Preparation method of nano calcium carbonate for reinforcing rubber

Abstract

The invention discloses a preparation method of nano calcium carbonate for reinforcing rubber, and relates to the technical field of nano calcium carbonate production.The preparation method comprises the steps that a refined lime milk solution is aged, the aged lime milk solution is sieved to remove impurities, and a lime milk diluent is obtained; sending the lime milk diluent to a carbonization kettle, then adding a compound dispersant and a first crystal form control agent into the carbonization kettle, and sending kiln gas into the carbonization kettle to prepare intermediate slurry; adding a second crystal form control agent, and feeding kiln gas into the carbonization kettle to obtain a calcium carbonate suspension; adding a coupling agent and a grafting agent into the calcium carbonate suspension, uniformly stirring, and then adding a surface treating agent for modification treatment to obtain modified nano calcium carbonate slurry; and carrying out filter pressing, drying and crushing on the modified nano calcium carbonate slurry to obtain the finished product nano calcium carbonate. Therefore, the first crystal form control agent and the second crystal form control agent guide the nano calcium carbonate to be converted into a cube-chain form, and the strength and fracture resistance of the rubber product are greatly enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-calcium carbonate production, and particularly to a preparation method of nano-calcium carbonate for reinforcing rubber. Background Art

[0002] With the increasing demand of the rubber industry for high-performance reinforcing materials, nano-calcium carbonate has become one of the important fillers in the rubber reinforcement field due to its high specific surface area, excellent dispersibility and low cost characteristics.

[0003] For example, the Chinese patent with the publication number "CN109911925B" discloses "a preparation method of nano-calcium carbonate for rubber special use", and its disclosed content is "The main steps are as follows: controlling the lime calcination temperature, the digestion lime-water ratio, the digestion temperature, and the aging time of the refined slurry to obtain the active lime milk required for producing nano-calcium carbonate; controlling the initial carbonization temperature and concentration of the lime milk, and adding specific dispersants and crystal form control agents in the early stage of entering the tower for carbonization to obtain specific chain-shaped nano-calcium carbonate particles, and adding a silicon source in the later stage of carbonization or at the end of carbonization; controlling the calcium carbonate slurry at 60 - 70 °C, first adding a surfactant for treatment, and after the treated slurry is dehydrated and dried until the moisture content is lower than 0.5%, it is depolymerized to obtain the first modified nano-calcium carbonate dry powder, and then added to a high-speed mixer and treated with a coupling agent, and depolymerized again to obtain the composite modified nano-calcium carbonate. The nano-calcium carbonate prepared by the present invention has good dispersibility, good compatibility with rubber substrates, and good mechanical properties, and can be used as an excellent reinforcing filler for rubber".

[0004] Although the nano-calcium carbonate provided by the above scheme can improve the mechanical properties of rubber, it is difficult to enhance the anti-aging ability of rubber. Summary of the Invention

[0005] Aiming at the above defects, the purpose of the present invention is to provide a preparation method of nano-calcium carbonate for reinforcing rubber, aiming to solve the problem of poor anti-aging ability of reinforcing rubber in the prior art.

[0006] To solve the above technical problems, the technical solution of the present invention is: A preparation method of nano-calcium carbonate for reinforcing rubber, comprising the following steps: Step 1, aging the refined lime milk solution for 24 - 48 h, and then configuring the aged lime milk solution and deionized water according to a mass ratio of 1:6 - 7.5 and sieving to remove impurities to obtain a lime milk dilution; Step 2: Send the diluted lime milk to the carbonization kettle. Subsequently, add a compound dispersant and a first crystal form control agent to the carbonization kettle. At the same time, send kiln gas with a carbon dioxide volume concentration of 22% - 30% into the carbonization kettle to carry out the primary carbonization reaction. Stop the delivery of kiln gas when the pH value of the liquid in the carbonization kettle is 7.5 - 8.2 to obtain an intermediate slurry. Step 3: Add a second crystal form control agent to the intermediate slurry, and send kiln gas with a carbon dioxide volume concentration of 30% - 35% into the carbonization kettle to carry out the secondary carbonization reaction. Stop the delivery of kiln gas when the pH value in the carbonization kettle ≤ 7 to obtain a calcium carbonate suspension. Step 4: Add a coupling agent and a grafting agent to the calcium carbonate suspension, stir evenly, and then add a surface treatment agent for modification treatment to obtain a modified nano calcium carbonate slurry. Step 5: Obtain the finished nano calcium carbonate after filtering, drying, and crushing the modified nano calcium carbonate slurry.

[0007] Among them, in Step 1, the calcium hydroxide concentration in the diluted lime milk is 8% - 12%.

[0008] Among them, in Step 2, the kiln gas flow rate for the primary carbonization reaction is 3 - 5m 3 / h, and the temperature inside the carbonization kettle is 18 - 35°C.

[0009] Among them, in Step 3, the kiln gas flow rate for the secondary carbonization reaction is 2 - 4m 3 / h, and the temperature inside the carbonization kettle is 22 - 38°C.

[0010] Among them, in Step 2, the first crystal form control agent is composed of one or more of aluminum sulfate, aluminum chloride, magnesium sulfate, and barium sulfate, and the dosage of the first crystal form control agent is 0.8% - 2.5% of the mass fraction of calcium hydroxide dry matrix.

[0011] Among them, by weight, in Step 2, the compound dispersant is composed of 25 - 35 parts of sodium hexametaphosphate, 40 - 60 parts of sodium octadecenoate, and 8 - 15 parts of cetyltrimethylammonium bromide, and the dosage of the compound dispersant is 0.2% - 0.8% of the mass fraction of calcium hydroxide dry matrix.

[0012] Among them, by weight, in Step 3, the second crystal form control agent is composed of 5.4 - 8.6 parts of EDTA, 6.7 - 12.5 parts of calcium disodium edetate, 45 - 60 parts of sodium pyrophosphate, and 15.5 - 25.5 parts of nitrilotriacetic acid, and the dosage of the second crystal form control agent is 1.5% - 3.2% of the mass fraction of calcium hydroxide dry matrix.

[0013] Among them, in step four, by weight, the coupling agent consists of 10-20 parts of γ-methacryloxypropyltrimethoxysilane, 20-30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30-40 parts of triisostearoyl titanate isopropyl ester, and 20-40 parts of sodium stearate. The dosage of the coupling agent is 0.2%-0.8% of the mass fraction of the calcium carbonate dry matrix.

[0014] Among them, the surface treatment agent consists of 22-28 parts of ethylene bisstearamide, 15-20 parts of cetyltrimethylammonium bromide, 3-5 parts of styrene-acrylic polymer emulsion, and 50-60 parts of lauric acid amide. The dosage of the surface treatment agent is 0.15%-0.4% of the mass fraction of the calcium carbonate dry matrix.

[0015] Among them, the grafting agent consists of 70-80 parts of thioacrylic acid, 15-20 parts of dialkyl phosphate, and 2.3-5.5 parts of azobenzene derivatives. The dosage of the grafting agent is 0.34%-0.75% of the mass fraction of the calcium carbonate dry matrix.

[0016] After adopting the above technical solution, the beneficial effects of the present invention are as follows: First, the first crystal form control agent and the second crystal form control agent are used to guide the transformation of nano-calcium carbonate into a cubic-chain composite form. When in use, the nano-calcium carbonate can greatly enhance the strength, fracture resistance, and wear resistance of rubber products. Second, the compound dispersant endows the nano-calcium carbonate with excellent properties of low agglomeration and high fluidity, reducing the phenomenon of sticking to the roll during the rubber processing. Third, the azobenzene derivative undergoes cis-trans isomerization under ultraviolet light, endowing the rubber product with photo-controlled shape memory characteristics, which greatly enhances the resistance of the rubber product to ultraviolet light. Specific embodiments

[0017] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] Example: A preparation method of nano-calcium carbonate for reinforcing rubber includes the following steps: In step one, the refined lime milk solution is aged for 24-48 h, and then the aged lime milk solution and deionized water are configured according to a mass ratio of 1:6-7.5 and sieved to remove impurities to obtain a diluted lime milk solution; In step two, the diluted lime milk solution is sent to a carbonization kettle with a volume of 55 L and a slurry filling volume of 30 L. Then, a compound dispersant and a first crystal form control agent are added to the carbonization kettle. At the same time, kiln gas with a carbon dioxide volume concentration of 22%-30% is sent into the carbonization kettle for the first carbonization reaction. When the pH value of the slurry in the carbonization kettle is 7.5-8.2, the kiln gas supply is stopped to obtain an intermediate slurry; Step 3: Add a second crystal form control agent to the intermediate slurry, and feed kiln gas with a carbon dioxide volume concentration of 30 - 35% into the carbonization kettle for secondary carbonization reaction. Stop feeding the kiln gas when the pH value in the carbonization kettle ≤ 7 to obtain a calcium carbonate suspension. Step 4: Add a coupling agent and a grafting agent to the calcium carbonate suspension, stir evenly, and then add a surface treatment agent for modification treatment to obtain a modified nano calcium carbonate slurry.

[0019] Step 5: Filter, dry, and crush the modified nano calcium carbonate slurry to obtain the finished nano calcium carbonate.

[0020] In Step 1, the calcium hydroxide concentration in the lime milk dilution is 8% - 12%.

[0021] In Step 2, the flow rate of the kiln gas for the primary carbonization reaction is 3 - 5 m 3 / h, and the temperature inside the carbonization kettle is 18 - 35 °C.

[0022] In Step 3, the flow rate of the kiln gas for the secondary carbonization reaction is 2 - 4 m 3 / h, and the temperature inside the carbonization kettle is 22 - 38 °C.

[0023] In Step 2, the first crystal form control agent is composed of one or more of aluminum sulfate, aluminum chloride, magnesium sulfate, and barium sulfate, and the dosage of the first crystal form control agent is 0.8% - 2.5% of the mass fraction of the calcium hydroxide dry matrix. Using the first crystal form control agent to induce nano calcium carbonate to form a chain-like and needle-like structure, which can improve the impact resistance and bending strength of rubber.

[0024] By weight, in Step 2, the compound dispersant is composed of 25 - 35 parts of sodium hexametaphosphate, 40 - 60 parts of sodium octadecenoate, and 8 - 15 parts of cetyltrimethylammonium bromide, and the dosage of the compound dispersant is 0.2% - 0.8% of the mass fraction of the calcium hydroxide dry matrix. The compound dispersant can improve the electrostatic repulsion and steric hindrance between particles, promote the separation of nano calcium carbonate particles, and leave enough space for the shape mutation of nano calcium carbonate to form.

[0025] By weight, in Step 3, the second crystal form control agent is composed of 5.4 - 8.6 parts of EDTA, 6.7 - 12.5 parts of calcium disodium edetate, 45 - 60 parts of sodium pyrophosphate, and 15.5 - 25.5 parts of nitrilotriacetic acid, and the dosage of the second crystal form control agent is 1.5% - 3.2% of the mass fraction of the calcium hydroxide dry matrix. The role of the second crystal form control agent is to promote the shape of nano calcium carbonate to transform into a cube and chain shape, which makes nano calcium carbonate have better dispersibility. At the same time, when acting on rubber, it will make the rubber matrix have better connection ability.

[0026] In step four, by weight parts, the coupling agent consists of 10-20 parts of γ-methacryloxypropyltrimethoxysilane, 20-30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30-40 parts of triisostearoyl titanate isopropyl ester, and 20-40 parts of sodium stearate. The dosage of the coupling agent is 0.2%-0.8% of the mass fraction of the calcium carbonate dry matrix. The function of the coupling agent is to introduce sulfide and silicon source. When nano calcium carbonate is applied in rubber, it can enable the rubber to have better chemical bonding and stress dispersion ability.

[0027] The surface treatment agent consists of 22-28 parts of ethylene bisstearamide, 15-20 parts of cetyltrimethylammonium bromide, 3-5 parts of styrene-acrylic polymer emulsion, and 50-60 parts of lauric acid amide. The dosage of the surface treatment agent is 0.15%-0.4% of the mass fraction of the calcium carbonate dry matrix. The function of the surface treatment agent is to modify the nano calcium carbonate and improve the stability, weather resistance and fluidity of the nano calcium carbonate.

[0028] The grafting agent consists of 70-80 parts of thioacrylic acid, 15-20 parts of dialkyl phosphate ester, and 2.3-5.5 parts of azobenzene derivative. The dosage of the grafting agent is 0.34%-0.75% of the mass fraction of the calcium carbonate dry matrix. Thioacrylic acid has a sulfur cross-linking active group. Dialkyl phosphate ester can enhance the flame retardancy of nano calcium carbonate, while azobenzene derivative endows nano calcium carbonate with dynamic interface response characteristics, enabling nano calcium carbonate to have excellent resistance to ultraviolet irradiation.

[0029] Example 1: Prepare nano calcium carbonate using the above preparation method, with the differences being: In step one, age the refined lime milk solution for 24 h, and then prepare and screen out impurities by mixing the aged lime milk solution and deionized water at a mass ratio of 1:6 to obtain a lime milk dilution; In step two, feed kiln gas with a carbon dioxide volume concentration of 22% into the carbonization kettle for the first carbonization reaction. Stop feeding the kiln gas when the pH value of the liquid in the carbonization kettle reaches 7.5 to obtain an intermediate slurry; In step three, feed kiln gas with a carbon dioxide volume concentration of 30% into the carbonization kettle.

[0030] In step one, the calcium hydroxide concentration in the lime milk dilution is 8%.

[0031] In step two, the kiln gas flow rate for the first carbonization reaction is 3 m 3 / h, and the temperature in the carbonization kettle is 18°C.

[0032] In step three, the kiln gas flow rate for the second carbonization reaction is 2 m 3 / h, the temperature inside the carbonization kettle is 22 °C.

[0033] In step two, the first crystal form control agent is composed of a mixture of magnesium sulfate and barium sulfate, and the dosage of the first crystal form control agent is 0.8% of the mass fraction of the calcium hydroxide dry matrix.

[0034] By weight, in step two, the compound dispersant is composed of 25 parts of sodium hexametaphosphate, 40 parts of sodium octadecenoate, and 8 parts of cetyltrimethylammonium bromide, and the dosage of the compound dispersant is 0.2% of the mass fraction of the calcium hydroxide dry matrix.

[0035] By weight, in step three, the second crystal form control agent is composed of 5.4 parts of EDTA, 6.7 parts of calcium disodium edetate, 45 parts of sodium pyrophosphate, and 15.5 parts of nitrilotriacetic acid, and the dosage of the second crystal form control agent is 1.5% of the mass fraction of the calcium hydroxide dry matrix.

[0036] By weight, in step four, the coupling agent is composed of 10 parts of γ-methacryloxypropyltrimethoxysilane, 20 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30 parts of triisostearoyl titanate isopropyl ester, and 20 parts of sodium stearate, and the dosage of the coupling agent is 0.2% of the mass fraction of the calcium carbonate dry matrix.

[0037] The surface treatment agent is composed of 22 parts of ethylene bisstearamide, 15 parts of cetyltrimethylammonium bromide, 3 parts of styrene-acrylic polymer emulsion, and 50 parts of lauric acid amide, and the dosage of the surface treatment agent is 0.15% of the mass fraction of the calcium carbonate dry matrix.

[0038] The grafting agent is composed of 70 parts of thioacrylic acid, 15 parts of dialkyl phosphate ester, and 2.3 parts of azobenzene derivative, and the dosage of the grafting agent is 0.34% of the mass fraction of the calcium carbonate dry matrix.

[0039] Example 2: The difference between this example and Example 1 is as follows: In step one, the refined lime milk solution is aged for 28 h, and then the aged lime milk solution and deionized water are configured according to a mass ratio of 1:6.5 and screened to remove impurities to obtain a diluted lime milk solution; In step two, kiln gas with a carbon dioxide volume concentration of 24% is sent into the carbonization kettle for the primary carbonization reaction, and the kiln gas supply is stopped when the pH value of the slurry in the carbonization kettle is 7.8 to obtain an intermediate slurry; In step three, kiln gas with a carbon dioxide volume concentration of 32% is sent into the carbonization kettle.

[0040] In step one, the calcium hydroxide concentration in the diluted lime milk solution is 9%.

[0041] In Step 2, the kiln gas flow rate for the primary carbonization reaction is 3.5 m 3 / h, and the temperature inside the carbonization kettle is 20 °C.

[0042] In Step 3, the kiln gas flow rate for the secondary carbonization reaction is 2.5 m 3 / h, and the temperature inside the carbonization kettle is 24 °C.

[0043] In Step 2, the first crystal form control agent is composed of a mixture of aluminum sulfate and aluminum chloride, and the dosage of the first crystal form control agent is 1.5% of the mass fraction of the calcium hydroxide dry matrix.

[0044] By weight, in Step 2, the compound dispersant is composed of 28 parts of sodium hexametaphosphate, 45 parts of sodium octadecenoate, and 9 parts of cetyltrimethylammonium bromide, and the dosage of the compound dispersant is 0.25% of the mass fraction of the calcium hydroxide dry matrix.

[0045] By weight, in Step 3, the second crystal form control agent is composed of 5.8 parts of EDTA, 7.5 parts of calcium disodium edetate, 50 parts of sodium pyrophosphate, and 18.5 parts of nitrilotriacetic acid, and the dosage of the second crystal form control agent is 1.8% of the mass fraction of the calcium hydroxide dry matrix.

[0046] By weight, in Step 4, the coupling agent is composed of 12 sulfides, 35 parts of isopropyl triisostearoyl titanate, and 25 parts of sodium stearate, and the dosage of the coupling agent is 0.5% of the mass fraction of the calcium carbonate dry matrix.

[0047] The surface treatment agent is composed of 24 parts of ethylene bisstearamide, 16 parts of cetyltrimethylammonium bromide, 4 parts of styrene-acrylic polymer emulsion, and 55 parts of lauric acid amide, and the dosage of the surface treatment agent is 0.18% of the mass fraction of the calcium carbonate dry matrix.

[0048] The grafting agent is composed of 75 parts of thioacrylic acid, 17 parts of dialkyl phosphate, and 3.5 parts of azobenzene derivatives, and the dosage of the grafting agent is 0.45% of the mass fraction of the calcium carbonate dry matrix.

[0049] Example 3: In Step 1, the refined lime milk solution is aged for 38 h, and then the aged lime milk solution and deionized water are configured in a mass ratio of 1:7 and screened to remove impurities to obtain a diluted lime milk solution; In Step 2, kiln gas with a carbon dioxide volume concentration of 28% is fed into the carbonization kettle for the primary carbonization reaction, and the feeding of the kiln gas is stopped when the pH value of the liquid in the carbonization kettle reaches 8 to obtain an intermediate slurry; In Step 3, kiln gas with a carbon dioxide volume concentration of 34% is fed into the carbonization kettle.

[0050] In Step 1, the calcium hydroxide concentration in the diluted lime milk solution is 11%.

[0051] In Step 2, the kiln gas flow rate for the primary carbonization reaction is 4 m 3 / h, and the temperature inside the carbonization kettle is 32 °C.

[0052] In Step 3, the kiln gas flow rate for the secondary carbonization reaction is 3 m 3 / h, and the temperature inside the carbonization kettle is 35 °C.

[0053] In Step 2, the first crystal form control agent is aluminum sulfate, and the dosage of the first crystal form control agent is 2% of the mass fraction of the calcium hydroxide dry matrix.

[0054] By weight, in Step 2, the compound dispersant is composed of 32 parts of sodium hexametaphosphate, 53 parts of sodium octadecenoate, and 12 parts of cetyltrimethylammonium bromide. The dosage of the compound dispersant is 0.38% of the mass fraction of the calcium hydroxide dry matrix.

[0055] By weight, in Step 3, the second crystal form control agent is composed of 7.6 parts of EDTA, 11 parts of calcium disodium edetate, 54 parts of sodium pyrophosphate, and 20 parts of nitrilotriacetic acid. The dosage of the second crystal form control agent is 2.5% of the mass fraction of the calcium hydroxide dry matrix.

[0056] By weight, in Step 4, the coupling agent is composed of 18 parts of γ-methacryloxypropyltrimethoxysilane, 28 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 38 parts of triisostearoyl titanate isopropyl ester, and 38 parts of sodium stearate. The dosage of the coupling agent is 0.68% of the mass fraction of the calcium carbonate dry matrix.

[0057] The surface treatment agent is composed of 27 parts of ethylene bisstearamide, 18 parts of cetyltrimethylammonium bromide, 4.5 parts of styrene-acrylic polymer emulsion, and 58 parts of lauric acid amide. The dosage of the surface treatment agent is 0.21% of the mass fraction of the calcium carbonate dry matrix.

[0058] The grafting agent is composed of 76 parts of thioacrylic acid, 19 parts of dialkyl phosphate, and 5 parts of azobenzene derivatives. The dosage of the grafting agent is 0.7% of the mass fraction of the calcium carbonate dry matrix.

[0059] Example 4: In Step 1, the refined lime milk solution is aged for 48 h, and then the aged lime milk solution and deionized water are configured according to a mass ratio of 1:7.5 and screened to remove impurities to obtain a diluted lime milk solution; In Step 2, kiln gas with a carbon dioxide volume concentration of 30% is fed into the carbonization kettle for the primary carbonization reaction. When the pH value of the liquid in the carbonization kettle reaches 8.2, the feeding of kiln gas is stopped to obtain an intermediate slurry. In Step 3, kiln gas with a carbon dioxide volume concentration of 35% is fed into the carbonization kettle.

[0060] In Step 1, the calcium hydroxide concentration in the diluted lime milk is 12%.

[0061] In Step 2, the flow rate of the kiln gas in the primary carbonization reaction is 5 m 3 / h, and the temperature inside the carbonization kettle is 35°C.

[0062] In Step 3, the flow rate of the kiln gas in the secondary carbonization reaction is 4 m 3 / h, and the temperature inside the carbonization kettle is 38°C.

[0063] In Step 2, the first crystal form control agent is barium sulfate, and the dosage of the first crystal form control agent is 2.5% of the mass fraction of calcium hydroxide dry matrix.

[0064] By weight, in Step 2, the compound dispersant is composed of 35 parts of sodium hexametaphosphate, 60 parts of sodium octadecenoate, and 15 parts of cetyltrimethylammonium bromide. The dosage of the compound dispersant is 0.8% of the mass fraction of calcium hydroxide dry matrix.

[0065] By weight, in Step 3, the second crystal form control agent is composed of 8.6 parts of EDTA, 12.5 parts of calcium disodium edetate, 60 parts of sodium pyrophosphate, and 25.5 parts of nitrilotriacetic acid. The dosage of the second crystal form control agent is 3.2% of the mass fraction of calcium hydroxide dry matrix.

[0066] By weight, in Step 4, the coupling agent is composed of 20 parts of γ-methacryloxypropyltrimethoxysilane, 30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 40 parts of triisostearoyl titanate isopropyl ester, and 40 parts of sodium stearate. The dosage of the coupling agent is 0.8% of the mass fraction of calcium carbonate dry matrix.

[0067] The surface treatment agent is composed of 28 parts of ethylene bisstearamide, 20 parts of cetyltrimethylammonium bromide, 5 parts of styrene-acrylic polymer emulsion, and 60 parts of lauric acid amide. The dosage of the surface treatment agent is 0.4% of the mass fraction of calcium carbonate dry matrix.

[0068] The grafting agent is composed of 80 parts of thioacrylic acid, 20 parts of dialkyl phosphate, and 5.5 parts of azobenzene derivatives. The dosage of the grafting agent is 0.75% of the mass fraction of calcium carbonate dry matrix.

[0069] Comparative Example 1: The difference between this comparative example and Example 1 is that the primary carbonization is omitted.

[0070] Comparative Example 2: The difference between this comparative example and Example 1 is that no dispersant is used.

[0071] Comparative Example 3: The difference between this comparative example and Example 1 is that no coupling agent is used.

[0072] Comparative Example 4: The difference between this comparative example and Example 1 is that the second crystal form controlling agent is omitted.

[0073] The products in Examples 1 to 4 and Comparative Examples 1 to 4 were respectively used in rubber production, and the finished rubber products were compared. The rubber was tested according to the following formula:

[0074] 1. Instrument: (1) JSM-6700F scanning electron microscope, a product of Japan Electronic Instrument Co., Ltd., inspected by Shandong University of Technology; (2) Specific surface area meter, Beijing Biode Electronic Instrument TB-1000 BET specific surface area meter, which uses nitrogen adsorption to measure the product by an indirect method. The unit of specific surface area (SBET) is m² / g; (3) Tap density, tested by Dandong Better Instrument Co., Ltd. BT-1001 intelligent powder property tester; (4) Oil absorption value, measured by a microburette, by adding DOP and calculating the minimum amount of DOP required for ball formation; (5) Twin-roller mixing mill, produced by Jiangsu Mingtuo Company, with roller speed ratio of 1:1.35 and roller size of Φ160mm*1350mm; (6) Plate vulcanizer, produced by Jiangsu Mingtuo Company, with MT-160T plate vulcanizer, hydraulic system rated pressure of 14.5Mpa, nominal mold clamping MN1.6, hot plate spacing of 100mm, number of hot plate working layers of 2, and electric heating power of each plate of 2.2KW; (7) Mooney viscometer, produced by Jiangsu Mingtuo Company, model 7080-S2; (8) Rotorless vulcanizer, produced by Jiangsu Mingtuo Company, model 2000-A (9) Electronic tensile testing machine, AI-7000S type produced by Jiangsu Mingtuo Company; (10) Akron abrasion testing machine, MT4160 type produced by Jiangsu Mingtuo Company; (11) MT-300A type digital density meter produced by Jiangsu Mingtuo Company; (12) MT-4003 type rubber fatigue crack testing machine produced by Jiangsu Mingtuo Company; (13) QUV type ultraviolet aging tester produced by Q-Lab of the United States.

[0075] 2. Rubber compound mixing: The rubber compound mixing is carried out on an open mill. The temperature of the front roller is 55 °C, and the roller gap is 1.5 mm. The mixing process is as follows: plasticize various rubbers for 2 min → add small ingredients and mix for 2 min → add fillers and mix for 5 min → add sulfur and mix for 3 min → thin pass → make 5 triangle bales → take off the sheet → store. Then, it is vulcanized under pressure at 160 °C using a flat vulcanizer, taken out of the mold after 5 min, and cooled.

[0076] 3. Performance testing: 3.1 Determination of tensile properties: The tensile property standard is mainly based on GB / T 528-2009 (Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber). A universal tensile testing machine is used to measure the 300% modulus and strength at 23 °C.

[0077] 3.2 Compression set: According to the method specified in GB / T 7759.1-2015, the test specimen is measured. The test piece is compressed by 25% and kept in this state for 24 hours. After 24 hours, the external force is removed, and it is further left standing for 30 minutes. Then, the thickness of the test piece at this time is measured and the result is recorded.

[0078] 3.3 Abrasion resistance: An Akron abrasion testing machine is used, and the applied force is 26.7 N. (1) Prepare the test specimen: Cut a test specimen that meets the standard requirements from the material to be tested. The dimensions of the test specimen are usually width 12.7 ± 0.2 mm, thickness 3.2 ± 0.2 mm, and the length is the circumference of the rubber wheel. (2) Install the test specimen: Fix the test specimen on the clamping device of the testing machine to ensure that the surface of the test specimen is flat and there should be no cracks or impurities. (3) Set the parameters: Adjust the parameters such as the load, rotation speed, and stroke of the testing machine. The rotation speed of the rubber wheel shaft is generally 76 ± 2 r / min, and the rotation speed of the grinding wheel shaft is 34 ± 2 r / min. In the angle adjustment part, adjust the included angle between the rubber wheel shaft and the grinding wheel shaft to 15°. (4) Conduct the test: Start the testing machine to make the test specimen rub against the grinding wheel. After pre-grinding for 200 minutes, take down the test specimen, brush off the rubber chips, and weigh its mass. (5) Conduct the formal test: Fix the test specimen on the rubber wheel shaft again, set the number of test rotations to 3416 (equivalent to 1.61 km), and start the formal abrasion test. After the test is completed, take down the test specimen and weigh its mass again. (6) Measure the result: Calculate the wear volume or mass loss of the test specimen based on the mass change before and after the test. Usually, the abrasion amount of the material is expressed by the wear volume per unit travel (cm³ / 1.61 km) or mass loss (g / 1.61 km).

[0079] 3.4 Number of fatigue resistance cycles: According to GB / T 1687.4-2021, Determination of heat build-up and fatigue resistance of vulcanized rubber in flexometer testing - Part 4, the MT-4003 rubber fatigue cracking testing machine is used for determination.

[0080] 3.5 Resistance to ultraviolet aging performance According to the GB / T 14522-2008 standard, it is the national standard of "Artificial weathering test method for plastics, coatings and rubber materials used in mechanical industry products - Fluorescent ultraviolet lamp".

[0081] Experimental equipment: QUV test chamber.

[0082] Experimental conditions: The products in Examples 1 - 4 and Comparative Examples 1 - 4 are sent to the QUV test chamber, and the samples are irradiated with ultraviolet lamps with wavelengths of 200 - 275 nm, 275 - 320 nm and 320 - 400 nm for 7 days respectively. The ultraviolet light intensity is 20 W / cm 2 , the distance between the sample and the ultraviolet light is 40 cm. After 7 days of ultraviolet aging, the retention rates of tensile strength, elongation at break, tear strength and other indicators of the test specimens are tested.

[0083] The test results are as follows:

[0084] Remark: The average particle size is calculated according to the formula of specific surface area:

[0085] 6 is the powder shape factor, 2.7 is the specific gravity of calcium carbonate, dp = average diameter (μm), s = specific surface area (m 2 / g).

[0086] It can be seen from the above comparison that for Examples 1, 2, 3, 4 of the present invention and the products of Comparative Examples 1, 2, 3, 4, when used in rubber, they do not stick to the roller during processing, have good processing performance, have relatively high 300% modulus, tensile strength, elongation at break, tear strength, small compression set, low abrasion loss, many anti-fatigue cycle times, high retention rate of tensile strength after aging, high retention rate of tensile strength after aging, and high retention rate of tear strength after aging.

[0087] In summary, the advantages of this solution are as follows: First, the first crystal form control agent and the second crystal form control agent are used to guide the transformation of nano-calcium carbonate into a cubic-chain composite morphology. When in use, the nano-calcium carbonate can greatly enhance the strength, fracture resistance, and wear resistance of rubber products. Second, the compound dispersant endows the nano-calcium carbonate with excellent properties of low agglomeration and high fluidity, reducing the phenomenon of rubber sticking to the roller during the processing. Third, the azobenzene derivative undergoes cis-trans isomerization under ultraviolet light, endowing the rubber product with photo-controlled shape memory characteristics, which greatly enhances the resistance of the rubber product to ultraviolet light.

[0088] The present invention is not limited to the above specific embodiments. Those of ordinary skill in the art starting from the above concepts and making various transformations without creative labor fall within the protection scope of the present invention.

Claims

1. A method for preparing nano calcium carbonate for reinforcing rubber, characterized in that: The steps include: Step 1, aging the refined lime milk solution for 24 to 48 hours, then mixing the aged lime milk solution with deionized water in a mass ratio of 1:6 to 7.5 and sieving to remove impurities, to obtain a lime milk dilution; Step 2: sending the lime milk dilution to the carbonization kettle, then adding the compound dispersant and the first crystal form control agent to the carbonization kettle, and at the same time, sending kiln gas with a carbon dioxide volume concentration of 22-30% to the carbonization kettle to carry out the primary carbonization reaction, and stopping the kiln gas delivery when the pH value of the feed liquid in the carbonization kettle is 7.5-8.2 to obtain the intermediate slurry; Step 3, adding a second crystal form control agent to the intermediate slurry, and feeding kiln gas with a carbon dioxide volume concentration of 30-35% into the carbonization kettle to carry out a secondary carbonization reaction, and stopping the kiln gas feeding when the pH value in the carbonization kettle is ≤7 to obtain a calcium carbonate suspension; Step 4, adding a coupling agent and a grafting agent to the calcium carbonate suspension, stirring evenly, and then adding a surface treatment agent for modification to obtain a modified nano calcium carbonate slurry; Step 5: The modified nano calcium carbonate slurry is filtered, dried and crushed to obtain finished nano calcium carbonate.

2. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In step 1, the concentration of calcium hydroxide in the lime milk dilution is 8% to 12%.

3. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In step 2, the kiln gas velocity for the initial carbonization reaction is 3~5m 3 / h, the temperature in the carbonization kettle is 18~35℃.

4. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In step 3, the kiln gas velocity of the secondary carbonization reaction is 2~4m 3 / h, the temperature in the carbonization kettle is 22~38℃.

5. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In step 2, the first crystal form control agent is composed of one or more of aluminum sulfate, aluminum chloride, magnesium sulfate, and barium sulfate, and the amount of the first crystal form control agent is 0.8% to 2.5% of the mass fraction of the calcium hydroxide dry matrix.

6. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In terms of weight, in step 2, the compound dispersant is composed of 25 to 35 parts of sodium hexametaphosphate, 40 to 60 parts of sodium octadecenoate and 8 to 15 parts of hexadecyltrimethylammonium bromide. The amount of the compound dispersant is 0.2% to 0.8% of the mass fraction of the calcium hydroxide dry matrix.

7. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In terms of weight, in step three, the second crystal form controller is composed of 5.4 to 8.6 parts of EDTA, 6.7 to 12.5 parts of calcium sodium edetate, 45 to 60 parts of sodium pyrophosphate and 15.5 to 25.5 parts of aminotriacetic acid, and the amount of the second crystal form controller is 1.5% to 3.2% of the mass fraction of the calcium hydroxide dry matrix.

8. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: In terms of weight, in step 4, the coupling agent is composed of 10 to 20 parts of γ-methacryloxypropyl trimethoxy, 20 to 30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30 to 40 parts of triisostearyl titanate isopropyl and 20 to 40 parts of sodium stearate, and the amount of the coupling agent is 0.2% to 0.8% of the mass fraction of the dry calcium carbonate matrix.

9. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: The surface treatment agent is composed of 22-28 parts of ethylene bisstearic acid amide, 15-20 parts of hexadecyl trimethyl ammonium bromide, 3-5 parts of styrene-acrylic acid polymer emulsion, and 50-60 parts of lauric acid amide. The amount of the surface treatment agent is 0.15%-0.4% of the mass fraction of the calcium carbonate dry matrix.

10. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, characterized in that: The grafting agent is composed of 70-80 parts of thioacrylic acid, 15-20 parts of dialkyl phosphate and 2.3-5.5 parts of azobenzene derivatives, and the amount of the grafting agent is 0.34%-0.75% of the mass fraction of the calcium carbonate dry matrix.

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