KR20190042927A - Smart window for controlling visible light and infrared - Google Patents

Abstract

The present invention relates to a smart window in which the arrangement of cholesteric liquid crystals and dichroic dyes is determined according to an applied voltage. More specifically, according to an applied voltage, cholesteric liquid crystals are arranged in a planar, focal conic, and homeotropic manner so that the transmittance of infrared light may be controlled, and dichroic dyes are arranged in a homogeneous, random, and homeotropic manner so that the visible light transmittance may be controlled. The amount of transmitted infrared light and visible light is controlled to efficiently maintain proper indoor temperature and to control indoor illuminance.

Description

[0001] SMART WINDOW FOR CONTROLLING VISIBLE LIGHT AND INFRARED [0002]

The present invention relates to a smart window for controlling visible light and infrared rays, and more particularly, to a smart window for controlling visible light and infrared rays, and more particularly to a smart window for adjusting visible light and infrared rays, And to a smart window for control.

Recently, reducing energy consumption due to resource depletion and enforcement of environmental regulations has become a top priority in the world. Particularly, this is also the case in many optical application technologies that require optical properties to be electrically controlled. For example, a smart window has been attracting attention as a user freely adjusting the amount of light transmission to improve energy efficiency.

One of the most important things in the indoor environment is the natural light transmitted through the windows. There is a problem in that the indoor temperature rises due to excessive infrared ray transmittance in the winter, and excessive use of energy due to the operation of the air conditioner.

In the conventional smart window, the driving body coheres with the pad of the electrode according to whether the voltage is applied or not to block the incident light, or the refraction layer having different refractive index is formed on the substrate to control the light transmission amount through the infrared reflection layer. However, in the case of the present invention, the arrangement of the cholesteric liquid crystal molecules and the dichroic dye is changed according to the applied voltage to control the light transmission amount.

Korean Patent Publication No. 2016-0117326 Korean Patent Publication No. 2017-0024830

It is an object of the present invention to provide a smart window for controlling the visible and infrared transmittance by switching the arrangement of cholesteric liquid crystals and dichroic dyes by controlling the voltage.

A smart window for controlling visible light and infrared rays, comprising: a lower substrate;

A cholesteric liquid crystal and a dichroic dye provided on the lower substrate;

And an upper substrate,

The cholesteric liquid crystal is arranged in planar, focal conic, and homeotropic states according to an applied voltage,

The dichroic dye is arranged in a homogeneous, random, and homeotropic state according to an applied voltage.

The cholesteric liquid crystal is characterized by being formed by adding a chiral dopant to a nematic liquid crystal.

And the content of the chiral dopant is 10 to 20 wt%.

And the content of the nematic liquid crystal is 80 to 90 wt%.

And the pitch length of the cholesteric liquid crystal is 600 to 800 nm.

And the average refractive index of the cholesteric liquid crystal is 1.4 or more.

The dichroic dyes may be azo dyes, azo-stilbene dyes, benzothiazolyl polyazomethyl dyes, methine-arylidene dyes, tetrazine dyes, oxadiazine dyes, carbazole-azo dyes, amino dyes or anthraquinone dyes And the like.

The content of the dichroic dye is 0.5 to 5 wt%.

And a liquid crystal cell gap of 3 to 10 mu m.

The smart window of the present invention has an infrared blocking effect by switching the arrangement of cholesteric liquid crystal molecules and controls the visible light transmittance using dichroic dyes following the behavior of cholesteric liquid crystals.

1 is a schematic diagram showing a smart window for controlling visible light and infrared rays according to the present invention.
FIG. 2A is a schematic view showing a smart window in a state before voltage application according to an embodiment of the present invention, in which cholesteric liquid crystal molecules are arranged in a planar state, and dichroic dyes are arranged homogeneously.
FIG. 2B is a schematic view illustrating a smart window in a low voltage applied state according to an embodiment of the present invention, in which cholesteric liquid crystal molecules are arranged in a focal conic state, dichroic dyes are arranged in a random state .
FIG. 2C is a schematic view illustrating a smart window in a high voltage applied state according to an embodiment of the present invention, wherein the cholesteric liquid crystal molecules and the dichroic dye are arranged in a homeotropic state.
3 is a graph showing the transmittance in the visible light region according to the voltage.
4A and 4B are cross-sectional views of the smart window according to the embodiment of the present invention. FIG. 4A is a cross-sectional view of FIG. 4A when the liquid crystal behaves as shown in FIG. (Opaque state), and FIG. 4C shows the liquid crystal behavior as shown in FIG. 4 (transparent state).
5 is a schematic diagram of a phase change of a liquid crystal according to a voltage application when a dual frequency LC is used.

BRIEF DESCRIPTION OF THE DRAWINGS The visible light and infrared smart windows of the present invention will now be described with reference to the accompanying drawings. The width and thickness of the layers or regions illustrated in the accompanying drawings may be somewhat exaggerated for clarity and ease of description.

Referring to FIG. 1, the smart window of the present invention includes a cholesteric liquid crystal mixture 200 between an upper substrate 100 and a lower substrate 200, and the upper substrate 100 and the lower substrate 300 Substrates 101 and 301, transparent electrodes 102 and 302, and horizontal alignment films 103 and 303 are laminated.

The transparent electrode may be a known electrode or a transparent conductive thin film such as ITO (Indium Tin Oxide) coated on a polyethylene terephthalate (PET) film. In the present invention, the transparent electrode is connected to an external power source of the smart window to generate an electric field.

A horizontal alignment film may be stacked on the transparent electrode and may be used without limitation as long as the orientation of the adjacent cholesteric liquid crystal mixture 200 can be appropriately adjusted.

On the other hand, the cholesteric liquid crystal mixture 200 includes a cholesteric liquid crystal (CLC) and a dichroic dye, and the cholesteric liquid crystal can be prepared by doping a chiral compound with a nematic liquid crystal, Or by bonding a chiral group to a nematic liquid crystal molecule. Since cholesteric liquid crystals use ambient light as a light source, unlike ordinary liquid crystals, no polarizer is required.

The cholesteric liquid crystal has a Bragg reflection effect that selectively reflects light according to the twist direction of the helix and the pitch of the repeating structure. At this time, when the light incident on the cholesteric liquid crystal is expressed by the sum of the two circularly polarized lights whose directions of rotation are opposite to each other, the circularly polarized light in the same direction as the twisted structure of the cholesteric liquid crystal is reflected, The polarized light has a transmission characteristic, and the wavelength? _O of the reflected light is represented by the following equation 1 Satisfies.

λ _o = nP _o ... (Equation 1)

In the above formula (1), n denotes the average refractive index of the cholesteric liquid crystal, and P _o denotes the pitch of the cholesteric liquid crystal. When the cholesteric liquid crystal having various pitches is produced, the wavelength range of the reflected light is widened.

Since the smart window of the present invention selectively reflects light in the infrared region, a combination of a nematic liquid crystal and a chiral dopant must be determined so as to have a pitch reflecting the light of the region. Specifically, a chiral dopant is added to a nematic liquid crystal to form a cholesteric liquid crystal. The chiral dopant used in this case is a compound having an optically active group such as a cholesterol derivative or a 2-methylbutyl group, But the present invention is not limited thereto.

The content of chiral dopant added to the nematic liquid crystal is preferably 10 to 20 wt%. If the content of the chiral dopant is less than 10 wt%, the pitch value required for forming the cholesteric liquid crystal can not be realized. If the content of the chiral dopant exceeds 20 wt%, excess residual chiral dopant There is a problem that the infrared transmittance is decreased.

In the present invention, a nematic liquid crystal is preferably a dual frequency liquid crystal capable of controlling the dielectric anisotropy of the liquid crystal in positive or negative using an AC frequency change. In general, however, the nematic liquid crystal has a positive dielectric anisotropy LCDs can be used without limitation.

The content of nematic liquid crystals in cholesteric liquid crystal formation is 80 to 90 wt%. If the content of the nematic liquid crystal does not reach 80 wt%, the blocking effect of the infrared wavelength region is not exhibited and the transmittance is too high or too low to exhibit the optical characteristics required by the present invention. If the content exceeds 90 wt% The cholesteric liquid crystal can not be formed and it is difficult to implement a smart window.

On the other hand, when a voltage is applied in the present invention, the pitch of the cholesteric liquid crystal is loosened to increase the infrared transmittance, and when the voltage is cut off, a pitch is formed and the infrared transmittance is decreased. Therefore, the pitch length of the cholesteric liquid crystal has a large influence on the infrared transmittance, so it is necessary to specify the pitch length. The preferred pitch length of the cholesteric liquid crystal is 600 to 800 nm. If the pitch of the cholesteric liquid crystal is less than 600 nm, the wavelength of the infrared ray band can not be reflected, and if the pitch exceeds 800 nm, the performance of the smart window of the present invention can not be optimized.

In the present invention, the reflection wavelength band is changed according to the refractive index of the liquid crystal, and the required average refractive index of the cholesteric liquid crystal is 1.4 or more. If the average refractive index does not reach 1.4, the amount of the chiral dopant increases and the infrared ray transmittance decreases due to the residual chiral dopant.

A dichroic dye means a material capable of anisotropic absorption of light in at least a part or the entire range in a visible light region (wavelength of light of 400 to 700 nm). The dichroic dye absorbs or transmits light depending on the direction in which the light absorptance according to the direction changes, and has a characteristic that it can be oriented in accordance with the orientation of the cholesteric liquid crystal. In the present invention, dichroic dyes can use all kinds of dyes having the maximum absorbance in the visible light range. Examples thereof include azo dyes, azo-stilbene dyes, benzothiazolyl polyazomethyl dyes, methine- A tetrazine series, an oxadiazine series, a carbazole-azo series, an amino series or an anthraquinone series dichroic dye may be selected and used.

The content of the dichroic dye used is 0.5 to 5 wt% of the cholesteric liquid crystal mixture. If the content of the dichroic dye is less than 0.5 wt%, it is difficult to control the transmittance in the visible light region. If the content exceeds 5 wt%, the initial transmittance is too low.

In the present invention, the liquid crystal cell gap is 3 to 10 mu m. If the cell gap is less than 3 mu m, the amount of dichroic dye existing in the cell becomes excessively large. If the cell gap is more than 10 mu m, The transmittance of the line is lowered.

2A to 2C show the arrangement of cholesteric liquid crystal molecules according to a voltage application state. As shown in FIG. 2A, when the cholesteric liquid crystal is in the planar state before the voltage application, when the chiral pitch coincides with the wavelength of the infrared region, the light in the infrared region can not be transmitted through the window and is selectively reflected. They are arranged in the horizontal direction and can not transmit visible light.

However, when a high voltage is applied to the liquid crystal cell as shown in FIG. 2C, the cholesteric liquid crystal and the dichroic dye have a homeotropic structure, so that all incident light passes through the window. When a low voltage is applied as shown in FIG. Since the steric liquid crystal is arranged in a focal conic state and the dichroic dye is also arranged in a random state, only a part of the incident light is reflected. When the cholesteric liquid crystal is arranged in the focal conic state, light is scattered and the transmittance is lowered (see FIG. 3B).

Hereinafter, the present invention will be described in more detail with reference to Examples. This is for further illustrating the present invention, and the scope of the present invention is not limited to these examples.

≪ Example 1 >

The glass substrate is washed with ethanol and deionized water and dried on a hot plate for 100 to 5 minutes. As the heater of the cholesteric liquid crystal cell, an ITO film was deposited on the glass substrate by RF magnetron sputtering. The ITO film was composed of In ₂ O ₃ (90 wt%) and SnO ₂ (10 wt%). The thickness of the ITO film formed was 0.7 mm, and the surface resistance of the glass substrate on which the ITO film was deposited was 25 OMEGA / sq.

The cholesteric liquid crystal molecules used in this experiment are formed by adding chiral dopants (TCI, S-811) to nematic liquid crystal molecules (Merck, MDA-00-3969). The chiral dopant is 4 - {[(1-methylheptyl) oxy] carbonyl} phenyl-4- (hexyloxy) benzoate. Physical properties of the nematic liquid crystal molecule are shown in Table 1 below.

Clearing Point (℃) 110 n _e (20 캜, 589.3 nm) 1.7192 n _o (20 DEG C, 589.3 nm) 1.4978 (20 DEG C, 589.3 nm) 0.0865 Δε (20 ° C., 1 kHz) 2.98 Δε (20 ° C., 50 kHz) -2.75

The helical twist power of the chiral dopant used for cholesteric liquid crystal formation is 11 탆 ^-1 .

The physical properties of the liquid crystal cell prepared in Example 1 are shown in Table 2 below.

Dichroic dye 2wt% Driving frequency 1kHz, 50kHz Driving voltage 0V to 70V
(50V to 0V when driving at 50kHz) Electric field 0V / μm to 7V / μm Cell gap and temperature 10 μm, 25 ° C.

≪ Example 2 >

A liquid crystal cell was prepared in the same manner as in Example 1 except that the dichroic dye content in Example 1 was 4 wt%.

≪ Comparative Example 1 &

A liquid crystal cell was prepared in the same manner as in Example 2 except that nematic liquid crystal having no chiral dopant was used in Example 2.

≪ Comparative Example 2 &

A liquid crystal cell was prepared in the same manner as in Example 1, except that the dichroic dye was not included in Example 1.

<Experimental Example>

1. Measurement of light transmittance

The transmittance is measured by a method in which a light source-sample-detector is arranged in a straight line using a UV-Vis spectrophotometer (Scinco corporation, S-3100), and light emitted from the light source is detected by a detector through a sample.

<Transmittance according to wavelength of liquid crystal cell manufactured by Example 1>

<Transmittance in the visible light region (400 nm to 700 nm) of the liquid crystal cell manufactured according to Example 1>

<Transmittance in the infrared region (900 nm to 1100 nm) of the liquid crystal cell manufactured according to Example 1>

<Transmittance according to the wavelength of the liquid crystal cell manufactured in Example 2>

<Transmittance in the visible light region (400 nm to 700 nm) of the liquid crystal cell manufactured according to Example 2>

<Transmittance in the infrared region (900 nm to 1100 nm) of the liquid crystal cell manufactured according to Example 2>

<Transmittance of Examples 1 and 2 and Comparative Example 1 according to wavelength>

Initial transmittance (%) Maximum transmittance (%) Lowest Transmittance (%) Visible ray infrared ray Visible ray infrared ray Visible ray infrared ray Example 1 20.05
(at 0V) 35.37
(at 0V) 51.21
(at 70V) 59.26
(at 70V) 6.63
(at 16V) 11.39
(at 22V) Example 2 4.09
(at 0V) 33.56
(at 0V) 40.00
(at 70V) 62.28
(at 70V) 0.90
(at 14V) 2.66
(at 24V) Comparative Example 1 21.92
(at 0V) 52.85
(at 0V) 52.26
(at 70V) 52.85
(at 0V) 21.92
(at 0V) 52.85
(at 0V) Comparative Example 2 74.92
(at 0V) 36.23
(at 0V) 74.92
(at 0V) 60.33
(at 70V) 74.92
(at 0V) 15.23
(at 22V)

In Examples 1 and 2 of the present invention, the liquid crystal changes from an initial semi-transparent state to a opaque state when a voltage is applied (0 V? 30 V) in response to an electric field, and the transmittance of visible light and infrared light is reduced at this time. However, when the voltage is further applied (30V? 70V), the twist of the cholesteric liquid crystal is released, and all the liquid crystal molecules are aligned vertically, and the transmittance is increased.

Comparing Example 1 and Example 2, the initial transmittance and the maximum transmittance in the infrared region are similar but the lowest transmittance is different. This is because light scattering occurs well in Example 2 and the concentration of dichroic dye is high The lowest transmittance of the ground infrared region is further lowered. The transmittance in the visible light region is lower in the case of Example 2 where the ratio of the dichroic dye in the cholesteric liquid crystal mixture is higher, and the higher the dichroic dye ratio, the more the external light is absorbed.

100 upper substrate
101 substrate
102 Electrode
103 Horizontal alignment film
200 cholesteric liquid crystal mixture
201 cholesteric liquid crystal molecule
202 dichroic dye
300 lower substrate
301 substrate
302 Electrode
303 horizontal alignment film
400 AC voltage

Claims (9)

A lower substrate;
A cholesteric liquid crystal and a dichroic dye provided on the lower substrate;
And an upper substrate,
The cholesteric liquid crystal is arranged in planar, focal conic, and homeotropic states according to an applied voltage,
Wherein the dichroic dye is a homogeneous, random, and homeotropic visible light ray according to an applied voltage and a smart window for controlling infrared rays. The smart window for visible light and infrared rays according to claim 1, wherein the cholesteric liquid crystal is formed by adding a chiral dopant to a nematic liquid crystal. The smart window for visible light and infrared rays according to claim 2, wherein the content of the chiral dopant is 10 to 20 wt%. The smart window for visible light and infrared rays according to claim 2, wherein the content of the nematic liquid crystal is 80 to 90 wt%. The smart window for visible light and infrared rays according to claim 1, wherein the pitch length of the cholesteric liquid crystal is 600 to 800 nm. The smart window for visible light and infrared rays according to claim 1, wherein the cholesteric liquid crystal has an average refractive index of 1.4 or more. The dichroic dye according to claim 1, wherein the dichroic dye is selected from the group consisting of azo series, azo-stilbene series, benzothiazolyl polyazomethyl series, methine-arylidene series, tetrazine series, oxadiazine series, carbazole- An amino-based or an anthraquinone-based one or more selected from the group consisting of a visible light ray and an infrared ray. The smart window for visible light and infrared rays according to claim 1, wherein the content of the dichroic dye is 0.5 to 5 wt%. The smart window for visible light and infrared rays according to claim 1, wherein the liquid crystal cell gap is 3 to 10 占 퐉.

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