A preparation method of nano calcium carbonate for reinforcing rubber

Abstract

The invention discloses a preparation method of nano-calcium carbonate for reinforcing rubber, which relates to the field of nano-calcium carbonate production technology, including: aging a refined lime milk solution, sieving the aged lime milk solution to remove impurities, and obtaining a lime milk dilution; sending the lime milk dilution to a carbonizing kettle, then adding a composite dispersant and a first crystal form control agent to the carbonizing kettle, and feeding kiln gas into the carbonizing kettle to obtain an intermediate slurry; adding a second crystal form control agent, and feeding kiln gas into the carbonizing kettle to obtain a calcium carbonate suspension; 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; the modified nano-calcium carbonate slurry is subjected to filter pressing, drying, and crushing to obtain a finished product of nano-calcium carbonate. By this, the first crystal form control agent and the second crystal form control agent guide the nano-calcium carbonate to transform into a cubic chain form, greatly enhancing the strength and fracture resistance of rubber products.

Description

Technical Field

[0001] The invention relates to the technical field of nano calcium carbonate production, in particular to a method for preparing nano calcium carbonate for reinforcing rubber. Background Art

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

[0003] For example, the Chinese patent with publication number "CN109911925B" discloses "a method for preparing nano-calcium carbonate for rubber", and its disclosure content is "the main steps are: controlling the lime calcination temperature, the digestion ash-water ratio, the digestion temperature, and the refined pulp aging time to obtain the active lime milk required for the production of nano-calcium carbonate; controlling the initial carbonization temperature and concentration of the lime milk, and adding specific dispersants and crystal control agents for carbonization in the early stage of entering the tower to obtain specific chain-like 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, dehydrating and drying the treated slurry to a moisture content of less than 0.5%, and then depolymerizing to obtain a modified nano-calcium carbonate dry powder, which is then added to a high-speed mixer, treated with a coupling agent, and depolymerized again to obtain a composite modified nano-calcium carbonate. The nano-calcium carbonate prepared by the present invention has good dispersibility, good compatibility with the rubber substrate, good mechanical properties, and can be used as an excellent reinforcing filler for rubber."

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

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

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] A method for preparing nano calcium carbonate for reinforcing rubber comprises the following steps:

[0008] 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;

[0009] Step 2: The lime milk dilution is fed to a carbonization kettle, and 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 fed into the carbonization kettle to carry out a primary carbonization reaction. When the pH value of the feed liquid in the carbonization kettle reaches 7.5-8.2, the kiln gas supply is stopped to obtain an intermediate slurry.

[0010] 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 to carry out a secondary carbonization reaction. When the pH value in the carbonization kettle is ≤7, stop feeding the kiln gas to obtain a calcium carbonate suspension;

[0011] 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;

[0012] Step 5: The modified nano-calcium carbonate slurry is filtered, dried, and crushed to obtain finished nano-calcium carbonate.

[0013] Wherein, in step 1, the concentration of calcium hydroxide in the lime milk dilution is 8% to 12%.

[0014] Among them, in step 2, the kiln gas velocity of the initial carbonization reaction is 3~5m 3 / h, the temperature in the carbonization kettle is 18~35℃.

[0015] Among them, 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℃.

[0016] Wherein, 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 dry matrix of calcium hydroxide.

[0017] Wherein, in step 2, the compound dispersant is composed of a mixture of 25 to 35 parts of sodium hexametaphosphate, 40 to 60 parts of sodium octadecenoate and 8 to 15 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.2% to 0.8% of the mass fraction of the dry calcium hydroxide matrix.

[0018] Wherein, in step three, the second crystal form control agent 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 control agent is 1.5% to 3.2% of the mass fraction of the dry matrix of calcium hydroxide.

[0019] Wherein, in step 4, the coupling agent is composed of 10 to 20 parts of γ-methacryloyloxypropyltrimethoxy, 20 to 30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30 to 40 parts of triisostearyl isopropyl titanate 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.

[0020] The surface treatment agent is composed of a mixture of 22 to 28 parts of ethylene bisstearamide, 15 to 20 parts of cetyltrimethylammonium bromide, 3 to 5 parts of styrene-acrylic polymer emulsion, and 50 to 60 parts of lauric acid amide, and the amount of the surface treatment agent is 0.15% to 0.4% of the mass fraction of the dry calcium carbonate matrix.

[0021] 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 dry calcium carbonate matrix.

[0022] After adopting the above technical solution, the beneficial effects of the present invention are:

[0023] First, the first and second crystal form control agents are used to guide the transformation of nano-calcium carbonate into a cubic-chain composite form. During use, nano-calcium carbonate can greatly enhance the strength, fracture resistance, and wear resistance of rubber products. Second, the compounded dispersant imparts nano-calcium carbonate with excellent low-agglomeration and high fluidity, reducing rubber sticking during processing. Third, azobenzene derivatives undergo cis-trans isomerization under ultraviolet light, imparting light-controlled shape memory properties to rubber products, significantly enhancing their resistance to ultraviolet rays. DETAILED DESCRIPTION

[0024] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Example:

[0026] A method for preparing nano calcium carbonate for reinforcing rubber comprises the following steps:

[0027] 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;

[0028] Step 2: The lime milk dilution is sent to a carbonization kettle with a volume of 55 L and a slurry volume of 30 L. Subsequently, 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 to carry out a primary carbonization reaction. When the pH value of the feed liquid in the carbonization kettle reaches 7.5-8.2, the kiln gas supply is stopped to obtain an intermediate slurry.

[0029] 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 to carry out a secondary carbonization reaction. When the pH value in the carbonization kettle is ≤7, stop feeding the kiln gas to obtain a calcium carbonate suspension;

[0030] 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 to obtain a modified nano-calcium carbonate slurry.

[0031] Step 5: The modified nano-calcium carbonate slurry is filtered, dried, and crushed to obtain finished nano-calcium carbonate.

[0032] In step 1, the concentration of calcium hydroxide in the lime milk dilution is 8% to 12%.

[0033] 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℃.

[0034] 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℃.

[0035] 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 is used in an amount of 0.8% to 2.5% by weight of the dry calcium hydroxide matrix. The first crystal form control agent induces the nano-calcium carbonate to form chain-like and needle-like structures, which can improve the impact resistance and flexural strength of the rubber.

[0036] In step 2, the compound dispersant is composed of a mixture of 25-35 parts sodium hexametaphosphate, 40-60 parts sodium octadecenoate, and 8-15 parts cetyltrimethylammonium bromide, by weight, with the amount of compound dispersant being 0.2% to 0.8% by weight of the dry calcium hydroxide matrix. The compound dispersant enhances electrostatic repulsion and steric hindrance between particles, promoting the separation of nano-calcium carbonate particles and leaving sufficient space for shape mutation in nano-calcium carbonate formation.

[0037] In step 3, the second crystal form control agent 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 control agent is 1.5% to 3.2% by weight of the dry calcium hydroxide matrix. The function of the second crystal form control agent is to promote the shape of the nano-calcium carbonate to change to a cubic or chain shape, which makes the nano-calcium carbonate have better dispersibility. At the same time, when acting on the rubber, it will make the rubber matrix have better bonding ability.

[0038] In step 4, the coupling agent consists of 10-20 parts by weight of γ-methacryloyloxypropyltrimethoxy, 20-30 parts of bis-[3-(triethoxysilyl)propyl] disulfide, 30-40 parts of isopropyl triisostearyl titanate, and 20-40 parts of sodium stearate. The coupling agent is used in an amount of 0.2% to 0.8% by weight of the dry calcium carbonate matrix. The coupling agent introduces sulfide and silicon sources into rubber, which, when applied to the rubber, enhances chemical bonding and stress dissipation.

[0039] The surface treatment agent is composed of a mixture of 22-28 parts ethylene bisstearamide, 15-20 parts cetyltrimethylammonium bromide, 3-5 parts styrene-acrylic acid polymer emulsion, and 50-60 parts lauric acid amide. The amount of the surface treatment agent is 0.15% to 0.4% by weight of the dry calcium carbonate matrix. The surface treatment agent is used to modify the nano-calcium carbonate, improving its stability, weather resistance, and fluidity.

[0040] The grafting agent is composed of a mixture of 70-80 parts of thioacrylic acid, 15-20 parts of dialkyl phosphate, and 2.3-5.5 parts of an azobenzene derivative. The amount of the grafting agent is 0.34% to 0.75% by weight of the dry calcium carbonate matrix. The thioacrylic acid has sulfur cross-linking active groups, the dialkyl phosphate can enhance the flame retardancy of the nano-calcium carbonate, and the azobenzene derivative imparts dynamic interfacial response properties to the nano-calcium carbonate, making it highly resistant to ultraviolet radiation.

[0041] Example 1:

[0042] The above preparation method is used to prepare nano calcium carbonate, the difference being that:

[0043] In step 1, the refined lime milk solution is aged for 24 hours, and then the aged lime milk solution is mixed with deionized water in a mass ratio of 1:6 and sieved to remove impurities to obtain a lime milk dilution;

[0044] In step 2, kiln gas with a carbon dioxide volume concentration of 22% is fed into the carbonization kettle to carry out the primary carbonization reaction. When the pH value of the liquid in the carbonization kettle reaches 7.5, the kiln gas feeding is stopped to obtain an intermediate slurry.

[0045] In step 3, kiln gas with a carbon dioxide volume concentration of 30% is fed into the carbonization kettle.

[0046] In step 1, the concentration of calcium hydroxide in the lime milk dilution is 8%.

[0047] In step 2, the kiln gas velocity for the initial carbonization reaction is 3m 3 / h, the temperature in the carbonization kettle is 18℃.

[0048] In step 3, the kiln gas velocity of the secondary carbonization reaction is 2m 3 / h, the temperature in the carbonization kettle is 22℃.

[0049] In step 2, the first crystal form control agent is a mixture of magnesium sulfate and barium sulfate, and the amount of the first crystal form control agent is 0.8% of the mass fraction of the calcium hydroxide dry matrix.

[0050] In step 2, the compound dispersant is composed of a mixture of 25 parts of sodium hexametaphosphate, 40 parts of sodium octadecenoate and 8 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.2% of the mass fraction of the dry calcium hydroxide matrix.

[0051] In step 3, the second crystal form control agent is composed of 5.4 parts of EDTA, 6.7 parts of calcium sodium edetate, 45 parts of sodium pyrophosphate and 15.5 parts of aminotriacetic acid, and the amount of the second crystal form control agent is 1.5% of the mass fraction of the calcium hydroxide dry matrix.

[0052] In step 4, the coupling agent is composed of 10 parts of γ-methacryloyloxypropyltrimethoxy, 20 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30 parts of triisostearyl isopropyl titanate and 20 parts of sodium stearate, and the amount of the coupling agent is 0.2% of the mass fraction of the dry calcium carbonate matrix.

[0053] The surface treatment agent is composed of a mixture 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. The amount of the surface treatment agent is 0.15% of the mass fraction of the dry calcium carbonate matrix.

[0054] The grafting agent is composed of a mixture of 70 parts of thioacrylic acid, 15 parts of dialkyl phosphate and 2.3 parts of azobenzene derivatives, and the amount of the grafting agent is 0.34% by mass of the dry calcium carbonate matrix.

[0055] Example 2:

[0056] The difference between this embodiment and embodiment 1 is that:

[0057] In step 1, the refined lime milk solution is aged for 28 hours, and then the aged lime milk solution is mixed with deionized water in a mass ratio of 1:6.5 and sieved to remove impurities to obtain a lime milk dilution;

[0058] In step 2, kiln gas with a carbon dioxide volume concentration of 24% is fed into the carbonization kettle to carry out the primary carbonization reaction. When the pH value of the liquid in the carbonization kettle reaches 7.8, the kiln gas feeding is stopped to obtain an intermediate slurry.

[0059] In step 3, kiln gas with a carbon dioxide volume concentration of 32% is fed into the carbonization kettle.

[0060] In step 1, the concentration of calcium hydroxide in the lime milk dilution is 9%.

[0061] In step 2, the kiln gas velocity for the initial carbonization reaction is 3.5m 3 / h, the temperature in the carbonization kettle is 20℃.

[0062] In step 3, the kiln gas velocity of the secondary carbonization reaction is 2.5m 3 / h, the temperature in the carbonization kettle is 24℃.

[0063] In step 2, the first crystal form control agent is a mixture of aluminum sulfate and aluminum chloride, and the amount of the first crystal form control agent is 1.5% of the mass fraction of the calcium hydroxide dry matrix.

[0064] In step 2, the compound dispersant is composed of a mixture of 28 parts of sodium hexametaphosphate, 45 parts of sodium octadecenoate and 9 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.25% of the mass fraction of the calcium hydroxide dry matrix.

[0065] In step 3, the second crystal form control agent is composed of 5.8 parts of EDTA, 7.5 parts of calcium sodium edetate, 50 parts of sodium pyrophosphate and 18.5 parts of aminotriacetic acid, and the amount of the second crystal form control agent is 1.8% of the mass fraction of the calcium hydroxide dry matrix.

[0066] In step 4, the coupling agent is composed of 12 sulfide, 35 parts of triisostearyl isopropyl titanate and 25 parts of sodium stearate, and the amount of the coupling agent is 0.5% of the mass fraction of the dry calcium carbonate matrix.

[0067] The surface treatment agent is composed of a mixture 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. The amount of the surface treatment agent is 0.18% of the mass fraction of the dry calcium carbonate matrix.

[0068] The grafting agent is composed of a mixture of 75 parts of thioacrylic acid, 17 parts of dialkyl phosphate and 3.5 parts of azobenzene derivatives, and the amount of the grafting agent is 0.45% of the mass fraction of the dry calcium carbonate matrix.

[0069] Example 3:

[0070] In step 1, the refined lime milk solution is aged for 38 hours, and then the aged lime milk solution is mixed with deionized water in a mass ratio of 1:7 and sieved to remove impurities to obtain a lime milk dilution;

[0071] In step 2, kiln gas with a carbon dioxide volume concentration of 28% is fed into the carbonization kettle to carry out the primary carbonization reaction. When the pH value of the liquid in the carbonization kettle reaches 8, the kiln gas feeding is stopped to obtain an intermediate slurry.

[0072] In step 3, kiln gas with a carbon dioxide volume concentration of 34% is fed into the carbonization kettle.

[0073] In step 1, the concentration of calcium hydroxide in the lime milk dilution is 11%.

[0074] In step 2, the kiln gas velocity for the initial carbonization reaction is 4m 3 / h, the temperature in the carbonization kettle is 32℃.

[0075] In step 3, the kiln gas velocity of the secondary carbonization reaction is 3m 3 / h, the temperature in the carbonization kettle is 35℃.

[0076] In step 2, the first crystal form control agent is aluminum sulfate, and the amount of the first crystal form control agent is 2% of the mass fraction of the calcium hydroxide dry matrix.

[0077] In terms of weight, in step 2, the compound dispersant is composed of a mixture of 32 parts of sodium hexametaphosphate, 53 parts of sodium octadecenoate and 12 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.38% of the mass fraction of the calcium hydroxide dry matrix.

[0078] In step 3, the second crystal form control agent is composed of 7.6 parts of EDTA, 11 parts of calcium sodium edetate, 54 parts of sodium pyrophosphate and 20 parts of aminotriacetic acid, and the amount of the second crystal form control agent is 2.5% of the mass fraction of the dry matrix of calcium hydroxide.

[0079] In step 4, the coupling agent is composed of 18 parts of γ-methacryloyloxypropyltrimethoxy, 28 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 38 parts of triisostearoyl isopropyl titanate and 38 parts of sodium stearate, and the amount of the coupling agent is 0.68% of the mass fraction of the dry calcium carbonate matrix.

[0080] The surface treatment agent is composed of a mixture 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 amount of the surface treatment agent is 0.21% of the mass fraction of the dry calcium carbonate matrix.

[0081] The grafting agent is composed of 76 parts of thioacrylic acid, 19 parts of dialkyl phosphate and 5 parts of azobenzene derivatives. The amount of the grafting agent is 0.7% of the mass fraction of the dry calcium carbonate matrix.

[0082] Example 4:

[0083] In step 1, the refined lime milk solution is aged for 48 hours, and then the aged lime milk solution is mixed with deionized water in a mass ratio of 1:7.5 and sieved to remove impurities to obtain a lime milk dilution;

[0084] In step 2, kiln gas with a carbon dioxide volume concentration of 30% is fed into the carbonization kettle to carry out the primary carbonization reaction. When the pH value of the liquid in the carbonization kettle reaches 8.2, the kiln gas feeding is stopped to obtain an intermediate slurry.

[0085] In step 3, kiln gas with a carbon dioxide volume concentration of 35% is fed into the carbonization kettle.

[0086] In step 1, the concentration of calcium hydroxide in the lime milk dilution is 12%.

[0087] In step 2, the kiln gas velocity for the initial carbonization reaction is 5m 3 / h, the temperature in the carbonization kettle is 35℃.

[0088] In step 3, the kiln gas velocity of the secondary carbonization reaction is 4m 3 / h, the temperature in the carbonization kettle is 38℃.

[0089] In step 2, the first crystal form control agent is barium sulfate, and the amount of the first crystal form control agent is 2.5% of the mass fraction of the calcium hydroxide dry matrix.

[0090] In the second step, the compound dispersant is composed of a mixture of 35 parts of sodium hexametaphosphate, 60 parts of sodium octadecenoate and 15 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.8% of the mass fraction of the calcium hydroxide dry matrix.

[0091] In step 3, the second crystal form control agent is composed of 8.6 parts of EDTA, 12.5 parts of calcium sodium edetate, 60 parts of sodium pyrophosphate and 25.5 parts of aminotriacetic acid, and the amount of the second crystal form control agent is 3.2% of the mass fraction of the calcium hydroxide dry matrix.

[0092] In step 4, the coupling agent is composed of 20 parts of γ-methacryloyloxypropyltrimethoxy, 30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 40 parts of triisostearyl isopropyl titanate and 40 parts of sodium stearate, and the amount of the coupling agent is 0.8% of the mass fraction of the dry calcium carbonate matrix.

[0093] The surface treatment agent is composed of a mixture 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 amount of the surface treatment agent is 0.4% of the mass fraction of the dry calcium carbonate matrix.

[0094] The grafting agent is composed of 80 parts of thioacrylic acid, 20 parts of dialkyl phosphate and 5.5 parts of azobenzene derivatives. The amount of the grafting agent is 0.75% of the mass fraction of the dry calcium carbonate matrix.

[0095] Comparative Example 1:

[0096] The difference between this comparative example and Example 1 is that the initial carbonization is omitted.

[0097] Comparative Example 2:

[0098] This comparative example differs from Example 1 in that no dispersant is used.

[0099] Comparative Example 3:

[0100] This comparative example differs from Example 1 in that no coupling agent is used.

[0101] Comparative Example 4:

[0102] This comparative example is different from Example 1 in that the second crystal form controlling agent is omitted.

[0103] The products of 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:

[0104]

[0105] 1. Instrument:

[0106] (1) JSM-6700F scanning electron microscope, a product of Japan Electronic Instruments 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 determine the product by an indirect method. The unit of specific surface area (SBET) is m² / g; (3) Tap density, which was measured using Dandong Better Instrument Co., Ltd. BT-1001 intelligent powder property tester; (4) Oil absorption value, which was measured using a microburette. By adding DOP, the minimum amount of DOP required for spherical formation was calculated; (5) Twin-roller mill, manufactured by Jiangsu Mingtuo Company, with a roller speed ratio of 1:1.35 and roller dimensions of Φ160mm*1350mm; (6) Flatbed vulcanizer, manufactured by Jiangsu Mingtuo Company, with a hydraulic system rated pressure of 14.5 MPa, a nominal mold clamping pressure of MN1.6, a hot plate spacing of 100 mm, a number of hot plate working layers of 2, and an electric heating power of 2.2 kW per plate; (7) Mooney viscometer, manufactured by Jiangsu Mingtuo Company, model 7080-S2; (8) Rotorless vulcanizer, manufactured 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 display density meter produced by Jiangsu Mingtuo Company; (12) MT-4003 type rubber fatigue cracking testing machine produced by Jiangsu Mingtuo Company; (13) American Q-Lab type QUV type ultraviolet aging tester.

[0107] 2. Rubber mixing:

[0108] The rubber compound was mixed on an open mill with a front roller temperature of 55°C and a roller gap of 1.5 mm. The mixing process was as follows: plasticize each rubber compound for 2 minutes, add small materials and mix for 2 minutes, add fillers and mix for 5 minutes, add sulfur and mix for 3 minutes, thin the material, form triangle bags 5 times, remove the sheet, and allow to stand. The material was then vulcanized under pressure at 160°C on a flat-plate vulcanizer for 5 minutes, and the sheet was removed and cooled.

[0109] 3. Performance testing:

[0110] 3.1 Determination of tensile properties:

[0111] The tensile performance 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.

[0112] 3.2 Compression permanent deformation:

[0113] Measure the specimen according to the method specified in GB / T 7759.1-2015. Compress the specimen by 25% and maintain this condition for 24 hours. After 24 hours, remove the external force and allow the specimen to rest for an additional 30 minutes. Measure the thickness of the specimen at this point and record the result.

[0114] 3.3 Wear resistance:

[0115] An Akron abrasion tester was used, with a force of 26.7 N. (1) Sample preparation: Cut a sample that meets the standard requirements from the material to be tested. The sample size is usually 12.7 ± 0.2 mm in width, 3.2 ± 0.2 mm in thickness, and the length is the circumference of the rubber wheel. (2) Sample installation: Fix the sample on the clamping device of the tester to ensure that the sample surface is flat and should not have cracks or impurities. (3) Parameter setting: Adjust the load, speed, stroke and other parameters of the tester. The speed of the rubber wheel shaft is generally 76 ± 2 r / min, and the speed of the grinding wheel shaft is 34 ± 2 r / min. In the angle adjustment part, adjust the angle between the rubber wheel shaft and the grinding wheel shaft to 15°. (4) Test: Start the tester and rub the sample against the grinding wheel. After 200 minutes of pre-grinding, remove the sample, brush off the rubber scraps, and weigh its mass. (5) Formal Test: The specimen is re-fixed on the rubber wheel shaft, and the test number is set to 3416 revolutions (equivalent to 1.61 km). The formal wear test begins. After the test, the specimen is removed and weighed again. (6) Measurement Results: Based on the mass change before and after the test, the wear volume or mass loss of the specimen is calculated. The Akron wear loss of a material is usually expressed as wear volume per unit travel (cm³ / 1.61 km) or mass loss per unit travel (g / 1.61 km).

[0116] 3.4 Anti-fatigue cycles:

[0117] According to GB / T 1687.4-2021, determination of temperature rise and fatigue resistance of vulcanized rubber in flexure test - Part 4, the test is carried out using MT-4003 rubber fatigue crack testing machine.

[0118] 3.5 UV aging resistance

[0119] GB / T 14522-2008 is the national standard for "Artificial weathering test methods for plastics, coatings and rubber materials for mechanical industrial products - Fluorescent UV lamp".

[0120] Experimental equipment: QUV test chamber.

[0121] Experimental conditions: The products of Examples 1 to 4 and Comparative Examples 1 to 4 were placed in a QUV test chamber and irradiated with UV lamps of wavelengths of 200-275 nm, 275-320 nm, and 320-400 nm for 7 days, respectively. The UV intensity was 20 W / cm 2 The distance between the sample and the UV light is 40 cm. After 7 days of UV aging, the retention rate of the sample's tensile strength, elongation at break, tear strength and other indicators is tested.

[0122] The test results are as follows:

[0123]

[0124] Note: The average particle size is calculated according to the formula of specific surface area:

[0125]

[0126] 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).

[0127] From the above comparison, it can be seen that the products of Examples 1, 2, 3 and 4 of the present invention, as well as Comparative Examples 1, 2, 3 and 4, when used for rubber, do not stick to the roller during processing, have good processing performance, have high 300% modulus, tensile strength, elongation at break, tear strength, small compression permanent deformation, low wear, many fatigue resistance cycles, high tensile strength retention rate after aging, high tensile strength retention rate after aging, and high tear strength retention rate after aging.

[0128] In summary, the advantages of this solution are as follows: First, the first and second crystal form control agents are used to guide the transformation of nano-calcium carbonate into a cubic-chain composite form. During use, nano-calcium carbonate can greatly enhance the strength, fracture resistance, and wear resistance of rubber products. Second, the compounded dispersant gives nano-calcium carbonate excellent low-agglomeration and high-flowability properties, reducing the sticking of rubber to rollers during processing. Third, the azobenzene derivative undergoes cis-trans isomerization under ultraviolet light, giving the rubber product light-controlled shape memory properties, which greatly enhances the rubber product's resistance to ultraviolet rays.

[0129] The present invention is not limited to the above-mentioned specific implementation methods. Various changes made by ordinary technicians in this field based on the above-mentioned concept without creative work are all within the scope of protection 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: The lime milk dilution is fed to a carbonization kettle, and 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 fed into the carbonization kettle to carry out a primary carbonization reaction. When the pH value of the feed liquid in the carbonization kettle reaches 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 to carry out a secondary carbonization reaction. When the pH value in the carbonization kettle is ≤7, stop feeding the kiln gas 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: filtering, drying, and crushing the modified nano-calcium carbonate slurry to obtain finished nano-calcium carbonate; 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% by mass of the dry calcium carbonate matrix; 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% by mass of the dry calcium hydroxide matrix; In parts by weight, the second crystal form control agent 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 control agent is 1.5% to 3.2% of the mass fraction of the dry matrix of calcium hydroxide.

2. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, wherein 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, wherein 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, wherein 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, wherein: In step 2, the compound dispersant is composed of a mixture of 25 to 35 parts of sodium hexametaphosphate, 40 to 60 parts of sodium octadecenoate and 8 to 15 parts of cetyltrimethylammonium bromide, and the amount of the compound dispersant is 0.2% to 0.8% 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, wherein: In step 4, the coupling agent is composed of 10 to 20 parts of γ-methacryloyloxypropyltrimethoxy, 20 to 30 parts of bis-[3-(triethoxysilyl)propyl]-disulfide, 30 to 40 parts of triisostearyl isopropyl titanate 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.

7. The method for preparing nano calcium carbonate for reinforcing rubber according to claim 1, wherein: The surface treatment agent is composed of a mixture of 22 to 28 parts of ethylene bisstearamide, 15 to 20 parts of cetyltrimethylammonium bromide, 3 to 5 parts of styrene-acrylic polymer emulsion, and 50 to 60 parts of lauric acid amide. The amount of the surface treatment agent is 0.15% to 0.4% of the mass fraction of the dry calcium carbonate matrix.

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