WURSTER COATING- PROCESS AND PRODUCT VARIABLES - IJPI

INTERNATIONAL JOURNAL OFREVIEW ARTICLEPHARMACEUTICAL INNOVATIONS ISSN 2249-1031external to coating partition must beoccupied by the particles to be coated. Thismakes it possible to have sufficientquantity of particles inside the partition toaccumulate the maximum coating solutiondroplets and to avoid premature drying, ordepositing on the walls of the partition. Tocalculate load of particles to be introducedfollowing formula can be used-M= (r 1 2 -r 2 2 ) πLρ pWhere r 1 and r 2 are chamber radius andpartition radius, L is the length of thepartition; ρ p is bulk density of particles [7] .Air Distribution Plate: Suitable baseplate has to select to get consistentfluidization at minimum attrition. Thefluidization volume affects particlevelocity; the smaller particle requireslesser air volume to attain certain heightthan the bigger particles. The differentialpressure and air velocity at the airdistribution plate must be almost same.Therefore when we deal with the smallerparticle we have to use plate with lesseropening area to create the resistance at theAir Distribution Plate to have betterdistribution of the air [6, 1] .Fluidization Air Flow: The inlet airvolume is not to dry the product it has tobe used to achieve desired fluidizationpattern. The drying of the product can beachieved by adjusting the temperature. Fornon-aqueous coating a bubbling type offluidisation in down bed is suggested tominimize the generation of static chargeand particle friction, whereas for aqueouscoating more rigorous fluidization isneeded to have more drying efficiency. Atlow airflow rates the air passes through thebed without disturbing the solid particles,as air flow is increase some of particles getVolume 2, Issue 2, March− April 2012start to move upward. When the air flow isincrease up to certain value particles startmoving upward and fell through innercylinder like a fountain. During this thepressure drop and remain constant, andparticle moves in regular way [1, 6, 7] .Fluidization Air Humidity: Inlet airhumidity is the most critical factor. Itshould be considered because before itenters the HEPA filters, get heated andpass through the equipment air is drawnfrom the external environment. Thehumidity of air may vary from season toseason or day to day. The changes in dewpoint of air changes the evaporatingefficiency of that air.Lower humidity inthe inlet air will enhance the dryingcapacity of air even at low temperature butit will cause excessive static charge in theproduct. To eliminate static charge andprocess variability, the required specificand absolute level must be set at the initialstage of development itself. Too highabsolute humidity will result in adepression in air temperature below dewpoint, which will cause the condensationof water either on to machine or productsubstrate surface. It is not recommended tokeep high moisture for a highly watersoluble substrate at intial stage. Thehumidity can be increased after the initialcoating because the static charge developsonly once the pellets are coated withpolymers [2, 5,11] .Fluidization Air Temperature: It willdepend on the spray rate, type of solvent,tackiness of solution and have directimpact on product humidity and producttemperature. For aqueous solvent hightemperature is needed to avoidagglomeration of particles while for non-62 | P a g ehttp://www.ijpi.org