JPH0150889B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device that utilizes the cholesteric-nematic phase transition phenomenon.

The cholesteric-nematic phase transition type liquid crystal display panel has the structure of the cholesteric phase when no electric field is applied, as shown in Figure 1 (a) Grangian structure in which the helical axis is perpendicular to the substrate surface. (b) those with a focal conic structure in which the helical axis is tilted with respect to the substrate surface; The factors that differentiate these two initial states are the surface orientation treatment and d/p.

An example of the experimental results will be described below.

As the surface orientation treatment, as shown in Figure 2, 1
There are three types of processing: vertical alignment treatment on both sides of the substrate (vertical panel), vertical alignment treatment on two sides of the substrate, horizontal alignment treatment on the other substrate (hybrid panel), and horizontal alignment treatment on the three sides of the substrate (parallel panel). A panel was prepared, and a chiral nematic liquid crystal to which an optically active substance was added was sealed so that d/p=2.0. The parallel panel No. 3 is flat and transparent, and the hybrid panel No. 2 has a striped structure with the axis tilted in one direction, and is slightly cloudy compared to the parallel panel No. 3. The vertical panel 1 has a focal conic structure with randomly tilted axes and is cloudy. Next, we conducted an experiment to change d/p, and found that vertical panel 1
The boundary was approximately d/p = 1.5, below which a transparent structure appeared, and above that a white turbidity due to a focal conic structure appeared. The degree of cloudiness in the hybrid panel No. 2 varied, and the parallel panel No. 3 remained flat and transparent. As d/p was further increased, both the vertical panel 1 and the hybrid panel 2 began to exhibit an initial state close to transparency. The above is the initial state of each panel to which no electric field is ever applied. However, d/p≧1.5
The state when an electric field is applied and removed to the liquid crystal panel that satisfies the following does not match the above-mentioned initial state, no matter which alignment treatment is performed. After application and removal of the electric field, the vertical panel 1 becomes cloudy and cloudy, close to the initial state, but the tissue becomes finer and finger-squeezed, which does not match the initial state. The horizontal panel of No. 3 becomes cloudy and has a focal conic structure, which is completely different from its initial state, which was flat and transparent. The hybrid panel No. 2 returns to a cloudy state that is relatively the same as the initial state, but the striped structure does not completely match.

In this way, in the conventional phase change type liquid crystal display panel that satisfies d/p≧1.5, the area on the display segment electrode after the application and removal of the electric field and the background area in the initial state are not recognized to be the same on the display. , resulting in a decline in display quality. For this reason, at present, there is no choice but to use a region with a small d/p, or to accept a certain degree of deterioration in display quality.

The present invention eliminates such drawbacks and satisfies d/p≧
It was invented with the aim of achieving high display quality even in the 1.5 range.

Hereinafter, the present invention will be explained in detail based on Examples.

Example 1 Example 1 is an application of the present invention to a scattering type display device. Figure 3 is a conceptual diagram. The lower substrate has segment electrodes 6 on the upper side of the substrate 8.
A reflective film 9 is attached to the lower side of the background electrode 7 which is provided at an interval of 20 μm so as to surround it. The liquid crystal layer is sandwiched between this lower substrate and an upper substrate 4 having a common electrode 5 on the entire surface.

In this embodiment, the substrates 4 and 8 are made of flat Pyrex glass, the entire surface electrode 5, the segment electrode 6, and the background electrode 7 are made of a transparent conductive film of In ₂ O ₃ , and the reflective film 9 is made of a vapor-deposited aluminum film. The substrate was further vertically aligned using Surfine 150, a vertical alignment agent manufactured by Dainippon Ink and Chemicals, and was bonded using a 9μ nylon spacer. The sealed liquid crystal is a mixed liquid crystal of cyanobiphenyl liquid crystal and phenylcyclohexyl carbonate liquid crystal, and CB-15 manufactured by BDH.
4.0% by weight was added, and the pitch was 3.2μ.

Next, FIG. 3 will be explained. Figures a and f show a cross section a and a display f when a voltage sufficient to cause a nematic phase transition is applied to the segment electrodes 6 and the entire surface electrode 5 after filling the liquid crystal.

The liquid crystal molecules in the region 11 corresponding to the segment electrode 6 undergo a cholesteric-nematic phase transition due to the electric field, and are homeotropically aligned. On the other hand, the structure of the liquid crystal corresponding to the background area 10 is
The focal conic structure, which is the initial state after encapsulation, is maintained. Therefore, the segment area becomes optically homogeneous and transparent, and the background area becomes cloudy due to the focal conic structure. Because of the reflective plate 9, the segment area 11 is reflective;
The background area 10 becomes light-scattering and displays as shown in f.

FIGS. 3b and 3g are diagrams showing the cross section b and the display state g when the electric field is reduced to 0 from the electric field application states a and f. The liquid crystal molecules 13 in the region corresponding to the segment electrodes have a focal conic structure again, but the structure is slightly different from the focal conic structure in the initial state. FIG. 4 shows the structure of FIG. 3g. A corresponds to the segment electrode area, and B corresponds to the background area. In other words, A applies an electric field,
The focal conic structure after removal, B represents the focal conic structure in the initial state. From FIG. 4, it can be seen that the finger-squeeze-like pattern in A is finer than that in B. This indicates that the direction of inclination of the helical axis has become more random than in the initial state. Therefore, region A becomes cloudy with stronger light scattering than the initial state of B. Figures 3b and 3g show this situation. For this reason, when the display is in the OFF state, the segment area and the background area are distinguishable, leading to deterioration in display quality.

FIGS. 3c and 3h show the cross section and display when a voltage is applied between the background electrode, segment electrode, and upper electrode provided according to the present invention.
The liquid crystal molecules are homeotropically aligned, resulting in a reflective display similar to the segment electrode area of FIG. 3f. Next, the cross section and display state when the voltage is set to 0 are shown in FIGS. 3d and 3i. Liquid crystal molecules have a focal conic structure and become cloudy. Moreover, the focal conic structure exhibits a thin finger-like pattern shown in FIG. 4A. Regarding the display, it is in the same cloudy state as the segment electrode area in FIG. 3g. FIGS. 3e and 3j show cross sections and display states when a voltage is applied to the segment electrodes of the liquid crystal panel in states d and i. The regions corresponding to the segment electrodes undergo a nematic phase transition and become transparent.

The ON state and OFF state of the display in this embodiment correspond to e, j, d, and i in FIG. 3, respectively. The two states used for display are a cloudy state of a focal conic structure with a thin finger-like pattern shown in FIG. 4A, and a transparent state of a nematic phase with homeotropic orientation. Furthermore, the gap between the segment electrode and the background electrode is as small as 20 μm and cannot be visually recognized.

In this way, in this example, a scattering type display device was realized which provides a homogeneous display in the OFF state.

Example 2 Example 2 is an application of the present invention to a phase change type guest-host liquid crystal display device. FIG. 5 is a conceptual diagram thereof. A lower substrate with segment electrodes 6 and background electrodes 7 attached on the upper side, and a common electrode 5 on the entire surface.
It has a structure in which the liquid crystal layer is sandwiched between an upper substrate 4 having a substrate 4 and a liquid crystal layer. In this embodiment, the substrates 8 and 4 were made of flat Pyrex glass, and the entire surface electrodes 5, segment electrodes 6, and background electrodes 7 were made of transparent conductive films of In ₂ O ₃ . The substrate was vertically aligned and pressure bonded as in Example 1. The encapsulated liquid crystal composition is a cyanobiphenyl liquid crystal and a phenylcyclohexyl carbonate liquid crystal made by BDH.
It contains 3.0 wt% of CB-15 and an appropriate amount of dichroic dye D-35 manufactured by BOH. In addition, between the segment electrode and the background electrode, Example 1 was used.
Similarly, they are separated by a 20 μm gap.

In a guest-host liquid crystal display that utilizes cholesteric-nematic phase transition, the display is mainly
This is caused by a difference in absorption due to a change in the orientation of the dye molecules 14, but the light scattering effect due to the change in the orientation of the liquid crystal has a considerable influence on the display. In fact, in display panels with large d/p values aimed at high contrast, the cloudiness in the OFF state and the transparency in the ON state have a greater display effect than the difference in light absorption by dichroic dyes. There are cases. However, as described in Example 1, this cloudy state also has an initial state in which no electric field is applied, and an initial state in which an electric field is applied once.
The structure is somewhat different from the OFF state.

This also has a negative impact on the guest-host effect. In other words, the difference in structure becomes a difference in light absorption, and the difference in light scattering state is also combined, so that the segment electrode region 11 and the background region 10 can be distinguished from each other when OFF.

FIGS. 5a and 5d show the cross section and display when a voltage is applied between the segment electrode 6, the background electrode 7, and the entire surface electrode 5 of the upper substrate. This is a display state in which the liquid crystal molecules 13 and dye molecules 14 on the entire surface of the liquid crystal panel are homeotropically aligned, transparent, and light absorption by the dye is weak. b and e indicate when the voltages of a and d are set to 0. Liquid crystal molecules take on a focal conic structure, and as a result, absorption of light by dye molecules increases and the liquid becomes cloudy. This focal conic structure is observed as a finer finger-like pattern than in the cut state. This is Example 1
This corresponds to FIG. 4A of FIG. FIGS. 5c and 5f show the case where a voltage is applied between the segment electrode and the upper entire surface electrode. The segment electrode area is transparent and lightly colored by the dye, and the background area appears cloudy and darkly colored. This is the ON state. In the OFF state, as shown in FIGS. 5b and 5e described above, the entire surface of the liquid crystal panel displays a homogeneous display.

Example 3 Example 3, like Example 2, is applied to a phase change type guest-host liquid crystal display device.

The configuration is the same as in Example 2 and will therefore be omitted. The difference is that the substrate is aligned in parallel by applying polyimide and rubbing. The encapsulated liquid crystal composition was also the same as in Example 2.

When parallel alignment treatment is applied, the initial state is the first state.
This is a flat Grange Yang structure as shown in Figure a. Therefore, it is transparent and the pigments absorb light strongly. However, after application and removal of an electric field, it takes a long time to relax into a Grangian structure. This phenomenon is generally called a memory phenomenon.

Furthermore, in a region where d/p is large, there are cases in which there is almost no relaxation. At this time, the liquid crystal molecules have a focal conic structure and have light scattering properties. Therefore, the initial state is a Grangeyan structure,
Since the OFF state has a focal conic structure, the segment electrode area and the background area can be clearly distinguished, which is a major problem in display. According to the present invention, by applying and removing an electric field also to the background region and changing the Grangian structure to a focal conic state, the segment electrode region and the background region are not distinguished from each other on the display when the display is OFF.

This will be explained using FIG. 5 of the second embodiment. As shown in FIGS. 5a and 5d, a voltage is applied between the entire surface electrode 5, the segment electrode 6, and the background electrode 7, thereby causing the entire structure to be homeotropically oriented. Next, when the voltage is reduced to 0, the liquid crystal molecules assume a focal conic structure.
This state corresponding to FIGS. 5b and 5e is a cloudy, darkly colored OFF state, and the entire surface is homogeneous. Fifth
Figures c and f show an ON state in which a voltage is applied between the segment electrodes b and e and the upper entire surface electrode. In this way, as in the second embodiment, in this embodiment as well, it is possible to obtain a uniform OFF state over the entire surface.

In the case of the parallel alignment treatment of this embodiment, the time required for relaxation to the Grangian structure may be short depending on the liquid crystal used and the alignment treatment method. In such a case, the non-uniformity of the segment area and the background area in the OFF state can be eliminated by applying a voltage between the electrodes on the entire surface as necessary.

Although the present invention has been described above with reference to Examples, the present invention is not limited to the liquid crystal composition and alignment treatment in the Examples, and the display state of the background area is the same as that of the segment electrode area after applying and removing an electric field. Any phase change type liquid crystal display device that matches the above will be effective.

As described above, according to the present invention, since the background electrode is formed on almost the entire surface surrounding the segment electrode, it is possible to apply a voltage to the background region as well. Therefore, by first applying and removing a voltage to the entire area between the pair of substrates, it is possible to create a homogeneous liquid crystal alignment structure in the entire area. Next, since the pattern is displayed using segment electrodes, the contrast with the background area is improved, and high-quality display can be realized.

[Brief explanation of drawings]

FIGS. 1a and 1b are schematic diagrams of a Grangeyan structure and a focal conic structure. a...Grangian structure, b...focalconic structure, 1...substrate, 2...liquid crystal molecule, 3...axed. FIGS. 2a and 2b are schematic diagrams when the orientation treatment of the substrate is changed. 1...Vertical panel, 2...Hybrid panel, 3
...parallel panels, designation numbers in the figures are the same as in FIG. 1. Figure 3 a, b, c, d, e, f, g, h, i,
j is a conceptual diagram when implemented in a scattering type display device. a, f...conventional method ON state, b, g...conventional method
OFF state, c, h... segment, background When voltage is applied to both electrodes, d, i... OFF according to the present invention
State, e, j... ON state according to the present invention, 4... Upper substrate, 5... Upper entire surface electrode, 6... Segment electrode,
7... Background electrode, 8... Lower substrate, 9... Reflective film, 10
...background area, 11...segment area, 12...power supply, 13...liquid crystal molecule. FIGS. 4A and 4B are views of two finger-squeeze-like tissues observed with a polarizing microscope. A: Pattern after electric field application and removal, B: Pattern shown by the initial state. FIGS. 5a, b, c, d, e, and f are conceptual diagrams when implemented in a phase change type guest-host liquid crystal display device. a, d... When voltage is applied to the segment, background, and surface electrode, b, e... OFF state according to the present invention, c,
f... ON state according to the present invention, 14... dichroic dye molecule, other designation numbers in the figure are the same as in FIG. 3.

Claims (1)

[Claims] 1 A liquid crystal composition in which an optically active substance is added to a cholesteric liquid crystal or a nematic liquid crystal with positive dielectric anisotropy is sandwiched between a pair of substrates with electrodes formed on the opposing inner surfaces, and the cholesteric-nematic phase transition phenomenon is utilized. However, in a method for driving a phase change liquid crystal display device in which a cloudy state in a background region to which no voltage is applied is different from a cloudy state in a region removed by applying a voltage, segment electrodes formed on the inner surface of one substrate and , a background electrode formed on almost the entire surface surrounding the segment electrode, and a full surface electrode formed on almost the entire surface on the inner surface of the other substrate, the segment electrode and the background electrode, and the A method for driving a phase change type liquid crystal display device, comprising applying and removing a voltage between the segment electrode and the entire surface electrode, and then applying a voltage between the segment electrode and the entire surface electrode to display a pattern.