Preparation method of thermochromic coating and window film using thermochromic coating

Abstract

The invention relates to the technical field of thermochromic coatings, and discloses a preparation method of a thermochromic coating and a window film applying the thermochromic coating. Comprising the following operation steps: step 1, uniformly mixing sodium dodecyl sulfate and polyvinylpyrrolidone according to a mass ratio of 1: (0.3-0.4) to obtain a surfactant; step 2, adding modified polyurethane and acrylic resin into a solvent, heating and stirring at 50-60 DEG C for 1-2 hours, sequentially adding a surfactant, a pigment, a thermochromic microcapsule, a defoaming agent and a plasticizer, and continuously mixing for 40-60 minutes to obtain a thermochromic coating; carrying out melt extrusion, two-way stretching, shaping and cooling on a high polymer material to obtain a base film; setting the pressure to be 0.8-1N / cm < 2 > and the speed to be 1-2m / min, uniformly blade-coating the thermochromic coating on the base film, and drying at the temperature of 60-70 DEG C to prepare the intelligent window film, so that the energy consumption can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of thermochromic coatings, in particular to a preparation method of a thermochromic coating and a window film using the same. Background Art

[0002] Traditional windows have limited control over solar radiation, resulting in a large amount of heat entering the room in the summer, increasing air conditioning energy consumption; in the winter, indoor heat is easily lost, increasing heating energy consumption; thermochromic coatings can automatically adjust the optical properties of window films according to changes in ambient temperature, achieve adaptive control of solar radiation and thermal radiation, effectively regulate indoor temperature, and improve energy efficiency; using it as a coating for window films to make smart window films improves the energy consumption of traditional windows, and can be applied to a variety of scenarios such as building doors and windows, car windows, etc., which can not only meet the needs of building energy conservation, but also effectively regulate the temperature inside the car in the car, improving driving comfort, and has broad market prospects.

[0003] In summary, it is of great significance to prepare a thermochromic coating that can be used for window films. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a thermochromic coating and a window film using the same, so as to solve the problems in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a thermochromic coating comprises the following steps: Step 1: uniformly mixing sodium dodecyl sulfate and polyvinyl pyrrolidone in a mass ratio of 1:(0.3-0.4) to obtain a surfactant; Step 2: Add modified polyurethane and acrylic resin to the solvent, heat and stir at 50-60°C for 1-2 hours, add surfactant, pigment, thermochromic microcapsule, defoamer and plasticizer in sequence, continue mixing for 40-60 minutes, and obtain thermochromic coating.

[0006] More optimally, the raw materials of the thermochromic coating include the following components: by mass, 40 to 60 parts of solvent, 15 to 17 parts of acrylic resin, 10 to 20 parts of modified polyurethane, 10 to 18 parts of thermochromic microcapsules, 8 to 12 parts of plasticizer, 2 to 4 parts of surfactant, 2 to 2.5 parts of pigment, and 1 to 3 parts of defoaming agent.

[0007] More optimally, the solvent includes one or more of acetone, butanol or toluene; the plasticizer includes one or more of dioctyl phthalate, dibutyl sebacate or epoxidized soybean oil; and the defoamer is a polyether defoamer.

[0008] Preferably, the method for preparing the modified polyurethane is as follows: tetrafluorobutylene glycol and a catalyst are added to xylene and uniformly mixed to obtain a mixed solution; polycaprolactone polyol and dihydroxy-terminated polysiloxane are added to xylene and uniformly mixed, then toluene diisocyanate is added, and the reaction is carried out at 85-90 °C for 4-5 hours under a nitrogen atmosphere. After degassing by vacuum, the mixed solution is added and the reaction is continued for 1-2 hours to obtain the modified polyurethane.

[0009] Preferably, the raw materials of the modified polyurethane include the following components: by mass, 0.55-0.56 parts of toluene diisocyanate, 4.2-4.4 parts of polycaprolactone polyol, 0.55-0.57 parts of dihydroxy-terminated polysiloxane, 1.5-2 parts of tetrafluorobutylene glycol, 0.015-0.02 parts of catalyst, and 10-15 parts of xylene.

[0010] Preferably, the method for preparing the thermochromic microcapsules is as follows: (1) Aminated nano-titanium dioxide and dibutyltin dilaurate are ultrasonically dispersed in toluene, and dihydroxy-terminated polysiloxane is added. The mixture is stirred at 60-70 °C for 5-7 hours to obtain modified titanium dioxide; the modified titanium dioxide and polycaprolactone polyol are added to xylene and uniformly mixed to obtain a mixed solution; toluene diisocyanate is added to the mixed solution, and the reaction is carried out at 85-90 °C for 1-2 hours under a nitrogen atmosphere. Then, mixed solution A is added and the reaction is continued for 2-3 hours. After degassing by vacuum, a polyurethane prepolymer is obtained; (2) Crystal violet lactone, bisphenol A, and cetyl alcohol are uniformly mixed at 60-70 °C to obtain a ternary mixture; it is homogenized with styrene-maleic anhydride copolymer and deionized water to obtain an emulsion; (3) The polyurethane prepolymer is added to the emulsion and uniformly mixed, and a citric acid aqueous solution is added to adjust the pH to 4-5. The mixture is maintained at 80-90 °C for 2-3 hours, then a sodium hydroxide aqueous solution is added to adjust the pH to 7-8, and after washing and drying, thermochromic microcapsules are obtained.

[0011] Preferably, the raw materials of the modified titanium dioxide include the following components: by mass, 0.3-0.5 parts of aminated nano-titanium dioxide, 0.01-0.02 parts of dibutyltin dilaurate, and 1-1.5 parts of dihydroxy-terminated polysiloxane; the raw materials of the polyurethane prepolymer include the following components: by mass, 1.7-2 parts of polycaprolactone polyol, 0.2-0.3 parts of modified titanium dioxide, 0.17-0.25 parts of toluene diisocyanate, and 8-10 parts of xylene.

[0012] Preferably, the raw materials of the emulsion include the following components: by mass, 3 to 3.3 parts of crystal violet lactone, 1 to 1.2 parts of bisphenol A, and 40 to 60 parts of cetyl alcohol; the styrene-maleic anhydride copolymer accounts for 2 to 3 wt% of the emulsion; the mass ratio of the polyurethane prepolymer to the emulsion is (1 to 3):1; the concentration of the citric acid aqueous solution is 10 to 15 wt%, and the concentration of the sodium hydroxide aqueous solution is 10 to 15 wt%.

[0013] An application of a thermochromic coating, and the preparation method of the window film is as follows: melt-extrude a polymer material, perform biaxial stretching, and shape and cool to obtain a base film; set the pressure to 0.8 to 1 N / cm 2 , the speed is 1 to 2 m / min, scrape the thermochromic coating evenly on the base film, and dry it at 60 to 70 °C to obtain the window film; the polymer material includes one of PET particles and TPU particles.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, sodium dodecyl sulfate and polyvinylpyrrolidone are uniformly mixed in a mass ratio of 1:(0.3 to 0.4) to obtain a surfactant; the modified polyurethane and acrylic resin are added to a solvent, heated and stirred at 50 to 60 °C for 1 to 2 hours, and the surfactant, pigment, thermosensitive color-changing microcapsules, defoaming agent, and plasticizer are added in sequence, and the mixture is continued for 40 to 60 minutes to obtain a thermochromic coating.

[0015] In order to improve the performance of the thermochromic coating when applied to the window film; in the solution, polycaprolactone polyol, dihydroxy-terminated polysiloxane, and toluene diisocyanate are reacted for a period of time, then evacuated to remove bubbles, and a tetrafluorobutylene glycol chain extender and a catalyst are added, and the reaction is continued to obtain a modified polyurethane; among them, the addition of tetrafluorobutylene glycol can improve the antireflection property of the modified polyurethane, thereby being beneficial to enhancing the performance of the window film. Adding dihydroxy-terminated polysiloxane containing a polysiloxane structure to the fluoropolymer structure can effectively improve the anti-fouling property of the window film; while polycaprolactone polyol has a certain flexibility and strength, and dihydroxy-terminated polysiloxane can also endow the material with good elasticity and wear resistance, so the tear resistance of the window film can be improved.

[0016] In the solution, sodium dodecyl sulfate can reduce the surface tension of the liquid, enabling the uniform dispersion of macromolecular substances and solid particles in the solvent; it can also reduce the interfacial tension between the coating and the window film surface, allowing the coating to better wet the window film surface, promoting the penetration of the coating into the tiny pores on the window film surface, thereby enhancing the adhesion between the coating and the window film, ensuring that the coating adheres firmly to the window film and is not easily peeled off; polyvinylpyrrolidone is a non-ionic surfactant that can form a protective film on the particle surface and, in synergistic action with sodium dodecyl sulfate, further improve the dispersion stability of pigments, thermochromic microcapsules, etc. in the coating, preventing particle aggregation during storage and use, and maintaining the stability and uniformity of the coating; it can also participate in the film-forming process of the coating, improving the flexibility and density of the coating, enhancing the mechanical properties and weather resistance of the coating, enabling the window film to maintain good performance under different environmental conditions.

[0017] To enhance the film-forming property of the thermochromic coating; in the solution, acrylic resin is added to improve the film-forming performance and strengthen the formation of a firm coating on the window film surface by the thermochromic coating; although acrylic resin has good film-forming property, it will increase the resistance to heat transfer, slowing down the rate of external temperature change transmitted to the microcapsule core material, thereby prolonging the color-changing time of the window film.

[0018] To improve the influence of acrylic resin on the color-changing time of the window film, in the solution, the raw materials of modified polyurethane are used as the wall material of the thermochromic microcapsules, and the interfacial compatibility between the thermochromic microcapsules and the modified polyurethane is improved to improve the color-changing time of the window film; in the solution, bisphenol A, crystal violet lactone, and cetyl alcohol are used as the core material; to improve the combination of the polyurethane prepolymer wall material and the core material, in the solution, the core material is homogenized with styrene-maleic anhydride copolymer and deionized water to obtain an emulsion; making its surface contain active functional groups and increasing the content of hydroxyl groups in the polyurethane prepolymer, and then under acidic conditions, the anhydride bonds on the styrene-maleic anhydride copolymer are opened and combined with the hydroxyl groups in the polyurethane prepolymer under certain conditions to obtain the thermochromic microcapsules.

[0019] To improve the stability of the thermochromic microcapsules; in the solution, nano-titanium dioxide is added, but nano-titanium dioxide is prone to agglomeration in the polyurethane prepolymer. Therefore, in the solution, dihydroxy-terminated polysiloxane is grafted onto the surface of nano-titanium dioxide to improve the anti-ultraviolet performance of the thermochromic microcapsules, playing a role in protecting the core material, and appropriately reducing the dosage of polyisocyanate and increasing the proportion of polyol, which is beneficial to increasing the porosity of the wall material and achieving a synergistic heat insulation effect with nano-titanium dioxide. Therefore, the heat insulation performance of the thermochromic coating on the window film is improved, thereby enhancing the energy-saving effect of the window film. Specific implementation mode

[0020] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of 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] In the following specific embodiments, the parts are parts by mass. In this embodiment, it should be noted that there are no special restrictions on the purchase manufacturers of all raw materials involved in the present invention. Exemplarily, the CAS number of 3-aminopropyltriethoxysilane is 919-30-2; the product number of nano-titanium dioxide is 1317-80-2, purchased from Hubei Rishengchang New Material Technology Co., Ltd.; the CAS number of dibutyltin dilaurate is 77-58-7; the product number of dihydroxy-terminated polysiloxane is 171, purchased from Zhongshan Dixin Chemical Co., Ltd.; the polycaprolactone polyol model is 308, purchased from Liaoning Zhouqingchen Petrochemical Co., Ltd.; the CAS number of toluene diisocyanate is 26471-62-5; the product number of crystal violet lactone is 662223, purchased from Wuhan Shuer Biotechnology Co., Ltd.; the CAS number of bisphenol A is 80-05-7; the CAS number of cetyl alcohol is 36653-82-4; the product number of styrene-maleic anhydride copolymer is Y47209, purchased from Shanghai Yuanye Biotechnology Co., Ltd.; the CAS number of citric acid is 77-92-9; the CAS number of sodium dodecyl sulfonate is 2386-53-0; the product number of polyvinylpyrrolidone is S30268, purchased from Shanghai Yuanye Biotechnology Co., Ltd.; the product number of polyether defoamer is 003, purchased from Jinan Dehou Chemical Co., Ltd.; the product number of epoxidized soybean oil is S50881, purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0022] The preparation method of amino-functionalized nano-titanium dioxide is as follows: 1.3 parts of nano-titanium dioxide is ultrasonically dispersed in an ethanol aqueous solution (75 wt%), 0.4 part of 3-aminopropyltriethoxysilane is added, and hydrolysis is carried out at 75 °C for 3 hours, followed by washing and drying to obtain amino-functionalized nano-titanium dioxide.

[0023] Preparation method of temperature-sensitive color-changing microcapsules: (1) Ultrasonically disperse 0.37 parts of amino-functionalized nano-titanium dioxide and 0.01 part of dibutyltin dilaurate in toluene, add 1.2 parts of dihydroxy-terminated polysiloxane, and stir at 70 °C for 5 hours to obtain modified titanium dioxide; add 0.2 parts of modified titanium dioxide and 1.8 parts of polycaprolactone polyol to 8 parts of xylene and mix evenly to obtain a mixed solution; add 0.17 parts of toluene diisocyanate to the mixed solution, react at 85 °C for 2 hours under a nitrogen atmosphere, add mixed solution A, continue to react for 2 hours, and remove bubbles under vacuum to obtain a polyurethane prepolymer; (2) Uniformly mix 3.3 parts of crystal violet lactone, 1.2 parts of bisphenol A, and 45 parts of cetyl alcohol at 60 °C to obtain a ternary mixture; homogenize it with styrene-maleic anhydride copolymer (2.3 wt% of the emulsion) and deionized water to obtain an emulsion; (3) Weigh the polyurethane prepolymer and the emulsion according to a mass ratio of 2:1; add the polyurethane prepolymer to the emulsion and mix evenly, add citric acid aqueous solution (10 wt%), adjust the pH to 4.5, keep it at 80 °C for 2 hours, add sodium hydroxide aqueous solution (10 wt%), adjust the pH to 7.3, wash and dry to obtain temperature-sensitive color-changing microcapsules.

[0024] Preparation method of modified polyurethane: Add 1.8 parts of tetrafluorobutylene glycol and 0.015 part of catalyst to 5 parts of xylene and mix evenly to obtain a mixed solution; add 4.2 parts of polycaprolactone polyol and 0.55 part of dihydroxy-terminated polysiloxane to 10 parts of xylene and mix evenly, add 0.55 part of toluene diisocyanate, react at 85 °C for 4 hours under a nitrogen atmosphere, evacuate to remove bubbles, add the mixed solution, and react for 2 hours to obtain modified polyurethane.

[0025] Example 1: A preparation method of a thermochromic coating, comprising the following operation steps: Step 1: Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone according to a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 12 parts of modified polyurethane and 15 parts of acrylic resin to 40 parts of solvent, heat and stir at 60 °C for 1.5 hours, sequentially add 3 parts of surfactant, 2 parts of pigment, 10 parts of temperature-sensitive color-changing microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0026] Example 2: A preparation method of a thermochromic coating, comprising the following operation steps: Step 1: Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone according to a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 18 parts of modified polyurethane and 15 parts of acrylic resin into 40 parts of solvent, heat and stir at 60 °C for 1.5 hours, successively add 3 parts of surfactant, 2 parts of pigment, 15 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0027] Example 3: A preparation method of a thermochromic coating, comprising the following operating steps: Step 1: Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone in a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 18 parts of modified polyurethane and 17 parts of acrylic resin into 40 parts of solvent, heat and stir at 60 °C for 1.5 hours, successively add 3 parts of surfactant, 2 parts of pigment, 15 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0028] Comparative Example 1 is based on Example 2, and the wall material is changed to melamine and urea; Step 1: (1) Uniformly mix 3.3 parts of crystal violet lactone, 1.2 parts of bisphenol A, and 45 parts of cetyl alcohol at 60 °C to obtain a ternary mixture; homogenize it with styrene-maleic anhydride copolymer (accounting for 2.3 wt% of the emulsion) and deionized water to obtain an emulsion; (2) Add 3 parts of urea, 2 parts of melamine, and 12 mL of formaldehyde solution (35 wt%) into 15 mL of deionized water and mix evenly, adjust the pH to 10, stir at 70 °C for 2 hours to obtain a prepolymer; add it into the emulsion, keep it at 80 °C for 1 hour, adjust the pH to 4.5, continue to stir for 2 hours, wash, and dry to obtain thermochromic microcapsules; (3) Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone in a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 18 parts of modified polyurethane and 15 parts of acrylic resin into 40 parts of solvent, heat and stir at 60 °C for 1.5 hours, successively add 3 parts of surfactant, 2 parts of pigment, 15 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0029] Comparative Example 2 is based on Example 2, and the content of hydroxyl groups in the polyurethane prepolymer is reduced; Step 1: (1) Ultrasonically disperse 0.37 parts of amino-functionalized nano-titanium dioxide and 0.01 part of dibutyltin dilaurate in toluene, add 1.2 parts of dihydroxy-terminated polysiloxane, and stir at 70 °C for 5 hours to obtain modified titanium dioxide; add 0.2 part of modified titanium dioxide and 0.8 part of polycaprolactone polyol to 8 parts of xylene and mix evenly to obtain a mixed solution; add 0.17 part of toluene diisocyanate to the mixed solution, react at 85 °C for 2 hours under a nitrogen atmosphere, add mixed solution A, continue to react for 2 hours, and remove bubbles under vacuum to obtain a polyurethane prepolymer; (2) Uniformly mix 3.3 parts of crystal violet lactone, 1.2 parts of bisphenol A, and 45 parts of cetyl alcohol at 60 °C to obtain a ternary mixture; homogenize it with styrene-maleic anhydride copolymer (2.3 wt% of the emulsion) and deionized water to obtain an emulsion; (3) Weigh the polyurethane prepolymer and the emulsion according to a mass ratio of 2:1; add the polyurethane prepolymer to the emulsion and mix evenly, add a citric acid aqueous solution (10 wt%), adjust the pH to 4.5, maintain at 80 °C for 2 hours, add a sodium hydroxide aqueous solution (10 wt%), adjust the pH to 7.3, wash and dry to obtain thermochromic microcapsules; (4) Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone according to a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 18 parts of modified polyurethane and 15 parts of acrylic resin to 40 parts of a solvent, heat and stir at 60 °C for 1.5 hours, sequentially add 3 parts of surfactant, 2 parts of pigment, 15 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxy soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0030] Comparative Example 3 is based on Example 2, and dihydroxy-terminated polysiloxane is not introduced into the modified polyurethane; Step 1: (1) Uniformly mix 1.8 parts of tetrafluorobutylene glycol and 0.015 part of catalyst in 5 parts of xylene to obtain a mixed solution; add 4.5 parts of polycaprolactone polyol to 10 parts of xylene and mix evenly, add 0.55 part of toluene diisocyanate, react at 85 °C for 4 hours under a nitrogen atmosphere, evacuate to remove bubbles, add the mixed solution, and react for 2 hours to obtain modified polyurethane; (2) Uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone according to a mass ratio of 1:0.4 to obtain a surfactant; Step 2: Add 18 parts of modified polyurethane and 15 parts of acrylic resin to 40 parts of a solvent, heat and stir at 60 °C for 1.5 hours, sequentially add 3 parts of surfactant, 2 parts of pigment, 15 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxy soybean oil), and continue to mix for 60 minutes to obtain a thermochromic coating.

[0031] Comparative Example 4 is based on Example 2, without adding acrylic resin; Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are uniformly mixed at a mass ratio of 1:0.4 to obtain a surfactant; Step 2: 18 parts of modified polyurethane are added to 40 parts of a solvent, and heated and stirred at 60 °C for 1.5 hours. Then, 3 parts of the surfactant, 2 parts of pigment, 15 parts of thermosensitive color-changing microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxy soybean oil) are added in sequence, and mixing is continued for 60 minutes to obtain a thermochromic coating.

[0032] Comparative Example 5 is based on Example 2, without adding polyvinylpyrrolidone; 18 parts of modified polyurethane and 15 parts of acrylic resin are added to 40 parts of a solvent, and heated and stirred at 60 °C for 1.5 hours. Then, 3 parts of sodium dodecyl sulfonate, 2 parts of pigment, 15 parts of thermosensitive color-changing microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxy soybean oil) are added in sequence, and mixing is continued for 60 minutes to obtain a thermochromic coating.

[0033] Detection test: (1) TPU particles are melt-extruded, biaxially stretched, shaped and cooled to obtain a TPU film; the pressure is set to 0.8 N / cm 2 , and the speed is 2 m / min. The thermochromic slurries of Examples 1 to 3 and Comparative Examples 1 to 5 are uniformly scrape-coated on the TPU film and dried at 65 °C to obtain a window film; (2) Six window films prepared in Examples 1 to 3 and Comparative Examples 1 to 5 are taken respectively, the color-changing time is detected, and the average value is taken; and they are respectively placed in a drying oven at 70 °C for 30 minutes, then cooled at room temperature for 30 minutes, and after repeating 200 times, it is observed whether the coating peels off, and the tear strength before and after is recorded, and the tear strength reduction rate (%) is calculated; as shown in Table 1; (3) Two rooms with the same area (about 60 square meters) are selected as laboratories, equipped with separate electricity meters, and the same model of air conditioners are installed inside. One of the laboratories has the window film prepared in Example 2 pasted on the window; the other laboratory is not pasted (blank control); the operating parameters of the air conditioner are kept consistent (heating in winter), and the power consumption within the test time of the two laboratories on the same day is recorded, as shown in Table 2;

[0034] Table 1

[0035] Table 2 Conclusion: Comparative Example 1 is based on Example 2, with the wall material replaced by melamine and urea; this results in a decrease in the interfacial compatibility between the thermochromic microcapsules and the modified polyurethane, thus affecting the performance of the window film; Comparative Example 2 is based on Example 2, with the content of hydroxyl groups in the polyurethane prepolymer reduced; this leads to a decrease in the bonding between the wall material and the core material, thus affecting the performance of the window film; Comparative Example 3 is based on Example 2, without introducing dihydroxy-terminated polysiloxane into the modified polyurethane; this results in poor thermal stability of the thermochromic slurry coating, thus affecting the performance of the window film; Comparative Example 4 is based on Example 2, without adding acrylic resin; this leads to a decrease in the adhesion of the thermochromic coating. Although acrylic resin has good film-forming properties, it increases the resistance to heat transfer, slowing down the rate at which external temperature changes are transmitted to the microcapsule core material, thus slowing down the color-changing time of the window film in Comparative Example 4; Comparative Example 5 is based on Example 2, and it is found that adding polyvinylpyrrolidone also has a certain improvement on the performance of the window film.

[0036] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention.

Claims

1. A method for preparing a thermochromic coating, characterized in that: The steps include: Step 1: uniformly mixing sodium dodecyl sulfate and polyvinyl pyrrolidone in a mass ratio of 1:(0.3-0.4) to obtain a surfactant; Step 2: Add modified polyurethane and acrylic resin to the solvent, heat and stir at 50-60°C for 1-2 hours, add surfactant, pigment, thermochromic microcapsule, defoamer and plasticizer in sequence, continue mixing for 40-60 minutes, and obtain thermochromic coating.

2. The method for preparing a thermochromic coating according to claim 1, characterized in that: The raw materials of the thermochromic coating include the following components: by mass, 40 to 60 parts of solvent, 15 to 17 parts of acrylic resin, 10 to 20 parts of modified polyurethane, 10 to 18 parts of thermochromic microcapsules, 8 to 12 parts of plasticizer, 2 to 4 parts of surfactant, 2 to 2.5 parts of pigment, and 1 to 3 parts of defoaming agent.

3. The method for preparing a thermochromic coating according to claim 1, characterized in that: The solvent includes one or more of acetone, butanol or toluene; the plasticizer includes one or more of dioctyl phthalate, dibutyl sebacate or epoxidized soybean oil; and the defoamer is a polyether defoamer.

4. The method for preparing a thermochromic coating according to claim 1, characterized in that: The preparation method of the modified polyurethane comprises the following steps: adding tetrafluorobutanediol and a catalyst into xylene and mixing them uniformly to obtain a mixed solution; adding polycaprolactone polyol and dihydroxy-terminated polysiloxane into xylene and mixing them uniformly, adding toluene diisocyanate, reacting at 85-90° C. for 4-5 hours under a nitrogen atmosphere, vacuuming to remove bubbles, adding the mixed solution, reacting for 1-2 hours, and obtaining the modified polyurethane.

5. The method for preparing a thermochromic coating according to claim 4, characterized in that: The raw materials of the modified polyurethane include the following components: by mass, 0.55-0.56 parts of toluene diisocyanate, 4.2-4.4 parts of polycaprolactone polyol, 0.55-0.57 parts of dihydroxy-terminated polysiloxane, 1.5-2 parts of tetrafluorobutanediol, 0.015-0.02 parts of catalyst, and 10-15 parts of xylene.

6. The method for preparing a thermochromic coating according to claim 1, characterized in that: The preparation method of the thermochromic microcapsule is as follows: (1) ultrasonically dispersing amino nano-titanium dioxide and dibutyltin dilaurate in toluene, adding dihydroxy-terminated polysiloxane, and stirring at 60-70° C. for 5-7 hours to obtain modified titanium dioxide; The modified titanium dioxide and polycaprolactone polyol are added to xylene and mixed uniformly to obtain a mixed solution; toluene diisocyanate is added to the mixed solution, reacted at 85-90°C for 1-2 hours under a nitrogen atmosphere, mixed solution A is added, the reaction is continued for 2-3 hours, and vacuum degassing is performed to obtain a polyurethane prepolymer; (2) crystal violet lactone, bisphenol A, and hexadecanol are uniformly mixed at 60-70°C to obtain a ternary mixture; the mixture is homogenized with styrene-maleic anhydride copolymer and deionized water to obtain an emulsion; (3) the polyurethane prepolymer is added to the emulsion and mixed uniformly, citric acid aqueous solution is added, the pH is adjusted to 4-5, the mixture is kept at 80-90°C for 2-3 hours, sodium hydroxide aqueous solution is added, the pH is adjusted to 7-8, washed, and dried to obtain thermochromic microcapsules.

7. The method for preparing a thermochromic coating according to claim 6, characterized in that: The raw materials of the modified titanium dioxide include the following components: by weight, 0.3-0.5 parts of amino-modified nano titanium dioxide, 0.01-0.02 parts of dibutyltin dilaurate, and 1-1.5 parts of dihydroxy-terminated polysiloxane; the raw materials of the polyurethane prepolymer include the following components: by weight, 1.7-2 parts of polycaprolactone polyol, 0.2-0.3 parts of modified titanium dioxide, 0.17-0.25 parts of toluene diisocyanate, and 8-10 parts of xylene.

8. The method for preparing a thermochromic coating according to claim 6, characterized in that: The raw materials of the emulsion include the following components: 3-3.3 parts of crystal violet lactone, 1-1.2 parts of bisphenol A, and 40-60 parts of hexadecanol, by weight; the styrene-maleic anhydride copolymer accounts for 2-3wt% of the emulsion; the mass ratio of the polyurethane prepolymer to the emulsion is (1-3):1; the concentration of the citric acid aqueous solution is 10-15wt%, and the concentration of the sodium hydroxide aqueous solution is 10-15wt%.

9. A thermochromic coating prepared according to the method for preparing a thermochromic coating according to any one of claims 1 to 8.

10. An application of a thermochromic coating, characterized in that: The thermochromic coating according to claim 9 is applied to a window film, wherein the preparation method of the window film is: melt-extrude the polymer material, biaxially stretch, shape and cool to obtain a base film; set the pressure to 0.8~1N / cm 2 , the speed is 1~2m / min, the thermochromic coating is evenly scraped on the base film, and dried at 60~70℃ to obtain a window film; the polymer material includes one of PET particles and TPU particles.

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