Glass-ceramic cover plate, production method thereof, use thereof, and digital display device including that cover plate

Abstract

To provide a cover plate for electronic display devices that are producible in good optical quality using a robust production method.SOLUTION: A cover plate includes a silica-based glass ceramic. The cover plate has a thickness between 0.4 mm and 0.85 mm, has a transmittance of more than 80% in the range from 380 nm to 780 nm, is chemically tempered, has a CS of at least 250 MPa and / or a CS30 of at least 160 MPa, and a DoCL of at least 0.2 times the thickness of the cover plate, and includes at least one silica-based crystal phase having, in at least one near-surface layer, a unit cell volume of at least 1 vol.% larger than the crystal phase unit cell volume of a core, advantageously averaged after a tempering process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention generally relates to a glass ceramic cover plate, a method for manufacturing the same, a use thereof, and a digital display device including the cover plate. [Background technology]

[0002] Cover plates used in display devices have long been prior art. Such cover plates are often referred to as "covers" or "cover glass." In many cases, such cover plates are positioned to protect electronic components and display devices located behind them, for example, in smartwatches or smartphones, and include chemically strengthened glass to increase the mechanical resistance of the cover plate compared to an unstrengthened state. Furthermore, the use of glass-ceramic plates is also well known, in which case, glass-ceramic, which is already inherently more mechanically resistant than unstrengthened glass, is advantageous.

[0003] Depending on the precise composition of the glass ceramic, it can also be formed in a way that allows for strengthening. In principle, two mechanisms are possible. For example, glass ceramics contain not only crystalline components but also glassy components that can be referred to as "residual glass phase." Therefore, when glass ceramics are chemically strengthened, ion exchange may occur in the glass phase itself, and in this respect, the process proceeds very similarly to that of glass without crystalline components. However, ion exchange during chemical strengthening may also occur in the crystalline phase contained in the glass ceramic, and this can even be advantageous.

[0004] For example, GH Beall et al., "Ion-Exchange in Glass-Ceramics," Frontiers in Materials 2016, 3, Article 41, provides an overview of various mechanisms involved in strengthening glass-ceramics.

[0005] U.S. Patent Application Publication No. 2020 / 0346969 (US2020 / 0346969 A1) describes a chemically strengthened, three-dimensionally molded crystallized glass. The glass ceramic contains keytite as a crystalline phase. Its nucleation is preferably carried out via ZrO2 as a pure nucleating agent.

[0006] U.S. Patent Application Publication No. 2021 / 0292225 (US2021 / 0292225 A1) describes a chemically strengthened glass plate, a cover plate, and an electronic device comprising such a cover plate. The chemically strengthened glass may exist as a partially crystallized glass and may include, for example, keytite as a crystalline phase. In this case, nucleation advantageously occurs via nucleating agents ZrO2 and SnO2.

[0007] Glass ceramics containing keyite as a crystalline phase can already possess inherently high strength and can be chemically strengthened well, but they often exhibit noticeable cloudiness, making the manufacture of cover plates for display devices using such glass ceramics difficult, even if possible.

[0008] Therefore, there is a need for chemically strengthenable glass ceramics that can be manufactured with good optical quality using robust manufacturing methods, for use as cover plates for electronic display devices. A suitable manufacturing method for such glass ceramics, or for cover plates containing such glass ceramics, is also needed. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0346969 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0292225 [Non-patent literature]

[0010] [Non-Patent Document 1] GH Beall et al., “Ion-Exchange in Glass-Ceramics”, Frontiers in Materials 2016, 3, Article 41 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a cover plate containing silica-based glass ceramic that at least partially reduces the above-mentioned drawbacks of the prior art. Further embodiments relate to a method for manufacturing such a cover plate, and to the use thereof. [Means for solving the problem]

[0012] The problems of the present invention are solved by the subject matter of the independent claims. Specific and preferred configurations become apparent in the dependent claims, as well as in the specification and drawings of this disclosure.

[0013] Accordingly, the present invention relates to a cover plate having a thickness of 0.4 mm to 0.85 mm, comprising silica-based glass ceramic, and having a light transmittance τ of more than 80%, preferably more than 85%, in the range of 380 nm to 780 nm, which is advantageously specified for a cover plate thickness of 0.4 mm to 0.85 mm, and particularly advantageously specified for a cover plate thickness of 0.7 mm. visThe present invention relates to a cover plate having the following: The cover plate is chemically strengthened. The cover plate has a CS (compressive stress) of at least 250 MPa and preferably up to 1500 MPa, and / or a CS30 (compressive stress at a depth of 30 μm, specified from one of the two sides (or "surfaces") of the cover plate) of at least 160 MPa and preferably up to 525 MPa, and / or a DoCL (thickness of the strengthening layer) of at least 0.1 times the thickness of the cover plate and preferably less than half the thickness of the cover plate. The silica-based glass ceramic comprises at least one silica-based crystalline phase, the crystalline phase comprising at least one near-surface layer In particular, in a layer 20 μm to 70 μm deep, defined perpendicularly from one side of the cover plate, it is advantageous that, on average after the strengthening process, it has a unit cell volume at least 1 volume%, preferably at least 2 volume%, larger than the crystalline phase in the center. The center of the cover plate is understood as the structure of the cover plate in the layer below 70 μm, defined perpendicularly from one of the two sides of the cover plate. In other words, the center of the cover plate can also be understood as its "bulk". Generally, the smallest stress exists in the center of the cover plate.

[0014] The unit cell volume is determined via thin-film X-ray diffraction measurements. Depending on the angle of incidence Ω of the X-rays onto the planar sample surface (e.g., Ω=0.5° to Ω=5°), information about a depth of approximately 2 μm to 20 μm can be obtained. From the position of the measured X-ray diffraction reflection, the lattice constant and unit cell volume can be calculated using commonly available methods, and through this calculation, an average value along the optical path of the diffracted X-rays is provided in particular. By scraping the surface to the desired extent and then measuring again, the unit cell volume can be determined down to the region where ion exchange is no longer occurring. Relatively small changes in the lattice constant due to compressive or tensile stress in glass ceramics are negligible compared to the large changes in the lattice constant due to ion exchange in the crystal structure.

[0015] In the sense of this disclosure, the light transmittance at 380-780 nm measured in accordance with DIN 5033 is referred to as transmittance or light transmittance, or τvis It is shown as such. This is the same as the Y value in the CIE color system measured using a standard light source C at an observer angle of 2° for a 4 mm thick polished glass-ceramic sample. Since this light corresponds to white light with a color temperature of 6800 K, it represents average daylight.

[0016] The configuration of the cover plate as described above has many advantages.

[0017] Since the cover plate contains a silica-based glass-ceramic, it is already a chemically very resistant member. A silica-based glass-ceramic, within the scope of the present disclosure, is understood to be a glass-ceramic containing SiO2 and preferably containing SiO4 4- as a constituent tetrahedron, that is, a glass-ceramic containing so-called crystalline silica. Silica-based glass-ceramics already essentially have good mechanical resistance. Furthermore, the cover plate is chemically strengthened, that is, it has a CS (compressive stress) of at least 250 MPa and preferably at most 1500 MPa, and / or a CS30 of at least 160 MPa and preferably at most 525 MPa, and / or a DoCL of at least 0.1 times the thickness of the cover plate and preferably less than half the thickness of the cover plate. In this way, advantageous properties of the cover plate regarding mechanical use tests, for example, the so-called "set-drop test" regarding the behavior of the cover plate when incorporated into a device, can be achieved, so that a sufficiently thin and thus light cover plate can be used. Therefore, the cover plate has a thickness of 0.4 mm to 0.85 mm. This is also further advantageous because in this way a high light transmittance τ vis exceeding 80%, preferably exceeding 85%, is achieved in the wavelength range from 80 nm to 780 nm. Advantageously, the light transmittance value is specified for a cover plate thickness of 0.7 mm for comparison. To compare whether they meet this condition, thin plates can be laminated to achieve the corresponding thickness, and thicker plates can be made thinner. Generally, this light transmittance value is achieved for a cover plate thickness of 0.4 mm to 0.85 mm.

[0018] The silica-based glass ceramic contained in the cover plate includes at least one silica-based crystalline phase, which, in at least one near-surface layer, particularly in a thickness of 20 μm to 70 μm perpendicular to one side of the cover plate, has, on average after the strengthening process, a unit cell volume at least 1 volume%, preferably at least 2 volume%, larger than the unit cell volume of the crystalline phase in the center. In other words, the silica-based glass ceramic includes a crystalline phase, which exists as a strengthenable crystalline phase in its non-strengthened state, and in the chemically strengthened state of the cover plate according to the embodiment, is chemically strengthened in a form having the expanded unit cell volume as described above. In this case, the expansion of the unit cell of the crystalline phase in the chemically strengthened state does not exist over the entire thickness of the cover plate, but rather only within a specific region, i.e., only in the near-surface region of the cover plate. Therefore, a cover plate formed in a plate-like shape, meaning its thickness is at least an order of magnitude greater than its length and width, has two sides (or "sides"), the dimensions of which are specified by length and width, and extending perpendicularly inward from there toward the center of the cover plate, a near-surface layer is specified. This near-surface layer is formed on both sides of the cover plate. It is advantageously a layer with a depth of 20 μm to 70 μm. Here, the volume of the unit cell of the crystalline phase is different from the volume of the unit cell of the same crystalline phase in the center of the cover plate. Advantageously, the crystalline phase in which the unit cell in the near-surface layer is enlarged relative to the unit cell in the center is a silica-based crystalline phase.

[0019] Therefore, the expansion of the unit cell of the crystalline phase occurs at least in the region near the surface. Depending on the exact strengthening protocol, the ion exchange region can be up to a depth of 300 μm. Depending on the exact depth of the layer considered within the cover plate, it has been found that different proportions of ion-exchanged crystalline phases are brought about. In other words, this means that there is a thickness transition in the case of the cover plate according to the embodiment. For example, at the surface of the cover plate and advantageously up to the region of the near-surface layer, advantageously from 20 μm to 70 μm, almost complete exchange occurs up to a minimum as can be shown in the corresponding EDX profile. For a long strengthening protocol with a strengthening time of, for example, 12 hours, ion exchange up to a depth of about 300 μm is detectable. Here, the DoCL is 145 μm, and thus in the cover plate, the compressive stress curve is configured according to the ability of the material to accumulate tensile stress. The inventors believe that in the region below the crystal or microcrystal or crystalline phase where there is a DoCL identified using physical measurement techniques that is ion-exchanged, the proportion of the crystalline phase is small and thus does not contribute to the compressive stress. Therefore, strengthening exists because an increase in the volume of the crystalline phase in the near-surface region on both sides of the cover plate results in compressive stress in the central part inside the cover plate.

[0020] In other words, strengthening here is achieved not through exchange within the glass phase, but through exchange within the crystalline phase. Furthermore, it has been found that chemical strengthening by such ion exchange occurring within the crystalline phase results in highly efficient strengthening. Surprisingly, this is even better than ion exchange for non-crystallized glass materials with the same chemical composition. The same amount of ions are exchanged, but the strengthening formed in the cover plate according to the embodiment is better. In other words, in the cover plate according to the embodiment, which includes silica-based glass ceramic, the same amount of exchanged ions leads to higher strengthening. Therefore, the strengthening process is efficient with respect to the strengthening formed. This is evident, for example, in Figure 9 of the drawings, where the strengthening profile of a cover plate according to one embodiment is compared with the strengthening profile of a non-ceramicized cover plate containing the same chemical composition. Here, strengthening profile 5 corresponds to the cover plate according to one embodiment, and strengthening profile 6 corresponds to a cover plate containing the same chemical composition but formed in a glassy state and not ceramicized.

[0021] Therefore, when the degree of exchange is the same, that is, when the amount of ions exchanged from the exchange bath is essentially the same, more efficient strengthening is achieved. Thus, in the case of exchange into the crystalline phase, compressive stress can be built up more efficiently than in the case of exchange into the glass material. At the same time, it is also noted that the strengthening thus produced in glass ceramics has greater thermal and temporal stability than that of chemically strengthened glass of the same composition. For example, the strengthening brought into glass ceramics by ion exchange into the crystalline phase may not relax as rapidly as the chemical strengthening brought into glass materials. Furthermore, it has been found that the strengthening that can be accumulated in glass ceramic materials is higher than that in glass materials of the same chemical composition (see Figure 9 in the drawings of this disclosure for this as well).

[0022] The advantageous properties associated with the cover plates according to the embodiments of this disclosure are based on the fact that, under the same strengthening process, i.e., under the same strengthening time, a greater compressive stress can be generated in a cover plate made of or containing glass ceramic than in a cover plate made of or containing glass of the same chemical composition. Therefore, under the same strengthening process, the maximum tensile stress in the cover plate according to the embodiments is higher than in a cover plate made of or containing glass having the same chemical composition as the corresponding glass ceramic. Here, the composition of the glass or glass ceramic before the strengthening process is carried out, respectively.

[0023] For example, the maximum tensile stress was found to be 1.6 times greater than the maximum tensile stress (CT) in a corresponding glass-based or glass-based cover plate in one embodiment, where the cover plate had the same chemical composition and underwent the same strengthening process as a glass-based or glass-based cover plate.

[0024] For a cover plate according to one embodiment, and for a cover plate made of glass with the same chemical composition as the glass ceramic, the following values ​​were obtained as the maximum tensile stress (internal tensile stress CT): [Table 1]

[0025] The ratio of the CT value of the glass-ceramic cover plate to that of the glass cover plate is 1.48 (both cover plates were subjected to the same strengthening process).

[0026] Generally, the value of this ratio can be between 1.3 and 1.6, and especially up to 1.5.

[0027] This characteristic difference in CT values ​​can also be seen, for example, from the reinforcement profile diagram shown in Figure 9.

[0028] The particularly good strengthening achievable and achieved in the cover plate according to this disclosure is due precisely to strengthening to the crystalline phase, i.e., ion exchange. This, on the one hand, leads to an expansion of the crystalline unit cell, and thus is a special feature of the advantageous cover plate according to the embodiment. Furthermore, this also leads to particularly good results in so-called set-drop tests, for example, in the case of the cover plate according to the embodiment.

[0029] According to one embodiment of the cover plate, the crystalline phase contains a higher proportion of sodium oxide (Na2O) and / or potassium oxide (K2O) in at least the near-surface layer, i.e., after the strengthening process, than in the center. The inventors believe that in the near-surface region, the content of sodium oxide (Na2O) and / or potassium oxide (K2O) in the crystalline phase is increased to at least 1 mol%, preferably at least 2 mol%, and especially preferably up to 7 mol%, relative to the corresponding content of the crystalline phase in the center.

[0030] In that case, depending on the embodiment, sodium ions Na + This is particularly important because it is smaller than potassium ions and therefore can be exchanged more easily, thereby achieving a higher exchange depth, for example, about 0.1 to 0.4 times the thickness of the cover plate. Thus, an exchange depth of, for example, 70 μm or more is easily achievable. The strengthening value achieved at the surface of the cover plate is about 600 MPa or less, for example, about 500 MPa.

[0031] As mentioned above, potassium ions are larger than sodium ions, making it difficult for potassium ions to diffuse into the cover plate. Here, a small exchange depth is achieved, but the strengthening achieved by potassium exchange is also higher than that achieved by sodium exchange. In this way, the compressive stress value at the surface of the cover plate can be up to 1500 MPa, for example, 1100 MPa.

[0032] According to one embodiment, the glass ceramic of the cover plate contains more than 50 volume percent of crystalline phase, preferably more than 70 volume percent of crystalline phase, and particularly preferably up to 95 volume percent of crystalline phase. Thus, it is a glass ceramic containing only a small residue of glass material (so-called residual glass phase). In this way, particularly efficient strengthening has been found to be achievable. The reason for this is not yet fully understood, but it may be due to the large volume of crystalline phase present in the glass ceramic of the cover plate causing particularly good strengthening. In other words, the more crystals or microcrystals available for ion exchange, the higher the strengthening that can be achieved. Thus, as described above, exchange into the crystalline phase has been found to be very efficient. The inventors believe that, even at the same exchange rate, better chemical strengthening can be obtained because it is higher and more stable compared to glass materials of the same chemical composition. The good strengthening of the crystalline phase or into the crystalline phase is surprising even at high crystalline phase content of 95% by volume or more, because until now, it was thought that the exchange mechanism also occurred through the glass phase, since ions should be more mobile here than in a crystalline structure with rigid lattice sites. However, despite the high crystallinity of the glass-ceramic material, this embodiment advantageously allows for particularly good and efficient strengthening. Furthermore, despite the high crystalline phase content, very good permeability is still obtained for the glass-ceramic of the cover plate, and consequently for the cover plate itself as a whole.

[0033] The above crystal phase content rate relates to the overall content rate of the crystals in the glass ceramic, regardless of exactly which phases are present. According to a preferred embodiment, the glass ceramic contains keatite or keatite mixed crystals as the main crystal phase, which is generally understood to be present as the main crystal phase having a specific crystal structure, i.e., the keatite crystal structure in the case of keatite, with more than 50% by volume of the crystal phases generally contained in the glass ceramic. Advantageously, up to 98.5% by volume, or even 100% by volume, of the crystal phases contained in the glass ceramic can have a keatite crystal structure, i.e., exist as keatite or keatite mixed crystals. However, it is also possible for the glass ceramic to contain a secondary phase, such as a nucleating agent present as crystals.

[0034] According to a further embodiment, the cover plate has a chroma C of less than 4, preferably less than 3. * That is to say, the cover plate has very little color cast, so it is also possible to view the display behind it through the cover plate without disturbing color distortion. Chroma C * or C ab * is also shown as chroma, and chroma a * , b * is calculated as follows:

Equation

[0035] According to yet a further embodiment, the cover plate is characterized by a haze of 0.01% to 1% with respect to a thickness of the cover plate of 0.7 mm. Haze is understood as cloudiness. That is to say, the cover plate is formed with only slight cloudiness.

[0036] To achieve low chromaticity and / or low cloudiness, it may be advantageous to limit the TiO2 content of the glass ceramic. TiO2 is a known component of silica-based glass ceramics, such as so-called lithium aluminum silicate glass ceramics, and can be particularly useful for efficient nucleation. However, it has been found that this component, even if it does not color itself, can contribute to the coloration of the resulting glass ceramic through cloudiness. Therefore, according to one embodiment, the glass ceramic contains TiO2, advantageously up to 4 mass% of TiO2, and particularly preferably up to 3 mass% of TiO2.

[0037] Advantageously, according to one embodiment, the glass ceramic contained in the cover plate is formed as lithium aluminum silicate glass ceramic, and its crystalline phase is formed as a keytite mixed crystal. Lithium aluminum silicate glass ceramic is well known as a material that offers clear advantages in the manufacture of glass ceramics. Therefore, forming a glass ceramic containing a keytite mixed crystal as the crystalline phase (or crystalline phase) is even more advantageous because it has been found that not all crystalline phases in a lithium aluminum silicate glass ceramic system are configured to be strengthenable. However, keytite or keytite mixed crystal clearly has a crystalline structure that facilitates ion exchange, particularly the exchange of lithium for sodium and / or sodium and / or lithium for potassium. However, a drawback of known keytite mixed crystal glass ceramics, especially those that already possess inherently high strength, is that these glass ceramics often have a strong cloudiness. However, surprisingly, it has been found that cover plates containing keytite mixed crystal glass ceramics that simultaneously have slight cloudiness, only slight coloration, and even higher light transmittance are possible. The inventors do not yet fully understand the reason for this.

[0038] However, for lithium aluminum silicate glass ceramics and keytite mixed crystals of the crystalline phase, the keytite mixed crystal in the near-surface layer is 510 Å.3 Exceeding 515 Å, preferably 515 Å 3 It has been found that advantageous properties of the cover plate arise when the unit cell volume exceeds a certain level. The inventors believe that a mixed crystal with such a configuration has a composition in which the optical properties of the crystalline phase and the optical properties of the residual glass phase are optimally matched to each other in such a way that there is almost no difference in refractive index between the two phases. This reduces the effect of clouding.

[0039] In general, without being limited to a specific embodiment, according to one embodiment, the glass ceramic consists of the following components: SiO255-75, preferably 62-72 Al2O3 18-27, preferably 18-23 Li2O 2.8-5, preferably 3-5 It may contain in mass percent based on oxides.

[0040] This is a silica-based glass ceramic that is sufficiently meltable as glass and does not tend to crystallize immediately and disorderly. Within this general composition range, known lithium aluminum silicate glass ceramics, particularly those well known with respect to melting and ceramicization conditions, can be manufactured. A lithium content in the glass ceramic is even more advantageous because it allows for the exchange of sodium and / or potassium for lithium.

[0041] In further embodiments, the glass ceramic contains MgO, with a preferred upper limit of 8% by mass. Particularly preferably, the glass ceramic contains 4% by mass or less of MgO. MgO is a preferred component because it promotes the formation of keytite mixed crystals. This means that a certain percentage of MgO leads to a decrease in the ceramicization temperature. However, if the MgO content is too high, undesirable secondary phases, such as spinel and / or magnesium titanate, may be formed. This adversely affects the permeability of the resulting glass ceramic material, particularly with respect to its scattering. Therefore, the MgO content of the glass ceramic is advantageously limited to the limits described above.

[0042] According to one embodiment, the glass ceramic further contains ZnO in an advantageous maximum of 6% by mass, and particularly advantageously 2% by mass or less. Such a ZnO content can be advantageous because ZnO lowers the viscosity of the glass, making the green glass of the glass ceramic more easily meltable. However, too much ZnO leads to the formation of other phases, such as zinc spinel, and consequently, increased scattering.

[0043] Other alkaline earth metal oxides, such as CaO and BaO, can also have a positive effect on melting properties. However, the amount of such components RO (alkaline earth metal oxides, including ZnO) should generally be limited to avoid the formation of heterogeneous phases that can lead to greater scattering and, consequently, a decrease in transmittance. Furthermore, the use of heavy alkaline earth oxides, such as BaO and SrO, in particular, can be used to match the refractive index of the residual glass phase to that of the crystalline phase, thereby optimizing transmittance.

[0044] A special component of the glass ceramic according to one embodiment is SnO2. SnO2 can act, for example, as a clarifying agent in the molten material and then as a nucleating agent in the glass ceramic itself. Accordingly, according to one embodiment, the glass ceramic of the cover plate preferably contains SnO2, more preferably up to 2% by mass. A SnO2 content of at least 0.05% by mass, and preferably up to 1.6% by mass, is particularly preferred. Higher SnO2 content leads to a strong devitrification tendency, which worsens the productivity of the glass ceramic.

[0045] The components of ZrO2 and TiO2 can also act as nucleating agents in the glass ceramic according to the embodiment. Nucleation, particularly the content and relative ratio of the nucleating agents in the glass ceramic, has been found to be important for the formation of lightly colored silica-based glass ceramics having good light transmittance and slight cloudiness. Accordingly, according to one embodiment, the glass ceramic contains TiO2, advantageously up to 4 mass% of TiO2, particularly preferably up to 3 mass% of TiO2.

[0046] Furthermore, ZrO2 is also a very efficient nucleating agent in glass ceramics according to one embodiment. Accordingly, according to one embodiment, the glass ceramic contains ZrO2 in an advantageous amount of up to 5% by mass, particularly advantageously up to 4% by mass, and especially preferably at least 1.2% by mass.

[0047] The glass ceramic may further contain Fe2O3 up to a particularly large amount of 0.1 mass%. Fe2O3 is often present in the form of an unavoidable impurity in the glass ceramic according to the embodiment, but at the same time, it is beneficial for nucleation, so a certain content of Fe2O3 can also be beneficial. However, in order to obtain a glass ceramic that is as color neutral as possible, the content of Fe2O3 should be limited, and is advantageously 0.02 mass% or less. In particular, a content of 0.0001 mass% to 0.1 mass%, preferably 0.0001 to 0.02 mass%, is possible. In other words, generally, the Fe2O3 content of the glass ceramic of the cover plate according to one embodiment is less than 0.02 mass%.

[0048] Regarding the ratio of the important components TiO2 and ZrO2, according to one embodiment, the following relationship applies: 0 < Σ(TiO2 + ZrO2) < 9.5%, preferably 1.2 < Σ(TiO2 + ZrO2) < 9.5%.

[0049] It has been found that with such a ratio of TiO2 and ZrO2 as nucleating components to each other, particularly good values ​​regarding cloudiness and slight coloration can be achieved.

[0050] This can generally be achieved even better when the ratio of nucleating agents also incorporates an additional nucleating component, SnO2. According to preferred embodiments, the following generally applies: 0 ≤ SnO2 / (ZrO2 + TiO2) < 0.8, preferably 0.01 ≤ SnO2 / (ZrO2 + TiO2) < 0.7.

[0051] In particular, the glass ceramic according to one embodiment consists of the following components: SiO255-75, preferably 62-72 Al2O3 18~27 Li2O 2.8-5, preferably 3-5 Na2O 0-4, preferably 0-2 K2O 0-4, preferably 0-2 MgO 0-8, preferably 0-4 CaO 0-4, preferably 0-2 SrO 0-4, preferably 0-2 BaO 0-4, preferably 0-2 ZnO 0-6, preferably 0-2 TiO20-4, preferably 0-3 ZrO20~5, preferably 1.2~4 B2O30~2, preferably 0~0.1 Fe2O3 0.0001~0.1, preferably 0.0001~0.02 SnO20~2, preferably 0.05~1.6 This can be included in mass% on an oxide basis, where, advantageously, the total of the TiO2 and ZrO2 components, 0 < Σ(TiO2 + ZrO2) < 9.5%, preferably 1.2 < Σ(TiO2 + ZrO2) < 9.5% This applies.

[0052] According to one embodiment, the glass ceramic of the cover plate contains a crystalline phase having a microcrystal size of 120 nm or less. Advantageously, the microcrystals contained in the glass ceramic are up to 90 nm in size.

[0053] Embodiments in which the glass ceramic of the cover plate is As2O3 and / or Sb2O3-free are particularly preferred. Within the scope of this disclosure, “free” of these components is understood to mean that these components are present only in the form of unavoidable impurities or in trace amounts, at a maximum content of 500 ppm, preferably 100 ppm, of the mass.

[0054] According to a further embodiment, the cover plate is characterized by sharp impact strength for drop heights of at least 120 cm to 200 cm, as specified in a set drop test.

[0055] So-called "sharp impact" strength is understood, within the scope of this disclosure, to mean that a smartphone dummy containing the plate to be tested is dropped onto a rough surface using a drop device so that a number of small, sharp objects (e.g., grains of sand on asphalt, concrete, or sandpaper) can pierce the plate to be tested. In other words, this is the effect of one or more sharp objects, for example, particles with a very small radius of curvature or where the angle of part of the protrusion is less than 100°.

[0056] In this case, the keytight-type glass-ceramic cover plate with chemical strengthening in the crystalline phase achieved an average drop height of approximately 165 cm, which is about twice the height of the glass type, which is not ceramicized and chemical strengthening is conventionally constructed in the glass phase, and has an average drop height of 77 cm. When the same type of glass is unfavorably ceramicized (β-high temperature quartz mixed crystal), chemical strengthening cannot be sufficiently formed in either the crystalline or glass phase, so the drop height is insufficient at 20 cm.

[0057] This disclosure also relates to a method. A method for manufacturing a cover plate, and in particular a cover plate according to one embodiment, is as follows: • The process of manufacturing silica green glass through a melting process and subsequent hot forming, The heat treatment step of the silica green glass, wherein at least one nucleation step is performed at a temperature range of 690°C to 850°C for 5 minutes to 8 hours, preferably 30 minutes to 2 hours, and at least one ceramicization step is performed at a temperature range of 780°C to 1100°C for 3 minutes to 60 hours, preferably 3 minutes to 8 hours. The step of performing at least one ion exchange in an exchange bath having a composition of 100% to 0% by mass of KNO3, 0% to 100% by mass of NaNO3, and 0% to 5% by mass of LiNO3, at a temperature of 370°C to 500°C and for a period of 2 to 50 hours. Includes.

[0058] Generally, one or more further exchange steps can be carried out at a temperature of 370°C to 500°C for a period of 1 to 10 hours, using an exchange bath having a composition of 90% by mass of KNO3 and 10% by mass of NaNO3 to 100% by mass of KNO3, or 95% by mass of NaNO3 and 5% by mass of LiNO3 to 99% by mass of NaNO3 and 1% by mass of LiNO3.

[0059] The chemical strengthening characteristic values ​​CS0 (compressive stress on the surface of the cover plate), CS30 (compressive stress at a depth of 30 μm, or generally the stress), and DoCL (depth of the compressive stress layer, sometimes referred to as the exchange depth) can be determined using suitable measuring devices, such as the SLP-1000 and FSM6000. However, DoCL is not the same as the ion exchange depth.

[0060] Accordingly, this disclosure also generally relates to cover plates that have been manufactured or can be manufactured by a method according to one embodiment.

[0061] Furthermore, this disclosure relates to the use of a cover plate according to one embodiment and / or a cover plate manufactured by a method according to one embodiment in electronic devices, particularly in electronic display devices, particularly in mobile electronic display devices, such as mobile touch panels and / or mobile digital display devices, such as smartphones or smartwatches, and generally in touch panels. Furthermore, this disclosure also relates to display devices, particularly digital display devices, such as touch panels or smartwatches or smartphones, that include a cover plate according to one embodiment and / or a cover plate manufactured by a method according to one embodiment.

[0062] An exchange bath is understood to be a molten salt used in an ion exchange procedure for glass or glass articles. Within the scope of this disclosure, the terms exchange bath and ion exchange bath are used synonymously.

[0063] Typically, industrial-grade salts are used for exchange baths. This means that even if only sodium nitrate is used as the starting material for the exchange bath, certain impurities may also be present in the bath. In this case, the exchange bath is a molten salt, such as sodium nitrate, or a mixture of salts, such as a mixture of sodium and potassium salts. Here, the composition of the exchange bath is described in terms of its nominal composition, without taking into account any impurities that may be present. Therefore, within the scope of this disclosure, when 100% molten sodium nitrate is mentioned, this means that only sodium nitrate was used as the raw material. However, the actual sodium nitrate content of the exchange bath may deviate from this, and this is normal, because industrial raw materials, in particular, have certain proportions of impurities. However, this is usually less than 5% by mass, and especially less than 1% by mass, relative to the total mass of the exchange bath.

[0064] Accordingly, in the case of exchange baths having mixtures of different salts, the nominal content of these salts is stated without taking into account industrially occurring impurities in the starting materials. Therefore, an exchange bath having 90% by mass of KNO3 and 10% by mass of NaNO3 may also have small amounts of impurities, but these are due to the raw materials and should normally be less than 5% by mass, and especially less than 1% by mass, of the total mass of the exchange bath.

[0065] Furthermore, the composition of the exchange bath also changes during the ion exchange process, because continuous ion exchange causes lithium ions, in particular, to move from the glass or glass article into the exchange bath. However, such changes in the composition of the exchange bath due to aging are not taken into consideration here unless explicitly stated. Rather, within the scope of this disclosure, when the composition of the exchange bath is described, it is to match the nominal original composition. [Brief explanation of the drawing]

[0066] [Figure 1] This figure shows a cover plate 1 according to an embodiment of the present disclosure. [Figure 2]This figure shows a cover plate 1 according to an embodiment of the present disclosure. [Figure 3] This is a diagram illustrating the implementation of a set-drop test. [Figure 4] This is a diagram illustrating the implementation of a set-drop test. [Figure 5] This is a diagram illustrating the implementation of a set-drop test. [Figure 6] This is a diagram illustrating the implementation of a set-drop test. [Figure 7] This figure shows the evaluation of EDX measurement of glass ceramic cover plates. [Figure 8] This figure shows a comparison of the set drop strength of the cover plates. [Figure 9] This diagram compares exemplary reinforcement profiles of cover plates. [Examples]

[0067] The present invention will be described in more detail below using examples.

[0068] Table 1 shows the composition of the glass ceramic material according to the present invention.

[0069] The materials listed in Table 1 were melted at a temperature of approximately 1600-1680°C using standard raw materials in the glass industry, and then clarified. The melting of the mixture was first carried out in a sintered quartz glass crucible, then poured into a Pt / Rh crucible equipped with an inner quartz glass crucible, and homogenized by stirring at approximately 1550°C for 30 minutes. After standing at 1640°C for 2 hours, a mold measuring approximately 140mm × 100mm × 30mm was poured, relaxed in a cooling furnace at approximately 620-680°C, and then cooled to room temperature. From this mold, test samples were prepared for measuring the properties in the glass state and for ceramicization.

[0070] For ceramicization, a two-step program, as described in Table 1, was typically used. In this case, the starting glass was first heated from room temperature. gThe sample is heated to a nucleation temperature above a certain level and held there for a sufficient time for nucleation. Subsequently, the sample is heated to the ceramicization temperature and held there as well. Programs with three or more steps may also be used (Example 2 in Table 1). Furthermore, the holding time can be replaced by a slower heating rate. In the ceramicized sample, the crystalline phase and its content, as well as the transmittance τ in the visible range, are determined using XRD. vis The chrominance (in a sample with a thickness of 0.7 mm) and the chrominance in the Lab system (standard light source C) were determined.

[0071] The crystalline phase content listed in Table 1 was determined using X-ray diffraction measurements with a Panalytical X'Pert Pro Diffraktometer (Almelo, Netherlands). The generated CuKα rays (λ=1.5060 Å) were used as X-rays, filtered through a Ni filter. Standard X-ray diffraction measurements were performed on powder and solid samples under a Bragg-Brentano configuration (θ-2θ). X-ray diffraction patterns were measured from 10° to 100° (2θ angle). The relative proportion of the crystalline phase and the determination of microcrystal sizes were performed via Rietveld analysis. These measurements were performed on pulverized sample materials where the volume proportion of the central region was clearly dominant. Therefore, the measured phase proportions correspond to the phase distribution in the center of the glass ceramic. Samples marked with "V" correspond to comparative examples. Examples with only a number are examples of embodiments.

[0072] [Table 2-1]

[0073] [Table 2-2]

[0074] [Table 2-3]

[0075] For strengthening tests, ceramicized glass ceramic plates with a thickness of 0.7 mm were strengthened in various salt baths. Table 2 shows the changes in crystallographic data during the strengthening of glass ceramics according to the present invention.

[0076] [Table 3]

[0077] The aforementioned samples contained keytite mixed crystals as the main crystalline phase after ceramicization (96% keytite mixed crystals, 3% ZrTiO4). After strengthening (7.5 to 18 hours at a temperature of 420 to 440°C), all samples, regardless of the selected salt bath, showed a unit cell expansion of more than 1% in the near-surface layer compared to unstrengthened samples. Samples strengthened in 100% KNO3 even showed the formation of two different keytite mixed crystal structures in the near-surface layer, both of which had expanded unit cell volumes compared to unstrengthened keytite. Furthermore, all samples showed increased strength with DoCl values ​​of 102 μm (100% KNO3) to 154 μm (80% KNO3 / 20% NaNO3). The values ​​for CS30 were 195 MPa to 360 MPa.

[0078] A sample having the composition according to Example 9 was similarly prepared, ceramicized, and strengthened as described in Example 9 in Table 1. It contains nepheline ((Na,K)[AlSiO4]) as the main crystalline phase and trace amounts of rutile. From XRD measurements, the following crystallographic data were obtained for nepheline (hexagonal structure): a = 10.026 (5) Å, c = 8.372 (5) Å, unit cell volume V = 728.8 (10) Å 3 The following was obtained. After strengthening (100% KNO3, 500°C for 8 hours), calsilite (potassium-substituted end component of the nepheline mixed crystal system, KAlSiO4): a = 5.170 (5) Å, c = 8.730 (5) Å was obtained. For direct comparison, the lattice constant of the a axis must be doubled here, based on the difference in the size of the unit cells of the two structures (therefore, there are the same number of formula units in the unit cell). Thus, the unit cell volume V for calsilite is 808.3 (10) Å.3 This yields a result that corresponds to an expansion of approximately 10%.

[0079] The reinforcement conditions and, consequently, the reinforcement parameters achieved for different cover plates are shown in the table below.

[0080] [Table 4]

[0081] Here, CT represents internal tension and is expressed in MPa.

[0082] Description of the drawing Figure 1 shows a schematic, not to scale, diagram of the cover plate 1 according to an embodiment of the present disclosure. The cover plate 1 is formed in the form of a plate or sheet, in the sense that its thickness d (not shown in Figure 1) is at least an order of magnitude smaller than the length l and width b of the cover plate 1. The cover plate 1 may be flat or planar, as illustrated exemplary in Figure 1, or it may be a curved or bent plate. Generally, embodiments in which the cover plate has a small curvature only in the edge region are also conceivable. Both the length and width dimensions determine the two main faces or sides (sometimes referred to as "surfaces") of the cover plate 1.

[0083] Figure 2 shows a schematic, not-to-scale, cross-sectional view of the cover plate 1 according to an embodiment of this disclosure. The cover plate 1 has two sides 10 and 12 (these sides may also be referred to as the “surface” or “main surface” of the cover plate 1), with side 10 here being the top surface and side 12 being the bottom surface. Furthermore, the thickness d of the cover plate 1 is shown. The cover plate 1 has a layer 101 located between both sides 10 and 12, which is also referred to in the scope of this disclosure as the “near-surface layer”. The near-surface layer 101 is formed on both sides of the cover plate 1 and can be formed similarly, i.e., having the same thickness, for example, within the range of measurement accuracy. However, it is possible, and even preferable, for the thickness of the near-surface layer 101 belonging to one of the sides, for example side 10, to be different from the near-surface layer belonging to side 12. This may be the case, for example, when the chemical strengthening of the cover plate 1 is carried out in such a way that uneven replacement occurs.

[0084] A central region 102 is located between the two near-surface layers 101. Between the near-surface layers 101 and the central region 102, there may be further regions where ion exchange occurs but which do not contribute to, for example, compressive stress (though not shown in Figure 2). The central region is generally the region of minimum stress in the cover plate 1. In contrast, the near-surface layers 101 have higher stress, and in particular, they can be under compressive stress. The cover plate 1 generally contains silica-based glass ceramic, where the cover plate 1 generally has a thickness d of 0.4 mm to 0.85 mm. The light transmittance τ of the cover plate 1 is... visPreferably, the coverage is greater than 80% in the 380nm to 780nm range, and more preferably greater than 85%, specifically for a thickness of 0.4mm to 0.85mm, and more preferably for a thickness of 0.7mm. By chemical strengthening, the cover plate 1 is brought to such an extent that, in at least one or both near-surface layers 101, and particularly in layers of 20μm to 70μm perpendicular to the sides 10 and 11 of the cover plate 1, the crystalline phase contained in the glass ceramic of the cover plate 1 or contained therein has, on average after the strengthening process, a unit cell volume that is at least 1 volume%, preferably at least 2 volume%, larger than the crystalline phase in the central part 102. Advantageously, the crystalline phase contained in the glass ceramic of the cover plate 1 can be a silica-based crystalline phase. Through chemical strengthening, the cover plate 1 has a CS of at least 250 MPa and preferably up to 1500 MPa, and / or a CS30 of at least 160 MPa and preferably up to 525 MPa, and / or a DoCL of at least 0.2 times and preferably less than 0.5 times the thickness d of the cover plate 1 relative to the cover plate 1.

[0085] Figures 3-6 illustrate the implementation of a so-called set drop test to determine set drop intensity.

[0086] Here, the set-drop test is advantageously conducted as follows:

[0087] The cover plate is fixed to the sample container and dropped onto a defined surface from a cumulative drop height. An overview of the overall structure is shown in Figure 3. The cover plate used in the set drop test in Figure 5 has a length of 99 mm and a width of 59 mm and is magnetically fixed to the sample dummy in the sample container, as shown in Figure 4. However, for the experiments described in this disclosure, a cover plate format of 49.5 mm × 49.5 mm is used, unlike the sample illustration in Figure 4, and the principle configuration of the test implementation in Figures 3-6 is not affected by this.

[0088] First, a plastic plate is attached to a metal housing having the shape and weight of a holder for a mobile device, such as a smartphone, using double-sided adhesive tape. In this case, a plastic plate having a thickness of, for example, 4.35 mm to 4.6 mm is suitable (see Figure 5). The attachment is preferably done using double-sided adhesive tape having a thickness of approximately 100 μm. Next, a double-sided adhesive tape, preferably a double-sided adhesive tape having a thickness of 295 μm, in particular the double-sided adhesive tape of trademark tesa®, product number 05338, is attached to the plastic plate, such that a gap of 350 μm to 450 μm is maintained between the upper end of the housing or holder and the upper end of the glass article. The cover plate is higher than the frame of the housing, and there should be no direct contact between the cover plate and the aluminum housing. The "set," which mimics the attachment of a cover plate to a mobile device and is a kind of "dummy" of a real mobile device, in this case a smartphone, weighing 177.5g, is then dropped vertically from zero downwards with a certain initial velocity, glass-side down, onto a surface the size of DIN A4, the so-called impact surface. The impact surface is manufactured as follows: Sandpaper with an appropriate grit size, for example, grit 60 (#60), is attached to the base plate using double-sided adhesive tape, for example, adhesive tape with a thickness of 100 μm. Transparent double-sided Tesa (10m / 15mm), product number 05338, was used as the adhesive tape. Within the scope of this disclosure, particle size is defined in accordance with the standards of the Federation of European Producers of Abrasives (FEPA), for example see DIN ISO 6344, particularly DIN ISO 6344-2:2000-04, and Abrasives on substrates - Particle size analysis - Part 2: Specification of the particle size distribution of macroparticles pp. 12-220 (ISO 6344-2: 1998). In the case of the values ​​disclosed herein, the weight of the aluminum substrate base plate reaches approximately 3 kg.

[0089] The base plate must be rigid and preferably made of aluminum, or alternatively, steel. The sandpaper must be completely attached with adhesive tape and glued without air bubbles. The impact surface may be used only for five drop tests and should be replaced after five drop tests. The sample, i.e., the resulting set, is placed in the test apparatus and adjusted using a 2D level (circular bubble tube) so that the set is horizontal, with the cover plate facing the floor, i.e., towards the impact surface (see Figure 6). The first drop height is 25 cm, followed by drops from a height of 30 cm. If no fracture occurs, the drop height is increased by 10 cm increments until the glass fractures. The fracture height, the point of fracture, and the appearance of the fracture are recorded. The test is performed on 10 to 15 samples and the average value is taken.

[0090] Figure 7 shows the evaluation of EDX measurements on two different samples of glass-ceramic coverplates. Here, the glass-ceramic material of the coverplates had the same composition but was subjected to different strengthening protocols.

[0091] In the figure above, silica-based glass ceramic was chemically strengthened for 18 hours at 440°C in an exchange bath with a composition of 80% by mass KNO3 and 20% by mass NaNO3. According to EDX evaluation, the sodium oxide content at the sample surface is approximately 8 mol%. In the central or "bulk" region 102, a Na2O content of approximately 1 mol% can be assumed. This is also shown in Figure 7 (above). The above strengthening of the glass ceramic content in the cover plate can significantly increase the Na2O content, at least in the near-surface region 101, and can be increased to as much as 7 mol% in absolute terms in some cases, or advantageously to an average of 6 mol% in absolute terms over the thickness of the near-surface region 101 from Figure 2.

[0092] As already mentioned above, such an increase in potassium oxide content is more difficult for larger potassium ions. Here, depending on the exact configuration of the glass ceramic and / or strengthening protocol, an exchange depth of approximately 30 μm at the highest point is achieved, and the inventors believe that even greater exchange depths should be possible for optimal processes and materials. Although potassium exchange is more difficult to perform, it is also more efficient, so CS0 values ​​of, for example, 1200 MPa or 1100 MPa are considered possible, up to, for example, 1500 MPa. In the case of other strengthening protocols illustrated in the lower region of Figure 7, work was performed at very high potassium concentrations in the exchange bath. Here, the composition of the exchange bath was 99.5 mass% KNO3 and only 0.5 mass% NaNO3. The temperature of the exchange bath was 420°C, and the strengthening time was 7.5 hours. Here, as can be seen from the drawing in the lower part of Figure 7, despite the very small amount of NaNO3 content in the exchange bath, an increase in Na2O content occurs in the near-surface region 101 of the cover plate, particularly an increase to at least 5 mol% at the highest point. However, the K2O content also clearly increases, reaching a maximum of approximately 3 mol%. In contrast, in the central region 102, there are clearly lower concentrations of K2O and Na2O because they were not exchanged to the same extent.

[0093] A transitional region exists between region 101 and the central region 102, where exchange occurs, and it is suggested that at least a partial expansion of the unit cell volume also occurs. This "intermediate region" is a region where ion exchange occurs, but an increase in compressive stress is not necessarily required.

[0094] Finally, Figure 8 shows a comparison of the set-drop strengths of different cover plates having the same chemical composition but different crystalline phase content or different ceramicization. In the stress curve, 102 indicates the central region of the cover plate where the stress is minimum. Here, 2 shows the drop height results obtained for chemically strengthened green glass. 3 shows the results for glass ceramics containing a crystalline phase, in this case high-temperature quartz mixed crystal, which cannot be strengthened into the crystalline phase. The strength achieved in the set-drop test is completely insufficient. Finally, 4 shows the results for a cover plate according to one embodiment, here containing keytite as the crystalline phase. The results of the set-drop test are also summarized in the table below. The drop heights are given in cm.

[0095] [Table 5]

[0096] In Figure 9, exemplary reinforcement profiles of cover plates are compared with each other; that is, the reinforcement profile of a cover plate according to one embodiment is compared with the reinforcement profile of a cover plate containing the same chemical composition but not ceramicized. Here, reinforcement profile 5 corresponds to the cover plate according to one embodiment, and reinforcement profile 6 corresponds to a cover plate containing the same chemical composition but formed in a glassy state and not ceramicized. 102 indicates the central region where the stress is minimum. [Explanation of Symbols]

[0097] 1 Cover plate 10, 12 Side of the cover plate 101 Surface-neighboring layer of the cover plate 102 Center d. Thickness of the cover plate l Length of the cover plate b Width of the cover plate 2, 3, 4 Results of set-drop tests on different sample populations Enhanced profile according to 5 embodiments 6. Enhanced Profile of Comparative Example

Claims

1. A cover plate having a thickness of 0.4 mm to 0.85 mm, which comprises a silica-based glass ceramic, and which has a light transmittance τ of more than 80%, preferably more than 85%, in the range from 380 nm to 780 nm, preferably specified for a thickness of 0.4 mm to 0.85 mm, particularly preferably for a thickness of 0.7 mm. vis and has been chemically strengthened, and has a CS of at least 250 MPa and preferably at most 1500 MPa, and / or a CS30 of at least 160 MPa and preferably at most 525 MPa, and / or a DoCL for the cover plate of at least 0.2 times the thickness of the cover plate and preferably less than 0.5 times the thickness of the cover plate, wherein the silica-based glass ceramic comprises at least one silica-based crystalline phase, which in at least one near-surface layer, in particular in a layer of 20 μm to 70 μm perpendicularly from one of the side surfaces of the cover plate, preferably has a unit cell volume that is at least 1 vol. %, preferably at least 2 vol. %, greater on average after the strengthening process than the unit cell volume of the crystalline phase in the center, in particular in the region of stress minimum in the silica-based glass ceramic.

2. The crystalline phase contains a higher proportion of sodium oxide Na in at least the near-surface layer than in the center, especially in the region of the silica-based glass ceramic where the stress is at a minimum. 2 O and / or potassium oxide K 2 The cover plate of claim 1 including O.

3. 2. The cover plate according to claim 1, wherein the glass ceramic of the cover plate comprises more than 50% by volume of crystalline phase, advantageously more than 70% by volume of crystalline phase, and preferably up to 95% by volume of crystalline phase.

4. Chroma C less than 4, preferably less than 3 * The cover plate of claim 1 .

5. 10. The cover plate of claim 1, characterized by a haze of 0.01% to 1% for a cover plate thickness of 0.7 mm.

6. 2. The cover plate of claim 1, wherein the glass ceramic is formed as a lithium aluminum silicate glass ceramic and the crystalline phase is formed as a keatite mixed crystal.

7. The glass-ceramic may comprise: SiO 2 55 to 75, preferably 62 to 72 Al 2 O 3 18 to 27, preferably 18 to 23 Li 2 O 2.8 to 5, preferably 3 to 5 The cover plate of claim 1 , comprising, in mass % on an oxide basis:

8. The glass ceramic comprises the following components: SiO 2 55 to 75, preferably 62 to 72 <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> 18222 Li 2 O 2.8 to 5, preferably 3 to 5 Na 2 O 0 to 4, preferably 0 to 2 K 2 O 0 to 4, preferably 0 to 2 MgO 0 to 8, preferably 0 to 4 CaO 0-4, preferably 0-2 SrO 0-4, preferably 0-2 BaO 0-4, preferably 0-2 ZnO 0 to 6, preferably 0 to 2 TiO 2 0 to 4, preferably 0 to 3 ZrO 2 0 to 5, preferably 1.2 to 4 B 2 O 3 0 to 2, preferably 0 to 0.1 Fe 2 O 3 0.0001 to 0.1, preferably 0.0001 to 0.02 SnO 2 0 to 2, preferably 0.05 to 1.6 in wt. % on an oxide basis, where advantageously TiO 2 and ZrO 2 Regarding the sum of the components, 0 < Σ(TiO 2 + ZrO 2 ) < 9.5%, preferably 1.2 < Σ(TiO 2 + ZrO 2 ) <9.5% 2. The cover plate of claim 1, wherein:

9. Component SnO 2 , ZrO 2 and TiO 2 Regarding 0≦SnO 2 / (ZrO 2 + TiO 2 ) <0.8, preferably 0.01≦SnO 2 / (ZrO 2 + TiO 2 ) <0.7 2. The cover plate according to claim 1, wherein:

10. 2. The cover plate of claim 1, characterized in that it has a sharp impact strength determined in a set drop test up to a drop height of at least 120 cm to 200 cm.

11. 11. A method for manufacturing a cover plate according to any one of claims 1 to 10, comprising the following steps: - producing silica green glass by a melting process and subsequent hot forming; a heat treatment step of said silica green glass, wherein at least one nucleation step is carried out at a temperature in the range of 690°C to 850°C for a time period of from 5 minutes to 8 hours, preferably from 30 minutes to 2 hours, and at least one ceramming step is carried out at a temperature in the range of 780°C to 1100°C for a time period of from 3 minutes to 60 hours, preferably from 3 minutes to 8 hours; 100% by mass to 0% by mass of KNO 3 and 0% by weight to 100% by weight of NaNO 3 and 0% to 5% by weight of LiNO 3 carrying out at least one ion exchange in an exchange bath having a composition of the formula: The method comprising:

12. A cover plate produced or producible by the method of claim 11.

13. Use of a cover plate according to any one of claims 1 to 10 in an electronic device, in particular in an electronic display device, in particular in a mobile electronic display device, such as a mobile touch panel and / or a mobile digital display device, such as a smartphone or a smartwatch.

14. A display device, in particular a digital display device, comprising at least one cover plate according to any one of claims 1 to 10.

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