JPH1025477A - Ferrielectric liquid crystal composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ferrielectric liq. crystal compsn, which exhibits a ferrielectric phase in a wide temp, range and a high-speed responsively at room temp. or lower by mixing a specific optically active compd. With a specific liq. crystal compd. having a ferrielectric phase in its phase series. SOLUTION: This compsn. is prepd, by mixing an optically active compd. represented by formula I (wherein R<1> is a linear alkyl group; X<1> and X<2> are both H, or one of them is H and the other is F; Y<1> and Y<2> are both H, or one of them is H and the other is F; and m is 3-10) pref. in an amt. of 1-60mol% (based on the compsn.), still pref. 10-50mol%, with a liq. crystal compd. represented by formula II (wherein R<2> is R<1> ; Z<1> and Z<2> are both H, or one of them is H and the other is F; and p and q are each 2-4). In formula I, the number of carbon atoms of R<1> is pref. 8-10; and m is pref. 3-8. In formula II, the number of carbon atoms of R<2> is pref. 7-12; p is 3; and q is 2. The compsn. is useful for an active-matrix display element.

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 having a ferrielectric phase which is preferably used for an active matrix type liquid crystal display device driven for each pixel.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are already becoming popular mainly in portable devices as flat panel displays replacing conventional CRT displays. With the recent expansion of the functions of personal computers and word processors and the increase in the amount of processing information, LCDs also have higher functions, that is, larger display capacity, full color display,
A wide viewing angle, high-speed response, high contrast, and the like are required.

As a liquid crystal display system (liquid crystal driving system) that meets such demands, a thin film transistor is provided for each pixel of a screen.
An active matrix (AM) display element, in which a TFT (TFT) or a diode (MIM) is formed and a liquid crystal is independently driven for each pixel, has been proposed and implemented. In this display method, it is difficult to reduce the cost because of a low production yield.
Although there are problems such as difficulty in increasing the screen size, the display quality has surpassed the conventional mainstream STN display system due to its high display quality, and is approaching the CRT.

[0004]

However, in such an AM display element, the following problem occurs because a TN (twisted nematic) liquid crystal is used as a liquid crystal material. (1). TN liquid crystal is a nematic liquid crystal, and its response speed is generally slow (several tens of ms), and good image quality cannot be obtained when displaying moving images. (2). The display angle is narrow because the display is made using the twisted state (twist alignment) of the liquid crystal molecules. In particular, when gradation display is performed, the viewing angle sharply decreases. That is, the contrast ratio, color, and the like change depending on the viewing angle of the display.

In order to solve these problems, an AM using a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal instead of a TN liquid crystal.
Panel proposals have also been made in recent years (Japanese Unexamined Patent Publication No.
5-150257, 6-95080 etc.). However, these liquid crystals also have the following problems, and the wall for practical use is currently thick. (1) The ferroelectric liquid crystal has spontaneous polarization. However, since spontaneous polarization always exists, screen burn-in easily occurs and driving is difficult. Further, when the ferroelectric liquid crystal is displayed in the surface stabilization mode, only binary display of black and white can be performed, so that gradation display is extremely difficult. Special considerations are required when performing gradation display (for example, ferroelectric liquid crystal devices using monostable; Keiichi NITO et. Al, SI
D'94, Preprint, p48), the development of advanced practical technology is required. (2). Since the antiferroelectric liquid crystal does not have permanent spontaneous polarization, the burning problem described in (1) above is avoided.

However, AM driving requires a liquid crystal material that can be driven at least at 10 V or less. But,
Antiferroelectric liquid crystals generally have a large threshold voltage and are difficult to drive at low voltage. In addition, there is a problem that gradation display is difficult due to a history (hysteresis) in optical response. The present invention provides an AM that can solve the above problems.
It is to provide a new material suitable for driving. Ferrielectric liquid crystals can be considered as this new material.

A ferrielectric liquid crystal having a ferrielectric phase (SCγ * phase) was introduced in 1989 as 4- (4-octyloxyphenyl) benzoic acid = 4- (1-methylheptyloxycarbonyl) phenyl (abbreviation: MHPOBC) ) (Jap
anese Journal of AppliedPhysics, Vol.29, No.1, 199
0, pp. L131-137). The structural formula and phase sequence of MHPOBC are shown below. Structural formula: C ₈ H ₁₇ -O-Ph-Ph-COO-Ph-COO-C * H (CH ₃ ) C ₆ H ₁₃ where Ph represents a 1,4-phenylene group and C * represents an asymmetric carbon . Phase series: Cr (30) SIA * (65) SCA * (118) SCγ * (119) SC * (12
1) SCα * (122) SA (147) I where Cr is a crystalline phase, SIA * is a chiral smectic IA phase,
SCA * is chiral smectic CA phase (antiferroelectric phase), SCγ
* Indicates chiral smectic Cγ phase (ferrielectric phase), SC
* Is a chiral smectic C phase (ferroelectric phase), SCα * is a chiral smectic Cα phase, SA is a smectic A phase,
I indicates isotropic phase.

In order to explain a ferrielectric liquid crystal, FIG.
2 shows the molecular arrangement state in the ferrielectric phase, and FIG. 2 shows the optical response of the ferrielectric phase to a triangular wave. The ferrielectric phase has the molecular arrangement of FI (+) or FI (-) shown in FIG. In the absence of an electric field, FI (+) and FI (-) coexist because they are equivalent. Therefore, the average optical axis is in the direction of the normal to the layer, and is in a dark state under the conditions of the polarizing plate shown in FIG. In this state, the transmitted light intensity is 0 when the voltage is 0 in FIG.
Corresponds to FI (+) and FI (-) have spontaneous polarizations, respectively, as is apparent from the molecular arrangement state. However, in the coexistence state, the spontaneous polarizations cancel each other out, so that the average spontaneous polarization is zero. For this reason, the ferrielectric liquid crystal escapes the image sticking phenomenon observed in the ferroelectric liquid crystal, like the antiferroelectric liquid crystal.

[0009] When a voltage is applied to the ferrielectric liquid crystal, a region (domain) having an extinction position appears at a voltage lower than that attaining the ferroelectric state. This region has an optical axis in a direction inclined from the normal direction, though not so much as in the ferroelectric state. This intermediate state is considered FI (+) or FI (-). In this case, in FIG. 2, the transmitted light intensity on the stairs should be observed instead of a continuous change in the transmitted light intensity between the voltages 0 V and 4 V.
However, continuous transmitted light intensity was observed in FIG. This is probably because the threshold voltage of FI (+) → FO (+) or FI (-) → FO (-) is not clear. In the present invention, a liquid crystal phase in which the intermediate state described above is always observed is a ferrielectric phase, and a liquid crystal compound having the widest temperature range of the ferrielectric phase in the liquid crystal phase is a ferrielectric liquid crystal.

When the applied voltage is further increased, the ferroelectric phase (FO (+) or FO (-)) which is in a stable state according to the direction of the electric field is increased.
Phase transition. In other words, in FIG. 2, the transmission light intensity becomes saturated (left and right flat portions) are FO (+) and FO (-).
It is. It can be seen from FIG. 1 that in this ferroelectric state FO (+) or FO (-), a spontaneous polarization larger than that in the ferrielectric state FI (+) or FI (-) appears. As described above, in the ferrielectric phase, the coexistence state of FI (+) and FI (-) can be used as dark, and the ferroelectric states FO (+) and FO (-) can be used as light. Conventional ferroelectric liquid crystal switches between FO (+) and FO (-), while ferrielectric liquid crystal displays FO (+), FI (+), FI
It has the great feature of switching between the four states (-) and FO (-). All of the display principles use the birefringence of liquid crystal, and a display element with small viewing angle dependence can be manufactured.

In the ferrielectric phase, as shown in FIG. 2, the difference between the voltage changing from the ferrielectric state to the ferroelectric state and the voltage changing from the ferroelectric state to the ferrielectric state is generally small. That is, the width of the hysteresis tends to be very narrow, and has a V-shaped optical response, and has characteristics suitable for AM driving and gradation display in AM driving. Also, in the change due to the voltage of the ferrielectric phase, the threshold voltage, which is the voltage at which the ferrielectric state changes to the ferroelectric state, tends to be much smaller than that of the antiferroelectric liquid crystal. Therefore, it can be said that the ferrielectric liquid crystal is suitable for AM driving.

However, the number of liquid crystal compounds having a ferrielectric phase synthesized so far is extremely small. Furthermore, when a liquid crystal compound having a conventionally known ferrielectric phase alone is considered to be applied to an AM driving element, it is difficult to use the ferrielectric substance. No satisfactory has been found in terms of phase temperature range, hysteresis, and threshold voltage. For example, in general, the driving voltage of an AM driving element is low, and it is necessary to be able to drive at a high speed with an applied voltage of at least 10 V or less. From this point of view, the liquid crystal compound having a ferrielectric phase, which has been conventionally obtained, has a problem in response at a drive voltage of 10 V or less, and improvement in this aspect is strongly desired. The present invention has been made in view of this point, and provides a liquid crystal composition having a novel ferrielectric phase, which is suitable for AM driving and has excellent low voltage driving properties.

[0013]

That is, the present invention provides an optically active compound represented by the following general formula (1):
A ferrielectric liquid crystal composition represented by the formula (2), which is mixed with a liquid crystal compound having a ferrielectric phase in its phase series.

[0014]

Embedded image (Wherein R ¹ and R ² are linear alkyl groups, X ¹ and X ² are hydrogen atoms or one is a hydrogen atom and the other is a fluorine atom, Y ¹ and Y ² are a hydrogen atom or one is a hydrogen atom and the other is Fluorine atom, Z ¹ , Z ²
Is a hydrogen atom or one is a hydrogen atom and the other is a fluorine atom,
m is an integer of 3 to 10, p is an integer of 2 to 4, q is an integer of 2 to 4, and C * is an asymmetric carbon. )

In the optically active compound of the present invention, R ¹ in the general formula (1) preferably has 8 to 10 carbon atoms and m is an integer of 3 to 8. The mixing amount of the optically active compound represented by the general formula (1) is preferably 1 to 60 mol% of the composition,
Further, a range of 10 to 50 mol% is preferable. The liquid crystal compound having a ferrielectric phase used in the present invention has a general formula
(2) p in is 3, q is 2, the number of carbon atoms in R ² is 7-12 are preferred.

In the ferrielectric liquid crystal composition of the present invention, the transition temperature of the ferrielectric phase is preferably 40 ° C. or higher on the high temperature side and 0 ° C. or lower on the low temperature side, and more preferably 50 ° C. or higher on the high temperature side.
And it is preferable that the smectic A phase exists on the higher temperature side than the ferrielectric phase. In the ferrielectric phase, the threshold voltage at the time of transition from the ferrielectric state to the ferroelectric state is preferably 5 V / μm or less, and more preferably 3 V / μm or less.

The ferrielectric liquid crystal composition of the present invention is sandwiched between substrates on which a non-linear active element such as a thin film transistor or a diode is provided for each pixel, thereby forming an active matrix liquid crystal display element. The driving of the liquid crystal by the voltage using the active element is performed by switching between two ferrielectric states, two ferroelectric states, and an intermediate state.

The liquid crystal having a ferrielectric phase in the present invention can be obtained by the method disclosed by the present inventors (JP-A-3-2913).
No. 88). The outline of the manufacturing method is as follows. (B) AcO-Ph (X) -COOH + SOCl ₂ → AcO-Ph (X) -COCl (b) (b) + CF ₃ C * H (OH) (CH ₂ ) _m OC _n H _{2n + 1} → AcO-Ph (X) -COO-C * H (CF ₃ ) (CH ₂ ) _m OC _n H _{2n + 1} (c) (b) + (Ph-CH ₂ NH ₂ ) → HO-Ph (X)- COO-C * H (CF ₃ ) (CH ₂ ) _m OC _n H _{2n + 1} (d) RO-Ph-Ph-COOH + SOCl ₂ → RO-Ph-Ph-COCl (e) (b) + (d ) → Target liquid crystal compound In the formula, Ph represents a 1,4-phenylene group, and Ph (X) represents a 1,4-phenylene group which may be substituted with fluorine at the 2- or 3-position.

The above-mentioned manufacturing method is briefly described as follows. (A) Chlorination reaction of p-acetoxybenzoic acid with thionyl chloride. (B) Formation of ester by reaction between chloride (a) and optically active alcohol. (C) is an ester (b)
Deacetylation. (D) Chlorination of 4'-alkyloxybiphenyl-4-carboxylic acid. (E) Production of liquid crystal by reaction between phenol (c) and chloride (d).

The optically active compound used in the present invention can be prepared by the method already disclosed by the present inventors (Japanese Patent Application No. Hei 8-1-1187).
57) can be easily manufactured. The outline of the manufacturing method is as follows. (a) R * OH + p-TsCl → R * OTs (b) (a) + p-HO-Ph-O-CH ₂ Ph → PhCH ₂ -O-Ph-OR * (c) (b) + H ₂ → HOPhO-R * (d) R'COO-Ph-COOH + SOCl ₂ → R'COO-Ph-COCl (e) (d) + (C) → target optically active compound where R * OH is optical Active 2-alkanols, p-TsCl
p-Toluenesulfonyl chloride, Ph represents a 1,4-phenylene group, and PhCH ₂ -represents a benzyl group.

The above-mentioned manufacturing method is briefly described as follows. (a) Tosylation of an optically active alcohol. (b) is (a)
With p-benzyloxyphenol. (c) is a hydrogenated debenzyl group of (b). (d) Chlorination of 4-carbonyloxybenzoic acid. (e) Synthesis of the target optically active compound by reaction between (d) and (c).

[0022]

According to the present invention, there is provided a novel ferrielectric liquid crystal composition which has a ferrielectric phase in a wide temperature range and exhibits high-speed response at a temperature lower than room temperature.

[0023]

The present invention will be described in more detail with reference to the following examples. Note that the present invention is not limited to this. Examples 1 and 2 A phenyl ester compound represented by the following chemical structural formula (1
A) a ferrielectric liquid crystal (2A) represented by the following chemical structural formula
Was mixed with 30 mol% and 40 mol%, respectively. 1A: C ₉ H ₁₉ -COO-Ph (2F) -COO-Ph-OC * H (CH ₃ ) C ₅ H ₁₁ 2A: C ₉ H ₁₉ -O-Ph-Ph-COO-Ph (3F) -COO -C * H (CF ₃ ) (CH ₂ ) ₃ O
During C ₂ H ₅ Formula, Ph is 1,4-phenylene group, Ph (2F) is the 2-position (X ²⁾ the fluorine-substituted 1,4-phenylene group, Ph (3F) is the 3-position (Z ² ) Is a 1,4-phenylene group substituted with fluorine, and C * represents an asymmetric carbon.

Examples 3 and 4 Phenyl ester compounds (1) represented by the following chemical structural formula
B, 1C) was mixed with the ferrielectric liquid crystal (2A) used in Example 1 in an amount of 40 mol%. _{1B: C 9 H 19 -COO-} Ph (2F) -COO-Ph-OC * H (CH 3) C 3 H 7 1C: C 9 H 19 -COO-Ph (2F) -COO-Ph-OC * H (CH ₃ ) C ₇ H ₁₅

With respect to the compositions obtained in Examples 1 to 4,
The results of the identification of the liquid crystal phase and the examination of the optical response are shown in Table 1 below. The identification of the liquid crystal phase includes texture observation, conoscopic image observation, DSC (differential scanning calorimetry) measurement, and measurement of the area (domain) having an extinction position between the layer normal direction and the ferroelectric state optical axis direction. The presence was confirmed by observing the intermediate state (FI (±)). Observation of a conoscopic image is a powerful means for observing a ferrielectric phase. Observation of the conoscopic image followed the literature (J. Appl. Phys. 31. 793 (1992)). The ferrielectric phase is a domain (domain) having an extinction position between a normal parallel alignment cell for texture observation, conoscopic observation and DSC measurement, and observation of an intermediate state, that is, an optical axis direction of a layer normal and a ferroelectric state. Was recognized.

The cell whose optical response was examined was prepared in the following procedure. After a glass substrate having an insulating film (SiO ₂ : film thickness: 50 nm) and an ITO electrode was subjected to polyimide coating (film thickness: about 80 nm), only one of the pair of glass substrates was subjected to a rubbing treatment. Particle size
A pair of glass substrates were bonded via a 1.6 μm spacer to form a test cell. The cell thickness was 2 μm. The liquid crystal was heated to a temperature at which the liquid crystal became an isotropic phase, and the liquid crystal was injected into a test cell by capillary action. Thereafter, the liquid crystal was gradually cooled at a rate of 1 ° C./min to parallel align the liquid crystal.

Next, at a predetermined temperature, ± 10
V, 50mHz triangular wave voltage was applied to drive, and the change of transmitted light was examined. The threshold voltage I (unit: V / μm) is defined as the voltage at which the transmitted light intensity reaches 90% when the phase transition from the ferrielectric phase to the ferroelectric phase occurs, with the transmitted light intensity being 0% at the lowest and 100% at the highest.
, The voltage at which the transmitted light intensity becomes 90% during the phase transition from the ferroelectric phase to the ferrielectric phase is determined by the threshold voltage II (unit: V / μ
m) and the threshold voltage was measured. The response time was measured by defining the time required for the transmitted light intensity to change by 90% by applying a pulse voltage of 8 V and a frequency of 10 Hz as the response time.

[0028]

[Table 1] Threshold voltage response time Measurement phase sequence I II (μsec) Temperature Example 1 Cr (<-10) SCγ * (68) SA (87) I 1.3 1.2 64 30 ℃ 2 Cr (<- 10) SCγ * (55) SA (82) I 1.2 1.1 41 30 ° C 3 Cr (<-10) SCγ * (52) SA (86) I 1.2 1.2 50 30 ° C 4 Cr (<-10) SCγ * (54 ) SA (79) I 1.3 1.1 45 30 ° C Photoactive 1A Cr (25) I 1B Cr (37) I 1C Cr (5) SA (20) I Liquid crystal 2A Cr (34) SCγ * (101) SA (103) I 1.3 1.0 100 40 ° C The values in parentheses in the phase series in the table indicate the phase transition temperature (° C),
Cr indicates a crystal phase, SCγ * indicates a ferrielectric phase, SA indicates a smectic A phase, and I indicates an isotropic phase.

[Brief description of the drawings]

FIG. 1 is a diagram showing the molecular arrangement of a ferrielectric phase. FI
(+) And FI (-) represent a ferrielectric state, and FO (+) and FO (-) represent a ferroelectric state.

FIG. 2 shows an optical response of a ferrielectric phase to a triangular wave.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Motoyama 22nd Wadai, Tsukuba, Ibaraki Pref. Mitsubishi Gas Chemical Company, Ltd.

Claims (12)

[Claims] 1. A ferrielectric liquid crystal obtained by mixing an optically active compound represented by the following general formula (1) with a liquid crystal compound represented by the following general formula (2) and having a ferrielectric phase in its phase series: Composition. Embedded image (Wherein R ¹ and R ² are linear alkyl groups, X ¹ and X ² are hydrogen atoms or one is a hydrogen atom and the other is a fluorine atom, Y ¹ and Y ² are a hydrogen atom or one is a hydrogen atom and the other is Fluorine atom, Z ¹ , Z ²
Is a hydrogen atom or one is a hydrogen atom and the other is a fluorine atom,
m is an integer of 3 to 10, p is an integer of 2 to 4, q is an integer of 2 to 4, and C * is an asymmetric carbon. ) 2. The compound represented by the general formula (1), wherein R ¹ has 8 to 9 carbon atoms.
10. The ferrielectric liquid crystal composition according to claim 1, wherein m is an integer of 3 to 8. 3. The ferrielectric liquid crystal composition according to claim 1, wherein the amount of the optically active compound represented by the general formula (1) is 1 to 60 mol% of the composition. 4. The ferrielectric liquid crystal composition according to claim 1, wherein the amount of the optically active compound represented by the general formula (1) is 10 to 50 mol% of the composition. 5. In the general formula (2), p is 3, q is 2,
^2. The ferrielectric liquid crystal composition according to claim 1, wherein R2 has 7 to 12 carbon atoms. 6. The transition temperature of the ferrielectric phase is 40 ° C. on the high temperature side.
2. The ferrielectric liquid crystal composition according to claim 1, wherein the temperature is 0 ° C. or lower on the low temperature side. 7. The transition temperature of the ferrielectric phase is 50 ° C. on the high temperature side.
2. The ferrielectric liquid crystal composition according to claim 1, wherein the temperature is 0 ° C. or lower on the low temperature side. 8. The ferrielectric liquid crystal composition according to claim 1, which has a smectic A phase on a higher temperature side than the ferrielectric phase. 9. The semiconductor device according to claim 1, wherein the threshold voltage at the time of transition from the ferrielectric state to the ferroelectric state is 5 V / μm or less.
The ferrielectric liquid crystal composition according to the above. 10. The ferrielectric liquid crystal composition according to claim 1, wherein the threshold voltage at the time of transition from the ferrielectric state to the ferroelectric state is 3 V / μm or less. 11. An active matrix liquid crystal display device comprising the ferrielectric liquid crystal composition according to claim 1 sandwiched between substrates on which a non-linear active device such as a thin film transistor or a diode is provided for each pixel. 12. The method of driving a liquid crystal using a voltage using a nonlinear active element by two ferrielectric states and two ferroelectric states,
And switching to an intermediate state thereof.
An active matrix liquid crystal display device as described in the above.