Preparation process of special nano calcium carbonate for rubber and plastic

Abstract

The invention belongs to the technical field of nano calcium carbonate, and particularly relates to a preparation process of special nano calcium carbonate for rubber and plastic, which comprises the following steps: adjusting the density of refined lime milk, and adding a dispersing agent to obtain atomized slurry; a C02 / N2 mixed gas is introduced into the bottom of the carbonization tower, the atomized slurry is vertically sprayed out from the top, an amorphous intermediate is generated through a reaction, and a carbonized solution is obtained; transferring the carbonized solution to a carbonization kettle, adding a crystal form control agent, cyclohexane, a nonionic surfactant and a cosurfactant, and carrying out ultrasonic dispersion to form a water-in-oil microemulsion; introducing C02 / N2 mixed gas into the carbonization kettle, and carrying out carbonization reaction to obtain nano calcium carbonate slurry; the modified nano calcium carbonate slurry is subjected to dehydration, washing, drying and air jet pulverization, and the special high-specific-surface-area spherical-like network-shaped nano calcium carbonate particles for rubber and plastic are obtained. According to the process, integration of high reinforcing performance and long-acting anti-ultraviolet function of the nano calcium carbonate in the rubber is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano calcium carbonate, and particularly relates to a preparation process of nano calcium carbonate special for rubber and plastic. Background Art

[0002] Calcium carbonate is an important inorganic chemical product. As a filler, it is widely used in fields such as rubber, plastic, paper-making, coating, ink, and medicine. Nano calcium carbonate is an extremely important one in industrial calcium carbonate. In the filling application of polymer materials, its unique reinforcing property and toughening effect have significantly improved the material properties.

[0003] However, due to its ultra-fine particle size and extremely high surface energy, nano calcium carbonate is prone to spontaneous agglomeration during the rubber processing, and cannot be well compatible with the rubber matrix, resulting in limited reinforcing effect. Moreover, the agglomerated nano calcium carbonate will form stress concentration points inside the material, reducing the mechanical strength of rubber products. The specific surface area of ordinary nano calcium carbonate particles is 20 - 35m 2 / g, and the oil absorption value (DOP) is 20 - 35 ml / 100g. The contact area with polymers such as rubber and plastic is not enough, and it can only be used as a semi-reinforcing material, not meeting the standard of a reinforcing material yet.

[0004] On the other hand, ultraviolet radiation poses a major threat to rubber products. It causes a series of irreversible damages such as accelerating the aging process of materials, triggering physical property decline, chemical structure destruction, and appearance quality deterioration. Therefore, a certain amount of ultraviolet absorber is often added to the rubber formula. However, when the compatibility between the ultraviolet absorber and the rubber matrix is insufficient, under high temperature, high humidity or long-term stress, the absorber molecules may migrate to the material surface and volatilize, resulting in the gradual failure of the protection function. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, a preparation process of nano calcium carbonate special for rubber and plastic proposed by the present invention realizes the integration of high reinforcing performance and long-term anti-ultraviolet function of nano calcium carbonate in rubber, and is specifically realized through the following technical solutions: A preparation process of nano calcium carbonate special for rubber and plastic includes the following steps: (1) Obtaining refined lime milk by crushing, calcining, digesting, sieving, and aging limestone; (2) Adjusting the density of the refined lime milk to 1.04 - 1.15 g / cm 3 , adding 0.8% - 1.5% dispersant based on the dry basis mass of the refined lime milk, and uniformly dispersing to obtain an atomized slurry; (3)The temperature of the carbonization tower is 25 °C, a CO₂ / N₂ mixed gas is introduced from the bottom, the atomized slurry is vertically ejected from the top, and an amorphous intermediate is formed by reaction. When the pH of the system drops to 9.5, the mixed gas is interrupted, and the material at the bottom of the tower is collected to obtain a carbonized liquid; (4)The carbonized liquid is transferred to a carbonization kettle, 1% - 2% of a crystal form control agent is added based on the dry basis mass of the carbonized liquid, cyclohexane, a non-ionic surfactant, and a co-surfactant are added according to a mass ratio of (3 - 4):(1 - 2):(1 - 1.5), and the mass ratio of the carbonized liquid to cyclohexane is (2 - 3):(3 - 5). The temperature of the carbonization kettle is 25 °C, and ultrasonic dispersion is carried out at 20 kHz to form a water-in-oil microemulsion; (5)The temperature of the carbonization kettle is 35 °C, a CO₂ / N₂ mixed gas is introduced from the bottom of the kettle, and a carbonization reaction is carried out. When the pH drops to 8, the carbonization is stopped to obtain a nano-calcium carbonate slurry; (6)The temperature of the carbonization kettle is raised to 45 °C, 8% - 10% of modified titanium dioxide is added based on the dry basis mass of the nano-calcium carbonate slurry, ultrasonic dispersion is carried out to form a core-shell structure. Based on the addition amount of the modified titanium dioxide, 5% - 8% of polyacrylic acid is added, ultrasonic dispersion is carried out, and the temperature is raised to 55 °C and kept warm; (7)Ammonia is used to adjust the pH of the ethanol solvent to 9.0. Based on the dry basis mass of the nano-calcium carbonate slurry, 0.5% - 1% of stearic acid, 0.5% - 1% of a silane coupling agent, and 0.5% - 0.8% of phenyltrimethoxysilane are added, dispersed in the ethanol solvent, and ultrasonic dispersion is carried out. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is (0.2 - 0.5):(1 - 3) to obtain a modified liquid; (8)The modified liquid is added to the carbonization kettle and mixed with the nano-calcium carbonate slurry. The temperature of the carbonization kettle is 50 °C, high-shear dispersion is carried out, and the lower layer slurry is collected by standing and layered, and washed with ethanol to obtain a modified nano-calcium carbonate slurry; (9)The modified nano-calcium carbonate slurry is dehydrated, washed, dried, and airflow pulverized to obtain nano-calcium carbonate particles for special use in rubber and plastics.

[0006] Preferably, in step (3), the CO₂ / N₂ mixed gas is introduced 5 minutes before the atomized slurry is sprayed, the atomization rate is 0.5 - 1 m 3 / h, and the flow rate of the mixed gas is 2.5 - 5 m 3 / h.

[0007] Preferably, in step (3), the volume fraction of CO₂ is 50% - 60%.

[0008] Preferably, in step (5), the volume fraction of CO₂ is 30% - 40%, and the gas flow rate is 0.3 - 0.5 m 3 / min.

[0009] Preferably, the dispersant is compounded from sodium hexametaphosphate and sodium polyacrylate.

[0010] Preferably, the crystal form control agent is one or more of citric acid, citric acid monohydrate, trisodium citrate, tripotassium citrate, D-sodium gluconate, D-gluconic acid, maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid.

[0011] Preferably, the non-ionic surfactant is one or more of Span 20, Span 40, Span 60, Span 80, Span 83, and Span 85.

[0012] Preferably, the co-surfactant is one or more of n-butanol and isopropanol.

[0013] After adopting the above technical solution, the beneficial effects of the present invention are as follows: 1. The staggered spindle-shaped nano-calcium carbonate forms a multi-dimensional support in the rubber matrix. When the rubber product is subjected to an external force, the nano-calcium carbonate particles can effectively transmit stress and disperse stress concentration, enhancing the anti-deformation ability; 2. A hydrophobic layer is formed on the surface of the modified nano-calcium carbonate, reducing the surface energy of the particles and improving the compatibility with the rubber matrix. The rigid benzene ring of phenyltrimethoxysilane enhances the binding strength with the molecular chain of the rubber matrix through physical entanglement; 3. In the CaCO3@TiO2 core-shell structure, the surface TiO2 realizes full-band shielding by absorbing medium-wave ultraviolet rays and scattering long-wave ultraviolet rays, improving the anti-ultraviolet efficiency. TiO2 is combined with CaCO3 through chemical bonds, avoiding the migration or volatilization of traditional ultraviolet absorbers. Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0015] Figure 1 It is the scanning electron microscope photograph of Example 1; Figure 2 It is the scanning electron microscope photograph of Example 2; Figure 3 It is the scanning electron microscope photograph of Example 3; Figure 4 It is the scanning electron microscope photograph of the control group. Detailed Embodiments

[0016] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following specific embodiments are used to further describe the present invention in detail. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is only provided to provide a better understanding of the present invention by showing examples of the present invention.

[0017] Example 1 A preparation process of special nano calcium carbonate for rubber and plastic provided by the present invention includes the following steps: (1) Raw material treatment The limestone is processed according to the conventional treatment process, and refined lime milk is obtained after crushing, calcining, digesting, sieving, and aging.

[0018] (2) Preparation of atomized slurry The refined lime milk is adjusted to a density of 1.1 g / cm 3 through evaporation concentration or dilution with water. Based on the dry basis mass of the refined lime milk, 0.5% sodium hexametaphosphate and 0.3% sodium polyacrylate are added. Ultrasonic dispersion is carried out at 20 kHz for 20 minutes, and then sieved through a 400-mesh sieve to obtain the atomized slurry.

[0019] Sodium hexametaphosphate inhibits particle aggregation by chelating Ca 2+ and at the same time adsorbs on the particle surface to generate electrostatic repulsion. Sodium polyacrylate prevents particle aggregation through the long-chain steric hindrance effect and is compounded with sodium hexametaphosphate to enhance the dispersion stability.

[0020] (3) Preparation of modified titanium dioxide The nano titanium dioxide (powder) is soaked in a 0.1 mol / L hydrochloric acid solution for 1 hour to increase the surface hydroxyl density and improve the subsequent grafting efficiency. The treated nano titanium dioxide is mixed with absolute ethanol at a mass ratio of 1:5, and ultrasonic dispersion is carried out at 20 kHz for 10 minutes to obtain a suspension. Based on the mass of the nano titanium dioxide, 5% silane coupling agent (KH570) is added to the suspension, and glacial acetic acid is dropped to adjust the pH of the suspension to 4.5. Continuous stirring is carried out, and the reaction is carried out in a water bath at 60°C for 4 hours. Centrifugal separation is carried out, and it is washed 3 times with absolute ethanol and dried in vacuum at 60°C to obtain the modified titanium dioxide.

[0021] KH570 hydrolyzes to generate silanol under acidic conditions and condenses with the hydroxyl groups on the surface of the modified titanium dioxide to form a grafted hydrophobic layer on its surface. The hydrophobic layer improves its compatibility in the oil phase (cyclohexane) by reducing the interfacial tension between the modified titanium dioxide and cyclohexane.

[0022] The nano-titanium dioxide powder used is rutile type, with a particle size of 25 - 40 nm. Rutile titanium dioxide has excellent chemical stability and high scattering efficiency. In terms of ultraviolet shielding, for medium-wave ultraviolet rays, it mainly shields through absorption, while for long-wave ultraviolet rays, it is mainly through scattering and reflection, enhancing the anti-aging performance of the rubber matrix.

[0023] (4)Primary carbonization The internal temperature of the carbonization tower is controlled at 25 °C, aiming to inhibit the excessive growth of CaCO3 crystals through a low-temperature environment and promote homogeneous nucleation. A high-pressure atomizer with a pore diameter of 0.3 mm is set at the top of the carbonization tower, with an atomization pressure of 2 MPa and an atomization rate controlled at 0.6 m 3 / h. The pressure of the atomized slurry transfer pump is 15% higher than the atomization pressure to compensate for the pipeline resistance loss. A ring-shaped gas distributor is set at the bottom of the carbonization tower, and the gas flow rate is controlled at 3 m 3 / h.

[0024] During the carbonization reaction, a CO2 / N2 mixed gas (the volume fraction of CO2 is controlled at 55%) is introduced 5 minutes before the atomized slurry is sprayed. The mixed gas diffuses evenly through the bottom ring-shaped distributor to form a stable upward gas flow field. At the same time, introducing the mixed gas in advance can reduce the oxygen content in the tower and reduce oxidation side reactions.

[0025] After 5 minutes, the atomized slurry is vertically ejected from the high-pressure atomizer to form droplets with a particle size of 25 - 50 μm, aiming to increase the contact area between the liquid phase and the gas phase. The droplets are in reverse contact with the upward-moving CO2, and CO2 quickly diffuses to the surface of the droplets to form local supersaturation, inducing Ca 2+ and CO3 2- to undergo homogeneous nucleation and generate amorphous intermediates with a particle size of 5 - 10 nm.

[0026] After the atomized slurry spraying is completed, an on-line pH meter monitors the reaction process. When the pH of the system drops to 9.5, the mixed gas is interrupted, and the bottom material of the tower is collected to obtain the carbonized liquid.

[0027] (5)Microemulsion preparation Transfer the carbonized liquid to the carbonization kettle. Based on the dry basis mass of the carbonized liquid, add 1.3% crystal control agent. According to the mass ratio of 3.5∶1.5∶1.2, add cyclohexane, non-ionic surfactant, and co-surfactant. The mass ratio of the carbonized liquid to cyclohexane is 2∶3.5. The internal temperature of the carbonization kettle is controlled at 25 °C, and ultrasonic dispersion is carried out at 20 kHz for 30 minutes to form a water-in-oil (W / O) type microemulsion with a water core diameter of 35 - 50 nm.

[0028] Cyclohexane serves as the continuous oil phase, wrapping the water core formed by the aqueous solution phase to form a W / O type microemulsion. The water core serves as a "microreactor" for the subsequent carbonization reaction, and the chemical reaction is restricted within the water core of the microemulsion interfacial film.

[0029] The non-ionic surfactant is one or more of the Span series non-ionic surfactants, such as Span 20 (sorbitan monolaurate), Span 40 (sorbitan monopalmitate), Span 60 (sorbitan monostearate), Span 80 (sorbitan monooleate), Span 83 (sorbitan sesquioleate), and Span 85 (sorbitan trioleate). The non-ionic surfactant can reduce the oil-water interfacial tension and stabilize the microemulsion droplets. In this example, the non-ionic surfactant used is Span 80.

[0030] The co-surfactant is one or more of n-butanol and isopropanol, which is used to reduce the rigidity of the interfacial film, enhance the self-healing ability after droplet collision, and prevent droplet coalescence. In this example, the co-surfactant used is n-butanol.

[0031] The crystal form control agent is one or more of citric acid, citric acid monohydrate, trisodium citrate, tripotassium citrate, D-sodium gluconate, D-gluconic acid, maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid, which can induce the transformation of amorphous intermediates by selectively inhibiting and promoting the growth of different crystal planes. In this example, the crystal form control agent used is a compound of D-gluconic acid and fumaric acid in a mass ratio of 5:8.

[0032] When crystal form control agents such as citric acid, D-gluconic acid, and maleic acid are selected, they can chelate with calcium hydroxide to form calcium organic acids, increase the concentration of Ca 2+ in the microemulsion, which is beneficial to accelerating the reaction rate, promoting the formation of nano-calcium carbonate particles, and forming a network structure.

[0033] When crystal form control agents such as maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid are selected, the unsaturated double bonds contained therein can undergo cross-linking reactions with polymers during the later processing of polymers such as rubber and plastics, forming new covalent bonds and generating network-structured polymers, which is beneficial to increasing the strength and tear strength.

[0034] (6) Secondary carbonization The internal temperature of the carbonization kettle is controlled at 35 °C, and a CO2 / N2 mixed gas (the volume fraction of CO2 is controlled at 35%) is introduced from the bottom of the kettle at a gas flow rate of 0.35 m 3 / min for carbonization reaction. CO2 diffuses through the interfacial film into the water core, dissolves to form H2CO3, reduces the pH in the water core, and triggers the precipitation reaction of Ca 2+ and CO3 2- . The microemulsion confinement effect combined with the crystal form control agent inhibits abnormal grain growth. The reaction process is monitored by an on-line pH meter, and when the pH drops to 8, the carbonization is stopped to obtain a nano-calcium carbonate slurry with a chain-like composite crystal form.

[0035] Chain-like nanoparticles are formed into a chain-like network by stringing together individual fine particles, reducing the agglomeration phenomenon between particles, thus improving the dispersibility of the particles. They are easily mixed and dispersed with high-molecular polymers of rubber and plastics, and after dispersion, the end faces form a three-dimensional structure with active ends having chemical bonds with the high-molecular polymers of rubber and plastics, increasing the reinforcing property, and being a good reinforcing agent for rubber and plastics. Chain-like nanoparticles are more likely to form an interlaced network structure in the rubber matrix, forming multi-dimensional support. When a rubber product is subjected to an external force, the chain-like nanoparticles can effectively transfer stress and disperse stress concentration, thereby enhancing the tensile strength, tear strength and hardness of the rubber and increasing the anti-deformation ability.

[0036] (7) Primary modification After carbonization is completed, the carbonization kettle is heated to 45 °C. Based on the dry basis mass of the nano-calcium carbonate slurry, 8.5% of modified titanium dioxide is added and ultrasonic dispersion is carried out at 10 kHz for 20 minutes. The modified titanium dioxide is adsorbed on the surface of CaCO3 through the interfacial tension difference between oil and water and electrostatic attraction, forming a CaCO3@TiO2 core-shell structure. Based on the addition amount of the modified titanium dioxide, 6% of polyacrylic acid is added and ultrasonic dispersion is carried out at 10 kHz for 10 minutes. The carboxyl groups of polyacrylic acid are complexed with metal ions on the surfaces of CaCO3 and TiO2 to form chelation bonds, enhancing the core-shell interface stability and avoiding the migration or volatilization of traditional ultraviolet absorbers. The temperature is raised to 55 °C and kept warm for 30 minutes to promote the molecular chain segment movement of polyacrylic acid and improve the complexation efficiency of carboxyl groups with metal ions.

[0037] (8) Secondary modification The pH of the ethanol solvent is adjusted to 9.0 with 10% ammonia water by mass concentration. Based on the dry basis mass of the nano-calcium carbonate slurry, 0.8% of stearic acid, 0.8% of silane coupling agent (KH550) and 0.6% of phenyltrimethoxysilane are dispersed in the ethanol solvent, and ultrasonic dispersion is carried out at 10 kHz for 15 minutes. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is 2:11 to obtain a modified liquid. The modified liquid is added to the carbonization kettle and mixed with the nano-calcium carbonate slurry. The carbonization kettle is heated to 60 °C and high-shear dispersion (2000 rpm) is carried out for 30 minutes. After standing and separating layers, the lower-layer slurry is collected and washed 2-3 times with ethanol to obtain the modified nano-calcium carbonate slurry.

[0038] Ethanol is used as a solvent to dissolve stearic acid and silane coupling agent, promote uniform coating, and destroy the interfacial adsorption between the microemulsion oil film and CaCO3 particles through hydrogen bonds and van der Waals forces, promoting the separation of the oil phase (cyclohexane). Stearic acid, as a long-chain fatty acid, passes through the carboxyl group and Ca on the surface of nano-calcium carbonate 2+React to form a stable hydrophobic layer, reduce the surface energy of the particles, and enhance the compatibility with the rubber matrix. The silane groups generated by the hydrolysis of KH550 under alkaline conditions condense with the surface hydroxyl groups of CaCO3, and its amino groups crosslink with the hydrophobic layer of stearic acid through van der Waals forces to form a "hydrophobic - lipophilic" amphiphilic interfacial layer, enhancing the compatibility with rubber. The rigid benzene ring of phenyltrimethoxysilane enhances the binding strength with the molecular chains of the rubber matrix through physical entanglement.

[0039] (9)Final product treatment The modified nano - calcium carbonate slurry is dehydrated by a plate - and - frame filter press (pressure 0.6 MPa) to a moisture content of ≤25%, and then washed with water 2 - 3 times. After washing, it is dried in a fluidized bed (80 °C) and depolymerized and pulverized by an air - jet mill to obtain nano - calcium carbonate particles for rubber and plastics.

[0040] The specific surface area of the obtained nano - calcium carbonate particles is 71.23 m 2 / g, the oil absorption value is 54.5 ml / 100 g, and the scanning electron microscope (SEM) of the final product is attached Figure 1 , and the crystal form is a network of small spheres and a chain - rod network complex.

[0041] Example 2 A preparation process of nano - calcium carbonate for rubber and plastics provided by the present invention includes the following steps: (1)Raw material treatment The limestone is processed according to the conventional process, and refined lime milk is obtained after crushing, calcining, digestion, sieving, and aging.

[0042] (2)Preparation of atomized slurry Adjust the density of the refined lime milk to 1.04 g / cm 3 , and based on the dry - basis mass of the refined lime milk, add 0.5% sodium hexametaphosphate and 0.5% sodium polyacrylate. Disperse it by ultrasonic wave at 20 kHz for 15 minutes and sieve it through a 400 - mesh sieve to obtain the atomized slurry.

[0043] (3)Primary carbonization The temperature of the carbonization tower is controlled at 25 °C. Five minutes before the atomized slurry is sprayed in, a CO2 / N2 mixed gas (the volume fraction of CO2 is controlled at 50%) is introduced, and the gas flow rate is controlled at 2.5 m 3 / h. Five minutes later, the atomized slurry is vertically sprayed out from the high - pressure atomizer, and the atomization rate is 0.5 m 3 / h. When the pH of the system drops to 9.5, the mixed gas is interrupted, and the material at the bottom of the tower is collected to obtain the carbonized liquid.

[0044] (4)Preparation of micro - emulsion Transfer the carbonated solution into the carbonation kettle. Based on the dry basis mass of the carbonated solution, add 0.5% D-sodium gluconate and 0.5% trisodium citrate. Add cyclohexane, sorbitan monooleate, and n-butanol according to the mass ratio of 3∶1∶1, and the mass ratio of the carbonated solution to cyclohexane is 2∶3. Control the internal temperature of the carbonation kettle at 25°C and perform ultrasonic dispersion at 20 kHz for 20 minutes to form a water-in-oil (W / O) microemulsion.

[0045] (5)Secondary carbonation Control the internal temperature of the carbonation kettle at 35°C, introduce a CO₂ / N₂ mixed gas (the volume fraction of CO₂ is controlled at 30%) from the bottom of the kettle, and the gas flow rate is 0.3 m 3 / min, and carry out the carbonation reaction. Monitor the reaction process through an on-line pH meter, and stop carbonation when the pH drops to 8 to obtain a nano-calcium carbonate slurry.

[0046] (6)Primary modification After carbonation is completed, the temperature of the carbonation kettle is raised to 45°C. Based on the dry basis mass of the nano-calcium carbonate slurry, add 8% modified titanium dioxide (the modification method is the same as in Example 1), and perform ultrasonic dispersion at 10 kHz for 20 minutes. The modified titanium dioxide is adsorbed on the surface of CaCO₃ through the difference in oil-water interfacial tension and electrostatic attraction to form a CaCO₃@TiO₂ core-shell structure. Based on the addition amount of the modified titanium dioxide, add 5% polyacrylic acid, perform ultrasonic dispersion at 10 kHz for 10 minutes, raise the temperature to 55°C and keep it warm for 30 minutes.

[0047] (7)Secondary modification Adjust the pH of the ethanol solvent to 9.0 with 10% ammonia water by mass concentration. Based on the dry basis mass of the nano-calcium carbonate slurry, disperse 0.5% stearic acid, 0.5% KH550, and 0.5% phenyltrimethoxysilane in the ethanol solvent, and perform ultrasonic dispersion at 10 kHz for 10 minutes. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is 1∶5 to obtain a modified solution. Add the modified solution to the carbonation kettle and mix it with the nano-calcium carbonate slurry. Raise the temperature of the carbonation kettle to 50°C and perform high-shear dispersion (2000 rpm) for 30 minutes. After standing and separating layers, collect the lower-layer slurry and wash it with ethanol 2 - 3 times to obtain a modified nano-calcium carbonate slurry.

[0048] (8)Final product treatment Dehydrate the modified nano-calcium carbonate slurry with a plate-and-frame filter press (pressure 0.6 MPa) until the water content is ≤25%, and then wash it with water 2 - 3 times. After washing, perform fluidized bed drying (80°C) and use an air flow pulverizer to depolymerize and pulverize to obtain nano-calcium carbonate particles for special use in rubber and plastics.

[0049] The specific surface area of the obtained nano-calcium carbonate particles is 71.25 m 2 / g, the oil absorption value is 60.1 ml / 100 g, and the scanning electron microscope of the finished product is attached Figure 2, The crystal form is a reticular small ball and a chain rod net complex.

[0050] Example 3 A preparation process of special nanometer calcium carbonate for rubber and plastics provided by the present invention comprises the following steps: (1) Raw material treatment The limestone is processed according to the conventional process, and after being crushed, calcined, digested, sieved and aged, refined lime milk is obtained.

[0051] (2) Preparation of atomized slurry Adjust the density of the refined lime milk to 1.15 g / cm 3 , and based on the dry basis mass of the refined lime milk, add 1% sodium hexametaphosphate and 0.5% sodium polyacrylate. Disperse with 20 kHz ultrasonic for 25 minutes and sieve through a 400-mesh sieve to obtain the atomized slurry.

[0052] (3) Primary carbonization Control the temperature of the carbonization tower at 25 °C. 5 minutes before spraying the atomized slurry, introduce a CO2 / N2 mixed gas (the volume fraction of CO2 is controlled at 60%), and control the gas flow rate at 5 m 3 / h. After 5 minutes, the atomized slurry is vertically ejected from the high-pressure atomizer, and the atomization rate is 1 m 3 / h. When the pH of the system drops to 9.5, interrupt the mixed gas and collect the bottom material of the tower to obtain the carbonized liquid.

[0053] (4) Preparation of microemulsion Transfer the carbonized liquid to the carbonization kettle. Based on the dry basis mass of the carbonized liquid, add 1% D-sodium gluconate and 1% maleic anhydride. According to the mass ratio of 4:2:1.5, add cyclohexane, sorbitan monooleate, and n-butanol, and the mass ratio of the carbonized liquid to cyclohexane is 3:5. The internal temperature of the carbonization kettle is 25 °C, and disperse with 20 kHz ultrasonic for 30 minutes to form a water-in-oil (W / O) type microemulsion.

[0054] (5) Secondary carbonization Control the internal temperature of the carbonization kettle at 35 °C, introduce a CO2 / N2 mixed gas (the volume fraction of CO2 is controlled at 40%) from the bottom of the kettle, and the gas flow rate is 0.5 m 3 / min to carry out the carbonization reaction. Monitor the reaction process through an on-line pH meter, and stop carbonization when the pH drops to 8 to obtain the nanometer calcium carbonate slurry.

[0055] (6) Primary modification After carbonization is completed, the carbonization kettle is heated to 45 °C. Based on the dry basis mass of the nano-calcium carbonate slurry, 10% of modified titanium dioxide (the modification method is the same as that in Example 1) is added, and ultrasonic dispersion is carried out at 20 kHz for 20 minutes. The modified titanium dioxide is adsorbed on the surface of CaCO3 through the interfacial tension difference between oil and water and electrostatic attraction to form a CaCO3@TiO2 core-shell structure. Based on the addition amount of the modified titanium dioxide, 8% of polyacrylic acid is added, and ultrasonic dispersion is carried out at 10 kHz for 15 minutes, then the temperature is raised to 55 °C and kept warm for 45 minutes.

[0056] (7)Secondary modification Adjust the pH of the ethanol solvent to 9.0 with 10% ammonia water by mass concentration. Based on the dry basis mass of the nano-calcium carbonate slurry, 1% of stearic acid, 1% of KH550 and 0.8% of phenyltrimethoxysilane are dispersed in the ethanol solvent, and ultrasonic dispersion is carried out at 10 kHz for 20 minutes. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is 1:6 to obtain a modified liquid. The modified liquid is added to the carbonization kettle and mixed with the nano-calcium carbonate slurry. The carbonization kettle is heated to 50, and high-shear dispersion (2000 rpm) is carried out for 40 minutes. After standing and stratifying, the lower-layer slurry is collected and washed with ethanol 2-3 times to obtain the modified nano-calcium carbonate slurry.

[0057] (8)Finished product treatment The modified nano-calcium carbonate slurry is dehydrated with a plate-and-frame filter press (pressure 0.6 MPa) until the water content is ≤25%, and then washed with water 2-3 times. After washing, fluidized bed drying (80 °C) is carried out, and the airflow pulverizer is used for depolymerization and pulverization to obtain nano-calcium carbonate particles for special use in rubber and plastics.

[0058] The specific surface area of the obtained nano-calcium carbonate particles is 64.54 m 2 / g, the oil absorption value is 58.4 ml / 100 g, and the scanning electron microscope of the finished product is attached Figure 3 , and the crystal form is a grape cluster aggregate and a network spheroid complex.

[0059] Prepare experimental group rubber products By mass parts, 100 parts of styrene-butadiene rubber (SBR 1500) is plasticized to be softened on an open mill, 5 parts of zinc oxide, 2 parts of stearic acid, 20 parts of nano-calcium carbonate, and 1 part of antioxidant RD are added, and they are kneaded evenly (temperature 70 °C, time 25 minutes) to obtain a kneaded rubber. The kneaded rubber, 2.5 parts of sulfur and 1.5 parts of accelerator CZ are added to a vulcanizer, and after mixing, mold pressing and vulcanization are carried out (temperature 150 °C, pressure 15 MPa, time 30 minutes) to obtain rubber products. According to the raw material selection in Examples 1-3, the rubber products are respectively denoted as YX-A1 (nano-calcium carbonate from Example 1), YX-A2 (nano-calcium carbonate from Example 2), and YX-A3 (nano-calcium carbonate from Example 3).

[0060] Prepare control group rubber products By mass parts, 100 parts of styrene-butadiene rubber (SBR 1500) was plasticized on an open mill until softened, and 5 parts of zinc oxide, 2 parts of stearic acid, 20 parts of nano calcium carbonate, 1 part of antioxidant RD, and 5 parts of UV-326 (chlorobenzotriazole ultraviolet absorber) were added and mixed evenly (temperature 70 °C, time 25 minutes) to obtain a mixed rubber. The vulcanizer was added with the mixed rubber, 2.5 parts of sulfur and 1.5 parts of accelerator CZ, and after mixing, it was molded and vulcanized (temperature 150 °C, pressure 15 MPa, time 30 minutes) to obtain a rubber product, which was marked as YX-B1.

[0061] The nano calcium carbonate used was sourced from Shandong Yuxin Nano Technology Co., Ltd., and the scanning electron microscope of the finished product is attached Figure 4 , and the crystal form is cubic and quasi-spherical. The specific surface area of the nano calcium carbonate particles is 25.53 m 2 / g, and the oil absorption value is 28.4 ml / 100 g. The above four rubber product specimens were respectively subjected to performance tests, and the results are shown in the following table.

[0062]

[0063] The tensile strength and tear strength of the experimental groups (YX-A1 to A3) were significantly higher than those of the control group YX-B1. The chain-like nano calcium carbonate forms a three-dimensional network support, enhancing stress transfer through physical entanglement and chemical bonding. The cubic nano calcium carbonate (YX-B1) has poor isotropy and only disperses stress through van der Waals forces, resulting in weak reinforcement effect.

[0064] The weather resistance of the experimental groups (YX-A1 to A3) was significantly higher than that of the control group YX-B1. TiO2 inhibits surface yellowing, while UV-326 cannot prevent the formation of deep oxidation chromophore groups induced by long-wave ultraviolet rays. UV-326 mainly slows down aging by absorbing medium-wave ultraviolet rays, but has weak protection against long-wave ultraviolet rays, and small molecule ultraviolet absorbers are prone to migration or volatilization, resulting in obvious decline in long-term use performance.

[0065] The heat resistance stability of the experimental groups (YX-A1 to A3) was significantly higher than that of the control group YX-B1. At high temperatures, the movement of rubber molecular chains intensifies, the long axis direction of the grid-shaped small particles can slide and rearrange, dispersing thermal stress and inhibiting crack propagation caused by local thermal stress concentration. The extended structure of the spindle-shaped particles forms physical entanglement with the rubber molecular chains, delaying the slip and fracture of the molecular chains at high temperatures. The constructed three-dimensional network hinders the rapid transfer of heat in the matrix, reducing the overall thermal degradation rate. The cubic nano calcium carbonate has poor isotropy, and the particles are only combined through van der Waals forces, which are prone to agglomeration to form stress concentration points at high temperatures and cannot effectively inhibit heat conduction.

[0066] Overall, the chain-network nano-calcium carbonate has obvious reinforcement advantages. Through modification to optimize compatibility, three-dimensional network support, and core-shell interface optimization, it is easily dispersed during the mixing process, can avoid stress concentration, and thus its mechanical properties are significantly better than those of traditional cubic fillers. The core-shell structure can avoid the migration problem of ultraviolet absorbers and will not undergo phase separation during processing and use, maintaining long-term and stable ultraviolet absorption performance and extending the service life of the product.

[0067] According to the embodiments of the present invention as described above, these embodiments do not elaborate on all the details and do not limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made based on the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and its modified use based on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation process of nano calcium carbonate special for rubber and plastic, characterized in that, It includes the following steps: (1) Obtain refined lime milk by crushing, calcining, digesting, sieving, and aging limestone; (2) Adjust the density of the refined lime milk to 1.04 - 1.15 g / cm 3 , add 0.8% - 1.5% of the dispersant based on the dry basis mass of the refined lime milk, and disperse evenly to obtain the atomized slurry; (3) At a carbonization tower temperature of 25 °C, introduce a CO₂ / N₂ mixed gas from the bottom, and atomize the slurry to spray vertically from the top. React to form an amorphous intermediate. When the pH of the system drops to 9.5, interrupt the mixed gas, collect the bottom material of the tower to obtain a carbonized liquid; (4) Transfer the carbonized liquid to a carbonization kettle, add 1% - 2% crystal form control agent based on the dry basis mass of the carbonized liquid, add cyclohexane, non-ionic surfactant, and co-surfactant according to the mass ratio of (3 - 4):(1 - 2):(1 - 1.5). The mass ratio of the carbonized liquid to cyclohexane is (2 - 3):(3 - 5). The temperature of the carbonization kettle is 25 °C, and disperse it by ultrasonic wave at 20 kHz to form a water-in-oil microemulsion; (5) At a carbonization kettle temperature of 35 °C, introduce a CO₂ / N₂ mixed gas from the bottom of the kettle to carry out a carbonization reaction. Stop carbonization when the pH drops to 8 to obtain a nano-calcium carbonate slurry; (6) Raise the temperature of the carbonization kettle to 45 °C, add 8% - 10% modified titanium dioxide based on the dry basis mass of the nano-calcium carbonate slurry, disperse it by ultrasonic wave to form a core-shell structure. Based on the addition amount of the modified titanium dioxide, add 5% - 8% polyacrylic acid, disperse it by ultrasonic wave, and raise the temperature to 55 °C and keep it warm; (7) Adjust the pH of the ethanol solvent to 9.0 with ammonia water. Based on the dry basis mass of the nano-calcium carbonate slurry, add 0.5% - 1% stearic acid, 0.5% - 1% silane coupling agent, and 0.5% - 0.8% phenyltrimethoxysilane, disperse them in the ethanol solvent, and disperse it by ultrasonic wave. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is (0.2 - 0.5):(1 - 3) to obtain a modified liquid; (8) Add the modified liquid to the carbonization kettle to mix with the nano-calcium carbonate slurry. The temperature of the carbonization kettle is 50 °C, disperse it by high-shear, let it stand for layering, collect the lower-layer slurry, and wash it with ethanol to obtain a modified nano-calcium carbonate slurry; (9) Dehydrate, wash, dry, and pulverize the modified nano-calcium carbonate slurry by air flow to obtain nano-calcium carbonate particles for special use in rubber and plastics.

2. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1 is characterized in that: In the step (3), a CO₂ / N₂ mixed gas is introduced 5 minutes before the atomized slurry is sprayed, and the atomization rate is 0.5 - 1 m 3 / h, and the flow rate of the mixed gas is 2.5 - 5 m 3 / h.

3. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 2, wherein: In the step (3), the volume fraction of CO₂ is 50% - 60%.

4. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1 is characterized in that: In the step (5), the volume fraction of C02 is 30% to 40%, and the gas flow rate is 0.3 to 0.5 m 3 / min.

5. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1, characterized in that: The dispersant is compounded by sodium hexametaphosphate and sodium polyacrylate.

6. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1, characterized in that: The crystal form control agent is one or more of citric acid, citric acid monohydrate, trisodium citrate, tripotassium citrate, D-sodium gluconate, D-gluconic acid, maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid.

7. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1, characterized in that: The non-ionic surfactant is one or more of Span 20, Span 40, Span 60, Span 80, Span 83, and Span 85.

8. The preparation process of the special nano calcium carbonate for rubber and plastics according to claim 1 is characterized in that: The co-surfactant is one or more of n-butanol and isopropanol.

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