Thermochromic film based on liquid crystal and preparation method thereof

Abstract

The invention relates to the technical field of liquid crystal materials, in particular to a thermochromic film based on liquid crystal and a preparation method of the thermochromic film. The preparation method comprises the following steps: coating a liquid crystal mixed solution on a transparent flexible substrate, and curing to obtain a thermochromic liquid crystal layer; the liquid crystal mixed liquid is formed by mixing raw materials including a first liquid crystal mixture, a second liquid crystal mixture, a third chiral agent and a photoinitiator; according to the invention, the modified antioxidant and the hydroxyl-terminated polydimethylsiloxane are introduced into the polyurethane coating, and the transparent flexible substrates are coated with the polyurethane coating, so that the adhesion effect between the transparent flexible substrates is improved; the thermochromic film prepared by the invention is controllable in color, quick in response, wide in color gamut and good in moisture resistance, heat resistance and aging resistance, and can be applied to the fields of liquid crystal display, intelligent glass or anti-counterfeiting.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal materials, in particular to a liquid crystal-based thermochromic film and a preparation method thereof. Background Art

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

[0003] Thermochromic films prepared based on liquid crystals are often used for pipe temperature monitoring. In places such as home bathrooms, public bathrooms, swimming pools, and spas, existing solutions mostly use electronic sensors to monitor pipe stress, deformation and other parameters, and use temperature control valves to control the outlet water temperature. Not only do they rely on complex electronic equipment, they are also costly and difficult to maintain. 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 hot and humid environment for a long time, poor packaging will also shorten their service life. Therefore, it is very necessary to develop a thermochromic film based on liquid crystals. Summary of the invention

[0004] The object of the present invention is to provide a liquid crystal-based thermochromic film and a preparation method thereof to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a liquid crystal-based thermochromic film and a preparation method thereof, comprising the following steps: Step 1: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 50-60°C for 3-4h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 45-50°C for 3.5-4.5h with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 80-90°C for 4-5h, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; S2: The intermediate is mixed with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and reacted at 150-160°C for 8-9h with salicylic acid as a catalyst, and then chloroform is added to dilute, and salicylic acid is neutralized with a 3-5% mass concentration of sodium bicarbonate aqueous solution, and then petroleum ether is added to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and chloroform is removed by rotary evaporation, and the modified antioxidant is obtained by drying; S3: polytetrahydrofuran diol 2000, hydroxyl-terminated polydimethylsiloxane, modified antioxidant, and dimethylol propionic acid are mixed, isophorone diisocyanate and dibutyltin dilaurate are added, stirred, the temperature is raised to 70-80°C for reaction for 2-3 hours, 1,4-butanediol is added and the reaction is continued for 1-2 hours; then acetone and triethylamine are added and the reaction is continued for 5-10 minutes, ethylenediamine is added for chain extension reaction for 30 minutes, and impurities are evaporated to obtain a polyurethane coating with a solid content of 30-35%; S4: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer and the first chiral agent are uniformly mixed in a mass ratio of (2.5-10):1 to obtain a first liquid crystal mixture; the nematic phase liquid crystal and the second chiral agent are mixed in a mass ratio of 1:(0.15-0.8) to obtain a second 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) to obtain a liquid crystal mixed solution; two modified transparent flexible substrates are taken, the liquid crystal mixed solution is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator are mixed in a mass ratio of 100:(2-3) and then coated on the area of ​​the modified transparent flexible substrate that is not coated with the liquid crystal mixed solution, the two modified transparent flexible substrates are aligned with the patterned sides, and after compounding, ultraviolet light curing is performed to obtain a thermochromic film.

[0006] Furthermore, in S1, the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2.

[0007] Furthermore, 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).

[0008] Furthermore, 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.

[0009] Furthermore, in S4, the transparent flexible substrate is a PET film.

[0010] Furthermore, in step 2, the liquid crystal polymerizable monomer is 1,4-bis-[4-(3-acryloxypropoxy)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.

[0011] 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; and coats the liquid crystal mixture on a transparent flexible substrate, and solidifies and encapsulates to obtain a thermochromic film. The color of the thermochromic film prepared by the present invention is controllable, and has the advantages of fast response, wide color gamut, and large detection temperature range. In the temperature range of 0 to 60°C, the color of the thermochromic film will red shift as the temperature increases, and the full spectrum color can change reversibly; it is made into an ultra-thin film, which can be used flexibly and flexibly. With this technical effect, the thermochromic film of the present invention can be widely used in technical fields such as liquid crystal display, smart glass, and anti-counterfeiting labels.

[0012] 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, and the preparation method of the modified antioxidant is as follows: trimethylolpropane tris (mercaptopropionate) is used as a raw material, and it 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 is used to react with the amino group to access N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine with anti-aging performance, and the hydroxyl group is reacted to generate a hydroxyl group at the same time. The hydroxyl group can react with the isocyanate group in the polyurethane and is introduced into the polyurethane molecular chain segment in the form of a chemical bond, which improves the anti-aging performance of the polyurethane coating on the one hand, and avoids the migration of small molecule antioxidants outward on the other hand. The present invention also introduces hydroxyl-terminated polydimethylsiloxane into the polyurethane, and introduces silicone to improve the water resistance of the polyurethane, so that it maintains good adhesion performance in a hot and humid environment. During the curing process, the polyurethane coating coated on the transparent flexible substrate contains carbon-carbon double bonds, which are cross-linked with methyl methacrylate by ultraviolet irradiation to achieve better bonding. Another effect of the present invention is that under ultraviolet irradiation, the liquid crystal phase curing and encapsulation steps can be achieved simultaneously, which not only has a simple process, but also has better encapsulation performance of the obtained calorific value color-changing film. After the liquid crystal mixture is cured, a thermochromic liquid crystal layer is formed, and both sides of the thermochromic liquid crystal layer are combined with the polyurethane coating. In a hot and humid environment, the polyurethane coating can also play a waterproof, anti-aging, and anti-separation effect, thereby extending the life of the thermochromic film. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part 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 creative work are within the scope of protection of the present invention.

[0014] 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, item number 481939; PET film comes from Hefei Furen Technology Co., Ltd., item number FR-2008089; nematic liquid crystal E7 comes from Qingdao Qiujun Liquid Crystal Material Co., Ltd.

[0015] Embodiment 1: A liquid crystal-based thermochromic film and a method for preparing the same, comprising the following steps: Step 1: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 50°C for 3h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 45°C for 3.5h with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 80°C for 4h, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; wherein the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2; S2: Mix the epoxy group in the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in a molar ratio of 1:1.1, use salicylic acid as a catalyst, react at 150°C for 8h, add chloroform to dilute, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution, add petroleum ether to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain a modified antioxidant; S3: 182g of polytetrahydrofuran diol 2000, 19g of hydroxyl-terminated polydimethylsiloxane, 11g of modified antioxidant, and 22g of dimethylol propionic acid were mixed, 187g of isophorone diisocyanate and 0.7g of dibutyltin dilaurate were added and stirred, the temperature was raised to 70°C for reaction for 2h, 1.3g of 1,4-butanediol was added and the reaction was continued for 1h; then 21g of acetone and 5g of triethylamine were added and the reaction was continued for 5min, 3.4g of ethylenediamine was added for chain extension reaction for 30min, and impurities were evaporated to obtain a polyurethane coating with a solid content of 35%; S4: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0016] Embodiment 2: A liquid crystal-based thermochromic film and a method for preparing the same, comprising the following steps: Step 1: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 55°C for 3.5 hours, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 48°C for 4 hours with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 85°C for 4.5 hours, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; wherein the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2; S2: Mix the epoxy group in the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in a molar ratio of 1:1.1, use salicylic acid as a catalyst, react at 155°C for 8.5h, add chloroform to dilute, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution, add petroleum ether to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain a modified antioxidant; S3: 182g of polytetrahydrofurandiol 2000, 19g of hydroxyl-terminated polydimethylsiloxane, 11g of modified antioxidant, and 22g of dimethylol propionic acid were mixed, 187g of isophorone diisocyanate and 0.7g of dibutyltin dilaurate were added and stirred, the temperature was raised to 75°C for reaction for 2.5h, 1.3g of 1,4-butanediol was added and the reaction was continued for 1.5h; then 21g of acetone and 5g of triethylamine were added and the reaction was continued for 7min, 3.4g of ethylenediamine was added for chain extension reaction for 30min, and impurities were evaporated to obtain a polyurethane coating with a solid content of 35%; S4: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0017] Embodiment 3: A liquid crystal-based thermochromic film and a method for preparing the same, comprising the following steps: Step 1: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 60°C for 4 hours, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 50°C for 4.5 hours with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 90°C for 5 hours, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; wherein the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2; S2: Mix the epoxy group in the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in a molar ratio of 1:1.1, use salicylic acid as a catalyst, react at 160°C for 9 hours, add chloroform to dilute, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution, add petroleum ether to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain a modified antioxidant; S3: 182g of polytetrahydrofuran diol 2000, 19g of hydroxyl-terminated polydimethylsiloxane, 11g of modified antioxidant, and 22g of dimethylol propionic acid were mixed, 187g of isophorone diisocyanate and 0.7g of dibutyltin dilaurate were added and stirred, the temperature was raised to 80°C for reaction for 3h, 1.3g of 1,4-butanediol was added and the reaction was continued for 2h; then 21g of acetone and 5g of triethylamine were added and the reaction was continued for 10min, 3.4g of ethylenediamine was added for chain extension reaction for 30min, and impurities were evaporated to obtain a polyurethane coating with a solid content of 35%; S4: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0018] Comparative Example 1: The transparent flexible substrate is not modified, and other parameters are the same as those in Example 1.

[0019] The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0020] Comparative Example 2: The polyurethane coating was prepared without adding hydroxyl-terminated polydimethylsiloxane, and the other parameters were the same as those in Example 2.

[0021] Step 1: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 55°C for 3.5 hours, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 48°C for 4 hours with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 85°C for 4.5 hours, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; wherein the molar ratio of trimethylolpropane tris(mercaptopropionate), allyl isocyanate, epichlorohydrin, and sodium hydroxide is 1:1:2:2; S2: Mix the epoxy group in the intermediate with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine in a molar ratio of 1:1.1, use salicylic acid as a catalyst, react at 155°C for 8.5h, add chloroform to dilute, neutralize salicylic acid with a 3% sodium bicarbonate aqueous solution, add petroleum ether to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, remove chloroform by rotary evaporation, and dry to obtain a modified antioxidant; S3: 182g of polytetrahydrofuran diol 2000, 11g of modified antioxidant, and 22g of dimethylol propionic acid were mixed, 187g of isophorone diisocyanate and 0.7g of dibutyltin dilaurate were added and stirred, the temperature was raised to 75°C for reaction for 2.5h, 1.3g of 1,4-butanediol was added and the reaction was continued for 1.5h; then 21g of acetone and 5g of triethylamine were added and the reaction was continued for 7min, 3.4g of ethylenediamine was added for chain extension reaction for 30min, and impurities were evaporated to obtain a polyurethane coating with a solid content of 35%; S4: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0022] Comparative Example 3: No modified antioxidant was added, and the other parameters were the same as those in Example 3.

[0023] Step 1: S1: 182g of polytetrahydrofuran diol 2000, 19g of hydroxyl-terminated polydimethylsiloxane, and 22g of dimethylol propionic acid were mixed, 187g of isophorone diisocyanate and 0.7g of dibutyltin dilaurate were added and stirred, the temperature was raised to 80°C for reaction for 3h, 1.3g of 1,4-butanediol was added and the reaction was continued for 2h; then 21g of acetone and 5g of triethylamine were added and the reaction was continued for 10min, 3.4g of ethylenediamine was added for chain extension reaction for 30min, and impurities were evaporated to obtain a polyurethane coating with a solid content of 35%; S2: coating the polyurethane coating on the transparent flexible substrate to form a polyurethane coating, and baking and curing the coating to obtain a modified transparent flexible substrate; Step 2: The liquid crystal polymerizable monomer 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and the first chiral agent S811 are uniformly mixed 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 are 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 are mixed at a mass ratio of 1:1:0.26:0.06 to obtain a liquid crystal mixture; two modified transparent flexible substrates are taken, the liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and the photoinitiator 907 are mixed at a mass ratio of 100:3 and then coated on the area of ​​the modified transparent flexible substrate not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with the patterned sides, and UV curing is performed after compounding, and the UV irradiation intensity is 130mW / cm 2 The film was irradiated with ultraviolet light for 10 s to obtain a thermochromic film.

[0024] Experiment: The thermochromic films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, wherein: Thermochromic experiment: After the thermochromic film is dried on the polytetrafluoroethylene template, it is moved to the intelligent temperature-controlled electric heating plate and heated from 0°C to 65°C. The time of each color change is recorded.

[0025] Adhesion performance: Test the 180° peel strength between two transparent flexible substrates of the thermal color-changing film.

[0026] Moisture and heat resistance: The calorific value color-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 hours, and the packaging of the thermochromic film was observed.

[0027]

[0028] Conclusion: The thermochromic films in Examples 1 to 3 are sensitive to temperature and respond quickly; they have stable performance in a hot and humid environment. The data of Example 1 and Comparative Example 1 show that after the transparent flexible substrate is modified, the adhesion between the transparent flexible substrates is good, and the thermochromic film has a resistant to hot and humid conditions; the data of Example 2 and Comparative Example 2 show that after the addition of hydroxyl-terminated polydimethylsiloxane, the resistant to hot and humid conditions of the thermochromic film is better; the data of Example 3 and Comparative Example 3 show that after the introduction of the modified antioxidant, the adhesion between the transparent flexible substrates after curing is good, and at the same time, it has good resistance to hot and humid conditions.

[0029] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a thermochromic film based on liquid crystal, characterized in that: Step 1: Mixing the liquid crystal polymerizable monomer and the first chiral agent uniformly to obtain a first liquid crystal mixture; mixing the nematic liquid crystal and the second chiral agent to obtain a second liquid crystal mixture; mixing 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: A polyurethane coating is coated on a transparent flexible substrate to form a polyurethane coating, which is then baked and cured to obtain a modified transparent flexible substrate; two modified transparent flexible substrates are taken, a liquid crystal mixture is coated on the modified transparent flexible substrates to form a pattern, methyl methacrylate and a photoinitiator are mixed and then coated on the area of ​​the modified transparent flexible substrate that is not coated with the liquid crystal mixture, the two modified transparent flexible substrates are aligned with their patterned sides, and after compounding, ultraviolet light curing is performed to obtain a thermochromic film.

2. The method for preparing a thermochromic film based on liquid crystal 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 method for preparing a thermochromic film based on liquid crystal 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 method for preparing a thermochromic film based on liquid crystal according to claim 1, characterized in that: In step 2, the transparent flexible substrate is a PET film.

5. The method for preparing a thermochromic film based on liquid crystal according to claim 1, characterized in that: In step 2, the method for preparing the polyurethane coating comprises the following steps: S1: Disperse trimethylolpropane tris(mercaptopropionate) and allyl isocyanate in N,N-dimethylformamide, add dibutyltin dilaurate as a catalyst, react at 50-60°C for 3-4h, remove N,N-dimethylformamide by vacuum distillation, transfer the product to anhydrous methanol, add epichlorohydrin, react at 45-50°C for 3.5-4.5h with triethylamine as a catalyst, add sodium hydroxide solution with a mass concentration of 5% after rotary evaporation to remove impurities, react at 80-90°C for 4-5h, add methanol and ultrapure water, stand to separate the organic phase and the inorganic phase, rotary evaporation to remove impurities on the organic phase, and dry to obtain an intermediate; S2: The intermediate is mixed with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and reacted at 150-160°C for 8-9h with salicylic acid as a catalyst, and then chloroform is added to dilute, and salicylic acid is neutralized with a 3-5% mass concentration of sodium bicarbonate aqueous solution, and then petroleum ether is added to remove excess N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and chloroform is removed by rotary evaporation, and the modified antioxidant is obtained by drying; S3: Mix polytetrahydrofuran diol 2000, hydroxyl-terminated polydimethylsiloxane, modified antioxidant and dimethylol propionic acid, add isophorone diisocyanate and dibutyltin dilaurate, stir, heat to 70-80°C and react for 2-3h, add 1,4-butanediol and continue the reaction for 1-2h; then add acetone and triethylamine and continue the reaction for 5-10min, add ethylenediamine to extend the chain and react for 30min, evaporate impurities to obtain a polyurethane coating with a solid content of 30-35%.

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

2.

7. The method for preparing a thermochromic film based on liquid crystal according to claim 5, characterized in that: 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).

8. The method for preparing a thermochromic film based on liquid crystal according to claim 5, characterized in that: 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.

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

10. An application of the liquid crystal based thermochromic film as claimed in claim 9, 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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