Liquid Crystal Cell

Abstract

A liquid crystal cell, 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 and having an average current density of 30μA/cm.sup.2 to 60μA/cm.sup.2, wherein the average current density is an average value of current densities measured by applying an alternating-current voltage at a first voltage of 40 V and a frequency of 60 Hz to the liquid crystal cell from 0 ms to 8 ms after a fifth cycle.

2. The liquid crystal cell according to claim 1, wherein the liquid crystal layer comprises non-reactive liquid crystals and a conductivity control agent.

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

4. The liquid crystal cell according to claim 2, wherein the conductivity control agent comprises one or more selected from an anisotropic dye, reactive liquid crystals or an ionic compound.

5. The liquid crystal cell according to claim 2, wherein the conductivity control agent is included in a ratio of 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of the non-reactive liquid crystals.

6. 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.

7. The liquid crystal cell according to claim 6, 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 60V.

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

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

10. 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: adjusting the liquid crystal layer to have the average current density of 30μA/cm.sup.2 to 60μA/cm.sup.2 (provided that wherein the average current density is an average value of current densities measured by applying an alternating-current voltage at a voltage of 40 V and a frequency of 60 Hz to the liquid crystal cell from 0 ms to 8 ms after a fifth cycle.

11. The method for manufacturing a liquid crystal cell according to claim 10, wherein the liquid crystal cell is manufactured by injecting a heated liquid crystal composition between the two substrates and sealing edges of the heated liquid crystal composition injected between the substrates.

12. The method for manufacturing a liquid crystal cell according to claim 11, wherein the liquid crystal composition comprises: non-reactive liquid crystals; and an anisotropic dye, reactive liquid crystals and an ionic compound as a conductivity control agent, wherein when the reactive liquid crystals are in an amount of 8 wt % to 12 wt % in the liquid crystal composition, the heated liquid crystal is heated at a temperature of 90° C. to 110° C. for 20 hours to 30 hours.

13. The method for manufacturing a liquid crystal cell according to claim 11, wherein the liquid crystal composition comprises: non-reactive liquid crystals; and an anisotropic dye, reactive liquid crystals and an ionic compound as a conductivity control agent, wherein when the reactive liquid crystals are in an amount of 1 wt % to 5 wt % in the liquid crystal composition, the heated liquid crystal is heated at a temperature of 110° C. to 130° C. for 1 hour to 7 hours.

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

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] FIG. 1 is a diagram exemplarily showing a liquid crystal cell according to one example of the present application.

[0053] FIG. 2 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.

[0054] FIG. 3 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.

[0055] FIG. 4 is graphs measuring current densities of liquid crystal cells manufactured in Examples and Comparative Examples according to voltage application times.

[0056] FIG. 5 is graphs showing average current densities, transmittance-variable widths and haze in a scattering mode of liquid crystal cells prepared in Examples and Comparative Examples.

BEST MODE

[0057] 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

[0058] Manufacture of Liquid Crystal Cell

[0059] 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 9μm or so, a liquid crystal composition heated at 100° C. for 24 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 9μm.

[0060] Here, the vertical alignment film was formed 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 LC (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-methoxylphenyl 4-((6-(acryloyloxy)hexyl)oxy) benzoate (HCM-021, manufactured by HCCH) as reactive liquid crystals and CTAB (cetyltrimethylammonium bromide) as an ionic compound at a weight ratio of 90:1.6:10:1 (LC: anisotropic dye: RM: CTAB).

Examples 2 to 5 and Comparative Examples 1 to 4

[0061] Manufacture of Liquid Crystal Cell

[0062] Liquid crystal cells were manufactured in the same manner as in Example 1, except that the compositions of the liquid crystal compositions and the heating conditions shown in Table 1 below were used.

TABLE-US-00001 TABLE 1 Liquid crystal composition (weight ratio) Non-reactive Conductivity control agent liquid crystals Anisotropic Heating LC dye RM CTAB conditions Example 1 90 1.6 10 1 100° C., 24 hours Example 2 90 1.4 2.5 1 120° C., 2 hours Example 3 90 1.4 2.5 1 120° C., 3 hours Example 4 90 1.4 2.5 1 120° C., 4 hours Example 5 90 1.4 2.5 1 120° C., 6 hours Comparative 90 1.6 — — 100° C., Example 1 24 hours Comparative 90 1.6 10 — 100° C., Example 2 24 hours Comparative 90 1.4 2.5 1 120° C., Example 3 9 hours Comparative 90 1.4 2.5 1 120° C., Example 4 12 hours LC: 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

[0063] 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. 4. 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 average value of the measured current densities was shown in Table 3 below.

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

[0064] 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.

[0065] [Equation 1]

[0066] Transmittance-variable width=T.sub.0-T.sub.60

[0067] In Equation 1 above, To 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.

TABLE-US-00003 TABLE 3 Average Trans current Initial (0 V) 60 V mittance- density Trans- Trans- variable (μA/ mittance Haze mittance Haze width cm.sup.2) (%) (%) (%) (%) (%) Example 1 41.4 65.4 0.4 21.7 95.8 43.7 Example 2 47.5 68.5 0.8 25.1 95 43.4 Example 3 52.0 69.0 0.9 25.7 94.8 43.3 Example 4 55.5 68.4 0.9 25.6 95.5 42.8 Example 5 54.1 68.4 1.3 25.7 95.5 42.7 Comparative 11.7 63.8 0.9 28.2 36.5 35.6 Example 1 Comparative 24.1 64.8 0.8 23.1 85.7 41.7 Example 2 Comparative 79.5 68.1 1.4 29.6 94.9 38.5 Example 3 Comparative 78.7 67.0 1.2 27.4 95 39.6 Example 4

[0068] As shown in Table 3 and FIG. 5, as the liquid crystal cells manufactured in Examples 1 to 5 further comprised the conductivity control agent in the liquid crystal layer as compared to the liquid crystal cells manufactured in Comparative Examples 1 and 2, it was confirmed that they exhibited high current densities. Furthermore, as the liquid crystal cells manufactured in Examples 1 to 5 comprising the conductivity control agent in the liquid crystal layer heated for a lower time, that is, for less than 9 hours, as compared to the liquid crystal cells manufactured in Comparative Examples 3 and 4 having the same liquid crystal composition in the liquid crystal layer as that of the liquid crystal cells manufactured in Examples 1 to 5, it was confirmed that they exhibited low average current densities. That is, as the liquid crystal cells manufactured in Examples 1 to 5 satisfied all of the above-described conditions, it was confirmed that they satisfied the average current density of 30μA/cm.sup.2 to 60μA/cm.sup.2. In addition, as the liquid crystal cells manufactured in Examples 1 to 5 had a higher average current density than the liquid crystal cells manufactured in Comparative Examples 1 and 2, it was confirmed that they expressed high haze in the scattering mode.

[0069] In addition, as the liquid crystal cells manufactured in Examples 1 to 5 satisfied the average current density of 30μA/cm.sup.2 to 60μA/cm.sup.2, it was confirmed that they had more excellent transmittance-variable widths as compared to the liquid crystal cells manufactured in Comparative Examples 1 to 4 without satisfying the above-described average current density range.

EXPLANATION OF REFERENCE NUMERALS

[0070] 100, 300: substrate

[0071] 110, 310: base material

[0072] 120, 320: electrode layer

[0073] 130, 330: vertical alignment film

[0074] 200: liquid crystal layer