CN116218257A

CN116218257A - High-coverage calcium carbonate and preparation method and application thereof

Info

Publication number: CN116218257A
Application number: CN202310240632.4A
Authority: CN
Inventors: 徐永华; 甘昆秀; 温云祥; 吴永惠; 李永峰
Original assignee: Lianzhou Guangyuan Calcium Carbonate Co ltd; Qingyang Guangyuan New Material Co ltd; Jiangxi Guangyuan Chemical Co Ltd
Current assignee: Lianzhou Guangyuan Calcium Carbonate Co ltd; Qingyang Guangyuan New Material Co ltd; Jiangxi Guangyuan Chemical Co Ltd
Priority date: 2023-03-14
Filing date: 2023-03-14
Publication date: 2023-06-06

Abstract

The invention belongs to the technical field of inorganic fillers, and provides high-coverage calcium carbonate, a preparation method and application thereof, and solves the problem of excessive consumption of titanium dioxide in a coating. The method comprises the steps of carrying out wet grinding on calcium carbonate slurry and grinding aid to obtain primary slurry; wet grinding is carried out on the primary slurry and the grinding aid, so as to obtain wet heavy calcium carbonate; and carrying out modification treatment on the wet heavy calcium carbonate, the light calcium carbonate and the modifier to obtain the high-coverage calcium carbonate. The invention adopts a wet tandem grinding process, and prepares the superfine heavy calcium carbonate (the content of 2um is more than or equal to 85 percent) by adjusting the size and the filling rate of grinding media in two stages of wet grinding and selecting grinding aids. The calcium carbonate provided by the invention can reduce the titanium dioxide content by 15-20% in the emulsion paint formula system, and effectively reduce the formula cost.

Description

High-coverage calcium carbonate and preparation method and application thereof

Technical Field

The invention relates to the technical field of inorganic fillers, in particular to high-coverage calcium carbonate and a preparation method and application thereof.

Background

Titanium white is one of the best world hiding power white pigments found so far, and the hiding power is 5-10 times that of other white pigments. Therefore, the titanium pigment is widely applied to the fields of paint, plastics, paper making and the like to play the role of white pigment, wherein the paint field is the maximum application field of titanium pigment, and particularly the maximum use amount of inner and outer wall emulsion paint.

However, the price of the titanium dioxide is fluctuating in the interval of more than 1 ten thousand yuan/ton for a long time, the price is high, the cost of the formula is often large when the titanium dioxide is applied downstream, the cost of the formula is high when the adding amount is excessive, and the use of the titanium dioxide is more and more limited along with the EU to list the titanium dioxide as suspected carcinogen. Therefore, development of partial titanium dioxide substitutes is increasingly urgent from the standpoint of formulation cost and sustainable development.

At present, the main titanium dioxide substitution ideas in the interior and exterior wall emulsion paint mainly comprise two: 1. the covering power of a paint film is improved by introducing the dry covering power of air; 2. ultrafine mineral filler is adopted to be compounded with the titanium dioxide, so that flocculation of the titanium dioxide is reduced, and the utilization rate of the titanium dioxide is improved. The air dry covering power is introduced by adopting superfine filler, but when the adding amount of the superfine filler is too small, the generated porosity is insufficient, the covering power of a paint film is not obviously improved, and when the adding amount of the superfine filler is too large, the porosity is enough, but the washing resistance of the paint is easily obviously reduced due to larger oil absorption of the superfine filler, and the use requirement cannot be met; the idea of compounding the mineral filler and the titanium dioxide is generally carried out in a wet state, and particles are easy to agglomerate in the subsequent drying process, so that the compounding effect is greatly reduced, and the covering performance of a final product is affected. Therefore, the current mainstream research is to replace titanium dioxide in the direction of path 1. However, if partial substitution of titanium pigment is to be realized by the idea of the path 1, it is necessary to control the oil absorption of the ultra-fine filler used within a certain range while improving the porosity of the coating, so as to ensure that the properties such as the washing resistance of the paint film are not degraded.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides high-coverage calcium carbonate and a preparation method and application thereof.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of high-coverage calcium carbonate, which comprises the following steps:

(1) Carrying out wet grinding on the calcium carbonate slurry and the grinding aid to obtain primary slurry;

(2) Wet grinding is carried out on the primary slurry and the grinding aid, so as to obtain wet heavy calcium carbonate;

(3) And carrying out modification treatment on the wet heavy calcium carbonate, the light calcium carbonate and the modifier to obtain the high-coverage calcium carbonate.

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

the grinding aid is sodium polyacrylate;

the mass of the grinding aid is 2-5 per mill of the mass of calcium carbonate in the calcium carbonate slurry.

Preferably, the wet grinding in the step (1) has a medium filling rate of 50 to 60 percent;

the wet grinding medium comprises zirconia balls with the diameter of 1.8-2.2 mm and zirconia balls with the diameter of 2.3-2.7 mm;

the mass ratio of the zirconia balls with the diameters of 1.8-2.2 mm to the zirconia balls with the diameters of 2.3-2.7 mm is 1:2 to 3;

the wet grinding time is 20-30 min, and the rotating speed is 45-55 HZ.

Preferably, 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 dispersing agent and the ethylene glycol is 1-4: 1 to 4:0.5 to 1.5;

the mass of the grinding aid in the step (2) is 4-8 per mill of the mass of the calcium carbonate in the calcium carbonate slurry in the step (1).

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

the wet grinding medium comprises zirconia balls with the diameter of 0.6-1 mm and zirconia balls with the diameter of 1.2-1.8 mm;

the mass ratio of the zirconia balls with the diameters of 0.6-1 mm to the zirconia balls with the diameters of 1.2-1.8 mm is 2-5: 1, a step of;

the wet grinding time is 20-30 min, and the rotating speed is 45-55 HZ.

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

the mass ratio of the light calcium carbonate to the wet heavy calcium carbonate is 1:3 to 5.

Preferably, the modifier in step (3) comprises distyryl biphenyl type whitening agent, bis (dioctyl pyrophosphoryloxy) ethylene titanate and sodium stearate;

the mass ratio of the distyryl biphenyl brightening agent to the bis (dioctyl pyrophosphoryloxy) ethylene titanate to the sodium stearate is 0.5-2.5: 4-12: 1 to 10;

the mass of the modifier is 4-10 per mill of the mass sum of wet heavy calcium carbonate and light calcium carbonate.

Preferably, the temperature of the modification treatment in the step (3) is 70 to 90 ℃ and the time is 15 to 25min.

The invention also provides the high-coverage calcium carbonate obtained by the preparation method.

The invention also provides application of the high-coverage calcium carbonate in a coating.

The invention provides a preparation method of high-coverage calcium carbonate, which comprises the following steps: carrying out wet grinding on the calcium carbonate slurry and the grinding aid to obtain primary slurry; wet grinding is carried out on the primary slurry and the grinding aid, so as to obtain wet heavy calcium carbonate; and carrying out modification treatment on the wet heavy calcium carbonate, the light calcium carbonate and the modifier to obtain the high-coverage calcium carbonate. The invention adopts a wet tandem grinding process, and prepares the superfine heavy calcium carbonate (the content of 2um is more than or equal to 85 percent) by adjusting the size and the filling rate of grinding media in two stages of wet grinding and selecting grinding aids.

According to the invention, the light calcium carbonate with the spindle-shaped crystal morphology and the wet heavy calcium carbonate are selected for compounding, the spindle-shaped particles can furthest improve the porosity in the process of stacking the particles, when the composite material is applied to emulsion paint, enough air dry covering power can be provided under the condition of less additive amount, meanwhile, the porosity of a product is strictly controlled by controlling the proportion of the light calcium carbonate to the heavy calcium carbonate, the conditions of too high porosity, reduced water resistance, washing resistance and the like of a paint film, too low porosity, insufficient covering power and the like are avoided, and meanwhile, the specific modifier is adopted, so that the functions of increasing whiteness, improving dispersibility, reducing oil absorption and the like can be simultaneously realized.

The calcium carbonate provided by the invention is high-coverage calcium carbonate for emulsion paint, and the flocculation of titanium dioxide is reduced, the utilization rate of titanium dioxide is improved, the titanium dioxide content of 15-20% in an emulsion paint formula system can be reduced under the condition that the performances of paint film such as brushing resistance, water resistance and the like are not reduced by properly introducing the dry coverage of air, and the formula cost of the emulsion paint is effectively reduced.

Detailed Description

In the invention, the calcium carbonate is prepared from limestone ore, and the calcium carbonate content of the limestone ore is preferably more than or equal to 80%, more preferably more than or equal to 85%, and even more preferably more than or equal to 90%; the limestone ore is cleaned and naturally dried, and then coarse stone is obtained through two coarse crushing; and (3) carrying out ring roller grinding and classification on the coarse stone to obtain calcium carbonate.

In the invention, limestone ore is selected as raw ore, and the limestone ore has a denser texture than calcite ore, so that the oil absorption is lower under the condition of the same particle size, and the produced product has obvious improvement on the washing resistance when being applied to emulsion paint because the limestone ore component generally contains 1-3% of silicon dioxide.

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

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

In the invention, the grinding aid in the step (1) is sodium polyacrylate, and plays a role in reducing the viscosity of the slurry and improving the solid content of the slurry.

In the present invention, the mass of the grinding aid is preferably 2 to 5% by mass, more preferably 3 to 4% by mass, and even more preferably 3.4 to 3.6% by mass of the calcium carbonate in the calcium carbonate slurry.

In the invention, the calcium carbonate slurry and the grinding aid are mixed and then subjected to wet grinding, wherein the rotation speed of the mixing is preferably 45-55 HZ, more preferably 46-54 HZ, and even more preferably 48-52 HZ; the time is preferably 5 to 15 minutes, more preferably 6 to 14 minutes, and still more preferably 8 to 12 minutes.

In the present invention, the dielectric filling rate of the wet grinding in the step (1) is preferably 50 to 60%, more preferably 52 to 58%, and still more preferably 54 to 56%.

In the present invention, the wet-grinding medium preferably contains zirconia balls having a diameter of 1.8 to 2.2mm and zirconia balls having a diameter of 2.3 to 2.7mm, more preferably contains zirconia balls having a diameter of 1.9 to 2.1mm and zirconia balls having a diameter of 2.4 to 2.6mm, and still more preferably contains zirconia balls having a diameter of 2mm and zirconia balls having a diameter of 2.5 mm.

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

In the invention, because the particle size of the calcium carbonate is large, a large-size grinding medium is needed to provide enough kinetic energy for crushing, for example, the grinding medium is too small in size and insufficient in kinetic energy, and a separation system of the grinding medium and slurry is easy to be blocked.

In the present invention, the wet grinding time is preferably 20 to 30 minutes, more preferably 22 to 28 minutes, and still more preferably 24 to 26 minutes; the rotation speed is preferably 45 to 55HZ, more preferably 46 to 54HZ, and still more preferably 48 to 52HZ.

In the invention, after wet grinding in the step (1), the primary slurry has the following particle size after detection: d50 is 4.5-5.5 mu m, D97 is 8.5-10.0 mu m, and the mass of the component smaller than 2 mu m is more than or equal to 35%.

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

In the present invention, the acrylic ester high molecular weight dispersant is of the type HD2021.

In the invention, the mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersing agent and the ethylene glycol is preferably 1-4: 1 to 4:0.5 to 1.5, more preferably 2 to 3: 2-3: 0.6 to 1.4, more preferably 2.4 to 2.6:2.4 to 2.6:0.8 to 1.2.

In the invention, the sodium polycarboxylate is an anionic dispersing agent, has excellent water resistance and can prevent particle agglomeration through electrostatic repulsion; the acrylate high molecular weight dispersant can provide a remarkable steric hindrance effect and further prevent agglomeration among ultrafine particles; the glycol mainly plays a role of assisting in reducing the surface energy of the particles.

In the present invention, the mass of the grinding aid in the step (2) is preferably 4 to 8% by weight, more preferably 5 to 7% by weight, and still more preferably 5.5 to 6.5% by weight of the calcium carbonate in the calcium carbonate slurry in the step (1).

In the invention, the primary slurry and the grinding aid are mixed and then subjected to wet grinding; the stirring speed of the mixing is preferably 45 to 55HZ, more preferably 46 to 54HZ, still more preferably 48 to 52HZ, and the stirring time is preferably 5 to 10min, more preferably 6 to 9min, still more preferably 7 to 8min.

In the present invention, the wet-grinding medium filling rate in the step (2) is preferably 60 to 75%; more preferably 65 to 70%, still more preferably 66 to 68%.

In the present invention, the wet-grinding medium preferably contains zirconia balls having a diameter of 0.6 to 1mm and zirconia balls having a diameter of 1.2 to 1.8mm, more preferably contains zirconia balls having a diameter of 0.7 to 0.9mm and zirconia balls having a diameter of 1.3 to 1.7mm, and still more preferably contains zirconia balls having a diameter of 0.8mm and zirconia balls having a diameter of 1.4 to 1.6 mm.

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

in the invention, the secondary wet superfine grinding stage adopts the grinding medium with small particle size, so that the contact area is large, superfine wet grinding is more facilitated, and the grinding efficiency is improved.

In the invention, after wet grinding in the step (2), a slurry system is obtained, and the slurry system is detected to have the following particle size: d50 is 1.0-1.5 mu m, D97 is 2.0-2.5 mu m, and the mass of the component smaller than 2 mu m is more than or equal to 90%.

In the invention, the slurry system is subjected to flash evaporation drying, cloth bag collection and sieving to obtain wet heavy calcium carbonate; the particle size is detected as follows: d50 is 1.2-1.7 mu m, D97 is 2.3-2.8 mu m, and the mass of the component smaller than 2 mu m is more than or equal to 80%.

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

In the invention, the crystal morphology of the light calcium carbonate is selected as spindle morphology, compared with spherical and cubic light calcium carbonate, the spindle morphology can improve the porosity to the greatest extent in the stacking process, and when the light calcium carbonate is applied to emulsion paint, the light calcium carbonate can provide enough air dry covering power under the condition of less addition amount.

In the invention, the mass ratio of the light calcium carbonate to the wet heavy calcium carbonate is preferably 1:3 to 5, more preferably 1:3.5 to 4.5, more preferably 1:3.8 to 4.2.

In the invention, when the ratio of the light calcium carbonate to the wet heavy calcium carbonate is too high in a reasonable mass ratio range, the oil absorption of the composite powder is larger, the porosity in stacking is too high, and when the composite powder is applied to downstream emulsion paint, although the dry coverage of a paint film is higher, indexes such as washing resistance, water resistance and the like can show obvious descending trend due to obvious descending of the compactness of the paint film, if the ratio of the light calcium carbonate is too low, enough porosity cannot be provided, and the introduced air is insufficient in dry coverage, so that the coverage is not obviously promoted.

In the invention, light calcium carbonate and wet heavy calcium carbonate are mixed firstly, and modifier is added for modification after the mixing is finished; the temperature of the mixing is preferably 70 to 90 ℃, more preferably 75 to 85 ℃, and even more preferably 78 to 82 ℃; the time is preferably 10 to 15 minutes, more preferably 11 to 14 minutes, and still more preferably 12 to 13 minutes.

In the present invention, the modifier in step (3) preferably comprises distyryl biphenyl type whitening agent, bis (dioctyl pyrophosphoryloxy) ethylene titanate and sodium stearate.

In the present invention, the distyryl biphenyl type whitening agent is FBA351.

In the invention, the model of the bis (dioctyl pyrophosphoryloxy) ethylene titanate is HY-311.

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

In the invention, the distyryl biphenyl brightening agent improves the whiteness of the product, and prevents the influence on the hue of the product due to dark paint film caused by lower whiteness of limestone; the addition of the di (dioctyl pyrophosphoryloxy) ethylene titanate can improve the dispersibility of calcium carbonate to titanium dioxide; sodium stearate mainly plays a role in reducing the oil absorption of the product.

In the present invention, the mass of the modifier is preferably 4 to 10% by mass, more preferably 5 to 9% by mass, and even more preferably 7 to 8% by mass of the sum of the mass of the wet heavy calcium carbonate and the mass of the light calcium carbonate.

In the invention, the modifier is added in a mode of mixing the modifier with water and then spraying the mixture, and the mass ratio of the modifier to the water is preferably 1:1 to 3, more preferably 1:1.5 to 2.5, more preferably 1:1.8 to 2.2.

In the present invention, the temperature of the modification treatment in the step (3) is preferably 70 to 90 ℃, more preferably 75 to 85 ℃, still more preferably 78 to 82 ℃; the time is preferably 15 to 25 minutes, more preferably 16 to 24 minutes, and still more preferably 18 to 22 minutes.

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

Example 1

And (3) cleaning and naturally airing limestone ore with the calcium carbonate content of 85%, crushing the limestone ore to obtain coarse stone through two times, and then carrying out ring roller grinding and classification to obtain the calcium carbonate with the particle size of 400 meshes. Preparing calcium carbonate into slurry with the solid content of 60%, and then adding sodium polyacrylate with the mass of 2%o of that of the calcium carbonate, stirring and dispersing for 10min at the rotating speed of 50 HZ; wet grinding is carried out, the medium filling rate of the wet grinding is 50%, and the mass ratio of the zirconia balls with the thickness of 2mm to the zirconia balls with the thickness of 2.5mm is 1:3, grinding for 20min at 49HZ rotation speed to obtain primary slurry, wherein the detected granularity is D50:5.47mm, D97:9.82mm, less than 2um content 36.25%. Adding a grinding aid into the primary slurry, wherein the mass of the grinding aid is 4 per mill of the mass of calcium carbonate in the calcium carbonate slurry, and the mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersant HD2021 and the ethylene glycol in the grinding aid is 2:1:1, stirring for 5min at a rotation speed of 55HZ, then carrying out wet grinding, wherein the medium filling rate of the wet grinding is 60%, and the mass ratio of the zirconia balls of 0.8mm to 1.5mm is 2:1, grinding for 20min at a rotating speed of 50HZ to obtain a slurry system, wherein the detected granularity is D50:1.46um, D97:2.44um, the content of less than 2um is more than or equal to 90.18 percent; flash drying, cloth bag collecting and sieving the slurry system to obtain wet heavy calcium carbonate, wherein the particle size of the detected dry powder is D50:1.68um, D97:2.76um, less than 2um content not less than 81.32%. The spindle morphology of light calcium carbonate (oil absorption 55, sedimentation volume 2.8) and the obtained wet heavy calcium carbonate were mixed according to a ratio of 1:5, mixing for 10min at 70 ℃, preparing a modifier (the mass ratio of the distyryl biphenyl brightening agent FBA351 to the bis (dioctyl pyrophosphoryloxy) ethylene titanate HY-311 to the sodium stearate is 1:5:2), wherein the mass of the modifier is 4 per mill of the mass sum of wet heavy calcium carbonate and light calcium carbonate, and mixing the weighed modifier with water according to the weight ratio of 1:1, then adding the diluted calcium carbonate into the mixed light calcium carbonate and heavy calcium carbonate in a spray mode, and continuously mixing for 15min to finish modification to obtain the high-coverage calcium carbonate.

Example 2

And (3) cleaning and naturally airing limestone ore with the calcium carbonate content of 82%, crushing the limestone ore to obtain coarse stone through two times, and then carrying out ring roller grinding and classification to obtain the calcium carbonate with the particle size of 320 meshes. Preparing calcium carbonate into slurry with 70% of solid content, adding sodium polyacrylate with 3%o of calcium carbonate mass, stirring and dispersing for 15min at a rotating speed of 45 HZ; wet grinding is carried out, the medium filling rate of the wet grinding is 55%, and the mass ratio of the zirconia balls with the thickness of 2mm to the zirconia balls with the thickness of 2.5mm is 1:2, grinding for 25min at a rotating speed of 50HZ to obtain primary slurry, wherein the detected granularity is D50:5.02mm, D97:9.14mm, less than 2um content 39.83%. Adding a grinding aid into the primary slurry, wherein the mass of the grinding aid is 6 per mill of the mass of calcium carbonate in the calcium carbonate slurry, and the mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersant HD2021 and the ethylene glycol in the grinding aid is 2:2:1, stirring for 10min at a rotating speed of 50HZ, then carrying out wet grinding, wherein the medium filling rate of the wet grinding is 65%, and the mass ratio of the zirconia balls of 0.8mm to 1.5mm is 3:1, grinding for 25min at a rotating speed of 55HZ to obtain a slurry system, wherein the detected granularity is D50:1.22um, D97:2.18um, less than 2um content more than or equal to 92.02 percent; flash drying, cloth bag collecting and sieving the slurry system to obtain wet heavy calcium carbonate, wherein the particle size of the detected dry powder is D50:1.42um, D97:2.48um, less than 2um content is more than or equal to 82.67 percent. The spindle morphology of light calcium carbonate (oil absorption 60, sedimentation volume 3.1) and the obtained wet heavy calcium carbonate were mixed according to a ratio of 1:4, mixing for 15min at 80 ℃, preparing a modifier (the mass ratio of the distyryl biphenyl brightening agent FBA351 to the bis (dioctyl pyrophosphoryloxy) ethylene titanate HY-311 to the sodium stearate is 1:11:4), wherein the mass of the modifier is 8 per mill of the mass sum of wet heavy calcium carbonate and light calcium carbonate, and weighing the modifier and water according to the weight ratio of 1:2, diluting the mixture in a mass ratio, then adding the diluted mixture into the mixed light calcium carbonate and heavy calcium carbonate in a spray mode, and continuously mixing for 20 minutes to finish modification to obtain the high-coverage calcium carbonate.

Example 3

And (3) cleaning and naturally airing limestone ore with 83% of calcium carbonate content, crushing the limestone ore twice to obtain coarse stone, and carrying out ring roller grinding and classification to obtain the calcium carbonate with 480 meshes. Preparing calcium carbonate into slurry with the solid content of 75%, and then adding sodium polyacrylate with the mass of 4%o of that of the calcium carbonate, stirring and dispersing for 10min at the rotating speed of 55 HZ; wet grinding is carried out, the medium filling rate of the wet grinding is 60%, and the mass ratio of the zirconia balls with the thickness of 2mm to the zirconia balls with the thickness of 2.5mm is 1:3, grinding for 30min at a 45HZ rotating speed to obtain primary slurry, wherein the detected granularity is D50:4.62mm, D97:8.71mm, less than 2um content 44.32%. Adding a grinding aid into the primary slurry, wherein the mass of the grinding aid is 8 per mill of the mass of calcium carbonate in the calcium carbonate slurry, and the mass ratio of the sodium polycarboxylate, the acrylic ester high molecular weight dispersant HD2021 and the ethylene glycol in the grinding aid is 3:4:1, stirring for 10min at a rotating speed of 50HZ, then carrying out wet grinding, wherein the medium filling rate of the wet grinding is 70%, and the mass ratio of the zirconia balls of 0.8mm to 1.5mm is 2:1, grinding for 30min at 49HZ rotation speed to obtain a slurry system, wherein the detected granularity is D50:1.09um, D97:2.04um, less than 2um content more than or equal to 95.66 percent; flash drying, cloth bag collecting and sieving the slurry system to obtain wet heavy calcium carbonate, wherein the particle size of the detected dry powder is D50:1.26um, D97: the content of less than 2um is more than or equal to 84.22 percent and is 2.31 um. The spindle morphology of light calcium carbonate (oil absorption 58, sedimentation volume 2.5) and the obtained wet heavy calcium carbonate were mixed according to a ratio of 1:3, mixing for 15min at 90 ℃, then preparing a modifier (the mass ratio of the distyryl biphenyl brightening agent FBA351, the bis (dioctyl pyrophosphoryloxy) ethylene titanate HY-311 and sodium stearate is 2:9:9), wherein the mass of the modifier is 10 per mill of the mass sum of wet heavy calcium carbonate and light calcium carbonate, and weighing the modifier and water according to the weight ratio of 1:3, diluting the mixture according to the mass ratio, then adding the diluted mixture into the mixed light calcium carbonate and heavy calcium carbonate in a spray mode, and continuously mixing for 25 minutes to finish modification to obtain the high-coverage calcium carbonate.

The high coverage calcium carbonate prepared in examples 1 to 3 was subjected to correlation index detection according to HG/T3249-2013, and the results are shown in Table 1.

TABLE 1 index detection results

	Example 1	Example 2	Example 3
				Whiteness degree	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
				Content of less than or equal to 2um (%)	76.32	71.62	65.88
Oil absorption (ml/100 g)	22	24	26
				Moisture (%)	0.21	0.20	0.22

The high coverage calcium carbonate prepared in examples 1-3 was used in latex paints to replace 20% of the titanium dioxide in the formulation, compared to the original formulation and tested against the relevant standards, and the latex paint formulation is shown in table 2.

Table 2 latex paint formulation

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The latex paints described above were subjected to performance testing and the results are reported in table 3.

TABLE 3 latex paint Performance test results

	0#	1#	2#	3#	Test standard
						Contrast ratio	0.9562	0.9566	0.9588	0.9590	GB/T23981.1-2019
Number of times of washing resistance	526	570	552	530	GB/T9266-2009
						Water permeability/ml	1.0	1.0	0.9	1.0	GB/T9755-2014
Alkali resistance (48 h)	No abnormality	No abnormality	No abnormality	No abnormality	GB/T9755-2014

From the above examples, the present invention provides a method for preparing high coverage calcium carbonate, wherein a primary slurry is obtained by wet grinding a calcium carbonate slurry and a grinding aid; wet grinding is carried out on the primary slurry and the grinding aid, so as to obtain wet heavy calcium carbonate; and carrying out modification treatment on the wet heavy calcium carbonate, the light calcium carbonate and the modifier to obtain the high-coverage calcium carbonate. When the calcium carbonate prepared by the invention is applied to emulsion paint, 20% of titanium dioxide content in the formula can be replaced under the condition that indexes such as contrast ratio, washing resistance times, water permeability and alkali resistance of the product are not reduced, and the formula cost is effectively reduced.

The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims

1. A method for preparing high coverage calcium carbonate, which is characterized by comprising the following steps:

2. The method according to claim 1, wherein the solid content of the calcium carbonate slurry in the step (1) is 60 to 80%, and the particle size of the calcium carbonate in the calcium carbonate slurry is 300 to 500 mesh;

the grinding aid is sodium polyacrylate;

3. The method of claim 1 or 2, wherein the wet-milled medium filling rate in step (1) is 50 to 60%;

the wet grinding time is 20-30 min, and the rotating speed is 45-55 HZ.

4. The method of claim 3 wherein in step (2) the grinding aid comprises sodium polycarboxylate, acrylate high molecular weight dispersant and ethylene glycol;

5. The method according to claim 1 or 4, wherein the wet-grinding medium filling rate in step (2) is 60 to 75%;

the wet grinding time is 20-30 min, and the rotating speed is 45-55 HZ.

6. The method of claim 5, wherein the morphology of the crystals of the light calcium carbonate in step (3) is spindle morphology;

7. The method of preparing according to claim 6, wherein the modifier in step (3) comprises distyryl biphenyl type whitening agent, bis (dioctyl pyrophosphoryloxy) ethylene titanate, and sodium stearate;

8. The method according to claim 1, 6 or 7, wherein the temperature of the modification treatment in the step (3) is 70 to 90℃for 15 to 25 minutes.

9. The high coverage calcium carbonate obtained by the process of any one of claims 1 to 8.

10. Use of the high hiding calcium carbonate as claimed in claim 9 in a coating material.