Thin glass and methods for manufacturing thin glass

Abstract

The invention relates to a thin glass with a usable area having a thickness t of 15 to 300 µm and at least one side edge region, wherein the side edge region is in the form of a thickening with a maximum thickness T max with 1 <T max The invention relates to a manufacturing process for the thin glass, wherein the surface of the side edge region is continuously curved and connects to the usable area. The invention further relates to a manufacturing process for the thin glass.

Description

[0001] The invention relates to a thin glass with a thickness of 15 to 300 µm with high edge strength and a method for producing the thin glass. Description

[0002] Thin glass is typically drawn from molten glass in vertical or horizontal drawing processes, forming ribbons. These ribbons have rims along their lateral edges that are significantly thicker than the actual usable area of ​​the glass. For very thin glass below approximately 300 µm, the thickness of the rim area is usually several times greater than the glass thickness in the middle of the ribbon. These thick rim areas are generally removed directly during or after the cooling of the glass ribbon in a continuous process. Further processing of thin glass often requires cutting or separation, for which a variety of methods can be used, such as scoring, thermal laser cutting, or the insertion of filaments along a dividing line with an ultrashort pulse laser followed by breaking along the dividing line.The propagation of an initial crack by thermally induced tensile stresses using a CO2 laser is also known.

[0003] Many separation processes can lead to the formation of microcracks or other pre-existing damage at the separation edge of the thin glass. Under subsequent mechanical stress, this damage can result in a crack propagating into the thin glass. Tensile stresses at the edge can occur, for example, when the thin glass is bent along its convex outer edge.

[0004] Therefore, it is desirable to provide a method for increasing the edge strength of thin glass. Several methods for increasing the edge strength of thin glass are already known in the art. Edge strength can be increased with suitable mechanical grinding and polishing processes; however, such mechanical processes become increasingly difficult with decreasing thickness and intrinsic stability of thin glass, especially when high process speeds are required, which necessitates high forces. Similarly, the edge surface can be removed by an etching process, e.g., with hydrofluoric acid, but this is very time-consuming and material-intensive and requires subsequent cleaning of the thin glass to remove etching residues. Processing the glass edge with gas burners is also known, but typically has many disadvantages.Gas flames are prone to flickering and instability, which directly impacts processing quality. Furthermore, gas burners emit environmentally harmful gases such as CO2 and, due to the high heat generated, always pose a risk of injury to production personnel in a manufacturing environment.

[0005] In the patent application KR20220035606, the treatment of the glass edge with a vacuum plasma is proposed, but the introduction of the thin glass into a vacuum is also very complex and inefficient.

[0006] WO2020 / 123226 proposes treating the side surface of a glass article with an atmospheric pressure plasma generated by a plasma torch via a pulsed arc discharge at a frequency of 10 kHz to 1000 kHz. An increase in the flexural strength of the thin glass is disclosed, which is attributed to the generation of compressive stress in the edge surface. Plasmas using a gas with high thermal conductivity, such as helium or hydrogen, are said to be particularly advantageous. Typically, the treated edge can exhibit a SiO2 content that is at least 10 mol% higher and an Al2O3 content that is at least 25 mol% lower. This results in a significant chemical modification of the glass surface, which can cause various problems in subsequent processes, as the chemically modified glass may exhibit altered properties with regard to chemical stability, thermal properties, and even crystallization.

[0007] The object of the present invention is to provide an efficient method for increasing the edge strength of a thin glass which does not have the disadvantages of the prior art, and to provide a thin glass with a correspondingly increased edge strength.

[0008] The problem is solved by the independent claims. Preferred embodiments are described in the dependent claims.

[0009] The thin glass according to the invention comprises a usable area and at least one side-edge area, wherein the thin glass in the usable area has a first main surface and a second main surface as well as a thickness t of 15 to 300 µm, wherein the side-edge area has a surface which connects the first main surface and the second main surface, wherein the side-edge area is in the form of a thickening with a maximum thickness T max with T max / t > 1 and a width W, the surface of the side edge region is continuously curved and connects to the first and second main surfaces, and where the ratio T max / t < 10 is.

[0010] The thin glass according to the invention can be produced using the inventive method, wherein the side edge region is melted by means of a plasma stream, the plasma stream being generated with an atmospheric pressure plasma torch which is generated by a high-frequency field in the frequency range of 500 MHz to 5 GHz, and wherein the plasma stream is moved along the untreated side edge region at a relative velocity v. The edge strength K of the thin glass can thereby be increased from an initial value K' to a higher value K.

[0011] The processed thin glass exhibits characteristic features.

[0012] The thin glass according to the invention exhibits a significantly improved edge strength K compared to untreated thin glass. Surprisingly, the highest edge strengths can be achieved when the side edge region is formed by a thickening with a maximum thickness T. max with T max / t > 1 and T max / t < 10 is trained.

[0013] The thin glass according to the invention thus has a secondary border which is significantly thinner and narrower than the border known to those skilled in the art, which results from the primary drawing process and which can be referred to as the primary border. Due to its very small thickness and width, this secondary border will also be referred to as the minimal border in the following.

[0014] Thin glass can be in the form of glass sheets or ribbons with a thickness of 15 µm to approximately 1 mm. Examples include SiO2-based glasses such as borosilicate glasses, soda-lime glasses, and alkali-containing or alkali-free aluminosilicate glasses. Such thin glasses are typically produced from a glass melt via drawing processes such as downdraw, overflow fusion, or float processes, but can also be manufactured using cold finishing processes such as sawing, grinding, and polishing.

[0015] The thin glass can be in the form of a glass sheet with a rectangular, hexagonal, round, or any other freeform shape, or in the form of a glass ribbon, characterized by a length-to-width ratio of at least 10:1, preferably at least 50:1. Thin glass in the form of glass ribbons can also be in a rolled-up form, i.e., in the form of a glass roll.

[0016] According to the invention, the surface of the side edge region is continuously curved and adjoins the first and second main surfaces. Continuously curved in this context means that the thin glass exhibits a continuously changing curvature in a cross-sectional view perpendicular to the side edge region.

[0017] The usable area of ​​the thin glass is characterized by a thickness that is at least partially constant. Preferably, the two main surfaces have a roughness depth R. a < 1 nm, as is typically found on a fire-polished surface from a hot forming process.

[0018] The thin glass can have one or more side edge regions, e.g., an orthogonal basic shape with four side edge regions or a rounded shape with a single circumferential side edge region. At least one of the side edge regions is designed according to the invention, but in a preferred embodiment, two opposing side edge regions of a glass strip or glass sheet, or all four side edge regions of a glass strip or glass sheet, can also be designed according to the invention. In a further preferred embodiment, the glass sheet has a freeform or wafer shape (round shape with a notch or flattened edge for wafer alignment), wherein preferably the entire circumference of the thin glass is designed according to the invention.

[0019] Preferably, the side edge region designed according to the invention is at least partially straight; more preferably, the thin glass has two opposing and mutually parallel side edge regions designed according to the invention.

[0020] The maximum thickness T max and the width W of the side edge area may be subject to a variation along the side edge area. Unless otherwise specified, T max and W is determined as the mean of several individual measurements along a section of the side edge area.

[0021] The maximum thickness T can be determined in this case. max The thickness of the side edge can be determined at a specific point on the side edge, for example using a micrometer screw, or by means of a measuring microscope on a prepared cross-section or fracture. Typically, the thickness T is measured. maxof the side edge area is determined as the mean value of 5 to 10 individual measurements distributed across the side edge area.

[0022] The width W of the lateral edge region is determined using a measuring microscope on a prepared cross-section or fracture. The boundary of the lateral edge region towards the functional area is defined by the fact that the thickness is significantly greater than in the functional area itself.

[0023] In a preferred embodiment, the ratio T is max / t < 5, preferably < 3, more preferably < 2 or < 1.5 and / or T max / t > 1.01, preferably > 1.05, more preferably > 1.10, and / or the ratio W / t < 50, preferably < 10, more preferably < 3. These embodiments are characterized by particularly high edge strength, and the bendability and flexibility of the thin glass, which is significantly reduced in a thicker side edge area with T, is largely eliminated. max / t > 5 is severely restricted. The thin glass can thus, for example, be rolled up with a tight bending radius. Preferably, the ratio of the width W of the side edge region to the thickness t of the thin glass t in the usable range W / t < 100, preferably < 10, more preferably < 3. Surprisingly, such a small width or such a small ratio can be achieved with the method according to the invention, which allows, on the one hand, the flexibility and pliability of the thin glass corresponding to the thinner usable range and also a large remaining usable range.

[0024] In another preferred embodiment, the side edge region has a thickening with T max / t < 1.2 in combination with a width-to-thickness ratio W / t < 3, as well as rounded edges at the transition to the first and second main surfaces (2, 3). In a preferred embodiment, the surface of the side edge region has a roughness depth R over a surface fraction of at least 10%, at least 30%, more preferably at least 80%, and most preferably completely. a < 2 nm or < 1 nm. A roughness depth of < 2 nm or even < 1 nm is characteristic of fire-polished glass surfaces. The area fraction of the glass surface with a roughness depth R aThe value < 2 nm thus reflects whether the side edge region has been only partially or completely melted. Therefore, preferably the side edge region is at least partially melted; preferably, a larger section of the side edge region or the entire surface of the side edge region is melted by the method according to the invention. The glass exhibits a roughness depth R at the melted surface of the side edge region. a < 2 nm. The term "roughness" used here refers to the average roughness R. a , which is a measure of the quality of a surface. Typically, amplitude parameters characterize the surface based on the vertical deviations of the roughness profile from the center line. R a This is the arithmetic mean of the absolute values ​​of these vertical deviations. The value can be determined according to DIN EN ISO 4287:2010-07.

[0025] In a further preferred embodiment, the side edge region, with the exception of the adjoining usable area, is approximately circular in a cross-sectional view, and the width-to-thickness ratio (W / t) is typically >3, preferably >4. An approximately circular cross-sectional shape is understood here to be a cross-sectional shape that is convex over at least 200°, preferably at least 270°, with uniform curvature, to which the usable area adjoins in the remaining section of the circumference. Advantages of this embodiment include the highly reliable removal of microcracks in the side edge region, as well as the stabilization of the thin glass by the thicker side edge region, resulting in higher inherent strength and improved handling of the thin glass overall.

[0026] In a preferred embodiment, the surface of the side edge region has two concavely curved sub-surfaces, each adjoining the first and second main surfaces, as well as a convexly curved sub-surface that connects the concavely curved sub-surfaces. This shape exhibits maximum strength and can advantageously be achieved with the plasma stream according to the invention.

[0027] The plasma flow according to the invention is characterized by a very high energy input combined with a low process gas flow. Thus, the molten glass is not displaced by the process gas flow, which would lead to rapid solidification of the molten glass in a colder area with uneven surface structures. Instead, the molten side edge area can form the described advantageous shape under the influence of the surface tension of the molten glass.

[0028] In a preferred embodiment, the side edge region in the convexly curved portion of the surface contains no tungsten, and preferably no other metals that are not part of the bulk glass composition of the thin glass. Tungsten or metals can cause problems in various thin glass applications, can reduce edge strength in particle form, and are therefore undesirable. While the use of an RF plasma torch based on a high-frequency arc discharge introduces tungsten or another electrode material into the glass surface, this can be avoided with the method according to the invention, since the plasma is generated not by means of an arc discharge, but solely via the microwave field.

[0029] The inventors have discovered that an undesirable chemical change in the convexly curved portion of the side edge region, which is most exposed to the atmospheric pressure plasma burner, can surprisingly be avoided with the inventive method. Such chemical changes are undesirable because they can, for example, lead to a change in the coefficient of thermal expansion of the thin glass in the edge region, which can, for example, lead to the build-up of mechanical stresses and a reduction in edge strength, or to other undesirable properties of the altered glass composition, such as reduced chemical resistance. A chemical change is understood to mean a deviation of the chemical composition of the thin glass from the bulk glass composition.The bulk glass composition corresponds to the composition of the thin glass in a central plane of the thin glass within the usable area, e.g., at a distance of at least 10 mm from the side edge region. This bulk glass composition can be determined, for example, in a cross-section through the thin glass using EDX, XPS, or another surface-sensitive measurement method. In a preferred embodiment, the SiO₂ content in a surface layer (measured with EDX) of the convexly curved sub-surface of the side edge region therefore deviates by less than 10 wt%, preferably less than 5 wt%, from the SiO₂ content of the bulk glass composition. Furthermore, in a preferred embodiment, the Al₂O₃ content in a surface layer of the convexly curved sub-surface deviates by less than 10 wt%, preferably less than 5 wt%, from the Al₂O₃ content of the bulk glass composition.

[0030] In a preferred embodiment, the surface of the side edge region exhibits bubble inclusions with an average size in the range of 0.5 to 5 µm, preferably at least 10 bubbles per 5 mm length of the side edge region. Such bubble inclusions can form, for example, if the untreated thin glass is previously separated by a laser filamentation process. In this process, laser filaments are introduced into the thin glass along a dividing line, and the glass is then fractured along the dividing line. Individual laser filaments, which result in low edge strength of the thin glass, can be sealed by the resulting glass melt, thus forming bubble inclusions. Surprisingly, these bubble inclusions do not reduce the edge strength.

[0031] In a preferred embodiment, the bulk glass composition has an Al₂O₃ content of at least 5 wt%, preferably at least 15 wt%, and / or a Na₂O content of at least 10 wt%, preferably at least 15 wt%. Such thin glasses can be characterized by chemical hardenability and are used, among other things, in the field of displays.

[0032] In a preferred embodiment, the usable area of ​​the thin glass has a thickness t of 15 µm to 110 µm and / or a TTV of less than 15 µm, preferably less than 10 µm, and more preferably less than 5 µm and / or a relative TTV TTV rel of less than 15% preferably less than 10%, where TTV rel= TTV / t. The TTV (total thickness variation) is the difference between the maximum and minimum thickness in the usable area of ​​the thin glass. The inventors have found that small thickness variations in the untreated side edge area, as well as a small TTV, rel important for the formation of a side edge region of constant maximum thickness T max and are therefore also important for high edge strength of the thin glass.

[0033] In a preferred embodiment, the edge strength K of the thin glass after plasma treatment is at least 250 MPa, preferably at least 300 MPa and more preferably at least 400 MPa.

[0034] The edge strength K of the thin glass is determined using a two-point bending method, which is known, for example, from ST Gulati: “Two Point Bending of Thin Glass Substrate”, SID Symposium, Techn. Papers Vol. 42, pp. 652-654 (2011). In this method, a thin glass sample is clamped in a U-shape between two parallel support plates and bent ever more tightly by bringing these plates closer together. From the plate spacing at which fracture occurs, the fracture stress in the edge region of the thin glass is calculated, which was present at the time of fracture. In this description, the edge strength K denotes the arithmetic mean of the fracture stress values ​​determined by the two-point bending method for at least 10, preferably at least 20, thin glass samples.

[0035] The inventive method for producing thin glass with high edge strength comprises the following steps: - Provision of an untreated thin glass, wherein the untreated thin glass comprises a usable area and an untreated side edge area with an untreated surface, wherein the untreated thin glass has an edge strength K' and has in the usable area a first main surface and a second main surface and a thickness t of 15 µm to 300 µm. - Directing a plasma stream onto the untreated surface of the side edge area, wherein the plasma stream is generated with an atmospheric pressure plasma burner which is generated by a high frequency field in the frequency range of 500 MHz to 5 GHz. - Moving the plasma stream along the untreated side edge region 10' at a relative velocity v, wherein the thin glass has an edge strength K after plasma treatment.

[0036] An untreated edge region is understood to be an edge region that has no thickening compared to the usable area of ​​the thin glass and is preferably formed essentially by a flat edge surface connecting the first and second main surfaces. The untreated edge region is preferably formed by separation processes such as diamond cutting, scoring, crack propagation by thermal stress, or similar separation processes known to those skilled in the art for separating the primary edge of a thin glass.

[0037] Surprisingly, the inventive method achieves a very rapid melting of the glass surface, which, on the other hand, does not introduce any new defects, impurities, or mechanical weaknesses. In particular, excessive melting of the thin glass can also be avoided, so that only a thin surface layer is melted.

[0038] In a preferred embodiment, the atmospheric pressure plasma burner has a radio frequency field between 1 GHz and 3 GHz, preferably between 2.3 and 2.5 GHz. Particularly powerful and cost-effective microwave generators exist in this frequency range. The microwave signal can be supplied to the burner head of the atmospheric pressure plasma burner either via a waveguide or via a suitable coaxial cable; the use of a coaxial cable allows for particularly flexible process control.

[0039] In a preferred embodiment, the atmospheric pressure plasma burner or microwave generator has a power input of 50 to 500 watts, preferably only 100 to 200 watts. The power can be delivered continuously or in pulses. The inventors have found that, surprisingly, even a very low power is sufficient to achieve the preferred edge shapes according to the invention. It is assumed that, firstly, the energy of the plasma is transferred very efficiently to the thin glass, and secondly, a very low gas flow of the process gas can be used, resulting in a very high energy flux density for the plasma and minimal heat dissipation by convection. Advantageously, the immediate vicinity of the plasma stream even remains cold.

[0040] Untreated or dried air can be used as the process gas supplied to the atmospheric pressure plasma burner, where it is converted into a plasma state. The use of H₂ or He, or any other process gas with a thermal conductivity greater than 0.1 W / (m·K), can be advantageously avoided, especially since the use of H₂ poses a safety risk and the use of He is very expensive.

[0041] In a particularly preferred embodiment, the gas flow rate of the plasma stream is between 0.1 and 40 l / m, preferably between 2 and 15 l / m (l / m = standard liters per minute). With such a low gas flow rate, the plasma stream exhibits a very high energy density, and unwanted displacement or blowing of the molten glass can be avoided by appropriately adjusting the burner opening. The thin glass then deforms essentially by minimizing its surface energy and typically forms the edge shape described above with a high surface quality.

[0042] The method according to the invention is preferably used for thin glass with a side edge region whose untreated surface has defects. A defect is understood to mean any irregularity in the untreated surface that reduces the edge strength, such as microcracks ("flaws"), laser filaments, or conchoidal fracture structures from previous cutting processes. The edge strength K' of the untreated thin glass is typically less than approximately 200 MPa.

[0043] Preferably, the untreated side edge region has a chamfered edge, more preferably a scribing-chopped edge. Such edges are characterized by characteristic fracture structures on the fracture surface as well as residues from the scribing, which can be carried out, for example, with a diamond or a carbide wheel. Likewise, the untreated side edge region can have a plurality of parallel laser filaments, which preferably extend over the entire thickness of the thin glass, with the fracture surface then extending between the laser filaments.

[0044] Such edges are also characterized by the fact that the untreated surface does not transition into the first main surface and / or second main surface with a continuous curvature, but preferably has sharp-edged overcuts.

[0045] The untreated side edge area has a thickness T max ' on, where T max' / t < 1.15, preferably T max ' / t < 1.05, more preferred T max ' / t -1.00. The untreated side edge area therefore preferably has no thickening compared to the usable area.

[0046] After plasma treatment, the thin glass exhibits at least one of the following features, as has already been described for the thin glass according to the invention. - the side edge area is formed in the form of a thickening, where the ratio T max / t < 5, < 3, < 1.5, < 1.2, < 1.1 and / or T max / t >1.04 , preferably > 1.1 - the side edge area is formed in the form of a thickening, wherein the ratio W / t is < 100, preferably < 10, more preferably < 3. - the side edge area has a thickening T max / t < 1,2 and W / t < 3, as well as rounded edges at the transition to the first and second main surfaces (2, 3) - the surface is completely fire-polished. - the edge strength K is at least about 250 MPa, preferably at least 300 MPa and more preferably at least 400 MPa.

[0047] In the method according to the invention, the atmospheric pressure plasma torch is moved relative to the side edge region of the thin glass, whereby either the thin glass or the atmospheric pressure plasma torch can be moved. The plasma stream is directed towards the untreated surface of the side edge region. The distance between the atmospheric pressure plasma torch and the surface is preferably between 2 and 20 mm, more preferably between 4 and 15 mm.

[0048] The plasma stream can have an approximately cylindrical, jet-like shape with a visible length of approximately 20 to 50 mm. Unlike a burner flame, the plasma stream is typically very dimensionally stable, so that the plasma stream has a beam axis.

[0049] The direction from which the plasma stream strikes the side-edge region can be described by two angles α and β, where α is the angle between the beam axis of the plasma stream and the first main surface of the thin glass in a cross-sectional view perpendicular to the side-edge region, and where β is the angle between the beam axis and a perpendicular on the side-edge region in a top view of the first main surface. The angle α is preferably chosen to be less than 30°, preferably less than 10°, and the angle β less than 45°, preferably less than 15°. With a side-edge surface perpendicular to the main surfaces, the plasma stream thus strikes the side-edge surface almost perpendicularly. With these angles of incidence, side-edge regions can be created in the form of thickenings with only a small width.

[0050] In a preferred embodiment of the process, the relative velocity v between the plasma stream and the thin glass is at least 1 m / min, preferably > 6 m / min, and particularly preferably between 12 and 30 m / min for a glass thickness of 30 to 50 µm. Particularly high process speeds are made possible by preheating the untreated thin glass before it comes into contact with the plasma stream, but this is relatively complex. Preferably, the untreated thin glass is not preheated before it comes into contact with the plasma stream.

[0051] The method according to the invention is thus characterized by numerous advantages over the prior art. The edge strength of a thin glass can be significantly improved by extremely rapid, at least partial, melting of a side edge region, wherein, according to the invention, the treated side edge region has a greater thickness than the thin glass, but can nevertheless have a minimal width and thickness. No metallic impurities are introduced, and the surface of the thin glass is not chemically altered or contaminated.

[0052] The invention is explained in more detail below with reference to the enclosed figures. These show: Fig. 1 Schematic cross-sectional representation through the side edge region of the thin glass in a first embodiment Fig.2 Photographic recording of a fracture cross-section through the side edge region of the thin glass in a first embodiment with T / t ~ 1.5 Fig. 3 Photographic recording of a fracture cross-section through the side edge region of the thin glass in the first embodiment with T / t ~ 4 Fig. 4. Schematic cross-sectional representation through the side edge area of ​​an untreated thin glass. Fig. 5a Photographic image of a fracture cross-section through the side edge region of an untreated thin glass with a scratch-broken edge Fig. 5b Photographic image of the side edge area of ​​an untreated thin glass with a scratched edge Fig. 5c Photographic image of the side edge area of ​​a (treated) thin glass with laser-filamentated and broken edge Fig. 6 Schematic representation of the process for producing thin glass Fig.7 Dependence of the edge strength K of a thin glass treated according to the invention with a thickness of 30 µm as a function of the edge thickness Tmax

[0053] Fig. Figure 1 shows a schematic cross-sectional representation of the thin glass 1. The usable area 7 of the thin glass, with an approximately constant thickness t, adjoins the side edge area 10, which takes the form of a thickening with T. maxThe surface 4 of the side edge region 10 has two concave regions 8 adjoining the usable area 7, and a convex region 9 connecting the two concave regions 8. The side edge region 10 is approximately circular, except for the adjoining usable area 7. The ratio of the width W of the side edge region 10 to the thickness t is approximately 2.5. The surface 4 of the side edge region 10 adjoins the first and second main surfaces 2, 3 of the usable area 7 with a continuously changing curvature.

[0054] Fig. 2 and Fig. Figure 3 shows photographic images of a fracture cross-section through the side edge region of an embodiment with T / t ~ 1.5 ( Fig. 2), or with T / t ~ 4 ( / Fig. 3)

[0055] Fig.Figure 4 shows a schematic cross-sectional view through the untreated side edge region 10' of a thin glass with an obliquely fractured edge. The side edge region 10' adjoins the usable area 7, has a maximum thickness corresponding to the glass thickness t and a width W', and an end face that connects sharply to the first and second main surfaces 2, 3, i.e., without a continuously changing curvature. Defects 20 are schematically indicated in the untreated surface 4'. For illustrative purposes, the fracture surface is shown obliquely.

[0056] Fig. 5a and Fig. Figure 5b shows a photographic image of the fracture cross-section and a top view of the end face of an untreated thin glass 1' with a scratch-broken edge, as it may be before the application of the inventive method.

[0057] Fig.Figure 5c shows a top-down photograph of an end face of a thin glass, which was produced by introducing equidistant laser filaments along a dividing line followed by fracturing along the dividing line. An untreated thin glass can also exist in this form before the application of the inventive method.

[0058] Fig. Figure 6 shows a schematic representation of the process for producing thin glass with high edge strength.

[0059] Fig. Figure 7 shows the edge strength K as a function of the maximum thickness T. max of the side edge area for a thin glass sample with a glass thickness of approximately 30 µm. Examples of implementation:

[0060] Small glass sheets measuring 50 mm × 30 mm were produced from a thin glass ribbon made of chemically hardenable aluminosilicate glass with a glass thickness of approximately 30 µm using a slot-down drawing process.

[0061] A first batch of thin glass samples was cut from glass ribbons using a scribing fracture process and exhibited an edge strength K of approximately 199 MPa + / - 23 MPa in a number of 36 samples.

[0062] A second batch of thin glass samples was produced using a laser filamentation process followed by fracturing along the filament line. These samples exhibited an edge strength / characteristic fracture strength / Weibull modulus of 182 MPa ± 17 MPa in a sample size of 34.

[0063] Subsequently, further samples from the first and second batches were treated using the inventive method. A Heuermann HF-Technik APP-Jet PC-PS 500 plasma torch, which can be operated with a power input of 100 to 500 watts, was used. Dried compressed air (5 bar) was supplied to the atmospheric pressure plasma torch as the process gas.

[0064] The thin-glass samples were positioned on a table so that a side edge of the thin glass extended beyond the table edge. The atmospheric pressure plasma torch was moved along the edge region, with the plasma stream directed towards the side edge at an angle α of 180° in the plane of the thin glass and perpendicular to the side edge at an angle β of 90° when viewed from above.

[0065] The following table lists the process parameters used: Case No.: #1 #2 #3 #4 Burner output [watts] 120 130 120 120 Gas flow [l / min] 9 6 10 10 Freestanding glass overhang: 3 8 2.5 2.5 Working distance d [mm] 8,5 8 8,5 10 angle α 180° 180 180° 180 Angle β 90° 90° 90° 90 Relative speed [rpm] 3000 3000 6m / min Result: Edge diameter T max [µm] ~50 ~80 70 69

[0066] The average maximum thickness of the side edge region T was determined on the processed glass samples. max as well as the width W of the side edge area and the edge strength K are determined.

[0067] In Fig. 7 is the edge strength K as a function of the thickness T maxas well as the width W of the side edge area. It can be seen that the edge strength could be significantly increased by the method according to the invention.

[0068] The edge strength K of the thin glass before carrying out the process according to the invention was 182 + / - 17 MPa. After carrying out the process according to the invention, the edge strength K has increased significantly and, depending on the thickness T, amounts to max of the secondary bore, at least 300 MPa, sometimes > 450 MPa. Reference symbol list 1 (treated) thin glass 1' untreated thin glass 2 first main surface 3 second main surface 4 4' Surface (of the side edge area) Surface (of the untreated side edge area) 7 Usable area 8 concave curved partial surface 9 convex curved partial surface 10 side edge area 10' untreated side edge area 20 defects 21. Bladder inclusion 30 atmospheric pressure plasma burners 31 Nozzle opening 32 Plasma current QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] KR 20220035606

[0005] WO 2020 / 123226

[0006] Cited non-patent literature

[0000] DIN EN ISO 4287:2010-07

[0024] ST Gulati: “Two Point Bending of Thin Glass Substrate”, SID Symposium, Techn. Papers Vol. 42, pp. 652-654 (2011

[0034]

Claims

[1] Thin glass (1) comprising a usable area (7) and at least one side edge area (10), wherein the thin glass in the usable area (7) has a first main surface (2) and a second main surface (3) and a thickness t of 15 to 300 µm, wherein the side edge region (10) has a surface (4) which connects the first main surface (2) and the second main surface (3), wherein the side edge region (10) is in the form of a thickening with a maximum thickness T max with T max / t > 1 and a width W is formed and the surface (4) of the side edge region (10) is continuously curved to the first (2) and second main surface (3), and wherein the ratio T max / t < 10 is. [2] Thin glass according to the preceding claim, wherein the thin glass comprises at least one of the following features: - the ratio T max / t is < 5, preferably < 3, more preferably < 2, or <1.5 - the ratio T max / t is >1.01, preferably >1.05, more preferably >1.10 - the W / t ratio is < 50, preferably < 10, more preferably < 3. [3] Thin glass according to one of the preceding claims, wherein the side edge region (10) comprises at least one of the following features: - the side edge area (10) has a thickening with T max / t < 1,2 and W / t < 3, as well as rounded edges at the transition to the first and second main surfaces (2, 3) - the surface (4) of the side edge region (10) has a roughness depth R over a surface fraction of at least 10%, preferably at least 30%, more preferably at least 80% and most preferably completely. a < 2 nm or R a < 1 nm. - the side edge area (10) is approximately circular in a cross-sectional view, with the exception of the adjoining usable area (7). [4] Thin glass according to one of the preceding claims, wherein the surface (4) of the side edge region (10) has two concavely curved sub-surfaces (8) which each adjoin the first (2) and second (3) main surface, and has a convexly curved sub-surface (9) which connects the concavely curved sub-surfaces (8). [5] Thin glass according to one of the preceding claims, wherein the side edge region (10) comprises at least one of the following features: - in the convexly curved partial surface (9) of the surface (4) no tungsten is present, preferably no metals at all, which are not part of the bulk glass composition of the thin glass. - a SiO2 content in a surface layer (measured by EDX) of the convexly curved sub-surface (9) deviates by less than 10 wt% from a SiO2 content of the bulk glass composition. - an Al2O3 content in a surface layer (measured by EDX) of the convexly curved sub-surface (9) deviates by less than 10 wt% from an Al2O3 content of the bulk glass composition. - the surface (4) of the side edge region (10) has bubble inclusions (21) with an average size in the range of 0.5 to 5 µm, preferably at least 10 bubbles on a length of 5 mm of the side edge region (10) [6] Thin glass according to any one of the preceding claims, wherein the thin glass (1) comprises at least one of the following features - the bulk glass composition has an Al2O3 content of at least 5 wt%, preferably at least 15 wt% - the bulk glass composition has a Na2O content of at least 10 wt%, preferably at least 15 wt% [7] Thin glass according to one of the preceding claims, wherein the usable area (7) of the thin glass (1) comprises at least one of the following features - a thickness t from 15 µm to 110 µm - a TTV (Total Thickness Variation) of less than 15 µm, preferably less than 10 µm, and more preferably less than 5 µm - a relative Total Thickness Variation (TTV) rel of less than 15% preferably less than 10%, where TTV rel = TTV / t [8] Thin glass according to any of the preceding claims, wherein the edge strength K' is at least 200 MPa, preferably at least 300 MPa and more, preferably at least 400 MPa (more precisely via Weibull distribution?) [9] Method for producing thin glass with high edge strength, comprising the following steps: - Provision of an untreated thin glass (1') wherein the untreated thin glass (1') comprises a usable area (7) and an untreated side edge area (10') with an untreated surface (4'), wherein the untreated thin glass (1') has an edge strength K' and in the usable area (7) has a first main surface (2) and a second main surface (3) and a thickness t of 15 to 300 µm - Directing a plasma stream (32) onto the untreated surface (4') of the side edge region (13), wherein the plasma stream (32) is generated with an atmospheric pressure plasma burner (30) which is generated by a high frequency field in the frequency range of 500 MHz - 5 GHz - Moving the plasma stream (32) along the untreated side edge region 10' at a relative velocity v, wherein the thin glass has an edge strength K after plasma treatment. [10] Method according to claim 9, comprising at least one of the following features, - The atmospheric pressure plasma burner has a high-frequency field frequency between 1 GHz and 3 GHz, preferably between 2.3 and 2.5 GHz. - The atmospheric pressure plasma burner has a power consumption of 50 watts to 500 watts, preferably 100 to 200 watts. - The atmospheric pressure plasma burner uses untreated air or dried air as process gas. - The atmospheric pressure plasma burner uses as process gas a gas or gas mixture with a thermal conductivity of < 0.1 W / (m·K), and preferably no H2 and no He - the gas flow of the plasma stream (32) is between 0.1 and 40 l / min, preferably between 2 and 15 l / m [11] Method according to any one of claims 9 to 10, wherein the untreated side edge region (10') comprises at least one of the following features, - the untreated surface (4') has defects (20) - the edge strength K' is less than approximately 200 MPa - the untreated side edge area (10') has a broken edge, preferably a scribed edge, - the untreated surface (4') does not transition into the first main surface (2) and / or second main surface (3) with a continuous curvature, but preferably with sharp edges - the untreated side edge area (10') has a thickness T max ' on, where T max ' / t < 1.15, preferably T max ' / t < 1.05, more preferred T max ' / t -1.00 is, - the untreated side edge area (10') shows no thickening compared to the usable area (7). [12] Method according to any one of claims 9 to 11, wherein the thin glass (1) after plasma treatment has at least one of the following features: - the side edge region (10) is formed in the form of a thickening, where the ratio T max / t < 5, < 3, < 1.5, < 1.2, < 1.1 and / or T max / t >1.04 , preferably > 1.1 - the side edge region (10) is formed in the form of a thickening, wherein the ratio W / t < 100, preferably < 10, more preferably < 3. - the side edge area (10) has a thickening T max / t < 1,2 and W / t < 3, as well as rounded edges at the transition to the first and second main surfaces (2, 3) - the surface (4) is completely fire-polished. - the edge strength K is at least about 200 MPa, preferably at least 300 MPa and more preferably at least 400 MPa. [13] Method according to any one of claims 9 to 12, comprising at least one of the following features, - the distance between atmospheric pressure plasma burner (20) and surface (4') is between 2 and 20 mm, preferably between 4 and 15 mm. - the plasma stream has an approximately cylindrical, jet-like shape with a visible length of approximately 20 to 50 mm. [14] Method according to any one of claims 9 to 13, wherein the plasma stream has a beam axis (33), wherein the plasma stream strikes the side edge region (10') at angles α and β, where the angle α is the angle between the beam axis (33) and the first principal surface (2) in a cross-sectional view perpendicular to the side edge region (10'). where the angle β is the angle between the beam axis (33) and a perpendicular on the side edge region (10') in a top view of the first main surface (2), and where α is less than 30°, preferably less than 10° and / or β is less than 45°, preferably less than 15°. [15] Method according to any one of claims 9 to 14, comprising at least one of the following features, - the relative velocity v between plasma stream and thin glass is at least 1 m / min, preferably at least 6 m / min, and more preferably even at least 12 m / min to 30 m / min for a glass thickness of 30 to 50 µm - The untreated thin glass is not preheated before it comes into contact with the plasma stream.

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