Takao Umeda

Influences of Alignment Materials and LC Layer Thickness on AC Field-Stabilization Phenomena of Ferroelectric Liquid Crystals

The influences of alignment materials and LC layer thickness on an AC-field stabilization phenomena have been studied. Ferroelectric LC material with a dielectric anisotropy of -2.7 and two kinds of polyimide resins (A,B) for alignment materials were prepared. Polyimide resin A has a rigid structure and its molecular chain is rod-like, while polyimide resin B has a somewhat zigzag structure and a molecular chain which is flexibly coiled. The amplitude Eh of an AC electric field which is necessary for stabilizing LC molecules was measured and the following results were obtained: (1) Eh of the LC cell using polyimide resin B was smaller than that of the LC cell using polyimide resin A. (2) As the LC layer thickness became smaller, the amplitude of Eh became larger.

Method of Evaluating Tilt Domain in a Twisted Nematic Cell

The conditions for the formation of tilt domains in a twisted nematic cell have been studied in relation to the rubbing direction, the distribution of electric field at the electrode edges and the pretilt angle of liquid crystal molecules. The method of evaluating tilt domains in a twisted nematic cell using an electrode consisting of several segments with various angles to the rubbing directions was devised and some experiments were carried out. It is estimated that tilt domains are never induced when the pretilt angle is more than 1.2 degrees in a liquid crystal cell in the case where the angle between the upper surface rubbing direction and the lower surface rubbing direction, which is called the twisted angle, is 80 degrees.

Physical Properties of Ferroelectric Liquid Crystals and AC Field-Stabilization Effect

The relation between physical properties of ferroelectric liquid crystals (FLCs) and the AC field stabilization effect is described. The AC field-stabilization effect depends on a dielectric anisotropy Δe and a tilt angle θ. We introduced the parameter α defined by α=-Δesin 2θ and experimentally clarified that the FLCs with a large value of the parameter α showed a large AC field-stabilization effect. This is confirmed by using a FLC mixture with a large value of α so that the alignment state reset by a DC electric field is completely maintained for a certain time by superposing a high-frequency AC electric field to the DC electric field, even if the polarity of the DC electric field changes.

The influence of the spontaneous polarization and viscosity of ferroelectric liquid crystals on the AC field-stabilization effect

The influences of the spontaneous polarization (P/sub s/) and reorientational viscosity ( eta ) on the AC field-stabilization effect were studied experimentally by using four ferroelectric liquid-crystal (FLC) compounds that have different P/sub s/ and eta values. Delays in the response time originating from the AC field-stabilization effect were measured. Those FLC compounds with small P/sub s/ and low eta were found to be suitable for realizing both a large AC field-stabilization effect and quick response. >

A liquid-crystal display panel using polarizers as panel substrates

A liquid-crystal display (LCD) using polarizers as the panel substrates is investigated. The optical properties of TN LCDs using biaxially drawn polyester films and uniaxially drawn polyester films are evaluated. As a result, the latter films are selected as supporting films of the polarizers. Since both uniaxially drawn polyester films and LC molecules are optically anisotropic, interference colors may result due to birefringence. Also, as these polyester films are thermally anisotropic, warping of the LCD panel may occur after heat treatment. The influence of the arrangement of the polarizers on the optical and thermal properties of the LCD is discussed and the most suitable structure is determined. The developed plastic LCD is 0.5 mm in thickness and has better optical characteristics than those of a conventional LCD using glass substrates.

New Evaluation Method of Dielectric Materials Using a Microwave Technique

A new nondestructive method of evaluating changes in characteristics or detecting internal defects in insulation materials with microwave techniques is discussed. The main feature of the method is that the amplitude and phase angle of a detected signal are displayed in a polar co-ordinate system, which allows changes in both the dielectric constant and loss tangent of a dielectric material to be obtained at the same time. The results of experiment on deterioration, the detection of foreign materials, and differences in the inner structure of complex insulation materials are shown.

Effect of spontaneous polarization and viscosity of ferroelectric liquid crystals on AC field-stabilization phenomena

The influence of spontaneous polarization, P/sub s/ and rotational viscosity, eta , on the AC field-stabilization effect are studied by using four ferroelectric liquid crystal (FLC) compounds which have different P/sub s/ and eta . In the experiments, the delay of the response time originating from the AC field-stabilization effect is measured. It is found that FLC compounds with small P/sub s/ and low eta are suitable for realizing both large AC field-stabilization effect and quick response.<<ETX>>

AC Field-Stabilization Phenomena of Ferroelectric Liquid Crystals

AC field-stabilization phenomena of ferroelectric LC cells have been studied. The amplitude Eh of an AC electric field which is necessary for stabilizing an LC cell under a DC electric field with reverse polarity, has been obtained by theoretical discussions. Eh is expressed by the following equation: Eh2=Eho2+R\frac{P_{\text{s}}{\cdot}E_{\text{b}}}{|\Delta\epsilon| \sin^{2}\theta_{t}} where Eho is the AC electric field which is necessary for stabilizing an LC cell without an electric field, Ps is the spontaneous polarization, Eb is the DC electric field, Δe is the dielectric anisotropy, θt is the tilt angle and R is a constant. This equation represents the experimental results well.