Color-changing polypropylene composite material for new energy automobile as well as preparation method and application of color-changing polypropylene composite material

Abstract

The invention relates to the technical field of polymer composite materials, in particular to a novel polypropylene (PP) composite material with high light transmittance, long-acting weather resistance and an intelligent response type dynamic color changing function and a preparation method thereof, and belongs to the technical field of polymer composite materials. The composite material comprises the following components in parts by weight: 50-90 parts of polypropylene, 5-25 parts of a toughening agent, 1-4 parts of core-shell-shell structure color-changing microspheres, 1-5 parts of reactive nano shielding powder, 5-15 parts of a micron-sized reinforcing phase, 1-3.0 parts of an antioxidant light-stable compound system, 1-3 parts of a compatilizer and 0.3-0.8 part of a processing aid. Triple synergy of scattering inhibition, mechanical maintenance and weather resistance enhancement is achieved through multi-scale structure design and interface engineering, high light transmittance is kept, good mechanical performance and weather resistance are also considered, and the core problems that a color changing agent is inactivated under injection molding high-temperature shearing and the long-term weather resistance function is attenuated are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer modified materials for automobiles, specifically relating to a novel polypropylene (PP) composite material and its preparation method that combines high light transmittance, long-lasting weather resistance, and intelligent responsive dynamic color-changing function. Background Technology

[0002] With the rapid iteration of the global new energy vehicle industry, intelligence, personalization, and functional integration have become the core competitive focus for automakers. Automotive interior and exterior materials are upgrading from traditional "basic functional" to "intelligent responsive" materials. Polypropylene (PP) materials, with their advantages of low density (0.90-1.05 g / cm³), balanced mechanical properties, excellent processing fluidity, and controllable cost, have long held the top position in the use of interior and exterior materials in new energy vehicles, and are widely used in key components such as dashboards, door panels, charging port components, and ambient lighting housings. However, the limited functionality of traditional polypropylene materials is showing significant shortcomings in meeting the growing demand for high-end products. Specifically, in key aspects of new energy vehicles such as status monitoring, human-machine interaction feedback, and adaptive adjustment to the external environment, there is an urgent need for materials with "color-changing energy indication": materials need to have dynamic color-changing capabilities to achieve intelligent scenarios such as status indication, early warning, and ambient lighting creation. At present, the realization of such functions mostly relies on surface coating or coating on the substrate. This process has the following prominent problems: (1) Interface problem - poor adhesion between the coating and the PP substrate; (2) Durability problem: easy to peel and crack after long-term use; (3) Process complexity: multiple steps, high cost, environmental risks; (4) Performance degradation: problems such as response speed and color uniformity decrease over time.

[0003] To address these issues, the industry has explored relevant technologies, and some patents have disclosed targeted solutions. For example, CN202110234567A imparts photochromic capabilities to materials by directly incorporating spiropyran-based organic color-changing dyes into a high-transmittance polypropylene matrix. Its core mechanism utilizes the ring-opening isomerization reaction of dye molecules under ultraviolet light irradiation to achieve color change. However, the small dye molecules added by this method are prone to migration and aggregation in the matrix, leading to uneven color change, rapid efficiency decay, and poor heat resistance (long-term operating temperature below 80℃), failing to meet the stringent requirements of automotive exterior parts. CN115403860A uses inorganic WO3 photochromic powder as its core, preparing nanoscale color-changing materials via a hydrothermal method, and supplementing it with LDPE and nucleating agent NA88 to refine the grains and form a photochromic composite material with a color difference ΔE reaching 11. This scheme avoids the shortcomings of insufficient heat resistance of organic color change agents by using an inorganic system, and at the same time uses nucleating agents to refine the grains to improve light transmission efficiency. However, although the hydrothermal method can prepare high-purity WO3 powder, the production efficiency is low; it is easy to agglomerate, resulting in uneven dispersion and affecting the consistency of color change; and the batch stability is difficult to control during scale-up production.

[0004] Against this backdrop, developing a new type of composite material that combines high light transmittance, long-lasting weather resistance, stable dynamic color-changing function, excellent compatibility with PP matrix, and good processing performance has become the key to resolving the contradiction between the intelligent upgrading of new energy vehicles and the bottleneck of material performance. It is of great practical significance for promoting the technological innovation of interior and exterior materials of new energy vehicles. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing polypropylene materials, such as monotonous color and limited functionality, which fail to meet the personalized and intelligent requirements of new energy vehicles for interior and exterior trim parts. This invention proposes a composite material integrating color-changing properties and excellent mechanical properties, along with its preparation method. By combining a "core-shell-shell structured photochromic microsphere + reactive nano-shielding masterbatch synergistic compounding" system, an integrated structure of "high light transmittance - dynamic response - long-term stability" is constructed. This achieves rapid photochromic response and intelligent switching between high light transmittance and natural color while simultaneously considering the material's mechanical properties and weather resistance stability. This adapts to the lightweight, personalized, and intelligent interaction application scenarios of new energy vehicles, ultimately meeting the usage requirements of automotive interior and exterior injection molded parts. Specifically, this is achieved through the following technical solution:

[0006] A color-changing polypropylene composite material for new energy vehicles, characterized in that, by weight, it comprises the following components: high-flowability polypropylene: 50-90 parts; toughening agent: 5-25 parts; core-shell-shell structured photochromic microspheres: 1-4 parts; reactive nano-shielding masterbatch: 1-5 parts; antioxidant and light-stabilized compound system: 0.5-1.0 parts; compatibilizer: 1-3 parts; micron-scale reinforcing phase: 5-15 parts; processing aid: 0.3-0.8 parts.

[0007] Preferably, the photochromic polypropylene composite material exhibits a high-transmittance natural color state when there is no light irradiation, with a light transmittance ≥78% (2mm). It rapidly develops color when irradiated with 315-400nm light (response time ≤5s), and its color difference ΔE can reach 13.8. It recovers its transparent natural color within 2 minutes under conditions of cessation of irradiation / darkness.

[0008] Preferably, the reactive nano-shielding masterbatch is prepared by mixing redstone-type nano-titanium dioxide and cerium oxide nanocrystals at a mass ratio of 4:1, adding 1-2% of a silane coupling agent (based on the total amount of the mixed powder), premixing at 50-60°C in a high-speed mixer at 600-800 r / min for 5-8 min to obtain pretreated nano-mixed powder. The pretreated nano-mixed powder is then mixed with a dry PP matrix (at a 4:5 ratio) in a high-speed mixer for 10-15 min, followed by extrusion granulation using a twin-screw extruder.

[0009] Preferably, the high-flowability polypropylene is one or more of homopolymer polypropylene or random copolymer polypropylene, with a melt flow rate of 20-100 g / 10 min at 230℃@2.16 kg, balancing processing flowability and light transmittance, such as Zhenhai Refining & Chemical's M60T.

[0010] Preferably, the coupling agent is a silane coupling agent, including one of aminosilane, epoxysilane, methylpropionyloxysilane, vinylsilane, etc.

[0011] Preferably, the antioxidant and light-stabilizing compound system is a mixture of hindered amine light stabilizer, phosphite antioxidant, and ultraviolet absorber in a mass ratio of 2:2:1 to 4:2:1, and the ultraviolet absorber is at least one of benzophenone and benzotriazole.

[0012] Preferably, the micron-scale reinforcing phase is a surface-modified whisker, including one of modified magnesium sulfate whiskers or calcium sulfate whiskers.

[0013] Preferably, the compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH) with a grafting rate of 0.8%-1.5%.

[0014] Preferably, the toughening agent is one or both of the block copolymer elastomers SEBS (hydrogenated styrene-butadiene-styrene triblock copolymer) and ethylene-octene copolymer (POE).

[0015] Preferably, the processing aid lubricant is one of calcium stearate, magnesium stearate, zinc stearate, etc.

[0016] Preferably, the method for preparing the color-changing polypropylene composite material for new energy vehicles is characterized by comprising the following steps:

[0017] (1) Preparation of core-shell-shell structured photochromic microspheres

[0018] S1, preparation of spiropyran seed liquid: 0.5-1.5g of spiropyran derivative is dissolved in 10-30mL of dichloromethane (oil phase), and 0.2-1.0g of polyvinyl alcohol is dissolved in 50-100mL of water (aqueous phase). Under light-protected conditions, the oil phase is injected into the aqueous phase, and shear emulsification is performed at 8000rpm for 5-10min. The solvent is removed by rotary evaporation at 30-40℃, followed by vacuum drying for 1-2h to completely remove the solvent.

[0019] S2, PMMA shell coating: The spiropyran seed liquid obtained in S1, sodium dodecyl sulfate, methyl methacrylate (MMA) and azobisisobutyronitrile are polymerized at 60-80℃ in the dark for 6-8 hours under a nitrogen atmosphere to obtain a core-shell microsphere emulsion (the shell thickness is controlled by the mass ratio of MMA / spiropyran 5:1 to 8:1).

[0020] S3. Polysiloxane Surface Modification: Hydroxyl-terminated polydimethylsiloxane (molecular weight ≈ 2000) was dissolved in tetrahydrofuran (siloxane: THF = 1:5~1:8) and added dropwise to a microsphere emulsion. Dibutyltin dilaurate was added at 1%-3% of the siloxane mass, and the reaction was carried out at 50℃ for 4 h. The mixture was then centrifuged (7000-8000 rpm, 15 min), washed three times with ethanol / water, and vacuum dried at 40-60℃ for 24 h. The entire process was carried out in the dark, and the product was stored in a sealed, light-protected container.

[0021] (4) Preparation of modified whiskers: The whiskers are dispersed in an ethanol solution to form a dispersion with a solid-liquid ratio of 1:10-1:20. A coupling agent of 1% to 3% of the weight of the whiskers is added. The mixture is ultrasonically treated at 65 to 80°C for 0.5 to 2 hours, washed, and vacuum dried to obtain surface-modified whiskers.

[0022] (3) Reactive nano-shielding masterbatch: Rutile nano-titanium dioxide and cerium oxide nanocrystals are mixed at a mass ratio of 4:1, and a coupling agent accounting for 1-2% of the total mixed powder is added. The temperature is controlled at 50-60℃, and the mixture is premixed in a high-speed mixer at 600-800 r / min for 5-8 min to obtain pretreated nano-mixed powder. The pretreated nano-mixed powder is then fed into a dry PP matrix (at a ratio of 4:5) and mixed in a high-speed mixer for 10-15 min. Finally, it is extruded and granulated using a twin-screw extruder.

[0023] (4) Raw material premixing

[0024] Weigh out the polypropylene, toughening agent, core-shell-shell structured photochromic microspheres, reactive nano-shielding masterbatch, antioxidant and light-stabilized compound system, compatibilizer, and processing aid by weight percentage and add them to a high-speed mixer. Mix at 800-1200 r / min for 5-10 min and then mix the mixture for 10-15 min.

[0025] (5) Melt blending extrusion

[0026] The premixed material is added to a twin-screw extruder. The extruder barrel temperature is set in the following sections: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, Zone 4 190-200℃, and Die head 185-195℃. The screw speed is 300-450 r / min, and the vacuum degree is ≤-0.08MPa. Melt blending extrusion is then performed.

[0027] (6) Granulation and drying

[0028] The extruded material is granulated by an underwater pelletizer to a particle size of 2-4 mm, and then dried at 80-100℃ for 2-4 hours to obtain a high-transmittance, weather-resistant, and color-changing polypropylene composite material.

[0029] This method uses highly crystalline homopolymer PP as a matrix, constructs a primary UV protection barrier through the synergistic compounding of reactive nano-shielding masterbatch (TiO2 / CeO2 heterostructure), integrates a weather-resistant functional system (high molecular weight hindered amine light stabilizer compounded with benzotriazole UV absorber) to build a long-lasting chemical protection network, and anchors a smart dynamic color-changing component (core-shell-shell structured photochromic microspheres) as the core of the photoresponsive function, forming a three-in-one functional synergistic system of "physical shielding - chemical anti-aging - smart color changing", and prepares a functionalized polypropylene composite material with high transparency, long-lasting aging resistance and reversible dynamic color changing properties. It is suitable for automotive intelligent lighting systems, dynamic display decorative parts and interior and exterior functional integrated components, specifically including: luminous car logos, ambient light translucent masks, indicator light housings and other exterior components, as well as intelligent dashboard trim strips, dynamic trim strips for door interior panels and other components. It can present dynamic visual response effects with the help of light changes, significantly enhancing the technological quality and personalized experience of automotive products, and bringing users a more interactive driving and riding visual enjoyment.

[0030] The beneficial effects of this invention are as follows:

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) It realizes the intelligent unity of dynamic color-changing function and light transmission function: The material prepared by the present invention has unique light response characteristics. Under light conditions, the material can exhibit dynamic color changes to meet the personalized appearance requirements; in the absence of light, the material exhibits excellent high light transmission characteristics and can be used as a functional lighting cover or light guide component. This "one-body dual-state" characteristic allows it to replace the traditional single color-changing trim and independent light transmission parts at the same time, providing a brand-new material solution for the integrated and intelligent design of automotive interior and exterior trim. (2) Excellent mechanical properties and durability: The thermoplastic elastomer and compatibilizer in the formula work together to effectively improve the impact resistance and toughness of the material. The compounded antioxidant and light stabilizer system ensures the aging resistance of the material in long-term use and complex environment. The color is stable and fully meets the stringent requirements of automotive interior and exterior trim. (3) Simple preparation process and easy to industrialize: The melt blending extrusion and injection molding process adopted by the present invention has good compatibility with the existing polypropylene modification and parts manufacturing system. The process is stable and suitable for large-scale promotion and application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be noted that these embodiments are merely illustrative, and the description is only intended to explain the invention, but is not intended to limit the invention.

[0033] The main representative materials used in the following embodiments and comparative examples are as follows:

[0034] In the composite material formulations of the examples and comparative examples, the polypropylene resin in the PP composite material is preferably homopolymer polypropylene resin, with the commercial brand name M60T (melt flow rate of 60 g / 10 min at 230℃, 2.16 kg) provided by Sinopec; and the commercial brand name Y26 (melt flow rate of 25 g / 10 min at 230℃, 2.16 kg) provided by Zhenhai Refining & Chemical. Nano-titanium dioxide and cerium oxide nanocrystals were provided by Hangzhou Jiupeng New Materials Co., Ltd. The coupling agent was epoxy silane, provided by Hangzhou Jessica Chemical Co., Ltd.; the whisker filler was provided by Shanghai Fengzhu Composite New Materials Technology Co., Ltd., with the commercial brand name NP-YW2; the hydrogenated styrene-butadiene-block copolymer (SEBS) was provided by Baling Petrochemical, with the commercial brand name SEBS YH-503; and the antioxidant and UV absorber were provided by BASF and ICE (UK), with the commercial brands Irganox 1010, Negonox DSTP, and UV329. The compatibilizer is polypropylene grafted with maleic anhydride, sourced from Shanghai Huawen New Materials Co., Ltd. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0035] The content (mass percentage) of each component in the embodiments and comparative examples of the present invention is shown in Tables 1-2. The performance test results of the high light transmittance, weather-resistant, and color-changing polypropylene composite materials of Embodiments 1-7 and Comparative Examples 1-3 of the present invention are shown in Table 3.

[0036] The preparation methods of the color-changing polypropylene composite materials in the examples and comparative examples are as follows:

[0037] (1) Preparation of core-shell-shell structured photochromic microspheres

[0038] S1, preparation of spiropyran seed liquid: 0.5-1.5g of spiropyran derivative is dissolved in 10-30mL of dichloromethane (oil phase), and 0.2-1.0g of polyvinyl alcohol is dissolved in 50-100mL of water (aqueous phase). Under light-protected conditions, the oil phase is injected into the aqueous phase, and shear emulsification is performed at 8000rpm for 5-10min. The solvent is removed by rotary evaporation at 30-40℃, followed by vacuum drying for 1-2h to completely remove the solvent.

[0039] S2, PMMA shell coating: The spiropyran seed liquid obtained in S1, sodium dodecyl sulfate, methyl methacrylate (MMA) and azobisisobutyronitrile are polymerized at 60-80℃ in the dark for 6-8 hours under a nitrogen atmosphere to obtain a core-shell microsphere emulsion (the shell thickness is controlled by the mass ratio of MMA / spiropyran 5:1 to 8:1).

[0040] S3. Polysiloxane Surface Modification: Hydroxyl-terminated polydimethylsiloxane (molecular weight ≈ 2000) was dissolved in tetrahydrofuran (siloxane: THF = 1:5~1:8) and added dropwise to a microsphere emulsion. Dibutyltin dilaurate was added at 1%-3% of the siloxane mass, and the reaction was carried out at 50℃ for 4 h. The mixture was then centrifuged (7000-8000 rpm, 15 min), washed three times with ethanol / water, and vacuum dried at 40-60℃ for 24 h. The entire process was carried out in the dark, and the product was stored in a sealed, light-protected container.

[0041] (5) Preparation of modified whiskers: The whiskers are dispersed in an ethanol solution to form a dispersion with a solid-liquid ratio of 1:10-1:20. A coupling agent of 1% to 3% of the weight of the whiskers is added. The mixture is ultrasonically treated at 65 to 80°C for 0.5 to 2 hours, washed, and vacuum dried to obtain surface-modified whiskers.

[0042] (3) Reactive nano-shielding masterbatch: Rutile nano-titanium dioxide and cerium oxide nanocrystals are mixed at a mass ratio of 4:1, and a coupling agent accounting for 1-2% of the total mixed powder is added. The temperature is controlled at 50-60℃, and the mixture is premixed in a high-speed mixer at 600-800 r / min for 5-8 min to obtain pretreated nano-mixed powder. The pretreated nano-mixed powder is then fed into a dry PP matrix (at a ratio of 4:5) and mixed in a high-speed mixer for 10-15 min. Finally, it is extruded and granulated using a twin-screw extruder.

[0043] (4) Raw material premixing

[0044] Weigh out the polypropylene, toughening agent, core-shell-shell structured photochromic microspheres, reactive nano-shielding masterbatch, antioxidant and light-stabilized compound system, compatibilizer, and processing aid by weight percentage and add them to a high-speed mixer. Mix at 800-1200 r / min for 5-10 min and then mix the mixture for 10-15 min.

[0045] (5) Melt blending extrusion

[0046] The premixed material is added to a twin-screw extruder. The extruder barrel temperature is set in the following sections: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, Zone 4 190-200℃, and Die head 185-195℃. The screw speed is 300-450 r / min, and the vacuum degree is ≤-0.08MPa. Melt blending extrusion is then performed.

[0047] (6) Granulation and drying

[0048] The extruded material is granulated by an underwater pelletizer to a particle size of 2-4 mm, and then dried at 80-100℃ for 2-4 hours to obtain a high-transmittance, weather-resistant, and color-changing polypropylene composite material.

[0049] The high-transmittance, weather-resistant, and color-changing polypropylene composite materials prepared in Examples 1-6 and Comparative Examples 1-3 were used to prepare standard specimens (size: 100mm×50mm×2mm) using an injection molding machine. The specimens were made with smooth surfaces, free of bubbles and scratches. The transmittance, tensile strength, flexural strength, flexural modulus, cantilever beam notched impact strength, color development, and weather resistance were tested. Light transmittance was tested according to GB / T 2410-2008 for each sample of injection-molded square plate (2.0 mm thick); tensile strength was tested according to ISO 527 test method at a test speed of 50 mm / min; flexural modulus was tested according to ISO 178 standard at a bending speed of 2 mm / min; cantilever beam notched impact was tested according to ISO 179 standard at a test temperature of 23℃; under ultraviolet light (emission center wavelength λ = 365 nm) irradiation, the color difference value (ΔE) was quantified according to GB / T 15608-2006 standard (D65 light source simulating natural sunlight, 10° observation angle) to evaluate the photochromic effect and stability. Weather resistance was mainly assessed by evaluating the color difference value (ΔE) of the material after thermo-oxidative aging and 2000 hours of ultraviolet irradiation (tested every 5 minutes). The intensity of photochromism of the material was judged by the change in color difference. ΔE = ((L2-L1)) 2 +(a2-a1) 2 +(b2-b1) 2 ) 1 / 2 Where L1, a1, and b1 are the initial color values ​​of the samples (before UV irradiation), and L2, a2, and b2 are the color values ​​after irradiation / thermal oxidation. Before testing each batch of samples, the same standard color chart is measured 5 times repeatedly, and the coefficient of variation of ΔE is ≤1%.

[0050] Table 1. Components and contents of each component in Examples 1-7

[0051]

[0052]

[0053] Table 2 shows the distribution ratios (parts by weight) for each group in Comparative Examples 1–3.

[0054] Components Comparative Example 1 Comparative Example 2 Comparative Example 3 polypropylene 61.2 60.2 59.2 toughening agent 25 25 25 Photochromic microspheres 1 Micron-scale enhanced phase 10 10 10 Nano shielding masterbatch 2 Antioxidant and photostable compound system 0.8 0.8 0.8 compatibilizer 2.5 2.5 2.5 Processing aids 0.5 0.5 0.5

[0055] Table 3 Performance data of Examples 1-7 and Comparisons 1-3

[0056]

[0057]

[0058] Comparing the test results of Examples 1-7 with those of Comparative Examples 1-3, it can be seen that: Comparative Examples 1 and 3, without the addition of photochromic microspheres, had an ultraviolet irradiation ΔE value of 0 (no color change effect); while Examples 1-7 and Comparative Example 2, after adding the microspheres, had ΔE values ​​of 7.2-17.3 (showing obvious color change). This directly proves that photochromic microspheres are a necessary condition for composite materials to have color change ability. Moreover, within the addition amount of 4 parts, the higher the microsphere content, the more spiropyran color change sites and the stronger the color change intensity, without the effect attenuation caused by saturation or agglomeration.

[0059] Regarding light transmittance, compared with Comparative Example 1 (no functional component, light transmittance 78.51%), although the introduction of functional components in Examples 1 to 7 led to a decrease in light transmittance, they all maintained an application benchmark of over 70%. In particular, Examples 2 and 7 (2 parts microspheres + 2 parts shielding masterbatch) achieved a triple synergy of scattering suppression, mechanical maintenance, and weather resistance enhancement through multi-scale structural design and interface engineering. They not only maintained high light transmittance but also took into account good mechanical properties and weather resistance, achieving the best balance between high light transmittance, functionality, and weather resistance.

[0060] This balanced effect is due to precise structural and performance control: (1) Optical stealth: The transmittance is determined by the "scattering intensity of light by particles". The particle size and content of microspheres and shielding masterbatch jointly control the degree of scattering, thereby maximizing the preservation of the transmittance of the matrix. The D50 particle size (0.5-2μm) of the photochromic microspheres is in the Rayleigh scattering critical region of visible light (scattering intensity decreases exponentially when d<1μm). The core-shell-shell structure further weakens scattering through gradient refractive index matching. The refractive index deviation between the PMMA shell (refractive index 1.49) and the PP matrix (1.488-1.492) is very small. The outermost hydroxyl-terminated polysiloxane (n=1.48) further reduces the interfacial energy, causing the microspheres to tend to be "optically stealthy" in the matrix. After the nano-shielding masterbatch is surface modified by silane coupling agent, an organic layer is formed, which inhibits the strong scattering of TiO2 / CeO2, thereby maximizing the preservation of the transmittance of the matrix under functional load. (2) Mechanical property retention: The “interface modification design” of microspheres and shielding masterbatch enhances the bonding force with the PP matrix and avoids particles becoming stress concentration points: In the core-shell-shell structure, the PMMA shell and PP are polarly matched, and the hydroxyl groups of the outer HTPDMS can interact with the compatibilizer to achieve a tight bond between the “matrix-microsphere” interface and achieve efficient stress transfer; at the same time, the nano-shield is pretreated with silane coupling agent, the organic groups of the coupling agent entangle with PP, and the inorganic groups bond with the nanoparticles, eliminating the interface defects of the nanoparticles and producing a nano-reinforcement effect. (3) Synergistic weather resistance mechanism: The free radical scavenging of cerium oxide, the ultraviolet shielding of TiO2, and the protection of the spiropyran core by the PMMA shell of the microspheres achieve long-term stability.

[0061] In summary, the "core-shell-shell structure photochromic microspheres + reactive nano-shielding masterbatch synergistic compounding" system is adopted. Specifically, photochromic microspheres with spiropyran as the core, PMMA as the shell, and HTPDMS surface modification are introduced into the PP matrix, combined with redstone-type TiO2-cerium oxide (4:1) nano-shielding masterbatch pretreated with silane coupling agent, in an optimal ratio of 2 parts microspheres + 2 parts shielding masterbatch. During high-speed mixing and twin-screw extrusion granulation, the precise matching of the refractive indices of the microspheres and the matrix, along with the interface modification optimization of the nanoparticles, achieves uniform dispersion of functional particles and tight bonding with the matrix. Simultaneously, relying on the photochromic isomerization dynamic color-changing function of the microspheres and the synergistic anti-aging effects of the UV shielding and free radical scavenging of the nano-shielding masterbatch, an integrated structure of "high light transmittance - dynamic response - long-term stability" is constructed. The novel polypropylene (PP) composite material prepared by this invention possesses high light transmittance stability, long-term weather resistance, and intelligent responsive dynamic color-changing function. This "one-piece dual-state" characteristic allows it to simultaneously replace traditional single color-changing trim pieces and independent light-transmitting parts, providing a brand-new material solution for the integrated and intelligent design of automotive interior and exterior trim products.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An injection moulding grade light transmitting colour shifting polypropylene composite material, characterised in that, The high flow polypropylene includes the following components by weight: 50-90 parts; toughening agent: 5-25 parts; core-shell-shell structure photochromic microspheres: 1-4 parts; reactive nano shielding masterbatch: 1-5 parts; anti-oxidation light stable compound system: 0.5-1.0 parts; compatibilizer: 1-3 parts; micron-sized reinforcing phase: 5-15 parts; processing aid: 0.3-0.8 parts; the material is in a high light transmittance natural color state under no light irradiation, the light transmittance is greater than or equal to 78% (2mm), and the color difference ΔE can reach 12.6 under 315-400nm light irradiation.

2. An injection moulding grade light transmitting colour shifting polypropylene composite material according to claim 1, characterized in that: The high flow polypropylene is one or a combination of the following compositions: homopolymer polypropylene or random copolymer polypropylene, and the melt flow rate is 20-70g / 10min at 230℃ and 2.16kg, which balances the processing flowability and light transmittance.

3. An injection moulded, light transmitting, colour shifting polypropylene composite material according to claim 1, characterised in that: The core-shell-shell structure photochromic microspheres sequentially include, from the inside to the outside: a spiropyran photochromic compound as the core, polymethyl methacrylate as the shell, and a shell layer surface modified with a hydroxyl-terminated polysiloxane (HTPDMS), the shell layer thickness is 200-500nm, and the particle size D50 is 0.5-2μm.

4. The injection molding grade light transmitting color shifting polypropylene composite of claim 1, wherein: The preparation method of the reactive nano shielding masterbatch is as follows: after mixing the rutile type nano titanium dioxide and cerium oxide nanocrystals in a mass ratio of 4:1, adding 1-2% of the total amount of the mixed powder of a coupling agent, controlling the temperature at 50-60℃, and pre-mixing in a high-speed mixer at 600-800r / min for 5-8min, the pre-processed nano mixed powder is obtained. The pre-processed nano mixed powder and dry PP matrix are put into a high-speed mixer in a weight ratio of 4:5, mixed for 10-15min, and then extruded and granulated in a twin-screw extruder.

5. The injection molding grade light transmitting color shifting polypropylene composite of claim 1, wherein: The anti-oxidation light stable compound system is a compound of a high molecular weight hindered amine light stabilizer, a phosphite antioxidant, and a UV absorber in a mass ratio of 2:2:1-4:2:

1.

6. The injection molding grade light transmitting color shifting polypropylene composite of claim 1, wherein: The compatibilizer is maleic anhydride grafted polypropylene (PP-g-MAH) with a grafting rate of 0.8%-1.5%.

7. The injection molding grade light transmitting color shifting polypropylene composite of claim 1, wherein: The toughening agent is one or both of the following block copolymer elastomers: SEBS (hydrogenated styrene-butadiene-styrene triblock copolymer) and ethylene-octene copolymer (POE).

8. The preparation method of the color-changing polypropylene composite material for new energy vehicles according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) Preparation of core-shell-shell structure photochromic microspheres: S1, spiropyran seed liquid preparation: 0.5-1.5g of spiropyran derivative is dissolved in 10-30mL of dichloromethane (oil phase), and 0.2-1.0g of polyvinyl alcohol is dissolved in 50-100mL of water (aqueous phase); the oil phase is injected into the water phase under light protection, and sheared and emulsified at 8000rpm for 5-10min, and then vacuum dried at 30-40℃ for 1-2h to completely remove the solvent; S2, PMMA shell coating: the spiropyran seed liquid obtained in S1, sodium dodecyl sulfate, methyl methacrylate (MMA), and azobisisobutyronitrile are polymerized under nitrogen atmosphere at 60-80℃ in the dark for 6-8h to obtain a core-shell microsphere emulsion (the shell thickness is controlled by adjusting the mass ratio of MMA / spiropyran to 5:1-8:1); S3, polysiloxane surface modification: hydroxyl-terminated polydimethylsiloxane (molecular weight ≈ 2000) is dissolved in tetrahydrofuran (silicone: THF = 1:5-1:8), and is added dropwise to the microsphere emulsion, 1%-3% of dibutyltin dilaurate based on the mass of the silicone is added, and the reaction is carried out at 50°C for 4h; centrifugal separation (7000-8000rpm, 15min), ethanol / water washing 3 times, vacuum drying at 40-60°C for 24h; the whole process is carried out in the dark, and the product is sealed and stored in the dark; (2) Preparation of modified whiskers: The whiskers are dispersed in an ethanol solution to form a dispersion liquid with a solid-liquid ratio of 1:10-1:20, 1%-3% of a coupling agent based on the weight of the whiskers is added, and ultrasonic treatment is carried out at 65-80°C for 0.5-2h, then the whiskers are washed and vacuum dried to obtain surface-modified whiskers; (3) Reactive nano-shielding masterbatch: Rutile-type nano-titanium dioxide and cerium oxide nanocrystals are mixed in a mass ratio of 4:1, then 1-2% of a coupling agent based on the total amount of the mixed powder is added, the temperature is controlled at 50-60°C, and the pre-mixed nano-mixed powder is obtained by pre-mixing in a high-speed mixer at 600-800r / min for 5-8min. The pre-treated nano-mixed powder and dried PP matrix (4:5) are put into a high-speed mixer and mixed for 10-15min, and then extruded and granulated in a twin-screw extruder. (4) Raw material pre-mixing: Polypropylene, toughening agent, core-shell-shell photochromic microspheres, reactive nano-shielding masterbatch, anti-oxidation and light stabilization compound system, compatibilizer, and processing aid are weighed according to the weight percentage, and then added to a high-speed mixer and mixed at a speed of 800-1200r / min for 5-10min to obtain a mixture; (5) Melt blending and extrusion: The pre-mixed material is added to a twin-screw extruder, and the barrel temperature of the extruder is set in sections as follows: zone 1, 160-170°C; zone 2, 175-185°C; zone 3, 185-195°C; zone 4, 190-200°C; and die head, 185-195°C. The screw speed is 300-450r / min, and the vacuum degree is ≤-0.08MPa. Melt blending and extrusion are carried out; (6) Granulation and drying: The extruded material is granulated by an underwater pelletizer, and the particle size is 2-4mm. Then, the granules are dried at 80-100°C for 2-4h to obtain a high-transmittance weatherable and color-changing polypropylene composite material.

9. The production method according to claim 8, characterized by, In step (1), polypropylene, compatibilizer, and toughening agent are dried in an oven at 60-100°C for 0.5-2h to remove water. 10.The color-changing polypropylene composite material for new energy vehicles according to claim 1, characterized in that, The processing aid is one of calcium stearate, magnesium stearate, and zinc stearate.

11. Use of the color-changing polypropylene composite material for new energy vehicles according to any one of claims 1-10, characterized in that, The composite material is suitable for the application scenarios of new energy vehicles, such as lightweight, individualization, and intelligent interaction, and finally meets the requirements of automobile interior and exterior injection molding.

Images