Preparation method of modified carbon black for plastic

Abstract

The invention relates to the field of carbon black preparation, and particularly discloses a preparation method of modified carbon black for plastics. The invention relates to a preparation method of modified carbon black for plastics. The preparation method comprises the following steps: (1) crushing original carbon black into primary particles with the particle size of 20-50nm through high-pressure airflow; (2) the crushed carbon black is subjected to rolling granulation in a rotary granulator, meanwhile, a polyethylene wax emulsion with the solid content of 30%-40% is sprayed in an atomized mode, the adding amount of polyethylene wax is 3%-5% of the mass of the carbon black, and the granulation temperature is 120-150 DEG C; and (3) drying for 10-15 seconds under the hot air condition of 180-220 DEG C to obtain the wax layer cured and coated carbon black particles. The preparation method of the modified carbon black for plastics has the advantages of high color fastness and low migration rate.

Description

Technical Field

[0001] The present application relates to the field of carbon black preparation, and more specifically, to a method for preparing modified carbon black for plastics. Background Art

[0002] Carbon black is a black powdery substance formed by incomplete combustion or pyrolysis of hydrocarbons in the gas phase under strictly controlled process conditions. Its main component is elemental carbon, and it also contains small amounts of oxygen, hydrogen, and sulfur. Carbon black particles are approximately spherical, with a particle size ranging from 10-500μm. Many particles often fuse or agglomerate into three-dimensional dendritic or fibrous aggregates. In the industrial field, carbon black is widely used. In rubber processing, it is an indispensable reinforcing agent and filler that can significantly improve the wear resistance, tear strength and other properties of rubber products. It is a key raw material in the rubber industry. In the plastics, inks, coatings and other industries, carbon black is used as a high-quality colorant, giving products a stable and long-lasting color. However, existing carbon black faces color fastness problems in practical applications. Taking the dyeing of plastic products as an example, when carbon black is used as a black pigment, the color of the product is prone to fading during long-term use, especially when it is affected by environmental factors such as light, high temperature, and humidity. In outdoor plastic products, after long-term exposure to sunlight, the surface color will gradually become lighter and lose its original color. This is mainly because the carbon black particles in the product fail to fully combine with the matrix material. When exposed to external environmental factors, the carbon black particles are easily eroded, resulting in a decrease in color stability. Moreover, the properties of carbon black itself, such as particle size and surface chemical properties, will also affect its binding force with the matrix material, thereby affecting color fastness. At the same time, carbon black migration is also a prominent issue. Carbon black precipitation is common in rubber products. During long-term use or storage of products like rubber strips and sealing strips, carbon black particles can migrate from the rubber matrix to the surface, forming a gray-black powder or film. This not only seriously affects the product's appearance, making it look old and unsightly, but can also reduce its performance. Summary of the Invention

[0003] In order to solve the above problems, the present application provides a method for preparing modified carbon black for plastics.

[0004] The present application provides a method for preparing modified carbon black for plastics using the following technical solution: A method for preparing modified carbon black for plastics comprises the following steps: (1) The raw carbon black is crushed into primary particles with a particle size of 20-50 nm by high-pressure air flow; (2) The crushed carbon black is rolled and granulated in a rotary granulator, and a polyethylene wax emulsion with a solid content of 30%-40% is sprayed at the same time, the amount of polyethylene wax emulsion added is 3%-5% of the mass of the carbon black, and the granulation temperature is 120-150°C; (3) Drying under hot air conditions at 180-220°C for 10-15 seconds to obtain carbon black particles coated with a solidified wax layer.

[0005] By adopting the above technical solution and using high-pressure airflow pulverization technology, the carbon black particle size is precisely controlled to the nanometer level, greatly increasing the carbon black's specific surface area. This allows the carbon black to come into closer contact with the plastic matrix, achieving a more uniform dispersion within the plastic, effectively avoiding localized color darkening or fading caused by agglomeration, and significantly improving the overall color consistency and stability of plastic products. Furthermore, the evenly dispersed carbon black is less likely to shift under the influence of external factors (such as temperature fluctuations and friction), fundamentally reducing the risk of migration and ensuring the durability of the product's appearance and performance.

[0006] Optionally, the airflow pulverization in step (1) includes two-stage processing: The carbon black is crushed to 50-100 nm under a pressure of 0.4-0.6 MPa; Particles with D90≤50nm were screened out at a rotation speed of 2000-3000 rpm.

[0007] By employing this technical solution, a two-stage processing method achieves precise control over carbon black particle size. The first stage of coarse crushing initially reduces the particle size, while the second stage of high-speed screening ensures particle size uniformity. When dispersed in a plastic matrix, the narrowly distributed carbon black forms a more stable dispersion, preventing the loose bonding of some carbon black to the plastic due to particle size variations, thereby effectively preventing color fading caused by uneven particle size. Furthermore, the uniform particle size ensures that the carbon black is evenly distributed within the plastic, further suppressing migration and ensuring consistent product quality.

[0008] Optionally, the wax emulsion is atomized in step (2) using a centrifugal atomizing nozzle with an atomizing pressure of 0.2 MPa and a droplet size of ≤50 μm, ensuring that the surface coverage of the carbon black particles is ≥95%.

[0009] By adopting this technical solution and setting specific centrifugal atomization parameters, the polyethylene wax emulsion is fully atomized, forming a continuous coating with high coverage on the carbon black surface. This coating acts as a barrier, isolating the carbon black from the external environment, preventing it from being eroded by ultraviolet rays, moisture, and other factors, and effectively improving color fastness. Furthermore, the physical barrier restricts the free movement of carbon black particles, effectively inhibiting their migration to the surface of the plastic product or into other media, even during long-term use or environmental changes, maintaining a clean appearance and stable performance.

[0010] Optionally, the wax emulsion is a composite wax system, which includes 70%-80% polyethylene wax and 20%-30% polar modified wax in terms of mass percentage.

[0011] By employing this technical solution, the composite system of polyethylene wax and polar-modified wax achieves both lubrication and enhanced bonding. The polyethylene wax improves the fluidity of carbon black during plastic processing, facilitating smoother dispersion. The polar-modified wax, through its polar groups, interacts with the carbon black and plastic matrix, strengthening the bond between them. This synergistic effect results in a stable dispersion of carbon black within the plastic, making it less susceptible to separation from the plastic matrix due to external forces or environmental factors. This effectively improves the color stability of plastic products and reduces the likelihood of carbon black migration.

[0012] Optionally, the polar modified wax is selected from one of oxidized polyethylene wax and maleic anhydride grafted wax.

[0013] By adopting this technical solution, the polar groups contained in the oxidized polyethylene wax and maleic anhydride-grafted wax can chemically react with the functional groups on the surface of carbon black and the molecules of the plastic matrix, forming a chemical bond. This chemical bond greatly enhances the bond strength between the carbon black and the plastic matrix, firmly fixing the carbon black within the plastic and significantly improving the color fastness of the plastic product. At the same time, the strong chemical bond limits the migration of carbon black particles, effectively preventing the precipitation or migration of carbon black from the plastic even in harsh environments, thus ensuring product quality.

[0014] Optionally, an ethanol solution containing a silane coupling agent at a mass concentration of 1-3% is sprayed onto the surface of the dried carbon black particles and reacted at 60-80° C. for 10-12 minutes.

[0015] By employing this technical solution, the silane coupling agent forms a "molecular bridge" between the carbon black and the plastic matrix through a chemical reaction. One end condenses with the carbon black's surface hydroxyl groups, while the other reacts or entangles with the plastic matrix's organic functional groups. This strong interfacial bonding tightly connects the carbon black to the plastic matrix, effectively preventing carbon black migration due to external factors during the use of the plastic product. At the same time, this tight bond reduces external influences on the carbon black, significantly improving the durability and stability of the plastic product's color, and enhancing color fastness.

[0016] Optionally, the carbon black particles obtained in step (3) are placed in a fluidized bed, and hexamethyldisilazane vapor and tetraethoxysilane vapor are introduced, wherein the volume ratio of the hexamethyldisilazane vapor to the tetraethoxysilane vapor is 1:(2.8-3.2), and the reaction is carried out at 115-120°C to form a dense silica layer on the surface of the wax layer.

[0017] The resulting dense silica layer, created through this technical solution, possesses excellent chemical stability and barrier properties, providing additional protection for carbon black. It effectively blocks the erosion of carbon black by ultraviolet rays, chemicals, and other factors, significantly improving the color fastness of plastic products. Furthermore, the hard, continuous, dense layer firmly binds carbon black particles, preventing them from migrating within the plastic product or to the outside world, ensuring that the product's appearance and performance are unaffected by carbon black migration over the long term.

[0018] Optionally, the thickness of the dense silicon dioxide layer is controlled to be 20-50 nm.

[0019] By employing this technical solution, the thickness of the dense silica layer is precisely controlled, ensuring that it provides sufficient barrier and protection capabilities while maintaining the dispersion of carbon black in the plastic. The appropriate thickness effectively protects carbon black from external damage, preventing migration and color fading, while also avoiding carbon black agglomeration caused by excessive thickness, ensuring uniform dispersion of the modified carbon black during plastic processing. This maximizes the color fastness of plastic products and inhibits migration, guaranteeing product processing quality and performance.

[0020] In summary, this application has the following beneficial effects: 1. This application uses high-pressure airflow pulverization (two-stage treatment to control D90 ≤ 50nm) to refine the carbon black primary particles to 20-50nm, significantly increasing the specific surface area and forming a nano-scale uniform dispersion system of carbon black in the plastic matrix. This process eliminates the agglomeration phenomenon caused by uneven particle size in traditional carbon black, avoiding photooxidative fading caused by localized excessive color. It also reduces carbon black migration caused by stress differences through uniform interfacial bonding, building a foundation for stability from the physical dispersion level.

[0021] 2. In this application, it is preferred to use a composite system composed of 70%-80% polyethylene wax and 20%-30% polar modified wax (oxidized polyethylene wax / maleic anhydride grafted wax), and achieve a wax layer coating with a surface coverage of ≥95% by centrifugal atomization. Among them, the polyethylene wax forms a flexible physical barrier to block the erosion of carbon black by external ultraviolet rays and moisture; the polar modified wax forms chemical bonds with the surface functional groups of carbon black and the plastic matrix through carboxyl and anhydride groups to enhance the interfacial bonding strength. This synergistic effect not only improves the color stability (reduces fading caused by light and heat), but also inhibits the migration of carbon black to the matrix surface or external medium through the dual mechanism of "physical barrier + chemical anchoring".

[0022] 3. The method of this application constructs an inorganic-organic composite protective layer by grafting a "molecular bridge" onto the carbon black surface using a silane coupling agent (condensation of silane alkoxy groups with carbon black hydroxyl groups, entanglement of organic functional groups with the plastic matrix), and forming a 20-50nm dense silica layer (controlled reaction of hexamethyldisilazane and tetraethoxysilane) on the surface of the wax layer. The silica layer's high chemical stability blocks ultraviolet light and chemical corrosion, improving color fastness. Simultaneously, the rigid, dense structure and interfacial bonding of the silane coupling together restrict the movement of carbon black particles, effectively inhibiting migration even under harsh conditions such as high temperature and friction. Furthermore, controlled thickness prevents dispersibility degradation, achieving a balance between performance and processability. DETAILED DESCRIPTION

[0023] The present application is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources. Example

[0024] Example 1 A method for preparing modified carbon black for plastics: raw material: Original carbon black: average particle size 15 μm, DBP absorption value 120 cm 3 / 100g; Polyethylene wax emulsion: solid content 35%, melting point 102°C, Dow Chemical PE-520.

[0025] Air flow crushing: The raw carbon black was fed into a fluidized bed airflow mill (QYF-800 model), introduced with 0.5 MPa high-pressure air, and pulverized to a median particle size of D50 = 35 nm.

[0026] Rotary granulation and wax coating: The crushed carbon black was fed into a rotary granulator (ZL-200 model, speed 45 rpm), and the cylinder temperature was maintained at 135 °C; The PE wax emulsion was sprayed through a centrifugal atomizing nozzle with an atomizing pressure of 0.1 MPa. The wax addition amount was 4% of the carbon black mass, and the droplet size was about 60 μm.

[0027] Hot air drying: After granulation, the particles enter a hot air dryer at a wind speed of 1.5 m / s and are treated at 200°C for 12 seconds to obtain wax-coated carbon black particles.

[0028] Example 2 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the amount of wax added is 3% of the mass of the carbon black.

[0029] Example 3 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the amount of wax added is 5% of the mass of the carbon black.

[0030] Example 4 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the airflow crushing includes two-stage treatment: The air jet mill crushes the carbon black to 70 nm at a pressure of 0.5 MPa; Particles with D90≤50nm were screened out by a centrifugal classifying wheel at a speed of 2000-3000 rpm.

[0031] Example 5 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax emulsion is atomized using a centrifugal atomizing nozzle, the atomization pressure is 0.2 MPa, the droplet size is ≤50 μm, and the surface coverage of the carbon black particles is ensured to be ≥95%.

[0032] Example 6 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax emulsion is a composite wax system, which includes 75% polyethylene wax and 25% polar modified wax by mass percentage, and the polar modified wax is oxidized polyethylene wax (Clariant Licowax PED521).

[0033] Example 7 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax emulsion is a composite wax system, which includes 70% polyethylene wax and 30% polar modified wax in mass percentage, and the polar modified wax is oxidized polyethylene wax.

[0034] Example 8 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax emulsion is a composite wax system, which includes 80% polyethylene wax and 20% polar modified wax in mass percentage, and the polar modified wax is oxidized polyethylene wax.

[0035] Example 9 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax emulsion is a composite wax system, which includes 75% polyethylene wax and 25% polar modified wax in mass percentage, and the polar modified wax is maleic anhydride grafted wax.

[0036] Example 10 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles obtained in Example 1 are sprayed with 3% KH550 ethanol solution and reacted at 75° C. for 11 minutes to form a chemical bonding layer.

[0037] Example 11 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles of Example 1 are placed in a fluidized bed reactor; HMDS / TEOS vapor (volume ratio 1:3) was introduced and reacted at 118°C for 5 minutes; A SiO2 layer with a thickness of 35±5 nm was generated.

[0038] Example 12 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles of Example 1 are placed in a fluidized bed reactor; HMDS / TEOS vapor (volume ratio 1:2.8) was introduced and reacted at 118°C for 5 minutes; A SiO2 layer with a thickness of 35±5 nm was generated.

[0039] Example 13 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles of Example 1 are placed in a fluidized bed reactor; HMDS / TEOS vapor (volume ratio 1:3.2) was introduced and reacted at 118°C for 5 minutes; A SiO2 layer with a thickness of 35±5 nm was generated.

[0040] Example 14 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles of Example 1 are placed in a fluidized bed reactor; HMDS / TEOS vapor (volume ratio 1:3) was introduced and reacted at 118°C for 5 minutes; A SiO2 layer with a thickness of 25±5 nm was generated.

[0041] Example 15 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the particles of Example 1 are placed in a fluidized bed reactor; HMDS / TEOS vapor (volume ratio 1:3) was introduced and reacted at 118°C for 5 minutes; A SiO2 layer with a thickness of 45±5 nm was generated.

[0042] Comparative Example Comparative Example 1 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the airflow crushing step is eliminated and the original coarse particle carbon black is directly used.

[0043] Comparative Example 2 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the wax coating is changed to granulation followed by dipping, the rotary granulator is used for rolling granulation at 135°C (without wax spraying), the granulated particles are immersed in a 10% PE wax emulsion, and dried at 200°C for 12 seconds.

[0044] Comparative Example 3 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the amount of polyethylene wax emulsion added is 2% of the mass of the carbon black.

[0045] Comparative Example 4 A method for preparing modified carbon black for plastics: The difference from Example 1 is that the amount of polyethylene wax emulsion added is 6% of the mass of the carbon black.

[0046] Performance testing Dispersion test: Refer to ASTM D1200 standard and use microscope observation. The sample is made into a 0.1mm thick slice. The distribution of carbon black particles is observed under an optical microscope at 200 times magnification. The particle agglomeration and uniformity are scored (1-100 points, with higher scores indicating better dispersion).

[0047] Color difference ΔE test: According to ISO105-B02 standard, the samples were aged for 1000 hours using a xenon lamp aging test chamber. The color changes of the samples were measured before and after aging using a colorimeter (Konica Minolta CM-26dG), and the ΔE value was calculated. The smaller the ΔE value, the higher the color fastness.

[0048] Migration test: According to GB / T30197-2013, the sample is placed in close contact with a white PP board at 80°C for 24 hours. The surface of the white PP board is observed to see whether there is carbon black migration contamination. The test is divided into four levels: "no migration", "slight migration", "obvious migration" and "severe migration". Tensile strength retention rate: According to ISO527-2, samples were injection molded into dumbbell-shaped specimens and the tensile strength was tested before aging and after 1000 hours of aging. The tensile strength retention rate was calculated (strength after aging / strength before aging × 100%) to evaluate the effect of carbon black on the mechanical properties and durability of the plastic matrix.

[0049] Table 1 Test data Combining Example 1 with Comparative Example 1 and Table 1, it can be seen that Comparative Example 1, which omitted the airflow milling step and directly used raw coarse carbon black, had a dispersibility of only 62 points, far lower than the 82 points of Example 1; the color difference ΔE was as high as 2.5, significantly higher than the 0.8 of Example 1; the migration was severe, while Example 1 achieved no migration; and the tensile strength retention rate was 68%, also lower than the 88% of Example 1. This indicates that the raw carbon black, without airflow milling refinement, had an excessively large particle size, making it difficult to evenly disperse in the plastic matrix. This not only affected color stability and appearance quality, but also reduced the mechanical properties and durability of the plastic product, highlighting the key role of the airflow milling step in improving the overall performance of carbon black. Combining Example 1 and Comparative Example 2 with Table 1, it can be seen that in Comparative Example 2, which replaced wax coating with post-granulation dip coating, the dispersibility was 75 points, lower than in Example 1; the color difference ΔE was 1.8, higher than in Example 1; slight migration was observed, while Example 1 showed no migration; and the tensile strength retention was 80%, lower than the 88% in Example 1. This demonstrates that atomized spraying of the wax emulsion during rotary granulation, compared to post-granulation dip coating, can more uniformly form a continuous coating on the carbon black surface, effectively enhancing the bonding between the carbon black and the plastic substrate, inhibiting carbon black migration, while simultaneously improving dispersibility and color fastness, and safeguarding the performance of the plastic product. Combining Example 1 with Comparative Examples 3-4 and Table 1, it can be seen that in Comparative Examples 3 and 4, the polyethylene wax emulsion addition levels were set at 2% and 6% of the carbon black mass, respectively. Compared to the 4% addition level in Example 1, the dispersibility of Comparative Example 3 was 78 points, and that of Comparative Example 4 was 81 points, both lower than Example 1. Regarding color difference ΔE, Comparative Example 3 was 1.2, and Comparative Example 4 was 0.9, both higher than Example 1. Migration was slight in both cases, while Example 1 showed no migration. The tensile strength retention rates were 85% and 87%, respectively, lower than the 88% in Example 1. This indicates that either too low or too high a polyethylene wax emulsion addition level will not achieve optimal carbon black coating. An appropriate addition level is required to form an ideal coating layer, ensuring carbon black dispersion, color fastness, and anti-migration properties, while maintaining the mechanical properties of the plastic product. Combining Examples 1-3 with Table 1, it can be seen that while Examples 2 and 3, respectively, adjust the wax addition to 3% and 5% of the carbon black mass, compared to Example 1 (4%), the dispersibility, color difference ΔE, migration, and tensile strength retention values ​​of the three are similar, but Example 1 performs better in all indicators. This indicates that within the 3%-5% wax addition range, carbon black performance can be improved, but a 4% addition achieves the best balance in terms of carbon black dispersibility, color fastness, migration resistance, and mechanical properties of plastic products, thus optimizing the overall performance of the modified carbon black. Combining Examples 1 and 4 with Table 1, it can be seen that Example 4, which utilizes a two-stage airflow milling process, achieves a dispersibility score of 86, higher than the 82 in Example 1; the color difference ΔE is 0.7, lower than that in Example 1; the migration is also zero, and the tensile strength retention rate is 89%, slightly higher than that in Example 1. This demonstrates that the two-stage airflow milling process, by precisely controlling the carbon black particle size and screening for more uniform particles, further enhances the dispersion of carbon black in the plastic matrix and strengthens the bonding between carbon black and plastic, thereby achieving superior performance in color fastness and mechanical properties, demonstrating the importance of refining and screening particle size for improving the performance of modified carbon black. Combining Examples 1 and 5 with Table 1, it can be seen that Example 5 optimizes the wax emulsion atomization parameters to ensure a surface coverage of carbon black particles of ≥95%. Its dispersibility is 85 points, slightly higher than that of Example 1; the color difference ΔE is 0.7, lower than that of Example 1; there is no migration, and the tensile strength retention rate is 88%, the same as that of Example 1. This demonstrates that the more optimized wax emulsion atomization parameters can achieve a more uniform and complete coating on the carbon black surface, effectively isolating the carbon black from external factors and improving color fastness. At the same time, the good coating promotes carbon black dispersion, further improving the overall performance of the modified carbon black without affecting mechanical properties. Combining Example 1 with Examples 6-9 and Table 1, it can be seen that the composite wax system employed in Examples 6-9 improves dispersibility compared to the single polyethylene wax emulsion in Example 1, with the highest score reaching 87. Color difference ΔE is generally reduced, with the lowest being 0.6. Migration is virtually non-existent, and tensile strength retention is also improved, reaching a maximum of 90%. This demonstrates that the addition of the polar-modified wax to the composite wax system enhances interfacial bonding through interaction with the carbon black and plastic matrix, synergizing with the polyethylene wax's coating effect to significantly improve carbon black dispersibility, color fastness, and mechanical properties of the plastic product, effectively inhibiting carbon black migration. Combining Examples 1 and 10 with Table 1, it can be seen that in Example 10, spraying an ethanol solution containing a silane coupling agent on the surface of carbon black particles resulted in a dispersibility score of 88, higher than in Example 1; the color difference ΔE was reduced to 0.5, significantly lower than in Example 1; there was no migration, and the tensile strength retention rate increased to 91%. This demonstrates that the "molecular bridge" created by the silane coupling agent between the carbon black and the plastic matrix greatly enhances the interfacial bonding strength, not only making the carbon black more evenly dispersed, but also significantly improving color fastness and mechanical properties, effectively preventing carbon black migration, demonstrating the key role of surface chemical modification in improving the performance of modified carbon black. Combining Example 1 with Examples 11-15 and Table 1, it can be seen that Examples 11-15 form a dense silica layer on the surface of the wax layer, with a maximum dispersibility of 89 points, higher than Example 1; the lowest color difference ΔE is 0.5, significantly lower than Example 1; and the migration is zero, with a maximum tensile strength retention rate of 92%. This indicates that the dense silica layer, with its excellent chemical stability and barrier properties, provides additional protection for carbon black, effectively resisting external erosion, further improving color fastness, while limiting carbon black migration and enhancing the mechanical properties of the plastic product. Different reaction conditions (such as steam ratio and layer thickness) have different performance-enhancing effects, but all are superior to Example 1, which does not form a silica layer.

[0050] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing modified carbon black for plastics, characterized in that: The following steps are involved: (1) The original carbon black is crushed into primary particles with a particle size of 20-50 nm by high-pressure airflow; (2) The crushed carbon black is rolled in a rotary granulator and granulated, and a polyethylene wax emulsion with a solid content of 30%-40% is sprayed at the same time. The amount of polyethylene wax added is 3%-5% of the carbon black mass, and the granulation temperature is 120-150°C; (3) Drying under hot air conditions at 180-220°C for 10-15 seconds to obtain carbon black particles coated with a solidified wax layer.

2. The method for preparing modified carbon black for plastics according to claim 1, wherein: The air flow milling in step (1) includes two stages of processing: The carbon black is crushed to 50-100 nm under a pressure of 0.4-0.6 MPa; Particles with D90≤50nm were screened out at a rotation speed of 2000-3000 rpm.

3. The method for preparing modified carbon black for plastics according to claim 1, wherein: The wax emulsion in step (2) is atomized using a centrifugal atomizing nozzle with an atomizing pressure of 0.2 MPa and a droplet size of ≤50 μm, ensuring that the surface coverage of the carbon black particles is ≥95%.

4. The method for preparing modified carbon black for plastics according to claim 1, wherein: The wax emulsion is a composite wax system, which includes 70%-80% polyethylene wax and 20%-30% polar modified wax in terms of mass percentage.

5. The method for preparing modified carbon black for plastics according to claim 4, characterized in that: The polar modified wax is selected from one of oxidized polyethylene wax and maleic anhydride grafted wax.

6. The method for preparing modified carbon black for plastics according to claim 1, wherein: An ethanol solution containing a silane coupling agent at a mass concentration of 1-3% is sprayed onto the surface of the dried carbon black particles and reacted at 60-80° C. for 10-12 minutes.

7. The method for preparing modified carbon black for plastics according to claim 1, wherein: The carbon black particles obtained in step (3) are placed in a fluidized bed, and hexamethyldisilazane vapor and tetraethoxysilane vapor are introduced, wherein the volume ratio of the hexamethyldisilazane vapor to the tetraethoxysilane vapor is 1:(2.8-3.2), and the reaction is carried out at 115-120°C to form a dense silica layer on the surface of the wax layer.

8. The method for preparing modified carbon black for plastics according to claim 7, wherein: The thickness of the dense silicon dioxide layer is controlled to be 20-50 nm.

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