Light Modulation Element

Abstract

A light modulation element that can vary between a bright transparent mode and a dark scattering mode is provided. The light modulation element has a first light modulation layer and a second light modulation layer comprising nematic liquid crystals and a dichroic dye in a scattering mode when a voltage is applied. The first light modulation layer and the second light modulation layer are disposed to overlap each other. The light modulation element has an improved contrast ratio and haze-variable characteristics, without precipitation of dichroic dyes and an increase in power consumption.

Claims

1. A light modulation element comprising: a first light modulation layer comprising nematic liquid crystals and a dichroic dye, wherein the first light modulation layer is in a scattering mode when a voltage is applied and a second light modulation layer comprising nematic liquid crystals and a dichroic dye, wherein the second light modulation layer is in a scattering mode when a voltage is applied, wherein the first light modulation layer and the second light modulation layer are disposed to overlap each other.

2. The light modulation element according to claim 1, wherein the light modulation element has a contrast ratio (CR) of 10 or more as calculated by Equation 1 below:
CR=T(0V)/T(60V)  [Equation 1] wherein, T (0V) is a total transmittance (%) of the light modulation element in a state when no voltage is applied to each of the first light modulation layer and the second light modulation layer, and T (60V) is a total transmittance (%) of the light modulation element in a state when a voltage of 60V is applied to each of the first light modulation layer and the second light modulation layer.

3. The light modulation element according to claim 1, wherein the light modulation element has a haze difference (ΔH) of 50% or more as calculated by Equation 2 below:
ΔH=H(60V)−H(0V)  [Equation 2] wherein, H (0V) is haze (%) of the light modulation element in a state when no voltage is applied to each of the first light modulation layer and the second light modulation layer, and H (60V) is haze (%) of the light modulation element in a state when a voltage of 60V is applied to each of the first light modulation layer and the second light modulation layer.

4. The light modulation element according to claim 1, wherein the first light modulation layer and the second light modulation layer each comprise the nematic liquid crystals and the dichroic dye in a vertically oriented state when no voltage is applied.

5. The light modulation element according to claim 1, wherein the nematic liquid crystals included in each of the first light modulation layer and the second light modulation layer have negative dielectric constant anisotropy.

6. The light modulation element according to claim 1, wherein the first light modulation layer and the second light modulation layer each further comprise a conductive additive.

7. The light modulation element according to claim 6, wherein the electrical conductivity of the conductive additive is from 2×10.sup.−4 μS/cm to 5×10.sup.−3 μ/cm.

8. The light modulation element according to claim 6, wherein the conductive additive comprises a reactive mesogen.

9. The light modulation element according to claim 6, wherein the conductive additive is a compound represented by Formula 1 below: ##STR00003## wherein, P is a (meth)acrylate group, a carboxyl group, a hydroxyl group, a vinyl group, an epoxy group or a nitro group, X is a single bond, a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, or a substituted or unsubstituted alkoxylene group having 1 to 10 carbon atoms, L is a single bond, a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkynylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxylene group having 1 to 10 carbon atoms, —O— or —COO—, and Y is hydrogen, halogen, a cyano group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms unsubstituted or substituted with one or more substituents selected from the group consisting of a cyano group, halogen and alkenyl group.

10. The light modulation element according to claim 1, wherein a concentration of the dichroic dye included in each of the first light modulation layer and the second light modulation layer is from 0.01 wt % to 5 wt %.

11. The light modulation element according to claim 1, wherein the first light modulation layer and the second light modulation layer each have a thickness from 4 μm to 25 μm.

12. The light modulation element according to claim 1, further comprising a first substrate and a second substrate disposed opposite to both sides of the first light modulation layer and a third substrate and a fourth substrate disposed opposite to both sides of the second light modulation layer, wherein the first substrate, the second substrate, the third substrate and the fourth substrate each comprise a base layer, an electrode layer and a vertical alignment film sequentially.

13. The light modulation element according to claim 12, wherein the second substrate and the third substrate are attached via a pressure-sensitive adhesive or an adhesive.

14. The light modulation element according to claim 12, wherein the base layers included in the first substrate, the second substrate, the third substrate and the fourth substrate are each independently a glass base material or a plastic film base material.

Description

DESCRIPTION OF DRAWINGS

[0075] FIG. 1 exemplarily shows a light modulation element of the present application.

[0076] FIG. 2 is a graph of experimental results in Table 1.

[0077] FIG. 3 is a graph of experimental results in Table 2.

[0078] FIG. 4 is a graph of experimental results in Table 3.

[0079] FIG. 5 is a graph of experimental results in Table 4.

MODE FOR DISCLOSURE

[0080] Hereinafter, the present application will be described in detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the following examples.

Measurement Example 1. Measurement of Electrooptic Characteristics

[0081] For the light modulation elements produced in Examples and Comparative Examples, haze and transmittance depending on voltage application were measured according to ASTM D1003 standard, using a hazemeter (NDH-5000SP). EC1000S model equipment from NF was used for the voltage application, when an AC power was connected to the upper and lower ITO layers, and a square wave voltage was applied at a frequency of 60 Hz and a size of 0 to 70 Vrms.

[0082] Specifically, light is transmitted through the measurement object and incident into the integrating sphere, when in this process, the light is divided into diffusion light (DT, which means the sum of all diffused and emitted light) and parallel light (PT, which means exit light in the front direction excluding the diffusion light), and these lights are focused on the light receiving element in the integrating sphere, whereby the haze can be measured through the focused light. The total transmitted light (TT) by the above process is the sum (DT+PT) of the diffusion light (DT) and the parallel light (PT), where haze can be defined as a percentage (Haze (%)=100×DT/TT) of the diffusion light to the total transmitted light. In the following test examples, the total transmittance means the total transmitted light (TT).

Comparative Example 1: Production of Single Cell

[0083] An ITO (indium tin oxide) layer was formed on a PET (polyethylene terephthalate) film to prepare a PET-ITO film (Hansung Co., Ltd.) having a thickness of 50 μm. A release film of PET material is attached to the PET side of the PET-ITO film as a protective film. A first substrate was produced by coating a composition (RN-3954, Nissan) for forming a vertical alignment film on the ITO layer of the film using a 3 # bar, and then curing it at 150° C. for 20 minutes to form a vertical alignment film having a thickness of about 200 nm.

[0084] On the ITO layer of the same PET-ITO film as the PET-ITO film, column spacers having a height of 8 μm and a diameter of 15 μm were disposed at intervals of 250 μm. Next, a second substrate was prepared by forming a vertical alignment film in the same method as the first substrate.

[0085] In a 10 mL vial, 3.6 g of nematic liquid crystals (HNG726200-100, HCCH, dielectric constant anisotropy: −4.0, refractive index anisotropy: 0.225), 0.4 g of a conductive additive of Formula A below and 0.06 g of a dichroic dye (X12, BASF) were placed and then stirred at 100° C. for 24 hours to prepare a liquid crystal composition. The concentration of the dichroic dye can be a percentage of the weight of the dichroic dye to the total weight of the nematic liquid crystals and the conductive additive, where the concentration of the dichroic dye is 1.5 wt %.

[0086] A sealant was drawn on the edge of the alignment film surface of the second substrate with a seal dispenser. After the liquid crystal composition was applied onto the alignment film of the second substrate, the first substrate was laminated to produce a light modulation element with a single cell structure having a cell gap of 8 μm and an area of width×length=4.0 cm×2.2 cm.

##STR00002##

Comparative Examples 2 to 14

[0087] Light modulation elements with a single cell structure were produced in the same method as in Comparative Example 1, except that the cell gap size and dye concentration were changed as shown in Tables 1 to 4 below.

[0088] For Comparative Examples 1 to 14, the total transmittance (T (0V)) in a state when no voltage was applied and the total transmittance (T (60V)) in a state when a voltage of 60V was applied were measured, and the results were described in Tables 1 to 4 below. In Tables 1 to 4, the contrast ratio (CR) is a ratio of T (0V)/T (60V). FIGS. 2, 3, 4 and 5 are graphs of the experimental results of Table 1, Table 2, Table 3 and Table 4, respectively. In the experimental result graphs, the y-axis represents the total transmittance (T.T) (%), and the x-axis represents the concentration (%) of the dichroic dye.

TABLE-US-00001 TABLE 1 Cell Dye Concen- T(0 V) T(60 V) Gap tration (wt %) (%) (%) CR Comparative 1 8 μm 1.5 68.52 30.2 2.27 Example 2 8 μm 2 62.84 21.83 2.88 3 8 μm 2.55 57.94 16.73 3.46

TABLE-US-00002 TABLE 2 Cell Dye Concen- T(0 V) T(60 V) Gap tration (wt %) (%) (%) CR Comparative 4 10 μm 1 71.39 35.09 2.03 Example 5 10 μm 1.5 66.17 25.91 2.55 6 10 μm 2 58.98 17.73 3.33 7 10 μm 2.55 52.17 12.12 4.30

TABLE-US-00003 TABLE 3 Cell Dye Concen- T(0 V) T(60 V) Gap tration (wt %) (%) (%) CR Comparative 8 12 μm 1 59.3 19.56 3.03 Example 9 12 μm 2 53.08 12.97 4.09 10 12 μm 2.55 45.3 7.99 5.70

TABLE-US-00004 TABLE 4 Cell Dye Concen- T(0 V) T(60 V) Gap tration (wt %) (%) (%) CR Comparative 11 15 μm 1 50.28 14.85 3.39 Example 12 15 μm 1.5 43.08 8.32 5.18 13 15 μm 2 30.79 3.58 8.60 14 15 μm 2.55 21.53 2.26 9.53

Comparative Examples 15 to 18

[0089] Using the trend lines of the experimental result graphs in FIGS. 2, 3, 4 and 5, the concentration of the dichroic dye in each cell gap that the total transmittance was 40% in a state (0V) when no voltage was applied was obtained, and the total transmittance at the concentration upon applying a voltage of 60V was obtained and described in Table 5 below. In the exponent y=ae.sup.−bx of FIGS. 2 to 5, y means the total transmittance (T.T) (%), and x means the concentration of dichroic dye (%).

TABLE-US-00005 TABLE 5 Cell Dye Concen- T(0 V) T(60 V) Gap tration (wt %) (%) (%) CR Comparative 15  8 μm 4.845 40 4.56 8.77 Example 16 10 μm 3.88 40 4.85 8.25 17 12 μm 3.46 40 5.17 7.74 18 15 μm 1.503 40 7.80 5.13

[0090] From Table 5 above, the lower the cell gap, the more the CR value increases, but it can be seen that a CR of 10 or more cannot be obtained. In order to set the CR value to 10 or more, the concentration of the dichroic dye should be 5 wt % or more, and the cell gap should be lowered to 8 μm or less. However, this may cause a problem of dye precipitation (the saturation concentration of the dye is about 3 wt % for the host liquid crystal), and may cause a problem of processability due to the cell gap reduction.

Comparative Example 19

[0091] A light modulation element with a single cell structure was produced in the same method as in Comparative Example 1, except that the size of the cell gap was set to 10 μm and the concentration of the dichroic dye was changed to 1.71 wt %.

Comparative Example 20

[0092] A light modulation element with a single cell structure was produced in the same method as in Comparative Example 1, except that the size of the cell gap was set to 8 μm and the concentration of the dichroic dye was changed to 2.2 wt %.

Example 1

[0093] A first liquid crystal cell and a second liquid crystal cell were each produced in the same method as in Comparative Example 1, except that the cell gap was set to 10 μm and the concentration of the dichroic dye was changed to 1.71 wt %. The first liquid crystal cell and the second liquid crystal cell were attached via an OCA (LGC, V310) adhesive to produce a light modulation element with a double cell structure.

Example 2

[0094] A first liquid crystal cell and a second liquid crystal cell were each produced in the same method as in Comparative Example 1, except that the cell gap was set to 8 μm and the concentration of the dichroic dye was changed to 2.2 wt %. The first liquid crystal cell and the second liquid crystal cell were attached via an OCA (LGC, V310) adhesive to produce a light modulation element with a double cell structure.

Example 3

[0095] A first liquid crystal cell was produced in the same method as in Comparative Example 1, except that the cell gap was set to 10 μm and the concentration of the dichroic dye was changed to 1.71 wt %. A second liquid crystal cell was produced in the same method as in Comparative Example 1, except that the cell gap was set to 8 μm and the concentration of the dichroic dye was changed to 2.2 wt %. The first liquid crystal cell and the second liquid crystal cell were attached via an OCA (LGC, V310) adhesive to produce a light modulation element with a double cell structure.

Example 4

[0096] A first liquid crystal cell was produced in the same method as in Comparative Example 1, except that the cell gap was set to 10 μm and the concentration of the dichroic dye was changed to 1.71 wt %. A second liquid crystal cell was produced in the same method as in Comparative Example 1, except that the cell gap was set to 12 μm and the concentration of the dichroic dye was changed to 1 wt %. The first liquid crystal cell and the second liquid crystal cell were attached via an OCA (LGC, V310) adhesive to produce a light modulation element with a double cell structure.

[0097] For Comparative Examples 19 and 20, and Examples 1 to 4, the total transmittance T (0V) and the haze H (0V) in a state when no voltage was applied, and the total transmittance T (60V) and the haze H (60V) in a state when a voltage was applied were measured, and the results were described in Tables 6 to 11 below.

TABLE-US-00006 TABLE 6 Total Transmittance (%) Haze (%) Comparative T(0 V)  60.4 H(0 V)  6.84 Example 19 T(60 V) 18.86 H(60 V) 87.56 (Single Cell) CR [T(0 V)/T(60 V)] 3.20 ΔH [H(60 V) − 80.81 H(0 V)]

TABLE-US-00007 TABLE 7 Total Transmittance (%) Haze (%) Example 1 T(0 V)  39.6 H(0 V)  9.32 (Double T(60 V) 3.62 H(60 V) 93.92 Cell) CR [T(0 V)/T(60 V)] 10.94 ΔH [H(60 V) − H(0 V)] 84.6

TABLE-US-00008 TABLE 8 Total Transmittance (%) Haze (%) Comparative T(0 V)  59.7 H(0 V)  6.71 Example 20 T(60 V) 17.67 H(60 V) 87.15 (Single Cell) CR [T(0 V)/T(60 V)] 3.4 ΔH [H(60 V) − 80.44 H(0 V]

TABLE-US-00009 TABLE 9 Total Transmittance (%) Haze (%) Example 2 T(0 V)  41.32 H(0 V)  9.51 (Double T(60 V) 3.61 H(60 V) 94.01 Cell) CR [T(0 V)/T(60 V)] 11.45 ΔH [H(60 V) − H(0 V] 84.5

TABLE-US-00010 TABLE 10 Total Transmittance (%) Haze (%) Example 3 T(0 V)  40.12 H(0 V)  9.17 (Double T(60 V) 3.65 H(60 V) 93.43 Cell) CR [T(0 V)/T(60 V)] 10.99 ΔH [H(60 V) − H(0 V] 84.26

TABLE-US-00011 TABLE 11 Total Transmittance (%) Haze (%) Example 4 T(0 V)  41.31 H(0 V)  9.43 (Double T(60 V) 4.03 H(60 V) 93.66 Cell) CR [T(0 V)/T(60 V)] 10.25 ΔH [H(60 V) − H(0 V] 84.23

[0098] The light modulation elements with the single cell structure of Comparative Examples 19 and 20 and the light modulation elements with the double cell structure of Examples 1 to 4 all have no problem of dye precipitation and processability, but it can be seen that Examples 1 to 4 have significantly excellent contrast ratios (CR) and haze-variable characteristics as compared to Comparative Examples 1 and 2.

EXPLANATION OF REFERENCE NUMERALS

[0099] 100: first light modulation layer, 200: second light modulation layer.