Glass, method for manufacturing glass and glass melting apparatus

Abstract

The invention relates to a glass element, preferably made of borosilicate glass. Wherein the glass element has 50 or less inclusions with a size of 2 [mu] m to 10 [mu] m per kilogram of glass.

Description

This application is a divisional application of patent application 202080081103.9 filed on November 20, 2020, with the invention name of “Glass, method for making glass and glass melting equipment”. Technical Field

[0001] The invention relates to a glass element, preferably a glass element made of borosilicate glass.

[0002] The invention furthermore relates to a method for producing a glass element, preferably a glass element made of borosilicate glass.

[0003] The invention further relates to a glass melting apparatus, a method for operating a glass melting apparatus and a glass element, preferably a glass element made of borosilicate glass, preferably in the form of a borosilicate glass sheet, produced using the method and / or the glass melting apparatus.

[0004] Although the present invention is generally applicable to any glass element, the present invention will be described with respect to a glass element in the form of a glass sheet. Background Art

[0005] Glass melting equipment for producing glass usually consists of a melting or heating zone, in which a liquid glass melt is formed from raw materials (so-called glass mixture), a downstream refining zone, in which the glass melt is refined, so that residual bubbles remaining after the melting process or heating process are removed from the glass melt and from the downstream conditioning zone, which is used to further condition the refined glass melt. The temperature required for the entire melting process depends to a large extent on the type of glass. Soda-lime glass, such as soda-lime glass used for producing window glass and glass containers, has a significantly lower melting temperature than special glasses or glass ceramics used for display applications, for example. The conditioning zone of such a glass melting equipment can be designed as a working trough or channel system and a distribution system. Refractory materials are usually used as wall materials for glass melting equipment, mainly including aluminum zirconium silicate materials. However, it is known that the use of such materials as wall materials or melting contact materials can lead to the formation of bubbles and / or streaks in the glass melt and ultimately lead to waste in the final glass product.

[0006] Other defects, such as particles detached from the wall material of the molten tank and the like, lead to inclusions in the corresponding micrometer range, for example in float borosilicate glass, which make such glass unsuitable for various applications. Glass sheet samples made of float borosilicate glass produced in a known manner have disruptive metallic and non-metallic inclusions as well as bubbles with a broad size distribution and a high number. Inclusions larger than 50 µm can be sorted out with the aid of conventional optical inspection methods. On the other hand, inclusions with a size of 50 µm or less are difficult to detect and can usually only be identified, quantified and identified with great effort by trained personnel. Summary of the invention

[0007] It is therefore an object of the present invention to provide a glass element, preferably a glass sheet, having a reduced number of inclusions in the micrometer range; and a method for producing a glass element, preferably a glass sheet; a glass melting device, and a method for operating a glass melting device, which method significantly reduces the number of inclusions in the micrometer range.

[0008] Another object of the present invention is to provide an alternative glass element, preferably a glass sheet, an alternative method for producing a glass element, preferably a glass sheet, an alternative glass melting device and an alternative method for operating a glass melting device.

[0009] The invention achieves the above-mentioned objects with a glass element, preferably a glass element made of borosilicate glass, wherein the glass element has 50 or fewer inclusions per kilogram of glass having a size of 2 μm or more and 10 μm or less.

[0010] The invention achieves the above-mentioned object by a method for producing a glass element, preferably a glass element made of borosilicate glass, preferably according to any one of claims 1 to 12, comprising the following steps: i) providing a mixture, in weight %, comprising: SiO2 60% to 90%, preferably 76% to 90%; B2O3 0 to 20%; Al2O3 0 to 20%; Li2O 0 to 10%; Na2O 0 to 10%; K2O 0 to 10%; MgO 0 to 10%; CaO 0 to 10%, SrO 0 to 10%; and BaO 0 to 10%; ii) heating the mixture to form a glass melt, iii) conditioning the glass melt, and iv) cooling the glass melt to provide the glass element, Wherein, during step ii) and / or iii), at least one, preferably all, of the following conditions are met: a) the glass melt is heated at least partially by means of a resistance heater by applying a heating current to electrodes, wherein an alternating current with a frequency between 1 kHz and 200 kHz is used as the heating current; b) the contact surface in contact with the glass melt comprises 30% or more of the contact material in the form of a fused-cast zirconia material having a ZrO2 proportion of more than 70% by weight, preferably a fused-cast zirconia material having a ZrO2 proportion of more than 85% by weight; and c) 1% to 50% of the volume flow of bottom material of the glass melt is removed in the bottom region of the glass melt.

[0011] The present invention achieves the above-mentioned object by a glass melting device for implementing the method according to any one of claims 13 to 17, comprising: A heating device for heating the mixture to form a glass melt, a regulating device for regulating the glass melt, and A bottom extraction device for extracting bottom material of the glass melt, wherein the heating device and / or the regulating device comprises a heating device having at least two electrodes for a resistance heater; and in A) designing or controlling the heating device so that a heating current in the form of an alternating current with a frequency between 1 kHz and 200 kHz is applied to the at least two electrodes; and / or B) configuring the contact surface with the glass melt such that it comprises 30% or more of a contact material in the form of a fused-cast zirconium oxide material having a ZrO2 proportion of more than 70% by weight, preferably a fused-cast zirconium oxide material having a ZrO2 proportion of more than 85% by weight; and / or C) The bottom extraction device is designed to extract a volume flow of 1% to 50% of bottom material of the glass melt in the bottom region of the heating device and / or the regulating device.

[0012] The present invention also achieves the above object by a method for operating a glass melting apparatus according to claim 16, wherein at least one, preferably all, of the following steps are performed: I) operating the heating device by applying a heating current to the electrodes, wherein an alternating current with a frequency between 1 kHz and 200 kHz is used as the heating current, II) contacting the glass melt with a contact surface with which the glass melt contacts, the contact surface comprising 30% or more of a fused-cast zirconia material having a ZrO2 proportion exceeding 70% by weight, preferably a fused-cast zirconia material having a ZrO2 proportion exceeding 85% by weight; and III) The bottom extraction device is operated such that a volume flow of 1% to 50% of the bottom material of the glass melt is extracted in the bottom region.

[0013] Furthermore, the present invention also achieves the above-mentioned object by using a glass element manufactured by the method according to any one of claims 13 to 17 and / or by means of a glass melting device according to claim 18, preferably a glass element made of borosilicate glass, preferably in the form of a borosilicate glass plate, preferably a glass element according to any one of claims 1 to 12.

[0014] The term zirconium oxide is understood herein to mean ZrO2.

[0015] Unless otherwise defined, % herein equals % by weight.

[0016] One of the advantages achieved thereby is that inclusions, namely metallic and non-metallic inclusions and bubbles, can be significantly reduced. Preferably, when steps ii) to iii) are carried out and all conditions a) to c) or A) to C) are met or steps I) to III) are carried out, the number of metallic inclusions, in particular of recrystallized products of corrosion products dissolved in the glass, and the number of non-metallic inclusions can be significantly reduced. In this respect, it has been recognized according to the invention that, preferably, when condition a) or A) is met or step I) is carried out, the number of metallic inclusions is reduced. If the frequency range according to the invention is lowered, it has been recognized that the number of metallic inclusions increases dramatically, while an increase in frequency beyond the above-mentioned frequency range can only be achieved in an extremely complex and therefore cost-intensive manner. If condition b) or B) is met or step II) is carried out, it has been recognized according to the invention that this enables a reduction in non-metallic inclusions of the refractory material. If condition c) or C) is met or step III) is carried out, it has been recognized according to the invention that this leads to a reduction in inclusions of recrystallized products of corrosion products dissolved in the glass.

[0017] Preferred embodiments are those in which condition(s) or step(s) a, A or I; b, B or II; c, C or III; a, A or I and b, B or II; a, A or I and c, C or III; b, B or II and c, C or III; or a, A or I and b, B or II and c, C or III are satisfied or performed.

[0018] According to a preferred embodiment, the glass element is a glass pane; a pharmaceutical primary package made of glass, preferably a glass vial, a glass syringe, a glass ampoule and / or a glass cartridge; or a glass tube, preferably a glass element made of borosilicate glass.

[0019] The term "bottom material" in connection with the term "glass melt" refers to a material region of the glass melt which can be extracted through an opening in the bottom, for example through an opening in a heating device and / or a regulating device, preferably in a groove of the regulating device. In general, in the bottom region of the glass melt, extracting a certain percentage of the volume flow from the bottom material of the glass melt means that a certain volume percentage ratio of the glass melt is extracted per unit time in the bottom region. Only the protruding part of the glass melt is used to form a glass element, preferably in the form of a glass sheet. The extraction from the one or more openings in the bottom and the extraction from the protruding part of the glass melt result in a total of 100% of the volume flow. For example, if 25 liters of the bottom material of the glass melt in the bottom region of the glass melt are extracted in a time interval and 75 liters of the glass melt are extracted in the same time interval to form a glass element, preferably a glass sheet, this corresponds to an extraction of 25% of the volume flow from the bottom material of the glass melt in the bottom part of the glass melt.

[0020] The term "contact surface" in connection with the term "glass melt" refers to a surface which comes into contact with the molten glass. This includes, for example, the inner wall of the melting tank, also called working tank, with the usual filling level, stirrers, electrode holders and electrodes, inlets and outlets of the corresponding tanks (segments), channels within the melting tank and the like. In particular, contact surfaces here do not include the surfaces of the feed device for the mixture into the melting tank and contact surfaces immediately after the outlet of the melting tank, such as float tanks and / or cooling channels.

[0021] The term "glass element" is to be understood as a three-dimensional object of any shape, which is at least partially, preferably mainly, preferably completely made of glass, more preferably made of borosilicate glass, and can preferably be configured as a glass plate; as a primary pharmaceutical packaging made of glass, preferably as a glass vial, glass syringe, glass ampoule and / or glass cartridge; or as a glass tube.

[0022] The term "glass pane" is to be understood as a three-dimensional object made of glass, which in the simplest case is essentially constructed as a cuboid with thickness, length and width. The smallest dimension is the thickness, the two largest dimensions represent the faces with length and width. The viewing plane is along the normal to the face.

[0023] The thickness, length and width can be freely selected. The thickness is preferably between 0.01 cm and 10 cm, more preferably between 0.1 cm and 5 cm, more preferably between 0.15 cm and 2.5 cm, most preferably between 0.2 and 0.4 cm. The length and width are preferably between 1 cm and 500 cm, more preferably between 3 cm and 400 cm, more preferably between 5 and 100 cm, more preferably between 20 and 70 cm, most preferably between 40 cm and 60 cm, respectively. This has the advantage of providing a thin, transparent glass sheet, for example as a transparent cover or the like.

[0024] The term "glass tube" is to be understood as a three-dimensional object made of glass, which in the simplest case is essentially constructed as an elongated hollow body with an outer diameter, a length and a wall thickness. For example, the smallest dimension is the wall thickness, the two larger dimensions are the outer diameter and the length. The observation plane is along the normal to the outer surface of the tube.

[0025] The outer diameter, length and wall thickness can be freely selected. Preferably, the length of the glass tube is 2 cm or more, preferably 10 cm or more, more preferably 20 cm or more, more preferably 30 cm or more, more preferably 40 cm or more, more preferably 50 cm or more, more preferably 110 cm or more and / or 500 cm or less, preferably 400 cm or less, more preferably 300 cm or less, more preferably 200 cm or less, more preferably 100 cm or less, more preferably 50 cm or less. Preferably, the outer diameter is 3 mm or more, preferably 4 mm or more, more preferably 5 mm or more, more preferably 6 mm or more, more preferably 7 mm or more, more preferably 8 mm or more, more preferably 9 mm or more, more preferably 10 mm or more, more preferably 15 mm or more, more preferably 20 mm or more and / or 20 cm or less, preferably 15 cm or less, more preferably 10 cm or less, more preferably 5 cm or less, more preferably 4 cm or less, more preferably 3 cm or less, more preferably 2 cm or less. Preferably, the wall thickness is 0.1 mm, preferably 0.5 mm, more preferably 0.8 mm, more preferably 1.0 mm, more preferably 1.5 mm, more preferably 2.0 mm, more preferably 3.0 mm and / or 10.0 mm or less, preferably 5.0 mm or less, more preferably 5.0 mm or less, more preferably 4.0 mm or less, more preferably 3.0 mm or less, more preferably 2.0 mm or less, more preferably 1.0 mm or less.

[0026] The transmittance of the glass element is not particularly limited. Preferably, the glass element is standardized to a glass element, preferably a glass sheet or a glass tube, with a thickness or wall thickness of 6.5 mm and a transmittance of 70% or more, more preferably 80% or more, more preferably 90% or more, most preferably 95% or more at a wavelength of 400 nm to 800 nm. The transmittance is usually measured using a UV-visible spectrophotometer, such as a Specord 250 Plus spectrophotometer (from Analytik Jena). The transmittance of the sample is measured in the wavelength range of 250 to 1050 nm; the measurement is usually evaluated according to DIN EN 410:2011-04 (Glass in building construction - Determination of photometric and radiation-physical parameters of glass; German version EN 410:2011).

[0027] The determination of the number of inclusions and the size of inclusions according to an embodiment of the present invention is carried out by means of the method described below: In a dark room, visible light is directed perpendicularly to the extension of the glass sheet thickness, preferably at the straight cut edge, and parallel to the plane formed by the two largest dimensions (length and width) into the glass element to be inspected, in this case the glass sheet. Inclusions are identified by the reflection of light at the inclusions in the glass sheet. A handheld microscope, such as the handheld microscope "Wide Stand Microscope" from PEAK, can be used to distinguish dust and inclusions in the glass sheet, such as small particles in the size range <20µm. The particles optically identified in this way are visibly marked. The glass sheet marked in this way is observed under an optical microscope (e.g. Axio Imager M2m from Zeiss, with LD EC Epiplan 50x / 0.55 HD DIC objective and PI10x / 2 eyepiece) along the normal of the surface, whereby the inclusions are classified and their size is measured. The size of the inclusions and particles here refers to the longest dimension visible in the observation plane. With this type of measurement, it is consciously accepted that three-dimensionally structured inclusions can also extend in the measurement at their maximum elongation in the direction of the optical axis of the microscope, i.e. along the normal to the observation plane, and that in this case the smaller measured value of the inclusion is obtained as the actual value of the current elongation of the inclusion (e.g. crystal or crystallite). The smallest inclusion size that can be measured or measured with the Axio Imager M2m from Zeiss is approximately 2 µm. Therefore, smaller inclusions with a size of less than 2 µm are not taken into account when calculating the inclusions.

[0028] Although not described in detail, a person skilled in the art has no problem applying the above method to a glass element, such as a glass tube.

[0029] For example, smaller inclusions with a size of less than 2µm up to and including 50nm can be measured with the help of the Xradia 800 Ultra X-ray microscope from Carl Zeiss. Therefore, even smaller inclusions with a size of less than 50nm are not calculated or taken into account in the sense of inclusions.

[0030] If the weight of the glass element is less than one kilogram, the inclusions are calculated proportionally. If the weight of the glass element exceeds one kilogram, the number of inclusions is multiplied accordingly. The weight of the glass element is not particularly limited. The weight of the glass element is preferably 5 g to 400 kg, more preferably 0.01 kg to 350 kg, more preferably 0.1 kg to 20 kg, more preferably 0.2 kg to 18 kg, more preferably 0.5 kg to 15 kg, and most preferably 1.0 kg to 10 kg.

[0031] Unless otherwise indicated, all percentages herein are understood to be percentages by weight, abbreviated as wt %.

[0032] The term “inclusions” is to be understood here in the broadest sense and comprises in particular inclusions in the form of metallic and non-metallic inclusions, also called particles, and inclusions in the form of gaseous(ies), for example air, ie bubbles.

[0033] The term "metal inclusions" is to be understood in the broadest sense herein. Metal inclusions are here in particular inclusions which comprise particles of one or more metals which are present predominantly in elemental form. The metal or metals of the metal inclusions therefore have an oxidation state equal to 0. Metal inclusions include in particular noble metals and refractory metals.

[0034] The term "non-metallic inclusions" should be understood in the broadest sense. Non-metallic inclusions are inclusions comprising cations (oxidation level>0) and anions (oxidation level<0), also called salts. In particular, non-metallic inclusions comprise a crystal from the glass constituent and particles in the form of one or more refractory metal and noble metal salts, in particular crystals from the glass constituent and one or more refractory metal and noble metal silicates or oxides.

[0035] If the inclusion consists essentially of elemental metal, ie, approximately 100% elemental metal (oxidation level equal to 0), the inclusion is considered a metallic inclusion, otherwise the inclusion is considered a non-metallic inclusion. Metals and non-metals can be optically distinguished, for example, in the manner described above.

[0036] Examples of refractory metals are the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten.

[0037] The noble metal herein includes semi-noble metals and is exemplified by ruthenium, rhodium, palladium, osmium, iridium, platinum, silver, gold, copper, technetium, rhenium, antimony, bismuth and polonium.

[0038] Other examples of metals that may be contained in inclusions are magnesium, calcium, aluminum, silicon, tin (metallic inclusions) and their salts (non-metallic inclusions).

[0039] The term "bubble" should be understood in the broadest sense. Bubbles are formed by gas inclusions in the glass, where the gas can be gaseous at room temperature (20°C) or condense after cooling to produce bubbles with negative pressure. Examples of gases forming inclusions include oxygen, nitrogen, nitrogen oxides, carbon dioxide, sulfur dioxide, etc.

[0040] Unless otherwise defined, all preferred parameters and embodiments of the glass element apply here also to both methods and glass melting devices, and vice versa.

[0041] Further features, advantages and further embodiments of the invention will be described below or will be apparent from the invention.

[0042] According to a preferred refinement, the glass element has 50 or fewer inclusions per kilogram of glass having a size of 500 nm or more and 10 μm or less, preferably 50 nm or more and 10 μm or less, more preferably 10 μm or less. This has the advantage that a higher quality glass is preferably provided for high-energy laser applications.

[0043] According to a preferred embodiment, the glass element has 2000 or fewer inclusions per kg of glass, preferably 1000 or fewer inclusions, more preferably 500 or fewer inclusions, more preferably 250 or fewer inclusions, more preferably 100 or fewer inclusions, more preferably 50 inclusions, with a size of 20 μm or less, preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less, and a size of 2 μm or more, preferably 50 nm or more. This has the advantage of providing a higher quality glass preferably for high energy laser applications. If the number of inclusions remains constant but varies over a larger size range, high energy laser applications will be less affected.

[0044] Please note the following: For example, if the number of inclusions per kilogram of glass is limited to 50 or less and the size is 10 μm or less, a glass element according to an embodiment of the present invention may have 50 inclusions of 5 μm and 50 inclusions of 40 μm per kilogram of glass. However, if the number of inclusions per kilogram of glass is limited to 50 or less and the size is 50 μm or less, for example, a glass element having 50 inclusions of 5 μm and 50 inclusions of 40 μm per kilogram of glass does not satisfy this condition, but, for example, a glass element having 10 inclusions of 5 μm, 20 inclusions of 25 μm, and 15 inclusions of 45 μm does satisfy this condition.

[0045] The glass element may have any number of other larger inclusions. Large inclusions can be easily detected with the aid of common measurement techniques, for example directly after the production of the glass element and / or before further processing, and the glass element can be completely or partially sorted out. Large inclusions can also be significantly reduced by the embodiments of the invention described herein. Thus, the glass element has no inclusions with a size greater than 50 μm, more preferably greater than 40 μm, more preferably greater than 30 μm, more preferably greater than 20 μm, most preferably greater than 10 μm.

[0046] According to a preferred embodiment, the glass element has 50 or fewer inclusions per kilogram of glass, preferably 40 or fewer inclusions, preferably 30 or fewer inclusions, more preferably 20 or fewer inclusions, most preferably 10 or fewer inclusions, wherein these inclusions may have a size of 10 μm or less, preferably 20 μm or less, preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less. This has the advantage that the quality of the glass element is preferably improved for high-energy laser applications. The fewer inclusions per kilogram of glass, the less influence on high-energy laser applications. The quality of the glass element is improved.

[0047] Depending on the variation of the parameters, namely the frequency of the alternating current, the percentage extraction of the volume flow and the proportion of zirconium oxide in the contact surface, both the number and the size of the inclusions are influenced. Even when only conditions a) or A), b) or B) and c) or C) are met or only one step I), II) or III) is performed, at least one parameter among the size of the inclusions and / or the number of inclusions per kg of glass is reduced.

[0048] According to a preferred embodiment, the inclusions include metal inclusions, and wherein the glass element has 40 or fewer metal inclusions per kilogram of glass, preferably 30 or fewer metal inclusions, more preferably 20 or fewer metal inclusions, more preferably 10 or fewer metal inclusions, most preferably 5 or fewer metal inclusions, the size of which is 5 μm or less, preferably 10 μm or less, more preferably 20 μm or less, more preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less. As a result, the glass element has fewer inclusions overall due to the metal particles, which further improves the quality of the glass element. Frequently occurring metal inclusions include, in particular, metals such as tungsten, zirconium, platinum, rhodium, iridium, molybdenum, tin and copper, because these metals come into contact with the glass during the manufacture of the glass element.

[0049] According to a preferred embodiment, the inclusions include non-metallic inclusions, wherein the glass element has 25 or less non-metallic inclusions per kg of glass, preferably 15 or less non-metallic inclusions, more preferably 8 or less non-metallic inclusions, more preferably 1 or less non-metallic inclusions, more preferably 0.1 or less non-metallic inclusions, more preferably 0.05 or less non-metallic inclusions, most preferably 0.00 non-metallic inclusions, the size of which is 2 μm or more and 10 μm or less, preferably 2 μm or more and 20 μm or less, more preferably 2 μm or more and 30 μm or less, more preferably 2 μm or more and 40 μm or less, most preferably 2 μm or more and 50 μm or less. This reduces the number and size of non-metallic inclusions, thereby improving the quality of the glass element. Frequently occurring non-metallic inclusions include, in particular, crystals formed from glass components and / or oxides of one or more silicates and / or refractory metals and / or precious metals. For example, crystals crystallize from a glass melt, while silicates and / or oxides of refractory metals and / or noble metals are formed from contact materials in contact with the glass melt.

[0050] According to a preferred embodiment, the inclusions comprise bubbles, wherein the glass element has 25 bubbles or less, preferably 15 bubbles or less, more preferably 8 bubbles or less, more preferably 1 bubble or less, more preferably 0.1 bubbles or less, more preferably 0.05 bubbles or less, most preferably 0.00 bubbles per kg of glass, the size of which is 10 μm or less, preferably 20 μm or less, more preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less and / or 2 μm or more, preferably 50 nm or more. Thus, the overall quality of the glass element is also improved by inclusions in the form of bubbles.

[0051] According to a preferred embodiment, the glass element comprises, in weight %,: SiO2 60% to 90%, more preferably 76% to 90%; B2O3 0 to 20%; Al2O3 0 to 20%; Li2O 0 to 10%; Na2O 0 to 10%; K2O 0 to 10%; MgO 0 to 10%; CaO 0 to 10%, SrO 0 to 10%; and BaO 0 to 10%.

[0052] In a further preferred embodiment, the glass element has the following composition in wt. %: SiO2 exceeds 76%; B2O3 0 to 15%; Al2O3 0 to 5 %; Li2O 0 to 4 %; Na2O 0 to 4 %; K2O 0 to 4 %; MgO 0 to 4 %; CaO 0 to 4 %, SrO 0 to 4 %; and BaO 0 to 4 %; and Unavoidable impurities, i.e. less than 0.01%.

[0053] In a further preferred embodiment, the glass element has the following composition in % by weight: SiO2 76% to 85%; B2O3 0 to 15%; Al2O3 0 to 5 %; Li2O 0 to 4 %; Na2O 0 to 4 %; K2O 0 to 4 %; MgO 0 to 4 %; CaO 0 to 4 %, SrO 0 to 4 %; and BaO 0 to 4 %; and Unavoidable impurities, i.e. less than 0.01%.

[0054] The glass element preferably has a weight proportion of less than 0.05% by weight, more preferably less than 0.01% by weight of iron, arsenic and / or antimony oxides. More preferably, the glass element is free of iron, arsenic and antimony oxides. An environmentally friendly glass element is obtained by an arsenic-free and antimony-free glass element. Iron oxide may occur as an impurity, which may affect the color of the glass element. This can be prevented by selecting suitable starting materials.

[0055] According to a preferred embodiment, the glass element has one or more of the following features: i) the weight of the glass element is from 0.01 kg to 350 kg, preferably from 0.1 kg to 20 kg, more preferably from 0.5 kg to 15 kg, most preferably from 1.0 kg to 10 kg; ii) when the glass element is provided in the form of a glass sheet, the glass element has a thickness of between 0.01 cm and 10 cm, preferably between 0.1 cm and 5 cm, more preferably between 0.15 cm and 2.5 cm, most preferably between 0.2 and 0.4 cm; iii) when the glass element is provided in the form of a glass sheet, the length and width of the glass element are respectively between 1 cm and 500 cm, preferably between 3 cm and 400 cm, more preferably between 5 and 100 cm, more preferably between 20 and 70 cm, most preferably between 40 cm and 60 cm; iv) the glass element is standardized to a glass element in the form of a glass plate having a thickness of 6.5 mm and a transmittance at a wavelength of 400 nm to 800 nm of 70% or more, more preferably 80% or more, more preferably 90% or more, most preferably 95% or more; and v) The glass element has no inclusions having a size greater than 50 μm, preferably greater than 40 μm, more preferably greater than 30 μm, more preferably greater than 20 μm, most preferably greater than 10 μm.

[0056] More preferably, the glass element has the above characteristics i; ii; iii; iv; v; i+ii; i+iii; i+iv; i+v; ii+iii; ii+iv; ii+v; iii+iv; iii+v; iv+v; ii+iii+v; ii+iv+v; iii+iv+v; i+ii+iii+iv; i+ii+iii+v; i+ii+iv+v; i+iii+iv+v or i+ii+iii+iv+v.

[0057] According to a preferred embodiment of the method, the viscosity of the glass melt is set to a value between 30 Pas and 450 Pas, preferably between 33 Pas and 400 Pas, more preferably between 35 Pas and 265 Pas and / or maintained at this value at least in step ii) and iii). According to a preferred embodiment of the method, the viscosity of the glass melt is set to a value between 33 Pas and 265 Pas, preferably between 35 Pas and 200 Pas, at least in step ii). According to a preferred embodiment of the method, the viscosity of the glass melt is set to a value between 70 Pas and 450 Pas, preferably between 100 Pas and 400 Pas and / or maintained at this value at least in step iii). One of the advantages achieved in this way is that the method can be used for a large number of different glasses produced at different temperatures during the production process.

[0058] According to a preferred embodiment, the glass element is provided in the form of a glass plate or a glass tube. This makes the glass element easy to manufacture and can be used flexibly for various applications.

[0059] According to a preferred embodiment, the glass element has 2000 or less, preferably 1000 or less, more preferably 500 or less, more preferably 250 or less, more preferably 100 or less, more preferably 50 or less inclusions of size 50 nm or more and 500 nm or less per kg of glass. This has the advantage of providing a higher quality glass preferably for high energy laser applications.

[0060] According to a preferred embodiment, the glass element has 2000 or fewer, preferably 1000 or fewer, more preferably 500 or fewer, more preferably 250 or fewer, more preferably 100 or fewer, more preferably 50 or fewer inclusions having a size of 500 nm or more and 2 μm or less per kg of glass. This has the advantage that the quality of the glass element is higher.

[0061] According to a preferred embodiment of the method, an alternating current with a frequency between 1 kHz and 100 kHz, preferably between 5 kHz and 50 kHz, more preferably between 8 kHz and 15 kHz is used as the heating current. If the frequency is 1 kHz or more, preferably 5 kHz or more, more preferably 8 kHz or more, the number of inclusions, especially metal inclusions, is reduced. However, when the frequency is 200 kHz or less, preferably 100 kHz or less, more preferably 50 kHz or less, more preferably 15 kHz or less, the frequency is easier to achieve and unexpected problems such as blistering due to local overheating occur less frequently.

[0062] According to a preferred embodiment of the method, the contact surface with the glass melt comprises 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more of the contact material in the form of fused-cast zirconia material, thereby reducing the number of inclusions, for example from refractory materials, and improving the quality of the glass or glass element.

[0063] According to a preferred embodiment of the method, the contact material comprises a fused-cast zirconium oxide material having a ZrO2 content of more than 90% by weight, preferably more than 95% by weight. This further reduces the number of inclusions from the refractory material and further improves the quality of the glass element.

[0064] According to a preferred embodiment of the method, 5% to 40%, preferably 20% to 40%, more preferably 25% to 35% of the volume flow of the bottom material of the glass melt is extracted in the bottom area. This has the advantage of reducing the number of inclusions from corrosion products, i.e., non-metallic inclusions, thereby improving the quality of the glass.

[0065] In a preferred embodiment, in a method for producing a glass element in the form of a glass sheet, preferably a borosilicate glass sheet, the following steps S1 to S4 are performed; preferably S1 is performed first, then S2, then S3 and finally S4.

[0066] In a first step S1, a mixture is provided according to an embodiment of the present invention. In a further step S2, the mixture is heated to form a glass melt. In a further step S3, the glass melt is conditioned and in a further step S4, the glass melt is cooled to provide a glass element.

[0067] During the execution of steps S2-heating- and S3-conditioning, at least one of the following conditions, preferably all of them, is met: a) the glass melt is heated at least partially by means of a resistance heater by applying a heating current to electrodes, wherein an alternating current with a frequency between 1 kHz and 200 kHz is used as the heating current; b) the contact surface in contact with the glass melt comprises 30% or more of the contact material in the form of a fused-cast zirconium oxide material having a ZrO2 proportion exceeding 70% by weight; and c) 1% to 50% of the bottom material of the glass melt is extracted in the bottom region of the glass melt.

[0068] Further preferred features and advantages of the invention emerge from the dependent claims, the drawings and the associated figure description.

[0069] It is self-evident that the features mentioned above and explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Preferred designs and embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein the same reference numerals designate the same or similar or functionally identical components or elements.

[0071] In the attached figure: Figure 1 A glass melting apparatus according to an embodiment of the present invention is shown; and Figure 2 A method for producing a glass element according to one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0072] Figure 1 A glass melting apparatus according to one embodiment of the present invention is shown.

[0073] Figure 1 The glass melting device 1 is shown in detail. The glass melting device 1 comprises a heating device 2 in which the starting material, the so-called mixture, is heated and melted. For this purpose, the heating device 2 has a trough 2a provided with a bottom extraction device 6a for extracting bottom material 11 of the glass melt 10.

[0074] In order to ensure sufficient homogeneity and absence of bubbles, the glass melt 10 is refined after melting in a refining device 23 located downstream, which can also serve as a conveying area for conveying the glass melt 10 to downstream sections. The basic goal of refining the glass melt 10 is to remove gases that are physically and chemically bound in the glass melt 10 from the glass melt 10. After the refining is completed, the formation of new bubbles in the melt should at least be reduced or even prevented. In principle, the refining can be carried out in the same tank 2a or in a separate tank. The refining device 23 is followed by the conditioning device 3, in which the glass melt 10 is further conditioned and / or homogenized. At the bottom of the conditioning device 3 is another bottom extraction device 6b.

[0075] The wall 20 of the above-mentioned means 2, 23, 3 of the glass melting apparatus 1 comprises a refractory material, for example the above-mentioned fused cast zirconia material. Figure 1 , the heating device 2 is separated from the refining device 23 by means of a flow-influencing element 15, which in this region extends transversely to the flow direction over the entire width of the glass-melting device 1 and substantially completely blocks this region, except for a slight protrusion relative to the glass level. Alternatively or additionally, the flow-influencing element 15 can also be arranged in the transition region between the refining device 23 and the regulating device 3.

[0076] In addition, the glass melting device 1 has a heating device 4 with electrodes 5 for resistance heating. They are connected to an AC power supply 8, which provides an AC power supply with a frequency between 1kHz and 200kHz as a heating current. In addition, the glass melt can be heated, for example, by a gas burner (not shown). The control device 30 controls the regulating device 3, the heating device 2, the AC power supply 8, and the refining device 23 and the bottom extraction device 6a, 6b if necessary, so that on the one hand, the bottom material of the glass melt is extracted between 1% and 50% of the volume flow of the glass melt 10, for example, 25%, and can be sent back to the heating device 2 if necessary, and on the other hand, the glass melt 10 is resistively heated at least in the regulating device 3. In addition, the contact surface 7 in contact with the glass melt 10 has a contact material 7a in the form of a fused cast zirconium oxide material with a proportion of ZrO2 exceeding 70% by weight, preferably a fused cast zirconium oxide material with a proportion of ZrO2 exceeding 85% by weight.

[0077] Figure 2 The steps of a method for producing a glass element according to one embodiment of the invention are shown.

[0078] The method comprises the following steps: In a first step S1 a mixture is provided according to an embodiment of the invention. In a further step S2 the mixture is heated to form a glass melt. In a further step S3 the glass melt is conditioned and in a further step S4 the glass melt is cooled to provide a glass element.

[0079] In a preferred embodiment, the following steps S1 to S4 are performed in a method according to any one of claims 9 to 13 for manufacturing a glass element according to any one of claims 1 to 12 in the form of a glass plate, preferably a borosilicate glass plate; preferably S1 is performed first, then S2, then S3, and finally S4.

[0080] Example In the following table, the total number of inclusions of the comparative example and the example according to the embodiment of the present invention is shown in different categories, divided into bubbles, non-metallic inclusions and metallic inclusions: a Comparative Example b. Example of an embodiment according to the present invention The particle size distribution of metal inclusions in the range of 0 to 50 μm per kilogram of glass of Examples 3 to 6 is shown in the following table, wherein the size interval of 0 μm to 5 μm given in the following table only considers inclusions with a size of 2 μm or more: b. Example of an embodiment according to the present invention In Comparative Example 1 and Example 2, the size distribution of inclusions was not accurately determined. In Examples 2 and 3, the total number of inclusions per kg of glass was just over 50 (e.g., Example 2: 0.3 + 0.2 + 53.2 = 53.7 per kg), but some of the inclusions had a size of over 50 µm, so that the number of inclusions with a size of 50 µm or less and therefore the number of inclusions with a size of 10 µm or less was less than 50 inclusions per kg of glass (see Table 2; Example 3: 10.5 + 10.5 + 10.5 + 7.0 + 3.5 + 3.5 = 45.5 per kg). In addition to the inclusions in Table 2, inclusions with a size greater than 100 μm were found in Example 3. In Examples 3 to 6, the number of inclusions with a size of 50 μm or less was less than 50 inclusions per kg (see Table 2). In Examples 4 to 6, there are even fewer than 10 inclusions per kilogram. In addition, the glass sheets of Examples 4 to 6 have no other inclusions larger than 50 μm in size (as can be seen by comparing Table 1 with Table 2).

[0081] Comparative Example 1 is an example of a glass element in the form of a glass plate, in which the improvements to the glass melting device described here were not used, in other words a glass melting device known in the past or a production method known in the past was used. The total number of inclusions here clearly exceeded 50, and the number of inclusions of the corresponding type was also high. Even though the exact size of each individual inclusion was not determined in Comparative Example 1, it can be assumed that due to the large number of inclusions also in the range below 50 μm, the number of inclusions must have clearly exceeded 50 inclusions per kilogram. On this basis, the experimental glass melting device was successively improved.

[0082] First, in the experiment of the glass melting device, a part of the contact surface (about 70% or more) in contact with the glass melt was provided with a contact material made of a fused-cast zirconia material having a proportion of more than 70% by weight. At the same time, the glass melting device was operated to extract a volume flow of 1% to 50% of the bottom material of the glass melt in the bottom area of ​​the glass melt. This resulted in a significant reduction in bubbles and non-metallic inclusions (see, for example, Example 2). The number of metal inclusions in Example 2 exceeded 50 (number = 53.2), where, as described above, although most of the inclusions were 50 μm or less in size, some of the inclusions were also larger than 50 μm in size. Therefore, the glass sheet manufactured in this way had 50 or less inclusions of 10 μm or less in size per kilogram of glass. Even if the special contact material was added to a small part of the contact surface (30% or more of the contact surface), it resulted in a reduction in bubbles and non-metallic inclusions. 0 bubbles and non-metallic inclusions having a size of 50 µm or less are found per kg of glass in a glass sheet manufactured using a glass melting apparatus, wherein most of the contact surface with the glass melt (90% or more, even 95% or more) is a fused-cast zirconia material having a high proportion (85% or more, even 95% or more) of ZrO2, and further, in the bottom region of the glass melt, most of the bottom material of the glass melt (between 25 volume % and 35 volume %) is extracted (see Examples 3 to 6).

[0083] The resistance heater is likewise optimized. For this purpose, a new resistance heater according to an embodiment of the invention was installed in a glass melting device for test purposes. In comparative example 1, a conventional resistance heater was used, and a large number of metal inclusions were found in the glass sheets produced with it. In examples 2 to 6, the glass melt was at least partially heated and / or heated with a resistance heater by applying a heating current to the electrodes, wherein an alternating current with a frequency between 1 kHz and 200 kHz was used as the heating current, wherein the number of metal inclusions could be reduced. By adjusting the frequency between 1 kHz and 100 kHz, the number of metal inclusions could be further significantly reduced, until finally particularly few metal inclusions were found between 8 kHz and 15 kHz (see examples 4 to 6).

[0084] It can also be seen from the examples that the best results are achieved when all three improvement steps described in this article are applied.

[0085] In summary, at least one embodiment of the present invention has at least one of the following advantages: - Reduce inclusions, preferably metal particle inclusions, with a size of 50µm or less; - Increase the flexibility of glass in various applications, - Higher quality glass; - less waste; and - Reduced number of volumetric defects or lower volumetric defect density.

[0086] The glass or glass element produced by the embodiments of the present invention can be preferably used for the following applications: - High energy density laser applications; - Large-format, homogeneous and / or low-defect photomasks for lithography applications; - Nanoimprint lithography, for imprinting precision lenses or nanostructures down to the nm range, such as molds for magnetic layers in hard disks and the like; - Substrates for planar metal lens concepts and metal lens optics; - Super glass wafers; and - Precision windows in displays, preferably for OLEDs.

[0087] Although the present invention has been described based on the preferred embodiments, the present invention is not limited thereto but can be modified in various ways.

[0088] Reference numerals list 1 Glass melting equipment 2 Heating device Slot 2a 3 Adjustment device 4 Heating device 5 Electrodes 6a, 6b Bottom extraction device 7 Contact surface 7a Contact materials 8 AC power supply 10 Glass melt 11 Bottom material 20 wall 23 Refining unit 30 Control device

Claims

1. A glass element, preferably a glass element made of borosilicate glass, in, The glass element has 50 or fewer inclusions having a size of 2 μm or more and 10 μm or less per kilogram of glass.

2. The glass element according to claim 1, wherein The glass element has 2000 or fewer inclusions per kilogram of glass, preferably 1000 or fewer inclusions, more preferably 500 or fewer inclusions, more preferably 250 or fewer inclusions, more preferably 100 or fewer inclusions, more preferably 50 or fewer inclusions, and the size of the inclusions is 500 nm or more and 10 μm or less, preferably 50 nm or more and 10 μm or less, more preferably 10 μm or less.

3. The glass element according to any one of claims 1 or 2, wherein: The glass element has 50 or fewer inclusions per kg of glass having a size of 20 μm or less, preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less and / or a size of 2 μm or more, preferably 50 nm or more.

4. The glass element according to any one of claims 1 to 3, wherein: The glass element has 40 inclusions or less, preferably 30 inclusions or less, more preferably 20 inclusions or less, and most preferably 10 inclusions or less per kilogram of glass.

5. The glass element according to any one of claims 1 to 4, wherein The inclusions include metallic inclusions, and wherein the glass element has 40 or fewer metallic inclusions per kilogram of glass, preferably 30 or fewer metallic inclusions, more preferably 20 or fewer metallic inclusions, more preferably 10 or fewer metallic inclusions, most preferably 5 or fewer metallic inclusions, and the metallic inclusions are 5 μm or less in size, preferably 10 μm or less, more preferably 20 μm or less, more preferably 30 μm or less, more preferably 40 μm or less, and most preferably 50 μm or less.

6. The glass element according to any one of claims 1 to 5, wherein The inclusions include non-metallic inclusions, and wherein the glass element has 25 or fewer non-metallic inclusions per kilogram of glass, preferably 15 or fewer non-metallic inclusions, more preferably 8 or fewer non-metallic inclusions, more preferably 1 or fewer non-metallic inclusions, more preferably 0.1 or fewer non-metallic inclusions, more preferably 0.05 or fewer non-metallic inclusions, and most preferably 0.00 non-metallic inclusions, and the non-metallic inclusion size is 2 μm or more and 10 μm or less, preferably 2 μm or more and 20 μm or less, more preferably 2 μm or more and 30 μm or less, more preferably 2 μm or more and 40 μm or less, and most preferably 2 μm or more and 50 μm or less.

7. The glass element according to any one of claims 1 to 6, wherein The inclusions include bubbles, wherein the glass element has 25 bubbles or less, preferably 15 bubbles or less, more preferably 8 bubbles or less, more preferably 1 bubble or less, more preferably 0.1 bubbles or less, more preferably 0.05 bubbles or less, most preferably 0.00 bubbles per kilogram of glass, and the bubble size is 10 μm or less, preferably 20 μm or less, more preferably 30 μm or less, more preferably 40 μm or less, most preferably 50 μm or less and / or 2 μm or more, preferably 50 nm or more.

8. The glass element according to any one of claims 1 to 7, wherein In terms of weight %, the glass element comprises: SiO2 60% to 90%, preferably 76% to 90%; B2O3 0 to 20%; Al2O3 0 to 20%; Li2O 0 to 10%; Na2O 0 to 10%; K2O 0 to 10%; MgO 0 to 10%; CaO 0 to 10%, SrO 0 to 10%; and BaO 0 to 10%.

9. The glass element according to any one of claims 1 to 8, wherein The glass element has one or more of the following features: i) the weight of the glass element is from 0.01 kg to 350 kg, preferably from 0.1 kg to 20 kg, more preferably from 0.5 kg to 15 kg, most preferably from 1.0 kg to 10 kg; ii) when the glass element is provided in the form of a glass sheet, the glass element has a thickness of between 0.01 cm and 10 cm, preferably between 0.1 cm and 5 cm, more preferably between 0.15 cm and 2.5 cm, most preferably between 0.2 and 0.4 cm; iii) when the glass element is provided in the form of a glass sheet, the length and width of the glass element are both between 1 cm and 500 cm, preferably between 3 cm and 400 cm, more preferably between 5 and 100 cm, more preferably between 20 and 70 cm, most preferably between 40 cm and 60 cm; iv) the glass element is standardized to a glass element in the form of a glass plate having a thickness of 6.5 mm, and has a transmittance of 70% or more, more preferably 80% or more, more preferably 90% or more, most preferably 95% or more at a wavelength of 400 nm to 800 nm; as well as v) The glass element has no inclusions having a size greater than 50 μm, preferably greater than 40 μm, more preferably greater than 30 μm, more preferably greater than 20 μm, most preferably greater than 10 μm.

10. The glass element according to any one of claims 1 to 9, wherein: The glass element is provided in the form of a glass sheet or a glass tube.

11. The glass element according to any one of claims 1 to 10, wherein: The glass element has 2000 or fewer, preferably 1000 or fewer, more preferably 500 or fewer, more preferably 250 or fewer, more preferably 100 or fewer, more preferably 50 or fewer inclusions having a size of 50 nm or more and 500 nm or less per kilogram of glass.

12. The glass element according to any one of claims 1 to 11, wherein: The glass element has 2000 or fewer, preferably 1000 or fewer, more preferably 500 or fewer, more preferably 250 or fewer, more preferably 100 or fewer, more preferably 50 or fewer inclusions having a size of 500 nm or more and 2 μm or less per kilogram of glass.

13. A method for producing a glass element, in particular according to any one of claims 1 to 12, preferably a glass element made of borosilicate glass, comprising the following steps: i) providing (S1) a mixture comprising, in weight %, SiO2 60% to 90%, preferably 76% to 90%; B2O3 0 to 20%; Al2O3 0 to 20%; Li2O 0 to 10%; Na2O 0 to 10%; K2O 0 to 10%; MgO 0 to 10%; CaO 0 to 10%, SrO 0 to 10%; and BaO 0 to 10%; ii) heating (S2) the mixture to form a glass melt (10), iii) conditioning (S3) the glass melt (10), and iv) cooling (S4) the glass melt (10) to provide the glass element, Wherein, during step ii) and / or step iii), at least one, preferably all, of the following conditions are met: a) the glass melt (10) is heated and / or heated at least partially by means of a resistance heater by applying a heating current to the electrodes (5), wherein an alternating current with a frequency between 1 kHz and 200 kHz is used as the heating current; b) the contact surface (7) in contact with the glass melt (10) comprises 30% or more of a contact material (7a) in the form of a fused-cast zirconium oxide material having a ZrO2 proportion exceeding 70% by weight; and c) 1% to 50% of the volume flow of bottom material (11) of the glass melt (10) is removed in the bottom region of the glass melt (10).

14. The method according to claim 13, wherein: The viscosity of the glass melt (10) is set and / or maintained at a value between 30 Pas and 450 Pas, preferably between 33 Pas and 400 Pas, more preferably between 35 Pas and 265 Pas, at least in step ii) and / or iii).

15. The method according to claim 13 or 14, wherein: An alternating current having a frequency between 1 kHz and 100 kHz, preferably between 5 kHz and 50 kHz, more preferably between 8 kHz and 15 kHz, is used as the heating current.

16. The method according to any one of claims 13 to 15, wherein: The contact surface (7) in contact with the glass melt (10) comprises 60% or more, preferably 80% or more, more preferably 90% or more, and most preferably 95% or more of a contact material (7a) in the form of a fused-cast zirconium oxide material having a ZrO2 proportion of 75% by weight or more, preferably 85% by weight or more, and more preferably 95% by weight or more.

17. The method according to any one of claims 13 to 16, wherein: 5% to 40%, preferably 20% to 40%, more preferably 25% to 35% of the volume flow of the bottom material (11) of the glass melt (10) is removed in the bottom region.

18. A glass melting apparatus (1) for carrying out the method according to any one of claims 13 to 17, comprising: a heating device (2) for heating the mixture to form a glass melt (10), a regulating device (3) for regulating the glass melt (10), and a bottom extraction device (6a, 6b) for extracting a bottom material (11) of the glass melt (10), Wherein, the heating device (2) and / or the regulating device (3) comprises a heating device (4) having at least two electrodes for a resistance heater; and in A) designing or controlling the heating device (4) so ​​that a heating current in the form of an alternating current with a frequency between 1 kHz and 200 kHz is applied to the at least two electrodes (5); and / or B) constructing the contact surface (7) in contact with the glass melt (10) so that it comprises 30% or more of a contact material (7a) in the form of a fused-cast zirconium oxide material having a ZrO2 proportion of more than 70% by weight, preferably a fused-cast zirconium oxide material having a ZrO2 proportion of more than 85% by weight; and / or C) The bottom extraction device (6a, 6b) is designed to extract a volume flow of 1% to 50% of the bottom material (11) of the glass melt (10) in the bottom region of the heating device (2) and / or the regulating device (3).

19. A method for operating a glass melting apparatus (1) according to claim 18, wherein at least one, preferably all, of the following steps are performed: I) operating the heating device (4) by applying a heating current to the electrode (5), wherein an alternating current with a frequency between 1 kHz and 200 kHz is used as the heating current, II) bringing the glass melt (10) into contact with a contact surface (7) with which the glass melt (10) contacts, the contact surface comprising 30% or more of a fused-cast zirconia material having a ZrO2 proportion exceeding 70% by weight, preferably a fused-cast zirconia material having a ZrO2 proportion exceeding 85% by weight; and III) The bottom extraction device (6a, 6b) is operated such that a volume flow of between 1% and 50% of the bottom material (11) of the glass melt (10) is extracted in the bottom region of the glass melt (10).

20. A glass element, preferably a glass element made of borosilicate glass, preferably in the form of a borosilicate glass plate, preferably a glass element according to any one of claims 1 to 12, produced using the method according to any one of claims 13 to 17 and / or with the aid of a glass melting device (1) according to claim 18.

Images