FR3105212A1 - Process for rapid thermal treatment of thin films on tempered glass substrates - Google Patents

Abstract

The present invention relates to a process for the thermal treatment of at least one continuous thin coating deposited on a first face of a glass substrate, in which each point of said thin coating is heated for a period of less than 1 second at a temperature of at least 300 ° C while maintaining a temperature less than or equal to 150 ° C, preferably less than 100 ° C, at any point on the second face of said glass substrate, opposite to said first face, said method being characterized by the fact that the glass substrate is of reinforced glass and remains in the reinforced state during the heat treatment process.

Description

Process for rapid heat treatment of thin layers on tempered glass substrates

The present invention relates to a process for the rapid heat treatment of thin films deposited on reinforced glass substrates, in which the intensity and duration of the heat treatment are such that the treatment does not cause the reinforced glass to be annealed, the reinforced glass remaining thus in the reinforced state. The invention also relates to reinforced glass substrates coated with thin films treated by the method of the invention.

Some functional layers deposited on glass substrates require heat treatments, either to improve their properties, or even to give them their functionality. Examples include low-emissivity functional layers based on silver or transparent conductive oxides (TCO) whose emissivity and electrical resistivity are lowered following heat treatments. Photocatalytic layers based on cold-deposited titanium oxide generally require activation by heat treatment. Heat treatments also make it possible to create porosity in silica-based layers to lower their light reflection factor.

It is known, for example, from international application WO2008/096089 to expose thin mineral films, for example coatings comprising metallic films or transparent conductive oxide coatings, for a fraction of a second at very high temperatures so as to cause changes in thin films without affecting the supporting substrate of the thin film. The main advantage of heat treatment is the increase in the crystallization rate of the thin film, without the need to subject the entire substrate/film to an annealing step followed by a slow and controlled cooling.

In particular, application WO2010/139908 discloses a method of thermal treatment of thin layers by means of radiation, in particular infrared laser radiation focused on the layer. Such a treatment makes it possible to heat the layer very quickly without significantly heating the underlying substrate. Typically, the temperature at any point on the face of the substrate opposite that carrying the layer does not exceed 150° C., or even 100° C. during the treatment. Other types of radiation, such as that from flash lamps can also be used for the same purpose.

The rapid heat treatment process described in WO2008/096089 and WO2010/139908 is presented as being especially useful for non-tempered or non-curved substrates. Thermal toughening and/or bending makes it possible to obtain the crystallization of a thin film, deposited on the surface of the glass, thanks to the supply of heat essential for thermal toughening or bending. Heat treatment of the thin film is then superfluous.

However, for certain applications, in particular for facade glazing, thin films are deposited on tempered pre-cut glasses with fixed measurements (“cut size”), these glasses possibly being enamelled. If the thin film requires a heat treatment > 300° C. to improve or obtain the desired properties, the mechanical reinforcement of the tempered substrate will then be reduced, or even completely eliminated if it is subjected to a heat treatment in an oven.

Furthermore, not all thin films lend themselves to thermal quenching. One can cite for example the silver layers deposited by magnetron whose emissivity increases following the dewetting induced by the increase in temperature.

Finally, the chemical toughening of the glass is necessarily done before the deposition of a thin functional coating, such as a transparent electrode, a photocatalytic coating or even an anti-reflective layer and the person skilled in the art is then confronted with the problem of having to carry out a heat treatment of said thin coating, deposited on a substrate which has undergone chemical toughening, without significantly reducing the state of stress of the tempered glass substrate.

The present invention is based on the discovery that the rapid heat treatment process described for example in WO2008/096089 or WO2010/139908 is also suitable for thin coatings deposited on reinforced glass substrates (chemically or thermally) and then makes it possible to essentially retain the stress state of the reinforced glass while causing the desired structural change in the thin film, for example the increase in the crystallization rate.

The subject of the present application is therefore a process for the heat treatment of at least one continuous thin coating deposited on a first face of a glass substrate, in which each point of said thin coating is heated for a period of less than 1 second at a temperature of at least 300°C while maintaining a temperature less than or equal to 150°C, preferably less than 100°C, at any point on the second face of said glass substrate, opposite to said first face, said method being characterized in that the glass substrate is made of reinforced glass and remains in the reinforced state during the heat treatment process.

In the present application, the term " reinforced glass " encompasses glasses which have undergone a heat treatment for reinforcement and those which have undergone a chemical treatment for reinforcement.

Among the reinforced glasses having undergone a heat treatment of reinforcement, a distinction is made mainly between tempered glasses and semi-tempered glasses.

Tempered glasses: During thermal toughening, the glass is brought to a high temperature by passing through an oven until it reaches a temperature close to its softening point, generally around 570°C to 700°C depending on its composition. The glass is then rapidly cooled on the surface, for example by means of low-temperature air jets. In this way, the outer part of the glass sheet cools before the inner part, which induces permanent stresses in the glass: the central zone is put in tension while the parts close to the surface of the glass sheet are subjected to compressive stresses. Tempered glass has a higher resistance to mechanical and thermal stresses than annealed glass.

Thermally tempered glass can no longer be reworked. It can no longer be cut, shaped or drilled. It is therefore important that the machining and final sizing take place before quenching.

When thermally toughened glass breaks, it shatters into many small pieces with few or no sharp edges.

It is considered in this application that a reinforced glass of the thermally toughened type satisfies the fragmentation test as defined in point 8 of standard NF EN 12150-1 (2019).

When the rapid heat treatment method of the present invention is implemented on a tempered glass, the glass substrate complies with the fragmentation test of standard NF EN 12150-1 (2019) before and after said rapid heat treatment.

Semi-tempered glasses, also called “heat-strengthened glasses” or “heat-strengthened glasses”:

These are glasses which have undergone a heat treatment similar to thermal tempering but for which the compressive stresses are lower than those of tempered glass, because the cooling has been carried out more slowly.

Thermal quenching leads to a surface stress greater than 90 MPa, generally between 90 and 200 MPa. A semi-tempered, or heat-strengthened, glass has a surface stress generally in the range of 30 to 90 MPa, in particular in the range of 30 to 60 MPa. These compressive stresses can be measured for example by the Autogasp2 device marketed by the company Strainoptics.

Semi-tempered glass, or heat-strengthened glass, has undergone a cycle of heating and cooling that has made it generally twice as strong as annealed glass of the same type and thickness.

Thermally toughened glass has a greater resistance to thermal stress than annealed glass, but is not suitable for the same uses as tempered glass (safety glass), because when it breaks, the fragments are generally larger than those of the tempered glass and often remain in the frame after breakage.

Thermally toughened glass can be used for glazing that requires additional strength to withstand wind or snow loads and thermal stresses. It is also used in at least one of the glasses of a laminated glazing when it is necessary to obtain a reinforced laminate. Its large fragments after breakage allow the glass to remain in the frame until it can be replaced.

Like tempered glass, heat-strengthened glass cannot be cut or drilled after heat treatment. It can cause injury if broken.

Semi-tempered glasses are defined in standard NF EN 1863-1 (2012) and in this application it is considered that a semi-tempered glass substrate retains its reinforced state when, after having undergone the rapid heat treatment process of the present invention, it still satisfies the fragmentation test described in point 8 of this standard.

When the substrate is made of heat-strengthened glass (tempered or semi-tempered glass), its thickness is advantageously between 1.6 mm and 20 mm, preferably between 2 mm and 14 mm, in particular between 2.6 and 10 mm.

Glasses that have undergone a chemical strengthening treatment (chemical toughening): During chemical toughening, the glass is placed in a hot bath (350°C – 550°C) of potassium salts. Under the effect of heat, the sodium ions on the surface of the glass are replaced by potassium ions from the bath. Since potassium ions are larger than sodium ions, compressive stresses appear on the surface of the glass during cooling, improving its mechanical properties, in terms of impact resistance.

The surface compressive stresses of chemically toughened glasses and the thickness of the ion exchange layer can be determined using photoelastic measurement methods, for example using a stratorefractometer or a polarizing microscope equipped of a Babinet compensator.

The compressive stresses of chemically toughened glasses are generally between 100 and 1000 MPa, preferably between 150 and 800 MPa.

Thermal toughening requires a minimum thickness of glass, which is not the case with chemical toughening, which can be achieved on thicknesses of less than 2 millimetres.

The chemical hardness of tempered or chemically strengthened glass is mainly used for the solidification of thin and ultra-thin glass (UTG, ultra thin glass ). Given its very high resistance, chemically tempered glass is little used in construction and is mainly intended for applications such as aeronautics, lighting and electronics.

In the present application, it is considered that a chemically reinforced glass substrate retains its reinforced state when the rapid heat treatment of the invention does not reduce the value of the compressive stresses, determined using a stratorefractometer and confirmed by polarizing microscope, by more than 20%.

When the substrate is a chemically reinforced glass, it advantageously has a thickness comprised between 200 μm and 20 mm, preferably between 250 μm and 2000 μm, in particular between 300 μm and 1000 μm.

The continuous thin coating may consist of a single layer or of a stack of several layers. Its physical thickness is preferably between 0.5 nm to 10.0 μm, more preferably between 1 nm and 5.0 μm and in particular between 2 nm and 2.0 μm, in particular between 10 nm and 1.0 μm.

The continuous thin coating, also called a functional coating, preferably provides the coated substrate with at least one functionality chosen from low emissivity, low electrical resistivity, an antireflection effect, a self-cleaning function or ease of cleaning.

The continuous thin coating is advantageously based on a metal, an oxide, a nitride, or a mixture of oxides chosen from the group formed by silver, molybdenum, niobium, oxide titanium, mixed oxides of indium and zinc or tin, zinc oxide doped with aluminum or gallium, nitrides of titanium, aluminum or zirconium, titanium oxide doped with niobium, cadmium and/or zinc stannate, fluorine and/or antimony doped tin oxide.

Preferably, the functional layer(s) contained in the continuous thin coating or constituting the continuous thin coating are chosen from

• layers based on a metal in the metallic state,
• layers based on titanium oxide,
• electroconductive transparent oxide-based layers,
• silica-based layers.

According to a first preferred embodiment, the functional layer is based on a metal, typically silver, or even gold, molybdenum or niobium. The functional layer is preferably made of this metal. Such metals have properties of low emissivity and low electrical resistivity, so that the coated substrates can be used to manufacture glazing with reinforced thermal insulation, heated glazing or even electrodes. The thickness of the functional layer is then preferably comprised in the range going from 2 to 20 nm.

In this embodiment, the coating comprises at least one metallic functional layer, for example one, two or three metallic functional layers, each being generally arranged between at least two dielectric layers, typically layers of oxide, nitride or oxynitride, for example layers of silicon nitride, zinc and/or tin oxide, titanium oxide etc. This type of coating is preferably deposited by sputtering, in particular assisted by a magnetic field (magnetron process).

According to a second preferred embodiment, the functional layer is a layer based on titanium oxide, in particular a layer consisting of or essentially consisting of titanium oxide.

Thin layers based on titanium oxide have the particularity of being self-cleaning, by facilitating the degradation of organic compounds under the action of ultraviolet radiation (photocatalysis) and the elimination of mineral dirt under the action of runoff. of water. Titanium dioxide crystallized in the anatase form is much more effective in terms of degrading organic compounds than amorphous titanium dioxide or titanium dioxide crystallized in the rutile or brookite form. The titanium oxide can optionally be doped with a metal ion, for example a transition metal ion, or with nitrogen, carbon, fluorine, etc. atoms. Titanium oxide can also be under-stoichiometric or over-stoichiometric in oxygen (TiO ₂ or TiO _x ).

The layer based on titanium oxide is preferentially deposited by magnetron sputtering. However, this technique does not make it possible to obtain very active layers, because the titanium oxide is not there, or only very little crystallized. The heat treatment of the invention is then necessary to confer appreciable self-cleaning properties.

According to a third preferred embodiment, the functional layer is a layer based on an electrically conductive transparent oxide. The electrically conductive transparent oxide is preferably chosen from layers of indium tin oxide (ITO), layers of zinc oxide doped with aluminum or gallium and layers of zinc oxide. pewter doped with fluorine or antimony.

This type of layer confers electrical conduction properties but also low emissivity, allowing the material to be used in the manufacture of insulating glazing, anti-condensation glazing, or electrodes, for example for photovoltaic cells, for display screens or for lighting devices.

Finally, according to yet another fourth preferred embodiment, the functional layer is a porous silica-based layer.

The silica-based layer is preferably, after heat treatment, essentially made up or even made up of silica. The silica-based layer is advantageously antireflection, in the sense that the light reflection factor on the layer side is at most 6%, in particular 5% after heat treatment, when the layer is deposited on a single face of a glass substrate (the value therefore takes into account the reflection of the uncoated opposite face, which is approximately 4%).

According to a first variant, the silica-based layer comprises, before heat treatment, silicon, oxygen, carbon and optionally hydrogen, these last two elements being at least partially eliminated during the heat treatment so as to obtain a porous layer essentially made up of silica. This layer is preferably deposited by magnetron sputtering of a silicon or silica target or by plasma-assisted chemical vapor deposition using an organometallic compound such as hexamethyldisiloxane as silicon precursor.

According to a second variant, the silica-based layer comprises, before heat treatment, a matrix of silica and pore-forming agents, the latter being eliminated during the heat treatment so as to obtain a porous layer essentially consisting of silica. The blowing agents are preferably organic, in particular polymeric, for example polymethyl methacrylate, their average size preferably being within a range ranging from 20 to 200 nm. This layer is preferably deposited by a method of the sol-gel type.

The functional layer can be obtained by any type of thin layer deposition process. These may for example be processes of the sol-gel type, pyrolysis (liquid or solid), chemical vapor deposition (CVD), in particular assisted by plasma (APCVD), possibly under atmospheric pressure (APPECVD), evaporation, sputtering cathodic, in particular assisted by a magnetic field (magnetron process). In this last process, a plasma is created under a high vacuum in the vicinity of a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, tear off said elements, which are deposited on the substrate, forming the desired thin layer. This process is said to be “reactive” when the layer is made of a material resulting from a chemical reaction between the elements torn from the target and the gas contained in the plasma. The major advantage of this process lies in the possibility of depositing on the same line a very complex stack of layers by successively scrolling the substrate under different targets, generally in a single device.

In a preferred embodiment of the method of the invention, the heating of the thin layer is carried out by means of a laser device, preferably a laser device emitting laser radiation focused on the continuous thin coating.

The laser device preferably creates, at the level of the first face carrying the continuous thin coating, a single laser line under which the glass substrate carrying the continuous thin coating runs.

The laser radiation is preferably generated by modules comprising one or more laser sources as well as shaping and redirection optics.

The laser sources are typically laser diodes or fiber lasers, in particular fiber, diode or disc lasers. Laser diodes make it possible to economically achieve high power densities in relation to the electrical power supply, for a small footprint. The size of fiber lasers is even smaller, and the linear power obtained can be even higher, but at a higher cost. By fiber lasers is meant lasers in which the place of generation of the laser light is spatially offset with respect to its place of delivery, the laser light being delivered by means of at least one optical fiber. In the case of a disc laser, the laser light is generated in a resonant cavity in which the emitting medium is located, which is in the form of a disc, for example a thin disc (about 0.1 mm in diameter). thickness) in Yb:YAG. The light thus generated is coupled into at least one optical fiber directed towards the place of treatment. The laser can also be fiber, in the sense that the amplification medium is itself an optical fiber. Fiber or disc lasers are preferably optically pumped using laser diodes. The radiation from the laser sources is preferably continuous. It can alternatively be pulsed.

The wavelength of the laser radiation, therefore the treatment wavelength, is preferably within a range ranging from 200 to 2500 nm, preferably 500 to 1300 nm, in particular from 800 to 1100 nm.

Infrared laser radiation with a wavelength in the range from 900 to 1100 nm, in particular from 915 to 1050 nm is particularly preferred.

Power laser diodes emitting at one or more wavelengths chosen from 808nm, 880nm, 915nm, 940nm or 980nm have proven to be particularly well suited. In the case of a disk laser, the treatment wavelength is for example 1030 nm (emission wavelength for a Yb:YAG laser). For a fiber laser, the treatment wavelength is typically 1070nm.

The number of laser lines and their arrangement are advantageously chosen so that the entire width of the substrate is treated.

Several disjoint lines can be used, for example arranged in staggered rows or in the flight of a bird. In general, however, the laser lines are combined to form a single laser line.

In the case of narrow substrates, this laser line can be generated by a single laser module. For very wide substrates, on the other hand, for example greater than 1 m, or even 2 m and even 3 m, the laser line advantageously results from the combination of a plurality of elementary laser lines each generated by independent laser modules. The length of these elementary laser lines typically ranges from 10 to 100cm, in particular from 30 to 75cm, or even from 30 to 60cm. The elementary lines are preferably arranged so as to overlap partially in the direction of the length and preferably have an offset in the direction of the width, said offset being less than the half-sum of the widths of two adjacent elementary lines.

In one embodiment of the method of the invention, several glass substrates are juxtaposed and aligned in a direction perpendicular to the running direction of the substrates and the single laser line has a length at least equal to the width of all the aligned substrates. .

By “length” of the laser line is meant the largest dimension of the line, measured on the surface of the coating in a first direction, and by “width” the dimension along the second direction, perpendicular to the first direction. As is customary in the field of lasers, the width w of the line corresponds to the distance (in this second direction) between the axis of the beam (where the intensity of the radiation is maximum) and the point where the intensity of the radiation is equal to 1/e² times the maximum intensity. If the longitudinal axis of the laser line is named x, we can define a distribution of widths along this axis, named w(x).

The average width of the laser line or of each laser line is advantageously between 40 μm and 500 μm, preferably between 45 μm and 300 μm, in particular between 50 and 200 μm.

Throughout this text, “average” means the arithmetic mean. Over the entire length of the line, the distribution of widths is preferably narrow in order to limit as much as possible any heterogeneity of processing. Thus, the difference between the largest width and the smallest width is preferably worth at most 10% of the value of the average width. This figure is preferably at most 5% and even 3%. In certain embodiments this difference may be greater than 10%, for example from 11 to 20%.

The linear power of the laser line is preferably at least 50W/cm, advantageously at least 100W/cm or at least 150W/cm, in particular at least 200W/cm, or even at least 300W/cm and even at least 350W/cm. It is advantageously less than 1000 W/cm, preferably less than 800 W/cm and more preferably less than 600 W/cm. Linear power is measured where the, or each, laser line is focused on the coating. It can be measured by placing a power detector along the line, for example a calorimetric power meter, such as in particular the Beam Finder S/N 2000716 power meter from the company Coherent Inc. The power is advantageously distributed in such a way homogeneous over the entire length of the line or each line. Preferably, the difference between the highest power and the lowest power is less than 10% of the average power.

The energy density supplied to the thin coating by the laser device is preferably between 10 J/cm² and 300 J/cm², preferably between 15 J/cm² and 200 J/cm² .

According to another advantageous embodiment, the heating of the thin coating is carried out by means of a flash lamp.

Whenever mention is made of a "flash lamp" in the present application, this term designates a single flash lamp or a set of flash lamps, for example 5 to 20 lamps, or even 8 to 15 lamps, preferably arranged parallel to each other, and associated with one or more mirrors. Such a set of flash lamps and mirrors is used for example in the method disclosed in WO 2013/026817. The function of the mirrors is to direct all the light emitted by the lamps in the direction of the substrate and to give the light intensity profile a desired truncated bell shape with a central plateau of approximately constant intensity (varying from less than 5%) and lateral flanks where the intensity gradually decreases. These mirrors can be plane mirrors or focusing mirrors.

The lamps that can be used in the present process are generally in the form of sealed glass or quartz tubes filled with a rare gas, provided with electrodes at their ends. Under the effect of a short electrical pulse, obtained by discharging a capacitor, the gas ionizes and produces a particularly intense incoherent light. The emission spectrum usually has at least two emission lines; it is preferably a continuous spectrum exhibiting an emission maximum in the near ultraviolet and extending up to the near infrared. In this case, the heat treatment implements a continuum of treatment wavelengths.

The lamp is preferably a xenon lamp. It can also be an argon, helium or krypton lamp. The emission spectrum preferably comprises several lines, in particular at wavelengths ranging from 160 to 1000 nm.

The duration of the light pulse ( flash ) is preferably within a range ranging from 0.05 to 20 milliseconds, in particular from 0.1 to 5 milliseconds. The repetition rate is preferably within a range ranging from 0.1 to 5Hz, in particular from 0.2 to 2Hz.

The radiation can come from several lamps arranged side by side, for example 5 to 20 lamps, or even 8 to 15 lamps, so as to simultaneously treat a wider area. All the lamps can in this case emit flashes simultaneously.

The or each lamp is preferably arranged transversely to the longer sides of the substrate. The lamp or each lamp has a length of preferably at least 1 m, in particular 2 m and even 3 m so as to be able to process large substrates.

The capacitor is typically charged to a voltage of 500V to 500kV. The current density is preferably at least 4000A/cm².

The total energy density emitted by the flash lamps, relative to the surface of the coating, is preferably between 1 and 100J/cm², in particular between 1 and 30J/cm², or even between 5 and 20J/cm².

The method according to the invention has the advantage of only briefly heating the coating, without significant heating of the substrate. It is thus possible to preserve the state of reinforcement of the glass, in other words the compressive stresses of the reinforced glass. Throughout the heat treatment step, the temperature at any point on the face of the substrate opposite that bearing the functional layer is preferably at most 150° C., in particular 100° C. and even 50° C.

The maximum temperature to which the coating is heated during the heat treatment of the present invention is preferably at least 300° C., in particular 350° C., even 400° C., and even 500° C. or 600° C., and preferably less than 800°C, or even less than 700°C. The maximum temperature is generally reached when the point of the coating under consideration passes under the laser line or is irradiated by the flash lamp light pulse. At any given time, only the points on the surface of the coating located under the laser line or under the flash lamp and in its immediate surroundings (for example within one millimeter) are normally at a temperature of at least 300°C . For distances to the laser line (measured according to the direction of travel) greater than 2mm, in particular 5mm, including downstream of the laser line, the coating temperature is normally at most 50°C, and even 40°C or 30°C.

Each point of the coating is heated to the maximum temperature for a duration advantageously comprised in a range ranging from 0.05 to 20 ms, in particular from 0.1 to 10 ms, or from 0.15 to 5 ms. In the case of treatment by means of a laser line, this duration is fixed both by the width of the laser line and by the speed of relative movement between the substrate and the laser line. In the case of treatment using a flash lamp, this duration corresponds to the duration of the flash.

The substrate can be set in motion using any mechanical conveying means, for example using bands, rollers, translation plates. The conveying system makes it possible to control and regulate the speed of movement. If the substrate is made of flexible polymeric organic material, the movement can be carried out using a film advance system in the form of a succession of rollers.

All relative positions of the substrate and of the laser are of course possible, as long as the surface of the substrate can be suitably irradiated. The substrate will most generally be arranged horizontally, but it can also be arranged vertically, or at any possible inclination. When the substrate is arranged horizontally, the treatment device is generally arranged so as to irradiate the upper face of the substrate. The treatment device can also irradiate the underside of the substrate. In this case, the substrate support system, possibly the substrate conveying system when the latter is in motion, must allow the radiation to pass into the zone to be irradiated. This is the case, for example, when laser radiation and conveyor rollers are used: the rollers being separate, it is possible to place the laser in an area located between two successive rollers.

The speed of the relative displacement movement between the substrate and the radiation source or sources is advantageously at least 2m/min, in particular 5m/min and even 6m/min or 7m/min, or even 8m/min and even 9m/min. min or 10m/min. This can be adjusted according to the nature of the functional layer to be treated and the power of the radiation source used.

The heat treatment device can be integrated into a line for depositing layers, for example a line for deposition by cathode sputtering assisted by magnetic field (magnetron process), or a line for chemical vapor deposition (CVD), in particular assisted by plasma (PECVD), vacuum or atmospheric pressure (APPECVD). The line generally includes substrate handling devices, a deposition installation, optical control devices, stacking devices. The substrates, in particular made of glass, pass, for example on conveyor rollers, successively in front of each device or each installation.

The heat treatment device is preferably located just after the coating deposition installation, for example at the outlet of the deposition installation. The coated substrate can thus be treated in line after the deposition of the coating, at the outlet of the deposition installation and before the optical control devices, or after the optical control devices and before the substrate stacking devices.

The heat treatment device can also be integrated into the deposition installation. For example, the laser or the flash lamp can be introduced into one of the chambers of a sputtering deposition installation, in particular into a chamber where the atmosphere is rarefied, in particular under a pressure of between 10-6 mbar and 10- 2 mbar. The heat treatment device can also be arranged outside the deposition installation, but in such a way as to treat a substrate located inside said installation. It suffices to provide for this purpose a window transparent to the wavelength of the radiation used, through which the radiation would come to treat the layer. It is thus possible to treat a functional layer (for example a layer of silver) before the subsequent deposition of another layer in the same installation.

The present invention also relates to a reinforced glass substrate carrying a thin coating, which can be obtained by the process described above.

The reinforced glass substrate obtained by the process according to the invention can form or be integrated into a glazing, in particular for building or transport. It can be, for example, multiple glazing (double, triple, etc.), monolithic glazing, curved glazing, laminated glazing.

In the case of layers based on self-cleaning titanium oxide, the material can in particular constitute the first sheet of a multiple glazing, the functional layer being positioned on face 1 of said glazing. In the case of silver-based layers, the functional layer is preferably positioned inside the multiple glazing.

The substrate obtained by the process according to the invention can also be integrated into a photovoltaic cell. In the case of anti-reflective silica-based layers as mentioned above, the material coated with them can form the front face of a photovoltaic cell.

The reinforced glass substrate obtained by the method according to the invention can also be integrated into a display screen or a lighting device or a photovoltaic cell, as a substrate provided with an electrode.

Example 1

Formation of an anti-reflective layer on a thermally toughened glass substrate

A liquid composition hereinafter called “sol” is prepared by mixing 20.8 g of tetraethoxysilane, 18.4 g of absolute ethanol and 7.2 g of an aqueous solution (pH 2.5 by addition of HCl) . The molar ratio of the components is 1:1:4. This mixture is stirred for 4 h at room temperature so as to hydrolyze the tetraethoxysilane.

Submicron beads of poly(methyl methacrylate) (PMMA) having an average diameter of 80 nm ± 10 nm (dynamic light scattering, Malvern Nano ZS) are then added to this sol in the form of a 20% dispersion. in ethanol, so as to obtain a dispersion containing 55% by volume of PMMA beads. The dispersion is filtered through a 0.45 μm filter and deposited by centrifugation ( spin coating ) at 1000 revolutions per minute, on the atmosphere side of a heat-tempered soda-lime glass 4 mm thick. The thermally toughened substrate has a surface stress of 95 ± 10 MPa determined using an Autogasp2 device from the company Strainoptics.

The layer of sol containing the PMMA beads is then dried for 15 minutes at 100° C. in an infrared oven so as to obtain a silica strain containing PMMA beads.

After drying, an absorbent layer of inorganic black pigments dispersed in an organic binder (DV154140 marketed by Prince) is deposited by screen printing on the silica/PMMA layer. After drying for 15 minutes at 150°C, the absorbent layer has a thickness of 15 µm and a light transmission of 0%, i.e. all the laser energy will be converted into heat.

The tempered substrate bearing the silica/PMMA layer and the absorbent layer of black pigments is then subjected to laser treatment. Laser radiation has a wavelength of 980 nm. The laser device used produces a laser line, focused at the level of the treatment surface (absorbing layer), with a width of 50 µm, with a linear power of 10 W/mm along the perpendicular axis of the movement of the glass. During this laser annealing, the absorber layer absorbs the energy of the laser beam, causing the underlying silica/PMMA layer to heat up enough to break down the PMMA nanobeads and leave pores in place. The absorbent layer of black pigments is then removed by washing. The presence of the pores decreases in a known manner the refractive index of the silica layer and reduces the light reflection of the glass bearing the anti-reflective layer.

By varying the running speed of the substrate under the laser line, the inventors have shown that the light reflection of the final substrate is all the lower as the running speed is low.

All substrates successfully pass the fragmentation test of standard NF EN 12150-1 (2019). Laser annealing therefore does not alter the quenching state of the substrate.

Scroll speed Reflection
luminous Fragmentation test
EN 12150-1 (2019) Surface stresses No laser treatment 8% OK 95±10MPa 15m/min 7% OK 95±10MPa 10m/min 6.3% OK 95±10MPa 8m/min 5.7% OK 95±10MPa

When the tempered substrate bearing the two layers (silica/PMMA & absorbent layer) is subjected to annealing for 24 hours in an oven at 470°C, the light reflection is 5.5%. After this slow annealing, the surface stresses have disappeared and the substrate bearing the anti-reflective coating does not pass the fragmentation test of standard NF EN 12150-1 (2019).

Example 2

Formation of an anti-reflective layer on a chemically toughened glass substrate

Example 1 above is repeated except that instead of the thermally toughened glass substrate, a 4 mm soda-lime glass substrate chemically toughened and having compressive stresses, measured using of a polarizing microscope, 180 MPa +/- 20 MPa. The chemical toughening is carried out by immersing the glass substrate in a bath of potassium nitrate brought to a temperature of 490° C. for a period of 6 days.

As for example 1, the substrate is then covered successively with the sol-silica gel layer containing PMMA beads and then with the absorbent layer based on black pigments. It is then subjected to the same laser treatment as the substrate of Example 1 at a running speed under the laser line of 8 m/min, then the absorbent layer is removed by washing. The substrate thus obtained has a light reflection of 5.7% (instead of 8% without laser treatment).

The characterization of the final substrate does not highlight any modification of the mechanical properties of the chemical tempered glass substrate: the compressive stresses are equal to 180 +/- 20 MPa.

When the same chemically toughened substrate bearing the two layers (silica/PMMA & absorbent layer) is subjected to annealing in an oven at 470°C for 24 hours, the light reflection (after elimination of the absorbent layer by washing) is between 5.5 and 6%. After this slow annealing the surface stresses have disappeared.

Examples 1 and 2 thus show that the rapid annealing process of the present invention makes it possible to obtain desired changes in the functional layer, in this case the silica-based anti-reflection layer, without modifying the state of reinforcement. thermally or chemically toughened substrates.

Claims (13)

Process for the heat treatment of at least one continuous thin coating deposited on a first face of a glass substrate, in which each point of said thin coating is heated for a period of less than 1 second at a temperature of at least 300°C maintaining a temperature of less than or equal to 150°C, preferably less than 100°C, at any point on the second face of said glass substrate, opposite to said first face, said method being characterized in that the glass substrate is made of toughened glass and remains in a toughened state during the heat treatment process. Heat treatment process according to Claim 1, characterized in that the substrate is made of chemically reinforced glass. Heat treatment process according to Claim 2, characterized in that the substrate has a thickness of between 200 µm and 20 mm, preferably between 250 µm and 2000 µm, in particular between 300 µm and 1000 µm. Heat treatment process according to Claim 1, characterized in that the glass is made of heat-strengthened glass. Heat treatment process according to Claim 4, characterized in that the substrate has a thickness of between 1.6 mm and 20 mm, preferably between 2 mm and 14 mm, in particular between 2.6 and 10 mm. Heat treatment process according to any one of the preceding claims, characterized in that the said thin coating is heated to a maximum temperature of between 300 and 800°C, preferably between 400 and 700°C. Heat treatment process according to any one of the preceding claims, characterized in that the heating of the thin coating is carried out by means of a laser device, preferably a laser device emitting infrared laser radiation of a wavelength in the range from 900 to 1100 nm, in particular from 915 to 1050 nm, focused on the continuous thin coating. Heat treatment process according to any one of the preceding claims, characterized in that the heating of the thin coating is carried out by means of a laser device creating, at the level of the first face bearing the continuous thin coating, a laser line under which passes the glass substrate bearing the continuous thin coating. Treatment process according to Claim 7 or 8, characterized in that the energy density supplied to the thin coating by the laser device is between 10 J/cm² and 300 J/cm², preferably between 15 J/cm² and 200 J/ cm² . Heat treatment process according to Claim 8, characterized in that several glass substrates are juxtaposed and aligned in a direction perpendicular to the direction of travel of the substrates and that the laser line has a length at least equal to the width of the assembly aligned substrates. Heat treatment process according to any one of Claims 8 to 10, characterized in that the laser line has an average width of between 40 µm and 500 µm, preferably between 45 µm and 300 µm, in particular between 50 and 200 µm. Heat treatment process according to any one of the preceding claims, characterized in that the continuous thin coating is based on a metal, an oxide, a nitride, or a mixture of oxides chosen from the group formed by silver, molybdenum, niobium, titanium oxide, mixed oxides of indium and zinc or tin, zinc oxide doped with aluminum or gallium, nitrides of titanium, aluminum or zirconium, titanium oxide doped with niobium, cadmium and/or zinc stannate, tin oxide doped with fluorine and/or with antimony. A reinforced glass substrate carrying a continuous thin coating obtained by a method according to any preceding claim.