CN112130362A

CN112130362A - Bistable light modulator

Info

Publication number: CN112130362A
Application number: CN201910554691.2A
Authority: CN
Inventors: 卢遵胜; 陈凯; 武少彬; 周孟超; 李栋; 张宏伟; 王飞
Original assignee: Jiangsu Jitri Smart Liquid Crystal Sci and Tech Co Ltd
Current assignee: Jiangsu Jitri Smart Liquid Crystal Sci and Tech Co Ltd
Priority date: 2019-06-25
Filing date: 2019-06-25
Publication date: 2020-12-25

Abstract

The invention discloses a bistable light modulator, which comprises a first transparent conductive base layer, a liquid crystal layer and a second transparent conductive base layer which are sequentially stacked, and further comprises a first alignment layer which is subjected to orientation treatment and is arranged between the first transparent conductive base layer and the liquid crystal layer, wherein the liquid crystal layer comprises a cholesteric liquid crystal mixture, and the bistable light modulator comprises two stable states with zero electric field: a transmissive state in which incident light is substantially directed and a foggy state in which incident light is substantially scattered. The invention also discloses a method for preparing the bistable light modulator. The bistable light modulator can further improve the overall uniformity of optical performance while improving the fog state haze and reducing the transmission state haze, avoids loss of privacy, and has a simple preparation method and easy operation.

Description

Bistable light modulator

Technical Field

The invention relates to the field of liquid crystal-based dimming, in particular to a bistable dimming device.

Background

The liquid crystal-based dimming device is mainly composed of a transparent base material and a liquid crystal material, and the arrangement state of liquid crystal molecules is regulated and controlled in an external electric field mode, so that the conversion between full transparency and non-transparency is realized. Due to the unique dimming characteristic, liquid crystal-based dimming devices, such as intelligent glass, are widely applied to industries such as buildings, houses and automobiles, and are used for achieving the functions of adjusting light transmittance, increasing privacy, blocking ultraviolet rays or infrared rays and the like. The bistable or multistable dimming glass has the characteristic of no need of electric field maintenance, and has energy-saving safety and wider application prospect.

Bistable light control glasses based on cholesteric liquid crystals generally have two states of zero electric field stability: a transparent transmission state and an opaque fog state. Due to the characteristics of high transparency, high haze and no viewing angle problem, the bistable cholesteric liquid crystal dimming glass has become dimming glass with market potential. Generally, in such light control glass, cholesteric liquid crystal is in a periodic spiral structure, but the structure is greatly influenced by interface conditions and external environment, and in use, the liquid crystal molecules are not aligned uniformly often due to defects and nonuniformity of an interface or influence of the external environment, so that the overall uniformity of the optical performance of the light control glass is poor, the appearance of a product is influenced, privacy is easier to leak, and further application of the light control glass is limited.

Disclosure of Invention

In order to solve the above problems, the present invention provides a bistable light modulator, which includes a first transparent conductive substrate, a liquid crystal layer, a second transparent conductive substrate, and a first alignment layer processed by alignment, the first alignment layer is disposed between the first transparent conductive substrate and the liquid crystal layer, the liquid crystal layer includes a cholesteric liquid crystal mixture, and the bistable light modulator includes two stable states with zero electric field: which of the direct transmission states the incident light is made to be substantially and the fog state the incident light is made to be substantially scattered.

In a preferred embodiment, the cholesteric liquid crystal mixture comprises a bimesogenic compound, a nematic liquid crystal compound and a chiral compound.

In an alternative embodiment, the bistable light modulating device further comprises a second alignment layer, which is not oriented, disposed between the second transparent conductive substrate layer and the liquid crystal layer.

In a preferred embodiment, the orientation treatment manner includes a rubbing orientation method, a photo-orientation method, an evaporation method, and an LB film method.

In a preferred embodiment, the first alignment layer and/or the second alignment layer is of a substantially planar alignment type or a substantially homeotropic alignment type.

In a preferred embodiment, the thickness of the liquid crystal layer is 5 to 60 μm.

In an alternative embodiment, the first transparent conductive base layer and the second transparent conductive base layer include a transparent substrate and a transparent electrode, respectively. In a preferred embodiment, the transparent substrate is transparent glass or a transparent polymeric material.

The invention also discloses a method for preparing the bistable light modulator, which comprises the following steps: arranging a first alignment layer on the inner surface of the first transparent conductive base layer, and performing rubbing orientation on the first alignment layer along a direction, wherein the inner surface of the first transparent conductive base layer is provided with a transparent electrode; aligning the first transparent conductive base layer and the second transparent conductive base layer in a manner that the inner surfaces are opposite, wherein the inner surface of the second transparent conductive base layer is provided with a transparent electrode and is not subjected to rubbing orientation; adding a spacer between the first transparent conductive base layer and the second transparent conductive base layer, and attaching the first transparent conductive base layer and the second transparent conductive base layer which are arranged in an aligned manner by using frame sealing glue; filling the cholesteric liquid crystal mixture between the first transparent conductive base layer and the second transparent conductive base layer to form a liquid crystal layer; and curing the seal to form the bistable dimming device.

In a preferred embodiment, the rubbing orientation is performed by a single sheet intermittent rubbing method or a roll-to-roll continuous rubbing method.

In an alternative embodiment, the inner surface of the second transparent conductive base layer is provided with a second alignment layer, which is not subjected to a rubbing alignment treatment.

According to the bistable light modulator disclosed by the invention, the bimesogenic compound is introduced, and only one orientation layer subjected to orientation treatment is arranged, so that the overall uniformity of optical performance can be further improved while the haze and the transmission haze are improved, and the loss of privacy is avoided. The preparation method is simple and easy to operate, and the yield can be improved.

Drawings

The invention may be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, in which:

fig. 1 is a schematic diagram of a bistable light modulator device according to an embodiment of the present invention;

FIG. 2 is a schematic diagram illustrating the operation of the bistable dimmer device disclosed herein;

fig. 3 is a schematic diagram of a bistable light modulator device according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a bistable dimming device according to an embodiment of the present invention.

Detailed Description

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. The illustrated exemplary embodiments of the invention are provided for purposes of illustration only and are not intended to be limiting of the invention. Therefore, it is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Referring first to fig. 1, there is shown a bistable light modulating device having a structure including a first transparent conductive substrate layer 10, a second transparent conductive substrate layer 20 and a liquid crystal layer 30 interposed therebetween, and further including an alignment-treated first alignment layer 40 disposed between the first transparent conductive substrate layer 10 and the liquid crystal layer 30, and no alignment layer is disposed between the second transparent conductive substrate layer 20 and the liquid crystal layer 30, and no alignment treatment is performed on a surface of the second transparent conductive substrate layer 20 in contact with the liquid crystal layer 30. Of course, the alignment-treated first alignment layer 40 may be disposed between the second transparent conductive substrate layer 20 and the liquid crystal layer 30, and correspondingly, no alignment layer is disposed between the first transparent conductive substrate layer 10 and the liquid crystal layer 30, and no alignment treatment is performed on the surface of the first transparent conductive substrate layer 10 contacting the liquid crystal layer 30. The orientation treatment is used for restraining the liquid crystal molecules near the surface of the liquid crystal molecules from orderly arranging, and can adopt orientation arrangement processes commonly used in the liquid crystal industry, including a friction orientation method, a photo-orientation method, an evaporation method and an LB membrane method. In the following examples, the alignment treatment is preferably performed by a rubbing alignment method.

As shown in fig. 2, the liquid crystal layer 30 comprises a cholesteric liquid crystal mixture, in which cholesteric liquid crystal molecules 31 are spirally arranged in the liquid crystal layer, so that the bistable light-modulating device has two states of zero electric field stabilization: a transmissive state in which incident light is substantially directed (fig. 2(a)) and a foggy state in which incident light is substantially scattered (fig. 2 (b)). In the transmission state, the cholesteric liquid crystal molecules 31 are basically parallel to the surface of the light modulation device, and the spiral axis of the cholesteric liquid crystal molecules is vertical to the surface of the light modulation device, so that a planar texture of cholesteric liquid crystal is formed, and in the transmission state, incident light basically keeps the original incident angle to pass through the light modulation device without being influenced; in the foggy state, the cholesteric liquid crystal molecules 31 form a focal conic texture, and at this time, incident light is substantially scattered, resulting in a state with a large haze. In an embodiment of the invention, the cholesteric liquid crystal mixture comprises a bimesogenic compound, a nematic liquid crystal compound and a chiral compound, wherein the bimesogenic compound is a liquid crystal compound comprising two mesogens in the molecule, that is to say a bimesogenic compound comprising two groups in the molecule which induce liquid crystal phase capability. Due to the special elastic coefficient of the bimesogenic compound, the uniformity of the planar arrangement of cholesteric liquid crystal molecules can be improved, and the texture defects are reduced, so that the haze of the bistable light modulation device in a transmission state is reduced, and the haze of a haze state is improved. The weight percentage of the bimesogenic compound in the cholesteric liquid crystal mixture is 5-50%. Preferably, the bimesogenic compound accounts for 10-50% of the cholesteric liquid crystal mixture by mass. The nematic liquid crystal is a common liquid crystal compound or liquid crystal mixture having a nematic phase in a certain temperature range, such as 5CB, 2CB or E7. However, the nematic liquid crystal compound in the present invention does not include bimesogenic compounds that induce a nematic phase. The thickness of the liquid crystal layer 30 is generally 5 to 60 μm.

As shown in fig. 3, the first and second transparent

conductive base layers

10 and 20 may include

transparent substrates

11 and 21, respectively, and

transparent electrodes

12 and 22, respectively, wherein the

transparent electrodes

12 and 22 are disposed on the sides of the transparent conductive base layers that are in contact with the liquid crystal layer 30. The

transparent substrates

11 and 21 may be transparent glass or transparent polymer material, such as PET, PEN, PC, PP, PMMA, PBT, PVC, PI, cellulose, etc., respectively. However, the present invention is not limited thereto, and other materials having a transmittance meeting the requirement may be used. The

transparent electrodes

12 and 22 may be formed as a thin film covering the entire inner surface of the transparent substrate as shown in fig. 3, or may be further etched into a specific shape or divided into a plurality of corresponding sub-electrodes as required. The transparent electrode may include a carbon-based conductive film, a metal nanowire conductive film, a metal oxide conductive film, and the like, according to conductive materials. The carbon-based conductive material mainly includes graphene oxide and carbon nanotubes, the metal nanowire conductive film usually adopts silver nanowires or copper nanowires, and the metal oxide conductive film is mainly made of a mixed system of Indium Tin Oxide (ITO), indium oxide, tin oxide, zinc oxide and other metal oxides. In the following examples, the transparent electrode is an ITO electrode.

The bistable light modulating device may further be provided with a second alignment layer 50, as shown in fig. 4, the second alignment layer 50 being disposed between the second transparent conductive base layer 20 and the liquid crystal layer 30, wherein the second alignment layer 50 is not subjected to an orientation treatment. Of course, when the first alignment layer 40 is disposed between the second transparent conductive base layer 20 and the liquid crystal layer 30, the second alignment layer 50 may be disposed between the first transparent conductive base layer 10 and the liquid crystal layer 30, accordingly.

Depending on the pre-tilt angle (i.e., the angle between the long axis of the liquid crystal molecules and the surface of the alignment layer when the liquid crystal molecules are orderly arranged on the surface of the alignment layer), the first alignment layer 40 and/or the second alignment layer 50 may be of a substantially planar alignment type, i.e., the long axis of the liquid crystal molecules on the surface of the alignment layer is substantially parallel to the surface of the alignment layer, such as IPS, TN, STN types; it may also be of the substantially vertical alignment type, i.e. the long axes of the liquid crystal molecules are substantially perpendicular to the surface of the alignment layer, such as the VA mode.

In an embodiment of the present invention, a method for manufacturing a bistable light modulator device may include the following steps.

First, a first alignment layer is arranged on the inner surface of a first transparent conductive base layer, and rubbing orientation is carried out on the first alignment layer along a direction, wherein the inner surface is provided with a transparent electrode. The types of the first alignment layer include a substantially planar alignment type and a substantially vertical alignment type. The alignment layer is generally formed by uniformly applying an alignment agent on the transparent conductive base layer by a spin coating method, a dipping method, a letterpress printing method, a spraying method or a slit coating method, and curing. The rubbing orientation method includes a single-sheet intermittent rubbing method and a roll-to-roll continuous rubbing method, but the present invention is not limited thereto, and other general orientation operations may be used.

And aligning the first transparent conductive base layer and the second transparent conductive base layer in a mode of inner surface opposite, wherein the inner surface of the second transparent conductive base layer is also provided with a transparent electrode, but the inner surface of the second transparent conductive base layer is not subjected to rubbing orientation. In an alternative embodiment, the inner surface of the second transparent conductive base layer may be provided with a second alignment layer, which is not subjected to a rubbing alignment treatment. The types of the second alignment layer also include a substantially planar alignment type and a substantially vertical alignment type.

And then, adding a spacer between the first transparent conductive base layer and the second transparent conductive base layer, and attaching the first transparent conductive base layer and the second transparent conductive base layer which are arranged in an aligned mode by using frame sealing glue. The spacers can ensure a certain thickness between the two transparent conductive base layers and ensure the uniformity of the two transparent conductive base layers. The material of the spacer includes resin, glass fiber, and inorganic material. The shape of the spacers may be spherical, rod-like, or a mixture thereof. The frame sealing glue can be thermosetting glue, such as common epoxy resin; also can be light-cured glue, such as common UV glue; or UV heating of the hybrid glue.

Then, the cholesteric liquid crystal mixture is filled between the first transparent base layer and the second transparent conductive base layer to form a liquid crystal layer. Wherein the cholesteric liquid crystal mixture may include bimesogenic compounds, nematic liquid crystal compounds, and chiral compounds. The general steps of filling are: firstly, preparing a cholesteric liquid crystal mixture according to a certain proportion, and forming uniform liquid in a heating and stirring manner; and cooling to room temperature, and filling the liquid crystal mixture between the two transparent conductive base layers in a vacuum injection mode, a dripping spraying mode or a coating mode. The thickness of the liquid crystal layer is controlled by the size of the spacers, and the range of the thickness is 5-60 micrometers.

And finally, curing and sealing the frame sealing glue to form the bistable dimming device. According to the type of the frame sealing glue, the curing mode can be thermal curing or light curing.

The structure and optical performance of the bistable light modulator will be described in detail with reference to specific embodiments. In the following examples, the first transparent conductive substrate and the second transparent conductive substrate are made of glass/ITO, and the haze in the transmission state and the haze in the fog state are measured by a WGT-S type haze meter.

In the following examples, the formulations of the selected cholesteric liquid crystal mixtures (including bimesogenic compounds, nematic liquid crystal compounds and chiral compounds) are shown in table 1. Wherein, the component proportions are all in mass percent.

Table 1: cholesteric liquid crystal mixture formula

Comparative example

The bistable light modulator in this comparative example comprises first and second transparent conductive base layers, first and second alignment layers, and a liquid crystal layer, wherein the first and second alignment layers are both subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 20 microns, the transparent conductive base layer is made of glass/ITO, and the types of the first alignment layer and the second alignment layer are both VA types. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 2.

TABLE 2 haze in each of the Stable states

Example 1

The bistable light modulator in this embodiment comprises first and second transparent conductive substrates, first and second alignment layers, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment, and the second alignment layer is not subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 20 microns, the transparent conductive base layer is made of glass/ITO, and the types of the first alignment layer and the second alignment layer are both VA types. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 3.

TABLE 3 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	1.04	1.12	1.08	1.23	1.18	1.22	1.09	1.14	1.05	0.079
Fog state	90.05	90.06	90.09	90.03	90.10	90.09	90.07	90.10	90.06	0.024

Example 2

The bistable light modulator in this embodiment comprises first and second transparent conductive substrates, first and second alignment layers, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment, and the second alignment layer is not subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 20 micrometers, the transparent conductive base layer is made of glass/ITO, and the types of the first alignment layer and the second alignment layer are TN types. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 4.

TABLE 4 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	1.96	1.89	2.03	2.10	1.99	1.89	2.13	2.01	2.12	0.091
Fog state	89.86	90.02	89.95	90.10	89.96	89.85	90.08	89.78	90.04	0.111

Example 3

The bistable light modulator in this embodiment comprises first and second transparent conductive substrates, first and second alignment layers, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment, and the second alignment layer is not subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 20 micrometers, the transparent conductive base layer is made of glass/ITO, the type of the first alignment layer is VA type, and the type of the second alignment layer is TN type. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 5.

TABLE 5 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	2.56	2.33	2.68	2.12	2.71	2.28	2.37	2.41	2.19	0.207
Fog state	89.87	89.53	90.12	89.67	90.01	90.05	89.97	89.76	90.11	0.207

Example 4

The bistable light modulator in this embodiment comprises first and second transparent conductive base layers, a first alignment layer, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 20 microns, the transparent conductive base layer is glass/ITO, and the type of the first alignment layer is VA type. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 6.

TABLE 6 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	2.79	2.31	2.23	2.65	2.18	2.56	2.25	2.43	2.36	0.208
Fog state	89.66	90.12	90.21	89.97	90.23	89.87	90.15	90.07	90.17	0.187

Example 5

The bistable light modulator in this embodiment comprises first and second transparent conductive substrates, first and second alignment layers, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment, and the second alignment layer is not subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 6 microns, the transparent conductive base layer is made of glass/ITO, and the types of the first alignment layer and the second alignment layer are both VA types. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 7.

TABLE 7 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	2.21	2.36	2.29	2.58	2.33	2.87	2.09	2.28	2.40	0.228
Fog state	81.17	80.89	81.03	81.34	80.56	81.41	81.18	80.94	80.66	0.289

Example 6

The bistable light modulator in this embodiment comprises first and second transparent conductive substrates, first and second alignment layers, and a liquid crystal layer, wherein the first alignment layer is subjected to rubbing alignment treatment, and the second alignment layer is not subjected to rubbing alignment treatment. The thickness of the liquid crystal layer is 50 microns, the transparent conductive base layer is glass/ITO, and the types of the first alignment layer and the second alignment layer are both VA types. And selecting proper voltage to drive the bistable light modulation device to a transmission state and a fog state. The optical properties of each point were measured by selecting a number of positions on the bistable dimmer device, and the results are shown in table 8.

TABLE 8 haze in each of the Stable states

	1	2	3	4	5	6	7	8	9	Standard deviation of
											Transparent state	4.77	4.39	4.91	4.15	4.17	4.82	4.30	4.67	4.19	0.306
Fog state	92.86	93.08	93.59	92.97	93.22	93.14	93.55	93.11	93.12	0.243

Through the above comparative examples and examples, it can be seen that the bistable light modulator of the present invention can improve the overall uniformity of the optical properties (haze) in two stable states, so that the bistable light modulator has a more uniform and clear transmission state and a more private haze state in use.

Although several exemplary embodiments have been described above in detail, the disclosed embodiments are merely exemplary and not limiting, and those skilled in the art will readily appreciate that many other modifications, adaptations, and/or alternatives are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications, adaptations, and/or alternatives are intended to be included within the scope of the present disclosure as defined by the following claims.

Claims

1. A bistable light modulator comprising a first transparent conductive substrate, a liquid crystal layer, a second transparent conductive substrate, and a first alignment layer having been subjected to an alignment treatment, the first alignment layer being disposed between the first transparent conductive substrate and the liquid crystal layer, wherein the liquid crystal layer comprises a cholesteric liquid crystal mixture, the bistable light modulator comprising two zero-electric-field stable states: a transmissive state in which incident light is substantially directed and a foggy state in which incident light is substantially scattered.

2. The bistable dimming device of claim 1, wherein said cholesteric liquid crystal mixture comprises bimesogenic compounds, nematic liquid crystal compounds and chiral compounds.

3. The bistable dimming device of claim 1, further comprising a second alignment layer without said orientation treatment, said second alignment layer disposed between said second transparent conductive base layer and said liquid crystal layer.

4. A bistable light-adjusting device as claimed in any one of claims 1-3, wherein said orientation treatment comprises rubbing orientation, photo-orientation, evaporation and LB film.

5. A bistable dimming device as claimed in any one of claims 1 to 3, wherein the first and/or second alignment layers are substantially planar or substantially homeotropic.

6. The bistable light modulator of claim 1, wherein said liquid crystal layer has a thickness of 5-60 microns.

7. The bistable dimming device of claim 1, wherein the first transparent conductive base layer and the second transparent conductive base layer comprise a transparent substrate and a transparent electrode, respectively.

8. A method of manufacturing a bistable dimming device as claimed in any one of claims 1 to 7, comprising:

1) arranging a first alignment layer on the inner surface of a first transparent conductive base layer, and performing rubbing orientation on the first alignment layer along a direction, wherein the inner surface of the first transparent conductive base layer is provided with a transparent electrode;

2) aligning the first transparent conductive base layer and the second transparent conductive base layer in a mode that inner surfaces are opposite, wherein the inner surface of the second transparent conductive base layer is provided with a transparent electrode and is not subjected to rubbing orientation;

3) adding a spacer between the first transparent conductive base layer and the second transparent conductive base layer, and attaching the first transparent conductive base layer and the second transparent conductive base layer which are arranged in an aligned manner by using frame sealing glue;

4) filling a cholesteric liquid crystal mixture between the first transparent conductive base layer and the second transparent conductive base layer to form a liquid crystal layer;

5) and curing the seal to form the bistable dimming device.

9. The method of claim 8, wherein the rubbing orientation is by a single sheet intermittent rubbing method or a roll-to-roll continuous rubbing method.

10. The method of claim 8, wherein the inner surface of the second transparent conductive base layer is provided with a second alignment layer that is not subjected to a rubbing orientation process.