JPH11337946A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal color display device suitable for gradation display. SOLUTION: In the liquid crystal display device A, a signal electrode member 6 is constituted by successively laminating a protective film 2, a signal electrode 3, an insulating film 4 and an alignment layer 5 on a transparent substrate 1. Otherwise a scanning electrode member 7 is constituted by laminating the protective film 9, a colored layer 10 and a light shielding layer 11 on a transparent substrate 8 and further laminating an overcoat film 12, a scanning electrode 13, the protective film 14 and the oriented film 15 thereon. Further the scanning electrode 13 and the signal electrode 3 are patterned so as to intersect with each other to make a pixel region 16 and the signal electrode member 6 and the scanning electrode member 7 are disposed to face each other via chiral nematic liquid crystal 17. Respective pixel regions 16 are provided with regions 22, 23 in which twist angles of the chiral nematic liquid crystal 17 in an initial state are different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a memory-type bistable liquid crystal display using a chiral nematic liquid crystal.

[0002]

2. Description of the Related Art JP-A-6-230751 and JP-A-6-230751.
JP-A-235920 and JP-A-7-248485 propose a memory-type bistable liquid crystal display device using a chiral nematic liquid crystal, and a practical driving method in initial alignment conditions, two metastable states, and switching between the two. Such techniques are described.

According to the memory-type bistable liquid crystal display device, two metastable states (0 ° or 360 °) after the Freedericksz transition are sandwiched between unstable states (a mixture of the 0 ° state and the 360 ° state). It is displayed by switching with.

[0004]

In order to perform multi-color display with the above-mentioned bistable liquid crystal display device, it is necessary to realize gradation display. For this purpose, there are the following methods.

Switching between the two metastable states is performed by a difference in the magnitude of the selection voltage applied after the reset voltage. The OFF state (φ ₀ + π) is set by setting the selection voltage smaller than a certain threshold value Vth1, and the other state is set. If the selection voltage is set higher than a certain threshold value Vth2, the ON state (φ
_0- π) can be realized, but when the selection voltage is set between Vth1 and Vth2, the display state becomes a mixture of two metastable states, and gradation display can be performed using this state. .

However, there is a problem that it is difficult to set the selection voltage between Vth1 and Vth2 as required to control the ratio of the mixture of the two states, thereby achieving the gradation. In addition, when the two states are close to each other and reach a certain area, an unstable state in the form of a stripe that is not related to the display image has been developed.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device capable of gradation display.

Another object of the present invention is to provide a liquid crystal display device which achieves excellent color display.

[0009]

According to the liquid crystal display device of the present invention, an electrode pattern in which a large number of transparent electrodes are arranged on a transparent substrate and an alignment film are sequentially formed. The other member in which the electrode pattern in which the transparent electrodes are arranged and the alignment film are sequentially formed is arranged so as to face each other via the chiral nematic liquid crystal so as to intersect both electrode patterns and form a large number of pixels, Each pixel is provided with a plurality of regions having different twist angles in the initial state of the chiral nematic liquid crystal.

For example, when the liquid crystal display device of the present invention is a color display, colored layers are arranged in a matrix on a transparent substrate, a light shielding layer is arranged between the colored layers, and A member in which an overcoat film, an electrode pattern in which a number of transparent electrodes are arranged and an alignment film are sequentially formed, and a member in which an electrode pattern in which a number of transparent electrodes are arranged on a transparent substrate and an alignment film are sequentially formed. Are arranged opposite each other via a chiral nematic liquid crystal so that both electrode patterns cross each other to form a large number of pixels, and a plurality of regions having different twist angles in the initial state of the chiral nematic liquid crystal are provided for each pixel. .

In the liquid crystal display device having the above-described structure, the chiral nematic liquid crystal is applied to the plurality of regions having different twist structures in the initial state by applying a voltage that causes a Freedericksz transition in the initial state, and thereafter applied. It has two metastable states different from the initial state due to the voltage difference.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A bistable liquid crystal display device according to the present invention will be described with reference to FIGS.

FIG. 1 is an enlarged sectional view of a main part of a liquid crystal display device A of the present invention, FIG. 2 is an explanatory view showing a rubbing state of an alignment film forming two regions having different twist angles in each pixel, and FIG. FIG. 4 shows an applied voltage waveform, and FIG. 5 is an explanatory view showing another rubbing state of the alignment film forming two regions having different twist angles in each pixel.

In the liquid crystal display device A of the present invention, 1 is a transparent substrate made of glass or the like, 2 is a protective film made of SiO ₂ or the like, 3 is a signal electrode made of ITO or the like, and 4 is an insulating material made of SiO ₂ or the like. The film 5 is an alignment film, which constitutes the signal electrode member 6. The other scanning electrode member 7 is a transparent substrate 8 made of glass or the like.
9 is a protective film made of SiO ₂ or the like, 10 is a colored layer arranged in a matrix (in the figure, R, G and B indicate red, green and blue colored layers, respectively), and 11 is provided between the colored layers Light shielding layer made of metal such as chromium, black resin, etc.
Reference numeral 12 denotes an overcoat film covering the coloring layer 10 and the light-shielding layer 11, 13 denotes a scan electrode made of ITO or the like, 14 denotes an insulating film made of SiO ₂ or the like, and 15 denotes an alignment film. The alignment films 5 and 15 are made of polyimide, and are obtained by rubbing the films.

The scanning electrode 3 and the signal electrode 13 are patterned so as to intersect with each other so that each intersection becomes a rectangular pixel region 16 (for example, 300 μm × 300 μm), and the signal electrode member 6 and the scanning electrode member 7 are formed. Is 1.5 layer thickness
μm chiral nematic liquid crystal 17 (a liquid crystal composition exhibiting a nematic phase at room temperature [ZLI manufactured by E. Merck Ltd.]
-1557] and an optically active additive [E. Merck:
S-811] and the helical pitch P is adjusted).

Further, a seal member for enclosing the chiral nematic liquid crystal 17 is provided between the two members 6 and 7 around the display area. Further, retardation films 18 and 19 and polarizing plates 20 and 21 are disposed outside the transparent substrates 1 and 8.

According to the liquid crystal display device A having the above-described structure, the chiral nematic liquid crystal has a twisted structure in the initial state, and the chiral nematic liquid crystal has a twisted structure in the initial state. Is a memory-type bistable type having two different metastable states. For example, the twist angle φ ₀ (=
180 °), the twisted state of φ ₀ + π (= 360 °) is in a dark state, and the positional relationship (crossed Nicols) of the polarizers 20 and 21 is such that the twist angle φ ₀ −π in the bright state. (= 0 °).

Then, 0 ° and 360 ° across the unstable state
° Switching. That is, when the selection voltage after applying the voltage that causes the Freedericksz transition in the initial state is lower than Vl, the state becomes 360 °, and when the selection voltage is higher than V2, the state becomes 0 °. An unstable state where 0 ° and 360 ° coexist.

For example, when the polarizers 20 and 21 are made into crossed Nicols, the twist angle φ ₀ in the initial state = (180 °)
If the twisted state of φ ₀ + π = (360 °) is a dark state and the state of φ ₀ −π = (0 °) is a bright state, there are two unstable states (a bright state and a black state). States) are mixed, and such a mixed state indicates a state between white and black.

Normally, a voltage is set between V1 and V2,
It is difficult to control the mixed state of 0 ° and 360 °, thereby performing gradation display. Further, when the mixed state reaches a certain wide area, the pixels in the unstable state may interact with each other. And it was easy to develop unstable stripe-like defects in the displayed image.

Therefore, in the liquid crystal display device A of the present invention, in response to the unstable state of black and white, the regions 22 having different twist angles of the chiral nematic liquid crystal as shown in FIG. 23 are formed.

That is, in each pixel region 16 in the alignment films 5 and 15, the rubbing directions of the alignment films 5 are different between the regions 22 and 23 as indicated by arrows, and the alignment films 15 have a common rubbing direction between the regions 22 and 23. Rubbing direction. Such rubbing is formed by mask rubbing.

Next, FIG. 3 shows the relationship between the twist angle and the threshold value. However, d / p is constant.

The threshold voltage changes depending on the twist angle.
In the region 23, the initial twist angle is set to [180 + α].
°.

The initial twist angle is 180 ° and the dark state is 36
0 ° (180 ° + π), the bright state is 0 ° (180 ° -π)
, The threshold voltages in the regions 22 and 23 are Vth1 = 6.0 V and Vth1 = 4.2, respectively.
V, Vth2 = 7.8V and Vth2 = 6.0, respectively.
If Vs = 6.0 V because of V, Vd = + 2.0 V to make a complete light state, Vd = 0 V to make a dark state only in the region 22, and a complete dark state By setting Vd = −2.0 V, three gradation display was realized. By the way, 27-color display was possible because three gradations could be displayed.

Therefore, the liquid crystal display device A is driven by applying a scanning waveform and a signal waveform as shown in FIG. (A) is a voltage waveform applied to the scanning electrode,
(B) is a voltage waveform applied to the signal electrode, and (c) is a voltage waveform actually applied to the liquid crystal cell obtained by combining these two waveforms. The display state of each pixel is determined by the voltage of Vw (± (Vs ± Vd)) shown in (c), and the peak value of the voltage corresponding to the selected display state is controlled by the voltage value of the signal voltage applied voltage.

Thus, according to the liquid crystal display device A of the present invention, the regions 22 and 23 having different twist angles of the chiral nematic liquid crystal are formed in each pixel region 16 so that the light in the unstable state in the pixel region 16 is obtained. The expression ratio between the state and the dark state was controlled, and as a result, gradation display was realized.

It should be noted that the present invention is not limited to the above embodiment, and various changes and improvements may be made without departing from the scope of the present invention. For example, in the above embodiment, the rubbing direction is different between the regions 22 and 23 for the alignment film 5 and the rubbing direction is common to the regions 22 and 23 in the alignment film 15 for each pixel region 16. Instead of the alignment films 5 and 15, both regions 22 and
The rubbing direction may be different between the 23, thereby realizing a wider viewing angle. Further, besides making the areas 22 and 23 1: 1, the area ratio may be changed, and three or four areas having different twist angles for each pixel,
Alternatively, the area may be increased to a larger area. Furthermore,
In the embodiment of the present invention, a color liquid crystal display device has been described as an example. However, a monochrome liquid crystal display device can provide the same function and effect.

[0029]

As described above, according to the memory-type bistable liquid crystal display device of the present invention, each pixel is provided with a plurality of regions having different rubbing directions and different twist angles.
The expression ratio of the bright state and the dark state in the unstable state in each pixel region was controlled, whereby gradation display was realized, and as a result, a liquid crystal display device which achieved excellent color display was provided.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a liquid crystal display device of the present invention.

FIG. 2 is an explanatory diagram showing a rubbing state of an alignment film forming two regions having different twist angles in each pixel.

FIG. 3 is a diagram showing a relationship between a twist angle and a threshold value.

FIG. 4 is a waveform diagram of a voltage applied to the liquid crystal display device of the present invention.

FIG. 5 is an explanatory diagram showing another rubbing state of the alignment film forming two regions having different twist angles in each pixel.

[Explanation of symbols]

 Reference Signs List A Liquid crystal display device 1, 8 Transparent substrate 2, 9 Protective film 3 Signal electrode 4, 14 Insulating film 5, 15 Alignment film 6 Signal electrode member 7 Scanning electrode member 10 Coloring layer 11 Light shielding layer 12 Overcoat film 13 Scanning electrode 16 pixel Area 17 Chiral nematic liquid crystal 18, 19 Retardation film 20, 21 Polarizer 22, 23

Claims (1)

[Claims] A member formed by sequentially forming an electrode pattern in which a number of transparent electrodes are arranged on a transparent substrate and an alignment film; an electrode pattern in which a number of transparent electrodes are arranged on a transparent substrate; and an alignment film. And the other member, which is formed successively, is disposed to face each other via a chiral nematic liquid crystal so that a large number of pixels are formed by intersecting both electrode patterns, and each pixel is twisted in the initial state of the chiral nematic liquid crystal. A liquid crystal display device comprising a plurality of regions having different angles.