Wet grinding, dispersion and grading of titanium dioxide

Titanium dioxide pigment wet milling fractionation prior to the surface treatment is a very important part, since the titanium dioxide coarse particles by pulverization after calcination although Raymond, but still there is a coarse particles or aggregates of particles of a certain number of 10μm ~ No It is crushed, especially when crushed with Raymond mill. Many crushed fine particles are pressed together to form agglomerated particles due to rolling, which requires a large amount of energy to separate. Usually, the fineness of the sieve is measured, usually using a 325 mesh standard sieve, and the pore diameter is about 45 μm. The titanium dioxide pulverized by the Raymond mill generally contains large particles of 0.05% to 0.15% and more than 45 μm, so the coarse particles of 1 to 10 μm are used. by sieve method is not measured out, especially rutile type titanium dioxide particles hard, coarse particles are more easily mixed. DPFields et al. of DuPont Chemicals Department of the United States believe that large particles of 30μm or more mixed in titanium dioxide are sufficient to cause flaws and streaks on the surface of coating film and plastic profiles; particles above 5μm have a significant effect on dispersion; 0.5μm or more Any large particles have a great influence on the gloss of the coating film; the particles of 0.1~0.5μm mainly affect the optical properties such as hiding power, tinting strength and background color (see Figure 1).
The average primary particle size of the industrial titanium dioxide pigment is about 0.15~0.35μm. It is difficult to pulverize the aggregate to the original particle size by a general mechanical pulverizer, and the steam pulverizer can achieve the requirement of pulverizing to the primary particle, but Since the titanium dioxide particles are very fine, the surface area is large, and the surface free energy is high, the bonding force between the collected particles is very strong, and the crushing energy consumption by the steam jet mill is high and uneconomical. Some studies have done a comparison: If the limit of the fineness of the ordinary mechanical crusher is 10 μm, then the steam mill can be used to crush to 1 μm, and the wet sand mill can be crushed to less than 0.5 μm. Since the surface treatment of titanium dioxide generally adopts a wet coating, a certain dispersion and concentration of TiO 2 aqueous dispersion is required before coating, so wet grinding is the most effective ultrafine pulverization method for titanium dioxide so far, and the sand mill is wet pulverized. The main equipment for the preparation of high dispersions.
Wet grinding has special requirements for slurry concentration, viscosity, Ph dispersion state and ball loading (beads). The slurry concentration when wet-milling titanium dioxide is generally controlled at 600~1200g/L, pH value 8~11, bead volume (net volume percentage); sealed vertical 70%~80%, open vertical 60%~70%; Horizontal 80%~85%. It is generally recommended that the diameter of the smallest bead must be more than 2.5 times the size of the exit filter slit, and the spacing between the outer edge of the dispersion disc and the inner liner of the sander must be four times the diameter of the largest bead. Due to the high density of the zirconium beads, from the kinetics, the beads with high density can obtain a large impact energy, so that the rotation speed is not too high, and the linear velocity of the dispersion disk is generally about 14 m/s.
For materials that are difficult to pulverize or have coarser particles, two sand mills can be operated in series because titanium dioxide is not destroyed by excessive grinding. On the contrary, organic pigments have ionic bonds between inorganic pigment crystals due to their intermolecular bonding. Covalent bond bonding is weak, and excessive grinding can affect the quality of organic pigments. For products with higher water-soluble salts, it is best to choose hot wash 1 time before wet grinding, while chlorinated titanium dioxide can be directly ground by sand mill due to the fine particle size of the product after gas phase oxidation. After the classification, the surface treatment is carried out, and the wet pulverization is also advantageous for removing the residual chlorine in the product, but it is preferably steam dechlorination and then wet grinding.
In the wet grinding, the titanium dioxide slurry is kept in a dispersed state, and the effect of wet grinding is good. At the same time, the titanium dioxide must be subjected to a good dispersion state in the surface treatment of the coating. The pH of the uncoated titanium dioxide in the best dispersion state in water is 8-11, so it can be adjusted to the process specified value by alkali (NaOH) or sodium silicate (water glass) before being wet-ground. In addition to adjusting the pH, the dispersing agents may also be added such as: triethanolamine, diisopropanolamine, sorbitol, phosphate, sodium hexametaphosphate, sodium pyrophosphate, sodium carbonate and the like. Sodium hexametaphosphate has a strong dispersion of solid particles in the fine dispersion because it is a linear polyphosphate glass body that forms a soluble complex with metal ions such as calcium and magnesium in the dispersion medium. , to shield the multivalent cations, prevent these positively charged ions from electrically neutralizing with the negatively charged titanium dioxide, and its substructure is as follows:
Gravity-type settling classifier In China, we used water tanks in the past, calculated the sedimentation height and settling time of the particles according to the Stokes formula, and then separated the two kinds of suspended matter with different particle size distributions at the specified height. Taking rutile titanium dioxide as an example, when it is not a dispersion medium, the viscosity of water at room temperature is η=0.01 poise, the relative density ρ=1, and the relative density of rutile-type titanium dioxide ρ=4.2, calculated according to the Stokes formula, the diameter is It takes 4 min for the 5 μm rutile-type titanium dioxide particles to settle to a height of 1 cm. This method is simple and easy to operate. The disadvantages are gap operation, long settling time, low water selectivity and limited suspension stability. In the past, the gravity settlement of foreign countries generally adopts the Dorr Hydroseparator. Its principle is similar to that of the general Doer type settlement bucket. It is mainly graded by controlling the speed of overflow. One settlement area is 16m 2 and the settlement height is 2.7. The continuous gravity sedimentation classifier of m can classify 20t titanium dioxide every day. The overflow liquid can contain no large particles of more than 6μm. This equipment can be operated continuously, but the equipment is heavy, the floor space is large, and the slurry concentration is dilute. Less adopted.
It can be seen from the above formula that increasing the centrifugal force only by increasing Vt (increasing the feed pressure) to increase the flow rate and reducing the diameter of the cyclone is solved. Therefore, the diameter of the cyclone is generally small, usually 10 to 40 mm. The largest is only 100mm, the feed pressure is 0.15~0.7MPa, and the concentration of pulp washing clothes is 150~300g/L. The hydrocyclone designed by China Institute of Chemical Industry Coatings was used in titanium dioxide factories in Nanjing and Xiamen. 95 porcelain, its specifications are: cyclone diameter D = 15mm; cylinder height H = 34mm; feed port size = 2 × 8mm; overflow nozzle diameter ф = 3.5mm; bottom nozzle diameter ф = 1.4mm; The cone angle of the flow cone is 10°. Using this type of hydrocyclone to classify large particles of rutile-type titanium dioxide of 5 μm, the slurry concentration is controlled to be TiO 2 :H 2 O=1:8, and the dispersant (polyphosphate) is added in an amount of 0.3% to 0.6%. 2h, in the case of a feed pressure of 0.15MPa, the primary classification rate can reach 85%, and the single production capacity is 100t/a.
The working principle of the horizontal screw discharge sedimentation centrifuge (see Fig. 5) is that the suspension enters the hollow shaft of the screw conveyor at full speed and rotates along the feed pipe, and flows into the drum through the discharge port due to the centrifugal force. The coarse particles in the suspension settle on the inner wall of the drum and gradually fill the gap between the drum and the screw conveyor. Since the rotation speed of the screw is slightly lower than the rotation speed of the drum, the coarse particles are pushed by the screw to the drum. The discharge port of the end is discharged, and then enters the sand mill for wet grinding to form a closed loop system. The filtrate (fine particle portion) is located at the central portion of the drum, and the spiral passage formed along the auger flows to the large end of the drum and is discharged through the overflow baffle.

Pavement Hot Melt Road Marking Machine 

Latest aptitude program controller from Germany and human-friendly contrarily are adopted in the  vibrating  marking machine which it possible the prominent marking and prime mark painted at the same time and for just once .It is also equipped with step-less speed changing which makes the movement is  carried out at will.It  greatly promotes the implementing efficiency and makes the marking accurately fit the shape ,height and space between.It meets the requirement of various road condition and measures up to international norms.The road marks made by it can resist transformation ,abrasion and strikes.
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Features of fixing
Compulsory deceleration,reminding by shakes,glistening in rainy days and anti-slippery
1.Compulsory deceleration:remind the driver to slow down in dangerous section such as turn and slopes;
2.Reminding by shakes:Remind and warn the diver who drivers in fatigue or absent-mindedly;
3.Glistening in rainy days:Mark driving safe with clearer visual.
4.Anti-slippery:Magnify the friction with road and slow down the vehicle.
Major functions
When the driver is driving in fatigue or absent –mind-eely,the car shakes when it passes over the prominent lines giving out harsh noise.As a result,the driver comes back to sense promptly and readjusts the direction of the car thus preventing accidents.The prominent lines have better tree-dimensional reflection of light  so that  the driver can tell the direction and lane in rainy days.The mark lines guarantee the security of driver and provide compulsory deceleration and anti-slip-pery.

Main scope: Concrete Grinding machines, Floor Polishing Machines, Road Line Marking Machines, Truck Cranes, Road Rollers, excavators, Concrete Leveling Machines, Power Trowels and other Construction machinery .

Jining oking tec co.,ltd, established in 2010, is a professional manufacturer engaged in the research, development, production, sale and service of Concrete Grinding machines, Floor Polishing Machines, Road Line Marking Machines, Truck Cranes, Road Rollers, Excavators, Concrete Leveling Machines, Power Trowels and other Construction machinery .

We are located in Jining city,Shandong province with convenient transportation access. Dedicated to strict quality control and thoughtful customer service, our experienced staff members are always available to discuss your requirements and ensure full customer satisfaction.

In recent years, we have introduced a number of advanced production equipment, and also have an excellent production team and a complete quality assurance system to ensure that each batch of goods is delivered to customers in a timely and high quality.

We also have an excellent management team, experienced technical staffs and professional sales team to solve all problems you encountered before and after sales. In addition, we have obtained I S O 9 0 0 1:2 0 1 5 certificates. Selling well in all cities and provinces around China, our products are also exported to clients in such countries and regions as United States, Europe,Australia, Southeast Asia,Russia,the Middle East,Africa. We also welcome OEM and ODM orders. Whether selecting a current product from our catalog or seeking engineering assistance for your application, you can talk to our customer service center about your sourcing requirements.

Thermoplastic Road Line Marking Machine

Thermoplastic Road Line Marking Machine

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