Projection device for head-up display (HUD) with p-polarized radiation

Abstract

The invention relates to a projection device for a head-up display (HUD), comprising at least a windshield pane (10) with a HUD region (B), comprising an outer pane (1) and an inner pane (2) joined to one another via a thermoplastic intermediate layer (3); and a projector (4) directed toward the HUD region (B) and emitting p-polarized radiation; wherein a reflective coating (20) suitable for reflecting p-polarized radiation and comprising precisely one conductive layer (21) based on silver is arranged on the surface (II, III) of the outer pane (1) or the inner pane (2) facing the intermediate layer (3) or in the intermediate layer (3); and an emissivity-reducing coating (30) comprising a conductive layer (31) based on a transparent conductive oxide is arranged on the surface (IV) of the inner pane (2) facing away from the intermediate layer (3).

Description

[0001] The invention relates to a projection device for a head-up display and a use thereof.

[0002] Modern cars are increasingly equipped with so-called head-up displays (HUDs). Using a projector, typically in the dashboard area, an image is projected onto the windshield, where it is reflected and perceived by the driver as a virtual image behind the windshield. This allows important information, such as current speed, navigation, or warnings, to be projected into the driver's field of view without him having to take his eyes off the road. As a result, head-up displays can significantly contribute to improving road safety.

[0003] HUD projectors operate primarily with s-polarized radiation and illuminate the windshield at an angle of incidence of approximately 65%, which is close to the Brewster angle of the air-to-glass transition (56.5° for soda-lime glass). The problem that arises here is that the projector image is reflected on both outer surfaces of the windshield. As a result, in addition to the desired main image, a slightly offset secondary image, the so-called "phantom image," appears. This problem is often alleviated by arranging these surfaces at an angle to one another, particularly by laminating windshields designed as composite glass panes using a wedge-shaped interlayer so that the main image and the phantom image overlap. Composite glass with wedge-shaped films for HUDs is known, for example, from WO 2009 / 071135 A1, EP 1 800 855 B1, or EP 1 880 243 A2.

[0004] Wedge films are expensive, so the manufacture of such composite glass panes for HUDs is quite expensive. Therefore, there is a need for a HUD projection device that can suffice through a windshield without a wedge film. For example, a HUD projector can be operated with p-polarized radiation, which has no significant reflection on the surface of the glass pane. Instead, the windshield pane has a reflective coating as a reflective surface for p-polarized radiation. DE102014220189A1 discloses such a HUD projection device that operates with p-polarized radiation. As a reflective structure, a single metal layer, for example made of silver or aluminum, with a thickness of 5 nm to 9 nm is proposed. WO2019046157A1 also discloses a HUD with p-polarized radiation, in which a reflective coating with at least two metal layers is used.

[0005] US2017242247A1 discloses another HUD projection device with a reflective coating for p-polarized radiation. This reflective coating may contain one or more conductive silver layers and a dielectric layer. However, the reflectance spectrum has a pronounced curvature within the relevant spectral range, resulting in a relatively strong dependence of reflectivity on wavelength. This is detrimental to color-neutral HUD projection.

[0006] Many projection devices with improved reflective properties have been proposed, wherein these reflective properties are achieved in particular by optimizing the reflective coating. For example, WO2019179683A1, WO2020094422A1, and WO2020094423A1 propose reflective coatings with multiple silver layers.

[0007] WO2021004685A1 and the subsequently published WO2021104800A1 disclose reflective coatings having a single silver layer, which achieve good reflective properties for p-polarized radiation. Compared to reflective coatings having multiple silver layers, reflective coatings having a single silver layer have the advantage that they are less complex and can therefore be produced more simply and cost-effectively.

[0008] CN 106630688 A and CN 106646874 A disclose projection devices comprising a windshield and a projector with p-polarized radiation. The windshield has a purely dielectric reflective coating on the interior-facing surface of the inner pane for reflecting p-polarized radiation. Furthermore, the windshield is provided with a heatable coating containing a silver layer.

[0009] Also known are vehicle glazing panels equipped with a low-emissivity coating (so-called low-E coatings) that improve the thermal comfort of the vehicle interior by reflecting thermal radiation. Transparent low-emissivity coatings may, for example, contain a functional layer based on indium tin oxide (ITO). For example, see WO2013131667A1 and WO2018206236A1.

[0010] There is still a need for improved projection devices for HUDs that operate with p-polarized radiation, wherein the windshield has a further improved reflection behavior for p-polarized radiation. In particular, the windshield should have high transmittance in the visible spectral range and high reflectivity for p-polarized radiation and allow for a color-neutral display. Furthermore, the windshield should ensure high thermal comfort in the vehicle. The object of the present invention is to provide such an improved projection device.

[0011] According to the invention, this object is achieved by a projection device according to claim 1. Preferred embodiments are derived from the dependent claims.

[0012] The core of the present invention lies in the fact that a windshield pane is equipped with a combination of a reflective coating comprising precisely one silver layer and an emissivity-reducing coating comprising a TCO layer. To produce the HUD image, p-polarized radiation is used. The reflective coating is designed to reflect p-polarized radiation. Since the typical angle of incidence for HUD projection devices is approximately 65°, relatively close to the Brewster angle of the air-to-glass transition (56.5° for soda-lime glass), p-polarized radiation is barely reflected by the glass pane surface and is instead primarily reflected by the conductive coating. Consequently, ghost images are not visible or are barely perceptible, eliminating the need for expensive wedge films. Furthermore, wearers of polarization-selective sunglasses, which typically only allow p-polarized radiation to pass and block s-polarized radiation, can still see the HUD image. It is known that the reflective coating comprising a single silver layer according to the present invention is suitable for good, color-neutral HUD displays. This single silver layer does not excessively reduce light transmittance, so the glass pane can still be used as a windshield pane. The inventors have now surprisingly discovered that the presence of the emissivity-reducing coating leads to further improvements in reflective properties, in particular, a smoothing of the reflection spectrum, thereby enabling an even more color-neutral HUD display. Furthermore, the emissivity-reducing coating improves the thermal comfort of the vehicle by reducing the incoming thermal radiation in summer and reducing the outgoing heat in winter. This is a great advantage of the present invention.

[0013] The projection device for a head-up display (HUD) according to the present invention comprises at least one windshield and a projector (HUD projector). As is common with HUDs, the projector illuminates an area of the windshield where the radiation is reflected toward the observer (driver), thereby generating a virtual image that the observer perceives from behind the windshield. The area of the windshield that can be illuminated by the projector is called the HUD area. The beam direction of the projector can usually be varied by means of a reflector, particularly vertically, to adapt the projection to the observer's body dimensions. The area within which the observer's eyes must be located at a given mirror position is called the eye window. This eye window can be moved vertically by adjusting the mirrors, and the entire area accessible by it (i.e., the sum of all possible eye windows) is called the eye range. Observers within the eye range can perceive the virtual image. Of course, this means that the observer's eyes must be within the eye range, rather than, for example, their entire body.

[0014] The technical terms used here are well-known to those skilled in the art from the field of HUDs. For a detailed description, reference can be made to Alexander Neumann's doctoral dissertation, "Simulations basierte Messtechnik zur Prüfung von Head-Up Displays," from the Institute for Informatics at the Technical University of Munich (Munich: University Library of the Technical University of Munich, 2012), in particular Chapter 2, "Das Head-Up Display."

[0015] The windshield comprises an outer glass pane and an inner glass pane, which are joined together via a thermoplastic interlayer. The windshield is provided for separating an interior from the exterior environment in a window opening of a vehicle. In the context of the present invention, the inner glass pane refers to the glass pane of the windshield facing the interior of the vehicle. The outer glass pane refers to the glass pane facing the exterior environment. The windshield is preferably a windshield of a motor vehicle, in particular a passenger vehicle or a truck.

[0016] A windshield panel has an upper edge and a lower edge, and two side edges extending therebetween. The upper edge refers to the edge that is configured to point upward in the installed position. The lower edge refers to the edge that is configured to point downward in the installed position. The upper edge is often also called the top edge, and the lower edge is called the engine edge.

[0017] The outer and inner glass panes each have an outer side surface and an interior-facing surface, with a circumferential side edge extending therebetween. Within the meaning of the present invention, the outer side surface is understood to be the main surface that is intended to face the exterior environment in the installed position. Within the meaning of the present invention, the interior-facing surface is understood to be the main surface that is intended to face the interior in the installed position. The interior-facing surface of the outer glass pane and the outer side surface of the inner glass pane face one another and are joined to one another via a thermoplastic interlayer.

[0018] The projector is directed toward the HUD area of the windshield. It illuminates the HUD area with radiation in the visible range of the electromagnetic spectrum, specifically in the 450 nm to 650 nm spectral range, such as wavelengths of 473 nm, 550 nm, and 630 nm (RGB), to produce the HUD projection. According to the present invention, the projector emits p-polarized radiation.

[0019] According to the present invention, the windshield is equipped with a reflective coating suitable for reflecting p-polarized radiation. This generates a virtual image from the projector radiation, which the vehicle driver can perceive from his perspective behind the windshield. According to the present invention, the reflective coating comprises precisely one conductive layer based on silver. This conductive layer can also be simply referred to as a silver layer. It has been shown that even with this relatively simple reflective coating, very good reflective properties can be achieved. The reflective coating is disposed on the interior of the windshield, as is common with corrosion-sensitive coatings comprising a silver layer. The reflective coating can be disposed or applied to one of the surfaces of the two glass panes facing the interlayer, namely, the interior-facing surface of the outer glass pane or the outer surface of the inner glass pane. Alternatively, the reflective coating can be disposed within the thermoplastic interlayer, for example, applied to a carrier film disposed between two thermoplastic bonding films.

[0020] The projector radiation directed toward the windshield pane is primarily reflected at the reflective coating, so the reflection with the highest intensity occurs there. This means that the intensity of the projector radiation reflected at the reflective coating is higher than the intensity of the radiation reflected at all other interfaces, in particular, higher than the intensity of the projector radiation reflected at the interior-facing surface of the inner pane and the exterior surface of the outer pane.

[0021] Due to the conductive silver layer, the reflective coating according to the present invention has IR-reflecting properties and thus acts as a sun protection coating, reducing the temperature rise of the vehicle interior by reflecting the infrared portion of solar radiation, particularly in the near-infrared range, for example, in the range of 800 nm to 1500 nm. The reflective coating can also function as a heating coating if electrical contact is made with the reflective coating so that an electric current flows through it and this current heats the reflective coating.

[0022] According to the present invention, the windshield is also provided with an emissivity reducing coating. The emissivity reducing coating is also known as a heat radiation reflecting coating, a low emissivity coating or a low-emissivity coating ( Low emissivity). Emissivity is a measure of how much thermal radiation is emitted into the interior of the glass pane in the installed state compared to an ideal thermal radiator (black body). Emissivity-reducing coatings have the function of preventing heat from being radiated into the interior (the IR portion of solar radiation, in particular the thermal radiation of the glass pane itself) and of preventing thermal radiation from being emitted from the interior. They have reflective properties for infrared radiation, in particular for thermal radiation in the spectral range of 5 µm - 50 µm (see standard DIN EN 12898:2019-06). This effectively improves thermal comfort in the interior. When the outside temperature is high and the solar radiation is high, the emissivity-reducing coating can at least partially reflect the thermal radiation emitted by the entire glass pane toward the interior. When the outside temperature is low, it can reflect the thermal radiation emitted from the interior and thus reduce the effect of the cold glass pane as a heat sink. This is particularly advantageous in electric vehicles that generate less waste heat that can be used to heat the interior.

[0023] According to the invention, the emissivity-reducing coating is arranged on the interior-facing surface of the inner glass pane and comprises at least one, preferably precisely one, conductive layer based on a transparent conductive oxide (TCO). This conductive layer can also be referred to as a TCO layer.

[0024] A windshield pane equipped with a reflective coating and an emissivity-reducing coating preferably has an average reflectivity for p-polarized radiation of at least 10%, particularly preferably at least 15%, in the spectral range from 450 nm to 650 nm. This produces a sufficiently high-intensity projected image. Due to the wavelengths relevant for HUD displays (RGB: 473 nm, 550 nm, 630 nm), the spectral range from 450 nm to 650 nm is used to characterize the reflective properties. The high reflectivity with a relatively simple layer structure is a major advantage of the present invention. Particularly good results are achieved when the reflectivity over the entire spectral range from 450 nm to 650 nm is at least 10%, preferably at least 15%, so that the reflectivity at no point within the indicated spectral range falls below the indicated values.

[0025] The reflectivity describes the proportion of the total incident radiation that is reflected. It is shown in % (based on 100% of the incident radiation) or as a unitless number from 0 to 1 (normalized according to the incident irradiance). Plotted according to wavelength, it forms a reflection spectrum. In the context of the present invention, statements about the reflectivity for p-polarized radiation refer to the reflectivity measured at an angle of incidence of 65° to the surface normal on the interior side (which roughly corresponds to radiation passing through a conventional projector). Data on reflectivity or reflection spectra relate to reflectivity measurements using a light source that radiates uniformly with a normalized radiation intensity of 100% in the spectral range considered.

[0026] To achieve a display of the projector image that is as color-neutral as possible, the reflection spectrum should be as smooth as possible and have no distinct local minima or maxima. In the spectral range of 450 nm to 650 nm, the difference between the maximum reflectivity occurring and the reflectivity mean value, as well as the difference between the minimum reflectivity occurring and the reflectivity mean value, should in a preferred embodiment be at most 1%, particularly preferably at most 0.5%, and very particularly preferably at most 0.2%. Here, the reflectivity for p-polarized radiation measured at an angle of incidence of 65° to the surface normal on the interior side is used. The differences shown are to be understood as absolute deviations in the reflectivity (in %), not as percentage deviations relative to the mean value.

[0027] Alternatively, the standard deviation in the spectral range from 450 nm to 650 nm can be used as a measure of the smoothness of the reflection spectrum. It is preferably less than 1%, particularly preferably less than 0.5%, and very particularly preferably less than 0.2%.

[0028] It is particularly advantageous if the average reflectivity over the entire visible spectral range from 380 nm to 780 nm is at least 10%, preferably at least 15%, and if the difference between the maximum reflectivity occurring in this spectral range and the average reflectivity and the difference between the minimum reflectivity occurring in this spectral range and the average reflectivity is at most 2%, preferably at most 1.5%. The standard deviation in the spectral range from 380 nm to 780 nm is preferably less than 1%, particularly preferably less than 0.5%. The smoothest possible reflection spectrum in the visible spectral range ensures a color-neutral overall impression of the windshield pane without color deviations.

[0029] The reflective coating is transparent, which, within the meaning of the present invention, means that it has an average transmittance of at least 70%, preferably at least 80%, in the visible spectral range (380 nm to 780 nm) and therefore does not significantly restrict the view through the glass pane. In principle, it is sufficient if the HUD area of the windshield is provided with a reflective coating. However, other areas may also be provided with a reflective coating, and the windshield may be provided with a reflective coating substantially over its entire surface, which may be preferred for manufacturing reasons. In one embodiment of the present invention, at least 80% of the surface of the glass pane is provided with the reflective coating according to the present invention. In particular, the reflective coating is applied over the entire surface of the glass pane, with the exception of surrounding edge regions and optional localized regions that serve as communication, sensor, or camera windows to ensure transmittance of electromagnetic radiation through the windshield pane and are therefore not provided with a reflective coating. For example, the width of the uncoated surrounding edge region can be up to 20 cm. This prevents direct contact between the reflective coating and the surrounding atmosphere, thereby protecting the reflective coating from corrosion and damage within the windshield. The reflective coating is particularly preferably on the outer surface of the inner glass pane, because the projector radiation must then travel the shortest possible path through the windshield pane until it strikes the reflective coating. This is advantageous in terms of the quality of the HUD image.

[0030] The reflective coating is a thin-layer stack, i.e., a sequence of thin monolayers. This thin-layer stack comprises exactly one silver-based conductive layer. The silver-based conductive layer imparts the reflective coating with its basic reflective properties, as well as its infrared reflection effect and electrical conductivity. The reflective coating comprises exactly one silver layer, i.e., no more than one silver layer, and no further silver layers are arranged above or below the reflective coating. A particular advantage of the present invention is that the desired reflective properties can be achieved with a silver layer without excessively reducing the transmittance, as would be the case when using multiple conductive layers. However, further conductive layers may be present that do not significantly contribute to the electrical conductivity of the reflective coating but instead serve other purposes. This applies in particular to metal barrier layers having a geometric thickness of less than 1 nm, which are preferably arranged between the silver layer and the dielectric layer sequence.

[0031] The conductive layer is constructed based on silver (Ag). The conductive layer preferably contains at least 90% by weight of silver, particularly preferably at least 99% by weight of silver, very particularly preferably at least 99.9% by weight of silver. The silver layer may have dopants, for example palladium, gold, copper or aluminum. The geometric layer thickness of the silver layer is preferably at most 15 nm, particularly preferably at most 14 nm, very particularly preferably at most 13 nm. This allows for advantageous reflectivity in the IR range without excessively reducing transmittance. The geometric layer thickness of the silver layer is preferably at least 5 nm, particularly preferably at least 8 nm. Thinner silver layers can lead to dewetting of the layer structure. The geometric layer thickness of the silver layer is particularly preferably from 10 nm to 14 nm or from 11 nm to 13 nm.

[0032] The present invention is not limited to a specific design of the reflective coating. Rather, the reflective coating can be freely selected by those skilled in the art according to the requirements of the individual case, as long as it comprises a single silver layer. Typically, a lower dielectric layer or layer sequence is arranged below the silver layer. Similarly, an upper dielectric layer or layer sequence is typically arranged above the silver layer. The optical properties of the reflective coating, in particular the transmission and reflection spectra, can be influenced by those skilled in the art, in particular by the layer structure, i.e., by selecting the materials and thicknesses of the individual layers and the structure of the dielectric layer sequence. Thus, the reflective coating can be appropriately adjusted. Preferred embodiments of the reflective coating that achieve particularly good results are described below.

[0033] In the context of the present invention, the refractive index is generally given at a wavelength of 550 nm. In principle, the refractive index is independent of the measurement method and can be determined, for example, by ellipsometry. Ellipsometry instruments are commercially available, for example from Sentech. The optical thickness is the product of the geometric thickness and the refractive index (at 550 nm). The optical thickness of a layer sequence is calculated as the sum of the optical thicknesses of the individual layers.

[0034] If the first layer is arranged above the second layer, this means in the sense of the present invention that the first layer is arranged further away from the substrate on which the coating is applied than the second layer. If the first layer is arranged below the second layer, this means in the sense of the present invention that the second layer is arranged further away from the substrate than the first layer.

[0035] If a layer (thin layer) of the coating is formed on the basis of a material, then this layer consists predominantly of this material, in particular essentially of this material and possible impurities or dopants.

[0036] In one advantageous embodiment, the upper and lower dielectric layers or layer sequences each have a refractive index of at least 1.9. This allows for a high reflectivity for p-polarized radiation in the spectral range of 450 nm to 650 nm, which is relevant for HUD displays (HUD projectors typically operate with wavelengths of 473 nm, 550 nm, and 630 nm (RGB)). This results in a high-intensity HUD image. The ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is preferably at least 1.7. Surprisingly, it has been shown that this asymmetry in the optical thickness results in a significantly smoother reflection spectrum for p-polarized radiation, resulting in a relatively constant reflectivity across the entire relevant spectral range (450 nm to 650 nm). This ensures a color-neutral display of the HUD projection. The optical thickness ratio is calculated as the quotient of the optical thickness of the upper dielectric layer or layer sequence (dividend) divided by the optical thickness of the lower dielectric layer or layer sequence (divisor). In a particularly preferred embodiment, the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.8, particularly preferably at least 1.9. Particularly good results are achieved thereby.

[0037] In a particularly advantageous embodiment, the reflective coating does not include any dielectric layers with a refractive index of less than 1.9. All dielectric layers of the reflective coating therefore have a refractive index of at least 1.9. A particular advantage of the present invention is that the desired reflective properties can be achieved using only relatively high-refractive-index dielectric layers. Because silicon oxide layers, which have a low deposition rate in magnetic-field-assisted cathode deposition, are particularly suitable for low-refractive-index layers with a refractive index of less than 1.9, the reflective coating according to the present invention can be produced quickly and cost-effectively.

[0038] The reflective coating generally comprises, independently of one another, a dielectric layer or a sequence of dielectric layers having a refractive index of at least 1.9 above and below the silver layer. The dielectric layer can be constructed, for example, on the basis of silicon nitride, zinc oxide, zinc tin oxide, silicon-metal mixed nitrides, such as silicon zirconium nitride, zirconium oxide, niobium oxide, hafnium oxide, tantalum oxide, tungsten oxide or silicon carbide. The oxides and nitrides mentioned can be deposited stoichiometrically, substoichiometrically or superstoichiometrically. They can have dopants, such as aluminum, zirconium, titanium or boron. By means of the dopants, a certain electrical conductivity can be imparted to the material, which is itself dielectric. However, a person skilled in the art will recognize them as dielectric layers in terms of their function, as is common in the field of thin films. The material of the dielectric layer preferably has a relative density of less than 10 -4 The material of the conductive layer preferably has an electrical conductivity greater than 10 4 The conductivity is S / m.

[0039] The optical thickness of the upper dielectric layer or layer sequence is preferably 100 nm to 200 nm, particularly preferably 130 nm to 180 nm, and very particularly preferably 160 nm to 180 nm. The optical thickness of the lower dielectric layer or layer sequence is preferably 50 nm to 120 nm, particularly preferably 50 nm to 100 nm or 80 nm to 120 nm, and very particularly preferably 80 nm to 100 nm. This achieves good results.

[0040] In a particularly advantageous embodiment, a dielectric layer is arranged above and below the silver layer, which can be referred to as an antireflection layer and is preferably based on an oxide, for example tin oxide and / or a nitride, for example silicon nitride, particularly preferably based on silicon nitride (Si3N4). Silicon nitride has proven to be advantageous due to its optical properties, its easy availability and its high mechanical and chemical stability. Silicon is preferably doped, for example with aluminum or boron. In the case of a dielectric layer sequence, the layer based on silicon nitride is preferably the uppermost layer of the upper layer sequence or the lowermost layer of the lower layer sequence. The geometric thickness of the upper antireflection layer is preferably 50 nm to 100 nm, particularly preferably 55 nm to 80 nm, in particular 60 nm to 70 nm. The geometric thickness of the lower antireflection layer is preferably 10 nm to 50 nm, particularly preferably 15 nm to 40 nm, very particularly preferably 20 nm to 35 nm, in particular 20 nm to 30 nm.

[0041] In addition to the antireflection layer, further dielectric layers with a refractive index of at least 1.9 may optionally be present. Thus, the upper and lower layer sequences may independently comprise an adaptation layer which improves the reflectivity of the silver layer. The adaptation layer is preferably constructed based on zinc oxide (ZnO), particularly preferably zinc oxide ZnO. 1-δ , where 0 ≤ δ ≤ 0.01. The adaptor layer also preferably contains a dopant. The adaptor layer may comprise, for example, aluminum-doped zinc oxide (ZnO:Al). The zinc oxide is preferably deposited in a substoichiometric amount with respect to oxygen to prevent excess oxygen from reacting with the silver-containing layer. The adaptor layer is preferably arranged between the silver layer and the antireflection layer. The geometric thickness of the adaptor layer is preferably 5 nm to 30 nm, particularly preferably 8 nm to 12 nm.

[0042] A refractive index-increasing layer having a higher refractive index than the antireflection layer may also be present, likewise independently of one another in the upper and lower layer sequences. This allows the optical properties, in particular the reflective properties, to be further improved and fine-tuned. The refractive index-increasing layer preferably comprises a silicon-metal mixed nitride, such as a silicon-zirconium mixed nitride, a silicon-aluminum mixed nitride, a silicon-titanium mixed nitride or a silicon-hafnium mixed nitride (SiHfN), particularly preferably a silicon-zirconium mixed nitride (SiZrN). The proportion of zirconium is preferably 15 to 45% by weight, particularly preferably 15 to 30% by weight. Contemplated alternative materials are, for example, WO3, Nb2O5, Bi2O3, TiO2 and / or AlN. The refractive index-increasing layer is preferably arranged between the antireflection layer and the silver layer or between the adaptor layer (if present) and the antireflection layer. The geometric thickness of the refractive index-increasing layer is preferably 5 nm to 30 nm, particularly preferably 5 nm to 15 nm.

[0043] In one embodiment of the reflective coating, exactly one lower dielectric layer with a refractive index of at least 1.9, preferably based on silicon nitride, is arranged below the conductive layer. Similarly, exactly one upper dielectric layer with a refractive index of at least 1.9, preferably based on silicon nitride, is arranged above the conductive layer. This results in the following layer sequence, originating from the substrate: lower antireflection layer - silver layer - upper antireflection layer. The reflective coating preferably contains no further dielectric layers.

[0044] In another embodiment of the reflective coating, a first lower dielectric layer (antireflection layer) and a second lower dielectric layer (matching layer) are arranged below the conductive layer. Similarly, a first upper dielectric layer (antireflection layer) and a second upper dielectric layer (matching layer) are arranged above the conductive layer. The refractive index of the antireflection layer and the matching layer is at least 1.9. The antireflection layer is preferably constructed from silicon nitride, and the matching layer is constructed from zinc oxide. The matching layer is preferably arranged between the respective antireflection layer and the silver layer, resulting in a layer sequence starting from the substrate: lower antireflection layer - lower matching layer - silver layer - upper matching layer - upper antireflection layer. The reflective coating preferably contains no further dielectric layers.

[0045] In another embodiment of the reflective coating, a first lower dielectric layer (antireflection layer), a second lower dielectric layer (adaptation layer), and a third lower dielectric layer (refractive index increasing layer) are arranged below the conductive layer. Similarly, a first upper dielectric layer (antireflection layer), a second upper dielectric layer (adaptation layer), and a third upper dielectric layer (refractive index increasing layer) are arranged above the conductive layer. The antireflection layer, the adaptation layer, and the refractive index increasing layer have a refractive index of at least 1.9. The refractive index increasing layer has a higher refractive index than the antireflection layer, preferably at least 2.1. The antireflection layer is preferably constructed based on silicon nitride, the adaptation layer is constructed based on zinc oxide, and the refractive index increasing layer is based on a silicon-metal mixed nitride, such as a silicon-zirconium mixed nitride or a silicon-hafnium mixed nitride. The adaptation layer is preferably at a minimum distance from the silver layer, while the refractive index increasing layer is arranged between the adaptation layer and the antireflection layer. The resulting layer sequence starting from the substrate is: lower antireflection layer-lower refractive index increasing layer-lower adaptation layer-silver layer-upper adaptation layer-upper refractive index increasing layer-upper antireflection layer. The reflective coating preferably contains no further dielectric layers.

[0046] Since the upper and lower dielectric layer sequences can be formed independently of one another, combinations of the above-mentioned embodiments are also possible, wherein the upper dielectric layer / layer sequence is formed according to one embodiment and the lower dielectric layer / layer sequence is formed according to another embodiment.

[0047] In one advantageous embodiment, the reflective coating includes at least one metallic barrier layer. The barrier layer can be arranged below and / or above the silver layer and is preferably in direct contact with the silver layer. In this case, the barrier layer is located between the silver layer and the dielectric layer / layer sequence. The barrier layer serves to protect the silver layer from oxidation, particularly when the coated glass pane is subjected to temperature treatment, as typically occurs during bending. The barrier layer preferably has a geometric thickness of less than 1 nm, for example, 0.1 nm to 0.5 nm. The barrier layer is preferably constructed from titanium (Ti) or a nickel-chromium alloy (NiCr). It is particularly effective if the barrier layer is directly above the silver layer. Therefore, in one preferred embodiment, the reflective coating has a barrier layer above the silver layer and no barrier layer below it. The silver layer is in direct contact with the lower dielectric layer(s) and indirectly with the upper dielectric layer(s) via the barrier layer. The barrier layer only slightly alters the optical properties of the reflective coating and is preferably present in all of the above-described embodiments. Particularly preferably, the barrier layer is arranged directly above the silver layer, i.e., between the silver layer and the upper dielectric layer(s), where it is particularly effective.

[0048] In a particularly advantageous embodiment, the reflective coating comprises or consists of the following individual layers, proceeding from the substrate surface:

[0049] - a lower antireflection layer, preferably based on Si3N4, preferably having a geometric thickness of 20 nm to 30 nm,

[0050] - a lower refractive index-increasing layer, which is preferably based on SiZrN or SiHfN, preferably having a geometric thickness of 8 nm to 12 nm,

[0051] - a lower adaptor layer, which is preferably based on ZnO and preferably has a geometric thickness of 8 nm to 12 nm,

[0052] - a silver layer, which preferably has a thickness of 11 nm to 13 nm,

[0053] - a barrier layer, which is preferably based on Ti or NiCr and preferably has a geometric thickness of 0.1 nm to 0.5 nm,

[0054] - an upper adaptor layer, which is preferably based on ZnO and preferably has a geometric thickness of 8 nm to 12 nm,

[0055] - an upper refractive index-increasing layer, which is preferably based on SiZrN or SiHfN, preferably having a geometric thickness of 8 nm to 12 nm,

[0056] - an upper antireflection layer, which is preferably based on Si3N4 and preferably has a geometric thickness of 60 nm to 70 nm.

[0057] The emissivity-reducing coating according to the present invention is also transparent, i.e., has an average transmittance of at least 70%, preferably at least 80%, in the visible spectrum. The emissivity-reducing coating is typically applied to the entire surface of the substrate, possibly with the exception of surrounding edge regions and / or other locally defined areas that may be used, for example, for data transmission. The coated proportion of the substrate surface is preferably at least 80%.

[0058] According to the invention, the emissivity-reducing coating comprises a conductive TCO layer. Such a coating is corrosion-resistant and can be applied to exposed surfaces. The refractive index of the TCO layer is preferably between 1.7 and 2.3. The conductive layer is preferably constructed based on indium tin oxide (ITO), which has proven to be particularly useful, in particular due to its low specific resistivity and low deviation in sheet resistance. Alternatively, the conductive layer can also be constructed, for example, based on indium-zinc mixed oxide (IZO), gallium-doped tin oxide (GZO), fluorine-doped tin oxide (FTO, SnO2:F), antimony-doped tin oxide (ATO, SnO2:Sb) or niobium-doped titanium oxide (TiO2:Nb).

[0059] The thickness of the TCO layer is preferably 50 nm to 130 nm, particularly preferably 60 nm to 100 nm, for example 65 nm to 80 nm. This achieves particularly good results with respect to electrical conductivity while at the same time maintaining sufficient optical transparency.

[0060] The invention is also not limited to a specific design of the emissivity-reducing coating, as long as it comprises a TCO layer. Typically, dielectric layers or layer sequences are arranged below and / or above the TCO layer, which significantly influence the optical properties, in particular the transmittance and reflectivity. The emissivity-reducing coating is also a thin-layer stack, i.e., a sequence of thin individual layers. Preferred embodiments of the emissivity-reducing coating that achieve particularly good results are described below.

[0061] So-called anti-radiation or anti-reflection layers, which have a lower refractive index than the TCO layer and are arranged below and above it, have a particular influence on the optical properties. Due in particular to interference effects, these anti-reflection layers can increase the transmittance through the glass pane and reduce the reflectivity. The effect depends primarily on the refractive index and the layer thickness.

[0062] In one advantageous embodiment, the emissivity-reducing coating comprises a dielectric lower antireflection layer arranged below the TCO layer. The refractive index of the lower antireflection layer is preferably at most 1.8, for example, 1.3 to 1.8, particularly preferably at most 1.6, for example, 1.3 to 1.6. The thickness of the lower antireflection layer is preferably 5 nm to 50 nm, preferably 10 nm to 30 nm, for example 10 nm to 20 nm.

[0063] In one advantageous embodiment, the emissivity-reducing coating comprises a dielectric upper antireflection layer arranged above the TCO layer. The refractive index of the upper antireflection layer is preferably at most 1.8, for example, 1.3 to 1.8, particularly preferably at most 1.6, for example, 1.3 to 1.6. The thickness of the upper antireflection layer is preferably 10 nm to 100 nm, particularly preferably 30 nm to 70 nm, for example 45 nm to 55 nm.

[0064] In a particularly advantageous embodiment, the emissivity-reducing coating has a lower antireflection layer located below the TCO layer and an upper antireflection layer located above the TCO layer.

[0065] In particular, the antireflection layer contributes to the favorable optical properties of the glass pane. This increases the transparency of the windshield pane and promotes a neutral color impression. The antireflection layer is preferably based on an oxide or fluoride, particularly preferably on silicon oxide, magnesium fluoride, or calcium fluoride, and in particular on silicon oxide (SiO2). Silicon oxide may have dopants and is preferably doped with aluminum (SiO2:Al), boron (SiO2:B), titanium (SiO2:Ti), or zirconium (SiO2:Zr).

[0066] The upper antireflection layer can be the topmost layer of the coating. In this case, it is at its greatest distance from the substrate surface (the surface of the inner glass pane facing the interior space) and is the final layer of the layer stack, being exposed, accessible, and touchable. However, one or more further individual layers can also be arranged above the upper antireflection layer. Such further layers can, for example, serve to improve scratch protection and be constructed based on zirconium oxide, titanium oxide, or hafnium oxide.

[0067] It has been shown that the oxygen content of the TCO layer has a significant impact on its properties, particularly its transparency and electrical conductivity. The production of glass sheets often involves temperature treatments, such as thermal prestressing and / or bending, during which oxygen can diffuse into the TCO layer and oxidize it. In one advantageous embodiment, the emissivity-reducing coating between the TCO layer and the upper antireflection layer includes a dielectric barrier layer having a refractive index of at least 1.9 to regulate oxygen diffusion. The barrier layer serves to optimize the oxygen supply. Particularly good results are achieved when the barrier layer has a refractive index of 1.9 to 2.5.

[0068] The dielectric barrier layer for regulating the diffusion of oxygen is preferably constructed on the basis of a nitride or carbide. The barrier layer can be constructed, for example, on the basis of a nitride or carbide of tungsten, niobium, tantalum, zirconium, hafnium, chromium, titanium, silicon or aluminum. In a preferred embodiment, the barrier layer is constructed on the basis of silicon nitride or silicon carbide, in particular silicon nitride (Si3N4), whereby particularly good results are achieved. The silicon nitride can have dopants and, in a preferred extension, is doped with aluminum (Si3N4:Al), zirconium (Si3N4:Zr), titanium (Si3N4:Ti) or boron (Si3N4:B). In the case of a temperature treatment after application of the coating according to the invention, the silicon nitride can be partially oxidized. After the temperature treatment, the barrier layer deposited as Si3N4 now contains Si x N y O z , wherein the oxygen content is generally 0 atomic % to 35 atomic %.

[0069] The thickness of the barrier layer is preferably 5 nm to 20 nm, particularly preferably 7 nm to 15 nm, very particularly preferably 7 nm to 12 nm, for example 8 nm to 12 nm or 8 nm to 10 nm. This allows for particularly advantageous adjustment of the oxygen content of the TCO layer. The thickness of the barrier layer is selected based on oxygen diffusion and, to a lesser extent, on the optical properties of the glass pane. However, it has been shown that barrier layers with thicknesses within the indicated ranges are compatible with the emissivity-reducing coating according to the invention and its optical requirements.

[0070] In one advantageous embodiment, the emissivity-reducing coating comprises a dielectric barrier layer below the TCO layer and, optionally, below the lower antireflection layer, which prevents alkali metal diffusion. The barrier layer reduces or prevents the diffusion of alkali metal ions from the glass substrate into the layer system. Alkali metal ions can adversely affect the properties of the coating. Furthermore, the barrier layer, in interaction with the lower antireflection layer, advantageously contributes to adjusting the optical properties of the entire layer structure. The refractive index of the barrier layer is preferably at least 1.9. Particularly good results are achieved when the refractive index of the barrier layer is between 1.9 and 2.5. The barrier layer is preferably based on an oxide, nitride, or carbide, preferably an oxide, nitride, or carbide of tungsten, chromium, niobium, tantalum, zirconium, hafnium, titanium, silicon, or aluminum, for example oxides such as WO3, Nb2O5, Bi2O3, TiO2, Ta2O5, Y2O3, ZrO2, HfO2, SnO2, or ZnSnOx, or nitrides such as AlN. The barrier layer is particularly preferably constructed on the basis of silicon nitride (Si3N4), which achieves particularly good results. The silicon nitride can have dopants and, in a preferred embodiment, is doped with aluminum (Si3N4:Al), titanium (Si3N4:Ti), zirconium (Si3N4:Zr) or boron (Si3N4:B). The thickness of the barrier layer is preferably 10 nm to 50 nm, particularly preferably 20 nm to 40 nm, for example 25 nm to 35 nm. The barrier layer is preferably the lowest layer of the layer stack and is therefore in direct contact with the substrate surface, where it can optimally exert its effect.

[0071] In a particularly preferred embodiment, the coating consists exclusively of the layers described and contains no further layers. In this case, the emissivity-reducing coating consists of the following layers in the order indicated, starting from the substrate surface (the surface of the inner glass pane facing the interior):

[0072] - Barrier layer to prevent alkali metal diffusion

[0073] - Lower anti-reflective layer

[0074] - Conductive TCO layer

[0075] - Barrier layer to regulate oxygen diffusion

[0076] - Upper anti-reflective layer.

[0077] In one embodiment of the present invention, a windshield panel includes a region in which the thermoplastic interlayer is tinted or dyed. This occurs particularly in so-called panoramic windshields, which, compared to conventional windshields, extend toward the upper edge, have a significant curvature there, and appear to be drawn into the roof area of the vehicle. Such panoramic windshields provide vehicle occupants with a sense of "wide openness." In this case, the region with the tinted interlayer is arranged above the central visual field, i.e., between the central visual field and the upper edge of the windshield panel, particularly near or adjacent to the opaque overprint at the upper edge. The central visual field is defined as visual field B according to Economic Commission for the European Union (UN / ECE) Regulation No. 43 (ECE-R43, "Uniform conditions for the approval of safety glazing materials and their installation in vehicles"). Visual field B is defined in Annex 18 thereto. The interlayer may have a tinting profile in this region, where, for example, the tinting becomes stronger from the bottom toward the upper edge, resulting in a lower light transmittance through the windshield panel. In the colored areas, the light transmittance (total transmittance according to ECE-R 43) is preferably at least partially less than 70%, particularly preferably less than 50%, very particularly preferably less than 30%, and in particular less than 10%. For example, the colored areas of the interlayer can be produced by using portions of a colored polymer film instead of a clear polymer film. Alternatively, the colored film can also be placed on a clear PVB film.

[0078] The tinted areas have an enhanced absorption of solar radiation and therefore a greater warming. This can lead to an increase in the temperature of the vehicle interior due to the emission of thermal radiation. The emissivity-reducing coating according to the invention reduces this effect and improves thermal comfort. The advantages of the invention are therefore particularly evident in such glass panes.

[0079] The projector is arranged on the interior side of the windshield and illuminates the windshield through the interior-side surface of the inner pane. It is directed toward the HUD area and illuminates it to produce the HUD projection. The radiation of the projector is at least partially p-polarized, that is, it has a p-polarized radiation proportion. The radiation of the projector is preferably predominantly p-polarized, that is, it has a p-polarized radiation proportion of greater than 50%. The higher the proportion of p-polarized radiation in the total radiation of the projector, the greater the intensity of the desired projected image and the lower the intensity of undesired reflections on the surface of the windshield. The p-polarized radiation proportion of the projector is preferably at least 70%, particularly preferably at least 80%, and in particular at least 90%. In a particularly advantageous embodiment, the radiation of the projector is essentially purely p-polarized - so the p-polarized radiation proportion is 100% or only deviates from it insignificantly. The description of the polarization direction is based on the plane of incidence of the radiation on the windshield. 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 incident plane is defined by the incident vector and the windshield surface normal at the geometric center of the illuminated area.

[0080] The polarization, i.e., in particular the ratio of p- and s-polarized radiation, is determined at the location of the HUD area, preferably at its geometric center. Since windshield panes are generally curved, which affects the plane of incidence of the projector radiation, slightly different polarization ratios may occur in other areas, which is unavoidable for physical reasons.

[0081] The radiation of the projector preferably strikes the windshield at an angle of incidence of 45° to 70°, in particular 60° to 70°. In an advantageous embodiment, the angle of incidence deviates from the Brewster angle by a maximum of 10°. At this point, the p-polarized radiation is only insignificantly reflected on the surface of the windshield, so that no ghost images are produced. The angle of incidence is the angle between the incident vector of the projector radiation and the surface normal of the interior space side at the geometric center of the HUD area (i.e., the surface normal on the outer surface of the interior space side of the windshield). In the case of soda-lime glass (which is usually commonly used for window glass sheets), the Brewster angle of the air-glass transition is 56.5°. Ideally, the angle of incidence should be as close to this Brewster angle as possible. However, an angle of incidence of, for example, 65° can also be used, which is common for HUD projection devices, can be implemented in vehicles without any problems, and deviates from the Brewster angle only to a small extent, so that the reflection of the p-polarized radiation only increases insignificantly.

[0082] Since the reflection of the projector radiation occurs primarily at the reflective coating rather than at the outer surfaces of the glass panes, it is not necessary to arrange the outer surfaces of the glass panes at an angle to each other to avoid ghost images. Therefore, the outer surfaces of the windshield panes are preferably arranged essentially parallel to each other. For this purpose, the thermoplastic interlayer is preferably not designed in a wedge-shaped manner, but rather has a substantially constant thickness, particularly in the vertical direction between the upper and lower edges of the windshield pane, as well as in the inner and outer panes. In contrast, a wedge-shaped interlayer has a variable, typically increasing, thickness in the vertical direction between the lower and upper edges of the windshield pane. The interlayer is typically constructed from at least one thermoplastic film. Since standard films are significantly more cost-effective than wedge-shaped films, the windshield panes are thus more economical to manufacture.

[0083] The outer and inner panes are preferably made of glass, in particular soda-lime glass, as is common for window panes. However, in principle, the panes can also be made of other glass types (e.g., borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (e.g., polymethyl methacrylate or polycarbonate). The thickness of the outer and inner panes can vary widely. Glass panes with a thickness of 0.8 mm to 5 mm, preferably 1.4 mm to 2.5 mm, such as standard thicknesses of 1.6 mm or 2.1 mm, are preferably used.

[0084] The outer pane, inner pane, and thermoplastic interlayer can be clear and colorless, but can also be tinted or dyed. In a preferred embodiment, the total transmittance through the windshield pane (including the reflective coating) is greater than 70%. The term total transmittance is based on the method for testing the light transmittance of automotive glass panes specified in ECE-R 43, Annex 3, Section 9.1. The outer pane and inner pane can be independently non-prestressed, partially prestressed, or prestressed. If at least one of the panes is prestressed, this may be thermal or chemical.

[0085] In one advantageous embodiment, the outer pane is tinted or dyed. This reduces the reflectivity of the windshield's exterior, making the appearance of the pane more pleasant to outside observers. However, to ensure the desired light transmittance of 70% (total transmittance) for the windshield, the outer pane should preferably have a light transmittance of at least 80%, particularly preferably at least 85%. The inner pane and the interlayer are preferably clear, i.e., not tinted or dyed. For example, green- or blue-tinted glass can be used as the outer pane. Light transmittance describes the proportion of radiation in the visible spectrum that passes through the pane, at an angle of incidence of 0° relative to the surface normal. It can be measured, for example, using a Perkin Elmer "Lambda 900" spectrometer.

[0086] The windshield is preferably curved in one or more directions in space, as is common for automotive glass panes, with typical radii of curvature being approximately 10 cm to approximately 40 m. The windshield can also be flat, for example when it is provided as glass pane for a bus, train or tractor.

[0087] The thermoplastic interlayer comprises at least one thermoplastic polymer, preferably ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), or polyurethane (PU), or mixtures, copolymers, or derivatives thereof, particularly preferably PVB. The interlayer is typically constructed from a thermoplastic film, particularly based on PVB, EVA, or PU. This means that the film consists largely of the polymer (in a proportion greater than 50% by weight). In addition to the polymer, the film may also contain other additives, particularly plasticizers. The thickness of the interlayer is preferably 0.2 mm to 2 mm, particularly preferably 0.3 mm to 1 mm.

[0088] Windshield panes can be produced by methods known per se. The outer and inner glass panes are laminated to one another via an intermediate layer, for example, by means of an autoclave process, a vacuum bag process, a vacuum ring process, a calendaring process, a vacuum laminator, or a combination thereof. The outer and inner glass panes are typically joined under the action of heat, vacuum, and / or pressure.

[0089] The reflective coating and the emissivity-reducing coating are preferably applied to the respective glass pane surfaces by physical vapor deposition (PVD), particularly preferably by cathode sputtering ("sputtering"), and very particularly preferably by magnetic field-assisted cathode sputtering ("magnetron sputtering"). In principle, however, the coatings can also be applied, for example, by chemical vapor deposition (CVD), such as plasma-assisted vapor deposition (PECVD), by evaporation, or by atomic layer deposition (atomic layer deposition, ALD). The coatings are preferably applied prior to lamination. Instead of applying the reflective coating to the glass pane surfaces, it is also possible to provide it on a carrier film arranged in an intermediate layer.

[0090] If the windshield pane is to be bent, the outer and inner panes are preferably subjected to a bending process before lamination and preferably after any coating process. The outer and inner panes are preferably bent simultaneously (i.e., simultaneously and using the same tool) to ensure that the shapes of the panes are optimally matched to each other for the subsequent lamination. Typical temperatures for the glass bending process are, for example, 500°C to 700°C. This temperature treatment also increases transparency and reduces the surface resistance of the reflective coating.

[0091] The present invention also includes the use of the projection device according to the invention as a HUD in a motor vehicle, in particular a passenger vehicle or a truck.

[0092] The present invention will be explained in more detail below with reference to the accompanying drawings and examples. The drawings are schematic and not to scale. The drawings do not limit the present invention in any way.

[0093] It shows:

[0094] Figure 1 A top view of a composite glass panel of a universal projection device,

[0095] Figure 2 A section through the universal projection device,

[0096] Figure 3 a section through a composite glass pane of a projection device according to the invention,

[0097] Figure 4 a section through an embodiment of a reflective coating and an emissivity-reducing coating according to the invention on an inner glass pane,

[0098] Figure 5 Reflection spectra of the composite glass panes according to the example and comparative examples 1 and 2 for p-polarized radiation.

[0099] Figure 1 and Figure 2 Details of a generic projection device for a HUD are shown. The projection device comprises a windshield 10, in particular a windshield of a passenger vehicle. The projection device further comprises a projector 4, which is directed toward a region of the composite glass pane 10. In this region, generally referred to as the HUD region B, the projector 4 can generate an image that is perceived by an observer 5 (the vehicle driver) as a virtual image on the side of the composite glass pane 10 facing away from him when his eyes are within the so-called eye range E.

[0100] A windshield 10 is formed from an outer glass pane 1 and an inner glass pane 2, which are joined together by a thermoplastic interlayer 3. Its lower edge U is oriented downwardly, toward the engine of a passenger vehicle, while its upper edge O is oriented upwardly, toward the roof. In the installed position, the outer glass pane 1 faces the exterior, while the inner glass pane 2 faces the vehicle interior.

[0101] Figure 3An embodiment of a windshield 10 constructed according to the present invention is shown. The outer pane 1 has an outer surface I, which faces the exterior when in the installed position, and an interior-facing surface II, which faces the interior when in the installed position. Similarly, the inner pane 2 has an outer surface III, which faces the exterior when in the installed position, and an interior-facing surface IV. The outer and inner panes 1 and 2 are composed, for example, of soda-lime glass and have a thickness of, for example, 2.1 mm. The interlayer 3 is formed, for example, of a PVB film with a thickness of 0.76 mm. The PVB film has a substantially constant thickness, except for any surface roughness common in this field – the film is not designed as a so-called wedge film.

[0102] The outer side surface III of the inner pane 2 is provided with a reflective coating 20 according to the invention, which is provided as a reflective surface for projector radiation (and possibly also as an IR-reflective coating).

[0103] According to the present invention, the radiation from projector 4 is p-polarized, in particular, substantially pure p-polarized. Since projector 4 illuminates windshield pane 10 at an angle of incidence close to the Brewster angle, approximately 65°, the radiation from the projector is only insignificantly reflected from outer surfaces I, IV of composite glass pane 10. In contrast, reflective coating 20 according to the present invention is optimized for reflecting p-polarized radiation. It serves as a reflective surface for the radiation from projector 4 to produce the HUD projection.

[0104] The interior-facing surface IV of the inner glass pane 2 is provided with an emissivity-reducing coating 30 according to the invention. This emissivity-reducing coating 30 improves thermal comfort in the vehicle interior by reflecting thermal radiation. Surprisingly, the presence of the emissivity-reducing coating 30 also leads to improved reflection performance for p-polarized radiation, thus enabling improved display of HUD images.

[0105] Figure 4 The layer sequences of embodiments of a reflective coating 20 according to the present invention and an emissivity-reducing coating 30 according to the present invention are shown. The reflective coating 20 and the emissivity-reducing coating 30 are stacks of thin layers. The reflective coating 20 comprises a silver-based conductive layer 21. A metallic barrier layer 24 is arranged directly above the conductive layer 21. Above this, an upper dielectric layer sequence is arranged, which consists, from bottom to top, of an upper adapting layer 23b, an upper refractive index-increasing layer 23c, and an upper antireflection layer 23a. Below the conductive layer 21, a lower dielectric layer sequence is arranged, which consists, from top to bottom, of a lower adapting layer 22b, a lower refractive index-increasing layer 22c, and a lower antireflection layer 22a.

[0106] The layer structure shown is to be understood only as an example. The dielectric layer sequence can therefore also include more or fewer layers. The dielectric layer sequence also does not have to be symmetrical. Exemplary materials and layer thicknesses can be found in the following examples.

[0107] The emissivity-reducing coating 30 comprises a conductive layer 31 based on indium tin oxide (ITO). Below the conductive layer 31, a barrier layer 32 is arranged to prevent the diffusion of alkali metals, and above this, a lower antireflection layer 33 is arranged. Above the conductive layer 31, a barrier layer 34 is arranged to regulate oxygen diffusion, and an upper antireflection layer 35 is arranged. The layer structure shown is again to be understood as merely exemplary. Exemplary materials and layer thicknesses can be found in the following examples.

[0108] Table 1 shows the layer sequence of a windshield panel 10 according to an embodiment of the present invention, comprising a reflective coating 20 on the outer surface III of the inner pane 2 and an emissivity-reducing coating 30 on the interior-facing surface IV of the inner pane 2, as well as the materials and geometric layer thicknesses of the individual layers. The dielectric layers can be doped independently of one another, for example with boron or aluminum. The materials do not necessarily need to be deposited stoichiometrically; deviations from the stoichiometry of the molecular formula are also possible. For comparison, two comparative examples are also shown in Table 1. In comparative example 1, the windshield panel 10 comprises only the reflective coating 20, and in comparative example 2, only the emissivity-reducing coating 30.

[0109] Table 1

[0110]

[0111] The optical thickness of the dielectric layer sequence can be calculated as the product of the indicated geometric thickness and the refractive index (Si3N4: 2.0; SiZrN: 2.2, ZnO: 2.0; SiO2: 1.5).

[0112] Figure 5 Shown as Figure 3 Reflection spectra of windshield panes 10 in FIG. 1, each having the layer structures according to the exemplary embodiment of the invention and comparative examples 1 and 2 according to Table 1. The reflection spectra were recorded using a light source emitting p-polarized radiation with uniform intensity in the observed spectral range, with illumination through the inner pane 2 at an angle of incidence of 65° to the interior-side surface normal (so-called interior-side reflection). The reflectivity measurement thus approximates the conditions in a projection system.

[0113] As can already be seen from the graphical display of the spectra, the embodiments according to the present invention have improved reflection spectra compared to the comparative examples. Comparative Example 1 achieves similar reflectivity, but the reflection spectrum is less constant ("flat"), resulting in the HUD display appearing less color-neutral because the blue component, in particular, is strongly reflected. Furthermore, the visual appearance of the windshield pane 10 may have a color shift. Comparative Example 2 does not result in a sufficiently high reflectivity for high-intensity display of the HUD projection.

[0114] The spectral range of 450 nm to 650 nm is particularly interesting for evaluating HUD displays, as conventional HUD projectors 4 use radiation in this range (RGB: 473 nm, 550 nm, 630 nm). Table 2 summarizes the average reflectivity for p-polarized radiation and the differences between the maximum and minimum values in this spectral range and the average reflectivity. The standard deviation of the reflectivity spectra is also shown.

[0115] Table 2

[0116] Example Comparative Example 1 Comparative Example 2 Average reflectivity for p-polarized radiation, 450 nm-650 nm 17.0% 17.8% 3.2% The difference between the maximum reflectivity and the average 0.1% 1.2% 0.6% The difference between the minimum reflectivity and the average reflectivity 0.2% 0.5% 1.6% Standard deviation, 450 nm-650 nm 0.09% 0.55% 0.68%

[0117] As from Figure 5 As can be seen from the graphical display of the reflectance spectra, Comparative Example 1 results in a similar average reflectance as the embodiment according to the present invention, but with a greater variance in reflectance. Consequently, the HUD display is similarly intense, but less color-neutral. The average reflectance of Comparative Example 2 is too low.

[0118] The entire visible spectral range from 380 nm to 780 nm is of interest for evaluating the overall optical impression of windshield pane 10. Table 3 summarizes the average reflectivity for p-polarized radiation and the differences between the maximum and minimum values and the average reflectivity within this spectral range. Furthermore, the standard deviations of the reflectivity spectra are shown.

[0119] Table 3

[0120] Example Comparative Example 1 Comparative Example 2 Average reflectivity for p-polarized radiation, 380 nm-780 nm 16.8% 18.0% 2.9% The difference between the maximum reflectivity and the average 0.3% 1.3% 0.9% The difference between the minimum reflectivity and the average reflectivity 1.4% 1.3% 1.9% Standard deviation, 380 nm-780 nm 0.33% 0.66% 0.86%

[0121] As from Figure 5 As can already be seen from the graphical display of the reflection spectra, the embodiments according to the present invention result in a lower variance in reflectivity. As a result, the overall optical impression is more color-neutral, avoiding disruptive color deviations. All glass panes have a light transmittance of greater than 70%, making them suitable for use as windshield panes.

[0122] List of reference numerals:

[0123] (10) Windshield

[0124] (1) Outer glass panel

[0125] (2) Inner glass panel

[0126] (3) Thermoplastic middle layer

[0127] (4) Projector

[0128] (5) Observer / vehicle driver

[0129] (20) Reflective coating

[0130] (21) Silver-based conductive layer (silver layer)

[0131] (22a) First lower dielectric layer / anti-reflection layer

[0132] (22b) Second lower dielectric layer / adaptive layer

[0133] (22c) Third lower dielectric layer / refractive index increasing layer

[0134] (23a) First upper dielectric layer / anti-reflection layer

[0135] (23b) Second upper dielectric layer / adaptive layer

[0136] (23c) Third upper dielectric layer / refractive index increasing layer

[0137] (24) Metal barrier layer

[0138] (30) Emissivity reducing coating

[0139] (31) TCO-based conductive layer (TCO layer)

[0140] (32) Barrier layer to prevent alkali metal diffusion

[0141] (33) Lower anti-reflection layer

[0142] (34) Barrier layer for regulating oxygen diffusion

[0143] (35) Upper anti-reflection layer

[0144] (O) Upper edge of the windshield plate 10

[0145] (U) Lower edge of windshield plate 10

[0146] (B) HUD area of the windshield plate 10

[0147] (E) Eye movement range

[0148] (I) The outer surface of the outer glass pane 1 facing away from the intermediate layer 3

[0149] (II) Surface of the outer glass pane 1 facing the interior space side of the intermediate layer 3

[0150] (III) The outer surface of the inner glass sheet 2 facing the intermediate layer 3

[0151] (IV) The surface of the inner glass pane 2 facing away from the interior space side of the intermediate layer 3 .

Claims

1. A projection device for a head-up display (HUD), comprising at least A windshield pane (10) with a HUD region (B), comprising an outer pane (1) and an inner pane (2) joined to one another via a thermoplastic intermediate layer (3); and - a projector (4) directed towards the HUD area (B) and emitting p-polarized radiation; in - a reflective coating (20) suitable for reflecting p-polarized radiation is arranged on the surface of the outer pane (1) or the inner pane (2) facing the intermediate layer (3) or in the intermediate layer (3), said reflective coating comprising precisely one electrically conductive layer (21) containing at least 90% by weight of silver; and An emissivity-reducing coating (30) having an electrically conductive layer (31) based on indium tin oxide (ITO) is arranged on the surface of the inner glass pane (2) facing away from the intermediate layer (3).

2. The projection device according to claim 1, wherein the reflective coating (20) is configured such that - a lower dielectric layer or layer sequence is arranged below the electrically conductive layer (21) of the reflective coating (20), said lower dielectric layer or layer sequence having a refractive index of at least 1.9, and - an upper dielectric layer or layer sequence is arranged above the electrically conductive layer (21) of the reflective coating (20), the upper dielectric layer or layer sequence having a refractive index of at least 1.9, The ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is at least 1.

7. 3 . The projection device according to claim 2 , wherein the optical thickness of the upper dielectric layer or layer sequence is 100 nm to 200 nm and the optical thickness of the lower dielectric layer or layer sequence is 50 nm to 100 nm.

4. The projection device according to any one of claims 1 to 3, wherein the conductive layer (21) of the reflective coating (20) has a geometric thickness of 10 nm to 14 nm.

5. The projection device according to any one of claims 1 to 3, wherein - arranging a first lower dielectric layer, a second lower dielectric layer and a third lower dielectric layer below the conductive layer (21) of the reflective coating (20), the first lower dielectric layer, the second lower dielectric layer and the third lower dielectric layer having a refractive index of at least 1.9, and / or - arranging a first upper dielectric layer, a second upper dielectric layer and a third upper dielectric layer above the conductive layer (21) of the reflective coating (20), the first upper dielectric layer, the second upper dielectric layer and the third upper dielectric layer having a refractive index of at least 1.

9.

6. The projection device according to claim 5, wherein - said first lower dielectric layer is based on silicon nitride, - the second lower dielectric layer is based on zinc oxide, - the third lower dielectric layer is based on silicon-zirconium mixed nitride or silicon-hafnium mixed nitride, - said first upper dielectric layer is based on silicon nitride, - the second upper dielectric layer is based on zinc oxide, The third upper dielectric layer is based on silicon-zirconium mixed nitride or silicon-hafnium mixed nitride.

7. The projection device according to claim 1, wherein the reflective coating (20) comprises the following layers: - an antireflection layer based on silicon nitride, having a thickness of 20 nm to 30 nm, a refractive index-increasing layer based on silicon-zirconium mixed nitride or silicon-hafnium mixed nitride and having a thickness of 8 nm to 12 nm above the antireflection layer, - an adapting layer above the refractive index-increasing layer, based on zinc oxide and having a thickness of 8 to 12 nm, - a conductive layer (21) above the adapting layer, the thickness of which is 11 nm to 13 nm, - a barrier layer on top of the conductive layer (21), based on Ti or NiCr and having a thickness of 0.1 nm to 0.5 nm, - an adapting layer on top of the barrier layer, based on zinc oxide and having a thickness of 8 to 12 nm, an upper refractive index-increasing layer above the adapting layer, based on silicon-zirconium mixed nitride or silicon-hafnium mixed nitride and having a thickness of 8 nm to 12 nm, - an upper antireflection layer above the upper refractive index-increasing layer, based on silicon nitride and having a thickness of 60 to 70 nm.

8. The projection device according to any one of claims 1 to 3, wherein the reflective coating (20) comprises at least one metal barrier layer, which is arranged directly above and / or below the conductive layer (21) and has a geometric thickness of less than 1 nm.

9. The projection device according to claim 1, wherein the conductive layer (31) of the emissivity-reducing coating (30) is constructed on the basis of indium tin oxide (ITO) and has a thickness of 60 nm to 100 nm.

10. The projection device according to any one of claims 1 to 3, wherein the emissivity reducing coating (30) comprises a barrier layer (32) against alkali metal diffusion having a refractive index of at least 1.9, - a dielectric lower antireflection layer (33) with a refractive index of 1.3 to 1.8 above the barrier layer (32) against diffusion of alkali metals, - a conductive layer (31) above the dielectric lower anti-reflection layer (33), - a dielectric barrier layer (34) with a refractive index of at least 1.9 above the conductive layer (31) for regulating oxygen diffusion, - a dielectric upper antireflection layer (35) with a refractive index of 1.3 to 1.8 above the dielectric barrier layer (34).

11. The projection device according to claim 10, wherein - the dielectric lower anti-reflection layer (33) and the dielectric upper anti-reflection layer (35) are constructed based on silicon oxide, - the dielectric lower anti-reflection layer (33) has a thickness of 5 nm to 50 nm, and - The dielectric upper antireflection layer (35) has a thickness of 10 nm to 100 nm.

12. The projection device as claimed in claim 10, wherein the dielectric barrier layer (34) is constructed on the basis of silicon nitride or silicon carbide and has a thickness of 5 nm to 20 nm.

13. The projection device according to claim 10, wherein the barrier layer (32) preventing alkali metal diffusion is formed based on silicon nitride and has a thickness of 10 nm to 50 nm.

14. The projection device according to claim 10, wherein the windshield pane (10) has a region in which the intermediate layer (3) is tinted or dyed.

15. The projection device according to any one of claims 1 to 3, wherein the outer glass pane (1) is tinted or dyed and has a light transmittance of at least 80%.

16. The projection device according to any one of claims 1 to 3, wherein outer surfaces of the windshield glass panels (10) are arranged substantially parallel to each other.

Images