JP2011248074A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease brightness of a black color displayed by a normally-white type liquid crystal display device employing a TN (twisted nematic) mode, when the device is driven at a low voltage.SOLUTION: The liquid crystal display device includes: a positive-A type retardation layer 23a having a slow axis A1 that obliquely crosses a transmission axis A1 of a polarizing plate 22a and an alignment direction D1; and a positive-A type retardation layer 23b having a slow axis A2 in an symmetric relation to the slow axis A1 with respect to a direction D3 that bisects alignment directions D1 and D2 and giving the same retardation as that of the retardation layer 23a. The retardation and the direction of the slow axis A1 of the retardation layer 23a are determined in such a manner that, when the polarizing plate 22a is illuminated with natural light at a wavelength of 550 nm while applying a drive voltage, which is applied for displaying the lowest gradation level, to between first and second transparent electrodes, the light transmitting through a liquid crystal layer 212 becomes linearly polarized light having an oscillation direction of an electric field vector tilted by 45° with respect to the direction D3 at an intermediate position between alignment layers.

Description

  The present invention relates to a liquid crystal display device.

  For a liquid crystal display device, particularly a liquid crystal display device that operates with electric power supplied from a battery, a low drive voltage is desired. Lowering the drive voltage enables power consumption to be reduced, and also allows a wider voltage range to be allocated to overdrive or use a source driver with a smaller output, that is, a lower price. .

  However, in a normally white liquid crystal display device employing a twisted nematic (TN) mode, black may be displayed brightly when the drive voltage is lowered. This is because the liquid crystal molecules are not completely vertically aligned at a low driving voltage, and therefore the liquid crystal layer causes a change in the polarization state of the transmitted light.

  Patent Document 1 describes a normally white liquid crystal display device adopting a TN mode. In this liquid crystal display device, the twist angle of the liquid crystal molecules is 80 ° or less, the refractive index anisotropy Δn of the liquid crystal layer is in the range of 0.02 to 0.12, and the thickness d and the refractive index of the liquid crystal layer. The product Δnd with the anisotropy Δn is in the range of 0.2 to 1.2 μm. Further, this liquid crystal display device includes a retardation plate between one polarizing plate and the liquid crystal layer, or between each of the two polarizing plates and the liquid crystal layer. In the latter case, these retardation plates are installed so that each optical axis intersects the rubbing direction of the alignment film. Patent Document 1 describes Examples 1 and 2 as specific examples using two retardation plates, and in each of these Examples, each optical axis is an alignment film. It is arranged so as to form an angle of 90 ° with respect to the rubbing direction.

JP-A-6-43452

  Inventing the technology described herein, the present inventors have found that there is room for improvement in the brightness of black in a liquid crystal display device adopting the above-described configuration when driven at a low voltage.

  Therefore, an object of the present invention is to reduce the brightness of black displayed by a normally white liquid crystal display device adopting a TN mode when driven at a low voltage.

  According to an aspect of the present invention, the first and second transparent electrodes facing each other, a liquid crystal layer including a nematic liquid crystal material interposed between the first and second transparent electrodes, the first transparent electrode, A first alignment film that is interposed between the liquid crystal layer and aligns liquid crystal molecules contained in the liquid crystal material in the first direction in the vicinity of the first transparent electrode when no voltage is applied; the second transparent electrode; A second alignment film that is interposed between the liquid crystal layer and aligns the liquid crystal molecules in a second direction in the vicinity of the second transparent electrode when no voltage is applied, the second direction of the first transparent electrode When viewed from the thickness direction perpendicular to the main surface, the second alignment film twists the liquid crystal molecules in the liquid crystal layer together with the first alignment film when no voltage is applied. Second alignment film to be aligned, first transparent electrode, and first alignment A first transmission axis that is obliquely intersected with a third direction that bisects the angle formed by the first and second directions when viewed from the thickness direction. The first linearly polarizing plate, the second transparent electrode, and the second alignment film are sandwiched between the liquid crystal layer and the third linear direction when viewed from the thickness direction. A second linear polarizing plate having a second transmission axis that is symmetrical to the first transmission axis, and interposed between the first alignment film and the first linear polarizing plate, and from the thickness direction. A first retardation layer of positive A type having a first slow axis obliquely intersecting the first transmission axis and the first direction when viewed, the second alignment film, and the first It is interposed between two linearly polarizing plates, and has a symmetrical relationship with the first slow axis with respect to the third direction when viewed from the thickness direction. A positive A type second retardation layer having a second slow axis and giving the same retardation as the first retardation layer, and a driving voltage having a magnitude corresponding to the gradation to be displayed. A driving circuit applied between the first and second transparent electrodes and a driving voltage smaller than the voltage required for the liquid crystal material to be vertically aligned when displaying the lowest gray scale level. A controller for controlling the operation of the driving circuit so as to be applied between the transparent electrodes, and the driving voltage to be applied when displaying the lowest gradation is applied between the first and second transparent electrodes. In this state, when the first linearly polarizing plate is illuminated with natural light having a wavelength of 550 nm from the thickness direction, the light transmitted through the liquid crystal layer is an electric field at an intermediate position between the first and second alignment films. The vibration direction of the vector is inclined 45 ° with respect to the third direction. So that the linearly polarized light is, the first retardation layer liquid crystal display device retardation and normally white type orientation is defined in the first slow axis of the can is provided.

  According to the present invention, it is possible to reduce the brightness of black displayed by a normally white liquid crystal display device adopting a TN mode when driven at a low voltage.

1 is a plan view schematically showing a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of a pixel included in the liquid crystal display device shown in FIG. 1. Sectional drawing of the liquid crystal display device shown in FIG. The disassembled perspective view of the liquid crystal display device shown in FIG. The graph which shows an example of the influence which the maximum drive voltage has on the relationship between an observation direction and contrast ratio in the liquid crystal display device which concerns on a prior art example. A Poincare sphere showing a change in polarization state that occurs when light transmitted through one polarizing plate enters the other polarizing plate when one polarizing plate is illuminated from the normal direction in a liquid crystal display device according to a conventional example. In a liquid crystal display device according to a conventional example, when one polarizing plate is illuminated from a direction that forms an angle of 18 ° with respect to the normal direction, light that has passed through the polarizing plate is generated before entering the other polarizing plate. The graph which shows the change of a polarization state. The graph which shows the example of the change of the twist angle according to the position of the thickness direction in a liquid-crystal layer. The graph which shows a part of data of FIG. The Poincare sphere which shows an example of the change of the polarization state produced until the linearly polarized light which permeate | transmitted one polarizing plate in the liquid crystal display device shown in FIG. 1 injects into the other polarizing plate. The graph which expanded and depicted the curve shown in FIG. The graph which shows the example of the change of the contrast ratio according to an observation direction. The graph which shows the example of the relationship between the wavelength and the transmittance | permeability at the time of white display. The graph which shows the example of the relationship between the wavelength at the time of black display, and the transmittance | permeability. 3 is a graph showing an example of viewing angle characteristics of the liquid crystal display device shown in FIG. 1. The graph which shows the example of the transmittance | permeability change according to an applied voltage. In the liquid crystal display device shown in FIG. 1, when the transmission axes of the polarizing plates are crossed obliquely, an example of a change in polarization state that occurs until the linearly polarized light transmitted through one polarizing plate enters the other polarizing plate is shown. A graph drawn by enlarging a part of the Poincare sphere. Sectional drawing which shows schematically the liquid crystal display device which concerns on the 2nd aspect of this invention. The disassembled perspective view of the liquid crystal display device shown in FIG. FIG. 19 is a diagram schematically showing an example of an alignment state of liquid crystal molecules in the liquid crystal display device shown in FIG. 18. The graph which shows an example of the viewing angle characteristic which can be achieved by the liquid crystal display device shown in FIG. The graph which shows an example of the viewing angle characteristic which can be achieved by the liquid crystal display device which has the same structure as having shown in FIG. 18 except having changed the position of the optical compensation film.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same referential mark is attached | subjected to the component which exhibits the same or similar function through all the drawings, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a plan view schematically showing a liquid crystal display device according to the first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of a pixel included in the liquid crystal display device shown in FIG. FIG. 3 is a cross-sectional view of the liquid crystal display device shown in FIG. 4 is an exploded perspective view of the liquid crystal display device shown in FIG.

  The liquid crystal display device 1 is a normally white type liquid crystal display device employing a TN mode. As shown in FIG. 1, the liquid crystal display device 1 includes a display panel 2, a gate driver 3, a source driver 4, and a controller 5. The liquid crystal display device 1 further includes a backlight (not shown).

  The display panel 2 includes a liquid crystal cell 21 shown in FIG. The liquid crystal cell 21 includes an active matrix substrate 211a, a counter substrate 211b, a seal layer (not shown), and a liquid crystal layer 212.

  The active matrix substrate 211a includes a transparent substrate 2111a, a pixel electrode 2112a, and an alignment film 2113a.

  The transparent substrate 2111a is electrically insulating. The transparent substrate 211a is made of, for example, glass or plastic.

  The pixel electrodes 2112a are two-dimensionally arranged on one main surface of the transparent substrate 2111a. The arrangement of the pixel electrodes 2112a defines the display area AA shown in FIG.

  The pixel electrode 2112a is a transparent electrode. The pixel electrode 2112a is made of a conductive oxide such as indium tin oxide, for example.

  As shown in FIG. 3, the alignment film 2113a covers the pixel electrode 2112a. The alignment film 2113a is, for example, a polyimide film that has been rubbed. As shown in FIG. 4, the alignment film 2113a aligns liquid crystal molecules LC1 included in the liquid crystal layer 212, for example, rod-shaped molecules in the first direction D1, for example, in the vicinity thereof.

  A circuit including the pixel electrode 2112a is provided between the transparent substrate 2111a and the alignment film 2113a. As shown in FIG. 2, this circuit includes a gate line 2114, a source line 2115, an auxiliary capacitance line 2116, a thin film transistor 2117, and a capacitor 2118.

  The gate line 2114 and the source line 2115 are arranged so as to cross each other. The pixel electrode 2112 a, the thin film transistor 2117, and the capacitor 2118 are arranged corresponding to the intersection of the gate line 2114 and the source line 2115.

  A gate and a source of the thin film transistor 2117 are connected to a gate line 2114 and a source line 2115, respectively. A pixel electrode 2112 a and one electrode of the capacitor 2118 are connected to the drain of the thin film transistor 2117. The other electrode of the capacitor 2118 is connected to the auxiliary capacitance line 2116.

  As illustrated in FIG. 3, the counter substrate 211b includes a transparent substrate 2111b, a counter electrode 2112b, and an alignment film 2113b.

  The transparent substrate 2111b faces the alignment film 2113a. The transparent substrate 2111b is electrically insulating. The transparent substrate 2111b is made of glass or plastic, for example.

  The counter electrode 2112b is provided on the surface of the transparent substrate 2111b facing the alignment film 2113a so as to face the pixel electrode 2112a. The counter electrode 2112b is a transparent electrode. The counter electrode 2112b is made of a conductive oxide such as indium tin oxide, for example.

  The alignment film 2113b covers the counter electrode 2112b. The alignment film 2113b is, for example, a polyimide film that has been rubbed. As shown in FIG. 4, the alignment film 2113b aligns the liquid crystal molecules LC1 included in the liquid crystal layer 212 in the second direction D2, for example, in the vicinity thereof. The second direction D2 is a direction perpendicular to the main surface of the pixel electrode 2112a, here, a direction intersecting with the first direction D1 when viewed from the Z direction.

  Typically, the counter substrate 211b further includes a color filter layer. The color filter layer may be provided on the active matrix substrate 211a instead of being provided on the counter substrate 211b.

  In the display area AA shown in FIG. 1, granular spacers (not shown) are arranged between the active matrix substrate 211a and the counter substrate 211b shown in FIG. These granular spacers serve to separate the active matrix substrate 211a and the counter substrate 211b from each other with a certain gap therebetween. Instead of using the granular spacer, a columnar spacer may be provided on at least one of the active matrix substrate 211a and the counter substrate 211b.

  A seal layer (not shown) is interposed between the active matrix substrate 211a and the counter substrate 211b, and the substrates 211a and 211b are bonded to each other. The seal layer is provided so as to surround the display area AA shown in FIG. 1, and forms a hollow structure together with the active matrix substrate 211a and the counter substrate 211b shown in FIG.

  The liquid crystal layer 212 is made of a liquid crystal material that satisfies the above hollow structure. This liquid crystal material is a nematic liquid crystal material having positive dielectric anisotropy. The liquid crystal molecules LC1 contained in the liquid crystal material exhibit twist alignment when no voltage is applied.

  As shown in FIGS. 3 and 4, the display panel 2 further includes a first linear polarizing plate 22a, a second linear polarizing plate 22b, a first retardation layer 23a, and a second retardation layer 23b. It is out.

The linearly polarizing plates 22a and 22b are typically absorption type linearly polarizing plates. As shown in FIG. 3, the linearly polarizing plates 22a and 22b face the active matrix substrate 211a and the counter substrate 211b, respectively. As shown in FIG. 4, the linearly polarizing plate 22a obliquely intersects the third direction D3 that bisects the angle formed by the first direction D1 and the second direction D2 when viewed from the Z direction. One transmission axis A _T 1 is provided. On the other hand, the linearly polarizing plate 22b has a second transmission axis A _T 2 that is symmetrical to the first transmission axis A _T 1 with respect to the third direction D3 when viewed from the Z direction.

  As shown in FIG. 3, the retardation layer 23a is interposed between the polarizing plate 22a and the active matrix substrate 211a. The retardation layer 23a may be interposed between the transparent substrate 2111a and the alignment film 2113a. That is, the retardation layer 23 a may be a part of the liquid crystal cell 21.

The retardation layer 23a is a positive A type retardation layer. As shown in FIG. 4, the retardation layer 23 a has a first slow axis A _S 1 that obliquely intersects the first transmission axis A _T 1 and the first direction D 1 when viewed from the Z direction. ing.

  As shown in FIG. 3, the retardation layer 23b is interposed between the polarizing plate 22b and the counter substrate 211b. The retardation layer 23b may be interposed between the transparent substrate 2111b and the alignment film 2113b. That is, the retardation layer 23 b may be a part of the liquid crystal cell 21.

The retardation layer 23b is a positive A type retardation layer. As shown in FIG. 4, the retardation layer 23b has a second slow axis A _S 2 that is symmetrical to the first slow axis A _S 1 with respect to the third direction D3 when viewed from the Z direction. Have. The retardation layer 23b gives the same retardation as the retardation layer 23a to light having the same wavelength.

  The gate driver 3 and source driver 4 shown in FIG. 1 and the circuit shown in FIG. 2 constitute a drive circuit. This drive circuit applies a drive voltage having a magnitude corresponding to the gradation to be displayed between the electrodes 2112a and 2112b shown in FIGS.

  The gate driver 3 shown in FIG. 1 is connected to the gate line 2114 and the auxiliary capacitance line 2116 shown in FIG. The gate driver 3 supplies a scanning signal as a voltage signal to the gate line 2114. Specifically, the gate driver 3 makes the first scanning signal and the thin film transistor 2117 non-conductive to each gate line 2114 so that the first scanning signal for making the thin film transistor 2117 conductive is sequentially supplied to the gate line 2114. The second scanning signal to be in a state is supplied alternately. In addition, the gate driver 3 supplies a reference voltage to the auxiliary capacitance line 2116.

  The source driver 4 shown in FIG. 1 is connected to the source line 2115 shown in FIG. The source driver 4 outputs a driving voltage having a magnitude corresponding to the gradation to be displayed to the source line 2115. Specifically, the source driver 4 adjusts the size so that a relatively small voltage is applied between the electrodes 2112a and 2112b when the gradation to be displayed is high, that is, when a bright image is displayed. The drive voltage thus supplied is supplied to the source line 2115. The source driver 4 is a drive whose size is adjusted so that a relatively large voltage is applied between the electrodes 2112a and 2112b when the gradation to be displayed is low, that is, when a dark image is displayed. A voltage is supplied to the source line 2115.

  The controller 5 is connected to the gate driver 3 and the source driver 4 as shown in FIG. The controller 5 controls the operations of the gate driver 3 and the source driver 4. Specifically, the controller 5 controls the timing at which the gate driver 3 outputs the first scanning signal and the timing at which the source driver 4 outputs the driving voltage, and in addition, controls the magnitude of the driving voltage output by the source driver 4. To control. Then, the controller 5 applies the driving voltage smaller than the voltage necessary for the vertical alignment of the liquid crystal material between the electrodes 2112a and 2112b when displaying the lowest gradation, for example, black. The operation of the drive circuit is controlled. For example, the controller 5 controls the operation of the drive circuit described above so that a drive voltage of 1.5 V to 3.5 V is applied between the electrodes 2112a and 2112b when displaying the lowest gradation.

  A backlight (not shown) is provided on the back side of the display panel 2. The backlight typically illuminates the back surface of the display panel 2, here the polarizing plate 22a, with white light.

In the liquid crystal display device 1, in addition to adopting the above configuration, a voltage having the same magnitude as the drive voltage applied when displaying the lowest gradation is applied between the electrodes 2112 a and 2112 b from the Z direction. When the linear polarizing plate 22a is illuminated with natural light having a wavelength of 550 nm, the light transmitted through the liquid crystal layer 212 is linearly polarized light inclined at 45 ° with respect to the third direction at an intermediate position between the alignment films 2113a and 2113b. Thus, the retardation of the retardation layer 23a and the orientation of the first slow axis A _S 1 are determined. When this configuration is adopted, the contrast ratio in the front direction is improved, and it is possible to suppress black from being displayed brightly during low voltage driving.

  FIG. 5 is a graph showing an example of the influence of the maximum drive voltage on the relationship between the observation direction and the contrast ratio in the liquid crystal display device according to the conventional example.

  FIG. 5 shows data obtained by simulation for a typical normally white liquid crystal display device employing the TN mode. In this simulation, an optical simulation software LCD-MASTER made by Shintech Co., Ltd. was used, and the following conditions were assumed.

That is, the liquid crystal display device does not include a retardation layer, and the transmission axes of the linear polarizing plates are orthogonal to each other. The rubbing directions of the alignment films on the light source side and the viewer side were parallel to the transmission axes of the linear polarizing plates on the light source side and the viewer side, respectively. Further, the liquid crystal material has a refractive index anisotropy Δn of 0.13 for light having a wavelength of 550 nm, a dielectric anisotropy Δε of 12.7, and elastic moduli k ₁₁ , k _22, and k ₃₃ , The values were 10.5 pN, 7.1 pN, and 22.3 pN, respectively. The thickness of the liquid crystal layer was 3.8 μm, and the pretilt angle of the liquid crystal molecules was 1.0 °. Here, the voltage (maximum driving voltage) applied to the liquid crystal layer when displaying black is set to 5.0V, 3.0V, 2.5V, 2.0V, and 1.5V. Assuming such conditions, the relationship between the viewing direction and the contrast ratio was simulated.

  In FIG. 5, the horizontal axis represents the angle formed by the observation direction with respect to the direction perpendicular to the display surface, and the vertical axis represents the contrast ratio. As shown in FIG. 5, when the maximum drive voltage is lowered, the observation direction in which the contrast ratio is maximized deviates from the normal direction. The lower the maximum drive voltage, the greater the deviation from the normal direction of the observation direction where the contrast ratio is maximum.

  FIG. 6 shows a change in polarization state that occurs before light transmitted through one polarizing plate enters the other polarizing plate when one polarizing plate is illuminated from the normal direction in a liquid crystal display device according to a conventional example. Poincare sphere. FIG. 7 shows that when one polarizing plate is illuminated from a direction forming an angle of 18 ° with respect to the normal direction in a liquid crystal display device according to a conventional example, light transmitted through this polarizing plate enters the other polarizing plate. It is a graph which shows the change of the polarization state which arises by this. 6 and 7, P1 represents a polarization state when the previous light is incident on the liquid crystal layer, and P2 represents a polarization state when the previous light is emitted from the liquid crystal layer.

  6 and 7 show data obtained by performing a simulation under the same conditions as described above with reference to FIG. In these simulations, it is assumed that a voltage of 2.0 V is applied to the liquid crystal layer.

  As shown in FIG. 6, the light traveling in the normal direction is greatly different in the polarization state when entering the liquid crystal layer and the polarization state when exiting from the liquid crystal layer. That is, the light traveling in the normal direction is greatly different from the polarization state immediately after passing through the light source side polarizing plate and the polarization state immediately before entering the observer side polarizing plate. Therefore, when the display surface is observed from the normal direction under these conditions, the screen does not appear sufficiently dark.

  On the other hand, the light traveling in the direction forming 18 ° with respect to the normal direction draws a symmetrical S-shaped polarization locus as shown in FIG. There is no big difference between the state. Therefore, when the display surface is observed from a direction that forms 18 ° with respect to the normal direction under these conditions, the screen looks relatively dark.

  Based on the above results, the present inventors have adopted a design in which a symmetrical S-shaped locus similar to that shown in FIG. Even so, I thought it was possible to suppress the appearance of black light. The basis for this will be described below.

  In order to realize an ideal black display, it is necessary to completely block the light incident on the polarizing plate on the viewer side. That is, immediately before the light enters the polarizing plate on the observer side, the oscillation direction of the electric field vector of the light (hereinafter referred to as the polarization direction) must be linearly polarized light perpendicular to the polarizing plate transmission axis. In order to realize this change in the polarization state, the inventors paid attention to the symmetry of the locus shown in FIG. In FIG. 7, P3 is the polarization state at the center of the liquid crystal cell. The polarization state of the transmitted light has a symmetrical S-shaped trajectory centered on P3, and P3 is located approximately at the midpoint between the incident polarization state P1 and the exit polarization state P2. By utilizing this feature, the target emission polarization state can be obtained by adjusting the polarization state at the center of the liquid crystal cell on the Poincare sphere. For example, if the target exit polarization state is linearly polarized light whose polarization direction is perpendicular to the transmission axis of the observer-side polarizing plate, an ideal black display can be realized.

  In obtaining a symmetrical S-shaped locus for light traveling in the normal direction, as described below, an optical equivalent to increasing the twist angle of the liquid crystal molecules to be larger than the angle formed by the transmission axis of the polarizing plate. Is important.

  FIG. 8 is a graph showing an example of a change in twist angle according to the position in the thickness direction in the liquid crystal layer. FIG. 9 is a graph showing a part of the data of FIG.

  8 and 9 show data obtained by performing a simulation under the same conditions as described above with reference to FIG. In this simulation, it is assumed that a voltage of 2.0 V is applied to the liquid crystal layer.

  8 and 9, the horizontal axis represents the distance in the thickness direction from one alignment film, and the vertical axis represents the twist angle. 8 and 9, a curve C3 represents data obtained for light traveling in the normal direction, and a curve C4 is obtained for light traveling in a direction forming an angle of 18 ° with respect to the normal direction. Data.

  As shown in FIGS. 8 and 9, for light incident from the normal direction, the twist angle of the liquid crystal molecules is 90 °. On the other hand, for light traveling in a direction that forms an angle of 18 ° with respect to the normal direction, the effective twist angle of the liquid crystal molecules is 92.2 °.

  As suggested by this, in order to obtain a symmetrical S-shaped trajectory similar to that shown in FIG. 7 for light traveling in the normal direction, the transmission axis of the polarizing plate forms the twist angle of the liquid crystal molecules. It is important to obtain an optical effect equivalent to increasing the angle.

  In the liquid crystal display device 1 described with reference to FIGS. 1 to 4, the retardation layers 23a and 23b are used to obtain this optical effect. When the phase difference layers 23a and 23b are used and the configuration described with reference to FIGS. 1 to 4 is employed, it is possible to suppress the appearance of black light even when the drive voltage is lowered.

  FIG. 10 is a Poincare sphere showing an example of a change in polarization state that occurs until linearly polarized light that has passed through one polarizing plate enters the other polarizing plate in the liquid crystal display device shown in FIG. FIG. 11 is a graph drawn by enlarging the curve shown in FIG.

10 and 11 show data obtained by performing a simulation assuming the following conditions. That is, here, the liquid crystal material has the same physical properties as those described with reference to FIG. The thickness of the liquid crystal layer 212 was 3.8 μm, and the pretilt angle of the liquid crystal molecules LC1 was 1.0 °. The angle −α formed by the first direction D1 with respect to the third direction D3 was −45 °, and the angle α formed by the second direction D2 with respect to the third direction D3 was 45 °. The angle −β formed by the transmission axis A _T 1 with respect to the third direction D3 was −45 °, and the angle β formed by the transmission axis A _T 2 with respect to the third direction D3 was 45 °. The retardation of each of the phase difference layers 23a and 23b with respect to light having a wavelength of 550 nm is 113 nm. The angle −γ formed by the slow axis A _S 1 with respect to the third direction D3 was −138 °, and the angle γ formed by the slow axis A _S 2 with respect to the third direction D3 was 138 °. In this simulation, it is assumed that a voltage of 2.5 V is applied to the liquid crystal layer.

  In order to realize an ideal black display under the above polarizing plate conditions, the polarization state immediately before entering the second linearly polarizing plate 22b has an angle of −45 ° with respect to the third direction D3. The linearly polarized light to be formed, that is, the same polarization state as that immediately after passing through the first linearly polarizing plate needs to be obtained. Therefore, the polarization state of the light at the intermediate position between the alignment films 2113a and 2113b may be the same as that immediately after passing through the first linearly polarizing plate.

  10 and 11, P4 indicates a polarization state when light transmitted through the linearly polarizing plate 22a enters the retardation layer 23a, a polarization state of light at an intermediate position between the alignment films 2113a and 2113b, and a phase difference. The polarization state of the light immediately after being emitted from the layer 23b is shown. P5 represents the polarization state of light immediately after exiting from the retardation layer 23a, and P6 represents the polarization state of light immediately after exiting from the liquid crystal layer 212.

  When the polarization state of the transmitted light is changed as shown in FIGS. 10 and 11, the polarization state of the light immediately after the linearly polarizing plate 22a exits and the polarization state of the light at the intermediate position between the alignment films 2113a and 2113b. Further, the polarization state of the light immediately before entering the linearly polarizing plate 22b can be made equal. Therefore, as exemplified below, it is possible to suppress black from being brightly displayed at the time of low voltage driving, and therefore it is possible to simultaneously realize low voltage driving and a high contrast ratio.

FIG. 12 is a graph illustrating an example of a change in contrast ratio according to the observation direction.
In FIG. 12, the horizontal axis represents the angle formed by the observation direction with respect to the normal direction of the display surface, and the vertical axis represents the contrast ratio. In FIG. 12, a curve C5 is data obtained by performing a simulation under the same conditions as described above with reference to FIGS. Curve C6 is data obtained by performing a simulation under the same conditions except that the retardation layers 23a and 23b are omitted.

  As is clear from the comparison between the curves C5 and C6 shown in FIG. 12, when the configuration described with reference to FIGS. 1 to 4 is adopted, the normal direction is different from the case where the retardation layers 23a and 23b are omitted. The contrast ratio can be maximized. In the former case, a higher maximum contrast ratio can be achieved as compared with the latter case.

  FIG. 13 is a graph showing an example of the relationship between wavelength and transmittance during white display. FIG. 14 is a graph showing an example of the relationship between wavelength and transmittance during black display.

  13 and 14, the horizontal axis represents the wavelength of light, and the vertical axis represents the transmittance of the display panel. In FIGS. 13 and 14, curves C7 and C9 are data obtained by performing a simulation under the same conditions as described above with reference to FIGS. Curves C8 and C10 are data obtained by performing a simulation under the same conditions except that the retardation layers 23a and 23b are omitted.

  As is clear from the comparison of the curves C7 and C8 shown in FIG. 13, when the configuration described with reference to FIGS. 1 to 4 is adopted, the white color substantially the same as when the retardation layers 23a and 23b are omitted is displayed. can do. As is apparent from the comparison of the curves C9 and C10 shown in FIG. 14, when the configuration described with reference to FIGS. 1 to 4 is adopted, the phase difference layers 23a and 23b are omitted compared to the case where the retardation layers 23a and 23b are omitted. Can display dark black.

  FIG. 15 is a graph showing an example of viewing angle characteristics of the liquid crystal display device shown in FIG.

  FIG. 15 shows data obtained by performing a simulation under the same conditions as described above with reference to FIGS. 10 and 11. As shown in FIG. 15, under this condition, in addition to being able to achieve a high contrast ratio in the normal direction, a wide viewing angle can be realized, particularly in the left-right direction.

In the liquid crystal display device 1 described with reference to FIGS. 1 to 4, the retardation layers 23 a and 23 b have their slow axes A _S 1 and A _S 2 in the first direction when viewed from the Z direction. It arrange | positions so that D1 and the 2nd direction D2 may cross | intersect diagonally. The angle formed by the slow axis A _S 1 with respect to the first direction D1 and the angle formed by the slow axis A _S 2 with respect to the second direction D2 are in the range of 1 ° to 179 ° excluding 90 °, for example. Typically, it is in the range of 75 ° to 105 ° excluding 1 ° to 15 ° or 90 °.

As described below, when such a configuration is adopted, the phase difference layers 23a and 23b are arranged so that the slow axes A _S 1 and A _S 2 are orthogonal to the first direction D1 and the second direction D2, respectively. A much higher contrast ratio can be achieved compared to

FIG. 16 is a graph showing an example of transmittance change according to the applied voltage.
In FIG. 16, the horizontal axis represents the voltage applied to the liquid crystal layer 212, and the vertical axis represents the transmittance of the display panel 2 as a relative value with the value when the applied voltage is 0V being 100.

  FIG. 16 shows data obtained by performing a simulation assuming the following conditions.

That is, in obtaining the curve C11, the liquid crystal material has a refractive index anisotropy Δn for light having a wavelength of 550 nm of 0.13, a dielectric anisotropy Δε of 12.7, an elastic modulus k ₁₁ , k ₂₂ and k ₃₃ were 10.5 pN, 7.1 pN, and 22.3 pN, respectively. The thickness of the liquid crystal layer was 3.3 μm, and the pretilt angle of the liquid crystal molecules was 1.0 °.

The angle −α formed by the first direction D1 with respect to the third direction D3 was −50 °, and the angle α formed by the second direction D2 with respect to the third direction D3 was 50 °. The angle −β formed by the transmission axis A _T 1 with respect to the third direction D3 was −45 °, and the angle β formed by the transmission axis A _T 2 with respect to the third direction D3 was 45 °.

The angle formed by the slow axis A _S 1 of the retardation layer 23a with respect to the first direction D1 and the angle formed by the slow axis A _S 2 of the retardation layer 23b with respect to the second direction D2 are each 90. While changing within the range other than 0 °, the retardation of the phase difference layers 23a and 23b was changed, and the conditions under which the transmittance in the normal direction was minimized when the applied voltage was 2.5V were obtained.

  As a result, when the angles −γ and γ are −142 ° and 142 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 80 nm, transmission in the normal direction is performed when the applied voltage is 2.5V. The rate was minimized. Curve C11 represents the transmittance distribution obtained under this condition.

In obtaining the curve C12, the angle formed by the slow axis A _S 1 of the retardation layer 23a with respect to the first direction D1 and the angle formed by the slow axis A _S 2 of the retardation layer 23b with respect to the second direction D2. Except that each of and was set to 90 °, a condition that the transmittance in the normal direction was minimized when the applied voltage was 2.5 V was determined by the same method as described above for the curve C11. As a result, when the retardation of each of the retardation layers 23a and 23b was 105 nm, the transmittance in the normal direction was minimized when the applied voltage was 2.5V. A curve C12 represents the transmittance distribution obtained under this condition.

  Curve C13 represents the transmittance distribution obtained under the same conditions as described above for curve C11 except that retardation layers 23a and 23b are omitted.

As is apparent from the comparison between the curves C12 and C13, when the slow axes A _S 1 and A _S 2 are orthogonal to the first direction D1 and the second direction D2, respectively, the phase difference layers 23a and 23b are omitted; In comparison, driving at a lower voltage is possible. However, the contrast ratio that can be achieved in the former case is equivalent to the contrast ratio that can be achieved in the latter case. Specifically, when the slow axes A _S 1 and A _S 2 are orthogonal to the first direction D1 and the second direction D2, respectively, the contrast in the front direction achieved when the maximum drive voltage is 2.5V. The ratio is about 600 at maximum.

On the other hand, when the slow axes A _S 1 and A _S 2 are crossed obliquely with respect to the first direction D1 and the second direction D2, respectively, as is clear from the comparison of the curves C11 to C13, the retardation layer In addition to being able to drive at a lower voltage compared with the case where 23a and 23b are omitted, the case where the phase difference layers 23a and 23b are omitted and the slow axes A _S 1 and A _S 2 are respectively set to the first. A much higher contrast ratio can be realized as compared with the case of being orthogonal to the direction D1 and the second direction D2. Specifically, when the slow axes A _S 1 and A _S 2 are crossed obliquely with respect to the first direction D1 and the second direction D2, respectively, this is achieved when the maximum drive voltage is 2.5V. The contrast ratio in the front direction is 1100 at the maximum.

As described above, when the slow axes A _S 1 and A _S 2 are obliquely intersected with the first direction D1 and the second direction D2, respectively, the slow axes A _S 1 and A _S 2 are respectively set in the first direction. A much higher contrast ratio can be realized as compared with the case of being orthogonal to D1 and the second direction D2.

  The optimum values of the angles −γ and γ and the retardation of each of the retardation layers 23a and 23b vary according to the angles −α and α as illustrated below.

  Except that the angles -α and α are set to -45 ° and 45 °, respectively, the transmittance in the normal direction is obtained when the applied voltage is 2.5 V by the same method as described with respect to the curve C11 of FIG. The minimum condition was determined. As a result, when the angles −γ and γ are −138 ° and 138 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 113 nm, transmission in the normal direction is performed when the applied voltage is 2.5V. The rate was minimized. In this case, when the maximum drive voltage was 2.5 V, the contrast ratio in the front direction could be 1000 or more.

  A similar simulation was performed on a liquid crystal display device similar to the above except that the retardation layers 23a and 23b were omitted, and the contrast ratio in the front direction that could be achieved when the maximum drive voltage was 2.5 V was as follows. 70. Further, in order to achieve a sufficient contrast ratio in the liquid crystal display device in which the retardation layers 23a and 23b are omitted, it is necessary to set the maximum drive voltage to 4.0 V or higher.

  As described above, the optimum values of the retardations of the angles −γ and γ and the retardation layers 23a and 23b change according to the angles −α and α. Further, the optimum values of the retardations of the angles −γ and γ and the retardation layers 23a and 23b change according to the maximum drive voltage, as will be exemplified below.

  Except that the angles -α and α are set to -45 ° and 45 °, respectively, the transmittance in the normal direction when the applied voltage is 2.0 V is the same as that described with respect to the curve C11 in FIG. The minimum condition was determined. As a result, when the angles −γ and γ are −142 ° and 142 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 144 nm, transmission in the normal direction is performed when the applied voltage is 2.0V. The rate was minimized. In this case, when the maximum drive voltage was 2.0 V, the contrast ratio in the front direction could be 1000 or more.

  When the same simulation was performed for a liquid crystal display device similar to this except that the phase difference layers 23a and 23b were omitted, the contrast ratio in the front direction that could be achieved when the maximum drive voltage was 2.0V was 18 Further, in order to achieve a sufficient contrast ratio in the liquid crystal display device in which the retardation layers 23a and 23b are omitted, it is necessary to set the maximum drive voltage to 4.0 V or higher.

  Thus, the optimum values of the retardations of the angles −γ and γ and the phase difference layers 23a and 23b change according to the maximum drive voltage. Further, the optimum values of the retardations of the angles −γ and γ and the retardation layers 23a and 23b vary according to the physical properties of the liquid crystal material, as exemplified below.

Except that the angles −α and α were −45 ° and 45 °, respectively, and that the liquid crystal material had the following physical properties, the same method as described with respect to the curve C11 in FIG. The conditions under which the transmittance in the normal direction was minimized when the applied voltage was 2.0V were determined. That is, here, the liquid crystal material has a refractive index anisotropy Δn of 0.20 for light having a wavelength of 550 nm, a dielectric anisotropy Δε of 16.5, and an elastic modulus k ₁₁ , k ₂₂ and k. ₃₃ were determined to be 15.7 pN, 6.8 pN and 14.8 pN, respectively.

  As a result, when the angles −γ and γ are −139 ° and 139 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 122 nm, transmission in the normal direction is performed when the applied voltage is 2.0V. The rate was minimized. In this case, when the maximum drive voltage was 2.0 V, the contrast ratio in the front direction could be 1000 or more.

  When the same simulation was performed for a liquid crystal display device similar to this except that the phase difference layers 23a and 23b were omitted, the contrast ratio in the front direction that could be achieved when the maximum drive voltage was 2.0V was 37. Further, in order to achieve a sufficient contrast ratio in the liquid crystal display device in which the retardation layers 23a and 23b are omitted, it is necessary to set the maximum drive voltage to 3.2 V or more.

  As described above, the optimum values of the retardations of the angles −γ and γ and the retardation layers 23a and 23b vary depending on the physical properties of the liquid crystal material to be used.

In the example described above, the linearly polarizing plates 22a and 22b are arranged so that their transmission axes A _T 1 and A _T 2 are orthogonal when viewed from the Z direction. In addition, in the above-described example, the linear polarizing plate 22a has a wavelength of 550 nm from the Z direction in a state where a voltage having the same magnitude as the driving voltage applied when displaying the lowest gradation is applied between the electrodes 2112a and 2112b. When illuminated with natural light, the light transmitted through the liquid crystal layer 212 is at the intermediate position between the alignment films 2113a and 2113b so as to have the same polarization state as the polarized light incident on the retardation layer 23a. The orientation of the retardation and the first slow axis A _S 1 is defined.

Instead of adopting this configuration, the following configuration may be employed. That is, the linearly polarizing plates 22a and 22b may be arranged such that their transmission axes A _T 1 and A _T 2 are orthogonal to each other when viewed from the Z direction, or may be arranged so as to cross obliquely. Good. In this case, when the linearly polarizing plate 22a is illuminated with natural light having a wavelength of 550 nm from the Z direction in a state where a driving voltage applied when displaying the lowest gradation is applied between the transparent electrodes 2112a and 2112b, the liquid crystal layer 212 The retardation of the retardation layer 23a and the light passing through the phase difference layer 2113a and 2113b are linearly polarized light whose electric field vector oscillation direction is inclined by 45 ° with respect to the third direction D3. The direction of the slow axis A _S 1 may be determined. This will be described with reference to FIGS. 4, 11 and 17.

  FIG. 17 shows the change in the polarization state that occurs before the linearly polarized light transmitted through one polarizing plate enters the other polarizing plate when the transmission axes of the polarizing plates are obliquely crossed in the liquid crystal display device shown in FIG. It is the graph which expanded and drawn a part of Poincare sphere which shows an example.

FIG. 17 shows data obtained by performing a simulation assuming the following conditions. That is, here, the liquid crystal material has the same physical properties as those described with reference to FIG. The thickness of the liquid crystal layer 212 was 3.8 μm, and the pretilt angle of the liquid crystal molecules LC1 was 1.0 °. The angle −α formed by the first direction D1 with respect to the third direction D3 was −50 °, and the angle α formed by the second direction D2 with respect to the third direction D3 was 50 °. The angle −β formed by the transmission axis A _T 1 with respect to the third direction D3 was −50 °, and the angle β formed by the transmission axis A _T 2 with respect to the third direction D3 was 50 °. The retardation of each of the retardation layers 23a and 23b with respect to light having a wavelength of 550 nm is assumed to be 48 nm. The angle −γ formed by the slow axis A _S 1 with respect to the third direction D3 was −38 °, and the angle γ formed by the slow axis A _S 2 with respect to the third direction D3 was 38 °. In this simulation, it is assumed that a voltage of 2.5 V is applied to the liquid crystal layer.

  In FIG. 17, P7 represents the polarization state of the light immediately after being emitted from the linearly polarizing plate 22a. P8 represents the polarization state of the light immediately after being emitted from the retardation layer 23a. P9 represents the polarization state of light at an intermediate position between the alignment films 2113a and 2113b. P10 represents the polarization state of the light immediately after being emitted from the liquid crystal layer 212. P11 represents the polarization state immediately before entering the linearly polarizing plate 22b.

When displaying the lowest gradation, it is ideal that linearly polarized light whose polarization direction is perpendicular to the transmission axis A _T 2 is incident on the linearly polarizing plate 22b. That is, in this case, in the structure shown in FIG. 4, the angle formed by the polarization direction of the linearly polarized light incident on the linearly polarizing plate 22b with respect to the polarization direction of the linearly polarized light emitted by the linearly polarizing plate 22a is β-90 °. Ideally. This polarization state shown on the Poincare sphere corresponds to P11 in FIG.

In the liquid crystal display device 1 shown in FIG. 4, when each set of the transmission axes A _T 1 and A _T 2, the slow axes A _S 1 and A _S 2, and the directions D 1 and D 2 is viewed from the Z direction, While adopting a symmetric configuration with respect to the third direction, the retardation layers 23a and 23b have the same retardation. In such a liquid crystal display device 1, when displaying the lowest gradation, the polarization state of light at the intermediate position between the alignment films 2113a and 2113b is the polarization state emitted by the linearly polarizing plate 22a on the Poincare sphere, The polarization direction may be located at an intermediate point between the linear polarization state perpendicular to the transmission axis A _T 2, that is, the state of P9 in FIG. This state is a linearly polarized light whose polarization direction is (−β + (β−90 °)) / 2 with respect to the third direction D3, that is, the polarization direction is 45 ° with respect to the third direction D3. The linearly polarized light that is formed. If this design is adopted, an ideal black display is possible.

On the other hand, when the transmission axes A _T 1 and A _T 2 are orthogonal when viewed from the Z direction, the angle β is 45 °. Therefore, as described with reference to FIG. 11, when displaying the lowest gradation, the polarization state of the light immediately after the linearly polarizing plate 22a is emitted and the polarization of the light at the intermediate position between the alignment films 2113a and 2113b. By adopting a configuration in which the state coincides with the polarization state of the light immediately before entering the linearly polarizing plate 22b, an ideal black display can be achieved.

Next, the second aspect of the present invention will be described.
FIG. 18 is a cross-sectional view schematically showing a liquid crystal display device according to the second aspect of the present invention. FIG. 19 is an exploded perspective view of the liquid crystal display device shown in FIG. FIG. 20 is a diagram schematically showing an example of the alignment state of liquid crystal molecules in the liquid crystal display device shown in FIG.

  The liquid crystal display device according to the second aspect is the same as the liquid crystal display device 1 according to the first aspect except that the liquid crystal display device further includes a first optical compensation film 24a and a second optical compensation film 24b.

  For example, as shown in FIG. 18, the first optical compensation film 24a is disposed between the first retardation layer 23a and the transparent substrate 211a. As shown in FIG. 20, the first optical compensation film 24a includes a uniaxial compound LC2 having a negative refractive index anisotropy, for example, a discotic molecule. In the first optical compensation film 24a, the uniaxial compound LC2 has an optical axis parallel to a plane parallel to the first direction D1 and the thickness direction of the first optical compensation film 24a, here, the Z direction. In addition, hybrid orientation is performed so that the angle formed by the optical axis and the thickness direction of the first optical compensation film 24a increases from the first retardation layer 23a side toward the transparent electrode 2112a side.

  Here, the uniaxial compound LC2 is in the region near the liquid crystal layer 212 in the first optical compensation film 24a and in the region near the first optical compensation film 24a in the optical axis of the uniaxial compound LC2 and the liquid crystal layer 212. Hybrid alignment is performed so that the angle formed by the optical axis of the liquid crystal molecule LC1 positioned at a minimum is minimized. Note that the fourth direction D4 shown in FIG. 19 for the first optical compensation film 24a is orthogonal to the plane perpendicular to the Z direction of the average optical axis of the uniaxial compound LC2 in the first optical compensation film 24a. The direction is parallel to the direction.

  For example, as shown in FIG. 18, the second optical compensation film 24b is disposed between the second retardation layer 23b and the transparent substrate 2111b. As shown in FIG. 20, the second optical compensation film 24b includes a uniaxial compound LC2 having a negative refractive index anisotropy. In the second optical compensation film 24b, the uniaxial compound LC2 is such that its optical axis is parallel to a plane parallel to the second direction D2 and the thickness direction of the second optical compensation film 24b, here the Z direction. In addition, hybrid orientation is performed such that the angle formed by the optical axis and the thickness direction of the second optical compensation film 24b increases from the second retardation layer 23b side toward the transparent electrode 2112b side.

  Here, the uniaxial compound LC2 is in the region near the liquid crystal layer 212 in the second optical compensation film 24b, and in the region near the second optical compensation film 24b in the liquid crystal layer 212 and the optical axis of the uniaxial compound LC2. Hybrid alignment is performed so that the angle formed by the optical axis of the liquid crystal molecule LC1 positioned at a minimum is minimized. Note that the fifth direction D5 shown in FIG. 19 for the second optical compensation film 24b is orthogonal to the plane perpendicular to the Z direction of the average optical axis of the uniaxial compound LC2 in the second optical compensation film 24b. The direction is parallel to the direction.

  When the configuration described with reference to FIGS. 18 to 20 is employed, a wider viewing angle can be achieved as compared with the case where the optical compensation films 24a and 24b are omitted. When the configuration described with reference to FIGS. 18 to 20 is adopted, the optical compensation films 24a and 24b are respectively arranged between the linear polarizing plate 22a and the retardation layer 23a, and between the linear polarizing plate 22b and the retardation layer 23b. A wider viewing angle can be achieved as compared with the case of being arranged between the two.

  FIG. 21 is a graph showing an example of viewing angle characteristics that can be achieved by the liquid crystal display device shown in FIG. FIG. 22 is a graph showing an example of viewing angle characteristics that can be achieved by a liquid crystal display device having the same structure as that shown in FIG. 18 except that the position of the optical compensation film is changed.

  FIG. 21 shows data obtained by performing a simulation under the following conditions.

Specifically, the following matters were assumed for the liquid crystal display device adopting the structure described with reference to FIGS. That is, the liquid crystal material has a refractive index anisotropy Δn of 0.13 for light having a wavelength of 550 nm, a dielectric anisotropy Δε of 12.7, and elastic moduli k ₁₁ , k _22, and k ₃₃ , The values were 10.5 pN, 7.1 pN, and 22.3 pN, respectively. The thickness of the liquid crystal layer was 3.8 μm, and the pretilt angle of the liquid crystal molecules was 1.0 °.

The angle −α formed by the first direction D1 with respect to the third direction D3 was −45 °, and the angle α formed by the second direction D2 with respect to the third direction D3 was 45 °. The angle −β formed by the transmission axis A _T 1 with respect to the third direction D3 was −45 °, and the angle β formed by the transmission axis A _T 2 with respect to the third direction D3 was 45 °. The angle −δ formed by the fourth direction D4 with respect to the third direction D3 was −45 °, and the angle δ formed by the fifth direction D5 with respect to the third direction D3 was 45 °.

The angle -γ formed by the slow axis A _S 1 with respect to the third direction D3 and the angle γ formed by the slow axis A _S 2 with respect to the third direction D3 are changed, and the phase difference layer 23a and The retardation of 23b was changed, and the conditions under which the transmittance in the normal direction was minimized when the applied voltage was 2.5V were determined. As a result, when the angles −γ and γ are −37 ° and 37 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 37 nm, transmission in the normal direction is performed when the applied voltage is 2.5V. The rate was minimized.

  Under these conditions, the contrast ratio corresponding to the observation direction when the maximum drive voltage was 2.5 V was obtained. FIG. 21 shows the viewing angle characteristics obtained in this way.

  FIG. 22 shows data obtained by performing a simulation under the conditions described above with reference to FIG. 21 except that the following configuration is adopted.

Specifically, here, the optical compensation films 24a and 24b are respectively disposed between the linearly polarizing plate 22a and the retardation layer 23a and between the linearly polarizing plate 22b and the retardation layer 23b. did. The angle -γ formed by the slow axis A _S 1 with respect to the third direction D3 and the angle γ formed by the slow axis A _S 2 with respect to the third direction D3 are changed, and the phase difference layer 23a and The retardation of 23b was changed, and the conditions under which the transmittance in the normal direction was minimized when the applied voltage was 2.5V were determined. As a result, when the angles −γ and γ are −138 ° and 138 °, respectively, and the retardation of each of the retardation layers 23a and 23b is 112 nm, transmission in the normal direction is performed when the applied voltage is 2.5V. The rate was minimized.

  Under these conditions, the contrast ratio corresponding to the observation direction when the maximum drive voltage was 2.5 V was obtained. FIG. 21 shows the viewing angle characteristics obtained in this way.

  As is clear from the comparison between FIG. 15 and FIG. 22, the optical compensation films 24a and 24b are respectively arranged between the linearly polarizing plate 22a and the retardation layer 23a and between the linearly polarizing plate 22b and the retardation layer 23b. When arranged, the viewing angle characteristics deteriorate. On the other hand, when the structure described with reference to FIGS. 18 to 20 is employed, a high contrast ratio can be maintained and the viewing angle can be expanded particularly in the vertical direction.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Display panel, 3 ... Gate driver, 4 ... Source driver, 5 ... Controller, 21 ... Liquid crystal cell, 22a ... 1st linear polarizing plate, 22b ... 2nd linear polarizing plate, 23a ... 1st Phase difference layer, 23b ... second phase difference layer, 24a ... first optical compensation film, 24b ... second optical compensation film, 211a ... active matrix substrate, 211b ... counter substrate, 212 ... liquid crystal layer, 2111a ... transparent substrate, 2111b ... Transparent substrate, 2112a ... Pixel electrode, 2112b ... Counter electrode, 2113a ... Alignment film, 2113b ... Alignment film, 2114 ... Gate line, 2115 ... Source line, 2116 ... Auxiliary capacitance line, 2117 ... Thin film transistor, 2118 ... Capacitor, AA ... display area, A _S 1 ... first slow axis, A _S 2 ... second slow axis, A _T 1 ... first transmission axis, A _T 2 ... second transmission shaft C1 ... Curve, C2 ... Curve, C3 ... Curve, C4 ... Curve, C5 ... Curve, C6 ... Curve, C7 ... Curve, C8 ... Curve, C9 ... Curve, C10 ... Curve, C11 ... Curve, C12 ... Curve, C13 ... Curve, D1 ... first direction, D2 ... second direction, D3 ... third direction, D4 ... fourth direction, D5 ... fifth direction, LC1 ... liquid crystal molecule, LC2 ... uniaxial compound, P1 ... polarization state, P2 ... Polarization state, P3 ... polarization state, P4 ... polarization state, P5 ... polarization state, P6 ... polarization state, P8 ... polarization state, P9 ... polarization state, P10 ... polarization state, P11 ... polarization state.

Claims (4)

First and second transparent electrodes facing each other;
A liquid crystal layer interposed between the first and second transparent electrodes and including a nematic liquid crystal material;
A first alignment film that is interposed between the first transparent electrode and the liquid crystal layer and aligns liquid crystal molecules contained in the liquid crystal material in the first direction in the vicinity of the first transparent electrode when no voltage is applied;
A second alignment film that is interposed between the second transparent electrode and the liquid crystal layer and aligns the liquid crystal molecules in a second direction in the vicinity of the second transparent electrode when no voltage is applied; Is a direction intersecting with the first direction when viewed from the thickness direction perpendicular to the main surface of the first transparent electrode, and the second alignment film is the liquid crystal layer together with the first alignment film when no voltage is applied. A second alignment film for twist-aligning the liquid crystal molecules in the film,
Facing the liquid crystal layer with the first transparent electrode and the first alignment film in between, in a third direction that bisects the angle formed by the first and second directions when viewed from the thickness direction A first linear polarizing plate having a first transmission axis obliquely intersecting with respect to the first linear polarizing plate;
The second transparent electrode and the second alignment film are opposed to the liquid crystal layer, and the first transparent axis is symmetrical with respect to the third direction when viewed from the thickness direction. A second linear polarizing plate having two transmission axes;
A first slow axis that is interposed between the first alignment film and the first linearly polarizing plate and obliquely intersects the first transmission axis and the first direction when viewed from the thickness direction. A positive A-type first retardation layer having:
A second delay layer interposed between the second alignment film and the second linearly polarizing plate and symmetrical to the first slow axis with respect to the third direction when viewed in the thickness direction. A positive A-type second retardation layer having a phase axis and providing the same retardation as the first retardation layer;
A drive circuit for applying a drive voltage having a magnitude corresponding to a gradation to be displayed between the first and second transparent electrodes;
The operation of the driving circuit is such that a lower driving voltage is applied between the first and second transparent electrodes than the voltage required for the liquid crystal material to be vertically aligned when displaying the lowest gradation. And a controller for controlling
The first linear polarizing plate was illuminated with natural light having a wavelength of 550 nm from the thickness direction in a state where the driving voltage applied when displaying the lowest gradation was applied between the first and second transparent electrodes. Sometimes, the light transmitted through the liquid crystal layer is linearly polarized at an intermediate position between the first and second alignment films, and the vibration direction of the electric field vector is inclined by 45 ° with respect to the third direction. A normally white liquid crystal display device in which the retardation of the first retardation layer and the orientation of the first slow axis are defined. A first optical compensation film comprising a uniaxial compound having a negative refractive index anisotropy interposed between the first transparent electrode and the first retardation layer, wherein the uniaxial compound has an optical property The axis is parallel to a plane parallel to the first direction and the thickness direction of the first optical compensation film, and the optical axis and the thickness direction of the first optical compensation film are formed. A first optical compensation film that is hybrid-oriented so that an angle increases from the first retardation layer side toward the first transparent electrode side;
A second optical compensation film comprising a uniaxial compound having a negative refractive index anisotropy interposed between the second transparent electrode and the second retardation layer, wherein the uniaxial compound is optical The axis is parallel to a plane parallel to the second direction and the thickness direction of the second optical compensation film, and the optical axis and the thickness direction of the second optical compensation film are formed. The liquid crystal display device according to claim 1, further comprising: a second optical compensation film that is hybrid-aligned so that an angle increases from the second retardation layer side toward the second transparent electrode side.   3. The liquid crystal display device according to claim 1, wherein the first and second directions are directions that obliquely intersect each other when viewed from a direction perpendicular to a main surface of the first transparent electrode.   3. The liquid crystal display device according to claim 1, wherein the first and second directions are directions orthogonal to each other when viewed from a direction perpendicular to a main surface of the first transparent electrode.

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