GLASS, METHOD FOR MAKING GLASS AND GLASS MELTING PLANT

Description

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

[0002] The invention further relates to a method for producing a glass element from borosilicate glass.

[0003] The invention further relates to a glass melting plant and a method for operating a glass melting plant.

[0004] Although the present invention is generally applicable to any glass element, the present invention will be explained with reference to a glass element in the form of a glass plate.

[0005] Glass melting plants for the production of glass typically consist of a melting or heating section in which the raw materials, known as the glass batch, are converted into a liquid molten glass; a subsequent refining section in which the molten glass is refined so that any residual gas bubbles remaining after the melting or heating process are removed from the molten glass; and a downstream conditioning section for further conditioning the refined molten glass. The temperatures required for the entire melting process depend heavily on the type of glass. Soda-lime glasses, for example, used in the production of window glass and glass containers, are melted at significantly lower temperatures than, for example, specialty glasses for display applications or glass ceramics.The conditioning area of ​​such a glass melting plant can be designed as a working tank or as a trough and distribution system. Typically, a refractory material, usually consisting of aluminum zirconium silicate, is used as the wall material in a glass melting plant. However, it is known that the use of such materials as wall material or melt contact material can lead to the formation of bubbles and / or streaks in the glass melt and ultimately to rejects in the final glass product.

[0006] Other defects, such as particles detached from the melting tank wall material or similar, also lead to corresponding inclusions in the micrometer range, for example in floated borosilicate glass, which then renders this glass unsuitable for various applications. Samples of glass plates made of floated borosilicate glass produced in a known manner exhibit disruptive metallic and non-metallic inclusions and bubbles with a broad size distribution and a high number. Inclusions larger than 50 µm can be sorted out using conventional optical detection methods. In contrast, inclusions with a size of 50 µm or smaller are very difficult to detect and can usually only be identified, quantified, and qualified by trained personnel with great effort.

[0007] Known glass elements and methods for their production are known, for example, from US 6,829,908 B2 or US 2006 / 144089 A1.

[0008] An object of the present invention is therefore to provide a glass element, preferably a glass plate, with a reduced number of inclusions in the micrometer range and to provide a method for producing the glass element, preferably a glass plate, a glass melting plant, and a method for operating the glass melting plant, which significantly reduces the number of inclusions in the micrometer range.

[0009] A further object of the present invention is to provide an alternative glass element, preferably a glass plate, an alternative method for producing a glass element, preferably a glass plate, an alternative glass melting plant, and an alternative method for operating the glass melting plant.

[0010] The present invention solves the above-mentioned problems with a glass element according to claim 1.

[0011] The present invention achieves the above-mentioned objects with a method for producing a glass element according to claim 11.

[0012] The present invention achieves the above-mentioned objects with a glass melting plant according to claim 13.

[0013] The present invention also achieves the above-mentioned objects with a method for operating a glass melting plant according to claim 14.

[0014] Furthermore, the present description also discloses a glass element, preferably a glass element made of borosilicate glass, preferably in the form of a borosilicate glass plate, preferably according to one of claims 1 to 10, produced by a method according to one of claims 11 to 12 and / or by means of a glass melting plant according to claim 13.

[0015] The term zirconium oxide refers here to ZrO 2.

[0016] Unless otherwise defined, % herein equals wt%.

[0017] One of the advantages achieved in this way is that inclusions, i.e. metallic and non-metallic inclusions as well as bubbles, can be considerably reduced. Preferably when steps ii) to iii) are carried out and if all conditions a) and c) or A) and C) are met or steps I) to III) are carried out, both the number of metallic inclusions and the number of non-metallic inclusions, in particular of refractory material and of recrystallization products of corrosion products dissolved in the glass, can be considerably reduced. In this case, it has been recognized according to the invention that the number of metallic inclusions is preferably reduced when condition a) or A) is met or step I) is carried out.If the frequency range according to the invention is exceeded, it has been found that, surprisingly, the number of metallic inclusions has increased, whereas an increase in frequency beyond the aforementioned frequency range can only be implemented with great effort and thus at great expense. Through step II), it has been found according to the invention that this enables a reduction in non-metallic inclusions in refractory material. If condition c) or C) is met or step III) is carried out, it has been found according to the invention that this leads to a reduction in inclusions of recrystallization products of corrosion products dissolved in the glass.

[0018] Embodiments are those in which condition(s) or step(s) a, A or I and II; c, C or II and III; or a, A or I and II and c, C or III; are met or carried out.

[0019] According to a preferred embodiment, the glass element is a glass plate; a pharmaceutical primary packaging made of glass, preferably a glass vial, a glass syringe, a glass ampoule and / or a glass carpule; or a glass tube, preferably made of borosilicate glass.

[0020] The term "bottom material" in relation to the term "glass melt" refers to that portion of the glass melt that can be withdrawn through openings in the bottom, for example, through an opening in a tank of the heating device and / or the conditioning device, preferably the conditioning device. In general, withdrawing a certain % of the volume flow from the bottom material of the glass melt in a bottom region of the glass melt means that a certain vol. % of the glass melt in the bottom region is withdrawn per unit of time. Only the protruding portion of the glass melt serves to form the glass element, preferably in the form of a glass plate. The withdrawal from the opening(s) in the bottom and the withdrawal of the protruding portion of the glass melt total 100% of the volume flow. For example,If, within a time interval, 25 liters are withdrawn from the bottom material of the glass melt in a bottom region of the glass melt and, within the same time interval, 75 liters of the glass melt are withdrawn to form the glass element, preferably the glass plate, this corresponds to a withdrawal of 25% of the volume flow from the bottom material of the glass melt in a bottom region of the glass melt.

[0021] The term "contact surface" in relation to the term "glass melt" refers to the surface that is in contact with molten glass. This includes, for example, the inner wall of the melting tank, also called the working tank, at the usual filling level, stirrers, electrode holders and electrodes, inlets and outlets of the respective tank (sections), troughs within the melting tank, and the like. The contact surface does not include, in particular, surfaces of a feed device for the mixture into the melting tank and contact surfaces downstream of the direct outlets from the melting tank, e.g., the float bath and / or the cooling channel.

[0022] The term "glass element" refers to a three-dimensional object of any shape, which is made at least partially, preferably predominantly, preferably entirely of glass, more preferably borosilicate glass, and can preferably be designed as a glass plate; as pharmaceutical primary packaging made of glass, preferably as a glass vial, as a glass syringe, as a glass ampoule and / or as a glass carpule; or as a glass tube.

[0023] The term "glass plate" refers to a three-dimensional object made of glass, which, in the simplest case, is essentially a cuboid with a thickness, a length, and a width. The smallest dimension is the thickness, and the two largest dimensions represent a surface with a length and a width. The viewing plane is along a normal to the surface.

[0024] Thickness, length, and width are freely selectable. 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, and most preferably between 0.2 and 0.4 cm. The length and width are preferably each 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, and most preferably between 40 cm and 60 cm. The advantage of this is the provision of a thin, transparent glass plate, for example, as a transparent cover or the like.

[0025] The term "glass tube" refers to a three-dimensional object made of glass, which, in the simplest case, is essentially an elongated hollow body with an outer diameter, a length, and a wall thickness. The smallest dimension is the wall thickness, for example, while the two larger dimensions are the outer diameter and length. The viewing plane is along a normal to the outer surface of the tube.

[0026] The outer diameter, length, and wall thickness are freely selectable. The length of the glass tube is preferably 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.The outer diameter is preferably 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. The wall thickness is preferably 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.

[0027] The transmittance of the glass element is not specifically limited. The transmittance of the glass element, standardized to a glass element, preferably a glass plate or glass tube, with a thickness or wall thickness of 6.5 mm at a wavelength of 400 nm to 800 nm, is preferably 70% or more, more preferably 80% or more, more preferably 90% or more, most preferably 95% or more.

[0028] Transmittance is typically measured using a UV-VIS spectrometer, e.g., a Specord 250 Plus spectrophotometer (Analytik Jena). The sample's transmittance is measured in the wavelength range from 250 to 1050 nm; the measurement is typically evaluated according to DIN EN 410:2011-04 (Glass in building - Determination of photometric and radiation characteristics of glazing; German version EN 410:2011).

[0029] The determination of the number and size of inclusions according to embodiments of the invention was carried out using the method described below: In a dark room, visible light is directed into a glass element to be examined, in this case a glass plate, perpendicular to the thickness of the glass plate, preferably along a straight cut edge, and parallel to the surface formed by the two largest dimensions (length and width). The inclusions are identified by the reflection of the light from the inclusions in the glass plate. To distinguish between dust and inclusions in the glass plate of small particles, approximately in the size range < 20 µm, a handheld microscope, for example a "Wide Stand Microscope" from PEAK, can be used. The optically identified particles are visibly marked.The glass plate marked in this way is viewed along the normal to the surface under a light microscope, for example the Axio Imager M2m from Zeiss, with an LD EC Epiplan 50x / 0.55 HD DIC objective and a PI 10x / 2 eyepiece, whereby the inclusions are classified and their size measured. The size of the inclusions and particles refers to the longest dimension visible in the viewing plane. With this type of measurement, it is consciously accepted that three-dimensional inclusions may extend with their maximum longitudinal extent during measurement in the direction of the optical axis of the microscope, i.e. along the normal to the viewing plane, and in this case a smaller measured value for the inclusion is obtained than the actual value of the longitudinal extent of the inclusion, for example of the crystal or crystallite.The minimum size of inclusions that are or can be measured with the Zeiss Axio Imager M2m is approximately 2 µm. Smaller inclusions below 2 µm are therefore not considered in the inclusion count.

[0030] Even if not described in detail, a person skilled in the art will have no difficulty applying the method described above to a glass element, such as a glass tube.

[0031] Smaller inclusions, ranging from 2 µm down to 50 nm, can be measured using the Zeiss Xradia 800 Ultra X-ray microscope, for example. Even smaller inclusions, measuring less than 50 nm, are therefore not counted or considered inclusions.

[0032] If a glass element weighs less than one kilogram, the inclusions are calculated proportionally. If the glass element weighs more than one kilogram, the number of inclusions is multiplied accordingly. There are no specific restrictions on the weight of the glass element. The glass element preferably weighs 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.

[0033] Unless otherwise stated, all percentages herein are to be understood as percentages by weight, abbreviated to wt.%.

[0034] The term "inclusion" is to be understood in the broadest sense and includes in particular inclusions in the form of metallic and non-metallic inclusions, also called particles, and in the form of gas(es), e.g. air, i.e. bubbles.

[0035] The term "metallic inclusion" is to be understood in the broadest sense. Metallic inclusions are, in particular, inclusions of particles made of one or more predominantly elemental metals. The metal(s) of the metallic inclusions thus have an oxidation state of 0. Metallic inclusions include, in particular, precious metals and refractory metals.

[0036] The term "non-metallic inclusion" should be understood in the broadest sense. Non-metallic inclusions are inclusions consisting of cations (oxidation state >0) and anions (oxidation state <0), also called salts. In particular, non-metallic inclusions include particles in the form of crystals composed of glass components and one or more salts of refractory metals and precious metals, especially crystals composed of glass components and one or more silicates or oxides of refractory metals and precious metals.

[0037] Inclusions are counted as metallic if they consist primarily of elemental metal, i.e., approximately 100% elemental metal (oxidation state equal to 0); otherwise, the inclusions are counted as non-metallic. A distinction between metallic and non-metallic inclusions can be made optically, as described above. Refractory metals include, for example, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten.

[0038] Precious metals include semi-precious metals and are, for example, ruthenium, rhodium, palladium, osmium, iridium, platinum, silver, gold, copper, technetium, rhenium, antimony, bismuth and polonium.

[0039] Other examples of metals that may be present in the inclusions are magnesium, calcium, aluminum, silicon, tin (metallic inclusions) and salts thereof (non-metallic inclusions).

[0040] The term "bubbles" should be understood in the broadest sense. Bubbles are formed by gas inclusions in the glass, whereby the gas can be gaseous at room temperature (20°C) or condense upon cooling, forming a bubble with negative pressure. Gases that form inclusions include, for example, oxygen, nitrogen, nitrogen oxides, carbon dioxide, sulfur dioxide, and the like.

[0041] Unless otherwise defined, all preferred parameters and embodiments of the glass element also apply to the two processes and the glass melting plant and vice versa.

[0042] Further features, advantages and further embodiments of the invention are described below or will become apparent thereby.

[0043] According to a preferred embodiment, the glass element has 50 inclusions or fewer per kg of glass with a size of 500 nm or more and 10 µm or less, preferably with a size of 50 nm or more and 10 µm or less, more preferably 10 µm or less. The advantage of this is that a higher quality of the glass is provided, preferably for high-energy laser applications.

[0044] According to a preferred embodiment, the glass element has 2000 inclusions or fewer, preferably 1000 inclusions or fewer, more preferably 500 inclusions or fewer, more preferably 250 inclusions or fewer, more preferably 100 inclusions or fewer, more preferably 50 inclusions or fewer, with a size of 20 µm or fewer, preferably 30 µm or fewer, more preferably 40 µm or fewer, most preferably 50 µm or fewer, and a size of 2 µm or more, preferably 50 nm or more, per kg of glass. The advantage of this is that a higher quality of glass is provided, preferably for high-energy laser applications. If the number of inclusions remains the same but varies over a wider size range, high-energy laser applications are less affected.

[0045] The following should be noted: If, for example, the number of inclusions per kg of glass is limited to 50 inclusions or less with a size of 10 µm or less, a glass element according to an embodiment of the present invention may have 50 inclusions with a size of 5 µm and 50 inclusions with a size of 40 µm per kg of glass. However, if the number of inclusions per kg of glass is limited to 50 inclusions or less with a size of 50 µm or less, a glass element which, for example, has 50 inclusions with a size of 5 µm and 50 inclusions with a size of 40 µm per kg of glass would not meet this condition, but a glass element which, for example, has 10 inclusions with a size of 5 µm, 20 inclusions with a size of 25 µm and 15 inclusions with a size of 45 µm would.

[0046] The glass element can have any number of additional larger inclusions. Large inclusions can be easily detected using conventional measuring technology, 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. With the embodiments of the invention described herein, larger inclusions can also be significantly reduced. Therefore, the glass element preferably has no inclusions with a size of more than 50 µm, more preferably more than 40 µm, more preferably more than 30 µm, more preferably more than 20 µm, and most preferably more than 10 µm.

[0047] According to a preferred embodiment, the glass element has 50 inclusions or fewer, preferably 40 inclusions or fewer, preferably 30 inclusions or fewer, more preferably 20 inclusions or fewer, most preferably 10 inclusions or fewer, per kg of glass, wherein these inclusions may have a size of 10 µm or fewer, preferably 20 µm or fewer, preferably 30 µm or fewer, more preferably 40 µm or fewer, most preferably 50 µm or fewer. The advantage of this is that the quality of the glass element is increased, preferably for high-energy laser applications. The fewer inclusions there are per kg of glass, the less high-energy laser applications are impaired. The quality of the glass element is improved.

[0048] Depending on the variation of the parameters, i.e., the frequency of the alternating current, the percentage of the volume flow rate, and the proportion of zirconium oxide in the contact surface, both the number of inclusions and their size can be influenced. Even if only one of conditions a) or A), b) or B) and c) or C) is met, or if only one of steps I), II) or III) is performed, at least one of the parameters (size of the inclusions and / or number of inclusions per kg of glass) is reduced.

[0049] According to a preferred embodiment, the inclusions comprise metallic inclusions, wherein the glass element has 40 metallic inclusions or fewer, preferably 30 metallic inclusions or fewer, more preferably 20 metallic inclusions or fewer, more preferably 10 metallic inclusions or fewer, most preferably 5 metallic inclusions or fewer, with a size of 5 µm or fewer, preferably 10 µm or fewer, more preferably 20 µm or fewer, more preferably 30 µm or fewer, more preferably 40 µm or fewer, most preferably 50 µm or fewer, per kg of glass. Thus, the glass element overall has few inclusions due to metallic particles, which further improves the quality of the glass element. Frequently occurring metallic inclusions include, in particular, metals such as tungsten, zirconium, platinum, rhodium, iridium, molybdenum, tin and copper, since these come into contact with the glass during the production of glass elements.

[0050] According to a preferred embodiment, the inclusions comprise non-metallic inclusions, wherein the glass element has 25 non-metallic inclusions or less, preferably 15 non-metallic inclusions or less, more preferably 8 non-metallic inclusions or less, more preferably 1 non-metallic inclusion or less, more preferably 0.1 non-metallic inclusions or less, more preferably 0.05 non-metallic inclusions or less, most preferably 0.00 non-metallic inclusions, with a size of 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, per kg of glass. This reduces both the number and size of non-metallic inclusions, which in turn increases the quality of the glass element.Frequently occurring non-metallic inclusions include, in particular, crystals from glass components and / or one or more silicates and / or oxides of refractory metals and / or precious metals. The crystals crystallize, for example, from the glass melt, while silicates and / or oxides of refractory metals and / or precious metals form from the contact material in contact with the glass melt.

[0051] According to a preferred embodiment, the inclusions comprise bubbles, wherein the glass element has 25 bubbles or fewer, preferably 15 bubbles or fewer, more preferably 8 bubbles or fewer, more preferably 1 bubble or fewer, more preferably 0.1 bubbles or fewer, more preferably 0.05 bubbles or fewer, most preferably 0.00 bubbles, with a size of 10 µm or fewer, preferably 20 µm or fewer, more preferably 30 µm or fewer, more preferably 40 µm or fewer, most preferably 50 µm or fewer, and / or 2 µm or more, preferably 50 nm or more, per kg of glass. The quality of the glass element is thus increased overall, even for inclusions in the form of bubbles.

[0052] According to a preferred embodiment, the composition of the glass element comprises, in wt.%: SiO2 60 to 90%, more preferably 76 to 90%; B2O3 0 to 20%; Al 2 O 3 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%.

[0053] In a further preferred embodiment, the glass element has the following composition, in wt.%: SiO2 more than 76%; B2O3 0 to 15%; Al 2 O 3 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, ie less than 0.01%.

[0054] In a further preferred embodiment, the glass element has the following composition in wt.%: SiO2 76% to 85%; B2O3 0 to 15%; Al 2 O 3 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, ie less than 0.01%.

[0055] The glass element preferably contains iron, arsenic, and / or antimony oxide in a weight fraction of less than 0.05 wt.%, more preferably less than 0.01 wt.%. More preferably, the glass element is free of iron, arsenic, and antimony oxide. An arsenic- and antimony-oxide-free glass element results in an environmentally friendly glass element. Iron oxide can occur as an impurity, which can impair the color of the glass element. This can be prevented by appropriate selection of the starting materials.

[0056] According to a preferred embodiment, the glass element has one or more of the following features: i) the weight of the glass element is 0.01 kg to 350 kg, preferably 0.1 kg to 20 kg, more preferably 0.5 kg to 15 kg, most preferably 1.0 kg to 10 kg; ii) the thickness of the glass element, when provided in the form of a glass plate, is 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) the length and width of the glass element, when provided in the form of a glass plate, are each 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 40 cm to 60 cm; iv) the transmission of the glass element, normalised to a glass element in the form of a glass plate with a thickness of 6.5 mm at a wavelength of 400 nm to 800 nm, is 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 with a size of more than 50 µm, preferably more than 40 µm, more preferably more than 30 µm, more preferably more than 20 µm, most preferably more than 10 µm. ;

[0057] More preferably, the glass element has the aforementioned features 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; i+ii+iii; i+ii+iv; i+ii+v; i+iii+iv; i+iii+v; i+iv+v; ii+iii+iv; 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.

[0058] According to a preferred embodiment of the method, the viscosity of the glass melt is brought 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 the value is maintained at least in steps ii) and iii). According to a preferred embodiment of the method, the viscosity of the glass melt is brought to a value between 33 Pas and 265 Pas, preferably between 35 Pas and 200 Pas, and / or the value is maintained at least in steps ii). According to a preferred embodiment of the method, the viscosity of the glass melt is brought to a value between 70 Pas and 450 Pas, preferably between 100 Pas and 400 Pas, and / or the value is maintained at least in steps iii). One of the advantages achieved thereby is that the method can be used for a large number of different glasses to be produced with different temperatures during production.

[0059] According to a preferred embodiment, the glass element is provided in the form of a glass plate or a glass tube. This enables simple production and flexible use of the glass element for a wide variety of applications.

[0060] According to a preferred embodiment, the glass element has 2000 inclusions or fewer, preferably 1000 inclusions or fewer, more preferably 500 inclusions or fewer, more preferably 250 inclusions or fewer, more preferably 100 inclusions or fewer, more preferably 50 inclusions or fewer, with a size of 50 nm or more and 500 nm or less per kg of glass. The advantage of this is that a higher quality of the glass is provided, preferably for high-energy laser applications.

[0061] According to a preferred embodiment, the glass element has 2000 inclusions or fewer, preferably 1000 inclusions or fewer, more preferably 500 inclusions or fewer, more preferably 250 inclusions or fewer, more preferably 100 inclusions or fewer, more preferably 50 inclusions or fewer, with a size of 500 nm or more and 2 µm or less per kg of glass. The advantage of this is an even higher quality of the glass element.

[0062] 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, particularly metallic inclusions, is reduced. However, if the frequency is 200 kHz or lower, preferably 100 kHz or lower, more preferably 50 kHz or lower, more preferably 15 kHz or lower, it is easier to achieve this frequency, and unexpected problems, such as blistering due to local overheating, occur less frequently.

[0063] According to a preferred embodiment of the method, the contact surface with which the glass melt is in contact 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 molten zirconium oxide material. This reduces the number of inclusions, for example, of refractory material, and increases the quality of the glass or glass element.

[0064] According to a preferred embodiment of the method, the contact material comprises fused-cast zirconium oxide material with a content of more than 90 wt.% ZrO 2 , preferably more than 95 wt.% ZrO 2 . This further reduces the number of refractory inclusions and further increases the quality of the glass element.

[0065] According to a preferred embodiment of the method, between 5% and 40%, preferably between 20% and 40%, more preferably between 25% and 35%, of the volume flow is removed from the bottom material of the glass melt in a bottom region of the glass melt. The advantage of this is that the number of inclusions of corrosion products, i.e., non-metallic inclusions, is reduced, thus increasing the quality of the glass.

[0066] In a preferred embodiment, in the method for producing a glass element in the form of a glass plate, preferably a borosilicate glass plate, the following steps S1 to S4 are carried out; preferably first S1, then S2, then S3 and finally S4.

[0067] In a first step S1, a mixture is prepared according to an embodiment of the present invention. In a further step S2, the mixture is heated to 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 the glass element.

[0068] During the execution of steps S2 - heating - and S3 - conditioning, at least one, preferably all, of the following conditions are met: a) the glass melt is at least partially heated and / or warmed by electrical resistance heating 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 with which the glass melt is in contact comprises 30% or more of contact material in the form of molten zirconium oxide material with a proportion of more than 70% by weight of ZrO 2 ; and c) between 1% by volume and 50% by volume of the bottom material of the glass melt is withdrawn in a bottom region of the glass melt.

[0069] Further preferred features and advantages of the invention emerge from the subclaims, from the drawings and the associated description of the figures.

[0070] It is understood that the features mentioned above and those explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0071] Preferred embodiments and embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components or elements.

[0072] It shows: Figure 1 shows a glass melting plant according to an embodiment of the present invention; and Figure 2 shows a method for producing a glass element according to an embodiment of the present invention.

[0073] Figure 1 shows a glass melting plant according to an embodiment of the present invention.

[0074] In detail, Figure 1 A glass melting plant 1 is shown. The glass melting plant 1 comprises a heating device 2, in which the heating and melting of starting material, the so-called mixture, takes place. For this purpose, the heating device 2 has a tank 2a, which is equipped with a bottom removal device 6a for removing bottom material 11 from the glass melt 10.

[0075] To ensure sufficient homogeneity and freedom from bubbles, the melting process is followed by refining the glass melt 10 in a downstream refining device 23, which can also be used as a transport area for transporting the glass melt 10 to a downstream section. A key objective of refining the glass melt 10 is to remove the gases physically and chemically bound in the glass melt 10 from the glass melt 10. After refining is complete, the formation of new bubbles in the melt should at least be reduced or even prevented. Refining can generally take place within the same tank 2a or in a separate tank. The refining device 23 is followed by a conditioning device 3, in which the glass melt 10 is further conditioned and / or homogenized.At the bottom of the conditioning device 3 there is another bottom extraction device 6b.

[0076] The walls 20 of the aforementioned devices 2, 23, 3 of the glass melting plant 1 are made of a refractory material, such as the fused zirconium oxide material described above. Figure 1 The heating device 2 is separated from the refining device 23 by a flow-influencing element 15 that extends transversely to the flow direction across the entire width of the glass melting plant 1 in this area and essentially completely blocks this area, with the exception of a slight overhang from the glass level line. Alternatively or additionally, the flow-influencing element 15 can also be arranged in the transition area between the refining device 23 and the conditioning device 3.

[0077] The glass melting plant 1 also has a heating device 4 with electrodes 5 for resistance heating. These are connected to an alternating current source 8, which provides alternating current with a frequency between 1 kHz and 200 kHz as heating current. In addition, the glass melt can be heated, for example, with gas burners (not shown). A control device 30 controls the conditioning device 3, the heating device 2, the alternating current source 8 and, if applicable, the refining device 23 as well as the bottom removal devices 6a, 6b in such a way that, on the one hand, between 1% and 50% of the volume flow of the glass melt 10 is removed from the bottom material, for example 25%, and can optionally be fed back to the heating device 2, and, on the other hand, that resistance heating of the glass melt 10 takes place at least in the conditioning device 3.Furthermore, the contact surfaces 7 which are in contact with the glass melt 10 have contact material 7a in the form of molten zirconium oxide material with a proportion of more than 70 wt.% ZrO 2 , preferably molten zirconium oxide material with a proportion of more than 85 wt.% ZrO 2 .

[0078] Figure 2 shows steps of a method for producing a glass element according to an embodiment of the present invention.

[0079] The method comprises the following steps: In a first step S1, a mixture is prepared according to an embodiment of the present invention. In a further step S2, the mixture is heated to 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 the glass element.

[0080] In a preferred embodiment, in a method according to one of claims 9 to 13 for producing a glass element, preferably in the form of a glass plate, preferably a borosilicate glass plate, according to one of claims 1 to 12, the following steps S1 to S4 are carried out; preferably first S1, then S2, then S3 and finally S4. Examples

[0081] The following table shows the total number of inclusions of a comparative example and examples according to embodiments of the invention in different categories divided into bubbles, non-metallic inclusions and metallic inclusions: Example Blow Non-metallic inclusions Metallic inclusions [Unit] Number / kg Number / kg Number / kg 1 a< 4,7 33,5 66,8 2 b< 0,3 0,2 53,2 3 b< 0 0 52,4 4 b< 0 0 8,8 5 b< 0 0 7,7 6 b< 0 0 6,4 a Comparative example b Example according to embodiments of the invention

[0082] The size distribution of metallic inclusions per kg of glass from Examples 3 to 6 in the range of 0 to 50 µm is shown in the following table, whereby only inclusions with a size of 2 µm or more in the specified size interval 0 µm to 5 µm of the following table were taken into account: Example Size in µm 0 to 5 5 to 10 10 to 20 20 to 30 30 to 40 40 to 50 [Unit] Number / kg Number / kg Number / kg Number / kg Number / kg Number / kg 3 b< 10,5 10,5 10,5 7,0 3,5 3,5 4 b< 6,9 1,9 0 0 0 0 5 b< 7,0 0,7 0 0 0 0 6 b< 5,1 1,3 0 0 0 0 b Example according to embodiments of the invention

[0083] In Comparative Example 1 and Example 2, the size distribution of the inclusions was not precisely determined. In Examples 2 and 3, although the total number of inclusions was just over 50 (e.g. Example 2: 0.3 + 0.2 + 53.2 = 53.7 per kg) per kg of glass, the size of some inclusions was over 50 µm, so that the number of inclusions with a size of 50 µm or less, and thus also the number of inclusions with a size of 10 µm or less, was below 50 inclusions per kg of glass (see second table; Example 3: 10.5 + 10.5 + 10.5 + 7.0 + 3.5 + 3.5 = 45.5 per kg). In addition to the inclusions listed in the second table, inclusions with a size over 100 µm were also 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 second table); in Examples 4 to 6, it was even less than 10 inclusions per kg.In addition, the glass plates of Examples 4 to 6 did not show any further inclusions with a size larger than 50 µm (as can be seen from the comparison of the first and second tables).

[0084] Comparative Example 1 is an example of a glass element in the form of a glass plate in which none of the improvements to the glass melting system described herein were used; in other words, a previously known glass melting system or a previously known manufacturing process was used. The total number of inclusions here was well over 50, and the number of inclusions in each category was also very high. Even though the exact size of each individual inclusion in Comparative Example 1 was not determined, it can be assumed that, due to the high number of inclusions, even in the range below 50 µm, the number of inclusions must be well over 50 inclusions per kg. Based on this, a test glass melting system was successively improved.

[0085] First, in an experiment in the glass melting plant, a portion of the contact surface (approximately 70% or more) with which the glass melt was in contact was provided with contact material made of fused zirconium oxide material containing over 70 wt.% ZrO2. At the same time, the glass melting plant was operated in such a way that between 1% and 50% of the volume flow was drawn off from the bottom material of the glass melt in a bottom region of the glass melt. This led to a significant reduction in bubbles and non-metallic inclusions (see, for example, Example 2). The number of metallic inclusions in Example 2 is over 50 (number = 53.2), of which, as already described above, although the majority of the inclusions were 50 µm or less in size, some inclusions were also larger than 50 µm. Thus, a glass plate produced in this way has 50 inclusions or fewer with a size of 10 µm or less per kg of glass.Even covering a small portion of the contact surface with the special contact material (30% of the contact surface or more) led to a reduction in bubbles and non-metallic inclusions. 0 bubbles and non-metallic inclusions per kg with a size of 50 µm or less were found in glass plates produced using a glass melting system in which a large portion of the contact surface (90% or more, or even 95% or more) with which the glass melt was in contact was fused-cast zirconium oxide material with a high proportion (85 wt.% or more, or even 95 wt.% or more) of ZrO 2, and in addition, a large proportion (between 25 vol.% and 35 vol.%) was drawn off from the bottom material of the glass melt in a bottom region of the glass melt (see examples 3 to 6).

[0086] The electrical resistance heating was also optimized. For this purpose, a new electrical resistance heating system according to an embodiment of the present invention was installed in the glass melting system for testing purposes. In Comparative Example 1, a conventional resistance heating system was used, and a high number of metallic inclusions was detected in the glass plate produced with it. In Examples 2 to 6, the glass melt was at least partially heated and / or warmed with electrical resistance heating by applying a heating current to electrodes. The heating current used was an alternating current with a frequency between 1 kHz and 200 kHz, whereby the number of metallic inclusions could be reduced.The number of metallic inclusions could be further significantly reduced by adjusting the frequency between 1 kHz and 100 kHz, until finally particularly few metallic inclusions were found at a frequency between 8 kHz and 15 kHz (see examples 4 to 6).

[0087] The examples also show that the best results are achieved when all three improvement steps described here are applied.

[0088] In summary, at least one of the embodiments of the invention has at least one of the following advantages: Reduction of inclusions, preferably inclusions of metallic particles, with a size of 50 µm or less; increased flexibility of the glass for various applications, higher quality of the glass; less scrap; and reduced number of bulk defects or lower bulk defect density.

[0089] The glass or glass element produced by means of embodiments of the invention can preferably be used for the following applications: High-energy-density laser applications; large-format, homogeneous, and / or low-defect photomasks for lithographic applications; nanoimprint lithography, molds for imprinting precision lenses or nanostructures down to the nm range, e.g., hard disk magnetic layers or the like; substrates for flat metal lens concepts and optics; superglass wafers; and precision windows in displays, preferably for OLEDs.

Claims

1. Glass element made of borosilicate glass, wherein the glass element has per kg of glass 50 inclusions or less having a size of 2 µm or more and 10 µm or less, in particular wherein the glass element has per kg of glass 2000 inclusions or less, preferably 1000 inclusions or less, more preferably 500 inclusions or less, more preferably 250 inclusions or less, more preferably 100 inclusions or less, more preferably 50 inclusions or less, having a size of 500 nm or more and 10 µm or less, preferably having a size of 50 nm or more and 10 µm or less, more preferably of 10 µm or less.

2. Glass element according to claim 1, wherein the glass element has per kg of glass 50 inclusions or less 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.

3. Glass element according to any one of claims 1 to 2, wherein the glass element has per kg of glass 40 inclusions or less, preferably 30 inclusions or less, more preferably 20 inclusions or less, most preferably 10 inclusions or less.

4. Glass element according to any one of claims 1 to 3, wherein the inclusions comprise metal inclusions, and wherein the glass element has per kg of glass 40 metal inclusions or less, preferably 30 metal inclusions or less, more preferably 20 metal inclusions or less, more preferably 10 metal inclusions or less, most preferably 5 metal inclusions or less, having a size of 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.

5. Glass element according to any one of claims 1 to 4, wherein the inclusions comprise non-metal inclusions, and wherein the glass element has per kg of glass 25 non-metal inclusions or less, preferably 15 non-metal inclusions or less, more preferably 8 non-metal inclusions or less, more preferably 1 non-metal inclusion or less, more preferably 0.1 non-metal inclusions or less, more preferably 0.05 non-metal inclusions or less, most preferably 0.00 non-metal inclusions, having a size of 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.

6. Glass element according to any one of claims 1 to 5, wherein the inclusions comprise bubbles, wherein the glass element has per kg of glass 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, having a size of 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.

7. Glass element according to any one of claims 1 to 6, wherein the composition of the glass element comprises in % by 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%.

8. Glass element according to any one of claims 1 to 7, 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 0.1 kg to 20 kg, more preferably 0.5 kg to 15 kg, most preferably 1.0 kg to 10 kg; ii) the thickness of the glass element, when it is provided in the form of a glass plate, is 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 cm and 0.4 cm; iii) the length and width of the glass element, when it is provided in the form of a glass plate, is in each case 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 from 40 cm to 60 cm; iv) the transmission of the glass element standardised to a glass element in the form of a glass plate having a thickness of 6.5 mm at a wavelength of from 400 nm to 800 nm is 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 of more than 50 µm, preferably more than 40 µm, more preferably more than 30 µm, more preferably more than 20 µm, most preferably more than 10 µm.

9. Glass element according to any one of claims 1 to 8, wherein the glass element is provided in the form of a glass plate or a glass pipe.

10. Glass element according to any one of claims 1 to 9, wherein the glass element has per kg of glass 2000 inclusions or less, preferably 1000 inclusions or less, more preferably 500 inclusions or less, more preferably 250 inclusions or less, more preferably 100 inclusions or less, more preferably 50 inclusions or less having a size of 50 nm or more and 500 nm or less and / or wherein the glass element has per kg of glass 2000 inclusions or less, preferably 1000 inclusions or less, more preferably 500 inclusions or less, more preferably 250 inclusions or less, more preferably 100 inclusions or less, more preferably 50 inclusions or less having a size of 500 nm or more and 2 µm or less.

11. Method for producing a glass element from boron silicate glass according to any one of claims 1 to 10, comprising the steps of: i) providing (S1) an admixture comprising in % by 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 admixture 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 the contact face (7) with which the glass melt (10) is in contact comprises at a rate of 30% or more contact material (7a) in the form of fusion cast zirconium oxide material having a proportion of over 70% by weight ZrO2 and in particular wherein at least one, preferably all of the following conditions a) and c) is / are complied with during the steps ii) and / or iii): a) the glass melt (10) is at least partially heated and / or warmed with an electrical resistance heating by acting on electrodes (5) with a heating current, wherein as the heating current an alternating current is used at a frequency between 1 kHz and 200 kHz; and c) between 1% and 50% of the volume flow of the base material (11) of the glass metal (10) is removed in a base region of the glass melt (10), in particular wherein the viscosity of the glass melt (10) at least in the steps ii) and / or iii) is brought 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 the value is maintained.

12. Method according to claim 11, wherein as the heating current an alternating current at 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 and / or wherein the contact face (7) with which the glass melt (10) is in contact comprises at a rate of 60% or more, preferably 80% or more, more preferably 90% or more, most preferably 95% or more contact material (7a) in the form of fusion cast zirconium oxide material having a proportion of 75% by weight or more, preferably 85% by weight or more, more preferably 95% by weight or more ZrO2 and / or wherein between 5% and 40%, preferably between 20% and 40%, more preferably between 25% and 35% of the volume flow of the base material (11) of the glass melt (10) is removed in a base region.

13. Glass melt installation (1) for carrying out a method according to any one of claims 11 to 12, comprising: a heating device (2) for heating an admixture to form a glass melt (10), a conditioning device (3) for conditioning the glass melt (10), and a base removal device (6a, 6b) for removing base material (11) of the glass melt (10), wherein the heating device (2) and / or the conditioning device (3) comprises a heating device (4) having at least two electrodes for resistance heating; and wherein the contact face (7) with which the glass melt (10) is in contact is constructed in such a manner that it comprises at a rate of 30% or more contact material (7a) in the form of fusion cast zirconium oxide material having a proportion of over 70% by weight ZrO2, preferably fusion cast zirconium oxide material having a proportion of over 85% by weight ZrO2, and in particular wherein at least one of the conditions A) and C) is complied with: A) the heating device (4) is constructed or controlled in such a manner that the at least two electrodes (5) are acted on with a heating current in the form of an alternating current at a frequency between 1 kHz and 200 kHz; and / or C) the base removal device (6a, 6b) is constructed to remove between 1% and 50% of the volume flow from the base material (11) of the glass melt (10) in a base region of the heating device (2) and / or conditioning device (3).

14. Method for operating a glass melt installation (1) according to claim 13, wherein at least steps I) and II) or steps II) and III) or steps I), II) and III) are carried out: I) operating the heating device (4) by acting on the electrodes (5) with a heating current, wherein as the heating current an alternating current is used at a frequency between 1 kHz and 200 kHz, II) bringing the glass melt (10) into contact with a contact face (7) with which the glass melt (10) is in contact and which comprises at a rate of 30% or more fusion cast zirconium oxide material having a proportion of over 70% by weight ZrO2, preferably fusion cast zirconium oxide material having a proportion of over 85% by weight ZrO2; and III) operating the base removal device (6a, 6b) in such a manner that between 1% and 50% of the volume flow is removed from the base material (11) of the glass melt (10) in a base region.