Glass ceramic substrate for cooking appliances and glass ceramic items

Abstract

Glass ceramic substrate (12) for a cooking appliance, comprising a main surface (16) intended for receiving cooking elements by direct contact, wherein the main surface (16) has a textured zone (18) wherein the textured zone (18) has a number of RPc peaks less than or equal to 115 and a mean arithmetic deviation Ra greater than or equal to 1 µm and less than or equal to 6 µm.

Description

TECHNICAL AREA

[0001] This presentation concerns a glass-ceramic substrate for a cooking appliance. STATE OF THE ART

[0002] It is known that a main surface of a glass-ceramic substrate for a cooking appliance is textured to give it scratch-resistant and dirt-repellent properties.

[0003] Document FR3140623 describes a chemical texturing process for the surface of glass before ceramic heat treatment or for glass ceramics after ceramic heat treatment of glass.

[0004] Glass-ceramic substrates for cooking appliances are generally black and have a certain degree of light transmission to allow the indicator lights to be seen. However, under certain lighting conditions, the electronic components of the cooking appliance can become visible due to light reflection from the light source positioned above the appliance.

[0005] To solve this problem, it was proposed to apply an opaque coating, for example a layer of paint, to the underside of the glass-ceramic substrate, i.e., to the surface opposite the surface intended for direct contact with cooking elements such as pans and / or pots.

[0006] However, there is a risk of delamination of the opaque coating, particularly due to differences in the coefficient of thermal expansion between the glass ceramic and the opaque coating. Furthermore, this step of adding a coating complicates the manufacturing process of the glass ceramic substrate.

[0007] Furthermore, there is a need for a glass-ceramic substrate that is easy to manufacture and has a transparency that allows the user to see the indicator lights without revealing the electronic components. SUMMARY OF THE INVENTION

[0008] This presentation aims to address at least some of these disadvantages.

[0009] This presentation relates to a glass-ceramic substrate for a cooking appliance, comprising a main surface for receiving cooking elements by direct contact, wherein the main surface includes a textured zone, the textured zone having a number of RPc peaks less than or equal to 115 and a mean arithmetic deviation Ra greater than or equal to 1 µm and less than or equal to 6 µm.

[0010] While this is a glass-ceramic substrate, it is important to understand that it is not a glass-ceramic substrate with a coating applied to it. The textured zone is also not a coating applied to the substrate, but rather a zone created by treating the substrate itself. Therefore, there is no risk of delamination between the glass-ceramic substrate and any coating applied to it, particularly due to the difference in the coefficient of thermal expansion between the glass-ceramic substrate and the coating. This reduces the risk of defects in the glass-ceramic article that incorporates the glass-ceramic substrate. However, the textured zone may include decorative elements applied to it, such as screen-printed glaze layers.

[0011] The risks of chemical, thermal, mechanical and / or thermomechanical deterioration are reduced because the glass ceramic substrate is monolithic.

[0012] The risks of leaching of elements present in an additional layer and / or the risks of discoloration of the glass-ceramic substrate are reduced. The risk of leaching and / or discoloration can be attributed to chemical attacks caused by hot or cold soiling and / or hot or cold cleaning agents and / or thermo-oxidative reactions when the glass-ceramic substrate is heated.

[0013] The number of RPc peaks is defined in the standard DIN EN ISO 4287:2010 and is measured over an evaluation length of 4 mm to 12.5 mm.

[0014] The mean arithmetic deviation Ra is defined in the standard DIN EN ISO 4287:2010 and is measured over an evaluation length of 4 mm to 12.5 mm.

[0015] The textured zone is essentially isotropic, meaning that the variation in the measurement of the number of RPc peaks varies only slightly depending on the measurement direction.

[0016] It can be understood that the number of RPc peaks in the textured zone is less than or equal to 115, regardless of the measurement direction.

[0017] A number of RPc peaks less than or equal to 115 makes it possible to obtain a glass-ceramic substrate that reduces the visibility of the electronic components of a glass-ceramic article comprising the glass-ceramic substrate.

[0018] The scratch resistance properties of the glass-ceramic substrate improve with a higher mean arithmetic deviation (Ra) value. Since the mean arithmetic deviation is less than or equal to 6 µm, any decoration applied to the textured surface will be clearly visible.

[0019] In some embodiments, the number of RPc peaks is less than or equal to 60.

[0020] In some embodiments, the mean arithmetic deviation Ra is greater than or equal to 2 µm, preferably greater than or equal to 3 µm.

[0021] In some embodiments, the textured zone exhibits a blur of greater than or equal to 10% and less than or equal to 80%.

[0022] Blurring, also known as haze, is defined and measured according to the ISO 14782:1999 standard.

[0023] In some embodiments, the textured zone exhibits a color deviation ΔE* of less than or equal to 3, where the color of the textured zone is measured on white and black backgrounds.

[0024] The color deviation ΔE* is calculated according to the following equation. ΔE*=(L2*−L1*)2+(a2*−a1*)2+(b2*−b1*)2

[0025] The coordinates L1*, L2*, a1*, a2*, b1*, and b2* are the color reflection coordinates measured under illumination type D65 / 10 in the CIELAB 1976 room. The index 1 represents the coordinates on a white background, and the index 2 represents the coordinates on a black background.

[0026] The color deviation ΔE* is a parameter used to measure the opacity of the glass-ceramic substrate. The lower the value of the color deviation ΔE* (black / white), the more opaque the glass-ceramic substrate is considered.

[0027] In some embodiments, the textured zone includes a glaze decoration with a glaze line resolution of less than or equal to 1.6.

[0028] A glaze line is applied using screen printing. After the glaze has dried and been fired, the boundary between the glazed and unglazed areas is not straight, but forms a line with a certain wavy shape. The length of this boundary is measured using an optical microscope. The glaze line resolution, denoted by r, corresponds to the ratio between the measured length and the theoretical length of this boundary (a glaze line with perfectly straight edges).

[0029] In some embodiments, the glass-ceramic substrate has a thickness greater than or equal to 3.2 mm and less than or equal to 4.5 mm.

[0030] This presentation also relates to a glass-ceramic article comprising a glass-ceramic substrate as defined above.

[0031] For example, the glass ceramic article may include a glass ceramic substrate as defined above and a control panel for the glass ceramic article.

[0032] This presentation also relates to a glass-ceramic substrate as defined above, obtainable by a process comprising the following steps: - Ceramicization of a glass substrate to obtain the glass-ceramic substrate; - chemical treatment of a zone to be textured on the glass ceramic substrate in order to obtain the textured zone.

[0033] The chemical treatment enables a relatively uniform texturing of the textured zone. The textured zone is therefore essentially isotropic.

[0034] Chemical treatment makes it possible to treat large areas of the glass ceramic substrate or even the entire main surface of the glass ceramic substrate.

[0035] In some embodiments, the chemical treatment is carried out at a temperature greater than or equal to 30 °C and less than or equal to 60 °C.

[0036] In some embodiments, the chemical treatment is carried out over a period of 100 seconds or more and 1000 seconds or less.

[0037] In some embodiments, the glass substrate comprises, in mass percent, 58-75% silicon dioxide, 16-25% aluminum oxide, 2-4.5% lithium oxide, 0-2% sodium oxide, 0-2% potassium oxide, 0-4% calcium oxide, 0-5% magnesium oxide, 0-5% barium oxide, 0-5% zinc oxide, 0-5% strontium oxide, 1-6% titanium oxide, 0-3% zirconium oxide, 0-6% phosphorus pentoxide, 0-2% boron oxide, 0-2% iron oxide, 0-2% chromium oxide, 0-2% cobalt oxide, 0-2% refining agent, 0-2% colorant.

[0038] For example, the refining agent can, without restriction, include tin oxide and / or arsenic oxide and / or antimony oxide.

[0039] For example, without restriction, the dye may include vanadium oxide and / or chromium oxide and / or iron oxide and / or cobalt oxide.

[0040] In some embodiments, the chemical treatment is carried out with an aqueous solution containing hydrofluoric acid, ammonium fluoride, and fluorosilicic acid.

[0041] The mixture makes it possible to obtain a textured surface.

[0042] In some embodiments, the area of ​​the glass ceramic substrate to be textured is subjected to a mechanical surface treatment by sandblasting before the chemical treatment step.

[0043] Mechanical surface treatment by sandblasting can texture the area to be textured and shorten the chemical treatment time of the area to be textured.

[0044] In some embodiments, the chemical treatment is carried out with an aqueous solution containing hydrofluoric acid.

[0045] In some embodiments, a glaze decoration is applied to the textured zone, for example by screen printing.

[0046] This step is performed after the chemical treatment step. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further features and advantages of the subject of this presentation will become apparent from the following description of embodiments, which are given as non-restrictive examples with reference to the accompanying figures. [ Fig. 1] Fig. Figure 1 is a schematic perspective view of a glass ceramic article according to one embodiment. [ Fig. 2] Fig. Figure 2 is a schematic cross-sectional view of a textured zone according to one embodiment. [ Fig. 3] Fig. Figure 3 is a flowchart that illustrates the steps of a manufacturing process as described above.

[0048] In all figures, the common elements are identified by identical numerical reference symbols. DETAILED DESCRIPTION

[0049] Fig. Figure 1 is a schematic longitudinal sectional view of a glass ceramic article 10 according to an embodiment.

[0050] In the embodiment according to Fig. 1. The glass-ceramic article 10 comprises a glass-ceramic substrate 12 and a control panel 14 of the glass-ceramic article. The glass-ceramic article 10 may only comprise the glass-ceramic substrate 12; i.e., the glass-ceramic article may not have a control panel.

[0051] In the embodiment according to Fig.The glass-ceramic substrate 12 comprises a main surface 16 which has a textured zone 18. The main surface 16 of the glass-ceramic substrate 12 can comprise several textured zones 18. The main surface 16 of the glass-ceramic substrate 12 can also comprise a single textured zone 18 whose surface is identical to the surface of the glass-ceramic substrate 12. The glass-ceramic substrate 12 has a thickness E.

[0052] In the embodiment according to Fig. 1. The textured zone 18 includes a glaze decoration 20. The textured zone 18 can include several glaze decorations 20.

[0053] Fig. Figure 2 is a schematic cross-sectional view of textured zone 18 of Fig. 1.

[0054] Fig. Figure 3 is a flowchart that illustrates the steps of a manufacturing process 100 of the glass ceramic substrate 12.

[0055] The manufacturing process 100 comprises a ceramicization step 102 of a glass substrate to obtain the glass ceramic substrate 12 and the chemical treatment 104 of a zone of the glass ceramic substrate 12 to be textured to obtain the textured zone 18.

[0056] The chemical treatment step 104 may be preceded by a mechanical surface treatment step 106 by sandblasting.

[0057] The manufacturing process 100 can also include a step of applying 108 glaze decorations 20 to the textured zone 18, for example by screen printing. Examples 1 to 3 (Ex1 to Ex3)

[0058] Examples 1 to 3 are performed on glass-ceramic substrates whose textured zone is obtained by chemical treatment of the area to be textured. The aqueous chemical treatment solution contains hydrofluoric acid (HF), ammonium fluoride (NH4F), and fluorosilicic acid (H2SiF6). The composition of the solution, along with the temperature and duration of the chemical treatment, is given in Table 1 below. Examples 4 to 8 (Ex4 to Ex8)

[0059] Examples 4 to 8 are carried out on glass-ceramic substrates, whereby the textured zone is obtained by mechanical surface treatment and subsequent chemical treatment of the zone to be textured.

[0060] Mechanical surface treatment is carried out by sandblasting. The abrasive consists of garnet particles with a grit size of 120. The particles are sprayed onto the area to be textured through nozzles at a pressure between 2 and 5 bar. The feed rate is between 6 and 36 mm / s, and the vertical movement speed of the nozzles is between 250 and 500 mm / s. The area to be textured is processed in a single pass.

[0061] The aqueous chemical treatment solution contains hydrofluoric acid (HF). The composition of the solution and the duration of the chemical treatment, expressed in relative time, are listed in Table 1 below.

[0062] Table 1 contains the data on the chemical treatment for examples 1 to 8 as well as the values ​​for thickness E (in mm), RPc, Ra (µm), blur (in %), ΔE* and line resolution r for examples 1 to 8.

[0063] The values ​​of the various roughness parameters, Ra and Rpc, were measured with a Mitutoyo SJ401 mechanical probe with a stylus of type “12AAC731” and evaluated according to ISO 4287:2010 over an evaluation length of 4 mm to 12.5 mm.

[0064] The values ​​of ΔE* are measured using a 45 / 0 gloss spectroguide from Byk Gardner.

[0065] The data for the chemical treatment include the hydrofluoric acid concentration (in M), the NH4F and HF concentrations (in g / L), and the H2SiF6 concentration (in mol / L). The temperature T (in °C) of the chemical treatment bath is between 30 °C and 60 °C, and the time t (in relative time) of the chemical treatment is between 50 seconds and 1200 seconds. [Table 1] Ex1 Ex2 Ex3 Ex4 Ex5 Ex6 Ex7 Ex8 E 3,94 3,94 3,94 3,53 3,66 3,67 3,73 3,92 HF 9,4 22 9,4 14,3 14,2 13,9 14,5 13,9 NH4F, HF 500 500 500 H2SiF6 0,1 0,1 0,1 Time 7,5 t 5 t 5 t 1 t 2,5 t 4t 5,5 t 7,5 t RPc 69,97 51,93 110,06 36,11 25,23 20,90 18,21 19,53 Ra 1,63 2,89 1,49 4,88 5,53 4,81 5,16 5,05 Blur 69,81 70,89 66,53 72,59 49,36 31,26 18,16 13,24 ΔE* 0,51 0,48 0,59 0,57 0,65 1,2 1,95 2,26 r 1,57 1,43 1,38 1,3 1,3

[0066] It can be observed that the mechanical surface treatment step by sandblasting makes it possible to shorten the chemical treatment time while simultaneously creating a textured zone with good blur and ΔE* values. Furthermore, the resolution values ​​of line r allow for the application of glaze decorations with optically correct quality to the textured zone. Comparison examples 1 to 4 (ExC1 to ExC4)

[0067] Comparative examples 1 to 4 are performed on glass-ceramic substrates that have been treated in a rolling mill using a known method. The rollers of the rolling mill are themselves textured to imprint a pattern onto the laminated glass material.

[0068] Table 2 lists the values ​​for thickness E (in mm), RPc, Ra (µm), blur (in %), ΔE* and line resolution r for comparison examples 1 to 4. [Table 2] ExC1 ExC2 ExC3 ExC4 E 3,98 3,54 3,41 3,29 RPc 80,04 80,50 88,10 83,73 Ra 0,16 0,16 0,14 0,13 Blur 7,50 4,74 3,35 2,71 ΔE* 1,83 3,02 3,34 3,90 r 1,2 1,2 1,2 1,2

[0069] Although this presentation describes a specific embodiment, it is obvious that various modifications and changes can be made to these examples without departing from the general scope of the invention as defined in the claims. Furthermore, individual features of the different embodiments can be combined to form additional embodiments. Therefore, the description and drawings should be considered illustrative rather than limiting. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] FR 3140623

[0003] Cited non-patent literature

[0000] Standard DIN EN ISO 4287:2010

[0013]

Claims

[1] Glass ceramic substrate (12) for a cooking appliance comprising a main surface (16) intended for receiving cooking elements by direct contact, wherein the main surface (16) has a textured zone (18) wherein the textured zone (18) has a number of RPc peaks less than or equal to 115 and a mean arithmetic deviation Ra greater than or equal to 1 µm and less than or equal to 6 µm. [2] Glass ceramic substrate (12) according to claim 1, wherein the textured zone (18) has a blur of greater than or equal to 10% and less than or equal to 80%. [3] Glass ceramic substrate (12) according to claim 1 or 2, wherein the textured zone (18) has a color deviation ΔE* of less than or equal to 3, wherein the color of the textured zone (18) is measured on a white and black background. [4] Glass ceramic substrate (12) according to one of claims 1 to 3, wherein the textured zone (18) has a glaze decoration (20) with a glaze line resolution of less than or equal to 1.

6. [5] Glass ceramic substrate (12) according to any one of claims 1 to 4 having a thickness (E) greater than or equal to 3.2 mm and less than or equal to 4.5 mm. [6] Glass ceramic article (10) comprising a glass ceramic substrate (12) according to any one of claims 1 to 5. [7] Glass ceramic substrate (12) according to any one of claims 1 to 5, obtainable by a method comprising the following steps: - Ceramicization (102) of a glass substrate to obtain the glass ceramic substrate (12); - chemical treatment (104) of a zone of the glass ceramic substrate (12) to be textured in order to obtain the textured zone (18). [8] Glass ceramic substrate (12) according to claim 7, wherein the chemical treatment (104) is carried out with a solution containing hydrofluoric acid, ammonium fluoride and fluorosilicic acid. [9] Glass ceramic substrate (12) according to claim 7, wherein the zone of the glass ceramic substrate (12) to be textured is subjected to a mechanical surface treatment (106) by sandblasting prior to the chemical treatment step (104). [10] Glass ceramic substrate (12)) according to claim 9, wherein the chemical treatment (104) is carried out with a solution containing hydrofluoric acid.

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