Projection arrangement for one vehicle, comprising one side window

Description

[0001] The invention relates to a projection arrangement for a vehicle, in particular intended as an entertainment system, and the use of a vehicle side window for such a projection arrangement.

[0002] Automotive entertainment systems are becoming increasingly popular. It's common practice to equip the backs of the front seats with screens that allow rear passengers to watch movies or play computer games, for example.

[0003] Projection arrangements using the window panes are common in the automotive sector as so-called head-up displays (HUDs). These use a projector to project images onto the windshield, reflect them, and then the driver perceives them as a virtual image (as seen from the driver's perspective) behind the windshield. This allows important information to be projected into the driver's field of vision, such as the current speed, navigation information, or warnings, which the driver can perceive without having to take their eyes off the road.

[0004] If the projectors use s-polarized radiation, it is reflected off both external surfaces of the windshield. This results in a slightly offset secondary image, the so-called "ghost image," appearing alongside the desired main image. This problem is typically mitigated by arranging the surfaces at an angle to each other, particularly by using a wedge-like intermediate layer to laminate the windshields, which are designed as a composite pane, so that the main image and the ghost image are superimposed. Laminated glass with wedge films for HUDs are known, for example, from WO2009 / 071135A1, EP1800855B1, or EP1880243A2.

[0005] Alternatively, projectors with p-polarized radiation can be used. If the angle of incidence is close to the Brewster angle, p-polarized radiation is not reflected by the windshield surfaces, thus avoiding the problem of ghosting. Instead, the windshields have a reflective coating that generates the projection image. Such a HUD is known, for example, from DE 10 2014 220 189 A1.

[0006] It is also known to provide vehicle windows with transparent, electrically conductive coatings. These coatings can act as IR-reflective coatings to reduce heating of the vehicle interior and thereby improve thermal comfort. The coatings can also be used as heatable coatings by connecting them to a voltage source so that a current flows through the coating. Suitable coatings contain conductive metallic layers, for example, based on silver or aluminum. These coatings can, in principle, be used to reflect p-polarized radiation to generate a HUD projection image.Since windshields are subject to stringent legal requirements regarding transparency, the electrically conductive coatings are formed as complex thin-film stacks, ensuring not only reflective properties, particularly in the IR range, but also high transmission in the visible spectral range. Silver-containing transparent coatings are known, for example, from WO 03 / 024155, US 2007 / 0082219 A1, US 2007 / 0020465 A1, WO2013 / 104438, or WO2013 / 104439.

[0007] CN 104 267 498 A discloses a projection arrangement comprising a windshield and a projector that irradiates the windshield with p-polarized radiation. The windshield has a reflective coating that alternates between layers with a high optical index and layers with a low optical index.

[0008] EP 3 187 917 A2 discloses such a projection arrangement, wherein the reflective coating comprises silver layers and optically highly refractive dielectric layers.

[0009] US 2006 / 023315 A1 discloses a projection arrangement comprising a vehicle window, which may be a side window. The vehicle window is irradiated with s-polarized radiation by a projector. The radiation is converted by a polarization-modifying layer into p-polarized radiation, which is then reflected by a reflective layer.

[0010] The invention is based on the object of providing a projection system for a vehicle that can be used, in particular, as an entertainment system for rear vehicle occupants. The projection system should be as cost-effective to manufacture as possible and create an exceptional impression on the viewer.

[0011] The object of the present invention is achieved by a projection arrangement according to claim 1. Preferred embodiments are evident from the subclaims.

[0012] The projection arrangement for a vehicle according to the invention comprises at least one vehicle side window equipped with a reflective coating, and a projector. The projector is arranged on the interior side of the side window, is directed onto a region of the side window, and illuminates this region. The projector generates a virtual image visible behind the side window. The projector uses p-polarized radiation, which is not significantly reflected by the surfaces of the side window if the angle of incidence is selected close to the Brewster angle for an air-to-glass transition (57.2°, soda-lime glass). This avoids double reflections and eliminates the use of a wedge-like intermediate layer, which simplifies and reduces the cost of manufacturing the side window. The reflective coating is designed to reflect the p-polarized radiation to generate the projection image.Since there are significantly lower or no legal requirements for the transparency of rear side windows, the coating does not need to ensure high transmission in the visible spectral range. Therefore, simpler and less costly coatings can be used than, for example, in the case of windshields. The projection display as a virtual image behind the side window provides the viewer with an exceptional entertainment experience. These are major advantages of the present invention.

[0013] The side window according to the invention is intended to separate the interior from the outside environment in a window opening of a vehicle, in particular a side window opening. The side window is preferably a rear vehicle side window (in particular of a motor vehicle, for example a car or truck), i.e. a side window that is not assigned to the driver or front passenger, but rather to the rear occupants of the vehicle in the back seat. The side window comprises two external surfaces (main surfaces), which in the sense of the invention are referred to as an outside surface and an inside surface, and a circumferential side edge running between them. In the sense of the invention, the term outside surface refers to the surface which is intended to face the outside environment in the installed position.For the purposes of the invention, the interior-side surface refers to the main surface which is intended to face the interior in the installed position.

[0014] The vehicle side window can be designed as a monolithic glass or plastic pane, in particular as thermally toughened single-pane safety glass (ESG). In this case, the reflective coating is preferably applied to the interior surface, where it is exposed to lower mechanical and corrosive stresses than on the exterior surface. In a preferred embodiment, however, the vehicle side window is designed as a composite pane. The composite pane comprises an outer pane and an inner pane, which are connected to one another via a thermoplastic intermediate layer. For the purposes of the invention, the inner pane refers to the pane of the composite pane facing the interior (in particular the vehicle interior). The outer pane refers to the pane facing the exterior environment.The outer pane and the inner pane each have an outer surface, an inner surface, and a circumferential side edge extending therebetween. The inner surface of the outer pane and the outer surface of the inner pane face each other and are connected by the thermoplastic intermediate layer.

[0015] If the side window is designed as a composite window, the reflective coating is preferably applied to a surface of the two panes facing the intermediate layer, i.e., the interior-facing surface of the outer pane or the exterior-facing surface of the inner pane. Alternatively, the reflective coating can also be arranged within the thermoplastic intermediate layer, for example, applied to a carrier film arranged between two thermoplastic bonding films. Between the panes, the reflective coating is protected from corrosion, mechanical damage, and other adverse effects. This is particularly advantageous if the reflective coating comprises one or more metal-containing layers, for example, silver-containing layers, which are susceptible to corrosion and therefore should not have contact with the surrounding atmosphere.

[0016] Since the reflection of the projector radiation occurs essentially at the reflective coating and not at the external pane surfaces, it is not necessary to arrange the external pane surfaces at an angle to one another in order to avoid ghosting. The external surfaces of the side pane are therefore preferably arranged essentially parallel to one another. If the side pane is designed as a composite pane, the thermoplastic intermediate layer is preferably not wedge-shaped, but has an essentially constant thickness, just like the inner pane and the outer pane. A wedge-shaped intermediate layer, on the other hand, would have a variable, in particular increasing, thickness in the vertical direction between the lower edge and upper edge of the side pane. The intermediate layer is typically formed from at least one thermoplastic film.Since standard films are significantly cheaper than wedge films, the production of the side window is made more cost-effective.

[0017] The projector's radiation is predominantly p-polarized. The angle of incidence of the projector radiation on the side window is preferably between 45° and 70°. In a particularly advantageous embodiment, the angle of incidence deviates from the Brewster angle by a maximum of 10°. The p-polarized radiation is then reflected only insignificantly by the surfaces of the side window, so that no ghost image is created. The angle of incidence is the angle between the incidence vector of the projector radiation and the interior-side surface normal (i.e., the surface normal to the interior-side external surface of the side window) in the geometric center of the irradiated area of ​​the side window. 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°. Ideally, the angle of incidence should be as close to this Brewster angle as possible.However, angles of incidence of 65°, for example, can also be used, which are common for HUD projection arrangements, can be easily implemented in vehicles and deviate only slightly from the Brewster angle, so that the reflection of the p-polarized radiation increases only insignificantly.

[0018] The higher the proportion of p-polarized radiation in the total radiation of the projector, the more intense the desired projection image and the less intense unwanted reflections on the surfaces of the side window. The p-polarized radiation component of the projector is preferably at least 50%, more preferably at least 70%, most preferably at least 80%, and in particular at least 90%. In a particularly advantageous embodiment, the radiation from the projector is essentially purely p-polarized - the p-polarized radiation component is therefore 100% or deviates only insignificantly therefrom. The direction of polarization refers to the plane of incidence of the radiation on the side window. 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 defined by the incidence vector and the surface normal of the side plate at the geometric center of the irradiated area.

[0019] According to the invention, the side pane is provided with a reflective coating suitable for reflecting p-polarized radiation. The side pane provided with the reflective coating preferably has an average reflectance of at least 15%, particularly preferably at least 20%, and most particularly preferably at least 25%, relative to p-polarized radiation in the spectral range from 400 nm to 650 nm, which is particularly interesting for display by entertainment projectors. This produces a sufficiently intense projection image. The reflectance is measured at an angle of incidence of 65° to the interior surface normal, which roughly corresponds to the irradiation by conventional projectors.

[0020] The reflectance describes the proportion of the total incident radiation that is reflected. It is expressed as a percentage (relative to 100% incident radiation) or as a unitless number from 0 to 1 (normalized to the incident radiation). Plotted as a function of wavelength, it forms the reflection spectrum.

[0021] To achieve the most color-neutral display of the projector image, the reflection spectrum should be as smooth as possible and exhibit no pronounced local minima and maxima. Deviations at the edge of the relevant spectral range from 400 nm to 650 nm are less disruptive and can be accepted, but in the spectral range from 450 nm to 600 nm, the difference between the maximum reflectance and the mean reflectance, as well as the difference between the minimum reflectance and the mean reflectance, should, in a preferred embodiment, be no more than 7%, more preferably no more than 3%, and most preferably no more than 2.5%. Here, too, the reflectance relative to p-polarized radiation, measured at an angle of incidence of 65° to the interior surface normal, should be used.In a particularly advantageous embodiment, the above-mentioned preferred values ​​apply to the spectral range from 420 nm to 600 nm, instead of only from 450 nm to 600 nm.

[0022] The information on the reflectance or the reflection spectrum refers to a reflection measurement with a light source that radiates uniformly in the spectral range under consideration with a standardized radiation intensity of 100%.

[0023] Preferably, at least 80% of the pane surface is provided with the reflective coating according to the invention. In particular, the reflective coating is applied over the entire surface of the pane, optionally with the exception of a peripheral edge region and / or local areas that serve as communication, sensor, or camera windows to ensure the transmission of electromagnetic radiation through the composite pane and are therefore not provided with the coating. The peripheral uncoated edge region has a width of up to 20 cm, for example. It prevents direct contact of the coating with the surrounding atmosphere, so that the coating inside the composite pane is protected from corrosion and damage. An uncoated peripheral edge region and any communication windows are particularly useful when the reflective coating comprises electrically conductive, metal-containing layers.

[0024] The reflective coating is preferably a thin-film stack, i.e., a sequence of thin individual layers. The layer sequence comprises alternating layers with high refractive index and low refractive index. By appropriately selecting the materials and layer thicknesses, the reflective behavior of such a layer sequence can be specifically adjusted due to interference effects. This makes it possible to realize a reflective coating with effective reflection of p-polarized radiation in the visible spectral range. The layers with a high refractive index (optically high-index layers) have a refractive index greater than 1.8. The layers with a low refractive index (optically low-index layers) have a refractive index less than 1.8. The top and bottom layers of the thin-film stack are preferably optically high-index layers.

[0025] In one embodiment (not claimed), all high- and low-refractive-index layers, in particular all layers of the reflective coating, are formed as dielectric layers. The optically high-refractive-index layers are preferably based on silicon nitride, tin-zinc oxide, silicon zirconium nitride, or titanium oxide, particularly preferably based on silicon nitride. The optically low-refractive-index layers are preferably based on silicon oxide. Other materials on which the optically high-refractive-index layers can be formed are zirconium oxide, niobium oxide, hafnium oxide, tantalum oxide, tungsten oxide, silicon carbide, or diamond-like carbon (DLC). Other materials on which the optically low-refractive-index layers can be formed are aluminum oxide, magnesium fluorite, silicon oxynitride, or calcium fluorite. The total number of high- and low-refractive-index layers is preferably from 8 to 15.This makes it possible to design the reflection properties appropriately without making the layer structure too complex.

[0026] The layer thicknesses of the dielectric layers should preferably be from 30 nm to 500 nm, particularly preferably from 50 nm to 300 nm.

[0027] If a layer is formed on the basis of a material, the layer consists predominantly of this material in addition to any impurities or dopants.

[0028] According to the invention, the reflective coating comprises, in addition to the dielectric layers, at least one electrically conductive layer, in particular a metal-containing layer. Preferably, the reflective coating comprises precisely one electrically conductive layer. It has been shown that such a conductive layer is suitable for smoothing the reflection spectrum of the reflective coating in the visible range, thus achieving a more color-neutral display of the projector image. Furthermore, electrically conductive layers reflect IR radiation, thus improving thermal comfort by reflecting IR components of solar radiation and consequently reducing the amount of heat that can be generated in the interior. The total number of high- and low-refractive-index layers is preferably between 5 and 10. This allows for a suitable design of the reflective properties without making the layer structure too complex.The presence of the electrically conductive layer reduces the number of layers required to achieve a suitable design of the reflection properties.

[0029] According to the invention, at least one, in particular exactly one, of the optically low-refractive-index layers is formed as a metal-containing layer, while the remaining optically high- and low-refractive-index layers are formed as dielectric layers. The conductive layer is then arranged between two optically high-refractive-index dielectric layers, without an optically low-refractive-index layer being arranged between the conductive layer and said high-refractive-index layers. The above statements apply to the preferred materials and layer thicknesses of the dielectric layers.

[0030] The electrically conductive layer is preferably based on silver. The conductive layer preferably contains at least 90 wt.% silver, more preferably at least 99 wt.% silver, most preferably at least 99.9 wt.% silver. Alternatively, other electrically conductive materials can also be provided, for example gold, copper, or aluminum, or transparent conductive oxides (TCO) such as indium tin oxide (ITO). Commonly used silver-based conductive layers have a refractive index of approximately 0.015 and are therefore well suited as optically low-refractive-index layers. The layer thickness of the conductive layer is preferably from 5 nm to 20 nm, more preferably from 8 nm to 12 nm.

[0031] It is generally preferred that adjacent high and low refractive index layers have direct contact with each other and that no further layers are arranged in between.

[0032] In one embodiment (not claimed), the reflective coating comprises the following layer sequence starting from the substrate on which the coating is deposited: an optically high-refractive-index layer with a thickness of 80 nm to 100 nm, preferably from 92 nm to 95 nm, an optically low-refractive-index layer with a thickness of 40 nm to 60 nm, preferably from 50 nm to 53 nm, an optically high-refractive-index layer with a thickness of 120 nm to 140 nm, preferably from 126 nm to 129 nm, an optically low-refractive-index layer with a thickness of 100 nm to 120 nm, preferably from 106 nm to 109 nm, an optically high-refractive-index layer with a thickness of 60 nm to 80 nm, preferably from 67 nm to 70 nm, an optically low-refractive-index layer with a thickness of 100 nm to 120 nm, preferably from 120 nm to 115 nm, an optically high-refractive-index layer with a thickness of 60 nm to 80 nm, preferably from 68 nm to 71 nm, an optically low-refractive-index layer with a thickness of 100 nm to 120 nm, preferably from 107 nm to 110 nm, an optically highly refractive layer with a thickness of 30 nm to 50 nm, preferably from 40 nm to 43 nm,an optically low-refractive layer with a thickness of 50 nm to 70 nm, preferably from 60 nm to 63 nm, an optically high-refractive layer with a thickness of 200 nm to 220 nm, preferably from 211 nm to 214 nm. ,

[0033] The optically high-refractive-index layers have a refractive index greater than 1.8, while the optically low-refractive-index layers have a refractive index less than 1.8. The reflective coating particularly preferably consists of the aforementioned layers. The optically high-refractive-index and low-refractive-index layers are preferably dielectric layers. Preferred materials for the optically high-refractive-index layers are silicon nitride, tin-zinc oxide, silicon zirconium nitride, zirconium oxide, niobium oxide, hafnium oxide, tantalum oxide, tungsten oxide, titanium oxide, silicon carbide, or diamond-like carbon (DLC). Preferred materials for the optically low-refractive-index layers are silicon oxide, aluminum oxide, magnesium fluorite, silicon oxynitride, or calcium fluorite. The optically high-refractive-index and low-refractive-index layers are therefore preferably formed from these materials.

[0034] In one embodiment (not claimed), the reflective coating comprises the following layer sequence starting from the substrate on which the coating is deposited: an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 80 nm to 100 nm, preferably from 92 nm to 95 nm, an optically low-refractive-index layer based on silicon dioxide with a thickness of 40 nm to 60 nm, preferably from 50 nm to 53 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 120 nm to 140 nm, preferably from 126 nm to 129 nm, an optically low-refractive-index layer based on silicon dioxide with a thickness of 100 nm to 120 nm, preferably from 106 nm to 109 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, Silicon zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 60 nm to 80 nm, preferably 67 nm to 70 nm,an optically low-refractive-index layer based on silicon dioxide with a thickness of 100 nm to 120 nm, preferably from 120 nm to 115 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 60 nm to 80 nm, preferably from 68 nm to 71 nm, an optically low-refractive-index layer based on silicon dioxide with a thickness of 100 nm to 120 nm, preferably from 107 nm to 110 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 30 nm to 50 nm, preferably from 40 nm to 43 nm, an optically low-refractive-index layer based on silicon dioxide with a thickness of 50 nm to 70 nm, preferably from 60 nm to 63 nm, an optically highly refractive layer based on silicon nitride, tin-zinc oxide, silicon zirconium nitride or titanium oxide, preferably silicon nitride,with a thickness of 200 nm to 220 nm, preferably from 211 nm to 214 nm. The reflective coating particularly preferably consists of the layers mentioned above. ,

[0035] In a particularly advantageous embodiment, with which particularly good results are achieved, the reflective coating comprises the following layer sequence, starting from the substrate on which the coating is deposited: an optically high-refractive-index layer with a thickness of 260 nm to 280 nm, preferably from 268 nm to 271 nm, an optically low-refractive-index layer with a thickness of 110 nm to 130 nm, preferably from 121 nm to 124 nm, an optically high-refractive-index layer with a thickness of 80 nm to 100 nm, preferably from 89 nm to 92 nm, a metal-containing optically low-refractive-index layer, in particular based on silver, with a thickness of 5 nm to 15 nm, preferably from 8 nm to 10 nm, an optically high-refractive-index layer with a thickness of 230 nm to 250 nm, preferably from 236 nm to 239 nm, an optically low-refractive-index layer with a thickness of 190 nm to 210 nm, preferably from 197 nm to 200 nm, an optically high-refractive-index layer with a thickness of 120 nm to 140 nm, preferably from 132 nm to 136 nm.

[0036] The optically high-refractive-index layers have a refractive index greater than 1.8, while the optically low-refractive-index layers have a refractive index less than 1.8. The reflective coating particularly preferably consists of the aforementioned layers. The optically high-refractive-index and low-refractive-index layers are preferably dielectric layers, with the exception of the metal-containing optically low-refractive-index layer. Preferred materials for the optically high-refractive-index layers are silicon nitride, tin-zinc oxide, silicon zirconium nitride, zirconium oxide, niobium oxide, hafnium oxide, tantalum oxide, tungsten oxide, titanium oxide, silicon carbide, or diamond-like carbon (DLC). Preferred materials for the dielectric optically low-refractive-index layers are silicon oxide, aluminum oxide, magnesium fluorite, silicon oxynitride, or calcium fluorite. The optically high-refractive-index and low-refractive-index layers are therefore preferably formed from these materials.

[0037] In a particularly advantageous embodiment, with which particularly good results are achieved, the reflective coating comprises the following layer sequence, starting from the substrate on which the coating is deposited: an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 260 nm to 280 nm, preferably from 268 nm to 271 nm, an optically low-refractive-index layer based on silicon dioxide with a thickness of 110 nm to 130 nm, preferably from 121 nm to 124 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 80 nm to 100 nm, preferably from 89 nm to 92 nm, a layer based on silver with a thickness of 5 nm to 15 nm, preferably from 8 nm to 10 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 230 nm to 250 nm, preferably from 236 nm to 239 nm,an optically low-refractive-index layer based on silicon dioxide with a thickness of 190 nm to 210 nm, preferably from 197 nm to 200 nm, an optically high-refractive-index layer based on silicon nitride, tin-zinc oxide, silicon zirconium nitride or titanium oxide, preferably silicon nitride, with a thickness of 120 nm to 140 nm, preferably from 132 nm to 136 nm. The reflective coating particularly preferably consists of the aforementioned layers.

[0038] If a first layer is arranged above a second layer, this means, within the meaning of the invention, that the first layer is arranged further away from the substrate to which the coating is applied than the second layer. If a first layer is arranged below a second layer, this means, within the meaning of the invention, that the second layer is arranged further away from the substrate than the first layer. If a first layer is arranged above or below a second layer, this does not necessarily mean, within the meaning of the invention, that the first and second layers are in direct contact with one another. One or more further layers can be arranged between the first and second layers, unless this is explicitly excluded.

[0039] The given values ​​for refractive indices are measured at a wavelength of 550 nm.

[0040] The side pane, or in the case of a composite pane the outer pane and the inner pane, is preferably made of glass, in particular soda-lime glass, which is common for window panes. The side pane, or its individual panes, can in principle 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 side pane can vary widely. In the case of a composite pane, individual panes with a thickness in the range of 0.8 mm to 5 mm, more preferably 1.4 mm to 2.5 mm, are preferably used, for example those with the standard thicknesses of 1.6 mm or 2.1 mm. In the case of a monolithic pane, thicknesses of 2 mm to 5 mm are common.

[0041] The side window, or individual or all of its components, can be clear and colorless, but also tinted or colored. Non-tempered, semi-tempered, or tempered glass can be used. The side window is preferably curved in one or more directions, as is common for automotive windows, with typical radii of curvature ranging from approximately 10 cm to approximately 40 m. However, the side window can also be flat, for example, if it is intended for buses, trains, or tractors.

[0042] In the case of a composite pane, the thermoplastic intermediate layer contains at least one thermoplastic polymer, preferably ethylene-vinyl acetate (EVA), polyvinyl butyral (PVB), or polyurethane (PU), or mixtures or copolymers or derivatives thereof, particularly preferably PVB. The intermediate layer is typically formed from a thermoplastic film. The thickness of the intermediate layer is preferably from 0.2 mm to 2 mm, particularly preferably from 0.3 mm to 1 mm.

[0043] The projector is preferably an LCD projector, in particular a TFT projector, an LED projector, or an OLED projector. The projector is particularly a film projector, i.e., a projector suitable for playing films. The projector is particularly preferably designed as a dual projector, capable of simultaneously illuminating the two opposite side panels.

[0044] The invention further encompasses a method for producing a projection arrangement according to the invention, wherein a vehicle side window is provided with a reflective coating suitable for reflecting p-polarized radiation, and then a projector, whose radiation is predominantly p-polarized, is directed onto a region of the side window in a defined relative arrangement. The above-described statements regarding preferred embodiments apply accordingly.

[0045] The reflective coating is preferably applied by physical vapor deposition (PVD), particularly preferably by cathode sputtering, most preferably by magnetic field assisted cathode sputtering.

[0046] If the side window is a composite pane, the reflective coating is applied to the inner pane or the outer pane, or alternatively, provided on a carrier film. The outer pane and the inner pane are laminated together via the intermediate layer, for example, using an autoclave process, vacuum bag process, vacuum ring process, calender process, vacuum laminator, or combinations thereof. Any carrier film with a reflective coating is inserted between two thermoplastic films of the intermediate layer. The bonding of the outer pane and the inner pane is usually achieved under the influence of heat, vacuum, and / or pressure.

[0047] If the side pane is to be curved, it is preferably subjected to a bending process after any coating processes. In the case of a composite pane, the individual panes are preferably bent before lamination. Preferably, the outer and inner panes are bent congruently together (i.e., simultaneously and using the same tool), as this ensures the shape of the panes is optimally matched for subsequent lamination. Typical temperatures for glass bending processes are, for example, 500°C to 700°C.

[0048] The invention further encompasses the use of a vehicle side window equipped with a reflective coating suitable for reflecting p-polarized radiation as a projection surface for a projector whose radiation is predominantly p-polarized. The reflective coating comprises alternating optically high-refractive-index layers with a refractive index greater than 1.8 and optically low-refractive-index layers with a refractive index less than 1.8. At least one of the optically low-refractive-index layers is designed as an electrically conductive layer, while the optically high-refractive-index layers and the remaining optically low-refractive-index layers are designed as dielectric layers. The projection arrangement thus realized is preferably used for displaying entertainment content, in particular films, for the rear vehicle occupants. The preferred embodiments described above apply accordingly.The projection arrangement is preferably used in a motor vehicle, in particular a passenger car or truck, wherein the side window is a rear side window.

[0049] 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.

[0050] They show: Fig. 1 a schematic representation of an embodiment of the projection arrangement according to the invention, Fig. 2 a cross section through an embodiment of a vehicle side window as a component of the projection arrangement according to the invention, Fig. 3 a cross section through an embodiment of the reflective coating (not claimed), Fig. 4 a cross section through an embodiment of the reflective coating according to the invention, Fig. 5 reflection spectra of composite panes which are provided with coatings of theFigures 3 and 4 are equipped.

[0051] Figure 1shows an example of a projection arrangement according to the invention. The projection arrangement comprises a projector 4, which is mounted in the area of ​​a vehicle roof 6. The projector is a dual-film projector that emits p-polarized radiation (indicated by dashed arrows). The projection arrangement further comprises the two rear side windows 10 of the vehicle, which serve as a projection surface for the projector 4. The side windows 10 are provided with a reflective coating (not specifically shown) which is suitable for reflecting the p-polarized radiation of the projector 4. The reflection of the radiation from the projector 4 by the side windows 10 generates virtual images 7, which are perceived by the viewers 5 - the rear vehicle occupants - on the sides of the side windows 10 facing away from them. The projector 4 can thus display a film that appears, as it were, behind the windows in the surrounding landscape.

[0052] The projector 4 illuminates the side windows 10 at an angle of incidence of, for example, approximately 65°, which is close to the Brewster angle. Therefore, the p-polarized radiation is barely reflected by the external window surfaces. Instead, reflection occurs almost exclusively at the reflective coating as the sole reflective surface. Ghost images, which would be caused by reflection from both external surfaces of the side window 10 when using s-polarized radiation, can thus be avoided.

[0053] Figure 2shows the structure of one embodiment of the vehicle side window 10. The side window 10 is designed as a composite pane and is composed of an outer pane 1 and an inner pane 2, which are connected to one another via a thermoplastic intermediate layer 3. The outer pane 1 faces the outside environment in the installed position, and the inner pane 2 faces the vehicle interior. The outer pane 1 has an outside surface I, which faces the outside environment in the installed position, and an inside surface II, which faces the interior in the installed position. Likewise, the inner pane 2 has an outside surface III, which faces the outside environment in the installed position, and an inside surface IV, which faces the interior in the installed position. A reflective coating 20, which is suitable for reflecting p-polarized radiation, is applied to the outside surface III of the inner pane 2.The outer pane 1 and the inner pane 2 are made of soda-lime glass, for example. The outer pane 1 has a thickness of 2.1 mm, for example, and the inner pane 2 has a thickness of 1.6 mm. The intermediate layer 3 is made of a PVB film, for example, with a thickness of 0.76 mm.

[0054] Figure 3shows the layer sequence of a reflective coating 20 not according to the invention. The coating 20 is a stack of thin films, with a total of six dielectric, optically high-refractive-index layers 21 (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) and five dielectric, optically low-refractive-index layers 22 (22.1, 22.2, 22.3, 22.4, 22.5) being deposited alternately on the substrate (inner pane 2). The optically high-refractive-index layers 21.1, 21.2, 21.3, 21.4, 21.5, 21.6 are based on silicon nitride (SiN) with a refractive index of 2.04. The optically low-refractive layers 22.1, 22.2, 22.3, 22.4, 22.5 are based on silicon oxide (SiO) with a refractive index of 1.47.

[0055] The layer sequence is shown schematically in the figure. The layer sequence of a side pane 10 formed as a composite pane with the coating 20 on the outer surface III of the inner pane 2 is also shown in Table 1, along with the materials and layer thicknesses of the individual layers. Table 1 material Reference symbol Layer thickness Soda-lime glass 1 2.1 mm PVB 3 0.76 mm SiN 21.6 212.8 nm SiO 22.5 61.8 nm SiN 21.5 41.7 nm SiO 22.4 108.8 nm SiN 21.4 69.7 nm SiO 20 22.3 113.2 nm SiN 21.3 68.6 nm SiO 22.2 107.4 nm SiN 21.2 127.4 nm SiO 22.1 51.3 nm SiN 21.1 93.1 nm Soda-lime glass 2 1.6 mm

[0056] Figure 4shows the layer sequence of an advantageous embodiment of the reflective coating 20 according to the invention. The coating 20 is a stack of thin films, with a total of four dielectric, optically high-refractive-index layers 21 (21.1, 21.2, 21.3, 21.4) and three optically low-refractive-index layers 22 (22.1, 22.2, 22.3) being deposited alternately on the substrate (inner pane 2). The optically high-refractive-index layers 21.1, 21.2, 21.3, 21.4 are also based on silicon nitride (SiN). The middle optically low-refractive-index layer 22.2 is formed as an electrically conductive layer based on silver (Ag), while the remaining optically low-refractive-index layers 22.1, 22.3 are formed as dielectric layers based on silicon oxide (SiO).

[0057] The layer sequence is shown schematically in the figure. The layer sequence of a side pane 10 formed as a composite pane with the coating 20 on the outer surface III of the inner pane 2 is also shown in Table 2, along with the materials and layer thicknesses of the individual layers. Table 2 material Reference symbol Layer thickness Soda-lime glass 1 2.1 mm PVB 3 0.76 mm SiN 20 21.4 134.0 nm SiO 22.3 198.1 nm SiN 21.3 237.8 nm Ag 22.2 9.1 nm SiN 21.2 90.4 nm SiO 22.1 122.1 nm SiN 21.1 269.7 nm Soda-lime glass 2 1.6 mm

[0058] Figure 5 shows reflection spectra of a composite pane 10 as in Figure 2, each with a layer structure according to Table 1 and Table 2. The reflection spectrum was recorded with a light source emitting p-polarized radiation of uniform intensity in the spectral range under consideration, with irradiation via the inner pane (the so-called interior reflection) at an incidence angle of 65° to the interior surface normal. The reflection measurement thus approximates the situation in the projection setup.

[0059] The purely dielectric layer structure according to Table 1 results in an average reflectance of 27% in the spectral range from 400 nm to 650 nm, while the layer structure with the silver layer according to Table 2 results in an average reflectance of 27%. Both reflective coatings 20 are therefore suitable for effectively reflecting the p-polarized radiation of typical film projectors in the spectral range and thus producing the desired projection image.

[0060] It can be seen that the silver layer of the reflective coating leads to a significant smoothing of the reflection spectrum according to Table 2. In the spectral range from 450 nm to 600 nm, the mean value for the dielectric layer structure according to Table 1 is 28%, the minimum is 23%, and the maximum is 32%. The difference between the maximum reflectance and the mean is therefore 4%, and the difference between the minimum reflectance and the mean is 5%. In contrast, the mean value for the layer structure according to Table 2 is 30%, the minimum is 28%, and the maximum is 32%. The difference between the maximum reflectance and the mean is therefore 2%, and the difference between the minimum reflectance and the mean is also 2%. In the spectral range from 420 nm to 600 nm, the mean value for the dielectric layer structure according to Table 1 is 29%, the minimum is 23% and the maximum is 32%.The difference between the maximum reflectance and the mean is 3%, and the difference between the minimum reflectance and the mean is 6%. In contrast, the mean for the layer structure according to Table 2 is 30%, the minimum is 28%, and the maximum is 32%. The difference between the maximum reflectance and the mean is 2%, and the difference between the minimum reflectance and the mean is also 2%. The smoothing of the reflection spectrum by the silver layer results in a more color-neutral reproduction of the projector image.

[0061] Table 3 lists some optical values ​​of the coated side windows that are familiar to those skilled in the art and are commonly used to characterize vehicle windows. RL stands for the integrated light reflection and TL for the integrated light transmission (according to ISO 9050). The values ​​after RL or TL indicate the light source used, where A stands for light source A and HUD stands for a HUD projector with radiation wavelengths of 473 nm, 550 nm, and 630 nm (RGB), which was used here as an example model for a film projector. The angle specified after the type of light indicates the angle of incidence of the radiation to the outside surface normal. Angles of incidence less than 90° therefore indicate outside irradiation, and angles of incidence greater than 90° indicate interior irradiation.The specified angle of incidence of 115° corresponds to an angle of incidence to the interior surface normal of 65° (=180°-115°) and simulates irradiation with the projector according to the invention. When determining the integral reflection values ​​RL, the observation angle is 2°. Below the reflection values ​​are the corresponding color values ​​a* and b* in the L*a*b* color space, followed by the light source used (D65 light source and HUD projector) and the observation angle (angle at which the light beam enters the eye and hits the retina).

[0062] TTS ISO 13837 stands for the total solar energy received, measured according to ISO 13837, and is a measure of thermal comfort.

[0063] The panes exhibit relatively low light transmission and a distinct color cast when reflected from the outside. This plays a minor role for rear side windows, because the requirements for transmission and color neutrality are less stringent here than for windshields and front side windows. Good reflection values ​​and good color neutrality are achieved for the projector image shown (RL HUD p-pol. 115°). The TTS value is advantageously low for both coatings, whereby the layer structure shown in Table 2, due to the silver layer, further reduced the incident solar energy despite a smaller total number of layers. Table 3 Layer structure Table 1 Layer structure Table 2 RLA 8° / % 58,3 40,2 a* (D65 / 10°) -5,6 -15,9 b* (D65 / 10°) 36,4 22,3 RL A60° / % 53,5 43,0 a* (D65 / 10°) -4,2 0,4 b* (D65 / 10°) 3,1 -0,5 RL HUD p-pol. 115° / % 28,7 29,7 a* (HUD / 10°) -3,5 -0,4 b* (HUD / 10°) 1,5 -0,1 TL A 0° / % 38,7 56,1 TTS ISO 13837 / % 57,3 55,7 List of reference symbols:

[0064] (10) Vehicle side window (1) Outer pane (2) Inner pane (3) Thermoplastic intermediate layer (4) Projector (5) Viewer (6) Vehicle roof (7) Virtual image (20) Reflective coating (21) Optically high-refractive-index layer (21.1), (21.2), (21.3), (21.4), (21.5), (21.6) 1st, 2nd, 3rd, 4th, 5th, 6th optically high-refractive-index layer (22) Optically low-refractive-index layer (22.1), (22.2), (22.3), (22.4), (22.5) 1st, 2nd, 3rd, 4th, 5th optically low-refractive-index layer (I) Outside surface of the outer pane 1 facing away from the intermediate layer 3 (II) Interior surface of the outer pane 1 facing towards the intermediate layer 3 (III) Outside surface facing towards the intermediate layer 3 facing surface of the inner pane 2 (IV) interior-side surface of the inner pane 2 facing away from the intermediate layer 3

Claims

1. Projection arrangement for a vehicle, at least comprising - a vehicle window provided with a reflective coating (20), and - a projector (4) directed at a region of the vehicle window, wherein the radiation of the projector (4) is predominantly p-polarised and the reflective coating (20) is suitable for reflecting p-polarised radiation, and wherein the reflective coating (20) alternately comprises optically high-refractive layers (21) with a refractive index greater than 1.8 and optically low-refractive layers (22) with a refractive index less than 1.8, characterised in that - the vehicle window is a vehicle side window (10) and - at least one of the optically low-refractive layers (22.2) is designed as an electrically conductive layer, while the optically high-refractive layers (21) and the remaining optically low-refractive layers (22.1, 22.3) are designed as dielectric layers.

2. Projection arrangement according to claim 1, wherein the vehicle side window (10) having the reflective coating (20), in the spectral range from 400 nm to 650 nm, has an average reflectance with respect to p-polarised radiation of at least 15%, preferably at least 20%, particularly preferably at least 25%.

3. Projection arrangement according to claim 2, wherein in the spectral range from 450 nm to 600 nm, the difference between the maximum reflectance and the mean value of the reflectance as well as the difference between the minimum reflectance and the mean value of the reflectance is at most 3%.

4. Projection arrangement according to any of claims 1 to 3, wherein the radiation of the projector (4) is substantially purely p-polarised.

5. Projection arrangement according to any of claims 1 to 4, wherein the radiation of the projector (4) strikes the vehicle side window (10) at an angle of incidence of 45° to 70°.

6. Projection arrangement according to any of claims 1 to 5, wherein the dielectric optically high-refractive layers (21) are formed based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide and wherein the dielectric optically low-refractive layers (22) are formed based on silicon oxide.

7. Projection arrangement according to any of claims 1 to 6, wherein the electrically conductive layer is formed based on silver.

8. Projection arrangement according to any of claims 1 to 7, wherein the reflective coating (20) comprises the following layers: - an optically high-refractive layer (21.1) based on silicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, having a thickness of 260 nm to 280 nm, preferably of 268 nm to 271 nm, - thereupon, an optically low-refractive layer (22.1) based onsilicon dioxide, having a thickness of 110 nm to 130 nm, preferably of 121 nm to 124 nm, - thereupon, an optically high-refractive layer (21.2) based onsilicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, having a thickness of 80 nm to 100 nm, preferably of 89 nm to 92 nm, - thereupon, an optically low-refractive layer (22.2) based onsilver, having a thickness of 5 nm to 15 nm, preferably of 8 nm to 10 nm, - thereupon, an optically high-refractive layer (21.3) based onsilicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, having a thickness of 230 nm to 250 nm, preferably of 236 nm to 239 nm, - thereupon, an optically low-refractive layer (22.3) based onsilicon dioxide, having a thickness of 190 nm to 210 nm, preferably of 197 nm to 200 nm, - thereupon, an optically high-refractive layer (21.4) based onsilicon nitride, tin-zinc oxide, silicon-zirconium nitride or titanium oxide, preferably silicon nitride, having a thickness of 120 nm to 140 nm, preferably of 132 nm to 136 nm.

9. Projection arrangement according to any of claims 1 to 8, wherein the vehicle side window (10) is designed as a composite pane, comprising an outer pane (1) and an inner pane (2) which are connected to one another via a thermoplastic intermediate layer (3), and wherein the reflective coating (20) is arranged on the surface (II, III) of the outer pane (1) or the inner pane (2) that faces the intermediate layer (3) or within the intermediate layer (3).

10. Projection arrangement according to claim 9, wherein the external surfaces (I, IV) of the vehicle side window (10) are arranged substantially in parallel with one another.

11. Use of a vehicle side window (10) which is provided with a reflective coating (20) which is suitable for reflecting p-polarised radiation, as a projection surface for a projector (4) of which the radiation is predominantly p-polarised, wherein the reflective coating (20) alternately comprises optically high-refractive layers (21) with a refractive index greater than 1.8 and optically low-refractive layers (22) with a refractive index less than 1.8, and wherein at least one of the optically low-refractive layers (22.2) is designed as an electrically conductive layer, while the optically high-refractive layers (21) and the remaining optically low-refractive layers (22.1, 22.3) are designed as dielectric layers.

12. Use according to claim 11, wherein the projector (4) is used to display entertainment content, in particular films, for the rear vehicle occupants.