Apparatus and method for producing flat glass

Abstract

The invention relates to an apparatus and a method with which a particularly uniform thickness of flat glass can be obtained. The method is a stretching method in which a glass ribbon is stretched. In the method a spacer is used which allows a very small gap to be defined between the glass ribbon and the spacer even when the position of the glass ribbon changes.

Description

[0001] This application is a divisional application of Chinese patent application No. 201880069975.6 filed on October 17, 2018 and entitled “Device and method for producing flat glass”. Technical Field

[0002] The invention relates to a device and a method for producing flat glass and flat glass. Background Art

[0003] The flat glass according to the invention is in particular thin glass and the thinnest glass, which is suitable, for example, for the production of OLED cover plates, filters and other optical components, MEMS, substrates or cover glasses for sensors, displays. Such glass is produced by a stretching process. The thinner the glass, the more difficult it is to obtain a flat glass with uniform thickness and thus low TTV. One reason for uneven thickness of glass products is temperature fluctuations during hot forming. The viscosity of the glass depends on the temperature, so fluctuations in temperature lead to fluctuations in viscosity. During the stretching process, fluctuations in the viscosity of the glass body lead to high TTV.

[0004] In the prior art, attempts have been made to produce flat glass with particularly low TTV using different measures. For this purpose, baffles are also used that are intended to separate the hot forming area from the surrounding environment as much as possible (see WO 2017 / 095791 A1, WO 2012 / 166446 A1).

[0005] In the prior art, partitions are also used to prevent dirt from penetrating into the hot forming area (see WO 2016 / 085778 A1).

[0006] An important property of flat glass for the above-mentioned fields of application is a flawless surface. The surfaces of flat glass which can be produced by drawing processes such as downdrawing, overflow melting and redrawing are characterized by particularly flawless properties. These surfaces are so-called "fire-polished" surfaces. In order to protect these flawless surfaces, any contact of device parts with the drawn glass ribbon is avoided. Therefore, in the prior art, relatively large partition openings are always maintained in order to exclude undesired contact between the partition and the glass ribbon. Summary of the invention

[0007] The object of the present invention is to provide a device and a method making it possible to obtain flat glass whose thickness uniformity exceeds that of the glasses of the prior art.

[0008] This object is achieved by the subject matter of the claims.

[0009] method

[0010] The present invention provides a method for producing flat glass having at least two fire-polished surfaces, wherein a hot forming zone is provided, in which the glass of a glass ribbon passes through a temperature range including a processing temperature Va of the glass, wherein a partition is provided for forming a gas space between a region of the glass ribbon having its processing temperature Va and a region of the glass having its transition temperature Tg The method is characterized in that the partitions contact the hot glass ribbon at at least one point on at least two sides, respectively.

[0011] According to the invention, the method preferably comprises a forming step, in which a thinned glass ribbon is obtained by the action of a tensile force on a formable glass portion of the glass ribbon. Preferably, a thermoforming zone is provided, in which the glass passes through a temperature range including the processing temperature Va of the glass. Preferably, the thermoforming zone comprises at least one partition for thermal separation of the air chamber of the thermoforming zone, wherein the partition forms an opening through which the glass ribbon can move, and the partition contacts the glass ribbon at at least one point on at least two sides, respectively.

[0012] By definition, "flat glass" is a glass body whose width and length are much greater than its thickness. According to the invention, the thickness is particularly preferably less than 5 mm, more preferably less than 2 mm, further preferably less than 1 mm, more preferably less than 750 μm, further preferably less than 500 μm and particularly preferably less than 250 μm. The width is preferably at least 100 mm, further preferably at least 200 mm, more preferably at least 300 mm and particularly preferably at least 400 mm. In principle, the length is not subject to any restrictions, since very long glass can be produced by many stretching methods. The length is generally greater than 100 mm, preferably greater than 250 mm and particularly preferably greater than 500 mm. The flat glass according to the invention can have a rectangular bottom surface. However, the present invention also encompasses round or arbitrarily shaped flat glass.

[0013] According to the present invention, the tensile force preferably acting on the formable glass portion of the glass ribbon during the method is preferably at least 1 N, in particular at least 5 N or at least 10 N. The minimum tensile force that can sufficiently deform the glass ribbon is preferred. The required tensile force depends on the viscosity of the glass at the selected temperature. When the glass is stretched with too much tensile force, the required glass thickness cannot be obtained, and the glass ribbon may tear. Therefore, the maximum tensile force is preferably limited to 400 N, in particular 200 N and particularly preferably 100 N.

[0014] In the method according to the invention, a thinned glass ribbon is obtained in particular from a glass ribbon. The glass ribbon can have any shape. In the context of the redrawing method, the term "glass ribbon" includes a so-called preform, which is drawn into a thinned glass ribbon during the forming process. In the context of the downdraw method or overflow melting method, the glass ribbon is a glass melt that is initially still liquid after it emerges from the grooved (geschlitzten) drawing groove (downdraw) or after converging at the end of the drawing groove (overflow melting) or below the drawing groove (redrawing). The thinned glass ribbon is the product of a hot forming step before an optional post-processing step, in particular before cutting and / or removing the thick edges (Randborten).

[0015] In a particularly preferred embodiment, the method according to the invention is a redrawing method and the glass ribbon is a preform. In this case, the preform is drawn from a starting thickness D and a starting width B to a target thickness d and a target width b. During this drawing process, the glass becomes thinner, so that d is much smaller than D. The width B decreases less than the thickness D. Therefore, D / d is greater than B / b.

[0016] The processing temperature Va is the viscosity of the glass forming the glass ribbon is 10 4 The temperature at which the softening point EW corresponds to a viscosity of 10 7.6 dPas. The transition temperature Tg is the temperature at which the viscosity of the glass is 10 13 Temperature at dPas.

[0017] According to the invention, the partition, which is preferably arranged essentially horizontally, contacts the glass ribbon on at least two sides. It is thus achieved that the distance between the partition and the glass ribbon remains constant during the method and that the air chambers above and below the partition are separated as much as possible. This results in a limited vertical convection between the two air chambers and thus in small temperature fluctuations. During production, the glass ribbon and in particular the thinned glass ribbon tends to change its position slightly. The reason for this is that, on the one hand, very thin glass ribbons can be produced by the stretching method concerned here, and the position of the glass ribbon is influenced by air movements. On the other hand, the devices used in these methods are usually constructed at least partially from metal, which expands relatively strongly under the influence of heat. Therefore, this leads to changes in the position of the glass ribbon in the device. In the case of the re-stretching method (which is preferred in the context of the present invention), it is also the case that the absolute fluctuations in the thickness of the preform can be significant, so that these fluctuations must be taken into account for the partition between the preheating zone and the hot forming zone. In the prior art, the opening that enables the glass body to enter and / or leave the hot forming zone must be selected to be large enough to allow these changes in position without collisions between the glass ribbon and the partition. The solution according to the invention always ensures a uniform distance between the intermediate plate and the glass ribbon.

[0018] In one embodiment, the partition contacts the glass ribbon exactly on both sides. The sides contacted by the partition are in particular the sides with the largest surface, which are referred to herein as the upper side and the lower side. For this purpose, the partition can include a contact portion, which contacts the side of the glass ribbon. Here, the contact portion is a component of the partition, which protrudes beyond the spacing portion and in particular all other components of the partition in the direction of the glass ribbon and can therefore contact the glass ribbon, while other parts of the partition are not in contact with the glass ribbon. The contact portion can be made of any material that withstands the high temperatures of the glass and avoids contamination of the glass. Preferred materials for the contact portion are hexagonal boron nitride, aluminum oxide, fused quartz, silica glass or a combination thereof.

[0019] In one embodiment, the partition comprises two or more contact portions, respectively, for the upper side and the lower side of the glass body. As an alternative or in addition, the partition may comprise one or more contact portions, respectively, for the two narrow sides of the glass ribbon passing through the partition opening. In one embodiment, the partition comprises six contact portions, two contact portions respectively for the upper side and the lower side, and one contact portion respectively for the narrow sides. The contact portion may be a component protruding in the direction of the glass ribbon, which in principle may have any shape and may preferably be inclined (guide nose), which means that the contact portion comprises at least one face inclined in the direction of the glass ribbon.

[0020] In an alternative embodiment, the spacer can include a cylindrical spacer member, such as a roller, a tube or a rod, wherein the contact portion is formed in particular by a region of such a spacer member having a larger cylindrical diameter. In this embodiment, the spacing portion is preferably formed by a region having a cross-sectional diameter that is smaller than the cross-sectional diameter in the region of the contact portion. In this design, the gap width between the glass ribbon and the spacing portion, in particular half of the difference between the cross-sectional diameter in the region of the contact portion and the cross-sectional diameter in the region of the spacing portion. The advantage of the cylindrical design is that the cylinder rests on the glass ribbon in a roller-like manner, resulting in particularly low resistance because it rolls on the surface of the glass ribbon as the glass ribbon moves. The cylindrical spacer member can be arranged on a support having an inclined surface in the direction of the glass ribbon so that the minimum gap width is always achieved. This design allows the spacer member to be always correctly oriented without intervening in the production process.

[0021] The contact area (through which the contact portion contacts the glass ribbon) is preferably as small as possible. In particular, the range of the contact area of ​​each contact portion in the width direction of the glass ribbon is less than 10 cm, in particular less than 5 cm, more preferably less than 2 cm or less than 1 cm. In a particularly preferred embodiment, the range of each contact portion in the width direction is not more than 0.5 cm or even not more than 0.3 cm. The range of each contact portion in the length direction of the glass ribbon is preferably less than 10 cm, in particular less than 5 cm, more preferably less than 2 cm or less than 1 cm. In a particularly preferred embodiment, the range of each contact portion in the length direction is not more than 0.5 cm or even not more than 0.3 cm. The smaller the contact area, the lower the resistance of the contact portion to the tensile movement.

[0022] Preferably, the spacer contacts the glass ribbon at the edge of the glass ribbon, in particular in an area extending from the edge of the glass ribbon over a width corresponding to at most 30% or at most 20%, in particular at most 15%, more preferably at most 10% or at most 5% of the entire width of the thinned glass ribbon, respectively. The edge of the glass ribbon is discarded in the stretching process, in which the goal is a particularly high surface quality and a particularly high thickness uniformity, because the edge of the glass ribbon has a greater thickness (thick edge) compared to the middle part of the glass ribbon. This is why it is acceptable for the spacer member to contact the glass ribbon in these areas, especially the improvement of the TTV of the flat glass prepared by the method according to the invention is very significant. The edge of the thinned glass ribbon can be removed in a post-processing step. Therefore, it is preferred that the contact portion contacts the glass ribbon outside the clear area.

[0023] Preferably, the partition comprises a contact portion and a spacing portion. Preferably, the contact portion of the partition contacts the glass ribbon, and the partition comprises a spacing portion, which does not contact the glass body and forms a gap between the glass ribbon and the spacing portion of the partition, wherein the width of the gap is preferably at most 5 mm, in particular at most 4 mm, preferably at most 3 mm, more preferably at most 2 mm. In a particularly preferred embodiment, the gap is <2 mm, more preferably <1 mm, particularly preferably <0.5 mm or even <0.1 mm. The width of the gap is the horizontal distance between the glass ribbon and the spacing portion of the partition. The particularly small gap between the spacing portion and the glass ribbon reduces convection and ensures a particularly sharp temperature gradient between the hot forming zone and the area outside the hot forming zone beyond the partition. The reduction in convection allows a particularly small TTV. The sharp temperature gradient allows the method to be performed in a particularly short hot forming zone, which counteracts the width shrinkage of the glass ribbon and thus increases the yield.

[0024] In one embodiment, the method is a down-draw method or an overflow melting method. In a preferred embodiment, in particular when the method is designed as a down-draw method or an overflow melting method, a partition is arranged at the glass outlet of the shell (Einhausung) of the hot forming zone. The partition at the glass outlet (which is located in the stretching direction from the hot forming zone) thermally shields the area below the hot forming zone, so that the glass ribbon that has left the hot forming zone for a short time can be cooled in a controlled manner. Thus, for example, particularly rapid cooling can be achieved. Of course, this can also be an advantage for the re-stretching method.

[0025] In a preferred embodiment, the method according to the invention is a re-stretching method. In particular, the re-stretching method benefits from the design of the separator according to the invention, since the re-stretching device requires a holder for the preform, which holder usually comprises a metal element, which expands under the influence of heat and thus changes the position of the preform. The design of the separator according to the invention takes these position changes into account.

[0026] In a preferred design of the method, a partition is arranged at the glass inlet of the housing of the thermoforming zone, in particular between the area in which the glass has its transition temperature Tg and the thermoforming zone. The arrangement of a partition at the glass inlet is particularly preferred for the re-stretching method. Preferably, the preform is preheated in a preheating zone before entering the thermoforming zone. In the preheating zone, the glass is heated in particular to a temperature which is lower than the temperature in the thermoforming zone and in particular lower than the processing temperature but higher than the transition temperature. In order to achieve uniform thermoforming only in the thermoforming zone by effective thermal separation of the thermoforming zone from the preheating zone, it has proven valuable to use the partition described herein.

[0027] In a preferred embodiment of the method, the uniformity of the temperature in the hot forming zone is characterized by an interquartile range of less than 2 K, more preferably less than 1.5 K and particularly preferably less than 1 K. It has been shown that the setting of such a low interquartile range leads to the low TTV desired according to the invention. In order to determine the interquartile range, the temperature in the hot forming zone is measured with a thermocouple element, in particular with a fast-responding thermocouple element. The thermocouple elements used in the example section are suitable for this. They are characterized by a wire gauge of less than 0.1 mm and a nominal diameter (Perlendurchmessern) <0.3 mm. Temperature sensors with low thermal inertia can be used. In particular, such sensors are cooled with an initial cooling rate of more than 5 K / s after being taken out of a furnace heated to 600° C. to ambient air with a temperature of 20° C.

[0028] The thermocouple element is arranged in the glass plane at a distance of less than 40 mm from the partition and less than 20 mm from the glass edge. Alternatively, the thermocouple element can also be arranged in the glass ribbon plane in the middle of the deformation zone and less than 20 mm from the glass edge. However, any other position in the deformation zone of the glass ribbon at a distance of less than 20 mm from the glass ribbon is also feasible.

[0029] In a preferred design of the method, the partition is at least partially movable relative to the housing of the hot forming zone. In the prior art, the partition is usually firmly connected to the stretching device, for example the housing of the hot forming zone. By the preferred design of the partition according to the invention, which is movable relative to the housing of the hot forming zone, it can be ensured that the partition is always optimally oriented, so that flat glass of excellent quality can be produced. For example, the partition is slidable on the plate or can be slid on the plate and then pushed into the desired position, so that the partition follows the movement of the glass ribbon without changing the gap width. The plate can be part of the housing of the hot forming zone.

[0030] Device

[0031] Features described in the above method description, which are also reflected in the device features, are preferably also features of the device, even if they are not described again below. The device is particularly suitable and intended for carrying out the method according to the invention and for producing the flat glass according to the invention.

[0032] According to the present invention, there is also an apparatus for producing flat glass, the apparatus having at least one glass storage, at least one hot forming zone, at least one stretching device adapted to apply tension to a glass ribbon in the apparatus, wherein the hot forming zone comprises at least one partition for thermal separation of an air chamber of the hot forming zone, wherein the partition forms an opening through which the glass ribbon can be guided, and the partition comprises a contact portion arranged to contact the glass ribbon at at least one point on at least two sides. Preferably, the apparatus is a redraw apparatus, a downdraw apparatus or an overflow melting apparatus.

[0033] A "spacer" is any component capable of creating a thermal separation between the thermoforming zone and the area above and / or below it. It may comprise one or several parts. In a preferred design, the spacer comprises a spacing part which is arranged at a distance from the glass ribbon so that a gap is formed between the glass ribbon and the spacing part. Preferably, the spacer is at least partially movable relative to the housing of the thermoforming zone. Particularly preferred is a design in which the spacer comprises one or several, in particular two, cylindrical spacer members (in particular rollers) arranged on a support, and in which the support comprises an inclined surface in the direction of the glass ribbon.

[0034] Preferably, the partition is arranged at the glass outlet of the shell of the thermoforming zone and / or the partition is arranged at the glass inlet of the shell of the thermoforming zone. In a preferred embodiment, partitions of the type described here are arranged both at the inlet into the thermoforming zone and at the outlet from the thermoforming zone in order to adjust the temperature distribution as evenly as possible and thus adjust the preferred interquartile range according to the invention.

[0035] Preferably, the stretching device comprises a guide member. The guide member is preferably a roller, a caterpillar, a roll, a clamp or a combination thereof. The guide member preferably has a cylindrical basic shape. In particular, the guide member comprises at least one contact area through which the guide member contacts the glass ribbon.

[0036] The apparatus preferably comprises a heating device for heating the glass ribbon. The heating device is preferably selected from the group consisting of a resistance heater, an IR heater, a burner and a laser and combinations thereof. In a preferred embodiment, the apparatus comprises a cooling device to cool the glass ribbon after deformation.

[0037] There is a certain distance between the heating device and the glass. The space created by this distance is filled with gas, usually air, and is referred to herein as an air chamber. In this air chamber, convection occurs due to the temperature gradient. However, the air chamber does not necessarily have to be equipped with a heating device. The term "air chamber" simply means that the glass is not in a vacuum, but in a space filled with gas (especially air), so that convection can occur. The air chamber can be defined by a heating device or in other ways. It is particularly important for the present invention that the air chamber above and below the partition is thermally separated by the partition, so that the vertical convection between the two air chambers is limited, so that temperature fluctuations are small.

[0038] In one embodiment, the device is a redrawing device, wherein the glass reservoir is thus formed by a preform made of glass or the device comprises a holder for a preform made of glass. In another embodiment, the device is a downdraw device or an overflow melting device, wherein the glass reservoir is formed by a drawing trough. In the case of a downdraw device, the drawing trough comprises a gap nozzle at its lower end. The device may comprise one or more guide bodies in the region below the gap nozzle.

[0039] In addition, the device may include other components known to those skilled in the art, which are not described in detail here. This includes in particular at least one cooling device. In addition, in the case of a down-draw method or an overflow melting method, a melting device, such as a melting crucible or a melting pool, may be provided.

[0040] The method may comprise one or several post-processing steps, in particular cutting, trimming and / or finishing of the glass, in order to obtain a flat glass having the desired properties.

[0041] plate glass

[0042] The features described below, which are material properties of the glass, apply not only to the flat glass as final product of the method, but also to the glass used as starting material in the method.The flat glass is preferably producible and / or produced by the method according to the invention.

[0043] According to the present invention, there is also a flat glass having at least two fire-polished surfaces and a thickness of less than 0.01-3*10 -5 *(1 / K)*(Va-EW)+2.8*10 -8 *(1 / K 2 )*(Va-EW) 2 Relative TTV of , where Va is the processing temperature and EW is the softening point.

[0044] Furthermore, according to the invention, there is also a flat glass having at least two fire-polished surfaces and a relative TTV of less than 0.01. Preferably, the difference between the processing temperature Va and the softening point EW of the glass is at least 50 K, in particular at least 100 K, at least 150 K or even at least 200 K. In particular, the difference is at most 500 K, preferably at most 450 K and particularly preferably at most 250 K or at most 150 K. It has been shown that flat glasses having the advantageous properties described herein, in particular the TTV described herein, can be obtained from glasses having these properties. In a particularly preferred design, the flat glass is a glass ribbon, a glass plate or a glass wafer.

[0045] Preferably, the flat glass is a glass with a thickness of less than 2 mm, in particular less than 0.75 mm, less than 0.5 mm or less than 0.25 mm. In a particularly preferred embodiment, the thickness of the flat glass is no more than 100 μm, no more than 50 μm, no more than 30 μm, no more than 20 μm or no more than 10 μm. In a preferred embodiment, the width of the flat glass is 10 to 1000 mm, in particular at least 50 mm, at least 100 mm or at least 200 mm. Preferably, it should not exceed a value of 800 mm, in particular 700 mm, 600 mm, 450 mm or 304.8 mm.

[0046] Flat glass having a relative TTV of less than 0.009, less than 0.007 or less than 0.005 is preferred. The relative TTV is determined by continuously measuring the thickness of the thinned glass body in a 2 mm wide strip in the center of the glass ribbon and is calculated for sections of length 160 mm respectively. The relative TTV is the TTV of such a 2 mm wide and 160 mm long section divided by its average thickness. The average thickness is the average of all thickness values ​​measured for such a 2 mm wide and 160 mm long section. The TTV is derived from the difference between the maximum and minimum thickness values ​​measured for such a 2 mm wide and 160 mm long section.

[0047] Preferably, the thickness values ​​are measured in traces (Spuren) that are orthogonal to the stretching direction. Preferably, within each trace, one measurement value is recorded per millimeter. Preferably, in the stretching direction, the distance between the traces is 10 mm. Therefore, preferably, in the case of the above-mentioned cross-section of 2 mm width and 160 mm length, two thickness values ​​are measured for each trace (preferably at the width position 0.5 mm and 1.5 mm of the cross-section). Preferably, 16 traces are measured (preferably at the length position 5 mm, 15 mm, 25 mm, ..., 155 mm of the cross-section). Therefore, for a cross-section of 2 mm width and 160 mm length, 2×16=32 thickness values ​​are preferably measured.

[0048] A "fire-polished surface" is a surface which is characterized by a particularly low roughness. The production method according to the invention makes it possible to produce flat glass with specific surface properties. Due to the production methods which make it possible to obtain flat glass, the flat glass has at least one, in particular two, fire-polished surfaces. In contrast to mechanical polishing, in the case of fire polishing the surface is not ground, but the material to be polished is heated to such a high temperature that it flows smoothly. The costs for producing smooth surfaces by fire polishing are therefore significantly lower than the costs for producing mechanically polished surfaces. The roughness of a fire-polished surface is lower than that of a mechanically polished surface. For the flat glass according to the invention, a "surface" refers to the top and / or bottom side, that is to say the two surfaces which are largest in comparison with the remaining surfaces.

[0049] The fire-polished surface of the flat glass of the invention preferably has a root mean square roughness (Rq or RMS) of at most 5 nm, preferably at most 3 nm and particularly preferably at most 1 nm. The roughness depth Rt of the flat glass is preferably at most 6 nm, further preferably at most 4 nm and particularly preferably at most 2 nm. The roughness depth is determined in accordance with DIN EN ISO 4287. According to the invention, the roughness Ra is preferably less than 1 nm.

[0050] In the case of mechanically polished surfaces, the roughness values ​​are even worse. In addition, in the case of mechanically polished surfaces, polishing marks can be seen under an atomic force microscope (AFM). In addition, residues of mechanical polishing agents (e.g., diamond powder, iron oxide, and / or CeO2) can also be seen under AFM. Since the mechanically polished surface must always be cleaned after polishing, some ions on the glass surface are leached. The reduction of some ions can be detected by secondary ion mass spectrometry (ToF-SIMS). Such ions are, for example, Ca, Zn, Ba, and alkali metals.

[0051] The glass is preferably selected from the group of silicate glass, phosphate glass, borate glass, germanate glass or chalcogenide glass. Particularly preferred glasses are borosilicate glass, alkali metal silicate glass, alkaline earth metal silicate glass, aluminosilicate glass, titanium silicate glass, lanthanum borate glass or fluorophosphate glass. Particularly preferably, the glass is an optical glass, in particular heavy flint glass, colored glass or borosilicate glass.

[0052] Preferably, the glass has

[0053] - at least 20% by weight and at most 85% by weight of SiO2,

[0054] - at least 3% by weight of alkali metal oxides,

[0055] - up to 5% by weight of Al2O3,

[0056] - up to 15% by weight of B2O3, and / or

[0057] - up to 3% by weight of ZrO2.

[0058] Particularly preferably, the glass comprises the following components

[0059] Best More preferred <![CDATA[SiO2]]> 20 to 50% by weight 20 to 30% by weight <![CDATA[Na2O]]> 5 to 20% by weight 8 to 15% by weight <![CDATA[K2O]]> 5 to 20% by weight 8 to 15% by weight CaO 5 to 20% by weight 8 to 15% by weight BaO 5 to 20% by weight 8 to 15% by weight <![CDATA[TiO2]]> 20 to 50% by weight 20 to 30% by weight <![CDATA[ZrO2]]> 0.1 to 3 wt% 0.5 to 2% by weight <![CDATA[Nb2O5]]> 3 to 10% by weight 4 to 7 wt%

[0060] Also preferably, the glass comprises the following components

[0061] Best More preferred <![CDATA[SiO2]]> 60 to 85% by weight 75 to 83% by weight <![CDATA[B2O3]]> 10 to 20% by weight 11 to 16 wt% <![CDATA[Na2O]]> 2 to 10 wt% 3 to 6 wt% <![CDATA[K2O]]> 0.1 to 10% by weight 0.25 to 2 wt% <![CDATA[Al2O3]]> 0.1 to 10% by weight 1 to 4 wt%

[0062] In a preferred embodiment, the glass is a colored glass, in particular a blue glass, which contains one or more coloring components, in particular copper and cobalt.

[0063] Preferred colored glass includes the following ingredients

[0064]

[0065]

[0066] ΣRO is the sum of alkaline earth metal oxides and ZnO. ΣR2O is the sum of alkali metal oxides.

[0067] In a preferred embodiment, the colored glass is a fluorine-containing colored glass, and specifically comprises the following components.

[0068] <![CDATA[P2O5]]> 25 to 75% by weight <![CDATA[Al2O3]]> 0.5 to 15 wt% CuO 1 to 20% by weight <![CDATA[F / F2]]> 1 to 30% by weight ΣRO 0 to 40% by weight <![CDATA[ΣR2O]]> 0.5 to 20% by weight

[0069] Due to the toxicity and ecological hazards of the following components, the glass is preferably free of Pb, Cd, Ni and As.

[0070] When it is mentioned in the present specification that there is no component in the glass or that the glass does not contain a certain component, it means that the component is only allowed to be present in the glass as an impurity. This means that it is not contained in a large amount and / or it is not added to the glass as a glass component. According to the present invention, a small amount is less than 1000 ppm, preferably less than 500 ppm and most preferably less than 100 ppm. Preferably, the glass also does not contain components that are not mentioned as glass components in the present specification. According to a preferred embodiment, the glass is preferably composed of at least 90% by weight, further preferably at least 95% by weight, further preferably at least 97.5% by weight, further preferably at least 99% by weight, further preferably at least 99.5% by weight, further preferably at least 99.9% by weight of the components mentioned herein.

[0071] Example

[0072] Example 1 (Comparative Example)

[0073] In the redrawing system, a flat glass preform made of heavy flint glass (NSF6) with dimensions of 1650 mm×340 mm×14 mm was redrawn to a thickness of 300 μm in the middle region. The glass had the following composition: 25 wt% SiO2, 10 wt% Na2O, 10 wt% K2O, 10 wt% CaO, 10 wt% BaO, 25 wt% TiO2, 1 wt% ZrO2, 5 wt% Nb2O5.

[0074] The re-stretching system is equipped with a heating and cooling device, which leads to a short deformation zone, so that the width loss of the strip is less than 80 mm. The heating device consists of two parallel SiC tubes, and the cooling device consists of a furnace facility through which a coolant flows. Fast thermocouple elements for measuring the current temperature are located between the SiC tubes and next to the deformation zone of the glass. The temperature of the SiC heating element is adjusted so that the glass body must be stretched with a force of 5-40 N. The temperature at the thermocouple element and the glass thickness in the net area are measured in a time-dependent manner. The temperature fluctuations show an interquartile range of 5.6 K (see Figures 5A to 5D ).

[0075] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a strip 2 mm wide and 160 mm long. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In Example 1, the relative TTV obtained was 0.015.

[0076] Example 2 (Comparative Example)

[0077] The furnace partition does not touch the preform

[0078] In the redrawing system, a flat glass preform made of heavy flint glass (NSF6) with dimensions of 1650 mm×340 mm×14 mm was redrawn to a thickness of 300 μm in the middle region. The glass had the following composition: 25 wt% SiO2, 10 wt% Na2O, 10 wt% K2O, 10 wt% CaO, 10 wt% BaO, 25 wt% TiO2, 1 wt% ZrO2, 5 wt% Nb2O5.

[0079] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the ribbon is less than 80 mm. The heating device consists of two parallel SiC tubes and the cooling device consists of a furnace facility through which a coolant flows. Fast thermocouple elements for measuring the current temperature are located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a partition connected to the furnace is installed, which leaves a gap of 3 mm with the preform. The temperature of the SiC heating element is adjusted so that the glass ribbon must be stretched with a force of 5-40 N. The temperature on the thermocouple element and the glass thickness in the clear area are measured in a time-dependent manner. The temperature fluctuations show an interquartile range (IQA) of 2.15 K (see Figures 5A to 5D ).

[0080] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.011.

[0081] Example 3

[0082] The furnace diaphragm is in contact with the preform

[0083] In the redrawing system, a flat glass preform made of heavy flint glass (NSF6) with dimensions of 1650 mm×340 mm×14 mm was redrawn to a thickness of 300 μm in the middle region. The glass had the following composition: 25 wt% SiO2, 10 wt% Na2O, 10 wt% K2O, 10 wt% CaO, 10 wt% BaO, 25 wt% TiO2, 1 wt% ZrO2, 5 wt% Nb2O5.

[0084] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the ribbon is less than 80 mm. The heating device consists of two parallel SiC tubes, the cooling device consists of a furnace facility through which a coolant flows. A fast thermocouple element for measuring the current temperature is located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a floating partition (schwimmende Blende) made of hexagonal boron nitride is installed, which contacts the preform in the edge area at the guide nose (contact part) and is therefore able to position itself relative to the preform so that the gap dimension relative to the preform outside the contact area between the glass body and the spacing part does not exceed 1.5 mm. The temperature of the SiC heating element is adjusted so that the glass ribbon must be stretched with a force of 5-40 N. The temperature on the thermocouple element and the glass thickness in the clear area are measured in a time-dependent manner. The fluctuations in temperature show an interquartile range (IQA) of 0.9 K (see Figures 5A to 5D ).

[0085] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0085.

[0086] Example 4

[0087] Furnace partition in contact with the preform, cylindrical partition element

[0088] In the redrawing system, a flat glass preform made of heavy flint glass (NSF6) with dimensions of 1650 mm×340 mm×14 mm was redrawn to a thickness of 300 μm in the middle region. The glass had the following composition: 25 wt% SiO2, 10 wt% Na2O, 10 wt% K2O, 10 wt% CaO, 10 wt% BaO, 25 wt% TiO2, 1 wt% ZrO2, 5 wt% Nb2O5.

[0089] The re-stretching system is equipped with heating and cooling devices that result in a short deformation zone, so that the width loss of the strip is less than 80 mm. The heating device consists of two parallel SiC tubes and the cooling device consists of a furnace facility through which a coolant flows. Fast thermocouple elements for measuring the current temperature are located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone are installed Figure 4A and Figure 4BThe glass ribbon is stretched with a spacer having a gap of 0.5 mm relative to the glass body. The temperature of the SiC heating element is adjusted in such a way that the glass ribbon must be stretched with a force of 5-40 N. The temperature on the thermocouple element and the glass thickness in the clear area are measured in a time-dependent manner. The temperature fluctuations show an interquartile range of 0.5 K.

[0090] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0063.

[0091] Example 5

[0092] The furnace diaphragm is in contact with the preform

[0093] In a redrawing system, a flat glass preform made of borosilicate glass (Borofloat) with dimensions of 1650 mm×340 mm×14 mm was redrawn to a thickness of 170 μm in the middle region. The glass had the following composition: 80 wt. % SiO2, 12.5 wt. % B2O3, 4 wt. % Na2O, 0.5 wt. % K2O, 2 wt. % Al2O3.

[0094] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the ribbon is less than 80 mm. The heating device consists of two parallel SiC tubes and the cooling device consists of a furnace facility through which a coolant flows. A fast thermocouple element for measuring the current temperature is located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a floating partition made of hexagonal boron nitride is installed, which contacts the preform in the edge area at the guide nose and is therefore able to position itself relative to the preform so that the gap size relative to the preform outside the contact area does not exceed 1.5 mm. The temperature of the SiC heating element is adjusted so that the glass ribbon must be stretched with a force of 5-40 N. The temperature on the thermocouple element and the glass thickness in the clear area are measured in a time-dependent manner. The fluctuations in temperature show an interquartile range (IQA) of 0.9 K.

[0095] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0041.

[0096] Example 6

[0097] The furnace partition is in contact with the preform

[0098] In the redrawing system, a flat glass preform made of blue glass (BG 66) with dimensions of 800 mm×200 mm×14 mm was redrawn to a thickness of 110 μm in the middle region.

[0099] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the strip is less than 80 mm. The heating device consists of two parallel SiC tubes, the cooling device consists of a furnace facility through which a coolant flows. A fast thermocouple element for measuring the current temperature is located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a floating partition made of hexagonal boron nitride is installed, which contacts the preform in the edge area at the guide nose and is therefore able to position itself relative to the preform so that the gap size relative to the preform outside the contact area does not exceed 1.5 mm. The temperature of the SiC heating element is adjusted in such a way that the glass body must be stretched with a force of 5-40 N. The temperature on the thermocouple element as well as the glass thickness in the clear area are measured in a time-dependent manner. The fluctuations in temperature show an interquartile range (IQA) of 0.9 K (see Figures 5A to 5D ).

[0100] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0094.

[0101] Example 7

[0102] The furnace diaphragm is in contact with the preform

[0103] In the redrawing system, a flat glass preform made of soda-lime float glass with dimensions of 1650 mm×400 mm×8 mm was redrawn to a thickness of 200 μm in the middle region. The glass had the following composition: 71.7 wt. % SiO2, 1.2 wt. % Al2O3, 0.2 wt. % Fe2O3, 0.1 wt. % TiO2, 0.4 wt. % SO3, 6.7 wt. % CaO, 4.2 wt. % MgO, 15 wt. % Na2O, 0.4 wt. % K2O.

[0104] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the strip is less than 80 mm. The heating device consists of two parallel SiC tubes, the cooling device consists of a furnace facility through which a coolant flows. A fast thermocouple element for measuring the current temperature is located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a floating partition made of hexagonal boron nitride is installed, which contacts the preform in the edge area at the guide nose and is therefore able to position itself relative to the preform so that the gap dimension relative to the preform outside the contact area does not exceed 1.5 mm. The temperature of the SiC heating element is adjusted in such a way that the glass body must be stretched with a force of 5-40 N. The temperature on the thermocouple element as well as the glass thickness in the clear area are measured in a time-dependent manner. The fluctuations in temperature show an interquartile range (IQA) of 0.9 K (see Figures 5A to 5D ).

[0105] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0051.

[0106] Example 8

[0107] The furnace diaphragm is in contact with the preform

[0108] In the redrawing system, a flat glass preform made of blue glass (BG 56) with the dimensions of 800 mm×200 mm×14 mm was redrawn to a thickness of 110 μm in the middle region. The glass had the following composition: 68 wt. % P2O5, 7 wt. % Al2O3, 1 wt. % Li2O, 5 wt. % Na2O, 6 wt. % K2O, 4 wt. % MgO, 2 wt. % La2O3, 6 wt. % CuO, 1 wt. % V2O5.

[0109] The re-stretching system is equipped with a heating and cooling device which results in a short deformation zone, so that the width loss of the strip is less than 80 mm. The heating device consists of two parallel SiC tubes, the cooling device consists of a furnace facility through which a coolant flows. A fast thermocouple element for measuring the current temperature is located between the SiC tubes and next to the deformation zone of the glass. Between the deformation zone and the preheating zone, a floating partition made of hexagonal boron nitride is installed, which contacts the preform in the edge area at the guide nose and is therefore able to position itself relative to the preform so that the gap dimension relative to the preform outside the contact area does not exceed 1.5 mm. The temperature of the SiC heating element is adjusted in such a way that the glass body must be stretched with a force of 5-40 N. The temperature on the thermocouple element as well as the glass thickness in the clear area are measured in a time-dependent manner. The fluctuations in temperature show an interquartile range (IQA) of 0.9 K (see Figures 5A to 5D ).

[0110] The thickness distribution measured during the experiment was evaluated with respect to the fluctuations in the stretching direction by analyzing the TTV of a 2 mm wide and 160 mm long strip. The relative TTV is the quotient of the current TTV (in microns) and the average thickness in the clear area. In this example, the relative TTV obtained is 0.0088.

[0111] Discussion of Examples

[0112] The results show that as the interquartile range of the temperature decreases, the median TTV value also decreases. It is therefore particularly advantageous to achieve the smallest possible gap distance. The processing point Va (viscosity 10 4 dPas) is 817℃, softening point EW(10 7.6 dPas) is 681°C. The processing point Va (viscosity 10 4 dPas) is 1270℃, softening point EW(10 7.6 dPas) is 820°C.

[0113] The following table summarizes the results:

[0114] experiment Va[℃] EW[℃] <![CDATA[V a --EW[K]]> <![CDATA[IQA 温度 [K]]]> Relative TTV Example 1 817 681 136 5.6 0.015 Example 2 817 681 136 2.15 0.0113 Example 3 817 681 136 0.9 0.0085 Example 4 817 681 136 0.5 0.0063 Example 5 1270 820 450 0.9 0.0041 Example 6 596 496 100 0.9 0.0095 Example 7 1030 695 335 0.9 0.0051 Example 8 610 490 120 0.9 0.0088

[0115] Thus, according to the invention, a relative TTV of <0.01 is achieved. In particular, the invention allows a relative TTV of <0.01 to be achieved for glasses where the difference between EW and Va is <500 K or <450 K or <150 K. The smaller the difference between Va and EW, the steeper the glass, i.e. the greater the slope of the viscosity curve in the event of temperature fluctuations and the more sensitive the TTV.

[0116] When the relative TTV is plotted against (Va-EW) ( Figure 6 , 7, 8), it can be seen that the relative TTV is less than 0.01-3*10 -5* (1 / K)*(Va-EW)+2.8*10 -8* (1 / K 2 )*(Va-EW) 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0117] Figure 1A The partition assembly of the device according to the invention is shown in a top view, with the glass body located in the partition.

[0118] Figure 1B Shows Figure 1A A side cross-sectional view of a baffle assembly.

[0119] Figure 2 A perspective view is shown of a baffle assembly in an apparatus according to the present invention.

[0120] Figure 3 A schematic side view of a baffle assembly in a device according to the invention is shown.

[0121] Figure 4A The baffle assembly of the device according to the invention is shown in a side cross-sectional view.

[0122] Figure 4B A cross-sectional perspective view of a device having a baffle assembly according to the present invention is shown.

[0123] Figures 5A to 5D Measured data of the temperature distribution in the method according to the invention are shown.

[0124] Figure 6 The relative TTV obtained in the experiments related to the difference between the processing temperature and the softening point is shown.

[0125] Figure 7 The relative TTV obtained in the experiments related to the difference between the processing temperature and the softening point is shown.

[0126] Figure 8 The relative TTV obtained in the experiments related to the difference between the processing temperature and the softening point is shown. DETAILED DESCRIPTION

[0127] The embodiments of the invention explained below serve to illustrate and do not limit the subject matter of the invention.

[0128] exist Figure 1A , 1BA possible embodiment is shown in Figures 1 and 2. The real spacer made of hexagonal boron nitride is located on a support plate, which has an opening larger than the spacer. The spacer can slide on the support plate and thus position itself relative to the glass ribbon. In this design, the spacer includes six protruding contact portions in the form of guide noses, which can contact the glass. Here, the guide noses are provided with inclined surfaces inclined in the direction of the glass ribbon, so that the glass ribbon can push the spacer into the correct position.

[0129] When multiple heaters are provided, the temperature of the hot zone is measured below the partition and between the heaters. For the measurement, a K-type thermocouple element with a wire diameter of 0.1 mm and a nominal diameter less than 0.3 mm is used. The sampling rate of the measurement is one second. This setup has a low thermal inertia and allows the measurement of fluctuations in the air temperature in the deformation zone.

[0130] Figure 1A The glass ribbon 1 is shown in the opening of the partition 2. The partition 2 includes a contact portion 3 that contacts the glass ribbon 1. The contact portion 3 is designed as a guide nose. Two guide noses contact the upper side and the lower side of the glass ribbon 1, respectively, and one guide nose contacts the two narrow sides, respectively. Here, at the position where the partition 2 does not contact the glass ribbon 1, a gap is formed between the glass ribbon 1 and the spacing portion of the partition 2. The partition 2 shown is formed in one piece. However, according to the present invention, the partition 2 can also be formed in multiple parts.

[0131] Figure 1B Shown with Figure 1A The same type of partition 2 is shown. The partition 2 comprises a contact portion 3 designed as a guide nose. The contact portion 3 is inclined in the direction of the glass ribbon 1. In addition, the partition assembly comprises a cover plate 7. The partition 2 is located on a bottom plate 5, which is part of the housing of the thermoforming zone 6.

[0132] Figure 2 Also shown is the glass ribbon 1 entering the thermoforming zone 6. The device shown comprises a housing including a bottom plate 5 for the spacer 2 and a cover plate 7 arranged on the spacer.

[0133] Figure 3 Shows something like Figure 2 , and shows the arrangement of thermocouple elements 8 for determining the temperature distribution in the hot forming zone.

[0134] Figure 4A and Figure 4BAnother embodiment is shown. The advantage of this embodiment is that the same gap size is produced on both sides of the glass ribbon. Round tubes or rods made of heat-resistant material (alumina, fused quartz, quartz glass, etc.) are located on an inclined plane inclined in the direction of the glass ribbon. Therefore, they roll towards the glass. These tubes are provided with contact portions in the form of spacers made of glass contact material (for example, hexagonal boron nitride), so that the defined gap can be adjusted. Here, the spacers are positioned so as not to contact the clear area of ​​the subsequent glass ribbon. The clear area is the part of the glass ribbon for the final product without the above-mentioned edges.

[0135] Figure 4A An alternative design of an apparatus with a spacer assembly according to the invention is shown. Here, a cylindrical spacer element 9 is used, which is arranged on a support 10 having an inclination in the direction of the glass ribbon 1. The support 10 is in turn arranged on a base plate 5, which can represent a component of the housing of the hot forming zone. The cylindrical spacer element 9 comprises a contact portion 11, which is designed as a region of increased diameter of the spacer element 9.

[0136] Figure 4B Also shown is a device having cylindrical spacer elements.

[0137] Figure 5A , Figure 5B , Figure 5C and Figure 5D The interquartile range of the temperature in the hot forming zone measured during the method according to the invention for Examples 1-3 is shown. Here, the upper curve shows the course of the temperature over time in the case of the separator of Example 3; the middle curve shows the course of the temperature over time in Example 2; the lower curve shows the course of the temperature over time in Example 1. The frequency of the measured temperatures is shown on the right. The width of the distribution reflects the fluctuations in the temperature values.

[0138] Figure 6 The relative TTV is shown as a function of the difference between the processing temperature Va and the softening point EW of the glass. It can be seen that the greater the difference, i.e. the "longer" the glass, the easier it is to obtain the best results with respect to the relative TTV. However, it can also be seen that, in the case of a given glass, the type of spacer has a crucial influence on the achievable relative TTV.

[0139] Figure 7 A graph of the equation characterizing the flat glass according to the invention is shown. The values ​​above the curve are achieved by the spacers of the prior art, and the values ​​below the curve are achieved according to the solution of the invention.

[0140] Figure 8Again the relative TTV is shown which depends on the difference between the processing temperature and the softening point and on the separator variant, reference being made here to the examples shown in this text.

[0141] Reference numerals list

[0142] 1 Glass belt

[0143] 2 partitions

[0144] 3. Contact part

[0145] 4 Clearance

[0146] 5. Bottom Plate

[0147] 6Hot forming area

[0148] 7 Cover

[0149] 8 Thermocouple elements

[0150] 9Cylindrical spacer element

[0151] 10 Support

[0152] 11. Contact portion of cylindrical spacer element.

Claims

1. A flat glass having at least two fire-polished surfaces and less than 0.01-3*10 -5 *(1 / K)*(Va-EW)+2.8*10 -8 *(1 / K 2 )*(Va-EW) 2 The relative TTV is the TTV of each 2 mm wide section with a length of 160 mm at the center of the glass ribbon divided by the average thickness of the section, and Va is the viscosity of the glass at 10 4 dPas is the processing temperature, EW is the softening point.

2. The flat glass according to claim 1, which has a thickness of less than 2 mm.

3. The flat glass according to claim 1, having a thickness of less than 0.75 mm.

4. The flat glass according to claim 1, having a thickness of less than 0.5 mm.

5. The flat glass according to claim 1, having a thickness of less than 0.25 mm.

6. The flat glass according to any one of claims 1 to 5, having a width of 10 to 1000 mm.

7. Flat glass according to any one of claims 1 to 5, having a width of at least 50 mm.

8. Flat glass according to any one of claims 1 to 5, having a width of at least 100 mm.

9. Flat glass according to any one of claims 1 to 5, having a width of at least 200 mm.

10. The flat glass according to any one of claims 1 to 5, wherein: The relative TTV is less than 0.

009.

11. The flat glass according to any one of claims 1 to 5, wherein: The relative TTV is less than 0.

007.

12. The flat glass according to any one of claims 1 to 5, wherein: The relative TTV is less than 0.

005.

13. Flat glass according to any one of claims 1 to 5, wherein the difference between Va and EW of the glass is at most 500K.

14. Flat glass according to any one of claims 1 to 5, wherein the difference between Va and EW of the glass is at most 450K.

15. Flat glass according to any one of claims 1 to 5, wherein the difference between Va and EW of the glass is at most 150K.

16. The flat glass according to any one of claims 1 to 5, having a root mean square roughness Rq of at most 5 nm; and having a roughness depth Rt of at most 6 nm.

17. The flat glass according to any one of claims 1 to 5, having a root mean square roughness Rq of at most 3 nm; and having a roughness depth Rt of at most 4 nm.

18. The flat glass according to any one of claims 1 to 5, having a root mean square roughness Rq of at most 1 nm; and having a roughness depth Rt of at most 2 nm.

19. Flat glass according to any one of claims 1 to 5, wherein the glass is selected from silicate glass, phosphate glass, borate glass, germanate glass, chalcogenide glass, borosilicate glass, lanthanum borate glass or fluorophosphate glass.

20. Flat glass according to any one of claims 1 to 5, wherein the glass is selected from alkali metal silicate glass, alkaline earth metal silicate glass, aluminosilicate glass or titanium silicate glass.

21. Flat glass according to any one of claims 1 to 5, wherein the glass is heavy flint glass.

22. Flat glass according to any one of claims 1 to 5, wherein the glass is coloured glass.

23. The flat glass according to any one of claims 1 to 5, wherein: Glass includes - at least 20% by weight and at most 85% by weight of SiO2, - at least 3% by weight of alkali metal oxides, - up to 5% by weight of Al2O3, - up to 15% by weight of B2O3, and / or - Up to 3% by weight of ZrO2.

24. The flat glass according to any one of claims 1 to 5, comprising the following components 。 25. The flat glass according to any one of claims 1 to 5, comprising the following components 26. The flat glass according to any one of claims 1 to 5, comprising the following components 。 27. The flat glass according to any one of claims 1 to 5, comprising the following components 。 28. The flat glass according to any one of claims 1 to 5, wherein the content of Pb, Cd, Ni or As in the glass is less than 1000 ppm.

29. The flat glass according to any one of claims 1 to 5, wherein the content of Pb, Cd, Ni or As in the glass is less than 500 ppm.

30. The flat glass according to any one of claims 1 to 5, wherein the content of Pb, Cd, Ni or As in the glass is less than 100 ppm.

31. The flat glass according to any one of claims 1 to 5, which is a glass ribbon, a glass plate or a glass wafer.

32. An optical component comprising the flat glass according to any one of claims 1 to 31.

33. A method for producing flat glass according to any one of claims 1 to 31, comprising, A heat forming zone (6) is provided, in which the glass of the glass ribbon (1) passes through a temperature range, wherein the temperature range includes a processing temperature Va of the glass. A partition (2) is provided for thermal separation of the gas space between a region of the glass ribbon (1) where the glass has its processing temperature Va and a region where the glass has its transition temperature Tg, wherein the partition (2) forms an opening through which the glass ribbon (1) can move, It is characterized in that The partition plate (2) contacts the hot glass ribbon (1) at at least one point on at least two sides, wherein the side in contact with the separator is the side having the largest surface, The contact portion (3, 11) of the partition (2) contacts the glass ribbon (1), and the partition (2) has a spacing portion which does not contact the glass ribbon (1) and forms a gap (4) between the glass ribbon (1) and the spacing portion of the partition (2), wherein the width of the gap (4) is at most 5 mm.

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