Transmittance-variable film capable of controlling pretilt of liquid crystal interface

Abstract

A transmittance-variable film and a use thereof, where the transmittance-variable film can control pretilt of a liquid crystal interface by applying a liquid crystal alignment film containing splay oriented liquid crystal molecules, and can vertically and horizontally orient a liquid crystal layer or a liquid crystal interface according to an average tilt angle of the liquid crystal alignment film to ensure uniformity of driving and fast response speed. In addition, by applying a liquid crystal alignment film, the transmittance-variable film can be implemented in various modes with a simple coating-drying-curing method excluding the rubbing process by controlling an arrangement of liquid crystal molecules in a liquid crystal alignment film other than the pretilt control method using the conventional rubbing method.

Claims

1. A transmittance-variable film comprising: a first substrate, a transmittance-variable liquid crystal layer comprising non-reactive liquid crystals and a dichroic dye, and a second substrate in sequence, wherein the non-reactive liquid crystals are liquid crystals that have no polymerizable group, wherein the first substrate comprises a first alignment film, wherein the first alignment film does not contain a liquid crystal, wherein the second substrate comprises a second alignment film, wherein the second alignment film contains reactive liquid crystals, wherein the reactive liquid crystals are in a splay oriented state where a tilt angle of the reactive liquid crystals changes along a thickness direction of the second alignment film, wherein an average tilt angle of the reactive liquid crystals ranges from 0.2 degrees to 20 degrees, wherein the first alignment film is directly on the transmittance-variable liquid crystal layer, wherein the second alignment film is directly on the transmittance-variable liquid crystal layer, wherein the non-reactive liquid crystals have a horizontal orientation when no voltage is applied, wherein the non-reactive liquid crystals of transmittance-variable liquid crystal layer are horizontally oriented when no voltage is applied by the average tilt angle of the reactive liquid crystals being in the splay oriented state in the second alignment film.

2. The transmittance-variable film according to claim 1, wherein the first substrate further comprises a first electrode film and the first alignment film is formed on the first electrode film, and the second substrate further comprises a second electrode film and a third alignment film formed on the second electrode film, wherein the third alignment film does not contain a liquid crystal, and the second alignment film is formed on the third alignment film.

3. The transmittance-variable film according to claim 2, wherein the first and third alignment films are each a photo-alignment film.

4. The transmittance-variable film according to claim 1, further comprising a ball spacer between the first substrate and the second substrate.

5. The transmittance-variable film according to claim 4, wherein the ball spacer comprises at least one selected from the group consisting of a carbon-based material, a metal-based material, an oxide-based material, and a composite material.

6. The transmittance-variable film according to claim 1, wherein reactive liquid crystals are liquid crystal compounds having at least one polymerizable functional group.

7. The transmittance-variable film according to claim 1, wherein the transmittance-variable film realizes a clear state upon horizontal orientation of the non-reactive liquid crystals and a dark state upon vertical orientation of the non-reactive liquid crystals, wherein a transmittance of the transmittance-variable film at the clear state is 40% or more and the transmittance at the dark state is 5% or less.

8. A transmittance-variable film comprising a first substrate, a transmittance-variable liquid crystal layer and a second substrate in sequence, wherein at least one of the first substrate or the second substrate comprises an alignment film containing splay oriented liquid crystals, wherein the alignment film has an average tilt angle of 30 degrees to 90 degrees and the transmittance-variable liquid crystal layer has vertical orientation when no voltage is applied.

9. The transmittance-variable film according to claim 1, wherein the second alignment film has a thickness of 300 nm to 3000 nm.

10. The transmittance-variable film according to claim 1, wherein the transmittance-variable liquid crystal layer has a reverse tilt domain size of 80 μm or less.

11. The transmittance-variable film according to claim 1, wherein the transmittance-variable liquid crystal layer has a reverse tilt domain size of 10 μm to 80 μm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram illustratively showing a transmittance-variable film according to one embodiment of the present application.

(2) FIG. 2 is a diagram showing transmittance-variable films of Examples 1 and 2.

(3) FIG. 3 is a diagram showing a transmittance-variable film of Example 3.

(4) FIG. 4 is a driving image of Example 1.

(5) FIG. 5 is a driving image of Example 2.

(6) FIG. 6 is a driving image of Comparative Example 1.

(7) FIG. 7 is a graph showing the evaluation results of transmittance according to the driving voltage of Example 3.

(8) FIG. 8 is a graph showing the evaluation results of transmittance according to the viewing angle of Example 3.

BEST MODE

(9) Hereinafter, the present application will be described in detail by way of the following examples, but the scope of the present application is not limited by the following examples.

Example 1

(10) Preparation of First Non-Liquid Crystal Alignment Film Composition

(11) 9.675 g of a solvent (cyclohexanone), 0.325 g of a photo-orientable material (5-norbornene-2-methyl-4-methoxy cinnamate) and 0.01 g of nanoparticles (PMMA, SEKISUI, average particle diameter: 370 nm) were added to a 20 ml vial and then mixed to prepare a first non-liquid crystal alignment film composition.

(12) Preparation of Ball Spacer Composition

(13) 9.675 g of a solvent (cyclohexanone), 0.065 g of a photo-orientable material (5-norbornene-2-methyl-4-methoxy cinnamate) and 0.1 g of a ball spacer (KBN-510, SEKISUI, average particle diameter: 10 μm) were added to a 20 ml vial and then mixed to prepare a ball spacer composition.

(14) Fabrication of First Substrate

(15) The first non-liquid crystal alignment film composition was coated on an ITO layer of a first electrode film (PC/ITO film, width×length=100 mm×100 mm) to a thickness of about 300 nm using a mayer bar (#4). The coated composition was dried at about 80° C. for about 2 minutes. The dried composition was vertically (0°) irradiated with a polarized ultraviolet ray having an intensity of 200 mW/cm.sup.2 at room temperature (25±5° C.) for 10 seconds and cured to form a first non-liquid crystal alignment film. Thereafter, the ball spacer composition was coated on the first non-liquid crystal alignment film to a thickness after drying of about 60 nm using a mayer bar (#10). The coated composition was dried at about 100° C. for about 2 minutes. The dried composition was vertically (0°) irradiated with a polarized ultraviolet ray having an intensity of about 200 mW/cm.sup.2 for 10 seconds and the ball spacer was fixed on the first non-liquid crystal alignment film to fabricate a first substrate.

(16) Preparation of Second Non-Liquid Crystalline Alignment Film Composition

(17) 9.675 g of a solvent (cyclohexanone) and 0.325 g of a photo-orientable material (5-norbornene-2-methyl-4-methoxy cinnamate) were added to a 20 ml vial and then mixed to prepare a second non-liquid crystal alignment film composition.

(18) Fabrication of Second Substrate

(19) The second non-liquid crystal alignment film composition was coated on an ITO layer of a second electrode film (PC/ITO film, width×length=100 mm×100 mm) to a thickness after drying of about 300 nm using a mayer bar (#4). The coated composition was dried at about 80° C. for about 2 minutes. The dried composition was vertically (0°) irradiated with a polarized ultraviolet ray having an intensity of 200 mW/cm.sup.2 at room temperature (25±5° C.) for 10 seconds and cured to form a second non-liquid crystal alignment film. Thereafter, a splay orientable liquid crystal mixture (trade name: RMM667, manufacturer: MERCK) dissolved in toluene at 25 wt % was applied on the second non-liquid crystal alignment film using a mayer bar (#4) to form a liquid crystal alignment film. Thereafter, the liquid crystal alignment film was dried in an oven at 80° C. for 2 minutes. After drying, the alignment film was irradiated with an ultraviolet ray having an intensity of 300 mW/cm.sup.2 at 40° C. for about 10 seconds and cured to fabricate a second substrate on which the liquid crystal alignment film with a thickness of 1000 nm was formed.

(20) Cell Lamination

(21) After applying 1 g of a composition for a transmittance-variable liquid crystal layer (MDA-14-4145, Merck) containing positive liquid crystals and an azo-based dye on the first non-liquid crystal alignment film of the first substrate, the second substrate was laminated so that the second non-liquid crystal alignment film contacted the ball spacer to fabricate a liquid crystal cell as in FIG. 2.

Example 2

(22) A liquid crystal cell was fabricated in the same manner as in Example 1, except that when the second non-liquid crystal alignment film composition was coated, the curing temperature after drying was changed to 60° C.

Example 3

(23) Fabrication of First Substrate

(24) A first substrate was fabricated in the same manner as in Example 1, except that when the second non-liquid crystal alignment film composition was coated, the curing temperature after drying was changed to 80° C.

(25) Fabrication of Second Substrate

(26) A second substrate was fabricated in the same manner as in Example 1, except that when the second non-liquid crystal alignment film composition was coated, the curing temperature after drying was changed to 80° C.

(27) Cell Production

(28) On the second non-liquid crystal alignment film of the first substrate, a solution for a transmittance-variable liquid crystal layer, in which 100 mg of an azo-based dye (X12, BASF) and 1 g of a negative liquid crystal composition (MAT-13-1422, Merck) were mixed, and a ball spacer (KBN-510, SEKISUI) were applied, and then the first substrate was laminated with the second substrate to produce a liquid crystal cell as in FIG. 3.

Comparative Example

(29) A liquid crystal cell was produced in the same manner as in Example 1, except that a horizontal orientable liquid crystal mixture (RMM1290, Merck) was used in place of the splay orientable liquid crystal mixture upon fabrication of the second substrate.

Measurement Example 1: Measurement of Average Tilt Angle

(30) For the second non-liquid crystal alignment films of the second substrates in Examples 1 to 3 and Comparative Example, tilt angles were measured and the average values thereof were described in Table 1 below. The tilt angle of the second non-liquid crystal alignment film of the second substrate was measured by measuring and simulating the phase difference values at each angle using an Axoscan equipment from Axometics, and the average value thereof was calculated. Specifically, after fabricating the second non-liquid crystal alignment film of the second substrate, the phase difference was measured at 1° intervals from 60° to −60°, and then the tilt angle was measured through fitting simulation, and the average value was calculated.

(31) TABLE-US-00001 TABLE 1 Classification Average tile angle (unit: °) Example 1 5.8 Example 2 13.2 Example 3 44.5 Comparative Example 0.1

Evaluation Example 1: Domain Size Evaluation (Microscope Observation)

(32) It was evaluated whether or not the liquid crystal cells of Examples 1 and 2 and Comparative Example were uniformly driven. Specifically, the size of the reverse tilt domain in which the liquid crystal was expressed in the low voltage driving of 3 V, that is, the region in which the liquid crystal molecules had different directions at the time of tilting, was evaluated by a method of measuring it with a microscope.

(33) FIGS. 4 to 6 are micrographs (50 magnification) in which the liquid crystal cells of Examples 1 and 2 and Comparative Example were measured at a driving voltage of 3 V (AC), respectively. From FIG. 4, a reverse tilt domain having a size of about 30 μm to 80 μm was observed in Example 1, and from FIG. 5, a reverse tilt domain having a size of about 10 μm to 30 μm was observed in Example 2, and from FIG. 6, a reverse tilt domain having a size of about 150 μm to 500 μm was observed in Comparative Example. That is, as the average tilt angle shown in Table 1 is larger, a smaller reverse tilt domain is generated, and it can be seen that Examples are driven more uniformly than Comparative Example.

Evaluation Example 2: Evaluation of Transmittance According to Voltage

(34) For the liquid crystal cell of Example 3 showing the initial vertical orientation, the average transmittance according to the driving voltage application at a wavelength of 400 nm to 700 nm was measured and the results were shown in Table 2 and FIG. 7 below. It exhibited a clear mode at the transmittance of about 26.6% when no voltage was applied (0 V), and switched to a dark mode at the transmittance of about 4.52% when a voltage of about 20 V was applied. As a result, when the average tilt angle of the second non-liquid crystal alignment film was increased by about 45°, it could be seen that the vertical orientation was possible.

(35) TABLE-US-00002 TABLE 2 Driving voltage (V) Transmittance (%) 0 26.6 5 9.23 10 5.54 20 4.52

Evaluation Example 3: Evaluation of Transmittance According to Viewing Angle

(36) For the liquid crystal cell of Example 3, the average transmittance according to the viewing angle at a wavelength of 400 nm to 700 nm was measured, and the results were shown in FIG. 8. Specifically, the transmittance according to the viewing angle (polar angle) at an azimuthal angle of 90° upon no voltage application (0V). As a result of the measurement, it could be confirmed that the vertical orientation was well performed.

EXPLANATION OF REFERENCE NUMERALS

(37) 100: first substrate 110: first electrode film 120: first non-liquid crystal alignment film 121: cured product 130: liquid crystal alignment film 200: second substrate 210: second electrode film 220: second non-liquid crystal alignment film 230: liquid crystal alignment film 300: transmittance-variable liquid crystal layer 301: ball spacer 302: liquid crystal molecule