Dispersion milling importance

The solids feeder may be of aiw type Screw feeders, venturi sections, high-speed grinders, and dispersion mills are employed. For pneumatic conveyors, selection of the correct feeder to obtain thorough initial dispersion of solids in the gas is of major importance. For example, by employing an air-swept hammer mill in a drying operation, 65 to 95 percent of the total heat may be transferred within the mill itself if all the drying gas is passed through it. Fans may be of the... 

Kinetic Dispersion Mills. Another important mill is the Kady mill developed by Charles Kew of the Kinetic Dispersion Corp. (21). By many it is considered another high-speed dissolver because both use a high-speed impeller even though there are basic differences between the two mills. 

In the tape process, one of the most important steps is the dispersion milling procedure. This will be described in more detail later in this book. One of the primary purposes of this procedure is to break down soft agglomerates that have formed as a result of high surface area. Dry agglomerates are caused by weak interparticle forces, that is, van der Waals and H-bonds. If one looks at a scanning electron micrograph of a typical powder in the as-received condition, it will... 

The second process to finish phthalocyanine, which is more important for P-copper phthalocyanine, involves grinding the dry or aqueous form in a ball mill or a kneader (64). Agents such as sodium chloride, which have to be removed by boiling with water after the grinding, are used. Solvents like aromatic hydrocarbons, xylene, nitrobenzene or chlorobenzene, alcohols, ketones, or esters can be used (1). In the absence of a solvent, the cmde P-phthalocyanine is converted to the a-form (57,65) and has to be treated with a solvent to regain the P-modification. The aggregate stmcture also has an impact on the dispersion behavior of a- and P-copper phthalocyanine pigments (66). 

For the purpose of paint formulation the most important units of equipment are the laboratory ball mill, bead mills and high speed dispersers. The most common, the ball mill, consists of a cylindrical porcelain vessel a little more than half filled with steel, porcelain balls or pebbles. Pigment, together with sufficient binder and solvent to make a free-flowing mix, is loaded into the mill until it is approximately two-thirds full. The mill is then closed and fixed into a device whereby it is made to rotate about its major axis. Normally, a period of about 16 hours is required for thorough dispersion of the pigment, whereupon the mill-base is emptied out and blended with the remainder of the ingredients. 

P.O.36 is completely fast to overcoating. Bleeding into a white overcoat is only observed at baking temperatures above 160°C. P.O.36 is heat stable up to 160°C. In dispersing the opaque type, it is important to avoid excessive shearing forces and to closely monitor the temperature, especially if agitated ball mills are used. Faulty temperature control may lead to a dull color. 

Baking is currently performed by continuous operation. Modern variations involve using heated crushing or milling equipment, such as kneader dispersers or oscillating mills at approximately 200°C [9]. This technique significantly improves the reaction control over a batch process. If baking is performed by continuous process, phthalonitrile only remains within the reaction vessel for a very short period of time (between 3 and 20 minutes). It is important to remember that the temperature may not exceed 250°C. The product which evolves from this process is usually purified by acid treatment. 

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