GLASS OR GLASS CERAMIC PLATE

Abstract

The invention relates to a glass or glass-ceramic plate comprising a glass or glass-ceramic substrate coated with a metal oxide-based coating, characterized in that said coating has a coverage rate of 25% to 90% and the coated plate has a roughness RSm of less than or equal to 300 µm, preferably less than or equal to 250 µm.

Description

Title of the invention: GLASS OR VITRO-CERAMIC PLATE

[0001] The present invention relates to a glass or glass-ceramic plate. More specifically, it relates to a glass or glass-ceramic plate intended to serve as a furniture surface and / or a cooking surface as well as an article comprising such a glass or glass-ceramic plate.

[0002] Glass ceramic hobs are traditionally used as cooking plates. They also find applications in areas requiring heat resistance, for example to form fireplace inserts. Recently, their use has extended to other areas of daily life: glass ceramic hobs can thus be used as furniture surfaces, in particular to form worktops, central islands, consoles, etc. the surface area they occupy in these new applications being larger than in the past. Glass plates can, for certain applications, be an alternative to glass ceramic plates, in particular for furniture cladding but also, under certain conditions, for cooking plates.Depending on their use, glass or glass-ceramic plates may be equipped with keys, touch zones, buttons or other controls, their surface being in all cases (even in the case of a simple furniture surface) subject to multiple contacts linked to their uses, generally causing the appearance of unsightly fingerprints at the contact points, possibly leading to repeated cleaning, in particular when the plates are dark. These traces or dirt can also cause interference with other possible components (heating elements, light sources, displays, etc.) of the article.

[0003] To avoid fingerprints on the surface of products, it is known in certain fields to apply hydrophobic and oleophobic coatings to limit the quantity of liquid(s) (water, sebum) deposited upon contact with the finger. However, such coatings, which must be applied to the entire surface to be protected, are not thermally resistant, which poses problems for applications such as cooking plates.

[0004] In the field of glass ceramics, existing textures or coatings are generally not suitable for systematically remedying the problems of fingerprints. The most frequently used coatings are mainly coatings chosen to withstand high temperatures, such as enamels, used locally to form decorative patterns or to indicate, for example, areas of heating, or paints used rather flat as opacifiers. However, these traditional coatings do not generally prevent fingerprints linked to the handling and use of coated substrates. Enamels can also locally reduce the mechanical resistance of glass-ceramic plates and flake off. Paints are also not suitable for all heating methods for hobs due to their lower resistance, particularly thermal. It is also known to use other coatings based in particular on thin metallic layers deposited flat over a large part of the surface of the substrate, but such layers sometimes contribute to the problem of fingerprints.

[0005] The present invention provides an improved glass or glass-ceramic plate making it possible to limit the visibility of fingerprints on its surface, in particular a glass or glass-ceramic plate intended to be used with one or more heating elements such as a cooking plate, or intended to serve as a furniture surface. The plate according to the invention has anti-fingerprint properties, without harming the other properties sought for its use, in particular their ease of maintenance and cleaning, its mechanical resistance, in particular resistance to scratches and abrasion, and where appropriate its thermal resistance.

[0006] The present invention relates to a glass or glass-ceramic plate comprising a glass or glass-ceramic substrate coated with a coating based on metal oxide, in particular aluminum oxide or mixed aluminum oxide, characterized in that said coating has a coverage rate of 25% to 90% and the coated plate has a roughness RSm of less than or equal to 300 pm, preferably less than or equal to 250 pm.

[0007] The substrate is preferably a glass-ceramic substrate, in particular a lithium aluminosilicate glass-ceramic substrate. The chemical composition of the glass-ceramic substrate typically comprises (or consists essentially of) the following constituents within the limits defined below, expressed in weight percentages and the sum of which is between 97 and 100%: SiO2 52 - 75% A12O318 - 27% Li2O 2.5 - 5.5% K2O 0 - 3% Na2O 0 - 3% ZnO 0 - 3.5% MgO 0 - 3% CaO 0 - 2.5% BaO 0 - 3.5% SrO 0 - 2% TiO2l,2-5.5% ZrO2 0 - 3%

[0008] The substrate may also be a glass substrate whose composition is of the lithium aluminosilicate, borosilicate or alumino-borosilicate type.

[0009] The chemical composition of lithium aluminosilicate glass typically comprises (or consists essentially of) the following constituents, varying within the weight limits defined below: SiO2 49-75% A12O315-30% Li2O 1-8% K2O 0-5% Na2O 0-5% ZnO 0-5% MgO 0-5% CaO 0-5% BaO 0-5% SrO 0-5% TiO20-6% ZrO2 0-5% B2O3 0-5%.

[0010] The chemical composition of borosilicate glass typically comprises (or consists essentially of) the following constituents, varying within the weight limits defined below: SiO2 70-85% B2O3 8-16% Al2O30-5% RO 0-10% K2O 0-2% Na2O 1-8%.

[0011] The chemical composition of alumino-borosilicate glass typically comprises (or consists essentially of) the following constituents, varying within the weight limits defined below and the sum of which is between 97 and 100%: SiO2 45-68%, Al2O38-20% B2O34-18% RO 5-30% R2O at most 10%.

[0012] The expression “RO” designates the alkaline earth oxides MgO, CaO, SrO and BaO, while the expression "R2O" designates alkali oxides, in particular Na2O and K2O.

[0013] The expression "consists essentially of" within the meaning of the present invention means the oxides mentioned constitute at least 95%, or even 97% or even 99% by weight of the composition. Whatever the composition of the plate, it usually comprises additives used for refining. The refining agents are typically chosen from arsenic, antimony, tin, cerium oxides, halogens, metal sulfides, in particular zinc sulfide. The weight content of refining agents is normally at most 1%, preferably between 0.1 and 0.6%. The plate is generally colored in the mass. The composition thus generally comprises colorants chosen in particular from vanadium oxide, iron oxide, cobalt oxide, cerium oxide, selenium oxide, chromium oxide, or even nickel oxide, copper oxide and manganese oxide.In the case of a glass-ceramic plate, this is preferably a glass-ceramic colored with vanadium oxide. It may comprise from 0.01 to 0.5% by weight of vanadium oxide, optionally in combination with other colorants such as iron oxide, cobalt oxide or manganese oxide.

[0014] The glass or glass-ceramic substrate typically has a light transmission of less than 65%, or even less than 40%, or less than 20%, or even less than 10%. It is preferably less than 5%, in particular in the case of a glass-ceramic substrate, in particular colored with vanadium oxide. The light transmission is measured according to standard EN 410:2011, under illuminant D65, taking into account both direct and diffuse transmission. It can be measured using a spectrometer equipped with an integrating sphere.

[0015] The substrate is preferably a dark substrate, that is to say it has a clarity L*, as defined in the CIE L*a*b* system, of less than 50, preferably less than 40, more preferably less than 30.

[0016] The substrate is in the form of a plate typically having a thickness of 2 to 15 mm, in particular 3 to 10 mm, for example 4, 5, 6, 7 or 8 mm. The dimensions (length and width) of the plate depend on the application for which it is intended: it generally has dimensions of 20 to 120 cm, in particular for applications in cooking devices, but can also have larger dimensions, for example a width of up to 120 cm, or even 180 cm, and a length greater than 200 cm, for worktop applications.

[0017] The substrate preferably has a coefficient of linear thermal expansion of at most 50.107 K1. In the case of a glass substrate, it typically has a coefficient of linear thermal expansion of 25 to 45.107 K1. In the case of a glass-ceramic substrate, the absolute value of the coefficient of expansion is typically in lower than 25.107 K1, or even lower than 15.107 K or even lower than 5.107 K1. The coefficient of linear thermal expansion is measured according to ISO 7991:1987 between 20 and 300°C.

[0018] The coating is preferably based on aluminum oxide, titanium oxide, niobium oxide, zirconium oxide or a mixed oxide thereof, in particular mixed aluminum oxide, more preferably based on aluminum oxide or mixed aluminum oxide. The term "based on" means that the coating generally comprises at least 50% by weight of the oxide in question, preferably at least 60% and even 70% or 80%, or even 90%, 95% or 99% by weight of this element. In certain cases, the coating may consist of this oxide, except for impurities.

[0019] The mixed aluminum oxide is preferably chosen from binary or ternary aluminum oxides, in particular from mixed aluminum and titanium oxides, mixed aluminum and zirconium oxides and mixed aluminum, titanium and silicon oxides, preferably from mixed aluminum and titanium oxides and mixed aluminum, titanium and silicon oxides. The coating preferably comprises at least 30% by weight, preferably at least 40% to 80%, of alumina relative to the total weight of the oxides. Interestingly, a coating based on mixed aluminum and titanium oxide makes it possible to maintain a relatively low clarity and a relatively high gloss, particularly appreciated for applications such as a cooktop.

[0020] The coating according to the invention is typically obtained by spraying a material based on metal oxide, in particular aluminum oxide or mixed aluminum oxide, in powder form. These deposition methods consist of spraying powder particles, preferably molten, at very high speed. The particles arriving on a surface to be coated are crushed in the form of drops (splats).

[0021] The coating according to the invention is generally a discontinuous deposit. The coating is typically in the form of a surface distribution of solid drops of a metal oxide-based material, in particular aluminum oxide or mixed aluminum oxide, distributed randomly over the surface of the plate. As illustrated in [Fig.l] representing an SEM image of a coating according to the invention, at the scale of a few hundred microns (for example 500 μm), certain areas are covered with drops, which may overlap or superimpose, while other areas are not covered. The coverage rate is greater than or equal to 25%, preferably greater than or equal to 35% and less than or equal to 90%, preferably less than or equal to 80%. The coverage rate is more preferably 30 to 70%, or even 40 to 60%.In certain embodiments, it may be less than or equal to 50%, in particular from 35 to 50%, or greater than or equal to 50%, in particular from 60 to 90%. The term “recovery rate” is understood to mean within the meaning of the . present invention, the ratio, expressed as a percentage, of the surface area of ​​the plate actually covered by the surface dispersion of drops of material based on aluminum oxide or mixed aluminum oxide to the total surface area theoretically covered by the coating (the surface area of ​​the plate on which the coating has been deposited). The coverage rate is measured by image analysis taken under an optical microscope, followed by image processing by thresholding and binarization. The coverage rate corresponds to the ratio of pixels corresponding to the coating (generally white pixels) to all pixels.

[0022] The average diameter of the drops is preferably from 10 to 200 pm, more preferably from 20 to 160 pm. The average diameter of the drops is measured by image analysis from optical microscopies.

[0023] The plate according to the invention has a roughness RSm of less than or equal to 300 pm, preferably from 50 to 250 pm. The ratio Ra / Rsm is preferably greater than or equal to 0.0030, and typically less than or equal to 0.1000, and more preferably from 0.0030 to 0.0500, or even from 0.0035 to 0.0100. It generally has a roughness Ra of less than or equal to 2.5 pm, preferably less than or equal to 2.0 pm, or even less than or equal to 1.5 pm, and typically greater than or equal to 0.3 pm. The roughness Rdq is preferably from 3.0 to 25.0°. The coated plate preferably has a roughness Rz greater than or equal to 3.0 pm, or even greater than or equal to 3.5 pm and typically less than or equal to 20 pm, preferably less than or equal to 15 pm. The roughness Rt is typically greater than or equal to 5 pm and preferably less than or equal to 15 pm or less than or equal to 9 pm.

[0024] The roughnesses RSm, Ra, Rdq, Rz and Rt are defined in a conventional manner according to ISO 4287:1997. RSm represents the average width of the elements of the roughness profile corresponding to the average value of the widths of the elements of the profile within a base length. Ra represents the average deviation of the roughness profile corresponding to the arithmetic mean of the absolute values ​​of the deviations between the successive peaks and troughs within a base length. Rdq represents the root mean square slope of the roughness profile corresponding to the root mean square value of the local slopes within a base length. Rz represents the maximum height of the roughness profile corresponding to the sum of the largest of the projection heights of the roughness profile and the largest of the trough depths of the roughness profile within a base length.Rt represents the total height of the roughness profile corresponding to the sum of the largest of the roughness profile protrusion heights and the largest of the roughness profile trough depths within the evaluation length. The roughnesses RSm, Ra, Rdq and Rz are measured over a base length of 0.8 mm and the roughness Rt over a 4 mm evaluation length using a contact roughness tester such as the SJ-401 roughness tester. of the Mitutoyo company.

[0025] In certain embodiments, the coating has a coverage rate of 30 to 70%, preferably 40 to 60%, and the plate has a roughness RSm of less than or equal to 250 pm, a roughness Ra of less than 1.5 pm and a ratio Ra / RSm of 0.003 to 0.01. It has in fact been observed that these embodiments, in addition to reducing the visibility of fingerprints, provide improved mechanical properties to the glass or glass-ceramic plate (improved scratch resistance and / or reduced visibility of scratches) and do not generate excessive blurring, thus ensuring good visibility of the displays placed below the plate.

[0026] Another object of the present invention relates to a method for manufacturing a glass or glass-ceramic plate as described above comprising the deposition of a metal oxide-based coating by projection on the surface of a glass or glass-ceramic substrate, characterized in that the surface of the substrate is at a temperature above 300°C during the deposition of the coating.

[0027] Coating methods using so-called thermal spraying are well known to those skilled in the art. These may include plasma spraying, oxy-gas flame spraying or high-speed thermal spraying (or HVOF: High Velocity Oxy-Fue!). The particles of the powder to be sprayed are heated to temperatures above the melting temperature of the powder. The deposited drops adhere to the substrate mainly due to the diffusion of atoms at the substrate / drop interface or mechanically due to the plastic deformation of the particles, and to a lesser extent by Van der Waals forces.

[0028] The coating according to the invention is preferably obtained by plasma spraying. The spraying parameters such as the electrical power, the total flow rate of plasma gases, the composition of the plasma gases, the powder flow rate, the linear speed of the torch and the number of passes are adjusted in a manner well known to those skilled in the art, depending on the type of torch and the characteristics of the powder used, to generate a flow of correctly melted particles at an adequate speed so as to obtain non-burst, adherent and little cracked droplet spreads and to obtain a coating according to the invention.For example, in particular in the case of plasma projection using a plasma torch of the Proplasma HP8 type marketed by Saint-Gobain Coating Solutions, the electrical power can be from 30 to 65 kW, the total gas flow rate from 40 to 80 L / min, the powder flow rate from 0.5 to 15 g / min, the linear speed of movement of the torch from 1000 to 5000 mm / s, the feed step is from 3 to 15 mm and the number of passes from 1 to 10. The powder flow rate, the linear speed of movement of the torch, the feed step (distance separating 2 lines of movement of the torch) as well as the number of passes make it possible in particular to modulate the coverage rate and the roughness of the coating according to the invention.

[0029] The powder used in the method according to the invention is generally of a nature identical to the desired coating, that is to say a metal oxide powder, in particular an aluminum oxide or mixed aluminum oxide powder, preferably chosen from binary or ternary aluminum oxides, in particular from mixed aluminum and titanium oxides and mixed aluminum, titanium and silicon oxides.

[0030] The powder typically has a particle size such that the diameter Di0 is between 3 and 20 μm, and such that the diameter D90 is between 20 and 75 μm. The diameters Di0, respectively D90, are understood to mean that 10%, respectively 90%, by number of the particles of the powder have a diameter less than the value Di0, respectively D90. They are determined by laser diffraction.

[0031] The powder is preferably a powder with dense grains, i.e. having a porosity of less than 1%. It is preferably a powder resulting from a melting process (melted-ground) in order to improve the adhesion of the coating.

[0032] When depositing the coating according to the invention, the surface of the substrate is at a temperature above 300°C, preferably above 360°C, for example from 400 to 800°C, or even from 450 to 700°C. For this, the substrate is heated before and / or during the deposition step. It has indeed been noted that the temperature of the substrate impacts the roughness of the deposit obtained.

[0033] A heat treatment may also be carried out after the deposition of the coating according to the invention to improve its adhesion. In particular, in the case of a glass-ceramic plate, it may prove advantageous to deposit the coating on the mother glass, i.e. before the ceramization heat treatment, to take advantage of the beneficial effect of the heat treatment on the adhesion of the coating.

[0034] The plate according to the invention may, if necessary, be coated with other functional coatings (anti-overflow layer, opacifying layer, etc.) and / or decorative coatings, in particular localized ones, such as usual enamel-based patterns. For example, the plate may have a localized coating of decorative enamel, generally on the same face as the coating according to the invention, and generally above it, (to form, for example, patterns or logos or to delimit / indicate certain zones, in particular heating zones), and / or an opacifying layer on all or part of the face of the plate opposite the coating according to the invention (to conceal, for example, internal elements arranged under the plate).

[0035] The plate according to the invention can be used for different applications such as worktops, cooking devices, for example cooking plates, in particular induction, fireplace inserts, fire-resistant glazing or even as a decorative element. Thus, the present invention also relates to an article, in particular a worktop, a cooking device, a fireplace insert, a fire-resistant glazing or a decorative element, comprising a glass or glass-ceramic plate as described above or obtained by the method described above. It is preferably a cooking device. Whatever the application, the plate according to the invention is such that, in the use configuration, the coating according to the intention is arranged on the surface of the plate facing the user.

[0036] The article according to the invention may also comprise internal elements comprising a heating means, a display device and / or a control device. The display device may be a light source, in particular light-emitting diodes or an LCD screen, possibly associated with optical filters or optical guides. The heating means may be chosen from radiant or halogen heating means, atmospheric gas burners, and induction heating means. The control device may be an electronic control panel with sensitive keys. The article may also be provided with (or associated with) additional functional element(s) such as a frame, stiffener(s), connector(s), cable(s), control element(s), etc.

[0037] The present invention is illustrated by the following non-limiting examples.

[0038] Dark glass-ceramic plates of the KeraBlack+ type marketed by Eurokera were coated by plasma spraying with different coatings based on aluminum oxide and mixed aluminum oxides. The coatings were deposited on substrates heated to between 400 and 720°C using an HP 8 torch marketed by Saint-Gobain Coating Solutions. The spraying parameters for sample II were as follows: - Electrical power: 53 kW - Total flow rate of plasma gases: 68 L / min - Torch-substrate distance: 130 mm - Powder flow rate: 2.5 g / min - Linear speed of the torch: 3000 mm / s - Advance step: 7 mm - Number of passes: 1

[0039] Samples C1 to C3 and 12 to 15 are obtained in an identical manner to sample II except for certain projection parameters, in particular the powder flow rate, the linear speed of the torch and the number of passes.

[0040] The aluminum oxide powders used are dense grain powders (melted-ground) with the following characteristics: Composition AlTiOx AlTiSiOx Particle diameters Dio-Dqo (pm) 15-45 5-25

[0042] The coverage rate of the different coatings obtained was measured by image analysis taken with an optical microscope (Leica DMC 2900), followed by image processing using the Image! software. The processing consists of using the threshold function of the software, adjusting the gray levels and then binarizing the image so that the drops appear as white pixels and the uncovered surface appears in black. [Fig.2] shows an image of a sample taken with an optical microscope and [Fig.3] shows the corresponding image after image processing allowing the calculation of the coverage rate.

[0043] The visibility of fingerprints on the coated samples was evaluated compared to the uncoated glass-ceramic reference sample according to the following protocol. Several fingerprints were made on the coated samples and on the uncoated glass-ceramic taken as a reference. The observers' evaluations were carried out on the same day as the finger application, under the same illumination conditions with the Daylight illuminant in a SpectraLight III light booth marketed by X-Rite, at an angle of 60° to normal. The results are presented in Table 2. (-) indicates a visibility of fingerprints identical to that of the uncoated glass-ceramic. (+) indicates a visibility of fingerprints lower than that of the uncoated glass-ceramic.

[0044] The results are summarized in Table 2. Samples II to 15 are examples according to the invention and Examples C1 to C3 are comparative examples. Sample Cl C2 C3 H] 12 13 14 15 Coating AlTiSiOx AlTiOx Coverage rate (%) 32 16 24 31 42 87 47 70 RSm (pm) 336 417 338 233 130 86 170 154 Ra / RSm 0.0011 0.0013 0.0025 0.0037 0.0057 0.018 0.0037 0.0067 Visibility of fingerprints (-) (-) (-) (+) (+) (+) (+) (+)

[0046] Samples II to 15 exhibit significantly improved anti-fingerprint properties compared to samples C1 to C3 which are no better than the uncoated reference glass-ceramic.

Claims

Claims

1. Glass or glass-ceramic plate comprising a glass or glass-ceramic substrate coated with a metal oxide-based coating, characterized in that said coating has a coverage rate of 25% to 90% and the plate has a roughness RSm of less than or equal to 300 pm, preferably less than or equal to 250 pm.

2. Plate according to claim 1, characterized in that it has a roughness Ra such that the ratio Ra / RSm is greater than or equal to 0.0030.

3. Plate according to any one of claims 1 or 2, characterized in that it has a roughness Ra less than or equal to 2.5 pm.

4. Plate according to any one of claims 1 to 3, characterized in that said coating has a coverage rate of 30 to 70%.

5. Plate according to any one of claims 1 to 4, characterized in that said coating is based on aluminum oxide, titanium oxide, niobium oxide, zirconium oxide or mixed oxide thereof, in particular mixed aluminum oxide.

6. Plate according to any one of claims 1 to 5, characterized in that the substrate has a light transmission of less than 65%, preferably less than 5%.

7. Plate according to any one of claims 1 to 6, characterized in that the substrate has a clarity L* of less than 50, preferably less than 40, more preferably less than 30.

8. Plate according to any one of claims 1 to 7, characterized in that the substrate is a glass-ceramic substrate having a chemical composition comprising the following constituents within the limits defined below expressed in weight percentages and the sum of which is between 97 and 100%: SiO2 52 - 75% A12O318 - 27% Li2O 2.5 - 5.5% K2O 0 - 3% Na2O 0 - 3% ZnO 0 - 3.5% MgO 0 - 3% CaO 0 - 2.5% BaO 0 - 3.5% SrO 0 - 2% TiO2l.2-5.5% ZrO2 0 - 3%.

9. Plate according to any one of claims 1 to 7, characterized in that the substrate is a glass substrate whose composition is of the lithium aluminosilicate, borosilicate or alumino-borosilicate type, preferably a borosilicate type glass substrate having a chemical composition comprising the following constituents within the limits defined below expressed in weight percentages: SiO2 70-85% B2O3 8-16% Al2O30-5% RO 0-10% K2O 0-2% Na2O 1-8%.

10. Method of manufacturing a glass or glass-ceramic plate according to one of claims 1 to 9 comprising the deposition of a metal oxide-based coating by projection on the surface of a glass or glass-ceramic substrate, characterized in that the surface of the substrate is at a temperature above 300°C during the deposition of the coating.

11. An article comprising a glass or glass-ceramic plate as defined in one of claims 1 to 9 and internal elements comprising a heating means, a display device and / or a control device.

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