JP5072520B2 - 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 characteristic 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. On the other hand, it is required to reduce the thickness and cost of the entire apparatus.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a liquid crystal display device which can be reduced in thickness and cost and has a 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;
A first polarizing plate provided on one outer surface of the liquid crystal display panel, and a first retardation plate and a second retardation plate disposed between the first polarizing plate and the liquid crystal display panel; One optical element;
A second optical element including a second polarizing plate provided on the other outer surface of the liquid crystal display panel,
The first retardation plate is a retardation plate in which a predetermined phase difference is given to light having a predetermined wavelength and nematic liquid crystal molecules are immobilized in a hybrid alignment state along a normal direction.

  According to the present invention, it is possible to provide a liquid crystal display device which can be reduced in thickness and cost and has a good display quality.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, a liquid crystal display device including a transmissive display unit that selectively transmits backlight and displays an image 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 arranged to face the array substrate AR, and between the array substrate AR and the counter substrate CT. And a held 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, a 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 surface opposite to the surface in contact with the liquid crystal layer LQ of the counter substrate CT) is provided. Further, the 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 through a contact hole formed in the organic insulating film 18. 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 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 light having an elliptical polarization state that is almost linearly polarized is incident on the liquid crystal layer LQ. Therefore, 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 emitted from the first optical element OD1 is incident on the liquid crystal layer LQ while maintaining a predetermined polarization state. When a voltage for black display (black display voltage) is applied to the liquid crystal layer LQ, the polarization state of the light incident on the liquid crystal display panel LPN is affected by the phase difference of the liquid crystal layer LQ and is substantially linearly polarized. Changed to polarization state.

  Further, the second optical element OD2 controls the polarization state of light passing through the liquid crystal layer LQ so that light having a polarization state of linearly polarized light (or elliptically polarized light that is almost as linearly polarized as possible) enters the liquid crystal layer LQ. Therefore, the polarization state of the light incident on the second optical element OD2 is converted into a predetermined polarization state, that is, linearly polarized light when passing through the second optical element OD2.

  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). It is substantially linearly polarized light having Ep). Here, the substantially linearly polarized light is light having a polarization state with an ellipticity of 0.1 or less, preferably 0.02 or less. 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.

  Below, each structure is demonstrated more concretely.

  The first optical element OD1 includes one first polarizing plate 51, and a first retardation plate RF1 and a second retardation plate RF2 disposed between the first polarizing plate 51 and the liquid crystal display panel LPN. Configured. 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 is configured by one second polarizing plate 52.

  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 has an optically positive uniaxial refractive index anisotropy as shown in FIG. 4A. It has a liquid crystal film layer 60 in which nematic liquid crystal molecules 61 are immobilized in a hybrid orientation along the normal direction (that is, the thickness direction of the retardation plate) in the liquid crystal state.

  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 large tilt angle with respect to the interface (that is, the liquid crystal molecules 61A are substantially aligned with the interface). In the vicinity of the interface on the second retardation plate RF2 side, the liquid crystal molecules 61B are aligned so as to form a relatively small tilt angle with respect to the interface (that is, the liquid crystal molecules 61B). Are oriented almost parallel to the interface). That is, in the liquid crystal display panel LPN, the orientation direction of the liquid crystal molecules on the array substrate AR side when a voltage is applied is different from the hybrid direction of the liquid crystal molecules included in the first retardation plate RF1 by 180 °.

As such a first retardation plate RF1, an NH film (manufactured by Nippon Oil Corporation) is applicable. 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 indexes of the ordinary ray and extraordinary ray 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 of the liquid crystal layer LQ (retardation). ) 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 of the retardation plate (front retardation) is R = (Nx−ny) · d.

  The first retardation plate RF1 and the second retardation plate RF2 included in the first optical element OD1 have a slow axis and a fast axis that are orthogonal to each other, and have a predetermined front phase difference. Yes.

  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 direction orthogonal thereto as a fast axis. It has a function as a phase difference plate that gives a predetermined phase difference (λ is a wavelength, and m is a positive number) between light having a predetermined wavelength (for example, 550 nm) to be transmitted. Yes.

  The second retardation plate RF2 has a predetermined phase difference (λ is a wavelength and λ is a positive number) between light of a predetermined wavelength (for example, 550 nm) that transmits the fast axis and the slow axis. / N phase difference). As such second retardation plate RF2, Zeonore (manufactured by Optes Co., Ltd.), Arton (manufactured by JSR) or the like can be applied.

  In the first optical element OD1, the absorption axis A1 of the first polarizing plate 51, the slow axis D1 in the plane of the first retardation plate RF1, and the slow axis D2 in the plane of the second retardation plate RF2 are set. Each component is arranged so as to have a predetermined angle relationship. That is, the second retardation plate RF2 is disposed on the first polarizing plate 51 so that the slow axis D2 thereof is approximately 45 ° with respect to the absorption axis A1 of the first polarizing plate 51. The first phase difference plate RF1 is disposed on the second phase difference plate RF2 such that the slow axis D1 is substantially 90 ° with respect to the slow axis D2 of the second phase difference plate RF2. When the first optical element OD1 is disposed on the liquid crystal display panel LPN, the first optical element OD1 is configured such that the slow axis D1 of the first retardation plate RF1 having a viewing angle widening function is the liquid crystal molecule 40 of the liquid crystal layer LQ. The direction (the rubbing direction of the alignment film 20 on the array substrate AR side) is substantially parallel to the director, and the direction in which the liquid crystal molecules 61 are hybrid aligned in the first retardation plate RF1 and the rubbing direction of the alignment film 20 on the array substrate AR side are Are arranged in the opposite direction.

  Further, in the second optical element OD2, the second polarizing plate 52 is arranged so that the absorption axis A2 thereof is orthogonal to the absorption axis A1 of the first polarizing plate 51 (substantially 90 degrees).

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

  In particular, the birefringent material constituting the retardation plate has a characteristic that its main refractive index depends on the wavelength of light. For this reason, the phase difference R of the phase difference plate depends on the wavelength of light passing therethrough. Therefore, as described above, by applying the first optical element OD1 having a configuration in which at least two types of retardation plates are combined, the wavelength dependency of the retardation R can be relaxed and used for color display. In all wavelength ranges, a predetermined phase difference is given to form a desired polarization state.

  That is, the backlight light that has passed through the first optical element OD1 is converted into substantially linearly polarized light and enters the liquid crystal layer LQ. It is assumed that the major axis direction of the substantially linearly polarized light is parallel to the X axis. In the liquid crystal layer LQ, by applying a phase difference of λ / 2 to the substantially linearly polarized light incident on the liquid crystal layer LQ when no voltage is applied (or when a low voltage is applied), the light passing through the liquid crystal layer LQ is It is converted into linearly polarized light that is orthogonal to the substantially linearly polarized light incident on the liquid crystal layer. That is, the plane of vibration of this linearly polarized light is parallel to the Y axis orthogonal to the X axis. Therefore, by applying the second polarizing plate 52 having the absorption axis parallel to the X axis in the second optical element OD2, the linearly polarized light that has passed through the liquid crystal layer LQ can be increased without using another retardation plate. It can be transmitted with transmittance (white display).

  On the other hand, in the liquid crystal layer LQ, when a voltage is applied (or when a high voltage is applied), the phase difference imparted to the substantially linearly polarized light incident on the liquid crystal layer LQ is made substantially zero, thereby passing through the liquid crystal layer LQ. The maintained light maintains a polarization state equivalent to substantially linearly polarized light before entering the liquid crystal layer. That is, the vibration plane of the substantially linearly polarized light is parallel to the X axis. Therefore, by applying the second polarizing plate 52 having the absorption axis parallel to the X axis in the second optical element OD2, the linearly polarized light that has passed through the liquid crystal layer LQ can be increased without using another retardation plate. It can be absorbed by the absorption rate (black display). As described above, since the second optical element OD2 is composed of only the second polarizing plate 52 without applying a retardation plate, it is possible to reduce the thickness and cost and obtain good optical characteristics. It becomes possible.

  Next, regarding a method for obtaining further good optical characteristics, particularly optical compensation at the time of black display, the front phase difference R (RF1) of the first phase difference plate RF1 and the second phase difference plate in the first optical element OD1. The relationship between the front phase difference R (RF2) of RF2 and the residual phase difference R (LQ) of the liquid crystal layer LQ during black display will be examined.

  Here, the residual phase difference R (LQ) of the liquid crystal layer LQ will be described. When a voltage for black display (black display voltage) is applied to the liquid crystal layer LQ, the liquid crystal molecules 40 located at the center (midplane) away from the substrate interface in the cross section of the liquid crystal layer LQ are in the direction of the electric field. They are arranged so that their major axis directions are substantially parallel. For this reason, the front phase difference of the midplane of the liquid crystal layer LQ can be regarded as substantially zero (nm). However, the liquid crystal molecules 40 that are aligned adjacent to the substrate interface are affected by the alignment regulating force (anchoring) of the interface, have a slow response to voltage, and maintain an initial alignment state. For this reason, the front phase difference in the vicinity of the substrate interface of the liquid crystal layer LQ is not zero (nm). Therefore, even when a sufficiently high black display voltage for black display is applied to the liquid crystal layer LQ, the front phase difference remains in the liquid crystal layer LQ due to the influence of anchoring at the substrate interface. This is generally called residual phase difference.

  In the present embodiment, (1) the applied liquid crystal layer LQ, the first retardation plate RF1, and the second retardation plate RF2 all have a positive retardation, (2) The director of the liquid crystal molecules 40 in the liquid crystal layer LQ and the slow axis D1 of the first retardation plate RF1 are set substantially parallel to each other. (3) The slow axis D1 and the second position of the first retardation plate RF1. Since the slow axis D2 of the phase difference plate RF2 is set at an angle of about 90 degrees, the front phase difference R (RF1) of the first phase difference plate RF1 and the second phase difference plate RF2 of the first optical element OD1 are set. The total phase difference R (total) of the front phase difference R (RF2) and the residual phase difference R (LQ) of the liquid crystal layer LQ is R (total) = R (LQ) + R (RF1) −R It can be expressed as (RF2).

  In this equation, the first optical element OD1 and the liquid crystal are set by setting each phase difference so that R (total) becomes zero, that is, R (LQ) + R (RF1) = R (RF2). Optical compensation can be realized with the layer LQ. That is, in this embodiment, the first optical element OD1 alone does not convert the polarization state of the backlight light into substantially linearly polarized light, but emits from the liquid crystal display panel LPN in consideration of the residual phase difference of the liquid crystal layer LQ. The polarization state of the emitted light is converted into substantially linearly polarized light (ellipticity <0.1).

  That is, by setting the sum of the residual phase difference of the liquid crystal layer LQ and the front phase difference of the first phase difference plate RF1 to be substantially equal to the front phase difference of the second phase difference plate RF2, the backlight unit BL After the backlight light passes through the first optical element OD1 and the liquid crystal layer LQ during black display, it can be converted into light having a polarization state that is almost as linearly polarized as possible. Therefore, not only in the case of white display as described above, but also in the case of black display, a straight line having an ellipticity very close to zero in the polarization state of light that has passed through the first optical element OD1 and the liquid crystal layer LQ. Since it can be approximated to polarized light, it is possible to obtain good optical characteristics only by applying the second polarizing plate 52 in the second optical element OD2.

  Next, the arrangement of the first optical element OD1 and the second optical element OD2 on the liquid crystal display panel LPN will be considered.

  Here, description will be made based on FIG. 4B 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 is arranged so that its slow axis D1 is oriented in the direction of 45 ° -225 ° so that it is substantially parallel to the rubbing direction of the alignment film 20. At this time, the hybrid direction of the liquid crystal molecules included 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 retardation plate RF2 is disposed so as to be substantially orthogonal to the slow axis D1 of the first retardation plate RF1 (that is, directed to a 135 ° azimuth). Further, the first polarizing plate 51 has, for example, 90 ° -270 ° so that the absorption axis A1 forms an angle of about 45 ° with respect to the slow axes of the first retardation plate RF1 and the second retardation plate RF2. It is arranged to face the direction of

  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 substantially linearly polarized light transmitted through the liquid crystal layer LQ during black display (in this case, the direction parallel to the X axis). Is done. In other words, in the second optical element OD2, the second polarizing plate 52 has an absorption axis A2 in the elliptical long axis direction of the polarization state of light (substantially linearly polarized light) after passing through the first optical element OD1 and the liquid crystal layer LQ. Are arranged so as to be substantially parallel to each other. That is, the second polarizing plate 52 may be arranged so that the absorption axis A2 is oriented in the 0 ° -180 ° direction.

  FIG. 5 shows the polarization state of light after the backlight is transmitted through the first optical element OD1 and the liquid crystal layer LQ having the above-described configuration when a black display voltage (for example, 4.8 V) is applied to the liquid crystal layer LQ. Is shown. As described above, in the black display state, the polarization state of the light transmitted through the first optical element OD1 and the liquid crystal layer LQ has the minor axis direction amplitude (Es) with respect to the major axis direction amplitude (Ep). The ellipticity was about 0.017. Further, it has been found that the major axis direction of such substantially linearly polarized light is substantially 0 ° azimuth (X axis). This indicates that the absorption axis A2 of the second polarizing plate 52 is preferably set to an orientation of 0 ° in order to display a black image with good quality.

(Example)
Next, examples of the liquid crystal display device according to this embodiment will be described. This liquid crystal display device is designed as follows, for example.

  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 4.9 μm. Note that the voltage applied to the liquid crystal layer LQ to realize black display was set to 4.8 (V), and at this time, the residual phase difference of the liquid crystal layer LQ was 60 (nm).

  First, in order to compensate for the birefringence caused by the liquid crystal molecules 40, the slow axis D1 of the first retardation plate RF1 (that is, the first retardation plate RF1) of the first optical element OD1 to be arranged on the outer surface of the array substrate AR. The orientation azimuth of the liquid crystal molecules 61 constituting the azimuth is set to an orientation (for example, 225 ° orientation) substantially antiparallel to the rubbing direction of the array substrate AR so as to be in a relationship of successive compensation. The front phase difference of the first retardation plate RF1 is set to 100 nm, for example.

  Subsequently, the slow axis D2 of the second retardation plate RF2 is set to an orientation (eg, 135 ° orientation) substantially perpendicular to the liquid crystal molecules 40 and the slow axis D1 of the first retardation plate RF1. Note that the front phase difference of the second phase difference plate RF2 is set to, for example, 160 nm so as to correspond to the sum of the residual phase difference of the liquid crystal layer LQ and the front phase difference of the first phase difference plate RF1.

  Subsequently, the absorption axis A1 of the first polarizing plate 51 intersects with the slow axis D1 of the first retardation plate RF1 and the slow axis D2 of the second retardation plate RF2 at an angle of approximately 45 ° (for example, 90 °). Set to (azimuth of °).

  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 oriented so as to be substantially orthogonal to the absorption axis A1 of the first polarizing plate 51 (for example, 0 °). Set to (azimuth). The orientation of the slow axis of the retardation plate and the orientation of the absorption axis of the polarizing plate are defined by the angle formed with the X axis, as shown in FIG. 4B.

  The residual phase difference R (LQ) of the liquid crystal layer LQ, the phase difference R (RF1) of the first phase difference plate RF1, and the phase difference R (RF2) of the second phase difference plate RF2 are limited to these values. However, as long as the relationship R (LQ) + R (RF1) = R (RF2) is satisfied, the same result is obtained.

  As the first retardation plate RF1, an NH film (manufactured by Nippon Oil Corporation) with an average inclination angle β of 37 degrees was applied. Here, the average inclination angle β 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 [(high tilt angle + low tilt angle) / 2 + low tilt angle. ] Is defined as the value given by In the first retardation plate RF1 described above, for example, as shown in FIG. 4A, the “high tilt angle” is a liquid crystal that rises with the greatest inclination from the main surface of the array substrate among the liquid crystal molecules that are hybrid-aligned. This corresponds to the tilt angle (tilt with respect to the main surface) of the molecule 61A, and “low tilt angle” refers to the liquid crystal molecules 61B that have risen 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. ZEONOR (manufactured by Optes Co., Ltd.) was applied as the second retardation film RF2.

  According to such an example, the viewing angle dependence of the contrast ratio was measured, and the result shown in FIG. 6 was obtained. Here, in the figure showing the measurement results regarding the viewing angle dependence of the contrast ratio, the center corresponds to the normal direction of the liquid crystal display panel LPN, and the concentric circles centered on the normal direction are the tilt angle (viewing angle) with respect to the normal line. ) Corresponds to 10 ° to 80 °. The characteristic diagram shown here is obtained by connecting regions of equal contrast ratio for each direction.

  As shown in FIG. 6, according to the embodiment, the viewing angle range of the equal contrast ratio (CR) = 10: 1 realizes a sufficiently wide viewing angle of 160 ° both on the top and bottom of the screen and on the left and right of the screen. It was confirmed that it was made. The contrast in the normal direction of the screen was 400.

  On the other hand, FIG. 7A is a diagram showing the configuration of Comparative Example 1, and the configuration of the liquid crystal display panel LPN is the same as that of the example, but the first optical element OD1 includes a first polarizing plate, a half-wave plate, and The second optical element OD2 is configured to include a second polarizing plate, a ½ wavelength plate, and a ¼ wavelength plate, and includes an NH film having an average inclination angle β of 28 degrees. is there.

  FIG. 7B shows the result of measuring the viewing angle dependency of the contrast ratio of Comparative Example 1 having the configuration shown in FIG. 7A. The viewing angle range of the equal contrast ratio (CR) = 10: 1 is The angle was 140/145 ° on the screen top / bottom / screen left / right, respectively. Further, the contrast in the normal direction of the screen was 250, which was inferior to the example.

  According to this example, improvement was confirmed in both the contrast in the normal direction of the screen and the viewing angle range of the equal contrast ratio. In addition, about each measurement, the contrast in the normal line direction of a screen was measured by BM5-A (made by Topcon), and the viewing angle characteristic was measured by Ez-Contrast (made by ELDIM).

  Next, the configuration shown in FIG. 8 based on the same concept as the present embodiment is used as Comparative Example 2 to clarify the difference from the present embodiment and to obtain a favorable viewing angle characteristic in the present embodiment. Explain why.

  The difference between the present embodiment and the second comparative example shown in FIG. 8 is that the second retardation plate RF2 is included in the first optical element OD1 in the present embodiment, whereas the second difference in the second comparative example is the first. The only difference is that the two retardation plate RF2 is included in the second optical element OD2. The relationship between the liquid crystal layer LQ and the axial angle between the first polarizing plate 51 and the first retardation plate RF1 in the first optical element OD1, Axial angle relationship between the first phase difference plate RF1 and the director of the liquid crystal molecules 40 included in the liquid crystal layer LQ, the front phase difference R (RF1) of the first phase difference plate RF1, and the average inclination of the first phase difference plate RF1 The corners are all the same. In addition, the arrangement angle of the absorption axis A2 of the second polarizing plate 52 included in the second optical element OD2 to the liquid crystal display panel LPN, the front phase difference R (RF2) of the second retardation plate RF2 included in the second optical element OD2. ), And the relationship between the axis angles of the slow axis D2 of the second retardation plate RF2 and the slow axis D1 of the first retardation plate RF1 are all set to be the same. Therefore, it is clear that the TV characteristics (that is, the relationship of the transmittance with respect to the voltage applied to the liquid crystal layer LQ) in the front of this embodiment and the comparative example 2 shown in FIG. 8 are the same. .

  FIG. 9A shows the simulation result of the viewing angle characteristic of the present embodiment, and FIG. 9B shows the simulation result of the viewing angle characteristic of Comparative Example 2. From these results, both have substantially the same characteristics in the front, but are completely different in the viewing angle characteristics, and the present embodiment shows a favorable viewing angle characteristic, whereas the comparative example 2 has a viewing angle. It turns out that becomes narrow.

  In order to explain this result, for each configuration, the polarization state of the light after the backlight passes through the first optical element OD1 and the liquid crystal layer LQ, and after the external light passes through the second optical element OD2. Analysis was performed on the coincidence with the polarization state of light.

  It is assumed that a predetermined voltage (= 4.8 V) is applied to the liquid crystal layer LQ for black display. FIG. 10A is a characteristic diagram showing the coincidence of both in the vertical direction of the screen in the present embodiment, and FIG. 10B is a characteristic diagram showing the coincidence of both in the vertical direction of the screen in Comparative Example 2. The horizontal axis is the angle formed with respect to the normal line in the vertical direction of the screen, and the vertical axis is the ellipticity at a wavelength of 550 nm as a parameter indicating the polarization state. Further, “A” in the figure corresponds to the polarization state of the light after the backlight is transmitted through the first optical element OD1 and the liquid crystal layer LQ, and “B” is the external light transmitted through the second optical element OD2. It corresponds to the polarization state of the later light.

  Since the liquid crystal molecule orientation of the liquid crystal layer LQ is set to 45 degrees, FIGS. 10A and 10B show the viewing angle characteristics in the vertical direction of the screen, but the same viewing angle characteristics are also shown in the horizontal direction of the screen. Show. In order to realize good viewing angle compensation, the polarization state of the light after the backlight passes through the first optical element OD1 and the liquid crystal layer LQ, and the light after the outside light passes through the second optical element OD2. It is important that the polarization state of the two is substantially the same.

  As is clear from FIG. 10A, in the present embodiment, the two are almost the same, whereas in Comparative Example 2, as shown in FIG. The front polarization state of Comparative Example 2 is elliptical polarization with an ellipticity> 0.7, whereas the front polarization state of the present embodiment is substantially linearly polarized with an ellipticity <0.1. It turns out that it is a near polarization state. That is, in the present embodiment, linearly polarized light (or elliptically polarized light having a relatively small ellipticity) is mainly used, whereas in Comparative Example 2, circularly polarized light (or elliptically polarized light having a relatively large ellipticity) is mainly used. ) Is different.

  When applying elliptically polarized light having a relatively large ellipticity in the normal direction of the screen as in Comparative Example 2, the main refractive indexes nx, ny, and nz are normally nx = ny> nz in the second optical element OD2. A third retardation plate RF3 (negative C plate; n-C) having a relationship is added, or a negative biaxial film (NB) having a relationship of nx> ny> nz as the second retardation plate RF2. If this is not applied, good display quality cannot be obtained.

FIG. 11A is a view angle characteristic diagram when a negative C plate (manufactured by Nitto Denko Corporation) is arranged as a third retardation plate between the second optical element OD2 and the liquid crystal layer LQ in the configuration of the comparative example 2. Is shown. In the negative C plate, the normal direction retardation (Rth) defined by “Rth = [ (nx + ny) / 2−nz] × film thickness” was set to 80 nm.

  FIG. 11B illustrates a configuration in which a negative C plate (Rth = 80 nm) is disposed between the second optical element OD2 and the liquid crystal layer LQ, after the backlight passes through the first optical element OD1 and the liquid crystal layer LQ. This shows the coincidence between the polarization state of the light and the polarization state after external light has passed through the second optical element OD2. It can be seen that the coincidence between the two is good and that the viewing angle characteristic is also good.

  On the other hand, in the present embodiment, in the polarization state of the light after the backlight is transmitted through the first optical element OD1 and the liquid crystal layer LQ, the polarization is linearly polarized with an ellipticity <0.1 in the normal direction of the screen. Since it can be converted into near elliptically polarized light, only the second polarizing plate 52 can be used without applying a negative C plate (n-C) or a negative biaxial film (NB) as the second optical element OD2. Viewing angle compensation is possible. Therefore, it is possible to reduce the thickness and cost, and to provide a high-quality liquid crystal display device.

  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.

  The second optical element OD2 may include a third retardation plate corresponding to a negative C plate between the second polarizing plate 52 and the liquid crystal display panel LPN. That is, as shown in FIG. 12A, in the liquid crystal display device according to the modification, the second optical element OD2 is disposed between one second polarizing plate 52 and the second polarizing plate 52 and the liquid crystal display panel LPN. And a third phase difference plate RF3.

  The third retardation plate RF3 has a relationship of nx = ny> nz, 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 normal direction. It has refractive index anisotropy. In the third retardation plate RF3, the phase difference Rth in the normal direction was set to 80 nm.

  In the modified example of such a configuration, as shown in FIG. 12B, the measurement result of the viewing angle dependency of the contrast ratio in the configuration of the example in which the third retardation plate RF3 is not disposed (that is, the configuration shown in FIG. 3). Compared with (ie, the measurement result of FIG. 6), a region with a low contrast ratio (for example, CR = 10: 1) has a substantially equivalent viewing angle, but a region with a high contrast ratio (for example, CR = 50). 1 or more), it can be seen that a wider viewing angle can be obtained with the configuration of the example in which the third retardation plate RF3 is not disposed. Although not shown, even if a negative biaxial film (NB) is applied as the third retardation plate RF3, the same characteristics as shown in FIG. 12B can be obtained.

  Based on the above results, in particular, in order to enlarge the region of high contrast ratio, the second optical element is implemented rather than the configuration including the third retardation plate made of a negative C plate or a negative biaxial film. It was confirmed that the example configuration (that is, the configuration in which the second optical element does not include both the negative C plate and the negative biaxial film) is more advantageous.

  In the above-described embodiment, it is desirable that the first retardation plate RF1 is constituted only by the liquid crystal film layer 60. In other words, in the embodiment, the first retardation plate RF1 is formed by the liquid crystal film layer 60 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). It is configured. 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. For reference, the viewing angle dependency of the contrast ratio when an NH film having the same structure as that of the example and having a base film is applied as the first retardation plate RF1 was measured. As shown in FIG. Results were obtained.

  As the low contrast ratio region (for example, CR = 10: 1), a viewing angle substantially equivalent to the configuration of the base filmless example shown in FIG. 6 was obtained, but the high contrast ratio region (for example, CR = 10). 50: 1 or more), it can be seen that the configuration of the base film-less example can obtain a wider viewing angle. Based on the above-described results, in particular, in order to enlarge the region of high contrast ratio, the configuration of the embodiment (base film-less (rather than the configuration of the first retardation plate RF1 having the base film (TAC)) is applied. It was confirmed that the configuration using the first retardation plate RF1 (without TAC) is more advantageous.

  In the above-described embodiment, it is desirable to apply the first retardation plate RF1 having a relatively large average tilt angle β, for example, having the liquid crystal film layer 60 of about β = 37 degrees. For reference, the viewing angle dependency of the contrast ratio when the first retardation plate (NH film) having the liquid crystal film layer of β = 28 degrees was applied while having the same configuration as the example was measured. Results as shown in FIG. 14 were obtained.

  As the low contrast ratio region (for example, CR = 10: 1), a viewing angle substantially equivalent to the configuration of the embodiment of β = 37 degrees shown in FIG. 6 was obtained, but the high contrast ratio region (for example, CR = 10: 1). = 50: 1 or more), it can be seen that a wider viewing angle can be obtained with the configuration of the embodiment of β = 37 degrees. Based on the above-described results, in particular, in order to enlarge a region with a high contrast ratio, the configuration of the example (average tilt) is more than the configuration to which the first retardation plate RF1 having a liquid crystal film having a small average tilt angle is applied. It was confirmed that the configuration using the first retardation plate RF1 having a liquid crystal film having a large angle is more advantageous.

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 a configuration of a first optical element and a second optical element applicable to the liquid crystal display device shown in FIG. FIG. 4A is a diagram for explaining the relationship between the orientation of liquid crystal molecules in the liquid crystal display panel and the orientation of liquid crystal molecules in the first retardation plate when a voltage is applied. FIG. 4B 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 characteristic diagram showing a polarization state after backlight passes through the first optical element and the liquid crystal layer in the liquid crystal display device according to the present embodiment. FIG. 6 is a characteristic diagram obtained by measuring the viewing angle dependency of the contrast ratio in the liquid crystal display device according to the example of the present embodiment. FIG. 7A is a diagram schematically showing a configuration of a liquid crystal display device according to Comparative Example 1. FIG. 7B is a characteristic diagram in which the viewing angle dependence of the contrast ratio in the liquid crystal display device according to Comparative Example 1 is measured. FIG. 8 is a configuration diagram schematically showing a configuration of a liquid crystal display device according to Comparative Example 2. FIG. 9A is a characteristic diagram that simulates the viewing angle dependence of the contrast ratio in the liquid crystal display device according to the example of the present embodiment. FIG. 9B is a characteristic diagram simulating the viewing angle dependence of the contrast ratio in the liquid crystal display device of Comparative Example 2. FIG. 10A shows the change in ellipticity in the vertical direction of the screen in the polarization state after the backlight passes through the first optical element and the liquid crystal layer, and the external light is the second optical element in the example of the present embodiment. FIG. 6 is a characteristic diagram showing matching with a change in ellipticity in the vertical direction of the polarization state after passing through the beam. FIG. 10B shows the change in the ellipticity in the vertical direction of the screen in the polarization state after the backlight light passes through the first optical element and the liquid crystal layer in Comparative Example 2, and after the external light passes through the second optical element. It is the characteristic view which showed matching with the change of the ellipticity of the up-down direction of the polarization state of this. FIG. 11A is a characteristic diagram in which the viewing angle dependence of the contrast ratio is measured when a negative C plate is disposed between the second optical element and the liquid crystal layer in Comparative Example 2. FIG. 11B shows the vertical direction of the polarization state after backlight passes through the first optical element and the liquid crystal layer when a negative C plate is disposed between the second optical element and the liquid crystal layer in Comparative Example 2. FIG. 6 is a characteristic diagram showing matching between a change in ellipticity in FIG. 5 and a change in ellipticity in the vertical direction of the polarization state after external light passes through the second optical element. FIG. 12A corresponds to a modification of the present embodiment, and a liquid crystal to which a second optical element having a configuration example in which a third retardation plate (negative C plate) is disposed between a second polarizing plate and a liquid crystal layer is applied. It is a block diagram which shows the structure of a display apparatus roughly. FIG. 12B is a characteristic diagram obtained by measuring the viewing angle dependency of the contrast ratio in the modification shown in FIG. 12A. FIG. 13 is a characteristic diagram in which the viewing angle dependence of the contrast ratio is measured in a configuration example in which an NH film including a base film is applied as the first retardation plate in the present embodiment. FIG. 14 is a characteristic diagram in which the viewing angle dependency of the contrast ratio is measured in a configuration example in which an NH film having an average inclination angle of 28 degrees is applied as the first retardation plate in the present embodiment.

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 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;
Provided on one outer surface of the liquid crystal display panel, a first polarizer, and, viewed including the first phase difference plate and the second phase difference plate disposed between the first polarizer and the liquid crystal display panel A first optical element that controls a polarization state of light passing through the liquid crystal layer so that light having a polarization state of substantially linear polarization enters the liquid crystal layer ;
A second optical element including a second polarizing plate provided on the other outer surface of the liquid crystal display panel,
The first retardation plate is a liquid crystal film layer that is in contact with the outer surface of the second retardation plate and the liquid crystal display panel, respectively, and gives a predetermined retardation to light having a predetermined wavelength, and nematic liquid crystal molecules in a normal direction. Consists of a liquid crystal film layer fixed in a state of hybrid alignment along ,
In the first optical element, an angle formed between the absorption axis of the first polarizing plate and the slow axis of the second retardation plate is set to approximately 45 degrees, and the slow axis of the first retardation plate and the The director of the liquid crystal molecules contained in the liquid crystal layer is set substantially in parallel, and the angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is approximately 90 degrees. Set,
In the second optical element, an angle formed between the absorption axis of the second polarizing plate and the absorption axis of the first polarizing plate is set to approximately 90 degrees,
The liquid crystal display device , wherein the sum of the residual retardation of the liquid crystal layer and the front retardation of the first retardation plate is substantially equal to the front retardation of the second retardation plate . The second optical element includes a third retardation plate between the second polarizing plate and the liquid crystal display panel,
The third retardation plate has a refractive index of nx = ny> nz, 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 normal direction. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has rate anisotropy.   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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