Low-alkalinity dolomite powder as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of inorganic materials, and provides low-alkalinity dolomite powder as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing coarse dolomite powder and a grinding aid solution, and carrying out ball milling to obtain superfine dolomite powder; mixing the superfine dolomite powder with the modifier solution I, and carrying out surface modification to obtain primary modified dolomite powder; and mixing the primary modified dolomite powder with the modifier solution II, and carrying out surface modification. According to the invention, dibutyl phosphate and a polymeric dispersant containing an acidic group are compounded as a wear-resistant auxiliary agent, so that the wear-resistant auxiliary agent has a grinding aiding effect, and meanwhile, the pH value of the particle surface is adjusted, and the alkalinity is reduced; polyester is firstly adopted for primary modification, and then a compound modifier of amino epoxy phosphate and methacryloyloxyethyl phosphate is adopted for secondary modification, so that the flowability of the dolomite powder and the compatibility of the dolomite powder and resin in the coil coating are improved; the crosslinking density and the leveling property of a coating film can be considered, and the solvent wiping resistance and the ultraviolet aging resistance of the coating film are improved.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic materials, and in particular to low-alkalinity dolomite powder and a preparation method and application thereof. Background Art

[0002] The main components of dolomite are CaCO3 and MgCO3. It is a trigonal carbonate mineral with a crystal structure similar to that of calcite. It is widely used in building materials, ceramic materials, glass and refractory materials. Dolomite has the characteristics of high whiteness, dense particles, low price and easy availability, and the price of raw ore is significantly lower than that of calcite. Therefore, dolomite is often used as a raw material for the production of heavy calcium carbonate, which is used in coatings, plastics, rubber, adhesives and other fields. The content of magnesium carbonate in dolomite is relatively high, and the solubility of magnesium carbonate in water is significantly higher than that of calcium carbonate. The pH value of heavy calcium carbonate produced with dolomite as raw material is generally higher (8.5-9.0), which is significantly higher than that of heavy calcium carbonate produced with calcite as raw material (pH value is 7.5-8.0). This leads to certain restrictions on the use of dolomite in the field of materials sensitive to alkalinity.

[0003] Coil coating is a professional coating used to coat the surface of steel plates and aluminum plates and used after making pre-coated coils. It is generally a one-component baking paint system with saturated polyester resin as the main resin and amino resin as the curing agent. The coating is generally thin (<20μm), and the main performance requirements are film flexibility and weather resistance. The fillers in coil coatings are mainly barium sulfate, calcium carbonate, kaolin, silica powder, feldspar powder, etc., and calcium carbonate has become the preferred filler for low-grade coil coatings due to its obvious cost advantage. Acid catalysts are usually added to coil coatings to promote the cross-linking reaction of the coating film. It is sensitive to the pH value of the filler. Fillers with too high alkalinity will absorb acid catalysts, affect the cross-linking density of the coating film, and thus affect the various resistance properties of the coating film. Therefore, most of the calcium carbonate used in coil coatings is produced from calcite as raw material. However, since the particles of calcite are relatively loose and have a large oil absorption, it has a greater impact on the viscosity of the coil coating, thereby affecting the gloss of the coating film and the flow properties of the coil coating. Although dolomite has high particle density and low oil absorption, it has high alkalinity, which will affect the cross-linking and curing of the coating.

[0004] Therefore, the development of low-alkalinity dolomite powder has broad application prospects for coil coatings. Summary of the invention

[0005] The purpose of the present invention is to provide a low-alkalinity dolomite powder and a preparation method and application thereof in view of the deficiencies in the prior art.

[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 low-alkali dolomite powder, comprising the following steps:

[0008] 1) Mix coarse dolomite powder and a grinding aid solution, and perform ball milling to obtain ultrafine dolomite powder;

[0009] 2) Mix the ultrafine dolomite powder and modifier solution I, and perform surface modification to obtain primary-modified dolomite powder;

[0010] 3) Mix the primary-modified dolomite powder with modifier solution II, and perform surface modification to obtain low-alkali dolomite powder.

[0011] Preferably, in step 1), the particle size of the coarse dolomite powder is 325-400 mesh, and the coarse dolomite powder is obtained by sequentially crushing and grinding dolomite raw ore.

[0012] Preferably, in step 1), the solvent in the grinding aid solution is anhydrous ethanol, and the mass ratio of the grinding aid to anhydrous ethanol is 1:4-5;

[0013] The grinding aid comprises dibutyl phosphate and a polymer dispersant containing acidic groups, and the mass ratio of dibutyl phosphate to the polymer dispersant containing acidic groups is 1:3-5;

[0014] The mass of the grinding aid is 6-8‰ of the mass of the coarse dolomite powder.

[0015] Preferably, in step 1), the ball milling medium used is ceramic balls, and the medium filling rate is 50-60%.

[0016] Preferably, in step 2), the solvent in the modifier solution I is anhydrous ethanol, and the mass ratio of modifier I to anhydrous ethanol is 1:4-5;

[0017] Modifier I is a polyester, the molecular weight of the polyester is 2000-3000 Da, and the acid value of the polyester is 2-4 mgKOH / g;

[0018] The mass of modifier I is 4-6‰ of the mass of the ultrafine dolomite powder.

[0019] Preferably, in step 2), the surface modification is carried out under stirring conditions, the stirring speed is 600-800 r / min, the surface modification temperature is 60-80 °C, and the surface modification time is 20-30 min.

[0020] Preferably, in step 3), the solvent in the modifier solution II is anhydrous ethanol, and the mass ratio of modifier II to anhydrous ethanol is 1:4-5;

[0021] The modifier II comprises amino epoxy phosphate and methacryloyloxyethyl phosphate, and the mass ratio of amino epoxy phosphate to methacryloyloxyethyl phosphate is 1:2-3;

[0022] The mass of the modifier II is 3-5‰ of the mass of the primary modified dolomite powder.

[0023] Preferably, in step 3), the mixing is that the modifier solution II is mixed with the primary modified dolomite powder by spray atomization, the temperature of the spray atomization is 50-60°C, and the pressure of the spray atomization is 4-6 MPa;

[0024] Step 3) The surface modification is carried out in a pin disk mill, the temperature of the surface modification is 80-90°C, the time of the surface modification is 10-15 min, and the rotor speed of the pin disk mill is 200-300 m / s.

[0025] The present invention also provides the low-alkali dolomite powder prepared by the described preparation method.

[0026] The present invention also provides the application of the described low-alkali dolomite powder in coil coatings.

[0027] The beneficial effects of the present invention include the following points:

[0028] 1) The present invention uses the compounding of dibutyl phosphate and a polymer dispersant containing acidic groups as a wear-resistant aid. While the polymer dispersant containing acidic groups plays a role in assisting grinding, it can also adjust the pH value of the particle surface, reduce the alkalinity of the material, and will not react with the acid catalyst in the coil coating system; first, polyester with a molecular weight of 2000-3000 Da and an acid value of 2-4 mgKOH / g is used for primary modification, and then a compounding modifier of amino epoxy phosphate and methacryloyloxyethyl phosphate is used for secondary modification. The two modification treatments improve the fluidity of the dolomite powder and its compatibility with the resin in the coil coating.

[0029] 2) The pH value of the low-alkali dolomite powder of the present invention is lower than 7.5, D 50 is 2-2.3 μm, D 97 is 4.8-5.1 μm, D 100 ≤8.5 μm, wherein the mass content of particles with a diameter ≤2 μm is ≥55%, the oil absorption is ≤20 mL / 100 g. When applied to coil coatings, it can take into account the crosslinking density and leveling property of the coating film, effectively improve the solvent resistance wiping and ultraviolet aging resistance of the coating film, and solve the problems existing in traditional dolomite powder and calcite powder in coil coatings. Description of the Drawings

[0030] Figure 1 It is the process flow chart of the preparation of the low-alkali dolomite powder of the present invention. Detailed Embodiments

[0031] The present invention provides a method for preparing low-alkali dolomite powder, comprising the following steps:

[0032] 1) Mixing dolomite coarse powder and a grinding aid solution, and performing ball milling to obtain ultrafine dolomite powder;

[0033] 2) Mixing the ultrafine dolomite powder and modifier solution I, and performing surface modification to obtain primary-modified dolomite powder;

[0034] 3) Mixing the primary-modified dolomite powder with modifier solution II, and performing surface modification to obtain the low-alkali dolomite powder.

[0035] In the present invention, the particle size of the dolomite coarse powder in step 1) is preferably 325-400 mesh, more preferably 350-375 mesh; the dolomite coarse powder is preferably prepared by sequentially crushing and grinding dolomite ore.

[0036] In the present invention, the mass content of calcium oxide in the dolomite ore is preferably ≥31%, more preferably ≥35%; the mass content of magnesium oxide is preferably ≥31%, more preferably ≥35%. The higher the purity of the dolomite ore, the higher the density of the particles, and the lower the oil absorption of the prepared dolomite powder.

[0037] In the present invention, the crushing is preferably carried out by jaw crushing and hammer crushing in sequence. After the dolomite ore is crushed, dolomite particles are obtained, and the dolomite particles are ground to obtain dolomite coarse powder; the diameter of the dolomite particles is preferably 10-50 mm, more preferably 20-40 mm, and even more preferably 30 mm.

[0038] In the present invention, the solvent in the grinding aid solution in step 1) is preferably anhydrous ethanol, and the mass ratio of the grinding aid to anhydrous ethanol is preferably 1:4-5, more preferably 1:4.2-4.8, and even more preferably 1:4.5;

[0039] The grinding aid preferably comprises dibutyl phosphate and a polymer dispersant containing acidic groups, and the mass ratio of dibutyl phosphate to the polymer dispersant containing acidic groups is preferably 1:3-5, more preferably 1:3.5-4.5, and even more preferably 1:4;

[0040] The mass of the grinding aid is preferably 6-8‰ of the mass of the dolomite coarse powder, more preferably 6.5-7.5‰, and even more preferably 7‰.

[0041] In the present invention, the ball milling medium used in step 1) is preferably ceramic balls, and the medium filling rate is preferably 50-60%, more preferably 52-58%, and even more preferably 55%.

[0042] In the present invention, the ball-to-material ratio in step 1) is preferably 3:2 to 3, more preferably 3:2.5; the rotation speed of the ball milling is preferably 20 to 30 r / min, more preferably 25 r / min; the time of the ball milling is preferably 20 to 30 min, more preferably 25 min.

[0043] In the present invention, the ball milling is preferably carried out in a double-chamber ball mill, and the ceramic balls are preferably ceramic balls with different particle sizes compounded. In the front chamber, the mass ratio of the ceramic balls with a diameter of 30 to 40 mm (including 30 mm and 40 mm), the ceramic balls with a diameter of 40 to 50 mm (excluding 40 mm, including 50 mm), and the ceramic balls with a diameter of 50 to 60 mm (excluding 50 mm, including 60 mm) is preferably 1:1 to 2:3 to 4, more preferably 1:1.5:3.5; in the rear chamber, the mass ratio of the ceramic balls with a diameter of 20 to 30 mm (excluding 20 mm and 30 mm), the ceramic balls with a diameter of 10 to 20 mm (excluding 10 mm, including 20 mm), and the ceramic balls with a diameter of 0 to 10 mm (excluding 0 mm, including 10 mm) is preferably 1:1 to 2:3 to 4, more preferably 1:1.5:3.5.

[0044] In the present invention, after the grinding in step 1) is completed, it is preferable to classify and collect the ground material through a classifier to obtain ultrafine dolomite powder; the D 50 of the ultrafine dolomite powder is preferably 2 to 2.3 μm, and the D 97 is preferably 4.8 to 5.1 μm, and the D 100 is preferably ≤8.5 μm, and the mass content of the particles with a particle size ≤2 μm in the ultrafine dolomite powder is preferably ≥55%.

[0045] In the present invention, the solvent in the modifier solution I in step 2) is preferably anhydrous ethanol, and the mass ratio of the modifier I to anhydrous ethanol is preferably 1:4 to 5, more preferably 1:4.2 to 4.8, and even more preferably 1:4.5;

[0046] the modifier I is preferably a polyester, the molecular weight of the polyester is preferably 2000 to 3000 Da, more preferably 2200 to 2800 Da, and even more preferably 2500 Da; the acid value of the polyester is preferably 2 to 4 mgKOH / g, more preferably 2.5 to 3.5 mgKOH / g, and even more preferably 3 mgKOH / g;

[0047] the mass of the modifier I is preferably 4 to 6‰ of the mass of the ultrafine dolomite powder, more preferably 4.5 to 5.5‰, and even more preferably 5‰. The modifier I has a low viscosity and good fluidity, and coating on the surface of the dolomite powder helps to improve the fluidity of the material and at the same time improve the compatibility with the resin in the coil coating.

[0048] In the present invention, the surface modification in step 2) is preferably carried out under stirring conditions. The stirring speed is preferably 600 - 800 r / min, more preferably 650 - 750 r / min, and even more preferably 700 r / min. The temperature of the surface modification is preferably 60 - 80 °C, more preferably 65 - 75 °C, and even more preferably 70 °C. The time of the surface modification is preferably 20 - 30 min, more preferably 22 - 28 min, and even more preferably 25 min.

[0049] In the present invention, the solvent in the modifier solution II in step 3) is preferably anhydrous ethanol. The mass ratio of the modifier II to anhydrous ethanol is preferably 1:4 - 5, more preferably 1:4.2 - 4.8, and even more preferably 1:4.5.

[0050] The modifier II preferably comprises amino epoxy phosphate and methacryloyloxyethyl phosphate. The mass ratio of amino epoxy phosphate to methacryloyloxyethyl phosphate is preferably 1:2 - 3, more preferably 1:2.2 - 2.8, and even more preferably 1:2.5.

[0051] The mass of the modifier II is preferably 3 - 5‰ of the mass of the once-modified dolomite powder, more preferably 3.5 - 4.5‰, and even more preferably 4‰.

[0052] In the present invention, the mixing in step 3) is preferably that the modifier solution II is mixed with the once-modified dolomite powder by spray atomization. The temperature of the spray atomization is preferably 50 - 60 °C, more preferably 52 - 58 °C, and even more preferably 55 °C. The pressure of the spray atomization is preferably 4 - 6 MPa, more preferably 4.5 - 5.5 MPa, and even more preferably 5 MPa.

[0053] The surface modification in step 3) is preferably carried out in a pin disk mill. The temperature of the surface modification is preferably 80 - 90 °C, more preferably 82 - 88 °C, and even more preferably 85 °C. The time of the surface modification is preferably 10 - 15 min, more preferably 11 - 14 min, and even more preferably 12 - 13 min. The rotor speed of the pin disk mill is preferably 200 - 300 m / s, more preferably 220 - 280 m / s, and even more preferably 250 m / s.

[0054] In the present invention, the pin disk mill preferably adopts a wide-chamber pin disk mill. A vortex two-phase flow is formed in the pin disk by the high-speed rotating rotor in the wide-chamber pin disk mill, and depolymerization and dispersion are carried out while the surface modification is carried out, effectively improving the agglomeration situation of the dolomite powder during the modification process.

[0055] The present invention also provides the low-alkali dolomite powder prepared by the preparation method described above.

[0056] The present invention also provides an application of the low-alkalinity dolomite powder in coil coatings.

[0057] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] The raw dolomite ore used in this embodiment is from Xiuyan Mine, Haicheng City, Liaoning Province. The polymer dispersant containing acidic groups is SN-2011N produced by Shanghai Shenzhu Chemical Technology Co., Ltd., and the polyester is CJ-560 produced by Laiyang Yalimei Coating Co., Ltd.

[0059] Example 1

[0060] In the grinding aid solution used in this embodiment, the mass ratio of the grinding aid to absolute ethanol is 1:4. The grinding aid is dibutyl phosphate and a polymer dispersant containing acidic groups with a mass ratio of 1:4, and the mass of the grinding aid is 8‰ of the mass of the dolomite coarse powder;

[0061] In the modifier solution I, the mass ratio of modifier I (polyester) to absolute ethanol is 1:5, and the mass of modifier I is 4‰ of the mass of the ultrafine dolomite powder.

[0062] In the modifier solution II, the mass ratio of modifier II to absolute ethanol is 1:4. Modifier II is amino epoxy phosphate and methacryloyloxyethyl phosphate with a mass ratio of 1:2.5, and the mass of modifier II is 3‰ of the mass of the once-modified dolomite powder.

[0063] In the front bin of the double-chamber ball mill, the mass ratio of ceramic balls with a diameter of 30 - 40 mm (including 30 mm and 40 mm), ceramic balls with a diameter of 40 - 50 mm (excluding 40 mm, including 50 mm), and ceramic balls with a diameter of 50 - 60 mm (excluding 50 mm, including 60 mm) is 1:1:4; in the rear bin, the mass ratio of ceramic balls with a diameter of 20 - 30 mm (excluding 20 mm and 30 mm), ceramic balls with a diameter of 10 - 20 mm (excluding 10 mm, including 20 mm), and ceramic balls with a diameter of 0 - 10 mm (excluding 0 mm, including 10 mm) is 1:2:3.

[0064] The preparation method of the low-alkalinity dolomite powder in this embodiment is as follows:

[0065] The raw dolomite ore with 31% calcium oxide content and 31% magnesium oxide content is cleaned and dried, and sequentially crushed by a jaw crusher and a hammer crusher to obtain dolomite particles with a diameter of 30 mm. The dolomite particles are transported to a HC-2000 pendulum mill by a spiral auger conveyor system for grinding to obtain dolomite coarse powder with a particle size of 350 mesh. A grinding aid solution is added at the front end of the spiral auger conveyor system, and the dolomite coarse powder is transported to a 1.83 m × 8 m double-chamber ball mill by this spiral auger conveyor system. Using ceramic balls as the ball milling medium, the filling rate of the ball milling medium is 50%, the ball-to-material ratio is 3:2, and after ball milling for 30 min at a speed of 25 r / min, the ball-milled material is classified and collected into a silo by a 6-head classifier (classifier frequency is 57 Hz) to obtain ultrafine dolomite powder. Detected by a BT-9300ST laser particle size analyzer, the D 50 is 2.20 m, the D 97 is 5.01 μm, the D 100 is 8.22 μm, and the mass content of the ultrafine dolomite powder with a particle size ≤ 2 μm is 57.34%.

[0066] Modifier solution I is added at the front end of the spiral auger conveyor system, and the ultrafine dolomite powder is transported to a high-speed mixer by this spiral auger conveyor system and surface-modified at 60 °C at a speed of 800 r / min for 30 min to obtain once-modified dolomite powder.

[0067] The once-modified dolomite powder is transported to an atomization chamber by a spiral auger conveyor system. Modifier solution II is added to the additive system in the atomization chamber. Modifier solution II is sprayed and atomized at 55 °C and 5 MPa and mixed with the once-modified dolomite powder to obtain a mixture. The mixture is transported to a wide-chamber nail disk mill and surface-modified at 85 °C with the rotor speed of the nail disk mill being 250 m / s for 10 min to obtain low-alkali dolomite powder.

[0068] Example 2

[0069] In the grinding aid solution used in this example, the mass ratio of the grinding aid to absolute ethanol is 1:5. The grinding aid is dibutyl phosphate and a polymer dispersant containing acidic groups with a mass ratio of 1:5, and the mass of the grinding aid is 7‰ of the mass of the dolomite coarse powder;

[0070] In modifier solution I, the mass ratio of modifier I (polyester) to absolute ethanol is 1:4.5, and the mass of modifier I is 5‰ of the mass of the ultrafine dolomite powder.

[0071] In modifier solution II, the mass ratio of modifier II to absolute ethanol is 1:5. Modifier II is amino epoxy phosphate and methacryloyloxyethyl phosphate with a mass ratio of 1:2, and the mass of modifier II is 4‰ of the mass of the once-modified dolomite powder.

[0072] In the front chamber of the double-chamber ball mill, the mass ratio of ceramic balls with a diameter of 30 - 40 mm (including 30 mm and 40 mm), ceramic balls with a diameter of 40 - 50 mm (excluding 40 mm, including 50 mm), and ceramic balls with a diameter of 50 - 60 mm (excluding 50 mm, including 60 mm) is 1:1:3; in the rear chamber, the mass ratio of ceramic balls with a diameter of 20 - 30 mm (excluding 20 mm and 30 mm), ceramic balls with a diameter of 10 - 20 mm (excluding 10 mm, including 20 mm), and ceramic balls with a diameter of 0 - 10 mm (excluding 0 mm, including 10 mm) is 1:2:3.

[0073] The preparation method of the low-alkali dolomite powder in this embodiment is as follows:

[0074] Clean and air-dry the original dolomite ore with a calcium oxide mass content of 35% and a magnesium oxide mass content of 35%, and successively crush it through a jaw crusher and a hammer crusher to obtain dolomite particles with a diameter of 50 mm. Convey the dolomite particles to an HC-2000 pendulum mill through a spiral auger conveyor system for grinding to obtain dolomite coarse powder with a particle size of 400 mesh. Add a grinding aid solution at the front end of the spiral auger conveyor system, and convey the dolomite coarse powder through this spiral auger conveyor system to a 1.83 m × 8 m double-chamber ball mill. Using ceramic balls as the ball milling medium, the ball milling medium filling rate is 60%, the ball-to-material ratio is 3:3, and after ball milling for 25 min at a rotational speed of 25 r / min, classify and collect the ball-milled material into a silo through a 6-head classifier (classifier frequency is 57 Hz) to obtain ultrafine dolomite powder. Detected by a BT-9300ST laser particle size analyzer, the D 50 of the ultrafine dolomite powder is 2.13 μm, the D 97 is 4.87 μm, the D 100 is 8.04 μm, and the mass content of the ultrafine dolomite powder with a particle size ≤ 2 μm is 59.63%.

[0075] Add modifier solution I at the front end of the spiral auger conveyor system, and convey the ultrafine dolomite powder through this spiral auger conveyor system to a high-speed mixer, and perform surface modification at 80°C at a rotational speed of 600 r / min for 20 min to obtain primary-modified dolomite powder.

[0076] Convey the primary-modified dolomite powder to an atomization chamber through a spiral auger conveyor system. Add modifier solution II to the additive system in the atomization chamber, spray and atomize modifier solution II at 50°C and 6 MPa, and mix it with the primary-modified dolomite powder to obtain a mixture. Convey the mixture to a wide-chamber nail disk mill, and perform surface modification at 80°C and a rotor speed of 300 m / s of the nail disk mill for 12 min to obtain the low-alkali dolomite powder.

[0077] Example 3

[0078] In the grinding aid solution used in this example, the mass ratio of the grinding aid to absolute ethanol is 1:4.5. The grinding aid is dibutyl phosphate and a polymer dispersant containing acidic groups with a mass ratio of 1:3, and the mass of the grinding aid is 6‰ of the mass of the coarse dolomite powder.

[0079] In the modifier solution I, the mass ratio of modifier I (polyester) to absolute ethanol is 1:4, and the mass of modifier I is 6‰ of the mass of the ultrafine dolomite powder.

[0080] In the modifier solution II, the mass ratio of modifier II to absolute ethanol is 1:4.5. Modifier II is amino epoxy phosphate and methacryloyloxyethyl phosphate with a mass ratio of 1:3, and the mass of modifier II is 5‰ of the mass of the once-modified dolomite powder.

[0081] In the front chamber of the double-chamber ball mill, the mass ratio of ceramic balls with a diameter of 30 - 40 mm (including 30 mm and 40 mm), ceramic balls with a diameter of 40 - 50 mm (excluding 40 mm, including 50 mm), and ceramic balls with a diameter of 50 - 60 mm (excluding 50 mm, including 60 mm) is 1:2:3; in the rear chamber, the mass ratio of ceramic balls with a diameter of 20 - 30 mm (excluding 20 mm and 30 mm), ceramic balls with a diameter of 10 - 20 mm (excluding 10 mm, including 20 mm), and ceramic balls with a diameter of 0 - 10 mm (excluding 0 mm, including 10 mm) is 1:2:4.

[0082] The preparation method of the low-alkali dolomite powder in this example is as follows:

[0083] Clean and dry the original dolomite ore with a calcium oxide mass content of 31% and a magnesium oxide mass content of 31%, and sequentially crush it through a jaw crusher and a hammer crusher to obtain dolomite particles with a diameter of 10 mm. Convey the dolomite particles to an HC-2000 pendulum mill through a spiral auger conveyor system for grinding to obtain coarse dolomite powder with a particle size of 325 mesh. Add the grinding aid solution at the front end of the spiral auger conveyor system, and convey the coarse dolomite powder through this spiral auger conveyor system to a 1.83 m × 8 m double-chamber ball mill. Using ceramic balls as the ball-milling medium, the filling rate of the ball-milling medium is 55%, the ball-to-material ratio is 3:2.5, and after ball-milling for 20 min at a rotation speed of 25 r / min, the ball-milled material is classified and collected into the bin through a 6-head classifier (classifier frequency is 57 Hz) to obtain ultrafine dolomite powder. Detected by a BT-9300ST laser particle size analyzer, the D 50 is 2.01 μm, D 97 is 4.81 μm, D 100It is 7.96 μm, and the mass content of the ultrafine dolomite powder with a particle size ≤ 2 μm is 61.14%.

[0084] Add modifier solution I at the front end of the spiral auger conveying system, and convey the ultrafine dolomite powder through this spiral auger conveying system to the high-speed mixer. Carry out surface modification at 70 °C at a rotation speed of 700 r / min for 25 min to obtain the once-modified dolomite powder.

[0085] Convey the once-modified dolomite powder to the atomization chamber through the spiral auger conveying system. Add modifier solution II to the additive system in the atomization chamber. Spray and atomize modifier solution II at 60 °C and 4 MPa, and mix it with the once-modified dolomite powder to obtain a mixture. Convey the mixture to a wide-chamber nail-disc mill, and carry out surface modification at 90 °C with the rotor speed of the nail-disc mill being 200 m / s for 15 min to obtain the low-alkali dolomite powder.

[0086] Test the pH value, particle size, oil absorption, whiteness and moisture content of the low-alkali dolomite powder prepared in Examples 1 to 3 and the CC-2800 dolomite powder produced by Jiangxi Guangyuan Chemical Co., Ltd. according to JC / T 2579-2020;

[0087] Test the pH value, particle size, oil absorption, whiteness and moisture content of the GY-716 calcite powder produced by Jiangxi Guangyuan Chemical Co., Ltd. according to HG / T 3249-2013. The test results are shown in Table 1.

[0088] Table 1 Performance test results of low-alkali dolomite powder and conventional powders

[0089]

[0090] As can be seen from Table 1, the pH value of the low-alkali dolomite powder prepared in Examples 1 to 3 is lower than 7.5, and the oil absorption is lower than 20 mL / 100 g, which is significantly lower than that of the CC-2800 dolomite powder and the GY-716 calcite powder. This result shows that the low-alkali dolomite powder of the present invention has the characteristics of low alkalinity and low oil absorption.

[0091] Apply the low-alkali dolomite powder, CC-2800 dolomite powder, and GY-716 calcite powder prepared in Examples 1 to 3 to coil coatings (topcoats) respectively. The formula of the coil coatings (topcoats) is shown in Table 2.

[0092] Table 2 Formula of coil coatings (topcoats)

[0093]

[0094]

[0095] The properties of the coil coatings and their coatings in Application Examples 1 to 3 and Comparative Application Examples 1 to 2 were tested separately, and the test results are shown in Table 3.

[0096] The process for preparing the coating film was as follows: The coil coating was sprayed onto an aluminized zinc steel sheet with a thickness of 0.27 mm and baked at 200 °C for 30 s to obtain a coating film with a thickness of 15 μm.

[0097] Table 3 Test results of the properties of the coil coating and its coating film

[0098]

[0099]

[0100] As can be seen from Table 3, when the low-alkali dolomite powder prepared in Examples 1 to 3 of the present invention was applied to the coil coating, the indexes such as the number of MEK rubbing resistance times, ultraviolet aging resistance performance, dispersibility and glossiness of the coating film were significantly better than those of CC-2800 dolomite powder and GY-716 calcite powder.

[0101] The above are only 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 of 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 low-alkali dolomite powder, characterized in that, It includes the following steps: 1) Mix the dolomite coarse powder and the grinding aid solution, and carry out ball milling to obtain ultrafine dolomite powder; 2) Mix the ultrafine dolomite powder and the modifier solution I, and carry out surface modification to obtain the once-modified dolomite powder; 3) Mix the once-modified dolomite powder with the modifier solution II, and carry out surface modification to obtain the low-alkalinity dolomite powder.

2. The preparation method according to claim 1, characterized in that, In step 1), the particle size of the dolomite coarse powder is 325-400 mesh, and the dolomite coarse powder is prepared by sequentially crushing and grinding the dolomite raw ore.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the solvent in the grinding aid solution is anhydrous ethanol, and the mass ratio of the grinding aid to anhydrous ethanol is 1:4-5; The grinding aid contains dibutyl phosphate and a polymer dispersant containing acidic groups, and the mass ratio of dibutyl phosphate to the polymer dispersant containing acidic groups is 1:3-5; The mass of the grinding aid is 6-8‰ of the mass of the dolomite coarse powder.

4. The preparation method according to claim 3, characterized in that, In step 1), the ball milling medium used for ball milling is ceramic balls, and the medium filling rate is 50-60%.

5. The preparation method according to claim 4, characterized in that, In step 2), the solvent in the modifier solution I is anhydrous ethanol, and the mass ratio of the modifier I to anhydrous ethanol is 1:4-5; The modifier I is a polyester, the molecular weight of the polyester is 2000-3000 Da, and the acid value of the polyester is 2-4 mgKOH / g; The mass of the modifier I is 4-6‰ of the mass of the ultrafine dolomite powder.

6. The preparation method according to claim 4 or 5, characterized in that, In step 2), the surface modification is carried out under stirring conditions, the stirring speed is 600-800 r / min, the surface modification temperature is 60-80 °C, and the surface modification time is 20-30 min.

7. The preparation method according to claim 6, characterized in that, In step 3), the solvent in the modifier solution II is anhydrous ethanol, and the mass ratio of the modifier II to anhydrous ethanol is 1:4-5; The modifier II contains amino epoxy phosphate and methacryloyloxyethyl phosphate, and the mass ratio of amino epoxy phosphate to methacryloyloxyethyl phosphate is 1:2-3; The mass of the modifier II is 3-5‰ of the mass of the once-modified dolomite powder.

8. The preparation method according to claim 7, wherein, In step 3), the mixing is that the modifier solution II is mixed with the once-modified dolomite powder by spray atomization, the spray atomization temperature is 50-60 °C, and the spray atomization pressure is 4-6 MPa; In step 3), the surface modification is carried out in a pin disk mill, the surface modification temperature is 80-90 °C, the surface modification time is 10-15 min, and the rotor speed of the pin disk mill is 200-300 m / s.

9. The low-alkalinity dolomite powder prepared by the preparation method according to any one of claims 1-8.

10. The application of the low-alkalinity dolomite powder according to claim 9 in coil coatings.

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