A method for the preparation of a thermochromic coating and its application to a window film

Abstract

This invention relates to the field of thermochromic coating technology, and discloses a method for preparing thermochromic coatings and a window film for their application; comprising the following steps: Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are uniformly mixed at a mass ratio of 1:(0.3~0.4) to obtain a surfactant; Step 2: Modified polyurethane and acrylic resin are added to a solvent, heated and stirred at 50~60℃ for 1~2 hours, and surfactant, pigment, thermochromic microcapsules, defoamer, and plasticizer are added sequentially, and mixing is continued for 40~60 minutes to obtain a thermochromic coating; the polymer material is melt-extruded, biaxially stretched, shaped and cooled to obtain a base film; the pressure is set to 0.8~1N / cm. 2 At a speed of 1~2m / min, the thermochromic coating is evenly applied to the base film and dried at 60~70℃ to produce a smart window film, which can effectively reduce energy consumption.

Description

Technical Field

[0001] This invention relates to the field of thermochromic coating technology, specifically a method for preparing thermochromic coatings and its application in window films. Background Technology

[0002] Traditional windows have limited ability to control sunlight, resulting in a large amount of heat entering the room in summer, increasing air conditioning energy consumption; in 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, achieving adaptive control of solar and thermal radiation, effectively regulating indoor temperature, and improving energy efficiency. Using it as a coating for window films, smart window films can be made to improve the energy consumption of traditional windows and can be applied to various scenarios such as building doors and windows and car windows. It can not only meet the needs of building energy conservation, but also effectively regulate the interior temperature of cars, improving driving and riding comfort, and has broad market prospects.

[0003] In conclusion, the development of a thermochromic coating that can be used for window films is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing thermochromic coatings and a window film for their application, in order to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a thermochromic coating includes the following steps:

[0007] Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:(0.3~0.4) to obtain a surfactant;

[0008] Step 2: Add the modified polyurethane and acrylic resin to the solvent, heat and stir at 50~60℃ for 1~2 hours, then add the surfactant, pigment, thermochromic microcapsule, defoamer and plasticizer in sequence, and continue mixing for 40~60 minutes to obtain the thermochromic coating.

[0009] In a more optimized form, the raw materials of the thermochromic coating include the following components: by mass parts, 40-60 parts solvent, 15-17 parts acrylic resin, 10-20 parts modified polyurethane, 10-18 parts thermochromic microcapsules, 8-12 parts plasticizer, 2-4 parts surfactant, 2-2.5 parts pigment, and 1-3 parts defoamer.

[0010] In a more optimized configuration, 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.

[0011] A more optimized method for preparing the modified polyurethane is as follows: tetrafluorobutane glycol and catalyst are added to xylene and mixed uniformly to obtain a mixture; polycaprolactone polyol and dihydroxy-terminated polysiloxane are added to xylene and mixed uniformly; toluene diisocyanate is added; the mixture is reacted at 85-90°C for 4-5 hours under a nitrogen atmosphere; the mixture is then defoamed under vacuum; the mixture is added; and the mixture is reacted for 1-2 hours to obtain the modified polyurethane.

[0012] In a more optimized form, the modified polyurethane raw materials include the following components: by mass parts, 0.55-0.56 parts toluene diisocyanate, 4.2-4.4 parts polycaprolactone polyol, 0.55-0.57 parts dihydroxy-terminated polysiloxane, 1.5-2 parts tetrafluorobutanediol, 0.015-0.02 parts catalyst, and 10-15 parts xylene.

[0013] A more optimized 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 mixed evenly to obtain a mixed solution; toluene diisocyanate is added to the mixed solution, and the mixture is reacted at 85-90°C for 1-2 hours under a nitrogen atmosphere; mixed solution A is added, and the reaction continues for 2 hours. (2) After 3 hours of vacuum degassing, polyurethane prepolymer is obtained; (3) Crystal violet lactone, bisphenol A and hexadecyl alcohol are uniformly mixed at 60-70℃ to obtain a ternary mixture; it is homogenized with styrene-maleic anhydride copolymer and deionized water to obtain an emulsion; (4) Polyurethane prepolymer is added to the emulsion and mixed uniformly, citric acid aqueous solution is added, pH is adjusted to 4-5, and it is kept at 80-90℃ for 2-3 hours. Sodium hydroxide aqueous solution is added, pH is adjusted to 7-8, and it is washed and dried to obtain thermochromic microcapsules.

[0014] In a more optimized form, the modified titanium dioxide raw material comprises the following components: by mass parts, 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 polyurethane prepolymer raw material comprises the following components: by mass parts, 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.

[0015] In a more optimized form, the raw materials of the emulsion include the following components: by mass parts, 3-3.3 parts crystal violet lactone, 1-1.2 parts bisphenol A, and 40-60 parts cetyl alcohol; the styrene-maleic anhydride copolymer accounts for 2-3 wt% 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 10-15 wt%, and the concentration of the sodium hydroxide aqueous solution is 10-15 wt%.

[0016] An application of a thermochromic coating, wherein the window film is prepared by: melting and extruding a polymer material, biaxially stretching it, and cooling it to obtain a base film; setting the pressure to 0.8~1 N / cm. 2 At a speed of 1~2m / min, the thermochromic coating is evenly applied to the base film and dried at 60~70℃ to obtain the window film; the polymer material includes one of PET particles and TPU particles.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] In this invention, sodium dodecyl sulfonate and polyvinylpyrrolidone are uniformly mixed at a mass ratio of 1:(0.3~0.4) to obtain a surfactant; modified polyurethane and acrylic resin are added to a solvent and heated and stirred at 50~60℃ for 1~2 hours; surfactant, pigment, thermochromic microcapsules, defoamer and plasticizer are added in sequence, and mixing is continued for 40~60 minutes to obtain a thermochromic coating.

[0019] To improve the performance of thermochromic coatings in window films, the following method involves reacting polycaprolactone polyol, dihydroxy-terminated polysiloxane, and toluene diisocyanate for a period of time, followed by vacuum degassing, the addition of tetrafluorobutylene glycol chain extender and catalyst, and continued reaction to obtain modified polyurethane. The addition of tetrafluorobutylene glycol enhances the anti-reflective properties of the modified polyurethane, thus improving the performance of the window film. The addition of dihydroxy-terminated polysiloxane containing a polysiloxane structure to the fluoropolymer structure effectively improves the stain resistance of the window film. Furthermore, polycaprolactone polyol possesses certain flexibility and strength, while dihydroxy-terminated polysiloxane imparts good elasticity and wear resistance to the material, thereby improving the tear resistance of the window film.

[0020] In this solution, sodium dodecyl sulfonate reduces the surface tension of liquids, allowing polymers and solid particles to disperse uniformly in the solvent. It also reduces the interfacial tension between the coating and the window film surface, enabling the coating to better wet the film surface and promote its penetration into the micropores of the film, thereby improving the adhesion between the coating and the window film and ensuring the coating adheres firmly to the film, preventing it from peeling off. Polyvinylpyrrolidone (PVP), a nonionic surfactant, forms a protective film on the particle surface. Working synergistically with sodium dodecyl sulfonate, it further improves the dispersion stability of pigments and thermochromic microcapsules in the coating, preventing particle aggregation during storage and use, and maintaining the stability and uniformity of the coating. PPVP also participates in the film-forming process, improving the coating's flexibility and density, enhancing its mechanical properties and weather resistance, ensuring the window film maintains good performance under various environmental conditions.

[0021] To enhance the film-forming properties of thermochromic coatings, acrylic resin is added to improve film-forming performance and enhance the formation of a firm coating on the window film surface. Although acrylic resin has good film-forming properties, it increases the resistance to heat transfer, slowing down the transfer of external temperature changes to the microcapsule core material, thereby prolonging the color-changing time of the window film.

[0022] To mitigate the impact of acrylic resin on the color-changing time of window film, this design uses modified polyurethane as the wall material for thermochromic microcapsules. By improving the interfacial compatibility between the thermochromic microcapsules and the modified polyurethane, the color-changing time of the window film is enhanced. The design uses bisphenol A, crystal violet lactone, and cetyl alcohol as core materials. To improve the bonding between the polyurethane prepolymer wall material and the core material, the core material is homogenized with a styrene-maleic anhydride copolymer and deionized water to obtain an emulsion. This emulsion contains active functional groups on its surface and increases the hydroxyl content in the polyurethane prepolymer. Then, under acidic conditions, the anhydride bonds on the styrene-maleic anhydride copolymer open and combine with the hydroxyl groups in the polyurethane prepolymer under certain conditions, thus obtaining the thermochromic microcapsules.

[0023] To improve the stability of thermochromic microcapsules, nano-titanium dioxide is added to the design. However, nano-titanium dioxide is prone to agglomeration in polyurethane prepolymers. Therefore, the design grafts dihydroxy-terminated polysiloxane onto the surface of nano-titanium dioxide to improve the UV resistance of the thermochromic microcapsules, thus protecting the core material. Furthermore, the amount of polyisocyanate is appropriately reduced while the proportion of polyols is increased, which helps to improve the porosity of the wall material. This, combined with the nano-titanium dioxide, creates a synergistic heat insulation effect, thereby improving the heat insulation performance of the thermochromic coating in window films and ultimately enhancing the energy-saving effect of the window film. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In the following specific embodiments, "parts" refers to parts by weight. It should be noted that there are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: 3-aminopropyltriethoxysilane (CAS number 919-30-2); nano-titanium dioxide (item number 1317-80-2), purchased from Hubei Rishengchang New Material Technology Co., Ltd.; dibutyltin dilaurate (CAS number 77-58-7); dihydroxyl-terminated polysiloxane (item number 171), purchased from Zhongshan Dixing Chemical Co., Ltd.; polycaprolactone polyol (model 308), purchased from Liaoning Zhouqingchen Petrochemical Co., Ltd.; toluene diisocyanate (CAS number 26471-62-5); crystal violet... The following products were purchased from Shanghai Yuanye Biotechnology Co., Ltd.: lactone (product number 662223); bisphenol A (CAS number 80-05-7); cetyl alcohol (CAS number 36653-82-4); styrene-maleic anhydride copolymer (product number Y47209); citric acid (CAS number 77-92-9); sodium dodecyl sulfonate (CAS number 2386-53-0); polyvinylpyrrolidone (product number S30268); polyether defoamer (product number 003); and epoxidized soybean oil (product number S50881).

[0026] The preparation method of aminated nano-titanium dioxide is as follows: 1.3 parts of nano-titanium dioxide are ultrasonically dispersed in an ethanol aqueous solution (75wt%), 0.4 parts of 3-aminopropyltriethoxysilane are added, and the mixture is hydrolyzed at 75℃ for 3 hours. After washing and drying, aminated nano-titanium dioxide is obtained.

[0027] Preparation method of thermochromic microcapsules: (1) 0.37 parts of aminated nano-titanium dioxide and 0.01 parts of dibutyltin dilaurate were ultrasonically dispersed in toluene, and 1.2 parts of dihydroxy-terminated polysiloxane were added. The mixture was stirred at 70°C for 5 hours to obtain modified titanium dioxide; 0.2 parts of modified titanium dioxide and 1.8 parts of polycaprolactone polyol were added to 8 parts of xylene and mixed evenly to obtain a mixed solution; 0.17 parts of toluene diisocyanate were added to the mixed solution and reacted at 85°C for 2 hours under a nitrogen atmosphere; mixed solution A was added and the reaction was continued for 2 hours; the mixture was defoamed under vacuum to obtain polyurethane prepolymer; (2) 3.3 parts crystal violet lactone, 1.2 parts bisphenol A, and 45 parts cetyl alcohol were uniformly mixed at 60°C to obtain a ternary mixture; it was homogenized with styrene-maleic anhydride copolymer (accounting for 2.3 wt% of the emulsion) and deionized water to obtain an emulsion; (3) the polyurethane prepolymer and the emulsion were weighed at a mass ratio of 2:1; the polyurethane prepolymer was added to the emulsion and mixed uniformly, citric acid aqueous solution (10 wt%) was added, the pH was adjusted to 4.5, and it was kept at 80°C for 2 hours. Sodium hydroxide aqueous solution (10 wt%) was added, the pH was adjusted to 7.3, and the mixture was washed and dried to obtain thermochromic microcapsules.

[0028] The modified polyurethane is prepared as follows: 1.8 parts of tetrafluorobutane glycol and 0.015 parts of catalyst are added to 5 parts of xylene and mixed evenly to obtain a mixture; 4.2 parts of polycaprolactone polyol and 0.55 parts of dihydroxy-terminated polysiloxane are added to 10 parts of xylene and mixed evenly; 0.55 parts of toluene diisocyanate are added, and the mixture is reacted at 85°C for 4 hours under a nitrogen atmosphere. After vacuum degassing, the mixture is added, and the mixture is reacted for 2 hours to obtain the modified polyurethane.

[0029] Example 1: A method for preparing a thermochromic coating, comprising the following steps:

[0030] Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0031] 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, then add 3 parts of surfactant, 2 parts of pigment, 10 parts of thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0032] Example 2: A method for preparing a thermochromic coating, comprising the following steps:

[0033] Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0034] Step 2: Add 18 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, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0035] Example 3: A method for preparing a thermochromic coating, comprising the following steps:

[0036] Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0037] Step 2: Add 18 parts of modified polyurethane and 17 parts of acrylic resin to 40 parts of solvent, heat and stir at 60°C for 1.5 hours, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0038] Comparative Example 1 is based on Example 2, except that the wall material is replaced with melamine and urea;

[0039] Step 1: (1) Mix 3.3 parts crystal violet lactone, 1.2 parts bisphenol A and 45 parts 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 urea, 2 parts melamine and 12 mL formaldehyde solution (35 wt%) to 15 mL deionized water and mix evenly, adjust the pH to 10, stir at 70°C for 2 hours to obtain a prepolymer; add it to the emulsion, keep at 80°C for 1 hour, adjust the pH to 4.5, continue stirring for 2 hours, wash and dry to obtain thermochromic microcapsules;

[0040] (3) Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0041] Step 2: Add 18 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, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0042] Comparative Example 2 is based on Example 2, but with a reduction in the hydroxyl content in the polyurethane prepolymer;

[0043] Step 1: (1) Disperse 0.37 parts of aminated nano-titanium dioxide and 0.01 parts of dibutyltin dilaurate in toluene using ultrasonication, 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 0.8 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 the reaction for 2 hours, and remove bubbles under vacuum to obtain polyurethane prepolymer; (2) Disperse 3.3 parts of toluene in toluene in toluene in toluene in toluene in toluene and 0.01 parts of dibutyltin dilaurate in toluene. 1 part crystal violet lactone, 1.2 parts bisphenol A, and 45 parts cetyl alcohol were uniformly mixed at 60°C to obtain a ternary mixture; it was homogenized with styrene-maleic anhydride copolymer (accounting for 2.3 wt% of the emulsion) and deionized water to obtain an emulsion; (3) the polyurethane prepolymer and the emulsion were weighed at a mass ratio of 2:1; the polyurethane prepolymer was added to the emulsion and mixed uniformly, citric acid aqueous solution (10 wt%) was added, the pH was adjusted to 4.5, and it was kept at 80°C for 2 hours. Sodium hydroxide aqueous solution (10 wt%) was added, the pH was adjusted to 7.3, and it was washed and dried to obtain thermochromic microcapsules;

[0044] (4) Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0045] Step 2: Add 18 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, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0046] Comparative Example 3 is based on Example 2, but without the introduction of dihydroxy-terminated polysiloxane into the modified polyurethane;

[0047] Step 1: (1) Add 1.8 parts of tetrafluorobutanediol and 0.015 parts of catalyst to 5 parts of xylene and mix evenly to obtain a mixture; add 4.5 parts of polycaprolactone polyol to 10 parts of xylene and mix evenly, add 0.55 parts of toluene diisocyanate, react at 85°C for 4 hours under a nitrogen atmosphere, remove bubbles by vacuum, add the mixture, react for 2 hours to obtain modified polyurethane;

[0048] (2) Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0049] Step 2: Add 18 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, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0050] Comparative Example 4 is based on Example 2, but without the addition of acrylic resin;

[0051] Step 1: Sodium dodecyl sulfonate and polyvinylpyrrolidone are mixed uniformly at a mass ratio of 1:0.4 to obtain a surfactant;

[0052] Step 2: Add 18 parts of modified polyurethane to 40 parts of solvent, heat and stir at 60°C for 1.5 hours, then 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) in sequence, and continue mixing for 60 minutes to obtain thermochromic coating.

[0053] Comparative Example 5 is based on Example 2, but without the addition of polyvinylpyrrolidone;

[0054] 18 parts of modified polyurethane and 15 parts of acrylic resin were added to 40 parts of 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 thermochromic microcapsules, 2 parts of defoamer (polyether defoamer), and 8 parts of plasticizer (epoxidized soybean oil) were added in sequence and mixed for another 60 minutes to obtain thermochromic coating.

[0055] Testing: (1) TPU particles were melt-extruded, biaxially stretched, shaped and cooled to obtain a TPU film; the pressure was set to 0.8 N / cm. 2 At a speed of 2 m / min, the thermochromic pastes of Examples 1-3 and Comparative Examples 1-5 were uniformly coated onto the TPU film and dried at 65°C to obtain the window film.

[0056] (2) Six window films prepared in Examples 1-3 and Comparative Examples 1-5 were taken, and the color change time was measured and the average value was taken. They were placed in a 70℃ drying oven for 30 minutes and then cooled at room temperature for 30 minutes. After repeating this process 200 times, the coating was observed to see if it peeled off. The tear strength before and after was recorded, and the tear strength reduction rate (%) was calculated. As shown in Table 1.

[0057] (3) Two rooms of the same size (about 60 square meters) were selected as laboratories, each with a separate electricity meter and an air conditioner of the same model installed inside. The window film prepared in Example 2 was affixed to the window of one laboratory; the window film was not affixed to the window of the other laboratory (blank control). The air conditioner operating parameters were kept consistent (heating in winter). The power consumption of the two laboratories during the test period on the same day was recorded as shown in Table 2.

[0058]

[0059] Table 1

[0060]

[0061] Table 2

[0062] Conclusions: Comparative Example 1, based on Example 2, replaced the wall material with melamine and urea, which reduced the interfacial compatibility between the thermochromic microcapsules and the modified polyurethane, thus affecting the performance of the window film. Comparative Example 2, based on Example 2, reduced the hydroxyl content in the polyurethane prepolymer, which decreased the direct bonding between the wall material and the core material, thus affecting the performance of the window film. Comparative Example 3, based on Example 2, did not introduce dihydroxyl-terminated polysiloxane into the modified polyurethane, which resulted in poor thermal stability of the thermochromic slurry coating, thus affecting the performance of the window film. Comparative Example 4, based on Example 2, did not add acrylic resin, which reduced 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 transferred to the microcapsule core material, thus slowing down the color-changing time of the window film in Comparative Example 4. Comparative Example 5, based on Example 2, found that the addition of polyvinylpyrrolidone also improved the performance of the window film to some extent.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for the preparation of a thermochromic paint, characterized in that: The method comprises the following steps: Step 1: uniformly mix sodium dodecyl sulfonate and polyvinylpyrrolidone at a mass ratio of 1:(0.3-0.4) to obtain a surfactant; Step 2: add the modified polyurethane and the acrylic resin into a solvent, heat and stir at 50-60°C for 1-2 hours, then sequentially add the surfactant, the pigment, the thermochromic microcapsule, the defoaming agent and the plasticizer, and continue to mix for 40-60 minutes to obtain the thermochromic paint; The modified polyurethane is prepared by the following method: uniformly mix tetrafluorobutanediol and a catalyst in dimethylbenzene to obtain a mixed solution A; uniformly mix polycaprolactone polyol and double-hydroxyl-terminated polysiloxane in dimethylbenzene, and then add toluene diisocyanate, and react at 85-90°C for 4-5 hours under a nitrogen atmosphere, vacuum degassing, and then add the mixed solution A and react for 1-2 hours to obtain the modified polyurethane; The thermochromic microcapsule is prepared by the following method: (1) ultrasonically disperse amino-nano-titanium dioxide and dibutyltin dilaurate in toluene, add double-hydroxyl-terminated polysiloxane, and stir at 60-70°C for 5-7 hours to obtain modified titanium dioxide; add the modified titanium dioxide and polycaprolactone polyol in dimethylbenzene to uniformly mix to obtain a mixed solution; add toluene diisocyanate to the mixed solution, and react at 85-90°C for 1-2 hours under a nitrogen atmosphere, add the mixed solution A, and continue to react for 2-3 hours, vacuum degassing to obtain a polyurethane prepolymer; (2) uniformly mix crystal violet lactone, bisphenol A and cetyl alcohol at 60-70°C to obtain a ternary mixture; homogenize the ternary mixture with a styrene-maleic anhydride copolymer and deionized water to obtain an emulsion; (3) uniformly mix the polyurethane prepolymer in the emulsion, add an aqueous citric acid solution to adjust the pH to 4-5, and keep at 80-90°C for 2-3 hours, add an aqueous sodium hydroxide solution to adjust the pH to 7-8, and wash and dry to obtain the thermochromic microcapsule.

2. A method of preparing a thermochromic paint according to claim 1, characterized in that: The raw materials of the thermochromic paint comprise the following components: 40-60 parts of a solvent, 15-17 parts of an acrylic resin, 10-20 parts of a modified polyurethane, 10-18 parts of a thermochromic microcapsule, 8-12 parts of a plasticizer, 2-4 parts of a surfactant, 2-2.5 parts of a pigment and 1-3 parts of a defoaming agent.

3. A method of preparing a thermochromic paint according to claim 1, characterized in that: The solvent comprises one or more of acetone, butanol or toluene; the plasticizer comprises one or more of dioctyl phthalate, dibutyl sebacate or epoxy soybean oil; and the defoaming agent is a polyether defoaming agent.

4. The method for preparing a thermochromic coating according to claim 1, characterized in that: The raw materials of the modified polyurethane comprise the following components: 0.55-0.56 parts of toluene diisocyanate, 4.2-4.4 parts of polycaprolactone polyol, 0.55-0.57 parts of double-hydroxyl-terminated polysiloxane, 1.5-2 parts of tetrafluorobutanediol, 0.015-0.02 parts of a catalyst and 10-15 parts of dimethylbenzene.

5. The method for preparing a thermochromic coating according to claim 1, characterized in that: The raw material of the modified titanium dioxide comprises the following components: 0.3-0.5 parts of amino-nano titanium dioxide, 0.01-0.02 parts of dibutyltin dilaurate, and 1-1.5 parts of bis-hydroxyl terminated polysiloxane.

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

7. The thermochromic coating prepared by the preparation method of the thermochromic coating according to any one of claims 1-6.

8. Use of a thermochromic paint, characterized in that: The thermochromic coating as described in claim 7 is applied to a window film, wherein the window film is prepared by: melting and extruding a polymer material, biaxially stretching it, and cooling it to obtain a base film; setting the pressure to 0.8~1 N / cm. 2 At a speed of 1~2m / min, the thermochromic coating is evenly applied to the base film and dried at 60~70℃ to obtain the window film; the polymer material includes one of PET particles and TPU particles.

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