Heating unit with one triple-glazed door

Description

[0001] The invention relates to a heating device comprising an enclosure defining a cavity, said cavity being closed by a door incorporating glazing that confines the heat within the cavity of the device. The invention also relates to such a door and its use as a component of such a device.

[0002] A heating device according to the invention comprises an enclosure delimited by one or more walls, including a glazed door. Heating means allow the cavity inside the enclosure to be heated to a high temperature. The heating devices may include, in particular, ovens, chimneys, furnaces, etc.

[0003] The glazing used as components of a door or, potentially, a wall of a heating device is generally multi-pane glazing, meaning glazing composed of several glass substrates, particularly quadruple glazing. Multi-pane glazing helps retain heat inside the heating device while keeping the outer surface of the glazing cool to the touch, thus protecting users from burns.

[0004] Such a multiple glazing comprises at least two substrates held apart to define a space. The glazing faces are conventionally designated from the inside of the heating device, with the substrate faces numbered from the inside out.

[0005] The glazing used as a component of a heating device may include substrates coated with functional coatings that reflect thermal radiation, particularly infrared (IR) radiation. These coatings reduce the amount of energy dissipated outside the heating device by reflecting heat back into the enclosure. The use of these coatings helps to reduce the energy consumption of the heating device as well as the heating of the external wall of the glazing forming the oven door.

[0006] For example, patent application EP1293726 A2 describes a glass barrier comprising on a first surface a heat-reflective coating deposited by pyrolysis and on a second surface a heat-reflective coating deposited by a physical vapor deposition (PVD) process.

[0007] Coatings incorporating functional silver-based metallic layers (or silver coatings) are known to be the most effective at reducing the emissivity of glazing while preserving the optical and aesthetic qualities of the wall or door, including good visibility through it. These coatings also ensure better user protection, lower energy consumption, and greater user comfort.

[0008] However, the thermal resistance of coatings containing these functional silver-based metallic layers is often insufficient. The poor chemical and thermal resistance of these coatings can lead, in the long term, to the appearance of defects such as corrosion spots, scratches, silver dewetting, or even total or partial delamination of the stack.

[0009] This phenomenon is exacerbated when such glazing incorporating thin layers of silver is used in heating devices, for example as oven doors, and is subjected to prolonged and repeated high-temperature heat treatment cycles in a humid environment, such as pyrolysis treatments. These heat treatment cycles in a humid environment accelerate the degradation of the silver layers, notably through demolding or corrosion of the silver.

[0010] Also, any defect or scratch, whether due to corrosion or mechanical stress, is likely to impair not only the energy and optical performance but also the aesthetics of the coated substrate.

[0011] US application 2012 / 0084963, however, discloses a multi-glazing system used as a component of a furnace door, comprising a transparent substrate coated with a stack of thin films including at least one functional silver-based metallic layer and a top protective zirconium oxide-based layer. The zirconium oxide-based layers protect the stack during high-temperature heat treatment. However, substrates coated with such protective layers are susceptible to corrosion in hot, humid environments.

[0012] Application WO2016 / 097560 describes a glazing comprising a transparent substrate coated with a stack of thin films comprising at least one functional silver-based metallic layer characterized in that the stack comprises a top protective layer based on titanium oxide and zirconium.

[0013] Publication WO2011 / 104034 describes a device for heating an oven door comprising three sheets of glass, including heat-reflecting coatings, the distance between the first two sheets being between 0.5 and 1 mm and 3 cm for the following spacing.

[0014] US patent application 2003 / 0113550 describes a multiple glazing that can serve as a furnace door and comprises a succession of glass substrates, with heat-reflecting stacks arranged on different faces of these glass substrates.

[0015] Although the stacks described in the previously reported publications can in principle satisfy the required criteria of chemical and mechanical resistance at the usual operating temperature of the furnace, furnace door configurations with optimal thermal insulation performance and ease of manufacture, preferably at a lower cost, are still being sought.

[0016] In particular, an architecture is sought that not only ensures a cool exterior surface of the wall, thus guaranteeing user safety against potential burns, but also effectively confines heat within the device's enclosure or cavity. Furthermore, the device is sought to be as energy-efficient as possible, specifically one whose wall cooling requires little or no additional effort, such as the ventilation of cooling air through the various substrates that make up the wall.

[0017] The object of the present invention is to provide a heating device according to claim 7 and a door or wall according to claim 1 equipping such a device, making it possible to effectively solve the problems previously described.

[0018] Heat refers to all or part of the radiation emitted by the oven's heating elements, including infrared radiation between 2 micrometers and 10 micrometers.

[0019] More specifically, the present invention relates to a heating device as described in the following claims, equipped with an enclosure delimiting a cavity, said device comprising a door or a wall, incorporating triple glazing comprising three transparent substrates.

[0020] Triple glazing refers to an assembly of three successive sheets of glass, but not linked together by spacers, particularly hermetically, as is the case in triple glazing typically used in the field of building glazing.

[0021] The glass substrates according to the present invention are intended for the manufacture of a heating device such as a furnace. Their surface area is therefore typically less than 0.5 m².

[0022] Further details of the implementation and / or preferred realization of the present invention are given below, which can of course be combined as appropriate: Faces 1 and 2 of the first substrate and 3 of the second substrate are covered with heat-reflective coatings, faces 4 to 6 preferably being without such coatings; e1 > e2; e2 > e1; e1 and e2 are between 4 and 15 mm; the ratio between the largest and smallest spacing is less than 5, preferably less than 4, and most preferably less than 3.5, or even less than 3.0. The intermediate spacings between the substrates are filled with air in contact with the outside atmosphere (and therefore with air at ordinary pressure). The substrates are parallel to each other. The triple glazing comprises: a) for the first substrate in contact with the cavity: on a first face 1, facing inwards and in direct contact with said cavity, a first stack reflecting heat essentially by means of one or more functional layers based on a transparent conductive oxide,preferably selected from mixed tin and indium oxides or fluorine-doped tin or Sb oxides, on the other face 2, facing outwards from said cavity, a second heat-reflecting stack essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver, b) for the second substrate: on the face 3 facing inwards from said cavity, a third heat-reflecting stack essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine-doped tin or Sb oxides, face 4 of the second substrate preferably being free of heat-reflecting coating, faces 5 and 6 of the third substrate being free of heat-reflecting coating; the triple glazing comprises: a) for the first substrate in contact with the cavity: on a first face 1,a) For the second substrate: on the inward-facing face 2, in direct contact with said cavity, a first stack reflecting heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine-doped tin or Sb oxides; on the other face 2, facing outwards from said cavity, a second stack reflecting heat essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver. b) For the second substrate: on the face 3 facing inwards from said cavity, a third stack reflecting heat essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver; face 4 of the second substrate preferably being devoid of a heat-reflecting coating.faces 5 and 6 of the third substrate being devoid of heat-reflecting coating; the first coating (or first stack) on face 1 comprises as a functional layer an indium tin oxide, the atomic percentage of Sn in the oxide of which is advantageously in the range of 5 to 70%, in particular 10 to 60%; the first coating (or first stack) on face 1 comprises as a functional layer an indium tin oxide layer preferably comprising a mass proportion of about 85 to 95% indium oxide and about 15 to 5% tin oxide; the first coating (or first stack) on face 1 comprises successively from the substrate: at least one sublayer of a dielectric compound, in particular selected from silicon nitride, silicon oxide, or zinc tin oxide, a functional layer of ITO,at least one overlayer of a dielectric compound, in particular selected from silicon nitride, silicon oxide, or tin and zinc oxide; the first coating (or first stack) on face 1 comprises successively from the substrate: at least one sublayer of a dielectric compound, in particular selected from silicon nitride, silicon oxide, tin and zinc oxide, a first functional layer of ITO, an intermediate layer of a dielectric compound, in particular selected from silicon oxide, silicon nitride or tin and zinc oxide, a second functional layer of ITO, at least one overlayer of a dielectric compound, in particular selected from silicon nitride, silicon oxide, or tin and zinc oxide; the second coating (or second stack) on face 2 comprises at least one functional silver-based metallic layer and at least two dielectric assemblies,each dielectric assembly comprising at least one dielectric layer, such that each silver-based layer is arranged between two dielectric layers; the third coating (or third stack) on face 3 or face 4 of the second substrate comprises at least one functional silver-based metallic layer and preferably at least two dielectric assemblies, each dielectric assembly comprising at least one dielectric layer, such that each silver-based layer is arranged between two dielectric layers; at least the coated substrate of the stack is domed and / or tempered, and preferably all the substrates of the glazing are tempered.

[0023] The invention also relates to a door or wall for a heating device as described in the following claims.

[0024] According to particular and preferred modes of a door according to the invention: Faces 1 and 2 of the first substrate and 3 of the second substrate are covered with heat-reflective coatings, faces 4 to 6 preferably being free of such coatings; e1 > e2; e2 > e1; said triple glazing comprises: a) for the first substrate in contact with the cavity: on a first face 1, facing inwards and in direct contact with said cavity, a first stack reflecting heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine-doped tin or Sb oxides, on the other face 2, facing outwards from said cavity, a second stack reflecting heat essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver. b) for the second substrate: on the face 3 facing inwards from said cavity,a third stack reflecting heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably chosen from mixed tin and indium oxides or fluorine-doped tin or Sb oxides; said triple glazing comprises: a) for the first substrate in contact with the cavity: on a first face 1, facing inwards and in direct contact with said cavity, a first stack reflecting heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably chosen from mixed tin and indium oxides or fluorine-doped tin or Sb oxides, on the other face 2, facing outwards from said cavity, a second stack reflecting heat essentially by means of one or more functional layers based on a metal chosen from gold or silver,preferably silver. b) for the second substrate: on face 3 facing the interior of said cavity, a third stack reflecting heat primarily by means of one or more functional silver-based layers.

[0025] The invention also relates to the use of triple glazing as described above as a constituent element of the wall or door of a heating device equipped with an enclosure and / or a cavity such as an oven.

[0026] Of course, all the characteristics described previously in relation to the heating device also apply to said wall or door, although they are not repeated here for reasons of brevity.

[0027] The transparent substrates used according to the invention are preferably made of a rigid mineral material, preferably glass, in particular soda-lime silicate, borosilicate, or aluminosilicate. They may also be made of glass-ceramic. In an advantageous embodiment, the substrates are borosilicate glasses that are highly resistant to very high temperatures.

[0028] The thickness of the substrate(s) generally varies between 0.5 mm and 19 mm. The thickness of the substrate(s) is preferably less than or equal to 6 mm, or even less than or equal to 4 mm.

[0029] The transparent substrates coated with the stacks may have undergone a high-temperature heat treatment, such as annealing (e.g., flash annealing like laser or flame annealing), quenching, and / or bending. The heat treatment temperature is above 400°C, preferably above 450°C, or even above 500°C. The coated substrate of the stack may therefore be bent and / or tempered. The first coated substrate of the stacks on each face is preferably tempered glass, particularly when it forms part of a glazing unit used as a component of a heating device or a fire door.

[0030] According to the invention, the glazing is triple-glazed and therefore comprises only three substrates, preferably also made of glass, namely an inner substrate (first substrate), a central or intermediate substrate (second substrate), and an outer substrate (third substrate). These three substrates define six faces. Face 1 faces the interior of the heating device and thus constitutes the inner wall of the glazing. Faces 2 through 5 are on the interior of the triple glazing. Face 6 faces the exterior of the heating device and thus constitutes the outer wall of the glazing.

[0031] Regarding the first stack, it preferably comprises one or more functional layers of a transparent conductive oxide as a heat-reflecting functional layer (and therefore does not include other conductive layers, particularly those made of a metal such as silver). According to the invention, any coating comprising a functional layer based on, and preferably made of, a transparent conductive oxide of the ITO type, i.e., based on a mixed oxide of tin and indium, is used. The expression "based on" means, in the context of the present invention, that the layer in question comprises at least 80%, or even 90% or 95% by weight of the compound in question. The layer may advantageously be made of, or essentially made of, such a compound. Preferably, the deposited stack is one in which the functional layer(s) are based on ITO.The atomic percentage of Sn in the oxide is advantageously within a range of 5 to 70%, particularly from 10 to 60%. More specifically, according to the invention, a layer of a mixture of indium(III) oxide (In₂O₃) and tin(IV) oxide (SnO₂) is preferably used, in the mass proportion of approximately 85 to 95% of the former and approximately 15 to 5% of the latter. These conductive yet transparent layers exhibit low emissivities, correlated with low resistivities or squared resistances. They are material layers obtained by vacuum deposition by sputtering, optionally assisted by a magnetic field ("Magnetron"). In particular, and unexpectedly, much higher performance was achieved when these ITO-based stacks were combined, on the other side of the glass substrate, with a low-emissivity coating including a functional (reflective) silver layer.

[0032] According to a preferred embodiment of the present invention, the stack deposited on the first face is a stack comprising two functional layers based on ITO, the two functional layers being separated by at least one layer of a dielectric material.

[0033] Each ITO-based layer can have a physical thickness in the range of 20 to 80 nm, particularly 30 to 80 nm. The cumulative physical thickness of all ITO-based layers is preferably in the range of 40 to 200 nm, particularly 60 to 160 nm.

[0034] The dielectric intermediate layer(s) is preferably based on a compound selected from the oxides, nitrides or oxynitrides of silicon, aluminum, titanium, tin, zinc, zirconium, niobium, nickel, chromium or a mixture thereof. It is preferably essentially made up of such a compound, or even made entirely of such a compound.

[0035] More specifically, the dielectric intermediate layer(s) preferably consist essentially of a compound selected from a silicon and / or aluminum oxide, nitride, or oxynitride, a titanium nitride or oxide, a nickel-chromium oxide, a niobium nitride, or a tin-zinc oxide. Preferably, each dielectric intermediate layer is based on (or essentially composed of) silicon oxide, silicon nitride, titanium oxide, or tin-zinc oxide. Silicon oxide or nitride is particularly preferred. Silicon nitride or tin-zinc oxide are especially valued because their refractive index is close to that of ITO, so their presence does not disrupt the optical properties of the stack.Preferably, the refractive index for a wavelength of 550 nm of the intermediate layer(s) (in particular of the single intermediate layer) is at least 1.8, in particular 1.9, advantageously within a range of 1.8 to 2.5, in particular 1.9 to 2.2. The number of intermediate layers separating the ITO-based layers preferably varies from 1 to 5, in particular from 1 to 3 or from 1 to 2. Advantageously, the thin-film stack comprises at least two layers (in particular two layers) based on a transparent, electrically conductive oxide separated by at most two intermediate layers, in particular by a single intermediate layer.

[0036] Among the preferred combinations, the stacking includes (or is made up of) successively from the substrate: an adhesion layer, for example based on or essentially made of silica, a first ITO layer, an intermediate dielectric layer, for example based on or essentially made of silica, silicon nitride or tin and zinc oxide, a second ITO layer, an oxygen barrier layer, for example based on or essentially made of silicon nitride, a low refractive index layer, for example based on or essentially made of silica.

[0037] As for the second stack, it reflects heat essentially through one or more functional layers based on a metal chosen from gold or preferably silver, arranged in particular on face 2 of the triple glazing.

[0038] Gold-based or, preferably, silver-based layers are deposited between dielectric coatings, which generally comprise several dielectric layers. These dielectric layers allow for fine-tuning the optical properties of the stack and provide sufficient light transmission for external visibility of the enclosure. Furthermore, these dielectric layers protect the silver layer from chemical and mechanical damage. The thin-film stack therefore advantageously comprises at least one functional silver-based metallic layer and at least two dielectric coatings, each dielectric coating containing at least one dielectric layer, such that each functional metallic layer is positioned between two dielectric coatings.

[0039] The stack is deposited by sputtering, notably assisted by a magnetic field (magnetron process). According to this advantageous embodiment, all the layers of the stack are deposited by sputtering assisted by a magnetic field.

[0040] Unless otherwise stated, the thicknesses mentioned in this document are physical thicknesses. A thin film is defined as a layer with a thickness between 0.1 nm and 200 micrometers, depending on its nature and composition.

[0041] Throughout this description, the substrate according to the invention is considered to be horizontally positioned. The stack of thin films is deposited on top of the substrate. The meanings of the terms "above" and "below," and "lower" and "upper," are to be understood in relation to this orientation. Unless otherwise specified, the terms "above" and "below" do not necessarily mean that two layers and / or coatings are in contact with each other. When it is specified that a layer is deposited "in contact" with another layer or coating, this means that there cannot be one or more layers interposed between these two layers.

[0042] The functional metal layer is typically silver-based and generally comprises at least 80%, preferably at least 90%, and better still at least 95%, or even at least 98% by mass of silver relative to the mass of the functional layer. Preferably, the silver-based functional metal layer comprises less than 1.0% by mass of metals other than silver relative to the mass of the silver-based functional metal layer.

[0043] The thickness of the silver-based functional layers is, in increasing order of preference, from 5 to 20 nm, from 8 to 15 nm.

[0044] The stack may include at least one blocking layer whose function is to protect the silver layers by preventing potential degradation due to the deposition of a dielectric coating or heat treatment. These blocking layers are preferably located in contact with the functional silver-based metallic layers.

[0045] The stack may include at least one blocking layer located below and in contact with a silver-based functional metallic layer and / or at least one blocking layer located above and in contact with a silver-based functional metallic layer.

[0046] Among the blocking layers traditionally used, we can mention blocking layers based on a metal chosen from niobium Nb, tantalum Ta, titanium Ti, chromium Cr or nickel Ni or based on an alloy obtained from at least two of these metals, in particular an alloy of nickel and chromium (NiCr).

[0047] The thickness of each overlay or underlay of the blocking layer is preferably: of at least 0.2 nm or at least 0.5 nm and / or at most 5.0 nm or at most 2.0 nm.

[0048] The dielectric coatings have a thickness greater than 15 nm, preferably between 15 and 50 nm and better from 30 to 45 nm.

[0049] Barrier dielectric layers are defined as layers made of a material capable of blocking the diffusion of oxygen and water at high temperatures, from the ambient atmosphere or the transparent substrate, into the functional layer. Barrier dielectric layers can be based on silicon and / or aluminum compounds selected from oxides such as SiO₂, nitrides such as silicon nitride Si₃N₄ and aluminum nitrides A₂N, and oxynitrides SiO₂XN₃Y, possibly doped with at least one other element. Barrier dielectric layers can also be based on zinc tin oxide.

[0050] Stabilizing dielectric layers are defined as layers made of a material capable of stabilizing the interface between the functional layer and this layer. Stabilizing dielectric layers are preferably based on a crystalline oxide, particularly zinc oxide, possibly doped with at least one other element, such as aluminum. The stabilizing dielectric layer(s) are preferably zinc oxide layers.

[0051] The stabilizing dielectric layer(s) may be located above and / or below at least one silver-based functional metal layer or each silver-based functional metal layer, either directly in contact with it or separated by a blocking layer.

[0052] According to an advantageous embodiment, the silicon and / or aluminum nitride-based dielectric layer is preferably in contact with the upper protective layer, which may advantageously be titanium oxide-based or titanium and zirconium oxide-based, as described in application WO2016 / 097560. The silicon and / or aluminum nitride-based dielectric layer has, in particular, a thickness of: less than or equal to 100 nm, less than or equal to 50 nm or less than or equal to 45 nm, and / or greater than or equal to 15 nm, greater than or equal to 20 nm or greater than or equal to 25 nm.

[0053] According to this embodiment, the stacking may, for example, include: a dielectric coating located below the silver-based functional metal layer, possibly a blocking layer, a silver-based functional metal layer, possibly a blocking layer, a dielectric coating located above the silver-based functional metal layer, a top protective layer.

[0054] According to one embodiment, the stacking comprises: a dielectric coating located below the silver-based functional metal layer comprising at least one silicon and / or aluminum nitride-based dielectric layer and optionally a zinc oxide-based stabilizing function dielectric layer, optionally a blocking layer, a silver-based functional metal layer, optionally a blocking layer, a dielectric coating located above the silver-based functional metal layer comprising at least one silicon and / or aluminum nitride-based dielectric layer, a top protective layer.

[0055] According to another possible embodiment of the invention, the second stack can comprise several functional layers based on a metal chosen from gold or preferably silver, and in particular two or three silver layers, each of them being separated from the next preferably by at least one layer of dielectric material in particular such as those previously described.

[0056] According to such an embodiment, the stacking may, for example, include: a dielectric coating located below the silver-based functional metal layer, possibly a blocking layer, a first silver-based functional metal layer, possibly a blocking layer, a dielectric coating located above the first silver-based functional metal layer, possibly a blocking layer, a second silver-based functional metal layer, possibly a blocking layer, a dielectric coating located above the second silver-based functional metal layer, a top protective layer.

[0057] Regarding the coating on face 3 or face 4 of the triple glazing, preferably on face 3, it is preferably a stack whose functional layer is based on fluorine-doped tin oxide (SnO2:F). This material is usually deposited chemically, for example by chemical vapor deposition (CVD), possibly enhanced by plasma vapor deposition (PECVD).

[0058] Alternatively and also preferably, the coating present on face 3 or face 4 of the triple glazing, preferably on face 3 of the triple glazing, is a stack whose functional layer is a silver-based heat-reflecting layer or a stack comprising several silver functional layers, in particular of the type described previously for face 2.

[0059] Various embodiments of the present invention are given below, in relation to the figure 1 Attached: The figure 1 illustrates an example of a heating device comprising triple glazing according to the invention.

[0060] Triple glazing according to the figure 1 It comprises three glass substrates arranged parallel to each other, thus defining, from the inside to the outside of the device's cavity, six successive glass surfaces conventionally numbered 1 to 6 from the inside out. A gap e1 is provided between the first glass substrate and the second glass gap. A gap e2, different from e1, is provided between the first glass substrate and the second glass gap. The gaps between the substrates are filled with air at ambient pressure and are in fluid communication with the outside. Three configurations according to the invention are shown in the figure. figure 1 : a) a spacing e1 of 14 mm and a spacing e2 of 5 mm (conf.1). b) a spacing e1 of 12 mm and a spacing e2 of 7 mm (conf.2). c) a spacing e1 of 5 mm and a spacing e2 of 14 mm (conf.3).

[0061] According to comparative configuration 4 (conf. 4), the three substrates are spaced at the same distance of 9.5 mm. Examples :

[0062] In all the following examples, oven doors were manufactured with triple glazing and conforming to the configurations described previously in relation to the figure 1 . More precisely :

[0063] On a first clear soda-lime glass substrate of a thickness of 4mm, stacks of thin films are deposited as defined below: On a first face 1 of the substrate, a stack conforming to example 1 of application WO2015 / 033067 is deposited.

[0064] More specifically, the stack was deposited by AC magnetron sputtering onto a 4 mm thick clear soda-lime-silicon glass substrate A following: Glass / SiN x (2nm) / SiO 2 (34nm) / ITO (118nm) / SiN x (6nm) / SiO 2 (65nm) / TiO 2 (3nm).

[0065] The numbers in parentheses correspond to the physical thicknesses deposited for each layer, expressed in nanometers.

[0066] Silicon oxide and silicon nitride layers were deposited using aluminum-doped silicon targets (8 atomic percent) under an argon plasma with the addition of oxygen and nitrogen, respectively. ITO layers were deposited using ITO targets under an argon plasma. The ITO layer consists of a mixture of indium(III) oxide (In₂O₃) and tin(IV) oxide (SnO₂), in a mass proportion of approximately 90% of the former and approximately 10% of the latter. The SiN barrier layer was deposited under a pressure of 2.0 µbar. The normal emissivity of this stack, as measured according to standard FR-EN 12898, is 18%.

[0067] On the second side 2 of this first substrate, the stack is deposited using conventional sputtering deposition techniques. Bfollowing comprising a functional layer of silver, and whose normal emissivity is 3%: Glass / SiN x (30nm) / ZnO (5nm) / NiCr (0.5nm) / Ag (12nm) / NiCr (0.5nm) / ZnO (5nm) / SiN x (30nm) / TiO 2 (3nm).

[0068] As a second substrate, we use a substrate marketed by the company AGC under the reference Planibel G ®<, comprising a clear soda-lime glass sheet 4mm thick on one face of which is deposited a C coating by pyrolysis-CVD, consisting of a layer of fluorine-doped tin oxide.

[0069] The third substrate is a 4mm thick sheet of clear soda-lime glass with bare faces, i.e. not covered by the previous coatings. Examples 1 to 3 (according to the invention):

[0070] The furnace doors are manufactured using traditional glassmaking techniques, comprising the assembly of the three glass substrates described previously, according to configurations A to C described in relation to the figure 1 of which : a first substrate as described above comprising the coating A on side 1 and the coating B on face 2 of the door, the second Planibel G ®< substrate, in such a way that the coating C is oriented towards the inside of the door, i.e. is located on face 3 of the triple glazing and the door, then the third glass substrate, whose bare faces are faces 5 and 6 of the triple glazing (cf. figure 1 ) and the door.

[0071] According to example 1, a spacing e 1 of 14 mm is provided between the first two substrates and a spacing e 2 of 5 mm between the second and third substrates.

[0072] According to example 2, a spacing e 1 of 12 mm is provided between the first two substrates and a spacing e 2 of 7 mm between the second and third substrates.

[0073] According to example 3, a spacing e 1 of 5 mm is provided between the first two substrates and a spacing e 2 of 14 mm between the second and third substrates. Example 4 (comparative):

[0074] According to this example 4, the same manufacturing steps are reproduced as in examples 1 to 3, but the three glass substrates are spaced at the same distance of 9.5 mm. Example 5 (comparative):

[0075] According to this example 5, a quadruple glazing is assembled this time for the manufacture of the oven door by taking the configuration of example 4 to which a fourth glass substrate is added on the outside, the fourth substrate being a clear glass substrate of thickness 4 mm and whose faces are bare, each substrate being spaced from the next by a distance of 6 mm in order to maintain a door thickness comparable to the previous examples. Example 6 (comparative):

[0076] According to this example 6, a triple-glazed unit is assembled for the manufacture of the furnace door, using three Planibel G® substrates. The Planibel substrates are all oriented so that coating C faces the inside of the door; that is, coating C is positioned on faces 1, 3, and 5 of the triple glazing. In this example 6, a gap e1 of 14 mm is maintained between the first two substrates and a gap e2 of 5 mm between the second and third substrates. Example 7 (comparative):

[0077] According to this example 7, a quadruple glazing unit is assembled for the furnace door, using three Planibel G® substrates as described in example 6. The Planibel substrates are used as the first three substrates of the quadruple glazing unit. They are all oriented so that coating C faces inwards towards the door; that is, coating C is positioned on faces 1, 3, and 5 of the quadruple glazing unit. The fourth substrate is a 4 mm thick clear glass substrate with bare faces. The substrates are spaced approximately 6 mm apart.

[0078] The cavity of an oven equipped with heating elements and fitted with the different doors according to examples 1 to 6 is then heated to a temperature of around 430 °C.

[0079] The results are reported in Table 1 below: In Table 1, A is a face coated by stacking A (including the ITO functional layer), B is a face coated by stacking B (including the silver functional layer), C is a face coated by coating C (including the SnO2:F pyrolytic layer) and X is an uncoated face.

[0080] It is stated that, according to GIFAM (Interprofessional Group of Household Appliance Manufacturers) criteria, the maximum temperature of the outer wall of an oven door must never exceed 70°C for the appliance to be considered "cool door". Table 1 Example F1 F2 F3 F4 F5 F6 F7 F8 e 1 e 2 e 3 Average cavity temperature (°C) External wall temperature (°C) 1* A B C X X X - - 14 5 - 430 67 2* A B C X X X - - 12 7 - 430 70 3* A B C X X X - - 5 14 - 430 70 4 A B C X X X - - 9,5 9,5 - 430 77 5 A B C X X X X X 6 6 6 430 65 6 C X C X C X - - 14 5 - 430 83 7 C X C X C X X X 6 6 6 430 73 *invention

[0081] In Table 1, the temperature of the outer wall of the door indicates the maximum temperature measured on the outer pane of glass of the door. e1 is the spacing between substrate 1 and substrate 2, and e2 is the spacing between substrate 2 and substrate 3 in triple glazing. In the case of quadruple glazing, e3 is the spacing between substrate 3 and substrate 4.

[0082] The results shown in Table 1 demonstrate the advantages of the present invention: Example 7 is representative of a furnace door currently in use. It comprises four panes of glass, with a heat-reflective coating applied to faces 1, 3, and 5 of the glass. For an average cavity temperature of 430°C, an external temperature of 73°C is observed.

[0083] Reference example 5 is a quadruple-glazed door in which heat-reflective coatings have been applied to faces 1, 2, and 3 of the different glass substrates. In this configuration, the maximum temperature measured on the outer face 6 of the door, in contact with the outside, is 65°C when the oven cavity is heated to 430°C. This temperature ensures user safety, even when the oven is heated to very high temperatures, such as during pyrolysis. However, the drawback of this configuration is the use of four glass substrates, which increases the door's weight and makes its manufacture significantly more expensive.

[0084] In example 4, the fourth substrate was removed, while the spacing e1 between the first and second substrates and e2 between the second and third substrates remained essentially the same. A significant increase in the external temperature of the door was then observed.

[0085] In examples 1 to 3 of the invention, the configuration of example 4 (triple-glazed configuration) has been modified by changing the respective spacings e1 and e2, while keeping the door thickness constant. A significant decrease in the external temperature of the door is observed, down to values ​​comparable to those of the reference example 5. A particularly advantageous configuration of the invention in which e1 is greater than e2 is illustrated by example 1.

[0086] Thus, according to the invention and thanks to a particular combination associating triple glazing with three stacks reflecting heat respectively on faces 1, 2 and 3 of said triple glazing and a particular and selected spacing between the three glass substrates, it is possible to offer lighter oven doors but still providing all the safety guarantees for the user.

[0087] Example 6 should be compared to example 7, which conforms to current practice. It can thus be observed that the removal of the fourth substrate (example 6) cannot, in this case, be compensated for by a different spacing between the three substrates, as observed by comparing examples 5 and 1 to 3.

[0088] It thus appears from these two examples that it is indeed the particular combination of the positioning of the reflective coatings and the selection of the spacing between the substrates that makes it possible to minimize the temperature of the outer face of the door.

Claims

1. Door or wall for a heating device, the door or wall comprising a triple-glazed unit, the three transparent substrates of which can define, from the inside to the outside of the cavity of said device, faces numbered 1 to 6 respectively, at least the faces 1 and 2 of the first substrate and 3 and / or 4 of the second substrate being covered with heat-reflecting coatings, in which door or wall the average spacing e1 between the first substrate and the second substrate and the average spacing e2 between the second substrate and the third substrate are different, the ratio between the larger spacing and the smaller spacing being greater than 1.1, preferably greater than 1.5 and very preferably greater than 2, or even greater than 2.5, e1 and e2 being between 2 and 20 mm.

2. Door or wall for a heating device as described in the preceding claim, wherein the faces 1 and 2 of the first substrate and 3 of the second substrate are covered with heat-reflecting coatings, the faces 4 to 6 having no such coatings.

3. Door or wall for a heating device as described in one of claims 1 or 2, wherein e1>e2.

4. Door or wall for a heating device as described in one of claims 1 or 2, wherein e2>e1.

5. Door or wall for a heating device as described in claim 1, wherein said triple-glazed unit comprises: a) for the first substrate which can be in contact with the cavity: - on a first face 1, which is intended to face inwards and is in direct contact with said cavity, a first stack which reflects heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine- or Sb-doped tin oxides, - on the other face 2, which is intended to face the outside of said cavity, a second stack which reflects the heat essentially by means of one or more functional layers based on a metal selected from gold or silver, b) for the second substrate: - on the face 3 intended to face the inside of said cavity, a third stack which reflects heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine- or Sb-doped tin oxides.

6. Door or wall for a heating device as described in claim 1, wherein said triple-glazed unit comprises: a) for the first substrate which can be in contact with the cavity: - on a first face 1, which is intended to face inwards and is in direct contact with said cavity, a first stack which reflects heat essentially by means of one or more functional layers based on a transparent conductive oxide, preferably selected from mixed tin and indium oxides or fluorine- or Sb-doped tin oxides, - on the other face 2, which is intended to face the outside of said cavity, a second stack which reflects the heat essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver, b) for the second substrate: - on the face 3 intended to face the inside of said cavity, a third stack which reflects the heat essentially by means of one or more functional layers based on a metal selected from gold or silver, preferably silver.

7. Heating device provided with an enclosure defining a cavity, said device comprising a door or a wall according to one of the preceding claims.

8. Heating device according to the preceding claim, wherein e1 and e2 are between 4 and 15 mm.

9. Heating device according to one of claims 7 or 8, wherein the face 4 of the second substrate preferably has no heat-reflecting coating, the faces 5 and 6 of the third substrate having no heat-reflecting coating.

10. Heating device according to any of claims 7 to 9, wherein the second coating on the second face 2 of the first substrate preferably comprises at least one silver-based functional metal layer and at least two dielectric assemblies, each dielectric assembly comprising at least one dielectric layer, so that each silver-based layer is arranged between two dielectric assemblies.

11. Heating device according to any of claims 7 to 10, wherein the third coating on the first face 3 of the second substrate or on the second face 4 of the second substrate comprises at least one silver-based functional metal layer and preferably at least two dielectric assemblies, each dielectric assembly comprising at least one dielectric layer, so that each silver-based layer is arranged between two dielectric assemblies.

12. Heating device according to any of claims 7 to 11, wherein at least the substrate coated with the stack is curved and / or tempered, and preferably wherein all the substrates of the glazed unit are tempered.