Nano calcium carbonate for car paint and preparation method thereof

Abstract

The present invention belongs to the field of nano-calcium carbonate technology, and specifically relates to nano-calcium carbonate for vehicle paint and a preparation method thereof. The preparation method comprises: adding a dispersant to a Ca(OH)2 slurry and thoroughly mixing to obtain a refined slurry; carbonizing a portion of the refined slurry to obtain a nano-calcium carbonate slurry A having a spherical crystal form; subjecting the remaining refined slurry to a secondary carbonization to obtain a nano-calcium carbonate slurry B having a chain-like crystal form; introducing the nano-calcium carbonate slurry A and the nano-calcium carbonate slurry B into a mixing kettle and performing a modification treatment to obtain a modified nano-calcium carbonate slurry; and drying, pulverizing, and sieving the modified nano-calcium carbonate slurry to obtain the nano-calcium carbonate for vehicle paint. By optimizing the preparation process of the nano-calcium carbonate, its dispersibility in vehicle paint and its compatibility with resin matrices and metal substrates are improved, thereby significantly improving the comprehensive properties of the vehicle paint, such as adhesion and impact resistance, and effectively solving the problems of topcoat peeling and primer shedding.

Description

Technical Field

[0001] The invention belongs to the technical field of nano calcium carbonate, and particularly relates to nano calcium carbonate for vehicle paint and a preparation method thereof. Background Art

[0002] Automotive primer, as the base coating in a car paint system, comes into direct contact with the metal substrate and provides a good foundation for subsequent topcoat application. Nano-calcium carbonate, due to its small particle size, large surface area, and high surface activity, exhibits excellent functional effects in car paint, such as improving the coating's hardness, wear resistance, and impact resistance.

[0003] However, the ultrafine particle size and extremely high surface energy of nano-calcium carbonate make it prone to spontaneous agglomeration during processing, making it difficult to achieve good compatibility with resin matrices and metal substrates. This agglomeration not only reduces the dispersion of nano-calcium carbonate in car paint but also creates stress concentration points within the coating. This can easily cause the topcoat to peel off, or even the primer to fall off, when impacted, seriously affecting the durability and aesthetics of the automotive coating. Summary of the Invention

[0004] In response to the problems existing in the prior art, on the one hand, the present invention provides a method for preparing nano-calcium carbonate for car paint, aiming to improve its dispersibility in car paint and its compatibility with resin matrix and metal substrate by optimizing the preparation process of nano-calcium carbonate, thereby significantly improving the comprehensive performance of car paint such as adhesion and impact resistance, and effectively solving the problems of topcoat peeling and primer shedding.

[0005] To achieve the above object, a method for preparing nano calcium carbonate for car paint comprises the following steps:

[0006] 1) After limestone is crushed, calcined, digested, aged, and filtered to obtain Ca(OH)2 slurry, a dispersant accounting for 0.8% to 1.2% of the dry weight of the Ca(OH)2 slurry is added and the mixture is thoroughly mixed to obtain a refined slurry;

[0007] 2) introducing 60% to 70% of the total volume of the refined slurry into a carbonization kettle A, maintaining the temperature at 18° C., introducing CO2 gas, and adding 0.5% to 1% of the dry weight of the refined slurry to the carbonization kettle A. When the pH of the slurry measured by the pH monitoring system drops to 8.5, stopping the ventilation, keeping the temperature for 15 minutes, adding 0.3% to 0.6% of the dry weight of γ-aminopropyltriethoxysilane, and mixing and stirring to obtain a spherical nano-calcium carbonate slurry A;

[0008] 3) introducing 30% to 40% of the total volume of the refined slurry into the carbonization kettle B, maintaining the temperature at 22° C., introducing CO2 gas, and adding 0.5% to 1.5% of the dry weight of the refined slurry to the carbonization kettle B. When the pH of the slurry measured by the pH monitoring system drops to 8.5, stopping the ventilation, keeping the temperature for 15 minutes, adding 0.3% to 0.5% of the dry weight of the titanate coupling agent, and mixing and stirring to obtain a nano-calcium carbonate slurry B with a chain-like crystal form;

[0009] 4) Nano-calcium carbonate slurry A and nano-calcium carbonate slurry B were introduced into a mixing kettle together, maintained at 60°C, and mixed and stirred for 45 minutes to obtain a nano-calcium carbonate slurry in a composite crystal form. The mixture was kept warm for 15 minutes, and a silane coupling agent and a surfactant were added in sequence, and mixed and stirred to obtain a modified nano-calcium carbonate slurry;

[0010] 5) Drying and crushing the modified nano-calcium carbonate slurry to obtain nano-calcium carbonate for car paint.

[0011] Preferably, the dispersant is sodium polyacrylate.

[0012] Preferably, the crystal form controlling agent A is sodium polyphosphate.

[0013] Preferably, the crystal form controlling agent B is prepared by compounding sucrose and magnesium chloride in a mass ratio of 3:2.

[0014] Preferably, the titanate coupling agent is TMC-201.

[0015] Preferably, the silane coupling agent is KH-550, and the addition amount is 0.3% to 0.6% of the dry basis weight of the nano-calcium carbonate slurry.

[0016] Preferably, the surfactant is sodium stearate, and the added amount is 0.5% to 0.8% of the dry weight of the nano-calcium carbonate slurry.

[0017] On the other hand, the present invention also provides nano calcium carbonate for vehicle paint, which is prepared by the above preparation method.

[0018] After adopting the above technical solution, the beneficial effects of the present invention are:

[0019] The present invention aims to optimize the preparation process of nano calcium carbonate, improve its dispersibility in car paint and its compatibility with resin matrix and metal substrate, thereby significantly improving the comprehensive performance of car paint, such as adhesion and impact resistance, and effectively solving the problems of topcoat peeling and primer shedding. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. 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.

[0021] Example 1

[0022] This embodiment provides a method for preparing nano calcium carbonate for car paint. The following are the specific preparation steps and technical details of the preparation method.

[0023] Refined slurry preparation

[0024] The limestone is crushed, calcined, digested, aged and filtered to obtain Ca(OH)2 slurry, to which sodium polyacrylate accounting for 0.8% of the dry basis weight of the Ca(OH)2 slurry is added and fully mixed to obtain a refined slurry.

[0025] By adding the dispersant sodium polyacrylate, the viscosity of the system can be reduced, its fluidity and stability can be improved, and particle agglomeration can be prevented. During the carbonization stage, the carbonization reaction can proceed more evenly, which helps to produce calcium carbonate products with small particle size and uniform distribution.

[0026] Preparation of spherical nano-calcium carbonate

[0027] 60% of the total volume of refined slurry was introduced into carbonization kettle A, the reaction temperature was controlled at 18°C, the stirring rate was 300 rpm, 0.5% of the dry weight of the refined slurry was added with sodium polyphosphate, and CO2 gas (volume fraction 35%) was introduced from the bottom at a flow rate of 0.5 L / min for carbonization.

[0028] When the pH of the slurry measured by the pH monitoring system dropped to 8.5, aeration was stopped and the mixture was kept at 25° C. for 15 minutes to stabilize the product crystal form and reduce lattice defects.

[0029] After carbonization, the reaction temperature was controlled at 40° C., γ-aminopropyltriethoxysilane was added based on 0.3% of the dry mass of the slurry for surface treatment, and the mixture was stirred at 200 rpm for 20 min to finally obtain a nano-calcium carbonate slurry A with a spherical crystal form.

[0030] Preparation of chain-like nano-calcium carbonate

[0031] The remaining 40% of the refined slurry was introduced into carbonization kettle B. The reaction temperature was controlled at 22°C and the stirring rate was 200 rpm. A crystal form control agent B, made from sucrose and magnesium chloride in a mass ratio of 3:2, was added, accounting for 0.5% of the dry weight of the refined slurry. CO2 gas (40% by volume) was introduced from the bottom at a flow rate of 0.8 L / min to carry out carbonization. When the pH of the slurry dropped to 9.0 as measured by the pH monitoring system, the temperature was raised to 30°C and the aeration rate was reduced to 0.3 L / min.

[0032] When the pH monitoring system measured that the pH of the slurry dropped to 8.5, the CO2 gas was stopped and the mixture was kept at 30°C for 15 minutes to stabilize the product crystal form and reduce lattice defects.

[0033] After carbonization, a titanate coupling agent TMC-201 was added based on 0.3% of the dry basis weight of the slurry for surface treatment, and the mixture was stirred at 200 rpm for 20 min to finally obtain a nano-calcium carbonate slurry B having a chain-like crystal form.

[0034] Mixed modification

[0035] Prepared nano-calcium carbonate slurries A and B were introduced into a mixing kettle, maintained at 45°C, and stirred at 200 rpm for 20 minutes to produce a composite nano-calcium carbonate slurry. During mixing, the ethoxy groups of γ-aminopropyltriethoxysilane hydrolyze in an aqueous environment to form silanol groups, which can chemically bond with the hydroxyl groups on the surface of metal oxides (such as Al2O3 on the vehicle body), thereby improving the adhesion of the primer to the metal substrate. The titanate ester of TMC-201 hydrolyzes to form titanium hydroxyl groups, which condense with the silanol groups to form a Si-O-Ti bridge structure at the interface between the two crystal forms, creating a stable nano-calcium carbonate slurry with a "grape bunch"-like crystal structure.

[0036] After 15 minutes of heat preservation, the mixture was cooled to room temperature. A silane coupling agent, KH-550, was added at a concentration of 0.3% by weight of the nano-calcium carbonate slurry on a dry basis, and the mixture was stirred at 200 rpm for 10 minutes. Subsequently, a surfactant, sodium stearate, was added at a concentration of 0.5% by weight of the nano-calcium carbonate slurry on a dry basis, and the mixture was stirred at 300 rpm for 10 minutes to obtain a modified nano-calcium carbonate slurry. Modification with KH-550 allows the slurry to chemically react with the organic resin, enhancing the interfacial bonding between the nano-calcium carbonate and the organic matrix (such as topcoat).

[0037] Finished product processing

[0038] The modified nano calcium carbonate slurry is dried and then deagglomerated and crushed by a jet mill to obtain nano calcium carbonate for vehicle paint.

[0039] Example 2

[0040] This embodiment provides a method for preparing nano calcium carbonate for car paint. The following are the specific preparation steps and technical details of the preparation method:

[0041] 1) After limestone is crushed, calcined, digested, aged, and filtered to obtain Ca(OH)2 slurry, sodium polyacrylate accounting for 1% of the dry weight of the Ca(OH)2 slurry is added and thoroughly mixed to obtain a refined slurry;

[0042] 2) 65% of the total volume of the refined slurry was introduced into the carbonization kettle A, the reaction temperature was controlled at 18°C, the stirring rate was 300 rpm, 0.8% of the dry basis weight of the refined slurry was added with sodium polyphosphate, and CO2 gas (volume fraction 35%) was introduced from the bottom at a flow rate of 0.5 L / min for carbonization. When the pH monitoring system measured that the pH of the slurry dropped to 8.5, the aeration was stopped, and the mixture was kept warm at 25°C for 15 minutes. The reaction temperature was controlled at 40°C, 0.5% of the dry basis weight of the slurry was added with γ-aminopropyltriethoxysilane for surface treatment, and the mixture was stirred at 200 rpm for 20 minutes to finally obtain a spherical nano-calcium carbonate slurry A;

[0043] 3) The remaining 35% of the refined slurry was introduced into the carbonization kettle B, the reaction temperature was controlled at 22°C, the stirring rate was 200rpm, and a crystal form control agent B made of sucrose and magnesium chloride in a mass ratio of 3:2, which accounted for 1% of the dry basis weight of the refined slurry, was added, and CO2 gas (volume fraction 40%) was introduced from the bottom at a flow rate of 0.8L / min for carbonization. When the pH monitoring system measured that the pH of the slurry dropped to 9.0, the temperature was raised to 30°C and the ventilation rate was reduced to 0.3L / min. When the pH monitoring system measured that the pH of the slurry dropped to 8.5, the CO2 gas was stopped from being introduced, and the temperature was kept at 30°C for 15min. A titanate coupling agent TMC-201 was added based on 0.35% of the dry basis weight of the slurry for surface treatment. The mixture was stirred at 200rpm for 20min to finally obtain a nano-calcium carbonate slurry B with a chain-like crystal form.

[0044] 4) introducing the prepared nano-calcium carbonate slurry A and nano-calcium carbonate slurry B into a mixing kettle, maintaining the temperature at 45° C. and stirring at 200 rpm for 20 minutes to obtain a composite nano-calcium carbonate slurry. After keeping the temperature for 15 minutes, the mixture was cooled to room temperature, and 0.5% of the dry weight of the nano-calcium carbonate slurry was added with a silane coupling agent KH-550. The mixture was stirred at 200 rpm for 10 minutes. 0.6% of the dry weight of the nano-calcium carbonate slurry was added with a surfactant, sodium stearate, and the mixture was stirred at 300 rpm for 10 minutes to obtain a modified nano-calcium carbonate slurry.

[0045] 5) The modified nano-calcium carbonate slurry is dried and then deagglomerated and crushed by a jet mill to obtain nano-calcium carbonate for car paint.

[0046] Example 3

[0047] This embodiment provides a method for preparing nano calcium carbonate for car paint. The following are the specific preparation steps and technical details of the preparation method:

[0048] 1) After limestone is crushed, calcined, digested, aged, and filtered to obtain Ca(OH)2 slurry, sodium polyacrylate accounting for 1.2% of the dry weight of the Ca(OH)2 slurry is added and thoroughly mixed to obtain a refined slurry;

[0049] 2) 70% of the total volume of the refined slurry was introduced into the carbonization kettle A, the reaction temperature was controlled at 18°C, the stirring rate was 300 rpm, 1% of the dry basis weight of the refined slurry was added with sodium polyphosphate, and CO2 gas (volume fraction 35%) was introduced from the bottom at a flow rate of 0.5 L / min for carbonization. When the pH monitoring system measured that the pH of the slurry dropped to 8.5, the aeration was stopped, and the mixture was kept warm at 25°C for 15 minutes. The reaction temperature was controlled at 40°C, 0.6% of the dry basis weight of the slurry was added with γ-aminopropyltriethoxysilane for surface treatment, and the mixture was stirred at 200 rpm for 20 minutes to finally obtain a spherical nano-calcium carbonate slurry A;

[0050] 3) The remaining 30% of the refined slurry was introduced into the carbonization kettle B, the reaction temperature was controlled at 22°C, the stirring rate was 200 rpm, and a crystal form control agent B made of sucrose and magnesium chloride in a mass ratio of 3:2, which accounted for 1.5% of the dry basis weight of the refined slurry, was added. CO2 gas (volume fraction 40%) was introduced from the bottom at a flow rate of 0.8 L / min for carbonization. When the pH monitoring system measured that the pH of the slurry dropped to 9.0, the temperature was raised to 30°C and the ventilation rate was reduced to 0.3 L / min. When the pH monitoring system measured that the pH of the slurry dropped to 8.5, the CO2 gas was stopped from being introduced, and the temperature was kept at 30°C for 15 minutes. A titanate coupling agent TMC-201 was added based on 0.5% of the dry basis weight of the slurry for surface treatment. The mixture was stirred at 200 rpm for 20 minutes to finally obtain a nano-calcium carbonate slurry B with a chain-like crystal form.

[0051] 4) introducing the prepared nano-calcium carbonate slurry A and nano-calcium carbonate slurry B into a mixing kettle, maintaining the temperature at 45° C. and stirring at 200 rpm for 20 minutes to obtain a composite nano-calcium carbonate slurry. After keeping the temperature for 15 minutes, the mixture was cooled to room temperature, and 0.6% of the dry weight of the nano-calcium carbonate slurry was added with a silane coupling agent KH-550. The mixture was stirred at 200 rpm for 10 minutes. 0.8% of the dry weight of the nano-calcium carbonate slurry was added with a surfactant, sodium stearate, and the mixture was stirred at 300 rpm for 10 minutes to obtain a modified nano-calcium carbonate slurry.

[0052] 5) The modified nano-calcium carbonate slurry is dried and then deagglomerated and crushed by a jet mill to obtain nano-calcium carbonate for car paint.

[0053] The car paint nano-calcium carbonate obtained in Examples 1-3 of the present invention and commercially available nano-calcium carbonate (Guangxi Huana New Materials Co., Ltd.; CCS-H) were used to fill the car primer. The specific preparation method of the car primer includes the following steps:

[0054] 1) Mix 30 parts of epoxy resin, 15 parts of polyurethane resin, and 20 parts of xylene by weight, raise the temperature to 50°C, and stir until completely dissolved to obtain a resin solution;

[0055] 2) Add 5 parts of titanium dioxide, 10 parts of nano calcium carbonate and 3 parts of zinc phosphate to the resin solution and disperse by ultrasonic to ensure that the filler is evenly dispersed;

[0056] 3) Add 0.5 parts of dispersant BYK-163, 0.5 parts of defoamer BYK-052, and 0.3 parts of leveling agent BYK-354 in sequence, stirring continuously. Add the additives every 10 minutes, and then stir at 800 rpm for 30 minutes to obtain the primer.

[0057] The four primer samples were applied to steel plates with a size of 10 cm × 5 cm, and the relevant properties of the steel plates were tested. The test results are shown in Table 1.

[0058] Table 1 Primer performance table

[0059]

[0060] The spherical particles provide good flowability, while the interlaced chain-like particles and "bunch of grapes" clusters disperse stress and improve impact resistance. The synergistic effect of TMC-201, KH-550, and γ-aminopropyltriethoxysilane strengthens the interfacial bonding between the primer and the metal substrate and organic resin, improving adhesion.

[0061] A layer of BSY-98 bright red acrylic polyurethane automotive topcoat was applied to each of the four steel plates coated with primer, and then relevant performance tests were performed. The test results are shown in Table 2.

[0062] Table 2 Topcoat performance

[0063]

[0064] The nano calcium carbonate in Examples 1-3 has enhanced interfacial bonding with the organic resin through surface treatment, providing favorable conditions for bonding between the topcoat and the primer, and ensuring close bonding between the topcoat and the primer.

[0065] 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 method for preparing nano calcium carbonate for car paint, characterized in that: The steps include: 1) After limestone is crushed, calcined, digested, aged, and filtered to obtain Ca(OH)2 slurry, a dispersant accounting for 0.8% to 1.2% of the dry weight of the Ca(OH)2 slurry is added and the mixture is thoroughly mixed to obtain a refined slurry; 2) introducing 60% to 70% of the total volume of the refined slurry into a carbonization kettle A, maintaining the temperature at 18° C., introducing CO2 gas, and adding 0.5% to 1% of a crystal form control agent A based on the dry weight of the refined slurry. When the pH of the slurry measured by the pH monitoring system drops to 8.5, stopping the aeration, maintaining the temperature for 15 minutes, adding 0.3% to 0.6% of γ-aminopropyltriethoxysilane based on the dry weight, and mixing and stirring to obtain a nano-calcium carbonate slurry A having a spherical crystal form; the crystal form control agent A is sodium polyphosphate; 3) introducing 30% to 40% of the total volume of the refined slurry into the carbonization kettle B, maintaining the temperature at 22° C., introducing CO2 gas, and adding 0.5% to 1.5% of the dry weight of the refined slurry. When the pH of the slurry measured by the pH monitoring system drops to 8.5, stopping the aeration, keeping the temperature for 15 minutes, adding 0.3% to 0.5% of the dry weight of a titanate coupling agent, and mixing and stirring to obtain a nano-calcium carbonate slurry B with a chain-like crystal form; the crystal form controlling agent B is prepared by compounding sucrose and magnesium chloride in a mass ratio of 3:2; 4) Nano-calcium carbonate slurry A and nano-calcium carbonate slurry B were introduced into a mixing kettle together, maintained at 60°C, and mixed and stirred for 45 minutes to obtain a nano-calcium carbonate slurry in a composite crystal form. The mixture was kept warm for 15 minutes, and a silane coupling agent and a surfactant were added in sequence, and mixed and stirred to obtain a modified nano-calcium carbonate slurry; The silane coupling agent is KH-550, and the addition amount is 0.3% to 0.6% of the dry basis weight of the nano-calcium carbonate slurry; the surfactant is sodium stearate, and the addition amount is 0.5% to 0.8% of the dry basis weight of the nano-calcium carbonate slurry; 5) Drying and crushing the modified nano-calcium carbonate slurry to obtain nano-calcium carbonate for car paint.

2. The method for preparing nano calcium carbonate for vehicle paint according to claim 1, wherein: The dispersant is sodium polyacrylate.

3. The method for preparing nano calcium carbonate for vehicle paint according to claim 1, wherein: The titanate coupling agent is TMC-201.

4. Nano calcium carbonate for vehicle paint prepared by the method for preparing nano calcium carbonate for vehicle paint according to any one of claims 1 to 3.

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