KR20010016326A - Nematic Liquid Crystal Compounds and Nematic Liquid Crystal Mixtures for Liquid Crystal Displays - Google Patents

Abstract

PURPOSE: A new nematic liquid crystal compound capable of increasing a birefringence rate and coefficient of elasticity, widening the temperature range of a nematic phase and increasing the response speed without increasing driving voltage, nematic liquid crystal composition containing the same and liquid crystal display device using the same are provided which improve afterglow and cross talk phenomenon and have an effect on reducing driving voltage. CONSTITUTION: The new nematic liquid crystal compound of formula (1) has a high speed response, low viscosity and a high voltage holding ratio. The nematic composition comprises at least one selected from the group consisting of the liquid crystal compound of the formula (1). In formula, R1 is CnH2n+1O, CnH2n+1 or CH3CnH2n+1 (n is an integer from 1 to 12) containing one double bond in the middle of an alkyl chain, m is selected from an integer from 0, 1, A is selected from formula 2, B is selected from a single bond or -CH2CH2-, -COO-, -C≡C-, -OCH2-, X is H or F.

Description

Nematic Liquid Crystal Compounds and Nematic Liquid Crystal Compositions Comprising the Same and Liquid Crystal Displays Using the Same {Nematic Liquid Crystal Compounds and Nematic Liquid Crystal Mixtures for Liquid Crystal Displays}

The present invention provides a novel nematic liquid crystal compound useful as an electro-optic information display material and a nematic liquid crystal composition having appropriately controlled characteristics such as North refractive index, viscosity, modulus of elasticity, temperature range of the nematic phase, and liquid crystal using the same. It relates to a display device.

Nematic liquid crystal composition is used as an important material of the liquid crystal display (LCD) used in electronic calculators, electronic notebooks, portable computers, and the like. A typical liquid crystal display device is a twisted nematic liquid crystal display device. Recently, it is widely used as a display device for high-speed information processing such as a word process and a personal computer.

Liquid crystal display devices are passive TN (Twist Nematic), STN (Super Twist Nematic) and ferroelectric liquid crystal display devices, active TFT (Thin Film Transitor), MIM (Metal Insulator Metal), and diode (diode). ) It can be divided into liquid crystal display device.

Active liquid crystal display devices with excellent display performance are used in flat panel display fields such as notebooks, computers, liquid crystal televisions and projectors. In the active method, a liquid crystal display device is driven by using a switching element such as a thin film transistor (TFT) or a metal insulator or metal (MIN) in each pixel, so a high voltage holding ratio with a low leakage current is important. In addition, the response speed required for the liquid crystal display device due to the increase in the amount of display information and the realization of moving images tends to be getting faster.

However, the nematic liquid crystal composition known so far has a problem that it is difficult to implement a moving image because of the slow response speed. In order to solve this problem, the necessity of developing nematic liquid crystal compounds satisfying the following conditions is increasing.

First, in order to improve the response speed quickly, lower the viscosity of the liquid crystal material.

It should be adjusted within the range from 25 mm 2 / s.

Second, in order to lower the driving voltage, the dielectric anisotropy (Δε) is increased to 10 to

It should be adjusted within 15 (35 ℃, 1kHz) range.

Third, the nematic phase must be built over a wide temperature range. Preferred Nematic Phase Temperature

The range is -30 to 80 ° C.

Fourth, the birefringence (Δn) value should be 0.20 (25 ° C) or more.

Thus, in order to solve these problems, new liquid crystal compounds or liquid crystal compositions having characteristics such as high speed response, low viscosity and high voltage holding ratio have been proposed.

It is well known that a liquid crystal material having a high birefringence (Δn) and a modulus of elasticity is required to improve the electro-optical properties of TN-LCD, STN-LCD and TFT-LCD. Examples of the liquid crystal having a large birefringence (Δn) known to date include the following compounds shown in Chemical Formula 3.

R represents an alkyl group, an alkoxy group, or an alkoxyalkyl group here.

Even if it is hard to improve the electro-optical properties of the liquid crystal material by adding or mixing such liquid crystal compounds, the chemical safety of the liquid crystal material, the driving temperature range of the liquid crystal display device, etc. are often not improved and remain a problem.

For example, when the liquid crystal compounds of Formulas (a) to (c) listed above are mixed, the birefringence (Δn) of the mixed liquid crystal increases, but the smectic phase tends to appear or the temperature of the nematic phase can be driven. Narrow range Therefore, it is difficult to produce a liquid crystal display device using a mixed liquid crystal of these compounds and having good electro-optical characteristics and capable of driving in a wide range of nematic temperature ranges.

In the case of a TFT-LCD, compounds such as (e) and (f) of Chemical Formulas 3 are used to obtain a low leakage voltage and a high voltage holding ratio in order to obtain uniform and high contrast display characteristics. However, with these liquid crystal compounds, the birefringence (Δn) and the elastic modulus (K ₁₁ , K ₃₃ ) cannot be increased, and the threshold voltage cannot be reduced.

The problem to be solved by the present invention is to increase the birefringence (Δn) and the modulus of elasticity (K ₁₁ , K ₃₃ ) without significantly increasing the driving voltage, and to increase the response speed to widen the temperature range of the nematic phase that can be driven, It is to provide a nematic liquid crystal compound and a nematic liquid crystal composition. In addition, the nematic liquid crystal composition is used as a constituent material to provide a liquid crystal display device having improved electro-optic characteristics.

The present invention provides a nematic liquid crystal compound represented by the formula (1) to solve the first problem.

[Formula 1]

Wherein R ₁ is C _n H _{2n + 1} O, C _n H _{2n + 1} or CH ₃ C _n H _2n-2 having one double bond in the middle of the alkyl chain, _where n is an integer from 1 to 12 , m is selected from an integer of 0, 1, A is selected from the group consisting of

[Formula 2]

B is a single bond or

-CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2-

Is selected from the group and X is H or F.

And, if B is selected from the group consisting of Formula (2),

[Formula 2]

A is a single bond or

-CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2-

Is selected from the group and X is H or F.

In Formula 1, m is 0 or 1, n is 3, 5, 7, A is a cyclonuclear chamber and benzene, B is an ethylene group and an acetylene group, X is preferably hydrogen and fluorine.

A second object of the present invention is a nematic liquid crystal composition comprising two or more liquid crystal compounds, with a nematic liquid crystal composition of 5 to 75% by weight relative to the total weight of the nematic liquid crystal composition.

It provides a nematic liquid crystal composition containing at least one compound selected from the compound group represented by the formula (1).

[Formula 1]

Wherein R ₁ is C _n H _{2n + 1} O, C _n H _{2n + 1} or CH ₃ C _n H _2n-2 having one double bond in the middle of the alkyl chain, _where n is an integer from 1 to 12 , m is selected from an integer of 0, 1, A is selected from the group consisting of

[Formula 2]

B is a single bond or

-CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2-

Is selected from the group and X is H or F.

And, if B is selected from the group consisting of Formula (2),

[Formula 2]

A is a single bond or

-CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2-

Is selected from the group and X is H or F.

In the nematic liquid crystal composition of the present invention, the nematic liquid crystal composition including a compound selected from the compound group represented by Chemical Formula 1 as an essential component has a high birefringence index (Δn) and an elastic modulus (K ₁₁ , K ₃₃ ) and a driving voltage. It has a low response speed and a large voltage holding ratio.

The nematic liquid crystal composition of the present invention is a nematic liquid crystal composition containing 5 to 60% by weight of a compound selected from the compound group represented by the formula (1). It is appropriate to add 30 to 70% by weight of this composition in order to increase the birefringence (Δn) and to increase the response speed.

In addition, the nematic liquid crystal composition comprising at least one liquid crystal compound selected from the compound group represented by (2) to (5) of Formula 4 in the nematic liquid crystal composition (A) including the compound selected from the compound group represented by Formula 1 The nematic liquid crystal composition to which the composition (B) was added is provided.

In the above formula, R ₃ to R ₆ are linear alkyls each having an integer of 3 to 7 carbon atoms or CH ₃ C _n H _2n-2 (n is an integer of 2 to 6) having one double bond in the middle of the alkyl chain. Chains are preferred.

This nematic liquid crystal composition is a compound selected from the compound group represented by (2) to (5) of formula (4) in 25 to 70% by weight of the nematic liquid crystal composition (A) prepared with a liquid crystal compound selected from the compound group represented by the formula (1). It is a nematic liquid crystal composition added by adding 30-50 weight%. In order to increase the birefringence (Δn) and the modulus of elasticity (K ₁₁ , K ₃₃ ) by adding the compounds represented by the formulas (2) to (5), it is appropriate to add 30 to 40% by weight.

This nematic liquid crystal composition comprising a compound selected from the compound group represented by the formula (1) as an essential component, the birefringence (Δn) is significantly higher than 0,20, and the temperature range of the nematic phase is very wide, about 140 ^° C or more. Because of this property of nemaktic liquid crystal composition (A), a liquid crystal compound selected from the group of compounds represented by formulas (2) to (5) in which fluorine is substituted, a tolan group is connected, and an isothiocyanate group is substituted at the terminal of the molecule It can be predicted that the addition of to the nematic liquid crystal composition (A) increases the elastic modulus (K ₁₁ , K ₃₃ ) value of the nematic liquid crystal composition to increase the response speed. In addition, the nematic liquid crystal compound containing the compound selected from the compounds represented by the formula (1) as essential components and the compounds selected from the compounds represented by the formula (2) to (5) of the general formula 4 because they are very compatible with each other essential components A nematic liquid crystal composition exhibiting excellent properties can be obtained without sacrificing the good properties of.

The liquid crystal composition of the present invention may be mixed with a generally known nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, etc. in order to improve the characteristics of the liquid crystal composition in addition to the liquid crystal compound represented by the formula (1). However, when a large amount of such liquid crystal compound is added, the property of the liquid crystal composition to be obtained may be reduced, so the amount of addition should be limited in accordance with the required characteristics of the nematic liquid crystal composition.

In addition, the present invention provides a TN, STN, TFT and IPS liquid crystal display using the nematic liquid crystal composition.

Table 1 shows the phase transition temperatures of representative compounds represented by the general formula (1) related to the present invention. In Table 1, m.p. is the temperature of phase transition from the crystal phase to the liquid crystal phase or the isotropic liquid phase, and c.p. represents each temperature of phase transition from the liquid crystal phase to the isotropic liquid phase.

Extrapolation method of birefringence of 85% (weight ratio) of 4- (4-hexylcyclohexyl) -1-isothiocyanatobenzene liquid crystal compound used as the mother liquid crystal and 15% by weight of each compound shown in Tables 1 and 2 The birefringence index (Δn) of the single liquid crystal compound was determined. Each compound was sufficiently purified by removing impurities using distillation, column purification, recrystallization, and the like.

The nematic liquid crystal composition of the present invention contains a compound selected from the compound represented by Formula 1 as essential components. The compound represented by the formula (1) and the compound represented by (2) to (5) of the formula (4) is very compatible with other liquid crystal compounds containing the functional group represented by the formula (5) as a partial structure of the liquid crystal molecular structure.

In order to confirm the effect of the liquid crystal compound represented by Formula 1 on the liquid crystal composition of the present invention, the following experiment was carried out. A mixed liquid crystal (A) was prepared at a mixing ratio with the liquid crystal compound represented by the formula (6) as a mother liquid crystal using a liquid crystal compound currently used in general purpose. A nematic liquid crystal composition (B) was selected from the group of liquid crystal compounds represented by the formula (1) of the present invention and prepared in a mixing ratio with the liquid crystal compound represented by the formula (6).

Mixed liquid crystal (A)

Mixed liquid crystal (B)

In order to compare the effect of the liquid crystal compound presented in the present invention, the compound No. 60 weight% of the mixed liquid crystal (B) which mixed 1, 2, 3, and 4 at the same ratio was mixed and prepared. The liquid crystal composition is injected into a TN cell having a thickness of 3.2 μm and the threshold voltage (V _th ), the time required for applying the voltage from the state where no voltage is applied (τ _on ) and the voltage is applied. The time required until the light was not transmitted by removing the voltage from the state (τ _off ) and the voltage holding ratio (Voltage holding ratio (VHR)) were measured. The nematic phase-isotropic liquid phase transition temperature (T _NI ) and birefringence (Δn) of these mixed liquid crystals were measured. In order to compare the electro-optical properties of the liquid crystal compounds proposed in the present invention, the liquid crystal compositions were injected into a twisted nematic cell having a thickness of 5.7 μm, and the threshold voltages V _th and γ (saturation voltages V _sat and V _th ratios). ), The time required for the light to pass through from the state where no voltage is applied (τ _on ), or the time required for the light to pass through when the voltage is removed from the applied state ( τ _off ), and voltage holding ratio (VHR) were measured.

From the results shown in Table 3, the nematic liquid crystal composition to which the compound selected from the compound group represented by the formula (1) was added showed a higher nematic phase-isotropic liquid phase transition temperature than the parent liquid crystal composition (A), and responded without significantly changing the threshold voltage. You can see that it has the effect of speeding up. The threshold voltage of the nematic liquid crystal composition can be operated at a sufficiently low driving voltage of 1.3 V or less. In addition, the liquid crystal composition of the present invention is chemically stable and exhibits a high voltage holding ratio, which is suitable for an active liquid crystal display device.

Since the compound represented by Chemical Formula 1 of the present invention can easily increase the birefringence (Δn) of the liquid crystal composition, the response speed can be increased by reducing the thickness (d) of the liquid crystal display device and optimizing the birefringence (Δn). have. In addition, the nematic phase of the nematic liquid crystal composition can be extended to the high temperature side and the low temperature side, and a high-speed response liquid crystal display device can be obtained without deteriorating the viscosity.

In addition, the liquid crystal composition of the present invention has the effect of maintaining and improving the above-mentioned electro-optic properties when the compound selected from the compound group represented by the formula (1) and the compound selected from the compound group represented by the formula (4) (2) to (5) You will get

Until now, as described above, the nematic liquid crystal composition of the present invention is a nematic liquid crystal composition having a high response speed and high chemical stability.

The nematic liquid crystal composition of the present invention is generally used to fill various display liquid crystal cells with appropriate additives as necessary to make a liquid crystal display device. The liquid crystal display device of the present invention has excellent high-speed response and heat resistance, and there are few afterimages and free phenomenon of the display screen, so that it can be used in any environment.

EXAMPLE

Although the following examples are listed and described in detail, the present invention is not limited to the listed examples.

Example 1 Nematic liquid crystal composition No. 16

Nematic liquid crystal composition consisting of 16 was prepared. Chemical stability of the liquid crystal composition was put into a test tube 1g of the liquid crystal composition to remove the bubbles by vacuum treatment, nitrogen gas was injected and heated at 150 ^o C for 2 hours to measure the phase transition temperature of the liquid crystal composition. Content "%" of a composition in an Example means "weight%. The liquid crystal composition is characterized by T _NI (isotropic liquid phase transition temperature from nematic phase: ^o C), T _N (phase transition temperature from solid phase or smectic phase to nematic phase: ^o C), and V _th (gap between two electrodes Threshold voltage measured by inject | pouring a liquid crystal into the twist nematic test cell of (Volt), (gamma (saturation voltage (V _sat ) and V _th ratio)), (DELTA) n (birefringence) was measured. The result is as follows.

T _NI ( ^o C): 89.6, Δn: 0.173, V _th (1 kHz, 5 V) / V: 1.46, γ = 1.75, VHR (30 Hz, 25 ^o C): 98%

Example 2 Nematic liquid crystal composition No. 17

Nematic liquid crystal composition consisting of 17 was prepared. Each physical property value and a characteristic value were measured by the method similar to Example 1. The result is shown below.

T _NII ( ^o C): 117.8, Δn: 0.188, V _th (1 kHz, 5 V) / V: 1.50, V ₉₀ (1 kHz, 5 V) / V: 2.80, γ = 1.86, VHR = 97%

Example 3 Nematic liquid crystal composition No. 18

Nematic liquid crystal composition consisting of 18 was prepared. Each physical property value and a characteristic value were measured by the method similar to Example 1. The result is shown below.

T _NII ( ^o C): 117.5, Δn: 0.190, V _th (1 kHz, 5 V) / V: 1.47, V ₉₀ (1 kHz, 5 V) / V: 2.90, γ = 1.97, VHR = 97%

Example 4 Nematic liquid crystal composition No. 19

Nematic liquid crystal composition consisting of 19 was prepared. Each physical property value and a characteristic value were measured by the method similar to Example 1. The result is shown below.

T _NII ( ^o C): 71.1, Δn: 0.1522, V _th (1 kHz, 5 V) / V: 1.40, V ₉₀ (1 kHz, 5 V) / V: 2.60, γ = 1.86, τ _on = 3.4 ms, τ _off = 11.2 ms, VHR = 98%

Example 5 Nematic liquid crystal composition No. 20

Nematic liquid crystal composition consisting of 20 was prepared. Each physical property value and a characteristic value were measured by the method similar to Example 1. The result is shown below.

T _NII ( ^o C): 115, Δn: 0.1645, V _th (1 kHz, 5 V) / V: 1.42, V ₉₀ (1 kHz, 5 V) / V: 2.50, γ = 1.76, VHR = 97%

The nematic liquid crystal compound and the composition of these compounds of the present invention have a large birefringence (Δn), a wide temperature range indicating a nematic phase, and a low threshold voltage (V _th ). In addition, the viscosity is low, the elastic modulus (K ₁₁ , K ₃₃ ) and the dielectric anisotropy (Δε) is large, the voltage holding ratio (Voltage Holding Ratio: VHR) is high, and the chemical stability is excellent. Therefore, the nematic liquid crystal composition in which these liquid crystal compounds are mixed is twisted nematic (TN), super-twist nematic (STN) liquid crystal display (LCD) or active matrix (active matrix). : It is possible to improve afterimage and cross talk phenomenon by using AM-type thin film transistor (TFT) liquid crystal display device, and to improve response speed because of low viscosity and large elastic modulus. It is effective in reducing the driving voltage.

Claims (10)

Nematic liquid crystal compound represented by Formula 1: [Formula 1] Wherein R ₁ is C _n H _{2n + 1} O, C _n H _{2n + 1} or CH ₃ C _n H _2n-2 having one double bond in the middle of the alkyl chain, _where n is an integer from 1 to 12 , m is selected from an integer of 0, 1, A is [Formula 2] When selected from the group consisting of B is a single bond or -CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2- Is selected from the group and X is H or F. And B is represented by Formula 2 [Formula 2] When selected from the group consisting of A is a single bond or -CH ₂ CH _2- , -COO-, -C≡C-, -OCH _2- Is selected from the group and X is H or F. A nematic liquid crystal composition containing at least one or more liquid crystal compounds selected from the group of nematic liquid crystal compounds represented by Chemical Formula 1 of claim 1 A nematic liquid crystal composition containing at least one or more liquid crystal compounds selected from the group of nematic liquid crystal compounds represented by formulas (2) to (5) The nematic liquid crystal composition A according to claim 2 is mixed with the additive B selected from the compound group represented by (2) to (5) of Formula 4 with the main liquid crystal, and the addition amount thereof is 5 to 70% by weight. Liquid crystal composition. The nematic liquid crystal composition according to claim 4, wherein the amount of the additive B added to the total weight of the nematic liquid crystal composition is 15 to 40%. A TFT type liquid crystal display device of an active matrix method using the nematic liquid crystal composition of claim 2. An active matrix method MIM liquid crystal display using the nematic liquid crystal composition of claim 2. An in-plane switching (IPS) type liquid crystal display device of an active matrix method using the nematic liquid crystal composition of claim 2. A simple matrix type twist nematic liquid crystal display using the nematic liquid crystal composition of claim 2. A simple matrix type super twist nematic liquid crystal display using the nematic liquid crystal composition of claim 2.