JPH0217599B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal composition, and more specifically, the present invention relates to a liquid crystal composition, and more specifically,
This invention relates to a liquid crystal material used in a liquid crystal display element using a dual-frequency driving method (Japanese Patent Application Laid-open Nos. 104043-1982 and 139394-1970) that utilizes the dielectric dispersion phenomenon of liquid crystals. Electro-optical display elements using liquid crystals have advantages such as low voltage drive, low power consumption, and high contrast, and are currently widely used in digital watches, calculators, measuring instruments, etc., but most of them are segment-based. It is a dot matrix display that can display several dozen characters, and can display several hundred characters.
It has been difficult to use liquid crystals in character displays, graphic displays, and even televisions. Conventionally, matrix display has been performed using dynamic drive such as voltage averaging, but this method limits the maximum number of digits to about 8 digits, making multiplex drive for character displays, graphic displays, etc. difficult. be. To compensate for this drawback, the dielectric anisotropy of liquid crystal changes depending on the frequency of the applied voltage, and the sign of the dielectric anisotropy changes with the frequency of the applied voltage. A dual-frequency drive system that controls the orientation of liquid crystal molecules by applying signals with different components and performs ON-OFF display is attracting attention. When driving with this method, typical characteristics required of the liquid crystal material are shown below. The absolute value of dielectric anisotropy at the driving frequency (especially higher frequencies than fc) is large. fc is relatively low over the operating temperature range. The temperature dependence of fc is small. The response speed (in this case, the dual-frequency drive method is used as described in Japanese Patent Application Laid-Open No. 139394/1983, and the average value of the sum of the rise speed and fall speed under constant conditions) is fast. The above characteristics will be briefly explained. In general, the greatest advantage of liquid crystal displays is that they can be driven at low voltages, consume low power, and provide high contrast, but in order to display a multi-digit matrix using dual-frequency drive, an applied voltage of several tens of volts is required. Also, the driving frequency is as high as several KHz on the high frequency side. Therefore, in order to reduce power consumption, it is very effective to increase the absolute value of dielectric anisotropy, especially to increase the absolute value of dielectric anisotropy on the higher frequency side than fc. →Characteristics In order to make the display smaller, the circuit is C-MOS-
There are limits to the drive voltage and drive frequency when incorporating and driving ICs, etc. fc is several KHz near room temperature
Even if the thigh can be driven satisfactorily with FC, if the temperature rises
Shifts to the high frequency side, making it impossible to display
The operating temperature range becomes narrower. Also fc at low temperature
If is too low, the dielectric anisotropy on the frequency side lower than fc will be smaller, and this will also become impossible to display.
This will narrow the operating temperature range. Therefore, a liquid crystal is required that has a small rate of increase in fc due to temperature changes and has a small fc value at high temperatures. →Characteristics: Along with contrast, responsiveness is the most important characteristic in terms of display quality, and this is the key to practical application, especially in applications such as televisions, which have fast ON-OFF switching speeds. →Characteristics Since there are almost no liquid crystals that can exhibit these characteristics either singly or as a mixture of homologues, compositions with the required characteristics are created by mixing several types of liquid crystal compounds or non-liquid crystal compounds. However, among the above characteristics, these are contradictory; for example, improving responsiveness increases fc, and many liquid crystals are characterized by the inability to display at temperatures higher than room temperature. Furthermore, it is obvious that the physical properties of liquid crystals are temperature dependent, but as mentioned above, temperature changes in fc are a particular problem in practice in dual-frequency drive systems, and in conventional liquid crystals, temperature dependence of fc is large. Therefore, it is difficult to widen the operating temperature range even if a temperature compensation circuit is installed. Conventionally, when the above characteristics ~ are satisfied in a well-balanced manner and dual-frequency drive is performed, the operating temperature range is wide (5℃ to 40℃ is considered practical) and the contrast is good (10:1 or higher). ), quick response (both rise and fall at room temperature,
300 mstc or less). The present invention has been made to improve these drawbacks, and its purpose is to provide a liquid crystal composition that can operate over a wide temperature range and has a fast response speed when driven at two frequencies. be. The liquid crystal composition for dual-frequency driving of the present invention has the general formula: (However, R ₁ is a straight-chain alkyl group having 3.5 carbon atoms,
R ₂ represents a straight chain alkyl group having 4, 5, 6, or 7 carbon atoms. ), and the chemical formula is At least one compound selected from group b compounds represented by and the general formula is (However, R ₂ represents a straight chain alkoxy group having 4, 5 or 6 carbon atoms, R ₃ represents a straight chain alkyl group having 4 or 5 carbon atoms, and X represents CN or Cl.) The compound and the general formula are (However, R ₄ is a straight-chain alkyl group having 5 to 7 carbon atoms, and A is

[expression] or

[Formula] or

[Formula], R ₅ represents a straight chain alkyl group having 5 to 7 carbon atoms, R ₆ represents a straight chain alkyl group having 5 to 8 carbon atoms, and R ₇ represents a straight chain alkyl group having 5 carbon atoms. ) and at least one compound of group (d-1) represented by

[Table] 〓
and at least one type of compound selected from the d-n group of compounds represented by: That is, component a shown below General (In the formula, R has 3 or 5 carbon atoms, and R' has 4 carbon atoms.
~7 straight chain alkyl). b A liquid crystal compound that has a cyano group at its terminal and has large positive dielectric anisotropy. c A liquid crystal compound that has negative dielectric anisotropy with a large absolute value, or a non-liquid crystal compound that has a rod-like molecular shape. d A liquid crystal compound or liquid crystal mixture that satisfies at least two of the following conditions. 1 fc is low. 2 The temperature dependence of fc is small. 3. Low viscosity. 4. Wide liquid crystal temperature range and low melting point. By blending the components of each group a to d in appropriate proportions, we succeeded in creating a liquid crystal composition that is sufficiently practical as a liquid crystal material for dual-frequency driving. Next, when mixing each of the components a to d above, how each component contributes to the characteristics required of the above-mentioned dual-frequency driving liquid crystal material will be explained. In general, the dielectric constant of a liquid crystal (ε=permittivity in the direction parallel to the long axis of the molecule, ε⊥=permittivity in the direction perpendicular to the long axis of the molecule) changes depending on the frequency of the applied voltage. That is, dielectric dispersion occurs as shown in FIG. In the figure, the frequency at which ε=ε⊥ is fc (crossing frequency), and the dielectric anisotropy of the liquid crystal (Δε=ε−
ε⊥) is more positive than ε−ε⊥>0 in the frequency region lower than fc, and ε−ε⊥＜ in the frequency region higher than fc.
It is more negative than 0. If a liquid crystal with such properties is sealed in a TN liquid crystal cell and signals with different frequency components are applied to the cell, the orientation direction of the liquid crystal can be changed. That is, as shown in Fig. 2, a, when a signal having the frequency component fL in Fig. 1 is applied,
Liquid crystal molecules are oriented perpendicular to the cell surface, and in a TN cell, it is in an ON state. Similarly, as shown in FIG. 2b, when a signal having a frequency component of fH in FIG. 1 is applied, the liquid crystal molecules are aligned horizontally to the cell surface and are in the OFF state. This is the basic principle of dual-frequency drive, but when displaying with dynamic drive like a character display, ON-OFF display is performed by applying a signal consisting of a composite component of low and high frequencies. The dielectric dispersion of such a liquid crystal is fc, ΔεL, ΔεH
It is characterized by (Figure 1). First, among the properties required of liquid crystal materials, the absolute value of dielectric anisotropy at the driving frequency (especially at frequencies higher than FC) must be large. This is to lower the drive voltage as described above, and the components that greatly contribute to this are the b and c groups among the a to d groups. That is, the component that increases and adjusts Δε _L is b
(a group of liquid crystal compounds that have a cyano group at the terminal and have large positive dielectric anisotropy) and have a considerable influence on the adjustment of Δε _L , but the main purpose is to adjust the absolute value of Δε _H. The increasing component is a C group compound (a liquid crystal compound having negative dielectric anisotropy with a large absolute value, or a group of non-liquid crystal compounds whose molecules have a rod-like shape). That is, ΔεL and ΔεH are mainly adjusted by the b group and c group. There are a wide variety of known liquid crystal compounds as group b compounds, but among them, those with the general formula (In the formula, R represents a straight-chain alkoxy group having 6 or 8 carbon atoms.) Examples include compounds having a CN group at the terminal. Other well-known

【formula】

[Formula], etc. are possible, but since these compounds have a high dispersion frequency as a single product, adding them to the composition will increase the dispersion frequency of the composition, so it may be difficult to meet the required characteristics described above. Considering balance, this is not very desirable. On that point, as mentioned above (in particular,
) has a low dispersion frequency and good balance with properties. These liquid crystal compounds have relatively high melting points and clearing points. When these compounds are added to a composition, it is possible to raise the clearing point of the composition, but if the amount is large, the melting point of the composition increases and crystals may precipitate at low temperatures. Therefore, it is not possible to add a large amount, but since Δε is large, a very small amount (10εt% or less, preferably 6εt%) can be added.
The magnitude of ΔεL of the composition can be adjusted to an appropriate value simply by adding (below). For the above reasons, the preferred compounds of group b are:
1) The melting point is 150°C or less, preferably 130°C or less, more preferably 100°C or less, 2) The total number of benzene rings and cyclohexane rings is 3 or more and 4 or less, 3) The bond between the benzene rings or cyclohexane rings is

[Formula] or C-C, the number of ester bonds in the compound is 0 to 3, it goes without saying that the terminal has -CN and Δε is large, and it is optically and chemically stable. No, but 1) above
As long as the compounds fall under ~3), compounds in Table 1 with different terminal alkyl chain lengths, and even compounds with structural formulas other than the general formula ~ above, correspond to Group b compounds. As such, it is sufficiently effective and practical. There are not as many types of compounds known as group c compounds as there are in the group b compounds mentioned above. Even a strong dipole such as a cyano group has the effect of increasing polarization in the same direction and increasing Δε if it is attached at the end of the long axis of the molecule in parallel with the long axis. When attached to a ring, the polarization in the same direction (at an angle of about 60° to the long axis) is not very large, so there are only a few negative liquid crystals with large absolute values. Therefore, even non-liquid crystal compounds have a rod-like shape, and when mixed with liquid crystal, they have negative dielectric anisotropy with a large absolute value and have a relatively low melting point. It is also sufficiently effective when used as an agent. As an example, the general formula

[Formula] (In the formula, R has 4 to 6 carbon atoms, and R' has 4.5 carbon atoms.
represents a straight-chain alkyl group, X represents CN, and Y represents -Cl or -CN. ) is a compound represented by
These compounds do not exhibit a liquid crystal phase. However, since it has a rod-like shape like liquid crystal molecules, when mixed with other liquid crystals, it exhibits dielectric anisotropy like liquid crystals. Therefore, it has good compatibility with liquid crystals and has a relatively low melting point, so it does not raise the melting point of the composition and can be aged at low temperatures. As described above, compounds of group c are desirable: 1) have a melting point of 150°C or lower, preferably 130°C or lower, more preferably 100°C or lower, 2) have a Δε of -4
or more, preferably -7 or more, more preferably -10
Above, 3) the number of benzene rings and cyclohexane rings is 2 to 3, 4) the bond between the benzene ring and cyclohexane ring is

[Formula] or C-C, the number of ester bonds in the compound is 0 or more and 2 or less, and the compound is optically and chemically stable, but if the compound falls under 1) to 4) above. ,
These compounds having different terminal alkyl chain lengths, and even compounds having structural formulas other than these, are sufficiently effective and practical as corresponding to the compounds of group c. In this way, group B (a group of liquid crystal compounds that have a cyano group at the terminal and a large positive dielectric anisotropy) and group C (a group of liquid crystal compounds that have a negative dielectric anisotropy with a large absolute value, or a group of molecular shapes) By mixing an appropriate amount of non-liquid crystal compounds (group of non-liquid crystal compounds having a rod shape) into the composition,
It is possible to create a liquid crystal composition that satisfies the conditions required for liquid crystal materials (the absolute value of dielectric anisotropy is large at the driving frequency (particularly at a frequency higher than fc)). Further, in FIG. 1, ΔεL/|ΔεH| is also an important condition for driving, but it can be adjusted by changing the blending ratio of group b and group c. Next, among the characteristics required for liquid crystal materials,
, but since these have a close correlation, their relationship with the components will be explained together. The dielectric dispersion phenomenon of liquid crystal molecules occurs in a relatively low frequency region compared to many polar polymers, and this phenomenon is mainly caused by the rotation of the entire molecule and the change of dipoles within the molecule. Here, the dispersion frequency is
When fr is the relaxation time, τ is the viscosity of the liquid crystal, and η is the viscosity of the liquid crystal, there is a relationship of fr=1/τ∝1/η. Furthermore, the response time for rising and falling becomes slower as the viscosity of the liquid crystal increases. Therefore, the dispersion frequency and response time are inversely proportional. In addition, fr is a function of the molecular length of the liquid crystal molecule, the shape of the molecule, the thermodynamic energy of the molecule, temperature, etc., and satisfies the required characteristics in a well-balanced manner, i.e., fast response and temperature dependence of fc. Naturally, in order to create a composition that has a low fc value and a relatively low fc value even at high temperatures, it is necessary to use well-balanced components. That is,
(General formula of component a group according to the present invention) (In the formula, R has 3.5 carbon atoms, R' has 4 to 4 carbon atoms.
A liquid crystal compound or liquid crystal mixture that satisfies at least two of the following conditions: 1. Low fc. 2. Low temperature dependence of fc. 3. Low viscosity. 4. Wide liquid crystal temperature range, low melting point). Condition 4 of the above group d is necessary for widening the operating temperature range and improving aging, especially low-temperature aging, not only for dual-frequency drive liquid crystals. Desirable compounds of group d have the general formula (In the formula, R ₁ has 3 to 5 carbon atoms, R ₂ has 1 carbon number,
2,4, _R3 represents a straight chain alkyl group having 5,8 carbon atoms, and _R4 represents a straight chain alkyl group having 5,7 carbon atoms. The compound has a low viscosity, a low melting point, a relatively wide liquid crystal temperature range, and a small temperature dependence of fc, that is, it simultaneously satisfies conditions 2, 3, and 4 of the requirements for a D group compound. It is an excellent liquid crystal compound. The compound has a very wide liquid crystal temperature range, low fc, and small temperature dependence, that is, satisfies conditions 1, 2, and 4, so
It is still an excellent liquid crystal compound. Compounds other than those listed above that are desirable as equivalent to group d compounds have the general formula: (In the formula, R ₅ is a straight chain alkyl group selected from 5 to 7 carbon atoms, R ₆ is a straight chain alkyl group having 6 carbon atoms or H, R ₇ is an alkoxy group having 6.8 carbon atoms, R ₈
is a straight-chain alkyl group having 5 carbon atoms or a straight-chain alkoxy group having 6 carbon atoms, _R9 is a straight-chain alkyl group having 5 to 7 carbon atoms, and X is -Cl or -H). . As a result of many experiments, the present inventors have found that a compound with good responsiveness, low fc, and small temperature dependence of fc is a liquid crystal compound having the following structure. That is, 1) the melting point is 150°C or lower, preferably 100°C or lower, more preferably 70°C or lower;
℃ or less, 2) The sum of the numbers of benzene rings and cyclohexane rings is 2 or more and 3 or less, preferably 3. More preferably, 2 benzene rings and 1 cyclohexane ring, 3) The bond between the benzene ring and the cyclohexane ring is

[Formula] or C-C, the number of ester bonds is 0 or more and 2 or less, more preferably 1 or more and 2 or more
The following are more desirable: 1. It is also an optically and chemically stable compound. That is, such compounds are those corresponding to the above d, and have the structural formula of ~, but as long as they fall under 1) to 3) above, these compounds may have a different number of carbon atoms, and is a compound with a structural formula other than ~ that is sufficiently effective as a compound of group b,
And practical. Group a/general formula (In the formula, R has 3.5 carbon atoms, R' has 4 to 7 carbon atoms.
(representing a straight chain alkyl) is a compound represented by
They are considered to be included in Group D compounds because they have good responsiveness, low fc, and small temperature dependence of fc, but they are especially important because they have excellent characteristics or balance. be. In this way, group a (general formula (In the formula, R has 3.5 carbon atoms, R' has 4 to 7 carbon atoms.
By mixing the d group (liquid crystal compound or liquid crystal mixture that satisfies at least two of the following conditions) with the c group and the d group, it is possible to meet the requirements for liquid crystal materials. This is the condition for (Drive frequency (especially higher frequency than FC)
(the absolute value of dielectric anisotropy is large). (fc
is relatively low within the operating temperature range). (The temperature dependence of fc is small). It is possible to create a liquid crystal composition that satisfies (fast response speed). Hereinafter, this liquid crystal composition for dual-frequency driving having excellent characteristics will be described in detail with reference to Examples. Example 1 A liquid crystal composition shown in Table 1 was prepared and sealed in a liquid crystal cell shown in FIG. 3, and the frequency of AC measurement voltage was 100
The dielectric constant of liquid crystal was measured in the range of Hz to 100KHz. (At this time, the DC bias voltage that controls the orientation of liquid crystal molecules is 60V, and the measurement voltage is 50mV)

【table】

[Table] The results are shown in Figure 4. However, the measurement temperature is 40℃
It is. In addition, this liquid crystal composition was sealed in a liquid crystal cell as shown in Fig. 3, in which the liquid crystal layer has a thickness of 8 μm, and the response was measured using the dual-frequency driving method described in JP-A-54-139394. As a result, the average rise and fall was 315Wsec. (However, the driving conditions are Temp = 20℃, Vt (timing voltage) = 30V,
fH (driving frequency on the high frequency side) = 50 KHz, fL (driving frequency on the low frequency side) = 100 Hz) Example 2 The liquid crystal composition shown in Table 2 was made and the dielectric constant was measured in the same manner as in Example 1. As a result, it turned out as shown in Figure 5.

【table】

[Table] Furthermore, when the response speed was measured in the same manner as in Example 1, the average rising and falling times were 275 msec. Example 3 The liquid crystal compositions shown in Table 3 were prepared, and the dielectric constants were measured in the same manner as in Example 1. The results are shown in FIG.

【table】

[Table] When the response speed was measured in the same manner as in Example 1,
The average of rising and falling times is 220msec each.
It was hot. Example 4 Liquid crystal compositions shown in Table 4 were prepared, and the dielectric constants were measured in the same manner as in Example 1. The results are shown in FIG.

【table】

[Table] Responsiveness was investigated using the same method as in Example 1, and the average of rising and falling times was
It was 140msec. As shown in Examples 1 to 4, all the components of these liquid crystal compositions (Example 1) It is an ester compound and is chemically and optically stable. Also energized aging, high (low) resistance
Temperature and humidity aging resistance also show good results. As described above, the liquid crystal composition for dual-frequency driving provided by the present invention has 1) a balance between fc and responsiveness, that is, an fc of more than 10 K at not only room temperature but also high temperature.
Hz and relatively low and stable, high frequency (50~60K
Since the dielectric anisotropy can be ensured even at Hz), low voltage driving is possible and responsiveness is excellent. 2) The temperature dependence of fc is small. (If you install a temperature compensation circuit, it will be 0°C to 40°C.
It is possible to display the temperature in °C. )3) It is very excellent as a liquid crystal composition for dual-frequency driving in terms of fast response speed, and is highly practical.

[Brief explanation of drawings]

FIG. 1 is a diagram showing dielectric dispersion due to frequency changes in liquid crystal. FIG. 2 is a diagram showing a schematic diagram of the alignment state of liquid crystal molecules when liquid crystal is sealed in a TN cell and low frequency and high frequency signals are applied. FIG. 3 is a diagram showing a liquid crystal cell structure in which various characteristics of this example were measured. Figures 4, 5, 6, and 7 show the relationship between measurement frequency and dielectric anisotropy at 40°C for the liquid crystal compositions shown in Example 1, Example 2, Example 3, and Example 4, respectively. Diagram showing. (In the figure, the horizontal axis is frequency, and the vertical axis is dielectric anisotropy) 1... Polarizing plate, 2... Pyrex glass, 3... Indium oxide film, 4... Polyimide film, 5... Liquid crystal,
6...Nylon spacer.

Claims (1)

[Claims] 1. The general formula is (However, R ₁ is a straight-chain alkyl group having 3.5 carbon atoms,
R ₂ represents a straight chain alkyl group having 4, 5, 6, or 7 carbon atoms. ), and the chemical formula is At least one compound selected from group b compounds represented by and the general formula is (However, R ₂ represents a straight chain alkoxy group having 4, 5 or 6 carbon atoms, R ₃ represents a straight chain alkyl group having 4 or 5 carbon atoms, and X represents CN or Cl.) The compound and the general formula are (However, R ₄ is a straight chain alkyl group having 5 to 7 carbon atoms, A is [Formula] or [Formula] or [Formula], R ₅ is a straight chain alkyl group having 5 to 7 carbon atoms, R ₆
represents a straight-chain alkyl group having 5,8 carbon atoms, and R ₇ represents a straight-chain alkyl group having 5 carbon atoms. ) and the general formula is [Table] 〓
A liquid crystal composition for dual-frequency driving, characterized in that it comprises at least one kind selected from compounds of the dn group represented by: