JP2600647B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] It is effective when driving a ferroelectric liquid crystal display device at a high time division ratio and performing gradation display.

[Summary of the Invention]

The present invention is characterized in that the threshold value of the entire device is set to a low voltage and a uniform value by providing dense and uniform projections on the surface of the alignment film of the ferroelectric liquid crystal display device.

[Conventional technology]

FIG. 1 shows a ferroelectric liquid crystal display device. A transparent electrode 2 is provided on two glass substrates 1, and a polymer film such as polyimide is rubbed thereon with a cloth or the like to form a thin film 3 for alignment control in which liquid crystal molecules are arranged in one direction. ing. The two glass substrates are kept at an arbitrary interval by a spacer 4, and a ferroelectric liquid crystal 5 is sealed therebetween, and is surrounded by a seal portion 6. A polarizing film is attached to each of the two glass substrates.

FIG. 2 shows the operation of the ferroelectric liquid crystal display device. The direction 1 of the spontaneous polarization possessed by the liquid crystal molecules is determined by the direction 2 of the electric field applied to the liquid crystal layer through the electrodes, and maintains the arrangement structure of the state (I) or (II) depending on the polarity of the electric field. The polarization axes of the upper and lower polarizers are set to be orthogonal to each other and parallel or perpendicular to the direction of the molecules in the state (I). For this reason, the state (I) is dark, but the state (I)
In (I), light transmission is observed due to the birefringence of the liquid crystal, and the liquid crystal becomes bright. When the driving waveform shown in FIG. 3A is applied to the liquid crystal layer, the state is switched to the state (I) with the first and third pulses and to the state (II) with the second pulse, so that the light shown in FIG. Is obtained. As the peak value of the pulse No. 4 increases, the state (I) is maintained at a certain voltage. FIG. 5 shows a change in the amount of light transmission with respect to the peak value of the pulse 4 shown in FIG. 3, and is shown as a representative example of the threshold characteristic. Assuming that the voltage indicating a 10% change is Vth and the voltage indicating a 90% change is Vsat, Vth and Vsat are as shown in FIG.
It varies greatly depending on the pulse width. In the case of driving at a high time division ratio, it is necessary to shorten the pulse width, so that a high driving voltage is required. In the case of performing gradation display, a method using a light quantity change by changing a pulse peak value as shown in FIG. 5 and a change in Vth and Vsat by changing a pulse width as shown in FIG. The method to use is considered.

[Problems and objects to be solved by the invention]

Conventionally, polyimide, polyamideimide, and the like are used as the material used for the alignment film. However, the electrical characteristics of the polymer are affected by the remaining polar groups such as a carboxyl group and an amine group. For this reason, the threshold characteristics and the response characteristics of the ferroelectric liquid crystal display element become non-uniform, and the threshold characteristics in particular cause display unevenness and deviation of gradation display, which is a serious problem. Particularly when driving at a high time division ratio, a high voltage is applied as described above, so that this effect is large.

In addition, the threshold characteristics of a ferroelectric liquid crystal display element are also affected by the alignment state of the molecules themselves, and a region in which the alignment is disordered due to surface scratches or small foreign matter is compared with other uniform alignment regions. Since a low threshold value is shown, similar display unevenness is caused.

An object of the present invention is to solve the problems of such alignment and to obtain a ferroelectric liquid crystal display element having uniform threshold characteristics and no display unevenness.

[Means for solving the problem]

The liquid crystal display device of the present invention is a liquid crystal display device in which a liquid crystal having a memory property is sandwiched between a pair of substrates having a plurality of electrodes on opposing substrate inner surfaces, and an alignment layer is formed on the substrate. The number of inversion domain nuclei of the liquid crystal is
0.05-0.2 so as to be formed at a rate of 400-500 pieces / mm ²
Fine particles having a particle size of μm are arranged on the alignment film.

[Example] Hereinafter, an example of the present invention will be described.

Example 0.2 to 0.0 in the polyimide used as the liquid crystal alignment film
After mixing polystyrene particles with a particle size of 5 μm, apply a film on the glass substrate to a thickness of 0.07 to 0.02 μm,
The one fired at 150 ° C. for 30 minutes was used as one electrode substrate, and the other electrode substrate was prepared using only polyimide containing no fine particles under the same conditions and rubbing one side with a cloth. To keep the two glass substrates parallel, a glass fiber having a diameter of about 2 μm was assembled as a spacer, and a ferroelectric liquid crystal having an Smc ^* phase was sealed. The threshold characteristics of this device were evaluated using the waveform of FIG. 3 (a). As a result, a difference as shown in the following table was observed as compared with the device having only the polyimide film. Also, a difference was observed in the number of nuclei of the inversion domain, which is a factor of the uniformity of the threshold characteristics.

As is clear from the above, it was effective to provide the protrusions on the surface, while improving the non-uniformity of the threshold characteristics due to the variation at the time of forming the alignment film.

〔The invention's effect〕

With the liquid crystal display device of the present invention having the above-described configuration, the following effects can be obtained.

That is, by arranging fine particles having a particle size of 0.05 to 0.2 μm on the alignment film so that the number of the inversion domain nuclei of the liquid crystal is formed at a rate of 400 to 500 / mm ² , the liquid crystal display element is formed. The threshold and saturation characteristics can be lowered and stabilized.

[Brief description of the drawings]

FIG. 1 is a side sectional view schematically showing a display device using a liquid crystal, and FIGS. 2 (I) and (II) show the characteristics of liquid crystal molecules when a voltage is applied to the ferroelectric liquid crystal display to drive it. FIG. 3 is a principle diagram for explaining the movement, and FIG. 3 is a response characteristic diagram of a drive waveform (a) for evaluating a threshold characteristic of a ferroelectric liquid crystal display device and a change in light transmittance (b) corresponding to the drive waveform. FIG. 4 is a characteristic diagram showing a change in the threshold value with the pulse width. The horizontal axis represents the pulse width in FIG. 3A, and the vertical axis represents the values of Vth and Vsat. FIG. 5 is a diagram showing one embodiment of the threshold characteristic of the liquid crystal display device of the present invention, in which the horizontal axis corresponds to the peak value of the pulse 4 in FIG. 3 (a), and the vertical axis represents the light transmission. Indicates the rate.

Claims (1)

(57) [Claims] 1. A liquid crystal having a memory property is sandwiched between a pair of substrates having a plurality of electrodes on inner surfaces of opposed substrates,
In a liquid crystal display device having an alignment layer formed on the substrate, a particle size of 0.05 to 0.2 μm is selected so that the number of inversion domain nuclei of the liquid crystal is formed at a rate of 400 to 500 / mm ^2. A liquid crystal display device, wherein fine particles having the same are arranged on the alignment film.