JP3405340B2 - Liquid crystal display device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art A conventional reflective STN mode has a feature that it requires no backlight and consumes less power, and has been widely adopted in various portable information devices.

FIG. 5 shows a sectional view of a conventional liquid crystal display element using a reflective STN mode. A conventional liquid crystal display element is composed of a liquid crystal cell 1, polarizing plates 2 and 3 arranged on both sides of the liquid crystal cell 1, and a reflector 4 provided outside the polarizing plate 3.

[0004]

However, the conventional liquid crystal display device using the reflective STN mode has problems that the display is dark and the coloring is large. In addition, there was a problem that the display is doubled, which is peculiar to the reflective mode.

FIG. 6 shows the spectral characteristics of a conventional reflective STN liquid crystal display device when the electric field is off and when it is on. 4 in the figure
Reference numeral 1 is a spectral characteristic when the electric field is off, and 42 is a spectral characteristic when the electric field is on. Here, the cell condition is that the twist angle is 255 degrees, the retardation Δn × d represented by the product of the birefringence Δn of the liquid crystal and the cell gap d is 0.85 μm, and the polarization axis direction and the rubbing direction are set. The angle is 45 degrees. In STN mode, yellow green when off and blue when on,
The display was markedly colored and the luminous reflectance was low at 65%, resulting in poor visibility.

The present invention is intended to solve such a problem, and an object thereof is to introduce a new reflective liquid crystal mode to obtain a liquid crystal display which is bright, has little coloring, and does not show double display. It is to provide an element.

[0007]

A liquid crystal display device according to the present invention comprises a liquid crystal cell in which an STN mode liquid crystal layer is sandwiched between a pair of substrates, a polarizing means disposed outside one of the substrates, and another polarizing device. A backlight arranged outside the substrate,
In the liquid crystal display element having, a semi-transmissive reflection plate is arranged between the liquid crystal layer and the backlight, and a polarizing means is arranged between the reflection plate and the backlight. It is characterized by Further, the liquid crystal display element of the present invention is characterized in that an optical anisotropic body is further arranged between the reflection plate and the backlight. Further, it is characterized in that two or more optical anisotropic bodies are used.

Further, a transparent electrode patterned by an insulating material is provided on the reflecting plate.

Further, the reflecting plate also serves as a pixel electrode. Further, it is characterized in that two or more optical anisotropic bodies are used.

The present invention will be described in detail below with reference to examples.

[0011]

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES Example 1 FIG. 1 is a sectional view of a liquid crystal display device of the present invention. In the figure, 1 is a liquid crystal cell, 2 is a polarizing plate,
Reference numeral 4 is a reflector, and 5 is an optically anisotropic body. Further, 11 is an upper substrate, 12 is a lower substrate, 13 is a transparent electrode, and 15 is a liquid crystal. The liquid crystal is ZLI-4506 (Δn = made by Merck).
0.1438) was used for twist alignment in a liquid crystal cell having a cell gap of 5.6 μm. The retardation value is 0.
It is 81 μm. A uniaxially stretched film of polycarbonate resin was used as the optically anisotropic body. The Δn is 0.0039, the film thickness is 80 μm, and the retardation value is 0.31 μm.

FIG. 3 is a diagram showing the relationship between the axes of the liquid crystal display device of the present invention as viewed from the viewing direction (that is, the upper direction of FIG. 1). 21 is the polarization axis direction of the polarizing plate, 22 is the stretching direction of the uniaxially stretched film used as an optically anisotropic body, 23 is the rubbing direction of the upper substrate, and 24 is the rubbing direction of the lower substrate. In addition, 31 is an angle formed by 21 and 23, and is 3 degrees to the left 40 degrees.
2 is an angle formed by 22 and 23, which is set to 22 degrees to the left, and 33 is a twist angle of the liquid crystal, which is set to 260 degrees to the left.

FIG. 4 is a diagram showing the spectral characteristics of the liquid crystal display device manufactured under the above conditions. In the figure, reference numeral 41 is a spectral characteristic when the electric field is off, and 42 is a spectral characteristic when the electric field is on. The off-state luminous reflectance Yoff is as high as 83%, and the display color thereof is very close to white. In addition, the luminous reflectance when turned on is 2.
Since it is as low as 0%, the maximum possible contrast ratio is 1:
42.

Since the liquid crystal display element of this embodiment has a large twist angle of 260 degrees and a very sharp voltage transmittance characteristic, it is as high as 1:20 even when 1/480 duty multiplex driving is performed. A display contrast was obtained.

(Embodiment 2) The liquid crystal display element of Embodiment 2 has the same structure as that of Embodiment 1. However, the liquid crystal cell 1 of FIG.
, A liquid crystal ZLI-4428 (Δn = 0.
1222) was used. The cell gap is 6.0 μm and the retardation value is 0.73 μm. Also,
As the optically anisotropic body 5, a uniaxially stretched film of PMMA resin was used. The Δn is 0.00061 and the film thickness is 60
The retardation value is 0.37 μm at 0 μm.
In FIG. 3, the angle 31 is 21 degrees to the left and the angle 32 is
Was set to 10 degrees to the left, and the twist angle 33 was set to 240 degrees to the left.

At this time, a relatively high luminous reflectance Yoff of 78% was obtained at the time of off, and the display color was close to white. Further, since the luminous reflectance when turned on is as low as 2.1%, the maximum possible contrast ratio is as large as 1:37.

Further, in the present embodiment, since the uniaxially stretched film of PMMA resin having optically negative uniaxiality is used as the optically anisotropic body, it is characterized by excellent viewing angle characteristics.

(Embodiment 3) FIG. 2 is a sectional view of a liquid crystal display element of this embodiment. In the figure, 1 is a liquid crystal cell, 2 is a polarizing plate, and 5 is an optically anisotropic body. Further, 11 is an upper substrate, 1
Reference numeral 2 is a lower substrate, 13 is a transparent electrode, 14 is a reflective film which also serves as a pixel electrode, and 15 is a liquid crystal. Liquid crystal ZLI-4427 (Δn = 0.127) manufactured by Merck was used for the liquid crystal cell 1, and the average retardation value was set to 0.69 μm. A uniaxially stretched film of polypropylene resin was used as the optically anisotropic body. The Δn is 0.001
8, film thickness is 200 μm, retardation value is 0.3
It is 6 μm. Further, in FIG. 3, the angle 31 is set to the left 1
3 degrees, angle 32 left 88 degrees, twist angle 33 left 225
Set in degrees.

At this time, a comparatively high luminous reflectance Yoff of 80% was obtained when off, and the display color was close to white. Also, since the luminous reflectance when turned on is as low as 2.2%,
The maximum possible contrast ratio is as large as 1:36.

Here, the reflection film 14 has a surface unevenness of 0.
This is a metal aluminum thin film provided on the surface of frosted glass of 5 μm by a sputtering method, and has a reflection characteristic with little directivity. In addition to aluminum, any material having a white silver color such as nickel or chromium may be used as the metal, and the surface irregularities may be provided by roughly polishing the surface of the metal or performing a chemical treatment.

When patterning the reflection film into a comb shape, a method of directly patterning the metal thin film,
There is a method in which a transparent electrode is provided on a metal thin film via an insulator and the transparent electrode is patterned. This insulator is
This is effective when the twist angle for alleviating surface irregularities is large and the d / p margin (d: cell gap, p: spontaneous pitch) is narrow.

As described above, by providing the reflection plate in the liquid crystal cell,
The problem that the display looks double can be solved. Further, a slight variation in the liquid crystal thickness has an additional effect of averaging the display colors and further reducing the coloring.

In the above embodiments, the optically anisotropic substance is placed between the liquid crystal cell and the polarizing plate, but it may be placed between the liquid crystal cell and the reflector. Further, not only one optically anisotropic body but also two or more optically anisotropic bodies can be used to obtain a higher contrast ratio and less colored display.

Further, when the rubbing directions 23 and 24 of the liquid crystal cell are set so that the uniaxially stretched film stretching direction 22 can be set in parallel with the horizontal direction of the display screen, the viewing angle in the left and right direction is widened so that a plurality of people can display. It's convenient to see.
On the contrary, if the rubbing direction is set so that the stretching direction 22 can be set parallel to the vertical direction of the display screen, the contrast ratio is improved. In any case, arranging the uniaxially stretched film in this way increases the number of expensive films taken,
It is also very effective in reducing manufacturing costs.

If the reflection plate 4 is of a semi-transmissive type and a backlight is provided on the opposite side of the liquid crystal cell with the reflection plate sandwiched, it can be used as a transmissive display in dark surroundings. You can make up for the shortcomings. However, in that case, it is necessary to provide a polarizing plate and an optically anisotropic body between the reflection plate and the backlight.

[0026]

The liquid crystal display device of the present invention comprises a liquid crystal cell in which an STN-mode liquid crystal layer is sandwiched between a pair of substrates, a polarizing means arranged outside one of the substrates, and the other substrate. In a liquid crystal display device having a backlight arranged outside, a semi-transmissive reflection plate is arranged between the liquid crystal layer and the backlight, and between the reflection plate and the backlight. Is characterized in that a polarizing means is arranged, so that it can be used as a transmissive display when the surroundings are dark.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display element in Examples 1 and 2 of the present invention.

FIG. 2 is a cross-sectional view of a liquid crystal display element in Example 3 of the present invention.

FIG. 3 is a diagram showing a relationship between axes of the liquid crystal display element of the present invention.

FIG. 4 is a diagram showing spectral characteristics of the liquid crystal display element in Example 1 of the present invention when the electric field is off and when the electric field is on.

FIG. 5 is a cross-sectional view of a conventional liquid crystal display element.

FIG. 6 is a diagram showing spectral characteristics of a conventional liquid crystal display element when the electric field is off and when the electric field is on.

[Explanation of symbols]

1. Liquid crystal cell 2. Polarizing plate (upper side) 3. Polarizing plate (lower side) 4. Reflector 5. Optically anisotropic body (uniaxially stretched film) 11. Upper substrate 12. Lower substrate 13. Transparent electrode 14. Reflective film that also serves as a pixel electrode 15. Liquid crystal 21. Polarization axis (absorption pongee or transmission axis) direction of polarizing plate 22. Optical axis direction of optically anisotropic body (stretching direction of uniaxially stretched film) 23. Rubbing direction of upper substrate 11 (liquid crystal alignment direction) 24. Rubbing direction of the lower substrate 12 (liquid crystal alignment direction) 31.21 forms an angle with 23. 32.22 forms an angle with 23. Liquid crystal 15 twist angle 41. Spectral characteristics of reflected light when electric field is off 42. Spectral characteristics of reflected light when electric field is on

Claims (3)

(57) [Claims] 1. A liquid crystal cell in which an STN-mode liquid crystal layer is sandwiched between a pair of substrates, a polarizing means disposed outside one of the substrates, and a backlight disposed outside the other substrate. In the liquid crystal display element having, a semi-transmissive reflection plate is arranged between the liquid crystal layer and the backlight, and a polarizing means is arranged between the reflection plate and the backlight. Liquid crystal display device characterized by. 2. The liquid crystal display device according to claim 1, further comprising an optical anisotropic body disposed between the reflection plate and the backlight. 3. The liquid crystal display element according to claim 2, wherein two or more optically anisotropic bodies are used.