Multifunctional transparent display and dark tinting composite film and preparation method thereof

Abstract

The application discloses a multifunctional transparent display and dark color dimming composite film and a preparation method thereof, and belongs to the technical field of dimming films. The multifunctional transparent display and dark color dimming composite film comprises, from top to bottom, an upper layer of conductive base material, a dark color dimming composite layer, a photochromic layer and a lower layer of conductive base material which are sequentially stacked. The preparation method of the composite film comprises the following steps: 1) preparing a dark color dimming composite layer slurry and a photochromic layer slurry; 2) assembling the dimming film; and 3) post-processing. In the application, the photochromic spirooxazine unit is in the form of a secondary ammonium salt, and is assembled with a supramolecular polymer matrix with a side chain hanging calabash [6] urea, and a dynamic and reversible non-covalent bond cross-linking and molecular inclusion protection mechanism is used, so that the key technical bottlenecks of traditional photochromic materials in the aspects of cycle stability, single function and processing compatibility are successfully solved, and the construction of a high-performance, multiple-stimulus-response intelligent material is realized.

Description

Technical Field

[0001] This invention relates to the field of dimming film technology, and in particular to a multifunctional transparent display and dark-tone light composite film and its preparation method. Background Technology

[0002] Photochromic materials have shown great potential in fields such as smart windows, information storage, and anti-counterfeiting. Among them, integrating photochromic molecules (such as spiroxazine) into polymer matrices to prepare dimming films is the mainstream technical route. However, traditional physical blending techniques have three inherent technical bottlenecks that severely restrict their practical application and development.

[0003] First, it exhibits poor cycling stability. The open-ring form of spiroxazine molecules, induced by light, possesses high reactivity. When directly exposed to the external environment within a conventional polymer matrix, it is susceptible to irreversible photodegradation due to attacks from oxygen and free radicals, leading to rapid photofatigue in the material.

[0004] Secondly, the material compatibility and dispersibility are poor. The hydrophobic photochromic molecules are poorly compatible with the hydrophilic polymer matrix, and are prone to phase separation or molecular aggregation, resulting in decreased film transparency, uneven response, and a decrease in color-changing efficiency due to aggregation quenching effect.

[0005] Finally, their functionality is limited. Traditional materials typically only respond to light stimuli, making it difficult to achieve intelligent regulation of multiple environmental stimuli, thus restricting their application scenarios.

[0006] Therefore, developing a novel material system capable of simultaneously endowing photochromic units with excellent stability, molecular-level dispersibility, and multiple responsiveness has become an urgent technological need in this field. Supramolecular chemistry, particularly host-guest assembly strategies based on macrocyclic hosts, offers a novel approach to solving these challenges. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a multifunctional transparent display and dark-tone light composite film and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention first proposes a multifunctional transparent display and dark-tone light composite film, comprising an upper conductive substrate, a dark-tone light composite layer, a photochromic layer and a lower conductive substrate stacked sequentially from top to bottom;

[0010] The conductive substrate is an indium tin oxide-polyethylene terephthalate composite film;

[0011] The dark-toned light composite layer is obtained by coating a mixture of dark azobenzene tinting compounds, polyurethane acrylate, bisphenol A epoxy diacrylate, nematic microcrystalline medium mixture, and photoinitiator in a mass ratio of 2-3:35-40:20-25:35-40:2.

[0012] The photochromic layer is obtained by coating poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium salt hexafluorophosphate in a mass ratio of 2-3:1.

[0013] Preferably, the preparation process of the spiroxazine-secondary ammonium salt hexafluorophosphate includes the following steps:

[0014] 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine] was dissolved in acetonitrile, dimethylamine was added, and the mixture was stirred at 38-42°C for 6-8 hours. The mixture was then rotary evaporated and dissolved in ice water. Ammonium hexafluorophosphate was added, and the white precipitate was collected and dried under vacuum to obtain spiroxazine-secondary ammonium hexafluorophosphate.

[0015] 1-(2-Bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine] undergoes a nucleophilic substitution reaction with dimethylamine, where the nitrogen atom of dimethylamine attacks the bromopentyl carbon atom of 1'-(5-bromopentyl)spiroxazine to form a secondary ammonium salt; subsequently, ammonium hexafluorophosphate is added, utilizing the hexafluorophosphate ion (PF6) - The exchange reaction with bromide ions produces a more stable hexafluorophosphate:

[0016] ;

[0017] Preferably, in the preparation of the spiroxazine-secondary ammonium hexafluorophosphate, the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:6-7:1.05-1.1.

[0018] Preferably, the preparation process of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbita[6]urea) includes the following steps:

[0019] (1) Dissolve cucurbit[6]urea and 1-butyl-3-methylimidazolium chloride in concentrated hydrochloric acid, add potassium persulfate at 58-62℃, stir for 3.5-4.5h, cool to room temperature, precipitate with cold deionized water, repeat dissolution and purification of the precipitate to obtain monohydroxycucurbit[6]urea;

[0020] (2) Dissolve monohydroxycucurbit[6]urea in N,N-dimethylformamide, under nitrogen protection and ice-water bath, add sodium hydride and stir for 25-35 min; add 4-chloromethylstyrene, stir at room temperature for 23-25 ​​h, precipitate the product with ice-cold ether, wash with tetrahydrofuran and ether alternately, and dry under vacuum to obtain 4-vinylbenzyloxycucurbit[6]urea;

[0021] (3) Dissolve 4-vinylbenzyloxycucurbit[6]urea, acrylamide and methacrylamide in deionized water, add 2,2'-azobisisobutylamidine dihydrochloride under nitrogen protection, react at 58-62℃ for 23-25h, and dialysis to purify to obtain poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea).

[0022] Potassium persulfate decomposes at 60°C to generate free radicals, which initiate the hydroxylation reaction of cucurbit[6]urea molecules, introducing a single hydroxyl active site to provide reactive groups for subsequent grafting; unreacted cucurbit[6]urea and potassium persulfate residues are removed by cold water stepwise precipitation purification.

[0023] Sodium chloride first reacts with the hydroxyl group of monohydroxycucurbita[6]urea to generate an oxonium (-O) - ); The oxygen anion acts as a nucleophile to attack the chloromethyl carbon atom of 4-chloromethylstyrene, resulting in a nucleophilic substitution reaction. The vinyl group (-CH=CH2) is grafted onto the cucurbit[6]urea molecule to obtain a cucurbit[6]urea derivative containing a polymerizable active group.

[0024] 2,2'-Azobisisobutylamidine dihydrochloride decomposes at 60°C to generate free radicals, which initiate copolymerization of acrylamide, methacrylamide and 4-vinylbenzyloxycucurbit[6]urea; the carbon-carbon double bonds of the three monomers are opened and interconnected to form the polymer backbone, and cucurbit[6]urea is linked to the backbone through benzyloxy groups to become side groups.

[0025] The specific reaction process is as follows:

[0026] ;

[0027] Preferably, in the preparation of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 85-90:8-10:1-3:1.

[0028] This invention also proposes a method for preparing a composite thin film with multifunctional transparent display and dark-tone light, comprising the following steps:

[0029] S1. Preparation of dark-tone light-reflecting composite layer paste and photochromic layer paste:

[0030] Under light-protected conditions, polyurethane acrylate and bisphenol A epoxy diacrylate are heated at 50-60℃ and mixed evenly to form a prepolymer matrix. Dark azobenzene tinting compounds are uniformly dispersed in a nematic microcrystalline medium mixture, and the prepolymer matrix is ​​added. The mixture is stirred at 50℃ for 2-4 hours to obtain a dark-tinted light-emitting composite layer slurry, which is then allowed to stand to degas for later use.

[0031] Poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium salt hexafluorophosphate were dissolved in N,N-dimethylformamide and stirred in the dark for 12-24 hours to obtain photochromic layer slurry.

[0032] Spirooxazine-secondary ammonium hexafluorophosphate, acting as a photochromic molecule, is encapsulated within the cavity of cucurbita, forming a host-guest complex. This provides a protective microenvironment for the photochromic molecule, shielding it from oxygen, solvents, etc., and significantly mitigating photofatigue.

[0033] ;

[0034] Spirooxazine-secondary ammonium hexafluorophosphate undergoes a photochromic reaction upon exposure to ultraviolet light:

[0035] ;

[0036] Spirooxazine molecules exhibit a spirocyclic structure, with two conjugated systems separated by a sp... 3 The hybrid spiro carbon atoms are separated and perpendicular to each other. This structure causes it to absorb only ultraviolet light and not in the visible light region, so it is colorless. After absorbing ultraviolet light, the chemical bond between the spiro carbon atom and the oxygen atom undergoes heterolytic cleavage and breaks. After the bond breaks, the molecular structure changes from a non-planar spiro ring to a planar, highly conjugated large π-bond structure. This planar conjugated structure causes its absorption spectrum to redshift and strongly absorb visible light, thus exhibiting a purple color.

[0037] After ultraviolet light is removed, the open-ring form is in a metastable state. It will spontaneously reverse into a lower-energy closed-ring state through thermal relaxation or by absorbing energy from visible light, and the color will disappear.

[0038] S2, Dimming film assembly:

[0039] Take a conductive substrate with the conductive side facing up, spin-coat a layer of photochromic slurry, and vacuum dry at 58-62℃ for 10-14 hours to form a photochromic layer; lay glass fiber or polymer microsphere spacers in the edge area of ​​the photochromic layer, cover with a dark-toned photochromic composite slurry, and perform photocuring.

[0040] S3, Post-processing:

[0041] After photocuring, the film is left to stand at room temperature and in a dark environment for 2-4 hours, or subjected to heat treatment at 28-42℃ for 25-35 minutes for thermal relaxation, to obtain a multifunctional transparent display and dark-tone light composite film.

[0042] Preferably, in S1, poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbita[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate are dissolved in N,N-dimethylformamide to obtain a solution with a solid content of 15-20%.

[0043] Preferably, in step S2, the wet film thickness of the photochromic layer is 1-3 μm, the thickness of the dark-tone composite layer is 15-25 μm, the curing light wavelength is 365 nm, and the light intensity is 50-100 mW / cm². 2 .

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. This invention utilizes the strong host-guest interaction between the macrocyclic cavity of cucurbita[6]urea (CB[6]) and the spiroxazine-secondary ammonium salt guest to stably encapsulate and fix the photochromic unit in the polymer network. The cavity of CB[6] provides a rigid "protective microenvironment" for the spiroxazine molecule, effectively shielding it from external factors such as oxygen and free radicals, which attack the highly reactive open-ring body and greatly suppress the occurrence of photodegradation side reactions. Compared with the technique of directly dispersing spiroxazine in a common polymer matrix, the photochromic layer prepared by this invention exhibits excellent fatigue resistance and service life.

[0046] 2. In the physical blending method, the hydrophobic photochromic molecules have poor compatibility with the hydrophilic polymer matrix, which easily leads to phase separation or molecular aggregation, resulting in decreased film transparency, turbidity, uneven color change response, and low efficiency. In this invention, cucurbita[6]urea is covalently grafted onto the water-soluble acrylamide polymer backbone, ensuring uniform dispersion of the host in the matrix. The photochromic guest molecules are dispersed in situ and at the molecular level in the host cavity through host-guest interaction. The confinement effect of the cucurbita[6]urea cavity prevents the face-to-face stacking of spiroxazine molecules, effectively suppressing fluorescence quenching and color change failure caused by aggregation. The uniform dispersion of photochromic molecules at the nanoscale or even molecular level in the polymer film is achieved, avoiding phase separation, thereby preparing a homogeneous film with high transparency and no defects. The polymer backbone provides excellent film-forming properties and mechanical strength, while supramolecular interaction endows intelligent response characteristics. The two work together to finally obtain a high-quality dimming film with excellent optical performance, good mechanical properties, and sensitive response.

[0047] In summary, this invention successfully solves the key technical bottlenecks of traditional photochromic materials in terms of cycle stability, functional singularity and processing compatibility by assembling the photochromic spiroxazine unit in the form of a secondary ammonium salt with a supramolecular polymer matrix of cucurbita[6]urea with side chains, combined with dynamic, reversible non-covalent crosslinking and molecular inclusion protection mechanism, thus realizing the construction of high-performance, multi-stimulus responsive smart materials. Attached Figure Description

[0048] Figure 1 The 1H NMR spectrum of the spiroxazine-secondary ammonium salt hexafluorophosphate proposed in this invention is shown. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0050] Preparation Example 1: The preparation process of spiroxazine-secondary ammonium salt hexafluorophosphate includes the following steps:

[0051] 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine] was dissolved in acetonitrile, dimethylamine was added, the mixture was stirred at 40°C for 7 h, rotary evaporated, dissolved in ice water, ammonium hexafluorophosphate was added, the white precipitate was collected, and dried under vacuum to obtain spiroxazine-secondary ammonium salt hexafluorophosphate.

[0052] In the preparation of the spiroxazine-secondary ammonium hexafluorophosphate, the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:7:1.05.

[0053] A portion of spiroxazine-secondary ammonium hexafluorophosphate was taken, purified, dissolved in dimethyl sulfoxide, and analyzed by 1H NMR spectroscopy. The results are as follows. Figure 1 As shown:

[0054] The peaks in the 6.5–8.0 ppm region correspond to aromatic ring hydrogens in the molecule (benzene ring hydrogens of the indoline ring and naphthooxazine ring). Because multiple hydrogens on the aromatic ring are in different chemical environments, the peaks are relatively dense, showing multiple sets of overlapping peaks. The multiple sets of peaks in the 1.0–1.5 ppm region correspond to multiple methyl hydrogens in the molecule, including the "3,3-dimethyl" at the 3-position of the indoline ring, and secondary ammonium salts (-NH...). + The peak at 2.24 ppm corresponds to the methylene (-CH2-) hydrogen atom linked to the N atom of indoline, while the peaks at 3.32 and 3.36 ppm correspond to the -NH group of the secondary ammonium salt.+ Hydrogen and adjacent methylene hydrogen: secondary ammonium salt (-NH + The chemical shift of the NH hydrogen in (CH3)2 is usually in the range of 3 to 4 ppm. The adjacent methylene group will also shift to this region due to the influence of the positive charge of N. 6.65 ppm corresponds to the hydroxyl (-OH) hydrogen in the molecule. The distribution of peaks and the range of chemical shifts in each region of the spectrum are consistent with the chemical environment of hydrogen atoms in the molecular structure of "spiroxazine-secondary ammonium salt", which can prove that this compound is the target spiroxazine-secondary ammonium salt.

[0055] The preparation process of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbita[6]urea) includes the following steps:

[0056] (1) Dissolve cucurbit[6]urea and 1-butyl-3-methylimidazolium chloride in concentrated hydrochloric acid, add potassium persulfate at 60°C, stir for 4 hours, cool to room temperature, precipitate with cold deionized water, repeat dissolution and purification of the product to obtain monohydroxycucurbit[6]urea;

[0057] (2) Monohydroxycucurbit[6]urea was dissolved in N,N-dimethylformamide, and under nitrogen protection and ice-water bath, sodium hydride was added and stirred for 30 min; 4-chloromethylstyrene was added and stirred at room temperature for 24 h. The product was precipitated with ice-cold ether, washed alternately with tetrahydrofuran and ether, and dried under vacuum to obtain 4-vinylbenzyloxycucurbit[6]urea.

[0058] (3) Dissolve 4-vinylbenzyloxycucurbit[6]urea, acrylamide and methacrylamide in deionized water, add 2,2'-azobisisobutylamidine dihydrochloride under nitrogen protection, react at 60°C for 24 h, and dialysis to purify to obtain poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea).

[0059] In the preparation of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 90:8:3:1.

[0060] Preparation Example 2: In the preparation of the spiroxazine-secondary ammonium hexafluorophosphate, the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:6.5:1.075.

[0061] In the preparation of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 87.5:9:2:1.

[0062] Preparation Example 3: In the preparation of the spiroxazine-secondary ammonium hexafluorophosphate, the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:6:1.1.

[0063] In the preparation of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 85:10:1:1.

[0064] Example 1: A method for preparing a multifunctional transparent display and dark-tone light composite film, comprising the following steps: The raw material obtained in Example 3 is prepared as follows:

[0065] S1. Preparation of dark-tone light-reflecting composite layer paste and photochromic layer paste:

[0066] Under light-protected conditions, polyurethane acrylate and bisphenol A epoxy diacrylate are heated at 50-60℃ and mixed evenly to form a prepolymer matrix. Dark azobenzene tinting compounds are uniformly dispersed in a nematic microcrystalline medium mixture, and the prepolymer matrix is ​​added. The mixture is stirred at 50℃ for 3 hours to obtain a dark-tinted light-emitting composite layer slurry, which is then allowed to stand to degas for later use.

[0067] Poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate were dissolved in N,N-dimethylformamide and stirred in the dark for 18 hours to obtain a photochromic layer slurry.

[0068] S2, Dimming film assembly:

[0069] Take a conductive substrate with the conductive side facing up, spin-coate a layer of photochromic slurry, and vacuum dry at 60°C for 12 hours to form a photochromic layer; lay glass fiber or polymer microsphere spacers in the edge area of ​​the photochromic layer, cover with a dark-toned photochromic composite slurry, and perform photocuring.

[0070] S3, Post-processing:

[0071] After photocuring, the film is left to stand at room temperature and in a dark environment for 3 hours for thermal relaxation, resulting in a multifunctional transparent display and dark-tone light composite film.

[0072] In S1, poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbita[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate are dissolved in N,N-dimethylformamide to obtain a solution with a solid content of 15%.

[0073] In S2, the wet film thickness of the photochromic layer is 3 μm, the thickness of the dark-tone composite layer is 15 μm, the curing light wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 .

[0074] Example 2: Preparation of the raw material obtained in Example 2, wherein in S1, poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate are dissolved in N,N-dimethylformamide to obtain a solution with a solid content of 17.5%.

[0075] In S2, the wet film thickness of the photochromic layer is 2 μm, the thickness of the dark-tone composite layer is 20 μm, the curing light wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 .

[0076] Example 3: Preparation of the raw material obtained in Example 1, wherein in S1, poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate are dissolved in N,N-dimethylformamide to obtain a solution with a solid content of 20%.

[0077] In S2, the wet film thickness of the photochromic layer is 1 μm, the thickness of the dark-tone composite layer is 25 μm, the curing light wavelength is 365 nm, and the light intensity is 100 mW / cm². 2 .

[0078] At the same time, the present invention also includes:

[0079] Comparative Example 1: Based on Preparation Example 2, the difference is that the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:2:1.075, and the rest is the same as in Example 2.

[0080] Comparative Example 2: Based on Preparation Example 2, the difference is that in the preparation of poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 87.5:9:5:1, and the rest is the same as in Example 2.

[0081] Comparative Example 3: Based on Example 2, the difference is that the wet film thickness of the chromogenic layer is 10 μm, and the rest is the same as in Example 2.

[0082] Comparative Example 4: Based on Example 2, the difference is that 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine] was used directly, without the synthesis of spiroxazine-secondary ammonium salt hexafluorophosphate, that is, the final molecule does not have a strongly polar terminal group, and the rest is the same as Example 2.

[0083] For each embodiment and comparative example, the dimming film of the present invention was tested according to GB / T 35847-2018 Electro-liquid crystal film dimming glass; GB / T 31370.5-2018 Flat panel display (FPD) color filter test method part 5: contrast ratio; GB / T 1040.3-2006 Plastics tensile properties determination part 3: test strips for thin plastics and sheets; ASTM D7791-12 Standard test method for uniaxial fatigue properties of plastics, and the driving voltage (threshold voltage Vth, saturation voltage Vsat), contrast ratio (CR), response time (on-ton, off-toff), transmittance (on-state T-on, off-state T-off), and other related properties, under energized conditions of 120mW / cm². 2 The transmittance was measured under ultraviolet light irradiation, and the corresponding results are shown in Table 1:

[0084] Table 1. Performance test data of the dimming film

[0085]

[0086] Data Analysis:

[0087] The electro-optic dimming performance is mainly determined by the dark-tone dimming composite layer, which is based on the principle of polymer dispersed microcrystalline media (PDLC). In this layer, the microcrystalline media droplets rearrange under an electric field to achieve the switching between light transmission and scattering (or absorption) states.

[0088] The driving voltages of Examples 1-3 were at a low level of 16-20V / 28-35V, showing good driveability. The driving voltage of Comparative Example 2 was significantly higher (25 / 45V), while Comparative Example 4 was slightly better or comparable to the Examples. The driving voltage is related to the size of the microcrystalline medium droplets and the interfacial anchoring energy. The smaller the droplets, the stronger the interfacial effect, and the higher the required driving voltage. In Comparative Example 2, the feed ratio of cucurbita[6]urea monomer was too high (molar ratio 5%), which may lead to excessive crosslinking density or the formation of an overly dense polymer network during polymerization, limiting the growth of microcrystalline medium droplets and forming more and smaller droplets, thus leading to an increase in driving voltage. The driving voltage of Comparative Example 4 (unmodified spiroxazine) was comparable to that of the Examples, indicating that the composition of the photochromic layer has little interference with the electric field driving process of the dark-toned light layer, which is in line with the design expectation—the two layers are relatively independent electrically.

[0089] Example 2 exhibited the best overall optical performance (CR=73, T-on=87.2%, T-off=1.2%). The CR of all examples was higher than that of Comparative Examples 1, 3, and 4. Comparative Example 4 had a significantly higher off-state transmittance (T-off), resulting in a lower CR value.

[0090] Contrast ratio (CR) is the ratio of transmittance in the on state to transmittance in the off state. High CR requires high T-on and low T-off. Thanks to optimized formulation and process, the microcrystalline media droplets scatter light and the azobenzene tinting compound absorbs light most fully in the off state (extremely low T-off); in the on state, the microcrystalline media molecules are arranged in an orderly manner, and the obstruction to light is minimal (extremely high T-on). In Comparative Example 1, the amount of dimethylamine was insufficient, resulting in incomplete quaternization of spiroxazine. The product still contained a large amount of unmodified, weakly polar bromoalkane precursors. This weakened the binding ability of spiroxazine molecules to the cucurbita[6] urea host, and some spiroxazine was unevenly distributed in the polymer matrix, possibly forming tiny crystals or aggregates. These defects would become additional light scattering centers in the off state, leading to an increase in T-off and thus a decrease in CR.

[0091] Comparative Example 3: The photochromic layer was too thick (10 μm). While this may enhance the color depth, more importantly, it introduced severe light scattering and intrinsic absorption, resulting in a significant decrease in overall transmittance (T-on and on-state transmittance (after UV exposure)) in both on and off states, thereby impairing CR.

[0092] Comparative Example 4 directly used the unquaternized spiroxazine precursor. This molecule lacks a strongly polar hexafluorophosphate counterion, has poor compatibility with polar polymer matrices (such as polyacrylamide), and cannot form a stable host-guest inclusion complex with cucurbita[6]urea. This leads to severe phase separation of the spiroxazine molecule during film formation, forming macroscopic or microscopic defects, significantly enhancing light scattering in the off state, resulting in a T-off of up to 4.0% and a sharp drop in CR to 18.

[0093] The response times of Examples 1-3 are relatively fast, ranging from 15-35 ms. Comparative Examples 2 (slower ton / toff) and 3 (significantly slower ton / toff) are the main focus of this study. The response speed is influenced by the viscoelasticity of the microcrystalline medium, the droplet size, and the elasticity of the polymer network.

[0094] As mentioned above, in Comparative Example 2, the excessively high cucurbit[6]urea content resulted in a dense polymer network. This network exerted an excessively strong constraint on the microcrystalline media droplets, requiring not only a higher voltage (high driving voltage) to drive the microcrystalline media to change direction, but also, after the electric field was removed, the microcrystalline media was hindered by a strong elastic recovery force and could not quickly return to a random state, resulting in slower on and off responses.

[0095] The extremely thick photochromic layer in Comparative Example 3 itself exhibits propagation delay and scattering effects on light, but this is not the primary cause. The main cause may be that the thick film experiences greater internal stress during curing, which could cause compression or interfacial interactions with adjacent dark-toned light layers, indirectly affecting the rearrangement dynamics of microcrystalline media droplets and leading to a slower response.

[0096] The photochromic properties are determined by the photochromic layer, and the core is the supramolecular interaction between spiroxazine-secondary ammonium salt hexafluorophosphate and poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea). The coloring response of the examples is 3-4 seconds, and the fading half-life is 22-28 seconds. The responses of Comparative Examples 1, 2, and 3 are all slower than those of the examples, especially Comparative Example 3, which has a fading half-life of up to 60 seconds. Comparative Example 4 has the fastest response (2.5s / 20s), but its fatigue resistance is extremely poor. In the examples, the coordination between the secondary ammonium salt cation of spiroxazine and the carbonyl group at the cucurbit[6]urea port, as well as the hydrophobic interaction, together form a stable host-guest inclusion complex. This inclusion effect:

[0097] For the coloring process (UV-on): the energy barrier for molecular conformational change is slightly increased, which may result in a coloring response that is a fraction of a second slower than that of pure spiroxazine molecules (Comparative Example 4), but this is a reasonable sacrifice in exchange for the huge stability.

[0098] For the fading process (UV-off): the fading half-life was significantly prolonged. Cucurbita[6]urea cavity stabilized the configuration of the open-ring spiroxazine (particulate cyanine), improving its thermodynamic stability and slowing its return to the closed-ring state. This is a desirable "memory effect" that allows the tinted state to be maintained for a longer period of time.

[0099] In Comparative Example 1, the quaternization was incomplete, and some spiroxazine failed to form ammonium salt terminals that strongly interact with cucurbita[6]urea. The coloring and fading behavior of these "free" molecules was closer to that of Comparative Example 4. However, due to the presence of some successfully modified molecules in the system, the overall performance was between that of the examples and Comparative Example 4. In Comparative Example 2, the excessively high cucurbita[6]urea density may lead to overly rigid polymer chains or the formation of multiple cross-linking points, which restricts the free volume and molecular mobility necessary for spiroxazine molecules to undergo ring-opening isomerization after photoexcitation, thus resulting in slower coloring and fading. Comparative Example 3: Thick film effect. The photochromic reaction occurs throughout the entire film layer. When ultraviolet light is incident, the surface molecules color rapidly, but the light propagates and gradually attenuates in the thick film, resulting in weaker light intensity received by the bottom layer molecules, and the overall coloring is slower. Similarly, during the fading process, the synergy of heat transfer and molecular conformational changes is more difficult in the thick film, resulting in an extremely slow fading process. In Comparative Example 4, the unencapsulated spiroxazine molecules move freely within the polymer matrix without additional energy barriers, resulting in the fastest coloring and fading. However, this "freedom" comes at the cost of stability.

[0100] Fatigue resistance is the most important indicator of the superiority of the design of this invention. The fatigue resistance of Example 2 is as high as 10,000 cycles, while that of Comparative Example 4 drops sharply to 500 cycles, and that of Comparative Example 1 is only 2,000 cycles. The fatigue of spiroxazine toning compounds mainly stems from the side reactions of the open-ring body (partial cyanine), such as oxidative degradation or irreversible cyclization reactions. The cavity of cucurbita[6]urea provides a confined, hydrophobic microenvironment for the open-ring body of spiroxazine. This microenvironment can:

[0101] Oxygen shielding: effectively reduces the contact between open-ring compounds and oxygen, inhibiting oxidative degradation.

[0102] Stable high-energy state: Through host-guest interactions, the reactivity of the open-ring body is reduced, making it less prone to irreversible chemical side reactions.

[0103] Preventing aggregation: Each spiroxazine molecule is isolated in its own cucurbit[6]urea “room”, avoiding inactivation caused by π-π stacking between molecules.

[0104] Comparative Example 4 had no protection from cucurbita[6]urea, and the spiroxazine molecule was directly exposed to oxygen and the external environment. The open-ring form degraded rapidly after multiple cycles, resulting in extremely poor fatigue resistance. Due to incomplete quaternization, only a portion of the spiroxazine in Comparative Example 1 was protected, while the rest fatigued rapidly like the molecules in Comparative Example 4. Therefore, its overall lifespan was far lower than that of the fully optimized examples.

[0105] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multifunctional transparent display and dark-tone light composite film, characterized in that, It includes an upper conductive substrate, a dark-toned light composite layer, a photochromic layer, and a lower conductive substrate, which are stacked from top to bottom; The conductive substrate is an indium tin oxide-polyethylene terephthalate composite film; The dark-toned light composite layer is obtained by coating a mixture of dark azobenzene tinting compounds, polyurethane acrylate, bisphenol A epoxy diacrylate, nematic microcrystalline medium mixture, and photoinitiator in a mass ratio of 2-3:35-40:20-25:35-40:

2. The photochromic layer is obtained by coating poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium salt hexafluorophosphate in a mass ratio of 2-3:1; The preparation process of poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) includes: cucurbit[6]urea reacting with 1-butyl-3-methylimidazolium chloride and potassium persulfate to obtain monohydroxycucurbit[6]urea; monohydroxycucurbit[6]urea reacting with 4-chloromethylstyrene to obtain 4-vinylbenzyloxycucurbit[6]urea; and copolymerizing 4-vinylbenzyloxycucurbit[6]urea, acrylamide and methacrylamide to obtain poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea); Spirooxazine-secondary ammonium salt hexafluorophosphate has the following structure: 。 2. The multifunctional transparent display and dark-tone light composite film according to claim 1, characterized in that, The preparation process of the spiroxazine-secondary ammonium salt hexafluorophosphate includes the following steps: 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine] was dissolved in acetonitrile, dimethylamine was added, and the mixture was stirred at 38-42°C for 6-8 hours. The mixture was then rotary evaporated and dissolved in ice water. Ammonium hexafluorophosphate was added, and the white precipitate was collected and dried under vacuum to obtain spiroxazine-secondary ammonium hexafluorophosphate.

3. The multifunctional transparent display and dark-tone light composite film according to claim 2, characterized in that, In the preparation of the spiroxazine-secondary ammonium hexafluorophosphate, the molar ratio of 1-(2-bromoethyl)-2-tert-butyl-3,3-dimethyl-6-nitrospiro[indoline-2,3'-naphtho[2,1-b][1,4]oxazine], dimethylamine and ammonium hexafluorophosphate is 1:6-7:1.05-1.

1.

4. The multifunctional transparent display and dark-tone light composite film according to claim 1, characterized in that, The preparation process of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbita[6]urea) includes the following steps: (1) Dissolve cucurbit[6]urea and 1-butyl-3-methylimidazolium chloride in concentrated hydrochloric acid, add potassium persulfate at 58-62℃, stir for 3.5-4.5h, cool to room temperature, precipitate with cold deionized water, repeat dissolution and purification of the precipitate to obtain monohydroxycucurbit[6]urea; (2) Dissolve monohydroxycucurbit[6]urea in N,N-dimethylformamide, under nitrogen protection and ice-water bath, add sodium hydride and stir for 25-35 min; add 4-chloromethylstyrene, stir at room temperature for 23-25 ​​h, precipitate the product with ice-cold ether, wash with tetrahydrofuran and ether alternately, and dry under vacuum to obtain 4-vinylbenzyloxycucurbit[6]urea; (3) Dissolve 4-vinylbenzyloxycucurbit[6]urea, acrylamide and methacrylamide in deionized water, add 2,2'-azobisisobutylamidine dihydrochloride under nitrogen protection, react at 58-62℃ for 23-25h, and dialysis to purify to obtain poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea).

5. The multifunctional transparent display and dark-tone light composite film according to claim 4, characterized in that, In the preparation of the poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea), the molar ratio of acrylamide, methacrylamide, 4-vinylbenzyloxycucurbit[6]urea and 2,2'-azobisisobutylamidine dihydrochloride is 85-90:8-10:1-3:

1.

6. A method for preparing a multifunctional transparent display and deep-tone light composite film as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Preparation of dark-tone light-reflecting composite layer paste and photochromic layer paste: Under light-protected conditions, polyurethane acrylate and bisphenol A epoxy diacrylate are heated at 50-60℃ and mixed evenly to form a prepolymer matrix. Dark azobenzene tinting compounds are uniformly dispersed in a nematic microcrystalline medium mixture, and the prepolymer matrix is ​​added. The mixture is stirred at 50℃ for 2-4 hours to obtain a dark-tinted light-emitting composite layer slurry, which is then allowed to stand to degas for later use. Poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium salt hexafluorophosphate were dissolved in N,N-dimethylformamide and stirred in the dark for 12-24 hours to obtain photochromic layer slurry. S2, Dimming film assembly: Take a conductive substrate with the conductive side facing up, spin-coate a layer of photochromic slurry, and vacuum dry at 58-62℃ for 10-14 hours to form a photochromic layer; lay glass fiber or polymer microsphere spacers in the edge area of ​​the photochromic layer, cover with a dark-toned photochromic composite slurry, and perform photocuring. S3, Post-processing: After photocuring, the film is left to stand at room temperature and in a dark environment for 2-4 hours, or subjected to heat treatment at 28-42℃ for 25-35 minutes for thermal relaxation, to obtain a multifunctional transparent display and dark-tone light composite film.

7. The method for preparing a multifunctional transparent display and dark-tone light composite film according to claim 6, characterized in that, In S1, poly(acrylamide-co-methacrylamide-g-4-vinylbenzyloxycucurbit[6]urea) and spiroxazine-secondary ammonium hexafluorophosphate are dissolved in N,N-dimethylformamide to obtain a solution with a solid content of 15-20%.

8. The method for preparing a multifunctional transparent display and dark-tone light composite film according to claim 6, characterized in that, In S2, the wet film thickness of the photochromic layer is 1-3 μm, the thickness of the dark-tone composite layer is 15-25 μm, the curing light wavelength is 365 nm, and the light intensity is 50-100 mW / cm². 2 .

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