Substrate having a functional coating and a temporary protection layer

0001The invention relates to the protection of substrates, preferably made of glass, carrying at least one functional coating. These substrates are intended to undergo transport, transformation and/or storage stages.

0002It is known to use articles comprising substrates carrying functional coatings in order to give said substrates optical properties (mirror or anti-reflective layers), thermal properties (low-emission, solar control or anti-solar layers, in particular based on silver layers ) or electrical (antistatic layers, transparent conductive layers).

0003Many functional coatings deposited on substrates have low mechanical strength, in particular high scratch ability and low abrasion resistance. Finally, some functional coatings are subject to corrosion during storage, particularly in a humid environment.

0004In particular, substrates bearing functional coatings based on metal layers, for example based on silver or on a silver-based alloy, have these drawbacks. These substrates are generally used in laminated or multiple, double or triple glazing, for so-called solar control and/or low emissivity applications. The functional coatings are then deliberately encapsulated in the glazing.

0005Glass substrates carrying functional coatings of this type are for example sold by the company Saint-Gobain under the name Cool Lite^®. These substrates have very good optical (TL, color) and thermal (solar factor) performance. These performances are obtained thanks to functional coatings comprising complex stacks with in particular more than ten thin layers of different thickness and nature.

0006These substrates undergo various transformation steps such as steps of cutting, washing, shaping of the edges, assembly and/or heat treatments of the quenching, annealing and/or bending type. It is common and practical to carry out the assembly and/or the various treatments at a place other than that where the substrate carrying the functional coating is manufactured. These substrates therefore also undergo storage and transport steps.

0007The mechanical stresses likely to generate scratch-type alterations are multiple and include in particular:<ul id="ul0001" list-style="dash" compact="compact"><li>the step of storing the substrates after deposition of the functional coating on the production site,</li><li>the step of moving the substrates, stacked or not, from the place of production to the place of transformation,</li><li>the shaping and storage stage at the processing site,</li><li>the step of washing in a humid environment carried out for example before a heat treatment or an assembly in double glazing (DGU) or triple glazing (TGU),</li><li>the steps of passing over rollers, for example over the rollers of the furnace with a view to heat treatment, in particular in the case of so-called bi-functionalized substrates carrying functional coatings on each face.</li></ul>

0008The visibility of the scratches once created increases considerably when the substrate is subjected to a tempering-type heat treatment. The scratchability of such substrates is detrimental from the point of view of aesthetics and production efficiency. In fact, scratches not visible before heat treatment, which only become apparent afterwards, can lead to an abnormally high scrap rate. The financial loss is then even higher because the discarded substrate includes the cost of the heat treatment.

0009Complex functional coatings and in particular those comprising thin metal layers based on silver also have low abrasion resistance. These mechanical stresses can induce defects other than scratches, such as the partial or total tearing of one or more layers of the functional coating.

0010Corrosion phenomena can also occur depending on the nature of the materials constituting the functional coatings. But above all, their occurrence is highly dependent on the conditions of humidity, temperature and the duration of the various stages of movement, storage, washing and/or heat treatment. Functional coatings comprising in particular metallic layers or layers based on hygroscopic oxides are sensitive to humidity.

0011Any defects or scratches in the functional coating, whether due to corrosion or mechanical stress, are likely to alter not only the aesthetics but also the optical and/or energy performance of the substrate. The handling of substrates bearing such coatings requires a great deal of care during the transport, transformation and/or storage stages.

0012It is known to protect the surface of the substrate with peelable adhesive polymer films. These films can be deposited in the solid state (as for example in the application<patcit id="pcit0001" dnum="EP1610940A"><text>EP-A-1 610 940</text></patcit>), or in a liquid state (patent<patcit id="pcit0002" dnum="US5866199A"><text>US 5,866,199</text></patcit>). These solutions using peelable films have the following disadvantages:<ul id="ul0002" list-style="dash" compact="compact"><li>high cost,</li><li>a long, tedious peeling step likely to leave traces of the agent providing the bond between the substrate and the film,</li><li>possible delamination of the functional coating during the peeling phase, and</li><li>the need to manage peeled film scrap.</li></ul>

0013The deposition of the same peelable film in the solid state on large substrates is sometimes difficult and may require the use of several films. Problems arise when joining the films:<ul id="ul0003" list-style="dash" compact="compact"><li>either part of the functional coating is not covered by one or the other of the films and in this case the protection is incomplete,</li><li>or the films overlap, which potentially leads to risks when cutting the substrate.</li></ul>

0014Polymer films obtained from a liquid phase and which can be removed by cleaning with aqueous solutions have also been developed. Requirement<patcit id="pcit0003" dnum="WO0050354A"><text>WO 00/50354</text></patcit> discloses, for example, films obtained from aqueous solutions of acrylic polymers which can easily be removed with water, since the polymer is itself soluble in water.

0015Requirement<patcit id="pcit0004" dnum="WO0102496A"><text>WO01/02496</text></patcit> discloses a coating intended to temporarily protect a substrate during a stage of transport, handling or storage, by the application of a removable protective coating. The coating can be a film obtained from aqueous solutions of polymers. The polymers constituting the film can be chosen from starch or casein homopolymers or copolymers, polymers derived from proteins, acrylic polymers, polyacrylamides, polyalkylene oxide polymers, polyvinyl acetate, polyvinyl alcohols , polyvinylpyrrolidone, styrene/acrylic acid copolymers, ethylene/acrylic acid copolymers, cellulosic copolymers and cellulose derivatives.

0016The protective coating is preferably removed by aqueous washing. According to a non-preferred embodiment, this coating can also be eliminated by thermal decomposition or combustion.

0017Temporary protective layers that can be removed during washing are not likely to protect the substrate against wet corrosion during storage. But above all, these layers do not protect the functional coating during the washing phases. In addition, they also have the disadvantage of causing pollution of the washing machine of the transformer.

0018The solutions of the prior art are not effective enough to limit the contact between the functional coating and the chemical elements including liquid water or water vapour, which can lead to cold corrosion during the various stages of storage and/or or transformation.

0019There is therefore a need to temporarily protect the substrates carrying a functional coating during the manufacturing, transformation, transport and/or storage stages. The temporary protection must be sufficiently durable to allow protection of the surface of the substrate both against physical alterations, against corrosion in a humid environment or during a washing step.

0020To this end, the subject of the invention is an article comprising a substrate comprising two main faces defining two main surfaces separated by edges, said substrate carrying:<ul id="ul0004" list-style="dash" compact="compact"><li>a functional coating deposited by sputtering assisted by a magnetic field on at least a part of a major surface and</li><li>a temporary protective layer deposited on at least part of the functional coating,</li></ul>characterized in that:<ul id="ul0005" list-style="dash" compact="compact"><li>the temporary protective layer has a thickness of at least 1 micrometer,</li><li>the temporary protective layer is insoluble in water,</li><li>the temporary protective layer is obtained from a composition comprising (meth)acrylate compounds,</li><li>the substrate bearing the functional coating has not undergone heat treatment at a temperature above 400°C.</li></ul>

0021The temporary protective layer is hardened by drying, by IR baking, by UV irradiation or by electron beam.

0022The temporary protective layer is obtained from a liquid composition comprising (meth)acrylate compounds chosen from monomers, oligomers, prepolymers or polymers comprising at least one (meth)acrylate function.

0023The temporary protective layer according to the invention is specifically intended to be removed during a heat treatment of the quenching, annealing and/or bending type at a temperature sufficient to allow its removal by thermal decomposition. Surprisingly, this temporary protective layer is eliminated without harming the optical properties of the substrate bearing the functional coating. One and the same step of heat treatment of the protected substrate makes it possible to eliminate the protection of the substrate and to confer on the substrate certain properties or conformation (tempered and/or curved substrate).

0024Preferably, the protected substrate, that is to say the substrate bearing the temporary protective layer, has not undergone heat treatment of the quenching, annealing and/or bending type, that is to say heat treatment at a temperature above 200°C or above 400°C. The protected substrate is not tempered and/or bent.

0025Preferably, the substrate bearing the functional coating has not undergone high temperature heat treatment of the quenching, annealing and/or bending type, that is to say heat treatment at a temperature above 200° C. or above at 400°C. This means that the article formed by the substrate and the functional coating has not undergone heat treatment at high temperature. This also means that the method does not include a high temperature heat treatment step, that is to say heat treatment at a temperature above 200°C or above 400°C, between the deposition of the functional coating and depositing the temporary protective layer.

0026This temporary protective layer essentially comprises organic materials of the (meth)acrylate polymer type. Its chemical formulation allows rapid and complete combustion during heat treatment and generates during its decomposition only volatile molecules that are easy to eliminate.

0027This water-insoluble layer provides effective protection during the washing step and against wet corrosion.

0028Surprisingly, the protection is retained even when the substrate undergoes successive cuts. Indeed, the substrates protected according to the invention seem protected from the corrosion mechanisms which could be initiated on the one hand in full face but also from the cutting edge. The substrates protected according to the invention can therefore be cut several times without requiring modification of the protective layer and without losing the functions of mechanical and chemical protection.

0029The invention also relates to the process for protecting said article. In the rest of the text, the preferred embodiments apply in the same way to the different subjects of the invention, the substrate and the method.

0030Requirement<patcit id="pcit0005" dnum="WO0102496A"><text>WO01/02496</text></patcit> does not mention polymers comparable to the (meth)acrylate compounds used according to the invention. This application preferentially discloses water-soluble organic protective layers, in particular based on easily hydrolysable polyvinyl alcohol. Such layers do not meet the problem of the invention which is in particular to resist corrosion in a humid environment and/or washing before transformation.

0031But above all, although this document envisages the elimination of a temporary organic protective layer by thermal decomposition during a tempering-type treatment, it discourages proceeding in this way. Indeed, it is expressly mentioned that elimination by combustion is not preferentially used when the substrates comprise a functional coating deposited by sputtering assisted by a magnetic field (magnetron).

0032Surprisingly, the temporary protective layer according to the invention can be completely removed during a heat treatment by decomposition without harming the optical, energetic or thermal properties imparted to the substrate by the functional coating. These advantageous properties are obtained even when the functional coating has been deposited by magnetron sputtering.

0033The temporary protective layer according to the invention is intended to be applied preferably at the outlet of the production line of substrates carrying functional coatings. The deposition step can be easily integrated into the process for manufacturing the substrate bearing the functional coating.

0034The application of a temporary protective layer obtained from a liquid composition essentially free of solvent and hardened preferably by UV irradiation, by IR curing or by electron beam is particularly advantageous. The choice of this solvent-free technology considerably simplifies the industrial implementation of a method comprising a step of applying such a layer. The absence of solvent makes it possible to avoid setting up a device for drying, recovering and treating the solvent vapors which must not be emitted into the atmosphere. The modifications to be made may be limited to inserting at the end of the line a deposition device, for example by coating with a “roller coater” roller, as well as a crosslinking device such as a UV lamp.

0035The liquid composition has, thanks to the judicious choice of the (meth)acrylate compounds, a suitable viscosity to make it possible to easily obtain a temporary protective layer with a thickness greater than or equal to 1 μm and a sufficient reactivity to allow almost instantaneous crosslinking on the whole thickness. The chemical nature, the degree of cross-linking, the density as well as the thickness of the temporary protective layer contribute to obtaining effective protection against abrasion, the appearance of scratches and corrosion. These protective properties are obtained for thicknesses less than 50 micrometers.

0036Finally, the absence of solvent coupled with almost instantaneous hardening, for example by UV irradiation or by electron beam, makes it possible to obtain protected substrates without affecting the production rates. Advantageously, the coating speeds are compatible with the deposition speeds of the functional coatings, which allows continuous manufacture of the substrates bearing a functional coating and a temporary protective layer according to the invention. For example, the speeds of application of the temporary protective layer, comprising for example coating and crosslinking, can be between 1 and 90 m/min on a substrate of width 1 m to 3.3 m.

0037Although the invention is particularly suitable for the protection of substrates bearing mechanically weak functional coatings, the solution of the invention can be applied to the protection of substrates bearing all types of functional coating.

0038The functional coating includes at least one functional layer. The functional layer is preferably a layer that can act on solar radiation and/or long wavelength infrared radiation. These functional layers are, for example, metal functional layers based on silver or on a metal alloy containing silver.

0039The substrate may comprise a functional coating comprising a stack of thin layers successively comprising, starting from the substrate, an alternation of n functional metal layers, in particular functional layers based on silver or on a metal alloy containing silver, and of ( n+1) antireflection coatings, each antireflection coating comprising at least one dielectric layer, so that each functional metal layer is disposed between two antireflection coatings.

0040The substrate may comprise a stack of thin layers successively comprising, starting from the substrate, an alternation of two functional metal layers, in particular functional layers based on silver or on a metal alloy containing silver, and three antireflection coatings, each antireflection coating comprising at least one dielectric layer, so that each functional metal layer is placed between two antireflection coatings.

0041The substrate may also comprise a stack of thin layers successively comprising, starting from the substrate, an alternation of three functional metal layers, in particular functional layers based on silver or on a metal alloy containing silver, and four anti-reflective coatings, each antireflection coating comprising at least one dielectric layer, so that each functional metal layer is placed between two antireflection coatings.

0042The thickness of the functional coating is:<ul id="ul0006" list-style="dash" compact="compact"><li>greater than 100 nm, preferably greater than 150 nm,</li><li>less than 300 nm, preferably less than 250 nm.</li></ul>

0043According to a particularly advantageous embodiment of the invention, the functional coating comprises an upper layer chosen from titanium, zirconium and/or hafnium nitrides, oxides or oxy-nitrides. The upper layer of the functional coating is the layer farthest from the substrate and/or the layer in direct contact with the temporary protective layer.

0044Surprisingly, the applicant has discovered that there is a synergy between an upper layer based on titanium, zirconium and/or hafnium and the temporary protective layer. This synergy is reflected in particular by the total absence of surface defects as well as by very small colorimetric variations between the product before and after hardening. Finally, the synergy also results in a very low haze after quenching.

0045The upper layer can in particular be a layer:<ul id="ul0007" list-style="dash" compact="compact"><li>titanium nitride; zirconium nitride; hafnium nitride; titanium zirconium nitride; titanium, zirconium and hafnium nitride;</li><li>titanium oxide; zirconium oxide; hafnium oxide; titanium oxide and zirconium; titanium oxide, zirconium and hafnium.</li></ul>

0046The thickness of these upper layers is preferably between 1 and 20 nm and better still between 1 and 5 nm.

0047According to a variant, the upper layer can be a layer of silicon nitride optionally doped with aluminium. The thickness of this upper layer is preferably between 5 and 50 nm and better still between 10 and 50 nm.

0048The functional coating can be deposited by any known means such as by cathode sputtering assisted by a magnetic field, by thermal evaporation, by CVD or PECVD, by pyrolysis, by chemical deposition, by sol-gel type or deposition of layers. inorganic wet process.

0049The functional coating is preferably deposited by sputtering assisted by a magnetic field. According to this advantageous embodiment, all the layers of the functional coating are deposited by sputtering assisted by a magnetic field. The temporary protective layer is advantageously directly in contact with the functional coating.

0050The temporary protective layer is essentially organic in nature. The reacted (meth)acrylate compounds represent at least 90% by mass of the mass of the temporary protective layer.

0051By (meth)acrylate is meant an acrylate or a methacrylate. The term “(meth)acrylate compounds” means esters of acrylic or methacrylic acid comprising at least one acroyl (CH2=CH—CO—) or methacrylic (CH2=CH(CH3)—CO—) function. These esters can be monomers, oligomers, pre-polymers or polymers. These (meth)acrylate compounds, when subjected to polymerization conditions, yield a polymer network with a strong structure.

0052The (meth)acrylate compounds used according to the invention can be chosen from monofunctional and polyfunctional (meth)acrylates such as mono-, di-, tri-, poly-functional (meth)acrylates. Examples of such monomers are:<ul id="ul0008" list-style="dash" compact="compact"><li>monofunctional (meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, n- or ter-butyl(meth)acrylate, hexyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth) acrylate, benzyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate, phenyloxyethyl(meth)acrylate, hydroxyethylacrylate, hydroxypropyl(meth)acrylate, vinyl(meth)acrylate caprolactone acrylate, isobornyl methacrylate, lauryl methacrylate, polypropylene glycol monomethacrylate,</li><li>difunctional (meth)acrylates such as 1,4-butanediol di(meth)acrylate, ethylene dimethacrylate, 1,6-hexandiol di(meth)acrylate, bisphenol A di(meth)acrylate, trimethylolpropane diacrylate, triethylene glycol diacrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate,</li><li>trifunctional (meth)acrylates such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tripropylene glycol triacrylate,</li><li>(meth)acrylates of higher functionality such as pentaerythritol tetra(meth)acrylate, ditrimethylpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate or hexa(meth)acrylate.</li></ul>

0053According to an advantageous embodiment, the temporary protective layer does not include mineral filling material such as fillers or pigments. The temporary protective layer also does not include additives that cannot be eliminated during the heat treatment, such as organic compounds comprising silicon of the siloxane type.

0054The temporary protective layer has a thickness:<ul id="ul0009" list-style="dash" compact="compact"><li>greater than 1 micrometer, preferably greater than 5 micrometers,</li><li>less than 100 micrometers, preferably less than 50 micrometers,</li><li>between 2 and 100 micrometers, between 5 and 50 micrometers or between 10 and 30 micrometers.</li></ul>

0055The temporary protective layer has a weight between 5 and 50 g/m², preferably between 10 and 30 g/m².

0056According to advantageous embodiments of the invention, the liquid composition has the following characteristics:<ul id="ul0010" list-style="dash" compact="compact"><li>the liquid composition comprises less than 20% by mass of solvent relative to the total mass of the liquid composition,</li><li>the liquid composition comprises less than 10% by mass of solvent relative to the total mass of the liquid composition,</li><li>the liquid composition is solvent-free,</li><li>the liquid composition has a viscosity measured at 25°C:<ul id="ul0011" list-style="dash" compact="compact"><li>at least 0.05 Pa.s, at least 0.08 Pa.s, at least 0.1 Pa.s, at least 0.50 Pa.s,</li><li>no more than 5 Pa.s, no more than 2 Pa.s,</li><li>between 0.05 and 5 Pa.s;</li></ul></li><li>the liquid composition comprises at least one polymerization initiator, preferably a photoinitiator,</li><li>the polymerization initiator represents 0.1 to 20%, or 1 to 15%, preferably 5 to 15% and better still 8 to 12% by mass of the total mass of the (meth)acrylate compounds,</li><li>the liquid composition further comprises at least one additive chosen from plasticizers, absorbers, separating agents, heat and/or light stabilizers, thickening agents or surface modifiers,</li><li>the sum of all additives is between 0 and 5% by mass of the mass of the liquid composition,</li><li>(meth)acrylate compounds chosen from esters of acrylic or methacrylic acid comprising at least two acroyl (CH2=CH-CO-) or methacroyl (CH2=CH(CH3)-CO-) functions,</li><li>the liquid composition comprises by mass relative to the total mass of the (meth)acrylate compounds, in increasing order of preference, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, 100% of (meth)acrylate compounds chosen from esters of acrylic or methacrylic acid comprising at least two acroyl (CH2=CH-CO-) or methacrylic (CH2=CH(CH3)-CO-) functions,</li><li>the liquid composition comprises:<ul id="ul0012" list-style="dash" compact="compact"><li>at least one aliphatic urethane-acrylic oligomer,</li><li>at least one (meth)acrylate monomer chosen from mono-, bi-, tri-functional (meth)acrylate monomers,</li><li>at least one polymerization initiator,</li></ul></li><li>the liquid composition comprises:<ul id="ul0013" list-style="dash" compact="compact"><li>at least one aliphatic urethane-acrylic oligomer,</li><li>at least one difunctional (meth)acrylate monomer,</li><li>at least one trifunctional (meth)acrylate monomer,</li><li>at least one polymerization initiator, preferably a photoinitiator,</li></ul></li><li>the liquid composition comprises by mass relative to the total mass of the (meth)acrylate compounds:<ul id="ul0014" list-style="dash" compact="compact"><li>30 to 80% by mass of at least one aliphatic urethane-acrylic oligomer,</li><li>20 to 70% by mass of at least at least one (meth)acrylate monomer chosen from a mono, bi or trifunctional (meth)acrylate.</li></ul></li></ul>

0057According to the invention, the polymerization initiators are not considered as additives.

0058The liquid composition can be applied at ambient temperature by any known means and in particular by roller coating, by spraying, by dipping, by curtain coating, or by spraying. The liquid composition is preferably applied by roller coating. The deposition rate of the liquid composition can be between 1 and 90 m/min.

0059The temporary protective layer can be hardened:<ul id="ul0015" list-style="dash" compact="compact"><li>by drying at a temperature below 200° C. for a period ranging for example from 10 s to 180 s,</li><li>by UV curing (different wavelengths) preferably in the open air and at room temperature or</li><li>by electron beam.</li></ul>

0060The liquid composition further comprises a polymerization initiator, the nature of which depends on the type of hardening chosen. For example, in the case of thermal hardening, initiators of the benzoyl peroxide type are used. In the case of curing by UV radiation, so-called photoinitiators are used.

0061The substrate to be protected must withstand a heat treatment above 200°C, preferably above 400°C. The invention therefore relates to any substrate made of materials resistant to these temperatures without major alteration. By way of substrate, mention may be made of glass substrates, glass-ceramic substrates, ceramic substrates, steel substrates, metal substrates with a melting point above 250° C. The substrate is preferably a glass substrate.

0062Advantageously, the substrate carrying the temporary protective layer has not undergone heat treatment of the quenching, annealing and/or bending type, that is to say heat treatment at a temperature above 200°C.

0063The glass substrate can be flat, colorless and/or tinted. The thickness of the substrate is preferably between 1 and 19 mm, more particularly between 2 and 10 mm, or even between 3 and 6 mm.

0064According to a variant of the invention, the temporary protective layer can be used to protect the functional coating during a step of depositing another coating. This other coating can be deposited on a part of the main surface of the substrate bearing the functional coating or on a part of the main surface of the substrate not bearing the functional coating.

0065It is known in particular that for obtaining bi-functionalized substrates bearing a functional coating on each main face, the contact of the functional coating deposited first with the rollers of the deposition device during the second passage allowing the deposition of the second coating leads to harmful alterations in the quality of the first coating (pollution, scratches). These alterations becoming visible after deposition of the second functional coating and possibly quenching. The invention makes it possible to overcome this problem by protecting the first coating with a protective layer intended to disappear during the quenching or bending of the bi-functionalized substrate.

0066According to another variant of the invention, the temporary protective layer can be used to protect the rear surface of the substrate during the deposition of a functional coating. Indeed, the passage over the rollers of the rear face of a substrate, for example made of glass, during the deposition of a functional coating, is capable of partially altering said surface (dirt, scratch). The invention makes it possible to overcome this problem by protecting the rear surface of the substrate before deposition of the first coating.

0067The temporary protective layer can be applied:<ul id="ul0016" list-style="dash" compact="compact"><li>on each of the main surfaces of the substrate, and/or</li><li>on at least one edge of the substrate, and/or</li><li>on each edge of the substrate.</li></ul>

0068When the temporary protective layer is deposited on each of the main surfaces of the substrate and on each of the edges of the substrate, the chemical and/or mechanical protection is then conferred on the entire surface of the substrate.

0069The temporary protective layer can be deposited on a glass substrate before or after a cutting step, that is to say on a glass substrate at the final size or close to the final size (primary).

0070Another subject of the invention is a method for protecting an article comprising a substrate comprising two main faces defining two main surfaces separated by edges, said glass substrate bearing a functional coating deposited on at least part of a main surface , said protection method comprising the following steps:<ul id="ul0017" list-style="dash" compact="compact"><li>preparing a liquid composition comprising (meth)acrylate compounds chosen from monomers, oligomers, prepolymers or polymers comprising at least one (meth)acrylate function,</li><li>apply the composition to at least part of the functional coating, preferably using a roller, to a thickness of at least 1 micrometer,</li><li>crosslinking the composition so as to form the temporary protective layer.</li></ul>

0071The protection method includes the step of removing said temporary protective layer by heat treatment at high temperature. The heat treatment temperature is greater than 200°C, greater than 300°C, or greater than 400°C. The heat treatments are chosen from annealing, for example by flash annealing such as laser or flame annealing, quenching, and/or bending.

0072The liquid composition preferably comprises less than 20% by mass of solvent relative to the total mass of the liquid composition and a viscosity of between 0.05 and 5 Pa.s

0073The process for protecting a substrate further comprises a step of removing said temporary protective layer by heat treatment. The heat treatments are chosen from annealing, for example by flash annealing such as laser or flame annealing, quenching, and/or bending. The heat treatment temperature is greater than 200°C, greater than 300°C, or greater than 400°C.

0074The heat treatment necessary to eliminate the protective layer can be annealing in a static or dynamic furnace. The heat treatment may then aim to improve the crystallization of one or more layers included in the stack to be protected.

0075The functional coating comprises at least one functional layer deposited during a magnetron deposition step.

0076The temporary protective layer is formed immediately after the step of depositing the functional coating. According to the invention, it is considered that the temporary protective layer can be formed "immediately afterwards", when the temporary protective layer can be formed less than 10 minutes, preferably less than 5 minutes and better still less than 1 minute after the functional coating deposition step.

0077The present description also relates to a production line for an article comprising a substrate comprising two main faces defining two main surfaces separated by edges, said substrate bearing:<ul id="ul0018" list-style="dash" compact="compact"><li>a functional coating deposited on at least a part of a major surface and</li><li>a temporary protective layer deposited on at least part of the functional coating, obtained from a liquid composition,</li></ul>characterized in that it comprises:<ol id="ol0001" compact="compact"><li>i) a device for depositing a functional coating,</li><li>ii) a device for depositing a liquid composition comprising a means for storing and a means allowing the application in the form of a layer of said liquid composition,</li><li>iii) a crosslinking device, for example thermal, by UV irradiation or by electron beam,</li><li>iv) means for moving said substrate from devices i) to iii).</li></ol>

0078The device for depositing a functional coating can be a device for depositing by pyrolysis, a device for depositing by chemical means and preferably a sputtering device assisted by a magnetic field (magnetron).

0079The device for depositing a liquid composition comprising a storage means and a means allowing the application in the form of a layer of said liquid composition is preferably a roller coating device. This device can comprise an application roller and a backing roller. The liquid composition can then be pumped into the space defined between the two rollers constituting a storage means and applied by driving the rollers.

0080Preferably, the crosslinking device is a UV lamp.

0081The protected glass substrate according to the invention can be stacked without cross-pollution, or appearance of mechanical scratches, immediately after deposition of the functional coatings.

0082The protected glass substrate according to the invention advantageously meets the following criteria:<ul id="ul0019" list-style="dash" compact="compact"><li>mechanical scratch protection resulting for example in a resistance to the Erichsen test at the tip (EST) of at least 7 N and to the Clement test greater than 20 N,</li><li>protection against mechanical processing stress resulting in increased resistance of the functional coating located under the protective layer to different storage modes, washing machine brush, shaping and cutting,</li><li>wet corrosion protection, in particular the corrosion mechanism of silver layers subjected to the condensation of a film of water during storage or transport.</li><li>resistance of the protective layer during tempering for a sufficient time for the glass to remain highly emissive for a time allowing a significant energy gain,</li><li>excellent adhesion of the protective layer to the functional coating to withstand all processing steps before hardening without delamination,</li><li>elimination of the temporary protective layer without leaving mineralized residues in the event of hardening or bending whatever the type of heating (radiative/convective).</li></ul>

EXAMPLES

I. Materials used

1. Substrates and functional layers

0083The substrates used are flat glass substrates approximately 6 mm thick obtained by a float process which consists in pouring the molten glass onto a bath of tin.

0084Functional coatings conferring solar control properties comprising a stack of thin layers were deposited using a cathode sputtering device assisted by magnetic field (magnetron).

0085The first functional coating, hereinafter called Ag tri-layers, successively comprises, starting from the substrate, an alternation of three silver layers (functional metal layers) and four antireflection coatings, each antireflection coating comprising at least one dielectric layer, so that each functional metal layer is disposed between two anti-reflective coatings. The total thickness of this functional coating is between 200 and 250 nm.

0086The second functional coating, hereinafter called Ag bi-layers, comprises a stack of thin layers comprising successively, starting from the substrate, an alternation of two silver layers and three antireflection coatings, each antireflection coating comprising several dielectric layers, so that each layer of silver is placed between two anti-reflective coatings. The total thickness of this functional coating is between 150 and 200 nm.

0087The upper layer of the first and second functional coatings is chosen from:<ul id="ul0020" list-style="dash" compact="compact"><li>OC1: a layer of titanium, zirconium and hafnium nitride obtained from targets of metallic titanium, metallic alloy of titanium and zirconium or metallic alloy of titanium, zirconium and hafnium (TiZrHfNx) from 2 to 5 nm,</li><li>OC2: a layer of titanium oxide obtained from a target of metallic titanium or titanium oxide TiOx substoichiometric (x&lt;2) of 2 to 5 nm or</li><li>OC3: a silicon nitride layer obtained from an optionally doped silicon target of 10 to 50 nm.</li></ul>

2. Temporary protective layer

0088Liquid compositions were made with mixtures of oligomers and monomers comprising at least one acrylate function marketed by the company Sartomer:<ul id="ul0021" list-style="none" compact="compact"><li>CN9276: tetra-functional aliphatic urethane-acrylate oligomer,</li><li>SR351: trimethylolpropane triacrylate, tri-functional acrylate monomer,</li><li>SR833S: tricyclodecane dimethanol diacrylate, di-functional acrylate monomer.</li></ul>

0089The presence of the urethane-acrylate oligomer makes it possible to modulate the properties of hardness and flexibility of the temporary protective layer.

0090The temporary protective layer is then hardened either by drying or by UV curing. A polymerization initiator is added and chosen according to the type of crosslinking. For example :<ul id="ul0022" list-style="dash" compact="compact"><li>for thermal crosslinking, the initiator is benzoyl peroxide,</li><li>for UV curing, the initiator can be chosen from the photoinitiators marketed by BASF under the name Irgacure^® such as the Iragure 500, by Lambson under the name Speedcure 500 or by Lamberti under the name Esacure HB.</li></ul><tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="41mm" /><colspec colnum="2" colname="col2" colwidth="12mm" /><colspec colnum="3" colname="col3" colwidth="12mm" /><colspec colnum="4" colname="col4" colwidth="12mm" /><colspec colnum="5" colname="col5" colwidth="12mm" /><thead valign="top"><row><entry>Compositions</entry><entry>AT</entry><entry>B</entry><entry>VS</entry><entry>D</entry></row></thead><tbody><row rowsep="0"><entry>Main constituent:</entry><entry /><entry /><entry /><entry /></row><row rowsep="0"><entry>- acrylate oligomer</entry><entry>40</entry><entry>40</entry><entry>60</entry><entry>36</entry></row><row rowsep="0"><entry>- di-functional acrylate</entry><entry>30</entry><entry>30</entry><entry>20</entry><entry>25</entry></row><row><entry>- tri-functional acrylate</entry><entry>30</entry><entry>30</entry><entry>20</entry><entry>25</entry></row><row><entry rowsep="0">Initiator:</entry><entry rowsep="0" /><entry rowsep="0" /><entry rowsep="0" /><entry rowsep="0" /></row><row><entry rowsep="0">- Thermal</entry><entry rowsep="0">3</entry><entry rowsep="0">-</entry><entry rowsep="0">-</entry><entry rowsep="0">-</entry></row><row><entry>-UV</entry><entry>-</entry><entry>5</entry><entry>5</entry><entry>5</entry></row><row><entry>Solvent: butyl acetate</entry><entry>-</entry><entry>-</entry><entry>-</entry><entry>9</entry></row><row><entry>Viscosity at 25°C(Pa.s)</entry><entry>0,71</entry><entry>0,50</entry><entry>1,08</entry><entry>0,15</entry></row></tbody></tgroup></table></tables>

0091The compositions are defined in parts by mass.

0092The main constituents consist of oligomers, monomers and possibly prepolymers.

0093The liquid compositions are applied to the glass substrates by roller coating. Thicknesses comprised between 10 and 20 μm are obtained by using speeds for the applicator roller comprised between approximately 15 and 25 m/min.

0094The temporary layers A hardened by drying are heated at 150° C. for 15 min and thus perfectly dry and hard.

0095The temporary layers D are dried beforehand in an IR type oven at a temperature of at least 120° C. but less than 170° C. before passing under UV for crosslinking.

0096The temporary layers B, C or D hardened by UV irradiation are crosslinked at a speed of 15 m/min by UV radiation supplied by a 120 W mercury lamp. Under these conditions, the polymerization of the mixture of monomers and oligomers is obtained in the thickness range of 10 to 20 µm.

0097Temporary layers cured by UV irradiation can also be cured using a UV LED curing system.

II. Evaluation of mechanical properties

0098These tests were carried out on glass substrates bearing:<ul id="ul0023" list-style="dash" compact="compact"><li>a silver three-layer functional coating,</li><li>a type C temporary protection layer.</li></ul>

0099The thicknesses tested for the functional layer are respectively 13 and 20 μm.

0100The substrates are subjected to thermal toughening under the following conditions: 685-695°C for 40-50s/mm of glass. Then, an Erichsen test at the Tip (EST) and a High Humidity (HH) test are carried out.

0101The Erichsen test consists in deferring the value of the force necessary, in Newtons, to produce a scratch in the stack (point of Van Laar, steel ball).

0102The following assessment indicators were used:<ul id="ul0024" list-style="none" compact="compact"><li>“+++”: no scratches,</li><li>“0”: non-continuous stripes,</li><li>"--": many non-continuous scratches,</li><li>“---”: continuous stripes.</li></ul>

0103The humidity test (HH) consists of storing samples for 8 days at 90% relative humidity and at 60°C and observing the possible presence of defects such as pitting corrosion. The following assessment indicators were used:<ul id="ul0025" list-style="none" compact="compact"><li>“+”: no sting,</li><li>“-”: many bites.</li></ul>

0104The tables below summarize the glazing, the assessment conditions and the assessment indicators. A reference substrate bearing a functional coating without a temporary protective layer is compared with two substrates bearing a functional coating and a temporary protective layer 13 and 24 μm thick. The test was carried out on two different places on the surface of the same substrate. These examples clearly show the excellent resistance to scratching and to wet corrosion of the substrates protected according to the invention.<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="9"><colspec colnum="1" colname="col1" colwidth="24mm" /><colspec colnum="2" colname="col2" colwidth="11mm" /><colspec colnum="3" colname="col3" colwidth="11mm" /><colspec colnum="4" colname="col4" colwidth="11mm" /><colspec colnum="5" colname="col5" colwidth="11mm" /><colspec colnum="6" colname="col6" colwidth="11mm" /><colspec colnum="7" colname="col7" colwidth="11mm" /><colspec colnum="8" colname="col8" colwidth="11mm" /><colspec colnum="9" colname="col9" colwidth="9mm" /><thead valign="top"><row><entry>Erichsen test</entry><entry align="center">0,1</entry><entry align="center">0,5</entry><entry align="center">0,7</entry><entry align="center">1</entry><entry align="center">3</entry><entry align="center">5</entry><entry align="center">7</entry><entry align="center">10</entry></row></thead><tbody><row><entry morerows="1">Reference</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">0</entry><entry align="center">---</entry><entry align="center">---</entry><entry align="center">---</entry><entry align="center">---</entry></row><row><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">0</entry><entry align="center">---</entry><entry align="center">---</entry><entry align="center">---</entry><entry align="center">---</entry></row><row><entry morerows="1">C-13µm</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">--</entry></row><row><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">--</entry></row><row><entry morerows="1">C-24µm</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">0</entry><entry align="center">--</entry></row><row><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">+++</entry><entry align="center">--</entry></row></tbody></tgroup></table></tables><tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="20mm" /><colspec colnum="2" colname="col2" colwidth="23mm" align="center" /><thead valign="top"><row><entry>HH test</entry><entry>Appreciation</entry></row></thead><tbody><row><entry>Reference</entry><entry>-</entry></row><row><entry>C-13µm</entry><entry>+</entry></row><row><entry>C-24µm</entry><entry>+</entry></row></tbody></tgroup></table></tables>

0105The reference substrate according to the Erichsen test comprises from 1 N fine scratches and at 10 N numerous very visible continuous scratches, homogeneous in thickness. The same substrate protected by a temporary protective layer according to the invention comprises many fewer scratches after hardening for applied forces of 7 to 10 N. In addition, the scratches are non-continuous.

0106The substrates protected by a temporary protective layer according to the invention do not include any pitting corrosion. These tests show that a substrate bearing a functional coating 13 μm thick is effectively protected.

III. Evaluation of properties after quenching

0107The quenching tests carried out show the total removal of the temporary protective layer without deterioration of the substrates carrying the functional coatings. This aspect was verified by measuring the colorimetric coordinates. Glass substrates carrying functional coatings which differ in the choice of the top layer have been tested. They comprise respectively as upper layer OC1 (TiZrHfNx) and OC2 (TiOx).

0108Substrates hereinafter called OC1-Inv and OC2-Inv were protected by a temporary type C coating and subjected to tempering. To compare, reference substrates hereinafter called OC1-Ref and OC2-Ref were not protected and subjected to quenching.

0109The colorimetric variation at the color heat treatment on the functional coating side in reflection induced by quenching was calculated (ΔE). For that :<ul id="ul0026" list-style="dash" compact="compact"><li>the colors in reflection L*, a* and b* in the LAB system measured according to the illuminant D65, side layers are measured and</li><li>the variation is measured as follows: ΔE = (Δa*² + Δb*² + ΔL*²)^½.</li></ul>

0110Several ΔE measurements were performed for each glass substrate covered with a functional coating. The table below summarizes the results of these tests.

0111For the reference substrates, the ΔE represents the variation between the L, a* and b* values ​​obtained for an unprotected substrate before quenching and for an unprotected quenched substrate.

0112For the substrates of the invention, the ΔE corresponds to the variation between the values ​​L, a* and b* obtained for an unprotected substrate before tempering and for a protected substrate whose protective layer has been removed following tempering.<tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="19mm" /><colspec colnum="2" colname="col2" colwidth="17mm" /><colspec colnum="3" colname="col3" colwidth="19mm" /><colspec colnum="4" colname="col4" colwidth="17mm" /><colspec colnum="5" colname="col5" colwidth="19mm" /><thead valign="top"><row><entry><b>Substrate</b></entry><entry><b>OC1-Inv</b></entry><entry><b>OC1-Ref</b></entry><entry><b>OC2-Inv</b></entry><entry><b>OC2-Ref</b></entry></row></thead><tbody><row><entry morerows="2">ΔE</entry><entry>11,21</entry><entry>10,70</entry><entry>12,71</entry><entry>10,43</entry></row><row><entry>11,15</entry><entry>11,13</entry><entry>12,51</entry><entry>-</entry></row><row><entry>11,95</entry><entry>10,81</entry><entry>12,93</entry><entry>-</entry></row></tbody></tgroup></table></tables>

0113These tests show that the presence of the temporary protective layer according to the invention does not modify the colorimetric variations which can be induced by a treatment of the tempering type. Indeed, the difference between the values ​​of ΔE are not significant between a substrate according to the invention and a quenched reference substrate with respect to a non-quenched substrate.

0114Regardless of the nature of the upper layer, no colorimetric variation attributable to the presence of the temporary protective layer is observed. This means that the temporary protective layer does not induce colorimetric modification in the substrate after heat treatment.

IV. Upper Layer Influence

0115Comparative tests to evaluate the influence of the upper layer on the appearance after quenching have been carried out. Substrates carrying functional coatings of the silver tri-layer type with different upper layers were tested. Each of these substrates was covered with a temporary type C protective layer and then subjected to a tempering type heat treatment.

0116The observations of the surface after heat treatment depending on the nature of the upper layer are as follows:<ul id="ul0027" list-style="dash" compact="compact"><li>OC1 (TiZrHfNx): no fault,</li><li>OC2 (TiOx): no fault,</li><li>OC3 (Si3N4): no fault.</li></ul>

0117Other top layers have been tested. These layers have not made it possible to obtain results as good as those obtained with nitrides, oxides or oxy-nitrides of titanium, zirconium and/or hafnium. Functional coatings comprising upper layers based on titanium, zirconium and/or hafnium protected by temporary layers according to the invention show better resistance to corrosion and very low haze levels.