Backlight, lighting device, screen, optical film having an optical film

Abstract

The present invention relates to a backlight (13), said backlight having an optical film that extends in a planar shape, emits light, and controls and limits the viewing angle of a viewer. The optical film comprises: a first polarizing layer (1) having a first absorption axis that forms an angle of 0° to 30° with the surface normal of the optical film along the viewing direction; 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 present invention, there are various technical designs and combinations thereof in which a spatially uniform compensation layer composed of a single-axis or biaxial birefringent material is disposed, and the material and thickness of the compensation layer are specified such that the light density is minimized within a specific solid angle range that does not include the entire half space except for a concave cone along the entire viewing direction.

Description

Technology Field

[0001] The present invention relates to a backlight having an optical film that extends in a plane and emits light, and controls and limits the viewing angle of a viewer, and also to the optical film. The film comprises a first polarizing layer having a first absorption axis forming an angle of 0° to 30° with the surface normal of the optical film and a second polarizing layer having a second absorption axis parallel to the surface of the optical film. At least one phase shift compensation layer is disposed between them to improve the limitation of the viewing angle range. Along the viewing direction, the first polarizing layer or the second polarizing layer may form the layer closest to the viewer.

[0002] Over the past few years, the viewing angle range of LCDs has expanded significantly. However, a very wide viewing area often becomes a disadvantage. Information such as banking details and other personal and sensitive data is increasingly being provided on mobile devices like laptops and tablets. Consequently, people need to control who can view this sensitive data. For example, if you want to view vacation photos or share information on the display with others for advertising purposes, you should be able to select a wide viewing angle range or a viewing angle (public mode). On the other hand, if image information needs to be kept secret, a narrower viewing angle range or a viewing angle (private mode) is preferable.

[0003] The automotive industry faces a similar problem. When the engine is started, the driver must not be distracted by visual content such as digital entertainment, but passengers also want to watch visual content while driving. Therefore, a screen capable of switching between each display mode is required.

[0004] Microsheet-based laminated films have been used to protect visual data in mobile displays. However, these films cannot be replaced or converted, so they must always be attached and removed manually. Additionally, they must be shipped separately from the display when not in use. Another major disadvantage of using these sheet films is light loss.

[0005] US 6765550 B2 discloses a privacy protection method using micro lamellae. The main disadvantages of this technical solution are the mechanical removal and attachment of the filter and light loss in protection mode.

[0006] US Patent No. 5993940 A discloses a method for implementing a peeping prevention mode, that is, a limited viewing mode with a narrow field of view, by using a film having small striped prisms evenly distributed on its surface. However, this is technically very difficult to develop and manufacture.

[0007] WO 2012 / 033583 A1 implements switching between free and restricted fields of view by controlling liquid crystals between "chromophore" layers. This process results in light loss and is technically very difficult.

[0008] US 2012 / 0235891 A1 discloses a very complex screen backlight. FIGS. 1 and 15 of this application form light in the path from the backlight to the frontlight using multiple light guides as well as other complex optical components such as a micro-lens assembly (40) and a prism structure (50). This is expensive to implement, technically difficult, and also results in light loss. According to the variation shown in FIG. 17 of US 2012 / 0235891 A1, both light sources 4R and 18 generate light with a narrow illumination angle, and light from the backlight source 18 is converted into light with a wide illumination angle through a complex process. As mentioned above, this complex conversion significantly reduces brightness.

[0009] JP 2007-155783 A uses a special optical surface (19) that is complex to calculate and manufacture. This surface refracts light into a narrower or wider area depending on the angle of incidence. This structure is similar to a Fresnel lens. In addition, this surface has interfering sides and can refract light in undesirable directions. Therefore, it is uncertain whether truly reasonable light distribution can be achieved.

[0010] US 2013 / 0308185 A1 discloses a special stepped light guide that emits light in various directions across a wide surface depending on the direction of light shining from a narrow surface. When used with a transmissive image display device such as an LC display, it is possible to create a screen that can switch between a free viewing mode and a restricted viewing mode. A major disadvantage is that the restricted viewing effect can only be implemented in the left / right or up / down directions and cannot be implemented in all directions at once, such as in certain payment processes. Additionally, even in restricted viewing mode, afterglow may be visible if the viewing angle is obscured.

[0011] WO 2015 / 121398 A1 filed by the applicant describes a screen having two operating modes. To achieve switching between operating modes, scattering particles are present within the corresponding light guide. However, the polymer scattering particles selected in this application generally have the following disadvantages: light is output from two large surfaces and coupled, and about half of the effective light is emitted in the wrong direction, i.e., toward the backlight, and cannot be recovered to a sufficient level for structural reasons. Additionally, depending on the situation, particularly at high concentrations, scattering particles composed of polymers distributed within the light guide may result in a scattering effect that impairs the anti-peeping protection effect in the protective operating mode.

[0012] The basic concept of the "Electro-Induced Birefringence (EDB)" method is to utilize the switchable liquid crystal of an additionally applied LC panel to "filter" light that does not escape the imaging layer at a specific beam angle. The disadvantages of this technology are additional energy consumption, high cost, and the difficulty in shifting the sweet spot, which is the optimal viewing position at ±40°. Furthermore, the LC structure does not have sufficient absorption capacity because light intensity attenuation increases again when the viewing angle exceeds this sweet spot. Therefore, when the viewing angle exceeds ±40°, the light intensity is limited to a maximum of 3% of the maximum light intensity.

[0013] US 2019 / 0094626 A1 discloses an optical layer structure for controlling or limiting the viewing angle, wherein two phase difference plates are arranged as a compensation layer over a linear polarizer. These two phase difference plates, referred to as λ / 4 plates, are constructed from several structured optical anisotropic fin-shaped or strip-shaped layers, with a carrier material disposed between each layer. These layers may have the same structure but may differ in orientation after arrangement. The top layer forms a polarizing layer, i.e., a so-called "Z-polarizer," in which the absorption axis of the polarization transition dipole moment is oriented perpendicular to the surface of the layer. Even when using layers with such a fin-shaped structure, visual artifacts such as moiré patterns may still occur. Therefore, these layers can only be used on screens with known resolution and characteristics, such as size, sphere diameter, scattering characteristics, and distance from the screen surface, and cannot be used universally regardless of screen size.

[0014] These methods and configurations generally have disadvantages, such as significantly reducing native screen brightness, requiring complex and expensive optical components for mode switching, degrading resolution in free viewing mode, or causing visual artifacts when using very high-resolution displays. Another disadvantage is that the viewing angle is not completely restricted. Even with a restricted viewing angle, image content with significantly reduced brightness can still be perceived, which can interfere with vision, such as during night driving.

[0015] The purpose of the present invention is to develop a backlight that is generally combined with a screen and has an optical film for controlling and limiting the viewing angle range of a viewer, thereby improving the limitation of the viewing angle range, making it more difficult for unauthorized users to peek at protected image content, and further improving the so-called privacy protection effect.

[0016] In an optical film having the aforementioned layer structure and a backlight comprising such optical film, the present invention achieves the aforementioned objective through a special technical solution for at least one compensation layer. First, the first polarizing layer and the second polarizing layer are described in detail. The first polarizing layer has a first absorption axis that forms an angle of 0° to 30° with the surface normal of the optical film. When this angle is 0°, that is, when the absorption axis is parallel to the surface normal or perpendicular to the film surface, it is referred to as a "Z-polarizer." When the angle changes but remains within the aforementioned maximum range of 30°, it is referred to as "Z" below. *It is called a "polarizer." The absorption of the first polarizing layer is generally fixed, but a switchable solution that can turn absorption on and off depending on the angle may also be used. The second polarizing layer has a second absorption axis parallel to the surface of the optical film. Thus, the second polarizing layer is a conventional linear polarizer. At least one phase shift compensation layer is disposed between the first polarizing layer and the second polarizing layer to improve the viewing angle limitation. Both the first polarizing layer and the second polarizing layer can be positioned closest to the viewer. Preferably, all layers are fixedly connected by material methods such as welding or optical bonding.

[0017] For the sake of understanding, the following text assumes that in an orthogonal coordinate system formed in the x, y, and z directions, the film surface lies in a plane parallel to the xy plane formed in the x and y directions. Therefore, the surface normal is parallel to the z direction.

[0018] In order to improve the privacy effect, that is, to improve the limitation of the viewing angle range, at least one phase transition compensation layer can be configured using two methods in principle. In the first alternative (hereinafter also referred to as alternative (i)), a first B between the first polarization layer and the second polarization layer * A compensation layer is arranged, and this 1 B * The compensation layer consists of a first biaxial birefringent material. This biaxial birefringent material has two optical axes and three principal refraction axes, and each principal refraction axis has a refractive index n x , n y , n z It corresponds to one by one (birefringently) to. 1 B * Depending on the technical solution of the compensation layer and the direction of the 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. The first B * The reward layer satisfies the following conditions.

[0019]

[0020] Here, d represents the thickness of the first compensation layer, and Δph is the first B * It represents the phase transition generated by the compensation layer, represents any wavelength satisfying this condition. Thus, B * Defines an upper limit for the phase delay of the compensation layer, and B * Indirectly determines the maximum thickness of the compensation layer.

[0021] In the second alternative (hereinafter also referred to as alternative (ii)), two or more compensation layers composed of a uniaxial birefringent material are disposed between the first polarization layer and the second polarization layer. A spatially uniform first A * The compensation layer is composed of a first uniaxial birefringent material having two first principal refractive axes different from the first optical axis, wherein the first optical axis coinciding with one of the first principal refractive axes is perpendicular to or parallel to the first absorption axis of the first polarization layer. Spatially uniform second A * The compensation layer is positioned behind the observer and consists of a second uniaxial birefringent material having a second optical axis and two second principal refraction axes, wherein the second optical axis of the second material, which coincides with one of the second principal refraction axes, is perpendicular to the first optical axis of the first material. The optical axis of such a uniaxial material is also referred to as a special axis.

[0022] Here, "spatially uniform" means that the compensation layer is not structured in the internal or in areas parallel to the surface of the optical film, and thus exhibits uniform characteristics over the entire area. This differs from, for example, US 2019 / 0094626 A1. To prevent visual artifacts in such layered structures, one of the technical solutions of US 2019 / 0094626 A1 requires specifically adjusting the layer structure for each configuration in terms of resolution, distance, sphere diameter, surface, and scattering characteristics, which increases manufacturing costs. However, the optical film of the present invention having a spatially uniform compensation layer can be universally applied to various screen sizes and resolutions without special adjustments.

[0023] Here, 2 A's * Each reward layer satisfies the following conditions.

[0024]

[0025] Here, d is the corresponding A * Indicates the thickness of the compensation layer, and n e represents a specific refractive index, and n o represents the normal refractive index. Δph is the first A, respectively. * Compensation layer or 2nd A * It represents the phase transition generated by the compensation layer, and λ represents the wavelength satisfying this condition, which can be arbitrarily specified in principle.

[0026] In both alternatives, the material and thickness (d) of the compensation layer are defined such that the luminescence density is minimized within a predetermined solid angle range (R) when measured in a spherical coordinate system in which the origin is located on the surface of the film and the plane of the surface of the film, said solid angle includes an azimuth angle (φ) and a polar angle (θ), said azimuth angle (φ) is measured with respect to the preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limit azimuth angles (φ lim It is smaller than the absolute value of ). The preferred direction can be selected arbitrarily, but must be adjusted to suit the application of the optical film. For applications such as screens with a fixed orientation (e.g., vehicles), the preferred direction is generally selected to be parallel to the imaginary line between the vertical driver's eyes that extends horizontally.

[0027] Meanwhile, the solid angle range in which the luminescence density is minimized also includes the polar angle (θ). The polar angle (θ) is a specified limit polar angle (θ) where the absolute value measured with respect to the first absorption axis in the plane formed by the surface normal and the first absorption axis (where the two vectors share a common origin) is defined. lim It is greater than ). In other words, the limit polar angle (θ limAll solid angles outside the cone are measured around a first absorption axis (hereinafter referred to as the "zero axis") having a surface normal. When the surface normal and the first absorption axis are parallel, the polar angle is measured only with respect to the surface normal. When an optical film is applied to the screen described above, the light emission density is minimized within the solid angle range, so the viewing angle is effectively limited. Therefore, under ideal conditions, a viewer within the solid angle range with respect to the spherical coordinate system of the optical film will not be able to perceive the content of the screen due to the minimum light emission density within this range. The term "minimum light emission density" refers to a light emission density that is nearly zero, which is significantly reduced compared to the light emission density outside the solid angle range, and refers to a state in which the viewer ideally cannot see any image content.

[0028] In order to define the solid angle range more clearly, that is, to reduce the luminescence density within this solid angle range more significantly than the luminescence density outside this solid angle range, in this alternative (ii), a spatially uniform third C * The compensation layer is the 1st A * Compensation layer and 2 A * It is advantageously positioned between the compensation layers. This 3rd C * The compensation layer is composed of a third single-axis birefringent material having a third optical axis and two third principal refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer.

[0029] To achieve a symmetric reduction 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 on the screen, a viewer viewing the screen along the surface normal perceives a symmetric reduction in luminous density depending on whether the viewing angle is to the right, to the left, or the preferred direction. This reduction depends only on the absolute value of the polar angle. In this case, the limiting polar angle (θ lim Since it is measured based on the surface normal, it is the same at all azimuths, unlike when measured based on the first absorption axis.

[0030] When the first absorption axis takes the above orientation, the first polarization layer is called a Z-polarization layer. When the first absorption axis takes a different orientation within the above range, the first polarization layer is Z * It is also called a polarization layer. In other words, the use of the "*" symbol here indicates that the Z-polarization layer has been generalized.

[0031] As mentioned above, "A * The term "compensation layer" is a generalization of the term "A compensation layer," and "B * The term "compensation layer" is a generalization of the term "B-compensation layer." The definitions of the terms "Z-polarization layer," "A-compensation layer," and "B-compensation layer," which are commonly used in the prior art, are as follows: Ho-Jin Choi et al., Ho-Jin Choi et al. Optical anisotropy conversion of retarder film made of rodlike and crosslike reactive molecules, and its dependence on the relative ratio and the orientation of the constituent molecules See ". This was published online in Optical Materials 99(2020) and is reference number 109531.

[0032] When the first absorption axis is perpendicular to the film surface, that is, when the first polarization layer is composed of a Z-polarizer, there are several advantageous technical solutions. There are two solutions for the first alternative and a third solution for the second alternative. In order to achieve the desired viewing area limitation, the optical axis direction of the compensation layer must, in principle, coincide with the direction of the first absorption axis of the first polarization layer. For example, if a viewer, such as a driver, views the screen at an oblique angle rather than along the surface normal, it may be desirable to place the first absorption axis at a different location.

[0033] In the first technical solution based on the first alternative, 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 * The compensation layer is constructed as a -B compensation layer. These optical axes lie in a plane formed in the x and z directions, and the three principal refraction axes correspond to the directions of the orthogonal coordinate system. Here, n x >n y >nz and, n x is parallel to the second absorption axis of the second polarization layer. This latter condition applies even when the first absorption axis is tilted at a relatively small angle of up to about 10° with respect to the surface normal. Otherwise, the principal refraction axis is also tilted. The coordinate system directions in the x, y, and z directions are based on the direction of the first absorption axis corresponding to the z direction of the coordinate system. The most important feature is n x It is perpendicular to the first absorption axis.

[0034] In the second technical plan based on the first alternative, 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 plan, the first B * The compensation layer is constructed as a +B compensation layer. The optical axis lies in the plane formed in the y and z directions, and the three principal refraction axes correspond to the directions of the orthogonal coordinate system. Here, n z >n x >n y and, n y is parallel to the second absorption axis of the second polarization layer. This latter condition applies even when the first absorption axis is tilted at a relatively small angle of up to about 10° with respect to the surface normal. Otherwise, the principal refraction axis is also tilted. The coordinate system directions in the x, y, and z directions are based on the direction of the first absorption axis corresponding to the z direction of the coordinate system. The most important feature is n y It is perpendicular to the first absorption axis.

[0035] In the third technical plan based on the second alternative, the first absorption axis of the first polarization layer (1) is also perpendicular to the surface of the optical film. In this technical plan, the first A * The reward layer is constructed as a +A reward layer, and the 2 A * The reward layer is constructed as an -A reward layer, or vice versa. 3 C * If a reward layer is provided, it is constructed as a -C reward layer or a +C reward layer.

[0036] In order to keep manufacturing costs low, the 1 A * Compensation layer and 2 A * The compensation layers preferably have the same structure. That is, both compensation layers are constructed as either +A compensation layers or both as -A compensation layers and have the same thickness.

[0037] According to all the technical solutions above, a particularly desirable improvement, a liquid crystal layer switchable between at least two states is disposed between a second polarizing layer and a compensation layer closest to the second polarizing layer. The liquid crystal layer is configured to transmit light transmitted by the second polarizing layer in a first switching state as linear polarization that is unchanged or rotated by 90°, and in a second switching state as circular, elliptical, or linear polarization. In the first switching state, the 90° rotation is such that linearly polarized light changes to linear or elliptical polarization after passing through the switchable liquid crystal layer, at which point most of the electric field vector is rotated by 90°. That is, the polarization is not rotated exactly 90°. The addition of the switchable liquid crystal layer enables switching between a non-peeping mode and an open mode, which is particularly pronounced when an optical film is integrated into a screen. As described above, the reduction in luminous intensity within a specified solid angle range is permanent in the case of an optical film, but can be eliminated by using a switchable liquid crystal layer. The first switching state corresponds to a non-peeping mode in which the light maintains linear polarization. The second switching state corresponds to an open mode in which light is generally elliptically polarized but may adopt different polarization depending on the selected liquid crystal layer. In the open mode, the luminescence density within a specified solid angle range does not decrease or decreases only slightly. Therefore, if this arrangement is used on a screen, image content can be perceived regardless of the viewer's position (i.e., without limitation) within a technically feasible range. In the anti-peeping mode, a person standing sideways (with respect to the first absorption axis direction) cannot perceive the image content. Alternatively, the liquid crystal layer can be arranged between the first polarization layer and the nearest compensation layer.

[0038] This switchable liquid crystal layer is generally used in conjunction with a static first polarizing layer to form a switchable optical film. If the function of the switchable liquid crystal layer can be performed by the switchable first polarizing layer, the switchable liquid crystal layer may be omitted. In this case, the first polarizing layer may be composed, for example, of a liquid crystal layer in which a dye is embedded, so-called a "dye-LC-cell" (dye liquid crystal cell). This type of liquid crystal layer is particularly suitable when the first absorption axis, that is, the absorption axis of the first polarizing layer, is parallel to the surface normal of the optical film.

[0039] A line of sight restriction within a specified solid angle range is preferably achieved through the following method. The components of the optical film are coordinated with each other so that the loss function is minimized within the specified solid angle range (R).

[0040]

[0041] Here, T(φ, θ) is the angle-dependent transmittance, and Ω is the solid angle. Specifically, the natural logarithm of the angular resolution transmittance is calculated and integrated over the solid angle range where privacy is optimized. This logarithm implements weights to account for transmittances of various magnitudes during the optimization process. Other weighting schemes, such as linear weights, can also be used. In this case, it is not necessary to apply the logarithm to the transmittance. Uniglobe Kisco's LCD MASTER ® or INCROPS' Tecwiz LCD 3D ® The optical construction of the present invention can be implemented by using a commercially available optical design program such as [program name] to adjust the components and satisfy these conditions.

[0042] In general applications, preferably, the limiting azimuth (φ) lim ) is 30° to 40° centered on the primary direction, and / or the limit polar angle (θ lim ) is 40° to 50° centered on the surface normal or the first absorption axis (if tilted relative to the surface normal).

[0043] If the switchable liquid crystal layer is not disposed on the film, the backlight having the optical film can be embedded in the lighting device of the screen. If the switchable liquid crystal layer is disposed on the film, the backlight can be embedded in the screen.

[0044] Specifically, a non-switchable optical film, i.e., a backlight without a switchable liquid crystal layer, can be integrated into a lighting device for a transmissive screen (specifically an LC display), wherein the lighting device is configured to operate in two modes of operation: B1 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is emitted within a more restricted solid angle range than in free viewing mode. The lighting device includes a planar backlight that emits light, and the backlight has a backlight light source and the non-switchable optical film. When the second polarizing layer of the optical film is positioned in front of the first polarizing layer in the viewing direction, the backlight light source of the backlight emits unpolarized light for the entire backlight (and in the case of other technical schemes described below). In the opposite arrangement, the light emitted from the backlight light source of the backlight may be (partially) polarized. A plate-shaped light guide is positioned in the viewing direction in front of the backlight so that the viewer looks at the lighting device. The light guide has two large surfaces connected by a narrow face, and has a coupling element on at least one of the large surfaces and / or within it. A light-emitting element is positioned laterally on at least one of the narrow faces of the light guide. A linear polarization filter is placed in front of the backlight or light guide in the direction of observation. Optionally, the polarization filter may correspond to a second polarization layer of the optical film or use a special construction. This limits the direction of propagation of light originating from the backlight and passing through the linear polarization filter. In the limited viewing mode of operating mode B2, the backlight is turned on and the light-emitting element is turned off. Within the limited viewing angle range, only the backlight emits light. In operating mode B1, in free viewing mode or public viewing mode, at least the light-emitting element is turned on to compensate for or overcompensate for the limited illumination provided by the backlight alone. Thus, the backlight can be turned on or off in public viewing mode. In this case, a transmissive screen is placed in front of the lighting device.

[0045] The invention includes a screen capable of operating in two or more operating modes, such as B1 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is emitted to the viewer within a range of viewing angles or solid angles that is more restricted than in free viewing mode. In a technical configuration having a switchable liquid crystal layer capable of switching between the two states, the screen first includes a planar light-emitting backlight having the optical film. Optionally, the backlight may emit light directly, for example, as a so-called "direct matrix backlight." A linear polarization filter is positioned in front of the backlight in the viewing direction. Optionally, the polarization filter may correspond to a second polarization layer of the optical film. This restricts the direction of propagation of light originating from the backlight and passing through the linear polarization filter. A transmissive image display device is positioned in front of the backlight in the viewing direction. The linear polarization filter may be positioned within the transmissive image display device as part of the image display device. The polarization filter may be a standalone configuration, in which case it is positioned as close as possible to the image display device within the optical component stack. In a typical image display device, linear polarizers are positioned above and below the liquid crystal layer in the viewing direction. The previous description pertains to a straight polarizer positioned below in the direction of observation. An upper straight polarizer is essential for privacy protection applications. As previously mentioned, the liquid crystal layer, which is switchable between at least two states, is in the first switching state in operating mode B2 and in the 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 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is emitted to the viewer in a more restricted viewing angle range or stereoscopic angle range than in free viewing mode. The screen includes an image display device, such as an OLED, micro LED, or LCD, and an optical film placed in front of the image display device in the viewing direction. The optical film includes the liquid crystal layer that is switchable between at least two states. According to the definitions of the first and second switching states, the liquid crystal layer is in a first switching state in operating mode B1 and in a second switching state in operating mode B2.

[0047] Of course, within the scope of the present invention, the features described above and below may not only be combined in the manner described in this application, but may also be combined in other ways or used alone. Brief explanation of the drawing

[0048] The present invention will be described in detail with reference to the accompanying drawings and embodiments, which illustrate the essential features of the invention. These embodiments are for illustrative purposes only and are not limiting. For example, a description of an embodiment containing multiple elements does not imply that all elements are essential. Specifically, other embodiments may include alternative elements, reduced elements, or additional elements. Unless otherwise stated, elements of different embodiments may be combined with one another. Changes and variations described for one embodiment may also apply to other embodiments. To avoid duplication, identical or corresponding elements in different drawings are indicated by the same symbols and are not described again. Some of these are as follows: Figures 1a to 1c show various layer structures of optical films used to control and limit the viewing angle of a viewer. Figure 2 shows the limitation on the field of view range. Figure 3 is an example of how personal information protection is improved through the present invention. Figures 4a and 4b show the anti-peeping effect of the first technical method of the optical film. Figures 5a and 5b show the anti-peeping effect of the second technical method of the optical film. Figures 6a and 6b show the anti-peeping effect of the third technical method of the optical film. Figures 7a to 7g are polarization ellipses passing through an optical film. Figure 8 shows a switchable method for an optical film. Figures 9a and 9b show two operating states of a lighting device having a non-switchable optical film. Fig. 10 is a screen having a switchable optical film. Fig. 11 is another screen having a switchable optical film. Specific details for implementing the invention

[0049] FIGS. 1a through 1c are various principle diagrams of the layer structure of an optical film for controlling and limiting the viewing angle of a viewer. A viewer, not illustrated, is positioned on the top layer, which has a surface normal parallel to the long side of the drawing in the drawing plane. This top layer, viewed from the viewer's direction in all three viewpoints 1a through 1c, is the first polarizing layer (1). 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. At the 0° angle, the first polarizing layer (1) is a Z-polarizer. Depending on the magnitude of the angle, "Z * The term "polarizing plate" is used. An angle of 0° is suitable, for example, for a laptop where the user is positioned directly in front of the screen. For example, in the case of a car, an angle of 30° is advantageous because the screen is positioned between the driver's seat and the passenger seat, allowing relevant information to be visible only to the driver.

[0050] The bottom layer in FIGS. 1a to 1c is a second polarization layer (2) having a second absorption axis parallel to the surface of the optical film. That is, the second polarization layer (2) is a straight polarizer.

[0051] At least one phase shift compensation layer is disposed between the first polarization layer (1) and the second polarization layer (2) to improve the limitation of the viewing angle range. Depending on the type of compensation layer, a single compensation layer or multiple compensation layers are used. Such compensation layers are, for example, uniaxial or biaxial birefringent polymer films. Advantageously, these layers are fixedly connected to each other through optical bonding or other material bonding. For example, ultrasonic welding may be used. In cases where very smooth surfaces are in contact or pressed together, they may be connected by adhesive alone, and an anti-reflection layer may be used as needed. The anti-peeping effect can be improved by installing one or more compensation layers. In another alternative not illustrated, the second polarization layer (2) is disposed on the top layer in the viewing direction, and the first polarization layer (1) is disposed thereafter, in which case at least one phase shift compensation layer is always located between the first polarization layer (1) and the second polarization layer (2).

[0052] In the first technical method illustrated in FIG. 1a and hereinafter referred to as the first alternative or alternative (i), between the first polarization layer (1) and the second polarization layer (2), a first B * A compensation layer (3) is placed. 1 B * The compensation layer (3) is a spatially uniform layer composed of a biaxially birefringent material. Therefore, this material, i.e., the first B * The compensation layer (3) has two optical axes and three principal refraction axes. These three principal refraction axes each have a refractive index n x , n y , n zThis corresponds to... This is a common characteristic of biaxial birefringent materials. The symbols "x", "y", and "z" correspond to the axes of the Cartesian coordinate system. However, to achieve the anti-peeping effect, 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.

[0053] The direction of the first absorption axis determines the direction of all other absorption axes or the principal refractive axes of all types of compensation layers. If the first polarizing layer is, for example, a Z-polarizer and its first absorption axis is parallel to the surface normal or perpendicular to the film surface, this implies that the corresponding principal refractive axis corresponding to the minimum or maximum refractive index is also parallel to the surface normal. Therefore, the other two principal refractive axes lie in the plane of the optical film surface. In this case, the first B, which is the B compensation layer * The optical axis of the compensation layer (3) lies in a plane perpendicular to the surface of the optical film. In this case, the first B * Two construction methods are possible for the compensation layer (3).

[0054] Meanwhile, it can be constructed as a -B compensation layer. In this case, since it is a Z polarizer, a virtual orthogonal coordinate system (B * In defining the principal refractive axis and optical axis of the compensation layer, the z-direction corresponds to the direction perpendicular to the surface of the optical film. In this notation, the -B compensation layer is n x >n y >n z The condition is satisfied. Therefore, the minimum refractive index corresponding to the principal axis perpendicular to the surface of the optical film is n. z It is denoted as . Also, the maximum refractive index n x The principal refractive axis corresponding to is parallel to the second absorption axis of the second polarization layer (2).

[0055] On the other hand, it can be constructed as a +B compensation layer. Here, the z direction may be associated with the direction perpendicular to the surface of the optical film. In this notation, the +B compensation layer is n z >n x >n yThe condition is satisfied. Therefore, the maximum refractive index corresponding to the major axis perpendicular to the surface of the optical film is n. z It is denoted as . Also, the minimum refractive index (n y The principal refractive axis corresponding to ) is parallel to the second absorption axis of the second polarization layer (2) (see above).

[0056] Regarding all technical solutions of the first alternative, the first B * The compensation layer (3) satisfies the following conditions.

[0057]

[0058] Here, d is the first B * It indicates the thickness of the compensation layer (3), Δph indicates the phase transition generated by the first compensation layer, and λ indicates the wavelength satisfying this condition, which is, in principle, arbitrarily defined. This is the first B * Defines the upper limit of the phase delay of the compensation layer (3) and indirectly determines the maximum thickness.

[0059] In the second technical method, the basic structure of which is illustrated in FIG. 1b and hereinafter also referred to as the second alternative or alternative (ii), at least two compensation layers composed of a uniaxial birefringent material are arranged between the first polarization layer (1) and the second polarization layer (2). These are the first A * Compensation layer (4) and 2nd A * This is the compensation layer (5). This A * Compensation layer (4) and 2nd A * The compensation layer (5) is spatially uniformly configured in the manner defined above. The first A * The compensation layer (4) is composed of a first single-axis birefringent material having a first optical axis and two first principal refraction axes, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarization layer (1). 2 A * The compensation layer (5) is positioned on the rear side when viewed from the viewer's viewing direction and is composed of a second single-axis birefringent material having a second optical axis and two second principal refraction axes. The second A * The direction of the second optical axis of the compensation layer (5) is the first A* It is determined according to the direction of the first optical axis of the compensation layer (4), and the condition that the second optical axis must be perpendicular to the first optical axis must be satisfied. This A * Compensation layer (4) and A * Each of the compensation layers (5) satisfies the following conditions.

[0060]

[0061] Here, d represents the thickness of the corresponding compensation layer, and n e represents a specific refractive index, and n o represents the normal refractive index. Δph is the first A, respectively. * Compensation layer (4) or second A * It represents the phase transition generated by the compensation layer (5), where λ represents the wavelength satisfying this condition, which is, in principle, arbitrarily designated. This A * Compensation layer (4) and A * The compensation layer (5) can be made of the same material and / or the same thickness, thus simplifying the manufacturing process.

[0062] FIG. 1c illustrates an improved form of the second alternative. In order to define the solid angle range more clearly, that is, to reduce the luminescence density within this solid angle range more significantly than the luminescence density outside this solid angle range, or to provide greater flexibility when selecting elements of the compensation layer, this second alternative advantageously [is] the first A * Compensation layer and 2 A * Spatially uniform third C between compensation layers * A compensation layer (6) is placed. 3rd C * The compensation layer (6) is composed of a third single-axis birefringent material having a third optical axis and two third principal refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer (1). Third C * The optical axis direction of the compensation layer (6) material is also determined by the first absorption axis direction of the first polarization layer (1).

[0063] When the first polarization layer (1) is constructed as a Z-polarizer and the first absorption axis is perpendicular to the surface of the optical film, the first A * The compensation layer (4) is constructed as a +A compensation layer and the second A * The compensation layer (5) is constructed as a -A compensation layer or the first A * The compensation layer (4) is constructed as a -A compensation layer and the second A * The compensation layer (5) is constructed as a +A compensation layer. 3 C * When a compensation layer (6) is placed, it is constructed as a -C or +C compensation layer.

[0064] In the first and second alternatives, the material and thickness (d) of the compensation layer are specified such that the luminescence density is minimized only within a specified solid angle range (R) in a spherical coordinate system where the origin is located on the film surface and the film plane. This solid angle range (R) includes only a portion of the possible perceptible half-space, namely the azimuth angle (φ) of the film surface. Here, |φ| or |180°-φ|, which is a value measured relative to the preferred direction on the film surface plane, is the specified limit azimuth angle (φ lim It is smaller than the absolute value of ). The preferred direction can be selected arbitrarily, but it must be adjusted to suit the application of the optical film. For example, when using such optical films on a fixed-direction screen (e.g., a vehicle), the preferred direction is generally selected to be parallel to the imaginary line between the vertical driver's eyes that extends horizontally. Limit azimuth (φ lim The value is specified according to the application of the film. For example, for a laptop computer that needs to be protected from side vision in a vehicle such as a train, a typical value is 30° to 40° to the left and right of the preferred direction. Here, the preferred direction is generally parallel to the long side of the screen, and the first absorption axis is parallel to the normal of the screen, so the luminescence density drops symmetrically in all directions.

[0065] On the other hand, in the solid angle range where luminescence density is minimized, the polar angle (θ lim ) is also included, and this polar angle (θ lim) is measured with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, is measured with respect to the first absorption axis in the plane formed by the surface normal and the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle (θ lim It is greater than ). Preferably, the limit polar angle (θ lim The angle is between 40° and 50° depending on the purpose of use and the application. When this optical film is applied to the screen, the light emission density is minimized within the solid angle range, so the viewing angle is effectively limited. Therefore, ideally, a viewer located within the solid angle range relative to the spherical coordinate system of the optical film will not be able to perceive the content of the screen, or at least will not be able to perceive such content, due to the minimum light emission density within this range.

[0066] The line-of-sight restriction effect within a specified solid angle range, that is, the phenomenon where the emission density decreases or is minimized within this solid angle range, is a loss function It is desirable that this be achieved by adjusting the elements of the optical film so that it is minimized within a specified solid angle range (R). Here, θ represents the angle-dependent transmittance, and Ω represents the solid angle range. Specifically, the natural logarithm of the angle-resolved transmittance is calculated and integrated over the solid angle range to optimize anti-peeping protection. This includes not only the horizontal field of view but also field of view angles deviating from the 0° vertical viewing direction (along the surface normal) of the actual viewer, i.e., upward or downward field of view angles. For example, this includes a third viewer standing next to a device user sitting in anti-peeping mode. Ultimately, anti-peeping protection is significantly improved compared to the prior art for these field of view angles. Logarithmic weights are used to assign weights of various magnitudes, but linear or other weights may also be used.

[0067] This is illustrated by example with FIGS. 2 and FIGS. 3. FIGS. 2 shows a specified solid angle range (R) projected onto an optical film plane as a black area, which is also referred to as a conoscope image. Within this range, anti-peeping protection must be improved so that the luminescence density is as low as possible. In this example, the solid angle range (R) is the limiting azimuth (φ lim ) is specified to be 40° (forming a black area above and below the horizontal axis), and the limit polar angle (θ lim The angle is also specified to be 40° (corresponding to the concave regions to the right and left of the center). In this case, the inner concentric circles correspond to a polar angle (θ) = 40°. Within this specified solid angle range, the integral of the loss function, i.e., the logarithmic transmittance, is minimized. The components can be adjusted using the commercial optical design program mentioned above to satisfy this condition.

[0068] Finally, even in the case of a vertical viewing angle other than 0° (corresponding to viewing the surface of the optical film vertically), an enhanced anti-peeping effect can be obtained towards the side, referring to the vertical viewing angle of 30° and the second alternative optical film shown in FIG. 3, which has a +A compensation layer and a -A compensation layer on one side and an additional -C compensation layer on the other. 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 anti-peeping protection effect is shown in arbitrary units in the drawings, that is, the luminous density is normalized to an angle of 0° according to the horizontal viewing angle, thereby allowing one to check how the brightness of the screen changes in the anti-peeping protection angle range compared to the angle range without anti-peeping protection effect. For example, a 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 it. The solid line corresponds to the anti-peeping protection effect achievable in the prior art using only a Z-polarizer at a vertical viewing angle of 30° and without a spatially uniform compensation layer. The dotted line represents two types of A * It shows the anti-peeping protection effect combined with the compensation layers (-A compensation layer and +A compensation layer), and the dotted line shows the anti-peeping protection effect combined with the additional -C compensation layer. In this example, A * Since the reward layer is not fully optimized, combining it with the -C reward layer does not provide any improvement in this example. However, generally, C *Using a compensation layer provides improved anti-peeping protection at an angle of approximately 30°. Lateral anti-peeping protection is significantly improved at a maximum angle of approximately 60°. Anti-peeping protection improves slightly at large angles greater than 60°, but is still an improved level compared to prior art. Although this anti-peeping protection is exaggerated due to the logarithmic scale, it is not noticeable in practice. At a vertical viewing angle of 0°, which is not shown here, the conventional optical film and the optical films described above and below with an additional compensation layer generally achieve the same results, which generally correspond to the dotted or dashed lines.

[0069] The solid angle range (R) shown in FIG. 2 is illustrated for illustrative purposes only and can be adjusted as needed. For example, it can be adjusted to improve anti-peeping protection for the vertical viewing angle from a horizontal viewing angle of 0°. For example, in the case of a laptop computer, this corresponds to a viewer standing directly behind a seated user. In this case, the black solid angle range in FIG. 2 completely encompasses a concentric circle of a 40° angle.

[0070] More examples are illustrated in FIGS. 4a and 4b, FIGS. 5a and 5b, and FIGS. 6a and 6b, and the solid angle range (R) shown in FIG. 2 is specified. FIGS. 4a, 5a, and 6a show the anti-peeping protection effect for a vertical viewing angle of 0°, and FIGS. 4b, 5b, and 6b show the anti-peeping protection effect for a vertical viewing angle of 30°. The curve with a solid line is always the first Z * It corresponds to an optical film having only a polarization layer and no additional spatially uniform compensation layer.

[0071] FIGS. 4a and 4b illustrate the anti-peeping protective effect of an optical film having the first alternative structure shown in FIG. 1a, which is the first B * It has a compensation layer (3). x , n y and n zSince biaxial birefringent layers for multiple combinations achieve the same optical function, these layers are classified by two different parameters that take this into account, namely the transmission parameter.

[0072] and parameters .

[0073] A dashed curve is obtained in the green, mid-visible light wavelength range, where the human eye has maximum sensitivity at wavelength (λ) = 550 nm, with thickness (d) = 5.25 μm, Re = 132, and N = 3.84. The intrinsic correlation between refractive indices is n x It can be inferred from. For example, n x =1.6246, n y =1.6, n z = 1.5287. To produce a layer with this calculated refractive index, numerous manufacturing methods for highly controlling the refractive index are known in the prior art. By selecting a material with a desired refractive index ratio, the thickness (d) is N z It is adjusted to satisfy. In addition to the above parameters, significant improvements can be achieved with other combinations. This results in the anti-peeping protection characteristics indicated by the dotted line, where R e =75, N=3.84. These values ​​are provided for illustrative purposes only, and a tolerance of + / -20% is allowed; even if included in each case, the anti-peeping protection effect is not significantly reduced.

[0074] FIGS. 5A and 5B illustrate the anti-peeping effect of an optical film having a second alternative structure shown in FIG. 1C, and said structure is a first A * Compensation layer (4) and 2nd A * It has a compensation layer (5), and an additional third C between them. * It also has a compensation layer (6). Here, the first absorption axis of the first polarization layer (1) is also perpendicular to the surface to form a Z-polarizer. Therefore, the first A *The compensation layer (4) is constructed as a +A compensation layer having positive birefringence, and the second A * The compensation layer (5) is constructed as a -A compensation layer having negative birefringence, and the third C * The compensation layer (6) is constructed as a -C compensation layer having negative birefringence. Or, the first A * The compensation layer (4) can be constructed as a -A compensation layer having negative birefringence, and the second A * The compensation layer (5) can be constructed as a +A compensation layer having positive birefringence, and the third C * The compensation layer (6) can be constructed as a +C compensation layer having negative birefringence, where the negative birefringence is n e <n o It represents the case where, positive birefringence is n e >n o It represents the case where.

[0075] At a vertical viewing angle of 0° (Fig. 5a), which corresponds to viewing the film directly from above along the surface normal, there is no improvement even with the use of three additional compensation layers in addition to the Z-polarizer. However, at a vertical viewing angle of 30° (Fig. 5b), an improved anti-peeping protection effect is clearly visible. The improvements shown in Figs. 5A and 5B can be achieved using a series of compensation layers, and the first +A compensation layer is condition d·(n e -n o )=264nm is satisfied and the 2nd -A compensation layer is condition d·(n o -n e It satisfies )=-264nm, and the tolerance for each is 20%. The third -C compensation layer satisfies the condition d·(n e -n o It satisfies )=-22nm, and the tolerance is greater than + / -10nm. Relatively thin C * For the entire compensation layer, the tolerance is + / -10nm or 20%, depending on the larger of the two values. In the alternative using the first -A compensation layer, the sign is applied in reverse.

[0076] FIGS. 6a and 6b illustrate the anti-peeping protective effect of an optical film having the second alternative structure shown in FIG. 1c. This structure is the first A * Compensation layer (4) and 2nd A * It is composed of a compensation layer (5), and a third C in between. * A compensation layer (6) is additionally disposed. Unlike FIGS. 5a and 5b, the first absorption axis of the first polarization layer is tilted 20° toward the surface with respect to the surface normal Z * It forms a polarizing plate. This orientation is A to achieve an anti-peeping protection effect. * Compensation layer and C * It determines how the optical axis of the compensation layer should be aligned. To create such a tilted compensation layer, for example, photo-alignment and polymerization of LC liquid crystals can be used. Without loss of generality, the first A * The compensation layer (4) is -A * Constructed as a compensation layer, and the 2nd A * The compensation layer (5) is +A * It is constructed as a compensation layer, and accordingly, the 3rd C * The compensation layer (6) is -C * It is constructed as a compensation layer. The improvements shown in Figures 6a and 6b can be achieved using a series of compensation layers. The first +A * The reward layer is d·(n e -n o Satisfies the condition ) = 264nm, and the 2nd -A * The reward layer is d·(n e -n o It satisfies the condition )=-264nm, and the tolerance of each compensation layer is 20%. 3 -C * The reward layer is d·(n e -n o It satisfies the condition )=-82nm, and the tolerance is also 20%. 1 -A * In the alternative using a compensation layer, the sign is applied in reverse.

[0077] In FIGS. 7a through 7f, the second alternative optical film illustrated in FIG. 1c is described as an example, and the role of each layer is explained in detail through polarization ellipses, wherein the first absorption axis of the first polarization layer (1) is parallel to the surface normal of the optical film. For comparison, FIG. 7g shows the polarization of light when using a layer structure without an additional compensation layer in the prior art. The viewing direction of a hypothetical observer follows the surface normal of the optical film. FIGS. 7a through 7g each show a plurality of polarization ellipses distributed in a circle around the origin of the coordinate system. The position of each polarization ellipse corresponds to the viewing angle toward the surface of the optical film. The viewing angle from the origin of the coordinate system corresponds to the surface normal, that is, the plane perpendicular to the surface of the optical film. Without loss of generality, the direction parallel to the shorter side along the vertical edge of the drawing page with respect to the page plane is called the x-direction, and the direction perpendicular thereto is called the y-direction. Here, the x-direction also corresponds to the preferred direction and is parallel to the hypothetical line connecting the viewer's eyes, so it is also referred to as the horizontal direction hereinafter. That is, on the x-axis of the coordinate system of FIGS. 7a through 7g, there is a polarization ellipse corresponding to a viewing angle that deviates only horizontally from zero, corresponding to a viewer moving only laterally from the origin. On the y-axis, there is a polarization ellipse corresponding to a viewing angle that deviates only vertically from zero, corresponding to a viewer moving vertically up or down from the origin. Here, "vertical" movement or displacement 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 within the horizontal plane formed by the horizontal direction between the viewer's eyes and the surface normal. Rather, it means displacement perpendicular to that plane. For example, if a seated first viewer looks directly at the optical film along the surface normal, the viewing angle of a second viewer standing immediately behind the first viewer is offset only vertically along the y-axis. For illustrative purposes, FIGS. 7a through 7g each show two concentric circles.The inner circle limits the field of view to a maximum of 25° in each direction, and the outer circle limits the field of view to a maximum of 45° in each direction. The outermost field of view is 90°, which is practically undetectable.

[0078] FIG. 7a shows circularly polarized light emitted from a backlight to an optical film. This light first reaches a second polarization layer (2) having a second absorption axis, and is linearly polarized because the second absorption axis of the second polarization layer (2) is oriented parallel to the surface of the film, that is, in a horizontal direction, or generally along an imaginary connecting line connecting the observer's eye. This connecting line also coincides with the preferred direction.

[0079] The linearly polarized light after passing through the second polarization layer is the second A constructed with the -A compensation layer * It is incident on the compensation layer (5). The polarization is maintained almost constant, particularly in the horizontal and vertical directions. However, s-polarized light is obtained over a wider area when viewed from above within the viewing angle range. Referring to FIG. 7c, this s-polarization refers to light in which the associated electric field vector is perpendicular to the plane of incidence (the plane formed by the surface normal and the direction of incidence). FIG. 7d shows the next layer, the third C * After passing through the compensation layer (6), it exhibits angle-resolved polarization. This compensation layer is constructed as a +C compensation layer, but has low birefringence and C * Because it is a compensation layer, it is difficult to identify changes in the drawing. Fig. 7e shows the first A constructed with a +A compensation layer. * The polarization of light after passing through the compensation layer (4) is shown. Most of this light is approximately p-polarized, which means that the electric field vector is parallel to the plane of incidence. Therefore, the absorption of light propagating in a non-perpendicular direction is increased by the subsequent first polarization layer (1), which is a Z-polarization layer. This is achieved through the interaction of the three compensation layers. This significantly improves the anti-peeping protection effect.

[0080] Finally, FIG. 7f shows the polarization of light after passing through the first polarization layer (1), i.e., the Z-polarizer. In contrast, FIG. 7g shows the polarization of light of the prior art in which the Z-polarizer is directly connected to the second polarizer. As the polarization ellipse approaches the point, the luminescence density decreases. It is clearly evident here that the luminescence density in the black region of FIG. 2 is much smaller than that of the prior art, which indicates an improved anti-peeping effect. This is achieved in the following way: As with the prior art, the luminescence density is not minimized over the entire half-space range except for the narrow viewing angle cone, but is minimized only in the actual part of this half-space outside the viewing angle cone, i.e., within a specified solid angle range (R). Specifically, the loss function is minimized within the specified solid angle range (R).

[0081]

[0082] Here, T(φ, θ) is the angle-dependent transmittance and Ω is the solid angle. By doing this, the luminescence density is significantly reduced within the desired range, thereby improving anti-peeping protection.

[0083] FIG. 8 is a first A similar to FIG. 1b * Compensation layer (4) and 2nd A * A technical method for an optical film having a compensation layer (5) is illustrated, provided that the second polarization layer (2) and the second A * A liquid crystal layer (7) is additionally disposed between the compensation layers (5), and this liquid crystal layer (7) is capable of switching between at least two states. In the first switching state, the liquid crystal layer (7) transmits light transmitted from the second polarizing layer (2) in a state where the polarization does not change or is rotated 90°, and in the second switching state, transmits light transmitted from the second polarizing layer (2) in a state where it is circularly or elliptically polarized. Of course, the liquid crystal layer (7) using this switching method can also be applied to other optical film technology methods, particularly the methods illustrated in FIG. 1a and 1c.

[0084] As shown in the screens illustrated in FIGS. 10 and 11, FIG. 10 illustrates a screen capable of operating in two or more modes: B1 (free viewing mode) and B2 (restricted viewing mode). In the restricted viewing mode, light is emitted to the viewer with a more restricted viewing angle range than in the free viewing mode. To switch between these two modes of operation, the screen includes a flat backlight (8), which includes an optical film (not specifically illustrated herein) containing a liquid crystal layer (7), the liquid crystal layer (7) being able to switch between at least two states, which emit light represented here by a plurality of light sources (9). This is a simplified diagram. For example, a surface light emitter with a structured surface or an edge-type light guide may be used, and optionally, an optical layer such as a diffuser or a prism grating film may be included. Optionally, the backlight may emit light directly in the form of a "Direct Matrix Backlight Dimming" system. A linear polarizing filter (10) is placed in front of the backlight (8) in the direction of observation. This limits the direction of propagation of light emitted from the backlight (8) and passing through the linear polarization filter (10). The transmissive image display device (11) is positioned in front of the backlight (8) in the viewing direction. The linear polarization filter (10) is positioned behind the transmissive image display device (11) in the viewing direction. The polarization filter must be positioned as close as possible to the image display device. That is, no additional layer should be provided between the two devices. Preferably, the linear polarization filter (10) is positioned within the transmissive image display device 11. That is, it is part of or integrated into the transmissive image display device (11). In operating mode B2, the liquid crystal layer (7), capable of switching between at least two states, is in a first switching state. In operating mode B1, the liquid crystal layer (7), capable of switching between at least two states, is in a second switching state.That is, the switchable liquid crystal layer implements a switch between an open operation mode and a peeping prevention mode. In the open operation mode, image content displayed on the screen can be viewed without restriction from various viewing angles. In the peeping prevention mode, the displayed image content is seen with sufficient brightness only within a narrow viewing angle range of a cone surrounding the first absorption axis of the first polarization layer (1).

[0085] FIG. 11 illustrates another technical embodiment of a screen capable of operating in at least two operating modes (B1 (free viewing mode) and B2 (restricted viewing mode)). In restricted viewing mode, light is emitted to the viewer with a viewing angle range that is more restricted than in free viewing mode. The screen includes an image display device (12), which uses a structure known in the prior art and may be composed of, for example, an active light-emitting image display device (12) based on OLED or micro LED, or, for example, a passive light-emitting (i.e., illuminated) image display device (12) based on LCD. An optical film having a liquid crystal layer (7) switchable between at least two states is positioned in the forward viewing direction of the image display device (12). The optical film is constructed, for example, according to a first alternative embodiment, wherein a spatially uniform first B composed of a biaxial birefringent material * A compensation layer (3) is disposed between the first polarizing layer (1) and the second polarizing layer (2). The second polarizing layer (2) can also serve as a rear polarizer ("rear polarizer") of, for example, the LC display of the video playback device (12). Of course, all other previously mentioned technical methods, including an optical film having a switchable liquid crystal layer (7), may also be used. As with the screen, the liquid crystal layer (7), which can switch between at least two states, is in a first switching state in operating mode B2 and in a second switching state in operating mode B1. This technical method is particularly suitable for improving existing screens.

[0086] Alternatively, a lighting device for a screen can be manufactured using an optical film without a switchable liquid crystal layer (7). This device can be configured to operate in two operating modes: B1 (free viewing mode) and B2 (restricted viewing mode). In the restricted viewing mode, light is emitted over a more restricted solid angle range than in the free viewing mode. FIGS. 9A and 9B illustrate examples of such a lighting device in these two operating modes. By combining the lighting device with an image playback device that displays image content located upstream of the viewing direction, a screen capable of switching between the two operating modes B1 and B2 can be obtained.

[0087] The lighting device illustrated in FIGS. 9a and 9b includes a planar backlight (13), which incorporates a static, i.e., non-switchable optical film as exemplarily illustrated in FIGS. 1a through 1c. A plate-shaped light guide (14) is positioned in front of the backlight (13) in the viewing direction. The light guide (14) has a coupling element within at least one large surface and / or volume. In the illustrated example, the coupling element (15) is positioned within the volume of the light guide (14). A linear polarization filter (16) is positioned in front of the backlight (13) or the light guide (14) in the viewing direction. This essentially limits the direction of propagation of light emitted from the backlight (13), passing through the optical film, and then passing through the linear polarization filter (16). Optionally, the linear polarization filter (16) may perform the function of an equivalent second polarization layer (2). A light-emitting element (17) arranged laterally on at least one narrow side (here, both narrow sides) of a light guide (14) injects light into the light guide (14) when turned on. The light incident on the light-emitting element (17) is reflected back and forth by total reflection from the light guide (14) and reaches an output coupling element (15). This output coupling element deflects the light and passes it through the surface of the light guide (14) to be transmitted outward toward the viewer. The output coupling element (15) is configured to deflect almost all of the light in this direction so that the light from the backlight (13) is transmitted with almost no obstruction.

[0088] FIG. 9a shows the lighting device in operating mode B2 of the restricted viewing mode. In this mode, only a relatively small and generally conical solid angle range, indicated by an arrow on the surface of the light guide (14), is illuminated. In this case, only the backlight (13) is turned on. The light-emitting element (17) must be turned off. FIG. 9b shows the lighting device in operating mode B1 of the open viewing mode. In this mode, light is emitted over a solid angle range that is much larger or wider than in operating mode B2, indicated by an arrow on the light guide (14). In this case, the light-emitting element (17) must be turned on. Light injected into the light guide (14) and combined by the output coupling element (15) serves to widen the illuminated solid angle range. The backlight (13) can be turned on or off in operating mode B1. When the backlight (13) is turned off, uniform illumination of the solid angle range is generally achieved in operating mode B1.

[0089] A passive image playback device illuminated from behind by the lighting device shown in FIGS. 9a and 9b generates a restricted viewing mode B2 or an open viewing mode B1 for a viewer viewing video content displayed on the video playback device, depending on whether the light-emitting element (17) is on or off.

[0090] By using a video playback device and, if necessary, a dedicated lighting device, the optical film can be widely used in all situations requiring the display and / or input of confidential information, such as PIN input, data display at ATMs or payment terminals, password input, and email verification on mobile devices. The present invention is particularly applicable to automobiles to selectively block video content that is distracting to the driver or passengers. Explanation of the symbols

[0091] 1: First polarization layer 2: Second polarization layer 3: Section 1 B * Compensation layer 4: 1 A * Compensation layer 5: 2nd A* Compensation layer 6: 3rd C * Compensation layer 7: Liquid crystal layer 8: Backlight 9: Light source 10: Linear polarizing filter 11: Video playback device 12: Video playback device 13: Backlight 14: Light guide 15: Output combining element 16: Linear polarizing filter 17: Light-emitting element R: Range of solid angle

Claims

Claim 1 A backlight (13) having an optical film that extends in a planar shape, emits light, and controls and limits the viewing angle of a viewer, wherein the optical film comprises: a first polarizing layer (1) having a first absorption axis forming 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 parallel to the surface of the optical film; wherein, between the first polarizing layer (1) and the second polarizing layer (2), at an alternative (i), a first biaxial birefringent material having two optical axes and three principal refractive axes is composed of a spatially uniform first B * Compensation layers (3) are arranged, and the main refractive axis has a respective refractive index n x , n y , n z Corresponding to, where, 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 the first B * The compensation layer (3) satisfies the following conditions, In the above formula, the first B * Compensation layer (3) includes thickness (d), phase shift (Δph), and a predetermined wavelength (λ); alternative (ii), at least two compensation layers composed of uniaxial birefringent materials are arranged, and a spatially uniform first A * The compensation layer (4) is composed of a first single-axis birefringent material having two first principal refraction axes different from the first optical axis, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarization layer (1), and a spatially uniform second A on the rear side when viewed from the viewer's direction * The compensation layer (5) is arranged, and the second A * The compensation layer is composed of a second single-axis 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, and wherein each of the compensation layers satisfies the following conditions, In the above equation, the thickness (d) of the compensation layer and the special refractive index (n e ) and normal refractive index (n o ), including a phase shift (Δph) and a predetermined wavelength (λ); and in the alternatives (i) and (ii), the material and thickness (d) of the compensation layer are defined such that the luminescence density is minimized within a predetermined solid angle range (R) when measured in a spherical coordinate system in which the origin is located on the surface of the film and the plane of the surface of the film, the solid angle includes an azimuth angle (φ) and a polar angle (θ), the azimuth angle (φ) is measured with respect to the preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limit azimuth angles (φ lim It is smaller than the absolute value of ); the polar angle (θ) is measured with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, is measured with respect to the first absorption axis in the plane formed by the surface normal and the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle (θ lim Backlight (13), characterized by being larger than ). Claim 2 In paragraph 1, the above 1 A * Compensation layer and the above 2 A * Spatially uniform third C between compensation layers * A compensation layer (6) is arranged, and the third C * The backlight (13) is composed of a third single-axis birefringent material having a third optical axis and two third principal refraction axes, wherein the third optical axis is parallel to the first absorption axis of the first polarization layer (1). Claim 3 A backlight (13) characterized in that, in claim 1 or 2, the first absorption axis is perpendicular to the surface of the film. Claim 4 In paragraph 3, the principal refraction axis corresponding to the minimum refractive index is parallel to the first absorption axis, and the first B * The compensation layer (3) is the minimum refractive index n z The principal axis of refraction corresponding to is parallel to the normal of the surface, and the maximum refractive index n x A -B compensation layer is constructed such that the principal refraction axis corresponding to is parallel to the second absorption axis of the second polarization layer (2), where, n x >n y >n z Backlight (13) characterized by being. Claim 5 In paragraph 3, the principal refraction axis corresponding to the maximum refractive index is parallel to the first absorption axis, and the first B * The compensation layer (3) is the maximum refractive index n z The principal refraction axis corresponding to is parallel to the normal of the surface, and the minimum refractive index n y A +B compensation layer is constructed such that the principal refraction axis corresponding to is parallel to the second absorption axis of the second polarization layer (2), where, n z >n x >n y Backlight (13) characterized by being. Claim 6 In paragraph 3, the above 1 A * The compensation layer (4) is constructed as a +A compensation layer, and the above second A * The compensation layer (5) is constructed as a -A compensation layer, or the above-mentioned first A * The compensation layer (4) is constructed as a -A compensation layer, and the above-mentioned second A * The compensation layer (5) is constructed as a +A compensation layer, and the third C * When the compensation layer (6) is placed, the above 3 C * Backlight (13), characterized in that the compensation layer (6) is constructed as a -C compensation layer or a +C compensation layer. Claim 7 In paragraph 1, the above 1 A * Compensation layer (4) and the second A * Backlight (13), characterized by having the same structure as the compensation layer (5). Claim 8 In claim 1, a liquid crystal layer (7) capable of switching between at least two states is disposed between the second polarizing layer (2) and the compensation layer closest to the second polarizing layer (2), and the liquid crystal layer (7) is configured to transmit light that has passed through the second polarizing layer (2) in a first switching state as no polarization or rotated by 90°, and to transmit light that has passed through the second polarizing layer (2) in a second switching state as circular polarization, elliptical polarization, or linear polarization, characterized in that it is a backlight (13). Claim 9 In claim 1, a liquid crystal layer (7) capable of switching between at least two states is disposed between the first polarizing layer (1) and the compensation layer closest to the first polarizing layer (1), and the liquid crystal layer (7) is configured to transmit light that has passed through the first polarizing layer (1) in a first switching state as no polarization or rotated by 90°, and to transmit light that has passed through the first polarizing layer (1) in a second switching state as circular polarization, elliptical polarization, or linear polarization, characterized in that it is a backlight (13). Claim 10 In claim 1 or 2, within the range of the predetermined solid angle (R), the loss function is minimum, and here, A backlight (13) characterized in that represents an angle-dependent transmittance and Ω represents the range of the solid angle. Claim 11 In claim 1 or 2, the limiting azimuth (φ) lim ) is 30° to 40° to the left and right of the priority direction, and / or the limit polar angle (θ lim Backlight (13), characterized in that ) is 40° to 50°. Claim 12 As a lighting device for a screen, the lighting device is arranged to be operable in at least two operating modes, namely B1 (used for free viewing mode) and B2 (used for restricted viewing mode), and in the restricted viewing mode, light is irradiated within a range of solid angles more restricted than in the free viewing mode, and the lighting device comprises: a backlight (13) according to claim 1 or 2; a plate-shaped light guide (14) having an output coupling element (15) on at least one surface and / or inside and positioned in front of the backlight (13) along the viewing direction; a light-emitting member (17) positioned laterally on at least one narrow side of the light guide (14); and a linear polarizing filter (16) positioned in front of the backlight (13) or in front of the light guide along the viewing direction; A lighting device for a screen, comprising, thereby, light emitted from the backlight (13) and transmitted through the linear polarization filter (16) is restricted in its direction of travel, wherein, in operation mode B2, the backlight (13) is turned on and the light-emitting member (17) is turned off, and in operation mode B1, at least the light-emitting member (17) is turned on. Claim 13 As a screen, the screen is capable of operating in at least two operating modes, namely a free viewing mode B1 and a restricted viewing mode B2, and in the restricted viewing mode, light is projected within a range of solid angles more restricted than in the free viewing mode for an observer, and the screen is characterized by: a backlight (8) having a liquid crystal layer (7) capable of switching between at least two states according to claim 8 or 9; a linear polarizing filter (10) disposed in front of the backlight (8) along the viewing direction; a transmissive image playback device (11) disposed in front of the backlight (8) along the viewing direction - wherein the linear polarizing filter (10) is disposed inside or after the transmissive image playback device (11) -, wherein in the operating mode B2, the liquid crystal layer (7) capable of switching between at least two states is in a first switching state, and in the operating mode B1, the liquid crystal layer (7) capable of switching between at least two states is in a second switching state. Claim 14 As a screen, the screen is operable in at least two operating modes, namely B1 (used for free viewing mode) and B2 (used for restricted viewing mode), and in the restricted viewing mode, light is irradiated to an observer within a range of solid angles more restricted than in the free viewing mode, and the screen comprises: an image playback device (12); and an optical film disposed in front of the image playback device (12) along the viewing direction, having a liquid crystal layer (7) capable of switching between at least two states, wherein in operating mode B2, the liquid crystal layer (7) is in a first switching state, and in 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 forming 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 parallel to the surface of the optical film. A first biaxial birefringent material having two optical axes and three principal refractive axes, comprising, between the first polarizing layer (1) and the second polarizing layer (2), at an alternative (i), a spatially uniform first B * Compensation layers (3) are arranged, and the main refractive axis has a respective refractive index n x , n y , n z Corresponding to, where, 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 the first B * The compensation layer (3) satisfies the following conditions, In the above formula, the first B * Compensation layer (3) includes thickness (d), phase shift (Δph), and a predetermined wavelength (λ); alternative (ii), at least two compensation layers composed of uniaxial birefringent materials are arranged, and a spatially uniform first A * The compensation layer (4) is composed of a first single-axis birefringent material having two first principal refraction axes different from the first optical axis, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarization layer (1), and a spatially uniform second A on the rear side when viewed from the viewer's direction * The compensation layer (5) is arranged, and the second A * The compensation layer is composed of a second single-axis 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, and wherein each of the compensation layers satisfies the following conditions, In the above equation, the thickness (d) of the compensation layer and the special refractive index (n e ) and normal refractive index (n o ), including a phase shift (Δph) and a predetermined wavelength (λ); and in the alternatives (i) and (ii), the material and thickness (d) of the compensation layer are defined such that the luminescence density is minimized within a predetermined solid angle range (R) when measured in a spherical coordinate system in which the origin is located on the surface of the film and the plane of the surface of the film, the solid angle includes an azimuth angle (φ) and a polar angle (θ), the azimuth angle (φ) is measured with respect to the preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limit azimuth angles (φ lim It is smaller than the absolute value of ); the polar angle (θ) is measured with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, is measured with respect to the first absorption axis in the plane formed by the surface normal and the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle (θ lim (greater than ), and wherein, between the second polarization layer (2) and the compensation layer closest to the second polarization layer (2), a liquid crystal layer (7) capable of switching between at least two states is disposed, and the liquid crystal layer (7) is constructed to transmit light that has passed through the second polarization layer (2) in a first switching state with no polarization or by rotating it 90°, and to transmit light that has passed through the second polarization layer (2) in a second switching state as circular polarization, elliptical polarization, or linear polarization, or wherein a liquid crystal layer (7) capable of switching between at least two states is disposed between the first polarization layer (1) and the compensation layer closest to the first polarization layer (1), and the liquid crystal layer (7) is constructed to transmit light that has passed through the first polarization layer (1) in a first switching state with no polarization or by rotating it 90°, and to transmit light that has passed through the first polarization layer (1) in a second switching state as circular polarization, elliptical polarization, or linear polarization A screen characterized by being constructed to allow transmission. Claim 15 A screen according to claim 14, wherein a third C* compensation layer (6) is spatially uniform between the first A* compensation layer and the second A* compensation layer, and the third C* compensation layer (6) is composed of a third single-axis birefringent material having a third optical axis and two third principal refraction axes, and the third optical axis is parallel to the first polarization layer (1). Claim 16 delete

Images