WO2023242040A1

WO2023242040A1 - Method for obtaining curved laminated glazing

Info

Publication number: WO2023242040A1
Application number: PCT/EP2023/065325
Authority: WO
Inventors: Jalal BACHAROUCHE; Juliette JAMART; Alexia YON
Original assignee: Saint-Gobain Glass France
Priority date: 2022-06-15
Filing date: 2023-06-08
Publication date: 2023-12-21
Also published as: FR3136756A1

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

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

Laminated glazing is glazing in which two sheets of glass are adhesively bonded using a lamination interlayer. The latter makes it possible in particular to retain shards of glass in the event of breakage, but also provides other functionalities, in particular in terms of burglary resistance or improvement of acoustic properties.

Layers of enamel, generally black and opaque, are often deposited on part of the glazing, generally in the form of a peripheral strip intended to conceal and protect against ultraviolet radiation the polymeric seals used for fixing and positioning the glazing on the body bay. Enamelled areas also conceal the mounting areas for the interior mirror and various connectors and sensors.

In laminated glazing, these layers of enamel are generally arranged on face 2, the faces being traditionally numbered from the face intended to be positioned outside the vehicle. Face 2 is therefore a face 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 automobile 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 glass with a low melting point, which soften under the effect of a cooking heat treatment and adhere to the glass sheet. A mineral layer is thus formed, generally opaque, with strong chemical and mechanical resistance, adhering perfectly to the glass while maintaining the pigment particles. The cooking step is generally carried out simultaneously with the bending of the glass sheet.

In the context of the manufacture of laminated glazing, the two sheets of glass of the glazing are often curved together, the sheet of glass intended to be positioned inside the vehicle generally being placed above the other sheet of glass, which bears enamel. It is then necessary for the enamel to have non-stick properties in order to prevent any sticking between the two sheets of glass during bending. To do this, we usually use enamels containing bismuth, that is to say obtained from glass frits containing bismuth oxide.

Despite the choice of this type of enamel, and despite the deposition 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 experienced by the sheets of glass, or the pressure applied to the sheet of glass carrying the enamel (either because the process provides for the application of pressure, or simply because of the weight of the sheet of glass located above), that part of the enamel is transferred from one glass to another in certain areas of the glazing, leading to aesthetic defects or, in extreme cases, breakage of the glazing.

The invention aims to obviate these drawbacks.

To this end, the subject of the invention is a process for obtaining laminated curved glazing, in particular a windshield or a roof of a motor vehicle, comprising the following steps:
- the supply of a first sheet of glass, then
- a step of depositing, on at least part of a first face of said first sheet of glass, a first layer of enamel, then
- a step of deposition by digital printing, only on part of said first layer of enamel, of a second layer of enamel which is not electro-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 simultaneous bending of 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 sheet of glass with the additional sheet of glass by means of a lamination interlayer.

The invention also relates to 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 one part of a first face of 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.

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

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

The first sheet of glass may be clear glass or tinted glass, preferably tinted glass, for example green, gray or blue. To do 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 include other coloring agents, such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or even selenium.

The first sheet of glass preferably has a thickness in a range ranging 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.

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.

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

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

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

The stack preferably comprises at least one functional layer, in particular an electro-conductive functional layer. The functional layer is preferably between two thin dielectric layers, at least one of which is a nitride-based layer. Other possible dielectric layers are for example layers of oxides or oxynitrides.

At least one electro-conductive functional layer is advantageously chosen from:
- the metallic layers, in particular silver or niobium, or even gold, and
- the 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 aluminum or gallium).

These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In the glazing fitted to land vehicles, particularly automobiles, railways, or even air or maritime vehicles, low-emissive glazing allows part of the solar radiation to be reflected outward in hot weather, and therefore to limit the heating of the the passenger compartment of said vehicles, and where applicable to reduce air conditioning expenses. Conversely, in cold weather, these glazings help retain heat within the passenger compartment, and therefore reduce heating energy costs. It is the same in the case of glazing fitted to buildings.

According to a preferred embodiment, the stack of thin layers comprises at least one layer of silver, in particular one, two or three, or even four layers of silver. 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.

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.

In order to protect the or each thin electroconductive 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 and tin.

At least part of the stack of thin layers 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).

The stack of thin layers is preferably deposited by cathodic 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 plasma species, 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 up of a material resulting from a chemical reaction between the elements torn from 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 scrolling the glass sheet under different targets, generally in a single device.

The aforementioned stacks have electrical conduction and infrared reflection properties useful for providing a heating function (defrosting, defogging) and/or a thermal insulation function.

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

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

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

The second layer of enamel is deposited only on part of said first layer of enamel. It is therefore not deposited elsewhere than on the first layer of enamel, and it is not deposited on the entire first layer of enamel. It is notably deposited on 3 to 50%, or even 4 to 30%, even 5 to 20%, of the surface of the first layer of enamel.

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

Whatever the configuration, the second layer of enamel preferably extends from the edges of the first sheet of glass to a distance ranging from 1 to 10 cm, in particular from 2 to 5 cm, or even from 2 to 4 cm of said edges. The distance is measured from the nearest edge. The second layer of enamel does not normally extend beyond this, as enamel transfers do not usually 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.

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 include lead oxide.

The pigments preferably comprise one or more oxides chosen from chromium, copper, iron, manganese, cobalt and nickel oxides. For example, these may be copper and/or iron chromates.

The enamel composition (of each of the enamel layers) generally also 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 eliminated during the firing of the enamel. The medium typically includes solvents, diluents, oils and/or resins. In this text, the liquid composition which is used to deposit, on the sheet of glass, a layer of wet enamel is referred to as “enamel composition”. The term “ink” can 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.

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

According to one example, the first layer of enamel is based on bismuth silicate, bismuth borosilicate or bismuth borate. Even if these compositions generally give so-called “anti-stick” enamels, that is to say do not generate sticking during bending, enamel transfer can still occur in certain cases.

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:
B ₂ O ₃ 2-20%, notably 4-10%
SiO ₂ 20-45%, notably 25-40%
Bi ₂ O ₃ 0
ZnO 8-25%, notably 10-20%.

The composition may also comprise at least one alkaline 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 (TiO ₂ ), in contents ranging from 1 to 10%, in particular from 2 to 7%. The composition also includes pigments, for example copper chromates. In this case the typical contents of Cr ₂ O ₃ and CuO range from 8 to 20% and 3 to 12% respectively.

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 the glass frit used to form the enamel.

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

In particular, its chemical composition includes in particular the following oxides, in weight contents varying within the limits mentioned below:
B ₂ O ₃ 1-15%, notably 2-10%
SiO ₂ 10-35%, notably 15-30%
Bi ₂ O ₃ 15-50%, notably 25-45%
ZnO 5-25%, notably 8-20%,
Na ₂ O+K ₂ O 0-5%.

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 includes 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 composition to enamel to pass through the screen in areas where the mesh of the screen is not blocked, 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.

The step of depositing the second layer of enamel is carried out by digital printing. Digital printing techniques include, for example, inkjet printing or transfer printing using laser radiation.

Inkjet printing is preferably carried out using a print head whose movement (particularly position and speed) is controlled by computer or using a series of print heads. 'fixed impression against which the glass scrolls at a controlled speed. To do this, the or each print head includes nozzles through which drops of ink are projected locally onto the sheet of glass. 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.

The digital printing technique can also be transfer printing, in particular by laser transfer. For example, a support, in particular rotating, coated with ink is placed opposite the sheet of glass 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 sheet of glass.

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.

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 process 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 which 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.

The process preferably comprises, before the bending step, a step of pre-baking the first sheet of glass coated with the first and second layers of enamel, 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.

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

The glass sheets can be kept apart by placing between them an interlayer powder 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 sticking between the glass sheets.

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

During bending, the interior sheet of glass (intended to be positioned inside the passenger compartment) is normally placed above the exterior sheet of glass. Thus, the first glass sheet is preferably located under the additional glass sheet. In laminated curved glazing, the first sheet of glass is preferably located on the convex side of the glazing and the first face is turned towards the lamination spacer. The enamel layers are then placed on face 2 of the glazing.

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

As said previously, the additional sheet is preferably the interior sheet of the laminated glazing, that is to say the sheet located on the concave side of the glazing, intended to be positioned inside the passenger compartment of the vehicle.

The additional glass sheet can be soda-lime-silico glass, or even borosilicate or aluminosilicate glass. It can be clear or tinted glass. Its thickness is preferably between 0.5 and 4 mm, in particular between 1 and 3 mm.

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) a stack of additional 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.

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

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

The lamination interlayer can advantageously have acoustic absorption properties in order to absorb sounds of airborne or solid-borne origin. It can in particular be made up 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.

The lamination interlayer can also have thermal insulation properties, in particular reflection of infrared radiation. For this purpose, it may comprise a coating of thin layers with low emissivity, 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.

The thickness of the lamination interlayer is generally in a range ranging from 0.3 to 1.5 mm, in particular from 0.5 to 1 mm. The lamination spacer 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 vision system, known as HUD ( head-up display).

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

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

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

represents a detail of the .

In these figures, the first sheet of glass 1 is shown after deposition of 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.

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

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.

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 must be adjusted according to the areas where enamel transfers are likely to occur.

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

Glass sheets 2.1 mm thick were coated by screen printing with a first layer of enamel (Ferro 14303) based on bismuth and sodium silicate with a wet thickness of 20 µm, depending on the configuration presented in .

In a comparative test, the glass sheet thus coated then underwent drying then a pre-baking treatment at 640°C for 180 seconds, then finally a bending step (640°C, 600 seconds) by gravity with a sheet of additional glass 2.1 mm thick placed on the first sheet of glass, enamel side. No interlayer powder was interposed between the two sheets of glass. During crowning, a force of 5 N was applied to the corners. After bending, a transfer of enamel to the additional glass sheet was observed at corners, as well as breakages.

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

Process for obtaining laminated curved glazing, in particular a windshield or a roof of a motor vehicle, comprising the following steps:
- the supply of a first sheet of glass (1), then
- a step of depositing, on at least part of a first face of said first sheet of glass (1), a first layer of enamel (11), then
- a step of deposition by digital printing, only on a part of said first enamel layer (11), of a second enamel layer (12) which is not electro-conductive, said second enamel layer (12) having a composition different from that of the first enamel layer (11) and comprising bismuth, then
- a step of simultaneous bending of 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 glass sheet (1) with the additional glass sheet by means of a lamination interlayer.
Method according to claim 1, in which the step of depositing the first layer of enamel (11) is carried out by screen printing.
Method according to 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).
Method according to one of the preceding claims, comprising, before the bending step, a step of pre-baking the first sheet of glass (1) coated with the first (11) and the second layer of enamel (12). ).
Method according to one of the preceding claims, in which 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).
Method according to one of the preceding claims, in which 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, in which 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, in which the second layer of enamel (12) is also deposited on all of the edges of the first sheet of glass (1).
Method according to one of claims 7 or 8, in which the second layer of enamel (12) extends from the edges of the first sheet of glass (1) up to a distance ranging from 1 to 10 cm, in particular 2 to 5 cm from said edges.
Method according to one of the preceding claims, in which the second layer of enamel (12) is black and opaque.
Method according to one of the preceding claims, in which the second enamel layer (12) is based on bismuth borosilicate.
Method according to one of the preceding claims, in which the second layer of enamel (12) is deposited by inkjet printing or by transfer under the effect of laser radiation.
Method according to one of the preceding claims, in which during bending, the first glass sheet (1) is located under the additional glass sheet.
Method according to one of the preceding claims, in which, in the laminated curved 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.
Laminated curved glazing, in particular windshield or roof of a motor vehicle, obtainable according to the method of one of the preceding claims, comprising a first sheet of glass (1) coated on at least part of a first face a first layer of enamel (11), itself partially coated with a second layer of enamel (12) which is not electro-conductive having a composition different from that of the first layer of enamel ( 11) and comprising bismuth, said first glass sheet (1) being laminated with an additional glass sheet by means of a lamination interlayer.