JP3342417B2 - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve viewing angle characteristics of the display device without sacrificing its manufacturing yield and transmissivity by providing a liquid crystal layer of the device in each of its pixel regions with and second domains having different alignments of the liquid crystal molecules from each other and placing a phase compensator between a liquid crystal cell and each of polarizing plates placed on the both side of the liquid crystal cell. SOLUTION: In this display device, a liquid crystal layer 101 is provided in each of its pixel regions with first and second domains 101a and 101b having different alignments of the liquid crystal molecules from each other and on both side of the liquid crystal layer 101, first and second phase compensators 102 and 103 each having positive refractive-index anisotropy are placed respectively in such a way that each of the slow axes is parallel to the substrate surface and also to the other slow axis and almost orthogonally intersects the slow axis of the liquid crystal layer 101 at the time of applying no voltage. Further, third phase compensators 104 and 105 are placed between a first polarizing plates 108 and the first phase compensator 102 and between a second polarizing plate 109 and the second phase compensator 103, respectively. The first to third phase compensators 102 to 105 are formed so as to compensate the refractive-index anisotropy of liquid crystal molecules of the liquid crystal layer 101, which are aligned almost parallel to the substrate surface at the time of applying no voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitor display for a computer and a liquid crystal display device for displaying video images and the like, and more particularly to a liquid crystal display device having excellent viewing angle characteristics.

[0002]

2. Description of the Related Art In order to increase the viewing angle of a liquid crystal display device,
Various display modes have been proposed. As a typical example, IPS (In-P1aneSwitch) that moves liquid crystal molecules in parallel to the substrate surface by using a lateral electric field is used.
ng) mode, a liquid crystal display device in which liquid crystal molecules are oriented substantially perpendicular to the substrate surface when no voltage is applied and the tilt direction of the liquid crystal molecules is divided when a voltage is applied (Japanese Patent Laid-Open No. 7-280).
No. 68) or a liquid crystal display device in which a liquid crystal molecule is oriented substantially horizontally on the substrate surface when no voltage is applied, and a region where the rising direction of the liquid crystal molecule rises when a voltage is applied is formed to enlarge the viewing angle (Japanese Patent Laid-Open No. -3081)
Can be mentioned.

[0003]

In the IPS mode,
Since it is necessary to provide a plurality of non-transparent electrodes in a display picture element, the number of openings is reduced and the transmittance (display luminance) of the display device is reduced.
There was a problem that it became low. JP-A-7-2806
No. 8 discloses a liquid crystal display device having a negative dielectric anisotropy (n-type liquid crystal) and a substrate which has been subjected to a vertical alignment process. There is a problem that the time required for injecting the liquid crystal material is more than twice as long as the case where the substrate (p-type liquid crystal) and the substrate subjected to the horizontal alignment treatment are used, and the manufacturing efficiency is reduced. JP-A-10-308
In the liquid crystal display device disclosed in Japanese Patent Laid-Open Publication No. 1 (1993) -1994, liquid crystal molecules are driven by transparent electrodes disposed above and below the substrate, so that the transmittance, which is a problem in the IPS mode, does not decrease, and the dielectric anisotropy is positive. Since the liquid crystal material and the substrate subjected to the horizontal alignment treatment are used, there is no problem that the manufacturing efficiency is reduced, which is a problem in JP-A-7-28068, but the viewing angle characteristics are reduced.
There is a problem that it is inferior to the liquid crystal display device disclosed in Japanese Patent No. 8068. The liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 10-3081 has a problem that the gradation characteristics in the vertical direction of the display surface are asymmetric.

The present invention has been made to solve the above-mentioned problems of the prior art, and has as its object to provide a liquid crystal display device having excellent viewing angle characteristics without sacrificing manufacturing efficiency and transmittance. And

[0005]

According to the liquid crystal display device of the present invention, both are sandwiched between transparent first and second substrates, and the first and second substrates have a positive dielectric anisotropy. A liquid crystal layer comprising a nematic liquid crystal material having first and second electrodes provided on the first and second substrates, respectively, for applying an electric field substantially perpendicular to the first and second substrates to the liquid crystal layer; In a liquid crystal display device having first and second polarizers provided outside each of the first and second substrates and arranged in a crossed Nicols state, the liquid crystal layer comprises liquid crystal molecules for each display pixel region. A first phase difference compensating element having a positive refractive index anisotropy between the first polarizing plate and the first substrate. A second phase difference compensating element having a positive refractive index anisotropy is provided between the two polarizing plates and the second substrate. The slow axes of the first phase difference compensating element and the second phase difference compensating element are arranged parallel to the substrate surface and parallel to each other so as to be substantially orthogonal to the slow axis of the liquid crystal layer in a state where no voltage is applied. And disposing at least one third phase difference compensating element between the first polarizing plate and the first phase difference compensating element or between the second polarizing plate and the second phase difference compensating element. And the refractive index ellipsoid of the third phase difference compensating element is 3
Has two main axes a, b, c, and each main axis a, b, c
Are defined as na, nb, and nc, and nc>na>
nb, the main axis a and the main axis b are in a plane parallel to the substrate, the main axis c is parallel to the normal direction of the substrate surface, and the main axis a is adjacent to the phase difference compensating element. And the first, second, and third phase difference compensating elements are oriented substantially parallel to the substrate surface when no voltage is applied. The above-mentioned object is achieved by having a configuration for compensating the characteristics.

The retardation value of the liquid crystal layer is represented by d _lc · Δ
n, the refractive indices in the directions of the principal axes a, b, c of the refractive index ellipsoid of the third phase difference compensating element are na, nb,
nc, the in-plane retardation of the third phase difference compensating element is d · (na−nb), the retardation in the thickness direction is d · (na−nc), and the parameters RL and NZ are respectively RL = d · (Na−nc) / (d _lc · Δn), N
Z = (na−nc) / (na−nb), wherein the third phase difference compensating element is provided between the first polarizing plate and the first phase difference compensating element and between the second polarizing plate and the second compensating element. And the sum of RL of the two third phase difference compensating elements is represented by R
When defined as Lsum, 0 ≦ | RLsum | ≦ 2, and each of the two third phase difference compensating elements has log (| NZ |) ≧ 2.0 · | RL | −1.2. Is satisfied, provided that RL <0 and NZ <0.

Preferably, RL and NZ of the two third phase difference compensating elements are equal to each other.

Hereinafter, the operation will be described.

In the liquid crystal display device according to the present invention, a substantially vertical electric field is applied to a liquid crystal layer made of a nematic liquid crystal material having a positive dielectric anisotropy disposed between a pair of polarizing plates disposed in a crossed Nicols state. Thus, a normally black mode (black display when no voltage is applied) is performed. The liquid crystal layer
The first liquid crystal molecules having different orientations are different for each display picture element region.
And at least the second domain, the display quality in the viewing angle direction can be improved.

[0010] By providing a phase difference compensating element between the liquid crystal cell and the polarizing plate, the refractive index anisotropy of the liquid crystal molecules oriented substantially parallel to the surface of the substrate when no voltage is applied is compensated for. In all viewing angle directions including the direction, black display with extremely little viewing angle dependency is realized. That is, the first phase difference compensating element and the second phase difference compensating element having positive refractive index anisotropy are respectively provided on both sides of the liquid crystal cell, and their slow axes are parallel to the substrate surface. By arranging the liquid crystal molecules so that their axes are parallel and perpendicular to the slow axis of the liquid crystal layer, the refractive index anisotropy of the liquid crystal molecules when viewed from the front can be effectively compensated. Further, by disposing a third phase difference compensating element having a positive refractive index anisotropy in such a manner that its slow axis is parallel to the normal direction of the substrate surface, the transmittance change accompanying the viewing angle change is compensated, Black floating can be eliminated. In addition, the elliptically polarized light can be obtained by arranging the principal axis of the third phase difference compensating element having the maximum refractive index in the plane so as to be substantially orthogonal to the polarization axis of the polarizing plate closer to the phase difference compensating element. Can be compensated for, and a display with further excellent viewing angle characteristics can be provided.

The retardation value of the liquid crystal layer (d _lc ·
Δn), in-plane retardation (d · (na−nb)) of the third phase difference compensating element, and retardation in the thickness direction (d · (na−nc)). RL = d · (na−nc) / (d _lc · Δn) NZ = (na−nc) / (na−nb) By appropriately selecting and combining the parameters RL and NZ, It is possible to realize a liquid crystal display device having extremely excellent viewing angle characteristics in all directions and obtaining a desired contrast ratio.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, parameters that are commonly used in the description of the following embodiments and that characterize the structures of a liquid crystal layer, a polarizing plate, and a retardation plate are defined as follows.

The definition of each parameter, particularly the value of the angle, is based on an XYZ orthogonal coordinate system appropriately set on the liquid crystal panel. As shown in FIGS. 1A to 1C, the reference coordinate system only needs to have the XY plane parallel to the liquid crystal panel surface, and the directions of the X axis and the Y axis are not limited at all.
(A) to (c)). However, in one liquid crystal display device, a common axis is used for all of the liquid crystal layer, the polarizing plate, and the retardation plate. In the following description, X_REF, Y_REF, Z_RE
F.

The parameters that characterize the alignment state of the liquid crystal molecules in the liquid crystal layer will be described with reference to FIG. FIG. 2 (a)
FIG. 3 is a perspective view of a liquid crystal cell. In the following description, domains in a uniform alignment state will be described for simplicity. In the configuration in which the picture element region is orientation-divided into a plurality of domains,
The parameters that characterize the liquid crystal layer in each domain are the retardation value of the liquid crystal layer, the twist angle of the liquid crystal layer, and the orientation direction of liquid crystal molecules (liquid crystal molecules located in the middle of the thickness direction of the liquid crystal layer) (slow axis of the liquid crystal layer). is there.

FIG. 2B is a sectional view of the liquid crystal layer. The retardation value of the liquid crystal layer is equal to the refractive index anisotropy of the liquid crystal 5103 of the liquid crystal layer sandwiched between the substrates 5101 and 5102.
And the product d _lc · △ n of the distance (the thickness of the liquid crystal layer = cell gap) d _lc between the substrate 5101 (for example, the substrate on which the color filter is formed) and the substrate 5102 (for example, the substrate on which the TFT array is formed) I do.

FIG. 2C is a plan view when the liquid crystal cell is observed from the observer side. The straight line 5104 is the light source side substrate 5
A straight line parallel to the long axis of the liquid crystal molecule adjacent to 102;
The straight line 5105 is a straight line parallel to the long axis of the liquid crystal molecules adjacent to the observer-side substrate 5101. For simplicity, a case where the twist angle of the liquid crystal molecules is 90 ° or less will be described. In this case, the twist angle of the liquid crystal layer is changed from the straight line 5104 to the straight line 510.
4 is a rotation angle when rotated until it coincides with the straight line 5105, and a counterclockwise rotation is defined as positive. This angle is shown as θtwist in the figure.

The orientation direction of the liquid crystal layer is defined as follows.
The straight line bisecting θtwist shown in FIG.
106. This straight line 5106 coincides with the direction in which the liquid crystal molecules located in the middle of the thickness direction of the liquid crystal layer rise due to the electric field, and is called the orientation direction or slow axis of the liquid crystal layer. When a voltage (halftone voltage) giving an intermediate transmittance is applied to the liquid crystal layer, the liquid crystal molecules in the liquid crystal layer whose major axis is parallel to the straight line 5106 are considered. Liquid crystal cell straight line 5
A cross-sectional view parallel to 106 is shown in FIG. The rising direction of the liquid crystal molecules is indicated by an arrow, and the arrow parallel to the straight line 5106 is indicated by 5107. The orientation direction of the liquid crystal layer is an angle β formed with the reference axis X_REF when counterclockwise is defined as positive.

The parameter of the polarizing plate is a polarization axis (transmission axis).
Direction (angle). A method of defining the direction of the polarization axis will be described (not shown). The direction of the polarization axis is the reference axis X_RE.
The angle was defined as an angle with F, and the counterclockwise direction was defined as positive. Of course, a polarizing plate represented by any polarization axis direction α,
The directions of the polarization axes of the polarizing plates represented by α + 180 ° and α−180 ° are all equivalent.

The parameters of the phase difference plate are defined.
The parameters of the retardation plate include an in-plane retardation value (in a plane parallel to the display surface), a thickness direction retardation value (a direction perpendicular to the liquid crystal display surface), an angle of the main axis a (an angle between X_REF and the main axis a), and a parameter. RL (the ratio of the retardation value in the thickness direction to the retardation value of the liquid crystal layer) and the parameter NZ (the ratio of the retardation value in the thickness direction to the in-plane retardation value).

FIG. 3 shows a refractive index ellipsoid of the retardation plate. The three main axes of the refractive index ellipsoid of the retardation plate used in this embodiment are a, b, and c. The main axes a, b and c form an orthogonal coordinate system. The main axes a and b are in a plane parallel to the phase plate surface, that is, in a plane parallel to the display surface. At this time, the spindle a,
The values of the refractive index along b and c are defined as na, nb and nc, respectively. Further, the thickness of the phase difference plate is d.

The in-plane retardation of the retardation plate is d
-It is defined as (na-nb).

The retardation in the thickness direction is d · (n
a-nc).

The angle of the main axis a is defined as an angle γ between the reference axis X_REF and the main axis a. The sign of the angle is positive in the counterclockwise direction.

The parameter RL is d · (na−n
c) / (d _lc · Δn)

The parameter NZ is (na−nc) /
(Na-nb).

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the operation principle of the liquid crystal display device of the present invention will be described with reference to FIG.

FIG. 4 shows a liquid crystal display device 100 according to the present invention.
It is the figure which represented typically. FIG. 4 illustrates a transmission type liquid crystal display device.

The liquid crystal display device 100 includes a liquid crystal layer 101,
A pair of electrodes 100a and 100b for applying a voltage to the liquid crystal layer 101, and a pair of retardation plates disposed on both sides of the liquid crystal layer 101 (of course, having a suitable refractive index anisotropy such as a retardation compensation film and a liquid crystal cell). Anything can be used.)
102 and 103, and further, retardation plates 102 and 10
3 and retarders 104 and 1 provided outside each of
05, a pair of polarizing plates 108 and 109 sandwiching these components and arranged in a crossed Nicols state.
Arrows in the polarizers 108 and 109 in FIG. 4 indicate the polarization axis (transmission axis) of the polarizer.

The liquid crystal layer 101 shown in FIG. 4 shows the orientation of liquid crystal molecules in one display picture element region when no voltage is applied. The ellipses in FIG. 4 schematically represent liquid crystal molecules. As a liquid crystal material, a nematic liquid crystal material having a positive dielectric anisotropy (abbreviated as Np liquid crystal material) is used. The liquid crystal molecules are aligned substantially parallel to the surfaces of the pair of substrates (not shown) and the electrodes when no voltage is applied. By applying a voltage to the electrodes 100a and 100b formed on the liquid crystal layer 101 side of the pair of substrates so as to sandwich the liquid crystal layer 101, an electric field in a direction substantially perpendicular to the surface of the substrate is applied to the liquid crystal layer.

As shown in FIG. 4, the liquid crystal layer 101 has first alignment states different from each other in each display picture element region.
It has a domain 101a and a second domain 101b. In the example of FIG. 4, the directors of the liquid crystal molecules in the first domain 101a and the directors of the liquid crystal molecules in the second domain 101b are oriented in azimuthal directions different from each other by 180 °. When a voltage is applied between the electrodes 100a and 100b, the liquid crystal molecules in the first domain 101a rise clockwise,
The orientation of the liquid crystal molecules in the second domain 101b is controlled so as to rise in the counterclockwise direction, that is, in the directions opposite to each other. Such director alignment of liquid crystal molecules can be realized using a known alignment control technique using an alignment film. By forming a plurality of first domains and second domains in which the director orientations differ by 180 ° in one display pixel region, the viewing angle characteristics can be made more uniform.

As described above, the luminance change of the image obtained by observing the halftone display image of the liquid crystal display device 100 having the display pixels divided in the orientation direction from the normal direction of the display surface to the first domain 101a side. And the luminance change of the image observed while tilted toward the second domain 101b is symmetric. It is preferable that the area of the first domain 101a and the area of the second domain 101b are substantially the same. It is not always necessary to make the area of each domain the same for each display picture element region, and the sum of the area of the first domain 101a and the sum of the area of the second domain 101b are equal to each other over the entire display surface. Is also good. The configuration of the orientation division is not limited to the above example.

As shown in FIG. 4, the first domain 101
a of the liquid crystal molecules in a and the second domain 101b
The azimuth directions are different from each other by 180 ° with respect to the director of the liquid crystal molecules in this case.
It is parallel to the direction represented by the arrow 609 in the middle. In the specification of the present application, the direction 609 is the slow axis direction of the liquid crystal layer in the state where no voltage is applied. More generally, the direction of the slow axis of the liquid crystal layer in the state where no voltage is applied is defined as the azimuthal direction in which the liquid crystal molecules near the center in the thickness direction of the liquid crystal layer rise by voltage. This definition can be applied not only to a liquid crystal layer in which liquid crystal molecules are aligned parallel to the substrate surface (including antiparallel), but also to a liquid crystal layer in which liquid crystal molecules are twisted.

The first phase difference compensating element 102 and the second phase difference compensating element 103 typically have a positive uniaxial refractive index anisotropy, and the maximum refractive index of the index ellipsoid. (That is, the slow axis) (the directions of arrows 125 and 126 in FIG. 4) are parallel to the substrate surface, and the liquid crystal layer 10 when no voltage is applied.
It is arranged to be orthogonal to one slow axis. Therefore,
Light leakage due to the refractive index anisotropy of the liquid crystal molecules in a state where no voltage is applied is suppressed, and as a result, excellent black display (normally black characteristics) is obtained.

The third phase difference compensating elements 104 and 105
Typically has biaxial refractive index anisotropy, and its slow axis (in the directions indicated by arrows 121 and 122 in FIG. 4) is arranged parallel to the normal direction of the substrate surface, and the viewing angle Compensate for the change in transmittance due to the change. Further, the third phase difference compensating element 104
And 105, the principal axes having the larger refractive index (indicated by arrows 123 and 12 in FIG. 4) among the principal axes of the refractive index ellipsoid parallel to the surface of the substrate.
4) is arranged so as to be orthogonal to the polarization axis of the polarizing plate on the side close to the respective phase difference compensating elements, thereby compensating for rotation of the polarization axis of elliptically polarized light and providing a display with excellent viewing angle characteristics. It is possible to do. Note that only one of the third phase difference compensating elements 104 and 105 may be arranged.

Hereinafter, the components of the present invention will be described in more detail.

(Nematic Liquid Crystal Material Having Positive Dielectric Anisotropy: Np Liquid Crystal Material) In the present invention, like a TN mode liquid crystal display device widely used at present, a substrate subjected to a horizontal alignment treatment and an Np liquid crystal material are used. Is used. Therefore, the time required for injecting the liquid crystal material can be reduced to about に or less as compared with the case where the substrate subjected to the vertical alignment treatment and the Nn liquid crystal material are used as in the liquid crystal display device of JP-A-7-28068.
Generally, the Np liquid crystal material has a lower viscosity than the Nn liquid crystal material, and the horizontal alignment processing substrate surface has higher wettability to the liquid crystal material than the vertical alignment processing substrate surface. The factors have a synergistic effect, and as a result, the liquid crystal material can be injected at a high speed. Injection time of liquid crystal material accounts for a large percentage of the time required for each process of manufacturing a liquid crystal display device, and greatly reducing the time leads to a significant improvement in manufacturing efficiency of the liquid crystal display device. .

(Vertical Electric Field) In the present invention, a liquid crystal molecule is driven by applying a vertical electric field (perpendicular to the substrate) to the liquid crystal layer by a pair of electrodes disposed so as to sandwich the liquid crystal layer.
That is, since the same aperture ratio as that of the conventional TN mode liquid crystal display device can be obtained, it is not necessary to form an opaque electrode in the display pixel region unlike the IPS mode.
A liquid crystal display device having a higher pixel aperture ratio than the liquid crystal display device in the mode can be obtained.

(Orientation Division) At present, T is widely used.
In a liquid crystal display device that changes the transmittance by moving liquid crystal molecules in the thickness direction of the liquid crystal layer, including the N mode,
There is a problem that viewing angle dependence of display luminance is large (viewing angle characteristics are inferior). This problem will be described with reference to FIGS. 5A, 5B, and 5C. FIGS. 5A and 5B schematically show a liquid crystal display device having a liquid crystal layer 203 twisted. In these figures, a pair of electrodes 201 and 20 are disposed between a pair of polarizing plates 206 and 207 arranged in a crossed Nicols state.
2 sandwiches the liquid crystal layer 203. The long axis of the liquid crystal molecules located near the center in the thickness direction of the liquid crystal layer 203 is drawn so as to be positioned in the plane of the drawing (looking longest). 5A shows a state where no voltage is applied, and FIG. 5B shows a state where a voltage is applied.

As shown in FIG. 5A, when no voltage is applied, the liquid crystal molecules 203a near the center in the thickness direction are oriented substantially parallel to the substrate surface. Even if this state is observed from the viewing angle directions 204 and 205, no difference is recognized. On the other hand, as shown in FIG. 5B, when a voltage for displaying a halftone is applied, the observed state differs depending on the viewing angle direction. This is because the liquid crystal molecules have a positive uniaxial refractive index anisotropy (cigar-shaped refractive index ellipsoid). When a voltage is applied, the liquid crystal molecules 203b rise in the direction determined by the pretilt (counterclockwise in this example). When the liquid crystal molecules 203b are observed from the 204 direction (coincident with the long axis direction of the liquid crystal molecules 203b), the anisotropy of the refractive index of the cigar-shaped liquid crystal molecules 203b disappears (the liquid crystal molecules 203b look circular). On the other hand, when the liquid crystal molecules 203b are observed from the 205 direction, the refractive index anisotropy becomes maximum.

Therefore, when the liquid crystal molecules 203b in the liquid crystal cell are viewed from the direction of the arrow 204, most of the liquid crystal molecules look circular, that is, the refractive index anisotropy of the liquid crystal layer becomes small. Therefore, the linearly polarized light transmitted through the polarizing plate 206 reaches the polarizing plate 207 without any change in the polarization state in the liquid crystal layer 203, and is blocked by the polarizing plate 207 having a polarizing axis orthogonal to the polarizing axis of the polarizing plate 206. Therefore, the transmittance decreases. On the other hand, the liquid crystal molecules 203 in the liquid crystal cell
When viewing b, most of the liquid crystal molecules look like rods. That is,
The liquid crystal layer 203 has the maximum refractive index anisotropy. Therefore, the polarization state of the polarized light that has passed through the polarizing plate 206 is changed by the liquid crystal layer 203, and the amount of light transmitted through the polarizing plate 207 is maximized.

As a result, as shown in FIG. 5C, the display when the viewing angle is changed in the rising direction of the liquid crystal molecules (the direction of arrow 204 in FIG. 5B) and in the opposite direction (the direction of arrow 205 in FIG. 5B). Brightness changes greatly. In general, the liquid crystal display device has an upward direction (12 o'clock direction) of 205 directions,
The downward direction (6 o'clock direction) is set to be the 204 direction. Note that each curve in FIG. 5 shows the transmittance for different applied voltages.

That is, in the conventional TN mode, when the viewing angle is changed along the alignment direction of the liquid crystal molecules, the luminance significantly changes. As understood from the above description, such asymmetry of the gradation characteristic is not limited to the TN mode.
This is common to display modes in which liquid crystal molecules move in the cell thickness direction of a liquid crystal cell, and in which alignment division is not performed.

By performing orientation division for each picture element region,
Improves the asymmetry of the gradation characteristics with respect to the viewing angle direction,
A symmetrical gradation characteristic (viewing angle characteristic) is obtained. This will be described with reference to FIGS. 6A and 6B
As shown in (1), for example, one pixel region is divided into two regions A and B (first domain and second domain) in which the rising directions of liquid crystal molecules by voltage differ by 180 °. In the state where no voltage is applied, as shown in FIG. 6A, the liquid crystal molecules in any region are oriented substantially parallel to the substrate surface (the pretilt angle is ignored for simplicity). When a voltage for halftone display is applied, as shown in FIG.
Of the liquid crystal molecules 303a of the region B are counterclockwise.
03b rises clockwise (the rising direction is determined by the pretilt direction). As described above, the tone characteristics of the regions A and B depend on the viewing angle directions 304 and 305, respectively, as shown in FIGS. 6C and 6D. Since the region A and the region B exist in one pixel region, the gradation characteristics of the whole one pixel region are calculated by averaging the gradation characteristics of FIGS. 6C and 6D in consideration of the area ratio of each region. It will be. Therefore, by setting the area SA of the area A and the area B of the area B to 1: 1,
As shown in FIG. 6E, symmetrical gradation characteristics are obtained in both directions of arrow 304 and arrow 305.

Next, the ratio between SA and SB and the gradation characteristics will be described in order to estimate the range in which the effect of the orientation division can be obtained. FIG. 7A shows the viewing angle dependency of a voltage application state where the transmittance at the front is 50% among the gradation characteristics shown in FIG. 6E.
6A and 6B, as a measure of vertical symmetry.
The relationship between the ratio TA / TB of the transmittances TA and TB at a viewing angle of 50 ° in the directions of 4 (upper) and 305 (lower) and the ratio SA / (SA + SB) of the areas SA and SB of the regions A and B is shown. As shown in FIG. 7B. FIG. 7B shows that the upper and lower gradation characteristics are almost symmetric (TA / TB = about 1) when the ratio of SA is around 0.5.

Note that the alignment division is not limited to the two divisions, and the liquid crystal molecules rise in the opposite direction when voltage is applied on the entire display surface.
It is sufficient that the sum of the areas of the two regions is substantially the same. In consideration of display uniformity, it is preferable that the unit of the alignment division is smaller, and it is preferable to perform the alignment division into two or more for each picture element region. Further, as shown in FIGS. 7C and 7D, a plurality of regions A and a plurality of regions B may be provided for each picture element region, and the two regions A and B may be alternately arranged. By forming a plurality of regions A and regions B for each pixel region and reducing the unit of orientation division, the viewing angle characteristics can be made more uniform. The reason is shown in FIG.
As shown in E, the light (arrow 402) transmitted only through the regions A and B when observing the liquid crystal display device from an oblique direction.
This is because the ratio of the light (arrow 401) transmitted across the AB2 region to A, 402B) increases.

(Normal Black Mode and Improvement of Contrast Ratio) In the present invention, a viewing angle characteristic is improved by using a third phase difference compensating element in a normally black mode in which a black display state is obtained when no voltage is applied. I do.
The viewing angle characteristic is an apparent change of a display image generated when the display image is observed from a direction (oblique direction) shifted from a direction perpendicular to the display surface of the liquid crystal display device. The apparent change of the display image includes a gradation change, a contrast ratio change, a color change, and the like. The gradation change can be improved by the orientation division as described above. Hereinafter, first, what must be done to suppress the change in contrast ratio will be described, then a method of realizing the normally black mode by the first and second phase difference compensating elements will be described, and finally, the third phase difference compensation will be described. The effect of suppressing the change in the contrast ratio (improvement of the dependence of the contrast ratio on the viewing angle) created by the combination with the element is explained. Finally, it is difficult to suppress the change in the normally white type contrast ratio for comparison. Some points will be described.

The contrast ratio (CR) is defined as a value obtained by dividing the maximum transmittance (the transmittance at the time of displaying white) by the minimum transmittance (the transmittance at the time of displaying black). In a normal liquid crystal display device, the change in transmittance due to observation in an oblique direction is larger in the black display state than in the white display state. Therefore, in order to improve the viewing angle characteristics of the contrast ratio, it is sufficient to improve the transmittance change (floating black) due to oblique observation during black display.

In order to realize the normally black mode, the liquid crystal layer which is horizontally aligned when no voltage is applied compensates for the refractive index anisotropy of the liquid crystal layer. In the present invention, this compensation is performed by the retarders 102 and 103 in FIG.
In FIG. 8A, retardation plates 502 and 503 are retardation plate 1
It plays the same role as 02,103. The liquid crystal layer of the present invention is substantially horizontally aligned when no voltage is applied as shown in FIG. 8A. When the liquid crystal layer is viewed from the front of the liquid crystal display device, the refractive index in the direction of the arrow 508 (orientation direction) in FIG. 8B is maximum, and the refractive index in the direction perpendicular thereto is minimum.
In the present invention, the value obtained by multiplying the difference between the maximum refractive index and the minimum refractive index by the thickness of the liquid crystal layer, that is, the retardation value of the liquid crystal layer is set to about 250 nm (50 nm to 500 nm). At this time, the first and second retardation plates 502 and 503 having positive uniaxial refractive index anisotropy are used to realize normally black characteristics. Specifically, the phase difference plate 5
The retardation values of 02 and 503 are approximately の of the retardation value of the liquid crystal layer, that is, approximately 125 nm.
What is necessary is just to make the slow axis coincide with the arrows 509 and 510 (perpendicular to 508). Thus, the birefringence effect of the liquid crystal layer when no voltage is applied can be canceled by the first and second retardation plates.

Next, in the liquid crystal display device of the present invention in which the alignment is divided, the normally black type can easily compensate for the phase difference for improving the floating of black as compared with the normally white type. A description will be given of the fact that a liquid crystal display device having a good contrast viewing angle change can be obtained with the type, but it is difficult with the normally white type.

As shown in FIG. 8A, in the case of a liquid crystal display device that displays black when no voltage is applied, the liquid crystal layers in the region A and the region B are in substantially the same alignment state. This orientation is parallel to the substrate surface. That is, both the regions A and B are in substantially the same alignment state, and one of the main axes of the refractive index ellipsoid representing the liquid crystal layer is parallel to the normal line of the substrate, and the two main axes are parallel to the substrate surface. In the plane. In addition, the first and second
One of the principal axes of the refractive index ellipsoid representing the retardation plate is also parallel to the normal line of the substrate, and the other two principal axes are in a plane parallel to the substrate surface.

FIG. 8C shows the change in the retardation value of each of the A and B regions when observed in the directions of arrows 520 and 521 in FIG. 8B, and the change of the retardation value in the case of being changed in the directions of arrows 522 and 523. 8G.

The angle dependence of the retardation value of the area A matches that of the area B. In addition, 520, 52
The extreme point of the retardation value (the downwardly convex point in the figure) coincides with the angle change in any direction of 1, 522 and 523. (0 deg in the figure). In order to suppress the floating of black (a change in the viewing angle of the contrast ratio) due to the change in the viewing angle, the above-described change in the retardation may be compensated.

As can be seen from the characteristic of the retardation change, in the liquid crystal display device of the present invention, the same phase difference compensating element (third phase difference plate) can be used for the regions A and B to compensate for the phase difference. In addition, the third retardation compensating element has a position where one of the principal axes of the refractive index ellipsoid is parallel to the normal to the retardation plate surface and the other two principal axes are in a plane parallel to the retardation plate surface. A phase difference plate can be used. A retardation plate having such characteristics can be easily and inexpensively manufactured using a conventional technique such as a stretching method. As described above, in the liquid crystal display device in which the alignment is divided, the normally black type liquid crystal display device is provided with a phase difference plate (third phase difference plate) having the same characteristics for any region, thereby providing contrast. It is one of the essences of the present invention to suppress the viewing angle dependence of the change.

On the other hand, a normally white type shown in FIG.
That is, when black display is performed when a voltage is applied, the orientations of the region A and the region B during black display are different, and the main axis of the refractive index ellipsoid representing the liquid crystal layer is inclined from the normal line of the substrate. Arrow 520 in normally white type shown in FIG. 8E
8F show changes in the retardation values of the A and B regions when observed from the directions of 522 and 523.
FIG. 8H shows a change in the retardation value when the observation is performed in a tilted direction.

According to FIG. 8F, the change in the retardation value with respect to the change in the angle in the directions of the arrows 520 and 521 is greatly different between the region A and the region B. As an example, the retardation value of the area A takes the minimum value when it is tilted in the direction of the arrow 520, whereas the retardation value of the area B takes the minimum value when it is tilted in the direction of the arrow 521.

As described above, in order to improve the floating of black in the liquid crystal display device of FIG. 8D, different phase difference compensating elements corresponding to the regions A and B are required. The regions A and B are regions obtained by dividing one picture element, and since their respective areas are very small, it is extremely difficult to actually manufacture a phase difference compensating element for improving black floating. Become.

(Viewing angle compensation by third phase difference compensating element)
As described above, by using a phase difference compensating element in which one of the main axes of the refractive index ellipsoid is parallel to the normal to the phase difference plate surface and the other two main axes are in a plane parallel to the phase difference plate surface. 4, the liquid crystal layer 101, the first phase difference compensating element 102,
A change in retardation due to oblique observation of the second phase difference compensating element 103, that is, an improvement in black floating can be achieved. In the present invention, the floating black is compensated for by the third phase difference compensating element.

The fact that black floating can be compensated for by the third phase difference compensating element will be described with reference to FIG. 9 while paying attention to the angle change of the liquid crystal molecules and the refractive index anisotropy of the phase difference compensating element. FIG. 9 shows a refractive index ellipsoid of the liquid crystal layer and the phase difference compensating element used in the present invention. In FIG.
In FIG. 4, reference numeral 601 denotes a refractive index ellipsoid of the liquid crystal layer 101, and reference numerals 602 and 603 denote refractive index ellipses of the first phase difference compensating element 102 and the second phase difference compensating element 103, respectively. Each of these refractive index ellipsoids has positive uniaxiality, and its optical axis is in a plane parallel to the surface of the liquid crystal display element. Further, the refractive index ellipsoids 604 and 605 of the third phase difference compensating elements 104 and 105 are all in a plane parallel to the normal to the surface of the liquid crystal display element.

The refractive index ellipsoid 706 (slow axis 70
4, a change in the refractive index when a circle 705) orthogonal to the slow axis is viewed from an oblique direction will be described with reference to FIGS.
First, consider a case where the liquid crystal display device is viewed from the front. The refractive index anisotropy that contributes to the birefringence of the liquid crystal layer or the retardation plate is biaxially 702 and 70 that are in a plane whose normal line is the traveling direction of the incident linearly polarized light and form 45 ° with the polarization axis 701 of the linearly polarized light.
3 is the refractive index difference in the direction parallel to 3. Accordingly, the refractive index anisotropy contributing to the transmittance in the front direction is na1 and n in FIG. 10A.
This is the difference na1-nb1 of b1.

When the viewing angle is inclined in the major axis direction of the refractive index ellipsoid of the liquid crystal molecules or the retardation plate, the refractive index anisotropy that contributes to the transmittance is the difference na2 between na2 and nb2 in FIG. 10B.
−nb2. In this case, as shown in FIG. 10B, the refractive index na2 is smaller than na1 shown in FIG. 10A. On the other hand, nb1 and nb2 are equal (nb1 = nb
2). That is, when the viewing angle is inclined along the major axis of the refractive index ellipsoid, the refractive index anisotropy is in a direction of decreasing.

As shown in FIG. 10C, when the viewing angle is changed along the minor axis of the refractive index ellipsoid, the refractive index anisotropy contributing to the transmittance is the difference na3-nb3 between na3 and nb3.
That is, when the viewing angle is changed along the minor axis direction of the refractive index ellipsoid, the refractive index anisotropy does not change.

Finally, consider the case where the main axis of the refractive index ellipsoid coincides with the normal of the display surface of the display device. The refractive index contributing to the transmittance when viewed from the front is shown in FIG. 10D.
Is the difference na4-nb4 between na4 and nb4. That is, when a retardation plate having a refractive index ellipsoid of na4 = nb4 is used, the transmittance in the front direction does not change at all. When the viewing angle is changed in an oblique direction, FIG.
Is the difference na5-nb5 between na5 and nb5. That is, in such a refractive index ellipsoid, the refractive index anisotropy increases as the viewing angle is inclined from the front direction. That is, there is an effect of compensating for the change in the refractive index shown in FIG. 10B.

In the above description, the refractive index ellipsoid in FIG. 10D has been described as a uniaxial refractive index ellipsoid. On the other hand, the corresponding phase difference compensating elements 104 and 105 in FIG. 4 also have a refractive index anisotropy in a plane parallel to the liquid crystal display element surface (arrow 1).
(Having a large refractive index in the direction of 23). However, even in this case, the above description has been made. This is because the arrow 123 is substantially orthogonal to the polarization axis of the incident linearly polarized light.

As shown in FIG. 4, if a biaxial phase difference compensating element is used, the rotation of the polarization axis of linearly polarized light entering from an oblique direction and the rotation of the principal axis of elliptically polarized light transmitted obliquely through the phase difference compensating element 103 will be described. , It is possible to obtain better viewing angle characteristics than in the case where a uniaxial phase difference compensating element is used. The specificity can be easily understood in the examples.

The phase difference compensation effect in the refractive index ellipsoid group of FIG. 9, which is one embodiment of the present invention, will be summarized based on the discussion on the single refractive index ellipsoid described in FIGS. 10A to 10E. In the refractive index ellipsoid group representing the liquid crystal layer and the retardation plate when no voltage is applied according to the embodiment of the present invention shown in FIG. 9, when linearly polarized light (polarization direction 607) is incident, two azimuth directions are used. Table 1 summarizes changes and increases / decreases in refractive index anisotropy that affect the transmittance when the viewing angle is changed in the azimuthal directions indicated by 608 and 609.

[0066]

[Table 1]

From the above table, it can be seen that oblique viewing angle changes can be compensated for by a retardation plate having a refractive index ellipsoid whose refractive index in the normal direction is larger than that in a plane parallel to the surface of the liquid crystal display device. I understand. Further, the refractive index that contributes to the transmittance is a refractive index in a direction forming 45 ° with the polarization axis of the incident linearly polarized light. Therefore, it can be easily understood that the refractive index in this direction should be smaller than the refractive index in the normal direction of the surface of the liquid crystal display device.

(Production of Liquid Crystal Cell / Orientation Division) A method of producing a liquid crystal cell used in this embodiment, particularly a method of orientation division will be described. The liquid crystal display device of the present invention can be manufactured by appropriately combining known manufacturing methods.

The liquid crystal cell is manufactured on a normal TFT (thin film transistor) substrate under substantially the same conditions as those for manufacturing a current TN liquid crystal cell. However, in this embodiment, the rubbing direction (angle) is different from the conventional TN type liquid crystal cell. Further, in order to form a two-divided alignment, the pretilt angle is controlled by irradiating the alignment film with UV light.

FIG. 11A is a schematic view of the liquid crystal cell in this embodiment as viewed from the observer side substrate. Arrow 12 in the figure
02 is the rubbing direction on the color filter substrate side;
03 is the rubbing direction on the TFT substrate side.

The alignment state of the liquid crystal molecules after the liquid crystal is injected into the substrate subjected to the rubbing process in the rubbing direction and subjected to the realignment process will be described. X- in FIG.
X 'cross section, that is, liquid crystal molecules 1 having a cross section parallel to the rubbing direction
It is considered that the orientation of 206 is schematically represented as shown in FIG. Liquid crystal molecules 1206 and observer side substrate 12
05 or the light source side substrate 1204, and the liquid crystal molecules in the intermediate layer of the liquid crystal cell are oriented substantially parallel to the substrate surface. If a voltage is applied to this liquid crystal layer, the liquid crystal molecules in the intermediate layer will become the arrows 1207 or 1
It can rotate (get up) in the direction of 208 with the same probability.

Therefore, in the present invention, rubbing was performed after irradiating one of the upper and lower substrates with UV light. FIG. 11 schematically shows the orientation of the liquid crystal molecules in the XX ′ section in this state.
It is shown in (c). One picture element was divided into two areas A and B, and UV irradiation was performed. In region A, the alignment film on the opposite substrate is irradiated with UV light, and in region B, only the alignment film on the TFT substrate side is irradiated with UV light. As a result of evaluating the optical characteristics of the liquid crystal cell subjected to such treatment, it was confirmed that the liquid crystal molecules in the intermediate layer in the region A rotated in the direction of arrow 1207 and the liquid crystal molecules in the region B rotated in the direction of arrow 1208. That is, the alignment (pretilt) of the liquid crystal molecules located near the middle in the thickness direction of the liquid crystal layer could be controlled. Note that UV irradiation may be performed after the rubbing treatment. Furthermore, U
Split orientation may be performed by means other than V irradiation and rubbing.

(Embodiment 1) One embodiment of the present invention is shown in FIG. In FIG. 4, reference numeral 101 denotes a liquid crystal cell;
Reference numerals 3, 104 and 105 denote retardation plates, and 108 and 109 denote polarizing plates.

The liquid crystal cell 101 is divided into two regions, A and B, for each picture element. The orientation parameters for each region are as follows.

[0075]

[Table 2]

The parameters of the polarizing plate are as follows.

[0077]

[Table 3]

The parameters of the phase difference plate are shown below.

[0079]

[Table 4]

FIG. 12 shows a value obtained by dividing the transmittance at an applied voltage of 4 V by the transmittance at an applied voltage of 0 V (contrast ratio).
FIG. The center of the circle is the normal direction of the display surface (viewing angle 0 °), and each concentric circle has a viewing angle of 20 ° from the inside,
40 °, 60 °, and 80 ° are shown, respectively. In addition, the horizontal axis of the drawing indicates the X_REF axis, and the vertical axis indicates Y_REF. The isocontrast curve is the contrast ratio (CR)
= 50. As is apparent from this figure, the liquid crystal display device of this embodiment has a CR = 50 in all azimuth directions.
It can be seen that the above display is obtained at a viewing angle of 60 ° or more, and has excellent viewing angle characteristics.

Comparative Example 1 Comparative Example 1 is shown in FIG. In FIG. 13, reference numeral 6301 denotes a liquid crystal cell, 6302 and 630.
Reference numeral 3 denotes first and second phase difference compensating elements, 6305 and 630
Reference numeral 6 denotes a polarizing plate.

The liquid crystal cell 6301 is orientation-divided into two regions A and B for each picture element. The orientation parameters for each region are as follows.

[0083]

[Table 5]

The parameters of the polarizing plate are as follows.

[0085]

[Table 6]

The parameters of the phase difference plate are shown below.

[0087]

[Table 7]

FIG. 14 shows a value obtained by dividing the transmittance at an applied voltage of 4 V by the transmittance at an applied voltage of 0 V (contrast ratio).
FIG. The center of the circle is the normal direction of the display surface (viewing angle 0 °), and each concentric circle has a viewing angle of 20 ° from the inside,
40 °, 60 °, and 80 ° are shown, respectively. In addition, the horizontal axis of the drawing indicates the X_REF axis, and the vertical axis indicates Y_REF. The isocontrast curve is the contrast ratio (CR)
= 50. As is clear from this figure, the liquid crystal display device of this comparative example has a poor viewing angle characteristic in the directions of X_REF and Y_REF.

(Embodiment 2) In the present embodiment, the range of parameters in which the phase difference compensating elements 104 and 105 function effectively is estimated. Here, the parameters are the in-plane retardation d · (na−nb) of the phase difference compensator, the retardation in the thickness direction d · (na−nc), and the angle of the na axis. Here, a preferable range of the retardation d · (na−nb) and d · (na−nc) of the phase difference compensating element is estimated.

In changing the above parameters, the parameters RL and NZ can be uniquely determined, and the parameters RL and NZ can be relatively compared with the retardation value ( _dlc · Δn) of the liquid crystal layer. As follows.

RL = d · (na−nc) / (d _lc · Δn) NZ = (na−nc) / (na−nb) The influence of retardation is examined using the same liquid crystal display device as in the first embodiment. did. Phase difference compensating elements 104 and 105
Were made equal to each other, and the parameters were changed in the following ranges.

0 <| RL | <1 and RL <0 0.1 <| NZ | <100 and NZ <0 The effect of the phase difference compensating element is based on the contrast ratio at a viewing angle of 60 ° of the liquid crystal display device. Was evaluated. X_REF and Y_R when the phase difference compensating element shown in the comparative example is not used
Contrast ratio CRrefX at a viewing angle of 60 ° in the EF direction
_REF and CRrefY_REF as the reference, and the contrast ratio CR corresponding to each using a retardation plate
The ratio between compX_REF and CRcompY_REF was defined as evaluation parameters ηX_REF and ηY_REF. That is, ηX_REF = CRcompX_REF / CRrefX
_REF ηY_REF = CRcompY_REF / CRrefY
_REF. If ηX_REF> 1 and ηY_REF> 1, it can be said that the contrast ratio has been improved by the phase difference compensating element.

FIGS. 15 and 16 show the results of ηX_REF and ηY_REF when the retardation is changed, respectively. The horizontal axis of FIG. 15 and FIG.
L, and the vertical axis is log (−NZ). ηX_R
The regions where EF> 1 and ηY_REF> 1 are indicated by hatching in the figure.

As is apparent from the figure, ηX_REF> 1
Is wider than the range of ηY_REF> 1. Therefore,
In order to evaluate the overall effect of the phase difference compensating elements 104 and 105, a range where the average value of ηX_REF and ηY_REF is larger than 1 (ηX_REF + ηY_REF) /
The range where 2> 1 was estimated. FIG. 17 shows the obtained results.
Shown in

The horizontal axis in FIG. 17 is -RL, and the vertical axis is
log (-NZ) and (ηX_REF + ηY_RE
The region where F) / 2> 1 is indicated by hatching in the figure.
Furthermore, (ηX_REF + ηY_R
The range where EF) / 2> 10 is indicated by double hatching.

From the above results, the range of the parameters in which the effects of the phase difference compensating elements 104 and 105 can be obtained is as shown in FIG.
It can be seen that the region is indicated by hatching in the middle.

In particular, the point A (-RL =
0.1, log (-NZ) =-1.0) and point B (-RL =
Area above the line containing 0.7, log (-NZ) = 0.2), that is, a region where the value of log (-NZ) is large,
0 <| -RL | <1 and log (| -NZ |)
It is practically preferable to use a phase difference compensating element having a parameter satisfying> 2.0 · | -RL | -1.2 because a margin for variation in characteristics of the phase difference compensating element can be increased.

In this embodiment, the phase difference compensating element 10
Although evaluation was performed using the same characteristics (same parameters) as 4 and 105, it can be easily inferred that the effects of the present invention are not limited to the above combinations. Respective parameters of the phase difference compensating plates 104 and 105 are represented by RL_104, NZ_104, RL_105, NZ_1.
05 and RLsum = RL_104 + RL_105, the range in which the effects of the present invention can be obtained is approximately 0 ≦
| RLsum | ≦ 2, and log (| NZ_104 |) ≧ 2.0 · | RL_104
| -1.2 log (| NZ_105 |) ≧ 2.0 · | RL_105
| −1.2 may be sufficient.

As shown in Example 1 and Comparative Example,
In the direction of X_REF ± 45 °, sufficiently good viewing angle characteristics are obtained regardless of the presence or absence of the phase difference compensating element. Further, good visual characteristics have been confirmed for all parameters studied in the present embodiment. Therefore, it is considered that the viewing angle characteristics can be improved if the parameters of the phase difference compensating elements 104 and 105 are in the above range.

[0100]

As described above, according to the present invention, a normally black mode liquid crystal display device in which a change in display quality depending on the viewing angle direction is extremely small is provided. The liquid crystal display device of the present invention does not sacrifice the manufacturing efficiency and transmittance unlike the conventional wide viewing angle liquid crystal display device. INDUSTRIAL APPLICABILITY The liquid crystal display device of the present invention is suitably used for a display device requiring a wide viewing angle, such as a monitor display for a computer and a liquid crystal display device for displaying video images and the like.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a definition of a main axis direction for describing a configuration of an embodiment.

FIG. 2 is a schematic diagram for explaining a configuration of an embodiment.

FIG. 3 is a diagram schematically showing a refractive index ellipsoid of a retardation plate used in an example.

FIG. 4 is a perspective view schematically showing one embodiment of the liquid crystal display device of the present invention.

FIG. 5A is a cross-sectional view schematically showing the liquid crystal molecule alignment when no voltage is applied.

FIG. 5B is a schematic diagram schematically showing the liquid crystal molecular alignment when a voltage is applied.

FIG. 5C is a graph showing the transmittance change of the area A when the viewing angle is changed in the cross section of the areas A and B, using the transmittance of the front as a parameter.

FIG. 6A is an alignment-divided liquid crystal region A in a black display state.
3A and 3B are cross-sectional views schematically showing alignment states of liquid crystal molecules in B.

FIG. 6B is a cross-sectional view schematically showing an alignment state of liquid crystal molecules in the liquid crystal regions A and B that have undergone alignment division in a halftone display state.

FIG. 6C is a graph showing a change in transmittance with respect to a change in viewing angle in a region A, using the transmittance of the front as a parameter.

FIG. 6D is a graph showing a change in transmittance with respect to a change in viewing angle in a region B, using the transmittance of the front as a parameter.

FIG. 6E is a graph showing a change in overall transmittance with respect to a change in viewing angle between regions A and B, using the transmittance of the front as a parameter.

FIG. 7A is a diagram illustrating a pixel division ratio (area ratio of areas A and B) and symmetry of gradation, and is a diagram illustrating a definition of transmittance used for evaluation of symmetry.

FIG. 7B is a diagram illustrating the pixel division ratio (area ratio of regions A and B) and the symmetry of gradation, and is a diagram illustrating the area ratio of regions A and B and the symmetry of gradation.

FIG. 7C is a diagram schematically showing a modified example of the orientation division of one display picture element region according to the present invention.

FIG. 7D is a diagram schematically showing another modified example of the orientation division of one display picture element region according to the present invention.

FIG. 7E: By reducing the unit of orientation division,
It is a schematic diagram for demonstrating the reason that a viewing angle characteristic can be made more uniform.

FIG. 8A is a schematic cross-sectional view of a liquid crystal molecule orientation during black display in a normally black liquid crystal display device.

FIG. 8B is a view showing a relative relationship among an absorption axis of a polarizing plate, an alignment axis of liquid crystal molecules, and a slow axis of a retardation plate for obtaining a normally black characteristic in a horizontal alignment cell.

FIG. 8C is a graph showing a change in a retardation value when a viewing angle is changed along the alignment direction of liquid crystal molecules in a black display state in a normally black display device.

FIG. 8D is a schematic cross-sectional view of the liquid crystal molecule alignment during black display in a normally white liquid crystal display device.

FIG. 8E is a diagram showing a relative relationship between an absorption axis of a polarizing plate and an alignment axis of liquid crystal molecules for obtaining a normally white characteristic in a horizontal alignment cell.

FIG. 8F is a graph showing a change in retardation value when the viewing angle is changed along the alignment direction of liquid crystal molecules in a normally white liquid crystal display device in a black display state.

FIG. 8G is a graph showing a change in a retardation value when a viewing angle is changed along a direction orthogonal to an alignment direction of liquid crystal molecules in a black display state in a normally black display device.

FIG. 8H is a graph showing a change in retardation value when a viewing angle is changed in a normally white liquid crystal display device in a black display state along a direction orthogonal to the alignment direction of liquid crystal molecules.

FIG. 9 is a diagram illustrating an improvement in viewing angle characteristics of contrast in the present invention. FIG. 3 shows a liquid crystal layer, a refractive index ellipsoid of a retardation plate group, and a polarization axis of incident linearly polarized light in one embodiment of the present invention.

FIG. 10A is a diagram showing a refractive index ellipsoid having a positive uniaxial refractive index anisotropy.

FIG. 10B is a diagram illustrating transmitted light when linearly polarized light having an angle of 45 ° with the slow axis from the normal direction of the plane is incident.

FIG. 10C shows a refractive index ellipsoid having a positive uniaxial refractive index anisotropy, in which the slow axis and the slow axis are inclined from the direction inclined along the slow axis with respect to the normal of a plane including the slow axis. Angle of 4
It is a figure explaining transmitted light at the time of injecting linearly polarized light which is 5 degrees.

FIG. 10D is a diagram illustrating transmitted light when linearly polarized light is incident on a refractive index ellipsoid having a positive uniaxial refractive index anisotropy from the direction of its slow axis.

FIG. 10E is a diagram illustrating transmitted light when linearly polarized light is incident on a refractive index ellipsoid having a positive uniaxial refractive index anisotropy from a direction inclined from its slow phase.

FIG. 11 is a schematic diagram illustrating a liquid crystal cell in the liquid crystal display device of the present invention. (A) is a diagram showing a rubbing direction, and (b) is a schematic diagram showing an alignment state of liquid crystal molecules in a cell thickness direction by the rubbing process of (a). (C)
FIG. 3A is a schematic diagram illustrating an alignment state of liquid crystal molecules in a cell thickness direction when the rubbing treatment of FIG.

FIG. 12 is an isocontrast diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 13 is a perspective view schematically showing a liquid crystal display device of a comparative example.

FIG. 14 shows an isocontrast diagram of a liquid crystal display device of a comparative example.

FIG. 15 is a graph showing a preferable range of retardation (X_REF direction) of the phase difference compensating element of the liquid crystal display device according to the example of the present invention.

FIG. 16 is a graph showing a preferable range of the retardation (Y_REF direction) of the phase difference compensating element of the liquid crystal display device according to the example of the present invention.

FIG. 17 is a graph showing a preferable range of the retardation (average value) of the phase difference compensating element of the liquid crystal display device according to the example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 100 Liquid crystal display device 100a, 100b Electrode 101 Orientation bipartite liquid crystal layer 101a, 101b Orientation-divided area | region 102, 103, 104, 105 Retardation plate 108, 109 Polarizer 1201 Rubbing direction of counter substrate 1202 Rubbing direction of TFT substrate 1204 TFT substrate 1205 Opposite substrate 1206 Liquid crystal molecules 1207 Arrow indicating the direction in which liquid crystal molecules rise when voltage is applied 1208 Arrow indicating the direction in which liquid crystal molecules rise when voltage is applied

Claims (3)

(57) [Claims] A first liquid crystal layer sandwiched between the first and second substrates, and a liquid crystal layer made of a nematic liquid crystal material having a positive dielectric anisotropy; First and second electrodes provided on the first and second substrates, respectively, for applying an electric field substantially perpendicular to the first and second substrates to the liquid crystal layer; provided on the outside of each of the first and second substrates And a first polarizer and a second polarizer arranged in a crossed Nicols state, wherein the liquid crystal layer includes first and second domains in which the orientation of liquid crystal molecules is different for each display picture element region. At least a first phase difference compensating element having a positive refractive index anisotropy between the first polarizing plate and the first substrate;
A second phase difference compensating element having a positive refractive index anisotropy is provided between the first phase difference compensating element and the second phase difference compensating element so that the slow axes of the first phase difference compensating element and the second phase difference compensating element are parallel to the substrate surface. The liquid crystal layer is disposed in parallel so as to be substantially orthogonal to the slow axis of the liquid crystal layer in a state where no voltage is applied, and is disposed between the first polarizing plate and the first phase difference compensating element, or between the second polarizing plate and the second polarizing plate. At least one third phase difference compensating element is disposed between the second phase difference compensating element, and the refractive index ellipsoid of the third phase difference compensating element has three principal axes a, b, and c. The refractive indices in the directions of the respective main axes a, b, and c are defined as na, nb, and nc, and the relation of nc>na> nb is established. The main axes a and b are in a plane parallel to the substrate. The main axis c is parallel to the normal direction of the substrate surface, and the main axis a is orthogonal to the polarization axis of the polarizing plate adjacent to the phase difference compensating element; Second and third retardation compensation element compensates the refractive index anisotropy of the liquid crystal molecules of the liquid crystal layer oriented substantially parallel to the substrate surface when no voltage is applied, the liquid crystal display device. 2. The liquid crystal layer having a retardation value of d _lc · Δ
n, the refractive indices in the directions of the principal axes a, b, c of the refractive index ellipsoid of the third phase difference compensating element are na, nb,
nc, the in-plane retardation of the third phase difference compensating element is d · (na−nb), the retardation in the thickness direction is d · (na−nc), and the parameters RL and NZ are RL = d · (Na−nc) / (d _lc · Δn), NZ = (na−nc) / (na−nb), wherein the third phase difference compensating element is a first polarizing plate and a first phase difference compensating element. And between the second polarizing plate and the second compensating element, and when the sum of RL of the two third phase difference compensating elements is defined as RLsum, 0 ≦ | RLsum | ≦ 2 And each of the two third phase difference compensating elements satisfies log (| NZ |) ≧ 2.0 · | RL | −1.2, provided that RL <0 and NZ <0 Claim 1
3. The liquid crystal display device according to 1. 3. The liquid crystal display device according to claim 2, wherein RL and NZ of the two third phase difference compensating elements are respectively equal to each other.