Display device

Abstract

To provide a display device capable of further suppressing light leakage in directions other than the front.SOLUTION: The display device includes: a liquid crystal display panel having a display region for outputting an image; a light source for emitting light from one side of the liquid crystal display panel; and a dimming unit interposed between the liquid crystal display panel and the light source, the dimming unit being configured to control the degree of light transmission between the liquid crystal display panel and the light source. The dimming unit includes a first liquid crystal panel and a second liquid crystal panel laminated in a direction in which the light source and the liquid crystal display panel face each other. The first liquid crystal panel is a TN-type liquid crystal panel, and the second liquid crystal panel is an ECB-type liquid crystal panel.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a display device. [Background technology]

[0002] In recent years, there has been a demand for display devices that allow the viewing angle range in which an image can be viewed to be changed. For example, in display devices mounted on vehicles such as four-wheeled automobiles, it is required to realize a viewing angle range in which an image can be viewed from the passenger seat, but cannot be viewed from the driver's seat only while driving. To realize such a viewing angle range, a technology has been proposed in which a light-control liquid crystal panel with a switchable viewing angle range is superimposed on an image display panel (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-195388 Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration described in Patent Document 1, the viewing angle range is controlled by strongly suppressing light emission to one side (the driver's seat side) across the front of the display device and not so much suppressing light emission to the other side. However, with the configuration described in Patent Document 1, in a range where the oblique angle to the front is so large that it does not contribute to the visibility of the image from the other side (the passenger seat side), light to the other side is reflected by a light-reflecting structure such as the side glass of a four-wheeled vehicle and directed toward one side, which can result in the image being visible from the one side. In order to suppress such visibility of the image from one side, it is necessary to suppress light leakage from the other side that does not contribute to the visibility of the image.

[0005] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a display device that can further suppress light leakage. [Means for solving the problem]

[0006] A display device according to one embodiment of the present disclosure includes a liquid crystal display panel having a display area for outputting an image, a light source for irradiating light from one side of the liquid crystal display panel, and a light control unit interposed between the liquid crystal display panel and the light source to control the degree of light transmission between the liquid crystal display panel and the light source, the light control unit having a first liquid crystal panel and a second liquid crystal panel stacked in a direction in which the light source and the liquid crystal display panel face each other, the first liquid crystal panel being a TN liquid crystal panel, and the second liquid crystal panel being an ECB liquid crystal panel. Here, the TN mode refers to the twisted nematic (TN) mode, and the ECB mode refers to the electrically controlled birefringence (ECB) mode, both of which refer to the driving mode of the liquid crystal panel. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of the main configuration of a display device according to an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of each of the components of the display device. [Figure 3] FIG. 3 is a diagram showing the optical effects that are exerted on the light generated by the light source 60 before it reaches the display panel side. [Figure 4] FIG. 4 is a diagram showing an example of the viewing angle characteristics of the display device 1 that are caused by the degree of light transmission when the first liquid crystal panel is in operation (ON). [Figure 5] Figure 5 is a schematic diagram showing an example of the relationship between the display device 1, a user U1 who can see the image DSP regardless of whether the liquid crystal panel is operating or not (ON / OFF), and a user U2 who cannot see the image DSP when the liquid crystal panel is operating (ON). [Figure 6] FIG. 6 is a schematic diagram showing the difference between the image DSP viewed by a user viewing the display device 1 from the front and a user viewing the display device 1 obliquely. [Figure 7]FIG. 7 is a graph showing the relationship between the polar angle of the first direction and the light transmittance of the first liquid crystal panel in operation. [Figure 8] FIG. 8 is a graph showing the relationship between the polar angle of the first direction and the light transmittance of the second liquid crystal panel in operation. [Figure 9] FIG. 9 is a graph showing the difference in brightness between the display device of the embodiment and a comparative example in which the liquid crystal panel provided in the light control section is only a TN liquid crystal panel. [Figure 10] FIG. 10 is a schematic diagram showing the difference between the E mode and the O mode. [Figure 11] FIG. 11 is a diagram showing the optical effect when the second liquid crystal panel is disposed closer to the light source than the first liquid crystal panel, and the layering order of the configuration that causes such a change. [Figure 12] FIG. 12 is a diagram showing the optical action of a light control section having a layered structure different from the structure described with reference to FIGS. 3 and 11, and the layering order of the structure that causes such a change. DETAILED DESCRIPTION OF THE INVENTION

[0008] Each embodiment of the present disclosure will be described below with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily conceive while maintaining the gist of the invention are naturally included within the scope of the present disclosure. Furthermore, to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0009] (Embodiment) FIG. 1 is a schematic diagram showing an example of the main configuration of a display device 1 according to an embodiment. The display device 1 includes a light control unit 10, a display panel 30, and a light source 60. The direction in which the light control unit 10, the display panel 30, and the light source 60 are stacked is defined as a third direction Z. One of two directions perpendicular to the third direction Z is defined as a first direction X, and the other is defined as a second direction Y. The first direction X and the second direction Y are perpendicular to each other. In the display device 1, the light source 60, the light control unit 10, and the display panel 30 are stacked in this order from one side to the other side of the third direction Z.

[0010] Fig. 2 is a schematic cross-sectional view of each of the components of the display device 1. Note that in Fig. 1 and Fig. 2, there are gaps between the components of the light source 60, the dimming unit 10, and the display panel 30. These gaps are provided for the purpose of making the drawings easier to understand, and are not essential in the actual display device 1. However, in the embodiment, gaps are provided as air gaps between the light source 60 and the dimming unit 10 and between the dimming unit 10 and the display panel 30.

[0011] The dimming unit 10 has a configuration in which a first polarizing layer 11, a first liquid crystal panel 20A, a second polarizing layer 12, a first retardation plate 13, a second liquid crystal panel 20B, and a second retardation plate 14 are stacked from one side to the other side in the third direction Z. The first polarizing layer 11 and the second polarizing layer 12, as well as a third polarizing layer 41 and a fourth polarizing layer 42 (described later), are optical components configured to maximize the transmission of light polarized in a specific direction. This specific direction is referred to as the transmission axis direction. The transmission axis direction is aligned with the polarizing plate. In other words, the transmission axis direction is perpendicular to the third direction Z. The direction perpendicular to the transmission axis direction and the third direction Z is referred to as the absorption axis direction. The absorption axis direction is the polarization direction through which light is least likely to be transmitted by the polarizing plate. The first retardation plate 13 and the second retardation plate 14 are optical components that change the phase of light entering from one side in the third direction Z and allow the light to pass to the other side in the third direction Z.

[0012] The first liquid crystal panel 20A and the second liquid crystal panel 20B are liquid crystal panels. Hereinafter, the term "liquid crystal panel" encompasses both the first liquid crystal panel 20A and the second liquid crystal panel 20B. The first liquid crystal panel 20A is a liquid crystal panel of the so-called twisted nematic (TN) type. In a TN type panel, the transmission axes (and absorption axes) of two polarizing layers (the first polarizing layer 11 and the second polarizing layer 12) facing each other across the liquid crystal panel intersect. In the TN type, when no voltage is applied, multiple liquid crystal molecules aligned in the third direction Z twist the polarization direction of light, establishing a state (chirality) in which light can pass through both transmission axes of the two polarizing layers. In the TN type, when a voltage is applied, this chirality is lost and light no longer passes through. The second liquid crystal panel 20B is a liquid crystal panel of the so-called electrically controlled birefringence (ECB) type. In the ECB mode, when no voltage is applied, the long axis direction (ne in FIG. 10) of the liquid crystal molecules is arranged to be parallel (horizontal alignment) to the first substrate 21 and the second substrate 22. When a voltage is applied to the liquid crystal in such an ECB mode liquid crystal panel, the liquid crystal molecules stand up so that the long axis direction of the liquid crystal molecules approaches the direction along the third direction Z, thereby changing the degree of light transmittance.

[0013] The liquid crystal panel has a configuration in which a first substrate 21 is provided on one side of a liquid crystal LM and a second substrate 22 is provided on the other side. The first substrate 21 and the second substrate 22 are light-transmitting substrates. The light-transmitting substrate is, for example, a glass substrate, but is not limited to this and may be a substrate made of another light-transmitting material. Hereinafter, when referring to one side, it refers to the surface on one side in the third direction Z in a plate-like configuration. Furthermore, when referring to the other side, it refers to the surface on the other side in the third direction Z in a plate-like configuration.

[0014] A first electrode FE1 is formed on the other surface of the first substrate 21. A second electrode FE2 is formed on one surface of the second substrate 22. The first electrode FE1 and the second electrode FE2 are electrodes provided to cover the display area AA. The other surface of the first electrode FE1 and the other surface of the first substrate 21 in an area where the first electrode FE1 is not formed are covered with an insulating layer 23. One surface of the second electrode FE2 and the one surface of the second substrate 22 in an area where the second electrode FE2 is not formed are covered with an insulating layer 24. The display area AA will be described later.

[0015] At least one of the first electrode FE1 and the second electrode FE2 is provided so that the potential can be changed depending on whether the liquid crystal panel is in operation or not. That is, the voltage generated between the first electrode FE1 and the second electrode FE2 differs when the liquid crystal panel is in operation (ON) and when it is not in operation (OFF).

[0016] Liquid crystal LM is interposed between insulating layer 23 and insulating layer 24, at least in display area AA. In addition, a seal 25 is interposed between insulating layer 23 and insulating layer 24 outside display area AA. Although not shown, seal 25 is a frame-shaped member that surrounds liquid crystal LM when viewed from the front on a plane (XY plane) perpendicular to third direction Z. Liquid crystal LM is enclosed within the liquid crystal panel by being surrounded by seal 25 between insulating layer 23 and insulating layer 24.

[0017] An alignment film 23a is provided on the other surface of the insulating layer 23 in an area that covers at least the display area AA. An alignment film 24a is provided on one surface of the insulating layer 24 in an area that covers at least the display area AA. The alignment films 23a and 24a orient the liquid crystal molecules contained in the liquid crystal LM in a specific direction. The alignment of the liquid crystal molecules changes when the potential difference between the first electrode FE1 and the second electrode FE2 changes.

[0018] The display panel 30 is a liquid crystal panel different from the first liquid crystal panel 20A and the second liquid crystal panel 20B. The display panel 30 has a plurality of pixels. The display panel 30 is a liquid crystal panel for displaying images that is provided so that the degree of light transmission at each position of the plurality of pixels can be individually controlled in response to input image data from the outside.

[0019] The display panel 30 shown in Fig. 2 is a so-called IPS (In Plane Switching) liquid crystal panel. The display panel 30 has a pixel substrate 31 on one side in the third direction Z with a liquid crystal LQ sandwiched therebetween, and a counter substrate 32 on the other side. Furthermore, a third polarizing layer 41 is provided on one surface of the pixel substrate 31. A fourth polarizing layer 42 is provided on the other surface of the counter substrate 32. Hereinafter, the term "panel section DP" refers to the portion of the display panel 30 excluding the third polarizing layer 41 and the fourth polarizing layer 42.

[0020] On the other surface of the pixel substrate 31, a common electrode CE, an insulating layer 33, a pixel electrode P, an insulating layer 34, etc. are laminated from one side to the other in the third direction Z. A color filter 35, etc. are laminated on one surface of the counter substrate 32. In addition, outside the display area AA, a seal 36 is interposed between the insulating layer 34 and the color filter 35. The seal 36 has the same shape as the seal 25 described above. The liquid crystal LQ is enclosed within the display panel 30 by being surrounded by the seal 36 between the insulating layer 34 and the color filter 35.

[0021] The display area AA is an area in the display panel 30 where multiple pixel electrodes P are arranged. The multiple pixel electrodes P are arranged two-dimensionally along the XY plane within the display area AA. The display panel 30 is a so-called active matrix display panel that is configured to be able to display and output any image by individually controlling the degree of light transmittance of each pixel electrode P. More specifically, in the display panel 30 of this embodiment, a reference potential is applied to the common electrode CE. Furthermore, individual potentials (pixel signals) are applied to the multiple pixel electrodes P, thereby individually controlling the degree of light transmittance of each pixel electrode P. Therefore, the display area AA can be said to be an area where images are displayed and output.

[0022] The light source 60 emits light toward the other surface on which the polarization generating layer 53 is provided. The polarization generating layer 53 is an optical element that polarizes the light emitted from the other surface of the light source 60 at a specific angle. The polarization generating layer 53 is, for example, a DBEF (Dual Brightness Enhancement Film), but is not limited to this, and may be any other element as long as it is capable of polarizing the light emitted from the other surface of the light source 60 at a specific angle. The light generated by the light source 60 passes through the polarization generating layer 53, the dimming unit 10, the third polarizing layer 41, the display panel 30, and the fourth polarizing layer 42, and is emitted to the other surface of the display device 1.

[0023] Next, a change in the deflection direction of light that occurs before the light generated by the light source 60 is emitted to the other surface side of the display device 1 will be described with reference to FIG.

[0024] FIG. 3 is a diagram showing the optical effects that are exerted on light generated by the light source 60 before it reaches the display panel 30. In the following description, polarization along the first direction X is referred to as 0° polarization. Furthermore, in the description with reference to FIG. 3, the polarization angle is shown based on the 0° polarization. Furthermore, in the description with reference to FIG. 3, among changes in the polarization direction of light, a change in counterclockwise rotation by r° along the XY plane is referred to as a "change of +r°." Furthermore, a "change of -r°" refers to a change in the opposite direction (clockwise) by r°. r is a real number greater than or equal to 0.

[0025] In this embodiment, the transmission axis of the polarization generating layer 53 is set so as to transmit light emitted from the other surface of the light source 60 as 45° polarized light. Therefore, the polarized light that passes through the polarization generating layer 53 and enters the first polarizing layer 11 is 45° polarized light. In Figure 3, this transmission axis is shown as optical property A1.

[0026] The transmission axis and absorption axis of the first polarizing layer 11 are set so as to transmit maximum light polarized at an angle of 45°. In Fig. 3, among the contents indicated as optical property A2, the solid arrow indicates the 45° transmission axis, and the dashed arrow indicates the 135° absorption axis.

[0027] The first liquid crystal panel 20A is provided between the first polarizing layer 11 and the second polarizing layer 12 so as to be able to affect the polarization direction of light. Specifically, the first liquid crystal panel 20A controls the degree of change in the polarization direction of light passing through in the third direction Z (magnitude of the twist angle) by controlling the orientation of the liquid crystal molecules contained in the liquid crystal LM.

[0028] In this embodiment, the refractive index difference (Δn) of the liquid crystal molecules and the thickness (d) of the liquid crystal LM are determined so that the maximum twist angle that the first liquid crystal panel 20A can impart to light is approximately 100°. The first liquid crystal panel 20A can, for example, polarize incident light at 323° and output it at 223°. More specifically, the first liquid crystal panel 20A is designed so that the refractive index difference (Δn) is 0.2 and the cell gap that determines the thickness (d) of the liquid crystal LM is between 3 μm and 10 μm (e.g., 8 μm). The twist angle that the first liquid crystal panel 20A imparts to light is not limited to the maximum angle but can be appropriately adjusted within a range less than the maximum angle depending on the voltage applied to the liquid crystal. Therefore, the first liquid crystal panel 20A can control the percentage of light that enters through the first polarizing layer 11 and passes through the second polarizing layer 12 by controlling the twist angle imparted to the light.

[0029] In Figure 3, among the drawn contents indicated as optical property A3, the solid straight arrow corresponds to the deflection direction of light entering from the first polarizing layer 11, the dashed arrow corresponds to the deflection direction of light to pass through the second polarizing layer 12, and the solid arc-shaped arrow connecting the solid straight arrow and the dashed arrow indicates an example of the twist angle by the first liquid crystal panel 20A.

[0030] The second polarizing layer 12 has a transmission axis and an absorption axis that are set to maximize the transmission of 135° polarized light. In the drawing indicated as optical property A4 in FIG. 3, the solid arrow indicates the 135° transmission axis, and the dashed arrow indicates the 45° absorption axis. The angle difference between the transmission axis of the first polarizing layer 11 and the transmission axis of the second polarizing layer 12 is 90°. Therefore, the first liquid crystal panel 20A can generate a twist angle that allows light from the first polarizing layer 11 to pass through the second polarizing layer 12 during operation.

[0031] The first retardation film 13 has a slow axis of 157.5° and a phase difference of 270 nm. The 135° polarized light that passes through the second polarizing layer 12 and enters the first retardation film 13 is polarized at 90° and exits toward the second liquid crystal panel 20B. In Figure 3, the dashed arrow indicating optical property A5 indicates the 157.5° slow axis.

[0032] The second liquid crystal panel 20B is provided between the first retarder 13 and the second retarder 14 so as to be able to affect the polarization direction of light. Specifically, the second liquid crystal panel 20B controls the degree of change in the polarization direction of light passing through in the third direction Z (the magnitude of the twist angle) by controlling the orientation of the liquid crystal molecules contained in the liquid crystal LM.

[0033] In this embodiment, the second liquid crystal panel 20B does not substantially affect the deflection direction of light. That is, the twist angle that the second liquid crystal panel 20B imparts to light is 0°. Specifically, the second liquid crystal panel 20B in this embodiment is designed, for example, to have a refractive index difference (Δn) of 0.2 and a cell gap that determines the thickness (d) of the liquid crystal LM of between 2 μm and 5 μm (e.g., 3 μm). More specifically, the second liquid crystal panel 20B shown in FIG. 3 is arranged so that the transmission axis is at 0° and the absorption axis is at 90°.

[0034] 3, among the contents indicated as optical property A6, the solid straight arrow corresponds to the rubbing direction on one of the first substrate 21 side and the second substrate 22 side of the second liquid crystal panel 20B, and the dashed arrow corresponds to the rubbing direction on the other of the first substrate 21 side and the second substrate 22 side of the second liquid crystal panel 20B. These rubbing directions optically act as slow axes.

[0035] The second retardation plate 14 is a negative-C retardation plate with a retardation set within the range of −50 nm to −300 nm. Light polarized at 90° entering the second retardation plate 14 becomes polarized at 0° and exits toward the third polarizing layer 41. This suggests a change in the polarization direction of light caused by the negative-C retardation plate, indicated as optical property A7 in FIG. 3.

[0036] The third polarizing layer 41 has a transmission axis determined to transmit 0° polarized light to the maximum extent possible. Therefore, light that has passed through the second retardation plate 14 can also pass through the third polarizing layer 41. Furthermore, the polarized light that passes through the third polarizing layer 41 and enters the panel unit DP is 0° polarized light. In FIG. 3, this transmission axis is indicated as optical property A8.

[0037] The specific configurations of the panel unit DP and the fourth polarizing layer 42, which are not shown in FIG. 3, are arbitrary. As an example, the panel unit DP is configured to impart a +90° change to polarized light transmitted from one side to the other side in the third direction Z. That is, a +90° change occurs in the polarized light upon transmission through the panel unit DP. Therefore, the polarized light transmitted through the panel unit DP and incident on the fourth polarizing layer 42 is 90° polarized. FIG. 3 shows the angle V10b of the polarized light incident on the panel unit DP and the angle V10a of the polarized light transmitted through the panel unit DP. In addition, in this example, the transmission axis direction V11 of the fourth polarizing layer 42 is determined so as to transmit 90° polarized light to the maximum extent. Therefore, light transmitted through the panel unit DP can be transmitted through the fourth polarizing layer 42.

[0038] Next, the optical effect produced by the liquid crystal panel will be described. When the liquid crystal panel is inactive (OFF), there is almost no difference in the degree of light transmission between one side in the first direction X and the other side in the first direction X. That is, when the first liquid crystal panel 20A and the liquid crystal panel are both inactive (OFF), when an image DSP (see FIG. 6) of the display device 1 is viewed from each of two viewpoints that are linearly symmetric in the first direction X with respect to a viewpoint viewing the display device 1 from the front, the brightness of the image perceived from the two viewpoints is almost the same. Hereinafter, the term "image DSP" refers to the image displayed and output by the display panel 30 of the display device 1. Furthermore, at this time, the image can be viewed from the viewpoint viewing the display device 1 from the front with greater brightness than from the other viewpoints. That is, when the liquid crystal panel is inactive (OFF), the degree to which light along the third direction Z passes through the liquid crystal panel is greater than the degree to which light intersecting the third direction Z passes through the liquid crystal panel.

[0039] On the other hand, when the liquid crystal panel is in operation (ON), the degree of light transmission differs between one side in the first direction X and the other side in the first direction X. The viewing angle characteristics of the display device 1 caused by the degree of light transmission when the liquid crystal panel is in operation (ON) will be described with reference to FIG.

[0040] Fig. 4 is a diagram showing an example of the viewing angle characteristics of the display device 1 that are caused by the degree of light transmittance when the first liquid crystal panel 20A is operating (ON). The centers of the concentric circles in Fig. 4 correspond to the normal line of the display device 1 along the third direction Z, and the concentric circles centered on this normal line indicate tilt angles with respect to the normal line of 20°, 40°, 60°, and 80°, respectively. The characteristic diagram shown here was obtained by connecting regions of equal transmittance for each direction.

[0041] As shown in Fig. 4, when the user's line of sight with respect to the display device 1 is tilted toward one side (0°) of the first direction X, a relatively high light transmittance is obtained. Furthermore, when the user's line of sight with respect to the display device 1 is along the normal direction, that is, when the user looks straight at the display device 1, a relatively high light transmittance is also obtained. In contrast, when the user's line of sight with respect to the display device 1 is tilted toward the other side (180°) of the first direction X, the light transmittance becomes significantly lower than that of the one side. In particular, when the angle of inclination of the line of sight toward the other side (180°) of the first direction X exceeds 30°, the transmittance becomes 3% or less in the example shown in Fig. 4, and the image becomes so dark that it is virtually unrecognizable to humans.

[0042] The viewing angle characteristics as described with reference to Fig. 4 can be used for display output control intended to make an image visible to a user viewing the display device 1 from the front or from one side in the first direction X, and to make an image invisible to a user viewing the display device 1 from the other side in the first direction X. An example of application of such display output control will be described with reference to Fig. 5.

[0043] Figure 5 is a schematic diagram showing an example of the relationship between the display device 1, a user U1 who can see the image DSP regardless of whether the liquid crystal panel is operating or not (ON / OFF), and a user U2 who cannot see the image DSP when the liquid crystal panel is operating (ON).

[0044] As shown in FIG. 5, the display device 1 and the user U1 face each other in the third direction Z. Although not shown in FIG. 5, the other side of the display device 1, i.e., the side of the fourth polarizing layer 42, is the user U1 side in FIG. 5. Therefore, image light LS1 directed toward the user U1 as a result of display output by the display device 1 is aligned along the third direction Z. In this positional relationship between the display device 1 and the user U1, the user U1 can be said to be at a viewpoint from which the display device 1 is viewed from the front. On the other hand, the user U2 is positioned to view the other side of the display device 1 obliquely from a direction tilted toward the other side of the first direction X with respect to the third direction Z. In other words, the image light LS2 directed toward the user U2 as a result of display output by the display device 1 is tilted toward the other side of the first direction X (180° in FIG. 4). In this positional relationship between the display device 1 and the user U2, the user U2 can be said to be at a viewpoint from which the display device 1 is viewed obliquely.

[0045] 5 is established when the display device 1 is installed in a four-wheeled vehicle in which the user U2 is seated in the driver's seat and the user U1 is seated in the passenger seat, but the case is not limited to this. For example, the positional relationship may also be established when the display device 1 is installed as a personal monitor for each passenger in an aircraft such as a passenger plane, and other cases may also be included.

[0046] 6 is a schematic diagram showing the difference in image DSP viewed by a user viewing the display device 1 from the front and a user viewing the display device 1 obliquely. A user viewing the display device 1 from the front is, for example, user U1 in FIG. 5. A user viewing the display device 1 obliquely is, for example, user U2 in FIG. 5. In the description with reference to FIG. 6, a state of the display device 1 in which an image is displayed and output by the display panel 30 and the liquid crystal panel is inactive (OFF) is referred to as a first state. A state of the display device 1 in which an image is displayed and output by the display panel 30 and the liquid crystal panel is active (ON) is referred to as a second state.

[0047] As described above, when the liquid crystal panel is not operating (OFF), the degree to which light traveling along the third direction Z passes through the liquid crystal panel is equal to or greater than the degree to which light intersecting the third direction Z passes through the liquid crystal panel. Furthermore, as described with reference to FIG. 4, even when the liquid crystal panel is operating (ON), a relatively high light transmittance is obtained when a user views the display device 1 from the front. Therefore, a user viewing the display device 1 from the front can view the image DSP shown in FIG. 6 regardless of whether the operating state of the display device 1 is the first state or the second state. Note that the form of the image DSP shown in FIG. 6 is merely an example and is not intended to be limiting. The display panel 30 can display and output any image.

[0048] On the other hand, as described with reference to FIG. 4, when the liquid crystal panel is in operation (ON), if the user's line of sight with respect to the display device 1 is tilted toward the other side (180°) in the first direction X, the light transmittance is significantly lower than that on one side. Therefore, when the operating state of the display device 1 is the second state, a user who views the display device 1 obliquely from the other side in the first direction X cannot substantially view the image DSP. Note that when the operating state of the display device 1 is the second state, the significant decrease in light transmittance as described with reference to FIG. 4 does not occur even on the other side (180°) in the first direction X. Therefore, when the operating state of the display device 1 is the first state, a user who views the display device 1 obliquely from the other side in the first direction X can view approximately the same image DSP as a user who views the display device 1 head-on.

[0049] As shown in FIG. 6, the image DSP is visually recognized as a rectangular image. That is, in the embodiment, when the display device 1 is viewed from the front, the display area AA has a rectangular shape corresponding to the image DSP shown in FIG. 6. Two of the four sides of the rectangle are aligned along the first direction X, and the other two sides are aligned along the second direction Y. The light control unit 10 of the embodiment uses the third direction Z as a reference to differentiate the degree of light transmission of rays of light inclined toward one side of the longitudinal direction of the rectangle (first direction X) from the degree of light transmission of rays of light inclined toward the other side of the longitudinal direction. In this way, the light control unit 10 generates a visual difference between the first state and the second state described with reference to FIG. 6.

[0050] The above describes the basic concept of controlling visibility of the image DSP for each of users U1 and U2 in the first and second states. However, even in the second state, a light route may be established that allows user U2 to view the image DSP. For example, consider a configuration in which light LS3 from display device 1 is reflected to generate light LS4, such as reflector 102 shown in FIG. 5. In this case, light LS4 may reach user U2, unintentionally creating a state in which the image DSP output by display device 1 in the second state is also visible to user U2. In this case, for example, if FIG. 5 shows an example of the interior of a four-wheeled vehicle, the passenger-side side window may function as reflector 102, thereby creating this situation.

[0051] Therefore, in the embodiment, a mechanism is adopted to suppress the generation of outgoing light from the display device 1 in an oblique direction, such as light LS4, which is light on one side (0°) in the first direction X and is not necessary for the user U1 to view the image DSP. Specifically, the second liquid crystal panel 20B, which is an ECB-type liquid crystal panel, is included in the configuration of the dimming unit 10, thereby suppressing the generation of such outgoing light.

[0052] Fig. 7 is a graph showing the relationship between the first direction polar angle and the light transmittance of the operating first liquid crystal panel 20A. In Figs. 7, 8, and 9, the horizontal axis indicates a viewing angle with a positive (+) value for a viewing angle from an angle tilted to one side of the first direction X, with the line of sight from the front of the display device 1 as the reference (viewing angle of 0°), and a viewing angle with a negative (-) value for a viewing angle from an angle tilted to the other side of the first direction X. Furthermore, the vertical axis in Figs. 7 and 8 indicates the light transmittance in percentage (%). The light transmittance here is synonymous with the brightness of emitted light relative to the brightness of incident light.

[0053] 7 indicates the cell gap (unit: μm) of the first liquid crystal panel 20A. That is, each of the graphs indicates the light transmittance generated by the first liquid crystal panel 20A of the cell gap corresponding to the numerical value attached to the graph. Note that the voltage applied to the liquid crystal LM in each of the first liquid crystal panels 20A having different cell gaps is the same (e.g., 2.5 V).

[0054] 7, when the first liquid crystal panel 20A is operated, the light transmittance from the negative (-) side, i.e., the other side of the first direction X, is significantly lower than the light transmittance from the positive (+) side, i.e., the one side of the first direction X. This indicates that when the display output image of the display device 1 is viewed from the other side of the first direction X, the image appears significantly darker than when the display output image of the display device 1 is viewed from the one side of the first direction X, making it difficult to recognize the content of the image. In particular, the light transmittance is essentially zero at a first direction polar angle of -30°, making it essentially impossible to view the display output image of the display device 1 from that polar angle.

[0055] On the other hand, as shown by the plus (+) side of the graph in Figure 7, the light transmittance to one side of the first direction X tends to decrease as the deviation from 0° increases, but even at a horizontal polar angle of 80°, the light transmittance is only about 10%. Such light transmittance on the plus (+) side can cause light, such as the light LS4 described above, to be emitted from the display device 1 in an oblique direction that is not necessary for the user U1 to view the image DSP, but is light on the one side (0°) of the first direction X. In other words, if the dimming unit 10 is configured only with a TN-type liquid crystal panel such as the first liquid crystal panel 20A, it will not be possible to sufficiently suppress such oblique light emission.

[0056] 8 is a graph showing the relationship between the first-direction polar angle and the light transmittance of the operating second liquid crystal panel 20B. The numerical values ​​attached to each of the graphs in FIG. 8 indicate the cell gap (unit: μm) of the second liquid crystal panel 20B. That is, each of the graphs indicates the light transmittance generated by the second liquid crystal panel 20B having the cell gap corresponding to the numerical value attached to the graph. Note that the voltage applied to the liquid crystal LM in each of the second liquid crystal panels 20B having different cell gaps is the same (e.g., 2.9 V).

[0057] As shown in Fig. 8, the operation of the second liquid crystal panel 20B can significantly reduce the transmittance of light on the plus (+) side compared to that of the first liquid crystal panel 20A. In particular, by setting the cell gap of the second liquid crystal panel 20B to 3 μm or less, the transmittance of light on the plus (+) side can be more reliably significantly reduced compared to that of the first liquid crystal panel 20A. Note that, as shown in Figs. 7 and 8, the larger the cell gap, the steeper the characteristics of both the first liquid crystal panel 20A and the second liquid crystal panel 20B, and the greater the degree of change (jump) in the transmittance in response to a change in the first direction polar angle tends to be.

[0058] 9 is a graph showing the difference in brightness between the display device 1 of the embodiment and a comparative example in which the liquid crystal panel provided in the dimming unit 10 is only a TN liquid crystal panel. In FIG. 9, brightness is shown as a normalized luminance (%) based on the normal direction along the vertical axis. In this expression using normalized luminance (%), the normal luminance of the panel surface of the TN liquid crystal panel, i.e., the luminance at a viewing angle of 0°, is considered to be 100% luminance, and the luminance at a viewing angle corresponding to the angle from the normal direction of 0° is expressed as a percentage. For example, if the normal luminance is 1000 nits and 100 nits at a viewing angle of +30°, the viewing angle of +30° is expressed as 10%. In the comparative example in which the liquid crystal panel provided in the dimming unit 10 is only a TN type liquid crystal panel, as shown in graph GLb, on the plus (+) side, i.e., on one side of the first direction X, the tendency of the decrease in brightness that occurs according to the degree of deviation from 0° is gradual, and it is not possible to sufficiently suppress the light emitted from the display device 1 in an oblique direction, such as the light LS4 described above, which is light on one side (0°) of the first direction X and is not necessary for the user U1 to view the image DSP.

[0059] In contrast, in an embodiment in which the dimming unit 10 includes both the first liquid crystal panel 20A and the second liquid crystal panel 20B, as shown by graph GLa, the degree of brightness reduction occurring in response to the degree of deviation from 0° can be significantly increased compared to the comparative example. In particular, at a first direction polar angle of 55° or greater, brightness can be reduced to a level so dark that the display output image of the display device 1 is virtually unrecognizable. Therefore, according to this embodiment, it is possible to suppress light emitted from the display device 1 in an oblique direction, such as the light LS4 described above, which is light on one side (0°) of the first direction X and is not necessary for the user U1 to view the image DSP. Note that, if it is desired to suppress reflected light such as the light LS4 to approximately 1%, it is necessary to consider the relationship between the reflectance of a configuration such as the reflector 102 and the brightness shown in FIG. 9. For example, if the reflectance of the reflector 102 is 8%, if the brightness is 12% or less, reflected light such as the light LS4 can be suppressed to 1% or less. In the example shown in FIG. 9, the brightness becomes 12% or less once the angle exceeds 43°, which is sufficient to suppress reflected light such as the light LS4.

[0060] In addition, the liquid crystal panels for light control such as the first liquid crystal panel 20A and the second liquid crystal panel 20B employ either the E mode or the O mode.

[0061] Figure 10 is a schematic diagram showing the difference between E mode and O mode. In Figure 10, the liquid crystal molecule contained in the liquid crystal LM is shown as liquid crystal molecule LM1. The liquid crystal molecule LM1 exhibits uniaxial optical anisotropy. Specifically, an axis ne with a higher refractive index (n) than the other directions occurs in one direction. The axis perpendicular to axis ne is axis no. The "e" in axis ne stands for extraordinary. The "o" in axis no stands for ordinary. The "n" in axes ne and no comes from the unit of refractive index (n).

[0062] In E mode, the orientation of the liquid crystal molecules LM1 is determined so that the vibration direction LV3 of the linearly polarized light after passing through the polarizer that allows light LV1 entering the liquid crystal panel to pass is parallel to the axis ne of the liquid crystal molecules LM1. Therefore, in E mode, the liquid crystal molecules LM1 are aligned so that the axis ne is perpendicular to the absorption axis LV2 of the polarizer.

[0063] In O mode, the orientation of the liquid crystal molecules LM1 is determined so that the vibration direction LV3 of the linearly polarized light after passing through the polarizer that allows light LV1 entering the liquid crystal panel to pass is perpendicular to the direction of the axis ne of the liquid crystal molecules LM1. Therefore, in O mode, the liquid crystal molecules LM1 are aligned so that the axis ne is parallel to the absorption axis LV2 of the polarizer.

[0064] The first liquid crystal panel 20A of the embodiment is, for example, an E-mode liquid crystal panel, and the second liquid crystal panel 20B of the embodiment is, for example, an O-mode liquid crystal panel.

[0065] (Variation) Modifications of the embodiment will be described below. For example, the first liquid crystal panel 20A may be an O-mode liquid crystal panel. Therefore, both the first liquid crystal panel 20A and the second liquid crystal panel 20B may be O-mode.

[0066] Furthermore, the second liquid crystal panel 20B may be an E-mode liquid crystal panel. Therefore, both the first liquid crystal panel 20A and the second liquid crystal panel 20B may be E-mode.

[0067] In addition, in the embodiment, the first liquid crystal panel 20A is disposed closer to the light source 60 than the second liquid crystal panel 20B, but the second liquid crystal panel 20B may be disposed closer to the light source 60 than the first liquid crystal panel 20A.

[0068] 11 is a diagram showing the optical effect when the second liquid crystal panel 20B is disposed closer to the light source 60 than the first liquid crystal panel 20A, and the stacking order of the configuration that causes such a change. Note that the configuration when the second liquid crystal panel 20B is disposed closer to the light source 60 than the first liquid crystal panel 20A may be either the first configuration or the second configuration shown in FIG. 11. In the description with reference to FIG. 11, the same components as those described with reference to FIG. 3 are denoted by the same reference numerals, and different components are denoted by different reference numerals.

[0069] In the first configuration, the polarization generating layer 53 in the embodiment described with reference to FIG. 3 is replaced with a polarization generating layer 53A. The polarization generating layer 53A has the same configuration as the polarization generating layer 53, except that the transmission axis is set so that light emitted from the other surface of the light source 60 is polarized at 90° and transmitted. In FIG. 11, this transmission axis is shown as optical property A11. In addition, in the first configuration, the configuration between the polarization generating layer 53A and the third polarizing layer 41 in FIG. 3, i.e., the configuration corresponding to the light control unit 10 in the embodiment, is replaced with a configuration in which the polarizing layer 41A, the second liquid crystal panel 20B, the second retarder 14, the retarder 13A, the first polarizing layer 11, the first liquid crystal panel 20A, the second polarizing layer 12, and the first retarder 13 are stacked in this order from one side to the other side in the third direction Z. Similar to the relationship between the polarized light generating layer 53 and the first polarizing layer 11 shown in FIGS. 2 and 3, an air gap is provided between the polarized light generating layer 53A and the polarizing layer 41A. The polarizing layer 41A has the same configuration as the third polarizing layer 41, except that its transmission axis is set to maximize the transmission of 90° polarized light. In FIG. 11, this transmission axis is indicated as optical property A81. The retardation plate 13A has a slow axis of 67.5° and a phase difference of 270 nm. In FIG. 11, the dashed arrow indicated as optical property A51 indicates the 67.5° slow axis. As described above, except for the differences noted above, the first configuration is the same as the configuration described with reference to FIG. 3.

[0070] In the second configuration, the polarization generating layer 53 in the embodiment described with reference to FIG. 3 is replaced with a polarization generating layer 53B. The polarization generating layer 53B has the same configuration as the polarization generating layer 53, except that its transmission axis is set so as to transmit light emitted from the other surface of the light source 60 as 0° polarized light. In FIG. 11, this transmission axis is shown as optical property A12. In addition, in the second configuration, the configuration between the polarization generating layer 53A and the third polarizing layer 41 in FIG. 3, i.e., the configuration corresponding to the light control unit 10 in the embodiment, is replaced with a configuration in which the third polarizing layer 41, the second liquid crystal panel 20B, the second retarder 14, the retarder 13B, the first polarizing layer 11, the first liquid crystal panel 20A, the second polarizing layer 12, and the first retarder 13 are stacked in this order from one side to the other side in the third direction Z. 2 and 3, an air gap is provided between the polarized light generating layer 53B and the third polarizing layer 41 facing the polarized light generating layer 53B in the third direction Z. The retardation plate 13B has a slow axis of 22.5° and a phase difference of 270 nm. In FIG. 11, the dashed arrow indicating optical property A51 indicates the 22.5° slow axis. Except for the points noted above, the second configuration is the same as the configuration described with reference to FIG. 3.

[0071] In the first and second configurations, the provision of the second polarizing layer 12 located between the first liquid crystal panel 20A and the first retardation film 13 more reliably suppresses obliquely emitted light. However, in the first and second configurations, the second polarizing layer 12 located between the first liquid crystal panel 20A and the first retardation film 13 is not necessary. The absence of the second polarizing layer 12 increases the overall light transmittance, enabling a brighter display output.

[0072] Fig. 12 is a diagram showing the optical action of a light control unit having a layered structure different from the configuration described with reference to Fig. 3 and Fig. 11, and the layering order of the configuration that causes such a change. In the description with reference to Fig. 12, the same components as those described with reference to Fig. 3 and Fig. 11 are denoted by the same reference numerals, and different components are denoted by different reference numerals.

[0073] The third configuration in FIG. 12 shows a case where a second liquid crystal panel 20B of E mode is employed. In the third configuration, the configuration between the polarized light generating layer 53 and the third polarizing layer 41 in FIG. 3, i.e., the configuration corresponding to the dimming unit 10 in the embodiment, is replaced with a configuration in which the first polarizing layer 11, the first liquid crystal panel 20A, the second polarizing layer 12, the first retardation film 13, the second liquid crystal panel 20B, and the second retardation film 14 are stacked in this order from one side to the other side in the third direction Z. Of these, it is noteworthy that the second liquid crystal panel 20B is in E mode. Except for the points noted above, the third configuration is the same as the configuration described with reference to FIG. 3.

[0074] The fourth configuration in FIG. 12 shows a case where the second liquid crystal panel 20B is disposed closer to the display panel 30 than the second retarder 14. In the fourth configuration, the configuration between the polarized light generation layer 53 and the third polarizing layer 41 in FIG. 3, i.e., the configuration corresponding to the light control unit 10 in the embodiment, is replaced with a configuration in which the first polarizing layer 11, the first liquid crystal panel 20A, the second polarizing layer 12, the first retarder 13, the second retarder 14, and the second liquid crystal panel 20B are stacked in this order from one side to the other side in the third direction Z. As described above, except for the points noted otherwise, the fourth configuration is the same as the configuration described with reference to FIG. 3.

[0075] The fifth configuration in FIG. 12 shows a case where a first liquid crystal panel 20A of O mode is employed. In the fifth configuration, the configuration between the polarized light generating layer 53 and the third polarizing layer 41 in FIG. 3, i.e., the configuration corresponding to the dimming unit 10 in the embodiment, is replaced with a configuration in which the first polarizing layer 11, the first liquid crystal panel 20A, the second polarizing layer 12, the retarder 13B, the second liquid crystal panel 20B, and the second retarder 14 are stacked in this order from one side to the other side in the third direction Z. Of these, it is noteworthy that the first liquid crystal panel 20A is in O mode. Except for the points noted above, the fifth configuration is the same as the configuration described with reference to FIG. 3.

[0076] In the embodiment, the second retardation film 14 is arranged closer to the display panel 30 than the second liquid crystal panel 20B, but as in the fourth embodiment, the second liquid crystal panel 20B may be arranged closer to the display panel 30 than the second retardation film 14.

[0077] As described above, the display device (display device 1) includes a liquid crystal display panel (display panel 30) having a display area for outputting an image, a light source (light source 60) that emits light from one side of the liquid crystal display panel, and a dimming unit (dimming unit 10) interposed between the liquid crystal display panel and the light source to control the degree of light transmission between the liquid crystal display panel and the light source. The dimming unit includes a first liquid crystal panel (first liquid crystal panel 20A) and a second liquid crystal panel (second liquid crystal panel 20B) stacked in the direction in which the light source and the liquid crystal display panel face each other. The first liquid crystal panel is a TN-type liquid crystal panel, and the second liquid crystal panel is an ECB-type liquid crystal panel. This significantly increases the degree of brightness reduction that occurs depending on the degree of deviation from the front of the display device 1 (0° in FIG. 9 ). In particular, at a first direction polar angle of 55° or more, brightness can be reduced to such a level that the display output image of the display device 1 is virtually invisible. Therefore, according to the embodiment, it is possible to suppress light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for the user U1 to view the image DSP.

[0078] Furthermore, by arranging the dimming unit (dimming unit 10) such that the first polarizing layer (first polarizing layer 11), first liquid crystal panel (first liquid crystal panel 20A), second polarizing layer (second polarizing layer 12), first retardation plate (first retardation plate 13), second liquid crystal panel (second liquid crystal panel 20B), and second retardation plate (second retardation plate 14) are arranged from the light source (light source 60) side toward the liquid crystal display panel (display panel 30) side, as described above, light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for user U1 to view the image DSP can be suppressed.

[0079] In addition, by arranging the dimming unit (dimming unit 10) in the order of the first retardation plate (first retardation plate 13), the second liquid crystal panel (second liquid crystal panel 20B), the second retardation plate (second retardation plate 14), the first polarizing layer (first polarizing layer 11A), the first liquid crystal panel (first liquid crystal panel 20C), and the second polarizing layer (second polarizing layer 12A) from the light source (light source 60) side toward the liquid crystal display panel (display panel 30) side, light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for user U1 to view the image DSP can be similarly suppressed.

[0080] In addition, by arranging the dimming unit (dimming unit 10) such that the first polarizing layer (first polarizing layer 11), first liquid crystal panel (first liquid crystal panel 20A), second polarizing layer (second polarizing layer 12), first retardation plate (first retardation plate 13), second retardation plate (second retardation plate 14), and second liquid crystal panel (second liquid crystal panel 20D) from the light source (light source 60) side toward the liquid crystal display panel (display panel 30) side, light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for user U1 to view the image DSP can be similarly suppressed.

[0081] Furthermore, since the first liquid crystal panel (first liquid crystal panel 20A) is in the E mode, as described above, it is possible to suppress light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for the user U1 to view the image DSP.

[0082] Furthermore, even if the first liquid crystal panel (first liquid crystal panel 20A) is in the O mode, it is possible to similarly suppress light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for the user U1 to view the image DSP.

[0083] Furthermore, even if the second liquid crystal panel (second liquid crystal panel 20B) is in the E mode, it is possible to similarly suppress light leakage such as light emitted from the display device 1 in an oblique direction that is not necessary for the user U1 to view the image DSP.

[0084] In addition, other effects and advantages brought about by the aspects described in this embodiment that are clear from the description in this specification or that can be appropriately thought of by a person skilled in the art are naturally understood to be brought about by the present disclosure. [Explanation of symbols]

[0085] 1 Display device 10 Dimming section 11 First polarizing layer 12 Second polarizing layer 13 1st retardation plate 14 Second retardation plate 20A 1st LCD panel 20B Second LCD panel 30 Display Panel 53 Polarization generation layer 60 light source

Claims

1. a liquid crystal display panel having a display area for outputting an image; a light source that irradiates light from one side of the liquid crystal display panel; a light control unit interposed between the liquid crystal display panel and the light source to control the degree of light transmission between the liquid crystal display panel and the light source, the light control unit includes a first liquid crystal panel and a second liquid crystal panel stacked in a direction in which the light source and the liquid crystal display panel face each other, the first liquid crystal panel is a TN liquid crystal panel, the second liquid crystal panel is an ECB type liquid crystal panel; Display device.

2. the light control unit includes a first polarizing layer, the first liquid crystal panel, a second polarizing layer, a first retardation plate, the second liquid crystal panel, and a second retardation plate, which are arranged from the light source side toward the liquid crystal display panel side; The display device according to claim 1 .

3. the light control unit includes a first retardation plate, the second liquid crystal panel, a second retardation plate, a first polarizing layer, the first liquid crystal panel, and a second polarizing layer, which are arranged from the light source side toward the liquid crystal display panel side; The display device according to claim 1 .

4. the light control unit includes a first polarizing layer, the first liquid crystal panel, a second polarizing layer, a first retardation plate, a second retardation plate, and the second liquid crystal panel, which are arranged from the light source side toward the liquid crystal display panel side; The display device according to claim 1 .

5. the first liquid crystal panel is in E mode; The display device according to claim 1 .

6. the first liquid crystal panel is in O mode; The display device according to claim 1 .

7. the second liquid crystal panel is in O mode; The display device according to claim 1 .

8. the second liquid crystal panel is in E mode; The display device according to claim 1 .

Images