Coating Science Popularization: how to achieve good dispersion effect of titanium dioxide

Dispersion is the premise of coating treatment on the surface of titanium dioxide particles The ideal dispersion is that particles are dispersed in the state of primary particles, so that the membrane can be coated on the primary particles Otherwise, due to poor dispersion, the membrane is coated on the periphery of the flocculation group When the flocculation group is subjected to ultra-fine crushing, the membrane will be incomplete and cannot achieve the expected effect In the process of dispersion, the materials (or oxide materials) after pre grinding (Raymond Mill) are firstly added into the desalted water to make slurry, which is dispersed by stirring In order to improve the dispersion effect, the dispersant needs to be added Generally, the difficulty of dispersion is related to the concentration of TiO2 Therefore, only from the perspective of dispersion, reducing the concentration is beneficial to dispersion However, the condition of the next process must be considered When the subsequent process is directly coated, the concentration only needs to meet the coating process requirements; when the subsequent process is connected to wet grinding, the conditions conducive to wet grinding must be fully considered In order to improve the grinding effect, the concentration of materials should be increased In the past, the concentration of pre dispersed slurry was controlled at about 30%, but now it has been increased to 40% There are still higher concentrations abroad Under the condition of satisfying the material flow performance, it is beneficial to increase the concentration In order to ensure the equipment is complete, the grinding time of materials should not be too long When it is really needed, measures such as external cooling and series connection should be taken The equipment of wet grinding usually adopts sand mill, which has high energy consumption and large investment However, it has significant dispersion function and can improve the shape of particles Therefore, it is used in most post-treatment devices There are many sand mills in China, whose products are widely used in paint and coating industries However, there are few sand mills for titanium white production, and the equipment specifications are relatively small For the ten thousand ton titanium white production plant, the imported large sand mills should be used The grinder can be divided into vertical and horizontal type The vertical type is operated under normal pressure, and the horizontal type can operate under certain pressure Both of them are used in the production of titanium dioxide abroad The cylinder of the grinding machine should be wear-resistant metal material or wear-resistant non-metal material Considering that the abrasion of the cylinder may cause pollution to the product, wear-resistant non-metal material should be preferred The working medium of the grinding machine is sand or bead The requirement of the working medium is wear resistance and high density The more suitable sand is Ottawa sand, and its diameter is less than 1mm The grinding effect of the grinding machine is the basic requirement for the selection of the grinding machine For the semi-finished product of titanium dioxide (the material or oxide material after Raymond), the particle size is required to be less than 325 mesh For the high-quality titanium white product, the particle size after grinding has been greatly improved compared with the 5 μ m controlled by the gravity sedimentation classification, which is required to be less than 1 μ m, which is difficult to be achieved only by mixing For the imported grinder, it can basically meet the requirements As for the calibration of the production capacity of sanding mill, due to the lack of experience of domestic manufacturers and the lack of foreign operation data, plus the factors related to the characteristics of materials and pre dispersion status, it is difficult to generalize It is customary for some manufacturers to use the residence time to determine the capacity, but it involves the factors such as the concentration of materials and the quality of grinding status, etc., when using the residence time It seems unscientific to calibrate the grinding machine in between Instead, the energy consumption of grinding injection is about 40kW H.ttio2 for the horizontal grinder (recommended by the manufacturer) That is to say, the production capacity of the grinder is obtained by dividing the actual power consumption of the grinder by the energy consumption per unit product For vertical sand mills, the grinding energy consumption (recommended by the manufacturer) is about 80kW H / ttio2 On the surface, the production capacity of horizontal and vertical sanding mills is quite different In fact, the production capacity of sanding mills should be determined according to the material characteristics and grinding requirements If necessary, it should be tested After sanding, TiO2 particles in the slurry have been well dispersed, which can meet the requirements of coating However, in the process of sanding, the abrasion of sand or ball is objective, and even sometimes it may break When the particle size of sand or ball is smaller than a certain size, it will flow out of the sanding machine with materials These particles have no pigment performance, and mixing products will have an impact on the quality, at the same time, it will also affect the subsequent processing equipment, and may even cause damage to the equipment This requires the removal of these foreign particles.