FR3163647A1 - SUBSTRATE COMPRISING A PROTECTED ENAMEL COATING - Google Patents

Abstract

The invention relates to a substrate comprising two main faces defining two main surfaces separated by edges, said substrate comprising an enamel layer deposited on at least a portion of one main surface and a temporary protective layer, obtained from a liquid composition comprising (meth)acrylate compounds, deposited on at least a portion of the enamel layer. The enamel layer is obtained by depositing a UV-curable enamel composition. The invention also relates to a method for manufacturing an article comprising a protected enamel coating.

Description

SUBSTRATE COMPRISING A PROTECTED ENAMEL COATING

The invention relates to the protection of substrates, preferably glass, bearing at least one enamel layer and optionally a functional coating. The invention particularly relates to articles comprising such a substrate and a manufacturing process. Where a functional coating is present, the enamel layer is located furthest from the substrate. These substrates are intended to undergo transport, processing, and/or storage.

It is known to supply articles with substrates bearing a decorative enamel coating. Such articles are described, for example, in document EP 0 695 727.

To obtain an enamel coating, an enamel composition is first prepared. In this text, the term "enamel composition" refers to the liquid composition used to deposit a "wet" layer of enamel onto the glass sheet. The term "ink" can also be used for compositions intended for digital printing.

The enamel composition generally comprises glass frit, a pigment, and an organic support medium, the organic support medium including a hardening component. The organic support medium is intended to facilitate the application of the enamel composition to the substrate and its temporary adhesion to it.

After the enamel composition is applied, a drying process is carried out to crosslink and/or dry the organic support medium and obtain a provisional layer sufficiently consistent for the glass substrate to continue its manufacturing cycle. This drying step thus results in the formation of an enamel layer. The enamel layer then comprises a polymer matrix resulting from the drying or crosslinking of the curable composition.

Currently, the layers of enamel obtained are distinguished as follows:
- following a drying step by heat treatment such as infrared (IR) radiation or hot air blowing to evaporate the solvents from the support medium and
- following crosslinking by ultraviolet (UV) radiation in order to polymerize the support medium.

The terms "provisional enamel layer" or "enamel layer" are used according to the invention to describe the dry intermediate state after crosslinking or drying but before firing or vitrification of the enamel.

The enamel layer is subsequently transformed into an enamel coating by a high-temperature heat treatment designed to vitrify the enamel.

The term "enamel coating" refers to the final layer, applied after firing or vitrification of the enamel . Enamel coatings are formed from an enamel composition comprising at least one pigment and at least one glass frit. Enamel coatings preferably do not contain lead oxide.

The enamel coating can be a flat layer applied over a large part of the substrate or to a specific area of the substrate. It can also form specific patterns, possibly with a small surface area.

Preferably, the enamel layer or coating forms patterns, including decorative patterns such as logos. The enamel layer or coating is deposited only on a portion of the substrate. The area covered by the enamel layer or coating preferably represents 2 to 90%, and in particular 3 to 60%, or even 5 to 40%, of the substrate surface.

The enamel layer is preferably applied by screen printing or digital printing. Digital printing techniques include, for example, inkjet printing.

For screen printing, a screen printing screen is placed on the glass sheet, which includes meshes, some of which are blocked, then the enamel composition is deposited on the screen, then a squeegee is applied to force the enamel composition through the screen in the areas where the screen meshes are not blocked, so as to form a wet enamel layer.

Other deposition methods can be used such as digital printing, such as inkjet printing or transfer under the effect of a laser beam, as well as roller and vaporization.

It is also possible to deposit an enamel layer on a functional coating, known to give said substrates optical (mirror or anti-reflective layers), thermal (low-emissive, solar control or anti-solar layers, especially based on silver layers) or electrical (anti-static layers, transparent conductive layers) properties.

The enamel layer, as well as the functional coating if present, exhibits low mechanical resistance, including high scratch resistance and low abrasion resistance.

These coated substrates undergo various processing steps, such as cutting, washing, edge shaping, assembly, and/or heat treatments like quenching, annealing, and/or bending. It is common and practical to perform the assembly and/or various treatments at a location other than where the substrate bearing the functional coating is manufactured. These substrates therefore also undergo storage and transportation.

The mechanical stresses that can cause scratch-type damage are numerous and include, in particular:
- the substrate storage stage after the functional coating has been applied at the production site,
- the stage of moving the substrates, stacked or not, from the place of production to the place of processing,
- the shaping and storage stage at the processing site,
- the washing stage in a wet environment carried out for example before heat treatment or assembly in double glazing (DGU) or triple glazing (TGU),
- the steps of passing over rollers, for example over the rollers of the oven for heat treatment, particularly in the case of so-called bi-functionalized substrates bearing functional coatings on each face.

These mechanical stresses can induce defects other than scratches, such as the partial or total removal of one or more layers of the functional coating.

The visibility of scratches, once created, can increase considerably when the substrate undergoes heat treatment such as quenching. The scratchability of such substrates is detrimental from both an aesthetic and production yield perspective. Indeed, scratches invisible before heat treatment, which only become apparent afterward, can lead to an abnormally high scrap rate. The financial loss is then even greater because the discarded substrate incorporates the cost of the heat treatment.

Any defects or scratches on the coating can impair not only the aesthetics but also the optical and/or energy performance of the substrate, when it has a functional coating. Handling substrates with such coatings requires great care during transport, processing, and/or storage.

Various methods of protecting the surface of substrates coated with functional coatings have already been described. EP-A-1 610 940 and US 5,866,199 describe the application of peelable adhesive polymer films. WO 01/02496 describes a coating intended to temporarily protect a substrate using aqueous polymer solutions. These protective coatings are removed by aqueous washing.

Document WO2015/019022 describes the temporary protection of substrates coated with a functional coating by depositing a layer primarily composed of organic matter. A liquid composition is applied and then cured either by drying, UV curing, or electron beam curing. The temporary protective layer is then removed during the thermal quenching step of the coated substrate.

For enamel coatings, document WO 2012/004337 describes the protection of the surface of an enamel-based coating by a wax layer, present on the enamel layer in the form of a film. The removal of this wax layer is a drawback of this method.

Document WO 2011/051459 describes a reinforced enamel layer with a high organic content. This protection does not appear to be sufficient. At greater thicknesses, delamination problems could occur, particularly after immersion in water, for example during a washing machine cycle, or post-firing defects could develop.

Document WO 2007/104752 also concerns the protection of enamel layers. It mentions the application of a UV- or IR-curable resin (20 to 150 µm thick in the liquid state). The enamel layer preferably contains an IR-curable organic medium (see [0017]). During hardening, the enamel layer vitrifies and the protective layer is partially or completely destroyed (see [0033]). The examples all use an IR-curable enamel layer dried at 150 or 220°C.

The applicant discovered that certain UV-cured organic temporary protective coatings did not effectively protect IR-cured enamel layers. In some cases, there appears to be an incompatibility between the protective coatings and the enamel layer, causing instabilities on the enamel surface. Specifically, the enamel may appear rough when a smooth surface is desired. Finally, when the enamel layer is patterned, the shape of the patterns may also be altered.

Therefore, there is a need for effective temporary protection of substrates coated with an enamel layer, and possibly a functional coating, during manufacturing, processing, transport, and/or storage. This temporary protection must be sufficiently durable to safeguard the substrate surface against physical alterations, corrosion in humid environments, and during washing. Crucially, however, it is essential that the temporary enamel layer itself is not damaged by the temporary protective coating.

The invention relates to an article comprising a substrate having two principal faces defining two principal surfaces separated by edges, said substrate comprising:
- a layer of enamel deposited on at least part of a main surface and
- a temporary protective layer applied to at least part of the enamel layer,
characterized in that:
- the enamel layer is made using a UV-curable enamel composition;
- the temporary protective layer comprises a polymeric matrix obtained from a liquid composition comprising (meth)acrylate compounds.

The invention has shown good compatibility between the enamel layer and the temporary protective layer and good resistance to mechanical stresses, such as scratches.

Preferably, the substrate including the enamel layer and the temporary protective layer has not undergone heat treatment at a temperature exceeding 400 °C.

The temporary protective layer may have the following characteristics, alone or in combination:
- it is insoluble in water, and/or
- it has a thickness of at least 1 micrometer, or between 1 and 50 µm, preferably between 6 and 25 µm, and/or
- it is obtained from a polymerizable liquid composition, and/or
- the polymerizable liquid composition includes (meth)acrylate compounds, and/or
- the polymer matrix is obtained by UV polymerization, and/or
- it is hardened by UV irradiation, and/or
- the (meth)acrylate compounds that have reacted with each other represent at least 90% by mass of the mass of the temporary protective layer, and/or
- the polymerizable liquid composition comprises less than 20% by mass of solvent relative to the total mass of the polymerizable liquid composition and/or
- the polymerizable liquid composition has a viscosity between 0.05 and 5 Pa.s, preferably between 0.5 and 2 Pa.s.

According to the invention, the temporary protective layer is insoluble in water. This means that the temporary protective layer is not washed away in water, particularly through dissolution, swelling, or peeling. The temporary protective layer therefore provides effective protection during the washing stage and against wet corrosion.

The enamel layer may exhibit the following characteristics alone or in combination:
- it comprises glass frit; a pigment; and the polymer matrix, and/or
- the polymer matrix obtained by UV irradiation, and/or
- it is obtained by hardening an enamel composition.

Glass frit is preferably based on bismuth and/or zinc borosilicate.

The pigments preferably comprise one or more oxides chosen from among chromium, copper, iron, manganese, cobalt, titanium, and nickel oxides. For example, copper and/or iron chromates may be used. The enamel layer can be of various colors, depending on the desired decoration: black, white, red, blue, green, etc.

According to the invention, a polymer matrix obtained by UV irradiation means that the polymer matrix is hardened or crosslinked by UV irradiation.

The enamel composition may exhibit the following characteristics alone or in combination:
- it comprises glass frit; a pigment; and an organic support medium, and/or
- the organic support medium comprises a UV-curable polymerizable composition and possibly solvents, and/or
- the polymer matrix can be obtained from a polymerizable composition comprising (meth)acrylate compounds, and/or
- the polymerizable composition may include photoinitiators, and/or
- the enamel layer has, at the time of deposition, a thickness of between 5 and 100 µm, preferably between 10 and 50 µm.

The polymerizable liquid composition of the temporary protective layer and the polymerizable composition of the support medium may be of the same nature. Preferably, both compositions are cured by UV irradiation.

The enamel layer can have, at the time of deposition, a thickness of between 5 and 150 µm, preferably between 10 and 120 µm.

The temporary protective layer can have a thickness of between 1 and 50 µm, preferably between 6 and 25 µm. Since this layer preferably contains little or no solvent, the thickness ranges at the time of deposition also correspond to the thickness ranges obtained after drying.

The polymerizable liquid composition preferably has a viscosity between 0.05 and 5 Pa.s, preferably between 0.5 and 2 Pa.s.

In some embodiments, the substrate also includes a functional coating. This functional coating is preferably located between the substrate and the enamel layer. This functional coating is the least distant from the substrate.

The enamel layer can be in direct contact with the substrate or separated from the substrate by the functional coating.

This functional coating can reflect infrared radiation. The functional coating may consist of a silver-based metallic functional layer or a conductive oxide layer.

The functional coating may comprise a stack of thin films successively comprising, from the substrate, an alternation of n silver-based functional metal layers and (n+1) dielectric coatings, each dielectric coating comprising at least one dielectric layer, such that each functional metal layer is arranged between two dielectric coatings.

The invention also relates to a method for manufacturing an article comprising a substrate having two principal faces defining two principal surfaces separated by edges, the method comprising the following steps:
- depositing a UV-curable enamel composition on at least part of the substrate;
- crosslinking of the enamel composition under UV irradiation to form an enamel layer;
- preparation of a polymerizable liquid composition comprising (meth)acrylate compounds,
- application of the polymerizable liquid composition to at least part of the enamel layer,
- crosslinking of the polymerizable liquid composition so as to form a temporary protective layer comprising a polymer matrix preferably having a thickness of at least 1 micrometer.

The cross-linking of the liquid composition comprising (meth)acrylate compounds can be carried out by UV irradiation.

Preferably, the polymerizable liquid composition is a liquid composition comprising (meth)acrylate compounds selected from monomers, oligomers, prepolymers or polymers comprising at least one (meth)acrylate function.

According to one embodiment, the process includes, prior to the deposition of the enamel composition, a step of deposition of a functional coating comprising a functional layer, generally by cathodic sputtering assisted by a magnetic field.

The item can then be transported and stored without damage.

The process may also include a high-temperature heat treatment step such as quenching, annealing, and/or doming, particularly at temperatures exceeding 200°C, 300°C, or 400°C. This allows, in a single step, the removal of the temporary protective layer and the vitrification of the enamel layer to form the enamel coating. This step may be carried out well after the article has undergone the previously described steps.

The process comprises a single step of heat treatment and deprotection of the article, including the removal of the temporary protective layer by heat treatment at a temperature above 200°C, preferably above 400°C, sufficient to vitrify the temporary enamel layer to form the enamel coating. This step can also be used to temper the article.

The process generally includes a cutting stage, prior to the heat treatment stage.

Advantageously, the enamel composition is applied by screen printing.

The preferred embodiments apply equally to the different objects of the invention, the substrate and the manufacturing process.

Preferably, the crosslinking of the polymerizable liquid composition comprising (meth)acrylate compounds is carried out by UV irradiation, and is carried out for a duration of between 5 and 20 sec, preferably between 8 and 12 sec.

The temporary protective layer according to the invention can be completely removed during a thermal decomposition treatment without affecting the aesthetic properties imparted to the substrate by the decorative coating. These advantageous properties are obtained even when the substrate has a functional coating deposited by magnetron sputtering.

The temporary protective layer according to the invention is intended to be applied preferably at the end of the manufacturing line for substrates bearing enamel coatings. The deposition step can be easily integrated into the manufacturing process of the coated substrate.

The application of a temporary protective layer obtained from a liquid composition that is essentially solvent-free and preferably cured by UV irradiation. In other embodiments, the protective layer can be cured by IR curing or by electron beam curing. The choice of a solvent-free technology considerably simplifies the industrial implementation of a process that includes a step of applying such a layer. The absence of solvents eliminates the need for a drying, recovery, or treatment system for solvent vapors that must not be released into the atmosphere. Modifications may be limited to adding a deposition device at the end of the line, for example, a roller coater, and a curing device such as a UV lamp.

Thanks to the judicious selection of (meth)acrylate compounds, the liquid composition exhibits a viscosity suitable for easily obtaining a temporary protective layer with a thickness of 1 µm or greater, and sufficient reactivity for near-instantaneous crosslinking throughout its entire thickness. The chemical nature, degree of crosslinking, density, and thickness of the temporary protective layer all contribute to achieving effective protection against abrasion, scratching, and corrosion. These protective properties are obtained for thicknesses less than 50 micrometers.

Finally, the absence of solvents, combined with near-instantaneous curing (for example, by UV irradiation), makes it possible to obtain protected substrates without impacting production rates. Advantageously, the coating speeds are compatible with the deposition rates of the functional coatings, allowing for the continuous production of substrates bearing a functional coating and a temporary protective layer according to the invention. For example, the application speeds of the temporary protective layer, including, for example, coating and curing, can range from 1 to 90 m/min on a substrate with a width of 1 m to 3.3 m.

Although the invention is particularly suitable for the protection of substrates bearing enamel layers, the solution of the invention also applies to substrates comprising a first functional coating and a second enamel layer.

The functional coating comprises at least one functional layer. Preferably, this functional layer is capable of acting on solar radiation and/or long-wavelength infrared radiation. Examples of such functional layers include metallic functional layers based on silver or silver-containing metallic alloys.

The substrate may include a functional coating comprising a stack of thin films successively comprising, from the substrate, an alternation of n functional metallic layers, in particular functional layers based on silver or silver-containing metallic alloys, and (n+1) anti-reflective coatings, each anti-reflective coating comprising at least one dielectric layer, such that each functional metallic layer is disposed between two anti-reflective coatings.

The thickness of the functional coating is:
- greater than 100 nm, preferably greater than 150 nm,
- less than 300 nm, preferably less than 250 nm.

The functional coating can be deposited by any known means such as magnetically assisted sputtering, thermal evaporation, CVD or PECVD, pyrolysis, chemical deposition, sol-gel deposition or wet deposition of inorganic layers.

The functional coating is preferably deposited by magnetic field-assisted sputtering. According to this advantageous embodiment, all layers of the functional coating are deposited by magnetic field-assisted sputtering.

The enamel layer is preferably deposited by screen printing. To do this, a screen printing screen is placed on the sheet of glass, which includes meshes, some of which are blocked, then the enamel composition is deposited on the screen, then a squeegee is applied to force the enamel composition through the screen in the areas where the screen meshes are not blocked, so as to form a wet enamel layer.

Other deposition techniques can be used, such as digital printing like inkjet printing or laser transfer. Inkjet printing is preferably carried out using a print head whose movement (in particular, its position and speed) is controlled by a computer, or using a series of fixed print heads past which the glass moves at a controlled speed. To achieve this, the print head(s) include nozzles through which droplets of ink are projected locally onto the glass sheet. This technique is sometimes called "drop on demand" (DOD).

Advantageously, the glass frit and pigments exhibit a particle size distribution by volume such that the D90 is at most 2 µm in the enamel composition. The D90 is determined, for example, by laser granulometry. In the final enamel coating, the D90 is generally <15 µm.

The temporary protective layer comprises a polymer matrix. The polymer matrix is organic in nature. The temporary protective layer is obtained from a polymerizable liquid composition. The polymerizable composition comprises at least some polymerizable organic compounds. The polymerizable organic compounds are preferably (meth)acrylate compounds selected from monomers, oligomers, prepolymers, or polymers comprising at least one (meth)acrylate functional group.

The (meth)acrylate compounds that reacted together represent at least 90% by mass of the mass of the temporary protective layer.

(Meth)acrylate refers to acrylate or methacrylate. "Meth)acrylate compounds" are defined as esters of acrylic or methacrylic acid containing at least one acroyl (CH2=CH-CO-) or methacroyl (CH2=C(CH3)-CO-) group. These esters can be monomers, oligomers, prepolymers, or polymers. When subjected to polymerization conditions, these (meth)acrylate compounds form a polymer network with a solid structure.

The (meth)acrylate compounds used according to the invention can be selected from monofunctional and polyfunctional (meth)acrylates such as mono-, di-, tri-, and polyfunctional (meth)acrylates. Examples of such monomers are:
- 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,
- 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,
- trifunctional (meth)acrylates such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tripropylene glycol triacrylate,
- (meth)acrylates of superior functionality such as pentaerythritol tetra(meth)acrylate, ditrimethylpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate or hexa(meth)acrylate.

According to an advantageous embodiment, the temporary protective layer does not include mineral fillers such as fillers or pigments. Nor does the temporary protective layer include additives that cannot be removed during heat treatment, such as organic compounds containing silicon of the siloxane type.

The temporary protective layer can have a weight between 5 and 50 g/ ^m² , preferably between 10 and 30 g/ ^m² .

According to advantageous embodiments of the invention, the liquid composition has the following characteristics:
- the liquid composition comprises less than 20% by mass of solvent relative to the total mass of the liquid composition,
- the liquid composition comprises less than 10% by mass of solvent relative to the total mass of the liquid composition,
- The liquid composition is solvent-free.
- The liquid composition has a viscosity measured at 25 °C:
- of at least 0.05 Pa.s, of at least 0.08 Pa.s, of at least 0.1 Pa.s or 0.50 Pa.s,
- at most 5 Pa.s, at most 2 Pa.s,
- between 0.05 and 5 Pa.s;
- the liquid composition comprises at least one polymerization initiator, preferably a photoinitiator, preferably a UV photoinitiator,
- the polymerization initiator represents 0.1 to 20%, or 1 to 15%, preferably 5 to 15% and better 8 to 12% by mass of the total mass of (meth)acrylate compounds,
-the liquid composition further comprises at least one additive selected from plasticizers, absorbers, separating agents, heat and/or light stabilizers, thickening agents or surface modifiers,
- the sum of all additives is between 0 and 5% by mass of the mass of the liquid composition,
- (meth)acrylate compounds selected from the esters of acrylic or methacrylic acid having at least two acroyl (CH2=CH-CO-) or methacroyl (CH2=C(CH3)-CO-) functions,
- the liquid composition comprises, by mass relative to the total mass of (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 selected from the esters of acrylic or methacrylic acid having at least two acroyl (CH2=CH-CO-) or methacroyl (CH2=C(CH3)-CO-) functions,
- The liquid composition includes:
- at least one aliphatic urethane-acrylic oligomer,
- at least one (meth)acrylate monomer chosen from among the mono, bi, tri-functional (meth)acrylate monomers,
- at least one polymerization initiator, preferably UV,
- The liquid composition includes:
-at least one aliphatic urethane-acrylic oligomer,
-at least one difunctional (meth)acrylate monomer,
-at least one trifunctional (meth)acrylate monomer,
-at least one polymerization initiator, preferably a photoinitiator,
- the liquid composition comprises, by mass relative to the total mass, (meth)acrylate compounds:
-30 to 80% by mass of at least one aliphatic urethane-acrylic oligomer,
-20 to 70% by mass of at least one (meth)acrylate monomer chosen from a mono, bi, tri functional (meth)acrylate.

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

The liquid composition can be applied at ambient temperature by any known method, including roller coating, spraying, dipping, curtain coating, or gun spraying. Roller coating is the preferred method of application. The deposition rate of the liquid composition can range from 1 to 90 m/min.

The temporary protective layer can be hardened:
- by drying at a temperature below 200°C for a duration ranging, for example, from 10 s to 180 s,
- by UV cross-linking (different wavelengths), preferably in open air and at room temperature or
- by electron beam.

The temporary protective layer is preferably hardened by UV cross-linking.

The liquid composition also includes a polymerization initiator, the nature of which depends on the type of curing chosen. For example, in the case of thermal curing, benzoyl peroxide-type initiators are used. In the case of UV curing, photoinitiators are used.

The substrate to be protected must withstand heat treatment above 200°C, preferably above 400°C. The invention therefore relates to any substrate made of materials resistant to these temperatures without significant alteration. Examples of suitable substrates include glass, glass-ceramic, ceramic, steel, and metal substrates with a melting point above 250°C. The substrate is preferably a glass substrate.

Advantageously, the substrate bearing the temporary protective layer has not undergone heat treatment of the quenching, annealing and/or bending type, i.e. heat treatment at a temperature above 200 °C.

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

According to one embodiment of the invention, the temporary protective layer can be used to protect the enamel layer during a step involving the deposition of another coating on a different side of the substrate not bearing the enamel layer. It is known that, in the production of dual-functionalized substrates with a coating or layer on each main side, contact between the first-deposited coating/layer and the rollers of the deposition device during the second pass, which deposits the second coating, causes damaging alterations to the quality of the first coating/layer (contamination, scratches). These alterations become visible after the deposition of the second coating and, if necessary, hardening. The invention addresses this problem by protecting the first coating/layer with a protective layer designed to disappear during the hardening or curing of the dual-functionalized substrate.

In addition to being deposited on one or both of the substrate's main surfaces, the temporary protective layer can be deposited on at least one edge of the substrate, and/or on each of the substrate's edges. When the temporary protective layer is deposited on each of the substrate's main surfaces and on each of the substrate's edges, chemical and/or mechanical protection is then provided over the entire surface of the substrate.

The temporary protective layer can be deposited on a glass substrate before or after a cutting step, i.e. on a glass substrate at the final size or close to the final size (primitive).

This temporary protective layer is removed by high-temperature heat treatment. The heat treatment temperature is above 200 °C, 300 °C, or 400 °C. Heat treatments are chosen from among annealing, for example by flash annealing such as laser or flame annealing, quenching, and/or bending.

The substrate protection process also includes a step of removing the temporary protective layer by heat treatment. Heat treatments are selected from annealing, for example by flash annealing such as laser or flame annealing, quenching, and/or bending. The heat treatment temperature is above 200 °C, above 300 °C, or above 400 °C.

The heat treatment required to remove the protective layer may involve annealing in a static or dynamic furnace. The heat treatment may then aim to improve the crystallization of one or more layers within the stack to be protected.

The temporary protective layer is formed after the step of depositing the provisional enamel layer.

The device for depositing a liquid composition, allowing for the application of said liquid composition in a layer, is preferably a roller coating device. This device may include an application roller and a counter-roller. The liquid composition can then be pumped into the space defined between the two rollers, which constitutes a storage means, and applied by driving the rollers.

Preferably, the crosslinking device is a UV lamp.

The glass substrate protected according to the invention can be stacked without cross-contamination or the appearance of mechanical scratches, immediately after the enamel layer has been deposited.

The protected glass substrate according to the invention advantageously meets the following criteria:
- mechanical protection against scratching, resulting for example in a resistance to the Erichsen point test (EST) of at least 3N,
- protection against the mechanical stresses of the transformation process, resulting in increased resistance of the functional layer or coating located beneath the protective layer to different storage methods, washing machine brushes, shaping and cutting,
- protection against wet corrosion, in particular the corrosion mechanism of silver layers subjected to condensation of a water film during storage or transport,
- resistance of the protective layer during tempering for a sufficient time to ensure that the glass remains highly emissive for a period allowing for significant energy savings,
- Excellent adhesion of the protective layer to enamel layers and coatings functional to withstand all transformation stages before hardening without delamination.
- Removal of the temporary protective layer without leaving mineralized residues in case of quenching or bulging regardless of the type of heating (radiative/convective).

The item can be a quarter window, a rear window or a side window of a motor vehicle.

EXAMPLES I. Materials used 1. Substrates

The substrates used are flat glass substrates approximately 6 mm thick obtained by a flotation process ("float") which consists of pouring molten glass onto a tin bath.

2. Substrate coated with a layer of enamel Example 1 (comparative)

An IR-curable enamel composition (trademark 144011-black, from Vibrantz) is deposited onto the substrate in a pattern of 6 mm dots spaced 50 mm apart. The deposit is made by screen printing using a "77T" type screen printing screen to obtain dots 25 µm thick (measured wet).

The hardening stage is carried out by IR drying at 160°C for 180 seconds in order to form an enamel layer.

Example 2 (according to the invention)

A light gray UV-curable enamel composition is deposited in the same pattern using the same screen-printing method as in Example 1. The deposited dots have a thickness of 25 µm (measured wet). The enamel composition comprises a glass frit, pigments, and a support medium including a UV-curable polymerizable composition as described, for example, in patent application WO 2023/068923.

The hardening stage is carried out by UV radiation, for 10 seconds to form an enamel layer.

3. Substrate coated with a layer of enamel and a temporary protective layer

A polymerizable liquid composition was prepared with a mixture of oligomers and monomers comprising at least one acrylate function, marketed by the company Sartomer:

CN9276: tetrafunctional aliphatic urethane-acrylate oligomer,

SR351: trimethylolpropane triacrylate, tri-functional acrylate monomer,

SR833S: tricyclodecane dimethanol diacrylate, difunctional acrylate monomer.

The presence of the urethane-acrylate oligomer allows the hardness and flexibility properties of the temporary protective layer to be modulated.

A polymerization initiator is added. It can be chosen from among the photoinitiators marketed by BASF under the name Irgacure® such as Irgacure 500 or Irgacure® 184.

The liquid composition includes the following acrylate compounds:
- 60 parts by mass of acrylate oligomer,
- 20 parts by mass of difunctional acrylate and
- 20 parts by mass of tri-functional acrylate.
5 to 10 parts by mass of a UV initiator are added for 100 parts by mass of acrylate compounds.
The viscosity of the composition, measured at 25°C, is 1.08 Pa.s.

The liquid composition is applied to glass substrates previously coated with enamel layers (example 1 and example 2). The liquid composition is applied by roller coating to form a layer 13 µm thick. This layer is then cured by UV radiation until completely dry and hard.

This forms two protected substrates called:
- Example 1 protected and
- Example 2 protected.

II. Compatibility

There FIG. 1 represents substrates coated with a temporary enamel layer and a protective layer according to example 1 on the left (Protected Example 1) and according to example 2 on the right (Protected Example 2).
For the protected example 1, defects appear quickly. The enamel spots become irregular. The surface of the enamel layer is rough.
For example 2, the protected enamel dots are perfectly clear. The surface of the enamel layer is completely smooth.
The inventors therefore observed that the temporary protective layer is not compatible with an IR-curable type enamel layer, whereas it is fully compatible with a UV-curable type enamel layer.

III. Evaluation of mechanical properties

These tests were carried out on:
- Example 2: a substrate comprising the enamel layer according to example 2, UV crosslinked but without a protective layer;

- Example 2 protected: a protected substrate comprising the enamel layer according to Example 2 cured with UV, and a temporary protective layer;
- a reference example (Ref.): a substrate with a temporary protective layer as described above.

The substrates are subjected to an Erichsen test which consists of reporting the value of the force required, in Newtons, to make a scratch in the layers (Van Laar point, tungsten carbide ball diameter 0.75 mm) according to the ISO 1518 standard.

The following evaluation indicators were used, averaging over 3 samples:
- "NOK": clearly visible scratches
- “+/-”: slightly visible scratches on the edge of the enamel dots,
- "OK": no visible scratches Erichsen test 1N 2N 3N 4N Ref OK OK OK NOK Example 2 without protective layer OK NOK NOK NOK Ex 2 with protective layer OK OK +/- NOK

There FIG. 2 represents two photographs of the two different spots in example 2 after 2N scratches. As shown in the FIG. 2 On the substrate coated according to example 2 without a protective layer, scratches appear. These scratches are irreversible. However, on the same substrate with a protective layer (not shown), no scratches appear.

There FIG. 3 represents three photographs of the same pad from Example 2, protected after scratching at 3N. The first photograph (left) is taken immediately after generating the scratch (left figure). The middle photograph is taken 2 minutes after the test. The third photograph (right) is taken 1 day after the test. Slight scratches appear on the enamel pads immediately after the test ( FIG. 3 (left). However, 2 minutes after the test, the scratches diminish ( FIG. 3 (middle) and 1 day after the test the scratches disappeared ( FIG. 3 (right). Scratches are absorbed thanks to the protective layer.

IV. Evaluation of properties after quenching

The samples according to example 1, protected example 1, example 2, and protected example 2 were subjected to a quenching heat treatment (220 seconds at 690°C). The temporary protective layer was completely removed, and the enamel layers were thus transformed into vitreous enamel coatings.

Figures 4 and 5 show the sample from Example 1 on the left and according to protected Example 1 on the right.
The sample in Example 1 is free of defects, but the protected sample in Example 1 has an uneven enamel coating. The enamel coating does not adhere properly to the substrate.
It was therefore observed that the temporary protective layer degraded the enamel layer according to example 1. One hypothesis would be that the heat treatment resulted in the combustion of the protective layer which penetrated into the enamel layer, causing deterioration of the latter.
It appears that the temporary protective layer does not effectively protect the enamel layer in example 1.

THE FIG. 6 and 7 show the sample from Example 2 on the left and according to the protected Example 2 on the right.
Unlike the coating in Example 1, the coating in Example 2 is free of defects. The substrate on the right, which had received the temporary protective layer, is exactly as clean as the substrate in Example 1 without a temporary protective layer. After tempering, the enamel coating adheres perfectly to the substrate.
It appears that the temporary protective layer effectively protects the enamel layer in example 2.

Claims (18)

An article comprising a substrate having two principal faces defining two principal surfaces separated by edges, said substrate comprising:
- a layer of enamel deposited on at least part of a main surface and
- a temporary protective layer applied to at least part of the enamel layer,
characterized in that:
- the enamel layer comprises a polymeric matrix obtained by UV irradiation;
- the temporary protective layer comprises a polymeric matrix obtained from a polymerizable liquid composition comprising (meth)acrylate compounds. Article according to the preceding claim, characterized in that the substrate comprising the enamel layer and the temporary protective layer has not undergone heat treatment at a temperature exceeding 400 °C. Article according to any one of the preceding claims, characterized in that the temporary protective layer is insoluble in water. Article according to any one of the preceding claims, characterized in that the temporary protective layer is hardened by UV irradiation. Article according to any one of the preceding claims, characterized in that the temporary protective layer has a thickness between 1 and 50 µm, preferably between 6 and 25 µm. Article according to any one of the preceding claims, characterized in that the (meth)acrylate compounds having reacted between themselves represent at least 90% by mass of the mass of the temporary protective layer. Article according to any one of the preceding claims, characterized in that the polymerizable liquid composition comprises less than 20% by mass of solvent relative to the total mass of the polymerizable liquid composition. Article according to any one of the preceding claims, characterized in that the polymerizable liquid composition has a viscosity between 0.05 and 5 Pa.s, preferably between 0.5 and 2 Pa.s. Article according to any one of the preceding claims characterized in that the enamel layer comprises glass frit, pigment and polymer matrix. Article according to any one of the preceding claims characterized in that the enamel layer has, at the time of deposition, a thickness of between 5 and 100 µm, preferably between 10 and 50 µm. Article according to any one of the preceding claims, characterized in that the substrate further comprises a functional coating, preferably located between the substrate and the enamel layer. Article according to the preceding claim, characterized in that the functional coating comprises a silver-based metallic functional layer. Article according to claim 11 or 12, characterized in that the functional coating comprises a stack of thin films comprising successively from the substrate an alternation of n silver-based functional metal layers and (n+1) anti-reflective coatings, each dielectric coating comprising at least one dielectric layer, such that each functional metal layer is arranged between two dielectric coatings. A method for manufacturing an article comprising a substrate having two principal faces defining two principal surfaces separated by edges, the method comprising the following steps:
- deposition of a UV-curable enamel composition on at least part of the substrate;
- crosslinking of the enamel composition under UV irradiation to form an enamel layer;
- preparation of a polymerizable liquid composition comprising (meth)acrylate compounds,
- application of the polymerizable liquid composition to at least a portion of the enamel layer to a thickness of at least 1 micrometer,
- crosslinking of the polymerizable liquid composition so as to form a temporary protective layer comprising a polymer matrix preferably having a thickness of at least 1 micrometer. Manufacturing process according to the preceding claim, characterized in that it comprises prior to the deposition of the enamel composition, a step of deposition of a functional layer, by cathodic sputtering assisted by a magnetic field. A manufacturing process according to any one of claims 14 and 15, characterized in that it further comprises a high-temperature heat treatment step of the quenching, annealing and/or bending type, in particular at a temperature above 200 °C, above 300 °C, or above 400 °C, enabling, in a single step, the removal of said temporary protective layer and the vitrification of the enamel layer to form the enamel coating. Manufacturing process according to any one of claims 14 to 16, characterized in that the deposition of the enamel composition is carried out by screen printing. A manufacturing process according to any one of claims 14 to 17, characterized in that the crosslinking of the liquid composition comprising (meth)acrylate compounds is carried out by UV irradiation.