Silicon dioxide coated calcium carbonate spherical powder and preparation method thereof

Abstract

The invention provides a preparation method of spherical powder of silicon dioxide coated calcium carbonate, which comprises the following steps: dispersing calcium carbonate into water, and uniformly stirring to obtain a calcium carbonate suspension; adding acidic silica sol into the calcium carbonate suspension, and stirring for reaction; adding alkaline silica sol, and adjusting the pH value to 7-9 to obtain gel; carrying out filter pressing separation on the gel, and drying to form a compact silicon dioxide layer on the surface; and crushing the silicon dioxide coated calcium carbonate to obtain the spherical powder of the silicon dioxide coated calcium carbonate. When the spherical powder is used as a toothpaste abrasive, the spherical powder does not damage enamel through rolling friction on the surfaces of teeth, and meanwhile, the compatibility with fluoride is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of silica preparation, and particularly relates to a spherical powder of silica-coated calcium carbonate and a preparation method thereof. Background Art

[0002] The abrasive in toothpaste is one of its main components, accounting for about 20%-50% of the total weight of toothpaste. The main function of the abrasive is to remove dental plaque, food residues and pigment deposits on the tooth surface through physical friction during the brushing process, while helping to clean the teeth and polish the tooth surface. Selecting a suitable abrasive is crucial for ensuring the cleaning effect of toothpaste and protecting tooth enamel.

[0003] The function of toothpaste abrasive in toothpaste is to clean and disperse dental calculus and tartar on the tooth surface by friction to achieve the purpose of cleaning teeth. It is required to be safe, non-toxic, odorless, white in appearance, uniform in particle size, with a hardness between tooth enamel and tartar, moderate friction value and pH value, particle size concentrated in 5-20 microns, small solubility product, good chemical stability, and does not react with other components of toothpaste. Currently, the commonly used toothpaste abrasives in China are dicalcium hydrogen phosphate dihydrate, silica, natural calcium carbonate, light calcium carbonate, etc. Toothpaste natural calcium carbonate (i.e., toothpaste calcite powder or toothpaste heavy calcium carbonate) is prepared by washing and pulverizing calcite ore. Toothpaste with natural calcium carbonate as the abrasive currently accounts for about 50% of the toothpaste market sales in China, and has an important impact on the oral health level of Chinese people. The quality requirements for calcium carbonate used as toothpaste abrasive are much higher than the standards of ordinary calcium carbonate.

[0004] The RDA value of natural calcium carbonate is as high as about 250, which is relatively high and easily wears tooth enamel. The dosage of calcium carbonate as a toothpaste abrasive in toothpaste is usually 40-50%, and the dosage is also relatively large. In addition, natural calcium carbonate has a rhombic crystal structure, and its acute angles are extremely easy to damage tooth enamel after long-term use, exposing nerve endings. When exposed to different external conditions such as acid, cold, sweet, and heat, the exposed nerves are stimulated and painful, commonly known as tooth hypersensitivity. In addition, natural calcium carbonate will produce carbon dioxide when encountering acidic substances in toothpaste, resulting in toothpaste swelling. At the same time, the calcium ions generated by calcium carbonate are easily combined with fluoride ions to form more insoluble calcium fluoride and continuously consume fluoride ions, resulting in poor compatibility with fluorides such as sodium fluoride. The main purpose of adding fluoride in toothpaste is to reduce the probability of dental caries. And the fluoride in fluoride can only play an anti-caries role when it is in an ionic state. Calcium carbonate-based abrasives will rob fluoride ions in toothpaste, thereby reducing the efficacy of fluoride toothpaste. To sum up, the calcium carbonate powder obtained from natural calcite is difficult to meet the needs of medium and high-grade toothpaste, especially toothpaste added with various active substances, which seriously affects the stability and shelf life of toothpaste. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing spherical powder of calcium carbonate coated with silica. Acidic silica sol and basic silica sol are added to a calcium carbonate suspension, and a dense silica layer is formed on its surface by pressure filtration, etc. The RDA value of the spherical powder is lower than that of natural calcium carbonate, so as to reduce the wear on tooth enamel. When used as a toothpaste abrasive, it rolls and rubs on the tooth surface without damaging the tooth enamel on the tooth surface. At the same time, its compatibility with fluoride is improved. The toothpaste prepared with the spherical powder of calcium carbonate coated with silica obtained by the present invention has a smooth and delicate paste body and good stability.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for preparing spherical powder of calcium carbonate coated with silica, comprising the following steps: S1: Disperse calcium carbonate in water and stir evenly to obtain a calcium carbonate suspension; S2: Add acidic silica sol to the calcium carbonate suspension obtained in step S1 and stir for reaction; S3: Then add basic silica sol and adjust the pH to 7-9 to obtain a gel; S4: Press-filter and separate the gel obtained in step S3, and dry it to form a dense silica layer on the surface; S5: Crush the calcium carbonate coated with silica to obtain spherical powder of calcium carbonate coated with silica.

[0007] Preferably, in step S1, the solid-liquid ratio of calcium carbonate to water is 1 g: 10-20 ml, and it is stirred at a rate of 400-500 r / min for 15-25 min at a temperature of 80-100 °C to obtain a calcium carbonate suspension.

[0008] Preferably, in step S2, the proportion of acidic silica sol in the calcium carbonate suspension is 1-3%.

[0009] Preferably, the preparation process of the acidic silica sol in step S2 is: mix basic silica sol and cation exchange resin according to a mass ratio of 2-5: 1, and react at a temperature of 60-70 °C for 30-50 min to obtain acidic silica sol; the pH of the acidic silica sol is 1.5-3.

[0010] Preferably, in step S3, the proportion of basic silica sol added in the calcium carbonate suspension is 2.5-3.5%.

[0011] Preferably, the silica content in the basic silica sol is 35-50%, and the particle size is 80-100 nm.

[0012] Preferably, the preparation process of the alkaline silica sol is as follows: Put 500 - 700 parts of deionized water into a reaction kettle, heat it up to 65 - 75 °C, add 10 - 15 parts of silicon powder and 2 - 4 parts of sodium hydroxide thereto, and stir and react for 1 - 1.5 h; continue to heat it up to 75 - 85 °C, add 30 - 40 parts of silicon powder and 1 - 3 parts of sodium hydroxide, and stir and react for 1.5 - 2.5 h; then heat it up to 90 - 95 °C, add 50 - 70 parts of silicon powder and 2 - 4 parts of sodium hydroxide, and stir and react for 2.5 - 3.5 h to obtain the alkaline silica sol.

[0013] Preferably, in step S3, the pressure filtration temperature is 20 - 30 °C, the pressure is 0.3 - 0.5 Mpa, and the thickness of the silicon dioxide layer is 30 - 50 nm.

[0014] Preferably, in step S4, the particle size D of the spherical powder product 50 is 10 - 13 um.

[0015] For the spherical powder of calcium carbonate coated with silicon dioxide prepared by any one of the above, the friction value RDA (Relative Dentin Abrasion) of the spherical powder is 190 - 220, and the compatibility with fluoride is 50 - 70%.

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: Silicon dioxide can be stably compounded with various active substances, but its price is relatively high, about 7 - 20 times that of calcite powder. The raw materials of silica sol are easy to obtain and the cost is low, which is very suitable for making silicon dioxide for coating calcium carbonate, and has an obvious price advantage. In the present invention, acidic silica sol is added to the calcium carbonate suspension to eliminate the sharp parts of calcium carbonate and change the shape of calcium carbonate into a spherical shape or close to a spherical shape; alkaline silica sol is added, and its colloidal particles collide with the colloidal particles of acidic silica sol on the surface of calcium carbonate to undergo a neutralization reaction to form a gel, and a dense silicon dioxide layer is formed on the surface through pressure filtration, and spherical powder is obtained through drying and pulverization.

[0017] Compared with the friction value RDA of natural heavy calcium carbonate which is as high as about 250, the friction value RDA of the spherical powder of calcium carbonate coated with silicon dioxide is 190 - 220, and it has no damage to dentin when used as a toothpaste abrasive; in addition, the fluoride compatibility of natural heavy calcium carbonate is 0, while the fluoride compatibility of the spherical powder of calcium carbonate coated with silicon dioxide prepared by the present invention is 50 - 70%, and the fluoride compatibility is significantly improved; moreover, the stability and acid resistance of the spherical powder of calcium carbonate coated with silicon dioxide in toothpaste are also significantly improved. Specific embodiments

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] Example 1 This example provides a method for preparing spherical powder of calcium carbonate coated with silica, comprising the following steps: S1: Mix calcium carbonate and water according to a solid-liquid ratio of 1 g: 10 ml, stir at a rate of 400 r / min for 15 min at a temperature of 80 °C to obtain a calcium carbonate suspension; S2: Put 500 g of deionized water into a reaction kettle, heat it up to 65 °C, add 10 g of silicon powder and 2 g of sodium hydroxide thereto, and stir and react at a rate of 400 r / min for 1 h; continue to heat up to 75 °C, add 30 g of silicon powder and 1 g of sodium hydroxide, and continue to stir and react for 1.5 h; then heat up to 90 °C, add 50 g of silicon powder and 2 g of sodium hydroxide, and continue to stir and react for 2.5 h to obtain an alkaline silica sol; Mix the alkaline silica sol and the cation exchange resin Dowex™ 50W according to a mass ratio of 2 - 5:1, react at a temperature of 60 °C for 30 min to obtain an acidic silica sol; add 1% of the acidic silica sol based on the proportion to the calcium carbonate suspension described in step S1, and stir and react at a rate of 400 r / min for 40 min; S3: Then add 2.5% of the alkaline silica sol based on the proportion, adjust the pH to 7.5, and let it stand for 25 min to obtain a gel; S4: At a temperature of 20 °C and a pressure of 0.3 Mpa, perform pressure filtration separation on the gel described in step S3, and dry it at 80 °C, that is, a dense silica layer with a thickness of 30 - 40 nm is formed on the surface; S5: Crush the calcium carbonate coated with silica to a particle size D 50 of 10 - 13 um to obtain spherical powder of calcium carbonate coated with silica; the friction value RDA of this powder is 195 and the fluorine compatibility is 68%.

[0020] Example 2 This example provides a method for preparing spherical powder of calcium carbonate coated with silica, comprising the following steps: S1: Mix calcium carbonate and water according to a solid-liquid ratio of 1 g: 20 ml, stir at a rate of 500 r / min for 25 min at a temperature of 100 °C to obtain a calcium carbonate suspension; S2: Put 700 g of deionized water into a reaction kettle, heat it up to 75 °C, add 15 g of silicon powder and 4 g of sodium hydroxide to it, and stir and react at a rate of 500 r / min for 1.5 h; continue to heat up to 85 °C, add 40 g of silicon powder and 3 g of sodium hydroxide, and continue to stir and react for 2.5 h; then heat up to 95 °C, add 70 g of silicon powder and 4 g of sodium hydroxide, and continue to stir and react for 3.5 h to obtain alkaline silica sol; Mix the alkaline silica sol and the cation exchange resin Purolite C100 according to a mass ratio of 5:1, and react at a temperature of 70 °C for 50 min to obtain acidic silica sol; add 3% acidic silica sol by proportion to the calcium carbonate suspension described in step S1, and stir and react at a rate of 600 r / min for 60 min; S3: Then add 3.5% alkaline silica sol by proportion, adjust the pH to 8.5, and let it stand for 35 min to obtain a gel; S4: At a temperature of 30 °C and a pressure of 0.5 Mpa, filter and separate the gel described in step S3, and dry it at 80 °C, that is, a dense silica layer with a thickness of 40 - 50 nm is formed on the surface; S5: Crush the calcium carbonate coated with silica to a particle size D 50 of 10 - 13 um to obtain spherical powder of calcium carbonate coated with silica; the friction value RDA of this powder is 210 and the fluorine compatibility is 55%.

[0021] Example 3 This example provides a method for preparing spherical powder of calcium carbonate coated with silica, which includes the following steps: S1: Mix calcium carbonate and water according to a solid-liquid ratio of 1 g:15 ml, and stir at a rate of 450 r / min at a temperature of 95 °C for 22 min to obtain a calcium carbonate suspension; S2: Put 650 g of deionized water into a reaction kettle, heat it up to 70 °C, add 12 g of silicon powder and 3 g of sodium hydroxide to it, and stir and react at a rate of 600 r / min for 1.2 h; continue to heat up to 82 °C, add 35 g of silicon powder and 2 g of sodium hydroxide, and continue to stir and react for 2 h; then heat up to 92 °C, add 65 g of silicon powder and 3 g of sodium hydroxide, and continue to stir and react for 2.5 - 3.5 h to obtain alkaline silica sol; Mix the alkaline silica sol and the cation exchange resin Amberlite™ IR-120 according to a mass ratio of 3.5:1, and react at a temperature of 65 °C for 40 min to obtain acidic silica sol; add 2% acidic silica sol by proportion to the calcium carbonate suspension described in step S1, and stir and react at a rate of 550 r / min for 55 min; S3: Then add 3% alkaline silica sol by proportion, adjust the pH to 8.1, and let it stand for 30 min to obtain a gel; S4: At a temperature of 25 °C and a pressure of 0.4 Mpa, the gel described in step S3 is subjected to pressure filtration and separation, and dried at 80 °C, i.e., a dense silica layer with a thickness of 35 - 45 nm is formed on the surface; S5: The calcium carbonate coated with silica is crushed to a particle size D 50 of 10 - 13 um, and spherical powder of calcium carbonate coated with silica can be obtained; the friction value RDA of this powder is 220 and the fluorine compatibility is 65%.

[0022] Comparative Example 1 The difference from Example 1 is that in step S1, the solid-liquid ratio of calcium carbonate to aqueous solution is 1 g: 30 ml, and other steps remain unchanged.

[0023] Comparative Example 2 The difference from Example 1 is that in step S1, the solid-liquid ratio of calcium carbonate to aqueous solution is 1 g: 5 ml, and other steps remain unchanged.

[0024] Comparative Example 3 The difference from Example 1 is that in step S3, the pH is 6, and other steps remain unchanged.

[0025] Comparative Example 4 The difference from Example 1 is that in step S3, the pH is 11, and other steps remain unchanged.

[0026] Comparative Example 5 The difference from Example 1 is that in step S4, the pressure filtration temperature is 50 °C and the pressure is 0.6 Mpa, and other steps remain unchanged.

[0027] Comparative Example 6 The difference from Example 1 is that in step S4, the pressure filtration temperature is 10 °C and the pressure is 0.1 Mpa, and other steps remain unchanged.

[0028] Performance test: Referring to GB / T 32661-2016, the apparent density, specific surface area, and median particle size of the spherical powders prepared in each example and comparative example are detected; the RDA (Relative Dentin Abrasion) friction value of silica is measured by the radioactive tracer method; the results are shown in the following table.

[0029] Table 1

[0030] As can be seen from the above performance test results, the spherical powders prepared in Examples 1-3 are spherical, with a relatively large apparent density, a relatively small specific surface area, and good friction performance; the appropriate RDA value enables their application in toothpaste without damaging tooth enamel. In particular, Example 3 has better comprehensive performance. Comparative Examples 1-6, however, do not adopt the necessary technical solutions, resulting in significantly poorer performance in the corresponding performance tests than the examples. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0031] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of spherical silica-coated calcium carbonate powder, characterized in that, It includes the following steps: S1: Disperse calcium carbonate in water and stir evenly to obtain a calcium carbonate suspension; S2: Add acidic silica sol to the calcium carbonate suspension described in step S1 and stir to react; S3: Then add basic silica sol and adjust the pH to 7 - 9 to obtain a gel; S4: Filter and separate the gel described in step S3 by pressure filtration and dry it to form a dense silica layer on the surface; S5: Crush the calcium carbonate coated with silica to obtain spherical powder of calcium carbonate coated with silica.

2. The preparation method of a spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that, In step S1, the solid - liquid ratio of calcium carbonate to water is 1g:10 - 20ml, and it is stirred at a rate of 400 - 500r / min at a temperature of 80 - 100°C for 15 - 25min to obtain a calcium carbonate suspension.

3. The preparation method of a spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that, In step S2, the proportion of acidic silica sol in the calcium carbonate suspension is 1 - 3%.

4. The preparation method of a spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that, The preparation process of the acidic silica sol described in step S2 is: mix basic silica sol and cation exchange resin according to a mass ratio of 2 - 5:1, react at a temperature of 60 - 70°C for 30 - 50min to obtain acidic silica sol; the pH of the acidic silica sol is 1.5 - 3.

5. The preparation method of a spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that, In step S3, the proportion of basic silica sol added in the calcium carbonate suspension is 2.5 - 3.5%.

6. The preparation method of the spherical powder of calcium carbonate coated with silica according to claim 5, characterized in that, The silica content in the basic silica sol is 35 - 50%, and the particle size is 80 - 100nm.

7. The preparation method of the spherical powder of calcium carbonate coated with silica according to claim 5, characterized in that, The preparation process of the basic silica sol is: put 500 - 700 parts of deionized water into a reaction kettle, heat it up to 65 - 75°C, add 10 - 15 parts of silicon powder and 2 - 4 parts of sodium hydroxide, stir and react for 1 - 1.5h; continue to heat it up to 75 - 85°C, add 30 - 40 parts of silicon powder and 1 - 3 parts of sodium hydroxide, stir and react for 1.5 - 2.5h; then heat it up to 90 - 95°C, add 50 - 70 parts of silicon powder and 2 - 4 parts of sodium hydroxide, stir and react for 2.5 - 3.5h to obtain basic silica sol.

8. The preparation method of the spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that, In step S3, the pressure filtration temperature is 20 - 30°C, the pressure is 0.3 - 0.5Mpa, and the thickness of the silica layer is 30 - 50nm.

9. The preparation method of the spherical powder of calcium carbonate coated with silica according to claim 1, characterized in that The particle size D of the spherical powder product in step S4 50 is 10 - 13 μm.

10. The spherical powder of calcium carbonate coated with silica prepared according to any one of claims 1-9, characterized in that, The friction value RDA of the spherical powder is 190 - 220, and the compatibility with fluoride is 50 - 70%.

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