Method for obtaining curved laminated glazing

Abstract

The invention relates to a method for obtaining curved laminated glazing involving supplying a first sheet of glass (1) and then applying, to at least part of a first face of said first sheet of glass (1), a first coat of enamel (11), then using digital printing to apply, to just part of said first coat of enamel (11), a second coat of enamel (12) which is not electrically conducting, said second coat of enamel (12) having a different composition from that of the first coat of enamel (11) and containing bismuth, then simultaneously bending the first sheet of glass (1) and an additional sheet of glass, said first face facing toward said additional sheet of glass, then laminating said first sheet of glass (1) with the additional sheet of glass using a lamination interlayer.

Description

Process for obtaining laminated curved glazing

[0001] The invention relates to the field of laminated curved glazing for motor vehicles, for example roofs or windshields.

[0002] Laminated glass is a type of glass in which two sheets of glass are adhesively bonded together using a lamination interlayer. This interlayer not only helps retain shards of glass in the event of breakage, but also provides other features, particularly in terms of burglary resistance and improved acoustic properties.

[0003] Layers of enamel, usually black and opaque, are often applied to part of the glazing, generally in the form of a peripheral strip intended to conceal and protect from ultraviolet radiation the polymer seals used to fix and position the glazing on the bodywork opening. Enameled areas also conceal the fixing areas of the interior rearview mirror and various connectors and sensors.

[0004] In laminated glazing, these enamel layers are generally arranged on side 2, the sides being traditionally numbered starting from the side intended to be positioned on the outside of the vehicle. Side 2 is therefore a side in contact with the lamination interlayer. The aesthetic appearance of the enamel layer seen from the outside of the vehicle is of particular importance for car manufacturers. The enamel is generally obtained by firing above 500°C a composition comprising a glass frit and pigments. A glass frit consists of fine particles of a low-melting 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 firing step is generally carried out simultaneously with the bending of the glass sheet.

[0005] In the context of laminated glazing manufacturing, the two sheets of glass in the glazing are often bent together, with the sheet of glass intended to be positioned inside the vehicle generally being placed on top of the other sheet of glass, which carries the enamel. It is then necessary for the enamel to have non-stick properties to prevent any sticking between the two sheets of glass during bending. To achieve this, enamels containing bismuth are usually used, i.e. obtained from glass frits containing bismuth oxide.

[0006] Despite the choice of this type of enamel, and despite the deposit of an interlayer powder intended to create a (small) distance between the glass sheets, it may happen, depending on the bending process used, the temperature undergone by the glass sheets, or even the pressure applied to the glass sheet bearing the enamel (either because the process provides for the application of pressure, or simply due to the weight of the glass sheet located above), that part of the enamel is transferred from one glass to the other in certain areas of the glazing, leading to aesthetic defects or even, in extreme cases, breakage of the glazing.

[0007] The invention aims to overcome these drawbacks.

[0008] For this purpose, the invention relates to a method for obtaining laminated curved glazing, in particular a windshield or a roof of a motor vehicle, comprising the following steps: - providing a first sheet of glass, then - a step of depositing, on at least a portion of a first face of said first sheet of glass, a first layer of enamel, then - a step of depositing by digital printing, only on a portion of said first layer of enamel, a second layer of enamel which is not electrically conductive, said second layer of enamel having a composition different from that of the first layer of enamel and comprising bismuth, then - a step of simultaneously bending the first sheet of glass and an additional sheet of glass, said first face being turned towards said additional sheet of glass,then - a step of laminating said first glass sheet with the additional glass sheet by means of a laminating interlayer.,

[0009] The invention also relates to a laminated curved glazing, in particular a windshield or a roof of a motor vehicle, obtained or capable of being obtained according to the method of the invention, comprising a first sheet of glass coated on at least part of a first face with a first layer of enamel, itself partially coated with a second layer of enamel having a composition different from that of the first layer of enamel and comprising bismuth, said first sheet of glass being laminated with an additional sheet of glass by means of a lamination interlayer.

[0010] The first sheet of glass can be flat or curved. The glass sheet is usually flat when the enamel layers are deposited, and is then curved.

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

[0012] The first glass sheet may be clear glass or tinted glass, preferably tinted glass, for example green, gray or blue. To achieve this, the chemical composition of the glass sheet advantageously comprises iron oxide, in a weight content ranging from 0.5 to 2%. It may also comprise other coloring agents, such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0013] The first 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.

[0014] The lateral dimensions of the first sheet of glass must be adapted according to those of the laminated glazing into which it is intended to be integrated. The first sheet of glass preferably has a surface area of ​​at least 1 m².

[0015] According to one embodiment, the first layer of enamel is in direct contact with the first sheet of glass.

[0016] According to another embodiment, the first glass sheet is coated, under the first layer of enamel, with a stack of thin layers, in particular over at least 70%, in particular over at least 90%, or even over the entirety of its surface.

[0017] In this case, the stack of thin layers is preferably in contact with the first glass sheet and the first enamel layer is preferably in contact with the stack of thin layers. In this text, "contact" means physical contact.

[0018] The stack preferably comprises at least one functional layer, in particular an electrically conductive functional layer. The functional layer is preferably comprised between two thin dielectric layers, at least one of which is a nitride-based layer. Other possible dielectric layers are, for example, oxide or oxynitride layers.

[0019] At least one electroconductive functional layer is advantageously chosen from:- metallic layers, in particular silver or niobium, or even gold, and- layers of a transparent conductive oxide, in particular chosen from indium and tin oxide, doped tin oxides (for example with fluorine or antimony), doped zinc oxides (for example with aluminum or gallium).

[0020] These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In glazing used in land vehicles, particularly cars, railways, or even aircraft or maritime vehicles, low-emissivity glazing allows part of the solar radiation to be reflected outwards in hot weather, and therefore limits the heating of the passenger compartment of said vehicles, and where appropriate reduces air conditioning costs. Conversely, in cold weather, these glazings help to retain heat within the passenger compartment, and therefore reduce the energy effort required for heating. The same is true for glazing used in buildings.

[0021] According to a preferred embodiment, the stack of thin layers comprises at least one silver layer, in particular one, two or three, or even four silver layers. The physical thickness of the silver layer or, where appropriate, the sum of the thicknesses of the silver layers is preferably between 2 and 20 nm, in particular between 3 and 15 nm.

[0022] According to another preferred embodiment, the stack of thin layers comprises at least one layer of indium and tin oxide. Its physical thickness is preferably between 30 and 200 nm, in particular between 40 and 150 nm.

[0023] In order to protect the or each electrically conductive thin layer (whether metallic or based on transparent conductive oxide) during the bending step, each of these layers is preferably framed by at least two dielectric layers. The dielectric layers are preferably based on oxide, nitride and / or oxynitride of at least one element chosen from silicon, aluminum, titanium, zinc, zirconium, tin.

[0024] At least part of the thin-film stack can be deposited by various known techniques, for example by chemical vapor deposition (CVD), or by cathode sputtering, in particular assisted by a magnetic field (magnetron process).

[0025] The stack of thin layers is preferably deposited by cathode sputtering, in particular assisted by a magnetic field. In this process, a plasma is created under a high vacuum in the vicinity of a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, tear off said elements, which are deposited on the glass sheet, forming the desired thin layer. This process is called "reactive" when the layer is made of a material resulting from a chemical reaction between the elements torn off the target and the gas contained in the plasma. The major advantage of this process lies in the possibility of depositing a very complex stack of layers on the same line by successively moving the glass sheet under different targets, generally in a single device.

[0026] The aforementioned stacks have electricity conduction and infrared reflection properties useful for providing a heating function (defrosting, demisting) and / or a thermal insulation function.

[0027] When the stack of thin layers is intended to provide a heating function, current leads must be provided. These may include strips of silver paste deposited by screen printing on the stack of thin layers, at two opposite edges of the glass sheet.

[0028] Preferably, the first layer of enamel (particularly in the final glazing) is opaque, black in color, and forms a band on the periphery of the first sheet of glass. The peripheral band is preferably a self-enclosed band which, from each point on the periphery of the sheet of glass, extends towards the inside of the sheet of glass over a certain width, typically between 1 and 30 cm, a width which may be different depending on the areas of the glazing. The width may, for example, be greater in the lower part of the glazing (in the position of use) than in the lateral parts. As explained previously, the main purpose of this peripheral band is to conceal and / or protect various elements, in particular the glazing mounting joints in the bodywork bay of the vehicle as well as the base of the interior rearview mirror.The peripheral strip may provide openings, particularly in the upper part of the glazing (in the position of use), in order to allow the use of sensors, such as rain sensors, light sensors, cameras or lidars.

[0029] The second layer of enamel is also preferably black and opaque. In this text, the black tint preferably corresponds to a clarity in reflection on the glass side (L*, illuminant D65, CIE-1964 reference observer) of less than 10, in particular less than 5. As indicated previously, the second layer of enamel is not electrically conductive.

[0030] The second layer of enamel is deposited only on a part of said first layer of enamel. It is therefore not deposited anywhere other than on the first layer of enamel, and it is not deposited on the entire first layer of enamel. In particular, it is deposited on 3 to 50%, or even on 4 to 30%, or even on 5 to 20%, of the surface of the first layer of enamel.

[0031] The second layer of enamel is preferably deposited at least at the corners of the first glass sheet. It is in these areas that the transfer of the enamel to the opposite glass is most likely to occur. The first glass sheet generally has a substantially trapezoidal or rectangular shape, and then comprises four corners. The second layer of enamel can be deposited only in the corners, or in addition on at least part of the edges. It can also be deposited both in the corners and on all of the edges, thus forming a peripheral frame.

[0032] Regardless of the configuration, the second layer of enamel preferably extends from the edges of the first pane of glass to a distance of 1 to 10 cm, in particular 2 to 5 cm, or even 2 to 4 cm from said edges. The distance is measured from the nearest edge. The second layer of enamel does not normally extend beyond this, since enamel transfers do not generally occur in the center of the glazing. The second layer of enamel is normally deposited only in the corners, or even on at least part of the edges, but not elsewhere.

[0033] The first and second enamel layers are preferably formed from a composition comprising at least one pigment and at least one glass frit. The enamel layers preferably do not comprise lead oxide.

[0034] The pigments preferably comprise one or more oxides selected from chromium, copper, iron, manganese, cobalt and nickel oxides. These may be, for example, copper and / or iron chromates.

[0035] The enamel composition (of each of the enamel layers) generally further comprises an organic medium, intended to facilitate the application of the composition to the substrate as well as its temporary adhesion to the latter, and which is removed during the firing of the enamel. The medium typically comprises solvents, diluents, oils and / or resins. In this text, the term "enamel composition" refers to the liquid composition that is used to deposit, on the glass sheet, a wet enamel layer. The term "ink" may also be used in the case of compositions intended for digital printing. The term "enamel layer" is used to describe the final layer, after firing, while the term "wet enamel layer" is used to describe the enamel layer before firing.

[0036] The first enamel layer is preferably based on silicate, borosilicate or borate, bismuth and / or zinc. The glass frit of the composition used for the first enamel layer is then a silicate, borosilicate or borate, bismuth and / or zinc.

[0037] For example, the first layer of enamel is based on bismuth silicate, bismuth borosilicate or bismuth borate. Although these compositions generally produce so-called "non-stick" enamels, i.e., enamels that do not form sticky coatings during bending, enamel transfer can still occur in certain cases.

[0038] According to another example, the first layer of enamel is based on zinc borosilicate. Its chemical composition includes in particular the following oxides, in weight contents varying within the limits mentioned below: B2O32-20%, in particular 4-10% SiO220-45%, in particular 25-40% Bi2O30ZnO 8-25%, in particular 10-20%.

[0039] The composition may also comprise at least one alkali metal oxide, in particular potassium, in contents of at most 5% and / or sodium, in contents ranging from 2 to 15%, in particular from 5 to 13%. The composition preferably contains titanium oxide (TiO2), in contents ranging from 1 to 10%, in particular from 2 to 7%. The composition also comprises pigments, for example copper chromates. In this case the typical contents of Cr2O3 and CuO range from 8 to 20% and from 3 to 12% respectively.

[0040] The chemical composition of enamel can be determined by conventional chemical analysis methods, particularly from fired enamel. It is therefore the chemical composition of the fired enamel layer, and not of the glass frit used to form the enamel.

[0041] The second enamel layer comprises bismuth. It is preferably based on bismuth borosilicate. The glass frit of the composition used for the second enamel layer is then a bismuth borosilicate, or even a bismuth and zinc borosilicate. These compositions have proven particularly effective in preventing enamel transfer during bending. Compared to the composition of the first enamel layer, the second enamel layer preferably comprises more bismuth oxide, more zinc oxide and fewer alkali oxides.

[0042] In particular, its chemical composition includes the following oxides, in weight contents varying within the limits mentioned below: B2O3 1-15%, in particular 2-10% SiO2 10-35%, in particular 15-30% Bi2O3 15-50%, in particular 25-45% ZnO 5-25%, in particular 8-20%, Na2O+K2O 0-5%.

[0043] The step of depositing the first layer of enamel is preferably carried out by screen printing. To do this, 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. The thickness of the first layer of wet enamel is preferably between 15 and 30 µm.

[0044] The second layer of enamel is applied using digital printing. Digital printing techniques include inkjet printing or laser transfer printing.

[0045] Inkjet printing is preferably carried out using a print head whose movement (in particular the position and speed) is controlled by a computer or using a series of fixed print heads opposite which the glass moves at a controlled speed. To achieve this, the or each print head comprises nozzles through which drops of ink are projected locally onto the glass sheet. This technique is sometimes called "drop on demand" (DOD). Advantageously, the glass frit and the pigments have a volume particle size distribution such that the D90 is at most 2 µm. The D90 is for example determined by laser particle size analysis. The viscosity of the ink is preferably between 1 and 50 mPa.s.

[0046] The digital printing technique can also be transfer printing, particularly laser transfer. For example, a support, particularly a rotating one, coated with ink is placed opposite the glass sheet and the print head locally emits a laser beam focused on a part of the support, resulting in the creation of a drop of ink which is deposited on the glass sheet.

[0047] The thickness of the second layer of wet enamel is preferably between 5 and 25 µm, in particular between 10 and 15 µm. It is preferably less than the thickness of the first layer of wet enamel.

[0048] The step of depositing the second layer of enamel is preferably followed by a drying step, typically at a temperature between 100 and 200°C. Preferably, the method does not include a drying step between the deposition of the first layer of enamel and the deposition of the second layer of enamel. The second layer of enamel is then deposited on the first layer of enamel while it is still wet. According to an alternative embodiment, the method may include a drying step between the deposition of the first layer of enamel and the deposition of the second layer of enamel.

[0049] The method preferably comprises, before the bending step, a step of pre-firing the first glass sheet coated with the first and second enamel layers, preferably at a temperature between 450 and 600°C. Such pre-firing makes it possible to eliminate the organic medium, or generally any organic component possibly present in the enamel layers, and makes it possible to improve the adhesive properties of the second enamel layer.

[0050] Bending can be carried out by gravity (the glass deforms under its own weight) or by pressing, at temperatures typically ranging from 550 to 650°C.

[0051] The 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 and / or magnesium carbonate, and is intended to reduce the risk of sticking between the glass sheets.

[0052] However, the invention makes it possible to do without this interlayer powder, which provides an advantage in terms of the environment and safety. Preferably, during bending, no interlayer powder is therefore placed between the glass sheets.

[0053] During bending, the inner glass sheet (intended to be positioned inside the passenger compartment) is normally placed above the outer glass sheet. Thus, the first glass sheet is preferably located below the additional glass sheet. In laminated curved glazing, the first glass sheet is preferably located on the convex side of the glazing and the first face is turned towards the lamination interlayer. The enamel layers are then arranged on face 2 of the glazing.

[0054] The lamination step can be carried out by autoclave treatment, for example at temperatures of 110 to 160°C and under a pressure of 10 to 15 bars. Prior to autoclave treatment, the air trapped between the glass sheets and the lamination interlayer can be removed by calendering or by vacuum.

[0055] As previously stated, the additional sheet is preferably the inner sheet of the laminated glazing, i.e. the sheet located on the concave side of the glazing, intended to be positioned inside the passenger compartment of the vehicle.

[0056] The additional glass sheet can be made of soda-lime-silica glass, or borosilicate or aluminosilicate glass. It can be clear or tinted glass. Its thickness is preferably between 0.5 and 4 mm, especially between 1 and 3 mm.

[0057] According to one embodiment, the additional glass sheet carries on the face opposite the face facing the lamination interlayer (preferably face 4, the additional sheet being the inner sheet) an additional stack of thin layers, in particular a low-emissivity stack, comprising a transparent conductive oxide, in particular indium tin oxide (ITO). In this embodiment, the lamination interlayer and / or the additional glass sheet is preferably tinted, the glass sheet carrying the coatings possibly being made of clear glass. The glazing obtained is preferably a motor vehicle roof.

[0058] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0059] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0060] The lamination interlayer can advantageously have sound absorption properties in order to absorb sounds of airborne or solid-borne origin. It can in particular be made for this purpose of three polymeric sheets, including two so-called external PVB sheets framing an internal polymeric sheet, possibly made of PVB, of lower hardness than that of the external sheets.

[0061] The lamination interlayer may also have thermal insulation properties, in particular infrared radiation reflection. For this purpose, it may comprise a coating of low-emissivity thin layers, for example a coating comprising a thin layer of silver or a coating alternating dielectric layers of different refractive indices, deposited on an internal PET sheet framed by two external PVB sheets.

[0062] The thickness of the lamination interlayer is generally in the range of 0.3 to 1.5 mm, in particular 0.5 to 1 mm. The lamination interlayer may have a thinner thickness on one edge of the glazing than in the center of the glazing in order to avoid the formation of a double image when using a head-up display (HUD) system.

[0063] The following exemplary embodiments, as well as Figures 1 to 3 below, illustrate the invention in a non-limiting manner.

[0064] illustrates a first glass sheet coated with the first and second layers of enamel, according to a first embodiment.

[0065] illustrates a first glass sheet coated with the first and second enamel layers, according to a second embodiment.

[0066] represents a detail of the.

[0067] In these figures, the first sheet of glass 1 is shown after depositing the two layers of enamel and before bending. It is therefore still flat, here of a substantially trapezoidal shape, but other shapes are obviously possible, for example substantially rectangular or triangular shapes, depending on the final design of the glazing.

[0068] The first layer of enamel 11 is shown in hatched form for clarity of the figure, but it is generally black (after firing). It can also have gradients of dots in places for aesthetic purposes. It is presented here in the form of a peripheral band.

[0069] In the embodiment of the, the second layer of enamel 12, shown in black, is deposited only at the four corners of the first sheet of glass.

[0070] As shown in, the second layer of enamel 12 extends, from the edges of the first sheet of glass 1, up to a distance d, for example of the order of 2 to 3 cm. The distance is to be adjusted according to the areas where enamel transfers are likely to occur.

[0071] In the embodiment of the, the second enamel layer 12 is also deposited on the edges of the first glass sheet, thus forming a peripheral frame, but of smaller size than the frame of the first enamel layer. Other variants are of course possible, in which for example only a part of the edges is coated with the second enamel layer.

[0072] Glass sheets 2.1 mm thick were screen-coated with a first layer of enamel (Ferro 14303) based on sodium bismuth silicate with a wet thickness of 20 µm, according to the configuration presented in.

[0073] In a comparative test, the coated glass sheet was then dried and pre-fired at 640°C for 180 seconds, followed by a gravity bending step (640°C, 600 seconds) with an additional 2.1 mm thick glass sheet placed on the first glass sheet, enamel side. No interlayer powder was placed between the two glass sheets. During bending, a force of 5 N was applied to the corners. After bending, additional enamel transfer to the glass sheet was observed at the corners, as well as breakage.

[0074] In a test according to the invention, a second layer of enamel was deposited by digital printing on the periphery (as shown in) of the first layer of enamel while still wet, up to a distance of 2 to 3 cm from the edges. The ink used was based on bismuth and zinc borosilicate. After drying, pre-firing and bending, carried out under the same conditions as for the comparative test, no enamel transfer and no breakage were observed.

Claims

A method for obtaining curved laminated glazing, in particular a windshield or a motor vehicle roof, comprising the following steps: - supplying a first sheet of glass (1), then - a step of depositing, on at least a part of a first face of said first sheet of glass (1), a first layer of enamel (11), then - a step of depositing by digital printing, only on a part of said first layer of enamel (11), a second layer of enamel (12) which is not electrically conductive, said second layer of enamel (12) having a different composition from that of the first layer of enamel (11) and comprising bismuth, then - a step of simultaneously curving the first sheet of glass (1) and an additional sheet of glass, said first face being turned towards said additional sheet of glass,then a step of laminating said first sheet of glass (1) with the additional sheet of glass by means of a laminating interlayer. Method according to claim 1, wherein the step of depositing the first layer of enamel (11) is carried out by screen printing. A method according to any one of the preceding claims, not comprising a drying step between the deposition of the first layer of enamel (11) and the deposition of the second layer of enamel (12). A method according to any one of the preceding claims, comprising, before the bending step, a pre-firing step of the first sheet of glass (1) coated with the first (11) and second layer of enamel (12). A method according to any one of the preceding claims, wherein the second layer of enamel (12) is deposited on 3 to 50%, or even on 4 to 30%, of the surface of the first layer of enamel (11). A method according to any one of the preceding claims, wherein the first layer of enamel (11) is opaque, black in color, and forms a band around the periphery of the first sheet of glass (1). Method according to the preceding claim, wherein the second layer of enamel (12) is deposited at least at the corners of the first sheet of glass (1). Method according to the preceding claim, wherein the second layer of enamel (12) is also deposited on the entire edges of the first sheet of glass (1). A method according to any one of claims 7 or 8, wherein the second layer of enamel (12) extends from the edges of the first sheet of glass (1) to a distance of 1 to 10 cm, in particular 2 to 5 cm, from said edges. A method according to any one of the preceding claims, wherein the second layer of enamel (12) is black and opaque. A method according to any one of the preceding claims, wherein the second enamel layer (12) is based on bismuth borosilicate. A method according to any one of the preceding claims, wherein the second layer of enamel (12) is deposited by inkjet printing or by transfer under the effect of laser radiation. A method according to any one of the preceding claims, wherein during the bending, the first glass sheet (1) is located under the additional glass sheet. A method according to any one of the preceding claims, wherein, in the curved laminated glazing, the first sheet of glass (1) is located on the convex side of the glazing and the first face is turned towards the lamination interlayer. Curved laminated glazing, in particular windscreen or roof of motor vehicle, capable of being obtained according to the process of one of the preceding claims, comprising a first sheet of glass (1) coated on at least part of a first face with a first layer of enamel (11), itself partially coated with a second layer of enamel (12) which is not electrically conductive having a composition different from that of the first layer of enamel (11) and comprising bismuth, said first sheet of glass (1) being laminated with an additional sheet of glass by means of a lamination interlayer.

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