JPH0132274B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid crystal composition, and more particularly, to a liquid crystal composition used in a liquid crystal display device that utilizes dielectric dispersion of liquid crystal. Calculators, wristwatches, and other items that had existed since then began to be sold in large quantities. Although liquid crystal display elements were statically driven in the early days, most of them are now dynamically driven. The dynamic drive system currently in use is
This method is called voltage averaging, and advances in liquid crystal materials, circuit technology, etc. have improved it to the extent that it can drive by three to four orders of magnitude. However, the improvement with this method is limited to this extent, and there is a limit to its application to character displays, graphic displays, televisions, etc., which require multi-digit driving. Two-frequency dynamic drive has emerged as a method to improve such voltage averaging method.
(Hereinafter abbreviated as 2F method.) Some liquid crystals cause dispersion at relatively low frequencies.
In some cases, the dielectric anisotropy (Δε) is positive at low frequencies, but reverses and becomes negative at high frequencies. (See Figure 1) At this time, there is a frequency at which Δε becomes 0, and this frequency is called the crossover frequency (c) and is characterized as a physical property value of the liquid crystal. The feature of the 2F method is that it uses two AC power supplies, one with a lower frequency and one with a higher frequency than c, as the driving power supply, and takes advantage of the difference in the behavior of liquid crystals at low and high frequencies. Generally, in the case of dynamic driving, the ratio of the voltage applied to the display during lighting to the voltage when not lighting is required to be at least a certain value, and the larger the ratio, the better. In the voltage averaging method, this value depends only on the number of digits, and there is little room for improvement. On the other hand,
It is known that the 2F method depends on the dielectric constant of the liquid crystal and the driving voltage, and theoretically it can be driven by many orders of magnitude. However, in reality, no liquid crystal composition has been obtained that can be used at room temperature and has a practical response speed that satisfies these requirements. [Problems to be Solved by the Invention] The following properties are required for a liquid crystal composition that has an appropriate response speed at room temperature and is used in the above-mentioned 2F method liquid crystal display element. 1. In order to lower the drive voltage, the absolute values of dielectric anisotropy on the low frequency side and on the high frequency side must be large. In particular, the absolute value of dielectric anisotropy on the high frequency side is large. 2. Small c and low viscosity. An object of the present invention is to provide a liquid crystal composition that satisfies these requirements. [Means for Solving the Problems] The liquid crystal composition for dual-frequency dynamic driving of the present invention has the general formula: (However, R ₁ represents a straight chain alkyl group having 5 or 8 carbon atoms.) At least one of the compounds represented by 23.6 to 70
Weight% and general formula (However, R ₂ represents a straight chain alkyl group having 6 or 7 carbon atoms, and R ₃ represents a straight chain alkyl group having 4 or 5 carbon atoms.) At least one of the compounds represented by
In a liquid crystal composition consisting of % by weight, the general formula (However, R ₄ represents a straight chain alkyl group having 3 or 4 carbon atoms.) 31.4% by weight or less of two types of compounds represented by the chemical formula 7.9% by weight or less of a compound represented by the chemical formula 5.5% by weight or less of a compound represented by the chemical formula 7.9% by weight or less of a compound represented by the chemical formula It is characterized in that the compound represented by is added in an amount of 7.9% by weight or less. The amount of each compound added was determined for the following reason. If it is less than 23.6% by weight, the crossover frequency will increase, and if it exceeds 70% by weight, the temperature characteristics will deteriorate. Also, If it is less than 15.8% by weight, the dielectric dispersion on the high frequency side will not be very large, and if it exceeds 30% by weight, the temperature-temperature characteristics and cross frequency will deteriorate. Furthermore, general formula or chemical formula (3), (4), (5), (6),
When each of the compounds represented by (7) exceeds a predetermined amount, the dielectric anisotropy on the low frequency side becomes extremely small and the crossover frequency increases. The characteristics of the compound used in the present invention are as follows:
It is as shown in Table 1.

[Table] Although the compounds shown in Table 1 do not have a liquid crystal phase, the desired liquid crystal composition can be obtained by appropriately mixing these compounds. Table 2 lists examples of suitable liquid crystal compounds that can be mixed with the compounds listed in Table 1.

【table】

〔Example〕

Example 1 A liquid crystal composition shown in Table 3 was prepared, and how the dielectric anisotropy of this liquid crystal composition changed with frequency was investigated. The results at 30°C are shown in Figure 1.

[Table] According to this figure, |△ε on the high frequency side of this composition
It turns out that | is 3.9, Since it is 2.3 before the addition of , it can be seen that |△ε| on the high frequency side becomes extremely large by adding this. Also, instead of the above compounds, similar compounds, e.g. |△εH| of the liquid crystal composition when 30 weight percent of is added is +3.2, so It can be seen that it is more effective to add Example 2 A liquid crystal composition shown in Table 4 was prepared, and how the dielectric anisotropy of this liquid crystal composition changed with frequency was investigated. The results at 25.7°C are shown in Figure 2. When this liquid crystal composition was filled into a liquid crystal cell and tested under the conditions shown in Table 5, very good results were obtained.

【table】

[Table] The driving voltage at this time was ±30V, and the response speed was as fast as 300 milliseconds at 25°C, with the sum of the rise, fall, and delay times being sufficiently durable for use.

【table】

[Comparative example]

Similar to Example 2, the general formula is not used. The results of comparing the compositions blended in the proportions shown in Table 6 are shown below.

【table】

[Table] The driving voltage at this time was ±30V, and the response time was 430 milliseconds at 25°C, the sum of the rise, fall, and delay times. [Effects of the Invention] As described above, the dual-frequency dynamic driving liquid composition of the present invention has the following general formula: For the compound represented by the general formula By mixing the compound represented by the formula in a predetermined ratio, the dielectric anisotropy |△ε| on the high frequency side becomes about 4, compared to about 2 before adding the compound in (2) above. , it shows a very remarkable effect of increasing the absolute value of the dielectric anisotropy mentioned above, and as the absolute value of the dielectric anisotropy increases, the driving voltage can be lowered by about 20 to 25%, making it possible to use a lower voltage. It is possible to drive the In addition, the compositions (1) and (2) above have a predetermined alkyl group, and chemical formula By mixing the compound represented by the formula in a predetermined proportion, the crossover frequency can be set to an extremely low practical value of approximately KHz, and the response time is also 430 milliseconds at 25°C without using the composition of the present application. In contrast, in the present invention, the time is 300 milliseconds, which can be shortened by more than 100 milliseconds.A dual-frequency dynamic drive liquid crystal display using such a liquid crystal composition can be used in multi-digit drive displays such as character displays. It exerts its power in

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the relationship between dielectric anisotropy (Δε) and frequency (KHz) of the liquid crystal composition of the present invention. In the figure, the vertical axis shows dielectric anisotropy and the horizontal axis shows frequency.

Claims (1)

[Claims] 1. General formula (However, R ₁ represents a straight chain alkyl group having 5 or 8 carbon atoms.) At least one of the compounds represented by 23.6 to 70
Weight% and general formula (However, R ₂ represents a straight chain alkyl group having 6 or 7 carbon atoms, and R ₃ represents a straight chain alkyl group having 4 or 5 carbon atoms.) At least one of the compounds represented by
In a liquid crystal composition consisting of % by weight, the general formula (However, R ₄ represents a straight chain alkyl group having 3 or 4 carbon atoms.) 31.4% by weight or less of two types of compounds represented by the chemical formula 7.9% by weight or less of a compound represented by the chemical formula 5.5% by weight or less of a compound represented by the chemical formula 7.9% by weight or less of a compound represented by the chemical formula 1. A liquid crystal composition for dual-frequency dynamic drive, characterized in that a compound represented by the following is added in an amount of 7.9% by weight or less.