Modified calcium carbonate for use in the manufacture of toothpaste abrasives and process for the preparation thereof

Abstract

The present application provides modified calcium carbonate for preparing toothpaste abrasive and a preparation method thereof, wherein the modified calcium carbonate is a core-shell structure, taking calcium carbonate particles as the core, and the surface of the core is coated with a silica layer; the silica layer is formed by sequentially reacting acidic silica sol and alkaline silica sol on the surface of the calcium carbonate particles. The method comprises the following steps: S1, raw material pretreatment; S2, preparation of calcium carbonate suspension; S3, acidic silica sol pretreatment; S4, alkaline silica sol forms a silica layer coating; S5, solid-liquid separation and drying, to obtain modified calcium carbonate. Through the process of acidic silica sol pretreatment and alkaline silica sol step-by-step coating, the present application realizes uniform, dense and thickness-controllable silica layer coating on the surface of calcium carbonate particles, improves the dispersibility and fluidity of calcium carbonate, reduces moisture absorption and agglomeration, thereby avoiding blockage during discharging, and optimizing the cleaning effect and paste stability of the modified calcium carbonate as toothpaste abrasive.

Description

Technical Field

[0001] This invention belongs to the field of raw material technology for daily chemical products, specifically relating to modified calcium carbonate for preparing toothpaste abrasives and its preparation method. Background Technology

[0002] Calcium carbonate is one of the most widely used ingredients in toothpaste abrasives. It is inexpensive, readily available, non-toxic, and odorless, and can account for 20-50% of toothpaste formulations. The main function of abrasives is to remove plaque, pigment deposits, and food debris from the tooth surface through physical friction, while simultaneously polishing the tooth surface. Natural calcium carbonate, also known as heavy calcium carbonate, is usually obtained from calcite ore through washing, beneficiation, and crushing; its quality directly affects oral health. An ideal toothpaste abrasive should possess safe physicochemical properties, including being non-toxic, odorless, white in color, with uniform and moderate particle size, a hardness between that of tooth enamel and tartar, and good chemical stability, not easily reacting adversely with other components in toothpaste such as fluoride and foaming agents.

[0003] However, natural calcium carbonate has several drawbacks in practical applications. First, its abrasive value is usually high, which can easily lead to excessive wear of tooth enamel and may damage dentin with long-term use. Second, natural calcium carbonate usually has a prismatic crystal structure, and its sharp edges can easily scratch tooth enamel during brushing. More importantly, calcium carbonate is chemically unstable and easily produces carbon dioxide gas when it comes into contact with acidic substances, causing toothpaste to swell; at the same time, the calcium ions dissolved from calcium carbonate can combine with fluoride ions added to the toothpaste to form insoluble calcium fluoride, thus consuming free fluoride ions and severely weakening the anti-caries effect of fluoride toothpaste.

[0004] Furthermore, in the actual production process of toothpaste, natural calcium carbonate raw materials have a certain degree of hygroscopicity. During storage and transportation, especially in the feeding stage, they easily absorb moisture from the air, leading to moisture absorption and agglomeration. This phenomenon can cause problems such as bridging and blockage in the feeding equipment, seriously affecting the continuity and efficiency of the production line, and may lead to inconsistent quality between batches of the final product.

[0005] In existing technologies, several improvements have been made to address the shortcomings of calcium carbonate abrasives. For example, one approach proposes completely replacing calcium carbonate with silica as the abrasive. Silica possesses stable chemical properties, excellent cleaning effects, and good compatibility with fluoride. However, silica is significantly more expensive than calcium carbonate, which would undoubtedly increase the production cost of toothpaste. Another approach suggests surface modification of calcium carbonate, such as coating it with silica to improve its acid resistance and compatibility with fluoride. However, these existing technologies primarily focus on improving the chemical properties of calcium carbonate during toothpaste use, such as preventing reactions with fluoride or reducing enamel wear. Their motivation and evaluation of effectiveness are concentrated on enhancing oral care performance.

[0006] The existing technology generally tends to solve the problem of feeding calcium carbonate raw materials into toothpaste by improving the hardware of the feeding equipment, such as using physical means such as mechanical vibrators, fluidization devices or changing the design of the hopper. However, these methods do not change the characteristics of the calcium carbonate raw materials themselves.

[0007] From a technical perspective, those skilled in the art typically address the issue of raw material agglomeration by optimizing the equipment—a conventional approach using physical solutions. However, fundamentally altering the surface properties of calcium carbonate particles through chemical modification to enhance their flowability and anti-agglomeration ability is not a standard choice in toothpaste abrasive preparation. While existing technologies involve silica-coated calcium carbonate processes, their objectives are primarily focused on resolving chemical issues such as acid resistance or fluoride compatibility. They do not reveal or imply that this coating structure can significantly improve the physical flow properties of the raw material, nor do they connect it to solving the feeding difficulties in toothpaste production. Therefore, there is a need to design modified calcium carbonate for preparing toothpaste abrasives and its preparation method. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, a modified calcium carbonate for preparing toothpaste abrasives and a method for preparing the same are provided.

[0009] To achieve the above objectives, the present invention provides the following technical solution: Modified calcium carbonate used to prepare toothpaste abrasives has a core-shell structure, with calcium carbonate particles as the core and a silica layer on its surface. The silica layer is formed by the sequential reaction of acidic silica sol and alkaline silica sol on the surface of calcium carbonate particles.

[0010] The thickness of the silicon dioxide layer is 25 to 55 nanometers.

[0011] The modified calcium carbonate has an angle of repose of no more than 35 degrees and a particle size D50 of 8 to 15 micrometers.

[0012] A method for preparing modified calcium carbonate for use in toothpaste abrasives, the method comprising the following steps: S1. Raw material pretreatment: Wash, crush, and grind natural calcium carbonate ore to obtain calcium carbonate powder; S2. Suspension preparation: Disperse the calcium carbonate powder obtained in step S1 into process water to form a calcium carbonate suspension under stirring conditions. S3, Acidic environment pretreatment: Add acidic silica sol to the calcium carbonate suspension in step S2 and stir to react; S4. Silica Coating: Add alkaline silica sol to the reaction system of step S3, adjust the pH of the system to alkaline, and continue the reaction to form a gel, so that silica coats the surface of calcium carbonate. S5. Solid-liquid separation and drying: The gel obtained in step S4 is separated by pressure filtration. The resulting filter cake is dried and crushed to obtain modified calcium carbonate.

[0013] In step S1, the grinding is carried out using a ring roller mill, and the grinding parameters are controlled so that the particle size D50 of the resulting calcium carbonate powder is 5 to 12 micrometers.

[0014] In step S2, the solid-liquid mass-volume ratio of the calcium carbonate suspension is 1 gram: 8 to 22 milliliters, the stirring temperature is 75 to 95°C, and the stirring speed is 300 to 500 rpm.

[0015] In step S3, the amount of acidic silica sol added accounts for 0.5% to 4.0% of the total mass of the calcium carbonate suspension, the reaction temperature is 75 to 95°C, and the reaction time is 15 to 35 minutes.

[0016] In step S4, the amount of alkaline silica sol added accounts for 2.0% to 4.5% of the total mass of the calcium carbonate suspension; the pH value of the system is adjusted to 7.5 to 9.0.

[0017] The preparation process of the alkaline silica sol includes the following steps: adding 500 to 750 parts by weight of process water to a reaction vessel, heating to 60 to 80°C, first adding 8 to 18 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 0.8 to 1.8 hours; then heating to 70 to 90°C, adding 25 to 45 parts by weight of silicon powder and 0.8 to 3.5 parts by weight of sodium hydroxide, and stirring for 1.2 to 2.8 hours; finally heating to 85 to 98°C, adding 45 to 80 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 2.0 to 4.0 hours to obtain the alkaline silica sol.

[0018] In step S5, the pressure of the filter press is 0.2 to 0.6 MPa and the temperature is 15 to 35°C; the drying temperature is 80 to 120°C and the time is 1 to 5 hours.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: Silica can form a uniform "isolating film" on the surface of calcium carbonate particles. On the one hand, it reduces the friction and adhesion between particles, making the powder easier to slide; on the other hand, it can fill the gaps between calcium carbonate particles and destroy the "arch structure" formed by the material due to moisture absorption, adsorption, static electricity, etc., thereby preventing blockage during feeding. The specific beneficial effects are as follows: 1. This invention improves the flowability and anti-caking properties of modified calcium carbonate powder. Natural calcium carbonate particles have a certain degree of polarity and hygroscopicity, easily adsorbing moisture from the air, leading to liquid bridging forces between particles, thus causing agglomeration and difficulties in feeding. In this invention, the silica coating effectively alters the surface properties of the particles; its lower surface energy and the resulting steric hindrance weaken the cohesive forces between particles and the moisture adsorption effect. This allows the powder to exhibit better dispersibility and flowability during storage and transportation, especially in the feeding stage of toothpaste production, effectively alleviating bridging and clogging problems, and ensuring production continuity and efficiency.

[0020] 2. The silica coating layer of this invention acts as a physical barrier, increasing the stability of calcium carbonate. It reduces the direct contact between the calcium carbonate core and other sensitive components in the toothpaste, thereby lowering the likelihood of adverse chemical reactions. This barrier effect helps maintain the stability of the toothpaste system. For example, the dense silica layer, to a certain extent, prevents direct contact between the calcium carbonate core and acidic components and active ingredients such as fluoride. This not only helps reduce the occurrence of toothpaste swelling but also provides favorable conditions for the stable presence of active ingredients such as fluoride ions, allowing their anti-caries effect to be maintained for a longer period.

[0021] 3. This invention effectively improves the surface structure and overall frictional properties of calcium carbonate as an abrasive by coating a natural calcium carbonate core with a silica layer. Because silica itself has suitable hardness and a smooth spherical structure, when coated on the surface of prismatic calcium carbonate particles, it can buffer and disperse the frictional force acting on the tooth surface during brushing to a certain extent. This structure makes the abrasive more prone to generating rolling friction during cleaning, rather than simple scraping, thus helping to reduce the potential risk of enamel abrasion. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the specific embodiments of this application, the sources of various main raw materials are briefly described as follows: Natural calcium carbonate ore: Guangxi Hezhou Kelong Powder Co., Ltd. Acidic silica sol: Guangdong Huihe Silicon Products Co., Ltd. Silicon powder: Wuhan Jiyesheng Chemical Co., Ltd. Sodium hydroxide: Hubei Xingyinhe Chemical Co., Ltd. The technical solution of this application is as follows: Modified calcium carbonate used to prepare toothpaste abrasives has a core-shell structure, with calcium carbonate particles as the core and a silica layer on its surface. The silica layer is formed by the sequential reaction of acidic silica sol and alkaline silica sol on the surface of calcium carbonate particles.

[0024] The thickness of the silicon dioxide layer is 25 to 55 nanometers.

[0025] The modified calcium carbonate has an angle of repose of no more than 35 degrees and a particle size D50 of 8 to 15 micrometers.

[0026] A method for preparing modified calcium carbonate for use in toothpaste abrasives, the method comprising the following steps: S1. Raw material pretreatment: Wash, crush, and grind natural calcium carbonate ore to obtain calcium carbonate powder; S2. Suspension preparation: Disperse the calcium carbonate powder obtained in step S1 into process water to form a calcium carbonate suspension under stirring conditions. S3, Acidic environment pretreatment: Add acidic silica sol to the calcium carbonate suspension in step S2 and stir to react; S4. Silica Coating: Add alkaline silica sol to the reaction system of step S3, adjust the pH of the system to alkaline, and continue the reaction to form a gel, so that silica coats the surface of calcium carbonate. S5. Solid-liquid separation and drying: The gel obtained in step S4 is separated by pressure filtration. The resulting filter cake is dried and crushed to obtain modified calcium carbonate.

[0027] In step S1, the grinding is carried out using a ring roller mill, and the grinding parameters are controlled so that the particle size D50 of the resulting calcium carbonate powder is 5 to 12 micrometers.

[0028] In step S2, the solid-liquid mass-volume ratio of the calcium carbonate suspension is 1 gram: 8 to 22 milliliters, the stirring temperature is 75 to 95°C, and the stirring speed is 300 to 500 rpm.

[0029] In step S3, the amount of acidic silica sol added accounts for 0.5% to 4.0% of the total mass of the calcium carbonate suspension, the reaction temperature is 75 to 95°C, and the reaction time is 15 to 35 minutes.

[0030] In step S4, the amount of alkaline silica sol added accounts for 2.0% to 4.5% of the total mass of the calcium carbonate suspension; the pH value of the system is adjusted to 7.5 to 9.0.

[0031] The preparation process of the alkaline silica sol includes the following steps: adding 500 to 750 parts by weight of process water to a reaction vessel, heating to 60 to 80°C, first adding 8 to 18 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 0.8 to 1.8 hours; then heating to 70 to 90°C, adding 25 to 45 parts by weight of silicon powder and 0.8 to 3.5 parts by weight of sodium hydroxide, and stirring for 1.2 to 2.8 hours; finally heating to 85 to 98°C, adding 45 to 80 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 2.0 to 4.0 hours to obtain the alkaline silica sol.

[0032] In step S5, the pressure of the filter press is 0.2 to 0.6 MPa and the temperature is 15 to 35°C; the drying temperature is 80 to 120°C and the time is 1 to 5 hours.

[0033] This invention achieves a uniform, dense, and controllable silica layer coating on the surface of calcium carbonate particles through a stepwise process of acidic silica sol pretreatment and alkaline silica sol coating. This improves the dispersibility and flowability of modified calcium carbonate, reduces moisture absorption and agglomeration, thereby avoiding blockage during feeding and optimizing its cleaning effect and paste stability as an abrasive in toothpaste.

[0034] The present invention will be described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited to these examples. Unless otherwise specified, the chemical reagents and raw materials used in the following examples and comparative examples are all conventional commercially available products.

[0035] Example 1 Natural calcium carbonate ore was washed, crushed, and then ground using a ring roller mill. The grinding parameters were controlled to achieve a particle size (D50) of 12 micrometers for the resulting calcium carbonate powder. 1000 grams of this calcium carbonate powder was dispersed in 22000 ml of process water and stirred at 95°C at 500 rpm to form a calcium carbonate suspension. 4.0% (by mass) of acidic silica sol was added to this suspension, and the mixture was stirred at 95°C for 35 minutes. Subsequently, 4.5% (by mass) of alkaline silica sol was added to the reaction system to adjust the pH to 9.0, and the reaction continued to form a gel. The preparation process of alkaline silica sol is as follows: 750 parts by mass of process water are added to a reaction vessel, the temperature is raised to 80°C, 18 parts by mass of silica powder and 4.5 parts by mass of sodium hydroxide are added first, and the mixture is stirred and reacted for 1.8 hours; then the temperature is raised to 90°C, 45 parts by mass of silica powder and 3.5 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 2.8 hours; finally, the temperature is raised to 98°C, 80 parts by mass of silica powder and 4.5 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 4.0 hours. The resulting gel is separated by pressure filtration at 0.6 MPa and 35°C. The resulting filter cake is dried at 120°C for 5 hours and then crushed to obtain the modified calcium carbonate product.

[0036] Example 2 In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: Natural calcium carbonate ore was washed, crushed, and then ground using a ring roller mill. The grinding parameters were controlled to achieve a particle size (D50) of 5 micrometers for the resulting calcium carbonate powder. 1000 grams of this calcium carbonate powder was dispersed in 8000 ml of process water and stirred at 75°C at 300 rpm to form a calcium carbonate suspension. 0.5% (by mass) of acidic silica sol was added to this suspension, and the mixture was stirred at 75°C for 15 minutes. Subsequently, 2.0% (by mass) of alkaline silica sol was added to the reaction system, adjusting the pH to 7.5, and the reaction continued to form a gel. The preparation process of alkaline silica sol is as follows: 500 parts by mass of process water are added to a reaction vessel, and the temperature is raised to 60°C. First, 8 parts by mass of silica powder and 1.5 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 0.8 hours. Then, the temperature is raised to 70°C, and 25 parts by mass of silica powder and 0.8 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 1.2 hours. Finally, the temperature is raised to 85°C, and 45 parts by mass of silica powder and 1.5 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 2.0 hours. The resulting gel is separated by pressure filtration at 0.2 MPa and 15°C. The resulting filter cake is dried at 80°C for 1 hour and then crushed to obtain the modified calcium carbonate product.

[0037] Example 3 In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows: Natural calcium carbonate ore was washed, crushed, and then ground using a ring roller mill. The grinding parameters were controlled to achieve a particle size (D50) of 8.5 micrometers for the resulting calcium carbonate powder. 1000 grams of this calcium carbonate powder was dispersed in 15000 ml of process water and stirred at 85°C at 400 rpm to form a calcium carbonate suspension. 2.25% (by mass) of acidic silica sol was added to this suspension, and the mixture was stirred at 85°C for 25 minutes. Subsequently, 3.25% (by mass) of alkaline silica sol was added to the reaction system to adjust the pH to 8.25, and the reaction continued to form a gel. The preparation process of alkaline silica sol is as follows: 625 parts by mass of process water are added to a reaction vessel, the temperature is raised to 70°C, 13 parts by mass of silica powder and 3.0 parts by mass of sodium hydroxide are added first, and the mixture is stirred and reacted for 1.3 hours; then the temperature is raised to 80°C, 35 parts by mass of silica powder and 2.15 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 2.0 hours; finally, the temperature is raised to 91.5°C, 62.5 parts by mass of silica powder and 3.0 parts by mass of sodium hydroxide are added, and the mixture is stirred and reacted for 3.0 hours. The resulting gel is separated by pressure filtration at 0.4 MPa and 25°C. The resulting filter cake is dried at 100°C for 3 hours and then crushed to obtain the modified calcium carbonate product.

[0038] Comparative Example 1 In this comparative example, the similarities with Example 1 will not be repeated, and the differences are as follows: Without performing an acidic silica sol pretreatment step, alkaline silica sol is directly added to the calcium carbonate suspension after preparation for the coating reaction.

[0039] Comparative Example 2 In this comparative example, the similarities with Example 2 will not be repeated, and the differences are as follows: The alkaline silica sol coating step is not performed; only acidic silica sol pretreatment is performed, and no subsequent alkaline silica sol coating is performed.

[0040] Comparative Example 3 In this comparative example, the similarities with Example 3 will not be repeated, and the differences are as follows: The silica coating is 15 nanometers thick.

[0041] Comparative Example 4 In this comparative example, the similarities with Example 1 will not be repeated, and the differences are as follows: The silica coating is 65 nanometers thick.

[0042] Comparative Example 5 In this comparative example, the similarities with Example 1 will not be repeated, and the differences are as follows: The unmodified natural calcium carbonate used had the same particle size D50 as in Example 2, which was 5 micrometers.

[0043] Performance Test Results and Analysis Modified calcium carbonate was prepared according to the parameters of the examples and comparative examples, respectively. To comprehensively evaluate the performance of the modified calcium carbonate, the following test methods were used: the angle of repose was determined by the injection method, reflecting the powder flowability; the particle size distribution was determined by a laser particle size analyzer; the fluoride stability was determined by measuring the free fluoride ion retention rate after mixing the abrasive with sodium monofluorophosphate solution; the abrasion resistance was determined by the radioactive enamel abrasion test; the hygroscopicity was determined by measuring the mass gain rate after placing the sample in an environment with 80% relative humidity for 24 hours; and the paste stability was determined by observing whether the paste produced gas through accelerated testing. Specific test results are shown in Table 1.

[0044] Table 1 Analysis of Test Results

[0045] As shown in Table 1, the modified calcium carbonate prepared in the three embodiments of this invention exhibits significant advantages in all performance indicators. Regarding flowability, the angle of repose of the products in the embodiments does not exceed 35 degrees, significantly lower than that of the comparative samples. This result confirms the positive effect of the silica coating layer on improving the flowability of calcium carbonate particles. Example 3 has the lowest angle of repose at only 31.2 degrees, indicating it has the best flowability. Comparative Example 1, lacking an acidic silica sol pretreatment step, suffers from compromised coating uniformity, resulting in an increased angle of repose of 38.6 degrees. Comparative Example 2, without alkaline silica sol coating, has an angle of repose as high as 42.3 degrees, further demonstrating the necessity of a complete coating process.

[0046] Regarding fluoride stability, all the products in the examples achieved a stability of over 90%, significantly higher than the comparative samples. This performance is crucial for the anti-caries efficacy of fluoride toothpaste. Example 3 exhibited the best fluoride stability at 95.1%, indicating that its uniformly thick silica coating effectively prevents calcium ion dissolution without compromising other properties due to excessive coating thickness. Comparative Example 3, due to insufficient coating thickness, had a fluoride stability of only 89.5%, demonstrating the direct impact of coating thickness on fluoride stability. Comparative Example 5, without any modification, had the lowest fluoride stability at only 68.4%, fully revealing the limitations of using natural calcium carbonate in fluoride toothpaste.

[0047] In the abrasion resistance test, the enamel abrasion values ​​of the products in the examples were all controlled below 0.41 micrometers, significantly lower than those of the comparative samples. This result confirms the effective role of the silica coating in reducing the abrasiveness of calcium carbonate. Example 3 had the lowest abrasion value of 0.35 micrometers, indicating that its coating structure was the most ideal. Comparative Example 2, without coating treatment, had an abrasion value as high as 0.68 micrometers, close to the 0.82 micrometers of Comparative Example 5 (natural calcium carbonate), demonstrating the importance of coating treatment in protecting tooth enamel.

[0048] Regarding hygroscopicity, the moisture absorption rates of the products in the examples were all below 0.6%, while those of the comparative samples were generally above 0.9%. Low hygroscopicity is directly related to the powder's ability to resist agglomeration during storage and transportation. Example 3 had the lowest moisture absorption rate, at only 0.38%, which is consistent with its angle of repose test results. The moisture absorption rate of Comparative Example 5 was as high as 3.67%, fully demonstrating the characteristic of natural calcium carbonate being prone to hygroscopic agglomeration.

[0049] The results of the paste stability test further verified the advantages of the product of this invention. The pastes in all three embodiments showed no change after accelerated testing, while Comparative Examples 1, 2, and 3 all exhibited varying degrees of gas production, with Comparative Example 5 showing the most severe gas production. This result corroborates the fluorine stability test data, indicating that the silica coating layer can indeed effectively block the contact between calcium carbonate and acidic substances, preventing the generation of carbon dioxide gas.

[0050] Test results show that the modified calcium carbonate prepared by the present invention through sequential coating with acidic silica sol and alkaline silica sol exhibits significant improvements in fluidity, fluorine stability, wear resistance, hygroscopicity, and paste stability.

[0051] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. Modified calcium carbonate for preparing toothpaste abrasives, characterized in that, The modified calcium carbonate has a core-shell structure, with calcium carbonate particles as the core and a silica layer on its surface. The silica layer is formed by the sequential reaction of acidic silica sol and alkaline silica sol on the surface of calcium carbonate particles.

2. The modified calcium carbonate for preparing toothpaste abrasives according to claim 1, characterized in that, The thickness of the silicon dioxide layer is 25 to 55 nanometers.

3. The modified calcium carbonate for preparing toothpaste abrasives according to claim 1, characterized in that, The modified calcium carbonate has an angle of repose of no more than 35 degrees and a particle size D50 of 8 to 15 micrometers.

4. A method for preparing modified calcium carbonate for toothpaste abrasives as described in any one of claims 1-3, characterized in that, The method includes the following steps: S1. Raw material pretreatment: Wash, crush, and grind natural calcium carbonate ore to obtain calcium carbonate powder; S2. Suspension preparation: Disperse the calcium carbonate powder obtained in step S1 into process water to form a calcium carbonate suspension under stirring conditions. S3, Acidic environment pretreatment: Add acidic silica sol to the calcium carbonate suspension in step S2 and stir to react; S4. Silica Coating: Add alkaline silica sol to the reaction system of step S3, adjust the pH of the system to alkaline, and continue the reaction to form a gel, so that silica coats the surface of calcium carbonate. S5. Solid-liquid separation and drying: The gel obtained in step S4 is separated by pressure filtration. The resulting filter cake is dried and crushed to obtain modified calcium carbonate.

5. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 4, characterized in that, In step S1, the grinding is carried out using a ring roller mill, and the grinding parameters are controlled so that the particle size D50 of the resulting calcium carbonate powder is 5 to 12 micrometers.

6. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 4, characterized in that, In step S2, the solid-liquid mass-volume ratio of the calcium carbonate suspension is 1 gram: 8 to 22 milliliters, the stirring temperature is 75 to 95°C, and the stirring speed is 300 to 500 rpm.

7. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 4, characterized in that, In step S3, the amount of acidic silica sol added accounts for 0.5% to 4.0% of the total mass of the calcium carbonate suspension, the reaction temperature is 75 to 95°C, and the reaction time is 15 to 35 minutes.

8. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 4, characterized in that, In step S4, the amount of alkaline silica sol added accounts for 2.0% to 4.5% of the total mass of the calcium carbonate suspension; the pH value of the system is adjusted to 7.5 to 9.

0.

9. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 8, characterized in that, The preparation process of the alkaline silica sol includes the following steps: adding 500 to 750 parts by weight of process water to a reaction vessel, heating to 60 to 80°C, first adding 8 to 18 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 0.8 to 1.8 hours; then heating to 70 to 90°C, adding 25 to 45 parts by weight of silicon powder and 0.8 to 3.5 parts by weight of sodium hydroxide, and stirring for 1.2 to 2.8 hours; finally heating to 85 to 98°C, adding 45 to 80 parts by weight of silicon powder and 1.5 to 4.5 parts by weight of sodium hydroxide, and stirring for 2.0 to 4.0 hours to obtain the alkaline silica sol.

10. The method for preparing modified calcium carbonate for toothpaste abrasives according to claim 4, characterized in that, In step S5, the pressure of the filter press is 0.2 to 0.6 MPa and the temperature is 15 to 35°C; the drying temperature is 80 to 120°C and the time is 1 to 5 hours.

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