JP2966234B2 - Manufacturing method of ferroelectric liquid crystal display element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for manufacturing a ferroelectric liquid crystal display device, and more particularly, to a method for injecting a ferroelectric liquid crystal between substrates.

[0002]

2. Description of the Related Art Clark and Lagerwall have proposed a liquid crystal device that controls transmitted light by combining it with a polarizer using the refractive index anisotropy of a ferroelectric liquid crystal. (JP-A-56-107216, U.S. Pat.
67924, etc.). This ferroelectric liquid crystal has bistability and generally has a chiral smectic C phase (SmC ^* ) or a chiral smectic H phase (SmH ^* ) having a non-helical structure in a specific temperature range. When an electric field is applied to the ferroelectric liquid crystal, the ferroelectric liquid crystal takes one of a first optically stable state and a second optically stable state in response to the electric field. It has a property of maintaining a state, that is, has bistability, and has a quick response to a change in an electric field, and is expected to be widely used as a high-speed and storage-type liquid crystal.

[0003]

The liquid crystal in such a liquid crystal display element is injected after assembling the liquid crystal cell. However, when this injection is performed in a high-temperature ISO phase, the liquid crystal has a low viscosity. There is a problem that a portion (pixel) that has not been completely filled remains without being completely injected. Further, at this temperature, since the liquid crystal molecules are oriented in random directions, there is a problem that poor alignment is caused and display quality of the entire liquid crystal element is impaired. On the other hand, if the liquid crystal is injected at a slightly lower temperature in the SmA phase, there is a problem that the injection time becomes longer due to the high viscosity, thereby lowering the productivity or not being injected at all.

Accordingly, the present invention realizes uniform injection of liquid crystal and improves display quality by eliminating alignment unevenness.
It is another object of the present invention to provide a method of manufacturing a ferroelectric liquid crystal display device, which improves the productivity by shortening the injection time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a method of manufacturing a ferroelectric liquid crystal display device in which a ferroelectric liquid crystal is injected between a pair of opposed substrates. The method, wherein the ferroelectric liquid crystal is Is
The phase transition to the o phase, SmA phase, and SmC ^* phase, and the injection of the ferroelectric liquid crystal is performed in a temperature range in which the Iso phase and the SmA phase are mixed. In this case, the transition from the SmA phase to the Iso phase occurs When the temperature is T ₀ and the temperature at the time of injecting the ferroelectric liquid crystal is T, T ₀ −2.5 ° C. ≦ T ≦ T ₀ +
It is preferable to satisfy the relationship of 2.5 ° C.

The time required for injecting the ferroelectric liquid crystal into the entire area between the substrates is represented by D, and the time during which the ferroelectric liquid crystal is in a temperature range in which the Iso phase and the SmA phase coexist is defined as D. When t is set, the relationship t ≧ 0.5 * D may be satisfied.

Further, an orientation control film may be formed on the substrate, the orientation control film may be subjected to a uniaxial orientation treatment, and the pretilt angle may be 5 degrees or more.

[0008]

When the ferroelectric liquid crystal is injected in a temperature range where the Iso phase and the SmA phase coexist, the viscosity of the liquid crystal is reduced and uniform injection can be performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

First, the structure of a liquid crystal display device will be described with reference to FIG.
(a) It will be described along (b).

The liquid crystal display device has a pair of substrates 11a and 11b which are arranged in parallel as shown in FIG. 1 (b), and has a thickness of about 40 on these substrates 11a and 11b.
Transparent electrodes 12a and 12b of 0 to 2000 degrees are formed respectively. Further, these transparent electrodes 12a, 12b
On top of this, SiO ₂ having a thickness of 100 to 2000 ° is formed as an insulating film (not shown).
A polymer organic film (for example, polyimide, polyamide, or PVA resin) having a thickness of 10 to 1000 degrees
e, 13b. This alignment control film 13
e and 13b are subjected to a uniaxial orientation treatment, and the pretilt angle is set to 5 degrees or more. Also, as described above, the transparent electrode 1
A large number of spacer particles 14,... And an epoxy-based particulate adhesive 15,... Are interposed between the substrates 11a, 11b formed with 2a, 12b and the like. Among them, the spacer particles 14,... Have an average particle size of 1.5 μm (generally 0.1 μm).
(3.5 [mu] m) is used, and the gap between the substrates 11a and 11b is defined to be constant. Further, as the epoxy-based particulate adhesive 15, for example, “Toray Pearl” (trade name) manufactured by Toray Industries, Inc. is used with an average particle size of 5 μm. 11a and 11b are adhesively held.
On the other hand, the ends of the transparent electrodes 12a and 12b are
(For example, epoxy-based adhesive),
The gap between the substrates is sealed.

The ferroelectric liquid crystal 17 is injected into the liquid crystal cell assembled as described above. As the ferroelectric liquid crystal 17 in this embodiment, a mixed liquid crystal mainly composed of DOBAMBC having the following phase transition temperature is used.

[0013]

[Outside 1] Then, in this example, the temperature T _{0 at} which the SmA phase transitions to the Iso phase was confirmed by observation with an optical microscope (T ₀ = 117 ° C. in the above-mentioned liquid crystal), and T ₀ −2.5 ° C. ≦ T ≦ T _0. + 2.5 ° C. (T) T was injected in the temperature range of liquid crystal at the time of injection (for example, 115 to 119).
° C). In this temperature range, the Iso phase and the SmA phase are mixed. In addition, the temperature control during liquid crystal injection was realized by performing the injection step in a thermostatic bath large enough to accommodate the entire liquid crystal cell. 2 (a), 2 (b) and 2 (c) show the outline of the liquid crystal injection temperature profile used in this embodiment. Here, the time D indicates the time from when the ferroelectric liquid crystal starts to enter the injection port to when the liquid crystal reaches the entire liquid crystal cell end opposite to the injection port (hereinafter, referred to as “injection time D”). . In this embodiment, the time t during which the liquid crystal is maintained in the above-mentioned temperature range (T ₀ −2.5 ° C. ≦ T ≦ T ₀ + 2.5 ° C.) at the time of injection is represented by t ≧ 0.5 * D. Temperature control.

As a result, when the liquid crystal was injected in the above temperature range, the liquid crystal was injected into all the pixels, and no unfilled pixels were generated. In addition, alignment defects generated in the liquid crystal cell were reduced. As a result, the contrast was improved, the driving voltage range was widened, and the display quality was improved as compared with the liquid crystal cell in which only the Iso phase was injected. Also, Sm
The injection time can be reduced as compared with the case where the injection is performed in the A phase, and the productivity of the liquid crystal display element can be improved.

The inventor of the present invention, in order to confirm the effect of the present embodiment, has been carried out with the Iso phase (120 to 125 ° C.) and the SmA phase (1
(08-113 ° C.). And
When the injection was performed in the Iso phase state, it was confirmed that the liquid crystal was not completely filled and unfilled pixels remained. Pixels due to such injection are different from driving characteristics of surrounding pixels,
For this reason, it was also confirmed that the driving voltage width of the liquid crystal cell was reduced, and that the uniformity of the alignment state in the pixel was disturbed and the contrast was lowered. On the other hand, when injection was performed in the state of the SmA phase, almost no injection was performed because the viscosity of the liquid crystal was high.

Next, another embodiment of the present invention will be described.

As the ferroelectric liquid crystal in this embodiment, a ferroelectric liquid crystal TFK-8616 manufactured by Teikoku Chemical Industry Co., Ltd. having the following phase transition temperature was used.

[0018]

[Outside 2] Then, in this example, after confirming the temperature range where the Iso phase and the SmA phase are mixed by optical microscope observation,
Injection was performed in the temperature range (61 to 67 ° C). The temperature control during the injection was performed in the same manner as in the above-described embodiment.

As a result, the liquid crystal was injected into all the pixels, and no unfilled pixels were generated. In addition, alignment defects generated in the liquid crystal cell were reduced, and a liquid crystal display element having a uniform in-plane was realized. Further, the injection time can be reduced as compared with the case where the injection is performed in the SmA phase, and the productivity of the liquid crystal display element can be improved.

By using a material different from the phase transition temperature of the liquid crystal in the previous embodiment, the above-described effect is not caused by the effect unique to the phase transition temperature of the liquid crystal, but is injected in a region where the Iso phase and the SmA phase are mixed. It was confirmed that the effect was obtained.

In order to confirm the effect of the present embodiment, the present inventor has determined that the Iso phase (70 to 75 ° C.) and the SmA phase (55 to 55 ° C.)
(60 ° C.). Then, it was confirmed that when the injection was performed in the Iso phase state, the liquid crystal was not completely filled, and unfilled pixels remained. And the pixel by such injection differs from the driving characteristic of the surrounding pixels,
For this reason, it was also confirmed that the driving voltage width of the liquid crystal cell was reduced, and that the uniformity of the alignment state in the pixel was disturbed and the contrast was lowered. On the other hand, when injection was performed in the state of the SmA phase, almost no injection was performed because the viscosity of the liquid crystal was high.

[0022]

As described above, according to the present invention, S
The viscosity can be made lower than in the case where only the mA phase is present, and the time for the injection step can be shortened. Further, in a temperature range where the Iso phase and the SmA phase coexist, the ferroelectric liquid crystal molecules receive a force to form a phase between the upper and lower substrates, thereby suppressing pixels in which liquid crystal has not been completely filled, thereby preventing the occurrence of poor alignment. Can be eliminated.

[Brief description of the drawings]

FIG. 1A is a plan view showing the entire structure of a liquid crystal display element,
(b) is the BB sectional view.

FIGS. 2A, 2B and 2C are diagrams showing temperature profiles at the time of liquid crystal injection, respectively, according to the present invention.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Transparent electrode 13a, 13b Alignment control film 17 Ferroelectric liquid crystal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1341 G02F 1/13 101

Claims (4)

(57) [Claims] 1. A method of manufacturing a ferroelectric liquid crystal display device, comprising injecting a ferroelectric liquid crystal between a pair of substrates opposed to each other, wherein the ferroelectric liquid crystal includes an Iso phase, a SmA phase,
A method for producing a ferroelectric liquid crystal display element, wherein a phase transition to an SmC ^* phase and the injection of the ferroelectric liquid crystal are performed in a temperature range where an Iso phase and an SmA phase are mixed. 2. When the temperature at which the SmA phase transitions to the Iso phase is T ₀ and the temperature at the time of injecting the ferroelectric liquid crystal is T, T ₀ −2.5 ° C. ≦ T ≦ T ₀ +2 2. The method for manufacturing a ferroelectric liquid crystal display device according to claim 1, wherein the following relationship is satisfied. 3. A time required for injecting the ferroelectric liquid crystal into the entire space between the substrates is represented by D, and a time in which the ferroelectric liquid crystal is in a temperature range in which the Iso phase and the SmA phase are mixed at the time of the injection. 2. The method for manufacturing a ferroelectric liquid crystal display device according to claim 1, wherein, when t is satisfied, a relationship of t ≧ 0.5 * D is satisfied. 4. The method according to claim 1, wherein an orientation control film is formed on the substrate, the orientation control film is subjected to a uniaxial orientation treatment, and a pretilt angle is 5 degrees or more. A method for manufacturing a ferroelectric liquid crystal display device.