A high-covering calcium carbonate and its preparation method and application

Abstract

The present invention belongs to the technical field of inorganic fillers, and provides a high-hiding calcium carbonate and its preparation method and application, which solves the problem of excessive titanium dioxide usage in coatings. The method wet-grinds calcium carbonate slurry and a grinding aid to obtain a primary slurry; wet-grinds the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate; and modifies the wet-process heavy calcium carbonate, light calcium carbonate and a modifier to obtain the high-hiding calcium carbonate. The present invention adopts a wet tandem grinding process, and by adjusting the grinding medium size, filling rate and selection of grinding aids in two wet grinding stages, an ultrafine heavy calcium carbonate (2um content ≥85%) is prepared. Compared with the traditional one-stage wet grinding process, the product has a more concentrated particle size distribution, a higher fine powder content and a higher grinding efficiency. The calcium carbonate provided by the present invention can reduce the titanium dioxide content in the latex paint formula system by 15-20%, effectively reducing the formula cost.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic fillers, in particular to high-hiding calcium carbonate and a preparation method and application thereof. Background Art

[0002] Titanium dioxide is one of the world's best-hiding white pigments, boasting 5 to 10 times the hiding power of other white pigments. Therefore, it is widely used as a white pigment in coatings, plastics, and papermaking. Coatings are the largest application area for titanium dioxide, particularly in interior and exterior latex paints.

[0003] However, the price of titanium dioxide has long fluctuated above 10,000 yuan per ton, making it expensive. In downstream applications, it often accounts for a significant portion of the formulation cost, and excessive addition increases the formulation cost. Furthermore, with the EU designating titanium dioxide as a suspected carcinogen, its use is becoming increasingly restricted. Therefore, the development of alternatives to titanium dioxide is becoming increasingly urgent, both for formulation cost and sustainable development considerations.

[0004] Currently, there are two main approaches to replacing titanium dioxide in interior and exterior latex paints: 1. Improving the hiding power of the paint film by introducing the dry hiding power of air; 2. Compounding titanium dioxide with ultrafine mineral fillers to reduce titanium dioxide flocculation and improve titanium dioxide utilization. Introducing dry hiding power requires the use of ultrafine fillers. However, when the ultrafine filler dosage is too low, the resulting porosity is insufficient, and the paint film's hiding power is not significantly improved. When the ultrafine filler dosage is too high, the porosity is sufficient, but due to the high oil absorption of the ultrafine filler, the paint's scrub resistance is significantly reduced, failing to meet application requirements. Compounding mineral fillers with titanium dioxide generally requires a wet process, and during the subsequent drying process, the particles tend to agglomerate, significantly reducing the compounding effect and affecting the hiding performance of the final product. Therefore, the current mainstream research on titanium dioxide replacement is still focused on path 1. However, if you want to achieve partial replacement of titanium dioxide through the idea of ​​Path 1, you need to take into account both increasing the porosity of the coating and controlling the oil absorption of the ultrafine filler used within a certain range, so as to ensure that the washability and other properties of the paint film are not reduced. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a high-hiding calcium carbonate and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing high-hiding calcium carbonate, comprising the following steps:

[0008] (1) wet grinding the calcium carbonate slurry and the grinding aid to obtain a primary slurry;

[0009] (2) wet-grinding the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate;

[0010] (3) The wet-process heavy calcium carbonate, light calcium carbonate and a modifier are subjected to modification treatment to obtain the high-hiding calcium carbonate.

[0011] Preferably, the solid content of the calcium carbonate slurry in step (1) is 60-80%, and the particle size of the calcium carbonate in the calcium carbonate slurry is 300-500 mesh;

[0012] The grinding aid is sodium polyacrylate;

[0013] The mass of the grinding aid is 2-5‰ of the mass of calcium carbonate in the calcium carbonate slurry.

[0014] Preferably, the medium filling rate of the wet grinding in step (1) is 50-60%;

[0015] The wet grinding media includes zirconia balls with a diameter of 1.8 to 2.2 mm and zirconia balls with a diameter of 2.3 to 2.7 mm;

[0016] The mass ratio of the zirconia balls with a diameter of 1.8 to 2.2 mm to the zirconia balls with a diameter of 2.3 to 2.7 mm is 1:2 to 3;

[0017] The wet grinding time is 20 to 30 minutes, and the rotation speed is 45 to 55 Hz.

[0018] Preferably, the grinding aid in step (2) comprises sodium polycarboxylate, an acrylate high molecular weight dispersant and ethylene glycol;

[0019] The mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersant and the ethylene glycol is 1-4:1-4:0.5-1.5;

[0020] The mass of the grinding aid in step (2) is 4 to 8‰ of the mass of the calcium carbonate in the calcium carbonate slurry in step (1).

[0021] Preferably, the medium filling rate of the wet grinding in step (2) is 60-75%;

[0022] The wet grinding media includes zirconia balls with a diameter of 0.6 to 1 mm and zirconia balls with a diameter of 1.2 to 1.8 mm;

[0023] The mass ratio of the zirconia balls with a diameter of 0.6 to 1 mm to the zirconia balls with a diameter of 1.2 to 1.8 mm is 2 to 5:1;

[0024] The wet grinding time is 20 to 30 minutes, and the rotation speed is 45 to 55 Hz.

[0025] Preferably, the crystal morphology of the light calcium carbonate in step (3) is a spindle morphology;

[0026] The mass ratio of the light calcium carbonate to the wet-process heavy calcium carbonate is 1:3-5.

[0027] Preferably, the modifier in step (3) comprises distyryl biphenyl whitening agent, bis(dioctyl pyrophosphate)ethylene titanate and sodium stearate;

[0028] The mass ratio of the distyryl biphenyl whitening agent, bis(dioctyl pyrophosphate acyloxy)ethylene titanate and sodium stearate is 0.5-2.5:4-12:1-10;

[0029] The mass of the modifier is 4 to 10‰ of the sum of the mass of the wet-process heavy calcium carbonate and the light calcium carbonate.

[0030] Preferably, the temperature of the modification treatment in step (3) is 70-90° C., and the time is 15-25 minutes.

[0031] The present invention also provides high-hiding calcium carbonate obtained by the preparation method.

[0032] The present invention also provides application of the high-hiding calcium carbonate in coatings.

[0033] The present invention provides a method for preparing high-obscuration calcium carbonate, comprising the following steps: wet-grinding a calcium carbonate slurry and a grinding aid to obtain a primary slurry; wet-grinding the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate; and modifying the wet-process heavy calcium carbonate, light calcium carbonate, and a modifier to obtain the high-obscuration calcium carbonate. The present invention utilizes a wet tandem grinding process, adjusting the grinding media size, fill rate, and grinding aid selection in two wet grinding stages to produce an ultrafine heavy calcium carbonate (2 μm content ≥ 85%). Compared to traditional one-stage wet grinding processes, the product has a more concentrated particle size distribution, a higher fine powder content, and improved grinding efficiency.

[0034] The present invention selects light calcium carbonate with a spindle-shaped crystal morphology and wet-process heavy calcium carbonate for compounding. During the accumulation process of the particles, the spindle-shaped particles can maximize the porosity. When applied to latex paint, they can provide sufficient air-dry hiding power with a relatively small addition amount. At the same time, the porosity of the product is strictly controlled by controlling the ratio of light calcium carbonate to heavy calcium carbonate, so that the porosity is not too high, which causes a decrease in the water resistance and scrub resistance of the paint film, and the porosity is not too low, which causes insufficient hiding power. At the same time, the use of a specific modifier can simultaneously increase whiteness, improve dispersibility, and reduce oil absorption.

[0035] The calcium carbonate provided by the present invention is a high-hiding calcium carbonate used in latex paint. The dry hiding power of air appropriately introduced can reduce the flocculation of titanium dioxide and improve the utilization rate of titanium dioxide. While ensuring that the performance of the paint film, such as scrub resistance and water resistance, is not reduced, the titanium dioxide content in the latex paint formula system can be reduced by 15-20%, effectively reducing the formulation cost of the latex paint. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing high-hiding calcium carbonate, comprising the following steps:

[0037] (1) wet grinding the calcium carbonate slurry and the grinding aid to obtain a primary slurry;

[0038] (2) wet-grinding the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate;

[0039] (3) The wet-process heavy calcium carbonate, light calcium carbonate and a modifier are subjected to modification treatment to obtain the high-hiding calcium carbonate.

[0040] In the present invention, calcium carbonate is prepared from limestone ore, and the calcium carbonate content of the limestone ore is preferably ≥80%, more preferably ≥85%, and more preferably ≥90%; the limestone ore is cleaned and naturally dried, and then subjected to two coarse crushing steps to obtain coarse stone; the coarse stone is subjected to ring roller grinding and classification to obtain calcium carbonate.

[0041] In the present invention, the raw ore selected is limestone ore. Since the texture of limestone ore is denser than that of calcite ore, its oil absorption is lower under the condition of the same particle size. Moreover, since the composition of limestone ore generally contains 1 to 3% of silicon dioxide, the product produced can be used in latex paint to significantly improve the wash resistance.

[0042] In the present invention, the solid content of the calcium carbonate slurry in step (1) is preferably 60-80%, more preferably 65-75%, and more preferably 68-72%; the particle size of the calcium carbonate in the calcium carbonate slurry is preferably 300-500 mesh, more preferably 350-450 mesh, and more preferably 380-420 mesh.

[0043] In the present invention, the grinding aid is preferably sodium polyacrylate.

[0044] In the present invention, the grinding aid in step (1) is sodium polyacrylate, which plays the role of reducing the viscosity of the slurry and increasing the solid content of the slurry.

[0045] In the present invention, the mass of the grinding aid is preferably 2-5‰ of the mass of calcium carbonate in the calcium carbonate slurry, more preferably 3-4‰, and more preferably 3.4-3.6‰.

[0046] In the present invention, the calcium carbonate slurry and the grinding aid are mixed and then wet-ground. The mixing speed is preferably 45 to 55 Hz, more preferably 46 to 54 Hz, and more preferably 48 to 52 Hz; the mixing time is preferably 5 to 15 min, more preferably 6 to 14 min, and more preferably 8 to 12 min.

[0047] In the present invention, the medium filling rate of the wet grinding in step (1) is preferably 50-60%, more preferably 52-58%, and even more preferably 54-56%.

[0048] In the present invention, the wet grinding media preferably comprises zirconia balls with a diameter of 1.8 to 2.2 mm and zirconia balls with a diameter of 2.3 to 2.7 mm, further preferably comprises zirconia balls with a diameter of 1.9 to 2.1 mm and zirconia balls with a diameter of 2.4 to 2.6 mm, and more preferably comprises zirconia balls with a diameter of 2 mm and zirconia balls with a diameter of 2.5 mm.

[0049] In the present invention, the mass ratio of the zirconia balls with a diameter of 1.8 to 2.2 mm to the zirconia balls with a diameter of 2.3 to 2.7 mm is preferably 1:2 to 3, more preferably 1:2.2 to 2.8, and even more preferably 1:2.4 to 2.6.

[0050] In the present invention, since the particle size of calcium carbonate is relatively large, a large-sized grinding medium must be selected to provide sufficient kinetic energy for crushing. If the size of the grinding medium is too small, the kinetic energy is insufficient and the separation system of the grinding medium and the slurry is easily blocked.

[0051] In the present invention, the wet grinding time is preferably 20 to 30 min, more preferably 22 to 28 min, more preferably 24 to 26 min; the rotation speed is preferably 45 to 55 Hz, more preferably 46 to 54 Hz, more preferably 48 to 52 Hz.

[0052] In the present invention, after the wet grinding in step (1), the particle size of the primary slurry is detected to be: D50 is 4.5-5.5 μm, D97 is 8.5-10.0 μm, and the mass of the component less than 2 μm is ≥35%.

[0053] In the present invention, the grinding aid in step (2) preferably comprises sodium polycarboxylate, an acrylate high molecular weight dispersant and ethylene glycol.

[0054] In the present invention, the model of the acrylate high molecular weight dispersant is HD2021.

[0055] In the present invention, the mass ratio of the sodium polycarboxylate, the high molecular weight acrylate dispersant and the ethylene glycol is preferably 1-4:1-4:0.5-1.5, more preferably 2-3:2-3:0.6-1.4, and more preferably 2.4-2.6:2.4-2.6:0.8-1.2.

[0056] In the present invention, sodium polycarboxylate is an anionic dispersant with excellent water resistance, which can prevent particle agglomeration through electrostatic repulsion; the high molecular weight acrylate dispersant can provide a significant steric hindrance effect, further preventing agglomeration between ultrafine particles; and ethylene glycol mainly plays the role of assisting in reducing the surface energy of the particles.

[0057] In the present invention, the mass of the grinding aid in step (2) is preferably 4-8‰ of the mass of the calcium carbonate in the calcium carbonate slurry in step (1), more preferably 5-7‰, and more preferably 5.5-6.5‰.

[0058] In the present invention, the primary slurry and the grinding aid are mixed and then wet-ground; the stirring speed of the mixing is preferably 45 to 55 Hz, more preferably 46 to 54 Hz, more preferably 48 to 52 Hz, and the stirring time is preferably 5 to 10 min, more preferably 6 to 9 min, more preferably 7 to 8 min.

[0059] In the present invention, the medium filling rate of the wet grinding in step (2) is preferably 60-75%, more preferably 65-70%, and even more preferably 66-68%.

[0060] In the present invention, the wet grinding media preferably comprises zirconia balls with a diameter of 0.6 to 1 mm and zirconia balls with a diameter of 1.2 to 1.8 mm, further preferably comprises zirconia balls with a diameter of 0.7 to 0.9 mm and zirconia balls with a diameter of 1.3 to 1.7 mm, and more preferably comprises zirconia balls with a diameter of 0.8 mm and zirconia balls with a diameter of 1.4 to 1.6 mm.

[0061] In the present invention, the mass ratio of the zirconia balls with a diameter of 0.6 to 1 mm to the zirconia balls with a diameter of 1.2 to 1.8 mm is preferably 2 to 5:1, more preferably 3 to 4:1, and even more preferably 3.4 to 3.6:1.

[0062] In the present invention, small-particle grinding media are selected in the secondary wet ultrafine grinding stage, which has a large contact area and is more conducive to ultrafine wet grinding and improves grinding efficiency.

[0063] In the present invention, the wet grinding time is preferably 20 to 30 min, more preferably 22 to 28 min, more preferably 24 to 26 min; the rotation speed is preferably 45 to 55 Hz, more preferably 46 to 54 Hz, more preferably 48 to 52 Hz.

[0064] In the present invention, after the wet grinding in step (2) is completed, a slurry system is obtained. The slurry system is tested and the particle size is: D50 is 1.0-1.5 μm, D97 is 2.0-2.5 μm, and the mass of the component less than 2 μm is ≥90%.

[0065] In the present invention, the slurry system is flash dried, bagged and sieved to obtain wet-process heavy calcium carbonate; the particle size is detected to be: D50 is 1.2-1.7 μm, D97 is 2.3-2.8 μm, and the mass of the component less than 2 μm is ≥80%.

[0066] In the present invention, the crystal morphology of the light calcium carbonate in step (3) is preferably a spindle morphology; the oil absorption is preferably 55 to 60, more preferably 56 to 59, more preferably 57 to 58; the sedimentation volume is preferably 2.4 to 3.2, more preferably 2.6 to 3.0, more preferably 2.7 to 2.9.

[0067] In the present invention, the crystal morphology of light calcium carbonate is selected to be a spindle morphology. Compared with spherical and cubic light calcium carbonate, the spindle morphology can maximize the porosity during the stacking process. When used in latex paint, it can provide sufficient air-dry hiding power with a smaller addition amount.

[0068] In the present invention, the mass ratio of the light calcium carbonate to the wet-process heavy calcium carbonate is preferably 1:3-5, more preferably 1:3.5-4.5, and even more preferably 1:3.8-4.2.

[0069] In the present invention, light calcium carbonate and wet-process heavy calcium carbonate need to be within a reasonable mass ratio range. When the proportion of light calcium carbonate is too high, the oil absorption of the composite powder is large, and the porosity during stacking is too high. When applied to downstream latex paint, although the dry hiding of the paint film is high, the density of the paint film is significantly reduced, and its indicators such as scrub resistance and water resistance will show a significant downward trend. If the proportion of light calcium carbonate is too low, it cannot provide sufficient porosity, the introduced air dry hiding is insufficient, and the improvement in hiding is not obvious.

[0070] In the present invention, light calcium carbonate and wet-process heavy calcium carbonate are first mixed, and a modifier is added after the mixing is completed for modification; the mixing temperature is preferably 70-90°C, more preferably 75-85°C, and more preferably 78-82°C; the mixing time is preferably 10-15 min, more preferably 11-14 min, and more preferably 12-13 min.

[0071] In the present invention, the modifier in step (3) preferably comprises a distyryl biphenyl whitening agent, bis(dioctylpyrophosphate)ethylene titanate and sodium stearate.

[0072] In the present invention, the model of the distyryl biphenyl brightener is FBA351.

[0073] In the present invention, the model of the bis(dioctyl pyrophosphate)ethylene titanate is HY-311.

[0074] In the present invention, the mass ratio of the distyryl biphenyl whitening agent, bis(dioctyl pyrophosphate)ethylene titanate and sodium stearate is preferably 0.5-2.5:4-12:1-10, more preferably 1-2:6-10:2-8, and more preferably 1.4-1.6:7-9:4-6.

[0075] In the present invention, the distyryl biphenyl whitening agent improves the whiteness of the product, preventing the paint film from being dark due to the low whiteness of limestone, thereby affecting the product hue; the addition of bis(dioctylpyrophosphate)ethylene titanate can improve the dispersibility of calcium carbonate in titanium dioxide; and sodium stearate mainly plays a role in reducing the oil absorption of the product.

[0076] In the present invention, the mass of the modifier is preferably 4-10‰ of the sum of the mass of wet-process heavy calcium carbonate and light calcium carbonate, more preferably 5-9‰, and even more preferably 7-8‰.

[0077] In the present invention, the modifier is added by spraying after mixing the modifier and water. The mass ratio of the modifier to water is preferably 1:1-3, more preferably 1:1.5-2.5, and even more preferably 1:1.8-2.2.

[0078] In the present invention, the temperature of the modification treatment in step (3) is preferably 70-90°C, more preferably 75-85°C, and more preferably 78-82°C; the time is preferably 15-25 min, more preferably 16-24 min, and more preferably 18-22 min.

[0079] The present invention also provides high-hiding calcium carbonate obtained by the preparation method.

[0080] The present invention also provides application of the high-hiding calcium carbonate in coatings.

[0081] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0082] Example 1

[0083] Limestone ore with a calcium carbonate content of 85% is washed and naturally dried, then crushed twice to obtain coarse stone. This is then roller milled and classified to obtain calcium carbonate with a particle size of 400 mesh. The calcium carbonate is then prepared into a slurry with a solid content of 60%. Then, sodium polyacrylate (2‰ by weight of the calcium carbonate) is added and stirred and dispersed at 50 Hz for 10 minutes. Wet grinding is then performed, with a media filling ratio of 50% and a mass ratio of 2mm to 2.5mm zirconia balls of 1:3. After grinding at 49 Hz for 20 minutes, the primary slurry is obtained. The particle sizes tested are D50: 5.47mm, D97: 9.82mm, and the content of particles less than 2µm is 36.25%. A grinding aid is added to the primary slurry, the mass of the grinding aid is 4‰ of the mass of calcium carbonate in the calcium carbonate slurry, the mass ratio of sodium polycarboxylate, acrylic ester high molecular weight dispersant HD2021 and ethylene glycol in the grinding aid is 2:1:1, and the mixture is stirred at a speed of 55HZ for 5 minutes, and then wet grinding is carried out. The medium filling rate of wet grinding is 60%, the mass ratio of 0.8mm and 1.5mm zirconia balls is 2:1, and the slurry system is obtained by grinding at a speed of 50HZ for 20 minutes. The particle size is detected to be D50: 1.46um, D97: 2.44um, and the content of less than 2um is ≥90.18%; the slurry system is flash dried, bag collected and sieved to obtain wet-process heavy calcium carbonate, and the dry powder particle size is detected to be D50: 1.68um, D97: 2.76um, and the content of less than 2um is ≥81.32%. The light calcium carbonate with spindle morphology (oil absorption 55, sedimentation volume 2.8) and the obtained wet-process heavy calcium carbonate were mixed at a mass ratio of 1:5 at 70°C for 10 minutes, and then the modifier was prepared (the mass ratio of distyryl biphenyl brightener FBA351, bis(dioctyl pyrophosphate) ethylene titanate HY-311 and sodium stearate was 1:5:2). The mass of the modifier was 4‰ of the sum of the mass of wet-process heavy calcium carbonate and light calcium carbonate. The weighed modifier was diluted with water at a mass ratio of 1:1, and then added to the mixed light calcium carbonate and heavy calcium carbonate in the form of a spray. The mixing was continued for 15 minutes to complete the modification and obtain high-hiding calcium carbonate.

[0084] Example 2

[0085] Limestone ore with a calcium carbonate content of 82% was washed and naturally dried, then crushed twice to obtain coarse stone. This was then roller milled and classified to obtain calcium carbonate with a particle size of 320 mesh. The calcium carbonate was then prepared into a slurry with a solids content of 70%. Sodium polyacrylate (3‰ by weight of the calcium carbonate) was then added and dispersed at 45 Hz for 15 minutes. Wet grinding was then performed with a media fill rate of 55%, a mass ratio of 2mm to 2.5mm zirconia balls of 1:2, and grinding at 50 Hz for 25 minutes to obtain a primary slurry. The particle sizes were tested to be 5.02mm (D50), 9.14mm (D97), and 39.83% (less than 2µm). A grinding aid is added to the primary slurry, the mass of the grinding aid is 6‰ of the mass of calcium carbonate in the calcium carbonate slurry, the mass ratio of sodium polycarboxylate, acrylic high molecular weight dispersant HD2021 and ethylene glycol in the grinding aid is 2:2:1, and the mixture is stirred at a speed of 50HZ for 10 minutes, and then wet grinding is carried out. The medium filling rate of wet grinding is 65%, the mass ratio of 0.8mm and 1.5mm zirconia balls is 3:1, and the slurry system is obtained by grinding at a speed of 55HZ for 25 minutes. The particle size is detected to be D50: 1.22um, D97: 2.18um, and the content of less than 2um is ≥92.02%; the slurry system is flash dried, bag collected and sieved to obtain wet-process heavy calcium carbonate, and the dry powder particle size is detected to be D50: 1.42um, D97: 2.48um, and the content of less than 2um is ≥82.67%. The light calcium carbonate with spindle morphology (oil absorption 60, sedimentation volume 3.1) and the obtained wet-process heavy calcium carbonate were mixed at a mass ratio of 1:4 at 80°C for 15 minutes, and then the modifier was prepared (the mass ratio of distyryl biphenyl brightener FBA351, bis(dioctyl pyrophosphate) ethylene titanate HY-311 and sodium stearate was 1:11:4). The mass of the modifier was 8‰ of the sum of the mass of wet-process heavy calcium carbonate and light calcium carbonate. The weighed modifier was diluted with water at a mass ratio of 1:2, and then added to the mixed light calcium carbonate and heavy calcium carbonate in the form of a spray. The mixing was continued for 20 minutes to complete the modification and obtain high-hiding calcium carbonate.

[0086] Example 3

[0087] Limestone ore with a calcium carbonate content of 83% was washed and naturally dried, then crushed twice to obtain coarse stone. This was then roller milled and classified to obtain calcium carbonate with a particle size of 480 mesh. The calcium carbonate was then prepared into a slurry with a solids content of 75%. Sodium polyacrylate (4‰ by weight of the calcium carbonate) was then added and dispersed at 55 Hz for 10 minutes. Wet grinding was then performed with a media fill rate of 60% and a mass ratio of 2mm to 2.5mm zirconia balls of 1:3. After grinding at 45 Hz for 30 minutes, the primary slurry was obtained. The particle sizes were tested to be D50: 4.62mm, D97: 8.71mm, and 44.32% of the particles were less than 2µm. A grinding aid is added to the primary slurry, the mass of the grinding aid is 8‰ of the mass of calcium carbonate in the calcium carbonate slurry, the mass ratio of sodium polycarboxylate, acrylic ester high molecular weight dispersant HD2021 and ethylene glycol in the grinding aid is 3:4:1, and the mixture is stirred at a speed of 50HZ for 10 minutes, and then wet grinding is carried out. The medium filling rate of wet grinding is 70%, the mass ratio of 0.8mm and 1.5mm zirconia balls is 2:1, and the slurry system is obtained by grinding at a speed of 49HZ for 30 minutes. The particle size is detected to be D50: 1.09um, D97: 2.04um, and the content of less than 2um is ≥95.66%; the slurry system is flash dried, bag collected and sieved to obtain wet-process heavy calcium carbonate, and the dry powder particle size is detected to be D50: 1.26um, D97: 2.31um, and the content of less than 2um is ≥84.22%. The light calcium carbonate with spindle morphology (oil absorption 58, sedimentation volume 2.5) and the obtained wet-process heavy calcium carbonate were mixed at a mass ratio of 1:3 at 90°C for 15 minutes, and then the modifier was prepared (the mass ratio of distyryl biphenyl brightener FBA351, bis(dioctyl pyrophosphate) ethylene titanate HY-311 and sodium stearate was 2:9:9). The mass of the modifier was 10‰ of the sum of the mass of wet-process heavy calcium carbonate and light calcium carbonate. The weighed modifier was diluted with water at a mass ratio of 1:3, and then added to the mixed light calcium carbonate and heavy calcium carbonate in the form of a spray. The mixing was continued for 25 minutes to complete the modification and obtain high-hiding calcium carbonate.

[0088] The high hiding calcium carbonate prepared in Examples 1 to 3 was tested for relevant indicators according to HG / T3249-2013. The results are shown in Table 1.

[0089] Table 1 Index test results

[0090] Example 1 Example 2 Example 3 Whiteness 96.32 96.65 96.82 D50(um) 1.70 1.88 2.07 D97(um) 3.49 3.84 4.95 D100(um) 10.22 10.31 10.27 ≤2um content (%) 76.32 71.62 65.88 Oil absorption (ml / 100g) 22 24 26 Moisture (%) 0.21 0.20 0.22

[0091] The high hiding calcium carbonate prepared in Examples 1 to 3 was applied to latex paint to replace 20% of the titanium dioxide content in the formula, and compared with the original formula and tested according to relevant standards. The latex paint formula is shown in Table 2.

[0092] Table 2 Latex paint formula

[0093]

[0094]

[0095] The above latex paint was subjected to performance testing, and the results are recorded in Table 3.

[0096] Table 3 Latex paint performance test results

[0097] 0# 1# 2# 3# Test standards Contrast ratio 0.9562 0.9566 0.9588 0.9590 GB / T23981.1-2019 Washing times 526 570 552 530 GB / T9266-2009 Water permeability / ml 1.0 1.0 0.9 1.0 GB / T9755-2014 Alkali resistance (48h) No abnormalities No abnormalities No abnormalities No abnormalities GB / T9755-2014

[0098] As can be seen from the above examples, the present invention provides a method for preparing high-hiding calcium carbonate, comprising wet-grinding a calcium carbonate slurry and a grinding aid to obtain a primary slurry; wet-grinding the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate; and modifying the wet-process heavy calcium carbonate, light calcium carbonate, and a modifier to obtain the high-hiding calcium carbonate. When the calcium carbonate prepared by the present invention is used in latex paint, it can replace 20% of the titanium dioxide content in the formulation while ensuring that the product's contrast ratio, wash resistance, water permeability, and alkali resistance are not reduced, effectively reducing the formulation cost.

[0099] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing high-hiding calcium carbonate, characterized in that: It includes the following steps: (1) wet grinding the calcium carbonate slurry and the grinding aid to obtain a primary slurry; (2) wet-grinding the primary slurry and the grinding aid to obtain wet-process heavy calcium carbonate; (3) modifying the wet-process heavy calcium carbonate, light calcium carbonate and the modifier to obtain the high-hiding calcium carbonate; Calcium carbonate is prepared from limestone ore; The grinding aid in step (2) comprises sodium polycarboxylate, an acrylate high molecular weight dispersant and ethylene glycol; The mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersant and the ethylene glycol is 1-4:1-4:0.5-1.5; The mass of the grinding aid in step (2) is 4 to 8‰ of the mass of the calcium carbonate in the calcium carbonate slurry in step (1); The crystal morphology of the light calcium carbonate in step (3) is a spindle morphology; The mass ratio of the light calcium carbonate to the wet-process heavy calcium carbonate is 1:3-5; The modifier in step (3) comprises a distyryl biphenyl whitening agent, bis(dioctyl pyrophosphate)ethylene titanate and sodium stearate; The mass ratio of the distyryl biphenyl whitening agent, bis(dioctyl pyrophosphate acyloxy)ethylene titanate and sodium stearate is 0.5-2.5:4-12:1-10; The mass of the modifier is 4 to 10‰ of the sum of the mass of the wet-process heavy calcium carbonate and the light calcium carbonate.

2. The preparation method according to claim 1, wherein The solid content of the calcium carbonate slurry in step (1) is 60-80%, and the particle size of the calcium carbonate in the calcium carbonate slurry is 300-500 mesh; The grinding aid is sodium polyacrylate; The mass of the grinding aid is 2-5‰ of the mass of calcium carbonate in the calcium carbonate slurry.

3. The preparation method according to claim 1 or 2, wherein The medium filling rate of the wet grinding in step (1) is 50-60%; The wet grinding media includes zirconia balls with a diameter of 1.8 to 2.2 mm and zirconia balls with a diameter of 2.3 to 2.7 mm; The mass ratio of the zirconia balls with a diameter of 1.8 to 2.2 mm to the zirconia balls with a diameter of 2.3 to 2.7 mm is 1:2 to 3; The wet grinding time is 20 to 30 minutes, and the rotation speed is 45 to 55 Hz.

4. The preparation method according to claim 3, wherein The medium filling rate of the wet grinding in step (2) is 60-75%; The wet grinding media includes zirconia balls with a diameter of 0.6 to 1 mm and zirconia balls with a diameter of 1.2 to 1.8 mm; The mass ratio of the zirconia balls with a diameter of 0.6 to 1 mm to the zirconia balls with a diameter of 1.2 to 1.8 mm is 2 to 5:1; The wet grinding time is 20 to 30 minutes, and the rotation speed is 45 to 55 Hz.

5. The preparation method according to claim 4, wherein The temperature of the modification treatment in step (3) is 70-90° C. and the time is 15-25 minutes.

6. The high-hiding calcium carbonate obtained by the preparation method according to any one of claims 1 to 5.

7. Use of the high hiding calcium carbonate according to claim 6 in coatings.

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