Reflective liquid crystal device and use thereof

Abstract

A liquid crystal device and the use thereof are provided. The liquid crystal device has an advantage in terms of power consumption since a normally transparent mode may be realized in a state in which an external electric field is not applied, and can exhibit an excellent light blocking characteristic when an external electric field is applied.

Claims

1. A reflective liquid crystal device comprising: a first substrate layer; a first electrode layer disposed below the first substrate layer; a first pretilt homeotropic alignment film disposed below the first electrode layer; a guest-host liquid crystal layer comprising a liquid crystal compound and a dichroic dye, and disposed below the first pretilt homeotropic alignment film; a second pretilt homeotropic alignment film disposed below the guest-host liquid crystal layer; a second electrode layer disposed below the second pretilt homeotropic alignment film; a second substrate layer disposed below the second electrode layer; a quarter-wave plate disposed below the second substrate layer; and a reflective plate disposed below the quarter-wave plate, wherein an optical axis of the quarter-wave plate is formed at an angle of 40 to 50 with respect to an optical axis of the liquid crystal compound included in the horizontally aligned guest-host liquid crystal layer when an external electric field is applied, wherein the thicknesses of the guest-host liquid crystal layer, the first and second substrate layers and the first and second electrode layers satisfy the following Equation 1:
0.015<b/a<0.6[Equation 1] wherein b represents a thickness of the guest-host liquid crystal layer, and a represents the sum of thicknesses of the first and second substrate layers and the first and second electrode layers, and wherein the reflective liquid crystal device satisfies the following Equation 2:
AB>40%[Equation 2] wherein A represents a reflectance in a state in which an external electric field is not applied, and B represents a reflectance in a state in which an external electric field is applied.

2. The reflective liquid crystal device of claim 1, wherein the liquid crystal compound is an N-type nematic liquid crystal compound.

3. The reflective liquid crystal device of claim 1, wherein the guest-host liquid crystal layer comprises the dichroic dye at 0.3 to 3 parts by weight, based on 100 parts by weight of the liquid crystal compound.

4. The reflective liquid crystal device of claim 1, wherein a pretilt angle of the liquid crystal compound included in the guest-host liquid crystal layer is in a range of 70 to 90 in a state in which an external electric field is not applied.

5. The reflective liquid crystal device of claim 1, wherein the guest-host liquid crystal layer has a thickness ranging from 3 m to 30 m.

6. The reflective liquid crystal device of claim 1, wherein the pretilt homeotropic alignment film is a rubbing alignment film or an optical alignment film.

7. The reflective liquid crystal device of claim 1, which is maintained in a transmission mode such that the reflective liquid crystal device has a reflectance of 30% or more in a state in which an external electric field is not applied.

8. The reflective liquid crystal device of claim 1, which is maintained in a block mode such that the reflective liquid crystal device has a reflectance of less than 30% in a state in which an external electric field is applied.

9. The reflective liquid crystal device of claim 1, which is realized in a transparent mode such that the reflective liquid crystal device has a haze of less than 10% in a state in which an external electric field is applied.

10. A mirror comprising the reflective liquid crystal device defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view showing a conventional reflective liquid crystal device;

(2) FIGS. 2 and 3 are schematic views showing a liquid crystal device according to one exemplary embodiment of the present invention; and

(3) FIGS. 4 and 5 are diagrams showing an operation principle of the liquid crystal device according to one exemplary embodiment of the present invention.

DESCRIPTION OF DRAWING NUMBER

(4) 100: a polarizing plate

(5) 200: a liquid crystal cell

(6) 300: a reflective plate

(7) 401a, 401b: substrate layers

(8) 402: electrode layers

(9) 500: alignment films

(10) 600: a guest-host liquid crystal layer

(11) 700: a quarter-wave plate

(12) 800: light incident on a lower substrate

(13) 801: light parallel with an alignment direction of a dichroic dye

(14) 802: light perpendicular to an alignment direction of a dichroic dye

BEST MODE FOR CARRYING OUT THE INVENTION

(15) Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, and can be implemented in various forms. The following embodiments are described in order to enable those of ordinary skill in the art to embody and practice the present invention.

EXAMPLE 1

Manufacture of Reflective Liquid Crystal Device (A1)

(16) A pretilt homeotropic alignment film having an pretilt angle of 86 was formed on a pair of polyethylene terephthalate (PET) films on which an indium tin oxide (ITO) transparent electrode layer was deposited, and then coated with a composition for forming a guest-host liquid crystal layer (including a liquid crystal compound (HCM009 commercially available from HCCH) and an anisotropic dye (X12 commercially available from BASF) at a weight ratio of 100:1) to form a guest-host liquid crystal layer. Thereafter, a quarter-wave plate having an optical axis formed at an angle of approximately 45 with respect to an optical axis of the liquid crystal compound in the liquid crystal layer which was horizontally aligned when an external electric field was applied was formed on a surface of the PET film on which no transparent electrode layer was formed, and a reflective plate was additionally positioned on an opposite surface of a surface of the quarter-wave plate at which the guest-host liquid crystal layer existed, thereby manufacturing a reflective liquid crystal device (A1) having the same structure as shown in FIG. 2.

EXAMPLE 2

Manufacture of Reflective Liquid Crystal Device (A2)

(17) A reflective liquid crystal device (A2) was manufactured in the same manner as in Example 1, except that a guest-host liquid crystal layer was formed using a guest-host liquid crystal composition (including a liquid crystal compound (HCM009 commercially available from HCCH) and an anisotropic dye (X12 commercially available from BASF) at a weight ratio of 100:0.7.

EXAMPLE 3

Manufacture of Reflective Liquid Crystal Device (A3)

(18) A reflective liquid crystal device (A3) was manufactured in the same manner as in Example 1, except that the reflective liquid crystal device having the same structure as shown in FIG. 3 was manufactured using only one PET film.

COMPARATIVE EXAMPLE 1

Reflective Liquid Crystal Device (B1) Including no Quarter-Wave Plate

(19) A reflective liquid crystal device (B1) was manufactured in the same manner as in Example 1, except that the reflective liquid crystal device having a structure in which no quarter-wave plate was present in the structure as shown in FIG. 2 was manufactured.

COMPARATIVE EXAMPLE 2

Reflective Liquid Crystal Device (B2) Including Angle-Adjusted Quarter-Wave Plate

(20) A reflective liquid crystal device (B2) was manufactured in the same manner as in Example 1, except that a quarter-wave plate having an optical axis formed at an angle of approximately 20 with respect to an optical axis of the liquid crystal compound which was horizontally aligned when an external electric field was applied was formed.

EXPERIMENTAL EXAMPLE

Measurement of Reflection Rate

(21) Reflectances of the liquid crystal devices manufactured in Examples and Comparative Examples were measured when an electric field was not applied and when an electric field was applied.

(22) Specifically, the reflectances of the liquid crystal devices manufactured in Examples and Comparative Examples compared to the reflectance of the reflective plate when an electric field was not applied and when an electric field was applied were measured under a D65 light source using a spectrum colorimeter (CM-2500d commercially available from Konica Minolta Co., Ltd.)., and then converted into percentages. In this case, the external electric field applied was 30V.

(23) TABLE-US-00001 TABLE 1 Examples Comparative Examples 1 2 3 1 2 Reflectance (%) upon 60 69 62 53 60 application of no electric field Reflectance (%)upon 11 23 11 32 20 application of electric field