Normally-on flexible liquid crystal dimming film and preparation method thereof

Abstract

The invention relates to the technical field of liquid crystal devices, and particularly discloses a normally-on flexible liquid crystal dimming film and a preparation method thereof. The structure of the normally-on flexible liquid crystal dimming film sequentially comprises a first flexible transparent substrate, a first vertical alignment layer, a dye liquid crystal layer, a second vertical alignment layer and a second flexible transparent substrate from top to bottom, wherein the materials of the first vertical alignment layer and the second vertical alignment layer are selected from side chain type transparent polyimide materials; the dye liquid crystal layer comprises black dichroic dye and negative phase liquid crystal. By accurately controlling the orientation arrangement of liquid crystal molecules, a high-precision pretilt angle is realized, the light modulation amplitude in a visible light broadband range reaches 45% or above, and the photoelectric property is equivalent to that of a normally dark (forward) mode liquid crystal dimming film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid crystal devices, in particular to a constant-brightness flexible liquid crystal dimming film, and a preparation method thereof. BACKGROUND

[0002] The liquid crystal dimming film is a functional film based on the photoelectric properties of liquid crystals, which can change the arrangement state of liquid crystal molecules by applying voltage, thereby realizing dynamic regulation of light transmittance. The existing liquid crystal dimming film is mainly divided into two categories of polymer liquid crystal dimming film and guest-host liquid crystal dimming film according to the material system; and is mainly divided into constant-dark mode and constant-brightness mode according to the display mode. Unlike the polymer liquid crystal dimming film which presents a hazy light transmission in the dark state, the guest-host liquid crystal dimming film can maintain transparency in both bright and dark states, so it has a broader application prospect in the fields of vehicle windows, rail transit and aviation transparent parts.

[0003] In the face of the technical needs of green development and the natural pursuit of environmental comfort, the demand for dimming glass in the fields of civil buildings, vehicle sunroofs, rail transit windows, military ships, aviation transparent parts and the like is increasing. However, the current guest-host liquid crystal dimming film is mostly based on inorganic glass as the substrate, and usually adopts a constant-dark mode design, which needs to be continuously powered to maintain the transparent state in the use process, resulting in high energy consumption and great safety hazards. On the other hand, the rigid characteristics of the inorganic glass substrate limit its application in curved dimming windows, and it is difficult to meet the demand for flexible and lightweight materials in modern transportation tools and building design.

[0004] The constant-brightness flexible liquid crystal dimming film maintains a natural transparent state when powered off, and becomes opaque only when powered on, which is both energy-saving and safe. At the same time, the use of flexible substrates enables it to perfectly fit various curved structures. However, the existing constant-brightness flexible dimming film has a small light modulation amplitude in a specific waveband range, but a small light modulation amplitude in a wide visible light waveband range. Therefore, developing a constant-brightness liquid crystal dimming film with a wide waveband and high light modulation amplitude suitable for flexible substrates has become a key problem to be solved. SUMMARY

[0005] To overcome the above problems, the present application provides a constant-brightness flexible liquid crystal dimming film, which realizes a high-precision pre-tilt angle by precisely controlling the orientation and arrangement of liquid crystal molecules, and has photoelectric performance comparable to that of a constant-dark (forward) mode liquid crystal dimming film.

[0006] In addition, the present application also provides a preparation method of the constant-brightness flexible liquid crystal dimming film.

[0007] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions: In a first aspect, the present application provides a constant brightness flexible liquid crystal dimming film, the structure of the constant brightness flexible liquid crystal dimming film comprises, from top to bottom, a first flexible transparent substrate, a first vertical alignment layer, a dye liquid crystal layer, a second vertical alignment layer and a second flexible transparent substrate. The material of the first vertical alignment layer and the second vertical alignment layer is selected from a side-chain type transparent polyimide material, the curing temperature of the side-chain type transparent polyimide material is ≤ 150℃, and the side chain comprises at least one of an alkane chain, an alicyclic group, a fluorinated alkyl group or an aromatic group. The dye liquid crystal layer comprises black dichroic dye and negative phase liquid crystal; the black dichroic dye is selected from at least one of Licristar XHR-300K, OrgaSol Black K12 and Kayaset B-SHD; or, the black dichroic dye comprises at least one orange dye, at least one red dye and at least one blue dye; the dichroic ratio of the black dichroic dye is ≥ 12; the light bright point temperature of the negative phase liquid crystal is ≥ 85℃, and the dielectric anisotropy △ε at 1KHz frequency and 25℃ is -10~ -1.

[0008] The present application adopts a composite system of high dichroic ratio black dye and negative phase liquid crystal, realizes wide-band light absorption regulation through the synergistic effect of different absorption effects of the dichroic dye in different axial directions and the negative dielectric property of the liquid crystal. At the same time, the side-chain type transparent polyimide material vertical alignment layer can form a precisely controllable alignment field on the surface of the flexible organic substrate, induce the liquid crystal molecules to form an arrangement structure nearly perpendicular to the substrate, and make the dye molecules present an optimal orientation in the off state, so as to obtain high transmittance and reduce the driving threshold; after power-on, the electric field drives the liquid crystal molecules to arrange horizontally, and then drives the dye molecules to turn synchronously, and based on the flexible organic transparent material, high-efficiency light modulation is realized. The constant brightness flexible organic liquid crystal dimming film provided by the present application not only ensures the light modulation amplitude effect in a wide spectral range (450~650nm), but also can realize the dimming product in a curved configuration, greatly widening the application range.

[0009] Preferably, the black dichroic dye comprises an anthraquinone type orange dye, an anthraquinone type red dye and an anthraquinone type blue dye.

[0010] Further preferably, the black dichroic dye is composed of the following components in mass percentage: 20~60wt% of anthraquinone type orange dye, 20~60wt% of anthraquinone type red dye and 20~60wt% of anthraquinone type blue dye.

[0011] The anthraquinone type orange dye, the anthraquinone type red dye and the anthraquinone type blue dye all comprise a structural formula shown in formula (I): (I).

[0012] In the case of the anthraquinone orange dye of formula (I), the substituents R1, R4, R5, R8 are each independently selected from the group consisting of a hydrogen atom, a hydroxyl group or a halogen, and R2, R3, R6, R7 are each independently selected from the group consisting of a substituent A or a hydrogen atom; the substituent A has the following formula (II): (II); In formula (II), j is 0 or 1; k is an integer and 0≤k≤25.

[0013] Preferably, the anthraquinone orange dye has the following formula (III): (III); In formula (III), k is an integer and 0≤k≤25.

[0014] In the case of the anthraquinone red dye of formula (I), the substituents R1, R4, R5, R8 are each independently selected from the group consisting of a hydrogen atom, a hydroxyl group or a halogen, and R2, R3, R6, R7 are each independently selected from the group consisting of a substituent A or a hydrogen atom; the substituent A has the following formula (II): (II); In formula (II), j is 0 or 1; k is an integer and 0≤k≤25.

[0015] Preferably, the anthraquinone red dye has the following formula (IV): (IV); In formula (IV), k is an integer and 0≤k≤25.

[0016] In the case of the anthraquinone blue dye of formula (I), the substituents R1, R5 are each independently selected from the group consisting of a hydrogen atom, a hydroxyl group, an amino group, a nitro group or a halogen; R4, R8 are each independently selected from the group consisting of a hydrogen atom, a hydroxyl group, an amino group, a nitro group, a halogen or a substituent C; R2, R3, R6, R7 are each independently selected from the group consisting of a substituent D or a hydrogen atom; the substituent C has the following formula (V): (V); In formula (V), m is 0 or 1; n is an integer and 0≤n≤25.

[0017] The substituent D has the following formula (VI): (VI); In formula (VI), x is 0 or 1; y is 0 or 1; z is an integer and 0≤z≤25.

[0018] Preferably, the anthraquinone blue dye has the following formula (VII): (Ⅶ); In formula (Ⅶ), z is an integer, and 0≤z≤25, n is an integer, and 0≤n≤25.

[0019] Further preferably, in the black dichroic dye, the anthraquinone type orange dye has a structural formula as shown in formula (1), the anthraquinone type red dye has a structural formula as shown in formula (2), and the anthraquinone type blue dye has a structural formula as shown in formula (3): (1); (2); (3).

[0020] Preferably, the black dichroic dye and the negative phase liquid crystal form a mixture, wherein the concentration of the black dichroic dye is 0.1-1wt%.

[0021] Preferably, the material of the first flexible transparent substrate and the second flexible transparent substrate is selected from polyethylene terephthalate film, polyimide film or inorganic glass with a thickness of 0.1-0.7mm and a square resistance of 5-30Ω / □.

[0022] Preferably, the surface of the first flexible transparent substrate and the second flexible transparent substrate is provided with a conductive layer.

[0023] Preferably, the conductive layer is selected from one of ITO film, silver nanowire or polymer conductive layer.

[0024] Preferably, microbeads are distributed between the first vertical alignment layer and the second vertical alignment layer, the dye liquid crystal layer is filled in the gap between the microbeads, the diameter of the microbeads is 5-25μm, and the distribution density is 30-50g / m².

[0025] The present application controls the size and distribution density of the microbeads, ensures the uniformity of the substrate spacing, provides a stable arrangement space for the liquid crystal molecules, effectively prevents the deformation of the substrate under pressure, improves the bending resistance of the light modulation film, and is suitable for various bending application scenarios.

[0026] Preferably, the microbeads are selected from silica microbeads and / or polystyrene microbeads.

[0027] Preferably, the thickness of the first vertical alignment layer and the second vertical alignment layer is 1-20μm, and the liquid crystal pre-tilt angle under zero electric field is 89-90°.

[0028] Preferably, the glass transition temperature (Tg) of the film formed by the side chain type transparent polyimide material is 200-300℃. Tg≥160℃, dielectric constant is 2-3@1 kHz, dielectric loss is 0.001-0.003.

[0029] Preferably, the side chain type transparent polyimide material can be selected from commercially available polyimide materials, such as SVT series of Upilex® of Ube Industries, LF series of Pyralux® of DuPont, PIXEO TM OP-1000, CPI of Kolon Industries TM -100F, DL-4000 series of Dalton Electronic Materials Co., Ltd., etc., but not limited to these materials.

[0030] Preferably, the negative liquid crystal can be selected from commercially available liquid crystal materials, such as HNG30400-200, HNG30900-100 and HNG30500-100 of Jiangsu Hengxin New Material Co., Ltd., SLC10V323-000, SLC10V321-200 and SLC10V321-400 of Yongshenghuaqing Liquid Crystal Material Co., Ltd., BHR22400-000 and BHR22500-000 of Beijing Bihui Shikong Liquid Crystal Technology Co., Ltd., etc., but not limited to these materials.

[0031] In a second aspect, the present application provides a preparation method of the above-mentioned constant-brightness flexible liquid crystal dimming film, comprising the following steps: S1. Coating a side chain type transparent polyimide material on the inner side (i.e. the side opposite to the other substrate and used for forming a liquid crystal dye layer) surface of the first flexible transparent substrate and the second flexible transparent substrate respectively, and then performing a curing treatment to obtain a first flexible transparent substrate with a first vertical alignment layer on the surface and a second flexible transparent substrate with a second vertical alignment layer on the surface; S2. Performing a rubbing treatment on the first vertical alignment layer surface of the first flexible transparent substrate and the second vertical alignment layer surface of the second flexible transparent substrate treated in step S1, and cleaning; wherein the roller angle is 45°±20', the roller shaft rotation speed is 800-1200 rpm, and the rubbing frequency is 2-10 times; S3. Spraying microbeads on the first vertical alignment layer surface of the first flexible transparent substrate and the second vertical alignment layer surface of the second flexible transparent substrate treated in step S2 respectively, and the microbead distribution density is 30-50 g / m²; S4. Coating a sealant on the four peripheral edges of the first flexible transparent substrate and the second flexible transparent substrate treated in step S3 respectively, and performing a heat pressing and curing composite treatment to obtain a liquid crystal cell with a cavity in the middle; S5. Filling the mixture of the black dichroic dye and the negative phase liquid crystal into the cavity of the liquid crystal cell treated in step S4 to form a dye liquid crystal layer, obtaining the constant light flexible liquid crystal dimming film.

[0032] The present application adopts a low-temperature curing process to prepare a polyimide vertical alignment layer on a flexible substrate, realizes high uniformity and stability of the alignment layer by precisely controlling the rubbing process parameters and the distribution density of microbeads. On this basis, an optimized vacuum filling process is used to complete the uniform filling of the liquid crystal material, and ensures that the cell thickness tolerance is controlled within ±0.5 μm. The whole preparation process is compatible with the existing liquid crystal display production line, and can realize large-scale production.

[0033] Preferably, in step S1, the temperature of the curing treatment is 120-150°C, and the curing treatment time is 1-3h.

[0034] Preferably, the coating method is selected from the group consisting of coating, mask printing and letterpress printing.

[0035] Preferably, in step S4, the temperature of the hot-pressing curing composite treatment is 70-100°C, and the time is 0.5-1h.

[0036] In summary, compared with the prior art, the present application has the following beneficial effects: The constant light flexible liquid crystal dimming film provided by the present application realizes a high-precision pre-tilt angle of 89-90° by precisely controlling the orientation and arrangement of liquid crystal molecules, the light modulation amplitude reaches more than 45% in a wide band (450-650nm) of visible light, and the photoelectric performance is comparable to that of a constant dark (positive) mode liquid crystal dimming film. Secondly, the optimized structure design reduces the driving voltage threshold to below 15V, greatly reducing the energy consumption. The preparation process is simple, and the existing liquid crystal cell production line can be used for production, which is conducive to large-scale popularization and application. At the same time, the flexible dimming film is not only suitable for planar shapes, but also can be applied to curved surfaces, and has a wide application prospect in the fields of vehicle-mounted, rail transit and aviation transparent parts. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a structure schematic diagram of the constant light flexible liquid crystal dimming film prepared in Example 1 of the present application; Figure 2 is a process flow diagram for preparing the constant light flexible liquid crystal dimming film in Example 1 of the present application; Figure 3 is a pre-tilt angle data diagram of the constant light flexible liquid crystal dimming film prepared in Examples 1-3 of the present application; Figure 4 is a transmittance-wavelength curve diagram of the constant light flexible liquid crystal dimming film prepared in Examples 1-3 of the present application. DETAILED DESCRIPTION

[0038] The present application now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the application are shown. Like numbers refer to like elements throughout. Well-known structures have not been described in detail in order to avoid obscuring the present application. This application can take form in various specific implementations as described and claimed.

[0039] Before further description of the application, it is understood that the application is not limited in scope to the specific embodiments described herein; and that various modifications and changes can be made thereto without departing from the spirit and scope of the application.

[0040] When numerical ranges are given, understand that the range is inclusive of the two endpoints and any number in between, unless otherwise specified. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0041] The side chain type transparent polyimide material used in the embodiments of the present application is a side chain connected to the main chain of diamine monomer through methylene, ether bond or direct connection, which can be obtained by commercial means or synthesized according to known methods.

[0042] It should be noted that the embodiments are only an example of implementation, and any black dichroic dye, negative liquid crystal, and side chain type transparent polyimide material that meets the above performance requirements are suitable for the present application.

[0043] Embodiment 1 The present embodiment provides a constant light flexible liquid crystal dimming film, the structure is as shown in Figure 1 The first layer 1 is a first flexible transparent substrate, the second layer 2 is a first vertical alignment layer, the third layer 3 is a dye liquid crystal layer, the fourth layer 4 is a second vertical alignment layer, and the fifth layer 5 is a second flexible transparent substrate.

[0044] The inner side surface (i.e. the side opposite to the other substrate and used for forming the liquid crystal dye layer) of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 is provided with a conductive layer formed by magnetron sputtering ITO film on the surface of the substrate; the material of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 is selected from polyethylene terephthalate film (PET film, square resistance 30Ω / □).

[0045] The thickness of the first vertical alignment layer 2 and the second vertical alignment layer 4 is 8μm, and the material is selected from Upilex®-SVT-F of Ube, and the curing temperature is 130℃, Tg= 165℃, dielectric constant = 2.8@1 kHz, dielectric loss is 0.002@1 kHz. The polystyrene microbeads are evenly distributed between the first vertical alignment layer 2 and the second vertical alignment layer 4, the diameter of the microbeads is 6 μm, and the distribution density is 30 g / m².

[0046] The dye liquid crystal layer 3 comprises black dichroic dye and negative phase liquid crystal, and the concentration of the black dichroic dye in the mixture formed by the black dichroic dye and the negative phase liquid crystal is 0.5 wt%.

[0047] The black dichroic dye is a self-made dye, which comprises an anthraquinone type orange dye as shown in formula (1), an anthraquinone type red dye as shown in formula (2), and an anthraquinone type blue dye as shown in formula (3), wherein the mass percentage of the anthraquinone type orange dye, the anthraquinone type red dye, and the anthraquinone type blue dye is 30%, 30%, and 40%, respectively. (1); (2); (3).

[0048] The clearing point temperature of the negative phase liquid crystal is 85℃, and the dielectric anisotropy △ε at 1 kHz and 25℃ is -5. The negative phase liquid crystal is selected from HNG30400-200.

[0049] The preparation method of the constant-brightness flexible liquid crystal dimming film provided in the embodiment is shown in the process flow as shown in Figure 2 The preparation method of the constant-brightness flexible liquid crystal dimming film provided in the embodiment is shown in the process flow as shown in (1) A transparent substrate is prepared, and an ITO thin film is prepared on the inner side surface (the side which will be opposite to the other substrate in the subsequent process) of the transparent substrate by magnetron sputtering to form a conductive layer, thereby obtaining a first flexible transparent substrate and a second flexible transparent substrate; (2) A transparent polyimide material containing a phenyl side chain is spin-coated on the inner side surface (the side which will be opposite to the other substrate in the subsequent process) of the first flexible transparent substrate and the second flexible transparent substrate, respectively, at a spin-coating speed of 500 rpm, a spin-coating time of 8 s, and an acceleration of 100 rpm / s, and then cured at 130℃ for 1.5 h to form a first vertical alignment layer on the surface of the first flexible transparent substrate and a second vertical alignment layer on the surface of the second flexible transparent substrate; (3) The first flexible transparent substrate and the second flexible transparent substrate treated in step (2) are placed on a rubbing machine, and the surface of the first vertical alignment layer and the surface of the second vertical alignment layer are subjected to rubbing treatment. The angle of the roller is adjusted to 45°, the roller shaft rotates at a speed of 1200 rpm, and the roller shaft rolls from one side of the substrate to the other side for 2 times. Then, the rubbed substrate is cleaned in an ultrasonic cleaning machine filled with ultrapure water for 10 min. (4) Dissolve the microbeads with a diameter of 6 μm in an ethanol solution at a mass fraction of 5 wt%, and fill into a spraying machine. Fix the first flexible transparent substrate and the second flexible transparent substrate treated in step (3) and checked to be qualified on the spraying machine, and start the spraying machine to spray the prepared microbead ethanol solution on the surfaces of the first vertical alignment layer and the second vertical alignment layer. After completion, detect the interval bead spraying density by a spraying density detector, and the distribution density is 30 g / m2. (5) Use silk screen printing to coat a sealant with a width of about 5 mm at the periphery of the first flexible transparent substrate and the second flexible transparent substrate treated in step (4) at a distance of ≤10 mm from the edge; place the first flexible transparent substrate and the second flexible transparent substrate completed in production in the hot press for curing and compounding by aligning the alignment marks, the curing temperature is 80 °C, and the time is 0.5 h, to obtain a liquid crystal cell with a cavity in the middle. (6) Place the liquid crystal cell in an injection tank, and then introduce nitrogen into the injection tank; subsequently, use a vacuum pump to make the vacuum in the injection tank be 1 x 10 -2 Pa. After vacuumizing, immerse the liquid crystal cell in a dye liquid crystal (i.e. a mixture of black dichroic dye and negative phase liquid crystal) pool, so that the liquid surface covers the liquid crystal cell and is injected, and after the cavity of the liquid crystal cell is filled with the dye liquid crystal, close the vacuum, and charge, to obtain a constant-brightness flexible liquid crystal dimming film.

[0050] Example 2 This example provides a constant-brightness flexible liquid crystal dimming film, the structure of which is shown in Figure 1 and includes five layers of materials stacked in sequence, the first layer 1 is a first flexible transparent substrate, the second layer 2 is a first vertical alignment layer, the third layer 3 is a dye liquid crystal layer, the fourth layer 4 is a second vertical alignment layer, and the fifth layer 5 is a second flexible transparent substrate.

[0051] The inner side surfaces (i.e. the side opposite to the other substrate and used for forming the liquid crystal dye layer) of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 are each provided with a conductive layer formed by magnetron sputtering ITO film on the substrate surface; the materials of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 are selected from polyethylene terephthalate film (PET film, square resistance 10 Ω / □).

[0052] The thicknesses of the first vertical alignment layer 2 and the second vertical alignment layer 4 are both 12 μm, and the materials are selected from Pyralux® LF-031 of DuPont, the curing temperature is 140 °C, Tg = 170 °C, the dielectric constant = 2.6 @ 1 kHz, and the dielectric loss is 0.0015 @ 1 kHz. The first vertical alignment layer 2 and the second vertical alignment layer 4 are uniformly distributed with polystyrene microbeads, the diameter of the microbeads is 10 μm, and the distribution density is 40 g / m2.

[0053] The dye liquid crystal layer 3 comprises black dichroic dye and negative phase liquid crystal; the black dichroic dye comprises at least one orange dye, at least one red dye and at least one blue dye, and the dichroic ratio is ≥12; the concentration of the black dichroic dye in the mixture formed by the black dichroic dye and the negative phase liquid crystal is 1wt%.

[0054] The black dichroic dye is a self-made dye, which comprises an anthraquinone type orange dye as shown in formula (1), an anthraquinone type red dye as shown in formula (2) and an anthraquinone type blue dye as shown in formula (3), wherein the mass percentage of the anthraquinone type orange dye, the anthraquinone type red dye and the anthraquinone type blue dye is 30%, 30% and 40% respectively. (1); (2); (3).

[0055] The clearing point temperature of the negative phase liquid crystal is 88℃, and the dielectric anisotropy △ε is -3.2 at a frequency of 1KHz and a temperature of 25℃. The negative phase liquid crystal is selected from HNG30900-100.

[0056] The preparation method of the constant-brightness flexible liquid crystal dimming film provided in the embodiment comprises the following steps: (1) A transparent substrate is prepared, and an ITO thin film is prepared on the inner side surface (the side which will be opposite to the other substrate in the future) of the transparent substrate by magnetron sputtering to prepare a conductive layer, so as to obtain a first flexible transparent substrate and a second flexible transparent substrate; (2) A transparent polyimide material containing a dodecyl side chain is spin-coated on the inner side surface (the side which will be opposite to the other substrate in the future) of the first flexible transparent substrate and the second flexible transparent substrate respectively, the spin-coating speed is 1000rpm, the spin-coating time is 5s, the acceleration is 100rpm / s, and then the first flexible transparent substrate is cured at 140℃ for 2h to form a first vertical alignment layer on the surface of the first flexible transparent substrate, and the second flexible transparent substrate is cured at 140℃ for 2h to form a second vertical alignment layer on the surface of the second flexible transparent substrate; (3) The first flexible transparent substrate and the second flexible transparent substrate treated in step (2) are placed on a rubbing machine, and the surface of the first vertical alignment layer and the surface of the second vertical alignment layer are subjected to rubbing treatment, the angle of the roller is adjusted to 45°, the roller shaft rotates at a speed of 1200rpm, the roller shaft rolls from one side of the substrate to the other side, and the rubbing is performed for 5 times; then the rubbed substrate is placed in an ultrasonic cleaning machine filled with ultrapure water for cleaning, and the cleaning time is 10min; (4) Dissolve microbeads with a diameter of 10 μm in an ethanol solution at a mass fraction of 5 wt%, and fill into a spraying machine. Fix the first flexible transparent substrate and the second flexible transparent substrate treated in step (3) and checked to be qualified on the spraying machine, and start the spraying machine to spray the prepared microbead ethanol solution on the surfaces of the first vertical alignment layer and the second vertical alignment layer. After completion, detect the interval bead spraying density by a spraying density detector, and the distribution density is 40 g / m2; (5) Use silk screen printing to coat a sealant with a width of about 5 mm at a distance of ≤10 mm from the edge of the first flexible transparent substrate and the second flexible transparent substrate treated in step (4); place the first flexible transparent substrate and the second flexible transparent substrate completed in production in a hot press for curing and compounding by alignment with the alignment marks, and the curing temperature is 80 °C and the time is 0.5 h, to obtain a liquid crystal cell with a cavity in the middle; (6) Place the liquid crystal cell in an injection tank, and then introduce nitrogen into the injection tank; then, use a vacuum pump to make the vacuum in the injection tank be 1 x 10 -2 Pa, and after vacuum extraction, immerse the liquid crystal cell in a dye liquid crystal (i.e. a mixture of black dichroic dye and negative phase liquid crystal) pool, so that the liquid surface covers the liquid crystal cell and is injected, and after the cavity of the liquid crystal cell is filled with dye liquid crystal, the vacuum is closed, and the gas is filled, to obtain a constant-brightness flexible liquid crystal dimming film.

[0057] Example 3 This example provides a constant-brightness flexible liquid crystal dimming film, and the structure is as shown in Figure 1 The five layers of materials are sequentially superimposed, the first layer 1 is a first flexible transparent substrate, the second layer 2 is a first vertical alignment layer, the third layer 3 is a dye liquid crystal layer, the fourth layer 4 is a second vertical alignment layer, and the fifth layer 5 is a second flexible transparent substrate.

[0058] The inner side surfaces (i.e. the side opposite to the other substrate and used for forming the liquid crystal dye layer) of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 are each provided with a conductive layer formed by magnetron sputtering ITO film on the substrate surface; and the materials of the first flexible transparent substrate 1 and the second flexible transparent substrate 5 are selected from polyethylene terephthalate film (PET film, square resistance 25 Ω / □).

[0059] The thicknesses of the first vertical alignment layer 2 and the second vertical alignment layer 4 are both 8 μm, and the materials are selected from Upilex®-SVT-F of Ube, and the curing temperature is 130 °C, Tg =165 °C, the dielectric constant =2.8 @1 kHz, and the dielectric loss is 0.002 @1 kHz. The first vertical alignment layer 2 and the second vertical alignment layer 4 are uniformly distributed with polystyrene microbeads, the diameter of the microbeads is 12 μm, and the distribution density is 50 g / m2.

[0060] The dye liquid crystal layer 3 comprises black dichroic dye and negative phase liquid crystal; the black dichroic dye is selected from Kayaset B-SHD. The concentration of the black dichroic dye in the mixture of the black dichroic dye and the negative phase liquid crystal is 0.3 wt%.

[0061] The light bright spot temperature of the negative liquid crystal is 88℃, and the dielectric anisotropy Δε is-3.2 at a frequency of 1KHz and a temperature of 25℃. The negative phase liquid crystal is selected from HNG30900-100.

[0062] The preparation method of the constant-brightness flexible liquid crystal dimming film provided in the embodiment comprises the following steps: (1) A transparent substrate is prepared, and an ITO thin film is prepared on the inner side surface (the side which will be opposite to the other substrate in the subsequent process) of the transparent substrate by magnetron sputtering to prepare a conductive layer, thereby obtaining a first flexible transparent substrate and a second flexible transparent substrate; (2) A cyclohexyl side chain-containing transparent polyimide material is spin-coated on the inner side surface (the side which will be opposite to the other substrate in the subsequent process) of the first flexible transparent substrate and the second flexible transparent substrate, respectively, at a spin-coating speed of 1000 rpm, a spin-coating time of 5 s, and an acceleration of 100 rpm / s, and then cured at 130℃ for 1.5 h, thereby forming a first vertical alignment layer on the surface of the first flexible transparent substrate and a second vertical alignment layer on the surface of the second flexible transparent substrate; (3) The first flexible transparent substrate and the second flexible transparent substrate treated in step (2) are placed on a rubbing machine, and the surface of the first vertical alignment layer and the surface of the second vertical alignment layer are subjected to rubbing treatment, the angle of the roller is adjusted to 45°, the roller shaft rotates at a speed of 1200 rpm, the roller shaft rolls from one side of the substrate to the other side, and the rubbing is performed for 10 times; then the rubbed substrate is placed in an ultrasonic cleaning machine filled with ultrapure water for cleaning, and the cleaning time is 10 min; (4) Microbeads with a diameter of 12μm are dissolved in an ethanol solution at a mass fraction of 6wt%, and filled into a spraying machine. The first flexible transparent substrate and the second flexible transparent substrate treated in step (3) and passed the inspection are fixed on the spraying machine, and the prepared microbead ethanol solution is sprayed on the surface of the first vertical alignment layer and the surface of the second vertical alignment layer by starting the spraying machine. After completion, the interval bead spraying density is detected by a spraying density detector, and the distribution density is 50g / m²; (5) A sealing glue with a width of about 5mm is coated around the first flexible transparent substrate and the second flexible transparent substrate treated in step (4) at a distance of ≤10mm from the edge by silk screen printing; the first flexible transparent substrate and the second flexible transparent substrate completed are aligned by the alignment marks, and placed in a hot press for curing and compounding, the curing temperature is 80℃, and the time is 0.5h, thereby obtaining a liquid crystal cell with a cavity in the middle; (6) Place the liquid crystal cell in the injection tank, then inject nitrogen into the injection tank; then, use a vacuum pump to make the vacuum in the injection tank 1x10 -2 Pa, after vacuumizing, immerse the liquid crystal cell into the dye liquid crystal pool, so that the liquid surface (a mixture of black dichroic dye and negative phase liquid crystal) is above the liquid crystal cell and is injected, after the cavity of the liquid crystal cell is filled with dye liquid crystal, close the vacuum, inflate, and obtain a constant light flexible liquid crystal dimming film.

[0063] Performance test Manufacture the electrode: coat silver paste with a width of 10mm at the step of the first flexible transparent substrate and the second flexible transparent substrate, after the silver paste is coated and solidified, connect the pin to the circuit.

[0064] The pre-tilt angles of the dimming films prepared by examples 1-3 were tested by using a liquid crystal parameter tester, and the results are shown in Figure 3 The left, middle and right are the pre-tilt angles of the first vertical alignment layer, the dye liquid crystal layer and the second vertical alignment layer, respectively.

[0065] The transmittance of the dimming films prepared by examples 1-3 at 450~652nm wavelength under the condition of applying an external field (on state, 25℃, 40V alternating current field) and not applying an external field (off state) was tested by using a liquid crystal parameter tester, and the results are shown in Figure 4 As can be seen from the figure, under the condition of no external field, the overall transmittance in the visible light band is greater than 50%, after applying an electric field, the overall visible light transmittance is reduced to within 30%, and the dimming amplitude is >45%.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, any modification, equivalent replacement or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A constant flexible liquid crystal dimming film, characterized in that, The structure of the constant flexible liquid crystal dimming film comprises, from top to bottom, a first flexible transparent substrate, a first vertical alignment layer, a dye liquid crystal layer, a second vertical alignment layer, and a second flexible transparent substrate. The material of the first vertical alignment layer and the second vertical alignment layer is selected from a side-chain type transparent polyimide material, the curing temperature of the side-chain type transparent polyimide material is ≤ 150℃, and the side chain comprises at least one of an alkane chain, an alicyclic group, a fluorinated alkyl group, or an aromatic group. The dye liquid crystal layer comprises black dichroic dye and negative phase liquid crystal; the black dichroic dye is selected from at least one of Licristar XHR-300K, OrgaSol Black K12, and Kayaset B-SHD; or the black dichroic dye comprises at least one orange dye, at least one red dye, and at least one blue dye; the dichroic ratio of the black dichroic dye is ≥ 12; the light bright point temperature of the negative phase liquid crystal is ≥ 85℃, and the dielectric anisotropy Δε at 1KHz frequency and 25℃ is -10~ -1.

2. The homeotropic flexible liquid crystal switchable film according to claim 1, wherein, The black dichroic dye comprises an anthraquinone type orange dye, an anthraquinone type red dye, and an anthraquinone type blue dye. The anthraquinone type orange dye, the anthraquinone type red dye, and the anthraquinone type blue dye each comprise a structural formula as shown in formula (I): （I）； When formula (I) represents the anthraquinone type orange dye, the substituents R1, R4, R5, and R8 in the structural formula are each independently selected from a hydrogen atom, a hydroxyl group, or a halogen, and R2, R3, R6, and R7 are each independently selected from a substituent A or a hydrogen atom; the structural formula of the substituent A is as shown in formula (II): （Ⅱ）； In formula (II), j is 0 or 1; k is an integer, and 0≤k≤25; Preferably, the structural formula of the anthraquinone type orange dye is as shown in formula (III): （Ⅲ）； In formula (III), k is an integer, and 0≤k≤25; When formula (I) represents the anthraquinone type red dye, the substituents R1, R4, R5, and R8 in the structural formula are each independently selected from a hydrogen atom, a hydroxyl group, or a halogen, and R2, R3, R6, and R7 are each independently selected from the substituent A or a hydrogen atom; Preferably, the structural formula of the anthraquinone type red dye is as shown in formula (IV): （Ⅳ）； In formula (IV), k is an integer, and 0≤k≤25; When formula (I) represents the anthraquinone type blue dye, the substituents R1 and R5 in the structural formula are each independently selected from a hydrogen atom, a hydroxyl group, an amino group, a nitro group, or a halogen; R4 and R8 are each independently selected from a hydrogen atom, a hydroxyl group, an amino group, a nitro group, a halogen, or a substituent C; R2, R3, R6, and R7 are each independently selected from a substituent D or a hydrogen atom; the structural formula of the substituent C is as shown in formula (V): （Ⅴ）； In formula (V), m is 0 or 1; n is an integer, and 0≤n≤25; The structural formula of the substituent D is as shown in formula (VI): （Ⅵ）； In formula (VI), x is 0 or 1; y is 0 or 1; z is an integer, and 0≤z≤25; Preferably, the structural formula of the anthraquinone type blue dye is as shown in formula (VII): （Ⅶ）； In formula (VII), z is an integer, and 0≤z≤25; n is an integer, and 0≤n≤25.

3. The homeotropic flexible liquid crystal switchable film according to claim 1 or 2, wherein, The black dichroic dye and the negative phase liquid crystal form a mixture, wherein the concentration of the black dichroic dye is 0.1-1 wt%.

4. The homeotropic flexible liquid crystal switchable film according to claim 1, wherein, The material of the first flexible transparent substrate and the second flexible transparent substrate is selected from polyethylene terephthalate film, polyimide film or inorganic glass with a thickness of 0.1-0.7 mm and a square resistance of 5-30 Ω / □.

5. The homeotropic flexible liquid crystal switchable film according to claim 1, wherein, The surface of the first flexible transparent substrate and the second flexible transparent substrate is provided with a conductive layer.

6. The homeotropic flexible liquid crystal switchable film according to claim 5, wherein, The conductive layer is selected from one of ITO film, silver nanowire or polymer conductive layer.

7. The homeotropic flexible liquid crystal switchable film according to claim 1, wherein, Microbeads are distributed between the first vertical alignment layer and the second vertical alignment layer, the dye liquid crystal layer is filled in the gap between the microbeads, the diameter of the microbeads is 5-25 μm, and the distribution density is 30-50 g / m².

8. The homeotropic flexible liquid crystal switchable film according to claim 1, wherein, The thickness of the first vertical alignment layer and the second vertical alignment layer is 1-20 μm, and the liquid crystal pre-tilt angle under zero electric field is 89-90°.

9. The constant flexible liquid crystal switchable film according to claim 1, wherein, The glass transition temperature of the side chain type transparent polyimide material after film formation is ≥160℃, the dielectric constant is 2-3, and the dielectric loss is 0.001-0.

003.

10. A method of producing the homeotropic flexible liquid crystal switchable film according to any one of claims 1 to 9, characterized in that, The method comprises the following steps: S1. Coating a side chain type transparent polyimide material on the inner side surface of the first flexible transparent substrate and the second flexible transparent substrate, respectively, and then performing a curing treatment to obtain a first flexible transparent substrate with a first vertical alignment layer on the surface and a second flexible transparent substrate with a second vertical alignment layer on the surface; S2. Performing a rubbing treatment on the first vertical alignment layer surface of the first flexible transparent substrate and the second vertical alignment layer surface of the second flexible transparent substrate treated in step S1, and cleaning; wherein the roller angle is 45°±20', the roller shaft rotation speed is 800-1200 rpm, and the rubbing frequency is 2-10 times; S3. Spraying microbeads on the first vertical alignment layer surface of the first flexible transparent substrate and the second vertical alignment layer surface of the second flexible transparent substrate treated in step S2, respectively, and the microbead distribution density is 30-50 g / m²; S4. Coating a sealant on the four edges of the first flexible transparent substrate and the second flexible transparent substrate treated in step S3, respectively, and performing a heat pressing and curing composite treatment to obtain a liquid crystal cell with a cavity in the middle; S5. Filling the mixture of the black dichroic dye and the negative phase liquid crystal into the cavity of the liquid crystal cell treated in step S4 to form a dye liquid crystal layer, and obtaining the constant light flexible liquid crystal dimming film.

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