Liquid crystal cell

Abstract

A liquid crystal cell and a manufacturing method thereof and a use thereof are provided in the present disclosure. The liquid crystal cell is in a normally transparent mode, and has excellent transmittance-variable characteristics in a transparent mode and a scattering mode and excellent haze characteristics in the scattering mode. Such liquid crystal cell may be applied to various light modulation devices, such as a smart window, a window protective film, a flexible display element, a light shielding plate for transparent displays, an active retarder for 3D image displays or a viewing angle control film.

Claims

1. A liquid crystal cell comprising: two substrates disposed opposite to each other; and a liquid crystal layer present between the two substrates, wherein the liquid crystal layer comprises non-reactive liquid crystals and a conductivity control agent, wherein the conductivity control agent is included in a ratio of 0.1 parts by weight to 30 parts by weight relative to 100 parts by weight of the non-reactive liquid crystals, wherein upon measuring current densities over time, a current density peak appears after 2 ms, wherein the current densities are measured during a positive half cycle after a fifth cycle and the current densities are measured by applying an alternating-current voltage at a first voltage of 40 V and a frequency of 20 Hz to 120 Hz to the liquid crystal cell, and the current density peak is a maximum value of the current densities appeared after 0.5 ms.

2. The liquid crystal cell according to claim 1, wherein the non-reactive liquid crystals have negative dielectric constant anisotropy.

3. The liquid crystal cell according to claim 1, wherein the conductivity control agent comprises one or more selected from an anisotropic dye, reactive liquid crystals or an ionic compound.

4. The liquid crystal cell according to claim 1, wherein the liquid crystal layer has a transparent mode in an initial state and a scattering mode at the time of applying a second voltage.

5. The liquid crystal cell according to claim 4, wherein the liquid crystal layer has a difference of 40% or more between transmittance in the initial state and transmittance at the time of applying the second voltage of 60 V.

6. The liquid crystal cell according to claim 4, wherein the liquid crystal layer has haze of 90% or more at the time of applying the second voltage of 60 V.

7. The liquid crystal cell according to claim 1, wherein the two substrates each comprise an electrode layer and a vertical alignment film.

8. An optical modulation device comprising the liquid crystal cell of claim 1.

9. A method for manufacturing a liquid crystal cell comprising two substrates disposed opposite to each other and a liquid crystal layer present between the two substrates, wherein the method comprises: heating a liquid crystal composition at a temperature of 100° C. to 120° C., and injecting the heated liquid crystal composition between the two substrates to form the liquid crystal cell, wherein upon measuring current densities of the liquid crystal layer over time, a current density peak appears after 2 ms, wherein the current densities are measured during a positive half cycle after a fifth cycle and the current densities are measured by applying an alternating-current voltage at a voltage of 40 V and a frequency of 20 Hz to 120 Hz to the liquid crystal cell, and the current density peak is a maximum value of the current densities appeared after 0.5 ms.

10. The method for manufacturing the liquid crystal cell according to claim 9, further comprising sealing the edges of the heated liquid crystal composition injected between the substrates.

11. The method for manufacturing the liquid crystal cell according to claim 10, wherein the heated liquid crystal composition comprises non-reactive liquid crystals and a conductivity control agent, wherein the conductivity control agent comprises an anisotropic dye and reactive liquid crystals, wherein the heated liquid crystal composition is heated for 25 hours to 30 hours.

12. The method for manufacturing the liquid crystal cell according to claim 10, wherein the heated liquid crystal composition comprises: non-reactive liquid crystals; and a conductivity control agent, wherein the conductivity control agent comprises an anisotropic dye, reactive liquid crystals and an ionic compound, and when the reactive liquid crystals are included in an amount of 2.5 wt % to 7.5 wt % in the liquid crystal composition, and the heated liquid crystal composition is heated for 30 minutes to 15 hours.

13. The method for manufacturing the liquid crystal cell according to claim 10, wherein the heated liquid crystal composition comprises: non-reactive liquid crystals and a conductivity control agent comprising an anisotropic dye, reactive liquid crystals and an ionic compound, and when the reactive liquid crystals are included in an amount of 7.5 wt % to 12.5 wt % in the liquid crystal composition, the heated liquid crystal composition is heated for 30 minutes to 4 hours.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram exemplarily showing a liquid crystal cell according to one example of the present application.

(2) FIG. 2 is a graph exemplarily showing waveforms according to time of an alternating-current voltage applied when measuring a current density of a liquid crystal cell according to one example of the present application.

(3) FIG. 3 is a diagram exemplarily showing a liquid crystal cell implementing a transparent mode in an initial state according to one example of the present application.

(4) FIG. 4 is a diagram exemplarily showing a liquid crystal cell implementing a scattering mode when a voltage is applied according to one example of the present application.

(5) FIG. 5 is graphs measuring current densities of liquid crystal cells manufactured in Examples and Comparative Examples according to voltage application times.

BEST MODE

(6) Hereinafter, the present application will be described in detail with reference to Examples, but the scope of the present application is not limited by the following Examples.

Example 1

(7) Manufacture of Liquid Crystal Cell

(8) After two glass substrates, in which ITO (indium tin oxide) transparent electrode layers and vertical alignment films were sequentially formed, were disposed apart from each other so that the vertical alignment films faced each other and the interval was about 9 μm or so, a liquid crystal composition heated at 110° C. for 30 hours was injected between the two glass substrates disposed apart from each other and the edges were sealed to manufacture a liquid crystal cell having an area of 2.5 cm×3.0 cm and an interval of 9 μm.

(9) Here, the vertical alignment film was produced by coating a vertical alignment composition (Nissan 5661) on the ITO transparent electrode layer and baking it at a temperature of 100° C. for 10 minutes. As shown in Table 1 below, the liquid crystal composition was prepared by mixing commercial liquid crystals LC1 (HNG740600-100, manufactured by HCCH) having dielectric constant anisotropy of −3.1 and refractive index anisotropy of 0.188, an anisotropic dye (X12, manufactured by BASF) and 4-methoxylphenyl 4-((6-(acryloyloxy)hexyl)oxy) benzoate (HCM-021, manufactured by HCCH) as reactive liquid crystals at a weight ratio of 90:1.3:5 (LC1: anisotropic dye: RM).

Examples 2 to 3 and Comparative Examples 1 to 3

(10) Manufacture of Liquid Crystal Cell

(11) Liquid crystal cells were manufactured in the same manner as in Example 1, except that the compositions of the liquid crystal composition and the heating conditions were changed as in Table 1 below.

Example 4

(12) Manufacture of Liquid Crystal Cell

(13) A liquid crystal cell was manufactured in the same manner as in Example 1, except that as the liquid crystal composition, commercial liquid crystals LC2 (HCCH 7262, manufactured by HCCH) having dielectric constant anisotropy of −5.0 and refractive index anisotropy of 0.1995, an anisotropic dye (X12, manufactured by BASF), 4-methoxyphenyl 4-((6-(acryloyloxy)hexyl)oxy) benzoate (HCM-021, manufactured by HCCH) as reactive liquid crystals and CTAB (cetyltrimethylammonium bromide) as an ionic compound, as shown in Table 1 below, were mixed at a weight ratio of 90:1.4:10:1 (LC2: anisotropic dye: RM: CTAB).

(14) TABLE-US-00001 TABLE 1 Liquid crystal composition (weight ratio) Non-reactive liquid crystals Conductivity control agent Heating LC1 LC2 Anisotropic dye RM CTAB conditions Example 1 90 — 1.3 5 — 110° C., 30 hours Example 2 90 — 1.3 5 1 110° C., 1 hour Example 3 90 — 1.3 5 1 110° C., 12 hours Example 4 — 90 1.4 10 1 115° C., 2 hours Comparative 90 — 1.3 5 1 60° C., 4 hours Example 1 Comparative 90 — 1.3 — 1 25° C., 4 hours Example 2 Comparative — 90 1.4 10 1 115° C., 6 hours Example 3 LC1: commercial liquid crystals (HNG740600-100, manufactured by HCCH) LC2: commercial liquid crystals (HCCH 7262, manufactured by HCCH) Anisotropic dye: X12, manufactured by BASF RM (reactive liquid crystals): 4-methoxyphenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate (HCM-021, manufactured by HCCH) CTAB: cetyltrimethylammonium bromide

Evaluation Example 1. Current Density Evaluation

(15) For liquid crystal cells manufactured in Examples and Comparative Examples, the instantaneous current-voltage (I-V) was measured using a semiconductor characteristic analyzer, Keithly 4200, having a driving waveform shown in Table 2 below. Specifically, currents flowing at the time of applying an alternating-current voltage of 40 V and 60 Hz to two substrates disposed opposite to each other in the liquid crystal cells manufactured in Examples and Comparative Examples were measured and shown in FIG. 5. At this time, the current value measured after the fifth cycle (Cycle) was taken for stabilization. After voltage application, the current at 8 ms divided by the area was called the final current density, and the average value of the current densities measured from 0 ms to 8 ms was defined as the average current density. The current density peak time point appearing upon the current density measurement and the average value of the measured current densities were shown in Table 3 below. In this case, the current density peak means the maximum value of the current density values after 0.5 ms.

(16) TABLE-US-00002 TABLE 2 DSLC cell Keithly 4200 driving waveform (60 Hz, 40 V, square waveform) Value Unit Period 0.0167 Sec Pulse Width 0.00833 Sec Rise Time 0.0001 Sec Fall Time 0.0001 Sec Base Voltage −40 Volt Amplitude −80 Volt

Evaluation Example 2. Haze and Transmittance Evaluation

(17) For the liquid crystal cells manufactured in Examples and Comparative Examples, haze and transmittance were measured by an ASTM method using a haze meter, NDH-5000SP. Specifically, AC power was connected to two substrates disposed opposite to each other so as to apply a vertical electric field to each of the liquid crystal cells manufactured in Examples and Comparative Examples, and the haze in the transparent mode at the time of applying no initial voltage and the scattering mode applying a voltage of 60 V and 60 Hz was measured and shown in Table 3 below. In addition, the transmittance in the transparent mode at the time of applying no initial voltage (0 V) and the transmittance in the scattering mode applying a voltage of 60 V and 60 Hz were measured as the transmittance, and then the difference between them was defined as the transmittance-variable width, as shown in the following equation 1, and shown in Table 3 below.
Transmittance-variable width=T.sub.0−T.sub.60  [Equation 1]

(18) In Equation 1 above, T.sub.0 is transmittance at the time of applying no initial voltage (0V), and T.sub.60 means transmittance at the time of applying a voltage of 60 V and 60 Hz.

(19) TABLE-US-00003 TABLE 3 Peak time Average Initial (0 V) 60 V Transmittance- point current density Transmittance Haze Transmittance Haze variable width (ms) (μA/cm.sup.2) (%) (%) (%) (%) (%) Example 1 2.781 44.9 66.4 1.6 26.4 95.3 40.0 Example 2 2.781 45.8 64.6 1.9 22.7 95.2 41.9 Example 3 2.336 54.2 64.4 1.9 22.2 95.5 42.2 Example 4 2.695 49.5 67.8 0.7 26.6 95.7 41.2 Comparative 0.977 40.3 66.5 1.8 26.5 79.5 40.0 Example 1 Comparative 1.138 41.0 63.6 1.6 23.4 74.7 40.2 Example 2 Comparative 1.113 79.8 67.9 1.0 30.3 95.1 37.6 Example 3

(20) As shown in Table 3 above, it was confirmed that the liquid crystal cells manufactured in Examples 1 to 4 in which the current density peak appeared after 2 ms expressed excellent haze in the scattering mode and simultaneously had excellent transmittance-variable widths as compared to the liquid crystal cells manufactured in Comparative Examples 1 and 2 in which the current density peak appeared before 2 ms.

EXPLANATION OF REFERENCE NUMERALS

(21) 100, 300: substrate 110, 310: base material 120, 320: electrode layer 130, 330: vertical alignment film 200: liquid crystal layer