JP2768234B2 - Liquid crystal display device using optical compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display.

[0002]

2. Description of the Related Art A liquid crystal display device has an inherent problem of viewing angle dependence of a displayed image. In particular, with the recent increase in the size of liquid crystal display devices and the expansion of applications such as in-vehicle use, this viewing angle dependency is becoming a major issue. In particular, a twisted nematic (TN) mode is widely used because a high contrast can be easily obtained, but a wider viewing angle is required.

As one means for solving this problem, an optical compensator is attached to a liquid crystal display device. This optical compensator is mainly used for the purpose of reducing the viewing angle dependence during black display. In particular, two optical compensation systems using an optical compensator to expand the viewing angle range of the TN mode are mainly proposed. Hereinafter, these two optical compensation methods will be described.

The first optical compensation method is for a normally black TN mode, and is described in "Wide Viewing Angle LCD LCD Using Retardation Films", Yamagishi, H .; Watanabe, Y. Yokoyama, Japan Display, 89, 316 pages (1
989) ("Wide-Viewing Angle LCD Using Retardatio
n Films ", N. Yamagishi, H. Watanabe, K. Yokoyama,
JAPANDISPLAY'89, 316 (1989)). This method will be described with reference to FIG. In this method, the uniaxial optical compensators are arranged orthogonally. by this,
It can mainly widen the left and right viewing angle range. FIG. 14 shows a state in which the viewing angle range in the left, right, up and down directions reprinted from the above-mentioned document is expanded.

The second type of optical compensation system is for a normally white TN mode, and is described in "New Normally Negative Birefringence Film Film."
Compensated Twisted Nematic LC
Ds With Largest Viewing Angle
Performance ”, On, Japan Display '
92, 247 (1992) ("New Normally Whit
e NegativeBirefringence Film Compensated Twisted N
ematic LCDs with Largest ViewingAngle Performanc
e ", HL Ong, JAPAN DISPLAY '92, 247 (1992)). This method will be described with reference to FIG. 15. In this method, a negative light having an optical axis in the normal direction of the film surface is used. Fig. 15 shows an enlarged view angle range in the left, right, up and down directions, which is reprinted from the above-mentioned document.

[0006]

However, the above-described optical compensation system cannot completely eliminate the viewing angle dependence of the black display state. The reason will be described below.

Generally, when a liquid crystal display device is viewed from an oblique direction, birefringence different from that when viewed from the front is generated. Therefore, if an optical compensator whose birefringence changes in a direction opposite to the viewing angle dependency of the liquid crystal display device is attached, the birefringence of the sum of the two (the liquid crystal display device and the optical compensator) does not have the viewing angle dependency. However, since the two above-mentioned optical compensators use uniaxial optical films, it is not possible to completely compensate for an optically anisotropic body having a twist angle such as TN.
For this reason, the above-mentioned two optical compensators cannot increase the viewing angle range in the vertical direction.

As described above, in the conventional optical compensation means,
It was not possible to completely compensate for the viewing angle dependency with respect to the liquid crystal alignment state of black display, and it was not possible to significantly expand the viewing angle range.

[0009]

The liquid crystal display device of the present invention comprises a liquid crystal display panel having a twisted liquid crystal alignment.
Consists molecules having refractive index anisotropy of the refractive index anisotropy and opposite sign of the liquid crystal molecules, Ri yet an oriented structure was twisted liquid crystal orientation structure opposite direction twisted shows a black display in which the liquid crystal molecules takes bets, The twist pitch is visible light
A long optical compensation plate than the wavelength of the liquid crystal alignment in the adjacent surface
In-plane orientation of structure and substrate surface of orientation structure in optical compensator
It consists of attaching so that the inner directions match .

[0010]

First, a liquid crystal display system using the optical compensator of the present invention will be described. The liquid crystal display panel in the present invention needs to have a twisted structure. The optical compensator according to the present invention can be obtained by modifying the liquid crystal alignment structure to be compensated according to the procedure shown in FIG. First, as shown in FIG. 1A, the same structure as the liquid crystal alignment structure at the time of black display is assumed as an optical compensator. Next, as shown in FIG. 1B, the twist angle direction is reversed. Thereby, the right twist becomes the left twist (the left twist becomes the right twist). Further, as shown in FIG. 1C, the refractive index anisotropy is reversed. In general, the refractive index anisotropy Δn of a used liquid crystal has a positive sign, and thus Δn has a negative sign. As shown in FIG. 1D, the compensator 102 obtained as described above is
Attached to 1 is a liquid crystal display device of the present invention.

Next, the operation of the compensator when light is vertically incident will be described. FIG. 2 shows a combination of the compensator 102 and the liquid crystal 101 obtained by the above-described procedure. In general, the incident polarized light 103 enters the liquid crystal 101 and exits as elliptically polarized light 104. After that, the elliptically polarized light 104 enters the compensator 102. The changes in polarization in the liquid crystal 101 and the compensator 102 are shown in FIG. 2 at points A1, A2,... An and B1, B2.
-Consider dividing into sections of Bn. In this way, each section of the liquid crystal and the compensator can be regarded as a uniaxially anisotropic optical element.

The elliptically polarized light 104 has a point A at point B1.
It will return to the state of n-1. This is the interval B0-B1
This is because the optical element No. and the optical element in the section An-1 -An are always parallel to each other and have the opposite sign in the refractive index anisotropy. When the light further reaches point B2, the state returns to point An-2. This is because the twist directions of the liquid crystal 101 and the compensator 102 are opposite, so that the optical elements in the section B1-B2 and the sections An-2 -An-
This is because the optical axes of the first optical element become parallel. As a result of the progress of the above process, at the point Bn, the light returns to the state of the point A0, and the light 105 emitted from the compensator returns to the original polarization state. As described above, by attaching the liquid crystal display device and the compensating plate between the orthogonal polarizing plates, black display can be performed.

Next, the effect of the present invention when the line of sight is inclined will be described with reference to FIG. When the incident polarized light 103 is incident obliquely, the same process as in the case of normal incidence occurs. That is, the elliptically polarized light 104 has a state of light at the point B1 at the point An-1.
It becomes the same as the state of light at. This is because the optical axis of the section B0-B1 and the optical element of the section An-1 -An are parallel to each other, and the refractive index anisotropy has the opposite sign. Similarly, the light is restored.
For this reason, the viewing angle dependency is eliminated in the black display realized by the liquid crystal display device inserted between the orthogonal polarizing plates and the optical compensator of the present invention. Therefore, a high contrast ratio can be maintained over a wide viewing angle range. As can be seen from the above description, any orientation structure of the liquid crystal can be selected. Therefore, the present invention can be applied to black display of any liquid crystal.

Although the description has been made in a somewhat schematic manner, the compensator for the widely used TN structure will be described in further detail. In the display using TN, black display is performed when no voltage is applied to TN (normally black) and TN
When black is displayed when voltage is applied (normally white)
Divided into Therefore, the structure of the compensator differs between the normally black and the normally white cases.

First, the case of normally black TN will be described. Normally, in the black display in the normally black TN mode, the transmittance is wavelength-dependent, and a perfect black display cannot be obtained. In this case, the compensator has a structure in which the refractive index anisotropy has the opposite sign and the twist direction is opposite by the procedure of FIG. In this case, completion is achieved by disposing the TN liquid crystal 107 and the compensator 102 as shown in FIG. At this time, the two polarizing plates 100 are arranged so as to be vertical. In this manner, as described above, not only the viewing angle dependency of the black display is eliminated, but also a complete black display can be obtained.
This is because the elliptically polarized light emitted from the TN liquid crystal is restored by the compensator.

Next, the case of normally white TN will be described. Normally, as shown in FIG.
90 ° when the twist angle is set from 5 ° to 135 °
The 270 ° azimuth is defined as the vertical direction of the display surface. On the other hand, 0 °-
The 180 ° azimuth is defined as the left and right azimuth of the display surface.

In the case of normally white, black display is performed when a voltage is applied, and the liquid crystal orientation in the TN liquid crystal 107 is deformed by an electric field. The state shown in FIG. 1 is deformed by this electric field to obtain the compensator 102. FIG. 5 shows the arrangement of the compensator 102 and the TN liquid crystal 107 obtained in this manner. The reason why the viewing angle dependency of the black display in this case is eliminated will be described.

First, a change in the line of sight in the vertical direction of the display surface will be described with reference to FIG. TN liquid crystal 10 in black display state
7 has a rising direction by the electric field. Therefore, when the viewing angle is changed upward and downward, the transmittance changes asymmetrically, and the viewing angle dependency becomes sharp. However, T
In the combination of the N liquid crystal 107 and the compensator 102, since both the TN liquid crystal and the compensator have a rising direction, the birefringence changes with respect to the vertical viewing angle change cancel each other out,
Shows mild viewing angle dependence.

Next, a change in the line of sight in the left-right direction of the display surface will be described with reference to FIG. In this case, the TN liquid crystal 107 and the compensator 102 have a substantially symmetric structure in the left-right direction.
For this reason, the transmittance shows a gradual change.

As described above, if the optical compensator of the present invention is applied to normally white TN, a wide viewing angle range can be obtained in both the vertical and horizontal directions.

Although the above description has been made with reference to the TN structure, the twist angle is not limited. from now on,
It can be seen that the method can be immediately applied to the super twist TN (STN).

According to the above description, the structure of the compensator is different depending on the target liquid crystal alignment structure in the black display state. Therefore, a case in which it is actually difficult to realize a compensator is considered. In this case, it can be approximated by a combination of several compensating plates. In an extreme case, as shown in FIG. 9, the structure of the compensator obtained by the procedure of FIG. 1 is divided into fine sections in the thickness direction of the compensator, and each fine section is replaced with a uniaxial birefringent body. Things are fine.

[0023]

Next, an embodiment of the present invention will be described. In the present embodiment, the TN mode is selected as a compensation target.

First, a TN mode liquid crystal panel will be described. An amorphous silicon thin film transistor array substrate (TFT substrate) having a pixel size of 100 μm × 150 μm and a counter substrate having a color filter were prepared, and a polyimide solution was applied to both substrates and baked to form an alignment film. Thereafter, both substrates were rubbed, and the two substrates were bonded so that the rubbing directions were orthogonal. At the time of this lamination, 5.
By interposing the 6 μm latex spacer, the gap between both substrates could be finally reduced to 5.2 μm. Next, the liquid crystal ZLI mixed with the left chiral dopant
-4792 (manufactured by Merck) was injected into the gap between both substrates by vacuum injection. The refractive index anisotropy of this liquid crystal is 0.1.
94.

Next, as shown in FIG.
Zero polystyrene films 108 are laminated while being shifted clockwise by 9 °. Since polystyrene has side chains, when it is stretched in the uniaxial stretching direction 109, the refractive index anisotropy becomes negative. In this way, a right twisted TN structure having pseudo-negative refractive index anisotropy can be obtained. The thickness of each film is about 85 μm. The product Δnd of the refractive index anisotropy (Δn) and the thickness (d) of the TN liquid crystal is 0.488 μm.
m. In order to make the absolute value of Δnd equal to the absolute value of the compensator as a whole, the uniaxial stretching step is adjusted so that the refractive index anisotropy of each film becomes −0.000575.

As shown in FIG. 11, the TN liquid crystal panel 110 obtained from the above process is bonded to the polycrystalline compensation plate 111, and two polarizing plates 100 are bonded so as to be orthogonal to each other. Thereafter, the display was illuminated by a backlight unit, and the viewing angle dependence of the black display state when no voltage was applied was measured using a luminance meter. The result is shown in FIG. Each iso-transmittance curve is shown. For comparison, FIG. 13 shows the viewing angle dependence of the black display state of a TN liquid crystal panel in which two polarizing plates are stuck in parallel (conventional normally black TN panel). As can be seen from this, it can be seen that the viewing angle dependence of the black display has been largely eliminated.

The same effect can be obtained by applying a similar compensator to an STN liquid crystal panel.

[0028]

As described above, it is possible to obtain the liquid crystal display device of the present invention having high visibility and wide viewing angle dependence. Also, as described in the embodiment, a sufficient effect can be obtained even when applied to the TN and other liquid crystal modes.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the present invention.

FIG. 2 is a cross-sectional view for explaining the operation of the present invention.

FIG. 3 is a cross-sectional view for explaining the operation of the present invention.

FIG. 4 is a perspective view for explaining an example in which the present invention is applied to a normally black TN.

FIG. 5 is a perspective view for explaining an example in which the present invention is applied to a normally white TN.

FIG. 6 is a perspective view for explaining a vertical and horizontal relationship in the TN display panel.

FIG. 7 is a cross-sectional view illustrating an example in which the present invention is applied to a normally white TN.

FIG. 8 is a cross-sectional view for explaining an example in which the present invention is applied to a normally white TN.

FIG. 9 is a perspective view for explaining an embodiment of the present invention.

FIG. 10 is a perspective view for explaining an embodiment of the present invention.

FIG. 11 is a perspective view for explaining an embodiment of the present invention.

FIG. 12 is an iso-transmittance curve showing the viewing angle dependency of the example of the present invention.

FIG. 13 is an iso-transmittance curve showing the viewing angle dependency of TN.

FIG. 14 is an iso-transmissivity curve diagram showing the viewing angle dependence of TN of the first conventional example.

FIG. 15 is an iso-transmittance curve diagram showing the viewing angle dependence of TN of the second conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 polarizing plate 101 liquid crystal 102 compensator 103 incident polarized light 104 elliptically polarized light 105 compensator outgoing light 106 combination of uniaxial compensators 107 TN liquid crystal 108 polystyrene film 109 uniaxial stretching direction 110 TN liquid crystal panel 111 polystyrene compensator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335 G02F 1/1347 G02F 1/133 500

Claims (3)

(57) [Claims] 1. A liquid crystal display panel having a twisted liquid crystal orientation , comprising a molecule having a refractive index anisotropy of a sign opposite to that of a liquid crystal molecule , wherein the liquid crystal molecule exhibits a black display. the Ri door a liquid crystal alignment structure and orientation structure was a twist in the opposite direction, yet the twist pitch
Ji is a long optical compensation plate than the wavelength of visible light, the adjacent surfaces smell
Orientation of the liquid crystal alignment structure and the alignment structure in the optical compensator.
A liquid crystal display device attached so that the in-plane directions of the substrates match . 2. The liquid crystal display device according to claim 1, wherein the optical compensator has a normally black twisted nematic structure that displays black when no voltage is applied. 3. The liquid crystal display device according to claim 1, wherein the optical compensator has a normally white twisted nematic structure that displays black when a voltage is applied .