Method for controlling powder particles in titanium dioxide

Abstract

The invention relates to the technical field of production, and provides a method for controlling powder particles in titanium dioxide, which comprises the following steps: pulping a metatitanic acid crude product, calcining, carrying out roll milling, pulping, colloid milling and ceramic milling, screening, sanding, screening, and separating by a cyclone to obtain an intermediate material, adding a modified dispersant and alkali liquor into the slurry; finally, adding tetraethoxysilane into the intermediate material, reacting for a period of time, then continuously adding sodium hexametaphosphate and zirconium sulfate into the slurry, and carrying out surface coating treatment; according to the control method, titanium dioxide particles with uniform particle size and high whiteness quality can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of production, and in particular to a method for controlling powder particles in titanium dioxide. Background Art

[0002] Titanium dioxide is an important chemical material widely used in various fields. Its performance and quality are closely related to its particle size. The particle size of titanium dioxide refers to the size of titanium dioxide particles, which is mainly measured by a laser particle size analyzer.

[0003] The production process of titanium dioxide has very high requirements for the fineness and distribution of particles. In order to ensure that the required particle size index can be obtained, the crushing, grinding and classification control of medium powder are particularly important. Medium powder is usually expressed by the parameter D50 value (median diameter or median particle size), that is, the particle size corresponding to the cumulative particle size distribution percentage of the sample reaches 50%. Its physical meaning is that particles with a particle size larger than it account for 50%, and particles with a particle size smaller than it also account for 50%. The uniform and concentrated particle size distribution of the slurry after classification is the prerequisite for determining the quality of the surface treatment coating, and has a vital impact on the quality of the product.

[0004] Therefore, controlling the particle size of titanium dioxide powder is the core and key link in controlling the type and quality grade of titanium dioxide finished products. How to control the particle size of titanium dioxide and optimize the particle size distribution has become an urgent problem to be solved. Summary of the invention

[0005] In order to better control the particle size of the medium powder, the present invention focuses on the research from the aspects of raw material, slurry dispersion, wet grinding process route, grinding media, etc., and explores the optimal process control conditions for raw product grinding through production practice. Specifically, the purpose of the present invention is to provide a method for controlling the particles of titanium dioxide medium powder, which can obtain titanium dioxide particles with uniform particle size and high whiteness quality.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] A method for controlling powder particles in titanium dioxide comprises the following steps:

[0008] S1. Take crude metatitanic acid with a phosphorus content of 700ppm to 2000ppm, crush it in a crusher, add H3PO4 solution, and stir for 30 minutes to make a slurry with a concentration of 500 to 600g / L; wherein the amount of H3PO4 solution added is 0.1 to 0.2% of the mass of titanium dioxide in the metatitanic acid in terms of phosphorus pentoxide;

[0009] S2, calcining the slurry, then roller milling (80-200r / min), and then low-speed beating (20-50r / min), which helps to avoid the generation of bubbles and ensures uniform mixing of materials; during the low-speed beating process, adding modified dispersant and alkali solution to the slurry; then sequentially performing colloid milling and ceramic milling, after the treatment, sieving, sand milling, and sieving again, and separating by a cyclone, an intermediate material is obtained; the qualified intermediate material after grinding is used for surface treatment; the modified dispersant is a copolymer synthesized by solution polymerization using acrylic acid, maleic acid, and polyethylene glycol monomethyl ether of acrylic acid as monomers;

[0010] The titanium dioxide particles treated with modified dispersants have better uniformity and better dispersibility. This is mainly due to the fact that the hydrophilic polyether chain contained in acrylic acid polyethylene glycol monomethyl ether plays a steric hindrance role in the dispersion, making the modified dispersant coating the particle surface more complete and the dispersion and viscosity reduction effect stronger. Under the action of acrylic acid and maleic acid, the adsorption of acrylic acid polyethylene glycol monomethyl ether is enhanced, so that its hydrophilic chain increases and the steric resistance is stronger, thereby enhancing its dispersibility, making the particle size distribution uniform, without excessively large or small particle agglomerates.

[0011] S3. Add ethyl orthosilicate to the intermediate material obtained in S2, react for a period of time, and coat the surface of titanium dioxide with a dense silicon dioxide film layer by a sol-gel method; the coated intermediate material shows lower acid solubility and activity, and has higher density and weather resistance; then continue to add sodium hexametaphosphate and zirconium sulfate to carry out surface coating treatment; finally, wash the intermediate material after the coating treatment with water to obtain a filter cake; then flash evaporation and steam powder are carried out to obtain a titanium dioxide finished product.

[0012] After the above-mentioned coating treatment, the present invention forms a uniform and continuous dense protective film on the surface of titanium dioxide, which can not only effectively shield metal ion impurities, improve the whiteness of titanium dioxide, inhibit excessive growth of TiO2 grains, and ensure the particle size distribution of titanium dioxide, but also reduce the surface energy of titanium dioxide, improve the dispersibility of titanium dioxide, and show better optical properties, whiteness, brightness and weather resistance.

[0013] Furthermore, in S1, the phosphorus content in the crude product is 800 ppm to 1000 ppm.

[0014] Further, in S2, the preparation method of the modified dispersant is:

[0015] (1) After maleic acid, polyethylene glycol monomethyl ether of acrylic acid and an initiator are mixed, an organic solvent is added to fully dissolve them, and then nitrogen is introduced into the reaction system and the temperature is raised to 70-90° C. and reacted for a period of time;

[0016] (2) dissolving acrylic acid and an initiator in an organic solvent and mixing them uniformly, then slowly adding them dropwise to the reaction system of step (1), and evaporating the organic solvent after a period of reaction; dissolving the obtained product in water and adding an appropriate amount of alkaline solution to adjust the pH to 6-7, and obtaining a modified dispersant after purification.

[0017] Furthermore, in step (1), the molar amount of the initiator is 0.5% to 2% of the total molar amount of maleic acid and polyethylene glycol monomethyl ether of acrylic acid; and in step (2), the molar amount of the initiator is 0.1% to 0.5% of the molar amount of acrylic acid.

[0018] Furthermore, in step (1), the amount of the organic solvent used is 50% to 100% of the total weight of the reactants (i.e., maleic acid, polyethylene glycol monomethyl ether of acrylic acid and initiator); in step (2), the amount of the organic solvent used is 50% to 100% of the total weight of the reactants (i.e., acrylic acid and initiator).

[0019] Furthermore, the molar ratio of acrylic acid, maleic acid and acrylic acid polyethylene glycol monomethyl ether is 2-8:3-9:10-15; preferably, it is 5:6:10.

[0020] Furthermore, the organic solvent is ethyl acetate or propylene glycol methyl ether.

[0021] Furthermore, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile or dimethyl azobisisobutyrate.

[0022] Further, in S2, 2.0‰ to 3.0‰ of a modified dispersant is added to the obtained slurry, and the pH value is adjusted to 9.5-10 with a dilute alkali.

[0023] Furthermore, in S2, the calcination temperature during calcination is 935-945°C. Under the salt treatment method of the present invention, the titanium dioxide particles obtained by the calcination temperature of 935-945°C are approximately round in shape, the particle size is relatively uniform, and the titanium dioxide particle size can reach 260nm. The particle size distribution is narrow, the tinting power is greater than 1500, and the blue phase is greater than 40; otherwise, if the temperature is too low, the particles are small and the specific surface area is small, and relatively uniform medium powder particles cannot be obtained; if the calcination temperature is too high, the particles are sintered, agglomeration will occur, and the growth rate of the titanium dioxide particles is inconsistent, resulting in a wide particle size distribution and poor pigment performance.

[0024] The filling amount of the grinding media of the ceramic mill and the sand mill has a great influence on the grinding particle size. The larger the diameter of the grinding media, the coarser the particle size of the slurry, but the production capacity will increase; conversely, the smaller the diameter of the grinding media, the finer the slurry particle size, and the production capacity will decrease. In order to balance production capacity and quality, in S2, the ceramic balls of the ceramic mill are selected in sizes of 10mm, 8mm, 6mm, and 4mm, and the addition ratio is 2:2:2:1. The concentration of the ceramic mill slurry is 500-600g / L, the viscosity is controlled at 80mpa·s~100mpa·s, and it is regularly supplemented at 60~80mg / ton. The grinding effect is the best, and then the residues are all passed through the 300-350 mesh sieve.

[0025] In addition, in S2, when sanding, the sand mill uses a NETZSCH 1000L sand mill, and the sand milling medium uses zirconium beads or zirconium oxide beads with a diameter of 5-10mm, with a one-time filling amount of 2300kg. Preferably, 6mm, 8mm, and 10mm zirconium beads are selected respectively, and the addition ratio is 3:2:1; the slurry concentration is controlled at 500-600g / L, and the viscosity is controlled at 20mpa·s~50mpa·s, and it is regularly supplemented at 80mg~120mg / ton to detect whether the slurry particle size after sand milling can meet the production quality index requirements; when sand milling, adjust the speed to 1000-2000r / min and stir for 0.5-1h. In addition, when sand milling, two-stage sand milling is performed, the first-stage sand mill uses 4-6mm zirconium beads as the sand milling medium, and the second-stage sand mill uses 6-10mm zirconium oxide beads as the sand milling medium. This combination has the best grinding effect, and the particle size distribution of the obtained medium powder is the most uniform and concentrated.

[0026] Further, in S2, before sand grinding, the material is passed through a 300-350 mesh screen; after sand grinding, the material is passed through a 450-550 mesh screen.

[0027] Furthermore, in S3, the amount of ethyl orthosilicate added is 1-5% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1-3% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.5-1% of the mass of the intermediate material.

[0028] Further, in S3, the surface coating process is controlled at 50-70°C, and the specific operation is as follows: ethyl orthosilicate is added to the intermediate material at a uniform speed, and then matured for 0.5-1h; then sodium hexametaphosphate and zirconium sulfate are added at a uniform speed. During this process, acid or alkali solution is added dropwise to control the pH of the system to be between 6.5 and 8.5, and matured for 0.5-1h. After maturation, it is washed and dried.

[0029] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0030] The present invention controls titanium dioxide from aspects such as raw material, slurry dispersion, wet grinding process route, grinding media, etc., to obtain titanium dioxide particles with uniform particle size and high whiteness quality. More specifically, the present invention adds a modified dispersant during the grinding process to make the titanium dioxide particles have better uniformity and better dispersibility, and performs surface coating treatment on the titanium dioxide particles to form a uniform and continuous dense protective film on the surface of the titanium dioxide, which can not only effectively shield metal ion impurities, improve the whiteness of titanium dioxide, inhibit excessive growth of TiO2 grains, and ensure the particle size distribution of titanium dioxide, but also reduce the surface energy of titanium dioxide, improve the dispersibility of titanium dioxide, and show good optical properties, whiteness, brightness and weather resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 This is a particle size distribution diagram of the titanium dioxide product obtained in Example 1 of the present invention;

[0033] Figure 2 This is the particle size distribution diagram of the titanium dioxide finished product obtained in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0035] Example 1

[0036] A method for controlling powder particles in titanium dioxide comprises the following steps:

[0037] S1. Take crude metatitanic acid with a phosphorus content of 1000ppm, crush it in a crusher, add 0.1% H3PO4 solution (0.1% of the mass of titanium dioxide in metatitanic acid in terms of P2O5), and stir for 30 minutes to make a slurry with a concentration of 550g / L;

[0038] S2, the slurry is calcined at 940 ° C, then roller milled at a roller speed of 150 r / min, and then low-speed beating is performed at 35 r / min. During the low-speed beating process, 2‰ of a modified dispersant is added to the slurry, and the pH value is adjusted to 9.8 with a sodium bicarbonate solution; then the slurry is processed in sequence by colloid milling (speed 2000 r / min) and ceramic milling. The ceramic balls of the ceramic mill are selected in sizes of 10 mm, 8 mm, 6 mm, and 4 mm, and the addition ratio is 2:2:2:1, the concentration of ceramic grinding slurry is 550g / L, the viscosity is controlled at 90mpa·s, and 70mg / ton is added regularly; then the residue is passed through a 330-mesh sieve, and then two-stage sand milling is carried out. The first-stage sand mill uses 4mm and 6mm zirconium beads, and the addition ratio is 3:2. The second-stage sand mill uses 6mm, 8mm, and 10mm zirconium beads, and the addition ratio is 3:2:1. Then it passes through a 500-mesh sieve and is separated by a cyclone to obtain the intermediate material.

[0039] The modified dispersant is a copolymer synthesized by solution polymerization using acrylic acid, maleic acid, and polyethylene glycol monomethyl ether of acrylic acid as monomers in a molar ratio of 5:6:10. Specifically, the preparation method of the modified dispersant is as follows: (1) maleic acid, polyethylene glycol monomethyl ether of acrylic acid, and azobisisobutyronitrile are mixed, and ethyl acetate is added to fully dissolve them, and then nitrogen is introduced into the reaction system and the temperature is raised to 80° C., and the reaction is carried out for 0.5 h; (2) acrylic acid and azobisisobutyronitrile are dissolved in ethyl acetate and mixed, and then slowly added dropwise to the reaction system of step (1), and the ethyl acetate is evaporated after the reaction is carried out for 0.5 h. Ester; the product is dissolved in water and an appropriate amount of sodium bicarbonate is added to adjust the pH to 6.5, and the modified dispersant is obtained after purification; wherein, in step (1), the molar amount of the initiator is 1% of the total molar amount of maleic acid and polyethylene glycol monomethyl ether of acrylic acid; in step (2), the molar amount of the initiator is 0.3% of the molar amount of acrylic acid; in step (1), the amount of the organic solvent is 90% of the total weight of the reactants (i.e., maleic acid, polyethylene glycol monomethyl ether of acrylic acid and the initiator); in step (2), the amount of the organic solvent is 80% of the total weight of the reactants (i.e., acrylic acid and the initiator);

[0040] S3. At 60°C, add ethyl orthosilicate to the intermediate material obtained in S2 at a uniform speed, and then mature for 0.5h; then add sodium hexametaphosphate and zirconium sulfate at a uniform speed. During this process, add hydrochloric acid or sodium hydroxide to control the pH of the system to about 7. After aging for 0.5h, wash and dry; wherein, the amount of ethyl orthosilicate added is 3% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 2% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.7% of the mass of the intermediate material; finally, wash the intermediate material after the above coating treatment with water to obtain a filter cake; then flash evaporation and steam powder are carried out to obtain a titanium dioxide finished product; the L value of the obtained titanium dioxide finished product is 98.43%, the a value is -0.75, and the b value is -0.19.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that in S2, the molar ratio of acrylic acid, maleic acid and polyethylene glycol monomethyl ether is 3:7:12; the L value of the obtained titanium dioxide product is 98.38%, the a value is -0.73, and the b value is -0.24.

[0043] Example 3

[0044] The difference between this embodiment and embodiment 1 is that: in S3, the amount of tetraethyl orthosilicate added is 2% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1.5% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.9% of the mass of the intermediate material; the L value of the obtained titanium dioxide product is 98.40%, the a value is -0.71, and the b value is -0.22.

[0045] Example 4

[0046] The difference between this embodiment and embodiment 1 is that: in S3, the surface coating process is controlled at 65°C, and the specific operation is as follows: ethyl orthosilicate is added to the intermediate material at a uniform speed, and then matured for 1 hour; then sodium hexametaphosphate and zirconium sulfate are added at a uniform speed. During this process, acid or alkali solution is added dropwise to control the pH of the system to about 7.5, and matured for 1 hour. After maturation, it is washed and dried; the L value of the obtained titanium dioxide finished product is 98.24%, the a value is -0.74, and the b value is -0.22.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that in S2, sodium citrate is used as a dispersant; the L value of the obtained titanium dioxide product is 98.12%, the a value is -0.82, and the b value is -0.43.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that in S3, the intermediate material is not subjected to surface coating treatment, that is, the intermediate material is directly washed with water to obtain a filter cake; then flash evaporation and steam powder are performed to obtain a titanium dioxide finished product; the L value of the obtained titanium dioxide finished product is 98.03%, the a value is -0.83, and the b value is -0.43.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 1 is that in S2, the sand milling process only includes the first-stage sand milling and does not include the cyclone separation step. The L value of the titanium dioxide product obtained is 98.15%, the a value is -0.80, and the b value is -0.39.

[0053] Experimental Example 1

[0054] The particle size of the titanium dioxide products prepared in each embodiment and comparative example was tested. The results are shown in Table 1 and the particle size distribution diagram is shown in Figure 1 ;

[0055] Table 1 - Comparison of particle sizes of titanium dioxide products obtained in various embodiments and comparative examples

[0056]

[0057]

[0058] It can be seen from the data in Table 1 that the growth rate of the titanium dioxide particles in Comparative Example 1 that were not dispersed by the modified dispersant of the present invention was inconsistent, resulting in a wider particle size distribution, and ions agglomerated, resulting in larger particle size and specific surface area; in Comparative Example 2, the intermediate material was not coated, and a uniform and continuous dense protective film could not be formed on the surface of the titanium dioxide, resulting in excessive grain growth and uneven particle size distribution; the particle size obtained in Comparative Example 3 was relatively coarse relative to that in Example 1, which was mainly due to the fact that the slurry was not fully ground and screened.

[0059] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for controlling powder particles in titanium dioxide, characterized in that: The following steps are involved: S1. Take crude metatitanic acid with a phosphorus content of 700ppm to 2000ppm, crush it with a high-efficiency crusher, add H3PO4 solution, and stir for 30 minutes to prepare a slurry with a concentration of 500-600g / L; S2, calcining the slurry, then roller milling, and then beating. During the beating process, a modified dispersant and alkali solution are added to the slurry; then the slurry is sequentially subjected to colloid milling and ceramic milling. After treatment, the slurry is sieved, sand milled, and sieved again, and separated by a cyclone to obtain an intermediate material; the modified dispersant is a copolymer synthesized by solution polymerization using acrylic acid, maleic acid, and polyethylene glycol monomethyl ether as monomers; S3. Add ethyl orthosilicate to the intermediate material obtained in S2, react for a period of time, and then continue to add sodium hexametaphosphate and zirconium sulfate to the slurry for surface coating treatment.

2. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S1, the phosphorus content in the crude product is 800 ppm to 1000 ppm.

3. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S2, the preparation method of the modified dispersant is: (1) maleic acid, polyethylene glycol monomethyl ether of acrylic acid and an initiator are mixed, and an organic solvent is added to fully dissolve them. Then, nitrogen is introduced into the reaction system and the temperature is raised, and the reaction is continued for a period of time; (2) dissolving acrylic acid and an initiator in an organic solvent and mixing them uniformly, then slowly adding them dropwise to the reaction system of step (1), and evaporating the organic solvent after a period of reaction; dissolving the obtained product in water and adding an appropriate amount of alkaline solution to adjust the pH to 6-7, and obtaining a modified dispersant after purification.

4. The method for controlling powder particles in titanium dioxide according to claim 3, characterized in that: The molar ratio of acrylic acid, maleic acid and polyethylene glycol monomethyl ether is 2-8:3-9:10-15.

5. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S2, 2.0‰ to 3.0‰ of a modified dispersant is added to the obtained slurry, and the pH value is adjusted to 9.5-10 with a dilute alkali to obtain an intermediate material.

6. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S2, the calcination temperature during calcination is 935 to 945°C.

7. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S2, when ceramic grinding is performed, the grinding medium is porcelain balls with diameters of 10mm, 8mm, 6mm, and 4mm, and the addition ratio is 2:2:2:1; when sand grinding, the grinding medium is zirconium beads or zirconium oxide beads with a diameter of 5-10mm, and zirconium beads of 6mm, 8mm, and 10mm are selected, and the addition ratio is 3:2:

1.

8. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: During sand grinding, two-stage sand grinding is performed. The first-stage sand grinder uses 0.4-0.6mm zirconia beads as sand grinding media, and the second-stage sand grinder uses 0.6-0.8mm zirconia beads as sand grinding media.

9. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S2, before sanding, pass through a 300-350 mesh screen; after sanding, pass through a 450-550 mesh screen.

10. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that: In S3, the amount of ethyl orthosilicate added is 1-5% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1-3% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.5-1% of the mass of the intermediate material.

Images