JP2732765B2 - Ferroelectric liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device using a ferroelectric liquid crystal composition.

[0002]

2. Description of the Related Art
The most widely used liquid crystal display device utilizes a nematic phase of liquid crystal. However, in a twisted nematic (TN) type liquid crystal display device, since the contrast decreases with an increase in the number of lines, it is 2,000 × 2000.
It is difficult to make a large-capacity display element such as a line. In order to improve the TN type liquid crystal display element, a super twisted nematic (STN) type liquid crystal display element and a double super twisted nematic (DSTN) type liquid crystal display element have been developed. At the moment,
The display capacity of about 800 x 1024 lines is the limit.

A thin film transistor (TF) is formed on a substrate.
An active matrix type liquid crystal display device in which T) is arranged has also been developed, and a large-capacity display such as 1000 × 1000 lines has become possible. However, it has disadvantages such as a long manufacturing process, a reduction in yield, and an extremely high manufacturing cost. In recent years, various display modes using a smectic phase in addition to the liquid crystal display element using the nematic phase have been actively studied, and in particular, a ferroelectric liquid crystal display element is expected to be promising. Such a display element is disclosed, for example, in N. A. Clark, et a
l.), Appl. Phys. Lett., 36 , 899 (1980). This display method uses a ferroelectric liquid crystal, such as a chiral smectic C phase and a chiral smectic I phase, and uses a memory property. Therefore, the display capacity can be increased with an increase in response speed. It is possible. Further, since no active element such as a thin film transistor is required, the manufacturing cost is not increased. Further, the above-mentioned ferroelectric liquid crystal element also has an advantage of a wide viewing angle, and is greatly expected as a liquid crystal element for large-capacity display such as 2000 × 2000 lines.

There are various problems to be solved in order to put a ferroelectric liquid crystal display into practical use. Above all, it is very important to find a technique for achieving high contrast in simple matrix driving. To address this problem, a method of obliquely depositing an alignment film, a method of using a high pretilt alignment film, a method of applying an AC electric field, a method of using a naphthalene-based compound,
Methods using a uniform alignment and a method using a liquid crystal material having negative dielectric anisotropy have been proposed.

The "method for obliquely depositing an alignment film" is a method proposed by Uemura et al., T. Uemura et al., Proc. SID, 175 (1987). , Mass production and large area are difficult. "Method using high pretilt alignment film" is described in Yamamoto et al. N. Yamamoto et al., Jp.
Although this is a method proposed by nJAppl. Phys., 28 , 524 (1989), it is not easy to form a large area and uniform alignment using a high pretilt alignment film.

The “method of performing an AC electric field application process” is as follows.
Sato et al., Y.Sato et al., Jpn.J. Appl.Phys., 28 , L483 (198
9) and H. Rieger et al., Proc. SID, 396 (199
0), which applies a low-frequency, high-voltage AC electric field to a normal ferroelectric liquid crystal cell to forcibly change the chevron layer structure in the cell to a near ideal pseudo-bookshelf layer structure. It is to let. This method has advantages such as easy high contrast and wide memory angle and bright display.However, on the other hand, there are still problems in practical use such as a decrease in response speed and a change in characteristics during driving with time. ing.

"Method using a naphthalene compound"
Mochizuki et al., Ferroelectrics., 122 ,
37 (1991). It has been reported that by using a specific naphthalene-based compound, a pseudo bookshelf layer structure close to ideal could be obtained and high contrast was realized. However, since the compounds that can be used are extremely limited, it is expected to be extremely difficult to realize a practical large-screen large-display-capacity ferroelectric liquid crystal display using this technique.

[0008] "C1-Method Using Uniform Alignment" is described by Mukaiden et al. [Mukoden, "Next-Generation Liquid Crystal Materials: Ferroelectric Liquid Crystals and Antiferroelectric Liquid Crystals" (Supervised by Atsuo Fukuda), pp114 (1992)
A high contrast is obtained by utilizing a specific alignment state of C1-uniform obtained in a parallel rubbing liquid crystal cell using a high pretilt alignment film. However, in this method, it is difficult to selectively form a C1-uniform orientation in a large area.

On the other hand, the “method using a liquid crystal material having negative dielectric anisotropy” is described in Surguy et al., PWHSurguy et al.
L., Ferroelectrics., 122 , 63 (1991)), which is a promising method for realizing high contrast, and is a promising method for PWRoss, Proc. SID, 217 (199).
2) discloses a ferroelectric liquid crystal display using this technique. Hereinafter, the ferroelectric liquid crystal display will be described in detail.

An ordinary ferroelectric liquid crystal composition having a non-negative dielectric anisotropy exhibits a τ-V characteristic as shown in FIG. That is, as the voltage increases, τ (pulse width required for memory) monotonously decreases. On the other hand, in the case of a ferroelectric liquid crystal composition having a negative dielectric anisotropy, a τ-V characteristic showing a minimum value (τ-V _min ) as shown in FIG. 9B is obtained. Surguy et al. Report the driving method shown in FIG. 10 as a driving method using the τ-V characteristic. In the figure, one waveform is a column waveform, two waveforms are a vertical waveform, and three waveforms are a result waveform. Fig. 1 shows the principle of this driving method.
Briefly shown in FIG. This driving method is, | V _s -V _d | of the voltage is switched to the memory state of the ferroelectric liquid crystal device when applying a is the voltage higher than the voltage | V _s + V _d | time was applied and the voltage When a lower | V _d | is applied, switching is not performed.

However, a major problem with this method is that the driving voltage is high. Ross et al. PWRoss, Proc.SID, 217 (1
According to the report of 992), the drive voltage of the prototype ferroelectric liquid crystal display is 55V. Since the price of an IC driver for driving a ferroelectric liquid crystal display increases as the voltage increases, a high drive voltage is a major factor in increasing costs. In order to manufacture a ferroelectric liquid crystal display with a reduced price, it is necessary to drive the display using a general-purpose IC driver that is not so expensive, and for this purpose, it is necessary to reduce the drive voltage to at least 40 V or less. is there. The reason for requiring a high drive voltage at this time is that τ−V
This is because the voltage value (V _min ) in the characteristics is high,
In order to drive the following it is necessary to develop a ferroelectric liquid crystal composition showing a V _min around 30 V.

According to Surguy et al., V _min is obtained by the following equation. V _min = E _min · d = Ps · d / (√3 · ε ₀ · Δε · sin 2θ) where E _min is the minimum value of the electric field strength, d is the cell thickness, Ps is spontaneous polarization, and Δε is the dielectric constant difference. Anisotropy, θ is the tilt angle. As can be seen from this equation, obtaining a low value of V _min requires a large negative dielectric anisotropy and a small spontaneous polarization. On the other hand, since the response speed of the ferroelectric liquid crystal is related to spontaneous polarization, it is difficult to obtain a high-speed response when the spontaneous polarization is reduced. Therefore, a low-viscosity material having negative dielectric anisotropy is required as a liquid crystal material. Of course, in order to obtain a good ferroelectric liquid crystal display element, the following four conditions which have been conventionally known must be satisfied. The conditions are as follows: in order to exhibit a smectic C phase over a wide temperature range around room temperature, and to obtain good alignment and phase stability, the liquid crystal material must have an IAC (Isotropic-
Smectic A-Smectic C) or INAC (Isotropic-Nem
atic-Smectic A-SmecticC), that the helical pitch of the nematic phase and the smectic C phase is sufficiently longer than the cell thickness, and that they have good chemical stability and light stability. Further, the tilt angle, the refractive index, the specific resistance and the like can be optimized as needed.

Various compounds are known as ferroelectric liquid crystal compounds used in ferroelectric liquid crystal display devices. For example, a phenylnaphthalene compound having fluorine at a position adjacent to a benzene ring is known (Japanese Patent Application Laid-Open No. 4-504571).
The present invention has been made under the above-mentioned conditions, and provides a ferroelectric liquid crystal display device using a ferroelectric liquid crystal composition exhibiting a low _Vmin value.

[0014]

According to the present invention, an electrode is formed on each of a pair of insulating substrates, and an alignment film is formed thereon. It is arranged so as to face each other, a ferroelectric liquid crystal is interposed therebetween, at least one of the electrodes is arranged in a direction intersecting a plurality of scanning electrodes and a plurality of signal electrodes for constituting a pixel, and the scanning electrode and A ferroelectric liquid crystal display device comprising: an application / drive means for selectively applying a voltage to a signal electrode to switch an optical axis of the ferroelectric liquid crystal; and a means for optically identifying switching of the optical axis. Wherein the ferroelectric liquid crystal composition has the general formula (I)

[0015]

Embedded image (Wherein R ¹ and R ² are the same or different and have 1 to 1 carbon atoms)
5 is a straight or branched alkyl group or the same or
Is a linear or branched chain having 1 to 15 carbon atoms
It is a lucoxy group. ) Less fluorine compound
And has a negative dielectric anisotropy.
Provided is a ferroelectric liquid crystal display device. Furthermore, the present invention
According to the method, electrodes are formed on each of a pair of insulating substrates.
And an alignment film is formed on it to form a pair of insulating
Substrates are arranged to face each other, and ferroelectric liquid crystal
And at least one of the electrodes constitutes a pixel
Multiple scanning electrodes and multiple signal electrodes to intersect each other
The scanning electrodes and the signal electrodes.
And a switch for switching the optical axis of the ferroelectric liquid crystal.
Means for optically discriminating switching between the drive / drive means and the optical axis
A ferroelectric liquid crystal display device comprising :
The liquid crystal composition has the general formula (I)

Embedded image (Wherein R ¹ and R ² are the same or different and have 1 to 1 carbon atoms)
A straight-chain or branched alkyl group having 5 or a straight-chain or branched alkoxy group having the same or different and having 1 to 15 carbon atoms. At least one and represented by general formula fluorine compound) (II)

[0016]

Embedded image (Wherein R ³ and R ⁴ are the same or different and each have 1 to 1 carbon atoms)
A straight-chain or branched alkyl group having 5 or a straight-chain or branched alkoxy group having the same or different and having 1 to 15 carbon atoms. The present invention provides a ferroelectric liquid crystal display device containing at least one fluorine compound represented by the formula (1) and having a negative dielectric anisotropy.

The general formulas (I) and (II) have two fluorine groups in a direction perpendicular to the molecular long axis, and the two fluorine groups are bonded to the same phenyl ring. Large negative dielectric anisotropy can be expected. Further, since it does not have a high-viscosity substituent such as an ester, low viscosity can be expected. In addition, by appropriately selecting R ¹ , R ² , R ³ and R ⁴ , the smectic C phase can be stably expressed. Further, by combining the compound of the general formula (I) and the compound of the general formula (II), a liquid crystal composition containing the compound of the general formula (I) or the compound of the general formula (II) alone is used. , The temperature range, phase series, orientation, and the like of the smectic C phase can be improved.

Examples of the same or different linear or branched alkyl groups having 1 to 15 carbon atoms which can be used for R ¹ , R ² , R ³ and R ⁴ include methyl, ethyl, propyl, butyl, pentyl, Hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, 1-methylpropyl, 1-methylbutyl, 1-methylpentyl, 1-methylhexyl, 1-methyloctyl, 1-methylnonyl, 1- Methyldecyl, 1-methylundecyl, 1-methyldodecyl, 1-methyltridecyl, 1-methyltetradecyl,
4-methylpentyl, 5-methylhexyl, 6-methylheptyl, 7-methyloctyl, 8-methylnonyl, 9
-Methyldecyl, 10-methylundecyl, 11-methyldodecyl, 12-methyltridecyl, 13-methyltetradecyl, 3-ethylpentyl, 4-ethylhexyl, 5-ethylheptyl, 6-ethyloctyl, 7-ethylnonyl, 8 -Ethyldecyl, 9-ethylundecyl, 10-ethyldodecyl, 11-ethyltridecyl and the like.

The same or different linear or branched alkoxy groups having 1 to 15 carbon atoms include methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, Decyloxy, undecyloxy,
Dodecyloxy, tridecyloxy, tetradecyloxy, pentadecyloxy, 1-methylpropoxy, 1-
Methylbutoxy, 1-methylpentyloxy, 1-methylhexyloxy, 1-methylheptyloxy, 1-methyloctyloxy, 1-methylnonyloxy, 1-methyldecyloxy, 1-methylundecyloxy, 1-
Methyl dodecyloxy, 1-methyltridecyloxy,
1-methyltetradecyloxy, 4-methylpentyloxy, 5-methylhexyloxy, 6-methylheptyloxy, 7-methyloctyloxy, 8-methylnonyloxy, 9-methyldecyloxy, 10-methylundecyloxy, 11-methyldodecyloxy, 12-methyltridecyloxy, 13-methyltetradecyloxy, 3-ethylpentyloxy, 4-ethylhexyloxy, 5-
Ethylheptyloxy, 6-ethyloctyloxy, 7
-Ethylnonyloxy, 8-ethyldecyloxy, 9-
Ethylundecyloxy, 10-ethyldodecyloxy,
11-ethyltridecyloxy and the like.

Among these, as a combination of R ¹ and R ² , when R ¹ is a hexyl, heptyl, octyl, nonyl, decyl, hexyloxy, heptyloxy, octyloxy, nonyloxy or decyloxy group, R ² is hexyl. , Heptyl, octyl, nonyl, decyl, hexyloxy, heptyloxy, octyloxy, nonyloxy or decyloxy group. It is preferable to use these compounds in combination of several kinds.

The combination of R ³ and R ⁴ is as follows:
When R ³ is a hexyl, heptyl, octyl, nonyl, decyl, hexyloxy, heptyloxy, octyloxy, nonyloxy or decyloxy group, R ⁴ is hexyl, heptyl, octyl, nonyl, decyl, hexyloxy, heptyloxy, octyl. An oxy, nonyloxy or decyloxy group is preferred. It is preferable to use these compounds in combination of several kinds.

In the ferroelectric liquid crystal composition of the present invention, when the amount of the compound of the general formula (I) is more than 80% by weight, the added compound crystallizes in the liquid crystal composition for practical use. Problems often arise. Therefore, the general formula (I)
The compound is suitably added in an amount of 5 to 80% by weight, and 10 to 50% by weight.
% By weight is particularly preferred. When the amount of the compound represented by the general formula (II) is more than 80% by weight, practical problems such as crystallization of the added compound in the liquid crystal composition and the inability to obtain an INAC phase series occur. Often. Therefore, the addition amount of the compound of the general formula (II) is suitably from 5 to 80% by weight, and particularly preferably from 10 to 50% by weight.

The compound of the general formula (I) and the compound of the general formula (I
The compounding ratio with the compound of I) is generally 9.5: 0.5 to 6:
4, preferably from 8: 2 to 7: 3. Here, examples of the method of synthesizing the compounds of the general formulas (I) and (II) are shown below. The compounds of the general formulas (I) and (II) can be obtained, for example, according to the method described in JP-A-4-504571.

First, the method for synthesizing the compound of the general formula (I) is as follows. The case where R ¹ is hexyloxy and R ² is octyl will be described as an example. First, a solution of 1-bromohexane dissolved in 3-pentanone is added dropwise to a stirred refluxing mixture of 6-bromo-2-naphthol and potassium carbonate in 3-pentanone. The stirred mixture is heated under reflux for 24 hours. The potassium carbonate is filtered off, water is added to the filtrate and the product is extracted with ether. Washing the ether extract with water, 5% aqueous sodium hydroxide and water,
Dry over sodium sulfate. After removing sodium sulfate by filtration, the residue obtained by evaporating the solvent is purified by column chromatography (silica gel / hexane), and recrystallized with methanol to obtain 2-bromo-6-hexyloxynaphthalene. . Next, 2-bromo-6-hexyloxynaphthalene was dissolved in ethanol, and the solution was dissolved in a benzene solution of 2,3-difluoro-4-octylphenylborate and tetrakis (triphenylphosphine) palladium and a 2M aqueous solution of sodium carbonate. The mixture is added dropwise to the stirred mixture at room temperature under an argon gas atmosphere. The stirred mixture is heated under reflux for 20 hours. The product is extracted with ether, and the ether extract is washed with brine and dried over sodium sulfate. The sodium sulfate was removed by filtration, the solvent was distilled off, and the residue obtained was purified by column chromatography (silica gel / hexane-ethyl acetate = 40: 1), and recrystallized with ethanol, whereby R ¹ was hexyloxyl. , R ² is octyl.

[0025]

Embedded image

Next, the synthesis method of the compound of the general formula (II) is as follows. The case where R ³ is octyl and R ⁴ is decyloxy will be described as an example. 1-bromo-4- (tra
ns-4'-octylcyclohexyl) benzene was dissolved in ethanol, and the resulting solution was stirred and mixed with a benzene solution of 2,3-difluoro-4-decyloxyphenylborate and tetrakis (triphenylphosphine) palladium and a 2M aqueous solution of sodium carbonate. The solution is added dropwise at room temperature under an argon gas atmosphere. The stirred mixture is refluxed.
Heat for 20 hours. The product is extracted with ether, and the ether extract is washed with brine and dried over sodium sulfate. The sodium sulfate was removed by filtration, and the residue obtained by evaporating the solvent was subjected to column chromatography (silica gel / hexane-hexane).
The compound of the general formula (II) in which R ³ is octyl and R ⁴ is decyloxy can be obtained by purifying with ethyl acetate = 40: 1) and recrystallizing with ethanol.

[0027]

Embedded image The liquid crystal composition of the present application may contain a component compound other than the compound of the general formula (I) and / or the general formula (II). In order for the liquid crystal composition to exhibit ferroelectric liquid crystal, it is necessary that the liquid crystal composition exhibit optical activity, and for that, at least one component in the composition must be an optically active compound. Therefore, when the compound of the general formula (I) and / or the compound of the general formula (II) does not show optical activity, an optical component other than the compound of the general formula (I) and / or the general formula (II) is contained in the composition. It is necessary to add at least one active compound. As the optically active compound, for example,

[0028]

Embedded image (Wherein R ⁵ and R ⁶ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ),

[0029]

Embedded image (Wherein R ⁷ and R ⁸ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ),

[0030]

Embedded image (Wherein R ⁹ and R ¹⁰ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ),

[0031]

Embedded image (Wherein R ¹¹ and R ¹² are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ), And the like.

When the optically active compound is added, it is suitably added in an amount of 0.5 to 5% by weight, and 0.5 to 3% by weight.
Is particularly preferred. Further, in the liquid crystal composition, the compound represented by the general formula (I)
And / or as a compound that may be contained as a component other than the compound of the general formula (II) and the optically active compound as described above, for example,

[0033]

Embedded image (Wherein R ¹³ and R ¹⁴ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ),

[0034]

Embedded image (Wherein R ¹⁵ and R ¹⁶ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ),

[0035]

Embedded image (Wherein, R ¹⁷ and R ¹⁸ are the same or different and each have 4 to 12 carbon atoms)
Or a straight-chain or branched-chain alkoxy group having the same or different and having 4 to 12 carbon atoms. ) And the like.

In order for the ferroelectric liquid crystal composition to exhibit a low _Vmin , it is necessary to reduce spontaneous polarization to some extent. Therefore, the spontaneous polarization is preferably 10 nC / cm ² or less. In order to obtain good alignment, it is preferable that the ferroelectric liquid crystal composition shows at least a nematic phase, a smectic A phase, and a smectic C phase. Next, the ferroelectric liquid crystal display device of the present invention will be described with reference to FIG.

FIG. 1 is a sectional view of a liquid crystal display device using the ferroelectric liquid crystal composition of the present invention, and is an example of a transmission type display device. In the figure, 1 and 2 are insulating substrates, 3 and 4 are conductive films, 5 is an insulating film, 6 is an alignment film (alignment control layer), 7 is a sealant, 8 is ferroelectric liquid crystal, and 9 is polarized light. Show the board. As the insulating substrates 1 and 2, a light-transmitting substrate is used, and a glass substrate is usually used. On this insulating substrate, for example, InO ₃ , SnO ₂ , ITO (Indium-Tin Oxide)
The transparent electrodes 3 and 4 having a predetermined pattern made of a conductive thin film such as the above are formed. This is known as CVD (Chemical Vapor D)
eposition) method or a sputtering method. The thickness of the conductive thin film is preferably 50 to 200 nm.

An insulating film 5 having a thickness of 50 to 200 nm is formed on the transparent electrode. For example, Si
Inorganic thin films such as O ₂ , SiN _x , and Al ₂ O ₃ , and organic thin films such as polyimide, photoresist resin, and polymer liquid crystal can be used. When the insulating film is an inorganic thin film, it can be formed by an evaporation method, a sputtering method, a CVD method, a solution coating method, or the like. In the case where the insulating film is an organic thin film, a solution in which an organic substance is dissolved or a precursor solution thereof is applied by a spinner coating method, a dip coating method, a screen printing method, a roll printing method, etc. By curing under curing conditions (heating, light irradiation, etc.), or by vapor deposition, sputtering, CVD, LB (Langumuir-
(Blodgett) method or the like. However, this insulating film can be omitted.

On the insulating film 5, an alignment film (alignment control layer) 6 having a thickness of 10 to 100 nm is formed. However, when the insulating film is omitted, the alignment film is formed directly on the conductive films 3 and 4. As the alignment film 6, an inorganic or organic film can be used. Silicon oxide or the like can be used for the inorganic alignment film, and as a film forming method, for example, an oblique evaporation method, a rotary evaporation method, or the like can be used. Nylon, polyvinyl alcohol, polyimide, or the like can be used for the organic alignment film, and rubbing is usually performed thereon. Also, a polymer liquid crystal, an LB film, or the like can be used.
Orientation by a magnetic field, orientation by the spacer edge method, and the like are also possible. Furthermore, SiO ₂ , SiN
It is also possible to use a method in which _X or the like is formed by a vapor deposition method, a sputtering method, a CVD method, or the like, and rubbing is performed thereon. Thereafter, two insulating substrates are bonded together, and a liquid crystal composition is injected to manufacture a ferroelectric liquid crystal display device.

The above is the description of the switching element having one pixel based on FIG. 1.
The present invention is applicable to a large-capacity matrix display device. In this case, as shown in a schematic plan view of FIG. There are various methods for aligning a ferroelectric liquid crystal element, and the most realistic method is a rubbing method in consideration of mass production and the like. There are mainly three rubbing methods: parallel rubbing, anti-parallel rubbing, and single rubbing. Parallel rubbing is a rubbing method in which upper and lower substrates are rubbed, and the rubbing directions are parallel. Anti-parallel rubbing is a rubbing method in which upper and lower substrates are rubbed, and the rubbing directions are antiparallel. Single rubbing is a method of rubbing only one of the upper and lower substrates.

Among them, one-side rubbing has a drawback that it is difficult to form good uniform orientation. Because the ferroelectric liquid crystal composition exhibits optical activity, if the liquid crystal composition has a nematic phase on the high temperature side, the nematic phase necessarily has a helical structure, and the helical structure has a uniform orientation. This is because it inhibits. If the ferroelectric liquid crystal composition does not have a nematic phase on the high temperature side, this problem does not occur, but conversely, a smectic phase appears directly from the isotropic liquid state, and in this case also a good It is difficult to obtain a uniform orientation.

Next, the antiparallel rubbing has a disadvantage that a linear defect is likely to be generated along the rubbing direction, so that it is difficult to obtain a uniform orientation. Therefore, the preferred method for the alignment method in the present invention is a rubbing method, but the most preferable alignment method for obtaining uniform alignment is to combine a cell subjected to parallel rubbing with a ferroelectric liquid crystal composition having an INAC phase series. Is the way. In this case, a spiral structure exists in the nematic phase, but since the orientation direction of the molecules is regulated from both sides of the upper and lower substrates, uniform orientation is easily obtained in the nematic phase, and from that state, the smectic A phase and the chiral smectic C phase are changed. If the temperature is lowered, it is possible to easily obtain a uniform orientation in the direction of the layer normal.

However, even in the ferroelectric liquid crystal display device of the parallel rubbing, the alignment state generated in the chiral smectic C phase is not one. There are two causes of non-uniformity over the entire surface. One is related to the bending of the smectic phase. It is well known that a ferroelectric liquid crystal cell exhibits a bent layer structure (chevron layer structure), and there may be two regions as shown in FIG. Kobe et al. Named them C1 and C2 in relation to pretilt. In the figure, θ _p is a pretilt angle.

The other is a uniform (U) and a twist (T). The uniform is an orientation showing an extinction position, and the twist is an orientation showing no extinction position. Mukodono et al., In a parallel rubbing ferroelectric liquid crystal cell using a high pretilt alignment film, C1U (C1-uniform),
M. Koden et al., Jpn. JA reporting that three orientation states of C1T (C1-twist) and C2 were obtained.
ppl. Phys., 30 , L1823 (1991). As a result of further detailed investigation, the present inventors have found that there are four alignment states of C1U, C1T, C2U, and C2T in a parallel rubbing ferroelectric liquid crystal cell. FIG. 13 shows the molecular orientation in these orientation states.

A comparison of four alignment states obtained in a ferroelectric liquid crystal cell having negative dielectric anisotropy shows that:
Since C1T and C2T have no extinction position and the black state is not black, good contrast cannot be obtained. Further, the C1U orientation is difficult to switch, and even if it is switched, there is a disadvantage that the C2U state changes to an orientation in which the C2 state is mixed during driving. In contrast, the present inventors have found that good contrast is provided in the C2U state.

The appearance of the C1 and C2 orientations is related to the pretilt, but the C2 state can occur when the pretilt angle is in the range of 0 to 15 °. As Mukaidon and others report,
When the pretilt angle is high, the C2 state is preferable because there is only one state indicating the extinction position. However, C1 tends to be easier to take than C2 as the pretilt angle increases. In addition, the lower the pretilt angle, the lower the C2
However, if it is too low, the C2T state is likely to occur. Therefore, the most preferable range of the pretilt angle in the present invention is 5 to 10 °, whereby the C2U state can be obtained.

When the ferroelectric liquid crystal composition of the general formula (I) or the general formula (I) and the general formula (II) is used in the above-mentioned alignment method and pretilt angle, the alignment state of the ferroelectric liquid crystal is C2U. In this state, the orientation of the layer normal is uniform, and the direction of the bending of the smectic layer structure of the ferroelectric liquid crystal and the direction of the pretilt of the ferroelectric liquid crystal molecules at the interface between the ferroelectric liquid crystal and the alignment film are the same.

Next, the driving method will be described in detail. As a driving method of the present invention, a voltage that does not switch the optical axis to the scanning electrode and a voltage that switches the optical axis to the signal electrode are applied. Then, a voltage that does not switch the optical axis to the signal electrode and a voltage that switches the optical axis to the scanning electrode are applied. Is applied to the pixel formed by the intersection of the scanning electrode and the signal electrode, and the voltage in the region where the negative effect of the dielectric anisotropy acting on the ferroelectric liquid crystal molecules at a positive or negative high voltage of 40 V or less is large. A method of applying a voltage waveform consisting of two types of voltages in a region where the negative effect of the dielectric anisotropy acting on the ferroelectric liquid crystal molecules is small at a negative or positive low voltage corresponding to the voltage can be used. .

As a driving method that can be used in the present invention, the method shown in FIG. 10 can be used, and a more preferable driving method includes the method shown in FIG. This driving method is a driving method capable of partially rewriting, and is a preferable driving method for manufacturing a display having a large display capacity of 2000 × 2000 lines using this ferroelectric liquid crystal element. In this driving method, the waveform (1) is applied to the scanning electrode coupled to the pixel to be rewritten, and the waveform (2) is applied to the other scanning electrodes. As a waveform of the signal electrode, a waveform (3) is applied to a pixel to be rewritten, and a waveform (4) is applied to a pixel not to be rewritten. The voltage waveform applied to the pixel is (5)-
(8), waveforms when no rewriting is performed (6) to
When the voltage of (8) is applied, τ is equal and the amount of transmitted light is substantially equal, so that good display without flicker can be obtained.

[0050]

EXAMPLES Example 1 Compounds Nos. 1 to 7 represented by general formulas (I) and (II) were synthesized. The structures and transition temperatures of the compounds are shown in Tables 1 and 2.

[0051]

[Table 1]

[0052]

[Table 2] Example 2 Using the compounds shown in Tables 1 and 2, ferroelectric liquid crystal compositions No. 1 and No. 2 having the compositions shown in Table 3 were produced. Table 4 shows the transition temperatures of the manufactured ferroelectric liquid crystal compositions.

[0053]

[Table 3]

[0054]

[Table 4] Example 3 Using the ferroelectric liquid crystal compositions shown in Tables 3 and 5, Table 6 was used.
No. 3 to No. 7 of the ferroelectric liquid crystal composition shown in FIG. Table 7 shows the transition temperatures of the manufactured ferroelectric liquid crystal compositions.

[0055]

[Table 5]

[0056]

[Table 6]

[0057]

[Table 7] Example 4 An orientation film of PSI-A-2101 (manufactured by Chisso Corporation) with a thickness of 50 nm was applied on two glass substrates and rubbed. A cell thickness of 50 μm is applied to the two glass substrates so that the rubbing directions are antiparallel.
Nematic LCD E-8 (Merck)
Was injected. Magnetic field capacity method K. Suzuki, K. Toriyama and A.
PS by Fukuhara., Appl.Phys.Lett ,. 33 (1987) 561
When the pretilt angle of the IA-2101 alignment film was measured, it was 5 °
Met.

Example 5 A transparent electrode made of ITO (conductive thin film) having a thickness of 100 nm was formed on two glass substrates, and a Si electrode was formed on the transparent electrode.
A 120 nm-thick insulating film made of O ₂ was formed, and a PSI-A-2101 (manufactured by Chisso Corporation) alignment film was applied on the insulating film with a thickness of 50 nm and rubbed. Next, the two glass substrates were bonded with a cell thickness of 2 μm so that the rubbing directions were the same, and the ferroelectric liquid crystal composition prepared in Example 3 was injected. After the injection, the cell is once heated to a temperature at which the ferroelectric liquid crystal composition changes into an isotropic liquid, and then cooled to room temperature at 5 ° C./min to obtain a ferroelectric liquid crystal display device having good C2U orientation. Obtained.

This ferroelectric liquid crystal display device was placed between two orthogonal polarizers, a voltage was applied, and the characteristics were evaluated. Table 8 shows the evaluation conditions and the obtained characteristics. Further, the [tau] _-Vmin characteristics of this ferroelectric liquid crystal display element were evaluated, and the results are shown in FIGS. As can be seen from FIGS.
_min is obtained below 30V. In the obtained ferroelectric liquid crystal display device, the direction of the bending of the smectic phase structure of the ferroelectric liquid crystal composition was the same as the direction of the pretilt of the ferroelectric liquid crystal molecules at the interface between the ferroelectric liquid crystal and the alignment film. Was.

[0060]

[Table 8] Comparative Example 1 A transparent electrode made of ITO having a thickness of 100 nm was formed on two glass substrates, and a film made of SiO ₂ was formed on the transparent electrode.
A 120 nm insulating film is formed, and PSI-A-21 is formed on this insulating film.
An 01 (manufactured by Chisso) alignment film was applied to a thickness of 50 nm and rubbed. Next, the two glass substrates were stuck together at a cell thickness of 2 μm so that the rubbing directions were the same, and the ferroelectric liquid crystal compositions shown in Table 5 were respectively injected. After injection, the cell is heated to a temperature at which the ferroelectric liquid crystal composition changes to an isotropic liquid, and then cooled to room temperature at 5 ° C./min to obtain a ferroelectric liquid crystal display device having good alignment. Was.

The ferroelectric liquid crystal display device was placed between two orthogonal polarizers, a voltage was applied, and the characteristics were evaluated. Table 9 shows the evaluation conditions and the obtained characteristics. Further, the τ-V _min characteristics of this ferroelectric liquid crystal display device were evaluated, and the results are shown in FIG. As can be seen from FIG. 14, τ−V
_{Although min} characteristics were obtained, V _min was 30 V or more.

[0062]

[Table 9]

[0063]

According to the present invention, formula (I), or one
When the ferroelectric liquid crystal compositions of the general formulas (I) and (II) are used, the bending direction of the smectic layer structure of the ferroelectric liquid crystal and the ferroelectric liquid crystal molecules at the ferroelectric liquid crystal-alignment film interface It is possible to obtain a large-capacity ferroelectric liquid crystal display device having a high pre-tilt direction, a good orientation, a high contrast and a low driving voltage.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a ferroelectric liquid crystal device using the ferroelectric liquid crystal composition of the present invention.

FIG. 2 is a schematic view of a method for manufacturing a large-capacity ferroelectric liquid crystal display device.

FIG. 3 is a diagram showing driving waveforms for driving a ferroelectric liquid crystal display device.

FIG. 4 shows τ-V characteristics of the ferroelectric liquid crystal display device of the present invention.

FIG. 5 shows τ-V characteristics of the ferroelectric liquid crystal display device of the present invention.

FIG. 6 shows τ-V characteristics of the ferroelectric liquid crystal display device of the present invention.

FIG. 7 shows a τ-V characteristic of the ferroelectric liquid crystal display device of the present invention.

FIG. 8 shows τ-V characteristics of the ferroelectric liquid crystal display device of the present invention.

FIG. 9 is a diagram showing τ-V characteristics of a ferroelectric liquid crystal material.

FIG. 10 is a diagram showing driving waveforms for driving a ferroelectric liquid crystal display element.

11 is a diagram illustrating the principle of the driving method in FIG.

FIG. 12 is an explanatory diagram of a C1 orientation and a C2 orientation of a ferroelectric liquid crystal display element.

FIG. 13 is a molecular orientation model of an orientation state of a ferroelectric liquid crystal display device.

FIG. 14 shows τ-V characteristics of a conventional ferroelectric liquid crystal display device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 insulating substrate 3 conductive film 4 conductive film 5 insulating film 6 alignment film (alignment control layer) 7 sealant 8 ferroelectric liquid crystal 9 polarizing plate

Claims (7)

(57) [Claims] An electric circuit is provided on each of a pair of insulating substrates.
A pole is formed, an alignment film is formed thereon, and these pair
Insulating substrates are placed facing each other, and ferroelectric
With a liquid crystal interposed, at least one of the electrodes forms a pixel
A plurality of scanning electrodes and a plurality of signal electrodes
Arranged in a direction that intersects with
And switching the optical axis of the ferroelectric liquid crystal.
Optically distinguishes the switching between the application / driving means and the optical axis
Wherein the ferroelectric liquid crystal composition has a general formula (I) : (Wherein R ¹ and R ² are the same or different and have 1 to 1 carbon atoms)
5 is a straight or branched alkyl group or the same or
Is a linear or branched chain having 1 to 15 carbon atoms
It is a lucoxy group. ) Less fluorine compound
And has a negative dielectric anisotropy.
Ferroelectric liquid crystal display device. 2. An electrode is formed on each of a pair of insulating substrates, an alignment film is formed thereon, and the pair of insulating substrates is disposed so as to face each other. With a liquid crystal interposed, at least one of the electrodes is arranged with a plurality of scanning electrodes and a plurality of signal electrodes in a direction crossing each other to form a pixel, and selectively applies a voltage to the scanning electrodes and the signal electrodes, and A ferroelectric liquid crystal display device comprising an application / driving means for switching an optical axis of the ferroelectric liquid crystal and a means for optically identifying switching of the optical axis, wherein the ferroelectric liquid crystal composition has a general formula (I) (Wherein R ¹ and R ² are the same or different and have 1 to 1 carbon atoms)
A straight-chain or branched alkyl group having 5 or a straight-chain or branched alkoxy group having the same or different and having 1 to 15 carbon atoms. At least one and represented by general formula fluorine compound) (II) ## STR2 ## (Wherein R ³ and R ⁴ are the same or different and each have 1 to 1 carbon atoms)
A straight-chain or branched alkyl group having 5 or a straight-chain or branched alkoxy group having the same or different and having 1 to 15 carbon atoms. A ferroelectric liquid crystal display device comprising at least one fluorine compound represented by the formula (1) and having a negative dielectric anisotropy. 3. An application / driving means applies a voltage that does not switch the optical axis to the scanning electrode and a voltage that switches the optical axis to the signal electrode, and then applies a voltage that does not switch the optical axis to the signal electrode and an optical axis to the scanning electrode. Is applied to the pixel formed at the intersection of the scanning electrode and the signal electrode.
A voltage in a region where the negative effect is large on the ferroelectric liquid crystal molecules acting on the ferroelectric liquid crystal molecules at a positive or negative high voltage of V or less, and the ferroelectric liquid crystal molecules at a negative or positive low voltage corresponding to the voltage. A method for driving a ferroelectric liquid crystal display device, characterized by applying two kinds of voltage waveforms of a voltage in a region where a negative effect of dielectric anisotropy acting on the liquid crystal is small. 4. A ferroelectric liquid crystal composition, a ferroelectric liquid crystal display device according to claim 1 or 2 shows the 10 nC / cm ² or less spontaneous polarization. 5. A ferroelectric liquid crystal composition comprising at least a nematic phase, a smectic A phase and a smectic C.
Any one of claims 1, 2 or 4 consisting exhibit phase
Ferroelectric liquid crystal display device according to. 6. The ferroelectric liquid crystal display device according to claim 1 , wherein a pretilt angle at an interface between the ferroelectric liquid crystal and the alignment film is 10 ° or less. 7. A ferroelectric bending direction and the ferroelectric liquid crystal smectic layer structure of the liquid crystal - direction of pretilt of the ferroelectric liquid crystal molecules in the orientation film interface are the same claim 1, 2, 4, 5 or 7. The ferroelectric liquid crystal display device according to any one of 6 .