JPH0210326A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the degradation of image quality such as flickering of a screen and unequal display by using a high polymer having the electric conductivity within a 10<-18>-10<-15>Q<-1>cm<-1> range as an oriented film. CONSTITUTION:The conductive high polymer having 10<-18>-10<-15>Q<-1>cm<-1> electrical conductivity is used as the oriented film in order to prevent accumulation of unnecessary charges in the liquid crystal display element. Investigation is made on polyethylene and polypyrrole having an alkyl chain and polyacetylene having a benzene ring in the side chain. As a result, these high polymers dissolve easily in solvents and the easy formation of the high-polymer films on a substrate is possible. The charges are less accumulated in this case and the accumulation of the charges on these high-polymer films arises hardly with these films themselves. The good electrolytic driving characteristic is, therefore, obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display device, and particularly to a liquid crystal display device with an improved alignment film for controlling the alignment of liquid crystals.

Display elements using liquid crystal technology have the following advantages: 1) Low power consumption 2) Low driving voltage 3) Compact and lightweight, and are used in a variety of applications including calculators and watches. It is being

In order to obtain good characteristics in such a liquid crystal display element, it is necessary to align the liquid crystal in a certain direction and form a monodomain. In order to form liquid crystals into monodomains, it is necessary to align the liquid crystals in a certain direction due to interfacial effects, and for this reason, liquid crystal display elements are always provided with an alignment film. Typical liquid crystal alignment film processing methods include oblique evaporation,
One example is the rubbing method.

In the oblique evaporation method, an oxide such as SiO or a metal such as Pt is deposited on the substrate surface at an angle of several hundred to several tens of amps from an oblique direction.
An alignment film is created by vapor deposition to a thickness of 0OA.

The reason why a specific molecular arrangement can be achieved using the oblique evaporation method is that
This is due to the interaction between the ripple-shaped surface formed on the substrate surface by oblique vapor deposition and liquid crystal molecules, and the subtle difference in the shape causes the difference between parallel alignment and tilted alignment.

On the other hand, in the rubbing method, an alignment process can be performed by rubbing an organic polymer film formed on a substrate surface in a certain direction with a cloth or the like. The mechanism of liquid crystal alignment by the rubbing method is not completely understood, but by applying shear stress to the surface of the alignment film by rubbing, alignment of polymer chains near the surface occurs, and the liquid crystal aligns according to the orientation of the polymer chains. It is considered.

Among these alignment treatment methods, from the viewpoint of ease of preparing an alignment film and stability of alignment, the following alignment methods are used for liquid crystal display elements:
Rubbing methods for polyimide films are widely used.

Problems to be Solved by the Invention However, the rubbing method for polyimide films also has the following problems. Since polyimide resin generally has high insulating properties, when it is used as an alignment film for display, unnecessary charges are accumulated in the liquid crystal, the alignment film, or the interface thereof. If the amount of charge accumulated on one substrate of the liquid crystal element differs from that on the other substrate, the effective voltage applied to the liquid crystal layer will differ depending on the polarity, which can cause screen flickering and display unevenness, especially in active matrix systems. It causes In addition to such deterioration in image quality such as screen flickering and display unevenness, there is also a problem in long-term reliability.

Similarly, when this polyimide alignment film is used in a ferroelectric liquid crystal display element, abnormal display occurs when polarity is reversed due to charges accumulated in the element, such as display burnout.
In some cases, the memory properties characteristic of ferroelectric liquid crystals cannot be sufficiently obtained.

One way to prevent charge accumulation in the liquid crystal, alignment film, or their interface is to increase the electrical conductivity of the alignment film. For example, this is generally done using conductive resin or film. One possible method is to disperse carbon grains in an alignment film. However, when carbon grains are mixed, it is difficult to disperse the fine particles of around 100A, and there are problems with opposing shorts and light transmission due to the carbon grains, so this is not an appropriate countermeasure.

An object of the present invention is to provide a liquid crystal display element that solves the problems of conventional liquid crystal display elements.

Means for Solving the Problems The present invention has an electric conductivity of 10-19 to t□-1sΩ-1.
The above object is achieved by using a liquid crystal display element whose alignment film is made of a polymer within the range of cm-1.

Effect The present invention uses a highly conductive polymer as a liquid crystal alignment film, which makes it difficult for charges to accumulate.
Good electric field drive characteristics can be obtained.

EXAMPLES The present invention will be explained below with reference to drawings showing examples thereof.

Currently, in order to prevent unnecessary charges from accumulating in a liquid crystal display element, a method of using a conductive polymer as an alignment film is considered. In the case of conductive polymers, as represented by polyacetylene, they are generally insoluble in solvents, but recently soluble conductive polymers have been developed. Among these, polythenylene and polypyrrole with alkyl chains,
We investigated polyacetylene with a benzene ring on the side chain and found that it dissolves easily in solvents, allows easy formation of a polymer film on a substrate, and also shows that even when used as an alignment film for liquid crystals, the alignment of liquid crystals does not improve. I confirmed that it was good. They also discovered that liquid crystal display devices using this alignment film have less accumulated charge. When the electrical conductivity of these polymer films was measured, it was within the range of 10-1'' to 10-+5Ω-'cm-', and since the electrical resistance is approximately the same or lower than the resistance of liquid crystal, the film itself It is also thought that charge is difficult to accumulate.

Therefore, by using a highly conductive polymer as the liquid crystal alignment film, charges are less likely to be accumulated, and therefore good electric field drive characteristics can be obtained. Furthermore, it can be applied to ferroelectric liquid crystal displays very easily.

Next, the present invention will be explained in more detail.

The polymer used in the liquid crystal display element of the present invention can be easily formed into a film using a spin cord or the like, similar to conventionally used polymer alignment films (polyimide polymer films, polyvinyl alcohol films, etc.). Furthermore, by performing a rubbing treatment thereafter, the liquid crystal can be easily aligned.

The electrical conductivity of a polymer is as follows:
Sandwiched between electrodes with an area of 1ffIff12, to
The applied voltage was determined by applying an ov voltage.

A luminance modulation degree m expressed by the following formula was defined as a quantity representing the degree of flickering on the screen of a liquid crystal display element.

Average transmitted light intensity In this example, the driving waveform is f = 30 Hz and a rectangular wave.
The m value was measured by applying a voltage v51I required to change the light transmittance of the liquid crystal display element by 50%. The 30 Hz component of the transmitted light fluctuation was separated using a spectrum analyzer (Atopantest Co., Ltd.!! TR-9406).

The level at which flicker can be felt varies greatly from person to person, but
In the case of flz, flicker is not recognized in most cases when the luminance modulation degree m<0.01.

Example 1 FIG. 1 shows the structure of a liquid crystal display element according to the present invention. A device having this structure was created as follows. First, IT
On the substrates 1 and 9 having O electrodes 2 and 8, Ni chill-2-
Hi 90 words “Non (NMP) has one volume and 0 (0)
-Tourunoe: Lu? Cefton) was applied by a spin code method so that the thickness of the alignment films 3 and 4 after drying was 50 OA, and dried at 100° C. for 1 hour. Ne°su(0-MethiJ
The electrical conductivity of the alignment film is 7X
The 10th inch was Ω-'am-'.

Next, the alignment film on this glass substrate is rubbed, and then bonded together via a bead spacer 6 so that the rubbed directions are twisted 90 degrees to each other, and the cell gap is 5.871 m. The surrounding area was surrounded with sealing resin 5 except for the area where . Next, as the liquid crystal 7, a nematic liquid crystal (LIXON 9150 nematic liquid crystal manufactured by Chisso Petrochemical Co., Ltd.) was injected into the device under reduced pressure at room temperature, and the injection port was sealed.

When this device was observed using a polarizing microscope, it was found that the liquid crystals were uniformly aligned.

Next, the voltage-transmittance characteristics of each element were measured at 20° C. using a Canon liquid crystal evaluation device, and the voltage V′l required for a 50% change in light transmittance was determined.

After applying a DC voltage of 5 cm for 30 minutes, the degree of brightness modulation m at 30 Hz was measured by the multiplex method. As a result, m=
0.0060, there were no abnormal displays such as flickering, and there was almost no charge accumulation.

Example 2 An alignment film was prepared in the same manner as in Example 1 using a solution of 3-hexyl (3-hexyl) dissolved in toluene as the alignment film. The electrical conductivity of the +7 (3-hexyl) alignment film was 8×10-”Ω-’Cm-’.

When the device was assembled and nematic liquid crystal was injected, the liquid crystal was aligned uniformly. In addition, when the brightness modulation degree m was determined in the same manner as in Example 1, it was 0.0075, and there was no flickering.
There was also almost no charge accumulation.

Example 3 As an alignment film, NJ (electrical conductivity: 9X10-'θΩ-'c) dissolved in NMP was used.
When a cell was prepared in the same manner as in Example 1 using tn-'), the liquid crystal was uniformly aligned, m=o, 0065, and there was almost no charge accumulation.

Example 4 As an alignment film, phos(p-(o-I) dissolved in NMP was used as an alignment film.
Chill) Noenishishi) (Electrical conductivity: 3X10-"Ω-'
A cell was prepared in the same manner as in Example 1 using the following method. The liquid crystal was uniformly aligned, m = 0, 0077, and there was almost no charge accumulation.

Example 5 An alignment film was prepared in the same manner as in Example 1 using Ness (O-methy 11 pheni 117 cetiton) as the alignment film.

Next, the alignment film on this glass substrate was rubbed and bonded together with a 2.07 zm spacer in between so that the rubbing directions of the alignment film on the upper r substrate were opposite to each other. As the liquid crystal, a ferroelectric liquid crystal having the following phase transition was injected into the device at 90° C. (I phase) under reduced pressure.

→(11-+511A-+ 5m("When this device was observed using a polarizing microscope, a uniformly aligned ferroelectric liquid crystal display device with no defects was obtained. This did not occur and there was no charge accumulation.

Example 6 An alignment film was prepared in the same manner as in Example 5 using this film (3-hehesyl ft nitoshi) as the alignment film.

When the device was assembled with a gap of 2.0 μm and ferroelectric liquid crystal was injected, the liquid crystal was aligned uniformly.

Further, no burnt-up phenomenon occurred, and there was almost no charge accumulation.

Example 7 When a cell was prepared in the same manner as in Example 5 using a liquid crystal solution (N-) dissolved in NMP as an alignment film, the liquid crystal was aligned uniformly and no stickiness was observed. There was also almost no charge accumulation.

Example 8 As an alignment film, a solution of glue (p-(o-r) dissolved in NMP was used.
A ferroelectric liquid crystal cell was prepared in the same manner as in Example 5 using a ferroelectric liquid crystal cell. The liquid crystal was aligned uniformly, there was no burnt phenomenon, and there was almost no charge accumulation.

Comparative Example 1 Polyimide (electrical conductivity: 8×l) was used as a polymer alignment film.
A liquid crystal display element was fabricated in the same manner as in Example 1 using a conductive material with a diameter of 6Ω-'cm.

In this device, the liquid crystal was uniformly aligned, but the brightness modulation degree m
is as large as 0.0353, and you can see the flickering on the display.
Electric charge had accumulated.

Comparative Example 2 As a polymer alignment film, poly(o-me f11 stitoshi) (
A ferroelectric liquid crystal display element was prepared in the same manner as in Example 3 using electrical conductivity: 4×10 Ω 7 Ω cm−’.

In this element, the longer the voltage was applied, the more abnormal display occurred due to the burnt phenomenon.

Effects of the Invention The liquid crystal display element of the present invention can easily solve conventional problems such as screen flickering and display unevenness due to accumulated charges by using a polymer with limited electrical conductivity. In addition, even in the case of a ferroelectric liquid crystal display element, it is a good display element that does not cause display burning phenomenon.

[Brief explanation of the drawing]

The figure is a sectional view showing the structure of a liquid crystal display element in an embodiment of the present invention. 1.9...Glass substrate, 2,8...I
TO electrode, 3, 4... alignment film, 5...
Seal resin, 6... Bead spacer, 7...
···liquid crystal.

Claims (3)

[Claims] (1) Electrical conductivity is 10^-^1^0~10^-^1^
A liquid crystal display element whose alignment film is made of a polymer within the range of 5Ω-^1cm^-^1. (2) The polymer of the alignment film is polythenylene, polypyrrole, polycyanoacetylene, polymethylazomethine, polyphenylacetylene, poly(p-phenylene), poly(m-phenylene), and derivatives thereof, or a mixture thereof. Claim 1: The polymer is a polymer or a copolymer.
The liquid crystal display element described above. (3) The liquid crystal display element according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal.