Nano calcium carbonate for vehicle paint and preparation method of nano calcium carbonate

Abstract

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.The preparation method comprises the steps that a dispersing agent is added into Ca (OH) 2 slurry and fully mixed, and refined slurry is obtained; carbonizing part of the refined slurry to obtain nano calcium carbonate slurry A with a spherical crystal form; carrying out secondary carbonization on the residual refined slurry to obtain nano calcium carbonate slurry B with a chain-shaped crystal form; introducing the nano calcium carbonate slurry A and the nano calcium carbonate slurry B into a mixing kettle together, and carrying out modification treatment to obtain modified nano calcium carbonate slurry; and drying, crushing and sieving the modified nano calcium carbonate slurry to obtain the nano calcium carbonate for the vehicle paint. By optimizing the preparation process of the nano calcium carbonate, the dispersity of the nano calcium carbonate in the vehicle paint and the compatibility of the nano calcium carbonate with a resin matrix and a metal base material are improved, so that the comprehensive properties such as adhesive force and impact resistance of the vehicle paint are remarkably improved, and the problems of surface paint stripping and primer falling are effectively solved.

Description

Technical Field

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

[0002] As the base coat in the automotive coating system, the automotive primer directly contacts the metal substrate and provides a good foundation for the subsequent topcoat painting. Due to its small particle size, large specific surface area, high surface activity and other characteristics, nano calcium carbonate exhibits excellent functional effects in car paint, such as improving the hardness, wear resistance, impact resistance, etc. of the coating.

[0003] However, the ultra-fine particle size and extremely high surface energy of nano calcium carbonate make it prone to spontaneous agglomeration during the processing, and it is difficult to be well compatible with the resin matrix and the metal substrate. This agglomeration phenomenon not only reduces the dispersibility of nano calcium carbonate in car paint, but also causes stress concentration points inside the coating, making the car paint prone to topcoat peeling or even primer peeling when impacted, seriously affecting the durability and aesthetics of the automotive coating. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, on the one hand, the present invention provides a preparation method of nano calcium carbonate for car paint, aiming to optimize the preparation process of nano calcium carbonate, improve its dispersibility in car paint and its compatibility with the resin matrix and the metal substrate, so as to significantly enhance the comprehensive properties such as the adhesion and impact resistance of the car paint, and effectively solve the problems of topcoat peeling and primer peeling.

[0005] To achieve the above object, a preparation method of nano calcium carbonate for car paint includes the following steps: 1) Limestone is crushed, calcined, digested, aged, and filtered to obtain a Ca(OH)2 slurry. A dispersant accounting for 0.8% - 1.2% of the dry basis mass of the Ca(OH)2 slurry is added, and fully mixed to obtain a refined slurry; 2) 60% - 70% of the total volume of the refined slurry is introduced into carbonization kettle A, the temperature is maintained at 18°C, CO2 gas is introduced, and a crystal form control agent A accounting for 0.5% - 1% of the dry basis mass of the added refined slurry is added. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas supply is stopped, and it is kept warm for 15 minutes. γ-aminopropyltriethoxysilane accounting for 0.3% - 0.6% of the dry basis mass is added, and mixed and stirred to obtain nano calcium carbonate slurry A with a spherical crystal form; 3) Introduce refined slurry with a total volume of 30% - 40% into carbonization kettle B, maintain the temperature at 22°C, introduce CO2 gas, add crystal form control agent B accounting for 0.5% - 1.5% of the dry basis mass of the added refined slurry. When the pH of the slurry measured by the pH monitoring system drops to 8.5, stop ventilation, keep warm for 15 min, add titanate coupling agent accounting for 0.3% - 0.5% of the dry basis mass, mix and stir to obtain nano calcium carbonate slurry B with a chain-like crystal form; 4) Introduce nano calcium carbonate slurry A and nano calcium carbonate slurry B into the mixing kettle together, maintain the temperature at 60°C, mix and stir for 45 min to obtain nano calcium carbonate slurry with a composite crystal form, keep warm for 15 min, add silane coupling agent and surfactant in sequence, mix and stir to obtain modified nano calcium carbonate slurry; 5) Dry and crush the modified nano calcium carbonate slurry to obtain nano calcium carbonate for car paint.

[0006] Preferably, the dispersant is sodium polyacrylate.

[0007] Preferably, the crystal form control agent A is sodium polyphosphate.

[0008] Preferably, the crystal form control agent B is compounded by sucrose and magnesium chloride according to a mass ratio of 3:2.

[0009] Preferably, the titanate coupling agent is TMC - 201.

[0010] Preferably, the silane coupling agent is KH - 550, and the addition amount is 0.3% - 0.6% of the dry basis mass of the nano calcium carbonate slurry.

[0011] Preferably, the surfactant is sodium stearate, and the addition amount is 0.5% - 0.8% of the dry basis mass of the nano calcium carbonate slurry.

[0012] On the other hand, the present invention also provides a nano calcium carbonate for car paint, which is prepared by the above preparation method.

[0013] After adopting the above technical solution, the beneficial effects of the present invention are: The present invention aims to optimize the preparation process of nano calcium carbonate, improve its dispersibility in car paint and compatibility with resin matrix and metal substrate, thereby significantly enhancing the comprehensive properties such as adhesion and impact resistance of car paint, and effectively solving the problems of topcoat peeling and primer falling off. Specific embodiments

[0014] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be 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 some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by showing examples of the present invention.

[0015] Example 1 This embodiment provides a preparation method of nano calcium carbonate for car paint. The following are the specific preparation steps and technical details of this preparation method.

[0016] Preparation of refined slurry The limestone is crushed, calcined, digested, aged, and filtered to obtain a Ca(OH)2 slurry. Sodium polyacrylate accounting for 0.8% of the dry basis mass of the Ca(OH)2 slurry is added and fully mixed to obtain a refined slurry.

[0017] 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. In the carbonization stage, the carbonization reaction can proceed more evenly, which helps to generate calcium carbonate products with small particle size and uniform distribution.

[0018] Preparation of spherical nano calcium carbonate 60% of the total volume of the refined slurry is introduced into carbonization kettle A. The reaction temperature is controlled at 18 °C, the stirring rate is 300 rpm, sodium polyphosphate accounting for 0.5% of the dry basis mass of the refined slurry is added, and CO2 gas (volume fraction 35%) is introduced at a flow rate of 0.5 L / min from the bottom for carbonization.

[0019] When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas supply is stopped and kept at 25 °C for 15 min to stabilize the crystal form of the product and reduce lattice defects.

[0020] After carbonization is completed, the reaction temperature is controlled at 40 °C, and γ-aminopropyltriethoxysilane is added for surface treatment based on 0.3% of the dry basis mass of the slurry, and stirred at a rate of 200 rpm for 20 min to finally obtain nano calcium carbonate slurry A with a spherical crystal form.

[0021] Preparation of chain-like nano calcium carbonate Introduce the remaining 40% of the refined slurry into carbonization kettle B. Control the reaction temperature at 22°C, the stirring rate at 200 rpm. Add crystal form control agent B which is made of sucrose and magnesium chloride in a mass ratio of 3:2 and accounts for 0.5% of the dry basis mass of the refined slurry. Introduce CO2 gas (volume fraction 40%) at a flow rate of 0.8 L / min from the bottom for carbonization. When the pH of the slurry measured by the pH monitoring system drops to 9.0, raise the temperature to 30°C and reduce the ventilation rate to 0.3 L / min.

[0022] When the pH of the slurry measured by the pH monitoring system drops to 8.5, stop introducing CO2 gas, keep it at 30°C for 15 min to stabilize the crystal form of the product and reduce lattice defects.

[0023] After carbonization is completed, add titanate coupling agent TMC-201 based on 0.3% of the dry basis mass of the slurry for surface treatment, stir at a rate of 200 rpm for 20 min, and finally obtain nano-calcium carbonate slurry B with a chain-like crystal form.

[0024] Mixed modification Introduce the prepared nano-calcium carbonate slurry A and nano-calcium carbonate slurry B into the mixing kettle together, maintain the temperature at 45°C, stir at a rate of 200 rpm for 20 min to obtain the nano-calcium carbonate slurry of the composite. During mixing, the ethoxy groups of γ-aminopropyltriethoxysilane hydrolyze to form silanol groups in an aqueous environment, which can form chemical bonds with the hydroxyl groups on the surface of metal oxides (such as Al2O3 on the vehicle body surface), thereby improving the adhesion between the primer and the metal substrate. The titanate of TMC-201 hydrolyzes to form titanium hydroxyl groups, which condense with the silanol groups to form a Si-O-Ti bridging structure at the interface of the two crystal forms, constructing a stable nano-calcium carbonate slurry with a "grape cluster" - shaped composite crystal form.

[0025] After keeping warm for 15 min, cool it to room temperature, add silane coupling agent KH-550 based on 0.3% of the dry basis mass of the nano-calcium carbonate slurry, and stir at a rate of 200 rpm for 10 min. Subsequently, add sodium stearate, a surfactant, based on 0.5% of the dry basis mass of the nano-calcium carbonate slurry, and stir at a rate of 300 rpm for 10 min to obtain the modified nano-calcium carbonate slurry. After being modified by KH-550, it can undergo a chemical reaction with the organic resin to enhance the interfacial bonding between the nano-calcium carbonate and the organic matrix (such as the topcoat).

[0026] Finished product treatment Dry the modified nano-calcium carbonate slurry, and then depolymerize and pulverize it with a jet mill to obtain nano-calcium carbonate for vehicle paint.

[0027] Example 2 This example provides a preparation method of nano-calcium carbonate for vehicle paint. The following are the specific preparation steps and technical details of this preparation method: 1) Limestone is crushed, calcined, digested, aged, and filtered to obtain a Ca(OH)2 slurry. Sodium polyacrylate accounting for 1% of the dry basis mass of the Ca(OH)2 slurry is added and thoroughly mixed to obtain a refined slurry; 2) 65% of the total volume of the refined slurry is introduced into carbonization kettle A. The reaction temperature is controlled at 18 °C, the stirring rate is 300 rpm, sodium polyphosphate accounting for 0.8% of the dry basis mass of the refined slurry is added, and CO2 gas (volume fraction 35%) is introduced from the bottom at a flow rate of 0.5 L / min for carbonization. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas supply is stopped, and it is kept warm at 25 °C for 15 min. The reaction temperature is controlled at 40 °C, and γ-aminopropyltriethoxysilane is added for surface treatment based on 0.5% of the dry basis mass of the slurry, and it is stirred at a rate of 200 rpm for 20 min to finally obtain nano-calcium carbonate slurry A with a spherical crystal form; 3) The remaining 35% of the refined slurry is introduced into carbonization kettle B. The reaction temperature is controlled at 22 °C, the stirring rate is 200 rpm, crystal form control agent B made of sucrose and magnesium chloride in a mass ratio of 3:2 and accounting for 1% of the dry basis mass of the refined slurry is added, and CO2 gas (volume fraction 40%) is introduced from the bottom at a flow rate of 0.8 L / min for carbonization. When the pH of the slurry measured by the pH monitoring system drops to 9.0, the temperature is raised to 30 °C and the gas supply rate is reduced to 0.3 L / min. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the supply of CO2 gas is stopped, and it is kept warm at 30 °C for 15 min. A titanate coupling agent TMC-201 is added for surface treatment based on 0.35% of the dry basis mass of the slurry, and it is stirred at a rate of 200 rpm for 20 min to finally obtain nano-calcium carbonate slurry B with a chain-like crystal form; 4) The prepared nano-calcium carbonate slurry A and nano-calcium carbonate slurry B are introduced into a mixing kettle together. The temperature is maintained at 45 °C, and it is stirred at a rate of 200 rpm for 20 min to obtain a composite nano-calcium carbonate slurry. After keeping warm for 15 min, it is cooled to room temperature. Silane coupling agent KH-550 accounting for 0.5% of the dry basis mass of the nano-calcium carbonate slurry is added, and it is stirred at a rate of 200 rpm for 10 min. Sodium stearate, a surfactant accounting for 0.6% of the dry basis mass of the nano-calcium carbonate slurry, is added, and it is stirred at a rate of 300 rpm for 10 min to obtain a modified nano-calcium carbonate slurry; 5) The modified nano-calcium carbonate slurry is dried and then depolymerized and pulverized by a jet mill to obtain nano-calcium carbonate for car paint.

[0028] Example 3 This example provides a preparation method of nano-calcium carbonate for car paint. The following are the specific preparation steps and technical details of this preparation method: 1) Limestone is crushed, calcined, digested, aged, and filtered to obtain a Ca(OH)2 slurry. Sodium polyacrylate accounting for 1.2% of the dry basis mass of the Ca(OH)2 slurry is added and thoroughly mixed to obtain a refined slurry; 2) 70% of the total volume of the refined slurry is introduced into carbonization kettle A. The reaction temperature is controlled at 18°C, the stirring rate is 300 rpm, sodium polyphosphate accounting for 1% of the dry basis mass of the refined slurry is added, and CO2 gas (volume fraction 35%) is introduced from the bottom at a flow rate of 0.5 L / min for carbonization. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas supply is stopped, and it is kept warm at 25°C for 15 min. The reaction temperature is controlled at 40°C, and γ-aminopropyltriethoxysilane is added for surface treatment based on 0.6% of the dry basis mass of the slurry, and it is stirred at a rate of 200 rpm for 20 min to finally obtain nano-calcium carbonate slurry A with a spherical crystal form; 3) The remaining 30% of the refined slurry is introduced into carbonization kettle B. The reaction temperature is controlled at 22°C, the stirring rate is 200 rpm, a crystal form control agent B made of sucrose and magnesium chloride in a mass ratio of 3:2 and accounting for 1.5% of the dry basis mass of the refined slurry is added, and CO2 gas (volume fraction 40%) is introduced from the bottom at a flow rate of 0.8 L / min for carbonization. When the pH of the slurry measured by the pH monitoring system drops to 9.0, the temperature is raised to 30°C and the gas supply rate is reduced to 0.3 L / min. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the supply of CO2 gas is stopped, and it is kept warm at 30°C for 15 min. A titanate coupling agent TMC-201 is added for surface treatment based on 0.5% of the dry basis mass of the slurry, and it is stirred at a rate of 200 rpm for 20 min to finally obtain nano-calcium carbonate slurry B with a chain-like crystal form; 4) The prepared nano-calcium carbonate slurry A and nano-calcium carbonate slurry B are jointly introduced into a mixing kettle, the temperature is maintained at 45°C, and it is stirred at a rate of 200 rpm for 20 min to obtain a composite nano-calcium carbonate slurry. After being kept warm for 15 min, it is cooled to room temperature. Silane coupling agent KH-550 accounting for 0.6% of the dry basis mass of the nano-calcium carbonate slurry is added, and it is stirred at a rate of 200 rpm for 10 min. Sodium stearate, a surfactant accounting for 0.8% of the dry basis mass of the nano-calcium carbonate slurry, is added, and it is stirred at a rate of 300 rpm for 10 min to obtain a modified nano-calcium carbonate slurry; 5) The modified nano-calcium carbonate slurry is dried and then depolymerized and pulverized by a jet mill to obtain nano-calcium carbonate for automotive paint.

[0029] The nano-calcium carbonate for automotive paint obtained in Examples 1-3 of the present invention and commercially available nano-calcium carbonate (Guangxi Warner New Materials Co., Ltd.; CCS-H) are filled into automotive primer. The specific preparation method of the automotive primer includes the following steps: 1) By mass parts, 30 parts of epoxy resin, 15 parts of polyurethane resin and 20 parts of xylene are mixed, and the temperature is raised to 50 °C and stirred until completely dissolved to obtain a resin solution; 2) 5 parts of titanium dioxide, 10 parts of nano calcium carbonate and 3 parts of zinc phosphate are added to the resin solution, and ultrasonic dispersion is carried out to ensure uniform dispersion of the fillers; 3) 0.5 part of dispersant BYK-163, 0.5 part of defoamer BYK-052 and 0.3 part of leveling agent BYK-354 are added in sequence, and continuous stirring is carried out. The interval between the addition of additives is 10 minutes, and then stirring is carried out at a rate of 800 rpm for 30 minutes to obtain a primer.

[0030] The above four primer specimens are respectively applied to steel plates with a specification of 10 cm × 5 cm, and relevant performances of the above steel plates are detected. The detection results are shown in Table 1.

[0031] Table 1 Primer performance table

[0032] Spherical particles provide good fluidity. Interlaced chain-like particles and "grape cluster" cluster complexes can disperse stress and improve impact resistance. The synergistic effect of TMC-201, KH-550 and γ-aminopropyltriethoxysilane can enhance the interfacial bonding between the primer and the metal substrate and the organic resin, and improve the adhesion.

[0033] A layer of BSY-98 bright red acrylic polyurethane automotive topcoat is respectively applied to the above four steel plates coated with primer, and then relevant performances are detected. The detection results are shown in Table 2.

[0034] Table 2 Topcoat performance table

[0035] In Examples 1-3, the interfacial bonding force between nano calcium carbonate and organic resin is enhanced through surface treatment, which provides favorable conditions for the bonding between the topcoat and the primer, and ensures the tight bonding between the topcoat and the primer.

[0036] In accordance with the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor limit the invention to only the specific embodiments. Obviously, according to the above description, many modifications and variations can be made. These embodiments are selected and specifically described in this specification in order to better explain the principle and practical application of the present invention, so that those skilled in the art can make good use of the present invention and its modified use based on the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of nano calcium carbonate for car paint, characterized in that, It includes the following steps: 1) Limestone is crushed, calcined, digested, aged, and filtered to obtain a Ca(OH)2 slurry. A dispersant accounting for 0.8% - 1.2% of the dry basis mass of the Ca(OH)2 slurry is added and fully mixed to obtain a refined slurry; 2) 60% - 70% of the total volume of the refined slurry is introduced into carbonization kettle A. The temperature is maintained at 18°C, and CO2 gas is introduced. A crystal form control agent A accounting for 0.5% - 1% of the dry basis mass of the added refined slurry is added. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas introduction is stopped, and it is kept warm for 15 minutes. γ-aminopropyltriethoxysilane accounting for 0.3% - 0.6% of the dry basis mass is added, and it is mixed and stirred to obtain nano-calcium carbonate slurry A with a spherical crystal form; 3) 30% - 40% of the total volume of the refined slurry is introduced into carbonization kettle B. The temperature is maintained at 22°C, and CO2 gas is introduced. A crystal form control agent B accounting for 0.5% - 1.5% of the dry basis mass of the added refined slurry is added. When the pH of the slurry measured by the pH monitoring system drops to 8.5, the gas introduction is stopped, and it is kept warm for 15 minutes. A titanate coupling agent accounting for 0.3% - 0.5% of the dry basis mass is added, and it is mixed and stirred to obtain nano-calcium carbonate slurry B with a chain-like crystal form; 4) Nano-calcium carbonate slurry A and nano-calcium carbonate slurry B are introduced into a mixing kettle together. The temperature is maintained at 60°C, and it is mixed and stirred for 45 minutes to obtain nano-calcium carbonate slurry with a composite crystal form. It is kept warm for 15 minutes, and a silane coupling agent and a surfactant are added in sequence and mixed and stirred to obtain modified nano-calcium carbonate slurry; 5) The modified nano-calcium carbonate slurry is dried and pulverized to obtain nano-calcium carbonate for car paint.

2. The preparation method of nano calcium carbonate for automotive paint according to claim 1, characterized in that: The dispersant is sodium polyacrylate.

3. The preparation method of nano calcium carbonate for car paint according to claim 1, characterized in that: The crystal form control agent A is sodium polyphosphate.

4. The preparation method of nano calcium carbonate for car paint according to claim 1, characterized in that: The crystal form control agent B is compounded by sucrose and magnesium chloride according to a mass ratio of 3:

2.

5. The preparation method of nano calcium carbonate for car paint according to claim 1, characterized in that: The titanate coupling agent is TMC-201.

6. The preparation method of nano-calcium carbonate for automotive paint according to claim 1, characterized in that: The silane coupling agent is KH-550, and the addition amount is 0.3% - 0.6% of the dry basis mass of the nano-calcium carbonate slurry.

7. The preparation method of nano calcium carbonate for car paint according to claim 1, characterized in that: The surfactant is sodium stearate, and the addition amount is 0.5% - 0.8% of the dry basis mass of the nano-calcium carbonate slurry.

8. Nano-calcium carbonate for car paint prepared by the preparation method of nano-calcium carbonate for car paint according to any one of claims 1 - 7.

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