1 Introduction
Titanium white powder is an excellent quality white pigment powder, having good light scattering ability, and thus good whiteness, high color strength, hiding power, while having high chemical stability and good weather resistance, non-toxic, odorless It has no stimulating effect on human body and is widely used in industrial fields such as coatings, plastics, papermaking and ink. In solvent-based coatings, titanium dioxide, as a white pigment, is a secondary film-forming material that not only imparts a bright white color to the surface of the object but also has weather resistance, chalking resistance and rheology. Certain role. The oil dispersibility of titanium dioxide is very concerned about solvent coatings and plastics. Its advantages and disadvantages will greatly affect the production process, production equipment and product quality. Based on the surface properties of titanium dioxide, combined with the composition of solvent-based coatings, the dispersion mechanism of titanium dioxide in solvent-based coatings was discussed, and the factors of shadow orientation were analyzed. This provides a theoretical basis for improving the dispersibility of titanium dioxide in solvent-based coatings, and has certain reference significance.
2 Titanium dioxide surface properties
Titanium dioxide is an inorganic compound that is insoluble in water and insoluble in oil, but is capable of being dispersed in a water or oil medium. Titanium dioxide has a small particle size and a high specific surface energy, so it exhibits strong agglomeration characteristics in a single solid phase to reduce surface energy and form relatively stable sub-aggregated particles. Studies have shown that the adsorption of water in the surface of titanium dioxide will form a basic "terminal" hydroxyl group and an acidic "bridge" hydroxyl group with water. From the detection of zeta potential, the surface is highly electronegative ( The anatase titanium dioxide has a Zeta potential of about -50 mv), which forms an adsorption layer of the same charge and has a strong adsorption effect. The titanium dioxide exhibits strong high dispersibility and strong surface adsorption in the two phases.
3 Dispersion mechanism of titanium dioxide in solvent-based coatings
3.1 Basic composition of solvent-based coatings Solvent-based coatings mainly include film-forming base oils or resins, dispersion medium volatile organic solvents and pigments. The film-forming base material is the main film-forming material of the paint, and the pigment is a coloring and covering effect to the object, and belongs to a secondary film-forming material. The dispersion medium is such that the film-forming binder and pigment are well dispersed to form a viscous liquid. Therefore, the dispersion mechanism of titanium dioxide in solvent-based coatings is to discuss the wetting and dispersing process of titanium dioxide in the mixed coating of film-forming base and dispersion medium (volatile organic solvent).
3.2 Interaction between titanium dioxide, resin and solvent oil Solvent oil can completely dissolve the resin to form a mixed paint. The strong surface adsorption of titanium dioxide can adsorb the resin and solvent oil. In the dispersion process of titanium dioxide, the resin is required to adsorb as much as possible on the surface of the titanium dioxide as much as possible, and the solvent oil is not adsorbed as much as possible, which is beneficial to the solubility of the solvent oil to the resin and the solubility of the resin. The coating formed with titanium dioxide is highly stabilized. Therefore, titanium dioxide, resin and solvent oil interact with each other and restrict each other. The abnormality of any one component will affect the performance of the whole system.
3.3 Dispersion mechanism of titanium dioxide in solvent-based coatings In solvent-based coatings, solvent oils are generally non-polar solvents or solvents with very weak polarity. The electrical properties are very weak, and the electric double layer formed on the surface of titanium dioxide is weak. A strong electric double layer effect is formed on the whole system to reduce the surface energy and reach a stable state. In this system, titanium dioxide is adsorbed by the polymer resin, and the polymer is solvated by the solvent oil. Therefore, the adsorbed resin has a solvated long chain, and these solvated long chains are neatly arranged on the surface of the titanium dioxide particles. Arranged to form a shield of a certain area. When two oxidized long-chain-coated titanium dioxide particles are close to each other, the solvated long chains interpenetrate, and during the intercalation process, the concentration of the polymer resin in the intercalation region increases, and the osmotic pressure difference is formed in the adjacent region due to the difference in osmotic pressure. The effect is to force the solvent oil to flow out to the region with low pressure difference, forcing the particles to separate, so as to achieve the purpose of dispersing the titanium dioxide in the mixed paint of the resin and the solvent oil.
Therefore, the dispersion mechanism of titanium dioxide in solvent-based coatings can be explained by the surface adsorption shielding effect. [next]
4 Factors affecting the dispersion of titanium dioxide In solvent-based coatings, when the resin and solvent oil are determined, the degree of dispersion and dispersion stabilization of titanium dioxide in the mixed paint is determined by its own application properties and surface properties.
4.1 Average particle size and particle size distribution of titanium dioxide The average particle size and particle size distribution of titanium dioxide are comprehensive indicators reflecting the performance and application properties of titanium dioxide pigments. Through a large number of experiments, the zeta potential is about -70mv when the mass percentage of titanium dioxide is less than 200nm, and the zeta potential is about -40mv. If the mass percentage is less than 20%, the zeta potential is about -40mv, which indicates that titanium dioxide is The particle size situation seriously affects the surface electrical properties, which affects the surface adsorption properties. However, the particle size should not be too small, otherwise it will affect the performance of other pigments, so it is necessary to control the appropriate particle size range, and generally control the particle size at (0.15-0.3) μm.
See Table 1 for the effect of titanium dioxide average particle size and particle size distribution on oil dispersibility.
Table l Effect of average particle size and particle size distribution on oil dispersibility Titanium dioxide origin Average particle size nm Distribution width Oil dispersibility/μm
Panzhihua 273.5 0.102 35
Henan 467.7 0.323 75
Yunnan 378.2 &n
Table 1 shows the oil dispersibility test of titanium dioxide powders with different particle size distributions. It is found that the average particle size and the width of the particle size distribution (mass percentage normal distribution map) have a great influence on the dispersibility of titanium dioxide oil. According to a large number of experimental data statistics, the following conclusions can be drawn; when the particle size distribution width of titanium dioxide is less than 0.1, it is detected by a squeegee fineness meter, and the fineness is (40-30) p. m, when the peak width is 0.2, the fineness is about 60 gm, and if the distribution width is more than 0.3, basically the product cannot be used in the solvent-based paint, and treatment measures must be taken. Therefore, the particle size distribution is required to be as uniform as possible, to increase the grinding strength of the product, to reduce the distribution width, and to improve oil dispersibility.
4.2 Soluble substances in titanium dioxide The level of soluble substances in titanium dioxide also seriously affects the application performance of titanium dioxide. Titanium dioxide In the mixed paint dispersion system, the soluble salt is generally a very strong inorganic ion, which will offset the charge on the surface of the titanium dioxide, but can not form a strong electric double layer, but weaken the surface of the titanium dioxide. The adsorption inhibits the resin from being firmly adsorbed on the surface of the titanium dioxide particles, which reduces the degree of dispersion stabilization, resulting in the coarsening of the titanium dioxide in the solvent-based coating. In addition, in some insulating paints, the high solubility of the soluble substance reduces the electrical resistivity of the system and reduces the insulation properties of the surface of the coated object. At the same time, the electrochemical properties of the coating are obvious, and the chemical resistance and corrosion resistance are lowered. . See Table 2 for the effect of titanium dioxide soluble materials on oil dispersibility.
Table 2 Effect of soluble matter of titanium dioxide on oil dispersibility Sample Purified water Water soluble substance /% Distribution width Oil dispersibility / μm
Sample 1 deionized water 0.45 0.122 40
Sample 2 Production water 0.82 0.150 60
Sample 3 Deionized water 0.35 0.102 30
As can be seen from the data in Table 2, the water-soluble substance does have a certain influence on the oil dispersibility of the product. According to the quality assurance requirements of titanium dioxide products, the content of soluble substances must be controlled to be less than 0.5%. Therefore, deionized water must be used in the titanium dioxide purification process to remove impurity ions. [next]
4.3 Oil absorption of titanium dioxide Experiments have shown that if titanium dioxide has a high oil absorption, the titanium dioxide is definitely poorly dispersed or unstable in solvent oil and tends to aggregate. In the solvent-based coating, the high-oil absorption titanium dioxide is proportioned, ground and dispersed according to the original formula, and a part of the solvent oil is absorbed by the titanium white powder, so that the oil of the dissolved resin is insufficient, the degree of solvation of the resin is lowered, and the titanium dioxide is affected to the resin. The adsorption causes a decrease in dispersibility and dispersion stability.
5 Ways to improve the dispersibility of titanium dioxide in solvent-based coatings 5.1 Strict control of particle size and particle size distribution The factors affecting the particle size and particle size distribution of titanium dioxide are complex. Firstly, the hydrolysis process and technology are improved to ensure uniform formation of primary particles. . The second is to strengthen the control of the critical temperature point of calcination, so that the titanium dioxide particles grow evenly. Finally, the powder of the product is carried out. At present, most of the crushing processes of titanium dioxide enterprises adopt Raymond system, and it is also possible to use a jet mill with high efficiency and good classification effect to further control the particle size of titanium dioxide and stabilize the surface characteristics.
5.2 Control of oil absorption and water-soluble substances The oil absorption of titanium dioxide is mainly related to the calcination atmosphere or the high temperature of calcination during calcination. If improperly controlled, it will cause lattice defects and irregular particle shape of titanium dioxide particles. Therefore, it is necessary to control the appropriate Calcination temperature, reasonable adjustment of feed amount and kiln rotation speed, reducing lattice defects of particles and regular geometric shape of particles.
5.3 Surface treatment
The surface of the titanium dioxide is treated or a certain dispersant is added. The dispersant can be firmly adsorbed on the surface of the titanium dioxide, and can provide a long chain of resin solvation, which is more favorable for the adsorption of titanium dioxide and resin, and increases. The degree of dispersion stabilization. The composition of the dispersant generally having such characteristics is relatively complicated, and most of them are polyalkylamine alkylammonium salts.
Currently, the majority of domestic manufacturers is the low level of anatase type products, in the solvent-borne coatings generally poor dispersibility, thus applied in paint industry is gradually replaced by rutile product. The anatase titanium dioxide can be surface-treated to change its surface properties, which can be comparable to the oil dispersion of rutile products to some extent, and the price is low and the rutile products have certain market competitiveness. Comparative domestic surface treatment agent are favored: silicone, coupling agent, or some nitrogen poly phosphates and the like, wherein more silicone treatment applications, and have been successful in the industry.
6 Conclusion Based on the surface characteristics of titanium dioxide, the role and dispersion mechanism of titanium dioxide in solvent-based coatings were discussed. The factors affecting the dispersion of titanium dioxide in solvent-based coatings were also analyzed. It was proposed to improve the solubility of titanium dioxide in solvents. A new way of dispersibility in coatings.
Titanium white powder is an excellent quality white pigment powder, having good light scattering ability, and thus good whiteness, high color strength, hiding power, while having high chemical stability and good weather resistance, non-toxic, odorless It has no stimulating effect on human body and is widely used in industrial fields such as coatings, plastics, papermaking and ink. In solvent-based coatings, titanium dioxide, as a white pigment, is a secondary film-forming material that not only imparts a bright white color to the surface of the object but also has weather resistance, chalking resistance and rheology. Certain role. The oil dispersibility of titanium dioxide is very concerned about solvent coatings and plastics. Its advantages and disadvantages will greatly affect the production process, production equipment and product quality. Based on the surface properties of titanium dioxide, combined with the composition of solvent-based coatings, the dispersion mechanism of titanium dioxide in solvent-based coatings was discussed, and the factors of shadow orientation were analyzed. This provides a theoretical basis for improving the dispersibility of titanium dioxide in solvent-based coatings, and has certain reference significance.
2 Titanium dioxide surface properties
Titanium dioxide is an inorganic compound that is insoluble in water and insoluble in oil, but is capable of being dispersed in a water or oil medium. Titanium dioxide has a small particle size and a high specific surface energy, so it exhibits strong agglomeration characteristics in a single solid phase to reduce surface energy and form relatively stable sub-aggregated particles. Studies have shown that the adsorption of water in the surface of titanium dioxide will form a basic "terminal" hydroxyl group and an acidic "bridge" hydroxyl group with water. From the detection of zeta potential, the surface is highly electronegative ( The anatase titanium dioxide has a Zeta potential of about -50 mv), which forms an adsorption layer of the same charge and has a strong adsorption effect. The titanium dioxide exhibits strong high dispersibility and strong surface adsorption in the two phases.
3 Dispersion mechanism of titanium dioxide in solvent-based coatings
3.1 Basic composition of solvent-based coatings Solvent-based coatings mainly include film-forming base oils or resins, dispersion medium volatile organic solvents and pigments. The film-forming base material is the main film-forming material of the paint, and the pigment is a coloring and covering effect to the object, and belongs to a secondary film-forming material. The dispersion medium is such that the film-forming binder and pigment are well dispersed to form a viscous liquid. Therefore, the dispersion mechanism of titanium dioxide in solvent-based coatings is to discuss the wetting and dispersing process of titanium dioxide in the mixed coating of film-forming base and dispersion medium (volatile organic solvent).
3.2 Interaction between titanium dioxide, resin and solvent oil Solvent oil can completely dissolve the resin to form a mixed paint. The strong surface adsorption of titanium dioxide can adsorb the resin and solvent oil. In the dispersion process of titanium dioxide, the resin is required to adsorb as much as possible on the surface of the titanium dioxide as much as possible, and the solvent oil is not adsorbed as much as possible, which is beneficial to the solubility of the solvent oil to the resin and the solubility of the resin. The coating formed with titanium dioxide is highly stabilized. Therefore, titanium dioxide, resin and solvent oil interact with each other and restrict each other. The abnormality of any one component will affect the performance of the whole system.
3.3 Dispersion mechanism of titanium dioxide in solvent-based coatings In solvent-based coatings, solvent oils are generally non-polar solvents or solvents with very weak polarity. The electrical properties are very weak, and the electric double layer formed on the surface of titanium dioxide is weak. A strong electric double layer effect is formed on the whole system to reduce the surface energy and reach a stable state. In this system, titanium dioxide is adsorbed by the polymer resin, and the polymer is solvated by the solvent oil. Therefore, the adsorbed resin has a solvated long chain, and these solvated long chains are neatly arranged on the surface of the titanium dioxide particles. Arranged to form a shield of a certain area. When two oxidized long-chain-coated titanium dioxide particles are close to each other, the solvated long chains interpenetrate, and during the intercalation process, the concentration of the polymer resin in the intercalation region increases, and the osmotic pressure difference is formed in the adjacent region due to the difference in osmotic pressure. The effect is to force the solvent oil to flow out to the region with low pressure difference, forcing the particles to separate, so as to achieve the purpose of dispersing the titanium dioxide in the mixed paint of the resin and the solvent oil.
Therefore, the dispersion mechanism of titanium dioxide in solvent-based coatings can be explained by the surface adsorption shielding effect. [next]
4 Factors affecting the dispersion of titanium dioxide In solvent-based coatings, when the resin and solvent oil are determined, the degree of dispersion and dispersion stabilization of titanium dioxide in the mixed paint is determined by its own application properties and surface properties.
4.1 Average particle size and particle size distribution of titanium dioxide The average particle size and particle size distribution of titanium dioxide are comprehensive indicators reflecting the performance and application properties of titanium dioxide pigments. Through a large number of experiments, the zeta potential is about -70mv when the mass percentage of titanium dioxide is less than 200nm, and the zeta potential is about -40mv. If the mass percentage is less than 20%, the zeta potential is about -40mv, which indicates that titanium dioxide is The particle size situation seriously affects the surface electrical properties, which affects the surface adsorption properties. However, the particle size should not be too small, otherwise it will affect the performance of other pigments, so it is necessary to control the appropriate particle size range, and generally control the particle size at (0.15-0.3) μm.
See Table 1 for the effect of titanium dioxide average particle size and particle size distribution on oil dispersibility.
Table l Effect of average particle size and particle size distribution on oil dispersibility Titanium dioxide origin Average particle size nm Distribution width Oil dispersibility/μm
Panzhihua 273.5 0.102 35
Henan 467.7 0.323 75
Yunnan 378.2 &n
Table 1 shows the oil dispersibility test of titanium dioxide powders with different particle size distributions. It is found that the average particle size and the width of the particle size distribution (mass percentage normal distribution map) have a great influence on the dispersibility of titanium dioxide oil. According to a large number of experimental data statistics, the following conclusions can be drawn; when the particle size distribution width of titanium dioxide is less than 0.1, it is detected by a squeegee fineness meter, and the fineness is (40-30) p. m, when the peak width is 0.2, the fineness is about 60 gm, and if the distribution width is more than 0.3, basically the product cannot be used in the solvent-based paint, and treatment measures must be taken. Therefore, the particle size distribution is required to be as uniform as possible, to increase the grinding strength of the product, to reduce the distribution width, and to improve oil dispersibility.
4.2 Soluble substances in titanium dioxide The level of soluble substances in titanium dioxide also seriously affects the application performance of titanium dioxide. Titanium dioxide In the mixed paint dispersion system, the soluble salt is generally a very strong inorganic ion, which will offset the charge on the surface of the titanium dioxide, but can not form a strong electric double layer, but weaken the surface of the titanium dioxide. The adsorption inhibits the resin from being firmly adsorbed on the surface of the titanium dioxide particles, which reduces the degree of dispersion stabilization, resulting in the coarsening of the titanium dioxide in the solvent-based coating. In addition, in some insulating paints, the high solubility of the soluble substance reduces the electrical resistivity of the system and reduces the insulation properties of the surface of the coated object. At the same time, the electrochemical properties of the coating are obvious, and the chemical resistance and corrosion resistance are lowered. . See Table 2 for the effect of titanium dioxide soluble materials on oil dispersibility.
Table 2 Effect of soluble matter of titanium dioxide on oil dispersibility Sample Purified water Water soluble substance /% Distribution width Oil dispersibility / μm
Sample 1 deionized water 0.45 0.122 40
Sample 2 Production water 0.82 0.150 60
Sample 3 Deionized water 0.35 0.102 30
As can be seen from the data in Table 2, the water-soluble substance does have a certain influence on the oil dispersibility of the product. According to the quality assurance requirements of titanium dioxide products, the content of soluble substances must be controlled to be less than 0.5%. Therefore, deionized water must be used in the titanium dioxide purification process to remove impurity ions. [next]
4.3 Oil absorption of titanium dioxide Experiments have shown that if titanium dioxide has a high oil absorption, the titanium dioxide is definitely poorly dispersed or unstable in solvent oil and tends to aggregate. In the solvent-based coating, the high-oil absorption titanium dioxide is proportioned, ground and dispersed according to the original formula, and a part of the solvent oil is absorbed by the titanium white powder, so that the oil of the dissolved resin is insufficient, the degree of solvation of the resin is lowered, and the titanium dioxide is affected to the resin. The adsorption causes a decrease in dispersibility and dispersion stability.
5 Ways to improve the dispersibility of titanium dioxide in solvent-based coatings 5.1 Strict control of particle size and particle size distribution The factors affecting the particle size and particle size distribution of titanium dioxide are complex. Firstly, the hydrolysis process and technology are improved to ensure uniform formation of primary particles. . The second is to strengthen the control of the critical temperature point of calcination, so that the titanium dioxide particles grow evenly. Finally, the powder of the product is carried out. At present, most of the crushing processes of titanium dioxide enterprises adopt Raymond system, and it is also possible to use a jet mill with high efficiency and good classification effect to further control the particle size of titanium dioxide and stabilize the surface characteristics.
5.2 Control of oil absorption and water-soluble substances The oil absorption of titanium dioxide is mainly related to the calcination atmosphere or the high temperature of calcination during calcination. If improperly controlled, it will cause lattice defects and irregular particle shape of titanium dioxide particles. Therefore, it is necessary to control the appropriate Calcination temperature, reasonable adjustment of feed amount and kiln rotation speed, reducing lattice defects of particles and regular geometric shape of particles.
5.3 Surface treatment
The surface of the titanium dioxide is treated or a certain dispersant is added. The dispersant can be firmly adsorbed on the surface of the titanium dioxide, and can provide a long chain of resin solvation, which is more favorable for the adsorption of titanium dioxide and resin, and increases. The degree of dispersion stabilization. The composition of the dispersant generally having such characteristics is relatively complicated, and most of them are polyalkylamine alkylammonium salts.
Currently, the majority of domestic manufacturers is the low level of anatase type products, in the solvent-borne coatings generally poor dispersibility, thus applied in paint industry is gradually replaced by rutile product. The anatase titanium dioxide can be surface-treated to change its surface properties, which can be comparable to the oil dispersion of rutile products to some extent, and the price is low and the rutile products have certain market competitiveness. Comparative domestic surface treatment agent are favored: silicone, coupling agent, or some nitrogen poly phosphates and the like, wherein more silicone treatment applications, and have been successful in the industry.
6 Conclusion Based on the surface characteristics of titanium dioxide, the role and dispersion mechanism of titanium dioxide in solvent-based coatings were discussed. The factors affecting the dispersion of titanium dioxide in solvent-based coatings were also analyzed. It was proposed to improve the solubility of titanium dioxide in solvents. A new way of dispersibility in coatings.
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