A liquid crystal-based thermochromic film, its preparation method, and applications

Abstract

The present invention relates to the technical field of liquid crystal materials, and specifically to a thermochromic film based on liquid crystal and a preparation method thereof. In the present invention, a liquid crystal mixture is coated on a transparent flexible substrate and cured to obtain a thermochromic liquid crystal layer; the liquid crystal mixture is formed by mixing raw materials including a first liquid crystal mixture, a second liquid crystal mixture, a third chiral agent, and a photoinitiator; in the present invention, a modified antioxidant and hydroxyl-terminated polydimethylsiloxane are introduced into a polyurethane coating and coated on a transparent flexible substrate to improve the adhesion effect between the transparent flexible substrates; the thermochromic film prepared in the present invention has a controllable color, fast response, wide color gamut, and good moisture resistance, heat resistance, and aging resistance, and can be applied to the fields of liquid crystal display, smart glass, or anti-counterfeiting.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal materials, and particularly to a thermochromic film based on liquid crystal, a preparation method thereof, and an application thereof. Background Art

[0002] Liquid crystal is a state of matter between liquid state and crystalline state. It has both the fluidity of liquid and the anisotropy of crystal. The characteristics of the liquid crystal molecules' different arrangements and orientations under different conditions can be utilized to achieve the color change of the material, and the liquid crystal material can be applied to fields such as display, smart glass, anti-counterfeiting identification, and temperature control monitoring.

[0003] The thermochromic film prepared based on liquid crystal is often used for pipeline temperature monitoring. In places such as home bathrooms, public bathrooms, swimming pools, and spas, existing solutions mostly use electronic sensors to monitor parameters such as the stress and deformation of pipelines, and use temperature control valves to control the outlet water temperature. This not only relies on complex electronic devices, but also has high costs and difficult maintenance. The temperature control effect is not intuitive enough, and there is a risk of scalding. In addition, the existing liquid crystal color-changing materials have the problem of complex and cumbersome production processes, and due to being in a humid and hot environment for a long time, poor encapsulation will also lead to a shortened service life. Therefore, it is very necessary to develop a thermochromic film based on liquid crystal. Summary of the Invention

[0004] The purpose of the present invention is to provide a thermochromic film based on liquid crystal, a preparation method thereof, and an application thereof, so as to solve the problems raised in the above background art.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A thermochromic film based on liquid crystal and a preparation method thereof, including the following steps:

[0006] Step 1:

[0007] S1: Disperse trimethylolpropane tris(mercaptoacetate) and allyl isocyanate in N,N-dimethylformamide, add the catalyst dibutyltin dilaurate, react at 50-60°C for 3-4 hours, distill off N,N-dimethylformamide under reduced pressure, transfer the product to anhydrous methanol, add epichlorohydrin, react at 45-50°C for 3.5-4.5 hours with triethylamine as the catalyst, remove impurities by rotary evaporation, then add a 5% sodium hydroxide solution by mass concentration, react at 80-90°C for 4-5 hours, add methanol and ultrapure water, let it stand to separate the organic phase and the inorganic phase, and perform rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate;

[0008] S2: Mix the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, use salicylic acid as a catalyst, react at 150 - 160 °C for 8 - 9 h, add chloroform for dilution, neutralize salicylic acid with an aqueous sodium bicarbonate solution with a mass concentration of 3 - 5%, then add petroleum ether to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, rotary evaporate to remove chloroform, and dry to obtain the modified antioxidant;

[0009] S3: Mix polytetrahydrofuran diol 2000, hydroxyl-terminated polydimethylsiloxane, the modified antioxidant, and dimethylolpropionic acid, add isophorone diisocyanate and dibutyltin dilaurate and stir, raise the temperature to 70 - 80 °C and react for 2 - 3 h, add 1,4-butanediol and continue to react for 1 - 2 h; then add acetone and triethylamine and continue to react for 5 - 10 min, add ethylenediamine for chain extension reaction for 30 min, and distill off impurities to obtain a polyurethane coating with a solid content of 30 - 35%;

[0010] S4: Coat the polyurethane coating on a transparent flexible substrate to form a polyurethane coating, and bake and cure to obtain a modified transparent flexible substrate;

[0011] Step 2:

[0012] Mix the liquid crystalline polymerizable monomer and the first chiral agent in a mass ratio of (2.5 - 10):1 to obtain a first liquid crystal mixture; mix the nematic liquid crystal and the second chiral agent in a mass ratio of 1:(0.15 - 0.8) to obtain a second liquid crystal mixture; mix the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent, and the photoinitiator in a mass ratio of 1:(0.95 - 1):(0.25 - 0.3):(0.05 - 0.12) to obtain a liquid crystal mixture; take two modified transparent flexible substrates, coat the liquid crystal mixture on the modified transparent flexible substrates to form a pattern, mix methyl methacrylate and the photoinitiator in a mass ratio of 100:(2 - 3) and coat it on the area of the modified transparent flexible substrate where the liquid crystal mixture is not coated, align the sides with patterns of the two modified transparent flexible substrates, and perform ultraviolet curing after lamination to obtain a thermochromic film.

[0013] Further, in S1, the molar ratio of trimethylolpropane tris(mercaptoacetate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2.

[0014] Further, in S2, mix the intermediate and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine according to a molar ratio of 1:(1.1 - 1.2) of the epoxy group in the intermediate to N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0015] Further, in S3, the dosages of the components are as follows in parts by weight: 160 - 196 parts of polytetrahydrofuran diol 2000, 15 - 23 parts of hydroxyl-terminated polydimethylsiloxane, 8 - 12 parts of modified antioxidant, 19 - 27 parts of dimethylolpropionic acid, 180 - 240 parts of isophorone diisocyanate, 0.5 - 1 part of dibutyltin dilaurate, 1.2 - 1.6 parts of 1,4-butanediol, 18 - 24 parts of acetone, 4 - 7 parts of triethylamine, and 2.6 - 3.8 parts of ethylenediamine.

[0016] Further, in S4, the transparent flexible substrate is a PET film.

[0017] Further, in step 2, the liquid crystal polymerizable monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene; the nematic liquid crystal is any one or more of E7 and SLC1717; the first chiral agent, the second chiral agent, and the third chiral agent are one or more of R5011, R1011, R811, S5011, S1011, and S811.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: When preparing the thermochromic film, the present invention first mixes the first liquid crystal mixture and the second liquid crystal mixture; mixes the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent, and the photoinitiator to obtain a liquid crystal mixture solution; coats the liquid crystal mixture solution on a transparent flexible substrate, and cures and encapsulates it to obtain a thermochromic film. The thermochromic film prepared by the present invention has controllable color, and has the advantages of fast response, wide color gamut, and large detection temperature range. In the temperature range of 0 - 60 °C, as the temperature of the thermochromic film increases, the color will redshift, and the full-spectrum color changes reversibly; when it is made into an ultra-thin film, it can be used in a flexible and flexible manner. Utilizing this technical effect, the thermochromic film of the present invention can be widely applied to technical fields such as liquid crystal displays, smart glass, and anti-counterfeiting labels.

[0019] In order to improve the adhesion effect between the liquid crystal mixture and the transparent flexible substrate, the present invention coats a polyurethane coating containing a modified antioxidant on the surface of the transparent flexible substrate. The preparation method of the modified antioxidant is as follows: trimethylolpropane tris(mercapto propionate) is used as the raw material, which is first reacted with allyl isocyanate to introduce a carbon-carbon double bond; then reacted with epichlorohydrin and sodium hydroxide to introduce an epoxy group, and the epoxy group reacts with an amino group to introduce N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine with anti-aging properties. At the same time, a hydroxyl group is generated, and the hydroxyl group can react with the isocyanate group in the polyurethane and be introduced into the polyurethane molecular chain segment in a chemical bond manner. On the one hand, the anti-aging performance of the polyurethane coating is improved, and on the other hand, the outward migration of small molecule antioxidants is avoided. The present invention also introduces hydroxyl-terminated polydimethylsiloxane into the polyurethane to introduce silicone to improve the water resistance of the polyurethane and keep good adhesion performance in a humid and hot environment. During the curing process, the polyurethane coating coated on the transparent flexible substrate contains carbon-carbon double bonds, and through ultraviolet irradiation, it crosslinks with methyl methacrylate to achieve better bonding. Another effect of the present invention is that under the irradiation of ultraviolet light, the liquid crystal phase curing and encapsulation steps can be realized synchronously. Not only is the process simple, but the obtained heat value color-changing film has better encapsulation performance. After the liquid crystal mixture is cured, a thermochromic liquid crystal layer is formed, and both sides of it are combined with the polyurethane coating. In a humid and hot environment, the polyurethane coating can also play the roles of waterproofing, anti-aging, and preventing separation and shedding, and extend the life of the thermochromic film. Detailed implementation mode

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] The materials used in the present invention and their sources: polytetrahydrofuran diol 2000 comes from Jining Baiyi Chemical Co., Ltd.; hydroxyl-terminated polydimethylsiloxane comes from Sigma-Aldrich, product number 481939; PET film comes from Hefei Furen Technology Co., Ltd., product number FR-2008089; nematic liquid crystal E7 comes from Qingdao Qiuyun Liquid Crystal Materials Co., Ltd.

[0022] Example 1: A thermochromic film based on liquid crystal and its preparation method, including the following steps:

[0023] Step 1:

[0024] S1: Disperse trimethylolpropane tris(mercapto propionate) and allyl isocyanate in N,N-dimethylformamide, add the catalyst dibutyltin dilaurate, react at 50 °C for 3 h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, use triethylamine as the catalyst and react at 45 °C for 3.5 h. After rotary evaporation to remove impurities, add a sodium hydroxide solution with a mass concentration of 5%, react at 80 °C for 4 h, add methanol and ultrapure water, let it stand to separate the organic phase and the inorganic phase, and perform rotary evaporation on the organic phase to remove impurities, and dry to obtain the intermediate; wherein, the molar ratio of trimethylolpropane tris(mercapto propionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2;

[0025] S2: Mix the intermediate and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine according to a molar ratio of 1:1.1 of the epoxy groups in the intermediate, use salicylic acid as the catalyst, react at 150 °C for 8 h, add chloroform for dilution, neutralize salicylic acid with an aqueous sodium bicarbonate solution with a mass concentration of 3%, and then add petroleum ether to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. Rotary evaporate to remove chloroform and dry to obtain the modified antioxidant;

[0026] S3: Mix 182 g of polytetrahydrofuran diol 2000, 19 g of hydroxyl-terminated polydimethylsiloxane, 11 g of the modified antioxidant, and 22 g of dimethylolpropionic acid, add 187 g of isophorone diisocyanate and 0.7 g of dibutyltin dilaurate and stir, heat up to 70 °C and react for 2 h, add 1.3 g of 1,4-butanediol and continue to react for 1 h; then add 21 g of acetone and 5 g of triethylamine and continue to react for 5 min, add 3.4 g of ethylenediamine for chain extension reaction for 30 min, and distill off impurities to obtain a polyurethane coating with a solid content of 35%;

[0027] S4: Coat the polyurethane coating on a transparent flexible substrate to form a polyurethane coating, and bake and cure to obtain a modified transparent flexible substrate;

[0028] Step 2:

[0029] The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 were mixed evenly at a mass ratio of 2.5:1 to obtain a first liquid crystal mixture; the nematic liquid crystal E7 and the second chiral agent S5011 were mixed at a mass ratio of 1:0.1 to obtain a second liquid crystal mixture; the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011 and the photoinitiator 907 were mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates were taken, the liquid crystal mixture was coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 were mixed at a mass ratio of 100:3 and then coated on the area of the modified transparent flexible substrates where the liquid crystal mixture was not coated, the two modified transparent flexible substrates with the patterned sides were aligned, and after lamination, ultraviolet curing was carried out, and the ultraviolet irradiation intensity was 130mW / cm 2 Ultraviolet light with an intensity of was irradiated for 10 s to obtain a thermochromic film.

[0030] Example 2: A liquid crystal-based thermochromic film and its preparation method, comprising the following steps:

[0031] Step 1:

[0032] S1: Trimethylolpropane tris(mercaptoacetate) and allyl isocyanate were dispersed in N,N-dimethylformamide, dibutyltin dilaurate as a catalyst was added, and the reaction was carried out at 55 °C for 3.5 h. N,N-dimethylformamide was removed by vacuum distillation, the product was transferred to anhydrous methanol, epichlorohydrin was added, and the reaction was carried out at 48 °C for 4 h using triethylamine as a catalyst. After rotary evaporation to remove impurities, a 5% sodium hydroxide solution by mass concentration was added, and the reaction was carried out at 85 °C for 4.5 h. Methanol and ultrapure water were added, and the organic phase and the inorganic phase were separated by standing, and the organic phase was rotary evaporated to remove impurities and dried to obtain an intermediate; wherein, the molar ratio of trimethylolpropane tris(mercaptoacetate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2;

[0033] S2: The intermediate epoxy group and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine were mixed at a molar ratio of 1:1.1, salicylic acid was used as a catalyst, and the reaction was carried out at 155 °C for 8.5 h. Chloroform was added for dilution, salicylic acid was neutralized with a 3% sodium bicarbonate aqueous solution by mass concentration, and then petroleum ether was added to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. Chloroform was rotary evaporated to obtain a modified antioxidant;

[0034] S3: Mix 182 g of polytetrahydrofuran diol 2000, 19 g of hydroxyl-terminated polydimethylsiloxane, 11 g of modified antioxidant, and 22 g of dimethylolpropionic acid. Add 187 g of isophorone diisocyanate and 0.7 g of dibutyltin dilaurate and stir. Heat up to 75 °C and react for 2.5 h. Then add 1.3 g of 1,4-butanediol and continue to react for 1.5 h. Subsequently, add 21 g of acetone and 5 g of triethylamine and continue to react for 7 min. Add 3.4 g of ethylenediamine for chain extension reaction for 30 min. Evaporate the impurities to obtain a polyurethane coating with a solid content of 35%.

[0035] S4: Coat the polyurethane coating on a transparent flexible substrate to form a polyurethane coating, and bake and cure it to obtain a modified transparent flexible substrate.

[0036] Step 2:

[0037] Mix the liquid crystalline polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 evenly according to a mass ratio of 2.5:1 to obtain a first liquid crystal mixture. Mix the nematic liquid crystal E7 and the second chiral agent S5011 according to a mass ratio of 1:0.1 to obtain a second liquid crystal mixture. Mix the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011, and the photoinitiator 907 according to a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture. Take two modified transparent flexible substrates, coat the liquid crystal mixture on the modified transparent flexible substrates to form a pattern, coat the mixture of methyl methacrylate and photoinitiator 907 with a mass ratio of 100:3 on the area of the modified transparent flexible substrates where the liquid crystal mixture is not coated. Align the sides with patterns of the two modified transparent flexible substrates, and after lamination, perform ultraviolet curing. The intensity of ultraviolet irradiation is 130 mW / cm 2 and irradiate with ultraviolet light for 10 s to obtain a thermochromic film.

[0038] Example 3: A liquid crystal-based thermochromic film and its preparation method, including the following steps:

[0039] Step 1:

[0040] S1: Disperse trimethylolpropane tris(mercapto propionate) and allyl isocyanate in N,N-dimethylformamide, add the catalyst dibutyltin dilaurate, react at 60 °C for 4 h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, use triethylamine as the catalyst and react at 50 °C for 4.5 h. After removing impurities by rotary evaporation, add a 5% sodium hydroxide solution by mass concentration and react at 90 °C for 5 h. Add methanol and ultrapure water, let it stand to separate the organic phase and the inorganic phase, and remove impurities from the organic phase by rotary evaporation, then dry to obtain the intermediate; wherein, the molar ratio of trimethylolpropane tris(mercapto propionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2;

[0041] S2: Mix the intermediate and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine according to a molar ratio of 1:1.1 of the epoxy groups in the intermediate, use salicylic acid as the catalyst, react at 160 °C for 9 h, add chloroform for dilution, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution by mass concentration, then add petroleum ether to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain the modified antioxidant;

[0042] S3: Mix 182 g of polytetrahydrofuran diol 2000, 19 g of hydroxyl-terminated polydimethylsiloxane, 11 g of the modified antioxidant, and 22 g of dimethylolpropionic acid, add 187 g of isophorone diisocyanate and 0.7 g of dibutyltin dilaurate and stir, heat up to 80 °C and react for 3 h, then add 1.3 g of 1,4-butanediol and continue to react for 2 h; subsequently add 21 g of acetone and 5 g of triethylamine and continue to react for 10 min, add 3.4 g of ethylenediamine for chain extension reaction for 30 min, and distill off impurities to obtain a polyurethane coating with a solid content of 35%;

[0043] S4: Coating the polyurethane coating on a transparent flexible substrate to form a polyurethane coating, and baking and curing to obtain a modified transparent flexible substrate;

[0044] Step 2:

[0045] The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 were mixed evenly at a mass ratio of 2.5:1 to obtain the first liquid crystal mixture; the nematic liquid crystal E7 and the second chiral agent S5011 were mixed at a mass ratio of 1:0.1 to obtain the second liquid crystal mixture; the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011 and the photoinitiator 907 were mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates were taken, the liquid crystal mixture was coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 were mixed at a mass ratio of 100:3 and then coated on the area of the modified transparent flexible substrates where the liquid crystal mixture was not coated, the two modified transparent flexible substrates with the patterned sides were aligned, and after lamination, ultraviolet curing was carried out. The ultraviolet irradiation intensity was 130 mW / cm 2 of ultraviolet light was irradiated for 10 s to obtain a thermochromic film.

[0046] Comparative Example 1: The transparent flexible substrate was not modified, and the other parameters were the same as those in Example 1.

[0047] The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 were mixed evenly at a mass ratio of 2.5:1 to obtain the first liquid crystal mixture; the nematic liquid crystal E7 and the second chiral agent S5011 were mixed at a mass ratio of 1:0.1 to obtain the second liquid crystal mixture; the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011 and the photoinitiator 907 were mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates were taken, the liquid crystal mixture was coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 were mixed at a mass ratio of 100:3 and then coated on the area of the modified transparent flexible substrates where the liquid crystal mixture was not coated, the two modified transparent flexible substrates with the patterned sides were aligned, and after lamination, ultraviolet curing was carried out. The ultraviolet irradiation intensity was 130 mW / cm 2 of ultraviolet light was irradiated for 10 s to obtain a thermochromic film.

[0048] Comparative Example 2: Polyurethane coating was prepared without adding hydroxyl-terminated polydimethylsiloxane, and the other parameters were the same as those in Example 2.

[0049] Step 1:

[0050] S1: Disperse trimethylolpropane tris(mercapto propionate) and allyl isocyanate in N,N-dimethylformamide, add the catalyst dibutyltin dilaurate, react at 55 °C for 3.5 h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 48 °C for 4 h using triethylamine as the catalyst, remove impurities by rotary evaporation, then add a 5% sodium hydroxide solution by mass concentration, react at 85 °C for 4.5 h, add methanol and ultrapure water, let it stand to separate the organic phase and the inorganic phase, and remove impurities from the organic phase by rotary evaporation, and dry to obtain the intermediate; wherein, the molar ratio of trimethylolpropane tris(mercapto propionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2;

[0051] S2: Mix the intermediate and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine according to a molar ratio of 1:1.1 of the epoxy groups in the intermediate, use salicylic acid as the catalyst, react at 155 °C for 8.5 h, add chloroform for dilution, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution by mass concentration, then add petroleum ether to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain the modified antioxidant;

[0052] S3: Mix 182 g of polytetrahydrofuran diol 2000, 11 g of the modified antioxidant, and 22 g of dimethylolpropionic acid, add 187 g of isophorone diisocyanate and 0.7 g of dibutyltin dilaurate and stir, raise the temperature to 75 °C and react for 2.5 h, add 1.3 g of 1,4-butanediol and continue to react for 1.5 h; then add 21 g of acetone and 5 g of triethylamine and continue to react for 7 min, add 3.4 g of ethylenediamine for chain extension reaction for 30 min, and distill off impurities to obtain a polyurethane coating with a solid content of 35%;

[0053] S4: Coat the polyurethane coating on a transparent flexible substrate to form a polyurethane coating, and bake and cure to obtain the modified transparent flexible substrate;

[0054] Step 2:

[0055] The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 were mixed evenly at a mass ratio of 2.5:1 to obtain the first liquid crystal mixture; the nematic liquid crystal E7 and the second chiral agent S5011 were mixed at a mass ratio of 1:0.1 to obtain the second liquid crystal mixture; the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011 and the photoinitiator 907 were mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates were taken, the liquid crystal mixture was coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 were mixed at a mass ratio of 100:3 and then coated on the area of the modified transparent flexible substrates where the liquid crystal mixture was not coated, the two modified transparent flexible substrates with the patterned sides were aligned, and after lamination, ultraviolet curing was carried out, and the ultraviolet irradiation intensity was 130mW / cm 2 of ultraviolet light was irradiated for 10 s to obtain a thermochromic film.

[0056] Comparative Example 3: The modified antioxidant was not added, and the other parameters were the same as those in Example 3.

[0057] Step 1:

[0058] S1: 182 g of polytetrahydrofuran diol 2000, 19 g of hydroxyl-terminated polydimethylsiloxane, and 22 g of dimethylolpropionic acid were mixed, 187 g of isophorone diisocyanate and 0.7 g of dibutyltin dilaurate were added and stirred, the temperature was raised to 80 °C and reacted for 3 h, 1.3 g of 1,4-butanediol was added and the reaction continued for 2 h; then 21 g of acetone and 5 g of triethylamine were added and the reaction continued for 10 min, 3.4 g of ethylenediamine was added for chain extension reaction for 30 min, and impurities were removed by evaporation to obtain a polyurethane coating with a solid content of 35%;

[0059] S2: The polyurethane coating was coated on the transparent flexible substrate to form a polyurethane coating, and baking curing was carried out to obtain a modified transparent flexible substrate;

[0060] Step 2:

[0061] The liquid crystalline polymerizable monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 were mixed evenly in a mass ratio of 2.5:1 to obtain the first liquid crystal mixture; the nematic liquid crystal E7 and the second chiral agent S5011 were mixed in a mass ratio of 1:0.1 to obtain the second liquid crystal mixture; the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent S1011 and the photoinitiator 907 were mixed in a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates were taken, the liquid crystal mixture was coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 were mixed in a mass ratio of 100:3 and then coated on the area of the modified transparent flexible substrates where the liquid crystal mixture was not coated, the two modified transparent flexible substrates with the patterned sides were aligned, and after lamination, ultraviolet curing was carried out, and the ultraviolet irradiation intensity was 130mW / cm 2 of ultraviolet light was irradiated for 10 s to obtain a thermochromic film.

[0062] Experiment: The thermochromic films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, where:

[0063] Thermochromic experiment: After the thermochromic film was dried on a polytetrafluoroethylene template, it was transferred to an intelligent temperature-controlled electric hot plate, and the temperature was raised from 0 °C to 65 °C, and the color change time was recorded each time.

[0064] Adhesion performance: The 180° peel strength between the two transparent flexible substrates of the calorific value-changing film was tested.

[0065] Damp heat resistance performance: The calorific value-changing film was placed in a constant temperature and humidity chamber with a relative humidity of 95% and a temperature of 50 °C for 240 h, and the encapsulation condition of the thermochromic film was observed.

[0066]

[0067] Conclusion: The thermochromic films in Examples 1 to 3 are sensitive to temperature and respond quickly; they have stable performance in a humid and hot environment. The data of Example 1 and Comparative Example 1 show that after the transparent flexible substrates are modified, the adhesion performance between the transparent flexible substrates is good, and the thermochromic film has damp heat resistance performance; the data of Example 2 and Comparative Example 2 show that after adding hydroxyl-terminated polydimethylsiloxane, the damp heat resistance performance of the thermochromic film is better; the data of Example 3 and Comparative Example 3 show that after introducing a modified antioxidant, the adhesion performance between the cured transparent flexible substrates is good, and at the same time, it has good damp heat aging resistance performance.

[0068] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a liquid crystal-based thermochromic film, characterized in that: Step 1: Mix the liquid crystalline polymerizable monomer and the first chiral agent evenly to obtain a first liquid crystal mixture; mix the nematic liquid crystal and the second chiral agent to obtain a second liquid crystal mixture; mix the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent and the photoinitiator to obtain a liquid crystal mixture; Step 2: Coat the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and bake and cure to obtain a modified transparent flexible substrate; take two modified transparent flexible substrates, coat the liquid crystal mixture on the modified transparent flexible substrate to form a pattern, mix methyl methacrylate and the photoinitiator and coat it on the area of the modified transparent flexible substrate where the liquid crystal mixture is not coated, align the sides with patterns of the two modified transparent flexible substrates, and after lamination, carry out ultraviolet curing to obtain the thermochromic film; In Step 2, the preparation method of the polyurethane coating includes the following steps: S1: Disperse trimethylolpropane tris(mercaptoacetate) and allyl isocyanate in N,N-dimethylformamide, add the catalyst dibutyltin dilaurate, react at 50-60 °C for 3-4 h, distill off N,N-dimethylformamide under reduced pressure, transfer the product to anhydrous methanol, add epichlorohydrin, and react at 45-50 °C for 3.5-4.5 h with triethylamine as the catalyst. After rotary evaporation to remove impurities, add a 5% sodium hydroxide solution by mass concentration and react at 80-90 °C for 4-5 h. Add methanol and ultrapure water, let it stand to separate the organic phase and the inorganic phase, and carry out rotary evaporation to remove impurities from the organic phase, and dry to obtain an intermediate; S2: Mix the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, use salicylic acid as the catalyst, react at 150-160 °C for 8-9 h, dilute with chloroform, neutralize salicylic acid with an aqueous sodium bicarbonate solution with a mass concentration of 3-5%, and then add petroleum ether to remove the excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. Rotary evaporate to remove chloroform and dry to obtain a modified antioxidant; S3: Mix polytetrahydrofuran diol 2000, hydroxyl-terminated polydimethylsiloxane, the modified antioxidant, and dimethylolpropionic acid, add isophorone diisocyanate and dibutyltin dilaurate and stir, raise the temperature to 70-80 °C and react for 2-3 h, add 1,4-butanediol and continue to react for 1-2 h; then add acetone and triethylamine and continue to react for 5-10 min, add ethylenediamine for chain extension reaction for 30 min, and distill off impurities to obtain a polyurethane coating with a solid content of 30-35%.

2. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In step 1, in the first liquid crystal mixture, the liquid crystal polymerizable monomer and the first chiral agent are mixed in a mass ratio of (2.5~10):1; in the second liquid crystal mixture, the nematic liquid crystal and the second chiral agent are mixed in a mass ratio of 1:(0.15~0.8); in the liquid crystal mixture, the first liquid crystal mixture, the second liquid crystal mixture, the third chiral agent and the photoinitiator are mixed in a mass ratio of 1:(0.95~1):(0.25~0.3):(0.05~0.12); the liquid crystal polymerizable monomer is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene; the nematic liquid crystal is E7; the first chiral agent, the second chiral agent and the third chiral agent are one or more of R5011, R1011, R811, S5011, S1011 and S811.

3. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In step 2, methyl methacrylate and photoinitiator are in a mass ratio of 100:(2~3).

4. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In step 2, the transparent flexible substrate is a PET film.

5. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In the preparation of the polyurethane coating, in S1, the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:

2.

6. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In the preparation of the polyurethane coating, in S2, the epoxy group in the intermediate and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine are mixed in a molar ratio of 1:(1.1~1.2).

7. The preparation method of a liquid crystal-based thermochromic film according to claim 1, characterized in that: In the preparation of the polyurethane coating, in S3, the amount of each component, by weight, is 160-196 parts of polytetramethylene glycol 2000, 15-23 parts of hydroxyl-terminated polydimethylsiloxane, 8-12 parts of modified antioxidant, 19-27 parts of dihydroxymethylpropionic acid, 180-240 parts of isophorone diisocyanate, 0.5-1 parts of dibutyltin dilaurate, 1.2-1.6 parts of 1,4-butanediol, 18-24 parts of acetone, 4-7 parts of triethylamine, and 2.6-3.8 parts of ethylenediamine.

8. The liquid crystal-based thermochromic film prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a liquid crystal-based thermochromic film as described in claim 8, characterized in that: The liquid crystal-based thermochromic film is applied to the fields of liquid crystal display, smart glass, anti-counterfeiting identification, and temperature control monitoring.

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