Liquid crystal composition and its application

This application is a 371 U.S. National Stage of International Application No. PCT/CN2014/083002, filed Jul. 25, 2014, which claims the benefit of Chinese Patent Application No. 201410269923.7, filed Jun. 17, 2014. The disclosures of the above applications are incorporated herein by reference.

The present invention relates to liquid crystal materials, particularly to the use of liquid crystal compositions for liquid crystal display devices.

Currently, liquid crystal has been applied in information display and some progress has been made in optical communication (S. T. Wu, D. K. Yang. Reflective Liquid Crystal Displays. Wiley, 2001). In recent years, applications of liquid crystal compounds have significantly broadened to various types of display devices, electro-optical devices, electronic components, sensors and the like. For these purposes, a plurality of different structures has been proposed, particularly in nematic phase liquid crystals. Nematic phase liquid crystal compound so far has been widely used in flat panel displays, especially in thin film transistor (TFT) active matrix liquid crystal display (AMLCD) systems.

It has been a long path of development since the discovery of liquid crystals. In 1888, Friedrich Reinitzer, an Austrian botanist, discovered the first liquid crystal material, i.e., cholesteryl benzoate. Manguin invented a rubbing orientation for the production of single domain liquid crystal and initiated the research on optical anisotropy in 1917. E. Bose established Swarm doctrine in 1909, which was supported by experiments of L. S. Ormstein and F. Zernike et al (1918) and later was explained as statistical fluctuations by De Gennes. In 1933, G. W. Oseen and H. Zocher founded continuum theory which was modified by F. C. Frank later in 1958. M. Born (1916) and K. Lichtennecker (1926) found and studied liquid crystal dielectric anisotropy respectively. In 1932, W. Kast accordingly divided the nematic phase into positive and negative two categories. In 1927, V. Freedericksz and V. Zolinao discovered that nematic liquid crystal would be deformed and presented a voltage threshold (Freederichsz change) in the electric field or magnetic field. The discovery provides a basis for liquid crystal displays.

In 1968, R. Williams in Radio Corporation of America (RCA) found that nematic phase liquid crystals formed domain structure and had light scattering phenomenon in the electric field. G. H. Heilmeir then developed a dynamic scattering mode, the first liquid crystal display in the world. In the early 1970s, Helfrich and Schadt invented twist-nematic (TN) principle. The combination of the TN photoelectric effect and integrated circuit made a display device (TN-LCD), which has opened up a broad prospect for the application of liquid crystals. Since then, due to the development of large scale integrated circuits and the advancement of liquid crystal material, the liquid crystal display, in the art, has made a breakthrough. Super Twist Nematic (STN) mode was proposed successively by T. Scheffer et al. in 1983 through 1985 and an AMLCD mode proposed by P. Brody in 1972 were re-adopted. Conventional TN-LCD technology has been transferred to STN-LCD and TFT-LCD technologies. Although STN scanning lines can be up to 768 lines, there are still some shortcomings such as response speed, viewing angle and gray scale when the temperature rises. Therefore, for a large panel, high information content, high color quality display, an active matrix display becomes the first choice. TFT-LCD has been widely used in direct-view TV, large-screen projection television, computer monitor and certain military instrument display. It is believed that TFT-LCD technologies will have even broader applications.

There are two types of “active matrix” structures: firstly, metal oxide semiconductor (MOS) on a silicon wafer as the substrate. Secondly, thin film transistor (TFT) fabricated on a glass substrate.

Monocrystalline silicon as the substrate has a limitation with its display size due to the fact that there were many problems at junctions of each part of the display unit or module assembly. Accordingly, the second type of TFT active matrix is promising. The photoelectric display effect is generally TFT-TN mode. TFT substrate includes a compound semiconductor, such as of CdSe, a polycrystalline silicon as well as amorphous silicon.

For small and medium-size displays such as monitors and smart phones, the in-plane switching (IPS) and fringe field switching (FFS) mode is very interesting for its large viewing angle compared with TFT-TN display. With respect to the IPS, FFS has a higher transmittance. The liquid crystal mixture of those displays lies in the compounds with positive dielectric anisotropy, and optionally, neutral compounds.

It is desirable that the LCs inside the display cell structure should have the following advantages:

1. wide temperature range of nematic phase (in particular, low-temperature range)

2. fast response time (outdoor use, automobiles, avionics) switching at very low temperatures

3. superior resistance to UV radiation (longer service life)

4. low threshold voltage (to save energy)

5. high transmittance.

The present invention is directed to synthesizing liquid crystals for TN, ADS, FFS or IPS display applications. In particular, the liquid crystal medium should have a fast response time and a low rotational viscosity while having a high birefringence. The liquid crystal media should also have a high clearing point, and a suitable dielectric anisotropy.

It is discovered that the above-mentioned performances can be achieved by using a liquid crystal mixture comprising one or more compounds of formula I. The novel compound is characterized by a higher clearing point, better mutual solubility, more stable, while its physical parameters such as optical anisotropy, dielectric anisotropy and rotational viscosity are moderate adjustable. By combining with other suitable liquid crystal compounds, excellent overall electro-optical performances have already been achieved.

Specifically the present invention provides a liquid crystal composition comprising:

a) 1 to 90 weight percents of one or more compounds represented by the general formula I;

b) 1 to 85 weight percents of one or more compounds represented by the general formula II to III;

c) at most 80 weight percents of one or more compounds represented by the general formula IV to XIII;

d) at most 30 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) at most 30 weight percents of one or more compounds represented by the general formula XVII to XXI;

f) at most 15% of one or more compounds represented by the general formula XXII to XXV;

wherein the above a) to f) sum to 100%;

R-A 1 -Z 1 -A 2 -Z 2 -A 3 -Z 3 -A 4 -Z 4 -A 5 -O(CH 2 )nF   I

wherein,

R is selected from H and unsubstituted or substituted alkyl or alkoxy containing 1 to 12 carbon atoms, one or more CH 2 groups thereof being independently replaced by —C≡C—, —CF 2 O—, —CH═CH—, —O—, —CO—O—, —O—CO— in a manner of not directly being bonded each other to oxygen atoms, and one or more H atoms thereof being replaced by halogen;

A 1 , A 2 , A 3 , A 4 and A 5 are each independently selected from a single bond; 1,3-cyclopentylene, 1,4-cyclohexylene, 1,4-cyclohexenyl; 1,4-piperidine group; 1,4-bicyclo [2.2.2] octyl; 1,4-phenylene, naphthalene-2,6-diyl; trans-decalin-2,6-diyl; tetrahydronaphthalene-2,6-diyl; indan; indene; phenanthrenyl and dibenzofuran; 1,4-cyclohexylene, one or two nonadjacent CH 2 thereof being replaced by O or S; 1,4-phenylene, one or two nonadjacent CH being replaced by N; and hydrogen may independently be substituted with halogen in each case; while A 1 , A 2 , A 3 , A 4 and A 5 cannot be all a single bond;

Z 1 , Z 2 , Z 3 and Z 4 are each independently selected from a single bond, —(CH 2 ) 2 —, —(CH 2 ) 4 —, —CH═CHCH 2 CH 2 —, —CH 2 CH 2 CH═CH—, CF 2 O, OCF 2 , CF 2 CF 2 , CF═CF, CH 2 CF 2 , CF 2 CH 2 , OCF 2 CF 2 O, C 2 H 1 CF 2 O, CH 2 CF 2 OCH 2 , CH 2 OCF 2 CH 2 , OCF 2 C 2 H 4 , C 3 H 6 O, OC 3 H 6 , C 2 H 4 OCH 2 , CH 2 OC 2 H 4 , CH 2 O, OCH 2 , —CH═CH—, —C≡C— and COO;

n is 2, 3 or 4;

wherein,

R 2 and R 3 are each independently selected from alkyl or alkoxy containing 1-7 carbon atoms, one or more CH 2 groups thereof may each, independently be replaced by —CH═CH— and one or more H atoms thereof may be replaced by fluorine element;

A and B are each independently selected from 1,4-cyclohexylene; 1,4-phenylene, one or more H atoms thereof may be replaced by fluorine element;

C and D are each independently selected from 1,4-cyclohexylene, one or two nonadjacent —CH 2 — thereof may be replaced by O;

Y 1 -Y 7 each independently denotes H or F;

Z 5 denotes a single bond, —C 2 H 4 —, —(CH 2 ) 4 —, —CH═CH, —CF═CF, —C 2 F 4 —, —CH 2 CF 2 —, —CF 2 CH 2 —, —CH 2 O—, —OCH 2 , —COO—, —CF 2 O— or —OCF 2 —;

X 1 denotes F, OCF 3 , OCHF 2 , CF 3 , CF 2 H, CL, OCH═CF 2 or OCF 2 CF═CF 2 .

Preferably, the liquid crystal composition provided in present invention comprising:

a) 2 to 55 weight percents of one or more compounds represented by the general formula I;

b) 17 to 82 weight percents of one or more compounds represented by the general formula II to III;

c) at most 57 weight percents of one or more compounds represented by the general formula IV to XIII;

d) at most 30 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) at most 26 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%.

More preferably,

a) 3 to 50 weight percents of one or more compounds represented by the general formula I;

b) 20 to 80 weight percents of one or more compounds represented by the general formula II to III;

c) 5 to 50 weight percents of one or more compounds represented by the general formula IV to XIII;

d) 1 to 15 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) 1 to 25 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%.

Most preferably, the liquid crystal composition provided in is the present invention comprising:

a) 5 to 50 weight percents of one or more compounds represented by the general formula I;

b) 20 to 60 weight percents of one or more compounds represented by the general formula II to III;

c) 10 to 50 weight percents of one or more compounds represented by the general formula IV to XIII;

d) 3 to 15 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) 3 to 20 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%;

or

a) 10 to 38 weight percents of one or more compounds represented by the general formula I;

b) 23 to 42 weight percents of one or more compounds represented by the general formula II to III;

c) 34 to 45 weight percents of one or more compounds represented by the general formula IV to a XIII;

d) at most 12 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) at most 8 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%;

or

a) 28 to 46 weight percents of one or more compounds represented by the general formula I;

b) 23 to 56 weight percents of one or more compounds represented by the general formula II to III;

c) at most 20 weight percents of one or more compounds represented by the general formula IV to a XIII;

d) 8 to 14 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) 8 to 19 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%;

or

a) 15 to 41 weight percents of one or more compounds represented by the general formula I;

b) 20 to 42 weight percents of one or more compounds represented by the general formula II to III;

c) 22 to 33 weight percents of one or more compounds represented by the general formula IV to XIII;

d) 14 to 30 weight percents of one or more compounds represented by the general formula XIV to XVI;

e) 3 to 24 weight percents of one or more compounds represented by the general formula XVII to XXI;

wherein the above a) to e) sum to 100%.

The liquid crystal composition of the present invention provides the compounds of formula I exhibits a good miscibility, excellent overall performances, especially high clearing point.

Wherein the compound of formula I which is preferably represented, R is selected from H and unsubstituted or substituted alkyl or alkoxy group each containing 1 to 7 carbon atoms, wherein these groups one or more CH 2 groups may also be substituted independently by —CH═CH—, —O—, in a manner not directly bonded to each other to O atoms, and wherein one or more H atoms may be replaced by halogen;

A 1 , A 2 , A 3 , A 4 and A 5 are each independently selected from: a single bond; 1,3-cyclopentyl, 1,4-cyclohexylene, 1,4-cyclohexenyl; 1,4-phenyl, naphthalene 2,6-diyl; trans-decalin-2,6-diyl; tetrahydronaphthalene-2,6-diyl; indan, wherein, in a 1,4-cyclohexylene CH 2 or two CH 2 not directly connected may be replaced by O or S; 1,4-phenylene in a CH or two CH not directly connected may be replaced by N; and hydrogen may be independently in each case substituted by fluorine; while A 1 , A 2 , A 3 , A 4 and A 5 cannot be all a single bond;

Z 1 , Z 2 , Z 3 and Z 4 are each independently selected from: a single bond, —(CH 2 ) 2 —, —(CH 2 ) 4 —, CF 2 O, OCF 2 , CF═CF, CH 2 CF 2 , CF 2 CH 2 , CH 2 O, OCH 2 , —CH═CH—;

n is 2, 3 or 4;

More preferably:

R is selected from H and unsubstituted or substituted alkyl or alkoxy containing 1 to 6 carbon atoms, wherein these groups with one or more CH 2 groups may each, independently replaced by —CH═CH—, —O—, with O atoms not directly bonded, and wherein one or more H atoms may also be replaced by fluorine;

A 1 , A 2 , A 3 , A 4 and A 5 are each independently selected from: a single bond; 1,4-cyclohexylene; 1,4-cyclohexenyl; phenyl-1,4; wherein 1,4-cyclohexylene one or two CH 2 not directly connected may be replaced by O; and hydrogen may independently be substituted by one or more fluorine in each case; while A 1 , A 2 , A 3 , A 4 and A 5 cannot be all a single bond;

Z 1 , Z 2 , Z 3 and Z 4 are each independently selected from: a single bond, —(CH2) 2-, CF2O;

n is 2, 3 or 4;

More preferred compounds of formula I can be selected from at least one compounds listed as follows:

wherein R 1 is selected from alkyl or alkoxy group containing 1 to 6 carbon atoms,

wherein these groups one or more CH 2 groups may each, independently be replaced by —CH═CH—, one or more H atom may be replaced by fluorine;

n is 2, 3 or 4.

The most preferred compounds of formula I are as follows:

Two ring structures of the compounds with general formula II or III, provided in the present invention, are non-polar components. Such compounds have a significant effect on reducing the systematic viscosity and enhancing response speed, which is essential for a mixture of liquid crystal compounds to achieve fast response time of the display. The compounds with formula II provided by the invention are of negative dielectric anisotropy (−Δε), and have characteristics of low viscosity at low temperature. Adding to a liquid crystal composition with positive dielectric anisotropy, such compounds can effectively improve transmittance characteristics of the liquid crystal displays.

Wherein, preferably the formula II and/or III compound represented by the one or more compounds selected from the following:

The compounds with general formula IV to XIII, provided in the present invention, are polar compounds, the structure has a large dielectric anisotropy, which will be able to reduce display's driving voltage and enhance energy conservation, when applied to the liquid crystal composition.

Preferably the compound of Formula IV to XIII is selected from the compounds represented by one or more of:

wherein R 2 and X 1 represents supra, Y 1 -Y 7 represents H or F independently of one another.

The general formula XIV to XVI, provided in the present invention, is of biphenyl or terphenyl structure that has a large optical anisotropy, which may increase the optical anisotropy, thereby reduce the cell thickness and improve the response speed, when applied to the liquid crystal composition.

Wherein the compound of Formula XIV to XVI is preferably represented by a compound selected from one or more of:

wherein R 2 , R 3 , Y 1 , Y 2 and X 1 represents supra.

The general formula XVII to XXI, provided in the present invention, is of tetracyclic structure, which has a high clearing point, applied to the liquid crystal composition may improve temperature range of the device.

Wherein said compound of Formula XXI to XVII preferably represents one or more compounds selected from the following:

wherein R 2 , R 3 and X 1 represents supra.

And the compound is preferably, to the general formula XXII, XXV selected from compounds represented by one or more of:

wherein R 2 and R 3 represent supra.

There is no methodological limitation for preparing the liquid crystal composition in the present invention. A conventional method of mixing two or more compounds may be adopted, such as a method for preparing the different components mixed at a high temperature and dissolved each other; the liquid crystal composition may also prepared by dissolving and mixing the compound in a solvent, and then the solvent may be distilled off under reduced pressure. In present invention, a liquid crystal composition can be prepared according to a conventional method, such as that the smaller percentage component is dissolved into a larger percentage main component at high temperature, or that respective components are dissolved in an organic solvent, such as acetone, chloroform or methanol, and the mixture are obtained after removal of the solvent. Nevertheless, the present invention is not particularly limited to the above-mentioned methods.

Furthermore, the present invention further relates to apply the state-of-art liquid crystal composition in a LCD device, wherein the device is preferably TN, ADS, FFS or IPS display. The liquid crystal composition of the present invention has characteristics of low viscosity, high resistivity, good low-temperature miscibility, fast response and excellent transmission, which can be used for a variety of fast response display modes. The working temperature of a LCD is subject to the temperature range of liquid crystal. Information can only be displayed in a specific temperature range of the liquid crystal phase. At low temperature, the viscosity of liquid crystal increases exponentially, a hurdle of LCD, which remarkably reduces the response speed and overall performances of LCD. The liquid crystal composition according to the present invention overcomes these problems. Characterized by its low viscosity, good low-temperature performance and excellent transmission allows the liquid crystals to use in TN, IPS or FFS displays with remarkably improved performances.

The following examples illustrate the embodiment of the invention but the applicants do not intend to limit the scope of the present invention.

The embodiment of the invention for preparing the liquid crystal compositions is described as follows:

To prepare a homogeneous liquid crystal solution, a well-known thermo dissolution approach in the field was introduced: firstly, weight the liquid crystal compounds on the weighting scales; secondly, mixing the liquid crystal compounds without specific sequential requirement, but usually in order of higher melting point first; thirdly, stir the compounds at 60-100 C, such that the components melted uniformly. After filtration, rotary evaporation and packaging, the final target sample is obtained.

Unless otherwise indicated, percentages are by weight and temperatures are given in degrees Celsius in the contest. The following abbreviations are used:

Δn is optical anisotropy (20° C.), Δε dielectric anisotropy (25° C., 1000 Hz), γ 1 for the bulk viscosity (mPa·s, 25° C.), Cp is the clearing point of liquid crystal composition (° C.). For ease of illustration, in the following examples, the group structure of the liquid crystal compound is represented by the code shown in Table 1:

The following structure, as an example,

can be represented as CDUQU-3.O3F.

The following structure, as another example,

can be represented as CCPU-5.F.

The following examples describe in detail the percentage ratio of the liquid crystal compounds prepared according the present invention and the performance parameters of the resulting liquid crystal composition as shown in the following tables.

The liquid crystal composition of the present invention has characteristics of low viscosity, high resistivity, good low-temperature mutual solubility, fast response and excellent transmission, which can be used for a variety of fast response display modes. The working temperature of a LCD is subject to the temperature range of liquid crystal. Information can only be displayed in a specific temperature range of liquid crystal phase. At low temperature, the viscosity of liquid crystal increases exponentially, a hurdle of LCD, which substantially reduces the response speed and overall performances of LCD. The liquid crystal composition according to the present invention overcomes these problems. Characterized by its low viscosity, good low-temperature performance and excellent transmission, the liquid crystal composition is applicable in TN, IPS or FFS displays with remarkably improved performances.