JPH04320218A - Liquid crystal optical element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal optical element which responds with electric fields at a high speed, allows easy gradation display and has a memory characteristic. CONSTITUTION:This liquid crystal optical element is constituted by crimping a smectic A liquid crystal compsn. 1 which contains a ferroelectric high-polymer liquid crystal and a ferroelectric high-polymer liquid crystal or low-molecular ferroelectric liquid crystal having the spontaneous polarization of the code varying from the spontaneous polarization of this ferroelectric high-polymer liquid crystal and exhibits such electric field induced tilt as to change the tilt angle by the magnitude of the impressed electric field and to maintain this tilt angle even if the electric field is removed between electrodes 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element suitably used in liquid crystal display elements, liquid crystal memory elements, and the like.

0002

BACKGROUND OF THE INVENTION As a liquid crystal optical element using a smectic A liquid crystal exhibiting electric field-induced tilt, for example,
Japanese Patent No. 3632 describes an optical modulation method and device for changing the tilt angle of a liquid crystal composition containing a ferroelectric liquid crystal in a smectic A phase state by an external electric or magnetic field. This uses the usual electroclinic effect and has excellent high-speed response, but it has no memory, so the tilt angle disappears immediately when the applied external field is removed. There are problems such as low productivity because low-molecular liquid crystals are used, and orientation is performed by a normal rubbing method.

0003

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal optical element that responds quickly to an electric field, can easily display gradations, and has memory properties. Another object of the present invention is to provide a liquid crystal optical element having the above-mentioned properties with excellent film formability and orientation.

0004

[Means for Solving the Problems] As a result of extensive research in order to solve the above problems, the present inventors have developed a smectic film that exhibits an electric field-induced tilt in which the electric field-induced tilt angle is maintained even when the electric field is removed. It has been discovered that the object can be achieved by a liquid crystal optical element using the liquid crystal composition A, and the present invention has been completed based on this knowledge.

That is, the present invention provides a smectic A that exhibits an electric field-induced tilt in which the tilt angle changes depending on the magnitude of the applied electric field and is maintained even when the electric field is removed.
The present invention provides a liquid crystal optical element characterized in that a liquid crystal composition is sandwiched between electrodes.

The liquid crystal composition used in the present invention is a smectic A liquid crystal composition exhibiting an electric field-induced tilt in which the tilt angle changes depending on the magnitude of the applied electric field and is maintained even when the electric field is removed. be. Since the tilt angle of this liquid crystal composition changes depending on the magnitude of the applied electric field, the response to the electric field is fast and gradation display is easy. Furthermore, since the tilt angle induced by the electric field is maintained even when the electric field is removed, it has memory properties.

In general, all ferroelectric liquid crystals exhibiting a smectic A phase can be mentioned as smectic A liquid crystals exhibiting electric field-induced tilt, but normally, the electric field-induced tilt disappears immediately when the electric field is removed. This electric gradient (
(Electroclinic) effect is related to fluctuations in the tilt angle of the liquid crystal called soft mode. The relaxation frequency of this fluctuation is on the order of kHz or higher for ordinary liquid crystals, so when the external field (electric field) applied to the liquid crystal is removed, the tilt angle induced by the electric field is immediately relaxed, and the liquid crystal The average tilt angle of is zero. Therefore, a liquid crystal optical element using a smectic A liquid crystal that exhibits a normal electric field-induced tilt has a gradation property in which the tilt angle can be controlled by the magnitude of the electric field, but as mentioned above, it does not have a memory property. This has been a practical impediment to liquid crystal optical elements using smectic A liquid crystals that exhibit electric field-induced tilt. However, the liquid crystal composition used in the present invention is a smectic A liquid crystal composition that exhibits an electric field-induced tilt in which the tilt angle changes depending on the magnitude of the applied electric field and the electric field-induced tilt angle is maintained even when the electric field is removed. The liquid crystal optical element of the present invention achieves gradation performance and memory performance at the same time.

[0008] The tilt angle after the electric field is removed is preferably maintained at 50% or more of the tilt angle when the electric field is applied;
In particular, it is preferably kept at 70% or more. If it is less than 50%, the contrast difference before and after removing the electric field becomes too large. Further, the holding time of the tilt angle is preferably 10 ms or more, and particularly preferably 30 ms or more for use in displaying a good moving image. If the time is less than 10 ms, practically sufficient memory performance cannot be obtained.

Specifically, such a liquid crystal composition is preferably one in which the relaxation frequency of the soft mode is kept low to 20 Hz or less, taking into account that the tilt angle is reduced to some extent. When the relaxation frequency is set to 20 Hz or less, the tilt angle can be maintained for a practically necessary time even when the electric field is removed. In particular, it is preferable to set the frequency to 15 Hz or less.

[0010] There are no particular restrictions on the composition of the liquid crystal composition as long as it has the above-mentioned characteristics at the operating temperature, but from the viewpoint of film formability, orientation, etc. It is preferable. In particular, at least one type of ferroelectric polymer liquid crystal and at least one type of ferroelectric polymer liquid crystal or low molecular weight ferroelectric liquid crystal having a spontaneous polarization of a sign different from the spontaneous polarization of the ferroelectric polymer liquid crystal. It is preferable to contain. In this case, the molecular weight of the polymeric ferroelectric liquid crystal is preferably a number average molecular weight of 1000 or more.

[0011] A suitable mixing ratio when mixing liquid crystals with positive and negative signs of spontaneous polarization is as follows: the spontaneous polarization value of liquid crystals with positive signs of spontaneous polarization is Ps(+), and the weight fraction is M(+). ,
The spontaneous polarization value of the liquid crystal whose spontaneous polarization sign is negative is Ps(-),
If the weight fraction is M(-), then 0.05≦{Ps(+)・M(+)}/{Ps(-
)・M(-)}≦20. If this ratio is less than 0.05, the response time may become long, and if it exceeds 20, memory properties may not be developed. Generally, it is not necessary to completely cancel spontaneous polarization.

Specific examples of suitable ferroelectric polymer liquid crystals include repeating units [I] and [I
I]

[Formula 1] (However, in the formula, a is 2 or 3, p is 0 or 1, and k is 2 to
20 integer, m is an integer from 0 to 3, n is an integer from 2 to 7,
t is an integer of 0 to 3, and u is an integer of 2 to 7. ), and the molar ratio of repeating units [I] and [II] ([I]/
[II]) is selected from copolymers having a ratio of (1/99) to (99/1).

More specifically, the following copolymers may be mentioned.

[Case 2]

[0014] Further, as a suitable low-molecular ferroelectric liquid crystal, for example, when mixed with the above-mentioned copolymer, it is preferable to use one whose spontaneous polarization sign is negative (-). In this case, the low-molecular ferroelectric liquid crystal may be one component or a multi-component mixture. Examples include those shown below.

embedded image Other commercially available low molecular weight ferroelectric liquid crystal compositions, such as CS-1015 and CS-1026 manufactured by Chisso Corporation, can also be suitably used. In this case, it is preferable that the sign of the spontaneous polarization is different from that of the polymeric ferroelectric liquid crystal. Furthermore, the liquid crystal composition used in the present invention may contain a non-ferroelectric liquid crystal material or a dielectric material as long as the smectic A phase does not disappear.
Non-liquid crystal substances such as chromatic dyes may also be added.

FIG. 1 is a sectional view showing an example of a liquid crystal optical element of the present invention. The liquid crystal optical element of the present invention is formed by sandwiching the above liquid crystal composition 1 between electrodes 2. As electrode 2,
Those commonly used in liquid crystal optical elements, such as ITO electrodes, can be suitably used. Preferably, the electrode 2 is supported by a substrate 3. The substrate 3 is not particularly limited, but when a composition containing polymeric liquid crystal is used as the liquid crystal composition 1, it is preferable to use a flexible substrate. Furthermore, a polarizing plate can be provided on the outside of the substrate 3 if necessary.

The liquid crystal optical element of the present invention can be suitably manufactured by using a known method for manufacturing a liquid crystal optical element, by sandwiching a liquid crystal composition between electrodes and performing an alignment treatment. for example,
When using a liquid crystal composition containing a polymeric liquid crystal, a long flexible substrate with electrodes is used because the liquid crystal composition has excellent film forming properties and alignment properties for mechanical alignment treatment.
It can be suitably manufactured with high productivity by a series of continuous high-speed processes such as applying a liquid crystal composition onto the electrode surface of a substrate, laminating it with a counter substrate, and bending and aligning the substrate.

[0017]

EXAMPLES The present invention will be explained in detail below based on Examples, but the present invention is not limited thereto. Example 1 (1) Production of ferroelectric polymer liquid crystal Ferroelectric polymer liquid crystal A having the following repeating units and characteristics was produced by the following method.

[Chemical 4] Phase transition behavior [Iso: isotropic phase, SmC*: chiral smectic C
phase, Sm1: unidentified smectic phase] Spontaneous polarization Ps (+) = +80 nC/cm2 (25°C) (1-
1) Production of monomer a Monomer a having the following structure was produced according to the following reaction.

embedded image While flowing argon gas, 1.1 mol of NaH (purity 60%) was gradually added to 200 ml of anhydrous THF and stirred. Next, 1, dissolved in 200 ml of anhydrous THF,
1 mol of 5-hexadien-3-ol was added dropwise with stirring. The reaction solution was stirred for about 2 hours, and after confirming that the generation of hydrogen gas had stopped, 2 mol of 1,10-dibromodecane dissolved in 200 ml of anhydrous THF was added at once, and the mixture was stirred under reflux for 8 hours. Next, the obtained reaction solution was filtered and heated to 50°C.
, concentrated for 1 hour at 3 torr or less, diluted 3 times with hexane, and purified by liquid chromatography to obtain compound (1). The yield was about 50%.

[0018]

[Chemical formula 6] 80 g of compound ■, 45.8 g of methyl 4-hydroxybenzoate, 124 g of potassium carbonate (anhydrous), and 400 ml of methyl ethyl ketone (MEK) were placed in a 1 liter 4-necked flask, and heated under argon gas.
The mixture was stirred at 0°C for 14 hours. The reaction mixture cooled to room temperature was filtered to remove salts such as potassium carbonate, and the resulting filtrate was applied to a rotary evaporator, and MEK was distilled off at a bath temperature of 50° C. while reducing the pressure with an electric aspirator. Next, about 300 ml of methylene chloride was added to the obtained residue, which was stirred, and then filtered again to remove insoluble salts. The obtained filtrate was applied to a rotary evaporator, and methylene chloride was distilled off under reduced pressure at a bath temperature of 50°C to obtain 91 g of a crude product of compound (1).

45 g of this crude product was diluted with 30 ml of methylene chloride to obtain a homogeneous solution, which was then subjected to liquid chromatography using a pre-column (capacity 270 ml) packed with activated alumina and a main column (capacity 1 liter) packed with silica gel. Fractionation was carried out using graphics. The eluate containing the target product was applied to a rotary evaporator, and the solvent was distilled off at 50° C. under reduced pressure. The remaining crude product was also collected under the same conditions.
Both fractions were combined to obtain compound (2). The yield is 84.4g (
The yield was 87%).

[0020]

##STR00007## According to Reaction 3 above, compound (1) was synthesized as follows. Compound ■42.4g, potassium hydroxide 24g,
Pour 20 ml of water and 60 ml of methanol into a 1 liter 4-necked flask, and while flowing argon gas,
The mixture was heated under stirring and refluxed at 0°C for 30 minutes. Next, after cooling the temperature of the reaction mixture to below 40° C., 600 ml of water was added into the reaction mixture. Thereafter, the temperature was raised to 90° C., and heating and stirring were continued for 4 hours. After confirming that the reaction mixture had become pale blue and transparent, the reaction was completed and the mixture was cooled to room temperature.

The reaction mixture was transferred to a 2 liter beaker, and purified water was added to bring the volume to 1.5 liters. After uniformly dissolving, a 3N aqueous hydrochloric acid solution was added to adjust the pH of the system to 2. Next, the suspension in which the white solid was precipitated was filtered, and the recovered white solid was suction filtered and washed several times with pure water. This solid was transferred to a 2 liter beaker, 1 liter of pure water was added, and the solid was stirred in a suspended state for 10 minutes. After suction filtering this suspension again and washing it several times with pure water,
The mixture was dried overnight in a vacuum dryer at 50°C to obtain Compound ①. The yield was 36.8 g (yield 90%).

[0022]

embedded image Monomer a was synthesized as follows according to Reaction 4 above. Carboxylic acid obtained in reaction 3 (compound ■) 27.
5g, 21ml thionyl chloride and 80ml dry toluene
The mixture was placed in a 500 ml four-necked flask equipped with a reflux condenser and stirred to form a homogeneous solution. Next, after adding 0.02 ml of pyridine, the reaction temperature was raised to 65° C., and heating and stirring was continued for 4 hours. Note that argon gas was constantly flowed through the flask. After this, in order to remove excess thionyl chloride and toluene as a solvent in the reaction mixture, the reaction mixture was heated to 65°C using an aspirator equipped with a dry ice trap in the middle, and over 1 hour most of the thionyl chloride and toluene were removed. was removed. Finally, the temperature was raised to 80°C and the remaining thionyl chloride was removed over 30 minutes.

To the reaction mixture cooled to room temperature, one portion of toluene was added.
Add 60 ml and 7.5 ml of pyridine to make a homogeneous solution,
Among them is the compound ■ (4'-hydroxybiphenyl-4-
Optically active 1-methylheptyl ester of carboxylic acid)2
160 ml of a toluene solution containing 4.1 g was added dropwise over 30 minutes with stirring. Thereafter, the reaction was completed by stirring at room temperature overnight. During the reaction, argon gas was flowed to prevent moisture from entering the reaction vessel.

The reaction mixture thus obtained was filtered to remove precipitated pyridine salt. Next, the filtrate was applied to a rotary evaporator, and the solvent was distilled off under reduced pressure at a bath temperature of 50° C. to obtain 50.9 g of a concentrate containing monomer a. Next, 50 g of methylene chloride was added to this concentrate and stirred to obtain a homogeneous and transparent solution.

This solution was fractionated by liquid chromatography using a precolumn (capacity: 270 ml) packed with activated alumina and a main column (capacity: 1 liter) packed with silica gel. The eluate containing the target product was applied to a rotary evaporator, and the solvent was distilled off under reduced pressure at a bath temperature of 50°C. The yield of crude product was 44.1 g (yield 88%).

The crude product was transferred to a 1 liter flask and 500 ml of ethanol was added. Next, attach a reflux condenser to the flask and
Stir for a minute. After confirming that the white solid had completely dissolved to form a homogeneous solution, the flask was naturally cooled to near room temperature. Next, this flask was stoppered to prevent moisture from entering, and then placed in a refrigerator and allowed to stand for 4 hours or more. After this, the flask was taken out, the precipitated white solid was collected by suction filtration, and the collected solid was washed several times with cold ethanol.

Finally, this solid was dried overnight in a vacuum dryer at 50°C to obtain monomer a. The yield was 36.9 g (yield 74%). The structure of monomer a is 1H-NMR
Confirmed by. A 1H-NMR chart is shown in FIG. (1-2) Production of monomer b Monomer b having the following structural formula was produced.

[Chemical formula 9] In reaction 4 for the production of monomer a, 24.1 g of compound
The process was carried out in the same manner as in the production of monomer a, except that 18.5 g of compound (1) having the following structure was used instead.

embedded image The yield of monomer b was 22.5 g (yield 50%). The structure of monomer b was confirmed by 1H-NMR. 1
A chart of H-NMR is shown in FIG.

(1-3) Copolymerization Add 1.82 g of the above monomer a to 14 ml of dry toluene.
(2.66 mmol), 0.18 g of the above monomer b (
0.30 mmol) and 0.26 g (1.94 mmol) of 1,1,3,3-tetramethyldisiloxane were uniformly dissolved by stirring while flowing argon gas. Next, after adding 2.0 mg of chloroplatinic acid hexahydrate,
The mixture was heated and stirred for hours. During stirring, a very small amount of argon gas was kept flowing to prevent moisture and oxygen from entering the reaction vessel.

After the polymerization reaction is completed, the reaction mixture is filtered,
Toluene was distilled off from the filtrate. The residue was diluted with 3 g of methylene chloride, and separated and purified by column chromatography using silica gel as a packing material to obtain the desired copolymer. Yield was 1.74g.

(1-4) Structure confirmation of the copolymer The structure of the copolymer was determined by 1H-NMR to be a copolymer in which the molar ratio of monomer a units and b units was 86:14, and the monomers were linked by disiloxane. It turned out to be a combination. The molar ratio was calculated using the integrated intensities of the peaks at 8.15 and 7.65 ppm. The 1H-NMR spectrum of the copolymer is shown in FIG. Moreover, the weight average molecular weight of the copolymer measured by GPC was 4,100.

(1-5) Properties as a liquid crystal The properties of this copolymer as a liquid crystal were as follows. Phase transition behavior Response time to electric field change τ10-90 (25°C, 20V) = 5.6ms Lowers the transition temperature from isotropic phase to chiral smectic C phase compared to homopolymer of monomer a having the same level of molecular weight. , and the response speed is improved.

(2) Production of liquid crystal composition Ferroelectric polymer liquid crystal A obtained above and low molecular weight ferroelectric liquid crystal composition B having the following properties (manufactured by Chisso Corporation:
CS-1015) in dichloromethane 2g each
The liquid crystal composition was dissolved and mixed in 0 ml, and the solvent was evaporated to obtain a liquid crystal composition. Phase transition behavior Iso ←→ N* ←→ SmA ←
→ SmC* ←→ Cryst (℃)
78 69
58 -17 [N*: chiral nematic phase, SmA: smectic A phase, Cryst
: Crystal phase] Spontaneous polarization Ps(-)=-7nC/cm2 (25℃) {P
s(+)・M(+)}/{Ps(-)・M(-)}=1
1.4

(3) Characteristics of the liquid crystal composition This liquid crystal composition was placed in a 10 m long tube with the electrode surface facing inside.
The liquid crystal cell was sandwiched between m x 20 mm x 1 mm glass substrates with ITO electrodes and subjected to alignment treatment, and the phase transition temperature was determined as follows using a polarizing microscope as a liquid crystal cell with a cell thickness of 2.5 μm. Phase transition behavior [SmA*: Smectic A showing electric field-induced tilt
Phase, g: glass state]

[0034] Here, the orientation treatment was performed by applying shear at 80°C. Since the composition was a smectic A liquid crystal composition exhibiting electric field-induced tilt, no zigzag defects were observed. Also, response time τ10-9 to electric field change at room temperature 25°C
0 is 200μs when a voltage of ±10V is applied between the electrodes.
The tilt angle θ at that time was 14.5°. Even if this 10V applied voltage is removed, the tilt angle θ remains 14.
It was almost kept at 0. This tilt angle θ did not change even one hour after the applied voltage was removed. Also, the applied voltage is ±2
Response time to electric field change when set to 0V τ10-9
0 was 205 μs, and the tilt angle θ was 27°. Even when this 20V applied voltage is removed, the tilt angle θ is 25
．． It was 5°. This tilt angle θ also remained unchanged one hour after the applied voltage was removed. From the above, in this liquid crystal composition,
It was clear that the tilt angle varied with the magnitude of the applied electric field and that the tilt angle was maintained when the electric field was removed. Furthermore, when we measured the dielectric dispersion of this liquid crystal cell, we found that the relaxation frequency of the soft mode of the liquid crystal composition was 3 at 40°C.
0 Hz, and at 25° C., it was below 20 Hz, which is the measurement limit on the measuring device, revealing the uniqueness of this liquid crystal composition.

(4) Manufacture of liquid crystal optical element Next, a liquid crystal optical element was prototyped as follows using the present liquid crystal composition. First, the present liquid crystal composition was made into a 25% by weight toluene solution,
Polyethersulfone (PES) substrate with ITO electrode (Sumitomo Bakelite FST: width 180mm, thickness 100μ
The solution was applied onto the surface of an ITO electrode with a length of 20 m) using a direct gravure coater. Immediately after drying the solvent, the same type of substrate to which nothing had been applied was laminated so that the ITO electrode surface was in contact with the liquid crystal composition to obtain an unoriented element. Then,
As shown in FIG. 2, the unoriented element 5 was subjected to an alignment treatment by passing through an alignment treatment apparatus consisting of four groups of three rolls to obtain an oriented element 6. Here, each roll was made of chrome-plated iron and had a diameter of 80 mm and a width of 300 mm. Also, the surface temperature of each roll is T1=100℃, T2
=80℃, T3=80℃, line speed is v=5m/
It was a minute. After the alignment treatment, a 300 mm length was cut out to obtain a desired liquid crystal optical element.

(5) Characteristics of liquid crystal optical element When the obtained liquid crystal optical element was observed under a polarizing microscope, no alignment defects were found. Furthermore, when this liquid crystal optical element was placed between orthogonal polarizing plates and rotated with respect to the polarizing plates, the contrast ratio of the transmitted light intensity was 200 or more. Also, ±10V between the electrodes
When the voltage was applied, the tilt angle θ was 15°C,
The contrast ratio was 120. Furthermore, even when the applied voltage was removed, the tilt angle θ was maintained at 14°C. This tilt angle θ was maintained for more than one hour after the applied voltage was removed, and it was clear that the device had a practically sufficient memory property. In this way, a liquid crystal optical element with a fast response to voltage, memory properties, and whose tilt angle is variable depending on the voltage was extremely easily obtained.

[0037]

Effects of the Invention The liquid crystal optical element of the present invention has a fast response to an electric field, can easily display gradations, and has memory properties. Moreover, it has excellent film formability and orientation.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a liquid crystal optical element of the present invention.

FIG. 2 is an explanatory diagram showing an alignment processing apparatus used in Examples.

FIG. 3 is a chart showing 1H-NMR measurement results of monomers produced in Examples.

FIG. 4 is a chart showing 1H-NMR measurement results of monomers produced in Examples.

FIG. 5 is a chart showing 1H-NMR measurement results of copolymers produced in Examples.

[Explanation of symbols]

1 Liquid crystal composition 2 Electrode 3 Board 4 roll 5 Unoriented element 6 Oriented element

Claims (3)

[Claims] [Claim 1] A smectic A liquid crystal composition that exhibits an electric field-induced tilt in which the tilt angle changes depending on the magnitude of the applied electric field and is maintained even when the electric field is removed is sandwiched between electrodes. A liquid crystal optical element characterized by: 2. The liquid crystal optical element according to claim 1, wherein the liquid crystal composition has a soft mode relaxation frequency of 20 Hz or less. 3. A liquid crystal composition comprising at least one ferroelectric polymer liquid crystal and a ferroelectric polymer liquid crystal or a low molecular weight liquid crystal having a spontaneous polarization having a sign different from that of the ferroelectric polymer liquid crystal. Claim 1 containing at least one dielectric liquid crystal.
Or the liquid crystal optical element according to 2.