JP5072481B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a transmissive liquid crystal display device including a liquid crystal layer containing liquid crystal molecules that are homogeneously aligned.

  Similar to a twisted nematic (TN) mode liquid crystal display device, a viewing angle compensation phase difference film is applied to a vertically aligned (VA) mode liquid crystal display device having excellent display characteristics when viewed from the front. Thus, a technique for realizing a wide viewing angle has been proposed (see, for example, Patent Document 1).

In addition, a technique for manufacturing a biaxial birefringent film that can be applied to a liquid crystal display device such as a super twisted nematic (STN) mode has been proposed (see, for example, Patent Document 2).
JP 2005-099236 A JP-A-2005-181451

  In recent years, liquid crystal display devices configured by holding a liquid crystal layer containing liquid crystal molecules that are homogeneously aligned between a pair of substrates have been required to improve display quality such as further improvement of contrast and expansion of viewing angle.

  An object of the present invention is to provide a liquid crystal display device with good display quality.

A liquid crystal display device according to an aspect of the present invention includes:
A liquid crystal display panel holding a liquid crystal layer containing homogeneously aligned liquid crystal molecules between a first substrate and a second substrate disposed to face each other;
The first polarizing plate is disposed on one outer surface of the liquid crystal display panel, and is disposed between the first polarizing plate and the liquid crystal display panel, and transmits light having a predetermined wavelength that passes through the fast axis and the slow axis. A first retardation plate in which nematic liquid crystal molecules are fixed in a hybrid alignment along a normal direction and a predetermined retardation is provided between the first polarizing plate and the first retardation plate A first optical element having a uniaxial or negative biaxial refractive index anisotropy,
A third retardation plate provided on the other outer surface of the liquid crystal display panel, disposed between the second polarizing plate and the liquid crystal display panel, and having a biaxial refractive index anisotropy; A second optical element having a fourth retardation plate disposed between the third retardation plate and the liquid crystal display panel and having a refractive index anisotropy equivalent to a negative C plate,
The polarization state of the light transmitted through the first optical element and the liquid crystal display panel is linearly polarized light having substantially the same ellipticity as the light transmitted through the second optical element.

  According to the present invention, a liquid crystal display device with good display quality can be provided.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, a transmissive liquid crystal display device that displays an image using backlight light (selectively transmits) will be described as an example.

  As shown in FIGS. 1 and 2, the liquid crystal display device is an active matrix type color liquid crystal display device and includes a transmissive liquid crystal display panel LPN. The liquid crystal display panel LPN includes an array substrate (first substrate) AR, a counter substrate (second substrate) CT disposed opposite to the array substrate AR, and a space between the array substrate AR and the counter substrate CT. And a liquid crystal layer LQ held in the liquid crystal layer LQ.

  In addition, the liquid crystal display device includes a first optical element OD1 provided on one outer surface of the liquid crystal display panel LPN (that is, an outer surface opposite to the surface in contact with the liquid crystal layer LQ of the array substrate AR), and a liquid crystal display. A second optical element OD2 provided on the other outer surface of the panel LPN (that is, the outer surface opposite to the surface in contact with the liquid crystal layer LQ of the counter substrate CT) is provided. Further, the transmissive liquid crystal display device includes a backlight unit BL that illuminates the liquid crystal display panel LPN from the first optical element OD1 side.

  Such a liquid crystal display panel LPN includes a display area DSP for displaying an image. The display area DSP is composed of a plurality of pixels PX arranged in an mxn matrix.

  The array substrate AR is formed using an insulating substrate 10 having optical transparency such as a glass plate or a quartz plate. In other words, the array substrate AR includes m × n pixel electrodes EP arranged for each pixel in the display area DSP, and n scanning lines Y () formed along the row direction of these pixel electrodes EP. Y1 to Yn), m signal lines X (X1 to Xm) formed along the column direction of these pixel electrodes EP, and regions including intersections of the scanning lines Y and the signal lines X in each pixel PX M × n switching elements W, etc.

  The array substrate AR is further connected to at least a part of the scanning line driver YD connected to the n scanning lines Y and the m signal lines X in the driving circuit area DCT around the display area DSP. At least a part of the signal line driver XD. The scanning line driver YD sequentially supplies scanning signals (driving signals) to the n scanning lines Y based on control by the controller CNT. Further, the signal line driver XD supplies video signals (drive signals) to the m signal lines X at the timing when the switching elements W in each row are turned on by the scanning signal based on the control by the controller CNT. Thereby, the pixel electrode EP of each row is set to a pixel potential corresponding to the video signal supplied via the corresponding switching element W.

  Each switching element W is, for example, an n-channel thin film transistor, and includes a semiconductor layer 12 disposed on the insulating substrate 10. The semiconductor layer 12 can be formed of, for example, polysilicon or amorphous silicon, and is formed of polysilicon here. The semiconductor layer 12 has a source region 12S and a drain region 12D on both sides of the channel region 12C. The semiconductor layer 12 is covered with a gate insulating film 14.

  The gate electrode WG of the switching element W is connected to the scanning line Y (or formed integrally with the scanning line Y). Both the gate electrode WG and the scanning line Y are disposed on the gate insulating film 14. These gate electrodes WG and scanning lines Y are covered with an interlayer insulating film 16.

  The source electrode WS and the drain electrode WD of the switching element W are disposed on both sides of the gate electrode WG on the interlayer insulating film 16. The source electrode WS is connected to the signal line X (or formed integrally with the signal line X) and is in contact with the source region 12S of the semiconductor layer 12. The drain electrode WD is connected to the pixel electrode EP (or formed integrally with the pixel electrode EP) and is in contact with the drain region 12D of the semiconductor layer 12. These source electrode WS, drain electrode WD, and signal line X are covered with an organic insulating film 18.

  The pixel electrode EP is disposed on the organic insulating film 18 and is electrically connected to the drain electrode WD. The pixel electrode EP is formed of a light-transmitting conductive material such as indium tin oxide (ITO). The pixel electrodes EP corresponding to all the pixels PX are covered with the alignment film 20.

  On the other hand, the counter substrate CT is formed using an insulating substrate 30 having optical transparency such as a glass plate or a quartz plate. That is, the counter substrate CT includes a counter electrode ET and the like in the display area DSP. The counter electrode ET is disposed so as to face the pixel electrode EP corresponding to the plurality of pixels PX. The counter electrode ET is made of a light-transmitting conductive material such as indium tin oxide (ITO). The counter electrode ET is covered with an alignment film 36.

  The color display type liquid crystal display device includes a color filter layer 34 provided on the inner surface of the liquid crystal display panel LPN corresponding to each pixel. In the example shown in FIG. 2, the color filter layer 34 is provided on the counter substrate CT. The color filter layer 34 is formed of a plurality of different colors, for example, colored resins that are colored in three primary colors such as red, blue, and green. The red colored resin, the blue colored resin, and the green colored resin are disposed corresponding to the red pixel, the blue pixel, and the green pixel, respectively. Such a color filter layer 34 may be arranged on the array substrate AR side.

  Each pixel PX is partitioned by a black matrix (not shown). This black matrix is arranged so as to face wiring portions such as the scanning lines Y, the signal lines X, and the switching elements W provided on the array substrate AR.

  When the counter substrate CT and the array substrate AR as described above are arranged so that the alignment film 20 and the alignment film 36 face each other, a spacer (for example, a resin material) arranged between them is arranged. A predetermined gap is formed by the formed columnar spacer. The liquid crystal layer LQ is composed of a liquid crystal composition including liquid crystal molecules 40 enclosed in a gap formed between the alignment film 20 of the array substrate AR and the alignment film 36 of the counter substrate CT. In this embodiment, the liquid crystal layer LQ includes liquid crystal molecules 40 having a twist angle of 0 deg (homogeneous alignment).

  In the liquid crystal display device according to this embodiment, as shown in FIG. 3, the first optical element OD1 and the second optical element OD2 control the polarization state of the light that has passed through them. That is, the first optical element OD1 controls the polarization state of the light passing through the first optical element OD1 so that the light having the polarization state of elliptical polarization or substantially linear polarization enters the liquid crystal display panel LPN. That is, the polarization state of the backlight light incident on the first optical element OD1 is converted into a predetermined polarization state when passing through the first optical element OD1. Thereafter, the backlight light that has passed through the first optical element OD1 is incident on the liquid crystal layer LQ while maintaining a predetermined polarization state. The outgoing light emitted from the liquid crystal display panel LPN has a polarization state of elliptically polarized light or substantially linearly polarized light.

  In addition, the second optical element OD2 controls the polarization state of the light passing through the second optical element OD2 so that the light having the polarization state of elliptical polarization or substantially linear polarization enters the liquid crystal display panel LPN. That is, the polarization state of the light incident on the second optical element OD2 is converted into a predetermined polarization state when passing through the second optical element OD2.

  At this time, the polarization state of the light passing through the second optical element OD2 substantially matches the polarization state of the light emitted from the liquid crystal display panel LPN. In other words, the polarization state of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN is substantially the same ellipticity as the light transmitted through the second optical element OD2 (= minor axis direction amplitude Es / major axis direction amplitude). Ep) and substantially linearly polarized light (ellipticity <0.1) or elliptically polarized light (ellipticity> 0.7). With such a configuration, the contrast in the normal direction of the liquid crystal display panel LPN can be improved and the viewing angle can be increased.

  The first embodiment using substantially linearly polarized light and the second embodiment using elliptically polarized light will be described below.

<< First Embodiment >>
As shown in FIG. 3, in the liquid crystal display device according to the first embodiment, the first optical element OD1 is disposed between one first polarizing plate 51 and the first polarizing plate 51 and the liquid crystal display panel LPN. The first phase difference plate RF1 and the second phase difference plate RF2 are provided. In the example shown in FIG. 3, the first retardation plate RF1 is disposed between the first polarizing plate 51 and the liquid crystal display panel LPN (array substrate AR). The second retardation plate RF2 is disposed between the first polarizing plate 51 and the first retardation plate RF1.

  The second optical element OD2 includes one second polarizing plate 52, and a third retardation plate RF3 and a fourth retardation plate RF4 disposed between the second polarizing plate 52 and the liquid crystal display panel LPN. Configured. In the example shown in FIG. 3, the third retardation plate RF3 is disposed between the second polarizing plate 52 and the liquid crystal display panel LPN (counter substrate CT). The fourth retardation plate RF4 is disposed between the third retardation plate RF3 and the liquid crystal display panel LPN (counter substrate CT).

  The first polarizing plate 51 and the second polarizing plate 52 applied here have an absorption axis and a transmission axis orthogonal to each other in a plane orthogonal to the light traveling direction. Such a polarizing plate extracts light having a vibrating surface in one direction parallel to the transmission axis, that is, light having a linearly polarized light state, from light having a vibrating surface in a random direction.

  The first retardation plate RF1 applied here is an optically anisotropic retardation plate, and nematic liquid crystal molecules 61 having optically positive uniaxial refractive index anisotropy are converted into a liquid crystal state. The liquid crystal film layer 60 is fixed in a state of being hybrid-aligned along the normal direction (that is, the thickness direction of the retardation plate).

  In such a liquid crystal film layer 60, for example, in the vicinity of the interface on the array substrate AR side, the liquid crystal molecules 61A are aligned so as to form a relatively small tilt angle with respect to the interface (that is, the liquid crystal molecules 61A are substantially aligned with the interface). On the other hand, in the vicinity of the sea surface on the second retardation plate RF2 side, the liquid crystal molecules 61B are aligned so as to form a relatively large tilt angle with respect to the interface (that is, the liquid crystal molecules 61B). Is oriented almost perpendicular to the interface). As such a first retardation plate RF1, an NH film (manufactured by Nippon Oil Corporation) can be applied. Such a liquid crystal film has a function of optically compensating for the retardation of the liquid crystal layer LQ that changes depending on the viewing angle due to the orientation of the liquid crystal molecules 40 included in the liquid crystal layer LQ, and has a function of expanding the viewing angle. This corresponds to the retardation plate.

In discussing birefringence in the liquid crystal layer LQ in which the alignment of the liquid crystal molecules 40 having refractive index anisotropy changes according to the applied voltage and the retardation plate having refractive index anisotropy, the refractive index is relatively The large axis corresponds to the slow axis, and the relatively small refractive index axis corresponds to the fast axis. The slow axis coincides with the vibration plane of the extraordinary ray. The fast axis coincides with the plane of vibration of ordinary rays. When the refractive indices of ordinary rays and extraordinary rays passing through the liquid crystal layer LQ are no and ne, respectively, and the thickness of the liquid crystal layer LQ along the traveling direction of each ray is d, the retardation value of the liquid crystal layer LQ ( The retardation value is defined by Δn · d (nm) = (ne · d−no · d) (that is, Δn = ne−no). For the phase difference plate, main refractive indexes corresponding to three axes orthogonal to each other are applied, and main refractive indexes corresponding to the axes orthogonal to each other in the plane of the phase difference plate are set to nx and ny, respectively. When the main refractive index corresponding to the axis in the normal direction (that is, the thickness direction of the retardation plate) is nz, and the thickness of the retardation plate is d, the front retardation value (front retardation value) of the retardation plate is , R = (nx−ny) × d. The normal phase difference value of the retardation plate is defined by Rth = [ (nx + ny) / 2−nz] × d.

  The first retardation plate RF1 and the second retardation plate RF2 included in the first optical element OD1, and the third retardation plate RF3 and the fourth retardation plate RF4 included in the second optical element OD2 are orthogonal to each other. It has a slow axis and a fast axis.

  That is, the first retardation plate RF1 has, in addition to the above-described viewing angle widening function, the orientation direction (director) of the liquid crystal molecules 61 as a slow axis and the in-plane direction orthogonal thereto as a fast axis. It functions as a phase difference plate that gives a predetermined phase difference (λ is the wavelength and m is a positive number) between light of a predetermined wavelength (for example, 550 nm) that passes through is doing.

  The second retardation plate RF2 has a uniaxial or negative biaxial refractive index anisotropy (that is, nx> ny ≧ nz). The second retardation plate RF2 has a fast axis and a slow axis in its plane, and has a predetermined position between light of a predetermined wavelength (for example, 550 nm) that passes through the fast axis and the slow axis. It has a function as a phase difference plate that gives a phase difference (λ / n phase difference where λ is a wavelength and n is a positive number).

  The third retardation plate RF3 has biaxial refractive index anisotropy. The third retardation plate RF3 has an Nz coefficient of 0.5 given by Nz = (nx−nz) / (nx−ny). The third retardation plate RF3 has a fast axis and a slow axis in the plane thereof, and has a predetermined position between light of a predetermined wavelength (for example, 550 nm) that transmits the fast axis and the slow axis. It has a function as a phase difference plate that gives a phase difference (λ / n phase difference).

  The fourth retardation plate RF4 has a refractive index anisotropy equivalent to a negative C plate (that is, nx = ny> nz). The fourth retardation plate RF4 has an optical axis in the normal direction (thickness direction).

  As such second retardation plate RF2 and third retardation plate RF3, ZEONOR (manufactured by Optes Co., Ltd.), Arton (manufactured by JSR), or the like can be applied. As the fourth retardation plate RF4, a VAC film (manufactured by Sumitomo Chemical Co., Ltd.), an NC film (manufactured by Nitto Denko Corporation), or the like is applicable.

  Next, a specific example of the arrangement of the first optical element OD1 and the second optical element OD2 in the liquid crystal display panel LPN in the first embodiment will be considered.

  Here, description will be made based on FIG. 4 in which the liquid crystal display device is observed from the counter substrate CT side. For convenience, an X axis and a Y axis orthogonal to each other are defined in a plane parallel to the main surface of the array substrate AR (or the counter substrate CT), and a normal direction of the plane is defined as a Z axis. In-plane corresponds to a plane defined by the X-axis and the Y-axis. Here, for example, the X axis corresponds to the horizontal direction of the screen, and the Y axis corresponds to the vertical direction of the screen. Further, the positive (+) direction (0 ° azimuth) of the X axis corresponds to the right side of the screen, and the negative (−) direction (180 ° azimuth) of the X axis corresponds to the left side of the screen. Furthermore, the positive (+) direction (90 ° azimuth) of the Y axis corresponds to the upper side of the screen, and the negative (−) direction (270 ° azimuth) of the Y axis corresponds to the lower side of the screen.

  In the liquid crystal display panel LPN, the rubbing direction of the alignment film 20 on the array substrate AR side is set at an angle of 45 ° with respect to the X axis.

  The arrangement of the first optical element OD1 on the liquid crystal display panel LPN is set based on the rubbing direction of the alignment film 20. That is, the first retardation plate RF1 has an orientation of 45 ° so that the slow axis D1 is substantially parallel to the rubbing direction of the alignment film 20 (that is, the director of the liquid crystal molecules 40 included in the liquid crystal layer LQ). It is arranged to face. That is, the first retardation plate RF1 is arranged so that the hybrid direction of the liquid crystal molecules contained in the first retardation plate RF1 is oriented in the direction of 225 ° which is opposite to the rubbing direction of the alignment film 20. Further, the slow axis D2 of the second phase difference plate RF2 is disposed so as to face a direction of 135 ° so as to be substantially orthogonal to the slow axis D1 of the first phase difference plate RF1. Further, the first polarizing plate 1 is 90 so that its absorption axis A1 forms an angle of approximately 45 ° with respect to the slow axis D1 of the first retardation plate RF1 and the slow axis D2 of the second retardation plate RF2. It is arranged to face the azimuth.

  On the other hand, the arrangement of the second optical element OD2 on the liquid crystal display panel LPN is set based on, for example, the direction of linearly polarized light transmitted through the liquid crystal layer LQ during black display (in this case, the direction parallel to the X axis). The That is, in the second optical element OD2, the second polarizing plate 52 has its absorption axis A2 substantially parallel to the major axis direction of the substantially linearly polarized light after passing through the first optical element OD1 and the liquid crystal layer LQ. Are arranged as follows. That is, the second polarizing plate 52 is arranged so that its absorption axis A2 is oriented at 0 ° so that the absorption axis A1 of the first polarizing plate 51 is substantially orthogonal to the absorption axis A1. The third retardation plate RF3 is arranged so that its slow axis D3 is oriented 90 ° so as to be substantially orthogonal to the absorption axis A2 of the second polarizing plate 52. The fourth retardation plate RF4 is formed on the third retardation plate RF3 by vapor deposition or coating.

  With such a configuration, the first optical element OD1 has a function of converting into substantially linearly polarized light or elliptically polarized light having a predetermined ellipticity. The second optical element OD2 has a function of converting into substantially linearly polarized light having an ellipticity (<0.1) substantially equal to the ellipticity of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN. is doing.

<< Second Embodiment >>
As shown in FIG. 5, in the liquid crystal display device according to the second embodiment, the first optical element OD1 is disposed between one first polarizing plate 51 and the first polarizing plate 51 and the liquid crystal display panel LPN. The first phase difference plate RF1 and the third phase difference plate RF3 are provided. In the example shown in FIG. 5, the first retardation plate RF1 is disposed between the first polarizing plate 51 and the liquid crystal display panel LPN (array substrate AR). The third retardation plate RF3 is disposed between the first polarizing plate 51 and the first retardation plate RF1.

  The second optical element OD2 includes one second polarizing plate 52, and a second retardation plate RF2 and a fourth retardation plate RF4 disposed between the second polarizing plate 52 and the liquid crystal display panel LPN. Configured. In the example shown in FIG. 5, the second retardation plate RF2 is disposed between the second polarizing plate 52 and the liquid crystal display panel LPN (counter substrate CT). The fourth retardation plate RF4 is disposed between the second retardation plate RF2 and the liquid crystal display panel LPN (counter substrate CT).

  All of the first polarizing plate 51 and the second polarizing plate 52, the first retardation plate RF1, the second retardation plate RF2, the third retardation plate RF3, and the fourth retardation plate RF4 applied here. This is the same as that applied in the first embodiment, and detailed description thereof is omitted.

  In the second embodiment, the arrangement of the first optical element OD1 and the second optical element OD2 on the liquid crystal display panel LPN is the same as that of the first embodiment shown in FIG.

  That is, in the liquid crystal display panel LPN, the rubbing direction of the alignment film 20 on the array substrate AR side is set to an azimuth of 45 ° with respect to the X axis.

  The arrangement of the first optical element OD1 on the liquid crystal display panel LPN is set based on the rubbing direction of the alignment film 20. That is, the first retardation plate RF1 has an orientation of 45 ° so that the slow axis D1 is substantially parallel to the rubbing direction of the alignment film 20 (that is, the director of the liquid crystal molecules 40 included in the liquid crystal layer LQ). It is arranged to face. That is, the first retardation plate RF1 is arranged so that the hybrid direction of the liquid crystal molecules contained in the first retardation plate RF1 is oriented in the direction of 225 ° which is opposite to the rubbing direction of the alignment film 20. Further, the slow axis D3 of the third phase difference plate RF3 is disposed so as to face a 90 ° azimuth so as to form an angle of approximately 45 degrees with the slow axis D1 of the first phase difference plate RF1. Further, the first polarizing plate 1 is disposed so as to face the 90 ° direction so that the absorption axis A1 thereof is substantially parallel to the slow axis D3 of the third retardation plate RF3.

  On the other hand, the arrangement of the second optical element OD2 on the liquid crystal display panel LPN is set based on, for example, the direction of linearly polarized light transmitted through the liquid crystal layer LQ during black display (in this case, the direction parallel to the X axis). The That is, in the second optical element OD2, the second polarizing plate 52 has its absorption axis A2 substantially parallel to the major axis direction of the substantially linearly polarized light after passing through the first optical element OD1 and the liquid crystal layer LQ. Are arranged as follows. That is, the second polarizing plate 52 is arranged so that its absorption axis A2 is oriented at 0 ° so that the absorption axis A1 of the first polarizing plate 51 is substantially orthogonal to the absorption axis A1. The second retardation plate RF2 has a slow axis D2 that forms an angle of about 45 degrees with respect to the absorption axis A2 of the second polarizing plate 52, and the slow retardation axis D1 of the first retardation plate RF1. It is arranged so as to face a direction of 135 ° so as to be substantially orthogonal. The fourth retardation plate RF4 is formed on the third retardation plate RF3 by vapor deposition or coating.

  With such a configuration, the first optical element OD1 has a function of converting into substantially linearly polarized light or elliptically polarized light having a predetermined ellipticity. Further, the second optical element OD2 has a function of converting into elliptically polarized light having an ellipticity (> 0.7) substantially equal to the ellipticity of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN. ing.

《View angle compensation by third retardation plate》
Next, the function of the third retardation plate RF3 applied in the first embodiment and the second embodiment described above will be described.

  That is, the third retardation film RF3 has an orientation in which the slow axis D3 is parallel to the absorption axis A1 of the first polarizing plate 51 (eg, 90 ° orientation) or an orthogonal orientation (eg, 0 ° orientation). ). Such a third retardation plate RF3 improves the viewing angle characteristics of the polarizing plate in the case where the absorption axis A1 of the first polarizing plate 51 and the absorption axis A2 of the second polarizing plate 52 are orthogonal to each other. It has a function.

  That is, the polarizing plate applied in this embodiment has the viewing angle dependence of the contrast ratio as shown in FIG.

  Here, in FIG. 6, the center corresponds to the normal direction of the liquid crystal display panel LPN, and concentric circles centering on the normal direction have tilt angles (viewing angles) of 20 °, 40 °, 60 ° with respect to the normal, And corresponds to 80 °. The characteristic diagram shown here is obtained by connecting regions of equal contrast ratio for each direction. The same applies to the simulation result regarding the viewing angle dependency of the contrast ratio described later.

  As shown in FIG. 6, in the viewing angle characteristics of the polarizing plate, isotropic characteristics cannot be obtained in all directions, and the viewing angle increases in the 45 ° -225 ° azimuth and 135 ° -315 ° azimuth directions. Along with this, the contrast sharply decreases. The third retardation plate RF3 has a function of improving the viewing angle characteristics of the polarizing plate when a polarizing plate having such viewing angle characteristics is applied.

  FIG. 7 shows a third phase difference plate RF3 with Nz coefficient = 1.0, a third phase difference plate RF3 with Nz coefficient = 0.5, and a third phase difference plate RF3 with Nz coefficient = 0.1, respectively. Viewing angle of the polarizing plate when the slow axis D3 is arranged so as to be parallel to the absorption axis A1 of the first polarizing plate 51 and at an angle of 90 ° with the absorption axis A2 of the second polarizing plate 52. It is the characteristic view which simulated the characteristic. In these simulations, the conditions other than the Nz coefficient of the third retardation plate RF3 are all the same.

  As is clear from FIG. 7, the Nz coefficient of the third retardation plate RF3 is preferably approximately 0.5. Thereby, the viewing angle dependency of the polarizing plate is improved, and a contrast ratio (CR) of 500: 1 or more is obtained in almost all directions. In addition, since the slow axis D3 of the third retardation plate RF3 is arranged parallel or orthogonal to the absorption axis A1 of the first polarizing plate 51, no phase difference is generated. Therefore, the phase difference value of the third retardation plate RF3 is not particularly limited.

<< Optimization of normal phase difference in the second optical element >>
Next, the optimum range of the normal phase difference Rth of the second optical element OD2 applied in the first embodiment and the second embodiment described above will be examined. The normal phase difference Rth of the second optical element OD2 corresponds to the normal phase difference of the fourth phase difference plate RF4 in the first embodiment shown in FIG. 3, and the second embodiment shown in FIG. In the form, this corresponds to the sum of the normal phase differences of the second retardation plate RF2 and the fourth retardation plate RF4. In the second embodiment, when the second retardation plate RF2 has uniaxial refractive index anisotropy (that is, nx> ny = nz), the normal phase difference Rth of the second optical element OD2 is This corresponds to the normal phase difference of the fourth retardation plate RF4.

  When the viewing angle dependence of the contrast ratio was simulated for the liquid crystal display device under the same conditions except for the normal phase difference Rth of the second optical element OD2, the result shown in FIG. 8 was obtained.

  From the simulation results shown here, by applying the second optical element OD2 whose normal phase difference Rth is not less than 100 nm and not more than 200 nm, a contrast ratio of 10: 1 or more is obtained in a viewing angle range within 60 ° in almost all directions. It was confirmed that More desirably, by applying the second optical element OD2 having a normal phase difference Rth of 150 nm or more and 170 nm or less, it is confirmed that a contrast ratio of 10: 1 or more can be obtained in a viewing angle range within 80 ° in almost all directions. It was done.

  Therefore, the optimum range of the normal phase difference Rth of the second optical element OD2 is 100 nm to 200 nm, more preferably 150 nm to 170 nm. By applying such a second optical element OD2, the viewing angle dependence of the polarization state of the light transmitted through the second optical element OD2 is determined based on the polarization state of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN. It becomes possible to match the viewing angle dependency.

  That is, the ellipticity of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN and the ellipticity of the light transmitted through the second optical element OD2 vary depending on the viewing angle. By applying the second optical element OD2 having a normal phase difference, the ellipticity of the light transmitted through the first optical element OD1 and the liquid crystal display panel LPN and the light transmitted through the second optical element OD2 regardless of the viewing angle. Is substantially equal to the ellipticity. This makes it possible to enlarge the viewing angle at which a high contrast ratio can be obtained, particularly during black display.

<< Optimization of the average tilt angle of liquid crystal molecules in the first retardation plate >>
Next, regarding the optimum range of the average inclination angle of the first retardation plate RF1 applied in the first embodiment and the second embodiment described above, the voltage applied to the liquid crystal layer LQ and the residual phase difference R (LQ) Consider based on relationships.

  That is, as shown in FIG. 9, the residual phase difference R (LQ) does not become zero even when a relatively high voltage (for example, 6 V) is applied to the liquid crystal layer LQ including liquid crystal molecules that are homogeneously aligned. Therefore, optical compensation is performed in consideration of the residual phase difference R (LQ) of the liquid crystal layer LQ. In other words, considering optimization during black display, when a relatively high black display voltage is applied to the liquid crystal layer LQ, the liquid crystal molecules are aligned at a relatively high tilt angle, so the residual retardation value is small. The liquid crystal molecules thus aligned are optically compensated by the first retardation plate RF1 including liquid crystal molecules hybrid-aligned with a relatively small tilt angle. Further, when a relatively low black display voltage is applied to the liquid crystal layer LQ, the liquid crystal molecules are aligned at a relatively low tilt angle, so that the residual retardation value becomes large. The liquid crystal molecules thus aligned are optically compensated by the first retardation plate RF1 including liquid crystal molecules hybrid-aligned with a relatively large tilt angle.

  Here, attention is focused on the average inclination angle of the first retardation plate RF1. The average tilt angle is defined as an angle formed by the main refractive index nz in the depth direction with respect to the normal direction, and is simply given by ((high tilt angle + low tilt angle) / 2 + low tilt angle). Define as a value. In the first retardation plate RF1 described above, for example, as shown in FIG. 3, “high tilt angle” means a liquid crystal that rises with the greatest inclination with respect to the main surface of the array substrate among liquid crystal molecules that are hybrid-aligned. This corresponds to the tilt angle (tilt with respect to the main surface) of the molecule 61B, and the “low tilt angle” refers to the liquid crystal molecule 61A that rises with the smallest tilt with respect to the main surface of the array substrate among the liquid crystal molecules that are hybrid aligned. Corresponds to the tilt angle.

  The first retardation plate necessary for optical compensation of the liquid crystal layer LQ having such a residual retardation value when a black display voltage is set such that the residual retardation value R (LQ) of the liquid crystal layer LQ is 50 nm or more. The average tilt angle of the liquid crystal molecules of RF1 is 35 degrees or more. With such a setting, it is possible to drive at a relatively low voltage, and it is possible to apply a low cost driving circuit with high versatility.

<< Description of Example 1 and Comparative Examples 1 to 3 Corresponding to the First Embodiment >>
First, the configuration of the first embodiment will be described. The basic configuration is as shown in FIG.

  For the liquid crystal display panel LPN, the liquid crystal layer LQ is composed of a liquid crystal composition containing homogeneously aligned liquid crystal molecules. For example, MJ041113 (Merck, Δn = 0.065) was applied as the liquid crystal composition. At this time, the director of the liquid crystal molecules 40 (the major axis direction of the liquid crystal molecules) was regulated by the rubbing direction of the alignment film 20 on the array substrate AR side, and was set to make an angle of 45 ° with respect to the X axis. The gap in the liquid crystal layer LQ was set to 4.5 μm. Note that the black display voltage applied to the liquid crystal layer LQ in order to realize black display is set to 4.0 (V). At this time, the residual phase difference value R (LQ) of the liquid crystal layer LQ is 60 (nm). Met.

  In order to compensate for the birefringence caused by the liquid crystal molecules 40, the slow axis D1 of the first retardation plate RF1 is set to an orientation of 225 ° for the first optical element OD1 to be arranged on the outer surface of the array substrate AR. . The front retardation value R (RF1) of the first retardation plate RF1 was set to 100 nm. The average tilt angle of the liquid crystal molecules constituting the first retardation plate RF1 was set to 35 degrees. An NH film (manufactured by Nippon Oil Corporation) was applied as the first retardation plate RF1.

  The slow axis D2 of the second phase difference plate RF2 is set to an orientation of 135 °. The front retardation value R (RF2) of the second retardation plate RF2 is the sum of the residual retardation value R (LQ) of the liquid crystal layer LQ and the front retardation value R (RF1) of the first retardation plate RF1. Was set to 160 nm. Therefore, since R (LQ) + R (RF1) = R (RF2) is satisfied, in the front black display, the liquid crystal layer LQ can be optically compensated only by the first optical element OD1. In this embodiment, the Nz coefficient of the second retardation plate RF2 is set to 1.0. As such second retardation plate RF2, ZEONOR (manufactured by Optes Co., Ltd.) was applied.

  The absorption axis A1 of the first polarizing plate 51 is set to a 90 ° azimuth. On the other hand, the absorption axis A2 of the second polarizing plate 52 of the second optical element OD2 to be arranged on the outer surface on the counter substrate CT side is set to an orientation of 0 °.

  The slow axis D3 of the third retardation plate RF3 is set to a 90 ° azimuth. Further, the Nz coefficient of the third retardation plate RF3 was set to 0.5. As such third retardation plate RF3, ZEONOR (manufactured by Optes Co., Ltd.) was applied. Since the fourth retardation plate RF4 does not have a slow axis in the XY plane, the axis angle with other optical elements is not particularly limited.

  According to Example 1 as described above, when the viewing angle dependency of the contrast ratio was simulated, the result shown in FIG. 10 was obtained. That is, it was confirmed that the viewing angle range with an equicontrast ratio of 10: 1 can realize a sufficiently wide viewing angle of 160 ° in almost all directions of the screen. It was also confirmed that the high contrast region with an equicontrast ratio of 100: 1 was enlarged in all directions.

  Next, a comparative example will be described. In Comparative Examples 1 to 3 described here, in the same manner as in Example 1, the polarization state of the light after passing through the first optical element OD1 and the liquid crystal display panel LPN is substantially a straight line with an ellipticity <0.1. It is comprised so that it may become polarized light.

  Comparative Example 1 is a liquid crystal display in which the fourth retardation plate is not applied and the Nz coefficient of the second retardation plate RF2 is changed in the range from 1.8 to 3.0 in the configuration of Example 1. Device. In Comparative Example 1, the viewing angle dependence of the contrast ratio was simulated. As shown in FIG. 11, the same effect as in Example 1 was obtained regardless of how the Nz coefficient of the second retardation plate RF2 was set. It turns out that it cannot be obtained.

  The comparative example 2 is a liquid crystal display device having a configuration in which the fourth retardation plate is not applied and the uniaxial second retardation plate RF2 (Nz coefficient = 1.0) is applied in the configuration of the first embodiment. . In the comparative example 2, when the viewing angle dependence of the contrast ratio is simulated, it can be seen that both the region with the equal contrast ratio of 10: 1 and the region with the ratio of 100: 1 become very narrow as shown in FIG.

  Comparative Example 3 is a liquid crystal display device having a configuration in which the third retardation plate is not applied in the configuration of Example 1. In the comparative example 3, when the viewing angle dependence of the contrast ratio is simulated, it can be seen that, in particular, the region having the equal contrast ratio of 100: 1 becomes very narrow as shown in FIG.

  From the above, in order to expand not only the region with the equal contrast ratio of 10: 1 but also the region with the equal contrast ratio of 100: 1 in all directions, the polarizing plates of the first polarizing plate 51 and the second polarizing plate 52 Applying the third retardation plate RF3 as viewing angle compensation, and the polarization state of the light transmitted through the first optical element and the liquid crystal display panel and the polarization state of the light transmitted through the second optical element are the same regardless of the viewing angle. In order to compensate optically, it is necessary to simultaneously satisfy the application of the negative C plate as the fourth retardation plate RF4.

<< Description of Example 2 and Comparative Examples 4 to 6 Corresponding to Second Embodiment >>
First, the configuration of the second embodiment will be described. The basic configuration is as shown in FIG. That is, the difference from the first embodiment is that the second retardation plate RF2 is disposed between the second polarizing plate 52 and the fourth retardation plate RF4, and the third retardation plate RF3 is disposed on the first polarizing plate 51. And the first phase difference plate RF1 are the only points that are arranged, and the relationship of the shaft angles is the same as in the first embodiment.

  According to Example 2 as described above, when the viewing angle dependency of the contrast ratio was simulated, the result shown in FIG. 14 was obtained. That is, it was confirmed that the viewing angle range with an equicontrast ratio of 10: 1 can realize a sufficiently wide viewing angle of 160 ° in almost all directions of the screen. It was also confirmed that the high contrast region with an equicontrast ratio of 100: 1 was enlarged in all directions.

  Next, a comparative example will be described. In Comparative Examples 4 to 6 described here, similarly to Example 2, elliptically polarized light in which the polarization state of light after passing through the first optical element OD1 and the liquid crystal display panel LPN has an ellipticity> 0.7. It is comprised so that.

  Comparative Example 4 is a liquid crystal display in which the fourth retardation plate is not applied and the Nz coefficient of the second retardation plate RF2 is changed in the range from 1.8 to 3.0 in the configuration of the second embodiment. Device. In Comparative Example 4, when the viewing angle dependence of the contrast ratio was simulated, as shown in FIG. 15, the same effect as in Example 2 was obtained regardless of how the Nz coefficient of the second retardation plate RF2 was set. It turns out that it cannot be obtained.

  Comparative Example 5 is a liquid crystal display device having a configuration in which the fourth retardation plate is not applied and the uniaxial second retardation plate RF2 (Nz coefficient = 1.0) is applied in the configuration of the second embodiment. . In the comparative example 5, when the viewing angle dependence of the contrast ratio was simulated, as shown in FIG. 16, it can be seen that both the 10: 1 region and the 100: 1 region are very narrow.

  Comparative Example 6 is a liquid crystal display device having a configuration in which the third retardation plate is not applied in the configuration of Example 2. In Comparative Example 6, when the viewing angle dependence of the contrast ratio was simulated, it can be seen that, in particular, the region having the equal contrast ratio of 100: 1 is very narrow as shown in FIG.

  From the above, also in Example 2, in order to expand not only the region with the equal contrast ratio of 10: 1 but also the region with the equal contrast ratio of 100: 1 in all directions, the first polarizing plate 51 and the second polarizing plate Applying the third retardation plate RF3 as the viewing angle compensation of the polarizing plate by the polarizing plate 52, the polarization state of the light transmitted through the first optical element and the liquid crystal display panel, and the polarization state of the light transmitted through the second optical element In addition, it is necessary to simultaneously satisfy the application of the negative C plate as the fourth retardation plate RF4 in order to optically compensate for the same regardless of the viewing angle.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the spirit of the invention in the stage of implementation. 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 the component covering different embodiment suitably.

  For example, although the example in which the switching element W is configured by an n-channel thin film transistor has been described, other configurations may be used as long as the same various drive signals can be generated.

  In the above-described embodiment, it is desirable that the first retardation plate RF1 is constituted only by the liquid crystal film layer 60. That is, in the embodiment, the first retardation plate RF1 is configured by the liquid crystal film layer 60 that is in contact with the second retardation plate RF2 and the outer surface of the liquid crystal display panel LPN (that is, the outer surface of the insulating substrate 10 constituting the array substrate AR). Has been. A phase difference plate having a liquid crystal film layer containing liquid crystal molecules hybrid-aligned such as an NH film is a state in which the liquid crystal molecules maintain a predetermined alignment state after applying an alignment treatment on the base film and applying a liquid crystal material. It is obtained by curing with. Triacetate cellulose (TAC) is widely used as the base film. However, since the base film itself has a retardation, it is necessary to compensate in consideration of the retardation of the base film in order to realize good optical compensation. Therefore, optical compensation can be easily realized by applying a base film-less NH film as in the above-described embodiment.

  In the second embodiment, the second retardation plate RF2 is included in the second optical element OD2, but may be included in the first optical element OD1. In that case, the second phase difference plate RF2 is disposed between the first phase difference plate RF1 and the third phase difference plate RF3, and the phase difference value R (RF3) and the slow axis D3 of the second phase difference plate RF2. Are the same as those in the second embodiment.

  In the second embodiment, the third retardation plate RF3 is included in the first optical element OD1, but may be included in the second optical element OD2. In that case, the third retardation plate RF3 is disposed between the second retardation plate RF2 and the second polarizing plate 2, and the slow axis D3 of the third retardation plate RF3 is the absorption axis A2 of the second polarizing plate. Arranged in a direction parallel to or orthogonal to.

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 cross-sectional structure of the liquid crystal display device shown in FIG. FIG. 3 is a diagram schematically showing the configuration of the first optical element and the second optical element of the first embodiment applicable to the liquid crystal display device shown in FIG. FIG. 4 is a diagram for explaining the orientation of the slow axis of each retardation plate shown in FIG. 3 and the orientation of the absorption axis of each polarizing plate. FIG. 5 is a diagram schematically showing configurations of the first optical element and the second optical element of the second embodiment applicable to the liquid crystal display device shown in FIG. FIG. 6 is a diagram showing the viewing angle characteristics of the polarizing plate. FIG. 7 is a diagram illustrating a result of simulating the viewing angle dependence of the contrast ratio for the liquid crystal display devices having different Nz coefficients of the third retardation plate illustrated in FIGS. 3 and 5. FIG. 8 is a diagram showing the results of simulating the viewing angle dependence of the contrast ratio for the liquid crystal display devices in which the normal phase difference Rth of the second optical element shown in FIGS. 3 and 5 is different. FIG. 9 is a diagram illustrating a relationship between a voltage applied to a liquid crystal layer including homogeneously aligned liquid crystal molecules and a residual retardation value. FIG. 10 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in the first embodiment. FIG. 11 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in Comparative Example 1. FIG. 12 is a diagram illustrating a result of simulating the viewing angle dependence of the contrast ratio in Comparative Example 2. FIG. 13 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in Comparative Example 3. FIG. 14 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in Example 2. FIG. 15 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in Comparative Example 4. FIG. 16 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in the comparative example 5. FIG. 17 is a diagram illustrating a result of simulating the viewing angle dependency of the contrast ratio in Comparative Example 6.

Explanation of symbols

  LPN ... liquid crystal display panel, AR ... array substrate, CT ... counter substrate, LQ ... liquid crystal layer, OD1 ... first optical element, OD2 ... second optical element, 51 ... first polarizing plate, RF1 ... first retardation plate, RF2 ... second retardation plate, 52 ... second polarizing plate, RF3 ... third retardation plate, RF4 ... fourth retardation plate, BL ... backlight unit, PX ... pixel

Claims (3)

A liquid crystal display panel holding a liquid crystal layer containing homogeneously aligned liquid crystal molecules between a first substrate and a second substrate disposed to face each other;
The first polarizing plate is disposed on one outer surface of the liquid crystal display panel, and is disposed between the first polarizing plate and the liquid crystal display panel, and transmits light having a predetermined wavelength that passes through the fast axis and the slow axis. A first retardation plate that is fixed in a state in which a predetermined phase difference is provided between the nematic liquid crystal molecules and the nematic liquid crystal molecules are hybrid-aligned along the normal direction and the average tilt angle of the nematic liquid crystal molecules is set to 35 degrees or more. A first optical element having a second retardation plate disposed between the first polarizing plate and the first retardation plate and having a uniaxial or negative biaxial refractive index anisotropy;
Provided on the other outer surface of the liquid crystal display panel, and disposed between the second polarizing plate and the second polarizing plate and the liquid crystal display panel, the refractive indexes in the directions perpendicular to each other are nx and When the refractive index in the normal direction is nz, the Nz coefficient given by Nz = (nx + nz) / (nx−ny) is set to 0.5 and has biaxial refractive index anisotropy. A second optical element comprising: a third retardation plate; and a fourth retardation plate disposed between the third retardation plate and the liquid crystal display panel and having a refractive index anisotropy equivalent to a negative C plate; With
The polarization state of the first optical element and the light transmitted through the liquid crystal display panel, Ri linearly polarized der with light substantially the same ellipticity having passed through the second optical element,
The angle formed by the absorption axis of the first polarizing plate and the slow axis of the second retardation plate is set to about 45 degrees, and the liquid crystal molecules contained in the liquid crystal layer and the slow axis of the first retardation plate And the angle between the slow axis of the first retardation plate and the slow axis of the second retardation plate is set to approximately 90 degrees, and The absorption axis and the slow axis of the third retardation plate are substantially orthogonal,
The liquid crystal display device , wherein the second optical element has a normal phase difference Rth of 150 nm to 170 nm . A liquid crystal display panel holding a liquid crystal layer containing homogeneously aligned liquid crystal molecules between a first substrate and a second substrate disposed to face each other;
The first polarizing plate is disposed on one outer surface of the liquid crystal display panel, and is disposed between the first polarizing plate and the liquid crystal display panel, and transmits light having a predetermined wavelength that passes through the fast axis and the slow axis. A first retardation plate that is fixed in a state in which a predetermined phase difference is provided between the nematic liquid crystal molecules and the nematic liquid crystal molecules are hybrid-aligned along the normal direction and the average tilt angle of the nematic liquid crystal molecules is set to 35 degrees or more. When the refractive index in the direction perpendicular to each other is arranged between the first polarizing plate and the first retardation plate is nx and ny, and the refractive index in the normal direction is nz And a third retardation plate having a biaxial refractive index anisotropy in which the Nz coefficient given by Nz = (nx + nz) / (nx−ny) is set to 0.5 , and a first optical element,
A second polarizing plate provided on the other outer surface of the liquid crystal display panel and disposed between the second polarizing plate and the liquid crystal display panel and having a uniaxial or negative biaxial refractive index anisotropy; A second optical element comprising: a two phase difference plate; and a fourth phase difference plate disposed between the second phase difference plate and the liquid crystal display panel and having a refractive index anisotropy equivalent to a negative C plate; With
The polarization state of the first optical element and the light transmitted through the liquid crystal display panel, Ri elliptical polarization der with light substantially the same ellipticity having passed through the second optical element,
The angle formed by the absorption axis of the first polarizing plate and the slow axis of the second retardation plate is set to about 45 degrees, and the liquid crystal molecules contained in the liquid crystal layer and the slow axis of the first retardation plate And the angle between the slow axis of the first retardation plate and the slow axis of the second retardation plate is set to approximately 90 degrees, and The absorption axis and the slow axis of the third retardation plate are substantially orthogonal,
The liquid crystal display device , wherein the second optical element has a normal phase difference Rth of 150 nm to 170 nm .   The liquid crystal display device according to claim 1, further comprising a backlight unit that illuminates the liquid crystal display panel from the first optical element side.

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