Glass ceramic plate with a liquid retention bead and method for producing such a plate

Description

[0001] The present invention relates to a ceramic glass cooktop for a cooking appliance comprising a liquid retention cord. When the ceramic glass cooktop is used in a cooking appliance, the retention cord prevents liquids that might overflow from cooking containers or utensils from reaching the surface of the cooktop.

[0002] Ceramic glass cooktops are now widely used as cooking surfaces in many cooking appliances. They are inorganic materials, most often based on silicates or aluminosilicates. Their main advantages are their flat surface, low coefficient of thermal expansion, and resistance to thermal shock.

[0003] When cooking food on a ceramic hob, liquids sometimes overflow from utensils or containers and quickly spread across the hob's surface due to its flatness. For safety reasons and to prevent damage to the environment where the cooking appliance is used, it is best to contain these spills on the hob before they run off its surface.

[0004] Food liquids are generally water, aqueous solutions, or organic solutions in which water is a component.

[0005] Various systems or devices aimed at retaining liquids on cooking surfaces are described in the prior art.

[0006] Document EP1178265 A1 describes a cooking device comprising a glass-ceramic plate on whose surface channels are directly engraved, through which the liquids to be retained flow. However, the engraving of such channels is likely to make the glass-ceramic plate locally more fragile and to cause unexpected fractures during machining or handling of the products.

[0007] Document FR2913098 A1 proposes an alternative solution: placing a level sensor on the rim of cooking containers to warn of any increase in liquid level before it overflows. The main drawback is that each container requires a sensor. If one sensor is forgotten or not activated, the liquids will not be contained.

[0008] Document WO2011056742 A1 describes a hydrophobic coating applied to the periphery of a cooking surface or surrounding certain areas of said surface, so as to create retention basins. These hydrophobic coatings have the advantage of retaining a certain volume of liquid within the basins they define. In this type of basin, the liquid generally takes the form of a film. The volume of the liquid is thus defined by the surface area of ​​the basin and the height of the film formed. However, research conducted on the flow of liquids in contact with hydrophobic coatings has found that the height reached by the film before the liquid overflows beyond the hydrophobic coating is less than the theoretical capillary height. Consequently, the volume of liquid retained is less than the desired volume and the retention time is shorter than expected.The reason for this is the inherent movement of the liquid during its flow, which causes local variations in internal pressure. At the interface between the liquid and the hydrophobic material, a local pressure variation can destabilize the liquid film, causing it to spill out of the reservoir.

[0009] Most of the retention volume measurements reported in the prior art for classifying cooktops with reservoirs defined by hydrophobic coatings were carried out using protocols in which there was no liquid flow. These protocols are called "static." The phenomenon described above, which corresponds to most real-world overflow cases, is therefore generally overlooked. Products with such reservoirs thus appear less efficient than advertised.

[0010] The present invention addresses these problems. The inventors have demonstrated that alternating hydrophobic and hydrophilic zones in a pattern satisfying certain geometric constraints improves the retention of moving liquids, notably slowing down or even stopping their flow. The constituents of the hydrophobic zones, when the parameters characterizing their hydrophobic nature meet certain criteria, can also increase this retention capacity.

[0011] The present invention therefore relates to a ceramic glass cooktop for a cooking device comprising: a first main face likely to come into contact with liquids when the plate is in use, a second main face and an edge, a liquid retention cord fixed on and in contact with said first main face.

[0012] The ceramic glass cooktop is characterized in that said retention cord: surrounds at least one region of said first main face so as to form a reservoir for the retention of liquids, and -includes at least two hydrophobic subcords inscribed within each other and separated by hydrophilic zones, the width of the hydrophilic zone between two consecutive subcords is everywhere between 500 µm and 2.5 cm, the hydrophobic subcords being such that when they are in contact with water, the hysteresis H of the contact angle between said hydrophobic subcords and the water is greater than or equal to 20°, said hysteresis H of the contact angle being defined as the difference between the advance angle Θa and the recoil angle Θr of the water on said hydrophobic subcords.

[0013] The phrase "when in use" means that the ceramic glass cooktop is being used in a cooking appliance and that cooking utensils or containers holding liquids are being used or handled on or over its surface which is suitable for contact with liquids.

[0014] In the following text, for the sake of clarity and conciseness, the expression "surface of the glass-ceramic hob" or its equivalents may be used. This expression refers to the surface of the front of the glass-ceramic hob.

[0015] The hydrophobic or hydrophilic nature of a material is usually defined by the contact angle formed by a static water droplet in contact with the material's surface. The contact line is the triple interface line between the water, the material, and the air. The static contact angle corresponds to the angle formed between the plane tangent to the surface of the water droplet and the plane of the material surface located beneath the water droplet. When the angle is less than 90°, the material is said to be hydrophilic; when it is equal to or greater than 90°, it is said to be hydrophobic.

[0016] Contact angle measurements are generally performed using a goniometer. The instrument deposits a calibrated drop of water onto a surface. Using a camera, image analysis software detects the shape of the drop, the location of the substrate, and then measures the contact angle. Examples of goniometers include the DSA100 and the MobileDrop GH11, both marketed by Krüss. An example of a measurement protocol is the one described in ASTM D7334-08(2013), Standard Practice for Surface Wettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement.

[0017] For the purposes of this invention, the hydrophobic or hydrophilic nature of a material is defined according to the preceding definition. Thus, the contact angle formed by a water droplet on hydrophilic areas is less than 90°. The contact angle formed by a water droplet on hydrophobic sub-cords is equal to or greater than 90°.

[0018] In one embodiment, the hydrophilic zones comprise one or more hydrophilic coatings deposited on the surface of the glass-ceramic cooktop. These hydrophilic coatings are intended to advantageously increase the hydrophilic nature of the cooktop surface in order to enhance its retention capacity.

[0019] These hydrophilic coatings can be organic or inorganic. The constituent(s) of hydrophilic coatings can be chosen from polyvinyls, polyacrylonitril, polymethyl acrylates, cellulose acetates, or copolymers of vinyl acetate and vinyl chlorides. Examples of inorganic materials include silica, alumina, and zirconia.

[0020] These coatings can be deposited using a deposition method chosen from liquid phase chemical deposition, vapor phase chemical deposition, vacuum phase chemical deposition, screen printing, centrifugal coating, dip coating, jet printing deposition, three-dimensional printing deposition.

[0021] In a preferred embodiment, the hydrophilic zones are formed by the surface of the glass-ceramic plate without any surface treatment, since the silicates and aluminosilicates composing most glass-ceramic plates are naturally hydrophilic materials. This embodiment is faster and simpler to implement.

[0022] According to the invention, the retention cord surrounds at least one area of ​​the ceramic glass cooktop surface onto which liquids may spill during cooking or food preparation. It thus delineates a liquid retention or containment reservoir. Liquid that overflows from a container or cooking utensil and spreads over this delimited area forms a film whose flow is blocked by the retention cord.

[0023] Cooking containers or utensils are generally placed on the areas of the ceramic glass cooktop surface beneath which heating elements are located when the cooktop is used in a cooking appliance. The retaining cord can advantageously encircle at least one of these areas.

[0024] In one embodiment, the retention cord is placed at most 3 cm, in particular at most 2 cm, or even at most 1 cm, from the edge of the ceramic glass cooktop. Positioned around the periphery of the cooktop in this way, a single retention cord is sufficient to encircle all the areas of the ceramic glass cooktop where utensils or cooking containers are used. This embodiment is particularly advantageous for cooking appliances in which the heating or cooking zones consist of one or more portions of the ceramic glass cooktop surface. It is also simpler and quicker to implement because it requires only one bead.

[0025] In an alternative embodiment, several retention cords are attached to the main surface of the ceramic glass cooktop that may come into contact with liquids during use. Each of these retention cords can surround different areas of the surface. These areas may be distant from each other or in contact. Some of these different retention cords may be separate or joined, that is, they may or may not have common portions. Preferably, these retention cords surround areas of the ceramic glass cooktop on which containers or cooking utensils that may contain liquids are used.

[0026] The area of ​​the ceramic glass plate region surrounded by at least one retention cord advantageously represents at least 60%, in particular 70%, preferably 80%, or even 90% of the area of ​​the face of the ceramic glass plate.

[0027] The width of a retention cord can advantageously be between 2 cm and 6 cm, in particular between 3 and 6 cm, or even between 3 and 5 cm.

[0028] The geometric shape of the area(s) delimited by the hydrophobic cords can be any shape: rectangular, circular, oval, triangular, trapezoidal, parallelepiped, or even follow the form of an aesthetic motif. The geometric shape is a matter of choice, depending on the technical constraints imposed by the cord application method and the use of the ceramic cooktop, or on the aesthetic preferences of the customers or the person implementing the invention.

[0029] According to the invention, the retention cords comprise at least two hydrophobic sub-cords inscribed one inside the other and separated by hydrophilic zones. In other words, each hydrophobic sub-cord individually delimits a region of the ceramic glass cooktop surface. The expression "inscribed one inside the other" applied to the hydrophobic sub-cords means that each hydrophobic sub-cord following another hydrophobic sub-cord from the edge of the ceramic glass cooktop is located within the region of the cooktop surface delimited by that other hydrophobic sub-cord.

[0030] The consecutive sub-cords must be close enough so that the height of the film formed by the liquid in the region delimited by the retention cord is greater than the height that would be obtained using a retention cord according to the prior art and which would include only one sub-cord.

[0031] Two consecutive subcords can be irregularly or regularly spaced as long as the width of the hydrophilic zone between two consecutive subcords is everywhere between 500 µm and 2.5 cm, in particular between 500 µm and 1.2 cm, or even between 700 µm and 1.2 cm.

[0032] Furthermore, the width of the hydrophobic sub-cords can advantageously range from 5 mm to 20 mm, particularly from 7 mm to 18 mm, or even from 10 mm to 15 mm, without affecting the retention effect. This characteristic thus reduces the amount of material required to form the hydrophobic sub-cords.

[0033] The contact of a liquid droplet with a material surface can also be characterized using two other contact angles: the leading angle θa and the recoil angle θr. These two angles are called dynamic because they correspond to the contact angles formed by a water droplet in contact with the material surface when its contact line with the material moves due to an increase or decrease in its volume. The contact line corresponds to the triple line formed at the interface between the water in the droplet, the material surface, and the atmosphere.

[0034] More precisely, the advance angle θa is the angle formed between the plane tangent to the surface of the water droplet and the plane of the surface of the material located below the water droplet before the contact line advances under the effect of the increase in the volume of water in the droplet.

[0035] The recoil angle θr is the angle formed between the plane tangent to the surface of the water droplet and the plane of the surface of the material located below the water droplet before the contact line recoils under the effect of a decrease in the volume of water in the droplet.

[0036] According to current knowledge available in the state of the art, the advance angle θa can be considered as a measure of the wetting or repulsive character of the surface, and the recoil angle θr as a measure of the adhesion of the water droplet to the surface.

[0037] The measurement of forward and backward angles is generally carried out using the same instruments as those used for measuring contact angle.

[0038] The volume of liquid retained depends on the surface area of ​​the region enclosed by the containment bead and the height or thickness of the film formed. Liquid flow from a container or utensil is generally continuous at a certain rate. Therefore, the time it takes for the liquid to spill out of the reservoir depends on the surface area of ​​the region enclosed by the containment bead, the flow rate, and the maximum height the liquid reaches in the reservoir.

[0039] In a preferred embodiment, when the hydrophobic sub-cords are in contact with water, the hysteresis H of the contact angle between said hydrophobic sub-cords and the liquid is greater than or equal to 20°, in particular greater than or equal to 25°, or even greater than or equal to 30°, said hysteresis H of the contact angle being defined as the difference between the leading angle θa and the recoil angle θr of the liquid on one of said hydrophobic sub-cords, in other words H = θa - θr. It has been observed, rather surprisingly, that when the value of this hysteresis is greater than or equal to 20°, in particular greater than or equal to 25°, or even greater than or equal to 30°, the maximum height of the liquid film, i.e., the volume of liquid retained, increases. The retention of the moving liquid is thus enhanced. The hysteresis value is preferably less than or equal to 100.

[0040] This surprising effect is particularly important when the angle of advance, θa, of the liquid on the subcords is also between 108 and 120°, especially between 110° and 120°.

[0041] There is a wide variety of hydrophobic materials or compounds suitable for making hydrophobic sub-beads. Among these materials, those skilled in the art can choose those whose other properties, particularly thermal and / or mechanical, are compatible with the application or the environment in which the ceramic glass cooktop is used.

[0042] For example, when a ceramic glass cooktop is used in a cooking appliance intended for domestic use, a person skilled in the art can choose hydrophobic material(s) that also withstand contact with hot liquids, typically at temperatures between 50°C and 150°C, without losing their hydrophobic properties. Similarly, it can be advantageous for hydrophobic materials to withstand thermal cycles of heating and cooling without deteriorating or losing their hydrophobic nature.

[0043] Hydrophobic materials can also be advantageously chosen to provide high mechanical resistance, particularly to abrasion. Indeed, when ceramic glass cooktops are used in domestic cooking appliances, they are subjected to considerable friction from the movement of utensils and / or cooking containers on their surface. If the hydrophobic sub-cords are positioned near areas of the ceramic glass cooktop surface where this movement is intense and frequent, they must also be abrasion-resistant. Conversely, if the hydrophobic sub-cords are located further from these areas, for example, when the retention cord is placed near the periphery of the ceramic glass cooktop, they will be subject to less friction. Therefore, high abrasion resistance is not always necessary, depending on the placement of the retention cord(s).

[0044] Hydrophobic materials suitable for constructing hydrophobic sub-cords can be organic or inorganic. Advantageously, hydrophobic sub-cords can comprise one or more organic or inorganic compounds with a surface tension of at most 20 mN·m⁻¹, in particular at most 15 mN·m⁻¹, or even at most 10 mN·m⁻¹. Such hydrophobic compounds generally also possess lipophobic or oleophobic properties, which can be useful when the liquids overflowing from containers or cooking utensils are rich in fats.

[0045] By way of non-limiting example, hydrophobic subcords may comprise one or more organic compounds selected from polysiloxanes, organosiloxanes, fluorosiloxanes, fluorocarbons, fluoropolymers, fluorosilanes and mixtures thereof.

[0046] Also, by way of non-limiting example, hydrophobic subcords may comprise one or more inorganic compounds selected from colloidal silica, nano-particulate silica, graphene and mixtures thereof.

[0047] Hydrophobic subcords can also be composites, meaning they comprise a mixture of materials that generally have hydrophobic properties. For example, they can be based on a mixture of non-hydrophobic materials and hydrophobic particles, the hydrophobic particles giving the mixture its hydrophobic character. These hydrophobic particles can be composed of the hydrophobic materials mentioned previously.

[0048] Generally, only the surfaces of the sub-cords are primarily in contact with liquids when they flow onto the ceramic glass cooktop. Therefore, it may be sufficient for only these surfaces to be hydrophobic. In such a case, the sub-cords can include a non-hydrophobic portion onto which a hydrophobic coating is deposited to impart a hydrophobic surface. For example, the non-hydrophobic portion can be an enamel, and the hydrophobic coating can be based on one of the hydrophobic materials mentioned above. This embodiment is particularly advantageous because the enamel can promote the adhesion of the hydrophobic coating to the ceramic glass cooktop surface and provide additional mechanical resistance.

[0049] In this embodiment, the hydrophobic sub-cords include a hydrophobic coating. The deposition of the hydrophobic sub-cords can then be carried out in two steps. A first step in which the enamel can be deposited on the surface of the glass-ceramic plate, and then a second step in which the hydrophobic coating is deposited on the enamel.

[0050] Besides the nature of the materials that compose them, the hydrophobic character of materials also depends on the morphology of their surface.

[0051] In one particular embodiment of the invention, the value of the roughness parameter, Ra, of the hydrophobic sub-cords is between 1 and 10 µm, preferably between 2 and 5 µm. In another embodiment of the invention, the value of the peak-to-valley parameter, Rz, of the hydrophobic sub-cords is between 5 and 50 µm, preferably between 10 and 20 µm. These two embodiments can be combined.

[0052] The specifications for measuring the Ra and Rz parameters are described in ISO 4288:1996, Geometrical Product Specifications (GPS) - Surface texture: Profile method - Terms, definitions and surface texture parameters. The wavelength cut-off used for measuring the Ra and Rz parameters in the present invention is 2.5 mm.

[0053] All the embodiments described can be combined.

[0054] The present invention also relates to a method for manufacturing a glass-ceramic plate as described above. In this manufacturing method, the hydrophobic sub-cords can be deposited according to one or more of the methods chosen from among liquid-phase chemical deposition, gas-phase chemical deposition, vacuum chemical deposition, such as spraying, screen printing, centrifugal coating, dip coating, jet printing deposition, wiping, flexography, magnetron sputtering, three-dimensional printing deposition.

[0055] The present invention also relates to a cooking device in which a ceramic glass plate equipped with a liquid retention cord as described above is used.

[0056] Cooking appliances also generally include control and / or display units for adjusting and / or displaying information related, for example, to the temperature or heating power. These units can be positioned below or above, in contact with or not, the ceramic glass cooktop. The terms "below" and "above" are defined in relation to the orientation of the main surface that may come into contact with liquids: the ceramic glass cooktop is oriented so that this surface is the upper surface of the cooking appliance on which the utensils or cooking containers are used.

[0057] For example, display units may include information projection means, placed below the glass-ceramic plate, which project light signals onto the side opposite the main side that may come into contact with liquids. The projected information is then visible through the glass-ceramic plate.

[0058] The control units may be touch-sensitive devices comprising detection means located beneath the ceramic glass cooktop. These means give certain areas of the cooktop a touch-sensitive function that can be activated by touching or pressing the fingers on the corresponding areas of the main surface likely to come into contact with liquids. Switching on the cooking appliance and adjusting the heating power can then be done simply by moving the fingers. Alternatively, the control units may be mechanical knobs located on the surface likely to come into contact with liquids and operated by rotation.

[0059] When liquid overflows from a cooking container and spills onto the ceramic cooktop, it is advantageous to prevent it from reaching the control units. If the control units are, for example, mechanical knobs, they will not be damaged. If they are touch-sensitive, the touch function will not be affected by the presence of liquid. The cooking appliance can then always be safely switched off.

[0060] Preferably, the cooking device according to the invention further includes a control unit which is not included in the region or regions of the ceramic glass plate delimited by the retention cord.

[0061] The advantages of the invention are illustrated by the figures and examples described below. There figure 1 is a schematic representation of a ceramic glass cooktop according to a first embodiment of the invention. figure 2is a schematic representation of a ceramic glass cooktop according to a second embodiment of the invention. figure 3 is a schematic representation of a cross-section along plane A of detail III of the figure 1 . There figure 4 is a schematic representation of a cross-section along plane B of detail IV of the figure 2 . There figure 5 is a schematic representation of a ceramic glass cooktop according to a third embodiment of the invention. figure 6 is a schematic representation of a cooking device comprising a ceramic glass plate according to a fourth embodiment of the invention.

[0062] There figure 1A ceramic glass plate 100 is shown according to a first embodiment of the invention. It comprises a main face 101 that is capable of coming into contact with liquids during use. For purely illustrative purposes, areas 102 of the face of the ceramic glass plate, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance, are also shown. The ceramic glass plate includes a single liquid retention cord 103 that surrounds a region 104 of the main face 101 of the plate that is capable of coming into contact with liquids. The retention cord 103 is located near the periphery of the ceramic glass plate and surrounds areas 102 of the face of the ceramic glass plate, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance.The liquid retention cord comprises two hydrophobic sub-cords 103a-103b separated by a hydrophilic zone 303. The alternation of the hydrophobic sub-cords and the hydrophilic zone is shown on the . figure 3 which corresponds to a cross-section of detail III according to plane A.

[0063] There figure 2A second embodiment of the invention represents a ceramic glass plate 100. It comprises a main face 101 that may come into contact with liquids during use. Areas 102 of the ceramic glass plate face, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance, are also shown. The ceramic glass plate includes a single liquid retention cord 201 surrounding a region 104 of the main face 101 of the plate that may come into contact with liquids. The retention cord 201 is located near the periphery of the ceramic glass plate and surrounds areas 102 of the ceramic glass plate face, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance.The liquid retention cord comprises three hydrophobic sub-cords 201a-201c separated by hydrophilic zones 401 and 402. The alternation of hydrophobic sub-cords and hydrophilic zones is shown on the . figure 4 which corresponds to a cross-section of detail IV according to plane B.

[0064] A cross-section of detail III along plane A of the figure 1 is represented on the figure 3The glass-ceramic hob 100 comprises a first main face 101, a second main face 302, and an edge 301. The main face 101 is likely to come into contact with liquids when the hob is in use. The retention cord 103 is fixed to and in contact with the main face 101 that is likely to come into contact with liquids. It comprises two hydrophobic sub-cords 103a-103b separated by a hydrophilic zone 303. The two consecutive sub-cords may be irregularly or regularly spaced. The width of the hydrophobic zone is everywhere between 500 µm and 2.5 cm, in particular between 500 µm and 1.2 cm, or even between 700 µm and 1.2 cm. The width of the hydrophobic sub-cords can advantageously be between 5 mm and 20 mm, in particular between 7 mm and 18 mm, or even between 10 mm and 15 mm.

[0065] There figure 4 represents a cross-section along plane B of detail IV of the figure 2The glass-ceramic hob 100 comprises a first main face 101, a second main face 302, and an edge 301. The main face 101 is likely to come into contact with liquids when the hob is in use. The retention cord 201 is fixed to and in contact with the main face 101 that is likely to come into contact with liquids. It comprises three hydrophobic sub-cords 201a-201c separated alternately by two hydrophilic zones 401 and 402. The three consecutive sub-cords may be irregularly or regularly spaced. The width of the hydrophobic zones is everywhere between 500 µm and 2.5 cm, in particular between 500 µm and 1.2 cm, or even between 700 µm and 1.2 cm. The width of the hydrophobic sub-cords can advantageously be between 5 mm and 20 mm, in particular between 7 mm and 18 mm, or even between 10 mm and 15 mm.

[0066] There figure 5A third embodiment represents a ceramic glass plate 100. The ceramic glass plate includes a face 101 that may come into contact with liquids during use. Areas 102 of the ceramic glass plate face, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance, are also shown. The ceramic glass plate includes two liquid retention cords 501 and 502 surrounding two regions 503 and 504 of the plate face that may come into contact with liquids. The retention cords surround areas 102 of the ceramic glass plate face, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance.Each liquid retention cord 501 and 502 comprises two hydrophobic sub-cords 501a-501b and 502a-502b respectively separated by hydrophilic zones 505 and 506.

[0067] A cooking device 600 comprising a ceramic glass plate according to a variant of the first embodiment of the invention of the figure 1 is shown in top view on the figure 6The ceramic glass plate 100 includes a main face 101 that may come into contact with liquids during use. For illustrative purposes only, areas 102 of the ceramic glass plate face, beneath which heating elements may be located when the ceramic glass plate is used in a cooking appliance, are also shown. The ceramic glass plate includes a single liquid retention bead 103 surrounding a region 104 of the main face 101 of the plate that may come into contact with liquids. The retention bead 103 is located near the periphery of the ceramic glass plate and surrounds areas 102 of the ceramic glass plate face, beneath which heating elements may be located. The liquid retention bead comprises two hydrophobic sub-beads 103a-103b separated by a hydrophilic zone 303.The cooking device includes a display unit 601 and two control units 602. The display unit 601 and control unit 602 are not included in the region 104 delimited by the retention cord 103. Examples

[0068] In order to illustrate the technical effect obtained by the invention, two examples of a glass-ceramic hob according to the invention are compared to two examples of a glass-ceramic hob equipped with a retention device or system according to the prior art.

[0069] The ceramic glass cooktop used in the examples is a commercially available lithium aluminosilicate ceramic glass cooktop.

[0070] In the examples according to the invention, a retention cord comprising two hydrophobic sub-cords is fixed to and in contact with the face of two glass-ceramic plates according to the arrangement illustrated in the figure 1For each glass-ceramic plate, the width of each of the hydrophobic sub-cords and the width of the hydrophilic zone separating them are shown in Table 1 (Examples 1 and 2). The hydrophilic zone consists of the surface of the glass-ceramic plate that has not undergone any treatment.

[0071] To produce the examples of glass-ceramic hobs according to the prior art, a retention cord comprising only a single hydrophobic sub-cord is fixed to and in contact with the face of two glass-ceramic hobs according to the same arrangement illustrated in the figure 1 (Examples 3 and 4). Examples 3 and 4 are comparative examples. In order to avoid any experimental bias related to the resizing of the retention cords, the width of the sub-cords was adjusted so that the area covered by the sub-cords and the area of ​​the region surrounded by the retention cord were identical to those of examples 1 and 2.

[0072] In all four examples, the area of ​​the region (104) surrounded by the retention cordon is identical.

[0073] The hydrophobic sub-cords are based on fluorinated trichlorosilane. They were deposited by evaporation under reduced pressure (chemical vapor deposition). During deposition, the areas of the glass-ceramic plate outside the hydrophobic sub-cords were protected using a mask impermeable to fluorinated compounds.

[0074] The retention performance of each ceramic glass plate was evaluated by pouring water into the center of the areas surrounded by the retention ring with an average flow rate of 2.4 to 2.5 mL / s. This flow rate is representative of the flow rate of a liquid overflowing from a cooking vessel.

[0075] The maximum retained volume and maximum retention time before overflowing beyond the retention barriers were measured. The results are reported in Table 1.

[0076] Comparison of examples 1 and 2 according to the invention and comparative examples 3 and 4 according to the prior art shows that a glass-ceramic plate according to the invention allows a gain of 7 to 8% on the volume of liquid retained and the retention time before overflow. Table 1 Example 1 Example 2 Example 3 (comparative) Example 4 (comparative) Number of hydrophobic sub-cords 2 2 1 1 Width of hydrophobic sub-cords (cm) 1 1 1,81 1,57 Width of hydrophilic zones (cm) 1 2 - - Time before overflow(s) 47 46 43 44 Maximum volume before overflow (mL) 112 113 105 105

[0077] Three examples of glass-ceramic hobs according to the invention were produced with hydrophobic sub-cords comprising different hydrophobic compounds. Some of these compounds are commercially available.

[0078] In each example, the same type of glass-ceramic cooktop is used, and the area of ​​the region (104) enclosed by the retaining cord is identical. The glass-ceramic cooktop is made of lithium aluminosilicate. It is representative of commercially available glass-ceramic cooktops.

[0079] Table 2 indicates for each example the trade name of the hydrophobic compound used for the subcords, the type of compound, the values ​​of contact angle θc, advance angle θa, recoil angle θc, and hysteresis H.

[0080] The contact angles, advance angle, and retreat angle were measured using a DSA100 goniometer marketed by the company Krüss.

[0081] In example 5, the hydrophobic sub-cords are silicone-based (Diamon Fusion Ultra (DFI)). They were deposited in two stages using a spray or wiping (liquid phase chemical deposition).

[0082] In example 6, the hydrophobic sub-cords are based on silica and fluorinated silane (SiF7E). They were deposited according to the following protocol: application of a 0.3% by weight hydrolyzed TEOS solution in isopropanol at pH 2 by spray (liquid phase chemical deposition), drying for 5 minutes, application of a SiF7E solution in isopropanol at pH 2 by spray or wiping (liquid phase chemical deposition), drying for 15 minutes.

[0083] In example 7, the hydrophobic sub-cords are based on the Nanofilm ABW product.

[0084] The retention performance of each ceramic glass plate was evaluated by pouring water into the center of the area surrounded by the retention cord and by measuring the maximum height, h, of the retained liquid film and the maximum retention time before overflowing beyond the cord.

[0085] Under static conditions, water is deposited slowly, taking care to minimize liquid movement, and the height of the water film formed is continuously measured until it overflows beyond the retention cord.

[0086] Under dynamic conditions, water is poured at a flow rate representative of the flow rate of a liquid overflowing from a cooking vessel, and the height of the water film formed and the time are continuously measured until the overflow exceeds the retention bead. Measurements were taken for three flow rate values: 1.8 mL / s (flow rate 1), 2.3 mL / s (flow rate 2), and 2.7 mL / s (flow rate 3).

[0087] The maximum measured values ​​are grouped in Table 2.

[0088] Examples show that a hysteresis value, H, greater than or equal to 20° increases the maximum height of the retained film and the retention time before overflow under dynamic conditions compared to static conditions. Retention times are notably 2 to 4 times longer, especially when the flow rate is high.

[0089] Comparing examples 5 and 7 on the one hand, and examples 7 and 8 on the other, shows that a high hysteresis value, especially above 30, allows for longer retention times.

[0090] Comparing examples 6 and 7 shows that, for similar advance angle values, an increase in the hysteresis value allows for longer retention times. Table 2 Example 5 Example 6 Example 7 Trade name of the hydrophobic compound of the subcords Diamond Fusion Ultra (DFI) Nanofilin ABW (Ferro) Type of compound silicone silica and SiF7E - Static Hmm) 3,4 4,4 4,1 Dynamic Flow rate 1 Hmm) 4,2 4,6 4,6 Time(s) 19,9 10,1 17,7 Flow rate 2 Hmm) 4,9 5,3 5 Time(s) 13,2 11,2 14,9 Flow rate 3 Hmm) 5 5,8 5,6 Time(s) 9,7 9,8 13,7 Contact angles θ 105 114 108 θa 108 120 117 θr 80 87 68 Hysteria H 20 33 49

[0091] Four further comparative examples, examples 8, 9, 10 and 11, were also carried out to illustrate the technical effect of the invention. In these examples, a retention cord comprising two hydrophobic sub-cords is fixed to and in contact with the surface of two glass-ceramic plates according to the arrangement illustrated in the figure 1For each of the glass-ceramic plates, the width of each of the hydrophobic sub-cords and the width of the hydrophilic zone separating them are reported in Table 1. In Examples 8, 9, and 10, the width of the hydrophilic zone between two consecutive sub-cords is within the range of 500 µm to 2.5 cm. In Example 11, the width of the hydrophilic zone is outside this range. The hydrophilic zone consists of the surface of the glass-ceramic plate that has not undergone any treatment. For comparison purposes, the area of ​​the hydrophilic zone (303) enclosed by the two sub-cords is identical for all Examples 8, 9, 10, and 11.

[0092] The hydrophobic sub-cords are based on fluorinated trichlorosilane. They were deposited by evaporation under reduced pressure (chemical vapor deposition). During deposition, the areas of the glass-ceramic plate outside the hydrophobic sub-cords were protected using a mask impermeable to fluorinated compounds.

[0093] The retention performance of each ceramic glass plate was evaluated by pouring water into the center of the hydrophilic zones defined by the consecutive sub-beads of the retention bead with an average flow rate of 2.4 to 2.5 mL / s. This flow rate is representative of the flow rate of a liquid overflowing from a cooking vessel.

[0094] The retained volume and maximum retention time before overflowing beyond the hydrophilic zone were measured. The results are reported in Table 3.

[0095] Comparing the results of Examples 8 and 9 of the invention with those of Example 10 shows that a glass-ceramic plate according to the invention provides a 23% reduction in the volume of liquid retained before overflow from the hydrophilic zone for Example 8 and a 40% reduction for Example 9 in the volume of liquid retained before overflow from the hydrophilic zone, compared to a plate with a retention bead comprising two consecutive sub-beads defining a hydrophilic zone width of 0.4 cm. Compared to the volume retained in Example 9, the reduction is 3% for comparative Example 11, which includes a retention bead with two consecutive sub-beads defining a hydrophilic zone width greater than 2.5 cm. The reduction in volume and time is particularly significant when the hydrophilic zone width is between 500 µm and 2.5 cm, and especially between 0.5 cm and 2.5 cm. Table 3 Example 8 Example 9 Example 10 Example 11 (comparative) Number of hydrophobic sub-cords 2 2 2 2 Width of hydrophobic sub-cords (cm) 1 1 1 1 Width of hydrophilic zones (cm) 1 2 0,4 3 Time before overflow of the hydrophilic zone(s) 27,1 30,5 21,7 31,6 Volume before overflow of the hydrophilic zone (mL) 66,4 75,4 53,9 77,3

Claims

1. A glass-ceramic plate (100) for a cooking device comprising: - a first main face (101) liable to be in contact with liquids when the plate is in the process of being used, a second main face (302) and an edge (301), - a liquid-retaining bead (103, 201, 501, 502) fastened to and in contact with said first main face (101), characterized in that said retaining bead (103, 201, 501, 502): - surrounds at least one region (104, 503, 504) of said first main face so as to form a liquid-retaining reservoir, and - comprises at least two hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) inscribed within one another and separated by hydrophilic zones (303, 401-402, 506, 505), the width of the hydrophilic zone between two consecutive sub-beads is throughout comprised between 500 µm and 2.5 cm. the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) being such that when they are in contact with water, the hysteresis H of the contact angle between said hydrophobic sub-beads and the water is greater than or equal to 20°, said hysteresis H of the contact angle being defined as the difference between the advancing angle θa and the receding angle θr of the water on said hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b).

2. The glass-ceramic plate (100) as claimed in claim 1, such that said advancing angle is between 108 and 120°, in particular between 110° and 120°.

3. The glass-ceramic plate (100) as claimed in claim 1 or 2, such that the width of the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) is between 5 mm and 20 mm, in particular between 7 mm and 18 mm, or even between 10 mm and 15 mm.

4. The glass-ceramic plate (100) as claimed in any one of claims 1 to 3, such that the value of the roughness parameter, Ra, of the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) is between 1 and 10 µm, preferably between 2 and 5 µm.

5. The glass-ceramic plate (100) as claimed in any one of claims 1 to 4, such that the value of the peak-to-valley parameter, Rz, of the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) is between 5 and 50 µm, preferably between 10 and 20 µm.

6. The glass-ceramic plate (100) as claimed in any one of claims 1 to 5, such that the width of the retaining bead (103, 201, 501, 502) is between 2 cm and 6 cm, in particular between 3 and 6 cm, or even between 3 and 5 cm.

7. The glass-ceramic plate (100) as claimed in any one of claims 1 to 6, such that the retaining bead (103, 201, 501, 502) is placed at at most 3 cm, in particular at most 2 cm, or even at most 1 cm from the edge of said glass-ceramic plate.

8. The glass-ceramic plate (100) as claimed in any one of claims 1 to 7, such that the surface area of the region (104, 503, 504) of the glass-ceramic plate surrounded by at least one retaining bead (103, 201, 501, 502) represents at least 60%, in particular 70%, preferably 80%, or even 90% of the surface area of the main face (101) of the glass-ceramic plate.

9. The glass-ceramic plate (100) as claimed in any one of claims 1 to 8, such that the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) comprise one or more organic or inorganic compounds, the surface tension of which is at most 20 mN.m-1, in particular at most 15 mN.m-1, or even at most 10 mN.m-1.

10. The glass-ceramic plate (100) as claimed in any one of claims 1 to 9, such that the hydrophobic sub-beads comprise one or more organic compounds chosen from polysiloxanes, organosiloxanes, fluorosiloxanes, fluorocarbons, fluoropolymers, fluorosilanes and a mixture thereof.

11. The glass-ceramic plate (100) as claimed in any one of claims 1 to 10, such that the hydrophilic zones (303, 401-402, 506, 505) are formed by the surface of the glass-ceramic plate that has not undergone any surface treatment.

12. The glass-ceramic plate (100) as claimed in any one of claims 1 to 11, such that the hydrophilic zones (303, 401-402, 506, 505) comprise one or more hydrophilic coatings deposited on one or more regions of the surface of the glass-ceramic plate.

13. A process for manufacturing a glass-ceramic plate (100) as claimed in any one of claims 1 to 12, wherein the hydrophobic sub-beads (103a-b, 201a-c, 501a-b, 502a-b) are deposited according to one or more of the methods chosen from chemical liquid deposition, chemical vapor deposition, vacuum chemical deposition, such as spraying, screen printing, centrifugal coating, dip coating, inkjet printing deposition, wiping, flexography, magnetron sputtering, 3D printing deposition.

14. A cooking device (600) comprising a glass-ceramic plate (100) as claimed in any one of claims 1 to 12.

15. The cooking device (600) as claimed in claim 14, further comprising a control unit (602), such that the control unit (602) is not within the region(s) (104, 503, 504) of the glass-ceramic plate (100) defined by the retaining bead (103, 201, 501, 502).