Most of the redispersible polymer powder uses the parallel spray drying process, that is, the motion direction of powder is the same with hot air. Some also uses the counter-current spray drying process, with air or nitrogen generally used as the drying medium. During spray drying, emulsion particles are prone to condensation, discoloration and other problems, so it is necessary to strictly control the emulsion additives, dispersion and solid content, as well as the spray form, spray pressure, droplet size, inlet and outlet hot air temperature, air speed and other process factors. In general, dual nozzle or multi nozzle has superior effects heat utilization to single nozzle. Usually the nozzle pressure is about 4 x 105Pa, the inlet temperature of hot air between 100 and 250℃, the outlet temperature about 80℃. Adding such inert mineral anti-caking agents as kaolin, diatomaceous earth and talcum powder can prevent caking. But if added before drying, then anti-caking agents may be encapsulated by polymers into microcapsules and lose power. Most are sprayed with emulsion respectively and independently at the top of dryer, but it is also easy to lose and crust on the dryer and pipeline by air currents. The better method for adding additives is a two-part method. One part is sprayed with compressed air at the top of dryer, and the other part enters with the cold air at the bottom. In order to prevent caking, the remaining part can be saponified during the emulsion polymerization process when polymerization reaches 80% to 90%. Or melamine-formaldehyde condensates may be added to the emulsion. Also, a certain kind of emulsifier emulsion can be utilized.
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