A reverse electro-controlled dimming film based on photopolymerizable monomers and a negative nematic liquid crystal system and its preparation method.

Abstract

This invention discloses a reverse electrically controlled dimming film based on a photopolymerizable monomer and a negative nematic liquid crystal system, and its preparation method. The film includes a liquid crystal cell or a liquid crystal film, and a liquid crystal composite system infused within the liquid crystal cell or liquid crystal film. The liquid crystal composite system comprises 50.0–96.0 wt% of a negative nematic liquid crystal mixture, 4.00–50.0 wt% of a photopolymerizable monomer, and 0.2–10.0% of a photo-leaving photoinitiator by mass of the total photopolymerizable monomer. The photo-leaving photoinitiator is an o-nitrophenyl compound, a benzothiophene iminophenylacetonitrile compound, or a mixture thereof. The reverse electrically controlled dimming film prepared by this invention has a visible light transmittance of less than or equal to 1% under a low-frequency electric field, a near-infrared light transmittance of less than or equal to 22%, and a visible light and near-infrared light transmittance of greater than or equal to 80% in the un-energized state. It has low energy consumption, low driving voltage and response time, and the preparation process is simple, energy-saving, and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of functional liquid crystal materials technology, and relates to an electrically controlled liquid crystal dimming film and its preparation method, specifically to an inverse electrically controlled dimming film based on a photopolymerizable monomer and a negative nematic liquid crystal system and its preparation method. Background Technology

[0002] Electro-controlled liquid crystal dimming films can switch between transparent and opaque states electronically, finding wide application in controlled shading technology, interior partitions, automotive windows and doors, and displays. Currently, commercially available electro-controlled liquid crystal dimming films are primarily polymer-dispersed liquid crystal (PDLC) films. In PDLC films without an applied electric field, the liquid crystal molecules exhibit a random distribution, resulting in strong light scattering. Under an electric field, the long axes of the liquid crystal molecules align parallel to the field, making the film transparent. PDLC films not only offer controllable states but are also easy to process in large areas. However, PDLC films are strictly electro-controlled dimming films, meaning they are normally in a state of strong light scattering but become light-transmitting when an external electric field is applied. This means their transmissive state requires a continuous electric field to maintain. However, in practical applications, such as building windows and doors, it is necessary to maintain a light-transmitting state most of the time and a light-shielding state only a few times. Using electro-controlled liquid crystal dimming films in these applications would inevitably lead to energy consumption. The electro-optical properties of inverted electro-controlled liquid crystal dimming films are that they are transparent when no electric field is applied, but exhibit strong light scattering when an electric field is applied. Therefore, in many applications, inverted electro-controlled liquid crystal dimming films better meet the requirements of energy conservation and environmental protection. Moreover, in some situations, the film becomes transparent when the power is off, posing no safety hazard to users. Therefore, inverted electro-controlled liquid crystal dimming films have a broader application prospect than conventional electro-controlled liquid crystal dimming films.

[0003] To date, research on inverted electro-controlled liquid crystal dimming films remains at the laboratory stage. Existing inverted electro-controlled dimming film systems are mainly based on polymer-stabilized liquid crystal (PSLC) systems, with preparation methods focusing on polymer-stabilized negative LC, dual-frequency liquid crystal (DFLC), and cholesteric liquid crystal (ChLC). However, PSLC systems suffer from low network content (typically only about 3-5 wt%), resulting in low bonding strength and poor stability between the two substrate layers, making them difficult to apply in practice. Furthermore, current methods for preparing electro-controlled dimming films using polymer-stabilized negative LC methods all require spin-coating an alignment layer on the inner side of the substrate, or using photomask methods that require the addition of salt ions to induce liquid crystal perturbation and light scattering under energized conditions, or using distribution polymerization methods, all of which are complex processes.

[0004] A polymer-dispersed and stabilized liquid crystal (PD&SLC) coexistence system combines the advantages of both PDLC and PSLC. This system enables large-area processing of flexible thin films with good stability, and also allows for different light-modulating properties.

[0005] Existing methods for preparing inverse electro-controlled dimming films using photo-initiated polymeric stable liquid crystal systems and polymeric dispersion-stabilized liquid crystal coexistence systems both employ initiators such as benzoin ether, benzophenone, thioanthrone, benzoyl dimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropanone, trimethylbenzoyl diphenylphosphine oxide, and benzoin diethyl ether. Furthermore, the orientation of the liquid crystal polymers in these systems requires substrate treatment, voltage application, or washing-in / washing methods, resulting in complex, energy-intensive, and environmentally polluting processes that rely on solvents. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an inverse electro-controlled dimming film based on photopolymerizable monomers and a negative nematic liquid crystal system, and its preparation method. The preparation process is simple and environmentally friendly, and the prepared inverse electro-controlled dimming film has low energy consumption, good stability, and strong practicality.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A reverse electro-controlled dimming film based on photopolymerizable monomers and negative nematic liquid crystal system, comprising a liquid crystal cell or liquid crystal film and a liquid crystal composite system infused in the liquid crystal cell or liquid crystal film.

[0009] The liquid crystal composite system comprises 50.0–96.0 wt% of a negative nematic liquid crystal mixture, 4.00–50.0 wt% of a photopolymerizable monomer, and 0.2–10.0% of a photo-leaking photoinitiator by mass of the total photopolymerizable monomer.

[0010] The photo-leaving photoinitiator includes o-nitrophenyl compounds, benzothiophene imino phenylacetonitrile compounds, or mixtures thereof in any proportion.

[0011] The present invention also has the following technical features:

[0012] Preferably, the photo-leaving photoinitiator comprises one or more of the following structural formulas in any proportion:

[0013]

[0014] In the formula n is 0 or 1.

[0015] Preferably, the photopolymerizable monomer is a liquid crystal photopolymerizable monomer, a non-liquid crystal photopolymerizable monomer, or a mixture of the two in any proportion.

[0016] Furthermore, the non-liquid crystal photopolymerizable monomer includes one or more of (meth)acrylates, polyurethane acrylates, polyester acrylates, polyether acrylates, waterborne acrylates, or vinyl ethers in any proportion.

[0017] Furthermore, the liquid crystal photopolymerizable monomer comprises one or more of the following substances in any proportion, with the specific structural formula as follows:

[0018]

[0019]

[0020] Where m and n take values ​​of 4 to 8, x and y take values ​​of 1 to 2, and E and Q are structural units of (meth)acrylate, vinyl ether, or polyurethane acrylate.

[0021] This invention also protects a method for preparing an inverse electro-controlled dimming film based on a photopolymerizable monomer and a negative nematic liquid crystal system as described above, comprising the following steps:

[0022] S1. Prepare a liquid crystal composite system by mixing the negative nematic liquid crystal mixture, photopolymerizable monomer and photo-leaking photoinitiator according to the mass ratio, and stir evenly.

[0023] S2. Heat the liquid crystal composite system prepared in S1 to a temperature 1-2°C higher than the clearing point of the composite system to form an isotropic liquid. Pour the isotropic liquid into a liquid crystal cell or place it between two conductive films and use glass microsphere spacers to control the thickness, and then extrude it into a film.

[0024] S3. Place the sample prepared in S2 at 5–40 mw / cm². 2 Irradiation under ultraviolet or visible light for 5–60 min at light intensity causes complete polymerization of polymerizable monomers in the system, constructing a negative nematic liquid crystal system anchored by polymer rods, resulting in a reverse electro-controlled dimming film that can simultaneously adjust visible and near-infrared light.

[0025] Preferably, the thickness of the liquid crystal cell or the particle size of the glass microspheres is 8–100 μm.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] This invention uses nitrophenyl compounds and benzothiophene imino phenylacetonitrile compounds as photo-leaking photoinitiators. The prepared inverse electrically controlled dimming film has a transmittance of less than or equal to 1% in the visible light region (400-760nm) and less than or equal to 22% in the near-infrared region under a low-frequency electric field. In the unpowered state, the transmittance of the film in both the visible and near-infrared regions is greater than or equal to 80%, and the contrast ratio of the sample in the visible light region is as high as 126. It has low energy consumption, with driving voltage and dynamic voltage not exceeding 30V, low response time, high polymer content, and strong adhesion. The wavelength-transmittance relationship curves of the sample after 100,000 electric field switching cycles in both powered and unpowered states are basically unchanged from the wavelength-transmittance relationship curve after one switching cycle, showing good stability and strong practicality. Moreover, the preparation process is simple, environmentally friendly, and does not require substrate alignment treatment. Attached Figure Description

[0028] Figure 1 The polymer microstructure of the inverse electro-controlled dimming film prepared in Example 1;

[0029] Figure 2 Electro-optic curve of the inverted electro-controlled dimming film prepared in Example 1;

[0030] Figure 3 The wavelength-transmittance curves of the inverted electro-controlled dimming film prepared in Example 1 under conditions of no electric field and with electric field;

[0031] Figure 4 The images show the physical effects of the inverted electro-controlled dimming film prepared in Example 1 in the un-energized state (a) and the physical effects under the applied electric field (20Hz, 24V) (b).

[0032] Figure 5 The wavelength-transmittance curves of the inverted electro-controlled dimming film prepared in Example 1 after one cycle of switching and 100,000 cycles of switching, under conditions of no electric field and with electric field. Detailed Implementation

[0033] The specific content of the present invention will be further explained in detail below with reference to the embodiments.

[0034] In the following embodiments, the names used, such as HNG726200-100, HNG30400-200, and HNG60700-200, are publicly disclosed negative nematic liquid crystal mixtures. Those skilled in the art can obtain them through publicly available documents or by purchasing them. They can also obtain other negative nematic liquid crystal mixtures with similar properties by mixing them themselves.

[0035] The structural formulas of the photo-leaving photoinitiators used in the following embodiments include:

[0036]

[0037] The liquid crystal photopolymerizable monomers used in the following embodiments include C6M, C4V, and C4N, whose structural formulas are as follows:

[0038]

[0039]

[0040] The non-liquid crystal photopolymerizable monomers used in the following embodiments include UV-1 and UV-2;

[0041] The composition of UV-1 includes BisA (70.0 wt%) and TGD (30.0 wt%);

[0042] The composition of UV-2 includes TMHA (42.0 wt%), IBMA (30.0 wt%), and TGD (10.0 wt%).

[0043] PEGDA600 (10.0wt%) and HME (8.0wt%);

[0044] The structural formulas of each component are as follows:

[0045]

[0046] Example 1

[0047] Step 1: Prepare a composite system of negative nematic liquid crystal / photopolymerizable monomer / photo-leaving photoinitiator by blending 80 wt% of negative nematic liquid crystal HNG726200-100, 20 wt% of photopolymerizable monomer C6M, and 0.2% of photoleaving photoinitiator by mass of the total photopolymerizable monomer in a specific ratio, and stir until homogeneous; the photoleaving photoinitiator is NPPOC-TMG, and its structure is as follows.

[0048] Step 2: Heat the liquid crystal composite system prepared in Step 1 to a temperature 1-2°C higher than the clearing point of the composite system to form an isotropic liquid. Pour the isotropic liquid into a liquid crystal cell or place it between two conductive films and extrude it into a film. The thickness is controlled by spacers or spacers. The thickness of the spacers or the particle size of the spacers is 15μm.

[0049] Step 3: Cure the filled liquid crystal cell or prepared sample film with ultraviolet light at an intensity of 40 mW / cm². 2 An irradiation time of 5 min was used to construct a negative nematic liquid crystal system anchored to a liquid crystal polymer rod, resulting in a reverse electro-controlled dimming film.

[0050] Figure 1The image shows the polymer microstructure of the inverse electro-optic dimming film in Example 1. It can be seen from the image that the polymer forms small rods, and that the polymer rods can accumulate into spheres. Figure 2 This is the electro-optic curve of the inverted electro-optic dimming film in Example 1, from... Figure 2 It can be seen that as the applied voltage increases, the average transmittance of the visible light region of the reverse electronically controlled dimming film gradually decreases. When the applied voltage is greater than 20V, the average transmittance of the visible light region of the reverse electronically controlled dimming film remains at 0.85%, indicating that the driving voltage of this electronically controlled dimming film is low and the contrast is high. Figure 3 The graphs shown are the wavelength-transmittance curves of the inverted electro-controlled dimming film in Example 1 under conditions of no electric field and with an electric field. Figure 3 It can be seen that the transmittance of the reverse electro-controlled dimming film in the visible and near-infrared regions is greater than or equal to 80% in the unpowered state. Under the condition of applying a 20Hz, 24V electric field, the transmittance of the sample in the visible region is less than 1%, and the transmittance in the near-infrared region is less than or equal to 22%. This indicates that the film has a high contrast in the visible region and has the function of shielding near-infrared light in the opaque state. Figure 4 The images show the physical effects of the reverse-type electrically controlled dimming film in Example 1: (a) without power, and (b) under an applied electric field (20Hz, 24V). Figure 4 It can be seen that the reverse electro-controlled dimming film is transparent when no electricity is applied, but when a certain electric field is applied, the transmittance of the film decreases and it becomes opaque. Figure 5 The figure shows the wavelength-transmittance curves of the inverted electro-controlled dimming film in Example 1 after one cycle of switching and 100,000 cycles of switching, under conditions of no electric field and with electric field. It can be seen from the figure that the wavelength-transmittance curves of the sample after 100,000 cycles of switching with and without electric field are basically unchanged from the wavelength-transmittance curve after one cycle of switching, indicating that the film has good stability.

[0051] Example 2

[0052] Step 1: Prepare a composite system of negative nematic liquid crystal / photopolymerizable monomer / photo-leaving photoinitiator by blending 96.0 wt% of negative nematic liquid crystal HNG30400-200, 4.0 wt% of photopolymerizable monomer, and 10.0 wt% of photoleaving photoinitiator (based on the total mass of photopolymerizable monomer) in a certain proportion and stirring until homogeneous. The photopolymerizable monomer consists of 90 wt% C6M and 10 wt% UV-1, and the photoleaving photoinitiator includes 20.0 wt% of compound number (1) and 80.0 wt% of compound number (2), with the following structure:

[0053]

[0054] Step 2: Heat the liquid crystal composite system prepared in Step 1 to a temperature 1-2°C higher than the clearing point of the composite system to form an isotropic liquid. Pour the isotropic liquid into a liquid crystal cell or place it between two conductive films and extrude it into a film. The thickness is controlled by spacers or spacers. The thickness of the spacers or the particle size of the spacers is 8μm.

[0055] Step 3: Photocur the filled liquid crystal cell or prepared sample film with a wavelength of 405 nm and a light intensity of 5 mW / cm². 2 An irradiation time of 60 min was used to construct a negative nematic liquid crystal system anchored to a liquid crystal polymer rod, resulting in a reverse electro-controlled dimming film.

[0056] Example 3

[0057] Step 1: Prepare a composite system of negative nematic liquid crystal / photopolymerizable monomer / photoleaving photoinitiator by blending 50 wt% of negative nematic liquid crystal HNG60700-200, 50 wt% of photopolymerizable monomer, and 1.0 wt% of photoleaving photoinitiator according to the total mass of photopolymerizable monomer, and stir until homogeneous. The photopolymerizable monomer consists of 80 wt% C4V and 20 wt% UV-2, and the photoleaving photoinitiator is compound number 2, with the following structure:

[0058] Step 2: Heat the liquid crystal composite system prepared in Step 1 to a temperature 1-2°C higher than the clearing point of the composite system to form an isotropic liquid. Pour the isotropic liquid into a liquid crystal cell or place it between two conductive films and extrude it into a film. The thickness is controlled by spacers or spacers. The thickness of the spacers or the particle size of the spacers is 100μm.

[0059] Step 3: Cure the filled liquid crystal cell or prepared sample film with ultraviolet light at an intensity of 15 mW / cm². 2 An irradiation time of 20 min was used to construct a negative nematic liquid crystal system anchored to a liquid crystal polymer rod, resulting in a reverse electro-controlled dimming film.

[0060] The above-described embodiments are merely illustrative of several implementations of the present invention and should not be construed as limiting the scope of the present invention. The photopolymerizable monomer and photo-leaving photoinitiator of the present invention can also be other substances or components given in the technical solutions, which are not listed here. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A trans electrically controlled light modulation film based on a photo- polymerizable monomer and a negative nematic liquid crystal system, characterized in that, The liquid crystal composite system comprises a liquid crystal cell or a liquid crystal film and a liquid crystal filled in the liquid crystal cell or the liquid crystal film. The liquid crystal composite system comprises 50.0-96.0 wt% of a negative nematic liquid crystal mixture, 4.00-50.0 wt% of a photopolymerizable monomer and 0.2-10.0 wt% of a photoreleasable photoinitiator. The photopolymerizable monomer comprises a liquid crystal photopolymerizable monomer and a non-liquid crystal photopolymerizable monomer. The photoreleasable photoinitiator comprises an o-nitrophenyl compound, a benzothiophene imine phenylacetonitrile compound or a mixture thereof. The photoreleasable photoinitiator comprises a mixture of one or more of the following structural formulae: wherein , or n is 0 or 1 ; The preparation method comprises the following steps: S1, blending the negative nematic liquid crystal mixture, the photopolymerizable monomer and the photoreleasable photoinitiator according to the mass ratio to prepare a liquid crystal composite system, and stirring uniformly; S2, heating the liquid crystal composite system prepared in S1 to a temperature of 1-2℃ higher than the clearing point of the composite system to form an isotropic liquid, filling the isotropic liquid into a liquid crystal cell or between two conductive films and using glass microspheres as spacers to control the thickness, and extruding into a film. S3, the sample prepared in S2 is placed under UV light or visible light with intensity of 5-40 mw / cm 2 The sample is irradiated under UV light or visible light with intensity of 5-60 min, so that the polymerizable monomers in the system are completely polymerized, a polymer rod-anchored negative nematic liquid crystal system is constructed, and a trans electrically controlled light modulation film capable of simultaneously adjusting visible light and near-infrared light is obtained.

2. The trans electrically controlled light modulation film based on a photopolymerizable monomer and a negative nematic liquid crystal system according to claim 1, wherein, The non-liquid crystal photopolymerizable monomer comprises one or more of a (meth)acrylate, a polyurethane acrylate, a polyester acrylate, a polyether acrylate, an aqueous acrylate or a vinyl ether in any proportion.

3. The trans electrically controlled light modulation film based on a photopolymerizable monomer and a negative nematic liquid crystal system according to claim 1, wherein, The liquid crystal photopolymerizable monomer comprises one or more of the following substances in any proportion, and the specific structural formula is as follows: wherein m and n are 4-8, x and y are 1-2, and E and Q are (meth)acrylate, vinyl ether or polyurethane acrylate structural units.

4. The trans electrically controlled light modulation film based on a photopolymerizable monomer and a negative nematic liquid crystal system according to claim 1, wherein, The thickness of the liquid crystal cell or the particle size of the glass microspheres is 8-100 μm.

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