WO2024165281A1 - Display system for a vehicle, having a p-polarised imaging unit - Google Patents

Abstract

The present invention relates to a display system for a vehicle, comprising: - a windscreen (10) comprising an outer pane (1) having an exterior-side surface (I) and an interior-side surface (II), and an inner pane (2) having an exterior-side surface (III) and an interior-side surface (IV), wherein the interior-side surface (II) of the outer pane (1) and the exterior-side surface (III) of the inner pane (2) are interconnected via a thermoplastic intermediate layer (3), wherein the windscreen (10) has at least one display region (A, B); and - at least one imaging unit (4) which is directed towards the display region (A) and irradiates said display region with p-polarised radiation, wherein a reflective coating (20) is arranged on the interior-side surface (IV) of the inner pane (2), which coating is suitable for reflecting p-polarised radiation and which comprises, in the specified sequence starting from the interior-side surface (IV) of the inner pane (2): - an optically highly refractive layer (21) having a refractive index greater than 1.9; - a metal- or semiconductor-based reflection-increasing layer (22); - an optically low-refractive layer (23) having a refractive index of less than or equal to 1.6.

Description

Display system for a vehicle with a p-polarized imaging unit

The invention relates to a display system for a vehicle.

Windshields for vehicles, particularly motor vehicles such as passenger cars, are designed as composite panes (laminated safety glass) which consist of an outer pane and an inner pane which are laminated together via a thermoplastic intermediate layer. They typically have an opaque masking area which is designed as a peripheral edge area and surrounds a central see-through area. The opaque masking area primarily serves to protect the adhesive used to bond the windshield to the vehicle body from UV radiation. The masking area is typically formed by a black masking print on the surface of the outer pane facing the intermediate layer.

Modern vehicles are increasingly being equipped with so-called head-up displays (HUDs). Using a projector, typically in the dashboard area, images are projected onto the visible area of the windshield, reflected there and perceived by the driver as a virtual image (from his perspective) behind the windshield. This means that important information can be projected into the driver's field of vision, such as the current driving speed, navigation or warning information, which the driver can perceive without having to take his eyes off the road. Head-up displays can therefore make a significant contribution to increasing road safety.

HUD projectors typically illuminate the windshield at an angle of incidence of about 65%, which is close to the Brewster angle for an air-glass transition (57.2° for soda-lime glass). This circumstance can be exploited for a clear display of the HUD projection: if the HUD projector is operated with p-polarized radiation, it hardly reflects the radiation on the external glass surfaces of the windshield. Instead, the windshield is equipped with a reflective coating which is suitable for reflecting the p-polarized radiation to produce the display image. Since there is only one significant reflection plane, namely the reflective coating, a clear display image is produced without ghost images (or with only weak ghost images which are due to residual reflection on the external glass surfaces if the angle of incidence differs slightly from Brewster angle). Examples include DE102014220189A1, EP3187917B1 and W02021104800A1.

It has also been proposed to use the opaque masking area as a display surface for a display system. For this purpose, a display area in the masking area is illuminated by an imaging unit such as a screen. For example, reference is made to DE102009020824A1, WO2022073894A1 and W02022073860A1. In this way, displays for the driver that were previously located in the area of the dashboard can be shown on the windshield itself. Examples of such displays are the driving speed, the time, the engine speed, the navigation system display, information on speed limits (traffic sign recognition), the image from a rear-facing camera and various status displays on the state of the vehicle. Such display systems in the masking area are also preferably operated with p-polarized radiation in order to avoid reflection on the glass surfaces and the resulting ghost images.

The reflective coating for a display area in the see-through area must have a high degree of transparency in order not to restrict visibility through the windshield to a critical extent. This circumstance typically limits the degree of reflection of the p-polarized radiation. Such a restriction does not apply to a display area in the masking area, since the masking area is opaque anyway. Reflective coatings with a higher degree of reflection can be used here, which leads to a more intense display of the display image. For this reason, different reflective coatings are typically used for a display in the see-through area (head-up display, HUD) and a display in the masking area.

Providing different reflective coatings poses problems for the glass manufacturer because it increases production costs. This is particularly true in the case where a vehicle is equipped with both a display area in the see-through area and a display area in the masking area, so that one and the same windshield must be provided with both coatings in certain areas. There is therefore a need for reflective coatings that can be used for both a display in the see-through area and a display in the masking area. CN113031276A discloses a display system, wherein the interior-side surface of the inner pane is provided with a reflective coating which comprises at least one sequence of a dielectric optically high-refractive index (refractive index > 1.8) and a dielectric optically low-refractive index (refractive index < 1.6) layer.

The invention is based on the object of providing an improved display system for a vehicle of the type mentioned at the beginning, which ensures a clear and high-intensity display, regardless of whether the display area is arranged in the see-through area or in the masking area. The windshield should be provided with an improved reflective coating which has a high degree of reflection with respect to the p-polarized radiation of the imaging unit.

The object of the present invention is achieved by a display system according to claim 1. Preferred embodiments emerge from the subclaims.

The core of the invention is an improved reflective coating. The reflective coating is corrosion-resistant and stable against mechanical stress, so that it can be used on the exposed interior surface of the inner pane. This achieves a particularly clear representation of the display image with only a very weakly intense ghost image in the event that the angle of incidence of the imaging unit does not exactly correspond to the Brewster angle. This ghost image is caused by a certain residual reflection on the outside surface of the outer pane, which is further weakened by passing through the reflective coating. If the reflective coating were instead arranged between the outer pane and the inner pane, there would be another ghost image from the interior surface of the inner pane. In addition, the reflective coating has a high degree of reflection with respect to the p-polarized radiation of the imaging unit, which ensures a high-intensity display image. The reflective coating can be used equally for display systems with a display area in the see-through area and for those with a display area in the masking area. On the other hand, the reflective coating is sufficiently transparent so that visibility through the viewing area is not significantly restricted and, in particular, the legal requirements for the transparency of windshields are still met. These are major advantages of the present invention. The high degree of reflection compared to p-polarized radiation with simultaneously high transparency is due in particular to the influence of the very thin reflection-enhancing layer based on a metal or semiconductor. The inventors have surprisingly discovered that the positioning of this reflection-enhancing layer is crucial: optimal properties are achieved when it is arranged between the optically high-refractive layer and the optically low-refractive layer. Otherwise, a lower light transmission and significantly lower reflection values compared to p-polarized radiation are achieved.

The display system according to the invention for a vehicle comprises at least one windshield and at least one imaging unit. As is usual with display systems of this type, the imaging unit irradiates an area of the windshield where the radiation is reflected in the direction of the viewer (driver), thereby creating a virtual image which the viewer perceives from behind the windshield. The area of the windshield which can be irradiated or is irradiated by the imaging unit is referred to as the display area. The windshield has at least one such display area. The at least one imaging unit is therefore directed at the at least one display area. During operation, the at least one imaging unit emits (at least partially) p-polarized radiation and irradiates the at least one display area with this p-polarized radiation.

The windshield is designed as a composite pane and comprises an outer pane and an inner pane that are connected to one another via a thermoplastic intermediate layer. The windshield is intended to separate the interior (vehicle interior) from the outside environment in the window opening of a vehicle that faces forward in the direction of travel. In the sense of the invention, the inner pane refers to the pane of the windshield that faces the interior. The outer pane refers to the pane that faces the outside environment.

The outer pane and the inner pane each have an outer surface and an inner surface and a circumferential side edge running between them. In the sense of the invention, the outer surface refers to the main surface which is intended to face the outside environment in the installed position. In the sense of the invention, the inner surface refers to the main surface which is intended to face the interior in the installed position. The The interior surface of the outer pane and the outside surface of the inner pane face each other and are connected to each other via the thermoplastic intermediate layer.

According to the invention, a reflective coating is arranged on the interior-side surface of the inner pane, which is suitable for reflecting p-polarized radiation. The reflective coating is particularly suitable and intended for reflecting the p-polarized radiation of the imaging unit to generate a display image that a viewer in the vehicle interior, in particular the vehicle driver, can perceive. The display image is in particular a virtual image that appears behind the reflection plane (i.e. the reflective coating) as seen by the viewer.

The reflective coating comprises, in the order given, starting from the interior surface of the inner pane:

- a (preferably dielectric) optically highly refractive layer with a refractive index greater than 1.9,

- a reflection-enhancing layer based on a metal or semiconductor,

- a (preferably dielectric) optically low-refractive layer with a refractive index of less than or equal to 1.6.

If a layer of the reflective coating is based on a material, the layer consists predominantly of this material in addition to any impurities or dopants (preferably with a proportion of less than 5 wt.-%).

Metallic doping (for example aluminum, boron, antimony, zirconium or titanium) can provide dielectric materials with a certain electrical conductivity. However, the expert will identify them as dielectric layers in terms of their function, as is usual in the field of thin layers. The material of the dielectric layers preferably has an electrical conductivity (reciprocal of the specific resistance) of less than 10' ⁸ S/m. The material of metallic layers (electrically conductive layers) preferably has an electrical conductivity of greater than 10 ⁴ S/m. The material of a semiconductor layer preferably has a conductivity between these values, i.e. from 10' ⁸ S/m to 10 ⁴ S/m. Another feature that distinguishes semiconductors from metals is the negative temperature coefficient of the specific resistance: the electrical conductivity of semiconductors decreases with increasing temperature. increases, while that of metals decreases with increasing temperature. The reason for this is the electronic band structure: semiconductors have a band gap between the valence and conduction bands, whereby electrons as free charge carriers must be thermally excited from the valence band to the conduction band in order to provide electrical conductivity. In metals, there is no band gap, the valence and conduction bands overlap, so that free charge carriers are present regardless of temperature. An increase in temperature leads to an excitation of movements of the atomic cores, which limits the mobility of the electrons.

In the context of the present invention, the refractive index is given in relation to a wavelength of 550 nm, unless explicitly stated otherwise. The refractive index is fundamentally independent of the measurement method. It can be determined using ellipsometry, for example. Ellipsometers are commercially available, for example from Sentech.

The reflective coating is in particular a transparent coating made of thin layers (thin layer stack, thin layer sequence). A transparent coating is understood to be a coating that has an average transmission in the visible spectral range of at least 70%, which therefore does not significantly restrict the view through the pane. In principle, it is sufficient if the reflective coating is only present in the display area on the interior surface of the inner pane. For manufacturing reasons and to ensure a homogeneous appearance, however, at least 80%, particularly preferably at least 90% of the interior surface of the inner pane is provided with the reflective coating. In particular, the reflective coating is applied over the entire surface of the interior surface of the inner pane, optionally with the exception of a peripheral edge area and/or local areas that are intended to ensure the transmission of electromagnetic radiation through the windshield as communication, sensor or camera windows. The peripheral uncoated edge area, if present, has a width of up to 20 cm, for example. For example, it can be used to bond the windshield to the vehicle body, so that the adhesive used for this purpose and any sealing elements can be arranged directly on the interior surface of the inner pane.

According to the invention, the optically highly refractive layer has a refractive index of more than 1.9. The refractive index is preferably more than 2.0, i.e. is greater than 2.0, particularly preferably greater than 2.1, most preferably from 2.1 to 2.5, in particular from 2.1 to 2.3.

In an advantageous embodiment, the optically highly refractive layer is based on silicon nitride, on a silicon-metal mixed nitride (preferably silicon-zirconium nitride, silicon-titanium nitride or silicon-hafnium nitride), on an aluminum nitride, on a niobium oxide or on a titanium oxide basis. This achieves good results. The materials have a suitably high refractive index and are easy to deposit. Silicon nitride, silicon-metal mixed nitride (preferably silicon-zirconium nitride, silicon-titanium nitride or silicon-hafnium nitride) and aluminum nitride are particularly preferred. In addition to a suitably high refractive index, these materials have the advantage that thin layers on their basis are bendable. The coated inner pane can therefore be subjected to a bending process to give it a curved shape (usually spherical) that is common in the automotive sector, without cracks or haze forming in the coating. Niobium oxide still has acceptable properties in terms of bendability, while titanium oxide is less bendable and should only be used on panes with less complex bends.

Silicon-metal mixed nitrides are particularly preferred because the metal content increases the refractive index and in particular allows it to be set to a desired value. Silicon-zirconium nitride is particularly preferred. The proportion of zirconium is preferably between 5 and 45% by weight, particularly preferably between 10 and 30% by weight.

The optically highly refractive layer can contain dopants, preferably aluminum or boron.

If a dielectric layer has metallic additives, these are referred to as doping in the sense of the invention if their proportion is less than 5% by weight. If the proportion is 5% by weight or more, a layer is referred to as a mixture, for example as a silicon-metal mixed nitride.

The optically highly refractive layer preferably has a thickness of 40 nm to 100 nm, particularly preferably 50 nm to 90 nm. This applies in particular if the optically highly refractive layer is the only layer below the reflection-enhancing layer. The specification of layer thicknesses or thicknesses refers, unless otherwise stated, to the geometric thickness of a layer.

If a first layer is arranged above a second layer, this means in the sense of the invention that the first layer is arranged further away from the interior-side surface of the inner pane than the second layer. If a first layer is arranged below a second layer, this means in the sense of the invention that the second layer is arranged further away from the interior-side surface of the inner pane than the first layer.

In one embodiment of the invention, the reflective coating below the reflection-enhancing layer comprises, in addition to the necessary optically high-refractive layer, a further (preferably dielectric) optically high-refractive layer. This further optically high-refractive layer can also be referred to as an optically high-refractive secondary layer. The further optically high-refractive layer can be arranged below the necessary optically high-refractive layer or between the necessary optically high-refractive layer and the reflection-enhancing layer. The necessary optically high-refractive layer in this embodiment preferably has a refractive index greater than 2.0, particularly preferably greater than 2.1, very particularly preferably from 2.1 to 2.5, in particular from 2.1 to 2.3. It is preferably made from the materials mentioned above. The further optically high-refractive layer preferably has a refractive index greater than 1.9, particularly preferably from 1.9 to 2.1. The further optically high-refractive layer is preferably based on silicon nitride, which can optionally be doped, for example with aluminum or boron.

In this embodiment, the required optically high-refractive layer preferably has a thickness of 10 nm to 80 nm, particularly preferably 20 nm to 70 nm. The further optically high-refractive layer preferably has a thickness of 10 nm to 80 nm, particularly preferably 20 nm to 70 nm. The two optically high-refractive layers should be combined in such a way that the total optical thickness is preferably 85 nm to 225 nm, particularly preferably 110 nm to 200 nm. In one embodiment, both optically high-refractive layers have a thickness of less than 40 nm, for example between 10 nm and 40 nm or between 20 nm and 40 nm (each (excluding the mentioned limit values). In a further embodiment, both High-refractive-index layers have a maximum thickness of 35 nm, for example from 10 nm to 35 nm or from 20 nm to 35 nm.

According to the invention, the reflection-enhancing layer is based on a metal or a semiconductor. It is preferably a very thin layer with a thickness of 1 nm to 10 nm, particularly preferably 2 nm to 9 nm, very particularly preferably 3 nm to 8 nm, in particular 5 nm to 8 nm. These thicknesses are sufficient to significantly increase the degree of reflection of the reflective coating and, on the other hand, do not reduce the light transmission of the windshield to a critical extent.

When selecting the metal, it is important to ensure that it is corrosion-resistant (as a thin layer), because the reflective coating is applied to the interior surface of the inner pane, which is typically exposed to the atmosphere. Some metals that are commonly used for thin-layer coatings on glass panes (for example for IR-reflective sun protection coatings) are therefore not suitable for the reflection-enhancing layer, such as silver or copper. If the reflection-enhancing layer is based on a metal, the metal is preferred:

- a precious metal (in the chemical-technical sense as a metal with a more positive standard potential than hydrogen), in particular selected from the group consisting of platinum, ruthenium, rhodium, palladium, osmium and iridium;

- a (base) transition metal, in particular selected from the group consisting of titanium, zirconium, hafnium, niobium, tantalum, nickel and chromium;

- Aluminum.

If the reflection-enhancing layer is based on a semiconductor, the semiconductor is preferred:

- an element semiconductor or a semimetal, in particular selected from the group consisting of silicon, germanium and tin in the α-modification (α-tin);

- an alloy or mixture of one of the said semi-metals with aluminium, in particular a silicon-aluminium alloy.

Alloys or mixtures of the above materials can also be used for the reflection-enhancing layer. It is possible to subject the reflective coating to a heat treatment after deposition, for example as part of a glass bending process. This regularly improves the optical properties of the coating, in particular increasing the light transmission. This can lead to partial oxidation of the metallic or semi-metallic reflection-enhancing layer.

According to the invention, the optically low-refractive layer has a refractive index of at most 1.6. The refractive index is preferably less than 1.6, i.e. less than 1.6, particularly preferably from 1.3 to 1.6, in particular from 1.4 to 1.6.

In an advantageous embodiment, the optically low-refractive layer is based on silicon oxide, magnesium fluoride or calcium fluoride, particularly preferably silicon oxide.

The optically low-refractive layer can contain dopants or mixed compositions, preferably aluminum, titanium, hafnium, zirconium.

The optically low-refractive-index layer preferably has a thickness of at least 50 nm, particularly preferably at least 90 nm. The thickness of the low-refractive-index layer is preferably at most 200 nm. The thickness of the low-refractive-index layer can be from 50 nm to 200 nm, in particular from 90 nm to 160 nm, in preferred embodiments. This applies in particular in the case that the optically low-refractive-index layer is the only layer above the reflection-enhancing layer.

The nitrides (silicon nitride, silicon-metal mixed nitride, aluminum nitride), oxides (silicon oxide) and fluorides (magnesium fluoride, calcium fluoride) listed as preferred dielectric materials can be deposited stoichiometrically, substoichiometrically or superstoichiometrically with regard to the nitrogen, oxygen or fluorine content.

In principle, there can be several optically high-refractive layers (i.e. a sequence of optically high-refractive layers) below the reflection-enhancing layer and/or several optically low-refractive layers (i.e. a sequence of optically low-refractive layers) above the reflection-enhancing layer. However, there is preferably no optically low-refractive layer below the reflection-enhancing layer and no optically high-refractive layer above the reflection-enhancing layer. The optical thickness of the optically high-refractive layer or layer sequence is preferably from 85 nm to 225 nm, particularly preferably 110 nm to 200 nm. The optical thickness of the optically low-refractive layer or layer sequence is preferably from 70 nm to 290 nm, particularly preferably 130 nm to 235 nm. The optical thickness in the sense of the invention results from the product of the geometric thickness and the refractive index at 550 nm, the optical thickness of a layer sequence being the sum of the optical thicknesses of the individual layers.

The preferred geometric and optical layer thicknesses specified in the context of the present invention are advantageous for the reflection properties of the reflection coating with respect to p-polarized radiation. In particular, they lead to the maximum of the reflection spectrum being approximately in the middle of the visible spectral range, in particular around 550 nm. In this way, a high degree of reflection and a comparatively color-neutral representation can be achieved.

In principle, it is also possible for the reflective coating to have further sequences of alternating optically high and low refractive layers, with or without intervening reflection-enhancing layer(s).

In particularly preferred embodiments, however, the reflective coating consists only of the following layers, in the specified order starting from the interior surface of the inner pane:

- the optically high-refractive layer with a refractive index greater than 1.9 - the reflection-enhancing layer based on a metal or semiconductor - the optically low-refractive layer with a refractive index less than or equal to 1.6;

- the optically high-refractive layer with a refractive index greater than 1.9 (preferably greater than 2.1) - an optically high-refractive secondary layer with a refractive index greater than 1.9 (preferably from 1.9 to 2.1) - the reflection-enhancing layer based on a metal or semiconductor - the optically low-refractive layer with a refractive index less than or equal to 1.6; or

- an optically high-refractive secondary layer with a refractive index greater than 1.9 (preferably from 1.9 to 2.1) - the optically high-refractive layer with a refractive index greater than 1.9 (preferably greater than 2.1) - the reflection-enhancing layer based on a metal or semiconductor - the optically low-refractive layer with a refractive index less than or equal to 1.6. The windshield typically has a transparent see-through area and an opaque masking area. The see-through area is intended for viewing. In the sense of the invention, the masking area refers to an area of the windshield through which it is not possible to see through. The light transmission of the masking area is less than 5%, preferably less than 2% and very particularly preferably essentially 0%. The masking area is typically formed by an opaque masking print on a surface of the outer pane and/or the inner pane, preferably on the interior surface of the outer pane. The masking print is in particular made of an enamel which contains glass frits and a pigment and is printed on using a screen printing process and then fired into the pane surface. The pigment is typically a black pigment, for example pigment black (carbon black), aniline black, bone black, iron oxide black, spinel black and/or graphite. The masking print preferably has a thickness of 5 pm to 50 pm, particularly preferably 8 pm to 25 pm. Alternatively, opaque films can be used in the intermediate layer to form the masking area.

In a typical embodiment, the masking area surrounds the see-through area like a frame. The masking area is therefore arranged all the way around the see-through area. Typically, the masking area forms the all-round edge area of the windshield and borders on the side edge of the windshield. In a preferred embodiment, the masking area is therefore arranged in a all-round edge area of the windshield and surrounds the central see-through area.

The opaque element that forms the masking area (in particular the cover print or the opaque polymer film) is arranged behind the reflective coating in the line of sight from the vehicle interior to the external environment so that the latter can be irradiated by the imaging unit. The reflective coating is therefore closer to the imaging unit and the vehicle interior than the opaque element and further away from the external environment.

The windshield has an upper edge and a lower edge as well as two side edges running between them. The upper edge is the edge that is intended to point upwards in the installation position. The lower edge is the edge which is designed to point downwards in the installation position. The upper edge is often referred to as the roof edge and the lower edge as the motor edge.

In one embodiment of the invention, the display area is arranged in the viewing area. This means that a display is generated directly in the field of vision of the user (in particular the driver), which he can see without having to take his eyes off the road. Such display systems are also known as head-up displays (HUD).

In a further embodiment of the invention, the display area is arranged in the masking area. It is preferred if the display area is arranged between the viewing area and the lower edge of the windshield. Displays that are traditionally shown in the area of the dashboard can be shown there. This is aesthetically pleasing and the driver does not have to look as far away from the road, which can be advantageous for reasons of driving safety. Such display systems can also be referred to as black print displays.

A combination of the two above embodiments is also possible. In a further embodiment of the invention, the windshield therefore has two display areas, whereby

- a first display area is arranged in the masking area and

- a second display area is arranged in the see-through area.

This design corresponds to the combination of a head-up display with a black print display. The invention develops its advantages in a special way because the reflective coating is suitable for both display areas. Only a single coating is therefore required, which ensures the reflection of the radiation from the imaging unit in both the first and second display areas. It is not necessary to provide a separate reflective coating or a separate reflective element for each display area. In this design, the display system preferably comprises two imaging units, with a first imaging unit (in particular a screen) being directed at the first display area and irradiating it, and a second imaging unit (in particular a projector) being directed at the second display area and irradiating it. Both imaging units emit p-polarized radiation during operation. In embodiments of the invention, it may be preferred if the display area is arranged in the masking area. In addition, a second display area can optionally be present in the see-through area.

The windshield provided with the reflective coating preferably has a reflection factor against p-polarized radiation of at least 10%, preferably at least 15%. The said reflection factor is measured with an angle of incidence of 65° and the standard light source A. The reflection factor is determined as an integrated reflection factor, whereby the observation angle corresponds to the angle of incidence. The light transmission of the windshield in the viewing area is preferably at least 70%. Light transmission means the total transmission, determined by the method for testing the light transmission of motor vehicle windows specified in ECE-R 43, Annex 3, Section 9.1.

The display system according to the invention is operated with p-polarized radiation. This means that the radiation from the at least one imaging unit has a p-polarized radiation component. In a preferred embodiment, the radiation from the at least one imaging unit is predominantly p-polarized, i.e. has a proportion of p-polarized radiation of more than 50%, preferably at least 80%, particularly preferably at least 95%. In particular, the radiation is essentially purely p-polarized - the p-polarized radiation component is therefore 100% or deviates only insignificantly from this. The indication of the direction of polarization refers to the plane of incidence of the radiation on the composite pane. P-polarized radiation refers to radiation whose electric field oscillates in the plane of incidence. S-polarized radiation refers to radiation whose electric field oscillates perpendicular to the plane of incidence. The plane of incidence is spanned by the incidence vector and the surface normal of the windshield at a point within the display area, preferably in the geometric center of the display area. Due to the curvature of the window that is common in the vehicle sector, which affects the plane of incidence and thus the definition of the polarization, the polarization components (in particular the ratio of p-polarized radiation to s-polarized radiation or vice versa) can be different from this reference point at other points. To generate the desired polarized radiation, for example, a polarization filter or a polarizing beam splitter can be arranged between the imaging unit and the windshield in the beam path if the imaging unit does not already provide radiation of the desired polarization direction. In a preferred embodiment, the radiation from the imaging unit is purely p-polarized. Then the reflection on the external pane surfaces is negligible and the display is essentially due solely to the reflection on the reflective coating, which can prevent a ghost image. In a further preferred embodiment, the radiation has both p-polarized and s-polarized radiation components. The proportion of p-polarized and s-polarized radiation can, for example, be from 20% to 80% or from 40% to 60%. This can increase the intensity of the display image because the s-polarized radiation components are reflected from the pane surfaces, which then also contributes to the overall intensity of the display image.

The imaging unit is preferably a projector or a screen (“display”, electronic display). In principle, any type of screen can be used for the display system according to the invention, for example a field emission screen (FED), a liquid crystal display (LCD), a thin film transistor display (TFT-LCD), a cathode ray tube display (CRT), a plasma display, an organic light-emitting diode (OLED), a (true) LED display or a surface conduction electron emitter display (SED). OLED and LCD screens are particularly common. Projectors are particularly common and preferred for head-up displays, screens for black print displays.

In HUD projectors, the beam direction can typically be varied using mirrors, particularly vertically, in order to adapt the projection to the height of the viewer. The area in which the viewer's eyes must be located for a given mirror position is called the eyebox window. This eyebox window can be moved vertically by adjusting the mirrors, whereby the entire area accessible in this way (i.e. the superposition of all possible eyebox windows) is called the eyebox. A viewer located inside the eyebox can perceive the virtual image. This of course means that the viewer's eyes must be inside the eyebox, not the entire body. The technical terms used here from the field of HUDs are generally known to the expert. For a detailed description, please refer to the dissertation "Simulation-based measurement technology for testing head-up displays" by Alexander Neumann at the Institute of Computer Science at the Technical University of Munich (Munich: University Library of the TU Munich, 2012), in particular to Chapter 2 "The head-up display". The at least one imaging unit is directed at the at least one display area of the windshield. It is arranged on the inside of the windshield and irradiates the windshield via the inside surface of the inner pane. When the display system is in operation, the radiation emitted by the imaging unit irradiates the display area to generate the projection or display image. The radiation from the imaging unit is in the visible spectral range of the electromagnetic spectrum, in particular in the spectral range from 450 nm to 650 nm - typical imaging units work with the wavelengths 473 nm, 550 nm and 630 nm (RGB). The angle of incidence of the radiation on the windshield is preferably from 45° to 70°, particularly preferably from 60° to 70°, for example about 65°. These angles of incidence deviate only slightly from the Brewster angle. The Brewster angle for an air-glass transition in the case of soda-lime glass, which is generally used for window panes, is 57.2° (with a refractive index of soda-lime glass of 1.55 at a wavelength of 550 nm). The angle of incidence can also be referred to as the angle of incidence. It is the angle between the incidence vector of the radiation and the interior-side surface normal (i.e. the surface normal to the interior-side surface of the inner pane) determined at a point in the display area, preferably in the geometric center of the display area. If the angle of incidence corresponds exactly to the Brewster angle, only s-polarized radiation is reflected, not p-polarized radiation. In an advantageous embodiment, the angle of incidence deviates from the Brewster angle by a maximum of 10°.

Since the angle of incidence typically does not deviate significantly from the Brewster angle, p-polarized radiation is generally not reflected or only reflected to a small extent on the external surfaces of the windshield (outer surface of the outer pane and interior surface of the inner pane). The reflection on the interior surface of the inner pane is practically solely due to the reflective coating. No (significant) further reflection takes place on the outer surface of the outer pane, which would lead to a ghost image when using s-polarized radiation. It is therefore not necessary to arrange the external surfaces at an angle to one another, as is usual when using s-polarized radiation, in order to superimpose the two reflections or to make them coincide as much as possible. Instead, the windshield and its components (outer pane, inner pane, intermediate layer) preferably have a constant thickness. The outer surface of the outer pane and the interior surface of the inner pane are preferably aligned parallel to each other. The use of relatively expensive wedge foils or wedge-shaped panes can be dispensed with. However, it is not impossible to use a wedge foil anyway, for example to bring a low-intensity ghost image, which is caused by reflection on the outside surface of the outer pane as a result of a deviation from the Brewster angle, into alignment with the main image.

In addition to avoiding ghost images, the use of p-polarized radiation also has the advantage that the displayed image is recognizable to wearers of polarization-selective sunglasses, which typically only allow p-polarized radiation to pass and block s-polarized radiation.

If the radiation from the imaging unit also contains s-polarized radiation components, the external surfaces of the windshield (outer surface of the outer pane and interior surface of the inner pane) are arranged at an angle (wedge angle) to one another in a further development of the invention in order to superimpose the reflections on the two said surfaces and thus avoid a ghost image. The distance between the surfaces increases from the lower edge towards the upper edge of the display area. This applies in particular if the display area is arranged in the see-through area of the windshield. The lower edge of the display area faces the lower edge of the windshield, the upper edge of the display area faces the upper edge of the windshield. The wedge angle can be achieved by using a wedge-shaped film as an intermediate layer or as a component of the intermediate layer, alternatively by using a wedge-shaped outer pane and/or inner pane.

The outer pane and the inner pane are preferably made of glass, in particular soda-lime glass, which is common for window panes. In principle, however, the panes can also be made of other types of glass (e.g. borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (e.g. polymethyl methacrylate or polycarbonate). The thickness of the outer pane and the inner pane can vary widely. Preferably, panes with a thickness in the range of 0.8 mm to 5 mm, preferably from 1.1 mm to 2.9 mm, for example with the standard thicknesses 1.6 mm or 2.1 mm, are used. The outer pane, the inner pane and the thermoplastic interlayer can be clear and colorless, but also tinted or colored. The outer pane and the inner panes can independently be non-tempered, partially tempered or tempered (thermally or chemically).

The windshield is preferably curved in one or more directions of space, as is usual for motor vehicle windows (particularly windows of passenger cars), with typical radii of curvature being in the range of about 10 cm to about 40 m. However, the windshield can also be flat, for example if it is intended as a windshield for buses, trains or tractors.

The thermoplastic intermediate layer contains at least one thermoplastic polymer, preferably polyvinyl butyral (PVB), ethylene vinyl acetate (EVA) or polyurethane (PU) or mixtures or copolymers or derivatives thereof, particularly preferably PVB. The intermediate layer is typically made of at least one thermoplastic film (connecting film), preferably based on one of the said polymers, in particular based on PVB. In the sense of the invention, this means that the film contains predominantly the said material (proportion of greater than 50% by weight) and can optionally contain further components, for example plasticizers, stabilizers, UV or IR absorbers. The thickness of the intermediate layer is preferably from 0.2 mm to 2 mm, particularly preferably from 0.5 mm to 1 mm.

The windshield can be manufactured using processes known per se. The outer pane and the inner pane are laminated together via the intermediate layer, for example using autoclave processes, vacuum bag processes, vacuum ring processes, calender processes, vacuum laminators or combinations thereof. The connection between the outer pane and the inner pane is usually carried out using heat, vacuum and/or pressure.

The reflective coating is preferably applied to the inner pane by physical vapor deposition (PVD), particularly preferably by cathode sputtering (“sputtering”), and most preferably by magnetic field-assisted cathode sputtering (“magnetron sputtering”). In principle, however, the coating can also be applied, for example, by chemical vapor deposition (CVD), for example plasma-assisted vapor deposition (PECVD), by vapor deposition or by atomic layer deposition. (atomic layer deposition, ALD). The coating is preferably deposited on the inner pane before lamination and before any bending process.

If the windshield is to be curved, the outer pane and the inner pane are preferably subjected to a bending process before lamination and preferably after any coating processes. The outer pane and the inner pane are preferably bent congruently together (i.e. lying on top of each other, at the same time and using the same tool), because this ensures that the shape of the panes is optimally coordinated for the subsequent lamination. Typical temperatures for glass bending processes are, for example, 500°C to 700°C. All standard bending methods can be used, for example gravity bending, press bending and/or suction bending.

The invention also includes a vehicle which is equipped with the display system according to the invention. The vehicle can be a land, air or water vehicle. The vehicle is preferably a motor vehicle, rail vehicle, aircraft or ship, in particular a passenger car or truck.

The invention also includes the use of a windshield designed according to the invention as a projection surface of a display system in a vehicle, wherein at least one imaging unit is directed at the at least one display area. The preferred embodiments described above apply accordingly to the use.

The invention further comprises the use of a display system according to the invention in a vehicle on land, on water or in the air, preferably a motor vehicle, rail vehicle, aircraft or ship, in particular a passenger car or truck. The invention is explained in more detail below with reference to a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

They show:

Fig. 1 is a plan view of a windshield of a first embodiment of a generic display system,

Fig. 2 shows a cross section through the display system of Figure 1 ,

Fig. 3 is a plan view of a windshield of a second embodiment of a generic display system,

Fig. 4 a cross-section through the display system from Figure 3,

Fig. 5 is a plan view of a windshield of a third embodiment of a generic display system,

Fig. 6 a cross-section through the display system from Figure 5,

Fig. 7 is a cross-section through the windshield of a display system according to the invention,

Fig. 8 is an enlarged view of section Z from Figure 7 in two embodiments according to the invention.

Figure 1 and Figure 2 each show a detail of a first embodiment of a generic display system for a vehicle. The display system comprises a windshield 10 of a passenger car. The display system also comprises an imaging unit 4, which is directed at a display area A of the windshield 10. In the display area A, the imaging unit 4 can generate images which are perceived by an observer 5 (vehicle driver) as virtual images on the side of the windshield 10 facing away from him when his eyes are within the so-called eyebox E.

The windshield 10 is made up of an outer pane 1 and an inner pane 2, which are connected to one another via a thermoplastic intermediate layer 3. Its lower edge U is arranged downwards in the direction of the engine of the passenger car, its upper edge O upwards in the direction of the roof. In the installed position, the outer pane 1 faces the outside environment, the inner pane 2 faces the vehicle interior. The outer pane 1 and the inner pane 2 are made of soda-lime glass with a thickness of 2.1 mm. The intermediate layer 3 is made of a 0.76 mm thick PVB film. The windshield 10 is shown flat for the sake of simplicity, although real windshields typically have a spherical curvature.

The outer pane 1 has an outer surface I that faces the external environment and an interior surface II that faces the vehicle interior. Likewise, the inner pane 2 has an outer surface III that faces the external environment and an interior surface IV that faces the vehicle interior.

The windshield 10 has an opaque masking area M, which is arranged in a peripheral edge area and surrounds a transparent see-through area D in a frame-like manner. Such masking areas M are common in vehicle windows - they primarily serve to protect the adhesive used to bond the windshield 10 to the vehicle body from UV radiation.

The display area A is arranged in the masking area M between the transparent area D and the lower edge U. Such a display system can also be referred to as a "black print display". This display area A is used to show a display for the vehicle occupants. This can in particular be status information about the vehicle (for example the driving speed or a fuel gauge), navigation instructions (for example speed limits or directions) or the image from a rear-facing camera. Entertainment content can also be shown (for example films, Internet data or computer games), in particular on the passenger side.

The imaging unit 4 is, for example, an LCD screen or a plurality of LCD screens arranged next to one another. The imaging unit 4 irradiates the display area A with an angle of incidence a, which is measured to the surface normal of the inner pane on the interior side. The angle of incidence a is, for example, 65°, which is comparatively close to the Brewster angle (about 57° for an air - soda-lime glass transition). The radiation from the imaging unit 4 is p-polarized - it is therefore hardly reflected on the glass surfaces.

In an embodiment of the display system according to the invention, the interior-side surface IV of the inner pane 2 is provided essentially over its entire surface with a reflective coating according to the invention, which is not shown in Figures 1 and 2 and will be described later. The reflective coating reflects the p-polarized radiation of the imaging unit 4 to produce the display image. Since it represents the only significant reflective interface, a clear display image is produced with no (or only very low intensity) ghost images.

Figure 3 and Figure 4 each show a detail of a second embodiment of a generic display system for a vehicle. The display system again comprises a windshield 10 of a passenger car and an imaging unit 4. The windshield 10 is designed in the same way as in the first embodiment according to Figure 1 and Figure 2.

In contrast to the first embodiment, the display area B is arranged in the viewing area of the windshield 10. The imaging unit 4 is a projector that is operated with p-polarized radiation. The imaging unit 4 irradiates the display area B, whereby a display image is projected directly into the field of vision of the observer 5 (vehicle driver) - again as a virtual image on the side of the windshield 10 facing away from him if his eyes are within the so-called eyebox E. Such a display system is also referred to as a "head-up display" (HUD). This allows the observer 5 to be shown status information (for example the driving speed), navigation instructions (for example speed limits or directions) or warning symbols in particular without him having to take his eyes off the road.

The imaging unit 4 again irradiates the display area B with an angle of incidence a which is, for example, 65°. The p-polarized radiation of the imaging unit 4 is therefore not significantly reflected on the glass surfaces. For reflection, a windshield 10 designed according to the invention has the same reflective coating as the first embodiment according to Figure 1 and Figure 2. This produces a clear display image without (or only with very low-intensity) ghost images.

Figure 5 and Figure 6 each show a detail of a third embodiment of a generic display system for a vehicle. The third embodiment represents a combination of the first embodiment according to Figure 1 and Figure 2 and the second embodiment according to Figure 3 and Figure 4. The display system again comprises a windshield 10 of a passenger car and an imaging unit 4. The windshield 10 is designed in the same way as in the first and second embodiments.

The windshield has a first display area A in the masking area M and a second display area B in the see-through area D. The display system comprises a first imaging unit 4.1 which is directed at the first display area A, for example an LCD screen or a plurality of LCD screens arranged next to one another. The display system also comprises a second imaging unit 4.2 which is directed at the second display area B, for example a projector. Both imaging units 4.1, 4.2 are operated with p-polarized radiation and irradiate the associated display area A, B with an angle of incidence a of, for example, 65°. For reflection, a windshield 10 designed according to the invention in turn has a reflective coating according to the invention. It is a great advantage of the present invention that the same reflective coating is suitable both for a head-up display with a display area B in the see-through area D and for a black print display with a display area A in the masking area M.

Figure 7 shows a cross section through an inventive design of the windshield 10 with the outer pane 1 (soda-lime glass, 2.1 mm), the inner pane 2 (soda-lime glass, 2.1 mm) and the thermoplastic intermediate layer 3 (PVB, 0.76 mm). The masking area M is formed by a black print on the interior-side surface II of the outer pane 1. The print consists of an enamel with glass frits and a black pigment that has been applied using a screen printing process and then burned into the pane surface. The reflective coating 20 according to the invention is arranged on the interior-side surface IV of the inner pane 2.

Figure 8 shows the section Z from Figure 7 in an enlarged view in two embodiments of the reflective coating 20 according to the invention.

Figure 8a shows a first embodiment of the reflective coating 20. The reflective coating 20 consists of

- an optically highly refractive layer 21 with a refractive index greater than 2.0,

- a reflection-enhancing layer 22 based on a metal or semiconductor and

- an optically low-refractive layer 23 with a refractive index less than or equal to 1.6, which are deposited, in particular sputtered, on the inner pane 2 in the specified order starting from the interior surface IV.

Figure 8b shows a second embodiment of the reflective coating 20. The reflective coating 20 consists of

- an optically highly refractive secondary layer 24 with a refractive index of 1.8 to 2.1,

- an optically highly refractive layer 21 with a refractive index greater than 2.1,

- a reflection-enhancing layer 22 based on a metal or semiconductor and

- an optically low-refractive layer 23 with a refractive index of less than or equal to 1.6, which are deposited, in particular sputtered, on the inner pane 2 in the specified order starting from the interior-side surface IV.

The layer sequences can be seen schematically in the figure. The layer sequence of a windshield 10 with the reflective coating 20 on the interior-side surface IV of the inner pane 2 is shown in Table 1 together with the materials and layer thicknesses of the individual layers for three examples 1 to 3 according to the invention. Examples 1 and 2 correspond to the structure according to Figure 8a, example 3 to the structure according to Figure 8b.

Table 1

In Table 2, however, the layer sequences of two windshields 10 with reflective coatings 20 not according to the invention are shown (Comparative Examples 1 and 2). Table 2

In Comparative Example 1, the reflection coating is formed only from an optically high-refractive layer 21 and an optically low-refractive layer 23; the reflection-enhancing layer 22 according to the invention is missing. In Comparative Example 2, such a reflection-enhancing layer 22 is present, but not between the optically high-refractive layer 21 and the optically low-refractive layer 23, but below the optically high-refractive layer 21.

The optically high-refractive layers 21 are each based on a silicon-zirconium mixed nitride (SiZrN) that was deposited in a nitrogen atmosphere with argon addition using a silicon-zirconium target with a zirconium content of 17% by weight. The optically high-refractive secondary layer 24 in example 3 is based on silicon nitride (SiN). The optically low-refractive layers 23 are each based on silicon oxide (SiO). The reflection-enhancing layer 22 is based on the metal titanium (Ti) in examples 1 and 3 and in comparative example 2, but in example 2 it is based on the semiconductor or semi-metal silicon (Si).

Table 3 shows materials and layer thicknesses for three further examples 4 to 6 according to the invention. They also correspond to the structure according to Figure 8a. In examples 4 to 6, niobium oxide (NbO) or titanium oxide (TiO) was used as the optically high-refractive layer 21. The optically low-refractive layers 23 are each based on silicon oxide (SiO), the reflection-enhancing layers 22 are based on the metal titanium (Ti). Table 3

The oxides SiO, NbO and TiO and the nitrides SiN and SiZrN can be deposited stoichiometrically, substoichiometrically or superstoichiometrically in terms of oxygen or nitrogen content, which is why a stoichiometric formula was not given. In the examples and the comparative example, however, the same stoichiometric ratio was chosen for layers based on the same material. The layers can also contain doping and impurities. The doping for layers based on the same material was also the same in the examples and the comparative example. The layers based on SiO, SiN and SiZrN were doped with aluminum.

The dielectric layers 21, 23, 24 have the following refractive indices at 550 nm: SiN (2.00), SiZrN (2.22), NbO (2.38), TiO (2.45), SiO (1.45). The refractive indices can be used to calculate the optical thicknesses of the layers, with the optical thickness being the product of the refractive index and the geometric thickness, which is given in Tables 1 to 3.

Table 4 shows the reflectance R _p-po i. of the windshield 10 with respect to p-polarized radiation at three different angles of incidence a. An angle of incidence a of 65° corresponds to the embodiments from Figures 1 to 6. R _p-po i. indicates the integrated light reflection with respect to p-polarized radiation, measured with a p-polarized light source of light type A. The observation angle corresponded to the angle of incidence in each case. Table 4

At all angles of incidence a, the inventive examples 1 to 3 have significantly higher reflection values R _p-po i. than the comparative example 1. This is due to the influence of the reflection-enhancing layer 22. Surprisingly, however, this effect does not occur in comparative example 2, in which the reflection-enhancing layer 22 was arranged below the optically highly refractive layer 21. Quite the opposite: here even lower reflection values are observed than in comparative example 1 without reflection-enhancing layer 22.

In Examples 4 to 6, slightly higher reflection values R _p-po i. can be observed than in Examples 1 to 3. This is due in particular to the use of materials of the optically highly refractive layers 21 with a higher refractive index.

In the examples according to the invention, the reflectance R _p-po i. is sufficiently high at all angles of incidence a, so that a high-intensity display image is produced. It can be seen that the reflectance R _p-po i. increases with increasing angle of incidence a. This is due in particular to the fact that the deviation from the Brewster angle increases, so that the reflection on the glass surfaces becomes stronger.

Table 4 also shows the light transmission TL, which means the integrated light transmission according to ISO 9050, measured with a light source of illuminant A. In the examples according to the invention and in comparative example 1, the light transmission was more than 70%, so that the legal requirements for windshields 10 are met. In comparative example 2, a lower Light transmission was observed, so that this windshield 10 cannot be placed on the market.

All values in Table 4 were determined in the viewing area D of the windshield 10.

List of reference symbols:

(10) Windshield

(1) Outer pane

(2) Inner pane

(3) thermoplastic intermediate layer

(4) imaging unit

(4.1), (4.2) first, second imaging unit

(5) Viewer / vehicle driver

(6) Cover printing

(20) Reflective coating

(21) optically highly refractive layer (refractive index > 2.0)

(22) reflection-enhancing layer

(23) optically low refractive index layer (refractive index < 1.6)

(24) optically highly refractive secondary layer (refractive index > 1 .8)

(O) Upper edge of the windscreen 10

(U) Lower edge of the windscreen 10

(D) See-through area

(M) Masking area

(A) Display area of the windshield 10 in the masking area M

(B) Display area of the windshield 10 in the viewing area D

(E) Eyebox

(a) Angle of incidence

(I) outside surface of the outer pane 1

(11) interior surface of the outer pane 1

(III) outside surface of the inner pane 2

(IV) interior surface of the inner pane 2

X -X‘ cutting line

Y -Y‘ intersection line

Z - Z‘ cutting line

Z enlarged section

Claims

Patent claims 1 . Display system for a vehicle, comprising - a windshield (10) comprising an outer pane (1) with an outer surface (I) and an interior surface (II) and an inner pane (2) with an outer surface (III) and an interior surface (IV), wherein the interior surface (II) of the outer pane (1) and the outer surface (III) of the inner pane (2) are connected to one another via a thermoplastic intermediate layer (3), wherein the windshield (10) has at least one display area (A, B), and - at least one imaging unit (4) which is directed at the display area (A) and irradiates it with p-polarized radiation, wherein a reflective coating (20) is arranged on the interior-side surface (IV) of the inner pane (2), which is suitable for reflecting p-polarized radiation and which comprises in the specified order starting from the interior-side surface (IV) of the inner pane (2): - an optically highly refractive layer (21) with a refractive index greater than 1.9 - a reflection-enhancing layer (22) based on a metal or semiconductor, - an optically low-refractive layer (23) with a refractive index of less than or equal to 1.6. 2. Display system according to claim 1, wherein the optically highly refractive layer (21) is based on silicon nitride, on the basis of a silicon-metal mixed nitride, preferably silicon zirconium nitride, silicon titanium nitride or silicon hafnium nitride, on the basis of aluminum nitride, on the basis of niobium oxide or on the basis of titanium oxide. 3. Display system according to claim 1 or 2, wherein the optically highly refractive layer (21) has a thickness of 40 nm to 100 nm, preferably 50 nm to 90 nm. 4. Display system according to claim 1 or 2, wherein the reflection coating (20) below the optically highly refractive layer (21) or between the optically highly refractive layer (21) and the reflection-enhancing layer (22) comprises a dielectric optically highly refractive secondary layer (24), wherein the optically high-refractive layer (21) has a refractive index greater than 2.1 and the optically high-refractive secondary layer (24) has a refractive index of 1.9 to 2.1. 5. Display system according to claim 4, wherein - the optically highly refractive layer (21) has a thickness of 10 nm to 80 nm, preferably 20 nm to 70 nm, - the optically highly refractive secondary layer (24) has a thickness of 10 nm to 80 nm, preferably 20 nm to 70 nm, and is preferably formed on the basis of silicon nitride. 6. Display system according to one of claims 1 to 5, wherein the reflection-enhancing layer (22) has a thickness of 1 nm to 10 nm, preferably from 2 nm to 9 nm, particularly preferably from 3 nm to 8 nm, most particularly preferably from 5 nm to 8 nm. 7. Display system according to one of claims 1 to 6, wherein the reflection-enhancing layer (22) is based on platinum, ruthenium, rhodium, palladium, osmium, iridium, titanium, zirconium, hafnium, niobium, tantalum, nickel, chromium, aluminum, silicon, germanium, a-tin or a silicon-aluminum alloy. 8. Display system according to one of claims 1 to 7, wherein the optically low-refractive layer (23) has a thickness of 50 nm to 200 nm, preferably 90 nm to 160 nm. 9. Display system according to one of claims 1 to 8, wherein the optically low-refractive layer (23) is based on silicon oxide, magnesium fluoride or calcium fluoride, preferably based on silicon oxide. 10. Display system according to one of claims 1 to 9, wherein the windshield (10) has a transparent see-through area (D) and an opaque masking area (M) and wherein the display area (B) is arranged in the see-through area (D). 11. Display system according to one of claims 1 to 9, wherein the windshield (10) has a transparent viewing area (D) and an opaque Masking area (M) and wherein the display area (B) is arranged in the masking area (M). 12. Display system according to one of claims 1 to 9, wherein the windshield (10) has a transparent viewing area (D), an opaque masking area (M), a first display area (A) and a second display area (B) and wherein - the first display area (A) is arranged in the masking area (M) and - the second display area (B) is arranged in the see-through area (D). 13. Display system according to one of claims 1 to 12, wherein the at least one imaging unit (4) irradiates the at least one display area (A, B) with an angle of incidence (a) of 60° to 70°. 14. Display system according to one of claims 1 to 13, wherein the imaging unit (4) is a projector or a screen. 15. Display system according to one of claims 1 to 14, wherein the outer pane (1) and the inner pane (2) are made of soda-lime glass.