Problems and Remedies for Tablet Coating in Just 5 Minutes

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Problems and Remedies for Tablet Coating in Just 5 Minutes
Understand Problems and Remedies for Tablet Coating
Blistering , Chipping , Cratering, Picking, Pitting , Blooming, Blushing, Colour variation, Infilling, Orange peel/Roughness, Splitting .
Chipping
Definition: It is defect where the film becomes chipped and dented, usually at the edges of the tablet.
Reason: Decrease in fluidizing air or speed of rotation of the drum in pan coating.
CAUSE: High degree of attrition associated with the coating process.
REMEDY: Increase hardness of the film by increasing the molecular weight grade of polymer.
Sticking / Picking

Definition: It is defect where isolated areas of film are pulled away from the surface when the tablet sticks together and then part.
Reason: Conditions similar to cratering that produces an overly wet tablet bed where adjacent tablets can stick together and then break apart.
CAUSE: Inefficient drying.
Higher rate of application of coating solution
REMEDY: Use optimum and efficient drying conditions or increase the inlet air temperature.
Decrease the rater of application of coating solution by increasing viscosity of coating solution.
Blistering
Definition: It is local detachment of film from the substrate forming blister.
Reason: Entrapment of gases in or underneath the film due to overheating either during spraying or at the end of the coating run.
CAUSE:
Effect of temperature on the strength, elasticity and adhesion of the film.
REMEDY:
Use mild drying condition.

Cracking/Splitting
Definition: It is defect in which the film either cracks across the crown of the tablet (cracking) or splits around the edges of the tablet (Splitting)
Reason: Internal stress in the film exceeds tensile strength of the film.
CAUSE:
Use of higher molecular weight polymers or polymeric blends.
REMEDY
Use lower molecular weight polymers or polymeric blends. Also adjust plasticizer type and concentration.
Cratering
Definition: It is defect of film coating whereby volcanic-like craters appears exposing the tablet surface.
Reason: The coating solution penetrates the surface of the tablet, often at the crown where the surface is more porous, causing localized disintegration of the core and disruption of the coating.
CAUSES: Inefficient drying.
Higher rate of application of coating solution.
REMEDIES: Use efficient and optimum drying conditions.
Increase viscosity of coating solution to decrease spray application rate.
Blooming
Definition: It is defect where coating becomes dull immediately or after prolonged storage at high temperatures.
Reason: It is due to collection on the surface of low molecular weight ingredients included in the coating formulation. In most circumstances the ingredient will be plasticizer.
CAUSE: High concentration and low molecular weight of plasticizer.
REMEDY: Decrease plasticizer concentration and increase molecular weight of plasticizer.
Pitting
Definition: It is defect whereby pits occur in the surface of a tablet core without any visible disruption of the film coating.
Reason: Temperature of the tablet core is greater than the melting point of the materials used in the tablet formulation.
CAUSE
Inappropriate drying (inlet air ) temperature
REMEDY
Dispensing with preheating procedures at the initiation of coating and modifying the drying (inlet air) temperature such that the temperature of the tablet core is not greater than the melting point of the batch of additives used.





Colour variation
Definition: A defect which involves variation in colour of the film.
Reason: Alteration of the frequency and duration of appearance of tablets in the spray zone or the size/shape of the spray zone.
CAUSE
Improper mixing, uneven spray pattern, insufficient coating, migration of soluble dyes-plasticizers and other additives during drying.
REMEDY
Go for geometric mixing, reformulation with different plasticizers and additives or use mild drying conditions.
Orange peel/Roughness
Definition: It is surface defect resulting in the film being rough and nonglossy. Appearance is similar to that of an orange.
Reason: Inadequate spreading of the coating solution before drying.
CAUSES: Rapid Drying
High solution viscosity
REMEDIES: Use mild drying conditions
Use additional solvents to decrease viscosity of solution.
Bridging
This occurs when the coating fills in the lettering logo on the tablet
Cause: High spray rate, High viscosity of solution
High percentage solids in the solution
Improper atomization pressure

Cause:
Reduce spray rate, Reduce viscosity of solution
Reduce percentage solids in the solution
Use proper atomization pressure

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