JPS5842446B2 - Phase change type liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal whose main component is a mixed liquid crystal of nematic liquid crystal and one or both of cholesteric liquid crystal and chiral nematic liquid crystal (hereinafter abbreviated as nematic-cholesteric mixed liquid crystal).

[Relating to a phase change type liquid crystal display device using [].

A phase change type liquid crystal display device using a nematic-cholesteric mixed liquid crystal utilizes light scattering in the focal conic state when a voltage is applied, and has the characteristic that a bright display can be obtained because it does not use a polarizing plate.

Phase change type liquid crystal display devices using a nematic-cholesteric mixed liquid crystal are divided into p-type and n-type, respectively, depending on the positive or negative dielectric anisotropy of the nematic liquid crystal used.

FIG. 1 is a light transmission intensity-voltage characteristic diagram of a phase change type liquid crystal display device using an n-type nematic-cholesteric mixed liquid crystal.

In the initial state when no voltage is applied, the surface alignment treatment results in a transparent or nearly transparent light scattering state, but as the voltage is increased, the light scattering state changes to a strong light scattering state, and this light scattering state remains for a long time even after the voltage is removed. Retained.

In order to return this light scattering state to its initial state, it is necessary to apply a high voltage with a high frequency.

Phase change type liquid crystal display devices using a p-type nematic/cholesteric mixed liquid crystal are classified into parallel alignment type and vertical alignment type depending on the alignment treatment.

FIG. 2 is a light transmission intensity-voltage characteristic diagram of a horizontal alignment type phase change type liquid crystal display device.

In the initial state when no voltage is applied, the substrate surface exhibits a transparent or weakly light-scattering state due to the horizontal alignment process, and as the voltage is increased, it becomes a focal conic state with strong light-scattering state, and when the voltage is further increased, it becomes transparent. It becomes a homeotropic nematic state.

If the voltage is lowered at a very slow rate (as shown in Figure 2), it will return to its initial state along the voltage increase curve.

FIG. 3 is a light transmission intensity-voltage characteristic diagram of a vertical alignment type phase change type liquid crystal display device using a p-type nematic-cholesteric mixed liquid crystal.

In the initial state with no voltage applied, it is slightly cloudy and transparent; when the voltage is increased, it becomes a focal conic state with strong light scattering, and when the voltage is further increased, it becomes a transparent homeotropic nematic state.

As shown in Figure 3, this vertical alignment type phase change type liquid crystal display device is characterized by a relaxation process, and when the voltage that exhibits a homeotropic nematic state is abruptly turned off, light emitted as shown by ■. After going through the scattering state, it returns to the initial state, and when the voltage is slowly lowered, it becomes a focal conic state, as shown by ■, and the light scattering state continues to accumulate.

As mentioned above, there are various types of phase change type liquid crystal display devices, and active research and development is currently underway to reduce power consumption, improve responsiveness, and improve contrast in order to put them into practical use.

In particular, in the case of a phase change type liquid crystal display device, a display in which the background part is in a light scattering state and the display parts such as numbers and characters are transparent (hereinafter referred to as negative type display).

), the display becomes easier to see, and various methods are being considered, such as providing electrodes also in the background.

An object of the present invention is to provide a phase change type liquid crystal display device with a negative type display using a simple electrode pattern that does not include means for applying an electric field to parts other than display pattern parts such as numbers and characters.

The present invention will be described below.

The present invention has discovered that the light scattering state due to the thermo-optic effect of a nematic-cholesteric mixed liquid crystal is accumulated semi-permanently unless the liquid crystal flows due to an external force or an electric field or magnetic field is applied. This is intended for application to phase change type liquid crystal display devices.

A nematic-cholesteric mixed liquid crystal sandwiched between two substrates that have been subjected to various alignment treatments exhibits a light scattering state when the liquid crystal is heated above its liquid transition temperature and then returned to the liquid crystal state. This is known as the thermo-optic effect, and research has been carried out to apply it to large displays where the display is written in a liquid state (transparent) by heating with laser light.

As a result of various experiments and research, this state of light scattering due to the thermo-optic effect has been found to be caused by temperature changes below the transition temperature of the liquid crystal, shock and vibration caused by dropping, as well as high temperature and high humidity conditions, and light irradiation conditions. It was confirmed that the liquid crystal does not change when left alone, and accumulates semi-permanently unless a strong electric or magnetic field is applied or an external force on the substrate causes the liquid crystal to flow.

The present invention realizes an easy-to-see negative type display by utilizing this semi-permanently accumulated light scattering state due to the thermo-optic effect as the background part of the display of a phase change type liquid crystal display device that displays the display by applying a normal voltage. It is.

As a result of various experiments, this phenomenon of accumulation of light scattering states due to the thermo-optic effect was observed in most liquid crystal cells subjected to surface alignment treatment other than rubbing treatment.

Normally, a phase change type liquid crystal display device exhibits a transparent state or a weak light-scattering state close to that due to the flow of the liquid crystal at the time of injection, when a nematic-cholesteric mixed liquid crystal is injected and sealed. When the material is heated above its liquid transition temperature and then returned to the liquid crystal state, a nearly uniform light scattering state is obtained, although it varies slightly depending on the treatment of the substrate surface.

The light scattering state obtained in this way becomes non-accumulative when the electric field is removed, and shows a history similar to that shown in FIGS. 1 to 3.

Therefore, only the display pattern portion to which the voltage is applied changes between the transparent state and the light scattering state depending on the voltage, and the background portion continues to maintain the light scattering state.

The explanation will be based on the drawings.

FIG. 4 shows an example of a phase change type liquid crystal display device of the present invention, in which 1 is a glass substrate, on which transparent electrodes 2 and alignment films 5 are formed.

Nematic/cholesteric mixed liquid crystal 4a. 4b (Although the liquid crystal is the same, for the sake of explanation, it is divided into a part 4b sandwiched between electrodes and the other part 4a.

: is sandwiched between the substrates by spacers 3.

The phase change type liquid crystal display device of the present invention is obtained by heating the liquid crystal having such a structure above the transition temperature of the nematic-cholesteric mixed liquid crystal to a liquid and returning it to room temperature. 4a,
The entire portion 4b accumulates a light scattering state, but when a voltage is applied, the portion of 4b to which an electric field is applied changes as shown in FIG. 1 to FIG. 3 depending on the type and orientation of the liquid crystal.

In the portion indicated by 4a, the light scattering state due to the thermo-optic effect is maintained.

FIG. 5 shows an example of application to numerical display. The part indicated by 6 is
This is a light scattering state due to the thermo-optic effect, 7 is a focal conic light scattering state due to voltage application, and 8 is a transparent state such as a Grangen state or a homeotropic nematic state.

By appropriately selecting the composition of the alignment film and the nematic/cholesteric mixed liquid crystal, the light scattering states of 6 and 7 can be made similar, and an easy-to-read negative type display in a transparent state with the light scattering state as a background can be obtained.

As described above, a negative type phase change type liquid crystal display device can be obtained with a simple electrode pattern similar to that of a TN type liquid crystal display device without providing a means for applying an electric field to the background portion, and an electric field can also be applied to the background portion. This has a great advantage in that power consumption can be reduced compared to the conventional case.

It was confirmed that the phenomenon of accumulation of light scattering states due to the thermo-optic effect in a phase change type liquid crystal display device using a nematic-cholesteric mixed liquid crystal can be obtained with most surface alignment treatments except rubbing treatment. Even in a phase change type liquid crystal display device composed of two substrates that had only been subjected to surface polishing, electrode formation, and cleaning, an accumulation phenomenon of light scattering states due to thermo-optic effects was observed.

Uses the light scattering state due to the thermo-optic effect to create a background part
The light scattering state is slightly different between the part sandwiched between the electrode and the substrate material surface and the part sandwiched between the substrate material surfaces on both sides, and the uniformity of the light scattering state in the background part is slightly inferior.

However, it has the advantage of omitting the alignment process in manufacturing the liquid crystal cell, which helps reduce costs.

In addition, an accumulation phenomenon of light scattering due to the thermo-optic effect was also observed in a phase change type liquid crystal display device composed of two substrates that have been subjected to alignment treatment by vapor deposition of an inorganic material. Therefore, there was no non-uniformity in the light scattering state in the background area unlike in the case where the above-mentioned alignment treatment was not performed, and a uniform and beautiful light scattering state was obtained.

Furthermore, the light scattering state of the thermo-optic effect created by the vapor-deposited inorganic film changes by changing the vapor deposition angle (the angle between the substrate surface and the direction of the vapor deposition source), so by appropriately selecting the vapor deposition angle, It is possible to make the light scattering state due to the thermo-optic effect similar to the light scattering state in the focal conic state due to voltage application to the display pattern portion.

Therefore, an extremely uniform and beautiful display can be obtained for the entire background area other than the portion displayed in a transparent state.

Examples of inorganic vapor deposition materials that can be used in the phase change type liquid crystal display device according to the present invention include oxides such as silicon oxide, silicon dioxide, calcium oxide, tungsten trioxide, titanium oxide, and magnesium oxide, magnesium fluoride, calcium fluoride, Fluorides such as barium fluoride and nitrides such as boron nitride have been experimentally confirmed.

An inert and non-conductive inorganic substance that can be deposited can be used as a deposition material for the alignment film of the phase change type liquid crystal display device of the present invention.

Furthermore, an accumulation phenomenon of light scattering states due to the thermo-optic effect was also confirmed in a phase change type liquid crystal display device constituted by two substrates subjected to an alignment treatment using an organic silane compound.

Regarding organic silane compounds, an accumulation phenomenon of light scattering states due to the thermo-optic effect was confirmed for compounds such as.

The orientation treatment using the above-mentioned organic silane compound is 0.01
The process was carried out by immersing it in an aqueous solution of ~5.0% by weight, followed by washing and drying, which is characterized by a relatively simple process.

The light scattering state due to the thermo-optic effect produced by this organic silane compound orientation treatment is a uniform light scattering state, similar to the above-described vapor deposition orientation treatment of an inorganic substance.

Furthermore, in the alignment treatment using an organic silane compound, by selecting the organic silane compound appropriately, either vertical alignment type or horizontal alignment type is possible.
This has the advantage that the increase in current value over time due to high voltage driving is small.

As described above, a phase change type liquid crystal display device that utilizes the phenomenon of accumulation of light scattering states due to the thermo-optic effect produced by alignment treatment of an organic silane compound has various advantages in addition to being able to obtain beautiful display.

The details will be described below using examples.

Example 1 A tin oxide film was formed by spraying on two Pyrex glass substrates whose surfaces had been polished, and electrodes were formed by etching.

These two substrates were ultrasonically cleaned with pure water and alcohol,
After steam cleaning with Guiflon and drying, it was assembled by thermocompression bonding of nylon, and a liquid crystal mixture of 94% biphenyl liquid crystal material E7 manufactured by Merck and 6% cholesteryl nonanoate was injected and sealed.

When this liquid crystal cell was heated to 70° C. and slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

By applying a 9V AC electric field to the electrode you want to display to make it transparent, and by applying a 3V AC electric field to the electrode you want to erase to create a focal conic light scattering state, a transparent state display with the light scattering state in the background can be created. Obtained.

By placing a gold-deposited reflector on the back, we were able to obtain an extremely beautiful display with a fully mirrored display against a pale yellow light-scattering background.

Example 2 After forming transparent electrodes on two glass substrates, -silicon oxide was deposited at an angle of 800 degrees to the surfaces of the substrates, and the glass substrates were sealed and assembled using spacers.

In this liquid crystal cell, biphenyl liquid crystal material E-
A mixed liquid crystal containing 792% and 8% P-2-methylbutyl-P'-cyanobiphenyl was injected and sealed.

When this liquid crystal cell was heated to 70° C. and slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

Applying a 12V, 50Hz AC electric field to the electrode you want to display makes it transparent, and applying a 4V AC electric field to the electrode you want to erase, creating a focal conic light scattering state, creates a uniform and even light scattering state in the background. A transparent display was obtained.

When a reflective plate made of vapor-deposited aluminum was placed on the back, an extremely beautiful display with a silver mirror surface against a silver-white light scattering background was obtained.

Example 3 After forming transparent electrodes by vapor-depositing indium oxide on two glass substrates, NH2(CH2)sSi(QC2H,)
It was immersed in a 300.1% solution, washed with pure water and alcohol, sealed with a spacer, and assembled.

In this liquid crystal cell, biphenyl liquid crystal material E-
794%, cholesteryl chloride 3%, and P-2-methylbutyl-P'-cyanobiphenyl 3% were injected and sealed.

When this liquid crystal cell was heated to 70° C. and slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

Apply a 9V AC electric field to the electrode you want to display to make it transparent, and apply a 3V AC electric field to the electrode you want to erase to create a focal conic light scattering state. A transparent display was obtained.

Although this liquid crystal cell is of the horizontal alignment type, it exhibited long-term memory properties even when the voltage was removed from the focal conic state.

By placing a dark blue colored ceramic plate on the back and shining a strong light source on the side of the liquid crystal cell, an easy-to-read dark blue display against a white light scattering background was obtained.

Example 4 The liquid crystal cell assembled in Example 3 was injected with a liquid crystal mixture of 85% liquid crystal mixed with MBBA and EBBA at a ratio of 3:2 and 15% cholesteryl oleate and sealed.

When this liquid crystal cell was heated to 80° C. and slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

Apply an electric field of 120 kHz at 5 KHz to the electrode you want to display to make it transparent, and apply an electric field of 3 kHz at 100 Hz to the electrode you want to erase.
When an electric field of 0 V was applied to create a focal conic light scattering state, a transparent state display with a uniform and even light scattering state background was obtained.

After applying an electric field and writing a display, even when the electric field was removed, memory and display were accumulated for a long time in both the light scattering state and the transparent state.

When a copper plate with a mirror surface was placed on the back, a beautiful display with a copper mirror surface against a background that scattered light in a pale copper color was obtained.

Example 5 After sputtering indium oxide onto two glass substrates to form transparent electrodes as shown in Figure 6, (CH30)3Si
(CH2)3 N+(CH3)2(CH2)I
7 It was immersed in a 0.1% aqueous solution of CH3.CI-(DMOAP), washed with pure water and alcohol, and sealed with a spacer and assembled.

In this liquid crystal cell, biphenyl liquid crystal material E-7 manufactured by Merck & Co., Ltd.
A mixed liquid crystal containing 90% cholesteryl oleate and 10% cholesteryl oleate was injected and sealed.

When this liquid crystal cell was heated to 70° C. and slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

This liquid crystal cell exhibited vertical alignment type behavior and was capable of line-sequential scanning.

By sequentially scanning lines with an appropriate voltage, the electrodes to be displayed are made transparent, and the electrodes to be erased are made to be in a focal conic light scattering state, as shown in Figure 7.
A transparent negative type display with a uniform light scattering background was obtained.

A phase change type liquid crystal display device using a normal vertical alignment type P-type nematic-cholesteric mixed liquid crystal that does not utilize the heating-light scattering and accumulation phenomenon of the present invention can also provide a negative type display with a dot matrix, but the voltage between the strip electrodes is The parts that are not covered remain transparent, making it impossible to obtain a background with uniform light scattering.Also, in order to obtain a negative type character of 5 x 7 dots as shown in Figure 7, one more electrode is needed around the area. , and 7×9 dots are required.

As described above, there are great advantages in applying the present invention to dot matrix display.

Example 6 Of two substrates on which electrodes were formed, magnesium fluoride was deposited on one at an angle of 80° to the substrate surface, and the silane compound CH3(CH2)451 (OCH3)300 was deposited on the other.
．． It was immersed in a 2% aqueous solution and washed with pure water and alcohol.

Seal these two boards with a spacer and assemble them.
A mixed liquid crystal containing 93% Schiff liquid crystal material RO-200 manufactured by Rossier and 7% cholesteryl oleate was injected and sealed.

When this liquid crystal cell was heated to 80° C. and then slowly cooled in air, the entire surface of the liquid crystal cell exhibited a uniform light scattering state.

Apply an AC electric field of IIV to the electrode you want to display to make it transparent, and apply an AC electric field of 3μ to the electrode you want to erase to create a focal conic light scattering state.A uniform and even light scattering state is created in the background. By arranging various types of reflective plates with colored mirrors on the back, very beautiful displays in a variety of colors were obtained.

As shown in the examples above, according to the present invention, TN-F
With a simple electrode structure similar to that of E-type liquid crystal display devices, beautiful negative-type display with uniform light scattering is now possible.

By appropriately selecting the reflector, various colors are possible, and when applied to displays on calculators and electronic wristwatches, extremely fashionable displays are possible.

As described above, the present invention dramatically improves the appearance of phase change type liquid crystal display devices, and has a great effect of promoting the spread of phase change type liquid crystal display devices.

[Brief explanation of the drawing]

Figures 1 to 3 show the light of phase change type liquid crystal display devices of N-type nematic-cholesteric mixed liquid crystal, horizontal alignment type of P-type nematic-cholesteric mixed liquid crystal, and vertical alignment type of P-type nematic-cholesteric mixed liquid crystal, respectively. FIG. 4 is a vertical cross-sectional view showing an embodiment of the phase change type liquid crystal display device of the present invention; FIG.
The figure is a plan view showing one embodiment of a phase change type liquid crystal display device of the present invention, FIG. 6 is a plan view showing an electrode pattern of Example 5,
FIG. 7 is a plan view showing an example of the fifth embodiment. 9...Transparent electrode.

Claims (1)

[Scope of Claims] 1. A pixel constituted by two substrates, at least one of which is transparent, arranged to face each other, and electrodes arranged on opposing surfaces of the two substrates; In a phase change type liquid crystal display device that includes a nematic-cholesteric mixed liquid crystal held between the pixels and performs display by applying a voltage to the pixel, the liquid crystal is made transparent by applying a predetermined voltage to the selected pixel. By applying a voltage lower than the predetermined voltage to non-selected pixels, the liquid crystal becomes a light-scattering focal conic phase, and the liquid crystal existing in the background area other than the pixel absorbs light due to the thermo-optic effect. A phase change type liquid crystal display device characterized by being in a scattering accumulation state. 2. A pixel composed of two substrates, at least one of which is transparent, arranged to face each other, and electrodes arranged on opposing surfaces of the two substrates, and a nematic film held between the two substrates. - In a phase change type liquid crystal display device that includes a cholesteric mixed liquid crystal and performs display by applying a voltage to the pixel, the liquid crystal is made transparent by applying a predetermined voltage to the selected pixel and then removing this voltage. By applying another predetermined voltage to non-selected pixels, the liquid crystal is made into a light-scattering focal conic phase, and the liquid crystal existing in the background area other than the pixels is made into a light-scattering focal conic phase due to the thermo-optic effect. A phase change type liquid crystal display device characterized by being in an accumulation state. 3. The phase change type liquid crystal display device according to claim 1 or 2, wherein at least one of the two substrates sandwiching the liquid crystal is subjected to alignment treatment. 4. The phase change type liquid crystal display device according to claim 3, wherein the alignment treatment is performed by vapor deposition of an inorganic substance. 5. The phase change type liquid crystal display device according to claim 3, which is subjected to alignment treatment using an organic silane compound.