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

Abstract

The present invention relates to a backlight (13), which has an optical film that extends planarly and emits light to control and limit the viewer's viewing angle range. The optical film includes a first polarizing layer (1) having a first absorption axis that makes an angle of 0° to 30° with respect to the normal to the surface of the optical film when viewed from the viewer's direction; at least one phase-shift compensation layer to improve 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, in various technical proposals and combinations thereof in which spatially uniform compensation layers composed of uniaxial or biaxial birefringent materials are arranged, the material and thickness of the compensation layers are specified such that the light density is minimized within a range of a specific solid angle that does not include the entire half-space except for a concave cone along the line of sight.

Description

[Technical Field]

[0001] The present invention relates to a backlight, which has an optical film that extends in a planar manner and emits light to control and limit the viewer's viewing angle range. The present invention also relates to an optical film, which includes a first polarizing layer having a first absorption axis at an angle of 0° to 30° with respect to the normal to the surface 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 the first and second polarizing layers to improve the limitation of the viewing angle range. When viewed from the viewer's direction, the first or second polarizing layer may form the layer closest to the viewer.

[0002] In recent years, significant progress has been made in expanding the viewing angle range of LCDs. However, there are many situations where a very wide display area on a screen can be disadvantageous. Information such as banking details, other personal information, and confidential data is increasingly being used on mobile devices such as laptops and tablets. Therefore, it is necessary to control who can view this confidential data, and when sharing information on the display with others, such as vacation photos or advertisements, it is necessary to be able to select a wide viewing angle or viewing angle (public mode). On the other hand, when image information needs to be kept confidential, a narrower viewing angle or viewing angle (private mode) is preferable.

[0003] A similar problem exists in the automotive industry. After starting the engine, the driver should not be distracted by visual content such as digital entertainment programs. On the other hand, passengers also want to watch visual content while driving. Therefore, a screen that allows switching between these display modes is necessary.

[0004] In mobile displays, microsheet-like add-on films are used to protect visual data. However, these films cannot be switched or replaced and must always be manually applied and removed. Furthermore, they must be transported separately from the display when not in use. Another major drawback of using sheet-like films is light loss. [Background technology]

[0005] US 6,765,550 B2 describes how such micro-slicing can be used to achieve privacy protection. The main drawbacks of this solution are the mechanical removal and installation of the filter, as well as the light loss in protection mode.

[0006] US 5,993,940 A discloses the use of film to achieve an anti-peeping mode, i.e., a restricted viewing mode with a narrow viewing angle. However, the technical difficulties in research and development and manufacturing are considerable.

[0007] In WO 2012 / 033583 A1, switching between free-field and limited-field views is achieved by controlling the liquid crystals between the so-called "color-producing" layers. However, light loss occurs during this process, making it technically quite challenging.

[0008] US 2012 / 0235891 A1 describes a highly complex screen backlight. According to Figures 1 and 15, not only are multiple light guides used, but other complex optical units such as a microlens unit 40 and a prism structure 50 are also employed. These elements shape the light emitted from the backlight in the path of the front illumination. This proposed technology is costly, technically complex, and results in significant light loss. According to a modification shown in Figure 17 disclosed in US 2012 / 0235891 A1, both of the two light sources 4R and 18 produce light with a narrow illumination angle, while the light from the rear light source 18 is converted to light with a wide illumination angle through a complex process. Such a complex conversion significantly reduces brightness, as previously mentioned.

[0009] According to JP 2007-155783 A, it uses a special optical surface 19 that is complex to calculate and manufacture, and deflects light to different, narrower, or wider areas depending on the angle of incidence. These structures are similar to Fresnel lenses. Furthermore, the presence of interference surfaces can deflect light in unintended directions. Therefore, it is not determined whether a truly rational light distribution can be achieved.

[0010] US 2013 / 0308185 A1 describes how a special light guide with stepped sections radiates light in different directions across a large surface, specifically from narrow sides and from which direction the light guide is illuminated. By working in conjunction with transmissive image playback devices such as LC displays, it is possible to generate screens that can switch between free viewing mode and restricted viewing mode. The main drawback is that the restricted viewing effect can only occur to the left / right or up / down, but not simultaneously, which is necessary for certain payment processes, for example. Furthermore, even in restricted viewing mode, residual rays are still visible despite the restricted viewing angle.

[0011] Applicant WO 2015 / 121398 A1 describes a screen display having two operating modes, in which scattering particles are present in the volume of the corresponding light guide to enable switching between operating modes. However, the polymer scattering particles selected in this invention have the drawback that, because light is typically emitted and combined from two large surfaces, about half of the light is irradiated in the wrong direction, i.e., towards the backlight, and cannot be structurally recovered sufficiently. In addition, in some cases, especially at high concentrations, scattering particles made of polymer distributed in the volume of the light guide may result in a scattering effect that weakens the anti-peeping effect in the protected operating mode.

[0012] The fundamental principle of the "electric birefringence (EDB)" technique is to "filter" all beam that does not exit the imaging layer at a specific beam angle using the switchable liquid crystals of an added LC panel. The drawbacks of this technique are the high additional energy consumption and cost, and the difficulty in changing the optimal point within + / -40°. The absorption of the LC structure is also insufficient because, once the observation angle exceeds the sweet spot, the luminosity attenuates and then rises again, so the luminosity at observation angles greater than + / -40° is less than 3% of the maximum luminosity.

[0013] US 2019 / 0094626 A1 describes an optical layer structure for controlling the viewing angle, in which two phase difference plates are placed as compensation layers on a linear polarizer. The two phase difference plates refer to λ / 4 plates, and have a structure, optical anisotropy, and a fin-like or strip-like layer, with carrier material placed between each of these layers. The structure may be the same, but the orientation differs once the arrangement is complete. The uppermost layer constitutes a polarizing layer, a so-called "Z polarizer," in which the absorption axis that gives rise to the polarization transition dipole moment is oriented perpendicular to the layer surface. Such layers structured with fins may produce visual artifacts such as moiré fringes, and therefore such layers can only be applied to screens with known properties such as resolution and size, pore size, scattering characteristics, and distance from the screen surface, and cannot be used universally independently of the screen size.

[0014] The above methods and arrangements generally have drawbacks: they significantly reduce the brightness of the base screen, require complex and expensive optical components for mode conversion, reduce the resolution in the common free-view mode, and produce visual artifacts when using displays with extremely high resolution. Another drawback is that the limitation of the viewing angle range is incomplete, meaning that despite the need to limit the viewing angle range, it may still be possible to perceive image content with significantly reduced brightness. [Overview of the Initiative]

[0015] The object of the present invention is to further improve the so-called privacy effect, which makes it more difficult for unauthorized users to peek at protected image content, by developing a backlight having an optical film that is generally combined with a screen to control and limit the viewer's viewing angle range.

[0016] In an optical film having the aforementioned layer structure and a backlight having such an optical film, the solution for achieving the above objectives of the present invention is a specific embodiment of the at least one compensation layer. First, the first polarizing layer and the second polarizing layer will be described in detail. The first polarizing layer has a first absorption axis that makes an angle of 0° to 30° with respect to the normal to the surface of the optical film. When the angle is 0°, that is, when the absorption axis is parallel to the surface normal or perpendicular to the film surface, it is also called a so-called "Z polarizer". When the angle is different and within the range of up to 30°, it is hereinafter referred to as "Z *Also called a "polarizer". The absorption of the first polarizing layer is usually static, but a switchable scheme may be employed to turn angle-dependent absorption on and off. The second polarizing layer has a second absorption axis parallel to the surface of the optical film. Thus, this second polarizing layer is a conventional linear polarizer. At least one phase-shift compensation layer is placed between the first and second polarizing layers to improve the limitation of the viewing angle range. Both the first and second polarizing layers are closest to the observer. Preferably, all layers are fixedly connected by, for example, material bonding, welding or optical bonding.

[0017] For ease of understanding, we will assume that, generally, in a Cartesian coordinate system consisting of x, y, and z directions, the film surface lies within a plane, and that this plane is 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, that is, to improve the limitations on the viewing angle range, the at least one phase shift compensation layer can be constructed using, in principle, two methods. In the first alternative (hereinafter also called alternative (i)), a first B made of a first biaxial birefringent material is placed between the first polarizing layer and the second polarizing layer. * A compensation layer is provided. This biaxial birefringent material has two optical axes and three principal refractive axes, each principal refractive axis having a refractive index n x , n y , n z Each corresponds to one. The first B * Depending on the proposed 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. Here, the first B * The compensation layer satisfies the following conditions.

number

[0019] In the second alternative (hereinafter also referred to as alternative (ii)), at least two compensation layers made of uniaxial birefringent materials are arranged between the first polarizing layer and the second polarizing layer, among which the first A that is spatially uniform * The compensation layer is made of a first uniaxial birefringent material having a first optical axis and two different first principal refractive axes, and the first optical axis overlapping with one of the first principal refractive axes is perpendicular or parallel to the first absorption axis of the first polarizing layer. As viewed by an observer, the second A that is spatially uniform * The compensation layer is arranged rearward, and this second A * The compensation layer is made of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes, and the second optical axis overlapping with one of the second principal refractive axes of the second material is perpendicular to the first optical axis of the first material. The optical axes of these uniaxial materials are also called special axes.

[0020] Here, "spatially uniform" means that the corresponding compensation layer is not structured within an area parallel to its interior or the surface of the optical film and has the same characteristics within the entire area range. This is different from US2019 / 0094626 A1. In order to prevent visual artifacts from occurring in such a sheet-like structured laminate, the layer structure according to one technical solution of US2019 / 0094626 A1 requires special adjustment for each component regarding resolution, distance, aperture, surface, and scattering characteristics. The optical film of the present invention having a spatially uniform compensation layer can be widely applied to various screen sizes and screen resolutions and does not require special adjustment.

[0021] The compensation layer is

Number

[0022] In these two 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 in a spherical coordinate system where the origin lies on the film surface and the film plane. The solid angle range R includes only a portion of the perceptible half-space, i.e., the azimuth angle φ, where the preferred direction measurement in the plane relative to the film surface is such that |φ| or |180°-φ| is less than the absolute value of a predetermined limiting azimuth angle φlim. In principle, the preferred direction can be arbitrarily selected, but should be done according to the application of the optical film. When such an optical film is applied to a screen with a fixed direction (e.g., a vehicle), the preferred direction is thus selected so as to be parallel to the imaginary line between the eyes of a seated driver.

[0023] On the other hand, the range of solid angles in which the emission density is minimized includes the first absorption axis and the polar angle θ measured in the plane formed by the surface normal and the first absorption axis (whose vectors share a common origin), and includes all solid angles except for cones that have a limiting polar angle θlim around the first absorption axis (here referred to as the zero axis), where the absolute value of the polar angle θ is greater than a predetermined limiting polar angle θlim. When the surface normal and the first absorption axis are parallel, the polar angle is measured only with respect to the surface normal. When such an optical film is applied to the screen described above, the emission density is minimized within the range of solid angles described above, thus functioning as an effective field of view limiter. Therefore, ideally, an observer positioned within the range of solid angles described above with respect to the spherical coordinate system of the optical film will perceive nothing on the screen due to the minimum emission density within this range. The term "minimum emission density" means that the emission density is almost zero, and this emission density is significantly lower than the emission density outside the range of solid angles described above, so ideally, the observer cannot see any image content.

[0024] In order to more clearly define the range of the solid angle, that is, in order to achieve a greater decrease in emission density inside than outside the range of the solid angle, in the second alternative (ii), the first A * Compensation layer and second A * A third C that is spatially uniform between the compensation layer and the surrounding layer * It is advantageous to place a compensation layer, and this third C * The compensation layer consists of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes, the third optical axis being parallel to the first absorption axis of the first polarizing layer.

[0025] To achieve a symmetrical decrease in luminescence density with respect to the film surface, the first absorption axis is perpendicular to the film surface. When this optical film is used as the screen, an observer viewing the screen along the screen's surface normal perceives a symmetrical decrease in luminescence density in response to changes in the viewing angle to the right, left, or preferred direction; that is, it correlates only with the absolute value of the polar angle. In this case, the limiting polar angle θlim is measured with respect to the surface normal, and therefore differs from that measured with respect to the first absorption axis in that it is the same for all azimuth angles.

[0026] When the first absorption axis takes this orientation, the first polarizing layer is also called the Z polarizing layer. When the first absorption axis takes a different orientation within the aforementioned range, the first polarizing layer is Z * This is called the polarizing layer, and the use of the symbol "*" indicates a generalization of the Z-polarizing layer.

[0027] Similarly, name A * Compensation layer A represents a generalization of the term compensation layer, name B *The term "compensation layer" represents a generalization of the term "B compensation layer." To define the prior art terms "Z polarizing layer," "A compensation layer," and "B compensation layer," one can refer to "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" by Ho-Jin Choi et al., which is published online in Optical Materials 99 (2020), reference number 109531.

[0028] When the first absorption axis is perpendicular to the surface of the film, that is, when the first polarizing layer is constructed as a Z-polarizing layer, several useful technical proposals are generated. The orientation of the optical axes of these compensation layers must, in principle, correspond to the orientation of the first absorption axis of the first polarizing layer in order to achieve the desired visible region limitation. The first absorption axis may be in a different direction, for example, if an observer, such as a vehicle driver, is viewing the screen from an oblique direction rather than the surface normal.

[0029] In the first technical proposal 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 proposal, the first B * The compensation layer is constructed as the -B compensation layer. Here, the optical axis lies in the plane formed by the x and z directions, and the three principal refractive axes correspond to the directions of the Cartesian coordinate system, n x >n y >n z and n x It is parallel to the second absorption axis of the second polarizing layer. The latter condition can also be applied to the first absorption axis being tilted at a small angle of inclination of up to about 10° with respect to the surface normal; otherwise, the principal refractive axis will also be tilted, and the orientations in the x, y, and z directions of the coordinate system will correspond to the z direction of the coordinate system based on the orientation of the first absorption axis, and substantially nx The key point is that it is perpendicular to the first absorption axis.

[0030] In the second technical proposal 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 proposal, the first B * The compensation layer is constructed as a +B compensation layer. Here, the optical axis lies in the plane formed by the y-direction and the z-direction, and the three principal refractive axes correspond to each direction in the Cartesian coordinate system, n z >n x >n y n y It is parallel to the second absorption axis of the second polarizing layer. The latter condition can also be applied to the first absorption axis being tilted at a small angle of inclination of up to about 10° with respect to the surface normal; otherwise, the principal refractive axis will also be tilted, and the orientations in the x, y, and z directions of the coordinate system will correspond to the z direction of the coordinate system based on the orientation of the first absorption axis, and substantially n y The key point is that it is perpendicular to the first absorption axis.

[0031] In the third technical proposal based on the second alternative, the first absorption axis of the first polarizing layer (1) is similarly perpendicular to the surface of the optical film, and in this technical proposal, the first A * The compensation layer is constructed as a +A compensation layer, and the second A * The compensation layer is constructed as an A compensation layer, or vice versa. Third C * If a compensation layer is provided, it will be constructed as a -C compensation layer or a +C compensation layer.

[0032] In order to keep manufacturing costs at a low level, the first A * Compensation layer and second A * The preferred structure of the compensation layers is the same; that is, both compensation layers are constructed as +A compensation layers, or both are constructed as -A compensation layers, and have the same thickness.

[0033] In all of the aforementioned technical proposals, a particularly preferred improved technical proposal includes a liquid crystal layer that can switch between at least two states, positioned between the second polarizing layer and the compensation layer closest to the second polarizing layer. This liquid crystal layer is constructed such that, in the first switching state, it transmits light that has passed through the second polarizing layer either unpolarized or rotated by 90°, and in the second switching state, it transmits light that has passed through the second polarizing layer as circularly polarized, elliptically polarized, or linearly polarized light. The 90° rotation in the first switching state means that linearly polarized light passes through the switchable liquid crystal layer and becomes linearly or elliptically polarized, and most of the electric field vectors are rotated by 90°. That is, the polarization is not rotated by exactly 90°. By adding a switchable liquid crystal layer, it is possible to switch between an anti-peeping mode and a common mode, which is evident when the optical film is integrated into the screen. The reduction in luminous intensity within a predetermined solid angle range described above is permanent for the optical film, but can be eliminated by using a switchable liquid crystal layer. The first switching state corresponds to the privacy mode, where the light maintains linear polarization. The second switching state corresponds to the common mode, where the light is normally elliptically polarized, but other polarization methods may be employed depending on the selected liquid crystal layer. In the common mode, the luminescence density within a predetermined solid angle range does not decrease, or decreases only slightly, so that if this arrangement is used on the screen, the image content can be perceived to the extent that is technically feasible, regardless of (i.e., without limitations) the viewer's position. In the privacy mode, the image content cannot be perceived by a person standing to the side (in the direction of the first absorption axis). Alternatively, the liquid crystal layer may be placed between the first polarization layer and the nearest compensation layer.

[0034] This switchable liquid crystal layer is typically applied together with a static first polarizing layer to produce a switchable optical film. If the functionality of the switchable liquid crystal layer is realized by the switchable first polarizing layer, the switchable liquid crystal layer may not be provided. In this case, the first polarizing layer is configured, for example, as a dye-encapsulated liquid crystal layer, a so-called "Dye-LC-Zellen" (dye LC unit). Such a 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.

[0035] Preferably, the line-of-sight restriction effect within a predetermined solid angle range is achieved as follows: The elements of the optical film are coordinated with each other so that the light emission density decreases or becomes minimal within this solid angle range R, and the following loss function is minimized within this predetermined solid angle range R:

number

[0036] In normal use, the limiting azimuth angle φlim is preferably 30° to 40° to the left and right, and / or the limiting polar angle θlim is preferably 40° to 50° to the left and right with respect to the surface normal or the first absorption axis direction (when inclined with respect to the surface normal).

[0037] If the switchable liquid crystal layer is not disposed on the film, the backlight having the optical film can be incorporated into the screen's lighting device; if the switchable liquid crystal layer is disposed on the film, it can be incorporated into the screen.

[0038] Specifically, in an illumination device applied to a transmissive screen (particularly an LC display), a backlight is inserted that has an optical film that is not switchable and does not have a switchable liquid crystal layer, and is capable of operating in at least two operating modes, namely a free viewing mode B1 and a restricted viewing mode B2, and in this restricted viewing mode, the illumination is configured to irradiate light within a more limited solid angle range than in the free viewing mode. This illumination device comprises a backlight that extends in a planar manner and emits light, and this backlight has a backlight light source and the aforementioned non-switchable optical film. If the second polarization layer of the optical film is positioned in front of the first polarization layer along the observation direction, the backlight as a whole (and the other technical proposals described later as well) emits unpolarized light from the backlight light source of the backlight; if the opposite arrangement is adopted, the light emitted from the backlight light source of the backlight is also (partially) polarized. For an observer viewing the illumination device, a plate-shaped light guide is positioned in front of the backlight along the viewing direction, having two large surfaces and a narrow side connecting them, with an output coupling element on at least one of these large surfaces and / or within its volume. A light-emitting element is positioned laterally on at least one of the narrow sides of the light guide. A linear polarizing filter is positioned in front of the backlight or in front of the light guide. Selectively, this polarizing filter may correspond to a second polarizing layer of an optical film, or it may be a special type. This restricts the direction of propagation of light emitted from the backlight and transmitted through the linear polarizing filter. In operating mode B2, which is a restricted viewing mode, the backlight is on and the light-emitting element is off. The backlight illuminates the restricted viewing angle range. In operating mode B1, which is a free or common mode, the restricted illumination by the backlight alone can be compensated or overcompensated by turning on at least these light-emitting elements. This allows the backlight to be turned on or off in the common viewing mode. In this case, a transmissive screen is positioned in front of the illumination device.

[0039] Furthermore, the present invention includes a screen capable of operating in at least two operating modes B1 (for free viewing mode) and B2 (for restricted viewing mode), in which controlled light is irradiated within a more restricted viewing angle range or solid angle range for the observer than in free viewing mode. In a technical proposal having a switchable liquid crystal layer capable of switching between two states, such a screen has a backlight and an optical film that extend in a planar manner and emit light. Selectively, the backlight can emit light directly, for example, in the form of a so-called "direct matrix backlight". A linear polarizing filter is positioned in front of the backlight along the viewing direction. Selectively, this polarizing filter may correspond to a second polarizing layer of the optical film. This restricts the direction of propagation of light emitted from the backlight and transmitted through the linear polarizing filter. A transmissive image reproduction device is positioned in front of the backlight along the viewing direction. The linear polarizing filter is provided in the transmissive image reproduction device as part of the image reproduction device. The polarizing filter may employ an independent method, and the polarizing filter is positioned as close as possible to the image reproduction device in the stacking of optical assemblies. A typical image playback device has linear polarizers above and below the liquid crystal layer along the viewing direction, but here it is described as having a linear polarizer below the viewing direction. The linear polarizer located above is very important for anti-peeping protection applications. As described above, the liquid crystal layer, which can switch between at least two states, enters the first switching state in operating mode B2 and the second switching state in operating mode B2.

[0040] Finally, the present invention further includes a screen capable of operating in at least two operating modes, namely a free viewing mode B1 and a restricted viewing mode B2, in which light is projected onto the observer within a more restricted solid angle range than in the free viewing mode. Such a screen may be, for example, an image reproduction device such as an OLED, microLED, or LCD, and an optical film positioned in front of the image reproduction device along the viewing direction, the optical film having a liquid crystal layer capable of switching between the at least two states described above. The liquid crystal layer is determined to be in a first switching state and a second switching state in operating mode B2 according to the definitions of the first and second switching states to date.

[0041] Of course, within the scope of the present invention, the features described above and below may be combined in the manner provided by this application, combined in other ways, or used individually.

[0042] The present invention will be described in detail below, along with embodiments, with reference to the accompanying drawings which also clarify the essential features of the invention. These embodiments are for illustrative purposes only and are not limiting. For example, the description of an embodiment that includes multiple parts or assemblies does not mean that all such parts or assemblies are essential. Specifically, other embodiments may include alternative parts and assemblies, reduced parts or assemblies, or additional parts or assemblies. Unless otherwise specified, parts or assemblies of different embodiments can be combined with each other. Modifications and variations described for one embodiment may also be applicable to other embodiments. To avoid duplication, identical or corresponding parts in different figures are denoted by the same reference numerals, and redundant descriptions are omitted. [Brief explanation of the drawing]

[0043] Here, [Figure 1A] Figure 1A shows the layered structure of an optical film for controlling and limiting the viewer's field of view. [Figure 1B] Figure 1B shows the layered structure of an optical film used to control and limit the viewer's field of view. [Figure 1C] Figure 1C shows the layered structure of an optical film for controlling and limiting the viewer's field of view. [Figure 2] Figure 2 shows the limitations of the field of view. [Figure 3] Figure 3 shows an example of how the present invention improves privacy protection. [Figure 4A] Figure 4A shows the anti-peeping protection effect of the first embodiment of the optical film. [Figure 4B] Figure 4B shows the anti-peeping protection effect of the first embodiment of the optical film. [Figure 5A] Figure 5A shows the anti-peeping protection effect of the second embodiment of the optical film. [Figure 5B] Figure 5B shows the anti-peeping protection effect of the second embodiment of the optical film. [Figure 6A] Figure 6A shows the anti-peeping protection effect of the third embodiment of the optical film. [Figure 6B] Figure 6B shows the anti-peeping protection effect of the third embodiment of the optical film. [Figure 7A] Figure 7A shows the polarization ellipses passing through the optical film. [Figure 7B] Figure 7B shows the polarization ellipses passing through the optical film. [Figure 7C] Figure 7C shows the polarization ellipses passing through the optical film. [Figure 7D] Figure 7D shows the polarization ellipses passing through the optical film. [Figure 7E] Figure 7E shows the polarization ellipses passing through the optical film. [Figure 7F] Figure 7F shows the polarization ellipses passing through the optical film. [Figure 7G] Figure 7G shows the polarization ellipses passing through the optical film. [Figure 8] Figure 8 shows a switchable embodiment of the optical film. [Figure 9A]Figure 9A shows two operating states of a lighting device equipped with a non-switchable optical film. [Figure 9B] Figure 9B shows two operating states of an illumination device equipped with a non-switchable optical film. [Figure 10] Figure 10 shows a screen with a switchable optical film. [Figure 11] Figure 11 shows another screen with a switchable optical film. [Modes for carrying out the invention]

[0044] Figures 1A-1C show various layered structures of optical films for controlling and limiting the viewer's viewing angle. An observer (not shown) is positioned above the top layer, and the surface of the top layer has a plane normal parallel to the long side of the drawing within the plane of the drawing. Viewed from the observer's direction, this top layer is the first polarizing layer 1 in all three Figures 1A-1C. The first polarizing layer 1 has a first absorption axis that makes an angle of 0° to 30° with respect to the plane normal of the optical film. When the angle is 0°, the first polarizing layer 1 is a Z polarizer, and for different angles, the term "Z* polarizer" is used. An angle of 0° is suitable, for example, for a laptop computer where the user is directly in front of the screen. An angle of 30° is advantageous, for example, in a car where the screen is positioned between the driver's and passenger's seats and relevant information is visible only to the driver.

[0045] In Figures 1A-1C, the lower layer is a second polarizing layer 2 having a second absorption axis parallel to the surface of the optical film. In other words, the second polarizing layer 2 is a linear polarizer.

[0046] At least one phase-shift compensation layer is placed 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 or multiple compensation layers may be used. The compensation layer is, for example, a uniaxial or biaxial birefringent polymer film. It is advantageous to permanently connect these layers to each other by, for example, optical adhesion or other material adhesion. For example, ultrasonic welding can also be used. When bonding or pressing extremely smooth surfaces together, they can also be connected by adhesion alone, using an anti-reflective layer as needed. The anti-peeping effect can be improved by providing one or more compensation layers, as described later. As an alternative solution not shown, the second polarization layer 2 can be placed as the uppermost layer in the viewing angle direction, with the first polarization layer 1 behind it. In this case, at least one phase-shift compensation layer is always placed between the first polarization layer 1 and the second polarization layer 2.

[0047] In the first technical solution shown in Figure 1A (hereinafter also referred to as the first alternative or alternative (i)), the first B is placed between the first polarizing layer 1 and the second polarizing layer 2. * Compensation layer 3 is positioned. * Compensation layer 3 is a spatially uniform layer made of a biaxial birefringent material. Therefore, this material, i.e., the first B * The compensation layer 3 has two optical axes and three principal refractive axes. Each of the three principal refractive axes has a refractive index n x , n y , n z This corresponds to the axes of a Cartesian coordinate system. This is a common characteristic of biaxial birefringent materials. The symbols "x", "y", and "z" correspond to the axes of a Cartesian coordinate system. However, in order to obtain 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.

[0048] The orientation of the first absorption axis determines the orientation of all other absorption axes or principal refractive axes in any type of compensating layer. If the first polarizing layer is, for example, a Z polarizer, i.e., its first absorption axis is parallel to the surface normal or perpendicular to the film surface, then it means that the principal refractive axes corresponding to the minimum or maximum refractive index are also parallel to the surface normal. Thus, the other two principal refractive axes lie in the plane of the optical film surface. * The optical axis of compensation layer 3 (in this case, compensation layer B) lies in a plane perpendicular to the optical film surface. In this case, the first B * Compensation layer 3 can be constructed in two ways.

[0049] On the other hand, it can also be constructed as a -B compensation layer. In this case, since the -B compensation layer is a Z polarizer, the principal refractive axis and B * In the virtual Cartesian coordinate system in which the optical axis of the compensation layer is defined, the z-direction is associated with the direction perpendicular to the optical film surface. In this notation, the -B compensation layer is n x >n y >n z The following condition is met. Therefore, the minimum refractive index corresponding to the principal axis perpendicular to the optical film surface is n z It is expressed as follows. Furthermore, the maximum refractive index n x The corresponding principal refractive axis is parallel to the second absorption axis of the second polarizer layer 2.

[0050] On the other hand, it can also be constructed as a +B compensation layer. Here, the z-direction is also related to the direction perpendicular to the optical film surface. In this notation, the +B compensation layer is n z >n x >n y The following conditions are met. Therefore, the maximum refractive index corresponding to the principal axis perpendicular to the optical film surface is n z It is expressed as follows. Furthermore, the minimum refractive index n y The corresponding principal refractive axis is parallel to the second absorption axis of the second polarizing layer 2 (see above).

[0051] In all technical proposals of the first alternative, the first B * Compensation layer 3 satisfies the following conditions.

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[0052] In the second technical proposal (whose basic structure is shown in Figure 1B, and which will hereafter be called the second alternative or alternative (ii)), a compensation layer consisting of at least two uniaxial birefringent materials is placed between the first polarizing layer 1 and the second polarizing layer 2. These are the first A * Compensation layer 4 and second A * Compensation layer 5. Two A * Compensation layers 4 and 5 are configured spatially uniformly as defined above. * Compensation layer 4 is composed of a first uniaxial birefringent material having a first optical axis and two first principal refractive axes, the first optical axis being perpendicular or parallel to the first absorption axis of the first polarizing layer 1. * Compensation layer 5 is positioned behind the observer and consists of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes. * The azimuth of the second optical axis of correction layer 5 is the same as the first A * The second optical axis is determined according to the orientation of the first optical axis of the correction layer 4, and the condition that the second optical axis is perpendicular to the first optical axis must be met. * Correction layers 4 and 5 satisfy the following conditions, respectively.

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[0053] Figure 1C shows an improved version of the second alternative. To more clearly define the range of the solid angle, i.e., to reduce the light density within this solid angle range more significantly compared to the light density outside this solid angle range, and / or to increase flexibility in the assembly selection of the compensation layer, this second alternative is based on the first and second A * A third spatially uniform C is placed between the compensation layers. * It is preferable to include a compensation layer 6. Third C * Compensation layer 6 is composed of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes, the third optical axis being parallel to the first absorption axis of the first polarizing layer 1. * The orientation of the optical axis of the compensation layer 6 material is also determined by the orientation of the first absorption axis of the first polarizing layer 1.

[0054] When the first polarizing layer 1 is constructed as a Z polarizer and the first absorption axis is perpendicular to the optical film surface, the first A * Correction layer 4 is a +A correction layer, and the second A * Correction layer 5 is constructed as a -A correction layer, or vice versa. Third C * If a correction layer 6 is provided, it is constructed as a -C or +C correction layer.

[0055] In the first and second alternatives, the material and thickness d of the compensation layer are specified such that the light density is minimized only within a specified solid angle range R in a spherical coordinate system with the film surface and film plane as the origin. The solid angle range R includes only a portion of the perceptible half-space; that is, on the one hand, it includes the azimuth angle φ on the film surface, and when measured relative to the preferred direction on the plane of the film surface, |φ| or |180°-φ| is smaller than the absolute value of the specified limiting azimuth angle φlim. In principle, the preferred direction can be arbitrarily selected but must be determined according to the application of the optical film. If such an optical film is used, for example, in a fixed-direction screen (e.g., a vehicle), the preferred direction is selected to be parallel to the imaginary line between the eyes of a driver sitting upright, i.e., usually extending horizontally. The limiting azimuth angle φlim is specified according to the application of the film. For example, in the case of a laptop that needs to block side views in a vehicle such as a train, values ​​of 30° to 40° to the left and right of the preferred direction are common. The preferred direction here is usually parallel to the longer side of the screen, and the first absorption axis is parallel to the screen normal, so the decrease in light density on all sides is symmetrical.

[0056] On the other hand, the range of solid angles in which the light density is minimized also includes the polar angle θ, which is measured with respect to the first absorption axis and within the plane formed by the surface normal and the first absorption axis, or, if the first absorption axis is parallel to the surface normal, is measured only with respect to the surface normal, and the absolute value of this polar angle is greater than a predetermined limiting polar angle θlim. Preferably, the limiting polar angle θlim is in the range of 40° to 50°, depending on the application. When the optical film is applied to the above screen, the light density is minimized within the aforementioned range of solid angles, thus effectively restricting the line of sight. Therefore, ideally, an observer positioned within the aforementioned range of solid angles with respect to the spherical coordinate system of the optical film will not perceive any content on the screen, or at least will not be able to recognize such content, because the light density is minimized within this range.

[0057] The line-of-sight restriction effect within a specific solid angle range, i.e., the reduction or minimization of luminous intensity within this solid angle range, adjusts the components of the optical film and the loss function.

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[0058] This will be illustrated using Figures 2 and 3. Figure 2 shows the projection of a specified solid angle range R onto the optical film plane as a black region (also called a conoscope image). Within this range, the light density must be as low as possible to enhance privacy protection. In this example, the solid angle range R is specified such that the limiting azimuth angle φlim is 40° (forming black regions above and below the horizontal axis), and the limiting polar angle θlim is also 40° (corresponding to the concave regions to the left and right of the midpoint). In this case, the inner concentric circles correspond to the polar angle θ = 40°. Within this specified solid angle range, the loss function, i.e., the integral of the logarithmic transmittance, is minimized. By using the commercially available optical design program given as an example, the components can be adjusted to satisfy this condition.

[0059] Finally, even when the vertical viewing angle is not 0° (corresponding to viewing the surface of the optical film perpendicularly), the anti-peeping protection effect on the sides is improved. For the optical film with a vertical viewing angle of 30° and the second option optical film which has a +A correction layer and a -A correction layer on one side and an additional -C correction layer on the other, see Figure 3. Since the first polarization layer 1 is constructed as a Z polarizer, the first absorption axis is parallel to the surface normal of the optical film. This figure shows the anti-peeping protection effect in arbitrary units. That is, the light density is normalized to an angle of 0° according to the horizontal viewing angle in degrees, and this figure shows how the brightness of the screen in the anti-peeping protected angle range compares to the non-anti-peeping protected angle range. For example, a preferred direction parallel to the horizontal direction is selected in relation to the viewer's reference frame. That is, the horizontal direction corresponds to a hypothetical line connecting the viewer's two eyes, and the vertical direction is perpendicular to this. The solid line represents the anti-peeping protection effect achievable with conventional technology at a vertical viewing angle of 30°, using only a Z polarizer and without a spatially uniform compensation layer. The dashed line represents two types of A * The image shows the anti-peeping protection effect when the compensation layers (-A and +A) are combined, and the dotted line shows the anti-peeping protection effect when combined with an additional -C compensation layer. A in this example * Since the compensation layer is not fully optimized, combining it with the -C compensation layer does not result in improvement in this example. However, generally speaking, C * Using the compensation layer improves privacy protection at angles around 30°. Side-viewing privacy protection is significantly improved at angles up to approximately 60°. At angles greater than 60°, privacy protection is only slightly improved, but still better than conventional technology. This improvement in privacy protection may appear exaggerated due to the logarithmic scale, but is not noticeable in reality. At a vertical viewing angle of 0° (not shown here), conventional optical films and optical films with the compensation layer described above and below show roughly the same results, roughly corresponding to the dashed or dotted lines.

[0060] The solid angle range R shown in Figure 2 is illustrative and can be adjusted as needed. For example, it can improve privacy protection at a horizontal field of view of 0° for a viewer standing directly behind a seated user, such as on a laptop. In this case, a solid angle range of 40° in Figure 2 completely encloses the concentric circles.

[0061] Figures 4A and 4B, 5A and 5B, and 6A and 6B show further examples defining the solid angle range R shown in Figure 2. Figures 4A, 5A, and 6A show the anti-peeping protection effect at a vertical viewing angle of 0°, and Figures 4B, 5B, and 6B show the anti-peeping protection effect at a vertical viewing angle of 30°. The solid curves always correspond to optical films that have only the first Z* polarizing layer and no additional spatially uniform compensating layer.

[0062] Figures 4A and 4B show the anti-peeping protection effect of the optical film having the first alternative structure shown in Figure 1A. This optical film is the first B * It is equipped with a compensation layer 3. x , n y , n z Since multiple combinations of biaxial birefringent layers achieve the same optical function, these layers are classified by two other parameters, namely the transmittance parameter.

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[0063] In the green visible mid-wavelength range, where the human eye has maximum sensitivity at wavelength λ=550nm, a dotted curve is obtained with a thickness d=5.25μm, Re=132, and Nz=3.84. The necessary correlation between refractive indices can be inferred from nx. For example, n x = 1.6246, n y =1.6, n zIt is 1.5287. To produce a layer having these calculated refractive indices accurately, numerous manufacturing methods for highly controlling the refractive index are known in the art. By selecting a material with the desired refractive index ratio, the thickness d is adjusted to satisfy Nz. In addition to the aforementioned parameters, significant improvements can also be achieved with other combinations. As a result, the anti-peeping protection characteristics indicated by the dotted line are obtained, with Re = 75 and Nz = 3.84. These values are for illustrative purposes only. A tolerance of + / - 20% is permitted and is included in each case without significantly reducing the anti-peeping protection effect.

[0064] Figures 5A and 5B show the anti-peeping protection effect of a second optical film different from the structure shown in Figure 1C. This optical film has a first A * correction layer 4 and a second A * correction layer 5, and a third C * correction layer 6 is disposed therebetween. Here, since the first absorption axis of the first polarizing layer 1 is also perpendicular to the surface, a Z polarizer is formed. Therefore, the first A * correction layer 4 is constructed as a +A correction layer with positive birefringence, the second A * correction layer 5 is constructed as a -A correction layer with negative birefringence, and the third C * correction layer 6 is constructed as a -C correction layer with negative birefringence. Alternatively, the first A * correction layer 4 can be constructed as a -A correction layer with negative birefringence, the second A * correction layer 5 can be constructed as a +A correction layer with positive birefringence, and the third C * correction layer 6 can be constructed as a +C correction layer with negative birefringence. Here, negative birefringence refers to the situation where n e <n o and positive birefringence refers to the situation where n e >n o

[0065] ​When the vertical viewing angle is 0° (Figure 5A), that is, when the film is viewed directly from above along the surface normal, no improvement is observed even when three correction layers are added in addition to the Z polarizer. However, when the vertical viewing angle is 30° (Figure 5B), an improvement in the anti-peeping protection effect can be clearly confirmed. The improvement shown in Figures 5A and 5B is due to the first +A correction layer d·(n e -n o ) = 264 nm, d·(n) in the second -A correction layer o -n e This can be achieved by using a series of correction layers that satisfy the condition ) = -264nm (each with a 20% tolerance). In the third -C correction layer, d·(n e -n o The condition ) = -22nm is met, and the tolerance exceeds + / -10nm. Relatively thin carbon * For the correction layer as a whole, the tolerance is either + / -10nm or 20%, determined by which value is greater. In the alternative with the first -A correction layer, the sign is reversed accordingly.

[0066] Figures 6A and 6B show the anti-peeping protection effect of an optical film having the second alternative structure shown in Figure 1C. This optical film is the first A * Correction layer 4 and second A * It has a correction layer 5, with a third C between them * A correction layer 6 is positioned. Unlike Figures 5A and 5B, the first absorption axis of the first polarizing layer is tilted 20° toward the surface with respect to the surface normal, Z * It is a polarizer. This orientation is A to achieve an anti-peeping protection effect. * Correction layer and C * Determine how the optical axis of the correction layer should be positioned. To manufacture such a tilted correction layer, for example, optical alignment and polymerization of LC liquid crystals can be used. Without loss of generality, the first A * Correction layer 4 is -A * As a correction layer, the second A * Correction layer 5 is +A * As a correction layer, and accordingly the third C * Correction layer 6 is -C *It is constructed as a correction layer. The improvements shown in Figures 6A and 6B can be achieved by using a series of correction layers. The first +A * The correction layer is d·(n e -n o The condition ) = 264 nm is satisfied, and the second -A * The correction layer is d·(n o -n e The condition of ) = -264nm is met, and the tolerance is 20%. Third -C * The correction layer is d·(n e -n o The condition ) = -82nm is satisfied, and the tolerance is also 20%. First -A * In the alternative using a correction layer, the sign is reversed.

[0067] Figures 7A-7F illustrate the role of each layer using polarization ellipses, using the second alternative optical film shown in Figure 1C as an example. Here, the first absorption axis of the first polarization layer 1 is parallel to the surface normal of the optical film. For comparison, Figure 7G shows the polarization of light when using a layer structure without additional compensation layers in the prior art. The line of sight of a hypothetical observer is along the surface normal of the optical film. Figures 7A-7G each show multiple polarization ellipses distributed in a circular pattern around the origin of the coordinate system. The position of each polarization ellipse corresponds to the viewing angle relative to the surface of the optical film. The viewing angle at the origin of the coordinate system corresponds to the surface normal, i.e., the top view perpendicular to the surface of the optical film. Without loss of generality, the direction parallel to the shorter side of the drawing plane along the vertical edge of the drawing page is called the x-direction, and the direction perpendicular to it is called the y-direction. Here, the x-direction also corresponds to the preferred direction and is parallel to the hypothetical connecting line between the viewer's eyes, and is therefore also called the horizontal direction below. In other words, on the x-axis of the coordinate system in Figures 7A-7G, there is a polarization ellipse corresponding to the field of view angle deviating only horizontally from zero, which corresponds to a viewer moving only horizontally from the origin. On the y-axis, there is a polarization ellipse corresponding to the field of view angle deviating only vertically from zero, which corresponds to a viewer moving vertically up or down from the origin. Here, "vertical" movement, or displacement, does not mean that the observer 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 surface normal and the observer's eyes. Rather, it refers to displacement perpendicular to that plane. For example, if a seated observer is looking directly at the optical film along the surface normal, the field of view of a second observer standing immediately behind the first observer will be shifted only vertically on the y-axis. Figures 7A-7G each show two concentric circles for ease of understanding. The inner circle limits the field of view angle to a maximum of 25° in each direction, and the outer circle limits the field of view angle to a maximum of 45° in each direction. The outermost field of view is 90°, but this is actually imperceptible.

[0068] Figure 7A shows circularly polarized light irradiated onto an optical film from a backlight. This light first enters a second polarizing layer 2, which has a second absorption axis. Since the second absorption axis of this second polarizing layer 2 is oriented parallel to the film plane, the light becomes linearly polarized. In this case, the direction is horizontal, that is, generally along the imaginary line connecting the observer's two eyes, and this horizontal direction corresponds to the preferred direction.

[0069] Linearly polarized light passes through the second polarization layer and then through the second A-A compensation layer constructed as the A-A compensation layer. * Entering compensation layer 5. The polarization hardly changes, especially in the horizontal and vertical directions. However, within the viewing angle, s-polarization is obtained over a wider area when viewed from above (see Figure 7C). This refers to light where the electric field vector is perpendicular to the incident plane (the plane formed by the plane normal and the direction of incidence). Figure 7D shows the next layer, the third C. * This shows the angle-resolved polarization after passing through compensation layer 6. This compensation layer is constructed here as a +C compensation layer, but it has low birefringence and C * Because it is a compensation layer, the changes are difficult to see in the diagram. Figure 7E shows the first A constructed as a +A compensation layer. * This shows the polarization of light after passing through compensation layer 4. Most of this light is almost p-polarized, meaning its electric field vector is parallel to the plane of incidence. Therefore, the absorption of light propagating in directions other than perpendicular is increased by the subsequent first polarization layer 1, the Z-polarization layer. This is achieved through the interaction of the three compensation layers described above, and significantly improves the anti-peeping protection effect.

[0070] Finally, Figure 7F shows the polarization of light after passing through the first polarization layer 1, i.e., the Z polarizer. For comparison, Figure 7G shows the polarization of light in the conventional technique where the Z polarizer is directly connected to the second polarizer. The closer the polarization ellipse is to a point, the lower the light density. It is clear that the light density in the black region of Figure 2 is much lower than in the conventional technique, indicating an improved anti-peeping protection effect. This is achieved by minimizing the light density only in the actual portion of the half-space outside the viewing angle cone, i.e., within the range of a specified solid angle R, rather than the entire half-space excluding the narrow viewing angle cone as in the conventional technique. Specifically, within the given range of solid angle R, the loss function is minimized:

number

number

[0071] Figure 8 shows the first A, similar to the one shown in Figure 1B. * Compensation layer 4 and second A * The present invention provides a technical proposal for an optical film having a compensation layer 5, but the second polarizing layer 2 and the second A * The difference is that a liquid crystal layer 7 is further positioned between the compensation layer 5 and the liquid crystal layer 7. The liquid crystal layer 7 is switchable between at least two states. In the first switching state, the liquid crystal layer 7 transmits light that has passed through the second polarizing layer 2 without changing its polarization state, or with a 90° rotation. In the second switching state, it transmits light that has passed through the second polarizing layer 2 as circularly polarized or elliptically polarized light. Of course, the liquid crystal layer 7 employing this switching mechanism can also be applied to other optical film technologies, particularly those shown in Figures 1A and 1C.

[0072] This results in a screen like the one shown in Figures 10 and 11. Figure 10 shows a screen capable of operating in at least two operating modes, namely B1 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is projected to a more restricted viewing angle for the viewer than in free viewing mode. To switch between these two operating modes, the screen is equipped with a backlight 8. The backlight 8 extends in a planar manner and comprises an optical film with a liquid crystal layer 7 (not specifically shown here) that is switchable between at least two states, the liquid crystal layer 7 being represented by multiple light sources 9 that emit light. This is a simplified diagram, and for example, a surface emitter with a structured surface or an edge-illuminated light guide could also be used. These light guides may also include optical layers such as diffusers or prism grating films as needed. If necessary, the backlight may also project light directly, for example in the form of "direct matrix backlight dimming". A linear polarizing filter 10 is positioned in front of the backlight 8 in the viewing direction. The linear polarization filter 10 restricts the propagation direction of light emitted from the backlight 8 and passing through the linear polarization filter 10. The transmissive image reproduction 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 reproduction device 11 in the viewing direction. The polarization filter should be as close as possible to the image reproduction device, and no additional layers should be provided between them. Preferably, the linear polarization filter 10 is positioned inside the transmissive image reproduction device 11, i.e., it is part of or integrated with the transmissive image reproduction device 11. In operating mode B2, the liquid crystal layer 7, which is switchable between at least two states, is in the first switching state. In operating mode B1, the liquid crystal layer 7, which is switchable between at least two states, is in the second switching state. That is, the switchable liquid crystal layer enables switching between common mode and privacy mode. In common mode, the image content displayed on the screen can be freely observed from multiple viewing angles. In privacy mode, the displayed image content is visible with sufficient brightness only within the narrow viewing angle range of the cone surrounding the first absorption axis of the first polarizing layer 1.

[0073] Figure 11 shows another embodiment of a screen capable of operating in at least two operating modes, namely B1 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is shone to a more restricted viewing angle for the observer than in free viewing mode. The screen comprises an image playback device 12 employing a structure known in the prior art, which can be designed, for example, as an active light-emitting image playback device 12 based on OLED or microLED, or as a passive light-emitting (i.e., illuminated) image playback device 12 based on LCD, for example. An optical film having a liquid crystal layer 7 that can be switched between at least two states is positioned in front of the viewing direction of the image playback device 12. The optical film is configured, for example, according to the first alternative embodiment, and is spatially uniform, consisting of a biaxial birefringent material. * A compensation layer 3 is positioned between the first polarizing layer 1 and the second polarizing layer 2. The second polarizing layer 2 can also be designed, for example, as a rear polarizer for the liquid crystal display of an image playback device 12. Of course, all the other aforementioned embodiments of the optical film having a switchable liquid crystal layer 7 are also applicable. Similar to the screen described above, the liquid crystal layer 7, which is switchable between at least two states, is in the first switchable state in operating mode B2 and in the second switchable state in operating mode B1. This invention is particularly suitable for modifying existing screens.

[0074] Alternatively, a screen illumination device can be manufactured using an optical film that does not have a switchable liquid crystal layer 7. This device can be configured to operate in at least two operating modes, namely B1 (free viewing mode) and B2 (restricted viewing mode). In restricted viewing mode, light is irradiated over a more limited range of solid angles than in free viewing mode. Figures 9A and 9B show examples of such an illumination device in these two operating modes. By combining this illumination device with an image playback device that displays image content positioned upstream of the viewing direction, a screen can be obtained that can switch between the two operating modes B1 and B2.

[0075] The lighting device shown in Figures 9A and 9B comprises a planar backlight 13, which incorporates a static, i.e., non-switchable optical film, as illustrated in Figures 1A-1C. A plate-shaped light guide 14 is positioned in front of the backlight 13 in the viewing direction. The plate-shaped light guide 14 has an output coupling assembly on at least one large surface and / or internally. In the illustrated example, the output coupling assembly 15 is positioned within the region of the light guide 14. A linear polarizing filter 16 is positioned in front of the backlight 13 or the light guide 14 in the viewing direction. This substantially restricts the direction of propagation of light emitted from the backlight 13, passing through the optical film and then through the linear polarizing filter 16. Selectively, the linear polarizing filter 16 can also function as an equivalent second polarizing layer 2. A light-emitting member 17 is positioned laterally on at least one short side (both sides in this case) of the light guide 14, and when switched on, the light-emitting member 17 injects light into the light guide 14. The light incident on the light-emitting member 17 is reflected back and forth by total internal reflection within the light guide 14 and incident on the output coupling assembly 15. These output coupling assemblies deflect the light, which passes through the surface of the light guide 14 and is emitted towards the observer. The output coupling assembly 15 is configured to deflect the light almost completely in this direction, allowing light from the backlight 13 to pass through with almost no obstruction.

[0076] Figure 9A shows the lighting device in operating mode B2 in limited viewing mode, in which only a relatively narrow, typically conical solid angle range is illuminated, as indicated by the arrows on the surface of the light guide 14. In this case, only the backlight 13 needs to be on, and the light-emitting member 17 needs to be off. Figure 9B shows the lighting device in operating mode B1 in common mode, in which light is irradiated over a much wider solid angle range than in operating mode B2, as indicated by the arrows on the light guide 14. In this case, the light-emitting member 17 needs to be on. The light injected into the light guide 14 and coupled by the output coupling assembly 15 plays a role in broadening the range of solid angles that are illuminated. In operating mode B1, the backlight 13 can be turned on or off. Turning off the backlight 13 usually results in uniform illumination of the solid angle range in operating mode B1.

[0077] The passive image playback device, illuminated from behind by the lighting device shown in Figures 9A and 9B, generates either a restricted viewing mode B2 or a public viewing mode B1 for viewers of the image content displayed on the image playback device, depending on the ON state of the light-emitting member 17.

[0078] The optical film described above can be widely used in any situation requiring the display and / or input of confidential information, such as PIN entry, data display at ATMs or payment terminals, password entry, and viewing emails on mobile devices, by using an image playback device and, if necessary, a dedicated illumination device. The present invention can also be applied in automobiles to selectively block out distracting image content for the driver or passengers. [Explanation of symbols]

[0079] 1: First polarizing layer 2: Second polarizing layer 3: The first B * compensation layer 4: First A * compensation layer 5: Second A * compensation layer 6: Third C* compensation layer 7: Liquid crystal layer 8: Backlight 9:Light source 10: Linear Polarizing Filter 11: Image playback device 12: Image playback device 13: Backlight 14: Light guide 15: Output coupling assembly 16: Linear Polarizing Filter 17: Light-emitting component R: range of solid angle

Claims

1. A backlight (13) that extends in a planar manner and emits light, It has an optical film for controlling and limiting the observer's field of view, The optical film is A first polarizing layer (1) having a first absorption axis that forms an angle of 0° to 30° with respect to the normal to the surface 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; Between the first polarizing layer (1) and the second polarizing layer (2), In alternative (i), The first B is composed of a first biaxial birefringent material having two optical axes and three principal refractive axes, and is spatially uniform. ＊ Compensation layer (3) is placed, Each of the aforementioned principal refractive axes has a refractive index n ｘ , n ｙ , n ｚ In response to, 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 mentioned above ＊ Compensation layer (3) satisfies the following conditions: [Math 1] The formula includes the first B mentioned above. ＊ The compensation layer (3) includes a thickness d, a phase shift Δph, and a predetermined wavelength λ; In alternative (ii), A compensation layer consisting of at least two uniaxial birefringent materials is provided. The compensation layer is the first A ＊ Compensation layer (4) and second A ＊ Including compensation layer (5), First A that is spatially uniform ＊ The compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two different first principal refractive axes. The first optical axis is perpendicular or parallel to the first absorption axis of the first polarizing layer (1) and is located behind when viewed from the observer. The second A is spatially uniform. ＊ The compensation layer (5) is composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes, wherein the second optical axis is perpendicular to the first optical axis. Each of the aforementioned compensation layers is [Math 2] The formula includes 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; In 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 where the origin is located on the surface of the film and on 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 a preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limiting azimuth angles φ ｌｉｍ Smaller than the absolute value of; the polar angle θ is measured in the plane between the surface normal and the first absorption axis, with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, with respect to the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle θ ｌｉｍ A backlight (13) characterized by being larger than the above.

2. The first A mentioned above ＊ Compensation layer (4) and the second A ＊ Between the compensation layers (5), a third spatially uniform C ＊ A compensation layer (6) is placed, The third C ＊ The compensation layer (6) is composed of a third uniaxial birefringent material having a third optical axis and two third principal refractive axes. The backlight (13) according to alternative (ii) of claim 1, characterized in that 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 principal refractive axis corresponding to the minimum refractive index is parallel to the first absorption axis. The first B mentioned above ＊ The compensation layer (3) has the minimum refractive index n ｚ The principal refractive axis corresponding to is parallel to the normal of the surface, and the maximum refractive index n ｘ The corresponding principal refractive axis is constructed as a -B compensation layer such that it is parallel to the second absorption axis of the second polarizing layer (2), where n ｘ >n ｙ >n ｚ The backlight (13) according to claim 3 and alternative (i), characterized in that it is the same as the backlight (13) according to claim 3 and alternative (i).

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

6. The first A mentioned above ＊ The compensation layer (4) is constructed as a +A compensation layer, and the second A ＊ Compensation layer (5) is constructed as -A compensation layer, or Conversely, the first A ＊ Compensation layer (4) is constructed as an A compensation layer, and the second A ＊ Compensation layer (5) is constructed as a +A compensation layer, and The third C ＊ The backlight (13) according to claim 3 and alternative (ii), characterized in that, when a compensation layer (6) is provided, it is constructed as a -C or +C compensation layer.

7. The first A mentioned above ＊ Compensation layer (4) and the second A ＊ The structure of the compensation layer (5) is the same as that of the backlight (13) according to claim 1, alternative (ii).

8. Between the second polarizing layer (2) and the compensation layer closest to the second polarizing layer (2), a liquid crystal layer (7) capable of switching between at least two states is arranged. The aforementioned liquid crystal layer (7) is In the first switching state, the light transmitted through the second polarizing layer (2) is transmitted either unpolarized or rotated by 90°. In the second switching state, the backlight (13) according to claim 1 or 2 is constructed to transmit light transmitted through the second polarizing layer (2) as circularly polarized, elliptically polarized, or linearly polarized light.

9. Between the first polarizing layer (1) and the compensation layer closest to the first polarizing layer (1), a liquid crystal layer (7) capable of switching between at least two states is arranged. The aforementioned liquid crystal layer (7) is In the first switching state, the light transmitted through the first polarizing layer (1) is transmitted either unpolarized or rotated by 90°. In the second switching state, the backlight (13) according to claim 1 or 2 is constructed to transmit light transmitted through the first polarizing layer (1) as circularly polarized, elliptically polarized, or linearly polarized light.

10. Within the predetermined solid angle range R, the loss function [Math 3] This is the minimum, Here, [Math 4] The backlight (13) according to claim 1 or 2, wherein represents angle-dependent transmittance and Ω represents the range of the solid angle.

11. The limit azimuth angle φ ｌｉｍ The backlight (13) according to claim 1 or 2, wherein the angle is 30° to 40° to the left and right from the preferred direction, and / or the limiting polar angle θlim is 40° to 50°.

12. A lighting device for a screen, The lighting device is arranged to be capable of operating in at least two operating modes, namely B1 (for free viewing mode) and operating mode B2 (for restricted viewing mode). In the restricted viewing mode, light is shone within a more restricted solid angle range than in the free viewing mode. The aforementioned lighting device is A backlight (13) according to any one of claims 1 to 7, 10, or 11; A plate-shaped light guide (14) having an output coupling assembly (15) on and / or within the volume thereof, and positioned in front of the backlight (13) along the observation direction; A light-emitting member (17) is laterally positioned 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 observation direction; As a result, the light emitted from the backlight (13) and transmitted through the linear polarizing filter (16) is restricted in its direction of propagation. Herein, in operating mode B2, the backlight (13) is on and the light-emitting member (17) is off, and in operating mode B1, at least the light-emitting member (17) is on, a lighting device for a screen.

13. It is 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. In the restricted viewing mode, light is shone within a more restricted solid angle range for the observer than in the free viewing mode. The aforementioned screen is A backlight (8) according to claim 8 or 9, having a liquid crystal layer (7) capable of switching between at least two states; A linear polarizing filter (10) positioned in front of the backlight (8) along the observation direction; thus, the light emitted from the backlight (8) and transmitted through the linear polarizing filter (10) is restricted to its direction of travel; and A transmissive image regeneration device (11) positioned in front of the backlight (8) along the observation direction - the linear polarizing filter (10) is positioned inside or behind the transmissive image regeneration device (11); Herein, in the operation mode B2, the liquid crystal layer (7) that can be switched between at least two states is in a first switching state, and in the operation mode B1, the liquid crystal layer (7) that can be switched between at least two states is in a second switching state, the screen.

14. It is 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. In the restricted viewing mode, light is shone within a more restricted solid angle range for the observer than in the free viewing mode. The aforementioned screen is Image playback device (12); An optical film having a liquid crystal layer (7) capable of switching between at least two states, positioned in front of the image playback device (12) along the observation direction; Here, in operation mode B2, the liquid crystal layer (7) is in the first switching state, and in operation mode B1, the liquid crystal layer (7) is in the second switching state. The optical film is A first polarizing layer (1) having a first absorption axis that forms an angle of 0° to 30° with respect to the normal to the surface 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; Between the first polarizing layer (1) and the second polarizing layer (2), In alternative (i), The first B is composed of a first biaxial birefringent material having two optical axes and three principal refractive axes, and is spatially uniform. ＊ Compensation layer (3) is placed, Each of the aforementioned principal refractive axes has a refractive index n ｘ , n ｙ , n ｚ In response to, 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 mentioned above ＊ Compensation layer (3) satisfies the following conditions: [Math 5] The formula includes the first B mentioned above. ＊ The compensation layer (3) includes a thickness d, a phase shift Δph, and a predetermined wavelength λ; In alternative (ii), A compensation layer consisting of at least two uniaxial birefringent materials is provided. The compensation layer is the first A ＊ Compensation layer (4) and second A ＊ Including compensation layer (5), The first A is spatially uniform. ＊ The compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two distinct first principal refractive axes, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarizing layer (1) and is located behind the observer. The second A is spatially uniform. ＊ The compensation layer (5) is composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes, wherein the second optical axis is perpendicular to the first optical axis. Each of the aforementioned compensation layers is [Math 6] The formula includes 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; In 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 where the origin is located on the surface of the film and on 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 a preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limiting azimuth angles φ ｌｉｍ Smaller than the absolute value of; the polar angle θ is measured in the plane between the surface normal and the first absorption axis, with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, with respect to the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle θ ｌｉｍ Larger than, Here, a liquid crystal layer (7) that can switch between at least two states is placed between the second polarizing layer (2) and the compensation layer closest to the second polarizing layer, and the liquid crystal layer (7) is configured such that in the first switching state, it transmits light that has passed through the second polarizing layer (2) either with its original polarization or with a polarization rotated by 90°, and in the second switching state, it transmits circularly polarized, elliptically polarized, or linearly polarized light, or A screen comprising a liquid crystal layer (7) that can switch between at least two states, disposed between a first polarizing layer (1) and a compensation layer closest to the first polarizing layer, wherein the liquid crystal layer (7) is configured to transmit light transmitted through the first polarizing layer (1) in its original polarization or with polarization rotated by 90° in the first switching state, and to transmit circularly polarized, elliptically polarized, or linearly polarized light in the second switching state.

15. The first A mentioned above ＊ Compensation layer and the second A ＊ Between the compensation layer and the third C which is spatially uniform ＊ A compensation layer (6) is placed, The screen according to alternative (ii) of claim 14, comprising a third uniaxial 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).

16. An optical film for controlling and limiting the observer's field of view, The optical film is A first polarizing layer (1) having a first absorption axis that forms an angle of 0° to 30° with respect to the normal to the surface 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; Between the first polarizing layer (1) and the second polarizing layer (2), In alternative (i), The first B is composed of a first biaxial birefringent material having two optical axes and three principal refractive axes, and is spatially uniform. ＊ Compensation layer (3) is placed, Each of the aforementioned principal refractive axes has a refractive index n ｘ , n ｙ , n ｚ In response to, 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 mentioned above ＊ Compensation layer (3) satisfies the following conditions: [Number 7] The formula includes the first B mentioned above. ＊ The compensation layer (3) includes a thickness d, a phase shift Δph, and a predetermined wavelength λ; In alternative (ii), A compensation layer consisting of at least two uniaxial birefringent materials is provided. The compensation layer is the first A ＊ Compensation layer (4) and second A ＊ Including compensation layer (5), The first A is spatially uniform. ＊ The compensation layer (4) is composed of a first uniaxial birefringent material having a first optical axis and two distinct first principal refractive axes, wherein the first optical axis is perpendicular or parallel to the first absorption axis of the first polarizing layer (1) and is located behind the observer. The second A is spatially uniform. ＊ The compensation layer (5) is composed of a second uniaxial birefringent material having a second optical axis and two second principal refractive axes, wherein the second optical axis is perpendicular to the first optical axis. Each of the aforementioned compensation layers is [Number 8] The formula includes 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; In 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 where the origin is located on the surface of the film and on 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 a preferred direction on the plane on the surface of the film, and |φ| and |180°-φ| are predetermined limiting azimuth angles φ ｌｉｍ Smaller than the absolute value of; the polar angle θ is measured in the plane between the surface normal and the first absorption axis, with respect to the surface normal, or, if the first absorption axis is not parallel to the surface normal, with respect to the first absorption axis, and the absolute value of the polar angle is a predetermined limit polar angle θ ｌｉｍ An optical film characterized by being larger than [a certain size].

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