JPH035719A - Manufacture of ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To obtain the panel which has excellent bistability for a long period by holding the liquid crystal panel in a temperature range wherein ferroelectric liquid crystal has an isotropic phase, and no thermal denaturation is caused after the ferroelectric liquid crystal is injected. CONSTITUTION:The ferroelectric liquid crystal 6 is injected while heating between two glass substrates 2 and 9. After the injection is completed, this panel is held within the temperature range wherein the ferroelectric liquid crystal 6 has the isotropic phase and no thermal denaturation is caused. Threshold value characteristics are therefore improved. The holding time is preferable >=3 hours. Consequently, ions in ferroelectric liquid crystal molecules nearby the surface of an orienting film are dispersed to reduce the uneven distribution of ions, asymmetry in threshold value is not generated even after the panel is left for a long period in one stable state of the ferroelectric liquid crystal molecules, and the panel having excellent stability for a long period is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a ferroelectric liquid crystal panel used in a liquid crystal display device.

2. Description of the Related Art Liquid crystal display devices are used in wristwatches, calculators, etc. due to their advantages of being thin, lightweight, and capable of being driven at low voltage. However, the response speed of currently used nematic liquid crystals is a few milliseconds.
J to several tens of milliseconds, making high-speed response impossible.
Fields of use are limited. On the other hand, ferroelectric liquid crystals can be applied to fields such as high-speed display devices, memory type displays, and liquid crystal shutters due to their response speed on the microsecond scale and memory effect.

As shown in FIG. 6, the ferroelectric liquid crystal molecules 12 have spontaneous polarization Ps in the direction perpendicular to the long sleeve direction of the molecules.
When a voltage E is applied, an electrical energy density f(Ps) shown by the equation (2) is generated.

f(Ps)=PsKcosφ (φ: azimuth angle)...
...■ That is, when a voltage E higher than the threshold voltage Et is applied to the ferroelectric liquid crystal molecules 12, the ferroelectric liquid crystal moves in a cone-shaped locus, as shown in Figure 6. It assumes a stable state and maintains this state even if the voltage is removed due to the memory properties of the ferroelectric liquid crystal. When a voltage -E in the opposite direction is applied, the ferroelectric liquid crystal molecules 12 rotate 180 degrees on the cone (-1) and take the other stable state B as shown in Figure 5C. The dielectric liquid crystal molecules 12 switch between two states, a stable state and a stable state B.

FIG. 6 shows the amount of transmitted light when a voltage waveform as shown in FIG. 6 & is applied to the liquid crystal panel. Vk indicates the write pulse, α is the brightness when the write pulse is applied, that is, the brightness during driving, and β is the brightness after applying a constant non-selection pulse for 1000 lines, that is, during memory time. It shows the brightness of FIG. 7 shows changes in threshold characteristics when the voltage of this voltage waveform is changed. FIG. 7a shows the characteristics for positive pulses, and FIG. 7 shows the characteristics for negative pulses. Here, the voltage at which the brightness in the positive pulse becomes 10% is V. , V is the voltage at which the brightness in the negative pulse is 9o%. It is closed.

Problems to be Solved by the Invention In the conventional method for manufacturing a ferroelectric liquid crystal panel, the temperature drops immediately after the liquid crystal is injected. However, in this method, ferroelectric liquid crystal molecules in the liquid crystal move due to the polarization electric field and form a space charge polarization field, or deformation of the liquid crystal layer near the alignment film interface causes one stable state (for example, the sixth If you leave it for a long time in a stable state (previously stable), the left stable state becomes more stable than the other stable state B, and it becomes difficult to move from stable state B to stable state B. ,■,.

and V. When the threshold value is different, the threshold characteristic becomes asymmetric. In other words, good bistability cannot be obtained. In other words, the threshold characteristics differ when a positive pulse is applied and when a negative pulse is applied.

(FIG. 8) In view of these conventional drawbacks, the present invention aims to provide a ferroelectric liquid crystal panel that exhibits good bistability over a long period of time.

Means for Solving the Problems In order to achieve the above objects, the present invention provides that after injecting ferroelectric liquid crystal into a liquid crystal panel, the ferroelectric γ night crystal exhibits an isotropic phase and does not undergo thermal denaturation. After holding the liquid crystal panel within a temperature range, the temperature is lowered.

According to the present invention, after the ferroelectric liquid crystal is injected, the liquid crystal panel is maintained in a temperature range in which the ferroelectric liquid crystal exhibits an isotropic phase and does not undergo thermal denaturation. It is thought that the ions in the dielectric liquid crystal molecules are dispersed and the uneven distribution of ions is alleviated, so that even after leaving the ferroelectric liquid crystal molecules in one stable state for a long time, the threshold values of the positive and negative pulses remain asymmetry. It is possible to obtain a panel that exhibits good bistability over a long period of time without causing any oxidation.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. The ferroelectric liquid crystal panel shown in FIG. 2 is manufactured using the manufacturing process shown in FIG. 1. First, a transparent electrode 3 made of a transparent conductive film (ITO film) is placed on two transparent glass substrates 2 and 9.
．． form 8.

After cleaning this glass substrate 2.9, an alignment film 4 is placed on it.
, 7, a polyimide resin is applied using a spinner, and then a rubbing treatment is performed using a wrapping cloth made of rayon. After that, the alignment film 4 of the other glass substrate 2 is
5102 with a diameter of 2 μm is sprinkled as a spacer on the surface provided with the alignment film 7, and sealing resin 6 is printed on the edge of the surface of the other glass substrate 9 where the alignment film 7 is provided. , and the sealing resin 6 is cured by heating. Thereafter, vacuum degassing is performed, and ferroelectric liquid crystal 6 is injected between the two glass substrates 2 and 9 while being heated. After the injection is completely completed, the panel is heated at temperatures of 1.2, 3, 4, and 5.1 degrees, respectively, at a temperature range in which the ferroelectric liquid crystal 6 exhibits an isotropic phase and does not undergo thermal denaturation.
After holding for 0 hours, the temperature is lowered. The injection port is sealed, and the polarizing plates 1 and 10 are attached to the glass substrate 2.9. Further, as a comparative example of this example, a liquid crystal panel was also manufactured by a method in which the temperature was immediately lowered after the ferroelectric liquid crystal 6 was injected.

A voltage was applied to the seven types of liquid crystal panels made in this way, one of them was kept in a stable state, and the panel was left at room temperature for 336 hours, after which the threshold characteristics were measured. The results are shown in FIG. In Fig. 3, the horizontal axis shows the holding time in the isotropic phase during panel fabrication, and the vertical axis shows the voltage v1o at which the # degree in the positive pulse becomes 10% when the threshold value 6111 is constant.
and the voltage V at which the brightness in the negative pulse is 90%. The difference between V and -V.

It shows. As is clear from Fig. 3, when the holding time in the isotropic phase is set to 0.1.2 hours, the difference in threshold characteristics between the positive pulse and the negative pulse is large and the pulse is asymmetric, whereas the isotropic It can be seen that when the retention time in the phase was 3 hours or more, the threshold characteristics were symmetrical, indicating good bistability.

Next, we changed the type of liquid crystal and conducted a similar experiment, and the results were summarized in the fourth section.
As shown in the figure. From FIG. 4, the retention time in the isotropic phase is 0.1.
When the holding time was set to 2 and 3.4 hours, the threshold characteristics became asymmetric, but when the holding time was set to 6 hours or more, the threshold characteristics of the positive and negative pulses were symmetrical, resulting in good bistability. You can see what it shows. That is, although the holding time in the isotropic phase differs depending on the type of liquid crystal, the threshold characteristics can be improved by holding the liquid crystal in the isotropic phase without lowering the temperature immediately after injecting the liquid crystal. Note that the holding time is preferably 3 hours or more.

In the embodiments described above, at least one of the glass substrates 2.9 needs to be transparent, and polyimide is used as the alignment films 4, 7, but other materials may be used. Furthermore, the material of the rubbing cloth is not limited to rayon, but may also be nylon, polyester, etc.

Further, the method of forming the alignment films 4 and 7 is not limited to spin cord, but may also be printing, or other alignment methods such as oblique vapor deposition. Furthermore, the liquid crystal injection method is not limited to vacuum injection, and may also be an injection method using capillary action (Method 1) in which liquid crystal is dropped onto a substrate and then bonded.

Effects of the Invention As described above, according to the present invention, after injecting the ferroelectric liquid crystal, the liquid crystal panel is maintained in a temperature range in which the ferroelectric liquid crystal exhibits an isotropic phase and is not subject to thermal denaturation. The ions in the ferroelectric liquid crystal molecules near the surface of the alignment film are dispersed, and the uneven distribution of ions is relaxed.

Even after one of the ferroelectric liquid crystal molecules is left in a stable state for a long period of time, the threshold value does not become asymmetrical, and a panel that exhibits good bistable aluminum over a long period of time can be obtained.

[Brief explanation of drawings]

Figure 1 is a process diagram showing a method for manufacturing a liquid crystal panel according to an embodiment of the present invention, Figure 2 is a sectional view showing the structure of the same panel, and Figures 3 and 4 are retention times in isotropic phase, respectively. Figure 6 is a schematic diagram showing the operating state of the ferroelectric liquid crystal molecules, Figure 6 is the voltage waveform applied to the liquid crystal panel, and the voltage waveforms applied to the liquid crystal panel during driving and memory. A characteristic diagram showing the relationship between brightness. Figure 7 is a characteristic diagram showing the threshold characteristics of the liquid crystal panel when driving for positive pulses and driving for negative pulses are symmetrical. Figure 8 is a characteristic diagram showing the driving for positive pulses and driving for negative pulses. FIG. 3 is a characteristic diagram showing threshold characteristics of a liquid crystal panel when driving is asymmetrical. 1.1o...Polarizing plate, 2,9...Glass substrate, 3.8...Electrode, 4,7...Alignment film, 6... ... Seal resin, 6 ... Ferroelectric liquid crystal, 11 ... Spacer, 12 ...
・Ferroelectric liquid crystal molecules.

Claims (2)

[Claims] (1) After injecting a ferroelectric liquid crystal into a liquid crystal panel, the liquid crystal panel is held in a temperature range in which the ferroelectric liquid crystal exhibits an isotropic phase and does not undergo thermal denaturation, and then the temperature is lowered. A method for manufacturing a dielectric liquid crystal panel. (2) The method for manufacturing a ferroelectric liquid crystal panel according to claim 1, wherein the holding time in the temperature range is 3 hours or more.