JPH0369919A - Manufacture of ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To uniformly orient a liquid crystal over a large area by forming oriented films on the respective opposite surfaces of substrates facing each other and subjecting the films to rubbing by using a roller whose surface material is cotton. CONSTITUTION:An aq. soln. of polyvinyl alcohol is applied by spin coating on the cleaned glass substrates 1 to form the oriented films 3. After the substrates 1 formed with these oriented films 3 are dried and are rubbed by the rubbing roller 12 wound with a cotton fabric 11. Since the oriented films 3 are rubbed by the cotton, the films are softly rubbed and are oriented without breaking the layer structure of the ferroelectric liquid crystal. Thus, the uniform formation of the ferroelectric liquid crystal over a large area is attained.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method for manufacturing a ferroelectric liquid crystal display element, and particularly relates to a method of rubbing an alignment film formed on a substrate when manufacturing a ferroelectric liquid crystal element. The present invention aims to provide a method for uniformly aligning liquid crystal over a large area.

In a method of manufacturing a ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sealed between a pair of opposing parallel substrates, an alignment film is formed on each opposing surface of the opposing substrates, and the surface material is The method includes a step of rubbing using a cotton roller.

[Industrial application field]

The present invention relates to a method for manufacturing a ferroelectric liquid crystal display element, and more particularly to a method for rubbing an alignment film formed on a substrate.

[Conventional technology]

Liquid crystal displays (LCDs) have the characteristics of low power consumption, low driving voltage, and light weight and thinness, so they are widely used as small-capacity displays for watches, calculators, etc., but in recent years, they have become popular for use in office automation equipment such as personal computers and word processors. As demand increases, there is a need for the development of liquid crystal displays with a larger amount of information.

The LCDs currently mainly used are the TN type and STN type, in which the liquid crystal molecules sandwiched between two substrates are twisted by 90 to 270 degrees. There are a simple matrix driving method and an active matrix driving method in which one or two thin film transistors (TPT) are fitted into one pixel. Although the simple matrix method has low manufacturing costs, it
When turned off, there is no memory and the threshold characteristics are not steep, so when trying to display a large capacity (640 x 400 dots or more), there is a crosstalk problem where non-displayed areas become half-displayed due to cumulative response effect 1. There is. Furthermore, this simple matrix method has a problem in that it is impossible to display high-definition, large-capacity moving images because of the long response time. On the other hand, the active matrix method has a problem in that it is difficult to form thin film transistors over a large area at low cost and without causing defects.

A display device (FLCD) using ferroelectric chiral smectic C (hereinafter referred to as S00) liquid crystal has been proposed as a new LCD capable of displaying large-capacity moving images using a low-cost simple matrix method (Japanese Patent Application Laid-Open No. Showa 56-108
Publication No. 216). In the ferroelectric liquid crystal display element, the thickness of the liquid crystal layer is approximately the same as or smaller than the helical pitch of the Sc9 liquid crystal. At this time, the helix unwinds due to the orientation regulating force at the substrate interface, and a bistable state appears. Because of this bistability, ferroelectric liquid crystal display elements exhibit memory properties, and as a result, they do not have the problem of crosstalk caused by the cumulative response effect seen in conventional liquid crystals, making it possible to increase capacity. have. Furthermore, since the ferroelectric liquid crystal display element has spontaneous polarization, the driving electric field acts directly 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 stronger than in the case of conventional liquid crystals, so the response time can be shortened to about 10 μs. Therefore, a ferroelectric liquid crystal display that takes advantage of these features is expected to be applied to high-definition displays such as personal computers and word processors, since it is possible to display moving images and large-capacity displays.

However, in order to effectively operate this ferroelectric liquid crystal display element, it is necessary to form uniform domains of the Sc'' phase in which liquid crystal molecules are aligned parallel to the substrate in the liquid crystal panel.

FIG. 6 shows a schematic diagram of a ferroelectric liquid crystal display element.

A transparent electrode 2 made of IT○ (indium tin oxide) is formed on the surface of the glass substrate 1, and a polyimide (P
An alignment film 3 made of a polymer such as I) is applied.

These two substrates are pasted together with a spacer 4 having a thickness of about 2/a interposed therebetween, and a ferroelectric liquid crystal 5 is sealed in the gap. The liquid crystal molecules are uniformly aligned parallel to the substrate, and at this time, the spontaneous polarization 6 indicated by the arrow takes a bistable state of upward direction (up) and downward direction (down). The transparent electrode 2 is connected to a power source 7 by a lead wire or the like, and by applying a pulse voltage from the power source 7, one of the bistable states is selected depending on the polarity of the voltage. The light emitted from the light source 10 passes through the polarizer 8 and the liquid crystal, and is transmitted from the analyzer 9.

Therefore, since the molecular arrangement is different in each bistable state, the optical rotation changes, making it possible to display bright and dark images.

The alignment control method for uniformly aligning the liquid crystal molecules 5 parallel to the glass substrate 1 shown in FIG. A magnetic field alignment method in which the material is slowly cooled to the ScI phase, and a rubbing method in which the polymer film formed on the substrate is rubbed with a brush or the like are known. Among these control methods, the shearing method has a difficulty in increasing capacity, and the magnetic field orientation method is effective when the panel gap is large, but it is difficult to align panels as thin as 2-inches. On the other hand, the polymer film rubbing method, which is widely used as a conventional method for controlling the alignment of nematic liquid crystals, is Sc*
It is known to be extremely effective in uniformly aligning liquid crystals.

[Problem to be solved by the invention]

Unlike conventional TN liquid crystals, SCI liquid crystals have a layered structure, so the degree of liquid crystal alignment varies greatly depending on the material of the rubbing roller. It is believed that the alignment of liquid crystal molecules is induced because the main chains of the polymer forming the alignment film are rearranged in the rubbing direction by rubbing. Therefore, it is thought that the effect on stretching of the main chain varies depending on the material of the rubbing roller.

Nylon, polyester, and the like are often used as materials for conventional rubbing rollers. However, when rubbing is performed using these materials, it has not been possible to obtain satisfactory results in terms of uniformity of orientation and degree of memory performance.

Japanese Patent Application Laid-Open No. 62-1366 regarding Naorika liquid crystal display element
Publication No. 23 discloses a rubbing treatment using cotton cloth for a TN type display element.

An object of the present invention is to provide a method for uniformly aligning liquid crystal over a large area when manufacturing a ferroelectric liquid crystal element.

[Means to solve the problem]

According to the present invention, the above problem is solved in a method for manufacturing a ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sealed between a pair of opposing parallel substrates. The present invention is solved by a method for manufacturing a ferroelectric liquid crystal display element, which is characterized by including a step of rubbing with a roller having a cotton surface material.

[For production]

According to the present invention, since the alignment film is rubbed with cotton, the layered structure of the ferroelectric liquid crystal can be aligned without being damaged by the soft rubbing.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view for explaining one embodiment of the present invention.

Approximately 3% of polyvinyl aluminum was applied onto the cleaned glass substrate 1.
The aqueous solution was spin-coded to form an alignment film 2 having a thickness of about 1000 layers. Next, the substrate on which these alignment films were formed was
After drying at 50° C. for 1 hour, as shown in FIG. 1, it was rubbed with a rubbing roller 12 wrapped with four types of cloth 11: cotton, nylon, rayon, and polyester. The arrow indicates the rubbing direction. Next, a pair of glass substrates were bonded together so that the rubbing direction was antiparallel to (opposite to) the former, to produce a panel with a gap of 2μ. FIGS. 2 and 3 are schematic diagrams showing the rubbing directions of a pair of alignment films, and show cases of parallel rubbing and antiparallel rubbing, respectively. In this example, the case of antiparallel rubbing shown in FIG. 3 was used. A commercially available ferroelectric liquid crystal (C3-1
013, manufactured by Chisso Corporation) to produce a liquid crystal panel.

Next, these liquid crystal panels were observed under crossed nicol conditions to examine differences in liquid crystal orientation due to differences in the rubbing roller material.

Note that the rubbing conditions are as shown in condition (A) below.

・Rubbing roller radius (Ro) = 25u.

・Rubbing roller rotation speed (N) = 548 r/m.

・Table speed (V) = 6600mm/m.

- Number of times of rubbing (M) = 12, - Amount of pushing (L) = 0.4 mm0 Table 1 shows the contrast ratio of the liquid crystal orientation of the above panel. From Table 1, it can be seen that the contrast ratio is highest when the rubbing roller material is cotton.

Table 1 and FIG. 4 are diagrams showing oscilloscope images of the amount of transmitted light of a liquid crystal panel, showing a method for determining the contrast ratio (a:b) of liquid crystal alignment.

Figure 4 shows the relationship between voltage and light transmittance over time; for example, when 15V is applied for 3.5ms, the light transmittance becomes b, and then after 0.5 seconds = When a voltage of 15V is applied for 3.5ms, the light transmittance drops to a. A/b (or a:b) at this time is defined as a contrast ratio.

Figures 5 (a), (b), (c) and (d) are transmissions of liquid crystal panels obtained to determine the contrast ratio of cotton roller (invention), nylon, rayon, and polyester (conventional example), respectively. FIG. 3 is a diagram showing an oscilloscope image of the amount of light.

According to Figure 5, when the rubbing roller material is cotton, the amount of transmitted light attenuates the least when the voltage changes from on to off, and therefore, the memory property is the best when the rubbing roller material is cotton. I understand that.

If the rubbing density is defined by the following formula (I) N(2πRo) -V ρ= ML (I)■ using the symbol given in the rubbing condition (A) above, the rubbing density is 57.8 (mm) It is.

Change the above rubbing density from 15 to 75 (+nm),
As a result of conducting the same study as in the above example, results similar to those shown in Tables 1 and 5 were obtained.

From the above, it can be seen that good contrast and memory properties can be obtained by using cotton as the rubbing roller material.

〔Effect of the invention〕

As explained above, according to the present invention, ferroelectric liquid crystal can be uniformly formed over a large area, and as a result, it is possible to provide a ferroelectric liquid crystal display with good contrast and memory properties. Become.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining one embodiment of the present invention, FIGS. 2 and 3 are schematic diagrams showing the rubbing direction of a pair of alignment films, and FIG. 2 is a parallel rubbing, Fig. 3 shows the case of antiparallel rubbing, Fig. 4 shows an oscilloscope image of the amount of transmitted light of the liquid crystal panel showing the method of determining the contrast ratio (a:b) of liquid crystal alignment, and Fig. 5 (a) ), (b), (c) and (d) are cotton (invention), nylon, rayon, polyester (
FIG. 6 is a diagram showing an oscilloscope image of the amount of transmitted light of the liquid crystal panel obtained for determining the contrast ratio in the case of the prior art example, and FIG. 6 is a schematic cross-sectional view showing the liquid crystal display element. DESCRIPTION OF SYMBOLS 1... Substrate, 3... Alignment film, 5... Liquid crystal molecule, 7... Power supply, 9... Analyzer, 11... Cloth (cotton), 2... Transparent electrode, 4 ... Spacer, 6... Spontaneous polarization, 8... Polarizer, 10... Light source, 12... Rubbing roller.

Claims (1)

[Claims] 1. In a method for manufacturing a ferroelectric liquid crystal display element in which a ferroelectric liquid crystal is sealed between a pair of opposing parallel substrates,
A method for manufacturing a ferroelectric liquid crystal display element, comprising the steps of forming an alignment film on each of the facing surfaces of the facing substrates, and rubbing the film using a roller whose surface material is cotton.