JPH0139085B2 - - 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.

A cholesteric-nematic phase transition type liquid crystal display panel has a cholesteric phase structure when no electric field is applied, and as shown in Fig. (b) a focal conic structure in which the helical axis 3 is inclined with respect to the substrate surface;
It can be classified into The factors that differentiate these two initial states are the surface alignment treatment and the ratio d/P of the gap d between the substrates and the helical pitch P of the liquid crystal composition.
It is.

An example of the experimental results is described below. As shown in Figure 2, (1) vertical alignment treatment on both sides of the substrate (vertical panel);
(2) Three types of panels are prepared: vertical alignment treatment on one side of the substrate, horizontal alignment treatment on the other substrate (hybrid panel), and (3) horizontal alignment treatment on both sides of the substrate (parallel panel). It was sealed with a chiral nematic liquid crystal to which an optically active substance was added so that the ratio of 2.0 was obtained. The parallel panel (3) is flat and transparent, and the hybrid panel (2) has a striped structure with the helical axis tilted in one direction, and is slightly cloudy compared to the parallel panel (3). be. The vertical panel in (1) has a focal conic structure with randomly tilted helical axes and is cloudy. Next, we conducted an experiment to change d/P, and found that the vertical panel in (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 of the hybrid panel (2) changed, and the parallel panel (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, the state when an electric field is applied and removed to the liquid crystal panel that satisfies d/P≧1.5 and the above-mentioned initial state do not match in any alignment treatment. After applying and removing electric field,
The vertical panel (1) has a cloudy state that is close to the initial state, but the tissue has become more finely fingerprint-like, which does not match the initial state. (3) horizontal panel becomes cloudy;
The resulting focal conic structure is completely different from the initial state, which was flat and transparent. The hybrid panel (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 display segment electrodes after the application and removal of the electric field and the background portion in the initial state are recognized to be the same in the display. However, the display quality deteriorated. 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 structure consists of a lower substrate in which a full-surface electrode 8, an insulating film 7, and a segment electrode 6 are laminated on a substrate 9, an upper substrate 4 having a common electrode 5 on the entire surface, and a liquid crystal layer sandwiched therebetween. In this embodiment, the substrate 9 and the substrate 4 are flat Pyrex glass, the insulating film 7 is a SiO ₂ sputtered film of 8000 Å, the entire surface electrode 8 is a gold-chromium evaporated film that also serves as a reflector, and the segment electrode 6 and the entire surface electrode 5 is a transparent conductive film of In ₂ O ₃ .
The substrate was further subjected to vertical alignment treatment using Surfine-150, a vertical alignment treatment agent manufactured by Dainippon Ink Chemical.
It is crimped with a 9μ nylon spacer.
The sealed liquid crystal was a mixed liquid crystal of cyanobiphenyl liquid crystal and phenylcyclohexyl carbonate liquid crystal to which 4.0% by weight of CB-15 manufactured by BDH was added and the pitch was set to 3.2μ.

Next, FIG. 3 will be explained. a and a' are diagrams showing a cross section a and a display state b when a voltage sufficient to cause a nematic phase transition is applied to the segment electrode 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 region 10 maintains the focal conic structure which is the initial state after encapsulation. Therefore, the segment area becomes optically homogeneous and transparent, and the background area becomes cloudy due to the focal conic structure. Since the entire surface electrode 8 also serves as a reflector, the segment area 11 is reflective and the background area 10 is light scattering, resulting in the display shown at a'.

FIGS. 3b and 3b' are diagrams showing the cross section b and the display state b' when the electric field is reduced to 0 from the electric field application states a and a'. 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. 3b'. 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 compared to B, A has a finer fingerprint-like pattern. 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 b' 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 3c' show the cross section and display when a voltage is applied between the electrodes provided on the entire surface according to the present invention. The liquid crystal molecules in the area corresponding to the entire surface electrode are homeotropically aligned, resulting in a reflective display similar to that in the segment electrode area shown in FIG. 3a'.
Next, Fig. 3 d and d' show the cross section and display when the voltage is set to 0. The entire electrode area has a focal conic structure and becomes cloudy. The focal conic structure also exhibits a thin fingerprint-like pattern as shown in FIG. 4A. Regarding the display, see Figure 3.
This is the same cloudy state as the segment electrode area b'. FIGS. 3e and 3e' show the cross section and display when a voltage is applied to the segment electrodes of the liquid crystal panel in the states d and d'. 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, e', d, and d' in FIG. 3, respectively. The two states used for display are the cloudy state of a focalonic structure with a thin fingerprint-like pattern shown in FIG. 4A, and the transparent state of a homeotropically oriented nematic phase.

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 in which a full-surface electrode 8, an insulating film 7, and a segment electrode 6 are laminated on a substrate 9;
The liquid crystal layer is sandwiched between an upper substrate 4 having a common electrode 5 on the entire surface. In this embodiment, the substrate 9 and the substrate 4 are made of flat pyrex glass.
The insulating film 7 was a sputtered SiO ₂ film of 8000 Å, and the entire surface electrodes 5 and 8 and the segment electrodes 6 were 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 includes cyanobiphenyl liquid crystal, phenylcyclohexyl carbonate liquid crystal, and CB-15 manufactured by BDH.
Added 3.0wt% and further added dichroic dye D manufactured by BDH.
-35 in an appropriate amount.

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 cloudy state when OFF and the transparent state when ON affect the display effect more than the difference in light absorption by dichroic dyes. may be given. 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 a′ show a full-surface electrode 8 according to the present invention,
The cross section and display state when a voltage is applied between the electrodes 5 on the entire surface of the upper substrate are shown. 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, and the display is transparent and light absorption by the dye is weak. b and b' indicate when the voltages of a and a' 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 fingerprint-like pattern than the initial state. This corresponds to FIG. 4A of the first embodiment. FIGS. 5c and 5c' 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. The OFF state is shown in FIGS. 5b and b' described above, and 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 referred to as a memory phenomenon. Furthermore, in regions 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, since the initial state is a Grangeyan structure and the OFF state is 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 5a', a voltage is applied between the electrodes 5 and 8 on the entire surface to homeotropically align the entire surface.
Next, when the voltage is reduced to 0, the liquid crystal molecules assume a focal conic structure. This state corresponding to FIGS. 5b and b' is a cloudy, darkly colored OFF state, and the entire surface is homogeneous. Figure 5 c and c' show the ON state when voltage is applied between the segment electrodes b and b' and the upper entire surface electrode.
represents the state. 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 OFF-state segment and the background region can be eliminated by applying a voltage between the electrodes on the entire surface as necessary.

The present invention has been described above with reference to Examples, but the present invention is not limited to the liquid crystal compositions and alignment treatments in the Examples, and the present invention is applicable to a phase in which the display state of the background region matches the segment electrode region after the electric field is removed. This is effective for transition type liquid crystal display devices.

As described above, according to the present invention, one substrate has a full-surface electrode, an insulating thin film, and a segment electrode,
Since the other substrate has a full-surface electrode, first,
By applying and removing a voltage between the electrodes on the entire surface, it is possible to create a homogeneous alignment structure of the liquid crystal on the entire surface area. Next, the segment electrodes provide a good pattern, making it possible to achieve high-quality display.

[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...
...Spiral axis. 2. FIGS. 1, 2, and 3 are schematic diagrams when the orientation treatment of the substrate is changed. 1...Vertical panel, 2...Hybrid panel, 3...Parallel panel. The instruction numbers in the figure are the same as in FIG. Figure 3 a, a', b, b', c, c'd, d', e,
e' is a conceptual diagram when implemented in a scattering type display device. a, a'... ON state of conventional method, b, b'... OFF state of conventional method, c, c'... When voltage is applied to the entire surface electrode, d, d'... OFF state according to the present invention , e,
e′...ON state according to the present invention, 4... Upper substrate,
5... Upper entire surface electrode, 6... Segment electrode, 7
... Insulating thin film, 8 ... Lower entire surface electrode, 9 ... Lower substrate, 10 ... Background region, 11 ... Segment region, 12 ... Power supply, 13 ... Liquid crystal molecules. FIGS. 4A and 4B are views of two fingerprint-like structures observed using a polarizing microscope. A... Pattern after electric field application and removal, B...
The pattern indicated by the initial state. FIGS. 5a, a', b, b', c, and c' are conceptual diagrams when implemented in a phase change type guest-host liquid crystal display device. a, a′... When voltage is applied to the entire surface electrode, b,
b'...OFF state according to the present invention, c, c'...ON state according to the present invention, 14...Dichroic dye molecule. Other designation numbers in the figure are the same as in FIG.

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. In the method for driving a phase change liquid crystal display device, the cloudy state of a background region to which no voltage is applied is different from the cloudy state of a region to which a voltage is applied and removed. a full-surface electrode formed on the entire surface; an insulating thin film formed on almost the entire surface of the full-surface electrode formed on one substrate; and a segment electrode formed on the insulating thin film; A phase change type liquid crystal display characterized in that a voltage is applied between the entire surface electrodes and removed, and then a voltage is applied between the segment electrodes and the entire surface electrode formed on the other substrate to display a pattern. How to drive the device.