Process for obtaining curved glazing comprising a layer of enamel

Abstract

The subject of the invention is a method for obtaining curved glazing comprising a layer of enamel on the outer face of the glazing, comprising a step of depositing, on a part of a face of a glass sheet, a layer of enamel comprising refractory particles or topped with a layer comprising refractory particles or capable of forming refractory particles during bending of the glass, then a step of bending said glass sheet, during which the glass sheet is conveyed on rollers and said layer of enamel is in contact with said rollers.

Description

Title of the invention: Method for obtaining curved glazing comprising a layer of enamel

[0001] The invention relates to the field of glazing for motor vehicles comprising a sheet of glass. It relates more particularly to curved glazing such as quarter windows, rear windows or side windows.

[0002] In an effort to differentiate vehicles through their design, car manufacturers are looking for original decorations, particularly decorations that are visible from the exterior of the vehicle. Decorations that create a smooth transition zone between the bodywork and the viewport are, for example, sought.

[0003] The aim of the invention is to propose a method for obtaining motor vehicle glazing having an attractive decoration, in particular a decoration visible only from the outside of the vehicle.

[0004] To this end, the invention relates to a method for obtaining a curved glazing comprising a layer of enamel on the outer face of the glazing, comprising a step of depositing, on a part of a face of a glass sheet, a layer of enamel comprising refractory particles or topped with a layer comprising refractory particles or capable of forming refractory particles during bending of the glass, then a step of bending said glass sheet, during which the glass sheet is conveyed on rollers and said layer of enamel is in contact with said rollers.

[0005] Another object of the invention is a curved glazing comprising a layer of enamel on the outer face of the glazing, obtained (or simply capable of being obtained) by this method, said layer of enamel comprising refractory particles or being topped with a layer comprising refractory particles.

[0006] The glazing according to the invention is curved, so as to match the curvature of the vehicle. A distinction is thus made between the inner face of the glazing, intended to be located on the inner side of the vehicle, which is the concave face, and the outer face of the glazing, intended to be located on the outer side of the vehicle, which is the convex face. In this case, the enamel layer is deposited according to the invention on the outer face, also called "face 1" in the art, that is to say on the convex face, in contact with the exterior of the vehicle.

[0007] The glazing is preferably a quarter window, a rear window or a side window of a motor vehicle.

[0008] The glazing is preferably a monolithic glazing, that is to say it comprises only a single sheet of glass. Alternatively, the glazing may be laminated, the glazing then comprising an additional sheet of glass adhesively bonded to the first glass sheet using a thermoplastic lamination interlayer, in particular based on polyvinyl acetal. Whatever the variant, the enamel layer is always on the outer face of the glazing, i.e. on face 1.

[0009] Particularly when the glazing is a monolithic glazing, the glass sheet is preferably mechanically reinforced, in particular tempered or hardened in the final glazing. The bending step is in this case immediately followed by tempering or hardening of the glass. This step generally involves rapid cooling of the glass, for example by means of air nozzles, in order to create compressive stresses on the surface of the glass.

[0010] The glass sheet is generally flat at the time of deposition of the enamel layer.

[0011] The glass of the glass sheet is typically a soda-lime-silica glass, but other glasses, for example borosilicates or aluminosilicates, may also be used. The glass sheet is preferably obtained by floatation, that is to say by a process consisting of pouring molten glass onto a bath of molten tin.

[0012] The glass sheet is preferably made of tinted glass. It preferably has a light transmission factor of between 2 and 75%, in particular between 5 and 60%, or even greater than 30%, thus ensuring good contrast, and therefore good visibility of the decoration, but only from the outside.

[0013] To do this, the glass preferably comprises the following coloring elements, in the weight contents defined below: Fe2O3 (total iron) from 1.2 to 2.3%, in particular from 1.5 to 2.2%, CoO from 50 to 400 ppm, in particular from 200 to 350 ppm, Se from 0 to 35 ppm, in particular from 10 to 30 ppm. The redox is preferably between 0.1 and 0.4, in particular between 0.2 and 0.3. Redox is understood to mean the weight ratio between the ferrous iron content (expressed as FeO) and the total iron content (expressed as Fe2O3).

[0014] According to another embodiment, the glass preferably comprises as the only coloring element iron oxide in the weight contents defined below: Fe2O3 (total iron) from 0.1 to 1.1%, in particular from 0.5 to 1.0%. The redox is preferably between 0.1 and 0.4.

[0015] In the present text, the light transmission factors are expressed taking into account the illuminant D65 and the CIE-1931 reference observer. The light transmission factor of the glass sheet is obviously measured in the absence of any coating.

[0016] The glass sheet preferably has a thickness in a range from 0.7 to 19 mm, in particular from 1 to 10 mm, particularly from 2 to 6 mm, or even from 2 to 4 mm.

[0017] The lateral dimensions of the glass sheet (and where applicable of the additional glass sheet) must be adapted according to the vehicle in which the glazing is intended to be integrated, more particularly depending on the dimensions of the bodywork bay in which the glazing is intended to be mounted. The sheet preferably has a surface area of ​​at least 0.5 m2, in particular at least 1 m2.

[0018] The enamel layer is deposited on the glass sheet by depositing an enamel composition. In this text, the term "enamel composition" refers to the liquid composition that is used to deposit a (wet) enamel layer. The enamel composition typically comprises a glass frit, pigments, and an organic medium. The term "enamel layer" is used to describe the layer at each stage of the process, both the wet layer (before possible drying or pre-firing) and the final layer (after firing, produced during bending). In the final glazing, the enamel layer comprises pigments bound by a vitreous or vitrocrystalline binder obtained by melting and cooling the glass frit. The organic medium, intended to facilitate the application of the composition to the glass sheet as well as its temporary adhesion to the latter, is removed at the latest during the firing of the enamel.The medium typically includes solvents, diluents, oils and / or resins.

[0019] Given the positioning of the enamel on face 1, the enamel preferably has high durability, including good chemical, scratch and weather resistance.

[0020] The glass frit is preferably based on bismuth and / or zinc borosilicate.

[0021] The pigments preferably comprise one or more oxides chosen from chromium, copper, iron, manganese, cobalt, titanium and nickel oxides. These may be, for example, copper and / or iron chromates. The enamel layer may be of different colors, depending on the desired decoration: black, white, red, blue, green, etc.

[0022] The enamel layer is preferably in direct contact with the glass sheet.

[0023] Preferably, the enamel layer forms patterns, in particular decorative patterns, for example logos. The enamel layer is only applied to a part of the glass sheet. The part coated with the enamel layer preferably represents 2 to 90%, in particular 3 to 60%, or even 5 to 40% of the surface of the glass sheet.

[0024] The thickness of the enamel layer after bending is preferably at least 10 μm, in particular at least 15 μm, in particular between 20 and 50 μm. Such a thickness makes it possible to give three-dimensional effects to the decoration. In particular, the decoration can be perceived by touch, unlike decorations obtained using sol-gel inks, for which the layers are much thinner.

[0025] The visual aspect of the decoration can be adapted by playing on the shape of the patterns and on the surface appearance of the enamel layer. The latter can in particular be rough to create a matte appearance, which will contrast with the shine of the glass.

[0026] The deposition of the enamel layer is preferably carried out by screen printing or by im digital pressure. Digital printing technology is, for example, an inkjet type technique.

[0027] For screen printing deposition, a screen printing screen is placed on the glass sheet, which comprises meshes, some of which are closed, then the enamel composition is deposited on the screen, then a doctor blade is applied in order to force the enamel composition to pass through the screen in the areas where the meshes of the screen are not closed, so as to form a layer of wet enamel.

[0028] According to the invention, the enamel layer comprises refractory particles or is topped with a layer comprising refractory particles or capable of forming refractory particles during bending of the glass. The inventors were able to demonstrate that this arrangement made it possible to avoid any damage to the enamel layer by the rollers, during conveying in the bending furnace.

[0029] The refractory particles preferably have a size of at least 10 pm, in particular at least 20 pm, or even between 30 and 100 pm.

[0030] According to a first embodiment, the enamel layer comprises refractory particles or is topped with a layer comprising refractory particles.

[0031] The term "refractory particles" means particles whose morphology is not significantly affected during bending. These particles must have a melting or softening temperature well above the temperatures experienced during bending, and must also not be dissolved by the frit. The refractory particles are in particular based on metal oxides or metals. The metal oxides are in particular simple oxides, such as for example aluminum, titanium or zirconium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being in particular called "complex inorganic colored pigments" or CICP), in particular black inorganic pigments.

[0032] The refractory particles preferably have a size of at least 10 μm, in particular at least 20 μm, or even at least 30 μm. The size of the refractory particles is preferably at most 100 μm. The size of the particles is in particular determined by laser granulometry.

[0033] The refractory particles are preferably based on zirconia. By zirconia-based particles is meant particles comprising at least 80% by weight, in particular 85% by weight, of zirconium oxide (ZrO2). The zirconia is preferably stabilized, in particular using yttrium. It may also contain sintering aid additives, in particular chosen from Al2O3, TiO2, ZnO, SiO2 and mixtures thereof.

[0034] Preferably, the zirconia-based particles have a chemical composition comprising, in particular consisting of, the following constituents, in the following weight content ranges: - ZrO2: 83-97% - Y2O3: 2-8% - A12O3: 0-3% - black pigments: 0-6%, especially 1-6%.

[0035] The zirconia-based particles are preferably calcined, in particular at a temperature between 1100 and 1500°C.

[0036] The zirconia-based particles preferably have a volume particle size distribution, determined by laser particle size analysis, such that the D10 is at least 20 pm, in particular between 30 and 45 pm, the D50 is between 40 and 52 pm and the D90 is at most 65 pm, in particular between 55 and 65 pm.

[0037] The refractory particles, in particular based on zirconia, are preferably black. In particular, the clarity L* in reflection is preferably less than 3, and even preferably less than 1. The colorimetric coordinates a* and b* are each preferably less than 0.5, in particular 0.1. The colorimetric parameters are determined in accordance with standard ISO 7724 (D65-100). To this end, the particles, in particular based on zirconia, may contain black pigments, typically in a content of between 1 and 6% by weight.

[0038] The average sphericity of the refractory particles, in particular the black refractory particles, is preferably greater than 0.60, in particular 0.70, or even 0.80 and even greater than 0.85. The sphericity of a particle corresponds to the ratio between the smallest Feret diameter and the largest Feret diameter. The average roundness of the refractory particles is preferably greater than 0.6, in particular 0.7 and even 0.8 or 0.9. The average sphericity (or roundness) corresponds to the arithmetic mean of the sphericity (or roundness) of 50 to 200 particles. The roundness corresponds to 4.A / JZ.LP, Lf being the largest Feret diameter and A the projected area of ​​a particle. These different parameters, in particular the Féret diameters, are measured by dynamic image analysis, for example using a Camsizer XT particle analyzer marketed by the Horiba company.

[0039] It has been observed that the use of black particles, and / or spherical particles, without too many roughnesses, makes it possible to improve the aesthetics of the enamel after firing, in particular reducing the blur visible in reflection from face 1 under strong illumination.

[0040] In a first variant, the enamel layer comprises refractory particles. Preferably, the enamel layer comprises refractory particles having a diameter of at least 20 μm in a volume proportion of at least 0.5%. The volume proportion of refractory particles having a size (or diameter) of 20 μm and more is preferably determined by laser granulometry. This proportion is at least 0.5% and preferably at least 1%, in particular at least 2% and even at least less than 3%. Due to their size, large refractory particles create a morphology during bending in which the particles form peaks, with the molten or softened glass frit gathering in the valleys. This size of 20 pm and above is much larger than that of the glass frit and pigments conventionally used. Preferably, the enamel composition contains refractory particles with a diameter of at least 30 pm, in particular at least 40 pm, and even at least 50 pm, in the aforementioned volume proportions.

[0041] In the case of screen printing deposition, and in order to ensure homogeneous deposition of the large refractory particles, the mesh opening of the screen is preferably at least 40 μm, in particular at least 60 μm, or even at least 70 μm. Too small a mesh opening will trap the particles and prevent their homogeneous deposition, while too large an opening leads to an excessively high enamel thickness which risks weakening the glass mechanically. The mesh opening is preferably at most 100 μm, in particular at most 80 μm. In order to allow good screen printing deposition, the enamel composition preferably does not contain particles (refractory or not) with a diameter greater than 80 μm. The presence of such particles can be determined by laser granulometry or using a Hegman gauge.

[0042] In a second variant, the enamel layer is topped with a layer comprising refractory particles. The method therefore comprises a step of depositing, at least on said enamel layer, refractory particles. The quantity of particles is preferably at least 0.1 g / m2, in particular at least 0.5 g / m2. It is advantageously at most 10 g / m2.

[0043] The refractory particles can be deposited alone. Alternatively, the refractory particles can be deposited in a mixture with elements that absorb infrared radiation. These absorbent elements can be of organic or mineral nature. These elements make it possible, during bending or possible pre-firing, to homogenize the temperature experienced in the different zones of the glass sheet and thus avoid the appearance of defects, for example optical distortions, in the zones of the glass located near the enamel. This effect is maximal when the absorbent elements are deposited over the entire surface of the glass sheet or at least in the zones of the first glass sheet near the enamel layer. Alternatively, the absorbent elements can be deposited only on the enamel layer. It has been observed in this case that the enamel has a blacker tint.The absorbent elements can be a resin, which will burn during the bending step or a possible pre-baking step. It can also be absorbent particles, such as pigments or carbon black. Carbon black is particularly preferred due to its ability to be eliminated by combustion during bending or a possible pre-baking.

[0044] The refractory particles can be deposited by any means. According to one embodiment, the particles are deposited by spraying or by dusting, in particular by means of a sieve. This scenario is particularly suitable when the particles are deposited alone. It also makes it possible to deposit large particles. When the refractory particles are deposited in a mixture with absorbent elements such as those mentioned above, the mixture can be deposited by screen printing. In this case, the refractory particles preferably have a size of less than 60 μm so as not to block the openings of the screen printing screen. In a preferred embodiment, the step of depositing the refractory particles comprises the deposition by screen printing of a mixture comprising an organic medium, the refractory particles and possibly absorbent elements, in particular carbon black.

[0045] According to a second embodiment, the enamel layer is topped with a layer capable of forming refractory particles during bending of the glass. This layer may in particular be an enamel layer, the glass frit of which is capable of devitrifying during bending, so as to form crystals. It may in particular be frits based on bismuth borosilicate.

[0046] After deposition, the wet enamel layer is preferably dried in order to remove the solvent, in particular at a temperature ranging from 100 to 200°C.

[0047] The bending step is preferably preceded by a pre-baking step, preferably at a temperature between 500 and 650°C.

[0048] The bending step is preferably carried out in a bending furnace, in particular at a temperature between 550 and 650°C. The glass sheet is conveyed during this step on rollers, with which the enamel layer is in contact. The bending step is preferably carried out in a bending furnace. The bending step comprises a phase of heating the glass sheet and then shaping it. The glass sheet is not necessarily in contact with the rollers throughout the bending step. It may be in contact only during the heating phase.

[0049] The rollers are preferably made of silica. They can be solid or hollow.

[0050] The bending process can be said to be "on-the-go", that is to say that the glass sheet is bent during its conveyance in the bending furnace, while being in contact with rollers. Alternatively, the glass sheet can be bent by pressing, in particular between two dies, lower and upper. In this case, the glass sheet is no longer in contact with the rollers during pressing.

[0051] As indicated previously, the bending step is preferably immediately followed by thermal quenching or controlled cooling.

[0052] The following examples illustrate the invention in a non-limiting manner.

[0053] Sheets of soda-lime-silica glass were coated by screen printing with dif different enamel compositions. To assess possible damage by rollers during bending, the glass sheets were placed in a furnace heated to 640°C for 600 seconds, before moving silica rollers over the surface of the enamel.

[0054] In a comparative example, the enamel composition was a composition marketed by the company Ferro under the reference 14303. After removal from the oven, it was observed that the surface of the enamel had been damaged by rollers.

[0055] In a first example according to the invention, the enamel composition was a composition marketed by the company Ferro under the reference 144100, and the enamel layer was topped with a second enamel layer (1L6026, Ferro) capable of forming refractory particles by devitrification during bending. The assembly underwent pre-firing at 600°C for 120 seconds.

[0056] In a second example according to the invention, the enamel composition was a composition marketed by the company Ferro under the reference 144100 to which black spherical zirconia particles (15% by weight) were added. The enamel layer then underwent pre-firing at 600°C for 120 seconds.

[0057] In a third example according to the invention, the enamel composition was a composition marketed by the company Ferro to which spherical white alumina particles (15% by weight) were added. The enamel layer was then pre-baked at 600°C for 120 seconds.

[0058] In a fourth example according to the invention, the enamel composition was a composition marketed by the company Ferro and the enamel layer was topped with a layer comprising 25% by weight of white spherical alumina particles and 75% by weight of organic medium, deposited by screen printing. The assembly then underwent pre-baking at 600°C for 120 seconds.

[0059] In a fifth example according to the invention, the enamel composition was a composition marketed by the company Ferro under the reference 144100 and the enamel layer was topped with a layer comprising 25% by weight of white spherical alumina particles and 75% by weight of organic medium, deposited by screen printing. The assembly then underwent pre-baking at 600°C for 120 seconds.

[0060] No damage to the enamel layer by the rollers was observed for the examples according to the invention.

Claims

Claims

1. Method for obtaining curved glazing comprising a layer of enamel on the outer face of the glazing, comprising a step of depositing, on a part of a face of a glass sheet, a layer of enamel comprising refractory particles or surmounted by a layer comprising refractory particles or capable of forming refractory particles during bending of the glass, said refractory particles having a size of at least 10 μm, then a step of bending said glass sheet, during which the glass sheet is conveyed on rollers and said layer of enamel is in contact with said rollers.

2. A method according to claim 1, such that the enamel layer forms patterns.

3. Method according to one of the preceding claims, wherein the thickness of the enamel layer after the bending step is at least 10 μm.

4. Method according to one of the preceding claims, in which the deposition of the enamel layer is carried out by screen printing or by digital printing.

5. Method according to one of the preceding claims, in which the enamel layer comprises refractory particles or is topped with a layer comprising refractory particles.

6. Method according to the preceding claim, in which the refractory particles are based on metal oxides or metals.

7. A method according to either of claims 5 or 6, wherein the refractory particles have a size of at least 20 pm.

8. Method according to one of the preceding claims, in which the bending step is immediately followed by thermal quenching.