High refractive index heavy calcium carbonate composite for night road marking paint and method for its production

Abstract

The application discloses a high-refractive heavy calcium carbonate compound for night road sign paint and a preparation method thereof; the compound is of a core-shell structure, the core is heavy calcium with a particle size of 2-5 microns, and the shell is a rutile titanium dioxide layer with a mass ratio of 10%-18%, and the overall refractive index of the compound is greater than or equal to 1.68, and the core decomposition rate is less than or equal to 5%. The preparation method comprises the following steps: after the heavy calcium slurry is activated in an alkaline manner, tetrabutyl titanate is added dropwise for in-situ hydrolysis coating under the control of pH and temperature, the conversion from anatase to rutile is realized through stepwise temperature rising calcination, the surface is activated through argon plasma, and finally, chemical grafting is carried out with a silane coupling agent; through precise process control, the application solves the contradiction between high-refractive coating and core thermal decomposition, realizes the unity of high-refractive powder, excellent resin compatibility and long-acting weather resistance, and is suitable for the field of high-performance night road sign paint.

Description

Technical Field

[0001] This invention relates to the field of inorganic powder material modification and composite material technology, specifically to a core-shell structured heavy calcium carbonate composite with high refractive index for use in nighttime road marking paint, and its precise and controllable preparation method. Background Technology

[0002] This invention relates to the field of inorganic powder material modification and composite material technology, specifically to a core-shell structured heavy calcium carbonate composite with high refractive index for use in nighttime road marking paint, and its precise and controllable preparation method.

[0003] Heavy calcium carbonate, as an inexpensive, widely available, and chemically stable inorganic filler, is widely used in plastics, rubber, coatings, and other fields. In road marking paints, heavy calcium carbonate mainly serves as an extender filler, increasing film thickness, reducing costs, and improving mechanical properties. However, unmodified heavy calcium carbonate has two significant drawbacks that fundamentally contradict the high-end application requirements of road marking paints: First, its surface is hydrophilic and oleophobic, resulting in poor interfacial compatibility with organic polymer resins. This leads to uneven dispersion in the paint film, making it prone to agglomeration and sedimentation. This not only affects the uniformity and mechanical properties of the paint film but also induces shrinkage stress during drying, causing premature cracking and peeling of the paint film, severely impacting the lifespan of the road markings. Second, and more critically, heavy calcium carbonate itself has a low refractive index, limiting its ability to reflect and scatter light, which cannot meet the core requirement of high reflectivity in modern nighttime road marking paints.

[0004] The reflectivity of road marking paint is a key indicator for ensuring nighttime driving safety, and its performance mainly depends on the refractive index of the fillers contained in the paint film. According to optical principles, the higher the refractive index of the filler, the stronger its ability to reflect headlights, resulting in better visibility and clarity at night. A traditional strategy to improve reflectivity is to directly sprinkle high-refractive-index glass microspheres onto the surface and inside the paint film. While effective, this method is costly. The difference in thermal expansion coefficients between the glass microspheres and the organic resin matrix, along with weak interfacial bonding, can easily lead to interfacial failure and microsphere detachment under long-term outdoor thermal stress and mechanical loads, causing a sharp decline in reflectivity and posing potential environmental problems.

[0005] Therefore, developing a functional filler with high refractive index that can form a strong bond with road marking paint resin, capable of partially or completely replacing glass microspheres, has become an important research direction in the industry. In existing technologies, surface coating of calcium carbonate with high refractive index materials is a recognized technical approach, but specific implementation schemes still face many bottlenecks and challenges: Limited and unstable improvement in optical performance: Most existing coating technologies struggle to achieve a continuous, dense, and uniform TiO2 coating layer at the microscale. Common adsorption, precipitation, and simple hydrolysis methods often lead to uneven adhesion of TiO2 nanoparticles on the calcium carbonate surface and homogeneous nucleation in the liquid phase, resulting in free particles. Consequently, the overall refractive index improvement of the composite powder is limited, often only reaching below 1.65, with significant batch-to-batch fluctuations, failing to consistently meet the optical requirements of high-end road marking paints. More importantly, if complete coating is not formed, the exposed areas of the calcium carbonate nucleus become low-refractive-index gaps in optics, severely degrading overall performance.

[0006] The contradiction between high-temperature crystallization and core stability: To obtain rutile titanium dioxide with the best optical properties, high-temperature heat treatment is usually required. However, heavy calcium carbonate (CaCO3) begins to decompose significantly at high temperatures, generating calcium oxide (CaO) and releasing carbon dioxide. This process leads to multiple problems: powder mass loss, structural damage, and decreased yield; the generated CaO expands in volume upon hydration, damaging the paint film structure from the inside; and the powder whiteness decreases, affecting the color of road signs. Existing technologies often sacrifice core stability to pursue crystal form conversion rate, and to preserve the core, only anatase and amorphous TiO2 with poor optical properties can be obtained, making it difficult to achieve both.

[0007] Poor surface modification effects and lack of quantitative control: Even with a core-shell structure, the compatibility between the surface and the resin remains crucial. Traditional silane coupling agent treatments often rely on the inherent number and activity of hydroxyl groups on the powder surface. After high-temperature treatment, the number of hydroxyl groups on the powder surface decreases significantly, reducing activity and leading to low silanization efficiency. Physical adsorption becomes the primary method, failing to form a strong chemical bond (Si-OM). This weak interfacial bond is highly susceptible to failure under harsh outdoor conditions of humidity, heat, and UV aging, causing the filler to delaminate from the resin. This is one of the fundamental reasons why many modified filler road marking paints exhibit insufficient weather resistance and rapid degradation of reflectivity. Furthermore, existing technologies generally lack quantitative control and verification methods for key intermediate and final indicators such as coating integrity, grafting efficiency, and hydroxyl density, resulting in poor process reproducibility and unstable product quality.

[0008] Therefore, there is an urgent need in this field for an innovative and systematic technical solution that can stably and controllably construct a continuous, uniform, and highly crystalline titanium dioxide coating layer without destroying the core structure of heavy calcium carbonate. Based on this, through efficient and quantitative surface activation and grafting technology, a strong interfacial bond with the resin can be achieved, thereby preparing an ideal filler that can simultaneously meet the requirements of high refractive index, excellent compatibility, and outstanding durability, so as to promote the advancement of nighttime road marking paint technology. Summary of the Invention

[0009] Purpose of the invention The purpose of this invention is to overcome the shortcomings of the prior art and provide a core-shell structured heavy calcium carbonate composite with high refractive index, high compatibility, and stable structure, which can significantly improve the reflectivity and durability of nighttime road marking paint.

[0010] Another objective of this invention is to provide a method for preparing the above-mentioned complex, which achieves the construction of a complete coating layer, inhibition of core decomposition, and high-efficiency surface grafting under mild conditions through precise process control, and the process is stable and reproducible.

[0011] Technical solution To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-refractive-index heavy calcium carbonate composite for use in nighttime road marking paint. The composite has a core-shell structure, and its overall refractive index is not less than 1.68. The core consists of heavy calcium carbonate particles with a particle size distribution D50 of 2 μm to 5 μm, and the decomposition rate of the heavy calcium carbonate core after calcination is ≤5%. The shell is a rutile titanium dioxide layer coating the surface of the core, with a refractive index not less than 2.5, and the relative intensity of the rutile characteristic peak 2θ = 27.4° accounting for not less than 95%. The titanium dioxide accounts for 12%-18% of the total mass of the composite, and when the D50 of the heavy calcium carbonate is 4 μm to 5 μm, the mass percentage of the titanium dioxide is not less than 13%.

[0012] Preferably, the outer surface of the titanium dioxide layer is grafted with organic functional groups by chemical bonding. The improved compatibility caused by the grafting is characterized by a reduction in sedimentation volume of the grafted sample in epoxy resin of not less than 15% compared to the plasma-activated sample alone.

[0013] Secondly, the present invention provides a method for preparing the high refractive index heavy calcium carbonate composite. The method includes the following core steps: S1: Pretreatment and Activation: Disperse heavy calcium carbonate powder in deionized water to form a slurry with a solid content of 15%-25%; then activate it by heating to 50℃-65℃ at a pH of 7.5-8.5 to increase the hydroxyl density on the surface of the heavy calcium carbonate particles to not less than 1.2 hydroxyl groups / nm. 2 Then, the first surface modifier is added for pretreatment, and the slurry temperature is raised to 65℃-80℃.

[0014] S2: In-situ hydrolysis coating: Under nitrogen protection, temperature control at 65℃-80℃ and stirring conditions, anhydrous ethanol solution of tetrabutyl titanate is added dropwise to activated heavy calcium carbonate slurry at a controllable rate, while ammonia solution is dynamically added dropwise to maintain the pH of the system at 8.5-9.5. The in-situ hydrolysis reaction is carried out for 2.5-3.5 hours to form a TiO2 coating layer on the surface of heavy calcium carbonate.

[0015] S3: Adding a steric hindrance agent: Within 2-4 minutes after the reaction described in the initial step S2, begin adding an aqueous solution of polyvinylpyrrolidone. The amount added is 12%-20% of the theoretically generated titanium dioxide mass, in order to prevent the aggregation of TiO2 nanoparticles.

[0016] S4: Separation and drying: The reacted material is subjected to solid-liquid separation and washing, and then vacuum dried at 100℃±2℃ to obtain intermediate composite powder.

[0017] S5: Stepped Heating Crystallization: The intermediate composite powder obtained in step S4 is subjected to stepped heating calcination under a nitrogen atmosphere: first, the temperature is increased to 700℃ at 2℃ / min and held for 3 hours, then increased to 720℃ and held for no more than 1 hour. This process promotes the transformation of amorphous TiO2 into rutile, while strictly controlling the thermal decomposition rate of heavy calcium nuclei to within 5%.

[0018] S6: Plasma surface activation: The calcined powder obtained in step S5 is treated in argon plasma for 3-5 minutes under specific power, pressure and gas flow conditions to significantly increase the surface hydroxyl density to no less than 4.5 hydroxyl groups / nm. 2 Furthermore, ensure that the covering layer is continuous and intact, and that the exposed area accounts for no more than 1% of the total area.

[0019] S7: Surface grafting modification: The composite powder obtained in step S6 is reacted with a specific silane coupling agent under catalytic conditions to achieve chemical bonding grafting, and the final product is obtained through subsequent washing and drying. The silane coupling agent needs to undergo pretreatment steps such as dilution, water addition, and pH adjustment before use.

[0020] This invention replaces the addition of crystal form promoters with a long-duration, low-temperature, stepped calcination process, avoiding the introduction of foreign impurities and ensuring product purity. The dry treatment method of plasma activation effectively resolves the contradiction between insufficient surface hydroxyl groups after high-temperature calcination and the requirements for subsequent grafting. The entire process is ingeniously designed with precise parameter control, ensuring the stability and reproducibility of the final product's structure and performance.

[0021] This invention, by constructing a continuous, dense, and crystalline stable rutile titanium dioxide coating layer, successfully increased the overall refractive index of the composite from approximately 1.58 (of ordinary heavy calcium carbonate) to over 1.68. This achievement makes the composite itself a highly efficient reflective agent. Road sign paint with the composite of this invention exhibits an initial reflectivity of up to 285 mcd·m. -2 ·lx -1 It is 155 mcd·m higher than that of paint films filled with ordinary heavy calcium carbonate. -2 ·lx -1The improvement exceeded 80%. This significantly enhanced the visibility and clarity of road signs at night, thereby improving road traffic safety.

[0022] This invention introduces functional groups that can chemically bond with the resin matrix onto the surface of the composite through the synergistic effect of plasma activation and silane chemical grafting. XPS analysis confirmed the presence of chemically bonded grafting, rather than simple physical adsorption, thus solving the industry pain point of poor compatibility between inorganic fillers and organic resins.

[0023] This invention demonstrates excellent dispersibility in resins through the grafted modified composite. Quantitative evaluation shows that the grafting-induced reduction in sedimentation volume is no less than 15%. This means that during the storage and application of road marking paint, it can effectively prevent filler sedimentation and caking, ensuring batch uniformity and ease of application, while also making the paint film denser and more uniform, reducing defects.

[0024] This invention innovatively adopts a stepped low-temperature long-time roasting process by abandoning the traditional methods of high-temperature rapid roasting and adding external accelerators. This process achieves a high rutile conversion rate while strictly controlling the thermal decomposition rate of the heavy calcium nucleus to an extremely low level of ≤5%.

[0025] This invention, through its preparation method, achieves a low decomposition rate in the product. A low decomposition rate means that the chemical structure of the heavy calcium carbonate core (CaCO3) is well preserved, avoiding problems such as powder moisture absorption, clumping, and decreased water resistance of the paint film caused by the formation of calcium oxide (CaO). Simultaneously, this also ensures that the final product has higher whiteness and chemical stability, providing a pure base color and long service life for road marking paint. After 500 hours of accelerated aging under a xenon lamp, the road marking paint using the composite of this invention exhibits a reflectivity retention rate as high as 87%, far exceeding samples filled with ordinary heavy calcium carbonate and high-end industry standards. This proves that the product of this invention not only has initial brightness but also sustained brightness.

[0026] This invention utilizes rutile TiO2, whose coating layer possesses excellent UV shielding properties, protecting the internal resin and grafted layers. The robust chemically bonded interface effectively resists internal stress damage caused by humidity, heat, and UV radiation, preventing filler-resin interface failure. The complete core-shell structure prevents direct erosion of the heavy calcium carbonate core by moisture and corrosive media. These three factors work synergistically to give the road marking paint an exceptionally long service life.

[0027] This invention, through such refined process control, ensures that each batch of products has a highly consistent structure and performance, greatly reducing production fluctuations and meeting the stringent requirements of industrial production for product consistency and reliability. The product of this invention can partially or completely replace expensive glass microspheres, achieving the same or even better reflective effects while significantly reducing raw material costs. The entire preparation process does not use toxic or harmful crystal form promoters, employs precise dosage of silane coupling agents, and effectively removes residues through washing, making it environmentally friendly.

[0028] This invention provides road marking paint products with superior performance and longer lifespan, offering strong material support for reducing nighttime traffic accident rates and protecting people's lives and property, and has significant social value. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for preparing a high refractive index heavy calcium carbonate composite for nighttime road marking paint according to the present invention.

[0030] Figure 2 This is a scanning electron microscope (SEM) image of the high refractive index heavy calcium carbonate composite prepared in Example 1 of this invention.

[0031] Figure 3 This is a SEM image of ordinary TiO2 coated with heavy calcium carbonate in Comparative Example 1. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention will be described in further detail below with reference to the accompanying drawings. The following examples are for illustrative purposes only and are not intended to limit the scope of this invention. Unless otherwise specified, all raw materials and reagents are commercially available.

[0033] Example 1: High-refractive-index heavy calcium carbonate complex: This embodiment fully demonstrates a method for preparing a high-refractive-index heavy calcium carbonate composite for nighttime road marking paint. This embodiment prepares a high-refractive-index heavy calcium carbonate composite by chemically bonding amino functional groups to the surface of a titanium dioxide shell through plasma activation and silane coupling agent grafting treatment, and evaluates its compatibility improvement effect in epoxy resin. This embodiment follows the preparation method of the present invention, including alkaline activation, in-situ hydrolysis coating, steric hindrance agent addition, step-temperature crystallization, and plasma activation. Specific materials and preparation processes are as follows: Materials and proportions: Heavy calcium carbonate powder (D50=4μm): 200g; Deionized water: 800mL; 10% ammonia solution: appropriate amount, used to adjust pH to 8.0; Fatty alcohol polyoxyethylene ether (AEO-9): 0.8g; Tetrabutyl titanate: 40 mL, used to prepare a 1.0 mol / L anhydrous ethanol solution; 8% ammonia solution: appropriate amount, used to maintain pH=9.0; Polyvinylpyrrolidone (PVP): Appropriate amount, used to prepare a 10% aqueous solution, the amount added is 15% of the theoretical mass of TiO2 produced; Argon: For plasma treatment, flow rate 15 sccm; KH550 silane coupling agent: 1.2g; Anhydrous ethanol: 12g; Acetic acid: 0.006g; 95% (v / v) ethanol: appropriate amount, for washing, liquid-to-solid ratio 8:1.

[0034] This embodiment details the preparation method and complete process of high refractive index heavy calcium carbonate composite. 200g of heavy calcium carbonate with a D50 of 4μm was used as the raw material, with a target TiO2 mass percentage of 13%. The specific process steps are as follows: S1. Pretreatment and activation: Prepare a 20% solid content heavy calcium carbonate slurry, adjust the pH to 8.0 with 10% ammonia water, and activate it by stirring at 60°C for 30 minutes; add 0.4% fatty alcohol polyoxyethylene ether by the mass of heavy calcium carbonate, and continue stirring for 30 minutes; raise the system temperature to 70°C. S2. In-situ hydrolysis and coating: Under nitrogen protection, at 70℃ and 700 rpm stirring conditions, 40 mL of 1.0 mol / L tetrabutyl titanate anhydrous ethanol solution was added dropwise to the slurry at a constant rate of 2 mL / min; simultaneously, 8% ammonia solution was added dropwise at 1.2 mL / min, and the pH of the reaction system was dynamically controlled to be stable at 9.0±0.2; the reaction was continued for 3 hours. S3. Adding steric hindrance: Three minutes after the start of adding tetrabutyl titanate solution, begin adding a 10% (w / w) aqueous solution of polyvinylpyrrolidone at a rate of 1.0 mL / min. The amount added is 15% of the theoretical TiO2 mass generated in this batch. S4. Separation and drying: After the reaction is completed, the mixture is filtered and washed thoroughly with deionized water until the conductivity of the filtrate is <50 μS / cm. The filter cake is placed in a vacuum drying oven and dried at 100℃ for 1.5 hours to obtain intermediate composite powder. S5. Stepped temperature crystallization: The intermediate is placed in a tube furnace and heated to 700°C at a rate of 2°C / min under a nitrogen atmosphere. It is then calcined at this temperature for 3 hours. The temperature is then increased to 720°C and calcined at this temperature for another 0.5 hours. The furnace is then cooled after the program is completed. S6. Plasma surface activation: Place the calcined and cooled powder into the cavity of the plasma treatment equipment, introduce argon gas, adjust the pressure inside the cavity to 90 Pa, and treat it for 4 minutes at a radio frequency power of 350 W. S7. Silane Grafting and Post-treatment: Take 100g of plasma-treated powder, first disperse it ultrasonically at 20 kHz, 300W for 10 minutes, then pre-disperse it at 4500 rpm for 4 minutes using a high-speed disperser. Transfer it to a reactor equipped with stirring and condensation, and heat it to 100℃. Dilute 1.2g of KH550 aminosilane coupling agent with 12g of anhydrous ethanol, and add 0.006g of acetic acid (0.5% of silane mass) and 0.12g of deionized water (1% of ethanol mass). After stirring evenly, control the pH of the diluted solution to approximately 4.5. Add this diluted solution dropwise to the reactor at a rate of 1.5 mL / min to react with the powder. After the addition is complete, continue to heat and stir the reaction at 100℃ for 45 minutes. After the reaction, allow it to cool naturally to below 50℃, and wash it twice with 95% (v / v) ethanol at a liquid-to-solid mass ratio of 8:1. After each wash, centrifuge at 5000 rpm for 10 minutes to separate the solid. The collected solids were vacuum dried at 80°C for 1 hour, and then cooled to room temperature under flowing nitrogen protection to obtain the final product.

[0035] Core product performance: The overall refractive index of the product is 1.70, as measured by an Abbe refractometer. Thermogravimetric analysis (TGA) shows a core decomposition rate of 2.1%. XRD analysis shows that the relative intensity of the rutile characteristic peak (2θ=27.4°) accounts for 96.8%.

[0036] Surface grafting and compatibility: XPS analysis confirmed the presence of nitrogen on the surface, indicating successful chemical bonding of amino groups. The grafted sample was compared with a plasma-activated sample from the same batch in terms of epoxy resin dispersion and sedimentation; the sedimentation volume reduction rate was measured to be 18%.

[0037] Example 2 Experimental Group: This example aims to verify the applicability and performance stability of the present invention under different parameter combinations by adjusting the particle size of the heavy calcium nucleus (D50=2μm) and the mass ratio of TiO2.

[0038] Materials and proportions: Heavy calcium carbonate powder (D50=2μm): 200g; Deionized water: 800mL; 10% ammonia solution: appropriate amount, used to adjust pH to 8.0; Fatty alcohol polyoxyethylene ether (AEO-9): 0.8g; Tetrabutyl titanate: 36.9 mL, used to prepare a 1.0 mol / L anhydrous ethanol solution, calculated based on a TiO2 content of 12%; 8% ammonia solution: appropriate amount, used to maintain pH=9.0; Polyvinylpyrrolidone (PVP): Appropriate amount, used to prepare a 10% aqueous solution, the amount added is 15% of the theoretical mass of TiO2 produced; Argon: For plasma treatment, flow rate 15 sccm; KH550 silane coupling agent: 1.2g; Anhydrous ethanol: 12g, used to dilute silane; Acetic acid: 0.006g; 95% (v / v) ethanol: 1600 mL, for washing, liquid-to-solid ratio 8:1.

[0039] The preparation method is as follows: S1. Pretreatment and Activation: 200g of heavy calcium carbonate powder with a D50=2μm was dispersed in 800mL of deionized water to form a slurry with a solid content of 20%. The pH of the slurry was adjusted to 8.0 with a 10% ammonia solution, and activated by stirring at 60℃ for 30 minutes. Then, 0.8g of fatty alcohol polyoxyethylene ether was added, and stirring was continued for another 30 minutes. Finally, the system temperature was raised to 70℃.

[0040] S2. In-situ hydrolysis and coating: Under nitrogen protection, at 70℃ and with stirring at 700 rpm, 36.9 mL of a 1.0 mol / L tetrabutyl titanate anhydrous ethanol solution was added dropwise to the slurry at a constant rate of 2 mL / min. Simultaneously, an 8% ammonia solution was added dropwise at 1.2 mL / min, dynamically controlling the pH of the reaction system to remain stable at 9.0 ± 0.2. The reaction was continued for 3 hours.

[0041] S3. Adding steric hindrance: Three minutes after the start of adding tetrabutyl titanate solution, begin adding a 10% (w / w) aqueous solution of polyvinylpyrrolidone at a rate of 1.0 mL / min. The amount added is 15% of the theoretical TiO2 mass generated in this batch.

[0042] S4. Separation and Drying: After the reaction is complete, the mixture is filtered and washed thoroughly with deionized water until the conductivity of the filtrate is <50 μS / cm. The filter cake is then placed in a vacuum drying oven and dried at 100℃ for 1.5 hours to obtain the intermediate composite powder.

[0043] S5. Stepped temperature crystallization: The intermediate is placed in a tube furnace and heated to 700°C at a rate of 2°C / min under a nitrogen atmosphere. It is then calcined at this temperature for 3 hours. The temperature is then increased to 720°C and calcined at this temperature for another 0.5 hours. The furnace is then cooled after the program is completed.

[0044] S6. Plasma surface activation: Place the calcined and cooled powder into the cavity of the plasma treatment equipment, introduce argon gas, adjust the pressure inside the cavity to 90 Pa, and treat for 4 minutes at a radio frequency power of 350 W.

[0045] S7. Silane Grafting and Post-treatment: Take 100g of plasma-treated powder, first disperse it ultrasonically at 20 kHz, 300W for 10 minutes, then pre-disperse it at 4500 rpm for 4 minutes using a high-speed disperser. Transfer it to a reactor equipped with stirring and condensation, and heat it to 100℃. Dilute 1.2g of KH550 aminosilane coupling agent with 12g of anhydrous ethanol, and add 0.006g of acetic acid (0.5% of silane mass) and 0.12g of deionized water (1% of ethanol mass) to the diluted solution. After stirring evenly, control the pH of the diluted solution to approximately 4.5. Add this diluted solution dropwise to the reactor at a rate of 1.5 mL / min to react with the powder. After the addition is complete, continue to heat and stir the reaction at 100℃ for 45 minutes. After the reaction, allow it to cool naturally to below 50℃, and wash it twice with 95% (v / v) ethanol at a liquid-to-solid mass ratio of 8:1. After each wash, centrifuge at 5000 rpm for 10 minutes to separate the solid. The collected solids were vacuum dried at 80°C for 1 hour, and then cooled to room temperature under flowing nitrogen protection to obtain the final product.

[0046] Characterized using the same testing method as in Example 1, the final product had an overall refractive index of 1.71, a calcination decomposition rate of 1.8% for the heavy calcium core, and X-ray diffraction analysis showed that the relative intensity of the characteristic peak (2θ=27.4°) of rutile TiO2 accounted for 97.2%.

[0047] Example 3 Experimental Group: The aim was to verify that when using large-particle-size heavy calcium nuclei (D50=5μm), excellent overall performance could still be achieved by appropriately increasing the TiO2 coating amount.

[0048] Materials and proportions: Heavy calcium carbonate powder (D50=5μm): 200g; Deionized water: 800mL; 10% ammonia solution: appropriate amount, used to adjust pH to 8.0; Fatty alcohol polyoxyethylene ether (AEO-9): 0.8g; Tetrabutyl titanate: 46.2 mL, used to prepare a 1.0 mol / L anhydrous ethanol solution, calculated based on a TiO2 content of 15%; 8% ammonia solution: appropriate amount, used to maintain pH=9.0; Polyvinylpyrrolidone (PVP): Appropriate amount, used to prepare a 10% aqueous solution, the amount added is 15% of the theoretical mass of TiO2 produced; Argon: For plasma treatment, flow rate 15 sccm; KH550 silane coupling agent: 1.2g; Anhydrous ethanol: 12g, used to dilute silane; Acetic acid: 0.006g; 95% (v / v) ethanol: 1600 mL, for washing, liquid-to-solid ratio 8:1.

[0049] The preparation method is as follows: S1. Pretreatment and Activation: 200g of heavy calcium carbonate powder with a D50=5μm was dispersed in 800mL of deionized water to form a slurry with a solid content of 20%. The pH of the slurry was adjusted to 8.0 with a 10% ammonia solution, and activated by stirring at 60℃ for 30 minutes. Then, 0.8g of fatty alcohol polyoxyethylene ether was added, and stirring was continued for another 30 minutes. Finally, the system temperature was raised to 70℃.

[0050] S2. In-situ hydrolysis and coating: Under nitrogen protection, at 70℃ and with stirring at 700 rpm, 46.2 mL of a 1.0 mol / L tetrabutyl titanate anhydrous ethanol solution was added dropwise to the slurry at a constant rate of 2 mL / min. Simultaneously, an 8% ammonia solution was added dropwise at 1.2 mL / min, dynamically controlling the pH of the reaction system to remain stable at 9.0 ± 0.2. The reaction was continued for 3 hours.

[0051] S3. Adding steric hindrance: Three minutes after the start of adding tetrabutyl titanate solution, begin adding a 10% (w / w) aqueous solution of polyvinylpyrrolidone at a rate of 1.0 mL / min. The amount added is 15% of the theoretical TiO2 mass generated in this batch.

[0052] S4. Separation and Drying: After the reaction is complete, the mixture is filtered and washed thoroughly with deionized water until the conductivity of the filtrate is <50 μS / cm. The filter cake is then placed in a vacuum drying oven and dried at 100℃ for 1.5 hours to obtain the intermediate composite powder.

[0053] S5. Stepped temperature crystallization: The intermediate is placed in a tube furnace and heated to 700°C at a rate of 2°C / min under a nitrogen atmosphere. It is then calcined at this temperature for 3 hours. The temperature is then increased to 720°C and calcined at this temperature for another 0.5 hours. The furnace is then cooled after the program is completed.

[0054] S6. Plasma surface activation: Place the calcined and cooled powder into the cavity of the plasma treatment equipment, introduce argon gas, adjust the pressure inside the cavity to 90 Pa, and treat for 4 minutes at a radio frequency power of 350 W.

[0055] S7. Silane Grafting and Post-treatment: Take 100g of plasma-treated powder, first disperse it ultrasonically at 20 kHz, 300W for 10 minutes, then pre-disperse it at 4500 rpm for 4 minutes using a high-speed disperser. Transfer it to a reactor equipped with stirring and condensation, and heat it to 100℃. Dilute 1.2g of KH550 aminosilane coupling agent with 12g of anhydrous ethanol, and add 0.006g of acetic acid (0.5% of silane mass) and 0.12g of deionized water (1% of ethanol mass) to the diluted solution. After stirring evenly, control the pH of the diluted solution to approximately 4.5. Add this diluted solution dropwise to the reactor at a rate of 1.5 mL / min to react with the powder. After the addition is complete, continue to heat and stir the reaction at 100℃ for 45 minutes. After the reaction, allow it to cool naturally to below 50℃, and wash it twice with 95% (v / v) ethanol at a liquid-to-solid mass ratio of 8:1. After each wash, centrifuge at 5000 rpm for 10 minutes to separate the solid. The collected solids were vacuum dried at 80°C for 1 hour, and then cooled to room temperature under flowing nitrogen protection to obtain the final product.

[0056] Characterized using the same testing method as in Example 1, the final product had an overall refractive index of 1.69, a calcination decomposition rate of 2.5% for the heavy calcium core, and X-ray diffraction analysis showed that the relative intensity of the characteristic peak (2θ=27.4°) of rutile TiO2 accounted for 96.5%.

[0057] Example 4 Experimental Group: The purpose was to test whether the product performance could still meet the requirements under the conditions of medium particle size (D50=3μm) and low TiO2 mass ratio, in order to explore the boundaries of the technical solution.

[0058] Materials and proportions: Heavy calcium carbonate powder (D50=3μm): 200g; Deionized water: 800mL; 10% ammonia solution: appropriate amount, used to adjust pH to 8.0; Fatty alcohol polyoxyethylene ether (AEO-9): 0.8g; Tetrabutyl titanate: 30.8 mL, prepared as a 1.0 mol / L anhydrous ethanol solution, calculated based on a TiO2 content of 10%; 8% ammonia solution: appropriate amount, maintain pH=9.0; Polyvinylpyrrolidone (PVP): Appropriate amount, used to prepare a 10% aqueous solution, the amount added is 15% of the theoretical mass of TiO2 produced; Argon: For plasma treatment, flow rate 15 sccm; KH550 silane coupling agent: 1.2g; Anhydrous ethanol: 12g, used to dilute silane; Acetic acid: 0.006g; 95% (v / v) ethanol: 1600 mL, for washing, liquid-to-solid ratio 8:1.

[0059] The preparation method is as follows: S1. Pretreatment and Activation: 200g of heavy calcium carbonate powder with a D50=3μm was dispersed in 800mL of deionized water to form a slurry with a solid content of 20%. The pH of the slurry was adjusted to 8.0 with a 10% ammonia solution, and activated by stirring at 60℃ for 30 minutes. Then, 0.8g of fatty alcohol polyoxyethylene ether was added, and stirring was continued for another 30 minutes. Finally, the system temperature was raised to 70℃.

[0060] S2. In-situ hydrolysis and coating: Under nitrogen protection, at 70℃ and with stirring at 700 rpm, 30.8 mL of a 1.0 mol / L tetrabutyl titanate anhydrous ethanol solution was added dropwise to the slurry at a constant rate of 2 mL / min. Simultaneously, an 8% ammonia solution was added dropwise at 1.2 mL / min, dynamically controlling the pH of the reaction system to remain stable at 9.0 ± 0.2. The reaction was continued for 3 hours.

[0061] S3. Adding steric hindrance: Three minutes after the start of adding tetrabutyl titanate solution, begin adding a 10% (w / w) aqueous solution of polyvinylpyrrolidone at a rate of 1.0 mL / min. The amount added is 15% of the theoretical TiO2 mass generated in this batch.

[0062] S4. Separation and Drying: After the reaction is complete, the mixture is filtered and washed thoroughly with deionized water until the conductivity of the filtrate is <50 μS / cm. The filter cake is then placed in a vacuum drying oven and dried at 100℃ for 1.5 hours to obtain the intermediate composite powder.

[0063] S5. Stepped temperature crystallization: The intermediate is placed in a tube furnace and heated to 700°C at a rate of 2°C / min under a nitrogen atmosphere. It is then calcined at this temperature for 3 hours. The temperature is then increased to 720°C and calcined at this temperature for another 0.5 hours. The furnace is then cooled after the program is completed.

[0064] S6. Plasma surface activation: Place the calcined and cooled powder into the cavity of the plasma treatment equipment, introduce argon gas, adjust the pressure inside the cavity to 90 Pa, and treat for 4 minutes at a radio frequency power of 350 W.

[0065] S7. Silane Grafting and Post-treatment: Take 100g of plasma-treated powder, first disperse it ultrasonically at 20 kHz, 300W for 10 minutes, then pre-disperse it at 4500 rpm for 4 minutes using a high-speed disperser. Transfer it to a reactor equipped with stirring and condensation, and heat it to 100℃. Dilute 1.2g of KH550 aminosilane coupling agent with 12g of anhydrous ethanol, and add 0.006g of acetic acid (0.5% of silane mass) and 0.12g of deionized water (1% of ethanol mass) to the diluted solution. After stirring evenly, control the pH of the diluted solution to approximately 4.5. Add this diluted solution dropwise to the reactor at a rate of 1.5 mL / min to react with the powder. After the addition is complete, continue to heat and stir the reaction at 100℃ for 45 minutes. After the reaction, allow it to cool naturally to below 50℃, and wash it twice with 95% (v / v) ethanol at a liquid-to-solid mass ratio of 8:1. After each wash, centrifuge at 5000 rpm for 10 minutes to separate the solid. The collected solids were vacuum dried at 80°C for 1 hour, and then cooled to room temperature under flowing nitrogen protection to obtain the final product.

[0066] Characterized using the same testing method as in Example 1, the final product had an overall refractive index of 1.68, a calcination decomposition rate of 1.5% for the heavy calcium core, and X-ray diffraction analysis showed that the relative intensity of the characteristic peak (2θ=27.4°) of rutile TiO2 accounted for 96.0%.

[0067] Example 5 Control Group: Materials and proportions: Heavy calcium carbonate powder (D50=4μm): 200g; Deionized water: 800mL; 10% ammonia solution: appropriate amount, adjust pH to 8.0; Fatty alcohol polyoxyethylene ether (AEO-9): 0.8g; Tetrabutyl titanate: 40 mL, prepared as a 1.0 mol / L anhydrous ethanol solution; 8% ammonia solution: appropriate amount, maintain pH=9.0; Polyvinylpyrrolidone (PVP): Appropriate amount, prepared into a 10% aqueous solution, the amount added is 15% of the theoretical mass of TiO2 produced; Air: roasting atmosphere; KH550 silane coupling agent: 1.2g; Anhydrous ethanol: 12g, used to dilute silane; Acetic acid: 0.006g; 95% (v / v) ethanol: 1600 mL, for washing, liquid-to-solid ratio 8:1.

[0068] The preparation method in this embodiment is as follows: Take 200g of heavy calcium carbonate powder with D50=4μm, and control the target mass ratio of TiO2 to be 13%. The first four steps of its preparation process, S1 to S4, are exactly the same as in Example 1.

[0069] The key differences are: S5. High-temperature calcination: The intermediate obtained in S4 is directly calcined in air at 800°C for 1 hour, and then cooled. S6. The plasma activation treatment step S6 in Example 1 is omitted in this embodiment. S7. Silane grafting: The powder after calcination and cooling in S5 is directly grafted with silane and post-processed according to the steps and parameters of S7 in Example 1 without any additional activation treatment.

[0070] Characterized using the same detection method as in Example 1, the obtained product has an overall refractive index of 1.65, a high decomposition rate of calcined heavy calcium core of 8.3%, and X-ray diffraction analysis shows that the relative intensity of its rutile TiO2 characteristic peaks accounts for only 85.2%. XPS analysis also indicates that the surface nitrogen signal is extremely weak and the grafting efficiency is low.

[0071] Example of effect and performance comparison: Table 1 Key performance indicators of the products from the embodiments ; Data Analysis: All samples 2-4 in the examples showed a stable refractive index ≥1.68, demonstrating the rationality of the technical features.

[0072] Example 5 uses a traditional process with a refractive index of only 1.65 and a nucleus decomposition rate as high as 8.3%, which verifies the necessity of the process improvement of the present invention.

[0073] The rutile content is directly related to the stability of the process. Examples 2-4 all maintained ≥96%, while Example 5 (control example) only had 85.2%.

[0074] Table 2 Weather resistance test results of road marking paint ; Data Analysis: The reflectance coefficient decay curves of Examples 1-4 are flat, and they still maintain more than 85% of their performance after 500 hours.

[0075] The products obtained in Examples 2-5 were added to acrylic road marking paint resin at a filler content of 30% to prepare standard test panels for performance testing. The results showed that the refractive index of the products in Examples 2-4 was consistently ≥1.68, and the reflectivity retention rate reached 85-87% after 500 hours of xenon lamp aging. XPS confirmed high grafting efficiency, with a nitrogen element atomic percentage of 1.5-1.8%. In contrast, Comparative Example 5, due to incomplete coating, severe core decomposition, and low grafting efficiency, had a nitrogen element atomic percentage of only 0.3%, the lowest refractive index of 1.65, the worst weather resistance, and a reflectivity retention rate of only 75%. This indicates that the present invention, through precise control of material ratios and preparation processes, successfully achieved a synergistic improvement in high refractive index, excellent weather resistance, and stable grafting, solving the technical bottlenecks of traditional processes.

[0076] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-refractive-index heavy calcium carbonate composite for use in nighttime road marking paint, characterized in that, The composite has a core-shell structure and its overall refractive index is not less than 1.

68. The overall refractive index is determined using the Abbe refractometer method at 25℃±1℃, by mixing the composite with anhydrous ethanol (1:1 mass ratio) at a ratio of 1:

1. The core is a heavy calcium carbonate particle with a particle size distribution D50 of 2μm-5μm, and the decomposition rate of the heavy calcium carbonate core after calcination is ≤5%. The decomposition rate is determined by thermogravimetric analysis under nitrogen atmosphere, heating rate of 10℃ / min, and 800℃. The shell is a metal oxide layer covering the surface of the core. The metal oxide is rutile titanium dioxide with a refractive index of not less than 2.

5. Its rutile crystal form is detected by X-ray diffraction using a Cu target / Kα line at a scanning rate of 5° / min, and the relative intensity of the characteristic peak 2θ=27.4° accounts for not less than 95%. The titanium dioxide accounts for 12%-18% of the total mass of the composite, and when the D50 of the heavy calcium carbonate is 4μm-5μm, the mass percentage of the titanium dioxide is not less than 13%.

2. The high refractive index heavy calcium carbonate composite according to claim 1, characterized in that, The outer surface of the titanium dioxide layer is grafted with organic functional groups by chemical bonding; the improved compatibility caused by the grafting is characterized by the following: compared with the plasma-activated sample, the grafted sample, after being stirred and dispersed at 1000 rpm for 10 minutes in 10 wt% epoxy resin E51 and left to stand for 24 hours, has a sedimentation volume reduction rate of not less than 15%.

3. The high refractive index heavy calcium carbonate composite according to claim 2, characterized in that, The organic functional group is amino.

4. A method for preparing the high refractive index heavy calcium carbonate composite as described in claim 1, characterized in that, Includes the following steps: S1: Disperse heavy calcium carbonate powder in deionized water to form a slurry with a solid content of 15%-25%; then, adjust the pH of the slurry to 7.5-8.5 using a 10% ammonia solution, and activate it at 50℃-65℃ with stirring for 20-40 minutes to increase the hydroxyl density on the surface of the heavy calcium carbonate particles to not less than 1.2 hydroxyl groups / nm. 2 Then, a first surface modifier is added to the slurry for pretreatment. The first surface modifier is at least one of fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, and fatty alcohol alkyl phosphate, and its addition amount is 0.2%-0.8% of the mass of heavy calcium carbonate. Subsequently, the slurry temperature is raised to 65℃-80℃ to prepare for step S2. S2: Under nitrogen protection, stirring speed of 600-800 rpm, and heating conditions maintained at 65℃-80℃, anhydrous ethanol solution of tetrabutyl titanate prepared within 1 hour is added dropwise to the activated heavy calcium carbonate slurry at a rate of 1-3 mL / min, with a precursor solution concentration of 0.8-1.5 mol / L; simultaneously, a 5%-10% ammonia solution is added dropwise at a rate of 1.0-1.5 mL / min to dynamically maintain the pH value of the reaction system at 8.5-9.5; the in-situ hydrolysis reaction is carried out for 2.5-3.5 hours; S3: Within 2-4 minutes after the in-situ hydrolysis reaction described in step S2, begin adding a 5%-10% aqueous solution of polyvinylpyrrolidone dropwise at a rate of 0.5-1.5 mL / min. The amount added is 12%-20% of the theoretically generated titanium dioxide mass. S4: The reacted material is subjected to solid-liquid separation and washing, and then dried in a vacuum drying oven at 100℃±2℃ for 1-2 hours to obtain intermediate composite powder; the thermal stability of the intermediate composite powder is determined by thermogravimetric analysis under the following conditions: heating rate 10℃ / min, nitrogen atmosphere, and its mass retention rate at 720℃ is not less than 95%; S5: The intermediate composite powder obtained in step S4 is calcined under a nitrogen atmosphere: first, the temperature is raised to 700℃ at a heating rate of 2℃ / min, and then held at this temperature for 3 hours. Subsequently, the temperature was raised to 720℃ and held at this temperature for no more than 1 hour; after calcination, calcined composite powder was obtained; the hydroxyl density on the surface of titanium dioxide in the calcined composite powder was not less than 1.5 hydroxyl groups / nm. 2 ; S6: The calcined composite powder obtained in step S5 is placed in an argon plasma treatment device and treated for 3-5 minutes under the conditions of 300-400W power, 80-100Pa pressure, and 10-20 sccm argon flow rate to obtain the high refractive index heavy calcium carbonate composite; the hydroxyl density on the titanium dioxide surface in the composite is not less than 4.5 hydroxyl groups / nm. 2 Scanning electron microscopy revealed that the TiO2 coating layer was continuous without exposed heavy calcium nuclei, and the exposed area accounted for no more than 1% of the total area. The hydroxyl density was determined by temperature-programmed desorption-mass spectrometry under the following conditions: heating rate 10℃ / min, and high-purity nitrogen as the desorption gas.

5. A method for preparing the high refractive index heavy calcium carbonate composite as described in claim 2, characterized in that, Includes the following steps: Repeat steps S1-S6; S7: The composite powder obtained in step S6 is treated with an ultrasonic disperser at 20kHz and 300W for 10 minutes, and then pre-dispersed in a turbine high-speed disperser at 4000-5000 rpm for 3-5 minutes to ensure that the D50 of the pre-dispersed powder is no greater than 6μm; then it is reacted with a silane coupling agent in an air atmosphere at 90℃-110℃, stirring speed of 400-600 rpm, and relative humidity of 50%-65%; the silane coupling agent is an aminosilane of type KH550, and its addition amount is 0.8%-1.5% of the mass of the composite powder obtained in step S6; After the reaction was completed, the mixture was naturally cooled to below 50°C, then washed twice with 95% (v / v) ethanol at a liquid-to-solid ratio of 8:

1. The mixture was then centrifuged at 5000 rpm for 10 minutes. The solid was collected and vacuum dried at 80°C for 1 hour. After drying, the solid was cooled to room temperature in a nitrogen atmosphere to ensure that the ethanol residue in the final powder was not higher than 0.1%. The ethanol residue was determined by headspace gas chromatography.

6. The method for preparing the high refractive index heavy calcium carbonate composite according to claim 5, characterized in that, Before use, the silane coupling agent is diluted with 5-10 times its mass of ethanol with a water content ≤0.05%, and 0.5%-1% of deionized water (equivalent to the mass of ethanol) is added to the diluted solution to control the concentration of the silane solution after dilution to 0.1-0.2 mol / L. Acetic acid (equivalent to the mass of silane) is added to control the pH of the diluted solution to 4.0-5.

0. Acetic acid is added dropwise at a rate of 1-2 mL / min, and the reaction is maintained at the temperature for 30-60 minutes after the addition is complete.

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