Preparation process of modified calcium carbonate powder based on talcum powder

Abstract

The invention relates to the technical field of inorganic powder material modification, and discloses a preparation process of modified calcium carbonate powder based on talcum powder, which comprises the following steps: S1, raw material preparation: selecting high-purity natural calcium carbonate powder and talcum powder for subsequent modification composite treatment; s2, calcium carbonate powder pretreatment: screening and pickling the calcium carbonate powder to remove impurities and improve the surface reaction performance of the calcium carbonate powder; s3, pretreating talcum powder: screening and baking the talcum powder to remove moisture and impurities; s4, surface modification treatment: respectively carrying out surface modification on the pretreated calcium carbonate powder and talcum powder; and S5, compounding treatment: uniformly mixing the surface-modified calcium carbonate powder and talcum powder according to a set mass ratio to form the modified composite powder material. According to the invention, by constructing an organosilane modified layer and a polymer coating structure, the dispersion of the powder is improved, the interface stability is enhanced, and the processing fluidity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic powder material modification, and specifically to a preparation process of modified calcium carbonate powder based on talcum powder. Background Art

[0002] Under the background of the rapid development of polymer composites, filled functional powder materials are widely used in fields such as packaging, building materials, and automotive parts. Especially in general resins such as polypropylene and polyethylene, introducing inorganic powders can not only reduce the material cost but also improve the dimensional stability, rigidity, and heat distortion temperature of the products. Natural mineral powders such as calcium carbonate and talcum powder have become the most commonly used filler sources in polymer systems due to their rich resources and mature processing technologies. However, as the application scenarios shift from traditional structural filling to higher-performance composite reinforcement, how to improve the interfacial compatibility, processing stability, and mechanical uniformity between these powders and polymer matrices has become one of the key factors affecting the comprehensive performance of materials.

[0003] In the existing technologies, to improve the matching performance between powders and polymers, some solutions use organic additives such as surfactants and compatibilizers for compounding, and achieve a certain degree of compatibility improvement by adjusting the interfacial energy difference. At the same time, there are also studies on regulating the particle size of powders and controlling the blending of composite pellets to improve their dispersion uniformity and mechanical property output in the matrix. Some technologies use low-temperature drying or inert atmosphere treatment to retain the structural integrity of the powders and avoid the degradation of surface functional groups caused by heat treatment. In addition, many solutions use simple ball milling or mechanical shearing to achieve preliminary dispersion of particles, enabling some fillers to have better fluidity and processing adaptability during processes such as injection molding and calendering.

[0004] However, these technologies still have some deficiencies; firstly, many additive-based treatments rely on interfacial wetting effects and lack true chemical anchoring, so the fillers are prone to debonding during long-term use and the interface is unstable; secondly, most of the particle size control relies on physical screening, and the distribution range is relatively wide, which easily leads to fluctuations in mechanical properties and poor batch-to-batch consistency. In some processes, the stability of the powder modification layer is insufficient, and it is prone to depolymerization in a heat or melting environment, unable to guarantee the structural continuity of the finished product. Some drying methods seemingly retain the powder morphology, but cause agglomeration or bridging during subsequent use, ultimately affecting the molding flow; furthermore, in many ball milling treatments, due to improper control, the surface modification structure is instead damaged, weakening the interfacial effect. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technologies, the present invention provides a preparation process of modified calcium carbonate powder based on talcum powder, which solves the problems of poor interfacial bonding, uneven dispersion, and insufficient processing adaptability of powders in the existing technologies.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: A preparation process of modified calcium carbonate powder based on talcum powder, comprising the following steps: S1. Raw material preparation: Select high-purity natural calcium carbonate powder and talcum powder for subsequent modification and compounding treatment. Natural calcium carbonate has good dispersibility and filling properties, but its surface activity is low and it is prone to agglomeration. Talcum powder, as a layered silicate mineral, has natural lubricity and a flaky structure, which can improve the dispersibility and interfacial properties of the composite system. By selecting high-purity raw materials, it helps to reduce impurity interference and improve the controllability of the modification effect and the stability of the composite material; S2. Pretreatment of calcium carbonate powder: Screen and pickling-treat the calcium carbonate powder to remove impurities and improve its surface reaction performance. Calcium carbonate powder often contains soluble salts, metal impurities or coarser particles, which will affect the adsorption efficiency and dispersion performance of the surface modifier. By screening, the particle size distribution can be unified, and pickling can remove the alkaline impurities and active passivation layer on the surface of calcium carbonate, making its surface carry more reactive hydroxyl groups, which is beneficial to the grafting of subsequent functional groups or physical adsorption modification; S3. Pretreatment of talcum powder: Screen and bake the talcum powder to remove moisture and impurities. Due to its natural layered structure, talcum powder is easy to adsorb moisture and volatile impurities in the air. Through high-temperature baking, physical adsorbed water and some volatile impurities can be effectively removed, while improving the stability and reactivity of the powder. Screening ensures that the talcum powder has a uniform particle size and morphology, reduces the agglomeration phenomenon, and provides a uniform dispersion system for subsequent modification and compounding; S4. Surface modification treatment: Respectively perform surface modification on the pretreated calcium carbonate powder and talcum powder. The surfaces of calcium carbonate and talcum powder are both inorganic polar groups with high surface energy, and direct mixing is prone to agglomeration and phase interface incompatibility problems. Through surface modification, introducing γ-aminopropyltriethoxysilane alcohol solution can form a dense coating layer or charge layer on the particle surface, reduce the surface energy, and improve the organophilicity; S5. Compounding treatment: Uniformly mix the surface-modified calcium carbonate powder and talcum powder according to a set mass ratio to form a modified composite powder material. The surface-modified calcium carbonate powder and talcum powder have good dispersibility and interfacial compatibility. Among them, calcium carbonate provides volume and structural support as the main structure, and talcum powder provides characteristics such as lubrication, anti-sticking, and improving processing fluidity. The two form a stable composite system, effectively improving the processing adaptability and terminal performance of the composite powder; S6. Dispersion treatment: The modified composite powder material is subjected to ultrasonic-assisted dispersion treatment in a dispersion medium to ensure the uniform distribution of each component particle in the medium. In the solution system, through the cavitation effect and shear force generated by ultrasonic waves, the agglomeration state between particles can be effectively broken, enabling the particles to be uniformly dispersed in the dispersion medium while maintaining the independence of particle size, which is beneficial to the retention of the powder morphology and structure during the subsequent drying process; S7. Drying treatment: The dispersed composite material is subjected to freeze-drying treatment to remove the dispersion medium and maintain the particle structure. Freeze-drying uses the sublimation principle to remove moisture under low temperature and vacuum, which can effectively avoid the phenomena of powder agglomeration, structure collapse or secondary aggregation caused by water evaporation in traditional thermal drying; S8. Particle screening and optimization: The dried composite powder is ground and screened to a set particle size range. Through grinding, the particles can be further refined and the agglomerates can be depolymerized. Screening ensures that the final product particle size is controlled within a specific range to meet the precision requirements of downstream applications in terms of dispersibility, filling property or reactivity.

[0007] Preferably, the raw material preparation step includes: Select natural calcium carbonate powder with an average particle size of 0.5 μm to 5 μm, and the mass fraction is 80 parts to 95 parts; Select talc powder with an average particle size of 0.2 μm to 2 μm, and the mass fraction is 5 parts to 20 parts. As the main component of the composite system, the particle size range of calcium carbonate is controlled within 0.5 μm to 5 μm, which can provide appropriate filling property and volume contribution while maintaining good dispersibility, and avoid the agglomeration problem caused by too fine particles or uneven distribution caused by too coarse particles. Talc powder, as a functional additive, its flaky structure and lubricating performance can improve the interfacial characteristics and processing fluidity of the system. When the particle size is controlled within 0.2 μm to 2 μm, it can fully fill the gaps between calcium carbonate in the composite structure, improve the packing density and interfacial uniformity of the particles, and at the same time do not affect the fluidity and dispersion stability of the powder. A higher proportion of calcium carbonate can ensure cost control and structural support, while the introduction of an appropriate amount of talc powder plays a key role in enhancing interfacial wettability, improving processability and the performance of the final composite system.

[0008] Preferably, the pretreatment of the calcium carbonate powder includes: Use a vibrating screen with a mesh number of 200 to 400 to screen, and remove particles with a particle size greater than 10 μm. Through the screening process within this range of mesh numbers, particles that do not meet the particle size requirements can be effectively removed. Further setting the upper limit of particle size removal to 10 μm is to match the particle size of the subsequent talc powder and achieve a good inter-particle cooperative filling structure, enhancing the denseness and rheological stability of the composite material; A 1% to 3% hydrochloric acid solution and calcium carbonate powder are pickled at a liquid-solid ratio of 5mL:1g to 10mL:1g. The pickling time is 20 minutes to 40 minutes, and the pickling temperature is controlled at 25℃ to 35℃. The surface of natural calcium carbonate is usually attached with soluble impurities, trace metal ions or passivation layers, which will affect the adsorption efficiency of the surface modifier. Hydrochloric acid, as a weak acid, can react with calcium carbonate in a controlled slow manner, releasing CO2 and taking away surface impurities, while exposing more active hydroxyl sites, thereby improving surface chemical reactivity. Hydrochloric acid in a concentration range of 1%–3% can avoid excessive corrosion while ensuring the treatment effect. The setting of the liquid-solid ratio and time parameters balances the reaction depth and powder stability, preventing particle size loss or structural damage due to excessive dissolution. In addition, the pickling temperature of 25℃ to 35℃ is controlled in the range of room temperature to slightly high temperature, which helps the reaction to proceed uniformly while avoiding particle agglomeration or crystal phase transition.

[0009] Preferably, the talc pretreatment comprises: Use a vibrating screen with a mesh size of 250 to 400 to remove particles with a particle size greater than 60 microns. Talc is a layered silicate mineral, and its particle size and particle size distribution have a significant impact on the dispersion and composite uniformity of the powder. Too large a particle size is not only not conducive to structural interlocking or interface matching with calcium carbonate powder, but also easily agglomerates in subsequent processing, reducing the stability of the powder system. By controlling the screening interval from 250 mesh (about 60μm) to 400 mesh (about 38μm), coarse particles with a particle size greater than 60 microns can be effectively removed, so that the talc is kept in a finer submicron or micron range, thereby enhancing its particle size compatibility and specific surface area with calcium carbonate powder and improving composite efficiency; The screened talc powder is baked at a temperature of 170°C to 190°C for 60 to 90 minutes to reduce the moisture content of the powder to below 0.5% and remove volatile impurities. The layered structure of talc powder gives it a strong adsorption capacity and is easy to adsorb environmental moisture or residual crystal water; if it is not removed, it will release moisture during the subsequent surface modification or dispersion process, affecting the stability of the system and may induce reaction by-products. In addition, talc powder may also contain trace organic matter or volatile impurities, which will interfere with the interfacial properties of the composite system if not removed. By baking at a constant temperature under medium and high temperature conditions of 170°C to 190°C, the adsorbed water and some organic impurities can be effectively removed, while avoiding crystallization or phase change of the talc structure due to excessive temperature. The 60 to 90-minute insulation time ensures that the thermal field evenly penetrates into the talc particles, reducing the moisture content of the powder to below 0.5%, providing dry, clean and active basic conditions for subsequent surface modification treatment.

[0010] Preferably, the surface modification treatment comprises: Spray the surface of calcium carbonate powder evenly with a γ-aminopropyltriethoxysilane alcohol solution with a mass fraction of 0.8% to 1.5%, and react at 80°C to 100°C for 2 hours. γ-aminopropyltriethoxysilane (APTES) is a commonly used silicone coupling agent. Its molecular structure contains both ethoxy groups that can be hydrolyzed to form Si-OH and aminopropyl functional groups that can react with polymers or dispersion systems. Setting the spraying method can ensure the uniformity of the distribution of the modifier, and the reaction temperature of 80°C to 100°C and the reaction time of 2 hours provide sufficient kinetic conditions for the silane coupling reaction, which helps to improve the bonding stability and coverage density, making the modified calcium carbonate have better dispersibility and composite adaptability; Add talc powder to an aqueous solution containing 0.2% to 0.8% by mass of sodium polyacrylate and 0.1% to 0.3% by mass of polyvinyl alcohol, stir evenly, and react at 60°C to 70°C for 1 hour. By introducing an aqueous solution of PAA and PVA for coating modification, a hydrophilic / hydrophilic polymer composite polymer layer can be formed on the surface of talc powder. Sodium polyacrylate, as an anionic polymer, has excellent dispersibility and adsorption ability for inorganic particles; while polyvinyl alcohol can enhance the flexibility and uniformity of the modified film layer, improve the stable dispersion ability and interfacial wettability of the powder. Reacting at a mild temperature of 60°C to 70°C for 1 hour is beneficial for the adsorption and orientation arrangement and curing of PAA and PVA on the particle surface, forming a dense and continuous coating layer, while avoiding thermal decomposition or polymer structure damage.

[0011] Preferably, the composite treatment includes: Add the surface-modified calcium carbonate powder and talc powder to a high-speed stirrer at a mass ratio of 8:1 to 9:1, and mix at a speed of 600 rpm to 900 rpm for 30 minutes to 60 minutes. The mass ratio is set based on the balance design between the main and auxiliary functional materials. Calcium carbonate, as the main filling and structural framework material, provides volume support and physical stability; talc powder, as a modification aid, improves the interfacial properties, dispersibility and fluidity of the system. A higher proportion of calcium carbonate ensures the strength and composition stability of the composite system, while the addition of a small amount of talc powder can improve the overall performance, avoiding cost increase or powder system instability caused by its excessive amount. Using a high-speed stirrer and controlling the mixing speed between 600 rpm and 900 rpm, combined with a continuous mixing time of 30 minutes to 60 minutes, can provide sufficient shear force and flow disturbance, enabling powders with different particle sizes and densities to fully contact and be evenly distributed in three-dimensional space, avoiding the floating or aggregation of talc powder due to its smaller particle size or lower surface energy.

[0012] Preferably, the dispersion treatment includes: The composite powder is added to an ethanol aqueous solution with a volume fraction of 30% to 60%. The ultrasonic frequency is 20 kHz to 40 kHz, the ultrasonic time is 15 minutes to 30 minutes, and the power is 300 W to 600 W. After high-speed mechanical mixing, although preliminary uniform compounding is achieved, there are still micro-agglomerations or structural entanglements between the particles. Selecting a mixed solution of ethanol and water as the dispersion medium is mainly based on its moderate dielectric constant, good volatility, and moderate wetting effect on the inorganic modified powder. Using an ultrasonic frequency of 20 kHz to 40 kHz can generate strong "cavitation effects" and micro-jet disturbances in the liquid medium, effectively overcoming the weak van der Waals forces or electrostatic adsorption forces between the particles, thereby breaking up the powder agglomeration; while controlling the ultrasonic power at 300 W to 600 W and the action time at 15 to 30 minutes ensures that the ultrasonic energy is sufficient to be transmitted to the entire dispersion system, forming a uniform sound field distribution, and at the same time avoiding excessive ultrasound from causing particle structure damage or system temperature rise.

[0013] Preferably, the drying treatment includes: The dispersion slurry is frozen at -40°C to -60°C for 4 hours to 6 hours. Using this range of low-temperature freezing is to quickly transform the ethanol aqueous solution into solid ice crystals in a short time, locking the spatial distribution of the particles in the dispersed state. This process avoids excessive migration, agglomeration, or mutual contact of the powder during the cooling process, effectively maintaining the original dispersed structure of the particles; Under the condition of a vacuum degree of 0.1 MPa to 0.15 MPa, freeze-drying is carried out for 12 hours to 18 hours. Freeze-drying is a low-temperature sublimation drying technology, which is suitable for inorganic powders with high requirements for particle structure and dispersibility. Under this range of vacuum degree, the frozen ethanol-water mixed solvent will directly sublimate into a gas without passing through the liquid state, thereby reducing the capillary force pulling and adhesion between the particles, effectively maintaining the dispersed state, original particle size, and specific surface area of the particles.

[0014] Preferably, the particle screening and optimization include: The dried composite powder is ground in a ball mill at a speed of 200 rpm to 400 rpm for 30 minutes to 1 hour. Through ball milling, the powder can be depolymerized for the second time. Controlling the ball milling speed in the range of 200 rpm to 400 rpm is to provide appropriate mechanical shear force and impact energy, ensuring both the grinding effect and avoiding excessive damage to the powder structure or a decrease in the specific surface area. Setting the time between 30 minutes and 1 hour can achieve a balance between energy consumption and grinding efficiency, making the particles reach the required fineness and have good fluidity and dispersion performance; Screened through a sieve with 300 to 500 meshes, the particle size distribution of the obtained powder is D90≤10μm, D50 is 2μm to 5μm. High-precision screening through a sieve with 300 meshes (about 48μm) to 500 meshes (about 25μm) can effectively remove the coarse particles formed due to insufficient grinding or un-disintegrated agglomeration, improve the particle size consistency and quality stability of the product. The particle size control standard of D90≤10μm enables the particle fineness to meet the requirements of high dispersion, avoiding particle sedimentation or precipitation of coarse particles during application; while controlling D50 between 2μm and 5μm makes the powder have sufficient fineness to achieve good distribution, and at the same time retains a certain particle structure strength and processing fluidity.

[0015] The present invention provides a preparation process of modified calcium carbonate powder based on talcum powder. It has the following beneficial effects: 1. The present invention uses γ-aminopropyltriethoxysilane to modify the surface of calcium carbonate particles, introducing a silane molecular layer with polar functional groups, which improves the affinity between inorganic powder and polyolefin matrix. It achieves the effects of enhancing the interfacial bonding force and improving the mechanical properties of the composite material. Compared with the direct filling method of unmodified calcium carbonate in the prior art, it overcomes the problems of non-bonding at the interface and easy peeling, and solves the problem of the overall strength reduction of the material.

[0016] 2. The present invention introduces PAA / PVA flexible polymer as the talcum powder coating layer, and realizes the reconstruction of the surface polarity of the powder on the basis of maintaining the integrity of the filler particle structure. It achieves the purpose of enhancing the dispersibility and improving the system stability. Compared with the traditional method of directly mixing talcum powder with polymers, it breaks through the limitations of serious powder agglomeration and uneven filler distribution, and improves the appearance and molding consistency of the product.

[0017] 3. By combining freeze-drying and low-speed ball milling means, the present invention realizes that the modified composite powder obtains an ideal particle size distribution and particle morphology while maintaining the structural integrity. The technical effects are reflected in the improvement of powder fluidity and more stable loose bulk density. In traditional air drying or untreated powder systems, problems such as particle agglomeration and structural collapse generally exist, resulting in difficult flow and unsmooth transportation during the processing. The present invention effectively avoids such defects.

[0018] 4. The present invention adds a classification and screening link in the post-treatment stage, effectively controls the powder particle size range, and improves the dispersion uniformity and filling efficiency in the polymer matrix. Finally, the dual optimization of the mechanical properties and apparent quality of the product is realized. Compared with the solutions with insufficient particle screening or too wide particle size distribution in the existing process, it solves the problems of internal stress accumulation and performance fluctuation caused by abnormal particle size in the composite system. Description of the Drawings

[0019] Figure 1 It is a flow chart of the preparation process of the present invention. Detailed implementation manners

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0021] Please refer to the attached Figure 1 :[[]]END]] Example 1 Weigh 90 parts of natural calcium carbonate powder, and evenly spray 1.0% γ-aminopropyltriethoxysilane (APTES) ethanol solution on its surface, and react for 2 hours at 90 °C to perform silane surface modification treatment.

[0022] Weigh 10 parts of talc powder, add it to an aqueous solution containing 0.3% sodium polyacrylate (PAA) and 0.2% polyvinyl alcohol (PVA), and stir and react at 65 °C for 1 hour to achieve surface coating modification.

[0023] Mix the above-mentioned modified calcium carbonate powder and modified talc powder in proportion, add them to a high-speed stirrer, and stir and mix at a speed of 700 rpm for 45 minutes to obtain a preliminary composite powder.

[0024] Add the composite powder to an ethanol aqueous solution with a volume fraction of 50%, and perform dispersion treatment using ultrasonic waves. The ultrasonic frequency is 30 kHz, the power is 450 W, and the treatment time is 20 minutes.

[0025] Freeze the dispersion slurry at -50 °C for 5 hours, and then freeze-dry it at a vacuum degree of 0.12 MPa for 16 hours to obtain a dry powder.

[0026] Grind the obtained powder in a ball mill at 300 rpm for 45 minutes, and then screen it through a 400-mesh sieve to obtain a uniform powder with D90 ≤ 10 μm and D50 of about 3.5 μm.

[0027] Example 2 Weigh 80 parts of natural calcium carbonate powder, and perform surface treatment with 1.2% APTES ethanol solution. The treatment temperature is 85 °C, and the treatment time is 2 hours.

[0028] Weigh 20 parts of talc powder, add it to an aqueous solution containing 0.5% PAA and 0.3% PVA, and react at 70 °C for 1 hour.

[0029] Mix the two in proportion and mix them in a high-speed stirrer at a speed of 600 rpm for 60 minutes.

[0030] The composite powder is put into an ethanol aqueous solution with a volume fraction of 60% and subjected to ultrasonic dispersion at a frequency of 25 kHz, a power of 500 W, and a treatment time of 30 minutes.

[0031] The freezing conditions of the slurry are −60 °C for 6 hours, and then freeze-dried for 18 hours under a vacuum condition of 0.15 MPa.

[0032] After drying, ball milling is carried out at a rotation speed of 400 rpm for 60 minutes, and screening is performed through a 500-mesh sieve. The final particle size is D90 ≤ 9 μm, and D50 is about 3 μm.

[0033] Example 3 Weigh 95 parts of natural calcium carbonate powder and treat it with a 0.8% APTES alcohol solution. The treatment temperature is set at 80 °C, and the reaction lasts for 2 hours.

[0034] Weigh 5 parts of talc powder and disperse it in an aqueous solution containing 0.2% PAA and 0.1% PVA, and react at 60 °C for 1 hour.

[0035] After mixing the modified powders, they are mixed in a high-speed stirrer at a speed of 900 rpm for 30 minutes.

[0036] Then add it to an ethanol aqueous solution with a volume fraction of 30%, set the ultrasonic frequency at 20 kHz, the power at 300 W, and the ultrasonic time at 15 minutes.

[0037] Freeze the dispersed slurry at −40 °C for 4 hours and freeze-dry it under a vacuum degree of 0.1 MPa for 12 hours.

[0038] The ball milling conditions for the dried powder are 200 rpm and a grinding time of 30 minutes. Screening is carried out using a 300-mesh sieve, and finally a modified composite powder with a particle size distribution of D90 ≤ 10 μm and D50 of about 5 μm is obtained.

[0039] Comparative Example 1: Compared with Example 1, the difference is that the calcium carbonate powder is not subjected to γ-aminopropyltriethoxysilane modification treatment, and the rest are the same.

[0040] Comparative Example 2: Compared with Example 1, the difference is that ultrasonic dispersion treatment is not used, but direct static stirring dispersion is adopted, and the rest are the same.

[0041] Comparative Example 3: Compared with Example 1, the difference is that freezing and freeze-drying treatments are not carried out, but direct hot air drying is performed at 60 °C until constant weight, and the rest are the same.

[0042] Comparative Example 4: Compared with Example 2, the difference is that the talc powder is not subjected to PAA / PVA modification treatment, but the original talc powder is directly used, and the rest are the same.

[0043] Comparative Example 5: Compared with Example 2, the difference lies in that the mass ratio of modified calcium carbonate powder to talcum powder is adjusted to 6:4, exceeding the range of 8:1 to 9:1 specified in the claims, and the rest are the same.

[0044] Comparative Example 6: Compared with Example 2, the difference lies in that the ball milling step is cancelled and sieving is directly carried out after drying, and the rest are the same.

[0045] Comparative Example 7: Compared with Example 3, the difference lies in that the dosage of APTES is increased to 2.5%, exceeding the range of 0.8% to 1.5% in the claims, and the rest are the same.

[0046] Comparative Example 8: Compared with Example 3, the difference lies in that the freezing temperature is only -20°C, lower than the specified range of -40°C to -60°C, and the rest are the same.

[0047] Comparative Example 9: Compared with Example 3, the difference lies in that a 200-mesh sieve is used for the final sieving particle size, and the particle size D90 of the obtained powder is >20 μm, resulting in ineffective particle size control, and the rest are the same.

[0048] Test Example 1: Experimental purpose: By comparing the differences between the examples and the comparative examples in terms of dispersion treatment and particle size regulation, verify the importance of each step in the present invention (such as silane treatment, PAA / PVA modification, ultrasonic dispersion, freeze-drying, and component ratio) for improving the powder dispersibility and particle size uniformity.

[0049] Experimental steps: Sample preparation: Seven groups of powder samples were prepared according to the process routes of Example 1, Example 2, and Comparative Examples 1, 2, 3, 4, and 5.

[0050] Dispersibility test (sedimentation test): Take 1 g of each group of samples, add them to the same volume of distilled water (50 mL), use a glass test tube, ultrasonically disperse for 1 minute and then let it stand.

[0051] Record the height of the supernatant every 10 minutes, continuously observe for 1 hour, and record the final sedimentation height (sedimentation rate) as the dispersibility index.

[0052] Particle size distribution test: Take each group of powder samples and detect their particle size parameters such as D90 and D50 with a laser particle size analyzer (such as Mastersizer).

[0053] Calculate the standard deviation of the particle size for each group of test data to represent the degree of particle distribution dispersion.

[0054] Data recording and comparative analysis (the experimental results are shown in Table 1).

[0055] Table 1: Test Results of Dispersibility and Particle Size Control Performance of Different Samples It can be seen from Table 1 that: First of all, after the calcium carbonate in Examples 1 and 2 was modified with γ-aminopropyltriethoxysilane (APTES), organic functional groups were introduced on the powder surface, greatly improving the affinity and dispersion stability of the particles in the liquid phase. The mechanism is that after the ethoxy groups in the silane molecule are hydrolyzed to form silanols, they react with the hydroxyl groups on the calcium carbonate surface to form stable Si–O–Ca bonds, and at the same time form an organic functional layer on the particle surface, reducing the surface energy and agglomeration tendency of the particles. Therefore, obvious phenomena of accelerated sedimentation and increased particle size appeared in the samples in Comparative Example 1 where this treatment was omitted.

[0056] Secondly, the synergy of ultrasonic dispersion and freeze-drying treatment is another key link to achieve highly dispersed and uniform particle size. In Examples 1 and 2, through the ultrasonic cavitation effect of 20 kHz–40 kHz, the micro-agglomeration structure caused by van der Waals forces between particles can be effectively broken, and the powder can be fully and uniformly distributed in the liquid medium. Subsequently, deep freezing at -40 °C to -60 °C can quickly solidify the spatial position of the particles, freeze the liquid channels to form a microporous ice crystal structure, and cooperate with the vacuum sublimation drying process to avoid secondary agglomeration caused by liquid capillary force, thus realizing structure shaping and particle size retention. On the contrary, in the samples in Comparative Examples 2 and 3 where ultrasonic treatment was cancelled or conventional hot air drying treatment was used, the phenomenon of abnormally large particle size and increased particle size standard deviation generally appeared, indicating that when the energy input or temperature control link is missing, particles are extremely likely to re-agglomerate.

[0057] In addition, the reasonable control of the composite ratio and the coating modification of talc powder also play a significant role in improving the particle size distribution. In Example 2, talc powder was coated with PAA and PVA, making its surface have certain hydrophilicity and a stable interface layer, further improving the dispersion balance of the overall system. In Comparative Examples 4 and 5, untreated talc powder or an unreasonable mass ratio was selected, resulting in uneven distribution or significant deviation of the median particle size, which is closely related to the fact that the polymer adsorption film formed by the modification of talc powder mentioned above can hinder the adhesion between particles and improve the interface stability, reflecting the necessity of the collaborative design of components and interfaces.

[0058] Test Example 2: Experimental Purpose: To verify the effectiveness of the surface modification treatment process (especially APTES modification and PAA / PVA coating) in improving the compatibility between the powder and the matrix. The tests include two aspects: mechanical bonding strength and microscopic interface morphology observation.

[0059] Experimental Steps: Composite Material Preparation: The samples of each example and comparative example were respectively blended with a polypropylene (PP) matrix at a filling ratio (such as 20 wt%), and splines were prepared using a twin-screw extruder.

[0060] The dimensions of the splines were prepared with reference to the GB / T1040 standard, and a part of the cross-section was reserved for subsequent morphology observation.

[0061] Interface bonding strength test (shear test): Using a universal material testing machine, according to the constant-speed tensile mode (1 mm / min), the interfacial shear strength (MPa) of the powder-filled splines was tested.

[0062] Each group of samples was tested 5 times, and the average value was taken as the result, and the maximum shear strength was recorded.

[0063] Scanning electron microscopy (SEM) analysis: After metal spraying the fractured splines, the morphology of the interface cross-section was observed by SEM to evaluate the degree of particle embedding, peeling traces and interface crack paths. (The experimental results are shown in Table 2).

[0064] Table 2: Test results of the interface bonding properties of different sample-filled composites It can be seen from Table 2 that: After the calcium carbonate powder in Example 1 and Example 3 was treated with γ-aminopropyltriethoxysilane (APTES), a stable organosilane coupling layer was formed on the particle surface. The aminopropyl end of this layer can interact polarly or even chemically crosslink with the polypropylene or epoxy matrix, thus forming an effective "bridge structure" in the interface layer. This mechanism ensures the embedding stability of the particles in the matrix and the interface stress transfer efficiency, so it shows obvious advantages in the shear strength test. In contrast, in Comparative Example 1 without treatment, due to the lack of interface bonding, obvious powder debonding and brittle fracture phenomena of crack propagation along the interface occurred.

[0065] In addition, the surface coating modification of talc also plays a key synergistic role in improving the interface compatibility of the composite system. In the examples, a flexible polymer adsorption layer was constructed using sodium polyacrylate (PAA) and polyvinyl alcohol (PVA). This layer can not only improve the distribution state of talc in the matrix, but also generate hydrogen bonds or van der Waals forces with the organic matrix by forming a large number of polar functional groups, enhancing the bonding performance between the powder and the polymer. In Comparative Example 4, the untreated talc showed particle peeling and interface cavities in the fracture surface, which fully indicates that the interface stress cannot be effectively transferred, resulting in a decrease in mechanical properties.

[0066] The regulation of freezing conditions also plays a role in structural guarantee for the interfacial bonding performance. In Example 3, deep freezing at -40°C to -60°C locked the uniform dispersion state of the powder in the liquid phase, and subsequent vacuum sublimation avoided powder agglomeration and damage to the modified layer, ensuring the integrity of the particle surface coating and the continuity of the functional layer from the microscopic structure. In Comparative Example 8, due to insufficient freezing temperature, partial powder structure collapse and discontinuous modified layer occurred, ultimately manifested as low interfacial bonding force and incomplete powder embedding in SEM observation. This also verifies the mechanism basis of the temperature control process for the stability of the surface functional structure emphasized in the present invention.

[0067] Test Example III: Experimental purpose: To verify the actual effects of ball milling and reasonable screening steps on improving the powder particle morphology, particle size control, and its processing adaptability.

[0068] Experimental steps: Sample preparation: Prepare 3 groups of powder samples according to the process routes of Example 3, Comparative Example 6, and Comparative Example 9 respectively.

[0069] Ensure that each sample has undergone freeze-drying, with differences only in the post-treatment (ball milling, screening) process.

[0070] Flowability test (funnel method): Use a standard powder flowability test funnel with a bottom hole diameter of 5 mm. Measure 50 g of powder and place it into the funnel, record the time (seconds) taken for complete outflow, and calculate the powder flow rate (g / s). Each group is tested 3 times and the average value is taken.

[0071] Angle of repose test: Slowly pour the powder onto a glass plate to form a natural conical pile, and measure the angle of repose (degrees). Use the projection method to take pictures to assist in reading the value.

[0072] Bulk density test: Fill a 20 mL graduated cylinder with powder (without compaction), weigh it, and then calculate the bulk density (g / cm 3 ) (The experimental results are shown in Table 3) Table 3: Test results of the flowability and packing properties of different samples As can be seen from Table 3: The ball milling and screening process is not only a simple post-processing step, but also a key technical node to ensure that the powder has good fluidity and processing adaptability. After freeze drying, Example 3 is subjected to low-speed ball milling at 200-400rpm to fully disaggregate the residual agglomerates while maintaining the particle structure intact, thereby forming a micro-powder with a moderate particle size and a relatively smooth surface. This particle morphology can reduce the friction coefficient and locking effect between particles during the flow process, so that the powder has a higher flow rate and a smaller stacking angle. Comparative Example 6 was not ground, and the particles still had multi-level agglomerations and sharp corners, resulting in uneven stacking and obvious bridging effect, which was manifested as a decrease in flow rate and an increase in stacking angle.

[0073] Looking further, in Example 3, by accurately screening the dry powder in the range of 300 to 500 mesh, coarse particles, agglomerates and large particles mixed in the fine powder can be effectively removed, and the particle size range is unified to the target range of D90≤10μm and D50 of 2-5μm. This particle size distribution allows the powder to form a dense but not compacted arrangement structure when stacked, which improves the stability of the loose density and avoids local blockage and powder collapse during the flow process. However, Comparative Example 9 used 200 mesh screening, which failed to effectively remove overly coarse particles and uneven particle size components, resulting in a decrease in its loose density, and the coarse particles interfered with the overall arrangement of the particles, causing poor fluidity.

[0074] The above results are highly consistent with the mechanism of particle size control and post-processing structure optimization emphasized in the present invention. The dispersed structure maintained by freeze drying can easily lose its dispersion advantage during powder collection and use without further grinding and screening. Therefore, subsequent low-speed ball milling helps to maintain the particle size stability based on particle dispersion, while the screening process controls the particle size limit to achieve the regular distribution and structural synergy of the overall particle population, which jointly determines the flow behavior and processing performance of the final powder.

[0075] Test Example 4: Purpose of the experiment: This experiment aims to verify the enhanced and synergistic performance of the modified calcium carbonate / talc composite powder obtained in the present invention in the actual application system (such as polypropylene filling material), including the mechanical properties and product appearance uniformity, so as to fully reflect the influence of different powder processes on the terminal use effect.

[0076] Experimental steps: Sample preparation: The modified powders in Example 1, Example 2, Example 3 and Comparative Examples 1, 4, 6 and 9 were selected.

[0077] Each powder was mixed with polypropylene (PP) matrix at a filling ratio of 30wt% in a twin-screw extruder to prepare a filling masterbatch, which was then injection molded into a standard specimen.

[0078] Mechanical property test: Refer to the GB / T1040 standard to conduct tensile strength (MPa) and flexural strength (MPa) tests. Each group of samples is tested 5 times, and the average value is taken.

[0079] Observation of product uniformity: Observe whether there are phenomena such as powder precipitation, color difference, stripes, delamination, etc. on the surface of injection-molded products, and use subjective grading of "excellent / medium / poor" and supplement with high-definition images for recording (the experimental results are shown in Table 4).

[0080] Table 4: Performance of different sample-filled polypropylene systems It can be seen from Table 4 that: The surface silane modification process adopted in the examples introduced organic functional groups on the surface of calcium carbonate particles, improved the interfacial bonding force with hydrophobic matrices such as polypropylene, and effectively improved the interfacial stress transfer ability between the filler and the matrix. During the stress process of the composite material, this "chemical compatibility layer" can slow down the stress concentration phenomenon, avoid particle detachment or peeling from the interface, and improve the overall mechanical properties. Due to the lack of this key modification step in Comparative Example 1, weak interfacial bonding occurred after filling, resulting in obvious performance loss and structural defects.

[0081] In addition, the flexible polymer coating layer formed by PAA and PVA on talc not only improved the dispersion uniformity of the powder in the matrix, but also constructed an intermediate transition interfacial layer with certain polarity, making the originally surface-inert talc particles more likely to have physical or chemical interfacial interactions with the polymer. This synergistic effect is reflected in the filling system, which not only improves the interfacial activity of the filler itself, but also inhibits particle agglomeration and migration, and improves the molding surface and stability of the product. Looking at the sample of untreated talc in Comparative Example 4, although the mechanical strength was slightly improved, due to unstable interfaces, some powder precipitation and flow marks still occurred during the injection molding process, verifying the necessity of talc modification treatment.

[0082] Finally, particle optimization steps such as ball milling and screening also play a basic guarantee role in the final performance. By moderately low-speed ball milling, the residual micro-agglomerates after drying can be broken up, making the particle size distribution of the powder more concentrated. At the same time, screening ensures that D90≤10μm and D50 is controlled within the range of 2–5μm, enabling the filler to be more evenly distributed in the polymer matrix, reducing local concentration or filler bridging, thereby improving the overall processing stability and mechanical consistency of the composite material. The powder with rough screening in Comparative Example 9 led to larger filler particle size and wide distribution, ultimately manifested as uneven appearance and mechanical fluctuations in the molded products, further corroborating the supporting value of the particle regulation strategy in the present invention for application adaptability performance.

[0083] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Preparation process of modified calcium carbonate powder based on talcum powder, characterized in that, The following steps are involved: S1. Raw material preparation: select high-purity natural calcium carbonate powder and talcum powder for subsequent modification and composite treatment; S2, calcium carbonate powder pretreatment: screening and pickling the calcium carbonate powder to remove impurities and improve its surface reaction performance; S3, talcum powder pretreatment: sieving and baking the talcum powder to remove moisture and impurities; S4, surface modification treatment: surface modification of the pretreated calcium carbonate powder and talcum powder respectively; S5, composite treatment: uniformly mixing the surface-modified calcium carbonate powder and talcum powder according to a set mass ratio to form a modified composite powder material; S6, dispersion treatment: subjecting the modified composite powder material to ultrasonic-assisted dispersion treatment in a dispersion medium to ensure uniform distribution of particles of each component in the medium; S7, drying treatment: freeze-drying the dispersed composite material to remove the dispersion medium and maintain the particle structure; S8, particle screening and optimization: Grind the dried composite powder and sieve it to a set particle size range.

2. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The raw material preparation step comprises: Select natural calcium carbonate powder with an average particle size of 0.5 μm to 5 μm, with a mass fraction of 80 to 95 parts; The talc powder has an average particle size of 0.2 μm to 2 μm and the mass fraction is 5 to 20 parts.

3. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The calcium carbonate powder pretreatment comprises: Use a vibrating screen with a mesh size of 200 to 400 to screen and remove particles with a particle size greater than 10 μm; Use 1% to 3% hydrochloric acid solution and calcium carbonate powder with a liquid-to-solid ratio of 5mL:1g to 10mL:1g for pickling. The pickling time is 20 minutes to 40 minutes, and the pickling temperature is controlled at 25°C to 35°C.

4. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The talcum powder pretreatment comprises: Use a 250-400 mesh vibrating screen to screen and remove particles larger than 60 microns; The screened talc powder is baked at a temperature of 170° C. to 190° C. for 60 to 90 minutes to reduce the moisture content of the powder to below 0.5% and remove volatile impurities.

5. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The surface modification treatment comprises: The surface of the calcium carbonate powder is uniformly sprayed with a γ-aminopropyl triethoxysilanol solution having a mass fraction of 0.8% to 1.5%, and reacted at 80° C. to 100° C. for 2 hours; Add talcum powder to an aqueous solution containing 0.2% to 0.8% by mass of sodium polyacrylate and 0.1% to 0.3% by mass of polyvinyl alcohol, stir evenly, and react at 60° C. to 70° C. for 1 hour.

6. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The composite treatment includes: The surface-modified calcium carbonate powder and talcum powder are added into a high-speed stirrer at a mass ratio of 8:1 to 9:1, and mixed at a speed of 600 rpm to 900 rpm for 30 to 60 minutes.

7. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The decentralized processing includes: The composite powder is added to an ethanol aqueous solution with a volume fraction of 30% to 60%, the ultrasonic frequency is 20kHz to 40kHz, the ultrasonic time is 15 minutes to 30 minutes, and the power is 300W to 600W.

8. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The drying process comprises: Freeze the dispersed slurry at -40°C to -60°C for 4 to 6 hours. The particle screening and optimization include: The dried composite powder is ground in a ball mill at a speed of 200 rpm to 400 rpm for 30 minutes to 1 hour; Screened through a sieve with 300 to 500 mesh, the particle size distribution of the obtained powder is D90 ≤ 10 μm, and D50 is 2 μm to 5 μm; Freeze-dried for 12 hours to 18 hours under the condition of a vacuum degree of 0.1 MPa to 0.15 MPa.

9. The preparation process of the modified calcium carbonate powder based on talcum powder according to claim 1, characterized in that, The particle screening and optimization include: The dried composite powder is ground in a ball mill at a speed of 200 rpm to 400 rpm for 30 minutes to 1 hour; Screened through a sieve with 300 to 500 mesh, the particle size distribution of the obtained powder is D90 ≤ 10 μm, and D50 is 2 μm to 5 μm.

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