Crystallizable lithium aluminosilicate glass, class ceramic produced thereby, production method for glass ceramic and use of glass ceramic

Abstract

To provide the LAS glass ceramic which has an improved whiteness L* (also calling it brightness in refractive index different from brightness Y measured in permeability) and a low average linear expansion coefficient and does not include As2O3 and Sb2O3, and to provide an economical production method for the above glass ceramic.SOLUTION: Disclosed is a lithium aluminosilicate glass ceramic which does not include As2O3 and Sb2O3 except inevitable impurities. This glass ceramic includes keatite as a main crystal phase and has a keatite peak temperature TP of keatite solid solution formation in a range of 980°C to 1,090°C. The keatite peak temperature TP is obtained using the heating rate of 5K / min by a differential scan calorimetry (DSC) based on DIN51007:2019-04. Besides, a ceramic formation method is also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium aluminosilicate glass ceramic (LAS glass ceramic) according to the preamble of claim 1.

[0002] The invention also relates to a ceramming process for producing said glass-ceramics and to the use of said LAS glass-ceramics.

[0003] LAS glass ceramics are widely used due to their special material properties, such as a low coefficient of thermal expansion and the resulting high temperature difference and thermal shock resistance, high strength, chemical resistance and transparency. In principle, the thermal expansion behavior is determined by the material's temperature range, which is usually

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[0004] Common applications for LAS glass-ceramics are fire glazing, cooking utensils, transparent fireplace windows, oven windows, and cooktops. When used as cooktops, the transparent glass-ceramic plates are either colored with colored oxides or coated with an opaque, usually chromatic, underside coating to prevent technical equipment from showing through and to provide a colored impression. The uncoated areas within the underside coating allow for the installation of colored and white display devices, often light-emitting diodes or screens.

[0005] Transmission and scattering are important properties for the appearance and optical properties of glass-ceramics.

[0006] High transparency means high lightness and low saturation, both of which imply low absorption, since absorption bands decrease lightness and increase saturation depending on the position of the spectrum visible to the human eye. In the literature, lightness is also referred to as light transmittance or integrated transmittance.

[0007] Scattering is determined by the size of the crystals, their birefringence, and the difference in refractive index between the crystals and the rest of the glass. In principle, low scattering is desirable so that what is seen through them is not distorted and the display is clearly visible.

[0008] Lightness and light transmittance are measured as the lightness value Y (brightness) in the CIE standard color system, or the whiteness L in the CIELAB color system. * The definition of the color system used is specified in DIN 5033, the German version of the international CIE standard. The evaluation of measurement data using the CIELAB color model is based on DIN EN ISO 11664-4 "Colorimetry -- Part 4: CIE 1976 L * a * b * Measurements of transmittance and reflectance are described in "Color space".

[0009] The spectrophotometric measurements required for this purpose are carried out on polished samples in the spectral range of 380 to 780 nm in the present invention. From the measured spectral values ​​in the range showing the visible light spectrum, the lightness Y and whiteness L are calculated by selecting a standard light source and an observer angle at that thickness. * , and color coordinate a * and b * The lightness Y is determined from the spectral values ​​of a transmittance measurement carried out in accordance with DIN ISO 15368. In addition, the transmittance at a given wavelength is measured.

[0010] In the case of glass ceramics, the L is used as an indicator of the color impression for translucent and opaque variants. * , a * , b * It is customary to define the parameters L. These values ​​are determined from the spectral values ​​of reflectance measurements carried out in accordance with DIN ISO 15368. * represents the brightness (whiteness), and the coordinate a * and b * respectively represent the color shift, where +a * =shift to red -a * = Shift to green +b * = shift to yellow -b * = blue shift Shows.

[0011] a * and b * From the value called saturation, c * But, the formula

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[0012] Large-scale production of glass-ceramics involves several steps. First, a crystallizable starting glass is melted from a mixture of cullet and powdered batch raw materials and then subjected to a fining process. Here, the glass melt reaches temperatures ranging from 1550°C to a maximum of 1750°C, typically 1700°C. In some cases, high-temperature fining is also performed at temperatures above 1750°C, typically around 1900°C. For uncolored glass-ceramics, arsenic oxide and antimony oxide are fining agents that have proven industrially and economically effective in terms of good bubble quality at conventional fining temperatures below 1700°C. Arsenic oxide is particularly advantageous for the transparency (high brightness, low saturation) of glass-ceramics. Even when these fining agents are tightly incorporated into the glass framework, they present safety and environmental disadvantages. Therefore, special care must be taken during raw material collection, raw material refining, and glass production to avoid evaporation from the melt. As a result, many efforts are being made to replace these materials, but these efforts face technical and economic drawbacks.

[0013] After melting and fining, the glass is usually hot-formed by casting, pressing, rolling, or the float process. For many applications, glass-ceramics are required in flat forms, such as sheet glass. Sheets are produced using rolling and float processes. To produce these LAS glasses economically, they require low melting temperatures and low hot-forming processing temperatures V A Furthermore, the glass should not exhibit devitrification during forming, i.e., it should not form crystals larger than about 5 μm, which would reduce the strength or cause visual defects in the glass-ceramic article. Forming is performed at a processing temperature V A (viscosity 10 4Since the melt temperature is near the melting point (dPa·s), it is necessary to ensure that the upper devitrification temperature of the melt is close to, and preferably below, the processing temperature to avoid the formation of large crystals. In roll forming, the critical area is the contact between the glass melt and the draw nozzle, made of a precious metal (usually a Pt / Rh alloy), before the glass is rolled and cooled. In float forming, the critical areas are the contact between the glass and the spout lip and the front region of the float bath where the glass comes into contact with liquid tin, where the crystal growth rate is high.

[0014] Crystallizable LAS glasses are transformed into glass-ceramics through controlled crystallization (ceramization) during subsequent temperature processing. This ceramization is a multi-step temperature process, beginning with nucleation at temperatures between 680°C and 800°C, typically from a ZrO2 / TiO2 solid solution. SnO2 also participates in the nucleation. Further temperature increase leads to the formation of a high-purity quartz solid solution (HQ solid solution), which transforms to a keatite solid solution with continued temperature increase in the 900°C to 1250°C range. The temperature and time conditions for this transformation depend on the composition and, to a lesser extent, on the temperature pretreatment. The transformation to a keatite solid solution results in larger crystals, resulting in increased light scattering. The transformation also increases the mean linear expansion coefficient of the glass-ceramic.

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[0015] Longer residence times at high temperatures for keatite formation increase the opacity of the material. The structure of the glass-ceramic is then altered, resulting in changes in optical, physical, and chemical properties. Shorter ceramming times are advantageous for economical production.

[0016] The environmentally friendly fining agent SnO2 alone or in combination with one or more fining additives such as halides (F, Cl, Br), CeO2, MnO2, Fe2O3 and / or sulfur compounds is becoming increasingly popular as an alternative to arsenic oxide and antimony oxide.

[0017] However, the use of SnO2 does not come without drawbacks. SnO2 itself is industrially ineffective as a fining agent and requires high temperatures to release the fining active oxygen. High concentrations of SnO2, on the order of about 1 wt. % of the As2O3 used, are disadvantageous because they devitrify the Sn-containing crystals during hot forming. The second major drawback of replacing arsenic oxide with tin oxide as a fining agent for non-colored glass-ceramics is that SnO2 introduces additional absorption, reducing the color value b * This absorption is mainly due to the colored complex with the nucleating agent TiO2. 2+ The Sn / Ti coloring complexes are more strongly colored than known Fe / Ti coloring complexes, a drawback that has previously made it difficult to replace the arsenic oxide fining agent with tin oxide in non-colored glass-ceramics.

[0018] The formation of the aforementioned charge-transfer coloring complexes occurs primarily during crystallization. To reduce the concentration of the coloring complexes, it is advantageous to shorten the nucleation and crystallization times. This is because shortening the nucleation time increases light scattering, while shortening the crystallization time leads to unevenness in the article.

[0019] The molten raw material of industrial batches contains further coloring elements as impurities, such as Cr, Mn, Ni, V, and especially Fe. Besides the Fe / Ti coloring complexes, Fe 2+ and Fe 3+ However, due to the high cost of low-iron raw materials, it is not economical to reduce the Fe2O3 content below about 50 ppm.

[0020] Approaches to avoid (WO 2008 / 065167) or limit (WO 2008 / 065166) the nucleating agent TiO2, which contributes to color complexes in transparent, uncolored glass-ceramics containing high-purity quartz solid solution, also referred to in the literature as "β-quartz" or "β-eucryptite," as the predominant crystalline phase, have not yet reached technical realization. Alternative nucleating agents, ZrO2 and / or SnO2, require higher contents, which result in disadvantages during melting and forming, such as higher melting and forming temperatures, as well as insufficient devitrification resistance during forming.

[0021] Even in translucent to opaque, non-colored glass-ceramics containing keatite solid solution, also referred to in the literature as "β-spodumene," as the predominant crystalline phase, high TiO2 contents adversely affect the optical properties of the glass-ceramics.

[0022] For example, WO 2019 / 016338 describes white, milky white or opaque tin-fined LAS-type glass-ceramics containing β-spodumene as the main crystalline phase, in which the TiO content is limited to 1.75 wt. %, and the document states that a low TiO content contributes to the whiteness L * However, the TiO2 content must not fall below the lower limit of 1.3% by weight, because in this case the crystals become too large, impairing the strength and even the homogeneous appearance of the glass-ceramic. The ceramming cycle described in the document provides the following steps: a rapid temperature rise from 20°C to 670°C at a heating rate of 25°C / min; a temperature rise from 670°C to the nucleation temperature T n Heat up to T n Residence time at T at a heating rate of 7 °C / min n to the crystal growth temperature T c Heat up to T cand rapid cooling to 20°C at a cooling rate of 25°C / min. Furthermore, these known glass-ceramics typically have a high SnO2 content, which requires high temperatures to produce opaque glass-ceramics with high whiteness, thereby increasing production costs. A further drawback is that the known methods c The problem is that the heating rate to reach the temperature is so high that flat plates cannot be produced.

[0023] WO 2019 / 117122 describes an LAS-based glass ceramic containing a β-spodumene solid solution as the main crystalline phase. The glass ceramic disclosed in this document has a drawback in that it has a mean linear expansion coefficient of 1.5 μm.

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[0024] Therefore, in the development of glass ceramics, for example, the product quality of the glass ceramic, in particular the saturation, lightness Y, and mean coefficient of linear expansion at short ceramming times, are important.

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[0025] The object of the present invention is to improve the whiteness L * (It is also called brightness measured by reflectance, as opposed to brightness Y, which is measured by transmittance) and a low average coefficient of linear expansion

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[0026] This problem is solved by a lithium aluminosilicate glass ceramic having the features of patent claim 1.

[0027] LAS glass ceramics are produced from starting or green glasses by a ceramicization process, in which the transformation of the green glass into the keatite phase occurs at temperatures up to 1250°C.

[0028] The formation of the keatite phase was confirmed by differential scanning calorimetry (DSC, specifically hf-DSC) according to DIN 51007:2019-04 at 5 K min -1 Here, the peak temperature of keatite solid solution formation (keatite peak temperature T P (also called) indicates the temperature at which the maximum heat of transformation is recorded.

[0029] Keatite peak temperature T P Glass-ceramics with a temperature in the range of 980°C to 1090°C have good color neutrality, especially a large whiteness L * and low average linear expansion coefficient

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[0030] Required keatite peak temperature T P Within this range, the desired properties of the glass-ceramic can be easily optimized.

[0031] Required keatite peak temperature T P This range allows a wide range of glass ceramics to be produced, from opaque to translucent, with the translucent glass ceramics being able to be differentiated between visible and non-visible.

[0032] Preferably, the keatite peak temperature T Pis in the range of 980°C to 1070°C, particularly in the range of 990°C to 1055°C. Glass-ceramics with keatite peak temperatures in this temperature range can be economically converted from green glasses to glass-ceramics by a suitable ceramming method with moderate ceramming temperatures and times.

[0033] The LAS glass ceramic preferably contains the following components in the following proportions (in weight % on an oxide basis): Li2O 3~5 Al2O318~25 SiO260~70 SnO20 to 0.5, preferably 0.01 to 0.5, more preferably 0.05 to <0.3 Includes.

[0034] Li 2 O, Al 2 O 3 and SiO 2 The oxides Li2O, Al2O3 and SiO2 are essential components of the keatite solid solution phase. They should be present within the following limits:

[0035] In crystallizable glasses and glass-ceramics made therefrom, the LiO content is 3-5 wt. %. The minimum content is useful for achieving the desired low processing temperature of the glass. Preferably, the LiO content is 4.5 wt. % or less, more preferably 4.4 wt. % or less, and particularly preferably 4.3 wt. % or less. The minimum content is preferably 3.2 wt. % and particularly preferably 3.4 wt. %.

[0036] Furthermore, the proportion of Li2O increases with the keatite peak temperature T P It was found that the higher the Li2O content, the higher the keatite peak temperature T P will be lower.

[0037] Preferably, the glass ceramic contains 3.9 to 4.5 wt.% LiO, preferably up to 4.2 wt.% LiO. The keatite peak temperature TP The temperature is preferably in the range of 990°C to 1025°C.

[0038] Preferably, the glass ceramic contains 3.5 to <3.9 wt.% LiO. The keatite peak temperature T P The temperature is preferably in the range of 1015°C to 1060°C.

[0039] A low LiO content has the advantage that it reduces the resources and raw material costs required to produce such glass-ceramics and makes the green glass manufacturing process more robust due to a lower tendency to devitrification, thus enabling higher yields.

[0040] A high Li2O content has the advantage that lower temperatures can be used during the production of the green glass as well as during the ceramming of the green glass to a glass-ceramic.

[0041] The Al2O3 content is preferably 18 to 25% by weight. A content higher than 25% by weight is disadvantageous because it tends to devitrify mullite during molding.

[0042] The content of the main component SiO2 is preferably at least 60% by weight, since this is advantageous for the properties required of glass-ceramics, such as low thermal expansion and chemical resistance. A minimum content of 64% by weight is particularly advantageous. Preferably, the SiO2 content is at most 70% by weight, since this component increases the processing and melting temperatures of the glass. Preferably, the SiO2 content is at most 68% by weight.

[0043] SnO 2 Preferably, the glass ceramic contains 0-0.5 wt. % SnO2.

[0044] In certain embodiments, SnO2 may not be used at all. If the glass is subjected to high-temperature fining, the glass-ceramic preferably contains 0 wt. % SnO2. During high-temperature fining, the temperature of the glass melt is preferably 1750°C or higher, preferably 1850°C or higher.

[0045] According to a further embodiment, the glass ceramic comprises SnO2. Thus, the glass ceramic comprises more than 0 wt. % SnO2, preferably at least 0.01 wt. % SnO2, even more preferably at least 0.05 wt. % SnO2 and / or a maximum of 0.5 wt. % SnO2, preferably not more than 0.3 wt. % SnO2.

[0046] Even at low concentrations, SnO acts as a fining agent, ensuring the required bubble quality in conjunction with industrial melting tank procedures. It is an environmentally friendly alternative to the heavy metals AsO and SbO. Furthermore, SnO also functions as a nucleating agent, significantly aiding in the control of the transformation process. Preferably, the glass and glass-ceramics produced therefrom contain at least 0.03 wt. % SnO, particularly preferably at least 0.04 wt. %.

[0047] Preferably, the glass ceramic has a color space L determined from the spectral values ​​of the reflectance measurement. * , a * , b * Whiteness L * is 60 to 97, and the lightness Y obtained from the spectrum value of the transmittance measurement is 0.1% to 25%, where L * and Y were determined using standard illuminant D65 at a glass ceramic thickness of 4 mm and an angle of 2°.

[0048] A basic distinction can be made between the following types of materials: Variation A A relates to opaque LAS glass-ceramics with high whiteness and low lightness Y.

[0049] Preferably, the glass ceramic is opaque and has a keatite peak temperature T in the range of 980 ° C to 1070 ° C, in particular in the range of 990 ° C to 1055 ° C. P and the following values: L * =85 to 97, preferably 90 to 97, particularly preferably 90 to 96 a * =-1.5 to 0.5, preferably -1.2 to 0.5 b * = -6 to 0.5, preferably -4.5 to 0 and Y=0.1% to 2%, preferably 0.2% to 2% It has.

[0050] Variation B B relates to a translucent LAS glass-ceramic with low whiteness and high lightness Y.

[0051] It does not have the crisp outline of a 7-segment display, but it can show residual heat and other signals.

[0052] Preferably, the glass ceramic is translucent and has a keatite peak temperature T in the range of 980°C to 1070°C, in particular in the range of 990°C to 1055°C. P and the following values: L * =72 to 93, preferably 80 to 93 a * =-5.5 to 0, preferably -5 to 0 b * = -7 to 0.5, preferably -6.5 to 0, particularly preferably -6 to 0 and Y=>2%~10% It has.

[0053] Variation C Variant C relates to an LAS glass ceramic with a low whiteness and a high lightness Y, so that the outline of the red display is clearly visible.

[0054] Preferably, the glass ceramic is translucent and has a keatite peak temperature T in the range of 980°C to 1070°C, in particular in the range of 990°C to 1055°C. P and the following values: L * = 60 to 82, preferably 65 to 82, particularly preferably 68 to 81 a * =-7.5 to -2, preferably -6.5 to -2, particularly preferably -5.5 to -2 b * =-19 to -4.5, preferably -14 to -4.5, particularly preferably -13.5 to -4.5 and Y => 10% to 25%, preferably > 10% to 20% It has.

[0055] While variations A and B provide no or insufficient display capabilities, variation C is noteworthy.

[0056] The display capability is preferably evaluated by visually inspecting a glass ceramic plate having a thickness of about 4 mm placed on a 7-LED segment display.

[0057] Additionally, transmittance measurements in accordance with ISO 15368 can be preferably used to evaluate the display ability.

[0058] In the PvK (Probe vor der Kugel, sample in front of the sphere) measurement variant, the sample is placed in front of an integrating sphere, which is equipped with a detector. This detector detects light scattered from the sample at an angle of up to 10° in the forward direction. In the PiP (Probe im Probenraum, sample in the sample chamber) measurement variant, the sample is placed in front of the integrating sphere at a distance of 43 cm. Here, light scattered from the sample is not detected by the detector.

[0059] For evaluation of the display performance of red display, it is preferable to use the ratio (PvK-PiP) / PiP for light with a wavelength of 630 nm.

[0060] For the group of materials "semi-transparent" with a Y value above 2%, the following classification of display capabilities is possible: "Unviewable" indicates that the display is not visible regardless of the observer's viewing angle. The image of a 7-LED segment display is blurred. An indication of when this perception occurs is given by the ratio (PvK-PiP) / PiP, which is a value greater than 20.

[0061] "Slightly viewable" means that the clearest image of the 7 LED segment display is seen when the viewer's line of sight is at a 90° angle, i.e., perpendicular, to the display. When the angle between the viewer's line of sight and the display deviates from 90°, the display appears blurry but is still viewable. The ratio (PvK-PiP) / PiP, which is an indicator of this perception, is a maximum of 20, and preferably, this ratio is at least 4.

[0062] "Good visibility" means that the display is clearly visible from any viewing angle, and the contours are sharp, but the red part of the 7-LED segment display appears less vivid. The ratio (PvK-PiP) / PiP, which is an index of this perception, is a maximum of 5.5, and preferably at least 2.

[0063] "Very good display" means that the display is very visible from any angle, the contours are clear, and the red part of the 7-LED segment display looks more vivid, further improving readability. The ratio (PvK-PiP) / PiP, which is an index of this perception, is a maximum of 3, and preferably this ratio is 0.

[0064] Preferably, the glass ceramic has a ratio (PvK-PiP) / PiP for light with a wavelength of 630 nm of ≦20.

[0065] The display capacity data in Tables 3 and 4 are based on the classifications mentioned above. The numerical values ​​of the parameters PvK and PiP and ratios are rounded in the tables.

[0066] Keatite peak temperature T P All three embodiments of the glass-ceramic could be optimized because the temperature is in the range of 980°C to 1090°C. * Not only is it high, but the color value a * and b * The advantage is that the amount of is low, which has a positive effect on color neutrality.

[0067] The white appearance (translucent to opaque) is produced by controlling the manipulation of crystallization. In specialized applications, it is also desirable to control scattering, for example, to produce a translucent white appearance.

[0068] Preferably, the glass ceramic has a density of 0 to 2.0 × 10 -6 / K, preferably 0.5 × 10 -6 / K or more, and particularly preferably 0.6 × 10 -6 / K or higher mean linear expansion coefficient

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[0069] It has been found that this property can also be improved.This embodiment has the advantage that it can be subjected to significantly higher thermal cycling loads than is the case with prior art glass ceramics.

[0070] MgO Preferably, the glass ceramic contains 0.01 to <1 wt. % MgO.

[0071] The MgO content should be less than or equal to 1% by weight, preferably at most 0.5% by weight, particularly preferably at most 0.4% by weight, and very particularly preferably at most 0.35% by weight. The preferred MgO value range of 0.1% to 0.4% by weight allows a particularly good combination of the requirements for low coloration of the glass ceramic and low processing temperatures.

[0072] According to a further embodiment, the glass ceramic does not contain MgO, except for impurities. This MgO-free embodiment has an equivalent whiteness L with a deviation of, for example, ±1. * For example, color value c of -3.5 to -5.5 * The advantage is that an improvement in

[0073] ZnO Preferably, the glass ceramic contains 0.5 to 3 wt. % ZnO.

[0074] The ZnO component is advantageous for lowering the melting and processing temperatures of the glass. This component, like the component Li2O, reduces the thermal expansion of the glass ceramic. The ZnO content is preferably limited to a maximum value of 3% by weight due to its tendency to evaporate from the glass melt. Preferably, the ZnO content is a maximum of 2.7% by weight, particularly preferably a maximum of 2.5% by weight. Preferably, the minimum content is 0.5% by weight, particularly preferably 1% by weight or more. Particularly preferably, the ZnO content is 0.5% to <3% by weight.

[0075] Preferably, the ratio of Al2O3 to Li2O+MgO+ZnO (all oxides expressed in % by weight) is: 3≦Al2O3 / (Li2O+MgO+ZnO)<3.2 (condition B1a) where the glass-ceramic has a keatite peak temperature T in the range of 990°C to 1005°C. P It has.

[0076] Preferably, the ratio of Al2O3 to Li2O+MgO+ZnO (all oxides expressed in % by weight) is: 3.2≦Al2O3 / (Li2O+MgO+ZnO)<3.8 (condition B1b) where the glass-ceramic has a keatite peak temperature T in the range >1005°C to 1060°C. P It has.

[0077] Satisfying condition B1a has the advantage that the transformation into a glass-ceramic having keatite as the main crystalline phase can be carried out at an economical and energy-efficient temperature and / or time.

[0078] Satisfying condition B1b has the advantage that the temperature range and / or ceramming time can be selected more widely to set the desired optical properties, allowing for better control of the target properties of the glass-ceramic.

[0079] Conditions B1a and B1b preferably also hold true for MgO-free glass-ceramic compositions.

[0080] Alkaline Na 2 O and K 2 O Preferably, the glass ceramic comprises (in wt % on an oxide basis): Na2O 0-1, and K2O 0~1 , except that condition B2a 0.1≦Na2O+K2O≦1.5 holds true.

[0081] Preferably, the glass ceramic comprises (in wt % on an oxide basis): Na2O 0-1, and K2O >0~1 , except for condition B2b 0.05≦Na2O / K2O≦1.2 holds true.

[0082] Preferably, the condition B2b falls within the range of 0.05 to 0.7, particularly 0.1 to 0.65.

[0083] The alkalis Na2O and K2O lower the melting and processing temperatures during glass forming. They also facilitate the melting of poorly soluble raw materials such as ZrO2 and SiO2. The content of both alkalis Na2O and K2O must be limited to a maximum of 1 wt.% because these components remain in the residual glass phase of the glass-ceramic rather than being incorporated into the crystalline phase. Too high a content impairs the crystallization behavior during the transformation of the crystallizable starting glass into the glass-ceramic and adversely affects the time / temperature stability of the glass-ceramic.

[0084] Preferably, the NaO content is 0% or >0% by weight, particularly preferably the glass ceramic comprises at least 0.05% by weight of NaO, even more particularly preferably at least 0.07% by weight of NaO, very particularly preferably 0.1% by weight of NaO. The maximum proportion is preferably 1% by weight.

[0085] Preferably, the K2O content is 0% or >0% by weight, particularly preferably the glass ceramic contains at least 0.1% by weight of K2O. The maximum proportion is preferably 1% by weight.

[0086] The total amount of alkalis Na2O+K2O is more preferably at most 1.2% by weight. In order to further improve the melting properties and reduce the processing temperature, the total amount of alkalis Na2O+K2O is particularly preferably at least 0.2% by weight. It is particularly preferred that 0.4% by weight≦Na2O+K2O≦1.2% by weight.

[0087] Fe 2 O 3 Preferably, the glass ceramic contains a maximum of 0.06 wt. % Fe2O3.

[0088] Due to the high cost of low-iron batch raw materials, it is uneconomical to limit the Fe2O3 content of crystallizable glasses to 0.008 wt. % or less, i.e., 80 ppm or less. On the other hand, the concentration of Fe / Ti coloring complexes in the glass ceramic increases with Fe2O3 content, and whiteness decreases. Therefore, crystallizable glasses and glass ceramics produced therefrom preferably contain a maximum of 0.06 wt. % Fe2O3, particularly preferably a maximum of 0.025 wt. %. It is an advantage of the glass ceramics and / or ceramicization methods described herein that this relatively high iron content does not yet adversely affect whiteness. At contents above 600 ppm, the lightness in reflectance, i.e., whiteness L, decreases. * as well as an undesired color shift, i.e., a * value and b * A deviation in value from the neutral point and possibly a decrease in lightness Y may also occur.

[0089] Nd 2 O 3 Preferably, the glass-ceramic contains up to 0.065 wt. % Nd2O3. Higher values ​​result in a higher color value b * This leads to a decrease in the color of the glass-ceramic, which is normally low in color. * This can lead to an undesirable increase in values.

[0090] P 2 O 5 Preferably, the glass ceramic comprises 0 to 2% by weight of P2O5, preferably 0 to 1% by weight, particularly preferably 0 to 0.5% by weight and very particularly preferably 0 to 0.1% by weight of P2O5.

[0091] In order to improve meltability and devitrification resistance during molding, up to 2% by weight, preferably up to 1% by weight, of P2O5 may be contained. Higher contents are detrimental to chemical resistance.

[0092] When a percentage of a component is listed as 0% by weight, it means that the component is not present in the raw batch, although these components may be present as unavoidable impurities.

[0093] Bi 2 O 3 According to a further embodiment, the glass ceramic is free of Bi2O3, except for impurities.

[0094] Bi2O3 is a coloring substance that gives the glass-ceramic a dark brown to black color. Whiteness L * To maximize the σ, it is advantageous to intentionally exclude Bi2O3.

[0095] ZrO 2 Preferably, the glass ceramic contains at most 2.5 wt. % ZrO, in particular at most 2.4 wt. % ZrO, particularly preferably at most 2.2 wt. % ZrO. The basis for the upper limit of 2.5 wt. % is the requirement for resistance to devitrification, especially if the glass ceramic also contains other nucleating agents.

[0096] A minimum content of 1% by weight is necessary for nucleation to occur sufficiently fast.

[0097] In a preferred embodiment, both the crystallizable starting glass, also called green glass, and the glass-ceramic produced therefrom preferably contain the following components in the following proportions (in weight % on an oxide basis): TiO2>1.6~2.8 ZrO21~2.5 ZnO 0-3 MgO 0.01~1 SnO20.01~<0.3 with the proviso that (both in weight percent) B3a 0.005 <MgO×SnO2<0.1 holds true.

[0098] The numerical values ​​for condition B3a are (wt%) 2 It has dimensions of

[0099] MgO×SnO 2 The product of MgO x SnO2 is crucial to achieve low chroma, clarity, and low melting and molding temperatures. This allows for economical production of a color value of a * and b * can be further reduced and the lightness Y of the glass ceramic can be adjusted accordingly.

[0100] In the glass according to the present invention, and in turn in the glass-ceramic as well, the product of the components MgO × SnO2 (all in wt %) is preferably 0.1 or less, preferably 0.08 or less, preferably 0.07 or less. It is desirable that the product of the components be 0.005 or more, preferably 0.01 or more, more preferably 0.012 or more, and particularly preferably 0.015 or more.

[0101] Condition B3a is the glass's desirable advantageous manufacturing properties and its good color value a * and b * This is advantageous for achieving both high brightness and adjustable brightness.

[0102] TiO 2 / SnO 2 Furthermore, compared to the prior art, it is advantageous to increase the nucleating agent ratio TiO2 / SnO2, where SnO2 > 0% by weight. Preferably, 7≦TiO2 / SnO2 < 200 (condition B4) holds. Both components increase coloration, in particular by absorption of Sn / Ti coloring complexes. The low SnO2 content according to the invention reduces the concentration of these coloring complexes, achieving the desired high brightness and low coloration. Here, the TiO2 content can be selected at a high value, increasing this ratio. This allows for shorter ceramming times and improved devitrification resistance.

[0103] The upper limit is preferably 100 or less, particularly preferably 50 or less, and particularly preferably 40 or less.

[0104] TiO 2 +ZrO 2 +SnO 2 Preferably, for the total of the nucleating agents TiO2+ZrO2+SnO2, a value range of 3 to 4.8% by weight is applicable (Condition B5). The minimum content is necessary for the nucleation to proceed fast enough. Preferably, the minimum content is 3.5% by weight in order to be able to produce a translucent glass-ceramic that can be displayed upon rapid ceramization. The basis for the upper limit of 4.8% by weight is the requirement for devitrification resistance.

[0105] According to a further embodiment, the glass-ceramic has the following components (in % by weight based on the oxide basis): Li2O 3.2 to <4.5 Al2O3 19 to 23 SiO2 62 to 68 Na2O 0 to 1 K2O 0 to 1 Na2O+K2O 0.1 to 1.5 ZnO 0 to 3 MgO 0.01 to 1 CaO 0.05 to 2 TiO2 1.8 to 2.8 ZrO2 1 to <2.2 SnO2 0.01 to <0.3 TiO2+ZrO2+SnO2 3.5 to 4.8 Fe2O3 0.008 to 0.06 has a composition containing, provided that 0.005 < MgO × SnO2 < 0.1 (Condition B3a) is satisfied.

[0106] In this preferred composition, ZnO can also be included as an essential component. In that case, preferably 1 to 3% by weight is applicable for ZnO.

[0107] According to a further embodiment, the glass-ceramic has the following components (in % by weight based on the oxide basis): Li2O 3.2 to <4.5 Al2O3 19 - 23 SiO2 62 - 68 Na2O 0.05 - 1 K2O 0 - 1 Na2O + K2O 0.15 - 1.2 MgO 0.1 - 0.8 CaO 0.05 - 1 SrO 0 - 1.5 BaO 0 - 2.5 SrO + BaO 0.5 - 2.5 ZnO 1 - 2.9 B2O3 0 - 1 TiO2 1.8 - 2.8 ZrO2 1 - <2.2 SnO2 0.01 - <0.25 TiO2 + ZrO2 + SnO2 3.6 - 4.8 P2O5 0 - 2 Fe2O3 0.008 - 0.05 having a composition containing, provided that 0.005 < MgO × SnO2 < 0.1 (Condition B3a) is satisfied.

[0108] Preferably, a glass - ceramic, preferably an opaque or translucent glass - ceramic, preferably according to Modification Example A or B, after annealing the glass - ceramic at 700 °C for 10 hours of annealing time, the deviation of the lightness Y from the lightness Y before annealing of the glass - ceramic is at most ±0.3 (|ΔY| ≤ 0.3%).

[0109] Preferably, a glass - ceramic, preferably an opaque or translucent glass - ceramic, preferably according to Modification Example A or B, after annealing the glass - ceramic at 700 °C for 10 hours of annealing time, the whiteness L * from the whiteness L * of the glass - ceramic before annealing has a deviation of at most ±1.5 (|ΔL * | ≤ 1.5), preferably at most ±0.7 (|ΔL * | ≤ 0.7).

[0110] Preferably, the glass ceramic, preferably an opaque or translucent glass ceramic, preferably according to variant A or B, has a color value a before annealing of the glass ceramic after annealing the glass ceramic at 700 ° C for an annealing time of 10 hours. * Color value from a * The deviation of the maximum is ±0.3(|Δa * |≦0.3).

[0111] Preferably, the glass ceramic, preferably an opaque or translucent glass ceramic, preferably according to variant A or B, has a color value b before annealing of the glass ceramic after annealing the glass ceramic at 700 ° C for an annealing time of 10 hours. * Color value b from * The deviation of the maximum is ±1.2(|Δb * |≦1.2), preferably ±0.5(|Δb * |≦0.5).

[0112] This test, with a relatively short annealing time of 10 hours at a temperature significantly higher than the service temperature, allows for simulating a longer service period at a lower service temperature. The test results show that the optical properties Y, as well as L, of the tested glass-ceramics, preferably opaque or translucent glass-ceramics, are significantly higher than the service temperature. * , a * and b * was found to be stable within narrow limits over long periods of time.

[0113] How green glass is made The method for producing crystallizable lithium aluminosilicate glass comprises: a) providing a batch formulation from industrial raw materials; b) melting the batch formulation and subjecting it to a fining treatment at a temperature above 1600°C, preferably above 1650°C; c) Cool the glass melt to a processing temperature V Aand molding at a temperature close to d) Cooling the glass to room temperature in a stress relief furnace to remove unnecessary stresses in the glass. It is characterized by:

[0114] Room temperature means 20°C.

[0115] After method step b), it is also possible to carry out high-temperature fining at temperatures above 1750°C.

[0116] The batch formulation is designed to obtain, after melting, a glass having the composition and properties according to the present invention. The preferred cullet addition in the batch formulation is 20-80 wt. %, which aids melting and allows for higher furnace throughput. A high-temperature fining device can be used if necessary. During forming, a glass ribbon in a plate shape is preferably produced by rolling, and then cooled to room temperature in a cooling furnace to avoid stress. Plates of the desired size are produced from this glass ribbon after quality checks for bulk and surface defects.

[0117] For economical production, low melting temperatures are advantageous, which is ensured by the lower viscosity of the glass melt at high temperatures.

[0118] Lowering the temperature during forming is economically advantageous. It extends the life of the forming tools and reduces heat loss. Forming is usually performed by rolling or floating, and the viscosity of the glass melt is 10 4 This temperature is the processing temperature V A It is also called.

[0119] A crystallizable glass has sufficient resistance to devitrification when formed from the melt. During forming, upon contact with the forming material (e.g., the precious metal of the draw nozzle in the rolling process), no visually noticeable crystals, which are critical for the strength of the glass-ceramic, form in the glass. The limiting temperature, or upper devitrification limit (OEG), below which critical devitrification occurs is preferably above the processing temperature V A The processing temperature is preferably V A This minimum difference defines a sufficient process window for the molding process. A It is particularly advantageous if the temperature of the -OEG is at least 20°C. A The temperature difference between the OEG and the SiO2 is an index of devitrification resistance.

[0120] Forming methods suitable for plate shapes include rolling and float processing. A preferred forming method from a glass melt is the two-roll method, because this method allows rapid cooling, which is advantageous when the composition is prone to devitrification.

[0121] Ceramization Method The next process step is ceramization on a flat or shaped high-temperature stable support (kiln furniture). Preferably, ceramization is carried out in a roller kiln.

[0122] The method according to the invention for producing a glass ceramic, which provides a crystallizable lithium aluminosilicate glass free of As2O3 and Sb2O3, comprises carrying out a ceramming process comprising the following process steps in the following order: a) The temperature of the crystallizable glass is reduced to room temperature T within 3 to 60 minutes. RT to a temperature T in the range of 660-730°C a a step of raising the b) The temperature of the crystallizable glass is increased by T over a period of 5 to 100 minutes. a to a maximum temperature of 800°C; c) The temperature of the glass containing the crystal nuclei is raised to the initial HQ solid solution formation temperature range T b a step of increasing the temperature to 780 to 850°C; d) Temperature range T over 5 to 120 minutes b a step of staying at e) The temperature of the glass containing the HQ solid solution is raised to a temperature range T C a step of increasing the temperature to 900°C to 950°C; f) The temperature of the glass containing the HQ solid solution is increased to a temperature range of 950°C to 1250°C within 5 to 80 minutes. D a step of raising the g) Residence time t V >0 to 60 minutes over the temperature range T D a step of staying at h) quenching the resulting glass ceramic to room temperature within 150 minutes and the total time for ceramming the glass is less than 300 minutes.

[0123] Temperature range T D The temperature selected by is the temperature T D , maximum temperature T D It is also called.

[0124] The crystallizable LAS glass may be free of SnO2 or may preferably contain SnO2.

[0125] In method step d), crystals of the high-purity quartz solid solution type are grown on crystallization seeds consisting of a nucleating agent. In this step, the high-purity quartz solid solution structure is homogenized. This high-purity quartz solid solution structure has the optical properties Y, L. * , a * , and b * This affects the adjustability of the

[0126] In method step e), the growth of the high purity quartz solid solution continues. As the HQ solid solution grows, the scattering of light increases.

[0127] In method step f), keatite solid solution crystals are formed from high-purity quartz solid solution crystals.

[0128] In method step g), the keatite solid solution crystals are further matured and the properties of the glass-ceramic are optimized.

[0129] In order to optimize the properties, it is preferred to carry out the following method steps in method step g): 1. Embodiment The keatite peak temperature is T P It is preferable that the temperature is ≦1005°C.

[0130] To produce a glass ceramic, the following method steps are carried out in method step g): g11) Residence time of 5 to 20 minutes V Temperature T in the range of 1120℃ to 1180℃ D Steps that stay in It is preferable to carry out the following.

[0131] To produce a glass ceramic, the following method steps are carried out in method step g): g12) Residence time of 5 to 20 minutes V Temperature T in the range of 1060℃ to 1120℃ D Steps that stay in It is preferable to carry out the following.

[0132] To produce a glass ceramic, the following method steps are carried out in method step g): g13) Residence time of 5 to 20 minutes V Temperature T ranges from 1035℃ to 1080℃ D Steps that stay in It is preferable to carry out the following.

[0133] Preferably, a low temperature T D A longer residence time is selected for , and vice versa.

[0134] The temperature treatment of steps g11) to g13) optimizes the desired properties of the glass ceramic variants A to C, and the short dwell time t V and / or a low temperature T D It can be produced economically by

[0135] 2. Embodiment The keatite peak temperature is T P It is preferable that the temperature is >1005°C.

[0136] To produce a glass ceramic, the following method steps are carried out in method step g): g21) Residence time of 5 to 20 minutes V Temperature T in the range of 1145℃ to 1180℃ D Steps that stay in It is preferable to carry out the following.

[0137] To produce a glass ceramic, the following method steps are carried out in method step g): g22) Residence time of 5 to 20 minutes V Temperature T in the range of 1100℃ to 1150℃ D Steps that stay in It is preferable to carry out the following.

[0138] To produce a glass ceramic, the following method steps are carried out in method step g): g23) Residence time of 5 to 20 minutes V Temperature T in the range of 1050℃ to 1100℃ D Steps that stay in It is preferable to carry out the following.

[0139] Preferably, a low temperature T D A longer residence time is selected for , and vice versa.

[0140] The temperature treatment of steps g21) to g23) optimizes the desired properties of the glass ceramic variants A to C, and the short dwell time t V and / or a low temperature TD It can be produced economically by

[0141] A keatite peak temperature T in the range of 990°C to 1025°C, preferably in the range of 990°C to 1005°C P A particularly preferred embodiment for producing a glass ceramic having the formula g31) A residence time of at least 6 minutes t V A temperature T of at least 1145°C D or a residence time of at least 15 minutes t V and staying at a temperature of at least 1120°C for a period of time. g32) A residence time of at least 6 minutes t V A temperature T of at least 1100°C D or a residence time of at least 15 minutes t V and staying at a temperature of at least 1080°C for a period of time. g33) A residence time of at least 6 minutes t V Temperature T D or a residence time of at least 15 minutes t V The temperature remains at least 1065°C for a period of time.

[0142] The temperature treatment in the three preferred method steps g31) to g33) described above also leads to the optimization of the desired properties in the glass ceramic variants A to C. The glass ceramic variants A to C, as well as the glass ceramics with Y≦2% and L preferably produced according to g31), * ≥ 93, preferably 2% prepared according to g32) <Y≦10%および80≦L * ≦92, and preferably 10% prepared according to g33) <Y≦25%および62≦L * Glass ceramics with a temperature of ≤80 have a short residence time t V and / or a low temperature T D It can be produced economically by

[0143] > Keatite peak temperature T in the range of 1005°C to 1060°C, preferably in the range of 1015°C to 1060°C P A further particularly preferred embodiment for producing a glass ceramic having the following method steps: g41) A residence time of at least 6 minutes t V A temperature T of at least 1170°C D or a residence time of at least 15 minutes t V and staying at a temperature of at least 1120°C for a period of time. g42) A residence time of at least 6 minutes t V Over a temperature T of at least 1120°C D or a residence time of at least 15 minutes t V dwell at a temperature of at least 1100°C for a period of time; g43) Residence time of at least 6 minutes t V A temperature T of at least 1100°C D or a residence time of at least 15 minutes t V The temperature remains at least 1080°C for a period of time.

[0144] The temperature treatment in steps g41) to g43) also leads to the optimization of the desired properties of the glass ceramic variants A to C. The glass ceramic variants A to C, as well as those preferably produced according to g41), with Y≦2% and L * ≥ 90, preferably 2% prepared according to g42) <Y≦10%および80≦L * ≦93, and preferably g43) 10% <Y≦25%および67≦L * Glass ceramics with a temperature of ≤81°C have a short residence time t V and / or a low temperature T D It can be produced economically by

[0145] The above-mentioned object is also achieved by a glass-ceramic according to any one of claims 1 to 27, which is produced from an As2O3- and Sb2O3-free crystallizable lithium aluminosilicate glass by a ceramming method according to any one of claims 28 to 34.

[0146] The glass ceramic according to the invention is preferably in the form of a platelet with a thickness of 2 mm to 20 mm, which may preferably have protrusions or grooves on one side, or may be smooth and / or deformed or curved on both sides, and is preferably used as fire protection glass, as a cooktop, for example for induction-, radiant-, or gas-heated cooking appliances, as a cover in the lighting field, as a support plate, or as an oven lining for baking ovens, fireplace ovens, or microwave ovens. This application may be intended for the end user's personal household appliances or for industrial applications, for example, in the food and beverage industry. The glass ceramic is also used in many sizes and shapes as a grill cover and / or as a cover for a gas or rotisserie burner, or as an accessory in the form of a pizza stone or plancha.

[0147] Glass ceramics have been found to be suitable for coating, preferably in the form of panels or plates, with heat radiation blocking coatings being particularly preferred.

[0148] The coating has one layer, preferably at least two layers. In the case of a coating having two layers, the first layer is preferably an IR-reflecting layer.

[0149] A preferred layer comprises a doped transparent conductive oxide, preferably zinc oxide, which is preferably used as the first layer in a two-layer system.

[0150] A further preferred layer comprises an X-ray amorphous oxide or nitride. Preferably, the oxide layer is an aluminum oxide layer. Preferably, the nitride layer is an aluminum nitride layer. In the case of a two-layer system, this layer is preferably used as the second layer applied on the first layer.

[0151] Keatite peak temperature T P It has been found that the transformation temperature for keatite formation, indicated by the keatite peak temperature, can be influenced by the ceramming conditions, thereby optimizing the properties of the glass-ceramic.

[0152] In the following, exemplary embodiments are described on the basis of a single drawing and tables. [Brief explanation of the drawings]

[0153] [Figure 1] FIG. 1 is a temperature / time schematic diagram of a ceramming program.

[0154] The drawing shows a temperature / time diagram of the ceramming program, with the various method steps a) to h) shown against the time axis t.

[0155] In method step a), the green glass is heated to an initial temperature T RT = 20°C to temperature T a In the subsequent method step b), nucleation takes place and T a The temperature is continuously increased from 1000 to a maximum of 800°C.

[0156] In the next step c), the temperature range T b In this example embodiment, the temperature range T b Residence at 200° C. is accompanied by a continuous increase in temperature within this temperature range.

[0157] Next, step e) is performed to bring the temperature range T CIn step f), the temperature is increased to T C Temperature range from 950℃ to 1250℃ D The temperature is further increased to a temperature of

[0158] Temperature range T D Once this is reached, method step g) is performed to add the residence time t V The temperature is kept constant throughout the glass-ceramic. D and any residence time t V The preferred method of selecting is explained in connection with various embodiments with preferred method steps g11 to g43.

[0159] Finally, in method step h) it is quenched to room temperature.

[0160] Table 1 shows preferred glass compositions subjected to various ceramming methods 1, which are designated as g11) to g13) or g21) to g23) in Tables 2 to 4. Ceramming methods 2 designated as g31 to g33 or g41 to g43 indicate specific embodiments of ceramming method 1. The choice of which option for each ceramming method 2 to use depends on the given T. D and t V is indicated by the value of

[0161] Table 1 shows the composition in weight percent of the crystallizable starting glasses according to the present invention, as well as relevant glass properties, such as the glass transition temperature T g and keatite peak temperature T P where Glass 14 is a comparative example. The glass ceramic has the same composition as the starting glass.

[0162] The glasses were melted as follows: a) providing a batch formulation from industrial raw materials; b) The batch formulation is melted in a laboratory scale silica glass crucible at 1620°C, then held for 2 hours, stirred and homogenized at 1600°C for 1 hour, heated to 1640°C and held for 3 hours; c) producing a cast block; and d) Cool to room temperature in a stress relief furnace to remove unnecessary stress in the glass.

[0163] Table 2 shows the optical properties and average linear expansion coefficients of glass ceramics according to the invention produced by the appropriate ceramming method 1 (e.g. g11 or g21) and of comparative examples (opaque glass ceramics) of variant A with a thickness of about 4 mm and Y≦2%.

[0164] From these data, it can be seen that, compared with embodiment 2, embodiment 1 has a lower whiteness L measured by reflectance when the lightness Y measured by transmittance is the same or similar using the same ceramization method. * This is especially true at the maximum temperature T D is low and the residence time t V Furthermore, the comparative example shows a higher temperature than the glass ceramic according to the invention, especially at the maximum temperature T D When the temperature is high and the maximum temperature T D Low residence time t V When the time is short, the same or similar brightness Y and whiteness L * This is presumably related to the fact that the refining agent As2O3 acts as a "whitening agent" in this glass-ceramic. However, the maximum temperature T D When the temperature is low and the residence time is long, the first embodiment has the same or similar brightness Y and whiteness L compared to the second embodiment and the comparative example. * is found to be higher.

[0165] The glass ceramic according to the present invention has a lower average linear expansion coefficient than the comparative example.

number

[0166] In addition, two color values ​​a * and b* and c * In one embodiment, the whiteness L * The amount decreases with increasing * approaches 0, and b * approaches 0, and c * It is clearly shown that the color value b * and c * For these color values ​​and whiteness L * In addition, in the first embodiment, the whiteness L * The higher the color value b * and c * The reduction in the amount of values ​​is particularly evident.

[0167] Fe2O3 has a color value of a * It can be seen that the color value a is shifted to the positive range, i.e., the red side. Here, this glass system has the same or even smaller color value a than Comparative Examples 26 to 28 using the same ceramicization method. * From the above, a * It is noteworthy that the color value a appears to be less sensitive to increasing Fe2O3 content. * In contrast to the color values ​​of Fe2O3-rich glass-ceramics upon ceramming, b * It can be seen that the value of can be improved or even worsened. Therefore, for compositions with a high Fe2O3 content, a * and b * In order to optimally adjust both the maximum temperature T D Lower the residence time t V However, to ensure a good white impression, it is necessary to shorten the whiteness L * Particular attention should be paid to the whiteness L * is the maximum temperature T D The lower the retention time t V The shorter the time, the lower the

[0168] The addition of Nd2O3 in the glass according to the invention, in contrast to the comparative example also containing Nd2O3, results in a color value of a * and b * Compared to the other examples of embodiment 2 and compared to embodiment 1, the addition of Nd2O3 results in the same or similar color values ​​a regardless of the ceramming method. * and color value b * is significantly reduced.

[0169] In contrast, particularly in the first embodiment, when the proportion of SnO2 is increased, the color value a * and b * But, a * =0 and b * This means that the temperature will move away from the so-called neutral point where θ = 0.

[0170] Overall, compared to embodiment 2 and the comparative example, embodiment 1 has a color value of a when the SnO2 content is low and no Nd2O3 is included. * and b * and c * is found to be better.

[0171] When examining the transmittance values ​​at 700 nm, it can be seen that the values ​​for embodiment 2 in particular are higher than those for embodiment 1 and also compared to the comparative example, with the same ceramming method. The transmittance at 700 nm is proportional to the lightness Y, and is therefore an indicator of lightness Y. The advantage here is that this value is measured directly.

[0172] It is particularly clear that for the glass ceramics according to the invention shown here, the infrared transmittance at 1600 nm is, with some exceptions, significantly higher in both embodiments with the same ceramming method compared to the comparative examples.

[0173] From these examples, it can be seen that adding MgO gives an equivalent color value of a * and b * Whiteness L *It can be seen more clearly that MgO helps to shift the keatite peak temperature to lower values ​​(see Table 1), thus resulting in high whiteness L * Furthermore, the addition of MgO increases the transmittance at 1600 nm.

[0174] Table 3 shows the optical properties and average linear expansion coefficients of glass ceramics according to the invention produced by the appropriate ceramming method (g12 or g22) and of comparative examples 64 and 65 (translucent glass ceramics without display capabilities) of variant B with a thickness of about 4 mm and Y > 2% to 10%. These data show that, in this variant, too, embodiment 1 achieves a higher whiteness L at the same or similar lightness Y compared to embodiment 2 with the same ceramming method. * It can be seen that, compared to the first embodiment, the comparative example achieves a higher whiteness L using the same ceramming method. * Furthermore, compared to the second embodiment, the first embodiment achieves a lower maximum temperature T D , i.e. already at 1120 °C instead of 1145 °C, a very good whiteness L * has been achieved.

[0175] The glass ceramics of this variant are generally undetectable, as evidenced by the ratio (PvK - PiP) / PiP at 630 nm being greater than 39. Examples 48 and 71 are exceptions, being rated "slight." This visual optical impression is confirmed by the low ratio (PvK - PiP) / PiP at 630 nm of 10 or less.

[0176] The glass ceramic according to the invention has the advantage of a lower average coefficient of linear expansion compared to the comparative examples, which contributes to the thermal shock resistance of the glass ceramic.

[0177] In contrast to Variation A, Variation B uses color values ​​a in one embodiment, as described in connection with Table 2. * and b * and c * and whiteness L* In contrast, this correlation is clearly evident within a single composition. For example, the color value a * and b * and c * L * Furthermore, the addition of SnO2 in embodiment 1 results in the same or similar whiteness L * And the color value a * and b * and c * It can be seen that the amount of Fe2O3 increases significantly. * is the same or similar color value a * and c * There is a significant shift to lower values.

[0178] As already explained for variant A, also in variant B, the increase in the Fe2O3 content in the glass ceramic according to the invention leads to a higher color value a with the same ceramming method compared to comparative example 64. * It can be seen that the amount of

[0179] In variant B, embodiment 1 has a lower maximum temperature T with respect to embodiment 2, regardless of the ceramming method. D Even if there is already an identical or similar * Value b * The advantage is that the coloring components SnO2 and Fe2O3 can be reduced in the glass ceramic according to the invention, which allows the same ceramming process, especially T D At 1100°C, the color value a * and b * and c * In this way, the amount of color value a can be reduced, which is significantly improved (less amount) compared to the comparative example. * and b * and c * From the glass 12, the maximum temperature T D Rise and / or residence time t VBy extension, the color value a * and b * and c * It is clear that the amount of β-glucan can be reduced. This means that with this composition, the maximum temperature T D Rise and / or residence time t V When extending the whiteness L * This can be explained by an increase in

[0180] With the same ceramming method, both embodiments show higher transmittance at 700 nm and / or 1600 nm compared to the comparative example. For glass ceramics of the same composition, the same residence time t V At the highest temperature T D As the dwell time t decreases, the transmittance values ​​at 700 nm and 1600 nm increase. V When the time is extended, the maximum temperature T D can be reduced, resulting in an equivalent whiteness L * It was found that the same transmittance values ​​were obtained.

[0181] Table 4 shows the optical properties and average linear expansion coefficients of glass ceramics according to the invention produced by the appropriate ceramming method (g13 or g23) and comparative examples 95 and 96 (translucent glass ceramics with display capabilities) of variant C with a thickness of about 4 mm and Y > 10% to 25%. As already shown in the other two variants A and B, embodiment 1 achieves a higher whiteness L at the same or similar lightness Y with the same ceramming method compared to embodiment 2. * In particular, in this example, the whiteness L of the first embodiment is equivalent to that of the second embodiment. * To achieve this, a lower maximum temperature T D However, in this case, a higher brightness Y is achieved, which helps to improve the red display capability. Even in this variant, the comparative example achieves a higher whiteness L than both embodiments using the same ceramization method. * However, in some examples, the whiteness L *Some of them have better (good) display capabilities when the maximum temperature T is the same or higher. This can be explained by the fact that the ratio (PvK-PiP) / PiP at 630 nm is 7.3 in Comparative Example 96, but is smaller, at 2.2 to 4.0, in the embodiments. Compared to the comparative examples, both Embodiment 1 and Embodiment 2 have higher maximum temperatures T D and / or a longer residence time t V Higher whiteness with very good display ability * This improves the impression of white compared to the comparative example. D The higher the whiteness L * It has a higher display capacity but only a small amount of display capability.

[0182] High brightness Y but whiteness L * When the whiteness L is low, the display ability is very good. Even in this display ability category, the whiteness L is higher than that of the comparative example. * There are examples showing this, which promotes an improvement in the impression of white.

[0183] In the modified example C, the color value a * and b * and c * and whiteness L * There is a clear correlation between the V At the highest temperature T D The higher or lower the maximum temperature T D The residence time is t V The longer the color value a * and b * and c * The amount of will be less.

[0184] As with the other two variants A and B, decreasing the SnO2 content resulted in a color value of a * and b * and c * It is again clear that the amount of

[0185] Compared to the comparative example, in the first embodiment, when the SnO content is reduced by the same ceramicization method, the whiteness L * is significantly lower than the comparative example with the same ceramization method, but has significantly better color values ​​a * and b * and c * In other words, the maximum temperature T D or the same maximum temperature T D Residence time t V With the extension of * If the color value a * and b * and c * These examples show that with the appropriate composition, the color value a can be improved even when SnO2 is used as a refining agent. * and b * and c * indicates that it is not damaged.

[0186] Also, the color value a is similar to or even better than that of embodiment 1. * and b * and c * can also be achieved in the second embodiment. However, to achieve this, a higher maximum temperature T D and / or a longer residence time t V is necessary.

[0187] Compared to the comparative example, in embodiment 1, similar or even better display capabilities are achieved with the same ceramming method.

[0188] In the second embodiment, the maximum temperature T D However, in the first embodiment, the maximum temperature T is already lower than that in the second embodiment. D and / or a longer residence time t V With the same good display ability, the same or even higher whiteness L *can be achieved, whereby the white impression of embodiment 1 can be adjusted with better energy efficiency than embodiment 2.

[0189] Furthermore, variant C, like the other two variants A and B, has a lower maximum temperature T D and the same residence time t V The comparative example shows an increase in transmittance at 700 nm and / or 1600 nm with the same ceramming method. However, the comparative example shows a higher transmittance at 700 nm and / or 1600 nm than the example of the first embodiment. However, both the examples of the first embodiment and the second embodiment show a higher maximum temperature T D and / or residence time t V This indicates that the transmittance at 700 nm and / or 1600 nm is higher than that of the comparative example.

[0190] Furthermore, these examples demonstrate that by removing MgO from the composition of Variation C, a comparable whiteness L * The color neutrality of the glass ceramic is more pronounced (color value a * , b * and c * As already shown in the example of Variant A, in Variant C, the addition of MgO increases the transmittance at 1600 nm, but also increases the transmittance at 630 nm and 700 nm.

[0191] Increasing SnO2 for better fining of the glass melt results in a comparable whiteness L compared to a suitable composition with a lower SnO2 content. * Equivalent color value a * , b * and c * is obtained.

[0192] Table 5 shows the lightness Y, whiteness L, and the like of glass ceramics according to the invention having a thickness of about 4 mm according to variants A (embodiment 1) and B (embodiment 2), when annealed at 700° C. for an annealing time of 10 hours. * , and the color value a * and b* Therefore, the use of SnO2 as a fining agent does not pose any disadvantages compared to the comparative examples.

[0193] [Table 1-1]

[0194] [Table 1-2]

[0195] [Table 1-3]

[0196] [Table 1-4]

[0197] [Table 1-5]

[0198] [Table 1-6]

[0199] [Table 1-7]

[0200] [Table 1-8]

[0201] [Table 1-9]

[0202] Table 2-1

[0203] Table 2-2

[0204] Table 2-3

[0205] Table 2-4

[0206] Table 2-5

[0207] Table 2-6

[0208] Table 2-7

[0209] Table 2-8

[0210] Table 2-9

[0211] Table 2-10

[0212] Table 2-11

[0213] Table 3-1

[0214] Table 3-2

[0215] Table 3-3

[0216] Table 3-4

[0217] Table 3-5

[0218] Table 3-6

[0219] Table 3-7

[0220] Table 4-1

[0221] Table 4-2

[0222] Table 4-3

[0223] Table 4-4

[0224] Table 4-5

[0225] Table 4-6

[0226] Table 4-7

[0227] Table 4-8

[0228] Table 4-9

[0229] Table 4-10

[0230] Table 4-11

[0231] Table 5-1

[0232] Table 5-2

[0233] Table 5-3

Claims

1. As, excluding inevitable impurities ２ O ３ and Sb ２ O ３ A lithium aluminosilicate glass ceramic having keatite as the main crystal phase and not containing the above, wherein the glass ceramic has a keatite peak temperature T for keatite solid solution formation in the range of 980 °C to 1090 °C Ｐ and the keatite peak temperature T Ｐ is determined by differential scanning calorimetry (DSC) in accordance with DIN 51007:2019-04 using a heating rate of 5 K·min －１ A glass ceramic, characterized in that it is obtained using the above heating rate.

2. The key tit peak temperature T Ｐ is in the range of 980°C to 1070°C, and the glass ceramic according to claim 1.

3. The glass ceramic contains the following components in the following proportions (in weight % based on oxides): Li ２ O 3 - 5 Al ２ O ３ 18 - 25 SiO ２ 60 - 70 SnO ２ 0 to 0.5 The glass ceramic according to Claim 1, which contains

4. The glass ceramic contains 3.9 to 4.5% by weight of Li ２ O, and has a keyite peak temperature T in the range of 990°C to 1025°C Ｐ The glass ceramic according to claim 1

5. The glass ceramic contains 3.5 to < 3.9 wt% of Li ２ O and has a keyite peak temperature T in the range of 1015°C to 1060°C Ｐ The glass ceramic according to claim 1

6. The glass ceramic has a whiteness L ＊ in the color space L ＊ a ＊ b ＊ is 60 to 97, and has a lightness Y of 0.1% to 25%, where L ＊ and Y are determined using a standard light source D65 at a thickness of 4 mm and an angle of 2° of the glass ceramic. The glass ceramic according to claim 1

7. The glass ceramic is opaque and has a keyite peak temperature T in the range of 980°C to 1070°C Ｐ and the following values: L ＊ = 85 to 97 a ＊ = -1.5 to 0.5 b ＊ = -6 to 0.5 and Y = 0.1% to 2% The glass ceramic according to Claim 1, which has

8. The glass ceramic is translucent and has a keyite peak temperature T in the range of 980°C to 1070°C Ｐ and the following values: L ＊ = 72 to 93 a ＊ = -5.5 to 0 b ＊ = -7 to 0.5 and Y => 2% to 10% The glass ceramic according to Claim 1, which has

9. The glass ceramic is translucent and has a keyite peak temperature T in the range of 980°C to 1070°C Ｐ and the following values: L ＊ = 60 to 82 a ＊ = -7.5 to -2 b ＊ = -19 to -4.5 and Y => 10% to 25% The glass ceramic according to Claim 1, which has

10. The glass ceramic according to Claim 8, wherein the glass ceramic has a ratio (PvK - PiP) / PiP of ≤ 20 for light with a wavelength of 630 nm.

11. The glass ceramic has an average linear expansion coefficient of 0 to 2.0×10 －６ / K 【Number 1】 The glass ceramic according to Claim 1, which has

12. The glass ceramic according to Claim 1, wherein the glass ceramic contains 0.01 to < 1% by weight of MgO.

13. The glass ceramic according to Claim 1, wherein the glass ceramic contains 0.5 to 3% by weight of ZnO.

14. Al ２ O ３ and Li ２ Regarding the ratio with LiO + MgO + ZnO (all oxides are shown in units of weight %), as follows: 3 ≤ Al ２ O ３ / (Li ２ O + MgO + ZnO) < 3.2 (Condition B1a) is satisfied, where the glass ceramic has a keyite peak temperature T in the range of 990°C to 1005°C Ｐ The glass ceramic according to claim 3, having

15. Al ２ O ３ and Li ２ Regarding the ratio with LiO + MgO + ZnO (all oxides are shown in units of weight %), as follows: 3.2 ≤ Al ２ O ３ / (Li ２ O + MgO + ZnO) < 3.8 (Condition B1b) is satisfied, where the glass ceramic has a keyite peak temperature T in the range of > 1005°C to 1060°C Ｐ The glass ceramic according to claim 3, having this.

16. The glass ceramic contains the following components in the following proportions (in weight % based on oxides): Na ２ O 0 to 1 K ２ O 0 to 1 but with the proviso that condition B2a 0.1 ≤ Na ２ O + K ２ O ≤ 1.5 is satisfied. The glass ceramic according to Claim 1.

17. The glass ceramic contains the following components in the following proportions (in weight % based on oxides): Na ２ O 0 to 1 K ２ O > 0 to 1 but with the proviso that condition B2b 0.05 ≤ Na ２ O / K ２ O ≤ 1.2 is satisfied. The glass ceramic according to Claim 1.

18. The glass ceramic contains up to 0.06% by weight of Fe ２ O ３ The glass ceramic according to claim 1, which contains

19. The glass ceramic contains Nd of 0.065 wt% or less ２ O ３ The glass ceramic according to claim 1, which contains the same

20. The glass ceramic contains 0 to 2% by weight of P ２ O ５ The glass ceramic according to claim 1, containing the same.

21. The glass ceramic contains the following components (in weight % based on oxides): TiO ２ > 1.6 to 2.8 ZrO ２ 1 to 2.5 ZnO 0 to 3 MgO 0.01 to 1 SnO ２ 0.01 to <0.3 but with the proviso that (here, both in weight % units) condition B3a 0.005 < MgO × SnO ２ < 0.1 is satisfied. The glass ceramic according to Claim 1.

22. The glass ceramic contains the following components (in weight % based on oxides): Li ２ O 3.2 to <4.5 Al ２ O ３ 19 - 23 SiO ２ 62 to 68 Na ２ O 0 to 1 K ２ O 0 to 1 Na ２ O + K ２ O 0.1 to 1.5 ZnO 0 to 3 MgO 0.01 to 1 CaO 0.05 to 2 TiO ２ 1.8 to 2.8 ZrO ２ 1 to <2.2 SnO ２ 0.01 to <0.3 TiO ２ +ZrO ２ +SnO ２ 3.5 to 4.8 Fe ２ O ３ 0.008 to 0.06 but with the proviso that 0.005 < MgO × SnO ２ < 0.1 is satisfied. The glass ceramic according to Claim 1.

23. The glass ceramic contains the following components (in weight % based on oxides): Li ２ O 3.2 to <4.5 Al ２ O ３ 19 - 23 SiO ２ 62 to 68 Na ２ O 0.05 to 1 K ２ O 0 to 1 Na ２ O + K ２ O 0.15 to 1.2 MgO 0.1 to 0.8 CaO 0.05 to 1 SrO 0 to 1.5 BaO 0 to 2.5 SrO + BaO 0.5 to 2.5 ZnO 1 to 2.9 B ２ O ３ 0 to 1 TiO ２ 1.8 to 2.8 ZrO ２ 1 to <2.2 SnO ２ 0.01 to <0.25 TiO ２ +ZrO ２ +SnO ２ 3.6 to 4.8 P ２ O ５ 0 to 2 Fe ２ O ３ 0.008 to 0.05 but with the proviso that 0.005 < MgO × SnO ２ < 0.1 (Condition B3a) is satisfied. The glass ceramic according to Claim 1.

24. After annealing the glass ceramic at 700 °C for an annealing time of 10 hours, the deviation of the lightness Y from the lightness Y before annealing of the glass ceramic is at most ±0.3% (|ΔY| ≤ 0.3%), the glass ceramic according to claim 1.

25. After annealing the glass ceramic at 700 °C for an annealing time of 10 hours, the whiteness L of the glass ceramic before the annealing treatment ＊ from the whiteness L ＊ The deviation of is at most ±1.5 (|ΔL ＊ | ≤ 1.5), The glass ceramic according to claim 1.

26. After annealing the glass ceramic at 700 °C for an annealing time of 10 hours, the color value a of the glass ceramic before annealing ＊ from the color value a ＊ The deviation of is at most ±0.3 (|Δa ＊ | ≤ 0.3). The glass ceramic according to claim 1.

27. After annealing the glass ceramic at 700 °C for an annealing time of 10 hours, the color value b of the glass ceramic before annealing ＊ from the color value b ＊ The deviation is at most ±1.2 (|Δb ＊ | ≤ 1.2), the glass ceramic according to claim 1.

28. A method for manufacturing a glass ceramic according to any one of claims 1 to 27, wherein As ２ O ３ and Sb ２ O ３ In a method for providing a crystallizable lithium aluminosilicate glass free of, the ceramization having the following method steps is carried out in the following order: a) raising the temperature of the glass capable of crystallization within 3 to 60 minutes from room temperature T ＲＴ to a temperature T in the range of 660 to 730 °C ａ in a stepwise manner; b) raising the temperature of the glass capable of crystallization from T to a maximum temperature of 800 °C over 5 to 100 minutes ａ and c) raising the temperature of the glass containing the crystal nuclei to a temperature range T of 780 to 850 °C, which is the temperature range for initial HQ solid solution formation, within 5 to 80 minutes ｂ in a step; d) A step of staying within the temperature range T for 5 to 120 minutes ｂ and e) raising the temperature of the glass containing the HQ solid solution to a temperature range T of 900 °C to 950 °C, which has a high crystal growth rate, within 5 to 80 minutes Ｃ ; and f) raising the temperature of the glass containing the HQ solid solution to a temperature range T of 950°C to 1250°C within 5 to 80 minutes Ｄ and g) Residence time t Ｖ > A step of staying within a temperature range T over 0 to 60 minutes Ｄ and staying h) quenching the obtained glass ceramic to room temperature within 150 minutes A method, characterized in that the total time for ceramization of the glass is within 300 minutes.

29. Keyite peak temperature T of ≦ 1005 °C Ｐ The method according to claim 28 for manufacturing a glass ceramic having, in method step g), the following method steps: A residence time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1120°C to 1180°C Ｄ for residence A method of performing.

30. A key titanite peak temperature T of ≦ 1005 °C Ｐ The method according to claim 28 for producing a glass ceramic having, in method step g), the following method steps: Retention time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1060°C to 1120°C Ｄ for the step of retention A method of performing.

31. Key titanite peak temperature T ≤ 1005 °C Ｐ The method according to claim 28 for producing a glass ceramic having, in method step g), the following method steps: Retention time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1035°C to 1080°C Ｄ for the retention step A method of performing.

32. >1005 °C key titanite peak temperature T Ｐ The method according to claim 28 for producing a glass ceramic having, in method step g), the following method steps: Retention time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1145°C to 1180°C Ｄ for the retention step A method of performing.

33. > 1005 °C key titanite peak temperature T Ｐ The method according to claim 28 for manufacturing a glass ceramic having, in method step g) the following method steps: Retention time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1100°C to 1150°C Ｄ for the step of retention A method of performing.

34. >1005 °C key titanite peak temperature T Ｐ The method according to claim 28 for manufacturing a glass ceramic having a, wherein in said method step g) the following method steps: Retention time t of 5 to 20 minutes Ｖ at a temperature T in the range of 1050°C to 1100°C Ｄ for the step of retention A method of performing.

35. As ２ O ３ and Sb ２ O ３ A glass-ceramic produced by the ceramization method according to claim 28 from a crystallizable lithium aluminosilicate glass free of

36. In the form of a plate-like object with a thickness of 2 mm to 20 mm, as a fireproof glass, as a cooktop, as a cover in the lighting field, as a support plate, or as an oven lining for a baking oven, a furnace oven or a microwave oven, as a grill cover, as a cover for a gas burner or a rotisserie burner, or in the form of a pizza stone or a griddle, use of the glass ceramic according to any one of claims 1 to 27.

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