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Dip Coating

Dip coating is one of the simplest and oldest methods of painting industrial goods. It is easy to use to automate, has a much higher material yield when compared with spray coating and low capital costs. The process makes use of the adhesion properties of viscous paints on the objects to be painted. Its disadvantages are the lack of prpcessing window with regard to film thicknesses and the defects associated with it, such as runs and blisters, the costs and the need for special precautionary measures to avoid explosions or fires when using solventborne paints. As a result of these dangers and corresponding incidents practically only waterbased dip coats are now used in the few still operating conventional systems.

(Artur Goldschmidt, BASF Handbook On Basics Of Coating Technology,p.478)


Curtain coating

In curtain coating, the momentum of the falling curtain aids in holding the coating liquid against the web and opposing air entrainment. Thus the velocity of the faling curtain, determined by the height of the curtain and also by the velocity of the liquid film leaving the slide, helps determine of the maximum coating speed. Also, as with both slide and slot coating, the flow rate itself is very important, aside from the need for a minimum flow to form the curtain. If the web stationary, the curtain on striking the web will split in the opposite direction. As the web starts moving, more of the flows goes in the direction of the web.Above some speed, all the liquids moves in the web direction. But even when all the liquid moves in the  web direction, at speeds just above the minimum, some liquid still goes backward a short distance before turning forward, to form a heel, as shown by Kistler(1984).

 

(Edgar B. Gutoff, Edward D. Cohen, Coating and Drying Defects: Troubleshhoting Operating Problems, p. 127) 


Tribo Charging

Tribocharging is the process of electricity generation when two different materials rub against each other. Some materials easily give up or accept electrons from other materials under friction. A triboelectric series lists materials that give up electrons in order from easiest to hardest. For many materials, the dielectric constant determines the position of that materialon the triboelectric series. Additional materials such as rabbit fur have been added based on experimentation. The further aart the two materials are that rub against each other, the more charge is transferred.

(Laurabce W. McKeen, Fluorinated Coatings and Finishes Handbook, p.150)

Corona Charging

Corona charging of the dielectric surface is realized using a corona discharge in air. A discharge is initiated by high DC voltage(5- 10kv) appliedto a corona electrode, which is a thin wire or a needle located about 1cm above the wafer. The ions created in this discharge are predominantly and (  for negative and positive polarity respectively. The very short mean free path ( cm) of the ions ensures collisiondominated transport with ions becoming thermalized before reaching the wafer. Corona charge deposition is non-destructive for charge doses up to few µC/ . For larger doses and especially for high corona fluxes, prolonged charging can lead to generation of traps at the interface and within a dielectric resulting in stress induced leakage current(SILC) in a process analogous to the effect of biasing stress in MOS capacitors. With further increasing of corona flux and dose,corona induced reactions can occur including corona induced oxide growth at room temperature. Corona charging utilized in this wor is limited to non-destructive range.

(S. Kar,R. Singh, Physics And Technology of High-K Gate Dielectrics II,p.426)