Patent ID: 12227444

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to one preferred embodiment, the coloured, transparent LAS glass-ceramic comprises as main constituents the following components (in wt % on an oxide basis):

Li2O3.0-4.2Na2O + K2O0.2-1.5MgO0-1.5CaO + SrO0-4BaO0-3ZnO0-2.2Al2O319-23SiO260-69TiO22.5-4ZrO20.5-2SnO20.05-<0.6P2O50-3B2O30-2
And also the stated amounts of V2O5of 55 ppm to 200 ppm and of Fe2O3of 450 ppm to 1000 ppm with a ratio of Fe2O3/V2O5(both in wt %) of 3 to 9 and also, optionally, additions of chemical refining agents such as CeO2and refining additives such as sulfate compounds, chloride compounds, fluoride compounds in total amounts of up to 2.0 wt %.

The glass-ceramic preferably consists substantially of the stated components in the stated portions. By “consists substantially of . . . ” is meant that these components are included at not less than 98 wt % in the glass-ceramic.

The water content of the crystallizable glasses for producing the glass-ceramics is preferably between 0.015 and 0.06 mol/l, depending on the choice of the mix raw materials and on the operating conditions at melting. This corresponds to p-OH values of 0.16 to 0.64 mm−1. On conversion into the glass-ceramic, there is a change in the IR band, which is used for determining the water content. As a result, owing to the measurement process, the β-OH value for the glass-ceramic increases by a factor of around 1.6, without any accompanying change in the water content. This and the method for determining the β-OH values are described for example in EP 1 074 520 A1.

According to a further preferred embodiment, the coloured, transparent LAS glass-ceramic comprises as main constituents the following components (in wt % on an oxide basis):

Li2O3.2-4.0Na2O + K2O0.4-1.2MgO0.1-1.3CaO + SrO0.2-1BaO1.5-2.8ZnO1-2.2Al2O320-22SiO262-67TiO22.8-3.5ZrO21-1.8SnO20.1-0.4P2O50-0.1B2O30-1
and also, optionally, refining additives such as sulfate, chloride, fluoride compounds in total amounts of up to 1.0 wt %.

The glass-ceramic preferably consists substantially of the stated components in the stated portions. By “consists substantially of . . . ” is meant that these components are included at not less than 98 wt % in the glass-ceramic.

If SnO2is present as a nucleating agent, the glass-ceramic may also be refined by means of SnO2. For that purpose the compound is present in the proportions discussed above. Its refining effect may be supported by the above-stated defining additives.

In order to achieve a very good refining effect in conjunction with the required bubble qualities and tank throughputs, it may be advantageous to carry out high-temperature refining at above 1700° C., preferably above 1750° C. In that case a bubble quality of less than 2 bubbles/kg in the glass or in the glass-ceramic (measured for bubble sizes of greater than 0.1 mm in one dimension) is achieved.

A large number of compounds of elements such as, for example, the alkali metals Rb and Cs or elements such as Mn and Hf are customary impurities in the mix raw materials that are used industrially. Other compounds, such as those of the elements W, Nb, Y, Mo, Bi and the raw earths, for example, may likewise be included in small proportions.

The coloured, transparent, lithium aluminium silicate glass-ceramic customarily comprises high-quartz mixed crystals as the main crystal phase. The average crystallite size is preferably less than 50 nm.

The LAS glass-ceramic of the invention preferably exhibits light scattering, reported as the integral haze value for standard illuminant C, determined according to ASTM D1003-13, of less than 20%, preferably less than 15%, for 3.5 mm.

The thermal expansion, measured between 20° C. and 700° C., for this type of LAS glass-ceramic with high-quartz mixed crystals, is established preferably at values of less than 1·10−6/K, preferably of (0±0.3)·10−6/K.

The lithium aluminium silicate glass-ceramic with high-quartz mixed crystals as the main crystal phase may be converted, in a customary way known to the skilled person, into a glass-ceramic having keatite mixed crystals as the main crystal phase. Owing to the customarily larger average crystallite size of greater than 120 nm, this converted glass-ceramic is translucent or opaque. The glass-ceramic with high-quartz mixed crystals as the main crystal phase may also be converted into a glass-ceramic with keatite mixed crystals as the main crystal phase in such a way that its crystallites remain sufficiently small, so that the glass-ceramic is transparent. A glass-ceramic of this kind with keatite mixed crystals customarily has a thermal expansion, measured between 20° C. and 700° C., of 0.8·10−6/K to 1.5·10−6/K, preferably of more than 1·10−6/K to 1.5·10−6/K.

The preferred geometry for the glass-ceramic of the invention or for the articles produced from it is in the form of plates. The plate preferably has a thickness of 2 mm to 20 mm, because this opens up important applications. At lower thicknesses, the strength is impaired; higher thicknesses are less economic because of the higher consumption of material. Except for service as safety glass, where high strengths are an important factor, therefore, the thickness selected is generally below 6 mm. In the case of service as a cooking surface, preferred thicknesses selected are from 2 mm to 6 mm. For the customary, standard cooking surfaces, sizes of up to 0.5 m2are customarily preferred. For larger implementations, with colour displays for example or if the cooking surface is configured at the same time as a work surface and includes further functionalities as well as the cooking function, these functionalities being set out in more detail when the possible applications as a cooking surface are outlined, preference is given to formats of greater than 0.5 m2or even of greater than 0.8 m2.

Suitable shaping processes for the plate-like geometry are, in particular, rolling and floating.

The glass-ceramic plate and the articles preferably produced from it may not only be flat in their shaping, but may also have been three-dimensionally moulded. For example, chamfered, angled or arched plates may be used. The plates may be right-angled or have other shapes, and, in addition to flat regions, they may include three-dimensionally moulded regions, e.g. woks, or rolled-in webs or areas as elevations or depressions, respectively. The geometric moulding of the plates is undertaken at the hot forming stage, by means of structured shaping rollers, for example, or by subsequent hot forming on the initial glasses, by means of burners or by dropping under gravity, for example. Ceramization is operated with supporting ceramic moulds in order to avoid uncontrolled changes in the geometric shape.

The glass-ceramic plate and the articles preferably produced from it may be smooth on both sides or may be pimpled on one side.

As a result of the favourable optical and thermal properties associated with the low thermal expansion and the optimized transition profile, and also by virtue of the other properties, especially the mechanical properties, there are numerous applications that are catered for advantageously.

The coloured, transparent glass-ceramic articles of the invention find application in the form of a cooking surface, more particularly a cooking surface with underside coating, or of an underside-coated cooking surface with cut-outs, so-called spare-outs for lighting in the cold region, i.e. in the display/indication region, and/or in the hot region, in other words in the cooking region, with cover means, or of a cooking surface having a so-called diffuser layer, which evenly distributes the light emerging from the underside of the cooking surface towards the viewer, or of a cooking surface having a so-called colour compensation filter, applied in adhered or printed or coated form. Additionally, it may take the form of a cooking surface in one of the above-stated versions with opaque or transparent capacitive sensor structures, applied in bonded, printed or pressed-on form, for regulating and controlling operation. Additionally, it may take the form of a cooking surface in one of the above-stated implementations, with one or more holes for control buttons, gas burners, fume removal systems (so-called down-draft systems) or other functional modules, optionally implemented with a flat facet on one or more edges.

Furthermore, it may take the form of a cooking surface in one of the above-stated versions, having transmission, defined via the Y(D65, 2°) value, that is increased/modified locally in the display region and/or hot region. This transmission) Y(D65, 2° may be increased locally up to 50%, preferably up to 30%, more preferably up to 25%, relative to the base transmission or nominal transmission of the substrate.

In one especially preferred embodiment, the transmission is increased locally up to 5%, more preferably up to 2.5%, relative to the base transmission.

In one embodiment of the invention, the transmission may also be lowered locally by 4%, preferably by 3%, relative to the base transmission of the substrate.

This lowering of the base transmission may be accomplished by coating or by a film or by intrinsic local modification to the material.

In particular embodiments, the glass-ceramics may find application for cookers equipped with sensors for measuring the pan temperature. Sensors of this kind may be fitted, for example, directly in the pan or above the pan, or may detect the temperature of the pan base by means of IR sensors.

Such IR sensors operate preferably at a wavelength>1 μm, preferably ≥1500 nm. In one particular embodiment, such sensors operate at a wavelength of 3-5 μm. The cooking surface therefore has a corresponding transmission in the relevant wavelength range. Ways in which this is ensured include either a local cut-out in the cover means or sufficient transparency of the cover means in the relevant wavelength range.

In other particular embodiments, the glass-ceramics may find application for cookers equipped with a wireless data connection. This data connection may serve to integrate the cooker with a fume hood, with a central control unit for household appliances, or else for functional control of the cooker. Data connections may be made via IR sensors or from radio links in the GHz range, e.g. wifi, Bluetooth.

Preferably, such IR sensors operate at a wavelength of 0.9-1 μm, preferably 930-970 nm. The cooking surface therefore has a corresponding transmission in the relevant wavelength range. Ways in which this is ensured include either a local cut-out in the cover means or sufficient transparency of the cover means in the relevant wavelength range.

In further particular embodiments, the glass-ceramics may find application for cookers equipped with a contactless control technology. Such controls operate, for example, by means of capacitive sensor technology, IR sensors or else ultrasound sensors.

In further particular embodiments, the glass-ceramics may find application for cookers equipped with LED-based and/or segment-based display elements and/or graphic display elements. These graphic display elements may have a single colour or multiple colours. Preferred single-colour graphic displays are white. Display elements of this kind are preferably designed with a capacitive touch-sensor system.

In further particular embodiments, the glass-ceramics may find application for cookers equipped with a minimum of top face decoration. In one embodiment, there are only one or more brand logos and the on/off switch located on the top face. In this case the decorative function for cooking zone marking, for example, is taken on entirely via lighting elements.

Furthermore, the glass-ceramics are used in conjunction with a functional top-face coating.

These functional top-face coatings may be applied in order to improve the scratch resistance, to facilitate capacity for cleaning, to improve the visibility of displays, to prevent destructive reflections, to minimize fingerprints and/or to minimize noises from pot movement.

In one particular embodiment, the surface may be polished or have a stochastic structure.

Furthermore, the coloured, transparent glass-ceramic articles according to the invention may find use as chimney viewing panel/chimney oven lining or facing, covering in the lighting sector and as safety glass optionally in a laminate system, as support plate or oven lining. In the ceramics, solar or pharmaceutical industry or in medical technology, they are suitable especially for production processes under high-purity conditions, as linings of ovens in which chemical or physical coating processes are carried out, or as chemically resistant laboratory equipment. Furthermore, they find use as a glass-ceramic article for high-temperature or extreme low-temperature applications, as furnace windows for combustion furnaces, as a heat shield for shielding hot environments, as a covering for reflectors, floodlights, projectors, photocopiers, for applications with thermomechanical exposure, as for example in night vision devices, or as cover for heating elements, especially as a cooking or frying surface, as white ware, as heating element covering, as wafer substrate, as article with UV protection, as architectural facing plate or as construction constituent of an electronic device.

The entire disclosures of all applications, patents and publications, cited above and below, and of corresponding German application DE 10 2017 119 914.4 filed Aug. 30, 2017 and DE 10 2018 101 423.6 filed Jan. 23, 2018, are hereby incorporated by reference.

The present invention will be illustrated below by a series of examples. However, the present invention is not limited to the examples mentioned.

The present invention is illustrated further by means of the following examples.

EXAMPLES

In the case of working Example A1 to A6, the starting glasses were melted down from raw materials customary in the glass industry, at temperatures of around 1620° C., for 4 hours. After the mix had been melted down in crucibles made from refractory material with a high quartz content, the melts were poured into PtRh20 crucibles having a crucible liner made of silica glass, and were homogenized by stirring for 60 minutes at temperatures of 1600° C. Following this homogenization, the glasses were refined at 1640° C. for 3 hours. Then pieces with a size of around 170×120×25 mm3were cast and were cooled in a cooling oven, beginning at 640° C., to room temperature. The castings were divided into the sizes required for the investigations and for the ceramization.

Working Examples A7 to A11 were melted industrially with the parameters customary for Sn refined LAS glass-ceramics.

The samples were ceramized using the ceramization programme outlined later on below.

Table 1, for Examples A1 to A11, which represents working examples, and C1 to C8, which represent comparative examples, shows the compositions and properties of the crystallizable starting glasses and properties of the glass-ceramics produced from the glasses.

Owing to typical impurities in the industrial mix raw materials used, the compositions do not add up to precisely 100.0 wt %. Typical impurities, although not introduced deliberately into the composition, are compounds of Mn, Rb, Cs, Hf or else, if not used as refining agents, of CI and F, which customarily amount to not more than 0.1 wt %. They are often entrained via the raw materials for the related components—for example, Rb and Cs via the Na or K raw materials, or Hf via the Zr raw material.

The transmission measurements were carried out on polished plates with a thickness of 4 mm using standard illuminant C, 2°. The transmission values reported are those at selected wavelengths, namely at 465 nm, at 470 nm and at 630 nm, and also the light transmission. The terms “light transmission” and “brightness Y” correspond to the same measured parameter, measured according to DIN 5033 in the CIE colour system as Y(D65, 2°). Also reported is the difference τvis−τ465, i.e. Y−τ465.

The ceramization programme was as follows:a) Heating from room temperature to 600° C. in 5 min.b) Temperature increase from 600° C. to a nucleation temperature Tnuclof between 700° C. and 750° C. at a heating rate of 50 K/m in, hold time tnuclof 5 min.b1) Temperature increase to a crystallization temperature Tcrystof between 780° C. and 820° C. at a heating rate of 12 K/m in, hold time tcrystof 8 min at Tcryst.

c) Temperature increase from Tcrystto a maximum temperature Tmaxof between 910° C. and 950° C. to a heating rate of 20 K/m in, hold time tmaxof 7 min at Tmax.d) Cooling to around 800° C. at 10 K/min, then rapid cooling to room temperature.

TABLE 1Wt %A1A2A3A4A5A6A7A8A9Al2O320.520.520.520.520.520.520.620.5720.63BaO2.312.312.32.292.32.32.312.32.3CaO0.4200.420.420.420.420.420.410.410.41CoO—————————Cr2O3—————————F—————————Fe2O3(ppm)940940920910810710890887895HfO20.0250.0250.0250.0250.0250.0250.0240.0240.024K2O0.240.250.240.240.240.250.270.260.26Li2O3.913.913.893.923.913.953.83.83.79MgO0.320.310.310.320.320.310.30.30.3MnO20.0180.0230.0290.0190.0180.0180.0180.0180.018MoO3—————————Na2O0.60.610.60.590.60.590.620.620.62Nb2O5—————————NiO—————————P2O50.0290.0290.0290.0290.0290.0290.0620.0610.063Sb2O3—————————SiO265.165.165.165.265.265.265.1465.265.15SnO20.270.270.270.260.270.260.270.260.26SrO0.0180.0180.0180.0180.0180.0180.0290.0280.028TiO23.193.183.23.173.173.183.113.113.09V2O5(ppm)170150140190180180140131139ZnO1.541.561.551.541.561.561.511.51.49ZrO21.421.421.421.411.421.411.391.391.38Fe2O3/V2O55.5296.2676.5714.7894.53.9446.3576.7716.439Y(D65, 2°) [%]4.1253.3075.3472.63.12.84.15.24.416τ @ 470 [%]1.81.32.50.941.221.121.672.31.793τ @ 465 [%]1.81.32.50.951.231.131.6702.31.78τ @ 630 [%]10.178.6412.47.198.167.610.212.410.8Difference2.3252.00682.84711.651.871.672.432.92.6369Y(D65, 2°) −τ @ 465 [%]Wt %A10A11C1C2C3C4C5C6C7C8Al2O320.6120.920.220.319.319.320.920.320.320.9BaO2.312.032.412.360.80.82.32.62.62.23CaO0.140.410.360.440.420.50.50.43CoO——0.027——Cr2O3——0.032——F——0.14Fe2O3(ppm)8828309001400200020002000850850900HfO20.0250.0260.0250.024K2O0.270.240.210.210.20.20.27Li2O3.793.813.8303.853.53.53.713.83.83.82MgO0.30.30.190.351.11.10.370.40.40.29MnO20.0180.0190.0220.0230.250.025MoO3——<0.005<0.005——Na2O0.620.60.570.610.590.60.60.6Nb2O5———0.011NiO——<0.001<0.001P2O50.0600.110.086Sb2O3——<0.01<0.01SiO265.1565.265.865.468.8668.8665.1465.565.565SnO20.270.260.30.320.20.20.240.290.290.25SrO0.0290.0370.0030.0040.021TiO23.12.963.022.963.12.73.12.92.93.13V2O5(ppm)138190200400400400260300250230ZnO1.51.531.411.451.61.61.51.51.51.53ZrO21.391.481.391.351.81.81.341.31.31.4Fe2O3/V2O56.3914.3684.53.5557.6922.8333.43.913Y(D65, 2°) [%]4.5744.23.51.31542.526.74.56.02.2τ @ 470 [%]1.8771.31.90.03317.711.20.67τ @ 465 [%]1.8541.320.0232.716.711.81.11.60.67τ @ 630 [%]11.2510.754.632.3663.343.76n.d.n.d.6.62Difference2.72042.91.51.27712.325.814.93.44.41.53Y(D65, 2°) −τ @ 465 [%]n.d. = no data

Examples C1 to C8 in Table 1 are comparative glass-ceramics outside of the invention.

Though C1 does have a difference (Y−τ(at 465 nm)) of 3%, the transmission characteristics are nevertheless realized through addition of CoO.

C2 likewise has a difference (Y−τ(at 465 nm)) of 3%, but the transmission values in the visible range are so low that, except for red displays, no further colours are visible. This is due to the addition of Cr2O3, which significantly reduces the transmission in the visible range.

Examples C3 to C5 all have a difference (Y−τ(at 465 nm)) of >3%, partly due to regions with very high transmission values, which are attributable to so-called iron overcolouring.

C6 and C7 do exhibit a light transmission Y(D65, 2°) of 2.5-10% and a spectral transmission τ(at 465 nm)>1.0%. However, their difference (Y(D65, 2°)−τ(at 465 nm)) is also >3%.

C8, while it does exhibit a difference (Y(D65, 2°)−τ(at 465 nm))<3%, nevertheless exhibits low light transmission Y(D65, 2°) of 2.2% and low spectral transmission τ(at 465 nm)of 0.67%.

Working Examples A1 to A11 illustrate the fact that the glass-ceramics of the invention combine the transmission properties of light transmission Y(D65, 2°) of 2.5-10%, spectral transmission τ(at 465 nm)>1.0% and a difference (Y(D65, 2°)−τ(at 465 nm)) of ≤3% and therefore make it possible on the one hand for there to be effective visibility of the underside-mounted displays with on the other hand reduced sight into the hob interior and also a colour transmissibility which is such that not only red but also colours such as green are transmitted and the colour and lightness conveyed are very neutral, in other words unfalsified, meaning conveyance of light that is unchanged or virtually unchanged despite passage through the glass-ceramic plate. The working examples, as preferred embodiments, also exhibit advantageously high transmission in the red spectral range, as shown by a spectral transmission τ at 630 nm of 10.9%±3.8%.

The starting glasses of the glass-ceramics of the invention possess low melting and forming temperatures and can be produced from inexpensive mix raw materials. They exhibit high devitrification resistance. They can be converted into glass-ceramics within short ceramization times.

The glass-ceramics of the invention therefore have economic and eco-friendly manufacturing properties, the latter the result of omission of the environmentally harmful raw materials arsenic oxide, antimony oxide, cobalt oxide and chromium oxide. The glass-ceramics of the invention satisfy the requirements of the various applications. Thus they have chemical resistance, high mechanical strength, the desired transmission properties, little to no light scattering, high temperature robustness and a high long-term stability in respect of changes in their properties (such, for example, as thermal expansion, transmission, development of stresses).

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.