DE202022003019U1 - Composite pane for a head-up display system with p-polarized radiation - Google Patents

Abstract

Composite pane for a head-up display system, comprising at least
- a first disc (1) with a first surface (I) and a second surface (II), a second disc (2) with a first surface (III) and a second surface (IV) and a thermoplastic intermediate layer (3) which is arranged between the second surface (II) of the first disc (1) and the first surface (III) of the second disc (2),
- a first coating (20) on the surface (III) of the second pane (2) facing the intermediate layer (3),
- a second coating (30) on the surface (IV) of the second pane (2) facing away from the intermediate layer (3),
- a HUD area (B) having the first coating (20) and the second coating (30),
wherein the first coating (20) and the second coating (30) are intended to reflect p-polarized radiation,
wherein a refractive index of the first coating (20) is at least 1.9, wherein the second coating (30) comprises at least a first layer (30.1) of a dielectric material having a refractive index greater than or equal to 1.9 and a second layer (30.2) of a dielectric material having a refractive index less than or equal to 1.6, and
wherein the second disc (2) has a smaller thickness than the first disc (1).

Description

The invention relates to a composite pane for a head-up display system and a projection arrangement for a head-up display system.

Vehicles, especially passenger cars, are increasingly being equipped with so-called head-up displays. A head-up display (HUD) is a display system that projects additional information in the form of images into the driver's field of vision.

The head-up display consists of a projector (imaging unit) and several optical modules for redirecting or reflecting an image onto a projection surface or reflection surface. A composite pane of glass, in particular the vehicle's windshield, is usually used as the projection surface. Although the image is projected onto the windshield, the human eye perceives it as floating far above the vehicle's hood.

In this way, additional information can be projected into the driver's field of vision, such as the current driving speed and navigation or warning information, which the driver can perceive without having to change his or her direction of view. Head-up displays can therefore make a significant contribution to increasing road safety.

The image produced by the projector usually consists of polarized, particularly s-polarized light radiation. The s-polarized light hits the composite pane at a certain angle of incidence and is at least partially refracted into the composite pane and reflected as s-polarized light into the driver's field of vision. However, the reflected images are not colorfast or are displayed with undesirable reflection, so-called double images.

The angle of incidence of the s-polarized radiation is usually about 65%, which corresponds approximately to the Brewster angle for an air-glass transition (57.2° for soda-lime glass). The problem here is that the projector image is reflected at both outer transitions from air to glass and from glass to air. As a result, in addition to the desired main image, a slightly offset secondary image, the so-called ghost image, occurs. The problem is alleviated by arranging the surfaces of the windshield at an angle to one another. This is done by using a wedge-shaped intermediate layer when laminating the windshield, which is designed as a composite pane. This allows the main image and the ghost image to be superimposed.

Wedge films are expensive, so that the production of such a composite pane for a HUD is quite cost-intensive. There is therefore a need for HUD systems that can operate with windshields without wedge films. For example, it is possible to operate the HUD projector with predominantly p-polarized radiation, which is not significantly reflected on the pane surfaces due to the radiation being close to the Brewster angle. Instead, the windshield has a reflective coating as a reflection surface for the p-polarized radiation, in particular with metallic and dielectric layers. HUD projection arrangements with reflective coating are made of WO2019179682A1 , WO2019179683A1 , WO2019206493A1 and WO2021/104800 A1 known. While the reflection on the outside surface of the outer pane is weakened as a result of the radiation reflection on the reflective coating, the reflection on the interior surface of the inner pane in particular can appear as a weak but nevertheless disturbing ghost image. Since high-frequency signals are not transmitted through the reflective coating, the sending and receiving of electromagnetic radiation in the interior of a vehicle is no longer possible. Usually one or two localized areas of the reflective coating are stripped.

WO2021/209201 A1 discloses a composite pane comprising a HUD reflection layer which is suitable for reflecting p-polarized radiation. The HUD reflection layer is arranged on the surface (II, III) of the outer pane or the inner pane facing the intermediate layer or within the intermediate layer.

EP0844507A1 discloses a HUD system of a motor vehicle with two glass plates connected to each other via an intermediate film. A polarization direction changing layer is arranged on the inner surface of the outer glass plate.

The object of the present invention is to provide a composite pane for a head-up display system which improves the reflectivity for p-polarized radiation in the visible spectral range and is permeable to high-frequency signals.

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

The composite pane according to the invention for a head-up display (HUD) system has a first pane and a second pane which are connected to one another via a thermoplastic intermediate layer. The first pane has a first surface (I) and a second surface (II). The second pane also has a first surface (III) and a second surface (IV).

The composite pane further comprises a HUD region and a first coating as well as a second coating, wherein the HUD region comprises the first coating and the second coating. The first coating is arranged on the surface (III) of the second pane facing the intermediate layer and the second coating is arranged on the surface (IV) of the second pane facing away from the intermediate layer. A refractive index of the first coating is at least 1.9. The second coating comprises at least a first layer of a dielectric material with a refractive index greater than or equal to 1.9 and a second layer of a dielectric material with a refractive index less than or equal to 1.6. Both coatings, both the first coating and the second coating, are intended for reflecting p-polarized radiation. The inventors have found that a coating comprising a high-refractive index layer and a low-refractive index layer is particularly suitable in terms of high reflectivity for p-polarized light. The p-polarized radiation is then reflected by the first coating and the second coating. The transmitted part of the radiation is reflected by the first coating located in the composite pane. Since the second pane is thin, the two reflected images overlap almost completely. This increases the intensity of the HUD display (projector image) resulting from the two reflections.

The second coating does not have to be applied over the entire surface (IV) of the second pane, but at least in the HUD area of the composite pane.

The first pane is tinted, which improves the visibility of the HUD display, and in combination with the second pane, which is thinner than the first pane, the visibility of the HUD display can be further increased. Such a composite pane has the particular advantage that it has reflective properties in the visible spectral range, particularly for p-polarized radiation. In addition, the formation of unwanted reflections, so-called ghost images, is largely minimized and ensures transmission of high-frequency signals on almost the entire surface of the composite pane.

In other words, the invention provides that the composite pane has a first coating and a second coating for reflecting p-polarized radiation, the second pane having a small thickness and the two reflections overlapping as much as possible. This effect is further enhanced by the tinting or coloring of the first pane. Surprisingly, it has been shown that such a composite pane according to the invention enables significantly improved visibility of the main image compared to previously known composite panes.

In a particularly preferred embodiment, the first coating and the second coating have exclusively dielectric layers. In addition, the first coating and the second coating can be free of electrically conductive materials. This ensures very good transmission of electromagnetic radiation through the composite pane. For legal reasons, it may also be desirable for a composite pane, in particular a vehicle pane, to have no metallic layers.

In a preferred embodiment, the first coating comprises a dielectric layer based on silicon-zirconium mixed nitride, silicon nitride, silicon-titanium mixed nitride, silicon-hafnium mixed nitride and/or titanium oxide.

In a further embodiment, the first coating comprises exclusively a dielectric layer, in particular based on silicon-zirconium mixed nitride.

In a further preferred embodiment, the first layer of the second coating comprises a dielectric layer based on silicon-zirconium mixed nitride, silicon nitride, silicon-titanium mixed nitride, silicon-hafnium mixed nitride or titanium oxide and the second layer of the second coating comprises a dielectric layer based on a dielectric oxide, in particular silicon oxide (SiO ₂ ). The second coating is preferably formed only from these two layers. It preferably has no further layers below or above one of the two layers. Preferably, the first layer and the second layer together comprise two or more layers with a different refractive index. The refractive index is greater than or equal to 1.9 for each layer of the first, in particular high-refractive-index layer and less than or equal to 1.6 for the second, in particular low-refractive-index layer. The second coating is transparent with an average transmission of visible light (380 nm to 780 nm) of preferably at least 80% and in particular at least 85%.

The second coating may have a total material thickness of at most 200 nm (nanometers), preferably at most 185 nm.

The composite pane is intended to separate the interior from the outside environment in a window opening of a vehicle. The composite pane is preferably the windshield of a motor vehicle, in particular a passenger car or truck. From the perspective of a vehicle occupant, the second coating is arranged spatially in front of the first coating when viewed through the second pane (inner pane).

As is usual with HUDs, a projector shines on an area of the composite pane. Where the radiation is reflected in the direction of the viewer (driver), a virtual image is created which the viewer perceives from behind the composite pane. The area of the composite pane that can be illuminated by the projector is called the HUD area. The beam direction of the projector can be varied using optical elements (e.g. mirrors), especially vertically, in order to adapt the projection to the height of the viewer.

P-polarized radiation is used to generate a HUD image. Since the angle of incidence of about 65° typical for HUD projection arrangements is relatively close to the Brewster angle for an air-glass transition (57.2°, soda-lime glass), p-polarized radiation is hardly reflected by window surfaces, while s-polarized radiation is reflected much more strongly. The reflection of p-polarized radiation takes place mainly at the second coating.

The thermoplastic intermediate layer can also be a functional thermoplastic film, in particular a film with acoustically dampening properties, a film that reflects infrared radiation, a film that absorbs infrared radiation and/or a film that absorbs UV radiation. For example, the thermoplastic intermediate layer can also be a band filter film. In order to reduce the transmission of total thermal radiation, the intermediate layer has thermal radiation (total transmitted thermal radiation TTS) reducing properties. For this purpose, the intermediate layer can be designed as a film with absorbing properties in the near infrared range (NIR). Near infrared radiation (NIR) is electromagnetic radiation in a wavelength range of 780 nm to 3000 nm (nanometers). This minimizes the heating inside rooms or vehicles and reduces the energy required to create an ambient climate that is comfortable for the person inside.

In one embodiment, the intermediate layer can comprise a conductor system with heating function, in particular several resistance wires as heating conductors.

In a further embodiment, at least one covering layer, in particular an opaque covering print, is arranged on the interior-side surface (II) of the first pane in an edge region of the composite pane. The opaque covering layer can be arranged directly or indirectly on the pane surface. The covering layer can at least partially overlap with the HUD region in the direction of view through the composite pane.

The opaque cover layer is arranged in an area of the pane in which the first and second coatings are also located, so that the cover layer, the first coating and the second coating overlap at least partially in the direction of view through the composite pane. Since the HUD projector is arranged in the interior of a vehicle when the composite pane is installed, the light emitted by the HUD projector hits the first coating or second coating and is reflected there. The reflected light is recognizable as an image for a viewer in the vehicle interior. The The opaque cover layer lies behind the first coating when viewed from the perspective of the observer in the vehicle interior. This means that the image in the area of the first coating and second coating has a good contrast.

The cover layer covers, for example, an adhesive bond or electrical connection elements of the composite pane. This gives the composite pane a good aesthetic visual impression. The cover layer also serves as UV protection for, for example, adhesives in the edge area of the composite pane.

The at least one opaque covering layer in the sense of the invention is a layer that prevents visibility through the composite pane. In this case, a transmission of at most 5%, preferably at most 2%, particularly preferably at most 1%, in particular at most 0.1%, of the light of the visible spectrum through the opaque covering layer takes place. The covering layer can also be semi-transparent, at least in sections, for example as a dot grid, stripe grid or checkered grid. Alternatively, the covering layer can also have a gradient, for example from an opaque covering to a semi-transparent covering.

The opaque cover layer is preferably printed on the first pane (e.g. outer pane), in particular using a screen printing process. Screen printing processes for applying opaque cover layers to panes are known as such. Such printed cover layers are also referred to as screen printing, black printing or black print and contain an opaque pigment, for example a black pigment. Known black pigments are, for example, pigment black (carbon black), aniline black, bone black, iron oxide black, spinel black and graphite. The opaque cover layer can be formed in the edge region of the composite pane all the way around the peripheral edge of the composite pane, whereby the width of the opaque cover layer can vary. The opaque cover layer is preferably widened in at least one area. This widened area of the opaque cover layer is used to display images emitted by the HUD projector.

In a further preferred embodiment of the invention, the thermoplastic intermediate layer is opaque in at least the edge region of the composite pane. The thermoplastic intermediate layer is preferably colored black in the edge region section. Alternatively, the thermoplastic intermediate layer can also be formed by a first and a second thermoplastic composite film, the first thermoplastic composite film being transparent and extending over the entire surface of the composite pane with the exception of the edge region. The second thermoplastic composite film is opaque and colored black, for example, and extends at least, preferably exclusively, over the edge region of the composite pane.

In a further preferred embodiment of the invention, an opaque, preferably black-colored, film is arranged within the thermoplastic intermediate layer. The film extends at least over the edge region and preferably only over the edge region. The film is formed, for example, on the basis of polyethylene terephthalate.

The edge region is preferably a strip-shaped region that is arranged along the lower edge. The edge region therefore extends from the left side edge to the right side edge and along the lower edge of the composite pane. The edge region can also extend in a strip-shaped manner along the upper edge from the left to the right side edge and/or along the left and/or right side edge from the lower edge to the upper edge. The edge region particularly preferably borders directly on the upper, side and/or lower edge. The edge region can run in a frame-shaped manner all the way around the composite pane. The edge region is not arranged within the region of the composite pane that is intended as a see-through region, for example when used as a windshield in a vehicle. The width of the edge region is preferably from 10 cm to 50 cm. In the sense of the invention, “width” means the extent perpendicular to the direction of extent.

In principle, it is sufficient if the HUD area of the composite pane, in particular as a windshield, is provided with the first coating and second coating. However, other areas of the composite pane can also be provided with the first and second coating. The composite pane can essentially be provided with the first and second coating over its entire surface, which may be preferred for manufacturing reasons.

In one embodiment of the invention, at least 80% of the pane surface is provided with the first and second coating. In particular, the first and second coating is applied to the entire surface of the Applied to the pane surface with the exception of the surrounding edge area and optionally local area. The surrounding uncoated edge area has a width of 20 cm, for example.

The composite pane according to the invention provides high reflectivity to p-polarized radiation in the spectral range from 450 nm to 650 nm (nanometers), which is relevant for HUD displays. HUD projectors typically work with wavelengths of 473 nm, 550 nm and 630 nm (RGB). This results in a high-intensity HUD image.

The projector is arranged on the interior side of the composite pane and illuminates the composite pane via the second (interior side) surface of the second pane. The light emitted by the HUD projector hits the HUD area and/or the cover layer and is reflected there.

In the sense of the invention, the external surface refers to the surface which is intended to face the external environment in the installed position. In the sense of the invention, the internal surface refers to the surface which is intended to face the interior in the installed position.

The projector is aimed at the HUD area and/or the cover layer and irradiates it to generate the HUD projection. According to the invention, the radiation from the projector is predominantly p-polarized, i.e. it has a p-polarized radiation component of more than 50%. The higher the proportion of p-polarized radiation in the total radiation from the projector, the more intense the desired projection image.

The p-polarized radiation component of the projector is preferably at least 70%, particularly preferably at least 80% and especially preferably at least 90%. In a particularly advantageous embodiment, the radiation from the projector is essentially purely p-polarized, i.e. the p-polarized radiation component is 100% or deviates only insignificantly from this. The indication of the direction of polarization refers to the plane of incidence of the radiation on the composite pane, in particular 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 plane of incidence is spanned by the incidence vector and the surface normal of the windshield in the geometric center of the irradiated area.

The radiation from the projector preferably hits the windshield at an angle of incidence of 45° to 75°, in particular 60° to 70°. In an advantageous embodiment, the angle of incidence deviates from the Brewster angle by a maximum of 10°. 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 windshield) in the geometric center of the HUD area. 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 only increases insignificantly.

The external surfaces of the composite pane are therefore preferably arranged substantially parallel to one another. The thermoplastic intermediate layer is preferably not wedge-shaped, but has a substantially constant thickness, in particular in the vertical course between the upper edge and the lower edge of the windshield, just like the first pane and the second pane.

The composite pane has a peripheral edge, which particularly preferably comprises an upper edge and a lower edge as well as two side edges running between them with a left and a right side edge. The upper edge refers to the edge that is intended to point upwards in the installed position of the composite pane. The lower edge refers to the edge that is intended to point downwards in the installed position. The upper edge is often also referred to as the roof edge and the lower edge as the motor edge.

The intermediate layer is typically made of at least one thermoplastic film. Since standard films are significantly cheaper than wedge films, the production of the windshield is made more cost-effective.

The first pane and the second pane are preferably made of glass, in particular soda-lime glass, which is common for window panes. In principle, however, the panes can also be made of other types of glass (for example borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (for example polymethyl methacrylate or polycarbonate). The thickness of the first pane as the outer pane and the second pane as the inner pane can vary widely. Preferably, panes with a thickness in the range of 0.8 mm to 5 mm, preferably from 1.1 mm to 2.5 mm, are used, for example those with the standard thicknesses 1.6 mm or 2.1 mm, with the second pane having a thickness of less than or equal to 1.6 mm, preferably less than or equal to 1.4 mm, particularly preferably 1.1 mm.

The second pane and the thermoplastic intermediate layer can be clear and colorless. The total transmission through the composite pane as a windshield (including reflective coating) is greater than 70% in a preferred embodiment. The term total transmission refers to the procedure for testing the light transmission of motor vehicle windows specified in ECE-R 43, Annex 3, Section 9.1. The first pane and the second pane can be untempered, partially tempered or tempered independently of one another. If at least one of the panes is to be tempered, this can be thermal or chemical tempering.

In an advantageous embodiment, the first pane is tinted or colored. For example, green or blue colored glass can be used as the first pane (outer pane). Such tinted glass panes are also known as TSANx, TSA3+ glass panes. This can reduce the external reflectivity of the composite pane, making the impression of the pane more pleasant for an outside observer. At the same time, a good HUD display with high contrast is enabled.

However, in order to guarantee the prescribed light transmission of 70% for windshields (total transmission), the outer pane (here the first pane) should preferably have a light transmission of at least 80%, particularly preferably at least 85%. The second pane and the intermediate layer are preferably clear, i.e. not tinted or colored.

The composite pane is preferably curved in one or more directions of space, as is usual for vehicle windows, with typical radii of curvature in the range of about 10 cm to about 40 m. The composite pane can also be flat, for example if it is intended as a pane for buses, trains or tractors.

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. The thermoplastic intermediate layer can be formed by one or more thermoplastic films arranged one above the other, wherein the thickness of the thermoplastic intermediate layer after lamination of the layer stack is preferably from 0.25 mm to 1 mm, typically 0.38 mm or 0.76 mm. The thermoplastic intermediate layer can also be formed from a film that is colored in some areas and is therefore opaque. The intermediate layer can also be formed from more than one film, wherein the at least two films extend over different areas of the surface of the composite pane.

The composite pane can be manufactured using methods known per se. The first pane and the second pane are laminated together via the intermediate layer, for example using autoclave processes, vacuum bag processes, vacuum ring processes, calender processes, vacuum laminators or combinations thereof. The first pane (outer pane) and the second pane (inner pane) are usually joined together using heat, vacuum and/or pressure.

The first coating and the second coating are preferably deposited onto a disk surface by physical vapor deposition (PVD), particularly preferably by cathode sputtering, very particularly preferably by magnetic field-assisted cathode sputtering, or by chemical deposition processes, particularly at atmospheric pressure. The coatings are preferably applied before lamination.

If something is "based" on a polymeric material, it consists predominantly of this material, i.e. at least 50%, preferably at least 60% and especially at least 70%. It can therefore also contain other materials such as stabilizers or plasticizers.

The invention also includes a vehicle, preferably a road vehicle, in particular a passenger car (car), which is equipped with a composite pane according to the invention.

The invention also includes a projection arrangement for a head-up display system, wherein the projection arrangement comprises the composite pane according to the invention and a projector, wherein the projector is directed at the HUD area of the composite pane, wherein the second surface (IV) of the second pane is provided for irradiation by the projector and the radiation of the projector is predominantly p-polarized. The composite pane is arranged in relation to the projector such that the second surface (IV) of the second pane is the surface of the composite pane closest to the projector.

The p-polarized radiation is reflected in the HUD area towards a viewer, creating a virtual HUD display that the viewer sees from behind the laminated pane or on the cover layer. The beam direction of the projector can typically be varied using mirrors, particularly vertically, in order to adapt the projection to the viewer's height. The area in which the viewer's eyes must be for a given mirror position is called the eyebox window. This eyebox window can be moved vertically by adjusting the mirrors, with the entire area accessible in this way (i.e. the superposition of all possible eyebox windows) being called the eyebox. A viewer located inside the eyebox can perceive the virtual image. This of course means that the viewer's eyes must be inside the eyebox, not their entire body.

The projector is preferably a liquid crystal (LCD) display, thin film transistor (TFT) display, light emitting diode (LED) display, organic light emitting diode (OLED) display, electroluminescent (EL) display or microLED display.

The invention further extends to the use of the projection arrangement according to the invention in vehicles for traffic on land, in the air or on water, in particular in motor vehicles. The use of the composite pane as a vehicle windshield is preferred.

The various embodiments of the invention can be implemented individually or in any combination. In particular, the features mentioned above and those to be explained below can be used not only in the combinations given, but also in other combinations or on their own, without departing from the scope of the present invention.

The invention is explained in more detail below using figures and exemplary embodiments. The figures are a schematic representation and are not to scale. The figures do not limit the invention in any way.

• 1 eine Draufsicht auf eine Verbundscheibe einer gattungsgemäßen Projektionsanordnung,
• 2 einen Querschnitt durch die Verbundscheibe,
• 3 einen Querschnitt durch eine erste Ausgestaltung einer erfindungsgemäßen Verbundscheibe,
• 4 einen Querschnitt durch eine Ausgestaltung einer ersten Beschichtung und einer zweiten Beschichtung, und
• 5 ein Reflexionsspektrum der erfindungsgemäßen Verbundscheibe gegenüber p-polarisierter Strahlung.

Show it:

• 1 a plan view of a composite pane of a generic projection arrangement,
• 2 a cross-section through the composite pane,
• 3 a cross section through a first embodiment of a composite pane according to the invention,
• 4 a cross section through an embodiment of a first coating and a second coating, and
• 5 a reflection spectrum of the composite pane according to the invention with respect to p-polarized radiation.

As a rule, information with numerical values should not be understood as exact values, but also include a tolerance of +/- 1% up to +/- 10%.

1 shows schematically a composite pane 10 with an upper edge O, a lower edge U and a so-called HUD area B. When installed, the HUD area can be in the lower area near the lower edge of the composite pane 10. In a peripheral edge region of the composite pane 10 there can additionally be a frame-shaped peripheral opaque covering layer.

2 shows a schematic of a generic projection arrangement for a HUD system. The projection arrangement comprises a composite pane 10 which is designed as a windshield of a passenger car. The composite pane 10 separates an interior of the passenger car from an external environment. The projection arrangement also has a projector 4 which is directed at an area of the composite pane 10. This area is usually referred to as HUD area B. In this area, images generated by the projector 4 can be projected, which are perceived by a viewer 5 (e.g. vehicle driver) as virtual images on the side of the composite pane 10 facing away from him when his eyes are inside the so-called eyebox E.

The composite pane 10 is made up of a first pane 1 as the outer pane and a second pane 2 as the inner pane of the passenger car, which are connected to one another via a thermoplastic intermediate layer 3. Its lower edge U is arranged downwards in the direction of the engine of the passenger car, its upper edge O upwards in the direction of the roof. In the installed position, the first pane 1 faces the outside environment, the second pane 2 faces the vehicle interior. The composite pane 10 can have any suitable geometric shape and/or curvature. As a windshield, it typically has a convex curvature.

3 shows schematically a first embodiment of a composite pane 10 according to the invention in cross section. The first pane 1 has an outside surface I which, in the installed position, faces the outside environment, and an inside surface II which, in the installed position, faces the interior. The composite pane 10 also comprises the second pane 2 which has an outside surface III and an inside surface IV. The surface III faces the outside environment in the installed position. In contrast, the surface IV faces the outside environment in the installed position.

The first pane 1 as the outer pane when installed and the second pane 2 as the inner pane are made of soda-lime glass, for example. The first pane 1 has a thickness of 2.1 mm, for example. The second pane 2 has a thickness of 1.6 mm, making it significantly thinner than the inner panes usually used in windshields. Alternatively, the thickness of the second pane (2) can be 1.4 mm or 1.1 mm. The reduction in the thickness of the second pane 2, i.e. the inner pane when installed in a vehicle, is accompanied by an adjustment of the first reflection to the second reflection. This means that the image that is created on the second surface IV of the second pane 2 moves closer to the image resulting from the second reflection. The images overlap more, which improves the impression of the resulting HUD display.

The first pane 1 has at least one tint. Due to the tint of the first pane 1, a good HUD display (projector image) with high contrast is possible. The intermediate layer 3 is made, for example, from a PVB film with a thickness of 0.76 mm. The PVB film has an essentially constant thickness, apart from any surface roughness that is customary in the industry. The PVB film can be designed with absorbing properties in the NIR range.

The first (outer) surface III of the second pane 2 is provided with a first coating 20 according to the invention, which has a refractive index of at least 1.9. The first coating 20 has a layer of an optically highly refractive material. The optically highly refractive layer of the first coating 20 is preferably based on silicon nitride, silicon-metal mixed nitrides such as silicon zirconium nitride (SiZrNx), silicon-titanium mixed nitride or silicon-hafnium mixed nitride. The layer thickness of the optically highly refractive layer should preferably be 20 nm to 80 nm, particularly preferably 30 nm.

The second (inside) surface IV of the second pane 2 is provided with a second coating 30 according to the invention. The first coating 20 according to the invention and the second coating 30 are optimized for the reflection of p-polarized radiation. They serve as reflection surfaces for the radiation of the projector 4 to generate the HUD projection. A first reflection takes place on the first coating 20. However, since the angle of incidence of the projector radiation deviates slightly from the Brewster angle, a second reflection of the projector radiation also takes place at the air-glass transitions, which leads to the formation of a second image. The second image, which is generated by the second reflection on the interior surface IV of the pane 2, can overlap well with the first image, which is generated by the first reflection on the first coating 20, due to the very small thickness of the second pane 2. Since the intensity of the reflected radiation (in contrast to the reflection on the outside surface I of the outer pane 1) is not already weakened by passing through the first coating 20 and the second coating 30, the first image enhances the visibility of the second image.

When looking through the composite pane 10 from the interior of the passenger car, the first coating 20 and the second coating 30 are arranged in front of the tinted first pane 1 (outer pane). This creates a particularly high-contrast and visually easily perceptible HUD display when the first and second coatings 20, 30 are irradiated with p-polarized light from the projector 4.

The radiation from the projector 4 is essentially p-polarized. Since the projector 4 irradiates the composite pane 10 with an angle of incidence of approximately 65° to 75°, which is close to the so-called Brewster angle, the radiation from the projector is only insignificantly reflected on the first (outer) surface I of the composite pane 10. The projector 4 is, for example, a display, in this case an LCD display. It would also be possible, for example, for the composite pane 10 to be a roof pane, side pane or rear pane. The p-polarized radiation is light waves within the wavelength range of 380 nm to 780 nm that is visually perceptible to humans.

4 shows the layer sequence of an exemplary embodiment of the second coating 30. The second coating 30 has a first layer of a dielectric material 30.1 with a refractive index greater than or equal to 1.9 and a second layer of a dielectric material 30.2 with a refractive index less than or equal to 1.6. The first layer of the second coating 30 has a dielectric material 30.1 based on silicon nitride, silicon-metal mixed nitrides such as silicon zirconium nitride (SiZrNx), silicon-titanium mixed nitride or silicon-hafnium mixed nitride. The second layer 30.2 of the second coating 3 has a dielectric material 30.2 based on silicon oxide (SiO ₂ ). The second layer 30.2 is an optically low-refractive layer compared to the first layer 30.1 of the second coating 30. The layer thicknesses of the dielectric layers of the second coating should preferably be 50 nm to 200 nm, particularly preferably 70 nm to 115 nm.

The first layer 30.1 and the second layer 30.2 of the second coating 30 are arranged congruently one above the other, with the first layer 30.1 being applied to the second surface IV of the second pane 2 and the second layer 30.2 being applied to the first layer 30.1.

While it would be intuitively obvious to reduce the reflection on the second surface IV of the second pane 2 by means of a reflection-reducing coating (anti-reflection coating), according to the invention the interior-side surface IV of the second pane 2 is, on the contrary, provided with a reflection-enhancing coating 30 which increases the overall reflectivity of the second surface IV.

The layer sequences of a composite pane 10 with the first coating 20 on the first (outer) surface III of the second pane 2 and the second coating 30 on the second (inner) surface IV of the second pane 2 according to the example according to the invention are shown in Table 1 together with the materials and geometric layer thicknesses of the individual layers. Table 1: material Reference symbol Layer thickness _SiO2 30.2 30 115nm SiZrN 30.1 70nm Soda-lime glass 2 1.6mm SiZrN 20 30nm PVB 3 0.76mm Soda-lime glass 1 2.1mm

By additionally absorbing the heat radiation at the intermediate layer 3, the TTS value of the composite pane can be improved, i.e. reduced, by up to 3%. This result was unexpected and surprising for the expert.

In 5 a reflection spectrum of the composite pane 10 with a layer structure according to Table 1 is shown. The reflection spectrum was recorded with a light source that emits p-polarized radiation of uniform intensity in the spectral range under consideration, when viewed via the second pane 2 (the so-called interior-side reflection over the inner pane) at an angle of incidence of 65° to the interior-side surface normal. From the graphic representation of the spectrum, it can be seen that the composite pane 10 according to the invention, although it has no metallic layer, offers quite good reflectivity in the optical range. The two coatings 20, 30, in combination with the quite thin second pane 2 and the tinted first pane 1, result in high reflectivity to p-polarized radiation, particularly in the spectral range from 400 nm to 780 nm.

The optical parameters achieved are shown in the following Table 2. In addition, a comparative example of a generic composite pane that does not meet the features according to the invention is shown in Table 2. Table 2: Example according to the invention Comparison example TTS 61.1 TTS 58.5 TLO° 72.9 TL (A) 73.0 Rg8° 22.1 a*g 8° 1.2 RL (A) 17.2 b*g 8° -1.3 Rg60° 27.9 a*g -8.5 a*g 60° 0.8 b*g 60° 0.3 b*g -10.8 at -2.2 b*t 2.0 a*g 60° -1.3 R p-HUD 20.5 a* p-HUD 1.5 b*g 60° -6.4 b* p-HUD 0.5 TE 53.9 RE 29.2

• TTS-Wert (ein Maß für die totale transmittierte Wärmestrahlung durch die Scheibe) Lichttransmission gemäß Lichtart A: TL A,
• Lichtreflexion gemäß Lichtart A: RL A,
• Farbwerte a*g und b*g
• Farbwerte a*g und b*g gemäß Lichteinfallswinkel 60°

The following colorimetric coordinates and parameters are listed:

• TTS value (a measure of the total transmitted thermal radiation through the pane) Light transmission according to light type A: TL A,
• Light reflection according to illuminant A: RL A,
• Color values a*g and b*g
• Colour values a*g and b*g according to light incidence angle 60°

It is clear that the example according to the invention has improved optical parameters. A significant advantage of the composite pane 10 according to the invention is that high-frequency signals can penetrate the composite pane and at the same time the reflectivity is improved with regard to HUD displays. At the same time, the external reflection color is relatively neutral (bluish/green tint), so that the composite pane does not have an unpleasant color cast (e.g. reddish tint).

List of reference symbols:

1

first disc

2

second disc

3

thermoplastic intermediate layer

4

projector

5

Viewer / Driver

10

Composite pane

20

first coating

30

second coating

30.1

first layer of the second coating 30

30.2

second layer of the second coating 30

O

Upper edge of the laminated protective screen 10

U

Lower edge of the laminated protective screen 10

B

HUD area of the composite protective screen 10

E

Eye box

I

first surface of the first pane 1 facing away from the intermediate layer 3

II

second surface of the first pane 1 facing the intermediate layer 3

III

first surface of the second pane 2 facing the intermediate layer 3

IV

second surface of the second pane 2 facing away from the intermediate layer 3

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2019179682 A1 [0007]
• WO 2019179683 A1 [0007]
• WO 2019206493 A1 [0007]
• WO 2021104800 A1 [0007]
• WO 2021209201 A1 [0008]
• EP 0844507 A1 [0009]

Claims (15)

Composite pane for a head-up display system, comprising at least - a first pane (1) with a first surface (I) and a second surface (II), a second pane (2) with a first surface (III) and a second surface (IV) and a thermoplastic intermediate layer (3) which is arranged between the second surface (II) of the first pane (1) and the first surface (III) of the second pane (2), - a first coating (20) on the surface (III) of the second pane (2) facing the intermediate layer (3), - a second coating (30) on the surface (IV) of the second pane (2) facing away from the intermediate layer (3), - a HUD region (B) which has the first coating (20) and the second coating (30), wherein the first coating (20) and the second coating (30) are provided for reflecting p-polarized radiation, wherein a refractive index of the first coating (20) is at least 1.9, where the second coating (30) has at least a first layer (30.1) of a dielectric material with a refractive index greater than or equal to 1.9 and a second layer (30.2) of a dielectric material with a refractive index less than or equal to 1.6, and wherein the second pane (2) has a smaller thickness than the first pane (1). Composite pane according to Claim 1 , wherein the first coating (20) and the second coating (30) comprise exclusively dielectric layers. Composite pane according to Claim 1 or 2 , wherein the first coating (20) and the second coating (30) are free of electrically conductive materials. Composite pane according to one of the Claims 1 until 3 , wherein the first pane (1) has a tint. Composite pane according to one of the Claims 1 until 4 , wherein the first coating (20) comprises a dielectric layer based on silicon-zirconium mixed nitride, silicon nitride, silicon-titanium mixed nitride, silicon-hafnium mixed nitride and/or titanium oxide. Composite pane according to one of the Claims 1 until 5 , wherein the first layer of the second coating (30) comprises a dielectric layer based on silicon-zirconium mixed nitride, silicon nitride, silicon-titanium mixed nitride, silicon-hafnium mixed nitride, indium tin oxide or titanium oxide, the second layer of the second coating (30) comprises a dielectric layer based on a dielectric oxide, in particular silicon oxide (SiO ₂ ) or doped silicon oxide, and wherein the first layer (30.1) of the second coating (30) is arranged closer to the second disk (2) than the second layer (30.2) of the second coating (30). Composite pane according to one of the Claims 1 until 6 , wherein the second coating (30) has a total material thickness of at most 200 nm, preferably at most 185 nm. Composite pane according to one of the Claims 1 until 7 , wherein the intermediate layer (3) is a film with absorbing properties in the wavelength range from 780 nm to 3000 nm. Composite pane according to one of the Claims 1 until 8th , wherein the intermediate layer (3) comprises a conductor system with heating function, in particular several resistance wires as heating conductors. Composite pane according to one of the Claims 1 until 9 , wherein at least one cover layer, in particular an opaque cover print, is arranged on the second surface (II) of the first pane (1) in an edge region of the composite pane (10) and at least partially in the HUD region in the viewing direction of the composite pane (10). Composite pane according to one of the Claims 1 until 10 , wherein the second disc (2) has a thickness of less than or equal to 1.6 mm, preferably less than or equal to 1.4 mm, particularly preferably 1.1 mm. Composite pane according to one of the Claims 1 until 11 , wherein the first coating (20) and the second coating (30) were deposited by magnetron sputtering or by a chemical deposition process, in particular at atmospheric pressure. Composite pane according to one of the Claims 1 until 12 , wherein the composite pane (10) is a windshield of a passenger car. Vehicle, in particular passenger car, with a composite pane (10) according to one of the Claims 1 until 13 . Projection arrangement for a head-up display system, comprising at least • a composite pane (10) according to one of the Claims 1 until 13 and • a projector (4) directed at the HUD region (B) of the composite pane (10), wherein the second surface (IV) of the second pane (2) is provided for irradiation by the projector (4) and wherein the radiation of the projector (4) is predominantly p-polarized.

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