JP2003005223A - Method for manufacturing liquid crystal display device with high contrast ratio asymmetric electro-optical characteristics - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To reduce the operating voltage in an HV-FLCD,
High contrast and stable operation at high temperatures. SOLUTION: There is a substance that takes a series of phase transition of isotropic phase-chiral nematic liquid crystal phase-chiral smectic C liquid crystal phase. In this case, smectic A
The feature is that it does not take phase. It is known that an electro-optical cell using such a ferroelectric liquid crystal exhibits asymmetric electro-optical characteristics. This is a Half-V shape
This is called the ed switching phenomenon. Such a ferroelectric liquid crystal display is abbreviated as HV-FLCD. The present invention controls an azimuthal surface anchoring strength of liquid crystal molecules to reduce operating voltage and improve asymmetry, that is, an HV-FLCD characterized by an improvement in operating characteristics such as a reduction in light leakage during dark area operation. Provided is an element that exhibits stable operation at high temperatures.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing method for realizing a high contrast ratio in a liquid crystal display element, particularly in a ferroelectric liquid crystal electro-optic or display element.

[0002]

2. Description of the Related Art A ferroelectric liquid crystal display proposed by Clark and Lagerwall [JP-A-56-107216] shows bistability and has a high speed response, and is expected as a liquid crystal display device for displaying moving images. Came. However, defects such as zig-zag defects are likely to occur, which causes light leakage, and it has been difficult to realize liquid crystal display with a high contrast ratio. Even in the past, the definition of C-1 and C-2 uniform phases (J. Kanbe et al: Ferreroelec
trics, 114, 3-26, 1991; Kod
en et al: Jpn. J. Appl. Phys.
31,3632-3635 (1992), Pretilt value (Kanbe et al; Koden et al.
al; P. Watson, P.M. J. Bos; Phys.
Rev. E56 R3769-R3711 (199
7); Furue et al: Mol.
Cryst. Liq. Cryst. 328, 193-
200 (1999)), the relationship between the roughness of the alignment film surface (H. Furue et al; Mol. Cryst.
Liq. Cryst. 328, 193-200 (199
9)), photo-alignment technology (R. Kurihara et al.
al: SID Digestof Tech. Paper
There is a report about rs30, 807-809 (2000). Furthermore, in a system lacking the smectic A phase in the phase transition series, the so-called Half-V switch is used.
ing has been reported (Y. Asano
et al: Jpn. J. Appl. Phys. 38
5977-5983 (1999)). The present invention is based on the inventor's research relating to-the anchoring is not shown in the conventional technique in the HV-FLCD. HVFLC by controlling anchoring strength
The purpose is to give D favorable electro-optical characteristics. Strong anchoring (10 ^-3 J /
The anchoring strength was not controlled because it was about m ² ). The present invention presents a technique for realizing desirable properties by controlling the strength of anchoring and stabilizing high temperature properties by introducing a polymer stabilization method.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In an HV-FLCD, the operating voltage is reduced, the brightness (whiteness) of the bright state during operation is improved, the darkness (blackness) of the dark state during operation is improved, and the high temperature is increased. Is required to be stable. These matters are issues to be solved.

[0004]

[Means for Solving the Problems] Saturation operating voltage value is 5 V (pulse width 1 ms) due to reduced photo-alignment of operating voltage.
Can be about Improvement of brightness in bright state of operation The deflection angle of FLC molecules can be set to ψ = 45 ° by photo-alignment. The brightness and the deflection angle φ are I = I ₀ sin ² (2
ψ), the brightest state can be realized if ψ = 45 °. Improving the darkness (blackness) of the dark state during operation In order to obtain the best darkness (black) in the dark state during operation, rubbing that gives a medium degree of anchoring strength is desirable. Stabilization of operation at high temperature Polymer stabilization is effective for stabilizing operation at high temperature. However, about 1 wt% is preferable as the optimum addition amount of the monomer. If the amount of added monomer is more than that, high voltage operation and decrease in brightness in the bright state occur.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, in the liquid crystal display element according to the embodiment of the present invention, a pair of transparent substrates (for example, glass substrates) 1a and 1b constitute a liquid crystal cell substrate, and a liquid crystal layer 2 (in this case, a liquid crystal cell substrate) is formed therein. Ferroelectric liquid crystal smectic C
^* Phase) is retained. Transparent electrodes 3a (P
X) and 3b are arranged and a voltage is applied to the liquid crystal. ITO is usually used as the transparent conductive film.

Liquid crystal alignment films 4a and 4a are formed on the inner wall of the liquid crystal cell.
b is applied.

A color filter 5 is used for color display. No color filter is required in the field sequential method. In the active matrix display, a thin film transistor (TFT) Q (7), a pixel electrode PX (3a) and a black stripe BS are used.
A crystalline silicon transistor or the like may be used instead of the TFT. It is used in such a manner that a cell composed of two substrates and a liquid crystal for use as a liquid crystal display is sandwiched between two polarizing plates 6a and 6b. When the reflective type is used, a light reflecting plate may be arranged on the lower substrate 1a and one polarizing plate may be used.

EXAMPLES Hereinafter, the present invention will be described in more detail by showing Examples of the present invention. However, the invention is not limited to these examples.

Example 1 On a glass substrate with an ITO transparent electrode, a polyimide alignment film RN manufactured by Nissan Chemical Industries, Ltd.
After forming -1199 with a thickness of about 0.03 μm, rubbing treatment or photo-alignment treatment was performed to obtain glass substrates with polyimide alignment films having different anchoring energies. Here, the rubbing treatment was carried out by rubbing with a pushing amount of 0.02 mm and rubbing with a pushing amount of 0.15 mm from where the rubbing cloth and the polyimide film touched each other.
Two types of substrates were prepared. Centering wavelength 3 for photo-alignment
This was performed by irradiating the substrate with a non-polarized ultraviolet ray having an intensity of 26 mW / cm ² at 10 nm from an angle of 45 ° for 4 hours. A liquid crystal cell was produced by facing each of the two substrates of these three types so that the surfaces on which the alignment films were formed faced each other at an interval of 2 μm. At this time, the rubbing directions of the two substrates of the liquid crystal cell were set to be antiparallel alignment. Next, the ferroelectric liquid crystal “R2301 (P _s = 3.
² nC / cm ² ) ”(Clariant, Chiral Smectic C-Chiral Nematic Phase Transition Temperature 66
C, chiral nematic-isotropic liquid phase transition temperature 87
˜90 ° C.) was maintained at 100 ° C. while being injected as an isotropic liquid phase. A DC voltage of 5 V was applied to the cell from the chiral nematic phase to the chiral smectic C phase to confirm uniform alignment, and then the application of the DC voltage was stopped and the temperature was lowered to room temperature to prepare a ferroelectric liquid crystal cell. On one surface of this liquid crystal cell, the transmission axis of one polarizing plate was made to coincide with the alignment direction of liquid crystal molecules when no voltage was applied to the liquid crystal cell, and on the other surface, another A liquid crystal display device was produced by bonding the other polarizing plate so that the transmission axis thereof was orthogonal to the alignment direction of the liquid crystal molecules. Second
The figure shows the electro-optical characteristics of the liquid crystal display device manufactured as described above. As can be seen from this, the transmittance increased when the pushing amount during rubbing was small, that is, when the anchoring energy was small. Further, in the case of photo-alignment, the anchoring energy was smaller than that of rubbing, and therefore the transmittance was higher. The transmittance T and the deflection angle ψ are T = I
/ I ₀ = sin ² (2ψ). In the photo-alignment cell, ψ = 45 ° was confirmed at 6V. Further, the response speed from the voltage non-application state to the voltage application state and from the voltage application state to the voltage non-application state was 1 ms or less, and it was confirmed that extremely high-speed switching was possible.

Example 2 A liquid crystalline diacrylate monomer "2A" having a smectic A phase-nematic phase as a phase series and exhibiting a smectic A phase at 36 ° C.
363 "(manufactured by Dainippon Ink and Chemicals, Inc.) and a ferroelectric liquid crystal composition" R2301 (P _s = 8.9 nC / cm).
² ) ”(Clariant, Chiral Smectic C
-Chiral nematic phase transition temperature 66 ° C, chiral nematic-isotropic liquid phase transition temperature 85-87 ° C) 99
A liquid crystalline mixture was prepared, which was composed of parts by mass and 0.01 parts by mass of a photopolymerization initiator "Irgacure 651" (manufactured by Ciba Specialty Chemicals). Next, this liquid crystalline mixture was injected into the cell prepared in the same manner as in Example 1, and 5 was charged from the chiral nematic phase to the chiral smectic C phase.
After applying a DC voltage of V to confirm uniform orientation, the application of DC voltage was stopped and the temperature was lowered to room temperature. Next, the liquid crystal diacrylate monomer "2A363" was photo-cured by irradiating with ultraviolet rays having a central wavelength of 365 nm and an intensity of ² mW / cm ² for 50 seconds at room temperature. Regarding the electro-optical characteristics of this liquid crystal display device, it was confirmed that the smaller the anchoring energy, the higher the transmittance as in Example 1. Further, there was no problem in reliability at high temperature.

[0010]

According to the present invention, with the above-described structure, it is possible to reduce the operating voltage, improve the brightness of the operating bright state, improve the darkness of the operating dark state, and stabilize the operation at high temperature. Play.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a ferroelectric liquid crystal display cell of the present invention.

FIG. 2 is a diagram showing electro-optical characteristics (horizontal axis: applied voltage, vertical axis: transmittance) of a liquid crystal display element manufactured by the manufacturing method of the present invention in Example 1.

[Explanation of symbols]

1a, 1b substrate 2 liquid crystal 3a, 3b transparent conductive film 4a, 4b Liquid crystal alignment film 5 color filters 6a, 6b Polarizing plate Q7 transistor 3a (PX) electrode BS black stripe

Claims (5)

[Claims] 1. A pair having at least one transparent substrate having a positive alignment structure for aligning smectic liquid crystals, chiral smectic liquid crystals, ferroelectric liquid crystals, and antiferroelectric liquid crystal molecules in a predetermined direction within the substrate surface. 2. A liquid crystal display device having the transparent substrate or a pair of substrates, one of which is a transparent substrate, and a liquid crystal layer sandwiched between the pair of substrates, so that defects in the alignment of the liquid crystal are prevented as much as possible. 2. The positive alignment structure is a pair of polymer alignment film or inorganic alignment film. In the case of a polymer alignment film, a rubbing process or a photo alignment process is performed. The inorganic alignment film is usually attached on the substrate by oblique vapor deposition. 3. A Half-V-FLCD which is a ferroelectric liquid crystal display exhibiting such strong asymmetric electro-optical characteristics.
Is abbreviated. In the HV-FLCD cell, the direction of the pretilt angle generated by anti-parallel rubbing is given in order to prevent defects originating from the chevron layer structure of the ferroelectric liquid crystal having a thickness of about 1 μm to 2 μm. The same applies when the photo-alignment method is used. 4. A liquid crystal molecule is aligned by photo-alignment accompanied by pretilt in manufacturing an HV-FLCD cell. At that time, at least the azimuth anchoring strength is 1 to 9 × 1.
The operating voltage is reduced by applying anchoring with a strength of about 0 ⁻⁶ (J / m ² ). 5. A HV-FLCD cell is manufactured by subjecting it to a weak rubbing treatment to obtain an azimuth anchoring strength of 1 ×.
By setting it to about 10 ⁻⁵ (J / m ² ) to 1 × 10 ⁻⁴ (J / m ² ), stable operation can be performed at a low voltage.