JP2006208531A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of obtaining high contrast in a wide visual angle range in addition to symmetry of a field angle. <P>SOLUTION: The liquid crystal display device comprises an electrode substrate providing a plurality of pixel electrodes; an opposite substrate arranged oppositely to the electrode substrate and aligned in a substantially parallel direction to alignment processing of the electrode substrate; and a chiral nematic liquid crystal sandwiched between the electrode substrate and the opposite substrate and divided into at least two bend alignment regions in each pixel by an electric field between a pixel electrode and the opposite electrode. The electrode substrate and the opposite substrate further comprises a circular polarizing plate 11 on a reverse side face to a face sandwiching the chiral nematic liquid crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having excellent moving image display characteristics and a wide viewing angle.

  A liquid crystal display device that mainly displays a moving image such as a television or a multimedia monitor is required to have a faster response characteristic than a liquid crystal display device that mainly displays a still image such as a PC monitor. Several liquid crystal modes using bend alignment or alignment similar to bend alignment have been proposed as liquid crystal modes that realize high-speed response characteristics. In the present specification, the term “bend orientation” includes orientations similar to the bend orientation.

  The bend alignment will be described with reference to the cross-sectional view of the liquid crystal panel shown in FIG. The bend alignment means that the liquid crystal molecules 102 of the liquid crystal layer 101 are aligned in a bow shape as shown in FIG. The liquid crystal layer 101 is sandwiched between a glass substrate 105 on which an alignment film 103 and a transparent electrode 104 are stacked, and the alignment of the liquid crystal molecules 102 is performed depending on the voltage applied between the transparent electrodes 104 formed on the glass substrates 105 on both sides. The degree of bending is controlled. In the bend alignment, since no backflow occurs in the liquid crystal layer 101 in response to a voltage change, a high-speed response characteristic can be obtained in principle. Details are described in Non-Patent Document 1, for example.

  Next, among liquid crystal modes using bend alignment, a liquid crystal mode called OCB (Optically Compensated Bend) mode has both high-speed response characteristics and wide viewing angle characteristics. However, in the OCB mode, since the alignment in the initial alignment state (the alignment state when no voltage is applied) is the splay alignment, a high initialization voltage of 20 V or more is required to obtain the bend alignment necessary for display. There was a problem. Details are described in Non-Patent Document 2, for example.

  In the OCB mode, a biaxial film that compensates for one direction in the film plane and the thickness direction of the film may be used as the retardation film that compensates for the residual retardation of the liquid crystal layer 101. In this case, in the OCB mode, it has been found that the viewing angle characteristics are improved by using a circularly polarizing plate instead of the linearly polarizing plate used in a normal liquid crystal display device. Details are described in, for example, Patent Document 1 and Non-Patent Documents 3 and 4.

  Here, the linearly polarizing plate usually used has a characteristic of transmitting linearly polarized light, whereas the circularly polarizing plate has a characteristic of transmitting right circularly polarized light or left circularly polarized light. The circularly polarizing plate is composed of a linearly polarizing plate and a quarter wavelength plate (hereinafter also referred to as a λ / 4 plate) that generates a phase difference of about ¼ wavelength in the film plane. It is often used that the transmission axis of the linear polarizing plate and the slow axis of the λ / 4 plate are bonded to form an angle of 45 degrees. Further, the wavelength λ is a wavelength of visible light, and is a value around 550 nm, which has high visibility of human eyes.

  Next, among liquid crystal modes using bend alignment, there is a liquid crystal mode called a DDB (Dual-Domain Bend) mode other than the OCB mode. This DDB mode is a liquid crystal mode having at least two bend alignment regions in one pixel, and does not require a high voltage for obtaining bend alignment in addition to high-speed response characteristics. This is because the initial orientation of the DDB mode is a twist orientation of approximately 180 degrees, and thus the twist orientation is continuously changed to the bend orientation by applying a voltage. Further, since the DDB mode has at least two symmetrically aligned regions, it has a feature that a viewing angle characteristic with good symmetry can be obtained. Details are described in Patent Document 2.

US Patent Application Publication No. 2004/0223104 JP 2003-66491 A SHINYA ONDA, 2 others, "Mechanism of Fast Response and Recover in Bend Alignment Cell", Mol. Cryst. Liq. Cryst., 1999, Vol. 331, p.383-389 K. Sueoka, 2 others, "Initialization of Optically Compensated Bend-Mode LCDs", AM-LCD / IDW '96 Proceedings, p.133-136 Ting-Jui and Po-Lun Chen, "A Novel Optically Compensative Structure for Gray-Scale Inversionless OCB-LCDs", IDW '03 Proceedings, p.77-80 T.Ishinabe, 2 others, "Improvement of Transmittance and Viewing Angle of the OCB Mode LCD by using Wide-Viewing-Angle Circular Polarizer", SID '04 Proceedings, p.638-641

  The DDB mode liquid crystal display device has excellent symmetry in the horizontal direction and vertical direction with respect to the white transmittance distribution. However, although the DDB mode liquid crystal display device has a wide contrast direction in the vertical direction, the horizontal direction is narrower than other liquid crystal modes, and a sufficiently wide viewing angle characteristic cannot be obtained. That is, the DDB mode liquid crystal display device has a good viewing angle symmetry, but has a problem that the contrast viewing angle is narrow.

  Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a liquid crystal display device capable of obtaining high contrast in a wide viewing angle range in addition to the symmetry of the viewing angle. And

  The solution according to the present invention includes an electrode substrate provided with a plurality of pixel electrodes, and a counter electrode disposed opposite to the electrode substrate, and is aligned in a substantially antiparallel direction with respect to the alignment processing of the electrode substrate. And a chiral nematic liquid crystal sandwiched between the electrode substrate and the counter substrate and divided into at least two bend alignment regions in each pixel by an electric field between the pixel electrode and the counter electrode, The electrode substrate and the counter substrate further include a circularly polarizing plate on a surface opposite to the surface sandwiching the chiral nematic liquid crystal.

  In the liquid crystal display device according to the present invention, since the electrode substrate and the counter substrate further include a circularly polarizing plate on the surface opposite to the surface sandwiching the chiral nematic liquid crystal, in addition to the symmetry of the viewing angle, a wide viewing angle range is provided. With this, it is possible to obtain a high contrast.

(Embodiment 1)
First, a DDB mode liquid crystal display device will be described. FIG. 1A schematically shows an initial alignment state in a DDB mode liquid crystal display device. A liquid crystal panel 7 shown in FIG. 1A has a liquid crystal layer 1 sandwiched between glass substrates 5 on which an alignment film 3 and transparent electrodes 4 are laminated, and is applied between the transparent electrodes 4 formed on the glass substrates 5 on both sides. In this configuration, the orientation of the liquid crystal molecules 2 is controlled by the level of the applied voltage. In the DDB mode, the alignment film 3 surfaces on both glass substrates 5 are subjected to an alignment process in an antiparallel direction (opposite direction).

  The initial alignment state of the DDB mode shown in FIG. 1A is not a splay alignment like the OCB mode but a twist alignment of about 180 degrees. In the DDB mode, a nematic liquid crystal material having a chiral property (hereinafter referred to as chiral nematic liquid crystal) is used for the liquid crystal layer 1 in order to obtain this initial alignment.

  The liquid crystal panel 7 shown in FIG. 1B schematically shows the alignment state during display in the DDB mode liquid crystal display device. As shown in FIG. 1B, the alignment state at the time of display in the DDB mode is such that one pixel in the DDB mode has two bend alignment regions (region A and region B) in which the bending direction of the bend alignment is opposite. Consists of In order to divide the bent alignment region, there are a method of providing an oblique electric field by providing a slit or a projection structure on the electrode, a method of utilizing a pretilt angle difference caused by a difference in surface roughness, and the like. In FIG. 1B, description of structures for dividing the vent alignment region is omitted.

  Unlike normal bend alignment such as the OCB mode, in the DDB mode, the tilt (rise) direction of the liquid crystal molecules 2 at the interface of the alignment film 3 is opposite between the upper interface and the lower interface. In the case of FIG. 1B, the lower interface rises from the back side of the drawing, whereas the upper interface rises from the front side of the drawing. In normal bend alignment, the upper and lower interfaces of the liquid crystal molecules 2 rise from the same side. For example, in the case of FIG. 11, the liquid crystal molecules 2 rise from the right side of the drawing in both the upper interface and the lower interface.

  In the DDB mode, since the tilt direction of the liquid crystal molecules 2 is reversed at the upper and lower interfaces, the splay alignment portion 6 is formed near the interface on one side. In the case of FIG. 1B, the splay alignment portion 6 is formed in the vicinity of the lower interface in the region A and in the vicinity of the upper interface in the region B, respectively. Although not clearly shown in FIG. 1B, since a chiral nematic liquid crystal is used for the liquid crystal layer 1, a twist component remains in the liquid crystal layer 1 in the alignment state at the time of display. Different.

  Next, when the liquid crystal display device in the DDB mode is operated as a normally white that displays white on the low voltage side and black on the high voltage side, the liquid crystal layer 1 of the black display voltage (hereinafter also simply referred to as black voltage) is displayed. In order to compensate for the residual retardation, a retardation film is disposed outside the glass substrate 5. Further, in the DDB mode liquid crystal display device, a polarizing plate is disposed outside the retardation film. FIG. 2 shows a configuration example of an optical film in a DDB mode liquid crystal display device.

  Although not shown, the liquid crystal panel 7 shown in FIG. 2 has the same configuration as the liquid crystal layer 1, the alignment film 3, the transparent electrode 4, and the glass substrate 5 shown in FIGS. 1 (a) and 1 (b). In the liquid crystal display device shown in FIG. 2, a uniaxial film (hereinafter referred to as “a plate 8”) that is one type of retardation film and has a retardation in the film plane is provided outside the liquid crystal panel 7. The a plate 8 has a front slow axis a arranged in the direction of an arrow (a direction substantially orthogonal to the alignment processing direction b of the liquid crystal panel 7), and cancels the residual phase difference of the liquid crystal layer 1 that occurs in the alignment processing direction b. ing. In FIG. 2, the a plate 8 is disposed at the upper and lower positions of the liquid crystal panel 7, and the sum of the phase differences of the a plate 8 is set to be equal to the residual phase difference of the liquid crystal layer 1.

  Further, in the liquid crystal display device shown in FIG. 2, a uniaxial film (hereinafter referred to as a c plate 9) having a negative retardation in the thickness direction of the film is disposed outside the a plate 8. Since the c plate 9 has no phase difference in the film plane, it hardly affects the front transmittance, but has a function of suppressing light leakage in a direction oblique to the film plane. Further, in the liquid crystal display device shown in FIG. 2, a polarizing plate 10 is disposed outside the c plate 9. Here, the polarizing plate 10 refers to a linear polarizing plate, and the transmission axis c thereof is orthogonal to the upper polarizing plate 10 and the lower polarizing plate 10 as indicated by arrows. Further, the transmission axis c of the c plate 9 is arranged so as to form an angle of 45 degrees with the alignment processing direction b of the liquid crystal layer 1.

  FIG. 3 shows the white transmittance distribution of the DDB mode liquid crystal display device when the film configuration shown in FIG. 2 is used. The transmittance numbers shown in FIG. 3 are values normalized by the transmittance at the pixel opening of the liquid crystal display device to which the a plate 8, the c plate 9, and the polarizing plate 10 are not attached. In general, a liquid crystal display device requires symmetrical viewing angle characteristics in the left-right direction, but a DDB mode liquid crystal display device has excellent symmetry not only in the left-right direction but also in the up-down direction as shown in FIG. Have.

  On the other hand, FIG. 4 shows the contrast distribution of the DDB mode liquid crystal display device when the configuration of the optical film shown in FIG. 2 is used. The contrast number shown in FIG. 4 is the ratio of white luminance to black luminance. Regarding the contrast distribution, although the viewing angle has symmetry, unlike the white transmittance distribution shown in FIG. 3, a sufficiently wide viewing angle characteristic cannot be obtained. In particular, in the contrast distribution shown in FIG. 4, although the viewing angle characteristics in the vertical direction are wide, the viewing angle characteristics in the horizontal direction are narrower than those in other liquid crystal modes.

  Thus, in this embodiment, a DDB mode liquid crystal display device that solves the above-described problems and can obtain high contrast in a wide viewing angle range in addition to the symmetry of the viewing angle is provided.

  FIG. 5 shows a cross-sectional view of the liquid crystal display device according to the present embodiment. In the liquid crystal display device shown in FIG. 5, the configuration of the liquid crystal panel 7, the a plate 8, and the c plate 9 is the same as the configuration of the liquid crystal display device shown in FIG. Therefore, detailed description of the configuration of the part is omitted. In the liquid crystal display device shown in FIG. 5, a circularly polarizing plate 11 is disposed on the outer surface of the c plate 9.

  Here, the circularly polarizing plate 11 includes a linearly polarizing plate 12, a biaxial film 13, and a λ / 4 plate 14. The biaxial film 13 is a retardation film that causes a phase difference between the film in-plane direction and the film thickness direction. The λ / 4 plate 14 is a retardation film that causes a phase difference of approximately ¼ of the wavelength λ in the film plane. Note that the wavelength λ is the wavelength of visible light, and is a value around 550 nm, which is highly visible to human eyes.

  Next, as the linear polarizing plate 12, a layer in which polyvinyl alcohol (PVA) is stretched and dyed with iodine is used as a polarizer, and a protective layer of cellulose triacetate (TAC) is superposed on both sides thereof. As long as the transmittance in the transmission axis direction is high and the transmittance in the absorption axis direction is low, a hydrophilic polymer film other than PVA, a dichroic dye other than iodine, and a transparent film material other than TAC are used. The linearly polarizing plate 12 may be configured. Specifically, it is desirable that the two linear polarizing plates 12 arranged in parallel Nicols have a transmittance of 35% or more and the two linear polarizing plates 12 arranged in crossed Nicols have a transmittance of 0.04% or less.

  Next, the biaxial film 13 leaks light when the angle formed by the transmission axes of the two linear polarizing plates 12 is not a right angle when the two linear polarizing plates 12 in the crossed Nicols arrangement are viewed from an oblique direction. Used to suppress The retardation in the film plane of the biaxial film 13 is preferably about λ / 2, that is, in the range of 250 to 300 nm. Further, the front slow axis direction of the biaxial film 13 is arranged to be parallel or orthogonal to the transmission axis of the linear polarizing plate 12. In addition, it is desirable that the angle shift between the front slow axis direction of the biaxial film 13 and the transmission axis of the linear polarizing plate 12 is within ± 2 degrees.

  The retardation in the thickness direction of the biaxial film 13 is defined by the value of Nz defined below. Nz is (nx−nz) / (nx−ny) where the refractive index in the optical principal axis direction in the film plane is nx, ny (nx> ny), and the refractive index in the film thickness direction is nz. Defined. In the liquid crystal display device according to the present embodiment, when the front slow axis direction of the biaxial film 13 and the transmission axis of the linear polarizing plate 12 are arranged in parallel, Nz = 0.6 to 1.1, In the case where they are arranged so as to be orthogonal, it is desirable that Nz = 0.1 to 0.4.

  As described above, the linearly polarizing plate 12 protects both sides of the PVA as a polarizer with TAC. However, the TAC used for the protective layer of the linear polarizing plate 12 has a phase difference of several tens of nm in the thickness direction. Therefore, in the liquid crystal display device according to this embodiment, the biaxial film 13 is used as a protective layer without providing a TAC on the liquid crystal panel 7 side (electrode substrate side and counter substrate side) of the linearly polarizing plate 12. It is. However, the present invention is not limited to the configuration in which the TAC is not provided on the liquid crystal panel 7 side of the linear polarizing plate 12, and when the TAC is provided on the liquid crystal panel 7 side, the biaxial film 13 or the like is considered in consideration of the TAC phase difference. These optical parameters may be designed.

  Next, it is desirable that the λ / 4 plate 14 has an in-plane retardation of 125 to 150 nm. The slow axis direction of the λ / 4 plate 14 is arranged at an angle of 45 degrees with respect to the transmission axis of the linear polarizing plate 12. It is desirable that the angular deviation between the slow axis direction of the λ / 4 plate 14 and the transmission axis direction of the linear polarizing plate 12 is within ± 2 degrees.

  The optical films such as the biaxial film 13 and the linearly polarizing plate 12 are preferably fixed between the optical films with an adhesive or the like in order to prevent an axial shift or the like due to a temperature change in the use environment. . The adhesive is preferably transparent and has excellent weather resistance and heat resistance.

  Next, the DDB mode liquid crystal panel 7 will be described in detail. The liquid crystal panel 7 includes an electrode substrate, a counter substrate, and a liquid crystal layer 1 sandwiched between two substrates.

  As the electrode substrate, the pixel structure shown in FIG. 6 is formed on a glass substrate 5 or the like which is a transparent insulating substrate. A perspective view of an electrode substrate having a unit structure corresponding to one pixel is shown in FIG. In an actual liquid crystal display device, similar unit structures are arranged in a matrix in the vertical and horizontal directions. A gate wiring 15 is arranged in one direction (lateral direction in the figure) on a glass substrate 5 (not shown) of the electrode substrate. A gate electrode 16 is connected to the gate wiring 15. The signal wiring 17 is arranged in a direction (vertical direction in the drawing) different from the direction of the gate wiring 15. A source electrode 18 is connected to the signal wiring 17.

  The gate electrode 16, the source electrode 18, the drain electrode 19, a semiconductor layer (not shown), an insulating layer (not shown), and the like constitute a TFT section 20 that is a switching element. The drain electrode 19 is connected via a contact hole 21 to a pixel electrode 22 made of a transparent conductive material such as ITO (Indium Tin Oxide). An organic alignment film (hereinafter simply referred to as an alignment film) such as polyimide or polyamide is further formed (not shown) on the electrode substrate having the above configuration, and the surface thereof is in a specific alignment processing direction 23. Then, an orientation process such as a rubbing process is performed. In addition to the above structure, an auxiliary capacitance wiring, an auxiliary capacitance electrode, and the like are formed on the electrode substrate, but the description is omitted in FIG.

  On the other hand, the counter substrate has the structure shown in FIG. 7 formed on a glass substrate 5 or the like which is a transparent insulating substrate. FIG. 7 shows a perspective view of a counter substrate having a unit structure corresponding to one pixel. Each pixel is divided by a black matrix 24 (hereinafter referred to as BM 24) for shielding light, and a color material layer 25 of red, green, blue, or the like is formed in the pixel. An overcoat layer (not shown) made of a transparent organic film is provided on the color material layer 25, and a counter electrode (not shown) made of a transparent conductive material is further provided on the overcoat layer. .

  However, a monochrome liquid crystal display device or the like may not be provided with the color material layer 25 or the overcoat layer. In the counter electrode according to the present embodiment, a vertical slit 26 is provided in the center of the pixel. In addition, in the part in which the slit 26 is provided, it is provided so that a part of BM24 may overlap. Similar to the electrode substrate, an alignment film (not shown) is formed on the counter substrate having the above-described configuration, and the surface thereof is subjected to an alignment treatment in an alignment treatment direction 27 opposite to the alignment treatment direction 23 of the electrode substrate. Applied.

  The electrode substrate and the counter substrate are arranged so that the alignment film surfaces face each other and the gap (hereinafter referred to as panel gap: d) is substantially constant, and the liquid crystal layer 1 is sandwiched between the substrates. Yes. As the liquid crystal material used for the liquid crystal layer 1, a material having a birefringence Δn of approximately 0.12 or more and a chiral pitch p in the range of greater than 4d / 3 and less than 4d is used.

  Next, a method for manufacturing the liquid crystal display device according to the present embodiment will be described. First, a method for manufacturing an electrode substrate will be described. A metal chromium film having a thickness of 300 nm is formed on the glass substrate 5, and the gate wiring 15 and the gate electrode 16 are formed by photolithography. Next, a 400 nm silicon nitride film (insulating film) is formed on the gate wiring 15 and the like. Subsequently, an amorphous silicon film of 100 nm and a doped amorphous silicon film of 100 nm are continuously formed on the silicon nitride film, and the TFT portion 20 is formed by photolithography. Again, a metal chromium film having a thickness of 300 nm is formed on the TFT portion 20 and the like, and the signal wiring 17, the source electrode 18 and the drain electrode 19 are formed by photolithography. Next, a 400 nm silicon nitride film (insulating film) is formed on the signal wiring 17 and the like, and the contact hole 21 is formed by photolithography. Subsequently, an ITO film having a thickness of 100 nm is formed on the silicon nitride film, and the pixel electrode 22 is formed by photolithography.

  Next, a method for manufacturing the counter substrate will be described. A metal chromium film is formed to 300 nm on the glass substrate 5, and the BM 24 is formed by photolithography. The red, green, and blue color material layers 25 are formed on the portions partitioned by the BM 24 by repeating film formation and photolithography. Thereafter, an overcoat layer is formed on the color material layer 25 and the like. Further, an ITO film having a thickness of 100 nm is formed on the overcoat layer, and slits 26 are formed in the counter electrode by photolithography.

  A method for manufacturing the liquid crystal panel 7 using the electrode substrate and the counter substrate manufactured as described above will be described. First, an alignment film (Optomer (registered trademark) AL3046 manufactured by JSR Co., Ltd.) having a thickness of about 80 nm is formed on the electrode substrate and the counter substrate, and the surface of the alignment film is shown in FIGS. 6 and 7 using a roller rubbing apparatus. A rubbing process is performed in the alignment process directions 23 and 27. Next, a resin spacer (Micropearl (registered trademark) manufactured by Sekisui Chemical Co., Ltd.) is sprayed on the counter substrate side. On the other hand, a sealing agent is applied to the periphery of the substrate on the electrode substrate side. Subsequently, the electrode substrate and the counter substrate are overlapped in a predetermined direction, and bonded together by thermocompression bonding. Thereafter, a liquid crystal material is injected from the opening (liquid crystal injection port) of the sealing agent of the bonded substrates. After the injection, the opening (liquid crystal injection port) of the sealing agent is sealed using an ultraviolet curable resin.

  As described above, after the liquid crystal panel 7 is manufactured, a drive circuit is mounted on the gate wiring 15, the signal wiring 17, the counter electrode, and the like so that a predetermined voltage can be applied to each electrode. After the mounting process, an optical film such as the biaxial film 13 or the linearly polarizing plate 12 shown in FIG.

  In the liquid crystal display device according to the present embodiment, a liquid crystal material having a panel gap d of 7 μm and physical properties shown in Table 1 is used. In the case of the present embodiment, the phase difference set value Δnd of the liquid crystal layer 1 is 980 nm (0.14 × 7 μm).

  The liquid crystal display device according to the present embodiment has the configuration of the optical film shown in FIG. Table 2 shows the configuration and characteristic values of the optical film shown in FIG. In Table 2, the configuration and the characteristic values from the upper linear polarizing plate 12 shown in FIG. 5 to the lower linear polarizing plate 12 are shown in order. Note that directions such as the transmission axis and the front slow axis are represented by counterclockwise angles with the right hand as 0 degrees when the liquid crystal display device is viewed from the front. That is, the alignment treatment direction 23 of the alignment film shown in FIG. 6 corresponds to 90 degrees, and the alignment treatment direction 27 of the alignment film shown in FIG. 7 corresponds to 270 degrees. The phase difference in Table 2 is a value at a wavelength of 550 nm. In Table 2, the thickness direction average retardation Rth of the biaxial film 13 is defined by Rth = (nz− (nx + ny) / 2) df, where the film thickness is df.

  The liquid crystal display device according to the present embodiment has the following electro-optical characteristics by adopting the configuration of the optical film shown in FIG. 5 and Table 2. First, FIG. 8 shows applied voltage-transmittance characteristics in the front of the liquid crystal display device. Here, the applied voltage is a voltage applied between the pixel electrode 22 and the counter electrode. The transmittance is normalized by the transmittance at the opening of the liquid crystal display device to which no optical film is attached. From the results shown in FIG. 8, in the liquid crystal display device according to the present embodiment, the black voltage is set to 6.3V and the white voltage is set to 2.5V.

  FIG. 9 shows the contrast distribution of white and black in the liquid crystal display device according to the present embodiment. As shown in FIG. 9, in the liquid crystal display device according to the present embodiment, a contrast of 10 or more is realized in a viewing angle range of 160 degrees or more in the vertical direction and 140 degrees in the left and right direction. That is, the liquid crystal display device according to the present embodiment solves the problem that the viewing angle characteristic in the vertical direction is wide but the viewing angle characteristic in the horizontal direction is narrow as in the DDB mode liquid crystal display device shown in FIG. Thus, a DDB mode liquid crystal display device capable of obtaining high contrast can be obtained.

  FIG. 10 shows a white transmittance distribution in the liquid crystal display device according to the present embodiment. As shown in FIG. 10, the liquid crystal display device according to the present embodiment has symmetrical viewing angle characteristics that are excellent not only in the horizontal direction but also in the vertical direction, similar to the DDB mode liquid crystal display device shown in FIG. ing.

  As described above, in the liquid crystal display device according to the present embodiment, wide viewing angle characteristics can be realized by using the circularly polarizing plate 11 in the DDB mode. In particular, the circularly polarizing plate 11 used in the liquid crystal display device according to the present embodiment is a circularly polarizing plate having a wide viewing angle that transmits circularly polarized light regardless of the viewing angle direction by using the biaxial film 13. . In the DDB mode, each pixel is composed of two bent alignment regions (region A and region B), so that the splay alignment portion 6 exists at one alignment film interface of each vent alignment region, There were some differences in the alignment state compared to the OCB mode composed of one bend alignment region, such as the remaining twist component of nematic liquid crystal. Nevertheless, the liquid crystal display device according to the present embodiment shows that wide viewing angle characteristics can be realized by using the circularly polarizing plate 11 in the DDB mode.

  Further, in the liquid crystal display device according to the present embodiment, the viewing angle characteristics at which the contrast is 10 or more are 140 degrees in the left-right direction and 160 degrees or more in the up-down direction, the front white transmittance is 18.0%, the black voltage Is 6.3V.

(Embodiment 2)
The liquid crystal display device according to the present embodiment has the same configuration as that of the optical film shown in the first embodiment, but the front slow axis direction of the biaxial film 13 is the upper and lower linear polarizing plates 12. The point different from the first embodiment is that it is orthogonal to the transmission axis. Table 3 shows the configuration of the optical film and the characteristic values in the liquid crystal display device according to the present embodiment.

  Table 3 also shows the configuration and characteristic values from the upper linear polarizing plate 12 shown in FIG. 5 to the lower linear polarizing plate 12 in order. Note that directions such as the transmission axis and the front slow axis are represented by counterclockwise angles with the right hand as 0 degrees when the liquid crystal display device is viewed from the front. Further, the phase difference in Table 3 is also a value at a wavelength of 550 nm. In Table 3, the thickness direction average phase difference Rth of the biaxial film 13 is also the same definition as the thickness direction average phase difference Rth in Table 2. is there.

  The biaxial film 13 according to the present embodiment is adjusted so that Nz = 0.1 to 0.4 because the front slow axis direction is orthogonal to the transmission axes of the upper and lower linear polarizing plates 12. Has been. In Table 3, Nz is 0.3.

  As described above, in the liquid crystal display device according to the present embodiment, wide viewing angle characteristics can be realized by adopting the configuration of the optical film shown in Table 3 in the DDB mode. Further, in the liquid crystal display device according to the present embodiment, the viewing angle characteristics at which the contrast is 10 or more are 140 degrees in the left-right direction and 160 degrees or more in the up-down direction, the front white transmittance is 18.0%, black The voltage is 6.3V.

(Embodiment 3)
The liquid crystal display device according to the present embodiment has a configuration in which the a plate 8, the c plate 9, and the circularly polarizing plate 11 are provided on the liquid crystal panel 7 as in the first embodiment. However, unlike the first embodiment, the circularly polarizing plate 11 according to the present embodiment includes the linearly polarizing plate 12 and the λ / 4 plate 14 without providing the biaxial film 13. Further, in the linear polarizing plate 12 of the first embodiment, the TAC on the liquid crystal panel 7 side is not provided, but in the linear polarizing plate 12 according to the present embodiment, the TAC on the liquid crystal panel 7 side is provided.

  As described in the first embodiment, the TAC itself has a phase difference of several tens of nm in the thickness direction. In the present embodiment, this TAC itself is used in place of the biaxial film 13 by utilizing the phase difference. However, since the range that can be compensated by the phase difference of the TAC itself is smaller than that of the biaxial film 13, the liquid crystal display device according to the present embodiment has contrast viewing angle characteristics as compared with the liquid crystal display device according to the first embodiment. Etc. become narrower.

  Table 4 below shows the configuration of the optical film and the characteristic values in the liquid crystal display device according to the present embodiment.

  Table 4 also shows the configuration and characteristic values from the upper linear polarizing plate 12 to the lower linear polarizing plate 12 in order. Note that directions such as the transmission axis and the front slow axis are represented by counterclockwise angles with the right hand as 0 degrees when the liquid crystal display device is viewed from the front. The phase difference in Table 4 is also a value at a wavelength of 550 nm.

  As described above, in the liquid crystal display device according to the present embodiment, the circularly polarizing plate 11 composed of the linearly polarizing plate 12 and the λ / 4 plate 14 provided with the TAC layers (protective layers) on both sides in the DDB mode. By providing, wide viewing angle characteristics can be realized, and the number of optical film components of the circularly polarizing plate 11 can be reduced to reduce the manufacturing cost. Further, in the liquid crystal display device according to the present embodiment, the viewing angle characteristics at which the contrast is 10 or more are 120 degrees in the left-right direction and 120 degrees in the up-down direction, the front white transmittance is 18.0%, the black voltage Is 6.3V.

(Embodiment 4)
The liquid crystal display device according to the present embodiment is configured by using the circularly polarizing plate 11 including the linearly polarizing plate 12 and the λ / 4 plate 14 without providing the biaxial film 13 as in the third embodiment. However, unlike the first embodiment, the liquid crystal display device according to the present embodiment has a configuration in which a biaxial film is provided instead of providing the a plate 8 and the c plate 9 on the liquid crystal panel 7. In other words, in the present embodiment, the phase difference compensation performed by the a plate 8 and the c plate 9 is performed by one sheet of biaxial film. Note that the linear polarizing plate 12 according to the present embodiment is also provided with a TAC on the liquid crystal panel 7 side.

  Table 5 below shows the configuration of the optical film and the characteristic values in the liquid crystal display device according to the present embodiment.

  Table 5 also shows the configuration and characteristic values from the upper linear polarizing plate 12 to the lower linear polarizing plate 12 in order. Note that directions such as the transmission axis and the front slow axis are represented by counterclockwise angles with the right hand as 0 degrees when the liquid crystal display device is viewed from the front. Moreover, the phase difference of Table 5 is also a value at a wavelength of 550 nm. In Table 5, the thickness direction average phase difference Rth of the biaxial film has the same definition as the thickness direction average phase difference Rth in Table 2. .

  As described above, in the liquid crystal display device according to the present embodiment, the circularly polarizing plate 11 composed of the linearly polarizing plate 12 and the λ / 4 plate 14 provided with the TAC layers (protective layers) on both sides in the DDB mode. By providing, wide viewing angle characteristics can be realized, and the number of optical film components of the circularly polarizing plate 11 can be reduced to reduce the manufacturing cost. Furthermore, since the number of optical films provided between the circularly polarizing plate 11 and the liquid crystal panel 7 can be reduced from two to one, the manufacturing cost for attaching the optical film and the opportunity for occurrence of misalignment are reduced. Can do. Further, in the liquid crystal display device according to the present embodiment, the viewing angle characteristics at which the contrast is 10 or more are 120 degrees in the left-right direction and 120 degrees in the up-down direction, the front white transmittance is 18.0%, the black voltage Is 6.3V.

  In addition, although the thickness direction average phase difference Rth of the biaxial film shown in Table 5 is −275 nm, it is slightly different from the thickness direction phase difference (−260 nm) of the c plate 9 shown in Table 4. This difference is due to the difference between the two plates of the a plate 8 and the c plate 9 or the single plate of the biaxial film.

(Embodiment 5)
The liquid crystal display device according to the present embodiment has the same optical film configuration as that shown in FIG. 5 of the first embodiment, except that the panel gap d of the liquid crystal panel 7 is 9 μm. d = 7 μm). Since the panel gap d of the liquid crystal panel 7 is 9 μm, the liquid crystal material used for this is different from the liquid crystal material shown in Table 1 only in the chiral pitch (p = 30 μm (25 ° C.)). In this case, the retardation setting value Δnd of the liquid crystal layer 1 is 0.14 × 9000 nm = 1260 nm.

  In the liquid crystal display device according to the present embodiment, the applied voltage-transmittance characteristics change as the retardation setting value Δnd of the liquid crystal layer 1 increases from 980 nm to 1260 nm in the first embodiment, and is necessary for black display. The applied voltage is 7.9V. Further, in the liquid crystal display device according to the present embodiment, the viewing angle characteristic at which the contrast is 10 or more is 120 degrees in the left-right direction and 160 degrees or more in the up-down direction, which is inferior to the case of Embodiment 1 by about 20 degrees in the left-right direction. ing. However, in the liquid crystal display device according to the present embodiment, the front white transmittance is 28.0%, which is an improvement over the front white transmittance 18.0% of the first embodiment.

  The optical film configuration of the liquid crystal display device according to the present embodiment is the same as Table 2 shown in the first embodiment, except that the thickness direction retardation of the c plate 9 is −380 nm. .

  In the liquid crystal display device according to the present embodiment, since the white transmittance is improved as compared with the first embodiment, a brighter display is possible if the luminance of the backlight is the same as that of the first embodiment. However, the liquid crystal display device according to the present embodiment has a problem that it is difficult to drive a commonly used driver IC because the black voltage is as high as 7.9V. Therefore, in the present invention, in consideration of the above contents and past empirical rules, if the phase difference setting value Δnd of the liquid crystal layer 1 is 1100 nm or less, white transmission is performed while driving with a commonly used driver IC. I think it is possible to improve the rate. In consideration of past empirical rules, it is considered that sufficient optical characteristics cannot be obtained when the retardation setting value Δnd of the liquid crystal layer 1 is smaller than 900 nm.

  As described above, in the present invention, when the retardation setting value Δnd of the liquid crystal layer 1 is in the range of 900 nm to 1100 nm, wide viewing angle characteristics and high white transmittance can be obtained while driving with a commonly used driver IC. Can be realized.

(Embodiment 6)
In the liquid crystal display device according to the present embodiment, the liquid crystal panel 7 and the optical film have the same configurations as those of the first embodiment, but some of the characteristic values of the optical film are different. Table 6 below shows the configuration and characteristic values of the optical film in the liquid crystal display device according to the present embodiment.

  Table 6 also shows the configuration and characteristic values from the upper linear polarizing plate 12 shown in FIG. 5 to the lower linear polarizing plate 12 in order. Note that directions such as the transmission axis and the front slow axis are represented by counterclockwise angles with the right hand as 0 degrees when the liquid crystal display device is viewed from the front. Moreover, the phase difference of Table 6 is also a value at a wavelength of 550 nm. In Table 6, the thickness direction average phase difference Rth of the biaxial film is the same definition as the thickness direction average phase difference Rth in Table 2. .

  As can be seen from Table 6, in the liquid crystal display device according to the present embodiment, unlike the case of the first embodiment, the in-plane retardation of the a plate 8 is as small as 40 nm. That is, in the first embodiment, the total in-plane phase difference of the two a plates 8 is 100 nm, but in this embodiment, it is 80 nm. In the liquid crystal display device according to the present embodiment, the thickness direction retardation of the c plate 9 also changes to −290 nm by changing the in-plane retardation of the a plate 8.

  Thereby, the liquid crystal display device according to the present embodiment has a viewing angle characteristic with a contrast of 10 or more, 160 degrees or more in the horizontal direction, 160 degrees or more in the vertical direction, and a white transmittance of 21.7% in the front. Become. That is, in the liquid crystal display device according to the present embodiment, the viewing angle characteristic of contrast becomes wider and the white transmittance is improved as compared with the first embodiment. However, since the black voltage of the liquid crystal display device according to the present embodiment is as high as 7.7 V, there is a problem that it is difficult to drive the driver IC that is generally used. Therefore, in the present invention, in consideration of the above contents and past empirical rules, if the total in-plane retardation of the a plate 8 is larger than 90 nm, the contrast is driven while being driven by a commonly used driver IC. It is considered possible to improve the viewing angle characteristics and white transmittance.

  As described above, according to the present invention, the a-plate 8 that is a uniaxial film generates a phase difference larger than 90 nm in total, thereby driving a wide viewing angle characteristic and high whiteness while being driven by a commonly used driver IC. Transmittance can be realized. Even when a biaxial film is used instead of the a plate 8 as in the fourth embodiment, the same effect can be obtained as long as the total in-plane retardation is larger than 90 nm.

(Comparative example)
For comparison, the case of the liquid crystal display device shown in FIG. 2 will be described. In the comparative example, the optical film shown in Table 7 is used for the liquid crystal panel 7 having the same configuration as that of the first embodiment. That is, in the comparative example, the liquid crystal display device has a configuration in which the circularly polarizing plate 11 is not used.

  In the liquid crystal display device according to the comparative example, the viewing angle characteristics at which the contrast is 10 or more are 80 degrees in the left-right direction and 140 degrees in the up-down direction, the front white transmittance is 18.0%, and the black voltage is 6.3 V. It has become.

  Although the configuration of several optical films has been described in the above first to sixth embodiments, the configuration is an example, and in the above-described embodiment, a single retardation film is used. A similar function may be realized by two retardation films. For example, if it is difficult to manufacture an optical film having a large retardation, it may be realized by using two optical films having a small retardation. Conversely, the compensation function using two retardation films may be realized by using one retardation film.

  Further, in Embodiments 1 to 6, the liquid crystal display device is set so that the alignment processing directions 23 and 27 are in the vertical direction when the liquid crystal display device is viewed from the front. However, the present invention is limited to this direction. Instead, the electrode substrate side and the counter substrate side may be in opposite directions, and may be set in other directions such as the left-right direction.

It is a figure explaining the structure of the liquid crystal display device used as the premise of this invention. It is a figure explaining the structure of the liquid crystal display device used as the premise of this invention. It is a figure explaining the optical characteristic of the liquid crystal display device used as the premise of this invention. It is a figure explaining the optical characteristic of the liquid crystal display device used as the premise of this invention. It is sectional drawing explaining the structure of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a figure explaining the structure of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a figure explaining the structure of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a figure explaining the optical characteristic of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a figure explaining the optical characteristic of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a figure explaining the optical characteristic of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is sectional drawing explaining the structure of the liquid crystal display device of bent orientation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal layer, 2 Liquid crystal molecule, 3 Orientation film, 4 Transparent electrode, 5 Glass substrate, 6 Spray orientation part, 7 Liquid crystal panel, 8 a plate, 9 c plate, 10 Polarizing plate, 11 Circular polarizing plate, 12 Linearly polarizing plate , 13 Biaxial film, 14 λ / 4 plate, 15 Gate wiring, 16 Gate electrode, 17 Signal wiring, 18 Source electrode, 19 Drain electrode, 20 TFT section, 21 Contact hole, 22 Pixel electrode, 23, 27 Orientation processing direction , 24 Black matrix, 25 color material layer, 26 slits.

Claims (6)

An electrode substrate provided with a plurality of pixel electrodes;
A counter electrode disposed opposite to the electrode substrate, and a counter substrate oriented in a substantially antiparallel direction with respect to the alignment treatment of the electrode substrate;
A chiral nematic liquid crystal sandwiched between the electrode substrate and the counter substrate and divided into at least two bend alignment regions in each pixel by an electric field between the pixel electrode and the counter electrode;
The liquid crystal display device, wherein the electrode substrate and the counter substrate further include a circularly polarizing plate on a surface opposite to a surface sandwiching the chiral nematic liquid crystal. The liquid crystal display device according to claim 1,
The circularly polarizing plate includes a linearly polarizing plate, a first biaxial film that causes a phase difference in the first front slow axis direction and thickness direction in the plane, and a second front slow axis direction in the plane. A quarter-wave plate that generates a phase difference of approximately ¼ wavelength,
The first biaxial film is arranged so that the first front slow axis direction is parallel to or orthogonal to the transmission axis direction of the linearly polarizing plate,
The liquid crystal display device, wherein the quarter-wave plate is arranged such that the second front slow axis direction forms an angle of approximately 45 degrees with the transmission axis direction of the linearly polarizing plate. The liquid crystal display device according to claim 1,
The circularly polarizing plate generates a phase difference of approximately ¼ wavelength in the in-plane second front slow axis direction with a linearly polarizing plate provided with a protective layer on the electrode substrate side and the counter substrate side surfaces. A quarter wave plate,
The liquid crystal display device, wherein the quarter-wave plate is arranged such that the second front slow axis direction forms an angle of approximately 45 degrees with the transmission axis direction of the linearly polarizing plate. A liquid crystal display device according to any one of claims 1 to 3,
A uniaxial film that causes a phase difference in the in-plane third front slow axis direction between at least one of the counter substrate and the circularly polarizing plate and between the electrode substrate and the circularly polarizing plate. Prepared,
The liquid crystal display device, wherein the uniaxial film produces a total retardation larger than 90 nm. A liquid crystal display device according to any one of claims 1 to 3,
A phase difference is caused in the in-plane third front slow axis direction and thickness direction between at least one of the counter substrate and the circularly polarizing plate and between the electrode substrate and the circularly polarizing plate. Further comprising a second biaxial film;
The liquid crystal display device according to claim 2, wherein the second biaxial film causes a phase difference larger than 90 nm in total in the third front slow axis direction. A liquid crystal display device according to any one of claims 1 to 5,
A liquid crystal display device, wherein a retardation setting value of a liquid crystal layer obtained by a product of birefringence of the chiral nematic liquid crystal and a distance between the electrode substrate and the counter substrate is in a range of 900 nm to 1100 nm. .

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