JPH0518403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a liquid crystal device, and more particularly to a method for injecting ferroelectric liquid crystal into a liquid crystal cell.

[Prior Art] Conventionally, the method of injecting liquid crystal is to draw the inside of the liquid crystal cell to a low pressure, adhere the liquid crystal to the injection port of the liquid crystal cell, and return the outside of the liquid crystal cell to atmospheric pressure, thereby injecting the liquid crystal cell with the pressure difference. A common method was to inject liquid crystal inside.

However, in this method, the exhaust system inside the liquid crystal cell and the liquid crystal injection system that returns the pressure to atmospheric pressure and injects the liquid crystal are the same, and both processes are performed in the same device, so if the gap of the liquid crystal cell is thin or However, in the case of liquid crystal cells with a large area, it takes a very long time to inject the liquid crystal, making it unsuitable for mass production, and it is difficult to inject liquid crystal by pressurizing the liquid crystal. It was hot.

[Problems to be Solved by the Invention] The present invention improves the conventional liquid crystal injection method, and performs the evacuation of the inside of the liquid crystal cell and the injection of liquid crystal in separate systems. It is an object of the present invention to provide a liquid crystal element that can shorten injection time, can be mass-produced, and has good quality.

[Means for Solving the Problems] That is, the present invention provides: (a) by accommodating a cell provided with an injection port in a first container and reducing the pressure inside the first container, a first step of bringing the inside of the cell into a low pressure state; (b) heating the cell in the first container to a sufficiently low viscosity so as to shut off the inside and outside of the cell; a second step of sealing the injection port with a chiral smectic liquid crystal material that has produced a state; (c) the injection port of the second step is sealed with a chiral smectic liquid crystal material; a third step of taking out the cell from the first container while maintaining the same state;
and (d) accommodating the cell in the third step in a second container, making the pressure outside the cell higher than the pressure inside the cell in the second container, and opening the injection port. a fourth step of injecting the chiral smectic liquid crystal material into the cell by heating the encapsulating chiral smectic liquid crystal material to a phase state of sufficiently low viscosity to be injected into the cell; This is a method for manufacturing a liquid crystal element characterized by the following.

The present invention will be explained in detail below.

FIGS. 1A and 1B are explanatory diagrams showing an example of an apparatus used in the method of manufacturing a liquid crystal element of the present invention.

In FIG. 1A, the liquid crystal cell 1 is placed in a vacuum container 2.
After the internal pressure of the liquid crystal cell is reduced to 0.3 Torr or less by suction with the rotary pump 3 and the internal pressure is reduced to 0.3 Torr or less, the liquid crystal in the liquid crystal tank 7 heated by the heater 6 from the power source 5 is transferred to the liquid crystal injection port. The liquid crystal itself is applied to the liquid crystal cell to cut off the inside and outside of the liquid crystal cell. Next, the liquid crystal cell 1 with the liquid crystal attached to the injection port is taken out from the vacuum container 2 and placed in the pressurized container 8 shown in FIG. 1B. The inside of the pressurized container 8 is pressurized with N ₂ gas to maintain a high pressure system, and while replenishing liquid crystal from the liquid crystal reservoir 10 to the liquid crystal cell 1 placed on the liquid crystal cell holding stand 9, the liquid crystal is heated by the heater 6 and the liquid crystal is heated. Lower the viscosity and inject.

When injecting liquid crystal, the outside of the liquid crystal cell 1 is pressurized,
Since the interior is kept in a low-pressure vacuum state, entry into the liquid crystal cell is facilitated.

In the figure, reference numeral 11 indicates a fan for temperature variation, reference numeral 12 indicates a pressurizing lock for the container lid, and reference numeral 13 indicates a nitrogen gas cylinder.

A means for heating at least one of the liquid crystal and the liquid crystal cell can be installed in the high-pressure system, but in this case, the higher the heating temperature within a range that does not deteriorate the liquid crystal, the lower the viscosity is, so it is desirable.

In addition, in a high-pressure system, it _is necessary to pressurize the liquid crystal and liquid crystal cell at a pressure above atmospheric pressure, or below atmospheric pressure and above the cell internal pressure. It is desirable that the temperature be as high as possible without having any adverse effects on the environment.

It is desirable to install means for heating the sealing liquid crystal in the vacuum system of the vacuum container to reduce the viscosity of the liquid crystal.

A particularly suitable smectic liquid crystal as the liquid crystal material used in the present invention is a chiral smectic liquid crystal, which has ferroelectricity. Specifically, chiral smectic C phase (SmC*), chiral smectic G phase (SmG
*), chiral smectic F phase (SmF*), chiral smectic I phase (SmI*), or chiral smectic H phase (SmH*) liquid crystals can be used. A nematic phase or a chiral nematic phase can also be used.

For more information on ferroelectric liquid crystals, see for example “Le Géneurard de Feuisique L’Etre”.
(“LE JOURNAL DE PHYSIQUE
LETTRE”) 36 (L-69) 1975 “Feroelectric Liquid Crystal”
(Ferroelectric Liquid Crystals; “Applied
“Applied Physics Letters”
Letters”) 36 (11) 1980 “Submicro Second Bistable Electro-Optical
"Switching in Liquid Crystals"
(“Submicro Second Bistable Electrooptic
“Switching in Liquid Cystals”); “Solid State Physics” 16
(141) 1981 "Liquid Crystal" and the like, and among those disclosed in these publications, ferroelectric liquid crystals having negative dielectric anisotropy can be used in the present invention.

Particularly preferred ferroelectric liquid crystals include those exhibiting a cholesteric phase (chiral nematic phase) at high temperatures; for example, phenyl ester liquid crystals exhibiting a phase transition temperature listed in the Examples below. Liquid crystal can be used.

When constructing an element using these materials, the element can be supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the temperature at which the liquid crystal compound forms a desired phase.

Figure 3 is for explaining the operation of ferroelectric liquid crystal.
This is a schematic drawing of an example of a cell. Hereinafter, explanation will be given using SmC* as an example of the desired phase.

31a and 31b are In ₂ O ₃ or ITO
A substrate (glass plate) coated with a transparent electrode made of a thin film of (Indium Tin Oxide), etc., between which SmC* phase liquid crystal with a liquid crystal molecular layer 32 oriented perpendicular to the glass surface is sealed. There is. A thick line 33 represents a liquid crystal molecule, and the liquid crystal molecule 33 continuously forms a helical structure in the plane direction of the substrate. Central axis 3 of this helical structure
5 and the axial direction of the liquid crystal molecules 33 is expressed as Θ. This liquid crystal molecule 33 has a dipole moment (P ⊥) 34 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 31a and 31b, the helical structure of the liquid crystal molecules 33 is unraveled, and the dipole moment (P ⊥) 34
The alignment direction of the liquid crystal molecules 33 can be changed so that all of the liquid crystal molecules are oriented in the direction of the electric field.

The liquid crystal molecules 33 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and short axis direction. Therefore, for example, if crossed Nicol polarizers are placed above and below the glass surface, voltage can be applied. It is easily understood that the liquid crystal optical element is a liquid crystal optical element whose optical properties change depending on the polarity.

The liquid crystal cell preferably used in the liquid crystal optical element of the present invention can be, for example, 10 μm or less.
As the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure even when no electric field is applied, as shown in Figure 2, and its dipole moment Pa or Pb increases upward by 2.
4a or downward 24b.
A tilt angle is defined as 1/2 of the angle formed by the molecular axis of the liquid crystal molecular axis 23a and 23b.This tilt angle is equal to 1/2 of the apex angle formed by the cone when it has a helical structure. Voltage applying means 2 applies an electric field Ea or Eb of different polarity above a certain threshold to such a cell.
1a and 21b, the dipole moment changes direction upwards 24a or downwards 24b corresponding to the electric field vector of the electric field Ea or Eb, and the liquid crystal molecules accordingly move either into one stable orientation 23a or into the other stable orientation. It is oriented in one of the orientations 23b.

As mentioned earlier, there are two advantages to using such ferroelectricity as a liquid crystal optical element. The first is that the response speed is extremely fast, and the second is that the response speed is extremely fast.
is that the orientation of liquid crystal molecules has bistability. To further explain the second point, for example, with reference to FIG. 2, when an electric field Ea is applied, the liquid crystal molecules are aligned in a stable orientation 23a of 1, and this state remains stable even when the electric field is turned off. Furthermore, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are aligned to another stable orientation 23b and the orientation of the molecules is changed, but they remain in this state even after the electric field is turned off.

In order to effectively realize such fast response speed and bistability, it is preferable that the cell thickness be as thin as possible.

The biggest problem in forming devices using liquid crystals with such ferroelectric properties is, as mentioned earlier, that the layer having the SmC phase is aligned perpendicularly to the substrate surface and the liquid crystal It is difficult to form a highly monodomain cell in which molecules are oriented substantially parallel to the substrate surface.

Incidentally, in manufacturing large-area liquid crystal cells, a method has been known in which a uniaxial alignment treatment is applied to the surface of a substrate. Examples of the uniaxial alignment treatment method include rubbing the substrate surface in one direction with velvet, cloth, or paper, or obliquely depositing SiO or SiO ₂ on the substrate surface.

[Operation] When liquid crystal is injected into a liquid crystal cell using the injection method of the present invention, it can be assumed that the liquid crystal is at a constant speed in a certain short period of time. In this case, there is a pressure gradient inside the cell, and the pressure gradient decreases linearly as you go deeper from the injection port, and the speed at which the liquid crystal enters is thought to be proportional to the pressure gradient. Therefore, it is presumed that the more the external pressure is increased by pressurizing the outside of the liquid crystal cell, the more rapidly the liquid crystal cell will be injected.

[Examples] Hereinafter, the present invention will be explained in more detail by showing examples.

Example 1 Using the apparatus shown in FIG. 1A and FIG. 1B, a liquid crystal material was applied to a liquid crystal cell with a cell thickness of 1 μm and a cell internal space of 200 mm x 300 mm by the following method.
A liquid crystal element was obtained by injecting DOBAMBC (decyloxybenzylidene-P'-amino-2-methylbutyl cinnamate).

First, the liquid crystal cell is placed in a vacuum container and the temperature is 0.2Torr.
After reducing the pressure to 75°C, the injection of the liquid crystal cell was sealed with smectic phase liquid crystal DOBAMBC heated to 75°C.

Next, the pressure is returned to atmospheric pressure and the liquid crystal cell is taken out.
It was placed in a pressurized container, pressurized with 1 atm of N ₂ gas, heated to 120° C., and liquid crystal was injected in I _SO (isotropic phase). As a result, injection into the liquid crystal cell was completed in about 16 hours.

Further, in the present invention, the phase state during injection of the liquid material is preferably a smectic A phase, a cholesteric phase, a nematic phase, a chiral smectic C phase, or an isotropic phase. In particular, a low viscosity isotropic liquid, a nematic phase, or a cholesteric phase is suitable as the liquid in the liquid crystal reservoir 10 of FIG. 1B.

[Effects of the Invention] When injecting liquid crystal into a liquid crystal cell, the present invention lowers the pressure inside the liquid crystal cell in a vacuum system, and then injects the liquid crystal under pressure in a high pressure system. The liquid crystal injection speed is accelerated, the injection time can be greatly shortened, and large-scale processing is possible.

[Brief explanation of the drawing]

FIGS. 1A and 1B are explanatory diagrams showing an example of an apparatus used in the method for manufacturing a liquid crystal device of the present invention, and FIG. 2 is a schematic diagram of a liquid crystal device using a ferroelectric liquid crystal with a non-helical structure. FIG. 3 is a schematic diagram of a liquid crystal element using a ferroelectric liquid crystal with a spiral structure. 1...Liquid crystal cell, 2...Vacuum container, 3...Rotary pump, 4...Liquid crystal injection port, 5...Power source,
6... Heater, 7... Liquid crystal tank, 8... Pressurized container, 9... Liquid crystal cell holding stand, 10... Liquid crystal reservoir,
11...Temperature variation fan, 12...Container lid pressure lock, 13...Nitrogen gas cylinder, 21a,
21b... Voltage application means, Ea, Eb... Electric field, 2
3a, 23b...Liquid crystal molecular axis, 24a, Pa...
Upward dipole moment, 24b, Pb... Downward dipole moment, 31a, 31b... Substrate,
32...Liquid crystal molecule layer, 33...Liquid crystal molecule, 34,
PL...Dipole moment, 35...Central axis,
...Tilt angle.

Claims (1)

[Claims] 1 (a) A cell provided with an injection port is housed in a first container, and the inside of the first container is depressurized to bring the inside of the cell into a low pressure state. (b) heating the chiral smectic liquid crystal in the first container to a sufficiently low viscosity so as to cut off the inside and outside of the cell, resulting in a phase state under the heating; a second step of sealing the injection port with a substance; (c) maintaining the injection port of the second step sealed with a chiral smectic liquid crystal material to close the cell; a third container for removing the liquid from the first container;
and (d) accommodating the cell in the third step in a second container, making the pressure outside the cell higher than the pressure inside the cell in the second container, and opening the injection port. a fourth step of injecting the chiral smectic liquid crystal material into the cell by heating the encapsulating chiral smectic liquid crystal material to a phase state of sufficiently low viscosity to be injected into the cell; A method for manufacturing a liquid crystal element, characterized by the following.