Crystalline lithium aluminum silicate glass and glass ceramic produced therefrom, as well as methods for producing the glass and glass ceramic, and uses of the glass ceramic

Abstract

To provide a crystallizable lithium aluminosilicate glass for producing transparent glass ceramic.SOLUTION: This invention relates to a crystallizable lithium aluminum silicate glass that contains, in wt.% on an oxide basis, following components: Li2O: 3 to 5, Al2O3: 19 to 24, SiO2: 62 to 70, TiO2: 1.6 (exclusive) to 2.8, ZrO2: 1 to 2.5, MgO: 0.01 to 0.5 (exclusive), SnO2: 0.01 to 0.15 (exclusive), under the condition (wt.%) 0.005<MgO×SnO2<0.06 (condition B1a). This invention also relates to glass ceramic produced from the glass and use thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a crystalline lithium aluminum silicate glass capable of being transformed into a LAS glass-ceramic according to the preamble of claim 1.

[0002] The invention also relates to glass-ceramics produced from this glass, to methods for their production and to the use of such LAS glass-ceramics.

[0003] LAS glass ceramics are widely used due to their special material properties, such as low coefficient of expansion, high strength, chemical resistance and transparency, combined with high temperature difference and thermal shock resistance. Typically, the thermal expansion behavior of a material is such that within its application temperature range, it is usually α 20 / 700 <0±1.5·10 -6 / K. Requirements for high-temperature use include that the glass-ceramic retain the required properties (e.g., thermal expansion, transmittance, thermal stability) over its service life. With regard to thermal stability, the glass-ceramic's small, but very small, shrinkage (compaction) at high temperatures is a very important factor. Glass-ceramic articles are often heated unevenly during use, which usually results in stresses within the article over time due to locally varying degrees of shrinkage.

[0004] LAS glass-ceramics have a wide range of applications, including fire protection windows, cooking utensils, transparent fireplace windows, oven windows, and cooking surfaces. When used as cooking surfaces, transparent glass-ceramic plates are either colored with colored oxides to prevent technical components from showing through and to create a colored impression, or have an opaque, usually colored, coating on the underside. The absence of an underside coating allows the installation of colored and white display indicators, usually light-emitting diodes or screens.

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

[0006] One class of such glass-ceramics is transparent, unpigmented glass-ceramics, which are manufactured without the addition of coloring compounds. Another class of transparent, colored glass-ceramics is bulk-colored, typically with the addition of V2O5, to reduce the brightness and achieve a black appearance, which is typical of cooking surfaces with a black appearance.

[0007] For transparent, uncolored glass-ceramics, high transparency, i.e., high brightness and low color, is desired. Both mean low absorption, since absorption bands not only decrease brightness but also increase color depending on their position in the visible spectrum. Thus, the brightness of such glass-ceramics is typically greater than 80% at a thickness of 4 mm.

[0008] In the literature, brightness is also referred to as light transmittance or integral transmittance.

[0009] However, transparent, uncolored glass-ceramics have a small amount of color due to the nucleating agents TiO2, and sometimes SnO2, and impurities present in the batch raw materials, especially iron impurities. This is undesirable and is minimized by industrial measures.

[0010] Another essential feature of LAS glass-ceramics is scattering, which is determined by the crystal size, birefringence, and the difference in refractive index between the crystals and the remaining glass. Typically, low scattering is desired so that the view through the glass remains unchanged and the display is clearly visible. In special applications, controlled scattering is also desired, for example, to create a translucent white appearance.

[0011] Lightness or light transmittance is expressed as the luminance value Y (luminance) according to the CIE standard color system or L in the CIELAB color system. * The German domestic translation of the international CIE standard is specified in DIN 5033. The CIELAB color model is based on DIN EN ISO 11664-4 "Colorimetry - Part 4: CIE 1976 L * a * b * It is standardized as a "color space."

[0012] The spectrophotometric measurements required for this purpose are carried out in the spectral range of 380-780 nm on polished samples within the scope of the present invention. From the spectral values measured in this range, which is the visible light spectrum, the light transmittance is calculated by selecting a standard light source and observer angle for the thickness in question.

[0013] For glass ceramics, the coordinate L is calculated according to the following formula: * ,a * ,b * Value c according to the CIELAB color system using * It is common to use saturation as a measure of color:

number

[0014] The CIELAB color coordinates can be calculated from the CIE color coordinates and luminance Y as is known. * Values are determined by spectrophotometric measurements of transmittance using selected parameters for a standard illuminant and observer angle.

[0015] The scattering of glass-ceramics is determined by measuring the turbidity (haze), which, according to ASTM D1003-13, is the percentage of transmitted light that deviates, on average, from the incident luminous flux by more than 2.5°.

[0016] The industrial production of transparent glass-ceramics is carried out in several stages. First, a crystalline starting glass is melted and refined from a mixture of cullet and powdered batch raw materials. The molten glass reaches temperatures ranging from 1550°C up to 1750°C, usually up to 1700°C. In some cases, fining at temperatures above 1750°C, typically around 1900°C, is also used. For transparent glass-ceramics, arsenic oxide and antimony oxide are industrially and economically recognized fining agents for their good bubble quality at conventional fining temperatures below 1700°C. Arsenic oxide is particularly advantageous for the transparency (high brightness and low color) of glass-ceramics. Even when tightly integrated into the glass framework, these fining agents have safety and environmental disadvantages. Therefore, special precautions must be taken during raw material extraction, raw material processing, and glass production due to evaporation from the melt. Therefore, considerable development efforts have been made to replace these substances, but they face industrial and economic disadvantages.

[0017] After melting and fining, the glasses are generally subjected to hot forming by casting, pressing, rolling, or floating. Many applications require glass-ceramics in the form of flat plates, e.g., sheets. Rolling and floating are used to produce plates. For the economical production of these LAS glasses, low melting temperatures during hot forming and low processing temperatures (V) are required. A Furthermore, the glass should not exhibit devitrification upon forming, i.e., large crystals greater than about 5 μm should not form in the glass-ceramic article, which would reduce its strength or be visually objectionable. A (viscosity 10 4Since the melting temperature is usually close to the processing temperature (dPas), it is necessary to ensure that the maximum devitrification temperature of the melt is close to, and preferably lower than, the processing temperature to avoid the formation of larger crystals. When rolling, the critical area is the contact between the molten glass and the drawing slot (commonly made of a Pt / Rh alloy) after rolling and before cooling. In the case of floating, this is the contact between the glass and the spout lip, and the area before the float bath where the glass comes into contact with liquid Sn, where the glass has a high crystal growth rate.

[0018] The crystalline LAS glass is transformed into a glass-ceramic in a subsequent temperature process by controlled crystallization (ceramization). This ceramization is carried out in a two-stage temperature process. First, nuclei are formed at temperatures between 680°C and 800°C, typically from ZrO2 / TiO2 mixed crystals. SnO2 also participates in the nucleation. High-temperature quartz mixed crystals grow on these nuclei at elevated temperatures. The maximum manufacturing temperature of approximately 900°C homogenizes the structure of the glass-ceramic and adjusts its optical, physical, and chemical properties. A short ceramization time is advantageous for economical production.

[0019] Increasing the temperature in the range of approximately 950°C to 1250°C leads to a further transformation to keatite mixed crystals. This transformation increases the thermal expansion coefficient of the glass-ceramic, and further crystal growth and the accompanying light scattering cause it to change from transparent to translucent to opaque in appearance.

[0020] The crystalline phases are also referred to in the literature as "β-quartz" or "β-eucryptite" for high-temperature quartz mixed crystals, and "β-spodumene" for keatite mixed crystals.

[0021] As an alternative to arsenic oxide and antimony oxide, the environmentally friendly fining agent SnO2 is increasingly being promoted, either alone or in combination with one or more fining additives such as halides (F, Cl, Br), CeO2, MnO2, Fe2O3, sulfur compounds, etc.

[0022] However, the use of SnO2 does not come without disadvantages. SnO2 itself is industrially ineffective as a fining agent and requires higher temperatures to release the fining-active oxygen. High concentrations of SnO2, about 1 wt. % at the As2O3 application scale, are disadvantageous due to the devitrification of Sn-containing crystals during hot forming. The second major disadvantage of transparent glass-ceramics when arsenic oxide is replaced by tin oxide as a fining agent is that SnO2 causes additional absorption, resulting in an increase in color. The absorption is mainly due to colored complexes with the nucleating agent TiO2. Sn 2+ The absorption increases with increasing proportion of , and therefore is enhanced at higher fining temperatures. The Sn / Ti colored complexes are more strongly colored than the known Fe / Ti colored complexes, and because of this disadvantage, it has been difficult to replace the fining agent arsenic oxide with tin oxide in transparent glass-ceramics. The Fe / Ti colored complexes produce reddish-brown colors, while the Sn / Ti colored complexes produce yellow-brown colors. The absorption mechanism of both colored complexes is presumed to be based on electron transition (charge transfer) between two adjacent multivalent cations.

[0023] The formation of the charge-transfer colored complexes occurs mainly during crystallization. To reduce the concentration of the colored complexes, it is advantageous to shorten the nucleation time and crystallization time. However, shortening the nucleation time increases light scattering, and shortening the crystallization time leads to non-uniformity of the product.

[0024] The industrial batch raw materials for the melt contain further colouring elements as impurities, such as Cr, Mn, Ni, V and especially Fe. Fe is not only impurified by Fe / Ti coloured complexes, but also by Fe 2+ or Fe 3+ However, due to the high cost of low-iron raw materials, it is uneconomical to reduce the Fe2O3 content to values below about 50 ppm.

[0025] In some established applications of glass-ceramics, heat-resistant specialty glasses, such as aluminosilicate or borosilicate glasses, are increasingly being used. Additional industrial measures, such as air cooling in fireplace windows or electronic temperature control in induction cooking surfaces, can reduce the operating temperatures and sometimes make the use of these specialty glasses possible. Compared to these glasses, the color of transparent glass-ceramics is a significant disadvantage. Therefore, there is a need to develop transparent glass-ceramics with reduced color.

[0026] Approaches to avoid (WO 2008 / 065167) or limit (WO 2008 / 065166) the nucleating agent TiO2, which is partly responsible for colored complexes in glass-ceramics, have not yet reached industrial realization. Higher contents of alternative nucleating agents ZrO2 and / or SnO2 are required, which leads to disadvantages during melting and forming, such as increased melting and forming temperatures and poor devitrification resistance during forming.

[0027] WO 2013 / 124373 describes the physical bleaching of transparent glass-ceramics containing high-quartz mixed crystals as the primary crystalline phase, free of arsenic and antimony except for unavoidable raw material impurities, by adding 0.005 to 0.15 wt. % Nd2O3. The principle of this physical bleaching is based on the cancellation of existing absorption bands by complementary absorption bands of the bleaching agent. Naturally, this leads to a decrease in brightness due to increased light absorption. To achieve favorable manufacturing conditions, i.e., low melting and molding temperatures, the exemplary glasses in this publication contain a high content of MgO, a viscosity-reducing component, of 0.44 to 0.93 wt. %. In addition to the high MgO content, the relatively high SnO2 content of the exemplary glass-ceramics contributes to the color c * It is disadvantageous for

[0028] WO 2013 / 171288 discloses transparent, low-color, non-scattering glass-ceramic articles, glass-ceramics, and precursor glasses containing high-temperature quartz mixed crystals. The composition of the LAS glass-ceramic does not contain arsenic oxide, antimony oxide, or rare earth oxides such as Nd2O3, except in unavoidable trace amounts. For satisfactory fining, the glass has a higher SnO2 content. Exemplary glasses according to this invention do not contain MgO to improve color and require high melting temperatures, particularly at processing temperatures of V. A For forming by rolling, due to the higher temperatures, this means a narrow process window and a reduced service life of the equipment.

[0029] WO 2016 / 038319 discloses a transparent, colorless, non-light-scattering glass-ceramic plate containing high-quartz mixed crystals and a chemical composition selected to be free of As, Sb, and Nd oxides. To ensure sufficient bubble quality, the minimum content of the fining agent SnO2 is selected to be higher. The disclosed composition range is unfavorable for color. The disclosed color value b * is only 6.4.

[0030] Therefore, developments must reconcile the many conflicting requirements of glasses and glass ceramics, such as favorable manufacturing properties without disadvantages to the product quality of glass ceramics, such as color, brightness, and low scattering, especially with short ceramming times.

[0031] The present invention provides - have favorable manufacturing characteristics for economical production, It is desirable that the transparent glass ceramics produced therefrom have low color, high brightness and low scattering, whereby short ceramming times are sought; The objective is to find a crystalline lithium aluminum silicate glass.

[0032] This problem is solved by a crystalline lithium aluminum silicate glass having the features of claim 1 and a glass ceramic produced therefrom having the features of claim 21.

[0033] It is also an object of the present invention to find methods for producing glasses and glass ceramics and their uses. These problems are solved by further independent claims.

[0034] The crystalline lithium aluminum silicate glass according to the present invention and the glass ceramic according to the present invention that can be produced from or has been produced from this glass have the following components (in weight % based on the oxide): Li2O 3 - 5 Al2O3 19 - 24 SiO2 62 - 70 TiO2 more than 1.6 - 2.8 ZrO2 1 - 2.5 MgO 0.01 - less than 0.5 SnO2 0.01 - less than 0.15 under the conditions (both in weight %): 0.005 < MgO × SnO2 < 0.06 (condition B1a) and having.

[0035] The unit of the numerical values of condition B1a is (weight %) 2 is.

[0036] Li2O, Al2O3 and SiO2 The oxides Li2O, Al2O3 and SiO2 are essential components of the high-temperature quartz mixed crystal phase and / or the keatite mixed crystal phase within the above-mentioned ranges, or will become essential components.

[0037] For crystallizable glasses and glass-ceramics produced therefrom, a Li2O content of 3 to 5.0 wt. % is desirable. The minimum content is required to achieve the desired low processing temperatures of the glass. At contents greater than 5 wt. %, it has been shown that it is difficult to achieve the desired zero thermal expansion of the glass-ceramic. Also, contents greater than 5 wt. % result in the desired low color temperature of the glass-ceramic. * Preferably, the LiO content is less than 4.5% by weight, more preferably less than 4.2% by weight, and particularly preferably less than 4% by weight. The minimum content is preferably 3.2% by weight, and particularly preferably 3.4% by weight.

[0038] A preferred range is 3% by weight to less than 4.5% by weight.

[0039] The Al2O3 content is between 19 and 24 wt%. Contents higher than 24 wt% are disadvantageous because mullite tends to devitrify during molding. Furthermore, higher contents have been shown to increase scattering at short ceramming times. Therefore, a maximum content of 23 wt% is preferred. Al2O3 contributes to the low processing temperature and less color change of the glass-ceramic. * The minimum content of Al2O3 is preferably at least 20% by weight, since this is advantageous for the

[0040] The content of the main component SiO2 is preferably at least 62% by weight, since this is beneficial for the required properties of the glass-ceramic, such as low thermal expansion and chemical resistance. Furthermore, scattering is reduced during short ceramming times. A minimum content of 64% by weight is particularly advantageous. The SiO2 content is preferably at most 70% by weight, since this component increases the processing and melting temperatures of the glass. The SiO2 content is preferably at most 68% by weight.

[0041] Nucleating agents TiO2, ZrO2 The component TiO2 is an effective nucleating agent and is essential for the transparency of glass-ceramics. TiO2 results in a high nucleation rate and therefore sufficient nucleation even at short ceramming times, resulting in small average crystallite sizes. This makes it possible to obtain glass-ceramics without visually disturbing scattering, even at short ceramming times.

[0042] However, higher TiO2 contents have a significant effect due to the formation of Fe / Ti and Sn / Ti colored complexes. Therefore, a TiO2 proportion of more than 1.6% by weight and up to 2.8% by weight is desirable. A minimum TiO2 content of 1.8% by weight is preferred. This minimum content is advantageous for reducing the ceramming time and avoiding scattering. TiO2 contents of more than 2% by weight are particularly preferred.

[0043] A maximum of 2.6 wt. % TiO2 is preferably included to limit color effects.

[0044] ZrO2 is contemplated as an additional nucleating agent. The ZrO2 content is 1-2.5 wt. %. Preferably, the ZrO2 content is limited to less than 2.2 wt. %, more preferably less than 2 wt. %. This is because higher contents can lead to poor batch melting behavior during glass production and can cause devitrification during molding due to the formation of Zr-containing crystals. This component helps to avoid increasing the content of the alternative nucleating agent TiO2, thereby reducing the color c * The minimum content of ZrO2 is preferably 1.6% by weight.

[0045] SnO2 The selection of the SnO2 content is of particular importance within the scope of the present invention, as this component is particularly important for the color of the glass-ceramic due to the formation of Sn / Ti colored species during crystallization.

[0046] In particular, the manufacturing characteristics of conventional forming using water-cooled rolls have been attracting renewed attention. Industrial tests using SnO2-fined LAS glass containing 0.18 wt% SnO2, as disclosed in WO 2013 / 124373, have shown that Sn-containing roll coatings accumulate during forming. Due to the effect of tin oxide as a nucleating agent, this roll coating induces an increase in surface crystals on the cooled glass ribbon in contact with the molten glass. These crystals are visually noticeable and can reduce strength. Removal of the roll coating involves production loss. The present invention mitigates this economic disadvantage of roll coatings.

[0047] Even during the thermal deformation of glass plates by a burner, reheating due to the pressing of particles from the roll coating can induce crystals at the bend seams, which grow during ceramization and become visually disturbing. Glass-ceramic articles deformed in this way are used, for example, as angled fireplace windows.

[0048] To avoid these disadvantages, the SnO2 content is limited compared to the prior art to less than 0.15 wt. %, preferably less than 0.12 wt. %, more preferably less than 0.10 wt. %, even more preferably less than 0.08 wt. %, and particularly preferably less than 0.05 wt. With a decrease in the SnO2 content, the color and roll coating decrease continuously. A clear improvement in the formation of surface crystals during forming appears at SnO2 levels below 0.10 wt. %.

[0049] A minimum content of 0.01% by weight of SnO2 is required as a lower limit. Polyvalent tin oxide prevents bubble formation (reboiling) in the precious metal parts in the melting tank, especially when the fining agents arsenic oxide or antimony oxide are not used. Even at low contents, SnO2 acts as a fining agent and, in combination with industrial measures in the melting tank, ensures the required bubble quality. Preferably, the glass and glass-ceramics produced therefrom contain at least 0.03% by weight of SnO2, particularly preferably at least 0.04% by weight.

[0050] A particularly preferred range, taking into account all aspects related to low color and economical manufacturing characteristics, is 0.03 to less than 0.10 wt. % SnO2.

[0051] MgO Another important factor for achieving the desired properties of glass-ceramics is the MgO content. The component MgO has a strong influence on many properties because it is a constituent of both the mixed crystal and the residual glass phase. This component promotes economical production by lowering the melting and processing temperatures of the glass. The MgO content is at least 0.01 wt. %, preferably at least 0.05 wt. %, more preferably at least 0.1 wt. %, and especially preferably at least 0.15 wt. In glass-ceramics, this component increases thermal expansion, leading to particularly unfavorable color enhancement. This is due to the promotion of the formation of Fe / Ti and Sn / Ti color species.

[0052] The MgO content is preferably less than 0.5 wt. %, more preferably at most 0.4 wt. %, and particularly preferably at most 0.35 wt. The preferred MgO range of 0.1 wt. % to 0.4 wt. % allows for a particularly good compromise between the requirement for low color in the glass-ceramic and low processing temperatures, and allows for the thermal expansion of the glass-ceramic to be adjusted to near zero.

[0053] MgO×SnO2 The product of the components MgO x SnO2 is crucial for achieving a balance between low color, fining potential, and low melting and molding temperatures. Therefore, the color c of glass-ceramics can be obtained economically. * The luminance Y can be further improved by further reducing the luminance, and the disadvantages of special glass with a high lightness value and less color can be reduced.

[0054] In the glass according to the invention, the product of the components MgO×SnO2 (both in weight %) is less than 0.06, preferably less than 0.05, preferably less than 0.04, more preferably less than 0.03, and particularly preferably less than 0.025. The product of this component is desirably greater than 0.005, preferably greater than 0.01, more preferably greater than 0.012, and particularly preferably greater than 0.015.

[0055] This is an essential condition for achieving both the desired favorable manufacturing characteristics of the glass and low color and high lightness.

[0056] Advantageously, for the product of this component, 0.01 < MgO×SnO2 < 0.05 (Condition B1b) is applied.

[0057] In a series of tests using various MgO contents and SnO contents, it was found that the MgO content characteristically affects the absorption by the Sn / Ti colored complex. Optical evaluation of the spectrum showed that the Sn / Ti absorption band in the blue color is affected not only in intensity but also in its position in the visible spectrum. By reducing the MgO content, the maximum position of the absorption band shifts in the direction of the invisible UV range. Here, since the sensitivity of the human eye is relatively low, this results in a desired reduction in color and an increase in lightness. If the low SnO2 content reduces the intensity of the Sn / Ti absorption band, the overall effect is particularly advantageous. Therefore, the low contents of MgO and SnO2 according to the invention within the scope of Condition B1a, particularly within the scope of Condition B1b, are important for the desired transparency, high lightness, and low color c * for transparency, which is understood as high luminance Y and low color c * The preferred values are Y > 83% and c * ≤ 4.

[0058] A narrowly defined composition range has been found that combines favorable manufacturing characteristics with low color, high light transmittance, and low scattering of the LAS glass-ceramic. In particular, the low color of the transparent glass-ceramic according to the invention is color c *is typically less than 1, which approaches values typical for temperature-stable specialty glasses.

[0059] Favorable manufacturing characteristics for economical production include low cost batch materials, low melting and forming temperatures, devitrification resistance, and short ceramming times, which achieve high brightness without visually objectionable light scattering (turbidity).

[0060] Furthermore, the increased ratio of the nucleating agent TiO2 / SnO2 compared to the prior art is advantageous for this. Preferably, 18≦TiO2 / SnO2<200 (condition B2) applies. Even more preferably, this ratio should be at least 20, and particularly preferably at least 25. Both components increase the color, particularly through the absorption of Sn / Ti colored complexes. The low SnO2 content according to the present invention reduces the concentration of these colored complexes, achieving the desired high brightness and low color. A higher TiO2 content can then be selected, increasing the ratio. This allows for shorter ceramization times without problematic scattering and improves devitrification resistance. The preferred upper limit is less than 100.

[0061] Preferably, a value range of 3.8 to 4.8% by weight applies to the total of nucleating agents TiO2 + ZrO2 + SnO2 (condition B3). A minimum content is required for sufficiently rapid nucleation. To further reduce scattering during rapid ceramization, a minimum content of 4% by weight is preferred. The upper limit of 4.8% by weight is due to the requirement of resistance to devitrification.

[0062] alkali The alkalis Na2O and K2O lower the melting and processing temperatures during glass forming. They accelerate the melting of the sparingly soluble raw materials ZrO2 and SiO2. Because these elements are not incorporated into the crystalline phase but remain in the residual glass phase of the glass-ceramic, their content must be limited to a maximum of 1.5% by weight. Excessively high contents impair the crystallization behavior during the transformation of the crystalline starting glass into the glass-ceramic and adversely affect the time-temperature stability of the glass-ceramic.

[0063] Preferably, the Na2O content is 0 wt% or more than 0 wt%, and particularly preferably, the glass contains at least 0.1 wt% of Na2O. The maximum ratio is preferably 1.5 wt%, particularly 1 wt%. Preferably, the ratio of Na2O is 0.1 wt% to 1.5 wt%.

[0064] Preferably, the K2O content is 0 wt% or more than 0 wt%, and particularly preferably, the glass contains at least 0.1 wt% of K2O. The maximum ratio is preferably 1.5 wt%, particularly 1 wt%. Preferably, the ratio of K2O is 0.1 wt% to 1.5 wt%.

[0065] In a preferred embodiment, 0.2 wt% ≤ Na2O + K2O ≤ 1.5 wt% (Condition B4a) is applied. The total alkali Na2O + K2O is more preferably at most 1.2 wt%. In order to further improve the melting property and lower the processing temperature, it is particularly preferred that the total alkali Na2O + K2O is at least 0.4 wt%. Particularly preferably, 0.2 wt% ≤ Na2O + K2O ≤ 1.2 wt% (Condition B4b) is applied.

[0066] To lower the melting temperature, it has been shown that the component Na2O is more preferable than K2O. Therefore, it is preferable that the Na2O content is higher than the K2O content (both in wt%). It is particularly advantageous that 1 < Na2O / K2O ≤ 10 (Condition B5) is applied. The lower limit of the ratio Na2O / K2O is preferably 2. The preferred upper limit of Na2O / K2O is less than 8.

[0067] Alkaline earth Similar to the alkalis Na2O and K2O, the alkaline earths CaO, SrO and BaO are also not incorporated into the mixed crystal phase and remain in the residual glass phase of the glass-ceramic. These are advantageous for lowering the melting temperature and the processing temperature. An excessively high content rate impairs the nucleation behavior and crystallization behavior when the crystalline glass transforms into the glass-ceramic, and has an adverse effect on the time / temperature stability of the glass-ceramic.

[0068] The component CaO is treated at a temperature of V A It has been found to be advantageous for reducing the temperature and improving the devitrification resistance. However, CaO leads to an increase in color and scattering at short ceramming times. CaO is contained in a maximum content of 2% by weight, preferably a maximum of 1% by weight. In order to minimize scattering at short ceramming times, an upper limit of the CaO content of less than 0.8% by weight is particularly preferred. Preferably, 0% by weight or more than 0% by weight, particularly preferably 0.05% by weight or more, even more preferably at least 0.1% by weight, and particularly preferably at least 0.3% by weight of CaO is applied. A preferred range is 0.05% by weight to 2% by weight.

[0069] The BaO content is preferably up to 4 wt.%. The SrO content is preferably up to 2 wt.%. The BaO content is preferably up to 2.5 wt.%. The SrO content is preferably up to 1.5 wt.%. A BaO content of 0 wt.% or more than 0 wt.%, at least 0.2 wt.%, is particularly preferred.

[0070] The preferred range of BaO is 0.2% by weight to 2.5% by weight.

[0071] The proportion of SrO is preferably 0% by weight, particularly preferably more than 0% by weight, in particular 0.01% by weight or more.

[0072] The preferred range of SrO is 0.01% by weight to 2% by weight.

[0073] In order to reduce the melting and processing temperatures, the sum of the SrO and BaO contents is preferably 0.5 to 2.5 wt. % (condition B6). Higher contents are detrimental to the time / temperature stability of the glass ceramic.

[0074] The alkalis Na2O and K2O and the alkaline earths CaO, SrO, and BaO accumulate not only in the residual glass phase between the crystals but also on the surface of the glass-ceramic. During ceramization, a glassy surface layer approximately 50–1000 nm thick is formed, which is almost crystal-free, enriched in these elements, and depleted in Li2O. This glassy surface layer has a positive effect on the acid resistance of the glass-ceramic surface. A sufficient glassy layer thickness of at least 50 nm requires minimum contents of both classes of elements, i.e., alkalis and alkaline earths. Contents higher than the upper limit can increase the thickness of the glassy layer, which is detrimental to the strength of the glass-ceramic.

[0075] ZnO The component ZnO is advantageous for lowering the melting and processing temperatures of the glass and for reducing scattering during short ceramming times. ZnO is incorporated into the mixed crystal phase and partly remains in the residual glass phase. This component, like the component Li2O, contributes to a reduction in the thermal expansion of the glass-ceramic. Due to the tendency for ZnO to evaporate from the molten glass and the required zero expansion of the glass-ceramic, the ZnO content is limited to a maximum value of 3% by weight. A ZnO content of up to 2.5% by weight, particularly preferably up to 2.0% by weight, is preferred. A ZnO content of 0% by weight or greater than 0% by weight is preferred. A minimum content of 0.5% by weight, particularly preferably greater than 1% by weight, is preferred. The ZnO content is preferably between 0.5% and 3% by weight.

[0076] P2O5 To improve meltability and devitrification resistance during molding, up to 4% by weight of P2O5 can be included. Higher contents are detrimental to chemical resistance. Preferably, 0% or more by weight of P2O5 is used. A preferred lower limit is 0.01% by weight, particularly preferably 0.02% by weight. A preferred upper limit is 2% by weight of P2O5. A preferred range is 0.01% to 4% by weight.

[0077] B2O3 The addition of up to 1% by weight of B2O3 also improves the meltability and devitrification resistance, but this is detrimental to the time / temperature stability of the glass-ceramic. Preferably, the glass-ceramic is technically free of B2O3, i.e., the content is less than 1000 ppm.

[0078] Fe2O3 Due to the high cost of low-iron batch raw materials, it is uneconomical to limit the Fe2O3 content of the crystallizable glasses to values below 0.008 wt.%, i.e., below 80 ppm. On the other hand, with increasing Fe2O3 content, the concentration of Fe / Ti colored complexes in the glass-ceramic also increases. Color (saturation) c * and absorption reduces the luminance Y. Therefore, it is desirable that the crystallizable glass and the glass-ceramics produced therefrom contain a maximum of 0.025 wt. % Fe2O3, preferably 0.02 wt. % Fe2O3.

[0079] colored compounds Due to the decrease in light transmittance and the increase in color, it is preferable that the glass does not contain, apart from unavoidable impurities, further coloring compounds such as Ce, Cr, Ni, Cu, V, Mo, W and / or S, which result in yellow, orange or red coloration. The content is preferably less than 20 ppm. A maximum content of 0.1% by weight is also acceptable.

[0080] Clarifying agent Fining can be supported by adding chemical fining agents such as arsenic oxide, antimony oxide or cerium oxide, and fining additives such as manganese oxide, sulfate compounds, halide compounds, preferably in a total content of up to 2.0% by weight.

[0081] In a preferred embodiment, the crystallizable glass or the LAS glass-ceramic produced therefrom has an environmentally friendly composition, which is understood to mean that the composition is industrially free of the common fining agents arsenic oxide and antimony oxide, i.e., the content is preferably less than 1000 ppm.

[0082] Both components may be present as impurities in a content of less than 0.2% by weight, preferably less than 0.1% by weight, particularly preferably less than 500 ppm. Except in exceptional cases, when arsenic-containing foreign cullet is added to the transparent glass-ceramic during melting for recycling reasons, it is preferable not to add them.

[0083] It is also preferable not to add halide compounds as fining aids. These evaporate during melting and reach the atmosphere in the melting tank. This results in the formation of corrosive compounds such as HF, HCl, and HBr, which are detrimental to the corrosion of refractory bricks in the melting tank and exhaust pipe. Therefore, the glass and glass ceramic preferably do not contain F, Cl, or Br except for unavoidable impurities, and their individual contents are usually less than 500 ppm.

[0084] It is preferred not to use cerium oxide and antimony oxide as this will deteriorate the color of the transparent glass-ceramic.

[0085] CoO The addition of CoO in an amount of up to 30 ppm can support decolorization. A CoO content of 0.1 ppm to 20 ppm CoO is preferred. Above 30 ppm, CoO causes a reddish tint in transparent glass-ceramics.

[0086] Nd2O3 The proportion of Nd2O3 can be 0% by weight or greater than 0% by weight.

[0087] In transparent glass-ceramics made from the lithium aluminum silicate glass according to the present invention, the problematic color due to Fe / Ti colored complexes and / or Sn / Ti colored complexes is reduced by adding Nd2O3 in a content of 0.005 to 0.5% by weight in a preferred embodiment. Below 0.005% by weight, the decolorizing effect is insignificant, and the preferred lower limit for Nd2O3 is 0.01% by weight, especially 0.03% by weight. Above 0.5% by weight, the absorption of the Nd band in the visible light range unnecessarily reduces brightness. Therefore, additions up to 0.2% by weight are preferred. The preferred range for Nd2O3 is 0.005 to 0.5% by weight.

[0088] If a percentage of 0% by weight is specified for a component, it means that the component in question is not contained in the raw material mixture. However, these components may be present as unavoidable impurities.

[0089] In a preferred embodiment, the crystalline lithium aluminum silicate glass according to the invention or an article made therefrom, or a glass-ceramic according to the invention made from the glass, preferably has the following composition in wt. % on an oxide basis: Li2O 3.2 to less than 4.5 Al2O319~23 SiO262~68 Na2O 0~1 K2O 0~1 Na2O+K2O 0.2~1.5 (condition B4a) MgO 0.05 to less than 0.5 CaO 0.05~2 SrO 0~1.5 BaO 0~2.5 ZnO 0~2.5 TiO2 1.8~2.8 ZrO21~less than 2.2 SnO2 0.01 to less than 0.12 TiO2+ZrO2+SnO23.8~4.8 (condition B3) P2O50~4 Fe2O3 0.008~0.025 under the conditions (both in wt%): 0.005 < MgO × SnO2 < 0.06 (Condition B1a) and having

[0090] According to a further embodiment, the crystalline lithium aluminum silicate glass or an article made therefrom, or a glass ceramic made from the glass preferably has the following composition in oxide-based wt%: Li2O 3.2 to less than 4.2 Al2O3 20 to 23 SiO2 62 to 68 Na2O 0.1 to 1 K2O 0 to 1 Na2O + K2O 0.2 to 1.2 (Condition B4b) MgO 0.1 to 0.4 CaO 0.05 to 1 SrO 0 to 1.5 BaO 0 to 2.5 SrO + BaO 0.5 to 2.5 (Condition B6) ZnO 0 to 2.5 B2O3 0 to 1 TiO2 1.8 to 2.8 ZrO2 1 to less than 2.2 SnO2 0.01 to less than 0.10 TiO2 + ZrO2 + SnO2 3.8 to 4.8 (Condition B3) P2O5 0 to 2 Fe2O3 0.008 to 0.02 under the conditions (both in wt%): 0.005 < MgO × SnO2 < 0.06 (Condition B1a) and having

[0091] To further improve the objectives of high light transmittance, economic production, and low color simultaneously, the crystalline lithium aluminum silicate glass or an article made therefrom, or a glass ceramic made from the glass particularly preferably has the following composition in oxide-based wt%: Li2O 3.2 to less than 4 Al2O3 20 to 23 SiO2 64 to 68 Na2O 0.1 - 1 K2O 0 - 1 Na2O + K2O 0.2 - 1.2 (Condition B4b) MgO 0.1 - 0.4 CaO 0.1 - 1 SrO 0 - 1.5 BaO 0.2 - 2 SrO + BaO 0.5 - 2 (Condition B6) ZnO 0.5 - 2.5 B2O3 0 - 1 TiO2 2 - 2.8 ZrO2 1.6 - less than 2.2 SnO2 0.03 - less than 0.10 TiO2 + ZrO2 + SnO2 3.8 - 4.8 (Condition B3) P2O5 0 - 2 Fe2O3 0.008 - 0.02 with the conditions (both in wt%): 0.005 < MgO × SnO2 < 0.06 (Condition B1a) and has.

[0092] In the above composition, it should be understood that the described components are at least 98 wt%, usually 99 wt% of the total composition. Compounds of a number of elements, such as F, Cl, alkali metals Rb, Cs, or elements such as Mn, Hf, etc., are common impurities in batch raw materials used industrially. Other compounds, such as compounds of elements W, Nb, Ta, Y, Mo, rare earths, Bi, V, Cr, Ni, may be contained in a small proportion, usually in the ppm range.

[0093] The water content of the crystalline glass for manufacturing the glass - ceramic is preferably 0.015 - 0.06 mol / l, depending on the selection of batch raw materials and process conditions during melting. This is 0.16 - 0.64 mm -1This corresponds to the β-OH value of the glass-ceramic. Upon transformation to glass-ceramic, an IR band changes, which can be used to determine the water content. This changes the β-OH value of the glass-ceramic without changing the water content. A method for determining the β-OH value is described, for example, in EP 1 074 520 A1.

[0094] Preferably, the crystallizable glass is 10 times lower than 1760°C. 2 dPas temperature and / or processing temperature V up to 1330 °C A , and / or the processing temperature V A The upper devitrification limit OEG is at least 15°C below the

[0095] The bubble quality of the crystalline lithium aluminum silicate glasses and glass ceramics produced therefrom preferably meets the bubble count requirement of less than 5 bubbles / kg, preferably less than 2 bubbles / kg. This applies to bubbles with a size of more than 0.1 mm. This is preferably ensured by the low content of the fining agent SnO2 according to the invention and / or by preferably additional industrial measures, such as the configuration of the tank with its walls and / or blowing nozzles, the energy utilization and throughput of the tank.

[0096] Since typical measures for sufficient fining at the low SnO2 contents according to the invention, such as adapting the tank throughput or structural measures of the melting tank, can result in additional costs, the crystallizable glass is preferably refined by high-temperature fining at temperatures above 1750°C.

[0097] Glass ceramic Crystalline lithium aluminum silicate glass is transformed into a glass-ceramic by a multi-step temperature process.

[0098] The glass ceramic has the same composition as lithium aluminum silicate glass.

[0099] The glass ceramic is preferably transparent.

[0100] According to a first embodiment, the glass ceramic contains high quartz mixed crystals as the main crystalline phase.

[0101] To minimize scattering in glass-ceramics that contain high-quartz mixed crystals as the primary crystalline phase, it is advantageous to minimize the crystallite size. However, until now, this has typically required longer nucleation and ceramming times, which are economically disadvantageous. The use of the compositions of the present invention results in glass-ceramics in which the nucleation and crystallization processes proceed more rapidly, thereby reducing ceramming times.

[0102] Due to the short ceramming time, the high-temperature quartz mixed crystal of the glass ceramic preferably has an average crystallite size of at least 25 nm after ceramming.Particularly preferably, the average crystallite size is greater than 35 nm.The upper limit is preferably less than 50 nm for the increase in scattering.

[0103] The proportion of high-quartz mixed crystal crystalline phase in the glass ceramic is preferably at least 60% by weight, preferably at most 80% by weight, which range is advantageous for obtaining the desired mechanical and thermal properties of the glass ceramic.

[0104] For a 4 mm thick transparent glass ceramic, the brightness Y is preferably greater than 83%, preferably greater than 84%, particularly preferably greater than 85%.

[0105] color c * is preferably at most 4, preferably less than 3.5, particularly preferably less than 3.

[0106] The lightness and color values apply to measurements using standard light D65, 2° on polished samples of 4 mm thickness according to standard DIN 5033.

[0107] Scattering (haze) is measured on a 4 mm thick polished sample of the LAS glass ceramic in accordance with ASTM D1003-13. The haze value is preferably less than 2.5%, more preferably less than 2%, and particularly preferably less than 1.8%. Above 2.5%, the turbidity is usually visually problematic. Values of less than 2% are preferred, since scattering may be noticeable in the case of dark, i.e., black, undercoats.

[0108] For this reason, the transparent glass ceramic according to the invention does not have any optically significant light scattering, and as a result, the view of objects and underlying coatings is not distorted when viewed through them, and luminous displays, such as displays or screens, below the glass ceramic plate are therefore clearly visible with sharp contours and no scattering.

[0109] The characteristics of the glass ceramic according to the invention are based on the combination of a defined composition, which preferably corresponds to the composition of the green glass from which it is derived, with an adapted rapid ceramming with a total duration of less than 300 minutes, using the method according to the invention and as illustrated in the examples.

[0110] The thermal expansion of the glass ceramic is preferably 0±0.5·10 in the temperature range from room temperature to 700°C. -6 It will be adjusted to a value around / K.

[0111] In another embodiment, the glass-ceramic contains keatite mixed crystals as the predominant crystalline phase. For economic reasons, it would be advantageous to be able to produce both transparent glass-ceramics with high quartz mixed crystals as the predominant crystalline phase and glass-ceramics with keatite mixed crystals as the predominant crystalline phase from a crystalline lithium aluminum silicate glass of the same composition. By designing the ceramming program, in particular by selecting the maximum temperature and the holding time, the appearance in the latter case can be adjusted from transparent to translucent to opaque.

[0112] The terms opaque, translucent, and transparent are understood from an application perspective with respect to the display ability of LEDs through the glass-ceramic article. A range of low brightness Y of a glass-ceramic plate, less than 2% in transmission, is referred to as opaque, as the display ability is not satisfactory. A range of higher brightness, but with visible scattering, with a haze value greater than 2.5%, is considered translucent.

[0113] The average crystallite size is preferably greater than 60 nm. The proportion of crystalline phase is greater than 60 wt. %, preferably greater than 80 wt. The combination of different properties of the two glass-ceramic embodiments allows many applications to be economically addressed.

[0114] The preferred shape of the glass ceramic according to the invention or the article produced therefrom is in the form of a plate. The plate preferably has a thickness of 2 mm to 20 mm, since this allows for important applications. A smaller thickness impairs strength, while a larger thickness requires a higher amount of material and is therefore uneconomical. Therefore, a thickness of less than 6 mm is preferably chosen, except for applications as safety glass, where high strength is important.

[0115] The preferred article according to the invention is a rolled glass ceramic plate. The maximum surface size of the article is limited in production by the width of the belt during hot forming (rolling or floating) and the size of the ceramizing furnace. For certain applications, such as fire protection glass or kitchen counters with integrated cooking zones, dimensions up to 3 m in side length are preferred, as this size fits the floor height of windows and cooking surfaces in commercial kitchens.

[0116] In this case, the glass ceramic plate and preferably the article produced therefrom can not only be flat, but also be three-dimensionally deformed. For example, folded, angled, or curved plates can be used. The plate can be rectangular or other shapes, and in addition to flat areas, it can also have three-dimensionally deformed areas, such as woks, or indented webs, or surfaces as bumps or depressions. The geometric deformation of the plate is carried out, for example, during hot forming with structured forming rolls, or by downstream hot forming of the starting glass, for example, with burners, infrared radiators, or by gravity drop. In the case of ceramicization, a supporting ceramic mold, such as a flatbed, is used to avoid uncontrolled changes in the geometric form. If required for the application, subsequent polishing on one or both sides is optionally possible.

[0117] Glass manufacturing method The method according to the invention for producing crystalline lithium aluminum silicate glass comprises: a) preparing a compounded batch from industrial raw materials; b) melting the blended batch and high temperature fining at a temperature above 1750°C; c) Cool the molten glass to a processing temperature V A forming the mixture at a temperature in the vicinity of the melt melting point; d) Cooling to room temperature in a stress relief furnace to remove unwanted stresses in the glass. It is characterized by:

[0118] Room temperature is understood to be 20°C.

[0119] The blend batch is formed to produce glass having the composition and properties according to the present invention after melting. The addition of 20-80% by weight of cullet to the blend batch preferably aids melting, allowing for higher tank throughput. A high-temperature fining unit is used, with the temperature of the molten glass in the melting tank being above 1750°C, preferably above 1850°C. For forming, a glass ribbon, preferably in the shape of a plate, is produced by rolling and cooled to room temperature in an annealing kiln to avoid stress. Plates of the desired size are produced from this glass ribbon after quality assurance regarding volumetric and surface defects.

[0120] The low melting temperature is advantageous for economical production and is ensured by the lower viscosity of the molten glass at high temperatures. 2 The temperature at which the so-called 10 2 The dPas temperature for the glass according to the invention is preferably below 1760°C, preferably below 1755°C, particularly preferably below 1750°C. Due to the low viscosity of the molten glass at high temperatures, the temperature in the melting tank can be adjusted lower, thereby extending the service life of the melting tank. Energy consumption in relation to the amount of glass ceramic produced is reduced. A low glass viscosity is also advantageous for bubble quality, since it promotes bubble rise and thus clarification.

[0121] Lowering the forming temperature is economically advantageous. The forming tool has a longer life and less heat is dissipated. Forming, usually by rolling or floating, is performed at temperatures up to 10 4 The melt viscosity is V dPa. A and in the glass according to the invention is preferably at most 1330°C, preferably at most 1325°C.

[0122] Crystallizable glasses have sufficient resistance to devitrification when formed from the melt. When formed in contact with forming materials (e.g., precious metals in the case of the drawing slit in a rolling process), no visually noticeable crystals are formed in the glass, which would seriously affect the strength of the glass-ceramic. The limiting temperature below which significant devitrification occurs, i.e., the upper devitrification limit (OEG), is preferably set at the processing temperature V A and particularly preferably at a treatment temperature V A This minimum difference defines a sufficient process window for the molding process. A -OEG is particularly advantageous, i.e., the temperature difference V A -OEG is a measure of devitrification resistance.

[0123] Suitable forming methods for plate-shaped shapes are rolling and floating in particular. The preferred forming method from molten glass is the two-roll method, which has the advantage of more rapid cooling when the composition tends to devitrify.

[0124] Ceramicization Method The next process step is ceramization on a flat or three-dimensional high-temperature stable platform (furnace support). Preferably, ceramization is carried out in a roller furnace.

[0125] The method according to the invention for producing a glass ceramic comprises the following process steps in the following order: a) The temperature of the crystallizable glass is raised to a temperature T in the range of 660°C to 730°C for 3 to 60 minutes. a raising the temperature to b) The temperature of the crystallizable glass is set to T within the nucleation temperature range. a to 800°C for 10 to 100 minutes; c) increasing the temperature of the glass containing the crystal nuclei to a temperature range of 850°C to 950°C, at which the crystal growth rate is high, within 5 to 80 minutes; d) maintaining the maximum temperature within the temperature range of 850°C to 950°C for 0 to 60 minutes, during which high-temperature quartz mixed crystal type crystals grow on the crystal nuclei; e) quenching the resulting glass ceramic to room temperature in less than 150 minutes The total duration of the ceramming of the glass is less than 300 minutes.

[0126] Preferably, the holding time in process step d) is between 1 and 60 minutes.

[0127] The required high heating rates can be achieved industrially in roller kilns. The temperature range of 660°C to 730°C corresponds approximately to the glass transition temperature. Above temperatures of 730°C to 800°C, the nucleation rate is in the high range, with the nucleation rate reaching a maximum between 750°C and 760°C.

[0128] T for 10 to 100 minutes a The nucleation temperature range is set to 800°C. The temperature of the glass containing the crystal nuclei is then raised within 5 to 80 minutes to 850 to 950°C, a temperature at which the high-temperature quartz mixed crystal phase is characterized by a high crystal growth rate. The maximum temperature within the 850 to 950°C temperature range is maintained for 0 to 60 minutes. During this process, the structure of the glass ceramic is homogenized and its optical, physical, and chemical properties are adjusted.

[0129] The resulting glass ceramic is then quenched to room temperature in less than 150 minutes and more than 10 minutes.

[0130] The total ceramming time is less than 300 minutes, preferably less than 200 minutes, particularly preferably less than 150 minutes.

[0131] Furthermore, transparent LAS glass-ceramics made from crystallizable glass achieve certain properties: high luminance Y and color c, so that the view of objects or underlying coatings and displays does not darken or change color. *It is desirable that the transparent glass-ceramic be free of visually disturbing light scattering so that the view and display therethrough is clear and undisturbed, which is desirable to ensure even with the desired short ceramming times.

[0132] The contents of components involved in the formation of crystalline phases and residual glass are optimized so that high brightness values, low color, and low scattering are achieved even with short ceramming times, whereby short ceramming times are understood to mean that the glass ceramic is produced from the crystalline LAS glass in less than 300 minutes, preferably less than 150 minutes, particularly preferably less than 100 minutes.

[0133] These preferred ranges, along with the composition ranges detailed further below, allow for low melting and processing temperatures V A The desired effects of favorable manufacturing properties such as minimized color, increased brightness, and minimized light scattering upon rapid ceramization in combination with the above are particularly advantageously obtained.

[0134] Use of glass ceramic Preferably, transparent lithium aluminum silicate glass ceramics comprising high-temperature quartz mixed crystals as the main crystalline phase are used as fire protection glass, fireplace sight glasses, baking oven sight glasses, in particular those used in pyrolysis furnaces, cooking surfaces which may have an underside coating, covers for lighting areas, safety glass panes, carrier plates, preferably used in laminates, or linings for furnaces preferably used in thermal processes.

[0135] In the case of fireplace viewing windows, it is desirable to have a good view of the combustion chamber and flame. In the case of cooking surfaces with a colored underside coating, it is desirable that the color of the underside coating is not altered by the color of the glass ceramic. For the above applications, the high values of brightness Y and low color c according to the present invention are desirable. * A combination of low and unobtrusive light scattering is preferred.

[0136] By applying an opaque coating to the upper and / or lower sides, it is possible to produce colored cooking surfaces from transparent glass ceramics with the required visual cover, making the technical components underneath invisible. The cooking surface is heated as usual by gas burners, radiant heating or induction.

[0137] The absence of a coating allows for the attachment of sensor areas, colored and white indicators, and displays.

[0138] The transparent glass-ceramic plate can be combined with upper and lower coatings, including partially transparent layers, as well as markings of cooking zones, for example. Various known coating types can be combined, including organic or inorganic decorative paints, glossy paints, silicone and sol-gel-based paint coatings, sputtered layers, metal layers, oxynitride layers, oxycarbide layers, etc. Layers can also be applied one on top of the other.

[0139] In the case of fireplace or oven viewing windows, for example, a coating may be desired to opaquely cover the edges of the glass panes. The coating on the upper or lower side of the glass-ceramic plate is arranged according to aesthetic requirements and specific requirements for chemical and physical properties.

[0140] The display device consists of light-emitting electronic components, such as light-emitting diodes, OLEDs, LCDs, or fluorescent displays. All types of displays are possible, both dot and flat, including seven-segment displays. The emission spectrum of a photoluminescent display can have one or more maxima and a wide range, so that the display appears colored (e.g., blue, purple, red, green, yellow, orange) or white. The glass-ceramic colorless c *This allows monochrome and color displays or screens to be produced without significant color shifts. The color of the display can be optionally changed by a color filter or color layer applied underneath. The color tone of the display can thus be influenced, and in some cases even corrected, when changed by the glass ceramic. Similarly, control elements, sensor elements, and control / operating elements, for example of the capacitive or inductive type, can be attached to the glass ceramic plate.

[0141] Alternatively, these applications can also be realized by transparent, translucent, or opaque lithium aluminum silicate glass-ceramics containing keatite mixed crystals as the predominant crystalline phase. In the translucent or opaque forms, they are preferably used as cooking surfaces, carrier plates (setter plates) for thermal processes, cover plates for microwave ovens or radiant heaters, and linings for combustion chambers. In this case, the brightness Y is preferably less than 30%.

[0142] A further preferred application of both glass-ceramics, whether containing high-quartz or keatite mixed crystals as the predominant crystalline phase, is as carrier plates or furnace linings. In the ceramic, solar, or pharmaceutical industries, or in medical technology, they are particularly suitable for production processes under high-purity conditions, such as furnace linings for chemical or physical coating processes, or as chemically resistant laboratory equipment. Furthermore, they are used as glass-ceramic objects for high-temperature or cryogenic applications, as furnace windows for incinerators, as heat shields for shielding against high-temperature environments, as reflectors, floodlights, projectors, beamers, and copier covers, for thermomechanical stress applications, such as in night vision devices, or as covers for heating elements, especially as cooking, grilling, or frying surfaces, in white goods, as radiator covers, as wafer substrates, as UV-protected objects, as facade panels, or as materials for housing components for electronic devices and / or glass covers for IT applications, such as mobile phones, laptops, and scanner glasses, or as bulletproof components.

[0143] The invention is illustrated by the following examples. [Brief explanation of the drawings]

[0144] [Figure 1] FIG. 1 shows the transmission curve of the glass ceramic of Example 13 (glass number 11) in Table 1. [Figure 2] FIG. 1 is a diagram illustrating the shift of an absorption band.

[0145] The crystallizable LAS glasses 1-11 according to the invention and comparative glasses 12-18 were melted from batch raw materials common in the glass industry at a temperature of 1620° C. for 4 hours.

[0146] The batch raw materials optionally used were lithium carbonate, aluminum oxide, aluminum hydroxide, aluminum metaphosphate, silica sand, sodium and potassium nitrate, sodium and potassium carbonate, magnesium oxide, lime, dolomite, strontium carbonate, barium carbonate, zinc oxide, tin oxide, titanium oxide, zirconium silicate, zirconium oxide, and optionally neodymium oxide.

[0147] As the main and industrial raw materials for the introduction of LiO, quartz, aluminum oxide, aluminum hydroxide, lithium carbonate, etc., which contain less than 150 ppm of FeO, are preferably used. This selection makes it possible to harmonize the requirements for economical raw materials and low impurity contents of coloring compounds of Fe, Ni, Cr, V, Cu, Mo, and S.

[0148] After melting the batch in a sintered quartz glass crucible, the experimental melt was transferred to a Pt / Rh crucible with an inner quartz glass crucible and homogenized by stirring for 60 minutes at a temperature of 1600° C. After homogenization, the glass was fined for 3 hours at 1640° C. For experimental melts, no high-temperature fining was performed.

[0149] Next, about 120 x 140 x 30 mm 3 Ingots of 1100 mm in size were cast and cooled to room temperature in a slow-cooling kiln starting at 660 °C to relieve stress. The castings were divided into sizes required for testing and ceramicization. Glass 11 was industrially melted in a production tank.

[0150] Table 1 lists the compositions and properties of the crystallizable glasses. The component contents and the relationships between the relevant components are also shown. Glasses 1-11 are glasses according to the present invention, i.e., examples, and Glasses 12-18 are comparative glasses outside the present invention, i.e., comparative examples. The compositions of Comparative Glasses 12-18 are outside the scope of the present invention and exhibit the noted disadvantages in terms of manufacturing properties (melting temperature, processing temperature, devitrification resistance, roll coating) and / or color, brightness, and scattering after transformation into glass-ceramics. Due to typical impurities in the industrial batch raw materials used, the total of the composition does not add up to exactly 100% by weight. Typical impurities are F, Cl, B, Mn, Rb, Cs, and Hf, usually less than 0.2% by weight, even if not intentionally introduced into the composition. Impurities are often introduced by the raw materials of the related components, such as Rb and Cs from Na or K raw materials, or Hf from Zr raw materials.

[0151] The water content of the crystallizable glasses measured by IR spectroscopy is shown in Table 1.

[0152] The glass transition temperature Tg [℃] and the processing temperature V A [℃], 10 2 dPas temperature [℃], upper limit of devitrification OEG [℃] and devitrification resistance V A The OEG is also listed in Table 1. For the OEG measurement, the glass is melted in a Pt / Rh10 crucible. The crucible is then held at various temperatures within the processing temperature range for 5 hours. The OEG temperature is determined by the highest temperature at which the first crystals appear at the interface between the molten glass and the crucible wall.

[0153] Table 2 relates to glass-ceramics containing high quartz mixed crystals as the predominant crystalline phase, produced from the glasses of Table 1. Here, Examples 1 to 13 are working examples, and Examples 14 to 20 are comparative examples.

[0154] For each specified ceramicization program, i.e., Program 1 or Program 2, the glass-ceramic properties, i.e., spectral transmittance at 400 nm [%], infrared transmittance at 1600 nm [%], thermal expansion from 20 to 700 °C [10-6 / K], and the phase content [volume %] of the main crystalline phase consisting of high-temperature quartz mixed crystals, as well as the average crystallite size [nm], measured using X-ray diffraction, are shown in Table 2. The light transmittance Y according to the CIE color system and the value c as a measure of color (saturation) are also shown. * Color coordinates L in the CIELAB system using * ,a * ,b * , and the haze value as a measure of scattering is also shown in Table 2.

[0155] Table 3 shows examples 21 and 22 of glass-ceramics containing keatite mixed crystals as the predominant crystalline phase, produced from glass 10 of Table 1. In addition to the transmittance values, color values for diffuse reflectance measurements are also shown. Furthermore, the appearance of the examples is qualitatively described.

[0156] Ceramicization Program 1~3 Ceramization program 1 involves heating to 720 °C for 24 min in a laboratory furnace that allows for high heating rates. In the temperature range of 720 °C to 800 °C, the heating rate is reduced to allow for sufficient nucleation and to avoid visually disturbing scattering.

[0157] The heating rate is further reduced from 800°C to the maximum temperature of 890°C, due to the crystallization of high-quartz alloys in this range. The accompanying shrinkage process must not proceed too rapidly, otherwise irregularities in the article may result. This temperature range also increases the formation of problematic Fe / Ti and Sn / Ti colored complexes. The total time from 800°C to the maximum temperature of 890°C is 53 minutes, followed by a 10-minute hold time. At the maximum temperature, the composition of the crystals and residual glass is determined, homogenizing the microstructure. This determines the chemical and physical properties of the glass-ceramic. After controlled cooling to 600°C, the furnace door is opened and the sample is rapidly cooled to room temperature.

[0158] Ceramicization program 1 (ceramization time 136 min): a) From room temperature to T in 24 minutes aRapid heating to 720°C b) T in 20 minutes a = Heat from 720°C to 800°C (heating rate 4°C / min), c) Heating from 800°C to 890°C in 53 minutes (heating rate 1.7°C / min); d) a maximum temperature of 890°C with a holding time of 10 minutes; e) Cool from 890°C to 600°C (at 10°C / min) within 29 minutes, then rapidly cool to room temperature.

[0159] Ceramization Program 2 shortens the overall ceramization time and extends the nucleation time. Ceramization Program 2 involves heating to a temperature of 720°C in 24 minutes in the ceramization furnace. Between 720°C and 800°C, the heating rate is further reduced to allow for sufficient nucleation and avoid visually disturbing scattering. The total time from 720°C to 800°C is 33 minutes. Above 800°C, crystallization of the desired high-quartz mixed phase occurs. The total time from 800°C to the maximum temperature of 885°C is 28 minutes. A 10-minute hold time at the 885°C maximum temperature establishes the crystal and residual glass composition and homogenizes the microstructure. After controlled cooling to 800°C at a rate of 8.5°C / min for 10 minutes, the furnace door is opened and the sample is quenched to room temperature. In summary, Ceramicization program 2 (ceramization time 105 minutes): a) From room temperature to T in 24 minutes a Rapid heating to 720°C (heating rate 30°C / min), b) T in 33 minutes a = Heat from 720°C to 800°C (heating rate 2.4°C / min), c) Heat from 800°C to 885°C within 28 minutes, heating at 1°C / min to 820°C and then at 8°C / min to 885°C; d) a maximum temperature of 885°C with a holding time of 10 minutes; e) Cool to 800°C within 10 minutes, then rapidly cool to room temperature.

[0160] Additional ceramming program 3 transformed the crystallizable glass No. 10 (Table 1) into a glass-ceramic containing keatite mixed crystals as the predominant crystalline phase. This program followed the same procedure as program 2 up to 885 °C (step d), and then, unlike program 2, heated to a maximum temperature of T at a heating rate of 10 °C / min without a hold time at 885 °C. max Hold time t max (See Table 3 for details.) The sample was cooled from the maximum temperature to 800°C at 10°C / min, and then rapidly cooled to room temperature.

[0161] Transmission measurements were performed on 4 mm thick polished plates using a Perkin-Elmer Lambda 900 instrument under standard illuminant D65 at a 2° angle. From the measured spectral values in the visible light spectrum range of 380 nm to 780 nm, the luminance Y was calculated according to DIN 5033 for the selected standard illuminant D65 and an observer angle of 2°.

[0162] From these measurements, the color coordinates L in the CIELAB system are calculated. * ,a * ,b * , and the value c * Diffuse reflectance measurements were also carried out in accordance with DIN 5033 using these parameters.

[0163] The scattering of glass ceramics is determined by measuring the turbidity (haze), which is measured on double-polished 4 mm thick plates using a commercial measuring device "haze-guard plus" from BYK-Gardner under standard illuminant C in accordance with standard ASTM D1003-13 and characterized by the haze value.

[0164] Glass 11 was industrially melted. The composition was optimized according to the requirements for economical production and transparency of lithium aluminum silicate glass ceramics. It has a low 10 2 dPas temperature, low processing temperature V AThe glass melt was refined at a high temperature of approximately 1850°C for 15 minutes. The bubble quality of this glass was excellent, with less than 2 bubbles per kg of glass. During forming, a 4 mm thick glass ribbon with smooth surfaces was rolled and cooled in a slow-cooling kiln to avoid stress. The formation of Sn-containing roll coatings was reduced compared to glasses with higher SnO2 contents. Plates measuring 500 x 500 x 4 mm were cut from this glass ribbon and cerammed in an industrial roller furnace. The ceramming program corresponded to program 2, with the crystallizable glass plate mounted on a flat base plate. The resulting transparent glass-ceramic plate had very good flatness of less than 0.3% of its edge length. The properties of this glass-ceramic are listed in Table 2 as Example 13. The transmission curve of this glass-ceramic according to the invention is shown in Figure 1. The transparency was within the advantageous range of the invention, with a brightness Y of 84.7% and a color c. * The value was 3.1, and there was no visually significant scattering.

[0165] A further comparative glass 18 (see Table 1) essentially had the composition of glass 1, but the MgO content was increased to 0.77 wt. %. Comparative glass 18 was converted to a glass-ceramic using ceramming program 1 (see comparative example 20 in Table 2). This comparative example 20 is contrasted with inventive example 1 in Table 1 of FIG. 2, which is glass 1 similarly transformed according to the same ceramming program 1. FIG. 2 shows the described effect of the shift in absorption bands that can be attributed to different MgO contents. The Sn / Ti absorption band in the blue range of visible light is affected in terms of intensity and position in the visible spectrum. Depending on the MgO content and the product of the components MgO×SnO2 according to the invention, a higher spectral transmittance is achieved in the short-wave range of the spectrum, which is responsible for the color c * MgO × SnO2 = 0.22 and color c * Compared with Example 1 where MgO×SnO2=0.06 and c=2.6, the value of Comparative Example 20 is * =3.2.

[0166] Typical impurities analyzed were 0.04 wt% HfO2, 8 ppm As2O3, 1 ppm Cr2O3, 1 ppm CuO, 3 ppm MnO2, 4 ppm MoO3, 1 ppm NiO, and 3 ppm V2O5.

[0167] [Table 1-1]

[0168] [Table 1-2]

[0169] [Table 1-3]

[0170] [Table 2-1]

[0171] [Table 2-2]

[0172] [Table 2-3]

[0173] [Table 3]

Claims

1. A crystalline lithium aluminum silicate glass for producing a transparent glass-ceramic, comprising (in weight percent on an oxide basis): Li ２ O3~5 <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"> 1124 Yes ２ 62~70 TiO ２ 1.6~2.8 ZrO ２ 1~2.5 MgO 0.01 to less than 0.5 SnO ２ 0.01 to less than 0.15 and conditions (both wt%): 0.01<MgO×SnO 2 <0.05 (condition B1b), A crystalline lithium aluminum silicate glass, characterized in that said glass does not contain, apart from unavoidable impurities, further coloring compounds of V and Mo which would result in a yellow, orange or red coloration.

2. The component TiO ２ and SnO ２ To, 18≦TiO ２ SN ２ ≦200 (Condition B2) 2. The crystalline lithium aluminum silicate glass according to claim 1, wherein

3. The nucleating agent includes 3.8 wt% ≤ TiO ２ +ZrO ２ +SnO ２ ≦4.8 wt% (Condition B3) 3. The crystalline lithium aluminum silicate glass according to claim 1, wherein the following is applied:

4. Na in a proportion of 0.1% to 1.5% by weight ２ 4. The crystalline lithium aluminum silicate glass according to claim 1, further comprising O.

5. K in a proportion of 0.1% to 1.5% by weight ２ 5. The crystalline lithium aluminum silicate glass according to claim 1, further comprising O.

6. 0.2% by weight≦Na ２ O+K ２ 6. Crystalline lithium aluminum silicate glass according to claim 5, characterized in that O≦1.5 wt. % (condition B4a) applies.

7. 1≦Na ２ O / K ２ 6. Crystalline lithium aluminum silicate glass according to claim 5, characterized in that O≦10 (condition B5) applies.

8. 8. Crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains CaO in a proportion of 0.05% to 2% by weight.

9. 9. Crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains BaO in a proportion of 0.2% to 2.5% by weight.

10. 10. Crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains SrO in a proportion of 0.01% to 2% by weight.

11. 11. Crystalline lithium aluminum silicate glass according to claim 10, characterized in that 0.5% by weight≦SrO+BaO≦2.5% by weight (condition B6) applies.

12. 12. Crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains ZnO in a proportion of 0.5% to 3% by weight.

13. P in a proportion of 0.01% to 4% by weight ２ O ５ 13. The crystalline lithium aluminum silicate glass according to claim 1, wherein the glass contains:

14. 14. Crystalline lithium aluminum silicate glass according to claim 1, characterized in that the glass is technically free of arsenic oxide and antimony oxide.

15. Nd in a proportion of 0.005% to 0.5% by weight ２ O ３ 15. The crystalline lithium aluminum silicate glass according to claim 1, wherein the glass contains:

16. Consisting of the following (by weight on an oxide basis): Li ２ O 3.2 to less than 4.5 <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"> 11~23 Yes ２ 62~68 Na ２ O 0~1 K ２ O 0~1 Na ２ O + K ２ O 0.2 to 1.5 (Condition B4a) MgO 0.05 to less than 0.5 CaO 0.05 to 2 TO ２ 1.8~2.8 ZrO ２ 1 to less than 2.2 SnO ２ 0.01 to less than 0.12 TiO ２ + ZrO ２ + SnO ２ 3.8 to 4.8 (Condition B3) Fe ２ O ３ 0.008~0.025 2. The crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains MgO×SnO 2 in a ratio of 0.01<MgO×SnO 2 <0.05 (condition B1b).

17. Consisting of the following (by weight on an oxide basis): Li ２ O 3.2 to less than 4.2 <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"> 25~23 Yes ２ 62~68 Na ２ O0.1~1 K ２ O 0~1 Na ２ O+K ２ O 0.2~1.2(Condition B4b) MgO 0.1-0.4 CaO 0.05 to 1 SrO 0-1.5 BaO 0-2.5 SrO+BaO 0.5 to 2.5 (condition B6) ZnO 0-2.5 B ２ O ３ 0~1 TO ２ 1.8~2.8 ZrO ２ 1 to less than 2.2 SnO ２ 0.01 to less than 0.10 TiO ２ + ZrO ２ + SnO ２ 3.8 to 4.8 (Condition B3) P ２ O ５ 0~2 Fe ２ O ３ 0.008~0.02 2. The crystalline lithium aluminum silicate glass according to claim 1, characterized in that it contains MgO×SnO 2 in a ratio of 0.01<MgO×SnO 2 <0.05 (condition B1b).

18. 10 below 1760°C ２ dPas temperature, and / or Maximum processing temperature V of 1330°C Ａ and / or The processing temperature V Ａ Upper limit of devitrification OEG at least 15 ° C. below 18. The crystalline lithium aluminum silicate glass according to claim 1, wherein

19. 19. The crystalline lithium aluminum silicate glass according to claim 1, characterized by a bubble count of less than 5 bubbles / kg.

20. 20. A method for producing a glass-ceramic, comprising transforming the lithium aluminum silicate glass according to any one of claims 1 to 19 into a glass-ceramic by a multi-stage temperature process.

21. The method for producing a glass ceramic according to claim 20, wherein the glass ceramic is transparent.

22. The method for producing a glass ceramic according to claim 20 or 21, characterized in that the glass ceramic contains high quartz mixed crystal as the predominant crystalline phase.

23. The glass ceramic has a brightness Y of more than 83% at a thickness of 4 mm and / or a color c of up to 4. ＊ 23. A method for producing a glass ceramic according to claim 20, characterized in that the glass ceramic has a haze value of less than 2.5%.

24. The method for producing a glass ceramic according to claim 20, wherein the glass ceramic contains keatite mixed crystals as the predominant crystalline phase.

25. A method for producing a glass ceramic according to any one of claims 20 to 24, characterized in that the glass ceramic is in the form of a plate having a thickness of 2 mm to 20 mm.

26. A method for producing the crystalline lithium aluminum silicate glass according to any one of claims 1 to 19, comprising: a) preparing a blended batch from industrial raw materials; b) melting the blended batch and high temperature fining at a temperature above 1750°C; c) Cooling the molten glass to a processing temperature V Ａ forming the mixture at a temperature in the vicinity of the melt melting point; d) Cooling to room temperature in a stress relief furnace A method characterized by:

27. 26. The method for producing a glass ceramic according to any one of claims 20 to 25, wherein ceramming is carried out by the following method steps: a) The temperature of the crystallizable glass is increased to a temperature T in the range of 660 to 730°C within 3 to 60 minutes. ａ raising the temperature to b) The temperature of the crystallizable glass is adjusted to T within the nucleation temperature range. ａ to 800°C for about 10 to 100 minutes; c) increasing the temperature of the glass containing crystal nuclei to a temperature range of 850 to 950°C, at which the crystal growth rate is high, within 5 to 80 minutes; d) maintaining the maximum temperature in the temperature range of 850-950 ° C for 0-60 minutes, during which high-temperature quartz mixed crystal type crystals grow on the crystal nuclei, and then e) quenching the resulting glass ceramic to room temperature in less than 150 minutes; wherein the total duration of said ceramming of said glass is less than 300 minutes.

28. 26. Use of a transparent glass-ceramic plate produced by the method of claim 25 as fire protection glass, fireplace sight glass, baking oven sight glass, cooking surface, cover for lighting area, safety glass pane, carrier plate, or furnace lining.

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