Backlight and lighting device with optical film, screen and optical film

Abstract

The invention relates to a backlight (13) which extends in a planar manner, emits light and has an optical film for controlling and limiting the viewing angle range of a viewer. The optical film, viewed from a viewer direction, comprises: a first polarizing layer (1) having a first absorption axis that forms an angle of 0-30 DEG with a surface normal of the optical film; at least one phase shift compensation layer for improving the limitation of the viewing angle range; and a second polarizing layer (2) having a second absorption axis parallel to the surface of the optical film. According to the invention, various technical schemes and combination schemes are provided in which a spatially uniform compensation layer made of a uniaxial or biaxial birefringent material is provided, in which the material and thickness of the compensation layer are specified such that the luminous density is minimum within a specified solid angle range. The solid angle range does not comprise the whole half space except for the cone which is concave in the viewing direction.

Description

Technical Field

[0001] The present invention relates to a backlight that extends planarly, emits light, and includes an optical film for controlling and limiting a viewer's viewing angle. The film comprises a first polarizing layer with a first absorption axis and a second polarizing layer with a second absorption axis. The first absorption axis forms an angle of 0° to 30° with respect to the surface normal of the optical film, and the second absorption axis is parallel to the surface of the optical film. At least one phase-shift compensation layer is disposed therebetween to improve the limitation of the viewing angle. As viewed from the viewer, either the first polarizing layer or the second polarizing layer may form the layer closest to the viewer.

[0002] In recent years, significant progress has been made in extending the viewing angle range of LCDs. However, there are often situations where the screen's very large viewing area becomes a disadvantage. Information, such as banking details or other personal information, as well as sensitive data, is increasingly being provided on portable devices such as laptops and tablets. Consequently, people need to control who can see this sensitive data; they need to be able to select a wide viewing angle range or viewing angle—public mode—to share the information on the display with others, for example, when viewing holiday photos or for advertising purposes. On the other hand, if the image information needs to be kept confidential, a narrower viewing angle range or viewing angle—private mode—is required.

[0003] A similar problem exists in the automotive industry: after the engine is started, the driver must not be distracted by visual content such as digital entertainment, while passengers want to be able to watch visual content while driving. Therefore, a screen that can switch between corresponding presentation modes is required.

[0004] Microsheet-based additional films have been used in portable displays to provide visual data protection. However, these films are not switchable or convertible; they must always be applied and removed manually. They also must be shipped separately from the display when not in use. Another major drawback of using these sheet films is light loss. Background Art

[0005] US 6,765,550 B2 describes privacy protection using micro-lamellae. The major drawbacks of this solution are the mechanical removal and attachment of the filter, and the light loss in the protection mode.

[0006] US 5,993,940 A describes the use of a film with small stripe-shaped prisms evenly distributed on the surface of the film to achieve a privacy mode, that is, a limited viewing mode with a small viewing angle range. The technical difficulty in research and development and manufacturing is quite high.

[0007] In WO 2012 / 033583 A1, switching between free and restricted fields of view is achieved by controlling the liquid crystals between so-called "chromophoric" layers. This process results in light loss and is technically very difficult.

[0008] US2012 / 0235891 A1 describes an extremely complex screen backlight. According to Figures 1 and 15 of the case, not only are several light guides used, but other complex optical elements are also used, such as a microlens assembly 40 and a prism structure 50, which shape the light from the rear lighting on the path to the front lighting. Its implementation is costly and technically difficult, and it also results in light loss. According to a variant shown in Figure 17 of US 2012 / 0235891A1, both light sources 4R and 18 generate light with a narrow illumination angle, wherein the light from the rear light source 18 undergoes a complex process before being converted into light with a large illumination angle. As mentioned above, such a complex conversion significantly reduces brightness.

[0009] JP 2007-155783 A uses a special optical surface 19, which is complex to calculate and manufacture. This surface deflects light into different narrow or wide areas depending on the angle of incidence. This structure is similar to a Fresnel lens. Furthermore, there are interfering side surfaces that deflect light in undesirable directions. Therefore, it is uncertain whether truly reasonable light distribution can be achieved.

[0010] US2013 / 0308185 A1 describes a special light guide with stepped sections that emits light in different directions over a large surface, depending on the direction in which the light guide is illuminated from its narrow side. In combination with a transmissive image reproduction device, such as an LC display, this creates a screen that can be switched between a free-viewing mode and a restricted-viewing mode. A major drawback is that the restricted-viewing effect can only be achieved left / right or up / down, but not all at once, as is necessary for certain payment processes. Furthermore, even in restricted-viewing mode, residual light may still be visible from obstructed viewing angles.

[0011] WO 2015 / 121398 A1, filed by the present applicant, describes a screen with two operating modes. To achieve the switching between operating modes, scattering particles are present in the volume of the corresponding light guide. However, the polymer scattering particles selected in this application generally suffer from the disadvantage that light is outcoupled from two large surfaces, so that approximately half of the useful light is emitted in the wrong direction, toward the backlight, and, due to structural reasons, cannot be recovered to a sufficient degree there. Furthermore, depending on the circumstances, and particularly at high concentrations, the scattering particles composed of polymers distributed in the volume of the light guide may lead to scattering effects that reduce the privacy protection effect in the protected operating mode.

[0012] The basic concept behind the "electrically induced birefringence (EDB)" approach is to utilize the switchable liquid crystals of an additionally applied LC panel to "filter" all light beams that do not exit the imaging layer at a specific beam angle. The disadvantages of this approach are the additional energy consumption and high cost, as well as the difficulty in shifting the + / -40° sweet spot, the optimal viewing position. The LC structure also suffers from insufficient absorption, as the light intensity attenuation increases again once the viewing angle exceeds the sweet spot. Consequently, for viewing angles greater than + / -40°, the light intensity is limited to a maximum of 3% of the maximum intensity.

[0013] US2019 / 0094626 A1 describes an optical layer structure for controlling or limiting the viewing angle, in which two phase difference plates are arranged as compensation layers on a linear polarizer. The two phase difference plates are λ / 4 plates, which have several structured, optically anisotropic, fin-shaped or strip-shaped layers, between which a carrier material can be arranged. They can have the same structure, but differ in their orientation after arrangement. The top layer forms a polarization layer, in which the absorption axis of the transition dipole moment used to achieve polarization is oriented in a direction perpendicular to the layer surface, a so-called "Z polarizer". In such a layer structured with fins, visual artifacts such as moiré fringes may still occur. Therefore, such layers can only be applied to screens whose resolution and characteristics such as size, aperture, scattering properties, and distance from the screen surface are known, but cannot be used universally and independently of the screen size.

[0014] The above-described methods and configurations generally have the disadvantages of significantly reducing basic screen brightness and / or requiring complex and expensive optical components for mode switching, and / or reducing resolution in the free-viewing public mode and / or introducing visual artifacts when using very high-resolution displays. Another disadvantage is that the viewing angle range is not completely restricted. Despite the restricted viewing angle, it is still possible to perceive image content with significantly reduced brightness, which can be disruptive, for example, when driving at night. Summary of the Invention

[0015] The object of the present invention is to develop a backlight having an optical film for controlling and limiting the viewing angle range of a viewer looking at the film, which is usually combined with a screen, thereby improving the limitation of the viewing angle range and making it more difficult for unauthorized users to peek into protected image content, i.e., further improving the so-called privacy effect.

[0016] In the optical film having the aforementioned layer structure and a backlight having such an optical film, the present invention provides a solution for achieving the aforementioned objectives through a special technical solution for the at least one compensation layer. The first and second polarizing layers are first described in detail. The first polarizing layer has a first absorption axis that forms an angle of 0° to 30° with respect to the surface normal of the optical film. When the angle is 0°, i.e., the absorption axis is parallel to the surface normal or perpendicular to the film surface, it is referred to as a "Z polarizer." Different angles within the aforementioned range up to 30° are also referred to as "Z* polarizers." The absorption of the first polarizing layer is typically static, but a switchable solution can also be employed, allowing angle-dependent absorption to be switched on and off. The second polarizing layer has a second absorption axis that is parallel to the surface of the optical film. Therefore, the second polarizing layer is a conventional linear polarizer. At least one phase-shift compensation layer is disposed between the first and second polarizing layers to improve the viewing angle range. Both the first and second polarizing layers can be positioned closest to the viewer. Preferably, all layers are fixedly connected, for example, by material bonding, welding, or optical bonding.

[0017] For ease of understanding, the following generally assumes that in the rectangular coordinate system formed by the x-, y-, and z-directions, the film surface lies in a plane parallel to the xy plane formed by the x- and y-directions. Therefore, the surface normal is parallel to the z-direction.

[0018] In order to improve the privacy effect, i.e., to improve the limitation of the viewing angle range, the at least one phase shift compensation layer can be constructed in two ways in principle. In a first alternative solution, hereinafter also referred to as alternative solution i, a first B* compensation layer is arranged between the first polarizing layer and the second polarizing layer. The first B* compensation layer is composed of a first biaxial birefringent material. The biaxial birefringent material has two optical axes and three main refractive axes, each of which corresponds (birefringently) to a refractive index n. x 、n y 、n z Depending on the technical solution of the first B* compensation layer and the orientation of its optical axis, the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis.

[0019]

[0020] Here, d represents the thickness of the first compensation layer, Δph is the phase shift caused by the first B* compensation layer, and λ is the wavelength that satisfies this condition, which is arbitrarily defined in principle. This defines an upper limit for the phase retardation of the B* compensation layer, which indirectly also specifies the maximum thickness.

[0021] In a second alternative (hereinafter also referred to as alternative ii), at least two compensation layers composed of uniaxially birefringent materials are disposed between the first and second polarizing layers. The spatially uniform first A* compensation layer is composed of a first uniaxially birefringent material having a first optical axis and two mutually different first principal refractive axes, wherein the first optical axis, which coincides with one of the first principal refractive axes, is perpendicular or parallel to the first absorption axis of the first polarizing layer. A spatially uniform second A* compensation layer is disposed behind the viewer and is composed of a second uniaxially birefringent material having a second optical axis and two second principal refractive axes, wherein the second optical axis of the second material, which coincides with one of the second principal refractive axes, is perpendicular to the first optical axis of the first material. The optical axes of these uniaxial materials are also referred to as special axes.

[0022] "Spatial uniformity" here means that the corresponding compensation layer is unstructured within its interior or within the area parallel to the optical film surface, and thus exhibits uniform properties across the entire area, unlike, for example, US2019 / 0094626 A1. To prevent visual artifacts in such a lamellar structured layer, one of the technical solutions in US2019 / 0094626 A1 requires specific adjustments to the layer structure for each configuration in terms of resolution, distance, aperture, surface, and scattering properties, which increases manufacturing costs. However, the optical film of the present invention, with its spatially uniform compensation layer, can be universally applied to a wide range of screen sizes and resolutions without requiring specialized adjustments.

[0023] Among them, each of the two A* compensation layers meets the condition

[0024]

[0025] Where d represents the thickness of the corresponding A* compensation layer, n e represents the special refractive index, n o represents the normal refractive index, Δph represents the phase shift caused by the first A* compensation layer or the second A* compensation layer, and λ represents an arbitrarily specified wavelength that satisfies this condition.

[0026] In both alternatives, the material and thickness d of the compensation layer are specified so that in the spherical coordinate system with its origin on the film surface and in the film plane, the luminous density is minimum only within a specified solid angle range R. The solid angle range R only includes a part of the possible perceptible half space, i.e., on the one hand, the azimuthal angle where the preferred orientation is measured relative to the plane of the film surface, or Less than the specified limit azimuth angle φ limThe preferred direction is the absolute value of . In principle, the preferred direction can be chosen arbitrarily, but should be determined based on the application of the optical film. When such an optical film is used, for example, in a screen with a fixed orientation (e.g., in a vehicle), the preferred direction is chosen so that it is parallel to an imaginary line between the eyes of an upright driver, i.e., typically extends horizontally.

[0027] On the other hand, the solid angle range in which the luminous density is minimum also includes a polar angle θ, measured relative to the first absorption axis and in a plane formed by the surface normal and the first absorption axis (the vectors of which have a common origin), the absolute value of which is greater than the specified limit polar angle θ lim , that is, with a limiting polar angle θ around the first absorption axis (which is here called the "zero axis") lim All solid angles outside the cone. In the case where the surface normal and the first absorption axis are parallel to each other, the polar angle is measured only with respect to the surface normal. When the optical film is applied to the screen described in the above example, the optical film acts as an effective line of sight restriction because the luminous density is minimum within the aforementioned solid angle range. Therefore, under ideal conditions, a viewer who is located within the aforementioned solid angle range relative to the spherical coordinate system of the optical film will not perceive any content on the screen due to the minimum luminous density within this range. The term "minimum luminous density" refers to a luminous density that is approximately zero, wherein the luminous density is significantly reduced compared to the luminous density outside the above solid angle range, so that the viewer cannot see any image content under ideal conditions.

[0028] In order to more clearly define the solid angle range, i.e. to achieve a greater drop in the luminous density within this solid angle range compared to the luminous density outside of this solid angle range, in this second alternative ii, advantageously a spatially uniform third C* compensation layer is arranged between the first A* compensation layer and the second A* compensation layer, said layer consisting of a third uniaxial birefringent material having a third optical axis and two third main refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer.

[0029] In order to achieve a symmetrical decrease in luminous density with respect to the film surface, the first absorption axis is perpendicular to the film surface. When this optical film is used in the aforementioned screen, a viewer looking at the screen along the surface normal of the screen will perceive a symmetrical decrease in luminous density depending on the viewing angle, whether to the right or left or in the preferred direction, that is, only in dependence on the absolute value of the polar angle. In this case, the limiting polar angle θ lim It is measured relative to the surface normal and is therefore the same for all azimuth angles, unlike when it is measured relative to the first absorption axis.

[0030] When the first absorption axis adopts this orientation, the first polarizing layer is also called a Z polarizing layer. When the first absorption axis adopts a different orientation within the aforementioned range, the first polarizing layer is called a Z* polarizing layer. That is, the use of the symbol "*" here indicates the generalization of the Z polarizing layer.

[0031] Likewise, the term A*compensation layer is a generalization of the term A compensation layer, and the term B*compensation layer is a generalization of the term B compensation layer. For definitions of the terms "Z polarizer layer," "A compensation layer," and "B compensation layer" known in the prior art, see Ho-Jin Choi et al., "Optical anisotropy conversion of retarder films made of rodlike and crosslike reactive molecules, and its dependence on the relative ratio and the orientation of the constituent molecules," published online in Optical Materials 99 (2020), reference number 109531.

[0032] When the first absorption axis is perpendicular to the film surface, meaning the first polarizing layer is configured as a Z-polarizer, several advantageous technical solutions arise: two for the first alternative and a third for the second alternative. The orientation of the optical axis of this compensation layer must, in principle, correspond to the orientation of the first absorption axis of the first polarizing layer to achieve the desired viewing area limitation. For example, if a viewer, such as a vehicle driver, is viewing the screen from an oblique angle rather than along the surface normal, the first absorption axis may preferably adopt a different orientation.

[0033] In a first technical solution based on the first alternative solution, the first absorption axis of the first polarizing layer is perpendicular to the surface of the optical film and the principal refractive axis corresponding to the minimum refractive index is parallel to the first absorption axis. In this technical solution, the first B* compensation layer is constructed as a -B compensation layer. The optical axis is located in the plane formed by the x-direction and the z-direction, and the three principal refractive axes correspond to the directions of the rectangular coordinate system, where n x >n y >n z , and n x The second absorption axis is parallel to the second polarizing layer. The latter condition also applies to the first absorption axis being tilted with respect to the surface normal by a small angle of up to about 10°, otherwise the main refractive axis will also be tilted, and the orientation of the coordinate system in the x, y and z directions is based on the orientation of the first absorption axis, which corresponds to the z direction of the coordinate system, wherein the essence is that n x perpendicular to the first absorption axis.

[0034] In a second technical solution based on the first alternative solution, the first absorption axis of the first polarizing layer is perpendicular to the surface of the optical film and the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis. In this technical solution, the first B* compensation layer is constructed as a +B compensation layer. The optical axis is located in the plane formed by the y-direction and the z-direction, and the three principal refractive axes correspond to the directions of the rectangular coordinate system, where n z >n x >n y , and n y The second absorption axis is parallel to the second polarizing layer. The latter condition also applies to the first absorption axis being tilted with respect to the surface normal by a small angle of up to about 10°, otherwise the main refractive axis will also be tilted, and the orientation of the coordinate system in the x, y and z directions is based on the orientation of the first absorption axis, which corresponds to the z direction of the coordinate system, wherein the essence is that n y perpendicular to the first absorption axis.

[0035] In a third technical solution based on the second alternative solution, the first absorption axis of the first polarizing layer (1) is also perpendicular to the surface of the optical film. In this technical solution, the first A* compensation layer is constructed as a +A compensation layer, and the second A* compensation layer is constructed as a -A compensation layer, or vice versa. In the case where a third C* compensation layer is provided, it is constructed as a -C or +C compensation layer.

[0036] In order to keep the manufacturing costs low, the first A* compensation layer and the second A* compensation layer preferably have the same structure, ie, both compensation layers are either constructed as +A compensation layers or as −A compensation layers and have the same thickness.

[0037] Among all the aforementioned technical solutions, according to a particularly preferred embodiment, a liquid crystal layer switchable between at least two states is disposed between the second polarizing layer and the compensation layer closest to it. The liquid crystal layer is configured to transmit light transmitted by the second polarizing layer with unchanged or 90° rotated linear polarization in a first switching state, and transmit the light with circular, elliptically, or linear polarization in a second switching state. In the first switching state, the 90° rotation means that linearly polarized light becomes linearly or elliptically polarized light after passing through the switchable liquid crystal layer, with the majority of the electric field vectors rotated by 90°. In other words, the polarization is not rotated exactly 90°. The addition of a switchable liquid crystal layer enables switching between privacy mode and public mode, a feature that is particularly evident when the optical film is integrated into a screen. The previously described drop in luminous density within a specified solid angle range is permanent for optical films but can be eliminated by using a switchable liquid crystal layer. The first switching state corresponds to privacy mode, in which light remains linearly polarized. The second switching state corresponds to public mode, in which light is typically elliptically polarized, but other polarizations are possible depending on the selected liquid crystal layer. In public mode, the luminous density within the specified solid angle range does not decrease or decreases only slightly. Therefore, if this arrangement is used in a screen, the image content can be perceived regardless of the viewer's position (i.e., without restrictions) within the technically feasible range. In privacy mode, however, the image content cannot be perceived by people standing sideways (relative to the direction of the first absorption axis). Alternatively, the liquid crystal layer can be arranged between the first polarizing layer and the compensation layer closest to it.

[0038] This switchable liquid crystal layer is typically used together with a static first polarizing layer to produce a switchable optical film. If the functionality of the switchable liquid crystal layer can be fulfilled by the switchable first polarizing layer, then the switchable liquid crystal layer can also be omitted. In this case, the first polarizing layer can be designed, for example, as a liquid crystal layer embedded with a dye, a so-called "Dye-LC-Zellen" (dye LC cell). This type of liquid crystal layer is particularly suitable when the first absorption axis, i.e., the absorption axis of the first polarizing layer, is parallel to the surface normal of the optical film.

[0039] The sight-limiting effect within the specified solid angle range is preferably achieved by the following means: the components of the optical film are coordinated with each other so that within the specified solid angle range R, the loss function

[0040] C2=∫ R lnT(φ,θ)dΩ

[0041] Minimum, among which is the angle-dependent transmittance, and Ω is the solid angle. That is, the natural logarithm of the angularly resolved transmittance is calculated and integrated over the solid angle range for which the privacy protection is to be optimized. This logarithm implements weighting so that transmittances of different orders of magnitude are taken into account during the optimization. Other weighting methods, such as linear weighting, can also be used. In this case, there is no need to apply the logarithm to the transmittance. Commercially available optical design programs can be used to coordinate the components with each other in a way that satisfies this condition and implement the optical design of the present invention, such as the LCD program from Uniglobe Kisco. or TecwizLCD by INCROPS

[0042] In common applications, the limiting azimuth angle φ is preferably lim 30° to 40° to the left and right of the preferred direction, and / or the extreme polar angle θ lim The angle is 40° to 50° to the left and right of the surface normal or the first absorption axis (if it is tilted relative to the surface normal).

[0043] In the case where the film is not provided with the aforementioned switchable liquid crystal layer, the backlight having the aforementioned optical film can be integrated into the lighting device of the screen. In the case where the film is provided with the switchable liquid crystal layer, the backlight can be integrated into the screen.

[0044] Specifically, a backlight having a non-switchable optical film, i.e., one without a switchable liquid crystal layer, can be incorporated into an illumination device for a transmissive screen (particularly an LC display), wherein the illumination device is configured to operate in two operating modes: B1 (for free viewing mode) and B2 (for restricted viewing mode). In the restricted viewing mode, light is emitted into a solid angle range that is more limited than in the free viewing mode. The illumination device includes a planar backlight that emits light, the backlight having a backlight source and the aforementioned non-switchable optical film. If the second polarizing layer of the optical film is arranged in front of the first polarizing layer in the viewing direction, then for the backlight as a whole (and the same applies to other technical solutions described below), the backlight source emits unpolarized light; in the opposite arrangement, the light emitted by the backlight source can be (partially) polarized. A plate-shaped light guide is arranged in front of the backlight in the viewing direction for a viewer looking toward the lighting device. The light guide has two large surfaces connected by a narrow side and includes an outcoupling element on at least one of these large surfaces and / or within its volume. A light-emitting element is arranged laterally on at least one of the narrow sides of the light guide. A linear polarizing filter is arranged in front of the backlight or the light guide in the viewing direction. Optionally, this polarizing filter can correspond to the second polarizing layer of an optical film, or a special solution can be used. This restricts the propagation direction of light originating from the backlight and passing through the linear polarizing filter. In operating mode B2 for restricted viewing, the backlight is turned on and the light-emitting element is turned off. Only the backlight emits light within the restricted viewing angle range. In operating mode B1 for free or public viewing, at least the light-emitting element is turned on, thereby compensating for or overcompensating for the limited illumination provided solely by the backlight. Accordingly, the backlight can be turned on or off in public viewing mode. In this case, the transmissive screen is arranged in front of the lighting device.

[0045] The present invention also includes a screen capable of operating in at least two operating modes: B1 (for free viewing) and B2 (for restricted viewing). In the restricted viewing mode, light is emitted into a viewing angle or solid angle range that is more restricted for the viewer than in the free viewing mode. In a solution having a switchable liquid crystal layer that can be switched between two states, the screen first comprises a planar, light-emitting backlight having the aforementioned optical film. Optionally, the backlight can emit light directly, for example, as a so-called "direct matrix backlight." A linear polarization filter is arranged in front of the backlight in the viewing direction. Optionally, the polarization filter can also correspond to the second polarization layer of the optical film. This restricts the propagation direction of light originating from the backlight and penetrating the linear polarization filter. A transmissive image reproduction device is arranged in front of the backlight in the viewing direction. The linear polarization filter can be part of the image reproduction device and disposed within the transmissive image reproduction device. This polarization filter can also be implemented as a standalone solution, in which case it is positioned as close as possible to the image reproduction device within the stack of optical elements. Typical image reproduction devices have a linear polarizer located above and below the LC layer in the viewing direction. The previous description refers to the linear polarizer located below in the viewing direction. The upper linear polarizer is crucial for privacy protection applications. As previously mentioned, the liquid crystal layer, which is switchable between at least two states, is in a first switching state in operating mode B2 and in a second switching state in operating mode B3.

[0046] Finally, the present invention also includes another screen capable of operating in at least two operating modes, B1 (for free viewing) and B2 (for restricted viewing). In the restricted viewing mode, light is emitted into a viewing angle or solid angle range that is more limited for the viewer than in the free viewing mode. This screen comprises an image reproduction device, which may be of the type, for example, OLED, microLED, or LCD, and an optical film arranged in front of the image reproduction device in the viewing direction, the optical film comprising the aforementioned liquid crystal layer switchable between at least two states. According to the definitions of the first and second switching states, the liquid crystal layer is in the first switching state in operating mode B2 and in the second switching state in operating mode B2.

[0047] Of course, within the scope of the present invention, the features mentioned above and those yet to be described below can be combined not only in the manner given in this application but also in other combinations or used alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be described in detail below in conjunction with embodiments with reference to the accompanying drawings that reveal the essential features of the present invention. This embodiment is for illustrative purposes only and does not constitute a limitation. For example, the description of an embodiment comprising multiple elements or components does not mean that all such elements or components are indispensable. Specifically, other embodiments may also include alternative elements and components, reduced elements or components, or additional elements or components. Unless otherwise specified, elements or components of different embodiments may be combined with each other. Variations and variants described for one of the embodiments may also be applied to other embodiments. To avoid repetition, identical or corresponding elements in different drawings are represented by the same symbols and are not repeated. Among them:

[0049] Figures 1A to 1C Various layer structures of optical films used to control and limit the viewing angle of the viewer.

[0050] Figure 2 To limit the viewing angle,

[0051] Figure 3 As an example of improving privacy protection by the present invention,

[0052] Figure 4A and 4B The anti-peeping effect of the first technical solution of the optical film is

[0053] Figure 5A and 5B The anti-peeping effect of the second technical solution of the optical film is:

[0054] Figure 6A and 6B The anti-peeping effect of the third technical solution of the optical film is:

[0055] Figures 7A to 7G is the polarization ellipse passing through the optical film,

[0056] Figure 8 A switchable solution for optical films.

[0057] Figure 9A and 9B Two working states of a lighting device with a non-switchable optical film,

[0058] Figure 10 A screen with a switchable optical film, and

[0059] Figure 11 Another screen with a switchable optical film. DETAILED DESCRIPTION

[0060] Figures 1A to 1CVarious schematic diagrams of the layer structure of an optical film for controlling and limiting the viewing angle of a viewer. The viewer (not shown) is located above the uppermost layer, which has a surface with a surface normal that is parallel to the long edge of the drawing sheet in the drawing sheet plane. The uppermost layer, viewed from the viewer, is visible on all three viewing angles. Figures 1A to 1C The first polarizing layer 1 is shown in the figure. The first polarizing layer 1 has a first absorption axis that forms an angle of 0° to 30° with the surface normal of the optical film. When the angle is 0°, the first polarizing layer 1 is a Z polarizer; different angles are used, such as a "Z* polarizer." A 0° angle is suitable, for example, for laptops where the user is directly in front of the screen. A 30° angle is more advantageous, for example, in motor vehicles, where the screen is positioned between the driver's seat and the passenger seat, ensuring that only the driver can see the relevant information.

[0061] Figures 1A to 1C The bottom layer is a second polarizing layer 2 having a second absorption axis, which is parallel to the surface of the optical film. In other words, the second polarizing layer 2 here is a linear polarizer.

[0062] At least one phase-shift compensation layer is arranged between the first polarizing layer 1 and the second polarizing layer 2 to improve the limitation of the viewing angle range. A single compensation layer or multiple compensation layers are used, depending on the type of compensation layer. Such a compensation layer is, for example, a uniaxial or biaxial birefringent polymer film. Such layers are advantageously fixed to each other, for example, by optical bonding or other material bonding. For example, ultrasonic welding can also be used. When extremely smooth surfaces are placed or pressed together, the connection can also be achieved simply by adhesion, with an anti-reflection layer being used as required. The anti-peeping effect can be improved by implementing one or more compensation layers, which will be explained below. In an alternative solution not shown, the second polarizing layer 2 can also be arranged as the top layer in the viewing direction, with the first polarizing layer 1 arranged behind it, wherein the at least one phase-shift compensation layer is always located between the first polarizing layer 1 and the second polarizing layer 2.

[0063] exist Figure 1A In the first technical solution shown and hereinafter also referred to as the first alternative or alternative i, a first B* compensation layer 3 is arranged between the first polarizing layer 1 and the second polarizing layer 2. The first B* compensation layer 3 is a spatially uniform layer composed of a biaxial birefringent material. Accordingly, the material or the first B* compensation layer 3 has two optical axes and three principal refractive axes. Each of the three principal refractive axes corresponds to a refractive index n. x 、n y 、n zThis is a common property of biaxial birefringent materials. The symbols "x," "y," and "z" correspond to the axes of a rectangular coordinate system. However, to achieve privacy protection, the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index must be parallel to the first absorption axis.

[0064] The orientation of the first absorption axis determines the orientation of all other absorption axes or principal refractive axes of all types of compensation layers. If the first polarizing layer is, for example, a Z polarizer, whose first absorption axis is parallel to the surface normal or perpendicular to the film surface, this means that the principal refractive axis corresponding to the minimum or maximum refractive index is also parallel to the surface normal. Accordingly, the other two principal refractive axes lie in the plane of the optical film surface. The optical axis of the first B* compensation layer 3, in this case a B compensation layer, lies in a plane perpendicular to the optical film surface. In this case, two configurations are possible for the first B* compensation layer 3.

[0065] On the one hand, it can be constructed as a -B compensation layer. In this case, it is a Z polarizer, so in an imaginary rectangular coordinate system (where the main refractive axis and the optical axis of the B* compensation layer are defined), the z direction is associated with the direction perpendicular to the surface of the optical film. In this representation, the -B compensation layer satisfies the condition n x >n y >n z Therefore, the minimum refractive index corresponding to the principal axis perpendicular to the surface of the optical film is expressed as n z In addition, corresponding to the maximum refractive index n x The principal refraction axis of φ is parallel to the second absorption axis of the second polarizing layer 2 .

[0066] On the other hand, it can be constructed as a +B compensation layer. Here, the z direction can also be associated with the direction perpendicular to the optical film surface. In this representation, the +B compensation layer satisfies the condition n z >n x >n y Therefore, the maximum refractive index corresponding to the principal axis perpendicular to the surface of the optical film is expressed as n z Furthermore, the principal refractive axis corresponding to the minimum refractive index ny is parallel to the second absorption axis of the second polarizing layer 2 (see above).

[0067] For all technical solutions of the first alternative, the first B* compensation layer 3 satisfies the condition

[0068]

[0069] Here, d represents the thickness of the first B* compensation layer 3, Δph represents the phase shift caused by the first B* compensation layer, and λ represents an arbitrarily specified wavelength that satisfies this condition. This defines an upper limit for the phase retardation of the first B* compensation layer 3, which indirectly also specifies the maximum thickness.

[0070] exist Figure 1B In the second technical solution, the basic structure of which is shown in the figure and which is also referred to as the second alternative or alternative ii hereinafter, at least two compensation layers consisting of a uniaxial birefringent material are arranged between the first polarizing layer 1 and the second polarizing layer 2. They are a first A* compensation layer 4 and a second A* compensation layer 5. The two A* compensation layers 4 and 5 are spatially uniformly constructed in the manner defined previously. The first A* compensation layer 4 is composed of a first uniaxial birefringent material having a first optical axis and two first principal refractive axes, wherein the first optical axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer 1. The second A* compensation layer 5 is arranged at the rear when viewed from the viewer, and is composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes. The orientation of the second optical axis of the second A* compensation layer 5 is determined according to the orientation of the first optical axis of the first A* compensation layer 4, wherein the condition that the second optical axis is perpendicular to the first optical axis must be met. Each of the two A* compensation layers 4 and 5 meets the condition

[0071]

[0072] Where d represents the thickness of the corresponding compensation layer, n e represents the special refractive index, n o represents the normal refractive index. Δph represents the phase shift caused by the first or second A* compensation layer 4 , 5 , respectively, and λ represents an arbitrarily defined wavelength that satisfies this condition. Both A* compensation layers 4 , 5 can be made of the same material and / or have the same thickness, thereby simplifying the manufacturing process.

[0073] Figure 1C A refinement of the second alternative is shown. To more clearly define the solid angle range, i.e., to achieve a greater drop in luminous density within this solid angle range compared to the luminous density outside of this solid angle range, and / or to provide greater flexibility in selecting the components of the compensation layers, in this second alternative, a third C* compensation layer 6, also spatially uniform, is advantageously arranged between the first and second A* compensation layers. The third C* compensation layer 6 is composed of a third uniaxially birefringent material having a third optical axis and two third principal refractive axes, wherein the third optical axis is parallel to the first absorption axis of the first polarizing layer 1. The orientation of the optical axis of the material of the third C* compensation layer 6 is also determined by the orientation of the first absorption axis of the first polarizing layer 1.

[0074] If the first polarizing layer 1 is designed as a Z polarizer, and thus the first absorption axis is perpendicular to the optical film surface, either the first A* compensation layer 4 is designed as a +A compensation layer and the second A* compensation layer 5 is designed as a -A compensation layer, or vice versa. If a third C* compensation layer 6 is provided, it is designed as a -C or +C compensation layer.

[0075] In the first and second alternatives, the material and thickness d of the compensation layer are specified so that, in a spherical coordinate system with its origin on the film surface and in the film plane, the luminous density is minimum only within a specified solid angle range R. The solid angle range R only encompasses a part of the possible perceptible half space, i.e., on the one hand, the azimuthal angle in the film surface. where the preferred orientation is measured relative to the plane of the film surface, or Less than the specified limit azimuth The absolute value of . In principle, the preferred direction can be chosen arbitrarily, but it should be determined according to the application of the optical film. When such an optical film is used, for example, in a screen with a fixed orientation (e.g., in a vehicle), the preferred direction is chosen so that it is parallel to an imaginary line between the eyes of a driver sitting upright, i.e., it usually extends horizontally. The limiting azimuth angle is specified according to the intended use of the film. For example, for laptop computers that need to be protected from being viewed from the side in vehicles such as trains, common values ​​are 30° to 40° left and right of the preferred direction - the preferred direction here is usually parallel to the long side of the screen, and the first absorption axis is parallel to the normal of the screen, so that the drop in luminous density towards all sides is symmetrical.

[0076] On the other hand, the solid angle range in which the luminous density is minimum also includes a polar angle θ, measured relative to the first absorption axis and in a plane formed by the surface normal and the first absorption axis, or measured only relative to the surface normal when the first absorption axis is parallel to the surface normal, the absolute value of which is greater than the specified limit polar angle θ lim Preferably, the limit polar angle θ lim The angle of the optical film is 40° to 50°, depending on the intended use. When applied to the screen described above, the film effectively restricts viewing angles because the luminous density is at its lowest within the aforementioned solid angle range. Therefore, ideally, a viewer positioned within the aforementioned solid angle range relative to the optical film's spherical coordinate system will not perceive any content on the screen, or at least will be unable to recognize it, due to the minimum luminous density within this range.

[0077] Preferably, the sight-limiting effect within the specified solid angle range is achieved by the following means: the components of the optical film are coordinated with each other so that within the specified solid angle range R, the loss function C2 = ∫ R ln T(φ,θ)dΩ is the smallest, where Denotes the angle-dependent transmittance, and Ω denotes the solid angle range. That is, the natural logarithm of the angularly resolved transmittance is calculated and integrated over the solid angle range for which privacy protection needs to be optimized. This includes not only the viewing angle in the horizontal direction, but also the viewing angle that deviates from the actual viewer's 0° vertical viewing direction (along the surface normal), i.e., the viewing angle facing upward or downward. This also includes, for example, a third viewer standing next to a seated device user in privacy mode. Ultimately, a privacy protection that is significantly improved over the prior art is obtained in terms of this viewing angle. Logarithms are used to weight at different orders of magnitude, but linear weighting or other weightings may also be used.

[0078] Combine Figure 2 and Figure 3 To illustrate this point. Figure 2 The projection of the specified solid angle range R into the optical film plane is shown as a black area, also known as a conoscopic image. Within this range, privacy protection needs to be improved so that the luminous density is as low as possible. In this example, the solid angle range R is specified so that the limiting azimuth angle φ lim is 40° - thus forming a black area above and below the horizontal axis -, and the limiting polar angle θ lim Also 40°—corresponding to the concave areas to the right and left of the midpoint. In this case, the inner concentric circle corresponds to a polar angle of θ = 40°. For this specified solid angle range, the loss function, i.e., the integral of the logarithmic transmittance, is minimized. The components can be coordinated to meet this condition using the commercially available optical design programs mentioned above as an example.

[0079] Finally, even for vertical viewing angles different from 0° (corresponding to looking perpendicularly towards the optical film surface), an improved privacy protection effect towards the sides can be obtained, see Figure 330° vertical viewing angle in the figure and the optical film in the second alternative, which has a +A compensation layer and a -A compensation layer on the one hand and another -C compensation layer on the other hand. The first polarizing layer 1 is constructed as a Z polarizer, so that the first absorption axis is parallel to the surface normal of the optical film. The figure shows the privacy protection effect in arbitrary units, that is, the luminous density is normalized to an angle of 0° according to the horizontal viewing angle in degrees, from which it can be seen how the brightness of the screen in the privacy protection angle range is compared with the non-privacy protection angle range. For example, the preferred direction parallel to the horizontal direction is selected, which is related to the viewer's reference frame, that is, the horizontal direction corresponds to the imaginary connecting line between the viewer's eyes, and the vertical direction is perpendicular to this. The solid line corresponds to the privacy protection effect that can be achieved in the prior art using only a Z polarizer and no spatially uniform compensation layer at a 30° vertical viewing angle. The dotted line shows the privacy protection effect of the combination of two types of A* compensation layers, -A and +A, and the dot-dash line shows the privacy protection effect of the combination with an additional -C compensation layer. The A* compensating layer in this example is not fully optimized, so the combination with the -C compensating layer in this example does not provide an improvement; however, in general, the use of the C* compensating layer provides improved privacy protection at angles around 30°. Privacy protection toward the side is significantly improved at angles up to approximately 60°. Privacy protection is slightly improved at larger angles above 60°, but still an improvement over the prior art. This privacy protection is exaggerated due to the logarithmic scale, but is not noticeable in practice. At a vertical viewing angle of 0°, not shown here, the prior art optical film and the optical films described above and below with the additional compensating layer generally achieve the same results, generally corresponding to the dashed or dotted lines.

[0080] Figure 2 The solid angle range R shown is shown for illustrative purposes only and can be adjusted as needed, for example, to improve the privacy protection for vertical viewing angles at a horizontal viewing angle of 0°, for example, for a laptop computer, corresponding to a viewer standing directly behind a seated user. In this case, for example Figure 2 The black solid angle range in FIG completely surrounds the concentric circle at 40°.

[0081] Figure 4A and 4B 、 Figure 5A and 5B and Figure 6A and 6B More examples are shown in Figure 2 The solid angle range R shown is specified. Figure 4A 、 Figure 5A and Figure 6A Shows the anti-peeping effect for a 0° vertical viewing angle. Figure 4B 、 Figure 5B and Figure 6BThe privacy protection effect is shown for a vertical viewing angle of 30°. The curves with solid lines always correspond to optical films with only one first Z* polarizing layer and without an additional spatially uniform compensation layer.

[0082] Figure 4A and Figure 4B Shown with Figure 1A The anti-peeping effect of the optical film of the structure of the first alternative is shown, which has a first B* compensation layer 3. x 、n y and n z Since multiple combined biaxial birefringent layers achieve the same optical function, such layers are classified by two other parameters that take this into account, namely by the parameter

[0083] R e =(n x -n y )·d and parameters

[0084]

[0085] In the green and middle visible light wavelength range where the human eye has the highest sensitivity at wavelength λ = 550nm, the thickness is d = 5.25μm, Re = 132 and N z =3.84, a dotted curve is obtained. x It is inferred that there must be a relationship between the refractive indices. For example, n x =1.6246, n y =1.6 and n z = 1.5287. In order to produce a layer with exactly this refractive index calculated, a large number of production methods for highly controlling the refractive index are known in the prior art. If a material with the desired refractive index ratio is selected, the thickness d is adjusted so that N z In addition to the aforementioned parameters, other combinations can also be used to achieve significant improvements; resulting in the anti-peeping effect characteristics shown by the dotted line, where R e =75 and N z = 3.84. This value is for illustrative purposes only, and a tolerance of + / - 20% is possible and included in each case without significantly reducing the privacy protection effect.

[0086] Figure 5A and Figure 5B Shown with Figure 1CThe anti-peeping effect of the optical film of the structure of the second alternative is shown, which has a first A* compensation layer 4 and a second A* compensation layer 5 and an additional third C* compensation layer 6 located between the two layers. The first absorption axis of the first polarizing layer 1 is also perpendicular to the surface here, so it is a Z polarizer. Accordingly, the first A* compensation layer 4 is constructed as a +A compensation layer with positive birefringence, the second A* compensation layer 5 is constructed as a -A compensation layer with negative birefringence, and the third C* compensation layer 6 is constructed as a -C compensation layer with negative birefringence. Alternatively, the first A* compensation layer 4 can be constructed as a -A compensation layer with negative birefringence, the second A* compensation layer 5 is constructed as a +A compensation layer with positive birefringence, and the third C* compensation layer 6 is constructed as a +C compensation layer with negative birefringence, where negative birefringence refers to n e <n o In the case of positive birefringence, n e >n o situation.

[0087] At 0° vertical viewing angle, Figure 5A , corresponding to a direct top view of the film along the surface normal, the use of three additional compensation layers in addition to the Z polarizer does not lead to an improvement, while at a vertical viewing angle of 30°, Figure 5B , you can clearly see the improved anti-peeping effect. Figure 5A and Figure 5B The improvement shown can be achieved with a series of compensation layers which, for the first +A compensation layer, satisfies the condition d·(n e -n o )=264nm, the second-A compensation layer satisfies the condition d·(n o -n e )=-264nm, each with a tolerance of 20%. For the third-C compensation layer, the condition d·(n e -n o ) = -22 nm, with a tolerance greater than + / - 10 nm. For a relatively thin C* compensation layer overall, the tolerance is either + / - 10 nm or 20%, whichever is greater. In the alternative solution with a first -A compensation layer, the sign is reversed accordingly.

[0088] Figure 6A and Figure 6B Shown with Figure 1C The anti-peeping effect of the optical film of the second alternative structure is shown, which has a first A* compensation layer 4 and a second A* compensation layer 5 and an additional third C* compensation layer 6 located between the two layers. Figure 5A 、 Figure 5BIn contrast, the first absorption axis of the first polarizing layer here is tilted 20° toward the surface relative to the surface normal, resulting in a Z* polarizer. This orientation also dictates how the optical axes of the A* and C* compensation layers should be arranged to achieve the privacy protection effect. To produce such tilted compensation layers, for example, photo-alignment and polymerization of LC mesogens can be employed. Without limitation, the first A* compensation layer 4 is constructed as a -A* compensation layer, the second A* compensation layer 5 is constructed as a +A* compensation layer, and correspondingly, the third C* compensation layer 6 is constructed as a -C* compensation layer. Figure 6A and Figure 6B The improvement shown can be achieved with a series of compensation layers which, for the first +A* compensation layer, satisfies the condition d·(n e -n o )=264nm, for the second -A* compensation layer, the condition d·(n o -n e )=-264nm, each with a tolerance of 20%. For the third -C* compensation layer, the condition d·(n e -n o ) = -82 nm, the tolerance is also 20%. In the alternative embodiment with a first -A* compensation layer, the signs are correspondingly reversed.

[0089] exist 7A to 7F In Figure 1C Taking the optical film in the second alternative as an example, the role of each layer is explained in detail by means of polarization ellipsoids, where the first absorption axis of the first polarizing layer 1 is parallel to the surface normal of the optical film. For comparison, Figure 7G The polarization of light when the layer structure without additional compensation layer is used in the prior art is assumed to be along the surface normal of the optical film. Figures 7A to 7G Each of them shows a plurality of polarization ellipses distributed in a circle around the origin of the coordinate system. The position of each polarization ellipse corresponds to a viewing angle toward the surface of the optical film. The viewing angle in the origin of the coordinate system corresponds to the surface normal, that is, the top view perpendicular to the surface of the optical film. Without being generally limited, along the longitudinal edge of the plane of the drawing page, the direction parallel to the short side relative to the plane of the drawing page is called the x-direction, and the direction perpendicular thereto is called the y-direction. The x-direction here also corresponds to the preferred direction and is parallel to the imaginary connecting line between the two eyes of the viewer, so it is also referred to as the horizontal direction hereinafter. That is to say, in Figures 7A to 7GThere are several polarization ellipses on the x-axis of the coordinate system in , which correspond to viewing angles that deviate from zero only in the horizontal direction, corresponding to viewers who move away from the origin only in the lateral direction. There are several polarization ellipses on the y-axis, whose viewing angles deviate from zero only in the vertical direction, corresponding to viewers who move vertically up and down from the origin position. "Vertical" movement or displacement here does not mean that the viewer moves away from the optical film along the surface normal, that is, it does not mean displacement along the surface normal in the horizontal plane formed by the surface normal and the horizontal direction between the viewer's eyes. It refers to displacement perpendicular to the plane. For example, when a first viewer is sitting and looking directly at the optical film along the surface normal, the viewing angle of the second viewer standing directly behind the first viewer is only vertically offset on the y-axis. For ease of understanding, Figures 7A to 7G Two concentric circles are depicted in each figure. The inner circle limits the viewing angle to a maximum of 25° in each direction, while the outer circle limits the viewing angle to a maximum of 45° in each direction. The outermost viewing angle is 90°, which is not perceptible in reality.

[0090] Figure 7A The circularly polarized light emitted by the backlight into the optical film is shown. This light first strikes the second polarizing layer 2 having a second absorption axis and is linearly polarized because the second absorption axis of the second polarizing layer 2 is oriented parallel to the film surface, in this case along the horizontal direction or, more generally, along the imaginary connecting line between the viewer's eyes, which also corresponds to the preferred direction.

[0091] After passing through the second polarization layer, the linearly polarized light enters the second A* compensation layer 5 designed as an -A compensation layer. The polarization remains almost unchanged in the horizontal and vertical directions, but in the viewing angle range with different angles, after passing through - in top view - s-polarized light is obtained in a larger area, see Figure 7C , that is, light whose associated electric field vector is perpendicular to the plane of incidence (the plane formed by the surface normal and the incident direction). Figure 7D This is the angle-resolved polarization after passing through the next layer, the third C* compensation layer 6. This compensation layer is constructed as a +C compensation layer here; however, the change is difficult to see in the figure because of the low birefringence and the fact that it is a C* compensation layer. Figure 7E This represents the polarization of light after passing through the first A* compensation layer 4, constructed here as a +A compensation layer. This light is mostly approximately p-polarized, meaning the electric field vector is parallel to the plane of incidence. Therefore, absorption of light propagating in non-perpendicular directions is increased by the subsequent first polarization layer 1, also known as the Z-polarization layer. This is achieved through the interaction of the three aforementioned compensation layers, significantly enhancing the privacy protection effect.

[0092] at last, Figure 7F The polarization of the light after passing through the first polarization layer 1, ie, the Z polarizer, is shown in FIG. Figure 7GThe figure shows the light polarization in the prior art, where the Z polarization layer is directly connected to the second polarization layer. The closer the polarization ellipse is to a point, the smaller the luminous density. It can be clearly seen here that Figure 2 The luminous density of the middle black area is much lower than that of the previous technology, so the anti-peeping effect is improved. This is achieved by the following method: as in the previous technology, the luminous density is not minimized in the entire half-space range - except for the narrow viewing cone - but only in the actual part of this half-space outside the viewing cone, that is, the specified solid angle range R. Specifically, the loss function is minimized within the specified solid angle range R.

[0093] C2=∫ R lnT(φ,θ)dΩ

[0094] Minimize, where is the angle-dependent transmittance, and Ω is the solid angle. This significantly reduces the luminous density within the desired range, thereby improving privacy protection.

[0095] Figure 8 For a similar Figure 1B The present invention relates to a technical solution of an optical film comprising a first A* compensation layer 4 and a second A* compensation layer 5, but an additional liquid crystal layer 7 is arranged between the second polarizing layer 2 and the second A* compensation layer 5, which can be switched between at least two states. The liquid crystal layer 7 is constructed so that in the first switching state, it transmits the light transmitted by the second polarizing layer 2 with unchanged or 90° rotated polarization, and in the second switching state, it transmits the light transmitted by the second polarizing layer 2 with circular or elliptically polarized light. Of course, the liquid crystal layer 7 using this switching method can also be applied to other technical solutions of optical films, especially Figure 1A and Figure 1C In the technical solution shown.

[0096] Thus, for example, Figure 10 and Figure 11 The screen shown. Figure 10A screen is shown that can operate in at least two operating modes: B1 (for free viewing) and B2 (for restricted viewing). In the restricted viewing mode, light is emitted into a viewing angle range that is more restricted for the viewer than in the free viewing mode. To switch between these two operating modes, the screen includes a backlight 8, which is planar and includes an optical film (not specifically shown here) with a liquid crystal layer 7 that can be switched between at least two states and emits light, represented here by a plurality of light sources 9. This is merely a simplified diagram; for example, surface emitters or edge-lit light guides with structured surfaces can also be used, optionally including optical layers such as diffusers or prismatic grating films. Optionally, the backlight can also emit light directly, for example, in a "direct matrix backlight dimming" configuration. A linear polarization filter 10 is arranged in front of the backlight 8 in the viewing direction to restrict the propagation direction of light emitted from the backlight 8 and passing through the linear polarization filter 10. A transmissive image reproduction device 11 is arranged in front of the backlight 8 in the viewing direction. A linear polarizing filter 10 is arranged behind the transmissive image reproduction device 11 in the viewing direction. The polarizing filter should be as close to the image reproduction device as possible, with as few layers as possible between the two. Preferably, the linear polarizing filter 10 is arranged within the transmissive image reproduction device 11, being a part of or integrated into the latter. In operating mode B2, the liquid crystal layer 7, which is switchable between at least two states, is in a first switching state. In operating mode B1, the liquid crystal layer 7, which is switchable between at least two states, is in a second switching state. In other words, the switchable liquid crystal layer enables switching between a public operating mode and an anti-privacy mode. In the public operating mode, the image content displayed on the screen can be viewed unrestricted from multiple viewing angles. In the anti-privacy mode, the displayed image content is visible with sufficient brightness only within a narrow viewing angle range within a cone surrounding the first absorption axis of the first polarizing layer 1.

[0097] Figure 11Another embodiment of a screen is shown, which can be operated in at least two operating modes: B1 (for free viewing) and B2 (for restricted viewing). In this restricted viewing mode, light is emitted into a viewing angle range that is more restricted for the viewer than in the free viewing mode. The screen includes an image reproduction device 12, which employs the structure disclosed in the prior art and can be designed, for example, as an actively luminous image reproduction device 12 based on OLEDs or microLEDs, or as a passively luminous (i.e., illuminated) image reproduction device 12 based on, for example, LCDs. An optical film having a liquid crystal layer 7 switchable between at least two states is arranged in front of the image reproduction device 12 in the viewing direction. The optical film is constructed, for example, according to a first alternative embodiment, wherein a spatially uniform first B* compensation layer 3 composed of a biaxially birefringent material is arranged between a first polarizing layer 1 and a second polarizing layer 2. The second polarizing layer 2 can also be designed, for example, as a rear polarizer for an LC display of the image reproduction device 12. Of course, all other aforementioned embodiments of optical films having a switchable liquid crystal layer 7 are also applicable. As with the aforementioned screen, the liquid crystal layer 7, which can switch between at least two states, is also in the first switching state in the operating mode B2 and in the second switching state in the operating mode B1. This technical solution is particularly suitable for retrofitting existing screens.

[0098] Alternatively, an optical film without a switchable liquid crystal layer 7 can be used to manufacture an illumination device for a screen, which can be configured so that it can operate in at least two operating modes B1 (for a free viewing mode) and B2 (for a restricted viewing mode), in which the light is emitted into a solid angle range that is more limited than in the free viewing mode. Figure 9A and Figure 9B An example of such an illumination device in these two operating modes is shown in If the illumination device is combined with an image reproduction device located upstream in the viewing direction for displaying image content, a screen that can switch between these two operating modes B1 and B2 can be obtained.

[0099] Figure 9A and Figure 9B The lighting device shown comprises a planar extended backlight 13, in which a Figures 1A to 1CA static, i.e., non-switchable, optical film is shown by way of example. A plate-shaped light guide 14 is arranged in front of the backlight 13 in the viewing direction. This light guide 14 has an outcoupling element on at least one of its large surfaces and / or within its volume. In the example shown, an outcoupling element 15 is arranged within the volume of the light guide 14. A linear polarization filter 16 is arranged in front of the backlight 13 or in front of the light guide 14 in the viewing direction. This essentially limits the propagation direction of light emitted by the backlight 13, passing through the optical film, and then through the linear polarization filter 16. Optionally, the linear polarization filter 16 can also perform the function of a second polarization layer 2, equivalent thereto. Laterally arranged on at least one narrow side of the light guide 14—here, on both narrow sides—are luminous elements 17, which, when switched on, inject light into the light guide 14. Light incident on light-emitting element 17 is reflected back and forth by total internal reflection in light guide 14 until it strikes output coupling element 15, which deflects the light so that it passes through the surface of light guide 14 and outward toward the viewer. Output coupling element 15 is configured to deflect the light almost entirely in this direction, allowing light from backlight 13 to pass through almost unimpeded.

[0100] Figure 9A The lighting device is shown in operating mode B2 for a restricted viewing mode, in which only a small, generally conical solid angle range is illuminated, indicated by arrows on the surface of the light guide 14. In this case, only the backlight 13 is switched on and the light-emitting element 17 must be switched off. Figure 9B The lighting device is shown in operating mode B1 for public viewing. In this viewing mode, light is emitted over a much larger or wider solid angle range than in operating mode B2, also indicated by the arrow on light guide 14. In this case, light-emitting element 17 must be switched on. The light emitted by light guide 14 and coupled out by outcoupling element 15 serves to broaden the illuminated solid angle range. Backlight 13 can be switched off or on in operating mode B1. When backlight 13 is switched off, uniform illumination across the solid angle range is generally achieved in operating mode B1.

[0101] By being Figure 9A and Figure 9B The illustrated lighting device illuminates the passive image reproduction device from behind, generating a restricted viewing mode B2 or a public viewing mode B1 for viewers of the image content displayed on the image reproduction device, depending on whether the light emitting member 17 is switched on or off.

[0102] By utilizing an image reproduction device and, if necessary, a dedicated lighting device, the aforementioned optical film can be widely used in any situation where confidential information needs to be displayed and / or entered, such as PIN entry, data display at ATMs or payment terminals, password entry, or reading email on mobile devices. The present invention is particularly applicable to motor vehicles to selectively block disruptive video content for the driver or passengers.

[0103] [Explanation of symbols]

[0104] 1: First polarization layer

[0105] 2: Second polarization layer

[0106] 3: First B* compensation layer

[0107] 4: First A* compensation layer

[0108] 5: Second A* compensation layer

[0109] 6: Third C* compensation layer

[0110] 7: Liquid crystal layer

[0111] 8: Backlight

[0112] 9: Light Source

[0113] 10: Linear polarizing filter

[0114] 11: Image reproduction device

[0115] 12: Image reproduction device

[0116] 13: Backlight

[0117] 14: Light guide

[0118] 15: Output coupling element

[0119] 16: Linear polarizing filter

[0120] 17: Light-emitting component

[0121] R: Solid angle range

Claims

1. A backlight (13), which extends in a planar manner, emits light and has an optical film for controlling and limiting the viewing angle of a viewer, wherein the optical film comprises a first polarizing layer (1) having a first absorption axis, wherein the first absorption axis forms an angle of 0° to 30° with the surface normal of the optical film, at least one phase shift compensation layer for improving the limitation of the viewing angle range, and a second polarizing layer (2) having a second absorption axis, wherein the second absorption axis is parallel to the surface of the optical film, Its characteristics are: Between the first polarizing layer (1) and the second polarizing layer (2), in a first alternative i. In the embodiment, a first B* compensation layer (3) is arranged, which is spatially uniform and consists of a first biaxial birefringent material having two optical axes and three main refractive axes, Each of the principal refractive axes corresponds to a refractive index n x 、n y 、n z , wherein the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, and Wherein the first B* compensation layer (3) satisfies the condition The thickness d, the phase shift Δph and the specified wavelength λ of the first B* compensation layer (3) are included. ii. In a second alternative, at least two compensation layers consisting of a uniaxial birefringent material are arranged, wherein The spatially uniform first "A*" compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two mutually different first principal refraction axes, wherein the first optical axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1), and the first principal refraction axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1) when viewed from the viewer. A second spatially uniform "A*" compensation layer (5) is arranged, which is composed of a second uniaxial birefringent material having a second optical axis and two second main refraction axes, wherein the second optical axis is perpendicular to the first optical axis, Where each of the compensation layers satisfies the condition Including the thickness d of the compensation layer, the special refractive index n e and normal refractive index n o , phase shift Δph and specified wavelength λ, In both alternatives i and ii, the material and thickness d of the compensation layer are specified so that, measured in a spherical coordinate system with its origin on the surface of the film and in a plane of the surface of the film, the luminous density is minimum only within a specified solid angle range R, the solid angle range including: azimuth angle where the preferred direction is measured relative to the plane of the film's surface, and Less than the specified limit azimuth and a polar angle θ, relative to the surface normal, or when the first absorption axis is not parallel to the surface normal, relative to the first absorption axis and measured in the plane formed by the surface normal and the first absorption axis, the absolute value of the polar angle is greater than the specified limit polar angle θ lim .

2. The backlight (13) according to claim 1, alternative ii, wherein: A spatially uniform third "C*" compensation layer (6) is arranged between the first "A*" compensation layer and the second "A*" compensation layer, and is composed of a third uniaxial birefringent material having a third optical axis and two third main refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarizing layer (1).

3. The backlight (13) according to claim 1 or 2, wherein: The first absorption axis is perpendicular to the surface of the film.

4. The backlight (13) according to claim 3 and alternative i, wherein: The principal refractive axis corresponding to the minimum refractive index is parallel to the first absorption axis, characterized in that the first "B*" compensation layer (3) is constructed as a "-B" compensation layer, wherein n x >n y >n z , corresponding to the minimum refractive index n z The principal refractive axis is parallel to the surface normal, corresponding to the maximum refractive index n x The principal refraction axis is parallel to the second absorption axis of the second polarizing layer (2).

5. The backlight (13) according to claim 3 and alternative i, wherein The principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, characterized in that the first "B*" compensation layer (3) is constructed as a "+B" compensation layer, wherein n z >n x >n y , corresponding to the maximum refractive index n z The principal refractive axis is parallel to the surface normal, corresponding to the minimum refractive index n y The main refraction axis is parallel to the second absorption axis of the second polarizing layer (2).

6. The backlight (13) according to claim 3 and alternative ii, wherein The first "A*" compensation layer (4) is designed as a "+A" compensation layer, the second "A*" compensation layer (5) is designed as a "-A" compensation layer, or vice versa, and, in the case of a third "C*" compensation layer (6), the compensation layers are designed as "-C" or "+C" compensation layers.

7. The backlight (13) according to claim 1, alternative ii, wherein: The first "A*" compensation layer (4) and the second "A*" compensation layer (5) have the same structure.

8. The backlight (13) according to claim 1 or 2, wherein: A liquid crystal layer (7) capable of switching between at least two states is arranged between the second polarization layer (2) and the compensation layer closest to the second polarization layer. The liquid crystal layer is constructed to transmit the light transmitted by the second polarization layer (2) with unchanged or 90° rotated polarization in a first switching state, and transmit the light with circular, elliptical or linear polarization in a second switching state.

9. The backlight (13) according to claim 1 or 2, wherein: A liquid crystal layer (7) capable of switching between at least two states is arranged between the first polarization layer (1) and the compensation layer closest to the first polarization layer. The liquid crystal layer is constructed to transmit the light transmitted by the first polarization layer (1) with unchanged or 90° rotated polarization in a first switching state, and to transmit the light with circular, elliptical or linear polarization in a second switching state.

10. The backlight (13) according to claim 1 or 2, wherein: Within the specified solid angle range R, the loss function ∫ R ln T(φ,θ)dΩ is the smallest, where represents the angle-dependent transmittance, and Ω represents the solid angle range.

11. The backlight (13) according to claim 1 or 2, wherein: The limiting azimuth 30° to 40° to the left and right of the preferred direction and / or the extreme polar angle θ lim It is 40° to 50°.

12. An illumination device for a screen, the illumination device being configured to be operable in at least two operating modes: B1 (for a free viewing mode) and B2 (for a restricted viewing mode), wherein in the restricted viewing mode, light is emitted into a solid angle range that is more limited than in the free viewing mode, the illumination device comprising The backlight (13) according to any one of claims 1 to 7, 10 or 11, a plate-shaped light guide (14) located in front of the backlight (13) in the viewing direction, said light guide having an outcoupling element (15) on at least one of its large surfaces and / or within its volume, a light-emitting member (17) arranged laterally on at least one narrow side of the light guide (14), and a linear polarization filter (16) arranged in front of the backlight (13) or in front of the light guide in the viewing direction, so that light emitted from the backlight (13) and penetrating the linear polarization filter (16) is restricted in its propagation direction, in, In the operating mode B2, the backlight (13) is turned on and the light emitting component (17) is turned off, and in the operating mode B1, at least the light emitting component (17) is turned on.

13. A screen capable of operating in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), wherein in the restricted viewing mode, light is emitted into a viewing angle range that is more limited for a viewer than in the free viewing mode, the screen comprising The backlight (8) according to claim 8 or 9, comprising a liquid crystal layer (7) which can be switched between at least two states, a linear polarization filter (10) arranged in front of the backlight (8) in the viewing direction, so that light emitted from the backlight (8) and penetrating the linear polarization filter (10) is limited in its propagation direction, and A transmissive image reproduction device (11) is arranged in front of the backlight (8) in the viewing direction, and the linear polarization filter (10) is arranged in or behind the image reproduction device. Wherein, in the working mode B2, the liquid crystal layer (7) capable of switching between at least two states is in a first switching state, and wherein in the working mode B1, the liquid crystal layer (7) capable of switching between at least two states is in a second switching state.

14. A screen capable of operating in at least two operating modes, B1 (for free viewing mode) and B2 (for restricted viewing mode), wherein in the restricted viewing mode, light is emitted into a viewing angle range that is more limited for a viewer than in the free viewing mode, the screen comprising Image reproduction device (12), an optical film arranged in front of the image reproduction device (12) in the viewing direction, the optical film having a liquid crystal layer (7) capable of switching between at least two states, wherein in the operating mode B2, the liquid crystal layer (7) is in a first switching state, and wherein in the operating mode B1, the liquid crystal layer (7) is in a second switching state, The optical film comprises: A first polarizing layer (1) having a first absorption axis, wherein the first absorption axis forms an angle of 0° to 30° with the surface normal of the optical film; At least one phase shift compensation layer for improving the limitation of the viewing angle range; and a second polarizing layer (2) having a second absorption axis, the second absorption axis being parallel to the surface of the optical film, wherein between the first polarizing layer (1) and the second polarizing layer (2), in the first alternative i. In the embodiment, a first B* compensation layer (3) is arranged, which is spatially uniform and consists of a first biaxial birefringent material having two optical axes and three main refractive axes, Each of the principal refractive axes corresponds to a refractive index n x 、n y 、n z , wherein the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, and Wherein the first B* compensation layer (3) satisfies the condition comprising the thickness d, the phase shift Δph and the prescribed wavelength λ of the first B* compensation layer (3), ii. In a second alternative, at least two compensation layers consisting of a uniaxial birefringent material are arranged, wherein The spatially uniform first "A*" compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two mutually different first principal refraction axes, wherein the first optical axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1), and the first principal refraction axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1) when viewed from the viewer. A second spatially uniform "A*" compensation layer (5) is arranged, which consists of a second uniaxial birefringent material having a second optical axis and two second principal refraction axes, wherein the second optical axis is perpendicular to the first optical axis, Where each of the compensation layers satisfies the condition Including the thickness d of the compensation layer, the special refractive index n e and normal refractive index n o , phase shift Δph and specified wavelength λ, In the alternatives i and ii, the material and thickness d of the compensation layer are specified so that the luminous density is minimum only within a specified solid angle range R when measured in a spherical coordinate system with the origin located on the surface of the film and in a plane on the surface of the film. The solid angle range includes: azimuth angle where the preferred direction is measured relative to the plane of the film's surface, and Less than the specified limit azimuth and a polar angle θ, relative to the surface normal, or when the first absorption axis is not parallel to the surface normal relative to the first absorption axis and the surface normal and the first absorption axis formed in the plane measured, the absolute value of the polar angle is greater than the specified limit polar angle θ lim , And among them A liquid crystal layer (7) capable of switching between at least two states is arranged between the second polarization layer (2) and the compensation layer closest to the second polarization layer, the liquid crystal layer being configured to transmit the light transmitted by the second polarization layer (2) with unchanged or 90° rotated polarization in a first switching state, and to transmit the light with circular, elliptical or linear polarization in a second switching state. or, A liquid crystal layer (7) capable of switching between at least two states is arranged between the first polarization layer (1) and the compensation layer closest to the first polarization layer. The liquid crystal layer is constructed to transmit the light transmitted by the first polarization layer (1) with unchanged or 90° rotated polarization in a first switching state, and to transmit the light with circular, elliptical or linear polarization in a second switching state.

15. A screen according to claim 14 and alternative ii, wherein A spatially uniform third "C*" compensation layer (6) is arranged between the first "A*" compensation layer and the second "A*" compensation layer, which is composed of a third uniaxial birefringent material having a third optical axis and two third main refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarizing layer (1).

16. An optical film for controlling and limiting the viewing angle of a viewer, comprising a first polarizing layer (1) having a first absorption axis, wherein the first absorption axis forms an angle of 0° to 30° with the surface normal of the optical film, at least one phase shift compensation layer for improving the limitation of the viewing angle range, and a second polarizing layer (2) having a second absorption axis, wherein the second absorption axis is parallel to the surface of the optical film, Its characteristics are: Between the first polarizing layer (1) and the second polarizing layer (2), in a first alternative i. In the embodiment, a first B* compensation layer (3) is arranged, which is spatially uniform and consists of a first biaxial birefringent material having two optical axes and three main refractive axes, Each of the principal refractive axes corresponds to a refractive index n x 、n y 、n z , wherein the principal refractive axis corresponding to the minimum refractive index or the principal refractive axis corresponding to the maximum refractive index is parallel to the first absorption axis, and Wherein the first B* compensation layer (3) satisfies the condition comprising the thickness d, the phase shift Δph and the prescribed wavelength λ of the first B* compensation layer (3), ii. In a second alternative, at least two compensation layers consisting of a uniaxial birefringent material are arranged, wherein The spatially uniform first "A*" compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two mutually different first principal refraction axes, wherein the first optical axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1), and the first principal refraction axis is perpendicular to or parallel to the first absorption axis of the first polarizing layer (1) when viewed from the viewer. A second spatially uniform "A*" compensation layer (5) is arranged, which consists of a second uniaxial birefringent material having a second optical axis and two second principal refraction axes, wherein the second optical axis is perpendicular to the first optical axis, Where each of the compensation layers satisfies the condition Including the thickness d of the compensation layer, the special refractive index n e and normal refractive index n o , phase shift Δph and specified wavelength λ, In alternatives i and ii, the material and thickness d of the compensation layer are specified so that the luminous density is minimum only within a specified solid angle range R, measured in a spherical coordinate system with its origin on the surface of the film and in a plane of the surface of the film, wherein the solid angle range includes: azimuth angle where the preferred direction is measured relative to the plane of the film's surface, and Less than the specified limit azimuth and a polar angle θ, relative to the surface normal or when the first absorption axis is not parallel to the surface normal relative to the first absorption axis and measured in the plane formed by the surface normal and the first absorption axis, the absolute value of the polar angle is greater than the specified limit polar angle θ lim .

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