is set, is represented by the first top roller 12, 42, which is located at the beginning of the second float bath section 28, also referred to as Bay 2 or float bath section 2, but at a different distance from the flow control component than the distance at which the glass has reached its maximum width after impacting the float bath.The first top roller is located approximately 4.5 m away from the throughput control component, the tweel, in the flow or drawing direction Y. More precisely, the beginning of the thickness-related hot forming section, within which the glass undergoes its defined thickness change, is defined by the perpendicular 52 in the negative z-direction, starting from the symmetry axis 50 of the top roller 42 to the upper surface 36, thus to the upper main surface 48 of the glass 8 to be hot formed. However, the particularly defined thickness-related hot forming is only a part of the overall hot forming.In the context of the present disclosure, the upper surface and the lower surface are also referred to as the upper main surface and the lower main surface, respectively, since these main surfaces each have the largest areal extent compared to lateral surfaces, i.e. surfaces which extend perpendicularly or transversely to these main surfaces, in particular after the respective glass panes have been separated, perpendicularly or transversely to them.

[0056] The end of the hot-forming section is determined by the last top roller 40, 44, which exerts a shaping influence on the glass ribbon to be hot-formed in the flow or drawing direction, and is located approximately 10.5 m to 11.1 m away from the throughput control component, the twelfth roller 17, in the flow or drawing direction Y. More precisely, the end of the hot-forming section is defined by the perpendicular 53 in the negative z-direction, starting from the axis of symmetry 51 of the last forming top roller 44 to the upper surface, in particular to the main surface 48, of the glass 8 to be hot-formed. The aforementioned top rollers 12 and 42, as well as 40 and 44, can also be clearly seen, for example, in the attached Figures 3 and 4.

[0057] The lower surface or lower main surface 49 of the glass to be hot-formed rests on the float bath 7 during hot-forming.

[0058] Advantageously, according to one embodiment, the viscosity is set such that the decimal logarithm of the viscosity at the distance from a component for throughput regulation, at which the glass has attained its maximum width after it has hit the float bath, thus in particular at a distance in the drawing direction Y from a component for throughput regulation, the tweel, of 1.5 m and in particular at the beginning of a second float bath section (or float bath section 2), is at least 5.0, particularly preferably at least 5.1, and preferably less than 5.25, and preferably the decimal logarithm at the end of hot forming, in particular at a distance in the drawing direction of approximately 10.5 m to 11.1 m after the component for throughput regulation, the tweel, and in particular at the beginning of a fourth float bath section, is at least 6.2, preferably at least 6.3, particularly preferably at least 6.35, with a preferred upper limit being at most 6.5.

[0059] The inventors believe that, contrary to previous assumptions, the fine waviness of the glass surface can be significantly reduced by conducting relatively cold hot forming, especially at the beginning. Previously, it was assumed that a warm operating mode, particularly in the area of ​​a glass production unit where the glassy material is transferred from a melting unit to a hot forming area, is advantageous in reducing surface structures such as fine waviness.

[0060] In fact, it has been shown that a so-called “hot procedure”, i.e. a procedure in which the viscosity at the beginning of the hot forming process is low and, for example, significantly less than IO 5,0dPa*s, elongated elevations, also known as draw marks, which occur essentially in the direction of drawing of a float glass, can be reduced. These draw marks form cylindrical lens-like structures extending in the drawing direction, the refractive power of which then becomes noticeable essentially perpendicular to the drawing direction. However, it has been found that these draw marks, i.e. thickness fluctuations of the glass ribbon occurring transversely to the drawing direction and extending in the drawing direction, are not the cause of the fine waviness addressed here. Rather, there are other phenomena that overlay the formation of draw marks and which are essentially not influenced by measures that merely suppress the formation of draw marks.

[0061] Surprisingly, this observation has shown that in processes where the viscosity of the glassy material is deliberately set low when moving away from a component for flow control, at which point the glass has reached its maximum width after hitting the float bath, for example at below 10 5,0 dPa*s, the resulting glass ribbon exhibits fewer draw marks, but other surface structures, particularly those occurring in the drawing direction, may be more prominent. These are small-area structures that do not form elevations or depressions parallel to the drawing direction.

[0062] humiliations (as in the so-called stripes), but rather form irregular structures reminiscent of leopard skin or “orange peel”.

[0063] For the overall improved surface quality of glass ribbons or glass sheets produced in this way (after singulation), it is therefore not only the adjustment of the viscosity at the beginning of the hot forming process that is important, as previously thought. Rather, it is particularly advantageous to consider the overall viscosity during the hot forming process. It has been shown that the viscosity at the distance from a component for flow control, at which point the glass has reached its maximum width after impacting the float bath, as well as at the end of the hot forming process, is a good measure for evaluating the process. A simple measure for evaluating the process can be the sum of the decimal logarithms of the viscosity at the distance from a component for flow control, at which point the glass has reached its maximum width after impacting the float bath, 1g (r|A / dPa*s), and at the end of the hot forming process, 1g (r|E / dPa*s).According to the process, the sum of the decimal logarithms of the viscosity at the distance from a component for flow control, at which the glass has reached its maximum width after hitting the float bath and at the end of hot forming, is between a minimum of 11.4 and a maximum of 11.8.

[0064] Preferably, the decimal logarithm of the viscosity at the end of hot forming, in particular at the beginning of a fourth float bath section at a distance of approximately 10.5 m to 11.1 m from a component for regulating the flow of glass to be hot formed, is at least 6.2, preferably at least 6.3, particularly preferably at least 6.35, with a preferred upper limit being at most 6.5. At this point in the hot forming process, for example at the end of a fourth float bath section, the glass ribbon no longer contracts as strongly as before in a hot forming process, so that there it is drawn mainly in the drawing direction by means of so-called border rollers or top rollers, and the colder the glass ribbon, the stronger the drawing.While this is true in principle, it has been shown that, especially when the viscosity of the glass ribbon is already at least 5.0, particularly preferably at least 5.1, and less than 5.25 at the distance from a throughput regulation component, at which point the glass has reached its maximum width after hitting the float bath, in particular upstream of a throughput regulation component and / or at the beginning of a first float bath section, there must be strong pulling by the top rollers, especially by the last top roller. At this point, pull is preferably applied in the pulling direction. However, the top rollers are preferably positioned in the middle of the hot forming process at an angle of up to 15° to the outside. The high viscosity at the end of the forming process prevents the glass ribbon from narrowing (contracting), for example due to the pull of the cooling track rollers.

[0065] In a further preferred embodiment, the value of the difference between the decimal logarithms of the viscosity at the distance from a flow control component at which the glass has reached its maximum width after impacting the float bath 1g (r|A / dPa*s), and the viscosity at the end of hot forming 1g (r|E / dPa*s) is between at least 1.2 and at most 1.5, in particular between at least 1.2 and at most 1.45 and is preferably 1.42.

[0066] Until now, a "cold" operating mode, at least at the beginning of the hot forming process, has generally been considered unfavorable in glass production. This is due not only to the fact that it would allow for more precise monitoring of the entire manufacturing process, especially the hot forming process, but also because it only allows for a comparatively low throughput.

[0067] Such a process can advantageously be carried out by floating. However, other glass production processes, in particular a drawing process in general, can also be used to produce a glass pane with advantageously low fine waviness, in particular a glass pane according to embodiments. In such a process, in particular a continuous process, a glass ribbon is obtained, which can then be further processed after leaving a lehr. In particular, it is possible here to then separate this glass ribbon into a glass pane.

[0068] Advantageously, the process according to the present disclosure can, according to one embodiment, be carried out in plants designed for a throughput of less than 400 t of glass per day, preferably less than 200 t of glass per day and particularly preferably less than 1001 t of glass per day.

[0069] This is because the process is not only operated "cool", i.e. with a comparatively high viscosity, from a distance from the component for throughput regulation at which the glass has reached its maximum width after hitting the float bath, but the viscosity is also set very precisely at the end of the hot forming process. As explained, this is extremely advantageous for achieving an advantageously low level of fine waviness. The temperature in the hot forming process is generally set using heating units. However, if particularly cool temperatures are used, it must be taken into account that the glassy material itself also transports heat. From a certain throughput, and with further increasing throughputs, it may therefore be necessary to extract heat from the glassy material itself, for example using special cooling devices such as fans or similar.This not only means additional equipment and correspondingly higher costs, but can also lead to additional properties being imposed on the glassy material or the glass ribbon, such as thermal stresses.

[0070] However, if the throughput is limited, as stated above, for example, the heat transported by the glassy material itself can be dissipated more easily, for example, by adjusting the temperature of the tin bath in the respective float bath sections. Processes in units with relatively low throughputs are therefore particularly well suited for producing glass panes with advantageously low fine waviness and / or low near-surface refractive power, especially when the presently disclosed process is applied.

[0071] It is advantageous if the viscosity of the glass melt is also adjusted before transferring it to the hot forming device in front of a lip stone (or spout) or at the location of a lip stone.

[0072] Examples

[0073] Particularly advantageously, the described process can be used to produce glass panes made of or comprising a borosilicate glass. Exemplary compositions can be in the following composition range, given in wt. % on an oxide basis:

[0074] SiO2 70 to 87, preferably 75 to 85

[0075] B2O3 5 to 25, preferably 7 to 14

[0076] AI2O3 0 to 5, preferably 1 to 4

[0077] Na2O 0.5 to 9, preferably 0.5 to 6.5

[0078] K2O 0 to 3, preferably 0.3 to 2.0

[0079] CaO 0 to 3

[0080] MgO 0 to 2.

[0081] In particular, the glass of the glass pane may comprise the following components in wt% on an oxide basis:

[0082] SiO270 to 86

[0083] AI2O3 0 to 5

[0084] B2O3 9 to 25

[0085] Na2O 0.5 to 5

[0086] K2O 0 to 1 Furthermore, the glass of the glass pane may comprise the following components in wt.%:

[0087] SiO277 to 80

[0088] AI2O3 2 to 5

[0089] B2O3 9 to 11

[0090] Na2O 2.6 to 5.2

[0091] K2O 0.5 to 2.5

[0092] MgO 0 to 2

[0093] CaO 1.2 to 2.7

[0094] Description of the drawings

[0095] The invention is described in more detail below with reference to the accompanying drawings and with reference to preferred and particularly preferred embodiments.

[0096] They show:

[0097] Figure 1 is a schematic sectional view of an apparatus for producing a glass pane and for carrying out the method disclosed herein, in which the cutting plane runs vertically approximately through the center of the apparatus,

[0098] Figure 2 shows the schematic sectional view of Figure 1 in a highly simplified form, in which the section shown in Figure 4 is marked with the cutting planes A and B,

[0099] Figure 3 is a schematic plan view of a part of the device shown in Figures 1 and 2 for producing a glass pane, in particular a glass ribbon to be hot-formed on a float bath, in which, to simplify the illustration, only a part of the total top rollers used is shown by way of example, Figure 4 is a plan view, seen obliquely from above, of a part of the device shown in Figures 1 and 2 for producing a glass pane in the form of a section which extends between the cutting planes A and B,

[0100] Figure 5 is an exemplary representation of viscosity curves disclosed herein, in which in particular the viscosity values ​​r|A at a distance 56 from the component for flow regulation, at which the glass has reached its maximum width after impacting the float bath, and the viscosity values ​​r|E at the end of the hot-forming section, thus the location of the solder 53, can be seen. Figure 6 is the device shown in Figure 4 for producing a glass pane with measuring surfaces M1 to M8 indicated on the upper surface of the hot-formed glass ribbon, as well as a measuring line ML for determining the fine waviness of the upper surface of the hot-formed glass ribbon.

[0101] Figure 7a is a plan view of the upper surface of the glass ribbon after its hot forming within the section planes C and D shown in Figure 6 with the measuring surfaces M1 to M8, in each of which a measuring line ML is arranged,

[0102] Figure 7b is a plan view of the lower surface 49 of the glass ribbon 13 after its hot forming within the section planes C and D shown in Figure 6 with the measuring surfaces ML to M8', in each of which a measuring line ML is arranged,

[0103] Figure 8 shows a boxplot representation of the fine waviness values ​​obtained for various viscosity values ​​as a function of the viscosities 1g (r|A / dPa*s) and 1g (r|E / dPa*s), whereby these fine wavinesses are each given for fixed values ​​of the sum of the viscosities 1g (r|A / dPa*s) + 1g (r|E / dPa*s) and, in addition to these sums of the viscosities, their difference 1g (r|A / dPa*s) - 1g (r|E / dPa*s) is also given, whereby the value of all individual measurements leading to this boxplot representation is entered in each boxplot representation, Figure 9 shows a boxplot representation for various viscosity values ​​of obtained fine waviness values ​​as a function of the viscosities 1g (r|A / dPa*s) and 1g (r|E / dPa*s), whereby these fine wavinesses are each given for an interval of the sum of the viscosities 1g (r|A / dPa*s) + 1g (r|E / dPa*s) are given, and in addition to these sums of the viscosities, an interval of difference 1g (r|A / dPa*s) - 1g (r|E / dPa*s) is given,where the value of a single measurement is entered in the boxplot representation, which leads to the boxplot representation shown in Figure 9.

[0104] Detailed description of preferred embodiments

[0105] In the following description of preferred and particularly preferred embodiments, the same reference numerals in the various figures designate the same or equivalent components of the device disclosed here.

[0106] The information on the thickness D of the glass pane 33, 33', 33" corresponds to the distance between the two main surfaces, thus the top side 34 and the bottom side 35 of the glass pane 33, 33', 33" after its hot forming and is to be measured perpendicular to these main surfaces, as shown by way of example in Figure 4.

[0107] The float system shown in Figures 1, 2, and 3 for carrying out the presently disclosed method comprises a melting furnace 2, also referred to as a melting tank, into which a mixture to be melted, in particular glass mixture 3, is fed in a known manner and heated by burners 4 until a glass melt 5 of the desired composition is formed. Further devices for homogenizing the glass melt are known to those skilled in the art and will therefore not be described in detail.

[0108] The molten glass from the glass melt 5 flows through a channel 6, generally under the influence of gravity, into a float bath 7 containing liquid tin. The glass 8 to be hot-formed, as part of its hot-forming process, can spread laterally under the influence of gravity, reducing its height. To adjust the temperature of the glass to be hot-formed, the tin bath 7 can be arranged in a float bath furnace 9, which has electric ceiling heaters 10, by means of which the temperature of the glass to be hot-formed can be adjusted. Furthermore, the temperature of the tin bath 7 can be adjusted in a defined manner in the drawing direction, thus influencing the temperature of the glass to be hot-formed and thus its viscosity in a defined manner.

[0109] Upon leaving the melting tank 2, the molten glass 8 to be hot-formed is guided onto the tin bath 7 via an inlet lip 11, also referred to as a lip stone or spout, which runs diagonally downwards and on which it already begins to widen. At a distance of 1.5 m from the throughput regulation component, thus a distance of 1.5 m in the Y direction in the center Mi of the glass ribbon 13 with respect to the X direction, the glass ribbon 13 has its greatest width, which means its greatest extension in the X direction. In the disclosed embodiments, this distance is approximately 1.5 m and is indicated, for example, in Figure 4 with the reference numeral 56. Using roller-shaped top rollers 12 as a pulling device, the glass ribbon 13 forming on the tin bath 7 is influenced in a defined manner from the side as it expands.In Figure 1, only three top rollers are shown as examples, but more than two of these top rollers can be present and used as required, as can be seen, for example, in Figures 3 and 4.

[0110] A top roller is a substantially roller-shaped body well known to those skilled in the art, which, with its outer annular shoulder, is in contact with the main surface or upper surface 48 of the glass 8 to be hot-formed, facing away from the tin bath, and which, by rotating about its longitudinal or symmetry axis 50, 51, exerts a force on the glass 8 to be hot-formed. This symmetry axis 50, 51 is shown merely as an example for the top rollers 42 and 44. Within the scope of the present disclosure, the term "top roller" can also be understood as a substantially roller-shaped transport device for the glass to be hot-formed.In this case, the first top roller 12, 42 represents a substantially roller-shaped transport device for the glass to be hot-formed at the beginning of the section Hs of the, in particular, defined, thickness-related hot-forming section and the last top roller 40, 44 represents a substantially roller-shaped transport device for the glass to be hot-formed at the end of the section Hs of the hot-forming section. In the course of this thickness-related hot-forming section Hs, the thickness of the glass ribbon 13 is set in a defined manner, but this hot-forming section Hs does not include all hot-forming measures, since the glass 8 to be hot-formed of the glass ribbon 13 is already being formed from the distance 56 to the component for throughput regulation, at which distance the glass has reached its maximum width after hitting the float bath, up to the beginning of the gate Hs.

[0111] The part of the glass 8 to be hot-formed that is in contact with the outer annular shoulder of the respective top roller moves the glass in a defined manner. The top roller is driven in a defined manner by a motor-controlled, essentially rod-shaped axis.

[0112] In the context of the present disclosure, the location or position of the top roller, in particular in the flow direction Y of the glass 8, is understood to be the perpendicular 52, 53 in the negative z-direction starting from the respective axis of symmetry 50, 51 of the corresponding top roller 42, 44 to the surface, in particular to the main surface 48 of the glass 8 to be hot-formed.

[0113] The position or location of the first top roller 12, 42 defines the entry of the glass 8 into the section Hs for its hot forming with respect to its thickness.

[0114] The position or location of the last top roller 40, 44 defines the exit of the glass 8 from the section Hs for its thickness-related hot forming and thus for its overall hot forming.

[0115] For the sake of simplicity, in the context of this disclosure, the

[0116] The mention of the first top roller refers to the pair of top rollers, for example the top rollers 42, 12, which are located at the same location in the flow direction, and the mention of the last top roller refers to the pair of top rollers, for example the top rollers 44, 40, which are each located at the same location in the flow or y-direction.

[0117] The location of the entry of the glass 8 into the section Hs for thickness-related hot forming is therefore indicated by the dashed line 54, whereas the location of the exit of the glass 8 from the section Hs for hot forming is indicated by the dashed line 55.

[0118] A further dashed line indicates the location or distance 56 from the throughput control component at which the glass 8 to be hot-formed has reached its maximum width after hitting the float bath 7.

[0119] In the context of the present disclosure, the length Hsl of the section Hs for thickness-related hot forming is understood to be the distance in the flow or y-direction between the plumb line 52 of the first top roller 42 and the plumb line 53 of the last top roller 44.

[0120] After its hot forming, the glass ribbon 13 can optionally be transferred to a cooling furnace 14, which can also have electric ceiling and floor heaters 15 in order to subject the glass ribbon 13 to a defined temperature reduction, whereby only ceiling heaters are shown as an example in Figure 1.

[0121] After leaving the annealing furnace 14, the glass ribbon 13 is then available for further processing, in particular separation into glass panes 33, 33', 33".

[0122] In order to be able to more clearly illustrate spatial arrangements of various assemblies or properties, for example of glasses to be hot-formed or glass panes 33, 33', 33" separated after hot-forming, in the following description of preferred embodiments, reference is first made to the Cartesian coordinate system shown in Figures 1, 2, 3 and 4, which defines an orthogonal X, Y and Z direction, to which all information in the various figures subsequently refers.

[0123] The X and Y directions span a plane that extends horizontally and thus runs essentially parallel to the surface of the tin bath 7. Perpendicular to this plane, the Z direction extends upwards and thus also defines the normal direction with respect to the glass ribbon 13.

[0124] Reference is made below to Figure 1, which comprises, as a device for producing a glass ribbon 13 from which the presently disclosed glass panes 33, 33', 33" can be separated, the float system provided overall with the reference number 1, which has all the devices or apparatuses described with reference to Figures 2, 3 and 4.

[0125] The melting device 16 includes the melting tank or melting furnace 2, a feed device for the glass batch 3, and the burners 4. Furthermore, the melting tank 2 has a channel 6 for transferring the molten, hot-formed glass 8 to the tin bath 7.

[0126] For example, the control slide 17, thus the component for regulating the throughput of the glass flow, which is also referred to as a tweel, is arranged behind the channel 6. By moving the control slide or tweel 17, which form the component 17 for throughput regulation, in the direction of the double arrow shown next to the reference number 17, the cross-section of the channel 6 can be narrowed or enlarged, whereby the amount of molten glass 8 to be hot-formed emerging from the melting tank 2 per unit of time can be regulated and, in particular, set in a defined manner. Furthermore, a feeder trough can be arranged between the melting tank 2 and the float bath furnace 9, in particular upstream of the tweel 17, which in this case forms the channel 6, in particular over a longer distance than shown in Figure 1.A more detailed description of the flow rate regulation can be found in DE 10 2013 203 624 A1 of the same applicant, which is also made the subject of the present application by reference.

[0127] Viewed in the flow direction of the molten and hot-formed glass 8, a device 18 for the defined adjustment of the viscosity of the molten and hot-formed glass 8 is arranged upstream of the throughput regulation component 17 and upstream of the lip stone or spout 11.

[0128] This device 18 for the defined adjustment of the viscosity comprises a chamber 19, which is separated from the melting tank 2 or can also form a part of it and receives the molten glass 8 to be formed into a glass substrate for the defined adjustment of its viscosity.

[0129] Furthermore, the device 18 for the defined adjustment of the viscosity comprises fluid-flow regions 20, 21, in particular water-flow regions, which absorb heat from the glass 8 to be hot-formed and can be designed as a metallic pipe system. This metallic pipe system can also be colored for better heat absorption or provided with a temperature-resistant paint on its surface.

[0130] Alternatively or additionally, the walls 22, 23, 24 and 25 of the chamber 19 can also absorb heat from the glass 8 to be hot-formed by adjusting their temperature in a defined manner, for example by means of additional cooling devices.

[0131] The chamber 19, with its walls 22, 23, 24 and 25, can also be spatially separated from the melting tank 2 and have high-temperature-resistant metallic walls in order to provide improved heat dissipation.

[0132] As described above, the device 18 for the defined adjustment of the viscosity comprises at least one cooling device, by means of which the temperature and thus also the viscosity of the glass 8 to be hot-formed can be adjusted in a defined manner. Non-contact and, alternatively or additionally, direct temperature measurements in contact with the glass to be measured are known to those skilled in the art. Corresponding sensors are described, for example, with the sensor device or unit 26 within the scope of this disclosure.

[0133] The sensor device or unit 26 can be in direct contact with the glass and thus carry out a direct temperature measurement or can also comprise a radiation measuring device which measures the temperature by detecting the spectrum emitted by the glass 8 to be hot-formed on the basis of the spectrum itself and / or the intensity of the emitted radiation.

[0134] The device 1 comprises a device or device 47 for hot forming, which will be described in more detail below, which is located in the flow or drawing direction behind the device 18 for the defined adjustment of the viscosity and receives the glass 8 to be hot formed via the lip stone or spout 11.

[0135] The lip stone or spout 8 directs the glass 8 to be hot-formed onto a tin bath 7 which is held in the float bath furnace 9.

[0136] A further cooling device 57 is arranged at a distance from the throughput control component 17 of approximately 2 m relative to its center in the Y direction above the glass 8 to be hot-formed. This cooling device 57 protrudes above the melt and can be 300 mm wide in the Y direction, 80 mm high in the Z direction, and 2.5 m long in the X direction, and can be constructed in two parts. A part of the cooling device 57 protrudes from opposite sides in the X direction above the glass to be hot-formed, thus providing essentially complete coverage of the glass 8 to be hot-formed in the X direction and in some areas in the Y direction.

[0137] The cooling device 57 not only shades the glass 8 to be hot-formed from the ceiling heaters 10, but also creates a cooling air flow coming from above the glass 8, with which it is possible to cool the glass 8 located below the cooling device 57 by approximately 20 to 25 K. Given the already initially high viscosity of the glass 8, this allows an overall flatter viscosity curve to be generated in the further course in the drawing direction, as is also shown, for example, in Figure 5.

[0138] Above the glass ribbon 13 forming on the tin bath 7, as can also be clearly seen from Figure 3, further top rollers 38 to 44 are arranged next to the top roller 12 for the mechanical movement of the glass ribbon 13.

[0139] The number of top rollers shown in Figure 3 is merely exemplary, since in preferred embodiments of the invention, 10 to 12 pairs of top rollers are preferably used.

[0140] The top rollers 41 and 38 serve only to adjust the width of the glass ribbon Bg 13 resulting from the hot forming and are optional, since the width Bg can also be adjusted in other ways, for example by regulating the amount of glass 8 which is provided for hot forming.

[0141] Figure 3 further shows an alternative or additional embodiment of the device 18 for the defined adjustment of the viscosity. The molten glass 8 is located in a channel 6 which leads from the melting tank 2 (not shown in Figure 3) to the float bath furnace 9. The walls 45, 46 of the channel 6 are formed from a high-temperature-resistant metal, for example platinum, which can also be arranged as a metallic layer on a mineral refractory material. By defining the temperature of these walls, heat can be extracted from the glass 8 and its temperature and viscosity can also be defined. In this embodiment, too, the sensor unit 26 described above can preferably be arranged near the twelfth 17.

[0142] Above, a drawing device was described for the hot-forming device 47, which comprises a float device, in particular a float bath furnace 9 with a tin bath 7. The method disclosed here is described below using a float method as an example.

[0143] Figure 4 shows a section of the device 1 for producing a glass ribbon 13 for a glass pane 33, 33', 33" to be separated from it, extending between the sectional planes A and B, in which, for the sake of better visibility, only the glass 8 to be hot-formed and the float bath 7, which is designed as a tin bath, are shown.

[0144] The glass 8 moves from the left side of Figure 4 at an entry speed towards the first top roller 42, 12, at which the thickness-related hot forming disclosed here into a glass ribbon 13 for a glass pane 33, 33', 33" to be separated therefrom begins. This speed corresponds to the speed of the glass 8 at the first top roller 42, 12. The glass 8 moves after the last top roller 40, 44 thus, after its hot forming described here, into a glass ribbon 13 for a glass pane 33, 33', 33" to be separated therefrom with an exit thickness D, further in the flow direction.

[0145] Where, in the context of the present disclosure, only hot forming is referred to in abbreviated form, this refers, for the sake of linguistic simplicity, to the hot forming to form a glass ribbon 13, which is described in more detail below, for a glass pane 33, 33', 33" to be separated therefrom, in particular after the glass ribbon 13 has cooled, both along the section Hs of the thickness-related hot forming section, as well as further hot forming steps which may have already taken place before reaching the first top roller, such as when pouring the glass 8 onto the float bath 7, during which the glass can spread out over a large area and assume its equilibrium thickness Dg of approximately 7 mm + / - 1 mm.

[0146] After hot forming, the glass 8 has an exit thickness of D, which it has assumed after the last top roller 40, 44. During its entire thickness-related hot forming into a glass ribbon 13 for a glass sheet 33, 33', 33" to be separated therefrom, the glass 8 has a width Bg between the first top roller 42, 12 and the last top roller 40, 44, thus in section Hs, and thus an extension in the x-direction of Bg, which is preferably changed by less than 3% in the x-direction during this thickness-related hot forming. This can be ensured by adjusting the rotation speed and angle along the axis of symmetry (rotation axis) of the respective top rollers.In particular, the angle of the respective axis of symmetry of the corresponding top roller can be changed in such a way that during the transport of glass 8 to be hot-formed, in particular along the thickness-related hot-forming section Hs, more or less strong contributions of the movement of the glass 8 to be hot-formed or of parts of the glass ribbon 13 in the x-direction result.

[0147] At a distance 56 from a component for flow regulation 17, at which the glass has reached its maximum width after impacting the float bath, the viscosity r|A is adjusted, in particular by adjusting the temperature of the glass ribbon 13 at this location, such that it has a value of 1g (r|A / dPa*s), of at least 5.0, particularly preferably at least 5.1 and preferably less than 5.25.

[0148] At the end of the hot forming section Hs, the viscosity r|E is adjusted, in particular by adjusting the temperature of the glass ribbon 13 at this location, so that it has a value of 1g (r|E / dPa*s) which is at least 6.2, preferably at least 6.3, particularly preferably at least 6.35, with a preferred upper limit being at most 6.5.

[0149] According to the invention, the viscosity in the hot-forming device is adjusted such that the sum of the decimal logarithms of the viscosity 1g (r|A / dPa*s) and 1g (r|E / dPa*s) at the distance 56 from a component for flow regulation 17, at which the glass has reached its maximum width after impacting the float bath, and at the end of hot-forming is between at least 11.4 and at most 11.8 r| dPa*s. An exemplary representation of corresponding viscosity curves can be seen in Figure 5, which in particular also shows the viscosity values ​​r|A at the distance 56 from a component for flow regulation 17, at which the glass has reached its maximum width after impacting the float bath, and the viscosity values ​​r|E at the end of the hot-forming section, thus of the solder 53.

[0150] Reference is now made to Figure 6, which shows the apparatus illustrated in Figure 4 for producing a glass pane with measuring surfaces M1 to M8 indicated on the upper surface 48 of the hot-formed glass ribbon 13, as well as an exemplary measuring line ML for determining the fine waviness of the upper surface 48 of the hot-formed glass ribbon 13. Although the measuring line ML illustrated in Figure 6 is initially shown as a continuous line for the sake of simplicity, it consists of respective measuring lines ML of the measuring surfaces M1 to M8, as will be explained in more detail below with reference to Figures 7a and 7b.

[0151] Glass panes 33, 33', 33" isolated from the glass ribbon 13 can comprise one or more of these measuring surfaces or can also comprise portions of these measuring surfaces. From the data shown in Figures 8 and 9, which are explained in more detail below, it can also be seen that the fine waviness values ​​according to the invention are reliably achieved as soon as an isolated glass pane 33, 33', 33" with its dimensions in the X direction reaches at least the length of a measuring section ML, because even adjacent measuring sections ML, which do not each have to have been recorded over their entire length, essentially lead to the fine waviness according to the invention as soon as the total length of a measuring section ML is reached. The same applies to the measuring surfaces M1', M2', M3', M4', M'5', M6', M7' and M8' located on the underside 49. The dimensions of the glass panes 33' and 33" subsequently separated from the glass ribbon are shown in Figures 7a and 7b merely as an example.

[0152] In Figure 6, cutting planes C and D extending in the Z and X directions are also shown in dashed lines, through which the glass ribbon 13 passes in the drawing direction Y after its hot forming. The measuring surfaces M1 to M8 indicated on the upper surface of the hot-formed glass ribbon are shown as an example for a defined time t after the hot-forming of the glass ribbon 13 and migrate with the glass ribbon 13 in the drawing direction Y and form part of the upper surface of the hot-formed glass ribbon, in particular for its subsequent separation into glass panes 33, 33', 33". Since the glass ribbon is not subject to any further change in size after its hot-forming, the measurements were subsequently carried out on individual glass panes 33, in which a measured glass pane 33 each comprised one of the measuring surfaces M1, M2, M3, M4, M5, M6, M7 or M8 and comprised one of the measuring surfaces M1', M2', M3', M4', M5', M6', M7' or M8'.

[0153] The measuring surfaces M1, M2, M3, M4, M5, M6, M7, and M8 are shown arranged on the upper surface 48 in Figure 6 and each have a square shape with an extension of 260 mm in the X and Y directions. This dimension of 260 mm also represents the respective measuring length ML.

[0154] For the sake of clarity, the dimensions shown in the figures are not drawn to scale, but in particular the thickness D is initially shown greatly enlarged for the sake of easier recognition.

[0155] Fine waviness measurements were taken on the upper surface 48 and on the lower surface 49 along a measuring line ML shown in Figures 7a and 7b, respectively.

[0156] Since the measuring surfaces Ml, M2, M3, M4, M5, M6, M7 and M8 as well as the measuring surfaces Ml ', M2', M3', M4', M5', M6', M7' and M8' extend transversely to the extension of the glass ribbon 13 in the X direction, this enables the entire glass ribbon 13 used to separate the glass panes after hot forming to be recorded in the X direction.

[0157] Areas below the top rollers 38 to 44 were covered by the

[0158] Fine waviness measurements are not recorded and are, for example, delimited in the X direction by the lines Mtl and Mt2 from the area of ​​the glass ribbon 13 lying between these lines Mtl and Mt2, so that surface-altering effects of the top rollers were not recorded by the fine waviness measurements. Lateral edges, which may rise above the upper main surface 48 at the edge of the glass ribbon 13 in the Z direction, are located behind the top rollers 38 to 44 with respect to the center of the glass ribbon Mi and thus also lie outside a respective measuring range ML. These were therefore also not recorded by a respective fine waviness measurement.

[0159] Figure 7a shows a plan view of the upper surface 48 of the glass ribbon 13 after its hot forming within the sectional planes C and D shown in Figure 6 with the measuring surfaces M1 to M8, in each of which a measuring line ML is arranged, and Figure 7b shows a plan view of the lower surface 49 of the glass ribbon 13 after its hot forming within the sectional planes C and D shown in Figure 6 with the measuring surfaces ML to M8', in each of which a measuring line ML is arranged,

[0160] The measuring surfaces M1' to M8' indicated in Figure 7b on the lower surface 49 of the hot-formed glass ribbon 13 are also shown as an example for a defined time t after the hot-forming of the glass ribbon 13, migrate with the glass ribbon 13 in the drawing direction Y and form part of the lower surface 49 of the hot-formed glass ribbon 13, in particular for its subsequent separation into glass panes 33, 33', 33".

[0161] By way of example, glass panes 33 were in particular separated in such a way that each had a measuring surface of the measuring surfaces M1 to M8 on its upper surface and a measuring surface of the measuring surfaces M1' to M8' with numerical correspondence to the respective measuring surfaces on its lower surface.

[0162] To determine the fine waviness, the surface of a glass pane was measured using a Surfcom 1400-350 surface and contour measuring device from ZEISS (release P000083259) along a line perpendicular to the drawing direction Y, thus running in the X direction, on the top surface and the bottom surface of the respective glass pane within a measuring area M1 to M8 and M1' to M8'. The aforementioned X direction can be seen, for example, in the Cartesian coordinate system shown in Figures 1 to 4. For this device, a lower limit wavelength Ac (cut-off) of 0.25 mm and an upper limit wavelength f (cut-off) of 8 mm were selected. A Gaussian filter was used for filtering. The fine waviness values ​​output by this contour measuring device are also referred to in the art as Wfpd values ​​and are also output accordingly by this measuring device.

[0163] Figures 8 and 9 show boxplot representations known to those skilled in the art, which are each determined for a plurality of measured values, for example eight measured values ​​from eight measuring lines ML.

[0164] Just for the sake of completeness, it should be noted that a boxplot representation consists of a rectangular box with a line running across this box and "antennas" extending up and down from this box, which are also called "whiskers". This line running across the box corresponds to the median of the measured values, i.e. the value at which the first half of the measured values ​​are above or on this line and the second half of the measured values ​​are below or on this line. The upper limit of the box represents the three-quarters quartile of the measured values, at which three-quarters of the measured values ​​are below or on the upper limit of the box and one-quarter of the measured values ​​are above or on the upper limit of the box.The lower limit of the box represents the one-quarter quartile of the measured values, at which one-quarter of the measured values ​​are below or at the lower limit of the box and three-quarters of the measured values ​​are above or at the lower limit of the box. These antennae or whiskers, which extend upwards or downwards from the box, indicate expected values ​​with their lengths corresponding to 1.5 times the distance from the lower to the upper end of the box, unless the actually measured values ​​do not extend that far, in which case they extend from the lower end of the box to the respective measured minimum value or extend from the upper end of the box to the respective measured maximum value. Figure 8 shows a boxplot representation of the fine waviness obtained for various viscosity values ​​as a function of the viscosities 1g (r|A / dPa*s) and 1g (r|E / dPa*s).

[0165] As in Figure 9, the indication "Position Top" indicates the measured values ​​of the upper surface 48 of the glass ribbon 13, and in particular the measured values ​​of the surface of the top side 36 of glass panes 33, 33' and 33" separated from this glass ribbon. Also as in Figure 9, the indication "Position Bottom" indicates the measured values ​​of the lower surface 49 of the glass ribbon 13, and in particular the measured values ​​of the surface of the bottom side 37 of glass panes 33, 33' and 33" separated from this glass ribbon.

[0166] In Figure 8, the values ​​of the fine wavinesses are given as ordinate in a lower label line for fixed values ​​of the sum of the viscosities 1g (r|A / dPa*s) + 1g (r|E / dPa*s), and the values ​​of the difference of the viscosities 1g (r|A / dPa*s) - 1g (r|E / dPa*s) are given in an upper label line of the ordinate.

[0167] The sum of the viscosities given above was:

[0168] 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.15 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.17 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.31 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.37 1g ​​(r|A / dPa*s) + 1g (r|E / dPa*s) = 11.44 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.5 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.52

[0169] It can be seen that below a value of the sum of the viscosities of approximately 1g (T|A / dPa*s) + 1g (r|E / dPa*s) = 11.4, the values ​​of the fine waviness are above 26 nm, whereby this value of 26 nm is represented as a line labeled OSG in Figures 8 and 9. Above the value of the sum of the viscosities of 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.4, there is a range of decreasing fine waviness, in particular fine waviness with values ​​below 26 nm, in particular decreasing down to 10 nm.

[0170] For example, the values ​​of the fine waviness obtained on the underside for a sum of the viscosities of about 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.6 and a difference of the viscosities 1g (r|A / dPa*s) - 1g (r|E / dPa*s) = 1.42 certainly show values ​​between 10 nm and 15 nm.

[0171] The values ​​of the fine waviness increase again slightly from a value of the sum of the viscosities of about 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.42.

[0172] A preferred range arises in particular when the viscosity in the hot-forming device is adjusted such that the sum of the decimal logarithms of the viscosity at the distance from a component for throughput regulation, at which the glass has reached its maximum width after impacting the float bath 1g (r|A / dPa*s), and the viscosity at the end of hot-forming 1g (r|E / dPa*s) is between at least 11.4 and at most 11.6, because then the values ​​of the medians, for example of a plurality of glass panes, in particular of at least eight glass panes 33, 33', 33", in particular of glass panes 33, 33', 33" with the features of claims 1 to 4, each formed from the fine wavinesses measured along the line ML of a respective glass pane 33, 33', 33" of the ensemble, are each reliably at a fine waviness of 10 nm to 26 nm.It is assumed here that the respective glass pane 33, 33', 33" of the ensemble each comprised at least one dimension in the X-direction with the length of a complete measuring section Ml, even if this was not provided independently by a single measuring section ML, but rather from portions of, for example, two measuring sections ML. Up to a value of approximately 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.8, correspondingly measured values ​​of fine waviness of less than 26 nm could also be obtained.

[0173] Reference is made below to Figure 9, which shows a boxplot representation for different viscosity values ​​of obtained fine waviness values ​​as a function of the viscosities 1g (r|A / dPa*s) and 1g (r|E / dPa*s).

[0174] The values ​​of the fine wavinesses are given for an interval of the sum of the viscosities 1g (r|A / dPa*s) + 1g (r|E / dPa*s).

[0175] In addition to these sums of the viscosities, for the first interval, thus the interval on the left side of Figure 9, an interval of difference 1g (r|A / dPa*s) - 1g (r|E / dPa*s) is also given.

[0176] Surprisingly, the inventors have discovered a further advantageous criterion, which can be explained by way of example using the values ​​of the sums of the viscosities of 1g (r|A / dPa*s) + 1g (r|E / dPa*s) = 11.6 and the differences of the viscosities 1g (r|E / dPa*s) - 1g (r|A / dPa*s) shown in Figure 9.

[0177] In the interval of the middle representation of Figure 9, for which the sum of the viscosity values ​​is: 11.4 < 1g (r|A / dPa*s) + 1g (r|E / dPa*s) < 11.6, values ​​of less than 26 nm were already reliably achieved for the median of the ensemble described here for the fine waviness and, in particular, for the upper surface, 48 values ​​of the median of the fine waviness of the ensemble were measured, which are less than 20 nm and greater than 10 nm.

[0178] However, if an additional criterion was introduced, namely that the difference between the decadic logarithms of the viscosity at the distance from a component for flow regulation, at which the glass has reached its maximum width after hitting the float bath 1g (r|A / dPa*s), and the viscosity at the end of hot forming 1g (r|E / dPa*s) is between at least 1.25 and at most 1.45, preferably 1.42, then almost all measured values ​​of the fine waviness, in particular of an entire ensemble described here, were below 26 nm and the scatter of these values ​​was significantly reduced.

[0179] The fine waviness values ​​obtained with this additional criterion are shown in the left column of Figure 9.

[0180] In the interval of the left representation of Figure 9, for which the sum of the viscosity values ​​is: 11.4 < 1g (r|A / dPa*s) + 1g (r|E / dPa*s) < 11.6 and for the difference 1.25 < 1g (r|A / dPa*s) - 1g (r|E / dPa*s) < 1.45, values ​​of less than 20 nm were already reached for the median of the ensemble described here for the fine waviness for both the surface 48 and the surface 49 and the values ​​of the median were regularly greater than 10 nm.

[0181] Where median values ​​are given here, these were obtained for surface 48 from values ​​of the measuring surfaces M1 to M8, and for the underside from values ​​of the measuring surfaces M1' to M8'. However, if these values ​​did not include the outer measuring surfaces M1 and M8, as well as M1' and M8', the resulting fine waviness values ​​were generally smaller than those shown in Figures 8 and 9.

[0182] The value of the difference in viscosities 1g (r|E / dPa*s) - 1g (r|A / dPa*s) = 1.25 was achieved, for example, by the preferred viscosities 1g (r|A / dPa*s) = 5.1 and 1g (r|E / dPa*s) = 6.35. The value of the difference in viscosities 1g (r|E / dPa*s) - 1g (r|A / dPa*s) = 1.45 was achieved, for example, by the viscosities 1g (r|A / dPa*s) = 5.0 and 1g (r|E / dPa*s) = 6.45, whereby the above viscosity value at the end of hot forming of 6.45 is only slightly below the maximum limit of 6.5 specified as preferred and resulted from the process described here as its direct result.

[0183] However, if glass panes 30 were isolated which comprised the measuring surfaces M3 to M6 or M3' to M6' which are closer to the center line Mi in the X direction, then all values ​​of the fine waviness measured in these measuring surfaces along the respective measuring line ML were definitely below 26 nm. This means that all measured fine wavinesses were then below 26 nm within a positive and negative distance in the X direction to the center line Mi of 910 mm, as shown, for example, in the left column of Figure 9.

[0184] In particular, the statement of this paragraph also applies to intervals with 11.4 < 1g (r|A / dPa*s) + 1g (r|E / dPa*s) < 11.6 and 1.25 < 1g (r|A / dPa*s) - 1g (r|E / dPa*s) < 1.45, for which the value of the difference of the viscosities 1g (r|E / dPa*s) - 1g (r|A / dPa*s) = 1.5 was achieved, for example, by the viscosities 1g (r|A / dPa*s) = 5.0 and 1g (r|E / dPa*s) = 6.5,

[0185] It will be apparent to the person skilled in the art that such precise viscosity values ​​require both exact sensory detection of these viscosities, in particular by appropriate temperature measurements of the temperature of the glass ribbon 13 at the respective corresponding location, as well as suitable measures for the removal and supply of thermal energy.

[0186] For this purpose, the temperature of the glass can be detected by means of sensor devices or units 26, wherein these sensor units 26 not only preferably have to be arranged in the vicinity of the twelfth 17, but can also be located at other locations, in particular along the section Hsl for thickness-related hot forming, in order in particular to always detect the temperature of the glass ribbon 13 with the necessary accuracy and to be able to regulate it accordingly.

[0187] A corresponding heat supply can be carried out thermally locally controlled by means of the burners 4 and a sector-by-sector temperature-controlled float bath 7.

[0188] Appropriate heat dissipation can be achieved, for example, by special cooling devices such as fans, which are not shown in the figures but are known to those skilled in the art, or by cooling devices 57, which can be suitably arranged along the section Hs1 for thickness-specific hot forming. Sector-by-sector thermal control of the float bath 7 can also contribute to appropriate heat dissipation.

[0189] Furthermore, the amount of glass 8 to be hot-formed, in particular the glass ribbon 13 formed therefrom, can be adjusted per unit of time with the component for throughput regulation, in particular control slide or tweel 17, so that the temperature of the glass 8 to be hot-formed is always within a safe control range, which can be exceeded, for example, if the heat capacity of the glass, with increasing throughput, makes temperature control via the surface only more difficult due to the increasing glass volume.

[0190] Advantageously, the method according to the present disclosure can also be carried out in such a way that a throughput of less than 400 t of glass per day, preferably less than 2001 t of glass per day and particularly preferably less than 100 t of glass per day is obtained, wherein the throughput is determined on the basis of the amount of glass which is guided per unit of time through the component for throughput regulation, in particular the control slide or Tweel 17.

[0191] List of reference symbols

[0192] 1 float system

[0193] 2 melting tanks

[0194] 3 mixture to be melted, in particular glass mixture

[0195] 4 burners

[0196] 5 Glass melt

[0197] 6 channel

[0198] 7 Float Bath

[0199] 8 Hot-formed glass

[0200] 9 Float bath oven

[0201] 10 ceiling heaters

[0202] 11 Lipstone or Spout

[0203] 12 top rollers

[0204] 13 glass band

[0205] 14 Kühl of en

[0206] 15 ceiling and floor heaters

[0207] 16 Melting facility

[0208] 17 Component for flow regulation, in particular control slide or tweel

[0209] 18 Device for the defined adjustment of the viscosity of the molten and hot-formed glass 8 in front of the component for throughput regulation 17

[0210] 19 Chamber, which is separated from the melting tank 2 or can also form a part of it and receives the molten glass 8 to be formed into a glass ribbon 13 for the defined adjustment of its viscosity

[0211] 20 Fluid flow area

[0212] 21 Fluid flow area

[0213] 22 Wall of Chamber 19

[0214] 23 Wall of Chamber 19

[0215] 24 Wall of Chamber 19

[0216] 25 Wall of Chamber 19

[0217] 26 Sensory device or unit

[0218] 27 Bay or Tub Section 1

[0219] 28 Bay or Tub Section 2

[0220] 29 Bay or Tub Section 3

[0221] 30 Bay or Tub Section 4

[0222] 31 Bay or Tub Section 5

[0223] 32 Bay or Tub Section 6

[0224] 33 Glass pane, also with the reference symbols 33' or 33"

[0225] 34 Top of the glass pane 33

[0226] 35 Underside of the glass pane 33

[0227] 36 Surface of the top 34 of the glass pane 33

[0228] 37 Surface of the underside 35 of the glass pane 33

[0229] 38 Top Rollers 39 Top Rollers

[0230] 40 top rollers

[0231] 41 top rollers

[0232] 42 top rollers

[0233] 43 top rollers

[0234] 44 top rollers

[0235] 45 Wall of Canal 6

[0236] 46 Wall of Canal 6

[0237] 47 Device or apparatus for hot forming

[0238] 48 Upper surface, upper main surface of the glass 8 or glass ribbon 13 to be hot-formed

[0239] 49 Lower surface, lower main surface of the glass 8 or glass ribbon 13 to be hot-formed

[0240] 50 axis of symmetry

[0241] 51 axis of symmetry

[0242] 52 Lot in negative z-direction

[0243] 53 Plumb line in negative z-direction

[0244] 54 Location of entry of glass 8 into section Hs for thickness-related hot forming, shown with a dashed line

[0245] 55 Location of exit of glass 8 from section Hs for hot forming

[0246] 56 Distance to the flow control component at which the glass has reached its maximum width after hitting the float bath

[0247] 57 Additional cooling equipment

[0248] Ml to M8 Surface or measuring surface for determining the fine waviness of the upper surface 48 of the glass ribbon 13 and the upper surface 36 of the top side 34 of the glass panes 33, 33', 33"

[0249] M1 ' to M8' surface or measuring surface for determining the fine waviness of the lower surface 49 of the glass ribbon 13 and the surface 37 of the underside 35 of the glass panes 33, 33', 33"

[0250] ML measuring line with a length of 260 mm, arranged within a measuring area Ml to M8 or within a measuring area Ml ' to M8'

[0251] Mi center of the glass ribbon in X-direction

[0252] Mtl boundary line to the area of ​​the respective surface of the glass ribbon 13 covered by the top rollers 38 to 44

[0253] Mt2 boundary line to the area of ​​the respective surface of the glass ribbon covered by the top rollers 38 to 44 13 OSG line at a fine waviness value of 26 nm r| viscosity

[0254] T|A Viscosity at a distance to the component for

[0255] Flow rate regulation at which the glass has reached its maximum width after hitting the float bath r|E Viscosity at the end of hot forming

Claims

1. Glass pane, in particular a glass pane obtained by singulation from a floated glass ribbon formed by hot forming, in particular comprising a borosilicate glass, with a thickness D between at least 1.75 mm and at most 7 mm comprising an upper side and a lower side, characterized by a fine waviness on at least one surface of the upper side or the lower side of the glass pane of 10 nm to 26 nm, preferably between 10 nm and 15 nm, in at least one direction parallel to the surface of the glass pane.

2. Glass pane, in particular a glass pane obtained by singulation from a floated glass ribbon formed by hot forming, in particular comprising a borosilicate glass, with a thickness D between at least 0.7 mm and at most 7 mm, in particular between 1.1 mm and at most 7 mm, comprising an upper side and a lower side, characterized by a fine waviness on at least one surface of the upper side or the lower side of the glass pane of 10 nm to 26 nm, preferably between 10 nm and 15 nm, in at least one direction parallel to the surface of the glass pane.

3. Glass pane according to claim 1 or 2, wherein the fine waviness on the surface of the top side or the surface of the bottom side of the glass pane is measured along a line ML with a length of 260 mm, preferably within a square area (Ml to M8 and Ml 'to M8') of 260 mm by 260 mm.

4. A glass pane according to any one of the preceding claims, wherein the at least one direction corresponds to a direction perpendicular to the drawing direction used in hot forming the glass pane.

5. Glass pane according to one of the preceding claims, comprising a borosilicate glass comprising the following components in wt.%: SiO2 70 to 87, preferably 75 to 85 B2O3 5 to 25, preferably 7 to 14 AI2O3 0 to 5, preferably 1 to 4 Na2O 0.5 to 9, preferably 0.5 to 6.5 K2O 0 to 3, preferably 0.3 to 2.5, particularly preferably up to 2 CaO 0 to 3 MgO 0 to 2.

6. An ensemble of glass panes comprising a plurality of glass panes, in particular at least eight glass panes, according to claims 1 to 5, in which the median of the fine waviness of the ensemble has a value which is less than 20 nm.

7. A method for producing a glass pane, in particular for the continuous production of a glass pane, in particular a glass pane according to one of claims 1 to 5 or a glass pane of an ensemble of glass panes according to claim 6, comprising the steps - Providing a mixture comprising glass raw materials, - melting the mixture to obtain a glass melt, - Adjusting the viscosity of the glass melt, - Transferring the glass melt into a device for hot forming by means of floating to form a glass ribbon, - separating the hot-formed glass ribbon to obtain a glass sheet, the viscosity in the hot-forming device being adjusted such that the sum of the decimal logarithms of the viscosity at the distance from a component for flow regulation, at which the glass has reached its maximum width after impact with the float bath 1g (r|A / dPa*s) and the viscosity at the end of hot-forming 1g (r|E / dPa*s) is between at least 11.4 and at most 11.

8.

8. A method for producing a glass sheet according to claim 7, wherein the viscosity in the hot forming device is adjusted so that the sum of the decadic Logarithms of viscosity at the distance from a flow control component at which the glass has reached its maximum width after impacting the float bath 1g (r|A / dPa*s), and viscosity at the end of hot forming 1g (r|E / dPa*s) are between at least 11.4 and at most 11.6.

9. A method for producing a glass pane, in particular for the continuous production of a glass pane, in particular a glass pane according to one of claims 1 to 5 or a glass pane of an ensemble of glass panes according to claim 6, in particular with the features of the method according to claim 7 or 8, wherein the decimal logarithm of the viscosity at the distance from a component for flow regulation, at which the glass has reached its maximum width after its impact on the float bath, is 1g (r|A / dPa*s), in particular at a distance of about 1.5 m in the drawing direction after a component for flow regulation, in particular at the beginning of a second float bath section, is at least 5.0, particularly preferably at least 5.1, and preferably less than 5.25, and the decimal logarithm at the end of hot forming is 1g (r|E / dPa*s), in particular at a distance in the drawing direction of about 10.5 m to 11.1 m after the component for flow regulation, in particular at the beginning of a fourth float bath section, is at least 6.2, preferably at least 6.3, particularly preferably at least 6.35, with a preferred upper limit being at most 6.

5.

10. The method according to any one of claims 7 to 9, wherein the difference between the decimal logarithms of the viscosity at the distance from a flow control component, at which the glass has attained its maximum width after impacting the float bath 1g (r|A / dPa*s) and the viscosity at the end of hot forming 1g (r|E / dPa*s) is between at least 1.25 and at most 1.5, in particular between at least 1.25 and at most 1.45, and preferably 1.

42.

11. A process according to any one of claims 7 to 10, wherein a throughput of less than 400 t of glass per day, preferably less than 200 t of glass per day and particularly preferably less than 1001 t of glass per day is obtained.

12. Method according to one of claims 7 to 11, wherein the at least one direction is indicated on the glass pane or a packaging of the glass pane.

13. Glass pane according to one of claims 1 to 5 or glass pane of a Ensembles having the features of claim 6, preferably manufactured or producible by a method according to one of claims 7 to 12.

14. Use of a glass pane according to one of claims 1 to 5 or claim 13 or of a glass pane of an ensemble having the features of claim 6 in electronic devices, in particular as a cover pane of a display or indicator device.

15. Use of a glass pane according to one of claims 1 to 5 or claim 13 or of a glass pane of an ensemble having the features of claim 6 as glazing, in particular as architectural glazing of buildings.

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