JPH02275415A - Manufacture of ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To realize the liquid crystal element which is superior in contrast and memory performance by manufacturing the liquid crystal element by repeating a process wherein an orienting film is formed on a transparent electrode and rubbed. CONSTITUTION:A high polymer film for orienting film formation which is formed by coating is rubbed in a normal way and then a high polymer film is formed by coating and rubbed. Thus, the coating and rubbing of a high polymer film are repeated to form the orienting film 3 where a defect is generated at a low frequency. This is affected remarkably by the orientation of a lower orienting film 3 because the high polymer films which are formed one over another are extremely thin and the orientation is therefore considered to be improved. The number of times of the repetition is limited and the orientation is saturated speedily. Consequently, ferroelectric liquid crystal 5 can be formed uniformly to large area, and consequently the ferroelectric liquid crystal display element which has superior contrast and memory performance can be put in practical use.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for manufacturing a ferroelectric liquid crystal display element, the purpose of this invention is to put into practical use a liquid crystal display element with excellent contrast and memory properties. In a liquid crystal display element in which an alignment film is provided on a glass substrate, transparent electrodes are arranged perpendicularly to each other in a matrix via spacers, and ferroelectric liquid crystal is sealed between the transparent electrodes, the alignment film is formed on the transparent electrodes. A method for manufacturing a ferroelectric liquid crystal display element is constructed by repeating the rubbing process a plurality of times.

[Industrial application field]

The present invention relates to a method for manufacturing a ferroelectric liquid crystal display element with improved contrast and memory properties.

Liquid Crystal Display
y (abbreviated as LCD) has low power consumption and drive voltage, and it is possible to put a thin and light display element into practical use, so it is widely used as a small-capacity display for watches, calculators, etc., but recently it has become popular for use in personal computers, word processors, etc. Demand for use in office automation equipment (abbreviated as OA equipment) is increasing, and there is a need to develop liquid crystal display elements with a larger amount of information.

[Conventional technology]

The LCD currently mainly used is TN (Twis
tedNematic) is a TN type using liquid crystal,
Two glass substrates equipped with band-shaped transparent electrodes are placed facing each other with a spacer in between so that the band-shaped electrodes are perpendicular to each other, and TN liquid crystal molecules are sealed inside the glass substrates with a twist of several tens to hundreds of degrees. ing.

And this TN type LCD has ■ Simple matrix method and ■ There is an active matrix method.

Therefore, although the manufacturing cost of the simple matrix method (2) is low, there is no memory when the electric field is turned on and off, and the dark value characteristic is not steep, so it is not possible to perform large-capacity displays such as 640 x 400 dots or more. If you try to do so, there is a problem of crosstalk in which non-displayed areas become half-displayed due to cumulative response effects.

Another problem is that the response time is long, ranging from several milliseconds to several 1011 seconds, making it impossible to accurately display large amounts of moving images.

On the other hand, the active matrix method (■) has one thin film transistor (abbreviated as TPT) in one pixel, and there is no problem of crosstalk, but it is low cost and can be used over a large area without causing defects. The problem is that it is difficult to form.

Now, as a new LCD that uses the simple matrix method that is used in this TN type LCD and is low-cost and can display large-capacity video, it uses ferroelectric chiral smetic C liquid crystal (abbreviated as SC1 liquid crystal). Ferroelectric LiquidCry
stal Display (abbreviated as FLCD) has been proposed.

In this FLCD element, the thickness of the liquid crystal layer is made to be about the same as, but less than, the helical pitch of the Sc* liquid crystal, and when this is done, the helix is unraveled by the alignment regulating force, and spontaneous polarization and a bistable state appear.

Because of this bistability, the PLCD element has memory properties, and since there is no crosstalk due to the cumulative response effect seen in conventional TN type liquid crystals, large capacity display is possible.

Furthermore, since the FLCD element has spontaneous polarization, the driving electric field directly acts on the dipole moment of the liquid crystal molecules.

Therefore, the torque exerted on the liquid crystal molecules by the applied electric field is about 1000 times larger than that of TN liquid crystal, so the response time can be shortened from several microseconds to several tens of microseconds. Therefore, FLCD is suitable for displaying videos and large-capacity displays. It becomes possible.

[Problem to be solved by the invention]

However, in order to effectively operate a ferroelectric liquid crystal display element, the Sc' liquid crystal molecules must be aligned parallel to the substrate to form uniform domains.

FIG. 1 shows a cross-sectional structure of a FLCD element, in which an alignment film 3 made of a polymer such as polyimide is coated on a transparent electrode 2 patterned on a glass substrate l.

These substrates 1 are pasted together with a spacer 4 in between, and a ferroelectric liquid crystal 5 is sealed in this gap.

In addition, on both sides of the glass substrate 1, there are polarizers 6 on the light source side.
Further, an analyzer 7 is arranged on the opposite side.

A FLCD having such a configuration is characterized in that the liquid crystal molecules are oriented parallel to the substrate, and the spontaneous polarization of the liquid crystal molecules is bistable, either upward or downward.

Figure 2 explains the operation of FLC (ferroelectric liquid crystal).FLC molecules 8, shown as sticks, have spontaneous polarization in the direction perpendicular to the long axis, and are originally arranged in a spiral shape. By making the gap between the glass substrates 1 smaller than the helical pitch of the FLC, the arrangement direction of the FLC molecules 8 can be aligned parallel to the glass substrate 1.

Figure 2 (A) shows FLC molecules 8 aligned in this way.
It shows the direction of spontaneous polarization of , and shows the state facing upward ↑.

Next, as shown in Figure (B), a voltage is applied between the transparent electrodes 2 of the upper and lower glass substrates 1, and an electric field 9 is applied in the opposite direction to the spontaneous polarization, as shown in Figure (C). Like a cone (C
one) rotates to the opposite side along the outer periphery, and the spontaneous polarization becomes downward a.

This state is maintained even when the electric field is removed.

In this way, is the spontaneous polarization of FLC molecules ↓? Since it takes either direction, it has memory properties, and its response speed is fast because its spontaneous polarization responds directly to the electric field.

Now, in order to put FLCD devices into practical use, it is necessary to uniformly align the FLC molecules parallel to the substrate, and methods for this include the shearing method, which applies shear stress to the substrate in the temperature range of smectic physiognomy, and the Gaussian Known methods include a magnetic field arrangement method in which a strong magnetic field is not applied and then slowly cooled to the sc* phase, and a rubbing method in which a polymer film formed on a substrate is rubbed with a brush or the like.

Among these control methods, the shearing method has difficulty in increasing capacity, and the magnetic field distribution method is effective when the panel gap is large, but it has the problem that it is difficult to align panels as thin as 2μ. There is.

On the other hand, it is known that the polymer film rubbing method, which is widely used as a conventional alignment control method for nematic liquid crystals, is extremely effective for uniformly aligning Sc1 liquid crystals.

However, unlike conventional TN liquid crystals, Sc1 liquid crystals have a layered structure, so conventional rubbing methods cannot align them sufficiently uniformly, resulting in many linear defects, resulting in problems such as contrast and memory performance. The problem was that the display characteristics were poor.

[Means to solve the problem]

The above problem can be solved by providing an alignment film on two glass substrates each having a plurality of transparent electrodes, making the transparent electrodes orthogonal to each other in a matrix shape via a spacer, and sealing a ferroelectric liquid crystal between the transparent electrodes. This problem can be solved by manufacturing a ferroelectric liquid crystal display element by repeating the process of forming an alignment film on the transparent electrode and rubbing it several times in the liquid crystal display element.

[Effect]

There are various theories as to why the liquid crystal is aligned by the alignment film that has been subjected to rubbing treatment, and it is not yet confirmed, but the inventors believe that rubbing causes the polymer film to stretch slightly, which causes the polymer This is thought to be due to the main chains being aligned in the stretching direction.

Based on this idea, it seems that thorough rubbing is sufficient to completely align the FLC, but when liquid crystals that have been aligned using the conventional rubbing method are observed under a polarizing microscope, many linear defects are found. This indicates that defects such as distortion and bending have occurred in the FLC, which has a layered structure.

For these reasons, excessive rubbing results in more defects.

In the present invention, as a method for fully orienting FLC, after performing normal rubbing on the applied polymer film for forming an alignment film,
Furthermore, it has been discovered that alignment with fewer defects can be achieved by coating and forming a polymer film and rubbing it.

It is not clear why it is possible to form an alignment film with fewer defects by repeating coating and rubbing of polymer films in this way, but it is probably because the polymer films formed in layers are thinner and cause the formation of an alignment film with fewer defects. It is thought that the orientation of the side alignment film has a significant influence, and therefore the orientation improves.

However, there is a limit to the number of repetitions, and the orientation quickly saturates.

〔Example〕

Polyvinyl alcohol was selected as the alignment film forming material, and this 3% aqueous solution was spin coded onto four glass substrates to form a film approximately 1000 thick.

Next, after drying these substrates at 150°C for 1 hour, they were rubbed using a roller wrapped in nylon cloth, and two of these substrates were treated with 3% polyvinyl alcohol as before. An aqueous solution was formed to a thickness of about 1000 mm, dried under similar conditions, and then rubbed.

Next, the substrates that have been rubbed once and twice are pasted together so that the rubbing directions are antiparallel.
I made panels with a spacing of 2μ.

A commercially available ferroelectric crystal (product name C5-1) is placed in this gap.
013, manufactured by Chisso Corporation) to form a liquid crystal panel.

Next, these liquid crystal panels were observed under crossed nicol conditions to examine differences in the alignment state of the liquid crystal due to the difference in the number of times of rubbing treatment.

Table 1 shows the results.

Table 1

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of the FLCD, and FIG. 2 is an explanatory diagram of a state in which the FLC is inverted by an electric field. In the figure, 1 is a gas substrate, 2 is a transparent electrode, 3 is an alignment film,
8 is an FLC+ molecule. In this way, it can be seen that the properties of the product that has been rubbed twice are better in all respects than those that have been rubbed once.

Claims (1)

[Claims] In a liquid crystal display element in which an alignment film is provided on two glass substrates provided with a plurality of transparent electrodes, the transparent electrodes are arranged perpendicularly in a matrix shape via a spacer, and ferroelectric liquid crystal is sealed between the transparent electrodes. . A method for manufacturing a ferroelectric liquid crystal display element, characterized in that the step of forming an alignment film on the transparent electrode and rubbing it is repeated multiple times.