High-whiteness coating-grade calcium carbonate slurry and preparation method thereof

Abstract

The invention provides a preparation method of high-whiteness coating-grade calcium carbonate slurry, which comprises the following steps: mixing stone powder with the mass percentage of Fe2O3 less than or equal to 0.1% with water, adding a dispersing agent into the water before or during mixing, and uniformly stirring to prepare calcium carbonate slurry; putting the calcium carbonate slurry into a sand mill for multi-stage wet grinding, and adding a dispersing agent in the grinding process; and grinding until the content of calcium carbonate with the particle size range of less than or equal to 2 microns in the slurry is greater than or equal to 95.0% in percentage by mass, and sieving the slurry to obtain the high-whiteness coating-grade calcium carbonate slurry. According to the invention, the high-whiteness coating-grade calcium carbonate slurry is prepared by adopting the stone powder with a specific specification through multi-stage wet grinding and can be used for partially replacing pigment china clay in papermaking coatings, so that the whiteness, glossiness, hiding rate and other indexes of the coatings are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking coated calcium carbonate preparation, in particular to a high-whiteness coating-grade calcium carbonate slurry and a preparation method thereof. Background Art

[0002] China clay is one of the important pigments in papermaking coatings, but the price of China clay used in papermaking coatings is relatively high, which affects the production cost of papermaking. The use of ordinary calcium carbonate to replace the pigment China clay in coatings will affect the quality indicators of paper such as brightness and opacity.

[0003] Heavy calcium carbonate, also known as ground calcium carbonate (GCC); also known as Kotamite in the United States, common names: heavy calcium, single fly powder, double fly powder, triple fly powder, quadruple fly powder. There are two production processes for heavy calcium carbonate: (1) Dry method: First, hand-select calcite, limestone, chalk, shells, etc. shipped from the quarry to remove the gangue, then use a crusher to coarsely crush the limestone, and then use a Raymond (swing) mill to crush it into fine limestone powder. Finally, use a disperser to grade the ground powder, and package the powder that meets the fineness requirements as a product and put it into storage, otherwise it will be returned for re-grinding. (2) Wet method: First, make the dry fine powder into a suspension and place it in a mill for further crushing. After dehydration and drying, ultrafine heavy calcium carbonate is obtained.

[0004] Characteristics of heavy calcium carbonate: irregular particle shape, certain angularity, rough surface, wide particle size distribution, average particle size is generally 1-10μm. Heavy calcium carbonate is divided into coarse ground calcium carbonate>3μm; fine ground calcium carbonate 1-3μm; ultrafine calcium carbonate 0.5-1μm according to its original average particle size (d).

[0005] Physical and chemical properties of heavy calcium carbonate: Chemical formula: CaCO 3 ; Relative molecular mass: 100.09; relative density is 2.7-2.9, the Mohs hardness of calcite is 3, aragonite is 3.5-4, the sedimentation volume of heavy calcium carbonate is 1.2-1.9 mL / g, and the specific surface area is 1m 2 / g or so.

[0006] Deep processing of inorganic mineral calcite powder and limestone powder to replace pigment clay in paper coatings without affecting paper quality has become the focus of technical research in the papermaking industry. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-whiteness coating-grade calcium carbonate slurry and a preparation method thereof, which partially replaces pigment clay and overcomes the problem in the prior art that ordinary calcium carbonate slurry is used to replace pigment clay in papermaking coatings and cannot ensure the whiteness, brightness and opacity of paper.

[0008] The present invention is achieved by adopting the following technical solutions:

[0009] A method for preparing a high-whiteness coating-grade calcium carbonate slurry comprises the following steps:

[0010] S1, Fe 2 O 3 The stone powder with a mass percentage of ≤0.1% is mixed with water, and a dispersant is added to the water before or during mixing and stirred to form a calcium carbonate slurry;

[0011] S2, placing the calcium carbonate slurry into a sand mill for multi-stage wet grinding, and adding a dispersant during the grinding process;

[0012] S3. When the calcium carbonate with a particle size range of ≤2 μm in the slurry is ground to a mass percentage of ≥95.0%, the slurry is sieved to obtain the high-whiteness coating-grade calcium carbonate slurry.

[0013] The stone powder is calcite powder or limestone powder. The inventor unexpectedly found that in the conventional calcium carbonate slurry preparation process, calcite powder or limestone powder is made into slurry and then passed through a screen with a magnetic iron remover to remove impurities and reduce Fe 2 O 3 Compared with the content, the present invention directly selects Fe 2 O 3 The calcium carbonate slurry can be prepared by using stone powder with a mass percentage of ≤0.1%, which can greatly improve the whiteness and opacity of the calcium carbonate slurry. The inventors have completed the present invention based on the above findings.

[0014] Preferably, the Fe in step S1 2 O 3 The stone powder with a mass percentage of ≤0.1% is prepared by the following method: calcite or limestone is coarsely crushed by a crusher, primary iron removal is performed by a magnetic iron remover, then pulverized into fine powder by a grinding mill, secondary iron removal is performed by a magnetic iron remover, and finally the stone powder is obtained after passing the grading inspection.

[0015] Preferably, the stone powder has a fineness range of 100-1000 mesh and a whiteness of not less than 92%. Too coarse or too fine stone powder is not conducive to obtaining a calcium carbonate slurry with a narrow particle size distribution, thereby reducing the stability of product quality. Stone powder with too low whiteness is not conducive to obtaining a high-whiteness calcium carbonate slurry.

[0016] Preferably, based on the dispersant mass solid content of 42 wt%, the amount of dispersant added in step S1 is 0.1-1% of the mass of the stone powder.

[0017] Preferably, the multi-stage wet grinding is to use a sand mill to perform two or more stages of graded grinding, and more preferably, three or more stages of graded grinding are used.

[0018] Preferably, based on the dispersant mass solid content of 42 wt%, the amount of dispersant added in step S2 is 1.5-4% of the mass of the stone powder.

[0019] The dispersant used in steps S1 and S2 is not particularly limited, and a calcium carbonate grinding dispersant commonly used in the art can be used.

[0020] Preferably, in step S1, stone powder and water are mixed in a weight ratio of (2-3):1.

[0021] Preferably, in step S1, the stirring time is 5-30 minutes, with the stone powder being uniformly dispersed in water to form a uniform slurry.

[0022] Preferably, in step S3, the mesh number of the sieve used for sieving is ≥100 meshes.

[0023] The high-whiteness coating-grade calcium carbonate slurry of the present invention has the following characteristics: by mass percentage, the content of calcium carbonate particles with a particle size of ≤2μm in the slurry is ≥95%, the solid content is ≥74.0%, the 325-mesh sieve residue is ≤0.005%, the 635-mesh sieve residue is ≤0.02%, the acid-insoluble matter is ≤0.7%, the pH value is 8.0-11.0, the viscosity is ≤500cps, and the whiteness is ≥94.5%.

[0024] The invention adopts stone powder of specific specifications to prepare high-whiteness coating-grade calcium carbonate slurry, which can partially replace the pigment clay in papermaking coatings and significantly improve the whiteness, glossiness, hiding power and other indicators of the coatings. DETAILED DESCRIPTION

[0025] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only used as examples, but are not used to limit the scope of the present invention. Those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalent solutions, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0026] The instruments or raw materials in the present invention without indicating the manufacturer are all conventional commercial instruments or raw materials.

[0027] Unless otherwise mentioned, the detection indexes involved in the embodiments of the present invention are detected by conventional detection methods in the art. The whiteness (i.e., D65 brightness) of the paper sample is measured according to GB / T7974-2013, the opacity is measured according to GB / T1543-2005, and the particle size is measured by a fully automatic X-ray sedimentation particle size analyzer SediGraph III Plus-5125.

[0028] Example 1

[0029] 325 mesh calcite powder (whiteness ≥ 92%, Fe 2 O 3 (%) ≤0.1%) slurry, calcite powder and water, neutral polyacrylate dispersant in a weight ratio of 3:1:0.002. First add the water and dispersant in the set proportion, open the dispersion pot and stir at the same time, then start adding calcite powder, stir thoroughly, mix evenly, so that the slurry has good fluidity, and then use a wet ultrafine medium grinder for three-stage grinding. During the grinding process, each grinder drips the dispersant. The amount of dispersant used during the grinding process is 42% solid content dispersant and calcite powder dry ratio is 2.7%, and the dispersant in three grinders is divided into three equal parts and added in equal amounts. Grind into calcium carbonate slurry with a particle size of ≤2μm and a content of ≥96.5%. Then filter using a 400-mesh sieve suspension vibrating screen. The indicators of the high-whiteness coating-grade calcium carbonate slurry are as follows: the content of calcium carbonate particles with a particle size of ≤2μm is ≥96.5%; the solid content is ≥74.0%; the 325-mesh sieve residue is ≤0.005%; the 635-mesh sieve residue is ≤0.02%; the acid-insoluble matter is ≤0.4%; the pH value is 8.0-10.0; the viscosity is ≤500cps; and the whiteness is ≥94.5%.

[0030] Comparative Example 1

[0031] Calcite powder without prior iron removal is selected, and after the stone powder is dispersed, the slurry is passed through a screen with an iron remover to remove iron, and the other processes are the same as in Example 1. The specific steps are as follows:

[0032] The 325 mesh calcite powder (whiteness ≥ 92%) is slurried, and the weight ratio of calcite powder to water and neutral polyacrylate dispersant is 3:1:0.002. First, add the water and dispersant in the set proportion, open the dispersion pot and stir at the same time, then start to add calcite powder, stir well, mix evenly, so that the slurry has good fluidity, the slurry passes through the filter screen, and the combined magnet frame iron remover is installed in the screen to remove debris and iron; then use a wet ultrafine medium grinder for three-stage grinding, and each grinder is dripped with dispersant during the grinding process. The amount of dispersant used in the grinding process is 42% solid content dispersant and calcite powder dry ratio is 2.7%, and the dispersant is divided into three equal parts in three grinders and added in equal amounts. Grind into calcium carbonate slurry with a particle size of ≤2μm and a content of ≥96.5%. Then use a 400-mesh screen to filter. The indicators of the prepared ordinary coating-grade calcium carbonate slurry are: the content of calcium carbonate particles with a particle size of ≤2μm is ≥96.5%; the solid content is ≥74.0%; the 325-mesh sieve residue is ≤0.005%; the 635-mesh sieve residue is ≤0.02%; the acid-insoluble matter is ≤0.5%; the pH value is 8.0-10.0; the viscosity is ≤300cps; and the whiteness is ≥91%.

[0033] The whiteness (i.e., D65 brightness), opacity and other conventional indexes of each embodiment and comparative example sample were tested. The test results are shown in Table 1.

[0034] Table 1 Sample test data

[0035]

[0036]

[0037] It can be seen from the test results that the product obtained by the method of the present invention has higher whiteness and better opacity than that obtained by the conventional method.

[0038] It should be understood by those skilled in the art that the above embodiments are only examples and do not limit the present invention. The purpose of the present invention has been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and explained in the embodiments, and the embodiments of the present invention may be deformed or modified in any way without departing from the principles.

Claims

1. A method for preparing a high-whiteness coating-grade calcium carbonate slurry, characterized in that: The steps include: S1. Mixing stone powder with a Fe2O3 mass percentage of ≤0.1% with water, adding a dispersant to the water before or during mixing and stirring to form a calcium carbonate slurry; S2, placing the calcium carbonate slurry into a sand mill for multi-stage wet grinding, and adding a dispersant during the grinding process; S3. When the calcium carbonate with a particle size range of ≤2 μm in the slurry is ground to a mass percentage of ≥95.0%, the slurry is sieved to obtain the high-whiteness coating-grade calcium carbonate slurry.

2. The method according to claim 1, characterized in that The stone powder with a Fe2O3 mass percentage of ≤0.1% in step S1 is prepared by the following method: coarsely crushing the calcite or limestone with a crusher, performing primary iron removal with a magnetic iron remover, then grinding it into fine powder with a grinding mill, performing secondary iron removal with a magnetic iron remover, and finally obtaining the stone powder after passing the grading inspection.

3. The method according to claim 1, characterized in that The stone powder has a fineness range of 100-1000 meshes and a whiteness of not less than 92%.

4. The method according to claim 1, characterized in that Based on the dispersant mass solid content of 42wt%, the amount of dispersant added in step S1 is 0.1-1% of the mass of the stone powder.

5. The method according to claim 1, characterized in that The multi-stage wet grinding is to use a sand mill to perform two or more graded grindings.

6. The method according to claim 1, characterized in that Based on the dispersant mass solid content of 42wt%, the amount of dispersant added in step S2 is 1.5-4% of the mass of the stone powder.

7. The method according to claim 1, characterized in that In step S1, stone powder and water are mixed in a weight ratio of (2-3):

1.

8. The method according to claim 1, characterized in that In step S1, the stirring time is 5-30 minutes, with the stone powder being uniformly dispersed in water to form a uniform slurry.

9. The method according to claim 1, characterized in that In step S3, the mesh number of the sieve used for sieving is ≥100 meshes.

10. The high whiteness coating grade calcium carbonate slurry prepared by the method according to any one of claims 1 to 9, characterized in that: Calculated by mass percentage, the content of calcium carbonate particles with a particle size of ≤2 μm in the slurry is ≥95%, the solid content is ≥74.0%, the 325-mesh sieve residue is ≤0.005%, the 635-mesh sieve residue is ≤0.02%, the acid insoluble matter is ≤0.7%, the pH value is 8.0-11.0, the viscosity is ≤500 cps, and the whiteness is ≥94.5%.

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