COMPOSITION COMPRISING AT LEAST ONE TYPE OF LIQUID CRYSTAL

Abstract

The present invention relates to a composition comprising at least one type of liquid crystal, to a liquid crystal cell and liquid crystal display device comprising such composition and to a method of preparing such a composition and/or such a liquid crystal cell.

Description

In the following, reference is made to the figures, wherein

FIG. 1 shows a schematic representation of a typical liquid crystal test cell. The liquid crystal test cell depicted shows three possible orientations of the liquid crystal material contained therein. The representation is not meant to imply that a liquid crystal material may take a vertical (homeotropic), parallel (homogeneous) and twisted orientation at the same time. The boundary surfaces shown therein may be a special layer introduced for the very purpose of aligning the liquid crystal material that is in contact with such boundary surface. Examples of useful boundary surfaces in accordance with the present invention are rubbed/unrubbed ITO, rubbed/unrubbed polyimide, rubbed/unrubbed CTAB (cetyl trimethyl ammonium bromide), or obliquely/perpendicularly evaporated/sputtered SiOx. The cell is formed of a front plane and a backplane. At each of these planes there is an electrode, frequently formed by ITO, and on top of such electrode there is a boundary surface which, optionally, may be an additional layer or layers, or may be the surfaces of the electrodes themselves.

FIG. 2 shows two structures of example dopants in accordance with the present invention. The term “dopant” as used herein is meant to signify a compound that is added to a liquid crystal composition. In a more specific sense, the term “dopant” refers to the aromatic ether or diaromatic ether or aromatic thioether or diaromatic thioether or aromatic secondary amine or diaromatic secondary amine in accordance with the present invention.

FIG. 3 shows the rise time vs. average field strength (from E10 to E90) for 2%, 4% and 6% BrPhOPh doped negative liquid crystals. Measurements were carried out at 35° C.

FIG. 4 shows temperature dependent speed factors for 4% and 6% BrPhOPh doped negative liquid crystals. Measurements were carried out at 52, 55, 60, 65 and 70° C. 2 μm cells with SiO_x alignment layers. 4% & 6% doped mixtures are faster and their switching voltages are lower than the pure material.

FIG. 5 shows rise time vs. averaged field strength (from E10 to E90) for 10% BrPhOPh doped negative liquid crystals. Measurements were carried out at 35° C. 10% doped material is faster and its switching voltages are lower.

FIG. 6 shows decay time vs. applied voltage (from V10 to V90) for 0, 1, 2% & 4% BrPhOPh doped negative liquid crystals. Measurements were carried out at 35° C. There is no significant change in the decay times.

FIG. 7 shows response time improvements at different concentrations of BrPhOPh (10%, 6%, 4% and 2%) in negative liquid crystals, 5 μm thick cells at 35° C. Depending on the applied voltages and the amount of dopants used, response times are from 5% to more than 80% faster than the pure materials.

FIG. 8 shows off transmittance of the negative liquid crystalline material with and without BrPhOPh (1%, 2%, 4% and 6% concentrations). Measurements were carried out at 35° C. No change in the black level. Thus the liquid crystal's director orientation at the alignment layer (boundary surface) remains unaffected FIG. 9 shows Voltage-Transmittance diagram of 4% and 6% BrPhOPh doped negative liquid crystal. 2 μm thick cells with SiO_x alignment layer. Measurements were carried out at 50° C. Contrast ratio and brightness of the doped mixtures are as good as the pure material.

FIG. 10 shows V10 and V90 values of 4% and 6% BrPhOPh doped negative liquid crystal. 2 μm cells with SiO_x alignment layer at 35° C. Switching voltages are reduced upon doping.

FIG. 11 shows Concentration dependent percentage changes in dielectric anisotropy and rotational viscosity of negative type liquid crystal upon addition of 2%, 4% and 6% of BrPhOPh. Measurements were carried out at 20° C.

FIG. 12 shows rise time vs. averaged field strength (from E10 to E90) for 1%, 2% and 4% ClPhOPh doped negative liquid crystals. Measurements were carried out at 35° C. Doped mixtures are much faster, and the switching voltages are reduced.

FIG. 13 shows decay time vs. applied voltage (from V10 to V90) for 1%, 2% and 4% ClPhOPh doped negative liquid crystals. Measurements were carried out at 35° C. Decay time of the 1% doped mixture is almost the same as that of pure material. Decay times of 2% & 4% doped mixtures are faster than the pure material.

FIG. 14 shows response time improvements upon addition of 2%, 4% & 6% BrPhOPh to positive type liquid crystals. Measurements were carried out at 35° C. Rise time of the doped mixtures are faster.

FIG. 15 shows rise time vs. averaged field strength (from E10 to E90) for 10% BrPhOPh doped positive liquid crystals. Measurements were carried out at 35° C. Rise time of the 10% doped mixture is faster. Also, its switching voltage is lower.

FIG. 16 shows rise time vs. averaged field strength (from E10 to E90) for 2% and 4% ClPhOPh doped positive liquid crystals. Measurements were carried out at 35° C. Rise time of the doped mixtures are faster, and the switching voltages are lower.

FIG. 17 shows voltage holding ratios of 2%, 4% and 6% BrPhOPh doped positive liquid crystal. Measurements were carried out at 35° C. Voltage holding ratios remain unaffected and very high after doping.

FIG. 18 shows voltage holding ratios of 2% and 4% ClPhOPh doped positive liquid crystals. Measurements were carried out at 35° C. Voltage holding ratios remain unaffected and very high after doping.

FIG. 19 shows V10 and V90 values of 2%, 4% and 6% BrPhOPh doped positive liquid crystal. Switching voltages decrease upon doping.

FIG. 20 shows order parameters and dichroic ratios of BrPhOPh doped+LC.

FIG. 21 shows a transmission vs. voltage T-V curve of undoped D-SPDLC (top) and D-SPDLC doped with 5 wt % BrPhOPh (bottom). Reduction of hysteresis can be clearly seen with the doped system.

FIG. 22 shows a hysteresis reduction with BrPhOPh and ClPhOPh concentration. Both dopants reduce the D-SPDLC's hysteresis. Compared to BrPhOPh, a smaller amount of ClPhOPh is needed to achieve the same hysteresis reduction.

FIG. 23 shows hysteresis being defined as “voltage value for Transmission₅₀ when the voltage is increasing” minus “voltage value for Transmission₅₀ when the voltage is decreasing”, and

FIG. 24 shows a schematic graph summarizing an illustrative representation of turn-on (rise) and turn-off (decay or fall) response times.

Claims

1. A composition comprising at least one type of liquid crystal and at least one type of aromatic ether or diaromatic ether or aromatic thioether or diaromatic thioether or aromatic secondary amine or diaromatic secondary amine.

2. The composition according to claim 1, characterized in that said aromatic ether or aromatic thioether or aromatic secondary amine or diaromatic ether or diaromatic thioether or diaromatic secondary amine is represented by formula I Ar1—(CH2)l—X—(CH2)k—Ar2  formula I

3. The composition according to claim 2, characterized in that each of Ar1 and Ar2 is an aromatic ring system and is, at each occurrence, independently selected from the group comprising phenyl, naphthyl, biphenyl, binaphthyl, anthracenyl, triptycyl, and heteroaromatic rings, with one or several heteroatoms in them, selected from S, O and N such as pyridyl, pyrimidyl, pyridazyl, thienyl and furanyl.

4. The composition according to any of claims 2-3, characterized in that each of Ar1 and Ar2, independently, is an aromatic ring system which is unsubstituted or is substituted with one or several substituents.

5. The composition according to claim 4, characterized in that said one or several substituents is selected from the group comprising Cl, F, Br, I, OH, NH2, —O(CH2)nCH3, —(CH2)nCH3, wherein n is 0 to 22, preferably 0 to 10, —CYmH3-m, wherein Y is selected from Cl, F, Br and I, m is from 1 to 3, said one or several substituents being preferably selected from —CF3, —CN, —NO2, —COOH, carboxylic acid ester, substituted and unsubstituted cyclohexyl, substituted and unsubstituted cyclohexenyl, substituted and unsubstituted cyclopentadienyl, substituted and unsubstituted cyclopentyl.

6. The method according to any of claims 4-5, characterized in that one of Ar1 and Ar2 is substituted with one or several substituents, preferably as defined in claim 5, and the other one of Ar1 and Ar2 is not substituted.

7. The composition according to claim 6, characterized in that said diaromatic ether is selected from the group comprising 4-chlorodiphenylether, 4-bromodiphenylether and 4-fluorobiphenylether.

8. The composition according to any of claims 4-5, characterized in that both of Ar1 and Ar2 are substituted with one or several substituents, preferably as defined in claim 5.

9. The composition according to any of claims 4-5, characterized in that none of Ar1 and Ar2 are substituted.

10. The composition according to any of the foregoing claims, characterized in that the amount of said at least one type of aromatic ether or diaromatic ether or aromatic thioether or diaromatic thioether or aromatic secondary amine or diaromatic secondary amine is, with respect to the total weight of the composition, 0.05% (w/w) to 20% (w/w), preferably 0.1% (w/w) to 10% (w/w).

11. The composition according to any of the foregoing claims, characterized in that said at least one type of liquid crystal is a liquid crystalline compound or a mixture of liquid crystalline compounds of the negative type.

12. The composition according to any of claims 1-10, characterized in that said at least one type of liquid crystal is a liquid crystalline compound or a mixture of liquid crystalline compounds of the positive type.

13. The composition according to any of claims 1-10, characterized in that said at least one type of liquid crystal is a liquid crystalline compound or a mixture of liquid crystalline compounds of the dual-frequency type.

14. The composition according to any of the foregoing claims, characterized in that said at least one type of liquid crystal is a liquid crystalline compound or a mixture of liquid crystalline and non-liquid crystalline compounds where the liquid crystalline compound is preferably selected from nematic liquid crystals.

15. A liquid crystal cell comprising the composition according to any of the foregoing claims.

16. The liquid crystal cell according to claim 15, characterized in that it comprises a front- and a backplane, on each or either of said front- and backplane an electrode or multiplicity of electrodes, on each of said electrodes and/or on said front- and backplane, a boundary surface consisting of either the electrode and/or the front- and backplane, or consisting of an additional layer or layers of materials on said electrode and/or on said front- and backplane, and between said boundary surfaces said composition according to any of claims 1-14.

17. The liquid crystal cell according to any of claims 15-16, characterized in that it has a response time <40 ms, preferably <20 ms, more preferably <10 ms, and/or a voltage holding ratio >80%, more preferably >90%, more preferably >96%.

18. The liquid crystal cell according to claim 15, characterized in that it is a polymer dispersed liquid crystal (PDLC), dichroic polymer dispersed liquid crystal (D-PDLC), sponge polymer dispersed liquid crystal (SPDLC), dichroic sponge polymer dispersed liquid crystal cell (D-SPDLC), wherein the composition according to any of claims 1-14 has been used to prepare said cell.

19. The liquid crystal cell according to claim 18, characterized in that it has a hysteresis ΔV<0.1×V90, more preferably <0.05×V90, more preferably <0.01×V90, wherein V90 is a switching voltage at which T90, i.e. 90% of maximum transmission, is achieved, wherein the hysteresis ΔV is defined as the difference in voltage between the voltage value at half maximum transmission, T50, of said cell when the voltage is increasing and the voltage value at half maximum transmission, T50, of said cell when the voltage is decreasing, on a transmission vs. voltage graph, wherein T50 is defined as ½(Tmax+Tmin), wherein Tmax and Tmin are the maximum and minimum transmission achieved on said transmission vs. voltage graph.

20. A liquid crystal display device, comprising the composition according to any of claims 1-14 or comprising one or a multiplicity of interconnected or separate liquid crystal cells according to any of claims 15-19.

21. A method of preparing the composition according to any of claims 1-14, characterized in that at least one aromatic ether or diaromatic ether or aromatic thioether or diaromatic thioether or aromatic secondary amine or diaromatic secondary amine as defined in any of claims 1-14, is mixed with at least one type of liquid crystal as defined in any of claims 1-14.

22. A method of preparing the liquid crystal cell according to any of claims 15-20, characterized in that the composition according to any of claims 1-14 is used to fill a liquid crystal cell or D-SPDLC or SPDLC or D-PDLC or PDLC.