KR100853222B1 - Liquid crystal composition capable of operation low voltage and liquid crystal display using the same - Google Patents

Abstract

The present invention relates to a low-voltage driving liquid crystal composition and a liquid crystal display device using the same, and more particularly, including a nematic liquid crystal compound having an isocyanate group in a para position of an aromatic ring at its terminal as a main essential component to provide high-speed response characteristics. The present invention relates to a low voltage driving liquid crystal composition that satisfies and has a high phase transition temperature, a low driving voltage, and a nematic phase in a wide temperature range.

Nematic liquid crystal compound, high speed high temperature liquid crystal composition, low voltage, liquid crystal display device

Description

Low voltage driving liquid crystal composition and liquid crystal display device using the same {LIQUID CRYSTAL COMPOSITION CAPABLE OF OPERATION LOW VOLTAGE AND LIQUID CRYSTAL DISPLAY USING THE SAME}

The present invention relates to a low-voltage driving liquid crystal composition and a liquid crystal display device, and more particularly, high phase transition temperature of the liquid crystal, high birefringence and elastic modulus, and wide driving temperature range of the nematic phase that can be driven to realize high-speed response speed. A low voltage driving liquid crystal composition comprising an NCS compound effective for application to various devices requiring liquid crystals such as LCDs and the like.

Liquid crystal is a fluid having optical / dielectric anisotropy, and when used in a liquid crystal display (LCD), it changes the phase difference of light by varying the optical anisotropy according to the voltage applied to the cell, the basic unit of LCD. The display can be implemented. Typical examples of such LCDs include DS (dynamic scattering mode), TN (twisted nematic mode), STN (supertwisted nematic mode), IPS mode (inplane switching mode), OCB mode (optically compensated bend mode), and VA mode (vertical). alignment mode). Recently, the mainstream of LCD is LCD using TFT (thin film transistor) which is an active driving method.

Liquid crystals used in LCDs should basically ensure chemical stability, photochemical stability, and heat stability, and should also have good resistance to electric field and electromagnetic radiation. In addition, it should have low viscosity, low threshold voltage and high contrast, and the operating temperature should be as broad as possible above room temperature and below room temperature. Also, since liquid crystals are generally used in mixtures, it is important for the various components to be easily miscible with each other. In other words, in order to implement LCDs with high quality, physical properties of liquid crystals suitable for LCD characteristics are required. Basically, the basic property condition for liquid crystal to be used in LCD is as follows.

First, the wide nematic temperature range should be maintained. The melting point temperature should be at least below -20 ° C, and most commercial nematic liquid crystal mixtures maintain the nematic phase even at -40 ° C. In addition, most of the phase transition temperature is 80 ℃ or more, and as the nematic liquid crystal mixture is recently applied to a TV using a direct backlight (backlight), a mixture having a high phase transition temperature of 90 ℃ or more is required.

Second, the specific resistance must be high. In LCDs, liquid crystals require high resistance because they serve as dielectrics or capacitors, and in the case of LCDs using TFTs, a resistivity of 1012 Ωcm or more is required.

Third, the refractive anisotropy of the liquid crystal requires slightly different refractive anisotropy for each of the electro-optic display companies in consideration of the arrangement, driving conditions, contrast ratio, and viewing angle of the liquid crystal used in the electro-optical display. The refractive index anisotropy of is required.

Fourth, as shown in Equation 1 below for low voltage driving, a liquid crystal mixture having a large dielectric anisotropy is required. In addition, a nematic liquid crystal mixture having a low elastic modulus is required, but considering the response speed, an elastic modulus is required. In the case of liquid crystal mixtures used in notebooks and monitors, the threshold voltage is about 1.5 to 2.0 volts.

[Equation 1]

Where V _th is the threshold voltage, Δε is the dielectric anisotropy, and K is the elastic modulus.

In the LCD for mobile, low voltage driving is required to maintain a longer life of the battery, and the low voltage driving requires a material having a high dielectric constant and high phase transition temperature as described above.

TFT liquid crystal displays are widely adopted for information terminal devices due to the advantages of thin, light weight, and low power consumption, and the market has been gradually expanded. In recent years, the demand for TFT LCD displays has been increasing due to the development of new applications such as CRT replacement LCD monitors and LCD desktop PCs.

On the other hand, the TV market is expected as an application of TFT liquid crystal display. In order for TFT liquid crystal display to participate in the TV market and expand its market share, the demand for video visibility, high brightness, and high-speed response technology is very important. have. TN, IPS, and VA modes are mentioned as TV-product groups. However, IPS and VA have advantages of viewing angle, but are difficult to cope with moving images due to slow response speed. The TN mode has a narrow viewing angle, but if the compensation of the viewing angle and improvement in response speed by the development of a compensation film or the like, it will be the most competitive TV mode in terms of characteristics and production yield.

In order to prevent high luminance and deterioration of the liquid crystal, the phase transition temperature of the liquid crystal should be kept higher than the current in consideration of the increase in temperature due to the tube current of the backlight. For high speed response, there is a method of increasing the refractive index of the liquid crystal by reducing the rotational viscosity of the material or lowering the cell gap.

As described above, LCD products are currently being commercialized in various modes such as TN, IPS, and VA. Most of them use nematic liquid crystals, and the phase transition temperature is about 70 to 80 ° C., and the response speed is about 20 to 30 ms. . Therefore, in order to cope with TV applications and moving pictures, an improvement in response speed and an increase in phase transition temperature are urgently required.

Therefore, in order to solve the problems of the prior art as described above, a low voltage capable of realizing a high-speed response technology through the development of high-temperature high-speed liquid crystal by increasing the phase transition temperature of the liquid crystal and increasing the refractive index anisotropy, aiming at high brightness and high speed response technology It is an object to provide a nematic liquid crystal composition.

Another object of the present invention is to provide a liquid crystal display device using the liquid crystal composition.

In order to achieve the above object, the present invention provides a nematic liquid crystal composition comprising a nematic liquid crystal compound represented by the following formula (1).

[Formula 1]

Wherein R is C _n H _{2n + 1} O, C _n H _{2n + 1} , or C _n H _2n-1 , where n is an integer from 1 to 15; R ₁ is H or F; L is An integer from 0 to 2; A is a single bond, -CH ₂ CH _2- , -COO-, -C = C-, or -C≡C-; X is H, F, Cl or Br; Y is H, F, Cl or Br.)

In addition, the present invention provides a liquid crystal display device comprising the nematic liquid crystal composition described above.

Preferably, the liquid crystal display device is a liquid crystal display device of an active drive type TN (twist nematic), STN, TFT-TN mode, IPS (In plane switching) mode, AOC or COA liquid crystal display device, or optically corrected It is a liquid crystal display device in an optically compensated bend mode.

Hereinafter, the present invention will be described in detail.

The present invention provides a nematic liquid crystal composition capable of lowering the viscosity of the liquid crystal, increasing the dielectric anisotropy and birefringence, increasing the temperature range of the nematic phase to increase the response speed, and enabling low voltage driving.

The nematic liquid crystal composition of the present invention may include the compound of Chemical Formula 1 as a key material to increase phase transition temperature by at least 18 ° C. or more, and achieve a response speed of about 10 ms compared to conventional commercial liquid crystals.

Comparing the physical properties of the compound of Formula 1 and the conventional liquid crystal compound of the present invention is shown in Table 1.

Phase transition temperature (℃) Dielectric anisotropy Refractive anisotropy Compound a

207.3 16.2 0.274 Compound b

25 13 0.135 Formula 1a

160.1 19.4 0.201

Referring to Table 1, the compound of Formula 1a of the present invention has a higher dielectric constant than a conventional NCS compound (Compound a), and has a phase transition temperature of 100 degrees or more and a dielectric constant and refractive index anisotropy even when compared to a compound b substituted with fluorine only. You can see big thing.

As such, the compound of formula 1 of the present invention may be used as a material useful for preparing a low voltage driving liquid crystal mixture.

The content of the nematic liquid crystal compound represented by Formula 1 is preferably 1 to 80% by weight, and more preferably 1 to 30% by weight based on the total composition. At this time, when the amount of the chemical formula 1 is less than 1% by weight, the response speed is slow, and when it exceeds 80% by weight, there is a problem that a high phase transition temperature and a high speed response speed cannot be obtained.

More preferably, the liquid crystal composition of the present invention may include a compound selected from the group consisting of compounds represented by the following Chemical Formulas 2, 3, and 4 together with the compound of Formula 1 above.

[Formula 2]

R ₂ -A ₁ -B ₁ -X ₁

[Formula 3]

[Formula 4]

Wherein R ₂ is each independently or simultaneously C _n H _{2n + 1} , or C _n H _2n , where n is an integer from 1 to 15;

,

,또는

이며;A ₁ and B ₁ are each independently or simultaneously

,

,or

Is;

X ₁ is F, CF ₃ , OCF ₃ , CH = CF ₂ , or OCH = CF ₂ ;

또는

이며;A ₂ are each independently or simultaneously

or

Is;

A ₃ , B ₂ and C are each independently or simultaneously F, CF ₃ , OCF ₃ , or H.)

The content of at least one liquid crystal compound selected from the group consisting of the compounds represented by the formulas (2), (3) and (4) is preferably 20 to 99% by weight.

In addition, the liquid crystal composition of the present invention may be used in addition to the liquid crystal compound of Formula 1 in order to improve the properties of the liquid crystal composition generally known nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal and the like. However, when a large amount of such liquid crystal compound is added, the characteristics of the liquid crystal composition to be obtained may be reduced. Therefore, the addition amount should be limited in accordance with the required characteristics of the nematic liquid crystal composition.

Such a liquid crystal composition of the present invention may be usefully used even in the case of LCD having a cell gap of 3.0 μm or more. Therefore, by using the composition of the present invention as a liquid crystal material, it is possible to provide a liquid crystal display device of various LCD products by filling in various liquid crystal cells with appropriate additives. For example, an active matrix method liquid crystal display device including the nematic liquid crystal composition, an active matrix method MIM liquid crystal display device, and an active matrix method IPS ( In-plane switching type liquid crystal display device, Simple matrix type Twistnematic type liquid crystal display device, Simple matrix type Super twist nematic type liquid crystal display device , Thin film transistor-twist nematic (TFT-TN) liquid crystal display, array on color filter (AOC) or color filter on array (COA) liquid crystal display, liquid crystal in optically compensated bend mode A display device or the like can be manufactured.

Hereinafter, the Example and comparative example of this invention are described. However, the following examples illustrate the present invention and do not limit the present invention.

Comparative Example 1

A commercial mixture "GM1" constructed as shown in Table 2 was prepared (GM1 = G1 + G2 + G3 + G4). The content of each G1 to G4 represents weight percent.                     

compound sign Content (% by weight) G1

3CCP ^OCF3 2.5

2CCP ^F.OCF3 2.6

2CCP ^OCF3 7.4

2 "CCP ^OCF3 2.5 G2

2CCP ^FFF 7.0

3CCP ^FFF 2.5

2CP ^F P ^FFF 2.9

2 "CCP ^FF 11.1 G3 (X F)

2CCesP ^x 3.4

2CP ^F esP ^x 9.0

3CCesP ^x 9.4 G4                                             

5CC2 " 21.8

5CC3 4.1

3CCO1 7.6

3CC3 " 6.2

The liquid crystal mixture having the composition shown in Table 1 is a commercially available liquid crystal, and the response speed of the liquid crystal was measured as 16.2 ms at a cell gap of 4.5 μm. The phase transition temperature (Tni) was 80 ° C., Δn was 0.0772, and Δε was 5.9. (20 ° C).

Example 1

In Example 1, liquid crystals having the composition shown in Table 3 below were prepared using 9.8 wt% of the following Chemical Formula 1b compound, which is a key material, for changing physical properties of GM1. Then, the phase transition temperature, refractive index anisotropy, dielectric anisotropy, and response speed (cell gap 3.75 μm) of the liquid crystal were measured.

[Formula 1b]

The phase transition temperature (Tni) of Formula 1b was 136 ° C (100 ° C), Δn was 0.198, and Δε was 20.0 (20 ° C).

sign Content (% by weight) Formula 1b 9.8 GM1 90.2

In the case of using Formula 1b, the phase transition temperature Tni was 82 ° C., Δn was 0.087, Δε was 7.0 (25 ° C.), and the response speed τ was 10.3 ms.

Example 2

In the same manner as in Example 1, using 17.5% by weight of the compound of Formula 1b as a key material to prepare a liquid crystal of the composition shown in Table 4. Then, the phase transition temperature, refractive index anisotropy, dielectric anisotropy, and response speed (cell gap 3.75 μm) of the liquid crystal were measured.

sign Content (% by weight) Formula 1b 17.5 GM1 82.5

When using the formula 1b, the phase transition temperature (Tni) is 98.3 ℃, Δn is 0.101, Δε is 7.8 (25 ℃), the response speed (τ) is 9.8 ms, threshold voltage (V _th ) is 1.2V It was.

As such, when the liquid crystal of Chemical Formula 1b was mixed, the improved properties were shown as follows. As the phase transition temperature increased by 123%, high temperature reliability was improved, which is a very suitable performance for display devices requiring high temperature stability. In addition, the dielectric anisotropy increased to about 132%, thereby improving the characteristics of low-voltage driving of the liquid crystal. This could be confirmed by reducing the threshold voltage by 0.2V compared to the GM1 liquid crystal. In addition, the refractive anisotropy increased by about 130%, and the most important response speed was reduced by 61% compared to that of the GM1 liquid crystal.

As can be seen from the above results, the liquid crystal of the present invention can be applied to an LCD having a cell gap of 3.5 μm or more, including the compound of Chemical Formula 1, and can be sufficiently utilized as a high-speed high temperature liquid crystal because it is possible to drive a low voltage.

As described above, the liquid crystal composition according to the present invention has a higher birefringence (Δn) and a dielectric anisotropy (Δε), a lower threshold voltage (V _th ), and a higher phase transition temperature than a commercially available mixed liquid crystal. It can realize high speed response speed and can drive low voltage, so it can be applied to various devices requiring liquid crystal such as LCD.

Claims (5)

A nematic liquid crystal composition comprising the nematic liquid crystal compound represented by Formula 1 below: [Formula 1]

Wherein R is C _n H _{2n + 1} O, C _n H _{2n + 1} , or C _n H _2n-1 , where n is an integer from 1 to 15; R ₁ is H or F; L is an integer from 0 to 2; A is -CH ₂ CH _2- ; X is H, F, Cl or Br; Z is H, F, Cl or Br. The method of claim 1, 1 to 80% by weight of the nematic liquid crystal compound represented by Formula 1, and 20 to 99% by weight of at least one liquid crystal compound selected from the group consisting of compounds represented by Formulas 2, 3 and 4 Nematic liquid crystal composition comprising: [Formula 2] R ₂ -A ₁ -B ₁ -X ₁ [Formula 3]

[Formula 4]

In which R ₂ is each independently or simultaneously C _n H _{2n + 1} , or C _n H _2n , where n is an integer from 1 to 15; A ₁ and B ₁ are each independently or simultaneously

,

, or

Is; X ₁ is F, CF ₃ , OCF ₃ , CH = CF ₂ , or OCH = CF ₂ ; A ₂ are each independently or simultaneously

or

Is; A ₃ , B ₂ and C are each independently or simultaneously F, CF ₃ , OCF ₃ , or H. A liquid crystal display device comprising the nematic liquid crystal composition of claim 1. 4. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is a liquid crystal display device of a twisted nematic (TN), STN, TFT-TN, or IPS (In plane switching) mode. 4. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is an AOC or COA liquid crystal display device or an optically compensated bend mode liquid crystal display device.