LIQUID CRYSTAL DEVICE

Abstract

The present application relates to a liquid crystal device. The liquid crystal device of the present application may realize a transparent white state, a transparent black state and a scattering state according to a level of an applied voltage at a fixed frequency. The liquid crystal device may be applied to, for example, a window of a vehicle, a smart window, a window protective film, a display, a light cutoff panel for a display, an active retarder for a 3D image display or a viewing angle controlling film.

Claims

1. A triple state liquid crystal device, comprising: a liquid crystal layer having a parallel conductivity of 1.010.sup.4 S/cm or more, and which switches among first to third states described below, and is designed for the switching among the first to third states to be performed by changing a voltage level at the same frequency, wherein the parallel conductivity is a value measured along the direction of an electric field while a voltage is applied to allow an optical axis of the liquid crystal layer to be parallel to the direction of the electric field at a measurement frequency of 60 Hz, at a measurement voltage of 0.5 V, and converted to correspond to a liquid crystal layer having an area of 1 cm.sup.2 and a thickness of 1 cm: first state: parallel light transmittance of 50% or more and haze of 5% or less; second state: parallel light transmittance of 35% or less and haze of 5% or less; and third state: parallel light transmittance of 10% or less and haze of 80% or more.

2. The device of claim 1, wherein the parallel conductivity of the liquid crystal layer is 5.010.sup.2 S/cm or less.

3. The device of claim 1, wherein the parallel conductivity of the liquid crystal layer is 3.010.sup.2 S/cm or less.

4. The device of claim 1, wherein, in the liquid crystal layer, the ratio (PC/VC) of the parallel conductivity (PC) to a vertical conductivity (VC) is 0.2 or more.

5. The device of claim 1, wherein in the liquid crystal layer, the ratio (VC/PC) of the vertical conductivity (VC) to the parallel conductivity (PC) is 2.0 or less.

6. The device of claim 1, which has a parallel light transmittance of 55% or more and a haze of 3% or less in the first state, a parallel light transmittance of 30% or less and a haze of 3% or more in the second state, and a parallel light transmittance of 5% or less and a haze of 90% or more in the third state.

7. The device of claim 1, which satisfies Formula A:
20H1/H2[Formula A] where H1 is haze of the triple state liquid crystal device at a frequency of 60 Hz and a voltage of 60 V, and H2 is haze of the triple state liquid crystal device at a frequency of 60 Hz and a voltage of 10 V.

8. The device of claim 1, which satisfies Formula B:
5<T1/T2[Formula B] where T1 is parallel light transmittance of the triple state liquid crystal device at a frequency of 60 Hz and a voltage of 10 V, and T2 is parallel light transmittance of the triple state liquid crystal device at a frequency of 60 Hz and a voltage of 60 V.

9. The device of claim 1, wherein the liquid crystal layer comprises an unreactive liquid crystal compound and a reactive mesogen.

10. The device of claim 9, wherein the liquid crystal layer comprises the reactive liquid crystal compound (.fwdarw.reactive mesogen) at 1 to 30 parts by weight with respect to 100 parts by weight of the unreactive liquid crystal compound.

11. The device of claim 9, wherein the liquid crystal layer further comprises an ionic compound at 2 wt % or less.

12. The device of claim 1, wherein the liquid crystal layer is vertically aligned in the first state.

13. The device of claim 1, wherein the liquid crystal layer is horizontally, vertically, twist or hybrid aligned in the second state.

14. The device of claim 1, wherein the liquid crystal layer is in an electrohydrodynamic instability state in the third state.

15. A method of manufacturing a triple state liquid crystal device comprising a liquid crystal layer, the method comprising: adjusting parallel conductivity of the liquid crystal layer to 1.010.sup.4 S/cm or more to allow the triple state liquid crystal device to switch among first to third states described below by changing a voltage level at the same frequency, wherein the parallel conductivity is a value measured along the direction of an electric field while a voltage is applied to allow an optical axis of the liquid crystal layer to be parallel to the direction of the electric field at a measurement frequency of 60 Hz, at a measurement voltage of 0.5 V, and converted to correspond to a liquid crystal layer having an area of 1 cm.sup.2 and a thickness of 1 cm: first state: parallel light transmittance of 50% or more and haze of 5% or less; second state: parallel light transmittance of 20% or less and haze of 5% or less; and third state: parallel light transmittance of 10% or less and haze of 80% or more.

16. The method of claim 15, wherein the liquid crystal layer is formed such that an applied voltage (V1) for realizing the first or second state and an applied voltage (V2) for realizing the third state satisfy Condition 1 described below:
V1<V2.[Condition 1]

17. A method of driving a triple state liquid crystal device comprising a liquid crystal layer having a parallel conductivity of 1.010.sup.4 S/cm or more, comprising: adjusting a level of an applied voltage such that the liquid crystal device realizes any one of first to third states described below, where the parallel conductivity is a value measured along the direction of an electric field while a voltage is applied to allow an optical axis of the liquid crystal layer to be parallel to the direction of the electric field at a measurement frequency of 60 Hz, at a measurement voltage of 0.5 V, and converted to correspond to a liquid crystal layer having an area of 1 cm.sup.2 and a thickness of 1 cm: first state: parallel light transmittance of 50% or more and haze of 5% or less; second state: parallel light transmittance of 20% or less and haze of 5% or less; and third state: parallel light transmittance of 10% or less and haze of 80% or more.

18. The method of claim 17, further comprising: controlling the level of an applied voltage to switch any one of the first to third states into another.

19. The method of claim 18, wherein the applied voltage is controlled such that an applied voltage (V1) for realizing the first or second state and an applied voltage (V2) for realizing the third state satisfy Condition 1 described below:
V1<V2.[Condition 1]

20. A light modulator, comprising: the triple state liquid crystal device of claim 1.

Description

DESCRIPTION OF DRAWINGS

[0084] FIGS. 1 to 3 illustrate a liquid crystal device.

[0085] FIGS. 4 to 11 show total transmittance and haze measured in experimental examples.

DESCRIPTION OF REFERENCE NUMERALS

[0086] 1011, 1012: two substrates facing each other [0087] 102: liquid crystal layer [0088] 201, 202: alignment films [0089] 301, 302: electrode layers

Modes of the Invention

[0090] Hereinafter, the above descriptions will be explained in further detail with reference to examples and comparative examples, but the scope of the present application is not limited by the following descriptions.

[0091] 1. Evaluation of Conductivity

[0092] Conductivity values were measured on liquid crystal devices manufactured as examples and comparative examples at room temperature using an LCR meter (E4980A, Agilent) under conditions of a measurement frequency of 60 Hz and a measurement voltage of 0.5 V. Parallel conductivity was measured on a vertically-aligned liquid crystal layer by applying a vertical voltage, that is, a voltage in the thickness direction, and when needed, vertical conductivity was measured on a horizontally-aligned liquid crystal layer by applying a vertical voltage. A liquid crystal layer of each liquid crystal device was manufactured to have an area of 9 cm.sup.2 (width: 3 cm, length: 3 cm) and a thickness of 15 m for the measurements.

[0093] 2. Evaluation of Haze and Transmittance

[0094] Haze and transmittance were measured on liquid crystal devices manufactured as examples and comparative examples using a haze meter, NDH-5000SP, according to the ASTM D1003 specification. That is, when light is transmitted through a measurement target and incident on the entrance of an integrating sphere, the light is separated into light diffused by the measurement target (DT, the sum of light emitted in all directions by diffusion) and parallel light (PT, light emitted in the forward direction excluding the diffused light), and by concentrating the light on a light receiving device in the integrating sphere, haze can be measured using the concentrated light. That is, in this procedure, total transmitted light (TT) is the sum (DT+PT) of the diffused light (DT) and the parallel light (PT), and haze may be defined as a percentage (haze (%)=100DT/TT) of the diffused light with respect to the total transmitted light. Also, in the following experimental example, a total transmittance refers to the total transmitted light (TT), and parallel transmittance refers to the parallel light (PT).

Preparation Example 1

[0095] Two polycarbonate (PC) films each having sequentially formed transparent ITO electrode layer and a vertical alignment film were separated from each other to allow the vertical alignment films to face each other and to have a cell gap of approximately 15 m, a liquid crystal composition was injected between the two separated PC films, and their edges were sealed, thereby manufacturing a liquid crystal device having an area of 9 cm.sup.2 and a cell gap of 15 m. The liquid crystal composition used in the experiment included a liquid crystal compound (manufacturer: HCCH, trade name: HNG730600-200) having a refractive index anisotropy of 0.15 and a dielectric anisotropy of 5.0, a dichroic dye (manufacturer: BASF, trade name: X12) and an additive for controlling conductivity (manufacturer: HCCH, trade name: HCM-009) in a weight ratio (HNG730600-200:X12:HCM-009) of 89.9:0.1:10. An actual value of the parallel conductivity of the liquid crystal layer manufactured as described above was approximately 3.110.sup.6 S, and a result obtained by converting the above value into that corresponding to a liquid crystal layer having an area of 1 cm.sup.2 and a thickness of 1 cm using Formulas 1 to 3 was 5.210.sup.4 S/cm.

Experimental Example 1

[0096] Total transmittance and haze were evaluated on the liquid crystal device manufactured in Preparation Example 1 at a fixed driving frequency of 60 Hz and variable applied voltages, and the results are summarized in FIGS. 4 and 5. FIG. 4 shows total transmittance, and FIG. 5 shows haze. Referring to FIGS. 4 and 5, it can be confirmed that the liquid crystal device of Preparation Example 1 can realize the first and second states at approximately 60 Hz and 10 V or less, and transmittance and haze are saturated due to EHDI driving at an applied voltage of 60 V.

[0097] For such a device, suitable conditions for the first state (the state in which molecules of a liquid crystal compound are vertically aligned), the second state (the state in which molecules of a liquid crystal compound are horizontally aligned) and the third state (the EHDI state) are summarized and listed in Table 1.

TABLE-US-00001 TABLE 1 Total Parallel light Voltage Frequency transmittance transmittance Haze (V) (Hz) (%) (%) (%) First state 0 60 60.1 58.9 2.0 Second state 10 60 31.9 30.9 3.0 Third state 60 60 15.8 0.7 95.7

Preparation Example 2

[0098] A liquid crystal device was prepared in the same manner as in Preparation Example 1, except that a liquid crystal composition used in the experiment included a liquid crystal compound (manufacturer: HCCH, trade name: HNG730600-200) having a refractive index anisotropy of 0.15 and a dielectric anisotropy of 5.0, a dichroic dye (manufacturer: BASF, trade name: X12), a first additive for controlling conductivity (manufacturer: HCCH, trade name: HCM-009), and a second additive for controlling a conductivity (manufacturer: Aldrich, trade name: CTAB) in a weight ratio (HNG730600-200:X12:HCM-099:CTAB) of 89.9:0.1:9.5:0.5. An actual value of the parallel conductivity of the liquid crystal layer manufactured as described above was approximately 1.010.sup.5 S, and a result obtained by converting the above value into a value corresponding to a liquid crystal layer having an area of 1 cm.sup.2 and a thickness of 1 cm using Formulas 1 to 3 was 1.710.sup.3 S/cm.

Experimental Example 2

[0099] Total transmittance and haze were evaluated on the liquid crystal device manufactured in Preparation Example 1 at variable driving frequencies and voltages, and the results are summarized in FIGS. 6 and 11. FIGS. 6 to 8 show total transmittance values measured at variable applied voltages while the driving frequency was sequentially fixed at 30 Hz, 60 Hz or 100 Hz, and FIGS. 9 to 11 show haze measured at variably applied voltages while the driving frequency was sequentially fixed at 30 Hz, 60 Hz or 100 Hz. As confirmed in the drawings, in the liquid crystal device of Preparation Example 2, first to third states were realized according to the applied voltages at approximately 100 Hz.

[0100] The results are summarized and listed in Table 2.

TABLE-US-00002 TABLE 2 Total Parallel light Voltage Frequency transmittance transmittance Haze (V) (Hz) (%) (%) (%) First state 0 30 58 57.5 1 Second state 10 30 29 14.3 50.9 Third state 60 30 15 0.7 95.6 First state 0 60 58.3 57.7 1 Second state 10 60 29.9 24.9 17 Third state 60 60 14.9 0.6 95.8 First state 0 100 57.9 57.3 1 Second state 10 100 30.4 29.8 1.8 Third state 60 100 14.7 0.7 95.6