JP2019015928A - Liquid crystal display device - Google Patents

Abstract

To provide a liquid crystal display device in which dot matrix display and segment display can be suitably combined.SOLUTION: A liquid crystal display device includes: an active drive type liquid crystal display element capable of performing dot matrix display; a passive drive type liquid crystal display element capable of performing segment display and stacked on the back side of the active drive type liquid crystal display element; a top-side polarizer disposed on the top side of the active drive type liquid crystal display element; a back-side polarizer disposed on the back side of the passive drive type liquid crystal display element; a negative C-plate disposed between the active drive type liquid crystal display element and the top-side polarizer or between the passive drive type liquid crystal display element and the back-side polarizer; and a viewing angle compensation plate disposed adjacent to the negative C-plate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a liquid crystal display device in which a plurality of liquid crystal elements are stacked.

  For example, as an in-vehicle liquid crystal display device (LCD), an active matrix liquid crystal display device having a switching thin film transistor (TFT) in each pixel of a dot matrix is being mounted. In the active element, when a signal voltage is supplied and the switch of the element is turned off, display can be performed over almost the entire period by the accumulated voltage. In the dot matrix display, various shapes can be displayed by active driving for arbitrarily selecting dots.

  In the case of a dot matrix with dots arranged in the horizontal and vertical directions, horizontal and vertical lines can be displayed almost favorably, but diagonal lines and curves are a mixture of horizontal and vertical lines. Displayed, and the edges are easily jagged.

  The segment display type liquid crystal display element using the segment electrode is a fixed pattern, but can display a smooth outline (edge). A segment display type liquid crystal display element has a limited number of display elements, and selects one electrode of each of two intersecting electrodes arranged with a liquid crystal layer interposed therebetween to drive one pixel passively (direct multiplex, simple Driven by matrix) drive. In passive drive, the drive time of each pixel within one cycle is shortened.

  There has also been proposed a liquid crystal display device having a laminated structure in which segment display type passive drive type liquid crystal display elements are laminated on the surface side of an active matrix type dot matrix liquid crystal display element and having a backlight on the back side (for example, Patent Document 1). The dot matrix liquid crystal display element is composed of a transmissive TFT drive type liquid crystal display element so that it can be illuminated by a backlight. The segment type liquid crystal display element is configured in a transmissive normally white mode so that the segment type liquid crystal display element does not shield the dot matrix display portion. For example, it is disclosed that, for example, a navigation screen that changes sequentially is displayed using a full dot matrix, and a traveling speed, a turn signal, a warning display, and the like are displayed as segments on the navigation screen.

  In recent years, normally black mode liquid crystal display elements having excellent display quality have been widely adopted. For example, there is known a liquid crystal display element that can reduce a black level light transmittance and realize a high contrast by combining a vertically aligned liquid crystal layer and an orthogonally arranged polarizer. In this liquid crystal element, the non-display portion is light-shielding. If a normally black mode display element is superimposed on the dot matrix display device, the display state of the dot matrix arranged below the non-display portion is hidden. For this reason, the display content is limited.

JP 2003-043449 A (Patent No. 4801291)

  A liquid crystal display device capable of suitably combining dot matrix display and segment display is provided.

  A liquid crystal display device according to an embodiment includes an active drive type liquid crystal display element capable of performing dot matrix display, a passive drive type liquid crystal display element which is stacked on the back side of the active drive type liquid crystal display element and can perform segment display, A surface-side polarizer disposed on the front surface side of the active drive type liquid crystal display element, a back surface side polarizer disposed on the back side of the passive drive type liquid crystal display element, the active drive type liquid crystal display element, and the surface A negative C plate arranged between the side polarizers or between the passive drive type liquid crystal display element and the back side polarizer, and a viewing angle compensator arranged adjacent to the negative C plate; A backlight disposed on the back side of the back side polarizer, and the active drive type liquid crystal display element and the passive drive type liquid crystal table. One of the elements is formed by an in-plane switching type liquid crystal element, and the other is formed by a vertical alignment type liquid crystal element. The active drive type liquid crystal display element, the passive drive type liquid crystal display element, the surface side polarizer, The characteristics of the back side polarizer are set so as to be in a normally black state when no voltage is applied.

  A normally black passive drive type liquid crystal display element can be used on the back side of the active drive type liquid crystal display element, and the display quality can be improved. A sharp edge can be realized by using a segment display passive drive type liquid crystal display element. Also, good viewing angle characteristics are realized.

1A is a plan view showing a passive drive type liquid crystal display element LCD1 having a segment display unit, which is disposed on the lower side of the multilayer structure according to the first embodiment, and FIG. 1B is disposed on the upper side of the multilayer structure according to the first embodiment. FIG. 1C is a plan view showing an active drive type liquid crystal display element LCD2 having a dot matrix display portion, and FIG. 1C shows an array of pixels PX of the dot matrix display portion in which rectangular pixels are regularly arranged in the vertical and horizontal directions. It is a top view. FIG. 1D is a plan view showing monochromatic electrode regions PEr, PEg, and PEb having three color (R, G, B) color filters CFr, CFg, and CFb in each rectangular pixel PX of the dot matrix display unit according to the first embodiment. 1E is an equivalent circuit diagram showing the configuration of each monochromatic electrode region PE, and FIG. 1F is a cross-sectional view showing a cross-sectional structure of a liquid crystal display device including a laminated structure of liquid crystal display elements. 6 is a cross-sectional view showing a cross-sectional structure of a liquid crystal display device according to Example 2. FIG.

  1A to 1F are a plan view, an equivalent circuit diagram, and a cross-sectional view showing a configuration of a liquid crystal display device according to a first embodiment. FIG. 1A is a plan view showing a passive drive type liquid crystal display element LCD 1 having a segment display unit 10. A segment electrode having a fixed shape is arranged in the segment display section 10 in the effective display area. The segment electrode has a smooth continuous edge. The counter electrode has an area including the segment electrode and performs display corresponding to the segment electrode. An air conditioner display is illustrated, and the operating state of the air conditioner is shown at the center, and the temperatures of the driver seat area and the passenger seat area are shown on the left and right sides.

  FIG. 1B is a plan view showing an active drive type liquid crystal display element LCD 2 having a dot matrix display unit 20. A dot matrix display unit 20 is formed over the entire effective display unit. The segment display unit 10 overlaps a partial area of the dot matrix display unit.

  In a typical usage pattern, the dot matrix arranged in the segment display unit 10 does not perform independent display but performs arbitrary display outside the segment display unit 10. The segment display unit 10 and the dot matrix display unit 20 outside the segment display unit perform independent display, for example.

  FIG. 1C shows an example of a large number of pixels PX regularly arranged in the vertical and horizontal directions in the dot matrix display unit 20. Rectangular pixels PX are arranged in the vertical and horizontal directions. Each pixel includes a plurality of single color regions with color filters.

  FIG. 1D shows an example of the arrangement of monochromatic regions including the red filter region CFr, the green filter region CFg, and the blue filter region CFb in each pixel PX. A monochromatic area electrode PE including a red area electrode PEr, a green area electrode PEg, and a blue area electrode PEb is arranged corresponding to each monochromatic area. Although an example in which one pixel PX includes three single color areas extending in the vertical direction has been shown, a combination of single color areas extending in the horizontal direction may be used, or a combination of single color areas having other shapes may be used. You can also.

  As shown in FIG. 1E, the monochrome area electrode PE of each monochrome area includes a storage capacitor C and is connected to a thin film transistor TFT that switches an image signal. A switching signal is supplied to the gate electrode of the thin film transistor TFT, the image signal is accumulated in the storage capacitor C during the on period, and the image signal accumulated during the off period is maintained. The monochromatic area electrode PE is covered with a color filter CF.

  As shown in FIG. 1F, an active drive type liquid crystal display element LCD2 that is arbitrarily driven using TFTs is disposed on a passive drive type liquid crystal display element LCD1 having segment electrodes that are driven in a simple matrix. It is composed. The passive drive type liquid crystal display element LCD 1 includes a liquid crystal layer 13 between a pair of glass substrates 11 and 12. The active drive type liquid crystal display element LCD2 includes a TFT array 25 connected to each pixel electrode on the lower glass substrate 21, a common electrode 24 including a color filter on the upper glass substrate 22, and a liquid crystal layer. 23 is disposed between the pixel electrode connected to the TFT array 25 and the common electrode 24.

  The passive drive type liquid crystal display element LCD1 has an external connection terminal group on the upper side, and is connected to the passive drive circuit DR1. The active drive type liquid crystal display element LCD2 includes an external connection terminal group below and is connected to the active drive circuit DR2. The passive drive circuit DR1 controls the display of the passive drive type liquid crystal display element. The active drive circuit DR2 first controls the display of the active drive type liquid crystal display element outside the passive liquid crystal display element region.

  A first polarizer P1 is arranged on the back side of the passive drive type liquid crystal display element LCD1, and a second polarizer P2 is arranged on the front side of the active drive type liquid crystal display element LCD2. For example, the pair of polarizers P1 and P2 form an orthogonal arrangement. The backlight 2 is disposed on the back side of the first polarizer P1.

  The liquid crystal layer alignment direction and the polarizer arrangement are set so that the multilayer element is in a normally black mode that becomes black when no voltage is applied. For example, the active drive type liquid crystal element LCD2 arranged on the front side is composed of an in-plane switching mode liquid crystal element that switches liquid crystal molecules in the effective display plane direction, and the passive drive type liquid crystal element LCD1 arranged on the back side is monodomain vertical. An alignment type liquid crystal element is used. The absorption axis of the back side polarizer P1 and the absorption axis of the front side polarizer P2 are arranged orthogonal to each other.

  If the presence of the active drive type liquid crystal element LCD2 is ignored, a structure capable of realizing high contrast is formed by sandwiching the vertically aligned passive drive type liquid crystal element LCD1 between the orthogonally arranged polarizers P1 and P2. When no voltage is applied, the orthogonally arranged polarizer blocks light, and when a voltage is applied to tilt the liquid crystal molecules in a direction different from the absorption axis direction of the polarizer, transmitted light is generated.

  The absorption axis of the front side polarizer P2 is set to the horizontal direction, and the liquid crystal molecule orientation direction when no voltage is applied to the adjacent in-plane switching type active drive type liquid crystal element LCD2 is transmitted so that the transmitted light of the LCD2 is shielded by the polarizer P2. Set to horizontal orientation. Note that the orientation of the absorption axis of the back polarizer P1 is a vertical orientation. For example, the in-plane switching type active drive type liquid crystal element LCD2 has a liquid crystal molecule alignment direction at the time of applying a voltage to a horizontal direction and a direction that forms an angle of 45 degrees with the vertical direction, and the vertical alignment type liquid crystal element LCD1 has the same alignment processing direction. The direction.

  When displaying an image of an arbitrary shape, the active drive type liquid crystal element LCD2 is driven. When the passive drive type liquid crystal element LCD1 exists so as to overlap the active drive type liquid crystal display element LCD2, the vertical alignment type liquid crystal molecules of the passive drive type liquid crystal display element simply function to transmit light.

  When displaying the segment display unit, the segment display element is driven. The outside of the drive area is a black area. It was confirmed that a shape having a sharp boundary can be displayed.

  Note that the active drive type liquid crystal display element may be formed of a vertical alignment type liquid crystal element, and the passive drive type liquid crystal display element may be constituted of an in-plane switching type liquid crystal element. The absorption axis arrangement direction of the polarizer is not limited to horizontal and vertical.

  According to the inventors' investigation, the liquid crystal display device according to the first embodiment has room for improvement in viewing angle characteristics. The inventor has continuously studied to improve the viewing angle characteristics of a liquid crystal display device in which a plurality of liquid crystal elements are stacked.

  FIG. 2 is a cross-sectional view illustrating a configuration of the liquid crystal display device according to the second embodiment. The liquid crystal display device according to the second embodiment has a configuration in which two viewing angle compensation plates (optical compensation plates) 31 and 32 are further added to the liquid crystal display device according to the first embodiment shown in FIG. 1 (particularly FIG. 1F).

  The viewing angle compensation plate 31 is disposed, for example, between the passive drive type liquid crystal element LCD1 and the back side polarizer P1. Further, the viewing angle compensation plate 32 is disposed between the viewing angle compensation plate 31 and the back surface side polarizer P1. The viewing angle compensation plates 31 and 32 may be disposed between the active drive type liquid crystal element LCD2 and the surface side polarizer P2.

  Here, in the viewing angle compensation plate, the refractive index in the in-plane direction and in the slow axis direction is defined as nx, the refractive index in the fast axis direction is defined as ny, and the refractive index in the thickness direction is defined as nz. . The Nz factor of the viewing angle compensator is defined as (nx−nz) / (nx−ny).

  At this time, a viewing angle compensation plate (nx≈ny> nz) having an Nz factor of ∞ is referred to as a negative C plate. A viewing angle compensation plate (nx> ny> nz) having an Nz factor larger than 1 is called a biaxial plate having negative biaxial optical anisotropy or simply a negative biaxial plate. A viewing angle compensation plate (nx> ny≈nz) having an Nz factor of approximately 1 is referred to as a positive A plate. Furthermore, a viewing angle compensation plate having an Nz factor smaller than 1 is mainly referred to as a biaxial plate having positive biaxial optical anisotropy or simply as a positive biaxial plate. However, a viewing angle compensation plate (nz≈nx> ny) having an Nz factor of approximately 0 is referred to as a negative A plate, and a viewing angle compensation plate (nz> nx≈ny) having an Nz factor of −∞ is referred to as a positive C plate. Call.

  As the viewing angle compensation plate 31, for example, a negative C plate is used. In the following, if the in-plane retardation Re = (nx−ny) × d (d: the thickness of the viewing angle compensation plate) is 7 nm or less, it is referred to as a negative C plate.

  As the viewing angle compensation plate 32, for example, a positive A plate is used. The positive A plate has a slow axis (an orientation in which the refractive index nx is defined) parallel (horizontal orientation) to a liquid crystal molecule orientation orientation when no voltage is applied to the in-plane switching active drive liquid crystal element LCD2. It is preferably arranged so as to be orthogonal (vertical orientation) to the absorption axis of the back polarizer P1 or parallel (horizontal orientation) to the absorption axis of the front polarizer P2.

  A simulation analysis was performed on viewing angle characteristics when no voltage was applied when various parameters of the viewing angle compensation plates 31 and 32 were adjusted. The retardation of the vertically aligned passive drive type liquid crystal element LCD1 was set to about 320 nm.

  In addition, the liquid crystal material used for a liquid crystal element assumed the liquid crystal material by Merck which has a negative dielectric constant anisotropy and (DELTA) n = 0.0914. The polarizer assumed was SKN18243T manufactured by Polatechno. Further, the viewing angle compensation plate was assumed to use norbornene-based cyclic olefin as a material.

  As a result of the simulation analysis, the thickness direction retardation Rth = ((nx + ny) / 2−nz) × d (d: thickness of the viewing angle compensation plate) of the negative C plate 31 is about 220 nm, and the in-plane of the positive A plate 32 When the phase difference Re is about 140 nm, the viewing angle characteristics are optimized. Specifically, although there was some light omission, the light omission was remarkably suppressed in all directions, and excellent viewing angle characteristics were confirmed.

  Subsequently, simulation analysis was performed on viewing angle characteristics when no voltage was applied when the viewing angle compensation plate 32 was replaced with a positive A plate and a negative biaxial film (Nz factor = 1.5). The retardation of the vertically aligned passive drive type liquid crystal element LCD1 was set to about 360 nm.

  As a result of the simulation analysis, the thickness direction retardation Rth of the negative C plate 31 is about 220 nm, the in-plane retardation Re of the negative biaxial film 32 is about 100 nm, and the thickness direction retardation Rth is about 100 nm. When viewing angle characteristics were optimized. Specifically, light leakage was suppressed in all directions, and excellent viewing angle characteristics were confirmed.

  Subsequently, simulation analysis was performed on viewing angle characteristics when no voltage was applied when the viewing angle compensation plate 32 was replaced with a negative biaxial film and a positive biaxial film (Nz factor = 0.5). The retardation of the vertically aligned passive drive type liquid crystal element LCD1 was set to about 275 nm.

  As a result of the simulation analysis, when the thickness direction retardation Rth of the negative C plate 31 is about 220 nm, the in-plane retardation Re of the positive biaxial film 32 is about 227 nm, and the thickness direction retardation Rth is 0 nm. The viewing angle characteristics have been optimized. Specifically, light leakage was suppressed in all directions, and excellent viewing angle characteristics were confirmed.

  Finally, simulation analysis was also performed on the viewing angle characteristics when no voltage was applied when the viewing angle compensator 32 was replaced with a negative A plate instead of a positive biaxial film. The retardation of the vertically aligned passive drive type liquid crystal element LCD1 was set to about 230 nm.

  As a result of the simulation analysis, when the thickness direction retardation Rth of the negative C plate 31 is about 330 nm and the in-plane retardation Re of the negative A plate 32 is about 125 nm, the viewing angle characteristic is optimized. Specifically, light leakage was suppressed in all directions, and excellent viewing angle characteristics were confirmed.

  In a liquid crystal display device in which an in-plane switching type liquid crystal element and a vertical alignment type liquid crystal element are stacked, it was confirmed that the viewing angle characteristic is remarkably improved by providing a negative C plate. Furthermore, it was confirmed that viewing angle characteristics were further optimized by combining a positive A plate, a negative biaxial film, a positive biaxial film, or a negative A plate.

  Although the present application has been described with reference to the embodiments, these are not restrictive. For example, materials, numerical values, and the like are examples, and are not limited thereto. It will be apparent to those skilled in the art that other various modifications, substitutions, improvements, and the like are possible.

LCD ... Liquid crystal display element, LCD1 ... Passive drive type liquid crystal display element, DR1 ... Passive drive circuit, LCD2 ... Active drive type liquid crystal display element, PX ... Pixel, DR2 ... Active drive circuit, CF ... Color filter, CFr ... Red filter region , CFg ... green filter region, CFb ... blue filter region, PE ... monochromatic region electrode, TFT ... thin film transistor, C ... storage capacitor, P1, P2 ... polarizer, 10 ... segment display, 11,12 ... glass substrate, 13 ... Liquid crystal layer, 20 ... dot matrix display unit, 21, 22 ... glass substrate, 23 ... liquid crystal layer, 24 ... common electrode, 25 ... TFT array, 31 ... optical compensator (negative C plate), 32 ... optical compensator (positive) A plate, negative biaxial plate, positive biaxial plate, or negative A plate).

Claims (4)

An active drive type liquid crystal display element capable of performing dot matrix display;
A passive drive type liquid crystal display element that is laminated on the back side of the active drive type liquid crystal display element and capable of segment display;
A surface-side polarizer disposed on the surface side of the active drive type liquid crystal display element;
A back side polarizer disposed on the back side of the passive drive type liquid crystal display element;
A negative C plate disposed between the active drive type liquid crystal display element and the front surface side polarizer or between the passive drive type liquid crystal display element and the back side polarizer;
A viewing angle compensator disposed adjacent to the negative C plate;
A backlight disposed on the back side of the back side polarizer;
With
One of the active drive type liquid crystal display element and the passive drive type liquid crystal display element is formed by an in-plane switching type liquid crystal element, and the other is formed by a vertical alignment type liquid crystal element,
The liquid crystal display in which the characteristics of the active drive type liquid crystal display element, the passive drive type liquid crystal display element, the front surface side polarizer, and the back surface side polarizer are set to a normally black state when no voltage is applied. apparatus.   The viewing angle compensation plate is any one of a positive A plate, a biaxial film having negative biaxial optical anisotropy, a biaxial film having positive biaxial optical anisotropy, or a negative A plate. Item 2. A liquid crystal display device according to item 1.   The viewing angle compensation plate is arranged so that an in-plane slow axis thereof is along a liquid crystal molecular orientation direction of an in-plane switching type liquid crystal element of the active drive type liquid crystal display element or the passive drive type liquid crystal display element. Item 3. A liquid crystal display device according to item 2.   When observed from the normal direction of the display surface, the display device includes a region where the display unit of the active drive type liquid crystal element and the display unit of the passive drive type liquid crystal device overlap, and in the overlap region, the active drive type liquid crystal device and The liquid crystal device according to any one of claims 1 to 3, wherein when one of the passive drive type liquid crystal elements is switched and the other is not driven, the display portion of the liquid crystal element on the switched side becomes a bright state. Liquid crystal display device.

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