JP2009003432A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device applied with the OCB (optically compensated bend) mode capable of wide angle visualization. <P>SOLUTION: The liquid crystal display, which is provided with a plurality of pixels each of which is having a reflection part and transmission part, includes: the liquid crystal display panel 1 applied with the OCB mode, wherein the panel 1 has a liquid crystal layer held between a pair of substrates; and a pair of optical elements 40 and 50 for optically compensating retardation of the liquid crystal layer in such a specifically displaying state where the liquid crystal layer is impressed with a voltage while being arranged on each external surface of the liquid crystal display panel. The optical elements 40 and 50 include: the circular polarizers C provided with the polarizer plates PL and the first retardation plates R1 for giving 1/4 wave length phase difference while being arranged between the polarization plate PL and the liquid crystal display panel 1; and the second retardation plates R2 having the refractive index anisotropy with principal axis tilted to the normal line. Furthermore, the optical elements 40 and 50 are provided with the phase differences in the thickness directions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device using an optically compensated bend (OCB) alignment technique capable of realizing a wide viewing angle and a high response speed. About.

  Liquid crystal display devices are applied to various fields by taking advantage of features such as light weight, thinness, and low power consumption.

  In recent years, a liquid crystal display device using an OCB mode has attracted attention as a liquid crystal display device capable of improving the viewing angle and the response speed. Such an OCB mode liquid crystal display device has a configuration in which a liquid crystal layer including liquid crystal molecules that are bend-aligned in a state where a predetermined voltage is applied between a pair of substrates is held. Such an OCB mode can increase the response speed compared to the twisted nematic (TN) mode, and optically influences the birefringence of light passing through the liquid crystal layer depending on the alignment state of the liquid crystal molecules. Since self-compensation is possible, there is an advantage that the viewing angle can be expanded.

In recent years, a liquid crystal display device using an OCB mode has been developed in a transflective liquid crystal display device having a reflective portion and a transmissive portion. For example, Patent Document 1 discloses a circularly polarizing plate applicable to an OCB mode transflective liquid crystal display device. This circularly polarizing plate includes a polarizing plate and a liquid crystal film having a nematic hybrid alignment structure fixed as an optically anisotropic element.
JP 2005-164957 A

  However, at present, the optimization of the circularly polarizing plate applied when optical design peculiar to the OCB mode is not sufficiently discussed, and in particular, a high contrast ratio (for example, when transmissive display is performed) There is a problem that the viewing angle at which CR = 10: 1 or more is obtained is narrow.

  An object of the present invention is to provide a transflective liquid crystal display device to which an OCB mode capable of wide viewing angle is applied.

A liquid crystal display device according to an aspect of the present invention includes:
In a liquid crystal display device having a reflective portion and a transmissive portion in each of a plurality of pixels arranged in a matrix,
A liquid crystal display panel using an OCB mode configured to hold a liquid crystal layer between a pair of substrates;
A pair of optical elements that are arranged on the respective outer surfaces of the liquid crystal display panel and optically compensate for retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer;
The optical element is
A circularly polarizing element having a polarizing plate and a first retardation plate disposed between the polarizing plate and the liquid crystal display panel to give a quarter-wave phase difference;
A second retardation plate disposed between the circularly polarizing element and the liquid crystal layer and having a refractive index anisotropy having a principal axis inclined with respect to a normal line;
And further having a phase difference in the thickness direction.

  According to the present invention, it is possible to provide a transflective liquid crystal display device to which an OCB mode capable of wide viewing angle is applied.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, as the liquid crystal display device, a transmissive portion that displays an image by selectively transmitting backlight light in one pixel and a reflective portion that displays an image by selectively reflecting external light are provided. A transflective liquid crystal display device to which the OCB mode configured as described above is applied will be described.

  As shown in FIG. 1, the liquid crystal display device includes a liquid crystal display panel 1 to which the OCB mode is applied, and a pair of optical elements disposed on the outer surfaces of the liquid crystal display panel 1, that is, a first optical element 40 and a second optical element. 50. Further, the liquid crystal display device includes a backlight 60 that illuminates the liquid crystal display panel 1 from the first optical element 40 side. That is, the first optical element 40 is disposed between the liquid crystal display panel 1 and the backlight 60.

  2 and 3, the liquid crystal display panel 1 includes a pair of substrates, that is, an array substrate (a substrate facing the first optical element 40) 10 and a counter substrate (a substrate facing the second optical element 50, or A liquid crystal layer 30 is held between the viewing side substrate) 20 and an active area DSP for displaying an image. The active area DSP has a substantially rectangular shape, and includes a plurality of pixels PX arranged in a matrix.

  Each of the pixels PX has a reflection part PR that displays an image by selectively reflecting external light in the reflective display mode, and an image that selectively transmits backlight light from the backlight 60 in the transmissive display mode. And a transmissive portion PT for displaying.

  The array substrate 10 is formed using an insulating substrate 11 having optical transparency such as glass. The array substrate 10 includes a plurality of scanning lines Sc and columns of pixels PX arranged on one main surface of the insulating substrate 11, that is, a surface facing the liquid crystal layer 30 so as to extend along the row direction of the pixels PX. A plurality of signal lines Sg arranged so as to extend along the direction, a switching element 12 arranged for each pixel PX in the vicinity of the intersection of the scanning line Sc and the signal line Sg, and a pixel PX connected to the switching element 12 Each pixel electrode 13 is provided, and an alignment film 16 is provided so as to cover the pixel electrode 13.

  The scanning line Sc and the signal line Sg are arranged so as to intersect with each other via an insulating film.

  The switch element 12 is configured by, for example, a thin film transistor (TFT). The switch element 12 has a semiconductor layer formed of polysilicon, amorphous silicon, or the like. The gate of the switch element 12 is electrically connected to the corresponding scanning line Sc (or formed integrally with the corresponding scanning line). The source of the switch element 12 is electrically connected to the corresponding signal line Sg (or formed integrally with the corresponding signal line).

  The pixel electrode 13 is disposed on the insulating film 14. The insulating film 14 forms a gap difference of the liquid crystal layer 3 between the reflection part PR and the transmission part PT. Each pixel electrode 13 includes a reflective electrode 13R provided corresponding to the reflective part PR and a transmissive electrode 13T provided corresponding to the transmissive part PT. The reflective electrode 13R is formed of a light reflective conductive material such as aluminum. The transmissive electrode 13T is made of a light-transmitting conductive material such as indium tin oxide (ITO). The reflective electrode 13R and the transmissive electrode 13T are electrically connected to the drain of the switch element 12.

  The counter substrate 20 is formed using an insulating substrate 21 having optical transparency such as glass. The counter substrate 20 covers the counter electrode 22 and the counter electrode 22 which are arranged on one main surface of the insulating substrate 21, that is, the surface facing the liquid crystal layer 30 so as to be opposed to the pixel electrodes 13 of the plurality of pixels PX. , And the like. The counter electrode 22 is formed of a light-transmitting conductive material such as ITO.

  The array substrate 10 and the counter substrate 20 having the above-described configuration are interposed via spacers (not shown) (for example, columnar spacers integrally formed on one substrate) so that the alignment films 16 and 23 face each other. It arrange | positions in the state which maintained the predetermined gap mutually, and is bonded together by the sealing material. The liquid crystal layer 30 is sealed in a gap between the array substrate 10 and the counter substrate 20.

  In this embodiment, the liquid crystal display panel 1 is configured to apply an OCB mode, and the liquid crystal layer 30 includes liquid crystal molecules 31 having positive dielectric anisotropy and optically positive uniaxiality. It is composed of a liquid crystal material. In the liquid crystal layer 30, the liquid crystal molecules 31 are bend-oriented between the array substrate 10 and the counter substrate 20 in a predetermined display state where a voltage is applied to the liquid crystal layer 30, and in the example shown in FIG. In the transmission part PT and the reflection part PR, the liquid crystal molecules 31 are bend aligned.

In particular, in the liquid crystal display panel 1 to which the OCB mode is applied, as shown in FIG. 4, the cell gap dR in the reflection part PR is less than ½ of the cell gap dT in the transmission part, that is,
dR <dT / 2
Is set to Here, the cell gap substantially corresponds to the thickness of the liquid crystal layer 30 between the alignment film 16 of the array substrate 10 and the alignment film 23 of the counter substrate 20.

  That is, the alignment film and the liquid crystal layer are both dielectrics disposed between the pixel electrode 13 and the counter electrode 22. The liquid crystal material applied to the OCB mode has a relatively high relative dielectric constant (ε), for example, 14 or more. For this reason, when a voltage is applied between the pixel electrode 13 and the counter electrode 22 so that a predetermined voltage is applied to the liquid crystal layer of the transmission part PT, the alignment film 16 has a capacitance C30 of the liquid crystal layer 30. Since the contribution of the capacitor C16 and the capacitor C23 of the alignment film 23 is high, when the cell gap dR of the reflective part PR is set to ½ of the cell gap dT of the transmissive part PT, the liquid crystal layer 30 of the reflective part PR Cannot apply a necessary and sufficient voltage. For this reason, it is important to set the cell gap dR of the reflection part PR to be smaller than ½ of the cell gap dT of the transmission part PT, and to increase the ratio of the voltage distributed to the liquid crystal layer 30 in the reflection part PR. That is, the cell gap dR of the reflective part PR is set to a value that allows a sufficient voltage to be applied to the liquid crystal layer 30 of the reflective part PR.

  In this embodiment, the cell gap dT of the transmission part PT is 4.65 μm, and the cell gap dR of the reflection part PR is 2.1 μm which is smaller than ½ of the cell gap dT.

<< First Embodiment >>
First, the liquid crystal display device according to the first embodiment will be described. In the first embodiment, the first optical element 40 and the second optical element 50 perform retardation of the liquid crystal layer 30 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 in the liquid crystal display panel 1 as described above. It has a function to compensate optically. The first optical element 40 and the second optical element 50 are configured to have a phase difference in the thickness direction.

  As shown in FIG. 1, the first optical element 40 is disposed on the outer surface of the array substrate 10, and the second optical element 50 is disposed on the outer surface of the counter substrate 20. The first optical element 40 and the second optical element 50 have the same configuration. That is, the first optical element 40 and the second optical element 50 each include a circularly polarizing element C having a polarizing plate PL and a first retardation plate R1, a second retardation plate R2, and a third retardation plate R3. Configured. Further, the first optical element 40 and the second optical element 50 have a symmetric configuration with respect to the liquid crystal display panel 1. That is, in the first optical element 40 and the second optical element 50, the second retardation plate R2, the third retardation plate R3, the first retardation plate R1, and the polarizing plate PL are laminated in this order from the liquid crystal display panel 1 side. Has been.

  The polarizing plate PL has a configuration in which a polarizing layer formed of polyvinyl alcohol (PVA) or the like is held between a pair of support layers formed of, for example, triacetate cellulose (TAC) or the like. It has orthogonal transmission and absorption axes.

  The first retardation plate R1 is disposed between the polarizing plate PL and the liquid crystal display panel 1, and has a fast axis and a slow axis that are substantially orthogonal to each other in the plane. The first retardation plate R1 is a so-called quarter-wave plate that gives a quarter-wave phase difference between light of a predetermined wavelength (for example, light with a wavelength of 550 nm) that passes through the fast axis and the slow axis. is there. Such a combination of the polarizing plate PL and the first retardation plate (¼ wavelength plate) R1 is ideally a circle that converts linearly polarized light having a predetermined wavelength that has passed through the transmission axis of the polarizing plate PL into circularly polarized light. Functions as a polarizing plate.

  The second retardation plate R2 is disposed between the circularly polarizing element C and the liquid crystal display panel 1, and has a fast axis and a slow axis that are substantially orthogonal to each other. The second retardation plate R2 is an anisotropic film that compensates for the retardation of the liquid crystal layer 30. When the total refractive index anisotropy of the second retardation plate R2 itself is taken into consideration, the substantial retardation axis. Is an anisotropic film having refractive index anisotropy inclined with respect to the normal. As such second retardation plate R2, for example, a WV (wide view) film (manufactured by Fuji Photo Film Co., Ltd.) is applicable. This WV film is a hybrid alignment of discotic liquid crystal molecules having optically negative uniaxial refractive index anisotropy along the normal direction (that is, the thickness direction of the retardation plate) in the liquid crystal state. This is a liquid crystal film that is fixed in such a state (that is, a state in which the main axis is in a hybrid orientation). Such a second retardation plate R2 is a retardation plate equivalent to an A plate having a retardation in its plane, and optically compensates for the viewing angle dependence of the refractive index anisotropy of bend-aligned liquid crystal molecules. To do.

  The third retardation plate R3 is a retardation plate equivalent to a C plate that is disposed between the circularly polarizing element C and the second retardation plate R2 and has a retardation in the thickness direction thereof. In other words, the third retardation plate R3 has nx = ny> nz, where nx and ny are the refractive indexes of the directions orthogonal to each other in the in-plane direction, and nz is the refractive index of the normal direction. It has a refractive index anisotropy of (optically negative). That is, in the first embodiment, the retardation in the thickness direction of the optical element is provided by the third retardation plate R3. That is, the third retardation plate R3 compensates for the shortage of the refractive index (nz) in the thickness direction necessary for optical compensation by the second retardation plate R2.

  In the liquid crystal display device as described above, the respective components are arranged at the following axial angles, for example, with the rubbing direction of the alignment film 16 of the array substrate 10 and the alignment film 23 of the counter substrate 20 as the reference orientation. The axis angle is an angle formed by the absorption axis of the polarizing plate and the slow axis of the retardation film counterclockwise with respect to the reference orientation (X axis), and is defined by FIG. That is, when the liquid crystal display device is observed from the counter substrate 20 side, an X axis and a Y axis orthogonal to each other are defined for convenience in a plane parallel to the main surface of the array substrate 10 (or the counter substrate 20). The normal direction is defined as the Z axis. The in-plane corresponds to an XY plane defined by the X axis and the Y axis. The rubbing directions of the alignment film 16 and the alignment film 23 are parallel to the X axis, and the liquid crystal molecules 31 of the liquid crystal layer 30 are bend-aligned in the XZ plane.

  FIG. 6 shows a configuration example of the first embodiment.

  That is, in the liquid crystal display panel 1, the rubbing direction of the liquid crystal layer 30 is set to 0 ° azimuth. In each pixel PX, the cell gap dT of the transmissive part PT is set to 4.65 μm, and the cell gap dR of the reflective part PR is set to 2.1 μm. The pretilt angle Θp of the liquid crystal molecules in the liquid crystal layer 30 is set to 7 °.

  In the first optical element 40 on the array substrate side, the polarizing plate PL is arranged so that the absorption axis thereof faces the 0 ° azimuth. The first retardation plate R1 is arranged so that its slow axis faces the 135 ° azimuth. The second retardation plate R2 is a retardation plate in which discotic liquid crystal molecules are hybrid-aligned along the thickness direction, and the average tilt angle of the principal axis of the discotic liquid crystal molecules is 30 ° with respect to the normal line. Is set. The second retardation plate R2 is arranged so that the orthogonal projection of the overall principal axis onto the XY plane is parallel to the rubbing direction. That is, the inclination direction of the main axis of the second retardation plate R2 is set to 0 ° azimuth.

  In the second optical element 50 on the counter substrate side, the polarizing plate PL is disposed so that the absorption axis thereof faces the 90 ° azimuth. The first retardation plate R1 is arranged such that its slow axis faces the 45 ° azimuth. The second retardation plate R2 is set so that the inclination direction of the main axis thereof is directed to the 0 ° azimuth.

  Thus, in the first embodiment, in particular, the first retardation plate R1 of each of the first optical element 40 and the second optical element 50 has a slow axis of 45 ° with respect to the rubbing direction. None, and the slow axes are arranged so as to be orthogonal to each other. This makes it possible to reduce the influence of the wavelength dispersion of the first retardation plate R1 itself, and in particular, the contrast due to the wavelength dependency when the liquid crystal display device is observed from the front (normal direction of the liquid crystal display panel). It is possible to suppress the decrease.

  In addition, the polarizing plate PL included in each of the first optical element 40 and the second optical element 50 has an absorption axis of 45 ° with respect to the slow axis of the first retardation plate R1 constituting the circularly polarizing element. They are arranged at an angle and the respective absorption axes are orthogonal to each other.

  In addition, about the 1st optical element 40 and the 2nd optical element 50, the retardation value of each structure is as follows. Here, the retardation value at a wavelength of 550 nm is shown. That is, the retardation R of the first retardation plate R1 is 137.5 nm, the retardation (in-plane retardation) Re of the second retardation plate R2 is 45 nm, and the retardation (thickness direction position) of the third retardation plate R3. (Phase difference) Rth is 130 nm. Here, the retardation values of the first optical element 40 and the second optical element 50 arranged via the liquid crystal layer 30 are made equal, but in the present invention, the retardation values may not be equal.

  According to the first embodiment as described above, in the OCB mode transflective liquid crystal display device having the functions of reflection display by the reflection unit and transmission display by the transmission unit, the optical element including the circular polarization element C and the OCB The overall optical design with the liquid crystal display panel in the mode has been optimized, and in both the reflective display and the transmissive display, a high contrast ratio display can be realized not only in the front direction but also when viewed from an oblique direction. The viewing angle can be expanded.

  Next, the effects of the above configuration example of the first embodiment were verified.

  FIG. 7 shows the result of simulating the viewing angle dependence of the contrast ratio in the transmissive display in the liquid crystal display device of the first embodiment. Here, the center of the concentric circle corresponds to the normal direction (Z-axis) of the liquid crystal display panel, and the concentric circles centered on the normal direction are inclination angles (viewing angles) with respect to the normal, and are 20 °, 40 °, respectively. It corresponds to 60 ° and 80 °. The characteristic diagram shown here is obtained by connecting regions having the same contrast ratio (CR) for each orientation, and in particular, a region having a contrast ratio = 100: 1 and a region having a contrast ratio = 10: 1. It is shown.

  As shown in FIG. 7, according to the configuration example of the first embodiment, a contrast ratio = 10: 1 or more can be obtained in a range where the viewing angle is 60 ° or more, and 0 ° − With regard to the 180 ° azimuth and 90 ° -270 ° azimuth, it was confirmed that a contrast ratio = 10: 1 or more was obtained in the range of the viewing angle of 80 ° or more, and a sufficient viewing angle was obtained.

<< Second Embodiment >>
Next, a liquid crystal display device according to a second embodiment will be described. In the second embodiment, the first optical element 40 and the second optical element 50 are in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 in the liquid crystal display panel 1 as described above, as in the first embodiment. The liquid crystal layer 30 has a function of optically compensating for retardation of the liquid crystal layer 30. In particular, in the second embodiment, the circularly polarizing element C provided in one of the first optical element 40 and the second optical element 50 is disposed between the polarizing plate PL and the first retardation plate R1. And a fourth retardation plate R4. That is, the first optical element 40 and the second optical element 50 have an asymmetric configuration with respect to the liquid crystal display panel 1.

  In the example shown in FIG. 8, the circularly polarizing element C of the second optical element 50 disposed on the counter substrate 20 side (that is, the observation surface side) with respect to the liquid crystal display panel 1 includes the polarizing plate PL and the fourth phase difference. Although the plate R4 and the first retardation plate R1 are included, the circularly polarizing element C of the first optical element 40 may include the fourth retardation plate R4. Other configurations are the same as those in the first embodiment.

  The fourth retardation plate R4 has a fast axis and a slow axis that are substantially orthogonal to each other, and light having a predetermined wavelength that passes through the fast axis and the slow axis (for example, light having a wavelength of 550 nm). It is a so-called half-wave plate that gives a half-wave phase difference between the two. The fourth retardation plate R4 has a function of expanding the viewing angle by compensating for the viewing angle dependence of the retardation of the entire liquid crystal display device. In particular, the fourth retardation plate R4 is used in an OCB mode transflective liquid crystal display device. It is configured so as to mainly compensate for the viewing angle dependency of the retardation of the required quarter-wave plate (first retardation plate R1) of the circularly polarizing element C.

  That is, in the first embodiment described above, particularly when transmissive display is performed, a good display with high contrast is observed in the front. This is because the first retardation plate R1 functions as a quarter-wave plate for imparting a quarter-wave retardation to the light passing through it, and forms an ideal circularly polarized light in combination with the polarizing plate PL. This is because the optical design is performed.

  However, when transmissive display is performed, when viewing from an oblique direction, there is a limit to the viewing angle at which a high contrast ratio can be obtained. For example, in the example illustrated in FIG. 7, the viewing angles in the 45 ° -225 ° azimuth and the 135 ° -315 ° azimuth are narrower than the 0 ° -180 ° azimuth and the 90 ° -270 ° azimuth. This is mainly because the retardation of the first retardation plate R1 depends on the viewing angle, and the function as a quarter-wave plate cannot be obtained at a viewing angle in a certain direction (that is, the first retardation plate R1 itself is not used). This is because it becomes impossible to give a quarter-wave retardation to the light passing through the light. For this reason, at a certain viewing angle, an ideal circularly polarized light cannot be formed by the combination of the first retardation plate R1 and the polarizing plate PL, and a high contrast display cannot be obtained.

  Here, only the viewing angle dependency of the first retardation plate R1 has been described, but other configurations may also have the viewing angle dependency, as in the example shown in FIG. These complex factors can be considered as a cause of narrowing the viewing angle.

  Therefore, in this second embodiment, in order to compensate for the viewing angle dependency of the retardation of not only the first retardation plate R1 but the entire liquid crystal display device, even when observed from an oblique direction, it becomes an ideal circularly polarized light. The fourth retardation plate R4 is arranged so that retardation that can be approached can be provided. Thereby, the viewing angle at which a high contrast ratio can be obtained can be further expanded as compared with the first embodiment.

  FIG. 9 shows a configuration example of the second embodiment. The configuration other than the fourth retardation plate R4 is the same as the configuration example of the first embodiment shown in FIG.

  In this configuration example, the fourth retardation plate R4 has a biaxial refractive index anisotropy. That is, the fourth retardation plate R4 has a refractive index anisotropy of nx> ny> nz. In the second optical element 50, the fourth retardation plate R4 is disposed so that its slow axis faces the 90 ° azimuth. That is, the slow axis of the fourth retardation plate R4 and the absorption axis of the polarizing plate PL are set in parallel.

  For this reason, there is no influence of retardation of the fourth retardation plate R4 in the front direction, and a good display with high contrast is observed as in the first embodiment. In addition, when observed from an oblique direction, the retardation of the fourth retardation plate R4 acts effectively, so that the viewing angle dependence of the retardation of the entire liquid crystal display device can be compensated, and ideal circularly polarized light Therefore, it is possible to observe a high-contrast good display in a wide viewing angle range.

  For the first optical element 40 and the second optical element 50, the retardation value of each component is as shown in FIG. Here, as in the first embodiment, the retardation value at a wavelength of 550 nm is shown. The retardation R of the fourth retardation plate R4 is 275 nm, and the Nz coefficient given by Nz = (nx−nz) / (nx−ny) is set to 0.4.

  Here, with respect to the Nz coefficient of the fourth retardation plate R4, in particular, a retardation is provided so that the viewing angle of 60 ° or more with respect to the 45 ° -225 ° azimuth and the 135 ° -315 ° azimuth becomes close to ideal circularly polarized light. Therefore, it is desirable to set the Nz coefficient to 0.3 or more. In order to prevent over-compensation beyond the ideal circularly polarized light, it is desirable to set the Nz coefficient of the fourth retardation plate R4 to 0.6 or less.

  According to the second embodiment as described above, in the OCB mode transflective liquid crystal display device having the functions of reflection display by the reflection part and transmission display by the transmission part, the optical element including the circular polarization element and the OCB mode are provided. The overall optical design of the LCD panel has been optimized, and in both reflective and transmissive displays, high contrast ratio display can be achieved even when viewed from an oblique direction as well as in the front direction. Can be further expanded.

  Next, the effects of the configuration example of the second embodiment were verified.

  FIG. 10 shows the result of simulating the viewing angle dependence of the contrast ratio in transmissive display in the liquid crystal display device of the second embodiment. According to the configuration example of the second embodiment, it was confirmed that the contrast ratio = 10: 1 or more was obtained in the range where the viewing angle was 80 ° or more, and a sufficient viewing angle was obtained for all directions of the screen. Further, the area of the viewing angle with the contrast ratio = 10: 1 or more was 1.14 times that of the first embodiment.

  In the second embodiment described above, the fourth retardation plate R4 is disposed on the second optical element 50 on the counter substrate 20 side (viewing side), so that the fourth retardation is used not only in transmissive display but also in reflective display. Although the plate R4 acts, it does not affect the characteristics particularly in the reflective display. In order to effectively operate the fourth retardation plate R4 only for transmissive display, the polarizing plate PL constituting the circularly polarizing element C in the first optical element 40 on the array substrate 10 side (light incident side / backlight side). It is desirable to arrange the fourth retardation plate R4 between the first retardation plate R1 and the first retardation plate R1.

<< Third Embodiment >>
Next, a liquid crystal display device according to a third embodiment will be described. In the third embodiment, the fourth retardation plate R4 has a biaxial refractive index anisotropy. That is, the fourth retardation plate R4 has a refractive index anisotropy of nx>ny> nz. In the second optical element 50, the fourth retardation plate R4 is disposed between the polarizing plate PL and the first retardation plate R1, and is disposed such that its slow axis faces the 0 ° azimuth. . That is, the positional relationship between the slow axis of the fourth retardation plate R4 and the absorption axis of the polarizing plate PL is different from that of the second embodiment, and the fourth retardation plate R4 has the slow axis of absorption of the polarizing plate PL. It arrange | positions so that an axis | shaft may be orthogonally crossed.

  FIG. 11 shows a configuration example of the third embodiment. The configuration other than the fourth retardation plate R4 is the same as the configuration example of the second embodiment shown in FIG.

  In the third embodiment, the retardation R of the fourth retardation plate R4 is, for example, 275 nm as in the second embodiment, and is 0.4 or more so that the Nz coefficient has an inverse relationship. By setting it to .7 or less, the same effect as the above configuration example can be obtained. Here, the Nz coefficient of the fourth retardation plate R4 is set to 0.7, for example.

  In the third embodiment, when the viewing angle dependence of the contrast ratio in the transmissive display is simulated, as in the second embodiment, the contrast ratio = within a range of viewing angles of 80 ° or more for all azimuths of the screen. 10: 1 or more was obtained, and it was confirmed that a sufficient viewing angle was obtained.

<< 4th Embodiment >>
Next, a liquid crystal display device according to a fourth embodiment will be described. In the fourth embodiment, the first optical element 40 and the second optical element 50 perform retardation of the liquid crystal layer 30 in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 in the liquid crystal display panel 1 as described above. It has a function to compensate optically. The first optical element 40 and the second optical element 50 are configured to have a phase difference in the thickness direction.

  As shown in FIG. 12, the first optical element 40 is disposed on the outer surface of the array substrate 10, and the second optical element 50 is disposed on the outer surface of the counter substrate 20. The first optical element 40 and the second optical element 50 have the same configuration. That is, the first optical element 40 and the second optical element 50 are configured to include the circularly polarizing element C having the polarizing plate PL and the first retardation plate R1, and the second retardation plate R2, respectively. Further, the first optical element 40 and the second optical element 50 have a symmetric configuration with respect to the liquid crystal display panel 1. That is, in the first optical element 40 and the second optical element 50, the second retardation plate R2, the first retardation plate R1, and the polarizing plate PL are laminated in this order from the liquid crystal display panel 1 side.

  In particular, in the fourth embodiment, the first retardation plate R1 has a biaxial refractive index anisotropy, that is, has a refractive index anisotropy of nx> ny> nz. is doing. In the first retardation plate R1, the refractive index anisotropy is equivalent to a widely used quarter-wave plate having a uniaxial refractive index anisotropy and a C plate having a retardation in the thickness direction. It is set so as to have the function of the other retardation plate. That is, in the fourth embodiment, the retardation in the thickness direction of the optical element is provided by the first retardation plate R1.

  The second retardation plate R2 is the same as that applied in the first embodiment.

  FIG. 13 shows a configuration example of the fourth embodiment.

  That is, the configuration of the liquid crystal display panel 1 is the same as that of the first embodiment.

  In the first optical element 40 on the array substrate side, the polarizing plate PL is arranged so that the absorption axis thereof faces the 0 ° azimuth. The first retardation plate R1 is arranged so that its slow axis faces the 135 ° azimuth. The second retardation plate R2 is a retardation plate in which discotic liquid crystal molecules are hybrid-aligned along the thickness direction, and the average tilt angle of the principal axis of the discotic liquid crystal molecules is 30 ° with respect to the normal line. Is set. The second retardation plate R2 is arranged so that the orthogonal projection of the overall principal axis onto the XY plane is parallel to the rubbing direction. That is, the inclination direction of the main axis of the second retardation plate R2 is set to 0 ° azimuth.

  In the second optical element 50 on the counter substrate side, the polarizing plate PL is disposed so that the absorption axis thereof faces the 90 ° azimuth. The first retardation plate R1 is arranged such that its slow axis faces the 45 ° azimuth. The second retardation plate R2 is set so that the inclination direction of the main axis thereof is directed to the 0 ° azimuth.

  As described above, in the fourth embodiment, in particular, each of the first retardation plates R1 of the first optical element 40 and the second optical element 50 has an angle of 45 ° with respect to the rubbing direction of each slow axis. None, and the slow axes are arranged so as to be orthogonal to each other. This makes it possible to reduce the influence of the wavelength dispersion of the first retardation plate R1 itself, and in particular, the contrast due to the wavelength dependency when the liquid crystal display device is observed from the front (normal direction of the liquid crystal display panel). It is possible to suppress the decrease.

  In addition, the polarizing plate PL included in each of the first optical element 40 and the second optical element 50 has an absorption axis of 45 ° with respect to the slow axis of the first retardation plate R1 constituting the circularly polarizing element. They are arranged at an angle and the respective absorption axes are orthogonal to each other.

  In addition, about the 1st optical element 40 and the 2nd optical element 50, the retardation value of each structure is as follows. Here, the retardation value at a wavelength of 550 nm is shown. That is, the retardation R of the first retardation plate R1 is 137.5 nm, and the Nz coefficient is set to 2.5. The retardation (in-plane retardation) Re of the second retardation plate R2 is 45 nm. Here, the retardation values of the first optical element 40 and the second optical element 50 arranged via the liquid crystal layer 30 are made equal, but in the present invention, the retardation values may not be equal.

  Here, regarding the Nz coefficient of the first retardation plate R1, the Nz coefficient is preferably set to 2.3 or more and 2.7 or less. This is because the retardation in the thickness direction becomes too small when the Nz coefficient is smaller than 2.3, and the retardation in the thickness direction becomes too large when the Nz coefficient is larger than 2.7. This is because becomes smaller.

  According to the fourth embodiment as described above, in the OCB mode transflective liquid crystal display device having the functions of reflection display by the reflection part and transmission display by the transmission part, the number of members constituting the optical element is reduced. In addition, it is possible to optimize the overall optical design of the optical element including the circularly polarizing element and the OCB mode liquid crystal display panel. As a result, the cost can be reduced, and in both the reflective display and the transmissive display, a display with a high contrast ratio can be realized not only when viewed from the front but also from an oblique direction, and a viewing angle at which a high contrast ratio can be obtained. Can be expanded.

<< 5th Embodiment >>
Next, a liquid crystal display device according to a fifth embodiment will be described. In the fifth embodiment, the first optical element 40 and the second optical element 50 are in a predetermined display state in which a voltage is applied to the liquid crystal layer 30 in the liquid crystal display panel 1 as described above, as in the fourth embodiment. In the fifth embodiment, the circularly polarizing element C provided in one of the first optical element 40 and the second optical element 50 has a function of optically compensating for the retardation of the liquid crystal layer 30. Has a fourth retardation plate R4 disposed between the polarizing plate PL and the first retardation plate R1. That is, the first optical element 40 and the second optical element 50 have an asymmetric configuration with respect to the liquid crystal display panel 1.

  In the example illustrated in FIG. 14, the circularly polarizing element C of the first optical element 40 disposed on the array substrate 10 side with respect to the liquid crystal display panel 1 includes the polarizing plate PL, the fourth retardation plate R4, and the first optical element 40. Although the retardation plate R1 is included, the circularly polarizing element C of the second optical element 50 may include the fourth retardation plate R4. Other configurations are the same as those in the fourth embodiment.

  The fourth retardation plate R4 has a fast axis and a slow axis that are substantially orthogonal to each other, and light having a predetermined wavelength that passes through the fast axis and the slow axis (for example, light having a wavelength of 550 nm). It is a so-called half-wave plate that gives a half-wave phase difference between the two. The fourth retardation plate R4 has a function of expanding the viewing angle by compensating for the viewing angle dependence of the retardation of the entire liquid crystal display device. In particular, the fourth retardation plate R4 is used in an OCB mode transflective liquid crystal display device. It is configured so as to mainly compensate for the viewing angle dependency of the retardation of the required quarter-wave plate (first retardation plate R1) of the circularly polarizing element C. Of course, the configuration other than the first retardation plate R1 may also have viewing angle dependency, and these complex factors can be considered as the cause of the narrow viewing angle.

  Therefore, in the fifth embodiment, when transmissive display is performed, observation is performed from an oblique direction so as to compensate for the viewing angle dependency of the retardation of the entire liquid crystal display device as well as the first retardation plate R1. Even so, the fourth retardation plate R4 is arranged so that retardation can be provided so as to approach the ideal circularly polarized light. Thereby, the viewing angle at which a high contrast ratio can be obtained can be further expanded as compared with the fourth embodiment.

  FIG. 15 shows a configuration example of the fifth embodiment. The configuration other than the fourth retardation plate R4 is the same as the configuration example of the fourth embodiment shown in FIG.

  In this configuration example, the fourth retardation plate R4 has a biaxial refractive index anisotropy. That is, the fourth retardation plate R4 has a refractive index anisotropy of nx> ny> nz. In the first optical element 40, the fourth retardation plate R4 is arranged so that its slow axis faces the 0 ° azimuth. That is, the slow axis of the fourth retardation plate R4 and the absorption axis of the polarizing plate PL are set in parallel.

  For this reason, in the front direction, there is no influence of the retardation of the fourth retardation plate R4, and a good display with high contrast is observed as in the fourth embodiment. In addition, when observed from an oblique direction, the retardation of the fourth retardation plate R4 acts effectively, so that the viewing angle dependence of the retardation of the entire liquid crystal display device can be compensated, and ideal circularly polarized light Therefore, it is possible to observe a high-contrast good display in a wide viewing angle range.

  In addition, about the 1st optical element 40 and the 2nd optical element 50, the retardation value of each structure is as having shown in FIG. Here, as in the fourth embodiment, the retardation value at a wavelength of 550 nm is shown. For the fourth retardation plate R4, the retardation R is 275 nm, and the Nz coefficient is set to 0.6.

  Here, with respect to the Nz coefficient of the fourth retardation plate R4, in particular, a retardation is provided so that the viewing angle of 60 ° or more with respect to the 45 ° -225 ° azimuth and the 135 ° -315 ° azimuth becomes close to ideal circularly polarized light. Therefore, it is desirable to set the Nz coefficient to 0.5 or more. In order to prevent over-compensation beyond the ideal circularly polarized light, it is desirable to set the Nz coefficient of the fourth retardation plate R4 to 0.7 or less.

  According to the fifth embodiment as described above, in the OCB mode transflective liquid crystal display device having the functions of reflection display by the reflection part and transmission display by the transmission part, the number of members constituting the optical element is reduced. However, as compared with the fourth embodiment, it is possible to further optimize the overall optical design of the optical element including the circularly polarizing element and the OCB mode liquid crystal display panel. As a result, the cost can be reduced, and in both the reflective display and the transmissive display, a display with a high contrast ratio can be realized not only when viewed from the front but also from an oblique direction, and a viewing angle at which a high contrast ratio can be obtained. Can be further expanded.

  In addition, this invention is not limited to the said embodiment itself, In the stage of implementation, it can change and implement a component within the range which does not deviate from the summary. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  For example, the first optical element 40 and the second optical element 50 described above may be disposed outside the liquid crystal layer 30. That is, the first optical element 40 is not limited to the configuration of the above-described embodiment, but the first retardation plate that constitutes the first optical element 40 between the insulating substrate 11 that constitutes the array substrate 10 and the liquid crystal layer 30. At least one of R1, third retardation plate R3, and second retardation plate R2 may be disposed. Further, the second optical element 50 is not limited to the configuration of the above-described embodiment, but the first retardation plate that constitutes the second optical element 50 between the insulating substrate 21 that constitutes the counter substrate 20 and the liquid crystal layer 30. At least one of R1, third retardation plate R3, and second retardation plate R2 may be disposed.

  In the first to third embodiments, the third phase difference R3 is composed of one optically negative C plate. However, the third phase difference R3 is composed of two A plates arranged so that the slow axes are orthogonal to each other. It may be configured.

  Further, in each of the above-described embodiments, the retardation Rth of the third retardation plate R3 is the case where the main display is the transmission part, that is, the area of the transmission part is larger than the area of the reflection part (for example, the transmission part The area of the reflection part is 4 times the area of the reflection part), and the phase difference is canceled in the transmission part. However, when the main display is the reflection part, that is, when the area of the reflection part is larger than the area of the transmission part, the retardation Rth of the third retardation plate R3 constituting the second optical element 50 is You may optimize so that a phase difference may be canceled. Further, the retardation Rth of the third retardation plate R3 constituting the second optical element 50 is set so as to be optimized in the reflecting portion, while the retardation Rth of the third retardation plate R3 constituting the first optical element 40 is set. May be optimized in cooperation with the third retardation plate on the second optical element side so as to cancel the phase difference even in transmissive display.

FIG. 1 schematically shows a configuration of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a configuration of a liquid crystal display panel applicable to the liquid crystal display device shown in FIG. FIG. 3 is a diagram schematically showing a configuration of an OCB mode transflective liquid crystal display panel applicable to the liquid crystal display device shown in FIG. FIG. 4 is a diagram for explaining the relationship between the alignment film capacitance and the liquid crystal capacitance between the reflection portion and the transmission portion. FIG. 5 is a diagram for explaining the definition of the axis angle with respect to the rubbing direction of the alignment film in the liquid crystal display device shown in FIG. FIG. 6 is a diagram for explaining a configuration example of the liquid crystal display device according to the first embodiment. FIG. 7 is a diagram showing the result of simulating the viewing angle dependence of the contrast ratio during transmissive display in the liquid crystal display device according to the first embodiment. FIG. 8 is a diagram schematically showing the configuration of the liquid crystal display device according to the second embodiment. FIG. 9 is a diagram for explaining a configuration example of the liquid crystal display device according to the second embodiment. FIG. 10 is a diagram showing the result of simulating the viewing angle dependence of the contrast ratio during transmissive display in the liquid crystal display device according to the second embodiment. FIG. 11 is a diagram for explaining a configuration example of the liquid crystal display device according to the third embodiment. FIG. 12 is a diagram schematically showing the configuration of the liquid crystal display device according to the fourth embodiment. FIG. 13 is a diagram for explaining a configuration example of the liquid crystal display device according to the fourth embodiment. FIG. 14 is a diagram schematically showing a configuration of a liquid crystal display device according to the fifth embodiment. FIG. 15 is a diagram for explaining a configuration example of the liquid crystal display device according to the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display panel 10 ... Array substrate 20 ... Opposite substrate 30 ... Liquid crystal layer 31 ... Liquid crystal molecule 40 ... 1st optical element 50 ... 2nd optical element 60 ... Backlight PL ... Polarizing plate R1 ... 1st phase difference plate (1 / 4 wavelength plate)
R2 ... Second retardation plate (WV film)
R3 ... Third retardation plate (C plate)
R4 ... Fourth retardation plate (1/2 wavelength plate)
R5 ... Fifth retardation plate (positive C plate)
PX ... Pixel PR ... Reflection part PT ... Transmission part

Claims (12)

In a liquid crystal display device having a reflective portion and a transmissive portion in each of a plurality of pixels arranged in a matrix,
A liquid crystal display panel using an OCB mode configured to hold a liquid crystal layer between a pair of substrates;
A pair of optical elements that are arranged on the respective outer surfaces of the liquid crystal display panel and optically compensate for retardation of the liquid crystal layer in a predetermined display state in which a voltage is applied to the liquid crystal layer;
The optical element is
A circularly polarizing element having a polarizing plate and a first retardation plate disposed between the polarizing plate and the liquid crystal display panel to give a quarter-wave phase difference;
A second retardation plate disposed between the circularly polarizing element and the liquid crystal layer and having a refractive index anisotropy having a principal axis inclined with respect to a normal line;
And a liquid crystal display device characterized by having a retardation in the thickness direction.   The optical element further includes a third retardation plate corresponding to a C plate that is disposed between the circularly polarizing element and the second retardation plate and has a uniaxial refractive index anisotropy. The liquid crystal display device according to claim 1, wherein a phase difference is imparted.   The circularly polarizing element provided in one of the optical elements has a fourth retardation plate disposed between the polarizing plate and the first retardation plate to give a half-wave phase difference. The liquid crystal display device according to claim 2.   The fourth retardation plate has a biaxial refractive index anisotropy, and is arranged so that its slow axis is parallel to the absorption axis of the polarizing plate, and in the direction perpendicular to each other in the plane. When the refractive index is nx and ny and the refractive index in the thickness direction is nz, the Nz coefficient given by Nz = (nx−nz) / (nx−ny) is 0.3 or more and 0.6 or less. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is set.   The fourth retardation plate has a biaxial refractive index anisotropy, and is arranged so that its slow axis is perpendicular to the absorption axis of the polarizing plate, and refracting in directions orthogonal to each other in the plane. The Nz coefficient given by Nz = (nx−nz) / (nx−ny) is set to 0.4 or more and 0.7 or less, where nx and ny are the rates, and nz is the refractive index in the thickness direction. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is a liquid crystal display device.   The liquid crystal display device according to claim 3, wherein the fourth retardation plate is provided in the circularly polarizing element disposed on the observation surface side of the optical element.   The liquid crystal display device according to claim 1, wherein the first retardation plate has a biaxial refractive index anisotropy and is provided with a retardation in the thickness direction.   The first retardation plate has Nz = (nx−nz) / (nx) where nx and ny are the refractive indexes in the directions perpendicular to each other in the plane, and nz is the refractive index in the thickness direction. The liquid crystal display device according to claim 7, wherein the Nz coefficient given by −ny) is set to 2.3 or more and 2.7 or less.   The circularly polarizing element provided in one of the optical elements has a fourth retardation plate disposed between the polarizing plate and the first retardation plate to give a half-wave phase difference. The liquid crystal display device according to claim 7.   The fourth retardation plate has a biaxial refractive index anisotropy, and is arranged so that its slow axis is parallel to the absorption axis of the polarizing plate, and in the direction perpendicular to each other in the plane. When the refractive indexes are nx and ny and the refractive index in the thickness direction is nz, the Nz coefficient given by Nz = (nx−nz) / (nx−ny) is 0.5 or more and 0.7 or less. The liquid crystal display device according to claim 9, wherein the liquid crystal display device is set.   2. The liquid crystal display device according to claim 1, wherein the first retardation plate is disposed such that a slow axis thereof forms an angle of about 45 ° with respect to a rubbing direction of the liquid crystal layer. The cell gap dR of the reflection part is smaller than the cell gap dT of the transmission part.
dR <dT / 2
The liquid crystal display device according to claim 1, wherein

Images