Liquid crystal composition and display device thereof

The present invention relates to a liquid crystal composition, and specifically relates to a liquid crystal composition having a higher response speed, a broader range of a nematic phase and a favourable low-temperature storage stability and the use thereof.

Liquid crystal material is a mixture of organic rod-shaped small molecular compounds which has both liquid fluidity and anisotropy of crystal in a certain temperature. Because of its optical anisotropy and dielectric anisotropy characteristics, liquid crystal material is widely used in the liquid crystal display elements of the devices of electronic calculators, car dashboard, televisions, computers and the like. Based on the LCD modes, liquid crystal compositions can be classified into the types of twisted nematic (TN), super twisted nematic (STN), thin film transistor (TFT), guest-host (GH), dynamic scattering (DS) and the like. The most common display element therein is based on the Schadt-Helfrich effect and has a twisted nematic structure.

Liquid crystal materials are required to have good chemical and heat stability, a suitable optical anisotropy, a broader range of a nematic phase as well as the good stabilities to electric field and electromagnetic radiation. In addition, the liquid crystal materials should have low viscosity and produce low threshold voltage and high contrast ratio in the liquid crystal cell. Since liquid crystal material is normally used as a mixture of various components, it is especially important that these components are miscible with each other. However, as the optimization of each performance parameter of the mixed liquid crystal material may result in inter-contradictory, inter-constraint and inter-influence results, it is very difficult to achieve a broader range of a nematic phase, suitable refractivity and dielectric anisotropy, as well as low-temperature storage stability at the same time. For example, the obvious defects of the liquid crystal compositions of EP0667555, EP0673986, DE19528106, DE19528107 and WO962851 are having a longer response time, lower resistivity and overhigh operating voltage. Further, poor low-temperature storage stability is also a defect of various existing liquid crystal materials.

Therefore, in the field of liquid crystal material, there is a need for novel liquid crystal compositions with improved performances. Particularly, for many types of application, liquid crystal compositions should have a suitably broader range of a nematic phase, a suitable refractivity and dielectric anisotropy, and a low-temperature storage stability.

One object of the present invention is to provide a liquid crystal composition having a higher response speed, a broader range of a nematic phase and a favourable low-temperature storage stability through optimizing the combinations of various liquid crystal compositions and the formulations thereof. The liquid crystal compositions will not show the defects in the existing materials or at least only show the above defects in a significantly lower degree.

In order to achieve the aforementioned object of the invention, the present invention provides a liquid crystal composition which comprises four compounds conforming with the following structural general formulas I, II, III and IV, wherein:

(1) 1%-50% by weight of the total amount of the liquid crystal composition of a compound of general formula (I)

(2) 1%-60% by weight of the total amount of the liquid crystal composition of a compound of general formula (II)

(3) 1%-60% by weight of the total amount of the liquid crystal composition of a compound of general formula (III)

and

(4) 0%-50% by weight of the total amount of the liquid crystal composition of a compound of general formula (IV)

in which:

R 1 , R 2 , R 3 , R 4 , R 5 and R 6 can be same or different, and are independently selected from a group consisting of H, halogen, C 1 -C 7 alkyl, C 1 -C 7 alkoxy, C 2 -C 7 alkenyl and C 2 -C 7 alkenoxy, in which one or more H of the C 1 -C 7 alkyl, C 1 -C 7 alkoxy, C 2 -C 7 alkenyl and C 2 -C 7 alkenoxy can be independently substituted by F;

Z 1 -Z 5 can be same or different, and are independently selected from a group consisting of single bond, —CH═CH—, —C≡C—, —O—, —COO—, —COO—, —OCH 2 —, —C 2 H 4 —, —CH 2 O— and —CF 2 O—;

X 1 is selected from a group consisting of halogen, C 1 -C 7 alkyl, C 1 -C 7 alkoxy and C 2 -C 7 alkenoxy, in which one or more H of the C 1 -C 7 alkyl, C 1 -C 7 alkoxy and C 2 -C 7 alkenoxy can be independently substituted by F;

L 1 -L 6 can be same or different, and independently are H or F, in which, at lease two of the L 1 -L 6 are F;

are independently selected from a group consisting of

in which, one or more H of the

can be independently substituted by F;

m, n and s independently are 0 or 1, and n and s are not simultaneously 0.

In the embodiments of the present invention, preferably, the compound of general formula (I) accounts for 3%-45% by weight of the total amount of the liquid crystal composition; the compound of general formula (II) accounts for 2%-50% by weight of the total amount of the liquid crystal composition; the compound of general formula (III) accounts for 3%-45% by weight of the total amount of the liquid crystal composition; and the compound of general formula (IV) accounts for 5%-40% by weight of the total amount of the liquid crystal composition.

In the embodiments of the present invention, preferably, the compound of general formula (I) is one or more compounds selected from a group consisting of the following compounds:

in which:

R 1 is selected from a group consisting of C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy, in which one or more H of the C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy can be independently substituted by F;

X 1 is selected from a group consisting of —F, —Cl, —CH 2 F, —CH 2 CH 2 F, —CH 2 CH 2 CH 2 F, —CH 2 CH 2 CH 2 CH 2 F, —OCF 3 , —OCH 2 F, —CH 2 OCH 2 F, —CH 2 CH 2 OCH 2 F, —CH═CH 2 and —OCH═CF 2 .

In the embodiments of the present invention, preferably, the compound of general formula (II) is one or more compounds selected from a group consisting of the following compounds:

in which:

R 2 is selected from a group consisting of C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy, in which one or more H of the C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy can be independently substituted by F.

In the embodiments of the present invention, preferably, the compound of general formula (III) is one or more compounds selected from a group consisting of the following compounds:

in which:

R 3 is selected from a group consisting of C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy, in which one or more H of the C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy can be independently substituted by F.

In the embodiments of the present invention, preferably, the compound of general formula (IV) is one or more compounds selected from a group consisting of the following compounds:

in which:

R 5 is selected from a group consisting of C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy, in which one or more H of the C 1 -C 5 alkyl, C 1 -C 5 alkoxy, C 2 -C 5 alkenyl and C 2 -C 5 alkenoxy can be independently substituted by F.

More preferably, the compound of general formula (I) is one or more compounds selected from a group consisting of the following compounds:

More preferably, the compound of general formula (II) is one or more compounds selected from a group consisting of the following compounds:

More preferably, the compound of general formula (III) is one or more compounds selected from a group consisting of the following compounds:

More preferably, the compound of general formula (IV) is one or more compounds selected from a group consisting of the following compounds:

In another aspect of the present invention, it provides a use of the liquid crystal composition of the present invention in manufacturing electrooptic device.

In yet another aspect of the present invention, it provides an electrooptic liquid crystal display comprising the liquid crystal composition of the present invention.

A liquid crystal medium comprising the aforementioned liquid crystal compositions with a broader range of nematic phase, a suitable optical anisotropy, a favourable low-temperature storage stability and a faster response time was established by the inventors through doing the combined experiments for the above compounds and comparing with the Comparison Examples.

As stated above, the liquid crystal compositions of the present invention can be used for outdoor work. The image display effect thereof is good, and there is no smearing phenomenon. Moreover, the liquid crystal compositions of the present invention have a favourable low-temperature storage stability and a higher response speed.

Unless specifically indicated, in the present invention, all ratios are weight ratios; all temperatures are degree centigrade; and the test on the data of the response time uses a cell gap of 7 nm.

The present invention will be illustrated by combining the detailed embodiments below. It should be noted that, the following examples are exemplary embodiments of the present invention, which are only used to illustrate the present invention, not to limit it. Other combinations and various modifications within the conception of the present invention are possible without departing from the subject matter and scope of the present invention.

The liquid crystal displays employed in the following embodiments are all TN-TFT liquid crystal display apparatus which is comprised of elements, such as polarizers (polaroids), electrode substrates, etc., and the cell gap thereof d=7 μm. This display apparatus is in normally white (NW) mode, i.e., white pixel color is observed if there is no voltage difference applied between the row electrode and the column electrode. The axes of the upper and lower polaroids on the substrates are at a 90-degree angle. The optical liquid crystal material is filled full of the space between the two substrates.

For the convenience of the expression, the unit structures of the liquid crystal compounds in the following Examples are represented by the codes listed in Table 1:

Take the following structural formula as an example:

Represented by the codes listed in Table 1, this structural formula can be expressed as 3PTGQP3.

Another example:

it can be expressed as nCPTPm, in which, the n in the code represents the number of the carbon atoms of the alkyl group on the left, for example, n is “3” means the alkyl is —C 3 H 7 ; the C in the code represents a cyclohexyl; the P in the code represents phenylene; the T in the code represents alkynyl; the m in the code represents the number of the carbon atoms of the alkyl group on the right, for example, m is “1” means the right alkyl is —CH 3 .

The abbreviated codes of the test items in the following Examples are respectively represented as:

Cp ( ) clearing point (nematic-isotropy phase transition temperature)

Δn optical anisotropy (589 nm, 20° C.)

γ1 torque viscosity (mPa*s, below 20° C.)

K11 elastic constant (“splay”, pN below 20° C.)

K33 elastic constant (“bend”, pN below 20° C.)

t −30° C. storage lifetime at low-temperature (below −30° C.)

V90 saturation voltage=characteristic voltage at 90% relative contrast (NW mode)

V10 threshold voltage=characteristic voltage at 10% relative contrast (NW mode)

Test conditions of V10: C/1 KHZ, JTSB7.0.

The ingredients used in the following Examples are all synthesized by the inventors of the present application according to the methods known in the art. These synthetic techniques are routine, and the test results show that the liquid crystal compounds thus prepared meet the criteria for the electronic compounds.

Several liquid crystal compositions are prepared according to the formulations of the liquid crystal compositions specified in the following Examples. The preparation of the liquid crystal compositions is proceeded according to the conventional methods in the art, and as an example, the compositions are prepared by mixing the specified formulation via the processing modes, such as heating, ultrasonic processing, suspending processing and so on.

The liquid crystal composition specified in the following Examples are prepared and studied. The formulas of the liquid crystal compositions and their test results for the performance are shown below.

Table 2 and Table 5 show the formulations of the liquid crystal compositions of the Comparison Examples. The test results obtained from the liquid crystal display devices filled with the liquid crystal compositions of the Comparison Examples in the space between the two substrates of the liquid crystal display devices are also listed so that the performances of the liquid crystal composition of the present invention can be compared with those of the Comparison Examples clearly.

Comparison Example 1

The liquid crystal composition of the Comparison Example is prepared according to the formulation listed in Table 2, and is tested by filling the same between two substrates of a liquid crystal display device. The performance data are shown in the Table below: