TWI392725B - Method of producing liquid crystal composition - Google Patents

Description

Liquid crystal composition method

The present invention relates to a process for producing a liquid crystal composition which is a constituent of a liquid crystal display element.

The liquid crystal display element has evolved into a variety of measuring instruments, automobile panels, word processors, electronic PDAs, printers, computers, televisions, and the like, including timers and electronic desktop computers. Representative of liquid crystal display methods include: TN (twisted nematic) type, STN (super twisted nematic) type, DS (dynamic light scattering) type, GH (guest master) type or FLC (high dielectric) capable of high speed response Liquid crystal) and so on. In addition, the driving method has evolved from the previous static driving to the multiplexed driving method, and the simple matrix method has been adopted. Recently, the active matrix method has been put into practical application.

The liquid crystal composition used herein is usually produced by mixing two or more kinds of compounds, and the mixing ratio thereof is based on the physical properties of the liquid crystal composition (nematic phase temperature range, refractive index anisotropy (Δn), and dielectric constant). Directional (Δε), viscosity, elastic constant, etc. or photoelectric characteristics (response time, critical voltage, steepness of VT (voltage-temperature) curve, etc.) for the purpose of display mode or drive mode of liquid crystal elements to match various values It is decided, but almost the composition must have high reliability for heat, light, moisture, and the like. Further, especially in the case of the active matrix driving method, it is important that the voltage holding ratio (VHR) must be sufficiently high. In order to improve the reliability, resistivity, and voltage holding ratio (VHR) of the liquid crystal composition, it is necessary to achieve high reliability and voltage holding ratio (VHR) with respect to each liquid crystal compound constituting the composition. However, even when a liquid crystal compound having high reliability, resistivity, and voltage holding ratio (VHR) is used, when the liquid crystal composition of these mixtures is produced, there is a possibility that the quality is deteriorated.

In the production method of the liquid crystal composition, there has been proposed a method of removing the organic solvent by mixing after dissolution by heating or dissolving the liquid crystal compound in an organic solvent (see Patent Document 1). However, most of the methods disclosed in these proposals lead to quality degradation. For example, in the case of dissolved mixing by heating, the liquid crystal compound is oxidatively decomposed due to oxygen upon heating, so that the resistivity or voltage holding ratio (VHR) of the liquid crystal composition is remarkably lowered. Further, there is a possibility that the liquid crystal upper limit transfer temperature is lowered to cause a change in physical properties or photoelectric characteristics of the liquid crystal composition. Further, in the method of dissolving in an organic solvent, there is a possibility that the resistivity or voltage holding ratio (VHR) of the liquid crystal composition is remarkably lowered due to impurities or dopants of the organic solvent. Further, the organic solvent is not completely removed and remains, and as a result, the resistivity of the liquid crystal composition is lowered or the voltage holding ratio is remarkably lowered. On the other hand, there has also been proposed a method of heating at a relatively low temperature in a reduced pressure state, which is directed to the production of a liquid crystal composition having a low electric resistance value (refer to Patent Document 2). However, the method disclosed in the cited document, although it can be manufactured at a lower temperature, still requires heating, so that the adverse effects caused by heating cannot be completely eliminated, and equipment accompanying heating is also required. Moreover, the method disclosed in the cited document has a problem between large-scale devices that require decompression. In other words, in order to dissolve the liquid crystal compound while decompressing, the container which can withstand pressure reduction is required, so that the manufacturing apparatus must use a large-scale decompression. Further, although a vacuum pump is generally used for the pressure reduction, a well for preventing backflow of the oil mist and a cooling device for cooling the trap used in the vacuum pump are also required as an accessory device. As described above, the method of producing a liquid crystal composition under reduced pressure inevitably leads to an increase in size of the apparatus, which necessitates investment of excessive capital to correspond to the demand for the liquid crystal composition being increased.

In view of the above, it is currently desired to develop a method for efficiently producing a higher quality liquid crystal composition with a simple device.

(Patent Document 1) Japanese Laid-Open Patent Publication No. 5-105876 (the right column of page 5)

(Invention Patent Document 2) Japanese Laid-Open Patent Publication No. 2002-194356 (Example of page 4)

The technical problem to be solved by the present invention is to provide a liquid crystal composition which can be manufactured with high reliability and which can be efficiently produced in the production of a liquid crystal composition composed of two or more kinds of liquid crystal compounds.

The inventors of the present invention have finally achieved the present invention in order to solve the technical problems as described above and concentrate on the results. The present invention provides a process for producing a liquid crystal composition characterized in that at least one of liquid crystal compounds having a melting point higher than 30 ° C is irradiated with microwaves.

The method of the present invention can produce a high-quality liquid crystal composition having high reliability without requiring a large-scale apparatus such as a decompression device or a heating device. In other words, it is highly practical to manufacture a liquid crystal composition which is required to suppress a decrease in resistivity, a small amount of impurities, and a small change in physical property value, and which has high reliability.

[Best Embodiment of the Invention]

Hereinafter, an example of the present invention will be described.

The method of the present invention is to efficiently produce a liquid crystal composition by irradiating a microwave with a liquid crystal compound containing at least one liquid crystal compound having a melting point of higher than 30 ° C without using an organic solvent or the like. . In particular, it is effective to use two liquid crystal compositions in which two or more liquid crystal compounds having a melting point of higher than 30 ° C are used, and five or more liquid crystal compounds having a melting point higher than 30 ° C are used. The liquid crystal composition is more effective in the manufacture.

The content of the compound having a melting point of 30 ° C or higher is preferably 60% or more, more preferably 70% or more, and particularly preferably 80% or more.

The liquid crystal composition may contain additives other than the liquid crystal compound. As the additive, an antioxidant, an ultraviolet absorber, an antistatic agent, a surfactant, or the like can be used. Further, an optically active compound having liquid crystallinity or non-liquid crystallinity may also be contained. When the amount of the compound having no liquid crystal skeleton is too large, the effect on the liquid crystal is adversely affected. Therefore, when a compound having no liquid crystal skeleton is to be added, the total content is preferably 5% or less. More preferably, it is 3% or less, and particularly preferably 1% or less.

The irradiation time of the microwave is preferably 1 hour or less, more preferably 30 minutes or less. If the temperature at the time of irradiation with the microwave is too high, the quality of the manufactured composition will be lowered, and if it is too low, it takes time to manufacture, so of course, it has an optimum temperature. Therefore, it is preferably in the range of from 50 ° C to the liquid crystal phase upper limit temperature of the obtained liquid crystal composition + 50 ° C, more preferably in the range of + 30 ° C.

The frequency of the microwave used is preferably 300 MHz or more, 3 THz or less, and more preferably 500 MHz or more. The irradiation intensity is preferably 100 W or more, more preferably 1 kW or more.

According to the production method of the present invention, since a liquid crystal composition can be produced at a low temperature, a high-quality liquid crystal composition can be produced in a general atmosphere. However, in order to produce a higher quality liquid crystal composition, it is preferred to carry out the irradiation of the microwave under a sealed condition, and more preferably in an inert gas atmosphere. The inert gas system is suitable for using a rare gas such as helium, neon or argon, and nitrogen.

Although the production method of the present invention does not require the use of a pressure reducing measure, the production of the composition can be carried out under reduced pressure.

The liquid crystal composition obtained by the production method of the present invention is not particularly limited, but when it is produced under reduced pressure, it is particularly preferable to produce a liquid crystal composition containing a large amount of a liquid crystal compound having a small molecular weight which is volatilized.

The molecular weight of the liquid crystal compound is preferably a compound having 300 or less, more preferably a compound having 250 or less.

In order to produce the liquid crystal composition more efficiently, it is preferred that the liquid crystal molecules formed are polarized and shifted. Specifically, it can be produced more efficiently than when the liquid crystal compound to be formed has a specific structure or functional group. A preferred structure has at least one aromatic ring in the molecule of the liquid crystal compound. Further, a preferred functional group is an electron-attracting functional group such as a halogen or a cyano group, and is preferably a compound having such a functional group in the molecule, and more preferably has an electron-attracting functional group in the aromatic ring. compound of.

Specifically, the compound to be constituted is preferably a compound represented by the formula (I).

(wherein R ¹ and R ² each independently represent an alkyl group having 1 to 16 carbon atoms substituted by fluorine, an alkoxy group having 1 to 16 carbon atoms, and 2 carbon atoms; Alkenyl group to 16, alkenyloxy group having 3 to 16 carbon atoms, fluorine atom, chlorine atom or cyano group; A, B and C each independently represent 1,4-phenylene, 2 or 3-fluoro -1,4-phenylene, 2,3-difluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene, 2 or 3-chloro-1,4-stretch Phenyl, 2,3-dichloro-1,4-phenylene, 3,5-dichloro-1,4-phenylene, 2-methyl-1,4-phenylene, 3-methyl -1,4-phenylene, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, indole-2,7-diyl, trans-1,4-cyclohexylene, 1,2 , 3,4-tetrahydronaphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, trans-1,3-di Alkane-2,5-diyl, pyridine-2,5-diyl, pyrimidine-2,5-diyl, pyridyl -2,5-diyl, or 嗒 -2,5-diyl, and these groups may be further substituted with 1 to 3 fluorine atoms; m represents 0, 1 or 2; Z ¹ and Z ² each independently represent a single bond , -CH ₂ CH ₂ -, -(CH ₂ ) ₄ -, -OCH ₂ -, -CH ₂ O-, -COO-, -CH=CH-, -CF=CF-, -CH=NN=CH- Or -C≡C-. However, if m is 2, then the two Z ² and C systems may independently be the same or different. )

In the formula (I), at least one of A, B and C is preferably an aromatic ring, more preferably 1,4-phenylene, 2 or 3-fluoro-1,4-phenylene, 2, 3-difluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene, 2 or 3-chloro-1,4-phenylene, 2,3-dichloro-1 , 4-phenylene, 3,5-dichloro-1,4-phenylene, 2-methyl-1,4-phenylene, 3-methyl-1,4-phenylene, naphthalene- 2,6-diyl, phenanthrene-2,7-diyl, indole-2,7-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, pyridine-2,5- Dibasic, pyrimidine-2,5-diyl, pyridyl -2,5-diyl, or 嗒 -2,5-diyl; particularly preferably 1,4-phenylene, 2 or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene, 3, 5-difluoro-1,4-phenylene.

R ¹ and R ² preferably each represent a fluorine atom, a chlorine atom or a cyano group, and the other represents an alkyl group having 1 to 16 carbon atoms and an alkoxy group having 1 to 16 carbon atoms. A compound having an alkenyl group having 2 to 16 carbon atoms and an alkenyloxy group having 3 to 16 carbon atoms.

When the liquid crystal composition for TFT is produced by the process of the present invention, in the compound represented by the formula (I), R ¹ and R ² each preferably independently represent a fluorine atom and have a carbon number of from 1 to 16. An alkyl group or a compound having an alkenyl group having 2 to 16 carbon atoms. In this case, the obtained liquid crystal composition has a high voltage holding ratio.

"Embodiment"

In the following, the invention will be described in more detail by way of examples, but the invention is not limited by the examples. In addition, "%" in the compositions of the examples and comparative examples below means "% by weight".

The microwave irradiation was carried out using a microwave irradiation device (special order product) manufactured by Fuji Electronic Industrial Co., Ltd. (high-frequency output power: 6 kW, oscillation frequency: 2,450 MHz ± 50 MHz). The analysis of the obtained liquid crystal composition used the following devices:

Gas Chromatography: HP6890 manufactured by HEWLETT PACKARD. The reliability was confirmed by measuring the electrical resistivity of the liquid crystal composition, confirming the formation of impurities and decomposition of the mixed compound by gas chromatography, and measuring the voltage holding ratio, the current value, and the physical property value.

[Example 1] Production of liquid crystal composition

The production of a liquid crystal composition (STN1, liquid crystal upper limit temperature: 95.1 ° C) composed of the following compounds was carried out.

In a separate flask having a capacity of 150 ml, the respective compounds as described above and the amounts thereof are recited. The separation flask was mounted on a microwave generating device and irradiated with microwave heating at an output of 1 kW. After the irradiation for 10 minutes, the microwave irradiation was stopped, and the separation flask was cooled, and then taken out from the microwave irradiation device, whereby 100 g of the nematic liquid crystal state of STN1 was obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.1 × 10 ¹¹ Ωcm. Further, the obtained liquid crystal composition was analyzed by gas chromatography, and as a result, no substance other than the mixed compound was formed, and decomposition of the mixed compound was not observed. The physical properties of the obtained liquid crystal composition were measured, and as a result, the desired properties were obtained. The liquid crystal was injected into the STN panel and the photoelectric characteristics were measured, and as a result, the desired characteristics were obtained. From the results as described above, it is understood that the liquid crystal composition of Example 1 has a very high reliability.

The method of the present invention can produce a high quality liquid crystal composition in 40 minutes without requiring a large-scale apparatus.

[Comparative Example 1] Production of liquid crystal composition under reduced pressure

The liquid crystal composition (STN1) similar to that of Example 1 was produced by the method disclosed in Japanese Laid-Open Patent Publication No. 2002-194356.

Weigh the desired amount of liquid crystal compound in an eggplant type flask. Then, the eggplant type flask was mounted on a rotary evaporator. The eggplant type flask was immersed in a 50 ° C oil bath and rotated. The rotary evaporator was slowly depressurized to 20 kPa using a vacuum pump for 5 minutes. The temperature of the oil bath was set to 110 ° C and the temperature was raised at a rate of 5 ° C / min. After the liquid crystal was changed to a liquid state and was transparent for 30 minutes, the oil bath was changed to a water bath to be cooled. After lowering to room temperature, stop the rotation and stop the decompression. After replacing the inside of the flask with nitrogen to return to atmospheric pressure, the eggplant type flask was removed by a rotary evaporator, whereby 100 g of nematic liquid crystal STN1 was obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.2 × 10 ¹¹ Ωcm. The obtained liquid crystal composition was analyzed by gas chromatography, and as a result, no substance other than the mixed compound was formed, and decomposition of the mixed compound was not observed. The physical properties of the obtained liquid crystal composition were measured, and as a result, the desired properties were obtained. However, it has been confirmed that certain lower molecular weight compounds have volatilized to cause compositional changes. In addition, manufacturing requires the use of a pressure reducing device or a heating device that requires large-scale equipment, and requires a long manufacturing time.

[Comparative Example 2] Production of liquid crystal composition under the atmosphere

The liquid crystal composition (STN1) similar to that of Example 1 was produced by the method disclosed in Japanese Laid-Open Patent Publication No. 5-105876.

Weigh the desired amount of liquid crystal compound in an eggplant type flask. After placing a magnet rotor in the eggplant type flask, it was placed on a hot plate at 50 ° C, and the temperature of the hot plate was raised to 110 ° C at a rate of 5 ° C/min, and the rotor was rotated while stirring. . After the liquid crystal was changed to a liquid state and was transparent for 30 minutes, the heating of the hot plate was stopped, and the temperature was slowly returned to room temperature. Thereby, STN1 of a nematic liquid crystal state of 100 g can be obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.1 × 10 ⁹ Ωcm. The liquid crystal composition thus obtained was analyzed by gas chromatography, and as a result, many substances other than the mixed compound appeared, and it was found that the liquid crystal compound for constituting the liquid crystal composition had been oxidatively decomposed. When the liquid crystal upper limit point transfer temperature was measured, the result was reduced to 94.0 ° C, and thus the deterioration of quality was large. Regarding the production method of Comparative Example 2, it was significantly inferior to the examples in terms of the reliability of the obtained liquid crystal composition.

[Example 2] Production of liquid crystal composition

Production of a liquid crystal composition (TFT1, liquid crystal upper limit temperature: 68.0 ° C) composed of the lower layer compound was carried out.

In a separate flask having a capacity of 150 ml, the respective compounds as described above and the amounts thereof are recited. The separation flask was placed on a microwave generating device and heated by irradiating microwaves at an output of 1 kW. After the irradiation for 10 minutes, the microwave irradiation was stopped, and the separation flask was cooled, and then taken out from the microwave irradiation device, whereby 100 g of the nematic liquid crystal state TFT1 was obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.5 × 10 ¹⁴ Ωcm. Further, the obtained liquid crystal composition was analyzed by gas chromatography, and as a result, substances other than the mixed compound were not mixed, and decomposition of the mixed compound was not observed. The physical properties of the obtained liquid crystal composition were measured, and as a result, the desired properties were obtained. The liquid crystal was injected into the TFT panel and the photoelectric characteristics were measured, and as a result, the desired characteristics were obtained. In addition, the voltage holding ratio when used in a TFT panel is also sufficiently high.

The method of the present invention can produce a high quality liquid crystal composition in 40 minutes without requiring a large-scale apparatus. From the results as described above, it is understood that the liquid crystal composition of Example 2 has a very high reliability.

[Comparative Example 3] Production of liquid crystal composition under reduced pressure

The liquid crystal composition (TFT1) similar to that of Example 2 was produced by the method disclosed in Japanese Laid-Open Patent Publication No. 2002-194356.

Weigh the desired amount of liquid crystal compound in an eggplant type flask. Then, the eggplant type flask was mounted on a rotary evaporator. The eggplant type flask was immersed in a 50 ° C oil bath and rotated. The rotary evaporator was slowly depressurized to 20 kPa using a vacuum pump for 5 minutes. Then, the temperature of the oil bath was set to 85 ° C, and the temperature was raised at a rate of 5 ° C / min. After the liquid crystal was changed to a liquid state and was transparent for 30 minutes, the oil bath was changed to a water bath to be cooled. After lowering to room temperature, stop the rotation and stop the decompression. After replacing the inside of the flask with nitrogen to return to atmospheric pressure, the eggplant type flask was removed by a rotary evaporator, whereby 100 g of the nematic liquid crystal state of the TFT 1 was obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.2 × 10 ¹⁴ Ωcm. The obtained liquid crystal composition was analyzed by gas chromatography, and as a result, no substance other than the mixed compound was formed, and decomposition of the mixed compound was not observed. The physical properties of the obtained liquid crystal composition were measured, and as a result, the desired properties were obtained. However, it has been confirmed that certain lower molecular weight compounds have volatilized to cause compositional changes. In addition, manufacturing requires the use of a pressure reducing device or a heating device that requires large-scale equipment, and requires a long manufacturing time.

[Comparative Example 4] Production of liquid crystal composition under the atmosphere

A liquid crystal composition (TFT1) similar to that of Example 2 was produced by the method disclosed in Japanese Laid-Open Patent Publication No. 5-105876.

Weigh the desired amount of liquid crystal compound in an eggplant type flask. After placing a magnet rotor in the eggplant type flask, it was placed on a hot plate at 50 ° C, and the temperature of the hot plate was raised to 85 ° C at a rate of 5 ° C / min while the rotor was rotated to stir. . After the liquid crystal was changed to a liquid state and was transparent for 30 minutes, the heating of the hot plate was stopped, and the temperature was slowly returned to room temperature. Thereby, 100 g of the nematic liquid crystal state of the TFT 1 can be obtained.

The resistivity of the obtained liquid crystal composition was measured and found to be 1.3 × 10 ¹³ Ωcm. The liquid crystal composition thus obtained was analyzed by gas chromatography, and as a result, many substances other than the mixed compound appeared, and it was found that the liquid crystal compound for constituting the liquid crystal composition had been oxidatively decomposed. When the liquid crystal upper limit point transfer temperature was measured, the result was reduced to 66.8 ° C, and thus the deterioration of quality was large. Regarding the production method of Comparative Example 4, it was significantly inferior to the examples in terms of the reliability of the obtained liquid crystal composition.

Claims (6)

A method for producing a liquid crystal composition, characterized in that at least one of liquid crystal compounds having a melting point higher than 30 ° C is irradiated with microwaves. For example, in the method of claim 1, the melting point of at least two of the liquid crystal compounds is higher than 30 °C. For example, in the method of claim 1, the microwave irradiation time is 1 hour or less. For example, in the method of claim 1, the microwave irradiation is carried out under reduced pressure. For example, in the method of claim 1, the microwave irradiation is carried out under an inert gas atmosphere. For example, in the method of claim 4, an inert gas is used in returning the reduced pressure state to atmospheric pressure.