Method for obtaining curved laminated glazing

Abstract

A method for obtaining curved laminated glazing comprising depositing an enamel composition on a portion of a face of a first glass sheet to form a green enamel layer, then bending said first glass sheet coated with the green enamel layer with a second glass sheet, the green enamel layer facing the second glass sheet. The enamel composition comprises a glass frit capable of melting and adhering to the first glass sheet during the bending step, pigments, an organic medium and ground soda-lime-silica glass particles capable of retaining their shape during the bending step, said particles being such that their largest dimension is less than the thickness of the green enamel layer.

Description

Method for obtaining laminated curved glass

[0001] The invention relates to the field of glazing for transport vehicles, in particular for motor vehicles. It concerns more specifically laminated curved glazing.

[0002] Laminated glass is glazing in which two sheets of glass are bonded together with an adhesive interlayer. This interlayer helps to hold glass fragments together in case of breakage, but also provides other functionalities, particularly in terms of burglary resistance and improved acoustic properties.

[0003] These windows often include coatings of various types, designed to impart different properties.

[0004] Layers of enamel, usually black and opaque, are often applied to part of the glazing, generally as a peripheral band designed to conceal and protect against ultraviolet radiation the polymer seals used to fix and position the glazing to the body frame. Enameled areas also conceal the mounting points for the interior rearview mirror and various connectors and sensors.

[0005] In laminated glass, these enamel layers are generally arranged on surface 2, with surfaces traditionally numbered starting from the surface intended to face the exterior of the vehicle. Surface 2 is therefore in contact with the interlayer. The aesthetic appearance of the enamel layer as seen from the outside of the vehicle is of particular importance to car manufacturers. The enamel is generally obtained by firing a composition containing a glass frit and pigments at temperatures above 500°C. A glass frit consists of fine particles of low-melting-point glass, which, under the effect of a firing heat treatment, softens and adheres to the glass sheet. This forms a mineral layer, generally opaque, with high chemical and mechanical resistance, adhering perfectly to the glass while retaining the pigment particles.The baking stage is usually carried out simultaneously with the curving of the glass sheet.

[0006] In the manufacturing of laminated glass, the two glass sheets are curved together, with the sheet intended for the interior of the vehicle typically placed on top of the other sheet, which carries the enamel coating. The enamel must therefore possess non-stick properties to prevent the two glass sheets from sticking together during the curving process. To achieve this, bismuth-containing enamels are commonly used; these are made from glass frits containing bismuth oxide. The non-stick properties of these enamels are due to the glass frit's ability to devitrify, meaning it forms crystals when heated. However, developing these non-stick properties requires a pre-firing stage of the enamel at temperatures exceeding 300°C, even reaching 500°C, before the curving stage. This stage is costly in terms of both time and energy.

[0007] The invention aims to develop a process for obtaining enamelled, curved and laminated glazing that is less expensive and less energy-intensive, while avoiding the gluing of glass sheets.

[0008] To this end, the invention relates to a method for obtaining laminated curved glass comprising the following steps: a) the deposition of an enamel composition on part of one face of a first sheet of glass to form a raw enamel layer, b) the bending of said first sheet of glass coated with the raw enamel layer with a second sheet of glass, said first and second sheets of glass being arranged during the bending so that the raw enamel layer faces the second sheet of glass, said bending leading to the formation of a baked enamel layer, and c) the lamination of the first and second sheets of glass by means of a lamination interlayer, said method being such that said enamel composition comprises a glass frit capable of melting and adhering to the first sheet of glass during the bending step, pigments,an organic medium and crushed soda-lime-silicon glass particles capable of retaining their shape during the doming stage, said particles being such that their largest dimension is less than the thickness of the raw enamel layer.

[0009] The invention also relates to glazing obtained or capable of being obtained by the invention. Such glazing is a curved laminated glazing comprising a first sheet of glass bonded adhesively to a second sheet of glass, said first sheet of glass being coated on a part of its face facing the second sheet of glass with a layer of baked enamel comprising pigments and particles of ground soda-lime-silicon glass, the largest dimension of which is less than the thickness of the baked enamel layer.

[0010] The term "enamel composition" refers to a fluid or paste-like composition comprising glass frit, pigments, and ground soda-lime-silicon glass particles dispersed or suspended in an organic medium. This medium is removed during the firing of the enamel, specifically during the shaping of the glass sheets. The term "raw enamel layer" refers to the layer obtained by depositing the enamel composition onto the first glass sheet before firing, before and / or after any drying process, which will be described in more detail later in this text. In the raw enamel layer, the glass frit is always in powder form; the cohesion of the layer and its adhesion to the first glass sheet are achieved through the organic medium or a portion thereof. The firing of the enamel takes place during the shaping stage.At the beginning of this step, the first sheet is coated with the raw enamel layer, meaning that the process of the invention does not include a pre-firing step of the enamel layer before the doming step. After doming and thus firing the enamel, a fired enamel layer is obtained, in which the pigments and the ground soda-lime-silicon glass particles are bound by a vitreous or glass-crystalline binder resulting from the melting of the glass frit.

[0011] The inventors were able to demonstrate that the presence of fine particles of ground soda-lime silico-glass in the enamel made it possible to prevent the glass sheets from sticking together, even in the absence of a pre-firing step.

[0012] Step a)

[0013] The first sheet of glass is generally flat when the enamel composition is applied and is subsequently curved. It is therefore curved in the glazing according to the invention. The glass of the first sheet is typically a soda-lime silicate glass, but other glasses, for example borosilicates or aluminosilicates, can also be used. The first sheet of glass is preferably obtained by flotation, that is, by a process consisting of pouring molten glass onto a bath of molten tin.

[0014] The first sheet of glass can be clear or tinted, preferably tinted, for example in green, gray, or blue. To achieve this, the chemical composition of the glass sheet advantageously includes iron oxide, in a weight content ranging from 0.5 to 2.0%. It may also include other coloring agents, such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0015] The first sheet of glass preferably has a thickness in the range of 0.7 to 19 mm, in particular 1 to 10 mm, particularly 2 to 6 mm, or even 2 to 4 mm.

[0016] The lateral dimensions of the first sheet of glass must be adapted according to those of the laminated glass into which it is intended to be integrated. The sheet of glass preferably has a surface area of ​​at least 1 m².

[0017] The first pane of glass may have been pre-coated with a stack of thin films, in particular a stack comprising at least one electrically conductive functional layer. The electrically conductive functional layer is preferably a thin layer of a metal (in particular silver, or even gold or niobium) or a transparent conductive oxide (TCO, for example, indium tin oxide or doped tin or zinc oxide), in order to give the glazing solar control, low-emissivity, and / or electrical conductivity properties, in the latter case particularly for defrosting or demisting the glazing. This stack of thin films may be located on the face where the enamel composition is deposited, or on the opposite face.When the thin-layer stack is positioned on the surface where the enamel composition is deposited, it can be removed chemically or mechanically from the areas where the composition is deposited, or conversely, it can be held in place so that the enamel composition is deposited on top of the thin-layer stack. Depending on the case, the enamel layer (raw and fired) is in direct contact with the first sheet of glass, or in direct contact with a thin-layer stack.

[0018] The enamel composition includes at least one glass frit. It may include only one, or alternatively include several glass frits of different compositions.

[0019] The glass of the glass frit (or, where applicable, one or each) in the enamel composition is preferably a bismuth and / or zinc silicate, borosilicate, or borate. The enamel layer preferably does not contain lead or cadmium oxide. The glass frit (or each glass frit) preferably has a glass transition temperature below 500°C. Low glass transition temperatures allow the frit to soften sufficiently to adhere to the first sheet of glass and bind the pigment and soda-lime-silicon glass particles.

[0020] In one example, the first layer of enamel is based on bismuth silicate, bismuth borosilicate, or bismuth borate. In another example, the first layer of enamel is based on zinc borosilicate.

[0021] Each glass frit in the enamel composition preferably comprises 4-10% by weight of B2O3, 15-40% by weight of SiO2, 40-70% by weight of Bi2O3 and 0-12% by weight of ZnO.

[0022] The pigments preferably comprise one or more oxides selected from among the oxides of chromium, copper, iron, manganese, cobalt and nickel. These may be, for example, copper and / or iron chromates.

[0023] The organic medium is designed to facilitate the application of the composition to the substrate and its temporary adhesion to the substrate. It generally includes solvents, diluents, oils, and / or resins.

[0024] Soda-lime-silicon glass particles are particles of ground glass. They therefore have a morphology characteristic of glass obtained by grinding, with angular and irregular shapes.

[0025] Preferably, the ground glass particles have a volumetric roundness distribution such that the median roundness value is between 0.01 and 0.50, in particular between 0.05 and 0.40. Roundness characterizes the degree of angularity of the particles. Preferably, the ground glass particles also have a volumetric sphericity distribution such that the median sphericity value is at most 0.90, in particular at most 0.85, or even at most 0.80 and at most 0.75. Sphericity characterizes how closely the particle approximates a sphere. The volumetric roundness and sphericity distributions can be determined by dynamic image analysis, for example using a Camsizer X2 (Retsch-Microtrac).

[0026] The ground soda-lime-silicon glass particles are such that their largest dimension is less than the thickness of the raw glaze layer. When the process includes a drying step, the largest particle dimension is preferably less than the thickness of the glaze layer after drying. Preferably, the ratio between the largest dimension of the ground soda-lime-silicon glass particles and the thickness of the raw glaze layer is at most 0.9, in particular at most 0.8, for example between 0.2 and 0.7. The largest particle dimension is also preferably less than the thickness of the fired glaze layer. In cases where the thickness of the glaze layer is not perfectly uniform, the term "thickness" refers to the average thickness. These criteria can be verified by microscopy, in particular by scanning electron microscopy, the largest dimension then corresponding to the maximum Feret diameter.The particles are then perfectly encapsulated in the fired enamel, so that the enamel does not have any roughness that could impair its optical properties and, more generally, its appearance.

[0027] Preferably, the ground soda-lime-silicon glass particles have a particle size distribution by volume such that the D90 is at most 15 µm. The particle size distribution (also called diameters) is preferably determined by laser granulometry. The D90 corresponds to the size such that 90% of the particles by volume are smaller than this size. The D90 is even preferably at most 12 µm. The Dmax (maximum diameter) is preferably less than 20 µm, specifically at most 19 µm, which means in this case that the enamel composition does not include any ground soda-lime-silicon glass particles with a diameter of 20 µm or more.

[0028] The solution proposed by the invention therefore differs from previously proposed solutions in which the non-stick effect is achieved through the use of large refractory particles, larger than the thickness of the enamel layer and thus capable of forming peak-valley morphologies, with the peaks formed by these large particles and the molten frit collecting in the valleys. Such a solution is, for example, described in patent application EP2832704. The invention, on the contrary, uses smaller particles, and it appears that the morphology of the particles prevents sticking despite their small size, perhaps through an effect on the rheology of the enamel during firing.

[0029] Ground soda-lime-silica glass particles can be obtained, in particular, by grinding recycled glass (also called cullet), especially glass from glass manufacturing or processing plants. This can include, in particular, glass recovered during edge-shaping stages.

[0030] The sodium-calcium silico-glass of the particles preferably has a linear thermal expansion coefficient between 20 and 300°C of between 70 and 100.10 -7 / K, particularly between 80 and 95.10 -7 / K.

[0031] The chemical composition of soda-lime-silica glass preferably comprises 55 to 80%, particularly 65 to 75%, by weight of silica (SiO2), 8 to 20%, particularly 10 to 15%, by weight of sodium hydroxide (Na2O), and 3 to 15%, particularly 5 to 12%, by weight of lime (CaO). It may include other constituents, in particular alumina (Al2O3), typically between 0 and 5%, particularly between 0 and 3% by weight, magnesium oxide (MgO), particularly between 0 and 5% by weight, and potassium hydroxide (K2O), particularly between 0 and 5% by weight.

[0032] Soda-lime silicate glass can be clear or tinted. It is advantageously tinted when the enamel layer needs to be black. In this case, the chemical composition of the soda-lime silicate glass advantageously includes 0.5 to 2.0% by weight of iron oxide (expressed as Fe2O3), and possibly other colorants such as chromium oxide, cobalt oxide, and / or selenium.

[0033] The content of ground soda-lime silico-glass particles in the enamel composition is preferably between 1 and 20% by weight, in particular between 5 and 15% by weight.

[0034] The enamel composition is preferably applied by screen printing or digital printing.

[0035] In screen printing, a screen is placed on the glass sheet. This screen has a mesh, some of which is blocked. The enamel composition is then deposited onto the screen, and a squeegee is used to force the enamel composition through the open areas of the screen mesh, thus forming a wet enamel layer. For screen printing, the ground soda-lime-silicon glass particles preferably have a D90 size between 5 and 15 µm, particularly between 8 and 12 µm.

[0036] Examples of digital printing techniques include inkjet printing or laser transfer printing.

[0037] Inkjet printing is preferably carried out using a print head whose movement (in particular its position and speed) is computer-controlled, 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 ink droplets are locally projected onto the glass sheet. This technique is sometimes called "drop on demand" (DOD). Advantageously, the glass frit, pigments, and soda-lime-silica glass particles in this case have a volumetric particle size distribution such that the D90 is at most 2 µm, for example, between 0.5 and 2.0 µm. The D90 is determined, for example, by laser particle size analysis. The ink viscosity is preferably between 1 and 50 mPa·s.

[0038] Digital printing can also be a transfer printing technique, particularly laser transfer. For example, a substrate, often a rotating one, coated with ink is placed next to the sheet of glass, and the print head emits a focused laser beam onto a portion of the substrate, creating a droplet of ink that is deposited onto the sheet of glass.

[0039] In one preferred embodiment, the enamel composition comprises 10-25% by weight of organic medium, 40-65% by weight of glass frit, 10-25% by weight of pigments, and 1-20% by weight of ground soda-lime-silicon glass particles. This embodiment is particularly well-suited for screen printing. In another preferred embodiment, the enamel composition comprises 30-50% by weight of organic medium, 20-40% by weight of glass frit, 10-30% by weight of pigments, and 1-20% by weight of ground soda-lime-silicon glass particles. This embodiment is particularly well-suited for digital printing, especially inkjet printing.

[0040] The thickness of the raw enamel layer (before or after possible drying) is preferably between 15 and 30 µm, especially between 16 and 25 µm.

[0041] Preferably, the raw enamel layer forms a band around the periphery of the first pane of glass. This peripheral band is preferably a self-enclosed band that extends inward from each point on the periphery of the glass pane to a certain width, typically between 1 and 30 cm. This width may vary depending on the area of ​​the glazing. For example, the width may be greater in the lower part of the glazing (in the operating position) than in the lateral sections. As explained previously, the main purpose of this peripheral band is to conceal and / or protect various components, including the glazing mounting joints in the vehicle's body frame and the base of the interior rearview mirror.The peripheral band can provide openings, particularly in the upper part of the glazing (in the position of use), to allow the use of sensors, such as rain sensors, light sensors, cameras or lidars.

[0042] Before the doming stage, the enamel composition deposition stage is preferably followed by a drying stage, typically at a temperature between 100 and 200°C, intended to remove at least some of the solvents from the enamel layer before the doming stage.

[0043] As previously mentioned, the process does not include a pre-firing step between the application of the enamel composition and the bending step. A pre-firing step is defined as a step prior to bending in which the first sheet of glass is heated to a temperature above 400°C, particularly 500°C.

[0044] Step b)

[0045] The curvature is preferably achieved by gravity (the glass deforming under its own weight) or by pressing, at temperatures typically ranging from 550 to 650°C. The two sheets of glass in laminated glazing are curved together, so as to ensure that they have the same curvature.

[0046] During the curving process, the inner pane of glass (intended for the interior of the vehicle) is normally placed above the outer pane of glass. Thus, the first pane of glass is preferably located below the second pane, with the enamel layer positioned between the two panes. In laminated curved glass, the first pane of glass is preferably located on the convex side of the glazing, with its first face facing the lamination interlayer. The enamel layer is then positioned on the second surface of the glazing.

[0047] The two glass sheets can be kept apart by placing an interlayer powder between them, ensuring a space of a few tens of micrometers, typically 20 to 50 µm. The interlayer powder is, for example, based on calcium carbonate and / or magnesium, and aims to reduce the risk of the glass sheets sticking together.

[0048] The fired enamel layer is preferably opaque and black. A black tint preferably corresponds to a lightness on glass-side reflection (L*, illuminant D65, CIE-1964 reference observer) of less than 10, in particular less than 5. As previously stated, the fired enamel layer preferably forms a band around the periphery of the first sheet of glass.

[0049] Step c)

[0050] The lamination process can be carried out by autoclave treatment, for example at temperatures of 110 to 160°C and under a pressure of 10 to 15 bar. Prior to autoclave treatment, the air trapped between the glass sheets and the laminating interlayer can be removed by calendering or vacuum extrusion. The second glass sheet can (preferably) be made of soda-lime glass, or alternatively, borosilicate or aluminosilicate glass. It can be clear or tinted. Its thickness is preferably between 0.5 and 4 mm, particularly between 1 and 3 mm.

[0051] The lamination is normally carried out so that the layer of baked enamel is on the face of the first sheet of glass which is turned towards the second sheet of glass, therefore in contact with the lamination interlayer.

[0052] In one embodiment, the second glass pane carries on the face opposite the face facing the laminating interlayer (preferably face 4, the second glass pane being the inner pane) an additional stack of thin films, in particular a low-emissivity stack, comprising a transparent conductive oxide, in particular indium tin oxide (ITO). In this embodiment, the laminating interlayer and / or the second glass pane is preferably tinted, the glass pane bearing the coatings being able to be clear glass. The resulting glazing is preferably a motor vehicle roof.

[0053] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0054] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0055] The laminate interlayer can advantageously possess sound-absorbing properties to absorb airborne or structure-borne noise. It can, in particular, be composed of three polymer sheets, including two outer sheets of PVB framing an inner polymer sheet, possibly also made of PVB, with a lower hardness than the outer sheets.

[0056] The lamination interlayer can also possess thermal insulation properties, particularly infrared radiation reflection. For this purpose, it can comprise a low-emissivity thin-film coating, for example, a coating including a thin silver layer or a coating alternating dielectric layers with different refractive indices, deposited on an inner PET sheet sandwiched between two outer PVB sheets.

[0057] The thickness of the lamination interlayer is generally in the range of 0.3 to 1.5 mm, particularly 0.5 to 1 mm. The lamination interlayer may be thinner at one edge of the glazing than in the center of the glazing to avoid the formation of a double image when using a head-up display (HUD).

[0058] The glazing obtained is preferably vehicle glazing, in particular a windscreen, roof or canopy of a vehicle, especially a motor vehicle.

[0059] The following examples illustrate the invention in a non-limiting manner.

[0060] In the comparative examples, the enamel composition used was the composition marketed under the reference S2-IR by the Fenzi company, comprising a bismuth and zinc borosilicate glass frit and copper chromate-based pigments. In the examples according to the invention, ground soda-lime silico-glass particles were added to the S2-IR composition, in a weight content of 10%.

[0061] Soda-lime silico-glass particles were obtained by fragmentation into pieces smaller than 5 cm, followed by crushing to obtain particles smaller than 3 mm, then grinding in a ball mill and planetary mill until a D90 of 15 µm was obtained.

[0062] In a first series of tests, the bonding was evaluated. Four 2.1 mm thick sheets of soda-lime-silica glass were screen-printed using the enamel compositions described above. The thickness of the raw enamel layer before drying was 18 µm in the comparative examples and 21 µm in the examples according to the invention. The glass sheets were then dried in a tunnel oven for 2 minutes at 150°C. After drying, the glass sheets were paired with other glass sheets, and the assembly was then curved by gravity collapse using a curving frame. Depending on the test, weights were placed at the corners or magnesium carbonate interlayer powder was placed between the glass sheets.

[0063] In the comparative examples, bonding was observed in all cases. However, in the examples according to the invention, no bonding was observed. Only a slight transfer of enamel to the second sheet of glass was observed when weights were placed at the corners.

[0064] In a second series of tests, the three-point bending strength was evaluated. For this purpose, 30 sheets of 3.85 mm thick soda-lime-silicon glass were screen-printed using the enamel compositions described above. The thickness of the raw enamel layer before drying was 22 µm for all samples. The glass sheets were then dried in a tunnel kiln for 2 minutes at 150°C and subsequently heated to 640°C for 400 seconds. The thickness of the fired enamel was 13 µm in the comparative examples and 14 µm in the examples according to the invention.

[0065] This is a scanning electron microscopy image of a sample according to the invention, after firing. The soda-lime silico-glass particles, recognizable by their irregular and angular shape, are encapsulated in the fired enamel layer.

[0066] Three-point bending tests reveal that the samples according to the invention exhibit improved mechanical resistance, the breaking stress for a 50% probability being 84.0 MPa in the case of the samples according to the invention versus 80.6 MPa in the case of the comparative samples.

Claims

A process for obtaining laminated curved glass comprising the following steps: a) depositing an enamel composition on part of one face of a first sheet of glass to form a raw enamel layer; b) bending said first sheet of glass coated with the raw enamel layer with a second sheet of glass, said first and second sheets of glass being arranged during the bending so that the raw enamel layer faces the second sheet of glass, said bending leading to the formation of a fired enamel layer; and c) laminating the first and second sheets of glass by means of a laminating interlayer, said process being such that the enamel composition comprises a glass frit capable of melting and adhering to the first sheet of glass during the bending step, pigments,an organic medium and crushed soda-lime-silicon glass particles capable of retaining their shape during the doming stage, said particles being such that their largest dimension is less than the thickness of the raw enamel layer. A method according to claim 1, wherein the ground glass particles have a volumetric rounding distribution such that the median rounding value is between 0.01 and 0.

50. A method according to any one of the preceding claims, wherein the ground glass particles have a volumetric sphericity distribution such that the median value of the sphericity is at most 0.90, in particular at most 0.

85. A process according to any one of the preceding claims, wherein the ratio between the largest dimension of the ground soda-lime silico-glass particles and the thickness of the raw enamel layer is at most 0.9, in particular at most 0.

8. A process according to any one of the preceding claims, wherein the ground soda-lime silico-glass particles have a volume particle size distribution such that the D90 is at most 15 µm, in particular at most 12 µm. A process according to any one of the preceding claims, wherein the soda-lime silico-glass of the ground soda-lime silico-glass particles has a linear coefficient of thermal expansion between 20 and 300°C of between 70 and 100.10 -7 / K, particularly between 80 and 95.10 -7 / K. A process according to any one of the preceding claims, wherein the chemical composition of the soda-lime silico-glass comprises 55 to 80% by weight of silica, 8 to 20% by weight of soda and 3 to 15% by weight of lime. A process according to any one of the preceding claims, wherein the content of ground soda-lime silico-glass particles in the enamel composition is between 1 and 20% by weight, in particular between 5 and 15% by weight. A method according to any one of the preceding claims, wherein the enamel composition comprises a glass frit of which the glass is a silicate, a borosilicate or a borate, of bismuth and / or zinc. A method according to any one of the preceding claims, wherein the deposition of the enamel composition is carried out by screen printing or by digital printing. A method according to any one of the preceding claims, wherein the thickness of the raw enamel layer is between 15 and 30 µm. A method according to any one of the preceding claims, wherein, prior to the doming step, the enamel composition deposition step is followed by a drying step. A method according to any one of the preceding claims, wherein the baked enamel layer is opaque and black in color and forms a band around the periphery of the first sheet of glass. Curved laminated glazing comprising a first sheet of glass bonded adhesively to a second sheet of glass, said first sheet of glass being coated on a part of its face facing the second sheet of glass with a layer of baked enamel comprising pigments and particles of ground soda-lime silico-glass, the largest dimension of which is less than the thickness of the layer of baked enamel.

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