High-weather-resistance liquid crystal dimming film

Abstract

The invention provides a high-weather-resistance liquid crystal dimming film which is provided with a first conducting film, a liquid crystal dimming layer and a second conducting film, the liquid crystal dimming layer is located between the first conducting film and the second conducting film, the liquid crystal dimming layer contains liquid crystal, a polymer, a photoinitiator and a light stabilizer, the liquid crystal is nematic liquid crystal, and the polymer is a polymer. The polymer comprises at least one radical-initiated resin and at least one cation-initiated resin, the radical-initiated resin comprises at least one of acrylic resin or allyl resin, and the cation-initiated resin comprises at least one epoxy resin; the photoinitiator comprises at least one radical initiator and at least one cationic initiator, the mass percentage of the total mass of the photoinitiator and the liquid crystal dimming layer is 0.01-5%, the proportion of the cationic initiator is smaller than that of the radical initiator, and the weight percentage of the light stabilizer and the liquid crystal dimming layer is not higher than 0.05%. The liquid crystal dimming film disclosed by the invention is high in weather resistance.

Description

Technical Field

[0001] The present invention relates to the field of liquid crystal dimming films, and more particularly to a liquid crystal dimming film with high weather resistance. Background Art

[0002] Liquid crystal dimming film is an intelligent dimming material based on liquid crystal technology. It changes the orientation of liquid crystal molecules through an electric field to achieve arrangement control of liquid crystal molecules and adjust light transmittance.

[0003] Liquid crystal dimming film consists of two layers of transparent conductive film and a polymer liquid crystal layer in between. The polymer liquid crystal layer is formed by curing a prepolymer and liquid crystal. When powered off, the liquid crystal molecules are disordered, preventing light from penetrating, resulting in a milky white, opaque appearance. When powered on, the liquid crystal molecules rearrange under the influence of the electric field, allowing light to pass through, resulting in a transparent state.

[0004] Liquid crystal dimming films can be used in architectural glass, automotive windshields, commercial projectors, medical equipment, and other fields. For example, in buildings, they can be used as smart curtains or thermal insulation films; in cars, they can be used as privacy films or sunshade films. However, due to the relatively harsh application conditions in outdoor and automotive applications, the weather resistance of traditional liquid crystal dimming films cannot meet the requirements, limiting their application.

[0005] To improve weather resistance, the industry generally mixes fluorinated nematic liquid crystals with azo dyes and anthraquinone dyes in specific ratios. However, the photostability, color, and curing process of azo and anthraquinone dyes limit their application. Azo dyes have poor photostability. The nitrogen atoms on the azo group in their molecular structure have a high electron cloud density, making them susceptible to photooxidation and breakage. While anthraquinone dyes have higher photostability than azo dyes, they often exhibit distinct colors and are therefore not widely used in transparent dimming films. Because the absorption spectra of azo and anthraquinone dyes partially overlap with the absorption spectra of photoinitiators, the absorption efficiency of photocuring is reduced, placing higher demands on the curing process, making this method uneconomical.

[0006] Therefore, there is a lack of a technical solution that can achieve a highly weather-resistant liquid crystal dimming film. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a liquid crystal dimming film with high weather resistance.

[0008] The present invention provides a highly weather-resistant liquid crystal dimming film, comprising a first conductive film, a liquid crystal dimming layer, and a second conductive film. The liquid crystal dimming layer is located between the first conductive film and the second conductive film. The liquid crystal dimming layer contains liquid crystal, a polymer, a photoinitiator, and a light stabilizer. The liquid crystal is a nematic liquid crystal. The polymer includes at least one free radical initiating resin and at least one cationic initiating resin. The free radical initiating resin includes at least one of an acrylic resin or an allyl resin. The cationic initiating resin includes at least one epoxy resin. The photoinitiator includes at least one free radical initiator and at least one cationic initiator. The mass percentage of the photoinitiator to the total mass of the liquid crystal dimming layer is 0.01-5%, the proportion of the cationic initiator is less than that of the free radical initiator, and the weight percentage of the light stabilizer to the liquid crystal dimming layer is not higher than 0.05%.

[0009] Preferably, the first conductive film and the second conductive film are PET films containing ITO.

[0010] Preferably, the liquid crystal is a nematic liquid crystal; the nematic liquid crystal contains at least one liquid crystal monomer represented by the following formula (I): ; wherein X and Y each independently represent a C1-C12 alkyl, alkoxy, cyano, isothiocyanate or halogen, ring A and ring B each independently represent a benzene ring, a pyridine ring or a cyclohexane ring; m and n each independently represent an integer of 0-4; L is an acetylenic bond, an olefinic bond or an ester group; a represents 0 or 1.

[0011] Preferably, the mass of the polymer is 30%-70% of the total mass of the polymer and the liquid crystal; the mass percentage of the photoinitiator to the total mass of the liquid crystal dimming layer is 0.01-5%, and the proportion of the cationic initiator is less than that of the free radical initiator; the acrylic resin contains acrylic monomers or acrylic oligomers, and the acrylic monomers contain at least one of monofunctional acrylic monomers, difunctional acrylic monomers or multifunctional acrylic resins; the acrylic oligomer contains at least one acrylic group; and the epoxy resin contains at least one non-monofunctional epoxy monomer or epoxy oligomer.

[0012] Preferably, the light stabilizer is a triazine initiator, and the triazine initiator has a structure described by the following formula (II): ; wherein, R1 and R2 each independently represent a C1-C12 substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted phenyl, substituted or unsubstituted phenoxy or hydroxyl group, R3 represents a substituted or unsubstituted alkoxy or hydroxyl group; p and q each independently represent 0, 1, 2, 3, 4 or 5, and r represents 0, 1, 2, 3 or 4.

[0013] Preferably, the light stabilizer is selected from at least one of the compounds shown in the following structures: .

[0014] Preferably, the liquid crystal dimming layer further contains an ionic liquid, and the weight percentage of the total mass of the ionic liquid and the liquid crystal dimming layer is no more than 2%.

[0015] Preferably, the ionic liquid is one selected from a salt composed of an organic cation and an inorganic anion, a salt composed of an inorganic cation and an organic anion, or a salt composed of an organic cation and an organic anion; the organic cation of the ionic liquid is an imidazole, pyridine, pyrrolidine, piperidine, pyrazole, triazole, quaternary ammonium, quaternary phosphonium or thiazole organic cation; the organic anion or inorganic anion is a trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, hexafluorophosphate, tetrafluoroborate, methanesulfonate, acetate, trifluoroacetate, bisfluorosulfonyl imide, methylsulfate, methylcarboxylate, chloride, bromide, iodide, fluoride, nitrate, sulfate, hydrogensulfate, phosphate, decanoate or dicyanimide anion.

[0016] Preferably, the ionic liquid contains one of the following ionic liquids: 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluorosulfonate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluorosulfonate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), N-ethylpyridinium tetrafluoroborate, tetramethylammonium bis(trifluoromethanesulfonyl imide), trihexyltetradecylphosphonium chloride or hexadecyl-3-methylimidazolium bromide.

[0017] Preferably, the photoinitiator is TPO or 1173, the cationic initiator is diphenyliodonium hexafluorophosphate, diphenyliodonium trifluoromethanesulfonate, triphenylsulfonium tetrafluoroborate, tri-p-tolylsulfonium hexafluorophosphate, U-160, U-261 or U-180, the epoxy resin is 1,6-hexanediol diglycidyl ether or trimethylolpropane triglycidyl ether, and the light stabilizer is S-8, S-4 or S-3.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) By adding epoxy resin and cationic initiator, the temperature weather resistance of the liquid crystal dimming film is improved. (2) By adding light stabilizer, the light weather resistance of the liquid crystal dimming film is improved. (3) By adjusting the ratio of epoxy resin, cationic initiator and light stabilizer, the overall weather resistance of the liquid crystal dimming film is improved. The weather resistance of the liquid crystal dimming film is further improved by adding ionic liquid. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose, the following is a description with reference to embodiments.

[0020] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0021] The basic scientific principle of liquid crystal dimming film is very clear, that is, the orientation of liquid crystal molecules is changed by electric field, so as to realize the arrangement control of liquid crystal molecules and the adjustment of light transmittance. However, as a component of the liquid crystal dimming layer, since liquid crystal is a mixed component and polymer is also a mixed component, there are infinite possibilities for matching each other, and the technical complexity is relatively high. The function of liquid crystal dimming film is to be in a foggy state when no voltage is applied and in a transparent state when voltage is applied. Such a simple function enables it to be applied to various occasions. Therefore, weather resistance in various scenarios becomes very important. Regarding weather resistance, it is mainly affected by multiple factors such as water vapor, oxygen, ultraviolet light, temperature, noise, magnetic field, vibration, salt spray corrosion, etc. Among them, water vapor, oxygen, ultraviolet light and temperature have a relatively large impact on liquid crystal dimming film.

[0022] Moisture and oxygen primarily affect the curing process. After processing, since the LCD dimming film is laminated and edge-sealed, the effects of moisture and oxygen generally do not need to be considered. Temperature limits the use range of the LCD dimming film. This is determined by the product itself and is primarily determined by the operating range of the liquid crystal. It is not inherently weather-resistant. However, because temperature changes can cause thermal expansion and contraction of the material, long-term temperature fluctuations can lead to internal stress accumulation, causing cracking, deformation, and other problems. Therefore, even within the operating range, long-term use may result in performance changes. As a type of optical film, ultraviolet light has a relatively significant impact on the LCD dimming film. Ultraviolet light has high energy and can destroy the molecular structure of the material, causing discoloration, cracking, and reduced strength. It is considered the main aging factor of the LCD dimming film.

[0023] Therefore, the inventors believe that the influence of ultraviolet radiation on the liquid crystal dimming film is the main factor, and temperature is the secondary factor.

[0024] Weatherability refers to the ability of a material, product, or structure to maintain stable physical, chemical, and mechanical properties under certain environmental conditions over long periods of use. In other words, weatherability reflects the material or product's ability to resist aging and degradation under certain environmental factors. For liquid crystal dimming films, this primarily refers to their ability to maintain performance under UV exposure and temperature fluctuations.

[0025] Regarding the performance of liquid crystal dimming film, in terms of weather resistance, the main considerations are changes in transmittance, driving voltage and appearance, including color changes.

[0026] The present invention provides a highly weather-resistant liquid crystal dimming film, comprising a first conductive film, a liquid crystal dimming layer, and a second conductive film. The liquid crystal dimming layer is located between the first conductive film and the second conductive film. The liquid crystal dimming layer contains liquid crystal, a polymer, a photoinitiator, and a light stabilizer. The liquid crystal is a nematic liquid crystal. The polymer includes at least one free radical initiating resin and at least one cationic initiating resin. The free radical initiating resin includes at least one of an acrylic resin or an allyl resin. The cationic initiating resin includes at least one epoxy resin. The photoinitiator includes at least one free radical initiator and at least one cationic initiator. The mass percentage of the photoinitiator to the total mass of the liquid crystal dimming layer is 0.01-5%, the proportion of the cationic initiator is less than that of the free radical initiator, and the weight percentage of the light stabilizer to the liquid crystal dimming layer is not higher than 0.05%.

[0027] Preferably, the first conductive film and the second conductive film are PET films containing ITO, where ITO is indium tin oxide and PET is polyethylene terephthalate.

[0028] Preferably, the liquid crystal is a nematic liquid crystal; the nematic liquid crystal contains at least one liquid crystal monomer represented by the following formula (I): ; wherein X and Y each independently represent a C1-C12 alkyl group, an alkoxy group, a cyano group, an isothiocyanate group or a halogen group; ring A and ring B each independently represent a benzene ring, a pyridine ring or a cyclohexane ring; m and n each independently represent an integer from 0 to 4; L is an acetylenic bond, an olefinic bond or an ester group; and a represents 0 or 1.

[0029] The nematic liquid crystal of the present invention can be commercially available or homemade. In an embodiment of the present invention, the nematic liquid crystal is a positive liquid crystal. Examples of the liquid crystal of the present invention include, but are not limited to, E7, E8, SLC1717, SLC7011, ZLI-3239, or C7, all of which are well known to those skilled in the art. For example, the chemical composition of E7 has the following components and proportions:

[0030] For example, the chemical composition of E8 has the following components and proportions:

[0031] Preferably, the mass of the polymer is 30%-70% of the total mass of the polymer and the liquid crystal; the mass percentage of the photoinitiator to the total mass of the liquid crystal dimming layer is 0.01-5%, and the proportion of the cationic initiator is less than that of the free radical initiator; the acrylic resin contains acrylic monomers or acrylic oligomers, and the acrylic monomers contain at least one of monofunctional acrylic monomers, difunctional acrylic monomers or multifunctional acrylic resins; the acrylic oligomer contains at least one acrylic group; and the epoxy resin contains at least one non-monofunctional epoxy monomer or epoxy oligomer.

[0032] The polymer can be commercially available, such as the NOA series familiar to those skilled in the art, including, but not limited to, NOA60, NOA61, NOA63, NOA65, NOA68, NOA71, NOA72, NOA73, NOA74, NOA76, NOA81, NOA84, NOA85, NOA86, NOA87, NOA88, NOA89, NOA1625, and NOA108. The polymer can also be homemade.

[0033] For example, but not limited to, acrylic monomers include butyl acrylate (BA), isooctyl acrylate (2-EHA), isodecyl acrylate (IDA), lauryl acrylate (LA), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), glycidyl methacrylate (GMA), isobornyl methacrylate (IBMA), tetrahydrofuranyl methacrylate (THFFA), phenoxyethyl acrylate (POEA), vinyl acetate (VA), N-vinyl pyrrolidone (NVP), diethylene glycol diacrylate (DEGDA), triethylene glycol diacrylate (TEGDA), diethylene glycol dimethacrylate (DE ... Acrylates (TEGDA), dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), neopentyl glycol diacrylate (NPGDA), ethylene phthalate diacrylate (PDDA), trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate (PETA), pentaerythritol tetraacrylate (PETTA), ditrimethylolpropane tetraacrylate (DTMPTTA), dipentaerythritol pentaacrylate (DPPA), dipentaerythritol hexaacrylate (DPHA). Preferably, aliphatic acrylates are used.

[0034] The acrylic resins of the present invention include acrylic monomers and oligomers. Oligomers contain at least one polymerizable group, and their structure is not limited. They can include oligomers containing acrylic groups or other groups, such as polyester, polyether, and polyurethane oligomers. Acrylic groups also include methacrylic groups. Polymerizable groups refer to groups that can participate in polymerization reactions and include acrylic groups, allyl groups, isocyanate groups, hydroxyl groups, and amine groups. It is understood that when there are two or more polymerizable groups, the polymerizable groups may also include epoxy groups. The acrylic resins of the present invention may contain only acrylic monomers or only acrylic oligomers, that is, they may contain only acrylic monomers without acrylic oligomers, or only acrylic oligomers without acrylic monomers. When containing acrylic monomers, they may further contain non-acrylic oligomers. When containing acrylic oligomers, they may further contain non-acrylic oligomers.

[0035] The allyl resin in the present invention may be an allyl monomer containing an allyl group, or an oligomer containing an allyl group.

[0036] The epoxy resin in the present invention can be an epoxy monomer or an oligomer containing epoxy groups. The epoxy resin contains at least one non-monofunctional epoxy monomer or epoxy oligomer, that is, at least one difunctional epoxy monomer or epoxy oligomer, or at least one multifunctional epoxy monomer or epoxy oligomer. The multifunctional group is typically three or four. When the epoxy resin already contains a non-monofunctional epoxy monomer or epoxy oligomer, it may also contain a monofunctional epoxy monomer or epoxy oligomer.

[0037] Examples of allyl monomers include, but are not limited to, trimethylolpropane diallyl ether (TMPDE), trimethylolpropane monoallyl ether (TMPME), and pentaerythritol triallyl ether (APE).

[0038] By way of example and not limitation, epoxy resins, based on their chemical structure, include glycidyl ethers, glycidyl esters, glycidyl amines, and alicyclics. Glycidyl ethers are often further subdivided into bisphenol A, bisphenol F, bisphenol S, hydrogenated bisphenol A, and aliphatic glycidyl ethers. For more information on epoxy resins, see Epoxy Resins and Their Applications, edited by Chen et al. (Chemical Industry Press, 2004, ISBN 7-5025-5154-9). Preferably, aliphatic epoxy resins are used.

[0039] Examples of epoxy monomers include, but are not limited to, bisphenol A diglycidyl ether (BDEGA), bisphenol F diglycidyl ether (DGEBF), 1,6-hexanediol diglycidyl ether (HDDGE), ethylene glycol diglycidyl ether (EGDGE), neopentyl glycol diglycidyl ether (NPGDGE), biphenyl diglycidyl ether (DGEBP), butanediol diglycidyl ether (BDDGE), trimethylolpropane triglycidyl ether (TPGDA), and trimethylolpropane triglycidyl ether (TMPTA). Preferably, aliphatic epoxy monomers are used.

[0040] Regarding the type of initiator, it can be either free radical initiation or cationic initiation. Specific examples of free radical initiators include, but are not limited to, 2-hydroxy-2-methylpropiophenone (1173), 1-hydroxycyclohexyl benzophenone (184), benzoin dimethyl ether (651), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (819), and isopropylthioxanthone (ITX). Cationic initiators include diaryliodonium salts, triarylsulfonium salts, alkylsulfonium salts, iron arene salts, sulfonyloxy ketones and triarylsiloxanes, and specific examples, but not limited to, include: bis(4-tert-butylphenyl)iodonium hexafluorophosphate, bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate, cyclopropyldiphenylsulfonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, diphenyliodonium hexafluoroarsenate, diphenyl ... diphenyl Methanesulfonate, 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate, triphenylsulfonium tetrafluoroborate, tri-p-tolylsulfonium hexafluorophosphate, tri-p-tolylsulfonium trifluoromethanesulfonate, 4-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate (U-160), 4-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate (U-180), η6-isopropylferrocene(II) hexafluorophosphate (U-261).

[0041] Preferably, the light stabilizer is a triazine initiator, and the triazine initiator has a structure described by the following formula (II): ; wherein R1 and R2 independently represent a C1-C12 substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted phenoxy group or a hydroxyl group; R3 represents a substituted or unsubstituted alkoxy group or a hydroxyl group; p and q independently represent 0, 1, 2, 3, 4 or 5; and r represents 0, 1, 2, 3 or 4.

[0042] Preferably, the light stabilizer is selected from at least one of the compounds shown in the following structures: .

[0043] When liquid crystal dimming films were first developed, thermal curing was primarily used, using polymers primarily based on epoxy resins. However, thermal curing requires heating the liquid crystal dimming film to a certain temperature, resulting in high energy consumption. Furthermore, as the temperature rises, the polymers continue to polymerize. Unlike thermal curing, UV curing only undergoes a curing reaction when exposed to ultraviolet light, resulting in a short curing time. Therefore, it quickly replaced thermal curing, which now uses polymers primarily based on acrylic resins. However, in terms of weather resistance, the volume shrinkage of acrylates after free radical curing is much greater than that of epoxy resins, which affects the weather resistance of acrylate polymers. Furthermore, the adhesion of acrylic resins is inferior to that of epoxy resins, further affecting weather resistance. Of course, not all acrylic resins have inferior adhesion to epoxy resins, but the cost of modified acrylic resins is generally increased.

[0044] For liquid crystal dimming films, the difference before and after UV curing is quite obvious. Before curing, the liquid crystal dimming layer is transparent. As curing progresses, the liquid crystal separates from the polymer system, and the appearance gradually changes from transparent to white, and finally to a normal foggy state. Because the liquid crystal separates from the polymer system, light cannot propagate in a straight line, and the UV-irradiated surface and the bottom layer become inconsistent. This inconsistency is also the source of poor weather resistance.

[0045] Multiple curing can be used, curing with one wavelength first and then with another wavelength, which may reduce shrinkage. The advantage of this is that there is no need to adjust the formula, only the process, but the adhesion is more difficult to adjust. Dual curing can be used, adding epoxy resin and curing under the dual effects of UV and heat. However, whether UV and heat curing are carried out simultaneously or UV curing first and then heat curing, the energy consumption required for heating will inevitably increase. Increasing production energy consumption in pursuit of weather resistance will undoubtedly increase costs, which is uneconomical.

[0046] Therefore, under the premise of light curing, the use of free radical and cationic polymerization, which takes into account the advantages of both acrylates and epoxy resins, becomes the preferred choice. The cationic initiator of the present invention is also a photoinitiator, which also has the characteristic of dark reaction. Dark reaction refers to the ability to continue curing even after the light source is removed. Generally speaking, dark reaction is a disadvantage because it can cause the product to continue "curing" after the processing is completed, that is, the curing process is still ongoing, resulting in inconsistent quality.

[0047] The present invention uses epoxy resin to improve adhesion and reduce shrinkage. Epoxy resin is relatively suitable as a cationic initiator and can achieve the invention's objectives through a dark reaction. The inventors believe that the dark reaction is not a disadvantage of the present invention's technical solution, but rather a feature that can be fully utilized to achieve the invention's objectives.

[0048] Another disadvantage of cationic initiators is that they impart a slight color, which is considered disadvantageous for colorless liquid crystal dimming films. However, the inventors have discovered that a low addition ratio of cationic initiators has minimal effect on the color of the liquid crystal dimming film.

[0049] In the present invention, triazine light stabilizers are primarily used to enhance UV weathering resistance. Triazine light stabilizers, also known as UV absorbers, possess significant light resistance compared to benzophenone and triazole light stabilizers and can be used to enhance the UV weathering resistance of liquid crystal dimming films. Similar to cationic initiators, triazine light stabilizers have a slightly yellowish color, and yellowing is considered detrimental to colorless, transparent liquid crystal dimming films. However, experiments conducted in the present invention demonstrate that, at least when added in relatively low amounts, the effect on the color of the liquid crystal dimming film is minimal.

[0050] The thickness of the liquid crystal dimming film is relatively thin, and when the driving voltage is applied, the field strength is relatively high. Calculated based on a 36V driving voltage and a thickness of 20μm, which are common in the prior art, the field strength is 2 MV / m. If the thickness of the liquid crystal dimming film is reduced to 10μm and the driving voltage is increased to 48V, the field strength reaches 4.8 MV / m. The intrinsic breakdown field strength of the liquid crystal dimming film is 20-50 MV / m. To ensure the safe operation of the liquid crystal dimming film, it is generally recommended that the operating field strength does not exceed 30% of the breakdown value, that is, no more than 6 MV / m. However, when fillers are added, the breakdown field strength will most likely drop rapidly. In the present invention, although the cationic initiator is not a filler, it is a special salt that can provide positive and negative ions when exposed to ultraviolet light, making it possible to exhibit certain characteristics of the filler. For safe long-term use, it is necessary to reduce the driving voltage. Fortunately, the cationic initiator reduces the breakdown field strength, and because it can provide positive and negative ions, it can also reduce the driving voltage. Lowering the driving voltage is not only for safe use, but also reduces long-term power consumption.

[0051] To further reduce the driving voltage, ionic liquids can be added. Regarding voltage breakdown, one scenario involves an insulating system where the field strength is too high, causing the insulator to break down and become a conductor. Another scenario involves adding too much conductive material to the insulating system, turning it into a conductor. Therefore, while cationic initiators and ionic liquids can reduce the driving voltage, their content should not be too high. However, there is a lack of experimental data on the amounts of ionic initiators and ionic liquids added. Based on experiments, the present invention prefers the amounts of cationic initiators and ionic liquids added.

[0052] Regarding the relationship between ions, driving voltage and breakdown voltage, there is no systematic and complete explanation through theory and experiment, and the specific effect of the liquid crystal dimming film is unclear.

[0053] Preferably, the liquid crystal dimming layer further contains an ionic liquid, and the weight percentage of the total mass of the ionic liquid and the liquid crystal dimming layer is no more than 2%.

[0054] Preferably, the ionic liquid is one selected from a salt composed of an organic cation and an inorganic anion, a salt composed of an inorganic cation and an organic anion, or a salt composed of an organic cation and an organic anion; the organic cation of the ionic liquid is an imidazole, pyridine, pyrrolidine, piperidine, pyrazole, triazole, quaternary ammonium, quaternary phosphonium or thiazole organic cation; the organic anion or inorganic anion is a trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, hexafluorophosphate, tetrafluoroborate, methanesulfonate, acetate, trifluoroacetate, bisfluorosulfonyl imide, methylsulfate, methylcarboxylate, chloride, bromide, iodide, fluoride, nitrate, sulfate, hydrogensulfate, phosphate, decanoate or dicyanimide anion.

[0055] Preferably, the ionic liquid contains one of the following ionic liquids: 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluorosulfonate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluorosulfonate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), N-ethylpyridinium tetrafluoroborate, tetramethylammonium bis(trifluoromethanesulfonyl imide), trihexyltetradecylphosphonium chloride or hexadecyl-3-methylimidazolium bromide.

[0056] Preferably, the photoinitiator is TPO or 1173, the cationic initiator is diphenyliodonium hexafluorophosphate, diphenyliodonium trifluoromethanesulfonate, triphenylsulfonium tetrafluoroborate, tri-p-tolylsulfonium hexafluorophosphate, U-160, U-261 or U-180, the epoxy resin is 1,6-hexanediol diglycidyl ether or trimethylolpropane triglycidyl ether, and the light stabilizer is S-8, S-4 or S-3. Specific embodiment 1 50 parts of liquid crystal and 50 parts of polymer were mixed and stirred evenly. 1 part of free radical initiator TPO, 0.05 part of cationic initiator diphenyliodonium hexafluorophosphate, 0.05 part of light stabilizer S-8, and 0.5 parts of 20-micron glass beads were added and stirred evenly. The mixture was then roller-pressed with ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal was E7, and the polymer was 45 parts of commercially available NOA65 and 5 parts of 1,6-hexanediol diglycidyl ether. Specific embodiment 2 The same method as in Example 1 was used, except that the proportion of the light stabilizer was reduced to 0.01 parts. Specific embodiment 3 The same method as in Example 1 was used, except that the proportion of the light stabilizer was reduced to 0.03 parts. Specific embodiment 4 The same method as in Example 1 was used, except that the light stabilizer was changed to S-3 and the proportion was reduced to 0.03 parts. Specific embodiment 5 The same procedure as in Example 1 was used, except that the cationic initiator was changed to diphenyliodonium trifluoromethanesulfonate. Specific embodiment 6 The same procedure as in Example 1 was used except that the cationic initiator was changed to triphenylsulfonium tetrafluoroborate. Specific embodiment 7 The same procedure as in Example 1 was used except that the cationic initiator was changed to tri-p-tolylsulfonium hexafluorophosphate. Specific embodiment 8 50 parts of liquid crystal and 50 parts of polymer were mixed and stirred evenly. 1.2 parts of free radical initiator 1173, 0.1 parts of cationic initiator U-160, 0.05 parts of light stabilizer S-8, and 0.2 parts of 20-micron glass beads were added. Stirring was continued after addition and the mixture was rolled onto an ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal used was E8 liquid crystal, and the polymer was a commercially available mixture of 25 parts of NOA65, 10 parts of 1,6-hexanediol diacrylate, 5 parts of neopentyl glycol diacrylate, 5 parts of 1,6-hexanediol diglycidyl ether, and 5 parts of trimethylolpropane triglycidyl ether. Specific embodiment 9 The same procedure as in Example 8 was used, except that the cationic initiator was changed to U-261. Specific embodiment 10 The same method as in Example 8 was used, except that the liquid crystal was changed to 40 parts, the polymer was changed to 60 parts, and NOA65 was increased to 35 parts. Specific embodiment 11 The same method as in Example 8 was used, except that the cationic initiator was changed to U-180. Specific embodiment 12 The same method as in Example 8 was used, except that the photoinitiator was changed to S-4. Specific embodiment 13 The same method as in Example 8 was used except that 0.01 parts of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was added. Specific embodiment 14 The same method as in Example 8 was used except that 0.02 parts of the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate was added. Specific embodiment 15 35 parts of liquid crystal and 65 parts of polymer were mixed and stirred evenly. 1 part of free radical initiator 1173, 0.1 part of cationic initiator U-160, 0.05 part of light stabilizer S-8, and 0.2 parts of 20-micron glass beads were added. After continued stirring, the film was rolled onto an ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm2 and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal used was SLC1717, and the polymer was a mixture of 18 parts of 3,5,5-trimethylhexyl acrylate, 6 parts of 1,4-butanediol diacrylate, 30 parts of isomethyl methacrylate, 6 parts of polyethylene glycol diacrylate 600 (PEGDA600), and 5 parts of butanediol diglycidyl ether.

[0072] Comparative Example 1 50 parts of liquid crystal and 50 parts of polymer were mixed and stirred evenly. 1 part of free radical initiator TPO, 0.05 part of cationic initiator diphenyliodonium hexafluorophosphate, 0.5 part of light stabilizer S-8, and 0.5 parts of 20-micron glass beads were added. Stirring was continued until evenly distributed. The mixture was then roller-pressed with an ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal used was E7, and the polymer was 45 parts of commercially available NOA65 and 5 parts of 1,6-hexanediol diglycidyl ether.

[0073] Comparative Example 2 50 parts of liquid crystal and 50 parts of polymer were mixed and stirred evenly. 1 part of free radical initiator TPO, 0.05 parts of cationic initiator diphenyliodonium hexafluorophosphate, and 0.5 parts of 20-micron glass beads were added and stirred evenly. The mixture was then roller-pressed with ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal used was E7, and the polymer was 45 parts of commercially available NOA65 and 5 parts of 1,6-hexanediol diglycidyl ether.

[0074] Comparative Example 3 Mix 50 parts of liquid crystal and 50 parts of polymer, stirring evenly. Add 1 part of free radical initiator TPO, 0.05 parts of light stabilizer S-8, and 0.5 parts of 20-micron glass beads. Continue stirring until evenly combined. Roll-press the mixture with ITO-PET film to form a 20-micron film. Curing under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm, the resulting sample was tested for photoelectric properties. The liquid crystal was E7, and the polymer was 50 parts of commercially available NOA65.

[0075] Comparative Example 4 50 parts of liquid crystal and 50 parts of polymer were mixed and stirred evenly. 0.5 parts of free radical initiator 1173, 0.1 parts of cationic initiator U-160, 0.05 parts of light stabilizer S-8, 0.2 parts of 20-micron glass beads, and 0.5 parts of 1-ethyl-3-methylimidazolium hexafluorophosphate were added. After continued stirring, the mixture was rolled onto an ITO-PET film to form a 20-micron film. The film was cured under ultraviolet light at an intensity of 6 mW / cm² and a wavelength of 365 nm. The resulting sample was then tested for photoelectric properties. The liquid crystal used was E8 liquid crystal, and the polymer was a commercially available mixture of 25 parts of NOA65, 10 parts of 1,6-hexanediol diacrylate, 5 parts of neopentyl glycol diacrylate, 5 parts of 1,6-hexanediol diglycidyl ether, and 5 parts of trimethylolpropane triglycidyl ether.

[0076] Regarding the weather resistance of liquid crystal dimming films, the main considerations are changes in transmittance, driving voltage, and appearance, including color changes.

[0077] For colorless liquid crystal dimming films, color change primarily focuses on color change, specifically the degree of yellowing. Appearance change primarily examines whether there are any noticeable cosmetic defects. Visual inspection is used rather than machine testing because, in actual products, human eye perception outweighs machine-tested data. Transmittance change primarily examines transmittance changes under driving voltage. Driving voltage primarily examines the change in voltage at 95% of maximum transmittance.

[0078] Since weather resistance is mainly related to UV and temperature, weather resistance tests are conducted on these two factors.

[0079] UV irradiation testing: According to the "Electro-Liquid Crystal Film Switchable Glass" (GB / T 35847-2018) standard, after 100 hours of irradiation, observe changes in various indicators. The appearance should show no noticeable changes, including significant discoloration, bubbles, delamination, or other defects. The change in visible light transmittance while powered on should be no more than 3%. Visible light transmittance is tested both in the powered-on and powered-off states in accordance with GB / T 5137.2-2020.

[0080] Temperature change test: The sample is placed alternately in an environment of (-40±2)℃ and (72±2)℃ for a total of 10 cycles. After the test, there should be no obvious change in appearance, and the change in visible light transmittance in the power-on state should not be greater than 3%.

[0081] For driving voltage and color change, the deviation is also considered to be no more than 3%.

[0082] Regarding the UV radiation weathering test, the data are as follows:

[0083] Regarding the temperature change weathering test, the data are as follows:

[0084] The impact of UV on the performance of liquid crystal dimming film: when the amount of light stabilizer added is too large (Comparative Example 1), the color change caused by UV irradiation is obvious. When no light stabilizer is added (Comparative Example 2), the transmittance change exceeds the deviation value. When no epoxy resin is added (Comparative Example 3), UV irradiation does not produce unacceptable adverse effects. When the ratio of cationic initiator to free radical initiator is equivalent (Comparative Example 4), the liquid crystal dimming film debonds after UV irradiation. No other parameters were measured.

[0085] The effect of temperature on the performance of the liquid crystal dimming film: when the amount of light stabilizer added is too large (Comparative Example 1), the color change caused by temperature change is also obvious. When no light stabilizer is added (Comparative Example 2), the temperature change does not produce unacceptable adverse effects. When no epoxy resin is added (Comparative Example 3), the liquid crystal dimming film produces bubbles, and no other parameters are measured. When the ratio of cationic initiator and free radical initiator is equivalent (Comparative Example 4), the liquid crystal dimming film debonds, and no other parameters are measured.

[0086] It can be seen that when the amount of light stabilizer added is too large or no light stabilizer is added, ultraviolet radiation is likely to cause yellowing or large deviations in transmittance changes. When no epoxy resin is added or the proportion of cationic initiator is inappropriate, temperature changes are more likely to cause measurement deviations.

[0087] The embodiments of the present invention are illustrative. For example, the liquid crystal ratios of the present invention are only illustrative. Those skilled in the art can make specific adjustments within the scope of protection of this patent based on the content of this patent.

[0088] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art. The present invention is not limited to the embodiments shown herein, but is intended to be consistent with the principles and features disclosed herein.

Claims

1. A highly weather-resistant liquid crystal dimming film comprising a first conductive film, a liquid crystal dimming layer, and a second conductive film, wherein the liquid crystal dimming layer is located between the first conductive film and the second conductive film, characterized in that: The liquid crystal dimming layer contains liquid crystal, a polymer, a photoinitiator and a light stabilizer, the liquid crystal is a nematic liquid crystal, the polymer includes at least one free radical initiating resin and at least one cationic initiating resin, the free radical initiating resin includes at least one of an acrylic resin or an allyl resin, the cationic initiating resin includes at least one epoxy resin, the photoinitiator includes at least one free radical initiator and at least one cationic initiator, the mass percentage of the photoinitiator to the total mass of the liquid crystal dimming layer is 0.01-5%, the proportion of the cationic initiator is less than that of the free radical initiator, and the weight percentage of the light stabilizer to the liquid crystal dimming layer is not higher than 0.05%.

2. The liquid crystal dimming film according to claim 1, wherein: The first conductive film and the second conductive film are PET films containing ITO.

3. The liquid crystal dimming film according to claim 1, wherein: The liquid crystal is a nematic liquid crystal; the nematic liquid crystal contains at least one liquid crystal monomer represented by the following formula (I): ; wherein X and Y each independently represent a C1-C12 alkyl, alkoxy, cyano, isothiocyanate or halogen, ring A and ring B each independently represent a benzene ring, a pyridine ring or a cyclohexane ring; m and n each independently represent an integer of 0-4; L is an acetylenic bond, an olefinic bond or an ester group; a represents 0 or 1.

4. The liquid crystal dimming film according to claim 1, wherein: The mass of the polymer is 30%-70% of the total mass of the polymer and the liquid crystal; the acrylic resin contains acrylic monomers or acrylic oligomers, and the acrylic monomers contain at least one of monofunctional acrylic monomers, difunctional acrylic monomers or multifunctional acrylic resins; the acrylic oligomer contains at least one acrylic group; and the epoxy resin contains at least one non-monofunctional epoxy monomer or epoxy oligomer.

5. The liquid crystal dimming film according to claim 1, wherein: The light stabilizer is a triazine initiator, and the triazine initiator has a structure described by the following formula (II): ; wherein, R1 and R2 each independently represent a C1-C12 substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted phenyl, substituted or unsubstituted phenoxy or hydroxyl group, R3 represents a substituted or unsubstituted alkoxy or hydroxyl group; p and q each independently represent 0, 1, 2, 3, 4 or 5, and r represents 0, 1, 2, 3 or 4.

6. The liquid crystal dimming film according to claim 1, wherein: The light stabilizer is selected from at least one of the compounds shown in the following structures: 。 7. The liquid crystal dimming film according to claim 1, wherein: The liquid crystal dimming layer further contains an ionic liquid, and the weight percentage of the total mass of the ionic liquid and the liquid crystal dimming layer is no more than 2%.

8. The liquid crystal dimming film according to claim 7, wherein: The ionic liquid is one selected from a salt consisting of an organic cation and an inorganic anion, a salt consisting of an inorganic cation and an organic anion, or a salt consisting of an organic cation and an organic anion; the organic cation of the ionic liquid is an imidazole, pyridine, pyrrolidine, piperidine, pyrazole, triazole, quaternary ammonium, quaternary phosphonium or thiazole organic cation; the organic anion or inorganic anion is a trifluoromethanesulfonate, bistrifluoromethanesulfonyl imide, hexafluorophosphate, tetrafluoroborate, methanesulfonate, acetate, trifluoroacetate, bisfluorosulfonyl imide, methylsulfate, methylcarboxylate, chloride, bromide, iodide, fluoride, nitrate, sulfate, hydrogensulfate, phosphate, decanoate or dicyanimide anion.

9. The liquid crystal dimming film according to claim 7, wherein: The ionic liquid contains one of the following ionic liquids: 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluorosulfonate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluorosulfonate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide), N-ethylpyridinium tetrafluoroborate, tetramethylammonium bis(trifluoromethanesulfonyl imide), trihexyltetradecylphosphonium chloride or hexadecyl-3-methylimidazolium bromide.

10. The liquid crystal dimming film according to claim 7, wherein: The photoinitiator is TPO or 1173, the cationic initiator is diphenyliodonium hexafluorophosphate, diphenyliodonium trifluoromethanesulfonate, triphenylsulfonium tetrafluoroborate, tri-p-tolylsulfonium hexafluorophosphate, U-160, U-261 or U-180, the epoxy resin is 1,6-hexanediol diglycidyl ether or trimethylolpropane triglycidyl ether, and the light stabilizer is S-8, S-4 or S-3.

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