Preparation process of TPU color-changing film

Abstract

The application relates to the technical field of high polymer materials, in particular to a preparation process of a TPU color-changing film. The process comprises the following steps: mixing a zinc nitrate aqueous solution and a tetrabutyl titanate ethanol solution, stirring, adjusting the pH to 8-9, and then reacting; centrifuging, washing the solid, drying, dispersing the solid in an ethanol aqueous solution, and then ultrasonic dispersing to obtain a suspension; under the condition of stirring, adding ethyl silicate to the suspension, adjusting the pH to 9-10, and then reacting; centrifuging, washing the solid, drying, dispersing the solid in an ethanol aqueous solution, adding a silane coupling agent, and then reacting; centrifuging, washing the solid, drying, and obtaining composite nanoparticles; mixing TPU resin, color master batches, a dispersing agent and a modification aid after primary mixing, adding the composite nanoparticles, melting and extruding the mixed materials, calendering, and cooling and shaping. The method can improve the color saturation, ultraviolet resistance and anti-aging performance of the TPU color-changing film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and in particular to a preparation process of a TPU color-changing film. BACKGROUND

[0002] The TPU (thermoplastic polyurethane) color-changing film is widely used in the fields of car color-changing, home decoration, electronic device protection, etc. due to its excellent flexibility, wear resistance, weather resistance and recyclability. With the increasing performance requirements of the market for the color-changing film, it is not only required to have stable color performance, but also to have comprehensive properties such as anti-aging, yellowing resistance and mechanical strength.

[0003] In the prior art, the preparation of the TPU color-changing film is mostly by directly adding color master particles to blend with TPU resin to form a film, but the color stability is insufficient and the color-changing film is prone to fading after long-term use. Meanwhile, in order to improve the weather resistance and mechanical properties of the color-changing film, nano particles (such as ZnO and TiO2) are often introduced for modification, but the nano particles are prone to agglomeration in the TPU matrix due to high surface energy, which leads to poor interfacial adhesion and affects the mechanical properties and appearance quality of the film material. In addition, the traditional surface modification method (such as single coating or simple coupling) of the nano particles cannot simultaneously solve the problems of dispersion and compatibility, which limits the modification effect.

[0004] Therefore, it is a technical problem to be solved in the field to develop a preparation process of a TPU color-changing film which can have color stability, weather resistance, mechanical properties and uniform dispersion of nano particles. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a preparation process of a TPU color-changing film, which forms a multi-level structure of "core-shell-coupling agent" by preparing ZnO-TiO2 nano particles, a SiO2 coating layer and a silane coupling agent modified composite nano particle in steps. The ZnO-TiO2 nano particles provide excellent weather resistance and ultraviolet shielding capacity; the SiO2 coating layer can reduce the surface energy of the nano particles and avoid agglomeration; and the silane coupling agent KH550 connects the inorganic nano particles and the organic TPU matrix through chemical bonds, significantly improves the interfacial compatibility, ensures the uniform dispersion of the nano particles in the TPU, and avoids the performance degradation of the film material caused by agglomeration.

[0006] Therefore, the present application provides the following technical solutions,

[0007] In a first aspect, the present application provides, in an optional embodiment, a preparation process of a TPU color-changing film, comprising the following steps:

[0008] S1: mixing, stirring a zinc nitrate aqueous solution and a tetrabutyl titanate ethanol solution, adjusting pH to 8-9 to react, centrifuging after the reaction, washing and drying the solid to obtain ZnO-TiO2 nanoparticles;

[0009] S2: dispersing the ZnO-TiO2 nanoparticles in an ethanol aqueous solution to ultrasonically disperse to obtain a suspension, adding tetraethyl orthosilicate to the suspension under stirring, adjusting pH to 9-10 to react, centrifuging after the reaction, washing and drying the solid to obtain ZnO-TiO2@SiO2 nanoparticles;

[0010] S3: dispersing the ZnO-TiO2@SiO2 nanoparticles in an ethanol aqueous solution, adding a silane coupling agent to react, centrifuging after the reaction, washing and drying the solid to obtain composite nanoparticles;

[0011] S4: mixing TPU resin, color master batch, dispersant and modification aid, then adding the composite nanoparticles, then melt extruding the mixed material, calendering, cooling and shaping to obtain a TPU color-changing film.

[0012] In the present application, the composite nanoparticles have uniform particle size distribution, can serve as optical scattering centers to reduce irregular reflection of light in the film material. Meanwhile, the surface thereof is modified by a silane coupling agent, and the compatibility of the composite nanoparticles with TPU resin and color master batch is excellent, which can avoid local light shielding phenomenon caused by particle agglomeration, so that the color of the color master batch can be fully exhibited, thereby improving color saturation. ZnO and TiO2 are both wide-bandgap semiconductor materials, the band gap of ZnO is about 3.37 eV, and the band gap of TiO2 is about 3.2 eV, which can absorb ultraviolet light with a wavelength less than 380 nm. ZnO-TiO2 in the core-shell structure can effectively absorb ultraviolet light, reducing damage to TPU molecular chains and color master batch; the outer SiO2 shell layer can reduce the absorption of visible light by ZnO-TiO2, avoiding adverse effects on color presentation. In addition, the composite nanoparticles absorb ultraviolet light, reducing aging reactions such as TPU molecular chain rupture and crosslinking caused by ultraviolet light, the SiO2 shell layer has good chemical stability, can block the invasion of oxygen, moisture and the like to the film material, delaying the aging process, meanwhile, the composite nanoparticles interact with TPU molecular chains, which can enhance the stability of the molecular chains and improve the anti-aging performance of the film material.

[0013] Preferably, in step S1, the concentration of the aqueous zinc nitrate solution is 0.08-0.12 mol / L. The concentration of the tetrabutyl titanate ethanol solution is 0.04-0.06 mol / L. The volume ratio of the aqueous zinc nitrate solution to the tetrabutyl titanate ethanol solution is 1: (0.8-1.2). The stirring speed is 250-350 r / min. The solution added when adjusting the pH is ammonia water. The reaction temperature is 110-130℃, and the reaction time is 3.5-4.5 h. The washing method is: first washing with deionized water, and then washing with ethanol. The drying temperature is 75-85℃, and the drying time is 5.5-6.5 h.

[0014] Preferably, in step S2, the volume ratio of ethanol to water in the aqueous ethanol solution is (2-4): 1. The ultrasonic dispersion time is 25-35 min, and the ultrasonic power is 250-350 W. The volume concentration of the suspension is 0.4-0.6 g / L. The stirring speed is 350-450 r / min. The mass ratio of the tetraethyl orthosilicate to the ZnO-TiO2 nanoparticles is 1: 1.5-2.5. The solution added when adjusting the pH is ammonia water. The reaction temperature is 50-70℃, and the reaction time is 2.5-3.5 h. The washing method is: first washing with deionized water, and then washing with ethanol. The drying temperature is 70-90℃, and the drying time is 5.5-6.5 h.

[0015] Preferably, in step S3, the amount of the silane coupling agent added is 3-8% of the mass of the ZnO-TiO2@SiO2 nanoparticles. The type of the silane coupling agent is KH550. The reaction temperature is 70-90℃, and the reaction time is 1.5-2.5 h. Stirring is performed during the reaction, and the stirring speed is 200-300 r / min. The solution used for washing is an ethanol solution. The drying temperature is 70-90℃, and the drying time is 3.5-4.5 h.

[0016] Preferably, in step S4, the mass ratio of the TPU resin, color master batch, dispersant, modification aid and composite nanoparticles is 100: (5-8): (2-3): (0.5-1): (3-5). The dispersant is polyethylene wax. The modification aid is antioxidant 1010. The rotation speed of the initial mixing is 750-850 r / min, the temperature is 80-90℃, and the time is 5-8 min. The rotation speed of the mixing is 650-750 r / min, the temperature is 80-90℃, and the time is 3-5 min. In the melt extrusion, the equipment used is a double-screw extruder; the temperature of the feeding section is 160-170℃, the temperature of the compression section is 180-190℃, the temperature of the homogenization section is 200-210℃, the temperature of the die head is 190-200℃, and the rotation speed of the screw is 450-500 r / min. In the calendering, the equipment used is a calendering machine; the temperature of the calendering roller is 180-190℃, and the calendering speed is 3-5 m / min. The temperature of the cooling and setting is 40-50℃.

[0017] In the present application, the rotation speed of the screw is strictly limited to 450-500 r / min. On the one hand, at this rotation speed, the TPU resin, color master batch, dispersant, modification aid and composite nanoparticles can be fully mixed, the nanoparticles can be prevented from agglomeration, and the nanoparticles can be uniformly dispersed in the matrix, thereby ensuring the color uniformity and the stability of various properties. On the other hand, the shearing action at this rotation speed will not excessively damage the molecular chain structure of the TPU. If the rotation speed is too high, the excessive shearing force will cause the molecular chain of the TPU to break, thereby affecting the mechanical properties and anti-aging properties of the film material. If the rotation speed is too low, the mixing will not be sufficient, the nanoparticles will not be uniformly dispersed, the nanoparticles will not be able to fully play their role, and the color saturation, ultraviolet resistance and anti-aging properties will be affected.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The present application forms a multi-level structure of "core-shell-coupling agent" by preparing ZnO-TiO2 nanoparticles, SiO2 coating layer and silane coupling agent modified composite nanoparticles in steps. The ZnO-TiO2 nanoparticles provide excellent weather resistance and ultraviolet shielding capacity; the SiO2 coating layer can reduce the surface energy of the nanoparticles and avoid agglomeration; and the silane coupling agent KH550 connects the inorganic nanoparticles and the organic TPU matrix through a chemical bond, significantly improves the interfacial compatibility, ensures the uniform dispersion of the nanoparticles in the TPU, and avoids the performance degradation of the film material caused by agglomeration.

[0020] 2.The composite nanoparticles provided by the application, wherein the ZnO and TiO2 have excellent ultraviolet absorption and reflection capabilities, can reduce the degradation of the color master batch by ultraviolet rays, and delay discoloration; at the same time, the SiO2 coating layer forms a physical barrier to further block the erosion of oxygen and moisture to the film material, and cooperates with the synergistic effect of the antioxidant 1010 to significantly improve the long-term color stability of the color-changing film and prolong the service life.

[0021] 3.The composite nanoparticles provided by the application can form “enhanced points” in the TPU matrix through uniform dispersion and interfacial bonding, and synergistically improve the tensile strength, tear strength and wear resistance of the film material. Experiments show that compared with the TPU color-changing film without adding the composite nanoparticles, the tensile strength and tear strength of the film material prepared by the process are improved, meeting the use requirements of high-demand scenarios.

[0022] 4.The parameters of each step of the application are clear and controllable, and through ultrasonic dispersion, step-by-step washing, precise temperature control and other operations, the structural stability and batch consistency of the composite nanoparticles are ensured. At the same time, the parameters of melt extrusion and calendering are matched with the processing characteristics of the TPU resin, the production process is easy to control, and it is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application.

[0024] In the following examples and comparative examples, the silane coupling agent KH550 was purchased from Kangjin New Materials Technology Co., Ltd.; the TPU resin was purchased from Dongguan Benguan New Materials Co., Ltd., with the brand BG; the color master batch was purchased from Anhui Kenken Shenglin Environmental Protection Technology Co., Ltd.; the polyethylene wax was purchased from Shijiazhuang Jinhe Nanometer Chemical Co., Ltd.; and the antioxidant 1010 was purchased from Guangzhou Telei New Materials Co., Ltd.

[0025] The technical scheme of the application will be described below in combination with examples.

[0026] Example 1

[0027] The present embodiment provides a preparation process of a TPU color-changing film, including the following steps:

[0028] S1: 0.1 mol / L zinc nitrate aqueous solution and 0.05 mol / L titanium tetrabutoxide ethanol solution (volume ratio of zinc nitrate aqueous solution to titanium tetrabutoxide ethanol solution is 1:1) are mixed, stirred at a rotation speed of 300 r / min, and ammonia water is added to adjust the pH to 9, and the mixed solution is transferred to a reaction kettle and reacted at 120℃ for 4h. After the reaction is completed, the product is centrifuged, the solid is washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2 nanoparticles.

[0029] S2: 0.5g ZnO-TiO2 nanoparticles are dispersed in 1L mixed solution of ethanol and deionized water (volume ratio of ethanol to deionized water is 3:1), ultrasonic dispersion for 30min (power is 300W) to obtain a mixed suspension with a concentration of 0.5g / L, 0.25g tetraethyl orthosilicate is added to the suspension under stirring (rotation speed is 400r / min), the pH is adjusted to 10 with ammonia water, and the reaction is carried out at 60℃ for 3h. After the reaction is completed, the product is centrifuged, the solid is washed with ionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2@SiO2 nanoparticles.

[0030] S3: 50g ZnO-TiO2@SiO2 nanoparticles are dispersed in ethanol, 2.5g silane coupling agent KH550 is added, and the reaction is carried out at 80℃ under stirring (stirring rotation speed is 250r / min) for 2h. After the reaction is completed, the product is centrifuged, the solid is washed with ethanol, and finally dried at 80℃ for 4h to obtain composite nanoparticles.

[0031] S4: 100kg TPU resin, 6kg color master batch, 2.5kg polyethylene wax and 0.8kg antioxidant 1010 are added to a high-speed mixer and mixed at a rotation speed of 800r / min and a temperature of 85℃ for 6min to obtain a premix, then 4kg composite nanoparticles are added and continue to mix at a rotation speed of 700r / min and a temperature of 85℃ for 4min. The mixed material is introduced into a twin-screw extruder, and the temperature of each section of the extruder is set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw rotation speed is strictly controlled at 480r / min. After the material is melted and mixed sufficiently in the extruder, it is extruded from the die head in a molten state. The molten sheet is introduced into a calendering machine, the calendering roller temperature is set to 180℃, and the calendering speed is 4m / min. Finally, the calendered film is pulled by a traction machine to a cooling roller group for cooling, and the cooling roller temperature is controlled at 45℃ to reduce the film temperature to room temperature, thereby obtaining a TPU color-changing film.

[0032] Example 2

[0033] The embodiment provides a preparation process of a TPU color-changing film, and comprises the following steps.

[0034] S1: 0.1 mol / L zinc nitrate aqueous solution and 0.05 mol / L tetrabutyl titanate ethanol solution (the volume ratio of the zinc nitrate aqueous solution and the tetrabutyl titanate ethanol solution is 1:1) are mixed, stirring is carried out at a rotating speed of 300 r / min, ammonia water is added, the pH is adjusted to 9, the mixed solution is transferred into a reaction kettle, and reaction is carried out at 120 DEG C for 4 h. After the reaction is completed, the product is centrifugally separated, the solid is washed with deionized water and ethanol for three times, and finally drying is carried out at 80 DEG C for 6 h, so that ZnO-TiO2 nanoparticles are obtained.

[0035] S2: 0.5 g of the ZnO-TiO2 nanoparticles is dispersed in 1 L of a mixed solution of ethanol and deionized water (the volume ratio of the ethanol and the deionized water is 3:1), ultrasonic dispersion is carried out for 30 min (the power is 300 W), a mixed suspension with a concentration of 0.5 g / L is obtained, 0.25 g of tetraethyl orthosilicate is added to the suspension under stirring (the rotating speed is 400 r / min), the pH is adjusted to 10 by using ammonia water, and reaction is carried out at 60 DEG C for 3 h. After the reaction is completed, the product is centrifugally separated, the solid is washed with deionized water and ethanol for three times, and finally drying is carried out at 80 DEG C for 6 h, so that ZnO-TiO2@SiO2 nanoparticles are obtained.

[0036] S3: 50 g of the ZnO-TiO2@SiO2 nanoparticles is dispersed in ethanol, 2.5 g of silane coupling agent KH550 is added, stirring reaction is carried out at 80 DEG C for 2 h (the stirring rotating speed is 250 r / min), after the reaction is completed, the product is centrifugally separated, the solid is washed with ethanol, and finally drying is carried out at 80 DEG C for 4 h, so that composite nanoparticles are obtained.

[0037] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 are added into a high-speed mixer, mixing is carried out at a rotating speed of 800 r / min and a temperature of 85 DEG C for 6 min, so that a premix is obtained, then 3 kg of the composite nanoparticles are added, and mixing is continuously carried out at a rotating speed of 700 r / min and a temperature of 85 DEG C for 4 min. The mixed material is added into a double-screw extruder, the temperature of each section of the extruder is set as follows: the feeding section is 160 DEG C, the compression section is 190 DEG C, the homogenizing section is 200 DEG C, and the die head temperature is 200 DEG C. The rotating speed of the screw is strictly controlled at 480 r / min. After the material is melt plasticized and fully mixed in the extruder, the material is extruded into a melt state sheet from the die head. The melt state sheet is introduced into a calendering molding machine, the temperature of the calendering roller is set to 180 DEG C, and the calendering speed is 4 m / min. Finally, the calendered film is pulled to a cooling roller group to be cooled, the temperature of the cooling roller is controlled at 45 DEG C, so that the temperature of the film is reduced to room temperature, and a TPU color-changing film is obtained.

[0038] Example 3

[0039] The embodiment provides a preparation process of a TPU color-changing film, and comprises the following steps.

[0040] S1: 0.1 mol / L zinc nitrate aqueous solution and 0.05 mol / L tetrabutyl titanate ethanol solution (the volume ratio of the zinc nitrate aqueous solution and the tetrabutyl titanate ethanol solution is 1:1) are mixed, stirring is performed at a rotating speed of 300 r / min, ammonia water is added, the pH is adjusted to 9, the mixed solution is transferred into a reaction kettle, and reaction is performed at 120 DEG C for 4 h. After the reaction is completed, the product is centrifugally separated, the solid is washed with deionized water and ethanol for three times respectively, and finally drying is performed at 80 DEG C for 6 h, so that ZnO-TiO2 nanoparticles are obtained.

[0041] S2: 0.5 g ZnO-TiO2 nanoparticles are dispersed in 1 L mixed solution of ethanol and deionized water (the volume ratio of the ethanol and the deionized water is 3:1), ultrasonic dispersion is performed for 30 min (the power is 300 W), so that a mixed suspension with a concentration of 0.5 g / L is obtained, 0.25 g tetraethyl orthosilicate is added to the suspension under stirring (the rotating speed is 400 r / min), the pH is adjusted to 10 by using ammonia water, and reaction is performed at 60 DEG C for 3 h. After the reaction is completed, the product is centrifugally separated, the solid is washed with deionized water and ethanol for three times respectively, and finally drying is performed at 80 DEG C for 6 h, so that ZnO-TiO2@SiO2 nanoparticles are obtained.

[0042] S3: 50 g ZnO-TiO2@SiO2 nanoparticles are dispersed in ethanol, 2.5 g silane coupling agent KH550 is added, stirring reaction is performed at 80 DEG C for 2 h (the stirring rotating speed is 250 r / min), after the reaction is completed, the product is centrifugally separated, the solid is washed with ethanol, and finally drying is performed at 80 DEG C for 4 h, so that composite nanoparticles are obtained.

[0043] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added into a high-speed mixer, mixed at a speed of 800 r / min and a temperature of 85℃ for 6 min to obtain a premix, and then 5 kg of composite nanoparticles were added and mixed at a speed of 700 r / min and a temperature of 85℃ for 4 min. The mixed material was added into a twin-screw extruder, and the temperature of each section of the extruder was set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw rotation speed was strictly controlled at 480 r / min. The material was melted and mixed sufficiently in the extruder, and then extruded into a molten sheet from the die head. The molten sheet was introduced into a calendering machine, and the temperature of the calendering roller was set at 180℃ and the calendering speed was 4 m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling, and the temperature of the cooling roller was controlled at 45℃ to reduce the temperature of the film to room temperature, thereby obtaining a TPU color-changing film.

[0044] Example 4

[0045] The present embodiment provides a preparation process of a TPU color-changing film, which comprises the following steps:

[0046] S1: A 0.1 mol / L zinc nitrate aqueous solution and a 0.05 mol / L tetrabutyl titanate ethanol solution (the volume ratio of the zinc nitrate aqueous solution to the tetrabutyl titanate ethanol solution was 1:1) were mixed, stirred at a speed of 300 r / min, and ammonia water was added to adjust the pH to 9. The mixed solution was transferred to a reaction kettle and reacted at 120℃ for 4 h. After the reaction was completed, the product was centrifuged, washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2 nanoparticles.

[0047] S2: 0.5 g of ZnO-TiO2 nanoparticles were dispersed in 1 L of a mixed solution of ethanol and deionized water (the volume ratio of ethanol to deionized water was 3:1), ultrasonically dispersed for 30 min (the power was 300 W) to obtain a mixed suspension with a concentration of 0.5 g / L. Under stirring (the speed was 400 r / min), 0.25 g of tetraethyl orthosilicate was added to the suspension, the pH was adjusted to 10 with ammonia water, and the reaction was carried out at 60℃ for 3 h. After the reaction was completed, the product was centrifuged, washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2@SiO2 nanoparticles.

[0048] S3: 50 g of ZnO-TiO2@SiO2nanoparticles were dispersed in ethanol, 2.5 g of silane coupling agent KH550 was added, and the reaction was stirred at 80℃ for 2h (stirring speed was 250r / min). After the reaction was completed, the product was centrifuged, the solid was washed with ethanol, and finally dried at 80℃ for 4h to obtain the composite nanoparticles.

[0049] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added to a high-speed mixer and mixed at a speed of 800r / min and a temperature of 85℃ for 6 min to obtain a premix, then 4 kg of composite nanoparticles were added and mixed at a speed of 700r / min and a temperature of 85℃ for 4 min. The mixed material was added to a twin-screw extruder, and the temperature of each section of the extruder was set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw speed was strictly controlled at 450r / min. After the material was melted and mixed in the extruder, it was extruded into a molten sheet from the die head. The molten sheet was introduced into a calendering machine, the calendering roller temperature was set to 180℃, and the calendering speed was 4m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling, and the cooling roller temperature was controlled at 45℃ to reduce the film temperature to room temperature, obtaining a TPU color-changing film.

[0050] Example 5

[0051] The present embodiment provides a preparation process of a TPU color-changing film, comprising the following steps:

[0052] S1: A 0.1 mol / L zinc nitrate aqueous solution and a 0.05 mol / L titanium tetrabutoxide ethanol solution (volume ratio of zinc nitrate aqueous solution to titanium tetrabutoxide ethanol solution was 1:1) were mixed, stirred at a speed of 300r / min, and ammonia was added to adjust the pH to 9. The mixed solution was transferred to a reaction kettle and reacted at 120℃ for 4h. After the reaction was completed, the product was centrifuged, the solid was washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2nanoparticles.

[0053] S2: 0.5 g of ZnO-TiO2nanoparticles were dispersed in a mixed solution of 1 L of ethanol and deionized water (volume ratio of ethanol to deionized water was 3:1), ultrasonic dispersion was performed for 30 min (power was 300 W), a mixed suspension with a concentration of 0.5 g / L was obtained, 0.25 g of tetraethyl orthosilicate was added to the suspension under stirring (stirring speed was 400 r / min), the pH was adjusted to 10 with ammonia water, and reaction was performed at 60℃ for 3 h, after the reaction was completed, the product was centrifuged and separated, the solid was washed with ionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2@SiO2nanoparticles.

[0054] S3: 50 g of ZnO-TiO2@SiO2nanoparticles were dispersed in ethanol, 2.5 g of silane coupling agent KH550 was added, stirring reaction was performed at 80℃ for 2 h (stirring speed was 250 r / min), after the reaction was completed, the product was centrifuged and separated, the solid was washed with ethanol, and finally dried at 80℃ for 4 h to obtain composite nanoparticles.

[0055] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added to a high-speed mixer, mixed at a speed of 800 r / min and a temperature of 85℃ for 6 min to obtain a premix, then 4 kg of composite nanoparticles were added, and mixing was continued at a speed of 700 r / min and a temperature of 85℃ for 4 min, the mixed material was added to a twin-screw extruder, the temperature of each section of the extruder was set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw speed was strictly controlled at 500 r / min, the material was melted and plasticized in the extruder and fully mixed, then extruded into a molten sheet from the die head, the molten sheet was introduced into a calendering machine, the calendering roller temperature was set to 180℃, and the calendering speed was 4 m / min, finally the calendered film was pulled by a traction machine to a cooling roller group for cooling, the cooling roller temperature was controlled at 45℃, the film temperature was reduced to room temperature, and a TPU color-changing film was obtained.

[0056] Comparative Example 1

[0057] This comparative example provides a preparation process of a TPU color-changing film, including the following steps:

[0058] 100kg TPU resin, 6kg color masterbatch, 2.5kg polyethylene wax and 0.8kg antioxidant 1010 were added into a high-speed mixer and mixed at a speed of 800r / min and a temperature of 85℃ for 6min to obtain a premix, which was then added into a twin-screw extruder. The temperature settings of the extruder were as follows: 160℃ for the feeding section, 190℃ for the compression section, 200℃ for the homogenization section and 200℃ for the die head. The screw rotation speed was strictly controlled at 480r / min. After the material was melted, plasticized and fully mixed in the extruder, a molten sheet was extruded from the die head. The molten sheet was introduced into a calendering machine, the temperature of the calendering rollers was set at 180℃ and the calendering speed was 4m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling. The temperature of the cooling rollers was controlled at 45℃ to reduce the temperature of the film to room temperature, thereby obtaining a TPU color-changing film.

[0059] Comparative Example 2

[0060] The present comparative example provides a preparation process of a TPU color-changing film, which comprises the following steps:

[0061] S1: A 0.1mol / L zinc nitrate aqueous solution and a 0.05mol / L titanium tetrabutoxide ethanol solution (the volume ratio of the zinc nitrate aqueous solution to the titanium tetrabutoxide ethanol solution was 1:1) were mixed, stirred at a speed of 300r / min and adjusted to a pH of 9 by adding ammonia water. The mixture was transferred to a reaction kettle and reacted at 120℃ for 4h. After the reaction was completed, the product was centrifuged, washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2 nanoparticles.

[0062] S2: 50g of the ZnO-TiO2 nanoparticles were dispersed in ethanol, 2.5g of silane coupling agent KH550 was added, and the mixture was stirred and reacted at 80℃ for 2h (the stirring speed was 250r / min). After the reaction was completed, the product was centrifuged, washed with ethanol, and finally dried at 80℃ for 4h to obtain composite nanoparticles.

[0063] S3: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added into a high-speed mixer, mixed at a speed of 800 r / min and a temperature of 85℃ for 6 min to obtain a premix, and then 4 kg of composite nanoparticles were added and mixed at a speed of 700 r / min and a temperature of 85℃ for 4 min. The mixed material was added into a twin-screw extruder, and the temperature of each section of the extruder was set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw rotation speed was strictly controlled at 480 r / min. The material was melted and mixed in the extruder, and then extruded into a molten sheet from the die head. The molten sheet was introduced into a calendering machine, and the temperature of the calendering roller was set at 180℃ and the calendering speed was 4 m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling, and the temperature of the cooling roller was controlled at 45℃ to reduce the temperature of the film to room temperature, thereby obtaining a TPU color-changing film.

[0064] Comparative Example 3

[0065] The present comparative example provides a preparation process of a TPU color-changing film, comprising the following steps:

[0066] S1: A 0.1 mol / L zinc nitrate aqueous solution and a 0.05 mol / L tetrabutyl titanate ethanol solution (volume ratio of zinc nitrate aqueous solution to tetrabutyl titanate ethanol solution is 1:1) were mixed, stirred at a speed of 300 r / min, and ammonia water was added to adjust the pH to 9. The mixed solution was transferred to a reaction kettle and reacted at 120℃ for 4 h. After the reaction was completed, the product was centrifuged, washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2 nanoparticles.

[0067] S2: 0.5 g of ZnO-TiO2 nanoparticles were dispersed in 1 L of a mixed solution of ethanol and deionized water (volume ratio of ethanol to deionized water was 3:1), ultrasonically dispersed for 30 min (power was 300 W) to obtain a mixed suspension with a concentration of 0.5 g / L. Under stirring (speed was 400 r / min), 0.25 g of tetraethyl orthosilicate was added to the suspension, the pH was adjusted to 10 with ammonia water, and the reaction was carried out at 60℃ for 3 h. After the reaction was completed, the product was centrifuged, washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2@SiO2 nanoparticles.

[0068] S3: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added to a high-speed mixer and mixed at a speed of 800 r / min and a temperature of 85°C for 6 min to obtain a premix, and then 4 kg of ZnO-TiO2@SiO2nanoparticles were added and mixed at a speed of 700 r / min and a temperature of 85°C for 4 min. The mixed material was then added to a twin-screw extruder, and the temperature of each section of the extruder was set as follows: feeding section 160°C, compression section 190°C, homogenization section 200°C, and die head temperature 200°C. The screw speed was strictly controlled at 480 r / min. The material was melted and mixed in the extruder, and then extruded into a molten sheet from the die head. The molten sheet was introduced into a calendering machine, and the temperature of the calendering rollers was set to 180°C at a calendering speed of 4 m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling, and the temperature of the cooling rollers was controlled at 45°C to reduce the temperature of the film to room temperature, thereby obtaining a TPU color-changing film.

[0069] Comparative Example 4

[0070] The present comparative example provides a preparation process of a TPU color-changing film, including the following steps:

[0071] S1: A 0.1 mol / L zinc nitrate aqueous solution and a 0.05 mol / L tetrabutyl titanate ethanol solution (volume ratio of zinc nitrate aqueous solution to tetrabutyl titanate ethanol solution is 1:1) were mixed, stirred at a speed of 300 r / min, and ammonia water was added to adjust the pH to 9. The mixed solution was transferred to a reaction kettle and reacted at 120°C for 4 h. After the reaction was completed, the product was centrifuged, and the solid was washed with deionized water and ethanol for 3 times, and finally dried at 80°C for 6 h to obtain ZnO-TiO2nanoparticles.

[0072] S2: 0.5 g of ZnO-TiO2nanoparticles were dispersed in 1 L of a mixed solution of ethanol and deionized water (volume ratio of ethanol to deionized water is 3:1), and ultrasonic dispersion was performed for 30 min (power is 300 W) to obtain a mixed suspension with a concentration of 0.5 g / L. Under stirring (speed is 400 r / min), 0.25 g of tetraethyl orthosilicate was added to the suspension, the pH was adjusted to 10 with ammonia water, and the reaction was carried out at 60°C for 3 h. After the reaction was completed, the product was centrifuged, and the solid was washed with deionized water and ethanol for 3 times, and finally dried at 80°C for 6 h to obtain ZnO-TiO2@SiO2nanoparticles.

[0073] S3: 50 g of ZnO-TiO2@SiO2nanoparticles were dispersed in ethanol, 2.5 g of silane coupling agent KH550 was added, and the reaction was stirred at 80°C for 2 h (stirring speed was 250 r / min). After the reaction was completed, the product was centrifuged, the solid was washed with ethanol, and finally dried at 80°C for 4 h to obtain the composite nanoparticles.

[0074] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax, and 0.8 kg of antioxidant 1010 were added to a high-speed mixer and mixed at a speed of 800 r / min and a temperature of 85°C for 6 min to obtain a premix. Then 4 kg of composite nanoparticles were added and mixed at a speed of 700 r / min and a temperature of 85°C for 4 min. The mixed material was then added to a twin-screw extruder, and the temperature of each section of the extruder was set as follows: feeding section 160°C, compression section 190°C, homogenization section 200°C, and die head temperature 200°C. The screw speed was strictly controlled at 440 r / min. After the material was melted and fully mixed in the extruder, it was extruded into a molten sheet from the die head. The molten sheet was introduced into a calendering machine, and the temperature of the calendering rollers was set to 180°C at a calendering speed of 4 m / min. Finally, the calendered film was pulled by a traction machine to a cooling roller group for cooling. The temperature of the cooling rollers was controlled at 45°C to reduce the temperature of the film to room temperature, and a TPU color-changing film was obtained.

[0075] Comparative Example 5

[0076] This comparative example provides a preparation process of a TPU color-changing film, including the following steps:

[0077] S1: A 0.1 mol / L zinc nitrate aqueous solution and a 0.05 mol / L titanium tetrabutoxide ethanol solution (volume ratio of zinc nitrate aqueous solution to titanium tetrabutoxide ethanol solution was 1:1) were mixed, stirred at a speed of 300 r / min, and ammonia was added to adjust the pH to 9. The mixture was transferred to a reaction kettle and reacted at 120°C for 4 h. After the reaction was completed, the product was centrifuged, the solid was washed with deionized water and ethanol for 3 times, and finally dried at 80°C for 6 h to obtain ZnO-TiO2nanoparticles.

[0078] S2: 0.5 g of ZnO-TiO2nanoparticles were dispersed in a mixed solution of 1 L of ethanol and deionized water (volume ratio of ethanol to deionized water was 3:1), ultrasonic dispersion was performed for 30 min (power was 300 W), a mixed suspension with a concentration of 0.5 g / L was obtained, 0.25 g of tetraethyl orthosilicate was added to the suspension under stirring (rotation speed was 400 r / min), the pH was adjusted to 10 with ammonia water, and reaction was performed at 60℃ for 3 h, after the reaction was completed, the product was centrifuged and separated, the solid was washed with ionized water and ethanol for 3 times, and finally dried at 80℃ for 6 h to obtain ZnO-TiO2@SiO2nanoparticles.

[0079] S3: 50 g of ZnO-TiO2@SiO2nanoparticles were dispersed in ethanol, 2.5 g of silane coupling agent KH550 was added, stirring reaction was performed at 80℃ for 2 h (stirring rotation speed was 250 r / min), after the reaction was completed, the product was centrifuged and separated, the solid was washed with ethanol, and finally dried at 80℃ for 4 h to obtain composite nanoparticles.

[0080] S4: 100 kg of TPU resin, 6 kg of color master batch, 2.5 kg of polyethylene wax and 0.8 kg of antioxidant 1010 were added to a high-speed mixer, mixed at a rotation speed of 800 r / min and a temperature of 85℃ for 6 min to obtain a premix, then 4 kg of composite nanoparticles were added, and mixing was continued at a rotation speed of 700 r / min and a temperature of 85℃ for 4 min, the mixed material was added to a twin-screw extruder, the temperature of each section of the extruder was set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw rotation speed was strictly controlled at 510 r / min, the material was melt plasticized and fully mixed in the extruder, and then extruded into a melt state sheet from the die head, the melt state sheet was introduced into a calendering machine, the calendering roller temperature was set to 180℃, and the calendering speed was 4 m / min, finally the calendered film was pulled to a cooling roller group for cooling, the cooling roller temperature was controlled at 45℃, the film temperature was reduced to room temperature, and a TPU color-changing film was obtained.

[0081] Comparative Example 6

[0082] This comparative example provides a preparation process of a TPU color-changing film, including the following steps:

[0083] S1: 0.1 mol / L zinc nitrate aqueous solution and 0.05 mol / L titanium tetrabutoxide ethanol solution (volume ratio of zinc nitrate aqueous solution to titanium tetrabutoxide ethanol solution is 1:1) are mixed, stirred at a rotation speed of 300 r / min, and ammonia water is added to adjust the pH to 9, and the mixed solution is transferred to a reaction kettle and reacted at 120℃ for 4h. After the reaction is completed, the product is centrifuged, the solid is washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2 nanoparticles.

[0084] S2: 0.5g ZnO-TiO2 nanoparticles are dispersed in 1L mixed solution of ethanol and deionized water (volume ratio of ethanol to deionized water is 3:1), ultrasonic dispersion for 30min (power is 300W), to obtain a mixed suspension with a concentration of 0.5g / L, 0.25g tetraethyl orthosilicate is added to the suspension under stirring (rotation speed is 400r / min), the pH is adjusted to 10 with ammonia water, and the reaction is carried out at 60℃ for 3h. After the reaction is completed, the product is centrifuged, the solid is washed with ionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2@SiO2 nanoparticles.

[0085] S3: 50g ZnO-TiO2@SiO2 nanoparticles are dispersed in ethanol, 2.5g silane coupling agent KH550 is added, and the reaction is carried out at 60℃ under stirring (stirring rotation speed is 250r / min) for 2h. After the reaction is completed, the product is centrifuged, the solid is washed with ethanol, and finally dried at 80℃ for 4h to obtain composite nanoparticles.

[0086] S4: 100kg TPU resin, 6kg color master batch, 2.5kg polyethylene wax and 0.8kg antioxidant 1010 are added into a high-speed mixer, mixed at a rotation speed of 800r / min and a temperature of 85℃ for 6min to obtain a premix, then 4kg composite nanoparticles are added, and the mixture is further mixed at a rotation speed of 700r / min and a temperature of 85℃ for 4min. The mixed material is introduced into a twin-screw extruder, and the temperature of each section of the extruder is set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw rotation speed is strictly controlled at 480r / min. After the material is melted and plasticized and fully mixed in the extruder, it is extruded from the die head as a molten sheet. The molten sheet is introduced into a calendering machine, and the temperature of the calendering rollers is set to 180℃. The calendering speed is 4m / min. Finally, the calendered film is pulled by a traction machine to a cooling roller group for cooling. The temperature of the cooling roller is controlled at 45℃, and the film temperature is reduced to room temperature to obtain a TPU color-changing film.

[0087] Comparative Example 7

[0088] The comparative example provides a preparation process of a TPU color-changing film, including the following steps:

[0089] S1: 0.1 mol / L zinc nitrate aqueous solution and 0.05 mol / L tetrabutyl titanate ethanol solution (volume ratio of zinc nitrate aqueous solution to tetrabutyl titanate ethanol solution is 1:1) are mixed, stirred at a speed of 300 r / min, and ammonia water is added to adjust the pH to 9, and the mixed solution is transferred to a reaction kettle and reacted at 120℃ for 4h. After the reaction is completed, the product is centrifuged, and the solid is washed with deionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2 nanoparticles.

[0090] S2: 0.5g ZnO-TiO2 nanoparticles are dispersed in 1L mixed solution of ethanol and deionized water (volume ratio of ethanol to deionized water is 3:1), ultrasonic dispersion is carried out for 30min (power is 300W) to obtain a mixed suspension with a concentration of 0.5g / L, 0.25g tetraethyl orthosilicate is added to the suspension under stirring (speed is 400r / min), the pH is adjusted to 10 with ammonia water, and the reaction is carried out at 60℃ for 3h. After the reaction is completed, the product is centrifuged, and the solid is washed with ionized water and ethanol for 3 times, and finally dried at 80℃ for 6h to obtain ZnO-TiO2@SiO2 nanoparticles.

[0091] S3: 50g ZnO-TiO2@SiO2 nanoparticles are dispersed in ethanol, 2.5g silane coupling agent KH550 is added, and stirring reaction is carried out at 100℃ for 2h (stirring speed is 250r / min). After the reaction is completed, the product is centrifuged, and the solid is washed with ethanol, and finally dried at 80℃ for 4h to obtain composite nanoparticles.

[0092] S4: 100kg TPU resin, 6kg color master batch, 2.5kg polyethylene wax and 0.8kg antioxidant 1010 are added into a high-speed mixer, mixed at a speed of 800r / min and a temperature of 85℃ for 6min to obtain a premix, then 4kg composite nanoparticles are added, and the mixture is continuously mixed at a speed of 700r / min and a temperature of 85℃ for 4min. The mixed material is introduced into a twin-screw extruder, and the temperature of each section of the extruder is set as follows: feeding section 160℃, compression section 190℃, homogenization section 200℃, and die head temperature 200℃. The screw speed is strictly controlled at 480r / min. After the material is melted and plasticized and fully mixed in the extruder, it is extruded from the die head in a molten state. The molten sheet is introduced into a calendering machine, the calendering roller temperature is set to 180℃, and the calendering speed is 4m / min. Finally, the calendered film is pulled by a traction machine to a cooling roller group for cooling. The cooling roller temperature is controlled at 45℃, and the film temperature is reduced to room temperature to obtain a TPU color-changing film.

[0093] Experimental Examples

[0094] The TPU color-changing films prepared in Examples 1-5 and Comparative Examples 1-5 were tested for performance:

[0095] Color saturation: the TPU color-changing films were attached to standard white test panels and observed under sunny midday and cloudy conditions;

[0096] UV resistance: the TPU color-changing films were placed in a UV aging test chamber and irradiated for 1000 h under conditions of wavelength 340 nm, irradiance 0.71 W / (m²・nm), and temperature 60℃, and the color difference before and after placement in the UV aging test chamber was tested.

[0097] Tensile strength retention rate: the tensile strength before aging and after 1000 h of UV aging was tested in accordance with GB / T 1040.3-2006 “Determination of tensile properties of plastics - Part 3: test conditions for films and sheets”, and the tensile strength retention rate was calculated (strength after aging / strength before aging x 100%).

[0098] The test results are shown in Table 1:

[0099] Table 1: Performance test results of TPU color-changing films of Examples 1-5 and Comparative Examples 1-7

[0100] Group Color saturation Delta E0 (from standard color card) before aging Delta E 1 after aging 1000 h Delta E change (DE1 - DE0) Tensile strength before aging (MPa) Tensile strength after aging (MPa) Tensile strength retention rate (%) Example 1 High saturation, bright stable in sunny day / cloudy day 0.7 1.9 1.2 46.2 42.8 92.6 Example 2 High saturation, bright stable in sunny day / cloudy day 0.8 2.3 1.5 45.5 40.9 90.0 Example 3 High saturation, bright stable in sunny day / cloudy day 0.7 2.1 1.4 46.8 42.9 91.7 Example 4 High saturation, bright stable in sunny day / cloudy day 0.8 2.0 1.2 45.8 41.8 91.3 Example 5 High saturation, bright stable in sunny day / cloudy day 0.7 2.0 1.3 46.5 42.1 90.5 Comparative Example 1 Low saturation, slightly dark, more obvious in cloudy day 1.3 5.9 4.6 33.5 25.2 75.2 Comparative Example 2 Medium saturation, slightly light, light sensitive 1.2 4.4 3.2 39.2 32.1 81.9 Comparative Example 3 Medium saturation, slightly light, light sensitive 1.1 4.0 2.9 38.5 30.8 80.0 Comparative Example 4 Higher saturation, slightly whitish, obvious in cloudy day 0.9 3.4 2.5 41.5 35.6 85.8 Comparative Example 5 Higher saturation, slightly whitish, obvious in cloudy day 0.9 3.5 2.6 41.0 34.9 85.1 Comparative Example 6 Medium-high saturation, slightly whitish, more obvious in cloudy day 0.9 3.1 2.2 42.5 35.3 83.1 Comparative Example 7 Medium saturation, obvious whitish, slightly light in light 1.0 3.4 2.4 41.8 34.5 82.5

[0101] As can be seen from Table 1, the TPU color-changing films of Examples 1-5 maintain high saturation and brightness under strong light (sunny day) and weak light (overcast day), with ΔE change amount of only 1.2-1.5, far below the threshold value, the initial tensile strength (45.5-46.8 MPa) is significantly higher than that of the comparative examples, and the retention rate after aging is 90.0%-92.6%, among them, the particle dispersion is most uniform and the retention rate is highest at a screw speed of 480 r / min. The TPU color-changing film of Comparative Example 1 has low color master batch dispersion efficiency without nano-particles, and light is easily scattered by the TPU matrix, resulting in low saturation and poor visual stability. Since there is no nano-particle protection, ultraviolet light directly damages the chemical structure of the color master batch, resulting in a ΔE change amount of 4.6, and without nano-particle enhancement, the initial strength is low (33.5 MPa), and the retention rate after aging is only 75.2%, with the poorest mechanical properties. The color development enhancement effect of the TPU color-changing films of Comparative Examples 2-3 is weaker than that of Example 1, and color fading easily occurs under light, with ΔE change amount of 2.9-3.2, obvious color fading, and due to the structural defects of the nano-particles, the interface bonding with the TPU matrix is weak, the initial strength and retention rate are lower than those of Example 1. The TPU color-changing films of Comparative Examples 4-5 have a screw speed of 440 r / min and 510 r / min during preparation, resulting in uneven dispersion of composite nano-particles, and local light scattering, which appears as "slight whitening", especially under weak light on overcast days. Due to the improper screw speed, the nano-particles are not uniformly dispersed, and the local protection is weak, with ΔE change amount of 2.5-2.6, the performance is better than that of the traditional process but worse than that of Example 1, and the screw speed deviates from the optimal value, the uneven dispersion of particles leads to local stress concentration, and the retention rate after aging (85.1%-85.8%) is lower than that of Example 1. In Comparative Example 6, the reaction temperature of the silane coupling agent in step S3 is 60°C, which is too low, resulting in incomplete reaction of the silane coupling agent KH550 with the ZnO-TiO2@SiO2 nano-particles, insufficient surface modification, and decreased interface compatibility and dispersion uniformity of the composite nano-particles with the TPU matrix. It is shown that the color saturation is slightly lower than that of Example 1, and slight whitening occurs (especially under weak light on overcast days); at the same time, due to insufficient modification, the shielding effect of the nano-particles on ultraviolet light and the interface enhancement effect are weakened, the ΔE change amount is greater than that of Example 1, and the tensile strength retention rate is significantly lower than that of Example 1. In Comparative Example 7, the reaction temperature of the silane coupling agent in step S3 is 100°C, which is too high, resulting in partial decomposition or excessive cross-linking of the silane coupling agent, producing by-products, destroying the surface modification layer structure of the composite nano-particles, and further deteriorating the compatibility and dispersion uniformity of the composite nano-particles with the TPU matrix. It is shown that the color saturation is significantly decreased, the whitening phenomenon is prominent, and the color is pale under light; due to the instability of the modification layer, the protection and enhancement effect of the nano-particles on the film material are more significantly weakened, the ΔE change amount and the tensile strength retention rate are worse than those of Example 1, and the performance is worse than that of Example 1.

[0102] Although the principles of the present application have been described in connection with the preferred embodiments thereof, it will be understood clearly to those skilled in the art that the embodiments described above are merely illustrative of the present application and are not intended to limit the scope of the present application. The details in the embodiments are not intended to limit the scope of the present application, and any obvious changes, simple replacements, etc. based on the technical solutions of the present application without departing from the spirit and scope of the present application are all within the protection scope of the present application.

Claims

1. A process for preparing a TPU color conversion film, characterized by, The method comprises the following steps: S1: mixing and stirring a zinc nitrate aqueous solution and a tetrabutyl titanate ethanol solution, adjusting the pH to 8-9 for reaction, centrifuging after the reaction, washing and drying the solid to obtain ZnO-TiO2 nanoparticles; S2: dispersing the ZnO-TiO2 nanoparticles in an ethanol aqueous solution for ultrasonic dispersion to obtain a suspension, adding tetraethyl orthosilicate to the suspension under stirring, adjusting the pH to 9-10 for reaction, centrifuging after the reaction, washing and drying the solid to obtain ZnO-TiO2@SiO2 nanoparticles; S3: dispersing the ZnO-TiO2@SiO2 nanoparticles in an ethanol aqueous solution, adding a silane coupling agent for reaction, centrifuging after the reaction, washing and drying the solid to obtain composite nanoparticles; S4: mixing TPU resin, color master batch, dispersant and modification aid, then adding the composite nanoparticles, melting and extruding the mixed material, calendering, cooling and shaping to obtain a TPU color-changing film; The mass ratio of the TPU resin, color master batch, dispersant, modification aid and composite nanoparticles is 100: (5-8): (2-3): (0.5-1): (3-5). In step S3, the reaction temperature is 70-90℃, and the reaction time is 1.5-2.5h. In step S4, the melting and extruding is performed by using a double-screw extruder, the temperature of the feeding section is 160-170℃, the temperature of the compression section is 180-190℃, the temperature of the homogenizing section is 200-210℃, the temperature of the die head is 190-200℃, and the rotation speed of the screw is 450-500r / min.

2. The process for preparing a TPU color conversion film according to claim 1, characterized in that, In step S1, the concentration of the zinc nitrate aqueous solution is 0.08-0.12mol / L, and the concentration of the tetrabutyl titanate ethanol solution is 0.04-0.06mol / L; and / or, The volume ratio of the zinc nitrate aqueous solution and the tetrabutyl titanate ethanol solution is 1: (0.8-1.2); and / or, The rotation speed of the stirring is 250-350r / min.

3. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S1, the solution added for adjusting the pH is ammonia water; and / or, The reaction temperature is 110-130℃, and the reaction time is 3.5-4.5h; and / or, The washing mode is: first washing with deionized water, and then washing with ethanol; and / or, The drying temperature is 75-85℃, and the drying time is 5.5-6.5h.

4. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S2, the volume ratio of ethanol and water in the ethanol aqueous solution is (2-4):1; and / or, The ultrasonic dispersion time is 25-35min, and the ultrasonic power is 250-350W; and / or, The volume concentration of the suspension is 0.4-0.6g / L.

5. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S2, the rotation speed of the stirring is 350-450r / min; and / or, The mass ratio of the tetraethyl orthosilicate and the ZnO-TiO2 nanoparticles is 1:1.5-2.5; and / or, The solution added for adjusting the pH is ammonia water.

6. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S2, the temperature of the reaction is 50-70℃, and the time is 2.5-3.5h; and / or, The washing method is: first washing with deionized water, and then washing with ethanol; and / or, The drying temperature is 70-90℃, and the time is 5.5-6.5h.

7. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S3, the adding amount of the silane coupling agent is 3-8% of the mass of the ZnO-TiO2@SiO2 nanoparticles; and / or, The type of the silane coupling agent is KH550; and / or, The stirring speed during the reaction is 200-300r / min; and / or, The solution used for the washing is an ethanol solution; and / or, The drying temperature is 70-90℃, and the time is 3.5-4.5h.

8. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S4, the dispersing agent is polyethylene wax; and / or, The modifying auxiliary is antioxidant 1010; and / or, The rotating speed of the initial mixing is 750-850r / min, the temperature is 80-90℃, and the time is 5-8min; and / or, The rotating speed of the mixing is 650-750r / min, the temperature is 80-90℃, and the time is 3-5min.

9. The process for preparing a TPU color shifting film according to claim 1, wherein, In step S4, the equipment used during the calendering is a calendering machine; The temperature of the calendering roller is 180-190℃, and the calendering speed is 3-5m / min; and / or, The temperature of the cooling and shaping is 40-50℃.