Liquid crystal cell

Abstract

Provided are a liquid crystal cell and a use thereof. An exemplary liquid crystal cell can be implemented in a bistable mode switching between a haze mode and a non-haze mode even with low driving voltage. Such a liquid crystal cell can be applied to various optical modulation apparatus, such as a smart window, a window protection film, a flexible display element, an active retarder for a 3D visual display, and a viewing angle-controlling film.

Claims

1. A bistable liquid crystal cell comprising: two opposite substrates; and a liquid crystal layer provided between the two opposite substrates and including a smectic liquid crystal compound, and an ionic compound having an anion represented by the following Chemical Formula 1:
I.sub.n.sup.−  [Chemical Formula 1] where, in Chemical Formula 1, I represents iodine and n represents a number of 2 or more, wherein the bistable liquid crystal cell is capable of switching between a haze mode having a haze of 80% or more and a non-haze mode having a haze of 10% or less at a voltage of 80 V or less, and wherein a ratio of the ionic compound in the liquid crystal layer is within the range of 0.005 wt % to 5.0 wt %.

2. The bistable liquid crystal cell of claim 1, wherein the smectic liquid crystal compound is a smectic A liquid crystal compound.

3. The bistable liquid crystal cell of claim 1, wherein the smectic liquid crystal compound is a compound represented by the following Chemical Formula 2: ##STR00008## where, in Chemical Formula 2, A represents a single bond, —COO—, or —OCO—, and R.sub.1 to R.sub.10 each independently represent a hydrogen, a halogen, an alkyl group, an alkoxy group, an alkoxycarbonyl group, a cyano group, a nitro group, or a substituent represented by the following Chemical Formula 3, wherein, in Chemical Formulas 2 and 3, any one of R.sub.1 to R.sub.15 is an alkyl group, an alkoxy group, or an alkoxycarbonyl group having 5 or more carbon atoms, ##STR00009## where, in Chemical Formula 3, B represents a single bond, —COO—, or —OCO—, and R.sub.11 to R.sub.15 each independently represent a hydrogen, a halogen, an alkyl group, an alkoxy group, an alkoxycarbonyl group, a cyano group, or a nitro group.

4. The bistable liquid crystal cell of claim 1, wherein, in Chemical Formula 1, n represents a number within the range of 3 to 10.

5. The bistable liquid crystal cell of claim 1, wherein the ionic compound is a nitrogen-containing onium salt, a sulfur-containing onium salt, or a phosphorus-containing onium salt.

6. The bistable liquid crystal cell of claim 1, wherein the ionic compound includes a cation represented by any one of the following Chemical Formulas 4 to 7: ##STR00010## where, in Chemical Formula 4, R.sub.a represents a hydrocarbon group having 4 to 20 carbon atoms, and includes a heteroatom, and R.sub.b and R.sub.c each represent hydrogen, or a hydrocarbon group having 1 to 16 carbon atoms, and include a heteroatom, wherein R.sub.c is not included when the nitrogen atom has a double bond, ##STR00011## where, in Chemical Formula 5, R.sub.d represents a hydrocarbon group having 2 to 20 carbon atoms, and includes a heteroatom, and R.sub.e, R.sub.f, and R.sub.g each represent hydrogen, and a hydrocarbon group having 1 to 16 carbon atoms, and include a heteroatom, ##STR00012## where, in Chemical Formula 6, R.sub.h represents a hydrocarbon group having 2 to 20 carbon atoms, and includes a heteroatom, and R.sub.i, R.sub.j, and R.sub.k each represent hydrogen, and a hydrocarbon group having 1 to 16 carbon atoms, and include a heteroatom, ##STR00013## where, in Chemical Formula 7, Z represents a nitrogen, sulfur, or phosphorus atom, R.sub.1, R.sub.m, R.sub.n, and R.sub.o each represent a hydrocarbon group having 1 to 20 carbon atoms and include a heteroatom, wherein R.sub.o is not included when Z is a sulfur atom.

7. The bistable liquid crystal cell of claim 1, wherein the bistable liquid crystal cell is formed so that the bistable liquid crystal cell switches between a transmission mode having a transmittance of 85% or more and a white mode having a transmittance of 83% or less.

8. The bistable liquid crystal cell of claim 1, wherein the liquid crystal layer further includes an anisotropic dye.

9. The bistable liquid crystal cell of claim 8, wherein the anisotropic dye is included in the liquid crystal layer in the ratio within the range of 0.01 wt % to 2 wt %.

10. The bistable liquid crystal cell of claim 8, wherein the bistable liquid crystal cell is formed so that the bistable liquid crystal cell switches between a transmission mode having a transmittance of 50% or more and a black mode having a transmittance of 40% or less.

11. The bistable liquid crystal cell of claim 1, wherein the liquid crystal layer further includes a polymer network.

12. The bistable liquid crystal cell of claim 11, wherein the polymer network is included in the liquid crystal layer in a ratio of 40 wt % or less.

13. The bistable liquid crystal cell of claim 1, further comprising an alignment layer provided on a side of the liquid crystal layer of the opposite substrates.

14. The bistable liquid crystal cell of claim 1, further comprising an electrode layer provided on a side of a liquid crystal layer of the opposite substrates.

15. An optical modulation apparatus comprising the bistable liquid crystal cell of claim 1.

16. A smart window comprising the bistable liquid crystal cell of claim 1.

Description

DESCRIPTION OF DRAWINGS

(1) FIGS. 1(a) and (b), 2(a) and (b), and 3(a) and (b) illustrate the exemplary liquid crystal cells.

(2) FIGS. 4(a) and (b), 5(a) and (b), 6(a) and (b), and 7 illustrate the exemplary ways of driving the liquid crystal cell.

(3) FIG. 8 illustrates the state of the liquid crystal cell in a non-haze mode according to Example 1.

(4) FIG. 9 illustrates the state of the liquid crystal cell in a haze mode according to Example 1.

MODES OF THE INVENTION

(5) Hereinafter, the above contents will be described in more detail with reference to Examples and Comparative Example. However, the present application is not limited to the exemplary embodiments disclosed below.

(6) 1. Measurements of Transmittance and Haze

(7) The transmittances and hazes of the liquid crystal cells manufactured in Examples and Comparative Examples were measured according to ASTM standards using a hazemeter, NDH-5000SP.

EXAMPLE 1

(8) A liquid crystal cell was manufactured by arranging two polycarbonate (PC) films on which an Indium Tin Oxide (ITO) transparent electrode layer and a known vertical alignment layer forms sequentially apart from each other so that the alignment layers were opposite each other and the distance therebetween was to be about 9 μm; injecting a liquid crystal composition between the two PC films arranged apart from each other; and then sealing an edge. The liquid crystal composition was prepared by mixing the liquid crystal compound (HJA151200-000 manufactured by HCCH) exhibiting a smectic A phase, an anisotropic dye (X12 manufactured by BASF), and an ionic compound including the cation represented by the following Chemical Formula A and the anion represented by the following Chemical Formula B in the weight ratio of 99.2:0.7:0.1 (Liquid crystal compound:Anisotropic dye:Ionic compound), and then used. For the prepared liquid crystal cell, the transmittance and haze were about 62.39% and about 1.36%, respectively, when no voltage was supplied (this state may be referred to hereinafter as a non-haze mode).

(9) ##STR00007##

EXAMPLE 2

(10) A liquid crystal cell was manufactured in the same method as Example 1, except that a PC film without the alignment layers on the surfaces of the electrode layers was used. For the prepared liquid crystal cell, the transmittance and haze were about 36.31% and about 90.28%, respectively, when no voltage was supplied (this state may be referred to hereinafter as the non-haze mode).

COMPARATIVE EXAMPLE 1

(11) A liquid crystal cell was manufactured in the same method as Example 2, except that a compound including the cation represented by the above-described Chemical Formula A and the anion represented by the following Chemical Formula C were used as an ionic compound. For the prepared liquid crystal cell, the transmittance and haze were about 35.80% and about 88.28%, respectively, when no voltage was supplied (this state may be referred to hereinafter as the non-haze mode).
Br.sup.−  [Chemical Formula C]

TEST EXAMPLE 1

Evaluation of Driving Voltage

(12) The voltage required for switching was evaluated after electrical power was connected to the ITO transparent electrode layer in each of the liquid crystal cells prepared in Examples and Comparative Example, the modes were switched during supply of a driving voltage. In other words, in the non-haze mode of Example 1, the voltage required for switching the non-haze mode into the haze mode having the transmittance of 40% or less and the haze of 90% or more was measured; and in the haze mode of Comparative Example 1 or Example 2, the voltage required for switching the haze mode into the non-haze mode having the transmittance of 60% or more and the haze of 2% or less was measured. FIG. 8 illustrates the state of the liquid crystal cell in the non-haze mode according to Example 1, and FIG. 9 illustrates the state of the liquid crystal cell in the haze mode according to Example 1.

(13) As listed in the following Table 1, in the liquid crystal cell according to Example 1, a voltage of 80 V at a frequency of 60 Hz was required to convert the non-haze mode into the haze mode having the transmittance of about 37.37% and the haze of about 92.37%, and even when the external voltage was removed after converting the non-haze mode into the haze mode, the haze mode was stably maintained for about 240 hours or more. In addition, a voltage of 80 V at a frequency of 6 kHz was required to convert the haze mode into the original non-haze mode. In addition, in the liquid crystal cell according to Example 2, a voltage of 80 V at a frequency of 6 kHz was required to convert the haze mode into the non-haze mode having the transmittance of about 62.54% and the haze of about 1.39%, and even when the external voltage was removed after converting the haze mode into the non-haze mode, the non-haze mode was stably maintained for about 240 hours or more. In addition, a voltage of 80 V at a frequency of 60 Hz was required to convert the non-haze mode into the original haze mode. On the other hand, in the case of Comparative Example 1, a high driving voltage of about 120 V at the same frequency was required to convert between the similar haze mode and non-haze mode.

(14) TABLE-US-00001 TABLE 1 Vertical electric field Vertical electric field 80 V [60 Hz] applied 80 V [6 kHz] applied Example 1 Transmittance 37.37% Transmittance 62.39% Haze 92.37% Haze 1.36% Example 2 Transmittance 36.31% Transmittance 62.54% Haze 90.28% Haze 1.39% Vertical electric field Vertical electric field 120 V [60 Hz] applied 120 V [6 kHz] applied Comparative Transmittance 35.80% Transmittance 63.04% Example 1 Haze 88.23% Haze 1.9%

EXPLANATION OF REFERENCE NUMBERS

(15) 101A, 101B: Substrate

(16) 102: Liquid crystal layer

(17) 1021: Smectic liquid crystal compound

(18) 201, 301: Polymer network

(19) 302: Liquid crystal area

(20) 401A, 401B, 501A, 501B: Electrode layer

(21) 601A, 601B, 701A, 701B: Alignment layer