A preparation process of nano calcium carbonate for rubber and plastics

Abstract

The present invention belongs to the field of nano-calcium carbonate technology, and specifically relates to a process for preparing nano-calcium carbonate for rubber and plastics. The process comprises: adjusting the density of refined lime milk and adding a dispersant to obtain an atomized slurry; introducing a CO2 / N2 mixed gas into the bottom of a carbonization tower, and vertically ejecting the atomized slurry from the top to react and generate an amorphous intermediate to obtain a carbonized liquid; transferring the carbonized liquid to a carbonization kettle, adding a crystal form control agent, cyclohexane, a nonionic surfactant, and a cosurfactant, and ultrasonically dispersing the mixture to form a water-in-oil microemulsion; introducing a CO2 / N2 mixed gas into the carbonization kettle to undergo a carbonization reaction to obtain a nano-calcium carbonate slurry; and dehydrating, washing, drying, and airflow pulverizing the modified nano-calcium carbonate slurry to obtain a network of spherical nano-calcium carbonate particles with a high specific surface area for rubber and plastics. This process combines the high reinforcing properties of nano-calcium carbonate in rubber with long-lasting UV resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of nano calcium carbonate, and in particular 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 used as a filler in a wide range of applications, including rubber, plastics, papermaking, coatings, inks, and pharmaceuticals. Nano-calcium carbonate is a crucial form of industrial calcium carbonate. Its unique reinforcement and toughening properties significantly enhance material performance in polymer filling applications.

[0003] However, due to its ultra-fine particle size and extremely high surface energy, nano calcium carbonate is prone to spontaneous agglomeration during rubber processing, and is not well compatible with the rubber matrix, which limits the reinforcement effect. Moreover, the agglomerated nano calcium carbonate will form stress concentration points inside the material, reducing the mechanical strength of the rubber product. Ordinary nano calcium carbonate particles have a specific surface area of ​​20 to 35 m 2 / g, the oil absorption value (DOP) is 20-35ml / 100g, and the contact area with rubber, plastic and other polymers is insufficient. It can only be used as a semi-reinforcement material and does not meet the standards of reinforcement materials.

[0004] On the other hand, UV radiation poses a significant threat to rubber products, accelerating the aging process and causing a series of irreversible damage, including degradation of physical properties, chemical structure breakdown, and deterioration of appearance. Therefore, a certain amount of UV absorbers are often added to rubber formulations. However, if the UV absorber is not compatible with the rubber matrix, under conditions of high temperature, high humidity, or prolonged stress, the absorber molecules may migrate to the material surface and volatilize, gradually rendering the protective function ineffective. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention proposes a process for preparing nano-calcium carbonate for rubber and plastics, which integrates the high reinforcing performance of nano-calcium carbonate in rubber with long-lasting UV resistance. This is achieved through the following technical solutions:

[0006] A process for preparing nano calcium carbonate for rubber and plastics comprises the following steps:

[0007] (1) The limestone is crushed, calcined, digested, screened and aged to obtain refined lime milk;

[0008] (2) Adjust the density of refined lime milk to 1.04-1.15 g / cm 3 , adding 0.8% to 1.5% of a dispersant based on the dry mass of the refined lime milk, uniformly dispersing it to obtain an atomized slurry;

[0009] (3) The temperature of the carbonization tower is 25°C, a C02 / N2 mixed gas is introduced into the bottom, and the atomized slurry is sprayed vertically from the top to react and generate an amorphous intermediate. 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;

[0010] (4) The carbonized liquid was transferred to a carbonization kettle, and 1% to 2% of a crystal form control agent was added based on the dry weight of the carbonized liquid. Cyclohexane, a nonionic surfactant, and a cosurfactant were added in a mass ratio of (3 to 4): (1 to 2): (1 to 1.5). The mass ratio of the carbonized liquid to cyclohexane was (2 to 3): (3 to 5). The carbonization kettle temperature was 25°C, and ultrasonic dispersion was performed at 20 kHz to form an oil-in-water microemulsion.

[0011] (5) The temperature of the carbonization kettle is 35°C, and a CO2 / N2 mixed gas is introduced from the bottom of the kettle to carry out the carbonization reaction. When the pH drops to 8, the carbonization is stopped to obtain a nano-calcium carbonate slurry;

[0012] (6) The carbonization kettle is heated to 45°C. Based on the dry weight of the nano-calcium carbonate slurry, 8% to 10% modified titanium dioxide is added and ultrasonically dispersed to form a core-shell structure. Based on the amount of modified titanium dioxide added, 5% to 8% polyacrylic acid is added and ultrasonically dispersed. The temperature is raised to 55°C and kept warm.

[0013] (7) adjusting the pH of the ethanol solvent to 9.0 with ammonia water, adding 0.5% to 1% stearic acid, 0.5% to 1% silane coupling agent, and 0.5% to 0.8% phenyltrimethoxysilane based on the dry basis weight of the nano-calcium carbonate slurry, dispersing the mixture in the ethanol solvent, and ultrasonically dispersing the mixture. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is (0.2 to 0.5): (1 to 3), thereby obtaining a modified solution;

[0014] (8) The modified liquid is added to the carbonization kettle and mixed with the nano calcium carbonate slurry. The carbonization kettle is heated to 50°C and dispersed under high shear. The lower layer of slurry is collected and washed with ethanol to obtain the modified nano calcium carbonate slurry.

[0015] (9) The modified nano-calcium carbonate slurry is dehydrated, washed, dried, and air flow crushed to obtain nano-calcium carbonate particles specifically for rubber and plastics.

[0016] Preferably, in step (3), a C02 / N2 mixed gas is introduced 5 minutes before the atomized slurry is sprayed, and the atomization rate is 0.5 to 1 m 3 / h, the mixed gas flow rate is 2.5~5m 3 / h.

[0017] Preferably, in step (3), the volume fraction of CO2 is 50% to 60%.

[0018] Preferably, in step (5), the volume fraction of CO2 is 30% to 40%, and the gas flow rate is 0.3 to 0.5 m / s. 3 / min.

[0019] Preferably, the dispersant is compounded from sodium hexametaphosphate and sodium polyacrylate.

[0020] Preferably, the crystal form controlling agent is one or more of citric acid, citric acid monohydrate, trisodium citrate, tripotassium citrate, sodium D-gluconate, D-gluconic acid, maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid.

[0021] Preferably, the nonionic surfactant is one or more of Span 20, Span 40, Span 60, Span 80, Span 83, and Span 85.

[0022] Preferably, the co-surfactant is one or more of n-butanol and isopropanol.

[0023] After adopting the above technical solution, the beneficial effects of the present invention are:

[0024] 1. The interlaced spindle-shaped nano-calcium carbonate forms a multi-dimensional support in the rubber matrix. When the rubber product is subjected to external force, the nano-calcium carbonate particles can effectively transmit stress and disperse stress concentration, thereby enhancing the ability to resist deformation;

[0025] 2. A hydrophobic layer forms 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 bonding strength with the molecular chain of the rubber matrix through physical entanglement;

[0026] 3. In the CaCO3@TiO2 core-shell structure, the TiO2 on the surface achieves full-band shielding by absorbing medium-wave ultraviolet rays and scattering long-wave ultraviolet rays, thereby improving the anti-ultraviolet efficiency. TiO2 is combined with CaCO3 through chemical bonds to prevent the migration or volatilization of traditional ultraviolet absorbers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is a scanning electron microscope photograph of Example 1;

[0029] Figure 2 This is a scanning electron microscope photograph of Example 2;

[0030] Figure 3 This is a scanning electron microscope photograph of Example 3;

[0031] Figure 4 The scanning electron micrographs of the control group are shown. DETAILED DESCRIPTION

[0032] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail with the following specific examples. 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 the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the present invention.

[0033] Example 1

[0034] The present invention provides a process for preparing nano calcium carbonate for rubber and plastic, comprising the following steps:

[0035] (1) Raw material processing

[0036] Limestone is processed according to the conventional process, and then crushed, calcined, digested, screened and aged to obtain refined lime milk.

[0037] (2) Preparation of atomized slurry

[0038] The refined lime milk is concentrated by evaporation or diluted with water to adjust the density of the refined lime milk to 1.1g / cm 3 Based on the dry weight of the refined lime milk, 0.5% sodium hexametaphosphate and 0.3% sodium polyacrylate were added, and ultrasonic dispersion was performed at 20 kHz for 20 minutes. The mixture was sieved through a 400-mesh sieve to obtain an atomized slurry.

[0039] Sodium hexametaphosphate chelates Ca 2+ It inhibits particle agglomeration and simultaneously 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 dispersion stability.

[0040] (3) Preparation of modified titanium dioxide

[0041] Nano-titanium dioxide powder was soaked in a 0.1 mol / L hydrochloric acid solution for one hour to increase its surface hydroxyl density and enhance subsequent grafting efficiency. The treated nano-titanium dioxide was then mixed with anhydrous ethanol at a mass ratio of 1:5 and ultrasonically dispersed at 20 kHz for 10 minutes to obtain a suspension. A silane coupling agent (KH570) was added to the suspension at a concentration of 5% based on the mass of the nano-titanium dioxide. Glacial acetic acid was added dropwise to adjust the pH of the suspension to 4.5. The suspension was stirred continuously and reacted in a 60°C water bath for four hours. The mixture was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 60°C to obtain the modified titanium dioxide.

[0042] KH570 hydrolyzes under acidic conditions to generate silanols, which condense with the hydroxyl groups on the surface of the modified titanium dioxide to form a grafted hydrophobic layer. This hydrophobic layer reduces the interfacial tension between the modified titanium dioxide and cyclohexane, thereby improving its compatibility in the oil phase (cyclohexane).

[0043] The nano-titanium dioxide powder used is rutile, with a particle size of 25 to 40 nm. Rutile titanium dioxide has excellent chemical stability and high scattering efficiency. It primarily absorbs medium-wave UV rays and scatters and reflects long-wave UV rays, improving the rubber matrix's anti-aging properties.

[0044] (4) Primary carbonization

[0045] The internal temperature of the carbonization tower is controlled at 25°C, aiming to inhibit the excessive growth of CaCO3 crystals through the low temperature environment and promote homogeneous nucleation. A high-pressure atomizer with a pore size of 0.3mm is set on the top of the carbonization tower, the atomization pressure is 2MPa, and the atomization rate is controlled at 0.6m 3 / h. The pressure of the atomized slurry delivery pump is 15% higher than the atomization pressure to compensate for the pipeline resistance loss. An annular gas distributor is set at the bottom of the carbonization tower, and the gas flow rate is controlled at 3m 3 / h.

[0046] During the carbonization reaction, a CO₂ / N₂ mixture (CO₂ volume fraction controlled at 55%) is introduced five minutes before the atomized slurry is sprayed. This mixture diffuses evenly through the annular distributor at the bottom, creating a stable updraft. This early introduction of the mixed gas also reduces the oxygen content within the tower, minimizing oxidation side reactions.

[0047] After 5 minutes, the atomized slurry is sprayed vertically from the high-pressure atomizer to form droplets with a particle size of 25 to 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 droplet surface to form local supersaturation, inducing Ca 2+ With CO3 2- Homogeneous nucleation generates an amorphous intermediate with a particle size of 5 to 10 nm.

[0048] After the spraying of the atomized slurry is completed, the reaction progress is monitored by an online pH meter. When the pH of the system drops to 9.5, the mixed gas is interrupted and the bottom material is collected to obtain the carbonized liquid.

[0049] (5) Preparation of microemulsion

[0050] The carbonized liquid was transferred to a carbonization kettle. A crystal form control agent (1.3%) was added based on the dry weight of the carbonized liquid. Cyclohexane, a nonionic surfactant, and a cosurfactant were added at a mass ratio of 3.5:1.5:1.2, resulting in a carbonized liquid to cyclohexane mass ratio of 2:3.5. The internal temperature of the carbonization kettle was maintained at 25°C, and ultrasonic dispersion was performed at 20 kHz for 30 minutes to form a water-in-oil (W / O) microemulsion with a water core diameter of 35-50 nm.

[0051] Cyclohexane, the oily continuous phase, encapsulates the water core formed by the aqueous phase, forming a W / O microemulsion. The water core acts as a "microreactor" for the subsequent carbonization reaction, and the chemical reaction is confined to the water core of the microemulsion interface membrane.

[0052] The nonionic surfactant is a Span series nonionic surfactant, and can be one or more of Span 20 (sorbitan monolaurate), Span 40 (sorbitan monopalmitate), Span 60 (sorbitan monostearate), Span 80 (sorbitan monooleate), Span 83 (sorbitan sesquioleate), or Span 85 (sorbitan trioleate). Nonionic surfactants can reduce oil-water interfacial tension and stabilize microemulsion droplets. In this example, Span 80 is used.

[0053] 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-repairing ability of the droplets after collision, and prevent the droplets from coalescing. The co-surfactant used in this embodiment is n-butanol.

[0054] The crystal form control agent is one or more of citric acid, citric acid monohydrate, trisodium citrate, tripotassium citrate, sodium D-gluconate, D-gluconic acid, maleic acid, maleic anhydride, hydrolyzed polymaleic anhydride, and fumaric acid. It selectively inhibits and promotes the growth of different crystal planes, inducing the transformation of the amorphous intermediate. The crystal form control agent used in this example is a mixture of D-gluconic acid and fumaric acid in a mass ratio of 5:8.

[0055] 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 organic acid calcium, thereby increasing the Ca content in the microemulsion. 2+ The concentration is conducive to accelerating the reaction speed, promoting the formation of nano-calcium carbonate particles and forming a network structure.

[0056] 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 rubber, plastics, and other polymers to form new connecting bonds, thereby generating a network structure of polymers, which is beneficial to increase strength and tear strength.

[0057] (6) Secondary carbonization

[0058] The internal temperature of the carbonization kettle is controlled at 35°C, and a C02 / N2 mixed gas (the volume fraction of C02 is controlled at 35%) is introduced from the bottom of the kettle at a gas flow rate of 0.35m 3 / min, carbonization reaction occurs. CO2 interfacial film diffuses to the water core, dissolves to generate H2CO3, reduces the pH in the water core, and triggers Ca 2+ With CO3 2- The microemulsion's confinement effect combined with a crystal form control agent inhibits abnormal grain growth. The reaction progress is monitored by an online pH meter. Carbonization is stopped when the pH drops to 8, resulting in a nano-calcium carbonate slurry with a chain-like complex crystal form.

[0059] Chain-linked nanoparticles are composed of tiny individual particles strung together to form a chain network. This reduces particle agglomeration, improving particle dispersibility. They easily mix and disperse with rubber and plastic polymers. After dispersion, the surfaces form a three-dimensional structure with active chemically bonded ends, enhancing reinforcement and making them an excellent reinforcing agent for rubber and plastics. Chain-linked nanoparticles more easily form an interlaced network within the rubber matrix, creating a multi-dimensional support structure. When rubber products are subjected to external forces, the chain-linked nanoparticles effectively transfer stress and disperse stress concentrations, thereby increasing the rubber's tensile strength, tear strength, and hardness, enhancing its resistance to deformation.

[0060] (7) Primary modification

[0061] After carbonization is complete, the carbonization kettle is heated to 45°C. Based on the dry weight of the nano-calcium carbonate slurry, 8.5% modified titanium dioxide is added, and ultrasonic dispersion is performed at 10kHz for 20 minutes. The modified titanium dioxide adsorbs onto the CaCO3 surface through the oil-water interfacial tension difference and electrostatic attraction, forming a CaCO3@TiO2 core-shell structure. Based on the amount of modified titanium dioxide added, 6% polyacrylic acid is added, and ultrasonic dispersion is performed at 10kHz for 10 minutes. The carboxyl groups of the polyacrylic acid complex with the metal ions on the CaCO3 and TiO2 surfaces, forming chelate bonds, enhancing the stability of the core-shell interface and preventing the migration or volatilization of traditional UV absorbers. The temperature is raised to 55°C and maintained for 30 minutes to promote the movement of the polyacrylic acid molecular segments and improve the complexation efficiency of the carboxyl groups with the metal ions.

[0062] (8) Secondary modification

[0063] The pH of the ethanol solvent was adjusted to 9.0 with 10% aqueous ammonia. Based on the dry weight of the nano-calcium carbonate slurry, 0.8% stearic acid, 0.8% silane coupling agent (KH550), and 0.6% phenyltrimethoxysilane were dispersed in the ethanol solvent. Ultrasonic dispersion was performed at 10 kHz for 15 minutes, with a mass ratio of ethanol to nano-calcium carbonate slurry of 2:11 to obtain a modified solution. The modified solution was added to a carbonization kettle and mixed with the nano-calcium carbonate slurry. The carbonization kettle was heated to 60°C and high shear dispersion was performed at 2000 rpm for 30 minutes. After standing for demixing, the lower slurry was collected and washed two to three times with ethanol to obtain the modified nano-calcium carbonate slurry.

[0064] Ethanol is used as a solvent to dissolve stearic acid and silane coupling agent, promote uniform coating, and destroy the interface adsorption between microemulsion oil film and CaCO3 particles through hydrogen bonding and van der Waals force, promoting the separation of oil phase (cyclohexane). Stearic acid, as a long-chain fatty acid, binds to the surface of nano-calcium carbonate through carboxyl groups. 2+ The reaction forms a stable hydrophobic layer, reducing the particle surface energy and improving compatibility with the rubber matrix. The silane groups generated by the alkaline hydrolysis of KH550 condense with the surface hydroxyl groups of CaCO3. The amino groups crosslink with the hydrophobic layer of stearic acid through van der Waals forces, forming a "hydrophobic-lipophilic" amphiphilic interface layer and enhancing compatibility with rubber. The rigid benzene rings of phenyltrimethoxysilane strengthen the bond with the rubber matrix molecular chains through physical entanglement.

[0065] (9) Finished product processing

[0066] The modified nano-calcium carbonate slurry is dehydrated using 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 deagglomerated and pulverized in a jet mill to obtain nano-calcium carbonate particles specifically for rubber and plastics.

[0067] The specific surface area of ​​the obtained nano calcium carbonate particles is 71.23 m 2 / g, oil absorption value is 54.5ml / 100g, the scanning electron microscope (SEM) of the finished product is attached Figure 1 , the crystal form is a complex of mesh balls and chain rod nets.

[0068] Example 2

[0069] The present invention provides a process for preparing nano calcium carbonate for rubber and plastic, comprising the following steps:

[0070] (1) Raw material processing

[0071] Limestone is processed according to the conventional process, and then crushed, calcined, digested, screened and aged to obtain refined lime milk.

[0072] (2) Preparation of atomized slurry

[0073] Adjust the density of refined lime milk to 1.04g / cm 3 Based on the dry weight of the refined lime milk, 0.5% sodium hexametaphosphate and 0.5% sodium polyacrylate were added, ultrasonically dispersed at 20 kHz for 15 minutes, and sieved through a 400-mesh sieve to obtain an atomized slurry.

[0074] (3) Primary carbonization

[0075] The temperature of the carbonization tower is controlled at 25°C, and a C02 / N2 mixed gas (the volume fraction of C02 is controlled at 50%) is introduced 5 minutes before the atomized slurry is sprayed, and the gas flow rate is controlled at 2.5m 3 / h. After 5 minutes, the atomized slurry was sprayed vertically from the high-pressure atomizer at a rate of 0.5m 3 / h, when the pH of the system drops to 9.5, the mixed gas is interrupted and the bottom material is collected to obtain the carbonized liquid.

[0076] (4) Preparation of microemulsion

[0077] The carbonized liquid was transferred to a carbonization kettle. Based on the dry weight of the carbonized liquid, 0.5% sodium D-gluconate and 0.5% trisodium citrate were added. Cyclohexane, sorbitan monooleate, and n-butanol were added in a mass ratio of 3:1:1, with a mass ratio of carbonized liquid to cyclohexane of 2:3. The internal temperature of the carbonization kettle was maintained at 25°C, and ultrasonic dispersion was performed at 20 kHz for 20 minutes to form a water-in-oil (W / O) microemulsion.

[0078] (5) Secondary carbonization

[0079] The internal temperature of the carbonization kettle is controlled at 35°C, and a C02 / N2 mixed gas (the volume fraction of C02 is controlled at 30%) is introduced from the bottom of the kettle at a gas flow rate of 0.3m 3 / min, and the carbonization reaction was carried out. The reaction process was monitored by an online pH meter, and the carbonization was stopped when the pH dropped to 8 to obtain nano-calcium carbonate slurry.

[0080] (6) Primary modification

[0081] After carbonization was complete, the carbonization kettle was heated to 45°C. 8% modified titanium dioxide (modification method as in Example 1) was added to the dry weight of the nano-calcium carbonate slurry, and ultrasonic dispersion was performed at 10 kHz for 20 minutes. The modified titanium dioxide was adsorbed onto the CaCO3 surface through the oil-water interfacial tension difference and electrostatic attraction, forming a CaCO3@TiO2 core-shell structure. Based on the amount of modified titanium dioxide added, 5% polyacrylic acid was added, and ultrasonic dispersion was performed at 10 kHz for 10 minutes. The temperature was then raised to 55°C and maintained for 30 minutes.

[0082] (7) Secondary modification

[0083] The pH of the ethanol solvent was adjusted to 9.0 with 10% aqueous ammonia. Based on the dry weight of the nano-calcium carbonate slurry, 0.5% stearic acid, 0.5% KH550, and 0.5% phenyltrimethoxysilane were dispersed in the ethanol solvent. Ultrasonic dispersion was performed at 10 kHz for 10 minutes, with a mass ratio of ethanol to nano-calcium carbonate slurry of 1:5 to obtain a modified solution. The modified solution was added to a carbonization kettle and mixed with the nano-calcium carbonate slurry. The carbonization kettle was heated to 50°C and high shear dispersion was performed at 2000 rpm for 30 minutes. After standing and demixing, the lower slurry was collected and washed two to three times with ethanol to obtain the modified nano-calcium carbonate slurry.

[0084] (8) Finished product processing

[0085] The modified nano-calcium carbonate slurry is dehydrated using 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 deagglomerated and pulverized in a jet mill to obtain nano-calcium carbonate particles specifically for rubber and plastics.

[0086] The specific surface area of ​​the obtained nano calcium carbonate particles is 71.25 m 2 / g, oil absorption value is 60.1ml / 100g, the scanning electron microscope of the finished product is attached Figure 2 , the crystal form is a complex of mesh balls and chain rod nets.

[0087] Example 3

[0088] The present invention provides a process for preparing nano calcium carbonate for rubber and plastic, comprising the following steps:

[0089] (1) Raw material processing

[0090] Limestone is processed according to the conventional process, and then crushed, calcined, digested, screened and aged to obtain refined lime milk.

[0091] (2) Preparation of atomized slurry

[0092] Adjust the density of refined lime milk to 1.15g / cm 3 Based on the dry weight of the refined lime milk, 1% sodium hexametaphosphate and 0.5% sodium polyacrylate were added, ultrasonically dispersed at 20 kHz for 25 minutes, and sieved through a 400-mesh sieve to obtain an atomized slurry.

[0093] (3) Primary carbonization

[0094] The temperature of the carbonization tower is controlled at 25°C, and a C02 / N2 mixed gas (the volume fraction of C02 is controlled at 60%) is introduced 5 minutes before the atomized slurry is sprayed, and the gas flow rate is controlled at 5m 3 / h. After 5 minutes, the atomized slurry was sprayed vertically from the high-pressure atomizer at a rate of 1m 3 / h, when the pH of the system drops to 9.5, the mixed gas is interrupted and the bottom material is collected to obtain the carbonized liquid.

[0095] (4) Preparation of microemulsion

[0096] The carbonized liquid was transferred to a carbonization kettle. 1% sodium D-gluconate and 1% maleic anhydride were added to the carbonized liquid on a dry weight basis. Cyclohexane, sorbitan monooleate, and n-butanol were added in a mass ratio of 4:2:1.5, resulting in a carbonized liquid to cyclohexane ratio of 3:5. Ultrasonic dispersion was performed at 20 kHz for 30 minutes at a temperature of 25°C in the carbonization kettle to form a water-in-oil (W / O) microemulsion.

[0097] (5) Secondary carbonization

[0098] The internal temperature of the carbonization kettle was controlled at 35°C, and a C02 / N2 mixed gas (the volume fraction of C02 was controlled at 40%) was introduced from the bottom of the kettle at a gas flow rate of 0.5 m 3 / min, and the carbonization reaction was carried out. The reaction process was monitored by an online pH meter, and the carbonization was stopped when the pH dropped to 8 to obtain nano-calcium carbonate slurry.

[0099] (6) Primary modification

[0100] After carbonization was complete, the carbonization kettle was heated to 45°C. 10% modified titanium dioxide (modification method as in Example 1) was added to the dry weight of the nano-calcium carbonate slurry, and ultrasonic dispersion was performed at 20 kHz for 20 minutes. The modified titanium dioxide was adsorbed onto the CaCO3 surface through the oil-water interfacial tension difference and electrostatic attraction, forming a CaCO3@TiO2 core-shell structure. Based on the amount of modified titanium dioxide added, 8% polyacrylic acid was added, and ultrasonic dispersion was performed at 10 kHz for 15 minutes. The temperature was then raised to 55°C and maintained for 45 minutes.

[0101] (7) Secondary modification

[0102] The pH of the ethanol solvent was adjusted to 9.0 with 10% aqueous ammonia. Based on the dry weight of the nano-calcium carbonate slurry, 1% stearic acid, 1% KH550, and 0.8% phenyltrimethoxysilane were dispersed in the ethanol solvent. Ultrasonic dispersion was performed at 10 kHz for 20 minutes, with a mass ratio of ethanol to nano-calcium carbonate slurry of 1:6 to obtain a modified solution. The modified solution was added to a carbonization kettle and mixed with the nano-calcium carbonate slurry. The carbonization kettle was heated to 50°C and high shear dispersion was performed at 2000 rpm for 40 minutes. After standing and demixing, the lower slurry was collected and washed two to three times with ethanol to obtain the modified nano-calcium carbonate slurry.

[0103] (8) Finished product processing

[0104] The modified nano-calcium carbonate slurry is dehydrated using 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 deagglomerated and pulverized in a jet mill to obtain nano-calcium carbonate particles specifically for rubber and plastics.

[0105] The specific surface area of ​​the obtained nano calcium carbonate particles is 64.54 m 2 / g, oil absorption value is 58.4ml / 100g, the scanning electron microscope of the finished product is attached Figure 3 The crystal form is a complex of grape cluster attachment and network spheres.

[0106] Preparation of rubber products for the experimental group

[0107] 100 parts by mass of styrene-butadiene rubber (SBR 1500) were masticated on an open mill until softened. 5 parts of zinc oxide, 2 parts of stearic acid, 20 parts of nano-calcium carbonate, and 1 part of antioxidant RD were added and mixed uniformly (temperature 70°C, time 25 minutes) to produce a rubber mix. The rubber mix, 2.5 parts of sulfur, and 1.5 parts of accelerator CZ were added to a vulcanizer, mixed, and then press-vulcanized (temperature 150°C, pressure 15 MPa, time 30 minutes) to produce a rubber product. Based on the materials selected in Examples 1-3, the rubber products were designated YX-A1 (nano-calcium carbonate derived from Example 1), YX-A2 (nano-calcium carbonate derived from Example 2), and YX-A3 (nano-calcium carbonate derived from Example 3), respectively.

[0108] Preparation of rubber products for the control group

[0109] 100 parts by mass of styrene-butadiene rubber (SBR 1500) were masticated on an open mill until softened. 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 (a chlorobenzotriazole ultraviolet absorber) were added and mixed uniformly (temperature 70°C, time 25 minutes) to obtain a rubber mix. The rubber mix, 2.5 parts of sulfur, and 1.5 parts of accelerator CZ were added to a vulcanizer, mixed, and then press-vulcanized (temperature 150°C, pressure 15 MPa, time 30 minutes) to obtain a rubber product labeled YX-B1.

[0110] The nano calcium carbonate used is from Shandong Yuxin Nanotechnology Co., Ltd. The scanning electron microscope of the finished product is attached. Figure 4 The crystal form is cubic and spherical. The specific surface area of ​​nano calcium carbonate particles is 25.53m 2 / g, oil absorption value is 28.4ml / 100g,

[0111] The above four rubber product samples were tested for performance respectively, and the results are shown in the following table.

[0112]

[0113] The tensile and tear strengths 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 support network, enhancing stress transfer through physical entanglement and chemical bonding. However, due to its poor isotropy, the cubic nano-calcium carbonate (YX-B1) only disperses stress through van der Waals forces, resulting in a weaker reinforcement effect.

[0114] 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 is unable to prevent the formation of deep-layer oxidative chromophores triggered by long-wave UV rays. UV-326 primarily mitigates aging by absorbing medium-wave UV rays, but its protection against long-wave UV rays is weak. Furthermore, the small-molecule UV absorber is prone to migration or volatilization, resulting in significant performance degradation over long-term use.

[0115] The experimental groups (YX-A1 to A3) showed significantly higher thermal stability than the control group (YX-B1). At high temperatures, the movement of rubber molecular chains intensifies, allowing the long axis of the grid-shaped small particles to slide and rearrange, dissipating thermal stress and inhibiting crack propagation caused by localized thermal stress concentration. The extended structure of the spindle-shaped particles forms a physical entanglement with the rubber molecular chains, slowing their slippage and breakage at high temperatures. This constructed three-dimensional network hinders the rapid transfer of heat within the matrix, reducing the overall thermal degradation rate. Cubic nano-calcium carbonate exhibits poor isotropy, with particles bonded only by van der Waals forces. At high temperatures, they tend to agglomerate, forming stress concentration points and failing to effectively inhibit heat conduction.

[0116] Comprehensively analyzing the table, chain-net nano-calcium carbonate offers significant reinforcement advantages. Modified to optimize compatibility, three-dimensional network support, and core-shell interface optimization, it easily disperses during mixing, avoiding stress concentration and resulting in significantly superior mechanical properties to traditional cubic fillers. The core-shell structure avoids UV absorber migration issues, preventing phase separation during processing and use, maintaining long-lasting and stable UV absorption performance, and extending the product's service life.

[0117] While the embodiments of the present invention are described above, these embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to make good use of the present invention and its modifications and uses. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A process for preparing nano calcium carbonate for rubber and plastics, characterized in that: The steps include: (1) The limestone is crushed, calcined, digested, screened and aged to obtain refined lime milk; (2) Adjust the density of refined lime milk to 1.04-1.15 g / cm 3 , adding 0.8% to 1.5% of a dispersant based on the dry mass of the refined lime milk, uniformly dispersing it to obtain an atomized slurry; (3) The temperature of the carbonization tower is 25°C, a C02 / N2 mixed gas is introduced into the bottom, and the atomized slurry is sprayed vertically from the top to generate an amorphous intermediate with a particle size of 5 to 10 nm. 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; (4) The carbonized liquid was transferred to a carbonization kettle, and 1% to 2% of a crystal form control agent was added based on the dry weight of the carbonized liquid. Cyclohexane, a nonionic surfactant, and a cosurfactant were added in a mass ratio of (3 to 4): (1 to 2): (1 to 1.5). The mass ratio of the carbonized liquid to cyclohexane was (2 to 3): (3 to 5). The carbonization kettle temperature was 25°C, and ultrasonic dispersion was performed at 20 kHz to form an oil-in-water microemulsion with a water core diameter of 35 to 50 nm. (5) The temperature of the carbonization kettle is 35°C, and a CO2 / N2 mixed gas is introduced from the bottom of the kettle to carry out the carbonization reaction. The CO2 diffuses into the water core of the oil-in-water microemulsion to trigger the precipitation reaction. When the pH drops to 8, the carbonization stops and a chain-like composite nano-calcium carbonate slurry is obtained; (6) The carbonization kettle is heated to 45°C. Based on the dry weight of the nano-calcium carbonate slurry, 8% to 10% modified titanium dioxide is added and ultrasonically dispersed to form a core-shell structure. Based on the amount of modified titanium dioxide added, 5% to 8% polyacrylic acid is added and ultrasonically dispersed. The temperature is raised to 55°C and kept warm. (7) adjusting the pH of the ethanol solvent to 9.0 with ammonia water, adding 0.5% to 1% stearic acid, 0.5% to 1% KH550, and 0.5% to 0.8% phenyltrimethoxysilane based on the dry weight of the nano-calcium carbonate slurry, dispersing them in the ethanol solvent, and ultrasonically dispersing them. The mass ratio of the ethanol solvent to the nano-calcium carbonate slurry is (0.2 to 0.5): (1 to 3), to obtain a modified solution; (8) The modified liquid is added to the carbonization kettle and mixed with the nano calcium carbonate slurry. The carbonization kettle is heated to 50°C and dispersed under high shear. The lower layer of slurry is collected and washed with ethanol to obtain the modified nano calcium carbonate slurry. (9) The modified nano-calcium carbonate slurry is dehydrated, washed, dried, and air flow crushed to obtain nano-calcium carbonate particles specifically for rubber and plastics.

2. The process for preparing nano calcium carbonate for rubber and plastic according to claim 1, wherein: In the step (3), a C02 / N2 mixed gas is introduced 5 minutes before the atomized slurry is sprayed, and the atomization rate is 0.5 to 1 m 3 / h, the mixed gas flow rate is 2.5~5m 3 / h.

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

4. The process for preparing nano calcium carbonate for rubber and plastic according to claim 1, wherein: In step (5), the volume fraction of CO2 is 30% to 40%, and the gas flow rate is 0.3 to 0.5 m 3 / min.

5. The process for preparing nano calcium carbonate for rubber and plastic according to claim 1, wherein: The dispersant is prepared by compounding sodium hexametaphosphate and sodium polyacrylate.

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

7. The process for preparing nano calcium carbonate for rubber and plastic according to claim 1, wherein: The nonionic surfactant is one or more of Span 20, Span 40, Span 60, Span 80, Span 83, and Span 85.

8. The process for preparing nano calcium carbonate for rubber and plastic according to claim 1, wherein: The co-surfactant is one or more of n-butanol and isopropanol.

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