JP2003104947A - Method for purifying liquid crystal compound by magnetic field application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying a liquid crystal compound, with which the reliability of a liquid crystal compound is improved and to obtain a liquid crystal composition having excellent reliability using the compound obtained by the method as a constituent component and a liquid crystal element using the liquid crystal composition. SOLUTION: This method for purifying a liquid crystal compound comprises applying a magnetic field to a liquid crystal compound in a liquid state, in a liquid crystal state or in a dissolved state in a solvent and subjecting the liquid crystal compound to a process for washing in water. The liquid crystal compound purified by the method has high reliability and is useful as a constituent material for a liquid crystal composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel method for purifying a liquid crystal compound, a liquid crystal compound purified by the purification method, a liquid crystal composition containing the compound, and a liquid crystal display device using the composition.

[0002]

2. Description of the Related Art Liquid crystal display devices have come to be used in watches, calculators, various measuring instruments, automobile panels, word processors, electronic notebooks, printers, computers, televisions and the like. Typical liquid crystal display systems are TN (twisted nematic) type, STN (super twisted nematic) type, DS (dynamic light scattering) type, GH (guest host) type, or FLC capable of high-speed response. (Ferroelectric liquid crystal) and the like. Also, as the drive system, the conventional static drive has become more common, and the multiplex drive is becoming more common, and the simple matrix system and recently the active matrix system have been put into practical use. As liquid crystal materials used for these, a great variety of compounds have been synthesized so far, and they are used as a constituent component of a liquid crystal composition depending on the application.

Physical properties of liquid crystal compositions (nematic phase temperature range, refractive index anisotropy (Δn), dielectric anisotropy (Δε), viscosity,
Elastic constants) and electro-optical characteristics (response time, threshold voltage, V-
Various values are required for the steepness of the T curve, etc., depending on the target display system and drive system of the liquid crystal element. Further, in addition to this, in the case of the matrix driving method, high reliability against heat and light is required.

Regarding the reliability (specific resistance etc.) of the liquid crystal composition, it is necessary that the individual liquid crystal compounds constituting the composition have high reliability (specific resistance etc.) and high reliability in the panel. is there. However, in many cases, it is difficult to improve the reliability of the compound or the reliability in the panel due to the presence of trace impurities that are difficult to remove, and the purification method has been studied. Conventionally, in order to remove such impurities, it has been necessary to purify by combining operations such as recrystallization, column chromatography, adsorbent treatment, ion exchange treatment, or distillation, if necessary, to produce a liquid crystal compound. In the above, productivity was remarkably reduced. In addition, it is not possible to sufficiently improve the reliability (specific resistance etc.) of the liquid crystal compound alone or the reliability in the panel no matter how many times the above refining operation is repeated,
Therefore, there were some compounds that could not be put to practical use, although they had excellent physical properties and electro-optical properties.

[0005]

The problem to be solved by the present invention is to improve the reliability of a liquid crystal compound by a simple operation.
A liquid crystal composition excellent in reliability in a panel, which is to provide a refining method for improving the reliability in a panel (specific resistance, etc.) and a compound obtained thereby is used as a constituent component. And to provide a highly reliable liquid crystal display device using the liquid crystal composition.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a liquid crystal compound is in a liquid state or in a liquid crystal state or in a state of being dissolved in a solvent, and then a magnetic field is applied, followed by a water washing step. The present inventors have found a method for purifying a liquid crystal compound, which is characterized by adding

Further, by using the obtained compound as a constituent, a liquid crystal composition having high reliability (specific resistance etc.) and reliability in a panel can be prepared,
It has become possible to manufacture a highly reliable liquid crystal display device such as a simple matrix drive system and an active matrix drive system using this, and the present invention has been completed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The purification method of the present invention is characterized by applying a magnetic field in a liquid state or a liquid crystal state or in a state of being dissolved in a solvent as described above, and then adding a water washing step. Is.

The strength of the magnetic field used in the present invention is from 0.1 T to 10
T is preferable, 0.3T to 7T is more preferable, 0.5T to 5T
Is more preferable, and 1T to 3T is particularly preferable. Further, a permanent magnet, an electromagnet, a superconducting magnet or a composite magnet of these can be used as a magnetic field generation source.

The magnetic field application time is preferably 10 minutes to 24 hours, more preferably 15 minutes to 18 hours, and particularly preferably 1 hour to 6 hours.

When purification is carried out in a state of being dissolved in a solvent, the solvent is preferably a hydrocarbon solvent, and in the case of an aliphatic hydrocarbon solvent, n-hexane, heptane, octane, nonane, decane, an aromatic hydrocarbon solvent. Then, benzene, toluene and xylene are preferable, n-hexane, heptane, toluene and xylene are more preferable, and n-hexane and toluene are particularly preferable.

The step of washing with water is a step of washing and separating with a two-phase system of a liquid state, a liquid crystal state or a liquid crystal compound dissolved in a solvent and water.

The water used in the water washing step is preferably ion-exchanged water, distilled water or ultrapure water, and ion-exchanged water is particularly preferable. The electric conductivity of the deionized water is preferably 1.0 .mu.s / cm ² or less, 0.5 .mu.s / cm ² or less is particularly preferred.

In the purification step after the water washing step, it is preferable to carry out one or more selected from recrystallization, column chromatography and adsorbent treatment, more preferably adsorbent treatment, and more preferably adsorbent treatment. It is particularly preferred to carry out post-recrystallization.

The liquid crystal compound which is the object of the purification method of the present invention is represented by the general formula (I)

[Chemical 2] (In the formula, R is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms,
Alkoxyl group, alkoxyl alkyl group, alkenyl
Represents a group or alkenyloxy group, which has 1 carbon atom
Substituted with an alkoxyl group or an alkenyloxy group of
Any one or more hydrogen atoms in the chain
It may be substituted with a nitrogen atom. A, B, C and D are
Independently trans-1,4-cyclohexylene groups, 1 or more
1,4-phenylene optionally substituted with the above fluorine atoms
Group, naphth optionally substituted with one or more fluorine atoms
Talen-2,6-diyl group, substituted with one or more fluorine atoms
An optionally tetrahydronaphthalene-2,6-diyl group,
Decahydronaphthalene-2,6-diyl group, one or more fluorine
Phenanthrene-3,8-di, optionally substituted with atoms
Group, a group which may be substituted with one or more fluorine atoms.
Trahydrophenanthrene-3,8-diyl group, 1 or more
Octahydrophenane optionally substituted with a fluorine atom
Tren-3,8-diyl group, perhydrophenanthrene-3,8-
Diyl group, pyridine-2,5-diyl group, pyrimidine-2,5-di
Yl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group
Group or trans-1,3-dioxane-2,5-diyl group
Then L¹~ L^FourAre independently -COO-, -OCO-, -CH₂CH
₂-, -CH₂CH (CH₃)-,-CH (CH₃) CH₂-, -CH₂O-, -OCH₂-, -C
F₂O-, -OCF₂-, -CH₂CH₂CH₂CH₂-, -CH = CHCH₂CH₂-, -CH₂C
H = CHCH ₂-, -CH₂CH₂CH = CH-, -OCH₂CH₂CH₂-, -CH₂OCH₂CH₂
-, -CH₂CH₂OCH₂-, -CH₂CH₂CH₂O-, -CF₂OCH₂CH₂-, -CH₂C
H₂OCF₂-, -CF = CF-, -CH = CH-, -C≡C- or single bond
You a, b, c and d each independently represent 0 or 1,
At least one represents 1. Z is a cyano group, a fluorine atom,
Chlorine atom, trifluoromethyl group, trifluoromethoxy
Si group, difluoromethoxy group, fluorine having 2 to 3 carbon atoms
Substituted alkoxyl group, straight-chain alkenyl group having 2 to 7 carbon atoms
It represents a alkyl group or an alkenyl group. Compound represented by)
It is suitable for purification.

In the general formula (I), a compound in which R represents a linear alkyl group having 1 to 7 carbon atoms or a linear alkenyl group having 2 to 7 carbon atoms is preferable, and Z is a cyano group or a fluorine atom. Represents a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group, a difluoromethoxy group or a fluorine-substituted alkoxyl group having 2 to 3 carbon atoms, and exists L ¹ to
It is more preferable to purify a compound in which L ⁴ represents —COO—, —OCO—, —CF ₂ O—, —OCF ₂ — or —C≡C—. These compounds have a strong anisotropy of P
Since it is a type liquid crystal material and impurities are easily taken in, sufficient reliability could not be obtained by the conventional refining method.

In the present purification method, the liquid crystal compound may be purified alone or as a liquid crystal composition in which two or more kinds of liquid crystal compounds are mixed.

[0018]

The present invention will be further described below by showing Examples of the present invention. However, the present invention is not limited to these examples.

Evaluation of reliability of compound Base liquid crystal composition (H)

[Chemical 3] A liquid crystal composition was prepared by adding 10% by mass of the liquid crystal compound purified by the method of the present invention to (in the formula,% represents mass%) and heating and dissolving. Resistivity of prepared liquid crystal composition (Ωcm)
Was measured to evaluate the reliability of the compound.

The specific resistance value (Ω · cm) was measured with an electrometer MMAII-17A manufactured by Kawaguchi Electric Co., Ltd. by applying 1VDC using a liquid electrode LP-05 type having a cell gap of 1 mm.

Evaluation of reliability in panel Liquid crystal composition prepared for measuring specific resistance was used as a liquid crystal cell for TN.
(Cell gap 8.3 μm) was vacuum-injected and sealed with a UV curable resin (Three Bond 3026 manufactured by Three Bond Co., Ltd.) to prepare a liquid crystal cell. A sample whose current value was measured immediately after the liquid crystal cell was prepared was used as an initial sample (hereinafter abbreviated as initial). Using Suntest (Original Hanau) for liquid crystal cells
UV irradiation sample (UV
(Abbreviated as V). Use a liquid crystal cell at 210
A sample that has been heated for a period of time is a heated sample
And

The current value is measured by applying a rectangular wave (Vap = 2.5V) to the produced liquid crystal cell using the circuit shown in FIG. 1 and observing the voltage waveform applied across the 50KΩ resistor in the circuit. Went by. Calculate Vr (V) from the observed voltage waveform (Fig. 2), and use the following formula

[Equation 1] The current value was calculated by. At this time, three liquid crystal cells were produced under each condition, their current values were measured, and the values of the current values obtained from the three cells were averaged to obtain the current value.

Example 1 Specific resistance and current value when a 1.1 T magnetic field was applied for 1 hour

[Chemical 4] 5 g of compound (II) was dissolved in 25 mL of toluene, a magnetic field of 1.1 T was applied, and the mixture was stirred for 1 hour. 25 mL of ion-exchanged water (0.35 μS / cm
After washing the organic layer twice with ² ), 0.25 g of silica gel / 0.25 g of alumina was added as an adsorbent, and the mixture was stirred for 30 minutes. 1 μm
After the adsorbent was filtered off with a Millipore filter, the solvent was distilled off under reduced pressure. After recrystallizing from hexane and filtering the crystallized crystals,
4.7 g of the dried and purified compound (II) was obtained. The measurement results of the specific resistance and current value of the liquid crystal composition for evaluation using the obtained compound (II) are as follows.

[0024]

[Table 1]

(Example 2) Resistivity and current value when a magnetic field of 1.1 T was applied for 5 hours 5 g of compound (II) was dissolved in 25 mL of toluene, and a magnetic field of 1.1 T was applied, and the mixture was stirred for 5 hours. 25 mL of ion-exchanged water (0.35 μS / cm
After washing the organic layer twice with ² ), 0.25 g of silica gel / 0.25 g of alumina was added as an adsorbent, and the mixture was stirred for 30 minutes. 1 μm
After the adsorbent was filtered off with a Millipore filter, the solvent was distilled off under reduced pressure. After recrystallizing from hexane and filtering the crystallized crystals,
4.7 g of the dried and purified compound (II) was obtained. The measurement results of the specific resistance and current value of the liquid crystal composition for evaluation using the obtained compound (II) are as follows.

[0026]

[Table 2]

Comparative Example 1 5 g of the compound (II) was dissolved in 25 mL of toluene, and the organic layer was washed twice with 25 mL of ion-exchanged water (0.35 μS / cm ² ) and then 0.25 g of silica gel / 0.25 g of alumina as an adsorbent. g was added and stirred for 30 minutes. After the adsorbent was filtered off with a 1 μm Millipore filter, the solvent was distilled off under reduced pressure. The crystals were recrystallized from hexane, and the crystallized crystals were filtered and dried to obtain 4.6 g of purified compound (II). The measurement results of the specific resistance and current value of the liquid crystal composition for evaluation using the obtained compound (II) are as follows.

[0028]

[Table 3] The results of the compound obtained in Examples 1 and 2 by the purification method of the present invention and the compound of Comparative Example 1 obtained by purification by a known method are compared. In Examples 1 and 2, the specific resistance is more than doubled as compared with Comparative Example 1. Initial current value is about 30
%, UV is about 20%, and heating is about 10%.

Therefore, the purification method of the present invention is effective in improving the reliability of the liquid crystal compound and the reliability in the panel.

[0030]

The method for purifying a liquid crystal compound of the present invention is a liquid crystal compound in a liquid state or a liquid crystal state, which is difficult to improve reliability (specific resistance etc.) or reliability in a panel by a conventional purification method. Or after applying a magnetic field in the state of being dissolved in a solvent,
By adding the water washing step, it became possible to easily and easily improve the reliability of the liquid crystal compound and the reliability in the panel.

From the above, the liquid crystal composition containing the liquid crystal compound purified by the method of the present invention has high reliability.
It is useful as a constituent material for TN, STN, and TFT liquid crystal display devices.

[Brief description of drawings]

[Figure 1] Current value measurement circuit

[Figure 2] Observed waveform and Vr

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C09K 19/20 C09K 19/20 19/30 19/30 19/32 19/32 19/34 19/34 G02F 1/13 500 G02F 1/13 500 F term (reference) 4H006 AA02 AA03 AB64 AD16 AD17 BB11 4H027 BA01 BB03 BB04 BC04 BC05 BD04 BE07 CD04 CL01 CM04 CQ04

Claims (9)

[Claims] 1. A method for purifying a liquid crystal compound, which comprises applying a magnetic field in a liquid state or a liquid crystal state or in a state of being dissolved in a solvent, and then adding a water washing step. 2. The method according to claim 1, wherein the applied magnetic field is 0.1 T to 10 T, and the applied time is 10 minutes or more and 24 hours or less. 3. The conductivity in the water washing step is 1.0 μS / c.
The method according to claim 1 or 2, wherein ion-exchanged water of m ² or less is used. 4. A liquid crystal compound represented by the general formula (I) [Chemical 1] (In the formula, R is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms,
Alkoxyl group, alkoxyl alkyl group, alkenyl
Represents a group or alkenyloxy group, which has 1 carbon atom
Substituted with an alkoxyl group or an alkenyloxy group of
Any one or more hydrogen atoms in the chain
It may be substituted with a nitrogen atom. A, B, C and D are
Independently trans-1,4-cyclohexylene groups, 1 or more
1,4-phenylene optionally substituted with the above fluorine atoms
Group, naphth optionally substituted with one or more fluorine atoms
Talen-2,6-diyl group, substituted with one or more fluorine atoms
An optionally tetrahydronaphthalene-2,6-diyl group,
Decahydronaphthalene-2,6-diyl group, one or more fluorine
Phenanthrene-3,8-di, optionally substituted with atoms
Group, a group which may be substituted with one or more fluorine atoms.
Trahydrophenanthrene-3,8-diyl group, 1 or more
Octahydrophenane optionally substituted with a fluorine atom
Tren-3,8-diyl group, perhydrophenanthrene-3,8-
Diyl group, pyridine-2,5-diyl group, pyrimidine-2,5-di
Yl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group
Group or trans-1,3-dioxane-2,5-diyl group
Then L¹~ L^FourAre independently -COO-, -OCO-, -CH₂CH
₂-, -CH₂CH (CH₃)-,-CH (CH₃) CH₂-, -CH₂O-, -OCH₂-, -C
F₂O-, -OCF₂-, -CH₂CH₂CH₂CH₂-, -CH = CHCH₂CH₂-, -CH₂C
H = CHCH ₂-, -CH₂CH₂CH = CH-, -OCH₂CH₂CH₂-, -CH₂OCH₂CH₂
-, -CH₂CH₂OCH₂-, -CH₂CH₂CH₂O-, -CF₂OCH₂CH₂-, -CH₂C
H₂OCF₂-, -CF = CF-, -CH = CH-, -C≡C- or single bond
You a, b, c and d each independently represent 0 or 1,
At least one represents 1. Z is a cyano group, a fluorine atom,
Chlorine atom, trifluoromethyl group, trifluoromethoxy
Si group, difluoromethoxy group, fluorine having 2 to 3 carbon atoms
Substituted alkoxyl group, straight-chain alkenyl group having 2 to 7 carbon atoms
It represents a alkyl group or an alkenyl group. ) Claim 3 represented by
The described purification method. 5. In the general formula (I), Z is a cyano group, a fluorine atom, a chlorine atom, a trifluoromethyl group, a trifluoromethoxy group, a difluoromethoxy group or 2 carbon atoms.
Represent to 3 of fluorine-substituted alkoxy group, present L ¹ ~L ⁴ is -COO -, - OCO -, - CF 2 O -, - OCF 2 - or -C≡C- claim 4, wherein representing the Purification method. 6. The purification method according to claim 1, further comprising one or more purification steps selected from recrystallization, column chromatography and adsorbent treatment after the water washing step. 7. A liquid crystal compound purified by the method according to claim 1. 8. A liquid crystal composition containing the liquid crystal compound according to claim 7. 9. A liquid crystal display device comprising the liquid crystal composition according to claim 8 as a constituent element.