JPH063677A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To achieve, a uniform liquid crystal orientation over a large area and establish a good electrooptical responsiveness by using a cyano-substitute polymer of specific cellulose base as a molecule orientation film. CONSTITUTION:Cyano-substitute of a resin based on cellulose given by formula I or II is used as a molecule orientation film. In formulas, R represents CpH2p+1 CN (p is integer 1-17) while (n) and (m) represent degree of polymerization, preferably being an integer between 100-10000. To form a film from a resin to which cellulose-based cyano-radical is introduced, the cyano-resin CR-C of Shinestu Chemical Co. make is dissolved in gamma-butylolactone in a concentration of 1wt.%. The dissolution is performed by heating to 60 deg.C and agitating approx. for 3hr using a magnetic stirrer in the N2 atmosphere. The solution obtained is cooled to room temp. and applied to a base board by a spin coater, wherein no filtrating process takes place. The spin coating is made in the N2 atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a surface-stabilized ferroelectric liquid crystal device.

[0002]

2. Description of the Related Art With the progress of office automation, word processors, personal computers, etc. have become widespread. Since such equipment is mainly a personal equipment and a small scale is generally demanded, a small liquid crystal display (LCD) is exclusively used as the display device.

Currently, the most widely used LCD drive mode is Super Twisted Nematic (ST).
N) method, and this method enables a relatively large capacity display with a simple panel configuration (simple matrix panel), which is mainly advantageous in terms of cost, and the selling price is set to a relatively low price. It is often used for personal computers.

However, the above STN system has the following problems. That is, (1) the viewing angle is narrow (up and down with respect to the panel normal direction, ± 30 ° in the horizontal direction). (2) The contrast ratio is low (about 640 × 400 dots 8: 1). (3) The screen is dark (the light transmittance of the panel is low). (4) Coloring occurs in the basic drive mode (with optical rotation dispersion). (5) The response speed of the liquid crystal is slow (difficult for mouse).

Therefore, as a liquid crystal driving mode for overcoming the above-mentioned drawbacks of STN and realizing a display of higher image quality, a ferroelectric liquid crystal display, particularly a ferroelectric liquid crystal display by surface stabilization ( SSFLCD) system is attracting attention,
Has been actively studied. However, although this SSFLCD method is an excellent method in terms of potential, it is still in a situation where large technical problems must be overcome before its practical application.

[0006]

The problems required to put the above SSFLCD system into practical use are as follows. (1) Optimization of liquid crystal layer structure (from chevron layer structure to bookshelf layer structure). (2) Establishment of large area uniform alignment treatment technology. (3) Establishment of manufacturing technology for narrow panel gap cells.

Among the problems (1) to (3), the problem (1) can be solved by using the naphthalene type liquid crystal composition developed by the present inventors (A. Mochi).
zuki, et al., Proceedings of the SID vol.31, No. 2,
123-128 (1990)). The problem (3) is gradually improved by maintaining a clean room and developing a spacer agent having a good particle size distribution. On the other hand, there is still no drastic solution for the large area uniform alignment treatment technology of the problem (2). Therefore, it is strongly desired to establish an alignment treatment technique capable of uniformly aligning a large area of the ferroelectric liquid crystal.

Therefore, it is an object of the present invention to provide a ferroelectric liquid crystal display device excellent in alignment and electro-optical characteristics, and a liquid crystal molecule alignment film and a resin film used therein.

[0009]

According to the present invention, there is provided a liquid crystal display device having a molecular alignment film of a cyano substitution product of a cellulose-based resin represented by the following structure (I) or (II). It

[0010]

[Chemical 3]

[0011]

[Chemical 4]

(In the formulas (I) and (II), R is C _p H
_{2p + 1} CN (where p is an integer of 1 to 17), and n
And m each represent a degree of polymerization, preferably 100 to 100
It is an integer of 00. )

The reason why the ferroelectric liquid crystal is difficult to be uniformly aligned as compared with the conventional nematic liquid crystal is (1)
The liquid crystal has a layered structure, and (2) the liquid crystal has spontaneous polarization. In particular, the spontaneous polarizability (2) is considered to make alignment difficult because the interaction between the liquid crystal molecules and the alignment film at the interface between the electric energy is strong.

In view of these problems, it has been attempted to use a polymer film having a high dielectric constant (polymer rubbing film) as an alignment film to neutralize electric interactions to some extent and obtain good alignment. Yes, with some success. For example, it is known that nylon, which is a polyamide, polyvinyl alcohol (PVA) having a high degree of saponification, polyimide having a large polarity, or the like, can provide relatively good uniform orientation. However, nylon and PVA have low heat resistance, and there is a problem in that the applied heat during liquid crystal panel production causes a decrease in orientation.

On the other hand, polyimide has sufficient heat resistance, but has a large polarity, and therefore, a solvent having a high hygroscopic property such as N-methylpyrrolidone is generally used as the imide coating solution (solution for transfer printing or spin coating). Since there is no choice but to use it, water easily mixes in the coating film, which causes a serious change in film quality.

Therefore, it is necessary to develop a resin orientation film which has heat resistance as high as that of polyimide and has a large coating production margin. Particularly, on the premise that a large-area panel is mass-produced, at present, it is considered that the oriented coating cloth by transfer printing has the highest throughput. However, PVA (solvent: water)
Generally, only low boiling point solvents can be used for nylon and nylon (solvent: toluene, etc.), so it is extremely difficult to process a uniform alignment film by transfer printing. Therefore, the throughput in mass production is high and a large area uniform alignment is possible. It is considered that the molecular alignment film needs to satisfy at least the following conditions.

(1) High heat resistance (> 200 ° C) (2) High boiling point solvent can be used (3) High relative permittivity of film

As a result of studying a polymer which actually satisfies such conditions, the present inventors have found that the above-mentioned conditions are satisfied by the above-mentioned cellulose-based cyanoresin of the structural formula (I) or (II). It was As described above, a water-soluble polymer such as PVA or cellulose is originally a polymer having a large polarity because it is soluble in water which is a polar solvent. It is considered that this large polarity generally contributes to the molecular orientation of the ferroelectric liquid crystal having large polarization, especially spontaneous polarization. However, when a solvent such as water is used, the boiling point is low, and the so-called “wettability” is poor in terms of matching the surface energy with the glass substrate.
It is extremely difficult to form a thin film of 00 to 800 angstrom uniformly.

Therefore, a polymer having a large polarity, which can be formed into a film by using a solvent having a high boiling point and a good wettability, is required. As a result of various studies as such a polymer, the above formula (I) or (II) The inventors have found that the resin having a cyano group introduced satisfies the above conditions and have completed the present invention.

The polymers of formulas (I) and (II) above are:
It can be produced by a known method, for example, cyanoresin CR-C, CR-S, CR from Shin-Etsu Chemical Co., Ltd.
Commercially available as -V.

[0021]

INDUSTRIAL APPLICABILITY In the present invention, for example, as will be described in the following examples, in a ferroelectric liquid crystal display device, by using the above-mentioned cellulose-based cyano-substituted polymer as a molecular alignment film, Can be achieved over a large area, and good electro-optical response characteristics can be obtained.

[0022]

EXAMPLES The present invention will be described in more detail below with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

A glass substrate provided with a transparent conductive film (ITO) having a size of 50 × 60 × 1.1 (thickness) mm is washed with an alkaline detergent, rinsed and dried, and then, the following method is applied. A cellulose-based cyano group-introduced resin was formed into a film.

That is, cyanoresin CR manufactured by Shin-Etsu Chemical Co., Ltd.
-C was dissolved in a concentration of 1 wt% γ-butyrolactone solvent. This dissolution was performed by heating to 60 ° C. and stirring using a magnetic stirrer under N ₂ atmosphere for about 3 hours.
After that, the obtained solution was cooled to room temperature and coated on a substrate by a spin coater without filtering. This spin coating is 500rpm × 5s and 2,500rpm × 45s
At a relative humidity of 20% or less in an N ₂ atmosphere. After coating, it was pre-cured at a temperature of 90 ° C. for 10 minutes and then cured in N ₂ at 220 ° C. for 1 hour.

After cooling to room temperature, rubbing twice with a nylon cloth, and then rubbing directions opposite to each other (antiparallel rubbing), two substrates were put together, and a silica ball having a diameter of 1.6 μm was used as a spacer. A cell was prepared as A mixed liquid crystal composition (A. Mochizuki, et al Ferro) containing 30% by weight of a naphthalene liquid crystal having the following structure in each cell
Electrics Vol. 113, pp. 353-359 (see 1991) was injected to obtain SSFLCD.

[0026]

[Chemical 5]

In the same process as above, only the alignment film is CR-C.
Instead of CR-S, PVA, nylon 66 and polyimide (RN-713, manufactured by Nissan Kagaku Co., Ltd.), various liquid crystal cells were prepared by the same operation. For these liquid crystal cells, their orientation and electro-optical properties were evaluated. The evaluation contents and items are as follows. (1) Orientation observation by polarization microscope (2) Optical response time by pulse wave application (3) Memory property evaluation (contrast ratio evaluation) (4) Polarization reversal current measurement by triangular wave application (5) Change in orientation state with temperature change The evaluation results are shown below.

(1) Alignment Observation Table with Polarizing Microscope 1 ─────────────────────────────── Alignment film resin Alignment state ─ ───────────────────────────── CR-C Almost uniform domain, no significant defects CR-S ¹⁾ Almost homogeneous domain, very few Lines in PVA Almost uniform domain, no significant defects Nylon 66 Some linear defects RN-713 (PI) Zigzag defects Some ───────────────────── ────────── 1) CR-S is a cyano substitution resin manufactured by Shin-Etsu Chemical Co., Ltd., which is of the same system as CR-C, and 1.5% by weight of 1,6-diisocyanatehexane is used as a cross-linking agent during film formation. Was added to the resin solution.

(2) Optical response and pulse response due to pulse application
Mori of Table 2 ──────────────────────────────── alignment layer response time ^{1) (μs)} Memory properties contrast ratio ─ ─────────────────────────────── CR-C 44.5 Very good 42.1 CR-S 48.3 Very good 40.6 PVA 48.5 Very good 38.8 Nylon 66 49.1 Good 33.0 RN- 713 (PI) 65.5 Low 12.5 ───────────────────────────────── 1) 25 ℃ , Time required for 10-90% optical change when 15V pulse is applied.

(3) Measurement of polarization reversal current by applying triangular wave
Constant general polarization inversion at the time as an electric field is applied molecular orientation of the liquid crystal is uniform occurs smoothly. Therefore, the time required for the angular process of the polarization reversal peak current when the triangular wave shown in FIG. 1 is applied is shortened. Table 3 shows the results obtained by comparing the time required for each process of polarization reversal in FIG. 1 for each alignment film.

Table 3 ──────────────────────────────── Alignment film tw (μs) t ₅ (μs) tr ( μs) tp (μs) ──────────────────────────────── CR-C 40.2 66.5 39.8 150.0 CR-S 42.3 69.1 40.1 150.0 PVA 42.5 69.5 40.8 155.5 Nylon 66 43.8 78.7 55.5 165.0 RN- 713 (PI) 59.9 100.1 90.1 197.2 ──────────────────────────── ─────

From the results shown in Table 3, the values of CR-C and CR-S are smaller than those of the other comparative examples at each time, and it is clear that the polarization is smoothly inverted.

(4) Temperature Dependence of Alignment The liquid crystal composition used for evaluation of the alignment film is Sc ^* (ferroelectric phase)
→ The phase transition temperature (Tc) of SA (smectic A phase) is about 50 ° C, but it is generally known that a cell in which the liquid crystal molecular orientation is firm maintains a good orientation up to around Tc. . Table 4 compares the change in the state of liquid crystal molecule alignment with respect to the change in temperature.

Table 4 ──────────────────────────── Alignment film 25 ℃ (room temperature) 35 ℃ 45 ℃ ─────── ────────────────────── CR-C Uniform Uniform Uniform CR-S Uniform Uniform Uniform PVA Uniform Uniform Almost Uniform Nylon 66 Uniform Uniform Almost Uniform RN- 713 (PI ) Almost uniform Many defects Many defects ─────────────────────────────

As is clear from the results shown in Table 4, the temperature dependence of the orientation is similar to the other evaluation results, and the orientation films of CR-C and CR-S are uniformly oriented up to near Tc, and the molecular orientation Is good.

As is clear from the above evaluation results, the cyano group-substituted resin gives the ferroelectric liquid crystal good molecular orientation,
Furthermore, γ-butyrolactone, N-methylpyrrolidone,
Since a high boiling point solvent such as butyl cellosolve can be used, it is easy to form a large-area uniform alignment film by transfer printing.

In this example, a cellulose-based resin was used, but this is because the cyano-substituted resin has a significantly higher relative dielectric constant than conventional resins as shown in the table below.

[0038]

The most basic physical property that gives good orientation to the ferroelectric liquid crystal is that the relative dielectric constant of the film is high to some extent, and if a high boiling point solvent can be applied to other resins, the same effect can be obtained. Is expected.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between time and current in each tracking of a polarization antipole by applying a triangular wave in an example.

Claims (3)

[Claims] 1. A liquid crystal display device comprising a cellulose-based resin represented by the following structure (I) or (II) having a cyano substituent as a molecular alignment film. [Chemical 1] [Chemical 2] (However, in the formula (I) and (II), R is C _p H _{2p +} 1 C
N (in the formula, p is an integer of 1 to 17), n and m
Each represents an integer of 100 to 10,000. ) 2. A liquid crystal molecular alignment film comprising a resin represented by the structure (I) or (II) according to claim 1 and having a relative dielectric constant of 12 or more. 3. A resin film for a liquid crystal molecule alignment film of a surface-stabilized ferroelectric liquid crystal device, comprising the resin represented by the structure (I) or (II) according to claim 1.