JP2007178664A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transflective liquid crystal display device having superior viewing angle characteristics. <P>SOLUTION: The liquid crystal display device is equipped with a liquid crystal panel 100, having a domain in which liquid crystal molecules align radially with inclination, when a predetermined voltage is applied to a liquid crystal layer in a pixel, and having a transmissive region that displays with a transmission mode and a reflection region for displaying with a reflection mode in the pixel; a first polarizing layer POL1, a first retardation layer R1, a second retardation layer R2, and a third retardation layer R3, disposed in this order, starting from the viewer's side of the liquid crystal panel; and a second polarizing layer POL2, a fourth retardation layer R4, a fifth retardation layer R5, and a sixth retardation layer R6, disposed in this order, starting from the side opposite to the viewer's side of the liquid crystal panel. Typically the first and fourth retardation layers function as half-wave plates and the third and sixth retardation layers function as quarter-wave plates. The second and fourth retardation layers R2, R4 have 50 nm or smaller in-plane retardation Re and have negative refractive index anisotropy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

  A liquid crystal display device is widely used as one of thin display devices (flat panel display: FPD). Among them, as a liquid crystal display device for a mobile device, a transflective liquid crystal display device is widely used (for example, Patent Documents 1 and 2 by the applicant of the present application, hereinafter referred to as “bipolar liquid crystal”). Display device "). The dual-use liquid crystal display device has a transmissive area that displays in the transmissive mode and a reflective area that displays in the reflective mode in the pixel, enabling high-quality display not only indoors but also outdoors where the outside light is strong. is there.

  Also known as a liquid crystal display device having excellent viewing angle characteristics is a liquid crystal display device having domains in which liquid crystal molecules are aligned radially (axisymmetrically) when a predetermined voltage is applied to a liquid crystal layer in a pixel. (For example, Patent Documents 3 to 5). In this liquid crystal display device, liquid crystal molecules are arranged radially by applying an alignment regulating force such as an oblique electric field or a protrusion to a vertical alignment type liquid crystal layer typically made of a nematic liquid crystal material having a negative dielectric anisotropy. Are aligned (sometimes referred to as “radially inclined alignment domains”). Here, “radial tilt alignment” is synonymous with “axially symmetric alignment”, and the liquid crystal molecules form a disclination line around the center of the radial tilt alignment (center axis of the axially symmetric alignment). The liquid crystal molecules are aligned continuously and the major axis of the liquid crystal molecules is aligned radially and spirally. In either case, the major axis of the liquid crystal molecules has a component (component parallel to the oblique electric field) inclined radially from the center of alignment. In this radially tilted liquid crystal domain, the long axis (director) of the liquid crystal molecules is aligned in all directions (azimuth in the substrate plane), so that viewing angle characteristics are excellent.

Although the present applicant has developed a dual-use liquid crystal display device (see, for example, Patent Document 6) that employs a mode that adopts the above-described radial tilt alignment, the need for improving viewing angle characteristics in mobile devices is increasing. .
Japanese Patent No. 2955277 US Pat. No. 6,195,140 JP-A-6-301036 JP 2000-47217 A JP 2003-167253 A JP 2005-250431 A

  The conventional dual-use liquid crystal display device employs an optical film configuration such as the liquid crystal display devices 200A and 200B shown in FIGS. 12 (a) and 12 (b). Since the arrangement of the polarizing layer and the retardation layer is symmetrical with respect to the liquid crystal panel (liquid crystal layer), only the polarizing layer and the retardation layer on the viewer side are shown in the figure. In general, commercially available polarizing plates include a polarizing layer that selectively transmits linearly polarized light (typically a polyvinyl alcohol (PVA) layer containing iodine) and a protective layer (typically triacetyl cellulose). Roll (TAC) layer). Here, since the retardation of the TAC layer is also taken into consideration, the polarizing layer and the polarizing plate are distinguished. In addition, since the TAC layer is considered as a so-called retardation plate, the term retardation layer is used. Although not particularly shown, an adhesive layer may be provided between the respective layers. Conventionally, typically between a polarizing plate (TAC layer / PVA layer / TAC layer) and an adjacent retardation layer. In addition, an adhesive layer is provided between the retardation layers adjacent to each other.

  Here, the following parameters are used to describe the refractive index anisotropy of the retardation layer.

  The principal axis having the largest refractive index in the layer surface of the retardation layer is the a axis, the principal axis in the layer surface orthogonal to the a axis is the b axis, the other principal axis in the surface normal direction is the c axis, and each principal refractive index in each principal axis direction. , Na, nb and nc, its thickness is d, its in-plane retardation is Re = (na−nb) · d, and its retardation in the thickness direction is Rth = ([(na + nb) / 2] −nc) · d. And In addition, when showing the numerical value of retardation, unless otherwise indicated, it shall represent the retardation with respect to light of 550 nm.

  The vertical alignment type liquid crystal layer is aligned substantially perpendicular (85 ° or more and 90 ° or less) with respect to the substrate surface when no voltage is applied, and tilts as the voltage is applied. By controlling the voltage, the retardation is set to change from about 250 nm to about 450 nm. The liquid crystal layer when no voltage is applied exhibits the same refractive index anisotropy as the positive uniaxial retardation layer (na = nb <nc).

  The liquid crystal display device 200A has a negative uniaxial retardation layer (na = nb> nc), and has a 1/4 wavelength layer and a 1/2 wavelength layer in this order on the viewer side. The negative uniaxial retardation layer is provided to compensate for the positive uniaxial refractive index anisotropy of the liquid crystal layer when no voltage is applied, and is conventionally disposed at a position closest to the liquid crystal layer. It was. The ¼ wavelength layer is provided to make light passing through the liquid crystal layer circularly polarized in order to display in the reflection mode, and the ½ wavelength layer is provided to suppress coloring in the reflection mode. It has been. When the ½ wavelength layer is provided, although the coloration in the reflection mode display is suppressed, the viewing angle becomes narrow and sufficient viewing angle characteristics cannot be obtained.

  The liquid crystal display device 200B is an example in which the negative uniaxial retardation layer and the ¼ wavelength layer in the liquid crystal display device 200A are configured by a single biaxial retardation layer, and a sufficient field of view similar to the liquid crystal display device 200A. Angular characteristics could not be obtained.

  The present invention has been made in view of the above points, and has as its main object to provide a dual-use liquid crystal display device having excellent viewing angle characteristics.

  The liquid crystal display device of the present invention has a domain in which liquid crystal molecules are radially inclined when a predetermined voltage is applied to a liquid crystal layer in a pixel, and displays in a transmissive region and a reflective mode in the transmissive mode in the pixel. A liquid crystal panel having a reflective region, and a first polarizing layer, a first retardation layer, a second retardation layer, a third retardation layer arranged in this order from the viewer side of the liquid crystal panel, A second polarizing layer, a fourth retardation layer, a fifth retardation layer, and a sixth retardation layer, which are arranged in this order from the side opposite to the viewer side of the liquid crystal panel; The absorption axis is orthogonal to the absorption axis of the first polarizing layer, the fourth retardation layer has substantially the same refractive index anisotropy as the first retardation layer, and the fifth retardation layer is The sixth retardation layer has substantially the same refractive index anisotropy as the second retardation layer, and the sixth retardation layer is substantially the same as the third retardation layer. When the main axis having the same refractive index anisotropy and having the largest refractive index in the layer surface of each retardation layer is defined as the a-axis, the fourth retardation layer, the fifth retardation layer, and the sixth retardation layer Each a axis is arranged so as to be orthogonal to the a axis of each of the associated retardation layers. The a axis of the first retardation layer is defined as a1 axis, and the principal axis in the layer plane orthogonal to the a1 axis is defined as b1. Axis, other principal axis in the surface normal direction is the c1 axis, each principal refractive index in each principal axis direction is na1, nb1 and nc1, its thickness is d1, its in-plane retardation is Re1 = (na1-nb1) · d1, The retardation in the thickness direction is Rth1 = ([(na1 + nb1) / 2] −nc) · d1, the a axis of the second retardation layer is the a2 axis, the main axis in the layer plane orthogonal to the a2 axis is the b2 axis, The other principal axis in the surface normal direction is the c2 axis. The main refractive indexes are na2, nb2 and nc2, the thickness is d2, the in-plane retardation is Re2 = (na2-nb2) · d2, and the retardation in the thickness direction is Rth2 = ([(na2 + nb2) / 2]. −nc) · d2, the a axis of the third retardation layer is the a3 axis, the main axis in the layer plane orthogonal to the a3 axis is the b3 axis, the other main axis in the surface normal direction is the c3 axis, and each main axis direction is The main refractive indexes are na3, nb3 and nc3, the thickness is d3, the in-plane retardation is Re3 = (na3-nb3) · d3, and the retardation in the thickness direction is Rth3 = ([(na3 + nb3) / 2] −nc ) · D3, the absorption axis of the first polarizing layer is the X axis, the smaller of the crossing angles of the X axis and the a1 axis is θ (> 0), and the X axis is the reference Direction in which the crossing angle with the a1 axis is θ Assuming that the angle between the X axis and the a3 axis is γ (> 0) as the + direction, 40 ≦ | 2 · θ−γ | ≦ 50 or 130 ≦ | 2 · θ−γ | ≦ 140 is satisfied, and 30 nm ≦ Re1-1.5 · Re3 ≦ 100 nm, 70 nm ≦ Re3 ≦ 170 nm, and Re2 ≦ 50 nm are satisfied.

  In one embodiment, it is more preferable that Rth1 <Rth2 is satisfied and Rth1 <0.

  In one embodiment, it is more preferable that 0 nm <Rth2 ≦ 150 nm is satisfied, and 20 nm ≦ Rth2 ≦ 150 nm is satisfied.

  In one embodiment, an adhesive layer may not be provided between the first retardation layer and the second retardation layer and between the second retardation layer and the third retardation layer. .

  In an embodiment, an adhesive layer may not be provided between the first polarizing layer and the first retardation.

  In one embodiment, a configuration in which a further retardation layer having substantially the same refractive index anisotropy as the second retardation layer is provided between the first polarizing layer and the first retardation layer. Good.

  According to the present invention, the viewing angle characteristics of the dual-use liquid crystal display device can be improved.

  With reference to the drawings, a dual-use liquid crystal display device according to an embodiment of the present invention will be described.

  1A and 1B are schematic cross-sectional views of liquid crystal display devices 100A and 100B according to an embodiment of the present invention.

  The liquid crystal display devices 100A and 100B have domains in which liquid crystal molecules are radially inclined when a predetermined voltage is applied to the liquid crystal layer in the pixel, and display in a transmissive region and a reflective mode in the pixel in the transmissive mode. This is a dual-use liquid crystal display device including a liquid crystal panel 100 having a reflective region for performing the above. The configuration of the liquid crystal panel 100 will be described later.

  The liquid crystal display devices 100A and 100B include a first polarizing layer POL1, a first retardation layer R1, a second retardation layer R2, and a third retardation layer R3 arranged in this order from the viewer side of the liquid crystal panel 100. The second polarizing layer POL2, the fourth retardation layer R4, the fifth retardation layer R5, and the sixth retardation layer R6 are arranged in this order from the side opposite to the viewer side of the liquid crystal panel. . The fourth retardation layer R4 has substantially the same refractive index anisotropy as the first retardation layer R1, and the fifth retardation layer R5 has substantially the same refractive index anisotropy as the second retardation layer R2. The sixth retardation layer R6 has substantially the same refractive index anisotropy as the third retardation layer R3.

  The first polarizing layer POL1 of the liquid crystal display device 100A is sandwiched between a pair of protective layers P1 and P2. The protective layers P1 and P2 are typically TAC layers. On the other hand, the liquid crystal display device 100B is provided with the protective layer P1 on the viewer side of the first polarizing layer POL1, but is different from the liquid crystal display device 100A in that it does not have a protective layer on the liquid crystal panel 100 side. .

Here, the a-axis of the first retardation layer R1 is the a1 axis, the main axis in the layer plane orthogonal to the a1 axis is the b1 axis, the other main axis in the surface normal direction is the c1 axis, and each main refractive index in each main axis direction , Na1, nb1 and nc1, the thickness is d1, the in-plane retardation is Re1 = (na1-nb1) · d1, and the retardation in the thickness direction is Rth1 = ([(na1 + nb1) / 2] −nc) · d1 The a axis of the second retardation layer R2 is the a2 axis, the main axis in the layer plane orthogonal to the a2 axis is the b2 axis, the other main axis in the surface normal direction is the c2 axis, and each main refractive index in each main axis direction is na2. , Nb2 and nc2, the thickness is d2, the in-plane retardation is Re2 = (na2-nb2) · d2, the retardation in the thickness direction is Rth2 = ([(na2 + nb2) / 2] −nc) · d2, A of the third retardation layer R3 The axis is the a3 axis, the main axis in the layer plane orthogonal to the a3 axis is the b3 axis, the other main axis in the surface normal direction is the c3 axis, the main refractive indexes in each main axis direction are na3, nb3 and nc3, and the thickness is d3 When the in-plane retardation is Re3 = (na3-nb3) · d3 and the retardation in the thickness direction is Rth3 = ([(na3 + nb3) / 2] −nc) · d3,
30 nm ≦ Re1-1.5 · Re3 ≦ 100 nm,
70 nm ≦ Re3 ≦ 170 nm, and
Re2 ≦ 50 nm,
Satisfied with the relationship.

Here, the optical arrangement (axial arrangement) of the polarizing layer and the retardation layer will be described with reference to FIG. 2 shows the X direction which is the absorption axis direction of the first polarizing layer POL1 disposed on the viewer side of the liquid crystal panel 100, the a1 axis direction of the first retardation layer R1, and the a3 axis of the third retardation layer R3. The direction relationship is shown. The absorption axis of the first polarizing layer POL1 is the X axis, the smaller of the crossing angles of the X axis and the a1 axis is θ (> 0), and the crossing of the X axis and the a1 axis is based on the X axis. If the direction where the angle is θ is the + direction and the angle formed by the X axis and the a3 axis is γ (> 0),
40 ≦ │ 2 ・ θ−γ │ ≦ 50 or 130 ≦ │ 2 ・ θ−γ │ ≦ 140
Is set to satisfy.

  In order to briefly explain the meaning of this angle setting (optical arrangement), for example, the first retardation layer R1 is a half-wave plate and the third retardation plate R3 is a quarter-wave plate. If θ is 22.5 °, γ is 90 °. In this optical arrangement, natural light (non-polarized light) incident on the first polarizing layer POL1 from the surface normal direction passes only linearly polarized light having a polarization plane orthogonal to the X direction, and this linearly polarized light is transmitted through the first retardation layer. (1/2 wavelength plate) R1 converts the plane of polarization into linearly polarized light symmetric with respect to the a1 axis (slow axis). The plane of polarization of the converted linearly polarized light forms an angle of 45 ° with respect to the a3 axis (slow axis) of the third retardation layer (1/4 wavelength plate) R3, so that the third retardation layer (1/4 The light transmitted through the wave plate R3 becomes circularly polarized light. With respect to this basic optical arrangement, ± 5 ° is considered as an alignment margin. The alignment margin is preferably ± 3 °.

  The conditions of the above 30 nm ≦ Re1-1.5 · Re3 ≦ 100 nm and 70 nm ≦ Re3 ≦ 170 nm are that the first retardation layer R1 and the third retardation layer R3 serve as a half-wave plate and a quarter-wave plate. It is more preferable that the above-described basic functions are satisfied, and 50 nm ≦ Re1-1.5 · Re3 ≦ 80 nm and 100 nm ≦ Re3 ≦ 150 nm are satisfied.

  The first retardation layer R1 preferably satisfies Rth1 <Rth2. When Rth1 is larger than Rth2, the viewing angle is narrowed. Rth1 <0 nm is preferable.

  The second retardation layer R2 is basically for compensating for the positive uniaxial refractive index anisotropy of the liquid crystal layer, and has a negative refractive index anisotropy (nc <na, nc <nb). have. Moreover, it is preferable to satisfy 0 nm <Rth2 ≦ 150 nm, and it is further preferable to satisfy 20 nm ≦ Rth2 ≦ 150 nm. If it is out of the above range, the viewing angle becomes narrow.

  The in-plane retardation Re2 of the second retardation layer R2 is preferably zero (that is, na = nb), and FIG. 2 does not show the a2 axis with Re2 = 0 (the a2 axis and the b2 axis are in-plane) It is equivalent in any direction). When Re2 is not zero, the a2 axis is preferably coincident with the a1 axis of the first retardation layer or the a3 axis of the third retardation layer. At this time, the sum of the in-plane retardation (Re1 or Re3) of the retardation layer (R1 or R3) with the a2 axis matched and the in-plane retardation Re2 of the second retardation layer is the in-plane retardation of the retardation layer. It is preferable that the retardation is set so as to satisfy the above relationship regarding Re1 and Re3.

  The above-described conditions are obtained by simulation and experiment described later.

  The a-axis of the retardation layer disposed on the side opposite to the viewer side of the liquid crystal panel 100 is disposed so as to be orthogonal to the a-axis of each retardation layer disposed symmetrically with respect to the liquid crystal panel 100. That is, the a4 axis of the fourth retardation layer R4 is arranged to be orthogonal to the a1 axis of the first retardation layer R1, and the a5 axis of the fifth retardation layer R5 is the a2 axis of the second retardation layer R2. The a6 axis of the sixth retardation layer R6 is arranged to be orthogonal to the a3 axis of the third retardation layer R3.

  By satisfying the above relationship, a liquid crystal display device having better viewing angle characteristics than the conventional one can be obtained, as will be described later with reference to simulation results and experimental examples.

  The liquid crystal display device 100A and the liquid crystal display device 100B have a difference in whether or not they have a protective layer (TAC layer) between the pair of polarizing layers POL1 and POL2, but they have superior viewing angle characteristics. There is no difference. When the configuration of the liquid crystal display device 100B is employed, a laminated film including a protective layer P1, a first polarizing layer POL1, a second retardation layer R2, and a third retardation layer R3 (sometimes collectively referred to as an optical film). Can be produced by a roll-to-roll method. For example, the polarizing layer POL1 with the protective layer P1 is supplied in a roll shape in which the absorption axis direction (X direction) is the machine direction. The third retardation layer R3 is formed of a film that is biaxially stretched in the machine direction and a direction orthogonal to the machine direction, and has a second retardation layer R2 in a roll shape in which the a3 axis is orthogonal to the machine direction. Can be supplied in the state. Therefore, if these roll-shaped films are bonded together with the machine direction coincident, the X direction and the a3 axis are arranged as shown in FIG. Before the first retardation layer R1 is bonded to the polarizing layer POL1 with the protective layer P1 and the third retardation layer R3 with the second retardation layer R2, a liquid crystalline polymer material is coated on either surface. (See, for example, JP-A-2004-199045). The a1 axis direction can be controlled, for example, by subjecting the surface to be coated to a rubbing treatment in a predetermined direction before coating the liquid crystalline polymer material.

  The liquid crystal display devices 100A and 100B shown in FIGS. 1A and 1B are similar to the conventional liquid crystal display device in that the phase difference layers adjacent to each other between the polarizing plate and the phase difference layers adjacent thereto are used. Although an adhesive layer may be provided between them, as described above, an optical film can be manufactured by a roll-to-roll method, so that the yield of materials can be improved and the manufacturing cost can be reduced. Even when the configuration of the liquid crystal display device 100A is adopted, the optical film is manufactured by the roll-to-roll method by forming the first retardation layer R1 and the second retardation layer R2 by the coating method. can do.

  Next, with reference to FIG. 3, the structure of the dual-use liquid crystal panel 100 that is preferably used as the liquid crystal panel for the liquid crystal display device of the present embodiment will be described.

  3A and 3B are diagrams schematically showing the structure of one pixel region of the liquid crystal panel 100 in the present embodiment. In the following, a color filter and a black matrix are omitted for the sake of simplicity. 3A is a top view of the pixel region viewed from the substrate normal direction, and FIG. 3B corresponds to a cross-sectional view taken along line 3B-3B ′ in FIG. FIG. 3B shows a state where no voltage is applied to the liquid crystal layer.

  The liquid crystal panel 100 includes an active matrix substrate (hereinafter referred to as “TFT substrate”) 100a, a counter substrate (also referred to as “color filter substrate”) 100b, and a liquid crystal provided between the TFT substrate 100a and the counter substrate 100b. Layer 30. The liquid crystal molecules 30a of the liquid crystal layer 30 have negative dielectric anisotropy, and a vertical alignment film (not shown) as a vertical alignment layer provided on the surface of the TFT substrate 100a and the counter substrate 100b on the liquid crystal layer 30 side. Thus, when no voltage is applied to the liquid crystal layer 30, as shown in FIG. 3B, the liquid crystal layer 30 is aligned perpendicular to the surface of the vertical alignment film. At this time, the liquid crystal layer 30 is said to be in a vertically aligned state. However, the liquid crystal molecules 30a of the liquid crystal layer 30 in the vertical alignment state may be slightly inclined from the normal line of the surface of the vertical alignment film (substrate surface) depending on the type of the vertical alignment film and the type of the liquid crystal material. In general, a state in which liquid crystal molecular axes (also referred to as “axis orientation”) are aligned at an angle of about 85 ° or more with respect to the surface of the vertical alignment film is called a vertical alignment state.

  The TFT substrate 100a of the liquid crystal panel 100 has a transparent substrate (for example, a glass substrate) 11 and a pixel electrode 14 formed on the surface thereof. The counter substrate 100b includes a transparent substrate (for example, a glass substrate) 21 and a counter electrode 22 formed on the surface thereof. The alignment state of the liquid crystal layer 30 for each pixel region changes in accordance with the voltage applied to the pixel electrode 14 and the counter electrode 22 arranged so as to face each other via the liquid crystal layer 30. Display is performed using a phenomenon in which the polarization state and amount of light transmitted through the liquid crystal layer 30 change in accordance with the change in the alignment state of the liquid crystal layer 30.

  Each pixel region includes a transmissive region T that displays light in a transmissive mode using light incident from the TFT substrate 100a side (typically light from a backlight) and light incident from the counter substrate 100b side (typically And a reflection region R for displaying a reflection mode using external light. In the present embodiment, the pixel electrode 14 includes a transparent electrode formed from a transparent conductive material and a reflective electrode formed from a conductive material having light reflectivity, and the transmission region T is defined by the transparent electrode. The reflective region R is defined by the reflective electrode. In addition, when a minute uneven shape is provided on the surface of the reflective electrode, light can be diffusely reflected by the reflective electrode, so that white display close to paper white can be realized.

  In the transmissive mode display, the light used for display passes through the liquid crystal layer 30 only once, whereas in the reflective mode display, the light used for display passes through the liquid crystal layer 30 twice. As shown in FIG. 3B, by making the thickness dr of the liquid crystal layer 30 in the reflection region R smaller than the thickness dt of the liquid crystal layer 30 in the transmission region T, the light used in the reflection mode is converted to light. On the other hand, the retardation provided by the liquid crystal layer 30 can be close to the retardation provided by the liquid crystal layer 30 with respect to the light used in the transmission mode. When the thickness dr of the liquid crystal layer 30 in the reflective region R is approximately ½ of the thickness dt of the liquid crystal layer 30 in the transmissive region T, the retardation that the liquid crystal layer 30 gives to the light used in both display modes. Can be made substantially equal.

  The counter substrate 100b has a step having an upper step surface 100b1 located in the reflection region R, a lower step surface 100b2 located in the transmission region T, and a side surface 100b3 connecting the upper step surface 100b1 and the lower step surface 100b2. As a result, the thickness dr of the liquid crystal layer 30 in the reflective region R is smaller than the thickness dt of the liquid crystal layer 30 in the transmissive region T. Specifically, the step of the counter substrate 100b is formed by selectively providing the transparent dielectric layer 29 in the reflection region R of the counter substrate 100b. The step side surface 100 b 3 is located in the reflection region R and is covered with the counter electrode 22.

  Next, the structure and operation of the pixel electrode 14 included in the liquid crystal panel 100 will be described.

  As shown in FIGS. 3A and 3B, the pixel electrode 14 includes a solid portion 14a formed from a conductive film (for example, an ITO film or an aluminum film) and a non-solid portion where no conductive film is formed. 14b.

  The solid portion 14a has a plurality of regions (referred to as “unit solid portions”) 14a ′, each of which is substantially surrounded by the non-solid portion 14b. These unit solid portions 14a ′ have substantially the same shape and the same size, and each unit solid portion 14a ′ is substantially circular. The unit solid portions 14a ′ are typically electrically connected to each other within each pixel region. In the configuration illustrated in FIG. 3B, the pixel electrode 14 has nine unit solid portions 14 ′, three of which (center of the paper) are transparent electrodes, and the remaining six ( The upper and lower sides of the drawing are the reflective electrodes.

  The non-solid portion 14b has a plurality of openings 14b1. These openings 14b1 have substantially the same shape and the same size, and are arranged so that the centers thereof form a square lattice. The unit solid portion 14a ′ in the center of the pixel region is substantially surrounded by four openings 14b1 whose centers are located on four lattice points forming one unit lattice. Each opening 14b1 has a substantially star shape having four quarter-arc sides (edges) and a four-fold rotation axis at the center thereof.

  The non-solid portion 14b further has a plurality of notches 14b2. The plurality of notches 14b2 are arranged at the end of the pixel region. The notch part 14b2 arranged in the area corresponding to the side of the pixel area has a shape corresponding to about one half of the opening part 14b1, and the notch part arranged in the area corresponding to the corner of the pixel area. 14b2 has a shape corresponding to about one quarter of the opening 14b1. The unit solid portion 14a ′ disposed at the end of the pixel region is substantially surrounded by the notch 14b2 and the opening 14b1. The notches 14b2 are regularly arranged, and the openings 14b1 and the notches 14b2 form a unit cell over the entire pixel region (up to the end). The opening 14b1 and the notch 14b2 are formed by patterning a conductive film that becomes the pixel electrode 14.

  When a voltage is applied between the pixel electrode 14 having the above-described configuration and the counter electrode 22, an oblique electric field generated around the solid portion 14a (near the outer periphery), that is, at the edge portion of the non-solid portion 14b. As a result, a plurality of liquid crystal domains each having a radial tilt alignment are formed. One liquid crystal domain is formed in each of a region corresponding to the opening 14b1 and a region corresponding to the unit solid portion 14a ′.

  Here, the square pixel electrode 14 is illustrated, but the shape of the pixel electrode 14 is not limited thereto. Since the general shape of the pixel electrode 14 is approximated to a rectangle (including a square and a rectangle), the openings 14b1 and the notches 14b2 can be regularly arranged in a square lattice. Even if the pixel electrode 14 has a shape other than a rectangular shape, the openings 14b1 and the notches are regularly formed (for example, in a square lattice shape as illustrated) so that the liquid crystal domains are formed in all the regions in the pixel region. What is necessary is just to arrange | position the part 14b2.

  The mechanism by which liquid crystal domains are formed by the above-described oblique electric field will be described with reference to FIGS. 4 (a) and 4 (b). 4A and 4B show a state in which a voltage is applied to the liquid crystal layer 30, and FIG. 4A shows the orientation of the liquid crystal molecules 30a according to the voltage applied to the liquid crystal layer 30. FIG. 4 (b) schematically shows a state where the liquid crystal molecules 30a that have changed according to the applied voltage reach a steady state. Show. Curves EQ in FIGS. 4A and 4B show equipotential lines EQ. 4A and 4B correspond to cross-sectional views taken along the line 4-4 ′ in FIG. 3A, but the step of the counter substrate 100b is omitted for the sake of simplicity of description. As shown.

  When the pixel electrode 14 and the counter electrode 22 are at the same potential (a state where no voltage is applied to the liquid crystal layer 30), as shown in FIG. 3B, the liquid crystal molecules 30a in the pixel region Oriented perpendicular to the surfaces of the substrates 11 and 21.

  When a voltage is applied to the liquid crystal layer 30, a potential gradient represented by an equipotential line (perpendicular to the electric lines of force) EQ shown in FIG. 4A is formed. This equipotential line EQ is parallel to the surface of the solid portion 14a and the counter electrode 22 in the liquid crystal layer 30 located between the solid portion 14a of the pixel electrode 14 and the counter electrode 22, and the pixel region. The liquid crystal on the EG falls in the region corresponding to the non-solid portion 14b of the non-solid portion 14b and the edge portion of the non-solid portion 14b (the inner periphery of the non-solid portion 14b including the boundary between the non-solid portion 14b and the solid portion 14a). In the layer 30, an oblique electric field represented by an inclined equipotential line EQ is formed.

  A torque is applied to the liquid crystal molecules 30a having negative dielectric anisotropy so as to align the axial direction of the liquid crystal molecules 30a in parallel to the equipotential lines EQ (perpendicular to the lines of electric force). Accordingly, the liquid crystal molecules 30a on the edge portion EG are rotated clockwise in the right edge portion EG in the drawing and counterclockwise in the left edge portion EG in the drawing, as indicated by an arrow in FIG. Each direction is inclined (rotated) and oriented parallel to the equipotential line EQ.

  The liquid crystal panel used in the liquid crystal display device according to the embodiment of the present invention is not limited to the above example, and the configurations described in Patent Documents 3 to 5 and the like, including those described in Patent Document 6, can be used. A known liquid crystal display panel applied to the above can be used.

  Next, display characteristics of the liquid crystal display device of the present embodiment will be described by showing simulations and experimental examples. An LCD-MASTER manufactured by Shintech Co., Ltd. was used for the simulation. A liquid crystal panel having a liquid crystal layer thickness retardation Δn · d of about 380 nm was used.

  A viewing angle characteristic of the liquid crystal display device 100A according to the embodiment of the present invention is shown in FIG. 5, and a viewing angle characteristic of the liquid crystal display device 100B is shown in FIG. For comparison, the viewing angle characteristics of the liquid crystal display device 200A shown in FIG. 12 are shown in FIGS. 7 and 8, and the viewing angle characteristics of the liquid crystal display device 200B are shown in FIG. Although only simulation results are shown in FIGS. 5 to 9, similar results were obtained in experiments. Further, FIG. 10 shows the viewing angle characteristics of the liquid crystal display device 200C shown in FIG. 12C in which the second retardation layer R2 ′ is disposed closest to the viewer. Note that the display quality of the dual-use liquid crystal display device is dominated by the transmission mode display, and here, the evaluation results for the transmission mode are shown. Table 1 shows the parameters of the optical film configuration in the evaluated liquid crystal display device.

  Each of the diagrams shown in FIGS. 5 to 10 is an isocontrast diagram in which the azimuth angle is 0 ° in the X direction (X axis) in FIG. The polar angle (angle from the normal to the display surface) indicated by the outermost circle is 80 °. In each figure, the outermost isocontrast line is a line indicating the contrast ratio 10, and is the isocontrast line indicating the contrast ratios 20, 30, and 40 in order toward the inner side.

  As can be seen from FIGS. 5 and 6 for the liquid crystal display devices 100A and 100B of the present embodiment, the line having a contrast ratio of 10 has four directions with azimuth angles of 0 °, 90 °, 180 °, and 270 ° ( In a direction perpendicular or parallel to the absorption axis of the polarizing layer), it intersects with a circle with a polar angle of 80 °. That is, in these directions, a contrast ratio of 10 can be displayed even in a viewing angle direction where the polar angle exceeds 80 °. On the other hand, in the isocontrast diagrams shown in FIGS. 7 to 10, the isocontrast line having a contrast ratio of 10 is located inside the circle having a polar angle of 80 °.

  Thus, as is apparent from the comparison between FIGS. 5 and 6 and FIG. 8 or FIG. 10, the retardation layer R2 (and R5) is disposed between the retardation layer R1 and the retardation layer R3. It can be seen that the viewing angle characteristics are improved.

  From the comparison between FIG. 5 and FIG. 6, the protective layer P2 (TAC layer) in the liquid crystal display device 100A has substantially the same refractive index anisotropy as the second retardation layer R2, but the viewing angle. There is almost no contribution to the properties. As a matter of course, the protective layer P1 disposed outside the first polarizing layer POL1 has no optical effect.

  Conventionally, as described above, it has been common technical knowledge to arrange the second retardation layer R2 at a position closest to the liquid crystal layer. This is because the second retardation layer R2 (typically having negative uniaxial anisotropy) is intended to compensate for the positive uniaxial refractive index anisotropy of the liquid crystal layer, and thus should be compensated. It seems that it was thought that it was preferable to arrange in the position nearest to the object. However, as is apparent from the above results, unlike the conventional technical common sense, the viewing angle is increased by disposing the second retardation layer R2 between the first retardation layer R1 and the third retardation layer R3. The characteristics can be greatly improved.

  Next, the result of examining the influence on the display characteristics by the in-plane retardation Re of the second retardation layer R2 will be described with reference to FIG. FIG. 11 is a graph in which the in-plane retardation Re of the second retardation layer R2 is taken on the horizontal axis and the front transmittance is taken on the vertical axis, and the vertical axis is normalized by the value when Re = 0 nm.

  As can be seen from FIG. 11, the front transmittance decreases as the in-plane retardation Re of the second retardation layer R2 increases. It can be seen that the in-plane retardation Re of the second retardation layer R2 is preferably 50 nm or less in order to suppress the decrease in transmittance to 5% or less. As for the viewing angle characteristics, as a result of the same examination as described above, when the in-plane retardation Re is increased, the viewing angle characteristics are also decreased. However, if the in-plane retardation Re is 50 nm or less, the contrast ratio is increased to about 80 ° polar angle. 10 can be obtained.

  According to the present invention, a dual-use liquid crystal display device suitable as a liquid crystal display device for mobile devices is provided.

(A) And (b) shows typical sectional drawing of liquid crystal display device 100A and 100B of embodiment by this invention. It is a schematic diagram for demonstrating the optical arrangement | positioning of a polarizing layer and a phase difference layer. (A) And (b) is a figure which shows typically the structure of the dual-use type liquid crystal panel used for the liquid crystal display device of embodiment by this invention, (a) is a top view, (b) is ( It is sectional drawing along the 3B-3B 'line in a). (A) And (b) is sectional drawing along 4-4 'line | wire of the liquid crystal display device shown to Fig.3 (a), (a) is according to the voltage applied to the liquid crystal layer, The state (ON initial state) in which the orientation of liquid crystal molecules starts to change is schematically shown, and (b) schematically shows the state in which the orientation of the liquid crystal molecules changed according to the applied voltage has reached a steady state. Is shown. It is a figure which shows the viewing angle characteristic of the liquid crystal display device of embodiment by this invention. It is a figure which shows the viewing angle characteristic of the other liquid crystal display device of embodiment by this invention. It is a figure which shows the viewing angle characteristic of the conventional liquid crystal display device. It is a figure which shows the viewing angle characteristic of the liquid crystal display device for a comparison. It is a figure which shows the viewing angle characteristic of the other conventional liquid crystal display device. It is a figure which shows the viewing angle characteristic of the liquid crystal display device for a comparison. It is a graph which shows the in-plane retardation Re dependence of 2nd phase difference layer R2 of the front transmittance of a liquid crystal display device. (A) And (b) is sectional drawing which shows typically the optical film structure of the conventional dual use type liquid crystal display device, (c) is a schematic diagram of the optical film structure of the dual use type liquid crystal display device for comparison. It is sectional drawing shown.

Explanation of symbols

100A, 100B Liquid crystal display device 100 Liquid crystal panel POL1 First polarizing layer POL2 Second polarizing layer R1 First retardation layer R2 Second retardation layer R3 Third retardation layer R4 Fourth retardation layer R5 Fifth retardation layer R6 Sixth retardation layer P1 First protective layer P2 Second protective layer (further retardation layer)
P3 Third protective layer P4 Fourth protective layer (further retardation layer)

Claims (6)

A liquid crystal having a domain in which liquid crystal molecules are radially inclined when a predetermined voltage is applied to a liquid crystal layer in the pixel, and having a transmissive region for displaying in a transmissive mode and a reflective region for displaying in a reflective mode. A panel,
The first polarizing layer, the first retardation layer, the second retardation layer, the third retardation layer, which are arranged in this order from the viewer side of the liquid crystal panel,
A second polarizing layer, a fourth retardation layer, a fifth retardation layer, and a sixth retardation layer arranged in this order from the side opposite to the viewer side of the liquid crystal panel;
The absorption axis of the second polarizing layer is orthogonal to the absorption axis of the first polarizing layer, the fourth retardation layer has substantially the same refractive index anisotropy as the first retardation layer, The fifth retardation layer has substantially the same refractive index anisotropy as the second retardation layer, and the sixth retardation layer has substantially the same refractive index anisotropy as the third retardation layer. And, assuming that the main axis having the largest refractive index in the layer surface of each retardation layer is the a axis, the a axes of the fourth retardation layer, the fifth retardation layer, and the sixth retardation layer are related to each other. Arranged so as to be orthogonal to the a-axis of each retardation layer
The a axis of the first retardation layer is an a1 axis, the main axis in the layer plane orthogonal to the a1 axis is the b1 axis, the other main axis in the surface normal direction is the c1 axis, and each main refractive index in each main axis direction is na1, nb1 and nc1, its thickness is d1, its in-plane retardation is Re1 = (na1-nb1) · d1, its retardation in the thickness direction is Rth1 = ([(na1 + nb1) / 2] −nc) · d1,
The a-axis of the second retardation layer is the a2 axis, the principal axis in the layer plane orthogonal to the a2 axis is the b2 axis, the other principal axis in the surface normal direction is the c2 axis, and the principal refractive indexes in the principal axis directions are na2 and nb2. And nc2, its thickness is d2, its in-plane retardation is Re2 = (na2-nb2) · d2, its thickness direction retardation is Rth2 = ([(na2 + nb2) / 2] −nc) · d2,
The a-axis of the third retardation layer is the a3 axis, the principal axis in the layer plane orthogonal to the a3 axis is the b3 axis, the other principal axis in the surface normal direction is the c3 axis, and the principal refractive indexes in the principal axis directions are na3 and nb3. And nc3, its thickness is d3, its in-plane retardation is Re3 = (na3-nb3) · d3, its retardation in the thickness direction is Rth3 = ([(na3 + nb3) / 2] −nc) · d3,
The X axis is the absorption axis of the first polarizing layer, the smaller of the crossing angles of the X axis and the a1 axis is θ (> 0), and the crossing of the X axis and the a1 axis with respect to the X axis. If the direction where the angle is θ is the + direction and the angle formed by the X axis and the a3 axis is γ (> 0),
40 ≦ │ 2 ・ θ−γ │ ≦ 50 or 130 ≦ │ 2 ・ θ−γ │ ≦ 140
Satisfied, and
30 nm ≦ Re1-1.5 · Re3 ≦ 100 nm,
70 nm ≦ Re3 ≦ 170 nm, and
Re2 ≦ 50 nm,
A liquid crystal display that satisfies the requirements.   The liquid crystal display device according to claim 1, wherein Rth1 <Rth2 is satisfied.   The liquid crystal display device according to claim 1, wherein 0 nm <Rth2 ≦ 150 nm is satisfied.   4. The adhesive layer according to claim 1, wherein no adhesive layer is provided between the first retardation layer and the second retardation layer and between the second retardation layer and the third retardation layer. 5. Liquid crystal display device.   5. The liquid crystal display device according to claim 1, wherein no adhesive layer is provided between the first polarizing layer and the first retardation. 6.   5. The liquid crystal display according to claim 1, further comprising a further retardation layer having a refractive index anisotropy substantially the same as that of the second retardation layer between the first polarizing layer and the first retardation layer. 6. A liquid crystal display device according to claim 1.