A flexible liquid crystal dimming film and its preparation method

Abstract

The present invention discloses a flexible liquid crystal dimming film, which comprises, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment region, a second polyimide layer, and a lower flexible light-transmitting substrate; wherein the first and second polyimide layers contain polymerizable monomers; the adjustment region is filled with a liquid crystal mixture; and the liquid crystal mixture includes polymerizable monomers, negative liquid crystals, and a photoinitiator. The present invention can achieve brightness adjustment of the flexible liquid crystal dimming device by adjusting the magnitude of the applied voltage. Simultaneously, by introducing double-bond or epoxy-structured monomers into the orientation layer, during the photopolymerization process, the monomers in the orientation layer participate in the free radical polymerization or cationic polymerization reaction of the adjustment region material, resulting in a polymer firmly connected to the surfaces of the two light-transmitting substrates, greatly enhancing the adhesion between the polymer network and the interface and significantly improving the film's bending resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal devices, and in particular to a flexible liquid crystal dimming film and a preparation method thereof. Background Art

[0002] Currently, liquid crystal dimming devices are used in high-end buildings, office partitions, and other applications. By controlling the transparent and frosted states of the liquid crystal dimming devices, the path of ambient light is altered. However, traditional liquid crystal dimming devices use glass as a substrate, which is fragile and difficult to install and transport. They are also incompatible with curved windows and some special shapes, making them unsuitable for modern architectural applications. Therefore, flexible liquid crystal dimming films have attracted widespread attention from researchers.

[0003] For flexible liquid crystal dimming films, the problems that need to be solved are: (1) Polyimide is a commonly used vertical alignment layer material. Polyamic acid can be used to obtain a polyimide layer through complete imidization. However, complete imidization of polyamic acid requires a high temperature of more than 200°C, and flexible substrates cannot withstand such high temperatures; (2) The surface of the polyimide alignment layer is not easy to modify, resulting in a weak connection between the interface and the polymer network, weak adhesion, and the polymer network easily falls off the surface when bent.

[0004] In summary, there is an urgent need to develop a new technical solution to improve the performance of flexible liquid crystal dimming films and solve the problems existing in the existing technology. Summary of the Invention

[0005] Based on this, the present invention provides a flexible liquid crystal dimming film and a preparation method thereof. The present invention adds a polymerizable monomer to the polyimide layer as a vertical alignment layer, and adopts a liquid crystal mixture containing a specific negative liquid crystal, a photoinitiator and a polymerizable monomer. The layers can produce good synergistic effects, effectively enhancing the dimming ability of the device, while greatly improving the adhesion on the interface, so that the device has good flexibility.

[0006] One object of the present invention is to provide a flexible liquid crystal dimming film, wherein the structure of the flexible liquid crystal dimming film comprises, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment area, a second polyimide layer, and a lower flexible light-transmitting substrate;

[0007] in,

[0008] The first polyimide layer and the second polyimide layer contain polymerizable monomers;

[0009] The adjustment area is filled with a liquid crystal mixture;

[0010] The liquid crystal mixture includes a polymerizable monomer, a negative liquid crystal and a photoinitiator;

[0011] The polymerizable monomer is selected from one or more of the following structures:

[0012]

[0013] Wherein, m=1-10, n=1-10, X1 and X2 are selected from One of the following;

[0014] The polymerizable monomers in the first polyimide layer, the second polyimide layer and the liquid crystal mixture are the same or different.

[0015] Furthermore, the photoinitiator is selected from One or more of .

[0016] Furthermore, the material of the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate is selected from one of polyethylene terephthalate film, polycarbonate film or polymer film.

[0017] Furthermore, the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate further comprise a conductive layer, and the conductive layer is selected from one of ITO, silver nanowires and polymer conductive layers.

[0018] Furthermore, a spacer is further included between the first polyimide layer and the second polyimide layer, and the spacer is selected from one of a silicon ball spacer and a polystyrene spacer.

[0019] Furthermore, the polyimide is polyimide DL-4018.

[0020] Another object of the present invention is to provide a method for preparing the flexible liquid crystal dimming film, comprising the following steps:

[0021] S1, spin-coating a polyimide solution containing a polymerizable monomer on the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate, respectively, and then performing a heat-curing treatment to obtain a first polyimide layer and a second polyimide layer;

[0022] S2, spraying spacers between the first polyimide layer and the second polyimide layer to obtain an adjustment area;

[0023] S3, filling the adjustment area with a liquid crystal mixture, performing a heating treatment to fully orient the liquid crystal mixture, and then inducing polymerization by ultraviolet light irradiation to obtain the flexible liquid crystal dimming film.

[0024] Furthermore, in step S1, in the solution, the mass ratio of the polymerizable monomer to the polyimide is 0.0001:100-1:10.

[0025] Furthermore, in step S1, the heating and curing treatment is: first treating at 90-110° C. for 1-5 minutes, and then heating to 105-300° C. for 30-120 minutes.

[0026] Furthermore, in step S1, the spin coating speed is 2000-8000 rpm, and the spin coating time is 30-90 s.

[0027] Furthermore, in step S2, the size of the spacer is 5-30 μm.

[0028] Furthermore, in step S3, the liquid crystal mixture contains polymerizable monomers, photoinitiators and negative liquid crystals in a mass ratio of (1-9):(0.1-0.5):(90.5-98.5).

[0029] Furthermore, in step S3, the intensity of the ultraviolet light is 1-50 mW / cm 2 , time is 2-120min.

[0030] Furthermore, in step S3, the negative liquid crystal is selected from at least one of HNG30400-200, HNG60700-200, HNG741200-000, and HTW715600-000.

[0031] The present invention has the following beneficial effects:

[0032] 1. The present invention provides a method for preparing a flexible liquid crystal dimming film. Without changing the polyimide material as a vertical alignment layer, the method utilizes the property of polyamic acid that can still provide vertical alignment for liquid crystal molecules when it is not fully imidized, so that it can form a vertical alignment layer on a flexible substrate. At the same time, the monomer material in the polyimide alignment layer can participate in the polymerization reaction, thereby enhancing the adhesion between the polymer and the interface in the flexible liquid crystal dimming film. When no voltage is applied to the flexible liquid crystal dimming film provided by the present invention, the negative liquid crystal is arranged in a single domain, and the transmittance of light reaches the highest at this time. When a voltage is applied between two flexible transparent substrates, the negative liquid crystal turns in a direction parallel to the flexible transparent substrates. Due to the presence of the polymer network, the negative liquid crystal is randomly arranged under the action of the electric field force and the elastic force of the polymer network, so that the flexible liquid crystal dimming film is converted from a light-transmitting state to a light-scattering state. By adjusting the magnitude of the applied voltage, the brightness and darkness of the flexible liquid crystal dimming device can be adjusted.

[0033] 2. The present invention also introduces monomers containing double bonds or epoxy groups into the polyimide alignment layer, so that during the photopolymerization process, the monomers in the polyimide alignment layer participate in the free radical polymerization reaction or cationic polymerization reaction of the adjustment area material. The generated polymer is firmly connected to the surfaces of the two transparent substrates, which greatly enhances the adhesion between the polymer network and the interface and significantly improves the bending resistance of the film. The device can be bent, which greatly improves the application prospects of flexible liquid crystal dimming films. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic structural diagram of a flexible liquid crystal dimming film is shown;

[0035] in,

[0036] Figure 1 A is a schematic diagram of the structure of the flexible liquid crystal dimming film when no electric field is applied;

[0037] Figure 1 B is a schematic diagram of the structure of the flexible liquid crystal dimming film after an electric field is applied.

[0038] Figure 2 Shown is an electron microscope image of the polymer network in the flexible liquid crystal dimming film.

[0039] Figure 3 A physical diagram of the device bending in the switching state of the flexible liquid crystal dimming film is shown.

[0040] Figure 4 The electron microscope images of the polyimide layer and polymer network of Comparative Example 1 are shown.

[0041] Figure 5 The transmittance change diagram of the embodiment and the comparative example after bending is shown.

[0042] Figure numerals: 1-upper substrate; 11-upper flexible light-transmitting substrate; 12-ITO electrode; 13-first polyimide layer; 2-lower substrate; 21-lower flexible light-transmitting substrate; 22-ITO electrode; 23-second polyimide layer; 3-negative liquid crystal; 4-polymer network. DETAILED DESCRIPTION

[0043] In order to more clearly illustrate the technical solutions of the present invention, the following examples are given. Unless otherwise stated, the raw materials, reactions and post-processing methods mentioned in the examples are common raw materials on the market and technical methods well known to those skilled in the art.

[0044] The terms "preferred," "preferably," "more preferred," and the like, used herein, refer to embodiments of the invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[0045] It should be understood that, except in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties to be obtained by the present invention.

[0046] The flexible light-transmitting substrate material in the embodiment of the present invention is polyethylene terephthalate film.

[0047] The flexible light-transmitting substrate in the embodiment of the present invention includes a conductive layer, and the conductive layer is an ITO electrode.

[0048] The spacer material in the embodiment of the present invention is a silicon sphere spacer.

[0049] Example 1

[0050] A flexible liquid crystal dimming film, the structure of the flexible liquid crystal dimming film comprises, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment area, a second polyimide layer, and a lower flexible light-transmitting substrate;

[0051] in,

[0052] The first polyimide layer and the second polyimide layer contain polymerizable monomers;

[0053] The mass ratio of the polymerizable monomer to the polyimide DL-4018 in the first polyimide layer and the second polyimide layer is 1:1000;

[0054] The adjustment area is filled with a liquid crystal mixture;

[0055] The liquid crystal mixture includes a polymerizable monomer, a negative liquid crystal and a photoinitiator;

[0056] The structural formula of the polymerizable monomer is

[0057]

[0058] The negative liquid crystal is HNG30400-200;

[0059] The photoinitiator is

[0060] In the liquid crystal mixture, the mass ratio of the polymerizable monomer, the photoinitiator and the negative liquid crystal is 3:0.2:96.8.

[0061] The method for preparing the flexible liquid crystal dimming film comprises the following steps:

[0062] S1. Spin-coating a polyimide solution containing a polymerizable monomer on the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate (spin coating speed is 2500 rpm, and the spin coating time is 60 s), respectively, and then placing them on a hot plate at 90° C. for 1 min, and then heating to 150° C. and placing them on a hot plate for 90 min to obtain a first polyimide layer and a second polyimide layer;

[0063] S2, spraying spacers between the first polyimide layer and the second polyimide layer to obtain an adjustment area;

[0064] S3, the liquid crystal mixture was heated to 60 ° C and filled into the adjustment area, and then kept warm on a 60 ° C hot plate for 30 minutes, and then heated at 27 mW / cm 2 The flexible liquid crystal dimming film was obtained by irradiating the flexible liquid crystal dimming film with ultraviolet light for 5 minutes.

[0065] Figure 1 A schematic structural diagram of a flexible liquid crystal dimming film is shown;

[0066] in,

[0067] Figure 1 A is a schematic diagram of the structure of the flexible liquid crystal dimming film when no electric field is applied;

[0068] Figure 1 B is a schematic diagram of the structure of the flexible liquid crystal dimming film after an electric field is applied.

[0069] Figure numerals: 1-upper substrate; 11-upper flexible light-transmitting substrate; 12-ITO electrode; 13-first polyimide layer; 2-lower substrate; 21-lower flexible light-transmitting substrate; 22-ITO electrode; 23-second polyimide layer; 3-negative liquid crystal; 4-polymer network.

[0070] according to Figure 1 It can be seen that when no electric field is applied, the negative liquid crystal molecules are vertically oriented under the action of the polyimide layer containing monomer materials and the polymer network. At the same time, the monomer material in the orientation layer will also induce free radical polymerization and connect with the polymer network. After the electric field is applied, the negative liquid crystal molecules tend to align parallel to the substrate direction under the action of the electric field. Due to the restriction of the polymer network, the negative liquid crystal molecules are randomly arranged in the box.

[0071] Figure 2 Shown is an electron microscope image of the polymer network in the flexible liquid crystal dimming film.

[0072] according to Figure 2 It can be seen that the polyimide layer containing monomer material connects the polymer network to the upper and lower substrates, significantly enhancing the interfacial adhesion, so that the device can be bent.

[0073] Figure 3 A physical diagram of the device bending in the switching state of the flexible liquid crystal dimming film is shown.

[0074] Example 2

[0075] A flexible liquid crystal dimming film, the structure of the flexible liquid crystal dimming film comprises, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment area, a second polyimide layer, and a lower flexible light-transmitting substrate;

[0076] in,

[0077] The first polyimide layer and the second polyimide layer contain polymerizable monomer 1;

[0078] The mass ratio of the polymerizable monomer 1 to the polyimide DL-4018 in the first polyimide layer and the second polyimide layer is 1:500;

[0079] The structural formula of the polymerizable monomer 1 is

[0080]

[0081] The adjustment area is filled with a liquid crystal mixture;

[0082] The liquid crystal mixture includes a polymerizable monomer 2, a negative liquid crystal and a photoinitiator;

[0083] The structural formula of the polymerizable monomer 2 is

[0084]

[0085] The negative liquid crystal is HTW715600-000;

[0086] The photoinitiator is

[0087] In the liquid crystal mixture, the mass ratio of the polymerizable monomer 2, the photoinitiator and the negative liquid crystal is 8:0.5:96.8.

[0088] The method for preparing the flexible liquid crystal dimming film comprises the following steps:

[0089] S1. Spin-coating a polyimide solution containing a polymerizable monomer on the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate (spin-coating speed is 2500 rpm, and the spin-coating time is 60 s), respectively, and then placing on a 90° C. hot stage for 1 min, and then heating to 170° C. and placing for 100 min to obtain a first polyimide layer and a second polyimide layer;

[0090] S2, spraying spacers between the first polyimide layer and the second polyimide layer to obtain an adjustment area;

[0091] S3, the liquid crystal mixture was heated to 60 ° C and filled into the adjustment area, and then kept warm on a 60 ° C hot plate for 30 minutes, and then heated at 20 mW / cm 2 The flexible liquid crystal dimming film was obtained by irradiating the flexible liquid crystal dimming film with ultraviolet light for 90 minutes.

[0092] Comparative Example 1

[0093] A flexible liquid crystal dimming film, the structure of the flexible liquid crystal dimming film comprises, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment area, a second polyimide layer, and a lower flexible light-transmitting substrate;

[0094] in,

[0095] The first polyimide layer and the second polyimide layer are made of polyimide DL-4018;

[0096] The adjustment area is filled with a liquid crystal mixture;

[0097] The liquid crystal mixture includes a polymerizable monomer, a negative liquid crystal and a photoinitiator;

[0098] The structural formula of the polymerizable monomer is

[0099]

[0100] The negative liquid crystal is HNG30400-200;

[0101] The photoinitiator is

[0102] In the liquid crystal mixture, the mass ratio of the polymerizable monomer, the photoinitiator and the negative liquid crystal is 3:0.2:96.8.

[0103] The method for preparing the flexible liquid crystal dimming film comprises the following steps:

[0104] S1. Spin-coating a polyimide solution on the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate (spin coating speed is 2500 rpm, and the spin coating time is 60 s), respectively, and then placing them on a 90° C. hot stage for 1 min, and then heating to 150° C. and placing them on a hot stage for 90 min to obtain a first polyimide layer and a second polyimide layer;

[0105] S2, spraying spacers between the first polyimide layer and the second polyimide layer to obtain an adjustment area;

[0106] S3, the liquid crystal mixture was heated to 60 ° C and filled into the adjustment area, and then kept warm on a 60 ° C hot plate for 30 minutes, and then heated at 27 mW / cm 2 The flexible liquid crystal dimming film was obtained by irradiating the flexible liquid crystal dimming film with ultraviolet light for 5 minutes.

[0107] Figure 4 The electron microscope images of the polyimide layer and polymer network of Comparative Example 1 are shown.

[0108] according to Figure 4 It can be seen that when no electric field is applied, the negative liquid crystal molecules are vertically aligned under the action of the polyimide layer and the polymer network, but the connection ability between the polymer network and the substrate is weak.

[0109] Test Case

[0110] The performance tests were performed on the flexible liquid crystal dimming films prepared in the examples and comparative examples.

[0111] Test method:

[0112] The flexible liquid crystal dimming films of Examples 1-2 and Comparative Example 1 were bent five times, and then the transmittance of the devices was tested.

[0113] The test results are shown in Table 1 and Figure 5 As shown:

[0114] Table 1 Performance test results

[0115]

[0116] Figure 5 The transmittance change diagram of the embodiment and the comparative example after bending is shown.

[0117] According to Table 1 and Figure 5 It can be concluded that the transmittance of the flexible liquid crystal dimming films in Examples 1-2 did not change significantly after multiple flexing. This is primarily due to the adhesion of the polymer network to the substrate, which enhanced the interfacial adhesion. In contrast, after a single flexing, the transmittance of the sample in Comparative Example 1 decreased due to the detachment of the polymer network from the substrate, resulting in a mismatch between the refractive index of the liquid crystal molecules and that of the polymer network. These results demonstrate that the present invention exhibits excellent flex resistance and dimming performance.

[0118] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0119] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A flexible liquid crystal dimming film, characterized in that: The structure of the flexible liquid crystal dimming film includes, from top to bottom, an upper flexible light-transmitting substrate, a first polyimide layer, an adjustment area, a second polyimide layer, and a lower flexible light-transmitting substrate; in, The first polyimide layer and the second polyimide layer contain polymerizable monomers; The adjustment area is filled with a liquid crystal mixture; The liquid crystal mixture includes a polymerizable monomer, a negative liquid crystal and a photoinitiator; The polymerizable monomer is selected from one or more of the following structures: Wherein, m=1-10, n=1-10, X1 and X2 are simultaneously selected from One of the following; The polymerizable monomers in the first polyimide layer, the second polyimide layer and the liquid crystal mixture are the same or different; The material of the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate is selected from one of polymer films; The method for preparing the flexible liquid crystal dimming film comprises the following steps: S1, spin-coating a polyimide solution containing a polymerizable monomer on the upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate, respectively, and then performing a heat-curing treatment to obtain a first polyimide layer and a second polyimide layer; S2, spraying spacers between the first polyimide layer and the second polyimide layer to obtain an adjustment area; S3, filling the adjustment area with a liquid crystal mixture, heating the adjustment area, and then irradiating the adjustment area with ultraviolet light to obtain the flexible liquid crystal dimming film; The photoinitiator is selected from One or more of; The upper flexible light-transmitting substrate and the lower flexible light-transmitting substrate further comprise a conductive layer, wherein the conductive layer is selected from one of ITO, silver nanowires and polymer conductive layers; The spacer is selected from one of a silicon sphere spacer and a polystyrene spacer; In step S1, the heating and curing treatment is: first treating at 90-110° C. for 1-5 minutes, and then heating to 105-300° C. for 30-120 minutes.

2. The flexible liquid crystal dimming film according to claim 1, characterized in that: In step S1, in the solution, the mass ratio of the polymerizable monomer to the polyimide is 0.0001:100-1:

10.

3. The flexible liquid crystal dimming film according to claim 1, characterized in that: In step S3, the liquid crystal mixture contains a polymerizable monomer, a photoinitiator, and a negative liquid crystal in a mass ratio of (1-9):(0.1-0.5):(90.5-98.5).

4. The flexible liquid crystal dimming film according to claim 1, characterized in that: In step S3, the intensity of the ultraviolet light is 1-50 mW / cm 2 , time is 2-120min.

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