Stretchable PET color-changing film and production process thereof

Abstract

The invention discloses a stretchable PET color-changing film and a production process thereof, and relates to the technical field of color-changing films, the stretchable PET color-changing film comprises a modified PET base film, a color-changing layer and a film coating layer; the modified PET base film is prepared from the following raw materials in percentage by mass: 65 to 75 percent of polydimethylsiloxane copolymerized modified PET, 23 to 32 percent of thermoplastic polyurethane elastomer and 2 to 3 percent of auxiliaries; the color changing layer is prepared from the following raw materials in percentage by mass: 10 to 20 percent of photonic crystal dispersion liquid, 0.3 to 0.5 percent of polydimethylsiloxane, 0.1 to 1 percent of defoaming agent and the balance of waterborne polyurethane; and the film coating layer is nano silicon dioxide sol. The stretchable PET color-changing film provided by the invention has excellent tensile strength and elongation at break.

Description

Technical Field

[0001] This application relates to the field of color-changing film technology, and in particular to a stretchable PET color-changing film and its manufacturing process. Background Technology

[0002] Stretchable PET color-changing film is a high-performance film made of polyethylene terephthalate (PET) as the base material through a biaxial stretching process. Combined with color-changing materials, it achieves dynamic color adjustment function and is commonly used in the automotive, construction, home furnishing, and electronics industries.

[0003] Polyethylene terephthalate (PET), as the "industrial cornerstone" of synthetic polymers, dominates the packaging, textile, and electronics industries due to its excellent mechanical properties, low cost, heat resistance, light resistance, and resistance to microbial corrosion. However, its inherent defects significantly limit the application expansion of high-performance color-changing films. For example, PET's insufficient toughness and low elongation at break make it prone to cracking or stress concentration during stretching; its poor hydrophilicity results in weak coating adhesion, making it prone to delamination and edge lifting; and its highly oriented crystalline structure restricts molecular chain movement, reducing stretchability and self-healing ability. Summary of the Invention

[0004] To improve the toughness and stretchability of PET color-changing film, this application provides a stretchable PET color-changing film and its manufacturing process.

[0005] This application provides a stretchable PET color-changing film, which adopts the following technical solution: A stretchable PET color-changing film includes a modified PET base film, a color-changing layer, and a coating layer. The modified PET base film raw materials include, by weight percentage, 65-75% polydimethylsiloxane copolymerized modified PET, 23-32% thermoplastic polyurethane elastomer, and 2-3% additives. The color-changing layer raw materials include, by weight percentage, 10-20% photonic crystal dispersion, 0.3-0.5% polydimethylsiloxane, 0.1-1% defoamer, and the balance being waterborne polyurethane.

[0006] Preferably, the polydimethylsiloxane copolymerized modified PET is prepared from the following raw materials in parts by weight: 194.18-291.27 parts dimethyl terephthalate, 148.52-222.78 parts ethylene glycol, 0.08-0.12 parts zinc acetate, 7-10.5 parts polydimethylsiloxane, and 0.08-0.12 parts antimony trioxide.

[0007] Preferably, the method for preparing the polydimethylsiloxane copolymerized modified PET includes the following steps: Dimethyl terephthalate and ethylene glycol are mixed and heated to 175-185℃. Zinc acetate is then added, and nitrogen is used to replace the air in the reactor to initiate the transesterification reaction. The reaction temperature is maintained at 175-185℃, and the stirring speed is 60-80 rpm for 2-2.5 hours. Subsequently, polydimethylsiloxane is added, and the reaction continues for 0.5-1 hours. Antimony trioxide is then added. The pressure is then reduced from atmospheric pressure to 10-15 Pa, and the temperature is gradually increased to 270-280℃ and maintained for 30-50 minutes to obtain polydimethylsiloxane copolymerized modified PET.

[0008] Preferably, the method for preparing the photonic crystal dispersion includes the following steps: Anhydrous ethanol and ZnS@SiO2 photonic crystal powder were mixed at a mass ratio of 10-12:1 and then ultrasonically dispersed in an ice-water environment for 6-10 hours to obtain a photonic crystal dispersion.

[0009] Preferably, the ZnS@SiO2 photonic crystal powder is prepared from the following raw materials in parts by weight: 2-4 parts ZnS nanoparticles, 400-800 parts anhydrous ethanol, 30-60 parts ultrapure water, 15-30 parts ammonia water, and 10-20 parts tetraethyl silicate.

[0010] Preferably, the ZnS nanoparticles are prepared from the following raw materials in parts by weight: 5-10 parts polyvinylpyrrolidone, 0.1-0.2 parts concentrated nitric acid, 3.6-7.2 parts thioacetamide, 3-6 parts zinc nitrate hexahydrate, and 75-150 parts ultrapure water.

[0011] Preferably, the method for preparing the ZnS nanoparticles includes the following steps: Add 5-10 parts of polyvinylpyrrolidone to 45-90 parts of ultrapure water, sonicate for 30-45 min, then add 0.1-0.2 parts of concentrated nitric acid and magnetically stir for 5-10 min at room temperature; then add 3.6-7.2 parts of thioacetamide, sonicate for 40-50 min, and react at 75-85℃ and 500-700 rpm for 30-50 min; add 3-6 parts of zinc nitrate hexahydrate to 30-60 parts of ultrapure water, sonicate for 30-45 min, then add to the reaction system under a nitrogen atmosphere, stir at 600-800 rpm for 1-2 min, and react at 75-85℃ and 300-400 rpm for 11-13 h; after the reaction is complete, centrifuge and wash the reaction solution multiple times, and dry it to obtain ZnS nanoparticles.

[0012] Preferably, the preparation method of the ZnS@SiO2 photonic crystal powder includes the following steps: ZnS nanoparticles were dispersed in a mixed solution of anhydrous ethanol and ultrapure water and sonicated for 90-120 min. Then, ammonia was added to the mixed solution at 700-900 rpm and stirred for 5-7 min. Tetraethyl silicate was then injected and stirred at room temperature for 1-2 h. After washing several times with ultrapure water, ZnS@SiO2 photonic crystal powder was obtained by freeze drying.

[0013] Preferably, the coating layer is a nano-silica sol.

[0014] This application provides a manufacturing process for a stretchable PET color-changing film, which adopts the following technical solution: A manufacturing process for a stretchable PET color-changing film includes the following steps: S1. Polydimethylsiloxane copolymerized modified PET, thermoplastic polyurethane elastomer, and additives are dried, mixed and melted by a twin-screw extruder, and then extruded and cooled to obtain a cast sheet; the cast sheet is biaxially stretched, heat-set, wound, and slit to obtain a modified PET base film with a thickness of 25-150μm; S2. After mixing waterborne polyurethane, polydimethylsiloxane, photonic crystal dispersion and defoamer, a color-changing layer composite sol is obtained; S3. Mix tetraethyl orthosilicate and ethanol and stir for 30-40 min to obtain solution A; mix ammonia and ethanol and stir to obtain solution B. At a temperature of 60-70℃ and a stirring speed of 500-700 rpm, gradually add solution B dropwise to solution A and continue stirring for 1.5-2 h to obtain nano silica sol. S4. Coat the color-changing layer composite sol on both sides of the modified PET base film, controlling the thickness of each layer to be 10-15μm, and cure it at 70-90℃ to obtain the color-changing layer; coat the surface of the color-changing layer with nano-silica sol, controlling the thickness to be 8-12μm, and dry it at 60-70℃; then shape the film material by hot press rollers at a temperature of 70-90℃ and a pressure of 0.2-0.5MPa to obtain a stretchable PET color-changing film.

[0015] In summary, this application includes at least one of the following beneficial technical effects: 1. This application synthesizes polydimethylsiloxane copolymerized modified PET by introducing polydimethylsiloxane during the PET transesterification process. The introduction of polydimethylsiloxane solves the problems of insufficient toughness and poor hydrophilicity of PET, and effectively improves the tensile strength and elongation at break of PET base film. At the same time, thermoplastic polyurethane elastomer is added and melt-blended to form a PET-TPU interpenetrating network structure. By utilizing the elastic recovery characteristics of TPU, stress concentration is reduced in the stretch-recovery cycle, and cracks are avoided. 2. This application uses the sol-gel method to coat the surface of ZnS nanoparticles with a SiO2 shell to form a core-shell structured photonic crystal, which can achieve a change in transmittance through the change in the refractive index of the cavity when the PET film is stretched, thereby achieving a mechanochromic effect; 3. The nano-silica sol prepared by hydrolysis of tetraethyl orthosilicate in this application forms a dense network structure after coating, which effectively improves the hardness and wear resistance of the color-changing film and enhances the interfacial bonding strength of each layer. Detailed Implementation

[0016] The present application will be further described in detail below with reference to the embodiments.

[0017] The chemical reagents used in the preparation examples, embodiments, and comparative examples provided in this invention are all commercially available products, and their brands and manufacturers are as follows: Thermoplastic polyurethane elastomer, Guangdong Wengjiang Chemical Reagent Co., Ltd., Product No.: PA95766; Maleic anhydride-grafted polypropylene compatibilizer, Liyang Ruipu New Materials Co., Ltd.; Antioxidant 1010, Shanghai Maclean Biochemical Technology Co., Ltd., Product No.: P750268; Antioxidant 168, Shanghai Maclean Biochemical Technology Co., Ltd., Product No.: T822863; Dimethyl terephthalate, Shanghai Maclean Biochemical Technology Co., Ltd., Product No.: D807069; Polydimethylsiloxane, Shanghai Maclean Biochemical Technology Co., Ltd., Product No.: P822627; Polyvinylpyrrolidone, Shanghai Aladdin Biochemical Technology Co., Ltd., Product No.: P434439; Waterborne polyurethane, Shanghai McLean Biochemical Technology Co., Ltd., Product No.: W741922; Polyether-modified polysiloxane defoamer, Wuhan Baiyite Chemical Co., Ltd.

[0018] Preparation Example 1: Preparation of Polydimethylsiloxane Copolymerized Modified PET Preparation Example 1.1 194.18g of dimethyl terephthalate and 148.52g of ethylene glycol were mixed and heated to 175℃. Then, 0.08g of zinc acetate was added. After replacing the air in the reactor with nitrogen, the transesterification reaction was initiated. The reaction temperature was maintained at 175℃, and the stirring speed was 60rpm for 2 hours. Subsequently, 7g of polydimethylsiloxane was added and the reaction continued for 0.5 hours. Then, 0.08g of antimony trioxide was added. The pressure was then slowly reduced from atmospheric pressure to 10Pa, and the temperature was gradually increased to 270℃ and maintained for 30 minutes to obtain polydimethylsiloxane copolymerized modified PET.

[0019] Preparation Example 1.2 242.73g of dimethyl terephthalate and 185.65g of ethylene glycol were mixed and heated to 180℃. Then, 0.1g of zinc acetate was added, and the air in the reactor was replaced with nitrogen to start the transesterification reaction. The reaction temperature was maintained at 180℃, the stirring speed was 70rpm, and the reaction was continued for 2.25h. Subsequently, 8.75g of polydimethylsiloxane was added and the reaction was continued for 0.75h. Then, 0.1g of antimony trioxide was added. The pressure was then slowly reduced from atmospheric pressure to 12.5Pa, and the temperature was gradually increased to 275℃ and maintained for 40min to obtain polydimethylsiloxane copolymerized modified PET.

[0020] Preparation Example 1.3 291.27g of dimethyl terephthalate and 222.78g of ethylene glycol were mixed and heated to 185℃. Then, 0.12g of zinc acetate was added, and the air in the reactor was replaced with nitrogen to start the transesterification reaction. The reaction temperature was maintained at 185℃, the stirring speed was 80rpm, and the reaction was continued for 2.5h. Then, 10.5g of polydimethylsiloxane was added and the reaction was continued for 1h. Then, 0.12g of antimony trioxide was added. The pressure was then slowly reduced from atmospheric pressure to 15Pa, and the temperature was gradually increased to 280℃ and maintained for 50min to obtain polydimethylsiloxane copolymerized modified PET.

[0021] Preparation Example 2: Preparation of Photonic Crystal Dispersion Preparation Example 2.1 S1. Add 5g of polyvinylpyrrolidone to 45g of ultrapure water, sonicate for 30min, then add 0.1g of concentrated nitric acid and magnetically stir for 5min at room temperature; then add 3.6g of thioacetamide, sonicate for 40min, and react at 75℃ and 500rpm for 30min; add 3g of zinc nitrate hexahydrate to 30g of ultrapure water, sonicate for 30min, then add to the reaction system under a nitrogen atmosphere, stir at 600rpm for 1min, and react at 75℃ and 300rpm for 11h; after the reaction is complete, centrifuge and wash the reaction solution multiple times, and dry to obtain ZnS nanoparticles; S2. 2g of ZnS nanoparticles were dispersed in a mixed solution of 400g anhydrous ethanol and 30g ultrapure water and sonicated for 90min. Then, 15g of ammonia water was added to the mixed solution at 700rpm and stirred for 5min. 10g of tetraethyl silicate was then injected and stirred at room temperature for 1h. After washing three times with ultrapure water, ZnS@SiO2 photonic crystal powder was obtained by freeze drying. S3. After mixing anhydrous ethanol and ZnS@SiO2 photonic crystal powder at a mass ratio of 10:1, the mixture is ultrasonically dispersed in an ice-water environment for 6 hours to obtain a photonic crystal dispersion.

[0022] Preparation Example 2.2 S1. Add 7.5g of polyvinylpyrrolidone to 67.5g of ultrapure water, sonicate for 37min, then add 0.15g of concentrated nitric acid and magnetically stir for 7.5min at room temperature; then add 5.4g of thioacetamide, sonicate for 45min, and react at 80℃ and 600rpm for 40min; add 4.5g of zinc nitrate hexahydrate to 45g of ultrapure water, sonicate for 37min, then add to the reaction system under a nitrogen atmosphere, stir at 700rpm for 1.5min, and react at 80℃ and 350rpm for 12h; after the reaction is complete, centrifuge and wash the reaction solution multiple times, and dry to obtain ZnS nanoparticles; S2. 3g of ZnS nanoparticles were dispersed in a mixed solution of 600g anhydrous ethanol and 45g ultrapure water and sonicated for 105min. Subsequently, 22.5g of ammonia water was added to the mixed solution at 800rpm, and after stirring for 6min, 15g of tetraethyl silicate was injected and stirred at room temperature for 1.5h. After washing with ultrapure water 4 times, ZnS@SiO2 photonic crystal powder was obtained by freeze drying. S3. After mixing anhydrous ethanol and ZnS@SiO2 photonic crystal powder at a mass ratio of 11:1, the mixture is ultrasonically dispersed in an ice-water environment for 8 hours to obtain a photonic crystal dispersion.

[0023] Preparation Example 2.3 S1. Add 10g of polyvinylpyrrolidone to 90g of ultrapure water, sonicate for 45min, then add 0.2g of concentrated nitric acid and magnetically stir for 10min at room temperature; then add 7.2g of thioacetamide, sonicate for 50min, and react at 85℃ and 700rpm for 50min; add 6g of zinc nitrate hexahydrate to 60g of ultrapure water, sonicate for 45min, then add to the reaction system under a nitrogen atmosphere, stir at 800rpm for 2min, and react at 85℃ and 400rpm for 13h; after the reaction is complete, centrifuge and wash the reaction solution multiple times, and dry to obtain ZnS nanoparticles; S2. 4g of ZnS nanoparticles were dispersed in a mixed solution of 800g anhydrous ethanol and 60g ultrapure water and sonicated for 120min. Subsequently, 30g of ammonia water was added to the mixed solution at 900rpm, and after stirring for 7min, 20g of tetraethyl silicate was injected and stirred at room temperature for 2h. After washing 5 times with ultrapure water, ZnS@SiO2 photonic crystal powder was obtained by freeze drying. S3. After mixing anhydrous ethanol and ZnS@SiO2 photonic crystal powder at a mass ratio of 12:1, the mixture is ultrasonically dispersed in an ice-water environment for 10 hours to obtain a photonic crystal dispersion.

[0024] Example 1 S1. 65g of polydimethylsiloxane copolymerized modified PET prepared in Preparation Example 1.1, 32g of thermoplastic polyurethane elastomer, and 3g of additives were dried and mixed at 80rpm for 15min. The mixture was then melted and extruded at 280℃ using a twin-screw extruder. After cooling, a cast sheet was obtained. The cast sheet was first stretched longitudinally by 3.5 times, cooled, corona-treated, then stretched transversely by 3.6 times, heat-set, and then wound and slit to obtain a modified PET base film with a thickness of 25μm. The additives used in this application include 1.5g of maleic anhydride-grafted polypropylene compatibilizer, 1g of fumed silica, 0.25g of antioxidant 1010, and 0.25g of antioxidant 168. S2. Mix 89.6g of waterborne polyurethane, 0.3g of polydimethylsiloxane, 10g of photonic crystal dispersion prepared in Preparation Example 2.1, and 0.1g of defoamer to obtain a color-changing layer composite sol; S3. Mix 125 mL of tetraethyl orthosilicate with 5 mL of ethanol and stir for 30 min to obtain solution A; mix 10 mL of ammonia water with 2.5 mL of ethanol and stir to obtain solution B. At a temperature of 60℃ and a stirring speed of 500 rpm, gradually add solution B dropwise to solution A and continue stirring for 1.5 h to obtain nano silica sol. S4. Coat the color-changing layer composite sol on both sides of the modified PET base film, controlling the thickness of each layer to be 10μm, and cure at 70℃ to obtain the color-changing layer; coat the surface of the color-changing layer with nano-silica sol, controlling the thickness to be 8μm, and dry at 60℃; then shape the film material by hot press rollers at a temperature of 70℃ and a pressure of 0.2MPa to obtain the stretchable PET color-changing film.

[0025] Example 2 S1. 70g of polydimethylsiloxane copolymerized modified PET prepared in Preparation Example 1.2, 28g of thermoplastic polyurethane elastomer, and 2g of additives were dried and mixed at 85 rpm for 17 min. The mixture was then melted and extruded at 285°C using a twin-screw extruder. After cooling, a cast sheet was obtained. The cast sheet was first stretched longitudinally by 3.5 times, cooled, corona-treated, then stretched transversely by 3.6 times, heat-set, and then wound and slit to obtain a modified PET base film with a thickness of 50 μm. The additives used in this application include 1g of maleic anhydride-grafted polypropylene compatibilizer, 0.5g of fumed silica, 0.25g of antioxidant 1010, and 0.25g of antioxidant 168. S2. Mix 84.1g of waterborne polyurethane, 0.4g of polydimethylsiloxane, 15g of photonic crystal dispersion prepared in Preparation Example 2.2, and 0.5g of defoamer to obtain a color-changing layer composite sol; S3. Mix 130 mL of tetraethyl orthosilicate with 6 mL of ethanol and stir for 30 min to obtain solution A; mix 10 mL of ammonia water with 3 mL of ethanol and stir to obtain solution B. At a temperature of 65℃ and a stirring speed of 600 rpm, gradually add solution B dropwise to solution A and continue stirring for 1.75 h to obtain nano silica sol. S4. Coat the color-changing layer composite sol on both sides of the modified PET base film, controlling the thickness of each layer to be 13μm, and cure at 80℃ to obtain the color-changing layer; coat the surface of the color-changing layer with nano-silica sol, controlling the thickness to be 10μm, and dry at 65℃; then shape the film material by hot press rollers at a temperature of 80℃ and a pressure of 0.35MPa to obtain the stretchable PET color-changing film.

[0026] Example 3 S1. 75g of polydimethylsiloxane copolymerized modified PET prepared in Preparation Example 1.1, 23g of thermoplastic polyurethane elastomer, and 2g of additives were dried and mixed at 90rpm for 20min. The mixture was then melted and extruded through a twin-screw extruder at 275°C. After cooling, a cast sheet was obtained. The cast sheet was first stretched longitudinally by 3.5 times, cooled, corona-treated, then stretched transversely by 3.6 times, heat-set, and then wound and slit to obtain a modified PET base film with a thickness of 150μm. The additives used in this application include 1g of maleic anhydride-grafted polypropylene compatibilizer, 0.5g of fumed silica, 0.25g of antioxidant 1010, and 0.25g of antioxidant 168. S2. Mix 78.5g of waterborne polyurethane, 0.5g of polydimethylsiloxane, 20g of photonic crystal dispersion prepared in Preparation Example 2.1, and 1g of defoamer to obtain a color-changing layer composite sol; S3. Mix 135 mL of tetraethyl orthosilicate with 7 mL of ethanol and stir for 30 min to obtain solution A; mix 10 mL of ammonia water with 3.5 mL of ethanol and stir to obtain solution B. At a temperature of 70℃ and a stirring speed of 700 rpm, gradually add solution B dropwise to solution A and continue stirring for 2 h to obtain nano silica sol. S4. Coat the color-changing layer composite sol on both sides of the modified PET base film, controlling the thickness of each layer to be 15μm, and cure at 90℃ to obtain the color-changing layer; coat the surface of the color-changing layer with nano-silica sol, controlling the thickness to be 12μm, and dry at 70℃; then shape the film material by hot press rollers at a temperature of 90℃ and a pressure of 0.5MPa to obtain the stretchable PET color-changing film.

[0027] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the PET material used in Comparative Example 1 is commercially available polyethylene terephthalate, purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number: P697813.

[0028] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the modified PET base film raw material in Comparative Example 2 did not contain thermoplastic polyurethane elastomer, but was replaced by an equal amount of polydimethylsiloxane copolymerized modified PET obtained from Preparation Example 1.1.

[0029] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the color-changing layer material used in Comparative Example 3 does not contain polydimethylsiloxane, but is replaced by an equal amount of waterborne polyurethane.

[0030] Performance testing The tensile strength and elongation at break of the stretchable PET color-changing films prepared in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with the national standard GB / T 1040-2006 "Determination of tensile properties of plastics". The results are shown in Table 1.

[0031] The light transmittance and haze of the stretchable PET color-changing films prepared in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with the national standard GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics". The results are shown in Table 1.

[0032] The specific test results are as follows: Table 1 Performance Test Results As can be seen from the test results in Table 1, the stretchable PET color-changing film provided in this application has a large tensile strength and elongation at break, indicating that the PET color-changing film provided in this application has excellent mechanical properties, can be stretched, and the light transmittance of the film will decrease during the stretching process.

[0033] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A stretchable PET color-changing film, characterized in that: The product includes a modified PET base film, a color-changing layer, and a coating layer. The modified PET base film raw materials include, by weight percentage, 65-75% polydimethylsiloxane copolymerized modified PET, 23-32% thermoplastic polyurethane elastomer, and 2-3% additives. The color-changing layer raw materials include, by weight percentage, 10-20% photonic crystal dispersion, 0.3-0.5% polydimethylsiloxane, 0.1-1% defoamer, and the balance being waterborne polyurethane.

2. The stretchable PET color-changing film according to claim 1, characterized in that: The polydimethylsiloxane copolymerized modified PET is prepared from the following raw materials in parts by weight: 194.18-291.27 parts dimethyl terephthalate, 148.52-222.78 parts ethylene glycol, 0.08-0.12 parts zinc acetate, 7-10.5 parts polydimethylsiloxane, and 0.08-0.12 parts antimony trioxide.

3. The stretchable PET color-changing film according to claim 2, characterized in that: The preparation method of the polydimethylsiloxane copolymerized modified PET includes the following steps: Dimethyl terephthalate and ethylene glycol are mixed and heated to 175-185℃. Zinc acetate is then added, and nitrogen is used to replace the air in the reactor to initiate the transesterification reaction. The reaction temperature is maintained at 175-185℃, and the stirring speed is 60-80 rpm for 2-2.5 hours. Subsequently, polydimethylsiloxane is added, and the reaction continues for 0.5-1 hours. Antimony trioxide is then added. The pressure is then reduced from atmospheric pressure to 10-15 Pa, and the temperature is gradually increased to 270-280℃ and maintained for 30-50 minutes to obtain polydimethylsiloxane copolymerized modified PET.

4. The stretchable PET color-changing film according to claim 1, characterized in that: The preparation method of the photonic crystal dispersion includes the following steps: Anhydrous ethanol and ZnS@SiO2 photonic crystal powder were mixed at a mass ratio of 10-12:1 and then ultrasonically dispersed in an ice-water environment for 6-10 hours to obtain a photonic crystal dispersion.

5. The stretchable PET color-changing film according to claim 4, characterized in that: The ZnS@SiO2 photonic crystal powder is prepared from the following raw materials in parts by weight: 2-4 parts ZnS nanoparticles, 400-800 parts anhydrous ethanol, 30-60 parts ultrapure water, 15-30 parts ammonia water, and 10-20 parts tetraethyl silicate.

6. The stretchable PET color-changing film according to claim 5, characterized in that: The ZnS nanoparticles are prepared from the following raw materials in parts by weight: 5-10 parts polyvinylpyrrolidone, 0.1-0.2 parts concentrated nitric acid, 3.6-7.2 parts thioacetamide, 3-6 parts zinc nitrate hexahydrate, and 75-150 parts ultrapure water.

7. The stretchable PET color-changing film according to claim 1, characterized in that: The method for preparing the ZnS nanoparticles includes the following steps: Add 5-10 parts of polyvinylpyrrolidone to 45-90 parts of ultrapure water, sonicate for 30-45 min, then add 0.1-0.2 parts of concentrated nitric acid and magnetically stir for 5-10 min at room temperature; then add 3.6-7.2 parts of thioacetamide, sonicate for 40-50 min, and react at 75-85℃ and 500-700 rpm for 30-50 min; add 3-6 parts of zinc nitrate hexahydrate to 30-60 parts of ultrapure water, sonicate for 30-45 min, then add to the reaction system under a nitrogen atmosphere, stir at 600-800 rpm for 1-2 min, and react at 75-85℃ and 300-400 rpm for 11-13 h; after the reaction is complete, centrifuge and wash the reaction solution multiple times, and dry it to obtain ZnS nanoparticles.

8. The stretchable PET color-changing film according to claim 1, characterized in that: The preparation method of the ZnS@SiO2 photonic crystal powder includes the following steps: ZnS nanoparticles were dispersed in a mixed solution of anhydrous ethanol and ultrapure water and sonicated for 90-120 min. Then, ammonia was added to the mixed solution at 700-900 rpm and stirred for 5-7 min. Tetraethyl silicate was then injected and stirred at room temperature for 1-2 h. After washing several times with ultrapure water, ZnS@SiO2 photonic crystal powder was obtained by freeze drying.

9. A stretchable PET color-changing film according to claim 1, characterized in that: The coating layer is a nano-silica sol.

10. A production process for a stretchable PET color-changing film according to any one of claims 1-9, characterized in that: Includes the following steps: S1. Polydimethylsiloxane copolymerized modified PET, thermoplastic polyurethane elastomer, and additives are dried, mixed and melted by a twin-screw extruder, and then extruded and cooled to obtain a cast sheet; the cast sheet is biaxially stretched, heat-set, wound, and slit to obtain a modified PET base film with a thickness of 25-150μm; S2. After mixing waterborne polyurethane, polydimethylsiloxane, photonic crystal dispersion and defoamer, a color-changing layer composite sol is obtained; S3. Mix tetraethyl orthosilicate and ethanol and stir for 30-40 min to obtain solution A; mix ammonia and ethanol and stir to obtain solution B. At a temperature of 60-70℃ and a stirring speed of 500-700 rpm, gradually add solution B dropwise to solution A and continue stirring for 1.5-2 h to obtain nano silica sol. S4. Coat the color-changing layer composite sol on both sides of the modified PET base film, controlling the thickness of each layer to be 10-15μm, and cure it at 70-90℃ to obtain the color-changing layer; coat the surface of the color-changing layer with nano-silica sol, controlling the thickness to be 8-12μm, and dry it at 60-70℃; then shape the film material by hot press rollers at a temperature of 70-90℃ and a pressure of 0.2-0.5MPa to obtain a stretchable PET color-changing film.

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