Photochromic master batch as well as preparation method and application thereof

Abstract

The invention relates to the technical field of optical functional polymer materials, and discloses a photochromic master batch as well as a preparation method and application thereof, the photochromic master batch comprises a polycarbonate matrix, a spiropyrane photochromic agent, polyethylene wax and an Irganox1010 antioxidant; the preparation method comprises the following steps: drying the polycarbonate to reduce the moisture content of the matrix; the spiropyrane photochromic agent is subjected to surface modification, so that the dispersity of the spiropyrane photochromic agent is improved; sequentially adding the dried polycarbonate, the modified color-changing agent, the polyethylene wax and the antioxidant into a double-screw extruder for melting and mixing; and cooling and granulating the mixed melt to obtain the photochromic master batch. The antioxidant Irganox1010 is introduced into the photochromic agent, and surface modification treatment is performed on the photochromic agent, so that the color change response speed and the cycle durability are effectively improved, rapid color development in a short time is realized, and high color stability is maintained under multiple rounds of excitation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photo-functional polymer materials, in particular to a photochromic master batch and a preparation method and application thereof. BACKGROUND

[0002] In the fields of intelligent vision, light-responsive packaging, anti-counterfeiting labels, and high-end building window decorations, photochromic materials are widely used in the design of functional polymer products due to their ability to reversibly change color under UV excitation. In environments with varying temperature and humidity and frequent light switching, the light response speed, cycle life, and stability of the material directly determine its practical application performance. However, effectively combining photochromic agents with engineering plastics during large-scale thermal processing has always been a challenge.

[0003] Currently, various technical solutions have been explored to realize the function of photochromic agents. Some methods involve mixing photochromic molecules such as spiropyrans and spirostane ketones with thermoplastic matrices to achieve reversible color change under UV light. Under conditions of stable structure, these materials can meet the color development requirements in low-frequency and static scenarios. Some processes use conventional double-screw mixing or surface coating techniques to optimize the fixation of photochromic agents within the polymer, thereby improving heat resistance and partial environmental adaptability, and have achieved preliminary engineering applications. Meanwhile, there are products on the market that use inert fillers or adjust the viscosity of the matrix to control color development, which have shown certain market performance in specific applications.

[0004] However, existing technologies generally lack systematic treatment of photochromic agent dispersion uniformity and interface stability. Color development processes are prone to regional inconsistencies, surface spots, color deviation problems, and insufficient product appearance stability, making it difficult to scale up. Moreover, under high-temperature extrusion conditions, some untreated photochromic agents decompose, forming color impurities and carbon spots, which severely interfere with the reversible conversion of photochromic structures. Additionally, the strong hygroscopicity of polycarbonate matrices has not been fully considered, and the vaporization disturbance of residual moisture during processing not only affects the rheological behavior but also causes color development failure or material structure damage. Therefore, the present application provides a photochromic master batch and a preparation method and application thereof to solve the above problems. SUMMARY

[0005] To overcome the deficiencies of the prior art, the present application provides a photochromic master batch and a preparation method and application thereof, which solve the problems of uneven dispersion of photochromic agents, poor thermal processing stability, and decreased color change cycle performance in the prior art.

[0006] To achieve the above purposes, the present application is implemented by the following technical solutions: a photochromic master batch comprising the following components by weight: Polycarbonate matrix: 60-70 parts; Spiropyrans photochromic agent: 3-5 parts; Polyethylene wax: 1-3 parts; Irganox1010 antioxidant: 1-2 parts.

[0007] Polycarbonate matrix: Polycarbonate is a high-strength, high-transparency plastic material, which is used as the matrix material of the master batch. It not only gives the photochromic master batch excellent mechanical strength and thermal stability, but also ensures that the color-changing effect is stable in plastic products. The melt index of polycarbonate is controlled between 12-14 g / 10 min, which not only meets the flowability requirements of the material during the melting process, but also ensures the uniform dispersion of the photochromic agent in the matrix.

[0008] Spiropyrans photochromic agent: This kind of photochromic agent can change color under ultraviolet or visible light irradiation, and has a unique photochromic effect. In this invention, methyl red spiropyran or ethyl red spiropyran is selected as the photochromic agent. These substances can respond to changes in light sources and achieve color changes without reducing transparency. By precisely selecting the photochromic agent, the plastic product can exhibit ideal photochromic effect under different environmental light conditions.

[0009] Polyethylene wax: As a dispersant, polyethylene wax can effectively improve the dispersibility of the photochromic agent in the polycarbonate matrix. The wax has a low melting point and good lubricity, which helps to improve the compatibility of the components during mixing and ensures the uniform distribution of the photochromic agent. Through the addition of polyethylene wax, the flowability of the master batch in the subsequent processing process is enhanced, and the friction is reduced, thereby improving the stability during the forming process.

[0010] Irganox1010 antioxidant: Irganox1010 is a widely used antioxidant that can effectively prevent the oxidative degradation of the polycarbonate matrix during high-temperature processing. By adding this antioxidant, the service life of the master batch can be significantly extended, and its stability under long-term high-temperature conditions can be improved, ensuring that the photochromic effect of the master batch during the processing of plastic products is not affected by degradation.

[0011] Overall, the photochromic master batch ensures stable photochromic effect under changes in external light by matching the polycarbonate matrix and spiropyrans photochromic agent, combining the dispersing effect of polyethylene wax and the protection of the antioxidant. The comprehensive optimization of these components improves the adaptability of the master batch in various processing environments.

[0012] Preferably, the spiropyrans photochromic agent is selected from methyl red spiropyran or ethyl red spiropyran.

[0013] The methyl red spiropyran or ethyl red spiropyran is selected as the photochromic agent in the photochromic masterbatch, which can achieve stable color change under ultraviolet irradiation and provide obvious photochromic effect without affecting the transparency. Due to the molecular structure characteristics, the spiropyran photochromic agent can cause molecular orbital transition under specific wavelength of light, thereby causing the change of visible light absorption characteristics and exhibiting color change. The methyl red spiropyran and the ethyl red spiropyran have slight differences in molecular structure, but both can provide good stability and repeated color changing ability, and are suitable for photochromic products with high requirements.

[0014] Preferably, the Irganox 1010 antioxidant is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester.

[0015] The Irganox 1010 antioxidant is an antioxidant widely used in polymers, which can effectively inhibit the oxidative degradation reaction of the polycarbonate matrix caused by high temperature during processing and use. The antioxidant can react with free radicals through the phenolic group in its molecular structure, thereby interrupting the progress of the oxidation chain reaction and protecting other components in the photochromic masterbatch from thermal degradation. The innovation of using the Irganox 1010 antioxidant lies in its improvement of the thermal stability of the photochromic masterbatch, which ensures that the color changing effect of the masterbatch will not be affected under high temperature conditions during injection molding or film blowing, thereby improving the service life of the photochromic plastic product.

[0016] Preferably, the melt index of the polycarbonate is 12-14 g / 10 min, and the molecular weight of the polyethylene wax is 2000-4000.

[0017] The melt index of the polycarbonate and the molecular weight of the polyethylene wax directly affect the flowability and dispersibility of the masterbatch. The melt index of the polycarbonate is controlled between 12-14 g / 10 min to ensure smooth flow of the material during melting, avoiding the situation of too thick or difficult to handle. The molecular weight of the polyethylene wax is set between 2000-4000, so that the wax can provide effective dispersion and lubrication performance without damaging the matrix structure. The interaction of the two ensures the uniform dispersion of the photochromic agent in the matrix, and also ensures the processing stability of the photochromic masterbatch in the subsequent processing process.

[0018] A preparation method of a photochromic masterbatch, comprising the following steps: S1, drying the polycarbonate matrix to obtain a pretreated material with low moisture content; S2, surface modification treatment is performed on the spiropyran photochromic agent to improve its dispersibility in the matrix; S3, sequentially feeding the pretreated polycarbonate, surface-modified photochromic agent, polyethylene wax and antioxidant into a twin-screw extruder for melt mixing; S4, cooling the mixed melt and performing a granulation process to obtain a photochromic masterbatch.

[0019] Firstly, in the raw material preparation stage, the treatment of polycarbonate matrix and photochromic agent directly affects the performance of the final masterbatch. The melt index of polycarbonate matrix as the main material is precisely controlled to ensure the flowability of the matrix material in the molten state, which is crucial for the subsequent mixing process. The surface modification treatment of the photochromic agent as a functional component can significantly improve its dispersibility in the matrix and prevent the degradation of the photochromic effect. The role of polyethylene wax is to provide lubrication and enhance the compatibility between components, while the design of its molecular weight ensures the appropriate viscosity during the processing.

[0020] Secondly, in the mixing process, the fusion of polycarbonate matrix with other components is the key to the preparation process. The temperature control and screw speed setting in this process are very precise to ensure the uniform dispersion and sufficient reaction of each component. Specifically, the polycarbonate matrix is treated by appropriate temperature and speed conditions during the melting process, which not only improves the flowability of the matrix but also provides conditions for the uniform dispersion of the photochromic agent.

[0021] Preferably, the drying treatment of the polycarbonate matrix comprises: placing the polycarbonate particles in a vacuum drying oven and drying at 75-85℃ for 3-5 hours; the moisture content of the dried polycarbonate is controlled to be not more than 0.02wt%, and it is sealed and stored under nitrogen protection.

[0022] The drying treatment of the polycarbonate matrix plays an important role in the entire preparation method. High humidity of the polycarbonate matrix may cause hydrolysis reaction in the subsequent melting process, which affects the molecular structure of the polymer and the final processing performance. Therefore, the drying process must be strictly controlled to ensure that the polycarbonate exhibits the best performance in the melting process. In this invention, the polycarbonate matrix is placed in a vacuum drying oven, and the drying temperature is set at 75-85℃, which can effectively remove moisture without causing degradation of the polycarbonate. The moisture content of the dried polycarbonate is controlled in a very low range, avoiding the negative effects of hydrolysis reaction on the performance of the polymer, thereby ensuring that the photochromic effect of the masterbatch is not affected.

[0023] Preferably, the surface modification treatment of the spiropyran photochromic agent comprises: mixing the spiropyran photochromic agent with 1-3wt% KH-550 silane coupling agent; ultrasonic dispersion for 20-40 minutes in anhydrous ethanol; Then dry at 60-80℃ for 1-2 hours to obtain the surface-modified photochromic agent.

[0024] Since the photochromic agent itself may have poor dispersibility, direct addition to the polycarbonate matrix may lead to uneven distribution, thereby affecting its photochromic effect. In order to solve this problem, the present application uses KH-550 silane coupling agent for surface modification, which improves the dispersibility and stability of the photochromic agent in the polycarbonate matrix through chemical reaction between the silane coupling agent and the photochromic agent molecules. Surface modification not only enhances the compatibility of the photochromic agent with the matrix, but also prevents the aggregation or precipitation of the photochromic agent during the mixing process, ensuring its excellent photochromic effect.

[0025] Preferably, the pre-processed components are melt mixed, including: The dried polycarbonate is heated to 230-260℃ in an extruder for melting; During the melting process, the screw rotation speed is set to 200-400 rpm for 5-8 minutes; Polyethylene wax, surface-modified photochromic agent and Irganox1010 antioxidant are added in sequence; After adding the photochromic agent, the rotation speed is increased to 500-600 rpm and mixed for 4-6 minutes; After adding the antioxidant, the rotation speed is adjusted to 250-350 rpm and mixed for another 1-3 minutes to ensure uniform mixing and thermal stability.

[0026] The key to the melt mixing process is the precise control of temperature and rotation speed. By controlling the melting state of the polycarbonate matrix, it can achieve the desired fluidity within a certain temperature range, thereby ensuring uniform mixing of the components. The control of rotation speed is also very important. Appropriate screw rotation speed can improve the dispersibility of the photochromic agent in the matrix, while too high or too low rotation speed may lead to uneven dispersion or excessive shear, affecting the performance of the final masterbatch. In the present application, by adjusting the screw rotation speed and melting temperature, uniform distribution of the components is successfully achieved, ensuring the stability of the photochromic effect.

[0027] The cooled melt after mixing is cooled and granulated, including: The mixed melt is extruded from the die head into a water cooling tank, and the cooling water temperature is controlled at 20-30℃; After cooling and shaping, the masterbatch particles with a diameter of 2-3mm and a length of 3-5mm are obtained by underwater pelletizing system.

[0028] Cooling and granulation is the last step in the preparation of photochromic masterbatch, its main role is to ensure the stability and processability of the masterbatch. By controlling the water temperature in the water cooling tank in the range of 20~30℃, the good fluidity and stability of the masterbatch during cooling can be effectively ensured, and the quality instability of the masterbatch caused by uneven cooling can be avoided. In addition, the underwater cutting system can accurately cut the required particle size and length while quickly cooling, thereby ensuring the uniformity and processability of the masterbatch.

[0029] The application of a photochromic masterbatch in plastic products, the photochromic plastic products are injection molding or blown film products.

[0030] In the injection molding process, the photochromic masterbatch of the application can be uniformly dispersed in the polycarbonate matrix, and during the injection molding process, due to its excellent fluidity and molding stability, it can ensure that the masterbatch does not appear to be precipitated or layered during the entire injection molding process; in the blown film molding process, the photochromic masterbatch of the application also exhibits excellent performance, due to the uniform dispersion of the masterbatch, the surface of the plastic film during the blown film process can uniformly exhibit the photochromic effect.

[0031] In summary, the present application includes at least one of the following beneficial technical effects: 1. The application effectively improves the color response speed and cycle durability by introducing antioxidant Irganox1010 into the photochromic agent and surface modification treatment of the color changing agent, realizes fast color development in a short time and maintains high color stability under multiple excitation, compared with the photochromic material in the prior art which is not subjected to antioxidant treatment or surface modification, solves the problems of slow color response and performance degradation after multiple cycles, has better light response efficiency and long-term stability; 2. The application realizes uniform dispersion and morphology stability control of the photochromic component in the polycarbonate matrix by introducing polyethylene wax dispersant during the preparation of the masterbatch and combining high temperature and high shear extrusion process, so that the color development uniformity of the final product is improved, the ΔE fluctuation range is reduced, and the defects such as large color difference and obvious surface spots caused by agglomeration or uneven distribution of the color changing agent in the prior art are overcome, ensuring the consistency and appearance quality of the product; 3. The application selects a spiropyran color changing agent with higher thermal stability, and strictly controls the water content of the polycarbonate matrix, effectively avoids thermal degradation and gasification disturbance in the process by optimizing the heat processing conditions, compared with the color changing agent with poor thermal stability or the undried matrix used in the prior art, the application effectively improves the processing stability, significantly reduces the surface defects such as black spots and bubbles, improves the yield and predictability of the process. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1is a flow chart of the preparation method of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the specification of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0034] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0035] Please refer to the drawings of the present application Figure 1 : Example 1 Raw material ratio (by weight fraction): Polycarbonate (melt index 13 g / 10 min): 65 parts; Methyl red spiropyran: 3.5 parts; Polyethylene wax (molecular weight about 3000): 2 parts; Irganox 1010 antioxidant: 1.5 parts.

[0036] Preparation steps: 1. Drying of the substrate: The polycarbonate was placed in a vacuum drying oven and dried at 80°C for 4 hours. After drying, the moisture content was controlled to be ≤0.02wt%, and the polycarbonate was stored in a sealed container.

[0037] 2. Surface modification of the photochromic agent: Methyl red spiropyran was mixed with 2% KH-550 by mass fraction, ultrasonically dispersed in anhydrous ethanol for 30 minutes, and then dried at 70°C for 1.5 hours.

[0038] 3. Melt mixing: The polycarbonate was heated to 240°C to start melting, and the initial screw speed was set to 300 rpm. The polyethylene wax, modified spiropyran, and antioxidant were added in sequence, and the speed was adjusted to 550 rpm and 350 rpm in stages, and the total mixing time was about 10 minutes.

[0039] 4. Cooling and granulation: The extruded melt was cooled in a 25°C water tank, and an underwater pelletizing system was used to produce master batches with a particle size of 2.5 mm and a length of 4 mm.

[0040] Example 2 Raw material ratio (by weight fraction): Polycarbonate (melt index 12 g / 10 min): 60 parts; Ethyl red spiropyran: 5 parts; Polyethylene wax: 3 parts; Irganox 1010 antioxidant: 2 parts.

[0041] Preparation steps: 1. Matrix drying: The polycarbonate was dried at 75°C for 5 hours to ensure that the water content was less than 0.02 wt%.

[0042] 2. Photochromic agent treatment: Ethyl rubrospiran was mixed with 3 wt % KH-550, ultrasonicated in anhydrous ethanol for 40 minutes, and then dried at 60° C. for 2 hours.

[0043] 3. Mixing process: Polycarbonate was melted at 230°C, with an initial rotation speed of 200 rpm, which was gradually increased to 600 rpm. The order of addition was polyethylene wax → photochromic agent → antioxidant, and the mixing process was strictly controlled to be completed within 12 minutes.

[0044] 4. Cooling and pelletizing: The melt was extruded through the die head and cooled in a 20°C water tank, and then passed through a pelletizer to obtain masterbatch particles (particle size 3 mm, length 3.5 mm).

[0045] Example 3: Raw material ratio (by weight): Polycarbonate (melt index 14 g / 10 min): 70 parts; methyl erythrospiropyran: 4 parts; polyethylene wax: 1 part; Irganox 1010 antioxidant: 1 part.

[0046] Preparation steps: 1. Matrix drying: The polycarbonate was vacuum dried at 85°C for 3 hours to ensure a low humidity environment.

[0047] 2. Modification of color changing agent: Methyl rubrospiran and 1 wt% KH-550 were ultrasonically treated in ethanol for 20 minutes and dried at 80°C for 1 hour.

[0048] 3. Mixing process: The polycarbonate melt temperature was set at 260°C and the initial rotation speed was 250 rpm. The addition order was the same as above, but the peak screw speed was controlled at 500 rpm to ensure efficient mixing in a short time to inhibit thermal degradation.

[0049] 4. Granulation process: After the melt is extruded, it is rapidly cooled in a 30°C water tank and pelletized into 2 mm × 3 mm particles using an underwater pelletizing system.

[0050] Comparative Example 1: Compared with Example 1, the difference is that the Irganox 1010 antioxidant is not added, and the rest are the same.

[0051] Comparative Example 2: Compared with Example 2, no polyethylene wax dispersant was added, and the rest were the same.

[0052] Comparative Example 3: Compared with Example 2, no polyethylene wax dispersant was added, and the rest were the same.

[0053] Comparative Example 4: Compared with Example 2, the heating temperature was changed from 230-260°C to 200°C constant temperature, and the rest were the same.

[0054] Comparative Example 5: Compared with Example 3, the spiropyran color-changing agent was replaced by a general compound with poor thermal stability (spirostane ketone, same concentration), and the rest were the same.

[0055] Comparative Example 6: Compared with Example 3, the drying step was omitted, and a polycarbonate substrate at room temperature without pretreatment was used, and the rest were the same.

[0056] Experiment 1: Purpose of the experiment: To verify the effect of the antioxidant Irganox 1010 introduced in the present application and the surface modification treatment of the photochromic agent on improving the color-changing response speed, cycle stability, and color retention.

[0057] Experimental object: Example 1 (complete formula); Comparative Example 1 (without antioxidant); Comparative Example 2 (without surface modification).

[0058] Experimental equipment and materials: UV light source (365nm LED light source); color difference meter (to measure ΔE); constant temperature light box (for cycle irradiation); digital camera + image processing software (quantitative analysis of color change); hot air drying oven.

[0059] Experimental steps: 1. Sample preparation: According to the formula of Example 1, Comparative Example 1, and Comparative Example 2, master batches were prepared by a twin-screw extruder, and standard injection molding conditions were used to prepare flat samples with a thickness of 1mm.

[0060] 2. Color-changing response test: Under the conditions of constant temperature 23°C, light intensity 10mW / cm 2 The sample was exposed to 365nm UV light source, and the color-changing time was recorded by color difference meter (ΔE≥15 as the standard for color completion).

[0061] 3. Cycle stability test: The sample was placed in an alternating light / shade environment, 3 minutes per cycle (2 minutes of irradiation + 1 minute of shading), for a total of 100 cycles. The ΔE value was recorded every 20 times to test the deviation between the initial color and the recovered color.

[0062] 4. Color recovery integrity test: Compare whether the color after each shading can be recovered to the initial state, and express the recovery effect with the percentage of ΔE drop (experimental data is shown in Table 1).

[0063] Table 1: Test results of photochromic response and cycle stability From Table 1, it can be seen that: The response speed of the photochromic master batch in this experiment shows strong component dependence. By introducing a spiropyran photochromic agent and surface modifying it, Example 1 effectively improves its dispersion uniformity in the polycarbonate matrix, thereby speeding up the structure transition process induced by light response, so that the color change can be completed within 2 seconds. Without modification (Comparative Example 2), the response speed is significantly slowed down due to the high interface energy barrier.

[0064] In the color change cycle, the Irganox1010 antioxidant introduced in Example 1 effectively inhibits the oxidative degradation induced by light, delaying the photo fatigue process of the color changing agent. Therefore, it still maintains a high ΔE value and recovery integrity after 100 times of UV-dark cycles, while Comparative Example 1, which lacks the antioxidant, shows obvious performance degradation, with a significant drop in ΔE value and a color recovery rate of less than 75%, indicating that the antioxidant plays a key role in improving cycle stability.

[0065] Mechanically, spiropyran compounds undergo ring opening to generate colored structures under UV excitation, and recover to the closed ring state in the dark state. If the dispersion is insufficient or the structure is degraded, the molecules cannot efficiently complete the open-closed ring conversion, resulting in slow response and incomplete color recovery. The present application effectively avoids the above problems through precise interface control and thermal stability strategies, achieving the synergistic performance output of fast response, high stability and excellent cycle life.

[0066] Experiment 2: Purpose of the experiment: Verify the influence of dispersant (polyethylene wax) and extrusion temperature setting on the distribution uniformity and color development consistency of the photochromic agent in the polycarbonate matrix, further supporting the technical advantages of the present application in interface control and thermal processing parameter optimization.

[0067] Experimental object: Example 2 (complete formula); Comparative Example 3 (without polyethylene wax); Comparative Example 4 (reduced processing temperature).

[0068] Test equipment and materials: Scanning Electron Microscope (SEM); Digital image acquisition system (surface gray scale analysis); Color difference meter (multi-region delta E measurement); Injection molding equipment (preparation of test bars).

[0069] Experimental procedure: 1. Sample preparation: Masterbatch was prepared according to Example 2 and its Comparative Examples 3, 4, and injection molded into 1 mm thick standard bars for surface and internal structure testing.

[0070] 2. Color development uniformity analysis: After color development of the sample under UV light, high-resolution images were taken of the bar surface, and surface color development uniformity was calculated by image gray scale variance analysis.

[0071] 3. Microscopic distribution observation: The cross-section of the sample was selected, and the scanning electron microscope (SEM) was used to image the distribution state of the color change agent to evaluate the occurrence of agglomeration or interface defects.

[0072] 4. Multi-region delta E test: Nine positions were evenly selected on the surface of the bar, and the delta E value after color development was tested at each position, and the standard deviation was calculated to represent the color development consistency (experimental data is shown in Table 2).

[0073] Table 2: Color development consistency and dispersion test results Sample number Surface grayscale variance ΔE standard deviation SEM observation results (subjective score, 0-10) Example 2 5.3 0.84 9 (evenly distributed, with a small amount of micro-agglomeration) Comparative Example 3 12.8 2.71 4 (obvious agglomeration, interface stratification) Comparative Example 4 9.1 1.94 6 (uneven distribution, weak local enrichment) As shown in Table 2: In the design of the present application, the addition of polyethylene wax as a dispersant plays a key role in color development uniformity. The photochromic agent in Example 2 forms a good dispersion structure in the matrix, and the surface color distribution is consistent during color development, with significantly lower image gray scale variance and delta E standard deviation than the comparative sample. Comparative Example 3 lacks a dispersant, and the color change agent is unevenly distributed in the polymer matrix, showing severe agglomeration under a scanning electron microscope, indicating that the interface wetting and particle dispersion effect are severely impaired.

[0074] From the microscopic structure, low-temperature processing (Comparative Example 4) retains the formula structure, but due to insufficient energy input, the screw shear force is weak, and the color change agent particles are not fully dispersed, forming local enrichment areas. SEM imaging verifies that it produces larger particle agglomerates in local areas, affecting color development uniformity. This local enrichment also leads to significant fluctuations in the delta E value between different regions of the bar, and the color development consistency decreases.

[0075] Mechanistically, photochromic agents need to be well dispersed to be fully exposed to the light field to trigger the light-responsive sites in their molecular structure. When the photochromic agents are aggregated into groups or poorly adhered to the substrate interface, their response efficiency will be significantly reduced, and local stress inhomogeneity will also easily cause processing defects. By improving the interfacial tension and increasing the wettability of the photochromic agent in the substrate with polyethylene wax, and supplemented by high-temperature and high-shear mixing, the internal structure of the material system can be maximized to ensure uniformity, extensive light response area, and consistent performance and predictability of the final product.

[0076] Experiment 3: Purpose of the experiment: To evaluate the effects of spiropyran photochromic agents and drying treatment of polycarbonate before processing on thermal stability, energy consumption during processing, and defect control of the final product.

[0077] Experimental object: Example 3 (complete formulation); Comparative Example 5 (replace photochromic agent); Comparative Example 6 (cancel substrate drying).

[0078] Test equipment and materials: Thermogravimetric analyzer (TGA); torque recording system (built-in extrusion equipment); injection molding defect analysis system (high-definition imaging + defect classification).

[0079] Experimental steps: 1. Sample preparation and preliminary treatment: Prepare master batches according to the corresponding formulations. Example 3 and Comparative Example 6 only differ in whether the polycarbonate is dried or not; Comparative Example 5 replaces the spiropyran photochromic agent with an equal amount of spirostane material, and the others remain the same.

[0080] 2. Thermogravimetric analysis (TGA): Take each master batch sample and heat it from room temperature to 600°C under nitrogen atmosphere, and record the temperatures corresponding to 5% and 50% mass loss.

[0081] 3. Processing torque fluctuation test: Record the screw torque change trend during extrusion processing to evaluate the processing stability of the material (the greater the fluctuation, the more obvious the inhomogeneity of viscoelasticity or water content).

[0082] 4. Injection molding product defect statistics: Make standard size samples and record the proportion of surface bubbles, color spots, and carbonized particles in each batch of samples to evaluate the appearance quality (experimental data is shown in Table 3).

[0083] Table 3: Thermal stability and processing defect test results From Table 3, we can see that: Compared to traditional spirostanones, spiropyran-based color-changing agents possess higher photoresponsiveness and thermal stability in their molecular structure. The color-changing agent in Example 3 exhibited a high decomposition onset temperature and a slow decomposition rate. TGA results showed that its structural integrity under heating conditions was superior to that of Comparative Example 5. Comparative Example 5 was susceptible to structural cracking and carbonization under high temperature conditions, ultimately forming a large amount of black impurities in the injection-molded strips, severely impacting the product's appearance and mechanical uniformity. This demonstrates the tolerance of the color-changing agent system selected in this invention to processing heat and its decisive role in the stability of the final product.

[0084] Polycarbonate is highly hygroscopic. If processed without sufficient drying, moisture will rapidly vaporize during high-temperature extrusion, causing internal pressure disturbances. This can lead to dramatic fluctuations in extrusion torque and unstable processing. In Comparative Example 6, the torque fluctuations were significantly increased, and numerous bubbles and ripples appeared in the finished injection molded product, indicating that the presence of moisture significantly affects the material's controllable processing properties. However, the present invention effectively reduces internal stress sources through rigorous drying pretreatment.

[0085] This invention utilizes a systematic design from the perspective of processing mechanisms. The stable aromatic ring structure of the spiropyran color-changing agent makes its thermal responsiveness more controllable and less susceptible to inactivation under hot melt conditions. The fully dried polycarbonate provides a volatile-free background, avoiding micro-explosions and interfacial cracking, thereby enabling a continuous and predictable melt processing. These two factors work together to ensure the integrity of the masterbatch structure and the yield rate of downstream injection molded products, demonstrating the systemic advantages of this invention in matching material selection with process.

[0086] The examples of this specific embodiment are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, any equivalent changes made based on the structure, shape, and principle of this application should be included in the scope of protection of this application.

Claims

1. A photochromic masterbatch, characterized in that: The composition comprises the following components in parts by weight: Polycarbonate matrix: 60-70 parts; Spiropyran photochromic agent: 3-5 parts; Polyethylene wax: 1-3 parts; Irganox1010 antioxidant: 1 to 2 parts.

2. The photochromic masterbatch according to claim 1, characterized in that: The spiropyran photochromic agent is selected from methyl rubrospiropyran or ethyl rubrospiropyran.

3. The photochromic masterbatch according to claim 1, characterized in that: The Irganox 1010 antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

4. The photochromic masterbatch according to claim 1, characterized in that: The melt index of the polycarbonate is 12 to 14 g / 10 min, and the molecular weight of the polyethylene wax is 2000 to 4000.

5. A method for preparing a photochromic masterbatch, applied to the photochromic masterbatch according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Drying the polycarbonate substrate to obtain a pretreated material with low moisture content; S2. performing surface modification treatment on the spiropyran photochromic agent to improve its dispersibility in the matrix; S3, sequentially putting the pretreated polycarbonate, surface-modified photochromic agent, polyethylene wax and antioxidant into a twin-screw extruder for melt mixing; S4. Cooling the mixed melt and granulating it to obtain a photochromic masterbatch.

6. The method for preparing a photochromic masterbatch according to claim 5, characterized in that: The drying process of the polycarbonate substrate comprises: Place the polycarbonate pellets in a vacuum drying oven and dry them at 75-85°C for 3-5 hours; The moisture content of the polycarbonate after drying is controlled to be no more than 0.02 wt %, and the polycarbonate is sealed and stored under nitrogen protection.

7. The method for preparing a photochromic masterbatch according to claim 5, characterized in that: The surface modification treatment of the spiropyran photochromic agent comprises: Mixing a spiropyran photochromic agent with 1-3 wt% of a KH-550 silane coupling agent; Ultrasonic dispersion in anhydrous ethanol for 20 to 40 minutes; The reaction mixture is then dried at 60-80° C. for 1-2 hours to obtain a surface-modified photochromic agent.

8. The method for preparing a photochromic masterbatch according to claim 5, characterized in that: The pretreated components are melt-mixed and kneaded, comprising: The dried polycarbonate is heated to 230-260°C in an extruder to melt; During the melting process, the screw speed was set at 200–400 rpm for 5–8 minutes; polyethylene wax, surface-modified photochromic agent, and Irganox 1010 antioxidant were added in sequence; After adding the photochromic agent, increase the speed to 500-600 rpm and mix for 4-6 minutes; After adding the antioxidant, adjust the speed to 250-350 rpm and mix for another 1-3 minutes to ensure uniform mixing and thermal stability.

9. The method for preparing a photochromic masterbatch according to claim 5, characterized in that: The process of cooling the mixed melt and granulating the mixed melt comprises: The mixed melt is extruded from the die head and enters the water cooling tank, and the cooling water temperature is controlled at 20-30℃; After cooling and forming, the pellets are cut into masterbatch particles with a diameter of 2 to 3 mm and a length of 3 to 5 mm through an underwater pelletizing system.

10. Use of the photochromic masterbatch according to any one of claims 1 to 4 in a plastic product, wherein the photochromic plastic product is an injection molded or blown film product.

Images