JPH05216003A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain safe and excellent electrooptical characteristics by incorporating specific compds. into the above liquid crystal compsn. and providing the compsn. with a diaferroelectric smectic phase in a wide temp. range including room temp. CONSTITUTION:This compsn. contains at least one kinds of the compds. expressed by formula and exhibits the diaferroelectric smectic phase in a room temp. region. In the formula, R1 denotes 1 to 30C alkyl group; R2 denotes 2 to 20C alkyl group; X1 denotes a bond group of any among -O-, -OCO-, -COO-, etc.; X2, X3 respectively independently denote a bond group of any among -OCO-, -COO-, -CH2O-, etc.; (k), (m), (n) respectively independently denote an integer from 0 to 1; (Z) denotes CF3 or CH3; A1, A2, respectively independently denote a group of a carbon 6-membered ring substd. with 0 to 2C nitrogen atom or a group, etc., in which 2 to 3 pieces of the carbon 6-membered homogeneous or heterogeneous thereof are combined directly or via the bond group of any among -COO-, -OCO-, etc., in a para position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition used for displays, light valves and the like, and more particularly to a novel liquid crystal composition having improved electro-optical characteristics.

[0002]

2. Description of the Related Art Switching between three states of an antiferroelectric liquid crystal is expected and active as one of methods for solving some of the essential problems found in the conventional surface stabilized ferroelectric liquid crystal (SSFLC). Is being researched. (ADLCh
andani et al .: Jpn. J. Appl. Phys., 27, L729 (198
8), ADLChandani et al .: Jpn. J. Appl. Phys., 2
8, L1265 (1988), etc. )

The main characteristics of the above-mentioned three-state switching are: (1) The antiferroelectric-ferroelectric phase transition by voltage application as shown in FIG. 4 has a sharp threshold characteristic with respect to a DC voltage. .. (2) Since the antiferroelectric-ferroelectric phase transition is accompanied by a wide optical hysteresis as shown in FIG. 4, if the bias voltage is applied after selecting the antiferroelectric phase or the ferroelectric phase, the selection can be made. It is possible to retain the state that was set. (3) The two orientation states in the electric field induced ferroelectric phase can be made optically equivalent. (4) Since it is possible to prevent the bias of charges in the liquid crystal, SS
There is no change over time in electro-optical characteristics as seen in FLC. Etc. If these characteristics are used, time-divisional driving can be performed in the simple matrix without limitation of the duty ratio.

The display principle using the antiferroelectric liquid crystal will be described with reference to FIG. As shown in FIG. 3A, the optical axis OA in the antiferroelectric phase is orthogonal to the smectic phase. Figure 3
A cell having a liquid crystal layer 6 sandwiched between two glass substrates 1 and 2 provided with transparent electrodes 4 and 5 and liquid crystal alignment films 9 and 10 as shown in FIG. , 12 so that the optical axis OA is parallel to any of the polarization axes, the element is in a light-shielded state (provisionally OFF). In this state, the absolute value of the applied voltage of the hysteresis characteristic of FIG.
Even if a voltage pulse of V (A−F) t | or less is applied, the change in light transmittance is slight and the OFF state can be maintained. On the other hand, when a voltage pulse whose absolute value is | V (A−F) s | or more is applied, the optical axes are OF (+) and OF as shown in FIG. 3A depending on the polarity of the pulse.
(−), The spontaneous polarization is transferred to the ferroelectric phase (+) and the ferroelectric phase (−) having Ps (+) and Ps (−). Since the optical axis forms an angle θ (+) or θ (−) with the polarization axis, the light transmission state (provisionally ON) is obtained. Since the angles θ (+) and θ (−) are equal, both can be treated as optically equivalent. The liquid crystal phase exhibiting such properties is 4- (1-methylheptylox).
^{ycarbonyl) phenyl 4, -octyloxybiphenyl-4} -carb
It was first discovered in oxylate (MHPOBC) and is called the antiferroelectric chiral smectic C phase (S _CA ^* phase). Examples of compounds and liquid crystal compositions that have already been reported include JP-A-1-213390.

[0005]

However, the above-mentioned conventional techniques have the following two problems. One is the issue of stability of the antiferroelectric phase state. It is generally said that it has a steep threshold characteristic with respect to DC voltage, and when a bias voltage of one polarity is applied after selecting the antiferroelectric phase state in multiplex drive, the antiferroelectric phase state becomes It is believed that it can be retained. However, even if an electric field whose absolute value is below the threshold value (| V (A−F) t | Is known to affect the light transmittance. (M.Jo
hno et al .: Jpn. J. Appl. Phys. 29. L107 (199
0)). This phenomenon is called a phase transition precursor phenomenon in the antiferroelectric phase-ferroelectric phase transition, which lowers the contrast ratio of the device and is not preferable from an application point of view.

Another problem is that the relaxation rate from the ferroelectric state to the antiferroelectric state is slower than the response rate in the reverse switching and that the relaxation rate has temperature dependence. Is. The slow relaxation time leads to a slow response speed as an electric characteristic of the liquid crystal display device and causes a screen flicker. According to the conventional technique, the scanning frequency has to be set low in accordance with the response characteristics of the liquid crystal material used, so that there is a problem in that the screen cannot be scrolled and the pointing device cannot be moved smoothly. The present invention is to solve the above problems, and an object thereof is to provide a liquid crystal composition and an electro-optical element which are stable and have excellent electro-optical characteristics.

[0007]

The present invention provides (1)

[Chemical 2] A liquid crystal composition containing at least one compound represented by the formula (1) and exhibiting an antiferroelectric smectic liquid crystal phase at room temperature.
However, in the formula, R ₁ is an alkyl group having 1 to 30 carbon atoms, R ₂ is an alkyl group having 2 to 20 carbon atoms, X ₁ is —O—, —OCO.
-, - COO -, - OCO 2 -, - CO- or a linking group, X _2, X ₃ are each independently --OCO -, -
_{COO -, - CH 2 O -} , - OCH 2 - or a linking group, k, m, n, are each independently an integer of 0 or 1, Z is CF ₃ or CH _3, A _1, A ₂ Each independently represents a 6-carbon carbon ring group substituted with 0 to 2 nitrogen atoms, or two or three of the same or different carbon 6-membered rings at the para-position, or -COO- , -OCO-, -CH
_{It is} a group linked via any one of ₂ O- and -OCH _2- , or a group in which a hydrogen atom in the ring of these groups is substituted with any of fluorine, a methyl group and an ethyl group. C ^*
Represents an optically active center.

In the liquid crystal composition represented by the above formula, X
Each of ₁ , X ₂ and X ₃ is a bonding group, which is present when k, m and n take an integer of 1, and does not exist when O is O and an adjacent group is directly bound. A ₁ and A ₂ may be the same group or different groups, and when the carbon atom of the 6-membered carbon ring is not replaced by a nitrogen atom, it becomes a benzene ring and is replaced by 2 nitrogen atoms. In this case, for example, a pyrimidine ring is used. 6-membered carbon ring substituted or not with a nitrogen atom is 2
˜3 para-positions may be linked, and the mode of linkage may be either when they are directly bound or when they are bound via a linking group. An example of A ₁ and A ₂

[Chemical 3] However, it is not limited to these groups.

(2) In the present invention, the liquid crystal composition of the above (1) is mixed with a liquid crystal compound exhibiting a ferroelectric smectic phase having a spontaneous polarization value of 100 nC / cm ² or more near the lower limit temperature of the ferroelectric liquid crystal phase. It is characterized by the liquid crystal composition. The amount to be mixed is preferably about 0.1 to 30% by weight.
As examples of the liquid crystal compound to be mixed, in addition to the substance of compound 10 shown in Examples,

[Chemical 4] However, the compounds are not limited to these compounds.

(3) Furthermore, the present invention comprises mixing the liquid phase composition of the above (1) with a compound having a nematic phase and / or a smectic phase alone and having two aromatic rings in its chemical structural formula. The liquid crystal composition is Examples of compounds containing two aromatic rings include:

[Chemical 5] (However, R and R'each independently have 2 to 20 carbon atoms.
Examples thereof include an alkyl group and an alkoxy group having a linear or branched structure of a certain degree. ), Etc. (where H is shown in the hexagon indicates a cyclohexane ring), there are many liquid crystal compounds in which various bonding groups and substituents are introduced based on these structures, The applicable compound is not limited to the above.

(4) The phase transition sequence is an isotropic phase from the high temperature side.
It is characterized in that it is a smectic A phase-antiferroelectric smectic phase, or an isotropic phase-smectic A phase-chiral smectic C phase-antiferroelectric smectic phase.

[0012]

By using the compound of the above general formula as the main component, the practical temperature range of the S _CA ^* phase is secured and the phase transition series necessary for the alignment of liquid crystal molecules is adjusted. The spontaneous polarization value is 100 nC near the lower limit temperature of the ferroelectric liquid crystal phase.
The compound having a ratio of / cm ² or more has the effects of lowering the threshold voltage of the composition and suppressing the effect of the phase transition precursory phenomenon. Further, the compound containing two aromatic rings in the chemical structural formula has an action of lowering the viscosity of the composition, and is an effective component for shortening the relaxation time from the ferroelectric phase to the antiferroelectric phase.

From the high temperature side, the phase transition sequence of the liquid crystal composition is an isotropic phase-smectic A phase-antiferroelectric smectic phase or an isotropic phase-smectic A phase-chiral smectic C phase-antiferroelectric smectic phase. By doing so, in the process of enclosing the liquid crystal composition in the device in the isotropic phase and cooling, the liquid crystal molecules take a uniaxial orientation state when the smectic A phase appears, and the layer direction is changed even if the phase is changed to the low temperature side Since it is maintained, it is possible to obtain an antiferroelectric smectic phase having a uniform alignment with the optical axes aligned in the plane.

[0014]

EXAMPLES The present invention will be described in detail below with reference to specific examples. As a sample, a liquid crystal composition of this example was heat sealed and slowly cooled in a cell in which a polyimide alignment film was formed on a transparent electrode and subjected to a uniaxial alignment treatment by a rubbing method to form a gap of 1.7 to 2.0 μm. A material in which the environmental temperature was kept in the temperature range of the antiferroelectric chiral smectic C phase (S _CA ^* phase) was used. The structure of the device is shown in FIG. In order to evaluate the electro-optical characteristics at the time of multiplex driving, the contrast ratio I _ON / V when the driving waveform of FIG. 1 is applied to the above-mentioned element and each voltage level V _W , V _b and V _d and the pulse width are optimized I _OFF was measured. 1A is a voltage waveform applied to the scan electrodes, FIG. 1B is a voltage waveform applied to the signal electrodes, FIG. 1C is a voltage waveform applied to a liquid crystal segment, and FIG. It is a figure which shows the change of the transmittance | permeability of a segment, and the horizontal axis shows time in each case. Also,
As shown in FIG. 2A, the relaxation time from the ferroelectric phase to the antiferroelectric phase is T _d in FIG. 2B when the electric field is set to 0 level after the voltage ± V _S above the saturation value is applied. The values expressed were measured.

Example 1 With the following weight percent composition:
A liquid crystal composition was obtained.

[Chemical 6] The compound represented by (hereinafter referred to as "compound 6") is 3
0.

[Chemical 7] The compound represented by (hereinafter referred to as “compound 7”) is 2
0.

[Chemical 8] The compound represented by (hereinafter referred to as “compound 8”) is 5
0. The phase transition temperature when the temperature was lowered was I (77.1) S _A (59.3) S _CA ^* . In the parentheses, the phase transition temperature (° C.) is shown, I is the isotropic phase, S _A is the smectic A phase, and S _CA ^* is the antiferroelectric chiral smectic C phase. The paraelectric phase-antiferroelectric phase transition temperature T _c is 59.3 ° C.

The notation I () S _A () S _CA ^* indicates that the phase transition sequence of the composition is isotropic phase (I) -smectic A phase (S _A ) -antiferroelectric chiral smectic C phase (S).
_CA ^* ). The S _CA ^* phase is a form of chiral smectic C phase (S _C ^* ) and in a natural state, the dipole moments show antiferroelectricity in which adjacent layers cancel each other, but an electric field above the saturation value is applied. In this state, spontaneous polarization is induced and ferroelectricity is exhibited. The state of exhibiting ferroelectricity by applying an electric field is equal to the ordinary ferroelectric chiral smectic C phase (S _C ^* ). It is also known that the chiral smectic C phase exhibits only ferroelectricity in a high temperature region and exhibits antiferroelectricity in a low temperature region (for example, the above-mentioned known substance is MHPOBC). Phase transition series in this case, isotropic phase - smectic A phase - chiral smectic C phase (S _C ^*) - although the antiferroelectric chiral smectic C phase ^{_{(S CA *), S C}} * -S CA * Metastases are often indistinguishable under normal microscopy. It is considered that the compositions of the examples of the present invention also have these two types of phase series.

30 ° C. (converted temperature T _C -30 ° C. = 29.3
When operated with the driving waveform of FIG.
V _W = 22 v, V _d = 3 v, V _b = 13 v, pulse width 1
In the setting of 00 μs, I _ON / I _OFF = 15. The response relaxation time T _{d was} 2.2 ms, and the apparent tilt angle θ was 35 °. The amount I of light transmitted through the element depends on the apparent tilt angle θ according to the formula I = I ₀ sin ² (2θ) sin ² (πΔnd / λ).
A larger θ of 45 ° or less indicates that the display element has higher light utilization efficiency.

Example 2 With the following weight percent composition:
A liquid crystal composition was obtained. Compound 6 90.

[Chemical 9] 5. The compound represented by (hereinafter referred to as "compound 9").

[Chemical 10] The compound represented by 5 (hereinafter referred to as "compound 10") is 5. The compound 9 is a nematic phase and the compound 10 is a smectic phase, and the spontaneous polarization value P _S of the compound 10 is 240 nC / cm ² . The phase transition temperature when the temperature was lowered was I (72.4) S _A (62.9) S _CA ^* . Was operated by the driving waveforms of FIG. 1 at _{30 ℃ (T C -30 ℃ =} 32.9 ℃), V W = 18
I _ON / I _OFF = 23 was obtained at a setting of v, V _d = 3 v, V _b = 10 v pulse width 150 μs. Response relaxation time T _d = 1.8 ms. Apparent tilt angle θ = 3
It was 1 °.

(Example 3) With the following weight% composition,
A liquid crystal composition was obtained. Compound 6 to 70. Compound 8 to 10.

[Chemical 11] The compound represented by 10. Compound 9 to 5. Compound 10 to 5. The phase transition temperature at the time of temperature decrease was I (72.3) S _A (58.9) S _CA ^* . Was operated by the driving waveforms of FIG. 1 at _{30 ℃ (T C -30 ℃ =} 28.9 ℃), V W = 17
I _ON / I _OFF = 20 was obtained at a setting of v, V _d = 2 v, V _b = 10 v pulse width 150 μs. The response relaxation time T _d = 1.2 ms.

(Example 4) With the following weight% composition,
A liquid crystal composition was obtained. Compound 6 40. Compound 7 to 26.
Compound 8 to 13.

[Chemical 12] The compound represented by 15. Compound 10 to 6. The phase transition temperature when the temperature was lowered was I (68.4) S _A (55.8) S _CA ^* . When operated by the drive waveform of FIG. 1 at 30 ° C. (T _C −30 ° C. = 25.8 ° C.), V _W = 22
I _ON / I _OFF = 20 was obtained in the setting consisting of v, V _d = 3 v, V _b = 14 v, and pulse width 120 μs. Response relaxation time T _d = 1.7 ms. Apparent tilt angle θ =
It was 32 °.

[0021]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a liquid crystal composition having a phase transition series for obtaining good alignment and exhibiting a stable antiferroelectric smectic phase in a wide temperature range including room temperature. done. Since the electro-optical characteristics are improved, high contrast can be realized when used as a display body, and high-speed scanning is possible. The present invention can be applied to a high-definition liquid crystal display device, a light valve, a spatial light modulator, and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a drive voltage waveform used for evaluation of an example of the present invention.

FIG. 2 is a diagram showing a drive voltage waveform used for evaluation of an example of the present invention.

FIG. 3 is a schematic view of an element used in an example of the present invention.

FIG. 4 is a diagram for explaining electro-optical characteristics of elements used in Examples of the present invention.

[Explanation of symbols]

OA Optical axis in antiferroelectric phase OF (+) Molecular orientation direction in ferroelectric phase (+) (optical axis) OF (-) Molecular orientation direction in ferroelectric phase (-) (optical axis) 1, 2 Glass substrate 3 Spacer material 4, 5 Transparent electrode 6 Liquid crystal layer 9, 10 Liquid crystal alignment film 11, 12 Polarizing plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Iwane 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72) Inventor Soyoshi Ami-cho, Inashiki-gun, Ibaraki Chuo 8-3-1, Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute

Claims (4)

[Claims] Claims: A liquid crystal composition containing at least one compound represented by the formula (1) and exhibiting an antiferroelectric smectic liquid crystal phase at room temperature. However, in the formula, R ₁ is an alkyl group having 1 to 30 carbon atoms, R ₂ is an alkyl group having 2 to 20 carbon atoms, X ₁ is —O—, —OCO—, —COO—, —OCO ₂ —, —C.
Any linking group O-, X _2, X ₃ are each independently -OCO -, - COO -, - CH 2 O -, - OCH 2
- one linking group, k, m, n, are each independently an integer of 0 or 1, Z is CF ₃ or CH _3, A _1, A ₂
Each independently represents a 6-carbon ring group substituted with 0 to 2 nitrogen atoms, or a carbon 6 of the same or different type thereof.
2-3 membered ring directly in the para position or, -COO -, - OCO -, - CH 2 O -, - OCH 2 -
Or a group in which a hydrogen atom on the ring of these groups is substituted with any one of a fluorine group, a methyl group and an ethyl group. 2. The liquid crystal composition according to claim 1, which has a spontaneous polarization value of 100 nC near the lower limit temperature of the ferroelectric liquid crystal phase.
A liquid crystal composition containing a liquid crystal compound exhibiting a ferroelectric smectic phase of not less than 1 cm ² / cm ² . 3. A liquid crystal composition comprising the liquid crystal composition according to claim 1 mixed with a liquid crystal compound having two aromatic rings and exhibiting a nematic phase and / or a smectic phase. 4. The phase transition sequence is an isotropic phase-smectic A phase-antiferroelectric smectic phase or an isotropic phase-smectic A phase-chiral smectic C from the high temperature side.
The liquid crystal composition according to claim 1, 2 or 3, which exhibits a phase-antiferroelectric smectic phase.