Glass-Ceramic Plate

Abstract

The present invention relates to a glass-ceramic plate of the lithium aluminosilicate type, characterized in that it has a chemical composition comprising the following components, expressed in percentages by weight, within the ranges defined below: SnO2 0.05% or more and less than 0.35% V2O50.05% or more and 0.40% or less Fe2O3: over 0.32% and not more than 0.40% Cr2O3: 0.005% or more and 0.040% or less.

Description

[Technical field]

[0001] The present invention relates to the field of glass-ceramic plates and methods for their manufacture. [Background technology]

[0002] Glass-ceramic plates are produced by subjecting lithium aluminosilicate glass plates to a high-temperature heat treatment, also known as the ceramification cycle. This heat treatment produces crystals of the β-quartz or β-spodumene structure within the plate, which have a negative coefficient of thermal expansion. Thus, the glass-ceramic material is no longer a glass: it is made of crystals connected by a residual glassy phase and has a coefficient of thermal expansion close to zero.

[0003] Such glass-ceramic plates are used in particular in cooking appliances, also known as cooktops. These appliances are often built into a worktop or mounted in a stove. The glass-ceramic plates can also be used as worktops. In both cases, the aesthetic appearance of the plate is an important criterion for the consumer's choice.

[0004] Glass-ceramic plates, especially those used in cooking devices, are generally dark glass-ceramics, typically colored with vanadium oxide. They have the distinctive feature of low, or even very low, light transmittance, making it possible to hide internal components, such as heaters. Their use in cooking appliances also imposes certain requirements specific to these applications. Also, a good infrared transmittance is necessary for the operation of touch controls (around 950 nm) or radiant heaters (around 2400 nm). Summary of the Invention [Problem to be solved by the invention]

[0005] For both functional and aesthetic reasons, cooking appliances are generally equipped with displays, such as light-emitting diodes (LEDs) or screens. There is an increasing market demand for a relatively wide range of options, especially in terms of aesthetic appeal. In this context, one of the aspects of differentiation employed is the development of various aesthetic effects through the use of display means, such as LEDs, visible through the glass-ceramic plate. The required properties of the glass-ceramic plate, in particular with regard to light transmittance, can therefore be varied depending on the desired effect. To change the optical properties of the glass-ceramic, it is usually necessary to adjust the composition. Thus, the widespread availability of glass-ceramic plates entails significant additional production costs, for example due to the transition times required to change the composition in the melting furnace for the mother glass production and / or the need for inventory management. There is therefore a need for mother glasses that can be used to produce glass-ceramic plates, the properties of which, in particular light transmittance, can be adjusted, thereby meeting a relatively wide range of specifications, without the need to adapt the composition. [Means for solving the problem]

[0006] The present invention therefore relates to a lithium aluminosilicate-type glass-ceramic plate, characterized in that it has a chemical composition comprising the following components, expressed in percentages by weight, within the ranges defined below: SnO2 0.05% or more and less than 0.35% V2O50.05% or more and 0.40% or less Fe2O3: over 0.30% and 0.40% or less Cr2O3: 0.005% or more and 0.04% or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present invention also relates to a method for making a glass-ceramic plate, which includes providing a lithium aluminosilicate glass plate, known as a mother glass, and ceramming the glass plate.

[0008] Another object of the invention is a glass-ceramic precursor plate, or mother glass, according to the invention. This glass plate is an intermediate article for obtaining a glass-ceramic plate according to the invention.

[0009] For a given composition, there exists a ceramming window within which the ceramming parameters (particularly the temperature and time of the ceramming step) can be modified while still ensuring proper crystallization. Glass-ceramics are endowed with special mechanical properties, in particular a nearly zero coefficient of thermal expansion, typically 15.10°C from 20 to 700°C. -7 K -1 Below, or even 10.10 -7 K -1 Below, or 5.10 -7 K -1 The following thermal expansion coefficients are given: The Applicant has demonstrated that by selecting the contents of SnO2, V2O5, Fe2O3 and Cr2O3 in such a way as to respect the equilibrium defined according to the invention, it is possible to obtain from the same mother glass glass-ceramics having a relatively wide range of properties, in particular a relatively wide range of optical properties, while maintaining the necessary requirements for the desired application, in particular the application in cooking appliances. In particular, a relatively wide range of light transmittances can be achieved in the ceramization window.

[0010] Vanadium oxide (V2O5) is the main pigment of the glass-ceramics according to the invention. They have a V2O5 content of 0.05% to 0.40%, preferably 0.07% to 0.30%, more preferably 0.10% to 0.20%. In the presence of SnO2, V2O5 significantly darkens the glass during ceramming. V2O5 is mainly responsible for the absorption below 700 nm, and in its presence can maintain a sufficiently high transmittance at 950 nm and in the infrared.

[0011] The content of chromium oxide (Cr2O3) ranges from 0.005% to 0.040%, preferably from 0.010% to 0.032%, more preferably from 0.012% to 0.030%. In some embodiments, the Cr2O3 content is from 0.010% to 0.025%, or even 0.020%.

[0012] The glass-ceramics according to the present invention have a total iron oxide content (expressed as Fe2O3) that is strictly more than 0.30% and at most 0.40%. The Fe2O3 content is preferably strictly more than 0.32% and can be as high as 0.40%. It can be from 0.33% to 0.40%, more preferably from 0.35% to 0.40%.

[0013] The composition contains tin oxide (SnO2) as a refining agent. The more the amount of SnO2 present, the easier and more efficient the refining process becomes. However, it is speculated that SnO2 also affects coloring by modifying the oxidation-reduction balance with vanadium and iron during ceramization. Therefore, the SnO2 content is 0.05% or more and strictly less than 0.35%, preferably from 0.10% to 0.32%, more preferably from 0.15% to 0.30%.

[0014] The contents of SnO2, V2O5, and Fe2O3 satisfy the following condition: 14 < 1000×(2Fe2O3 - SnO2)×V2O5 / 2 < 40, preferably 20 < 1000×(2Fe2O3 - SnO2)×V2O5 / 2 < 35. This balance significantly improves the range of light transmission achievable on the ceramic window.

[0015] The contents of SnO2, V2O5, and Fe2O3 may also satisfy the following condition: 7.0 < Fe2O3 / (V2O5×SnO2) < 15, preferably 8.0 < Fe2O3 / (V2O5×SnO2) < 15. Maintaining this balance improves the optical properties of the glass-ceramics.

[0016] Silica (SiO2) is the main glass-forming oxide. A high content will cause the viscosity of the glass to increase beyond the acceptable range, while an excessively low content will increase the thermal expansion coefficient. The silica content is preferably in the range of 52-75%, in particular 64-70%, 65.0-70%.

[0017] Alumina (Al2O3) also causes an increase in the viscosity of the glass and therefore makes it relatively difficult to melt. However, if it is present in too low an amount, the glass becomes difficult to ceramize. The alumina content is preferably in the range of 18-27%, in particular 18-21%.

[0018] Lithium oxide (Li2O) is essential for the formation of β-quartz crystals. A minimum content level is also required, thereby reducing the viscosity of the glass at high temperatures. The Li2O content is preferably in the range of 2.5-5.5%, in particular 2.5-3.9%.

[0019] The content of soda (Na2O) and potash (K2O) is preferably less than 3%, more preferably less than 1.0%, each. Their sum, expressed as Na2O+K2O, is preferably limited to ensure a low thermal expansion coefficient. This sum is advantageously at most 1.5%, or even at most 1%.

[0020] The composition of the plate contains lime (CaO) and barium oxide (BaO) to ensure a suitable viscosity at high temperatures, making it possible to optimize both the melting and the formation of the mother glass. The CaO content is preferably at most 2.5%, more preferably at most 1.0%, thereby both preventing excessive corrosion of the furnace refractories and limiting the formation of potentially scattering crystals. The BaO content is preferably at most 3.5%, in particular at most 3%. The sum of the CaO and BaO contents (written CaO+BaO) is in the range of about 2% to 5%, in particular 2.5% to 4%.

[0021] The MgO content is preferably 3% or less, and the content is preferably 0.20% to 1.5%.

[0022] The SrO content is preferably max. 2%, or even max. 1.4%. It is even more advantageously zero.

[0023] The ZnO content is preferably up to 3.5%, or even between 1.2% and 2.8%. During ceramization, this oxide participates in the formation of crystals of the β-quartz structure and thus contributes to a reduction in the thermal expansion coefficient.

[0024] Titanium oxide (TiO2) and zirconium (ZrO2) function as nucleating agents and promote bulk crystallization of β-quartz structure crystals. The TiO2 content is preferably 1.2% to 5.5%, more preferably 1.8% to 3.2%. The ZrO2 content is preferably less than 3%, more preferably 1.0% to 2.5%. A high ZrO2 content may lead to an excessively high liquidus temperature. A combination of TiO2 and ZrO2 is advantageous. The sum of these contents (TiO2 + ZrO2) is preferably more than 3.80%, more preferably more than 4%. A low amount may promote excessive crystal growth, thereby resulting in undesirable light scattering.

[0025] The glass-ceramic plate according to the invention advantageously has a chemical composition comprising, in addition to SnO2, V2O5, Fe2O3 and Cr2O3, the following components, expressed in percentages by weight, within the ranges defined below: SiO2 52% to 75%, preferably 64% to 70%, Al2O3 18% to 27%, preferably 18% to 21%, Li2O 2.5% to 5.5%, preferably 2.5% to 3.9%, K2O 0% to 3%, preferably 0% to 1.0%, Na2O 0% to 3%, preferably 0% to 1.0%, ZnO 0% to 3.5%, preferably 1.2% to 2.8%, MgO 0% to 3%, preferably 0.20% to 1.5%, CaO 0% to 2.5%, preferably 0% to 1.0%, BaO 0% to 3.5%, preferably 0% to 3%, SrO 0% to 2%, preferably 0% to 1.4%, TiO2 1.2% to 5.5%, preferably 1.8% to 3.2%, ZrO20% to 3%, preferably 1.0% to 2.5%, P2O50%-8%, preferably 0%-3%.

[0026] The chemical composition of the glass-ceramic plate comprises the oxides indicated above. Preferably, it consists essentially of these oxides. The expression "consists essentially of" is understood to mean that the aforementioned oxides make up at least 96%, or even 98% or 99% of the weight of the glass-ceramic. The chemical composition of the glass-ceramic plate generally comprises only Fe2O3, V2O5, and Cr2O3 as pigments. Other pigments, such as MnO, Bi2O3, CoO, NiO, or CeO2, may be present in minor amounts, typically with a total content of less than 0.1%, or even less than 0.05%, or even less than 0.01%. In particular, the chemical composition of the glass-ceramic plate typically comprises less than 10 ppm, or even less than 5 ppm, of CoO.

[0027] The glass-ceramic plate typically has a thickness of 2 mm to 10 mm, in particular 2.5 mm to 8 mm, such as 3 mm, 4 mm, 5 mm or 6 mm, etc. The dimensions (length and width) of the glass-ceramic plate depend on the application for which it is intended: it generally has dimensions of 20 cm to 120 cm, in particular for those applications in cooking appliances, but may have relatively large dimensions, for example more than 200 cm, for worktop applications.

[0028] The glass-ceramic plate according to the present invention typically has a light transmittance of 0.5% to 8%, preferably 0.7% to 6%. The light transmittance is measured at the actual thickness of the glass-ceramic plate according to ISO 9050:2003. At the actual thickness, the plate has a light transmittance at 625 nm of more than 3.5%, preferably more than 4%, a light transmittance at 950 nm of 40% to 70%, and a light transmittance at 1600 nm of 45% to 75%.

[0029] The present invention also relates to a glass plate of the lithium aluminosilicate type, which is a precursor of the glass-ceramic plate according to the invention. The chemical composition of this glass plate is identical or substantially identical to that of the glass-ceramic plate according to the invention. Therefore, what has been stated above in relation to the composition of the glass-ceramic plate also applies to the composition of the glass plate according to the invention. In particular, the glass plate preferably has a chemical composition comprising the following components, expressed in percentages by weight, within the ranges defined below: SnO2 0.05% or more and less than 0.35% V2O50.05% or more and 0.40% or less Fe2O3: over 0.30% and 0.40% or less Cr2O3: 0.005% or more and 0.04% or less.

[0030] On the other hand, glass plates are exclusively vitreous in nature, i.e. do not contain crystals. It should be noted that the precursor glass advantageously has a light transmittance of more than 60% for any wavelength between 1000 and 2500 nm. This makes it easy to melt and refine.

[0031] A further object of the present invention is a method for producing a glass-ceramic plate according to the invention, which comprises providing a glass plate according to the invention and ceramming said glass plate. More specifically, providing the glass plate comprises a melting step and a forming step.

[0032] Melting is typically carried out in a refractory furnace with the aid of a burner, using air or preferably oxygen as oxidant and natural gas or heavy oil as fuel. Resistors, especially made of molybdenum or platinum, immersed in the molten glass, may also provide part or all of the energy used to obtain the molten glass. The raw materials (silica, spodumene, petalite, lithium carbonate, etc.) are introduced into the furnace and undergo various chemical reactions under the influence of high temperature, such as decarbonation, the actual melting reaction, etc. The maximum temperature reached by the glass is typically at least 1500°C, especially between 1600°C and 1700°C. The glass can be formed into plates in known ways, such as by rolling the glass between metallic or ceramic rollers, by drawing (upwards or downwards) or even by the float process, a technique that involves pouring the molten glass onto a bath of molten tin.

[0033] The ceramification step comprises a thermal cycle with a temperature rise to the crystallization temperature, preferably in the range of 850°C to 1000°C, for example 900°C to 980°C, or even 920°C to 960°C. The choice of temperature and / or ceramification time, adapted to each composition, makes it possible to adjust the thermal expansion coefficient of the material obtained by varying the size and amount of crystals. Preferably, the thermal cycle comprises a rise to a temperature of 650°C to 850°C over a period of 15 to 200 minutes (nucleation step), followed by a controlled rise to the crystallization temperature, typically over a period of 5 to 120 minutes, followed by a maintenance at the crystallization temperature for a period of 5 to 20 minutes (crystal growth step).

[0034] Another object of the invention is an article, in particular a cooking device or a worktop, comprising at least one glass-ceramic plate according to the invention.

[0035] The cooking appliance is preferably of the radiative or induction type. The plate is preferably able to hide the heating means (e.g. inductors), the electrical wiring as well as the control and control circuitry of the cooking appliance. For this purpose, at least a part of the plate surface may be provided with a coating that is deposited on the plate and / or underneath the plate, said coating having the ability to absorb and / or reflect and / or scatter optical radiation. The coating may be deposited underneath the plate, i.e. on the surface facing the internal elements of the appliance, also called the "lower face", and / or on the plate, i.e. on the upper face. The coating may be an organic-based layer, such as a paint layer, a resin layer or a lacquer layer, or an inorganic-based layer, such as an enamel, or a metallic or metal oxide, nitride, oxynitride or oxycarbide layer. Preferably, an organic layer will be deposited on the lower face, while an inorganic layer, in particular an enamel, will be deposited on the upper face. Besides the glass-ceramic plate and at least one inductor (preferably three, or four, or even five), the cooking appliance may have at least one light-emitting device, at least one control and monitoring device, this assembly typically being located in a housing. The light-emitting device or devices are advantageously selected from liquid crystal displays (LCD), light-emitting diode displays (e.g. seven-segment displays), possibly organic displays (OLED), fluorescent displays (VFD). These light-emitting devices may be purely decorative, for example to visually separate different areas of the plate. However, in many cases they will have a functional role, showing various information useful to the user, in particular an indication of the heating power, an indication of the temperature, an indication of the cooking program, an indication of the cooking time, an indication of zones of the plate that have exceeded a certain temperature, etc. The control and monitoring device generally includes a touch-sensitive control, for example of the capacitive type or of the infrared type. All the internal elements are generally mounted in a housing, often metallic, which constitutes the lower part of the cooking appliance and is usually hidden in the worktop or in the cooker body. EXAMPLES

[0036] The following examples provide non-limiting illustrations of the present invention.

[0037] Various glasses having the chemical compositions (oxide contents by weight) shown in Table 1 were melted in a known manner and a number of 4 mm thick mother glass plate samples were formed for each composition. The plates were then heated at different ceramming temperatures T c The ceramicization cycles consisted of rapid heating to 600° C., ramping to 820° C. at a rate of 17° C. / min, holding at this level for 10 minutes, and then ramping to the ceramicization temperature T c The temperature is raised to the ceramicization temperature T c for 10 minutes, and finally, controlled cooling of the glass-ceramic to room temperature.

[0038] The light transmittance (Tv) is measured for each sample according to ISO standard 9050:2003. For a given mother glass composition, Tv max and TV min represent, respectively, the maximum and minimum light transmittance measured in glass-ceramics obtained with different ceramming cycles.

[0039] Table 1 below summarizes the results obtained: - composition of the mother glass used; - for a given mother glass composition, the minimum light transmittance Tv of the resulting glass-ceramics as a function of the ceramming cycle min ; - Light transmittance amplitude Tv achieved in three ceramming cycles max -TV min .

[0040] [Table 1]

[0041] These results show that the composition according to the invention makes it possible to achieve a relatively wide range of light transmittances with the same mother glass composition, which is particularly useful in applications as cooking plates, making it possible to adapt the optical properties to different specifications without having to modify the composition of the mother glass.

Claims

1. A lithium aluminosilicate-type glass-ceramic plate comprising the following components, expressed in weight percent, within the ranges defined below: SnO ２ 0.05% or more and less than 0.35%; V ２ O ５ 0.05% or more and 0.40% or less, Fe ２ O ３ More than 0.32% and not more than 0.40%, Cr ２ O ３ 0.005% or more and 0.040% or less, The SnO ２ , the V ２ O ５ , and the Fe ２ O ３ The content of 14<1000×(2Fe ２ O ３ -SnO ２ ) × V ２ O ５ Glass-ceramic plate meeting JIS / 2<40.

2. The SnO ２ , the V ２ O ５ , and the Fe ２ O ３ The content of 20<1000×(2Fe ２ O ３ -SnO ２ ) × V ２ O ５ 2. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate satisfies the following: / 2<35.

3. 0.07 to 0.30%, more preferably 0.10 to 0.20% V ２ O ５ 3. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate comprises:

4. 0.35 to 0.40% Fe ２ O ３ 3. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate comprises:

5. 0.10 to 0.32%, more preferably 0.15 to 0.30% SnO ２ 3. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate comprises:

6. 0.010 to 0.032%, more preferably 0.012 to 0.030% Cr ２ O ３ 3. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate comprises:

7. The SnO ２ , the V ２ O ５ , the Fe ２ O ３ The content of: 7.0<Fe ２ O ３ / (V ２ O ５ ×SnO ２ ) < 15, preferably 8.0 < Fe ２ O ３ / (V ２ O ５ ×SnO ２ ) <15, 3. The glass-ceramic plate according to claim 1, wherein the glass-ceramic plate satisfies the above formula:

8. The chemical composition comprises the following components, expressed in weight percent, within the ranges defined below: SiO ２ 52% to 75%, preferably 65.0% to 70%, Al ２ O ３ 18% to 27%, preferably 18% to 21%, Li ２ O 2.5% to 5.5%, preferably 2.5% to 3.9%, K ２ O 0% to 3%, preferably 0% to 1.0%, Na ２ O 0% to 3%, preferably 0% to 1.0%, ZnO 0% to 3.5%, preferably 1.2% to 2.8%, MgO 0% to 3%, preferably 0.20% to 1.5%, CaO 0% to 2.5%, preferably 0% to 1.0%, BaO 0% to 3.5%, preferably 0% to 3%, SrO 0% to 2%, preferably 0% to 1.4%, TiO ２ 1.2% to 5.5%, preferably 1.8% to 3.2%, ZrO ２ 0% to 3%, preferably 1.0% to 2.5%, P ２ O ５ 0% to 8%, preferably 0% to 3%, 3. The glass-ceramic plate of claim 1, comprising:

9. An article, in particular a cooking device, comprising a glass-ceramic plate according to claim 1 or 2.

10. A lithium aluminosilicate type glass plate, precursor of the glass-ceramic plate according to claim 1 or 2, comprising the following components, expressed in percentages by weight, within the ranges defined below: SnO ２ 0.05% or more and less than 0.35%; V ２ O ５ 0.05% or more and 0.40% or less, Fe ２ O ３ More than 0.32% and not more than 0.40%, Cr ２ O ３ 0.005% or more and 0.04% or less, The SnO ２ , the V ２ O ５ , and the Fe ２ O ３ The content of 14<1000×(2Fe ２ O ３ -SnO ２ ) × V ２ O ５ A glass plate that satisfies / 2<40.

11. A method for producing the glass-ceramic plate of claim 1 or 2, comprising: a glass plate of lithium aluminosilicate type, precursor of the glass-ceramic plate according to claim 1 or 2, comprising the following components, expressed in percentages by weight, within the ranges defined below: SnO 2 0.05% or more and less than 0.35%; V 2 O 5 0.05% or more and 0.40% or less; Fe 2 O 3 more than 0.32% and 0.40% or less; Cr 2 O 3 0.005% or more and 0.04% or less; and the contents of the SnO 2 , the V 2 O 5 , and the Fe 2 O 3 satisfy 14<1000×(2Fe 2 O 3 −SnO 2 )×V 2 O 5 / 2<40; - ceramizing said glass plate; A method comprising: