Display device

Abstract

The invention relates to a display device (1) having two operating modes. The invention also relates to a transport means comprising such a display device (1). The display device (1) comprises a display panel (2), a first backlighting system (5), a second backlighting system (6), and an element (7) that is located between the first backlighting system (5) and the second backlighting system (6) in order to restrict an angular distribution of the light emitted by the second backlighting system (6). The display panel (2) has a first polarising filter (3) arranged on the front side from the perspective of an observer and a second polarising filter (4) arranged on the rear side from the perspective of the observer. The second polarising filter (4) has an anisotropically scattering component (40).

Description

[0001] Description

[0002] Display device

[0003] The present invention relates to a display device with two operating modes. The invention also relates to a means of transportation with such a display device.

[0004] With the increasing size and number of displays in motor vehicles, the risk of the driver being disturbed by display content not intended for them increases. Display devices currently under development offer the option of switching the display between a mode in which the image is visible to all viewers (public mode) and a mode with restricted visibility (privacy mode). An efficient approach to this is the use of liquid crystal displays (LCDs) with dual backlighting. A first backlight emits light with a wide angular distribution, while a second backlight emits light with a restricted angular distribution.

[0005] As an alternative to this approach, concepts are being developed in which the light characteristics are controlled by one or more additional liquid crystal cells. Visibility can be restricted in a specific area of ​​the screen by segmenting the liquid crystal cell. Furthermore, it is possible to restrict the light characteristics using a switchable louvre film. The various approaches described can also be combined.

[0006] Against this background, DE 102017 007 669 A1 describes a screen that can be operated on a first partial area of ​​its screen in two operating modes: a free view mode and a restricted view mode, wherein the remaining screen area outside the first partial area permanently has a free view mode. The screen comprises a first extensive backlight that emits light in an unrestricted angular range and is substantially not arranged below said first partial area, and a second extensive backlight that emits light in a restricted angular range and is substantially arranged below said first partial area.

[0007] Display devices with a limited visibility operating mode, which have a luminance that drops very steeply towards the driver's position, usually use so-called louver films to block radiation towards the driver. These films are integrated into the backlight. However, due to the special structural properties and structure sizes of the films and light guides used in the backlight, there is an optical overlap with the subpixel structures of the liquid crystal panel above, which is perceived as a disturbing structure, e.g. as a moiré pattern or so-called speckled effect. The effects described are particularly disturbing if an adjacent area has no means of restricting visibility and therefore does not display any disturbing structure.

[0008] In this context, US 2013 / 0 077 316 A1 describes a display device comprising a light source and an optical waveguide, a diaphragm, an anisotropic scattering film, and a transmissive liquid crystal panel arranged along the path of the light emitted by the light source. The anisotropic scattering film serves to reduce the moiré effect.

[0009] US 2017 / 0 205 663 A1 describes a reflective liquid crystal

[0010] Display device. The display device comprises a liquid crystal panel and a front light unit. The liquid crystal panel contains a planar anisotropic diffusion element with low-refractive-index regions and high-refractive-index regions. The purpose of the anisotropic diffusion element is to reduce the moiré effect.

[0011] It is an object of the present invention to provide an improved solution for the design of a display device with two operating modes.

[0012] This object is achieved by a display device having the features of claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0013] According to a first aspect of the invention, a display device comprises:

[0014] - a display panel with a first polarizing filter arranged at the front from the viewpoint of a viewer and a second polarizing filter arranged at the rear from the viewpoint of the viewer, wherein the second polarizing filter has an anisotropically scattering component;

[0015] - a first backlight;

[0016] - a second backlight; and

[0017] - an element arranged between the first backlight and the second backlight for restricting an angular distribution of the light emitted by the second backlight.

[0018] In the solution according to the invention, the system consists of a display panel, preferably a liquid crystal panel, with dual backlighting, in which the two operating modes—unrestricted visibility (public mode) and restricted visibility (privacy mode)—can be switched independently of one another. Unrestricted visibility is achieved by a specially structured, side-illuminated, full-surface light guide mounted behind the display panel. The rear polarizing filter of the display panel is equipped with an anisotropically scattering component. The relative position of the scattering elements and their design effectively prevent moiré effects.The anisotropic scattering component thus enables the suppression of visible cosmetic defects while maintaining the sharp shading characteristics created by the backlight for the limited visibility operating mode.

[0019] Optionally, the shading characteristics can be optimized by additional liquid crystal cells arranged between the first backlight and the display panel. In this case, the polarizing filter with an anisotropic scattering component can also be used there.

[0020] The inventive solution thus provides a display device that can be selectively switched to a mode with unrestricted visibility and a mode with restricted visibility. This display device exhibits a steep shading characteristic towards the viewer, e.g., the operator of a means of transport, without any loss of image quality. In particular, there is little or no noticeable difference in image quality between areas with and without restricted visibility. Further advantages include the high energy efficiency of the design and the ability to adopt existing architectures. There is little or no additional effort required for development and assembly.

[0021] According to one aspect of the invention, the first backlighting comprises a side-illuminated first planar light guide. The second backlighting comprises a side-illuminated second planar light guide or is configured as a matrix backlighting. For the limited-visibility mode, the backlighting can be realized either by another light guide with lateral coupling or, alternatively, by a matrix backlighting, e.g., by an LED matrix (LED: Light Emitting Diode). The type of backlighting used is at the discretion of the person skilled in the art.

[0022] According to one aspect of the invention, the element for restricting an angular distribution comprises a louvre film. Preferably, the restricted angular distribution for the restricted visibility mode is achieved by various optical films arranged between the two backlights. One of these films, preferably the topmost film, is a louvre film. The use of louvre films has the advantage that extensive experience with them already exists.

[0023] According to one aspect of the invention, a scattering profile of the anisotropically scattering component is configured such that a broad scattering characteristic is created in a first direction and a narrow scattering characteristic is created in a second direction perpendicular to the first direction. Preferably, the scattering profile is configured such that an ideally Gaussian or Lambertian characteristic is created in the first, vertical direction, while ideally no scattering occurs in the second, horizontal direction. In this way, a particularly sharp shading characteristic is achieved.

[0024] According to one aspect of the invention, the anisotropically scattering component is formed by scattering elements integrated into the second polarizing filter. The integration of scattering elements into the polarizing filter has the advantage that the polarizing filter has a flat surface, which facilitates handling of the polarizing filter during assembly of the display device. Furthermore, damage to the scattering elements can be avoided.

[0025] According to one aspect of the invention, the anisotropically scattering component is formed by scattering elements arranged on a surface of the second polarizing filter. The scattering elements can be incorporated into the surface of the polarizing filter, e.g., by embossing, but they can also be applied to the surface by a coating. In both cases, conventional polarizing filters can be used as the starting material.

[0026] According to one aspect of the invention, the anisotropically scattering component is formed by a scattering film arranged on a surface of the second polarizing filter. For example, an anisotropically scattering adhesive layer can be applied to the polarizing filter. This embodiment has the advantage that no additional processing of the polarizing filter is required.

[0027] According to one aspect of the invention, the scattering film is formed by a film with polymer-dispersed liquid crystals. In this embodiment, a PDLC film (PDLC: Polymer Dispersed Liquid Crystal;

[0028] In polymer-dispersed liquid crystals (PDLCs), the polymer matrix is ​​designed to form elongated structures in the horizontal direction. The use of PDLC films has the advantage that they are available in numerous forms on the market.

[0029] According to one aspect of the invention, the scattering elements of the anisotropic scattering component are designed identically or differently. In addition to embodiments with identical scattering elements, embodiments with individually designed scattering elements are also possible. These allow the scattering characteristics to be adapted very precisely depending on the application.

[0030] A display device according to the invention is preferably used in a means of transport. The means of transport may be, for example, a motor vehicle, but alternatively also an aircraft, a rail vehicle, or a watercraft.

[0031] Further features of the present invention will become apparent from the following description and the appended claims in conjunction with the figures. Figure Overview

[0032] Fig. 1 shows schematically a section through a first embodiment of a display device with two operating modes according to the prior art;

[0033] Fig. 2 shows schematically a section through a second embodiment of a display device with two operating modes according to the prior art;

[0034] Fig. 3 shows schematically a section through a third embodiment of a display device with two operating modes according to the prior art;

[0035] Fig. 4 shows schematically a section through a display device according to the invention with two operating modes;

[0036] Fig. 5 shows schematically a scattering profile of the polarizing filter of the display device according to the invention;

[0037] Fig. 6 shows schematically a plan view of a surface structure of the polarizing filter;

[0038] Fig. 7 shows schematically a first embodiment of the polarizing filter with scattering elements on the surface;

[0039] Fig. 8 schematically shows a second embodiment of the polarizing filter with scattering elements on the surface; Fig. 9 schematically shows an embodiment of the polarizing filter with scattering elements inside;

[0040] Fig. 10 shows schematically an embodiment of the polarizing filter with a scattering film; and

[0041] Fig. 11 shows schematically a means of transport in which a solution according to the invention is implemented.

[0042] Character description

[0043] To better understand the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. Like reference numerals are used in the figures for like or equivalent elements and are not necessarily described again for each figure. It is understood that the invention is not limited to the illustrated embodiments and that the described features can also be combined or modified without departing from the scope of the invention as defined in the appended claims.

[0044] Fig. 1 schematically shows a section through a first embodiment of a display device 1 with two operating modes according to the prior art. The display device 1 has a display panel 2, a first backlight 5, a second backlight 6, and an element 7 arranged between the first backlight 5 and the second backlight 6 for restricting an angular distribution of the light emitted by the second backlight 6. The display panel 2 has a first polarizing filter 3 arranged at the front from the viewpoint of an observer and a second polarizing filter 4 arranged at the rear from the viewpoint of the observer. The display panel 2 can, in particular, be a liquid crystal panel. The first backlight 5 has a first planar light guide 50, into which light is coupled from laterally arranged light sources 51, and is intended for the operating mode with unrestricted visibility.In this embodiment, the second backlight 6 has a second planar light guide 60, into which light is coupled from laterally arranged light sources 61, and is provided for the operating mode with limited visibility. A foil stack 9 is arranged on the second light guide 60. The foils of the foil stack 9 have the task of scattering, collecting, or directing the generated light. A blind foil serves as element 7 for limiting the angular distribution. Other components of the display device 1, such as a cover glass, a housing, etc., are not shown for the sake of simplicity.

[0045] Fig. 2 schematically shows a section through a second embodiment of a display device 1 with two operating modes according to the prior art. The display device 1 largely corresponds to the embodiment shown in Fig. 1, however, the second backlighting is not realized by means of a laterally illuminated second planar light guide, but rather by a matrix backlighting 62. The matrix backlighting 62 has a plurality of light sources 61 and a reflector 63, which directs the light emitted by the light sources 61 toward the display panel 2.

[0046] Fig. 3 shows a schematic section through a third embodiment of a display device 1 with two operating modes according to the prior art. The display device 1 largely corresponds to the embodiment shown in Fig. 1. However, to optimize the shading characteristics, an additional liquid crystal element 10 is provided, which is arranged together with an additional polarizing filter 11 between the first backlight 5 and the display panel 2, in this example between the second polarizing filter 4 and the display panel 2. Fig. 4 shows a schematic section through a display device 1 according to the invention with two operating modes. The display device 1 largely corresponds to the embodiment shown in Fig. 1, ie both the first backlight 5 and the second backlight 6 each have a laterally illuminated planar light guide 50, 60 with the corresponding light sources 51, 61.Alternatively, the second backlight 6 can also be implemented as a matrix backlight. According to the invention, the second polarizing filter 4 has an anisotropically scattering component 40, which can be implemented in different ways. A louver film preferably serves as the element 7 for limiting the angular distribution. Further components of the display device 1, such as light sources, a cover glass, a housing, etc., are again not shown for the sake of simplicity.

[0047] Fig. 5 schematically shows a scattering profile of the second polarizing filter of the display device from Fig. 4. The anisotropically scattering component of the polarizing filter is designed such that a broad scattering characteristic, ideally a Gaussian or Lambertian characteristic, is created in a first, vertical direction. In contrast, a narrow scattering characteristic is created in a second, horizontal direction perpendicular to the first direction, with ideally no scattering at all.

[0048] Fig. 6 schematically shows a top view of a surface structure of the polarizing filter 4. Numerous scattering elements 400 can be seen, which can be located on the surface 41 of the polarizing filter 4 or inside the polarizing filter 4. The scattering elements 400 each have a pronounced extension in the horizontal direction, i.e., along the X-axis, while they have only a small extension along the Y-axis and the Z-axis. In this way, the scattering profile shown in Fig. 5 is achieved.

[0049] Fig. 7 shows schematically a first embodiment of the polarizing filter 4 with

[0050] Scattering elements 400 on the surface 41. In this embodiment, all scattering elements 400 have the same cross-section. The scattering elements 400 can be incorporated into the surface 41 of the polarizing filter 4, for example, by embossing, but they can also be applied to the surface 41 by means of a coating.

[0051] Fig. 8 schematically shows a second embodiment of the polarizing filter 4 with scattering elements 400 on the surface 41. In this embodiment, the scattering elements 400 are individually designed, meaning they can have different cross-sections. This allows the scattering characteristics to be adapted very precisely depending on the application.

[0052] Fig. 9 schematically shows an embodiment of the polarizing filter 4 with scattering elements 400 inside. In this embodiment, the anisotropically scattering component is formed by scattering elements 400 integrated into the polarizing filter 4. In the example shown, the scattering elements 400 are again individually designed. Alternatively, however, they can also be designed identically, i.e., have the same cross-section.

[0053] Fig. 10 schematically shows an embodiment of the polarizing filter 4 with a scattering film 8. The scattering film 8 can, for example, be an anisotropically scattering adhesive layer applied to the polarizing filter 4. Alternatively, the scattering film 8 can be formed by a film with polymer-dispersed liquid crystals. In this embodiment, the polymer matrix of a PDLC film is designed to form elongated structures in the horizontal direction.

[0054] Fig. 11 schematically shows a means of transport 100 in which a solution according to the invention is implemented. In this example, the means of transport 100 is a motor vehicle. Data on the vehicle's surroundings can be acquired using a sensor system 101. The sensor system 101 can in particular comprise sensors for environmental detection, e.g., ultrasonic sensors, laser scanners, radar sensors, lidar sensors, or cameras. The information acquired by the sensor system 101 can be used to generate content to be displayed for the display device 1. Further components of the motor vehicle in this example are a navigation system 102, by which position information can be provided, as well as a

[0055] Data transmission unit 103. Using the data transmission unit 103, a connection to a backend can be established, for example, to obtain updated software for components of the motor vehicle. A memory 104 is provided for storing data. Data exchange between the various components of the motor vehicle takes place via a network 105.

[0056] List of reference symbols

[0057] 1 display device

[0058] 2 display panel

[0059] 3 First polarizing filter

[0060] 4 Second polarizing filter

[0061] 40 Anisotropic scattering component

[0062] 41 Surface

[0063] 400 scattering element

[0064] 5 First backlighting

[0065] 50 First flat light guide

[0066] 51 Light source

[0067] 6 Second backlight

[0068] 60 Second flat light guide

[0069] 61 Light source

[0070] 62 matrix backlight

[0071] 63 Reflector

[0072] 7 Element for restricting an angular distribution

[0073] 8 Scattering film

[0074] 9 stacks of slides

[0075] 10 liquid crystal element

[0076] 11 polarizing filters

[0077] 100 means of transport

[0078] 101 Sensor Technology

[0079] 102 Navigation system

[0080] 103 Data transmission unit

[0081] 104 memory

[0082] 105 Network

Claims

Patent claims 1. Display device (1 ) with: - a display panel (2) with a first polarizing filter (3) arranged at the front from the viewpoint of an observer and a second polarizing filter (4) arranged at the rear from the viewpoint of the observer, wherein the second polarizing filter (4) has an anisotropically scattering component (40); - a first backlight (5); - a second backlight (6); and - an element (7) arranged between the first backlight (5) and the second backlight (6) for restricting an angular distribution of the light emitted by the second backlight (6).

2. Display device (1) according to claim 1, wherein the first backlight (5) has a laterally illuminated first planar light guide (50) and the second backlight (6) has a laterally illuminated second planar light guide (60) or is designed as a matrix backlight (62).

3. Display device (1) according to claim 1, wherein the element (7) for restricting an angular distribution comprises a blind film.

4. Display device (1) according to one of the preceding claims, wherein a scattering profile of the anisotropically scattering component (40) is designed such that a wide scattering characteristic is created in a first direction and a narrow scattering characteristic is created in a second direction perpendicular to the first direction.

5. Display device (1) according to one of claims 1 to 4, wherein the anisotropically scattering component (40) is formed by scattering elements (400) integrated in the second polarizing filter (4).

6. The display device (1) according to one of claims 1 to 4, wherein the anisotropically scattering component (40) is formed by scattering elements (400) arranged on a surface (41) of the second polarizing filter (3).

7. The display device (1) according to one of claims 1 to 4, wherein the anisotropically scattering component (40) is formed by a scattering film (8) arranged on a surface (41) of the second polarizing filter (4).

8. Display device (1) according to claim 7, wherein the scattering film (8) is formed by a film with polymer-dispersed liquid crystals.

9. Display device (1) according to one of claims 5 to 8, wherein scattering elements (400) of the anisotropically scattering component (40) are designed the same or differently.

10. Means of transport (100) with a display device (1) according to one of the preceding claims.

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